title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"Is the field of mathematics boundless or is it resolvable?"
] | [
false
] | I just had a discussion about this with my brother. He speculated that given enough time (t approaches infinity) that math would ultimately be resolved. Whereas I was thinking of the field as something that would inevitably continue to differentiate into new areas of study. I know this is hard to validate using journals, but how would you weigh in on this as people who are fully immersed in the abstract bases of the field Edit: Additionally, if you find that it is boundless, how do those implications play in to the relative boundlessness of other fields of study (physics, chemistry, etc etc) | [
"Math, in the most abstract sense, is about systems with rules, and exploring the consequences of those rules. ",
"Godel's Incompleteness Theorem",
" proves that for a mathematical system of sufficient complexity, there will be statements that are true, but that cannot be proven to be true. This means that m... | [
"Please stop mangling these poor old Gödel's theorems. And, before looking at incompleteness theorems, meet ",
"Gödel's completeness theorem",
":",
"In first order logic, a statement is true if and only if it can be proved to be true.",
"Hence, the idea that there are \"statements that are true, but cannot ... | [
"While incompleteness is important here, I think the bigger question is how many formal systems there are to study. My intuition is that this collection has ",
" cardinality. If this is in fact the case, to put it in OP's language, we could never hope to \"resolve\" all of mathematics because we could never come ... |
[
"Does chewing affect the amount of calories that are obtained from food?"
] | [
false
] | Suppose you eat a bowl of oatmeal, but you swallow whole mouthfuls - will the amount of calories obtained be lesser than that from a bowl of oatmeal that was chewed well before swallowing? | [
"Digestion starts with mixing saliva with the food. Without that, the food is going to be only partially digested in the stomach and small intestine. Also chewing breaking up the food so that the later stomach fluids can make better contact with the inside of clumps."
] | [
"So, if you chew lesser, your body won’t absorb all of the nutrients?"
] | [
"Yes, that's right. Some foods, like soup, chewing doesn't do much except mix in some saliva. For most solid foods, once you chew enough, more chewing doesn't help. For oatmeal, the food particles are already pretty small, and chewing is mainly just to break up any lumps and mix in saliva.",
"Saliva has amylase, ... |
[
"Does tagging animals have any social effect on the animal's group that is being researched?"
] | [
false
] | In Meerkat Manor, the researchers tag the dominant female and males. Does the presence of these tags themselves have any effect on the individuals and how others in the group treat them? | [
"The identification bands they put around a bird's leg can actually make is more or less desirable to mates because of the color. At least that was the case with Zebra finches, who preferred males wearing red leg bands.\nsource: ",
"http://planetearth.nerc.ac.uk/news/story.aspx?id=657"
] | [
"This question seems relevant because we ",
" that some tetrachromatic birds use the fourth channel (in the ultraviolet range) specifically for mate selection (paper ",
"here",
", which is actually about zebra finches specifically)"
] | [
"This question seems relevant because we ",
" that some tetrachromatic birds use the fourth channel (in the ultraviolet range) specifically for mate selection (paper ",
"here",
", which is actually about zebra finches specifically)"
] |
[
"How does a server know my bandwidth when I'm downloading a file? i.e. how does it know how much data to send at a time?"
] | [
false
] | [deleted] | [
"To expand a little, TCP generally starts by sending a little data and waiting for a response from the other end acknowledging the data was received. The amount of data sent between acknowledgements is then gradually increased until a packet is not acknowledged. That gives an estimate of the bandwidth (actually t... | [
"It's in the header of the initial connection request. The client will send the request which will contain information like what it is after and where to send it, and will also state number of bytes it can recieve. If the server is able it will send that number of bytes at a time, however it can respond saying \"no... | [
"It doesn't.",
"From a high level view... TCP sends data and waits for acknowledgements from the remote end. When some acknowledgements don't make it back, it adjusts accordingly.\nThis way it naturally fills the available bandwidth.",
"Basically the protocol was designed on the assumption that packet loss was ... |
[
"Why is the entropy of the early universe considered low?"
