Subset (10)

eli5 · 25k rows

Split (1)

train · 25k rows

query stringlengths 20 300	positive listlengths 1 1	negative listlengths 1 1
When the police offer a reward for helping to catch a criminal where does that money come from?	[ "> Taxes? Does each police station have an allotment of funds? Yes." ]	[ "Theatres get paid by movie companies to screen that movie. That's why low budget films struggle to get a box office return, whereas Pirates of the Carribean can pull a billion across their movies. Having a big budget aides not only the production but the release." ]
I don't understand this movie title. Why is the movie "The Imitation Game" named this?	[ "The Imitation Game is referring to the Allied effort to produce a method of breaking the Enigma code, by producing a machine which can imitate the actions of the Enigma code machine. It also refers to the efforts of Turing to imitate his expected heterosexual role within society while actually being homosexual; ma...	[ "When a computer has to move it has a number of different moves that it can make. Each potential move has a score attached to it, reflecting how good the move is. For hardest play the computer would choose the move with the highest score. For less deterministic play the computer would choose from the top-scoring po...
Why do box fans have the off setting (0) right next to the highest setting (3)? Wouldn't it make more sense to have it by the lowest setting?	[ "It's more efficient, electrically, to start a motor at a high speed than it is to get it moving at a slow speed. It is simple to step down to the slower speeds while it is running." ]	[ "Imagine a bathtub full of water, the water represents electricity. The bathtub has a faucet, which represents the generation of electricity. Imagine now that there are little holes in the bottom of the bathtub, all plugged up. When ever a home needs power, unplug the drain and let the water flow out. Now imagine ...
Why do we so often say "sorry?", "what?", "pardon?" etc immediately after being asked a question even though we know what the other person said?	[ "Your \"hearing memory\" (which is the sensory memory of what you've just heard) lasts about 4 seconds. If someone is listening to more than one thing at once, the brain processes them separately, but can still process the other within four seconds. The asking of \"What?\" lets the speaker know they've been heard, ...	[ "If you ask for 1 pen, it costs you two dollars. If you ask for 100 000 pens, they will only cost you one dollar each. I prefer selling you 100 000 pens at half price, than selling you 1 at full price and have 99 999 sitting around doing nothing. In a similar way, if you ask for a small amount of money, you pay a b...
How the heck does someone check in a gun onto a domestic flight in America?	[ "Anyone can check in a gun to a domestic flight, providing it's in checked baggage. The gun has to be unloaded, ammunition stored separately and in original box, and the gun locked into a hard-sided container. It also has to be declared at check-in." ]	[ "One search isn't going to do much. They have hugely complicated algorithms in place to find what they are looking for. It might raise a flag, but a single flag isn't going to do much. By the way, just because you don't live here doesn't mean we aren't watching Creepy Smile." ]
Why does it seem like something spinning starts to go in reverse as it slows down?	[ "If I have a camera taking pictures 30 times a second and a wheel with a stripe on it spinning 1 time a second you will clearly see it slowly rotating with the stripe pointing up every 30 frames. As the wheel speeds up it looks very strange on camera. If the wheel spins 30 times a second then the camera will displ...	[ "Your eye sensors tire after a short while viewing a static image. In this example they're giving you a fixed point to focus on so that the image stays positioned in the same place on your retina. Notice how her lips are green in the negative. Staring at that wears our your green sensor there. Then, when you switch...
In the winter, why do my clothes get more static electricity?	[ "The air is much more humid in the summer, which makes the air more conductive. This means that the static electricity is dispersed into the air. The dry air in the winter doesn't allow that method of release, so the static charge builds up. A humidifier or air ionizer will do the same thing, making the air more co...	[ "Wow, lots of grammar nazis here. For lack of better words myself I'll leave this here for them: _URL_0_ There's a discusson on this here: _URL_1_ ...but I've also heard it is because your blood is flowing away from the cold areas, which exposes your nerves to the skin. Don't know about that now that I read that ot...
Which organism needs the most energy in order to survive, relative to its size (biggest energy:volume ratio) ?	[ "If I understand you correctly, you mean which organism has the highest mass-specific metabolism? i.e. metabolism per unit mass? Smaller animals tend to require more energy than larger animals per unit mass. Shrews are pretty famous for having one of the highest, if not the highest, mass specific metabolism ([one s...	[ "Compassion, like any reaction, has triggers. Humans and some other social species have some level of compassion instinct, and other animals can sometimes trigger it by resembling behaviors among their own kind that induce it. The most common example is infants. Although in the wild an orphaned animal is usually tr...
In music, what is an industry plant?	[ "I had never heard of this before but 90 seconds of googling gave me this; \" In general, \"industry plant\" is a pithy derogative that we (haters) wield to imply that a rapper or singer is an upstart fraud, a record label puppet, a focus group-tested vessel of creativity so-called. Any musician with a hazy or stra...	[ "Trailers are rated just like movies. As far as I know there are only red and green ratings for trailers. Green - Ok to play before any movie Red - Only can play before R or NC-17 movies Now the reason you've only really saw green up to this point is that (a) trailers cost money and why would the studio pay to have...
How do video games (i.e Chess) change the AI depending on the level set (Easy, Medium, Hard)?	[ "The harder you set it, the more time the computer gives itself to examine every possible future situation -- what you might do next, then what it might do in response, then what you might do after that, etc. On low difficulty it won't look too far ahead." ]	[ "In some cases, they do. For example, the SwiftKey keyboard for Android analyzes not only the way you use it, but also your most commonly used words and phrases in your emails and social networks. However, in general, it's better to base predictions off the population of word usage as a whole, rather than trying to...
How does healthcare in the US work?	[ "No. Hospitals are not allowed to turn people away or stop treating because they can't pay. Instead, the patient gets a bill that they cannot afford to pay. They then go into bankruptcy and have a slew of financial problems due to the unfortunate circumstances of getting sick. Sadly, even with insurance, many Ameri...	[ "This CGP Grey video does a really good job of explaining it all. _URL_3_" ]
How common are bacteria that cause food-borne illnesses? What are the actual chances of getting sick from undercooked food?	[ "Hello. Microbiologist here for the USDA. I research food-borne pathogens, focusing on produce. Bacteria are ubiquitous critters. Since much of the water used to irrigate is nasty, it contains these pathogens on some level. And since raw meat, poultry, and eggs are such good sources of nutrients, they are commonly ...	[ "Imagine you are made of genetic soup. Some people have ingredients that just don't go well together and make the soup taste bad. But that's ok, because when you have a kid, we just take some of my soup and some of my wife's soup and pour it in together. So even though my soup has some bad ingredients, her ingredie...
