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{ "a_id": [ "ehvoi1q", "ehw6l28", "ehwbaha" ], "score": [ 24, 7, 3 ], "text": [ "The “black box” isnt a single system, its made up of separate recording devices through the aircraft.\n\nIt doesnt record EVERYTHING, only the Time, Engine specifics and altitude, the other records cockpit voice and conversations.\n\nThe data recording systems on aircraft flights saves burst data, meaning it only starts actively storing information on systems during burst periods of input, as soon as altitude. Flight pattern. Engine function or flap position starts changing quickly, like a problem has occurred, it begins capturing the movement and data.\n\nIt doesnt record every aspect of the flight or its systems. Only those that are changed via pilot manual input basically.\n\n\nIts like trying to take a 30 second movie trailer and building the entire movie from it.\n\nEdit: spelling ", "So much bad info in here. On commercial planes, there's 2 'black boxes' (actually painted orange, not black, but the name stuck): the Flight Data Recorder (FDR), and the Cockpit Voice Recorder (CVR). Optionally there's a 3rd device, the Quick Access Recorder (QAR) but this is not always used. \n\nThese recorders are constant recording devices, recording up to thousands of data points. On the CVR, there are multiple high resolution audio channels in the cockpit, including each flight position and general cockpit noise. On the FDR, things are also tracking aspects of the flight, engines, attitude, etc. \n\nWhy can it take so long to read out? Because they are recovering vital data after a massive impact that usually shreds the plan to bits. The boxes have to be found first (e.g. for the recent Amazon flight, they were buried in mud, but they could also be deep in the ocean, or in supper-difficult terrain to access). Once found, they have to be very carefully preserved and shipped to properly equipped research labs (only a handful in the world). When the devices are relatively unharmed, and assuming modern solid-state digital recordings (versus the ancient tape recordings), they are usually downloaded, read, and validated within a couple of days or arrival at the lab. But then they have suffered a massive impact (e.g. over the defined 3400G limit, or 1100C fire for 30 mins), then the lab experts often have to extract individual data chips and then reconstruct data by very low-level recovery techniques.\n\nWhen you put it all together, these guys do an awesome job, and the lessons learned from the last minutes of a stricken flight make the skies safer for all of us. ", "If they find the black box in tact they can get the data pretty fast. But interpreting it isn't that easy. There isn't enough data to build a complete simulation of what happened. And even if there were it wouldn't really be cost effective to develop a simulator program to reliably make sense of it. Easier to just parse it and reconstruct what happened manually.\n\nThere are other systems aside from black box that they recover data from. They aren't necessarily water/damage proof. I work for a company that makes engine control units. If the unit is in tact we can pull the data off of it with our normal engine maintenance software easily.\n\nBut in the past they've brought water logged ECUs to us, and we've had to spend weeks recovering the data from them. We have to pull off the memory chips then come up with some hardware/software to be able to recover the data from them. We don't have this equipment laying around because it happens so seldom.\n\nOn top of that, even if you can get all the data immediately and it seems obvious what went wrong you're still going to want to finish your investigation and account for all factors. Does the physical damage agree with the aircraft data? If the problem was an engine failure, were there other factors that led to that engine failure? You're going to want to have all the answers before you start publicizing your findings." ] }

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{ "a_id": [ "eixvkoq", "eiz3kdl" ], "score": [ 6, 2 ], "text": [ "Freckles are actually over active melanocytes (cells responsible for melanin production.) when you tan you are also increasing the amount of melanin you have as a whole , while freckles do not do that. The reason freckles can appear on either unexposed or exposed skin is because it is less dependent on the sun. Sometimes melanocytes just go into overdrive producing melanin.\n\nEdit: I was wrong about tanning increasing the amount of melanocytes ", "Whether you tan or freckle is determined by genes. Some people have the freckle gene and will freckle. \n\nYou have melanocytes everywhere so you’ll develop color everywhere, which is why people freckle in areas not exposed to the sun and why people who have naturally darker skin won’t be ghostly white in areas not exposed to the sun. Sun exposure makes you darker or makes you freckle *more*. But you’ll still have a baseline of freckles and melanin in places where the sun don’t shine," ] }

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{ "a_id": [ "c3xk1mo" ], "score": [ 4 ], "text": [ "It was essentially to secure more power for himself and destroy anti-Mao sentiments. It was also an attempt to unify the country after a couple of failed nation building campaigns (Great Leap Forward being one of the bigger failures). He stated that capitalists were becoming more powerful, and could turn China away from communism. So he instituted many policies that would denounce capitalism, intellectuals, traditionalist, or really, any person that falls under the broad category of possibly forming a coup against him.\n\nIn the end, the Cultural Revolution was yet another failure. The country was set back yet again, many academic texts were lost, many people died (particularly party members that were alleged to be \"counter-revolutionary\" and students that were sent out of the city to \"further the cause\"), and lack of social, economic and political progress." ] }

