title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"can anyone explain why gravity exists?"
] | [
false
] | null | [
"We don’t know."
] | [
"oh, well i didn't take physics further than a levels so i thought maybe later on there'd be an explanation"
] | [
"Generally physics can't say \"why\" things exist. We try to create models for ",
" things work, but basic questions like \"Why is there gravity?\" is not something that physicists can necessarily answer."
] |
[
"Why do many hygienic and medical items have diluted concentrations of the active ingredient(s)?"
] | [
false
] | [deleted] | [
"The proposed mechanism for the disinfecting power of ethanol is that it diffuses into a bacteria, where the high concentration messes up the internal functions. A higher concentration is thought to denature proteins (since they are soluble in water), which can block the diffusion process once denatured. Kind of li... | [
"Because more doesn't mean better. In both of these cases, the application involves contact with people, so there's the extra consideration of safe doses. Always use enough to do the job, but not more than necessary.",
"Even for other applications with no human contact, more is not better. For example, disinfecti... | [
"Wow, how does that work?"
] |
[
"Why do installing/uninstalling some software take system restart (PC) while others don't? What is the basic difference in these software?"
] | [
false
] | null | [
"Some software needs to replace files that are normally in constant use while the computer is running. Since allowing a file that is actively being used to be written to can cause serious corruption (in extreme cases, unless the update is properly synchronized), the installation asks for a restart and updates the f... | [
"Technically, you could work around this and develop systems that would never require a reboot (even when updating the main kernel itself, the kernel being the software that runs all the other software), but it is extremely technically challenging and not worth doing for consumer software.",
"This ability has exi... | [
"Linux can even load a new kernel without rebooting, or patch a running kernel.",
"http://en.wikipedia.org/wiki/Ksplice",
"http://www.ibm.com/developerworks/linux/library/l-kexec/index.html",
"(whenever I have to manage a M$ server, I feel like I'm going back in time.)"
] |
[
"How does stretching before exercise prepare muscles (specifically muscle fibres) for periods of high levels of muscular activity?"
] | [
false
] | [deleted] | [
"Actually the science suggests that stretching prior to exercise has no impact on preparing muscles prior to exercise.",
"There are several articles in the literature that stretching does not reduce the chance of injury, here's one:\n",
"http://europepmc.org/abstract/MED/10593217/reload=0;jsessionid=UJQVSGChXyp... | [
"Already been said, but static stretching (touching your toes, leaning against a wall to stretch calves, etc) doesn't really do anything for you and can actually increase chance of injury but decrease strength. It's better to do what is called dynamic stretching: butt kicks, high knees, running in place, throwing p... | [
"Just confirming what everyone else is saying here; studies suggest it weakens the muscles. Bodybuilders for example do not stretch prior to exercise, instead do warm up sets with very light weights.",
"http://www.drgangemi.com/2011/04/stop-stretching/",
"http://science.slashdot.org/story/08/11/07/1421242/stret... |
[
"How can there be clouds when it's freezing?"
] | [
false
] | I always assumed that clouds where just evaporated water. And if you have a lot of evaporated water, you would get a cloud. Then when the cloud cools down, you get rain. So how can there be clouds when it's freezing outside? how can there still be evaporated( and thus warm water) still be in the air? | [
"Clouds are indeed made of microparticles of water; however these microparticles can either be droplets of water or crystals of ice. Several of the higher altitude cloud types (cirrus for instance) are made of ice micro-crysts, carried away as dust by the strong winds of the altitudes where they are found. "
] | [
"Okay so a large amount of water vapour is not the only condition for clouds to form. It is quite difficult (requires very high vapour pressures) for water to transfer from a vapour to a liquid by itself. If it has a surface around which to transfer this process is much easier. This is why Cloud Condensation Nuclei... | [
"When you get high enough in the atmosphere, the sun also helps keep the waters energy high enough to keep it from condensing into rain. "
] |
[
"I have a question about the moon. When did all those craters happen, and why isn't it happening now?"
] | [
false
] | The moon is full of craters, where are all the meteors? | [
"A lot formed during the Late Heavy bombardment, shortly after the moons formation. There have been a fairly constant stream since then. The reason you don't see the same cratering rate on Earth is that we have an atmosphere and active tectonics which recycle our crust, and erode the surface."
] | [
"Agreed with OrbitalPete. It should also be added that it is, to some extent, still happening now. Just to a much smaller extent, but it still gets hit.",
"Here",
" is a great video (halfway down page) on the moon's evolution. It is a great 8 minutes.",
"EDIT: ",
"where are all the meteors?",
"So the mo... | [
"Meteors are ",
"still crashing into the moon",
".",
"However, the number of large impacts will be much less than that those closer to the moons formation as the number of large meteors has decreased over the millions (billions) of years since then (as they have all already had time to crash into things if th... |
[
"When creating a supercooled ice water solution, why does the ice remain as ice?"
] | [
false
] | null | [
"Because there is too much ice for that to happen. Melting ice requires heat input, so heat is transferred from the salt solution to the ice. This has the effect of cooling down the liquid and melting part of the ice simultaneously. However, it takes a lot more heat to melt ice (about 333 kj/kg) than to cool down w... | [
"I think something else important to note is that for a well-mixed substance that consists of some solid and some liquid of the same substance (such as ice water), both substances will be at the same temperature - the melting/freezing point. (The same is true for a substance that is part liquid and part gas, such a... | [
"1) How does ice water actually lower in temperature?\nIt takes energy to break the bonds holding the water molecules together. A hefty 80 calories are to melt 1 gram of ice, and yet it takes only 1 calorie to change the temperature of liquid water by 1ºC. When ice melts it takes the energy from the surrounding env... |
[
"What are some examples of widespread, evolutionarily unbeneficial traits, which were preserved in a group, because they didn't negatively affect the population enough to cause them to die out?"
] | [
false
] | Edit: To clarify - when I said unbeneficial, what I meant was that it's typically (to the best of my understanding) the traits which lead to better adaptation to an environment which are passed on, because they make the species more able to survive. What I'm wondering is whether there is for instance an animal which came in to a new territory, a descendant of which adapted in a certain way that gave it a strong benefit, and then the descendants of that animal had such a much easier time surviving that there were a ton of shitty traits that different members of the species, or subspecies or new species developed, but which they were strong enough to get by with regardless. | [
"Can you express the idea \"evolutionarily unbeneficial\" in other words? Because there is no benefit-seeking mechanism in evolution, only survival, the term \"evolutionarily unbeneficial\" seems to be self-contradicting.",
"Consider native species being extincted by invading species. Would you deem the traits of... | [
"the term \"evolutionarily unbeneficial\" seems to be self-contradicting.",
"It's ugly and grammatically questionable but it is not contradictory at all. It just means a constraint or a neutral or nearly neutral trait. Here's some examples off the top of my head:",
"Fish swim using horizontal undulations. Repti... | [
"The blind spot in vertebrate eyes and nipples on male mammals are both evolutionarily beneficial in a strict sense. ",
"Changes to the genome severe enough to eliminate the blindspot in vertebrate offspring would also be severe enough to render the offspring eyeless, so preserving the previous generation's visua... |
[
"What has to be improved or invented that fusion reactors are efficient?"
] | [
false
] | null | [
"There are numerous other technological and scientific issues that need to be addressed. But one of the majors issues in magnetic confinement fusion is heat transfer. If you heat an object, the final temperature it reaches is determined by a balance between how much heating power you supply and how rapidly the heat... | [
"However cost's increase as you increase the size.",
"How? Does it increase with volume, surface area, or what?"
] | [
"The cost of a large high tech construction project depends on many factors. But, as I understand it, you can often get a fairly good 0-th order estimate of the cost simply by calculating the amount of concrete poured in the construction.",
"As you increase the size of the reactor, you're going to need a bigger r... |
[
"Why are very old paintings and manuscripts sensitive to light?"
] | [
false
] | I was watching a documentary about a 13th century manuscript called the Codex Gigas, and they noted that exposure to light could irreparably damage it. I also heard you aren't allowed to take flash photos of certain old paintings, what kind of damage exactly are we talking about in cases like this? (I flaired this as chemistry because I didn't really know what this falls under, hope that is ok) Edit: Thanks for all the responses! | [
"All things with color are sensitive to light and will bleach out over time, which is why vendors like Pantone only guarantee the accuracy of a color for just a few years. Now think about if you had something beat by the sun and other atmospheric conditions to the point it was brittle like saltine crackers and flak... | [
"Many old paintings and manuscripts use pigments that are light-sensitive; they undergo chemical reactions and change or lose their colour on exposure to light. Typically, light sources that are rich in blue or ultraviolet light (such as sunlight and camera flashes) are better able to induce these reactions, and so... | [
"I used to work with the conservation department at my University and the way it was explained to me is that ultraviolet light damages the materials that make up most pigments. It causes oils to fade, and acrylics to fade and harden to the point of cracking, and the older the material is the more heavily affected i... |
[
"Why is chiropractic medicine considered wacko in the US? It is respected in Canada and part of the health-care system."
] | [
false
] | Is it because they sometimes claim that keeping the joints cracked and aligned can help other organs or is it something deeper? Is this disrespect a cultural thing or are Canadian chiropractors more "professional"? | [
"Because most of the practice is based on the concept of ",
"subluxation",
", which they can't even prove is real.",
"Also, many insurance plans do cover some alternative medicines, including Chiropractic, within limits. Mine does."
] | [
"It's mostly because many chiropractors make claims about health benefits that are not supported by scientific evidence, and therefore might even be harmful to a patient.",
"I don't think many people in the US are disrespectful to chiropractors on a personal level (not that I've seen, anyway), but the profession ... | [
"Homeopathy is considered a legit practice in Brazil, and it's covered by national healthcare as well. There's definitely a cultural side of the approval of this sort of non-scientific medical practices."
] |
[
"Are the differences between breeds of dogs similar to the differences between ethnicities of humans?"
] | [
false
] | I understand that human ethnicities are virtually genetically identical, but there are still noticeable differences in facial structures, skin color, hair color, etc. Is this similar in any way to the phenomenon that has occurred within breeds of domesticated dog? And could humans hypothetically be selectively bred to create a range of breeds as diverse as dog breeds? | [
"The human species isn't exactly outbred - the ",
"effective population size",
" is on the order of 10,000 (meaning that our several billion people, breeding nonrandomly due to geographic and sometimes cultural constraints, have roughly the same genetic diversity as only 10,000 people breeding in perfect random... | [
"http://genome.cshlp.org/content/17/4/520",
"Estimated from handfuls of individual DNA samples' X chromosomes, they got ~3100 each for Europeans, Chinese, and Japanese, and ~7500 for the Yoruba people of Nigeria. That's consistent with the general decrease in diversity as you get farther from Africa, except Europ... | [
"http://genome.cshlp.org/content/17/4/520",
"Estimated from handfuls of individual DNA samples' X chromosomes, they got ~3100 each for Europeans, Chinese, and Japanese, and ~7500 for the Yoruba people of Nigeria. That's consistent with the general decrease in diversity as you get farther from Africa, except Europ... |
[
"I tried searching the subreddit, but couldn't find anything solid so. Are Solar Flares/ Geo Magnetic Storms really a realistic threat to our electronics?"
] | [
false
] | I thought I found something once about how it would only really affect long distance transistors or something. | [
"http://www.telegraph.co.uk/science/space/7819201/Nasa-warns-solar-flares-from-huge-space-storm-will-cause-devastation.html",
"“We know it is coming but we don’t know how bad it is going to be,” Dr Richard Fisher, the director of Nasa's Heliophysics division, said in an interview with The Daily Telegraph.",
"“I... | [
"Sorry but I was looking for some science on the mechanisms of how it would affect ordinary electronics. Any idea?"
