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[SOURCE: https://en.wikipedia.org/wiki/Special:BookSources/978-0-391-04155-4] | [TOKENS: 380] |
Contents Book sources This page allows users to search multiple sources for a book given a 10- or 13-digit International Standard Book Number. Spaces and dashes in the ISBN do not matter. This page links to catalogs of libraries, booksellers, and other book sources where you will be able to search for the book by its International Standard Book Number (ISBN). Online text Google Books and other retail sources below may be helpful if you want to verify citations in Wikipedia articles, because they often let you search an online version of the book for specific words or phrases, or you can browse through the book (although for copyright reasons the entire book is usually not available). At the Open Library (part of the Internet Archive) you can borrow and read entire books online. Online databases Subscription eBook databases Libraries Alabama Alaska California Colorado Connecticut Delaware Florida Georgia Illinois Indiana Iowa Kansas Kentucky Massachusetts Michigan Minnesota Missouri Nebraska New Jersey New Mexico New York North Carolina Ohio Oklahoma Oregon Pennsylvania Rhode Island South Carolina South Dakota Tennessee Texas Utah Washington state Wisconsin Bookselling and swapping Find your book on a site that compiles results from other online sites: These sites allow you to search the catalogs of many individual booksellers: Non-English book sources If the book you are looking for is in a language other than English, you might find it helpful to look at the equivalent pages on other Wikipedias, linked below – they are more likely to have sources appropriate for that language. Find other editions The WorldCat xISBN tool for finding other editions is no longer available. However, there is often a "view all editions" link on the results page from an ISBN search. Google books often lists other editions of a book and related books under the "about this book" link. You can convert between 10 and 13 digit ISBNs with these tools: Find on Wikipedia See also Get free access to research! Research tools and services Outreach Get involved |
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[SOURCE: https://en.wikipedia.org/wiki/Maor_Farid#cite_ref-:1_4-0] | [TOKENS: 1458] |
Contents Maor Farid Dr. Maor Farid (Hebrew: מאור פריד; born April 20, 1992) is an Israeli scientist, engineer and artificial intelligence researcher at Massachusetts Institute of Technology, social activist, and author. He is the founder and CEO of Learn to Succeed (Hebrew: ללמוד להצליח) for empowering of youths from the Israeli socio-economic periphery and youths at risk, a regional manager of the Israeli center of ScienceAbroad at MIT, and an activist in the American Technion Society. He is an alumnus of Unit 8200, and a fellow of Fulbright Program and the Israel Scholarship Educational Foundation [he]. Dr. Farid was elected to the Forbes 30 Under 30 list of 2019, and won the Moskowitz Prize for Zionism. Early life Maor was born in Ness Ziona, a city in central Israel, as the eldest son for parents from immigrating families of Mizrahi Jews from Iraq and Libya. Maor suffered from Attention deficit hyperactivity disorder (ADHD) from a young age, and was classified as a problematic and violent student. His ADHD issues were diagnosed only after he began his university studies. However, inspired by his parents' background, he aspired to excel at school for a better future for his family. During elementary school, Maor attended local quizzes about Jewish history and Zionism, which significantly shaped his identity and national perspective. Farid graduated high school with the highest GPA in school. Later he was recruited to the Israel Defense Forces and drafted to the Brakim Program [he] – an excellence program of the Israeli Intelligence Corps for training leading R&D officers for the Israeli military and defense industry. Maor graduated the program with honors and was elected by the Israeli Prime Minister's Office and Unit 8200, where he served as an artificial intelligence researcher, officer, and commander. During his Military service, he received various honors and awards, such as the Excellent Scientist Award, given to the top three academics serving in the Israel Defense Forces. In 2019, Farid completed his military service in the rank of a Captain. Education and academic career As part of the (4 years) Brakim Program, Maor completed his Bachelor's and Master's degrees at the Technion in Mechanical Engineering with honors. Then, he initiated his Ph.D. research as a collaboration with the Israel Atomic Energy Commission (IAEC) in parallel to his duty military service. The main goals of his Ph.D. research were predicting irreversible effects of major earthquakes on Israel's nuclear facilities, and improving their seismic resistance using energy absorption technologies. The mathematical models developed by Farid were able to forecast earthquake effects on facilities with major hazard potential, and predicted the failure of liquid storage tanks due to earthquakes took place in Italy (2012) and Mexico (2017). The energy absorption technologies used, increased in up to 90% the seismic resistance abilities of those sensitive facilities. The research results were published in multiple papers in peer-reviewed academic journals and presented in international academic conferences. Later, this research expanded to an official collaboration between the Technion and the Shimon Peres Negev Nuclear Research Center, which aims to implement the findings obtained on existing sensitive systems, and won funding of 1.5 million NIS from the Pazy foundation of the Israel Atomic Energy Commission and the Council for Higher Education. In 2017, Farid completed his Ph.D. and as the youngest graduate at the Technion for that year, at the age of 24. In the graduation ceremonies, he honored his parents to receive the diplomas on his behalf. At the same year, he served as a lecturer at Ben-Gurion University in an original course he developed as a solution for knowledge gaps he identified in the Israeli defense industry. In 2018, Dr. Farid served as an artificial intelligence researcher at a Data Science team of Unit 8200, where he developed machine learning-based solutions for military and operational needs. In 2019, Farid won the Fulbright and the Israel Scholarship Educational Foundation scholarships, and was accepted to post-doctoral position at Massachusetts Institute of Technology where he develops real-time methods for predicting earthquake effects using machine learning techniques. In 2020, Farid was accepted to the Emerging Leaders Program at Harvard Kennedy School in Cambridge, Massachusetts. At the same year, he received the excellence research grant of the Israel Academy of Sciences and Humanities for leading his research in collaboration between MIT and the Technion. Social activism Farid social activism focuses on empowering youths from disadvantaged backgrounds from an early age. In 2010–2015, he served as a mentor of a robotics team from Dimona in FIRST Robotics Competition, a mathematics tutor in "Aharai!" [he] program for high-school students at risk in Dimona and Be'er Sheva, and a mentor and private tutor of adolescence and reserve duty soldiers from disadvantaged backgrounds. In 2010, he initiated "Learn to Succeed" (Hebrew: ללמוד להצליח) project, for mitigating the social gaps in the Israeli society by empowering youths from the social, economical, and geographical periphery for excellence, self-fulfillment and gaining formal education. In 2018, Learn to Succeed became an official non-profit organization. At the same year, Farid led a crowdfunding project of 150,000 NIS in order to expand the organization to a national scale. In 2019, he published the book "Learn to Succeed", in which he describes his struggle with ADHD, the violent environment in which he grew up, and the changing process he went through from being a violent teenager to becoming the youngest Ph.D. graduate at the Technion. The book was given to more than two thousand youths at risk and became a top seller in Israel shortly after its publication. Maor dedicated the book to his parents and to the memorial of his friend Captain Tal Nachman who was killed in operational activity during his military service in 2014. The organization consists of hundreds of volunteers, gives full scholarships to STEM students from the periphery who serve as mentors of youths, both Jews and Arabs, from disadvantaged backgrounds, runs a hotline which gives online practical and mental support to hundreds of youths, parents and educators, initiates inspirational activities with military orientation to increase the motivation of its teen-age members for significant military service, and gives inspirational lectures to more than 5,000 youths each year. In 2019, Maor initiated a collaboration with Unit 8200 in which tens of the program's members are being interviewed to the unit. This opportunity is usually given to students with the highest grades in the matriculate exams in each class. In 2020, Dr. Farid established the ScienceAbroad center at MIT, aiming to strengthen the connections between Israeli researchers in the institute and the state of Israel. Moreover, he serves as a volunteer in the American Technion Society. Honors and awards Personal life Farid is married to Michal. Interviews and articles References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Mailto] | [TOKENS: 497] |
Contents mailto mailto is a Uniform Resource Identifier (URI) scheme for email addresses. It is used to produce hyperlinks on websites that allow users to send an email to a specific address directly from an HTML document, without having to copy and enter it into an email client. It was originally defined by Request for Comments (RFC) 1738 in December 1994, expanded by RFC 2368 in July 1998, and refined by RFC 6068 in October 2010. Syntax Mailto URIs are composed of the scheme mailto: and one or more recipient addresses separated with a comma. Additionally, email headers such as cc or subject can be added as attribute-value pairs in the query component of the email. Percent-encoding must be used for the local-part of the Email addresses and for the header values. The Domain parts of the addresses can also be encoded using percent-encoding but using IDNA-Encoding is recommended for interoperability with legacy software. Examples "mailto" can be used within an HTML document to generate a link for sending email: Clicking on the hyperlink automatically opens the default email client, with the destination email address pre-filled. It is possible to specify initial values for headers (e.g. subject, cc, etc.) and message body in the URL. Blanks, carriage returns, and line feeds cannot be directly embedded but must be percent-encoded: Multiple addresses can be specified: The address can be omitted: Only the initial header should be prepended with a question mark. All subsequent headers require an ampersand. If this convention is not followed, the scheme will not properly copy over the headers to the email client. Security and privacy A number of security issues are mentioned in RFC 6068, one of them being robotic address harvesting. Mailto constructs are locatable within HTML pages by automated means which typically include the use of DOM constructs or regular expressions. Addresses harvested by such means are liable to be added to spammers' mass-mailing lists and thus to receive large amounts of unwanted mail. While methods exist to "harden" mailto links against harvesting—address munging and JavaScript-based address obfuscation among them—these protections can be circumvented by sufficiently sophisticated harvesting robots. Other techniques, like walling the address behind a CAPTCHA or similar "humanity check", provide security on par with that available for other contact methods, most notably web forms, which experience similar challenges with preventing spam. References |
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[SOURCE: https://en.wikipedia.org/wiki/Christmas_elf] | [TOKENS: 1013] |
Contents Christmas elf In English-speaking cultures, Christmas elves are diminutive elves that live with Santa Claus at the North Pole and act as his helpers. Christmas elves are usually depicted as green- or red-clad, with large, pointy ears and wearing pointy hats. They are most often depicted as humanoids, but sometimes as furry mammals with tails. Santa's elves are often said to make the toys in Santa's workshop and take care of his reindeer, among other tasks. The association of Christmas presents with elves has precedents in the first half of the 19th century with the Scandinavian nisse or tomte, and Saint Nicholas himself is called an elf in A Visit from St. Nicholas (1823). Origin The English word elf derives from the álfar from Ancient Norse mythology. This folklore predates the Christmas characters by many hundred years. Elves originated from Germanic mythology. In various regions of Europe there were similar supernatural beings that can be connected to elves, such as kobolds from Germany and house spirits named brownies in Scotland. In medieval Europe, elves were seen as nefarious and were often linked to demons. The image of elves in the workshop was popularized by Godey's Lady's Book, with a front cover illustration for its 1873 Christmas issue showing Santa surrounded by toys and elves with the caption "Here we have an idea of the preparations that are made to supply the young folks with toys at Christmas time". During this time, Godey's was immensely influential to the birth of Christmas traditions, having shown the first widely circulated picture of a modern Christmas tree on the front cover of its 1850 Christmas issue. Additional recognition was given in Austin Thompson's 1876 work "The House of Santa Claus, a Christmas Fairy Show for Sunday Schools". In the 1823 poem A Visit from St. Nicholas (commonly known as 'Twas the Night Before Christmas), often attributed to Clement Clarke Moore, Santa Claus himself is described in line 45: "He was chubby and plump, a right jolly old elf". Prior to the influence of Saint Nicholas in Sweden, the job of giving out gifts was done by the Yule goat. By 1891, the saint had merged with Tomten, which was previously an elfish / dwarfish farm guardian. Following the work of Jenny Nyström, this hybrid figure became known as Jultomten. Contemporary pop culture In North America and the British Isles, the modern legend of Santa Claus typically includes diminutive elves at Christmas; green-clad elves with pointy ears and pointy hats as Santa's employees / assistants. They make the toys in Santa's workshop located in the North Pole. In recent years, other toys—usually high-tech toys like computers, video games, DVDs, and DVD players, and even mobile phones—have also been depicted as being ready for delivery, but not necessarily made, in the workshop as well. In this portrayal, elves slightly resemble nimble and delicate versions of dwarves. In recent films (e.g. The Santa Clause series and The Christmas Chronicles), the elves' jobs also include operating police and air forces protecting the North Pole, helping Santa outside the Pole when he is captured by the real-world police, and as Santa's secret-service-like bodyguards (Fred Claus). The elves are generally said to live for hundreds, or even thousands, of years, despite the fact that in some cases they appear eternally youthful as children. Christmas elves have had their role expanded in modern films and television. They are generally portrayed in live-action films either by little actors, children, forced perspective to make normal-sized actors appear diminutive, or computer-generated imagery (CGI); otherwise by traditional animation, stop-motion animation, or computer animation according to the format of the film. For instance: Valentine D'Arcy Sheldon's children's picture book, The Christmas Tree Elf, tells the origin story of how Santa met his elves. It also introduces Blink the elf, who introduces Santa to the elves and saves Christmas by extinguishing a Christmas tree fire. A strong connection to Christmas and elves can be found in the popular fairy tale "The Elves and the Shoemaker" published by the Brothers Grimm in 1812. In this tale a shoemaker, who had not been able to meet the demand to make more shoes, is greeted by several elves just before Christmas to finish all the shoes for him. Around the world In European countries, Santa has differing helpers depending on the country. In the Netherlands and Belgium, Saint Nicholas is accompanied by Zwarte Piet (Black Peter) whose inclusion has become a controversial issue for the blackface depiction of the character. In Germany, the companions are the Knecht Ruprecht and in Luxembourg, they are known as Hoesecker. In Nordic countries, Christmas Elves are considered nisser and not elves and they will usually wear only red instead of the green and red outfits that they are known for in English speaking countries. See also References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Special:EditPage/Template:Xbox_Game_Studios] | [TOKENS: 1447] |
Editing Template:Xbox Game Studios Copy and paste: – — ° ′ ″ ≈ ≠ ≤ ≥ ± − × ÷ ← → · § Sign your posts on talk pages: ~~~~ Cite your sources: <ref></ref> {{}} {{{}}} | [] [[]] [[Category:]] #REDIRECT [[]] <s></s> <sup></sup> <sub></sub> <code></code> <pre></pre> <blockquote></blockquote> <ref></ref> <ref name="" /> {{Reflist}} <references /> <includeonly></includeonly> <noinclude></noinclude> {{DEFAULTSORT:}} <nowiki></nowiki> <!-- --> <span class="plainlinks"></span> Symbols: ~ | ¡ ¿ † ‡ ↔ ↑ ↓ • ¶ # ∞ ‹› «» ¤ ₳ ฿ ₵ ¢ ₡ ₢ $ ₫ ₯ € ₠ ₣ ƒ ₴ ₭ ₤ ℳ ₥ ₦ ₧ ₰ £ ៛ ₨ ₪ ৳ ₮ ₩ ¥ ♠ ♣ ♥ ♦ 𝄫 ♭ ♮ ♯ 𝄪 © ¼ ½ ¾ Latin: A a Á á À à  â Ä ä Ǎ ǎ Ă ă Ā ā à ã Å å Ą ą Æ æ Ǣ ǣ B b C c Ć ć Ċ ċ Ĉ ĉ Č č Ç ç D d Ď ď Đ đ Ḍ ḍ Ð ð E e É é È è Ė ė Ê ê Ë ë Ě ě Ĕ ĕ Ē ē Ẽ ẽ Ę ę Ẹ ẹ Ɛ ɛ Ǝ ǝ Ə ə F f G g Ġ ġ Ĝ ĝ Ğ ğ Ģ ģ H h Ĥ ĥ Ħ ħ Ḥ ḥ I i İ ı Í í Ì ì Î î Ï ï Ǐ ǐ Ĭ ĭ Ī ī Ĩ ĩ Į į Ị ị J j Ĵ ĵ K k Ķ ķ L l Ĺ ĺ Ŀ ŀ Ľ ľ Ļ ļ Ł ł Ḷ ḷ Ḹ ḹ M m Ṃ ṃ N n Ń ń Ň ň Ñ ñ Ņ ņ Ṇ ṇ Ŋ ŋ O o Ó ó Ò ò Ô ô Ö ö Ǒ ǒ Ŏ ŏ Ō ō Õ õ Ǫ ǫ Ọ ọ Ő ő Ø ø Œ œ Ɔ ɔ P p Q q R r Ŕ ŕ Ř ř Ŗ ŗ Ṛ ṛ Ṝ ṝ S s Ś ś Ŝ ŝ Š š Ş ş Ș ș Ṣ ṣ ß T t Ť ť Ţ ţ Ț ț Ṭ ṭ Þ þ U u Ú ú Ù ù Û û Ü ü Ǔ ǔ Ŭ ŭ Ū ū Ũ ũ Ů ů Ų ų Ụ ụ Ű ű Ǘ ǘ Ǜ ǜ Ǚ ǚ Ǖ ǖ V v W w Ŵ ŵ X x Y y Ý ý Ŷ ŷ Ÿ ÿ Ỹ ỹ Ȳ ȳ Z z Ź ź Ż ż Ž ž ß Ð ð Þ þ Ŋ ŋ Ə ə Greek: Ά ά Έ έ Ή ή Ί ί Ό ό Ύ ύ Ώ ώ Α α Β β Γ γ Δ δ Ε ε Ζ ζ Η η Θ θ Ι ι Κ κ Λ λ Μ μ Ν ν Ξ ξ Ο ο Π π Ρ ρ Σ σ ς Τ τ Υ υ Φ φ Χ χ Ψ ψ Ω ω {{Polytonic|}} Cyrillic: А а Б б В в Г г Ґ ґ Ѓ ѓ Д д Ђ ђ Е е Ё ё Є є Ж ж З з Ѕ ѕ И и І і Ї ї Й й Ј ј К к Ќ ќ Л л Љ љ М м Н н Њ њ О о П п Р р С с Т т Ћ ћ У у Ў ў Ф ф Х х Ц ц Ч ч Џ џ Ш ш Щ щ Ъ ъ Ы ы Ь ь Э э Ю ю Я я ́ IPA: t̪ d̪ ʈ ɖ ɟ ɡ ɢ ʡ ʔ ɸ β θ ð ʃ ʒ ɕ ʑ ʂ ʐ ç ʝ ɣ χ ʁ ħ ʕ ʜ ʢ ɦ ɱ ɳ ɲ ŋ ɴ ʋ ɹ ɻ ɰ ʙ ⱱ ʀ ɾ ɽ ɫ ɬ ɮ ɺ ɭ ʎ ʟ ɥ ʍ ɧ ʼ ɓ ɗ ʄ ɠ ʛ ʘ ǀ ǃ ǂ ǁ ɨ ʉ ɯ ɪ ʏ ʊ ø ɘ ɵ ɤ ə ɚ ɛ œ ɜ ɝ ɞ ʌ ɔ æ ɐ ɶ ɑ ɒ ʰ ʱ ʷ ʲ ˠ ˤ ⁿ ˡ ˈ ˌ ː ˑ ̪ {{IPA|}} Wikidata entities used in this page Pages transcluded onto the current version of this page (help): |
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[SOURCE: https://en.wikipedia.org/wiki/Doppler_beaming] | [TOKENS: 1522] |
Contents Relativistic beaming In physics, relativistic beaming (also known as Doppler beaming, Doppler boosting, or the headlight effect) is the process by which relativistic effects modify the apparent luminosity of emitting matter that is moving at speeds close to the speed of light. In an astronomical context, relativistic beaming commonly occurs in two oppositely directed relativistic jets of plasma that originate from a central compact object that is accreting matter. Accreting compact objects and relativistic jets are invoked to explain x-ray binaries, gamma-ray bursts, and, on a much larger scale, active galactic nuclei (AGN; of which quasars are a particular variety). Beaming affects the apparent brightness of a moving object. Consider a cloud of gas moving relative to the observer and emitting electromagnetic radiation. If the gas is moving towards the observer, it will be brighter than if it were at rest, but if the gas is moving away, it will appear fainter. The magnitude of the effect is illustrated by the AGN jets of the galaxies M87 and 3C 31 (see images at right). M87 has twin jets aimed almost directly towards and away from Earth; the jet moving towards Earth is clearly visible (the long, thin blueish feature in the top image at right), while the other jet is so much fainter it is not visible. In 3C 31, both jets (labeled in the lower figure at right) are at roughly right angles to our line of sight, and thus, both are visible. The upper jet points slightly more in Earth's direction and is therefore brighter. Relativistically, moving objects are beamed due to a variety of physical effects. Light aberration causes most of the photons to be emitted along the object's direction of motion. The Doppler effect changes the energy of the photons by red- or blue shifting them. Finally, time intervals as measured by clocks moving alongside the emitting object are different from those measured by an observer on Earth due to time dilation and photon arrival time effects. How all of these effects modify the brightness, or apparent luminosity, of a moving object is determined by the equation describing the relativistic Doppler effect (which is why relativistic beaming is also known as Doppler beaming). A simple jet model The simplest model for a jet is one where a single, homogeneous sphere is travelling towards the Earth at nearly the speed of light. This simple model is also an unrealistic one, but it illustrates the physical process of beaming. Relativistic jets emit most of their energy via synchrotron emission. In our simple model, the sphere contains highly relativistic electrons and a steady magnetic field. Electrons inside the blob travel at speeds a tiny fraction below the speed of light and are whipped around by the magnetic field. Each change in direction by an electron is accompanied by the release of energy in the form of a photon. With enough electrons and a powerful enough magnetic field, the relativistic sphere can emit a huge number of photons, ranging from those at relatively weak radio frequencies to powerful X-ray photons. Features of a simple synchrotron spectrum include, at low frequencies, the jet sphere is opaque and its luminosity increases with frequency until it peaks and begins to decline. This peak frequency occurs at log ν = 3 {\displaystyle \log \nu =3} . At frequencies higher than this, the jet sphere is transparent. The luminosity decreases with frequency until a break frequency is reached, after which it declines more rapidly. The break frequency occurs when log ν = 7 {\displaystyle \log \nu =7} . The sharp break frequency occurs because at very high frequencies, the electrons which emit the photons lose most of their energy rapidly. A sharp decrease in the number of high energy electrons means a sharp decrease in the spectrum. The changes in slope in the synchrotron spectrum are parameterized with a spectral index. The spectral index, α, over a given frequency range is simply the slope on a diagram of log S {\displaystyle \log S} vs. log ν {\displaystyle \log \nu } . (Of course for α to have real meaning the spectrum must be very nearly a straight line across the range in question.) In the simple jet model of a single homogeneous sphere the observed luminosity is related to the intrinsic luminosity as S o = S e D p , {\displaystyle S_{o}=S_{e}D^{p}\,,} where p = 3 − α . {\displaystyle p=3-\alpha \,.} The observed luminosity therefore depends on the speed of the jet and the angle to the line of sight through the Doppler factor, D {\displaystyle D} , and also on the properties inside the jet, as shown by the exponent with the spectral index. The beaming equation can be broken down into a series of three effects: Aberration is the change in an object's apparent direction caused by the relative transverse motion of the observer. In inertial systems it is equal and opposite to the light time correction. In everyday life aberration is a well-known phenomenon. Consider a person standing in the rain on a day when there is no wind. If the person is standing still, then the rain drops will follow a path that is straight down to the ground. However, if the person is moving, for example in a car, the rain will appear to be approaching at an angle. This apparent change in the direction of the incoming raindrops is aberration. The amount of aberration depends on the speed of the emitted object or wave relative to the observer. In the example above this would be the speed of a car compared to the speed of the falling rain. This does not change when the object is moving at a speed close to c {\displaystyle c} . Like the classic and relativistic effects, aberration depends on: 1) the speed of the emitter at the time of emission, and 2) the speed of the observer at the time of absorption. In the case of a relativistic jet, beaming (emission aberration) will make it appear as if more energy is sent forward, along the direction the jet is traveling. In the simple jet model a homogeneous sphere will emit energy equally in all directions in the rest frame of the sphere. In the rest frame of Earth the moving sphere will be observed to be emitting most of its energy along its direction of motion. The energy, therefore, is ‘beamed’ along that direction. Quantitatively, aberration accounts for a change in luminosity of D 2 . {\displaystyle D^{2}.} Time dilation is a well-known consequence of special relativity and accounts for a change in observed luminosity of D 1 . {\displaystyle D^{1}.} Blue- or redshifting can change the observed luminosity at a particular frequency, but this is not a beaming effect. Blueshifting accounts for a change in observed luminosity of 1 D α . {\displaystyle {\frac {1}{D^{\alpha }}}.} A more-sophisticated method of deriving the beaming equations starts with the quantity S ν 3 {\displaystyle {\frac {S}{\nu ^{3}}}} . This quantity is a Lorentz invariant, so the value is the same in different reference frames. Terminology See also References External links |
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[SOURCE: https://en.wikipedia.org/wiki/PA-RISC] | [TOKENS: 1118] |
Contents PA-RISC Precision Architecture RISC (PA-RISC) or Hewlett Packard Precision Architecture (HP/PA or HPPA), is a general purpose computer instruction set architecture (ISA) developed by Hewlett-Packard from the 1980s until the 2000s. The architecture was introduced on 26 February 1986, when the HP 3000 Series 930 and HP 9000 Model 840 computers were launched featuring the first implementation, the TS1. HP stopped selling PA-RISC-based HP 9000 systems at the end of 2008 but supported servers running PA-RISC chips until 2013. PA-RISC was succeeded by the Itanium (originally IA-64) ISA, jointly developed by HP and Intel. History In the late 1980s, HP was building four series of computers, all based on CISC CPUs. One line was the IBM PC compatible Intel i286-based HP Vectra series, started in 1986. All others were non-Intel systems. One of them was the HP 9000 Series 300 of Motorola 68000 series based workstations, another HP 9000 Series 200 line of technical workstations based on a custom silicon on sapphire (SOS) chip design, the SOS based 16-bit HP 3000 classic series, and finally the HP 9000 Series 500 minicomputers, based on their own (16- and 32-bit) FOCUS microprocessor. The Precision Architecture is the result of what was known inside Hewlett-Packard as the Spectrum program. HP planned to use Spectrum to move all of their non-PC compatible machines to a single RISC CPU family. In early 1982, work on the Precision Architecture began at HP Laboratories, defining the instruction set and virtual memory system. Development of the first TTL implementation started in April 1983. With simulation of the processor having completed in 1983, a final processor design was delivered to software developers in July 1984. Systems prototyping followed, with "lab prototypes" being produced in 1985 and product prototypes in 1986. The first processors were introduced in products during 1986, with the first HP 9000 Series 840 units shipping in November of that year.: 6 They were also used in a new series of HP 3000 machines in the late 1980s: the 930 and 950, commonly known at the time as Spectrum systems, the name given to them in the development labs. These machines ran MPE-XL, whereas HP 9000 machines employing the PA-RISC processor ran the HP-UX version of Unix. The first implementation of the Precision Architecture was the TS1, a central processing unit built from discrete transistor–transistor logic (74F TTL) devices. Later implementations were multi-chip VLSI designs fabricated in NMOS processes (NS1 and NS2) and CMOS (CS1 and PCX), beginning with the HP 3000 Series 950, HP 9000 Model 850S and HP 9000 Model 825, introduced in late 1987. The HP Precision Architecture has thirty-two 32-bit integer registers, sixteen 64-bit floating-point registers, and has a single branch delay slot. This means that the instruction immediately following a branch instruction is executed before the program's control flow is transferred to the target instruction of the branch.: 10 An HP Precision processor also includes a Processor Status Word (PSW) register. The PSW register contains various flags that enable virtual addressing, protection, interruptions, and other status information.: 6 The number of floating-point registers was doubled in the 1.1 version to 32 once it became apparent that 16 were inadequate and restricted performance. The architects included Allen Baum, Hans Jeans, Michael J. Mahon, Ruby Bei-Loh Lee, Russel Kao, Steve Muchnick, Terrence C. Miller, David Fotland, and William S. Worley. Other operating systems ported to the PA-RISC architecture include Linux, OpenBSD, NetBSD, OSF/1, NeXTSTEP, and ChorusOS. An interesting aspect of the PA-RISC line is that most of its generations have no level 2 cache. Instead large level 1 caches are used, initially as separate chips connected by a bus, and later integrated on-chip. Only the PA-7100LC and PA-7300LC have L2 caches. Another innovation of the PA-RISC is the addition of vector instructions (SIMD) in the form of MAX, which were first introduced on the PA-7100LC. Precision RISC Organization, an industry group led by HP, was founded in 1992, to promote the PA-RISC architecture. Members included Convex, Hitachi, Hughes Aircraft, Mitsubishi, NEC, OKI, Prime, Stratus, Yokogawa, Red Brick Software, and Allegro Consultants, Inc. The ISA was extended in 1996 to 64 bits, with this revision named PA-RISC 2.0. PA-RISC 2.0 also added fused multiply–add instructions, which help certain floating-point intensive algorithms, and the MAX-2 SIMD extension, which provides instructions for accelerating multimedia applications. The first PA-RISC 2.0 implementation was the PA-8000, which was introduced in January 1996. CPU specifications See also References External links |
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[SOURCE: https://en.wikipedia.org/wiki/EssilorLuxottica] | [TOKENS: 2003] |
Contents EssilorLuxottica EssilorLuxottica SA is a Franco-Italian vertically integrated multinational holding company registered in Charenton-Le-Pont and headquartered in nearby Paris. It designs, produces and markets ophthalmic lenses, equipment and instruments, prescription glasses and sunglasses. It was founded on 1 October 2018 and its name is an amalgamation of the two major corporations which merged to create it; the French Essilor and the Italian Luxottica. The two companies have, since the merger, been restructured as subsidiaries of the new entity. Under the terms of the merger agreement, Essilor would purchase Luxottica, but Luxottica's leadership would be guaranteed prominent positions in the newly-formed corporation as well as some seats on its board of directors; Luxottica founder, Leonardo Del Vecchio, was notably designated chairman. The first few years of EssilorLuxottica post-merger were marred by disputes over leadership roles, but Del Vecchio was able to bring them to a satisfactory end. Essilor and Luxottica were respectively the world's leading manufacturers of ophthalmic lenses and of eyeglasses; upon the merger, EssilorLuxottica thus became a monopoly. Essilor contributed its numerous proprietary lens technologies as well as its subsidiaries to the new company. Meanwhile, the latter gained through Luxottica ownership over numerous eyewear brands including Ray-Ban, Oakley, Persol, Oliver Peoples, and Vogue Eyewear; eyewear retailers LensCrafters, Pearle Vision, and Sunglass Hut, eyewear insurance company EyeMed, and exclusive eyewear licensing deals to numerous fashion houses. The company is listed on the Euronext Paris stock exchange under the trading symbol "EL" and is part of the CAC 40 share index which includes the 40 largest capitalized companies traded on the Paris Stock Exchange and the Euro Stoxx 50 which includes the 50 largest companies in the Eurozone. According to Statista, in 2023, the company generated €25.4 billion in revenue. History In January 2017, Essilor and Luxottica announced the merger of their activities. After having received the necessary authorizations from the competition authorities of the United States, the European Union, Brazil, Canada and China, EssilorLuxottica was created on 1 October 2018. On a technical level, Essilor acquired Luxottica, though Luxottica founder and executive chairman Leonardo Del Vecchio became co-leader of the new conglomerate, which would change its name to contain both companies. Luxottica proceeded to delist its American depositary receipts from the New York Stock Exchange upon announcement of the merger. Del Vecchio's holding company, Delfin, then held 62.42% of Luxottica, a share that it contributed to EssilorLuxotica. Delfin also became a plurality shareholder of the new group with 38.9% of the capital. This merger gives birth to a giant of the optical industry, generating a turnover of more than €16 billion and a market capitalization of €57 billion. The merger did not occur without controversy from anti-trust researchers, however, and Turkish authorities, accusing the company of not fulfilling anti-trust obligations it had agreed to during the merger, fined EssilorLuxottica €17 million in late August 2023. Despite the merger being completed in 2018, the company still faced an internal leadership battle for control of the company, fought between old Essilor leadership and Del Vecchio, who went on to state in a March 2019 interview with Le Figaro that Essilor CEO Hubert Sagnières "only listened to himself", and had cost the company up to €600 million in savings from the merger. Sagnières responded to Del Vecchio by accusing the Luxottica founder of attempting to take control of the newly formed conglomerate without offering "a premium to shareholders" of EssilorLuxottica. Del Vecchio further accused Sagnières of inexperience when running an eyewear company. The terms of the merger provided that old Essilor leadership as well as Luxottica's officers would have equal control over the merged entity, though the company would select a new CEO, internally or externally, by the end of 2020. Ultimately, Del Vecchio won with the backing of EssilorLuxottica shareholders. Del Vecchio's choice of appointing Francesco Milleri as CEO and Paul du Saillant [fr] as deputy CEO. Saginères ultimately departed EssilorLuxottica after the feud, and Del Vecchio, who previously agreed to limit his voting rights to control the company, regained the full weight of such voting rights. A company statement to the Financial Times reflected the settled nature of the conflict, stating that the resolution of the leadership battle represented "the victory of a vision, the creation of an extraordinary business that is at the beginning of what it can achieve". Del Vecchio further reflected the new company's leadership by going on to state that his "life-long dream" of creating a dominant vertically integrated company in eyewear has "finally come true". At the beginning of 2019, EssilorLuxottica acquired German-based Brille24 GmbH. Essilor's partner Shamir acquired Union Optic, a prescription laboratory that also distributes optical instruments. Essilor also acquired a majority stake in Indulentes, one of Ecuador's leading prescription laboratories, and a majority stake in Metalizado Optico Argentino S.A. (MOA), one of Argentina's leading prescription laboratories. EssilorLuxottica acquired a 75% stake in the Dutch opticians group GrandVision, which owns Vision Express in the UK and For Eyes in the US, in 2019 for €28 per share, which would value the entirety of GrandVision at Euro 7.2 billion. Del Vecchio died in June 2022, leaving $350 million in shares to Milleri. In August 2022, Essilor bought the remaining 50 percent stake in Shamir Optical Industry. Additionally, the company announced it would acquire Israeli startup Nuance Hearing for an undisclosed amount. This was the first major strategy shift and industry expansion for the company after Del Vecchio's 2022 death, and it accompanied reports that the firm was planning to introduce hearing aid technology into its lenses. In July 2024, EssilorLuxottica agreed to buy US streetwear brand Supreme for US$1.5 billion, expanding its brand portfolio beyond eyewear and lenses for the first time. Days later, it was reported that Meta was in talks to purchase a 5% stake in EssilorLuxottica. In July 2024, EssilorLuxottica acquired an 80% shareholding in Heidelberg Engineering. The Germany-headquartered Heidelberg specializes in ophthalmic diagnostic instruments based around optical coherence tomography (OCT), confocal microscopy, and scanning lasers. May 2023 saw EssilorLuxottica confirm that it had suffered a data breach two years earlier in 2021; upon noticing the breach, the company immediately alerted the FBI and Italian law enforcement. A spokesperson for the company stated that the company was first aware of the data breach in November 2022, and the owner of the website Have I Been Pwned? stated that around 77 million accounts were released. Operations The company dominates the global eyewear market as the largest single player in that market. EssilorLuxottica is the largest company in retail sales, owning many of the largest eyewear retail chains in the world. By number of locations, EssilorLuxottica's largest store chain is Sunglass Hut, with 3,239 locations as of 2020. Its second largest and third largest chains are Oticas Carol at 1,402 locations and LensCrafters with 1,094 locations respectively. Online, the company further owns Clearly, Eyebuydirect, FramesDirect.com, and online properties under its brand names such as Ray-Ban and Oakley. The company, inherited mostly from the Luxottica side, has control over some of the most recognized brands in eyewear. Previous acquisitions from Luxottica include Vogue Eyewear in 1990, Persol in 1995, Ray-Ban and Arnette in 1999, Oakley and Oliver Peoples in 2007, Alain Mikli in 2012, and Bolon eyewear owner Xiamen Yarui Optical in 2013. Essilor also brought some eyewear brands to the combined company, the largest of which being Foster Grant, acquired in 2010, and Costa Del Mar, a part of Essilor since 2014. Despite ownership of brands, Luxottica also brought over exclusive eyewear manufacturing deals to the company, mostly with major European fashion houses. Armani was Luxottica's first major licensing deal in 1989, one that remains intact to this day, and the company additionally manufactures eyewear for many companies, including but not limited to brands owned by Tapestry, Capri Holdings, Ralph Lauren Corporation, and Ferrari. In addition to the brands it owns, EssilorLuxottica presently has exclusive manufacturing licensing for Armani, Brooks Brothers, Burberry, Chanel, Coach, Dolce & Gabbana, Ferrari (through a Ray-Ban partnership), Michael Kors' eyewear, Miu Miu, Prada, Ralph Lauren, Swarovski, Tiffany & Co., Tory Burch, and Versace. EssilorLuxottica also signed new licensing deals with Jimmy Choo and Kodak in 2023, though did not renew its license with LVMH-owned Bulgari, which expired at the end of 2023. According to its website, it owns the following lens technologies: References External links |
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[SOURCE: https://en.wikipedia.org/wiki/Encryption] | [TOKENS: 3025] |
Contents Encryption In cryptography, encryption (more specifically, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Despite its goal, encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor. For technical reasons, an encryption scheme usually uses a pseudo-random encryption key generated by an algorithm. It is possible to decrypt the message without possessing the key but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users. Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often used in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing. Modern encryption schemes use the concepts of public-key and symmetric-key. Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption. History One of the earliest forms of encryption is symbol replacement, which was first found in the tomb of Khnumhotep II, who lived in 1900 BC Egypt. Symbol replacement encryption is "non-standard," which means that the symbols require a cipher or key to understand. This type of early encryption was used throughout Ancient Greece and Rome for military purposes. One of the most famous military encryption developments was the Caesar cipher, in which a plaintext letter is shifted a fixed number of positions along the alphabet to get the encoded letter. A message encoded with this type of encryption could be decoded with a fixed number on the Caesar cipher. Around 800 AD, Arab mathematician al-Kindi developed the technique of frequency analysis – which was an attempt to crack ciphers systematically, including the Caesar cipher. This technique looked at the frequency of letters in the encrypted message to determine the appropriate shift: for example, the most common letter in English text is E and is therefore likely to be represented by the letter that appears most commonly in the ciphertext. This technique was rendered ineffective by the polyalphabetic cipher, described by al-Qalqashandi (1355–1418) and Leon Battista Alberti (in 1465), which varied the substitution alphabet as encryption proceeded in order to confound such analysis. Around 1790, Thomas Jefferson theorized a cipher to encode and decode messages to provide a more secure way of military correspondence. The cipher, known today as the Wheel Cipher or the Jefferson Disk, although never actually built, was theorized as a spool that could jumble an English message up to 36 characters. The message could be decrypted by plugging in the jumbled message to a receiver with an identical cipher. A similar device to the Jefferson Disk, the M-94, was developed in 1917 independently by US Army Major Joseph Mauborne. This device was used in U.S. military communications until 1942. In World War II, the Axis powers used a more advanced version of the M-94 called the Enigma Machine. The Enigma Machine was more complex because unlike the Jefferson Wheel and the M-94, each day the jumble of letters switched to a completely new combination. Each day's combination was only known by the Axis, so many thought the only way to break the code would be to try over 17,000 combinations within 24 hours. The Allies used computing power to severely limit the number of reasonable combinations they needed to check every day, leading to the breaking of the Enigma Machine. Today, encryption is used in the transfer of communication over the Internet for security and commerce. As computing power continues to increase, computer encryption is constantly evolving to prevent eavesdropping attacks. One of the first "modern" cipher suites, DES, used a 56-bit key with 72,057,594,037,927,936 possibilities; it was cracked in 1999 by EFF's brute-force DES cracker, which required 22 hours and 15 minutes to do so. Modern encryption standards often use stronger key sizes, such as AES (256-bit mode), TwoFish, ChaCha20-Poly1305, Serpent (configurable up to 512-bit). Cipher suites that use a 128-bit or higher key, like AES, cannot be brute-forced because the total number of keys is 3.4028237e+38 possibilities. The most likely option for cracking ciphers with large key sizes is to find vulnerabilities in the cipher itself, like inherent biases and backdoors or by exploiting physical side effects through Side-channel attacks. For example, RC4, a stream cipher, was cracked due to inherent biases and vulnerabilities in the cipher. Encryption in cryptography In the context of cryptography, encryption serves as a mechanism to ensure confidentiality. Since data may be visible on the Internet, sensitive information such as passwords and personal communication may be exposed to potential interceptors. The process of encrypting and decrypting messages involves keys. The two main types of keys in cryptographic systems are symmetric-key and public-key (also known as asymmetric-key). Many complex cryptographic algorithms often use simple modular arithmetic in their implementations. In symmetric-key schemes, the encryption and decryption keys are the same. Communicating parties must have the same key in order to achieve secure communication. The German Enigma Machine used a new symmetric-key each day for encoding and decoding messages. In public-key cryptography schemes, the encryption key is published for anyone to use and encrypt messages. However, only the receiving party has access to the decryption key that enables messages to be read. Public-key encryption was first described in a secret document in 1973; beforehand, all encryption schemes were symmetric-key (also called private-key).: 478 Although published subsequently, the work of Diffie and Hellman was published in a journal with a large readership, and the value of the methodology was explicitly described. The method became known as the Diffie-Hellman key exchange. RSA (Rivest–Shamir–Adleman) is another notable public-key cryptosystem. Created in 1978, it is still used today for applications involving digital signatures. Using number theory, the RSA algorithm selects two prime numbers, which help generate both the encryption and decryption keys. A publicly available public-key encryption application called Pretty Good Privacy (PGP) was written in 1991 by Phil Zimmermann, and distributed free of charge with source code. PGP was purchased by Symantec in 2010 and is regularly updated. Uses Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. For example, the Computer Security Institute reported that in 2007, 71% of companies surveyed used encryption for some of their data in transit, and 53% used encryption for some of their data in storage. Encryption can be used to protect data "at rest", such as information stored on computers and storage devices (e.g. USB flash drives). In recent years, there have been numerous reports of confidential data, such as customers' personal records, being exposed through loss or theft of laptops or backup drives; encrypting such files at rest helps protect them if physical security measures fail. Digital rights management systems, which prevent unauthorized use or reproduction of copyrighted material and protect software against reverse engineering (see also copy protection), is another somewhat different example of using encryption on data at rest. Encryption is also used to protect data in transit, for example data being transferred via networks (e.g. the Internet, e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. There have been numerous reports of data in transit being intercepted in recent years. Data should also be encrypted when transmitted across networks in order to protect against eavesdropping of network traffic by unauthorized users. Conventional methods for permanently deleting data from a storage device involve overwriting the device's whole content with zeros, ones, or other patterns – a process which can take a significant amount of time, depending on the capacity and the type of storage medium. Cryptography offers a way of making the erasure almost instantaneous. This method is called crypto-shredding. An example implementation of this method can be found on iOS devices, where the cryptographic key is kept in a dedicated 'effaceable storage'. Because the key is stored on the same device, this setup on its own does not offer full privacy or security protection if an unauthorized person gains physical access to the device. Limitations Encryption is used in the 21st century to protect digital data and information systems. As computing power increased over the years, encryption technology has only become more advanced and secure. However, this advancement in technology has also exposed a potential limitation of today's encryption methods. The length of the encryption key is an indicator of the strength of the encryption method. For example, the original encryption key, DES (Data Encryption Standard), was 56 bits, meaning it had 2^56 combination possibilities. With today's computing power, a 56-bit key is no longer secure, being vulnerable to brute force attacks. Quantum computing uses properties of quantum mechanics in order to process large amounts of data simultaneously. Quantum computing has been found to achieve computing speeds thousands of times faster than today's supercomputers. This computing power presents a challenge to today's encryption technology. For example, RSA encryption uses the multiplication of very large prime numbers to create a semiprime number for its public key. Decoding this key without its private key requires this semiprime number to be factored, which can take a very long time to do with modern computers. It would take a supercomputer anywhere between weeks to months to factor in this key. However, quantum computing can use quantum algorithms to factor this semiprime number in the same amount of time it takes for normal computers to generate it. This would make all data protected by current public-key encryption vulnerable to quantum computing attacks. Other encryption techniques like elliptic curve cryptography and symmetric key encryption are also vulnerable to quantum computing.[citation needed] While quantum computing could be a threat to encryption security in the future, quantum computing as it currently stands is still very limited. Quantum computing currently is not commercially available, cannot handle large amounts of code, and only exists as computational devices, not computers. Furthermore, quantum computing advancements will be able to be used in favor of encryption as well. The National Security Agency (NSA) is currently preparing post-quantum encryption standards for the future. Quantum encryption promises a level of security that will be able to counter the threat of quantum computing. Attacks and countermeasures Encryption is an important tool but is not sufficient alone to ensure the security or privacy of sensitive information throughout its lifetime. Most applications of encryption protect information only at rest or in transit, leaving sensitive data in clear text and potentially vulnerable to improper disclosure during processing, such as by a cloud service for example. Homomorphic encryption and secure multi-party computation are emerging techniques to compute encrypted data; these techniques are general and Turing complete but incur high computational and/or communication costs. In response to encryption of data at rest, cyber-adversaries have developed new types of attacks. These more recent threats to encryption of data at rest include cryptographic attacks, stolen ciphertext attacks, attacks on encryption keys, insider attacks, data corruption or integrity attacks, data destruction attacks, and ransomware attacks. Data fragmentation and active defense data protection technologies attempt to counter some of these attacks, by distributing, moving, or mutating ciphertext so it is more difficult to identify, steal, corrupt, or destroy. The debate around encryption The question of balancing the need for national security with the right to privacy has been debated for years, since encryption has become critical in today's digital society. The modern encryption debate started around the '90s when US government tried to ban cryptography because, according to them, it would threaten national security. The debate is polarized around two opposing views. Those who see strong encryption as a problem making it easier for criminals to hide their illegal acts online and others who argue that encryption keep digital communications safe. The debate heated up in 2014, when Big Tech like Apple and Google set encryption by default in their devices. This was the start of a series of controversies that puts governments, companies and internet users at stake. Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to protect the integrity and authenticity of a message; for example, verification of a message authentication code (MAC) or a digital signature usually done by a hashing algorithm or a PGP signature. Authenticated encryption algorithms are designed to provide both encryption and integrity protection together. Standards for cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security may be a challenging problem. A single error in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See for example traffic analysis, TEMPEST, or Trojan horse. Integrity protection mechanisms such as MACs and digital signatures must be applied to the ciphertext when it is first created, typically on the same device used to compose the message, to protect a message end-to-end along its full transmission path; otherwise, any node between the sender and the encryption agent could potentially tamper with it. Encrypting at the time of creation is only secure if the encryption device itself has correct keys and has not been tampered with. If an endpoint device has been configured to trust a root certificate that an attacker controls, for example, then the attacker can both inspect and tamper with encrypted data by performing a man-in-the-middle attack anywhere along the message's path. The common practice of TLS interception by network operators represents a controlled and institutionally sanctioned form of such an attack, but countries have also attempted to employ such attacks as a form of control and censorship. Even when encryption effectively conceals a message’s content and prevents tampering, the length of the ciphertext remains a form of metadata that can leak sensitive information. For instance, the well-known CRIME and BREACH attacks against HTTPS exploited information leakage through encrypted message length as a side-channel attack. Traffic analysis more broadly refers to techniques that use metadata—such as message size and timing—to infer information about communication patterns. Applying padding to a message before encryption can help obscure its true plaintext length, though this increases the ciphertext size and adds bandwidth overhead. Padding may be applied randomly or deterministically, each approach involving different trade-offs. Encrypting and padding data to produce padded uniform random blobs (PURBs) ensures that the ciphertext reveals no metadata about the plaintext’s structure, leaking only asymptotically minimal O ( log log M ) {\displaystyle O(\log \log M)} information through its length. See also References Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/Python_(programming_language)#cite_note-tutorial-chapter1-182] | [TOKENS: 4314] |
Contents Python (programming language) Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. Python is dynamically type-checked and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural), object-oriented and functional programming. Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language. Python 3.0, released in 2008, was a major revision and not completely backward-compatible with earlier versions. Beginning with Python 3.5, capabilities and keywords for typing were added to the language, allowing optional static typing. As of 2026[update], the Python Software Foundation supports Python 3.10, 3.11, 3.12, 3.13, and 3.14, following the project's annual release cycle and five-year support policy. Python 3.15 is currently in the alpha development phase, and the stable release is expected to come out in October 2026. Earlier versions in the 3.x series have reached end-of-life and no longer receive security updates. Python has gained widespread use in the machine learning community. It is widely taught as an introductory programming language. Since 2003, Python has consistently ranked in the top ten of the most popular programming languages in the TIOBE Programming Community Index, which ranks based on searches in 24 platforms. History Python was conceived in the late 1980s by Guido van Rossum at Centrum Wiskunde & Informatica (CWI) in the Netherlands. It was designed as a successor to the ABC programming language, which was inspired by SETL, capable of exception handling and interfacing with the Amoeba operating system. Python implementation began in December 1989. Van Rossum first released it in 1991 as Python 0.9.0. Van Rossum assumed sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his "permanent vacation" from responsibilities as Python's "benevolent dictator for life" (BDFL); this title was bestowed on him by the Python community to reflect his long-term commitment as the project's chief decision-maker. (He has since come out of retirement and is self-titled "BDFL-emeritus".) In January 2019, active Python core developers elected a five-member Steering Council to lead the project. The name Python derives from the British comedy series Monty Python's Flying Circus. (See § Naming.) Python 2.0 was released on 16 October 2000, featuring many new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and Unicode support. Python 2.7's end-of-life was initially set for 2015, and then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3. It no longer receives security patches or updates. While Python 2.7 and older versions are officially unsupported, a different unofficial Python implementation, PyPy, continues to support Python 2, i.e., "2.7.18+" (plus 3.11), with the plus signifying (at least some) "backported security updates". Python 3.0 was released on 3 December 2008, and was a major revision and not completely backward-compatible with earlier versions, with some new semantics and changed syntax. Python 2.7.18, released in 2020, was the last release of Python 2. Several releases in the Python 3.x series have added new syntax to the language, and made a few (considered very minor) backward-incompatible changes. As of January 2026[update], Python 3.14.3 is the latest stable release. All older 3.x versions had a security update down to Python 3.9.24 then again with 3.9.25, the final version in 3.9 series. Python 3.10 is, since November 2025, the oldest supported branch. Python 3.15 has an alpha released, and Android has an official downloadable executable available for Python 3.14. Releases receive two years of full support followed by three years of security support. Design philosophy and features Python is a multi-paradigm programming language. Object-oriented programming and structured programming are fully supported, and many of their features support functional programming and aspect-oriented programming – including metaprogramming and metaobjects. Many other paradigms are supported via extensions, including design by contract and logic programming. Python is often referred to as a 'glue language' because it is purposely designed to be able to integrate components written in other languages. Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management. It uses dynamic name resolution (late binding), which binds method and variable names during program execution. Python's design offers some support for functional programming in the "Lisp tradition". It has filter, map, and reduce functions; list comprehensions, dictionaries, sets, and generator expressions. The standard library has two modules (itertools and functools) that implement functional tools borrowed from Haskell and Standard ML. Python's core philosophy is summarized in the Zen of Python (PEP 20) written by Tim Peters, which includes aphorisms such as these: However, Python has received criticism for violating these principles and adding unnecessary language bloat. Responses to these criticisms note that the Zen of Python is a guideline rather than a rule. The addition of some new features had been controversial: Guido van Rossum resigned as Benevolent Dictator for Life after conflict about adding the assignment expression operator in Python 3.8. Nevertheless, rather than building all functionality into its core, Python was designed to be highly extensible via modules. This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. Van Rossum's vision of a small core language with a large standard library and easily extensible interpreter stemmed from his frustrations with ABC, which represented the opposite approach. Python claims to strive for a simpler, less-cluttered syntax and grammar, while giving developers a choice in their coding methodology. Python lacks do .. while loops, which Rossum considered harmful. In contrast to Perl's motto "there is more than one way to do it", Python advocates an approach where "there should be one – and preferably only one – obvious way to do it". In practice, however, Python provides many ways to achieve a given goal. There are at least three ways to format a string literal, with no certainty as to which one a programmer should use. Alex Martelli is a Fellow at the Python Software Foundation and Python book author; he wrote that "To describe something as 'clever' is not considered a compliment in the Python culture." Python's developers typically prioritize readability over performance. For example, they reject patches to non-critical parts of the CPython reference implementation that would offer increases in speed that do not justify the cost of clarity and readability.[failed verification] Execution speed can be improved by moving speed-critical functions to extension modules written in languages such as C, or by using a just-in-time compiler like PyPy. Also, it is possible to transpile to other languages. However, this approach either fails to achieve the expected speed-up, since Python is a very dynamic language, or only a restricted subset of Python is compiled (with potential minor semantic changes). Python is meant to be a fun language to use. This goal is reflected in the name – a tribute to the British comedy group Monty Python – and in playful approaches to some tutorials and reference materials. For instance, some code examples use the terms "spam" and "eggs" (in reference to a Monty Python sketch), rather than the typical terms "foo" and "bar". A common neologism in the Python community is pythonic, which has a broad range of meanings related to program style: Pythonic code may use Python idioms well; be natural or show fluency in the language; or conform with Python's minimalist philosophy and emphasis on readability. Syntax and semantics Python is meant to be an easily readable language. Its formatting is visually uncluttered and often uses English keywords where other languages use punctuation. Unlike many other languages, it does not use curly brackets to delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases than C or Pascal. Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block. Thus, the program's visual structure accurately represents its semantic structure. This feature is sometimes termed the off-side rule. Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces. Python's statements include the following: The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type. This is called dynamic typing—in contrast to statically-typed languages, where each variable may contain only a value of a certain type. Python does not support tail call optimization or first-class continuations; according to Van Rossum, the language never will. However, better support for coroutine-like functionality is provided by extending Python's generators. Before 2.5, generators were lazy iterators; data was passed unidirectionally out of the generator. From Python 2.5 on, it is possible to pass data back into a generator function; and from version 3.3, data can be passed through multiple stack levels. Python's expressions include the following: In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp, Scheme, or Ruby. This distinction leads to duplicating some functionality, for example: A statement cannot be part of an expression; because of this restriction, expressions such as list and dict comprehensions (and lambda expressions) cannot contain statements. As a particular case, an assignment statement such as a = 1 cannot be part of the conditional expression of a conditional statement. Python uses duck typing, and it has typed objects but untyped variable names. Type constraints are not checked at definition time; rather, operations on an object may fail at usage time, indicating that the object is not of an appropriate type. Despite being dynamically typed, Python is strongly typed, forbidding operations that are poorly defined (e.g., adding a number and a string) rather than quietly attempting to interpret them. Python allows programmers to define their own types using classes, most often for object-oriented programming. New instances of classes are constructed by calling the class, for example, SpamClass() or EggsClass()); the classes are instances of the metaclass type (which is an instance of itself), thereby allowing metaprogramming and reflection. Before version 3.0, Python had two kinds of classes, both using the same syntax: old-style and new-style. Current Python versions support the semantics of only the new style. Python supports optional type annotations. These annotations are not enforced by the language, but may be used by external tools such as mypy to catch errors. Python includes a module typing including several type names for type annotations. Also, mypy supports a Python compiler called mypyc, which leverages type annotations for optimization. 1.33333 frozenset() Python includes conventional symbols for arithmetic operators (+, -, *, /), the floor-division operator //, and the modulo operator %. (With the modulo operator, a remainder can be negative, e.g., 4 % -3 == -2.) Also, Python offers the ** symbol for exponentiation, e.g. 5**3 == 125 and 9**0.5 == 3.0. Also, it offers the matrix‑multiplication operator @ . These operators work as in traditional mathematics; with the same precedence rules, the infix operators + and - can also be unary, to represent positive and negative numbers respectively. Division between integers produces floating-point results. The behavior of division has changed significantly over time: In Python terms, the / operator represents true division (or simply division), while the // operator represents floor division. Before version 3.0, the / operator represents classic division. Rounding towards negative infinity, though a different method than in most languages, adds consistency to Python. For instance, this rounding implies that the equation (a + b)//b == a//b + 1 is always true. Also, the rounding implies that the equation b*(a//b) + a%b == a is valid for both positive and negative values of a. As expected, the result of a%b lies in the half-open interval [0, b), where b is a positive integer; however, maintaining the validity of the equation requires that the result must lie in the interval (b, 0] when b is negative. Python provides a round function for rounding a float to the nearest integer. For tie-breaking, Python 3 uses the round to even method: round(1.5) and round(2.5) both produce 2. Python versions before 3 used the round-away-from-zero method: round(0.5) is 1.0, and round(-0.5) is −1.0. Python allows Boolean expressions that contain multiple equality relations to be consistent with general usage in mathematics. For example, the expression a < b < c tests whether a is less than b and b is less than c. C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c. Python uses arbitrary-precision arithmetic for all integer operations. The Decimal type/class in the decimal module provides decimal floating-point numbers to a pre-defined arbitrary precision with several rounding modes. The Fraction class in the fractions module provides arbitrary precision for rational numbers. Due to Python's extensive mathematics library and the third-party library NumPy, the language is frequently used for scientific scripting in tasks such as numerical data processing and manipulation. Functions are created in Python by using the def keyword. A function is defined similarly to how it is called, by first providing the function name and then the required parameters. Here is an example of a function that prints its inputs: To assign a default value to a function parameter in case no actual value is provided at run time, variable-definition syntax can be used inside the function header. Code examples "Hello, World!" program: Program to calculate the factorial of a non-negative integer: Libraries Python's large standard library is commonly cited as one of its greatest strengths. For Internet-facing applications, many standard formats and protocols such as MIME and HTTP are supported. The language includes modules for creating graphical user interfaces, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals, manipulating regular expressions, and unit testing. Some parts of the standard library are covered by specifications—for example, the Web Server Gateway Interface (WSGI) implementation wsgiref follows PEP 333—but most parts are specified by their code, internal documentation, and test suites. However, because most of the standard library is cross-platform Python code, only a few modules must be altered or rewritten for variant implementations. As of 13 March 2025,[update] the Python Package Index (PyPI), the official repository for third-party Python software, contains over 614,339 packages. Development environments Most[which?] Python implementations (including CPython) include a read–eval–print loop (REPL); this permits the environment to function as a command line interpreter, with which users enter statements sequentially and receive results immediately. Also, CPython is bundled with an integrated development environment (IDE) called IDLE, which is oriented toward beginners.[citation needed] Other shells, including IDLE and IPython, add additional capabilities such as improved auto-completion, session-state retention, and syntax highlighting. Standard desktop IDEs include PyCharm, Spyder, and Visual Studio Code; there are web browser-based IDEs, such as the following environments: Implementations CPython is the reference implementation of Python. This implementation is written in C, meeting the C11 standard since version 3.11. Older versions use the C89 standard with several select C99 features, but third-party extensions are not limited to older C versions—e.g., they can be implemented using C11 or C++. CPython compiles Python programs into an intermediate bytecode, which is then executed by a virtual machine. CPython is distributed with a large standard library written in a combination of C and native Python. CPython is available for many platforms, including Windows and most modern Unix-like systems, including macOS (and Apple M1 Macs, since Python 3.9.1, using an experimental installer). Starting with Python 3.9, the Python installer intentionally fails to install on Windows 7 and 8; Windows XP was supported until Python 3.5, with unofficial support for VMS. Platform portability was one of Python's earliest priorities. During development of Python 1 and 2, even OS/2 and Solaris were supported; since that time, support has been dropped for many platforms. All current Python versions (since 3.7) support only operating systems that feature multithreading, by now supporting not nearly as many operating systems (dropping many outdated) than in the past. All alternative implementations have at least slightly different semantics. For example, an alternative may include unordered dictionaries, in contrast to other current Python versions. As another example in the larger Python ecosystem, PyPy does not support the full C Python API. Creating an executable with Python often is done by bundling an entire Python interpreter into the executable, which causes binary sizes to be massive for small programs, yet there exist implementations that are capable of truly compiling Python. Alternative implementations include the following: Stackless Python is a significant fork of CPython that implements microthreads. This implementation uses the call stack differently, thus allowing massively concurrent programs. PyPy also offers a stackless version. Just-in-time Python compilers have been developed, but are now unsupported: There are several compilers/transpilers to high-level object languages; the source language is unrestricted Python, a subset of Python, or a language similar to Python: There are also specialized compilers: Some older projects existed, as well as compilers not designed for use with Python 3.x and related syntax: A performance comparison among various Python implementations, using a non-numerical (combinatorial) workload, was presented at EuroSciPy '13. In addition, Python's performance relative to other programming languages is benchmarked by The Computer Language Benchmarks Game. There are several approaches to optimizing Python performance, despite the inherent slowness of an interpreted language. These approaches include the following strategies or tools: Language Development Python's development is conducted mostly through the Python Enhancement Proposal (PEP) process; this process is the primary mechanism for proposing major new features, collecting community input on issues, and documenting Python design decisions. Python coding style is covered in PEP 8. Outstanding PEPs are reviewed and commented on by the Python community and the steering council. Enhancement of the language corresponds with development of the CPython reference implementation. The mailing list python-dev is the primary forum for the language's development. Specific issues were originally discussed in the Roundup bug tracker hosted by the foundation. In 2022, all issues and discussions were migrated to GitHub. Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to GitHub in January 2017. CPython's public releases have three types, distinguished by which part of the version number is incremented: Many alpha, beta, and release-candidates are also released as previews and for testing before final releases. Although there is a rough schedule for releases, they are often delayed if the code is not ready yet. Python's development team monitors the state of the code by running a large unit test suite during development. The major academic conference on Python is PyCon. Also, there are special Python mentoring programs, such as PyLadies. Naming Python's name is inspired by the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. Monty Python references appear frequently in Python code and culture; for example, the metasyntactic variables often used in Python literature are spam and eggs, rather than the traditional foo and bar. Also, the official Python documentation contains various references to Monty Python routines. Python users are sometimes referred to as "Pythonistas". Languages influenced by Python See also Notes References Further reading External links |