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{ "a_id": [ "ejvx8bx", "ejvxezg", "ejvxo8t", "ejvxrna", "ejvxxfk", "ejwedie" ], "score": [ 7, 2, 2, 2, 2, 2 ], "text": [ "Refresh rate - how often the screen itself is refreshed. It is completely independent of frames per second since you still have refreshes even with a static image.\n\n & #x200B;\n\nFPS - How many frames per second of a moving picture are displayed.", "If you have a TV or monitor it could refresh at say 60hz so 60 times a second it refreshes the image with whatever the source tells it too, PC, DVD or Blu-ray etc.\n\nFrames per second is how many different images are being sent to the monitor or TV every second.\n\nThe two do not have to be the same so in the example of a TV refreshing 60hz the source may only send 30FPS to the TV. This causes the same frame to be refreshed twice.\n\nMostly things sync up so the TV may change and refresh 30 times a second. If it's a computer monitor they tend to match the output from the GFX source.", "Refresh Rate is how fast the individual little cells that make up your screen can refresh, or flicker at. Refresh rate is the maximum rate at which your screen could keep up with a graphics card output.\n\nComputer or console graphics cards are designed to calculate and shove pixesl into what's known as a frame buffer. The graphics card gets texture data, model geometry, lighting, viewpoint info (i.e. what you're looking at), movement etc. from the CPU, RAM etc. and can calculate - for each pixel in the frame buffer - what colour and brightness it should be based on everything going on in the screen view. Depending on how fancy your graphics are set to, how much is going on in your game etc. will impact how fast the graphics card can update this frame buffer. Once a frame is completed, the GPU flicks a switch and tells the HDMI port to send this to your monitor. If there's too much going on in your game, your GPU is only updating the frame buffer maybe 20 or 30 times per second. \n\nSo that means if your monitor is running at 72 Hz, it will display the same frame for 2-3 updates - i.e. until the next frame is ready from the GPU. This results in only a 20-30Hz screen update. More frames per second is smoother, more lifelike. Some monitors may be able to interpolate or \"smooth\" between successive frames to make it look better. \n\nObviously if you have a really good (or multiple) GPU and you're getting 100+ fps, but only have a 60 Hz monitor, you're not getting full potential out of your rig. If thats the case, you should crank up the graphics quality of your game, why not?", "Hertz (Hz) is a unit that means that something is happening a specific amount of times per second, so technically *x* FPS and *x* Hz are the same thing.\n\nHowever, FPS typically refers to the number of frames that an application can process per second, whereas refresh rate is the number of frames that the monitor is capable of displaying per second. They don't always match, and most monitors still operate at a fixed refresh rate. \n\nIf a monitor has a refresh rate of 60 Hz, it means that the monitor will always update the image it displays 60 times per second, regardless of whether the application can keep up or is in fact faster. If an application is too slow to compute the next frame, the monitor will simply show the same image during the next refresh cycle. If the application is too fast, then the monitor will not be able to present every frame and some computed frames will be lost.", "The frame rate is the rate at which the graphics card can render an image, and the refresh rate is how often the screen can actually change the image. So if you have a frame rate of 120 and a refresh rate of 60, the screen will only show every second image it rendered to the screen. The other way round, if you have a refresh rate of 60 Hz and just 30 fps, the screen will repeat every image once. And if your frame rate is somewhere inbetween, say 45 fps and 60 Hz, your screen will occasionally show a half finished image, an effect known as [tearing](_URL_0_). Which is why it makes sense to enable V-Sync if you can't reliably reach 60 fps with a 60 Hz screen, which synchronizes the graphics card with the refresh rate of the screen so this doesn't happen. So instead of dropping from 60 to 45 Hz, it'll go down to 30 Hz if the scene on the screen is too demanding.", "FPS is the number of frames that your CPU/GPU is calculating per second. Refresh rate is how fast your monitor is refreshing per second.\n\nNow you may think that FPS higher than your refresh frame is useless but the thing is that higher FPS will still reduce your input lag. So even if you have a 60 HZ monitor, you will still notice a huge difference between playing on 60 fps and 200 fps.\n\nV-sync will cut your frames to the monitor refresh rate; I suggest turning that off." ] }

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[ [], [], [], [], [ "https://upload.wikimedia.org/wikipedia/commons/thumb/0/03/Tearing_%28simulated%29.jpg/1280px-Tearing_%28simulated%29.jpg" ], [] ]

{ "a_id": [ "cp1alfc" ], "score": [ 4 ], "text": [ "Facebook gives you the option to use your email address book to look for people you know. If someone who has your email used this option, Facebook now knows there used to be a connection between you two. This other person might not have sent you a friend request, but Facebook still knows, so it might suggest this person to you." ] }

