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11,000 | Benzodiazepines are commonly used recreationally by poly-drug users. Mortality is higher among poly-drug users that also use benzodiazepines. Heavy alcohol use also increases mortality among poly-drug users. Dependence and tolerance, often coupled with dosage escalation, to benzodiazepines can develop rapidly among dru... | https://en.wikipedia.org/wiki?curid=4781 |
11,001 | A 1999–2005 Australian police survey of detainees reported preliminary findings that self-reported users of benzodiazepines were less likely than non-user detainees to work full-time and more likely to receive government benefits, use methamphetamine or heroin, and be arrested or imprisoned. Benzodiazepines are sometim... | https://en.wikipedia.org/wiki?curid=4781 |
11,002 | Overall, anecdotal evidence suggests that temazepam may be the most psychologically habit-forming (addictive) benzodiazepine. Non-medical temazepam use reached epidemic proportions in some parts of the world, in particular, in Europe and Australia, and is a major addictive substance in many Southeast Asian countries. T... | https://en.wikipedia.org/wiki?curid=4781 |
11,003 | Benzodiazepines are used in veterinary practice in the treatment of various disorders and conditions. As in humans, they are used in the first-line management of seizures, status epilepticus, and tetanus, and as maintenance therapy in epilepsy (in particular, in cats). They are widely used in small and large animals (i... | https://en.wikipedia.org/wiki?curid=4781 |
11,004 | K2, at above sea level, is the second-highest mountain on Earth, after Mount Everest (at ). It lies in the Karakoram range, partially in the Gilgit-Baltistan region of Pakistan-administered Kashmir and partially in a China-administered territory of the Kashmir region included in the Taxkorgan Tajik Autonomous County of... | https://en.wikipedia.org/wiki?curid=17359 |
11,005 | K2 also became popularly known as the "Savage Mountain" after George Bell—a climber on the 1953 American expedition—told reporters, "It's a savage mountain that tries to kill you." Of the five highest mountains in the world, K2 is the deadliest; approximately one person dies on the mountain for every four who reach the... | https://en.wikipedia.org/wiki?curid=17359 |
11,006 | The summit was reached for the first time by the Italian climbers Lino Lacedelli and Achille Compagnoni, on the 1954 Italian expedition led by Ardito Desio. In January 2021, K2 became the final eight-thousander to be summited in the winter; the mountaineering feat was accomplished by a team of Nepalese climbers, led by... | https://en.wikipedia.org/wiki?curid=17359 |
11,007 | K2 is the only 8,000+ metre peak that has never been climbed from its eastern face. Ascents have almost always been made in July and August, which are typically the warmest times of the year; K2's more northern location makes it more susceptible to inclement and colder weather. The peak has now been climbed by almost a... | https://en.wikipedia.org/wiki?curid=17359 |
11,008 | The name "K2" is derived from notation used by the Great Trigonometrical Survey of British India. Thomas Montgomerie made the first survey of the Karakoram from Mount Haramukh, some to the south, and sketched the two most prominent peaks, labelling them "K1" and "K2", where the "K" stands for "Karakoram". | https://en.wikipedia.org/wiki?curid=17359 |
11,009 | The policy of the Great Trigonometrical Survey was to use local names for mountains wherever possible and K1 was found to be known locally as Masherbrum. K2, however, appeared not to have acquired a local name, possibly due to its remoteness. The mountain is not visible from Askole, the last village to the south, or fr... | https://en.wikipedia.org/wiki?curid=17359 |
11,010 | With the mountain lacking a local name, the name "Mount Godwin-Austen" was suggested, in honour of Henry Godwin-Austen, an early explorer of the area. While the name was rejected by the Royal Geographical Society, it was used on several maps and continues to be used occasionally. | https://en.wikipedia.org/wiki?curid=17359 |
11,011 | The surveyor's mark, K2, therefore continues to be the name by which the mountain is commonly known. It is now also used in the Balti language, rendered as "Kechu" or "Ketu" ( ). The Italian climber Fosco Maraini argued in his account of the ascent of Gasherbrum IV that while the name of K2 owes its origin to chance, i... | https://en.wikipedia.org/wiki?curid=17359 |
