Subset (10)

eli5 · 25k rows

Split (1)

train · 25k rows

query stringlengths 20 300	positive listlengths 1 1	negative listlengths 1 1
With the German army massed of 2 million men, and barely any empire to justify it, why didn't Britain see WW1 coming and prepare her own army, rather than rely on the tiny BEF?	[ "They certainly saw it as a threat, there were several fiction books written predicting an invasion. First, for a long time the British hoped to remain neutral and to stay off the continent. Second, Britain was at risk of a revolution from communists and at risk of civil war in Ireland. They had to consider how bui...	[ "The human arm has 23 muscles, the human face has 43 muscles. Right there you're nearly doubling the number of muscles that you have to replicate. Additionally the mouth and face are all about little details. If an arm in a video game moves 3 ft from throwing a football, the developer can be an inch or 2 off and yo...
How did the dominant sports in the USA come to be so different from the rest of the world?	[ "The answer lies in the history of colonialism. Although baseball may have its origins in Native American sports and gridiron football developed out of rugby, all three sports were devised in the United States. The US lacked extensive colonies to which it could export sports, which was a typical vector of transmiss...	[ "Back then people still needed jobs, now they dont and can practice harder for longer. And science helps by showing then methods on improving motions. You cam find cool videos on youtube" ]
Why is it that some tasks are much more easily performed while not thinking about what you're doing?	[ "The short answer is that your consciousness is rather limited in processing power compared to your subconsciousness. If you practice a task enough while using your consciousness, a lot of the specifics in the task will be transferred to the subconsciousness. Until the task is practiced enough, you won't be able to...	[ "Muscle memory and learning. You don't instinctively know exactly how to throw a baseball to get it on target as a toddler. You can get it in the general direction, but only through practice and the brain having an opportunity to learn through experience do you become capable of throwing a ball accurately" ]
how do rivers sometimes get as curvy as racetracks? Example inside.	[ "Its Known as a meander, there are some great examples on the wiki page so im not gonna type them up, but [this picture](_URL_1_) shows how gradually the outside of the bend of the river erodes faster than the inside... water obviously erodes the outside of the bend faster then the inside since the water travels sl...	[ "Do you mean chromatic aberration, which looks something like [this](_URL_0_)? If so, that is caused by lenses (and materials that act as lenses, like water) having a refractive index which depends on the wavelength of the light. Since natural light contains many wavelengths of light, the colors focus to differ...
Why can't we just store energy in batteries until we need it?	[ "Part of it is that it is slightly impractical to build a big enough battery and partly because batteries do not hold a charge forever. They decay over time" ]	[ "Let's say you have a 7 lane interstate. At each end there is a toll booth. In the past payments were processed manually and there was a receipt that had to print, but the printers were slow. Only do much traffic could get through. Fast forward to the future where you pay with the touch of a button and get an insta...
How are meteorologists able to forecast the weather 15+ days in advance? How often are those forecasts accurate?	[ "A few models will show weather out a few weeks. Some models are for determining seasonal outlooks on monthly basis. Most Meteorologist use models as guidance to their skills, and all will tell you there are drop offs in model guidance at days 3 and 5. Most Mets will not talk about anything beyond day 5. Anyone w...	[ "Because critics are full of shit. Most of the art world for example called Jackson Pollock \"Jack the Dripper\" until a wealthy hotel magnate bough one of his works and put it in the lobby. Then Pollock was a genius. Critics hate to be on the wrong side of history so they never have an issue it seems changing thei...
During Colonialism, where there any colonies established by smaller European, or non-European nations?	[ "Belgium colonized the Congo, first as a personal possession of King Leopold II, then as a belgian colony. It was one the worst administrations in the history of european colonization, humanitarian-wise. _URL_0_" ]	[ "[Here](_URL_0_) are Roggeveen's logs during the time he visited Easter Island. Nowhere does he mention 'whites, indians and Polynesians living in harmony'; he does, however, describe the natives' complexions as varying, some paler than others. Also, 'Polynesia' was not a word until 1756, 27 years after Jacob Rogge...
Why are there so many different numbered ink cartridges?	[ "Printer companies make money selling ink. They need you to buy more ink from them. That means changing things so that ink cartridges from old printers don't work in new printers, because they've added DRM and/or expiration date technology to the processor chips in the ink cartridge. The new numbers are just so you...	[ "You are right. It is mostly just the advertising aimed at making you buy it. So go for generics. Do not pay extra for the advertising. Ibuprofen is the same drug whatever the brand name." ]
How fast does something have to spin before it looks like a blur?	[ "Your eyes can't detect any changes that happen under 10 milliseconds. Did you know the digits on your alarm clock aren't on all at the same time? They rotate every few milliseconds to save on power consumption / prolong life." ]	[ "Think of a marbel in a field at night, you know it is somewhere on the field but you just cannot make it out. Now imagine it's moving. On the other hand, imagine a street light with a fly buzzing around it. You cannot see the fly but if you look at the light long enough you can just make out something changing in ...
What causes us to have uncontrollable (and can't stop) kind of laughter?	[ "Good question. I hope you get an answer from someone who knows. It is an amazing stress reliever and always a surprise when it happens. There is a special connection you have with people with whom it happens often. It seems a very human experience." ]	[ "Scientists seem to disagree between themselves on the answer. I know of 4 main theories (but there could very well be others). 1: Brain overlap theory. Basically, the parts of the brain that control the sex organs are located near the parts of the brain that control other areas of the body like the feet. These adj...
An interesting third person to compare to Cao Cao and Han Wudi	[ "Han Wudi and Cao Cao are both martial rulers, the third person you choose might as well be a conqueror as well to make your life easier. Qin Shihuang, Genghis Khan, and Mao Zedong would fit the bill. (Mao especially liked to compare himself to Cao Cao and Qin Shihuang.) Other military leaders from that list are An...	[ "They don't have to resemble the actor very much, since the scenes are carefully planned to disguise the stunt double's face. Take [Vic Armstrong](_URL_0_) for example - he looks a lot like Harrison Ford, but he also served as the stunt double for Timothy Dalton, George Lazenby and Christopher Reeve. Now they can j...
