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5lw3qo
Before modern counterfeit measures how could people tell if their currency was counterfeit?
Economics
explainlikeimfive
{ "a_id": [ "dbyyktq", "dbyx6uj" ], "text": [ "Well if you go back far enough currency was a specific metal, like gold, silver or copper. These metals had a value in the metal itself that did not matter what country issued them, so there was not any issue of counterfeiting as we know it. However people still found ways to scam you out of money. If you look on the edge of a coin, you will typically see that the edge is not smooth. Thats called \"reeding\" and is used because people used to shave a small amount of gold or silver off the edge of a coin and melt it down to pocket the difference. The reeding on the edge tells people that this coin has not been shaved down.", "Counterfeit currency has always been a problem. For a while, just stamping a coin was good enough as few people had the tech to stamp their own. Of course crooks got smart and figured out how to make fakes or modify existing coins. Gold coins were especially vulnerable and traders would have balance scales to check the coins hadn't been drilled out. Acid tests were developed and complex patterning on the coin made it more difficult to fake." ], "score": [ 14, 9 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5lw55a
Why do some surgeries result in equipment being left behind in patients (e.g. scissors)?
How would a nurse or doctor forget that equipment is left behind? Doesn't the hospital check if equipment is lost at the operating theatre?
Biology
explainlikeimfive
{ "a_id": [ "dbyxrl3" ], "text": [ "This is very, very, very, nearly impossibly rare. I trained as an O R nurse in the US in the 1970's. We counted all the instruments before surgery and after. These numbers were written down both times. The patient's incision was not closed until the numbers were equal. Also, during surgery sponges were used. Not the kitchen variety. They look like wash clothes and each has a tiny metal tag. These are counted as they are used and again counted at the end of surgery. Rarely a sponge may be left in the patient. And let me repeat, rarely. On x-ray the tag will be seen. Another operation and the sponge removed." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lw932
Gödel's Incompleteness Theorem and why it is an argument against the Theory of Everything
Wikipedia has left me dazed to be honest.
Physics
explainlikeimfive
{ "a_id": [ "dbz4kw8" ], "text": [ "First off, the incompleteness theorems have absolutely nothing to do with a \"theory of everything\". A ToE is an idea in physics, something that can explain all physical phenomena within the bounds of a single theory. Goedel's incompleteness theorems are entirely mathematical/logical in nature, and do not argue against (or for) the existence of a ToE. A *mathematical* theory is different than a theory in physics. In mathematics, a theory is a collection of axioms, which are the basic assumptions that you make in order to prove other things. In a theory of arithmetic, you might have axioms like \"0 is a natural number\", \"for all natural numbers n, n+0 = n\", and so on. Theories can prove various statements using only the axioms and formal logical reasoning. Various fields of mathematics use different theories to discover properties about different mathematical structures. Mathematical logic studies the properties of theories themselves. There are two properties in particular that are very nice for theories to have: * Completeness: for any given statement, the theory can either prove the statement or prove the negation of that statement (or both). * Consistency: for any given statement, the theory cannot both prove the statement and also prove the negation of that statement. For example, a theory which could prove literally any statement about arithmetic (\"1+1 = 2\", \"1+1 = 3\", \"0 is a natural number\", \"0 is not a natural number\", etc.) would certainly be complete, but it would be inconsistent (and not very useful). On the other hand, if the theory could prove absolutely nothing about natural numbers, it would be consistent (no contradictions arise when you can't prove anything) but it would also not be very useful because it's extremely incomplete. Ideally we'd want a theory of arithmetic which is both complete and consistent. In such a system, we could choose any possible statement about the natural numbers, and the theory could either prove or disprove that statement (but not both). What Goedel's first incompleteness theorem shows is that for a very broad class of theories, it is impossible to fulfill both of these properties. Specifically, the theorem applies to any theory which is recursively enumerable (you could write a computer program that lists all the axioms) and which is capable of talking about arithmetic. Both of these conditions are necessary. It is valid to define the theory of true arithmetic, where the axioms are all true statements about the natural numbers. This must be both complete and consistent, but it's not recursively enumerable because no algorithm could possibly tell you what all the axioms are. On the other hand, there are theories like Tarski's axioms for geometry, which manage to be both complete and consistent but which are incapable of describing arithmetic. Goedel's second incompleteness theorem takes this a step farther. Goedel showed that any theory which could be used to prove its own consistency must actually be inconsistent. Remember than an inconsistent system contains mutually contradictory proofs by definition, so it shouldn't be too surprising that inconsistent systems can \"prove\" their own consistency in addition to proving their own inconsistency. The more surprising part is that theories which *are* consistent can't possibly prove that they have this property. This, once again, foiled the hopes that some mathematicians had for formulating a foundation for mathematics which could prove its own validity. Most mathematical theories used today are assumed to be consistent but incomplete. That said, because of the second incompleteness theorem they cannot prove their own consistency. You can use stronger theories to prove weaker ones; for example, the ZFC axioms of set theory can prove the consistency of the Peano axioms of arithmetic. However, it is always theoretically possible (but unlikely) that these stronger theories have some inconsistency buried in them, and that these consistency proofs are therefore invalid. The lack of completeness is less of an issue, since unprovable statements are less bad for a theory than contradictory proofs. There are some statements known to be unprovable in ZFC and other theories, but if necessary we can always add in new axioms to resolve them one way or another." ], "score": [ 7 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lwfev
Why do all old movie trailers have narration in them?
Other
explainlikeimfive
{ "a_id": [ "dbz0n54" ], "text": [ "Because people generally want to know what a movie is about before they go see it and in the ~2 minutes a trailer lasts voiceover narration is the best way to communicate to the viewers what the movie is about." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lwp25
Both the sun and moon appear flat, with no cues that one is further away than the other. What is the maximum distance that variations in depth can be perceived at, and why?
Biology
explainlikeimfive
{ "a_id": [ "dbz54c7" ], "text": [ "We don't have depth perception beyond about 10 meters. Anything further than that, your eyes are focused at infinity, and are pointing in the same direction. Beyond that, we use cues like its apparent size and brightness, or color shifts caused by the amount of air between you and the object (how a distant mountain looks more blue than a near one). We determine things are flat or round by their shadows." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lwvjd
Both of my Parents are type O blood type. I am AB+ how is that possible?
Biology
explainlikeimfive
{ "a_id": [ "dbz3vn0", "dbz7uab", "dbz3fby", "dbz54az", "dbz56ub", "dbz6b9o", "dbznzne", "dbzejjt" ], "text": [ "Its possible, but extremely rare, for a person to have different blood type sperm/egg than their actual blood type (a chimera). The odds of both parents being chimeras would be astronomical. Either someone's typed wrong, or you're adopted.", "There is a rare blood type called hh or Bombay phenotype. It will appear as type O because it does not have the A or B antigens on it. However, children of a parent with this type may still have type AB blood, because the genes for the antigens are there, but the hh is a mutation that keeps these antigens from being expressed when the blood cells actually develop. I am rather amazed that no one has brought this up yet. I learned this in Molecular Genetics class.", "> Both of my Parents are type O blood type. I am AB+ how is that possible? It's not. Either you are mistaken about your or your parents' blood types, or you are adopted. Two O parents cannot produce an AB child.", "One parent with O blood makes AB impossible, much less two. You have to get A from one parent and B from the other. While it is not unheard of for one mutation to occur, it is very rare. For two freak mutations to happen at the same time would probably be never before in history improbable. So, here are the other possibilities: * both parents are wrong about their blood types * mom is wrong about her blood type, a mutation occured, and the man you call dad is irrelevant to the genetic equation * neither mom nor dad are your genetic parents I'm betting on the first one.", "Are your parents O + or O- ? Having an AB from an O is still impossible ... I'm just curious. The chimerism thing doesn't work because it means you have cells from one or more zygotes. But any of the DNA you have has to come from the sperm or the egg. Neither of your parents have any copies of A or B unless they are both chimeras as well, but this would have been detected when your parents were blood typed. URL_0 Article is from the American journal of medical genetics 1996", "> Edit: can O be mistaken for AB on a blood type test? Not usually. Blood typing tests for proteins on the surface of RBC's that react to certain antibodies. * Having type A blood means that your RBC's have type A surface antigens and your body produces antibodies that attack cells with type B surface antigens. * Having type B blodo means that your RBC's have type B surface antigens and your body produces antibodies that attack cells with type A surface antigens. * Having type AB blood means that your RBC's have both A and B surface antigens and your body does not produce antibodies that attack cells with either surface antigen. * Having type O blood means that your RBC's do not have either A or B antigens and your body produces antibodies that attack cells with either A or B antigens. So when they test your blood type, they see how antibodies react to your blood. If a blood sample reacts to type A antibodies and the cells start to stick together, then that blood is not type A. The same goes for type B. If blood reacts to both A and B antibodies, then that is type O blood. If the blood doesn't react to either A or B antibodies, then that is type AB blood. So it's not likely type O could be mistaken for type AB, as their reaction to antibodies in the test are the exact opposite. Type O will react to A & B antibodies while type AB won't react to either.", "OP, be aware that most posters in this thread are **grossly overestimating** the certainty with which AB0 blood typing proves parenthood on its own, because they're relying on high school genetics knowledge. Much like fingerprinting and DNA testing, while the average person thinks it's foolproof, there are all sorts of details involved (bombay blood as mentioned by a poster, incorrect test results, other genetic disorders, etc.) which makes matters far more muddled. Avoid making early conclusions.", "Genetics testing for other reasons shows that about 3% of the time the putative father is not as thought. This is in a group where the testing is announced ahead of time to both parents, especially to the mother, for a full diagnosis of the child. In other words, the mother knows ahead of time that the truth will out, and she can avoid it with any excuse she can think of. So this number is probably lower than the actual incidence. Be sure to think through the consequences of any possible discovery. You do not want your supposed father shooting your supposed mother." ], "score": [ 46, 36, 30, 8, 5, 4, 3, 3 ], "text_urls": [ [], [], [], [], [ "http://www.tweelingenregister.org/nederlands/verslaggeving/NTR_publicaties/Dijk_AJMG_1996.pdf" ], [], [], [] ] }
[ "url" ]
[ "url" ]
5lwws3
Why is ice less dense than water even though most solids are more dense than their liquid forms?
Physics
explainlikeimfive
{ "a_id": [ "dbz3n4u" ], "text": [ "Water has a delightful property: when water solidifies it's bond angles extend and it aligns into a lattice usually. That does 2 things. It makes the solid less dense, because there's more space between molecules, and it makes it sort of see-through." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lwz7p
How do people in war zones have access to Internet?
Technology
explainlikeimfive
{ "a_id": [ "dbz46gn" ], "text": [ "One of the design goals for what became the Internet was to be tolerant of failure. If some lines get cut, the Internet just routes around them. As long as there is still power and one intact line connecting that area to the rest of the world (whether it's a physical cable or a satellite link), the Internet will continue to work." ], "score": [ 5 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lx71d
Why do we have imperial/metric units, and so many different languages, while time has a universally accepted measurement?
Other
explainlikeimfive
{ "a_id": [ "dbz5uqb" ], "text": [ "Historically, every culture had their own measurements. Over time, we developed organizations to standardize these. Except for one country, everyone in the world uses a single system (metric). Even in the US, many types of commerce are increasingly in metric. There have been attempts to standardize language (Esperanto, for example). As well as historic \"lingua francas\" (Greek, Persian, Latin, French, English) that at various times become the language of international commerce and academia. However, language has proven to be much more resilient: 1. It's a lot harder to teach people new languages than new measurements 2. Language is tied to nationalism, culture and identity" ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lxd0j
Why are nuclear bombs detonated in the air instead of on impact?
Other
explainlikeimfive
{ "a_id": [ "dbz7283", "dbzaive" ], "text": [ "Because it has a wider impact range. Detonating on the ground has quite a bit of energy absorbed into the ground below it, instead of on the target location. Detonating in air allows it to spread out more, dealing more damage.", "It's a bit like how artillery shells are often set to detonate before impact. If they detonate on inpact, most of the force will be directed upwards and they will do less damage (to soft targets). However, if detonated in the air, the pressure and shrapnel will be directed downwards over a larger area. The same goes for nukes. To maximize damage, you don't want ground features to redirect anyting upwards." ], "score": [ 18, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5lxdu2
Why do many word pairs sound "correct" in one order, but not when reversed? Is it just cultural, or is there a linguistic explanation?
Some examples: Comparing "apples and oranges" vs "oranges and apples." It's more correct chronologically to say you are putting on your "socks and shoes," but I've only ever said/heard "shoes and socks." When speaking of friends and family, I'll refer to couples by name in the same order every time. But it's not consistently the closer relative first, or the male first, or any other discernible pattern. e.g. < My Sister > & < Her Husband > for one couple, but < Husband > & < Sister > for the other. I'm sure there are countless pairs of words (mostly nouns?) that are frequently spoken together, that just sound better in a specific order.
Other
explainlikeimfive
{ "a_id": [ "dbze60p", "dbz8edz" ], "text": [ "Words that often appear together are called \"collocations\", and it's simply the way we've learned them. We tend to process them as indivisible units -- phrases, rather than separate words. For example, when we say \"apples and oranges\", we're not thinking of two different kinds of fruit and then putting them in a list; we're using the phrase \"apples-and-oranges\" as a single thing, a metaphor for things that shouldn't be compared to each other. If you were listing the fruit sold by a local greengrocer, you could list apples and oranges in any order -- usually, the order they occur to you: \"He's got... oranges... and apples... and bananas... and grapefruit...\"", "URL_0 URL_1 For a more advanced explanation, you might also try /r/linguistics." ], "score": [ 5, 4 ], "text_urls": [ [], [ "https://www.reddit.com/r/explainlikeimfive/comments/2noyqz/eli5_how_do_we_automatically_know_to_say_black/", "https://www.reddit.com/r/explainlikeimfive/comments/59ers7/eli5_why_do_some_words_sound_better_in_a/" ] ] }
[ "url" ]
[ "url" ]
5lxf0t
How are the quantity of standard SI units determined?
Is there some sort of worldwide agreement, or using an object, etc?
Physics
explainlikeimfive
{ "a_id": [ "dbzd4fu" ], "text": [ "Well, *originally*, it mostly dates back to the French \"Age of Reason\" after the French Revolution. They decided that it was going to be a whole new civilization and this was their chance to start over and do everything right. IIRC, they even took a crack at redefining the months of the calendar. In the end, the metric system was pretty much the only thing that \"stuck\". A meter was defined as a ten millionth of the distance from the North Pole to the equator. A liter was defined as a cubic decimeter. A kilogram was defined as the mass of a liter of water at 0℃. 0℃ was defined as the freezing point of water, and 100℃ defined as the boiling point. In the end, these measurements turned out not to be very accurate, and so these things were redefined. As /u/suckmydi points out, the meter was redefined in terms of the speed of light (and seconds were defined in terms of vibration of a Cesium atom, IIRC.) Mass used to be determined by a \"standard\" [metal cylinder]( URL_0 ) which was copied and the copies distributed to various standards bureaus. I believe they're in the middle of redefining the kilogram in terms of a specific number of Silicon atoms." ], "score": [ 3 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Kilogram#International_prototype_kilogram" ] ] }
[ "url" ]
[ "url" ]
5lxo8s
Is silver a real color or just an optical property of certain materials?
I'm wondering if the color of silver is really a color at all, or just a weird visual consequence of our brain intercepting light waves bouncing off of the surface of reflective materials. This question was inspired by the earlier post asking about the color of mirrors, but I hope it's different enough to merit a response. Thank you all!
Physics
explainlikeimfive
{ "a_id": [ "dbz9n45", "dbz9muj" ], "text": [ "Everything you can see has a real color. Silver is just gray, but it's surface is also shiny. We decided to not call it \"shiny gray\" but \"silver.\" Because it's used often enough to need its own name.", "If you're talking about like the shiny silver that I think you are then... kind of? Think of it as more of a shade. Silver is just the metallic shine off the color grey. If you were to take a very shiny silver ingot and put dirt and take away the shine then it'd turn out to be more grey. So if you'd like to call a different shading of grey (in this case a shiner version) a color then yes it is." ], "score": [ 9, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5lxsep
How are new organs still being discovered? Shouldn't they have all been found with modern technology/direct surgical 'exploration'?
Biology
explainlikeimfive
{ "a_id": [ "dbza579" ], "text": [ "[RT article]( URL_0 ) > It was previously thought that the organ was an unimportant group of structures, but it has now been classified as one single organ, which connects the abdomen to the intestine. It wasn't 'discovered' in the sense of some surgeon going 'Hey guys, what is this?' Researchers just found that a group of structures seem to work together more closely than was previously thought. The simile is a little weak, but try thinking of it like Pluto. It just got reclassified." ], "score": [ 15 ], "text_urls": [ [ "https://www.rt.com/news/372583-new-human-organ-mesentery-discovered/" ] ] }
[ "url" ]
[ "url" ]
5lxub1
How can airport scanners see through leather but not through skin?
I understand that the waves are not powerful enough or too short to not pass through human skin as to not hurt us. But how can they pass through leather? Is it part of the treating process of the cow hide that allows it to be seen or is leather not common enough to be an issue?
Technology
explainlikeimfive
{ "a_id": [ "dbzae9h" ], "text": [ "The scanners would be dangerous to humans, if you went through the machine. That is why they make you put your carry on bags on the belt and walk you through the metal detector without bags. Different technologies. Trust me, they would rather just stick you on the belt." ], "score": [ 6 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lxukm
How do the military counts and confirms kills?
You often hear in documentaries for example "John Doe had x numbers of confirmed kills", how do they know?
Other
explainlikeimfive
{ "a_id": [ "dbzcnpe" ], "text": [ "There is no formal procedure, nor an official record. It's essentially self-reporting. Most snipers operate with a spotter. The sniper says \"I killed 'em.\" The spotter either confirms (\"He killed 'em\") or doesn't (\"Couldn't see\"). This goes into after-action reports, and that's about it. \"Confirmed kills\" is basically just PR. It's not an official number. [A good Quora answer on the subject.]( URL_0 )" ], "score": [ 6 ], "text_urls": [ [ "https://www.quora.com/What-exactly-is-a-confirmed-kill-and-an-unconfirmed-kill-How-are-sniper-kills-confirmed" ] ] }
[ "url" ]
[ "url" ]
5lxw21
Does my stomach acid pass into the rest of my digestive tract when food leaves my stomach?
If not, how? If so, I don't think we have the same gut flora outside of our stomachs, so how am I not dead?
Biology
explainlikeimfive
{ "a_id": [ "dbzeq3a" ], "text": [ "Your duodenum (the part after your stomach in the digestive tract) has Brunner glands which secrete a lot of HCO3- and neutralize the acid. This is necessary to prevent damage to the intestinal mucosa and to keep the pH under optimal conditions for the action of intestinal enzymes. The remaining part of your intestines also have their own HCO3- secreting glands." ], "score": [ 10 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5ly506
Why does fuel not ignite in cars?