11,012 | K2 lies in the northwestern Karakoram Range. It is located in the Baltistan region of Gilgit–Baltistan, Pakistan, and the Taxkorgan Tajik Autonomous County of Xinjiang, China. The Tarim sedimentary basin borders the range on the north and the Lesser Himalayas on the south. Melt waters from glaciers, such as those south... | https://en.wikipedia.org/wiki?curid=17359 |
11,013 | K2 is ranked 22nd by topographic prominence, a measure of a mountain's independent stature. It is a part of the same extended area of uplift (including the Karakoram, the Tibetan Plateau, and the Himalaya) as Mount Everest, and it is possible to follow a path from K2 to Everest that goes no lower than , at the Kora La ... | https://en.wikipedia.org/wiki?curid=17359 |
11,014 | K2 is notable for its local relief as well as its total height. It stands over above much of the glacial valley bottoms at its base. It is a consistently steep pyramid, dropping quickly in almost all directions. The north side is the steepest: there it rises over above the K2 (Qogir) Glacier in only of horizontal dista... | https://en.wikipedia.org/wiki?curid=17359 |
11,015 | A 1986 expedition led by George Wallerstein made an inaccurate measurement showing that K2 was taller than Mount Everest, and therefore the tallest mountain in the world. A corrected measurement was made in 1987, but by then the claim that K2 was the tallest mountain in the world had already made it into many news repo... | https://en.wikipedia.org/wiki?curid=17359 |
11,016 | K2's height given on maps and encyclopedias is . In the summer of 2014, a Pakistani-Italian expedition to K2, named "K2 60 Years Later", was organized to commemorate the 60th anniversary of the first ascent of K2. One of the goals of the expedition was to accurately measure the height of the mountain using satellite na... | https://en.wikipedia.org/wiki?curid=17359 |
11,017 | The mountains of K2 and Broad Peak, and the area westward to the lower reaches of Sarpo Laggo glacier, consist of metamorphic rocks, known as the "K2 Gneiss," and part of the Karakoram Metamorphic Complex. The K2 Gneiss consists of a mixture of orthogneiss and biotite-rich paragneiss. On the south and southeast face of... | https://en.wikipedia.org/wiki?curid=17359 |
11,018 | Ar/Ar ages of 115 to 120 million years ago obtained from and geochemical analyses of the K2 Gneiss demonstrate that it is a metamorphosed, older, Cretaceous, pre-collisional granite. The granitic precursor (protolith) to the K2 Gneiss originated as the result of the production of large bodies of magma by a northward-di... | https://en.wikipedia.org/wiki?curid=17359 |
11,019 | The mountain was first surveyed by a British team in 1856. Team member Thomas Montgomerie designated the mountain "K2" for being the second peak of the Karakoram range. The other peaks were originally named K1, K3, K4, and K5, but were eventually renamed Masherbrum, Gasherbrum IV, Gasherbrum II, and Gasherbrum I, respe... | https://en.wikipedia.org/wiki?curid=17359 |
11,020 | The first serious attempt to climb K2 was undertaken in 1902 by Oscar Eckenstein, Aleister Crowley, Jules Jacot-Guillarmod, Heinrich Pfannl, Victor Wessely, and Guy Knowles via the Northeast Ridge. In the early 1900s, modern transportation did not exist in the region: it took "fourteen days just to reach the foot of th... | https://en.wikipedia.org/wiki?curid=17359 |
11,021 | After five serious and costly attempts, the team reached —although considering the difficulty of the challenge, and the lack of modern climbing equipment or weatherproof fabrics, Crowley's statement that "neither man nor beast was injured" highlights the relative skill of the ascent. The failures were also attributed t... | https://en.wikipedia.org/wiki?curid=17359 |
11,022 | The next expedition to K2, in 1909, led by Prince Luigi Amedeo, Duke of the Abruzzi, reached an elevation of around on the South East Spur, now known as the "Abruzzi Spur" (or Abruzzi Ridge). This would eventually become part of the standard route, but was abandoned at the time due to its steepness and difficulty. Afte... | https://en.wikipedia.org/wiki?curid=17359 |
11,023 | The next attempt on K2 was not made until 1938, when the First American Karakoram expedition led by Charles Houston made a reconnaissance of the mountain. They concluded that the Abruzzi Spur was the most practical route and reached a height of around before turning back due to diminishing supplies and the threat of ba... | https://en.wikipedia.org/wiki?curid=17359 |