Why is the 5-17 age group so valuable to advertisers versus other age groups?	[ "Becaus for most if them their frontal lobes aren’t developed yet and are very easily molded by repetition and hype. Adults have the ability and experience to see the BS in ads." ]	[ "There's already [evidence](_URL_1_) suggesting a [genetic component](_URL_3_) to human sexuality. I'm not sure that your idea would produce any more powerful evidence, since there are already all sorts of difficulties with mating animals in captivity, which would complicate any attempts to study sexual orientation...
Would the Byzantine Empire still eventually fall without the Turks invading?	[ "This ventures pretty far into /r/HistoricalWhatIf territory. There are simply too many variables to lay out a definite answer - 1400-2013 is a long period and Eurasia would fairly inevitably see massive, potentially empire-ending upheavals in every sphere of society, from religion to politics to technology to popu...	[ "To go against the grain of this thread, and from an archaeological perspective: absolutely. Archaeology is something of a zero sum game, and every dollar that goes to one site is one that doesn't go to another; or to put it in concrete terms, every hundred million injection into Pompeii, or more accurately into th...
What is the deal with China and Indian at the moment?	[ "It's just a random border dispute. In that part of the world the borders have never been properly defined and agreed on for two reasons. Firstly, at least traditionally, the areas are primarily tribal and the people there are not that bothered about borders that were decided on by the British et al. Secondly it is...	[ "Victoria (u/chooter) was let go/fired from Reddit today, and because she does a lot of the background work behind r/IAMA it left that subreddit and a few others that also require her in a state of clusterfuck. [Here](_URL_0_) is a link to the explanation given by u/karmanaut on the whole situation." ]
Is De Morgan's Theorem true for more than two things?	[ "Yes. You can show this directly via truth tables, but it is nicer to show this for three objects based on the result for two objects. We use the associativity of AND and the associativity of OR (which is important, as otherwise something like \"A and B and C\" which you reference above has no meaning without paren...	[ "If you are cooking potatoes you don't need to look at them to know when they're done. You can simply set a timer and take them off it rings. In the same way we usually know how many iterations of some calculation is needed until we should arrive at the correct result. In some instances this is not exactly the cas...
What is the most basic form of life that still displays sleep-like behavior?	[ "It seems to be the tiny roundworm C. elegans, not coincidentally one of the most intensely studied basic forms of life. It does something sleep-like called lethargus before each time it molts. This tends to suggest that sleep goes way back in our evolutionary history, for whatever reason." ]	[ "Yes, there are many examples. These are just a few: * Chimpanzees: [Ex. 1](_URL_2_), [Ex. 2](_URL_3_), [Ex. 3](_URL_0_); there are [many more](_URL_1_). * [Monkeys](_URL_6_) * Whales: [Ex. 1](_URL_5_), [Ex. 2](_URL_4_) * Birds: [Ex. 1](_URL_8_), [Ex. 2](_URL_7_)" ]
What is the difference between induced pluripotent stem cells and embryonic stem cells?	[ "Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of a blastocyst. Induced pluripotent stem cells are cells that have been reprogrammed from a differentiated to a pluripotent state by the introduction of ectopic transcription factors. Part of the definition of pluripotency is the a...	[ "Investment banks are selling stocks. Equity Research is figuring out what a stock is worth. The inherent conflict of interest is that if the same company is both selling the stock, and providing research about it, the buyer has no way to tell if the research has been influenced to improve the story about why the s...
If car antennas are receive-only, how do radio stations count their listeners?	[ "> If car antennas are receive-only, how do radio stations count their listeners? They don't. They rely on polls which are sent out to people who self-report what they listened to during a sample week. Radio stations themselves have no way to determine who is picking up their signal." ]	[ "They don't. It's a marketing ~~lie~~ gimmick. I used to work for a company that did a similar thing by mail. New customers were supposed to sign up by a certain time for special rates but as a specific matter of policy we'd give those rates to anyone who mailed back the special offer." ]
I've seen a few of those home science videos involving a metal spinning top being placed above a magnet, which causes it to spin indefinitely. Why couldn't something like this be industrialised to produce infinite power?	[ "It won't spin indefinitely... It is just using up the energy that was originally put into it to start spinning. Can't get more out than you put in, so if you tried to hook up a generator robot, it would stop very quickly. A much better ELI5:. _URL_0_" ]	[ "Calculus, for the most part. It turns out that you can represent the vast majority of things you need to calculate with what's called a power series. So you take a function and, through some algorithm, turn it into a power series. A power series is an infinite sum of some more easily solved function, where you j...
Why don't planes have multiple wings to generate more lift?	[ "Firstly, commercial airplanes generate enough lift. They don't need more. Now the question becomes: Why they have one wide wing instead of two shorter wings so that the strength and thickness of individual wing can be smaller, reducing overall drag and weight? The problem with bi-planes is that the lower wing is...	[ "Each builder is going to do what they want. Google pictures of Beijing some time, they have entire large blocks of buildings the same style and height. They also are far more regulated about how they build. I imagine in a more free market economy, each builder wants their building to be \"their building\" and not ...
Sunday Digest \| Interesting & Overlooked Posts \| December 14, 2015–December 20, 2015	[ "Weekly Rundown: * /u/Lich-Su on [\"Did the cold war \"Domino Theory\" have any merit?\"](_URL_0_) * /u/anthropology_nerd on [\"A lot of my history teachers have said that the early American colonists would never have survived without the help from Native Americans. Is this true?\"](_URL_1_) * /u/polybios on [\"Wha...	[ "The US Department of Energy published a study [pdf:[1]] in 2008, showing a decrease of one-half of one percent (0.5%) daytime energy usage during the extended DST hours established in 2005. Conversely, most of Indiana did not observe DST until 2006; when they switched, the result appeared to be an increase in ener...
How are banned cartoons that are never seen found and uploaded?	[ "Someone somewhere has access to the tapes. If it's banned, that means a panel or group of viewers have viewed it, then decided it's not suited for the general public. During this process, the studio that created the cartoon probably has sent copies of the episode to various organizations for review; so somewhere o...	[ "Country specific ones follow the laws of that country. You can search for Tibet freedom on _URL_0_. but not _URL_1_ or Google.can Google was given a choice by Chinese gov. Either you make the search engine follow our rules, or you don't do business in China at all and China blocks _URL_2_ entirely" ]
how far back in time could I go and still mostly understand the English language?	[ "Within a few decades to a couple hundred of years, slang would start being really weird, but on the whole you could probably grasp most of what is being said. The first major barrier is probably going to be the [great vowel shift](_URL_2_). By that time, pronunciations, and a fair amount of the vocabulary, is go...	[ "Ahoy! I'm [Dr Richard Blakemore](_URL_1_) ([@historywomble](_URL_3_) on twitter) from the [University of Reading's History Department](_URL_4_) and I'm excited to join you on the 18th of September for an AMA about [my areas of expertise](_URL_5_) \\- the Stuart and Tudor navies, sailors in the Early Modern period,...