Chemistry
explainlikeimfive
{ "a_id": [ "dbzc77s", "dbzcb4x" ], "text": [ "Petrol itself is not very flammable. It's when the petrol gas is mixed with air at just the right concentration that ignition can happen.", "For a fire you need 3 components: - Fuel - Heat - Oxygen In the fuel tank you're missing the heat. Only in the engine itself you have all 3 present. (the heat is the spark from the spark plug)" ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5ly7q1
How is it that we are able to remember a songs lyrics even when we haven't heard the song in a while?
I was in the car when a song came and immediately I was able to sing along without issue. So how is it possible that we can remember songs much easier than other memories?
Biology
explainlikeimfive
{ "a_id": [ "dbzctvh", "dbzct36" ], "text": [ "Because you associate the lyrics with a melody, and it's much easier for us to remember melodies than a sequence of text. Also because the lyrics rhyme and have a meter. A meter means a pattern of the number of syllables per line in a verse, with the stressed syllables alternating in a predictable way. Probably the most recognizable meter is what Shakespeare used, iambic pentameter. Penta means five, iambic means it starts with an unstressed syllable and then every alternating one is stressed: to BE or NOT to BE, that IS the QUEStion __ 1 ___ 2 ____ 3 _____ 4 ____ 5 _____ This creates a pattern of sound, and it is really easy for us to remember a pattern of sound rather than a pattern of text. If you look at the text of old Norse sagas, like Beowulf, they have a pattern where each line is two halves, and the halves rhyme, and they have a stressed-syllable meter as well. This was a mnemonic device to allow bards to remember really long stories exactly, before they could be easily written down and shared.", "We have what is called the conscious and subconscious mind. We don't really ever forget anything, it just isn't something that we use often enough to take up concious memory. Sounds, sights and smells have a way of bringing those memories from the subconscious to the conscious" ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5ly8oj
Why does nicotine enhance the realism of dreams? What are some other things that may have this effect?
If I dip right before I go to bed I have much more intense dreams. Likewise, there are instances all over the Internet of people falling asleep with nicotine patches on and having intense or easily remembered dreams. What causes this, and are there any other chemicals that would have the same effect? I would wager that nicotine somehow increases brain activity and focus and keeps a portion of your brain active as you sleep, because I remember a nutritional supplement I used to take in order to help me focus had a similar effect.
Biology
explainlikeimfive
{ "a_id": [ "dbzeug6" ], "text": [ "Vitamin B6 [certainly does]( URL_0 ) (I take it daily). I also happen to be wearing a nicotine patch to quit smoking and also take B12. Wow. This combination has added a realism to my dreams like none other. As to why nicotine aids in this, I can only find anecdotal reports in dream-related forums (like Reddit's) that because it has been shown to increase focus in the brain, nicotine somehow pivots to where the brain activity happens to be most active at the moment (i.e., REM sleep) and enhances focus there." ], "score": [ 3 ], "text_urls": [ [ "https://www.ncbi.nlm.nih.gov/pubmed/11883552" ] ] }
[ "url" ]
[ "url" ]
5lyfmr
Why do we expect technologically advanced extraterrestrial life to broadcast radio signals into space?
Technology
explainlikeimfive
{ "a_id": [ "dbzfws2" ], "text": [ "Of all the artificial methods we know to transmit information through a vacuum, the electromagnetic spectrum is pretty much what we can both send and receive; there may be other theoretical concepts, but radio, and light, and various other points along the electromagnetic spectrum are what we have to work with. It's not because we think aliens will use it, it's because it's what we can currently work with that isn't naturally occurring that is most likely for aliens to be using. So, you are correct: absence of data doesn't prove aliens do not exist, but in cases like this you can't prove a negative as you're noting, so people who say this is proof that aliens do not exist are making insubstantiated claims. It doesn't prove they're wrong, either, it means they're using the wrong info to reach the conclusion." ], "score": [ 6 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lyh18
Country borders are huge, how do they prevent people from sneaking past along the entire border?
Borders go for miles, there must be unguarded territory in which people could travel across right?
Other
explainlikeimfive
{ "a_id": [ "dbzenr0", "dbzes3f", "dbzhxfr", "dbzf1bp" ], "text": [ "Most of that territory is inaccessible. If you want to hike over mountains and through swamp, well, I guess we will catch you when you reach the town on the other end. A lot of borders actually do have some kind of fence all along them. It could just be wire that sends an alarm if tripped, and then a border guard patrol will investigate. Or it could be something hard to climb. Very often, country borders today are the historical borders that naturally arose between communities - geographical features like lakes or mountains.", "Just because it's relevant and potentially interesting - in Europe there is the [Schengen Area]( URL_0 ) which is essentially a series of open borders that allow for the free movement of individuals between (most of) the countries of mainland Europe. So, in much of Europe, they simply do not physically enforce their land borders anymore (though given recent terrorism and the rise of nationalist political parties the Schengen Area may not survive in the long term).", "They don't. It is practically impossible to control all the territory, so ideas like \"building a wall\" are sheer idiocy. What you CAN do is increase patrols, fences, and security at points where people are likely to cross. This includes roads, urban areas (like El Paso), and other points near civilization that make crossing easy. That makes it more likely that people will have to move through difficult and remote areas, which serves as a deterrent.", "The short answer is they don't, directly. People have mentioned various geographical measures and security measures, but in most parts of the world, there's not an awful lot of difference between neighbouring countries, and it's often difficult to just move, owing to language barriers and the paperwork that is needed to get on with life, especially when things go wrong .... you are sick, you are arrested, you need to claim benefits. You often can't access those things in a foreign country, easily, so it's often a bad move to go." ], "score": [ 7, 6, 5, 3 ], "text_urls": [ [], [ "https://en.wikipedia.org/wiki/Schengen_Area" ], [], [] ] }
[ "url" ]
[ "url" ]
5lyheh
The saying "feed a cold, starve a fever". Just an old wise tale or is it accurate? If so what is happening physically?
I ask because I currently have a cold and my girlfriend keeps reiterating this saying to me, but when I was younger my Grandma would also say this. I joined Reddit fairly recently and this is my favorite thread. Hoping some of you can help clarify!
Biology
explainlikeimfive
{ "a_id": [ "dbzeahq" ], "text": [ "Its an old wife's tale. A fever is a natural response from your immune system. If you starve yourself during that you also starve your immune system. It just people have a tenancy to throw up and keep nothing down during a fever so they tend to feed them less/they eat less. Not throwing up is important because it dehydrates you." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lyopu
Why does one person singing out of tune sound like ass, but 50,000 people singing out of tune sounds amazing?
Aside from the emotional impact of being together in a large group - do the different out-of-tune notes somehow cancel each other out, or combine to make new harmonics?
Other
explainlikeimfive
{ "a_id": [ "dbzfrco", "dbzujsm", "dbzvl4v" ], "text": [ "Because they all are randomly out of tune, but just slightly, so they add up around the proper notes. On average you get a sound that is more intense around the right notes and their harmonics (which makes it sound non-dissonant), and the out of tune sounds just becomes a bunch of overtones making the sound a richer and more complex timbre. [See this old comment I made]( URL_0 ) for some technical details and visuals.", "It's sometimes called \"detuning\", used in music recording when a whole bank of synthesizers are all tuned slightly differently, producing a very \"fat\" and \"soft\" waveform. Very similar is the difference between a solo violin and an orchestra full of them. Love the latter, not a fan of the former. In a group of violinists, each will be playing a slightly different tone, but they'll average out to the right one, so that's the one we hear. When a solo violinist is a little off key (which they often are), it's easy to hear and unpleasant to the trained ear.", "Can you give an example of 50,000 people singing out of tune which sounds amazing? I don't believe the premise." ], "score": [ 164, 14, 11 ], "text_urls": [ [ "https://www.reddit.com/r/askscience/comments/4mur7n/why_do_some_objects_emit_a_pitchless_sound_when/d3yqdk5/" ], [], [] ] }
[ "url" ]
[ "url" ]
5lz33j
Why do we like to raise two fingers (aka the "peace sign") when posing for a picture?
Other
explainlikeimfive
{ "a_id": [ "dbzhwr5" ], "text": [ "Because people don't know what to do with their hands. They choose to \"strike a pose\" instead of perhaps appearing awkward. EDIT: The peace sign is just an example. People the world over use a variety of different signs but for the same purpose." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lzdve
What rule of sound waves makes sounds that are 12 half steps away from each other read as the same note to us?
Physics
explainlikeimfive
{ "a_id": [ "dbzleri", "dbzkt9b", "dc03ox0", "dbzk6n8" ], "text": [ "The \"12 steps\" are arbitrary, but the relationship between the frequencies is not: at the distance which we call 'one octave' the higher of the two tones results from vibrations which are exactly twice as fast as the lower tone. This means that it sounds \"the same only higher\" to our ears. Meanwhile, we in the West decided that it would be best to divide that distance up into 12 divisions, which we call semitones. That's far from the only way to divide that space up, though. The easiest way to visualise this is probably get a string, measure it, and twang it. Then get a string half that length (or stop the first string half-way down its length) and twang it again.", "Your ear likes simple ratios. The simplest is 2:1 which is called an \"octave\". The next simplest is 3:2 which is called a \"perfect fifth\". Twelve perfect fifths are very close to seven octaves and that's why there are twelve semitones in an octave and seven notes in a scale. Also, there are seven semitones to a perfect fifth.", "Music theory can be complicated but the basic answer is that it really doesn't. In western music we have 12 notes in our scale, but other music systems may have more or less notes and none of them precisely divide the notes up with the doubling of frequencies. They may also have different tunings in terms of which frequency a note is. For instance standard western tuning has A as 440hz but classical (or stradivari) tuning puts an A at 432hz. To get around this problem in western tunings we use a technique called even (or equal) temperament. What this does it slightly detunes each note in the scale so that when you come around to the 12th note, it is exactly double the starting note. The down side to this is because each note is slightly out of tune, it is impossible to make perfect chords as the notes are slightly out of tune. This causes a slight pulsing or beating of the notes. On instruments such as the violin, cello, theramin or any other instruments without keys or frets, it is possible to play non western notes, and tunings other than even temperament since the pitch of each note is determined by the performer rather than by a fret, key, or note hole. [Here is a good video that explains this]( URL_0 )", "Each octave up doubles the frequency (hertz) of each note. The note \"A4\" is 440 hertz, while \"A5\" is 880 hertz. ig" ], "score": [ 32, 5, 4, 3 ], "text_urls": [ [], [], [ "https://www.youtube.com/watch?v=1Hqm0dYKUx4" ], [] ] }
[ "url" ]
[ "url" ]
5lzpj3
How is it possible to move a house/building?
I've come across [this picture]( URL_0 ) of a building being moved in Romania a few times now and have also seen movies where an entire house was moved by truck. It appears to be a somewhat normal occurrence in other countries, but I've never heard of such thing where I live. How is it normally done?
Other
explainlikeimfive
{ "a_id": [ "dbznnbg" ], "text": [ "So, we actually moved a house and the process is pretty cool. We bought a house at auction for less than 3000 dollars and moved it. This was about 15 years ago. Step 1 remove the roof. Labeling the pieces for easy reassembly. Step 2 depending on how many stories the house is you place supporting beams along the floor joists of each level, ours was a 1 story with a loft so it was a bit wonky. Step 3 section the house into parts that will fit on a traditional flatbed. Ours was divided into 4 sections Step 4) the actual drive is planned out ahead of time with the specific dimensions of each piece at the time we had to pay 50 dollars per powerline that had to be taken down and put back up. Step 5) deliver and put it on the foundation and put it back together. Edit: we moved the house over 20 miles so that may be a factor" ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lzr39
Why do we laugh more when we are around people witnessing something funny as opposed to being alone?
Biology
explainlikeimfive
{ "a_id": [ "dbzu8xt" ], "text": [ "Laughing is primarily a team building social activity so there's no real reason to laugh if no one else is in the room. It's similar to yawning in that when you laugh, others are more likely to feel good and laugh, and vice versa which makes group laughter a self reinforcing process. As I recall there are actually religious cults built around getting everyone out into giggle fits - it's a pretty powerful interaction when you think about it." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5lzvwi
Why is processed "regular" pasta cheaper than whole grain?
Wouldn't whole grain actually be cheaper, since it doesn't have to go through additional steps during the processing?
Other
explainlikeimfive
{ "a_id": [ "dbzp6b0", "dbzx995" ], "text": [ "Regular pasta is *much* more popular, so it is produced by many more factories, so there is more competition. Competition keeps the price down.", "No experience with such pasta, but I live in a rice country. Brown rice, the less-processed kind, is less popular and are made only by premium brands which target the health-conscious customers, who are willing to pay more for the extra nutrition. There is less competition (supply) yes, but the buyers are willing to pay more (demand) too." ], "score": [ 12, 9 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5lzyi5
Why are economic ideas called theories?
Collectivist and classical
Economics
explainlikeimfive
{ "a_id": [ "dbzoprn", "dbzoq4x", "dbzwypm" ], "text": [ "Generally speaking, in an academic setting a theory is a proposed explanation for a set of data points that provides insight into the underlying workings or at least underlying formula that produced that data. Hence the theory of plate tectonics explains various geological features by proposing plates floating on magma. Or the theory of evolution explains biodiversity via various mechanisms of selection. Economic theories have the same goal, and so use the same terminology.", "They're using the scientific definition of the word (gravity is a theory). Theory is being used to mean everything that is understood about a topic. Everything within it should be repeatable, and peer reviewed. If someone can make repeatable observations that don't follow the theory, as in science, it can be incorporated into the theory after they understand why this is happening.", "Because they (rightly or wrongly) use scientific terminologies for their ideas. Within science, a theory is initially a hypothesis (basically, an idea) that undergoes testing and is useful for making predictions about the way our universe works. For example, Einstein developed his hypothesis concerning Relativity, and made predictions with that hypothesis that differed very significantly from Newtonian mechanics. Those predictions were proven to be correct, at which point General Relativity graduated to become a theory, and since has been used to predict the existence of other really weird phenomena that we now know exists. In many fields (particularly business, economics, psychology, sociology and social studies, politics, etc.) within the liberal arts that involve extensive human interaction, they utilize the same general ideas on terminology, but the standard of proof concerning the predictions are a hell of a lot lower, and as a result those fields are referred to as soft sciences because their theories aren't nearly as bulletproof because of the lower standards they are essentially forced to adhere to. On another note, business is generally harder and more reputable mathematically and scientifically than the other soft sciences, although to us in STEM fields it's still not quite strong enough to qualify as \"true\" science." ], "score": [ 15, 3, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m08ap
Why do we cry? What is the connection of tears coming out of our eyes with sadness or even happiness.
Biology
explainlikeimfive
{ "a_id": [ "dbztlq6", "dbzttxo", "dc06ql8", "dc04seo", "dc0qbhj", "dc05was" ], "text": [ "Humans are very social animals (i.e. social interactions are crucial to our survival), so we have lots of traits that exist only to act as signals in communication. As far as I know, we cry for the same reason we smile or raise our eyebrows - to signal our emotions to others. I have also heard about there being pheromones in tears that can influence the behavior of other people exposed to them, but I don't know much about that.", "Crying is evolutionary beneficial. It shows that something is wrong. Most of the time we can simply make noise to show that something is wrong, but some times, when we are suffocating for example, we have no way to express that we are in danger. Here, crying can be the solution to let others know we need help. Now, crying or being extremely happy aren't 'normal' situations, so the body interprets this as 'wrong'. Even though being extremely happy isn't bad, it's still seen as abnormal by the body, and thus a potential danger to our survival.", "Crying releases excess stress hormones (like cortisol), which is why you often feel a sense of relief or calmness after a good cry.", "Crying, i've heard actually releases some of the anxiety producing hormones we make when we get upset out of our bodies within the production of tears. Accumulation of these hormones or chemicals caused by feelings of sadness or happiness can disrupt homeostasis, causing the body to find a way to regain balance in its chemistry. There is also a heavy social reason as many have previously listed and explained.", "When we're extremely stressed or laughing hard our lung muscles tighten up. We cry because sometimes when under extreme emotion we can't communicate it with sound so our body communicates it from ejecting water from our eyes and making it really obvious, so everyone else knows something is up even if we can't communicate it. A huge part of human survival roots in compassion and empathy. If something is wrong, you **have** to communicate it to others. Also, as some people have said, crying releases stress hormones through the tear duct so we can calm ourselves down.", "Tears are packed with stress hormones, so they're your body's way of calming you down by forcing your stress out of your system through your eyes." ], "score": [ 244, 134, 99, 30, 9, 5 ], "text_urls": [ [], [], [], [], [], [] ] }
[ "url" ]
[ "url" ]
5m08ey
Why are theatrical movies 2.40:1 or a similar aspect ratio but our TVs are only 16:9?
Technology
explainlikeimfive
{ "a_id": [ "dbzqut9", "dbzruh1" ], "text": [ "The 16:9 size was chosen as a compromise between the wider shape of most movies, and the narrower shape of older TV shows. This way neither one looks ridiculous.", "In the beginning, Edison decided that movies should be 4:3. Then television was developed and they followed the 4:3 convention. As television got popular movies started experimenting with wider screens to differentiate films from TV. After some very wide movies, cinema standardized on a few formats around 2.35:1 and 2.4:1. This made for a very small letter boxed picture on 4:3 TVs. When the HD standard was in development, it was decided to choose an aspect ratio that minimized the size of black bars required for 4:3 content and 2.35:1 content, which was 16:9. However once broadcasters shifted to digital broadcasts, they quickly expanded to use the full 16:9 aspect." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m0c52
What is a trust fund and how do trust funds work?
Economics
explainlikeimfive
{ "a_id": [ "dbzsb7r", "dbzwnuy" ], "text": [ "A trust fund is money someone has set aside for your *benefit* but it is not under your *control.* The money is under the control of the *trustee* who invests or spends it for the benefit of the *beneficiary*. This is typically done so that people can pass along wealth to their children, but without the risk that the children will squander the money or make foolish investments. So for instance, your parents if they were rather well off, might set up a trust for you, putting $2 million aside. They then hire a trustee run manage it. He'll invest the money so that it grows over time, and dispense money to you under the rules your parents set up. Perhaps they've told him to spend $1500 a month on your rent, and then give a $2000 a month allowance (just a cash dispersal to your bank account). Then, at the age of 35 (when your parents presumed you would have matured enough), the trust goes away and you are put under full control of the remaining amount.", "Example: I have a trust that was setup by my grandparents for sister, cousins, and myself. Honestly it's not a lot and we weren't able to collect on it until we were in our 30s. I personally didn't even cash it out. I moved it to a long term savings account and am now saving it for my own sons education." ], "score": [ 12, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m0fqi
Why do some people sleep like rocks, while others wake up at the sound of a pin drop?
