Subset (10)

eli5 · 25k rows

Split (1)

train · 25k rows

query stringlengths 20 300	positive listlengths 1 1	negative listlengths 1 1
Does/can two atoms of carbon form a covalent bond while each atom uses all four available electrons for that bond?	[ "A single bond between two covalent molecules can only contain 2 electrons. Therefore, each carbon atom must make 4 bonds to be stable. I've always been told a carbon-carbon quadruple bond is impossible because of the current orbital theory of electron bonding: the bond cannot form due to the relative locations fo...	[ "Coax can carry more bandwidth (as in frequency spectrum). RG-6 coax can carry somewhere 1-3Ghz while Cat 6 Ethernet (8 wires) can only carry about 500 Mhz. The reason is the shielding is so good and the impedance of the RG-6 coax cable is guaranteed over a long distance. HD TV channels only need 6Mhz so a single ...
What is it about brain death that precludes the possibility of a person from being awakened?	[ "Dying cells don't just stop in-place, motionless, waiting for the joy-juice to be brought back into their (un-)lives. When cells die, they go through sequences of somewhat patterned changes. They lose membrane voltage gradients. They stream in Ca^++ ions, they upregulate caspase enzymes, and they fragment their ow...	[ "Work is being done on getting spinal nerves to regrow and attach. So far its still in the rat testing stage but they are having good results. Also, there have been experiments with jumping the gap with electronics technology that are also showing promise. Turns out, if your can transmit the signals reliably across...
Is there a scientific explanation for falling in love with one person, but not with another?	[ "I know Japanese has a word for it: 片思い (kataomoi), meaning unrequited love or one-sided love. The opposite is 両思い (ryouomoi), or mutual love." ]	[ "The outside of cells and virus cells are covered in chemicals. Different cells are covered in different chemicals. Specific chemicals stick to other specific chemicals. Other chemicals don't do anything. It can help to think of it like many different colors of velcro. Blue velcro only sticks to blue velcro, it doe...
How frequently was the "smallpox blanket" tactic used again Native Americans? Did it actually work?	[ "There are some previous answers to this question [here](_URL_1_) and [here](_URL_0_)." ]	[ "I'm really frustrated that all my books are in storage right now. The author you want to find is [Henry Reynolds](_URL_1_). If you're in university you may be able to access some of his books & papers for free. He's famous for his work on frontier conflict, but he covers non-violent contact as well. This is one of...
Why did snuff tobacco fall out of fation?	[ "Technically it has not. Copenhagen which is called chew, is actually snuff, but very few people use it properly. If you read the lid, it’s says snuff." ]	[ "Or would you put it down to factors such as the Army, Parliament, the Major General rule, religion at the time?" ]
Why does it take sink water so much longer to warm up than shower or bath tap water?	[ "The shower or bath tap simply lets out more water than the sink. An easy way to test this is to fill up a container with each to see how fast it fills up. This allows the shower or bath to flush out all the cold water in the pipes between the faucet and the hot water boiler faster than the sink." ]	[ "You need the heat from the boiling to cook the starch/flour which is an ingredient of the pasta. Try this at home. Take some flour and mix it with cold water. do the same with boiling water. you'll notice the difference. only by cooking the pasta gets soft but still sticks together." ]
What is the difference between fuel economy and fuel efficiency?	[ "Although if you are having a conversation with a regular person, they are basically interchangeable, I think the difference is that while fuel economy means your cars mile per gallon, fuel efficiency is the percent of potential energy in the fuel a vehicle can turn into mechanical energy if that makes sense." ]	[ "Republican: Economic freedom, social control Democrat: Economic control, Social freedom Facism: Economic control, social control Libertarian: Economic freedom, social freedom" ]
Regardless of their views on climate change, why are a majority of politicians against efforts to improve/protect the environment?	[ "The environment doesn't donate money to campaigns. Also just generally not the biggest issue for voters in an awful economy." ]	[ "Short answer, money. Slightly longer answer: religion, anti-intellectual movement, funding, social issues, and things that are used to ‘measure’ performance. Tests are easy to use to see if a kid can produce the answer to a given question. Which is great if you are playing Jeopardy but generally useless day to day...
With web extensions, like the heavily-advertised "Honey" service, "automatically find[ing] and appl[ying] coupon codes at checkout with a single click," wouldn't this drive up prices at these websites?	[ "What lost income? If anything, they may see increased income. Having easy to access coupons can encourage buyers to buy more, or buy stuff they weren't planning to originally buy. It also attracts buyers who weren't going to buy anything. New sales can make up for the discount provided by the coupon. Not to mentio...	[ "Yes. Imagine you break a stick and then put pieces back together with duct tape. Is repaired stick same as new? Of course not. It's the same with auto parts. They are prepared to deform in specific ways during collision but they only can deform once. During that process internal bonds between atoms inside part are...
In every crime show it's a different profession investigating and solving crimes. Who actually does it in real life?	[ "When crimes are investigated there are different professions involved. There are your standard beat cop who is the first to respond. Then there are specialist cops called detectives who are assigned depending on the type of crime. These would be the division that deals with homicides, or in the case of SVU deal w...	[ "Generally, networks \"know\" their audience first by setting their programming approach to meet a certain demographic (think Lifetime channel in the US being aimed at women). Then as they continue to broadcast they use research firms to confirm their programming is meeting their target audience, how that audience ...
Who were the most important religious figures of the 20th century?	[ "Pope John XXIII who started Vatican II, one of the largest set of reforms in Catholic history. Reformed the liturgy, changed the way Mass was conducted, and the world view of the largest Christian denomination in the world. It was huge." ]	[ "Is this question limited in scope to Eastern Europe/Near East or are you asking about a much more global scale?" ]
What makes cigarettes dangerous: the tobacco, or the processing?	[ "Unprocessed tobacco is dangerous, both because of the nicotine it contains, and because of the compounds formed when it is burned. However, a large number of the additives in cigarettes are also harmful, many far more so than the actual tobacco. Still, because tobacco is the primary ingredient in cigarettes (and c...	[ "Depends on what level the study is at. Look at people who regularly eat lots of red meat and bacon, and compare it to people who don't If there is a difference in cancer rates between the two groups, something is causing a higher rate of cancer. Maybe work place exposure, food, lifestyle etc. Then take genetically...