] | [
false
] | As I understand it, entropy is a measure of disorder, or the number of different ways you can alter the microscopic arrangement of system without changing its macroscopic appearance. Why do we consider the early universe as ordered? What features suggest this order? Or do we just assume that since the universe has relitavly high entropy now, it must have had low entropy back then? | [
"I think \"order\" and \"disorder\" are the wrong concepts to use when trying to visualize and understand what entropy is. Order and disorder are really in the eye of the beholder -- I will demonstrate:",
"Consider the very early universe: a hot, dense, uniform quark-gluon plasma. Someone who is considering th... | [
"Or do we just assume that since the universe has relitavly high entropy now, it must have had low entropy back then?",
"The universe still has remarkably low entropy. According to the second law of thermodynamics states that the entropy of such a system should be expected to increase. However we remember yesterd... | [
"The Wonders of the Universe series [forget which season probably the 1st] by Brian Cox covers this well.",
"Take a pail and fill it with sand. The sand in the pail is in \"low entropy\" because there are few ways [comparatively] to order the sand in that pail. Now dump it out. It's a pretty sand castle. Stil... |
[
"Why do bad smells actually smell bad to us?"
] | [
false
] | null | [
"We smell different things differently because of the way the particles interact with receptor enzymes in our noses. ",
"Bad things smell bad because this is beneficial in an evolutionary sense. When you think about what “smells bad” it is often things like faeces or rotten food which are also harmful to humans i... | [
"That's actually logic but at the same time pretty smart. Nature finds a way ahah"
] | [
"To add. There's not a 1:1 relationship between odor molecules and olfactory receptors. A given molecule can activate multiple receptors and a given receptor bind to various different molecules. Our brains interpret the resulting \"profile\". This means odors not found in nature may nonetheless be smelled, and some... |
[
"Do animals produce adrenaline?"
] | [
false
] | null | [
"Yep. Adrenaline and other catecholamines are routinely measured in animal studies."
] | [
"Yes. Although the structure and precise location of the adrenal gland might vary significantly, ",
"all vertebrates have adrenal glands"
] | [
"Not all but many, specifically mammals, have adrenal glands or something that provides a similar effect."
] |
[
"When is a felled tree actually dead?"
] | [
false
] | When exactly could you categorize the trunk of a felled tree as being dead? | [
"Qualifications: Forester ",
"Depends on the definition of \"dead\" for a tree. There are fluctuating definitions in people (based on which organ is used for a metric). Trees also have a variety of \"organs\" that could be used as a metric for death. ",
"Trees only have a small percentage of the overall biomass... | [
"the roots re-growing aren't the only issue, some trees (such as manitoba maples) will grow new shoots from the trunks weeks after being cut down."
] | [
"Some will even regrow roots adventitiously from the fallen trunk, so I do not think that a felled tree can be described as dead.",
"There is no sure way of identifying death in a tree. Instead, I think they way to think of it is that you can say the tree is dead at any time but you always have a certain probabil... |
[
"When I was a kid, all my friends warned me before I tried on their glasses. They said that my prescription would get worse if I did so. Is there any truth to this?"
] | [
false
] | [deleted] | [
"There's no truth to this. The strength of prescription you need is determined by the shape of your eye (the lens itself, the dimensions of the interior, and the shape of the retina). ",
"Generally, vision deteriorates as a consequence of actual physical changes to the tissues involved:",
"The lens undergoes va... | [
"Can cause eye ",
" (which is a temporary problem caused by overtaxing the small muscles) and a headache, but not actually alter the physical structure of your eye.",
"I'm aware of some investigation into vision deterioration caused by 'excessive' use of computer monitors, but I'm not aware anyone has demonstra... | [
"Can cause eye ",
" (which is a temporary problem caused by overtaxing the small muscles) and a headache, but not actually alter the physical structure of your eye.",
"I'm aware of some investigation into vision deterioration caused by 'excessive' use of computer monitors, but I'm not aware anyone has demonstra... |
[
"How Is Amplitude/Energy of an Electromagnetic Wave Measured?"
] | [
false
] | As far as I’ve been reading, an individual frequency can vary in wave height and be more powerful the taller it is, ie. 25 Hz with a short amplitude versus 25 Hz with a much higher amplitude. If we were talking about sound, it would be louder (I think?) which is measured in decibels. What are the units you would use the measure the energy/power for ultra or infrasound. And could I have a few examples so I can see what the range is like? | [
"Intensity, power per area, is a common measure for electromagnetic radiation. As an example, sunlight is about 1 kW/m",
".",
"You can use the same sound but expressing it via the pressure variation and/or converting it to decibel is more common."