] | [
"It affects electronics in the same way it affects big devices. It causes large scale magnetic fluctuations which induce charge in conductors. Smaller things have less conductors so they aren't affected as much. ",
"A lesser storm might just turn your laptop or phone off. "
] |
[
"Hair growth"
] | [
false
] | Why does body hair only grow to a certain length? Compared to the hair on your head which grows pretty much indefinitely. | [
"How does it know when to stop or when its been cut?"
] | [
"I believe that hair will always grow for a certain amount of time, and thus be a set length, before the hair strand will fall out and it will start again. Hair on your arm will fall out after growing a small amount, while one on your head will grow for a long time before falling out. "
] | [
"When the hair strand falls out, does its follicle grow a new strand? Or does it die?"
] |
[
"Do all living things have a \"common ancestor\"?"
] | [
false
] | [deleted] | [
"All known living things do. "
] | [
"Short answer: yes.",
"Connections between Kingdom, Phylum, Class, Order, Family, Genus, and Species are often represented in a tree diagram such as this: ",
"http://upload.wikimedia.org/wikipedia/commons/1/11/Tree_of_life_SVG.svg",
". These connections are determined by genetic similarities within the specie... | [
"They might not share an ancestor with other animals, but they are pretty likely to be in the big overall group which contains plants, animals, and other eukaryotes."
] |
[
"In the Everett interpretation of Quantum Mechanics, where are the alternate universes physically located?"
] | [
false
] | null | [
"No that’s not a dumb question, unfortunately it isn’t one there is a current scientific answer to, there may never be one.",
"It’s very tied up in the hard problem of consciousness which is something you’d want to go to ",
"r/askphilosophy",
" for (after looking at some basic info).",
"The problem of “why ... | [
"No problem. I think they don’t address it because the answer is that nobody knows and practically everything about consciousness is unknown. There’s no physical problem until you come to the existence of subjects, but that seems true for any interpretation of quantum mechanics."
] | [
"It’s not that they’re in a different place, just they are completely decoupled.",
"From around minute 24 there is a decent (if heavily favourable) explanation here:\n",
"https://youtu.be/5hVmeOCJjOU"
] |
[
"Is there a relationship between the size of a possible meteor that is on an intercept trajectory with Earth and the probability that we haven't found it yet?"
] | [
false
] | What are the chances that a meteor 5-10x larger than the one that hit Russia several years ago hits Earth within the next 10 years? Is there a way to compute this? | [
"There is ",
" of a relationship, only because the smaller an asteroid is, the less likely we are to have noticed it yet. (That doesn't mean we know about all the big ones. There are surely some huge ones we haven't spotted yet.)",
"But we've cataloged and charted only a small portion of asteroids, even only a ... | [
"In the last 100 000 000 years we have been hit by a huge asteroid once",
"Ideally, you'd want a bigger sample size than that. Maybe the last 100 million years were lucky and the 100 million years before that saw 4 impacts.",
"But yeah, chances are extremely low for something that big."
] | [
"Meteors that are very large generally can't get too close to earth. There are a lot of reasons for this, but the biggest one is that Jupiter's gravity ",
"pulls many asteroids",
" out of their normal orbital paths.",
"Think about it like this:",
"Large asteroids are usually periodic asteroids and not \"roa... |
[
"Both cocaine and marijuana increase heart rate. Why does the former cause heart problems that are absent or otherwise rare with the latter?"
] | [
false
] | Both psychoactive substances increase heart rate and can cause tachycardia. I understand that other physiological effects of excercise make it so that physical activity doesn't cause heart conditions unless there is an underlying medical problem. However with cocaine (and other stimulants like methamphetamine) the risk of cardiotoxicity, cardiac arrest, and other cardiovascular issues is present even though both excercise and stimulants increase heart rate. Now marijuana does not replicate the physiological response that physical activity does, but cardiotoxicity from marijuana use is either unknown or at least far lower than many stimulants, even though it increases heart rate. Is this because stimulants increase blood pressure whereas marijuana tends to decrease it? If that is the case, then why does mixing alcohol, beta blockers, or other substances that lower blood pressure with stimulants increase risk of cardiovascular complications rather than negate the problem the increased blood pressure? Furthermore, if anyone is willing, I'd like to understand the specific biochemical process that makes cocaine cardiotoxic (e.g. damage to the heart ventricles with chronic use). How exactly does it damage the heart? Thank you for your time. | [
"Starting with your points in reverse.",
"Cocaine's cardiotoxicity isn't a result of the increased heart rate/blood pressure. There are a few ideas currently, but none of them are conclusive. Personally, the one I find most compelling is the fact that cocaine can act as an ion channel blocker in muscle cells, whi... | [
"Thank you for the answer!"
] | [
"Marijuana increases heart rate secondary to blood vessel dilation, a normal physiological response. Dilated blood vessels mean less resistance, and you need a higher heart rate to maintain blood pressure. The effect overall isn't strong enough to drive a heart attack.",
"Cocaine is a double whammy. It strongly c... |
[
"I’ve always seen these fun videos on YouTube about interesting science experiments and I’ve come across one that shows people making near-unbreakable glass “teardrops,” called, Prince Rupert’s Drops. Why do these drops take so much pressure to break?"
] | [
false
] | null | [
"These are really interesting. The drops are formed by dropping molten glass into water to rapidly cool it. When this happens the outer layer cool and sets while the inner glass is still molten. As this inner glass cools it begins to contract, but since the outside has already set and won't budge, this creates a lo... | [
"Thanks! Now I kinda get it. I’ll have to check that out."
] | [
"Prince Rupert's Drops are regular glass that have been tempered. Tempering is a heat treatment that causes a layer of glass to change its molecular arrangement into a very, very strong layer, directly above the more brittle layer of glass. That's why you can smack the hell out of the big end, it's protected. But i... |
[
"Why do high temperatures damage hardware, specifically cpu's and gpu's?"
] | [
false
] | [deleted] | [
"At the microscopic level, a CPU consists of hundreds of millions of transistors. A transistor is, at the most fundamental level, multiple layers of semiconductor material with different types of impurities. The transistors are only a few nanometers across, so the impurity atoms don't have to move far to render it ... | [
"Full disclosure, I am not in any way associated with the design or production of computer hardware, but I do have a good deal of experience with materials science and I can tell you that heat can bring on many problems, especially on small scales like the internal structures of a cpu.",
"As you probably know, al... | [
"The electrical properties of semiconductors change with their temperature. Increasing the temperature of a semiconductor narrows its band gap and decreases its resistance. The decreased resistance allows extra current to leak and impairs the ability of transistors to regulate the flow of current.",
"At even high... |
[
"How do our bodies build a tolerance to alcohol?"
] | [
false
] | null | [
"After getting used to a lot of alcohol, the neurons in your brain that detect GABA (a neurotransmitter) start processing the alcohol (or the chemical that's being detected because of the alcohol) faster than usual.",
"Yes, you add something important to the current top response! The most important \"tolerance\"... | [
"This is called cellular tolerance. There also is a tolerance of your brain cells who detect the alcohol (this makes you behave weird when drunk). After getting used to a lot of alcohol, the neurons in your brain that detect GABA (a neurotransmitter) start processing the alcohol (or the chemical that's being detect... | [
"This is called cellular tolerance. There also is a tolerance of your brain cells who detect the alcohol (this makes you behave weird when drunk). After getting used to a lot of alcohol, the neurons in your brain that detect GABA (a neurotransmitter) start processing the alcohol (or the chemical that's being detect... |
[
"Why don't all gas pipe flows end up at sonic speed?"
] | [
false
] | According to the 1D models of compressible fluid flow, the effects of and the effects of both drive a flow toward Mach 1 (i.e. the speed of sound). Whether the flow starts of supersonic (M > 1) or subsonic (M < 1), the M = 1 condition is the maximum entropy point. Wall friction will actually cause a subsonic flow of gas through a pipe to up to M = 1 (I still have difficulty wrapping my head around this). So why then don't we find that all gaseous flows through a pipe ultimately end up with sonic flow velocities? I also do not understand what happens after the flow reaches M = 1. The textbooks I've read just say "if there is still pipe length left or heat addition past the point of M = 1, then the inlet conditions must spontaneously change such that the flow reaches M = 1 at the end of the pipe." But they do not explain what these changes are or what mechanism enforces them. What if I am controlling the inlet conditions to be, say, a certain pressure? Then what happens at the end of a rough walled pipe if the flow reaches M = 1 in the middle? Entropy is maximized when a compressible fluid flow velocity through a pipe reaches the speed of sound. So why aren't all our natural gas pipelines carrying gas at the speed of sound? | [
"Under the “Additional relations” sections in the Wiki article you linked, you can see how all the various quantities change as a function of Mach number. Particularly in the Fanno flow article, there’s a nice graph.",
"As you mentioned, for subsonic flow at the inlet, the second law of thermodynamics implies tha... | [
"Thanks for taking the time to write out such a detailed reply! This helps a lot. A couple follow-up questions if you have time and are willing (no worries if not).",
"1 -- Decoupling energy loss from velocity loss was a big and helpful conceptual step. But I still do not understand what would actually ",
" if ... | [
"The inlet Mach number would change such that L",
" = L, L",
" being the location of M = 1, and L being the length of the pipe (in coordinates where the pipe starts at 0).",
"Well the area of the pipe determines the mass flow rate for a given density and flow speed. Since the area is assumed constant, that gi... |
[
"What relationship does entropy have with quantum mechanics? If a box of atoms can exist in all possible states simultaneously on the quantum level, does that eliminate entropy completely?"
] | [
false
] | If a box of atoms is not observed (like a Schrodinger's Cat, but using atoms instead of cats), does it technically exist in all possible states until observed? And if that is true, what would be the entropy of such a box? If all possible levels of entropy are being occupied simultaneously, does that make entropy redundant on a quantum level? | [
"In classical statistical mechanics, you assume some probability distribution for the system to be in certain classical states, and derive statistical (thermodynamic) properties.",
"In quantum statistical mechanics, you assume a probability distribution that the system is in certain quantum states. However, the q... | [
"Actually you ",
" quantum mechanics to get the correct relationship with entropy for a box of gas molecules (e.g. the Ideal Gas model), because you run into trouble (Gibbs paradox) with the fact that you have an infinite number of states for such a classical system. ",
"The solution to this (due to Sackur and ... | [
"As a technical issue, using the equipartition theorem results in a UV catastrophe. You need to use the fact that the energies are discrete, or at least not include energy levels larger than ~kT."
] |
[
"What makes following a pressure gradient \"bulk flow\" but following a concentration gradient \"diffusion\"?"
] | [
false
] | In , a distinction is drawn between diffusions and bulk flows using the example of breathing: air following its pressure gradient into the alveoli is a bulk flow, while oxygen following its concentration gradient from the alveoli to the blood is a diffusion. In both cases, however, the microscopic, statistical-mechanical model is a molecular random walk. What is the distinction between these two cases? | [
"When I think of the Gaussian process/Brownian motion that might be a statistical model for advection and diffusion, it seems that both the mechanical forcing element and the concentration gradient just end up being instantaneous mean (or \"drift\") terms in the stochastic differential equation. Is that incorrect, ... | [
"When I think of the Gaussian process/Brownian motion that might be a statistical model for advection and diffusion, it seems that both the mechanical forcing element and the concentration gradient just end up being instantaneous mean (or \"drift\") terms in the stochastic differential equation. Is that incorrect, ... | [
"In both cases, however, the microscopic, statistical-mechanical model is a molecular random walk. What is the distinction between these two cases?",
"On the continuum fluid side of things, I would say the distinction is that for advection (bulk flow) there's a mechanical forcing element, whereas for diffusion it... |
[
"Can someone answer this question about Stephen Hawking's quantum fluctuations \"something from nothing\" hypothesis?"