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{ "a_id": [ "cclqhbc", "cclu2wj", "cclyva6", "ccm5kpz" ], "score": [ 68, 3, 2, 2 ], "text": [ "I believe that a lot of it is not actually fat under your skin, but fat around your guts that causes them to stick out. This is actually a different kind of fat. The stuff under your skin is called *subcutaneous fat,* while the stuff around your guts is called *visceral fat.* They are actually different types, and can be affected by your *hormones*- chemicals in your body that tell it what to do.\n\nStress, a lack of exercise, genetics, diabetes (too much sugar in your blood), and other factors can cause an increase in the fat around your guts relative to fat under your skin, which is why some people can be skinny and have big bellies, and others can have a lot of body fat but not have their tummies stick out so much.\n\nYour skeletal system and muscles keep it from sticking out of your back, although if you get enough fat on your body, you can get a decent amount of 'back fat' also.\n\nThe actual distribution of fat underneath your skin is, as I understand it, mostly determined by your genetics. This means that 'spot reduction'- the idea that you can lose fat in a specific area more than others say by exercising muscles near that far more- is a myth. Some people's genes make them put more of their fat in their faces or stomachs or arms or legs than others. We're all a little different in that way.\n\nSitups, for example, won't reduce your tummy fat in a larger proportion than anywhere else on your body (or at all if you don't burn more Calories/kilojoules {energy} than you eat), although they can strengthen muscles that hold it in more. And doing squats or lunges won't take off leg fat, either.\n\nSorry if I'm going a little too far in explaining some terms- they did say EXPLAINLIKEIMFIVE, but more importantly, some terms may be difficult for people whose first language is not English.", "You might want to revisit the assumption in your question by reviewing some of the stuff on this website.\n\n_URL_0_", "Evolution has determined that the best place to carry excess fat for a human is around their waist. \n\nThe more you get, the more its distributed other places, but that is where we can best carry the majority of it.\n\n", "[backs dont get fat? NSFL](_URL_0_)" ] }

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[ [], [ "http://www.peopleofwalmart.com/" ], [], [ "http://myskinnybuns.files.wordpress.com/2011/12/back-fat.jpg" ] ]

{ "a_id": [ "d2uud2x" ], "score": [ 3 ], "text": [ "Squeezed out of a shaped hole, like toothpaste is squeezed out of a round hole. Then sliced off in bits and cooked. " ] }

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{ "a_id": [ "dsbvrmy", "dsbx8dz", "dsc2e9n" ], "score": [ 2, 3, 2 ], "text": [ "They pretend to be at war for a day or two. Use fake bullets and rockets. Sometimes bigger countries also use fewer troops / guns to train for more complicated situations ", "This is a very vague question, but we'll try to take a crack at it.\n\nFor large-scale, military-only exercises, the participating units are put on a war footing and made to perform tasks they normally would during a conflict against either imaginary/simulated enemy targets or friendly troops playing the role of enemy combatants. Indirect fire has real ammo, so they fire on imaginary targets, friendlies playing hostiles necessitate blank rounds to be used. The troops are positioned as they would during a conflict (forward camps, usually) and supplied similarly, with MREs and limited resources.\n\nFor those exercises that want to also simulate civilian operators acting in concert with military forces, those civilian units or organizations (for example, fire crews, police forces and political chains of command) are also put on the same alert as they would under a full-scale conflict and perform simulated tasks and operations similar to those they would in wartime. For fire crews, this may include buildings set on fire in a manner to simulate bomb strikes, police may train to counter enemy special operations forces, and political command chains may face similar dilemmas as those in wartime. Medical organizations may be put on high alert and perform simulated complicated or mass casualty operations.\n\nNormally, all organizations in a country won't hold war exercises (or war games) at the same time, but the results of these can be combined and/or extrapolated to provide a relatively accurate overview of the capabilities against certain levels of enemy action both in the field and on the home front.", "Often by wargaming through systems of the sort you can buy from board game shops; just on a much more complex level and with more accurate information. Computers may be used to assist.\n\nThere is a thing called a 'command post exercise' where officers will be in a room and send orders out to virtual units, then be informed of what happens. The larger ones can have hundreds of players.\n\nThe US Naval War College has run many big ones over the years: here's some information on their site: _URL_1_\n\n[Just be careful that you don't make your RL adversary think you're not playing a game.](_URL_0_)\n" ] }

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[ [], [], [ "https://en.wikipedia.org/wiki/Able_Archer_83", "https://usnwc2.usnwc.edu/Research---Gaming/War-Gaming/Documents/RAGE/Gaming/-Global-Title-X-Series.aspx" ] ]