] | [
"Coming from industry, if we are looking at a specific frequency in ultra or infrasound we will generally use Pressure, not dB. Pressure ( in Pascals ) is a linear, rather than exponential scale. All of our microphones are calibrated based on pressure->voltage.",
"Pressure is directly proportional to the ampl... | [
"All acoustic waves (infrasound, sound, and ultrasound) are pressure waves, so they are measured in pressure units (Pascals in SI). The standard threshold of audibility in the 20 Hz to 20 kHz range is 20 micro-Pascals. However, this hides a lot of complications: people are most sensitive to frequencies in the middl... |
[
"Teplizumab is an antibody that targets the CD3 receptor on T-cells to prevent the T-cells from attacking the Insulin-producing Beta cells in the pancreas. How is the teplizumab able to specifically inhibit only the T-cells targeting the B-cells without compromising the immune system?"
] | [
false
] | null | [
"Just for a point of clarity, when you say \"B-cells\" I assume you mean beta cells. The immune system also has B cells which make antibodies. ",
"The medication will make you somewhat immunocompromised. however the immune system has multiple different ways to activate. All drugs that work on autoimmune disorders... | [
"It does compromise the immune response, which is the trade-off with basically any immunomodulatory drug. The innate immune response will be left intact, and B cells won't be directly affected (though they rely on T cell help for some functions), but the T cell response to anything, not just beta cells, will be sho... | [
"Yes sorry, I meant the beta cells. Thanks for the explanation!",
"You say that the immune system has multiple different ways of activating, could please elaborate on this in context with type 1 diabetes?"
] |
[
"I'm 32. Is there a single cell, or even molecule, left in my body that was there when I was born or am I a completely physically different organism from who I was as an infant?"
] | [
false
] | Have all original molecules in my body from birth been replaced by now or do some remain? If they've all been replaced, approximately how often does this occur in a human lifespan, rendering one a completely different physical being from who we once were aside from the ties of continuity? | [
"There may be others, but on a molecular level I would say the enamel on your teeth teeth and cartilage on your bones. These are permanent structures that once formed, do not change (much) unless damaged somehow.",
"If you are talking about the cellular level however, then you can encompass a much wider range of ... | [
"The epidermis (top layer) is replaced, the dermis (lower layer) is not. Tattoos inject ink into the dermis. "
] | [
"The epidermis (top layer) is replaced, the dermis (lower layer) is not. Tattoos inject ink into the dermis. "
] |
[
"What's the difference between the weak and strong anthropic principles?"
] | [
false
] | null | [
"The weak anthropic principle: The universe is the way it is because if it weren't, nobody would be here to wonder why it isn't.",
"The strong anthropic principle: The universe is the way it is because it must be in order for there to be somebody here to wonder why it is."
] | [
"Ah. So, in layman's terms, it's a question of whether the universe defines us or we define the universe?"
] | [
"The strong anthropic principle seems to say that our existence is so important that the universe evolved in a way that would allow it. Whereas the weak anthropic principle sort of says that we're here simply because we fit into the universe."
] |
[
"Can Ferrofluids be gaseous?"
] | [
false
] | Hi ! I've been looking into ferrofluids, and have only seen examples and demonstrations where the fluid is a liquid. Is it possible for ferrofluid to be gaseous? Thank you, bramanWolf. | [
"Hey, a few thoughts on that:",
"1- Ferrofluids are small particles in a solvent. The small particle itselfs is too big to be in a gaseous state.\n2- Ferromagnetism is destroyable trough temperature, so if you try to evaporate it thermal you will destroy the magnetic properties, and you will most likely evaporate... | [
"Actually this is an interesting approach. But you'd need a pressure- AND gravitationfree room i suppose. The solvent would evaporade together with the magnetic nanoparticles (due to no gravitation... otherwise the solvent would be first to evaporate again). The question is: would the solvent still keep the magneti... | [
"Thank you for your reply!"
] |
[
"Whats the most minimal food one could live off without any nutrient deficiencies?"