Which legend about purgatory was Martin Luther referencing in thesis #29?	[ "> I can find several saints by those names, but after a bit of research I can't find any stories about any of them associated with purgatory. What is Luther referencing here? It seems to be accepted that Luther was referring to Saint [Severinus of Noricum](_URL_1_) and [Pope Paschal I](_URL_0_). The source of this...	[ "Before I answer, may I ask who the speaker is for this particular lecture? Or if you have a link for me to listen to? I would like to know where they are coming from in their argument." ]
Why do multilingual people usually have much better grammar than people who only speak/write one language?	[ "When learning a new language, you learn the grammar of it also, which makes you pay much more attention to the new grammar, as well as making you more aware of your native grammar. From my experience, there is also a greater attention to grammar in foreign language education rather than native one." ]	[ "\"Just about everyone here\" Where is \"here\" for you? It sounds like your question's premise is based on a small sample set based on personal observation. Before your question is addressed, you should be making sure the premise is valid..." ]
How can someone sue over potential profits?	[ "There is precedence in the concept of tortious interference. Let's say you arrange to sell some product to a potential buyer. But, before they actually buy the product, they bow out of the deal. You find out that some third party was spreading rumors or lies about you, and that directly led to the buyer not follow...	[ "In the USA, a patent has a proprietary time frame. (maybe the correct term) I believe it is 17 years. Once that time frame is up, they can't use your logo or brand name, but they can use the general aspects of your patent." ]
How was cocaine discovered/invented?	[ "This is one of those cliff-notes history questions designed as ELI5, so I suggest you check out Wikipedia's page on cocaine, specifically the history section. That said, here's a quick rundown: Indigenous people knew about the effects of chewing coca leaves, Spanish explorers were skeptical about its supposed effe...	[ "Since nobody has given you anything yet, I suggest that you check out Sidney Mintz's Sweetness and Power: The Place of Sugar in Modern History. Most the answers you seek will be there..." ]
How would a Janissary have been treated during the late 14th century? (By superiors and the general population.) How formal was the Devsirme system by this stage?	[ "I had a great Ottoman history professor who claimed that Janissaries were treated very well. According to this prof Christian parents would try to get their children taken into the Janissary program so that their kids would have more opportunity in life. They were respected at court, on the battlefield, and in the...	[ "Could you perhaps present us with your original source so we can see what the author writes about it? I think I know the answer, but I would like to know what exactly the author wrote. Also, could you remove the bonus question? We do not allow discussions of events after 1993." ]
Could exposure to radiation actually give someone superhuman abilities?	[ "no. it would just kill you. besides, most any superhuman ability defies physics itself, even if you were able to sculpt a dna sequence at will, there is no sequence that would produce an ability to fly or move at super speed ect." ]	[ "Here's something I didn't see referenced in the three posts linked in the FAQ. There's a genetic mutation called Delta 32 or [CCR5](_URL_1_) that is believed to impart resistance to the Bubonic plague (and possibly HIV). Apparently this gene is more prevalent in Scandinavian and Slavic bloodlines. There's another ...
Why is voicemail technology still so terrible?	[ "It does exist. The very first iPhone was the first phone to do this, which was in 2007, [Here is what it looked like back then.](_URL_1_) Here is what the [current version looks like.](_URL_0_) If you don't have this feature, you probably don't have a good smartphone and/or a carrier which allows it." ]	[ "It takes a while to implement the changes. How would you like it if the law changed overnight and you had to pay fees/go to jail next day without having a chance to adapt yet." ]
How does an athlete using smelling salts work?	[ "Smelling salts release ammonia gas. If you breathe in this gas, it irritates the insides of your nose and lungs to such an extent that it stimulates your sympathetic (\"fight-or-flight\") nervous system. This is an autonomous part of your nervous system that, when activated, has all sorts of arousing effects on yo...	[ "Bacteria on/in your skin metabolize the minerals in your sweat and create a by-product. TL;DR: sweat is bacteria farts." ]
the physics of popcorn	[ "Popcorn is dried corn kernels that still have a small amount of water inside the shell, contained in the stuff inside it, called endosperm. When the popcorn kernel is heated, the water boils and turns to steam, but there's no place for it to go, so it superheats the endosperm inside the shell- however, the press...	[ "In a cavity, yes. This happens in your microwave oven." ]
Why is 1066 and the Norman Invasion so significant?	[ "The Norman French came and conquered the existing Anglo Saxon English nobility. Most were killed or forced to swear loyalty (often involving intermarrying) and they were replace with French nobles. This fundamentally changed the structure of the government, and even the English language. The influx of French words...	[ "Politics. It's an easy issue to use to paint your opponent as \"evil\" regardless of which side of the debate they are on." ]
What is a Neoliberal?	[ "Neoliberals are open border capitalist, which breaks from traditional positions liberals held as this favors corporations over labor. Labor used to be the bread and butter of liberal policy." ]	[ "Paying an ISP more for more megabits is like UPS/FedEx/USPS charging more for heavier packages. Network non-neutrality is like having them open your packages and charging more if you buy certain things." ]
Why do cats like to be in confined places?	[ "Safety. Many animals instinctively like being in confined spaces because it usually means you're hidden, nothing can come up behind you, and nothing bigger than you can enter your little cave/nest/nook/home. Your cat probably isn't consciously thinking these things -- it's just developed an innate attraction to su...	[ "Its the easiest way to get out of the kitchen for a 5 minute break." ]
Do different cultures have different taste buds?	[ "There is no difference in tastes buds, but there is a difference in what is considered flavorful. This is determined by what the settlers of the area were able to eat during the early years of development. Things taste bad because your body believes that they are poisonous. Frequent exposure can reprogram this res...	[ "Survivor(ship) bias. Even with age correction, one of the most likely explanations is that survivor bias spans all age groups. In a less developed country with limited access to healthcare, everyday infections, diseases, and ailments in general become much more severe. Still, there are other factors that contribu...
Why does aluminium foil have a shiny side and a matte side?	[ "It's simply a result of the manufacturing process, which side comes into contact with the steel roller. There's no appreciable difference in the properties of the foil on either side, other than the shininess." ]	[ "Do you have a fly screen over the window? If so what you are observing is a [Moiré pattern](_URL_0_) being projected onto the window. Essentially the light is passing through the screen and the light waves get split up and then interact with each other causing spots of superposition where some regions are darker a...