What were some important historical figures who had substance abuse problems?	[ "Queen Victoria used a variety of drugs that are now illegal today." ]	[ "Hi readers! Since questions like these often attract anecdotal answers, just a quick reminder: you are in /r/AskHistorians, so do ensure that answers are comprehensive and informative, and based on solid source material. Personal anecdotes or other casual chitchat/speculation/opinion are not accepted as answers he...
Why do those anti-tobacco companies like _URL_0_ get such a bad rep every time a conversation about smoking happens?	[ "They are a special interest group that is not above misrepresenting the truth, or using \"scare tactics\" to achieve their objective. So when you talk to smokers about it... they are not going to think highly of them. That being said... they are sort of fighting a \"morally right\" fight... so it's tough to do to ...	[ "Sugar tastes good. When faced with a choice between that which is smart and that which is pleasing, most people will spend their money on the latter. A business exists to sell people what they want to buy, not what some might feel they should buy." ]
why do we sometimes react and believe our dreams happened, whilst the majority of the time we know it was a dream?	[ "I spent a long time in a depressed stupor where I'd sleep as much as possible, each dream was a continuation as the last and it felt like a lucid dream. I'd remember every detail. When I just couldn't sleep, or was out of bed I'd day dream about it and it went on fit an entire summer break between school years. It...	[ "I belieeeeve that your body releases a mild paralyzing agent to keep you from flopping around in your sleep. Some people (myself included) experience sleep paralasys when we wake up before said paralyIng agent has worn off and cannot move or speak upon waking up for a few minutes." ]
If we took all the animals out of the ocean, would the volume the ocean occupies decrease, like a person getting in and out of a bathtub? Would it be affected at all? If it were, by how much would it be?	[ "Yes, the volume would decrease (minimally though). Take the estimate of 2 billion tons of fish [wiki](_URL_1_) and assume that those fish have a density near 1 (ie. similar to water). That would be 2,000,000,000,000,000 cubic cm of volume (equals 2 cubic kilometers). Even though this sounds like a large number, co...	[ "RMS Titanic is not just a shipwreck: it's a resting place for dozens, if not hundreds, of passengers that went down with the ship. Doing anything to the Titanic at this point is equivalent to messing with a grave. RMS Titanic has been preserved in many ways: books, television shows, movies, etc. Artifacts from the...
I found this gravestone on a mountainside in northern Italy. Could this be left over from WWII?	[ "Dating such an item based solely on a picture is incredibly difficult. To my knowledge the Allies did not advance that far north during the Italian Campaign of WWII (This is nearly in the Alps on the Austrian Border). That being said it is possible that this grave stone is from the first world war based on it's de...	[ "Hi OP, I've temporarily removed your post per our rule to protect personal privacy - _URL_0_. Could you either remove the link to your grandfather's docs, or modify the images to block out his name (and the names of any other people not serving in an official capacity), and any other identifying information. Then ...
Why do some words have silent letters(knight, knitting, pterodactyl)?	[ "It has to do with our lovely mutt of a language. English has been influenced over the years by German (a case language, which means endings of words tell you what part of speech/sentence they play), French/Norman (synactical, where the order of words create meaning in sentence), Latin, and Norse. If you compare ol...	[ "We don't, but is Jurassic Park a better film with a T-Rex that roars, or one that clucks like a chicken or coos like a pigeon?" ]
What causes cross tolerance in narcotics?	[ "Morphine and tapentadol are both opioid analgesics. Their chemical structure is different but both act on the same opioid receptors in our body. Opioid tolerance is caused mainly by the decreased response from receptors after repeated stimulation. So after repeated stimulation with morphine, the response from opi...	[ "Having done some background research on the region for some project evaluation, I have come across the debate between impact vs. tectonic origins. IIRC, there have been no signs of impact-related geological features (shatter cones, high pressure minerals, etc.) and the best explanation is a terrestrial tectonic bo...
Whats the difference between f.lux and dimming my computer's screen?	[ "The higher frequencies (blue, violet) are responsible for suppressing melatonin production. In the case of a computer monitor, only blue. F-lux allows you to maintain an overall higher brightness by setting color temperature rather than uniform luminance, leaving green and red less affected than blue. Color consta...	[ "One gathers the files, one applies it. Depending on what it is, if you started installing before you had all the pieces of the file, and something happened to the download, bad things could potentially happen." ]
Where do pharmaceutical companies get the materials to manufacture opioids?	[ "They produce, purchase and/or import them in licensed facilities. Just because a drug is \"illegal\" to possess without a prescription, doesn't mean it's illegal to make - as long as it's properly licensed and regulated." ]	[ "Well some of the high end brands just destroy their leftover stock, though I know [that was an issue](_URL_0_) and some may have changed (mainly by selling them to a country they don't care about). The cheaper brands just sell it to other stores, TJ-Maxx and Marshalls basically exist for this, they buy up all the ...
Can a variable be inversely related to itself?	[ "Usually such terms are reserved for equations with at least a one-dimensional solution space. E.g. in y = 1/x you are free to choose x and for each x ≠ 0 there is a y that solves the equation. Since you have one degree of freedom, the solution space is one dimensional. It makes intuitive sense to say tha...	[ "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 do sacrificial zinc anodes work to prevent corrosion of other metals, such as a boat hull/motor in salt water?	[ "The specific type of corrosion that these anodes prevent is called [Galvanic Corrosion](_URL_0_). Galvanic corrosion occurs when you have two dissimilar metals in contact with each other in an electrolyte (like water). The anode metal \"steals\" electrons from the cathode metal. This weakens and eventually dissolv...	[ "I think to best answer this question one should first take a moment and think about the life cycle of plants, how they disperse, and what a seedling needs to survive. Fats are an excellent source of stored energy. Many seeds are very rich in fats/oils which are used as storage energy for the embryo within the seed...
How does glue not dry inside of the bottle?	[ "Let's take plan old white glue for an example. It is a bunch of sticky stuff in water. When the water evaporates, the stuff that's left behind is frozen into place. When it's in the bottle, there's nowhere for the water vapor to evaporate to, so it stays wet and sticky." ]	[ "It's all about having an atmosphere, since that's what helicopters need to fly. [This article explains it quite nicely ](_URL_0_) Here's a relevant quote: *\"Elysium was that—unlike an airplane cabin—its atmosphere wasn’t canned up in some hollow tube. A landing spacecraft could enter its air like it would on Eart...
