title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"Alternators convert kinetic energy into electrical energy, where does the energy go when the circuit is broken?"
] | [
false
] | An alternator in a car is connected to a battery charging system : the spinny motion, magnets and copper, charges the battery, and some noise and heat is generated. A cable between the alternator and battery is cut : the battery does not charge. What happens to this generated energy? It can't be noise/heat/light. Ener... | [
"I highly recommend playing with a pair of ",
"hand crank generator toys",
" and trying it yourself. If you do the answer becomes obvious.",
"Power is force times velocity, or in this case torque times rotation rate.",
", you have to work hard to get it to spin. ",
", almost no force is required so no... | [
"It's probably clearer to say an alternator USES kinetic energy to ",
" generate electrical energy rather than converts. The kinetic energy is still there... the part that doesn't get converted to heat energy by friction, anyway. When the circuit is broken, the alternator stops generating electrical energy from t... | [
"Hate to break it to you, but energy can both be created and destroyed.",
"It's actually a quantity called the Stress-Energy-Momentum Psuedotensor (some times called the Landau-Lifshitz psuedotensor) that is conserved across the entire universe. For most intents and purposes, it's ",
" similar to \"energy\" as ... |
[
"If we are able to take pictures of deep space (Hubble telescope or observatories), why can't we take videos? Would these provide new information?"
] | [
false
] | Even if it wouldn't provide useful information, I still think it would be very interesting if not eye-opening to see these stars and galaxies rotate and move. | [
"Most celestial objects are so large that they would appear basically motionless in any videos we might take. Galaxies, for example, can take hundreds of millions of years to complete a single rotation, and nebula can be light years across. ",
"There are some still frames taken long periods apart where we can s... | [
"There are two issues with getting video of celestial objects. The first, which others here have addressed, is that the time scales that these things move on are so long that you would not see anything. ",
"The second is that these pictures are often not pictures in the sense we often use the word. Instead, th... | [
"Yeah, important point. You need absurdly long exposures to take pictures of dim things like nebulas and galaxies. From our point of view when looking up, the Andromeda galaxy has a width of something like 8 full moons, but it's far too dim for our eyes to see. Most every deep space object is like this."
] |
[
"How do the millions of neurons, and multiple parts of our brain form a singular consciousness?"
] | [
false
] | null | [
"I think I can clarify: you are asking the answer to the ",
"binding problem",
" and whoever answers it is a nobel prize winner for ",
". "
] | [
"Very interesting, thanks! I just hope this problem is solved before I die.",
"By the way, you accidentally a bracket. "
] | [
"I hope they solve it too!"
] |
[
"Is it possible to create a sustainable, but completely isolated underground city?"
] | [
false
] | null | [
"Your question is fairly open-ended, so is likely more appropriate for ",
"/r/AskScienceDiscussion",
". But I'll suggest some possible issues and their resolutions:",
"Obviously, you need to get oxygen and remove carbon dioxide somehow. Happily, there are a number of compounds that appear in the Earth that ar... | [
"Well, that really depends on the tools you have available to you. If there's an underground water source and you have artificial solar lamps to grow crops and plants for oxygen then I would say yes. You would need some type of power source though. If the underground area was large enough and there was access to co... | [
"Unless you like the taste of worms, there's not a whole lot of food underground "
] |
[
"Why didn't incredibly condensed portions of the universe form black holes after the Big Bang?"
] | [
false
] | I've looked at similar posts on this subreddit asking why the whole universe didn't collapse into a black hole after the Big Bang and the most common answer was to not look at the universe as a whole because it was different then than it is now. If portions of the universe that were comprised of atoms were still within... | [
"This shouldn't matter though, right? Energy vs solid matter doesn't matter in terms of a black hole, as mentioned in another post about matter/antimatter collisions inside a black hole. I was under the (possibly mistaken) impression that if the density needed for a black hole was present a black hole would exist, ... | [
"https://en.wikipedia.org/wiki/Primordial_black_hole"
] | [
"If either of you could link sources to your information, that would really clear things up for me."
] |
[
"Is there any material that absorbs all sound waves like vantablack does for light?"
] | [
false
] | Are soundproofing materials even able to be as effective as vantablack? I know that sound deadening foams and stuff exists but from what I've had experience with they only muffle it at best. | [
"Vantablack works by having tiny nanoscale structures that the light bounces around inside. ",
"Here's a picture",
" of some Vantablack as seen through an electron microscope. You can see that it's made up of stacks of tiny tubes. Light enters the material and scatters repeatedly off the tubes. The actual tube ... | [
"A couple pieces of information to tag on this:",
"return waves to their source."
] | [
"To be sure, vantablack is is incredible, however vantablack doesn't absorb 100% of light, it absorbs close to 100%, but not quite. it actually absorbs approximately 99.965% of light by bouncing the visible spectrum of electromagnetic radiation between the carbon nanotube arrays until eventually absorbed and thus c... |
[
"Is there a numerical method to calculate the sine/cosine of a given number?"
] | [
false
] | Given a number x, is there an algorithm to calculate/approximate sin(x)? If so, could you explain how you arrive at this algorithm? | [
"If you have a not-shitty function, then when you zoom in enough onto a graph of a function, it'll look like a straight line. If we know a value of the function in this zoomed in space, then we can figure out the slope of this line and write it down. This is a ",
"Linear Approximation of the Graph",
". If you'v... | [
"If you have a not-shitty function",
"Going forward I will be using this terminology in formal correspondence. "
] | [
"The actual series definition of the sine function is sin(x)=x-((x",
" )/3!)+((x",
" )/5!)-((x",
" )/7!)... (Continues in that pattern forever.)",
"Also Looks like ",
"this.",
"The series definition of the cosine function is cos(x)=1-((x",
" )/2!)+((x",
" )/4!)-((x",
" )/6!)... (Continues in that ... |
[
"If energy neither can be created nor destroyed wouldn't that mean that the universe must be eternal and lack both a beginning and an end?"
] | [
false
] | [deleted] | [
"There's something called the zero-energy universe hypothesis. It postulates the net energy of the universe is zero, which means you can create one from essentially nothing. A beginning would be when \"nothing\" was split into positive energy (e.g., matter) and negative energy (e.g., gravity).",
"Currently it's a... | [
"Correct me if I'm wrong, but this is generally referred to as the \"heat-death\" of the universe? As in there are no interactions between particles and what-have-you to generate heat?"
] | [
"Correct me if I'm wrong, but this is generally referred to as the \"heat-death\" of the universe?",
"Yep!"
] |
[
"What are some of the most interesting and pressing challenges still facing humankind?"
] | [
false
] | I have the opportunity for a full ride scholarship to any science, engineering, or math PhD program I can get into. During my undergrad years I was rather partial to probability theory/stochastic processes, but I'm not bound to it (although delving deeper into non-financial applications of it would probably pique my i... | [
"Eliminating or drastically slowing the human rate of aging may allow us individuals to stick around longer and help solve other problems, so that's a pretty good candidate to start with."
] | [
"In my opinion, these are the most pressing challenges, and they are all related:",
"Energy, especially reliance on oil",
"Access to clean water",
"Family planning / overpopulation",
"Nuclear non-proliferation",
"EDIT: I don't work on any of these problems. I do medical research and epidemiology in the d... | [
"How fast would we run out of room? I think another solution would be increasing the efficiency with which humans use their resources, allowing us to build more/better shelters and accommodate more humans. Although, I also think some sort of reasonable limit should be imposed on the number of children a person can ... |
[
"EM waves can be generated from a perturbation of an Electric field. Does this mean that an electron wizzing about in the electron cloud emits light?"
] | [
false
] | null | [
"In the classical interpretation, yes. However this means that the atomic structure would be unstable, so clearly that is incorrect, it was realising this that lead to the understanding of quantum mechanics. We now understand that the electron is not in one specific place within the cloud, and therefore cannot be '... | [
"What is a free electron density?"
] | [
"The electron in the 'electron cloud' would not emit light autonomously. Cautioning that the idea of an 'electron cloud' isn't the most precise way to discuss electrons. The 'cloud' is just a practical way to visualize the idea that electrons are described by probability densities in space of where that electron ... |
[
"Once you locate a new asteroid and identify its trajectory, do you then have to keep revisiting it and confirming this data in case it was influenced by as-yet-undiscovered bodies?"
] | [
false
] | null | [
"Once you take a long enough observation of an asteroid to get an accurate measure of its trajectory, you know basically where it's going. There are no undiscovered bodies in the inner solar system strong enough to make very significant deflections to an asteroid's orbit. However, when we're doing things like predi... | [
"Just to add a little personal experience to this:",
"I did this as an undergrad research project: Imaging asteroids with 'known' trajectories, determining their brightness and position with respect to the background star field, and submitting the coordinates to the ",
"Minor Planet Center",
" (which keeps da... | [
"and even better that they're data points on a different night.",
"I do not know any statistics, but I am interested by your implication that there would actually be some use to taking multiple data points on the same night (even though, I assume, the object would not have made any meaningful motion). The implic... |
[
"As a black hole collapses, how does the resulting Hawking radiation affect its event horizon?"
] | [
false
] | null | [
"As Hawking radiation takes away mass from the black hole, the event horizon must necessarily decrease. As the event horizon decreases, the black hole gets hotter. As it gets hotter, it radiates more. Eventually the whole thing just evaporates away"
] | [
"Heat death does not necessarily mean cold. It means everything is at the same temperature, so no work can be done by a thermodynamic process. Since almost ecerythng is a heat engine that requires a temperature gradient to function, that would be the end of most physical processes as we know them."
] | [
"No those were raving lunatics or tabloid reporters.",
"Apparently it has created quark-gluon plasma, which is apparently the densest matter that is NOT a black hole.",
"http://news.nationalgeographic.com/news/2011/05/110524-densest-matter-created-lhc-alice-big-bang-space-science/"
] |
[
"Could you use carbon dating to find out how long a specific creature was alive?"
] | [
false
] | I know carbon dating can be used on fossils, but say a dead sea turtle washed up on shore. What would be an efficient way to find out how long it was living for? | [
"Carbon-14 dating is based on the premise that this radioactive isotope of carbon-12 is present as a specific portion of all the carbon present in living creatures. Once a creature dies, the carbon-14 content of its tissues is set and begins to convert to nitrogen-14 over thousands and thousands of years at a set r... | [
"carbon-14 content of its tissues is set and begins to convert to carbon-12 over thousands and thousands of years at a set rat",
"This is not correct. 14-carbon decays (by beta decay) to 14-nitrogen, not 12-carbon. However, SoBad is correct in saying you can only date the time since death."