] | [
false
] | So, maybe there's no good answer to this that a layman like me will understand, but I'm wondering if someone could explain WHY exactly nothingness would sometimes fluctuate into positive and negative particles. I get how it happens, and I get that it is mathematically possible, but I don't understand what would cause this. Or is it just a part of our reality? | [
"Are you familiar with the ",
"Casimir effect",
"?",
"Effectively the math says that since nothing == (positive something + negative something) we should sometimes expect pairs of virtual particles to appear, however if you place 2 metal plates very close to each other there isn't enough space for some pairs ... | [
"Nothingness or vacuum does not fluctuate into pairs of particles and anti-particles, and things do not just happen without cause like that. What Hawking is describing is an intermediate step of a calculation, and for some reason presenting this math as something real, something that he isn't alone in doing. See, e... | [
"Yeah, I know that quite well, and I know the theory/math behind it as well. And it is a good example of what I mean. The math does not really tell us that virtual pairs of particles appear out of the vacuum: this is just an \"artifact\" of the perturbation theory, or rather us reading to much into the perturbation... |
[
"I read that, on average, 3 supernovas will occur in the Milky Way galaxy every century. If that is the case why haven't we observed any since the last one in 1604?"
] | [
false
] | Source: | [
"This is an open question! (Sort of! It has a universally agreed upon answer, that isn't really \"proven\", but it pretty much has to be right.) So, the main thought as to why this is, is that there's a lot of dust in the Milky Way, particularly in the central couple of degrees of Galactic latitude where nearly all... | [
"More recently, we have another tool to discover supernovae - one without extinction: neutrinos. SN 1987A was a supernova ",
" the Milky Way, but still powerful enough to be picked up by detectors in 1987. With 30 years of detector improvements and the smaller distance, a new supernova in our galaxy will be immed... | [
"Also - ",
" can sign up to their ",
"Early Warning mailing list",
" so you get notified if they detect one. It's not reserved for just astronomers."
] |
[
"Will intentionally hyperventilating increase physical stamina for a short period compared with normal breathing?"
] | [
false
] | I'm in the military, and we have to take physical fitness tests. Two thirds of these tests are doing as many sit-ups and push-ups in two minutes (each) as one can do. Since the performance is over such a short period of time, would breathing heavily prior to doing push-ups (to the point that you start to get light headed) actually help you do more since you would have an excess of oxygen in your blood to begin with? | [
"In a way. I've thrown a few explanations around these forums about this before. I'll look for the links and edit my post to add them after I write this up.",
"Anyways, basically when you hyperventilate, you're purging the CO2 from your body. When you exercise, your muscles use up oxygen and release CO2 into your... | [
"Your blood pH level must remain at a certain level, or your blood starts to become basic (the opposite of acidic, the CO2 dissolves in blood to become an acid). You begin to get light headed because your brain is telling you that something is wrong (your blood is becoming toxic).",
"Here's some more reading via ... | [
"Interesting hypothesis, but I should warn you, eating lemons will not increase the pH of your blood appreciably. Your stomach acids are at roughly pH 2-3 (strongly acidic!) and eventually the food, along with the stomach acid gets processed and absorbed through the intestine (Sorry, the details here are a little f... |
[
"Why don't processors have flip flop circuits with both the set and reset bits turned on to generate random numbers?"
] | [
false
] | [deleted] | [
"You're confusing undefined operation with random operation.",
"A particular datasheet for an S/R flip flop might say that if both /S and /R are asserted, then the output is undefined. But undefined is not random. It might be that the output will be true every time, or false every time, or predictably true ever... | [
"You can't count on anything to happen. Two otherwise identical components from the same production run may do two different things. They might do the same thing as well. They might do nothing one time and then something else at a different time.",
"If the manufacturer truly cared they could define the behavio... | [
"The output would flip back and forth in a predictable way as a function of time, which is by definition not random. If you were to press a button to freeze the circuit somewhere it would appear random because we don't operate fast enough. Actual random numbers should never be predictable even when being called at ... |
[
"Issues with my biology professor?"
] | [
false
] | I just started taking a biology 101 class at the local community college. The prof has said a couple things that bothered me. I wanted to get reddits opinnion. First i missed a couple of the first days due to broncitis. On our test it asked "what can we safely conclude from the theory of evolution?" 1. Small changes occur (bacteria becoming resistent to drugs) 2. Large changes occur (man evolving from ape) 3. All life evolved from a single celled organism. 4. How life in the universe began. I put 3 assuming 1 and 2 were correct. I got it wrong. The correct answer was 1. Next she said that she didnt understand how if we evolved from single cells why are giraffes and monkeys still around. The other thing she said was that it isn't offensive when people say we evolved from monkeys. Its more offensive when people claim we evolved from bacteria. What do you all think? | [
"Next she said that she didnt understand how if we evolved from single cells why are giraffes and monkeys still around",
"This person should not be teaching biology."
] | [
"This person should not be teaching biology",
"This person ",
" not teaching biology."
] | [
"Absolutely. This is a nonsensical statement and displays a terrifying lack of knowledge and understanding.",
"Edit: Actually, I just can't think of ",
" point of view to which that statement could make any sense; are you sure that you heard or understood it correctly OP? I can envisage a confused point of view... |
[
"Why are reflections (especially in liquid) clearer when viewed at an angle, as opposed to straight-on?"
] | [
false
] | null | [
"In the simplest of terms, photons are more prone to bounce off a surface as the angle the impact decreases. Think about throwing a ball at a window, if you hit it straight on, it has a good chance of penetrating the window. If you hit the window with a glancing blow, the ball is more prone to bounce."
] | [
"A good example of this is total internal reflection, the basic principle used with fibre optics."
] | [
"Some partial good answers here. It has to do with the ",
"Fresnel equations",
" as mentioned, but what's important when you're viewing, for example, the reflection of the Sun in water, is that as the angle becomes smaller, the amount of the light that is reflected goes up non-linearly and approaches 100%. This... |
[
"Is it possible for an environment to be so cold, an existing fire would be extinguished?"
] | [
false
] | Assuming there was an infinite supply of oxygen and a fuel source. | [
"Absolutely. The fire needs to be hot enough to be self-sustaining. Each reaction has to give off enough energy to trigger the next reaction. If the surrounding environment absorbs this energy then it is not available to trigger the next reaction.",
"Just for a simple example, if you've ever tried to put out a... | [
"Just to be clear, it's the temperature of the fuel itself that effects reaction rates, and not directly the temperature of the environment, although the environment strongly effects the material's temperature. For instance, if you place the fuel/oxidizer in an excellent thermal insulator, the cold temperatures out... | [
"Just to expand on ",
"/u/Bayoris",
"'s idea with some made up numbers: if you light some paper on fire at room temperature, the fire will spread because the flame can heat each unburned portion of paper to the required 451 degree flashpoint. Drop the temperature far enough (and have a good enough conductor o... |
[
"What specific evidence is there that ADHD is an actual disorder, and not just the overhyped treatment of normal human behaviors?"
] | [
false
] | null | [
"When the behaviour is uncontrollable and interferes with the individual's life, it's a disorder. Anxiety, Depression, etc are all normal human emotions/behaviours, but when they become uncontrollable and impairing we call them disorders."
] | [
"We lack the technology to examine a person's brain to such a level of detail that would let us decide if it was a disorder or not. Even then, how do you define disorder vs normal behaviour? It's all just electro-chemical signals.",
"The only way to define disorder is what I posted above.",
"Over-diagnosis is... | [
"We lack the technology to examine a person's brain to such a level of detail that would let us decide if it was a disorder or not. Even then, how do you define disorder vs normal behaviour? It's all just electro-chemical signals.",
"The only way to define disorder is what I posted above.",
"Over-diagnosis is... |
[
"Why would a person get a fever if they aren't fighting off a bacteria or virus?"
] | [
false
] | Like when a baby is teething, they will get a fever. What is the reason for it? | [
"Fever is an inflammatory response; fever can thus arise from inflammation of all sorts, including sunburn, allergies, tumors, drugs, arthritis, etc. ",
"1",
" ",
"2",
" This is why taking anti-inflammatories like NSAIDs (acetominophen, ibuprofen, etc) work to reduce fever. Essentially, a messenger protein ... | [
"It is generally accepted that the pro-inflammatory chemicals 'cytokines' have a major role in the generation of a fever. As chondroitin states some form of insult be it cell damage from infection or the rapid proliferation and necrosis of tumour cells will trigger this cytokine cascade that will result in a fever.... | [
"In cases of brain disease/damage:",
"\nThe hypothalamus is the part of a person's brain that, among other functions, controls your body temperature. If a person has suffered some kind of brain damage brought on by something like cerebrovascular ischemia, for example, it could compromise a person's ability to ma... |
[
"Why is space described as a 2-dimensional thing and not as a 3-dimensional one in gravitational waves explanation?"
] | [
false
] | null | [
"Space is 3-dimensional, in or outside the treatment of gravitational waves. If a popularization fails to communicate this concept, it's crappy."
] | [
"Totally agree. But then.. Why they expain space as a sheet that bends with the mass of objects if space isn't 2-dimensional??"
] | [
"Because the actual theory is very hard and some people try their best at making it understandable; what they often end up with is the rubber sheet which you shouldn't take too literally, if at all. It has many flaws. The dimensionality of space is the least of those problems."
] |
[
"If you are shot, why is better for the bullet to go through you completely than to become lodged in your body?"
] | [
false
] | null | [
"If the bullet passes through, it left your body with a significant fraction of its energy. If it stays, that energy has been delivered to your tissues. If the bullet breaks into fragments and stays in your body an even larger area has been damaged."
] | [
"SO of an emergency nurse..",
"If a small caliber bullet goes through a body then it probably didn't hit bone, an organ or anything other than skin and fat. ",
"Also, it can be dangerously invasive to extract a bullet, especially if it's close to an organ or in the head. "
] | [
"Thank you for a good simple and proper explanation. "
] |
[
"Is the acquisition or loss of a plasmid in a bacterial population considered evolution?"
] | [
false
] | Or would it only be considered evolution if there were changes in the chromosomal DNA? | [
"Plasmids occur ",
"frequently in bacterial populations growing in the wild",
". Some even have ",
"mechanisms to ensure they are separated into each daughter cell",
". Plasmids often contain beneficial genes and are only maintained because they make the cell more fit, so they are a part of evolution. They ... | [
"Tough question. Bacteria have a fuckton of horizontal gene transfer and very short generation time. ",
"Plasmid acquisition/loss is a rather unstable change in general. While there are some cases of plasmid dependency, like the toxin-antitoxin system, a lot of plasmids can be lost for one reason or another.",
... | [
"Loss or aquisition of a plasmid could be regarded as an addition/change to an organism's ",
"mobilome",
".",
"I believe that qualifies enough as a genomic change to be considered \"evolution.\""
] |
[
"Is it possible to \"uncompile code\" from say an executable, to whatever language the code was written in?"
] | [
false
] | null | [
"The word is \"decompile\". And yes and no - usually, it can be done, but the result will be virtually unreadable compared to the original code. Usually, the decompiled source will suffer from most or all of the following problems.",
"double CachedContractRanking;",
"double 6m2jb;",
"There are reasons for dec... | [
"Note that this depends on the language. Java code is compiled to Java bytecode, and Java bytecode still has a lot of the information that helps it to decompile nicely - including names of things."
] | [
"The wiki has an in-depth answer ",
"here",
", but to summarise:"
] |
[
"Why are so many medications dangerous when taken with alcohol?"