Why does the English language have a word for an equilateral rectangle (square), but not a specific word for an equilateral triangle?	[ "Etymonline has this interesting snippet: > mid-13c., \"tool for measuring right angles, carpenter's square,\" from Old French esquire \"a square, squareness,\" from Vulgar Latin exquadra, back-formation from exquadrare \"to square,\" from Latin ex \"out\" (see ex-) + quadrare \"make square, set in order, co...	[ "Point a flashlight at the wall and turn it on. See the small circle? Now, let's say your flashlight is delivering xyz power to the wall. So xyz power is landing in that circle, right? Tilt the flashlight in any direction. The circle spreads out across the wall doesn't it? But you didn't change the batteries or any...
Why are so many Americans hooked on opiate pain pills?	[ "We are a pharma loving people. There is a newer prescription pill epidemic and I think it partially reflects that. People tend to think that because someone gets a prescription for these pills that they are safe and sanctioned. And in ways it is better than heroin in that it is regulated. However, many people are ...	[ "\"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..." ]
Along what axis are polarized sunglasses polarized, and why?	[ "When randomly polarized light reflects off a horizontal surface, the horizontal component is greater than the vertical. Roads and water are horizontal, so traditionally, sunglasses are vertically polarized. There may be specialized ones for viewing LCD screens with sunglasses." ]	[ "> 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...
Why are Christianity, Islam, Judaism etc. considered "real religions" while ancient Egyptian, Roman, and Greek polytheism considered mythology?	[ "Because it still has active believers. If Christianity had died out a thousand years ago we’d see it the same way we see the Norse gods. Jesus could have been a member of The Avengers if history had played out a little differently." ]	[ "A pyramid is the easiest type of building to make. Any group of people who want to make a large structure are always going to start with a pyramid. Staircases are always going to take more work. So, if you want to walk to the top you will always make one section a stair case which is always going to be straight up...
Slavery in ancient Greece	[ "Slaves in Greece were not a rare thing to see. It is certain that rural slavery was very common in Athens. It is estimated that every citizen in Athens had at least 1 slave so, to answer your question, high class people were not the only ones to have slaves. A slaves principal use was for agricultural purposes usu...	[ "[This previous discussion](_URL_0_) might help. In a nutshell: homosexuality was known to happen, but was frowned upon. Sex without the possibility of procreation was considered morally offensive to the divine guardians of fertility." ]
Differences between the Penn State child abuse scandal and the ones coming from the Catholic Church	[ "Because Penn State is more recent. There was equal outrage over the Catholic Church scandal. However, that was more than one person molesting a few boys and over a much longer time, so the outrage was spread out instead of being condensed into a news cycle. Where there is no difference is that Penn State autho...	[ "This might be easier for people to answer if you gave a specific time and place. Are we talking about Italian renaissance choir boys or Chinese imperial officials? Edit: specific time not a specific Tim" ]
If you were to fill any bottle entirely with liquid and close it off, would the liquid move around as you move/turn the bottle?	[ "Yes. Electrostatic interaction between the liquid and bottle would results in flow near the liquid/bottle interface. The amount of flow would be determined by the viscosity of the liquid, the rate at which the bottle is turned or spun, and the degree of electectrostatic force between the bottle and liquid at the ...	[ "When you shoot an arrow from a bow, the energy of the bow is transferred to the arrow. It gradually (doesn't seem like it, I know) pushes the arrow downrange, from a full stop at full draw, to full speed when the arrow leaves it. All that pent up energy of the bow at full draw is efficiently transferred to the arr...
If Earth were represented as one single pixel in size, how large would you have to make Antares for illustrating to scale?	[ "Pixels are two-dimensional while planets are three-dimensional, so that doesn't really work. Assuming you just want a cross-section, we can say that [the diameter of Antares is about 160,000 times that of Earth](_URL_0_), so you would need a circle 160,000 pixels across, or about 20 billion pixels total." ]	[ "Iirc: whenever you post to, say, Facebook, the platform compresses the picture, by default. So, you take a pic with your phone and post it... Suppose its quality is defined by a value which is defined at 1'000'000. You post it and it goes to 100'000. Someone saves it, and reposts it, and it goes to 10'000. Someone...
Movies breaking even	[ "when you say a movie \"grosses\" 1 billion dollars, youre takking about total ticket sales. this doesnt include the what the theater gets, sales taxes, or other expenses. for a $10 ticket, the studio sees about $4 of that." ]	[ "According to Wikipedia, they own the estates that are housing them. Also, they made partnerships with other businesses, like pizza delivery, hair salons, gas stations or fitness centers. And apparently their prices are really low ($2 or $3 for a new release). [This](_URL_0_) article deals exactly with the reasons ...
If the universe is 13.8B years old, what year could life start forming?	[ "Life requires many heavier elements and an environment where it can form. As far as we know, this means a planet with atmosphere, magnetosphere, flowing water, and rich in elemental compounds. Given that these elements need to be formed in stars, life would require at least one generation of star death to get the ...	[ "The biggest proof isn’t exactly mathematical but observed. There is a 4 kelvin background radiation uniformly spread everywhere we look. It is thought to be the remnants of the explosion. Nasa actually has a pretty comprehensive list _URL_0_ It was less like someone sat down and did the math and more like someone ...
Why are mice the preferred testing subject for research?	[ "1. They're mammals. Humans, being selfish, want all our research to somehow relate directly to us, so most biomedical research is focused on mammalian models (mice and rats). 2. They reproduce and age quickly. 3. History. There's a long history of research already done on mice. It often sounds weird to...	[ "Short answer: it's always been that way. And to change it is hard because it's in the constitution so it would take an amendment to change it. Back in the olden days, a direct count was impossible so you needed it. Also, your point of smaller states having a bigger say is true, but it might be a feature rather th...