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Contents Black hole A black hole is an astronomical body so compact that its gravity prevents anything, including light, from escaping. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. The boundary of no escape is called the event horizon. In general relativity, a black hole's event horizon seals an object's fate but produces no locally detectable change when crossed. General relativity also predicts that every black hole should have a central singularity, where the curvature of spacetime is infinite. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly. Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. In 1916, Karl Schwarzschild found the first modern solution of general relativity that would characterise a black hole. Due to his influential research, the Schwarzschild metric is named after him. David Finkelstein, in 1958, first interpreted Schwarzschild's model as a region of space from which nothing can escape. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971. Black holes typically form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can grow by absorbing mass from its surroundings. Supermassive black holes of millions of solar masses may form by absorbing other stars and merging with other black holes, or via direct collapse of gas clouds. There is consensus that supermassive black holes exist in the centres of most galaxies. The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter falling toward a black hole can form an accretion disk of infalling plasma, heated by friction and emitting light. In extreme cases, this creates a quasar, some of the brightest objects in the universe. Merging black holes can also be detected by observation of the gravitational waves they emit. If other stars are orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses. History The idea of a body so massive that even light could not escape was first proposed in the late 18th century by English astronomer and clergyman John Michell and independently by French scientist Pierre-Simon Laplace. Both scholars proposed very large stars in contrast to the modern concept of an extremely dense object. Michell's idea, in a short part of a letter published in 1784, calculated that a star with the same density but 500 times the radius of the sun would not let any emitted light escape; the surface escape velocity would exceed the speed of light.: 122 Michell correctly hypothesized that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies. In 1796, Laplace mentioned that a star could be invisible if it were sufficiently large while speculating on the origin of the Solar System in his book Exposition du Système du Monde. Franz Xaver von Zach asked Laplace for a mathematical analysis, which Laplace provided and published in a journal edited by von Zach. In 1905, Albert Einstein showed that the laws of electromagnetism would be invariant under a Lorentz transformation: they would be identical for observers travelling at different velocities relative to each other. This discovery became known as the principle of special relativity. Although the laws of mechanics had already been shown to be invariant, gravity remained yet to be included.: 19 In 1907, Einstein published a paper proposing his equivalence principle, the hypothesis that inertial mass and gravitational mass have a common cause. Using the principle, Einstein predicted the redshift and half of the lensing effect of gravity on light; the full prediction of gravitational lensing required development of general relativity.: 19 By 1915, Einstein refined these ideas into his general theory of relativity, which explained how matter affects spacetime, which in turn affects the motion of other matter. This formed the basis for black hole physics. Only a few months after Einstein published the field equations describing general relativity, astrophysicist Karl Schwarzschild set out to apply the idea to stars. He assumed spherical symmetry with no spin and found a solution to Einstein's equations.: 124 A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution. At a certain radius from the center of the mass, the Schwarzschild solution became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this radius, which later became known as the Schwarzschild radius, was not understood at the time. Many physicists of the early 20th century were skeptical of the existence of black holes. In a 1926 popular science book, Arthur Eddington critiqued the idea of a star with mass compressed to its Schwarzschild radius as a flaw in the then-poorly-understood theory of general relativity.: 134 In 1939, Einstein himself used his theory of general relativity in an attempt to prove that black holes were impossible. His work relied on increasing pressure or increasing centrifugal force balancing the force of gravity so that the object would not collapse beyond its Schwarzschild radius. He missed the possibility that implosion would drive the system below this critical value.: 135 By the 1920s, astronomers had classified a number of white dwarf stars as too cool and dense to be explained by the gradual cooling of ordinary stars. In 1926, Ralph Fowler showed that quantum-mechanical degeneracy pressure was larger than thermal pressure at these densities.: 145 In 1931, Subrahmanyan Chandrasekhar calculated that a non-rotating body of electron-degenerate matter below a certain limiting mass is stable, and by 1934 he showed that this explained the catalog of white dwarf stars.: 151 When Chandrasekhar announced his results, Eddington pointed out that stars above this limit would radiate until they were sufficiently dense to prevent light from exiting, a conclusion he considered absurd. Eddington and, later, Lev Landau argued that some yet unknown mechanism would stop the collapse. In the 1930s, Fritz Zwicky and Walter Baade studied stellar novae, focusing on exceptionally bright ones they called supernovae. Zwicky promoted the idea that supernovae produced stars with the density of atomic nuclei—neutron stars—but this idea was largely ignored.: 171 In 1939, based on Chandrasekhar's reasoning, J. Robert Oppenheimer and George Volkoff predicted that neutron stars below a certain mass limit, later called the Tolman–Oppenheimer–Volkoff limit, would be stable due to neutron degeneracy pressure. Above that limit, they reasoned that either their model would not apply or that gravitational contraction would not stop.: 380 John Archibald Wheeler and two of his students resolved questions about the model behind the Tolman–Oppenheimer–Volkoff (TOV) limit. Harrison and Wheeler developed the equations of state relating density to pressure for cold matter all the way through electron degeneracy and neutron degeneracy. Masami Wakano and Wheeler then used the equations to compute the equilibrium curve for stars, relating mass to circumference. They found no additional features that would invalidate the TOV limit. This meant that the only thing that could prevent black holes from forming was a dynamic process ejecting sufficient mass from a star as it cooled.: 205 The modern concept of black holes was formulated by Robert Oppenheimer and his student Hartland Snyder in 1939.: 80 In the paper, Oppenheimer and Snyder solved Einstein's equations of general relativity for an idealized imploding star, in a model later called the Oppenheimer–Snyder model, then described the results from far outside the star. The implosion starts as one might expect: the star material rapidly collapses inward. However, as the density of the star increases, gravitational time dilation increases and the collapse, viewed from afar, seems to slow down further and further until the star reaches its Schwarzschild radius, where it appears frozen in time.: 217 In 1958, David Finkelstein identified the Schwarzschild surface as an event horizon, calling it "a perfect unidirectional membrane: causal influences can cross it in only one direction". In this sense, events that occur inside of the black hole cannot affect events that occur outside of the black hole. Finkelstein created a new reference frame to include the point of view of infalling observers.: 103 Finkelstein's new frame of reference allowed events at the surface of an imploding star to be related to events far away. By 1962 the two points of view were reconciled, convincing many skeptics that implosion into a black hole made physical sense.: 226 The era from the mid-1960s to the mid-1970s was the "golden age of black hole research", when general relativity and black holes became mainstream subjects of research.: 258 In this period, more general black hole solutions were found. In 1963, Roy Kerr found the exact solution for a rotating black hole. Two years later, Ezra Newman found the cylindrically symmetric solution for a black hole that is both rotating and electrically charged. In 1967, Werner Israel found that the Schwarzschild solution was the only possible solution for a nonspinning, uncharged black hole, meaning that a Schwarzschild black hole would be defined by its mass alone. Similar identities were later found for Reissner-Nordstrom and Kerr black holes, defined only by their mass and their charge or spin respectively. Together, these findings became known as the no-hair theorem, which states that a stationary black hole is completely described by the three parameters of the Kerr–Newman metric: mass, angular momentum, and electric charge. At first, it was suspected that the strange mathematical singularities found in each of the black hole solutions only appeared due to the assumption that a black hole would be perfectly spherically symmetric, and therefore the singularities would not appear in generic situations where black holes would not necessarily be symmetric. This view was held in particular by Vladimir Belinski, Isaak Khalatnikov, and Evgeny Lifshitz, who tried to prove that no singularities appear in generic solutions, although they would later reverse their positions. However, in 1965, Roger Penrose proved that general relativity without quantum mechanics requires that singularities appear in all black holes. Astronomical observations also made great strides during this era. In 1967, Antony Hewish and Jocelyn Bell Burnell discovered pulsars and by 1969, these were shown to be rapidly rotating neutron stars. Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities, but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse. Based on observations in Greenwich and Toronto in the early 1970s, Cygnus X-1, a galactic X-ray source discovered in 1964, became the first astronomical object commonly accepted to be a black hole. Work by James Bardeen, Jacob Bekenstein, Carter, and Hawking in the early 1970s led to the formulation of black hole thermodynamics. These laws describe the behaviour of a black hole in close analogy to the laws of thermodynamics by relating mass to energy, area to entropy, and surface gravity to temperature. The analogy was completed: 442 when Hawking, in 1974, showed that quantum field theory implies that black holes should radiate like a black body with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as Hawking radiation. While Cygnus X-1, a stellar-mass black hole, was generally accepted by the scientific community as a black hole by the end of 1973, it would be decades before a supermassive black hole would gain the same broad recognition. Although, as early as the 1960s, physicists such as Donald Lynden-Bell and Martin Rees had suggested that powerful quasars in the center of galaxies were powered by accreting supermassive black holes, little observational proof existed at the time. However, the Hubble Space Telescope, launched decades later, found that supermassive black holes were not only present in these active galactic nuclei, but that supermassive black holes in the center of galaxies were ubiquitous: Almost every galaxy had a supermassive black hole at its center, many of which were quiescent. In 1999, David Merritt proposed the M–sigma relation, which related the dispersion of the velocity of matter in the center bulge of a galaxy to the mass of the supermassive black hole at its core. Subsequent studies confirmed this correlation. Around the same time, based on telescope observations of the velocities of stars at the center of the Milky Way galaxy, independent work groups led by Andrea Ghez and Reinhard Genzel concluded that the compact radio source in the center of the galaxy, Sagittarius A*, was likely a supermassive black hole. On 11 February 2016, the LIGO Scientific Collaboration and Virgo Collaboration announced the first direct detection of gravitational waves, named GW150914, representing the first observation of a black hole merger. At the time of the merger, the black holes were approximately 1.4 billion light-years away from Earth and had masses of 30 and 35 solar masses.: 6 In 2017, Rainer Weiss, Kip Thorne, and Barry Barish, who had spearheaded the project, were awarded the Nobel Prize in Physics for their work. Since the initial discovery in 2015, hundreds more gravitational waves have been observed by LIGO and another interferometer, Virgo. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope (EHT) in 2017 of the supermassive black hole in Messier 87's galactic centre. In 2022, the Event Horizon Telescope collaboration released an image of the black hole in the center of the Milky Way galaxy, Sagittarius A*; The data had been collected in 2017. In 2020, the Nobel Prize in Physics was awarded for work on black holes. Andrea Ghez and Reinhard Genzel shared one-half for their discovery that Sagittarius A* is a supermassive black hole. Penrose received the other half for his work showing that the mathematics of general relativity requires the formation of black holes. Cosmologists lamented that Hawking's extensive theoretical work on black holes would not be honored since he died in 2018. In December 1967, a student reportedly suggested the phrase black hole at a lecture by John Wheeler; Wheeler adopted the term for its brevity and "advertising value", and Wheeler's stature in the field ensured it quickly caught on, leading some to credit Wheeler with coining the phrase. However, the term was used by others around that time. Science writer Marcia Bartusiak traces the term black hole to physicist Robert H. Dicke, who in the early 1960s reportedly compared the phenomenon to the Black Hole of Calcutta, notorious as a prison where people entered but never left alive. The term was used in print by Life and Science News magazines in 1963, and by science journalist Ann Ewing in her article "'Black Holes' in Space", dated 18 January 1964, which was a report on a meeting of the American Association for the Advancement of Science held in Cleveland, Ohio. Definition A black hole is generally defined as a region of spacetime from which no information-carrying signals or objects can escape. However, verifying an object as a black hole by this definition would require waiting for an infinite time and at an infinite distance from the black hole to verify that indeed, nothing has escaped, and thus cannot be used to identify a physical black hole. Broadly, physicists do not have a precisely-agreed-upon definition of a black hole. Among astrophysicists, a black hole is a compact object with a mass larger than four solar masses. A black hole may also be defined as a reservoir of information: 142 or a region where space is falling inwards faster than the speed of light. Properties The no-hair theorem postulates that, once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, electric charge, and angular momentum; the black hole is otherwise featureless. If the conjecture is true, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another. The degree to which the conjecture is true for real black holes is currently an unsolved problem. The simplest static black holes have mass but neither electric charge nor angular momentum. According to Birkhoff's theorem, these Schwarzschild black holes are the only vacuum solution that is spherically symmetric. Solutions describing more general black holes also exist. Non-rotating charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a non-charged rotating black hole. The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum. The simplest static black holes have mass but neither electric charge nor angular momentum. Contrary to the popular notion of a black hole "sucking in everything" in its surroundings, from far away, the external gravitational field of a black hole is identical to that of any other body of the same mass. While a black hole can theoretically have any positive mass, the charge and angular momentum are constrained by the mass. The total electric charge Q and the total angular momentum J are expected to satisfy the inequality Q 2 4 π ϵ 0 + c 2 J 2 G M 2 ≤ G M 2 {\displaystyle {\frac {Q^{2}}{4\pi \epsilon _{0}}}+{\frac {c^{2}J^{2}}{GM^{2}}}\leq GM^{2}} for a black hole of mass M. Black holes with the maximum possible charge or spin satisfying this inequality are called extremal black holes. Solutions of Einstein's equations that violate this inequality exist, but they do not possess an event horizon. These are so-called naked singularities that can be observed from the outside. Because these singularities make the universe inherently unpredictable, many physicists believe they could not exist. The weak cosmic censorship hypothesis, proposed by Sir Roger Penrose, rules out the formation of such singularities, when they are created through the gravitational collapse of realistic matter. However, this theory has not yet been proven, and some physicists believe that naked singularities could exist. It is also unknown whether black holes could even become extremal, forming naked singularities, since natural processes counteract increasing spin and charge when a black hole becomes near-extremal. The total mass of a black hole can be estimated by analyzing the motion of objects near the black hole, such as stars or gas. All black holes spin, often fast—One supermassive black hole, GRS 1915+105 has been estimated to spin at over 1,000 revolutions per second. The Milky Way's central black hole Sagittarius A* rotates at about 90% of the maximum rate. The spin rate can be inferred from measurements of atomic spectral lines in the X-ray range. As gas near the black hole plunges inward, high energy X-ray emission from electron-positron pairs illuminates the gas further out, appearing red-shifted due to relativistic effects. Depending on the spin of the black hole, this plunge happens at different radii from the hole, with different degrees of redshift. Astronomers can use the gap between the x-ray emission of the outer disk and the redshifted emission from plunging material to determine the spin of the black hole. A newer way to estimate spin is based on the temperature of gasses accreting onto the black hole. The method requires an independent measurement of the black hole mass and inclination angle of the accretion disk followed by computer modeling. Gravitational waves from coalescing binary black holes can also provide the spin of both progenitor black holes and the merged hole, but such events are rare. A spinning black hole has angular momentum. The supermassive black hole in the center of the Messier 87 (M87) galaxy appears to have an angular momentum very close to the maximum theoretical value. That uncharged limit is J ≤ G M 2 c , {\displaystyle J\leq {\frac {GM^{2}}{c}},} allowing definition of a dimensionless spin magnitude such that 0 ≤ c J G M 2 ≤ 1. {\displaystyle 0\leq {\frac {cJ}{GM^{2}}}\leq 1.} Most black holes are believed to have an approximately neutral charge. For example, Michal Zajaček, Arman Tursunov, Andreas Eckart, and Silke Britzen found the electric charge of Sagittarius A* to be at least ten orders of magnitude below the theoretical maximum. A charged black hole repels other like charges just like any other charged object. If a black hole were to become charged, particles with an opposite sign of charge would be pulled in by the extra electromagnetic force, while particles with the same sign of charge would be repelled, neutralizing the black hole. This effect may not be as strong if the black hole is also spinning. The presence of charge can reduce the diameter of the black hole by up to 38%. The charge Q for a nonspinning black hole is bounded by Q ≤ G M , {\displaystyle Q\leq {\sqrt {G}}M,} where G is the gravitational constant and M is the black hole's mass. Classification Black holes can have a wide range of masses. The minimum mass of a black hole formed by stellar gravitational collapse is governed by the maximum mass of a neutron star and is believed to be approximately two-to-four solar masses. However, theoretical primordial black holes, believed to have formed soon after the Big Bang, could be far smaller, with masses as little as 10−5 grams at formation. These very small black holes are sometimes called micro black holes. Black holes formed by stellar collapse are called stellar black holes. Estimates of their maximum mass at formation vary, but generally range from 10 to 100 solar masses, with higher estimates for black holes progenated by low-metallicity stars. The mass of a black hole formed via a supernova has a lower bound: If the progenitor star is too small, the collapse may be stopped by the degeneracy pressure of the star's constituents, allowing the condensation of matter into an exotic denser state. Degeneracy pressure occurs from the Pauli exclusion principle—Particles will resist being in the same place as each other. Smaller progenitor stars, with masses less than about 8 M☉, will be held together by the degeneracy pressure of electrons and will become a white dwarf. For more massive progenitor stars, electron degeneracy pressure is no longer strong enough to resist the force of gravity and the star will be held together by neutron degeneracy pressure, which can occur at much higher densities, forming a neutron star. If the star is still too massive, even neutron degeneracy pressure will not be able to resist the force of gravity and the star will collapse into a black hole.: 5.8 Stellar black holes can also gain mass via accretion of nearby matter, often from a companion object such as a star. Black holes that are larger than stellar black holes but smaller than supermassive black holes are called intermediate-mass black holes, with masses of approximately 102 to 105 solar masses. These black holes seem to be rarer than their stellar and supermassive counterparts, with relatively few candidates having been observed. Physicists have speculated that such black holes may form from collisions in globular and star clusters or at the center of low-mass galaxies. They may also form as the result of mergers of smaller black holes, with several LIGO observations finding merged black holes within the 110-350 solar mass range. The black holes with the largest masses are called supermassive black holes, with masses more than 106 times that of the Sun. These black holes are believed to exist at the centers of almost every large galaxy, including the Milky Way. Some scientists have proposed a subcategory of even larger black holes, called ultramassive black holes, with masses greater than 109-1010 solar masses. Theoretical models predict that the accretion disc that feeds black holes will be unstable once a black hole reaches 50-100 billion times the mass of the Sun, setting a rough upper limit to black hole mass. Structure While black holes are conceptually invisible sinks of all matter and light, in astronomical settings, their enormous gravity alters the motion of surrounding objects and pulls nearby gas inwards at near-light speed, making the area around black holes the brightest objects in the universe. Some black holes have relativistic jets—thin streams of plasma travelling away from the black hole at more than one-tenth of the speed of light. A small faction of the matter falling towards the black hole gets accelerated away along the hole rotation axis. These jets can extend as far as millions of parsecs from the black hole itself. Black holes of any mass can have jets. However, they are typically observed around spinning black holes with strongly-magnetized accretion disks. Relativistic jets were more common in the early universe, when galaxies and their corresponding supermassive black holes were rapidly gaining mass. All black holes with jets also have an accretion disk, but the jets are usually brighter than the disk. Quasars, typically found in other galaxies, are believed to be supermassive black holes with jets; microquasars are believed to be stellar-mass objects with jets, typically observed in the Milky Way. The mechanism of formation of jets is not yet known, but several options have been proposed. One method proposed to fuel these jets is the Blandford-Znajek process, which suggests that the dragging of magnetic field lines by a black hole's rotation could launch jets of matter into space. The Penrose process, which involves extraction of a black hole's rotational energy, has also been proposed as a potential mechanism of jet propulsion. Due to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disk-like structure around the object.: 242 As the disk's angular momentum is transferred outward due to internal processes, its matter falls farther inward, converting its gravitational energy into heat and releasing a large flux of x-rays. The temperature of these disks can range from thousands to millions of Kelvin, and temperatures can differ throughout a single accretion disk. Accretion disks can also emit in other parts of the electromagnetic spectrum, depending on the disk's turbulence and magnetization and the black hole's mass and angular momentum. Accretion disks can be defined as geometrically thin or geometrically thick. Geometrically thin disks are mostly confined to the black hole's equatorial plane and have a well-defined edge at the innermost stable circular orbit (ISCO), while geometrically thick disks are supported by internal pressure and temperature and can extend inside the ISCO. Disks with high rates of electron scattering and absorption, appearing bright and opaque, are called optically thick; optically thin disks are more translucent and produce fainter images when viewed from afar. Accretion disks of black holes accreting beyond the Eddington limit are often referred to as polish donuts due to their thick, toroidal shape that resembles that of a donut. Quasar accretion disks are expected to usually appear blue in color. The disk for a stellar black hole, on the other hand, would likely look orange, yellow, or red, with its inner regions being the brightest. Theoretical research suggests that the hotter a disk is, the bluer it should be, although this is not always supported by observations of real astronomical objects. Accretion disk colors may also be altered by the Doppler effect, with the part of the disk travelling towards an observer appearing bluer and brighter and the part of the disk travelling away from the observer appearing redder and dimmer. In Newtonian gravity, test particles can stably orbit at arbitrary distances from a central object. In general relativity, however, there exists a smallest possible radius for which a massive particle can orbit stably. Any infinitesimal inward perturbations to this orbit will lead to the particle spiraling into the black hole, and any outward perturbations will, depending on the energy, cause the particle to spiral in, move to a stable orbit further from the black hole, or escape to infinity. This orbit is called the innermost stable circular orbit, or ISCO. The location of the ISCO depends on the spin of the black hole and the spin of the particle itself. In the case of a Schwarzschild black hole (spin zero) and a particle without spin, the location of the ISCO is: r I S C O = 3 r s = 6 G M c 2 , {\displaystyle r_{\rm {ISCO}}=3\,r_{\text{s}}={\frac {6\,GM}{c^{2}}},} where r I S C O {\displaystyle r_{\rm {_{ISCO}}}} is the radius of the ISCO, r s {\displaystyle r_{\text{s}}} is the Schwarzschild radius of the black hole, G {\displaystyle G} is the gravitational constant, and c {\displaystyle c} is the speed of light. The radius of this orbit changes slightly based on particle spin. For charged black holes, the ISCO moves inwards. For spinning black holes, the ISCO is moved inwards for particles orbiting in the same direction that the black hole is spinning (prograde) and outwards for particles orbiting in the opposite direction (retrograde). For example, the ISCO for a particle orbiting retrograde can be as far out as about 9 r s {\displaystyle 9r_{\text{s}}} , while the ISCO for a particle orbiting prograde can be as close as at the event horizon itself. The photon sphere is a spherical boundary for which photons moving on tangents to that sphere are bent completely around the black hole, possibly orbiting multiple times. Light rays with impact parameters less than the radius of the photon sphere enter the black hole. For Schwarzschild black holes, the photon sphere has a radius 1.5 times the Schwarzschild radius; the radius for non-Schwarzschild black holes is at least 1.5 times the radius of the event horizon. When viewed from a great distance, the photon sphere creates an observable black hole shadow. Since no light emerges from within the black hole, this shadow is the limit for possible observations.: 152 The shadow of colliding black holes should have characteristic warped shapes, allowing scientists to detect black holes that are about to merge. While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Therefore, any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon. Light emitted towards the photon sphere may also curve around the black hole and return to the emitter. For a rotating, uncharged black hole, the radius of the photon sphere depends on the spin parameter and whether the photon is orbiting prograde or retrograde. For a photon orbiting prograde, the photon sphere will be 1-3 Schwarzschild radii from the center of the black hole, while for a photon orbiting retrograde, the photon sphere will be between 3-5 Schwarzschild radii from the center of the black hole. The exact location of the photon sphere depends on the magnitude of the black hole's rotation. For a charged, nonrotating black hole, there will only be one photon sphere, and the radius of the photon sphere will decrease for increasing black hole charge. For non-extremal, charged, rotating black holes, there will always be two photon spheres, with the exact radii depending on the parameters of the black hole. Near a rotating black hole, spacetime rotates similar to a vortex. The rotating spacetime will drag any matter and light into rotation around the spinning black hole. This effect of general relativity, called frame dragging, gets stronger closer to the spinning mass. The region of spacetime in which it is impossible to stay still is called the ergosphere. The ergosphere of a black hole is a volume bounded by the black hole's event horizon and the ergosurface, which coincides with the event horizon at the poles but bulges out from it around the equator. Matter and radiation can escape from the ergosphere. Through the Penrose process, objects can emerge from the ergosphere with more energy than they entered with. The extra energy is taken from the rotational energy of the black hole, slowing down the rotation of the black hole.: 268 A variation of the Penrose process in the presence of strong magnetic fields, the Blandford–Znajek process, is considered a likely mechanism for the enormous luminosity and relativistic jets of quasars and other active galactic nuclei. The observable region of spacetime around a black hole closest to its event horizon is called the plunging region. In this area it is no longer possible for free falling matter to follow circular orbits or stop a final descent into the black hole. Instead, it will rapidly plunge toward the black hole at close to the speed of light, growing increasingly hot and producing a characteristic, detectable thermal emission. However, light and radiation emitted from this region can still escape from the black hole's gravitational pull. For a nonspinning, uncharged black hole, the radius of the event horizon, or Schwarzschild radius, is proportional to the mass, M, through r s = 2 G M c 2 ≈ 2.95 M M ⊙ k m , {\displaystyle r_{\mathrm {s} }={\frac {2GM}{c^{2}}}\approx 2.95\,{\frac {M}{M_{\odot }}}~\mathrm {km,} } where rs is the Schwarzschild radius and M☉ is the mass of the Sun.: 124 For a black hole with nonzero spin or electric charge, the radius is smaller,[Note 1] until an extremal black hole could have an event horizon close to r + = G M c 2 , {\displaystyle r_{\mathrm {+} }={\frac {GM}{c^{2}}},} half the radius of a nonspinning, uncharged black hole of the same mass. Since the volume within the Schwarzschild radius increase with the cube of the radius, average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass: supermassive black holes are much less dense than stellar black holes. The average density of a 108 M☉ black hole is comparable to that of water. The defining feature of a black hole is the existence of an event horizon, a boundary in spacetime through which matter and light can pass only inward towards the center of the black hole. Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach or affect an outside observer, making it impossible to determine whether such an event occurred.: 179 For non-rotating black holes, the geometry of the event horizon is precisely spherical, while for rotating black holes, the event horizon is oblate. To a distant observer, a clock near a black hole would appear to tick more slowly than one further from the black hole.: 217 This effect, known as gravitational time dilation, would also cause an object falling into a black hole to appear to slow as it approached the event horizon, never quite reaching the horizon from the perspective of an outside observer.: 218 All processes on this object would appear to slow down, and any light emitted by the object to appear redder and dimmer, an effect known as gravitational redshift. An object falling from half of a Schwarzschild radius above the event horizon would fade away until it could no longer be seen, disappearing from view within one hundredth of a second. It would also appear to flatten onto the black hole, joining all other material that had ever fallen into the hole. On the other hand, an observer falling into a black hole would not notice any of these effects as they cross the event horizon. Their own clocks appear to them to tick normally, and they cross the event horizon after a finite time without noting any singular behaviour. In general relativity, it is impossible to determine the location of the event horizon from local observations, due to Einstein's equivalence principle.: 222 Black holes that are rotating and/or charged have an inner horizon, often called the Cauchy horizon, inside of the black hole. The inner horizon is divided up into two segments: an ingoing section and an outgoing section. At the ingoing section of the Cauchy horizon, radiation and matter that fall into the black hole would build up at the horizon, causing the curvature of spacetime to go to infinity. This would cause an observer falling in to experience tidal forces. This phenomenon is often called mass inflation, since it is associated with a parameter dictating the black hole's internal mass growing exponentially, and the buildup of tidal forces is called the mass-inflation singularity or Cauchy horizon singularity. Some physicists have argued that in realistic black holes, accretion and Hawking radiation would stop mass inflation from occurring. At the outgoing section of the inner horizon, infalling radiation would backscatter off of the black hole's spacetime curvature and travel outward, building up at the outgoing Cauchy horizon. This would cause an infalling observer to experience a gravitational shock wave and tidal forces as the spacetime curvature at the horizon grew to infinity. This buildup of tidal forces is called the shock singularity. Both of these singularities are weak, meaning that an object crossing them would only be deformed a finite amount by tidal forces, even though the spacetime curvature would still be infinite at the singularity. This is as opposed to a strong singularity, where an object hitting the singularity would be stretched and squeezed by an infinite amount. They are also null singularities, meaning that a photon could travel parallel to the them without ever being intercepted. Ignoring quantum effects, every black hole has a singularity inside, points where the curvature of spacetime becomes infinite, and geodesics terminate within a finite proper time.: 205 For a non-rotating black hole, this region takes the shape of a single point; for a rotating black hole it is smeared out to form a ring singularity that lies in the plane of rotation.: 264 In both cases, the singular region has zero volume. All of the mass of the black hole ends up in the singularity.: 252 Since the singularity has nonzero mass in an infinitely small space, it can be thought of as having infinite density. Observers falling into a Schwarzschild black hole (i.e., non-rotating and not charged) cannot avoid being carried into the singularity once they cross the event horizon. As they fall further into the black hole, they will be torn apart by the growing tidal forces in a process sometimes referred to as spaghettification or the noodle effect. Eventually, they will reach the singularity and be crushed into an infinitely small point.: 182 However any perturbations, such as those caused by matter or radiation falling in, would cause space to oscillate chaotically near the singularity. Any matter falling in would experience intense tidal forces rapidly changing in direction, all while being compressed into an increasingly small volume. Alternative forms of general relativity, including addition of some quatum effects, can lead to regular, or nonsingular, black holes without singularities. For example, the fuzzball model, based on string theory, states that black holes are actually made up of quantum microstates and need not have a singularity or an event horizon. The theory of loop quantum gravity proposes that the curvature and density at the center of a black hole is large, but not infinite. Formation Black holes are formed by gravitational collapse of massive stars, either by direct collapse or during a supernova explosion in a process called fallback. Black holes can result from the merger of two neutron stars or a neutron star and a black hole. Other more speculative mechanisms include primordial black holes created from density fluctuations in the early universe, the collapse of dark stars, a hypothetical object powered by annihilation of dark matter, or from hypothetical self-interacting dark matter. Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. At the end of a star's life, it will run out of hydrogen to fuse, and will start fusing more and more massive elements, until it gets to iron. Since the fusion of elements heavier than iron would require more energy than it would release, nuclear fusion ceases. If the iron core of the star is too massive, the star will no longer be able to support itself and will undergo gravitational collapse. While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the reference frame of infalling matter, a distant observer would see the infalling material slow and halt just above the event horizon, due to gravitational time dilation. Light from the collapsing material takes longer and longer to reach the observer, with the delay growing to infinity as the emitting material reaches the event horizon. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away. Observations of quasars at redshift z ∼ 7 {\displaystyle z\sim 7} , less than a billion years after the Big Bang, has led to investigations of other ways to form black holes. The accretion process to build supermassive black holes has a limiting rate of mass accumulation and a billion years is not enough time to reach quasar status. One suggestion is direct collapse of nearly pure hydrogen gas (low metalicity) clouds characteristic of the young universe, forming a supermassive star which collapses into a black hole. It has been suggested that seed black holes with typical masses of ~105 M☉ could have formed in this way which then could grow to ~109 M☉. However, the very large amount of gas required for direct collapse is not typically stable to fragmentation to form multiple stars. Thus another approach suggests massive star formation followed by collisions that seed massive black holes which ultimately merge to create a quasar.: 85 A neutron star in a common envelope with a regular star can accrete sufficient material to collapse to a black hole or two neutron stars can merge. These avenues for the formation of black holes are considered relatively rare. In the current epoch of the universe, conditions needed to form black holes are rare and are mostly only found in stars. However, in the early universe, conditions may have allowed for black hole formations via other means. Fluctuations of spacetime soon after the Big Bang may have formed areas that were denser then their surroundings. Initially, these regions would not have been compact enough to form a black hole, but eventually, the curvature of spacetime in the regions become large enough to cause them to collapse into a black hole. Different models for the early universe vary widely in their predictions of the scale of these fluctuations. Various models predict the creation of primordial black holes ranging from a Planck mass (~2.2×10−8 kg) to hundreds of thousands of solar masses. Primordial black holes with masses less than 1015 g would have evaporated by now due to Hawking radiation. Despite the early universe being extremely dense, it did not re-collapse into a black hole during the Big Bang, since the universe was expanding rapidly and did not have the gravitational differential necessary for black hole formation. Models for the gravitational collapse of objects of relatively constant size, such as stars, do not necessarily apply in the same way to rapidly expanding space such as the Big Bang. In principle, black holes could be formed in high-energy particle collisions that achieve sufficient density, although no such events have been detected. These hypothetical micro black holes, which could form from the collision of cosmic rays and Earth's atmosphere or in particle accelerators like the Large Hadron Collider, would not be able to aggregate additional mass. Instead, they would evaporate in about 10−25 seconds, posing no threat to the Earth. Evolution Black holes can also merge with other objects such as stars or even other black holes. This is thought to have been important, especially in the early growth of supermassive black holes, which could have formed from the aggregation of many smaller objects. The process has also been proposed as the origin of some intermediate-mass black holes. Mergers of supermassive black holes may take a long time: As a binary of supermassive black holes approach each other, most nearby stars are ejected, leaving little for the remaining black holes to gravitationally interact with that would allow them to get closer to each other. This phenomenon has been called the final parsec problem, as the distance at which this happens is usually around one parsec. When a black hole accretes matter, the gas in the inner accretion disk orbits at very high speeds because of its proximity to the black hole. The resulting friction heats the inner disk to temperatures at which it emits vast amounts of electromagnetic radiation (mainly X-rays) detectable by telescopes. By the time the matter of the disk reaches the ISCO, between 5.7% and 42% of its mass will have been converted to energy, depending on the black hole's spin. About 90% of this energy is released within about 20 black hole radii. In many cases, accretion disks are accompanied by relativistic jets that are emitted along the black hole's poles, which carry away much of the energy. The mechanism for the creation of these jets is currently not well understood, in part due to insufficient data. Many of the universe's most energetic phenomena have been attributed to the accretion of matter on black holes. Active galactic nuclei and quasars are believed to be the accretion disks of supermassive black holes. X-ray binaries are generally accepted to be binary systems in which one of the two objects is a compact object accreting matter from its companion. Ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes. At a certain rate of accretion, the outward radiation pressure will become as strong as the inward gravitational force, and the black hole should unable to accrete any faster. This limit is called the Eddington limit. However, many black holes accrete beyond this rate due to their non-spherical geometry or instabilities in the accretion disk. Accretion beyond the limit is called Super-Eddington accretion and may have been commonplace in the early universe. Stars have been observed to get torn apart by tidal forces in the immediate vicinity of supermassive black holes in galaxy nuclei, in what is known as a tidal disruption event (TDE). Some of the material from the disrupted star forms an accretion disk around the black hole, which emits observable electromagnetic radiation. The correlation between the masses of supermassive black holes in the centres of galaxies with the velocity dispersion and mass of stars in their host bulges suggests that the formation of galaxies and the formation of their central black holes are related. Black hole winds from rapid accretion, particularly when the galaxy itself is still accreting matter, can compress gas nearby, accelerating star formation. However, if the winds become too strong, the black hole may blow nearly all of the gas out of the galaxy, quenching star formation. Black hole jets may also energize nearby cavities of plasma and eject low-entropy gas from out of the galactic core, causing gas in galactic centers to be hotter than expected. If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time as they lose mass by the emission of photons and other particles. The temperature of this thermal spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which is inversely proportional to the mass. Hence, large black holes emit less radiation than small black holes.: Ch. 9.6 A stellar black hole of 1 M☉ has a Hawking temperature of 62 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrinking. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the Moon. Such a black hole would have a diameter of less than a tenth of a millimetre. The Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth. A possible exception is the burst of gamma rays emitted in the last stage of the evaporation of primordial black holes. Searches for such flashes have proven unsuccessful and provide stringent limits on the possibility of existence of low mass primordial black holes, with modern research predicting that primordial black holes must make up less than a fraction of 10−7 of the universe's total mass. NASA's Fermi Gamma-ray Space Telescope, launched in 2008, has searched for these flashes, but has not yet found any. The properties of a black hole are constrained and interrelated by the theories that predict these properties. When based on general relativity, these relationships are called the laws of black hole mechanics. For a black hole that is not still forming or accreting matter, the zeroth law of black hole mechanics states the black hole's surface gravity is constant across the event horizon. The first law relates changes in the black hole's surface area, angular momentum, and charge to changes in its energy. The second law says the surface area of a black hole never decreases on its own. Finally, the third law says that the surface gravity of a black hole is never zero. These laws are mathematical analogs of the laws of thermodynamics. They are not equivalent, however, because, according to general relativity without quantum mechanics, a black hole can never emit radiation, and thus its temperature must always be zero.: 11 Quantum mechanics predicts that a black hole will continuously emit thermal Hawking radiation, and therefore must always have a nonzero temperature. It also predicts that all black holes have entropy which scales with their surface area. When quantum mechanics is accounted for, the laws of black hole mechanics become equivalent to the classical laws of thermodynamics. However, these conclusions are derived without a complete theory of quantum gravity, although many potential theories do predict black holes having entropy and temperature. Thus, the true quantum nature of black hole thermodynamics continues to be debated.: 29 Observational evidence Millions of black holes with around 30 solar masses derived from stellar collapse are expected to exist in the Milky Way. Even a dwarf galaxy like Draco should have hundreds. Only a few of these have been detected. By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. The defining characteristic of a black hole is its event horizon. The horizon itself cannot be imaged, so all other possible explanations for these indirect observations must be considered and eliminated before concluding that a black hole has been observed.: 11 The Event Horizon Telescope (EHT) is a global system of radio telescopes capable of directly observing a black hole shadow. The angular resolution of a telescope is based on its aperture and the wavelengths it is observing. Because the angular diameters of Sagittarius A* and Messier 87* in the sky are very small, a single telescope would need to be about the size of the Earth to clearly distinguish their horizons using radio wavelengths. By combining data from several different radio telescopes around the world, the Event Horizon Telescope creates an effective aperture the diameter size of the Earth. The EHT team used imaging algorithms to compute the most probable image from the data in its observations of Sagittarius A* and M87*. Gravitational-wave interferometry can be used to detect merging black holes and other compact objects. In this method, a laser beam is split down two long arms of a tunnel. The laser beams reflect off of mirrors in the tunnels and converge at the intersection of the arms, cancelling each other out. However, when a gravitational wave passes, it warps spacetime, changing the lengths of the arms themselves. Since each laser beam is now travelling a slightly different distance, they do not cancel out and produce a recognizable signal. Analysis of the signal can give scientists information about what caused the gravitational waves. Since gravitational waves are very weak, gravitational-wave observatories such as LIGO must have arms several kilometers long and carefully control for noise from Earth to be able to detect these gravitational waves. Since the first measurements in 2016, multiple gravitational waves from black holes have been detected and analyzed. The proper motions of stars near the centre of the Milky Way provide strong observational evidence that these stars are orbiting a supermassive black hole. Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source Sagittarius A*. In 1998, by fitting the motions of the stars to Keplerian orbits, the astronomers were able to infer that Sagittarius A* must be a 2.6×106 M☉ object must be contained within a radius of 0.02 light-years. Since then, one of the stars—called S2—has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass of Sagittarius A* to 4.3×106 M☉, with a radius of less than 0.002 light-years. This upper limit radius is larger than the Schwarzschild radius for the estimated mass, so the combination does not prove Sagittarius A* is a black hole. Nevertheless, these observations strongly suggest that the central object is a supermassive black hole as there are no other plausible scenarios for confining so much invisible mass into such a small volume. Additionally, there is some observational evidence that this object might possess an event horizon, a feature unique to black holes. The Event Horizon Telescope image of Sagittarius A*, released in 2022, provided further confirmation that it is indeed a black hole. X-ray binaries are binary systems that emit a majority of their radiation in the X-ray part of the electromagnetic spectrum. These X-ray emissions result when a compact object accretes matter from an ordinary star. The presence of an ordinary star in such a system provides an opportunity for studying the central object and to determine if it might be a black hole. By measuring the orbital period of the binary, the distance to the binary from Earth, and the mass of the companion star, scientists can estimate the mass of the compact object. The Tolman-Oppenheimer-Volkoff limit (TOV limit) dictates the largest mass a nonrotating neutron star can be, and is estimated to be about two solar masses. While a rotating neutron star can be slightly more massive, if the compact object is much more massive than the TOV limit, it cannot be a neutron star and is generally expected to be a black hole. The first strong candidate for a black hole, Cygnus X-1, was discovered in this way by Charles Thomas Bolton, Louise Webster, and Paul Murdin in 1972. Observations of rotation broadening of the optical star reported in 1986 lead to a compact object mass estimate of 16 solar masses, with 7 solar masses as the lower bound. In 2011, this estimate was updated to 14.1±1.0 M☉ for the black hole and 19.2±1.9 M☉ for the optical stellar companion. X-ray binaries can be categorized as either low-mass or high-mass; This classification is based on the mass of the companion star, not the compact object itself. In a class of X-ray binaries called soft X-ray transients, the companion star is of relatively low mass, allowing for more accurate estimates of the black hole mass. These systems actively emit X-rays for only several months once every 10–50 years. During the period of low X-ray emission, called quiescence, the accretion disk is extremely faint, allowing detailed observation of the companion star. Numerous black hole candidates have been measured by this method. Black holes are also sometimes found in binaries with other compact objects, such as white dwarfs, neutron stars, and other black holes. The centre of nearly every galaxy contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M–sigma relation, strongly suggests a connection between the formation of the black hole and that of the galaxy itself. Astronomers use the term active galaxy to describe galaxies with unusual characteristics, such as unusual spectral line emission and very strong radio emission. Theoretical and observational studies have shown that the high levels of activity in the centers of these galaxies, regions called active galactic nuclei (AGN), may be explained by accretion onto supermassive black holes. These AGN consist of a central black hole that may be millions or billions of times more massive than the Sun, a disk of interstellar gas and dust called an accretion disk, and two jets perpendicular to the accretion disk. Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, Messier 32, Messier 87, the Sombrero Galaxy, and the Milky Way itself. Another way black holes can be detected is through observation of effects caused by their strong gravitational field. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected, making objects behind them appear distorted. When the lensing object is a black hole, this effect can be strong enough to create multiple images of a star or other luminous source. However, the distance between the lensed images may be too small for contemporary telescopes to resolve—this phenomenon is called microlensing. Instead of seeing two images of a lensed star, astronomers see the star brighten slightly as the black hole moves towards the line of sight between the star and Earth and then return to its normal luminosity as the black hole moves away. The turn of the millennium saw the first 3 candidate detections of black holes in this way, and in January 2022, astronomers reported the first confirmed detection of a microlensing event from an isolated black hole. This was also the first determination of an isolated black hole mass, 7.1±1.3 M☉. Alternatives While there is a strong case for supermassive black holes, the model for stellar-mass black holes assumes of an upper limit for the mass of a neutron star: objects observed to have more mass are assumed to be black holes. However, the properties of extremely dense matter are poorly understood. New exotic phases of matter could allow other kinds of massive objects. Quark stars would be made up of quark matter and supported by quark degeneracy pressure, a form of degeneracy pressure even stronger than neutron degeneracy pressure. This would halt gravitational collapse at a higher mass than for a neutron star. Even stronger stars called electroweak stars would convert quarks in their cores into leptons, providing additional pressure to stop the star from collapsing. If, as some extensions of the Standard Model posit, quarks and leptons are made up of the even-smaller fundamental particles called preons, a very compact star could be supported by preon degeneracy pressure. While none of these hypothetical models can explain all of the observations of stellar black hole candidates, a Q star is the only alternative which could significantly exceed the mass limit for neutron stars and thus provide an alternative for supermassive black holes.: 12 A few theoretical objects have been conjectured to match observations of astronomical black hole candidates identically or near-identically, but which function via a different mechanism. A dark energy star would convert infalling matter into vacuum energy; This vacuum energy would be much larger than the vacuum energy of outside space, exerting outwards pressure and preventing a singularity from forming. A black star would be gravitationally collapsing slowly enough that quantum effects would keep it just on the cusp of fully collapsing into a black hole. A gravastar would consist of a very thin shell and a dark-energy interior providing outward pressure to stop the collapse into a black hole or formation of a singularity; It could even have another gravastar inside, called a 'nestar'. Open questions According to the no-hair theorem, a black hole is defined by only three parameters: its mass, charge, and angular momentum. This seems to mean that all other information about the matter that went into forming the black hole is lost, as there is no way to determine anything about the black hole from outside other than those three parameters. When black holes were thought to persist forever, this information loss was not problematic, as the information can be thought of as existing inside the black hole. However, black holes slowly evaporate by emitting Hawking radiation. This radiation does not appear to carry any additional information about the matter that formed the black hole, meaning that this information is seemingly gone forever. This is called the black hole information paradox. Theoretical studies analyzing the paradox have led to both further paradoxes and new ideas about the intersection of quantum mechanics and general relativity. While there is no consensus on the resolution of the paradox, work on the problem is expected to be important for a theory of quantum gravity.: 126 Observations of faraway galaxies have found that ultraluminous quasars, powered by supermassive black holes, existed in the early universe as far as redshift z ≥ 7 {\displaystyle z\geq 7} . These black holes have been assumed to be the products of the gravitational collapse of large population III stars. However, these stellar remnants were not massive enough to produce the quasars observed at early times without accreting beyond the Eddington limit, the theoretical maximum rate of black hole accretion. Physicists have suggested a variety of different mechanisms by which these supermassive black holes may have formed. It has been proposed that smaller black holes may have also undergone mergers to produce the observed supermassive black holes. It is also possible that they were seeded by direct-collapse black holes, in which a large cloud of hot gas avoids fragmentation that would lead to multiple stars, due to low angular momentum or heating from a nearby galaxy. Given the right circumstances, a single supermassive star forms and collapses directly into a black hole without undergoing typical stellar evolution. Additionally, these supermassive black holes in the early universe may be high-mass primordial black holes, which could have accreted further matter in the centers of galaxies. Finally, certain mechanisms allow black holes to grow faster than the theoretical Eddington limit, such as dense gas in the accretion disk limiting outward radiation pressure that prevents the black hole from accreting. However, the formation of bipolar jets prevent super-Eddington rates. In fiction Black holes have been portrayed in science fiction in a variety of ways. Even before the advent of the term itself, objects with characteristics of black holes appeared in stories such as the 1928 novel The Skylark of Space with its "black Sun" and the "hole in space" in the 1935 short story Starship Invincible. As black holes grew to public recognition in the 1960s and 1970s, they began to be featured in films as well as novels, such as Disney's The Black Hole. Black holes have also been used in works of the 21st century, such as Christopher Nolan's science fiction epic Interstellar. Authors and screenwriters have exploited the relativistic effects of black holes, particularly gravitational time dilation. For example, Interstellar features a black hole planet with a time dilation factor of over 60,000:1, while the 1977 novel Gateway depicts a spaceship approaching but never crossing the event horizon of a black hole from the perspective of an outside observer due to time dilation effects. Black holes have also been appropriated as wormholes or other methods of faster-than-light travel, such as in the 1974 novel The Forever War, where a network of black holes is used for interstellar travel. Additionally, black holes can feature as hazards to spacefarers and planets: A black hole threatens a deep-space outpost in 1978 short story The Black Hole Passes, and a binary black hole dangerously alters the orbit of a planet in the 2018 Netflix reboot of Lost in Space. Notes References Further reading External links |
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[SOURCE: https://en.wikipedia.org/wiki/Curupira] | [TOKENS: 4007] |
Contents Curupira The Curupira, Currupira or Korupira (Portuguese pronunciation: [kuɾuˈpiɾɐ]) is a forest spirit in the myth of the Tupí-Guaraní speaking areas in the Brazilian and Paraguaian Amazon and Guyanas. It is a guardian of the rainforest that punishes humans for overcutting. The name Curupira means "covered in wounds or blisters", and derives from an agglutination of Nheengatu: kuru "grain, rough", etc. and piré "skin" (cog. Guarani/Tupi: pí), thus "rough or pimply skin". This kurupire may have been passed on perhaps from Nheengatu-speakers in Brazil to the Tupinambá speakers, then to the Guaraní-speaking population in the south. It is often said to look like a short-statured tapuio or caboclo (civilized indigene or one of mixed race), but also said to be a bald but otherwise shaggy man (though the women have flowing hair). Some say it has blue or green teeth. The red-haired image has become fixture, perhaps due to conflation with the caipora. The Curupira according to early Jesuits was a feared being known to leave gruesomely scarred bodies, to be appeased by offerings. But it underwent a mutation via European influence, and was recast into more of a mischievous trickster type spirit, often bungling and letting humans outsmart it, though it could still cause misfortune and death. Origins The Curupira legend spans Venezuela, Guyana, Peru and Paraguay, and appears to have been passed from Karaib-speakers to Guarani-speaking populace. Nomenclature The lore of the Curupira is not only found in Brazil, but also in Paraguay and Guiana coinciding with the distribution of the Tupi–Guarani languages. The name Curupira means "covered in wounds or blisters", and derives from an agglutination of Nheengatu: kuru "grain, rough", etc. and piré "skin" (cog. Guarani/Tupi: pí), thus "rough or pimply skin". This kurupire may have been passed on perhaps from Nheengatu-speakers in Brazil to the Tupinambá speakers, then to the Guaraní-speaking population in the south. The name is normally styled "Curupira" (in Pará) and spelt "Currupira" in the south. It is also argued that curupira goes by other names depending on region, namely Çacy tapereré (Saci Pererê) in the south, Caipora in the central region ), and Maty-taperé in the North[a]. Sometimes transcribed "Korupira". Some commentators have argued the Curupira and Caipora to be the same, others say they are different. The usage is regional, for example, from Maranhão south to Espírito Santo, its persistent nickname is Caipora (cf. § Conflation with Caipora). Legend The Curupira is a "hominoid spirit" or god, perhaps a "wild man", considered the guardian of the forest. It punishes humans who wantonly harvest lumber by making him lose his way, wander timelessly in the forest, so he becomes unable to reach his home. The Curupira is described as a small-statured tapuio ("brown man"[b]), or a "caboclinho" (diminutive of caboclo), of similar meaning. Notably, the Curupira has his feet turned backwards,[c] to mislead trackers with footprints proceeding in the opposite direction, so that one trying to flee the Curupira actually pursues it.[d] The Curupira allegedly has family, a wife and children living in the hollow of dead trees. The women have long hair.[e] Sometimes they trespass upon a human roça (crop field) to steal the mandioca (manioc). Or else it is said that the wife is some old, ugly evil tapuya woman who plays accomplice to his misdeeds, and among their children, the youngest is the Saci[f] Note that Caipora (Kaapora) has been discussed as a variant of Curupira, and its wife is identified as Tatácy (in Amazonas) and Tatámanha (in Pará).[g] Curupira was blamed for causing bad thoughts and nightmares. It is also said to have been a "mischievous wood-sprite"[h] that engages in conversation with humans, foments distrust and dissent among individuals, and enjoy watching them fall into misfortune, but this description, taken to mean a "comical spirit" has been viewed unfavorably. The Curupira is attested as being regarded as a "god of thinking" or of "lies and deception" (cf. § History for further details), which may have to do with it being seen as playing with one's mind in general. The Curupira is fond of tobacco, and rewards hunters for offering it, but they must keep it secret from their wives. Besides tobacco it loves cachaça (sugarcane booze), and hunters are known to offer these as propitiation to the Curupira. Curupira can also be regarded as a rider of a deer, rabbit, or pig, or a peccary, variously given to be a white-lipped peccary (Tayassu pecari) or a collared peccary (T. tajacu ; cf. § Conflation with Caipora). In the lore of the state of Pernambuco, the Curupira or Korupira (though the sources consider these a variant of the caipora/caapora) rides a deer, and is accompanied by his dog named “Papa-mel". The physical appearance is described variously. He is said to have enormous ears and blue or green teeth (in the Solimões River basin). It is also said to be balding or bald-headed (Tupinambá: piroka[i]) but hairy-bodied with long body hair (in the Rio Negro basin). Naturalist Bates remarked that it was like an orangutan with shaggy hair, living in trees, so that in later commentary the curupira was generally attributed with red/orange hair.[j] Others have said it has a bright red face and cloven feet. Other regions held that it was one-eyed (Rio Tapajós basin), or that it has no anus hence becomes solidly or massively built (according to Pará lore).[k] While Bates considered the Curupira and Caipora as distinguishable, they were considered to be the same by German naturalist Martius. Long red body hair seems to have been ascribed originally to the Caipora, said to be similar to Curupira. The Caipora is said to ride a collared peccary (taitetú), and the Curupira has come to be commonly portrayed riding one also. The Curupira also confuses travelers in the woods by producing high pitched whistling sound mimicking the call of the tinamou (inambú) bird. The Curupira allegedly beats on the projecting root of the tree (sapopema, i.e., buttress root) to diagnose if it remains sturdy enough to resist storms. Thus when paddlers traveling by canoe in the rivers of Pará hear beating noises in the forest, they will say it is the sound of Curupira performing that chore. According to the fieldwork of Charles Wagley conducted in the 1950s, the Curupira was known not only to make "long shrill cries" from the depths of the forest, but could mimic human voices to lure rubber tappers or hunters and lead them astray. In an old anecdote of an actual encounter, the child-sized curupira was strong enough to throw the man up in the air and break his legs. The man took out holy wax from his pouch, causing the creature to come no closer, but it had such catinga (bad odor) about him it rendered the hunter unconscious.[l] Supposedly the Curupira sings a certain enchanting song that attracts humans, and the lyrics literally mean "I'm walking along my path, behind me come walking, walking". To counter against the Curupira's effect of losing one's way, the traveler must fashion a cross or a wheel made of liana vine (Portuguese: cipó), and while the spirit is engaged trying to unravel it, the traveler gains opportunity to escape. The naturalist Bates also records that the mameluco youth who frequently accompanied him refused to proceed without hanging a charm made of palm-leaf formed into a wheel, in order to ward against the curupira. Narratives Herbert Huntington Smith (1879) records a story[m] where a Curupira kills a native hunter and brings back the heart to the man's wife and child to eat. The wife realizes the deception at night and flees with the child. She is helped by a frog that spits a gummy substance, which lifts her up to a tree. The Curupira gets stuck on the frog's sticky goo trying to climb, and dies. Another story was given by Charles Frederick Hartt tells of a hunter who was asked to hand over his heart, but outwits the Curupira. The man passes off a monkey heart as his own, persuading Curupira to carve out its own heart, thus committing his own murder. Hartt compared it to the Norwegian folktale "About Askeladden who Stole from the Troll" ("Boots and the Troll"). The hunter later goes to collect the green teeth of the Curupira, and discovers it has revived, giving him a magic bow, but sworn to secrecy. The inquisitive of his wife loosens his tongue and the hunter dies. In a variant version, the hunter breaks the taboo against using the magic bow to hunt birds, and is pecked to death by a flock. The hunter is mended by the Curupira using wax to replace his flesh, but the warning not to eat hot foods thereafter goes unheeded by the hunter, who melts away due to the heat intake. History The oldest mention of his name is by the Jesuit José de Anchieta, in São Vicente, on 30 May 1560: "It's a well-known thing and it's rumored by everyone that there are certain demons, which the Brazilians call corupira, that often attack Indians in the bush, wound them with the whip, tormenting and killing them. Our Brothers are witnesses of this, having seen [the dead] killed by them. Therefore, the Indians [in order to appease the demons] traverse the path through the sertão hinterlands, full of rough woodland and steep hills, to reach the highest mountain, leaving bird feathers, fans, arrows and such things [as a kind of oblation], begging [the demons] to do them no harm". Other early mentions were made by Jesuit Fernão Cardim [pt] (1584), and by the Dutchman Johannes de Laet (director of Dutch West India Company, in 1640) Acuña (1641) is mentioned as an earlier testimony, but he writes on the Mutayu tribe, reputed to have feet facing backwards, known to be a great craftsmen of stone axes, whom Acuña said were a subbranch of the Tupinambá. However, Sérgio Buarque de Holanda (Caminhos e Fronteiras 1957) argued the "fabulous Mutayu" and the Curupira myth to be a product derived from the rainforest people's tactical practice of wearing shoes to throw enemies off their path. Cardim records that Curupira is the devil the indigenous people revere and fear above all else, but do not craft any idols of them. De Laet's mentions it, and together with his collaborator Marcgravius (Georg Marcgrave) wrote in Latin that the names for the Devil among the populace was "Anhanga, Jurupari, Curupari [sic]", of which the Curupira was called a nuomen mentis, perhaps meaning "spirit of thoughts" as glossed by Father Simão de Vasconcelos [pt] (1663).[n] But this Latin can also be construed as meaning the deity of “lies” and “deceptions” according to Gonçalves Dias (1867). Cascudo does not appear to warm to that interpretation, and writes that Father João Daniel (1797) would have disagreed. João Daniel had described a deity that shouted out loud demanding offerings, and the populace got straightforwardly "beaten" for being derelict in their propitiation obligations. As the "god of thoughts" (or "god of lies" perhaps), Curupira had been treated as a venerated part of the pantheon, but later got corrupted to a sort of "imp or buffoon" according to Daniel Garrison Brinton. Compare mythographer Hartley Burr Alexander who characterized Curupira as less Satan and more Pan-like. Martius's characterization as "mischievous wood-sprite", which were taken to mean a "comical spirit" has been cited by other scholars, but they may have taken exception to this view.[o] Martius's point that Curupira as less sinister than the Jurupari seems lost to them. Also, there used to be compartmentalization of the different gods' duties where Anhanga protected large game, Caipora/Caapora small game, and the Mboitatá the grasses and shrubbery. But this divide broke down, and Curupira later came to be regarded as the unchallenged ruler over not just the forestry but all the wonders in it, according to the analysis of Cascudo. Eduardo Galvão [pt] (1955) informs: "Currupira is a genius of the forest. In the city or in the capoeiras in its immediate neighborhood there are no currupiras. They live further away, far inside the forest. The people of the city believe in their existence, but they are not a reason for concern because currupiras don't like heavily populated places". Parallels Mapinguari has been paralleled with the Pokái in the tradition of Macushi[p] who inhabit the forests in the mountain chains of Roraimá state, is an identical myth. The Pokái is "a small, long-haired country urchin with a long nose, with feet turned backwards, lame in one leg, and using the heel of his foot to hit the drums". The lore about the Iuoroko or Iuoroco among the Pariqui[q] people of Jatapu River may also be the same myth. Other counterparts are the Máguare of In Venezuela; the Selvage of Columbia, the Incan Chudiachaque of Peru, and the Kauá of Kokamas of Bolivia. The Curupira has also been paralleled with Rübezahl the alpine god of the Sudeten Mountains. Charles Frederick Hartt named three foreign mythical beings comparable to the curupira: Norwegian troll as aforementioned, the Russian leshy, and the Algonquian "Manabozho/Manobozho" (cog. Ojibwa: Nanabozho).: note 1 In one narrative, Manabozho watches the moose man magically extract a large piece of meat from his own wife (but heals her afterwards using meeta or 'magical cure'); Manabozho then tries to imitate this on his own wife, nearly killing her. This parallels the motif in the narrative (cf. above) where the hunter tricks the curupira into carving out his own heart. A Russian Fairy Tales story collected by Afanasyev, about the fox that tricks the bear into smashing its own forehead and eating the contents, also exhibits the same motif. The Russian leshy ("lyeshy") with green hair and green teeth is only superficially similar to the Curupira. Modern commemorations The State of São Paulo, as decreed by law of September 11, 1970, signed by governor Roberto Costa de Abreu Sodré, "establishes the Curupira as the state symbol of the guardian of the forests and the animals that live in them". On Arbor Day, September 21 of that year, a statue monument of Curupira was placed in what was then Horto Florestal (now Albert Löfgren State Park), in the state capital São Paulo. The statuette was vandalized and removed to museum, but a new version was commissioned from Thirso Cruz, and the replacement restored to the park. Cruz had originally created the (since stolen) Curupira statue that stood in Fábio Barreto municipal forest, Ribeirão Preto, based on which the original Horto statue got created. In the municipality of Olímpia, in that state, for over thirty consecutive years, no official documents are signed during the week in which the Folklore Festival takes place, in the month of August, a period in which the municipal authority is represented by Curupira, which exercises its power by protecting the local population and visitors who come there, birds, forests, etc.[citation needed] The Fundaçao Brasileira para Conservação da Natureza (FBCN) has adopted the curupira as its official symbol in 1958. In popular culture A being called the Demon Curupira was featured in several episodes of the 1999–2002 television series Beastmaster. Played by Australian actress Emilie de Ravin, this Curupira, while still possessing the backwards feet, had the appearance of a young and deceptively sweet-faced blonde girl clad in green. She was a spirit of the forest and very capricious; she protected the animals, particularly tigers, and with a kiss she could drain humans of their lives, reducing their bodies to mere husks. She was an uneasy ally of the title character, Dar. In the 2020 animated film The Red Scroll, the character Idril is inspired by Curupira, although she does not have backwards feet, she clearly demonstrates the ability to leave inverted footprints on the ground in one of the scenes. The 2021 Netflix series Invisible City features numerous characters of Brazilian lore, including Curupira. Curupira, played by Fabio Lago, is portrayed as a homeless person who is actually an entity that guards and protects Brazilian forests, perceived by his backward feet, flaming head, and illusion-like high whistles that combine nature and human voices. See also Explanatory notes References "Cha uatá, uatá Ce rapé rupi Cha uatá, uatá, Ce rakakuera Yure uatá, uatá" |