Why does milk become spoiled when left in the heat but not when heated?	[ "Milk is spoiled by bacteria. Most bacteria grows fastest in a warm environment. Leaving milk to warm up over a long period of time gives the bacteria the warmth it needs, and plenty of time to multiply. When you heat milk quickly the bacteria doesn't have enough time to grow to substantial numbers and spoil the mi...	[ "Ah... sort of? Humidity is a measurement of how saturated the air is with water vapor. Warm air can hold more water than cold air. So if you have say, 10 liters of water vapor in a 100 m^3 room, and raised the temperature, the humidity would go down, as the air's capacity to hold water increases. So in theory, if ...
If most people are vaccinated, how can an unvaccinated person cause an outbreak?	[ "The outbreak will be among those who cannot be or are not vaccinated. Some people have compromised immune systems and cannot be vaccinated. Herd immunity protects those who cannot be vaccinated. Nobody cares about people who choose to not be vaccinated, with the notable exception of the incredibly unfortunate chil...	[ "A marketing campaign by Boroughs-Wellcome intentionally stigmatized the disease in the late 1970s in a successful bid to sell Zovirax. Until then, they had a drug no one really needed because no one really cared. It's the first known and classic example of intentional \"disease-mongering.\" In doing so, they chang...
How can a rocket propel itself in space if space is a vacuum?	[ "The rocket thrusts gasses behind the ship. Since every action has an equal and opposite reaction, thusting matter in one direction creates motion in the opposite direction. The rocket could thrust anything behind it to create forward motion, from rusty bathtubs to chicken fingers. But no, you are correct, wings in...	[ "With Spirit and Opportunity, there is a specific reason. It was expected that the solar panels would quickly become coated in Martian dust, and soon the rovers would not receive enough power to function. However, the Martian wind turned out to be quite effective at cleaning the solar panels, so while they look fai...
Can things explode in space?	[ "Certainly. They can even burn if an oxidizer is provided." ]	[ "only if it's structure is perfectly non-[amorphous](_URL_0_) so that it wouldn't start contorting with the inertial effect commonly known as the [centrifugal force](_URL_1_). This would rule out glass and many plastics Also it would have to also be in a perfect vacuum so that air resistance, or friction with the a...
Why Can We Only Breathe Oxygen	[ "When oxygen reacts with many chemicals, it does so in a way that releases energy. We use this energy to run our bodies. This is also the energy you use when you burn wood for heat or gas to power your car." ]	[ "That small spectrum is what the sun produces most. If we evolved near a star that primarily emitted a different spectrum, we would be evolved to see that spectrum." ]
If only the skull of a human is found during an archaeological dig, is it possible to determine the gender of the individual?	[ "Yes, it is. The skulls of men and women are shaped differently. You can see just in the facial bone structure of living human beings that there is a difference. A studied anthropologist looking at the skulls wouldn't have much trouble." ]	[ "Several reasons: * Better technology. Many chambers were detected by sonar or radar. They would send a signal through the stones and listen for irregular echoes. Today's sonar and radar imaging techniques are better than they were in the past. The equipment is more sensitive, uses different frequencies, and with d...
How does Fiji water justify their inflated price?	[ "The claim is that their water from Fiji “comes from an artesian aquifer .“ Their unstated premise is that this water is somehow more pure and better for you. Their price comes from peoples willingness to buy it despite the high price. And people's willingness to buy it comes from their unstated premise." ]	[ "You are right. It is mostly just the advertising aimed at making you buy it. So go for generics. Do not pay extra for the advertising. Ibuprofen is the same drug whatever the brand name." ]
Why do criminal offenses "expire", so that after a while the offender can't be charged for a crime anymore?	[ "What you're talking about is called a [statute of limitations](_URL_0_). There are three main reasons to have them: 1. To encourage prosecutors to press charges in a timely fashion. This streamlines the legal system and prevents bloated files of suspects-who-haven't-been-charged-yet. 2. The accused may have eviden...	[ "Some flavours intensify over time as they are released from the ingredients to mingle with one another. Other foods simply have what gives them flavour breakdown or otherwise become absent. The spices in a chili will release more flavour over time like the leaves in a tea. A cake however, dries out over time makin...
What does picturing someone naked do for someone mentally who gets nervous in front of people?	[ "It's supposed to make them vulnerable and weaker than you in the mind's eye so they're less intimidating." ]	[ "from what Ive found, the question has to many variables to nail down exactly, as each case is typically different. some research says its the swelling and shrinking of blood vessels, while others attribute it to memory association. In short, its a well documented phenoma with a variety of reasons and speculations ...
Why are urban centers almost always Democratic and rural ones Republican, in recent times?	[ "Exposure to different kinds of people and ways of living vs rural bubbles. Notice that ports and hubs along the water tend to be the most liberal often having to do a lot with immigration and travel." ]	[ "I feel like this question is a bit outside of this subreddit's scope, it's really more of an economics question, plus if you look at [this graph](_URL_0_) then you can see that they were at very similar levels until around 20 years ago when they diverged, so anything following that violates the subreddits 20 year ...
Double-Slit Experiment: How did early scientists "observe" the photons causing the interference to be destroyed?	[ "The wording can be misleading. The distinction is simply whether the measurement is made at the double-slit, or at the screen farther back. \"Measurement\" or \"observation\" simply implies that the photon has been interacted with in some way" ]	[ "> no such undisturbed sequence has actually been found, meaning that our fossil records are inaccurately formed. Can somebody disprove this? That's absolutely incorrect. There are such a fantastically large number of counter-examples that I don't know where to start. Modern lake beds, ocean beds, rivers, alluvial ...
Why does watching porn help people fall asleep faster/easier?	[ "Probably because they are masturbating and orgasms can help you sleep." ]	[ "I read an article a somewhere that said it was do the the \"roughness\" or randomness of the noise. As the fingers nails catch and slip it produces random variances in the amplitude and frequency of the noise. Our brains find the signal unpredictable and that somehow causes it the view it as a danger. There are a...