I heard diet soda with zero calories can still lead to weight gain. How?	[ "the studies only show that people who drink diet soda can weigh more, they don't control for food intake. the issue is people act like it's ok to eat cake for dinner if they have a diet soda with it." ]	[ "The carbon dioxide, the bubbles, is a gas at RT. Pouring it into an empty glass means the liquid falls from a higher distance, when it hits the bottom of the glass the impact provides enough energy for the gas to escape. Not only does the liquid in there reduce the distance but also softens the impact. If you were...
How does the newer generation of captcha determine I'm not a robot? (The one where all you must do is click)	[ "It tracks mouse movement. If it was a bot it would immediately click the checkbox after it was loaded. You as a human have to move your mouse cursor to the checkbox and this movement is not in a straight line. So basically they just check mouse movement and time between checkbox being rendered and when it is click...	[ "Some traffic lights are on a timer. Those are the lights that seem to take forever to change. Other signals are triggered by a pressure plate under the asphalt, you can usually spot these by a square \"patch\" looking piece of asphalt at the stop line. The mechanism used usually depends on the amount of traffic at...
It is commonly believed that primates migrated to South America on vegetation rafts from Africa. Why is this the best known explanation despite the fact that it sounds ridiculous?	[ "It does sound weird, but there's a good deal of evidence for it. The dispersal of terrestrial species to islands and other land masses shows a real correlation with ocean currents, as you would expect from rafting. And on a smaller scale, it's actually been seen with iguanas: _URL_0_" ]	[ "How is that any more \"ignorant of history\" than thinking Rome was founded by two brothers who were sucked by a wolf, or Thebes being founded by some dragon-slayer who followed a cow?" ]
How was a week, an hour and a minute initially defined?	[ "24 hours — Egiptians used a base-12 counting system (as opposed to our base-10). 12 hours during the day (which they could track using sun dials) and correspondingly 12 hours at night (which they could track using the movement of stars). 7 day week — religions. It started in Babylon 600BCE, then transformed from t...	[ "Sort of. Quarks can come in +/- 1/3 or 2/3 of the fundamental charge, but they are only found in groups where the total charge adds up to an integer value of e. SI units are defined the way they are so that they are easily replicatable, not because they are inherently fundamental (there's nothing special about the...
why didn't medevil paintings have any perspective?	[ "Artists had not developed the technique of perspective until the beginning of the 15th century with Italian architect and artist Fillipo Brunelleschi. Medieval paintings don’t have perspective because it was not a “thing” yet. A lot of artists attempted to create it but didn’t really understand how to. Brunellesc...	[ "You should read Anne Rice ' s Memnoch the devil. AND Milton ' s Paradise Lost. \"It's better to rule in Hell than serve in Heaven.\" Or something like that." ]
Could a foreigner rise in power in Ghengis Khans court like Marco Polo in the Netflix show? If so what were some prominent examples of foreigners that he trusted?	[ "It may or may not be worth pointing out that Marco Polo visited Kublai Khan's court, not that of Genghis." ]	[ "Guan Yu is a historical personage recorded in the \"Records of the Three Kingdoms\" which was written in the 3rd century and is considered a historical work. The \"Romance of the Three Kingdoms\" was written in the 14th century and is a fictionalized novel. Here is a link to Guan Yu's Biography in the SGZ (chinese...
Why do you get lightheaded when you breathe quickly?	[ "By hyperventilating you breathe out more CO2 than usual. The lower concentration of CO2 means that you become alkalotic - the pH of your blood become higher, so less acidic. As far as I know, this makes it harder for the red blood cells to let go of oxygen molecules. This means your brain gets less oxygen, causing...	[ "How do you know you don’t have exercise induced asthma?" ]
How realistic is the shot and the recovery from the bullet "into the lung" in the movie Focus (2015)?	[ "I don't know what kind of firearm and bullet were supposed to be used, but no, it's not realistic. A through and through wound would leave massive cavitation and other tissue damage as well as blowing a large exit hole - typically. It's a movies, they frequently are inaccurate ." ]	[ "If the use were actually considered fair use, then it doesn't matter if it's a movie or YouTube video. There are tons of infringing uses on YouTube. Having said that, movies have bigger budgets, though, and are more diligent. They're actually usually over-diligent and pay for things even though they shouldn't h...
What are the benefits of animal testing?	[ "> If we didn't test on animals what discoveries would we have missed? Nearly every medical discovery made in the last 100 years. > What impact would it have on the future if we only tested on willing humans? We test a lot of things on willing humans. However, we only do this after we test on animals. When a resea...	[ "Politics. It's an easy issue to use to paint your opponent as \"evil\" regardless of which side of the debate they are on." ]
Why are Hox genes found in the genome organized by body location?	[ "Id just like to thank you all for bringing the level of discourse to an extraordinarily high level in this post." ]	[ "> If timezones are determined by your position on the globe Time zones are purely man-made things, and don't always line up the way you might expect. Your position on the globe is just a guideline for determining time zones. And if you look at an actual [timezone map](_URL_0_), you'll see that France and Spain...
If temperature is a measure of movement and movement is restricted by the speed of light does that mean that there is an upper limit to how hot something can get?	[ "Not for the reasons you're stating. Temperature is related to energy, rather than speed. Now, for slow velocities, before relativity comes into play, kinetic energy is just 1/2 mv^2 so you'd think there's a maximum energy, but that equation is modified at high velocities. Energy is, as far as relativity is concern...	[ "The rules of thermodynamics can be loosely put as: Zero: The universe wants to play a game where it changes your internal energy. One: You can't beat the universe. You can only hope to tie it. Two: You can only tie the universe at absolute zero. Three: You can't get to absolute zero. Building a machine that never ...
Has there ever been a battle where the opposing soldiers simply refused to fight?	[ "Well, there was the Christmas Day Armistice of 1914, where during WWI, the British and German troops agreed to a ceasefire on Christmas Day, and stopped fighting, even going as far as to have a friendly soccer match. However, a few days later, the fighting picked up again, and didn't end until 1918." ]	[ "One verified account of a (relatively minor) public figure who DID fake his own death was that of the British Member of Parliament, and former government minister John Stonehouse. Stonehouse was a rather corrupt right-wing Labour Party MP who had gotten into financial trouble and so to escape his debts, one day i...
Why did Hitler hate the Swiss people so much?	[ "Germany, at the time, was a nationalist fascist dictatorship with all power concentrated in one party and one person. Hitler's vision for the Großdeutsches Reich was an racially-homogeneous state centered around the superiority of the German people. Switzerland, on the other hand, was a multilingual, multicultural...	[ "This does not quite fit the bill of \"rival country\" but in 1989, a self described \"ecoterrorist group\" known only as \"The Breeders\" took credit for the recent infestation of California by medflies, which began destroying crops. Opinion is divided today as to whether it was a real attack, an out of control pr...