] | [
"With turtles and humans, you can always look at our skeletons and get a good idea of how old we were when we died. When scientists examine human remains, I know they look at our teeth for more accurate estimates."
] |
[
"Are different antibiotics better for specific tasks than others?"
] | [
false
] | After having a small problem recently, the doctor gave me an antibiotic that I had never heard of before. It got me wondering whether different antibiotics are more effective than others in different situations. Are there classes of antibiotics that are best for one task over another? How careful do doctors need to ... | [
"I answered part of your question in a reply, but I felt it needed further clarification.",
"The answer to your first question is \"it depends\". Microbiologists/pharmacologists do studies in which certain antibiotics are used for certain types of infection/prophylaxis. ",
"We typically base therapy on what t... | [
"Yep - different classes (as mentioned above) have different mechanisms of action and differ slightly per drug.",
"For example treatment for MRSA (broad generalization here, non-community acquired) - our lovely Gram positive nuke: vancomycin. Mechanistically, vancomycin will bind in the cell wall (specifically t... | [
"There are many many classes and subclasses of bacteria. Some antibiotics are broad-spectrum and target most anything, others are narrow spectrum and target only specific families. Different antibiotics have different potencies and side-effect risks. Sometimes the choice of antibiotics is somewhat arbitrary, othe... |
[
"Why can a sun-synchronous orbit only exist around an oblate body?"
] | [
false
] | null | [
"There are 2 special cases where the oblateness of the body can be ignored to meet the technical definition of a sun-synchronous orbit. A ",
"Lissajous Orbit",
" about ",
"L1",
" and ",
"L2"
] | [
"The equatorial bulge causes inclined orbits to precess. When the satellite is overflying the equator, the gravitational force points exactly downwards; but when it's at the maximum latitude it can reach with its inclination, the bulge pulls perpendicularly to its velocity. It can be modeled ",
"like this",
", ... | [
"Why would the angle of the orbit need to precedes to maintain sun-synchronicity?"
] |
[
"If I were to somehow hover 300 feet in the air, could I be struck by lightning since I'm not grounded? Could it shock me? Could it kill me?"
] | [
false
] | [deleted] | [
"You can get struck by lightning in the air. Your body will be more electrically conductive than the surrounding air and thus electricity will take the path of least resistance through your body. Planes sometimes get struck by lightning in midair. ",
"You'd experience some sort of injury. Birds don't get electroc... | [
"Airplanes also have a metal skin that is fairly conductive, shunting most of the current flow around the outside. This is not true for humans. "
] | [
"Airplanes are being hit by lightning all the time. Just google \n'airplane' + 'lightning'. "
] |
[
"What causes the pain in your side when you run/jog? What exactly is it and can be done to prevent it from occurring?"
] | [
false
] | null | [
"A side stitch can be caused by a number of different things. The most likely cause is friction between the diaphragm and internal organs. It can also be caused by friction between organs within the abdominal cavity. Because the sensation of pain within the abdomen is referred to the exterior, sometimes in places t... | [
"Check out the references for several suggestions to prevent it. ",
"http://en.wikipedia.org/wiki/Side_stitch"
] | [
"That sounds like typical muscle pain from anaerobic exercise. I hardly think that's what side stitches are. Are your sides even working anaerobically when you run?"
] |
[
"Is it possible to attach a satellite to a comet or other traveling item in space to hitch a ride to somewhere in the galaxy?"
] | [
false
] | [deleted] | [
"If you can softly land your space probe on an object that is leaving the solar system, then you have already achieved enough speed to escape the solar system anyway, so the activity would be pointless."
] | [
"Couldn't you put the satellite on an intercept trajectory at one of the 'slower' points of the comet's orbit, get captured by its gravity, land, then use it's velocity to catapult yourself out of the solar system?"
] | [
"The gravity of basically any asteroid would be much too small to be used as a gravity assist. There are quite a few big objects in the solar system - like planets - that could achieve the same effect.",
"Remember - in space, you don't need to give it gas to keep going. You only need to get going and coast the ... |
[
"In historical,natural climate change, what caused temperature to drop after a while? Will this happen again with human caused climate change?"
] | [
false
] | So historically, the earths climate has gone trough various cycles of hot periods and cold periods. I know that this time is different, but I was wondering what exactly caused the climate to cool again after a hot period? I know that there are 'breakaway' climate change triggers and was wondering how those were reserve... | [
"The norm during the last several million years have been periodic oscillations in climate between glacial and interglacial periods that are primarily dictated by changes in the amount of solar radiation. As a basic primer, this page from ",
"NOAA",
" does a good job in covering the major points. The short vers... | [
"The colloquial use of \"theory\" is actually a hypothesis.",
"When the word \"theory\" is used in a science context, it basically means a scientifically accepted model."
] | [
"the oceans are a sink not a source for co2, Over geological time, most of the world's carbon (more than 90 percent) has settled into the ",
" *",
"https://earthobservatory.nasa.gov/features/OceanClimate/ocean-atmos_chem.php",
" The ",
" takes up ",
" through photosynthesis by plant-like organisms (phyt... |
[
"Every time I have a scratchy or sore throat, I am told to gargle salt water. Why?"
] | [
false
] | How does gargling salt water help your sore throat? Or does it even help? | [
"Believe it or not, this is actually a treatment commonly used for the great-great-grandaddy of all chest colds, cystic fibrosis. In CF, people get thick, sticky mucus because of a defect in their ability to secrete water into the airways. ",
"Normally, you secrete mucins (the proteins that make snot snotty) alon... | [
"Yes, this is a common remedy found in many cultures to soothe sore throats - it is also recommended after the removal of wisdom teeth as a way to help prevent infection and soothe pain in the area. ",
"The idea is that the salt creates a osmotic gradient. It draws the water out of the bacterial cells effectively... | [
"Awesome! Thanks! My mother (I won't give away her age) is always telling me gargle salt water and I never believe her because she always says \"it's what my father told me to do.\" I guess I should trust her, since she is a doctor.."
] |
[
"Why exactly do we become tolerant to drugs?"
] | [
false
] | Is there any benefit in it? Any evolutionary advantage that has in some point of our history proved useful? I can't think of a reason why it'd be good to develop tolerance to any drug (in the broad sense of the word). | [
"Can you be a little more specific with what you mean by \"tolerance\"? For example, your body could be come \"tolerant\" to illicit drugs, requiring higher doses to achieve the same affect. Or your body could become \"tolerant\" to some antibiotic, requiring more or different drugs to treat an infection. Both m... | [
"In regards to biological tolerance, in short: bacteria can become resistant to antibiotics because they are adaptive and all cells are different. Likely, the bacteria that survived the first wave of antibiotics possess some gene to cause them to be immune. Since these resistant ones survive they replicate their be... | [
"This ability would have evolved millions of years before 'drugs', therapeutic or recreational, were invented. Basically drugs are toxins. So I'm taking tolerance to mean the ability to withstand more of a toxin (e.g. alcohol) when exposed to it many times. This happens because our liver produces more of the enzyme... |
[
"Inspired by Shitty Ask Science: How long *is* a year on the Sun?"
] | [
false
] | The sun isn't actually at the exact center of the solar system after all. It (like everything else) revolves around the common center of mass. How long does that take? A quick Google search gets me the galactic revolution period of the Sun, but not its "solar" period. Now that I think about it, is the earth's period ac... | [
"http://en.wikipedia.org/wiki/Barycentric_coordinates_(astronomy)",
"This is known as the solar system's barycenter and it is constantly in motion and dependent on what vectors all the planets and other masses in the solar system are pulling on the sun. "
] | [
"Yeah, so there must an orbital mode at the same period as the year of each object in the solar system. This undoubedtly means that the sun's orbit around the barycenter is not ",
", which means it will not repeat the same pattern twice, and therefore there is no well-defined \"year\". ",
"Playing around with... | [
"I literally said that that is not what I'm looking for in the question."
] |
[
"Hypothetically: If our galaxy (all the planets and the sun) had somehow been shot across the universe, would we be able to tell?"
] | [
false
] | Referring to about blackholes. If I'm not mistaken theres one at our galaxy's center, what would happen if that was involved? I think I've gotten what I'm trying to ask across, help scientists of reddit. I should also say I meant to put the follow for the title. Would we be able to tell ? | [
"You must understand that galaxies are absolutely enormous. Any collision would take millions and millions of years to complete. We probably wouldn't notice anything significant here on earth.",
"If our galaxy was, in fact, suddenly moving in a different direction very quickly, we would begin to notice that loc... | [
"Gotcha, but let's expand on that real quick. Let's say we've been flying through space for a while and it got to the point that M31 is actually getting close. If different galaxy's blackholes were getting close to each others event horizon that would trigger massive acceleration of space-time in that area and woul... | [
"You can see space-time stretching whenever you look at the sun.",
"If that doesn't explode your mind, then I don't know what will. But really, astronomers measured stars' positions near the sun during a solar eclipse and they noticed measurable differences in the stars' positions. This is because of the space-... |
[
"What are the ripples next to the atoms in the movie 'A boy and his atom'? (link in description)"
] | [
false
] | [deleted] | [
"The CO molecules are being placed on a copper crystal to make that movie. In a metal, the electrons are free to move around. So placing the CO molecule on the copper perturbs the electron density a bit and makes the periodic ripples. ",
"If you line up the CO atoms in a circle, you can get the ripples from each ... | [
"IBM used a scanning tunnelling microsope to view the surface of their substrate making each frame of the film. The microscope detects current tunnelling of the free electrons from the substrate into the tip of the probe, so regions with more tunnelled current correspond to places where there is a localised charge... | [
"That seems odd, couldn't you indefinitely keep adding concentric circles (like an onion) to produce a bigger and bigger electron density in the center?"
] |
[
"Why does a ball bounce higher the more air pressure it has?"
] | [
false
] | null | [
"Distortion of the material of the surface of the ball absorbs energy as it bends and rebounds. Higher pressure reduces the movement of the surface and allows more energy to go into the bounce.",
"There are additional gains depending on the material of the ball, for example if the material is somewhat elastic, th... | [
"Yes, it's friction internally, much like how car tires get hot while driving."
] | [
"Where does the energy from elastic collision go? Heat?"
] |
[
"why \"Steam\" is the driving force of most of the power plants for more than 150 years? Does no other fluid has capability to replace it?"
] | [
false
] | null | [
"Don't underestimate the benefit of it being cheap, clean, readily available and well understood. Another fluid would have to have significant technical advantages over it before making the switch would be worthwhile. "
] | [
"Fuel and heat energy is the driving force. Steam or whatever medium used is just a method of transferring that heat. Water has the highest latent heat value (stores most heat energy) of its kind. There are \"closed circuit\" gas turbines that use air as a working fluid."