{ "a_id": [ "ertdkik", "ertyild", "eru4gta" ], "score": [ 2, 2, 7 ], "text": [ "There isn't good evidence that it is dangerous at levels coming from plastics containing food/drink. It affects the endocrine system, but it's fairly weak in that action. The EPA and the European Food Safety Authority both say it shouldn't be a problem at normal exposure, but some groups still express concern and studies trying to get more data are ongoing. BPA containing plastics leach it out more when it is warmed, so microwaving will increase leakage.", "Knowing the nature of business and the power of Money, in this Subject, the best course is NOT to use anything that has it in it-like bottled water. I always carry an Army Canteen, with my OWN filtered water- and never a bottled water, not even for the dog;; check that espy not for the dog.", "Picture a steel chain in your mind. Flexible, strong, super useful. A single link, however, doesn't really do all that much.\n\nPlastics are literally chemical chains. Individual molecules aren't all that remarkable, but when connected in regular patterns they have incredible properties. Specifically, when BPA is mixed with phosgene, it forms polycarbonate- strong, clear, flexible plastic.\n\nNow, if you ate pure polycarbonate, you'd be fine. Your body doesn't really recognize it and it would eventually be excreted with other waste.\n\nBut to make polycarbonate, you essentially take a bowl and mix BPA with phosgene. Unfortunately, no chemical process is 100% efficient. There's always a little leftover that doesn't end up reacting. So intermixed with the polycarbonate product are little bits of unreacted BPA, sticking to the plastic.\n\nIf that plastic is then used to make a water bottle, some of that BPA may then dissolve into the water. When food is heated in a microwave, the container gets warmed up too. This helps dislodge the BPA from the plastic and allows more of it to dissolve into your food/drink. I also think BPA is used in things like thermal paper receipts, and touching them can cause BPA to dissolve into you through your skin.\n\nThe problem is that while polycarbonate isn't that interesting to your body, BPA is.\n\nHave you taken ibuprofen before? When your body feels pain, a enzyme binds to a molecule, let's call it molecule X, and converts it into a chemical signal for the pain response. Ibuprofen looks enough like X that the enzyme tries to turn it into a signal too, but fails. So while the enzyme is wasting its time with ibuprofen, molecule X just sits around and nothing happens- no pain signal is created.\n\nBPA works the same way. Enzymes in your body called hormone receptors bind to hormones (a type of chemical signal) such as testosterone and estrogen. Obviously these enzymes are really important for development. Testosterone tells your body to do one thing, estrogen another.\n\nIf you drink water with BPA in it, your body may absorb the BPA. BPA happens to look a lot like estrogen, so it binds to those hormone receptors and your body thinks it's getting an estrogen signal, so starts to do things related to that signal.\n\nIs it dangerous? It's hard to say. We can give people more and more BPA until we notice bad things happen, but that isn't really useful. Nobody is eating pounds of BPA, so if eating a pound of BPA is toxic, it isn't that helpful to know that.\n\nThe problem is, what happens when you absorb tiny amounts of BPA over the course of years? If a few cells accidentally think they're getting an estrogen signal once, it probably doesn't do anything. But if they keep getting that response over and over and over again, does it add up? Does it matter for everyone, or just young people who haven't fully developed yet? \n\nThe ideal experiment would be to have two identical babies, feed them exactly the same food and expose them to exactly the same stuff - all BPA free, but feed only one of them a little bit of BPA as well, and see if there are any differences.\n\nObviously, we don't have 80 years to wait around and see those results, and it would be deeply unethical to experiment on babies like that, even if the experiment were possible.\n\nSo instead we have to make models that try to approximate things. The most common one is zebrafish, whose nervous systems are similar to ours. We can grow a lot of them, control their environments, and dissect their brains to study them.\n\nThere are more problems, though. How much BPA do we give them to be representative of how much BPA humans get? How does the BPA affect them and would it be the same in humans? Does it matter if the BPA comes from food or drink? etc etc etc\n\nSo ultimately, the answer is that we don't know. The plastic lobby is really powerful and they make it very hard for scientists to get funding to study this. I personally know a few people who study BPA with these models, and their lives have been turned upside down by plastic companies smearing them and attacking them.\n\nShould you be worried? Experiments in some models have shown pretty scary results if zebrafish embryos are exposed to BPA, but there haven't been enough experiments to know if that's really the fault of the BPA or if it's a design flaw in the experiment. Honestly, at this point it could truly be either, and trying to apply those results to humans would be pretty worthless.\n\n If you are a young child, have a hormone disorder, or are pregnant, it'd be something to avoid to be on the safe side. Otherwise.... do what you can if it makes you feel better. I can't say if it'll hurt you or do nothing.\n\n I personally avoid touching receipts because there is no reason to even get them most of the time, and I try to use BPA free plastic. However, if someone hands me a water bottle and I'm thirsty, I don't worry about it. In the grand scheme of things, it's more dangerous to be in the sun (skin cancer), or eat junk food (heart disease) than it is to get a little BPA exposure." ] }