Biology
explainlikeimfive
{ "a_id": [ "dc01sqg", "dc02rwv", "dc07nmf", "dc08ad0", "dc0933x", "dc01j93", "dc080w8", "dc0bcbe", "dc00s8y", "dc0dwx5", "dc0ctrx", "dc0iaii", "dc08avz" ], "text": [ "There are stages of sleep where you take in next to no outside information--you are dead to the world, basically. There are lighter stages of sleep where you take in more information and can be easily woken up. We cycle through many stages in a night of normal sleep, which means there will be several points during the night when sleep is light and you are more likely to be disturbed. Your brain also doesn't remember much in REM/deep sleep, while you remember more in lighter stages of sleep. You literally forget that you hit deep sleep. There are a lot of things that mess up deep stages of sleep: alcohol, sedative-hypnotics like benzos and z-drugs, some mental illness, some sleep disorders, etc. If you aren't hitting dead-to-the-world deep sleep, of course you will be woken up more easily. Problems like hypervigilance can disturb sleep because you are basically scanning for a reason to find a threat, and it's pretty hard to fall asleep with that sort of anxiety. Thay said, research suggests that outside of major sleep disorders, the difference between good sleep and bad sleep is highly subjective. Many people who consider themselves light or poor sleepers are actually quite average. **Edit: this got bigger than I thought it would, so I would like to take a minute to get on my own small soapbox:** If you are concerned about your own sleep, *please please please* talk to your doctor. There are thousands of things that impact sleep. Don't leave it to strangers on the internet. Your health and well-being are worth it. /u/none_shall_pass touched on sleep apnea, which I didn't mention, but I think it warrants extra attention. [The Mayo Clinic has a good overview.] ( URL_0 ) If you are concerned about anxiety, hypervigilance, or anything else related to mental health, *please please please* think about reaching out for help. Doctors, psychiatrists, psychologists, counsellors, social workers, mental health clinics, school counsellors, campus counsellors, online counselling resources, workplace employee assistance programs, mental health advocacy organizations, whatever is available in your area. Anyone can learn skills to feel better and handle the ups and downs of life more easily. And everyone deserves to feel well and healthy. / end soapbox", "It makes sense for a communication-based species to have members that can be in constant \"guard mode\" in case of any overnight danger so that they can alert their whole tribe. But because most of the time there is no danger and the light sleepers will wake up because a cat meowed, you don't want everybody to be light sleepers, because fully rested members of the tribe are more efficient for the daily work. So basically what happens it that evolutionary speaking, a humanoid sub-species with only light sleepers will lose in combat or any less brutal competition to well rested enemies and, over generations, eventually go extinct. A humanoid sub-species with only deep sleepers will get regularly robbed from their resources overnight or even murdered in their sleep by predators/competitors; eventually going extinct. The subspecies with a mix of both, however, will thrive; and that's our ancestors. Like many evolutionary traits, sleeping variety is an artefact of a time it was more useful than in nowadays' society. But since it's not really detrimental to our survival, that characteristic is still around.", "Ok seeing a few weird answers here, and some plain ridiculous ones. My anthropology knowledge isn't as strong as I'd like, but hopefully I can help. The short answer is, it's not fully known why this occurs. Humans have a wide range of variability in our species (by the way, current top comment keeps referring to subspecies of humans sleeping different, that's some false terminology), and thus behave and interact with the environment in an equally wide range of ways. Add to this situational events such as lack of recent sleep, stress, or even familiarity with the area you are sleeping in, and it is more understandable why this variation occurs. That's not to say there is or isn't one overarching reason, but mainly that many factors influence how a person sleeps.", "Brown University ran a [study]( URL_0 ) on sleep in unfamiliar places and found an 'on watch' effect where one hemisphere stays on alert. It's possible you were in this state permanently with your ex SO. You could ask yourself where you do sleep well, this might give a hint to the environment in which your alertness is switched off.", "It *highly* depends to what you wake up for. Young mothers wake up to anything that sounds like baby crying. While some other sounds don't seem to matter at all. For me, I'm a really deep sleeper and can easily shut down 7 alarms without even remembering I woke up to do this. I once woke up, lit a cigarette, got long-time-no-nicotine-dizziness, fall asleep again and didn't even wake up when half of my duvet burned down. Thank god my dog started barking like mad due smoke. But whenever I - before falling asleep - give myself mental command \"if it rings, get up, get up\", I jump up like a spring, sometimes even a minute BEFORE first alarm. And like a fool, wonder if I have a superpower like Jack Reacher or something to tell time in my head. Even weirder that it has nothing to do with tiredness level, sometimes I play games till 5 and still jump up at 8, just because I told myself to do this before falling asleep. Telling yourself to wake up doesn't sound very convincing when you're dead tired, but for some reason, it works. For me at least. 90% of time or so. There is antidote to this: cold room with super warm blankets. If that happens, and especially if room gets warmer in the morning, there's no sound or force in the world that can wake you up. My dad used to lit the stove in the early hours to warm the room up in our country house (military smarts, probably) and I remember those days as absolutely most luxurious sleep I've ever gotten. I woke up and felt like I've gained super health and energy. I think It's how brain and conscious are wired. I think your ears don't really turn off while you sleep, but your mind wires what ears should consider important and what not.", "I'm going to answer this based off of opinion and stuff I've heard from others my whole life. It all starts from how it was at home when you were a baby. If you are born and raised (first 5 years of your life-ish) where your Mother or Father or whoever was always noisy during naps/sleeping.. such as vacuuming, loud TV, and anything else that makes noise, you were prone to hearing loud noise while sleeping. You literally adapted to trying to sleep through loud noises. Now for those who wake up to a pin drop. As a baby trying to sleep.. maybe the Mother, Father or whoever tippy-toed around the house and silently shut doors and had the TV on low to make sure precious baby Gerald stayed asleep; this could be the reason why that person can be easily woken up to loud noises. I believe it's all how you were raised and what made you adapt to certain noise levels while trying to sleep.", "It's an evolutionary trait. If you were a caveman, you better pray that you are easily waken up. It's supposed to protect you from predators and other threats that could kill you if you stayed asleep. If you ever feel jealous that someone can sleep through anything, just remember they're more likely to die in the wilderness.", "Training. People who grew up in noisy environments or went through traumatic times where there were loud noises at night (i.e. soldiers), they've trained their brains to ignore superfluous sounds. You could do a bunch of work to try and train your brain, you'll be dead tired for a long time before your brain reaches the \"fuck it\" point and just sleeps through. Or, you can just put on some static/wave sounds so you're not disturbed by unimportant noises.", "[There are some good answers to this question in past threads]( URL_0 )", "Sort of covered, but not specifically mentioned - how *comfortable* you are in your sleeping surroundings is *vital* to how deeply you sleep. If it's your first time staying somewhere, and you're alone, you're (probably) going to sleep incredibly lightly. There's *unquestionably* an evolutionary aspect to all of this, but the what, how, and why are beyond ELI5 by a long shot. It boils down to \"we used to live outside\".", "I'm an insomniac and I sleep like the dead (when I get to) to the point that I have slept through: several fires + fire alarms, tornadoes, hurricanes, two earthquakes, fireworks, and a new years eve bash. What can wake me up: cat jumping on me and smothering me for food at 4am. :|", "Proper answer here!!! The answer is sleep spindles. Countless research has shown that it's not evolutionary, and no, you can't train yourself. No, it's sleep spindles that we are born with. The more spindles you produce during a sleep cycle, the better you can tolerate noise, and coincidentally, spindles are related to better memory - so ability to create sleep spindles - > better sleep - > better memory - > yada yada. URL_0", "I would love to know! The smallest thing wakes me up. For example: someone staring at me, the power going off... etc. My alarm clock is literally one light vibration and that's it." ], "score": [ 1528, 308, 140, 40, 38, 26, 12, 11, 6, 6, 5, 5, 4 ], "text_urls": [ [ "http://www.mayoclinic.org/diseases-conditions/sleep-apnea/basics/symptoms/con-20020286" ], [], [], [ "https://news.brown.edu/articles/2016/04/sleep" ], [], [], [], [], [ "https://www.reddit.com/r/explainlikeimfive/search?q=light+sleepers&amp;restrict_sr=on&amp;sort=relevance&amp;t=all" ], [], [], [ "https://www.wired.com/2010/08/sleep-spindles/" ], [] ] }
[ "url" ]
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5m0h55
Why does coconut oil and other oils soak into some people's skin, and sit on top of others?
Other
explainlikeimfive
{ "a_id": [ "dc0k4w9", "dc0906b", "dc0tup2" ], "text": [ "Now that you mention it...Coconut oil will absorb on my upper body but just sits on my legs. It doesn't even help with the ash. You can see the ash under the oil if you look closely.", "Do they? I have never heard of this", "I figure it depends on the oil used, and how much of it they use. AFAIK, oils do not get \"absorbed\", they just stick to your skin. I think this isn't the case for oils, but for creams and other such products, they have a big amount of water in it. The water eventually evaporates and all that remains is a thin layer of fat which prevents water from evaporating quickly, keeping your skin moist, thus preventing dryness. That's why your skin gets drier after taking a shower: you've taken all the fat from your skin so you dry quickly." ], "score": [ 13, 12, 4 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m0idi
Does the placebo effect prove that our minds have a lot more power than we can directly utilize?
Biology
explainlikeimfive
{ "a_id": [ "dbzu7je", "dc02hpt", "dbztznj", "dc00bxo", "dc00mof", "dc0jtax", "dbzzdna", "dc0qkhq", "dc03zu4", "dc0chbm" ], "text": [ "(Edit: I clarified my answer after many pointed out that it is misleading to say that the placebo effect *proves* wishful cures. Please also see other answers.) There are a ton of reasons why a placebo might work: * there is a mind-body connection and psychosomatic therapies are valid * people pretend or believe themselves to be sick when they are not * people misreport disease symptoms and therapy effects * diseases can cure themselves given time * diet and environment cure diseases * statistical data and double-blind tests are the only valid medical evidence and drug development method New-age and alternative medicine play up the possibility of mind-body connection and that positive thinking, prayer, energy etc. cure diseases. This approach is unprovable and not scientific. In addition to the various circumstantial and accidental factors, there is the pragmatic statistical approach that indirectly takes all factors and hypothesis into consideration. Thus, modern medicine focuses on validating (rather than explaining) drugs and therapies via placebo-controlled double-blind clinical trials.", "It has less to do with our minds being able to cure our ills, and more to do with changing our perception. Imagine a light is blinking steadily one second on, one second off. Now imagine that you are told every 3rd blink is slightly longer than the rest. You might then perceive this as so even though the light is blinking at a steady rate. What matters is that your perception of the event is altered. It is very difficult for us to make purely objective observations of things without measuring devices like a watch or instruments to measure things we want to observe. Since we don't have instruments like this that tell you how much pain you are in, or how healthy you are, or how stressed you are, it is much more subjective to your perception and other factors can easily influence your experience. Your body actually has 3 brains so to speak. There is your brain, your involuntary nervous system, and the enteric nervous system in your gut. Each has nerve communication with the other, but also each can operate independent of the others. So for instance if you feel threatened, you can force yourself to be calm, but you can't force your body not to produce adrenaline and prep you for fight or flight. That is an involuntary reaction you are powerless to control. However you can practice breathing techniques to try to control your heart rate which can affect body temperature and relaxation. That is a far cry from the mind healing wounds or telling your liver to metabolize alcohol faster etc.", "No, that's a hypothesis you are making based on the observation of the placebo effect. The placebo effect only proves that our expectations or beliefs can impact our body in some way or another. Transforming this into your hypothesis requires additional assumptions such as what is power and what means being able to utilize, and proving this hypothesis would require additional testing which I'm not aware of being done before.", "One thing people forget about a placebo group in a medical trial is that, even though they aren't getting a real drug, they are getting regular attention of medical professionals who are keeping a close eye on their condition than they would otherwise. Add to that, placebos primarily help with subjective symptoms; things like stress and self reported pain.", "There is a lot of misconceptions about the placebo effect. The placebo effect is only refers to any effect outside of the intended ones and is mostly a tool to analyze data during scientific research. This could include this mystical mind over body effect but it is mostly a mix of biases, from the patient and the scientist and external effects. For example, if I would conduct a research about a new pill for pain reduction and some of my patients take aspirin but don't report it, it will show up in my data set as positive even in my control group. It serves as a way to remove these factors if we assume they will effect all groups the same way. An example of researcher bias could be two doctors having slightly different idea of, let say, a cured tumor. Two different research on the same treatment will show different results but factoring the placebo effect with a control group should show the same results. This is also why, if you look at the control group of similar researches on the same treatment you will often see different effect, because they do not have the same way of looking at data. Then there is the problem of reported effect vs real effect. A patient can report positive effect of a placebo because, while they do not experience any physiological effect, they feel they must report it as working because, \"hey this must work right?\". You will thus see very strange results if you compare reported data of let say, asthma attacks with a bio metric measurement, here, lung strength. The placebo affect is a great tool of analysis because most medical experiments is done on humans by humans in an open environment and we need a way factor for all the implicit biases and uncontrollable factor that are not cause by what we are observing but it is not a therapeutic method and was never meant to be. There might be an influence of the body in healing, but we should not jump at this conclusion before considering all the others, more plausible influences.", "ELI(Actually)5: Let's use our imaginations and pretend that you and your best friend are playing outside on a sunny day, and you both fall down and get an owie (scientifically referred to as a boo-boo) in the exact same way. Your mommy is outside watering the lawn and she sees you when you start to cry. She comes over and kisses your boo-boo. Meanwhile your friend's mommy is in her house drinking Rosé and thinking about what a mistake it was to get married so young, so your best friend's has to settle for his weird aunt Placebo (you know she's weird because her name is Placebo and she has a weird mole on her face) kissing his boo-boo. Now you obviously feel better because mommy kisses are a very effective scientifically proven cure for boo-boos. But everyone knows weird aunt kisses don't actually do a thing to help fix a boo-boo, and your friend has also stopped crying! So what happened? Why does Aunt Placebo have such a noticeable effect? - Maybe both of your boo-boos would have felt better anyway after a few minutes. - Maybe the act of kissing the boo-boo, even from a weird aunt, somehow distracts your friend and makes him think his boo-boo is better even if the underlying boo-boo is still there. - Maybe your friend stops crying because his aunt is a grown-up and he knows that grown-ups like to think that they helped (the word \"Placebo\" comes from a Latin word that means \"I shall please\"). - Maybe in the process of your friend's aunt kissing his boo-boo, he (accidentally or on purpose) rubbed some dirt on it (another scientifically proven pain reliever almost as good as mommy kisses) and you didn't notice. - Maybe your friend's brain has an (as-yet unidentified by science) secret magic store of mommy kisses that it releases after getting a kiss from someone other than his mommy. - Maybe more than one of these could be happening at the same time! If you had to put these possibilities in order from the highest to lowest chance of being right, where would you put the magic brain one? Is it more likely that the brain has a secret magic power that science hasn't found yet? Or that something else caused your friend's boo-boo to feel better? Probably the \"something else\" right? It turns out that it's really hard to study boo-boo cures while getting rid of the things that are higher on the list, so there is a very good chance that something else besides the magic secret store of mommy kisses is going on. We should probably just assume that the Aunt Placebo effect is from one or more of those, before we jump to the conclusion that Aunt Placebo gives your brain magic powers. Now let's get a band-aid on that boo-boo and get you back outside, eh sport?", "It makes you feel better when there isn't an actual pathophysical process and the symptoms might resolve by itself anyway. Same reason why giving placebo as a treatment for Meningitis or cancer is highly unethical.", "The brain is amazing, it not only named itself, but you could say that psychology is the brain trying to figure itself out.", "No, it proves we don't really don't have the capacity to tell pain from no pain when we're supposed to feel no pain...", "No, it proves that you \"participate\" in your experience of things like the severity of pain. If you're convinced you're being treated, you also convince yourself that it doesn't hurt as bad. You actually just don't feel it as much." ], "score": [ 547, 146, 93, 53, 19, 12, 8, 4, 3, 3 ], "text_urls": [ [], [], [], [], [], [], [], [], [], [] ] }
[ "url" ]
[ "url" ]
5m0kdr
Why does a 2 hour movie take a year to make when a high quality TV show can make 45 minute ones every week.
Other
explainlikeimfive
{ "a_id": [ "dbzu62l", "dbzvh9u" ], "text": [ "Most of the filming for a movie can be done in a couple of months, the rest of the time is editing, adding CG effects, marketing and waiting for the right time to release the movie. A lot of work is also done beforehand to write and edit the script, scouting locations for filming and getting permits, hiring staff and making sure that your actors are available. A TV show uses a lot of the same locations, costumes and actors every show. The crew usually works exclusively on that show for the whole season. The scripts have been written in advance, or several writers are working on scripts for several episodes at a time. Scenes that take place in the same location over several episodes can all be filmed at the same time and then edited together as needed. Most of the hard work in filming something is getting all of the necessary parts together. Once a TV show has all the crew, actors, makeup artists etc. in one spot they can film as much material as they need somewhat easily.", "it's important to note that a TV show is *not* making a 45-minute episode per week - they're usually 4-6 weeks ahead of whichever episode is airing. as in, if episode 8 just aired, chances are the production is currently editing episode 12, 13, or 14 (or any combination), and they may be actively shooting episode 15 and up. a full season (20ish episodes) of a typical network drama will take 6-10 months to complete. movies require all footage to be shot in one long stretch (note: there may be re-shoots, but these are not common). this allows films to be made cheaper (it's cheaper to rent equipment in continuous stretches vs. intervals) and allows for easier personnel scheduling (which also reduces cost). TV episodes are (for the most part) shot on a rolling schedule. episode 1 is shot first, then episode 2, etc. note that there are exceptions - i believe Game of Thrones shoots each season as if it were a movie (i.e. all in one big chunk). TV shows shoot this way because you can enter post-production (editing, VFX, etc.) for episode 1 while episode 4 is shooting; the overlap reduces costs and enables easier scheduling. post-production time and cost varies wildly from show-to-show and movie-to-movie. if a show requires a lot of VFX work it typically has a much longer post-production schedule." ], "score": [ 27, 14 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m0l9n
How does the liver work? Like mechanically?
Say I eat some cyanide. Somehow that cyanide gets from my stomach to the places where it does that thing that it does that kills me. And somehow my liver does a thing where it gets to the cyanide and it turns the cyanide from dangerous cyanide into not dangerous cyanide. And then the cyanide leaves. What's happening here?