That aristocrat joke	[ "There is nothing funny in the joke itself, it evolved as a way for comedians to test thier skill, delivery and push thier boundaries - and was typically only told in the company of other comedians." ]	[ "Does this mean he would be in thrall to the rich since they would be the ones with the leftovers?" ]
Who creates computer viruses and why do they do it?	[ "Programmers do, and for a variety of reasons. You can sell peoples personal information for a decent amount, or steal their bank account number, or turn their computer into a proxy for attacking something else." ]	[ "This is a very common question. You can use search to find [all the other really good answers](_URL_0_ ). This is instant, and faster than ust typing in your question every time. It's a way of cheating elections. Read the others, and then ask a more specific question." ]
What are the origins of Homosexuality?	[ "You're wondering how there could be an evolutionary \"survival of the fittest\" advantage to homosexuality? Passing on your genes is not just living long enough to have children. It's looking after them until they are fully functional adults too. If you're not interested in babymaking, you don't have any children ...	[ "Well as far as I know it started with this prank video: _URL_0_ And after that it simply went viral." ]
Is Liquid Fluoride Thorium Reactor technology a plausible solution to the energy crisis?	[ "Yes. LFTRs would be able to supply our current energy needs for thousands of years, and do so cheaper than coal power plants. There are minor engineering problems to be solved, but I have not found any serious showstopper during my research. So I remain optimistic." ]	[ "Availability, cost, pollution. Water is cheap/free, readily available (that's why most power plants that use steam turbines are built on lakes) and don't pollute when boiled. If you closed the system it could work, but you would have to have a significant condenser that wouldn't restrict flow in any way or you wo...
Why do Presidential candidates "suspend" their campaign? Does this mean they could suddenly return at some future point?	[ "It has more to do with fundraising. A suspended campaign can still fundraise (usually from the remaining candidates, in exchange for endorsements or logistical support) in order to pay down incurred debt (typically losing candidates owe staffers a significant amount). A terminated campaign can no longer collect mo...	[ "There are three things to consider when thinking about dissolution. The solvent’s (water’s) interaction with itself (among nearby water molecules), the solute’s (salt or sugar’s) interaction with itself, and the interaction between the solvent and the solute. In order to dissolve, this last interaction must be str...
Why are Jews considered to be a race, when Judaism is a religion?	[ "It's both. People that are racially Jewish come from a group of people that primarily bred among themselves for thousands of years. This concentrated the genes for certain physical characteristics that make somebody look stereotypically Jewish." ]	[ "Scientists have to fix definitions. Time intervals, unit distances and the kg were all defined by physical objects or other concepts that can change which would change the physical constant we define from it too... in the case of distance we redefined it as the distance light travels in a certain time in a vaccuum...
How people from around the world are able to join up with ISIS with seemingly no issues.	[ "Its easy to join for many Europeans because all they have to do is chat with an online recruiter, purchase transportation to Syria and meet up with their recruiter. European recruits are also highly valued by groups like ISIS because its a big propaganda win to get a US citizen to join an antiwestern group. They c...	[ "What do you mean, you tried but got lost? Do you mean you watched some episodes of the [current] third season of a show and had no idea what was going on or who any of the characters were? Well yeah, obviously, try starting with season 1. Or do you mean you started watching the first few episodes and didn't unders...
How does the brain know where a nerve is in the body, especially when the nerve has been moved?	[ "Other answers aren't really answering your question... You are pressing the skin over your nerve which isn't actually stimulating the nerve. The nerve only gets stimulated when the pressure receptor on its end gets stimulated. These pressure receptors are embedded in the skin so if you press above your nerve you a...	[ "Imagine you're trying to find a coffee shop in a city. If you've been there recently, it should be pretty easy to find. If it's been 10 years since you've been to the coffee shop or the city, it might take you a LONG time to find. It also might take long to find if you've been to other, similar coffee shops in the...
why are tanks for liquid transport round instead of square?	[ "The cylinder (or sphere) equalizes the pressure of the liquid contents better." ]	[ "There are alternative wheel designs ([example](_URL_0_)), but they're expensive and not as easy to repair if something goes wrong. Rubber tires are a simple, cheapish solution that works quite well. \\* note: don't trust me, I am not an engineer" ]
What caused Robespierre to decide that the use of the Guillotine was okay?	[ "Capital punishment was very common in pre-revolutionary France. For nobles, the typical method of execution was beheading; for commoners, it was usually hanging, but [less common and crueler sentences were also practiced](_URL_0_). When Dr. Guillotine proposed the new method of execution to the National Assembly, ...	[ "People care less about obeying rules when they are about to die. At this point what do they have to lose? Did Jerry over in cell D12 make a rude comment about your mother? Maybe Jerry should get stabbed 12 times with a sharpened tooth brush. What are the guards going to do about it? Kill you? lol!" ]
is there a place in space that we can't observe because the light from it hasn't reached us yet?	[ "Yes. Any object between roughly 46 and 62 billion light-years away has not yet had time to reach us. Any object farther than 62 billion light-years will never be visible to us as it lies outside our universe's event horizon in the LambdaCDM model. * _URL_0_" ]	[ "Congrats, you've stumbled upon a major open question in astrophysics." ]
Why have video game developers mastered most life-like motor skills, but still haven’t figured out how to get mouths to move realistically, when the character is talking?	[ "The human arm has 23 muscles, the human face has 43 muscles. Right there you're nearly doubling the number of muscles that you have to replicate. Additionally the mouth and face are all about little details. If an arm in a video game moves 3 ft from throwing a football, the developer can be an inch or 2 off and yo...	[ "Often, the voices are recorded before the final animation. So the animation is done to match the voice, not the other way around." ]
Why is the US tax system more complex than other developed nations?	[ "The US tax system is not much more complex then in other nations. The main difference is that in most countries the taxes are calculated by the tax office with the help of banks and other businesses and then sent to citizens for review. However in the US it is the other way and citizens are required to gather all ...	[ "The IRS doesn't know exactly how much money you will make this year based on a single paycheck, you might have a second job or a rental property or you might get a raise. They also don't know what deductions you qualify for or are going to take when they issue your pay cheque." ]
Tyre's Armoured Warships	[ "Sorry for the delay in seeing this! Unfortunately, I'm not quite sure what section of Arrian you refer to - I'd be more than happy to take a look at the Greek, but I'd need a place to look, first :) Would you be able to get me the section or a quote of the passage you refer to?" ]	[ "No. Germany launched the aircraft carrier [Graf Zeppelin](_URL_0_) but it was never finished, and the Italians had the [Aquila](_URL_1_) which was also never completed." ]
Why do Scientists use the 'half life' of something, why not just say the full life?	[ "Because, mathematically speaking (it will eventually happen in practice), the full life of a radioactive substance is infinite. A half life is the time taken for half of a sample to decay. So, you wait one half-life, and you're down to 50% of what you had before. Wait that time again and you're down to 25%, and so...	[ "Stations charge by the second to run a commercial. Shaving down to the most recognizable parts after the long version has run saves money." ]
Why isn't blood pressure a determining factor in defining whether if someone is dead or not?	[ "It is. Having a heartbeat causes predictable fluctuations in blood pressure. When you check for a pulse, you're checking for fluctuations in blood pressure big enough that you can feel it with your fingers. Perhaps you meant to ask about some nuance of blood pressure?" ]	[ "That's the primary role of the heart. The heart is a pump that moves the blood all throughout the body. Think of it like a hose hooked up to an electric pump. The hose is full of water, completely full of water, and hooked up to the pump at both ends. While the pump is active, the pump is pushing the water through...