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[SOURCE: https://en.wikipedia.org/wiki/Peter_Thiel#Political_activism] | [TOKENS: 18110] |
Contents Peter Thiel Peter Andreas Thiel (/tiːl/ ⓘ; born 11 October 1967) is a German and American entrepreneur, venture capitalist, and political activist. A co-founder of PayPal, Palantir Technologies, and Founders Fund, he was the first outside investor in Facebook. According to The New York Times, as of December 2025, Thiel's estimated net worth stood at US$27.5 billion, making him among the 100-richest individuals in the world. Born in Germany, Thiel was taken to the US by his parents when he was one year old. In 1971, his family moved to South Africa then South West Africa, before moving back to the US in 1977. After graduating from Stanford, he worked as a clerk, a securities lawyer, a speechwriter, and subsequently a derivatives trader at Credit Suisse. He founded Thiel Capital Management in 1996 and co-founded PayPal with Max Levchin and Luke Nosek in 1998. He was the chief executive officer of PayPal until its sale to eBay in 2002 for $1.5 billion. Following PayPal, Thiel founded Clarium Capital, a global macro hedge fund based in San Francisco. In 2003, he launched Palantir Technologies, a big data analysis company, and has been its chairman since its inception. In 2005, Thiel launched Founders Fund with PayPal partners Ken Howery and Luke Nosek. Thiel became Facebook's first outside investor when he acquired a 10.2% stake in the company for $500,000 in August 2004. He co-founded Valar Ventures in 2010, founded Thiel Capital in 2011, co-founded Mithril Capital in 2012, was investment committee chair, in 2012, and was a part-time partner at Y Combinator from 2015 to 2017. He was granted New Zealand citizenship in 2011, which later became controversial in New Zealand. Thiel has been described as "perhaps America's leading public intellectual today" or an "intellectual architect of Silicon Valley's contemporary ethos". Others debate the consistency or morality of his views.[N 1] Variously described as a conservative libertarian and democracy-skeptic authoritarian, Thiel has made substantial donations to American right-wing figures and causes. Through the Thiel Foundation, Thiel governs the grant-making bodies Breakout Labs and Thiel Fellowship. In 2016, when the Bollea v. Gawker lawsuit ended up with Gawker losing the case, Thiel confirmed that he had funded Bollea (Hulk Hogan). Gawker had previously outed Thiel as gay. Emails related to the activities of convicted child sex offender Jeffrey Epstein released by the House Oversight Committee in 2026 revealed that Valar Ventures accepted $40 million from Epstein and that Thiel corresponded with Epstein for five years before Epstein’s death, including on the topic of Brexit. Early life and education Peter Andreas Thiel was born in Frankfurt am Main, Hesse, then part of West Germany, on 11 October 1967, to Klaus Friedrich Thiel and Susanne Thiel. The family emigrated to the United States when Peter was one year old and lived in Cleveland, Ohio, where his father worked as a chemical engineer. Klaus worked for various mining companies, which created an itinerant upbringing for Thiel and his younger brother, Patrick Michael Thiel. Thiel and his mother later naturalized as U.S. citizens, whereas his father did not. Before settling in Foster City, California, in 1977, the Thiel family lived in South Africa and South West Africa (modern-day Namibia) in the time of apartheid. Peter changed elementary schools seven times. He attended a German-language school in Swakopmund for two years that required students to wear uniforms and utilized corporal punishment, such as striking students' hands with a ruler. He said this experience instilled a distaste for uniformity and regimentation later reflected in his support for individualism and libertarianism. The German community in Swakopmund was known at the time for its continued glorification of Nazism. Thiel was noted as a smart, but lonely, withdrawn boy, with whom others would not mingle because they knew he would not stay long in the town. Thiel played Dungeons & Dragons and was an avid reader of science fiction, with Isaac Asimov and Robert A. Heinlein among his favorite authors. He is a fan of J. R. R. Tolkien's works, stating as an adult that he had read The Lord of the Rings over ten times. Thiel excelled in mathematics and scored first in a California-wide mathematics competition while attending Bowditch Middle School in Foster City. At San Mateo High School, he read Ayn Rand and, influenced by his parents, admired Nixon and Reagan. He was valedictorian of his graduating class in 1985. When at school, he reportedly charged $500 each to take the SAT for underclassmen, knowing this would cost him his spot at Stanford if discovered. Thiel studied philosophy at Stanford University. The replacement of a "Western Culture" program at Stanford with a "Culture, Ideas and Values" course that addressed diversity and multiculturalism prompted Thiel to co-found The Stanford Review, a conservative and libertarian newspaper, in 1987. The paper received funding from Irving Kristol. Thiel was The Stanford Review's first editor-in-chief until he graduated in 1989. Thiel has maintained his relationship with the paper, consulting with staff and donating to the newspaper. According to Marc Andreessen, Thiel's time at the Review marked the beginning of a career-long strategy: using provocative verbal cues – later delivered through talks, books and mottos – as a way to attract capable individuals to his projects, preferring this method over actively seeking out talent. The Review has spawned a large network of industry leaders, among whom Andrew Granato and the Fortune respectively identify around 300 people who have worked for or received investment from Peter Thiel or Joe Lonsdale, another prominent editor-in-chief and Thiel's mentee. A number of Review alumni have also become public officials, beginning with Jay Bhattacharya and Paula M. Stannard who were editors during Thiel's time as editor-in-chief. After graduation, Thiel attended Stanford Law School, graduating in 1992 with a Juris Doctor degree. While at Stanford, Thiel met René Girard, whose mimetic theory influenced him. Career After graduating from Stanford Law School, Thiel was a law clerk to Judge James Larry Edmondson of the U.S. Court of Appeals for the Eleventh Circuit from 1992 to 1993. Thiel then worked as a securities lawyer for Sullivan & Cromwell in New York. He left the law firm in under a year. He then took a job as a derivatives trader in currency options at Credit Suisse in 1993 while also working as a speechwriter for former United States secretary of education William Bennett. Thiel returned to California in 1996. Upon returning to the Bay Area, Thiel capitalized on the dot-com boom. With financial support from friends and family, he raised $1 million toward the establishment of Thiel Capital Management and embarked on his venture capital career. Early on, he experienced a setback after investing $100,000 in his friend Luke Nosek's unsuccessful web-based calendar project. Soon thereafter, Nosek's friend Max Levchin described to Thiel his cryptography-related company idea, which became their first venture called Fieldlink (later renamed Confinity) in 1998. Thiel provided the initial $100,000 for Fieldlink in 1998. In February 1999, they raised $500,000 largely from friends and family ($35,000 was from Thiel's parents). By middle 1999, they raised $4.5 million, with Nokia Ventures contributing $3 million. With Confinity, Thiel realized they could develop software to bridge a gap in making online payments. Although the use of credit cards and expanding automated teller machine networks provided consumers with more payment options, not all merchants had the necessary hardware to accept credit cards. Thus, consumers had to pay with exact cash or check. Thiel wanted to create a type of digital wallet for consumer convenience and security by encrypting data on digital devices, and in 1999 Confinity launched PayPal. PayPal promised to open up new possibilities for handling money. Thiel viewed PayPal's mission as liberating people from the erosion of the value of their currencies due to inflation.[N 2] When PayPal launched at a press conference in 1999, representatives from Nokia and Deutsche Bank sent $3 million in venture funding to Thiel using PayPal on their PalmPilots. PayPal then continued to grow through mergers in 2000 with Elon Musk's online financial services company X.com, and with Pixo, a company specializing in mobile commerce. These mergers allowed PayPal to expand into the wireless phone market and transformed it into a safer and more user-friendly tool by enabling users to transfer money via a free online registration and email rather than by exchanging bank account information. PayPal went public on 15 February 2002 and was bought by eBay for $1.5 billion in October of that year. Thiel remained CEO of the company until the sale. His 3.7% stake in the company was worth $55 million at the time of acquisition. In Silicon Valley circles, Thiel is colloquially referred to as the "Don of the PayPal Mafia". Thiel used $10 million of his proceeds to create Clarium Capital Management, a global macro hedge fund focusing on directional and liquid instruments in currencies, interest rates, commodities, and equities. Thiel stated that "the big, macroeconomic idea that we had at Clarium—the idée fixe—was the peak-oil theory, which was basically that the world was running out of oil, and that there were no easy alternatives." In 2003, Thiel successfully bet that the United States dollar would weaken. In 2004, Thiel spoke of the dot-com bubble having migrated, in effect, into a growing bubble in the financial sector, and specified General Electric and Walmart as vulnerable. In 2005, Clarium saw a 57.1% return as Thiel predicted that the dollar would rally. However, Clarium faltered in 2006 with a 7.8% loss. Thereafter, the firm sought to profit in the long-term from its petrodollar analysis, which foresaw the impending decline in oil supplies. Clarium's assets under management grew after achieving a 40.3% return in 2007 to more than $7 billion by the first quarter of 2008, but fell later in the year and again in 2009 after financial markets collapsed. By 2011, after missing out on the economic rebound, many key investors pulled out, reducing the value of Clarium's assets to $350 million, two thirds of which was Thiel's money. In May 2003, Thiel incorporated Palantir Technologies, a big data analysis company named after the Tolkien artifact. He continues as its chairman, as of 2022. Thiel stated that the idea for the company was based on the realization that "the approaches that PayPal had used to fight fraud could be extended into other contexts, like fighting terrorism". He also stated that, after the September 11 attacks, the debate in the United States was "will we have more security with less privacy or less security with more privacy?". He envisioned Palantir as providing the government the technology to find terrorism without operating illegally. Palantir's reputation is controversial. Although the software only analyzes data collected by the customers, some criticize it for enabling surveillance.[N 3] Professor Vasilis Galis notes that the software is not a mere tool, but shapes policing culture with new policing norms.[N 4] According to Geoff Shullenberger (managing director of Compact) and Moira Weigel (Assistant Professor of Comparative Literature, Harvard), Peter Thiel and Alex Karp built Palantir on the basis of their understanding of Leo Strauss and the Frankfurt School. After the first meeting with Zuckerberg in August 2004, Thiel made a $500,000 angel investment in the startup (then "a three-person dormroom") for a 10.2% stake in the company and joined Facebook's board. This was the first outside investment in Facebook and valued the company at $4.9 million. He also bought Zuckerberg a car. The investment was originally in the form of a convertible note, to be converted to equity if Facebook reached 1.5 million users by the end of 2004. Although Facebook narrowly missed the target, Thiel allowed the loan to be converted to equity anyway. Thiel said of his investment: "I was comfortable with them pursuing their original vision. And it was a very reasonable valuation. I thought it was going to be a pretty safe investment." Facebook employees reported that Thiel's influence was unusual for a board member who was not also the CEO. Some criticized Thiel for pushing his mentee Zuckerberg and the company to the right. Zuckerberg credited Thiel with helping him time Facebook's 2007 Series D, which closed before the 2008 financial crisis. Facebook's initial public offering was in May 2012, with a market cap of nearly $100 billion ($38 a share), at which time Thiel sold 16.8 million shares for $638 million. In August 2012, immediately upon the conclusion of the early investor lock-up period, Thiel sold almost all of his remaining stake for between $19.27 and $20.69 per share, or $395.8 million, for a total of more than $1 billion. In 2016, he sold a little under 1 million of his shares for around $100 million. In November 2017, he sold another 160,805 shares for $29 million, putting his holdings in Facebook at 59,913 Class A shares. As of April 2020, he owned less than 10,000 shares in Facebook. On 7 February 2022, Thiel announced he would not stand for re-election to the board of Facebook owner Meta at the 2022 annual stockholders' meeting and would leave after 17 years in order to support pro–Donald Trump candidates in the 2022 United States elections. In 2005, Thiel created Founders Fund, a San Francisco-based venture capital fund. Other partners in the fund include Sean Parker, Ken Howery, and Luke Nosek. The fund focuses on defense-related startups and technology. After Facebook, even though it was a big financial success, Thiel made the Founders Fund pivot to hard tech, with the reasoning that while companies like Twitter might have a high value, they would not take "civilization to the next level." The Economist notes that the fund and Thiel, personally, have a history of incubating startups that do hypersensitive work related to national security. The fund casts Palantir, Anduril and the newly minted nuclear startup General Matter as the three parts of a trilogy, to which it hopes to add others, among which a plan for onshoring ultraviolet light lithography. Business Insider reports that, among Thiel's inner circle (who know well the billionaire's fondness for Tolkien's works), the fund is nicknamed "the Precious", in reference to the One Ring of Sauron. In addition to Facebook, the Founders Fund made early-stage investments in numerous startups, including Airbnb, Slide.com, LinkedIn, Friendster, RapLeaf, Geni.com, Yammer, Spotify, Practice Fusion, MetaMed, Vator, SpaceX, IronPort, Votizen, Asana, Big Think, CapLinked, Nanotronics Imaging, Powerset (Thiel is on the board of Nanotronics and Powerset), Stripe, Bullish Global (the parent company Block.one had also received investment from Thiel ), AltSchool, Trade Republic, PsiQuantum (photonic quantum computing), and Rigetti Computing (superconducting quantum computing). Thiel also backed DeepMind, a UK start-up that was acquired by Google in early 2014 for £400 million. Founders Fund is an important backer of the Berlin-based platform ResearchGate. Since 2012, Founders Fund had been quietly buying bitcoin, with the investment totaling around $20 million" (Bloomberg remarked that, "the investment amounts to a rounding error for Thiel’s firm."). The company sold the majority of its crypto holdings for $1.8 billion in March 2022 (with bitcoin making up two-thirds of its holdings), right before the market crashed. Also in 2017, Thiel was one of the first outside investors in Clearview AI, a facial recognition technology startup that has raised concerns in the tech world and media for its risks of weaponization. In 2024, alongside General Catalyst and Red Cell Partners, the Founders Fund incubated the defense incubator Valinor Enterprises. The co-founders are former Palantir's senior vice president Julie Bush (CEO), Trae Stephens, General Catalyst's Paul Kwan and Red Cell's Grant Verstandig. In 2024, the Founders Fund led a massive US$85 million seed round for the UAE's decentralized, open-source AI platform SentientAGI (Sentient Foundation), which seeks to challenge Perplexity and OpenAI's closed models as well as handle the problem of AI proliferation, which concentrates power in the hands of large players like Google and Amazon. In 2024 it also invested in Impulse Space (in-space transportation services), Ramp, Crusoe (AI infrastructure using clean energy). In 2025, the Founders Fund invests in Erebor (a new digital bank which is founded by Palmer Luckey and has quickly reached a US$2 billion valuation), EnduroSat (Bulgarian startup that produces Gen3 satellites at scale), Varda (space medicine and hypersonic testbed startup, founded by the Thiel Fellow Delian Asparouhov, Trae Stephens and Will Bruey, and incubated at the Founders Fund), Hadrian Automation. Anduril is a defense hardware startup that was founded in 2017 by Palmer Luckey (who is Thiel's mentee), Joe Chen, Trae Stephens, Matt Grimm and Brian Schimpf (the latter three are Palantir and Founders Fund alumni). The Founders Fund backed the company since its inception, leading its 2017 seed round. The $1 billion (part of the $2.5 billion Series G funding round) the Founders Fund invested in Anduril in June 2025 was the largest investment in the fund's history. In December 2024, it was reported that Palantir and Anduril were forming a consortium of new generation defense companies (which included SpaceX, OpenAI, Scale AI, Saronic Technologies and others) that they would lead in order to challenge the dominance of traditional defense companies. In July 2025, when the Trump administration's budget bill included a provision that required border surveillance towers to be "tested and accepted by U.S. Customs and Border Protection to deliver autonomous capabilities", Edith Olmsted of The New Republic made the criticism that the government favoured Peter Thiel's business, as the provision (which only Anduril fulfilled) effectively ruled out Anduril's rivals, namely General Dynamics and the Israeli-based Elbit Systems. General Matter emerged from stealth in April 2025, focusing on "production and handling of High-Assay, Low-Enriched Uranium (HALEU)." Scott Nolan, who formerly worked for SpaceX, left the Founders Fund to focus on the company and become the CEO, Thiel is also on the company's board of directors, which is noted by the Economist to be a rare occurrence these days. The plant in Paducah, built by General Matter, will be the "first privately developed US uranium enrichment facility". Valar Ventures is an internationally focused venture firm Thiel cofounded with Andrew McCormack and James Fitzgerald in 2010. Valar's portfolio includes TransferWise (now Wise), reforestation-funding finance platform Treecard, fintech startup Atoa (Wise, Treecard and Atoa are based in London), Miami-headquartered Novo and Fortú (digital bank which focuses on underbanked Latino and Hispanic communities), fintech unicorn Qonto, fintech startup Hero, accounting automation software startup Regate (all three are Paris-based), Vienna-based crypto unicorn Bitpanda, Lagos- and London-based banking startup Kuda Bank, Indonesian fintech startup Bukuwarung, Nigerian banking platform Maplerad, Mexican banking startup Albo, banking unicorn N26, B2B paytech Mondu, spend management platform Moss, tax filling unicorn Taxfix, instant payment API startup Ivy (N26, Mondu, Moss, Taxfix and Ivy are all Berlin-based; Ivy is founded by the Thiel Fellow Ferdinand Dabitz), Dubai-based fintech startup Baraka. Valar also invested in New-Zealand based companies including in the software firm Xero, undersea communication company Pacific Fibre and e-reader platform Booktrack. Recent investments include Arkansas-based Panacea Financial (digital fintech for medical practitioners), Riyadh-based SILQ ("largest B2B commerce platform across the Gulf and South Asia", resulted from the recent merger between Bangladesh-based Shop-Up and Saudi-based Sary), Canadian startup Neo (fintech), London-based fertility care startup Gaia. Thiel Capital is a venture capital fund founded by Thiel in 2011 and based in Los Angeles, also referred to as Thiel's family office. It provides "strategic and operational support" for many of Peter Thiel's initiatives and ventures. It incubated and launched Founders Fund, Mithril, Valar, the Thiel Fellowship and Breakout Labs, and also sponsors Crescendo Equity Partners. The firm's investments include Alloy Therapeutics (with Founders Fund and 8VC), EnClear Therapies (Jason Camm became a board member in 2020), the German unicorn ATAI Life Sciences (found by Thiel's friend, the biotech billionaire Christian Angermayer; Jason Camm also became a director in 2020), Compass Pathways (also partly owned by ATAI), Pilgrim (dual-use biotech startup founded by Thiel Fellow Jake Adler), Hugoboom, Rhea, Bullish Global (Founders Fund and Angermeyer are also investors), FTX (also received investment from Rivendell LLC), QA Wolf, Rollup (software platform to develop complex hardware), Neros (military drone startup found by Thiel Fellow Soren Monroe-Anderson), Regent Craft (electric seaglider, invested together with Founders Fund). Thiel Capital is also an investor (including post-IPO financial investment as major backer) of the dual-use German laser communications startup Mynaric. Angermayer also backs Mynaric. Hugoboom's app 28 requires users to input the first day of their last period to calculate the menstrual phases. The app's pro-life rhetoric and scientific basis is controversial. Some of the firm's notable (past) employees include former Austrian chancellor Sebastian Kurz, American politician and entrepreneur Blake Masters, Kevin Harrington (Senior Director for Strategic Planning at the United States National Security Council) and Michael Kratsios. Thiel Capital's investment in the Gilching-based drone startup Quantum-Systems as well as Thiel's subsequent backing of the Berlin-based attack drone startup Stark are sometimes considered controversial, due to Thiel's politics. In May 2025, Quantum-Systems became Europe's first dual-use unicorn and third defense unicorn, after fellow Bavarian startup Helsing and the Portuguese Tekever (Thiel has a role in the success of Helsing too and the startup is considered a part of the "Thiel ecosystem", although he does not directly invest in it). Thiel's mentee Moritz Döpfner brokered the deal with Quantum-Systems on Thiel's behalf and sits on its board. His venture fund Doepfner Capital also invests in Stark. In June 2012, he launched Mithril Capital Management, named after the fictitious metal in The Lord of the Rings, with Jim O'Neill and Ajay Royan. Unlike Clarium Capital, Mithril Capital, a fund with $402 million at the time of launch, targets companies that are beyond the startup stage and ready to scale up. Thiel holds shares in the space-based intelligence company BlackSky through Mithril. It also invests in Helion Energy. The 1517 Fund was founded in 2015 by Danielle Strachman and Michael Gibson, who were both in the founding team of the Thiel Fellowship. The fund provides cash grants and investments, aiming at extending the support already granted by the Thiel Fellowship. It targets "dropouts, renegade students, and deep tech scientists". Peter Thiel backs the fund. Its portfolio companies include Luminar Technologies, Loom, Inc., Atom Computing and Durin Mining Technologies among others. Thiel is the co-founder of America's Frontier Fund, together with Eric Schmidt. The New York Times writes that, America's Frontier Fund is an organization committed to bring manufacturing back to the US, especially that of semiconductors, and the leaders are determined to carry out this mission whether the state helps them or not. InfluenceWatch notes the fund's bipartisan character, with the participation of Ashton B. Carter and H.R. McMaster and the fact that the two founders are left and right-of-center respectively. The chief executive is Gilman Louie. In December 2024, it got approval to get funding from the Small Business Investment Company Critical Technology Initiative (SBICCT), which is "a joint effort by the U.S. Small Business Administration and the Department of Defense." In July 2025, it reportedly raised US$315 million for its first fund. It backs Venus Aerospace, a company develops hypersonic flight using rotating detonation rocket engine (since November 2024) and Foundation Alloy. The fund is characterized by Intelligence Online as "China-sceptic". Around the early 2020s, the Bavarian startup Kleo-Connect successfully developed a highly advanced satellite technology, which is considered much more suitable for governmental and military use than that of Starlink, which was originally conceived for civilian use only. It was feared the technology would fall into the hand of the PLA through its Chinese investors (who invested in the startup since 2018) though. Thus, the German government banned the sale of the company to China, but 144 lawsuits worldwide deterred investors from helping the company to expand the constellation. The founders decided to bring in the US's "highest conservative circles" (which led to the formation of Rivada Space Networks, which drew its personnel mainly from Kleo-Connect, in 2022), among which Karl Rove participated as an investor and lobbyist, and former US secretary of state Mike Pompeo joined the board of the mother company in the US, alongside others like Richard Myers, Jeb Bush, James Loy, Lord Guthrie and the Democrat Martin O'Malley. Rivada Networks's chairman Declan Ganley notes in particular the power of Thiel's name (whose investment in the firm remains undisclosed) in negotiation with investors. The United States Department of Defense is also an investor. Newt Gingrich is noted to have lobbied for the firm too. By 2025, the "politically connected company" has already expanded to 33 countries and collected 16 billion dollars in investments, despite having not launched its satellites (deployment is set to begin in 2027 with initial tests set for 2026). Thiel reportedly works to help the company's development, especially regarding its legal battles. Thiel is an investor and strategic partner of the Oslo-based SNÖ Ventures, having joined the firm in 2021, accompanied by a group of international strategic advisors. In 2024, the fund made its first investment in the defense tech sector, an early funding for the Swedish startup Nordic Air Defence, which developed counter-drone missile technology and is staffed with former employees from Palantir and Quantum Systems. Arctic Today sees this as an evidence of Sweden's strong transatlantic bond which is "seeping into defence", which is also shown in Daniel Ek's Prima Materia's investment in Helsing (which is a strategic partner of Palantir), which happened three months before Russia's 2022 invasion of Ukraine. In 2020, Thiel became a strategic partner and anchor investor of Elevat3, which is set up by Christian Angermayer's Apeiron Investment Group to invest in startups in German-speaking countries. The fund focuses on "life sciences, deep tech, fintech (financial technology), property and insurance". The fund has a partnership with the Founder Fund. In 2020, Thiel invested into the Neunkirchen-based startup Neodigital through the fund. The fund also backs other European startups such as the London-based aggregator startup Olsam. In 2022, through Elevat3 and in partnership with the Founders Fund, the Apeiron Group bought shares from the Chinese Fosun International and others to become a shareholder in the Hamburg-based NAGA Group. Thiel also holds shares in Heidelberger Beteiligungsholding [de] (which will be renamed as SQD.AI Strategies AG), the first dedicated German crypto holding treasury, through the firm. Seoul-based Crescendo Equity is a private equity firm which focuses on mid-cap manufacturing and technology companies in Asia. According to the official website, "Crescendo was established in 2012 with the sponsorship of Peter Thiel". The fund is co-founded by Peter Thiel, Matt Danzeisen (who serves as a member of its investment committee and representative to selected portfolio companies), Andy Lee (company chairman), Matt Price (CEO) and Slava Zhakov (CTO). The president is Anand Chandrasekaran. General Catalyst is also heavily involved in its financing and organization. The fund invests in Line Next (a unit of the Line Corporation), a joint venture between Softbank and Naver. The Business Korea credits Crescendo Equity Partners with transforming Korea's HPSP, which it invested in since 2017, into a global player in the semiconductor equipment sector. In 2025, Crescendo initiated the sale of its 40.9% controlling equity stake in the semiconductor firm, often dubbed Korea's ASML. The three major global PEF firms, Kohlberg Kravis Roberts (KKR), Carlyle, and Blackstone, which are dubbed the "big three buyout funds", have submitted their bids. The firm also plays an important role in the Korean semiconductor industry through investments and support of other companies like Hanmi Semiconductor [ko], Samyang NCchem [ko]. and Movensys (originally known as Soft Servo Group or Soft Motions & Robotics; the name was changed to Movensys in 2021 after Crescendo's investment). The firm also invests in companies that make metal equipment, including Seojin System and Model Solution. Thiel began to explore investing in charter cities on land after his interest in seasteading faded. Thiel is the anchor backer of Pronomos Capital, a firm "set up like a venture capital fund" that seeks to establish experimental, semi-autonomous cities in vacant lands, with acceptance from the countries involved. The founder of the firm is Patri Friedman. Projects backed by the firm include Próspera in Honduras. The Próspera project attracted companies like Oklo Inc. (nuclear startup backed by Thiel's Mithril and Sam Altman) and biotech startups, but led to legal struggles when the new Honduran government changed the laws in 2022. Praxis is a company that seeks to establish a new city-state and has explored Greenland as a possible location. In 2025, when the Danish government was integrating Palantir into the country's military, police and intelligence services, a major argument put forth by opponents was that the Praxis project (backed by Thiel through Pronomos) was a threat to Greenland. Other arguments were concerned with Thiel's politics in the US and Palantir's association with American and other European intelligence services, as well as the security risk that might arise from handing citizens' data to Palantir. The Danish National Police answered with a reference to a 2021 response to the Folketing, but otherwise, the Police, the Danish Security and Intelligence Service and Minister of Justice Peter Hummelgaard refused to comment on the matter. The firm was found in 2023 by Jason Camm (Chief Medical Officer of Thiel Capital). The regulatory filing does not disclose the name of the single investor who provides US$100 million or Thiel's involvement beyond the use of his name. The fund has invested in Ataraxis AI and EnClear Therapies together with the Founders Fund. Reports about investments in October 2025 (infection therapeutics company Peptilogics and cancer treatment startup HistoSonics) confirm that the firm is Thiel's. Hannes Holste from Thiel Capital is a partner. Thiel owns multiple entities named Rivendell, such as Rivendell One LLC, Rivendell 7 and Rivendell 25. Rivendell 7 and Rivendell 25 are personal investment vehicles, which are also used to hold Palantir shares. ProPublica reports that Thiel’s $1,700 PayPal investment and later investments In Palantir and Facebook through a Roth IRA had grown tax-free to over $5 billion by 2019. The Roth was held in Rivendell Trust since 2018. Thiel bankrolled the satellite imaging startup HySpecIQ, known for serving government agencies but struggling financially, through Rivendell Fund. Rivendell entities are known to participate in his German or Korean investments. According to a 2020 article from Bloomberg, Thiel was at the time an investor in funds managed by 8VC and in the bank Disruptive Technology Advisers. A 2017 Globe and mail article names Thiel as a limited partner at Social Capital. He also sponsored Sam Altman's first venture fund, Hydrazine Capital as well as J.D.Vance's Narya Capital. He also backs Doepfner Capital, the venture fund of Moritz Döpfner, the son of Mathias Döpfner. He funded 90% of Zeev Ventures's first fund and has backed it ever since. The Founders Fund was also a backer of the second fund of the Indonesia-focused Intudo. The involvement helped Intudo to validate its mission. Founders Fund is also among the backers of the Israel-based Mensch Capital. Thiel also backs the Singaporean venture investment firm Syfe Group through Valar. The Founders Fund also invested in the Seattle-based private equity fund Privateer Holdings in 2015, thereby becoming the first institutional investor in the cannabis industry. His first investment in a hedge fund managed by an outside manager was made in 2011: the firm was Grandmaster Capital Management, founded by Patrick Wolff, former Clarium and Thiel Macro executive. Also in 2011, he backed the second fund of Joshua Kushner's Thrive Capital. In 2019, Thiel, together with Mark Cuban and Marc Andreessen, backed the San Francisco-based crypto investment fund 1Confirmation. Thiel gives backing to Vivek Ramaswamy's financial firm Strive Asset Management, also described as an activist fund. The firm aims to free "corporate America" of what they deem to be "stakeholder capitalism" ESG mandates created by the three companies BlackRock, Vanguard and State Street and accuse them of causing the energy crisis. The firm does not deny climate science. In 2021, Thiel backed the first fund of A-Star Partners, founded by Kevin Hartz, former partner at Founders Fund. In 2022, he backed B2B-focused Wischoff Ventures founded by solo GP Nichole Wischoff. Thiel is also a major backer of the venture debt firm Tacora, founded by Keri Findley. Its inaugural fund in 2022 raised US$350 million in total, including US$250 million from Thiel. Bloomberg comments that, "It's an unusually large investment for Thiel, the size of which hasn't been previously reported." Findley was originally an associate of Danzeisen, whom she met because she and Thiel Capital both invested in SoFi. Thiel agreed to fund her after she discussed the idea with him at a casual dinner. Alexandra Ulmer and Joseph Tanfani from Reuters remark that Thiel was an instrumental force behind the creation of 1789 Capital, which was co-founded in 2022 by Omeed Malik and Chris Buskirk, a confidant of Thiel's. Blake Masters is also a board member. The fund is intended to create a "parallel economy", a network that combines "businesses, media outlets and political organizations" associated with the America First movement. In 2024, it recruited Donald Trump Jr. as a partner. He personally invests in Quora (leading its Series B), Reddit, and nuclear startup Seaborg Technologies (now Saltfoss Energy). He served on AbCellera's board from 2020 to 2024, when he resigned for personal reasons. Both sides stated that there was no disagreement, with Thiel saying that he was proud to have helped the company and AbCellera's founder Carl Hansen thanking him for his mentorship. He also retains his stake in the company, as of November 2024. In March 2015, Thiel joined Y Combinator as one of 10 part-time partners. In November 2017, it was reported that Y Combinator had severed its ties with Thiel. In 2024, Thiel became the lead funder of the Enhanced Games, a proposed multi-sport event that will allow athletes to use performance-enhancing substances without being subject to drug tests. The founder is the Australian lawyer Aron D'Souza, who came to know and become Thiel's confidant in the process of leading the Gawker case for him. Angermayer, who was introduced to D'Souza by Thiel, also invested, even though, as per Wired, Thiel and Angermayer were not normally interested in sports. The startup agrees to cover legal expenses for any clean athletes who participate in the event and are banned from mainstream competitions as a result. In 2018, the Founders Fund invested in the Israeli company Carbyne (emergency service). Leaked emails (released by the hacker group Handala, which "likely operates out of Iran's Ministry of Intelligence", according to Reuters) show that in 2014, Jeffrey Epstein leveraged his relationship with former Israeli Prime Minister Ehud Barak to get access to Thiel. Epstein arranged for Barak to meet Thiel in New York on June 9, 2014. In 2016, Epstein pitched Reporty (later Carbyne) to Valar, but the proposal got rejected on account of being premature (Epstein invested in total 40 million in Valar in 2015 and 2016).). Valar's McCormack said they would try to reengage when the startup was more developed. In 2018, the Founders Fund joined Carbyne's $15 million Series B. Thiel said that the subsequent interactions with Epstein following their introduction in 2014 were due to the fact Epstein was a "crazed networker". One of the people introduced to Thiel by Epstein was the Russian diplomat Vitaly Churkin. Byline Times suggests that Epstein was one of contact points that Thiel used for his political network in the UK, including with on the Labour Party (UK), although there is no record of Thiel's social visits to Epstein's homes or flights on his jet. Documents reviewed by The Wall Street Journal in 2023 show that there were scheduled meetings (half a dozen between 2014 and 2016) between Thiel and Epstein, including with others such as Woody Allen and Obama's advisor Kathryn Ruemmler. Reid Hoffman, Thiel's friend from the PayPal Mafia and a big Democratic donor was the one who directly introduced Thiel to Epstein (for years Epstein acquaintances had tried to invite Thiel to meet Epstein but were rejected) and also participated. Documents from the US House of Representatives showed Epstein invited Thiel to his private island in 2018. A spokesperson for Thiel said he never visited the island. In 2025, Snopes criticized a claim on the internet that Epstein offered girls to Thiel and others as misleading by omitting context. Journalist Whitney Webb claims Palantir is a CIA front, and links Thiel to the CIA, Mossad, and Epstein's alleged plan for an "Orwellian nightmare." Webb has shared these theories via the Chinese website of MintPress News – known for being part of the "Russian web of disinformation" – and Trineday, a publisher founded by conspiracy theorist Kris Millegan. The Washington Report on Middle East Affairs lists her as a MintPress journalist. Euronews writes that there is no known major financial connection between Thiel and Epstein, but Thiel seemed to treat Epstein as a contact point. The San Francisco Standard comments that around the time, other Israeli officials (acting independently of Barak) tried to build contact with Thiel as well, often aiming at a "lucrative" job at Palantir. Gawker lawsuit In May 2016, Thiel confirmed in an interview with The New York Times that he had paid $10 million in legal expenses to finance several lawsuits brought by others, including a lawsuit by Terry Bollea (Hulk Hogan) against Gawker Media for invasion of privacy, intentional infliction of emotional distress, and infringement of personality rights after Gawker made sections of a sex tape involving Bollea public. The jury awarded Bollea $140 million, and Gawker announced it was permanently closing due to the lawsuit in August 2016. Thiel referred to his financial support of Bollea's case as one of the "greater philanthropic things that I've done." Thiel said he was motivated to sue Gawker after they published a 2007 article publicly outing him, headlined "Peter Thiel is totally gay, people." Thiel stated that Gawker articles about others, including his friends, had "ruined people's lives for no reason," and said, "It's less about revenge and more about specific deterrence." In response to criticism that his funding of lawsuits against Gawker could restrict the freedom of the press, Thiel cited his donations to the Committee to Protect Journalists and stated, "I refuse to believe that journalism means massive privacy violations. I think much more highly of journalists than that. It's precisely because I respect journalists that I do not believe they are endangered by fighting back against Gawker." Owen Thomas, the author of the Gawker article, stated that he did not think it was an outing in the conventional sense, as Thiel had been open about his homosexuality, but the "strangely conservative" Silicon Valley had refused to talk about it. Thiel said that the problem was less about the outing itself, but the troubles it caused with regard to his business in Saudi Arabia and his parents. On 15 August 2016, Thiel published an opinion piece in The New York Times in which he argued that his defense of online privacy went beyond Gawker. He highlighted his support for the Intimate Privacy Protection Act and said that athletes and business executives have the right to stay in the closet as long as they want to. In an open letter to Thiel after losing the case, Gawker's Nick Denton accused Thiel of making them "stripped naked", together with the warning "in the next phase, you too will be subject to a dose of transparency. However philanthropic your intention, and careful the planning, the details of your involvement will be gruesome." Later though, in 2025, Denton said that Thiel was right and did him a favor in forcing the sale of Gawker Media. Views and political activities Thiel is described by different authors and media sources in different ways. He identifies as a libertarian. He has been called an Ayn Rand libertarian, plutocratic reactionary, militarist techno-libertarian, and libertarian authoritarian. His attitude towards democracy has been described as democracy-skeptic, partly antidemocratic, or post-democratic. French economist Yann Algan links Peter Thiel and Elon Musk to the concept of "liquid democracy" and the rise of libertarian AI governance, which Algan defines as "a radically decentralized, algorithm-driven democracy", which "prioritizes efficiency and individual freedom over democratic safeguards". Thiel's biographer Max Chafkin notes that his thinking is a mix of libertarianism and authoritarianism, but describes what Thiel truly believes and wants as a mystery. Thiel describes himself as a political atheist. He opines that trying to radically alter the current U.S. government is unrealistic. He also suggests that Curtis Yarvin methods will lead to Xi's China or Putin's Russia. He does not deny the value of statemanship though,[N 5] but opines that "people should spend less time trying to change the system than simply creating things outside it". Journalist Murad Ahmed from Financial Times calls Thiel "philosopher king at the very top of Silicon Valley" (with France 24 using a similar description). German philosopher Peter Sloterdijk also remarks: "Peter Thiel can be seen as more of a philosopher king. He acts very coolly and strategically – a dazzling figure, far outside our left-liberal perception patterns", while Ross Douthat from New York Times describes him as "most influential right-wing intellectual of the last 20 years". Commenting on Douthat's description, Luke Munn of the University of Queensland notes that, "Thiel's influence on politics is at once financial, technical and ideological [...] his potent cocktail of networks, money, strategy and support exerts a rightward force on the political landscape." In 2025, the author Ijoma Mangold [de] wrote an article for Die Zeit, describing Thiel's theories as obscure and incoherent at first glance, but often displaying an accurate intuition, while noting that both the man and his ideas "simultaneously fascinates, repels, and outrages." Later the author René Martens wrote on Mitteldeutscher Rundfunk, criticizing Mangold and Die Zeit for masking their admiration with pseudo-criticism and called Thiel a disciple of Carl Schmitt. In 2009, The Guardian stated that Thiel was a member of the neoconservative, Reaganite/Thatcherite "TheVanguard.org". The outlet said Thiel believes the Enlightenment led humanity from nature's rule to a world where nature has been conquered, and also noted Thiel's philosophy disregarded art, beauty, love, pleasure, and truth. The Guardian linked Thiel's investment in projects like the Singularity Institute to his belief in life-extension technologies as an escape from humanity's "nasty, brutish, and short" life. It criticized him for seeking to replace the natural world with a virtual one. Vadym Kovalenko notes that during the 90s and 2000s, Silicon Valley followed the spirit of Steve Jobs, who saw technology as art. But later this has translated into Thielism, which emphasizes "truth, the ideal, ontology" and matters like flying to Mars, curing aging and creating a new world over the superficiality. Kovalenko sees Thiel as a humanitarian Über-artist. On the question of exotericism versus esoteticism, Paul Leslie writes that in "The Straussian moment", Thiel tries to "weave together Schmitt's political theology—with its emphasis on the friend/enemy distinction—and Strauss's advocacy for esoteric wisdom and hidden hierarchies." In the article "Exotericism and the Untroubled Race for the Future", Thiel discerns between ancient esotericism, in which "thrice-great Hermes revealed his magical recipes only to a few" and "modern esotericism of grantwriting". He remarks, though, that exotericism takes time, and Goethe was "perhaps [...] the last human being to command the sum total of human knowledge." Writing for the Quarterly Journal of Speech in 2024, James Rushing Daniel wrote that: (...) "a rhetor ambitiously capitalizing on the material crises and political disillusionment of the day, defending a "cultural revolution" to put an end not just to the progressivism of the long 1990s but the values of collectivism and social justice and the remnants of social democracy and the Keynesian welfare state, replacing them with Randian individualism and the absolute dominance of the capitalist project." According to Daniel, Thiel has financially supported the intellectual wing of "the reactionary, traditionalist turn of conservative politics" termed by some as "the New Right". The Nation notes that he advocates "for a dramatic, right-wing political turn to address technological stagnation". Nick Land attributed Thiel's 2009 essay "The Education of a Libertarian" and statement that "I no longer believe that freedom and democracy are compatible" as a watershed moment in the development of the Dark Enlightenment movement. Patrick Zarrelli argues the quote is misread as anti-democratic, when Thiel's real concern is that mass democracy could erode the freedoms essential for innovation, but notes that Thiel underestimates the limits of technocracy like lack of democratic accountability. Zarelli remarks that Thiel has partially realized his philosophy: "By aligning technology with national priorities like defense modernization, pandemic response, and intelligence fusion. He has built parallel governance inside the state itself.", and notes that critics call Thiel a "shadow oligarch". Zarelli opines that a solution might be a hybrid form between technocracy and democracy. Italian professor Giuliano da Empoli opines that Thiel represents the alliance between the post-modern Silicon Valley and the archaic Trump, that threatens democracy. The author recognizes that the Silicon Valley actors are gifted and have the means to govern more efficiently than democratic institutions in some respects. He argues that humanity must not respond to post-modern tech leaders like the Aztecs did to the conquistadors, but must instead make deliberate choices about which areas should still prioritize democratic decision-making, even at the risk of less efficient outcomes. In his book L'Empire de l'ombre, Da Empoli echoes the sentiment of Thiel's quote, "Darker questions still emerge in these dusky final weeks of our interregnum," interpreting the "apocalypse" not as the end of the world, but as a sudden unveiling of forces that had long been taking shape beneath the surface. Blue Labour founder Maurice Glasman (who first met Thiel at Oxford, where Glasman rebuked Thiel's description of the British Empire as the Antichrist) denounces Thiel's view on democracy but defends leftist politicians' interaction with Thiel, saying that parties which have no place in the AI conversation will be out of the game very fast. Danish politician Christopher Arzrouni [da] dismisses Dagbladet Information's description of Thiel as a Prussian warhorse (preussisk kamphest) or a bigot tech prince who would bring the end of democracy or the world, calling him "a smart European who finds better opportunities in the U.S.", and criticizes European intellectuals' fear of new technology. Jacob Silverman noted that Thiel's actual political work drifted away from libertarianism, but it remained his intellectual guiding star. Jack Nicastro of Reason notes that Thiel's solution for "the dangers of government overreach and a one-world state" is "surprisingly libertarian". George A. Dunn believes that Thiel is the pathbreaker in connecting the thoughts of Girard and Strauss to debates on the origins of modernity. Thiel is a self-described conservative libertarian. Since the late 2010s, he has espoused support for national conservatism, and criticized economically liberal attitudes towards free trade and Big Tech. Thiel advocates that companies should avoid competition and attention, and try to develop into monopolies by creating something new, dominate a niche market before expanding into slightly broader markets. He notes that years or even decades of profits can come from such specific markets. In The Straussian Moment, Thiel notes that, "Since 1920, the vast increase in welfare beneficiaries and the extension of the franchise to women – two constituencies that are notoriously tough for libertarians – have rendered the notion of 'capitalist democracy' into an oxymoron." After the statement caused controversies, he replied that, he had made a "commonplace statistical observation about voting patterns that is often called the gender gap", and that women's right to vote was not under siege nor would taking it away solve any problem, but people should focus on projects outside of voting and politics. Adam Rogers contends that this essay has prefigured the Department of Government Efficiency project. In the 2025 Douthat interview, Thiel stated that, "Reagan was consumer capitalism, which is oxymoronic. You don't save money as a capitalist; you borrow money. And Obama was low-tax socialism – just as oxymoronic as the consumerist capitalism of Reagan." In 2021, Thiel wrote an article for Die Welt, claiming that the extreme political experiments of fascism and communism in the 20th century had led Germany to fear extremism in both politics and technology. However, as "the decisive arena for the future of the West", being the land of poets and thinkers would not be enough for Germany in the new era. He criticized "green quietism" and opined that new ideas could be dangerous but would be the source of growth. In a 2015 conversation with Tyler Cowen, Thiel claimed that innovative breakthroughs were happening in computing/IT and not the physical world. He lamented the lack of progress in space travel, high-speed transit, and medical devices. As a cause for the discrepancy, he said: "I would say that we lived in a world in which bits were unregulated and atoms were regulated." The Founders Fund and Khosla Ventures are backers of the Hill & Valley Forum, a group that is described by the Wall Street Journal as an anti-China alliance between Silicon Valley and Capitol Hill. In an article named Silicon soldiers of fortune, the China Daily, the channel of the Central Propaganda Department of the Chinese Communist Party, identifies Thiel, Palmer Luckey and Jacob Helberg as tech hawks who are increasingly shaping the US policy towards China. The Xinhua News Agency, China's official state news agency, states that Palantir and its leaders like Thiel and Vice President Wendy R. Anderson as well as other companies like Anduril and Saronic Technologies, as representatives of "the new military industrial complex", are an unpredictable danger to the US and the international community. The tech-focused outlet 36Kr though praises his long-term vision and methods in breaking down the traditional barriers in the US military-industrial complex and government sector, and his contribution to leading startups like Palantir, Anduril and SpaceX. The Brazilian newspaper Brasil de Fato (described by The New York Times as part of a "global web of Chinese propaganda") portrays Thiel as "the brightest anti-communist in the US", part of the anti-China brigade, "the leader of the tech-based section of the military-industrial complex" as well as "the most geo-politically strategic tech billionaire" and "the most dangerous non-state figure in the world today". According to Brasil de Fato, among all the capitalists, Thiel has the strongest grip on the National Security Council. In 2019, Thiel called Google "seemingly treasonous" and urged a government investigation, citing Google's work with China and asking whether DeepMind or Google's senior management had been "infiltrated" by foreign intelligence agencies. In 2025, Thiel called for a drastic reset in economic relations with China, stressing that economic relations should be viewed from a geopolitical standpoint as well. In an discussion with Peter Robinson, he opined that the US should not let itself be stuck between two extreme views about China (that China itself encourages to promote an attitude of political inaction towards them): "It's China is super weak, and China is super strong. And I've been in meetings in China where in some sense you got both messages within 20 minutes of one another, and it's like logically inconsistent but psychologically it doubles up." In 2024, Palantir became a strategic partner of Israel in military technology in an occasion both Thiel and Karp visited the country. In a 2024 interview with Bari Weiss, Thiel advocated cooperation with Israel to deter Iran from getting nuclear weapons: One of the lessons I take of the mid-20th century was every time a country got a nuclear weapon, we got a regional war. The Soviet Union gets the bomb in 1949. The Korean War starts in 1950 because when the Soviet Union backs North Korea, we can't bomb Russia. Then they can back North Korea with impunity, and we get a massive, massive regional war. That's, in a way, the price for being asleep at the switch and letting the Soviets get the bomb. 1964, Communist China gets the bomb. Vietnam War explodes in 1965. And again, China can back North Vietnam with impunity. We can't reciprocate. And the way I understand why would an Iranian nuclear bomb be a catastrophe? Because the degree to which Iran can support this plethora of bad actors, the Houthis, the Hamas people, and Hezbollah, and on and on throughout the Middle East, you could not retaliate against Iran [...] And so we don't have to go to the crazy theocracy that said they'd use the bomb and would use it. Regarding the Russia-Ukraine war, he opined that "the relentless NATO expansion might not have been a good idea", but the US could not simply retreat from Ukraine, because it would become a rout. In 2025, writing for the Singapore-based think tank ThinkChina, Artyom Lukin, a leading Russian expert on Asia-Pacific geopolitical issues, wrote that Thiel, whom Lukin described as "the éminence grise of Trump's own deep state" and "the most anti-China figure in the US top elite", together with his allies, were pushing the American geostrategy towards focusing on China (a country Thiel saw as "a half fascist, half communist gerontocracy" with "a socialism of a nationalistic sort, and [...] extremely racist.") as the paramount threat. Lukin noted that Thiel had little sympathy for Russia, but viewed it as a lesser threat and did not want to push Moscow towards Beijing's arms. According to The Intercept, Thiel is the source of the warrior culture in Silicon Valley, one focused on an arms race with China, although the anti-China sentiment is found on both sides of the political spectrum. Alex Karp notes that Palantir has a warrior culture, which values excellence over money. Thiel is a member of the Steering Committee of the Bilderberg Group, a gathering of intellectual figures, political leaders, and business executives, characterized as focused on defense and espionage, as well as Atlanticist and Europhile. Thiel's outsized influence at the gathering has been noted. Thiel, together with Auren Hoffman, is also the founder of Dialog, which is often compared to Bilderberg, but focuses more on tech. It does not share the lists of participants but is known to have invited American tech and political leaders, as well as intellectual heavyweights, on both sides of the political spectrum, as well as representatives from Europe and Middle East. Past topics included "AI's energy demands, the future of health care, and political realignments" and "caring for aging parents, love, mental health and the afterlife." Palantir is partner of the World Economic Forum, but Thiel has not gone to the meeting since 2013, because he considers it a place without individuals – there are only representatives of companies, governments and NGOs. He opines that some types of global governance might work, but it is necessary to have dissenting views. The Thiel Foundation is a supporter of the Committee to Protect Journalists (CPJ), which promotes the right of journalists to report the news freely without fear of reprisal. Beginning in 2008, Thiel has donated over $1 million to the CPJ. He is also a supporter of the Human Rights Foundation, which organizes the Oslo Freedom Forum. In 2011 he was a featured speaker at the Oslo Freedom Forum, and the Thiel Foundation was one of the event's main sponsors. He also backs the Alliance of Democracies Foundation founded by Anders Fogh Rasmussen. Thiel has supported mostly conservative gay rights causes such as the American Foundation for Equal Rights and GOProud. He invited conservative columnist and friend Ann Coulter to Homocon 2010 as a guest speaker. Coulter later dedicated her 2011 book, Demonic: How the Liberal Mob Is Endangering America, to Thiel. In 2012, Thiel donated $10,000 to Minnesotans United for All Families, in order to fight Minnesota Amendment 1 that proposed to ban marriage between same-sex couples there. In 2009, it was reported that Thiel helped fund James O'Keefe's "Taxpayers Clearing House" video—a satirical look at the Wall Street bailout. O'Keefe went on to produce the ACORN undercover sting videos; Thiel denied involvement in the ACORN sting. In July 2012, Thiel made a $1 million donation to the Club for Growth, a fiscally conservative 501(c)(4) organization, becoming the group's largest contributor. He is a major backer of the conservative Rockbridge Network, which is now an international network with Asian branches. In 2023, Business Insider reported that Thiel became an FBI informant in 2021. Business Insider also noted the fact that politicians sponsored by Thiel, including Vance and Masters, had repeatedly attacked the FBI and its leadership in public. According to former FBI agent Jonathan Buma, Peter Thiel, Elon Musk and David Sacks have been targets of Russian intelligence. Buma notes that Thiel cooperated with the FBI to identify the foreign espionage network. He visited president of Argentina and fellow libertarian Javier Milei three times in 2024. The Noticias de América Latina y el Caribe (NODAL) remarks that the cooperation between Thiel and Milei marks the political alignment between Argentina and Washington and Silicon Valley, also through organizations like Endeavor. According to NODAL, the introduction of Argentina into Thiel's network is erasing traditional politics while promoting a tech-based order which increases efficiency but also puts sovereignty at stake. Matt Stoller, research director of American Economic Liberties Project, remarks that Thiel is a "really smart nihilist", and notes that his focus is entirely on power. Thiel's biographer Max Chafkin writes that this is a likely explanation for Thiel's activities. In 2017, Thiel reportedly refused the offer to become chairman of the president's intelligence advisory board, despite Trump's urging. In the same year, there were reports that he considered becoming U.S. Ambassador to Germany or a bid for governorship of California. At the time, he said that he was not interested in a full-time job in politics. In 2024, he said that he had gotten used to tech and a full-time job as a politician would lead to depression. Thiel is a member of the Republican Party. He contributes to both Libertarian and Republican candidates and causes. In December 2007, Thiel endorsed Ron Paul for President in the 2008 United States presidential election. After Paul failed to secure the Republican nomination, Thiel contributed to the John McCain campaign. In 2010, Thiel supported Republican Meg Whitman in her unsuccessful bid for the governorship of California. He contributed the maximum allowable $25,900 to the Whitman campaign. In 2012, Thiel, along with Nosek and Scott Banister, put their support behind the Endorse Liberty Super PAC. Collectively they gave $3.9 million to Endorse Liberty, whose purpose was to promote Ron Paul. After Paul again failed to secure the nomination in the 2012 United States presidential election, Thiel contributed to the Mitt Romney/Paul Ryan presidential ticket of 2012. Thiel initially supported Carly Fiorina's campaign during the 2016 GOP presidential primary elections. After Fiorina dropped out, Thiel supported Donald Trump and became one of the California delegates for Trump's nomination. He was a headline speaker during the 2016 Republican National Convention, during which he announced that he was proud to be gay, Republican, and American, for which the assembled Republicans cheered. On 15 October 2016, Thiel announced a $1.25 million donation in support of Donald Trump's 2016 presidential campaign. Thiel stated to The New York Times: "I didn't give him any money for a long time because I didn't think it mattered, and then the campaign asked me to." After Trump's victory, Thiel was named to the executive committee of the president-elect's transition team. In 2017, Gavin Newsom (then lieutenant governor of California), whose campaign and marijuana legalization effort Thiel had supported, noted that Thiel cared deeply about criminal justice reform and had done a lot of behind-the-scene good work on marriage equality, which he was also passionate about. Newsom remarked, though, that "None of us are jumping up and down that he's aligned himself with President Donald Trump." By February 2022, Thiel was one of the largest donors to Republican candidates in the 2022 election campaign. By November 2022 he had spent 32 million. He supported 16 senatorial and congressional candidates. Two of said senatorial candidates (Blake Masters (who lost his race) and later U.S. Vice President JD Vance) were also tech investors who had previously worked for Thiel. In 2023, Barton Gellman of The Atlantic wrote in an article interviewing Thiel that Thiel "has lost interest in democracy" and that "he wouldn't be giving money to any politician, including Donald Trump, in the next presidential campaign". According to Reuters this occurred after he disagreed with the Republican party's focus on cultural issues. In the same Atlantic interview, he stated that the first Trump administration failed even his initial low expectations. In 2024, he described Trump as a clown whom Reid Hoffman's lawsuit turned into a martyr. In 2025, when interviewed by Ross Douthat, Thiel indicated that Trump and the populists were a disruptive factor that would prepare the stage for the process of true rebuilding (in 2023, he also opined that Trump's election would "slash regulations, crush the administrative state – before the country could rebuild"). He stressed that the support of large parts of the Silicon Valley for Trump was not pro-Trump in nature. He stated that disruption did not equal progress, and even his thought of trying to having a conversation with Trump about it (in Trump's first term) later proved "a preposterous fantasy". But he was satisfied about the fact that in the second term, deregulation was happening, for example regarding nuclear energy. Thiel has his own political-action committee, Free Forever, which is committed to supporting political candidates who support stricter border control, restrictive immigration policy, funds for veterans, and anti-interventionist foreign policy, among other things. According to OpenSecrets, the PAC was active only during the 2020 election cycle and then only in support of Kansas attorney general Kris Kobach's failed U.S. Senate bid. The campaign by Kobach, who lost in the Republican primary, had received almost all of its contributions from Thiel himself. In 2025, Brendan Glavin, director of insights for OpenSecrets, remarked that Thiel's political donations have "an ideological agenda that's not strictly motivated by financial or business concerns [...] His views are libertarian generally, and he wants to elect people who are like minded." Philanthropy Thiel carries out most of his philanthropic activities through the Thiel Foundation. In 2006, Thiel provided $100,000 of matching funds to back the Singularity Challenge donation drive of the Singularity Institute for Artificial Intelligence (now known as the Machine Intelligence Research Institute), a nonprofit organization that promotes the development of friendly artificial intelligence. He provided half of the $400,000 matching funds for the 2007 donation drive, and as of 2013 the Thiel Foundation had donated over $1 million to the institute. Additionally, he has spoken at multiple Singularity Summits. At the 2009 Singularity Summit, he said his greatest concern is the technological singularity not arriving soon enough. In December 2015, OpenAI, a nonprofit company aimed at the safe development of artificial general intelligence, announced that Thiel was one of its financial backers. In September 2006, Thiel announced that he would donate $3.5 million to foster anti-aging research through the non-profit Methuselah Mouse Prize foundation. He gave the following reasons for his pledge: "Rapid advances in biological science foretell of a treasure trove of discoveries this century, including dramatically improved health and longevity for all. I'm backing Dr. [Aubrey] de Grey, because I believe that his revolutionary approach to aging research will accelerate this process, allowing many people alive today to enjoy radically longer and healthier lives for themselves and their loved ones." As of February 2017, he had donated over $7 million to the foundation. When asked "What is the biggest achievement that you haven't achieved yet?" by the moderator of a discussion panel at the Venture Alpha West 2014 conference, Thiel said he wants to make progress in anti-aging research. Thiel also said that he is registered to be cryonically preserved, meaning that he would be subject to low-temperature preservation in case of his legal death in hopes that he might be successfully revived by future medical technology, and is signed up with the Alcor Life Extension Foundation. Thiel has expressed interest in the science of parabiosis, including young blood transfusion for potential health benefits. He said in a 2016 Inc. interview that the technology had been found to work on mice before being strangely dropped after the 1950s. The same Inc. article reported that the Thiel Capital medical director Jason Camm had contacted the transfusion startup Ambrosia, but its founder Jesse Karmazin told TechCrunch in a 2017 article that they had never been contacted by Thiel or Thiel Capital. In a 2022 Jacobin article, Ben Burgis characterizes the blood transfusion story as part of a deliberate attempt by Thiel to portray himself as an "evil genius". On 15 April 2008, Thiel pledged $500,000 to the newly created non-profit Seasteading Institute, directed by Patri Friedman, whose mission is "to establish permanent, autonomous ocean communities to enable experimentation and innovation with diverse social, political, and legal systems." At one of the institute's conferences, he described seasteading as "one of the few technological frontiers that has the promise to create a new space for human freedom." In 2011, Thiel gave $1.25 million to the Seasteading Institute, but resigned from its board the same year. In a 2017 interview with The New York Times, Thiel said seasteads are "not quite feasible from an engineering perspective" and "still very far in the future". On 29 September 2010, Thiel created the controversial Thiel Fellowship, which annually offers them a total of $100,000 (raised to $200,000 since 2025) over two years to 20 people under the age of 23 in order to spur them to drop out of college and create their own ventures. According to Thiel, many young people choose college simply because they're unsure of what else to do with their lives. He envisions a future system that offers different paths for different people, and believes that change in the university system will require external pressure ("Reformation") before any internal