] | [
"This is the answer. Water has a huge specific heat capacity (the amount of energy required to increase its temperature - second only to ammonia) as well as a huge latent heat values (the energy required to change its state between solid/liquid/gas).",
"Superheated steam is therefore a great medium to transfer en... |
[
"Why do hamsters become flat when extremely relaxed? Does this occur in other rodents as well?"
] | [
false
] | null | [
"Similar to how your cat can flatten out when laying on its back, or stomach. The arms and legs splay out and that brings all the associated fur and skin with them. Gravity does the rest.",
"This question can be broken down into a few more complicated questions requiring more specific answers. But they can be gen... | [
"Wow! Thank you for taking the time to type such a long and detailed answer!",
"What would happen if the human shoulder is structured like that of rodents'? Would it be more prone to injuries such as sprains? Why didn't we evolve that way?",
"Once again thank you so much! I learn something new every day."
] | [
"We would likely not be able to do much of the stuff we do now, weight bearing. It works for a small quadruped to have a shoulder that is basically suspended within muscles and having no bony joints, because the relative strain on the should is so much less. The largest mammal without a clavicle is a whale, and it ... |
[
"What study is this?"
] | [
false
] | null | [
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"listed in our wiki!",
"You can find the basic answer with a google / wiki search. Please start there and come back with a more specific question.",
"If you disagree with this decision, please send a... | [
"Try ",
"/r/AskScienceDiscussion",
" perhaps?"
] | [
"Which sub would be appropriate? ",
"The last one seems most appropriate, but isn't it just for physical objects? ",
"I already posted in tip of my tongue, but I thought this sub would be more knowledgeable about this sort of thing. "
] |
[
"Why does Euler's sum of powers conjecture hold for the case where k=3 but not when k=4 or k=5? Does it hold true for k=6?"
] | [
false
] | From what I understand, the Conjecture itself was disproved in 1966 by finding a counterexample where 27 + 84 + 110 + 133 = 144 (case where k=5). It was also proven that there are infinite solutions for k=4 (1986, Noam Elkies). The smallest example for k=4 is 95800 + 217519 + 414560 = 422481 A few questions: 1) Whic... | [
"OP probably meant solutions for a,b,c,d,e which have no common divisor."
] | [
"1.) Number Theory, in particular ",
"Diophantine Equations",
" and ",
"Algebraic Geometry",
". (Sometimes called ",
"Diophantine Geometry",
")",
"2.) The case k=3 is equivalent to Fermat's Last Theorem when the power is 3. So why does Fermat's Last Theorem hold for this particular case? This actually... | [
"To follow up, I'm assuming people have used computer time to try and find a case for k=6. I'm assuming that computers today could brute force testing of very high values. ",
"If someone discovered a case where k=6 has a solution, would it be interesting enough to get noticed? Would it have any further applica... |
[
"In most models of the solar system, the planets are all show on the same flat plane - are they?"
] | [
false
] | to be more specific, we see that the planets all seem to be on a roughly flat slope going out from the sun in a straight line. My question is, are any of the planets 'above' or 'below' earth relative to our position and the sun? Most documentaries about the solar system seem to reinforce this, but I'm not sure if thi... | [
"There is a reason for this - when planets form there is usually a larger structure influencing the patterns. For instance, the dust planes of most proto systems we've seen tend to follow the Milky Way plane. I am not sure if we have seen this happen in other galaxies yet (they are kinda far...) - but it figures to... | [
"Conservation of angular momentum writ large."
] | [
"They are almost all co-planar, the highest inclination is from Mercury, at ~7 degrees. All the inclinations of the planets are listed here: ",
"http://en.wikipedia.org/wiki/Orbital_inclination",
"Most objects like comets are too small to alter the paths of planets significantly."
] |
[
"I have a HUGE maple tree in my backyard. It towers over our three story house. What measurements/data would I need for someone to give me a good guess about it's age?"
] | [
false
] | It makes delicious maple syrup too! | [
"I'm not a scientist but I can answer this.",
"Find someone with a friend/relative who works in the forestry industry/education/government etc and borrow their core sampler.",
"You basically drill a core sample from the center of the tree and count the rings. If the tree is really big, you might not be able to... | [
"Cool, thanks!",
"Edit: Wait, I'm in askscience, right?"
] | [
"Cool, thanks!",
"Edit: Wait, I'm in askscience, right?"
] |
[
"What do the dot product/the tensor product of two vectors represent geometrically?"
] | [
false
] | So the cross product isn't too hard to understand conceptually, since there's an actual geometric representation for what it is (if a x b = c, then c is perpendicular to a and b and has a magnitude equal to the area of the parallelogram made by a and b (E: that goes in the direction according to the right-hand rule)). ... | [
"The dot product of ",
" and ",
" is |",
"||",
"|cos(θ), where θ is the angle between ",
" and ",
".",
"The tensor product of ",
" and ",
" is a bit more complicated. This is also called the outer product of ",
" and ",
". If we represent ",
" as a column vector, then the outer product ",
... | [
"Short answer for dot products is: how close they are to pointing in the same direction.",
"Dot product will be zero if two vectors are perpendicular (orthogonal), increasingly positive if the vectors are going in the same direction, and increasingly negative if they are pointing in opposite directions.",
"If y... | [
"The dot product of A and B is the length of A times the amount of B that points in A's direction, or vice versa."
] |
[
"If clouds and fog are essentially the same thing, then why doesn't fog produce spontaneous thunder and lightning?"
] | [
false
] | null | [
"Difference in potential is what allows electricity to flow, fog essentially is at the same potential as the ground it covers. Any difference it might generate quickly dissipates to ground, in the case of clouds they are very high and to bridge the difference over an air gap they can build quite a charge before it... | [
"Fog is a type of cloud, but most clouds do not produce lightning.",
"For a cloud to produce lighting, the component droplets of the cloud have to acquire electric charges and to accumulate with similarly charged droplets. This only happens in tall clouds, i.e. \"thunderclouds\" or \"cumulonimbus\", both because ... | [
"Due to the altitude of fog, the charge that accumulates in the low laying cloud is constantly grounded and never builds up to the point in which lightning could occur. "
] |
[
"How does waste water testing identify specific viruses based on protein fragments, especially after hours or days of degradation?"
] | [
false
] | I'm having a very hard time establishing exactly what technology is used for waste water testing for viral fragments, most fact sheets just say things like The samples are analysed for viral fragments Which while perfectly fine as a public service announcement, leaves me craving a jucier explanation. What tests are act... | [
"It's a PCR test. The actual magic of a PCR test is the PCR part isn't actually the test. The PCR part is a trick we found where you can take basically anything, Mix it with some chemicals and free DNA bits and then heat and cool it a bunch and you'll end up with a billion copies of every single bit of DNA that wa... | [
"That is true for a pure sample, in a lab, under controlled conditions, and perfect reaction efficiency. Real world samples invariably have contaminants, PCR inhibitors, and other \"muck\" that can reduce DNA extraction yield, purification, and PCR amplification efficiency, which make it difficult to amplify a si... | [
"I’m not sure you are giving a good description of PCR generally or accurately describing how you test for the fragment you want. You take your DNA sample and add specific single stranded DNA sequences, called primers, which flank the regions you want to amplify. DNA requires these primers to synthesize a new stran... |
[
"Just because two animals have similar features like scorpions and spiders having eight legs does it mean that they came for the same or related ancestors that evolved differently?"
] | [
false
] | null | [
"In the case of spiders and scorpions, they came from the same ancestor, they're both arachnids.",
"But that's not true for every animal that looks like another animal. Two completely different species can evolve the same features in convergent evolution."
] | [
"All life came from the same ancestors if you follow it back enough, but convergent evolution is a thing. For example, birds and mammals evolved to be warm-blooded independently. Scorpions and spiders are not an example of that though. All arachnids have eight legs."
] | [
"If animals share phenotypical similarities (these can be obvious like number of legs, or less obvious like chemical composition of bodily fluids, etc.), there are two possibilities: either 1) the animals evolved from a common ancestor that had this trait, or 2) the animals \"convergently\" evolved this trait becau... |
[
"[Physics] How is momentum conserved if I throw a ball up in the air?"
] | [
false
] | null | [
"There is a net external force acting on the ball."
] | [
"Thanks for the answer. While this may seem trivial to someone of your expertise, can you please give some detail as to why this matters? Does conservation of momentum not apply with external forces? I don't remember this being a highlight of the idea when it was taught to me in high school and college, but it make... | [
"The momentum of an object is not conserved if there is a net external force acting on it.",
" = d",
"/dt. If ",
" is not zero, the momentum of the object will change with time."
] |
[
"Why does tomato sauce stain plastic so effectively?"
] | [
false
] | After arduously scrubbing my child's plate with little success, I find myself wondering what is in tomato sauce that so quickly and effectively stains plastic items such as plastic storage containers? Is it a chemical compound in tomatoes? Or something added to the sauce? | [
"Specifically it is a non polar molecule called lycopene that is causing the stains. The plastic is porous and it enters the pores and diffuses through the container. To help prevent this you can rub the container down with a little butter before dumping the sauce in."
] | [
"Thank you, kind internet stranger!"
] | [
"The plastic isn't porous in the sense that it has pits or cavities. The lycopene is very non-polar, as is the plastic. The lycopene simply dissolves into plastic from the water-based tomato sauce.",
"Sticking the plastic in the sun for a while will bleach the lycopene and at least make it not look orange/red a... |
[
"Why do humans have long hair?"
] | [
false
] | I think I read somewhere that humans are the only apes capable of growing hair as long as the hair on our scalps. The trait seems to be rare in the animal kingdom at large. Is there some evolutionary advantage to it, or is it just a fluke of sexual selection? | [
"Hmm.. some animals do have long hair on their \"heads\". ",
"Like horses and lions and other animals with manes."
] | [
"I am not an anthropologist, but this is what I found from reading ",
"Wikipedia's article on \"Long hair\"",
":",
"Anthropologists speculate that the functional significance of long head hair may be adornment, a by-product of secondary natural selection once other androgenic/somatic hair (body hair) had larg... | [
"Well, orangutans may have quite long hair, too: ",
"http://images.mylot.com/userImages/images/postphotos/2078254.jpg"
] |
[
"Question regarding band gap values of Germanium"
] | [
false
] | Alright scientists, I have a question that I haven't been able to make any headway solving. I've read academic papers, looked through books, asked class mates and I can't come up with anything. I am given two curves of the absorption coefficient (cm vs the photon energy (eV). These two curves consist of a sample at two... | [
"This will not answer your question, but you may find it informative nonetheless."