] | [
false
] | null | [
"Actually, the reason certain medications are dangerous when taken with alcohol, is because they are metabolized by the same first pass enzyme in the liver - CYP2E1. Now depending on how much of this enzyme is available, your body may become overloaded by both the drug and the alcohol, leading to adverse effects. ... | [
"Grapefruit has an effect on a lot of drugs, including common ones like DXM and DPH (Robitussin and Benadryl).",
"https://en.wikipedia.org/wiki/Grapefruit%E2%80%93drug_interactions"
] | [
"Alcohol is metabolized in the liver as well as certain medications. The liver can only metabolize so much at a time. The rest stays in your blood stream and has illicit effects. Therefore, taking meds with alcohol can both damage the liver and increase the amount in the blood stream."
] |
[
"Why can animals drink rancid and stale water without getting sick, but humans cannot?"
] | [
false
] | null | [
"This has been answered before. To sum it up with my bad paraphrasing, is animals DO get sick but also because the water they are drinking isn't all that dangerous. In places where water borne illnesses are common it is due to many organisms having contaminated the water through feces or other contaminates. In plac... | [
"Also they're exposing their immune systems to waterborne pathogens more frequently, so they're going to be more robust in having to fight off those germs constantly. Sort of like when I just arrived in Vietnam and ate some street food on Day One and was laid out for two days afterwards when a local would have had ... | [
"Most toilets are sterile. And you immediately flush any waste and replace it with sterile, fresh water.",
"It's also more likely that you would get sick from licking your keyboard than if you licked the toilet bowl. "
] |
[
"If photons have no mass, then how can microwaves be \"too big\" to escape the faraday cage of a conventional microwave?"
] | [
false
] | [deleted] | [
"Pretty sure the 'size' in question here is wavelength. Microwave ovens have a Faraday cage made of a perforated metal mesh. The fact that the holes in the metal are much smaller than the wavelength of the microwaves means that they don't escape."
] | [
"There is a cross-sectional area that describes the likelihood of a photon interacting with an electron (or any other charged particle). This cross-sectional area is determined by the photon's energy. This is usually what is meant when someone talks about the \"size\" of a photon. The greater energy the photon has,... | [
"OK. Same point, the \"size\" of the photon is determined by its energy (wavelength is dependent on energy and vice versa). The greater the energy, the smaller the size."
] |
[
"Why is there indigenous people in the Arctic but not the Antarctic? "
] | [
false
] | null | [
"As a student of geography, this is the simplest explanation I can come up with. The Antarctic is inaccessible by land, so as human migrations accelerated toward the end of the last Ice Age, reaching the South was impossible, whereas other groups like the Inuit could people the Far North."
] | [
"In a word: Cold. The land in the antarctic is almost entirely inside the 66th parallel south. The majority pf the land in the arctic is outside the 66th parallel north. You can see that by comparing these two pages: ",
"arctic",
" ",
"antarctic",
".",
"While humans live in latitudes in the north of green... | [
"But there are some flaws there. Humans have reached other places that are far more inaccessible than the Antarctic. Hawaii is a great example, historians believed they got there by rowing canoe-like boats across the Pacific Ocean. Thats so mindbogglingly absurd, that it took a long time to be accepted. ",
"This ... |
[
"What exactly is a supermassive black hole?"
] | [
false
] | What makes a black hole "supermassive"? The amount of material/mass between the singularity and the event horizon? The size of the accretion disk? EDIT Thank you, guys! Crystal clear. | [
"Typical black holes are about the mass of the sun, maybe a few times as big.",
"A supermassive black hole is millions of times more massive than the sun."
] | [
"The mass is made up of the original mass of the black hole upon creation, and other mass it has accumulated, so the matter that has entered the event horizon would count. It can also gain mass by merging with other black holes. "
] | [
"It's in the centre of the event horizon as an infinitely small point.",
"While it's true that no matter escapes the event horizon, black holes do 'glow' and emit radiation in the form of Hawking radiation in which due to the immense gravitational field it causes virtual particles to become 'real' or some shit i'... |
[
"Is there a paleontologist in the house? 325 MILLION YEARS AGO - something was going on in my back yard. My summer project is to find out what that was."
] | [
false
] | null | [
"That's not the right starting time for the Carboniferous, but you're right that this material is Carboniferous. It could very well be plant material, as the Carboniferous period was a very productive time for plants (in fact, many of the coals in PA were deposited in the Pennsylvanian subperiod). I've seen some ... | [
"That's not the right starting time for the Carboniferous, but you're right that this material is Carboniferous. It could very well be plant material, as the Carboniferous period was a very productive time for plants (in fact, many of the coals in PA were deposited in the Pennsylvanian subperiod). I've seen some ... | [
"laughs when your next submission is \"Help, I've removed the keystone that was holding back a landslide from hitting my house.\""
] |
[
"How long does a beam in the Large Hadron Collider last before they have to dump it?"
] | [
false
] | [deleted] | [
"The brief spikes you see occur when the operator needs to adjust the beam to counteract the moon's tides over the course of a day.",
"That's fascinating. ",
"By the way, since I imagine moon tides are quite regular, is there some reason why this is not compensated for automatically?"
] | [
"The brief spikes you see occur when the operator needs to adjust the beam to counteract the moon's tides over the course of a day.",
"That's fascinating. ",
"By the way, since I imagine moon tides are quite regular, is there some reason why this is not compensated for automatically?"
] | [
"In an ideal world, the beams would get dumped after ~15 hours, then the machine needs 2.5 hours until we get new collisions. The protons could be kept longer (the record is 37 hours), but the collision rate goes down over time, refilling after 15 hours maximizes the total number of collisions in this ideal world. ... |
[
"What does it mean when scientists isolate a virus?"
] | [
false
] | null | [
"If your friend has a cold, and you get them to sneeze in a test tube for you, you probably have a sample of their cold virus in that test tube. But you haven't isolated the virus.",
"When we talk about isolating a virus, we mean isolating it ",
" that's in the sample from a patient (including, potentially, oth... | [
"I'm pretty sure they it means they have found and grown the virus in the lab. ",
"An isolate is the name for a virus that we have isolated from an infected host and propagated in culture.",
"https://www.virology.ws/2021/02/25/understanding-virus-isolates-variants-strains-and-more/",
"As a guess, one might co... | [
"Surely it make a big difference if it’s an already-known virus, or an unknown one? If you already know the virus you’re looking for, isn’t it just a simple PCR?"
] |
[
"What caused the United States to have the highest infant mortality rate among western countries?"
] | [
false
] | I've been told by some people that this is caused by different methods of determining what counts as a live birth vs a still birth, but I've never been shown any evidence for this. Could this be a reason, or is it caused by something else? | [
"The ",
"Congressional Research Service",
" investigated whether inconsistent recording of births could be the cause of our bad infant mortality rates (IMR) and found that it does not ",
" fully explain the results. (There is some effect from the inconsistent recording, but it isn't significant to explain th... | [
"I'll also point out that \"\"we don't provide very good health care to our citizens\" isn't strictly true. The US does provide excellent health care, but ",
". The problem is that we don't provide ",
": in fact, that's the next sentence after what you quote: ",
"Researchers also have found that access to pr... | [
"Right. I never meant to imply that our actual facilities and doctors were sub-par. They are the best in the world as far as I know. I meant it in the sense that only providing health care to the rich is \"not providing good health care.\" "
] |
[
"Could cancer spread to an identical twin?"
] | [
false
] | The reason cancer isn't contagious, from what i understand, is that our immune system would kill any cells in general from someone else that happen to enter our bodies, including cancer cells. If someone had an identical twin with cancer, would it be possible to contract it from them? | [
"I'm not sure about in humans, but something close to what you propose is happening in animals. Tasmanian Devils are currently suffering badly from a contagious cancer that is spreading throughout the population. It can do this because Devils have a low level of genetic diversity and all have a similar immune syste... | [
"Wow. That is seriously an amazing question. It looks like it is possible in specific cases! This link gives a nice discussion: ",
"http://listonlab.blogspot.com/2009/10/infectious-cancer.html"
] | [
"Cancer transmission through transplants is actually a major worry during transplantation and unfortunately ",
"has happend",
"."
] |
[
"What effects (good/bad) do sugar substitutes in diet fizzy drinks do to us in the long/short term?"
] | [
false
] | null | [
"An obvious good effect is the lack of calories (and associated effects) that come with real sugar. Most diet sodas use aspartame as a sweetener which has been extensively studied and not shown to have negative effects in amounts that would be consumed by a normal person."
] | [
"Thank you! ",
"I think there is a lot of theoretical \"bad\" effects of sugar substitutes but i guess it depends on what substitute is used by the company!"
] | [
"Scishow uploaded a video about this about a week ago",
"https://www.youtube.com/watch?v=qQarsq-1ykE"
] |
[
"I'm not an avid coffee drinker, but when I do drink it I feel an immediate but short-lived sense of euphoria. What is that?"
] | [
false
] | null | [
"Well to put it simply, caffeine is no joke. It does affect your brain chemistry, both adenosine and dopamine. These guys will give you that sense of euphoria by increasing your heart rate, dilating your pupils, increasing blood pressure, and opening up your airway.",
"Read ",
"How Caffeine Works",
" to get t... | [
"Do you put a lot of ",
"sugar",
" in it?"
] | [
"Thank you. I've been under the impression that it takes more than several minutes for caffeine to take effect. The euphoria I feel is near instantaneous."
] |
[
"Do sharks (or other carnivorous animals for that matter) eat the bones of their catch?"
] | [
false
] | I've never seen video of a shark making any efforts to avoid the bony parts of a meal. So what happens when it inevitably eats bone? Do they regurgitate them or just digest them with some super stomach acid? | [
"Yes!",
"Tiger sharks, for example, eat just about everything (everything that will fit in their mouths). ",
"Wolves, as well, eat bones of their prey. The difference between them and us is their jaw strength. They don't digest the hardest part of the bone, but they can snap it into something that can be swa... | [
"My dogs do! And the stomach (at least in humans) contains hydrochloride acid, which would react with calcium to make calcium chloride. "
] | [
"Pinniped Biologist here. Yes, seals, sea lions, and fur seals eat all of their fish! They don't even chew!"
] |
[
"Why is it so difficult to solve the Schrodinger Equation for multi-electron species?"
] | [
false
] | In our inorganic chemistry class, we learned about how the solution of the Schrodinger equation leads to the shape of the atomic orbitals for Hydrogen, and other single electron species. Why is it so hard to solve for species that have more than one electron? Is it the math itself, or some other physical constraint? EDIT: Solve it exactly, not approximate | [
"It isn't an issue of Schrödinger equation it is an issue of the three-body problem. Basically, the issue isn't a physical constraint but it arises from our understanding of mathematics and how we do it. I am a physical chemist so I am aware of it and how to approximate around it but as for mathematical research in... | [
"Let's clairfy some stuff here: There's no ",
" analytical solution. But you can't equate \"analytical\" with \"exact\". What you're thinking of is a ",
", which is a sub-set of analytical solutions. The classical three-body problem has an analytical solution, but not any known closed-form one.",
"A numerical... | [
"Schrödinger's equation is a partial differential equation that depends in part on the potential energy of the system. In the single electron case we generally ignore the nuclear interaction except to treat it as the source of a potential, so that the potential energy term in Schrödinger's equation becomes a simple... |
[
"What is the maximum heat of any known solid?"