11,024 | The following year, the 1939 American expedition led by Fritz Wiessner came within of the summit but ended in disaster when Dudley Wolfe, Pasang Kikuli, Pasang Kitar, and Pintso disappeared high on the mountain. | https://en.wikipedia.org/wiki?curid=17359 |
11,025 | Charles Houston returned to K2 to lead the 1953 American expedition. The attempt failed after a storm pinned down the team for 10 days at , during which time climber Art Gilkey became critically ill. A desperate retreat followed, during which Pete Schoening saved almost the entire team during a mass fall (known simply ... | https://en.wikipedia.org/wiki?curid=17359 |
11,026 | The 1954 Italian expedition finally succeeded in ascending to the summit of K2 via the Abruzzi Spur on 31 July 1954. The expedition was led by Ardito Desio, and the two climbers who reached the summit were Lino Lacedelli and Achille Compagnoni. The team included a Pakistani member, Colonel Muhammad Ata-ullah, who had b... | https://en.wikipedia.org/wiki?curid=17359 |
11,027 | On 9 August 1977, 23 years after the Italian expedition, Ichiro Yoshizawa led the second successful ascent, with Ashraf Aman as the first native Pakistani climber. The Japanese expedition took the Abruzzi Spur and used more than 1,500 porters. | https://en.wikipedia.org/wiki?curid=17359 |
11,028 | The third ascent of K2 was in 1978, via a new route, the long and corniced Northeast Ridge. The top of the route traversed left across the East Face to avoid a vertical headwall and joined the uppermost part of the Abruzzi route. This ascent was made by an American team, led by James Whittaker; the summit party was Lou... | https://en.wikipedia.org/wiki?curid=17359 |
11,029 | Another notable Japanese ascent was that of the difficult North Ridge on the Chinese side of the peak in 1982. A team from the led by Isao Shinkai and put three members, Naoe Sakashita, Hiroshi Yoshino, and Yukihiro Yanagisawa, on the summit on 14 August. However Yanagisawa fell and died on the descent. Four other memb... | https://en.wikipedia.org/wiki?curid=17359 |
11,030 | The first climber to reach the summit of K2 twice was Czech climber Josef Rakoncaj. Rakoncaj was a member of the 1983 Italian expedition led by Francesco Santon, which made the second successful ascent of the North Ridge (31 July 1983). Three years later, on 5 July 1986, he reached the summit via the Abruzzi Spur (doub... | https://en.wikipedia.org/wiki?curid=17359 |
11,031 | The first woman to summit K2 was Polish climber Wanda Rutkiewicz on 23 June 1986. Liliane and Maurice Barrard who had summitted later that day, fell during the descent; Liliane Barrard's body was found on 19 July 1986 at the foot of the south face. | https://en.wikipedia.org/wiki?curid=17359 |
11,032 | In 1986, two Polish expeditions summitted via two new routes, the Magic Line and the Polish Line (Jerzy Kukuczka and Tadeusz Piotrowski). Piotrowski fell to his death as the two were descending. This latter route has never been repeated. | https://en.wikipedia.org/wiki?curid=17359 |
11,033 | Thirteen climbers from several expeditions died in the 1986 K2 disaster. Another six mountaineers died in the 1995 K2 disaster, while eleven climbers died in the 2008 K2 disaster. | https://en.wikipedia.org/wiki?curid=17359 |
11,034 | There are a number of routes on K2, of somewhat different character, but they all share some key difficulties, the first being the extremely high altitude and resulting lack of oxygen: there is only one-third as much oxygen available to a climber on the summit of K2 as there is at sea level. | https://en.wikipedia.org/wiki?curid=17359 |
11,035 | The second is the propensity of the mountain to experience extreme storms of several days duration, which have resulted in many of the deaths on the peak. The third is the steep, exposed, and committing nature of all routes on the mountain, which makes retreat more difficult, especially during a storm. Despite many att... | https://en.wikipedia.org/wiki?curid=17359 |
11,036 | The standard route of ascent, used by 75% of all climbers, is the Abruzzi Spur, located on the Pakistani side, first attempted by Prince Luigi Amedeo, Duke of the Abruzzi in 1909. This is the peak's southeast ridge, rising above the Godwin-Austen Glacier. The spur proper begins at an altitude of , where Advanced Base C... | https://en.wikipedia.org/wiki?curid=17359 |