Why does moist heat work better than dry heat when applied to sore muscles?	[ "I think it would be all about heat transfer/ heat capacity. Water can hold a lot of heat (it's thermal capacity is high), and water would conduct heat better to your body than just warm cloth." ]	[ "They're already cooked and just need to be rehydrated. Think like a chicken breast...You can boil it and it'll take 20 minutes to cook, but if it's already cooked you just need to warm it through and it takes 5...Same concept different medium." ]
What is the difference between NoSleep and CreepyPasta?	[ "NoSleep is supposed to be for true, scary stories. The problem is, you don't have to verify your stories, and no one can claim a story fake, thus people who want to give people a good scare post here. CreepyPasta is just scary campfire-like stories. I used to love NoSleep, but unsubbed a few months ago because t...	[ "This is more of an opinion or discussion question than a concept you're looking to have explained. Not really a topic for ELI5. Maybe /r/askreddit" ]
Have we discovered stone age archaeological sites underwater (where old coasts existed before sea level rise)? If so, what have we learned? Are efforts ongoing?	[ "There's certainly been stone and crafted antler artifacts found under the North Sea in the Dogger Bank, they've been appearing in fishing nets for decades, but I wouldn't say it's an actual site, there's been work on it since 1998. Report on peat samples dredged up: _URL_1_ Article on the digs and the artifacts r...	[ "Because of the rotating Earth's [Coriolis effect](_URL_0_), the surface of the ocean responds to wind in a funny way: it moves sideways to the wind direction: to the right of the wind in the northern hemisphere, to the left in the southern hemisphere. This is known as \"[Ekman flow](_URL_1_)\". In the tropics, t...
Has anyone ever created an algorithm for creating congressional districts?	[ "I'm sorry to be terse, but if you google \"algorithms for congressional districts\" you will find a large number of results that answer your question pretty directly. Different algorithms that could be used and the pros and cons associated with each. The moral of the story is basically, yes, you can. None of the ...	[ "How did they do it (back then?) or how do they do it now? By using experiments and logical reasoning. You can't put a cell under a microscope and watch its metabolic functions. Instead you have to extrapolate out based on the inputs/outputs of the cell. In fact, the citric acid cycle was first postulated from expe...
how do phone card codes work? I know you punch in a number to call, but how does it bypass your phone carrier so you don't get charged by them too?	[ "You dial a toll free number first to connect to the company that issued the card, then you type in the code and phone number to tell them who you are and who you want to call." ]	[ "Inflation is a big factor, particularly for things that come from consistent sources like food products. But there are a few industries that beat inflation. Thanks to high competition, computers remain competitively priced while still increasing in performance from year to year. A Commodore 64 originally cost $595...
What causes a particle to have charge?	[ "Charge is an intrinsic property of fundamental particles like electrons, just as are its other properties such as its spin. Frankly there's not a whole lot more we can meaningfully say about it than that." ]	[ "There is no sharp boundary (or well-defined shell) of an atom. It is not correct to think of them as tiny marbles or something like that. The atomic size or radius is defined by an electron \"cloud\". The clouds size is determined by probabilities of finding an electron at that location. Because of the uncertainty...
How do abusive mental health facilities exist? Don't the staff object?	[ "It's complicated, not a direct answer (and arguably not the most regarded source) but this _URL_0_ article about it is actually pretty good at explaining why it sometimes happens. http://www._URL_0_/personal-experiences-2365-i-was-psych-nurse-who-abused-patients-with-chokeholds.html" ]	[ "Through fear of being ostracized, individuals in groups tend not to voice unpopular opinions. Sometimes, these unpopular opinions are, actually, popular amongst the group, but other members doing the same thing means those opinions may never actually get expressed." ]
How does Quantum Entanglement work?	[ "There is no known mechanism by which the particles \"send a message\" to one another. The phenomenon is the result of creating a system of two or more particles whose wavefunctions depend upon one another. By measuring an aspect of one particle, its wavefunction is collapsed to known value, which causes the other ...	[ "_URL_0_ The wikipedia article is excellent and better than any of the answers in here so far. If you have specific parts you don't understand, ask away and I can help explain them to you." ]
Why does it seem like it's more the single women who get "accidentally" pregnant and worry so much about becoming pregnant, but it's the married couples that have to "try" really hard?	[ "* A married couple gets pregnant. Nobody is surprised. * A married couple can't get pregnant. It's really sad. * A single woman gets pregnant. It's probably sad news. * A single woman doesn't get pregnant. Probably nobody cares. Make sense? Nobody cares about a dog biting a man. But if they hear about a man biting...	[ "That's just it. It takes a while to amass information and use it. An animal just does whatever comes natural, aka 'instinct'. But humans are taught and trained and learn and practice and... and... Layers and layers of information and training to get us to the point where we can actually achieve more than the previ...
If gravity is curvature in spacetime, does that mean that when I throw a ball it is actually going straight in it's own space, but because of the earth that space is curved 'downward'?	[ "The short answer is yes, there is a whole branch of study of this in physics, the most relevant of these are geodesics. Standard procedure in GR is to use whatever geometry of spacetime due to the presence of mass or other parameters that we are interested in and reformulate the lagrangian, hamiltonian or other re...	[ "Put a slinky in a long glass tube and fix one end of the slinky to one end of the tube. Now lay the tube on your desk. The slinky is all curled up . Next, stand the tube upright. One end of the slinky is fixed to the top of the tube and the bottom of the slinky dangles down. What if you held the tube at an angle.....