How common was foot-binding in ancient China?	[ "it seems as if you have it reversed. Foot binding was not common before the Song (more accurately, before the Ming), so a movie portraying women in the Qin with bound feet would be inaccurate." ]	[ "Simply answer: Different culture means different views on stuff like that. Opinion: Even now, I feel like it was done as a result of foreign cultural influence." ]
If tears are salty, why don't our eyes burn when we cry, like they burn when sweat gets into our eyes?	[ "[Tears](_URL_0_) aren't just composed of a salt solution. The lacrimal glands (the glands that produces your tears) release a salt solution along with lipids (oils) and mucus. These last two probably coat your eyes and help prevent the burning senstation. [Sweat](_URL_1_), however, is just a salt solution (and pre...	[ "There are two things you need to know; how taste buds work, and how saliva works Saliva is the first part of digestion, believe it or not. The food is actually being broken down at a molecular level before you even swallow it! Taste buds are sort of similar to the nerves you have on your skin. Your hands are reall...
If 3 identical table fans were turned on at the same time, and set to high, medium, and low- which fan would be the most likely to burn out its motor first?	[ "I am in for the answer as well but my hypothesis is that the slow one would burn out its motor first. This is ignoring bearings and other parts failing on the actual fan and just looking at the motor. I think this because a lot of time motors use resistors and other ways to absorb the energy from the wall and diss...	[ "The _tip_? The tip is not the hottest part. The _base_ is. One only needs to look at the colour of the flame. The light emitted is due to blackbody radiation of soot and other molecules in the flame. Therefore, the hotter the flame, the lower the wavelength of photon emitted. Let's examine a typical [candle](_URL_...
Why can does bark what seems like forever but people can only scream for a hour or two?	[ "Because don'ts cant bark like never, so people seems like screaming less for some time." ]	[ "~~[Here's](_URL_1_)~~ a pretty good article that sums up a lot of the changes. Essentially, sleep is important for a number of different endocrine processes in your body to return to homeostasis, including the cortisol stress pathway. People who are sleep deprived have higher levels of cortisol, making them grouch...
Why Does America Have Better Netflix Than Canada	[ "I believe it has to do the the [CRTC](_URL_0_) and how they regulate what is broadcast in Canada. I don't really know what's going on, it seems to be a very convoluted situation. Google CRTC+Netflix for lots of related articles." ]	[ "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" ]
Why do commercials often get cut down from their original length to a much shorter version after being on the air for a few weeks?	[ "Stations charge by the second to run a commercial. Shaving down to the most recognizable parts after the long version has run saves money." ]	[ "The initial price is generally based on the exit value required by the investors. Depending on when you put your money in and what level of risk you assumed, you'll want a certain payout. You set the amount and price of the stock to get that payout. However, selling stock is really no different than selling anythi...
Does temperature have relativistic effects?	[ "With regard to special relativity, I think yes, increasing the temperature will [increase the mass](_URL_0_) of the system. With regard to general relativity, the increase in temperature should increase the gravitation around the system, due to the increase in energy of the system. Also, insofar as temperature is...	[ "> As far as I can tell, neither have been observed at all anywhere in the universe, so what are their relevance? The relevance is that if you plug those figures into some real models of the universe, it allows crazy things like exceeding the speed of light or time travel. It is significant because the media likes ...
Why isn't there gaps in light when seen from huge distances across space?	[ "When observing very faint sources in higher ends of the spectrum you can sometimes only detect one photon at a time." ]	[ "Congrats, you've stumbled upon a major open question in astrophysics." ]
What were relations between the USA and the Russian Empire like?	[ "You might want to check out Saul Norman's Distant Friends: The United States and Russia, 1763-1867. Suffice it to say this isn't the first time that question's been asked and there's a reasonable number of articles on it. since it's actually an interesting thought. The two, for the most part, were rather friendl...	[ "A follow up & relevant question, how close did the CSA come to being recognized by a European Power?" ]
the differences between Singles, EP's, and Albums.	[ "Singles were created before the Internet, to get popular songs out quickly. The artist wouldn't have enough material or time to release something longer at the time. Traditionally, just an A-side (single) and the B-side. 2 songs. Nowadays, a few remixes. Somewhere around 6-15 minutes. EP stands for extended play, ...	[ "Ask Reddit is for personal opinions, stories, and the like. Essentially subjective answers to questions without hard answers. Something like \"whats your favorite food\" is a good post there ELI5 is for getting a simplified answer or explanation to a question that you don't understand. A good thread here would som...
Is it just a coincidence that the colours of Universal Indicator (used to measure pH) are the same as the colours of rainbow (and same order)?	[ "Color corresponds to frequency; prisms etc. refract light by separating light by frequency. If you order light by frequency the colors are ROYGBIV. Rainbows are caused by light refraction. Universal indicator mixes several pH indicators such that they provide a smooth color shift. Lets say you choose three indicat...	[ "Why not actually try the experiment? Everything you need is available at your local drug store[1]. An irrigation syringe (one with a plunger) could work to help you separate the oil from the urine. Tests for cannabis don't usually measure THC, but rather a metabolite which is a bit more hydrophilic; however, that ...
Were entire villages in Europe deserted during the Black Death? If so, what became of them?	[ "Yes, entire villages were struck so hard that they were abandoned. In Sweden, there's a specific name for villages that were abandoned - \"böle\" was added to the name of the village when it was re-populated again. It might not have been entirely eradicated, but enough so that people could move in from the outside...	[ "Related question: what was the size and importance of the medieval bleach industry?" ]
How will the recent SCOTUS decision affect private universities, not just state universities?	[ "It won't. The decision upheld a state referendum on affirmative action policies at public universities." ]	[ "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...
Did anyone tried to "hack" the telegraph network during the 19th century?? If yes, any notable examples of telegrackers??	[ "While this is a little later than the 19th century, the classic example of hacking into the world wide cable system was when the British intercepted the Zimmerman Telegram, during World War One. First, the Royal Navy severed all of Germany's trans Atlantic cables. Then they intercepted a message the Germans sent f...	[ "Is this a homework question? It says in our [rules](_URL_2_): Our users aren't here to do your homework for you, but they might be willing to help. Remember: AskHistorians helps those who help themselves. Don't just give us your essay/assignment topic and ask us for ideas. Do some research of your own, then come t...