11,037 | On 1 August 2008, 11 climbers from several expeditions died during a series of accidents, including several ice falls in the Bottleneck. | https://en.wikipedia.org/wiki?curid=17359 |
11,038 | Almost opposite from the Abruzzi Spur is the North Ridge, which ascends the Chinese side of the peak. It is rarely climbed, partly due to very difficult access, involving crossing the Shaksgam River, which is a hazardous undertaking. In contrast to the crowds of climbers and trekkers at the Abruzzi basecamp, usually at... | https://en.wikipedia.org/wiki?curid=17359 |
11,039 | Besides the original Japanese ascent, a notable ascent of the North Ridge was the one in 1990 by Greg Child, Greg Mortimer, and Steve Swenson, which was done alpine style above Camp 2, though using some fixed ropes already put in place by a Japanese team. | https://en.wikipedia.org/wiki?curid=17359 |
11,040 | Because 75% of people who climb K2 use the Abruzzi Spur, these listed routes are rarely climbed. No one has climbed the East Face of the mountain due to the instability of the snow and ice formations on that side. Besides the East Face, the North Face has not yet been climbed either. In 2007 Denis Urubko and Serguey Sa... | https://en.wikipedia.org/wiki?curid=17359 |
11,041 | For most of its climbing history, K2 was not usually climbed with supplemental oxygen, and small, relatively lightweight teams were the norm. However, the 2004 season saw a great increase in the use of oxygen: 28 of 47 summitteers used oxygen in that year. | https://en.wikipedia.org/wiki?curid=17359 |
11,042 | K2's summit is well above the altitude at which high altitude pulmonary edema (HAPE), or high altitude cerebral edema (HACE) can occur. In mountaineering, when ascending above an altitude of , the climber enters what is known as the "death zone". | https://en.wikipedia.org/wiki?curid=17359 |
11,043 | The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit for the speed at which conventional matter or energy (and thus any signal carrying inf... | https://en.wikipedia.org/wiki?curid=28736 |
11,044 | All forms of electromagnetic radiation, including visible light, travel at the speed of light. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and very sensitive measurements, their finite speed has noticeable effects. Starlight viewed ... | https://en.wikipedia.org/wiki?curid=28736 |
11,045 | Ole Rømer first demonstrated in 1676 that light travels at a finite speed (non-instantaneously) by studying the apparent motion of Jupiter's moon Io. Progressively more accurate measurements of its speed came over the following centuries. In a paper published in 1865, James Clerk Maxwell proposed that light was an elec... | https://en.wikipedia.org/wiki?curid=28736 |
11,046 | Massless particles and field perturbations, such as gravitational waves, also travel at speed in a vacuum. Such particles and waves travel at regardless of the motion of the source or the inertial reference frame of the observer. Particles with nonzero rest mass can be accelerated to approach but can never reach it, re... | https://en.wikipedia.org/wiki?curid=28736 |
11,047 | In some cases, objects or waves may appear to travel faster than light (e.g., phase velocities of waves, the appearance of certain high-speed astronomical objects, and particular quantum effects). The expansion of the universe is understood to exceed the speed of light beyond a certain boundary. | https://en.wikipedia.org/wiki?curid=28736 |
11,048 | The speed at which light propagates through transparent materials, such as glass or air, is less than ; similarly, the speed of electromagnetic waves in wire cables is slower than . The ratio between and the speed at which light travels in a material is called the refractive index of the material (). For example, for v... | https://en.wikipedia.org/wiki?curid=28736 |
11,049 | The speed of light in vacuum is usually denoted by a lowercase , for "constant" or the Latin (meaning 'swiftness, celerity'). In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used for a different constant that was later shown to equal times the speed of light in vacuum. Historically, the symbol "V" was used as a... | https://en.wikipedia.org/wiki?curid=28736 |