] | [
false
] | Whats the most simple food that someone to consume for a prolonged period of time (bread and water only for example) without any health risks? | [
"One of the most nutritionally complete single foods is the sweet potato, but even eating this does not give complete nutrition. According to several ",
"nutrition ranking",
" systems the sweet potato tops the list. "
] | [
"Do you consider an animal to be a \"simple food\"? Because natives of far north latitudes can survive on basically nothing but seals.",
"Also, eggs are very nutritious, as long as you're careful not to get a biotin deficiency from the avidin."
] | [
"If you have a normal, varied diet, you'll piss out most of the vitamins. If you don't eat much healthy stuff, the multivitamins are great."
] |
[
"Do any of you [Science People] ever doubt yourself and think you shouldn't have your title as a science person?"
] | [
false
] | null | [
"Sounds to me like you have feelings consistent with ",
"Impostor Syndrome",
", a common thinking pattern among scientists or other \"successful\" people."
] | [
"I think we need more people like you. It seems like a lot of people use their credentials as a platform to give their opinions weight. Having studied science myself I am more aware of how little individuals know and how and opinion from a credential really shouldn't be given more legitimacy than someone else's. ",... | [
"Research scientist in the pharmaceutical industry here...",
"I feel the same way. I never did well in lecture... but I did great in the labs. I can't stay awake in meetings but I can zoom around the lab running experiments that I feel like I barely understand what they do because the pHDs that are supposed to be... |
[
"What are solar sails and how do they work?"
] | [
false
] | null | [
"Not just hypothetical; they've been employed many times, and 3 years ago, JAXA made the first spacecraft with solar sails as the primary method of propulsion.",
"http://en.wikipedia.org/wiki/NanoSail-D2",
"http://en.wikipedia.org/wiki/IKAROS",
"Also, just as sailboats can travel upwind, solar sails are not l... | [
"From ",
"http://en.wikipedia.org/wiki/Solar_sail",
" :",
"Solar sails (also called light sails or photon sails) are a form of spacecraft propulsion using the radiation pressure (also called solar pressure) of a combination of light and high speed ejected gasses from a star to push large ultra-thin mirrors to... | [
"Is any of this theoretically possible?",
"Ehh, not really. If you think about a ring, the net gravitational force on it will be zero (because for each element of the ring, the element on the opposite side is experiencing an equal force in the opposite direction, thus canceling out), so there's not much to hold i... |
[
"If one glass of water is 30 degrees Celsius and another glass is 10 degrees Celsius, which glass reaches 20 degrees Celsius first? (X-post from r/askreddit)"
] | [
false
] | [deleted] | [
"It depends. :)",
"If the glasses were sealed, they would reach 20 C at the same time.",
"If they are open, part of the water in the hot glass would evaporate, cooling it, and leaving less water to cool.",
"Unless it was a high humidity environment, in which case water would condense on the cool glass, heati... | [
"The 30 degree glass will have the advantage of evaporative cooling, in addition to the conductive & radiative warming & cooling enjoyed by both."
] | [
"The ",
"specific heat",
" of water is actually a tiny bit higher at 10 C (4.204 J/gK) than at 30 C (4.178 J/gK), so even with sealed glasses, it takes a tiny bit more heat to go from 10 C to 20 C than from 30 C to 20 C."
] |
[
"Can someone explain the ethics of testing potentially life saving medication?"
] | [
false
] | So I was watching a report on the effects of Ivermectin treatment for Covid-19 vs a control group. This caused me to wonder about a more drastic medical situation such as the need to test a potential life saving medication for the treatment of something like cancer. I'm a software developer by training and trade, so I have an understanding of the scientific process, but I tend to work in a field where if I make a mistake...no one will die. So assume I have a new drug that has the potential to be extremely effective at treating cancer. I believe due diligence would require to perform double blind randomized testing with this medication as well as a placebo. At this point, I feel like there's an ethical issue because are we not knowingly taking individuals with a life threatening illness and deliberately giving them a non treatment? I know there are all sorts of nuances to what I'm asking and I'm sure it's not as simple as saying the control group is receiving no treatment. But how do we test life saving medication knowing that part of our group is not going to receive any medication whatsoever? Or am I just drastically off base in how medicine is developed and studied? Edit: wow, thank you everyone! I really appreciate the great responses! It all makes a lot more sense to me now. | [
"You're right that there are ethical problems with giving sick people placebos, which is why new medicines are tested against the existing treatment wherever possible. ",
"The UK's NHS website has an easy-to-read guide to clinical trials."