How can a cup of water not spill in an airplane when the plane tips its wings to make a broad turn?	[ "The forces created by a plane that is banked causes water to be pulled to the bottom of the cup. It's hard to feel this force as it's very subtle in commercial aircraft. An example is if you hold a cup of water and spin yourself around with your arm and cup extended. You will notice the water will pull to the ou...	[ "Negative air pressure. Warmer air takes up more volume than cooler air. When food is hot, and you seal it in an airtight container, the remaining air in the airtight container is warmed by the hot food. As the food cools -- even a little -- the air temperature also cools. As the air temperature decreases, the co...
Why do so many species enjoy being rubbed or scratched?	[ "This has to do with sociality. In humans and other primates grooming is an important part of social bonding. In dogs and cats it may be more to do with having co-evolved with humans. If the dog likes to be petted then it will be friendlier and will be selectively bred. Cats have a natural urge to rub their heads o...	[ "There is an [Wiki entry overview](_URL_0_) for this. Part of a [series](_URL_1_). Part of a long series. In fact people have written so much about [this sort of thing](_URL_2_) that you could think, correctly, that Humanity has an obsession about it. [Not just Humanity](_URL_3_), for evolution has had a hand in ma...
Stem cells. The science and the controversy.	[ "Stem cells can grow to be any cell you want. If you need new cells for your heart, brain, liver, whatever, these cells can be used as a base for growing new parts or repairing old ones. The controversy is with embryonic stem cells, which are only found in a human embryo that is 4-5 days old. To gather these cells...	[ "Your best bet is to read this [document](_URL_0_). You won't find any scientific arguments against radiometric dating, because there aren't any. At least, no valid ones." ]
How is the heat produced in our bodies?	[ "When we break down food to make energy to run or to move (etc.), heat is made as a by-product. ELI15: From the breakdown of glucose in cellular respiration to make ATP, heat is a by-product of oxidative phosphorylation. Fun fact: your body shivers to get rid of the ATP so that it can make more, not to cause \"musc...	[ "When we sleep our bodies release waves of white blood cells. They find things to fix while we sleep, and many more are released when we sleep in complete darkness vs with a lamp. I'll try to find the study I read to back it up!" ]
Why is it easier to fall asleep when you're cold as opposed to it being harder when you're hot?	[ "Cells are more excited and move more when heated, when cooled they slow down. Sort of like when you microwave popcorn, if it's heated it'll pop and jump all around full of energy :) When there is an absence of heat (aka, cold) it is restful and unmoving. Your brain can rest easier when it isn't popping :)" ]	[ "There are a few factors at work here : Moſt chairs are deſigned to ſit at about knee height ; they generally ſupport your back, and more importantly, your butt and legs. Toilets are uſually lower, and they are made with a large hole in the middle, into which you ſink a little. This lower height, lack of ſupport,...
Why can't we think of new colours?	[ "There are none, we have mapped every frequency in our visual range." ]	[ "We do, its called soylent, though it comes in liquid form. _URL_0_ Humans crave variety in our diets, so most people wouldn't stick to a single food unless they had to." ]
How come Chinese don't get sick more frequently, or even start an epidemic, seeing as how they treat and handle meat?	[ "My wife is like a hyena. If you're exposed to the same bacteria constantly, your body becomes quite accustomed to it. Antibacterial living makes you weak." ]	[ "As a Brazilian I can tell you why: we do it because we don`t trust the government and because we all feel that if we were in power we would exploit it as well. So basically because most believe that , given the chance, they would say \"screw everyone\" and take as much advantage as possible, they do NOT find thems...
How do fiber optic gyros work?	[ "There is a coil of fiber optic cable. A laser light is split into both ends. When they get back out again they get merged into a single beam again. You would expect the light going through the coil from either ends having the same phase and therefore you get constructive interference. However if the coil is spinni...	[ "Thee same way airplanes do. They have a probe with a hole in the front of it. Air is forced into it by the movement of the helicopter or plane that pressure is read as airspeed" ]
Why do people have different "types"? How are our ideas of attractiveness created?	[ "A lot of the characteristics we are attracted to are from basic instincts in our brain. Hour glass figures on women are representative of a good body for childbirth. An upside down triangle body on a man is representative of a physically strong man, who is resistant to disease. Some people are attracted to differ...	[ "_URL_0_ There are many factors which affect at what temperature a person begins to feel cold. People who weigh more tend to feel warmer. Men tend to feel warmer than women. Etc Scientists believe there might be a genetic component. They also believe that where you grow up might play a factor. But nobody has prove...
How does having a ceiling fan switched on while the A/C is running affect the temperature of the room?	[ "It depends on where you measure the temperature. A fan will help to even out the temperature in the room. That could be a bad thing if, for example, you prefer the cold air to settle to the floor. It could be good if you're sitting in a hot spot. The fan will keep running even though the AC cycles off/on with th...	[ "I can only talk about this on an anatomical level, but our ears aren't designed to pick up every sound around us. When a sound registers in our inner ear, it activates one of 24(?) or so critical bands, which vacillate in the general area that the sound occurs. Because there are a limited number of critical bands,...
why kids think its gross to like members of the opposite sex.	[ "Alternative title: \"Explain Like I'm 5 the experience of being 5.\"" ]	[ "Our ancestors when in the wild would enjoy a fresh kill, body still warm. If you came across a dead animal that had been there a while, well you wouldn't want that would you. Evolution has taught us warm is preferable to cold. Unless of course you are eating mint chocolate chip ice cream." ]
How/why did the american accent form?	[ "What's an America accent? Americans have different accents based on location with the US." ]	[ "From what I've read they ate a lot more rough course foods. Chewing things that are hard scrape our teeth for us kind of like it does for other animals. The problem for our modern teeth is we eat a lot of soft refined foods and a lot of sugar. That stuff just sits there and gets stuck which causes tooth decay." ]
Why can a human limb not sense its own weight?	[ "You can feel its weight. However you just get used to it after years. Think about it externally: if you never wear a watch, and then you put on a big heavy one your arm feels heavy because of that extra weight. Now let's say you wear that watch every day. You even sleep and shower in it. Eventually, wearing the w...	[ "Building a car is easier than rebuilding a car that's been obliterated in a ghastly accident. You can follow the same steps to build the new car every time and it'll work every time. Rebuilding the totaled car is a lot trickier. Each case is unique. What's damaged? How badly? What can be saved? What needs to be ...