11,050 | Sometimes is used for the speed of waves in any material medium, and for the speed of light in vacuum. This subscripted notation, which is endorsed in official SI literature, has the same form as related electromagnetic constants: namely, "μ" for the vacuum permeability or magnetic constant, "ε" for the vacuum permitti... | https://en.wikipedia.org/wiki?curid=28736 |
11,051 | Since 1983, the constant has been defined in the International System of Units (SI) as "exactly" ; this relationship is used to define the metre as exactly the distance that light travels in a vacuum in of a second. By using the value of , as well as an accurate measurement of the second, one can thus establish a stand... | https://en.wikipedia.org/wiki?curid=28736 |
11,052 | In branches of physics in which appears often, such as in relativity, it is common to use systems of natural units of measurement or the geometrized unit system where . Using these units, does not appear explicitly because multiplication or division by1 does not affect the result. Its unit of light-second per second is... | https://en.wikipedia.org/wiki?curid=28736 |
11,053 | The speed at which light waves propagate in vacuum is independent both of the motion of the wave source and of the inertial frame of reference of the observer. This invariance of the speed of light was postulated by Einstein in 1905, after being motivated by Maxwell's theory of electromagnetism and the lack of evidence... | https://en.wikipedia.org/wiki?curid=28736 |
11,054 | Special relativity has many counterintuitive and experimentally verified implications. These include the equivalence of mass and energy , length contraction (moving objects shorten), and time dilation (moving clocks run more slowly). The factor "γ" by which lengths contract and times dilate is known as the Lorentz fact... | https://en.wikipedia.org/wiki?curid=28736 |
11,055 | The results of special relativity can be summarized by treating space and time as a unified structure known as spacetime (with "c" relating the units of space and time), and requiring that physical theories satisfy a special symmetry called Lorentz invariance, whose mathematical formulation contains the parameter "c". ... | https://en.wikipedia.org/wiki?curid=28736 |
11,056 | It is generally assumed that fundamental constants such as "c" have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time. No conclusive evidence for such changes h... | https://en.wikipedia.org/wiki?curid=28736 |
11,057 | It also is generally assumed that the speed of light is isotropic, meaning that it has the same value regardless of the direction in which it is measured. Observations of the emissions from nuclear energy levels as a function of the orientation of the emitting nuclei in a magnetic field (see Hughes–Drever experiment), ... | https://en.wikipedia.org/wiki?curid=28736 |
11,058 | According to special relativity, the energy of an object with rest mass "m" and speed "v" is given by , where "γ" is the Lorentz factor defined above. When "v" is zero, "γ" is equal to one, giving rise to the famous formula for mass–energy equivalence. The "γ" factor approaches infinity as "v" approaches "c", and it wo... | https://en.wikipedia.org/wiki?curid=28736 |
11,059 | More generally, it is impossible for signals or energy to travel faster than "c". One argument for this follows from the counter-intuitive implication of special relativity known as the relativity of simultaneity. If the spatial distance between two events A and B is greater than the time interval between them multipli... | https://en.wikipedia.org/wiki?curid=28736 |
11,060 | There are situations in which it may seem that matter, energy, or information-carrying signal travels at speeds greater than "c", but they do not. For example, as is discussed in the propagation of light in a medium section below, many wave velocities can exceed "c". The phase velocity of X-rays through most glasses ca... | https://en.wikipedia.org/wiki?curid=28736 |
11,061 | If a laser beam is swept quickly across a distant object, the spot of light can move faster than "c", although the initial movement of the spot is delayed because of the time it takes light to get to the distant object at the speed "c". However, the only physical entities that are moving are the laser and its emitted l... | https://en.wikipedia.org/wiki?curid=28736 |
11,062 | The rate of change in the distance between two objects in a frame of reference with respect to which both are moving (their closing speed) may have a value in excess of "c". However, this does not represent the speed of any single object as measured in a single inertial frame. | https://en.wikipedia.org/wiki?curid=28736 |