It is said that the purpose of Soviet judiciary sentences were to 're-educate the masses' rather than to specifically punish. How accurate was this in practice?	[ "I grew up in the Eastern Bloc and lived under a communist regime until I was 20 years old. All that \"re-education\" stuff was bullshit. Just one of the many aspects of propaganda. Prison was prison, and not very nice either. If you were convicted of political crimes, prison was really really nasty in fact. Ever h...	[ "This question is getting a lot of traffic after being [tweeted by @reddit](_URL_5_), so I thought I'd welcome those of you that haven't visited /r/AskHistorians before to the subreddit. Please do bear in mind that in order to keep the quality of answers here high we have [strict rules on comments](/r/AskHistorians...
Do sexually transmitted diseases exist in animals other than humans?	[ "Dogs are famous for being susceptible to a sexually transmitted [CANCER](_URL_0_)." ]	[ "There are some interesting examples of mutualistic viruses, as [summarized in this table](_URL_1_). One that I have read about before is the [polydnavirus](_URL_0_), which infects a particular part of the ovaries of parasitic wasps. When these wasps find a caterpillar they inject an egg into it along with many pol...
why do large wet spots remain around small leaves on pavement?	[ "The leaf (now dead or dying) excretes moisture. the leaf also traps existing moisture. The leaf shields the moisture directly below it from wind and sunlight as well as artificial heat. The pavement is porous so the moisture you see around the outside and under leaf has \"wicked\" out to the surrounding concrete. ...	[ "The spectrometer on the Mars Reconnaissance Orbiter was pointed at the Recurring Slope Lineae, and it found spectral signatures that are unique to perchlorate salts. Since these lineae flow downhill in the summer, it means that the salts are being brought to the surface and then transported by a liquid of some kin...
What did beer and wine taste like in the ancient world?	[ "Hops weren't used until the middle ages. As you say, the flavour of beer would be quite varied depending on the time period you're talking about, but lack of hops is the biggest difference between modern beer and ancient beer. (My source is the Oxford Guide to Beer) Fun fact: if you'd like to taste something sim...	[ "Do you have a particular geographical region or time period in mind? You're more likely to get a good answer if you are more specific than \"people in the past\"." ]
Why are diseases such as HIV transferable through blood transfusions, but a blood disease such as leukemia isn't?	[ "HIV is an infectious disease, a virus that can only reproduce in human cells. If you move HIV particles in blood to a new person's blood, it will keep infecting cells; it's the way it makes more virus. Leukemia is a cancer that begins in the bone marrow, which starts making abnormal white blood cells. Like all can...	[ "Beef has a higher density than chicken meat, and as such bacteria have a harder time penetrating the outer layers of the beef, compared to chicken meat. This means you just have to take care of the bacteria on the outside of the beef, and you can keep the inside red, if that's what you want. For the exact same rea...
Were Vikings who had a hard time growing facial hair and beards ostracized or ridiculed?	[ "Yes! There's an infamous bit of Njáls saga where Njál is referred to as skegglaus, or beardless, and his sons as the taðskegglingar, shit-bearded ones, because he famously couldn't (or wouldn't, it's not 100% clear) grow a beard. The passage in question: > Bergþóra mælti er menn sátu undir borðum: \"Gjafar ...	[ "As a followup question, what \"image\" did they project? By this I mean, was it like a sign of nobility? Was it to show loyalty to a particular faction/religion/craft? Was it considered low class or as brands for criminals? Thank you. Cool question OP." ]
How does cancer kill a person?	[ "I'm no expert, but I believe you're on the right track. * Tumors consume nutrients and calories the body needs, weakening you * A cancer may release toxins into the body or upset chemical balances. * A tumor may grow large enough that it puts pressure on sensitive areas (such as the brain or heart) * A tumor may o...	[ "When cells divide they make pretty much exact copies of themselves. Introduce radiation to the equation and the copying process goes screwy and the new cell is different. Rinse and repeat over and over and you end up with body cells which are completely different in shape size and function to what they were origin...
How does antibiotic resistance arise?	[ "Because the selective agent kills those without the resistance, it gives the strain with resistance greater access to resources rather than having to compete with non-resistant strains." ]	[ "This may not be truly answerable by current science. The speculation to this is that life and its biology/biochemistry wasn't nearly as complex as it is now. If you go back far enough, you'll end up with life, or at least something that looks like life that was able to replicate DNA/RNA without today's complex...
Towards the end of WW2, why did the Nazis not resort to chemical weapons on their retreat all the way to Berlin, especially on the eastern front? Did they have some sort of moral reasoning?	[ "Follow ups; Did the Nazis have meaningful stockpiles of chemical weapons? What was the allies’ planned response in the event of widespread deployment of chemical weapons?" ]	[ "The simple answer is that the majority of rivers in Western Europe run along a general North/South axis (_URL_0_), whereas the Russian axis of advance was East/West. Those Russian armies poised to invade Western Europe would have a number of river crossings to perform. I am not sure, however, why they should favou...
Were cloaks commonly used in medieval times, as depicted in Fantasy novels? When/why did they fall "out of style"?	[ "There was [a thread last year](_URL_0_) about the \"fall out of style\" part of your question. In particular, /u/japaneseknotweed discusses some practical considerations in [this comment](_URL_0_cty3brk/)." ]	[ "You're going to need to narrow down your time frame here, keep in mind you're asking about a time frame of 1000 years over a very, very large area of land with vastly different cultures. You'll be more likely to receive an answer if you narrow the question down to a more specific time." ]
Why Was New Hampshire Covered Under Section 5 Of the Voting Rights Act Of 1965?	[ "[Here's](_URL_0_) a report from WBUR's Radio Boston on why some towns in New Hampshire receive higher Federal scrutiny of their elections procedures under section 5 of the Voting Rights Act of 1965. tl;dl In 1970 New Hampshire had a literacy test and unusually low voter turnout triggered the oversight." ]	[ "So, I don't know if you know this, but Blackstone did just what you are suggesting. After the housing crash of 2009, they went out and bought up homes in different cities. They put them all under the umbrella of a REIT (real estate investment trust) called \"Invitation Homes\" and then spun it out in an IPO a few...