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{ "a_id": [ "d6l5jto", "d6l5mq6", "d6l5pn7", "d6l8hxt", "d6lcz3z", "d6ldiwb", "d6ldrmx", "d6li6k6", "d6licp5", "d6liv3d", "d6ljxcz", "d6lkwy8", "d6lkxrm", "d6lldtm", "d6llo0t", "d6lq4kk", "d6lroj8", "d6lse4w", "d6lsmyr", "d6lstlq", "d6lt4om", "d6ltjm9", "d6lubvp", "d6luw39", "d6luxs3", "d6lv34a", "d6lv4jq", "d6lvcf9", "d6lvvyt", "d6lx79w", "d6ly42i", "d6lygtx", "d6lzbfy", "d6lznnw", "d6m01tl", "d6m08ca" ], "score": [ 2325, 21, 308, 4, 47, 444, 8, 3, 12, 5, 7, 16, 11, 14, 381, 20, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 5, 2, 2, 2, 2, 2, 2, 2, 2, 4 ], "text": [ "The photon from the laser pointer will travel infinity until something stop it. But the laser itself contains million of photons, and the further they travel, the further they are away from each other. You can test it yourself by pointing at something and walk closer, the dot become smaller but more clear, walk back away, the dot become bigger but blurry. At some point, all the photons will scatter too much to form a clearly visible dot. So if you point the pointer to the moon, it will reach but not be visible enough to see.", "It will travel for all time until it's absorbed by something. The light will get fainter because the laser will spread out. Your ~2mm laser at 100m will be 7km wide by time it hits the moon. It's the same # of photons but spread over a much wider area so it'll appear much less bright.\n\n", "According to [xkcd](_URL_0_), a good laser pointer has a tight enough beam to hit the moon, but the spot would be spread over most of the moon so an astronaut wouldn't notice it.", "light travels forever until something blocks it\n\nthat's the reason you can see stars. because that's same light that's traveled over billion and billions of miles. \n\n", "OK - not the OP here... but to jump on the original question and modify it a little, how far does the light from a laser pointer travel before it gets too distorted to recognize? For example, if I stand 25 feet away from someone who is pointing a laser pointer at my shirt, I can see it. How about if I stand 1 mile away and nothing interferes (and it is dark enough)... would I be able to see it clearly? If so, then how about 3 miles away? At what point will it not be obvious that there is a laser pointing on my shirt?", "According to [Wikipedia](_URL_0_), the divergence on a high-quality laser beam can be less than 1 milliradian. There are a couple of tools to calculate divergence and beam diameter [online here](_URL_1_). Using the distance from the earth to the moon as 1.261e9 feet, a laser beam with divergence of 0.5 mRad would have a diameter of 11.93 miles when it got there - so no, the astronaut wouldn't see a little red dot at his feet.\n\nTL;DR: The further away you get, the bigger the light beam gets. By the time you reach the moon, a high-quality laser beam will be 12 miles across.\n\nEDIT: Forgot the ELI5 TLDR.", "How many people pointing a laser at the moon till we can see it? O.o what if everyone on earth pointed a laser pointer at the moon at the same time?!!", "I understand that the light from a laser will spread out over distance but what I don't understand is why it the photon has infinite energy and will go on forever \"light travels forever until something blocks it\".", "I have a relatively powerful laser pointer and one night I called a friend who lived about 10-15 km away (as the crow flies) and pointed it at his house. It was really difficult to aim by hand but when he saw it, it was lighting a good portion of his garden. That's what he told me. I didn't see it from his perspective. If it's true, it gives you an idea about how quickly the beam diverges.\n", "_URL_0_\n\nHopefully this article is of interest. I saw it when heading across the Thames near Greenwich one time. ", "According to Michio Kaku a laser pointer will create a spot about 5 miles wide when aimed at the moon.\n\nThe light travels forever but it diffuses quickly to a point where it cannot be seen. Military grade lasers diffuse less and can be detected with equipment quite far making them useful for targeting.", "[xkcd answered a similar question](_URL_0_), which I think you'll appreciate and may help answer more questions. ", "The short answer is: No\n\nThe long answer is:\n\nAs the light from your laser pointer leaves, it will slowly spread out. So it will be come more and more spread out. On top of that, particles in the air and even the air itself will slowly but steadily absorb and scatter the laser light. \n\nYou can have someone test this out for yourself. Have a friend wave a laser point at you a block a way at night. Even if you can see the light, it is definitely harder than when it is in the same room.", "A more accurately answerable question would be, \"How far does a photon travel from a light source?\" A laser is just a very focused set of photons concentrated to a tight point and of sufficient energy to be considered a laser. The photons still diverge from each other though and over even a short distance the beam is no longer focused enough to create a tightly defined dot or harm anything in its path. It takes a lot of calculation and a lot of energy to create a path of light with enough resistance to deviation to stay a small focused beam past probably a few meters, and in low power \"laser pointers\" you will lose definition of the dot after probably a few tens of meters. There are too many variables to use a laser pointer as an example of a light source to ask how for it travels.\n\n\nIf you look at a single photon, it will travel forever, at the speed of light in its current medium. The photon will be absorbed by objects, bent by gravity, and speed up or slow down depending on what it's traveling through - and in the case of absorption and re-emission it's technically not the same photon anymore, so passing through glass or a haze of dust for example. In a perfect situation though, light will travel on it's current trajectory forever, and it will only be affected by gravity or expansion of the universe as it's wavelength stretches.", "I want to talk about the \"Laser Thermometer\" and clear something up.\n\nIt is actually an Infrared thermometer and the laser is only there as a means of aiming the device. The Laser does not read the temperature.", "Here's what a 1w laser looks like from the ISS.