] | [
"Abrupt changes in the absorption coefficient will signal a transition, such as the band gap. "
] | [
"A plot of the data would be good, but I expect based on your description that there will be a small increase in the absorption at one photon energy and then later a much larger one. That would indicate the locations of the indirect and direct band gaps respectively.",
"As for temperature, you could try and do so... |
[
"A rod more than a lightyear long?"
] | [
false
] | [deleted] | [
"This question has been asked before. Please use the reddit search function to see if your question has been asked previously. Have a read through some of those answers, and if you still have any questions, feel free to ask them here. ",
"The following 2 results with similar intent to your question was obtained... | [
"Not an expert here however found this in ",
"r/sciencefaqs",
" ",
"http://www.reddit.com/r/sciencefaqs/comments/fj1qd/if_i_had_an_infinitely_stiff_rod_could_i_push_and/"
] | [
"Over in ",
"r/scienceFAQs",
":\n",
"http://www.reddit.com/r/sciencefaqs/comments/fj1qd/if_i_had_an_infinitely_stiff_rod_could_i_push_and/"
] |
[
"Where does the additional mass come from during a beta-plus decay when a neutron is formed?"
] | [
false
] | I've been reading up a bit on the basics of radioactivity, but there's something I just don't understand. When a nucleus undergoes beta-plus decay and converts a proton to a neutron while emitting a positron and electron neutrino, it seems to mysteriously gain mass as neutrons are slightly heavier than protons, but whe... | [
"Yes, that's right -- actually I had a discussion about this exact topic with a flaired nuclear physicist on this sub a while back, where he explained that it is never correct to think about the constituents of nuclei in a decay process; it is only correct to think about the parent and daughter nuclei as whole syst... | [
"In a beta-plus decay, it’s the nucleus as a whole that’s decaying. Even though the mass of a free neutron is higher than the mass of a free proton, the Q-value for beta-plus decay of a nucleus with A > 1 can still be positive."
] | [
"Where does the additional mass come from during a beta-plus decay when a neutron is formed?",
"It is already present in the initial state of the nucleus that is decaying.",
"Does the process of changing one of the up quarks to a down quark somehow increase the particle's mass, or are there other forces at work... |
[
"How does a population experience an increase in genetic diversity?"
] | [
false
] | Is it only mutations? How would a bottleneck population such as Native Americans increase their genetic diversity without interbreeding with some other population? My question is general, it does not necessarily pertain to race or Homo sapiens but any population. | [
"Either mutation or mingling with other populations"
] | [
"Yeah, it's either going to be via mutation or via introgression of new alleles from outside populations. If the population fails to admix with any outside populations, then it will recover to an equilibrium level of diversity in time, and will thus continue to become more genetically distant from other populations... | [
"So would it be wrong to conclude that as a general principle, that younger species will have less genetic diversity than there evolutionary ancestors?"
] |
[
"Do gravitational waves have frequencies?"
] | [
false
] | I feel like the obvious answer is they do, but I don't know the answer. And if so, what determines their frequencies? Mass? How noticeable are these frequencies, and what would the frequency of a gravitational wave from the sun be compared to the black hole collision that LIGO observed? | [
"Not only do they have frequencies, but the range of frequencies LIGO detects are partly within the limits of human hearing.",
"So you can listen to ",
"natural-pitch black hole merging noises.",
" ",
"The frequency they produce is related to how fast the holes are orbiting eachother. As they spiral towards... | [
"Yes, they do. Gravitational waves in free space obey the same kind of dispersion relation that electromagnetic waves do: ω(",
") = |",
"|c."
] | [
"Wow listening to a black hole sounds like someone making something up, that’s amazing!"
] |
[
"Has there ever been an estimate on how many planets there could possible be with the existence of Life?"
] | [
false
] | null | [
"A very simplistic but easy estimate can be made with the ",
"Drake equation",
".",
"The problem is that the values of things such as the fraction of planets that develop life and the fraction of life‐bearing planets that develop ",
" life are unknown and perhaps unknowable.",
"Here’s ",
"Wolfram|Alpha’... | [
"And ",
"here's",
" xkcd's interpretation. The Drake equation is worse than simplistic. It's ",
" worse than meaningless, it's actually ",
". "
] | [
"Stuff like ",
"The Drake equation consists of a large number of probabilities multiplied together. Since each factor is guaranteed to be somewhere between 0 and 1, the result is also guaranteed to be a reasonable-looking number between 0 and 1. ",
", making the result worse than useless."
] |
[
"Why are morphogens not capable of growing back lost parts of our bodies, without the risk of developing cancer?"
] | [
false
] | My question is why did our bodies develop in this way? Why didn't our body find a way to use morphogens to it's advantage in order to restructure or repair/grow back completely missing limbs? Why wouldn't morphogens be able to start or stop working only when needed, in order to not work continually - leading to cancer?... | [
"Evolution doesn’t routinely do luxuries. Can your current form and life-processes keep you alive in your current environment long enough to breed the next generation? Yes? Then you are “successful enough”. Rinse, repeat, refine through those generations.\nIf the need to regrow limbs and organs was the only thing k... | [
"Evolution is adaptability to an enviroment. We humans do not need to regenerate body parts (although some organs can regenerate) since we are not constantly getting amputeed or hunted by predators. The body of a living being necessitate conditions to modify, so maybe, if we were at the same conditions of prehistor... | [
"We have stem cells, which are totipotent and have the capability to become whatever the body needs. We are not capable of naturally regrowing body parts, but thanks to them we can work out new improvements and help everyone!"
] |
[
"Why isn't the Universe condensing, or at least decelerating, with the constant gradual pull of gravity?"
] | [
false
] | null | [
"One of the interesting things about the way the general theory of relativity extended our understanding of gravity is that gravity (i.e., the curvature of spacetime) need not be attractive. That is, the curvature can be such that the trajectories of objects through spacetime diverge rather than converge. When we m... | [
"Well, it's actually speeding up. Which really isn't what one would expect. So, this is where dark energy enters into the equation. Hopefully in the coming years we'll get a better idea of the nature of what dark energy is. What this dark energy actually IS is still a debated question."
] | [
"In the general theory of relativity, gravity is identified with the curvature of spacetime. In the absence of curvature, if you have two objects that start out at rest relative to one another they will remain at rest with respect to one another. That is, neither object will see the other object move as time goes b... |
[
"AskScience AMA: I’m Professor Brian Hare, a pioneer of canine cognition research, here to discuss the inner workings of a dog’s brain, including how they see the world and the cognitive skills that influence your dog's personality and behavior. AMA!"
] | [
false
] | Hi Reddit! I’m , and I’m here to talk about canine cognition and how ordinary and extraordinary dog behaviors reveal the role of cognition in the rich mental lives of dogs. The scientific community has made huge strides in our understanding of dogs’ cognitive abilities – I’m excited to share some of the latest and most... | [
"So sorry for your loss and what a fascinating observation. I would love to say there's an experiment or systematic study to cite for this one, but there is not. Scientist have written papers about other animals - like primates - that they interpret as grieving the loss of their offspring. That said dogs showing be... | [
"I am laughing right now. YES! Your dog knows how much you love them! I sort of spoke about this in one of the earlier answers, but dogs have hijacked the human oxytocin bonding pathway that is normally reserved for our actual babies. When you stare at your dog, both your oxytocin levels go up, same as if you pet t... | [
"Do dogs recognize other breeds of dogs (e.g. a chihuahua seeing a husky) as being one of \"them\", or do they see other types of dogs as separate species altogether?"
] |
[
"Why can't doctors fuse the two halves of a bone back together after a fracture instead of letting the body do it?"
] | [
false
] | null | [
"Bones need to tolerate a high degree of stress and large forces. We could glue bone fragments together or graft with mashed up bone but it won't be strong enough. To get sufficient strength for weight bearing we use metal rods, plates, and screws.",
"There may be a product that can join bones but I don't know of... | [
"Can you clarify what you mean by fuse? When a break occurs the fracture needs to be reduced and immobilized. For the bone to grow back together the two ends have to be in close proximity and not have any motion relative to each other. If either requirement is not met, you have nonunion of the bone which might requ... | [
"Vertebroplasty",
" is really for stress fractures, but it's kind of doing that: joining the bones across a fracture with a kind of glue. My mother had this done on her back and was pain free immediately. Before, she couldn't even tolerate riding in a car."
] |
[
"What would happen to oil if it didn't get extracted?"
] | [
false
] | If it were to remain dormant, what would become of the crude oil we humans extract? | [
"Really depends on where it is. If it is in a basin that is still subsiding, eventually the heat will cook it into a graphite like substance. Many times there are ",
"natural oil seeps",
" where the oil finds a way to the surface like in offshore California or in the Black Sea. ",
"In geologically 'inactive' ... | [
"Not to derail this good question too much, but tar sand extraction is directly causing a lot of habitat loss & trace amounts of heavy metals in the areas where digging occurs, is being swept away by rain & entering rivers, which fish & local people are becoming poisoned. Such a shame. I can't totally say oil is co... | [
"Sure, you can find the wiki article ",
"here",
" if you're interested in reading it. Basically it's just a highly viscous bitumen that is mixed in to some loose sand. The reason it is not seen as the best way to get oil is because you have to dig the sand out (you can't pump it), take the sand to a refining pl... |
[
"What makes certain metal ions suitable for use in biological systems?"
] | [
false
] | I was recently asked the fairly simple question of "Why is the calcium ion so important in Biology?", however it got me thinking - why are some ions used preferentially over others? What is it about Ca that makes it more suitable for signalling transients over Mg ? In an action potential why are sodium ions outside and... | [
"Abundance and chemical properties determine which elements we use.",
"Abundance isn't just for metal ions and so the explanation will be generalized. If you look at what elements living things use, you'll see that the most common elements used are also the most abundant elements in the universe. Because there's ... | [
"Thank you for the detailed reply! I understood most of the biological points you made (I'm currently a biochem undergrad) but was hoping you could elaborate on some of the chemistry:",
"What do you mean by the akali metals being good at staying in solution? Is that because they don't form many insoluble precipit... | [
"I love answering these questions; there's just so much stuff to know and to ask!",
"Yeah, alkali metals don't form precipitates since they are much more stable in solution. ",
"Lightness means that a light element will have a higher charge to mass ratio. This effectively means there is a high electrical force(... |
[
"What would a nuclear detonation on the surface of the Earth look like from the ISS or similar orbiting platform?"
] | [
false
] | [deleted] | [
"Okay. The ISS orbits between 200 and 250 miles high. A 20 megaton bomb will produce a fireball ",
"about 2 miles in diameter",
". It will cause a \"conflagration\" ",
"40 miles in diameter",
".",
"What would this look like from 200 miles away? Here's a place to start: imagine driving down the interstate ... | [
"Also. Here's a graph of ",
"mushroom cloud dimensions.",
" The left axis is thousands of feet, the bottom axis is megatons. So go back to that ISS photo and imagine a mushroom cloud 20 miles high and 60 miles in diameter..."