11,063 | Certain quantum effects appear to be transmitted instantaneously and therefore faster than "c", as in the EPR paradox. An example involves the quantum states of two particles that can be entangled. Until either of the particles is observed, they exist in a superposition of two quantum states. If the particles are separ... | https://en.wikipedia.org/wiki?curid=28736 |
11,064 | Another quantum effect that predicts the occurrence of faster-than-light speeds is called the Hartman effect: under certain conditions the time needed for a virtual particle to tunnel through a barrier is constant, regardless of the thickness of the barrier. This could result in a virtual particle crossing a large gap ... | https://en.wikipedia.org/wiki?curid=28736 |
11,065 | So-called superluminal motion is seen in certain astronomical objects, such as the relativistic jets of radio galaxies and quasars. However, these jets are not moving at speeds in excess of the speed of light: the apparent superluminal motion is a projection effect caused by objects moving near the speed of light and a... | https://en.wikipedia.org/wiki?curid=28736 |
11,066 | A 2011 experiment where neutrinos were observed to travel faster than light turned out to be due to experimental error. | https://en.wikipedia.org/wiki?curid=28736 |
11,067 | In models of the expanding universe, the farther galaxies are from each other, the faster they drift apart. This receding is not due to motion through space, but rather to the expansion of space itself. For example, galaxies far away from Earth appear to be moving away from the Earth with a speed proportional to their ... | https://en.wikipedia.org/wiki?curid=28736 |
11,068 | In classical physics, light is described as a type of electromagnetic wave. The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed "c" with which electromagnetic waves (such as light) propagate in vacuum is related to the distributed capacitance and induct... | https://en.wikipedia.org/wiki?curid=28736 |
11,069 | In modern quantum physics, the electromagnetic field is described by the theory of quantum electrodynamics (QED). In this theory, light is described by the fundamental excitations (or quanta) of the electromagnetic field, called photons. In QED, photons are massless particles and thus, according to special relativity, ... | https://en.wikipedia.org/wiki?curid=28736 |
11,070 | Extensions of QED in which the photon has a mass have been considered. In such a theory, its speed would depend on its frequency, and the invariant speed "c" of special relativity would then be the upper limit of the speed of light in vacuum. No variation of the speed of light with frequency has been observed in rigoro... | https://en.wikipedia.org/wiki?curid=28736 |
11,071 | Another reason for the speed of light to vary with its frequency would be the failure of special relativity to apply to arbitrarily small scales, as predicted by some proposed theories of quantum gravity. In 2009, the observation of gamma-ray burst GRB 090510 found no evidence for a dependence of photon speed on energy... | https://en.wikipedia.org/wiki?curid=28736 |
11,072 | In a medium, light usually does not propagate at a speed equal to "c"; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity "v". A phys... | https://en.wikipedia.org/wiki?curid=28736 |
11,073 | The phase velocity is important in determining how a light wave travels through a material or from one material to another. It is often represented in terms of a "refractive index". The refractive index of a material is defined as the ratio of "c" to the phase velocity "v" in the material: larger indices of refraction ... | https://en.wikipedia.org/wiki?curid=28736 |
11,074 | In transparent materials, the refractive index generally is greater than 1, meaning that the phase velocity is less than "c". In other materials, it is possible for the refractive index to become smaller than1 for some frequencies; in some exotic materials it is even possible for the index of refraction to become negat... | https://en.wikipedia.org/wiki?curid=28736 |
11,075 | A pulse with different group and phase velocities (which occurs if the phase velocity is not the same for all the frequencies of the pulse) smears out over time, a process known as dispersion. Certain materials have an exceptionally low (or even zero) group velocity for light waves, a phenomenon called slow light. | https://en.wikipedia.org/wiki?curid=28736 |