] | [
"This is how it's done. That's also what you ",
" to compare it against. It usually doesn't make sense to test a product that you expect to perform worse than what's already on the market."
] | [
"Most trials like this have interim reviews for exactly this reason. They take unfinished data at intervals - say, if it’s a 5-year study, they may look at 1 year in and so on - to see if the unknown treatment has already reached a statistically significant improvement over the standard of care (the usual control)... |
[
"Could i drug myself to enjoy anything?"
] | [
false
] | If i took drugs that made me feel pleasant or euphoric doing boring or unpleasant tasks, could i condition myself to enjoy anything? (I don't intend to ever do this of course) | [
"You couldn't necessarily make yourself enjoy any activity, but you could make yourself seek out and want to perform any activity so long as there was a good chance it would end with the drugs."
] | [
"You could probably classically condition yourself to enjoy those menial tasks, but the effect wears off if you apply the conditioned stimulus (the boring) too often without the unconditioned stimulus (drugs). This procedure would not be recommended for extended periods of time. "
] | [
"Sounds like a strain of cannabis "
] |
[
"Warmth needs matter, there is absolutely no matter in space(like air or something), how is it possible that space has about 3°K?"
] | [
false
] | First things first; English is my second language, so please excuse any mistakes i may make. Second thing is that im not too versed in physics, so please by patient if i don't understand everything at first. The question is pretty much in the title(= Thanks for every answer!! | [
"Your second point is incorrect. There ",
" matter in space. It is, however, very thin compared to what we are used to. ",
"You are correct however, in that 'space itself' would not have a temperature. The 3 Kelvin (Kelvin is not referred to with degrees, no ° symbol necessary) refers to the thermal black body... | [
"Few factors involved. Microwave background radiation that was left over from the formation of the universe. Decay of matter, photons floating through space, othet sources of energy such as galaxies, stars, gas."
] | [
"You're right that \"warmth needs matter.\" Temperature is literally a measurement of how how much ",
"kinetic energy",
" (movement) a sample of mass has. That said, you can't measure the temperature of ",
". Empty space isn't at 0K- it simply ",
" of its own.",
"The 3K number you're referring to is the m... |
[
"Is it true that the left side of the brain is logical and the right side is more creative?"
] | [
false
] | And further more. does being left or right handed effect your personality at all? It just sounds like a bunch of superstition. | [
"I know that linking to articles instead of responding is a bit discouraged on here, but Steve Novella gives a fabulous write-up of this myth, and how it has a grain of truth:",
"More Left Brain / Right Brain Nonsense",
"Here's a quote:",
"So while some specific functions do lateralize, our minds and personal... | [
"And as for the second question, in the body of OP's post: there appears to be no reason to assume differences in personality that have a significant basis in brain anatomy. ",
"The most significant difference in brain anatomy found so far is that left-handed people have less lateralised speech comprehension proc... | [
"And as for the second question, in the body of OP's post: there appears to be no reason to assume differences in personality that have a significant basis in brain anatomy. ",
"The most significant difference in brain anatomy found so far is that left-handed people have less lateralised speech comprehension proc... |
[
"If we were able to melt machine and brain, would we still feel stimulation?"
] | [
false
] | null | [
"We can't answer such hypothetical questions objectively."
] | [
"Ok wait is this better?",
"So you know how when we touch something, our brain can sense that cause of the nerves in our skin correct? Would we still \"feel\" that we touched something if we had our brain uploaded onto a computer?",
"Like we were in a \"robot\" that held our conscious! Would our robot body be a... | [
"We don't at present know what it means to \"upload a brain to a computer\" so we can't really answer that question."
] |
[
"Why isn't glucose C6H12O6 and not CH2O?"
] | [
false
] | In chemistry, we talk about how the atomic ratios are important in determining what type of compound we have. N2O and NO2 are different compounds as they have different atomic ratios (2:1 vs 1:2). I understand that a glucose C6H12O6 (1:2:1) molecule has 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms, but wouldn't a hypothetical molecule of CH2O be the same compound (with the same properties) as it has the same atomic ratio? | [
"You're ignoring the connectivity. Glucose acts like it does because of how the atoms are connected, not just because of how many atoms of which type it has or their ratio",
"CH20 is actually formaldehyde, which has completely different properties to glucose",
"Chemical properties are a function of what the mo... | [
"Here is a crude analogy: \"no\" and \"noon\" are two different words."