] | [
"Yea, let the scientist pop in on this :P"
] |
[
"How large would a telescope have to be to be able to see the closest known exoplanet, in decent detail?"
] | [
false
] | null | [
"Yes it would."
] | [
"We do exoplanet discovery and we use an 8.2 meter mirror. Currently we either infer the exoplanet (based on techniques such as dimming of the host star, etc) - or directly image it (only for the closest and largest exoplanets, but only about a pixels worth).",
"New instruments coming online will give us much be... | [
"Would a moon-based telescope give a better image due to a lack of atmosphere?"
] |
[
"Various cultures eat cow brains on a regular basis. Is this not dangerous? Why isn't there a high rate of BSE in these cultures?"
] | [
false
] | maybe I'm just ignorant? But I thought eating brains was a dangerous thing to do and carried the risk of contracting certain types of diseases Like bovine spongiform encephalitis? yet these cultures don't seem to have a high rate of that disease. Re: . Beef brains and veal (juvenile beef) or calf's brains are used in t... | [
"Eating brains does run a higher risk than eating muscle or other organs, but that risk is still very low. If you read about the epidemiology of Creutzfeldt–Jakob disease (CJD), the most common prion disease, the incidence was 1 in 1,000,000 from 1979 to 1994 and 5 in 1,000,000,000 in those under the age of 30 in t... | [
"Tougher for the prions to transmit from cows to humans, however, cultures like the \"Fore\" in Papua New Guinea experienced much higher rates of prion-related diseases, ",
"Kuru",
", because they used to consume the body and brains of their deceased. Ironically, they only would participate in this ritual if th... | [
"Any relation to whether or not the cattle herds in question ate cow products? I was under the impression that part of the problem in the US was that cows were being fed (among other detritus) ground-up cow leftovers."
] |
[
"Why do we measure precipitation in inches? It seems primitive to me."
] | [
false
] | null | [
"Why is it primitive? Do you suggest centimeters then?"
] | [
"At the very least I would suggest changing to metric measurement, but I was meaning the way that it is measured, as it is currently how much rain/snow falls in one particular spot. Possibilities I could think of were perhaps the amount of time that the rain fell, or some kind of measurement based on the size of th... | [
"Wouldn't you rather want to know how much rain fell?",
"Instead of how long it fell for or how big the clouds are (which doesn't tell you anything too conclusive about the amount of rain in it either).",
"I'd rather know how much rain fell yesterday, than how long it rained for -- especially when the rate of r... |
[
"How high bats can fly? Is the maximum altitude comparable to birds one?"
] | [
false
] | null | [
"https://en.wikipedia.org/wiki/R%C3%BCppell%27s_vulture",
"\n11km, can check prays from above",
"Bats",
"\nno real need of altitude except for migratory purposes, but the Plecotus auritus found near the Himalaya was seen up to 3.3km.",
"Also, just found bats got the record of horizontal speed (160km/h inste... | [
"Numbers are impressive, especially those 11+km, where weather conditions are so deadly. Thanks!",
"Worth to notice that at 160km/h bats may be faster than cheetah :-)"
] | [
"Hold-on, That might be a mistake",
"https://www.newscientist.com/article/2112044-speedy-bat-flies-at-160kmh-smashing-bird-speed-record/",
"\nsays",
"The fastest bird on record for level flight is the common swift (Apus apus), which reaches around 112 km/h.",
"But ",
"https://en.wikipedia.org/wiki/Fastest... |
[
"How do you calculate the average sum of dice rolls when a \"drop the lowest roll\" mechanic is used?"
] | [
false
] | In various tabletop role-playing games, game designers will often use a system to set character statistics that is some derivation of "roll an x-sided die y-times, drop the lowest z rolls, and sum up the results." The most common example of this is rolling a 6-sided dice 4 times and dropping the lowest result. Now, ca... | [
"Suppose we roll a die ",
" times and label the results as X",
", X",
", ..., X",
" and let ",
" denote the minimum roll. Then the sum of the best N-1 rolls is",
"S = X",
" + X",
" + .... + X",
" - M",
"Expectation is linear and all of the X",
"'s have expected value (d+1)/2 where d is the num... | [
"The formula for E(M) (the expected value of the minimum roll) is given above. Just put N = 2 and d = 20. It's about 7.2."
] | [
"This is a perfect response and exactly what I was looking for. Thanks!"
] |
[
"How is it that you can compress TBs of data into small easy to move zip files? Shouldn't the data take up the same amount of memory all the time?"
] | [
false
] | I don't get how you can make data take up less space even though it is the same amount of information. | [
"Imagine you had a file which consisted of a 4TB long string of \"1s\". You could compress that file into the following line:",
"\"This file consists of a 4TB long string of 1s\"",
"Basically compressing a 4TB file into something under 50bytes.",
"It's a silly example, of course, but the idea is that compress... | [
"Compression assigns shorter outputs to more probable inputs. Lets say my input was something like AAABCABAABA. I would assign A- 1 B- 10 and C-100, thus the sequence would be compressed as",
"1 1 1 10 101 1 10 1 1 10 1,",
"which is 16 bits long. If you were to going to use a naive binary scheme where each lett... | [
"More probable sequences are more heavily compressed.",
"And the corollary is that a truly random data stream cannot be compressed in this way. Compression algorithms take data with redundant data and turn them into shorter sequences of more random data, which is why you cannot zip a zip file repeatedly to make ... |
[
"How did the elements form after the big bang?"
] | [
false
] | null | [
"Stars. All elements heavier than helium (some lithium ?) are formed inside stars and released into the universe during nova's. Elements up to iron release energy when they fuse, and this help drive the stellar engine. Elements heavier than iron are formed during supernovae."
] | [
"It's hydrogen, not helium and the 'pressure' bringing it together is gravity. How does hydrogen form ? It's the simplest element there is. One proton and one electron. It was formed during the big bang. "
] | [
"As the universe cooled",
"Just to note, the net energy of the universe is always the same. The fact that the universe expanded is why we say \"the universe cooled\"."
] |
[
"Can someone explain this sentence? \"[Gravity] is just the differential rate of time between high places and low places.\""
] | [
false
] | [deleted] | [
"It's a not-necessarily-wrong but also highly unorthodox way of describing gravity. You might say that objects \"want\" to be in places where time runs slower, so if an object is in one place, and right next door is a place with a slower time rate, it will tend there, the way a ball on a hill \"wants\" to be in low... | [
"This is a very odd way to think about it, and without further explanation I think the author is being misleading to a layman. (and trying to sound fancy to get more books sold)",
"So in GR objects follow ",
"geodesics",
", which is a generalization of a straight line in a flat space. (shortest 'distance' bet... | [
"You might say that objects \"want\" to be in places where time runs slower, so if an object is in one place, and right next door is a place with a slower time rate, it will tend there, the way a ball on a hill \"wants\" to be in lower rather than higher places, so it falls to the lowest place available.",
"It se... |
[
"How is hairgrowth regulated?"
] | [
false
] | How come your body hair stops growing at a certain length, but after shaving it grows again? | [
"Pubic hair sheds after about 5 months, I believe. If you cut it to half length, it'll just keep growing until it's destined to fall off."
] | [
"This is actually pretty interesting. ",
"You see, each hair follicle follows it's own schedule. Put simply, it's either in a growing stage, or a resting stage. So, when you cut your hair, some of the hair you cut is still 'growing', and so grows back when you shave.",
"It seems like it stops growing at a certa... | [
"I don't really get this. My assumption is that e.g. pubic hair grows to a specific length and then it stops growing. Is this even correct?",
"Now if I cut all that hair to half length, wouldn't it grow again to its specific lenghth? How does it know that it was cut?"
] |
[
"If your looking through the window of a spaceship traveling at near light speed as a stationary observer what do you see?"
] | [
false
] | You are a stationary observer with a very powerful telescope. There is a spaceship traveling at near light speed. You point your telescope at the window. To you does it appear that the people in the spaceship are moving in slow motion? | [
"look compressed along the axis of movement",
"Nope, see ",
"Terrell rotation",
"."
] | [
"Yes, they would look like they are moving in slow motion as they ARE moving in slow motion. However, if you are looking from inside the ship at someone outside, they would be the ones moving in slow motion. ",
"The people in the ship would also look compressed along the axis of movement of the ship, making for a... | [
"Thanks for that. I was simplifying (perhaps over-simplifying) the optical effects of relativistic motion due to the OP having seemingly basic understanding of the subject.",
"The effects that contradict the statement regarding optical compression are only apparent when the object is viewed parallel to its moveme... |
[
"Do taller people die younger?"
] | [
false
] | This has only just occurred to me. I don't think I've ever seen a really tall person who's about 85+ years old, and it certainly seems that all the people who manage to get to 100 are typically very very small. I know that people "shrink" as they age but I cant imagine a 6"2 skeleton inside any of the elderly people I'... | [
"Yes.",
" There are a couple of reasons for this. One is that tall people's hearts have to work harder to circulate blood, which will wear them out more over time. Another reason is that tall people have a larger number of cells than short people, which will lead to a statistically increased risk of cancer. "
] | [
"There probably is an association between being tall and earlier death. One recent paper (",
"Shorter men live longer: association of height with longevity and FOXO3 genotype in American men of Japanese ancestry.",
") found a relative risk of 1.006 per cm of height, which is a very small though statistically s... | [
"tall people have a larger number of cells than short people, which will lead to a statistically increased risk of cancer.",
"By the same reasoning, whales shouldn't exist. This is known as Peto's paradox."
] |
[
"Could a person have two different sets of DNA due to early mutations?"
] | [
false
] | Please excuse my bad non scientific english, english is not my native language: Okay so as far as I know mutations can occur when cells are creating copies of themselfs. Now lets imagine an early fetus that has it's cells dividing and there is a mutation in one of the cells that changes its DNA. This cell keeps on repl... | [
"Not to nitpick, but are you sure? ",
"A chimera or chimaera is a single organism (usually an animal) that is composed of two or more different populations of genetically distinct cells that ",
"(My emphasis added.)",
"The cells in the OP didn't originate from different zygotes... "
] | [
"Your body does, in fact, have many \"different sets of DNA\" although phrasing it that way makes things sound exciting than they actually are. Most of the differences we're talking about are very tiny (for example a change to a single one out of the 6 billion bases of DNA that make up your genome) and will have no... | [
"Thanks for the answer!"
] |
[
"Could our universe be a 4 dimensional shape?"