] | [
false
] | My son asked me tonight if it was possible for something to be as hot as the sun and still be a solid and I couldn't give him an answer. Help! | [
"Currently the substance with the highest verified melting point is tantalum hafnium carbide (4263 K or 3990 °C or 7214 °F). In 2015, some theoretical calculations indicated that another substance (an alloy of hafnium, hydrogen and carbon) would have a higher melting temperature (about 4400 K), but that was not yet... | [
"Hey,",
"roughly what ",
"u/roketo",
" said. I found slightly higher numbers for tantalum hafnium carbide ",
"here",
":",
"Currently the record-holder is tantalum hafnium carbide (Ta4HfC5), a refractory compound with a melting point of 4488 K (4215 °C, 7619 °F).",
"As well as some numbers for Carbon ... | [
"A rather more exotic type of solid would be the matter composing the crust of a neutron star, which doesn't melt until temperatures above 1,000,000 K due to the crazy amount of pressure keeping the atoms in place. Of course, this solid would immediately explode into a plasma if the pressure were relieved, so wheth... |
[
"How Integrated circuit are designed ?"
] | [
false
] | I know that integrated circuit (like CPUs) are made from silicon wafers, but since they are like circuit board, they must have been "drawn" in some way before being printed, but CPUs contains million of transistors. Are they automatically generated with some patterns ? | [
"They are written in programming languages that specify the logical operations.",
"Then Synthesis is performed by (a usually very expensive) piece of software to map the\nlogic to the transistors.",
"Some example code",
"In the old days chip designers were drawing huge masks with some kind of cutting\nequipme... | [
"Typically when you build a CPU it ends up being a hierarchical composition of fairly simple components.",
"You might implement an adder once and use that in multiple places, or implement a single register, then implement a register file from those. Design tool vendors will have libraries of general purpose part... | [
"Wow I would never thought that chips were actually \"programmed\", how much lines of code would it take to make a modern CPU ?"
] |
[
"Why do lightbulbs always seem to burn out right when you turn them on, and not while they're already on?"
] | [
false
] | null | [
"http://www.reddit.com/r/askscience/comments/lym1l/what_happens_in_a_light_bulb_when_it_burns_out_is/",
"This might help."
] | [
"Sometimes lights do burn out when they're on but basically it's because at the moment of being turned on lightbulbs experience a small surge of power that's greater than they get when they are running. This can push them to burn out."
] | [
"Yes, you are right about fatigue. The repeated stress of heating and cooling (evaporation and condensation) weakens the filament material over time.",
"However the question was why it breaks at the exact moment of turning the light on. The force that brakes the filament is the Lorentz force, which is created in ... |
[
"Why do we think there is a graviton?"
] | [
false
] | I thought that gravity was created by the shape of physical space. That is the curvature of space around heavy objects changes. This change causes two objects to be attracted to each by the shape of physical space. This isn't a particle or a force instead its a fundamental property of space and space physical objects create "space" based on the amount of mass within a volume. So, why do we think there is a gravity particle or a particle that passes along gravity as a force? | [
"say it's raining on a pond. You have a bunch of ripples that originate from the impact of the water droplet, and then you have waves that come from the constructive and destructive interference of each individual ripple that makes the wave. Would an individual particle be a particular ripple? "
] | [
"say it's raining on a pond. You have a bunch of ripples that originate from the impact of the water droplet, and then you have waves that come from the constructive and destructive interference of each individual ripple that makes the wave. Would an individual particle be a particular ripple? "
] | [
"how would you describe a photon?"
] |
[
"Can we train EVERY SINGLE muscle in our body?"
] | [
false
] | I mean, we often go to the gym to make our body look stronger and better by training your "main" muscles, but the thing is, since our whole body is covered my muscle, can we train every single one of those muscles? | [
"It's worth clarifying here, that there are 3 types of muscle within the human body, ",
", ",
" and ",
". Smooth muscle is entirely autonomous and is found around blood vessels, your gut, your airways etc. Cardiac muscle is what the contractile parts of your heart is composed of. I'm going to assume here that... | [
"In the interests of completeness, an example of smooth muscle hypertrophy and hyperplasia is as a result of chronic hypertension in the tunica media of arterioles.",
"Arterioles exhibit myogenic tone i.e. they constrict in response to stretch from intravascular pressure. This occurs in all arterioles but is part... | [
"Feel free.",
"As a disclaimer, whilst I'm confident in the muscle physiology there, my knowledge of the anatomy is less sound. ",
"It may not actually be physically possible to engage muscles such as the intercostals (accessory to breathing), or even the diaphragm in a useful way, I honestly don't know. You sh... |
[
"How many mutations does the average human have, if <1 what % of people have at least 1 mutation present?"
] | [
false
] | null | [
"Everyone undergoes ~ 20ish during gestation. And throughout your life individual cells undergo mutations that may of may not be passed down to other cells. Apoptosis prevents most from being passed down to other cells. By the end of your life it is possible to sequence a cell from your left hand and a cell from yo... | [
"By the end of your life it is possible to sequence a cell from your left hand and a cell from your right hand and get very very close but ever so slightly different sequences. ",
"That is ",
" the info I am looking for"
] | [
"Yes, in fact I'd say its incredibly unlikely for the 2 cells right now to have exactly the same DNA sequence. Errors in replication dueing cell division and random damage due to many different sources means cells are always going to have differences in nucleotides. We are very fortunate that it takes alot of mutat... |
[
"Why is speciation believed to be higher in the tropics?"
] | [
false
] | [deleted] | [
"This is a great question, and there isn't a full consensus on the answer.",
"One of the suggestions that I know off the top of my head is:\nTropics have greater rates of Primary productivity (due to the abiotic factors such as light intensity, rain, temperature). Higher rates of productivity can support longer f... | [
"There's also the idea that tropics are older, therefore, evolution have being going on for a longer time than the temperate and arctic zones -if we assume evolution is happening at the same rate in all regions."
] | [
"As the quality of data increases, there is evidence that ",
"food chain length does not differ between tropical, temperate and polar environments",
". However, this does not contradict the idea that there is a higher diversity of niches in tropical environments, nor does it contradict the idea that this is dri... |
[
"Why, when considering life on other planets, do scientists generally look for conditions similar to earth? (water, carbon, oxygen, etc)"
] | [
false
] | Whenever I read about scientists looking for other life, they invariably bring up looking for conditions similar to earth, e.g. looking for water. Couldn't alien life thrive on other substances? Perhaps even elements that we've never discovered? | [
"Alien life could be, well, totally alien to us. So alien that we might not even recognize it. But when you're searching for life in the vast emptiness of the universe, you use what you know as a starting point. As fun as it is to speculate about alternatives, we have exactly one confirmed life-supporting planet... | [
"We have not observed life on any of the other dozen or so orbiting bodies we've landed craft or people on in the solar system. Those squares and triangles won't work for us circles and you can think of as a few entries in the 'no life here' column.",
"You've got the problem that we can play, \"what if,\" with t... | [
"Not an expert but a couple of points:",
"We have discovered all the stable elements. There are no empty spaces in the periodic table.",
"Life, as we understand, will require complex molecules which can encode information that can replicate itself. Carbon has brilliant capability of forming long chains and ring... |
[
"How vaccine effectiveness is affected by blood donation?"
] | [
false
] | Say a person has been vaccinated (specifically the mRNA vaccines for Covid-19 if necessary). What if blood is being taken away from that person by blood-donation or other methods (even trauma). How does it affect the levels of antibodies/t-cells (are those the correct terms) in the blood? Are those restored to the high levels they were before blood was taken away, along with the generation of other blood "components"? Does it matter if the blood was taken away after the first vaccine dose or after the second? To clarify - I'm speaking about the immunized person that lost blood it some way, not a recipient of blood donation or antibodies. | [
"Vaccines are injected in muscle and not in blood, so I do not think you would lose enough material to notice an effect in the efficacy of the vaccine.",
", it could be the case that the drop in blood pressure caused by donation and the side effects of the vaccine (potentially nausea, headache, etc.) add up toget... | [
"As for blood donation, at least in Sweden, you have a thorough questionnaire and a meeting with a nurse before each donation so if vaccination would be affected it would be caught there and you would not be allowed to donate. Not exactly what you are asking but I thought I would clarify that at least."
] | [
"Do we know about the COVID vaccine yet? I see “experimental” vaccines have a 12 month waiting period to donate blood. Should younger people be donating blood now before they get their COVID vaccine since there may be a waiting period? I’m guessing an actual science person has considered this."
] |
[
"Since there is a universal speed limit (speed of light), is there a universal acceleration limit?"
] | [
false
] | Somehow I would bet that if there were, it would somehow be related to the velocity of light, but I can't, for the life of me, figure out what that kind of math would look like. I'm guessing that it would involve the derivation relativistic equations? | [
"If you consider the physics of acceleration you can't avoid thinking about ",
" a particle is accelerated.",
"If it is ordinary matter being accelerated non-gravitationally you are talking about a potential gradient (example: you accelerate an electron by applying an electrical potential gradient).",
"And th... | [
"Not within the confines of special or general relativity, but some sort of quantum gravity might limit it.",
"Accelerating observers experience blackbody radiation. This is called the Unruh effect. Blackbody radiation emits pressure. The pressure experienced from Unruh radiation, I just derived, is hbar/(960 pi"... | [
"What about accelerating with other force than electrical?"
] |
[
"Scallops, oysters, mussels and clams apparently have between 40 and 200 eyes. Why?"
] | [
false
] | For animals that seem to sit around waiting to be eaten, that seems excessive. So why so many eyes? | [
"We usually refer to these animals as bivalves. The eyes aren't as complex as our eyes, and they are usually along the outer rim of the shell. They see mostly light and shadow. A large shadow over a bed of clams might mean a predator. When the eyes sense that, the bivalve snaps shut to avoid being easy prey. They a... | [
"They usually use a muscle \"foot\" (more like a tongue) to push themselves along.",
"I found this site quite informative and easy to read for someone just looking for an overview of the many species.",
"\n",
"http://www.molluscs.at/bivalvia/"
] | [
"Good explanation, thanks mate! So scallops can swim, but how do the other bivalves move?"
] |
[
"How long, on average, does it take a carbon dioxide molecule floating in the atmosphere to move 1 meter?"
] | [
false
] | So, during the day when energy is raining in on Earth's atmosphere and jostling molecules in the air around, how long, on average, does it take a molecule of CO2 to move 1 meter in any direction (assume it's at sea level at the equator)? | [
"We first assume 1-dimension. Our particles have an average speed of v and average velocity of 0.",
"Since we assume many collisions and thus many changes in velocity, we shall take a particles speed as always being v.",
"If the average time between collisions is t then the average distance travelled will be:",... | [
"In perfectly still air this is a diffusion problem. The diffusion coefficient D of ",
"CO2 in air is 16 mm",
" /s",
". Now the time to diffuse a given distance is t=x",
" /(2D), so plugging that in you get 31,250 s or about 9 hours. Diffusion is really slow at large distances.",
"But wait, isn't CO2 movi... | [
"In reality, there is some average collision frequency (a number of collisions per unit time). ",
"Let us not do fluid dynamics a disservice by pretending these collisions can be ignored. The reason a gas behaves like it does in air is because the mean free path is much smaller than the typical scale lengths of t... |
[
"If Betelgeuse goes Supernova, how will it affect Earths ecosystems?"
] | [
false
] | Recently, I've read that Betelgeuse could go Supernova as early as within the next 100 years. If that happens, it would be so bright it would be like having a second Sun in the sky and there'd be no darkness for weeks. We could just pull down the shades and go back to sleep, but what would be the effect on nocturnal flora and fauna in Earths ecosystems if there was no darkness for a month or so? | [
"Here's an impression of what the Constellation of Orion will look like during the Supernova",
". I thought it would help clarify your points. "
] | [
"Here's an impression of what the Constellation of Orion will look like during the Supernova",
". I thought it would help clarify your points. "
] | [
"In principle this is all correct, ",
" we assume the supernova is spherically even distributed (i.e. radiation/light/energy is send evenly in all directions). However we see more and more evidence that this is absolutely not the case.",
"There is a very good chance that most of the energy will be send out in a... |
[
"How does redshift explain an expanding universe?"