Biology
explainlikeimfive
{ "a_id": [ "dbzvmca" ], "text": [ "Poisons work in a lot of different ways. Cyanide. It doesn't get turned into a 'not poisonous' cyanide by the liver. There is no such thing. Cyanide works by blocking the cells ability to uptake oxygen. Very small amount, there's no issue, as the amount of cyanide can't effect enough cells to have a negative effect. Generally up to 0.5mg/L. Cyanide is present in certain fruits, nuts etc. After 0.5mg/L, there starts to be enough to mess with your body. It creates heart issues, brain problems, low blood pressure. Over 3mg/L will kill you, as your body cannot recover or deal with the lack of oxygen in the cells and you'll die of a heart attack shortly after." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m0n4w
Why is it impossible (very difficult) to reverse a password hash?
I understand that a lot of sites store password hashes rather than actual plain text passwords. And when the user types in their password, the plain text is put through a hashing process (like MD5 or SHA-256) and then the output (the hash) of that process is actually used to authenticate the user. So when someone hacks a website they usually end up with hashed passwords rather than actual passwords. I've always heard that it is impossible (or at least so difficult it is practically impossible) to reverse the hashing process (i.e. you can't take a hash and turn it into plain text) unless you just brute force a ton of plain text strings and compare the hashes. So my question is, why can't hashing be reversed? Related question - could machine learning be used to reverse hashing? If a computer using machine learning tried to find patterns between hashes and respective plain text, could it get there eventually? Thanks!
Technology
explainlikeimfive
{ "a_id": [ "dbzvem9", "dc0ubfs", "dbzxbzm", "dc0c2bv", "dbzuk9a", "dc0c1uv" ], "text": [ "Hashing is destructive. To take an easy example that's easier to wrap your head around, we can make our own hashing algorithm. For simplicity, imagine we have a password system where users have 4-digit pin codes as passwords. So a real simple hash would be something like this: 1. Pick a number between 1111 and 9999 (3456) 2. Multiply the number by itself (3456 * 3456 = 11 943 936) 3. Store the last three digits as the password (936) Turning 3456 into 936 was real simple - Turning 936 into 3456 is very hard. Beyond that, there are a few not-to-rare caveats that occur, such as the need to use salts to prevent identical passwords from rendering identical hashes and avoid excessive truncation of both the input data and the stored hash. In our system above, for instance, any input that results in 936 will be a valid password, which means we have a high rate of collisions, which is bad.", "> So my question is, why can't hashing be reversed? Because each calculation in hashing offers a single and straightforward option going forward; but multiple options in reverse. Have you heard of [Tesla's valvular conduit]( URL_0 ) & ndash; a valve without moving parts? A hash function is hard to reverse for similar reasons. Each step is more difficult in one direction than the other. When you chain enough steps together, the difficulty multiplies in a way that flow in the wrong direction is close to impossible. Imagine you're at one of the source flows that join a large river. It's very straightforward to go downstream and end up where the river meets the ocean. Every turn is obvious - you always go downstream. However, if you're starting at the ocean, it's very difficult to go back to the place you started. Going up, you have to make countless decisions where the origin streams diverge, and it's highly unlikely you'll make all of them right unless you already know exactly where you're headed.", "Two reasons. First, it is designed to be hard. In mathematics, there are functions that get harder when you reverse them. It is typically easier to multiply than divide, or to raise to a power rather than taking a root. A well designed hash takes this to the extreme, and is a function that is computationally infeasible to reverse. Second, hashes lose information. They aren't encoding the information, they are taking its fingerprint. The best you can to is find one of the infinite number of strings that created that hash. Now if that string turned out to be \"Password123\" and not \"a67ab5ba895526eb3a7695c7b16bd910\", you could be reasonably sure you had the password...just not completely.", "What is missing from all of the answers so far is a statement of just how hard cracking is. A hash function is a mathematical function, or algorithm, that takes some string as input, and produces a number as output. It has the property that given the same input, it produces the same output. A modern, cryptograhic hash function does this in a way that is hard to reverse. That is, given the output if the hash function it is hard to find an input that, if run through the hash function, will produce that output. How hard? Hard enough that mathematicians believe there is no algorithm for reversing the hash function that is faster than trying all possible inputs until you find one that works. (Note: belief is not the same as proof. No hash function has been proven to be this strong, yet.) The number of possible passwords is very, very large, so trying them all is not practical. Nor will it ever be practical. Passwords as a system are widely regarded as no longer secure, but not because people can reverse the hash algorithms. People have gotten too good at coming up with plausible passwords you might have used, or at stealing your password.", "Because there are multiple inputs that can produce the same hash. So there is no way to reverse that process to get the specific input that was used to create that hash. Now, in terms of passwords, this is irrelevant because the system only checks to see if the hash is correct, it really doesn't care what the submitted password is. However, getting any of the potential inputs is hard because the math used to generate the hash is difficult to do in reverse. It uses functions known as \"one-way\" or \"trap-door\" functions that are easy to do one way but hard to do in reverse. The prototypical example is multiplication. It is easy to multiply two numbers together, but it is harder to take a number and determined what two numbers were multiplied together to make it (factorization). If you choose your number carefully, there doesn't exist sufficient computing power to solve that problem. Various hashing algorithms use different methods, but the fundamental principle of easy-one-way-hard-the-other holds. Hackers get around this by precomputing all possible inputs and hashes using a technique known a rainbow tables. By doing all of the work ahead of time, they can easily look-up what input produces a given hash.", "Let's say instead of your password, it's the city you live in that we are trying to verify. If I want to verify that you live in the place you lived before but I don't want to save your actual home city in a database for security reasons, I could calculate something based on your city instead. One easy thing to do would be to store how many miles away your city is from a given spot, such as Chicago. When you tell me your city again, I can calculate the distance from your city to Chicago and check that against the distance stored in the database. This isn't a great hashing scheme though because you can easily figure out all cities that are X miles away from Chicago and guess what city the person is from. You can make this kind of check harder by making the distance calculation more complex. So instead of just straight line distance, maybe you map an actual travel route between the two cities, then maybe add 1 to your distance count for every mile traveled North, subtract one for every mile traveled West, etc. Now when someone sees \"42\" in the database, it's not clear if the city is 42 miles North, or 70 miles North and 28 miles West, etc. Ideally, the results for your calculation seems like a random number, so that if one city's code is 122, a city right next to it could just as easily be 25 as 429, there should be no correlation between similarities in the city geography and the code you generate. As long as it's just a set of simple math operations to calculate that distance number, the system can easily create a code for any city and then recalculate the same code later to verify. There's still a problem though. Let's say New York's distance code is 149. Since this distance calculation itself isn't secret (if it works well it would be used for all kinds of websites and software), someone could just make a list of every major city and its corresponding distance code when compared to Chicago. So later if you find 149 in a leaked database, you know every user with that code is probably from New York. The solution is salting, which basically makes each calculation more unique. So instead of calculating distance from Chicago every time, you could calculate from a random city every time. Instead of user1:149, user2:149, user3:149, for three users from New York being stored in the database, it could be user1:149 from Chicago, user2:418 from Miami, user3:12 from San Francisco, so that now every user from New York has a different code stored. Now if someone wants to be able to know every user that lives in New York, they have to do the work of calculating the distance to New York from every other possible city that the system uses. Edit: Said hash where I meant salt" ], "score": [ 207, 10, 9, 9, 7, 7 ], "text_urls": [ [], [ "http://fluidpowerjournal.com/2013/10/teslas-conduit/" ], [], [], [], [] ] }
[ "url" ]
[ "url" ]
5m0r94
The difference between hacking and guessing a password
I didn't really get the comments on the Shower Thoughts post
Technology
explainlikeimfive
{ "a_id": [ "dbzvmih" ], "text": [ "Hacking generally means using a computer to gain unauthorized access to data in a system. So anything where you steal files from someone's computer is hacking. In most cases when people hack passwords from a database, they steal what are called the hashed passwords. To understand what that means, you have to know what a hash function is. A hash function is an algorithm that takes input and gives output in such a way that it is very difficult if not impossible to figure out the input from output. So you put something like \"password123\" into a hash function and you get out something like \"0086 AC73 249E 7845.\" Every time you put \"password123\" into the function, you get that same output. However, the operation doesn't reverse. So you can't use \"0086 AC73 249E 7845\" to figure out that the original password was password123. Websites typically used hashed passwords for security. This means when you initially submit your password, the website hashes it and saves the output. It never saves your actual password. Every time you log in, it runs the hash function again and compares output. Those lists of outputs are what hackers are able to steal. Breaking into a database and getting that list is hacking. Now that a hacker has a huge list of hashed password, the guessing comes in. The hacker can't reverse any of the hashed passwords to see what the originals were, but what he can do is feed common passwords into the function and see if he finds any matches. Hackers know common passwords (things like \"password\" \"123456\" and \"asdf\") and will test those out first. So in our example, the hacker may put \"password\" into the hash and get out a string of characters that don't match aynthing. He may then try \"password123\" and get the string \"0086 AC73 249E 7845\". That matches the hashed password next to your username in his list, so now he knows what your password is because he guessed it and got confirmation. tl;dr - Hackers have to first guess passwords to see what they look like hashed and then match that to the lists of passwords they steal." ], "score": [ 8 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m0sah
Why do the web addresses for subreddits need an /r/ before them?
Technology
explainlikeimfive
{ "a_id": [ "dbzvd05" ], "text": [ "They don't \"need to\" necessarily, but that's just how Reddit has their site mapping set up" ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m0z05
Why do fish herd together into schools for protection?
Is this to appear larger and more formidable? It seems that individual fish still get caught by predators similarly to if they were alone in the first place. They don't seem to attack the predator once they're in schools; rather, they evade the predator together. The only reason I can think of is that being in a school decreases the chances of you being targeted since there are now thousands of other targets. Edit: Spelling
Other
explainlikeimfive
{ "a_id": [ "dbzx9k5", "dbzyu3o", "dc00ql6" ], "text": [ "If you are alone, what are your odds of being eaten when a predator comes along? 100% If you are in a school of 100 fish, what are the odds of being eaten when a predator comes along? 1%", "Schooling provides two benefits: First, it reduces the odds of any one individual being eaten. Two, many predators don't have that great of vision. So, instead of looking like a big group of small individuals, the school may look like one big individual, discouraging the predator from attacking.", "It is hard for the predator to focus on just one fish when there are so many about. So the predator goes to attack the school, but there are so many fish going in different directions that they get confused and can't follow a single fish." ], "score": [ 6, 5, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m12sb
What is a fiscal year and why do we need it.
Economics
explainlikeimfive
{ "a_id": [ "dbzy5pk", "dbzy4uc", "dbzyv6f", "dbzyhkx" ], "text": [ "Fiscal years are used by government and some businesses (usually mid-to-large businesses) concerning money. As to why they don't use a traditional calendar year, [here is one reason]( URL_0 ): > December is a really bad month to try to close out an entire year's accounting books. Accountants and execs are on vacation for large parts of the month, most retail stores are flooded with revenue (and then contra-revenue as items are returned) that takes time to account at the store level and then filter up to the corporate office, etc etc. It also doesn't tell the whole story for most retail outfits; December sales are usually inflated by purchases that are then returned in January after all the hullaballoo. As a result, a fiscal year end in January or even February keeps the entire season's revenues and expenses in one fiscal year.", "A fiscal year is an accounting tool where you can shift when your year starts for accounting purposes. For some companies, the calendar year is inconvenient to use, so they'd rather manage their finances according to a different year. For instance, if you're a company that sells school supplies, reporting your sales according to calendar years is annoying, because you'll be reporting half of one school year and half of another, so you might decide that your fiscal year is going to run from July to June instead.", "The idea is you want the end of your year and the start of the new one to be during the quietest time in your business cycle. If you sell snow shovels for a living, whether a blizzard hits on the last week of 2016 or the first of 2017 can skew sales from one year to the next. Much better to end your fiscal year on 6/30, instead of dividing up your busy season.", "A fiscal year is a way to financially split up a period in roughly a year. It may be aligned with an actual year or it may be easier to schedule the extra work which comes with closing and opening a financial year to other times. The main reasons you would want to work with financial units is so you can do analysis and planning on your entire business at once. A big company might not know how much money it have at a given time. If someone have unclaimed expenses or there is an unregistered sale then the company do not know how much money is in that. There is a lot of other reporting and calculations that needs to be done before a company knows how much money it have. So it does all this at a given time each year. It would also make sense to do comprehensive planning which would involve a lot of input from the different departments on what they need and an overall plan on what the company should do and where to invest the money. You also have smaller units like fiscal quarters and fiscal months that would serve similar roles but on smaller scales." ], "score": [ 36, 23, 3, 3 ], "text_urls": [ [ "https://money.stackexchange.com/questions/1002/why-do-companies-have-a-fiscal-year-different-from-the-calendar-year" ], [], [], [] ] }
[ "url" ]
[ "url" ]
5m12up
What makes Earth's core molten hot?
By the equation PV=nRT I understand that an increase in pressure without increasing the volume of the container will increase the heat of whatever is contained, but the pressure of the entire Earth compressing the core isn't enough to explain the heat. It's theorized that the core of a similar sized planet (Mars) is cold. What accounts for the difference of a molten hot and a cold core at the center of Earth vs Mars?
Physics
explainlikeimfive
{ "a_id": [ "dbzy142", "dbzy33h" ], "text": [ "> but the pressure of the entire Earth compressing the core isn't enough to explain the heat. Constant pressure doesn't cause an increase in heat either, so you are correct the pressure is irrelevant. The kinetic energy of the formation would have resulted in a lot of heat too but it would have cooled long ago. The core is molten primarily because of radioactive decay of heavy elements within the core. They are far more diffuse than in a nuclear reactor but the heat adds up.", "I don't believe a solid iron-nickel ball roughly the size of the Moon and under immense pressure qualifies as an ideal gas, so IGL isn't correct unless you're just talking conceptually. Earth's core is indeed hot in part because of pressure, as is Mars' core (\"cold\" in this context is still hot enough such that Mars has an entirely molten core). In addition, Earth's inner regions are pretty well insulated from outer space, so its going to take a really long time until the core cools, and there are some mild nuclear reactions in the Earth's core that provide additional heat." ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m186k
How do we get headaches if the brain has no pain receptor?
Biology
explainlikeimfive
{ "a_id": [ "dbzzq3j", "dc026gx" ], "text": [ "It's not your brain that hurts during a headache; it's the nerves and stuff around your head/scalp/skull that have pain receptors.", "\"A headache or cephalalgia is pain anywhere in the region of the head or neck. ... The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the pain-sensitive structures around the brain.\" Essentially the meninges or protective tissues surrounding the brain become inflamed and this is where the pain comes from. When someone catches meningitis for example this is the area that is being affected by the disease. It causes swelling and other complications and ultimately if not treated, death. Thanks google" ], "score": [ 8, 5 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m18de
Why would a computer replace a simple character (') into a complicated series of nonsense ( & #39;) when copying and pasting certain text?
Technology
explainlikeimfive
{ "a_id": [ "dc02hjf", "dc01k0z", "dc03jb6" ], "text": [ "Because the simple characters have special meaning in certain contexts. In a web page, for example, you use < > to tell the browser about the structure of the page. If I wanted to make a paragraph with red text, I would write < p style=\"color:red\" > This text would be red < /p > If I want a literal < or > , I need a way to tell the computer that \"this is a literal < , not the start of an instruction\", and it needs to be a sequence that won't be used anywhere else. The way web pages take care of this is to use an & followed by a description of the character to mean the literal character. So if I want a literal `'`, I can use ` & apos;` or ` & #39;` (an apostrophe is character number 39). If I want a literal ampersand, I can use ` & amp;` or ` & #38;`.", "Certain characters like punctuation have those codes like & #39 to differentiate between a displayed punctuation in text and something that's part of code to execute.", "All these are great answers. To add on, these are known as 'escape sequences'; every language (markup or programming) that deals with strings has them, and they generally differ from language to language." ], "score": [ 43, 4, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m18w3
What is the circle of fifths and how do you read it?
I'm really into metal music and I hear this term thrown around a lot. I really wanna get into music theory and then learn to play an instrument and this fascinates me.
Physics
explainlikeimfive
{ "a_id": [ "dbzzzgf" ], "text": [ "[The wiki article may be a good general place to start]( URL_0 ). In music, any chord of two notes (or more, but we'll just stick with two here) can be described as augmented, major, minor, or diminished in terms of the sound produced. However, there are two special chords (the fifth and the fourth) which are neither major or minor, and so are called \"perfect;\" if you take any piece of music, and pull out a single 4th (5 half steps) or 5th (7 half steps) chord from that song, and *just play that chord*, you would be completely unable to tell whether the parent song is major or minor (assuming the whole song is in the same key). In addition, certain numerical combinations of notes (so, chords with a given number of half/whole steps between them) always have certain sound qualities, regardless of the actual notes being played. For example, a C - Gb and a C# - G chord are both diminished 5ths, and will evoke the same general response in the listener, despite the fact that they're two different sets of notes. The point of the circle of 5ths is that you can easily see the interrelationships between given notes for any given key. You can also reverse the circle to get the circle of 4ths, which is generally more useful for jazz. However, unless you're more into progressive or experimental metal you probably won't need that version of it, and can just rely on the circle of 5ths (which is the mainstay used for classical music, which is going to be a little more relevant to metal in general). Also, if you're interested in the theory of it I'd actually start by getting a keyboard and learning a bit of piano, as music theory is fundamentally easiest to understand on a piano, and because piano theory translates very well to understanding basically any kind of music. Edit; on half/whole steps, see [this]( URL_1 ). So, any type of key for a given song is going to follow the same general rules, regardless of where you start. For example, for a C-major scale (which has no sharps or flats), you would play C-D-E-F-G-A-B-C, in that order. However, if you started in G-major, it would be G-A-B-C-D-F-F#-G, and you'd have to get into the black keys. However, both of these scales follow the same progression of 7 steps from the root (C for C-major);root-whole-whole-half-whole-whole-whole-half. For a whole step, you skip the neighboring key (black or white) and head to the next key (again, black or white). Similarly, for a half-step, you just hit the neighboring key. Using combinations of whole and half steps, you can figure out the notes of any given key for a piece. *Every* major scale will have the root-whole-whole-half-whole-whole-whole-half progression. Similarly, every *minor* scale will have a set progression, of which the simplest version (\"natural\" minor) is root-whole-half-whole-whole-half-whole-whole. Another form of minor (\"harmonic\" minor, which produces a sound that some people think of as sounding middle-eastern or Egyptian, and which shows up in metal at times) is root-whole-half-whole-whole-half-1.5-half, where 1.5 is a step and a half (so, skip 2 notes on the keyboard)." ], "score": [ 3 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Circle_of_fifths", "http://www.piano-keyboard-guide.com/wp-content/uploads/2015/05/36-key-keyboard-chart.jpg" ] ] }
[ "url" ]
[ "url" ]
5m1cf6
what do we actually see at the edge of the observable universe?