\n\n_URL_0_", "One night I was camping in the middle of nowhere with some friends. One of these friends had a cheap laser pointer and some night vision goggles. There was a mountain maybe 10 miles away. We could shine the laser on the mountain, and we couldn't see it with the naked eye, but put on those night vision goggles and with the amplification of light, it was like shining a flashlight on something from ten feet away. It was a fairly large mountain, and the dot of light on it was huge. So, yeah, the light spreads a lot, but it gets there. ", "The light photons (particles of light) will travel an infinite distance at the same speed (of course in certain mediums it can travel slower or faster), given theres nothing blocking it, or the light slowly scattering, techniqually a few particles of light will hit the moon, but because of the large distance and large amount of blockers, such as the sky (all the particles of air in the sky, reflect a given amount of light particles) not a 100% of that light particles get there, and on top of that since light is also a wave, it scatters slowly apart from the source, this causing the light to even further become weaker, you can't see the light, but some sensors that are sensitive enough can detect the few that get there. ", "Subsequent ELI5: Could someone in an airplane point a laser pointer into my living room and theoretically use it to play with my cat? How far can a laser pointer point before it doesn't point like a pointer anymore?", "The light will keep going - until it hits something. \n\nThe light from your laser pointer would reach distant galaxies if you pointed it up to the sky on a clear night. But, no one outside of a few hundred yards is going to see it. By the time it reaches distant galaxies, it will just be a stray photon here and there. Far, far, far too faint to see.", "Your thermometer only uses a laser to show where you're pointing it, the laser isn't involved in the temperature measurement process at all.\n\nThe \"temp gun\" has a sensor that detects the (infrared) heat emitted by whatever you're pointing it at. \n\n\n(Other people covered your actual question, I figured I'd add this information)", "Light will travel until it is absorbed, so if you were to aim at the moon it would essentially reach it in just above one second, but you wouldn't see a red dot even if you were next to it because of the scattering of the laser. \n \nIf you've tried pointing lasers at night at something fairly distant (100-200m) you'd see the dot appear much bigger in diameter _and_ fainter, because of all the scatter. For an astronaut on the moon to see your laser you would have to have a very powerful low-scatter laser, which focuses light incredibly well (and if the Earth's air wasn't disrupting and refracting the laser's photons).", "I took a few astronomy classes at my college over the summer and we talked about lasers. Basically if you have any regular laser that's legal strength for regular people to own, the light emitted probably wont make it through the atmosphere. This is just because of the amount of dust in the atmosphere. There isn't much if you look at one part but when you are looking through miles and miles of small dust it starts to add up. Laser tend to become larger the farther they go and when the light spreads out it becomes much dimmer. If you shine a regular red laser pen at you wall its usually a couple millimeters wide but if you shine it across football field it will double in size. You could imagine shining it thousands of miles into space it wouldn't be visible even if our atmosphere was clear of debris and dust. But then we have very powerful lasers used for doing exactly what you said, pointing to the moon. There are a few spots on the moon the have little mirrors on them and certain labs have lasers that they point at the tiny mirrors to get a read about the moon ever-changing distance from earth. Im not sure but i think that these dont enlarge very much like normal laser pens.\n\nsorry if im totally wrong this is what i was told in school a few months ago", "Ok, besides the obvious answer \"Would it hit the moon? -- Yes, if it was a good enough laser!\" There is another point to make. The moon is traveling at 2,228mph relative to the earth. So trying to see the laser would be like trying to see a bullet that flew past you. Totally impossible. ", "Random question. Which radio station?", "Moslty likely that laser only travels about 1/100 of the distance to the moon after that the photons are so far scattered apart that you really wouldn't see anything past that now a really atrong laser like the one nasa uses to shoot at the moon and measure the distance from us to the moon is extremely powerful and has less scattering then a typical handheld red laser", "The 'beam' from a laser pointer, or any laser for that matter isn't perfect, it does diffuse and the cheaper ones diffuse visibly if you just shine them across the street. A hand held laser pointer might be able to hit the moon, but the dot would be miles wide and the light would be lost among other nearby sources. Over longer distances it would get so diffuse that it wouldn't even register.\n\nThis is to say nothing of the atmosphere, just passing through air which we can't visibly discern still has a diffusing effect and traveling through the depth of the earth's atmosphere is likely to cause some pretty severe diffusion of any visible spectrum beam. ", "The photons would spread so far apart with standard lasers. Gaussian beam shapes and whatnot. ", "This was on EITM was it not?", "Light travels infinitely but it also scatters the further away from the source it gets. Best example of this is the flashlight. The average wouldn't light the ground on the moon just as a flashlight wouldn't light the ground after a few feet. Though if conditions are right, you could see the light source. If you were across a large pond, you'll see the flashlight but it wouldn't light up the area around you. Don't think the astronaut would see the laser as it would be hidden by city lights and the fact that it would be too small for our eyes. Though could be wrong.", "When I [built my 1.8W](_URL_0_) laser pointer, the thinking at the time was the diode and driver I was useing should send it 8-14 miles, depending on atmospheric conditions, before it dissipated to an unrecognizable blob.\n\nYou can see the blue beam next to a fairly bright green one [here](_URL_1_), and keep in mind that I can set stuff on fire from ~6 feet away with the blue one (eye protection is a must).\n\n**EDIT TO ADD**\n\nThe one I built used a blue light diode, which, while bright, is nothing compared to a green one. This has to do with the ability of our eyes to see some colors much better than others. A comparably powerful (based on mW) red laser vs a green one will show how much more easily we can see the green. In the image above, for example, that green is rated at 10mW (standard laser pointers are 5mW) and you can see the green light as a solid beam at night without any fog or other heavy sediment in the air. It's great for stargazing. The blue one, OTOH, is also visible, but truly requires care and protection because you can go blind in an instant if it hits a bug or a raindrop and reflects back into your unprotected eye.", "Well a 1 Watt laser is visible from the ISS, if that helps. \n_URL_0_", "It goes very fast. Faster than you can imagine. So fast you could never see it unless you were going as fast as it is, which is impossible because nothing else can go that fast. REALLY fast.", "I'm certainly not an expert, but I'm willing to give it a shot.\n\nI'm tempted to say that the light will travel forever, but that's perhaps not the case. Perhaps most of the light will get scattered by the atmosphere and absorbed by atoms/molecules, these will emit one or more photons. If, for the sake of argument, we count these new photons as a continuation of the laser beam, then the laser beam will continue forever as the photons are absorbed and emitted until the end of the universe. If, on the other hand, we treat the absorption of the photons as the end of the laser beam, then all of the photons that were emitted from the laser beam will probably get absorbed sooner or later by something, thus spelling the end of said laser beam. There isn't much matter in space to absorb photons; on the other hand, there's an awful lot of space. It should be possible to calculate the odds of whether there are any \"original\" photons after a certain amount of distance, taking all of these things into account.", "The short answer is forever, the beam will travel forever, but will it be detected when it gets where its going?