] | [
false
] | The light coming from galaxies that are further away is redshifted more than those that are close, in such a predictable pattern that for galaxies we can't measure distance for, we instead measure redshift and use that to establish an estimated distance. We also know that the light we are seeing from those further galaxies is older than the light we see from closer galaxies. We are seeing these galaxies as they were in the past, in fact, further in the past than the closer, less-redshifted galaxies. What I'm hoping to figure out is this: Doesn't that suggest that the expansion of the universe is slowing? Possibly, since Andromeda is blueshifted, if I'm not mistaken, the universe could actually be contracting. Thank you for any help in understanding the problem I'm having with this. | [
"If the universe is expanding at a constant rate, we'd expect redshift to increase exponentially with time. In the first million years, it would redshift 1%. In the next million, another 1%, etc. Based on variations from that, we can tell if the expansion is increasing or slowing. It's increasing."
] | [
"The galaxies aren't moving. Space is expanding. There's a difference. Although I guess if space is flat they probably are just two different ways of looking at the same thing.",
"If you want to look at the special relativity version, and say galaxies are moving away, the further ones are redshifted because furth... | [
"If the universe was expanding at uneven rates, then the redshift would be different in different directions. It's not. It only depends on distance. Either the expansion of the universe is synchronized across concentric spheres around us, or the expansion of the universe only depends on time. We know how the univer... |
[
"Is continental drift at all influenced by the gravity of the sun and moon like our oceans?"
] | [
false
] | [deleted] | [
"The easiest way to think about this is that plate tectonics relies on constant forces over thousands or millions of years. Tides change on an hourly basis, and even the suns influence averages out over a day as the earth rotates, so over the timescale of plate tectonics these forces will average out to be irreleva... | [
"No. Plate tectonics is mostly influenced by two mechanisms: slab pull and ridge push. I'm on my cell phone so I can't link anything but some light googling can explain how they work exactly. ",
"As an aside, continental drift was the theory before plate tectonics and is no longer the accepted theory. The two te... | [
"Thank you! Like I said I have a basic understanding of the geological processes involved. I didn't know that those terms weren't interchangeable, but now I do. "
] |
[
"Can someone please explain how an IQ test works?"
] | [
false
] | I know the IQ scale with 100 being average, 140 very good, 160 genius ect. I was just wondering if someone could explain how the test actually functions in detail. Note: (I am not looking to find out my IQ I already know that). Also if you wouldn't mind: How correct are online IQ tests? | [
"Start here",
". If you still have questions let me know. ",
"How correct are online IQ tests?",
"Not at all correct. They are unlikely to have undergone any form of standardization and/or normative analysis. A standardized measure of intellectual functioning administered and interpreted by a qualified pr... | [
"Poorly, for any sensible definition of I."
] | [
"The online tests are worthless. You can go to MENSA and take a pre-test to see if you qualify for the actual test.",
"edit: Mensa isn't completely capitalized; obviously I didn't get in."
] |
[
"We have hot air balloons, and helium balloons but why not hot helium balloons?"
] | [
false
] | I know that suggesting Hot Hydrogen is a no-no, but wouldnt heating helium provide more lift than traditional methods or is there something I am missing here? I know heating helium would not be as simple as heating air obviously, but Im sure there is a way. | [
"As with so many things: It would be possible, but what's the point?",
"A hot air balloon needs to be reheated regularly to compensate for the heat loss. Because the balloon contains just air, it can use a relatively simple design with the bottom being open, so the burner can easily heat up the air. ",
"If you'... | [
"Also, there are hybrid hot air/helium balloons, called ",
"Rozière balloons",
", enabling more fuel-efficient buoyancy control, and thus longer flights. ",
"One of these was used by Bertrand Piccard and Brian Jones to cirumnavigate the Earth in 1999, in 477 hours and 47 minutes.",
"Edit : added flight dura... | [
"At what point does it stop being \"going around the world\" and start being \"flying a circle around the pole\"? "
] |
[
"If red hair is caused by recessive genes, blonde hair is also caused by recessive genes and dark hair is caused by dominant genes, how is it possible for parents to have brunette, blonde, and redheaded children?"
] | [
false
] | For example, the Andrews Sisters, and I've got friends with siblings like this. Mind explaining, ? It just confuses me. | [
"Ohhh, I see your question now. Because the mom was sleeping with the mailman.... Ok, while that may be true, the real answer is that there are actually at least two genes that control hair color, one is a brown (dominant) vs. blond (recessive) gene, the other is a red (recessive) vs. not-red (dominant) gene. So ... | [
"Pictures",
" always help to explain this one, but essentially if both parents are carriers of the recessive gene, and both pass the recessive gene along, then two copies of the recessive gene= expression of recessive trait."
] | [
"Yes, I get it, but shouldn't the recessive gene for blonde hair and the one for red hair be different, since they're both recessive? If so, how would they have children with different recessive hair colours ",
" one with a dominant hair colour?"
] |
[
"Occasionally we see plans to “bring back” extinct mammals like Mammoths, but in reality they would be Mammoth-Elephant hybrids. Would this method work with non-mammals like bringing back the Moa using other ratites like the Emu or Ostrich?"
] | [
false
] | As noted in the title often when talking about bringing back an extinct species it’s usually in regards to a mammal that went extinct fairly recently due to (from my understanding) the fact species exist today that are closely related enough that it may be possible to produce a hybrid offspring. However I never see any talks about being back extinct birds or reptiles or other egg-laying creatures. Is there some biological reason why it would be harder to produce hybrids using egg-laying creatures. Is artificially inseminating egg-layers not a thing? Or is it simply a case of mammoths and Tasmanian tigers etc are easier “first steps” on the path to bringing back extinct animals? | [
"There’s talk right now of de-extincting the passenger pigeon (",
"genome sequenced late 2017",
") and the moa (",
"2018",
"). Although this is a smaller moa than the ",
" moa, where work is still ongoing.",
"By contrast, we’ve had a full mammoth genome since 2015. (It helps, a little, that mammoths occ... | [
"I worked at a research wing of a company that runs zoos and aquariums in the US. We were specifically working on using common or less threatened animals as surrogates for viable frozen embryos of endangered species. (Bongos from Eland, tigers from lions, and African black footed cats from domestic short hair (hou... | [
"We would defeat the clone army using your well known weakness for clowns and balloons. "
] |
[
"How does gravity affect our aging?"
] | [
false
] | null | [
"There is no separate biological effect that isn't due to how time itself passes. If you understand how time dilation affects clocks, then it's the same phenomenon that changes how we age."
] | [
"Thanks, but just one more question, does time dilation as a result of gravity have anything to do with the atoms present within the area concerned?"
] | [
"No, it's just the geometry of spacetime."
] |
[
"Do sports drinks actually have a positive effect during physical exercise longer than 90 minutes?"
] | [
false
] | According to "Robert Rogbergs, an exercise physiologist at the University of New Mexico who studied Gatorade, said that unless someone is exercising or competing in a sporting event for longer than 90 minutes, there is no reason to drink something with excess sugar and electrolytes." This would suggest that physical activities longer than 90 minutes to indeed profit of an additional input of glucose or carbohydrates during the exercise. However, a friend suggested that drinking any kind of sports drinks is pointless as your body has enough energy "stored" to keep you up and running until your next meal, while other athletes suggested that eating things high in sugar during lengthy training periods can give you an extra push. So I suppose my question is: Do sports drinks actually have a positive effect during physical exercise longer than 90 minutes, and if yes, why exactly is that the case? I'd also like to add that apple-juice and mineral water in a 1:3 ratio is considered a great sports-drink (and recommended by the Deutscher Olympischer Sportbund (German Olympic Sports Confederation) based on the theory that ingesting the carbohydrates of the apple-juice is indeed beneficial during long-term exercises. I've also heard that a large input of glucose can help with "muscle-burn" during longer exercise. If that is also correct, I'm wondering why exactly that would be the case. This basically all came up during/after my ten hour mountainbike-tour today, and I was wondering if someone could help me out. | [
"Since ",
"/u/Dr_on_the_Internet",
" covered the electrolytes, here's the deal with carbohydrates:",
"your body has enough energy \"stored\" to keep you up and running until your next meal",
"When doing aerobic exercise, like running, cycling, etc., your body gets a lot of the energy from glycogen, which is... | [
"I'm not sure about the sugar, but I think the most important aspect is that sports drinks replenish electrolytes. If you exercise and sweat over long periods of time not only do you lose water, but you lose salt. If you drink only water, you don't replenish the sodium you need and your muscles can't work if the so... | [
"\"unless you are exercising for a long time\" - please can you be more specific? What do you mean by a long time? "
] |
[
"What's going on on our head when we feel mental exhaustion? Why is it draining to perform numerous calculations one after another?"
] | [
false
] | null | [
"Hmm. When you say",
"getting tired from the calculations,\nNOT about calculations putting the brain under load as they are performed",
"I don't think of these things as being mutually exclusive*. I think I interpreted \"mental exhaustion\" as perhaps a layperson's phenomenological experience of what it feels l... | [
"The phenomenon you're describing is called ",
"cognitive load",
" among cognitive and attentional psych researchers. I know that's not an answer to your question of ",
" it occurs, but hopefully knowing that term for it will be a good starting point if you want to look into it further."
] | [
"As far as I understood, the question was more about getting tired from the calculations, not about calculations putting the brain under load as they are performed.",
"Is it because the neurons / synapses \"get tired\"? Is it mostly metabolic? Or is it an active process, as it seems to be the case for the ",
"s... |
[
"How do (in theory) Cosmic Super Strings form?"
] | [
false
] | null | [
"At the most basic level, cosmic superstrings are distinct from normal cosmic strings and should really be understood as normal fundamental superstrings from string theory \"stretched\" to cosmological size. The most popular mechanism for formation is in the context of brane inflation models, but other models can a... | [
"well, cosmic strings =/= cosmic superstrings and they don't need string theory. Cosmic strings are in general 1D topological defects (\"knots\") which happen because there is a spontaneous symmetry breaking. They're formed through a mechanism called the Kibble(-Zurek) mechanism.",
"Instead of me just awkwardly t... | [
"I heard them described as one dimensional \"cracks\" in the universe due to irregularities present a few microseconds after the big bang. What is meant by \"cracks\"? Are they one dimensional voids where there is no space time? How then do they have mass? A one km cosmic super string has the same mass as earth? So... |
[
"Would it be possible to compress water to form really dense ice?"
] | [
false
] | I know with preasure it is possible to freeze ice at higher temperatures. I have always wondered if it was possible to freeze water at a hightemperature for storage. If it were possible to freeze water at just below boiling point would the ice be really dense? would a gallons worth of water be substantially smaller? | [
"It is possible to freeze water at 100°C and even higher (check out ",
"this phase diagram",
"), and that ice structure is much denser than the stuff in your freezer, but you would need to keep it pressurized or else it will revert to a less dense structure or liquid. We're talking pressures above about a Gigap... | [
"Just applying the pressure is a big problem. There are only two types of device that can reach those pressures; the one with the larger sample capacity can compress less than a cubic centimeter to that pressure."
] | [
"If only it would stay a solid after pressure was gone. You could use it as a way to store water in emergency situations, or carry water backpacking"
] |
[
"What are Parrots trying to achieve by mimicking sounds they hear?"