How do we, physically, store visual memories? Is each neuron used as a "pixel", and if so, how do we have enough room in our brain for it all?	[ "Neurons do not just store one thing. A 'pixel,' in your analogy, would actually be represented by a specific combination of many different neurons. Each of those neurons may be used in many other combinations to represent many other pixels. And there are [around 140 million neurons in the primary visual cortex](_U...	[ "To show a moving picture you needs a bunch of individual pictures all shown after another. A short clip might be 30 pictures total. A gif is pretty much just that, 30 pictures with some extra information like how long to wait before showing the next one. A modern video file like you see on youtube is a lot more co...
Why did Oliver Cromwell refuse being crowned king?	[ "It is worth noting that Cromwell did take a number of months after The Humble Petition and Advice was presented to decide whether or not to accept the crown. It can be argued that this is evidence enough that he wanted the crown for himself, after all, he was King in all but name at this point. The fact of the mat...	[ "If you go back in time there certainly was. A classic example would be the battle of Agincourt where the English king Henry V led his army from the center of the battle line. You can read \"The face of battle\" by John Keegan for a fine account of the battle including many kingly deeds performed in the thick o...
Micro LEDs aka "fairy lights"	[ "Certain types of copper wire have a transparent enamel around them - so they look like naked copper but are actually insulated." ]	[ "What kind of cheese is it? I mean, there is some types of bacteria that are phosphorescent..." ]
The difference between legalization and decriminalization	[ "Legalization means you can use or do something without any legal consequences. Decriminalization means you can use or do something without getting criminal charges (i.e. jail time) but you can still get a fine or warning without special permission." ]	[ "This CGP Grey video does a really good job of explaining it all. _URL_3_" ]
When did women's breasts become hyper sexualized?	[ "The answer to your question is likely prehistoric. You may consider cross-posting to r/askanthropology as well." ]	[ "The popularity of comic book characters and acceptance of the geek subculture, mainly. people aren't scared to show that they enjoy these things anymore." ]
Why antibiotics doesn't work on viruses?	[ "Antibiotics damage the metabolism or some structural components of the bacteria. The trick to antibiotics is that they are specific enough to be harmful to bacteria but not to the cells of the host. Viruses on the other hand don't have a metabolism of their own and their structure is extremely simple. They take ov...	[ "Largely because news stories sensationalize science without fully understanding it. There is a relevant XKCD comic that has a guy in a lab coat standing over a petri dish with a gun that says, \"When you see a claim that a common drug or vitamin 'kills cancer cells in a petri dish', keep in mind: so does a handgu...
Why do all modern phones have stripes on the bottom? (Picture in text)	[ "If your talking about the thin lines that run all along the phone, them it's separation for the antennas in the phone. Your phone has different antennas for cellular/LTE connections, Bluetooth, wifi..... Those lines are either where the antennas are run or they separate different metallic parts of the phone that a...	[ "The outside of cells and virus cells are covered in chemicals. Different cells are covered in different chemicals. Specific chemicals stick to other specific chemicals. Other chemicals don't do anything. It can help to think of it like many different colors of velcro. Blue velcro only sticks to blue velcro, it doe...
Why is there such a demand in Asia for Rhino and Elephant tusks? How did it start?	[ "Traditional Chinese Medicine uses herbs and powders and other natural ingredients to cure various ailments. They believe it will cure things such as impotence or even cancer. So, there's high demand for these items." ]	[ "Nostalgia, too ~ a lot of older guys that now have lots of money are reliving their youth - they either had one when they were young & want another, or wanted one when they were young and can now afford to pay the big bucks to get one." ]
How can terms of services apply to teenagers when they are underage yet still old enough to use social media platforms?	[ "A term of service isn't a contract. It's just an agreement and one whose primarily function is to absolve platforms of responsibility. So if you go on their platform and violate their terms of service and do something illegal, they can point to it and say, \"They knew they weren't supposed to do that, we do did *o...	[ "Because they would get sued. The legal system isn't like some kind of beep-boop robot that overlooks totally obvious loopholes. Any company that claimed \"No, we were really advertising the endorsement of Bill Gates, plumber, from Bumfuck, Nebraska.\" would get laughed out of court. As /u/Snewzie pointed out with ...
what is a Power of Attorney? And what do they do?	[ "A power of attorney is a document naming someone as your agent -- they are entitled to make decisions as though they were you. For instance, they can sign your name to contracts, access your money, etc. You can of course overrule them and revoke the power of attorney at any time; the idea of the thing is that you ...	[ "This CGP Grey video does a really good job of explaining it all. _URL_3_" ]
Excluding all religion, why are we not going insane over the fact that one day we, and everything and everyone, will die?	[ "It is inevitable and there is nothing we can do about it. When you boil it down, you really only have two options. 1 - You can live your life for today, do what makes you happy, raise your family to continue your blood line and try to live a fulfilling life. 2- You can stress about the inevitable without actually...	[ "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...
In academic articles, why are units of area often shown as being multiplied to the power of -1?	[ "The word \"per\" implies \"divided by.\" For example, miles per hour can be represented as (miles)/(hour). Newtons per square meter (the SI unit of pressure, also known as the Pascal), can be represented as (N)/(m^2 ). m^2 is the SI unit of area. Also, to directly answer your question, a/b is equivalent to ab^-1. ...	[ "As a US teacher, here's what I've found. America is in an uninterrupted chain of nostalgia for the previous generation's form of schooling. Having had no major disruptive events to our institutions, we still essentially pine for the one-room schoolhouse model. Every school board I've seen has proudly boasted that,...
Why do programmers start iterating a list at index zero instead of one?	[ "In the old days you would have to manage your own memory. You would have to store an address to where your data is located in memory and then to arithmetic on that address to find the specific value you were after. So a list would be a pointer to the address of the first entry in the list. If you add one data size...	[ "Imagine you are a travelling salesman, and you spend most of your time driving from place to place across the country. Today you need to get from Denver to Dallas. You could use High Level Navigation. You know how to get from Denver to Wichita, Wichita to Oklahoma City, and Oklahoma City to Dallas. String those to...
How do magnets get their magnetic fields? How do electrons get their electric fields? How do these even get their force fields in the first place?	[ "Each electron fundamentally has its own intrinsic dipole moment. Then the electrons and nuclei combine to form atoms, which have some total dipole moment. Then many atoms assemble into a macroscopic piece of material. In a ferromagnetic material, neighboring magnetic dipoles interact strongly with each other so th...	[ "Yer not alone in askin', and kind strangers have explained: 1. [ELI5: Whistling ](_URL_6_) 1. [ELI5: How does whistling work? And how is it different from blowing? ](_URL_0_) 1. [ELI5: How does whistling work? (Wind/air pressure to sound with whistles, bottles, or lips.) ](_URL_4_) 1. [ELI5:How does whistling work...