willingness to adapt can arise. In November 2011, the Thiel Foundation announced the creation of Breakout Labs, a grant-making program intended "to fill the funding gap that exists for innovative research outside the confines of an academic institution, large corporation, or government." It offers grants of up to $350,000 to science-focused start-ups, "with no strings attached". In April 2012, Breakout Labs announced its first set of grantees. In total, 12 startups received funding, for a total of $4.5 million in grants. One of the first ventures to receive funding from Breakout Labs was 3Scan, a tissue imaging platform. Breakout Ventures is a privately held venture capital firm founded in 2016 out of Breakout Labs to invest in science. Based in San Francisco, California, it invests in early-stage companies in technology, biology, and chemistry focused on human health and sustainability. The program focuses on biotech with a mix of hardware. Its partners include Founders Fund, Formation 8, OATV, Lux Capital, Khosla Ventures among others. Some of its recent investments include Noetik (cancer treatment), Phantom Neuro (neurotechnology). Corpernic Catalysts (catalysts for ammonia production), EnPlusOne Biosciences (RNA therapeutics), Passkey Therapeutics (synergistic multifunctional therapeutics), Cytovale (medical diagnostics). In 2011, Thiel made a NZ$1 million donation to an appeal fund for the casualties of the Christchurch earthquake. In Girard's honour, he has established the Imitatio project (part of the philanthropic Thiel Foundation), which aims to "supports research, education, and publications building on Rene Girard's mimetic theory." Personal life Thiel resided in San Francisco, California, until 2018, when he moved to Los Angeles. He had criticized San Francisco for being "intolerant of conservatives, insular and overpriced". Both Thiel Capital and Thiel Foundation followed him to Los Angeles, but the Founders Fund remains in San Francisco. Mithril's headquarters moved to Austin. Thiel married his long-time partner, Matt Danzeisen, in Vienna, Austria, on Thiel's 50th birthday (October 2017), when he was reported to have proposed to Danzeisen. Danzeisen started his career as an investment banker at Bank of America Securities. By 2007, when the couple were dating, Danzeisen was vice president of BlackRock. By 2021, he was chairman of Bridgetown 1 and Bridgetown 2, sponsored by Thiel Capital and Richard Li's Pacific Century Group. Sam Altman also sat on the board. Danzeisen also participates in other Thiel enterprises related to the family of Li Ka-shing (father of Richard Li), such as the Malta-based EUM. In 2017 Danzeisen was working as head of private investments at Thiel Capital, with a primary focus on North America and Asia. Thiel and Danzeisen have two young daughters, aged five and three as of June 2024, born through a surrogate. Adrian Wooldridge from Bloomberg reported in August 2025 that Thiel had four children. In 2023, in an interview with the Atlantic, Thiel noted that Danzeisen had tried to dissuade him from donating money to Republicans. Thiel was in a long-term relationship with model Jeff Thomas until Thomas's suicide in March 2023. Media coverage of Thomas's death drew widespread attention, partly because of Thomas's involvement with Democratic researchers led by David Brock and Jack Bury. Puck.news wrote that the anti-Thiel campaign exposed an undercurrent in modern politics in which there is an increasing tendency towards using people's private problems to achieve political goals. Thiel is a self-described Christian and a promoter of René Girard's Christian anthropology. Girard, a Catholic, explained the role of sacrifice and the scapegoat mechanism in resolving social conflict, which appealed to Thiel as it offered a basis for his Christian faith without the fundamentalism of his parents. Thiel grew up in an evangelical household but, as of 2011, described his religious beliefs as "somewhat heterodox", stating: "I believe Christianity is true but I don't sort of feel a compelling need to convince other people of that." According to Thiel, "Christianity for me is the anti-identity. Your identity is in Christ [...] and it's in that context we can figure out things about the world and truth [...] [Truth] is not a social construct." Thiel has participated in Veritas Forum events with the theologian N. T. Wright discussing religion, politics, and technology. Thiel opines that wokeism or "the woke religion" is a type of secular religion, which is "in some ways [...] anti-Christian and some ways [...] hyper-Christian" and fills the void of a weakened Church because people are attached to post-Christian values rather than a "rationalist, atheist" worldview. He notes that wokeism has a concept of the original sin as well as demands confession and repentance, while offering no transcendental values, no forgiveness or chance of redemption through sacrifice. He claims that this strand of thinking, which attacks Christians for not doing enough for victims or the poor, is a continuation of communism and the social gospel, which also inherit some Christian characteristics while being anti-Christian at the same time. Mikhail Minakov writes that "Thiel's conception of will integrates Christian eschatology, Girardian mimetic theory, and Straussian elitism to critique the impotence of liberal democracy while proposing the efficiency of a techno-feudal alternative." Elke Schwarz, a professor of political theory, notes that Peter Thiel and Marc Andreessen are the foremost proponents of techno-eschatology, which demonstrates the sacralizing of AI and uses spiritualism to bolster the logic of venture capitalism. Thiel opines that, "Crypto is decentralizing, AI is centralizing. Or, if you want to frame it more ideologically, crypto is libertarian and AI is communist." A topic Thiel is interested in is the Antichrist, Armageddon and Apocalypse, about which he has given talks in multiple events, including a September 2025 series of off-the-record private lectures organized by David Wood's Acts 17 Collective in San Francisco, which drew a group of protesters. Thiel opines that different people are worried about different apocalyptic threats like environment degradation, nuclear wars or bioweapons. He recognizes these as credible threats, but sees a total one-world government as closer to the Antichrist. He sees humanity as facing the double threats of the Antichrist and the Armageddon, which is the collapse of civilization through global warfare. He sees salvation in the figure of the Katechon, a mysterious force that restrains the Antichrist. He has referred to individuals, organizations, communism or even anti-tech regulations as precursors of the Antichrist. For example, he referred to environmental activist Greta Thunberg and AI safety advocate Eliezer Yudkowsky as “legionnaires of the Antichrist”. Different commentators see his Antichrist theory as a narrative to highlight the role of a hero, or a framework to attack political opponents or an attempt to brand himself as tech's free thinker (who has also touched on topics such as the Kennedy assassination, Epstein's crimes or aliens). Kayla Carman from the Russian Strategic Culture Foundation writes that the hero Thiel describes is implied to be Thiel himself, and states that Thiel, "auditioning for a role in a cosmic drama that no one asked him to star in", will never be this savior of civilization he aspires to be and the true Katechon should be "our collective refusal to be restrained" by billionaire philosopher kings. German scholar Adrian Daub, Professor of German and Comparative Literature at Stanford University, describes the lectures as "amateurish talks" and a desperate effort from a man with immense power and full of contradiction to disassociate himself from his own power and even his attempts to be understood. Professor Matthew Avery Sutton, representing the Washington State University, notes that Thiel is sincere in his interest in Christianity and draws from serious sources, but suggests that leaders should stop dressing their political theories in apocalyptic dress, because this will "raise anxieties, delegitimize compromise and insinuate that democratic deliberation is spiritually suspect". Others contend that Thiel's arguments make no sense and that his "fixation on apocalyptic scenarios reveals less about looming biblical prophecy than about the anxiety of a tech elite resisting limits on capital and code at a moment when public pressure for accountability is rapidly growing". Thiel began playing chess at the age of six and was at one time one of the top junior players in the United States. He holds the title of Life Master, but he has not competed since 2003. On 30 November 2016, Thiel made the ceremonial first move in the first tiebreak game of the World Chess Championship 2016 between Sergey Karjakin and Magnus Carlsen. He said that he stopped trying to become better at chess, because once a certain level had been reached, chess created an alternate reality that made him lose sight of the real world. Thiel is an occasional commentator on CNBC, having appeared on both Closing Bell with Kelly Evans, and Squawk Box with Becky Quick. He has been interviewed twice by Charlie Rose on PBS. He has also contributed articles to The Wall Street Journal, First Things, Forbes, and Policy Review, a journal formerly published by the Hoover Institution, on whose board he sits. In The Social Network, Thiel was portrayed by Wallace Langham. He described the film as "wrong on many levels". His distaste for the portrayal led to the establishment of the Thiel Fellowship on a whim. Thiel was the inspiration for the Peter Gregory character on HBO's Silicon Valley. Thiel said of Gregory, "I liked him [...] I think eccentric is always better than evil". Jonas Lüscher stated in an interview with Basellandschaftliche Zeitung that he based the character Tobias Erkner in his novel Kraft ("Force") on Thiel. After he hired former Austrian chancellor Sebastian Kurz (following scandals that led to Kurz's resignation) for Thiel Capital in 2022, Jan Böhmermann of the ZDF wrote and performed the satirical song Right time to Thiel that portrayed Thiel as a James Bond villain. Thiel was a German citizen by birth and became an American citizen by naturalization. He received New Zealand citizenship in a private ceremony at the New Zealand consulate in Santa Monica, California, in August 2011; his citizenship status was not made public until 2017. Thiel had visited the country on four occasions prior to his application for citizenship, staying a total of 12 days; the typical residency requirement is 1,350 days in five years. When he applied, Thiel stated he had no intention of living in New Zealand, which is a criterion for citizenship. Then-Minister of Internal Affairs Nathan Guy waived those normal requirements, under an "exceptional circumstances" clause of the Citizenship Act. Thiel's application cited his contribution to the economy—he had founded a venture capital fund in Auckland before applying, and had invested $7 million in two local companies—as well as a $1 million donation to the 2011 Christchurch earthquake appeal fund. Rod Drury, founder of Xero, also provided a formal reference for Thiel's application. Thiel's case was cited by critics as an example of how New Zealand passports can be bought, something the New Zealand government denied. At the time that his citizenship was revealed, The New Zealand Herald came out with the report that the New Zealand Defence Force, the Security Intelligence Service, and the Government Communications and Security Bureau have long-standing links with Thiel's Palantir. In 2015, Thiel purchased a 193-hectare (477-acre) estate near Wānaka, which fit the classification of "sensitive land" and required foreign buyers to obtain permission from New Zealand's Overseas Investment Office. Thiel did not require permission, as he was a citizen. Works In 1995, the Independent Institute published The Diversity Myth: Multiculturalism and the Politics of Intolerance at Stanford, which Thiel co-authored along with fellow tech entrepreneur David O. Sacks, and with a foreword by the late Emory University historian Elizabeth Fox-Genovese. The book is critical of political correctness and multiculturalism in higher education and alleges that it has diluted academic rigor. The authors also argue that, "You don't have diversity when you gather people who look different but talk and think alike."[N 6] Thiel and Sacks's writings drew criticism from then-Stanford Provost Condoleezza Rice and then-Stanford President Gerhard Casper in describing Thiel and Sacks's view of Stanford as "a cartoon, not a description of our freshman curriculum", and their commentary as "demagoguery, pure and simple". In 2016, Thiel apologized for two statements involving the rape crisis movement and date rape that he made in the book. In spring 2012, Thiel taught the class CS 183: Startup at Stanford University. Notes for the course, taken by student Blake Masters, led to a book titled Zero to One: Notes on Startups, or How to Build the Future by Thiel and Masters, which was released in September 2014. Derek Thompson, writing for The Atlantic, stated Zero to One "might be the best business book I've read". He described it as a "self-help book for entrepreneurs, bursting with bromides" but also as a "lucid and profound articulation of capitalism and success in the 21st century economy." "The Straussian Moment" is an essay written by Thiel in 2004, sometimes considered to be a fundamental text in his political thinking and was the subject of a 2019 interview at the Hoover Institution. The essay draws on several thinkers and political theorists and argues that the September 11 attacks upset "the entire political and military framework of the nineteenth and twentieth centuries", and therefore "a reexamination of the foundations of modern politics" was needed. One of Thiel's favorite books is The Sovereign Individual, which was a little-known work before he helped to popularize it. He wrote the preface for the reprinted edition. Thiel also has a chapter giving advice in Tim Ferriss self-help book Tools of Titans: The Tactics, Routines, and Habits of Billionaires, Icons, and World-Class Performers. Notes References Further reading External links |
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Contents First government of Israel The first government of Israel was formed by David Ben-Gurion on 8 March 1949, a month and a half after the elections for the First Knesset. His Mapai party formed a coalition with the United Religious Front, the Progressive Party, the Sephardim and Oriental Communities and the Democratic List of Nazareth, and there were 12 ministers. Election results There were around 434,000 valid votes cast in the 1949 election. Cabinet History and policies A notable piece of legislation enacted during the term of the first government was an educational law in 1949 which introduced compulsory schooling for all children between the ages of 5 and 14. One of the promises made by Mapai was to sign the 1949 Armistice Agreements, which they duly did. This laid out the foundation for the Green Line, a idemarcation line set out in the agreements between the Israeli army and those of its neighbours (Egypt, Jordan, Lebanon, and Syria) after the 1948 Arab–Israeli War. It served as the de facto borders of the State of Israel from 1949 until the Six-Day War in 1967, and continues to represent Israel's internationally recognized borders with the two Palestinian territories: the West Bank and the Gaza Strip. During this government, they set out the terms for Israeli conscription. During the government, austerity policies began, and oversaw a socialist distribution and rationing system. These policies largely came about as Israel had interited the economy of Mandatory Palestine, which had operated under wartime rationing. Ben-Gurion resigned on 15 October 1950 after the United Religious Front objected to his demands that the Supply and Rationing Ministry be closed and a businessman appointed as Minister for Trade and Industry, as well as issues over education in the new immigrant camps. References External links |
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Contents United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous states border Canada to the north and Mexico to the south, with the semi-exclave of Alaska in the northwest and the archipelago of Hawaii in the Pacific Ocean. The United States also asserts sovereignty over five major island territories and various uninhabited islands in Oceania and the Caribbean.[j] It is a megadiverse country, with the world's third-largest land area[c] and third-largest population, exceeding 341 million.[k] Paleo-Indians first migrated from North Asia to North America at least 15,000 years ago, and formed various civilizations. Spanish colonization established Spanish Florida in 1513, the first European colony in what is now the continental United States. British colonization followed with the 1607 settlement of Virginia, the first of the Thirteen Colonies. Enslavement of Africans was practiced in all colonies by 1770 and supplied most of the labor for the Southern Colonies' plantation economy. Clashes with the British Crown began as a civil protest over the illegality of taxation without representation in Parliament and the denial of other English rights. They evolved into the American Revolution, which led to the Declaration of Independence and a society based on universal rights. Victory in the 1775–1783 Revolutionary War brought international recognition of U.S. sovereignty and fueled westward expansion, further dispossessing native inhabitants. As more states were admitted, a North–South division over slavery led the Confederate States of America to declare secession and fight the Union in the 1861–1865 American Civil War. With the United States' victory and reunification, slavery was abolished nationally. By the late 19th century, the U.S. economy outpaced the French, German and British economies combined. As of 1900, the country had established itself as a great power, a status solidified after its involvement in World War I. Following Japan's attack on Pearl Harbor in 1941, the U.S. entered World War II. Its aftermath left the U.S. and the Soviet Union as rival superpowers, competing for ideological dominance and international influence during the Cold War. The Soviet Union's collapse in 1991 ended the Cold War, leaving the U.S. as the world's sole superpower. The U.S. federal government is a representative democracy with a president and a constitution that grants separation of powers under three branches: legislative, executive, and judicial. The United States Congress is a bicameral national legislature composed of the House of Representatives (a lower house based on population) and the Senate (an upper house based on equal representation for each state). Federalism grants substantial autonomy to the 50 states. In addition, 574 Native American tribes have sovereignty rights, and there are 326 Native American reservations. Since the 1850s, the Democratic and Republican parties have dominated American politics. American ideals and values are based on a democratic tradition inspired by the American Enlightenment movement. A developed country, the U.S. ranks high in economic competitiveness, innovation, and higher education. Accounting for over a quarter of nominal global GDP, its economy has been the world's largest since about 1890. It is the wealthiest country, with the highest disposable household income per capita among OECD members, though its wealth inequality is highly pronounced. Shaped by centuries of immigration, the culture of the U.S. is diverse and globally influential. Making up more than a third of global military spending, the country has one of the strongest armed forces and is a designated nuclear state. A member of numerous international organizations, the U.S. plays a major role in global political, cultural, economic, and military affairs. Etymology Documented use of the phrase "United States of America" dates back to January 2, 1776. On that day, Stephen Moylan, a Continental Army aide to General George Washington, wrote a letter to Joseph Reed, Washington's aide-de-camp, seeking to go "with full and ample powers from the United States of America to Spain" to seek assistance in the Revolutionary War effort. The first known public usage is an anonymous essay published in the Williamsburg newspaper The Virginia Gazette on April 6, 1776. Sometime on or after June 11, 1776, Thomas Jefferson wrote "United States of America" in a rough draft of the Declaration of Independence, which was adopted by the Second Continental Congress on July 4, 1776. The term "United States" and its initialism "U.S.", used as nouns or as adjectives in English, are common short names for the country. The initialism "USA", a noun, is also common. "United States" and "U.S." are the established terms throughout the U.S. federal government, with prescribed rules.[l] "The States" is an established colloquial shortening of the name, used particularly from abroad; "stateside" is the corresponding adjective or adverb. "America" is the feminine form of the first word of Americus Vesputius, the Latinized name of Italian explorer Amerigo Vespucci (1454–1512);[m] it was first used as a place name by the German cartographers Martin Waldseemüller and Matthias Ringmann in 1507.[n] Vespucci first proposed that the West Indies discovered by Christopher Columbus in 1492 were part of a previously unknown landmass and not among the Indies at the eastern limit of Asia. In English, the term "America" usually does not refer to topics unrelated to the United States, despite the usage of "the Americas" to describe the totality of the continents of North and South America. History The first inhabitants of North America migrated from Siberia approximately 15,000 years ago, either across the Bering land bridge or along the now-submerged Ice Age coastline. Small isolated groups of hunter-gatherers are said to have migrated alongside herds of large herbivores far into Alaska, with ice-free corridors developing along the Pacific coast and valleys of North America in c. 16,500 – c. 13,500 BCE (c. 18,500 – c. 15,500 BP). The Clovis culture, which appeared around 11,000 BCE, is believed to be the first widespread culture in the Americas. Over time, Indigenous North American cultures grew increasingly sophisticated, and some, such as the Mississippian culture, developed agriculture, architecture, and complex societies. In the post-archaic period, the Mississippian cultures were located in the midwestern, eastern, and southern regions, and the Algonquian in the Great Lakes region and along the Eastern Seaboard, while the Hohokam culture and Ancestral Puebloans inhabited the Southwest. Native population estimates of what is now the United States before the arrival of European colonizers range from around 500,000 to nearly 10 million. Christopher Columbus began exploring the Caribbean for Spain in 1492, leading to Spanish-speaking settlements and missions from what are now Puerto Rico and Florida to New Mexico and California. The first Spanish colony in the present-day continental United States was Spanish Florida, chartered in 1513. After several settlements failed there due to starvation and disease, Spain's first permanent town, Saint Augustine, was founded in 1565. France established its own settlements in French Florida in 1562, but they were either abandoned (Charlesfort, 1578) or destroyed by Spanish raids (Fort Caroline, 1565). Permanent French settlements were founded much later along the Great Lakes (Fort Detroit, 1701), the Mississippi River (Saint Louis, 1764) and especially the Gulf of Mexico (New Orleans, 1718). Early European colonies also included the thriving Dutch colony of New Nederland (settled 1626, present-day New York) and the small Swedish colony of New Sweden (settled 1638 in what became Delaware). British colonization of the East Coast began with the Virginia Colony (1607) and the Plymouth Colony (Massachusetts, 1620). The Mayflower Compact in Massachusetts and the Fundamental Orders of Connecticut established precedents for local representative self-governance and constitutionalism that would develop throughout the American colonies. While European settlers in what is now the United States experienced conflicts with Native Americans, they also engaged in trade, exchanging European tools for food and animal pelts.[o] Relations ranged from close cooperation to warfare and massacres. The colonial authorities often pursued policies that forced Native Americans to adopt European lifestyles, including conversion to Christianity. Along the eastern seaboard, settlers trafficked Africans through the Atlantic slave trade, largely to provide manual labor on plantations. The original Thirteen Colonies[p] that would later found the United States were administered as possessions of the British Empire by Crown-appointed governors, though local governments held elections open to most white male property owners. The colonial population grew rapidly from Maine to Georgia, eclipsing Native American populations; by the 1770s, the natural increase of the population was such that only a small minority of Americans had been born overseas. The colonies' distance from Britain facilitated the entrenchment of self-governance, and the First Great Awakening, a series of Christian revivals, fueled colonial interest in guaranteed religious liberty. Following its victory in the French and Indian War, Britain began to assert greater control over local affairs in the Thirteen Colonies, resulting in growing political resistance. One of the primary grievances of the colonists was the denial of their rights as Englishmen, particularly the right to representation in the British government that taxed them. To demonstrate their dissatisfaction and resolve, the First Continental Congress met in 1774 and passed the Continental Association, a colonial boycott of British goods enforced by local "committees of safety" that proved effective. The British attempt to then disarm the colonists resulted in the 1775 Battles of Lexington and Concord, igniting the American Revolutionary War. At the Second Continental Congress, the colonies appointed George Washington commander-in-chief of the Continental Army, and created a committee that named Thomas Jefferson to draft the Declaration of Independence. Two days after the Second Continental Congress passed the Lee Resolution to create an independent, sovereign nation, the Declaration was adopted on July 4, 1776. The political values of the American Revolution evolved from an armed rebellion demanding reform within an empire to a revolution that created a new social and governing system founded on the defense of liberty and the protection of inalienable natural rights; sovereignty of the people; republicanism over monarchy, aristocracy, and other hereditary political power; civic virtue; and an intolerance of political corruption. The Founding Fathers of the United States, who included Washington, Jefferson, John Adams, Benjamin Franklin, Alexander Hamilton, John Jay, James Madison, Thomas Paine, and many others, were inspired by Classical, Renaissance, and Enlightenment philosophies and ideas. Though in practical effect since its drafting in 1777, the Articles of Confederation was ratified in 1781 and formally established a decentralized government that operated until 1789. After the British surrender at the siege of Yorktown in 1781, American sovereignty was internationally recognized by the Treaty of Paris (1783), through which the U.S. gained territory stretching west to the Mississippi River, north to present-day Canada, and south to Spanish Florida. The Northwest Ordinance (1787) established the precedent by which the country's territory would expand with the admission of new states, rather than the expansion of existing states. The U.S. Constitution was drafted at the 1787 Constitutional Convention to overcome the limitations of the Articles. It went into effect in 1789, creating a federal republic governed by three separate branches that together formed a system of checks and balances. George Washington was elected the country's first president under the Constitution, and the Bill of Rights was adopted in 1791 to allay skeptics' concerns about the power of the more centralized government. His resignation as commander-in-chief after the Revolutionary War and his later refusal to run for a third term as the country's first president established a precedent for the supremacy of civil authority in the United States and the peaceful transfer of power. In the late 18th century, American settlers began to expand westward in larger numbers, many with a sense of manifest destiny. The Louisiana Purchase of 1803 from France nearly doubled the territory of the United States. Lingering issues with Britain remained, leading to the War of 1812, which was fought to a draw. Spain ceded Florida and its Gulf Coast territory in 1819. The Missouri Compromise of 1820, which admitted Missouri as a slave state and Maine as a free state, attempted to balance the desire of northern states to prevent the expansion of slavery into new territories with that of southern states to extend it there. Primarily, the compromise prohibited slavery in all other lands of the Louisiana Purchase north of the 36°30′ parallel. As Americans expanded further into territory inhabited by Native Americans, the federal government implemented policies of Indian removal or assimilation. The most significant such legislation was the Indian Removal Act of 1830, a key policy of President Andrew Jackson. It resulted in the Trail of Tears (1830–1850), in which an estimated 60,000 Native Americans living east of the Mississippi River were forcibly removed and displaced to lands far to the west, causing 13,200 to 16,700 deaths along the forced march. Settler expansion as well as this influx of Indigenous peoples from the East resulted in the American Indian Wars west of the Mississippi. During the colonial period, slavery became legal in all the Thirteen colonies, but by 1770 it provided the main labor force in the large-scale, agriculture-dependent economies of the Southern Colonies from Maryland to Georgia. The practice began to be significantly questioned during the American Revolution, and spurred by an active abolitionist movement that had reemerged in the 1830s, states in the North enacted laws to prohibit slavery within their boundaries. At the same time, support for slavery had strengthened in Southern states, with widespread use of inventions such as the cotton gin (1793) having made slavery immensely profitable for Southern elites. The United States annexed the Republic of Texas in 1845, and the 1846 Oregon Treaty led to U.S. control of the present-day American Northwest. Dispute with Mexico over Texas led to the Mexican–American War (1846–1848). After the victory of the U.S., Mexico recognized U.S. sovereignty over Texas, New Mexico, and California in the 1848 Mexican Cession; the cession's lands also included the future states of Nevada, Colorado and Utah. The California gold rush of 1848–1849 spurred a huge migration of white settlers to the Pacific coast, leading to even more confrontations with Native populations. One of the most violent, the California genocide of thousands of Native inhabitants, lasted into the mid-1870s. Additional western territories and states were created. Throughout the 1850s, the sectional conflict regarding slavery was further inflamed by national legislation in the U.S. Congress and decisions of the Supreme Court. In Congress, the Fugitive Slave Act of 1850 mandated the forcible return to their owners in the South of slaves taking refuge in non-slave states, while the Kansas–Nebraska Act of 1854 effectively gutted the anti-slavery requirements of the Missouri Compromise. In its Dred Scott decision of 1857, the Supreme Court ruled against a slave brought into non-slave territory, simultaneously declaring the entire Missouri Compromise to be unconstitutional. These and other events exacerbated tensions between North and South that would culminate in the American Civil War (1861–1865). Beginning with South Carolina, 11 slave-state governments voted to secede from the United States in 1861, joining to create the Confederate States of America. All other state governments remained loyal to the Union.[q] War broke out in April 1861 after the Confederacy bombarded Fort Sumter. Following the Emancipation Proclamation on January 1, 1863, many freed slaves joined the Union army. The war began to turn in the Union's favor following the 1863 Siege of Vicksburg and Battle of Gettysburg, and the Confederates surrendered in 1865 after the Union's victory in the Battle of Appomattox Court House. Efforts toward reconstruction in the secessionist South had begun as early as 1862, but it was only after President Lincoln's assassination that the three Reconstruction Amendments to the Constitution were ratified to protect civil rights. The amendments codified nationally the abolition of slavery and involuntary servitude except as punishment for crimes, promised equal protection under the law for all persons, and prohibited discrimination on the basis of race or previous enslavement. As a result, African Americans took an active political role in ex-Confederate states in the decade following the Civil War. The former Confederate states were readmitted to the Union, beginning with Tennessee in 1866 and ending with Georgia in 1870. National infrastructure, including transcontinental telegraph and railroads, spurred growth in the American frontier. This was accelerated by the Homestead Acts, through which nearly 10 percent of the total land area of the United States was given away free to some 1.6 million homesteaders. From 1865 through 1917, an unprecedented stream of immigrants arrived in the United States, including 24.4 million from Europe. Most came through the Port of New York, as New York City and other large cities on the East Coast became home to large Jewish, Irish, and Italian populations. Many Northern Europeans as well as significant numbers of Germans and other Central Europeans moved to the Midwest. At the same time, about one million French Canadians migrated from Quebec to New England. During the Great Migration, millions of African Americans left the rural South for urban areas in the North. Alaska was purchased from Russia in 1867. The Compromise of 1877 is generally considered the end of the Reconstruction era, as it resolved the electoral crisis following the 1876 presidential election and led President Rutherford B. Hayes to reduce the role of federal troops in the South. Immediately, the Redeemers began evicting the Carpetbaggers and quickly regained local control of Southern politics in the name of white supremacy. African Americans endured a period of heightened, overt racism following Reconstruction, a time often considered the nadir of American race relations. A series of Supreme Court decisions, including Plessy v. Ferguson, emptied the Fourteenth and Fifteenth Amendments of their force, allowing Jim Crow laws in the South to remain unchecked, sundown towns in the Midwest, and segregation in communities across the country, which would be reinforced in part by the policy of redlining later adopted by the federal Home Owners' Loan Corporation. An explosion of technological advancement, accompanied by the exploitation of cheap immigrant labor, led to rapid economic expansion during the Gilded Age of the late 19th century. It continued into the early 20th, when the United States already outpaced the economies of Britain, France, and Germany combined. This fostered the amassing of power by a few prominent industrialists, largely by their formation of trusts and monopolies to prevent competition. Tycoons led the nation's expansion in the railroad, petroleum, and steel industries. The United States emerged as a pioneer of the automotive industry. These changes resulted in significant increases in economic inequality, slum conditions, and social unrest, creating the environment for labor unions and socialist movements to begin to flourish. This period eventually ended with the advent of the Progressive Era, which was characterized by significant economic and social reforms. Pro-American elements in Hawaii overthrew the Hawaiian monarchy; the islands were annexed in 1898. That same year, Puerto Rico, the Philippines, and Guam were ceded to the U.S. by Spain after the latter's defeat in the Spanish–American War. (The Philippines was granted full independence from the U.S. on July 4, 1946, following World War II. Puerto Rico and Guam have remained U.S. territories.) American Samoa was acquired by the United States in 1900 after the Second Samoan Civil War. The U.S. Virgin Islands were purchased from Denmark in 1917. The United States entered World War I alongside the Allies in 1917 helping to turn the tide against the Central Powers. In 1920, a constitutional amendment granted nationwide women's suffrage. During the 1920s and 1930s, radio for mass communication and early television transformed communications nationwide. The Wall Street Crash of 1929 triggered the Great Depression, to which President Franklin D. Roosevelt responded with the New Deal plan of "reform, recovery and relief", a series of unprecedented and sweeping recovery programs and employment relief projects combined with financial reforms and regulations. Initially neutral during World War II, the U.S. began supplying war materiel to the Allies of World War II in March 1941 and entered the war in December after Japan's attack on Pearl Harbor. Agreeing to a "Europe first" policy, the U.S. concentrated its wartime efforts on Japan's allies Italy and Germany until their final defeat in May 1945. The U.S. developed the first nuclear weapons and used them against the Japanese cities of Hiroshima and Nagasaki in August 1945, ending the war. The United States was one of the "Four Policemen" who met to plan the post-war world, alongside the United Kingdom, the Soviet Union, and China. The U.S. emerged relatively unscathed from the war, with even greater economic power and international political influence. The end of World War II in 1945 left the U.S. and the Soviet Union as superpowers, each with its own political, military, and economic sphere of influence. Geopolitical tensions between the two superpowers soon led to the Cold War. The U.S. implemented a policy of containment intended to limit the Soviet Union's sphere of influence; engaged in regime change against governments perceived to be aligned with the Soviets; and prevailed in the Space Race, which culminated with the first crewed Moon landing in 1969. Domestically, the U.S. experienced economic growth, urbanization, and population growth following World War II. The civil rights movement emerged, with Martin Luther King Jr. becoming a prominent leader in the early 1960s. The Great Society plan of President Lyndon B. Johnson's administration resulted in groundbreaking and broad-reaching laws, policies and a constitutional amendment to counteract some of the worst effects of lingering institutional racism. The counterculture movement in the U.S. brought significant social changes, including the liberalization of attitudes toward recreational drug use and sexuality. It also encouraged open defiance of the military draft (leading to the end of conscription in 1973) and wide opposition to U.S. intervention in Vietnam, with the U.S. totally withdrawing in 1975. A societal shift in the roles of women was significantly responsible for the large increase in female paid labor participation starting in the 1970s, and by 1985 the majority of American women aged 16 and older were employed. The Fall of Communism and the dissolution of the Soviet Union from 1989 to 1991 marked the end of the Cold War and left the United States as the world's sole superpower. This cemented the United States' global influence, reinforcing the concept of the "American Century" as the U.S. dominated international political, cultural, economic, and military affairs. The 1990s saw the longest recorded economic expansion in American history, a dramatic decline in U.S. crime rates, and advances in technology. Throughout this decade, technological innovations such as the World Wide Web, the evolution of the Pentium microprocessor in accordance with Moore's law, rechargeable lithium-ion batteries, the first gene therapy trial, and cloning either emerged in the U.S. or were improved upon there. The Human Genome Project was formally launched in 1990, while Nasdaq became the first stock market in the United States to trade online in 1998. In the Gulf War of 1991, an American-led international coalition of states expelled an Iraqi invasion force that had occupied neighboring Kuwait. The September 11 attacks on the United States in 2001 by the pan-Islamist militant organization al-Qaeda led to the war on terror and subsequent military interventions in Afghanistan and in Iraq. The U.S. housing bubble culminated in 2007 with the Great Recession, the largest economic contraction since the Great Depression. In the 2010s and early 2020s, the United States has experienced increased political polarization and democratic backsliding. The country's polarization was violently reflected in the January 2021 Capitol attack, when a mob of insurrectionists entered the U.S. Capitol and sought to prevent the peaceful transfer of power in an attempted self-coup d'état. Geography The United States is the world's third-largest country by total area behind Russia and Canada.[c] The 48 contiguous states and the District of Columbia have a combined area of 3,119,885 square miles (8,080,470 km2). In 2021, the United States had 8% of the Earth's permanent meadows and pastures and 10% of its cropland. Starting in the east, the coastal plain of the Atlantic seaboard gives way to inland forests and rolling hills in the Piedmont plateau region. The Appalachian Mountains and the Adirondack Massif separate the East Coast from the Great Lakes and the grasslands of the Midwest. The Mississippi River System, the world's fourth-longest river system, runs predominantly north–south through the center of the country. The flat and fertile prairie of the Great Plains stretches to the west, interrupted by a highland region in the southeast. The Rocky Mountains, west of the Great Plains, extend north to south across the country, peaking at over 14,000 feet (4,300 m) in Colorado. The supervolcano underlying Yellowstone National Park in the Rocky Mountains, the Yellowstone Caldera, is the continent's largest volcanic feature. Farther west are the rocky Great Basin and the Chihuahuan, Sonoran, and Mojave deserts. In the northwest corner of Arizona, carved by the Colorado River, is the Grand Canyon, a steep-sided canyon and popular tourist destination known for its overwhelming visual size and intricate, colorful landscape. The Cascade and Sierra Nevada mountain ranges run close to the Pacific coast. The lowest and highest points in the contiguous United States are in the State of California, about 84 miles (135 km) apart. At an elevation of 20,310 feet (6,190.5 m), Alaska's Denali (also called Mount McKinley) is the highest peak in the country and on the continent. Active volcanoes in the U.S. are common throughout Alaska's Alexander and Aleutian Islands. Located entirely outside North America, the archipelago of Hawaii consists of volcanic islands, physiographically and ethnologically part of the Polynesian subregion of Oceania. In addition to its total land area, the United States has one of the world's largest marine exclusive economic zones spanning approximately 4.5 million square miles (11.7 million km2) of ocean. With its large size and geographic variety, the United States includes most climate types. East of the 100th meridian, the climate ranges from humid continental in the north to humid subtropical in the south. The western Great Plains are semi-arid. Many mountainous areas of the American West have an alpine climate. The climate is arid in the Southwest, Mediterranean in coastal California, and oceanic in coastal Oregon, Washington, and southern Alaska. Most of Alaska is subarctic or polar. Hawaii, the southern tip of Florida and U.S. territories in the Caribbean and Pacific are tropical. The United States receives more high-impact extreme weather incidents than any other country. States bordering the Gulf of Mexico are prone to hurricanes, and most of the world's tornadoes occur in the country, mainly in Tornado Alley. Due to climate change in the country, extreme weather has become more frequent in the U.S. in the 21st century, with three times the number of reported heat waves compared to the 1960s. Since the 1990s, droughts in the American Southwest have become more persistent and more severe. The regions considered as the most attractive to the population are the most vulnerable. The U.S. is one of 17 megadiverse countries containing large numbers of endemic species: about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and over 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland. The United States is home to 428 mammal species, 784 birds, 311 reptiles, 295 amphibians, and around 91,000 insect species. There are 63 national parks, and hundreds of other federally managed monuments, forests, and wilderness areas, administered by the National Park Service and other agencies. About 28% of the country's land is publicly owned and federally managed, primarily in the Western States. Most of this land is protected, though some is leased for commercial use, and less than one percent is used for military purposes. Environmental issues in the United States include debates on non-renewable resources and nuclear energy, air and water pollution, biodiversity, logging and deforestation, and climate change. The U.S. Environmental Protection Agency (EPA) is the federal agency charged with addressing most environmental-related issues. The idea of wilderness has shaped the management of public lands since 1964, with the Wilderness Act. The Endangered Species Act of 1973 provides a way to protect threatened and endangered species and their habitats. The United States Fish and Wildlife Service implements and enforces the Act. In 2024, the U.S. ranked 35th among 180 countries in the Environmental Performance Index. Government and politics The United States is a federal republic of 50 states and a federal capital district, Washington, D.C. The U.S. asserts sovereignty over five unincorporated territories and several uninhabited island possessions. It is the world's oldest surviving federation, and its presidential system of federal government has been adopted, in whole or in part, by many newly independent states worldwide following their decolonization. The Constitution of the United States serves as the country's supreme legal document. Most scholars describe the United States as a liberal democracy.[r] Composed of three branches, all headquartered in Washington, D.C., the federal government is the national government of the United States. The U.S. Constitution establishes a separation of powers intended to provide a system of checks and balances to prevent any of the three branches from becoming supreme. The three-branch system is known as the presidential system, in contrast to the parliamentary system where the executive is part of the legislative body. Many countries around the world adopted this aspect of the 1789 Constitution of the United States, especially in the postcolonial Americas. In the U.S. federal system, sovereign powers are shared between three levels of government specified in the Constitution: the federal government, the states, and Indian tribes. The U.S. also asserts sovereignty over five permanently inhabited territories: American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. Residents of the 50 states are governed by their elected state government, under state constitutions compatible with the national constitution, and by elected local governments that are administrative divisions of a state. States are subdivided into counties or county equivalents, and (except for Hawaii) further divided into municipalities, each administered by elected representatives. The District of Columbia is a federal district containing the U.S. capital, Washington, D.C. The federal district is an administrative division of the federal government. Indian country is made up of 574 federally recognized tribes and 326 Indian reservations. They hold a government-to-government relationship with the U.S. federal government in Washington and are legally defined as domestic dependent nations with inherent tribal sovereignty rights. In addition to the five major territories, the U.S. also asserts sovereignty over the United States Minor Outlying Islands in the Pacific Ocean and the Caribbean. The seven undisputed islands without permanent populations are Baker Island, Howland Island, Jarvis Island, Johnston Atoll, Kingman Reef, Midway Atoll, and Palmyra Atoll. U.S. sovereignty over the unpopulated Bajo Nuevo Bank, Navassa Island, Serranilla Bank, and Wake Island is disputed. The Constitution is silent on political parties. However, they developed independently in the 18th century with the Federalist and Anti-Federalist parties. Since then, the United States has operated as a de facto two-party system, though the parties have changed over time. Since the mid-19th century, the two main national parties have been the Democratic Party and the Republican Party. The former is perceived as relatively liberal in its political platform while the latter is perceived as relatively conservative in its platform. The United States has an established structure of foreign relations, with the world's second-largest diplomatic corps as of 2024[update]. It is a permanent member of the United Nations Security Council and home to the United Nations headquarters. The United States is a member of the G7, G20, and OECD intergovernmental organizations. Almost all countries have embassies and many have consulates (official representatives) in the country. Likewise, nearly all countries host formal diplomatic missions with the United States, except Iran, North Korea, and Bhutan. Though Taiwan does not have formal diplomatic relations with the U.S., it maintains close unofficial relations. The United States regularly supplies Taiwan with military equipment to deter potential Chinese aggression. Its geopolitical attention also turned to the Indo-Pacific when the United States joined the Quadrilateral Security Dialogue with Australia, India, and Japan. The United States has a "Special Relationship" with the United Kingdom and strong ties with Canada, Australia, New Zealand, the Philippines, Japan, South Korea, Israel, and several European Union countries such as France, Italy, Germany, Spain, and Poland. The U.S. works closely with its NATO allies on military and national security issues, and with countries in the Americas through the Organization of American States and the United States–Mexico–Canada Free Trade Agreement. The U.S. exercises full international defense authority and responsibility for Micronesia, the Marshall Islands, and Palau through the Compact of Free Association. It has increasingly conducted strategic cooperation with India, while its ties with China have steadily deteriorated. Beginning in 2014, the U.S. had become a key ally of Ukraine. After Donald Trump was elected U.S. president in 2024, he sought to negotiate an end to the Russo-Ukrainian War. He paused all military aid to Ukraine in March 2025, although the aid resumed later. Trump also ended U.S. intelligence sharing with the country, but this too was eventually restored. The president is the commander-in-chief of the United States Armed Forces and appoints its leaders, the secretary of defense and the Joint Chiefs of Staff. The Department of Defense, headquartered at the Pentagon near Washington, D.C., administers five of the six service branches, which are made up of the U.S. Army, Marine Corps, Navy, Air Force, and Space Force. The Coast Guard is administered by the Department of Homeland Security in peacetime and can be transferred to the Department of the Navy in wartime. Total strength of the entire military is about 1.3 million active duty with an additional 400,000 in reserve. The United States spent $997 billion on its military in 2024, which is by far the largest amount of any country, making up 37% of global military spending and accounting for 3.4% of the country's GDP. The U.S. possesses 42% of the world's nuclear weapons—the second-largest stockpile after that of Russia. The U.S. military is widely regarded as the most powerful and advanced in the world. The United States has the third-largest combined armed forces in the world, behind the Chinese People's Liberation Army and Indian Armed Forces. The U.S. military operates about 800 bases and facilities abroad, and maintains deployments greater than 100 active duty personnel in 25 foreign countries. The United States has engaged in over 400 military interventions since its founding in 1776, with over half of these occurring between 1950 and 2019 and 25% occurring in the post-Cold War era. State defense forces (SDFs) are military units that operate under the sole authority of a state government. SDFs are authorized by state and federal law but are under the command of the state's governor. By contrast, the 54 U.S. National Guard organizations[t] fall under the dual control of state or territorial governments and the federal government; their units can also become federalized entities, but SDFs cannot be federalized. The National Guard personnel of a state or territory can be federalized by the president under the National Defense Act Amendments of 1933; this legislation created the Guard and provides for the integration of Army National Guard and Air National Guard units and personnel into the U.S. Army and (since 1947) the U.S. Air Force. The total number of National Guard members is about 430,000, while the estimated combined strength of SDFs is less than 10,000. There are about 18,000 U.S. police agencies from local to national level in the United States. Law in the United States is mainly enforced by local police departments and sheriff departments in their municipal or county jurisdictions. The state police departments have authority in their respective state, and federal agencies such as the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have national jurisdiction and specialized duties, such as protecting civil rights, national security, enforcing U.S. federal courts' rulings and federal laws, and interstate criminal activity. State courts conduct almost all civil and criminal trials, while federal courts adjudicate the much smaller number of civil and criminal cases that relate to federal law. There is no unified "criminal justice system" in the United States. The American prison system is largely heterogenous, with thousands of relatively independent systems operating across federal, state, local, and tribal levels. In 2025, "these systems hold nearly 2 million people in 1,566 state prisons, 98 federal prisons, 3,116 local jails, 1,277 juvenile correctional facilities, 133 immigration detention facilities, and 80 Indian country jails, as well as in military prisons, civil commitment centers, state psychiatric hospitals, and prisons in the U.S. territories." Despite disparate systems of confinement, four main institutions dominate: federal prisons, state prisons, local jails, and juvenile correctional facilities. Federal prisons are run by the Federal Bureau of Prisons and hold pretrial detainees as well as people who have been convicted of federal crimes. State prisons, run by the department of corrections of each state, hold people sentenced and serving prison time (usually longer than one year) for felony offenses. Local jails are county or municipal facilities that incarcerate defendants prior to trial; they also hold those serving short sentences (typically under a year). Juvenile correctional facilities are operated by local or state governments and serve as longer-term placements for any minor adjudicated as delinquent and ordered by a judge to be confined. In January 2023, the United States had the sixth-highest per capita incarceration rate in the world—531 people per 100,000 inhabitants—and the largest prison and jail population in the world, with more than 1.9 million people incarcerated. An analysis of the World Health Organization Mortality Database from 2010 showed U.S. homicide rates "were 7 times higher than in other high-income countries, driven by a gun homicide rate that was 25 times higher". Economy The U.S. has a highly developed mixed economy that has been the world's largest nominally since about 1890. Its 2024 gross domestic product (GDP)[e] of more than $29 trillion constituted over 25% of nominal global economic output, or 15% at purchasing power parity (PPP). From 1983 to 2008, U.S. real compounded annual GDP growth was 3.3%, compared to a 2.3% weighted average for the rest of the G7. The country ranks first in the world by nominal GDP, second when adjusted for purchasing power parities (PPP), and ninth by PPP-adjusted GDP per capita. In February 2024, the total U.S. federal government debt was $34.4 trillion. Of the world's 500 largest companies by revenue, 138 were headquartered in the U.S. in 2025, the highest number of any country. The U.S. dollar is the currency most used in international transactions and the world's foremost reserve currency, backed by the country's dominant economy, its military, the petrodollar system, its large U.S. treasuries market, and its linked eurodollar. Several countries use it as their official currency, and in others it is the de facto currency. The U.S. has free trade agreements with several countries, including the USMCA. Although the United States has reached a post-industrial level of economic development and is often described as having a service economy, it remains a major industrial power; in 2024, the U.S. manufacturing sector was the world's second-largest by value output after China's. New York City is the world's principal financial center, and its metropolitan area is the world's largest metropolitan economy. The New York Stock Exchange and Nasdaq, both located in New York City, are the world's two largest stock exchanges by market capitalization and trade volume. The United States is at the forefront of technological advancement and innovation in many economic fields, especially in artificial intelligence; electronics and computers; pharmaceuticals; and medical, aerospace and military equipment. The country's economy is fueled by abundant natural resources, a well-developed infrastructure, and high productivity. The largest trading partners of the United States are the European Union, Mexico, Canada, China, Japan, South Korea, the United Kingdom, Vietnam, India, and Taiwan. The United States is the world's largest importer and second-largest exporter.[u] It is by far the world's largest exporter of services. Americans have the highest average household and employee income among OECD member states, and the fourth-highest median household income in 2023, up from sixth-highest in 2013. With personal consumption expenditures of over $18.5 trillion in 2023, the U.S. has a heavily consumer-driven economy and is the world's largest consumer market. The U.S. ranked first in the number of dollar billionaires and millionaires in 2023, with 735 billionaires and nearly 22 million millionaires. Wealth in the United States is highly concentrated; in 2011, the richest 10% of the adult population owned 72% of the country's household wealth, while the bottom 50% owned just 2%. U.S. wealth inequality increased substantially since the late 1980s, and income inequality in the U.S. reached a record high in 2019. In 2024, the country had some of the highest wealth and income inequality levels among OECD countries. Since the 1970s, there has been a decoupling of U.S. wage gains from worker productivity. In 2016, the top fifth of earners took home more than half of all income, giving the U.S. one of the widest income distributions among OECD countries. There were about 771,480 homeless persons in the U.S. in 2024. In 2022, 6.4 million children experienced food insecurity. Feeding America estimates that around one in five, or approximately 13 million, children experience hunger in the U.S. and do not know where or when they will get their next meal. Also in 2022, about 37.9 million people, or 11.5% of the U.S. population, were living in poverty. The United States has a smaller welfare state and redistributes less income through government action than most other high-income countries. It is the only advanced economy that does not guarantee its workers paid vacation nationally and one of a few countries in the world without federal paid family leave as a legal right. The United States has a higher percentage of low-income workers than almost any other developed country, largely because of a weak collective bargaining system and lack of government support for at-risk workers. The United States has been a leader in technological innovation since the late 19th century and scientific research since the mid-20th century. Methods for producing interchangeable parts and the establishment of a machine tool industry enabled the large-scale manufacturing of U.S. consumer products in the late 19th century. By the early 20th century, factory electrification, the introduction of the assembly line, and other labor-saving techniques created the system of mass production. In the 21st century, the United States continues to be one of the world's foremost scientific powers, though China has emerged as a major competitor in many fields. The U.S. has the highest research and development expenditures of any country and ranks ninth as a percentage of GDP. In 2022, the United States was (after China) the country with the second-highest number of published scientific papers. In 2021, the U.S. ranked second (also after China) by the number of patent applications, and third by trademark and industrial design applications (after China and Germany), according to World Intellectual Property Indicators. In 2025 the United States ranked third (after Switzerland and Sweden) in the Global Innovation Index. The United States is considered to be a world leader in the development of artificial intelligence technology. In 2023, the United States was ranked the second most technologically advanced country in the world (after South Korea) by Global Finance magazine. The United States has maintained a space program since the late 1950s, beginning with the establishment of the National Aeronautics and Space Administration (NASA) in 1958. NASA's Apollo program (1961–1972) achieved the first crewed Moon landing with the 1969 Apollo 11 mission; it remains one of the agency's most significant milestones. Other major endeavors by NASA include the Space Shuttle program (1981–2011), the Voyager program (1972–present), the Hubble and James Webb space telescopes (launched in 1990 and 2021, respectively), and the multi-mission Mars Exploration Program (Spirit and Opportunity, Curiosity, and Perseverance). NASA is one of five agencies collaborating on the International Space Station (ISS); U.S. contributions to the ISS include several modules, including Destiny (2001), Harmony (2007), and Tranquility (2010), as well as ongoing logistical and operational support. The United States private sector dominates the global commercial spaceflight industry. Prominent American spaceflight contractors include Blue Origin, Boeing, Lockheed Martin, Northrop Grumman, and SpaceX. NASA programs such as the Commercial Crew Program, Commercial Resupply Services, Commercial Lunar Payload Services, and NextSTEP have facilitated growing private-sector involvement in American spaceflight. In 2023, the United States received approximately 84% of its energy from fossil fuel, and its largest source of energy was petroleum (38%), followed by natural gas (36%), renewable sources (9%), coal (9%), and nuclear power (9%). In 2022, the United States constituted about 4% of the world's population, but consumed around 16% of the world's energy. The U.S. ranks as the second-highest emitter of greenhouse gases behind China. The U.S. is the world's largest producer of nuclear power, generating around 30% of the world's nuclear electricity. It also has the highest number of nuclear power reactors of any country. From 2024, the U.S. plans to triple its nuclear power capacity by 2050. The United States' 4 million miles (6.4 million kilometers) of road network, owned almost entirely by state and local governments, is the longest in the world. The extensive Interstate Highway System that connects all major U.S. cities is funded mostly by the federal government but maintained by state departments of transportation. The system is further extended by state highways and some private toll roads. The U.S. is among the top ten countries with the highest vehicle ownership per capita (850 vehicles per 1,000 people) in 2022. A 2022 study found that 76% of U.S. commuters drive alone and 14% ride a bicycle, including bike owners and users of bike-sharing networks. About 11% use some form of public transportation. Public transportation in the United States is well developed in the largest urban areas, notably New York City, Washington, D.C., Boston, Philadelphia, Chicago, and San Francisco; otherwise, coverage is generally less extensive than in most other developed countries. The U.S. also has many relatively car-dependent localities. Long-distance intercity travel is provided primarily by airlines, but travel by rail is more common along the Northeast Corridor, the only high-speed rail in the U.S. that meets international standards. Amtrak, the country's government-sponsored national passenger rail company, has a relatively sparse network compared to that of Western European countries. Service is concentrated in the Northeast, California, the Midwest, the Pacific Northwest, and Virginia/Southeast. The United States has an extensive air transportation network. U.S. civilian airlines are all privately owned. The three largest airlines in the world, by total number of passengers carried, are U.S.-based; American Airlines became the global leader after its 2013 merger with US Airways. Of the 50 busiest airports in the world, 16 are in the United States, as well as five of the top 10. The world's busiest airport by passenger volume is Hartsfield–Jackson Atlanta International in Atlanta, Georgia. In 2022, most of the 19,969 U.S. airports were owned and operated by local government authorities, and there are also some private airports. Some 5,193 are designated as "public use", including for general aviation. The Transportation Security Administration (TSA) has provided security at most major airports since 2001. The country's rail transport network, the longest in the world at 182,412.3 mi (293,564.2 km), handles mostly freight (in contrast to more passenger-centered rail in Europe). Because they are often privately owned operations, U.S. railroads lag behind those of the rest of the world in terms of electrification. The country's inland waterways are the world's fifth-longest, totaling 25,482 mi (41,009 km). They are used extensively for freight, recreation, and a small amount of passenger traffic. Of the world's 50 busiest container ports, four are located in the United States, with the busiest in the country being the Port of Los Angeles. Demographics The U.S. Census Bureau reported 331,449,281 residents on April 1, 2020,[v] making the United States the third-most-populous country in the world, after India and China. The Census Bureau's official 2025 population estimate was 341,784,857, an increase of 3.1% since the 2020 census. According to the Bureau's U.S. Population Clock, on July 1, 2024, the U.S. population had a net gain of one person every 16 seconds, or about 5400 people per day. In 2023, 51% of Americans age 15 and over were married, 6% were widowed, 10% were divorced, and 34% had never been married. In 2023, the total fertility rate for the U.S. stood at 1.6 children per woman, and, at 23%, it had the world's highest rate of children living in single-parent households in 2019. Most Americans live in the suburbs of major metropolitan areas. The United States has a diverse population; 37 ancestry groups have more than one million members. White Americans with ancestry from Europe, the Middle East, or North Africa form the largest racial and ethnic group at 57.8% of the United States population. Hispanic and Latino Americans form the second-largest group and are 18.7% of the United States population. African Americans constitute the country's third-largest ancestry group and are 12.1% of the total U.S. population. Asian Americans are the country's fourth-largest group, composing 5.9% of the United States population. The country's 3.7 million Native Americans account for about 1%, and some 574 native tribes are recognized by the federal government. In 2024, the median age of the United States population was 39.1 years. While many languages and dialects are spoken in the United States, English is by far the most commonly spoken and written. De facto, English is the official language of the United States, and in 2025, Executive Order 14224 declared English official. However, the U.S. has never had a de jure official language, as Congress has never passed a law to designate English as official for all three federal branches. Some laws, such as U.S. naturalization requirements, nonetheless standardize English. Twenty-eight states and the United States Virgin Islands have laws that designate English as the sole official language; 19 states and the District of Columbia have no official language. Three states and four U.S. territories have recognized local or indigenous languages in addition to English: Hawaii (Hawaiian), Alaska (twenty Native languages),[w] South Dakota (Sioux), American Samoa (Samoan), Puerto Rico (Spanish), Guam (Chamorro), and the Northern Mariana Islands (Carolinian and Chamorro). In total, 169 Native American languages are spoken in the United States. In Puerto Rico, Spanish is more widely spoken than English. According to the American Community Survey (2020), some 245.4 million people in the U.S. age five and older spoke only English at home. About 41.2 million spoke Spanish at home, making it the second most commonly used language. Other languages spoken at home by one million people or more include Chinese (3.40 million), Tagalog (1.71 million), Vietnamese (1.52 million), Arabic (1.39 million), French (1.18 million), Korean (1.07 million), and Russian (1.04 million). German, spoken by 1 million people at home in 2010, fell to 857,000 total speakers in 2020. America's immigrant population is by far the world's largest in absolute terms. In 2022, there were 87.7 million immigrants and U.S.-born children of immigrants in the United States, accounting for nearly 27% of the overall U.S. population. In 2017, out of the U.S. foreign-born population, some 45% (20.7 million) were naturalized citizens, 27% (12.3 million) were lawful permanent residents, 6% (2.2 million) were temporary lawful residents, and 23% (10.5 million) were unauthorized immigrants. In 2019, the top countries of origin for immigrants were Mexico (24% of immigrants), India (6%), China (5%), the Philippines (4.5%), and El Salvador (3%). In fiscal year 2022, over one million immigrants (most of whom entered through family reunification) were granted legal residence. The undocumented immigrant population in the U.S. reached a record high of 14 million in 2023. The First Amendment guarantees the free exercise of religion in the country and forbids Congress from passing laws respecting its establishment. Religious practice is widespread, among the most diverse in the world, and profoundly vibrant. The country has the world's largest Christian population, which includes the fourth-largest population of Catholics. Other notable faiths include Judaism, Buddhism, Hinduism, Islam, New Age, and Native American religions. Religious practice varies significantly by region. "Ceremonial deism" is common in American culture. The overwhelming majority of Americans believe in a higher power or spiritual force, engage in spiritual practices such as prayer, and consider themselves religious or spiritual. In the Southern United States' "Bible Belt", evangelical Protestantism plays a significant role culturally; New England and the Western United States tend to be more secular. Mormonism, a Restorationist movement founded in the U.S. in 1847, is the predominant religion in Utah and a major religion in Idaho. About 82% of Americans live in metropolitan areas, particularly in suburbs; about half of those reside in cities with populations over 50,000. In 2022, 333 incorporated municipalities had populations over 100,000, nine cities had more than one million residents, and four cities—New York City, Los Angeles, Chicago, and Houston—had populations exceeding two million. Many U.S. metropolitan populations are growing rapidly, particularly in the South and West. According to the Centers for Disease Control and Prevention (CDC), average U.S. life expectancy at birth reached 79.0 years in 2024, its highest recorded level. This was an increase of 0.6 years over 2023. The CDC attributed the improvement to a significant fall in the number of fatal drug overdoses in the country, noting that "heart disease continues to be the leading cause of death in the United States, followed by cancer and unintentional injuries." In 2024, life expectancy at birth for American men rose to 76.5 years (+0.7 years compared to 2023), while life expectancy for women was 81.4 years (+0.3 years). Starting in 1998, life expectancy in the U.S. fell behind that of other wealthy industrialized countries, and Americans' "health disadvantage" gap has been increasing ever since. The Commonwealth Fund reported in 2020 that the U.S. had the highest suicide rate among high-income countries. Approximately one-third of the U.S. adult population is obese and another third is overweight. The U.S. healthcare system far outspends that of any other country, measured both in per capita spending and as a percentage of GDP, but attains worse healthcare outcomes when compared to peer countries for reasons that are debated. The United States is the only developed country without a system of universal healthcare, and a significant proportion of the population that does not carry health insurance. Government-funded healthcare coverage for the poor (Medicaid) and for those age 65 and older (Medicare) is available to Americans who meet the programs' income or age qualifications. In 2010, then-President Obama passed the Patient Protection and Affordable Care Act.