] | [
false
] | In the same way that we thought the earth was flat even though it's a sphere, could the universe that we perceive as 3 dimensional exist in 4 dimensional space? | [
"Technically we ",
" perceive it as 4-dimensional, with time being the fourth dimension. However, IIRC it is widely thought to be at least** a 4-dimensional shape. But we will never be able to perceive it as such because we live in a 3-dimensional (4 with time) world. The book ",
" does a great job ",
"explai... | [
"Currently it looks like space is flat and don't have curvature, or it's very small. Space can be infinite or not. ",
"http://map.gsfc.nasa.gov/universe/uni_shape.html"
] | [
"Currently it looks like space is flat and don't have curvature, or it's very small. Space can be infinite or not. ",
"http://map.gsfc.nasa.gov/universe/uni_shape.html"
] |
[
"Why are most amino acids found in the L configuration and most sugars in the D?"
] | [
false
] | My biochem prof briefly stated that they fit together well because they're opposite configurations, but said she didn't have time to get into it because it's only a 5 week course instead of 17. Is there a reason that it's this way and not flipped so that AAs are in D and carbs in L? Is there something fundamentally un... | [
"This is a huge unresolved question (sorry, couldn't resist a little chirality humor there). It has major implications for origin-of-life studies, but despite a great deal of research over the decades, there's no definitive answer. Various mechanisms have been proposed for those two optical series to have been slig... | [
"That is one of the big mysteries in chemistry. Until we find life on other planets, we won't know if luck or some deeper reason is responsible. ",
"One possibility is polarized light. Light in interstellar space is circularly polarized, so this might have an effect on enhancing or destroying one orientation o... | [
"There's no difference in stability or reactivity. The main reason is evolutionary - things get re-used both substances being re-use metabolically but also genes getting \"re-used\" evolutionarily. So there's a benefit if we all use the same stuff, which we do to a much higher extent than just chirality - we all us... |
[
"Ok, Scientists, Could engineers [et al] make a lead-shielded mechanical suit that could let a workers work on the Fukushima reactors? [Fukushima #2 blasting 73 SIEVERTS / hr]"
] | [
false
] | Just heard that Fukushima #2 is not a good place for a tea party, with the area just above the cooling water giving a healthy 73 Sieverts / Hr [that's Sieverts, NOT ] Someone has made a mechanical suit that lets a human lift lots of weight.. to wit So could you make a bigger, lead-armored suit that would let workers g... | [
"Why must it be a suit? A suit designed to track movements and give tactile responses could be used to control an unmanned vehicle with robot arms attached. We're at the point where it's so precise, we can perform surgery with it."
] | [
"Good point.. I'm hearing that this environment is too radiactive even for FUCKING ROBOTS to operate without extensive shielding... the radiation interfering with the electronics. I am interested to know how much lead would be needed to keep a person safe, or at least kind of safe for a while, in this kind of envi... | [
"I'm not the one that asked the question and I wasn't saying the title was at its most optimized and semantically-correct state (Jeez, who argues about this kind of stuff, really...)",
"I was just saying, it should be easy to understand what he was wanting to know (you understood just fine if you're able to sugge... |
[
"How do integral membrane proteins get associated within the membrane?"
] | [
false
] | Integral membrane proteins are tightly associated within the cells membrane but how do they get associated in the first place? Are there special chaperones that do this in the beginning of the cells life cycle? What are he stages between protein synthesis and membrane association? | [
"Many integral membrane proteins are transmembrane proteins (proteins that go through the lipid bilayer and have exposed parts on either side of the membrane).",
"Transmembrane proteins are inserted into the membrane as they are translated at the ER (",
"diagram",
"). For these proteins synthesis and membrane... | [
"Well, there's a chemical reason, and there's a mechanical reason that integral membrane proteins end up in the membrane.",
"First, the chemical reason: it all has to do with entropic favorability that integral membrane proteins want to be in the membrane in the first place. They have hydrophilic and hydrophobic ... | [
"Are there special chaperones that do this....",
"I believe you're looking for the ",
"translocon",
", at least for a number of cases IIRC."
] |
[
"What distinguishes wasabi (or any other horseradish) and hot peppers (such as tabasco) from each other in terms of their heat when we eat them?"
] | [
false
] | [deleted] | [
"Radish and peppers have different type of molecules that cause you to experience a hot sensation. Peppers contain the compound capsiacin which will directly bind to subset of temperature sensors and activate them. Rasishes on the other hand, generate allyl isothiocyanates as their \"hot\" compound. These two compo... | [
"Here are a couple previous threads on the subject:",
"Why do foods like wasabi, horseradish, and mustard make a person's sinuses burn? What is happening exactly to cause the sensation?",
"Why is the burn felt from eating a hot pepper different than that felt from eating horseraddish or wasabi?",
"Can someone... | [
"Spiciness as we know it is a function of the amount of a molecule called capsaicin. Spicier foods have a higher concentration of capsaicin. This is quantified (albeit in an incredibly subjective way) by the ",
"Scoville Scale",
". The Scoville number of a food indicates the dilution factor necessary to make no... |
[
"How is the original amount of C14 in a fossil determined?"
] | [
false
] | When it comes to carbon dating, I understand how the age of a fossil can be determined with the necessary information, being how much C14 is in the current fossil, how fast that C14 deteriorates, and the original amount of C14 in the animal. My question is how the original amount of C14 is determined? Looked everywhere... | [
"It's not the absolute amount of C",
" that matters, but the ratio of C",
" to C",
" in the sample. The atmospheric ratio is held more or less constant by the creation of C",
" from Nitrogen, but once stored inside a body, it will decay to ",
" N",
". The longer it has been since the body breathed or in... | [
"To add to this, the \"more or less constant\" originally threw off carbon dating a bit since it has not been perfectly constant. A calibration curve was created to correct for this using, among other things, dendrochronology from bristlecone pines. Bristlecones can live thousands of years (oldest currently alive... | [
"That's only a problem for dating plants that grew after there was a lot of nuclear testing. 1950 is considered the cutoff point. But for example wood from a tree cut down in 1610, we can still carbon date that, it's not affected by the later nuclear testing."
] |
[
"How do scientists \"figure out\" the chemical structure of things?"
] | [
false
] | How do we know water is made up of molecules with 2 hydrogen and 1 oxygen atom? How do we know the chemical structure of dextrose or propane or hexane? | [
"Ugh experimentalist....time to get a theorist in here to clean this up. ",
"Ok so the OP was asking how do we know there are two hydrogen and 1 oxygen atoms. While your answers aren't wrong, they aren't really answering enough. ",
"Yes in modern day we have techniques like NMR, IR, UV/VIS, etc to figure out s... | [
"So I will comment on the structure.",
"The two experimental gold standards for this are microwave spectroscopy and xray crystalography (other spectroscopic techniques exist but they are far less accurate).",
"In MW spectroscopy the spectrum is determined by 3 rotational constants that are inversely perportinal... | [
"I've rarely heard of many chemists using Microwave Spectroscopy regularly. And I know a lot of chemists who avoid using XRD for as long as they can. ",
"I'd say NMR (Nuclear Magnetic Resonance) and Mass Spectrometry are your main techniques. Both methods don't require much work up and give you quite a bit of dat... |
[
"Is it true that our eye needs to focus light for us to use it effectively, but our body doesn’t focus touch sensations, and yet we can still use our sense of touch effectively?"
] | [
false
] | null | [
"Some focus is needed, yes, but doesn't have to be perfect. Near and farsighted people can still see things even without their classes (although very blurry). You have different kinds of touch receptors, some are sensitive to more localized sensations (like pinpricks) and are more closely spaced (like on your fing... | [
"But is there any sense in which your body \"focuses\" touch sensations like the eye focuses incoming light?"
] | [
"No"
] |
[
"Since the outer layer of our skin is essentially dead cells, why isn't our skin a more attractive target for decomposing bacteria?"
] | [
false
] | Why wouldn't our outer skin normally rot? | [
"We have a protective layer of bacteria which prevents pathogenic bacteria that rot us from growing and our skin is quite acidic and low in moisture anyway which makes it hostile to invaders. The bacteria that live on us survive on compounds in sweat and oils."
] | [
"Probably, skin bacteria are adapted to our skin conditions and fight off any interlopers and, in general, other skin bacteria- they're quite antagonistic.",
"Skin cells falling off wouldn't kill bacteria, the acidic conditions and competition from other bacteria stops invading bacteria colonizing you. Symbiotic ... | [
"so, sort of a co-evolved/symbiotic relationship?\nalso, could it have anything to do with the fact that the dead cells are constantly falling off?"
] |
[
"How did we get the high resolution photos of the bright spots on Ceres?"
] | [
false
] | null | [
"The Dawn spacecraft, which went there."
] | [
"As ",
"u/rantonels",
" points out, it is from the Dawn spacecraft (a discovery class NASA mission operated by JPL/UCLA). The specific instrument in question on Dawn that took those pictures is the Framing Camera, an instrument from the German institution DLR. Dawn also has a visibile and near-infrared spectr... | [
"lol"
] |
[
"Do liquid form medications actually work faster than tablets?"
] | [
false
] | I see this in advertisements and packaging a lot, the claim that liquid form medicines (such as pain relief or cold medication liqui-gels, etc) are "fast acting", taking effect quicker than regular tablet formulations. Is there any truth to this? | [
"This question is surprisingly complicated.",
"Different routes of administration can result in different Tmax, which is the time to maximum concentration in plasma. I've seen a suspension formulation that beat a tablet, a gelcap that beat a liquid formulation, and a fast-acting tablet beat a liquid formulation.... | [
"Pharmacology PhD student here (finally, my time to shine!).",
"The short answer is, it depends on the medication. For a slow-release capsule, clearly it takes longer for all the medicine to get on board. But it's designed this way, because you have to take fewer pills throughout the day to get a steady state o... | [
"Can for example cold medicine react with other parts of the body which aren't interesting for recovery?",
"If I'm understanding you right, then the answer is yes. An example: ",
"pseudoephedrine",
" (Sudafed).",
"Pseudoephedrine is a sympathetic agonist (meaning it \"turns on\" the alpha and beta nerves o... |
[
"Why and how is it that the O blood type is recessive and yet O is the most common blood type?"
] | [
false
] | null | [
"So the percentages are 38% type O+ to 34% A+, so it's not ridiculously more common. Positive is also more common than negative. Some of these changes likely have to do with maternal incompatibilities making + more favorable. There have also been studies that type O is at lower risk of heart disease and certain can... | [
"Recessive doesn't have to mean \"bad\", although \"bad\" recessive alleles are widely known. There's little adaptive pressure on ABO blood types, at least prior to the invention of blood transfusions. I am unsure if ABO blood types have ",
" function.",
"In genetics, blood types are called I for \"isoagglutino... | [
"Those numbers change depending on what population you look at. Geographically or ethnically, the numbers can change. These days, it's not going to be some huge difference though. O is the older type, but A & B showed up a long time ago from a human perspective."