Why do asmr videos make you so relaxed and sleepy?	[ "Heuristically, meaning that they choose things that people self-report as relaxing and combine them together. Similar to self-reporting but still heuristic in nature is to have subjects watch videos in an MRI and map the relaxation directly. This is a neurophenomenological approach which seeks to trigger an impuls...	[ "I read an article a somewhere that said it was do the the \"roughness\" or randomness of the noise. As the fingers nails catch and slip it produces random variances in the amplitude and frequency of the noise. Our brains find the signal unpredictable and that somehow causes it the view it as a danger. There are a...
What is the cause of the genealogical relationships of US Presidents? Is this common?	[ "Once you get out past second or third cousin, there's a lot less general relationship between the people. I know I have several third and fourth cousins, but I've never once met them. As stated, a lot of those listed, especially close relatives (Second cousin, etc), are from the same geographical area. Social elit...	[ "Hi there, the mod team has already had to remove several responses in this thread because we do not allow [personal anecdotes](_URL_3_). While they're sometimes quite interesting, they're unverifiable, impossible to cross-reference, and not of much use without more context. [This comment](_URL_3_) explains the rea...
Why do people blame football (american) coaches, and fire them for their players mistakes?	[ "Football coaches are a lot more involved than in most other sports. They make decisions about plays, strategies, various aspects of the game that have a direct effect on the outcome." ]	[ "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." ]
Why humans are so ill equipped to handle the cold?	[ "It is how we are evolved. Humans are first evolved as [endurance runners](_URL_0_), being able track games through persistence hunting mid-day. We were able to do so by sacrificing our body fur - which regulates body temperature and allows us better cold endurance - for our hairless bodies that could fair better i...	[ "We didnt, we lived in warmer climates until we learned how slowly over time as we moved north" ]
How do homeless people generally end up in the inner city?	[ "Everything in the city is much closer together (they are on foot all the time), and there are more public spots to hang out at. In a city you can beg from a lot of people and hang out under a bridge or something, but in the suburbs you would be in someone's yard most likely." ]	[ "Oh man everywhere, cracks in the drywall especially around pipes (bathroom) the can come from the pipes if they are really intrepid. We had ants one summer coming from an electrical socket in the kitchen and the hole they go through was in the wall (so so tiny) that connected the stove bent out side. Homes are not...
Liverpool Football fans and why they and their team seem to be catching a lot of shade recently.	[ "The biggest club cup in football was last night, the champiins league, akin to a super superbowl, and the liverpool goalkeeper made 2 blunders that lost them the game." ]	[ "I have a question for you. Do you want the version that is super, super long and includes a write-up on what actually went down at Munich, and the subsequent responses back and forth? Or do you want the shorter version that only talks about media coverage of the incident and how it changed things?" ]
What ever happened to that 'fusion reactor' that was supposedly sold a while back	[ "It's not been 'proven' to be a hoax because the guy hasn't let anyone see the thing in detail. His larger demonstration suffered from the same basic measurement-methodology flaws as his smaller-scale one, so they didn't add anything." ]	[ "The major investors were parts of the government (Freddie Fannie and the Federal Home Loan Banks). Some of the settlement was paid to those investors. Other investors may have their own lawsuits/settlements." ]
Why do cold bottles of water get wet on the outside?	[ "Condensation, water vapour in the air gets cold when it gets close to the cold water bottle and condenses into liquid water." ]	[ "Your faucet has a screen on it sometimes referred to as a diffuser. If you unscrew the diffuser from the end of the faucet, that probably won't happen anymore." ]
Why are PETA, as an animal organization, seemingly doing everything it can to destroy pet's lives? Aren't they supposed to help animals?	[ "The key letter in PETA isn't A, for animals, it's E, for ethical. By this, I mean that their primary motivation isn't a love of animals in particular, it's adherence to a particular set of ideas that say it's wrong to act in a certain way toward creatures that can feel pain, or to treat some creatures worse than ...	[ "1. Being against abortion is a winning strategy for Republicans wanting other Republicans to vote for them. Planned Parenthood is an abortion provider. 2. Republicans want to control women's sexuality and Planned Parenthood provides basic health care for women by providing birth control advice, contraceptives, cer...
Monday Mysteries \| The Historical Foundations of Myth and Legend	[ "A big one is, well, most of the bible. Was there a united monarchy? If so, what did it look like? Is there something behind the Exodus narrative, or is it a myth to give the Israelites a history separate from the other Canaanite groups?" ]	[ "Congrats! You've asked what may be the single most-asked question on /r/AskHistorians. That's good news, because it means we have [a big FAQ file devoted to your question](_URL_1_). Check it out, and I hope it helps! Edit: And [here](_URL_0_) is a great answer from /u/talondearg, who answers it quite a bit." ]
Is it true that baling wet hay after a frost won't start on fire vs baling wet hay after rain will? If so, what makes the difference?	[ "The percentage of water moisture in the hay. Frost is very little actual water and just on the top whereas a typical rain will wet all the hay. The amount of water determines if the hay dries (no problem) or if there is enough moisture that the hay will begin to decompose (problem). The decomposition is what crea...	[ "eli5 explanation: The spin on the ball makes the wind move fast on one side, slow on the other. The ball then gets moved by the different speeds of wind on the ball. edit: I was explaining it like I was explaining it to a 5 year old. The laces do in fact help create the differences in \"wind\" (friction against th...
I go on r/conspiracy a lot and see some Holocaust denial.	[ "You might like this thread by /u/commiespaceinvader: [Monday Methods: Holocaust Denial and how to combat it](_URL_0_). It includes methods deniers use, how to notice denial, and how to combat it." ]	[ "I've always been fascinated by the wide variety of \"Fall of Rome\" arguments and how they're affected by historical perspective. I was wondering: **Does your historical specialty advocate a certain theory for the fall of the Roman Empire? or what's a unique argument for the fall of the Roman Empire that you've co...