11,076 | The opposite, group velocities exceeding "c", was proposed theoretically in 1993 and achieved experimentally in 2000. It should even be possible for the group velocity to become infinite or negative, with pulses travelling instantaneously or backwards in time. | https://en.wikipedia.org/wiki?curid=28736 |
11,077 | None of these options, however, allow information to be transmitted faster than "c". It is impossible to transmit information with a light pulse any faster than the speed of the earliest part of the pulse (the front velocity). It can be shown that this is (under certain assumptions) always equal to "c". | https://en.wikipedia.org/wiki?curid=28736 |
11,078 | It is possible for a particle to travel through a medium faster than the phase velocity of light in that medium (but still slower than "c"). When a charged particle does that in a dielectric material, the electromagnetic equivalent of a shock wave, known as Cherenkov radiation, is emitted. | https://en.wikipedia.org/wiki?curid=28736 |
11,079 | The speed of light is of relevance to communications: the one-way and round-trip delay time are greater than zero. This applies from small to astronomical scales. On the other hand, some techniques depend on the finite speed of light, for example in distance measurements. | https://en.wikipedia.org/wiki?curid=28736 |
11,080 | In computers, the speed of light imposes a limit on how quickly data can be sent between processors. If a processor operates at 1gigahertz, a signal can travel only a maximum of about in a single clock cycle — in practice, this distance is even shorter since the printed circuit board itself has a refractive index and s... | https://en.wikipedia.org/wiki?curid=28736 |
11,081 | Given that the equatorial circumference of the Earth is about and that "c" is about , the theoretical shortest time for a piece of information to travel half the globe along the surface is about 67 milliseconds. When light is traveling in optical fibre (a transparent material) the actual transit time is longer, in part... | https://en.wikipedia.org/wiki?curid=28736 |
11,082 | Although this distance is largely irrelevant for most applications, latency becomes important in fields such as high-frequency trading, where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to microwave... | https://en.wikipedia.org/wiki?curid=28736 |
11,083 | Similarly, communications between the Earth and spacecraft are not instantaneous. There is a brief delay from the source to the receiver, which becomes more noticeable as distances increase. This delay was significant for communications between ground control and Apollo 8 when it became the first crewed spacecraft to o... | https://en.wikipedia.org/wiki?curid=28736 |
11,084 | Receiving light and other signals from distant astronomical sources takes much longer. For example, it takes 13 billion (13) years for light to travel to Earth from the faraway galaxies viewed in the Hubble Ultra Deep Field images. Those photographs, taken today, capture images of the galaxies as they appeared 13 billi... | https://en.wikipedia.org/wiki?curid=28736 |
11,085 | Astronomical distances are sometimes expressed in light-years, especially in popular science publications and media. A light-year is the distance light travels in one Julian year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or ne... | https://en.wikipedia.org/wiki?curid=28736 |
11,086 | Radar systems measure the distance to a target by the time it takes a radio-wave pulse to return to the radar antenna after being reflected by the target: the distance to the target is half the round-trip transit time multiplied by the speed of light. A Global Positioning System (GPS) receiver measures its distance to ... | https://en.wikipedia.org/wiki?curid=28736 |
11,087 | There are different ways to determine the value of "c". One way is to measure the actual speed at which light waves propagate, which can be done in various astronomical and Earth-based setups. However, it is also possible to determine "c" from other physical laws where it appears, for example, by determining the values... | https://en.wikipedia.org/wiki?curid=28736 |