As far as I know, the structure of the observable universe is a 3D sphere which is a crosscut of 4 dimensional spacetime, such that as we look deeper into this "snapshot" of the universe, we're looking deeper into the past. So does this mean 14 billion light years away we can look at the big bang itself? Do we somehow see the same singularity everywhere in the edge of the observable universe in any direction? And anything else anywhere in the universe would see the same singularity at the boundary of their own observed snapshot of the universe? I'm struggling to see how all of this actually works.
Physics
explainlikeimfive
{ "a_id": [ "dc01fze", "dc00wni", "dc010la", "dc0v7a5", "dc01bux", "dc012q7" ], "text": [ "What is the Big Bang? --- The origin of your confusion seems to be the very common misconception that the big bang originated from one point in space. That is not true. But let's back up a little:The observable universe is the sum of all points in space that are causally connected to earth. That means, it is a sphere around earth encompassing all the space from which photons have had the time to reach earth since the big bang ~13 billion years ago. This observable universe was indeed compressed into a tiny portion of space shortly after the big bang. However, the observable universe is by far not all there is. Current data shows, that the universe is [probably at least 3\\*10^(23) times bigger]( URL_1 ) than the observable universe. And many cosmologists believe that the universe is infinitely big. Hence, the big bang did not occur at one point in space, but everywhere at one. Which is why the name big bang is horrible. Henry Reich from MinutePhysics argues that the Big Bang should be renamed into Everywhere Stretch in [this]( URL_0 ) video. (You should definitely check this video out, it does a good job explaining your very question.) The Cosmic Background Radiation is the residual radiation from a time shortly after the Big Bang, when the universe cooled down enough to become transparent to photons. And the photons we detect on earth have traveled since that moment and are reaching us just now. Can we see Background Radiation from everywhere in the universe, or is earth somehow special? --- One of the most fundamental assumptions of cosmology is that the universe is isotropic and homogeneous - which is called the [cosmological principle]( URL_2 ). That means by and large the universe looks the same in all directions and at all points. This suggests, that earth is *not* special in being able to see Cosmic Background Radiation. Indeed, every observer, anywhere in the universe is in the center of their own observable universe and will receive CMB (cosmic microwave background) from the edge of *their* observable universe. Thus, the question what it looks like to stand at the edge of the observable universe cannot be answered in any meaningful way. An observer is *always* at the center of their own observable universe, so - by definition - there cannot be an observer at the edge of an observable universe.", "> So does this mean 14 billion light years away we can look at the big bang itself? Yes! Although, due to the expansion of spacetime it is actually more like 46.6 billion light years away, and what we can actually see is the time when the universe was full of a hot, glowing plasma. That plasma was opaque (can't see much through glowing clouds) so we can't actually observe even more into the past because light from then ran into the glowing clouds at the time. > Do we somehow see the same singularity everywhere in the edge of the observable universe in any direction? Not quite, but sort of in the sense that everywhere was the singularity at one point. What we see is the period where the universe was close and very hot, but not when it was a singularity. > And this is visible anywhere in the universe for the boundary of the snapshot particular to that point? I'm not sure what you mean by this, but any other point in the universe would be able to see the same thing as we do relative to their location. Their visible universe would be centered on their location.", "The furthest, oldest light that can be seen by any of our telescopes is the cosmic microwave background. This is light that was emitted 360,000 years or so after the Big Bang, when the Universe cooled enough to form neutral atoms and photons could move freely without being absorbed by charged particles. Today, that light has been redshifted to microwave wavelengths by the expansion of the Universe. We can see no further back into the past than this.", "Say, we launch a mobile telescope that flies off in a straight line away from earth. It then flies one light-year away from earth. Can it then observe stuff that's one light year beyond the observable universe in that direction?", "The farthest back that we can see is the Cosmic Microwave Background Radiation. For the first 300,000 years or so, the universe was so hot and dense that light could not travel freely because it existed in a plasma together with electrons, protons and neutrons. When the universe cooled enough, the photons could separate from the plasma, and we see the light from the so called \"last scattering surface\" as a very uniform emission of light.", "The observable universe is the sphere within which objects are visible from earth, because light from those objects has had time to reach earth. Objects outside this boundary you will not see, because their light is still traveling towards earth, but not here yet. Far enough away, and you will *never* see objects, because the universe will expand faster than their light can approach us. The observable universe is much wider than 14 billion light years however, due to the expansion of the universe. We actually get a radius of about 45 billion light years. If you could see far enough back in time, the universe itself was very opaque, at an early age, to electromagnetic radiation, so seeing through that is impossible." ], "score": [ 61, 7, 5, 4, 4, 3 ], "text_urls": [ [ "https://www.youtube.com/watch?v=q3MWRvLndzs", "https://en.wikipedia.org/wiki/Observable_universe", "https://en.wikipedia.org/wiki/Cosmological_principle" ], [], [], [], [], [] ] }
[ "url" ]
[ "url" ]
5m1d7t
What is the point of SMS Short Codes?
I have read the basic about them [here]( URL_0 ). Is there any reason companies use them other than having a 5-6 digit number? Do they send bulk messages any faster?
Technology
explainlikeimfive
{ "a_id": [ "dc00j2h" ], "text": [ "They're a lot easier for people to remember and to key in. Which are you more likely to do: text \"FREEGIFT\" to 66066, or text it to 2068794482?" ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1gf6
How does the U.S. government owe money to itself?
I can't quite grasp this based on stuff I am finding through Google. I am not savvy with economics. Thanks in advance. Edit: Thanks to everyone for your responses. I need to study up on bond markets apparently.
Economics
explainlikeimfive
{ "a_id": [ "dc02a0h", "dc02pez" ], "text": [ "The Federal Government \"borrows\" money from the people by issuing Federal Bonds and printing more cash, which devalues whatever money you have in your pocket. Hypothetical situation. 2017 budget rolls around, we have a $1 trillion deficit. The Fed issues $1 trillion in bonds and prints that much in cash. If there's $100 trillion dollars in circulation, printing that $1T just devalued your dollar by 1%. This is a result of the official abolishment of the gold standard in 1971", "The US government may have a fund set up to hold money and disburse it later for a specific purpose (for example, the social security fund). Now, the government could just keep that money in a bank, earning no interest. But that would be stupid because inflation would cause the fund to lose its value (the price of everything else will go up to keep up with inflation but your dollar figure in the bank stays the same, so when you draw on fund years later, you will end up buying less of the goods than you could have years before). So the government has a choice on how to invest that money. With the financial world considering US government bonds to be essentially risk-free, and the interest on those bonds can in general keep up with inflation, the people running that specific fund will invest the money in US government bonds. Now the US government owes money (through its bonds) to itself (its own fund). The government is likely avoiding other investment strategies (stocks, corporate bonds, etc) because they could be perceived as too risky. For example, imagine if the social security fund was invested in large bank stocks or even real estate in 2008 when the market tumbled. The person who made that investment decision, and his overseers (ultimately Congress/President) would face lots of political scrutiny, to put it mildly, for the losses incurred. Granted the stock market rebounded, but at the time, people would be very angry at the losses mounting in the social security fund. They would see it as the government taxing them and then just losing the money. It's too politically risky. In the end, the government doesn't \"raid\" the social security fund. The fund managers are making a choice to buy government bonds." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m1lss
Why is there an enzyme in the human body that breaks down methanol into formaldehyde? How does this enzyme exist in the first place?
Methanol would act like a super-potent grain alcohol, but then these enzymes come along and turn it into a deadly toxin right inside our own bodies. What gives?
Biology
explainlikeimfive
{ "a_id": [ "dc08ob6", "dc09q4t" ], "text": [ "I would assume that you are talking about Alcohol deydrogenase. enzymes can be specific for certain molecules up to a point in their active site(where the molecule of interest attaches), they just kinda look for certain parts on a molecule, like groups like alcohol groups and their sizes, that sort of thing. So imagine an enzyme sort of like a puzzle that is complete except for one piece that is in the middle, now imagine that you have several pieces that are around the same size as the hole in the puzzle, all with at least one connecting piece that can connect to a slot in the hole. Not all of the pieces are necessarily what you are looking for, but they can to some degree fit into the puzzle. the same thing is true with Alcohol dehydrogenase, it \"looks\" for small alcohols, so although we would may want it to react with only ethanol, if we were to put it into the presence of methanol it would help carry out the reaction as the methanol fits well enough into its active site that it can react.", "Since this is a rather chemistry specific question, I'll go ahead and give you the ELI18 version. The name of the enzyme is Alcohol Dehydrogenase. The enzyme's function is to help to degrade a fairly wide range of alcohols, most of which are toxic. For example isopropanol and/or amyl alcohols found in some alcoholic beverages. Ethanol (grain alcohol) is probably the least toxic of the possible targets the enzyme can attach to. A.D. does this by converting the alcohol into an aldehyde, by removing two hydrogens next to the (OH) group. In most cases the resulting aldehyde is much less toxic than the alcohol. For example, the A.D. produces ethyl aldehyde (aka acetaldehyde) out of ethanol. (This has a characteristic odor of beer or bread dough you can smell from the breath of people who are intoxicated.) From there ethyl aldehyde is converted into acetic acid and then conjugated into the compound Acetyl-Coenzyme A. Acetyl-CoA is used in a wide variety of processes in cells, including energy production. But, in the case of methanol or ethylene glycol (antifreeze) the resulting aldehyde produced is formaldehyde. Not only is this more toxic than methanol by itself. The formaldehyde is subsequently converted into formic acid with is yet more toxic than either formaldehyde or methanol. Methanol is only found in small concentrations in nature. Most commonly as a trace side product in fermented foods. So few organisms have evolved mechanisms to deal with large amounts of it. Ethylene glycol is a wholly man-made chemical. *TL;DR: the main function of Alcohol Dehydrogenase is to detoxify a wide range of alcohols. But in the case of methanol or ethylene glycol, it does the opposite, creating products that are more toxic, not less. These two compounds are rarely or never found in nature so few organisms have evolved defenses against large amounts of them.*" ], "score": [ 8, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m1mdt
Why is Facebook advertising it's "Facebook Live" feature so heavily?
It seems like it's on TV a bunch and I get notifications for it all the time. & nbsp; It doesn't seem like they are currently monetizing it, are they setting it up to do that in the future?
Technology
explainlikeimfive
{ "a_id": [ "dc044yt", "dc031wv" ], "text": [ "If the social media market starts to gravitate towards Snapchats or livestreams, etc it means users could use other platforms to share content and information which means they become less relevant. They are also working on different ways to monetize the live streaming with ads so they maintain revenue. This is revenue they lose if people use other networks to do accomplish the same goal. Essentially, they are trying to protect their market share in case social media transitions to into this new live space.", "Twitter created Periscope -- which has been letting users effortlessly host their own live streams for quite a while now. Facebook is trying to make up for lost ground." ], "score": [ 7, 5 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m1ncz
Why can a psychological condition/state (like stress) cause physiological effects?
Biology
explainlikeimfive
{ "a_id": [ "dc03172" ], "text": [ "Your mind is not independent from your body. You \"feel\" stressed because your body is releasing chemicals, raising your heart rate, etc. Every emotion you have does something to your body. In some cases, like fear, your body causes the emotion before you have time to think about it." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1o9q
how did humans survive the ice age?
I'm sitting here typing this, in a thick Parker jacket, a hoodie and a t-shirt; I can barely feel my fingers to type and it's about 0 Celsius. When climbers frequently get frost bite from exposure for over 12 hours, how did humans survive the constantly freezing temperatures of the ice age?
Biology
explainlikeimfive
{ "a_id": [ "dc03u01" ], "text": [ "Fur, fire and fat. Humans quickly learned that stealing the skin from furry animals makes a nice cozy coat. Even today, a traditional fur parka will work better than even the higher tech synthetic varieties. When humans are moving around, we're pretty good in the cold. When we're sitting around, like at home, we sat around a fire. Or in a cave with fire. Or in a tent, next to a fire. Fire was life and we were around it whenever possible. We also weren't skinny. Early humans loved to have a bit of fat on them. It kept us ever more insulated and gave us a nice reserve of calories to burn for warmth." ], "score": [ 8 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1o9s
Why do colors combine to make other colors?
Why do we have colors and how does red and yellow make orange or other colors make other colors?
Physics
explainlikeimfive
{ "a_id": [ "dc0b1h9" ], "text": [ "Colors are a response your brain makes to picking up certain wavelengths of electromagnetic radiation striking receptor cells in your brain. When this happens, those cells send signals to your brain, and your brain creates the image. Certain combinations of stimulation on those cells cause your brain to generate different colors, to help further discriminate, because this is a beneficial evolutionary adaptation (harder for things to blend together). Color itself is not a property of light or anything. Rather, a product of your brain interpreting it." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1pi5
How does internet speed affect online gaming experience
Been online gaming for years, but never really understood what , ping, upload and download really mean, and how it affects online. Currently, on speedtest, my ping is 15, download 37.18 Mbps, and upload 9.04 Mbps. How do each these numbers affect online gaming, mainly CoD, which is the most influential number.
Technology
explainlikeimfive
{ "a_id": [ "dc051c5", "dc03rit" ], "text": [ "Long story short, bandwidth gets you fast downloads, low latency gets you fast gaming, and packet loss hurts both. Bandwidth is a limit of the network capacity, and data caps placed on your account by your network provider so that you get the speed you paid for but no more. Latency is a matter of the switching performance of the switches and routers, the number of network hops the packet makes, and the distance between your computer and the other end of the connection. And packet loss hurts both latency (due to re transmitted packets) and bandwidth and is mostly a result of un optimized network routing and equipment defects. Details: So there are several different types of data and each has different sensitivities to network issues. For instance downloading a file is asynchronous and it is okay for parts of it to arrive out of order or for there to be a lot of latency in the communication because it's the size of the packets, and the number of them that make it through without being discarded that affects how quickly a download can work. Contrast that with a skype call which doesn't use a lot of bandwidth, but the data that is sent, is time critical. If the packets arrive out of order it doesn't do you any good because by the time the system re-assembles them you've already moved on to the next sentence. We perceive these problems as jitter and sound dropping out or becoming noisy. So latency is somewhat important, not dropping packets is very important, and bandwidth is less important. Then you have gaming, where you and all of the people playing as well as the server all have to exchange packets quickly so that each user is updated on what the other users did for each slice of time, and the server calculates all of these, and then sends the results out to each client. For instance you shoot an enemy at the same time they shoot you, whichever packet makes it to the server first, that player gets the kill and the other doesn't. Then the server sends the results. So you might see you fire first, but if the server doesn't, then it doesn't matter. So the latency, or round trip time it takes a packet to be sent and responded to, is the most important. So what effects latency, bandwidth, and packet loss? Latency is affected mostly by how far away you are from the server, and how many hops the packet has to make along the way. Packets are switched and routed, and each time they hit a switch or router, they have to be copied and re-transmitted and this causes a slight delay in the round trip time. This is less about the amount of bandwidth, and more about the switching speed and performance of the switches and routers. Bandwidth is affected mostly by network traffic, and throttling such as paying for 500mbps internet, the cable company caps your bandwidth at this limit. Also if neighbors are downloading a lot of stuff and the cable network gets overloaded, it can slow down your speed for a bit. Packet loss and arriving out of order, is mostly a matter of provisioning the networking equipment to use the best route, not to exceed the packet size, your computer not using a packet size too large so it's not fragmented, and the quality of the connections between the different hops on the way to the other side of the connection. Line noise, thunder storms, corroded wires, radio interference, over worked equipment, and of course [the fiber seeking backhoe]( URL_0 ). All of these lead to packets being lost or corrupted. Also certain transfer protocols like UDP do NOT re transmit packets. If a packet is lost, it's lost.", "Ping is the time it takes a signal to go from your location, to the destination and back. For example, a \"ping\" to a spaceship on Mars would take several minutes because electronic signals cannot travel faster than the speed of light. Similarly, while the distance between the United States and China is negligible for the speed of light, it still requires time and is not instant. Additionally, at every node/server, there may be some computation or process to occur that redirects your signal to the proper location (which also may take time). Download speed is the amount of information you can download from another. For example, downloading a game/music to your harddrive. Upload speed is the amount of information you can transfer to another. Have a high upload speed means you can upload a video to youtube much quicker. For the purposes of COD, download speed is the most important item but once it is over a certain threshold, your hardware, and the server's hardware will limit you." ], "score": [ 5, 3 ], "text_urls": [ [ "http://www.urbandictionary.com/define.php?term=Fiber-seeking%20Backhoe" ], [] ] }
[ "url" ]
[ "url" ]
5m1pm6
what is that feeling when you stand up to fast
Biology
explainlikeimfive
{ "a_id": [ "dc03odh" ], "text": [ "I think you mean [orthostatic hypotension]( URL_0 ), which is basically just a quick drop in blood pressure while your heart catches up with the sudden need to work a bit harder now that you stood up. For the moment while it catches up, the low blood pressure in your brain can cause experiences close to fainting (dizziness, very brief loss of vision, etc)." ], "score": [ 13 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Orthostatic_hypotension" ] ] }
[ "url" ]
[ "url" ]
5m1uj2
what exactly does Obama care do? why do some people hate it so much and why do other people love it so much?
Other
explainlikeimfive
{ "a_id": [ "dc0650r", "dc053zx" ], "text": [ "\"Obamacare\" is actually called the \"Patient Protection and Affordable Care Act\", but was renamed \"Obamacare\" by Republicans in an attempt to make Republicans/Conservatives/Alt-Righters dislike the act before they knew what it was because is was being associated with Obama (whom they already hated for many reasons - another story completely). That being said, the Affordable Care Act did a few things, including: * **Forces people to get a health care policy** (*Conservatives/Republicans don't like this because they perceive that it infringes on their freedoms; Democrats/Liberals like this because it helps people get help for their health*). * **Does not allow insurance companies to deny coverage to someone with a [pre-existing condition]( URL_0 )** (*Democrats/Liberals like this because it helps people get help for their health; Republicans/Conservatives don't like this because it takes money out of their pockets and forces businesses to behave in a certain way*). * **Expanded Medicaid eligibility to include individuals and families with incomes up to 133% of the federal poverty level** (*Democrats/Liberals like this because it helps people get help for their health; Republicans/Conservatives don't like this because it takes money out of their pockets*). * **Subsidized insurance premiums** (give people money to help them pay their premiums; *Democrats/Liberals like this because it helps people get help for their health; Republicans/Conservatives don't like this because it takes money out of their pockets*). It did a lot more, and you can read about it [here]( URL_1 ). TL;DR - it's allowed a lot of poor people access to healthcare that they did not previously have access to. And then [those same people voted for someone who would dismantle it]( URL_2 ) without thinking about the implications of their actions.... but that's another story. **Generally Liberals like it because it means poor people can have access to healthcare, and Conservatives hate it because it forces behavior (\"curtails freedom\") and potentially takes money out of their pockets to help other people.** EDIT: Formatting", "Obamacare does a whole bunch of stuff, more than I care to lay out in detail, but critically it does one thing: it mandates people get private insurance. Initially Obamacare was supposed to be universal healthcare, and Obama said he would not waver on the public option, but he ended up scrapping it entirely in an effort to get the bill passed by congress. This is mostly why democrats are angry about it, if they're angry about it. Republicans are mostly angry about it because it's the government forcing them to get a healthcare policy, which they don't feel they should have to. The other reason many people dislike it is because it's basically a huge handout to insurance companies, in a way. The idea was originally, let's make everyone get insurance, and have a public option so that there's a baseline insurance companies have to compete with. Since that got scrapped, however, insurance companies are free to collude with one another and price policies at whatever the hell they want them to, since now people MUST buy their policy from somebody, but the companies don't need to compete with a public option. There have been cases of some peoples' policies rising in cost by up to 30%. EDIT: words r hard" ], "score": [ 25, 21 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Pre-existing_condition", "https://en.wikipedia.org/wiki/Patient_Protection_and_Affordable_Care_Act", "http://www.vox.com/science-and-health/2016/12/13/13848794/kentucky-obamacare-trump" ], [] ] }
[ "url" ]
[ "url" ]
5m1vse
The Boltzmann Brain Theory.