How does cellphone reception work?	[ "Phones emanate in all directions, they do not have directional antennas or you would have to specifically point it toward a tower to use it. So every thing is just floating out there and other cellphones just ignore it because it's not addressed for them. Towers may have general antennas that radiate everywhere, o...	[ "Likely based on maps of coverage area, overlaid with maps of where people live. The accuracy of either type of map isn't perfect (if coverage is blocked by a very specific hill in an otherwise-covered area, for example). But it's feasible to cover basically all of a big city, and these small urban areas contain ...
I've heard arguments both that "Irish need not apply" signs were largely a myth and that they were, in fact, common. Is there a consensus among historians on the issue?	[ "I talked about the historiography of “No Irish Need Apply” in [this earlier answer](_URL_0_), if you’re interested!" ]	[ "Hi - we as mods have approved this thread, because while this is a homework question, it is asking for clarification or resources, rather than the answer itself, which is fine according to [our rules](_URL_1_). This policy is further explained in this [Rules Roundtable thread](_URL_3_) and this [META Thread](_URL_...
Are we any closer to curing cancer?	[ "[This comic](_URL_0_) explains it well. \"Cancer is not one disease\"" ]	[ "A few things to realize before trying to draw conclusions like this: * Science is an evolving process that doesn't end with a single study. One study's results could be refined or contradicted by other studies, and it takes multiple iterations to suss out the truth. * Science journalism is terrible. University PR ...
Why do we feel really cold when we are sick?	[ "Your skin doesn't actually feel coldness or hotness, but rather the rate at which heat is entering or leaving your body. If you have a fever, you are even hotter than usual compared to the air around you, so the heat transfers faster, and you get chills." ]	[ "You have to be in bed long enough for your body heat to be trapped by the blankets." ]
given the existing infrastructure, why aren't passenger railroad companies more common in the United States?	[ "The US is much more spread out than Europe. Taking a train from Portland to San Francisco is a 12-16 hour journey. Since taking a plane is about the same price & only takes an hour, it's much more popular. Rail is popular in places where you have a bunch of cities close to each other (Portland/Seattle, Boston/New ...	[ "With trepidation, I will try my first posting of an image - one suitable for this question. This is [John Piper's Old Corner Bar](_URL_0_) in Virginia City, Nevada in late 1860, illustrated by Grafton Brown, an African American Artist who produced a Bird's Eye View of the town (with businesses illustrated around p...
What was the Amazon like when the Sahara was still green?	[ "The \"Green Sahara\" has to be taken with a grain of salt. It was never a climax forest but has varied between extreme desert that it is today and open savannah grassland in different climate periods. The Amazon forest has also grown and shrunk. [This diagram](_URL_1_) shows some of the variations between both of ...	[ "[This map](_URL_0_) is a plot of all ocean voyages contained in millions of entries contained in the Maury collection, a collection of ship logbook entries chronicling global shipping (and weather data) from 1792 to 1910, currently in the possession of NOAA National Climatic Data Center. The entire collection was ...
Why do sapling trees not lose their leaves in the winter while adult trees of the same species do?	[ "Some like beeches hold onto dead leaves to collect snow at their base for added water when it melts. Saplings in general hold onto their leaves longer than the larger trees to get some last minute sugar from the sun without the shading of the larger trees." ]	[ "Your cell's DNA is like a paper manual for what it needs to do. Every time that cell divides, it photocopies the manual and gives a copy to the new cell. However, every photocopy can only be as good as the original copy and may also result in a lower quality. The original copy may also get some wear as you flip th...
what happens if you owe debts and you die	[ "Depends. Usually creditors (the people you owe money to) collect from the estate, before any of your heirs get inheritance. If you die owing more money then you have in assets, then the creditors get less then they are owed." ]	[ "After the search is completed for next of kin unsuccessfully, they county will typically either cremate or bury them in a pauper's grave." ]
Can we see from earth the middle of the milky way, or do we kinda know where it is?	[ "It's in the constellation of Sagittarius. It's not visible to the naked eye because there are absorption nebulas covering it, but infrared and x-ray telescopes can see it. Astronomers at ESO have even observed the stars that orbit the supermassive black hole in the center of the Milky Way. _URL_0_" ]	[ "This question is pretty tough to imagine. Here's something that might help: Imagine you live on a [Möbius strip](_URL_0_). You're facing straight down at all times. You leave a ghost image of yourself as you go around the strip. Travel fully around and you get back to where you started, still looking the same way....
why pictures of computer screens have weird, changing patterns when you zoom in and out?	[ "These are called [moire interference patterns](_URL_0_) and are caused by non-uniformly sampling the grid of pixels on the screen. In computer graphics, we use [mipmaps](_URL_1_) to combat this." ]	[ "I was curious, so I dug a bit and Google Translated their about page. > And now arcane text that I do not understand. To create paintings using convolutional neural network algorithm and artistic style by Leon A. Gatys, Alexander S. Ecker, and Matthias Bethge. For more information on this portal can be found at t...
Do average people really produce $115,000 of stuff per year, yet take home only $26,000?	[ "I'll also point out that median is not average. If you considered five guys who made $10K, $20K, $30K, $40K and $1M, you could say, \"we made $1,100,000 last year amongst the five of us (or $220,000 per person) but out median wage is only $30,000. Where'd all the rest of it go?\"" ]	[ "Have you ever loaded a 4K UHD YouTube video on a 1080p device? Well, 3840x2160 has exactly 4x the amount of pixels as 1920x1080, so what happens is that every 4 pixels (imagine a 2x2 square) gets made into 1 pixel, the color of that pixel is the average color of all 4 pixels. Photos are more difficult as they ha...
Is light/sound affected at all by temperature?	[ "Yes, sound is directly affected by temperature. The speed of sound in a medium may be calculated as c=sqrt(kRT), where k is the ratio of specific heats, R is the gas constant, and T is temperature. Considering what you hear are effectively \"Mach waves\" traveling through air, changing the temperature of the air w...	[ "It kind of does. Picture and sound are actually recorded quiet separately. Usually they're literally recorded separately — using separate machines — but sometimes they're recorded in the camera but using separate recording mechanisms. What matters is just that picture and sound end up synchronized. The fundame...