Where do carnivores get their fiber?	[ "This was posted by a [Gil Stoewsand of Cornell University](_URL_0_): The carnivore bowel is much different than humans. Carnivores have a short, smooth, stovepipe shape compared to our much longer, puckering, pouched shape, with a twisted, convoluted pathway. Carnivores need very little fiber to move things along...	[ "Your answer was removed shortly before you posted this question. It did not meet our standards. We ask that answers in this subreddit be in-depth and comprehensive, and highly suggest that comments include citations for the information. In the future, please take the time to better familiarize yourself with [the ...
If we can prove that there are particles that actually move faster than light, will it REALLY be possible to travel throught time?	[ "That's a hard question, because you're asking for a hypothetical analysis of a hypothetical behaviour of a hypothetical particle. Based on what we know right now, reverse time travel is not achievable. However, when things change, so will our understanding. No-one knows what those changes will be until they happen...	[ "Currently, yes, we have no propulsion technology to get to a habitable exoplanet in a reasonable timeline. I worked out the math in a couple previous threads, and it's also done [here](_URL_0_)." ]
Is it end-to-end encryption if the servers (e.g. WhatsApp) generate the encryption keys?	[ "It's not end-to-end if the servers generate the keys. With WhatsApp the servers don't generate the keys. You and the receiver do. That's the whole point of specifying that it's end-to-end encryption." ]	[ "You and some of your friends are at your house playing a game. In this game you are all in different rooms, one in the bedroom, one in the kitchen and so on - the only rule is you can't leave the room you're in. You play the game by shouting messages from one room to the other, and it's all fun. But there's a prob...
Does Halley's comet get smaller after each orbit?	[ "From my understanding, comets shrink over time if their orbit goes into the inner solar system. The [comet tail](_URL_1_) is a result of solar radiation from the sun, blasting off material from the comet. Just like [this](_URL_0_). This would lead me to believe that material is left behind by the comet after every...	[ "The image you refer to is the result of an observation know as the 2dFGRS which stand for \"2 degree galaxy redshift survey\"- redshift being a measure of a galaxies distance. It's shape is like an hour glass because it was focused on the north and south galactic poles. They did that because the disk of our galaxy...
How can there be so many pedestrians killed by trains? How can people not see, feel or hear an oncoming train?	[ "Simple answer: Suicide. It's more definite to end your life via bring crushed by a train compared to being hit by a car." ]	[ "Fortune tellers do what's called cold reading, picking up on little nicks and things that you physically show. They are also great at reading on your vulnerabilities such as emotions. They then attempt to predict, based on information that you have provided, try to create a crazy, but understandable fortune that c...
What happens to the debt of a missing person?	[ "Looking for a way out of debt are we?" ]	[ "> but form a legal perspective how does this work? National and local laws apply with the usual law enforcement having jurisdiction. As far as immigration is concerned it might be \"outside the country\" but it is still the territory of the country. Police will just walk in and arrest whoever they want." ]
I've read Christopher Columbus was sailing to India to find a route that avoids the Middle East. Is this true? If it is, why did he want to avoid the Middle East?	[ "He wanted to find a shorter route to India, not necessarily avoid going through the Middle East." ]	[ "Lots of airlines use the hub and spoke model. Rather than have a flight from every city to every other city, they have flights from the small cities to a few big cities, called \"hubs\". You then fly from the hub to your destination city, or perhaps to another hub, from which you fly to your destination. So let's ...
How can I, an average guy without huge amounts of historical knowledge, learn the truth when the subject is controversial and heavily influenced by propaganda?	[ "I can't answer the question directly, though I can point you to the sub's reading list. Most specifically, the one on Russia. [Link](_URL_5_) Apologies to the mods if this violates." ]	[ "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_...
Why do whales die on land? They breathe air and do not have gills. So what is causing their death?	[ "Multiple things can go wrong when beached. I think the biggest reasons are their own weight (for really large whales, they can crush organs) and heat exhaustion. However, they can get dehydrated or even suffocate/drown if their blowholes are covered." ]	[ "As a geologist who studied in the midwest and also spent time as a student archaeologist in that region, I would say that I think you'd be surprised about all the cliffs around the Great Plains. I just spent a few minutes looking around the [USGS National Topographic Map](_URL_0_) and if you look at basically any ...
What does the U on this magnet mean?	[ "That's weird, I've never seen that. For some reason this is bugging me, so I've spent a good 15 minutes trying to find out the answer to this. So far I've found [this magnet](_URL_0_) that has the same symbol in the middle, except now it's rotated 90°. There's also the possibility that you are holding the magnet u...	[ "\"Use\" takes many fewer letters. Since the message isn't essential marketing to get you to buy the product, the less space it uses the more is available for Marketing." ]
How are theaters allowed to oversell tickets	[ "Unlike what other people are saying they didn't oversell. Their point of sale software has auditorium max capacity counts and won't let them sell more seats than they have. What usually happens is sometimes there are more one off empty seats than anticipated and they elected to not ask people to move down or make ...	[ "NPR recently did a piece on this. Part of it is if the artist charges $200 then the artist is a money grubber. If a scalper does it, it is expected. Here is the piece. _URL_0_" ]
how a microphone converts sound into data that represents pitch and tone of a note.	[ "The movement of the coil (or the ribbon, or the plates, depending on mic type) moves in the same way the sound does in the air. It's sort of like an auditory photocopy of the sound that travels through the air. The sound waves hit the coil (or whatever), the coil vibrates in the same way (then gets amped, etc). Si...	[ "If it's a coin it measures the size/weight of the coin as each is unique. At least in the US. As far as bills it actually uses an optical scanner to look at the money as well as a magnetic scanner. Money is written with magnetic ink and says it's denomination in multiple locations. The optical scanner shines a UV ...