] | [
false
] | Don't know how much Animal Behaviour fits this subreddit, but I think it is a scientific question nonetheless. I like watching videos of domestic parrots making dozens of different sounds, and sometimes it's hard to think they're being made at random. When a parrot mimics a sound, what are they trying to achieve? Are they trying to convey different things with different sounds? Are they learning what responses each sound they make may elicit in other individuals? Are they simply being playful, and enjoy reproducing some sounds they hear when stimulated? | [
"Many birds that mimic sounds they hear use those sounds in their mating calls. A female parrot of mockingbird will tend to be drawn to calls that they find interesting, unique, or just pretty. Birds can use these sounds for other purposes as well, such as mimicking predators or making sounds they have figured out ... | [
"Hi! I work in behavior analysis for humans. But it’s pretty similar to when a baby is learning to talk. They may not really understand the deeper meaning of all the sounds, but they have developed an imitiative repertoire that allows connections to form between them and the person who hears it. Just like the babbl... | [
"I’m probably gonna get flamed here, but I keep seeing this word spelled this way “ques”. It’s “cues” like in theater, when it’s your ",
" to do something.",
"Queues refers to lines in which you have to wait",
"Ques is spanish for “what”"
] |
[
"Why is thermal expansion different between different solids?"
] | [
false
] | I was looking at a grill thermometer which uses a bimetallic strip to change shape. I understand that the expansion itself comes from heat and thus movement of the atoms being more spaced apart meaning more volume. Does the different expansions mean the atoms are naturally more spaced apart, or just more prone to movement (ie less inertia?), or am I way off the mark? | [
"Broadly, the thermal expansion coefficient can depend on the crystal arrangement, lattice spacing, bond strength, electron interactions, magnetic interactions, and a variety of other effects. The details are still a topic of active research. (If you're familiar with the scientist Richard Feynman, one of his early ... | [
"It has to do with relative bond strengths at a given temperature. While many things may be a solid at room temperature some melt much sooner than others. As things get closer and closet to their liquid phase, they naturally start expanding (except water, and a few other 'weirdos')"
] | [
"Quite a few of metal alloys in the invar (Fe0.64Ni0.36) family exhibit negative thermal expansion over a narrow range of temperatures. These alloys were named for the very small thermal expansion (considered invariant, hence invar) and have lots of applications in precision optics and electronics. \nAnother exampl... |
[
"Why is eating raw egg considered dangerous when the egg itself is enclosed in a germ free state?"
] | [
false
] | You tend to hear people advise against eating raw food, one of those foods being eggs. The main concern is that any sort of parasite or infectious microbe which might inhabit your food won't be killed off if you don't cook it thoroughly. My question, why is raw egg considered a possibly unclean food when eaten raw? Obviously it tastes better cooked but I am simply asking from a perspective about germs. The egg itself is an enclosed system. Why would a sterile environment be considered a risk factor for anything? | [
"I still wouldn't recommend it, but yeah, you should be fine. I say should be fine, because there's still a risk. Also, I'm a geologist, I lick rocks to see if it contains salt, so take my advice with a grain of NaCl."
] | [
"In the US and a few other countries, we wash the eggs after they pop out of the chicken. This washes away the natural protective layer which can let some bad bacteria in through microscopic fractures in the egg. That's why we refrigerate the eggs to keep them from going bad. Also it's possible the chicken might... | [
"The main danger comes from the egg being contaminated by the outside of the shell, which is not sterile. "
] |
[
"What does \"sustained blast wave\" mean in the context of thermobaric weapons?"
] | [
false
] | null | [
"https://www.researchgate.net/profile/Robert_Weinheimer/publication/322553927/figure/fig3/AS:667606096834560@1536181105007/11-Pressure-change-over-time-in-a-thermo-and-conventional-explosive-6_Q640.jpg",
"Look at that picture. You can see that the high explosive has a much higher peak pressure, but it's a very sh... | [
"The vapour cloud is caused by the negative pressure phase, which from a thermobaric explosion can be just as strong as, if not strong than that of a conventional explosion of the same yield."
] | [
"It seems odd to me that thermobaric weapons create less pressure than the average high explosive yet thermobaric weapons have this signature vapour sphere following the shockwave"
] |
[
"How come other animals kept their tail and humans lost their tail during the events of evolution?"
] | [
false
] | [deleted] | [
"Tails in primate animals are mostly used for locomotive purposes, for balance and in other cases as a gripping prehensile extra limb. In some cases the tails may not be \"useful\" but they are kept around for sexual selection reasons; i.e. mates find the body shape attractive.",
"Within the Hominoidea branch of ... | [
"Because we evolved from apes, who also lack tails, I think the loss of the tail probably predates being bipedal.",
"I think it probably has to do with the evolution of monkeys into apes. As monkeys began to live more on the ground rather than in the trees, a grasping tail became extraneous, and so it was no long... | [
"Horses use the tail as a fly swatter . Some insects can bite or could possibly leave larva and or cause an infection.",
"Dogs use there tails as a social thing when in a pack along with the ears."
] |
[
"What causes the red color of rust (Fe2O3)?"
] | [
false
] | I was trying to understand why the material absorbs most wavelenghts except red on an atomic level. I know the PI electron-absorption of azo dyes can be calculated with the amounts of conjugated double bond next to the N=N, but I have no idea how we can deduce the colour of inorganic matter. | [
"From the perspective of a physicist:",
"the band gap of bulk Fe2O3 is approximately 2.2eV. That means that light with a higher energy than 2.2eV (that's green light) can excite electrons from the valence band to the conduction band and is thus absorbed. Light below that energy is transmitted/reflected.",
"This... | [
"Now I'm curious, how is it different? I may be misunderstanding the labels that are used in chemistry.",
"The light is just exciting the electron from the highest occupied State to the lowest unoccupied state. In a bulk material (so Fe2O3 would be the unit cell of a crystal lattice rather than a single molecule)... | [
"Thanks for explaining, it helps a lot!"
] |
[
"What is Dark Matter/Anti Matter?"
] | [
false
] | I've always been interested in it, but never really understand it. I know that you can get anti-hydrogen by freezing Hydrogen very close to 0 Kelvin, and how it makes up half of the matter in the Universe, but that's about it! | [
"Two different things. Anti-matter is just regular matter but the particles have opposite charge. For example, the anti-electron (or positron) weighs the same as an electron but is positively charged. When it meets an electron, the two of them annihilate and leave x-rays. This can be used to detect cancer in Positr... | [
"No, anti-matter and dark energy are two different things. Anti-matter is different electromagnetically from regular matter, but in terms of gravity it's the same."
] | [
"Sorry for the random question on a random thread 17 days after your response, but it's the most recent question here about anti-matter and dark matter and I noticed your flair so here goes:",
"Is there a possibility that the so-called 'Dark Energy\" of our universe could just be areas of space where instead of m... |
[
"How many times must I use a reusable bag for groceries before I off set the carbon footprint of one use bags?"
] | [
false
] | null | [
"Wow, really? Cool! Source?"
] | [
"They don't biodegrade or do so slowly so you won't ever offset the footprint. IMO we shouldstop using them. But that'sin shouldland. Just minimizeuse bybringing yourown durable reusable bag. What you may be talking about is the cost to make that bag. One use offsets that cost i would think. "
] | [
"Carbon footprint?",
"Paper bags have a negative carbon footprint. Nearly all of the weight is from compounds made from CO2 in the air. As long as you don't burn them and the wood comes from sustainable forestry, using paper bags reduces CO2 in the atmosphere."
] |
[
"CNN reports tuna with cesium levels 3% above background. Can anyone provide context as to how low this really is? (e.g compared to radioactivity in smoke detectors)"
] | [
false
] | Not rewarding the article with a link. I'm pretty sure the only reason the publish button was hit on that article was because they could stick Fukushima in the title. But it got me wondering - at an intuitive level what does 3% above background mean? At what level above background does the risk of exposure start to rise above the everyday risks we take? | [
"That's more or less right. Normally we measure radiation exposure in Sieverts(Sv). Background can vary but we generally assume the worse to be safe so we go for 6.2 mSv. 3% is .186 mSv.",
"To answer your question, the most radiation workers in the industry are allowed a year is 50 mSv. The amount normal people a... | [
"That's more or less right. Normally we measure radiation exposure in Sieverts(Sv). Background can vary but we generally assume the worse to be safe so we go for 6.2 mSv. 3% is .186 mSv.",
"To answer your question, the most radiation workers in the industry are allowed a year is 50 mSv. The amount normal people a... | [
"For when it starts working... Here is the link to the original research: ",
"DOI: 10.1073/pnas.1204859109",
". Note, will not work yet. I hate Doi links."
] |
[
"Black holes. If they did not exist, could galaxies sustain themselves?"
] | [
false
] | I am curious... Do galaxies depend on black holes to maintain its structure? How do these extraordinarily massive spinning star-frisbees stay so balanced like a fully functional solar system? | [
"Nope. The black hole in the middle of the Milky Way (Sagittarius A*) represents 0.04% of the mass of the galaxy, whereas the Sun (which the planets orbit) represents 99.8 - 99.9% the mass of the solar system.",
"So if Sag A* were to vanish tomorrow, the Galaxy would remain together, and the orbits of the vast ma... | [
"To add to this answer the nearby galaxy ",
"M33",
" is largely unremarkable by eye but it has no supermassive black hole at it's core. Current understanding of galaxy evolution says the black hole can be signficicant in shaping the evolution of massive galaxies (i.e. bigger than the Milky Way), but they have l... | [
"To add this answer somewhat, even the largest supermassive black holes (several billion solar masses) are only a tiny fraction of the mass of the entire Galaxy; the M-sigma relation describes the typical mass ratios: ",
"https://www.skyandtelescope.com/astronomy-news/black-holegalaxy-link-extended/"
] |
[
"Energy of the universe"
] | [
false
] | Hi fellow reddit scientist, i was wondering how much energy is in the universe (today)? And does is actually have the same exact value it did since the big bang? | [
"This question gets asked so much, please excuse me not writing up an answer for the tenth time. Instead, why don't you read this:",
"http://www.physics.uq.edu.au/download/tamarad/papers/SciAm_Energy.pdf"
] | [
"Law of conservation of ",
" energy states that ",
" energy can not be created nor destroyed. ",
"Mass can be created or destroyed (or rather converted to another form of energy), in nuclear fission, fusion, particle-antiparticle production etc."
] | [
"The total energy of the universe is something that is incredibly difficult to measure. What is easier to measure is the energy density, or energy per unit volume. The most recent data seems to imply that the energy density of the universe is constant. This is what we call dark energy. Interestingly, the volume of ... |
[
"Why do lasers spontaneously emit?"
] | [
false
] | I understand in general how lasers work, but I'm wondering why an electron would spontaneously "jump down" in energy levels? What about a photon passing through it causes the electron to jump down instead of up, i.e. spontaneously emit? And also, how do lasers pump up the electrical energy in order to have electrons at higher energy states, in a practical/circuitry sense? | [
"I'm wondering why an electron would spontaneously \"jump down\" in energy levels?",
"Because it is a lower energy state - the same reason a ball will roll downhill.",
"What about a photon passing through it causes the electron to jump down instead of up, i.e. spontaneously emit?",
"What you described here is... | [
"One more point, it is very difficult to have a laser with a single ground state and excited state as you can't get an inversion necessary for gain. In an optical laser, lasing happens when the gain term exceeds the loss term for light transiting the cavity. An optically pumped laser requires an appropriate confi... | [
"Only partially correct. The laser starts from spontaneously emitted photons. Those photons however, are reflected back into the gain material by mirrors. When they pass excited ions, they cause the excited ions to emit photons in a process called stimulated emission. This causes more and more photos to be generate... |
[
"Would it be possible to become so intoxicated that your brain stops inverting the image from your eyes?"