\n\nLaser beams slowly spread out as they travel, based on their initial width when they were \"collimated\" or when we made all the light rays parallel. They spread out because of Heisenbergs uncertainty principle essentially and we get a spread out beam after our laser travels some distance.\n\nHere's my crazy ranting calculations on the subject:\n\n\nIn a 1mW red laser pointer. Assuming zero bandwidth.\n\nThere would be N = 10^(-3) W/ (( 3x10^(8) m/s/6.328x10^(-7) m)x7x10^(-34) Js) photons/second coming out the end of the laser.\n\nBear in mind im doing this on my phone in a bathroom and approximating but should be:\n\n N/sec = 10^(-3) /(5x10^(14) x6.5x10^(-34) ) \n = 10^(-3)/(3.25 x 10^(-19) ) \n = 3000 x 10^(12) photons/sec\n \n =3000 trillion photons/second\n\n\nI really want to go check those numbers, seems way too high.\n\n\nUpdate:\n\nWell i tried it in matlab and it says it's 3183.4 Trillion photons/second.\n\n\nGuess i nailed it\n\n-------------------------------------------------\n\nOkay so now we know there are 3 quadrillion photons coming out this laser at 1mW.\n\nLets amp this laser up, we want it to go much further into space so we pump this thing until it hits 10 Watts of power.\n\n\n3.184x10^(19) photons per second!, we have to decide how wide this stream of photons is when it starts its journey.\n\n\nWe will use a dfb laser diode (distributed feedback) which will give us that narrow peak we wanted. We'd want to launch this thing from singlemode optical fibre with a collimating element at the end because the cone that usually pours out of the end of a fibre kinda ruins the concentrated beam we are after.\n\n\n(Continued on my pc in on minute)\n\n\nAssuming the collimating optic was somehow in the fibre to avoid any initial beam spread before we straighten up the beam.\nLight in an optical fibre travels in modes, not all together in the centre of the fibre.\nWhen I look at my old optical fibre notes im seeing for a fibre with core of 20microns, the fundamental (Gaussian) mode will leak into the cladding to become about 28microns across.\n\nBut let's assume we guide this fibre really well (and interestingly) and all the 10 W of red light comes through evenly distributed across a diameter of 20 microns.\n\nSo our irradiance outside the fibre (no 4% reflection at the end from Fresnel because we are clever and use anti-reflect coatings) is\n\n 10 W / pi *(10^-5)^2 or 32 GigaWatts/m^2\n\nsweet, let's beam that baby into space.\n\n------------------------------------------------------------------\n\nNow it's easier for me to assume the beam travels as a Gaussian distribution from this point even though I said evenly distributed earlier, so that's what ill be using to figure out how weak this beam is after say.. 1 light year.\n\n(continued in a minute)\n\n\nSo I've checked my laser beam notes and it turns out that Gaussian beams, once we check in with the uncertainty principle, give us angular spread, related to the width of the beam, let's hope having a really small beam didn't ruin us!.\n\nthe radius of the beam w0 after a distance z is equal to [this equation](_URL_0_)\n\nso let's plug the values in and see how wide the beam is once it passes the sun.\n\nEdit: corrected some errors from before\n\nSo once our beam travels the distance to the sun, 149.6 million kilometres we have moved from having a beam 20 microns across to one that is ... oh my..\n\n 6 million metres across.\n\nGiving us an irradiance of \n\n 8.764 x 10^-14 W/m^2\n\nor\n\n 0.08 picoWatts/m^2\n\nthat's not detectable, at all.\n\n\n\n---------------------------------------------------------------\n\nLet's do our calculation for the 1mW laser pointer then.\n\n\nMaking all the assumptions of no wavelength bandwidth, just a single wavelength coming out the end. I'm measuring a dot on a piece of paper right now brb.\n\n\n our starting beam radius is 1mm.\n\n The irradiance of the beam is then 318.3 W/m^2\n\nBy the time the beam passes the distance between us and the Sun, the width of our beam will be:\n\n 60 kilometres across\n\nwith an irradiance of\n\n 876 picoWatts/m^2\n \n\nwe did better anyway, still pretty weak, and we aren't even anywhere close to leaving our own solar system yet and of course we ignored absorptions by the atmosphere and all that.\n\n-----------------------------------------------------------------------------------\n\nAccording to our research here today, we will need to make a very, very powerful beam that is parallel (collimated) when it is very wide.\n\nMy notes also say that high frequency (lower wavelength) beams don't spread as much as lower frequency (longer wavelength) beams.\n\n\n----------------------------------------------------------------------------------\n\nOur friend Randall Munroe at XKCD, writer of \"What If?\" used thousands of National Ignition Facilities to light up the moon, we don't need that high of a power, so we'll just take one, and expand to 1 kilometre across with a giant lens across the sky. \n\n\nNIF can generate 500 TerraWatts, which is awesome and terrifying\n\nWe aren't using red anymore, we are using a much higher energy photon, ultraviolet at 350nm (half our previous wavelength at 632.8nm). This should improve the amount of spreading we see in the result.\n\nSo our irradiance is:\n\n 5x10^(14) / (pi*(0.5*10^3 )^2 )\n = 637 million W/m^2\n\n\nAfter travelling past the sun, the beam has only doubled to ~2km across so the irradiance is then:\n\n 5x10^(14) / (pi*(10^3 )^2 )\n = 160 million W/m^2\n\nWe're doing so much better, easily detectable here.\n\nLet's go the nearest star, according to google, the nearest star is 4.35 light years or 9.46 Terrakilometres away (strange unit) or 9.46 x 10^15 metres away.\n\nhow wide is our beam when it gets there?\n\n 2 billion metres across\n\nIrradiance?\n\n 35.821 picoWatts/m^2\n\nWe did pretty well, maybe aliens are pretty close by and actually have super sensitive detectors on board to get this beam detected.\n\nBut It's looking bleak.", "I'm a chemist who's been working in a laser lab for about 8 months, so this is all new to me still and I work with lasers a bit more powerful/dangerous than typical laser pointers. \n\nMy understanding is that your average laser pointer has a collimating lens, intended to focus the beam \"at infinity\" so ideally the beam would go directly straight and maintain it's size and shape, in practice it would still diverge (spread out and weaken) over distance and would weaken depending on the initial power. This is also disrupted by anything it's going through which would scatter the beam. This is why typically you can see only where the beam impacts (say, a laser pointed at a wall) and not the beam itself. But throw say, dry ice into the beampath and you would see the trail. So the distance traveled would depend on the power I would think." ] }