We drink chlorinated water because the Cl prevents bacteria like cholera. Does drinking it also have any effect on our gut bacteria?	[ "Your stomach is much more chlorinated than any water you put in it — stomach acid is ~.1M HCl, whereas chlorinated drinking water is on the order of 2 mg/L, which is 55 µM HCl. So, chlorinated water has negligible effect on your stomach chemistry. Which means that the important question is: how is stomach acid n...	[ "The Gulf Stream primarily exists because of the action of winds blowing across the subtropical Atlantic. A good (but small) map of the surface currents is [here](_URL_0_). Unfortunately, many people are taught this [image](_URL_1_) of ocean circulation which both dramatically simplifies the Thermohaline Circulati...
Why can't we remember anything from when we are very young (i.e less then a year old)	[ "Until the age of 3 much of the rain remains undeveloped, specifically the frontal lobe which is responsible for both short-term memory retention and long-term memory coding. The first part of the brain to develop is the most fundamental part (the medulla and the pons) which accounts for body functions such as brea...	[ "Physically developing we are close to a bobcat or other animals in terms of lifespan. We have a much, much more complex world than any other animal does though. We have to eat that play-doh and stick that key in the electric socket to learn that we want to be a philosophy major or an architect. Bobcats can't build...
What makes sarcomas so: 1) rare and 2) aggressive compared to carcinomas or other cancers?	[ "They're rare because they're not from tissue with high cell turnover. Cancer is a problem of unregulated growth and division, so it naturally tends to affect cells that grow and divide a lot. The more times you copy and recopy your genetic code, the more chances there are for errors to add up such that normal safe...	[ "Before RICO laws it was hard to take down an entire organization because the mob boss could never be connected to any specific crime. The Mob boss would talk to his under-boss about an illicit act. The under-boss would pass the info along to a caporegime (a sort of lieutenant) who would then instruct one of his ga...
- the difference between "UI" and "UX"	[ "User Interface versus User Experience. The former (UI) is the means a device (whether it's a machine as simple as a screwdriver, or a software application as complex as SAS or QuickBooks) makes available for the person using the program to interact with it. Buttons, knobs, levers, places to type text, etc. These a...	[ "Well most importantly how to survive in space. But if that doesn't grab you here is a list. _URL_0_" ]
Why do companies do mail- in rebates?	[ "Because most people won't go through the effort of submitting a rebate. It's an easy way to attract potential customers, and means that only a small group will be taking advantage of any savings." ]	[ "Along with all the other answers so far, I believe there is a social component. Having a conversation/interaction with another human is more fun and interesting than looking something up on Google. In addition, you might gain access to a perspective that isn't yet on the internet." ]
What happens if someone is born in international waters? What nationality would they be?	[ "A lot of international politics is decided between each country or on a case to case basis. In most cases if a baby is born in international waters or on a ship headed to or from international waters then the child gets the same nationality as the parents. If this causes problems then the nationality of the ship i...	[ "There are lots of ways for animals to traverse the earth, not to be trite. Addressing your specific example, this wiki. _URL_1_ Indonesia was at one time linked to the rest of the islands in that part of the world, when sea levels were lower due to so much water being bound up in polar glaciers. When the glaciers...
Why do you feel cold when you have a high fever?	[ "For the same reason you feel colder when you step out of a nice hot shower. Your internal body temperature is higher, therefore the air around you feels colder than normal." ]	[ "Nervous system is all about the action potential in the neurons. All neurons signalling is an active chemical function. Energy is required to produce this function, and as a result lower temperatures drive down the energy available for the reaction to occur. This also happens in cells, making it impossible to main...
Can someone explain string theory to me?	[ "Precocious child: \"What is everything made out of?\" Science: \"Little things called atoms.\" PC: \"Well, what are atoms made out of?\" Science: \"Smaller things called protons, neutrons, and electrons.\" PC: \"What are those made out of?\" Science: \"Even smaller things called quarks.\" PC: \"What are qua...	[ "Have to recommend you watch this video by \"vsauce\" on Youtube: _URL_0_" ]
What makes up space? (Besides black holes, planets, stars, planets etc., what is the black space?)	[ "> It is impossible for a state of nothing to exist Why do you think that \"a state of nothingness\" cannot exist? > so what the hell is out there? Neutrinos. Electromagnetic and gravitational fields. The occasional atom of hydrogen and helium. Perhaps dark matter/energy. Essentially, as close to \"nothingness\" a...	[ "The computer has files of varying sizes. These take up varying amounts of spaces on the hard drive. Say you write to the hard drive 3 different files. One takes up 5 \"spaces\" the next 2 spaces, and the last 5 spaces. Later, you delete the 2 space file. Now you've got 5 occupied spaces, 2 free spaces, 5 occupied...
Why are nut/peanut allergies more common now than they have been in the past?	[ "For a time the recommendation was for young kids to avoid peanuts because the allergy could be so serious. However, it appears that avoiding peanuts while young can cause you to later develop the allergy. The recommendation now is to expose kids to peanuts while they are young. So, we're likely living in the time ...	[ "My guess? When you're dealing with a lot of makeup, prosthesis, special effects its easier to hide flaws. You can see acne under makeup in high def, you couldn't really see that back in the day. Just a guess." ]
Why are routers and modems commonly sold separately rather than contained in one unit?	[ "Most ISPs today sell a combo modem+router unit. You can buy them from many computer outlets too. The reason though, is there are different technologies used to deliver Internet to your house: cable, ASDL, and fiber are the current popular ones. By selling a router that takes an ethernet connection in from a sepa...	[ "They aren't trying to make money on them. They are a loss leader to get people in the store, and to smell good so people will be hungry while they shop. If the shopper buys a roast chicken that the store makes no money on, they might also pick up a loaf of bread , some mac and cheese, and some salad to make a more...
How can a company justify paying a single individual 500 times the average salary?	[ "there are not very many people that can manage a company of that size and can keep it growing. that's why they are worth millions per year. look at GM in 2008 ish. bad management led to some catastrophic results. _URL_0_ but Ford was under pretty good management from this guy _URL_1_ and didn't have to get bailed...	[ "They reason they rank so high on the power list is their ability to finance essentially any project out there... as well as they have an extreme amount of connections. If they so wanted they could fund the massively expensive project of integrating seaweed into animal feed and cut all greenhouse gas emissions from...