] | [
"To use your example, you're correct that NO2 is a gas; but N2O4 is also a gas completely separate from the NO2 - i.e. it's not the equivalent of 2 NO2 molecules.",
"I think what you're implicitly alluding to is the concept of empirical vs. molecular formulas: you would be correct in saying that for glucose the e... |
[
"Is it possible to determine where in Africa modern humans originated?"
] | [
false
] | I'm aware of work that's been done to try to determine where humans arose in Africa using genetic data (the big contenders being East and South Africa). However, I've also heard that at one point a harsh climate forced modern Humans to live solely along the coast of South Africa. If that's true, how could we hope to use genetic data to determine the birthplace of humanity? | [
"Hmm... Okay, first things first: there is no such thing as a \"missing link\". This was a Victorian/Edwardian concept that arose due to a failed understanding of the ",
" nature of evolution.",
"Secondly, we can pretty much trace our ancestry back at least 55 million years - the earliest recognisable primate f... | [
"So, the population genetic evidence on this matter overwhelmingly supports the \"Out of Africa\" hypothesis. It's very clear from the data",
"1",
"2",
" that the genetic diversity present in modern human populations that are outside of Africa is a subset of the diversity within Africa, an observation that is... | [
"National Geographic",
": \"",
"\"",
"Human Origins Project",
" and the ",
"Genografic",
" will probably tell us more.",
"Nothing else so far."
] |
[
"Are there stars that radiate no visible light?"
] | [
false
] | Do such stars exist that they radiate maybe only ultraviolet parts of the spectrum because they are so hot, or vice versa? | [
"Black body radiation is continuous across the entire spectrum. The hotter a black body is the more intense the radiation at every wavelength. However, there is a shift towards a higher frequency in the ",
" intensity. See graph ",
"here",
". All stars have a combination of black body radiation, and individua... | [
"No, a hotter black body emits more radiation at ",
" wavelengths than a cooler one. Making the black body hotter will never make it emit less visible light."
] | [
"The hotter an object gets the brighter it gets, so you can't make a star too hot to emit light. The only way to make something emit little visible light is to make it too cold. Now, there are massive objects that have a low enough temperature to be \"dark\" (e.g. brown dwarfs, some black holes), which I think you ... |
[
"What happens to a light photon after it is perceived at the back of my eye?"
] | [
false
] | [deleted] | [
"It's not converted to electricity. The energy from the photon is used to ",
"isomerize retinal",
", and that structural change is detected by opsin, inducing a conformational change in the protein as well. At the end this is turned into a signal in your optic nerve."
] | [
"It is absorbed by your eye."
] | [
"It causes an action potential by opening ion gates within the cell membrane, this charge travels along the nerve, which triggers the release of a neurotransmitter at a synapse. This chemical release triggers a new action potential at the next nerve in line."
] |
[
"From a programmers point of view, how does artificial intelligence work?"
] | [
false
] | [deleted] | [
"It's as complicated as the human mind, put simply. Many complicated tasks for the most basic things. The hard part of AI is actually programatically engineering code that can some how learn or improve/correct itself.",
"I think what you are specifically referring to, though, is vision-based tracking. How this... | [
"tl;dr: There are many ways to solve this problem, all of which work differently. Most algorithms involve some level of statistics and/or heuristic-based search.",
"AI isn't one single algorithm or strategy. Computer Scientists have mostly abandoned the idea of a \"strong AI\" that emulates human thought (think H... | [
"Here's an example:",
"Suppose you tell a program, \"The grass is wet.\"",
"Well, the program would have massive amounts of information stored, including millions of rules, of the form \"if X, then Y,\" etc., such as \"If a person is happy then they are probably smiling.\"",
"So, the program might find, \"If ... |
[
"What did neanderthals evolve from, where did they live, how did they get there and how was their genetic code close enough to that of the homosapien that the two species could still procreate each other?"
] | [
false
] | [deleted] | [
"It is currently thought that both us (anatomically modern humans or Homo sapians) and neanderthals evolved from a close common ancestor. The fact that they could breed isn't actually that astonishing. The 2 species of African elephant manage it so well that most people think that there are only one. ",
"As for ... | [
"And the lastest copy of National Geographic talks about neanderthal art and possible culture, if you can find a copy."