[x] Abortion in the United States is not federally protected, and is illegal or restricted in 17 states. American primary and secondary education, known in the U.S. as K–12 ("kindergarten through 12th grade"), is decentralized. School systems are operated by state, territorial, and sometimes municipal governments and regulated by the U.S. Department of Education. In general, children are required to attend school or an approved homeschool from the age of five or six (kindergarten or first grade) until they are 18 years old. This often brings students through the 12th grade, the final year of a U.S. high school, but some states and territories allow them to leave school earlier, at age 16 or 17. The U.S. spends more on education per student than any other country, an average of $18,614 per year per public elementary and secondary school student in 2020–2021. Among Americans age 25 and older, 92.2% graduated from high school, 62.7% attended some college, 37.7% earned a bachelor's degree, and 14.2% earned a graduate degree. The U.S. literacy rate is near-universal. The U.S. has produced the most Nobel Prize winners of any country, with 411 (having won 413 awards). U.S. tertiary or higher education has earned a global reputation. Many of the world's top universities, as listed by various ranking organizations, are in the United States, including 19 of the top 25. American higher education is dominated by state university systems, although the country's many private universities and colleges enroll about 20% of all American students. Local community colleges generally offer open admissions, lower tuition, and coursework leading to a two-year associate degree or a non-degree certificate. As for public expenditures on higher education, the U.S. spends more per student than the OECD average, and Americans spend more than all nations in combined public and private spending. Colleges and universities directly funded by the federal government do not charge tuition and are limited to military personnel and government employees, including: the U.S. service academies, the Naval Postgraduate School, and military staff colleges. Despite some student loan forgiveness programs in place, student loan debt increased by 102% between 2010 and 2020, and exceeded $1.7 trillion in 2022. Culture and society The United States is home to a wide variety of ethnic groups, traditions, and customs. The country has been described as having the values of individualism and personal autonomy, as well as a strong work ethic and competitiveness. Voluntary altruism towards others also plays a major role; according to a 2016 study by the Charities Aid Foundation, Americans donated 1.44% of total GDP to charity—the highest rate in the world by a large margin. Americans have traditionally been characterized by a unifying political belief in an "American Creed" emphasizing consent of the governed, liberty, equality under the law, democracy, social equality, property rights, and a preference for limited government. The U.S. has acquired significant hard and soft power through its diplomatic influence, economic power, military alliances, and cultural exports such as American movies, music, video games, sports, and food. The influence that the United States exerts on other countries through soft power is referred to as Americanization. Nearly all present Americans or their ancestors came from Europe, Africa, or Asia (the "Old World") within the past five centuries. Mainstream American culture is a Western culture largely derived from the traditions of European immigrants with influences from many other sources, such as traditions brought by slaves from Africa. More recent immigration from Asia and especially Latin America has added to a cultural mix that has been described as a homogenizing melting pot, and a heterogeneous salad bowl, with immigrants contributing to, and often assimilating into, mainstream American culture. Under the First Amendment to the Constitution, the United States is considered to have the strongest protections of free speech of any country. Flag desecration, hate speech, blasphemy, and lese majesty are all forms of protected expression. A 2016 Pew Research Center poll found that Americans were the most supportive of free expression of any polity measured. Additionally, they are the "most supportive of freedom of the press and the right to use the Internet without government censorship". The U.S. is a socially progressive country with permissive attitudes surrounding human sexuality. LGBTQ rights in the United States are among the most advanced by global standards. The American Dream, or the perception that Americans enjoy high levels of social mobility, plays a key role in attracting immigrants. Whether this perception is accurate has been a topic of debate. While mainstream culture holds that the United States is a classless society, scholars identify significant differences between the country's social classes, affecting socialization, language, and values. Americans tend to greatly value socioeconomic achievement, but being ordinary or average is promoted by some as a noble condition as well. The National Foundation on the Arts and the Humanities is an agency of the United States federal government that was established in 1965 with the purpose to "develop and promote a broadly conceived national policy of support for the humanities and the arts in the United States, and for institutions which preserve the cultural heritage of the United States." It is composed of four sub-agencies: Colonial American authors were influenced by John Locke and other Enlightenment philosophers. The American Revolutionary Period (1765–1783) is notable for the political writings of Benjamin Franklin, Alexander Hamilton, Thomas Paine, and Thomas Jefferson. Shortly before and after the Revolutionary War, the newspaper rose to prominence, filling a demand for anti-British national literature. An early novel is William Hill Brown's The Power of Sympathy, published in 1791. Writer and critic John Neal in the early- to mid-19th century helped advance America toward a unique literature and culture by criticizing predecessors such as Washington Irving for imitating their British counterparts, and by influencing writers such as Edgar Allan Poe, who took American poetry and short fiction in new directions. Ralph Waldo Emerson and Margaret Fuller pioneered the influential Transcendentalism movement; Henry David Thoreau, author of Walden, was influenced by this movement. The conflict surrounding abolitionism inspired writers, like Harriet Beecher Stowe, and authors of slave narratives, such as Frederick Douglass. Nathaniel Hawthorne's The Scarlet Letter (1850) explored the dark side of American history, as did Herman Melville's Moby-Dick (1851). Major American poets of the 19th century American Renaissance include Walt Whitman, Melville, and Emily Dickinson. Mark Twain was the first major American writer to be born in the West. Henry James achieved international recognition with novels like The Portrait of a Lady (1881). As literacy rates rose, periodicals published more stories centered around industrial workers, women, and the rural poor. Naturalism, regionalism, and realism were the major literary movements of the period. While modernism generally took on an international character, modernist authors working within the United States more often rooted their work in specific regions, peoples, and cultures. Following the Great Migration to northern cities, African-American and black West Indian authors of the Harlem Renaissance developed an independent tradition of literature that rebuked a history of inequality and celebrated black culture. An important cultural export during the Jazz Age, these writings were a key influence on Négritude, a philosophy emerging in the 1930s among francophone writers of the African diaspora. In the 1950s, an ideal of homogeneity led many authors to attempt to write the Great American Novel, while the Beat Generation rejected this conformity, using styles that elevated the impact of the spoken word over mechanics to describe drug use, sexuality, and the failings of society. Contemporary literature is more pluralistic than in previous eras, with the closest thing to a unifying feature being a trend toward self-conscious experiments with language. Twelve American laureates have won the Nobel Prize in Literature. Media in the United States is broadly uncensored, with the First Amendment providing significant protections, as reiterated in New York Times Co. v. United States. The four major broadcasters in the U.S. are the National Broadcasting Company (NBC), Columbia Broadcasting System (CBS), American Broadcasting Company (ABC), and Fox Broadcasting Company (Fox). The four major broadcast television networks are all commercial entities. The U.S. cable television system offers hundreds of channels catering to a variety of niches. In 2021, about 83% of Americans over age 12 listened to broadcast radio, while about 40% listened to podcasts. In the prior year, there were 15,460 licensed full-power radio stations in the U.S. according to the Federal Communications Commission (FCC). Much of the public radio broadcasting is supplied by National Public Radio (NPR), incorporated in February 1970 under the Public Broadcasting Act of 1967. U.S. newspapers with a global reach and reputation include The Wall Street Journal, The New York Times, The Washington Post, and USA Today. About 800 publications are produced in Spanish. With few exceptions, newspapers are privately owned, either by large chains such as Gannett or McClatchy, which own dozens or even hundreds of newspapers; by small chains that own a handful of papers; or, in an increasingly rare situation, by individuals or families. Major cities often have alternative newspapers to complement the mainstream daily papers, such as The Village Voice in New York City and LA Weekly in Los Angeles. The five most-visited websites in the world are Google, YouTube, Facebook, Instagram, and ChatGPT—all of them American-owned. Other popular platforms used include X (formerly Twitter) and Amazon. In 2025, the U.S. was the world's second-largest video game market by revenue (after China). In 2015, the U.S. video game industry consisted of 2,457 companies that employed around 220,000 jobs and generated $30.4 billion in revenue. There are 444 game publishers, developers, and hardware companies in California alone. According to the Game Developers Conference (GDC), the U.S. is the top location for video game development, with 58% of the world's game developers based there in 2025. The United States is well known for its theater. Mainstream theater in the United States derives from the old European theatrical tradition and has been heavily influenced by the British theater. By the middle of the 19th century, America had created new distinct dramatic forms in the Tom Shows, the showboat theater and the minstrel show. The central hub of the American theater scene is the Theater District in Manhattan, with its divisions of Broadway, off-Broadway, and off-off-Broadway. Many movie and television celebrities have gotten their big break working in New York productions. Outside New York City, many cities have professional regional or resident theater companies that produce their own seasons. The biggest-budget theatrical productions are musicals. U.S. theater has an active community theater culture. The Tony Awards recognizes excellence in live Broadway theater and are presented at an annual ceremony in Manhattan. The awards are given for Broadway productions and performances. One is also given for regional theater. Several discretionary non-competitive awards are given as well, including a Special Tony Award, the Tony Honors for Excellence in Theatre, and the Isabelle Stevenson Award. Folk art in colonial America grew out of artisanal craftsmanship in communities that allowed commonly trained people to individually express themselves. It was distinct from Europe's tradition of high art, which was less accessible and generally less relevant to early American settlers. Cultural movements in art and craftsmanship in colonial America generally lagged behind those of Western Europe. For example, the prevailing medieval style of woodworking and primitive sculpture became integral to early American folk art, despite the emergence of Renaissance styles in England in the late 16th and early 17th centuries. The new English styles would have been early enough to make a considerable impact on American folk art, but American styles and forms had already been firmly adopted. Not only did styles change slowly in early America, but there was a tendency for rural artisans there to continue their traditional forms longer than their urban counterparts did—and far longer than those in Western Europe. The Hudson River School was a mid-19th-century movement in the visual arts tradition of European naturalism. The 1913 Armory Show in New York City, an exhibition of European modernist art, shocked the public and transformed the U.S. art scene. American Realism and American Regionalism sought to reflect and give America new ways of looking at itself. Georgia O'Keeffe, Marsden Hartley, and others experimented with new and individualistic styles, which would become known as American modernism. Major artistic movements such as the abstract expressionism of Jackson Pollock and Willem de Kooning and the pop art of Andy Warhol and Roy Lichtenstein developed largely in the United States. Major photographers include Alfred Stieglitz, Edward Steichen, Dorothea Lange, Edward Weston, James Van Der Zee, Ansel Adams, and Gordon Parks. The tide of modernism and then postmodernism has brought global fame to American architects, including Frank Lloyd Wright, Philip Johnson, and Frank Gehry. The Metropolitan Museum of Art in Manhattan is the largest art museum in the United States and the fourth-largest in the world. American folk music encompasses numerous music genres, variously known as traditional music, traditional folk music, contemporary folk music, or roots music. Many traditional songs have been sung within the same family or folk group for generations, and sometimes trace back to such origins as the British Isles, mainland Europe, or Africa. The rhythmic and lyrical styles of African-American music in particular have influenced American music. Banjos were brought to America through the slave trade. Minstrel shows incorporating the instrument into their acts led to its increased popularity and widespread production in the 19th century. The electric guitar, first invented in the 1930s, and mass-produced by the 1940s, had an enormous influence on popular music, in particular due to the development of rock and roll. The synthesizer, turntablism, and electronic music were also largely developed in the U.S. Elements from folk idioms such as the blues and old-time music were adopted and transformed into popular genres with global audiences. Jazz grew from blues and ragtime in the early 20th century, developing from the innovations and recordings of composers such as W.C. Handy and Jelly Roll Morton. Louis Armstrong and Duke Ellington increased its popularity early in the 20th century. Country music developed in the 1920s, bluegrass and rhythm and blues in the 1940s, and rock and roll in the 1950s. In the 1960s, Bob Dylan emerged from the folk revival to become one of the country's most celebrated songwriters. The musical forms of punk and hip hop both originated in the United States in the 1970s. The United States has the world's largest music market, with a total retail value of $15.9 billion in 2022. Most of the world's major record companies are based in the U.S.; they are represented by the Recording Industry Association of America (RIAA). Mid-20th-century American pop stars, such as Frank Sinatra and Elvis Presley, became global celebrities and best-selling music artists, as have artists of the late 20th century, such as Michael Jackson, Madonna, Whitney Houston, and Mariah Carey, and of the early 21st century, such as Eminem, Britney Spears, Lady Gaga, Katy Perry, Taylor Swift and Beyoncé. The United States has the world's largest apparel market by revenue. Apart from professional business attire, American fashion is eclectic and predominantly informal. Americans' diverse cultural roots are reflected in their clothing; however, sneakers, jeans, T-shirts, and baseball caps are emblematic of American styles. New York, with its Fashion Week, is considered to be one of the "Big Four" global fashion capitals, along with Paris, Milan, and London. A study demonstrated that general proximity to Manhattan's Garment District has been synonymous with American fashion since its inception in the early 20th century. A number of well-known designer labels, among them Tommy Hilfiger, Ralph Lauren, Tom Ford and Calvin Klein, are headquartered in Manhattan. Labels cater to niche markets, such as preteens. New York Fashion Week is one of the most influential fashion shows in the world, and is held twice each year in Manhattan; the annual Met Gala, also in Manhattan, has been called the fashion world's "biggest night". The U.S. film industry has a worldwide influence and following. Hollywood, a district in central Los Angeles, the nation's second-most populous city, is also metonymous for the American filmmaking industry. The major film studios of the United States are the primary source of the most commercially successful movies selling the most tickets in the world. Largely centered in the New York City region from its beginnings in the late 19th century through the first decades of the 20th century, the U.S. film industry has since been primarily based in and around Hollywood. Nonetheless, American film companies have been subject to the forces of globalization in the 21st century, and an increasing number of films are made elsewhere. The Academy Awards, popularly known as "the Oscars", have been held annually by the Academy of Motion Picture Arts and Sciences since 1929, and the Golden Globe Awards have been held annually since January 1944. The industry peaked in what is commonly referred to as the "Golden Age of Hollywood", from the early sound period until the early 1960s, with screen actors such as John Wayne and Marilyn Monroe becoming iconic figures. In the 1970s, "New Hollywood", or the "Hollywood Renaissance", was defined by grittier films influenced by French and Italian realist pictures of the post-war period. The 21st century has been marked by the rise of American streaming platforms, which came to rival traditional cinema. Early settlers were introduced by Native Americans to foods such as turkey, sweet potatoes, corn, squash, and maple syrup. Of the most enduring and pervasive examples are variations of the native dish called succotash. Early settlers and later immigrants combined these with foods they were familiar with, such as wheat flour, beef, and milk, to create a distinctive American cuisine. New World crops, especially pumpkin, corn, potatoes, and turkey as the main course are part of a shared national menu on Thanksgiving, when many Americans prepare or purchase traditional dishes to celebrate the occasion. Characteristic American dishes such as apple pie, fried chicken, doughnuts, french fries, macaroni and cheese, ice cream, hamburgers, hot dogs, and American pizza derive from the recipes of various immigrant groups. Mexican dishes such as burritos and tacos preexisted the United States in areas later annexed from Mexico, and adaptations of Chinese cuisine as well as pasta dishes freely adapted from Italian sources are all widely consumed. American chefs have had a significant impact on society both domestically and internationally. In 1946, the Culinary Institute of America was founded by Katharine Angell and Frances Roth. This would become the United States' most prestigious culinary school, where many of the most talented American chefs would study prior to successful careers. The United States restaurant industry was projected at $899 billion in sales for 2020, and employed more than 15 million people, representing 10% of the nation's workforce directly. It is the country's second-largest private employer and the third-largest employer overall. The United States is home to over 220 Michelin star-rated restaurants, 70 of which are in New York City. Wine has been produced in what is now the United States since the 1500s, with the first widespread production beginning in what is now New Mexico in 1628. In the modern U.S., wine production is undertaken in all fifty states, with California producing 84 percent of all U.S. wine. With more than 1,100,000 acres (4,500 km2) under vine, the United States is the fourth-largest wine-producing country in the world, after Italy, Spain, and France. The classic American diner, a casual restaurant type originally intended for the working class, emerged during the 19th century from converted railroad dining cars made stationary. The diner soon evolved into purpose-built structures whose number expanded greatly in the 20th century. The American fast-food industry developed alongside the nation's car culture. American restaurants developed the drive-in format in the 1920s, which they began to replace with the drive-through format by the 1940s. American fast-food restaurant chains, such as McDonald's, Burger King, Chick-fil-A, Kentucky Fried Chicken, Dunkin' Donuts and many others, have numerous outlets around the world. The most popular spectator sports in the U.S. are American football, basketball, baseball, soccer, and ice hockey. Their premier leagues are, respectively, the National Football League, the National Basketball Association, Major League Baseball, Major League Soccer, and the National Hockey League, All these leagues enjoy wide-ranging domestic media coverage and, except for the MLS, all are considered the preeminent leagues in their respective sports in the world. While most major U.S. sports such as baseball and American football have evolved out of European practices, basketball, volleyball, skateboarding, and snowboarding are American inventions, many of which have become popular worldwide. Lacrosse and surfing arose from Native American and Native Hawaiian activities that predate European contact. The market for professional sports in the United States was approximately $69 billion in July 2013, roughly 50% larger than that of Europe, the Middle East, and Africa combined. American football is by several measures the most popular spectator sport in the United States. Although American football does not have a substantial following in other nations, the NFL does have the highest average attendance (67,254) of any professional sports league in the world. In the year 2024, the NFL generated over $23 billion, making them the most valued professional sports league in the United States and the world. Baseball has been regarded as the U.S. "national sport" since the late 19th century. The most-watched individual sports in the U.S. are golf and auto racing, particularly NASCAR and IndyCar. On the collegiate level, earnings for the member institutions exceed $1 billion annually, and college football and basketball attract large audiences, as the NCAA March Madness tournament and the College Football Playoff are some of the most watched national sporting events. In the U.S., the intercollegiate sports level serves as the main feeder system for professional and Olympic sports, with significant exceptions such as Minor League Baseball. This differs greatly from practices in nearly all other countries, where publicly and privately funded sports organizations serve this function. Eight Olympic Games have taken place in the United States. The 1904 Summer Olympics in St. Louis, Missouri, were the first-ever Olympic Games held outside of Europe. The Olympic Games will be held in the U.S. for a ninth time when Los Angeles hosts the 2028 Summer Olympics. U.S. athletes have won a total of 2,968 medals (1,179 gold) at the Olympic Games, the most of any country. In other international competition, the United States is the home of a number of prestigious events, including the America's Cup, World Baseball Classic, the U.S. Open, and the Masters Tournament. The U.S. men's national soccer team has qualified for eleven World Cups, while the women's national team has won the FIFA Women's World Cup and Olympic soccer tournament four and five times, respectively. The 1999 FIFA Women's World Cup was hosted by the United States. Its final match was attended by 90,185, setting the world record for largest women's sporting event crowd at the time. The United States hosted the 1994 FIFA World Cup and will co-host, along with Canada and Mexico, the 2026 FIFA World Cup. See also Notes References This article incorporates text from a free content work. Licensed under CC BY-SA IGO 3.0 (license statement/permission). Text taken from World Food and Agriculture – Statistical Yearbook 2023, FAO, FAO. External links 40°N 100°W / 40°N 100°W / 40; -100 (United States of America) |
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Contents Extraterrestrial life Extraterrestrial life, or alien life (colloquially aliens), is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically or conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more, or far less, advanced than humans. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology. Speculation about inhabited worlds beyond Earth dates back to antiquity. Early Christian writers, including Augustine, discussed ideas from thinkers like Democritus and Epicurus about countless worlds in the vast universe. Pre-modern writers typically assumed extraterrestrial "worlds" were inhabited by living beings. William Vorilong, in the 15th century, acknowledged the possibility Jesus could have visited extraterrestrial worlds to redeem their inhabitants.: 26 In 1440, Nicholas of Cusa suggested Earth is a "brilliant star"; he theorized that all celestial bodies, even the Sun, could host life. Descartes wrote that there were no means to prove the stars were not inhabited by "intelligent creatures", but their existence was a matter of speculation.: 67 In comparison to the life-abundant Earth, the vast majority of intrasolar and extrasolar planets and moons have harsh surface conditions and disparate atmospheric chemistry, or lack an atmosphere. However, there are many extreme and chemically harsh ecosystems on Earth that do support forms of life and are often hypothesized to be the origin of life on Earth. Examples include life surrounding hydrothermal vents, acidic hot springs, and volcanic lakes, as well as halophiles and the deep biosphere. Since the mid-20th century, researchers have searched for extraterrestrial life and intelligence. Solar system studies focus on Venus, Mars, Europa, and Titan, while exoplanet discoveries now total 6,022 confirmed planets in 4,490 systems as of October 2025. Depending on the category of search, methods range from analysis of telescope and specimen data to radios used to detect and transmit interstellar communication. Interstellar travel remains largely hypothetical, with only the Voyager 1 and Voyager 2 probes confirmed to have entered the interstellar medium. The concept of extraterrestrial life, especially intelligent life, has greatly influenced culture and fiction. A key debate centers on contacting extraterrestrial intelligence: some advocate active attempts, while others warn it could be risky, given human history of exploiting other societies. Context Initially, after the Big Bang, the universe was too hot to allow life. It is estimated that the temperature of the universe was around 10 billion Kelvin at the one-second mark. Roughly 15 million years later, it cooled to temperate levels, though the elements of organic life were yet nonexistent. The only freely available elements at that point were hydrogen and helium. Carbon and oxygen (and later, water) would not appear until 50 million years later, created through stellar fusion. At that point, the difficulty for life to appear was not the temperature, but the scarcity of free heavy elements. Planetary systems emerged, and the first organic compounds may have formed in the protoplanetary disk of dust grains that would eventually create rocky planets like Earth. Although Earth was in a molten state after its birth and may have burned any organics that fell on it, it would have been more receptive once it cooled down. Once the right conditions on Earth were met, life started by a chemical process known as abiogenesis. Alternatively, life may have formed less frequently, then spread—by meteoroids, for example—between habitable planets in a process called panspermia. During most of its stellar evolution, stars combine hydrogen nuclei to make helium nuclei by stellar fusion, and the comparatively lighter weight of helium allows the star to release the extra energy. The process continues until the star uses all of its available fuel, with the speed of consumption being related to the size of the star. During its last stages, stars start combining helium nuclei to form carbon nuclei. The larger stars can further combine carbon nuclei to create oxygen and silicon, oxygen into neon and sulfur, and so on until iron. Ultimately, the star blows much of its content back into the stellar medium, where it would join clouds that would eventually become new generations of stars and planets. Many of those materials are the raw components of life on Earth. As this process takes place in all the universe, said materials are ubiquitous in the cosmos and not a rarity from the Solar System. Earth is a planet in the Solar System, a planetary system formed by a star at the center, the Sun, and the objects that orbit it: other planets, moons, asteroids, and comets. The sun is part of the Milky Way, a galaxy. The Milky Way is part of the Local Group, a galaxy group that is in turn part of the Laniakea Supercluster. The universe is composed of all similar structures in existence. The immense distances between celestial objects are a difficulty for studying extraterrestrial life. So far, humans have only set foot on the Moon and sent robotic probes to other planets and moons in the Solar System. Although probes can withstand conditions that may be lethal to humans, the distances cause time delays: the New Horizons took nine years after launch to reach Pluto. No probe has ever reached extrasolar planetary systems. The Voyager 2 left the Solar System at a speed of 50,000 kilometers per hour; if it headed towards the Alpha Centauri system, the closest one to Earth at 4.4 light years, it would reach it in 100,000 years. Under current technology, such systems can only be studied by telescopes, which have limitations. It is estimated that dark matter has a larger amount of combined matter than stars and gas clouds, but as it plays no role in the stellar evolution of stars and planets, it is usually not taken into account by astrobiology. There is an area around a star, the circumstellar habitable zone or "Goldilocks zone", wherein water may be at the right temperature to exist in liquid form at a planetary surface. This area is neither too close to the star, where water would become steam, nor too far away, where water would be frozen as ice. However, although useful as an approximation, planetary habitability is complex and defined by several factors. Being in the habitable zone is not enough for a planet to be habitable, not even to actually have such liquid water. Venus is located in the solar system's habitable zone, but does not have liquid water because of the conditions of its atmosphere. Jovian planets or gas giants are not considered habitable even if they orbit close enough to their stars as hot Jupiters, due to crushing atmospheric pressures. The actual distances for the habitable zones vary according to the type of star, and even the solar activity of each specific star influences the local habitability. The type of star also defines the time the habitable zone will exist, as its presence and limits will change along with the star's stellar evolution. The Big Bang occurred 13.8 billion years ago, the Solar System was formed 4.6 billion years ago, and the first hominids appeared 6 million years ago. Life on other planets may have started, evolved, given birth to extraterrestrial intelligences, and perhaps even faced a planetary extinction event millions or billions of years ago. When considered from a cosmic perspective, the brief times of existence of Earth's species may suggest that extraterrestrial life may be equally fleeting under such a scale. During a period of about 7 million years, from about 10 to 17 million years after the Big Bang, the background temperature was between 373 and 273 K (100 and 0 °C; 212 and 32 °F), allowing the possibility of liquid water if any planets existed. Avi Loeb (2014) speculated that primitive life might in principle have appeared during this window, which he called "the Habitable Epoch of the Early Universe". Life on Earth is quite ubiquitous across the planet and has adapted over time to almost all the available environments in it, extremophiles and the deep biosphere thrive at even the most hostile ones. As a result, it is inferred that life in other celestial bodies may be equally adaptive. However, the origin of life is unrelated to its ease of adaptation and may have stricter requirements. A celestial body may not have any life on it, even if it were habitable. Likelihood of existence Life in the cosmos beyond Earth has been observed. The hypothesis of ubiquitous extraterrestrial life relies on three main ideas. The first one, the size of the universe, allows for plenty of planets to have a similar habitability to Earth, and the age of the universe gives enough time for a long process analog to the history of Earth to happen there. The second is that the substances that make life, such as carbon and water, are ubiquitous in the universe. The third is that the physical laws are universal, which means that the forces that would facilitate or prevent the existence of life would be the same ones as on Earth. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere else other than Earth. This argument is embodied in the Copernican principle, which states that Earth does not occupy a unique position in the Universe, and the mediocrity principle, which states that there is nothing special about life on Earth. Other authors consider instead that life in the cosmos, or at least multicellular life, may actually be rare. The Rare Earth hypothesis maintains that life on Earth is possible because of a series of factors that range from the location in the galaxy and the configuration of the Solar System to local characteristics of the planet, and that it is unlikely that another planet simultaneously meets all such requirements. The proponents of this hypothesis consider that very little evidence suggests the existence of extraterrestrial life and that, at this point, it is just a desired result and not a reasonable scientific explanation for any gathered data. In 1961, astronomer and astrophysicist Frank Drake devised the Drake equation as a way to stimulate scientific dialogue at a meeting on the search for extraterrestrial intelligence (SETI). The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. The Drake equation is:: xix where: and Drake's proposed estimates are as follows, but numbers on the right side of the equation are agreed as speculative and open to substitution: 10,000 = 5 ⋅ 0.5 ⋅ 2 ⋅ 1 ⋅ 0.2 ⋅ 1 ⋅ 10,000 {\displaystyle 10{,}000=5\cdot 0.5\cdot 2\cdot 1\cdot 0.2\cdot 1\cdot 10{,}000} [better source needed] The Drake equation has proved controversial since, although it is written as a math equation, none of its values were known at the time. Although some values may eventually be measured, others are based on social sciences and are not knowable by their very nature. This does not allow one to make noteworthy conclusions from the equation. Based on observations from the Hubble Space Telescope, there are nearly 2 trillion galaxies in the observable universe. It is estimated that at least ten percent of all Sun-like stars have a system of planets. In other words, there are 6.25×1018 stars with planets orbiting them in the observable universe. Even if it is assumed that only one out of a billion of these stars has planets supporting life, there would be some 6.25 billion life-supporting planetary systems in the observable universe. A 2013 study based on results from the Kepler spacecraft estimated that the Milky Way contains at least as many planets as it does stars, resulting in 100–400 billion exoplanets. The Nebular hypothesis that explains the formation of the Solar System and other planetary systems would suggest that those can have several configurations, and not all of them may have rocky planets within the habitable zone. The apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilisations and the lack of evidence for such civilisations is known as the Fermi paradox. Dennis W. Sciama claimed that life's existence in the universe depends on various fundamental constants. Zhi-Wei Wang and Samuel L. Braunstein suggest that a random universe capable of supporting life is likely to be just barely able to do so, giving a potential explanation to the Fermi paradox. Biochemical basis If extraterrestrial life exists, it could range from simple microorganisms and multicellular organisms similar to animals or plants, to complex alien intelligences akin to humans. When scientists talk about extraterrestrial life, they consider all those types. Although it is possible that extraterrestrial life may have other configurations, scientists use the hierarchy of lifeforms from Earth for simplicity, as it is the only one known to exist. The first basic requirement for life is an environment with non-equilibrium thermodynamics, which means that the thermodynamic equilibrium must be broken by a source of energy. The traditional sources of energy in the cosmos are the stars, such as for life on Earth, which depends on the energy of the sun. However, there are other alternative energy sources, such as volcanoes, plate tectonics, and hydrothermal vents. There are ecosystems on Earth in deep areas of the ocean that do not receive sunlight, and take energy from black smokers instead. Magnetic fields and radioactivity have also been proposed as sources of energy, although they would be less efficient ones. Life on Earth requires water in a liquid state as a solvent in which biochemical reactions take place. It is highly unlikely that an abiogenesis process can start within a gaseous or solid medium: the atom speeds, either too fast or too slow, make it difficult for specific ones to meet and start chemical reactions. A liquid medium also allows the transport of nutrients and substances required for metabolism. Sufficient quantities of carbon and other elements, along with water, might enable the formation of living organisms on terrestrial planets with a chemical make-up and temperature range similar to that of Earth. Life based on ammonia rather than water has been suggested as an alternative, though this solvent appears less suitable than water. It is also conceivable that there are forms of life whose solvent is a liquid hydrocarbon, such as methane, ethane or propane. Another unknown aspect of potential extraterrestrial life would be the chemical elements that would compose it. Life on Earth is largely composed of carbon, but there could be other hypothetical types of biochemistry. A replacement for carbon would need to be able to create complex molecules, store information required for evolution, and be freely available in the medium. To create DNA, RNA, or a close analog, such an element should be able to bind its atoms with many others, creating complex and stable molecules. It should be able to create at least three covalent bonds: two for making long strings and at least a third to add new links and allow for diverse information. Only nine elements meet this requirement: boron, nitrogen, phosphorus, arsenic, antimony (three bonds), carbon, silicon, germanium and tin (four bonds). As for abundance, carbon, nitrogen, and silicon are the most abundant ones in the universe, far more than the others. On Earth's crust the most abundant of those elements is silicon, in the Hydrosphere it is carbon and in the atmosphere, it is carbon and nitrogen. Silicon, however, has disadvantages over carbon. The molecules formed with silicon atoms are less stable, and more vulnerable to acids, oxygen, and light. An ecosystem of silicon-based lifeforms would require very low temperatures, high atmospheric pressure, an atmosphere devoid of oxygen, and a solvent other than water. The low temperatures required would add an extra problem, the difficulty to kickstart a process of abiogenesis to create life in the first place. Norman Horowitz, head of the Jet Propulsion Laboratory bioscience section for the Mariner and Viking missions from 1965 to 1976 considered that the great versatility of the carbon atom makes it the element most likely to provide solutions, even exotic solutions, to the problems of survival of life on other planets. However, he also considered that the conditions found on Mars were incompatible with carbon based life. Even if extraterrestrial life is based on carbon and uses water as a solvent, like Earth life, it may still have a radically different biochemistry. Life is generally considered to be a product of natural selection. It has been proposed that to undergo natural selection a living entity must have the capacity to replicate itself, the capacity to avoid damage/decay, and the capacity to acquire and process resources in support of the first two capacities. Life on Earth may have started with an RNA world and later evolved to its current form, where some of the RNA tasks were transferred to DNA and proteins. Extraterrestrial life may still be stuck using RNA, or evolve into other configurations. It is unclear if our biochemistry is the most efficient one that could be generated, or which elements would follow a similar pattern. However, it is likely that, even if cells had a different composition to those from Earth, they would still have a cell membrane. Life on Earth jumped from prokaryotes to eukaryotes and from unicellular organisms to multicellular organisms through evolution. So far no alternative process to achieve such a result has been conceived, even if hypothetical. Evolution requires life to be divided into individual organisms, and no alternative organisation has been satisfactorily proposed either. At the basic level, membranes define the limit of a cell, between it and its environment, while remaining partially open to exchange energy and resources with it. The evolution from simple cells to eukaryotes, and from them to multicellular lifeforms, is not guaranteed. The Cambrian explosion took place thousands of millions of years after the origin of life, and its causes are not fully known yet. On the other hand, the jump to multicellularity took place several times, which suggests that it could be a case of convergent evolution, and so likely to take place on other planets as well. Palaeontologist Simon Conway Morris considers that convergent evolution would lead to kingdoms similar to our plants and animals, and that many features are likely to develop in alien animals as well, such as bilateral symmetry, limbs, digestive systems and heads with sensory organs. Scientists from the University of Oxford analysed it from the perspective of evolutionary theory and wrote in a study in the International Journal of Astrobiology that aliens may be similar to humans. The planetary context would also have an influence: a planet with higher gravity would have smaller animals, and other types of stars can lead to non-green photosynthesizers. The amount of energy available would also affect biodiversity, as an ecosystem sustained by black smokers or hydrothermal vents would have less energy available than those sustained by a star's light and heat, and so its lifeforms would not grow beyond a certain complexity. There is also research in assessing the capacity of life for developing intelligence. It has been suggested that this capacity arises with the number of potential niches a planet contains, and that the complexity of life itself is reflected in the information density of planetary environments, which in turn can be computed from its niches. It is common knowledge that the conditions on other planets in the solar system, in addition to the many galaxies outside of the Milky Way galaxy, are very harsh and seem to be too extreme to harbor any life. The environmental conditions on these planets can have intense UV radiation paired with extreme temperatures, lack of water, and much more that can lead to conditions that don't seem to favor the creation or maintenance of extraterrestrial life. However, there has been much historical evidence that some of the earliest and most basic forms of life on Earth originated in some extreme environments that seem unlikely to have harbored life at least at one point in Earth's history. Fossil evidence as well as many historical theories backed up by years of research and studies have marked environments like hydrothermal vents or acidic hot springs as some of the first places that life could have originated on Earth. These environments can be considered extreme when compared to the typical ecosystems that the majority of life on Earth now inhabit, as hydrothermal vents are scorching hot due to the magma escaping from the Earth's mantle and meeting the much colder oceanic water. Even in today's world, there can be a diverse population of bacteria found inhabiting the area surrounding these hydrothermal vents which can suggest that some form of life can be supported even in the harshest of environments like the other planets in the solar system. The aspects of these harsh environments that make them ideal for the origin of life on Earth, as well as the possibility of creation of life on other planets, is the chemical reactions forming spontaneously. For example, the hydrothermal vents found on the ocean floor are known to support many chemosynthetic processes which allow organisms to utilize energy through reduced chemical compounds that fix carbon. In return, these reactions will allow for organisms to live in relatively low oxygenated environments while maintaining enough energy to support themselves. The early Earth environment was reducing and therefore, these carbon fixing compounds were necessary for the survival and possible origin of life on Earth. With the little amount of information that scientists have found regarding the atmosphere on other planets in the Milky Way galaxy and beyond, the atmospheres are most likely reducing or with very low oxygen levels, especially when compared with Earth's atmosphere. If there were the necessary elements and ions on these planets, the same carbon fixing, reduced chemical compounds occurring around hydrothermal vents could also occur on these planets' surfaces and possibly result in the origin of extraterrestrial life. Planetary habitability in the Solar System The Solar System has a wide variety of planets, dwarf planets, and moons, and each one is studied for its potential to host life. Each one has its own specific conditions that may benefit or harm life. So far, the only lifeforms found are those from Earth. No extraterrestrial intelligence other than humans exists or has ever existed within the Solar System. Astrobiologist Mary Voytek points out that it would be unlikely to find large ecosystems, as they would have already been detected by now. The inner Solar System is likely devoid of life. However, Venus is still of interest to astrobiologists, as it is a terrestrial planet that was likely similar to Earth in its early stages and developed in a different way. There is a greenhouse effect, the surface is the hottest in the Solar System, sulfuric acid clouds, all surface liquid water is lost, and it has a thick carbon-dioxide atmosphere with huge pressure. Comparing both helps to understand the precise differences that lead to beneficial or harmful conditions for life. And despite the conditions against life on Venus, there are suspicions that microbial life-forms may still survive in high-altitude clouds. Mars is a cold and almost airless desert, inhospitable to life. However, recent studies revealed that water on Mars used to be quite abundant, forming rivers, lakes, and perhaps even oceans. Mars may have been habitable back then, and life on Mars may have been possible. But when the planetary core ceased to generate a magnetic field, solar winds removed the atmosphere and the planet became vulnerable to solar radiation. Ancient life-forms may still have left fossilised remains, and microbes may still survive deep underground. As mentioned, the gas giants and ice giants are unlikely to contain life. The most distant solar system bodies, found in the Kuiper Belt and outwards, are locked in permanent deep-freeze, but cannot be ruled out completely. Although the giant planets themselves are highly unlikely to have life, there is much hope to find it on moons orbiting these planets. Europa, from the Jovian system, has a subsurface ocean below a thick layer of ice. Ganymede and Callisto also have subsurface oceans, but life is less likely in them because water is sandwiched between layers of solid ice. Europa would have contact between the ocean and the rocky surface, which helps the chemical reactions. It may be difficult to dig so deep in order to study those oceans, though. Enceladus, a tiny moon of Saturn with another subsurface ocean, may not need to be dug, as it releases water to space in eruption columns. The space probe Cassini flew inside one of these, but could not make a full study because NASA did not expect this phenomenon and did not equip the probe to study ocean water. Still, Cassini detected complex organic molecules, salts, evidence of hydrothermal activity, hydrogen, and methane. Titan is the only celestial body in the Solar System besides Earth that has liquid bodies on the surface. It has rivers, lakes, and rain of hydrocarbons, methane, and ethane, and even a cycle similar to Earth's water cycle. This special context encourages speculations about lifeforms with different biochemistry, but the cold temperatures would make such chemistry take place at a very slow pace. Water is rock-solid on the surface, but Titan does have a subsurface water ocean like several other moons. However, it is of such a great depth that it would be very difficult to access it for study. Scientific search The science that searches and studies life in the universe, both on Earth and elsewhere, is called astrobiology. With the study of Earth's life, the only known form of life, astrobiology seeks to study how life starts and evolves and the requirements for its continuous existence. This helps to determine what to look for when searching for life in other celestial bodies. This is a complex area of study, and uses the combined perspectives of several scientific disciplines, such as astronomy, biology, chemistry, geology, oceanography, and atmospheric sciences. The scientific search for extraterrestrial life is being carried out both directly and indirectly. As of September 2017[update], 3,667 exoplanets in 2,747 systems have been identified, and other planets and moons in the Solar System hold the potential for hosting primitive life such as microorganisms. As of 8 February 2021, an updated status of studies considering the possible detection of lifeforms on Venus (via phosphine) and Mars (via methane) was reported. Scientists search for biosignatures within the Solar System by studying planetary surfaces and examining meteorites. Some claim to have identified evidence that microbial life has existed on Mars. In 1996, a controversial report stated that structures resembling nanobacteria were discovered in a meteorite, ALH84001, formed of rock ejected from Mars. Although all the unusual properties of the meteorite were eventually explained as the result of inorganic processes, the controversy over its discovery laid the groundwork for the development of astrobiology. An experiment on the two Viking Mars landers reported gas emissions from heated Martian soil samples that some scientists argue are consistent with the presence of living microorganisms. Lack of corroborating evidence from other experiments on the same samples suggests that a non-biological reaction is a more likely hypothesis. In February 2005 NASA scientists reported they may have found some evidence of extraterrestrial life on Mars. The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center, based their claim on methane signatures found in Mars's atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near the Rio Tinto river in Spain. NASA officials soon distanced NASA from the scientists' claims, and Stoker herself backed off from her initial assertions. In November 2011, NASA launched the Mars Science Laboratory that landed the Curiosity rover on Mars. It is designed to assess the past and present habitability on Mars using a variety of scientific instruments. The rover landed on Mars at Gale Crater in August 2012. A group of scientists at Cornell University started a catalog of microorganisms, with the way each one reacts to sunlight. The goal is to help with the search for similar organisms in exoplanets, as the starlight reflected by planets rich in such organisms would have a specific spectrum, unlike that of starlight reflected from lifeless planets. If Earth was studied from afar with this system, it would reveal a shade of green, as a result of the abundance of plants with photosynthesis. In August 2011, NASA studied meteorites found on Antarctica, finding adenine, guanine, hypoxanthine, and xanthine. Adenine and guanine are components of DNA, and the others are used in other biological processes. The studies ruled out pollution of the meteorites on Earth, as those components would not be freely available the way they were found in the samples. This discovery suggests that several organic molecules that serve as building blocks of life may be generated within asteroids and comets. In October 2011, scientists reported that cosmic dust contains complex organic compounds ("amorphous organic solids with a mixed aromatic-aliphatic structure") that could be created naturally, and rapidly, by stars. It is still unclear if those compounds played a role in the creation of life on Earth, but Sun Kwok, of the University of Hong Kong, thinks so. "If this is the case, life on Earth may have had an easier time getting started as these organics can serve as basic ingredients for life." In August 2012, and in a world first, astronomers at Copenhagen University reported the detection of a specific sugar molecule, glycolaldehyde, in a distant star system. The molecule was found around the protostellar binary IRAS 16293-2422, which is located 400 light years from Earth. Glycolaldehyde is needed to form ribonucleic acid, or RNA, which is similar in function to DNA. This finding suggests that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation. In December 2023, astronomers reported the first time discovery, in the plumes of Enceladus, moon of the planet Saturn, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life." Although most searches are focused on the biology of extraterrestrial life, an extraterrestrial intelligence capable enough to develop a civilization may be detectable by other means as well. Technology may generate technosignatures, effects on the native planet that may not be caused by natural causes. There are three main types of techno-signatures considered: interstellar communications, effects on the atmosphere, and planetary-sized structures such as Dyson spheres. Organizations such as the SETI Institute search the cosmos for potential forms of communication. They started with radio waves, and now search for laser pulses as well. The challenge for this search is that there are natural sources of such signals as well, such as gamma-ray bursts and supernovae, and the difference between a natural signal and an artificial one would be in its specific patterns. Astronomers intend to use artificial intelligence for this, as it can manage large amounts of data and is devoid of biases and preconceptions. Besides, even if there is an advanced extraterrestrial civilization, there is no guarantee that it is transmitting radio communications in the direction of Earth. The length of time required for a signal to travel across space means that a potential answer may arrive decades or centuries after the initial message. The atmosphere of Earth is rich in nitrogen dioxide as a result of air pollution, which can be detectable. The natural abundance of carbon, which is also relatively reactive, makes it likely to be a basic component of the development of a potential extraterrestrial technological civilization, as it is on Earth. Fossil fuels may likely be generated and used on such worlds as well. The abundance of chlorofluorocarbons in the atmosphere can also be a clear technosignature, considering their role in ozone depletion. Light pollution may be another technosignature, as multiple lights on the night side of a rocky planet can be a sign of advanced technological development. However, modern telescopes are not strong enough to study exoplanets with the required level of detail to perceive it. The Kardashev scale proposes that a civilization may eventually start consuming energy directly from its local star. This would require giant structures built next to it, called Dyson spheres. Those speculative structures would cause an excess infrared radiation, that telescopes may notice. The infrared radiation is typical of young stars, surrounded by dusty protoplanetary disks that will eventually form planets. An older star such as the Sun would have no natural reason to have excess infrared radiation. The presence of heavy elements in a star's light-spectrum is another potential biosignature; such elements would (in theory) be found if the star were being used as an incinerator/repository for nuclear waste products. Some astronomers search for extrasolar planets that may be conducive to life, narrowing the search to terrestrial planets within the habitable zones of their stars. Since 1992, over four thousand exoplanets have been discovered (6,128 planets in 4,584 planetary systems including 1,017 multiple planetary systems as of 30 October 2025). The extrasolar planets so far discovered range in size from that of terrestrial planets similar to Earth's size to that of gas giants larger than Jupiter. The number of observed exoplanets is expected to increase greatly in the coming years.[better source needed] The Kepler space telescope has also detected a few thousand candidate planets, of which about 11% may be false positives. There is at least one planet on average per star. About 1 in 5 Sun-like stars[a] have an "Earth-sized"[b] planet in the habitable zone,[c] with the nearest expected to be within 12 light-years distance from Earth. Assuming 200 billion stars in the Milky Way,[d] that would be 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if red dwarfs are included. The rogue planets in the Milky Way possibly number in the trillions. The nearest known exoplanet is Proxima Centauri b, located 4.2 light-years (1.3 pc) from Earth in the southern constellation of Centaurus. As of March 2014[update], the least massive exoplanet known is PSR B1257+12 A, which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is DENIS-P J082303.1−491201 b, about 29 times the mass of Jupiter, although according to most definitions of a planet, it is too massive to be a planet and may be a brown dwarf instead. Almost all of the planets detected so far are within the Milky Way, but there have also been a few possible detections of extragalactic planets. The study of planetary habitability also considers a wide range of other factors in determining the suitability of a planet for hosting life. One sign that a planet probably already contains life is the presence of an atmosphere with significant amounts of oxygen, since that gas is highly reactive and generally would not last long without constant replenishment. This replenishment occurs on Earth through photosynthetic organisms. One way to analyse the atmosphere of an exoplanet is through spectrography when it transits its star, though this might only be feasible with dim stars like white dwarfs. History and cultural impact The modern concept of extraterrestrial life is based on assumptions that were not commonplace during the early days of astronomy. The first explanations for the celestial objects seen in the night sky were based on mythology. Scholars from Ancient Greece were the first to consider that the universe is inherently understandable and rejected explanations based on supernatural incomprehensible forces, such as the myth of the Sun being pulled across the sky in the chariot of Apollo. They had not developed the scientific method yet and based their ideas on pure thought and speculation, but they developed precursor ideas to it, such as that explanations had to be discarded if they contradict observable facts. The discussions of those Greek scholars established many of the pillars that would eventually lead to the idea of extraterrestrial life, such as Earth being round and not flat. The cosmos was first structured in a geocentric model that considered that the sun and all other celestial bodies revolve around Earth. However, they did not consider them as worlds. In Greek understanding, the world was composed by both Earth and the celestial objects with noticeable movements. Anaximander thought that the cosmos was made from apeiron, a substance that created the world, and that the world would eventually return to the cosmos. Eventually two groups emerged, the atomists that thought that matter at both Earth and the cosmos was equally made of small atoms of the classical elements (earth, water, fire and air), and the Aristotelians who thought that those elements were exclusive of Earth and that the cosmos was made of a fifth one, the aether. Atomist Epicurus thought that the processes that created the world, its animals and plants should have created other worlds elsewhere, along with their own animals and plants. Aristotle thought instead that all the earth element naturally fell towards the center of the universe, and that would make it impossible for other planets to exist elsewhere. Under that reasoning, Earth was not only in the center, it was also the only planet in the universe. Cosmic pluralism, the plurality of worlds, or simply pluralism, describes the philosophical belief in numerous "worlds" in addition to Earth, which might harbor extraterrestrial life. The earliest recorded assertion of extraterrestrial human life is found in ancient scriptures of Jainism. There are multiple "worlds" mentioned in Jain scriptures that support human life. These include, among others, Bharat Kshetra, Mahavideh Kshetra, Airavat Kshetra, and Hari kshetra. Medieval Muslim writers like Fakhr al-Din al-Razi and Muhammad al-Baqir supported cosmic pluralism on the basis of the Qur'an. Chaucer's poem The House of Fame engaged in medieval thought experiments that postulated the plurality of worlds. However, those ideas about other worlds were different from the current knowledge about the structure of the universe, and did not postulate the existence of planetary systems other than the Solar System. When those authors talk about other worlds, they talk about places located at the center of their own systems, and with their own stellar vaults and cosmos surrounding them. The Greek ideas and the disputes between atomists and Aristotelians outlived the fall of the Greek empire. The Great Library of Alexandria compiled information about it, part of which was translated by Islamic scholars and thus survived the end of the Library. Baghdad combined the knowledge of the Greeks, the Indians, the Chinese and its own scholars, and the knowledge expanded through the Byzantine Empire. From there it eventually returned to Europe by the time of the Middle Ages. However, as the Greek atomist doctrine held that the world was created by random movements of atoms, with no need for a creator deity, it became associated with atheism, and the dispute intertwined with religious ones. Still, the Church did not react to those topics in a homogeneous way, and there were stricter and more permissive views within the church itself. The first known mention of the term 'panspermia' was in the writings of the 5th-century BC Greek philosopher Anaxagoras. He proposed the idea that life exists everywhere. By the time of the late Middle Ages there were many known inaccuracies in the geocentric model, but it was kept in use because naked eye observations provided limited data. Nicolaus Copernicus started the Copernican Revolution by proposing that the planets revolve around the sun rather than Earth. His proposal had little acceptance at first because, as he kept the assumption that orbits were perfect circles, his model led to as many inaccuracies as the geocentric one. Tycho Brahe improved the available data with naked-eye observatories, which worked with highly complex sextants and quadrants. Tycho could not make sense of his observations, but Johannes Kepler did: orbits were not perfect circles, but ellipses. This knowledge benefited the Copernican model, which worked now almost perfectly. The invention of the telescope a short time later, perfected by Galileo Galilei, clarified the final doubts, and the paradigm shift was completed. Under this new understanding, the notion of extraterrestrial life became feasible: if Earth is but just a planet orbiting around a star, there may be planets similar to Earth elsewhere. The astronomical study of distant bodies also proved that physical laws are the same elsewhere in the universe as on Earth, with nothing making the planet truly special. The new ideas were met with resistance from the Catholic church. Galileo was tried for the heliocentric model, which was considered heretical, and forced to recant it. The best-known early-modern proponent of ideas of extraterrestrial life was the Italian philosopher Giordano Bruno, who argued in the 16th century for an infinite universe in which every star is surrounded by its own planetary system. Bruno wrote that other worlds "have no less virtue nor a nature different to that of our earth" and, like Earth, "contain animals and inhabitants". Bruno's belief in the plurality of worlds was one of the charges leveled against him by the Venetian Holy Inquisition, which tried and executed him. The heliocentric model was further strengthened by the postulation of the theory of gravity by Sir Isaac Newton. This theory provided the mathematics that explains the motions of all things in the universe, including planetary orbits. By this point, the geocentric model was definitely discarded. By this time, the use of the scientific method had become a standard, and new discoveries were expected to provide evidence and rigorous mathematical explanations. Science also took a deeper interest in the mechanics of natural phenomena, trying to explain not just the way nature works but also the reasons for working that way. There was very little actual discussion about extraterrestrial life before this point, as the Aristotelian ideas remained influential while geocentrism was still accepted. When it was finally proved wrong, it not only meant that Earth was not the center of the universe, but also that the lights seen in the sky were not just lights, but physical objects. The notion that life may exist in them as well soon became an ongoing topic of discussion, although one with no practical ways to investigate. The possibility of extraterrestrials remained a widespread speculation as scientific discovery accelerated. William Herschel, the discoverer of Uranus, was one of many 18th–19th-century astronomers who believed that the Solar System is populated by alien life. Other scholars of the period who championed "cosmic pluralism" included Immanuel Kant and Benjamin Franklin. At the height of the Enlightenment, even the Sun and Moon were considered candidates for extraterrestrial inhabitants. Speculation about life on Mars increased in the late 19th century, following telescopic observation of apparent Martian canals – which soon, however, turned out to be optical illusions. Despite this, in 1895, American astronomer Percival Lowell published his book Mars, followed by Mars and its Canals in 1906, proposing that the canals were the work of a long-gone civilisation. Spectroscopic analysis of Mars's atmosphere began in earnest in 1894, when U.S. astronomer William Wallace Campbell showed that neither water nor oxygen was present in the Martian atmosphere. By 1909 better telescopes and the best perihelic opposition of Mars since 1877 conclusively put an end to the canal hypothesis. As a consequence of the belief in the spontaneous generation there was little thought about the conditions of each celestial body: it was simply assumed that life would thrive anywhere. This theory was disproved by Louis Pasteur in the 19th century. Popular belief in thriving alien civilisations elsewhere in the solar system still remained strong until Mariner 4 and Mariner 9 provided close images of Mars, which debunked forever the idea of the existence of Martians and decreased the previous expectations of finding alien life in general. The end of the spontaneous generation belief forced investigation into the origin of life. Although abiogenesis is the more accepted theory, a number of authors reclaimed the term "panspermia" and proposed that life was brought to Earth from elsewhere. Some of those authors are Jöns Jacob Berzelius (1834), Kelvin (1871), Hermann von Helmholtz (1879) and, somewhat later, by Svante Arrhenius (1903). The science fiction genre, although not so named during the time, developed during the late 19th century. The expansion of the genre of extraterrestrials in fiction influenced the popular perception over the real-life topic, making people eager to jump to conclusions about the discovery of aliens. Science marched at a slower pace, some discoveries fueled expectations and others dashed excessive hopes. For example, with the advent of telescopes, most structures seen on the Moon or Mars were immediately attributed to Selenites or Martians, and later ones (such as more powerful telescopes) revealed that all such discoveries were natural features. A famous case is the Cydonia region of Mars, first imaged by the Viking 1 orbiter. The low-resolution photos showed a rock formation that resembled a human face, but later spacecraft took photos in higher detail that showed that there was nothing special about the site. The search and study of extraterrestrial life became a science of its own, astrobiology. Also known as exobiology, this discipline is studied by the NASA, the ESA, the INAF, and others. Astrobiology studies life from Earth as well, but with a cosmic perspective. For example, abiogenesis is of interest to astrobiology, not because of the origin of life on Earth, but for the chances of a similar process taking place in other celestial bodies. Many aspects of life, from its definition to its chemistry, are analyzed as either likely to be similar in all forms of life across the cosmos or only native to Earth. Astrobiology, however, remains constrained by the current lack of extraterrestrial life-forms to study, as all life on Earth comes from the same ancestor, and it is hard to infer general characteristics from a group with a single example to analyse. The 20th century came with great technological advances, speculations about future hypothetical technologies, and an increased basic knowledge of science by the general population thanks to science divulgation through the mass media. The public interest in extraterrestrial life and the lack of discoveries by mainstream science led to the emergence of pseudosciences that provided affirmative, if questionable, answers to the existence of aliens. Ufology claims that many unidentified flying objects (UFOs) would be spaceships from alien species, and ancient astronauts hypothesis claim that aliens would have visited Earth in antiquity and prehistoric times but people would have failed to understand it by then. Most UFOs or UFO sightings can be readily explained as sightings of Earth-based aircraft (including top-secret aircraft), known astronomical objects or weather phenomenons, or as hoaxes. Looking beyond the pseudosciences, Lewis White Beck strove to elevate the level of public discourse on the topic of extraterrestrial life by tracing the evolution of philosophical thought over the centuries from ancient times into the modern era. His review of the contributions made by Lucretius, Plutarch, Aristotle, Copernicus, Immanuel Kant, John Wilkins, Charles Darwin and Karl Marx demonstrated that even in modern times, humanity could be profoundly influenced in its search for extraterrestrial life by subtle and comforting archetypal ideas which are largely derived from firmly held religious, philosophical and existential belief systems. On a positive note, however, Beck further argued that even if the search for extraterrestrial life proves to be unsuccessful, the endeavor itself could have beneficial consequences by assisting humanity in its attempt to actualize superior ways of living here on Earth. By the 21st century, it was accepted that multicellular life in the Solar System can only exist on Earth, but the interest in extraterrestrial life increased regardless. This is a result of the advances in several sciences. The knowledge of planetary habitability allows to consider on scientific terms the likelihood of finding life at each specific celestial body, as it is known which features are beneficial and harmful for life. Astronomy and telescopes also improved to the point exoplanets can be confirmed and even studied, increasing the number of search places. Life may still exist elsewhere in the Solar System in unicellular form, but the advances in spacecraft allow to send robots to study samples in situ, with tools of growing complexity and reliability. Although no extraterrestrial life has been found and life may still be just a rarity from Earth, there are scientific reasons to suspect that it can exist elsewhere, and technological advances that may detect it if it does. Many scientists are optimistic about the chances of finding alien life. In the words of SETI's Frank Drake, "All we know for sure is that the sky is not littered with powerful microwave transmitters". Drake noted that it is entirely possible that advanced technology results in communication being carried out in some way other than conventional radio transmission. At the same time, the data returned by space probes, and giant strides in detection methods, have allowed science to begin delineating habitability criteria on other worlds, and to confirm that at least other planets are plentiful, though aliens remain a question mark. The Wow! signal, detected in 1977 by a SETI project, remains a subject of speculative debate. On the other hand, other scientists are pessimistic. Jacques Monod wrote that "Man knows at last that he is alone in the indifferent immensity of the universe, whence which he has emerged by chance". In 2000, geologist and paleontologist Peter Ward and astrobiologist Donald Brownlee published a book entitled Rare Earth: Why Complex Life is Uncommon in the Universe.[better source needed] In it, they discussed the Rare Earth hypothesis, in which they claim that Earth-like life is rare in the universe, whereas microbial life is common. Ward and Brownlee are open to the idea of evolution on other planets that is not based on essential Earth-like characteristics such as DNA and carbon. As for the possible risks, theoretical physicist Stephen Hawking warned in 2010 that humans should not try to contact alien life forms. He warned that aliens might pillage Earth for resources. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans", he said. Jared Diamond had earlier expressed similar concerns. On 20 July 2015, Hawking and Russian billionaire Yuri Milner, along with the SETI Institute, announced a well-funded effort, called the Breakthrough Initiatives, to expand efforts to search for extraterrestrial life. The group contracted the services of the 100-meter Robert C. Byrd Green Bank Telescope in West Virginia in the United States and the 64-meter Parkes Telescope in New South Wales, Australia. On 13 February 2015, scientists (including Geoffrey Marcy, Seth Shostak, Frank Drake and David Brin) at a convention of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea; one result was a statement, signed by many, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent". Government responses The 1967 Outer Space Treaty and the 1979 Moon Agreement define rules of planetary protection against potentially hazardous extraterrestrial life. COSPAR also provides guidelines for planetary protection. A committee of the United Nations Office for Outer Space Affairs had in 1977 discussed for a year strategies for interacting with extraterrestrial life or intelligence. The discussion ended without any conclusions. As of 2010, the UN lacks response mechanisms for the case of an extraterrestrial contact. One of the NASA divisions is the Office of Safety and Mission Assurance (OSMA), also known as the Planetary Protection Office. A part of its mission is to "rigorously preclude backward contamination of Earth by extraterrestrial life." In 2016, the Chinese Government released a white paper detailing its space program. According to the document, one of the research objectives of the program is the search for extraterrestrial life. It is also one of the objectives of the Chinese Five-hundred-meter Aperture Spherical Telescope (FAST) program. In 2020, Dmitry Rogozin, the head of the Russian space agency, said the search for extraterrestrial life is one of the main goals of deep space research. He also acknowledged the possibility of existence of primitive life on other planets of the Solar System. The French space agency has an office for the study of "non-identified aero spatial phenomena". The agency is maintaining a publicly accessible database of such phenomena, with over 1600 detailed entries. According to the head of the office, the vast majority of entries have a mundane explanation; but for 25% of entries, their extraterrestrial origin can neither be confirmed nor denied. In 2020, chairman of the Israel Space Agency Isaac Ben-Israel stated that the probability of detecting life in outer space is "quite large". But he disagrees with his former colleague Haim Eshed who stated that there are contacts between an advanced alien civilisation and some of Earth's governments. In fiction Although the idea of extraterrestrial peoples became feasible once astronomy developed enough to understand the nature of planets, they were not thought of as being any different from humans. Having no scientific explanation for the origin of mankind and its relation to other species, there was no reason to expect them to be any other way. This was changed by the 1859 book On the Origin of Species by Charles Darwin, which proposed the theory of evolution. Now with the notion that evolution on other planets may take other directions, science fiction authors created bizarre aliens, clearly distinct from humans. A usual way to do that was to add body features from other animals, such as insects or octopuses. Costuming and special effects feasibility alongside budget considerations forced films and TV series to tone down the fantasy, but these limitations lessened since the 1990s with the advent of computer-generated imagery (CGI), and later on as CGI became more effective and less expensive. Real-life events sometimes captivate people's imagination and this influences the works of fiction. For example, during the Barney and Betty Hill incident, the first recorded claim of an alien abduction, the couple reported that they were abducted and experimented on by aliens with oversized heads, big eyes, pale grey skin, and small noses, a description that eventually became the grey alien archetype once used in works of fiction. See also Notes References Further reading External links |