] | [
false
] | null | [
"No. Even though the image on your retina is upside down relative to the object you're observing, the brain doesn't actually do any 'flipping'. It just knows (through early development) which neurons connected to cells on your retina are associated with which direction, and so in that sense it is hard-wired into yo... | [
"Read my answer to deathropenguin5. I'm not denying the brains ability to rewire itself (neural plasticity), but I'm saying that the changes alcohol makes to your brain (such as loss of balance) are different to the kind of ",
" change required to re-wire your neurons in such a way that your vision becomes invert... | [
"the brain doesn't actually do any 'flipping'",
"This is key. The location of the neurons doesn't matter. Your brain has spent years refining associations between the inputs. These associations are irrelevant to how the neural signal was obtained."
] |
[
"Is the plane of the Suns orbit around the galactic center the same as the plane of the planets orbit around the Sun ? If so when in the cycle of the earths orbit are we in the front of the Sun's path."
] | [
false
] | null | [
"No, the galactic and solar planes are not aligned.",
"If this were the case, then the Sun's (and moon's, and planets') path through the sky throughout the year would line up with the Milky Way. Rather, it lines up with a set of constellations known as the Zodiac. (There is nothing special about the zodiacal con... | [
"The astronomical arrangement described above is pretty difficult to visualize spatially. I'd prefer to describe it as \"when the direction of Sol and the direction of Sagittarius A* form a right angle\". And since the right ascension of Sagittarius A* appears to be 17h 45m, that means the date that OP is looking f... | [
"I'm not sure I'd call towards the center the front since presumably we aren't moving towards the center of the galaxy but perpendicular to that direction as we orbit the galactic core. The front would be solar prograde. Which direction that is I don't recall off the top of my head."
] |
[
"Are there any forests or fertile regions that once used to be deserts or barren lands? If yes, what caused the change?"
] | [
false
] | null | [
"Anywhere that a forest exists used to be barren land at some point in time. The process starts with mosses and fungi growing on bare rock and breaking it down over time to the point where small plants can take hold (e.g. shrubs and grasses). As the ground is broken down from rock to gravel to soil and is mixed wit... | [
"If a sandy desert area starts getting a bunch of rain, the sand is going to erode off pretty quickly due to lack of cover plants. "
] | [
"Okay that progression makes sense. But what happens if let's say the area is a desert where there's 20m of sand before you hit any clay/bed rock."
] |
[
"If you wear glasses that invert everything for a certain amount of time, could your brain eventually flip it right-side up?"
] | [
false
] | I was recently reading a book called "The Unidentified," and in it, someone invented goggles that inverted their vision, and they would live "flipped" for a week or so. After that, their brain interpreted visual signals upside-down, so they would see the world "normally" again. Then they could remove the goggles and the process would repeat. Would such a thing be possible, since our brain already interprets what the eyes see as upside-down anyways? | [
"Wow this is wrong. Please refrain from posting without specific knowledge to back up your point. Otherwise, the quality of this subreddit drops dramatically.",
"The brain ",
" flip your vision if you are continually exposed to upside down visual input. In fact, when you are born, your vision is upside down to ... | [
"Wow this is wrong. Please refrain from posting without specific knowledge to back up your point. Otherwise, the quality of this subreddit drops dramatically.",
"The brain ",
" flip your vision if you are continually exposed to upside down visual input. In fact, when you are born, your vision is upside down to ... | [
"if you've got 25$ you can try it out yourself, ",
"for science",
"!"
] |
[
"If you visited a random star, how could you quickly determine if there are planets orbiting it?"
] | [
false
] | Let's say you're a space tourist, zipping around the galaxy looking for interesting solar systems to visit. As you approach a star, what techniques could you use to ascertain whether there are planets orbiting it? As a space tourist with a short attention span, you're only going to spend a few hours studying the solar system before moving on to the next one. Since planets are small and dark compared to stars, with lots of space between them, would you even notice any of the planets? Put another way: how realistic is the Star Trek scenario in which moments after laying a course for a star system the Science Officer can report on the number of planets the star has and whether any of them are Earth-like? | [
"With today's science, you would have to photograph the system, while filtering out the star.",
"Repeat every few hours, comparing photographs.",
"Anything that moved is likely a planet.",
"Add 200 years to technology and your computer would automatically filter out all known background stars... Leaving plane... | [
"It depends on how fast you're moving, but if you were travelling at such speeds that journeys between planets in a solar system is in the order of days or hours, then you could quickly tell which 'stars' were stars and which 'stars' were planets because you'd see them move relative to the background of unmoving st... | [
"Once you're close enough to the star system, you could use ",
"angular diameter",
" measurements to quickly discover any planets. Even Pluto as seen from Earth appears much larger than even the biggest stars in the sky. ",
"If using a sufficiently advanced telescope, I imagine you could use ",
"spectroscop... |
[
"Is more expensive shampoo notably chemically different or having a measurably different effect?"
] | [
false
] | I accidentally used my wife’s obscenely expensive shampoo yesterday. My hair feels no different, I’m a simple man and I feel like there is no difference other than personal preference, am I right? What processes or effects, if any, is my wife paying for? | [
"While I can't speak to the science, there is a \"cost of goods\" or cogs, associated with making the shampoo. Basically, the cost of all the ingredients and the packaging added together. This often is where you begin to figure out your wholesale cost. Cogs + some profit margin. More expensive ingredients will, of ... | [
"Well I mixed it with the dregs of my other shampoo so I will be using it (slightly tainted) for a while yet, I will report back if I become Jennifer Aniston :)"
] | [
"Well I mixed it with the dregs of my other shampoo so I will be using it (slightly tainted) for a while yet, I will report back if I become Jennifer Aniston :)"
] |
[
"How do you compute DFT of noisy signals with nontrivial correlation?"
] | [
false
] | So far I've calculated that if I have a series of random values that are uncorrelated and Gaussian distributed with standard deviation \sigma, then each component of the discrete Fourier transform of that series is a complex random variable with real part distributed as a Gaussian with standard deviation \sigma / sqrt(2N) where N is the number of points in the series. I define my discrete Fourier transform as \sum_{n=0} v(n) \exp[ -i 2 pi k n / N] I don't know how to do a similar calculation in the case that the time series points have a non-trivial correlation function. How do you do it? | [
"Just a thought, this is a pretty specific question, and if you don't get a good response here you might want to check out scicomp.stackexchange.com."
] | [
"I am aware of this theorem but, as you say, I don't ",
" it solves the problem at hand."
] | [
"I am aware of this theorem but, as you say, I don't ",
" it solves the problem at hand."
] |
[
"Point of Origination of the Universe?"
] | [
false
] | null | [
"Okay, take a very elastic sheet of rubber. Draw cartesian coordinates on it, like you learned in geometry class, and spaced very close together, so the lines are almost on top of each other. Let's say every where the lines cross, there's a galaxy. This sheet of rubber is infinitely large, so you can fit as many... | [
"There is none. The universe expanded ",
"Galaxies are moving ",
" not away from a point in space."
] | [
"No such point exists. The big bang was not, despite what its name sounds like, an explosion at a point in space."
] |
[
"Is there a maximum or minimum frequency of light?"
] | [
false
] | null | [
"No, there isn't. The frequency of a light wave is a frame-dependent quantity, and you can change the frame of reference to make the frequency arbitrarily low/high. Since all frames of reference are equally valid, there can be no lower or upper limit in frequency."
] | [
"Not really.",
"Low frequencies have really large wavelengths. If you are much smaller than the wavelength it is difficult to detect such a wave -- it has incredibly little energy and interacts very little. Thus at the low frequency end, things taper off to a blur of \"why would I even care\" electromagnetic ener... | [
"It depends a bit on what you mean by 'maximum' and 'minimum'. There are theoretical limits - which (I know it's silly to say) depend on the theory you're using, and since there can only be a finite number of observations there will always be a maximum or minimum observed frequency.",
"On the high side, it is ge... |
[
"Chirality are there any examples of right handed in organisms?"
] | [
false
] | So my chem class was discussing chirality in organisms on earth. Apparently every organism has a left handed chirality structure and it was speculated that anything that is right handed could be from another planet or alien species. So reddit are there any organisms that have right handed chirality on earth? I believe sea bears are thought to be an alien species, but my professor had no idea about its chirality. | [
"I don't believe there is any organism that uses D-amino acids in its biology. Consider that such an organism would have to:",
"be entirely autotrophic: Since chirality is retained throughout most metabolic processes, the hypothetical D-organism would be unable to process any amino acids or sugars obtained from... | [
"'waterbear' can survive in space and being boiled "
] | [
"also known as tardigrades. Also known as non-alien life forms. WHere did this crazy assertion come from?!"
] |
[
"Straws in space?"
] | [
false
] | I have been pondering this for a few days now. Say you were in the vacuum of space, with a blob of some non-freezing liquid. If you inserted a straw into said blob, and sucked on the other end, what would happen? (and yes i realize how impossible this experiment would be to run - you can replace a human sucking with some sort of machine if it makes you feel better) milkshakes in space, possible? | [
"Liquids tend to boil in space due to the low pressure reducing the boiling point.",
"Beyond this if you had a liquid that did not boil then you would not be able to draw it through a straw since there is no net pressure to move it. A straw works by decreasing the pressure inside the straw relative to the enviro... | [
"Yup. So in a true vacuum, the moment you opened your lips to attempt to suck the liquid through the straw, the pressure from the air in your lungs/body would fill the straw and form bubbles in the blob of liquid. and after that I'm not sure. I'm assuming they'd push their way to the outside of the bubble, and disa... | [
"Vacuum? No result, there is no way to create a lower pressure than vacuum on the other end of the straw (to any significant degree. There are different levels of how pure a vacuum is).",
"Zero (micro) gravity in a pressurized space shuttle? it'd work just fine."
] |
[
"How do spiders decide where to erect their web?"
] | [
false
] | Just a few questions that popped in my mind after finding a spider hanging in a corner of my toilet. How does urban enviroment (flats/houses for example) alter their choices? How long do they stay at a specific place if there is no catch? Do they leave any cues for fellow spiders to indicate if an area is good to settle down? Thanks for your time! | [
"this is an interesting subject, and i had to find out for myself, so i did what any good college student does when wikipedia doesn't have enough information, and went to JSTOR. here's a very rough summary, in my very unprofessional opinion of what these actual experts are saying:\nIn ",
"research on a spider wh... | [
"Not an arachnologist, but here goes:",
"Wikipedia indicates that spiders cast a thin adhesive thread into a breeze in order to cross large distances. This could mean that webs will likely be smaller indoors, since such breezes are less likely to exist or to carry the web a sufficient distance. Spiders will also ... | [
"Some great answers, one thing though. Spiders will build webs just as large indoors (in cages for example) as they do outside. The easy answer to the question is, they build their web where ever they are, and as big as the space is where they are located. If they fail to catch prey, they tear down their web, by... |
[
"Can ohm in a wire be less than 1?"
] | [
false
] | Imagine you have a wire. Is it possible for the resistance to be less than 1? That would mean that voltage would give more ampere? I can't wrap my head around this. | [
"Yes. Suppose you had a length of wire with a resistance of one ohm. A wire half as long would have a resistance of half an ohm. One volt of electromotive force will yield two amperes of current.",
"Electricity is often compared to water. Voltage is water pressure and current is flow rate. If the pipe doesn't slo... | [
"Materials with zero resistance to electricity exists, they are called superconductors. "
] | [
"Since voltage and current are in different units, you can't really say that the current is bigger or smaller than the voltage. How the numbers compare is just an accident based on how the units were defined. An analogy: you might say that people are always weigh more than their height: 70 kg vs 1.8 m, for examp... |
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