11,088 | In 1983 the metre was defined as "the length of the path travelled by light in vacuum during a time interval of of a second", fixing the value of the speed of light at by definition, as described below. Consequently, accurate measurements of the speed of light yield an accurate realization of the metre rather than an a... | https://en.wikipedia.org/wiki?curid=28736 |
11,089 | Outer space is a convenient setting for measuring the speed of light because of its large scale and nearly perfect vacuum. Typically, one measures the time needed for light to traverse some reference distance in the Solar System, such as the radius of the Earth's orbit. Historically, such measurements could be made fai... | https://en.wikipedia.org/wiki?curid=28736 |
11,090 | Ole Christensen Rømer used an astronomical measurement to make the first quantitative estimate of the speed of light in the year 1676. When measured from Earth, the periods of moons orbiting a distant planet are shorter when the Earth is approaching the planet than when the Earth is receding from it. The distance trave... | https://en.wikipedia.org/wiki?curid=28736 |
11,091 | Another method is to use the aberration of light, discovered and explained by James Bradley in the 18th century. This effect results from the vector addition of the velocity of light arriving from a distant source (such as a star) and the velocity of its observer (see diagram on the right). A moving observer thus sees ... | https://en.wikipedia.org/wiki?curid=28736 |
11,092 | An astronomical unit (AU) is approximately the average distance between the Earth and Sun. It was redefined in 2012 as exactly . Previously the AU was not based on the International System of Units but in terms of the gravitational force exerted by the Sun in the framework of classical mechanics. The current definition... | https://en.wikipedia.org/wiki?curid=28736 |
11,093 | Previously, the inverse of expressed in seconds per astronomical unit was measured by comparing the time for radio signals to reach different spacecraft in the Solar System, with their position calculated from the gravitational effects of the Sun and various planets. By combining many such measurements, a best fit val... | https://en.wikipedia.org/wiki?curid=28736 |
11,094 | The relative uncertainty in these measurements is 0.02 parts per billion (), equivalent to the uncertainty in Earth-based measurements of length by interferometry. Since the metre is defined to be the length travelled by light in a certain time interval, the measurement of the light time in terms of the previous defini... | https://en.wikipedia.org/wiki?curid=28736 |
11,095 | A method of measuring the speed of light is to measure the time needed for light to travel to a mirror at a known distance and back. This is the working principle behind the Fizeau–Foucault apparatus developed by Hippolyte Fizeau and Léon Foucault, based on a suggestion by François Arago. | https://en.wikipedia.org/wiki?curid=28736 |
11,096 | The setup as used by Fizeau consists of a beam of light directed at a mirror away. On the way from the source to the mirror, the beam passes through a rotating cogwheel. At a certain rate of rotation, the beam passes through one gap on the way out and another on the way back, but at slightly higher or lower rates, the ... | https://en.wikipedia.org/wiki?curid=28736 |
11,097 | The method of Foucault replaces the cogwheel with a rotating mirror. Because the mirror keeps rotating while the light travels to the distant mirror and back, the light is reflected from the rotating mirror at a different angle on its way out than it is on its way back. From this difference in angle, the known speed of... | https://en.wikipedia.org/wiki?curid=28736 |
11,098 | Today, using oscilloscopes with time resolutions of less than one nanosecond, the speed of light can be directly measured by timing the delay of a light pulse from a laser or an LED reflected from a mirror. This method is less precise (with errors of the order of 1%) than other modern techniques, but it is sometimes us... | https://en.wikipedia.org/wiki?curid=28736 |
11,099 | An option for deriving "c" that does not directly depend on a measurement of the propagation of electromagnetic waves is to use the relation between "c" and the vacuum permittivity "ε" and vacuum permeability "μ" established by Maxwell's theory: "c" = 1/("ε""μ"). The vacuum permittivity may be determined by measuring t... | https://en.wikipedia.org/wiki?curid=28736 |
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