Is it possible to move the earth?	[ "In theory. If you want to go deep into it when you do a pushup you move the earth down a trillionth of a millimeter." ]	[ "This is actually actively being worked on, check out this really neat video about it: _URL_0_" ]
Why do we say "dehydrated" instead of "Malhydrated". And "malnourished" instead of "denourished"?	[ "Dehydration is the lack of hydration, whereas malnourishment doesn't mean you're not getting nourishment, just bad nourishment. One is the absence, the other is just low quality." ]	[ "A nut has a hard shell with a seed inside that usually does not open (Like an acorn). A drupe has a fleshy (soft) shell with the seed (or pit) inside like a cherry. A fruit is just the fleshy soft part surrounding the seeds. If you planted a peach pit it would grow because it is also the seed! At least thats my u...
Why do I stop smelling a scent after being exposed to it for a period of time?	[ "[Olfactory fatigue](_URL_0_). Basically the body becomes desensitized to stimuli to prevent the overloading of our nervous system, thus allowing it to respond to new stimuli that are ‘out of the ordinary’." ]	[ "Think of your brain like a billion streams of water that flow over the surface of a rock. The more you use a certain stream, the more \"powerful\" that stream becomes by digging away that rock. Now even if you have a nice dug place for a stream, sometimes randomly that stream won't have needed to flow for a while ...
What is the meaning of the red envelopes that Chinese families give money in?	[ "A red envelope is a symbol that you wish prosperity on whoever you give the 利市/利是(Cantonese, pronounced lay-see IIRC) to. Often the envelope will have the number 88, a Chinese number of good luck on it. ELI5 Its a simple way to give somebody a gift of money, where the gift is not only the cash but the wish of pro...	[ "Remember that when you're voting you need to give a preference to each party and can even decide to Vote 1 for a small party you haven't heard of before (or, if you live in the electorate of Grayndler, Meow-Ludo Disco Gamma Meow Meow because you like the name - but seriously don't do this without researching the p...
Why do some blood tests need to be done from a specific arm, when blood in the body circulates so quickly?	[ "Blood tests don't need to come from a specific arm. If you're having multiple draws performed, they may switch arms between the draws to reduce the amount of punctures in a single arm (though it's preferable to get all the necessary blood from a single draw). And if they're testing for an infection that could invo...	[ "You can use something like [this](_URL_0_). If you bounce light off a rotating mirror to a stationary mirror a long way away, then the rotating mirror has moved a bit by the time the light gets back and reflects off it a second time. By measuring the angle between the light source and where you see the reflected l...
How does the MLM system work ?	[ "A newcomer pays for the opportunity to acquire what amounts to a premade \"business kit\" and shoulders the responsibility for making it profitable. Most of the time, the money doesn't come to them from outside customers, but to the joiner's \"upline.\" That is, the person who sold them the starter kit and their s...	[ "I encourage you to check out this youtube video _URL_0_ Explains it better than I can" ]
What are the things holding back consumer robotics?	[ "If you're talking about the robots seen in I, Robot or Robot and Frank, then about 30 more years of development and another 10 years of market introduction and expansion. We're just too far away right now to be putting a Rosie in every living room. Once we are there, they'll be prohibitively expensive for most...	[ "Cost, at this time, it still requires an extreme amount of money/resources to launch something into orbit or beyond. There isn't anything that we need that badly that would justify mining an asteroid/etc." ]
visible veins during/right agter a workout	[ "Your blood vessels dilate to increase the volume of blood flowing around your body so they show up more prominently. During exercise, your heart beats harder and faster, your blood pressure goes up and your blood vessels dilate to facilitate more blood flow to your muscles. Circulation increases from 5L/minute to ...	[ "Some medications, vaccines, etc are meant to be injected intramuscularly. Your muscles have tons of blood vessels that can get the medication into your blood stream. _URL_0_" ]
Why is idling bad for your car?	[ "It's not terribly bad, but it does continue to operate the engine for no benefit. In some poorly designed older cars, the distribution of oil might not be as good as one would like when idling a long time. This could lead to increased friction and wear." ]	[ "Food takes time to reach the stomach, and you'll notice if you eat and then wait you'll be less hungry. Chewing more simply takes more time to do, and so you get full with less food" ]
How can websites like hotwire and priceline get you cheaper arline tickets and hotel rooms?	[ "It is beneficial for airlines to fill empty seats and hotels to fill empty rooms, rather than to leave them empty. They form agreements with these companies to offer lower priced rooms, but often do so in secret so that the consumer doesn't know precisely which hotel or flight they are getting such a deal on. This...	[ "> How do trains/airlines/etc decide the age to stop letting children on for free? It is a marketing decision where the marketing department guesses what ages would be enough incentive to gather business they might otherwise lose to competitors. > Wouldn't you be able to lie about their age? Maybe. It isn't a big ...
How does Cholera force food and liquids through the body so quickly, and why can't nutrients be absorbed?	[ "Cholera is caused by a bacteria that nestles itself in the small intestine, which is where the majority of our nutrients are absorbed. Once in place, the Cholera bacteria starts excreting a Toxin. This toxin gets inside the cells of your intestine and causes them to burst, which in turn releases the cell’s innards...	[ "Contraction of bowel into the anal canal is peristaltic meaning it comes in waves. The first anal sphincter is involuntary so when you need to go it relaxes letting poo to the canal. Then you tense your voluntary one. When the peristaltic wave passes you mo longer feel the urge even though the canal itself is full...
Can I get sick if I do a poo in a public toilet and splash goes straight up into my open date?	[ "Your bumhole doesn't open up completely. Poo gets squeezed out, it doesnt fall out. If some water does splash up it doesn't go into your bumhole, it stays on the outside. I'm going to do some experiments and I'll let you know exactly what happens." ]	[ "I could answer this for you, but since I found it so wonderfully explained in detail [elsewhere](_URL_0_), I will instead point you there instead of typing the full explanation here. A very brief explanation of what is there though is to say that each time the food is cooled from hot to cold and passes through tha...
How do laser distance meters work?	[ "the laser light beams out till it hits something, then the light bounces back to the meter. The time it takes the light to reach the object and get back to the meter tells you the distance because we know the speed of light." ]	[ "Yes, there are [SASERs](_URL_0_). [Here](_URL_1_) is an article from New Scientist about the first such device." ]

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