Why are there such frequent stampedes at the Hajj and why are the resulting fatalities so high?	[ "> Is there a scientific (e.g. flocking) or cultural (it seems like this often happens during the \"stoning of the devil\" ritual) explanation for why this happens with such frequency at the Hajj and not, for example, during Papal Masses or major concert festivals? I think the scale of the Hajj blows all of these e...	[ "You mean the Animal Planet one? Hype and marketing. Then it became a euphemism for menstruation (I'll fill you in if you want, but it's gross sex stuff...) and took on a life of its own." ]
why is fast forward and rewind so poor on video media stored on a flash drive?	[ "I have a feeling it depends on your flash drive and how fast it can load data. I use a 256Gb USB 3.0 drive to play movies through my PS4 and it can fast forward and rewind very smoothly. Most likely your device/port are a USB 2.0 type, and as such has much slower transfer speeds, not great for rapid loading of vid...	[ "A show like Jimmy Kimmel isn't on YouTube for the revenue, they're on YouTube because it's free advertising. They don't want you to watch all the back-episodes, they want you to tune in and watch the show as it's airing." ]
How do computers restart?	[ "Many computers do momentarily power off when restarting. However the capacitors on the motherboard have not been lacking power for long enough to completely discharge their power and so can still hold some things in memory. Sort of like when you unplug a power adapter from the wall but the little light on the bric...	[ "Believe it or not, Microsoft have an excellent page on this: _URL_1_ Also, the \"dummies\" series have a good one, too: _URL_0_" ]
If you were to have a perfectly spherical ball of water, and you were somehow able to poke the center of it, how would the "shockwave" from the ripples look and what direction would they travel in?	[ "You can actually do this by using a focused laser to create a collapsing vapour bubble at the center. The shockwaves propagate outward." ]	[ "What if instead of cars around the equator, they were giant rockets hooked to the ground all pointing the same direction? And we set them all off at once all facing the same way? Would that make a bigger effect?" ]
Why do we cover our mouths when we're shocked or upset?	[ "often, with bad news comes emotions that are difficult to stifle. for example, wailing and gasping are very hard to control, and cause us to make involuntary noises, and open our mouths very wide. although this action could be to try and muffle the sound of an individual's reaction, most of what i've read suggests...	[ "Read up on [Paul Ekman](_URL_1_) and his development of the [Facial Action Coding System](_URL_0_). A good introduction/explanation of his research is found in the book [Blink](_URL_2_) by Malcolm Gladwell. The short answer to your question is, 'no'. From the wikipedia article on Paul Ekman linked to above: > Ek...
Can milk curdle in your stomach?	[ "There is acid in your stomach already. So the milk will curdle up anyway." ]	[ "It's because what your eyes are telling your brain is not consistent with what your ears are telling your brain. This is why you get car sick, too (but the other way around). When there is inconsistent information like this, it could indicate that you've ingested poison. What's a good way to get rid of ingested po...
If I'm eating a lot of salty food one day, can I drink extra water that day to partly counteract it?	[ "He obviously means how water dilutes your bloods content of salt and although his question is technically right, eating excessive amounts of salty food isn’t a great idea, drinking tonnes of water with it will just help mitigate the concentration of salt and the effect on his body" ]	[ "There are a few aspects to this- behavioral, genetic and epigenetic. Behavioral- If you are raised in a family that over eats or eats unhealthy foods, it is not unlikely that you will carry those same eating habits into adulthood. This is an aspect you can change by conciously changing your own habits. Genetic- Th...
If 8 ounces is a cup, why does my 16 oz bag of shredded cheese say 4 cups?	[ "Ounces are a unit of weight, while cups are a unit of volume. Different materials have different densities (the ratio of weight to volume). For example, pillow stuffing has far fewer ounces per cup than steel. Adding some confusion to the issue, the \"fluid ounce\" is a unit of volume, equal to the volume of one w...	[ "The news is a pretty random thing. Some stories get picked up, others don't. Sometimes there's deliberate bias involved, because the media want to spin a certain narrative. But other times it really is just random. So this story about the pacsun shirt took off, the House of Cards logo didn't. Also, you have to r...
If the half life of DNA is 512 years, how are those russian/korean/japanese scientists planning to clone the wooly mammoth?	[ "That was a measured half life of DNA in bones buried in the ground in New Zealand at an average temperature of about 15C. It shouldn't be taken as an absolute half-life of DNA survival time, which will vary wildly based on environmental conditions." ]	[ "Rotated through MedOnc. We collect data for 5, 10 and 15 year benchmarks for most cancers to get a vague idea of the progression of a type of cancer, not to tell people how long they’ve got. One example of its use is to compare treatment modalities e.g. 5 year survival of women with p+e+her+ breast cancer on letro...
Windchill vs Temperature I don't get it...	[ "The warmth that radiates from your body acts like a kind of insulation. So let's say you're standing in 32 degrees weather with no wind and it feels a certain way. Once the wind blows against you, your \"insulation\" gets blown away and suddenly 32 degrees feels colder than before, even though the temperature tech...	[ "(F-32)5/9 = C (C1.8)+32=F It isn't a very direct equation to convert between the two. Half of one isn't equal to half of the other because there's some addition/subtraction involved before the multiplication/division. Interestingly enough, at -40 C, you're also at -40 F." ]
Can You Freeze a Bubble?	[ "Any substance? This is what glass blowing is. Frozen bubbles _URL_0_" ]	[ "I like this. However, pictures are awesome. Your pictures with the flame on the drawing board? Good stuff. The video with candle/flame? Good stuff. Your face? Great face for TV, but I don't want to see it the majority of the time. It makes the viewer lose interest over a period of time. Personally, I liked learnin...
Why conservatives recently try to prevent a detailed census?	[ "I'll probably get down voted for saying this because it sounds so preconceived, but the right does not want data. If you look at most credible data analysing right wing ideologies, it usually disagrees with them. Trickle down and Reaganomics, more jails = less crime, creationism, deregulation helps the middle ...	[ "American here, we don't like anything new near our buttholes. New things scare us, anything to do with buttholes scare us. We may be the best country in the world but we are very shy about our buttholes." ]
why is it sometimes we can't say a word or name even though we know it? When it's 'on the end of our tongue' but we literally just can't say it	[ "Error: Segmentation Fault Seriously though, I think that this is really what's going on. Our brains are constantly overwriting old information with new information. When it does so, there are some lingering neural pathways to concepts that were recently overwritten, akin to a dangling pointer in programming. The d...	[ "Simply put for the same reason drinking water when you're not thirsty isn't as refreshing as when you're REALLY thirsty. Anticipating the bodies' needs doesn't trigger the same reward responses in the brain as fulfilling a need that is already present. Your muscles don't NEED to stretch right now, so you can't ant...