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Contents Middle East The Middle East[b] is a geopolitical region encompassing the Arabian Peninsula, Egypt, Iran, Iraq, the Levant, and Turkey. The term came into widespread usage by Western European nations in the early 20th century as a replacement of the term Near East (both were in contrast to the Far East). The term "Middle East" has led to some confusion over its changing definitions. Since the late 20th century, it has been criticized as being too Eurocentric. The region includes the vast majority of the territories included in the closely associated definition of West Asia, but without the South Caucasus. It also includes all of Egypt (not just the Sinai region) and all of Turkey (including East Thrace). Most Middle Eastern countries (13 out of 18) are part of the Arab world. The three most populous countries in the region are Egypt, Iran, and Turkey, while Saudi Arabia is the largest Middle Eastern country by area. The history of the Middle East dates back to ancient times, and it was long considered the "cradle of civilization". The geopolitical importance of the region has been recognized and competed for during millennia. The Abrahamic religions (Judaism, Christianity, and Islam) have their origins in the Middle East. Arabs constitute the main ethnic group in the region, followed by Turks, Persians, Kurds, Jews, and Assyrians. The Middle East generally has a hot, arid climate, especially in the Arabian and Egyptian regions. Several major rivers provide irrigation to support agriculture in limited areas here, such as the Nile Delta in Egypt, the Tigris and Euphrates watersheds of Mesopotamia, and the basin of the Jordan River that spans most of the Levant. These regions are collectively known as the Fertile Crescent, and comprise the core of what historians had long referred to as the cradle of civilization; multiple regions of the world have since been classified as also having developed independent, original civilizations. Conversely, the Levantine coast and most of Turkey have relatively temperate climates typical of the Mediterranean, with dry summers and cool, wet winters. Most of the countries that border the Persian Gulf have vast reserves of petroleum. Monarchs of the Arabian Peninsula in particular have benefitted economically from petroleum exports. Because of the arid climate and dependence on the fossil fuel industry, the Middle East is both a major contributor to climate change and a region that is expected to be severely adversely affected by it. Other concepts of the region exist, including the broader Middle East and North Africa (MENA), which includes states of the Maghreb and the Sudan. The term the "Greater Middle East" also includes Afghanistan, Mauritania, Pakistan, as well as parts of East Africa, and sometimes Central Asia and the South Caucasus. Terminology The term "Middle East" may have originated in the 1850s in the British India Office. However, it became more widely known when United States naval strategist Alfred Thayer Mahan used the term in 1902 to "designate the area between Arabia and India". During this time the British and Russian empires were vying for influence in Central Asia, a rivalry that would become known as the Great Game. Mahan realized not only the strategic importance of the region, but also of its center, the Persian Gulf. He labeled the area surrounding the Persian Gulf as the Middle East. He said that, beyond Egypt's Suez Canal, the Gulf was the most important passage for Britain to control in order to keep the Russians from advancing towards British India. Mahan first used the term in his article "The Persian Gulf and International Relations", published in September 1902 in the National Review, a British journal. The Middle East, if I may adopt a term which I have not seen, will some day need its Malta, as well as its Gibraltar; it does not follow that either will be in the Persian Gulf. Naval force has the quality of mobility which carries with it the privilege of temporary absences; but it needs to find on every scene of operation established bases of refit, of supply, and in case of disaster, of security. The British Navy should have the facility to concentrate in force if occasion arise, about Aden, India, and the Persian Gulf. Mahan's article was reprinted in The Times and followed in October by a 20-article series entitled "The Middle Eastern Question", written by Sir Ignatius Valentine Chirol. During this series, Sir Ignatius expanded the definition of Middle East to include "those regions of Asia which extend to the borders of India or command the approaches to India." After the series ended in 1903, The Times removed quotation marks from subsequent uses of the term. Until World War II, it was customary to refer to areas centered on Turkey and the eastern shore of the Mediterranean as the "Near East", while the "Far East" centered on China, India and Japan. The Middle East was then defined as the area from Mesopotamia to Burma; namely, the area between the Near East and the Far East. This area broadly corresponds to South Asia. In the late 1930s, the British established the Middle East Command, which was based in Cairo, for its military forces in the region. After that time, the term "Middle East" gained broader usage in Europe and the United States. Following World War II, for example, the Middle East Institute was founded in Washington, D.C. in 1946. The corresponding adjective is Middle Eastern and the derived noun is Middle Easterner. While non-Eurocentric terms such as "Southwest Asia" or "Swasia" have been sparsely used, the classification of the African country, Egypt, among those counted in the Middle East challenges the usefulness of using such terms. The description Middle has also led to some confusion over changing definitions. Before the First World War, "Near East" was used in English to refer to the Balkans and the Ottoman Empire, while "Middle East" referred to the Caucasus, Persia, and Arabian lands, and sometimes Afghanistan, India and others. In contrast, "Far East" referred to the countries of East Asia (e.g. China, Japan, and Korea). With the collapse of the Ottoman Empire in 1918, "Near East" largely fell out of common use in English, while "Middle East" came to be applied to the emerging independent countries of the Islamic world. However, the usage "Near East" was retained by a variety of academic disciplines, including archaeology and ancient history. In their usage, the term describes an area identical to the term Middle East, which is not used by these disciplines (see ancient Near East).[citation needed] The first official use of the term "Middle East" by the United States government was in the 1957 Eisenhower Doctrine, which pertained to the Suez Crisis. Secretary of State John Foster Dulles defined the Middle East as "the area lying between and including Libya on the west and Pakistan on the east, Syria and Iraq on the North and the Arabian peninsula to the south, plus the Sudan and Ethiopia." In 1958, the State Department explained that the terms "Near East" and "Middle East" were interchangeable, and defined the region as including only Egypt, Syria, Israel, Lebanon, Jordan, Iraq, Saudi Arabia, Kuwait, Bahrain, and Qatar. Since the late 20th century, scholars and journalists from the region, such as journalist Louay Khraish and historian Hassan Hanafi have criticized the use of "Middle East" as a Eurocentric and colonialist term. The Associated Press Stylebook of 2004 says that Near East formerly referred to the farther west countries while Middle East referred to the eastern ones, but that now they are synonymous. It instructs: Use Middle East unless Near East is used by a source in a story. Mideast is also acceptable, but Middle East is preferred. European languages have adopted terms similar to Near East and Middle East. Since these are based on a relative description, the meanings depend on the country and are generally different from the English terms. In German the term Naher Osten (Near East) is still in common use (nowadays the term Mittlerer Osten is more and more common in press texts translated from English sources, albeit having a distinct meaning). In the four Slavic languages, Russian Ближний Восток or Blizhniy Vostok, Bulgarian Близкия Изток, Polish Bliski Wschód or Croatian Bliski istok (terms meaning Near East are the only appropriate ones for the region). However, some European languages do have "Middle East" equivalents, such as French Moyen-Orient, Swedish Mellanöstern, Spanish Oriente Medio or Medio Oriente, Greek is Μέση Ανατολή (Mesi Anatoli), and Italian Medio Oriente.[c] Perhaps because of the political influence of the United States and Europe, and the prominence of Western press, the Arabic equivalent of Middle East (Arabic: الشرق الأوسط ash-Sharq al-Awsaṭ) has become standard usage in the mainstream Arabic press. It comprises the same meaning as the term "Middle East" in North American and Western European usage. The designation, Mashriq, also from the Arabic root for East, also denotes a variously defined region around the Levant, the eastern part of the Arabic-speaking world (as opposed to the Maghreb, the western part). Even though the term originated in the West, countries of the Middle East that use languages other than Arabic also use that term in translation. For instance, the Persian equivalent for Middle East is خاورمیانه (Khāvar-e miyāneh), the Hebrew is המזרח התיכון (hamizrach hatikhon), and the Turkish is Orta Doğu. Countries and territory Traditionally included within the Middle East are Arabia, Asia Minor, East Thrace, Egypt, Iran, the Levant, Mesopotamia, and the Socotra Archipelago. The region includes 17 UN-recognized countries and one British Overseas Territory. Various concepts are often paralleled to the Middle East, most notably the Near East, Fertile Crescent, and Levant. These are geographical concepts, which refer to large sections of the modern-day Middle East, with the Near East being the closest to the Middle East in its geographical meaning. Due to it primarily being Arabic speaking, the Maghreb region of North Africa is sometimes included. "Greater Middle East" is a political term coined by the second Bush administration in the first decade of the 21st century to denote various countries, pertaining to the Muslim world, specifically Afghanistan, Iran, Pakistan, and Turkey. Various Central Asian countries are sometimes also included. History The Middle East lies at the juncture of Africa and Eurasia and of the Indian Ocean and the Mediterranean Sea (see also: Indo-Mediterranean). It is the birthplace and spiritual center of religions such as Christianity, Islam, Judaism, Manichaeism, Yezidi, Druze, Yarsan, and Mandeanism, and in Iran, Mithraism, Zoroastrianism, Manicheanism, and the Baháʼí Faith. Throughout its history the Middle East has been a major center of world affairs; a strategically, economically, politically, culturally, and religiously sensitive area. The region is one of the regions where agriculture was independently discovered, and from the Middle East it was spread, during the Neolithic, to different regions of the world such as Europe, the Indus Valley and Eastern Africa. Prior to the formation of civilizations, advanced cultures formed all over the Middle East during the Stone Age. The search for agricultural lands by agriculturalists, and pastoral lands by herdsmen meant different migrations took place within the region and shaped its ethnic and demographic makeup. The Middle East is widely and most famously known as the cradle of civilization. The world's earliest civilizations, Mesopotamia (Sumer, Akkad, Assyria and Babylonia), ancient Egypt and Kish in the Levant, all originated in the Fertile Crescent and Nile Valley regions of the ancient Near East. These were followed by the Hittite, Greek, Hurrian and Urartian civilisations of Asia Minor; Elam, Persia and Median civilizations in Iran, as well as the civilizations of the Levant (such as Ebla, Mari, Nagar, Ugarit, Canaan, Aramea, Mitanni, Phoenicia and Israel) and the Arabian Peninsula (Magan, Sheba, Ubar). The Near East was first largely unified under the Neo Assyrian Empire, then the Achaemenid Empire followed later by the Macedonian Empire and after this to some degree by the Iranian empires (namely the Parthian and Sassanid Empires), the Roman Empire and Byzantine Empire. The region served as the intellectual and economic center of the Roman Empire and played an exceptionally important role due to its periphery on the Sassanid Empire. Thus, the Romans stationed up to five or six of their legions in the region for the sole purpose of defending it from Sassanid and Bedouin raids and invasions. From the 4th century CE onwards, the Middle East became the center of the two main powers at the time, the Byzantine Empire and the Sassanid Empire. However, it would be the later Islamic Caliphates of the Middle Ages, or Islamic Golden Age which began with the Islamic conquest of the region in the 7th century AD, that would first unify the entire Middle East as a distinct region and create the dominant Islamic Arab ethnic identity that largely (but not exclusively) persists today. The 4 caliphates that dominated the Middle East for more than 600 years were the Rashidun Caliphate, the Umayyad caliphate, the Abbasid caliphate and the Fatimid caliphate. Additionally, the Mongols would come to dominate the region, the Kingdom of Armenia would incorporate parts of the region to their domain, the Seljuks would rule the region and spread Turko-Persian culture, and the Franks would found the Crusader states that would stand for roughly two centuries. Josiah Russell estimates the population of what he calls "Islamic territory" as roughly 12.5 million in 1000 – Anatolia 8 million, Syria 2 million, and Egypt 1.5 million. From the 16th century onward, the Middle East came to be dominated, once again, by two main powers: the Ottoman Empire and the Safavid dynasty. The modern Middle East began after World War I, when the Ottoman Empire, which was allied with the Central Powers, was defeated by the Allies and partitioned into a number of separate nations, initially under British and French Mandates. Other defining events in this transformation included the establishment of Israel in 1948 and the eventual departure of European powers, notably Britain and France by the end of the 1960s. They were supplanted in some part by the rising influence of the United States from the 1970s onwards. In the 20th century, the region's significant stocks of crude oil gave it new strategic and economic importance. Mass production of oil began around 1945, with Saudi Arabia, Iran, Kuwait, Iraq, and the United Arab Emirates having large quantities of oil. Estimated oil reserves, especially in Saudi Arabia and Iran, are some of the highest in the world, and the international oil cartel OPEC is dominated by Middle Eastern countries. During the Cold War, the Middle East was a theater of ideological struggle between the two superpowers and their allies: NATO and the United States on one side, and the Soviet Union and Warsaw Pact on the other, as they competed to influence regional allies. Besides the political reasons there was also the "ideological conflict" between the two systems. Moreover, as Louise Fawcett argues, among many important areas of contention, or perhaps more accurately of anxiety, were, first, the desires of the superpowers to gain strategic advantage in the region, second, the fact that the region contained some two-thirds of the world's oil reserves in a context where oil was becoming increasingly vital to the economy of the Western world [...] Within this contextual framework, the United States sought to divert the Arab world from Soviet influence. Throughout the 20th and 21st centuries, the region has experienced both periods of relative peace and tolerance and periods of conflict particularly between Sunnis and Shiites. Geography In 2018, the MENA region emitted 3.2 billion tonnes of carbon dioxide and produced 8.7% of global greenhouse gas emissions (GHG) despite making up only 6% of the global population. These emissions are mostly from the energy sector, an integral component of many Middle Eastern and North African economies due to the extensive oil and natural gas reserves that are found within the region. The Middle East region is one of the most vulnerable to climate change. The impacts include increase in drought conditions, aridity, heatwaves and sea level rise. Sharp global temperature and sea level changes, shifting precipitation patterns and increased frequency of extreme weather events are some of the main impacts of climate change as identified by the Intergovernmental Panel on Climate Change (IPCC). The MENA region is especially vulnerable to such impacts due to its arid and semi-arid environment, facing climatic challenges such as low rainfall, high temperatures and dry soil. The climatic conditions that foster such challenges for MENA are projected by the IPCC to worsen throughout the 21st century. If greenhouse gas emissions are not significantly reduced, part of the MENA region risks becoming uninhabitable before the year 2100. Climate change is expected to put significant strain on already scarce water and agricultural resources within the MENA region, threatening the national security and political stability of all included countries. Over 60 percent of the region's population lives in high and very high water-stressed areas compared to the global average of 35 percent. This has prompted some MENA countries to engage with the issue of climate change on an international level through environmental accords such as the Paris Agreement. Law and policy are also being established on a national level amongst MENA countries, with a focus on the development of renewable energies. Economy Middle Eastern economies range from being very poor (such as Gaza and Yemen) to extremely wealthy nations (such as Qatar and UAE). According to the International Monetary Fund, the three largest Middle Eastern economies in nominal GDP in 2023 were Saudi Arabia ($1.06 trillion), Turkey ($1.03 trillion), and Israel ($0.54 trillion). For nominal GDP per person, the highest ranking countries are Qatar ($83,891), Israel ($55,535), the United Arab Emirates ($49,451) and Cyprus ($33,807). Turkey ($3.6 trillion), Saudi Arabia ($2.3 trillion), and Iran ($1.7 trillion) had the largest economies in terms of GDP PPP. For GDP PPP per person, the highest-ranking countries are Qatar ($124,834), the United Arab Emirates ($88,221), Saudi Arabia ($64,836), Bahrain ($60,596) and Israel ($54,997). The lowest-ranking country in the Middle East, in terms of GDP nominal per capita, is Yemen ($573). The economic structure of Middle Eastern nations are different because while some are heavily dependent on export of only oil and oil-related products (Saudi Arabia, the UAE and Kuwait), others have a highly diverse economic base (such as Cyprus, Israel, Turkey and Egypt). Industries of the Middle Eastern region include oil and oil-related products, agriculture, cotton, cattle, dairy, textiles, leather products, surgical instruments, defence equipment (guns, ammunition, tanks, submarines, fighter jets, UAVs, and missiles). Banking is an important sector, especially for UAE and Bahrain. With the exception of Cyprus, Turkey, Egypt, Lebanon and Israel, tourism has been a relatively undeveloped area of the economy, in part because of the socially conservative nature of the region as well as political turmoil in certain regions. Since the end of the COVID pandemic however, countries such as the UAE, Bahrain, and Jordan have begun attracting greater numbers of tourists because of improving tourist facilities and the relaxing of tourism-related restrictive policies. Unemployment is high in the Middle East and North Africa region, particularly among people aged 15–29, a demographic representing 30% of the region's population. The total regional unemployment rate in 2025 is 10.8%, and among youth is as high as 28%. Demographics Arabs constitute the largest ethnic group in the Middle East, followed by various Iranian peoples and then by Turkic peoples (Turkish, Azeris, Syrian Turkmen, and Iraqi Turkmen). Native ethnic groups of the region include, in addition to Arabs, Arameans, Assyrians, Baloch, Berbers, Copts, Druze, Greek Cypriots, Jews, Kurds, Lurs, Mandaeans, Persians, Samaritans, Shabaks, Tats, and Zazas. European ethnic groups that form a diaspora in the region include Albanians, Bosniaks, Circassians (including Kabardians), Crimean Tatars, Greeks, Franco-Levantines, Italo-Levantines, and Iraqi Turkmens. Among other migrant populations are Chinese, Filipinos, Indians, Indonesians, Pakistanis, Pashtuns, Romani, and Afro-Arabs. "Migration has always provided an important vent for labor market pressures in the Middle East. For the period between the 1970s and 1990s, the Arab states of the Persian Gulf in particular provided a rich source of employment for workers from Egypt, Yemen and the countries of the Levant, while Europe had attracted young workers from North African countries due both to proximity and the legacy of colonial ties between France and the majority of North African states." According to the International Organization for Migration, there are 13 million first-generation migrants from Arab nations in the world, of which 5.8 reside in other Arab countries. Expatriates from Arab countries contribute to the circulation of financial and human capital in the region and thus significantly promote regional development. In 2009 Arab countries received a total of US$35.1 billion in remittance in-flows and remittances sent to Jordan, Egypt and Lebanon from other Arab countries are 40 to 190 per cent higher than trade revenues between these and other Arab countries. In Somalia, the Somali Civil War has greatly increased the size of the Somali diaspora, as many of the best educated Somalis left for Middle Eastern countries as well as Europe and North America. Non-Arab Middle Eastern countries such as Turkey, Israel and Iran are also subject to important migration dynamics. A fair proportion of those migrating from Arab nations are from ethnic and religious minorities facing persecution and are not necessarily ethnic Arabs, Iranians or Turks.[citation needed] Large numbers of Kurds, Jews, Assyrians, Greeks and Armenians as well as many Mandeans have left nations such as Iraq, Iran, Syria and Turkey for these reasons during the last century. In Iran, many religious minorities such as Christians, Baháʼís, Jews and Zoroastrians have left since the Islamic Revolution of 1979. The Middle East is very diverse when it comes to religions, many of which originated there. Islam is the largest religion in the Middle East, but other faiths that originated there, such as Judaism and Christianity, are also well represented. Christian communities have played a vital role in the Middle East, and they represent 78% of Cyprus population, and 40.5% of Lebanon, where the Lebanese president, half of the cabinet, and half of the parliament follow one of the various Lebanese Christian rites. There are also important minority religions like the Baháʼí Faith, Yarsanism, Yazidism, Zoroastrianism, Mandaeism, Druze, and Shabakism, and in ancient times the region was home to Mesopotamian religions, Canaanite religions, Manichaeism, Mithraism and various monotheist gnostic sects. The six top languages, in terms of numbers of speakers, are Arabic, Persian, Turkish, Kurdish, Modern Hebrew and Greek. About 20 minority languages are also spoken in the Middle East. Arabic, with all its dialects, is the most widely spoken language in the Middle East, with Literary Arabic being official in all North African and in most West Asian countries. Arabic dialects are also spoken in some adjacent areas in neighbouring Middle Eastern non-Arab countries. It is a member of the Semitic branch of the Afro-Asiatic languages. Several Modern South Arabian languages such as Mehri and Soqotri are also spoken in Yemen and Oman. Another Semitic language is Aramaic and its dialects are spoken mainly by Assyrians and Mandaeans, with Western Aramaic still spoken in two villages near Damascus, Syria. There is also an Oasis Berber-speaking community in Egypt where the language is also known as Siwa. It is a non-Semitic Afro-Asiatic sister language. Persian is the second most spoken language. While it is primarily spoken in Iran and some border areas in neighbouring countries, the country is one of the region's largest and most populous. It belongs to the Indo-Iranian branch of the family of Indo-European languages. Other Western Iranic languages spoken in the region include Achomi, Daylami, Kurdish dialects, Semmani, Lurish, amongst many others. The close third-most widely spoken language, Turkish, is largely confined to Turkey, which is also one of the region's largest and most populous countries, but it is present in areas in neighboring countries. It is a member of the Turkic languages, which have their origins in East Asia. Another Turkic language, Azerbaijani, is spoken by Azerbaijanis in Iran. The fourth-most widely spoken language, Kurdish, is spoken in the countries of Iran, Iraq, Syria and Turkey, Sorani Kurdish is the second official language in Iraq (instated after the 2005 constitution) after Arabic. Hebrew is the official language of Israel, with Arabic given a special status after the 2018 Basic law lowered its status from an official language prior to 2018. Hebrew is spoken and used by over 80% of Israel's population, the other 20% using Arabic. Modern Hebrew only began being spoken in the 20th century after being revived in the late 19th century by Elizer Ben-Yehuda (Elizer Perlman) and European Jewish settlers, with the first native Hebrew speaker being born in 1882. Greek is one of the two official languages of Cyprus, and the country's main language. Small communities of Greek speakers exist all around the Middle East; until the 20th century it was also widely spoken in Asia Minor (being the second most spoken language there, after Turkish) and Egypt. During the antiquity, Ancient Greek was the lingua franca for many areas of the western Middle East and until the Muslim expansion it was widely spoken there as well. Until the late 11th century, it was also the main spoken language in Asia Minor; after that it was gradually replaced by the Turkish language as the Anatolian Turks expanded and the local Greeks were assimilated, especially in the interior. English is one of the official languages of Akrotiri and Dhekelia. It is also commonly taught and used as a foreign second language, in countries such as Egypt, Jordan, Iran, Iraq, Qatar, Bahrain, United Arab Emirates and Kuwait. It is also a main language in some Emirates of the United Arab Emirates. It is also spoken as native language by Jewish immigrants from Anglophone countries (UK, US, Australia) in Israel and understood widely as second language there. French is taught and used in many government facilities and media in Lebanon, and is taught in some primary and secondary schools of Egypt and Syria. Maltese, a Semitic language mainly spoken in Europe, is used by the Franco-Maltese diaspora in Egypt. Due to widespread immigration of French Jews to Israel, it is the native language of approximately 200,000 Jews in Israel. Armenian speakers are to be found in the region. Georgian is spoken by the Georgian diaspora. Russian is spoken by a large portion of the Israeli population, because of emigration in the late 1990s. Russian today is a popular unofficial language in use in Israel; news, radio and sign boards can be found in Russian around the country after Hebrew and Arabic. Circassian is also spoken by the diaspora in the region and by almost all Circassians in Israel who speak Hebrew and English as well. The largest Romanian-speaking community in the Middle East is found in Israel, where as of 1995[update] Romanian is spoken by 5% of the population.[d] Bengali, Hindi and Urdu are widely spoken by migrant communities in many Middle Eastern countries, such as Saudi Arabia (where 20–25% of the population is South Asian), the United Arab Emirates (where 50–55% of the population is South Asian), and Qatar, which have large numbers of Pakistani, Bangladeshi and Indian immigrants. Culture The Middle East has recently become more prominent in hosting global sport events due to its wealth and desire to diversify its economy. The South Asian diaspora is a major backer of cricket in the region. See also Notes References Further reading External links 29°N 41°E / 29°N 41°E / 29; 41 |
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Contents David Remez David Remez (Hebrew: דוד רמז; 23 May 1886 – 19 May 1951) was an Israeli politician, the country's first Minister of Transportation, and a signatory of the Israeli declaration of independence. Biography Remez was born David Drabkin in the village of Kopys in the Mogilev Governorate of the Russian Empire (now in Belarus) in 1886. After attending high school he studied law in Turkey before starting work as a teacher. He moved to Ottoman Palestine in 1913, and worked as an agricultural laborer in Ben Shemen, Be'er Tuvia, Karkur and Zikhron Ya'akov. He became involved in politics and trade unionism soon after the Mandate era began, serving as Director of the Public Works Office of the Histadrut and Solel Boneh from 1921 to 1929 as well as on Tel Aviv's city council from 1921 to 1925, and was a founding member of David Ben-Gurion's Mapai party. He became Secretary of the Histadrut in 1930, a position he retained until 1946, and also chaired the Jewish National Council from 1944 to 1949. Having signed Israel's declaration of independence, Remez was appointed Minister of Transportation in David Ben-Gurion's provisional government on 14 May 1948, a position he retained after the formation of the first government following the first Knesset elections in 1949. When the first government collapsed in November 1950, Remez became Education Minister taking over from Zalman Shazar. Remez, along with the Knesset's speaker commissioned Ecole de Paris painter, Yitzhak Frenkel to paint a 50 square meter painting of the first Knesset and dignitaries. Following Remez's death the painting was decommissioned by his successor. He died in office in May 1951, the first Israeli minister to do so. His Knesset seat was taken by Menachem Cohen. After his death several places in Israel were named after him, among them the Haifa neighborhood Ramot Remez and Remez Square in Jerusalem. His son, Aharon Remez was the second commander of the Israeli Air Force. References External links |
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Contents Age of Empires Age of Empires is a series of historical real-time strategy video games, originally developed by Ensemble Studios and published by Xbox Game Studios. The first title in the series, Age of Empires, focused on events in Europe, Africa and Asia, spanning from the Stone Age to the Iron Age; the expansion game explored the formation and expansion of the Roman Empire. The sequel, Age of Empires II: The Age of Kings, was set in the Middle Ages, while its expansion focused partially on the Spanish conquest of the Aztec Empire. Age of Empires III and its two expansions explored the early modern period, when Europe was colonizing the Americas and several Asian nations were on the decline. Another installment, Age of Empires Online, takes a different approach as a free-to-play online game utilizing Games for Windows Live. A spin-off game, Age of Mythology, was set in the same period as the original Age of Empires, but focused on mythological elements of Greek, Egyptian, and Norse mythology. The fourth main installment in the series, Age of Empires IV, was released on October 28, 2021, also focusing on the Middle Ages. The Age of Empires series has been a commercial success, selling over 25 million copies. Critics have credited part of the success of the series to its historical theme and fair play; the artificial intelligence (AI) players have fewer advantages than in many of the series' competitors. Games The games in the series focus on historical events throughout time. Age of Empires covers the events between the Stone Age and the Classical period, in Europe and Asia. Its expansion, The Rise of Rome, follows the formation and rise of the Roman Empire. The Age of Kings and its Nintendo DS spin-off follow Europe and Asia through the Middle Ages. The Age of Kings' expansion pack, The Conquerors, is set during the same period, but also includes scenarios about the Spanish conquest of the Aztec Empire, El Cid, and Attila the Hun. Age of Empires III and its first expansion, The WarChiefs, take place during the European colonization of the Americas. Its second expansion, The Asian Dynasties, follows the rise of Asia in the same period. Age of Empires Online focuses on the Greek and Egyptian civilizations. The series' spin-off, Age of Mythology, and its expansion pack, The Titans, are set during the Bronze Age, but focus on mythology as their themes, rather than history. Age of Empires, released on October 15, 1997, was the first game in the series, as well as the first major release from Ensemble Studios. It was one of the first history-based real-time strategy games made, utilizing the Genie game engine. GameSpot described it as a mix of Civilization and Warcraft. The game gives players a choice of 12 civilizations to develop from the Stone Age to the Iron Age. The expansion pack, The Rise of Rome, published by Microsoft on October 31, 1998, introduced new features and four new civilizations, including the Romans. Although the two games had contained many software bugs, patches resolved many of the problems. Age of Empires was generally well received, despite some highly negative reviews. GameSpot criticized a confused design, while Computer and Video Games praised the game as strong in single and multiplayer. The Academy of Interactive Arts & Sciences named Age of Empires the 1998 "Computer Strategy Game of the Year". For several years, the game remained high on the sales charts, with over three million units sold by 2000. The Rise of Rome sold one million units in 2000 and attained 80% as an aggregate score from GameRankings. In June 2017, Adam Isgreen, creative director of Xbox Game Studios announced Age of Empires: Definitive Edition at the Electronic Entertainment Expo 2017. It features overhauled graphics with support for 4K resolution, a remastered soundtrack, and other gameplay improvements, and was planned to be released on October 19, 2017, but was delayed until February 20, 2018, when it was released on the Microsoft Store. On May 30, 2019, Microsoft announced that the Definitive Edition would be coming to Steam, along with the Definitive Editions of both Age of Empires II and Age of Empires III. Age of Empires II: The Age of Kings, released on September 30, 1999, used the Genie game engine, and had gameplay similar to its predecessor. Age of Kings is set in the Middle Ages, from the Dark Ages to the Imperial Age. It allows players to choose one of 13 civilizations, from Europe, Asia, and the Middle East. On August 24, 2000, Microsoft published the expansion, The Conquerors. It added new units and five new civilizations, including two Mesoamerican civilizations: the Maya and the Aztec. The Age of Kings was a bigger critical success than the first two games, with Game Rankings and Metacritic scores of 92%. Microsoft shipped out more than two million copies to retailers, and the game received numerous awards and accolades. Critics agreed that The Conquerors expanded well on The Age of Kings, though issues of unbalanced gameplay were raised. The Age of Kings and The Conquerors won the 2000 and 2001 "Computer Strategy Game of the Year" awards from the Academy of Interactive Arts & Sciences, respectively. In April 2013, Age of Empires II: HD Edition was released on the Steam digital distribution platform for Windows operating systems. The HD Edition includes both the original game and the expansion The Conquerors, as well as updated graphics for high-resolution displays. Originally a fan-made modpack made for The Conquerors, Age of Empires II: The Forgotten was an unofficial expansion that added a new campaign, playable civilizations, maps, and quality of service updates. The Forgotten was later developed into an official expansion with SkyBox Labs and Forgotten Empires, and in November 2013 The Forgotten HD was released by Microsoft exclusively for the HD Edition on Steam. A third expansion named The African Kingdoms was released by Microsoft in November 2015, also exclusively for the HD Edition. A fourth expansion entitled Rise of the Rajas was released on December 19, 2016. On August 21, 2017, Microsoft announced Age of Empires II: Definitive Edition. In June 2019, Adam Isgreen, now the Franchise Creative Director for Age of Empires, shared more information regarding the Age of Empires II: Definitive Edition at the Electronic Entertainment Expo 2019. He confirmed that the Definitive Edition was being developed by Forgotten Empires, Tantalus Media, and Wicked Witch Software. He announced that the game would feature new 4K graphics, Xbox Live support for multiplayer, exclusive achievements, four new civilizations (Bulgarians, Cumans, Lithuanians, Tatars), three new campaigns, a new spectator mode and tournament features, and additional quality of life improvements. It was released on November 14, 2019. Bert Beeckman, co-founder of Forgotten Empires, confirmed on June 12 that Age of Empires II: HD Edition would not be removed from sale after the release of Age of Empires II: Definitive Edition. Age of Empires III was released on October 18, 2005 and was built on an improved version of the Age of Mythology game engine with the most significant changes being the updated graphics engine and the inclusion of the Havok physics middleware engine. The game is set in the period between 1421 and 1850, and players can choose one of eight European nations. The game introduced a large number of features, such as home cities. Described by Ensemble Studios as "an important support system to your efforts in the New World", home cities help provide the player with resources, equipment, troops, and upgrades. They can be used across multiple games, and upgraded after each battle; the feature was compared to a role-playing game character by Ensemble Studios. The first expansion to Age of Empires III, The WarChiefs, was released October 17, 2006. Most gameplay changes in the expansion pack were small, but it introduced three new civilizations, with a focus on Native Americans. The second expansion, The Asian Dynasties, went on sale October 23, 2007. It was a jointly developed product; Big Huge Games helped Ensemble Studios develop the game, with Brian Reynolds joining Bruce Shelley as lead designer. The game expanded the Age of Empires III universe into Asia, and introduced three new civilizations. Reception towards Age of Empires III was mixed; Game Revolution described it as "about as much fun" as a history textbook, while GameZone argued it was "one of the best looking games, much less an RTS game, that is out on the market currently". It sold more than two million copies, and won the GameSpy "real-time strategy game of the year" award. The WarChiefs failed to equal the success of its predecessor, with a lower score on both Game Rankings and Metacritic, and The Asian Dynasties' score was lower still with 80%. Several collectors' editions of Age of Empires III included a hardcover artbook. The last page of the artbook has a pictorial depiction of the series; the Roman numerals below each panel range from I to V, indicating the series would include an Age of Empires IV and Age of Empires V. Ensemble Studios employee Sandy Petersen said that the image "was total speculation on [their] part". In 2008, Microsoft announced they were closing down Ensemble Studios following the completion of Halo Wars. Some of its employees would form a new team as part of Microsoft Studios. Kevin Unangst, director of Games for Windows, denied it was the end of the Age of Empires series, telling The San Francisco Chronicle "we're very excited about the future potential for Age of Empires". Edge confirmed, in an interview with Microsoft's corporate vice president of interactive entertainment, Shane Kim, that Microsoft continued to own Age of Empires and that they had plans to continue the series. However, Bruce Shelley wrote in his blog that he would not be part of any new studios formed. Following the announcement of remastered editions of previous games, Microsoft announced Age of Empires III: Definitive Edition on August 21, 2017. On May 30, 2019, the company revealed that the Definitive Edition would come to Steam in the future, along with the Definitive Editions of both Age of Empires and Age of Empires II. On August 28, 2020, Microsoft announced at Gamescom 2020 that Age of Empires III: Definitive Edition would release officially on October 15, 2020. On January 23, 2020, Microsoft announced a closed beta for early February of that year. Betas ran on Steam and the Microsoft Store, with each beta session including a small piece of the game. The first closed beta session began on February 11, 2020, and ended on February 19, 2020. The second closed multiplayer session began on March 31 and ran until April 7. The game was released on October 15, 2020. On August 21, 2017, Microsoft announced Age of Empires IV, developed by Relic Entertainment. The title was officially released on October 28, 2021, with eight civilizations available at launch: the Abbasid Dynasty, the Chinese, the Delhi Sultanate, the English, the French, the Holy Roman Empire, the Mongols, and the Rus. The game is set during the Early Middle Ages to the early Renaissance, with the earliest appearance of any civilization being in the year 750. The game features four Ages, the same as those in Age of Empires II — Dark Age, Feudal Age, Castle Age, and Imperial Age. This title incorporates several features and mechanics of Age of Empires II that were changed or removed in Age of Empires III. Like other Age of Empires games, Age of Empires IV has received several new civilizations in updates. Recent updates have added the Ottomans, Malians, Byzantines, and Japanese, along with several variants of civilizations already in the game: the Ayyubids, Jeanne d'Arc, Order of the Dragon, and Zhu Xi's Legacy, for a total of 16 civilizations at present. Age of Mythology shared many elements of gameplay with the main series, and was considered a part of the series, despite its different focus. The campaign in Age of Mythology tells the story of an Atlantean, Arkantos, and his quest to find why his people are out of favor with Poseidon. Microsoft published the game on October 30, 2002, and its expansion, The Titans, on October 21, 2003. The Titans featured the Atlanteans as a new civilization. Its campaign is shorter than previous expansions, and centers on Kastor, son of Arkantos, who falls for the lies of the titans and frees them from Tartarus. Age of Mythology sold more than one million units in four months. It scored 89% on Game Rankings and Metacritic. The Titans failed to equal the sales success of Age of Mythology, although critics rated it highly. Backbone Entertainment developed Age of Empires: The Age of Kings as a turn-based game for the Nintendo DS. Majesco Entertainment published the game on February 14, 2006. It is similar to other turn-based games, such as Advance Wars, but with a gameplay based on its PC counterpart. Age of Empires: The Age of Kings scored 80% on Game Rankings and Metacritic. Konami brought a game of the same title to the PlayStation 2 around five years earlier than the DS version, but the game had little promotion, and sold poorly. On August 16, 2010, Microsoft announced Age of Empires Online, which was a free-to-play Games for Windows Live online game, it developed in collaboration with Robot Entertainment. It featured Free-to-play experiences via Games for Windows LIVE as well as: A persistent online capital city that lives and grows even when you're offline, Cooperative multiplayer quests, trading and a level-based system that lets you progress at your own pace. Premium content could be earned or purchased, such as access to blueprints and special items, as well as more quests and features. In September 2013, it was announced that the game would remain functional until July 1, 2014, after which it would be shut down due to the content being too expensive to maintain. On August 25, 2014, Age of Empires: Castle Siege was announced. It is a touch-based game developed by Smoking Gun Interactive. It was released on September 17, 2014, for the Windows PC and Windows Phone 8. On April 13, 2014, Age of Empires: World Domination was announced. It was developed by KLab Games for the iOS, Android and Windows Phone. It was released on December 7, 2015, with the service terminated on November 30, 2016. On October 25, 2022, a new mobile entry called Age of Empires Mobile was announced. A free-to-play game developed by TiMi Studio Group, the game was released on Android and iOS on October 17, 2024. Development The development phases of the Age of Empires games were similar in several ways. Due to the games being based on historical events, the team often had to do large amounts of research. However, the research was not in depth, which, according to Age of Empires designer Bruce Shelley, is "a good idea for most entertainment products". Shelley also said that Ensemble Studios took most of the reference material from children's sections at libraries. He pointed out the goal was for the players of the game to have fun, "not [its] designers or researchers". At the Games Convention Developers Conference in 2007, Shelley continued with this thought and explained that the success of the series laid in "making a game which appealed to both the casual and hardcore gamer". Shelley also remarked the Age of Empires games were not about history in itself, but rather "about the human experience;" they focused not simply on what humans had done but on what they could do in the future such as "going into space". Ensemble Studios developed Age of Mythology in a different way than the previous two games. The team had worried they "couldn't get away" with a third historical-based game, and chose mythology as the setting after they had discussed several options. The artificial intelligence (AI) used in the Age of Empires series has been developed and improved regularly by designers. AI specialist Dave Pottinger noted the development team gave the AI in the original game a very high priority, and spent over a year working on it. He said that the AI in the game relies on tactics and strategies to win, instead of "cheating" by giving bonus resources to itself, or tweaking its units to be stronger than normal. Pottinger later noted that the Age of Empires series team took great pride in their AI playing a "fair game" and didn't know what the player was doing and had to play by the same rules as its human opponents. Age of Empires allows players to choose to play either along specialized, story-backed conditions or as individual battles against the AI (and other players). Choosing to battle against the AI – rather than following the storyline – allows the AI to adapt to players' strategies and even remember which games it won and lost. The AI eventually overcomes players' strategies and easily destroys their villages after several games. For instance, in Age of Empires III, this is referred to as playing a "Skirmish". However, Age of Empires III allows players to refine their strategies further against the AI by "building a Deck", which allows players to replace "Home City" shipments with improved alternatives. In Age of Empires II: The Conquerors the AI was given a high priority, the result being the "smart villager" feature, which was included in subsequent games of the series. After building a structure that stores or produces resources, smart villagers would proceed to collect resources related to the structure, such as crops from farms or ore from exposed deposits. Age of Mythology: The Titans lets players use an AI debugger when creating custom scenarios; players can change the settings of computer players and make them act according to certain patterns. More basic changes to the AI had previously been available in the series' first two games. The graphics and visuals of Age of Empires improved with each successive release. From the original release to the second, Age of Empires II: The Age of Kings, noteworthy improvements gained praise from several critics. With the release of Age of Mythology the praise continued, and the fourth release, Age of Empires III, garnered even more. GameSpot praised the improved graphics in the second release, Age of Empires II: The Age of Kings. Eurogamer welcomed its introduction of female villagers as compared with the original male only version. Allgame praised the advanced grouping and path-finding systems in the second release. Despite the improved graphics, Allgame complained that units in Age of Empires II: The Age of Kings were at times difficult to distinguish from one another, a point numerous reviewers agreed on. Nevertheless, Game Revolution wrote that the second release was "the best looking of the 2D RTS games out there right now". The graphics continued to improve in Age of Mythology and was praised by a majority of reviewers. IGN ranked the graphics in this third release "a joy to watch ... awesome". GameSpot agreed, also rating the graphics nine out of ten. Game Revolution also agreed, and PC Gamer stated that the graphics in the third release "are packed with detail". The trend in improved graphics continued well into the next release, Age of Empires III, much to the delight of reviewers. IGN stated: "After seeing the screenshots, our jaws hit the floor at the amount of detail." 1UP.com described Age of Empires III as "one of the most beautiful games you will put on your computer for the foreseeable future". GameSpy agreed, stating: "Age III's graphics are unmatched in the strategy genre." Age of Empires III builds on and introduces new features to the prior release, Age of Mythology, such as the inclusion of the award-winning Havok physics simulation middleware game engine for the Windows version and PhysX for the Mac OS X. The innovative result is that pre-created animations are avoided; instead events are calculated according to the physics engine. Consequently, views of events like building destruction and tree felling are not pre-recorded. GameSpot also admired the graphics in the fourth release but complained about "the awkward unit behavior". Other graphical features of the game include bloom lighting and support for pixel shader 3.0. GameSpy awarded Age of Empires III the "Best Graphics" award at GameSpy's "Game of the Year 2005". Stephen Rippy has been the series' music director since the first game. He has had occasional help from his brother, David Rippy, as well as Kevin McMullan. He created the original music in Age of Empires with sounds of instruments from the periods in the game. These sounds came from actual instruments, and their digital samples. The tunes were the result of extensive research on the cultures, styles, and instruments used. Rippy said that sound development on The Age of Kings was easy, since there was knowledge of the instruments used in the Middle Ages. Therefore, they were able to reproduce the tunes for the soundtrack of the game. In Age of Mythology, an orchestral instrumentation was used, instead. According to McMullan, the team also collected large numbers of audio recordings from zoos, and created "a massive sound library of [their] own material". The music of Age of Empires III was similar to The Age of Kings, in which the team used more historical instruments; Rippy noted the team used instruments such as "bagpipes and field drums" to give it a realistic feel. Ensemble Studios worked together with Big Huge Games to develop The Asian Dynasties, Age of Empires III's second expansion. This was the first joint venture for both teams. The reason for them doing so was compatible schedules: Ensemble Studios was busy with other projects—particularly Halo Wars—while Big Huge Games' real-time strategy team had few projects at that time. Big Huge Games did most of the work, but Ensemble Studios designers Greg Street and Sandy Petersen joined in the brainstorming, and had control over the final product. Both studios had roles in testing the game before its release. Reception and legacy The Age of Empires series has been a commercial success. As of 2008, five of its games have each sold more than one million copies. According to Gamasutra, Age of Empires had sold more than three million copies, and The Rise of Rome sold one million copies as of 2000. Around the same time, Microsoft announced that they shipped over two million copies of The Age of Kings. In 2003, Microsoft announced the sales of one million copies for Age of Mythology. By 2004, prior to the release of Age of Empires III, the Age of Empires franchise had sold over 15 million copies. On May 18, 2007, Ensemble Studios announced that two million copies of Age of Empires III had been sold. Games in the series have consistently scored highly on video game review aggregator websites GameRankings and Metacritic, which collect data from numerous review websites. As noted in the adjacent table, the highest rating game is Age of Empires II: The Age of Kings, receiving a 92% score from both sites. Critics have credited Age of Empires for influencing real-time strategy (RTS) games such as Rise of Nations, Empire Earth, and Cossacks. Star Wars: Galactic Battlegrounds was also influenced by the series: it utilized the Genie game engine, as Age of Empires and Age of Empires II: The Age of Kings had, and was considered by critics to be a very close replica to the games; IGN began their review with the statement "I love Age of Star Wars, I mean Star Empires. Whatever it's called, I dig it." and GameSpot wrote that "fundamentals of the Age of Empires II engine are so intact in Star Wars: Galactic Battlegrounds that veterans of that game can jump right in". In October 2005, Shelley commented on the impact of the series. In a GameSpy interview, he explained that parents would "tell Ensemble Studios that their kid is reading books about ancient Greece because they enjoy playing with the triremes so much, or that they want to check out books about medieval history because [the] game taught them what a trebuchet was". Shelley has said that the key to the success of the games was its innovation, rather than imitation of its peers. He also claimed the unique elements in the games "helped establish the reputation of Ensemble Studios as masters of the real-time strategy genre". Mark Bozon of IGN wrote in his review of The Age of Kings, "The Age of Empires series has been one of the most innovative real-time strategy games for PC in the last decade or so." Gamenikki called Ensemble Studios "the developer that started it all" when they talked about how much Age of Empires III had done to advance the real-time strategy genre. Shelley has acknowledged the success and innovation of Age of Empires helped to ensure Ensemble survive its early periods since startup. In 2005, Shelley complained of critics holding an "innovation bias" against the series; citing the 60% score from Computer Gaming World, he said that despite Age of Empires III being "perhaps the best selling PC game in the world" at the time, reviewers expected "something really new" and rated it harshly. Bungie chose Ensemble Studios to develop Halo Wars, an RTS game based on their Halo series. They said that one of the reasons they chose to work with Ensemble was because of the Age of Empires series. They also noted that Ensemble was the perfect choice "to realize the original vision of Halo", which started life as an RTS. In 2024, the Red Bull Wololo: El Reinado Age of Empires II tournament achieved the second-highest viewership in the game's history, with a peak of 85,800 concurrent viewers. The event, held at the Castle of Almodóvar, Spain, featured eight top players, including TheViper and Hera, who won the final 5-1. This marked a 12% increase in peak viewership compared to the previous series, reflecting the growing popularity of Age of Empires II in the esports scene. References External links |
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Contents Auren Hoffman Auren Raphael Hoffman (born 1974) is an American entrepreneur, angel investor, author and CEO of SafeGraph, a firm that gathers location data from mobile devices and sells information about places and the movements of people. Personal life Hoffman is a son of Amalia Hoffman of Larchmont, New York, and Edward M. Hoffman of Montvale, New Jersey. Amalia Hoffman is an author and illustrator of children’s books. Edward M. Hoffman works in New York as a software engineer and software consultant to the financial industry. Hoffman graduated from the University of California, Berkeley with a degree in Industrial Engineering in 1996. In 2011, Hoffman married an assistant U.S. Attorney, Hallie Alexandra Mitchell, who graduated from Princeton University, and received a Juris Doctor degree from Northwestern University School of Law. Business Hoffman founded Kyber Systems in his junior year at UC Berkeley, as a way to pay for school. Kyber was sold to Human Ingenuity in 1997. Hoffman founded Bridgepath Inc. in 1998, which was acquired by Bullhorn, Inc. in October 2002. In 2002 he sold the website GetRelevant to Lycos. He then became chair of the Stonebrick Group through 2006, which sponsored networking events in the San Francisco area such as the Silicon Forum. Hoffman's business style is sometimes referred to as a networker. Hoffman is a speaker at events in the technology industry. In 2006 Hoffman cofounded Rapleaf and served as its CEO until 2012, when he left the company to run a Rapleaf spinoff called LiveRamp after Rapleaf was acquired by email marketing company TowerData. On May 14, 2014 Acxiom announced that it had acquired Liveramp, for $310 Million. Gawker mentioned a controversy surrounding privacy practices at Rapleaf. Hoffman left LiveRamp a little more than a year after it was acquired. As of December 2016[update], Hoffman is chairman of Siftery, and was listed as CEO of a company called SafeGraph. Writer Hoffman was a contributor to the Huffington Post, often on political subjects, as well as Business Week and his own blog called Summation. Hoffman is a Republican and a political contributor. Hoffman contributed to Council on Foreign Relations papers in 2004. Controversy In 2006, Wikipedia editors detected that Hoffman may have been editing his own Wikipedia entry, violating its guidelines. Silicon Valley media publicized the evidence, which Hoffman eventually confirmed to VentureBeat in 2007. Anonymous Wikipedia editors later edited out these references. Hoffman has also been criticized for his personal and professional networking practices and presentation of his own reputation. From 2007 to 2013, Hoffman received significant backlash over the data collection practices and sale of individuals' personal information to advertisers by his company, RapLeaf. As a prolific blogger and public spokesperson for the company, much of the criticism was directed at Hoffman personally. A 2010 investigation by The Wall Street Journal revealed that the company transmitted identifying details about individuals to at least 12 companies, violating the terms of service of Facebook and MySpace. A spokesperson at Facebook said it had "taken steps... to significantly limit Rapleaf's ability to use any Facebook-related data." When confronted by The Wall Street Journal and CNet, it quietly revised its privacy policy both times. CNNMoney described RapLeaf as "selling your identity," and TechCrunch characterized its method of identifiable data extraction of Google and Microsoft employees as "creepy." RapLeaf later became known as LiveRamp, and is now known as TowerData after being acquired by Acxiom. Beginning in 2020, Hoffman's company Safegraph received criticism for its practice of collecting and selling location data from mobile phones. Public records requests by the Electronic Frontier Foundation revealed that between 2018 and 2020, Safegraph and its spin-off company Veraset sold or gave disaggregate, device-specific location data about millions of people to government agencies in the U.S. In 2021, Google banned Safegraph from its Android app marketplace for violating its policies. Developers who had installed Safegraph's software development kit (SDK) in their apps were forced to remove the code or have their apps taken down by Google. In May 2022, Motherboard was able to purchase data from Safegraph which revealed aggregate information about the movements of people who visited clinics that provide abortions, including Planned Parenthood. According to the report, the data showed "where groups of people visiting the locations came from, how long they stayed there, and where they then went afterwards." The report generated concern among pro-choice advocates due to news about the impending decision in Dobbs v. Jackson Women's Health Organization, which would make abortion illegal in many states. Shortly after Motherboard's report was published, Hoffman announced that Safegraph would stop selling data about movements to and from family planning centers, saying the data did not have commercial value. Hoffman and Peter Thiel co-founded Dialog, a private, invitation-only society. Investments Hoffman is an angel investor and briefly worked as a venture capitalist with the Founders Fund in the 2011 to 2012 timeframe. Some of Hoffman's investments include: Aardvark (search engine) (sold to Google), BackTweets by Backtype (sold to Twitter), Blip.tv, BrightRoll, Chomp (search engine) (sold to Apple), CrowdFlower, Flowtown (sold to Demandforce which was sold to Intuit), Founders Fund, LabPixies (sold to Google), Meebo (sold to Google), MerchantCircle (sold to Reply.com), mob.ly (sold to GroupOn), Pingboard, Scopely, Thumbtack (website), Zoom Systems, and others. References |