Physics
explainlikeimfive
{ "a_id": [ "dc06w5j" ], "text": [ "Take a puzzle with 1000 pieces, throw them on the ground. You'll probably generate a huge mess. Repeat this often. Sometimes two pieces that fit together will land next to each other. Repeat this really, really often. Once in a while, all 1000 pieces will land at their right spot. Our brain is a bit like a puzzle - just with even more pieces (atoms). Space is never completely empty, there are a few atoms and radiation flying around, so space is constantly \"throwing pieces around\". Wait long enough and have enough space, and eventually a human brain will appear just by random chance. It won't last long, but it can last long enough to have thoughts. Every other possible arrangement of atoms will happen as well. There is also a \"Boltzmann flower pot\" and so on." ], "score": [ 28 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1w0k
How comedy YT channels can find and piece together words from people or movies to make a song
Technology
explainlikeimfive
{ "a_id": [ "dc05hls" ], "text": [ "You get the transcript and search them (or better yet, the captions for a video, since it's already time tagged). There are commercial services that have the transcripts for practically everything and there is software that can DVR shows and stuff with closed captions which can be searched. There are ways to search the captions of youtube videos as well." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m1xz9
What's going on with "black money" in India?
Economics
explainlikeimfive
{ "a_id": [ "dc05rba", "dc09a44", "dc05yzk" ], "text": [ "A bunch of people aren't reporting their income, mostly because it's gained through illegal means (like the black market). This income is kept hidden in their homes generally, and isn't stored in banks. In order to combat this, the Indian government surprised everyone by suddenly announcing that all their most common bills no longer have value, and must be exchanged for new bills. It would be like if the US government said \"we're getting rid of the $10 and $20 bills and replacing them with $15 and $30 bills.\" Anyone who wants their money to have value must take it to a bank to exchange it, where the amount they exchange will be recorded. Those with a ton of \"black money\", i.e. money gained through illegal means and not reported for taxes, will be exposed.", "I'm an Indian. Our currency is a rupee. We're more like England than we like to admit. Our note denominations are like 10, 20, 50, 100, 500, 1000. Well it was like that for about 35 years or so. Before that we didn't have 1000 rupee notes. The 1000 rupee note was created to remove black money. In November 2016 the government discontinued the 1000 & 500 rupee notes and introduced new notes with denominations 2000 & 500. This was done to force people to come out and exchange their cash. We were given about 3 months with a daily cash exchange limit and also a daily deposit/withdrawal limit. Apart from the daily limit there was an additional total limit which was about 2-2.5 Lacs (200,000-250,000). Old 500 and 1000 rupee notes have been rendered useless after 31st December, 2016. This means if your money is already in the bank you're safe but if you have more cash lying around the house than you should then you're screwed. I don't know if you know this but 80% of the transactions in India are done in cash. Although I am inclined to believe that in the long run this is a bad move. This mostly affected the poor and the middle class. More than 80 people died standing in bank cues. We didn't manage to get the amount of black money that was expected, naturally. Plus statistics show that since the last time this happened the consumption of black money has increased. It looks to me like black money can now be stored in smaller briefcases. I'm sleepy or I would have gone into more detail.", "This makes for an odd time. As I recall the week before this happened and about a week after the retail location I work at had a massive influx of indian-national customers looking to buy predominately Apple products in bulk. We put a hard limit on ipad and macbook quickly as our stock diminished very quickly but I had people screaming at me that they NEEDED 50 Ipads and 10 Macbooks. They paid in USD but the announcement which occurred on a Wednesday really seemed to put two and two together." ], "score": [ 15, 8, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m1z49
Why does the military insist on saluting?
Other
explainlikeimfive
{ "a_id": [ "dc0ge8e", "dc05x5e", "dc05zb8" ], "text": [ "Saluting has a long history that is actually not written in stone. However one explanation is that it was originally used as a greeting between two knights to show their face and thus not be seen as an enemy. Additionally it would take away from their master hand to hold their weapon. This has progressed through to when officers would remove their headgear in the presence of a superior, and then became just a grabbing of the hat. This turned into the modern salute which now has enlisted men salute officers and junior officers saluting superior officers. The salute itself is in recognition of the Commander-in-Chief, for the Commonwealth the salute goes to the Queen, as recognised by the crown on the cap badge. Really though it's just a longheld tradition and the military loves tradition.", "Many militaries salute primarily as a matter of tradition, honour, or respect for higher ranking officials. Salutes vary greatly from military to military, for historical examples, think the Fascist right arm salute, the bow given in many Eastern cultures, even the variations of the basic salute are many.", "Chain of command is very important, especially in a hazardous situation. It is critical to know who is supposed to be giving the orders, and who is supposed to be receiving them. Saluting, highly visible rank insignia, and referring to each other by rank reinforces this. Personnel are always aware of the authority structure in any given circumstance, so when someone shouts \"we need to get out of here!\" they know the difference between a panicking private and a captain ordering a retreat." ], "score": [ 23, 3, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m20v7
Why does a website with a recipe often include a long preface before you get to the actual recipe?
Each time you find a recipe online, there will likely be a very very long preface to the recipe that is by the author-- which makes no difference to the dish (for example, "I first made this dish on a Saturday morning, when the leaves were falling on my porch...."). If it were ads, that would make some sense as part of the deal of getting the recipe. But, it is usually just a long story and far too many pictures of the completed dish. What's the deal?
Other
explainlikeimfive
{ "a_id": [ "dc068ww", "dc06xx0", "dc0659s" ], "text": [ "Imma answer your question, but first let me tell you about this time I watered the lawn on a warm july afternoon, there were clouds in the sky and childrens laughter.... ok seriously, who knows, maybe they just like to hear themselves type, or create an emotional connection to the recipe, perhaps they are just killing white space so the ad banner on the side fits the page. could be worse, you could be asking about youtube videos. *11minutes to review a potato peeler? how???*", "If the author is a decent writer, it can help set the mood for the food but even the best authors can sometime seem like they're waving their wonderfulness about like a 3 year old boy enjoys waving around his penis (I've got one - wheee!) I would rather see the recipe at the top of the post so I can immediately see if I want to read further instead of slogging through 42 glamor shots to discover I don't have a certain ingredient and won't dream of buying it anyway (fungus!) or am lacking XYZ gadget and wouldn't bother buying one or working around it.", "I would guess it's because these websites aren't cookbooks, they're blogs, which implies some degree of the author writing for themself." ], "score": [ 5, 4, 3 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m21th
If I'm thinking of a song, are my brainwaves moving at the frequency of the notes?
So let's say I'm thinking of a song (or really even a note) I know really well, and am playing it consistently in my head. Are the neurons themselves replicating the song/note frequency? Would it be possible to scan for that frequency using some type of medical device (existing or theoretical)?
Biology
explainlikeimfive
{ "a_id": [ "dc08nj2" ], "text": [ "The thing about brains is that there's always a lot of stuff happening all over, such that it's hard to tell what's going on at any given point. Getting useful data from them usually requires a lot of averaging; the colorful brain scans you often see really only represent slightly increased or decreased activation. In general, this noisiness is really important. Predictable, synchronized firing of neurons is what we see in epileptic seizures, which are bad. While brains may give the appearance of rhythm and order, their actual workings look like pure chaos. Anyway, the only way to tell what a single neuron is doing is by inserting a tiny electrode. It's an invasive procedure, and you can't tell which cell you're going to get, so it's kinda limited." ], "score": [ 8 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m22kt
Why does scratching a bug bite feel so amazingly good when I'm obviously damaging my skin?
Biology
explainlikeimfive
{ "a_id": [ "dc0tklx", "dc0lub2" ], "text": [ "URL_0 There's a link to the same question /u/js569 explains: There are two types of sensations, fine and crude. Pain is an example of a crude sensation and touch is an example of a fine sensation. Both crude and fine sensory pathways are activated together, and when they are, the fine sensations generally overwhelm the crude sensations. That's why when you feel pain, touching it makes it feel better.", "Because the brain thinks there is an irritation there and gives you a pleasure sensation to scratch that area." ], "score": [ 9, 4 ], "text_urls": [ [ "https://www.reddit.com/r/explainlikeimfive/comments/1md53w/why_does_scratching_a_bug_bite_feel_so_good/" ], [] ] }
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5m23is
How can expired food grow mold/fungus on it if it's in a sealed container so any air carrying spores can't come into contact with it?
Mold and fungus come from air carrying fungi spores, so wouldn't placing a food item in a sealed container make it impossible for that to happen since new air can't come into contact with it?
Biology
explainlikeimfive
{ "a_id": [ "dc06vn5", "dc0as3x", "dc06tru" ], "text": [ "The air doesn't have to be \"new.\" Mold spores can lay dormant for a significant amount of time before starting to grow. If there's mold growing inside a sealed container then the spores went in before it was sealed.", "They are in the container, because you put them in there, however unwillingly, along with whatever food and/or air you put in there in the first place.", "If there are mold/fungus in the air that is in the sealed container when it is sealed, that would cause growth. In containers where it's not easy to make them vacuum sealed (think cans of fish), they seal the food in and then heat it up to a high enough temperature to kill off the microbes." ], "score": [ 4, 3, 3 ], "text_urls": [ [], [], [] ] }
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5m272v
How exactly does an explosion kill you?
Other
explainlikeimfive
{ "a_id": [ "dc07y2v", "dc07m53" ], "text": [ "There is a whole list of ways. Shrapnel- basically really sharp bits of things flying through your body and tearing you apart. Heat- explosions generate a lot of heat. If you are close to the explosion and survive everything else the heat will most likely kill you. Shockwave- this is the big one. When there is an explosion it generates a massive shockwave in the air. Usually when you hear of people missing limbs it's because of this shockwave. Imagine a giant the air as a fluid a shockwave would be like a tsunami.", "Shrapnel. Fragmentation. Sharp bits of things that blew up penetrating you mostly. That and the shock wave can collapse your lungs." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
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5m2a80
Why does carbonated water (most notibly soda) build up pressure once shaked?
Chemistry
explainlikeimfive
{ "a_id": [ "dc0a3bx" ], "text": [ "Carbonated means that the liquid has Carbon Dioxide dissolved in it. When you shake a bottle of soda, the Carbon Dioxide is 'released' from the liquid and expands, building pressure in the bottle." ], "score": [ 4 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m2c9s
Why is it that even though my car weighs almost 3,000 lbs it still gets blown around like a feather (mild exaggeration) when I'm driving on a windy day?
Physics
explainlikeimfive
{ "a_id": [ "dc0902d", "dc0933i", "dc0tz1a" ], "text": [ "Because your car also has a big side profile and wind has a big force. 3000 pounds doesn't mean you're immovable. A gentle 10mph Wind can move sail ships tens of thousands of pounds given enough sail area.", "wind hit the sides and gets underneath, and while your car weighs 3000 lbs, it had shocks that are built to move/respond to force.", "The wind does not blow your car around, it changes the geometry of your steering system. That system is made up of the steering wheel, rack and front tires along with the suspension system. The pliability of the suspension allows your car to roll left and right a few degrees as well as up and down. High-performance suspensions are designed specifically to reduce the rolling movement because it tends to steer you toward from the compressed side, i.e. away from the wind or corner. In a turn, with the car rolling toward the outside, this is part of what causes the wheel to want to return to center. At low speeds, it takes large changes in control geometry to accelerate the car left or right. When making a turn onto a road from a stop you may need to turn the wheel almost to its stop. At high speed, increasingly smaller control inputs are needed to accelerate the car laterally. To change lanes on the freeway you only need to turn the wheel a little bit. This is where the small deviations the wind create have their most profound effect." ], "score": [ 28, 4, 4 ], "text_urls": [ [], [], [] ] }
[ "url" ]
[ "url" ]
5m2fi3
Can a planet stay hidden if it is placed in opposition of Earth in orbit and moving with the same speed ?
Like dis URL_0
Physics
explainlikeimfive
{ "a_id": [ "dc09ra2", "dc09uvs" ], "text": [ "It could stay hidden from direct observation from Earth, but it would be easy to detect with indirect methods. For example, its gravitational effects on other planets, asteroids, comets, and spacecraft would be immediately obvious.", "No. The solar system started to be discovered by direct observations but then we started to map everything out and calculate gravity and the effect on other bodies to predict solar eclipses and when we would be able to see other planets. We might no be able to see the hidden planet, but we would be able to see the effect of gravity on everything else in the solar system." ], "score": [ 10, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m2fqn
What is 4-dimensional space?
I read Wikipedia article about it, but still can't figure out what actually is the 4th dimension or how to imagine 4D space.
Physics
explainlikeimfive
{ "a_id": [ "dc0a99t" ], "text": [ "In three dimensional space, we can find three directions that are orthogonal to the other two direction. In four dimensional space, we can find four such directions. There really is no way for our three dimensional brains to visualize a four dimensional space, but is is absolutely trivial to describe it mathematically. Thus, math is the only way to understand abstract concepts like four dimensional space. P.S.: there are a lot of people claiming time is that fourth dimension. This is completely wrong, as time has an affine and directional structure while space does not. There is an important distinction betweem the four dimensional spacetime and a four dimensional space." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m2ja9
Why did motorcycle sidecars become less popular?
Or why have we not seen as many?
Other
explainlikeimfive
{ "a_id": [ "dc0c2oh" ], "text": [ "Motorcycles used to be more common as a daily driver and even utility vehicle. People might not afford a car or a car driver license. Adding a side car makes a motorcycle much more useful as a daily driver. A worker might have lots of tools in the sidecar, you could go grocery shopping with the bike and even take your wife and kids with you on trips. The Armies wanted sidecars on their bikes to allow two solders on a bike. However nowadays people buy a motorcycle for more recreational use. Most people have a car or access to one within their budgets. Even people who use their bike as a daily commuter might use a car for their weekly grocery shopping or their weekly getaway with the wife and kids. The sidecar makes the bike more heavy, harder to navigate narrow places, more expensive and less enjoyable to ride." ], "score": [ 6 ], "text_urls": [ [] ] }
[ "url" ]
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5m2jnp
how and why did "Bee Movie" become a meme?
Other
explainlikeimfive
{ "a_id": [ "dc0axsi" ], "text": [ "It's a bad movie with a bad script and, somehow, actors usually considered good. It's lameness, coupled with the effort taken to actually produce and distribute the thing, make it a unique candidate for recognition on an Internet that likes laughing at people who try too hard. That's my take on it, any way." ], "score": [ 3 ], "text_urls": [ [] ] }
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5m2mc1
Why are American postboxes/mailboxes usually detached from the house itself?
Other
explainlikeimfive
{ "a_id": [ "dc0b8on", "dc0b6ro", "dc0dbr7", "dc0fw8v" ], "text": [ "It can only be so the mail carrier doesn't have to get out and walk up to each house if they have extended lawns/driveways. With mailboxes right at the street they can drive straight down the line, saving tons of time and hitting more addresses in a day.", "In general, it makes it easier for the mail deliverer to do their job if the mailbox is closer to the street. So the practice of having the house be farther away from the street meant that having the mailbox be a separate thing was a good compromise. Though MANY houses keep their postboxes attached to the house itself. It varies depending on your neighborhood.", "Some new housing developments like mine have on big box for every one (lots of little boxes with keys) so the mailman makes one stop", "Because the carriers deliver by car because that is more efficient. They only deliver on foot in dense cities and in these situations houses normally have a box on or near the door of the house." ], "score": [ 10, 5, 4, 3 ], "text_urls": [ [], [], [], [] ] }
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5m2oom
Why do we (in the USA) never seem to hear about left-leaning survivalist groups seizing a facility or something of that nature? Do such groups not exist? Or are they simply not covered by the MSM? Been curious since the Bundy incident in Malheur County, Ore.
Other
explainlikeimfive
{ "a_id": [ "dc0bu2l", "dc0dac6" ], "text": [ "All things considered, the US is a really right wing country. To the point that Hillary Clinton would have been the equivalent of a tea party candidate in most European countries. In that sense, your question asking about left wing extremism is kinda moot since there basically aren't any left wing extremists. Radical communists is the closest thing I can think of, and there just aren't many commies in good ol' Uncle Sam.", "In the USA, leftists are usually supportive of *more* government services, and are comfortable with public (government) ownership of land. So seizing facilities from the government isn't consistent with their views. But why don't they seize facilities from big private corporations? Basically because the USA is extremely pro-corporate. They would not receive much support from the average member of the public, and none from the police. The general public doesn't even support protests that briefly interrupt freeway traffic to protest murder." ], "score": [ 5, 3 ], "text_urls": [ [], [] ] }
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5m2out
Why do cars only visible smoke while in idle when engine is cold?
When cars with cold engines are standing at the traffic light they create white smoke while in idle. When driving it doesnt smoke noticeable. How is this possible?
Other
explainlikeimfive
{ "a_id": [ "dc0fmi4" ], "text": [ "It's not smoke, it's particles of water vapour that are condensing and sublimating into minuscule droplets and ice crystals. The most plentiful product of combustion is water. It looks like smoke for the same reason you can see your breath when you exhale in the cold. When the car moves the water disperses in the cold, dry air more quickly." ], "score": [ 6 ], "text_urls": [ [] ] }
[ "url" ]
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5m2zcx
Why are some video games or updates released with major problems instead of being delayed?
Even with a deadline, surely they would understand that releasing what they've got will only hurt, no?