I've read that one of the reasons that the Romans were so keen on conquering Britian was because of the wealth of minerals to be found there. What was Roman mining like? Of more interest, what were Roman mining towns like? What sort of military presence might there have been?	[ "Thanks to /u/Krazyhades (with a wonderful name) for summoning me: he/she is right to point in the direction of Cornwall, where indigenous mining had been going on for centuries before (after after) the arrival of the Romans. I suggest that you need to be considering the topic to be about Roman-era British mining, ...	[ "The best resource maps we have are of our own Moon and of Mars, thanks to the Clementine, Lunar Prospector and Mars Odyssey missions. Here are a few abundance maps for several materials of interest on the Moon - such as: [Titanium] (_URL_1_), [Iron] (_URL_6_), [Silicon] (_URL_5_) and [Thorium] (_URL_3_). Not to me...
In World War II, what kind of variety were there in tanks, and what kind of use did they get?	[ "Actually, the concept and adoption of the modern Main Battle Tank didn't come into being until after WW2 - during the war, the Sherman and T-34 were one of many types of tanks fielded. There were tanks classified as heavy tanks - like the Soviet IS-2 and US M26 Pershing. These were designed to have equal or greate...	[ "This is such an incredibly vast question that I find it literally impossible to imagine your professor assigning it to you without something more specific in mind. As such, you should review the material from your class to look for your answer." ]
How do ruins become buried and what is it's relation to time?	[ "I would crosspost to /r/archaeology, they tend to get this question semi-regularly. Maybe /r/geology for the geological timeframe aspects of the question as well." ]	[ "Here's a discussion from 3 years ago: [Is there any historical precedent for a pre-modern culture constructing elaborate mechanical traps \\(as seen in many films such as \"Goonies\" or in various \"Indiana Jones\" films\\) that are disarmable by an artifact or by a sequence of actions? Where does this common fil...
How can there be a "hole" in the ozone layer if ozone is a gas? Won't it just fill in the hole?	[ "The \"hole\" is created by compounds that destroy ozone gas. The most common of which are known as CFC's (chlorofluorocarbons). They essentially \"eat\" the ozone, thus creating the hole. Ozone cannot fill in this gap, as it's occupied by these compounds." ]	[ "The middle of the United States, sometimes referred to as the Great Plains, is a large, relatively flat area. This allows colder, dryer air from Canada to head south while warm, moist air from the Gulf of Mexico moves north, eventually meeting in the middle. When these two air masses collide, powerful storms can f...
Why is Saudi Arabia not diversifying their economy to include solar or wind power?	[ "But they are: [Source 1](_URL_0_) [Source 2](_URL_2_) [Source 3](_URL_1_)" ]	[ "So, I don't know if you know this, but Blackstone did just what you are suggesting. After the housing crash of 2009, they went out and bought up homes in different cities. They put them all under the umbrella of a REIT (real estate investment trust) called \"Invitation Homes\" and then spun it out in an IPO a few...
How come when you put earphones in your nose and pop your ears you hear the music in your head?	[ "Our hearing apparatus consists of the external ear (which is our floppy ear pinna and ear canal) and the ‘internally hidden’ middle ear, and internal ear. Normally, the sounds from outside is transmitted from the external ear then towards the eardrum into the middle ear, and lastly, towards external ear, where the...	[ "Destructive interference. Imagine sound being ocean waves that travel in direction towards you. If you were to create waves with equal wavelength and height to the incoming waves, and send them towards the waves that travel towards you, then the waves would cancel each other. That would cause sea where the waves ...
Could electrolysis be used in a matter to purify water of radiation?	[ "I think this is like building a death ray to kill an ant; there are filters that can remove radiation from water. If water is contaminated, then the ionizing particles are dissolved in it (like strontium-90, radium-226 etc.). A proper filter should remove these particles through reverse osmosis. Adding procedures ...	[ "Watched Sum of All Fears last night? You might want to look into the Monitoring Capabilities of the Comprehensive Test Ban Treaty (CTBT). You can read a bit about it here: _URL_0_ Basically, radiochemical analysis can tell you information about the bomb design and the metallurgical refinement techniques of the fis...
Why does hot water make a tea bag blow up like a balloon?	[ "The bag has some air in it. When you pour on the water, this coats the surface of the bag and seals the air in. The temperature of the water heats the air inside, which expands, making the bag appear to have been blown up." ]	[ "I am sure there will be physics papers published on this during the next months just like with the glowing sticky tape. One theory is briefly explained in the original video. As the rubber is stretched the molecules have to align in certain ways. This constricts them which increases the internal pressure of the ru...
Why have some civilizations developed into modern societies while others haven't?	[ "Most people copy ideas. If the tribe A comes up with a good idea, then tribe B next door will copy it. Or tribe A's good idea may make it powerful enough to conquer tribe B and force them to adopt their idea. Isolated communities may not be exposed to outsiders' ideas (like modern technology) so they don't copy th...	[ "They mutate. Take H1N1 for example. Until recently, that particular brand of influenza was only found in animals. Then, on a pig farm in Mexico, one strain of the virus mutated to be communicable to humans, and then infected the farm boy and spread across the world. It's basically evolution happening at a speed fa...
How does a Hexbug Nano move forward? Isn't it a brownian ratchet?	[ "You see how the legs are bent? The spring force to drive the toy forward is greater than to drive it backwards as a result. The orientation of the motor's rotation might help by having the mass move forward to back and compressing the legs on each stroke." ]	[ "I've actually built one for a science fair before. I used _URL_0_ as a reference guide: _URL_2_ _URL_1_ It worked, but know going in that you will not get a huge amount thrust. Your setup would probably do better, but it will still most likely not be a lot. What I ended up doing that had a more striking visual eff...
How realistic is widespread nuclear energy? Does the Earth have enough uranium deposits to provide power long term?	[ "According to [this](_URL_0_) study, there's enough Uranium to power the world for a while. There has been enough Uranium identified to produce 2.9 x 10^22 J energy, and it's estimated that global reserves actually contain enough for 2.2 x 10^23 J. For reference, global energy consumption in 2010 was 5.0 x 10^20 J....	[ "In the case of oil, a special set of conditions has to apply for it to be formed and preserved in the subsurface: 1. Source of organic matter (marine plankton/algae ➡️shale) 2. Deep burial (heat and pressure) ♨️⬇️ 3. Reservoir rock (eg sandstone)🍰 4. 3D Structure to trap migrating oil🗻 5. Seal to prevent it leak...