] |
[
"Is time divided up into discrete quanta? Is time \"quantized\"?"
] | [
false
] | null | [
"No this is just wrong. It is not known if time is discrete but if it is then the units are much smaller than a Planck time. A Planck time is the scale at which quantum events happen, and a discrete unit would have to be much smaller than that"
] | [
"This is not what the Planck scale is.",
"It's simply the scale at which our current models don't yield meaningful values anymore and we'd need Full Quantum Gravity to provide an accurate description of these kinds of interactions..."
] | [
"This is not what the Planck scale is.",
"It's simply the scale at which our current models don't yield meaningful values anymore and we'd need Full Quantum Gravity to provide an accurate description of these kinds of interactions..."
] |
[
"Why can't neural cells divide while other somatic cells can?"
] | [
false
] | I know basic biology, and, as far as I can understand, neural cells, such as brain cells and spine cells, can't divide and regrow once they are destroyed. This is why people with spinal damage are permanently crippled. Why is this? Are there restriction proteins stopping the division process? if so, which ones? Is... | [
"Surprisingly, we now know that neurons can both repair themselves (neuroregeneration) and divide (neurogenesis), but only to a small extent and in limited contexts. Otherwise, they are termed \"postmitotic\" and are in the G-zero phase of the cell cycle. It's believed this is a result of how specialized they are. ... | [
"They are post-mitotic and enter Go, as stated below. Think about it. Neurons have made connections to other cells in the brain and while some of these connections can be altered or strengthened over time (google \"cells that fire together wire together), it wouldn't make sense for a neuron to divide. It would h... | [
"Could you explain the contexts in which they can multiply?\nOr, can you provide the names of any articles that cover neural regeneration?"
] |
[
"Do water droplets oscillate naturally and, if so, what amplitude and frequency do they oscillate at?"
] | [
false
] | So I have had an idea for a while now that I have recently started to explore properly and I am having trouble distilling the information out there into the information that I need. Since we have such a good variety of experts then maybe someone already knows what I need. Suppose you have a droplet of water or other ae... | [
"A while back I came across ",
"this paper",
", which seems close to your question. These guys (dia)magnetically levitated water drops of different sizes in a solenoid and looked at the vibrations as a function of the size. For example, for a drop about 6mm in diameter, the vibrations were on the order of 0-100... | [
"Wonderful, exactly the kind of stuff I was hoping for. ",
"They seem to be concerned with the effects of the trap on changing the frequencies but this is the knife needed to wedge open the literature seam I think.",
"edit for your edit: Yeah, seems reasonable. The question of amplitude remains, which I knew wa... | [
"Something that is sort of opposite this is a gas bubble in a liquid. The competing external pressure of the fluid and internal pressure of the bubble cause harmonic oscillations. These oscillate at what's called the Minnaert frequency, which is associated with the sound made by babbling brooks. The angular freque... |
[
"Why do firearms (especially fully automatic firearms) recoil upwards, instead of just recoiling directly backwards in the opposite direction of the bullet? Additionally, why do they recoil up instead of sideways or down?"
] | [
false
] | null | [
"Recoil pushes the gun backward towards the shooter, but the barrel is usually off-center compared to the handle and weight of the gun.",
"Your hand, holding the handle of the gun and looped into the trigger, creates a pivot point, which pulls the gun around, pointing upward.",
"If the gun barrel were somehow b... | [
"Older rifles",
" had the sights right on top of the barrel, which to fit to the shoulder required the stock to bend downwards. This of course ended up creating a torque and pushing the barrel upwards. ",
"Modern rifles",
" have the sights above the barrel so the stock goes directly back into the shoulder to... | [
"Yes, I have noticed in high speed movies of guns like a semi automatic pistol, the gun doesn't kick much until the slide travels backward and hits the stop. Then the gun flips upward. So the spring is absorbing the recoil, until it can't."
] |
[
"Why do some things burn and others don't?"
] | [
false
] | null | [
"Things that burn have a chemical structure that allows their molecules to form simpler, energy-stable molecules in a chain reaction that is started when heat energy is added. ",
"The heat provides the energy for the more complex molecules to form less complex ones. When they change, the new forms requires less e... | [
"\"Complex\" might not be the best adjective. Take for instance hydrogen, or pure metals, which can be very energetic fuels. Oh, and carbon. Come to think of it, I wonder if silicon burns well."
] | [
"O2 isn't the only oxidizer that can propagate a combustion reaction. The oxidizer just has to have a higher electronegativity than the substance it is oxidizing so it can win the 'battle' for the electrons. F2 can also be used to propagate a reaction when O2 is not present or isn't capable of oxidizing a substance... |
[
"What universal constants are in the range of size/time which humans can relate to?"
] | [
false
] | Most are far too huge (speed of light) or far too small (size of even the longest non-chain molecule) The only one I can think of is the few dozen half lives between Carbon 15 (2.449 seconds) and Nickle 63 (a hair over 100 years). This isn't very helpful for me, as a half life is by definition an average of a random ev... | [
"I always found it fascinating that a Planck unit of energy is about the same as a tank of gasoline.",
"There's also the ",
"barn-megaparsec",
"; a barn is a unit of nuclear cross-section and multiplying that area by one megaparsec produces a unit of volume equal to about 2/3 of a teaspoon."
] | [
"I'd just like to point out that the barn-megaparsec is ",
" a physical constant in the sense of Planck's constant or the speed of light."
] | [
"You must choose which units you work with, because the choice of units scales the universal constants. As a (boring) example, take the atomic units (",
"http://en.wikipedia.org/wiki/Atomic_units",
"), they are chosen so that\nelectron mass = electron charge, hbar, coloumbs constant = 1.",
"But assuming you w... |
[
"WiFi signals are electromagnetic radiation, which are photons. How do they travel through walls?"
] | [
false
] | As above. Where am I confused? Edit: thanks everyone! | [
"ELI5: Walls are see-through in a color we can't see."
] | [
"Photons are absorbed by different materials depending on their energy (proportional to the frequency of the electromagnetic wave that they represent). The reason for this is that when a photon is absorbed by an atom, its entire energy must be absorbed by an electron, which \"jumps\" up to a higher energy level ins... | [
"Yeah - that's how UV sunglasses work. They're opaque to UV but let visible wavelengths through."
] |
[
"If You Can Smell the Odor of something, Are You Breathing in Microscopic Particles of that Substance?"
] | [
false
] | null | [
"Yes, although when we say \"the smell of this thing\" we may be referring to a different microscopic particle which is associated with that thing's presence.",
"For example, the smell of rain is not tiny particles of rain, but rather ",
"geosmin",
", which \"occurs in the air when rain falls after a dry spel... | [
"And the smell of feces is mostly due to gasses that do not constitute \"poop\" in a literal sense."
] | [
"But more to the point here. When you smell poo you are smelling the gases emitted by poo. You are not inhaling microscopic bits of poo. I may be wrong but I think that was the real question/concern."
] |
[
"Scientists created a “radioactive powered diamond battery” that can last up to 28,000 years. What is actually going on here?"
] | [
false
] | null | [
"Link to the article in question",
"This battery is basically similar to the ",
"radioisotope thermoelectric generators",
" used in space probes: radioactive material decays, which produces heat, which is converted to electricity.",
"The researches here have found a way to make such a battery quite small, d... | [
"It's also old news and the specific power output is really low.",
"https://phys.org/news/2016-11-diamond-age-power-nuclear-batteries.html",
"https://theness.com/neurologicablog/index.php/nuclear-diamond-batteries/"
] | [
"https://theness.com/neurologicablog/index.php/nuclear-diamond-batteries/",
"Nice read. Quoting it:",
"Even with low power density, we could theoretically fill a warehouse-sized building with millions of NDBs and hook them up to the electrical grid. This would provide steady power for thousands of years.",
"P... |
[
"Given how difficult it is to get off our own planet, how would we go about bringing a team of people back from the surface of mars"
] | [
false
] | I realise that Earth's gravity is greater than that of mars but I assume it would still take a lot of fuel to get back off the martian surface. Would we send fuel ahead of the landing party or use ice from the surface to create fuel down there? It's been a slow day at work and my mind has started wandering to things li... | [
"There are a lot of plans to this effect. ",
"Some use multiple launches to land multiple objects on mars, including habitation modules, fuel, a rocket to get back, etc. ",
"Some want to send a small factory to mars which will produce the fuel necessary. ",
"Some don't want it to be a two way trip at all. I... | [
"Just off the back of this, would it not be more practical to build a kind of mini ISS in orbit around mars instead of going straight to the surface? Surely we could learn a huge amount about the planet from orbit and shipping supplies to a station is much easier and carries less risk to the payload? Could we then ... | [
"We don't need to send people to mars to study mars. That can be done with robots. ",
"We send people to mars as the first steps of colonization, the first steps at sending humans to permanently inhabit more than one world. It won't be an overnight process to colonize. It'll be long and difficult. But simply put:... |
[
"There has been an increase in electric car sales. How do we dispose of their batteries, once their lifespan ends? And would disposing batteries release less pollutants compared to gas engines?"
] | [
false
] | null | [
"Lithium-ion batteries used in electric cars get worn out when they can only retain about 80% of their charge. That being said these batteries are still perfectly good for other applications like backing up solar or wind power. So these batteries are first repurposed once they can no longer be used for electric car... | [
"Batteries would have to be properly disposed of and not dumped in a site, improperly disposed batteries could mix with rain water and release toxic chemicals into the soil and contaminate any nearby lakes or rivers making it more devastating than gas engines... "
] | [
"Thanks! That’s a very informative answer!"
] |
[
"As global temperatures increase, will cloud cover also increase and buffer temperature increases?"
] | [
false
] | If surface temperatures are hotter, there should be more evaporation leading to more cloud cover with a higher albedo. Will this buffer temperature rise, or am I missing something? | [
"Hello! We discourage addressing yourself as a source. A source should be external corroboration that independently verifies your statements. You being a graduate student in itself does not constitute a source."
] | [
"Hello! We discourage addressing yourself as a source. A source should be external corroboration that independently verifies your statements. You being a graduate student in itself does not constitute a source."
] | [
"It is entirely possible that clouds will be able to partially offset increasing surface temperatures, but the net effect that clouds will have has yet to be determined.",
"It's ",
", but there is mounting evidence that it is not true; in fact, clouds likely constitute a small, but ",
" feedback to warming. F... |
[
"Is the universe still growing?"