Technology
explainlikeimfive
{ "a_id": [ "dc0eaop", "dc0tyaj" ], "text": [ "Money. They need the income to fund the continued development of the game. This is a practice that software developers have been using for a very long time. It is not just games either but OS and network gear. They all do some amount of 'sell to fund' and it doesn't seem to hurt them because people still are buying.", "Let's say your boss gives you an assignment you need to get done by Friday. Thursday comes, and you know that it won't be done - you go to your boss and explain, but they insist that they need whatever you've got by Friday, because your assignment needs to go out to partner companies and other branches due to agreements and contracts. It works the same largely with games. For an example, let's go with Dragon Age 2. The game is *developed* by BioWare, but *published* by EA. EA is the \"boss\" in this scenario - they told BioWare, the \"employee,\" that they needed the game done by a certain release date. This is due to contracts with retail stores, advertisers, partners, etc. Despite the fact that the game was released with many flaws and a lot had to be cut, they had a strict deadline they had to meet, or the team could potentially be fired. The other reasons for set release dates can vary. They might want to get in the holiday rush, compete with a new console release as a sort of package deal, be bound by an exclusivity contract with a certain platform, or want to avoid crashing into other games they're developing (if a company has two blockbuster titles, it's better to release them apart than to have them both come out at once and have their audience split between them). If it's an online game, things like servers might come into play - you're paying for the server from a certain date, and if the game isn't out you're just throwing the money away. In certain very egregious examples, or if the developer and publisher are on good terms or are close enough, you might get a delay instead. If a game literally just will not work, they can delay it. Or if you have a smaller publisher that works more closely, they might understand. But the AAA companies tend to want what they want when they want it - and they have so much clout and name recognition that people will go out and buy it no matter how broken it is." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }
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5m301z
How did Humans create perfectly flat objects prior to the invention of advanced tools/machinery?
If they used necessary contemporary tools, how did they create those tools to be flat? EDIT: How were these primitive methods of getting a flat surface applied to large-scale constructions and objects? (i.e. furniture, construction materials, etc.)
Technology
explainlikeimfive
{ "a_id": [ "dc0en27" ], "text": [ "There are no *perfectly* flat objects being made today. Even the mirrors on giant telescopes have fluctuations on the surface. If one wanted to make a fairly flat stone surface with only stone tools available one could use water in a bucket and grind a disk (or whatever) so that the edges and surface are even with the still water. Metals can be pounded flat pretty easily. Polish them to see how flat they are and work at it some more if necessary." ], "score": [ 8 ], "text_urls": [ [] ] }
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5m32em
Why does our vision sometimes blackout when we stand up?
Biology
explainlikeimfive
{ "a_id": [ "dc0f08v", "dc0in9g" ], "text": [ "When you are lying or sitting your blood pressure rises slightly due to position. When you stand the pressure drops. Blood can pool in your legs making it unavailable for your brain. If this is happening often you should probably see a doctor. This isn't healthy.", "It's often caused by low blood pressure or dehydration. In the ER they test your blood pressure lying down, sitting, and then standing and if it changes too much then they do further testing. Usually the take away is you are dehydrated. Source: CMA/PA student/ER volunteer" ], "score": [ 9, 4 ], "text_urls": [ [], [] ] }
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5m3al7
How did they calculate votes in the early days of America without phones/Internet to convey the results. Wouldn't it lead to rigging?
Other
explainlikeimfive
{ "a_id": [ "dc0gvmt" ], "text": [ "Votes were tabulated on paper in each local polling place. Then the results from each place (signed by local authorities) were gathered and taken to a regional capital for totaling. Then, if necessary, *these* signed totaling sheets were gathered and taken to a bigger city for final totaling. Auditors could inspect the ballot collection and totaling and reporting, to ensure they had not been altered. However, fraud was common as paper is extremely insecure. A common form of fraud was to \"lose\" whole boxes of votes from an area known to favor a certain candidate, before counting." ], "score": [ 11 ], "text_urls": [ [] ] }
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5m3cn7
How does our "new organ", the Mesentery, work?
Biology
explainlikeimfive
{ "a_id": [ "dc0wtja", "dc0oon6", "dc106h0", "dc11vg6", "dc1159v", "dc0mf9r", "dc102s6" ], "text": [ "The mesentery got a promotion in name from supportive tissue (to the small and large intestines) to apparently the classification of organ. It's always been there. We've known about it for a long time. General surgeons who work in the abdomen cut and slice into the mesentery all the time when resecting bowel. It's not that mysterious in anatomy. In function, we think it provides structural tether to the bowels (anchors to midine of body inside belly cavity) and a soft tissue matrix to allow arteries and veins and lymphatic vessels to connect from bowel to central vasculature. Further organ-level physiology and function remains to be revealed. I'm a physician.", "The mesentery is a single mass of \"connective\" tissue that connects from the rectum to the small intestine beneath the stomach and to the backbone. It's function so far is to hold the intestines in place so they aren't sloshing around your abdomen. Whether it's an actual new organ remains to be seen as apparently most have a unique function and cell type distinguishing them from connective tissue or muscle etc.", "It's basically a fan shape (like the Asian ones which you flick open in Mulan) - the top part are your small intestines, the bottom bit is attached to a relatively small line across the back of your body. The fan bit is the mesentery. It anchors the small intestine (9m of tubing!) to a small area (about 15-30cm in length). It also conveys blood vessels to supply the small intestine along its course. The fan structure is then pleated like a Scottish kilt to fold into the abdomen. Having played around with it in the dissection room, it's a very smooth structure which allows some sliding and makes it difficult to tie knots in the small intestine. Source: Med Student trying to make sense of the world", "We've known about the mesentery for ages. If you think about the structure of your intestines, because they're so long they need bloody supply everywhere and you don't want them to get knotted up. The mesentery solves both these problems, its basically a massive sheet which is connected to the intestines everywhere to stop it folding it on itself and also providing a blood supply. The only reason this 'news' is surfacing is because it has been rebranded from supporting tissue to organ. The definition of organ is: a part of an organism which is typically self-contained and has a specific vital function. So I suppose you can call it an organ now, its vital function being supporting tissue for the bowels.", "It's basically the reverse of what happened to Pluto. Pluto got demoted while the Mesentery got promoted. Both do the same stuff they did before, they just have a different name.", "The brief article I read about it claimed that its function is not yet understood. Since no one really understood that it was an actual organ, no one has tried to study its function. Yet. You can bet that a lot of people will start doing so. It isn't often that PhD candidates and labs have a new organ to target. And once they understand what it is supposed to do, they can start understanding what might go on when it doesn't work correctly.", "How does one determine if something's an organ or not?" ], "score": [ 579, 143, 97, 20, 19, 16, 9 ], "text_urls": [ [], [], [], [], [], [], [] ] }
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5m3eo0
Why do humans like to kiss each other?
Biology
explainlikeimfive
{ "a_id": [ "dc0lpr0", "dc0ukjj" ], "text": [ "It releases hormones that feel good, such as oxytocin. Why does it release hormones like that? Because a kiss is a good way to determine the health and immunological compatibility of a mate. If it is good, hormone are released and you want to do it again, because you get a good response from the partner. This encourages mating with a good partner. Bad kisses do not release the hormone, and a single bad kiss early on can greatly diminish sexual attraction. A bad kiss can occur for a number of reasons, but an unpleasant hormone response serves as an early warning system for mating.", "In short: because of regurtiation! SciShow did a great video about this with plenty of sources. URL_0 Mothers used to chew the food for their children because adult saliva has enzymes thay breaks food down better than babies saliva. Moms transferred it in a kiss like fashion. Thus we felt that the touching of lips showed caring and nurturing. So they started doing it with the people they care for and then I guess the tradition stuck longer than the tradition of mom's spotting in their baby's mouths ;)" ], "score": [ 36, 4 ], "text_urls": [ [], [ "https://youtu.be/HZKvYbR3S9c" ] ] }
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5m3rz7
What allows heat to cast a shadow?
I stepped out into my garage and next to our heater, and I had the light on, and was looking at the wall and noticed the shadow being cast was barely visible, but it was there, and it was from the heat coming out. So, I'm just curious what of that is allowing it to cast a shadow.
Chemistry
explainlikeimfive
{ "a_id": [ "dc0m9px" ], "text": [ "Light is bent or refracted by whatever it passes through. In a room of uniform temperature, the light is bent the same way everywhere so you see a uniform image. Heat causes turbulence in the air so the light is bent in a more chaotic manner. You're seeing this as a wavy image in the shadow. This is also what causes mirages and the wavy pattern that one can see on top of a car hood when the engine is hot. This happens not only to light, but any part of the electromagnetic spectrum. Radio signals are disrupted in the morning and the evening, thermal inversion. As the air quickly heats up or cools down, the radio waves are distorted by the same effect. Thus causing a distorted signal and static in the radio program you're listening to at those times." ], "score": [ 10 ], "text_urls": [ [] ] }
[ "url" ]
[ "url" ]
5m3vr8
What's the difference between a quicksave and a normal save in a video game?
Is there actually any difference?
Other
explainlikeimfive
{ "a_id": [ "dc0mq23", "dc0tawz", "dc12dih" ], "text": [ "This is a huge generalisation and will work differently based on the game but generally a quick save on console will delete when you pick it back up whereas a normal save can be accessed at any time. On a pc a quick save would just mean you don't pick which save slot to use. Again, huge generalisation, that's just how I understand it in very broad terms. What game are you talking about?", "In most games, a quick-save is a single save slot that can hold one save file at a time. Quick-saving will overwrite whatever the last save state was, and quick-loading a save will only ever load the most recent quick-save. A normal save lets you create your own separate save file that can be recovered regardless of future saves or loads.", "Think of quick-saving as a bookmark you keep moving as you progress, and normal saving as leaving post it notes at various points throughout the book" ], "score": [ 63, 16, 9 ], "text_urls": [ [], [], [] ] }
[ "url" ]
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5m3w4r
How long should one use bulb mode to get a good picture of the stars in a completely dark setting?
Technology
explainlikeimfive
{ "a_id": [ "dc0mra5" ], "text": [ "There is the 500/600 rule. Basically take 600 (500 to be safe) and divide it by your lens' focal length, that will tell you how many seconds you can expose for without getting star trails (where you see the stars move). Now, that is for full frame (35mm) sensors, I believe Nikon sensors have a 1.5x crop radio, so it should be: 500 / (1.5 * focal length) = seconds If you are just posting to Facebook or Imgur, 600 should be good, but if doing prints, go with 500." ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
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5m3x63
How can Sony make an XBONE equivalent while being significantly smaller AND without a power brick?
Technology
explainlikeimfive
{ "a_id": [ "dc0mmtw" ], "text": [ "Look up Ben Hecks ps4 and xbox teardowns on YouTube, the main difference as I remember is the xbox has an oversized heat sink as a precaution against the overheating issues of the 360" ], "score": [ 3 ], "text_urls": [ [] ] }
[ "url" ]
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5m41hp
Why do essential oils dissolve paint?
I put a drop of lemongrass essential oil on my wood, painted bedroom vanity to freshen up the room and returned to it a few hours later only to find out that the paint was nearly completely dissolved! WHAT IS THE MEANING OF THIS ??? D:
Chemistry
explainlikeimfive
{ "a_id": [ "dc0ptvs", "dc0voh5" ], "text": [ "Paint is a liquid when you apply it and after a bit becomes a solid. What is happening is that the paint is dissolved in a solvent, which evaporates off as it is applied, allowing it to solidify. If you were to apply another solvent capable of dissolving the paint again, it will redissolve. The lemongrass essential oil was able to redissolve the paint.", "The chemistry rule of \"like dissolves like\": oils will dissolve oil paints and water will dissolve water based paints (think watercolors). It's because of the molecul's properties having affinities for eachother." ], "score": [ 10, 3 ], "text_urls": [ [], [] ] }
[ "url" ]
[ "url" ]
5m41lm
Why does being shot in the head actually kill a person
Biology
explainlikeimfive
{ "a_id": [ "dc0p71c", "dc0r181", "dc0o9as" ], "text": [ "So I'm assuming what you're asking is: why is it that a gunshot to the brain is so catastrophically fatal, when it's been shown that you can damage that organ and come out of it alive? Pointing to the example of [Phineas Gage]( URL_0 ), who survived an entire pole being thrust through his brain by an explosive charge. Well it's worth noting that gunshot wounds are particularly nasty injuries. It isn't the case that the bullet bores a [neat hole through the skull and then exits on the other side]( URL_1 ). The skull fragments follow the bullet into the wound and scatter. And the bullet itself deforms (usually) and tumbles through the soft tissue inside, shredding everything. And any material the bullet came into contact with (dirt, clothing, bacteria, etc) comes in with it. Now for an organ that's so delicate that it necessitated having it's own sealed container to protect it, this is generally extremely bad. It's a bull in a china shop scenario. It's not that the brain is destroyed with a single hit. It's more that the single hit is catastrophically damaging.", "Bullets do not pass through soft matter and simply make a hole the size of the bullet. [Here] ( URL_0 ) is a video of bullets passing through various softish items (warning, it's anti-gun propaganda). A bullet forces the matter to spread out in a fairly large diameter, with the damage depending on the speed, caliber, etc.. of the bullet and the firearm used. I have had the misfortune of arriving on the scene of a man who killed himself by shooting himself in the head. He used a small caliber hand gun, which he somehow shot himself with in the front of the skull (usually people will shoot themselves from the side). The exit wound was approximately four or five inches in diameter. That is a large area of damage to a very sensitive organ.", "So the bullet passes through the brain, slicing it's path. But it also traumatically impacts the surrounding brain tissue as well. It is like how slamming a sledge hammer into your brain can kill you, even if it doesn't penetrate. > Gunshot wound head trauma is the cause of an estimated 35 percent of all deaths attributed to TBI **[Traumatic Brain Injury]**. There is a 90% mortality rate, and whether or not you survive depends on variables like \"caliber of the gun, size and speed of the bullet, the trajectory and site the injury\". Further reading: URL_0" ], "score": [ 21, 6, 3 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Phineas_Gage", "https://boneclones.com/images/store-product/product-596-main-original-1415040160.jpg" ], [ "https://www.youtube.com/watch?v=emP5D9Klssg" ], [ "http://www.aans.org/patient%20information/conditions%20and%20treatments/gunshot%20wound%20head%20trauma.aspx" ] ] }
[ "url" ]
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5m41o5
how do airline alliances work
Other
explainlikeimfive
{ "a_id": [ "dc0olmp" ], "text": [ "Imagine you run a taxi business that runs from Point A to Point B. You take passengers between only these two points. You overhear that some of your passengers mention they like to travel from Point C to Point D with another taxi business on occasion. So you strike an agreement with the other business to allow your customers to ride on their route, and theirs to ride on yours, with streamlined service between cars, and even perks for riding with both. Overall, it's a way for airlines to expand their markets to other continents and continue to grow their brand in an international capacity, even if they don't have the resources to commit to actually flying the route themselves." ], "score": [ 7 ], "text_urls": [ [] ] }
[ "url" ]
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5m43bf
What are each programming language's real-world function?
Why use Java over C# or C++ in a specific scenario? This applies to even Python and Pascal as well Edit 1: I understand how software works and how a language is a different way to communicate to the computer. I understand that you can connect software languages to real-world languages (i.e. Grammar = Syntax) But I am wanting to know - during *insert problem here*, why should I use *insert language here* Why use one over another?
Technology
explainlikeimfive
{ "a_id": [ "dc0ocmb", "dc0zd5o" ], "text": [ "Programming languages are like real-life languages. There are times one may be easier to communicate in - like speaking French when you're in France - but for the most part they all communicate the same things. If you want to program a sensor to detect when you press a button on a remote and then do something, you'll probably have an easier time in C since it was designed to keep stuff like that simple. But if you don't know C, you can still use Java or C# or whatever you do know, it will just be expressed differently. So really, they all serve the same function to communicate what you want to do to the processor. The only things that change are how that's expressed and how familiar you are with how to express it.", "during **insert problem** here, why should I use **insert language** here? Here are some suggestions for common problems you may need to solve, as most would have a programming language that's more suitable than the rest. * You want to make one application that you can distribute which runs the same on all Mac, Linux and Windows versions? Your application doesn't need to do high performance or speed intensive things? **Java** * You want to write an application where you will compile and distribute different versions for Mac, Linux and Windows? Speed is important? **C** or **C++** * You want to do smart things like extract meaning from text, parse documents, compare documents for similarity, or experiment with machine learning algorithms? It's a program that you will run but you don't need to distribute it to others to run on their machine? Speed isn't that important? **Python** * Windows application only? **C++** or **C# and the .NET framework** * Android app only? **Java** * iOS app only? **Swift** * An app to distribute on Android and iOS? **Java** and **Swift** (you probably need to write your app twice, in fact double the work!) * You want a fast number crunching application that runs on Android and iOS? Use **C++** for the number crunching part and **Java** and **Swift** for the pretty part of the app (the *front end*). * You want an interactive website? **Javascript**, or **PHP and MySQL**, or **Ruby** * You're making a TV, a TV remote, an MRI machine, or a car diagnostic system (these are called embedded devices)? **C** Of course every language can do every operation, but some have better support for some tasks than others. I do not intend to imply that this or that language can't do this or that task. Rather I am trying to illustrate what I would recommend from a neutral point of view to a person who has a precise task in hand and has developers in all languages at his/her disposal. For example Python has very helpful libraries for interpreting text. So it would be the number 1 recommendation if you have to parse documents, etc, while doing this in C would be painful. Market share is also a factor. For example Java has many flaws as a programming language which Microsoft tried to fix in C#, however Java is still more popular than C# and it's also the language of choice for Android. This makes it a more natural choice for many tasks, which in turn increases its popularity! If you try to go against the flow and do things in an uncommon language, you encounter problems as you can't Google for help so often, or may find that a library (such as machine learning) isn't as well implemented. All other things being equal, a widely used language is a better choice." ], "score": [ 8, 4 ], "text_urls": [ [], [] ] }
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5m45o8
Why does starchy food stick so hard onto kitchenware?
Chemistry
explainlikeimfive
{ "a_id": [ "dc0u166" ], "text": [ "Starch is used as poster glue. The gluten in wheat additionally makes the strands of starch molecules link together to make a tough solid." ], "score": [ 5 ], "text_urls": [ [] ] }
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5m46ua
Why do some people find things like dolls and clowns scary?
Many people I know (usually including me) get "eery vibes" from typically harmless things like dolls, clowns and abandoned buildings. Is there a specific reason why these things appear creepy to people?