What is happening in Macedonia?	[ "ELI5 as possible: Kosovo scenario again. Meaning Albanians will take a part of Macedonia and make it a new state. And that was not a protest, but a terrorist attack." ]	[ "[Search before submitting, especially when asking about current events. The search box is in the upper righthand corner of the page.](_URL_0_)" ]
Why are people not vaccinating their kids ?	[ "Some people don't trust the government for anything and see the scientific community as an extension of it. That distrust can become paranoia. If someone is prone to faith then they're more likely to accept whatever sounds right to them than what has actually been observed by experts (see 'truthiness')." ]	[ "Horse meat isn't rare at all. You can get it in many parts of europe. Tastes ok too. Anyway, that's culture. The same reason we think that bacon and eggs is a breakfast food, and don't eat grasshoppers." ]
How does lightning "know" the path of least resistance?	[ "This is a misconception. Generally, electricity takes every path that creates a complete circuit. The myth arises due to the majority of the electrons passing through the path of least resistance, as per V/IR. Where if the paths resistance is low, then the power passing through that path is greater, this is where ...	[ "Elektricity is lazy and always takes thé shortest route back. Meaning from pin 1 of the taser to pin 2 of the taser" ]
What would be the effects on the human body after sitting in a bed for 20+ years, as seen in the original Charlie and the chocolate factory grandparents ?	[ "Muscle atrophy, serious bed sores or ulcers. Blood clots forming which could lead to strokes, heart attacks and pulmonary emboli. Nothing good." ]	[ "Yer not alone in askin', and kind strangers have explained: 1. [ELI5: how do the time differences between planets work in Interstellar? ](_URL_6_) 1. [ELI5:Interstellar's relativity of time. ](_URL_3_) 1. [ELI5:[Interstellar] Time moves faster is some places in space than others. ](_URL_0_) 1. [ELI5: Aging in the ...
Why do mosquito bites leave bumps and getting a shot at the doctors office doesn't?	[ "The bump isn't from the small hole, it comes from the chemical that the mosquito injects into you. The saliva chemical they use prevents the blood from clotting and clogging up their tube." ]	[ "Imagine a needle in a haystack that is 10 kilometers wide, and there are only 10 people designated to finding said needle. It would take them an insanely long time. They might find a few of the needles in their allotted time frame, but likely not all of them. When a game is released to the public, it's the same wa...
Why is it that whenever we stretch really good (i.e. after waking up or lying down for a while), it temporarily impairs our hearing, and we hear a strong "ring" sound?	[ "/r/EarRumblersAssemble There are tiny muscles inside your ears. Some people can \"flex\" these muscles at will. I personally can do it whenever I want... Many can't do it without some sort of associated movement - tightly closing your eyes is a common one. Almost like how some people can't move just their little t...	[ "I'm only speculating but it could be Pavlovian response. You've probably heard of Pavlov's dog where the scientist would ring a bell and then give the dog some food, repeat, repeat, repeat. Eventually the dog would associate the bell with food and begin salivating at the sound of the bell, whether there was any fo...
Why are we told for example it is -2 degrees Celsius but feels like -10 degrees Celsius?	[ "This has been asked before, but it helps to know the right buzzwords for search, \"wind chill\": _URL_0_" ]	[ "Because most people will see it as a lower value. Just like stuff are advertised for 19.99 and a lot of people will think of that as \"less than twenty.\" 3.699 gets rounded in people's heads as three-sixty, not three-seventy. In a couple of days you can train your self to see the real value, 19.99 actually means ...
Were soldiers really sent home to preserve their family line, as seen in Saving Private Ryan?	[ "An important incident was the loss of the [five Sullivan brothers](_URL_1_) aboard a single ship in 1942. The incident resulted in a 1944 [film](_URL_0_) and also helped inspire a change in [policy](_URL_2_)." ]	[ "While not a scientific answer to your question at all, I want to suggest the excellent movie [Before the Fall](_URL_5_) (German Titel: Napola – Elite für den Führer) to anyone interested in this topic, which is a story about pupils in an elite high school in the German Reich." ]
If extremely common viruses, like Hepatitis A, give humans post-exposure immunity, how do these viruses survive in places they are everywhere, such as India?	[ "Kids provide a perpetual source of people with no immunity. By age 10, 90% of kids are infected with Hep A and immune for the rest of their life, which means that the number of people who can get infected with Hep A is in the ballpark of 5-10% of the population. That's still plenty of people to pass the virus arou...	[ "Straight hair that lies flat tends to hold in heat. That's an advantage in cold climates. Curly hair allows heat to escape while still providing protection from the sun to the skin underneath. That's an advantage in hot climates. Melanin in skin (the part that makes it dark) tends to block what's needed to make vi...
[Europe] Medieval social contract between Lord and serfs	[ "The answer to this is going to vary with time and place, and have a lot to do with how desperately the lords needed someone to cultivate their land and how desperately the peasants wanted land to cultivate. If you were formally someone's serf, that is, you swore an oath of fealty to them, they did have the obligat...	[ "Yes. The middle ages are a construct of the renaissance. No one is sure when they start or stop, and they start or stop at different times in different places anyway. Most historians dislike the term." ]
What does it mean that quantum information cannot be destroyed?	[ "Quantum mechanics has a property called unitarity. Unitarity says that as a quantum system evolves in time, it does so in a reversible way. Thanks to unitarity, two different initial states cannot evolve into the same final state. When a measurement is made in quantum mechanics, we assert that something non-reve...	[ "If you know the full Hamiltonian for your system and the initial state, you in principle know how the system will evolve for all time. The time evolution is governed by the [time-dependent Schrodinger equation](_URL_0_). However you don't necessarily know what the results of measurements will be. For example, if y...
Since false starts are a thing in races, is there a reason they don't employ a rhythmic countdown instead?	[ "Music isn't a competition between band mates, but racing between racers is. Fast reaction to the start gun is part of that competition. Motorsport usually does use a form of countdown, but reaction time is still important, vitally so in the case of drag racing." ]	[ "This question is getting a lot of traffic after being [tweeted by @reddit](_URL_5_), so I thought I'd welcome those of you that haven't visited /r/AskHistorians before to the subreddit. Please do bear in mind that in order to keep the quality of answers here high we have [strict rules on comments](/r/AskHistorians...
Why do some viruses (like the flu) have vaccines that have to be administered yearly, while other viruses only need vaccinated against once?	[ "Influenza evolves rapidly over the course of a year, so the common vaccines become ineffective between seasons. Hence new vaccines have to be be developed and administered each year." ]	[ "Computers run on sets of instructions telling it how to run all the parts of the computer and build an interface so you can use those parts. Say you're following a recipe for a cake. Then you finish the cake and someone comes along with a better way to make a cake by adding another ingredient and changing how muc...
Why do some vaccines "last" longer than others? What's the difference?	[ "The primary difference is the disease. The Flu virus is more prevalent and it also mutates quicker than some other viruses, and so a vaccine that worked last year likely won't work this year as the virus has reproduced so much that it's too different from the previous version." ]	[ "Epigenomics is the simplest of answers, you should read about it, I think you'll find it interesting. The wiki page is a nice summary. It talks about processes that affect the translation/expression of our DNA. Simply put having the same DNA, as the twins do have, does not mean those genes that are key in developi...

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