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Contents River dolphin River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant river dolphins are placed in two superfamilies, Platanistoidea and Inioidea. They comprise the families Platanistidae (the South Asian dolphins), the possibly extinct Lipotidae (Yangtze River dolphin), Iniidae (the Amazonian dolphins) and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Artiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of dolphins can be pink. River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents. They range in size from the 5-foot (1.5 m) long South Asian river dolphin to the 8-foot (2.4 m) and 220-pound (100 kg) Amazon river dolphin. Several species exhibit sexual dimorphism, in that the females are larger than the males. They have streamlined bodies and two limbs that are modified into flippers. River dolphins use their conical-shaped teeth and long beaks to capture fast-moving prey in murky water. They have well-developed hearing that is adapted for both air and water; they do not really rely on vision since their eyes are very small and the water they swim in is usually very muddy. Instead, they tend to rely on echolocation when hunting and navigating. These species are well-adapted to living in warm, shallow waters, and, unlike other cetaceans, have little to no blubber. River dolphins are not very widely distributed; they are all restricted to certain rivers or deltas. This makes them extremely vulnerable to habitat destruction. River dolphins feed primarily on fish. Male river dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. River dolphins produce a variety of vocalizations, usually in the form of clicks and whistles. River dolphins are rarely kept in captivity; breeding success has been poor and the animals often die within a few months of capture. As of 2020[update], there was only one river dolphin in captivity. Taxonomy and evolution Four families of river dolphins (Iniidae, Pontoporiidae, Lipotidae and Platanistidae) are currently recognized, comprising three superfamilies (Inioidea, Lipotoidea and Platanistoidea). Platanistidae, containing the two subspecies of South Asian river dolphin, is the only living family in the superfamily Platanistoidea. Previously, many taxonomists had assigned all river dolphins to a single family, Platanistidae, and treated the Ganges and Indus river dolphins as separate species. A December 2006 survey found no members of Lipotes vexillifer (commonly known as the baiji, or Chinese river dolphin) and declared the species functionally extinct. The current classification of river dolphins is as follows: In 2012 the Society for Marine Mammalogy began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community, including the IUCN, continue to consider the Bolivian population to be a subspecies of Inia geoffrensis. In October 2014, the Society for Marine Mammalogy took Inia boliviensis and Inia araguaiaensis off their list of aquatic mammal species and subspecies and currently does not recognize these species-level separations. River dolphins are members of the infraorder Cetacea, which are descendants of land-dwelling mammals of the order Artiodactyla (even-toed ungulates). They are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago. The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later. It is unknown when river dolphins first ventured back into fresh water. River dolphins are thought to have relictual distributions, that is, their ancestors originally occupied marine habitats, but were then displaced from these habitats by modern dolphin lineages. Many of the morphological similarities and adaptations to freshwater habitats arose due to convergent evolution; thus, a grouping of all river dolphins is polyphyletic. Amazon river dolphins are actually more closely related to oceanic dolphins than to South Asian river dolphins. Isthminia panamensis is an extinct genus and species of river dolphin, living 5.8 to 6.1 million years ago. Its fossils were discovered near Piña, Panama. River dolphin has been considered a taxonomic description, suggesting an evolutionary relationship among the group, although it is now known that they form two distinct clades. 'True' river dolphins are descendants of ancient evolutionary lineages that evolved in freshwater environments. Some species of cetacean live in rivers and lakes, but are more closely related to oceanic dolphins or porpoises and entered fresh water more recently. Such species are considered facultative freshwater cetaceans as they can use both marine and freshwater environments. These include species such as the Irrawaddy dolphin, Orcaella brevirostris, found in the Mekong, Mahakam, the Irrawaddy Rivers, as well as the Yangtze finless porpoise Neophocaena asiaeorientalis. Some oceanic cetacean populations are known to live semi-permanently in river and estuarine systems, such as the Indo-Pacific bottlenose dolphin group resident in the Swan River of Western Australia which travel as far inland as Belmont. The tucuxi (Sotalia fluviatilis) in the Amazon River is another species descended from oceanic dolphins; however, it does not perfectly fit the label of 'facultative' either, as it occurs only in fresh water. The tucuxi was until recently considered conspecific with the Guiana dolphin (Sotalia guianensis), which inhabits marine waters. It may also be true for the Irrawaddy dolphin and the finless porpoise that, although the species may be found in both freshwater and marine environments, individual animals found in rivers may not be able to survive in the ocean, and vice versa. The tucuxi is currently classified as an oceanic dolphin (Delphinidae). The Franciscana (Pontoporia blainvillei) has shown a converse evolutionary pattern, and has an ancient evolutionary lineage in freshwater, but inhabits estuarine and coastal waters. Biology River dolphins have a torpedo shaped body with a flexible neck, limbs modified into flippers, non-existent external ear flaps, a tail fin, and a small bulbous head. River dolphin skulls have small eye orbits, a long snout and eyes placed on the sides of the head. River dolphins are rather small, ranging in size from the 5-foot (1.5 m) long South Asian river dolphin to the 8-foot (2.4 m) and 220-pound (100 kg) Amazon river dolphin. They all have female-biased sexual dimorphism apart from Amazon river dolphin, with the females being larger than the males. River dolphins are polygynous, meaning male river dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. River dolphins have conical teeth, used to catch swift prey such as small river fish. They also have very long snouts, with some measuring 23 inches (58 cm), four times longer than most of their oceanic counterparts. They have a two-chambered stomach that is similar in structure to that of terrestrial carnivores. They have fundic and pyloric chambers. Breathing involves expelling stale air from their blowhole, followed by inhaling fresh air into their lungs. They do not have the iconic spout, as this only forms when the warm air exhaled from the lungs meets cold external air, which does not occur in their tropical habitats. River dolphins have a relatively thin layer of blubber. Blubber can help with buoyancy, protection from predators (they would have a hard time getting through a thick layer of fat), energy for leaner times, and insulation from harsh climates. The habitats of river dolphins lack these needs. River dolphins have two flippers and a tail fin. These flippers contain five digits. Although river dolphins do not possess fully developed hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. River dolphins are slow swimmers in comparison to oceanic dolphins, which can travel at speeds up to 35 miles per hour (56 km/h); the tucuxi can only travel at about 14 miles per hour (23 km/h). Unlike other cetaceans, their neck vertebrae are not fused together, meaning they have greater flexibility than other non-terrestrial aquatic mammals, at the expense of speed. This means they can turn their head without actually moving their entire body. When swimming, river dolphins rely on their tail fins to propel themselves through the water. Flipper movement is continuous. River dolphins swim by moving their tail fins and lower bodies up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. All species have a dorsal fin. The ears of river dolphins have specific adaptations to their aquatic environment. In humans, the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In river dolphins, and other cetaceans, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, river dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The ear is acoustically isolated from the skull by air-filled sinus pockets, which allows for greater directional hearing underwater. Dolphins send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows river dolphins to produce biosonar for orientation.: 203–427 They are so dependent on echolocation that they can survive even if they are blind. Beyond locating an object, echolocation also provides the animal with an idea on the object's shape and size, though how exactly this works is not yet understood. The small hairs on the rostrum of the Amazon river dolphin are believed to function as a tactile sense, possibly to compensate for their poor eyesight. River dolphins have very small eyes for their size, and do not have a very good sense of sight. In addition, the eyes are placed on the sides of the head, so the vision consists of two fields, rather than a binocular view like humans have. When river dolphins surface, their lens and cornea correct the nearsightedness that results from the refraction of light. They have both rod and cone cells, meaning they can see in both dim and bright light. Most river dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on their eyelids and an outer corneal layer that act as protection for the cornea.: 505–519 Olfactory lobes are absent in river dolphins, suggesting that they have no sense of smell.: 481–505 River dolphins are not thought to have a sense of taste, as their taste buds are atrophied or missing altogether. However, some dolphins have preferences between different kinds of fish, indicating some sort of attachment to taste.: 447–454 Interactions with humans Development and agriculture have had devastating impacts on the habitats on river dolphins. The total population of Araguaian river dolphins is estimated to be between 600 and 1,500 individuals, and genetic diversity is limited. The ecology of their habitat has been adversely affected by agricultural, ranching and industrial activities, as well as by the use of dams for hydroelectric power. The inhabited section of the Araguaia River probably extends over about 900 miles (1,400 km) out of a total length of 1,300 miles (2,100 km). The Tocantins river habitat is fragmented by six hydroelectric dams, so the population there is at particular risk. Its probable eventual IUCN status is vulnerable or worse.: 54–58 Both subspecies of South Asian river dolphins have been very adversely affected by human use of the river systems in the subcontinent. Irrigation has lowered water levels throughout both subspecies' ranges. Poisoning of the water supply from industrial and agricultural chemicals may have also contributed to population decline. Perhaps the most significant issue is the building of more than 50 dams along many rivers, causing the segregation of populations and a narrowed gene pool in which the dolphins can breed. Currently, three subpopulations of Indus river dolphins are considered capable of long-term survival if protected.: 31–32, 37–38 As China developed economically, pressure on the baiji river dolphin grew significantly.: 41–46 Industrial and residential waste flowed into the Yangtze. The riverbed was dredged and reinforced with concrete in many locations. Ship traffic multiplied, boats grew in size, and fishermen employed wider and more lethal nets. Noise pollution caused the nearly blind animal to collide with propellers. Stocks of the dolphin's prey declined drastically in the late 20th century, with some fish populations declining to one thousandth of their pre-industrial levels. In the 1950s, the population was estimated at 6,000 animals, but declined rapidly over the subsequent five decades. Only a few hundred were left by 1970. Then the number dropped down to 400 by the 1980s and then to 13 in 1997 when a full-fledged search was conducted. On December 13, 2006, the baiji (Lipotes vexillifer) was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen. The last verified and widely accepted sighting was in September 2004, but it has been allegedly seen and photographed by Chinese citizens on four occasions since then. The region of the Amazon in Brazil has an extension of 3,100,000 mi2 (8,000,000 km2) containing diverse fundamental ecosystems. One of these ecosystems is a floodplain, or a várzea forest, and is home to a large number of fish species which are an essential resource for human consumption. The várzea is also a major source of income through excessive local commercialized fishing. Várzea consist of muddy river waters containing a vast number and diversity of nutrient-rich species. The abundance of distinct fish species lures the Amazon River dolphin into the várzea areas of high water occurrences during the seasonal flooding. In addition to attracting predators such as the Amazon river dolphin, these high-water occurrences are an ideal location to draw in the local fisheries.: 54–58 Human fishing activities directly compete with the dolphins for the same fish species, the tambaqui (Colossoma macropomum) and the pirapitinga (Piaractus brachypomus), resulting in deliberate or unintentional catches of the Amazon river dolphin. The local fishermen overfish, and when the Amazon river dolphins remove the commercialized fish from the nets and lines, it damages the equipment and the capture and causes a negative reaction from the local fishermen. The Brazilian Institute of Environment and Renewable Natural Resources prohibit fishermen from killing the Amazon river dolphin, yet they are not compensated for the damage to their equipment and the loss of their catch. During the process of catching the commercialized fish, the Amazon river dolphins get caught in the nets and exhaust themselves until they die, or the local fishermen deliberately kill the dolphins that become entangled in their nets. The carcasses are discarded, consumed, or used as bait to attract a scavenger catfish, the piracatinga (Calophysus macropterus). The use of the Amazon river dolphin carcass as bait for the piracatinga dates back from 2000. The increasing consumption demand by the local inhabitants and Colombia for the piracatinga has created a market for distribution of the Amazon river dolphin carcasses to be used as bait throughout these regions.: 54–58 For example, of the 15 dolphin carcasses found in the Japurá River in 2010–2011 surveys, 73% of the dolphins were killed for bait, disposed of, or abandoned in entangled gillnets. The data does not fully represent the actual overall number of deaths of the Amazon river dolphins, whether accidental or intentional, because a variety of factors make it extremely complicated to record and medically examine all the carcasses. Scavenger species feed upon them and the complexity of the river currents makes it nearly impossible to locate all the carcasses. More importantly, the local fishermen do not report these deaths out of fear that legal action will be taken against them, as the Amazon river dolphin and other cetaceans are protected under the Brazilian federal law, prohibiting any takes, harassments, and kills of the species. Conservation The Global Declaration for River Dolphins was signed by nine countries on 24 October 2023, a date chosen as it is known as the International River Dolphin Day. This pact is intended to promote research and cooperation between countries with river dolphin populations. It is hoped that five further countries will join. Marine biologist Fernando Trujillo co-founded the Omacha Foundation in 1993 to protect the pink river dolphins in the Amazon and Orinoco Rivers. Since 2013, Trujillo and his team have been measuring the mercury levels in river dolphins. Mercury, leeched into the river through illegal gold mining processes, is harmful to both dolphins and humans. As global temperatures rise, the Amazon has seen record level of drought and river temperatures. In 2023, within just two months (September–October), 330 river dolphins were found dead in the Amazon region due to extreme drought. A baiji conservation dolphinarium was established at the Institute of Hydrobiology (IHB) in Wuhan in 1992. This was planned as a backup to any other conservation efforts by producing an area completely protected from any threats, and where the baiji could be easily observed. The site includes an indoor and outdoor holding pool, a water filtration system, food storage and preparation facilities, research labs and a small museum. The aim is to also generate income from tourism which can be put towards the baiji plight. The pools are not very large, only kidney shaped tanks with dimensions of 82 feet (25 m) arc 23 feet (7.0 m) width and 11 feet (3.4 m) depth, 33 feet (10 m) diameter, 6.6 feet (2.0 m) deep and 39 feet (12 m) diameter, 11 feet (3.4 m) deep, and are not capable of holding many baijis at one time. Douglas Adams and Mark Carwardine documented their encounters with the endangered animals on their conservation travels for the BBC programme Last Chance to See. The book by the same name, published in 1990, included pictures of a captive specimen, a male named Qi Qi (淇淇) that lived in the Wuhan Institute of Hydrobiology dolphinarium from 1980 to July 14, 2002. Discovered by a fisherman in Dongting Lake, he became the sole resident of the Baiji Dolphinarium (白鱀豚水族馆) beside East Lake. A sexually mature female was captured in late 1995, but died after half a year in 1996 when the Shishou Tian-e-Zhou Baiji Semi-natural Reserve (石首半自然白鱀豚保护区), which had contained only finless porpoises since 1990, was flooded. The Amazon river dolphin has historically been kept in dolphinariums. Today, only three exist in captivity: one in Acuario de Valencia in Venezuela, one in Zoologico de Guistochoca in Peru, and one in Duisburg Zoo in Germany. Several hundred were captured between the 1950s and 1970s, and were distributed in dolphinariums throughout the US, Europe, and Japan. Around 100 went to US dolphinariums, and of that, only 20 survived; the last (named Chuckles) died in Pittsburgh Zoo in 2002.: 58–59 Mythology In Hindu mythology, the Ganges river dolphin is associated with Ganga, the deity of the Ganges river. The dolphin is said to be one of the creatures which heralded the goddess' descent from the heavens, and Ganga's mount, the Makara, is sometimes depicted as a dolphin. In Chinese mythology, the baiji has many origin stories. For example, near the mouth of the Yangtze, the baiji was a princess that had lost her parents and had lived with her stepfather, whom she had longed to get away from. The stepfather wanted to trade her since she would be sold for a great sum of money, but as they were crossing the river to get to the trader, a storm rolled in. The enraged stepfather tried to take her, but she plunged herself into the river, was transformed into a dolphin before she drowned, and swam away from her abusive stepfather, who also fell in and was transformed into a porpoise. In another story, the baiji was the daughter of a general deported from the city of Wuhan during a war who ran away while her father was in duty. Later, the general met a woman who told him how her father was a general. When he realized that she was his daughter, he threw himself into the river out of shame, and his daughter ran after him and also fell into the river. Before they were drowned, the daughter was transformed into a dolphin and the general into a porpoise. Amazon river dolphins, known by the natives as the boto, encantados or toninhas, are very prevalent in the mythology of the native South Americans. They are often characterized in mythology with superior musical ability, seductiveness and love of sex that often results in illegitimate children, and attraction to parties. Despite the fact that the Encante are said to come from a utopia full of wealth and without pain or death, the encantados crave the pleasures and hardships of human societies. Transformation into human form is said to be rare, and usually occurs at night. The encantado will often be seen running from a festa, despite protests from the others for it to stay, and can be seen by pursuers as it hurries to the river and reverts to dolphin form. When it is under human form, it wears a hat to hide its blowhole, which does not disappear with the shapeshift. Besides the ability to shapeshift into human form, encantados frequently wield other magical abilities, such as controlling storms, hypnotizing humans into doing their will, transforming humans into encantados, and inflicting illness, insanity, and even death. Shamans often intervene in these situations. Kidnapping is also a common theme in such folklore. Encantados are said to be fond of abducting humans with whom they fall in love, children born of their illicit love affairs, or just about anyone near the river who can keep them company, and taking them back to the Encante. The fear of this is so great among people who live near the Amazon River that both children and adults are terrified of going near the water between dusk and dawn, or entering water alone. Some who supposedly have encountered encantados while out in their canoes have been said to have gone insane, but the creatures seem to have done little more than follow their boats and nudge them from time to time. References Further reading |
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Contents Black hole A black hole is an astronomical body so compact that its gravity prevents anything, including light, from escaping. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. The boundary of no escape is called the event horizon. In general relativity, a black hole's event horizon seals an object's fate but produces no locally detectable change when crossed. General relativity also predicts that every black hole should have a central singularity, where the curvature of spacetime is infinite. In many ways, a black hole acts like an ideal black body, as it reflects no light. Quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly. Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. In 1916, Karl Schwarzschild found the first modern solution of general relativity that would characterise a black hole. Due to his influential research, the Schwarzschild metric is named after him. David Finkelstein, in 1958, first interpreted Schwarzschild's model as a region of space from which nothing can escape. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The first black hole known was Cygnus X-1, identified by several researchers independently in 1971. Black holes typically form when massive stars collapse at the end of their life cycle. After a black hole has formed, it can grow by absorbing mass from its surroundings. Supermassive black holes of millions of solar masses may form by absorbing other stars and merging with other black holes, or via direct collapse of gas clouds. There is consensus that supermassive black holes exist in the centres of most galaxies. The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter falling toward a black hole can form an accretion disk of infalling plasma, heated by friction and emitting light. In extreme cases, this creates a quasar, some of the brightest objects in the universe. Merging black holes can also be detected by observation of the gravitational waves they emit. If other stars are orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses. History The idea of a body so massive that even light could not escape was first proposed in the late 18th century by English astronomer and clergyman John Michell and independently by French scientist Pierre-Simon Laplace. Both scholars proposed very large stars in contrast to the modern concept of an extremely dense object. Michell's idea, in a short part of a letter published in 1784, calculated that a star with the same density but 500 times the radius of the sun would not let any emitted light escape; the surface escape velocity would exceed the speed of light.: 122 Michell correctly hypothesized that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies. In 1796, Laplace mentioned that a star could be invisible if it were sufficiently large while speculating on the origin of the Solar System in his book Exposition du Système du Monde. Franz Xaver von Zach asked Laplace for a mathematical analysis, which Laplace provided and published in a journal edited by von Zach. In 1905, Albert Einstein showed that the laws of electromagnetism would be invariant under a Lorentz transformation: they would be identical for observers travelling at different velocities relative to each other. This discovery became known as the principle of special relativity. Although the laws of mechanics had already been shown to be invariant, gravity remained yet to be included.: 19 In 1907, Einstein published a paper proposing his equivalence principle, the hypothesis that inertial mass and gravitational mass have a common cause. Using the principle, Einstein predicted the redshift and half of the lensing effect of gravity on light; the full prediction of gravitational lensing required development of general relativity.: 19 By 1915, Einstein refined these ideas into his general theory of relativity, which explained how matter affects spacetime, which in turn affects the motion of other matter. This formed the basis for black hole physics. Only a few months after Einstein published the field equations describing general relativity, astrophysicist Karl Schwarzschild set out to apply the idea to stars. He assumed spherical symmetry with no spin and found a solution to Einstein's equations.: 124 A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution. At a certain radius from the center of the mass, the Schwarzschild solution became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this radius, which later became known as the Schwarzschild radius, was not understood at the time. Many physicists of the early 20th century were skeptical of the existence of black holes. In a 1926 popular science book, Arthur Eddington critiqued the idea of a star with mass compressed to its Schwarzschild radius as a flaw in the then-poorly-understood theory of general relativity.: 134 In 1939, Einstein himself used his theory of general relativity in an attempt to prove that black holes were impossible. His work relied on increasing pressure or increasing centrifugal force balancing the force of gravity so that the object would not collapse beyond its Schwarzschild radius. He missed the possibility that implosion would drive the system below this critical value.: 135 By the 1920s, astronomers had classified a number of white dwarf stars as too cool and dense to be explained by the gradual cooling of ordinary stars. In 1926, Ralph Fowler showed that quantum-mechanical degeneracy pressure was larger than thermal pressure at these densities.: 145 In 1931, Subrahmanyan Chandrasekhar calculated that a non-rotating body of electron-degenerate matter below a certain limiting mass is stable, and by 1934 he showed that this explained the catalog of white dwarf stars.: 151 When Chandrasekhar announced his results, Eddington pointed out that stars above this limit would radiate until they were sufficiently dense to prevent light from exiting, a conclusion he considered absurd. Eddington and, later, Lev Landau argued that some yet unknown mechanism would stop the collapse. In the 1930s, Fritz Zwicky and Walter Baade studied stellar novae, focusing on exceptionally bright ones they called supernovae. Zwicky promoted the idea that supernovae produced stars with the density of atomic nuclei—neutron stars—but this idea was largely ignored.: 171 In 1939, based on Chandrasekhar's reasoning, J. Robert Oppenheimer and George Volkoff predicted that neutron stars below a certain mass limit, later called the Tolman–Oppenheimer–Volkoff limit, would be stable due to neutron degeneracy pressure. Above that limit, they reasoned that either their model would not apply or that gravitational contraction would not stop.: 380 John Archibald Wheeler and two of his students resolved questions about the model behind the Tolman–Oppenheimer–Volkoff (TOV) limit. Harrison and Wheeler developed the equations of state relating density to pressure for cold matter all the way through electron degeneracy and neutron degeneracy. Masami Wakano and Wheeler then used the equations to compute the equilibrium curve for stars, relating mass to circumference. They found no additional features that would invalidate the TOV limit. This meant that the only thing that could prevent black holes from forming was a dynamic process ejecting sufficient mass from a star as it cooled.: 205 The modern concept of black holes was formulated by Robert Oppenheimer and his student Hartland Snyder in 1939.: 80 In the paper, Oppenheimer and Snyder solved Einstein's equations of general relativity for an idealized imploding star, in a model later called the Oppenheimer–Snyder model, then described the results from far outside the star. The implosion starts as one might expect: the star material rapidly collapses inward. However, as the density of the star increases, gravitational time dilation increases and the collapse, viewed from afar, seems to slow down further and further until the star reaches its Schwarzschild radius, where it appears frozen in time.: 217 In 1958, David Finkelstein identified the Schwarzschild surface as an event horizon, calling it "a perfect unidirectional membrane: causal influences can cross it in only one direction". In this sense, events that occur inside of the black hole cannot affect events that occur outside of the black hole. Finkelstein created a new reference frame to include the point of view of infalling observers.: 103 Finkelstein's new frame of reference allowed events at the surface of an imploding star to be related to events far away. By 1962 the two points of view were reconciled, convincing many skeptics that implosion into a black hole made physical sense.: 226 The era from the mid-1960s to the mid-1970s was the "golden age of black hole research", when general relativity and black holes became mainstream subjects of research.: 258 In this period, more general black hole solutions were found. In 1963, Roy Kerr found the exact solution for a rotating black hole. Two years later, Ezra Newman found the cylindrically symmetric solution for a black hole that is both rotating and electrically charged. In 1967, Werner Israel found that the Schwarzschild solution was the only possible solution for a nonspinning, uncharged black hole, meaning that a Schwarzschild black hole would be defined by its mass alone. Similar identities were later found for Reissner-Nordstrom and Kerr black holes, defined only by their mass and their charge or spin respectively. Together, these findings became known as the no-hair theorem, which states that a stationary black hole is completely described by the three parameters of the Kerr–Newman metric: mass, angular momentum, and electric charge. At first, it was suspected that the strange mathematical singularities found in each of the black hole solutions only appeared due to the assumption that a black hole would be perfectly spherically symmetric, and therefore the singularities would not appear in generic situations where black holes would not necessarily be symmetric. This view was held in particular by Vladimir Belinski, Isaak Khalatnikov, and Evgeny Lifshitz, who tried to prove that no singularities appear in generic solutions, although they would later reverse their positions. However, in 1965, Roger Penrose proved that general relativity without quantum mechanics requires that singularities appear in all black holes. Astronomical observations also made great strides during this era. In 1967, Antony Hewish and Jocelyn Bell Burnell discovered pulsars and by 1969, these were shown to be rapidly rotating neutron stars. Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities, but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse. Based on observations in Greenwich and Toronto in the early 1970s, Cygnus X-1, a galactic X-ray source discovered in 1964, became the first astronomical object commonly accepted to be a black hole. Work by James Bardeen, Jacob Bekenstein, Carter, and Hawking in the early 1970s led to the formulation of black hole thermodynamics. These laws describe the behaviour of a black hole in close analogy to the laws of thermodynamics by relating mass to energy, area to entropy, and surface gravity to temperature. The analogy was completed: 442 when Hawking, in 1974, showed that quantum field theory implies that black holes should radiate like a black body with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as Hawking radiation. While Cygnus X-1, a stellar-mass black hole, was generally accepted by the scientific community as a black hole by the end of 1973, it would be decades before a supermassive black hole would gain the same broad recognition. Although, as early as the 1960s, physicists such as Donald Lynden-Bell and Martin Rees had suggested that powerful quasars in the center of galaxies were powered by accreting supermassive black holes, little observational proof existed at the time. However, the Hubble Space Telescope, launched decades later, found that supermassive black holes were not only present in these active galactic nuclei, but that supermassive black holes in the center of galaxies were ubiquitous: Almost every galaxy had a supermassive black hole at its center, many of which were quiescent. In 1999, David Merritt proposed the M–sigma relation, which related the dispersion of the velocity of matter in the center bulge of a galaxy to the mass of the supermassive black hole at its core. Subsequent studies confirmed this correlation. Around the same time, based on telescope observations of the velocities of stars at the center of the Milky Way galaxy, independent work groups led by Andrea Ghez and Reinhard Genzel concluded that the compact radio source in the center of the galaxy, Sagittarius A*, was likely a supermassive black hole. On 11 February 2016, the LIGO Scientific Collaboration and Virgo Collaboration announced the first direct detection of gravitational waves, named GW150914, representing the first observation of a black hole merger. At the time of the merger, the black holes were approximately 1.4 billion light-years away from Earth and had masses of 30 and 35 solar masses.: 6 In 2017, Rainer Weiss, Kip Thorne, and Barry Barish, who had spearheaded the project, were awarded the Nobel Prize in Physics for their work. Since the initial discovery in 2015, hundreds more gravitational waves have been observed by LIGO and another interferometer, Virgo. On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope (EHT) in 2017 of the supermassive black hole in Messier 87's galactic centre. In 2022, the Event Horizon Telescope collaboration released an image of the black hole in the center of the Milky Way galaxy, Sagittarius A*; The data had been collected in 2017. In 2020, the Nobel Prize in Physics was awarded for work on black holes. Andrea Ghez and Reinhard Genzel shared one-half for their discovery that Sagittarius A* is a supermassive black hole. Penrose received the other half for his work showing that the mathematics of general relativity requires the formation of black holes. Cosmologists lamented that Hawking's extensive theoretical work on black holes would not be honored since he died in 2018. In December 1967, a student reportedly suggested the phrase black hole at a lecture by John Wheeler; Wheeler adopted the term for its brevity and "advertising value", and Wheeler's stature in the field ensured it quickly caught on, leading some to credit Wheeler with coining the phrase. However, the term was used by others around that time. Science writer Marcia Bartusiak traces the term black hole to physicist Robert H. Dicke, who in the early 1960s reportedly compared the phenomenon to the Black Hole of Calcutta, notorious as a prison where people entered but never left alive. The term was used in print by Life and Science News magazines in 1963, and by science journalist Ann Ewing in her article "'Black Holes' in Space", dated 18 January 1964, which was a report on a meeting of the American Association for the Advancement of Science held in Cleveland, Ohio. Definition A black hole is generally defined as a region of spacetime from which no information-carrying signals or objects can escape. However, verifying an object as a black hole by this definition would require waiting for an infinite time and at an infinite distance from the black hole to verify that indeed, nothing has escaped, and thus cannot be used to identify a physical black hole. Broadly, physicists do not have a precisely-agreed-upon definition of a black hole. Among astrophysicists, a black hole is a compact object with a mass larger than four solar masses. A black hole may also be defined as a reservoir of information: 142 or a region where space is falling inwards faster than the speed of light. Properties The no-hair theorem postulates that, once it achieves a stable condition after formation, a black hole has only three independent physical properties: mass, electric charge, and angular momentum; the black hole is otherwise featureless. If the conjecture is true, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another. The degree to which the conjecture is true for real black holes is currently an unsolved problem. The simplest static black holes have mass but neither electric charge nor angular momentum. According to Birkhoff's theorem, these Schwarzschild black holes are the only vacuum solution that is spherically symmetric. Solutions describing more general black holes also exist. Non-rotating charged black holes are described by the Reissner–Nordström metric, while the Kerr metric describes a non-charged rotating black hole. The most general stationary black hole solution known is the Kerr–Newman metric, which describes a black hole with both charge and angular momentum. The simplest static black holes have mass but neither electric charge nor angular momentum. Contrary to the popular notion of a black hole "sucking in everything" in its surroundings, from far away, the external gravitational field of a black hole is identical to that of any other body of the same mass. While a black hole can theoretically have any positive mass, the charge and angular momentum are constrained by the mass. The total electric charge Q and the total angular momentum J are expected to satisfy the inequality Q 2 4 π ϵ 0 + c 2 J 2 G M 2 ≤ G M 2 {\displaystyle {\frac {Q^{2}}{4\pi \epsilon _{0}}}+{\frac {c^{2}J^{2}}{GM^{2}}}\leq GM^{2}} for a black hole of mass M. Black holes with the maximum possible charge or spin satisfying this inequality are called extremal black holes. Solutions of Einstein's equations that violate this inequality exist, but they do not possess an event horizon. These are so-called naked singularities that can be observed from the outside. Because these singularities make the universe inherently unpredictable, many physicists believe they could not exist. The weak cosmic censorship hypothesis, proposed by Sir Roger Penrose, rules out the formation of such singularities, when they are created through the gravitational collapse of realistic matter. However, this theory has not yet been proven, and some physicists believe that naked singularities could exist. It is also unknown whether black holes could even become extremal, forming naked singularities, since natural processes counteract increasing spin and charge when a black hole becomes near-extremal. The total mass of a black hole can be estimated by analyzing the motion of objects near the black hole, such as stars or gas. All black holes spin, often fast—One supermassive black hole, GRS 1915+105 has been estimated to spin at over 1,000 revolutions per second. The Milky Way's central black hole Sagittarius A* rotates at about 90% of the maximum rate. The spin rate can be inferred from measurements of atomic spectral lines in the X-ray range. As gas near the black hole plunges inward, high energy X-ray emission from electron-positron pairs illuminates the gas further out, appearing red-shifted due to relativistic effects. Depending on the spin of the black hole, this plunge happens at different radii from the hole, with different degrees of redshift. Astronomers can use the gap between the x-ray emission of the outer disk and the redshifted emission from plunging material to determine the spin of the black hole. A newer way to estimate spin is based on the temperature of gasses accreting onto the black hole. The method requires an independent measurement of the black hole mass and inclination angle of the accretion disk followed by computer modeling. Gravitational waves from coalescing binary black holes can also provide the spin of both progenitor black holes and the merged hole, but such events are rare. A spinning black hole has angular momentum. The supermassive black hole in the center of the Messier 87 (M87) galaxy appears to have an angular momentum very close to the maximum theoretical value. That uncharged limit is J ≤ G M 2 c , {\displaystyle J\leq {\frac {GM^{2}}{c}},} allowing definition of a dimensionless spin magnitude such that 0 ≤ c J G M 2 ≤ 1. {\displaystyle 0\leq {\frac {cJ}{GM^{2}}}\leq 1.} Most black holes are believed to have an approximately neutral charge. For example, Michal Zajaček, Arman Tursunov, Andreas Eckart, and Silke Britzen found the electric charge of Sagittarius A* to be at least ten orders of magnitude below the theoretical maximum. A charged black hole repels other like charges just like any other charged object. If a black hole were to become charged, particles with an opposite sign of charge would be pulled in by the extra electromagnetic force, while particles with the same sign of charge would be repelled, neutralizing the black hole. This effect may not be as strong if the black hole is also spinning. The presence of charge can reduce the diameter of the black hole by up to 38%. The charge Q for a nonspinning black hole is bounded by Q ≤ G M , {\displaystyle Q\leq {\sqrt {G}}M,} where G is the gravitational constant and M is the black hole's mass. Classification Black holes can have a wide range of masses. The minimum mass of a black hole formed by stellar gravitational collapse is governed by the maximum mass of a neutron star and is believed to be approximately two-to-four solar masses. However, theoretical primordial black holes, believed to have formed soon after the Big Bang, could be far smaller, with masses as little as 10−5 grams at formation. These very small black holes are sometimes called micro black holes. Black holes formed by stellar collapse are called stellar black holes. Estimates of their maximum mass at formation vary, but generally range from 10 to 100 solar masses, with higher estimates for black holes progenated by low-metallicity stars. The mass of a black hole formed via a supernova has a lower bound: If the progenitor star is too small, the collapse may be stopped by the degeneracy pressure of the star's constituents, allowing the condensation of matter into an exotic denser state. Degeneracy pressure occurs from the Pauli exclusion principle—Particles will resist being in the same place as each other. Smaller progenitor stars, with masses less than about 8 M☉, will be held together by the degeneracy pressure of electrons and will become a white dwarf. For more massive progenitor stars, electron degeneracy pressure is no longer strong enough to resist the force of gravity and the star will be held together by neutron degeneracy pressure, which can occur at much higher densities, forming a neutron star. If the star is still too massive, even neutron degeneracy pressure will not be able to resist the force of gravity and the star will collapse into a black hole.: 5.8 Stellar black holes can also gain mass via accretion of nearby matter, often from a companion object such as a star. Black holes that are larger than stellar black holes but smaller than supermassive black holes are called intermediate-mass black holes, with masses of approximately 102 to 105 solar masses. These black holes seem to be rarer than their stellar and supermassive counterparts, with relatively few candidates having been observed. Physicists have speculated that such black holes may form from collisions in globular and star clusters or at the center of low-mass galaxies. They may also form as the result of mergers of smaller black holes, with several LIGO observations finding merged black holes within the 110-350 solar mass range. The black holes with the largest masses are called supermassive black holes, with masses more than 106 times that of the Sun. These black holes are believed to exist at the centers of almost every large galaxy, including the Milky Way. Some scientists have proposed a subcategory of even larger black holes, called ultramassive black holes, with masses greater than 109-1010 solar masses. Theoretical models predict that the accretion disc that feeds black holes will be unstable once a black hole reaches 50-100 billion times the mass of the Sun, setting a rough upper limit to black hole mass. Structure While black holes are conceptually invisible sinks of all matter and light, in astronomical settings, their enormous gravity alters the motion of surrounding objects and pulls nearby gas inwards at near-light speed, making the area around black holes the brightest objects in the universe. Some black holes have relativistic jets—thin streams of plasma travelling away from the black hole at more than one-tenth of the speed of light. A small faction of the matter falling towards the black hole gets accelerated away along the hole rotation axis. These jets can extend as far as millions of parsecs from the black hole itself. Black holes of any mass can have jets. However, they are typically observed around spinning black holes with strongly-magnetized accretion disks. Relativistic jets were more common in the early universe, when galaxies and their corresponding supermassive black holes were rapidly gaining mass. All black holes with jets also have an accretion disk, but the jets are usually brighter than the disk. Quasars, typically found in other galaxies, are believed to be supermassive black holes with jets; microquasars are believed to be stellar-mass objects with jets, typically observed in the Milky Way. The mechanism of formation of jets is not yet known, but several options have been proposed. One method proposed to fuel these jets is the Blandford-Znajek process, which suggests that the dragging of magnetic field lines by a black hole's rotation could launch jets of matter into space. The Penrose process, which involves extraction of a black hole's rotational energy, has also been proposed as a potential mechanism of jet propulsion. Due to conservation of angular momentum, gas falling into the gravitational well created by a massive object will typically form a disk-like structure around the object.: 242 As the disk's angular momentum is transferred outward due to internal processes, its matter falls farther inward, converting its gravitational energy into heat and releasing a large flux of x-rays. The temperature of these disks can range from thousands to millions of Kelvin, and temperatures can differ throughout a single accretion disk. Accretion disks can also emit in other parts of the electromagnetic spectrum, depending on the disk's turbulence and magnetization and the black hole's mass and angular momentum. Accretion disks can be defined as geometrically thin or geometrically thick. Geometrically thin disks are mostly confined to the black hole's equatorial plane and have a well-defined edge at the innermost stable circular orbit (ISCO), while geometrically thick disks are supported by internal pressure and temperature and can extend inside the ISCO. Disks with high rates of electron scattering and absorption, appearing bright and opaque, are called optically thick; optically thin disks are more translucent and produce fainter images when viewed from afar. Accretion disks of black holes accreting beyond the Eddington limit are often referred to as polish donuts due to their thick, toroidal shape that resembles that of a donut. Quasar accretion disks are expected to usually appear blue in color. The disk for a stellar black hole, on the other hand, would likely look orange, yellow, or red, with its inner regions being the brightest. Theoretical research suggests that the hotter a disk is, the bluer it should be, although this is not always supported by observations of real astronomical objects. Accretion disk colors may also be altered by the Doppler effect, with the part of the disk travelling towards an observer appearing bluer and brighter and the part of the disk travelling away from the observer appearing redder and dimmer. In Newtonian gravity, test particles can stably orbit at arbitrary distances from a central object. In general relativity, however, there exists a smallest possible radius for which a massive particle can orbit stably. Any infinitesimal inward perturbations to this orbit will lead to the particle spiraling into the black hole, and any outward perturbations will, depending on the energy, cause the particle to spiral in, move to a stable orbit further from the black hole, or escape to infinity. This orbit is called the innermost stable circular orbit, or ISCO. The location of the ISCO depends on the spin of the black hole and the spin of the particle itself. In the case of a Schwarzschild black hole (spin zero) and a particle without spin, the location of the ISCO is: r I S C O = 3 r s = 6 G M c 2 , {\displaystyle r_{\rm {ISCO}}=3\,r_{\text{s}}={\frac {6\,GM}{c^{2}}},} where r I S C O {\displaystyle r_{\rm {_{ISCO}}}} is the radius of the ISCO, r s {\displaystyle r_{\text{s}}} is the Schwarzschild radius of the black hole, G {\displaystyle G} is the gravitational constant, and c {\displaystyle c} is the speed of light. The radius of this orbit changes slightly based on particle spin. For charged black holes, the ISCO moves inwards. For spinning black holes, the ISCO is moved inwards for particles orbiting in the same direction that the black hole is spinning (prograde) and outwards for particles orbiting in the opposite direction (retrograde). For example, the ISCO for a particle orbiting retrograde can be as far out as about 9 r s {\displaystyle 9r_{\text{s}}} , while the ISCO for a particle orbiting prograde can be as close as at the event horizon itself. The photon sphere is a spherical boundary for which photons moving on tangents to that sphere are bent completely around the black hole, possibly orbiting multiple times. Light rays with impact parameters less than the radius of the photon sphere enter the black hole. For Schwarzschild black holes, the photon sphere has a radius 1.5 times the Schwarzschild radius; the radius for non-Schwarzschild black holes is at least 1.5 times the radius of the event horizon. When viewed from a great distance, the photon sphere creates an observable black hole shadow. Since no light emerges from within the black hole, this shadow is the limit for possible observations.: 152 The shadow of colliding black holes should have characteristic warped shapes, allowing scientists to detect black holes that are about to merge. While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Therefore, any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon. Light emitted towards the photon sphere may also curve around the black hole and return to the emitter. For a rotating, uncharged black hole, the radius of the photon sphere depends on the spin parameter and whether the photon is orbiting prograde or retrograde. For a photon orbiting prograde, the photon sphere will be 1-3 Schwarzschild radii from the center of the black hole, while for a photon orbiting retrograde, the photon sphere will be between 3-5 Schwarzschild radii from the center of the black hole. The exact location of the photon sphere depends on the magnitude of the black hole's rotation. For a charged, nonrotating black hole, there will only be one photon sphere, and the radius of the photon sphere will decrease for increasing black hole charge. For non-extremal, charged, rotating black holes, there will always be two photon spheres, with the exact radii depending on the parameters of the black hole. Near a rotating black hole, spacetime rotates similar to a vortex. The rotating spacetime will drag any matter and light into rotation around the spinning black hole. This effect of general relativity, called frame dragging, gets stronger closer to the spinning mass. The region of spacetime in which it is impossible to stay still is called the ergosphere. The ergosphere of a black hole is a volume bounded by the black hole's event horizon and the ergosurface, which coincides with the event horizon at the poles but bulges out from it around the equator. Matter and radiation can escape from the ergosphere. Through the Penrose process, objects can emerge from the ergosphere with more energy than they entered with. The extra energy is taken from the rotational energy of the black hole, slowing down the rotation of the black hole.: 268 A variation of the Penrose process in the presence of strong magnetic fields, the Blandford–Znajek process, is considered a likely mechanism for the enormous luminosity and relativistic jets of quasars and other active galactic nuclei. The observable region of spacetime around a black hole closest to its event horizon is called the plunging region. In this area it is no longer possible for free falling matter to follow circular orbits or stop a final descent into the black hole. Instead, it will rapidly plunge toward the black hole at close to the speed of light, growing increasingly hot and producing a characteristic, detectable thermal emission. However, light and radiation emitted from this region can still escape from the black hole's gravitational pull. For a nonspinning, uncharged black hole, the radius of the event horizon, or Schwarzschild radius, is proportional to the mass, M, through r s = 2 G M c 2 ≈ 2.95 M M ⊙ k m , {\displaystyle r_{\mathrm {s} }={\frac {2GM}{c^{2}}}\approx 2.95\,{\frac {M}{M_{\odot }}}~\mathrm {km,} } where rs is the Schwarzschild radius and M☉ is the mass of the Sun.: 124 For a black hole with nonzero spin or electric charge, the radius is smaller,[Note 1] until an extremal black hole could have an event horizon close to r + = G M c 2 , {\displaystyle r_{\mathrm {+} }={\frac {GM}{c^{2}}},} half the radius of a nonspinning, uncharged black hole of the same mass. Since the volume within the Schwarzschild radius increase with the cube of the radius, average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass: supermassive black holes are much less dense than stellar black holes. The average density of a 108 M☉ black hole is comparable to that of water. The defining feature of a black hole is the existence of an event horizon, a boundary in spacetime through which matter and light can pass only inward towards the center of the black hole. Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach or affect an outside observer, making it impossible to determine whether such an event occurred.: 179 For non-rotating black holes, the geometry of the event horizon is precisely spherical, while for rotating black holes, the event horizon is oblate. To a distant observer, a clock near a black hole would appear to tick more slowly than one further from the black hole.: 217 This effect, known as gravitational time dilation, would also cause an object falling into a black hole to appear to slow as it approached the event horizon, never quite reaching the horizon from the perspective of an outside observer.: 218 All processes on this object would appear to slow down, and any light emitted by the object to appear redder and dimmer, an effect known as gravitational redshift. An object falling from half of a Schwarzschild radius above the event horizon would fade away until it could no longer be seen, disappearing from view within one hundredth of a second. It would also appear to flatten onto the black hole, joining all other material that had ever fallen into the hole. On the other hand, an observer falling into a black hole would not notice any of these effects as they cross the event horizon. Their own clocks appear to them to tick normally, and they cross the event horizon after a finite time without noting any singular behaviour. In general relativity, it is impossible to determine the location of the event horizon from local observations, due to Einstein's equivalence principle.: 222 Black holes that are rotating and/or charged have an inner horizon, often called the Cauchy horizon, inside of the black hole. The inner horizon is divided up into two segments: an ingoing section and an outgoing section. At the ingoing section of the Cauchy horizon, radiation and matter that fall into the black hole would build up at the horizon, causing the curvature of spacetime to go to infinity. This would cause an observer falling in to experience tidal forces. This phenomenon is often called mass inflation, since it is associated with a parameter dictating the black hole's internal mass growing exponentially, and the buildup of tidal forces is called the mass-inflation singularity or Cauchy horizon singularity. Some physicists have argued that in realistic black holes, accretion and Hawking radiation would stop mass inflation from occurring. At the outgoing section of the inner horizon, infalling radiation would backscatter off of the black hole's spacetime curvature and travel outward, building up at the outgoing Cauchy horizon. This would cause an infalling observer to experience a gravitational shock wave and tidal forces as the spacetime curvature at the horizon grew to infinity. This buildup of tidal forces is called the shock singularity. Both of these singularities are weak, meaning that an object crossing them would only be deformed a finite amount by tidal forces, even though the spacetime curvature would still be infinite at the singularity. This is as opposed to a strong singularity, where an object hitting the singularity would be stretched and squeezed by an infinite amount. They are also null singularities, meaning that a photon could travel parallel to the them without ever being intercepted. Ignoring quantum effects, every black hole has a singularity inside, points where the curvature of spacetime becomes infinite, and geodesics terminate within a finite proper time.: 205 For a non-rotating black hole, this region takes the shape of a single point; for a rotating black hole it is smeared out to form a ring singularity that lies in the plane of rotation.: 264 In both cases, the singular region has zero volume. All of the mass of the black hole ends up in the singularity.: 252 Since the singularity has nonzero mass in an infinitely small space, it can be thought of as having infinite density. Observers falling into a Schwarzschild black hole (i.e., non-rotating and not charged) cannot avoid being carried into the singularity once they cross the event horizon. As they fall further into the black hole, they will be torn apart by the growing tidal forces in a process sometimes referred to as spaghettification or the noodle effect. Eventually, they will reach the singularity and be crushed into an infinitely small point.: 182 However any perturbations, such as those caused by matter or radiation falling in, would cause space to oscillate chaotically near the singularity. Any matter falling in would experience intense tidal forces rapidly changing in direction, all while being compressed into an increasingly small volume. Alternative forms of general relativity, including addition of some quatum effects, can lead to regular, or nonsingular, black holes without singularities. For example, the fuzzball model, based on string theory, states that black holes are actually made up of quantum microstates and need not have a singularity or an event horizon. The theory of loop quantum gravity proposes that the curvature and density at the center of a black hole is large, but not infinite. Formation Black holes are formed by gravitational collapse of massive stars, either by direct collapse or during a supernova explosion in a process called fallback. Black holes can result from the merger of two neutron stars or a neutron star and a black hole. Other more speculative mechanisms include primordial black holes created from density fluctuations in the early universe, the collapse of dark stars, a hypothetical object powered by annihilation of dark matter, or from hypothetical self-interacting dark matter. Gravitational collapse occurs when an object's internal pressure is insufficient to resist the object's own gravity. At the end of a star's life, it will run out of hydrogen to fuse, and will start fusing more and more massive elements, until it gets to iron. Since the fusion of elements heavier than iron would require more energy than it would release, nuclear fusion ceases. If the iron core of the star is too massive, the star will no longer be able to support itself and will undergo gravitational collapse. While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the reference frame of infalling matter, a distant observer would see the infalling material slow and halt just above the event horizon, due to gravitational time dilation. Light from the collapsing material takes longer and longer to reach the observer, with the delay growing to infinity as the emitting material reaches the event horizon. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away. Observations of quasars at redshift z ∼ 7 {\displaystyle z\sim 7} , less than a billion years after the Big Bang, has led to investigations of other ways to form black holes. The accretion process to build supermassive black holes has a limiting rate of mass accumulation and a billion years is not enough time to reach quasar status. One suggestion is direct collapse of nearly pure hydrogen gas (low metalicity) clouds characteristic of the young universe, forming a supermassive star which collapses into a black hole. It has been suggested that seed black holes with typical masses of ~105 M☉ could have formed in this way which then could grow to ~109 M☉. However, the very large amount of gas required for direct collapse is not typically stable to fragmentation to form multiple stars. Thus another approach suggests massive star formation followed by collisions that seed massive black holes which ultimately merge to create a quasar.: 85 A neutron star in a common envelope with a regular star can accrete sufficient material to collapse to a black hole or two neutron stars can merge. These avenues for the formation of black holes are considered relatively rare. In the current epoch of the universe, conditions needed to form black holes are rare and are mostly only found in stars. However, in the early universe, conditions may have allowed for black hole formations via other means. Fluctuations of spacetime soon after the Big Bang may have formed areas that were denser then their surroundings. Initially, these regions would not have been compact enough to form a black hole, but eventually, the curvature of spacetime in the regions become large enough to cause them to collapse into a black hole. Different models for the early universe vary widely in their predictions of the scale of these fluctuations. Various models predict the creation of primordial black holes ranging from a Planck mass (~2.2×10−8 kg) to hundreds of thousands of solar masses. Primordial black holes with masses less than 1015 g would have evaporated by now due to Hawking radiation. Despite the early universe being extremely dense, it did not re-collapse into a black hole during the Big Bang, since the universe was expanding rapidly and did not have the gravitational differential necessary for black hole formation. Models for the gravitational collapse of objects of relatively constant size, such as stars, do not necessarily apply in the same way to rapidly expanding space such as the Big Bang. In principle, black holes could be formed in high-energy particle collisions that achieve sufficient density, although no such events have been detected. These hypothetical micro black holes, which could form from the collision of cosmic rays and Earth's atmosphere or in particle accelerators like the Large Hadron Collider, would not be able to aggregate additional mass. Instead, they would evaporate in about 10−25 seconds, posing no threat to the Earth. Evolution Black holes can also merge with other objects such as stars or even other black holes. This is thought to have been important, especially in the early growth of supermassive black holes, which could have formed from the aggregation of many smaller objects. The process has also been proposed as the origin of some intermediate-mass black holes. Mergers of supermassive black holes may take a long time: As a binary of supermassive black holes approach each other, most nearby stars are ejected, leaving little for the remaining black holes to gravitationally interact with that would allow them to get closer to each other. This phenomenon has been called the final parsec problem, as the distance at which this happens is usually around one parsec. When a black hole accretes matter, the gas in the inner accretion disk orbits at very high speeds because of its proximity to the black hole. The resulting friction heats the inner disk to temperatures at which it emits vast amounts of electromagnetic radiation (mainly X-rays) detectable by telescopes. By the time the matter of the disk reaches the ISCO, between 5.7% and 42% of its mass will have been converted to energy, depending on the black hole's spin. About 90% of this energy is released within about 20 black hole radii. In many cases, accretion disks are accompanied by relativistic jets that are emitted along the black hole's poles, which carry away much of the energy. The mechanism for the creation of these jets is currently not well understood, in part due to insufficient data. Many of the universe's most energetic phenomena have been attributed to the accretion of matter on black holes. Active galactic nuclei and quasars are believed to be the accretion disks of supermassive black holes. X-ray binaries are generally accepted to be binary systems in which one of the two objects is a compact object accreting matter from its companion. Ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes. At a certain rate of accretion, the outward radiation pressure will become as strong as the inward gravitational force, and the black hole should unable to accrete any faster. This limit is called the Eddington limit. However, many black holes accrete beyond this rate due to their non-spherical geometry or instabilities in the accretion disk. Accretion beyond the limit is called Super-Eddington accretion and may have been commonplace in the early universe. Stars have been observed to get torn apart by tidal forces in the immediate vicinity of supermassive black holes in galaxy nuclei, in what is known as a tidal disruption event (TDE). Some of the material from the disrupted star forms an accretion disk around the black hole, which emits observable electromagnetic radiation. The correlation between the masses of supermassive black holes in the centres of galaxies with the velocity dispersion and mass of stars in their host bulges suggests that the formation of galaxies and the formation of their central black holes are related. Black hole winds from rapid accretion, particularly when the galaxy itself is still accreting matter, can compress gas nearby, accelerating star formation. However, if the winds become too strong, the black hole may blow nearly all of the gas out of the galaxy, quenching star formation. Black hole jets may also energize nearby cavities of plasma and eject low-entropy gas from out of the galactic core, causing gas in galactic centers to be hotter than expected. If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time as they lose mass by the emission of photons and other particles. The temperature of this thermal spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which is inversely proportional to the mass. Hence, large black holes emit less radiation than small black holes.: Ch. 9.6 A stellar black hole of 1 M☉ has a Hawking temperature of 62 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrinking. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the Moon. Such a black hole would have a diameter of less than a tenth of a millimetre. The Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth. A possible exception is the burst of gamma rays emitted in the last stage of the evaporation of primordial black holes. Searches for such flashes have proven unsuccessful and provide stringent limits on the possibility of existence of low mass primordial black holes, with modern research predicting that primordial black holes must make up less than a fraction of 10−7 of the universe's total mass. NASA's Fermi Gamma-ray Space Telescope, launched in 2008, has searched for these flashes, but has not yet found any. The properties of a black hole are constrained and interrelated by the theories that predict these properties. When based on general relativity, these relationships are called the laws of black hole mechanics. For a black hole that is not still forming or accreting matter, the zeroth law of black hole mechanics states the black hole's surface gravity is constant across the event horizon. The first law relates changes in the black hole's surface area, angular momentum, and charge to changes in its energy. The second law says the surface area of a black hole never decreases on its own. Finally, the third law says that the surface gravity of a black hole is never zero. These laws are mathematical analogs of the laws of thermodynamics. They are not equivalent, however, because, according to general relativity without quantum mechanics, a black hole can never emit radiation, and thus its temperature must always be zero.: 11 Quantum mechanics predicts that a black hole will continuously emit thermal Hawking radiation, and therefore must always have a nonzero temperature. It also predicts that all black holes have entropy which scales with their surface area. When quantum mechanics is accounted for, the laws of black hole mechanics become equivalent to the classical laws of thermodynamics. However, these conclusions are derived without a complete theory of quantum gravity, although many potential theories do predict black holes having entropy and temperature. Thus, the true quantum nature of black hole thermodynamics continues to be debated.: 29 Observational evidence Millions of black holes with around 30 solar masses derived from stellar collapse are expected to exist in the Milky Way. Even a dwarf galaxy like Draco should have hundreds. Only a few of these have been detected. By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical Hawking radiation, so astrophysicists searching for black holes must generally rely on indirect observations. The defining characteristic of a black hole is its event horizon. The horizon itself cannot be imaged, so all other possible explanations for these indirect observations must be considered and eliminated before concluding that a black hole has been observed.: 11 The Event Horizon Telescope (EHT) is a global system of radio telescopes capable of directly observing a black hole shadow. The angular resolution of a telescope is based on its aperture and the wavelengths it is observing. Because the angular diameters of Sagittarius A* and Messier 87* in the sky are very small, a single telescope would need to be about the size of the Earth to clearly distinguish their horizons using radio wavelengths. By combining data from several different radio telescopes around the world, the Event Horizon Telescope creates an effective aperture the diameter size of the Earth. The EHT team used imaging algorithms to compute the most probable image from the data in its observations of Sagittarius A* and M87*. Gravitational-wave interferometry can be used to detect merging black holes and other compact objects. In this method, a laser beam is split down two long arms of a tunnel. The laser beams reflect off of mirrors in the tunnels and converge at the intersection of the arms, cancelling each other out. However, when a gravitational wave passes, it warps spacetime, changing the lengths of the arms themselves. Since each laser beam is now travelling a slightly different distance, they do not cancel out and produce a recognizable signal. Analysis of the signal can give scientists information about what caused the gravitational waves. Since gravitational waves are very weak, gravitational-wave observatories such as LIGO must have arms several kilometers long and carefully control for noise from Earth to be able to detect these gravitational waves. Since the first measurements in 2016, multiple gravitational waves from black holes have been detected and analyzed. The proper motions of stars near the centre of the Milky Way provide strong observational evidence that these stars are orbiting a supermassive black hole. Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source Sagittarius A*. In 1998, by fitting the motions of the stars to Keplerian orbits, the astronomers were able to infer that Sagittarius A* must be a 2.6×106 M☉ object must be contained within a radius of 0.02 light-years. Since then, one of the stars—called S2—has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass of Sagittarius A* to 4.3×106 M☉, with a radius of less than 0.002 light-years. This upper limit radius is larger than the Schwarzschild radius for the estimated mass, so the combination does not prove Sagittarius A* is a black hole. Nevertheless, these observations strongly suggest that the central object is a supermassive black hole as there are no other plausible scenarios for confining so much invisible mass into such a small volume. Additionally, there is some observational evidence that this object might possess an event horizon, a feature unique to black holes. The Event Horizon Telescope image of Sagittarius A*, released in 2022, provided further confirmation that it is indeed a black hole. X-ray binaries are binary systems that emit a majority of their radiation in the X-ray part of the electromagnetic spectrum. These X-ray emissions result when a compact object accretes matter from an ordinary star. The presence of an ordinary star in such a system provides an opportunity for studying the central object and to determine if it might be a black hole. By measuring the orbital period of the binary, the distance to the binary from Earth, and the mass of the companion star, scientists can estimate the mass of the compact object. The Tolman-Oppenheimer-Volkoff limit (TOV limit) dictates the largest mass a nonrotating neutron star can be, and is estimated to be about two solar masses. While a rotating neutron star can be slightly more massive, if the compact object is much more massive than the TOV limit, it cannot be a neutron star and is generally expected to be a black hole. The first strong candidate for a black hole, Cygnus X-1, was discovered in this way by Charles Thomas Bolton, Louise Webster, and Paul Murdin in 1972. Observations of rotation broadening of the optical star reported in 1986 lead to a compact object mass estimate of 16 solar masses, with 7 solar masses as the lower bound. In 2011, this estimate was updated to 14.1±1.0 M☉ for the black hole and 19.2±1.9 M☉ for the optical stellar companion. X-ray binaries can be categorized as either low-mass or high-mass; This classification is based on the mass of the companion star, not the compact object itself. In a class of X-ray binaries called soft X-ray transients, the companion star is of relatively low mass, allowing for more accurate estimates of the black hole mass. These systems actively emit X-rays for only several months once every 10–50 years. During the period of low X-ray emission, called quiescence, the accretion disk is extremely faint, allowing detailed observation of the companion star. Numerous black hole candidates have been measured by this method. Black holes are also sometimes found in binaries with other compact objects, such as white dwarfs, neutron stars, and other black holes. The centre of nearly every galaxy contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M–sigma relation, strongly suggests a connection between the formation of the black hole and that of the galaxy itself. Astronomers use the term active galaxy to describe galaxies with unusual characteristics, such as unusual spectral line emission and very strong radio emission. Theoretical and observational studies have shown that the high levels of activity in the centers of these galaxies, regions called active galactic nuclei (AGN), may be explained by accretion onto supermassive black holes. These AGN consist of a central black hole that may be millions or billions of times more massive than the Sun, a disk of interstellar gas and dust called an accretion disk, and two jets perpendicular to the accretion disk. Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, Messier 32, Messier 87, the Sombrero Galaxy, and the Milky Way itself. Another way black holes can be detected is through observation of effects caused by their strong gravitational field. One such effect is gravitational lensing: The deformation of spacetime around a massive object causes light rays to be deflected, making objects behind them appear distorted. When the lensing object is a black hole, this effect can be strong enough to create multiple images of a star or other luminous source. However, the distance between the lensed images may be too small for contemporary telescopes to resolve—this phenomenon is called microlensing. Instead of seeing two images of a lensed star, astronomers see the star brighten slightly as the black hole moves towards the line of sight between the star and Earth and then return to its normal luminosity as the black hole moves away. The turn of the millennium saw the first 3 candidate detections of black holes in this way, and in January 2022, astronomers reported the first confirmed detection of a microlensing event from an isolated black hole. This was also the first determination of an isolated black hole mass, 7.1±1.3 M☉. Alternatives While there is a strong case for supermassive black holes, the model for stellar-mass black holes assumes of an upper limit for the mass of a neutron star: objects observed to have more mass are assumed to be black holes. However, the properties of extremely dense matter are poorly understood. New exotic phases of matter could allow other kinds of massive objects. Quark stars would be made up of quark matter and supported by quark degeneracy pressure, a form of degeneracy pressure even stronger than neutron degeneracy pressure. This would halt gravitational collapse at a higher mass than for a neutron star. Even stronger stars called electroweak stars would convert quarks in their cores into leptons, providing additional pressure to stop the star from collapsing. If, as some extensions of the Standard Model posit, quarks and leptons are made up of the even-smaller fundamental particles called preons, a very compact star could be supported by preon degeneracy pressure. While none of these hypothetical models can explain all of the observations of stellar black hole candidates, a Q star is the only alternative which could significantly exceed the mass limit for neutron stars and thus provide an alternative for supermassive black holes.: 12 A few theoretical objects have been conjectured to match observations of astronomical black hole candidates identically or near-identically, but which function via a different mechanism. A dark energy star would convert infalling matter into vacuum energy; This vacuum energy would be much larger than the vacuum energy of outside space, exerting outwards pressure and preventing a singularity from forming. A black star would be gravitationally collapsing slowly enough that quantum effects would keep it just on the cusp of fully collapsing into a black hole. A gravastar would consist of a very thin shell and a dark-energy interior providing outward pressure to stop the collapse into a black hole or formation of a singularity; It could even have another gravastar inside, called a 'nestar'. Open questions According to the no-hair theorem, a black hole is defined by only three parameters: its mass, charge, and angular momentum. This seems to mean that all other information about the matter that went into forming the black hole is lost, as there is no way to determine anything about the black hole from outside other than those three parameters. When black holes were thought to persist forever, this information loss was not problematic, as the information can be thought of as existing inside the black hole. However, black holes slowly evaporate by emitting Hawking radiation. This radiation does not appear to carry any additional information about the matter that formed the black hole, meaning that this information is seemingly gone forever. This is called the black hole information paradox. Theoretical studies analyzing the paradox have led to both further paradoxes and new ideas about the intersection of quantum mechanics and general relativity. While there is no consensus on the resolution of the paradox, work on the problem is expected to be important for a theory of quantum gravity.: 126 Observations of faraway galaxies have found that ultraluminous quasars, powered by supermassive black holes, existed in the early universe as far as redshift z ≥ 7 {\displaystyle z\geq 7} . These black holes have been assumed to be the products of the gravitational collapse of large population III stars. However, these stellar remnants were not massive enough to produce the quasars observed at early times without accreting beyond the Eddington limit, the theoretical maximum rate of black hole accretion. Physicists have suggested a variety of different mechanisms by which these supermassive black holes may have formed. It has been proposed that smaller black holes may have also undergone mergers to produce the observed supermassive black holes. It is also possible that they were seeded by direct-collapse black holes, in which a large cloud of hot gas avoids fragmentation that would lead to multiple stars, due to low angular momentum or heating from a nearby galaxy. Given the right circumstances, a single supermassive star forms and collapses directly into a black hole without undergoing typical stellar evolution. Additionally, these supermassive black holes in the early universe may be high-mass primordial black holes, which could have accreted further matter in the centers of galaxies. Finally, certain mechanisms allow black holes to grow faster than the theoretical Eddington limit, such as dense gas in the accretion disk limiting outward radiation pressure that prevents the black hole from accreting. However, the formation of bipolar jets prevent super-Eddington rates. In fiction Black holes have been portrayed in science fiction in a variety of ways. Even before the advent of the term itself, objects with characteristics of black holes appeared in stories such as the 1928 novel The Skylark of Space with its "black Sun" and the "hole in space" in the 1935 short story Starship Invincible. As black holes grew to public recognition in the 1960s and 1970s, they began to be featured in films as well as novels, such as Disney's The Black Hole. Black holes have also been used in works of the 21st century, such as Christopher Nolan's science fiction epic Interstellar. Authors and screenwriters have exploited the relativistic effects of black holes, particularly gravitational time dilation. For example, Interstellar features a black hole planet with a time dilation factor of over 60,000:1, while the 1977 novel Gateway depicts a spaceship approaching but never crossing the event horizon of a black hole from the perspective of an outside observer due to time dilation effects. Black holes have also been appropriated as wormholes or other methods of faster-than-light travel, such as in the 1974 novel The Forever War, where a network of black holes is used for interstellar travel. Additionally, black holes can feature as hazards to spacefarers and planets: A black hole threatens a deep-space outpost in 1978 short story The Black Hole Passes, and a binary black hole dangerously alters the orbit of a planet in the 2018 Netflix reboot of Lost in Space. Notes References Further reading External links |