How are skaters and other extreme sports athletes able to absorb the impact from such huge drops?	[ "I think I need to make another post about how forward momentum will lessen the impact." ]	[ "I'm sorry that I'm no expert, but I remember reading about this the last time a similar question was asked: _URL_0_ Basically, you percieve time faster after your run because of endorphines released during the work out, which means that the music seems slower. This is apparently also why a lot of rock musicians pl...
Why can we not chemically manufacture the Beta Lactam ring found in antibiotics like Penicillin?	[ "As noted in the earlier comment, we can certainly synthesize beta-lactam antibiotics. But for a pure chemical synthesis at the industrial scale, you'll need to beat [the fermentation route](_URL_0_). Hopefully someone with more synthesis/process development knowledge will show up in this thread with the latest and...	[ "Nothing is stopping them. [ReactOS](_URL_0_) is a binary-compatible windows clone, for example. As for Apple's OS X, it itself is a clone/fork of [FreeBSD](_URL_1_)." ]
How do smelling salts work?	[ "\"smelling salts\" is actually a small ampule of ammonia, the smell is VERY strong and when inhaled causes an increased heart rate, counter acting fainting source: used them at work on several occasions" ]	[ "Bacteria on/in your skin metabolize the minerals in your sweat and create a by-product. TL;DR: sweat is bacteria farts." ]
How does having the engine in the back of a car change how it drives?	[ "Engines are extremely heavy. Moving all that weight from one end of the car to another is going to affect how the car handles." ]	[ "men treat cars the same way women treat name brand jewellry/clothes/shoes. a means to achieve a higher goal. they might serve as a topic for conversations, but they also may distinguish social status, improve your image among peers/opposite sex, better your self esteem. they are a tool that helps you accomplish ma...
If Neanderthals and early Humans could interbreed, why do we consider them different species?	[ "Neanderthals (homo sapiens neanderthalensis) and humans (Homo sapiens sapiens) are not different species they are different sub species." ]	[ "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 do humans have allergies, and why does it seem like they're so common in the US specifically?	[ "Popular question. Ye may enjoy these: 1. [ELI5: Why do so many people today have allergies in the modern US ](_URL_2_) 1. [ELI5: Why do people get allergies? ](_URL_1_) 1. [ELI5: why are grass and other pollen allergies so common? ](_URL_7_) 1. [ELI5:How are allergies developed and why aren't there any cures for ...	[ "We are exposed to millions of pathogens daily. Getting into a long answer will require explaining the entire immune process which can get lengthy, check out these pages: [Innate Immunity](_URL_4_) [T Helper Cell](_URL_1_) [Complement system](_URL_0_) [Adaptive Immunity](_URL_2_) [Generation of Antibody Diversity](...
That gut feeling we get sometimes and is it a true biological response in a dangerous situation?	[ "I remember reading a lot of those feelings are your brain remembering things that once hurt you. So when you get a bad feeling about someone or a situation and you can't place why, it's the brain tying to warn you." ]	[ "Everything your brain does requires energy, including \"nothing.\" Specifically, to stop yourself from having certain types of thoughts (let's call them \"dumb ideas\"), other parts of your brain capable of critical thinking, evaluation, scenario modeling & if-then extrapolation have to exert metabolic energy. Lat...
Can fuels (like gasoline and diesel) be stored indefinitely, or would they degrade in quality and/or become unusable over time?	[ "[BP pdf]( _URL_0_) that explains how to maximise fuel storage." ]	[ "It's a series of thermo-regulated systems, this regulation system is called vernalization, and some plant species strictly depend on it The plant embryo, contained within the seed, doesn't grow unless triggered to do so, since the nutrients contained within the seed's endosperm are just enough for the bud to d...
Is gelatin considered a solid, liquid, or some form of matter in between?	[ "It's something in between, called a [gel](_URL_0_). It has some fluid-like and some solid-like properties and actually consists of a relatively rigid matrix with fluid in between. Many things we deal with in our daily lives aren't really a solid in the crystalline sense of solid many people think of. Gels aren't i...	[ "Heres a fantastic video on the problem if you have time. _URL_0_ If not. Basically a the base of the water kettle the heater is well above 100°c this coverts the water into a gas, this gas then expands in the \"cold water\" of around it. But once it becomes too weak it starts to condense aka transform into a liqu...
The Watergate Scandal	[ "The Watergate Scandal led to Nixon's resignation. The reason he resigned was because he had LIED under oath (he tried covering up the scandal). No evidence was found of him ordering/being directly involved in the wiretapping, but he did in fact try to cover it up when he found out what they did. Because he lied un...	[ "Woodstock, moon landing, all sorts of cool stuff. _URL_0_" ]
What do our eyes do when they are unfocused?	[ "The muscle in your eye that controls focus has to use energy to keep you focused on something close, so when you are not actively looking at something the muscle will relax and focus way off in the distance. The double image is because you have 2 eyes and they see the world from 2 slightly different perspectives....	[ "Althoguh not an entirely scientific response, people can generally \"focus\" on one intensive thought process while also being able to perform a more \"automatic\" thing. Take your example of singing the song: if you know the song very well, the words just come naturally and doesn't cost a lot of brain processing,...
Can humans get apes pregnant?	[ "It's been tried but has not succeeded. Doesn't mean it's impossible, some hybrids have very low success rates." ]	[ "You know when iTunes, Facebook or your phone updates and how you know it's the same program as before but things have changed slightly and you are kind of lost. Well that's what it would be like going from animals to humans with the errors being death instead of frustration." ]
Why do some vaccines only need to be given once, while others such as the flu jab need to be done yearly?	[ "The flu virus is highly unstable, anytime a person have two types of virus at the same time, he can create a third hybrid type that wouldn’t respond as well to the vaccine. That is why it is given yearly, of the several hundred subtypes, each year your get the ones most likely to affect the next year. If it is a ...	[ "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...
My Professor claims linear algebra is used in the programming of search engines. How?	[ "basically using matrixes of data and calculating the corresponding eigenvalues allows for faster searching and comparison of data sets than some other methods." ]	[ "check out /r/darknetmarkets if youre surprised people doing illegal shit can still monetize it online. They sell drugs on the internet, and very rarely do people get caught. Shit's cray. and no, in the case of illegal internet sites (clearnet or darknet), the Identity of whoever runs the site is usually unknown. I...

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