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[ [], [], [ "https://what-if.xkcd.com/13/" ], [], [], [ "https://en.wikipedia.org/wiki/Collimated_light", "http://www.pseudonomen.com/lasers/calculators/" ], [], [], [], [ "http://www.thegreenwichmeridian.org/tgm/articles.php?article=14" ], [], [ "https://what-if.xkcd.com/13/" ], [], [], [], [ "http://www.universetoday.com/93987/amateur-astronomers-flash-the-space-station/" ], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [ "http://laserpointerforums.com/f65/image-heavy-maglite-455-1-8ma-1-xw-preserving-internals-82302.html", "http://img.photobucket.com/albums/v402/thinksnow/Mag17-Alltogether.jpg" ], [ "http://www.universetoday.com/93987/amateur-astronomers-flash-the-space-station/" ], [], [], [ "http://imgur.com/X6wwnYQ" ], [] ]

{ "a_id": [ "ck2i7fv", "ck2i8xn", "ck2i9we" ], "score": [ 5, 2, 2 ], "text": [ "Gasoline doesn't last that long, for one. \n\nYou can buy gasoline *futures* (paying now for gas later) but it's a poor way to invest money. There are better ways to invest. ", "Considering the amount of equipment you need to safely store gas and or have it all evaporate away or blow you into kingdom come. NO.\n\nBUT, what you can do is purchase petroleum futures, essentially, making money by betting that gas prices will increase X number of months down the line. It's a simple investment transaction, but you need to go through an investment company and you have to pay taxes on it tho.", "1. gasoline is a regulated material - you can't store much of it.\n2. you'd have to have a license to sell it.\n3. you'd have to be able to sell it at a cheaper price than the wholesale price the station pays for it. You'd have bought it at retail and then sold it below wholesale. It'd have to have gone up in price a lot.\n4. it degrades over time. it \"goes bad\".\n\nif you believe in this business idea, I'd suggest you buy stock in gas companies - they are going to be much better at this business than you are.\n" ] }

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{ "a_id": [ "ckir983", "ckirec3" ], "score": [ 2, 3 ], "text": [ "Sorry to ELI5 your ELI5, but just for those who have never stepped into a bookies... \n\nIf I bet £10 each on yes and no, do I understand right that a \"no\" result would get me £2.50, and a \"yes\" would get me £30?\n\nIf so, that's a pretty sizable difference.", "I expect that the odds are down to a significant number of people betting the outcome will be 'No'. Odds aren't just calculated by looking at what will *probably* happen, but also by the amount of money already taken in by people betting. If the odds were, say, both even (which is what the polls suggest), and a disproportionate number of people bet on 'no', then if 'no' is the outcome, the bookmaker will lose out significantly. By stacking these odds, they can encourage people to bet the other way." ] }

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