] | [
false
] | Apologies if this question has been asked before. I googled some other posts but they didn't seem to address this question directly or in a way I could understand. I vaguely recall someone somewhere making a comment that the universe itself is expanding and not simply that the distances between galaxies are increasing... | [
"Yes, ",
"the universe is still expanding",
". Hubble was built to answer the question of whether the universe is expanding or contracting, and how fast. It's evidence showed that the universe is expanding. In fact, the rate of expansion is ",
", so it is expanding faster and faster. How and why this is happe... | [
"Both evidence and theory suggest that the universe will never slow down in its rate of expansion. The \"still growing?\" question seems to assume the universe is growing from a smaller place to a larger, and this is not the case - it's not expanding INTO anything. Google \"universe big rip\" and check the Wikipedi... | [
"In fact, the rate of expansion is increasing, so it is expanding faster and faster.",
"So it's unknown whether or not it will slow down?"
] |
[
"Why does an oil/soap film look colored due to interference when everyday light is not coherent?"
] | [
false
] | null | [
"All light has some degree of coherence, even sunlight. One way to view coherence is to see when you split one beam into 2, how much of a difference in the optical path they would have and still interfere. Now the bigger that difference the bigger the coherence length. Coherence also depends on the spectrum:\n Lc =... | [
"Oh thank you! That is certainly very interesting! I learned something new today thanks!",
"What about the light from artificial sources like tubelights in our home etc? Do they have that much coherence lenght? "
] | [
"Here",
" you can read the article without paywall. I think its message is slightly different. Unfiltered sunlight has a coherence length of 600 nm which is about equal to the wavelength of yellow light, so it is hardly coherent. However, the photoreceptors in the eye (cone cells) contain filters with a narrow ba... |
[
"Can we do anything interesting with the weak force?"
] | [
false
] | We are pretty good at harnessing electromagnetism to do useful things. Can we make the weak force do anything interesting or useful? I don't mean wait around to see randomly occurring beta decays, I mean set up a weak field to harness the force in some way. | [
"There have been proposals to use neutrinos for communicating through the Earth or with submarines."
] | [
"Don't underestimate the power of beta decays. Voyager 1 and 2 spacecrafts that explored the solar system and now interstellar space are powered indirectly by weak force. They put around 13kg of plutonium. The weak force interaction makes beta decay happen and this generates a lot of heat which is then converted to... | [
"I've met someone who worked on neutrino detector to \"spy\" nuclear power plant (for example in Iran). The conclusion of her Ph.D work was that it's feasible but only very close to the detector meaning that (again for example the Iranians) could just build nuclear weapons 100 meters away. ",
" : Clarified the un... |
[
"How will the end of the universe be different from before the big bang? Will there be a discernible flow of time?"
] | [
false
] | [deleted] | [
"Nobody can answer this question because nobody knows anything about \"before the Big Bang\". In fact, it's generally accepted that the universe itself was created in the Big Bang, so asking \"What was the universe like beforehand?\" doesn't have any meaning.",
"That being said, one possible scenario for the end... | [
"Not really. Heat death may be a more precise definition, but they describe the same fate of the universe.",
"The heat death of the universe is a final state in which there is no thermodynamic free energy with which to perform any work, which is a very specific state. The Big Freeze more generally refers to the... | [
"Just because something would happen a long time from now doesn't make it speculative. Rather, our incomplete knowledge of the physics involved in the universe, make it speculative. An alternative to the big freeze is the Big Crunch, the opposite, in which gravity wins out, and everything gets pulled together into ... |
[
"Can a superconductor get trapped in it's own magnetic field?"
] | [
false
] | null | [
"But a superconductor is subject to the meissner effect."
] | [
"No, because the magnetic field has no affect on the object itself"
] | [
"You might first consider why ",
"this contraption",
" doesn't work. It's not an entirely trivial issue despite the joke nature of it. A self-suspended solenoid isn't very different than that."
] |
[
"What's the difference between Crigler-Najjar syndrome and Gilbert syndrome?"
] | [
false
] | I've read much about them, and all I know is they are the same: same mutation (2q31.1), same damaged protein (UDP-glucuronosyltransferase), same symptoms, same inheritance (autosomic recessive); what's the difference? | [
"Gilbert's Syndrome is a defect where the enzyme is still functional, but in a lower proportion. Thus, bilirubin will not accumulate unless under minor physiologic stress (that includes drinking, lack of sleep and so...) and neonates will not be usually affected. \nIn Type I Crigler-Najjar syndrome the enzyme is co... | [
"Thank you so much, you are smarter than the internet. Only thing I could find is that bilirrubin concentrations are 100 fold higher in the Crigler-Najjar. Now it all makes sense."
] | [
"You're very welcome!"
] |
[
"Water Pressure"
] | [
false
] | I was reading on deep sea creatures withstanding high water pressures, and a question came to me. If I were to take a vessel to a certain depth and seal it at that depth, would the water pressure in that vessel stay the same, or would it change when brought to the surface? Of course, this is all assuming some ideal ves... | [
"Water doesn't compress all that much, so the amount that it has to expand to change from 10 atm to 1 atm is miniscule.",
"So, if you had a perfectly rigid vessel to keep the water in, it would still be at 10 ATM when you brought it back to the surface, and wouldn't equalize to 1 ATM until you opened it. When yo... | [
"If you vessel had a valve on it that you then opened at sea level it would spew out water like nobody's business.",
"Water is pretty incompressible.",
"With a non-replenishing container, it would only take a small volume of water to escape to equalize the pressure. "
] | [
"The pressure in the vessel would remain the same at whatever level you sealed it at. If you took the vessel to 1000ft below sea level and filled it up the pressure would be about 445psi. In comparison the air pressure at sea level is about 14.7 psi. If you then brought this vessel back up to sea level the pressure... |
[
"Are emotions innate or learned ?"
] | [
false
] | I thought emotions were developed at a very early age (first months/ year) by one's first life experiences and interactions. But say I'm a young baby and every time I clap my hands, it makes my mom smile. Then I might associate that action to a 'good' or 'funny' thing, but how am I so sure that the smile = a good thing... | [
"Paul Ekman and Wallace Friesen demonstrated that there are universally understood facial expressions which transcend cultural knowledge. In one experiment they went to Papua New Guinea and showed Fore tribesmen photographs of people making faces of happiness, fear, anger, disgust, sadness and surprise. Despite 1... | [
"Ekman's work is highly controversial and oft-criticized, so this is really only a small part of a much larger answer. Indeed, to fully answer this question, you'd have to address not only Ekman's views, but also those of LeDoux, Barrett, Russell, Panksepp, Izard, and so on. To suggest that emotions are definitel... | [
"PhD student in psych who studies emotions here.",
"Paul Ekman had some studies that showed what appeared to be innateness (as cited in another answer), but recent work by Lisa Feldman Barrett has (imho) cast doubt on innateness hypotheses (and basic emotion views in general). ",
"Here",
" is a 2014 Emotion p... |
[
"Is there a theoretical ceiling to the human ability to learn?"
] | [
false
] | null | [
"I dunno, it seems like we've reached a point where our intelligence is so vastly greater than any potential competing species that there's really not much selection pressure in favor of even more powerful brains. "
] | [
"Certainly. One of the major anthropological findings we see in human evolution is that, over time, the size of the cranial cavity increased vastly.",
"It is therefore likely that future humans will be able to grasp even more complicated concepts than we could ever hope to. Who's to say that any alien races we en... | [
"It also ignores our growing ability for self-guided evolution."
] |
[
"What determines how our voices sound?"
] | [
false
] | I mean, I understand genes must play a role, but how? How can a husky voiced mother and a gruffy voiced dad have five adult daughters with high pitched voices? Why do I sound different from my sisters? How do we all get our unique sounding voices and rarely sound like anyone else? | [
"Voice is a factor of a few things. First is the larynx, or \"voice-box\" (your adam's apple). Inside the larynx are two flaps of tissue attached to small muscles--the vocal folds or vocal chords. The muscles and cartilage in the larynx puts the chords under various amounts of tension, and when air passes over them... | [
"To add, take a look at ",
"this video.",
" You can see how much the resonance in the vocal tract changes the sound coming from your vocal cords. "
] | [
"It has to do with the way sound resonates from the air being passed through your vocal folds in the larynx, the movement of your mouth and tongue, and even the sinuses within your skull. This ",
"video",
" is very explanatory."
] |
[
"Can you effectively cool your house using evaporation?"
] | [
false
] | Evaporation of water, being an endothermic process, cools the area around it. What I want to know is can this process be used as a cheap way to cool your house? Specifically, I would like to know if this process would be plausible in an apartment, and if so, what equipment would I need to get? | [
"Yes, in certain areas (you need low humidity ambient air). It's called a swamp cooler."
] | [
"Yes, but as nalc said it is most effective in dry areas because more evaporation means cooler AND a good thing to mention is you also have to consider humidity. If you have constant evaporation you better either have some way to get the humidity out or keep dry air coming in.",
"Evaporative cooling"
] | [
"thats how we lived in Death Valley in 1960s"
] |
[
"Could a nuclear powered Ships be feasible?"
] | [
false
] | null | [
"Yes there are several nuclear aricraft carriers and even nuclear ice breakers across the world. They do not have smokestacks because they use pumped seawater as cooling."
] | [
"I'm asking this because I'm doing a writing thingy so pardon me if this question is absolutely inane buuuuuuuuuuuuut",
"If there was a smokestack, would it have any benefits? Or would it be mostly cosmetic, and thus if damaged by lighting strike or something would the boat still be safe to function?"
] | [
"Well you don't need one so you don't put one on. But if you had one it would just be useless weight and it being damaged shouldn't affect the way the ship work too much."
] |
[
"Is there any evidence space actually curves in the presence of gravity and isn't just a field effect like magnetism?"
] | [
false
] | If space is empty how can nothing curve? Do they actually mean a fabric like the aether curving? | [
"\"ancient and medieval thinking, not modern science\"",
"\nIt was a legitimate theory proposed and investigated by founders of modern science - Newton, Huygens, Fresnel, Young... There is nothing unscientific about having a theory that turns out to be wrong."
] | [
"To play the devil's advocate, the \"curvature of the space-time\" is a very abstract concept. Claiming that the space itself curves has a very specific meaning that cannot be extrapolated intuitively.",
"We describe how particles move by putting them on top of a \"background geometry\" and calculating the shorte... | [
"That was ancient and medieval thinking, not modern science.",
"The aether was well within the tradition of modern physics. The Michelson-Morley experiment which put it to rest was done by the head of the American Chemical Society and a Nobel-winning physicist. It was no phlogiston or medieval music of the sphere... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.