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Contents Gravity In physics, gravity (from Latin gravitas 'weight'), also known as gravitation or a gravitational interaction, is a fundamental interaction, which may be described as the force that draws material objects towards each other. The gravitational attraction between clouds of primordial hydrogen and clumps of dark matter in the early universe caused the hydrogen gas to coalesce, eventually condensing and fusing to form stars. At larger scales this resulted in galaxies and clusters, so gravity is a primary driver for the large-scale structures in the universe. Gravity has an infinite range, although its effects become weaker as objects get farther away. Gravity is described by the general theory of relativity, proposed by Albert Einstein in 1915, which describes gravity in terms of the curvature of spacetime, caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is sufficiently well approximated by Newton's law of universal gravitation, which describes gravity as an attractive force between any two bodies that is proportional to the product of their masses and inversely proportional to the square of the distance between them. Scientists are looking for a theory that describes gravity in the framework of quantum mechanics (quantum gravity), which would unify gravity and the other known fundamental interactions of physics in a single mathematical framework (a theory of everything). On the surface of a planetary body such as on Earth, the force of gravity operates towards the center of the body and is modified by the centrifugal effects arising from the rotation of the body. In this context, gravity gives weight to physical objects and is essential to understanding the mechanisms that are responsible for surface water waves, lunar tides and substantially contributes to weather patterns. Gravitational weight also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms. Characterization Gravity is the word used to describe a physical law, a fundamental physical interaction that derives primarily from mass, and the observed consequences of that interaction on objects. Gravity is the law that every object with mass attracts every other object in the universe in proportion to each mass and inversely proportional to the square of the distance between them. The force of gravity, F is written using the gravitational constant, G, as F = G m m ′ r 2 {\displaystyle F=G{\frac {mm'}{r^{2}}}} for two masses, m, and m′ separated by a distance r. Gravity is considered to be one of four fundamental interactions. The electromagnetic force law is similar to the force law for gravity: both depend upon the square of the inverse distance between objects in typical interactions. The ratio of gravitational attraction of two electrons to their electrical repulsion is 1 to 4.17×1042. As a result, gravity can generally be neglected at the level of subatomic particles. Gravity becomes the most significant interaction between objects at the scale of astronomical bodies, and it determines the motion of satellites, planets, stars, galaxies, and even light. Gravity is also fundamental in another sense: the inertial mass that appears in Newton's second law is the same as the gravitational mass. This equivalence principle is a scientific hypothesis that has been tested experimentally to more than one part in a trillion. History The nature and mechanism of gravity were explored by a wide range of ancient scholars. In Ancient Greece, Aristotle believed that each of the classical elements had a natural place in the universe which it tends to move toward - earth at the center of the universe (the center of the Earth, which was known to be spherical); then water, air, fire, and aether in concentric shells from inner to outer. He also thought that the speed of a falling object should increase with its weight, a conclusion that was later shown to be false. While Aristotle's view was widely accepted throughout Ancient Greece, there were other thinkers such as Plutarch who correctly predicted that the attraction of gravity was not unique to the Earth. Although he did not understand gravity as a force, the ancient Greek philosopher Archimedes discovered the center of gravity of a triangle. He postulated that if two equal weights did not have the same center of gravity, the center of gravity of the two weights together would be in the middle of the line that joins their centers of gravity. Two centuries later, the Roman engineer and architect Vitruvius contended in his De architectura that gravity is not dependent on a substance's weight but rather on its "nature". In the 6th century CE, the Byzantine Alexandrian scholar John Philoponus proposed the theory of impetus, which modifies Aristotle's theory that "continuation of motion depends on continued action of a force" by incorporating a causative force that diminishes over time. In 628 CE, the Indian mathematician and astronomer Brahmagupta proposed the idea that gravity is an attractive force that draws objects to the Earth and used the term gurutvākarṣaṇ to describe it.: 105 In the ancient Middle East, gravity was a topic of fierce debate. The Persian intellectual Al-Biruni believed that the force of gravity was not unique to the Earth, and he correctly assumed that other heavenly bodies should exert a gravitational attraction as well. In contrast, Al-Khazini held the same position as Aristotle that all matter in the Universe is attracted to the center of the Earth. In the mid-16th century, various European scientists experimentally disproved the Aristotelian notion that heavier objects fall at a faster rate. In particular, the Spanish Dominican priest Domingo de Soto wrote in 1551 that bodies in free fall uniformly accelerate. De Soto may have been influenced by earlier experiments conducted by other Dominican priests in Italy, including those by Benedetto Varchi, Francesco Beato, Luca Ghini, and Giovan Bellaso which contradicted Aristotle's teachings on the fall of bodies. The mid-16th century Italian physicist Giambattista Benedetti published papers claiming that, due to specific gravity, objects made of the same material but with different masses would fall at the same speed. With the 1586 Delft tower experiment, the Flemish physicist Simon Stevin observed that two cannonballs of differing sizes and weights fell at the same rate when dropped from a tower. In the late 16th century, Galileo Galilei's careful measurements of balls rolling down inclines allowed him to firmly establish that gravitational acceleration is the same for all objects.: 334 Galileo postulated that air resistance is the reason that objects with a low density and high surface area fall more slowly in an atmosphere. In his 1638 work Two New Sciences, Galileo proved that the distance traveled by a falling object is proportional to the square of the time elapsed. His method was a form of graphical numerical integration since concepts of algebra and calculus were unknown at the time.: 4 This was later confirmed by Italian scientists Jesuits Grimaldi and Riccioli between 1640 and 1650. They also calculated the magnitude of the Earth's gravity by measuring the oscillations of a pendulum. Galileo also broke with incorrect ideas of Aristotelian philosophy by regarding inertia as persistence of motion, not a tendency to come to rest. By considering that the laws of physics appear identical on a moving ship to those on land, Galileo developed the concepts of reference frame and the principle of relativity.: 5 These concepts would become central to Newton's mechanics, only to be transformed in Einstein's theory of gravity, the general theory of relativity.: 17 In last quarter of the 16th century Tycho Brahe created accurate tools for astrometry, providing careful observations of the planets. His assistant and successor, Johannes Kepler analyzed these data into three empirical laws of planetary motion. These laws were central to the development of a theory of gravity a hundred years later. In his 1609 book Astronomia nova Kepler described gravity as a mutual attraction, claiming that if the Earth and Moon were not held apart by some force they would come together. He recognized that mechanical forces cause action, creating a kind of celestial machine. On the other hand Kepler viewed the force of the Sun on the planets as magnetic and acting tangential to their orbits and he assumed with Aristotle that inertia meant objects tend to come to rest.: 846 In 1666, Giovanni Alfonso Borelli avoided the key problems that limited Kepler. By Borelli's time the concept of inertia had its modern meaning as the tendency of objects to remain in uniform motion and he viewed the Sun as just another heavenly body. Borelli developed the idea of mechanical equilibrium, a balance between inertia and gravity. Newton cited Borelli's influence on his theory.: 848 In 1657, Robert Hooke published his Micrographia, in which he hypothesized that the Moon must have its own gravity.: 57 In a communication to the Royal Society in 1666 and his 1674 Gresham lecture, An Attempt to prove the Annual Motion of the Earth, Hooke took the important step of combining related hypothesis and then forming predictions based on the hypothesis. He wrote: I will explain a system of the world very different from any yet received. It is founded on the following positions. 1. That all the heavenly bodies have not only a gravitation of their parts to their own proper centre, but that they also mutually attract each other within their spheres of action. 2. That all bodies having a simple motion, will continue to move in a straight line, unless continually deflected from it by some extraneous force, causing them to describe a circle, an ellipse, or some other curve. 3. That this attraction is so much the greater as the bodies are nearer. As to the proportion in which those forces diminish by an increase of distance, I own I have not discovered it.... Hooke was an important communicator who helped reformulate the scientific enterprise. He was one of the first professional scientists and worked as the then-new Royal Society's curator of experiments for 40 years. However his valuable insights remained hypotheses and some of these were incorrect. He was unable to develop a mathematical theory of gravity and work out the consequences.: 853 For this he turned to Newton, writing him a letter in 1679, outlining a model of planetary motion in a void or vacuum due to attractive action at a distance. This letter likely turned Newton's thinking in a new direction leading to his revolutionary work on gravity. When Newton reported his results in 1686, Hooke claimed the inverse square law portion was his "notion". Before 1684, scientists including Christopher Wren, Robert Hooke and Edmund Halley determined that Kepler's third law, relating to planetary orbital periods, would prove the inverse square law if the orbits were circles. However the orbits were known to be ellipses. At Halley's suggestion, Newton tackled the problem and was able to prove that ellipses also proved the inverse square relation from Kepler's observations.: 13 In 1684, Isaac Newton sent a manuscript to Edmond Halley titled De motu corporum in gyrum ('On the motion of bodies in an orbit'), which provided a physical justification for Kepler's laws of planetary motion. Halley was impressed by the manuscript and urged Newton to expand on it, and a few years later Newton published a groundbreaking book called Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). The revolutionary aspect of Newton's theory of gravity was the unification of Earth-bound observations of acceleration with celestial mechanics.: 4 In his book, Newton described gravitation as a universal force, and claimed that it operated on objects "according to the quantity of solid matter which they contain and propagates on all sides to immense distances always at the inverse square of the distances".: 546 This formulation had two important parts. First was equating inertial mass and gravitational mass. Newton's 2nd law defines force via F = m a {\displaystyle F=ma} for inertial mass, his law of gravitational force uses the same mass. Newton did experiments with pendulums to verify this concept as best he could.: 11 The second aspect of Newton's formulation was the inverse square of distance. This aspect was not new: the astronomer Ismaël Bullialdus proposed it around 1640. Seeking proof, Newton made quantitative analysis around 1665, considering the period and distance of the Moon's orbit and considering the timing of objects falling on Earth. Newton did not publish these results at the time because he could not prove that the Earth's gravity acts as if all its mass were concentrated at its center. That proof took him twenty years.: 13 Newton's Principia was well received by the scientific community, and his law of gravitation quickly spread across the European world. More than a century later, in 1821, his theory of gravitation rose to even greater prominence when it was used to predict the existence of Neptune. In that year, the French astronomer Alexis Bouvard used this theory to create a table modeling the orbit of Uranus, which was shown to differ significantly from the planet's actual trajectory. In order to explain this discrepancy, many astronomers speculated that there might be a large object beyond the orbit of Uranus which was disrupting its orbit. In 1846, the astronomers John Couch Adams and Urbain Le Verrier independently used Newton's law to predict Neptune's location in the night sky, and the planet was discovered there within a day. Newton's formulation was later condensed into the inverse-square law: F = G m 1 m 2 r 2 , {\displaystyle F=G{\frac {m_{1}m_{2}}{r^{2}}},} where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant 6.674×10−11 m3⋅kg−1⋅s−2. While G is also called Newton's constant, Newton did not use this constant or formula, he only discussed proportionality. But this allowed him to come to an astounding conclusion we take for granted today: the gravity of the Earth on the Moon is the same as the gravity of the Earth on an apple: M earth ∝ a apple R radius of earth 2 = a moon R lunar orbit 2 {\displaystyle M_{\text{earth}}\propto a_{\text{apple}}R_{\text{radius of earth}}^{2}=a_{\text{moon}}R_{\text{lunar orbit}}^{2}} Using the values known at the time, Newton was able to verify this form of his law. The value of G was eventually measured by Henry Cavendish in 1797.: 31 Newton's theory of gravity ran counter to a key idea of science, both then and now: forces should not rely on instantaneous action at a distance. Newton was well aware of this issue and his decision to continue anyway marked a shift in scientific thinking away from philosophically sound but empirically flawed models.: 44 Scientists like Gottfried Wilhelm Leibniz complained about this aspect of the theory of gravity. : 339 The issue was not resolved until Einstein's work on relativity in the 20th century. Eventually, astronomers noticed an eccentricity in the orbit of the planet Mercury which could not be explained by Newton's theory: the perihelion of the orbit was increasing by about 42.98 arcseconds per century. The most obvious explanation for this discrepancy was an as-yet-undiscovered celestial body, such as a planet orbiting the Sun even closer than Mercury, but all efforts to find such a body turned out to be fruitless. In 1915, Albert Einstein developed a theory of general relativity which was able to accurately model Mercury's orbit. Einstein's theory brought two other ideas with independent histories into the physical theories of gravity: the principle of relativity and non-Euclidean geometry. The principle of relativity, introduced by Galileo and used as a foundational principle by Newton, led to a long and fruitless search for a luminiferous aether after Maxwell's equations demonstrated that light propagated at a fixed speed independent of reference frame. In Newton's mechanics, velocities add: a cannon ball shot from a moving ship would travel with a trajectory which included the motion of the ship. Since light speed was fixed, it was assumed to travel in a fixed, absolute medium. Many experiments sought to reveal this medium but failed and in 1905 Einstein's special relativity theory showed the aether was not needed. Special relativity proposed that mechanics be reformulated to use the Lorentz transformation already applicable to light rather than the Galilean transformation adopted by Newton. Special relativity, as in special case, specifically did not cover gravity.: 4 While relativity was associated with mechanics and thus gravity, the idea of altering geometry only joined the story of gravity once mechanics required the Lorentz transformations. Geometry was an ancient science that gradually broke free of Euclidean limitations when Carl Gauss discovered in the 1800s that surfaces in any number of dimensions could be characterized by a metric, a distance measurement along the shortest path between two points that reduces to Euclidean distance at infinitesimal separation. Gauss' student Bernhard Riemann developed this into a complete geometry by 1854. These geometries are locally flat but have global curvature.: 4 In 1907, Einstein took his first step by using special relativity to create a new form of the equivalence principle. The equivalence of inertial mass and gravitational mass was a known empirical law. The m in Newton's first law, F = m a {\displaystyle F=ma} , has the same value as the m in Newton's law of gravity on Earth, F = G M m / r 2 {\displaystyle F=GMm/r^{2}} . In what he later described as "the happiest thought of my life" Einstein realized this meant that in free-fall, an accelerated coordinate system exists with no local gravitational field. Every description of gravity in any other coordinate system must transform to give no field in the free-fall case, a powerful invariance constraint on all theories of gravity.: 20 Einstein's description of gravity was accepted by the majority of physicists for two reasons. First, by 1910 his special relativity was accepted in German physics and was spreading to other countries. Second, his theory explained experimental results like the perihelion of Mercury and the bending of light around the Sun better than Newton's theory. In 1919, the British astrophysicist Arthur Eddington was able to confirm the predicted deflection of light during that year's solar eclipse. Eddington measured starlight deflections twice those predicted by Newtonian corpuscular theory, in accordance with the predictions of general relativity. Although Eddington's analysis was later disputed, this experiment made Einstein famous almost overnight and caused general relativity to become widely accepted in the scientific community. In 1959, American physicists Robert Pound and Glen Rebka performed an experiment in which they used gamma rays to confirm the prediction of gravitational time dilation. By sending the rays down a 74-foot tower and measuring their frequency at the bottom, the scientists confirmed that light is Doppler shifted as it moves towards a source of gravity. The observed shift also supports the idea that time runs more slowly in the presence of a gravitational field (many more wave crests pass in a given interval). If light moves outward from a strong source of gravity it will be observed with a redshift. The time delay of light passing close to a massive object was first identified by Irwin I. Shapiro in 1964 in interplanetary spacecraft signals. In 1971, scientists made the first-ever discovery of a black hole, in the galaxy Cygnus. The black hole was detected because it was emitting bursts of x-rays as it consumed a smaller star, and it came to be known as Cygnus X-1. This discovery confirmed yet another prediction of general relativity, because Einstein's equations implied that light could not escape from a sufficiently large and compact object. Frame dragging, the idea that a rotating massive object should twist spacetime around it, was confirmed by Gravity Probe B results in 2011. In 2015, the LIGO observatory detected faint gravitational waves, the existence of which had been predicted by general relativity. Scientists believe that the waves emanated from a black hole merger that occurred 1.5 billion light-years away. On Earth Every planetary body (including the Earth) is surrounded by its own gravitational field, which can be conceptualized with Newtonian physics as exerting an attractive force on all objects. Assuming a spherically symmetrical planet, the strength of this field at any given point above the surface is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body. The strength of the gravitational field is numerically equal to the acceleration of objects under its influence. The rate of acceleration of falling objects near the Earth's surface varies very slightly depending on latitude, surface features such as mountains and ridges, and perhaps unusually high or low sub-surface densities. For purposes of weights and measures, a standard gravity value is defined by the International Bureau of Weights and Measures, under the International System of Units (SI). The force of gravity experienced by objects on Earth's surface is the vector sum of two forces: (a) The gravitational attraction in accordance with Newton's universal law of gravitation, and (b) the centrifugal force, which results from the choice of an earthbound, rotating frame of reference. The force of gravity is weakest at the equator because of the centrifugal force caused by the Earth's rotation and because points on the equator are farthest from the center of the Earth. The force of gravity varies with latitude, and the resultant acceleration increases from about 9.780 m/s2 at the Equator to about 9.832 m/s2 at the poles. Waves on oceans, lakes, and other bodies of water occur when the gravitational equilibrium at the surface of the water is disturbed by for example wind. Similar effects occur in the atmosphere where equilibrium is disturbed by thermal weather fronts or mountain ranges. Orbits Planets orbit the Sun in an ellipse as a consequence of the law of gravity. Similarly the Moon and artificial satellites orbit the Earth. Conceptually two objects in orbit are both falling off of the curve they would travel in if the force of gravity were not pulling them together. Since the force of gravity is universal, all planets attract each other with the most massive and closest pair have the most mutual affect. This means orbits are more complex than simple ellipses. Astrophysics During star formation, gravitational attraction in a cloud of hydrogen gas competes with thermal gas pressure. As the gas density increases, the temperature rises, then the gas radiates energy, allowing additional gravitational condensation. If the mass of gas in the region is low, the process continues until a brown dwarf or gas-giant planet is produced. If more mass is available, the additional gravitational energy allows the central region to reach pressures sufficient for nuclear fusion, forming a star. In a star, again the gravitational attraction competes, with thermal and radiation pressure in hydrostatic equilibrium until the star's atomic fuel runs out. The next phase depends upon the total mass of the star. Very low mass stars slowly cool as white dwarf stars with a small core balancing gravitational attraction with electron degeneracy pressure. Stars with masses similar to the Sun go through a red giant phase before becoming white dwarf stars. Higher mass stars have complex core structures that burn helium and high atomic number elements ultimately producing an iron core. As their fuel runs out, these stars become unstable producing a supernova. The result can be a neutron star where gravitational attraction balances neutron degeneracy pressure or, for even higher masses, a black hole where gravity operates alone with such intensity that even light cannot escape.: 121 General relativity predicts that energy can be transported out of a system through gravitational radiation also known as gravitational waves. The first indirect evidence for gravitational radiation was through measurements of the Hulse–Taylor binary in 1973. This system consists of a pulsar and neutron star in orbit around one another. Its orbital period has decreased since its initial discovery due to a loss of energy, which is consistent for the amount of energy loss due to gravitational radiation. This research was awarded the Nobel Prize in Physics in 1993. The first direct evidence for gravitational radiation was measured on 14 September 2015 by the LIGO detectors. The gravitational waves emitted during the collision of two black holes 1.3 billion light years from Earth were measured. This observation confirms the theoretical predictions of Einstein and others that such waves exist. It also opens the way for practical observation and understanding of the nature of gravity and events in the Universe including the Big Bang. Neutron star and black hole formation also create detectable amounts of gravitational radiation. This research was awarded the Nobel Prize in Physics in 2017. At the cosmological scale, gravity is a dominant player. About 5/6 of the total mass in the universe consists of dark matter which interacts through gravity but not through electromagnetic interactions. The gravitation of clumps of dark matter known as dark matter halos attract hydrogen gas leading to stars and galaxies. Gravity acts on light and matter equally, meaning that a sufficiently massive object could warp light around it and create a gravitational lens. This phenomenon was first confirmed by observation in 1979 using the 2.1 meter telescope at Kitt Peak National Observatory in Arizona, which saw two mirror images of the same quasar whose light had been bent around the galaxy YGKOW G1. Many subsequent observations of gravitational lensing provide additional evidence for substantial amounts of dark matter around galaxies. Gravitational lenses do not focus like eyeglass lenses, but rather lead to annular shapes called Einstein rings.: 370 In October 2017, the LIGO and Virgo interferometer detectors received gravitational wave signals 2 seconds before gamma ray satellites and optical telescopes seeing signals from the same direction, from a source about 130 million light-years away. This confirmed that the speed of gravitational waves was the same as the speed of light. There are some observations that are not adequately accounted for, which may point to the need for better theories of gravity or perhaps be explained in other ways. Models The physical models of gravity, like all physical models, are expressed mathematically. Physicists use several different models, depending on the problem to be solved or for the purpose of gaining physical intuition.: 44 Newton's inverse square law models gravity as a force F between two objects proportional to their mass, m: F 12 = G m 1 m 2 r 12 2 {\displaystyle F_{12}=G{\frac {m_{1}m_{2}}{{r_{12}}^{2}}}} This gravitational force causes the objects to accelerate towards each other unless balanced by other forces. The force is "nonlocal": it depends on the mass of an object at a distance.: 44 Scientists from Newton onwards recognized that this action at a distance does not explain the root cause of the force; this lack of a root cause was raised against Newton's theory at first.: 339 Nevertheless the model explains a vast number of physical effects including cannon ball trajectories, tidal motion and planetary orbits.: 4 Creating a theory independent of action at a distance requires combining the concept of relativity with gravity, an enormously complex task using the Newtonian model.: 48 A second equivalent approach to model gravity uses fields.: 44 In physics, a field represents a physical phenomenon using a mathematical entity associated with each point in a space. Different field theories use different entities and concepts of space. For classical field theories of gravity, the entities can be vectors associated with points in a 3-dimensional space. Each vector gives the force experienced by an insignificantly small test mass at that point in space. The force vector at each point can be computed as the direction of the highest rate of change in the gravitational potential, a single number at each point in space. The three-dimensional map of the potential or of the gravitational field provides a visual representation of the effect of the gravitational effect of all surrounding objects.[dubious – discuss] Field models are local: the field values on a sphere completely determine the effects of gravity with the sphere.: 45 Fields are also used in general relativity, but rather than vectors over Euclidean space, the entities are tensors over spacetime. The Einstein field equations relate the 10 independent values in the tensors to the distribution of mass and energy in space.[dubious – discuss] A third completely different way to derive a model of gravity is based on action principles. This formulation represents the effects of gravity on a system in a mathematically abstract way. The state of the system, for example the position and velocity of every particle, is expressed as a single mathematical entity. Each state has an associated energy property called the Lagrangian; the physically allowed changes to the state of the system minimize the value of this property. The path of the state is not a path in physical space, but rather in a high-dimensional state space: each point along the path corresponds to a different position and or velocity collectively for all particles in the system. This formulation does not express the forces or fields of the individual particles.: 46 Modern theories of physics rely on these action principles.: 396 The Einstein field equation for gravitation can be derived from the Einstein–Hilbert action.: 388 General relativity In modern physics, general relativity is considered the most successful theory of gravitation. Physicists continue to work to find solutions to the Einstein field equations that form the basis of general relativity and continue to test the theory, finding excellent agreement in all cases.: p.9 Any theory of gravity must conform to the requirements of special relativity and experimental observations. Newton's theory of gravity assumes action at a distance and therefore cannot be reconciled with special relativity. The simplest generalization of Newton's approach would be a scalar field theory with the gravitational potential represented by a single number in a 4-dimensional spacetime. However, this type of theory fails to predict gravitational redshift or the deviation of light by matter and gives values for the precession of Mercury which are incorrect. A vector field theory predicts negative energy gravitational waves so it also fails. Furthermore, no theory without curvature in spacetime can be consistent with special relativity. The simplest theory consistent with special relativity and the well-studied observations is general relativity. Unlike Newton's formula with one parameter, G, force in general relativity is terms of 10 numbers formed in to a metric tensor.: 70 In general relativity the effects of gravitation are described in different ways in different frames of reference. In a free-falling or co-moving coordinate system, an object travels in a straight line. In other coordinate systems, the object accelerates and thus is seen to move under a force. The path in spacetime (not 3D space) taken by a free-falling object is called a geodesic and the length of that path as measured by time in the objects frame is the shortest (or rarely the longest) one. Consequently the effect of gravity can be described as curving spacetime. In a weak stationary gravitational field, general relativity reduces to Newton's equations. The corrections introduced by general relativity on Earth are on the order of 1 part in a billion.: 77 The Einstein field equations are a system of 10 partial differential equations which describe how matter affects the curvature of spacetime. The system may be expressed in the form G μ ν + Λ g μ ν = κ T μ ν , {\displaystyle G_{\mu \nu }+\Lambda g_{\mu \nu }=\kappa T_{\mu \nu },} where Gμν is the Einstein tensor, gμν is the metric tensor, Tμν is the stress–energy tensor, Λ is the cosmological constant, G {\displaystyle G} is the Newtonian constant of gravitation and c {\displaystyle c} is the speed of light. The constant κ = 8 π G c 4 {\displaystyle \kappa ={\frac {8\pi G}{c^{4}}}} is referred to as the Einstein gravitational constant. The non-linear second-order Einstein field equations are extremely complex and have been solved in only a few special cases. These cases however have been transformational in our understanding of the cosmos. Several solutions are the basis for understanding black holes and for our modern model of the evolution of the universe since the Big Bang.: 227 Testing the predictions of general relativity has historically been difficult, because they are almost identical to the predictions of Newtonian gravity for small energies and masses. A wide range of experiments provided support of general relativity.: 1–9 Today, Einstein's theory of relativity is used for all gravitational calculations where absolute precision is desired, although Newton's inverse-square law is accurate enough for virtually all ordinary calculations.: 79 Despite its success in predicting the effects of gravity at large scales, general relativity is ultimately incompatible with quantum mechanics. This is because general relativity describes gravity as a smooth, continuous distortion of spacetime, while quantum mechanics holds that all forces arise from the exchange of discrete particles known as quanta. This contradiction is especially vexing to physicists because the other three fundamental forces (strong force, weak force and electromagnetism) were reconciled with a quantum framework decades ago. As a result, researchers have begun to search for a theory that could unite both gravity and quantum mechanics under a more general framework. One path is to describe gravity in the framework of quantum field theory (QFT), which has been successful to accurately describe the other fundamental interactions. The electromagnetic force arises from an exchange of virtual photons, where the QFT description of gravity is that there is an exchange of virtual gravitons. This description reproduces general relativity in the classical limit. However, this approach fails at short distances of the order of the Planck length, where a more complete theory of quantum gravity (or a new approach to quantum mechanics) is required. General relativity has withstood many tests over a large range of mass and size scales. When applied to interpret astronomical observations, cosmological models based on general relativity introduce two components to the universe, dark matter and dark energy, the nature of which is currently an unsolved problem in physics. The many successful, high precision predictions of the standard model of cosmology has led astrophysicists to conclude it and thus general relativity will be the basis for future progress. However, dark matter is not supported by the Standard Model of particle physics, physical models for dark energy do not match cosmological data, and some cosmological observations are inconsistent. These issues have led to the study of alternative theories of gravity. See also References Further reading External links |
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Contents Middle East The Middle East[b] is a geopolitical region encompassing the Arabian Peninsula, Egypt, Iran, Iraq, the Levant, and Turkey. The term came into widespread usage by Western European nations in the early 20th century as a replacement of the term Near East (both were in contrast to the Far East). The term "Middle East" has led to some confusion over its changing definitions. Since the late 20th century, it has been criticized as being too Eurocentric. The region includes the vast majority of the territories included in the closely associated definition of West Asia, but without the South Caucasus. It also includes all of Egypt (not just the Sinai region) and all of Turkey (including East Thrace). Most Middle Eastern countries (13 out of 18) are part of the Arab world. The three most populous countries in the region are Egypt, Iran, and Turkey, while Saudi Arabia is the largest Middle Eastern country by area. The history of the Middle East dates back to ancient times, and it was long considered the "cradle of civilization". The geopolitical importance of the region has been recognized and competed for during millennia. The Abrahamic religions (Judaism, Christianity, and Islam) have their origins in the Middle East. Arabs constitute the main ethnic group in the region, followed by Turks, Persians, Kurds, Jews, and Assyrians. The Middle East generally has a hot, arid climate, especially in the Arabian and Egyptian regions. Several major rivers provide irrigation to support agriculture in limited areas here, such as the Nile Delta in Egypt, the Tigris and Euphrates watersheds of Mesopotamia, and the basin of the Jordan River that spans most of the Levant. These regions are collectively known as the Fertile Crescent, and comprise the core of what historians had long referred to as the cradle of civilization; multiple regions of the world have since been classified as also having developed independent, original civilizations. Conversely, the Levantine coast and most of Turkey have relatively temperate climates typical of the Mediterranean, with dry summers and cool, wet winters. Most of the countries that border the Persian Gulf have vast reserves of petroleum. Monarchs of the Arabian Peninsula in particular have benefitted economically from petroleum exports. Because of the arid climate and dependence on the fossil fuel industry, the Middle East is both a major contributor to climate change and a region that is expected to be severely adversely affected by it. Other concepts of the region exist, including the broader Middle East and North Africa (MENA), which includes states of the Maghreb and the Sudan. The term the "Greater Middle East" also includes Afghanistan, Mauritania, Pakistan, as well as parts of East Africa, and sometimes Central Asia and the South Caucasus. Terminology The term "Middle East" may have originated in the 1850s in the British India Office. However, it became more widely known when United States naval strategist Alfred Thayer Mahan used the term in 1902 to "designate the area between Arabia and India". During this time the British and Russian empires were vying for influence in Central Asia, a rivalry that would become known as the Great Game. Mahan realized not only the strategic importance of the region, but also of its center, the Persian Gulf. He labeled the area surrounding the Persian Gulf as the Middle East. He said that, beyond Egypt's Suez Canal, the Gulf was the most important passage for Britain to control in order to keep the Russians from advancing towards British India. Mahan first used the term in his article "The Persian Gulf and International Relations", published in September 1902 in the National Review, a British journal. The Middle East, if I may adopt a term which I have not seen, will some day need its Malta, as well as its Gibraltar; it does not follow that either will be in the Persian Gulf. Naval force has the quality of mobility which carries with it the privilege of temporary absences; but it needs to find on every scene of operation established bases of refit, of supply, and in case of disaster, of security. The British Navy should have the facility to concentrate in force if occasion arise, about Aden, India, and the Persian Gulf. Mahan's article was reprinted in The Times and followed in October by a 20-article series entitled "The Middle Eastern Question", written by Sir Ignatius Valentine Chirol. During this series, Sir Ignatius expanded the definition of Middle East to include "those regions of Asia which extend to the borders of India or command the approaches to India." After the series ended in 1903, The Times removed quotation marks from subsequent uses of the term. Until World War II, it was customary to refer to areas centered on Turkey and the eastern shore of the Mediterranean as the "Near East", while the "Far East" centered on China, India and Japan. The Middle East was then defined as the area from Mesopotamia to Burma; namely, the area between the Near East and the Far East. This area broadly corresponds to South Asia. In the late 1930s, the British established the Middle East Command, which was based in Cairo, for its military forces in the region. After that time, the term "Middle East" gained broader usage in Europe and the United States. Following World War II, for example, the Middle East Institute was founded in Washington, D.C. in 1946. The corresponding adjective is Middle Eastern and the derived noun is Middle Easterner. While non-Eurocentric terms such as "Southwest Asia" or "Swasia" have been sparsely used, the classification of the African country, Egypt, among those counted in the Middle East challenges the usefulness of using such terms. The description Middle has also led to some confusion over changing definitions. Before the First World War, "Near East" was used in English to refer to the Balkans and the Ottoman Empire, while "Middle East" referred to the Caucasus, Persia, and Arabian lands, and sometimes Afghanistan, India and others. In contrast, "Far East" referred to the countries of East Asia (e.g. China, Japan, and Korea). With the collapse of the Ottoman Empire in 1918, "Near East" largely fell out of common use in English, while "Middle East" came to be applied to the emerging independent countries of the Islamic world. However, the usage "Near East" was retained by a variety of academic disciplines, including archaeology and ancient history. In their usage, the term describes an area identical to the term Middle East, which is not used by these disciplines (see ancient Near East).[citation needed] The first official use of the term "Middle East" by the United States government was in the 1957 Eisenhower Doctrine, which pertained to the Suez Crisis. Secretary of State John Foster Dulles defined the Middle East as "the area lying between and including Libya on the west and Pakistan on the east, Syria and Iraq on the North and the Arabian peninsula to the south, plus the Sudan and Ethiopia." In 1958, the State Department explained that the terms "Near East" and "Middle East" were interchangeable, and defined the region as including only Egypt, Syria, Israel, Lebanon, Jordan, Iraq, Saudi Arabia, Kuwait, Bahrain, and Qatar. Since the late 20th century, scholars and journalists from the region, such as journalist Louay Khraish and historian Hassan Hanafi have criticized the use of "Middle East" as a Eurocentric and colonialist term. The Associated Press Stylebook of 2004 says that Near East formerly referred to the farther west countries while Middle East referred to the eastern ones, but that now they are synonymous. It instructs: Use Middle East unless Near East is used by a source in a story. Mideast is also acceptable, but Middle East is preferred. European languages have adopted terms similar to Near East and Middle East. Since these are based on a relative description, the meanings depend on the country and are generally different from the English terms. In German the term Naher Osten (Near East) is still in common use (nowadays the term Mittlerer Osten is more and more common in press texts translated from English sources, albeit having a distinct meaning). In the four Slavic languages, Russian Ближний Восток or Blizhniy Vostok, Bulgarian Близкия Изток, Polish Bliski Wschód or Croatian Bliski istok (terms meaning Near East are the only appropriate ones for the region). However, some European languages do have "Middle East" equivalents, such as French Moyen-Orient, Swedish Mellanöstern, Spanish Oriente Medio or Medio Oriente, Greek is Μέση Ανατολή (Mesi Anatoli), and Italian Medio Oriente.[c] Perhaps because of the political influence of the United States and Europe, and the prominence of Western press, the Arabic equivalent of Middle East (Arabic: الشرق الأوسط ash-Sharq al-Awsaṭ) has become standard usage in the mainstream Arabic press. It comprises the same meaning as the term "Middle East" in North American and Western European usage. The designation, Mashriq, also from the Arabic root for East, also denotes a variously defined region around the Levant, the eastern part of the Arabic-speaking world (as opposed to the Maghreb, the western part). Even though the term originated in the West, countries of the Middle East that use languages other than Arabic also use that term in translation. For instance, the Persian equivalent for Middle East is خاورمیانه (Khāvar-e miyāneh), the Hebrew is המזרח התיכון (hamizrach hatikhon), and the Turkish is Orta Doğu. Countries and territory Traditionally included within the Middle East are Arabia, Asia Minor, East Thrace, Egypt, Iran, the Levant, Mesopotamia, and the Socotra Archipelago. The region includes 17 UN-recognized countries and one British Overseas Territory. Various concepts are often paralleled to the Middle East, most notably the Near East, Fertile Crescent, and Levant. These are geographical concepts, which refer to large sections of the modern-day Middle East, with the Near East being the closest to the Middle East in its geographical meaning. Due to it primarily being Arabic speaking, the Maghreb region of North Africa is sometimes included. "Greater Middle East" is a political term coined by the second Bush administration in the first decade of the 21st century to denote various countries, pertaining to the Muslim world, specifically Afghanistan, Iran, Pakistan, and Turkey. Various Central Asian countries are sometimes also included. History The Middle East lies at the juncture of Africa and Eurasia and of the Indian Ocean and the Mediterranean Sea (see also: Indo-Mediterranean). It is the birthplace and spiritual center of religions such as Christianity, Islam, Judaism, Manichaeism, Yezidi, Druze, Yarsan, and Mandeanism, and in Iran, Mithraism, Zoroastrianism, Manicheanism, and the Baháʼí Faith. Throughout its history the Middle East has been a major center of world affairs; a strategically, economically, politically, culturally, and religiously sensitive area. The region is one of the regions where agriculture was independently discovered, and from the Middle East it was spread, during the Neolithic, to different regions of the world such as Europe, the Indus Valley and Eastern Africa. Prior to the formation of civilizations, advanced cultures formed all over the Middle East during the Stone Age. The search for agricultural lands by agriculturalists, and pastoral lands by herdsmen meant different migrations took place within the region and shaped its ethnic and demographic makeup. The Middle East is widely and most famously known as the cradle of civilization. The world's earliest civilizations, Mesopotamia (Sumer, Akkad, Assyria and Babylonia), ancient Egypt and Kish in the Levant, all originated in the Fertile Crescent and Nile Valley regions of the ancient Near East. These were followed by the Hittite, Greek, Hurrian and Urartian civilisations of Asia Minor; Elam, Persia and Median civilizations in Iran, as well as the civilizations of the Levant (such as Ebla, Mari, Nagar, Ugarit, Canaan, Aramea, Mitanni, Phoenicia and Israel) and the Arabian Peninsula (Magan, Sheba, Ubar). The Near East was first largely unified under the Neo Assyrian Empire, then the Achaemenid Empire followed later by the Macedonian Empire and after this to some degree by the Iranian empires (namely the Parthian and Sassanid Empires), the Roman Empire and Byzantine Empire. The region served as the intellectual and economic center of the Roman Empire and played an exceptionally important role due to its periphery on the Sassanid Empire. Thus, the Romans stationed up to five or six of their legions in the region for the sole purpose of defending it from Sassanid and Bedouin raids and invasions. From the 4th century CE onwards, the Middle East became the center of the two main powers at the time, the Byzantine Empire and the Sassanid Empire. However, it would be the later Islamic Caliphates of the Middle Ages, or Islamic Golden Age which began with the Islamic conquest of the region in the 7th century AD, that would first unify the entire Middle East as a distinct region and create the dominant Islamic Arab ethnic identity that largely (but not exclusively) persists today. The 4 caliphates that dominated the Middle East for more than 600 years were the Rashidun Caliphate, the Umayyad caliphate, the Abbasid caliphate and the Fatimid caliphate. Additionally, the Mongols would come to dominate the region, the Kingdom of Armenia would incorporate parts of the region to their domain, the Seljuks would rule the region and spread Turko-Persian culture, and the Franks would found the Crusader states that would stand for roughly two centuries. Josiah Russell estimates the population of what he calls "Islamic territory" as roughly 12.5 million in 1000 – Anatolia 8 million, Syria 2 million, and Egypt 1.5 million. From the 16th century onward, the Middle East came to be dominated, once again, by two main powers: the Ottoman Empire and the Safavid dynasty. The modern Middle East began after World War I, when the Ottoman Empire, which was allied with the Central Powers, was defeated by the Allies and partitioned into a number of separate nations, initially under British and French Mandates. Other defining events in this transformation included the establishment of Israel in 1948 and the eventual departure of European powers, notably Britain and France by the end of the 1960s. They were supplanted in some part by the rising influence of the United States from the 1970s onwards. In the 20th century, the region's significant stocks of crude oil gave it new strategic and economic importance. Mass production of oil began around 1945, with Saudi Arabia, Iran, Kuwait, Iraq, and the United Arab Emirates having large quantities of oil. Estimated oil reserves, especially in Saudi Arabia and Iran, are some of the highest in the world, and the international oil cartel OPEC is dominated by Middle Eastern countries. During the Cold War, the Middle East was a theater of ideological struggle between the two superpowers and their allies: NATO and the United States on one side, and the Soviet Union and Warsaw Pact on the other, as they competed to influence regional allies. Besides the political reasons there was also the "ideological conflict" between the two systems. Moreover, as Louise Fawcett argues, among many important areas of contention, or perhaps more accurately of anxiety, were, first, the desires of the superpowers to gain strategic advantage in the region, second, the fact that the region contained some two-thirds of the world's oil reserves in a context where oil was becoming increasingly vital to the economy of the Western world [...] Within this contextual framework, the United States sought to divert the Arab world from Soviet influence. Throughout the 20th and 21st centuries, the region has experienced both periods of relative peace and tolerance and periods of conflict particularly between Sunnis and Shiites. Geography In 2018, the MENA region emitted 3.2 billion tonnes of carbon dioxide and produced 8.7% of global greenhouse gas emissions (GHG) despite making up only 6% of the global population. These emissions are mostly from the energy sector, an integral component of many Middle Eastern and North African economies due to the extensive oil and natural gas reserves that are found within the region. The Middle East region is one of the most vulnerable to climate change. The impacts include increase in drought conditions, aridity, heatwaves and sea level rise. Sharp global temperature and sea level changes, shifting precipitation patterns and increased frequency of extreme weather events are some of the main impacts of climate change as identified by the Intergovernmental Panel on Climate Change (IPCC). The MENA region is especially vulnerable to such impacts due to its arid and semi-arid environment, facing climatic challenges such as low rainfall, high temperatures and dry soil. The climatic conditions that foster such challenges for MENA are projected by the IPCC to worsen throughout the 21st century. If greenhouse gas emissions are not significantly reduced, part of the MENA region risks becoming uninhabitable before the year 2100. Climate change is expected to put significant strain on already scarce water and agricultural resources within the MENA region, threatening the national security and political stability of all included countries. Over 60 percent of the region's population lives in high and very high water-stressed areas compared to the global average of 35 percent. This has prompted some MENA countries to engage with the issue of climate change on an international level through environmental accords such as the Paris Agreement. Law and policy are also being established on a national level amongst MENA countries, with a focus on the development of renewable energies. Economy Middle Eastern economies range from being very poor (such as Gaza and Yemen) to extremely wealthy nations (such as Qatar and UAE). According to the International Monetary Fund, the three largest Middle Eastern economies in nominal GDP in 2023 were Saudi Arabia ($1.06 trillion), Turkey ($1.03 trillion), and Israel ($0.54 trillion). For nominal GDP per person, the highest ranking countries are Qatar ($83,891), Israel ($55,535), the United Arab Emirates ($49,451) and Cyprus ($33,807). Turkey ($3.6 trillion), Saudi Arabia ($2.3 trillion), and Iran ($1.7 trillion) had the largest economies in terms of GDP PPP. For GDP PPP per person, the highest-ranking countries are Qatar ($124,834), the United Arab Emirates ($88,221), Saudi Arabia ($64,836), Bahrain ($60,596) and Israel ($54,997). The lowest-ranking country in the Middle East, in terms of GDP nominal per capita, is Yemen ($573). The economic structure of Middle Eastern nations are different because while some are heavily dependent on export of only oil and oil-related products (Saudi Arabia, the UAE and Kuwait), others have a highly diverse economic base (such as Cyprus, Israel, Turkey and Egypt). Industries of the Middle Eastern region include oil and oil-related products, agriculture, cotton, cattle, dairy, textiles, leather products, surgical instruments, defence equipment (guns, ammunition, tanks, submarines, fighter jets, UAVs, and missiles). Banking is an important sector, especially for UAE and Bahrain. With the exception of Cyprus, Turkey, Egypt, Lebanon and Israel, tourism has been a relatively undeveloped area of the economy, in part because of the socially conservative nature of the region as well as political turmoil in certain regions. Since the end of the COVID pandemic however, countries such as the UAE, Bahrain, and Jordan have begun attracting greater numbers of tourists because of improving tourist facilities and the relaxing of tourism-related restrictive policies. Unemployment is high in the Middle East and North Africa region, particularly among people aged 15–29, a demographic representing 30% of the region's population. The total regional unemployment rate in 2025 is 10.8%, and among youth is as high as 28%. Demographics Arabs constitute the largest ethnic group in the Middle East, followed by various Iranian peoples and then by Turkic peoples (Turkish, Azeris, Syrian Turkmen, and Iraqi Turkmen). Native ethnic groups of the region include, in addition to Arabs, Arameans, Assyrians, Baloch, Berbers, Copts, Druze, Greek Cypriots, Jews, Kurds, Lurs, Mandaeans, Persians, Samaritans, Shabaks, Tats, and Zazas. European ethnic groups that form a diaspora in the region include Albanians, Bosniaks, Circassians (including Kabardians), Crimean Tatars, Greeks, Franco-Levantines, Italo-Levantines, and Iraqi Turkmens. Among other migrant populations are Chinese, Filipinos, Indians, Indonesians, Pakistanis, Pashtuns, Romani, and Afro-Arabs. "Migration has always provided an important vent for labor market pressures in the Middle East. For the period between the 1970s and 1990s, the Arab states of the Persian Gulf in particular provided a rich source of employment for workers from Egypt, Yemen and the countries of the Levant, while Europe had attracted young workers from North African countries due both to proximity and the legacy of colonial ties between France and the majority of North African states." According to the International Organization for Migration, there are 13 million first-generation migrants from Arab nations in the world, of which 5.8 reside in other Arab countries. Expatriates from Arab countries contribute to the circulation of financial and human capital in the region and thus significantly promote regional development. In 2009 Arab countries received a total of US$35.1 billion in remittance in-flows and remittances sent to Jordan, Egypt and Lebanon from other Arab countries are 40 to 190 per cent higher than trade revenues between these and other Arab countries. In Somalia, the Somali Civil War has greatly increased the size of the Somali diaspora, as many of the best educated Somalis left for Middle Eastern countries as well as Europe and North America. Non-Arab Middle Eastern countries such as Turkey, Israel and Iran are also subject to important migration dynamics. A fair proportion of those migrating from Arab nations are from ethnic and religious minorities facing persecution and are not necessarily ethnic Arabs, Iranians or Turks.[citation needed] Large numbers of Kurds, Jews, Assyrians, Greeks and Armenians as well as many Mandeans have left nations such as Iraq, Iran, Syria and Turkey for these reasons during the last century. In Iran, many religious minorities such as Christians, Baháʼís, Jews and Zoroastrians have left since the Islamic Revolution of 1979. The Middle East is very diverse when it comes to religions, many of which originated there. Islam is the largest religion in the Middle East, but other faiths that originated there, such as Judaism and Christianity, are also well represented. Christian communities have played a vital role in the Middle East, and they represent 78% of Cyprus population, and 40.5% of Lebanon, where the Lebanese president, half of the cabinet, and half of the parliament follow one of the various Lebanese Christian rites. There are also important minority religions like the Baháʼí Faith, Yarsanism, Yazidism, Zoroastrianism, Mandaeism, Druze, and Shabakism, and in ancient times the region was home to Mesopotamian religions, Canaanite religions, Manichaeism, Mithraism and various monotheist gnostic sects. The six top languages, in terms of numbers of speakers, are Arabic, Persian, Turkish, Kurdish, Modern Hebrew and Greek. About 20 minority languages are also spoken in the Middle East. Arabic, with all its dialects, is the most widely spoken language in the Middle East, with Literary Arabic being official in all North African and in most West Asian countries. Arabic dialects are also spoken in some adjacent areas in neighbouring Middle Eastern non-Arab countries. It is a member of the Semitic branch of the Afro-Asiatic languages. Several Modern South Arabian languages such as Mehri and Soqotri are also spoken in Yemen and Oman. Another Semitic language is Aramaic and its dialects are spoken mainly by Assyrians and Mandaeans, with Western Aramaic still spoken in two villages near Damascus, Syria. There is also an Oasis Berber-speaking community in Egypt where the language is also known as Siwa. It is a non-Semitic Afro-Asiatic sister language. Persian is the second most spoken language. While it is primarily spoken in Iran and some border areas in neighbouring countries, the country is one of the region's largest and most populous. It belongs to the Indo-Iranian branch of the family of Indo-European languages. Other Western Iranic languages spoken in the region include Achomi, Daylami, Kurdish dialects, Semmani, Lurish, amongst many others. The close third-most widely spoken language, Turkish, is largely confined to Turkey, which is also one of the region's largest and most populous countries, but it is present in areas in neighboring countries. It is a member of the Turkic languages, which have their origins in East Asia. Another Turkic language, Azerbaijani, is spoken by Azerbaijanis in Iran. The fourth-most widely spoken language, Kurdish, is spoken in the countries of Iran, Iraq, Syria and Turkey, Sorani Kurdish is the second official language in Iraq (instated after the 2005 constitution) after Arabic. Hebrew is the official language of Israel, with Arabic given a special status after the 2018 Basic law lowered its status from an official language prior to 2018. Hebrew is spoken and used by over 80% of Israel's population, the other 20% using Arabic. Modern Hebrew only began being spoken in the 20th century after being revived in the late 19th century by Elizer Ben-Yehuda (Elizer Perlman) and European Jewish settlers, with the first native Hebrew speaker being born in 1882. Greek is one of the two official languages of Cyprus, and the country's main language. Small communities of Greek speakers exist all around the Middle East; until the 20th century it was also widely spoken in Asia Minor (being the second most spoken language there, after Turkish) and Egypt. During the antiquity, Ancient Greek was the lingua franca for many areas of the western Middle East and until the Muslim expansion it was widely spoken there as well. Until the late 11th century, it was also the main spoken language in Asia Minor; after that it was gradually replaced by the Turkish language as the Anatolian Turks expanded and the local Greeks were assimilated, especially in the interior. English is one of the official languages of Akrotiri and Dhekelia. It is also commonly taught and used as a foreign second language, in countries such as Egypt, Jordan, Iran, Iraq, Qatar, Bahrain, United Arab Emirates and Kuwait. It is also a main language in some Emirates of the United Arab Emirates. It is also spoken as native language by Jewish immigrants from Anglophone countries (UK, US, Australia) in Israel and understood widely as second language there. French is taught and used in many government facilities and media in Lebanon, and is taught in some primary and secondary schools of Egypt and Syria. Maltese, a Semitic language mainly spoken in Europe, is used by the Franco-Maltese diaspora in Egypt. Due to widespread immigration of French Jews to Israel, it is the native language of approximately 200,000 Jews in Israel. Armenian speakers are to be found in the region. Georgian is spoken by the Georgian diaspora. Russian is spoken by a large portion of the Israeli population, because of emigration in the late 1990s. Russian today is a popular unofficial language in use in Israel; news, radio and sign boards can be found in Russian around the country after Hebrew and Arabic. Circassian is also spoken by the diaspora in the region and by almost all Circassians in Israel who speak Hebrew and English as well. The largest Romanian-speaking community in the Middle East is found in Israel, where as of 1995[update] Romanian is spoken by 5% of the population.[d] Bengali, Hindi and Urdu are widely spoken by migrant communities in many Middle Eastern countries, such as Saudi Arabia (where 20–25% of the population is South Asian), the United Arab Emirates (where 50–55% of the population is South Asian), and Qatar, which have large numbers of Pakistani, Bangladeshi and Indian immigrants. Culture The Middle East has recently become more prominent in hosting global sport events due to its wealth and desire to diversify its economy. The South Asian diaspora is a major backer of cricket in the region. See also Notes References Further reading External links 29°N 41°E / 29°N 41°E / 29; 41 |
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Contents Maor Farid Dr. Maor Farid (Hebrew: מאור פריד; born April 20, 1992) is an Israeli scientist, engineer and artificial intelligence researcher at Massachusetts Institute of Technology, social activist, and author. He is the founder and CEO of Learn to Succeed (Hebrew: ללמוד להצליח) for empowering of youths from the Israeli socio-economic periphery and youths at risk, a regional manager of the Israeli center of ScienceAbroad at MIT, and an activist in the American Technion Society. He is an alumnus of Unit 8200, and a fellow of Fulbright Program and the Israel Scholarship Educational Foundation [he]. Dr. Farid was elected to the Forbes 30 Under 30 list of 2019, and won the Moskowitz Prize for Zionism. Early life Maor was born in Ness Ziona, a city in central Israel, as the eldest son for parents from immigrating families of Mizrahi Jews from Iraq and Libya. Maor suffered from Attention deficit hyperactivity disorder (ADHD) from a young age, and was classified as a problematic and violent student. His ADHD issues were diagnosed only after he began his university studies. However, inspired by his parents' background, he aspired to excel at school for a better future for his family. During elementary school, Maor attended local quizzes about Jewish history and Zionism, which significantly shaped his identity and national perspective. Farid graduated high school with the highest GPA in school. Later he was recruited to the Israel Defense Forces and drafted to the Brakim Program [he] – an excellence program of the Israeli Intelligence Corps for training leading R&D officers for the Israeli military and defense industry. Maor graduated the program with honors and was elected by the Israeli Prime Minister's Office and Unit 8200, where he served as an artificial intelligence researcher, officer, and commander. During his Military service, he received various honors and awards, such as the Excellent Scientist Award, given to the top three academics serving in the Israel Defense Forces. In 2019, Farid completed his military service in the rank of a Captain. Education and academic career As part of the (4 years) Brakim Program, Maor completed his Bachelor's and Master's degrees at the Technion in Mechanical Engineering with honors. Then, he initiated his Ph.D. research as a collaboration with the Israel Atomic Energy Commission (IAEC) in parallel to his duty military service. The main goals of his Ph.D. research were predicting irreversible effects of major earthquakes on Israel's nuclear facilities, and improving their seismic resistance using energy absorption technologies. The mathematical models developed by Farid were able to forecast earthquake effects on facilities with major hazard potential, and predicted the failure of liquid storage tanks due to earthquakes took place in Italy (2012) and Mexico (2017). The energy absorption technologies used, increased in up to 90% the seismic resistance abilities of those sensitive facilities. The research results were published in multiple papers in peer-reviewed academic journals and presented in international academic conferences. Later, this research expanded to an official collaboration between the Technion and the Shimon Peres Negev Nuclear Research Center, which aims to implement the findings obtained on existing sensitive systems, and won funding of 1.5 million NIS from the Pazy foundation of the Israel Atomic Energy Commission and the Council for Higher Education. In 2017, Farid completed his Ph.D. and as the youngest graduate at the Technion for that year, at the age of 24. In the graduation ceremonies, he honored his parents to receive the diplomas on his behalf. At the same year, he served as a lecturer at Ben-Gurion University in an original course he developed as a solution for knowledge gaps he identified in the Israeli defense industry. In 2018, Dr. Farid served as an artificial intelligence researcher at a Data Science team of Unit 8200, where he developed machine learning-based solutions for military and operational needs. In 2019, Farid won the Fulbright and the Israel Scholarship Educational Foundation scholarships, and was accepted to post-doctoral position at Massachusetts Institute of Technology where he develops real-time methods for predicting earthquake effects using machine learning techniques. In 2020, Farid was accepted to the Emerging Leaders Program at Harvard Kennedy School in Cambridge, Massachusetts. At the same year, he received the excellence research grant of the Israel Academy of Sciences and Humanities for leading his research in collaboration between MIT and the Technion. Social activism Farid social activism focuses on empowering youths from disadvantaged backgrounds from an early age. In 2010–2015, he served as a mentor of a robotics team from Dimona in FIRST Robotics Competition, a mathematics tutor in "Aharai!" [he] program for high-school students at risk in Dimona and Be'er Sheva, and a mentor and private tutor of adolescence and reserve duty soldiers from disadvantaged backgrounds. In 2010, he initiated "Learn to Succeed" (Hebrew: ללמוד להצליח) project, for mitigating the social gaps in the Israeli society by empowering youths from the social, economical, and geographical periphery for excellence, self-fulfillment and gaining formal education. In 2018, Learn to Succeed became an official non-profit organization. At the same year, Farid led a crowdfunding project of 150,000 NIS in order to expand the organization to a national scale. In 2019, he published the book "Learn to Succeed", in which he describes his struggle with ADHD, the violent environment in which he grew up, and the changing process he went through from being a violent teenager to becoming the youngest Ph.D. graduate at the Technion. The book was given to more than two thousand youths at risk and became a top seller in Israel shortly after its publication. Maor dedicated the book to his parents and to the memorial of his friend Captain Tal Nachman who was killed in operational activity during his military service in 2014. The organization consists of hundreds of volunteers, gives full scholarships to STEM students from the periphery who serve as mentors of youths, both Jews and Arabs, from disadvantaged backgrounds, runs a hotline which gives online practical and mental support to hundreds of youths, parents and educators, initiates inspirational activities with military orientation to increase the motivation of its teen-age members for significant military service, and gives inspirational lectures to more than 5,000 youths each year. In 2019, Maor initiated a collaboration with Unit 8200 in which tens of the program's members are being interviewed to the unit. This opportunity is usually given to students with the highest grades in the matriculate exams in each class. In 2020, Dr. Farid established the ScienceAbroad center at MIT, aiming to strengthen the connections between Israeli researchers in the institute and the state of Israel. Moreover, he serves as a volunteer in the American Technion Society. Honors and awards Personal life Farid is married to Michal. Interviews and articles References External links |
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