Other
explainlikeimfive
{ "a_id": [ "dc0repu" ], "text": [ "As far as dolls and clowns go, the scary feeling might be due to the \"uncanny valley\". This refers to the observation that the more an inanimate object has human characteristics (in appearance and movement), the more an observer feels an affinity for it. For example, a stuffed animal elicits feelings of warmth and cuteness. A robot that looks more human inspires people to think of it as more human and feel more comfortable with it, even to like it more. But: there's a limit. At some point, when the thing starts to look very close to human, but slightly off, the feelings of affinity turn to feelings of revulsion, disgust, and fear. This is likely because it starts to look like it's *wrong*, that it's a diseased or menacing person. Things that this applies to are said to fall into the uncanny valley. \"Valley\" comes from imagining these ideas as a chart. On the X axis, the further right means the more human-looking. On the Y axis, the higher numbers mean greater affinity and feelings of warmth. The line thus charted rises as it goes to the right, until it abruptly falls down to its lowest point. Then it soon rises to its highest point as you get to the maximum of looking human and the maximum of feelings of affinity --for those who actually *are* human. Thus there's visually a valley in the data points. You can google \"uncanny valley\" and it will probably be easier to see this chart than for me to have explained this. So, clowns look human, but slightly wrong. Same with dolls--feelings of cuteness arise and are then snuffed out as you realize you're not looking at an actual baby, and the dead doll eyes evoke corpse more than cuteness. Zombies do this too -- it's one reason why the shuffling zombie gait is disturbing. At a distance it seems like a person, but as it approaches, you realize there's something wrong, and tense up to judge what it could be, only to realize that it's a dead thing. Another hypothesis as to why clowns may be scary is that, with a face covered in makeup, including a huge fake grin, you can't accurately assess what emotions the person dressed as the clown are actually feeling. You can't see if there's a danger to you that is being obscured by a mask." ], "score": [ 15 ], "text_urls": [ [] ] }
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5m473n
How does SSL Certificates work exactly?
How do they encrypt the data exactly and couldn't eventually be "crackable" Also, without the S. How would someone be able to gather the data once they're on your network / Host?
Technology
explainlikeimfive
{ "a_id": [ "dc0x5ih", "dc0upwf", "dc11lhw" ], "text": [ "Say a website is using an SSL certificate. That certificate is just something that says something like \"I am reddit and nobody can impersonate me\". Now obviously SSL certificates websites offer up can simply be copied, so to authenticate themselves, the certificate includes a public key, and they have their private key which isn't shared, and the keys are mathematically linked, but the one can't be derived from the other (feasibly) they can only be created together, and the odds of you randomly generating an already existing key is miniscule, and when something is encrypted with one key, the other can decrypt it, and vice versa. So what's to stop websites from simpy generating their SSL certificates? Nothing, so to actually prove that the website you're connecting to is the real deal, they have their certificates signed by a higher authority, and you automatically trust that authority, even though you have no idea because it comes preloaded in your browser. It's like government issued IDs, if someone shows you their driver's license, you have reasonable cause to believe their age on that card is the truth. The certificate authority signs other people's certificates with their own private key, which is also not shared, but can be verified with their public key. So how does signing work? It's basically hashing and encrypting put together. Hashing is a function where you take a block of data and trim it down to a unique result that it isn't feasible to find a different block of data that returns the same result, so hashing can't (generally) be broken. Then it works like this, websites have their certificate, the certificate authority hashes it, and then encrypts the hash with their private key, which in turn spits out the digital signature Now when you connect to a website, they serve you their signed certificate, which includes their public key and their digital signature which was signed by the certificate authority's private key, and you have the certificate authority's public key already preloaded in your browser. You take their certificate, hash it yourself, and then you take their digital signature, decrypt it with the certificate authority's public key. If they both match, then they're legit. Now this only proves that the website you're connecting to has a certificate that's correctly signed by a certificate authority. To prove that it is actually them you're connecting to, they send a verifiable block of data signed with their own private key, which you test with their public key. So at the end you have reasonable cause to believe that the website you're connecting to is who they say they are, and their story is confirmed by a higher authority at the same time. At this point you know you're actually connecting to the website you're trying to connect. So how is any further data you exchange protected? You generate a key, this time a symmetric key that's used for both encryption and decryption. You encrypt it with the website's public key and send it, and the website decrypts it with their private key, which only they can. This key can't be compromised because you confirmed the website's certificate (which contains their public key), and only that website can decrypt anything you encrypt with their public key, so at the end both you and the website have a key that was encrypted during transmission and it's used to encrypt any data you exchange from this point on. Which brings another question, after the certificate is verified why can't we just continue encrypting stuff with their public key? Why do we have to generate a symmetric key and send it to the server? Because while you'll be able to send data securely to the server, the server in turn can't because anything they encrypt with their public key will be readable by anyone, and also because the algorithm used for the public/private key encryption is very slow, so it's only used at the start, after a which a faster algorithm is used. What algorithm to use is decided during the initial phase by both the browser and server telling each other their capabilities. For some real world example, let's take reddit. If you click on the top left green locked key sign, you should be able to see reddit's certificate, and that it's signed by DigiCert Inc. If you go into more detail and view it, you should be able to see reddit's public key, and their digital signature signed by DigiCert Inc. Edit: Minor correction, thanks /u/a_2 Edit2: Added another reason for using symmetric keys for encryption, arguable the main reason.", "It's like passing encrypted notes back and forth to a friend in class. You use a cipher so the teacher or other students cannot read the message. Except your 3rd friend who is really good at math, created the cipher and is the only one who can verify if the note that you received was actually sent from your friend. It should be noted that you can trust this 3rd friend to verify the notes correctly because you guys have been best friends basically forever, and everyone else trusts him too because he is so trustworthy. Edit: As a follow-up to your other questions, SSL is technically crackable, it's just not feasible to do so because with modern SSL, each packet would take days or weeks to crack. So the more feasible thing to do is setup a proxy server that intercepts SSL traffic, decrypts it, records it, and re-encrypts it the same way so the receiver never knows it was intercepted in the first place. Businesses do this to spy on their employees encrypted traffic, and the NSA basically does this at major internet relay points so they can spy on everybody. SSL just makes it so the average computer nerd can't spy on you, you have to have money to do it.", "This may no longer be the case, but this style of encryption was explained to me like this. Imagine you have a message and you want to send it to your mate. You have a box with the message inside. You add a padlock to the box and lock it, then send the box to your mate. Your mate then adds his own padlock to the box and sends the box back to you, now with both locks locking it. You remove your padlock from the box and send the box to your mate (now only with their padlock locking the box). He removes his lock, opens the box and reads the message \"FU MFER!\" So, you've exchanged a message, no one in between was able to intercept it, and neither of you had to give each other sensitive stuff like keys and passwords. Replace the box with a packet of data (or a frame or whatever the term the network bods are using these days) and the padlocks with encryption and it's sort of the same thing." ], "score": [ 51, 29, 4 ], "text_urls": [ [], [], [] ] }
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5m474v
What is a Deep Space Radio Wave And How Does It Effect Us As A Species?
Technology
explainlikeimfive
{ "a_id": [ "dc0upky" ], "text": [ "A deep space radio wave is just what the name describes - a radio wave coming from deep space (one has recently been pinpointed to come from another galaxy some 3 billion light years away, which I assume is why you're asking this question). They're short, they're rare, they're mysterious, and nobody knows exactly what causes them - but knowing which galaxy sent one out helps us determine that. As for how they affect us as a species, they don't right now, and they likely won't ever, really. It's just one of space's mysteries and we like solving those mysteries - and maybe we'll get some new insight on physics that allows us to build all sorts of crazy shit. On the other hand, maybe it's \"just\" a remnant of a star crossing the event horizon of the supermassive black hole at a galaxy's center, which won't be very practically applicable at all. On the other hand, maybe it's a giant planet-destroying space laser, and the more of these we keep seeing, the more fucked we are. But it's probably not that." ], "score": [ 24 ], "text_urls": [ [] ] }
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5m4h3t
How is Voyager 1 still sending NASA information from interstellar space, 39 years after it's launch?
Other
explainlikeimfive
{ "a_id": [ "dc0ujzk", "dc0t8s4", "dc0vg8u", "dc0xoo4", "dc0rb1e", "dc0tfyq", "dc0xpl1", "dc0yrd1" ], "text": [ "Some other commenters have covered really well how it's still *transmitting*, so I'll cover a bit of how we're *receiving*. The signals Voyager transmits are really weak when they get here, and there's a lot of noise in the electromagnetic spectrum, so the signals are way weaker than the noise. \"But wait\" you might say, \"if the signals are weaker than the noise, how can we hear them?\" It's a challenge comparable to hearing your friend whispering from across a room full of people talking. We came up with a really clever way to hear them, though. Basically, it's like this: we take two giant receiver antennas. We point one directly at Voyager, and one just a fraction of a degree off. Both receivers get all of the noise from that area of the sky, but only the first gets Voyager's signal as well. If you subtract the noise signal from the noise + Voyager signal, what you've got left is just the Voyager signal. This methodology is combined with a lot of fancy error correction coding to eliminate reception errors, and the net effect is the pinnacle of communications technology: the ability to communicate with a tiny craft billions of miles away. edit: typo", "Its using radios waves powered by a radioisotope thermoelectric generator (Expected to power the satellite till 2025). It have 12 ft parabolic antenna. The signal is received by Deep Space Network located in California,Spain and Canberra, Australia. The other countries with DSN are ~~Europe~~, Russia, China, India, and Japan. It take a while for the radio waves to get here (~~I'm guessing more than a Day~~.**EDIT** As per u/TankerD18 its takes about 19 hours, 7 minutes, and 28 seconds. So its takes less than a day). The flight control always keep the antenna oriented towards the earth. You can see real time status [HERE]( URL_0 ) and Weekly reports [HERE]( URL_1 ) . Edit: DSN operated by European Space Agency (known as the European Space Tracking (ESTRACK)) is scattered across Australia, Belgium, French Guayana, Three in Spain, Sweden, Portugal, Argentina.", "For anyone interested in seeing, in real time, status of communications by the Deep Space Network (DSN), this is really cool: URL_1 I used to leave that up as a screensaver at work, in full screen mode. In fact, as I type this, antenna 63 in Madrid is communicating with Voyager 1 (probably the contact details of some alien life form, well, one can hope)! Edit: I just realized I could also post the link that shows the tracking schedules of the Voyagers... it's maintained quite well: URL_0 Edit 2: Seems like another commenter also shared the same resources :)", "You know how radioactive stuff is supposed to be radioactive for a long time, and radiation \"cooks\" things? It turns out that if you take something that's really radioactive and has a long half-life, you can use that \"cooking\" to generate electricity for half a century. This is called an RTG (Radioisotope thermoelectric generator), and Voyager 1 was launched with one decades ago. It's not perfect - the plutonium core has decayed enough to force NASA to shut down some instruments for lack of power - but it still works. The same type of generator powers the Curiosity rover, and many other spacecraft. As for radio, that's a little more straightforward: we have really big receivers and powerful transmitters on Earth, as well as really smart error correction. EDIT: Here's a picture of a similar plutonium core - it actually glows red-hot: URL_0 So, Voyager will continue running until its RTG stops making enough power, we give up on it, or it gets hit by a rock.", "Radioisotope thermoelectric generators which make electricity from the temperature differential created by the decay of radioactive material. In short, nuclear batteries.", "Nuclear powered machine sending information over radio which we listen for using very large antennas which are part of the deep space network. You can actually watch the dsn connect to these machines over Twitter at dsn_status - pretty amazing", "What do we learn from these signals they send us?", "Sub-question: I recently learned that there are still ~10 people on the Voyager team. What do they do? I'm assuming they work on signal processing algorithms and such." ], "score": [ 3372, 277, 216, 163, 129, 27, 6, 6 ], "text_urls": [ [], [ "http://voyager.jpl.nasa.gov/where/", "http://voyager.jpl.nasa.gov/mission/weekly-reports/" ], [ "http://voyager.jpl.nasa.gov/mission/weekly-reports/", "http://eyes.nasa.gov/dsn/dsn.html" ], [ "https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#/media/File:Radioisotope_thermoelectric_generator_plutonium_pellet.jpg" ], [], [], [], [] ] }
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5m4lnt
Where are everyone's passwords stored in websites?
Technology
explainlikeimfive
{ "a_id": [ "dc0secu" ], "text": [ "If you're asking about when your browser asks you if you want to save a password, it's saving it inside your browser's memory or inside your browser company's cloud-based databases. If you're asking about when you have an account on some website, they store all of your account information inside a database, which is basically just a fancy spreadsheet." ], "score": [ 4 ], "text_urls": [ [] ] }
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5m4mzf
How does an LED change colors?
Is there any mechanical or physical change? Are there multiple different colored LEDs in each "bulb" that are illuminated in various configurations to produce each color (similar to an RGB display)? Or can one unit actually produce light of variable wavelengths?
Technology
explainlikeimfive
{ "a_id": [ "dc0tofc", "dc0u2jt", "dc1buyc", "dc10e9v", "dc0v6c4" ], "text": [ "A color changing LED isn't one LED in a package but three LEDs along with a small computer to drive them. The LED is made up of red, green and blue LEDs each of which can be controlled by a microcontroller. Since the two legs on the LED that supply the power are connected to the microcontroller and not the LED elements a current limit resistor is not required. The microcontroller is able to turn each of the colors on or off, so if the red LED is turned on then the output from the color changing LED is red. When the blue LED is turned on it is blue, if both the blue and red LEDs are turned on then the color changing LED is a shade of purple (called magenta). Similarly combining red with green gives yellow and blue & green gives cyan. Although the color changing LED uses the six colors mentioned above, it slowly changes from one to another. This is still done using the three basic red, green & blue elements. If the red LED is combined with the blue LED, but the blue LED is only driven at 50% of its normal brightness then a color half way between red and magenta is generated. Whilst the red LED is left turned on, if the blue LED is slowly taken from 0% brightness to 100% brightness then the color will gradually change from red to magenta. If a standard LED is turned on and off very quickly, say 100 times every second then as far as the human eye is concerned it looks like it is constantly on. If the amount of time the LED is on for is the same as the time it is off for then it will be on for 50% of the time and 50% of its full brightness. This same method can be done with the three LED elements inside the color changing LED. This means it is possible to combine any amount of the red, green and blue to give the desired color. Looking once again at the change from red to magenta, if the blue LED starts mainly turned off, goes to being on and off in even amounts and then to mainly being on then the the color will change as required. [Source]( URL_0 )", "Masters Electrical Engineering. Most RGB LED have all three colors in them. You then light a specific one my applying power to the color you want. If you look at large LEDs that can do RGB, they have 4 prongs coming off. You then power the prong you want an bam! Color. One for ground, and then each color gets a prong. If you make a super small RGB LED and then combine a bunch into a massive array, you get a tv. You can do it with a single light source, then apply a polarizing filter. The filter is controlled by a small current. This can produce colors as well and is the idea behind LCD displays.", "Wow thanks everyone! That would have taken me hours of googling and synthesizing information from multiple sources. This is more than I wanted which is even better.", "As most have said, they typically contain a red, green, and blue LED in one package. Just wanted to point out: this is also how a TV or computer monitor works. There is a red, green, and blue pixel in a pattern over and over. By controlling each color, you can basically make any color.", "An older style of multi-colour LED is the type that have a red and a green LED in the one package. They usually have three legs. Despite having a red and green LED, they can actually display a third colour. Light them both and you get yellow, because red and green light combined give you yellow light." ], "score": [ 110, 50, 4, 4, 4 ], "text_urls": [ [ "https://www.kitronik.co.uk/blog/how-color-changing-leds-work/" ], [], [], [], [] ] }
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5m4n2j
How does the golden ratio follow the fibonacci sequence?
Mathematics
explainlikeimfive
{ "a_id": [ "dc0sugd", "dc0xoxk" ], "text": [ "Take two successive numbers of Fibonacci sequence, 13 and 21 for example. 21/13 will be close to golden ratio. Kepler proved that limit of ratio of two infinitely large successive Fibonacci numbers is golden ratio, or lim{n - > inf} F{n+1}/Fn = phi. EDIT: More general form, as wikipedia says, is lim{n - > inf} F{n+a}/Fn = phi^a, and it leads to phi^{n+1} = phi^n + phi^{n-1}.", "Well, let's look at what the golden ratio IS. It's the solution to the following equation: 1/phi + 1 = phi The fibonacci sequence can be written as: f(n) = f(n-1) + f(n-2). From this we can construct a function g(n) = f(n+1)/f (n) which becomes g(n) = [f(n) + f(n-1)] / f(n) = 1 + f(n-1)/f(n). This then turns into g(n) = 1 + 1/g(n-1). Why... that's very close to the definition of the Golden ratio! As it turns out, g(n) is a convergent sequence, which means the higher n gets, the closer to the golden ratio you get! And this isn't restricted to the Fibonacci sequence. Start with ANY two positive numbers... so long as it follows the rule f(n) = f(n-1)+f(n-2) it will converge on the golden ratio in the exact same way." ], "score": [ 14, 4 ], "text_urls": [ [], [] ] }
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5m4t6n
What is an axiom?
Can axioms be proven to be false? (mathematical axioms for instance)
Mathematics
explainlikeimfive
{ "a_id": [ "dc0u42g" ], "text": [ "Every theorem has a proof, an answer to the question of \"why is that true?\". For axioms, the \"why?\" is a non-provable value statement. It's true because we want it to be true, rather than due to any particular proof. In general, axioms will be so simple and fundamental that they are clearly never going to be discovered to be proven false entirely, as a blanket, but the concern is that when you claim that an axiom is true for all ___, you risk there being a REALLY obscure ___ which when the axiom is applied, proves a contradiction. If you can prove a contradiction, you can prove anything (proof of A: suppose not A - {contradiction} - therefore, A) - so when selecting our list of axioms, we seek ones that are so carefully constructed as to not permit the proving of any contradictions. Mathematics is based off of the axioms of ZFC. These are a minimal set of axioms which for over a hundred years have been scrutinized by mathematicians - and maybe there is a way to use them to prove a contradiction, but nobody's found one, and a whole lotta people have been looking, so they make for some pretty solid ground. Before that, we had naive set theory which said that for every assertion about a thing, there exists a set of things for which that assertion is true. It seems simple enough compared to ZFC, but it's just not good enough because it permits proof of contradictions. See [Russell's Paradox]( URL_0 )." ], "score": [ 3 ], "text_urls": [ [ "http://enwp.org/Russell's_Paradox" ] ] }
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5m4ty2
What causes irrational fear?
What causes people to feel irrationally afraid of certain things? Spiders, for example: small, mostly harmless and unobtrusive, yet just the sight of one can paralyze a grown man with fear. It makes no logical sense, so what's the origin/cause/purpose of it from a biological standpoint?
Biology
explainlikeimfive
{ "a_id": [ "dc0vwi6" ], "text": [ "Anxiety is a good thing. It's what kept us alive and what gave us our fight or flight response. So it's extremely useful and vital. However in a world where sleeping with spiders and sleeping in trees no longer exist, our Anxiety still does. Our brains haven't really caught up with our lives. And the complexity of our brains can give us odd fears that don't entirely relate to something primal but have similar roots of fear." ], "score": [ 9 ], "text_urls": [ [] ] }
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