] | [
"Current theory is that Homo Neandertalensis and homo Sapian share a common ancestor in a previous homo species. This species managed to be break of africa and thus evolved into neandertals. In Africa the same homo species eventually gave rise to Homo Spains.",
"Have a look at Neanderthals - Human Extinction (BBC... |
[
"Why is it that the skin on the human face is so much more sensitive and prone to problems like acne?"
] | [
false
] | null | [
"There are greater amount of nerve endings in the skin on our face. Add that with the lack of friction from external objects (Clothes, objects, even wind and sunlight) and you have sensitive skin! In contrast, your palms and fingers have a large amount of nerve endings as well but since you have been using your ha... | [
"Do other animals that produce sebum have problems with acne then?"
] | [
"But what about the back? I mean, they call it backne for a reason. "
] |
[
"Are there any few-celled organisms?"
] | [
false
] | Organisms seem to be divided into single cell or million+ celled, but are there any with fewer? Something like 2-100 cells? I tried googling this but all I got were creationist sites arguing against evolution. | [
"Sure, the one that popped into my head immediately was ",
", a type of nematode. It has ",
"~1,000 cells",
" in a mature adult male. And, of course, throughout evolution, there must have been intermediates between the unicellular eukaryotes still seen today (baker's yeast, for example) and the multicellula... | [
"Check out the bizzare mesozoans ",
"http://en.wikipedia.org/wiki/Mesozoa",
"and placozoa",
"http://en.wikipedia.org/wiki/Placozoa"
] | [
"http://www.ncbi.nlm.nih.gov/books/NBK28332/",
"There are many, just grab some swamp water and a microscope you will see tons of <100 celled organisms. "
] |
[
"If there was a massive mirror placed at the edge of the universe, and we had telescopes powerful enough to see to and through it, what would we see?"
] | [
false
] | null | [
"Basically the mirror would show us what we looked like in the past. For every light year the mirror is distant, it would show us what we were doing two years in the past. The photons for every point in time, would take a year to get to the mirror, and a year to return. So, once a mirror is placed beyond the halfwa... | [
"No, by \"through\" I meant seeing the reflection. Thanks, this was a really fantastic answer."
] | [
"This assumes the universe has a definite edge, which it very well may not, so your question is difficult to answer. If the universe existed in spherical coordinates, the entire universe ",
" be a mirror of sorts in that if you traveled in a straight line in any direction you would eventually end up exactly where... |
[
"Why did nuclear tests 'Bluestone' and 'Housatonic' have small fireballs surrounding the main fireballs?"
] | [
false
] | [deleted] | [
"Regarding your secondary question of why Housatonic lasted so long, I need to point out that the film you linked to shows the detonation ",
" So the 7 minute playback actually was recorded in about ",
".",
"The sphere that briefly appears surrounding the fireball early in the film looks like some sort of at... | [
"Are you referring to the \"sparkles\" that can be seen around the edge of the fireball between 0:05 and 0:18 in the Housatonic video? A lot of small bright spots forming a spherical shell?",
"My guess is that these are similar to the \"mottling\" described in ",
"this wikipedia article",
", which they say \"... | [
"OK, that's the mottling I mentioned."
] |
[
"What man made objects can be seen from earth to space?"
] | [
false
] | Hello, googling the same question shows me results from what can be seen from space to earth but not viceversa, I am not a flat earther btw, the earth is round, thank you. I am asking this because I am buying a telescope so I want to see something like the space station or such, is it possible? Thank you for your asnwers | [
"You can \"see\" the ISS as a brightish light with just the naked eye, and with a telescope you can at least make out it's shape. It moves fairly quickly and you'll only see it for a second, though. Other satellites are smaller and you won't be able to discern them as anything but blips of light moving across the s... | [
"The ISS is a very bright spot that is often visible a bit after sunset or a bit before sunrise. It can appear about as bright as Venus or Mars. Over 100 other satellites are bright enough to be visible to the naked eye if you don't have too much light pollution, with binoculars or a small telescope you can see hun... | [
"Just to add a quick note about GEO objects... During \"glint season\" (which is around the equinoxes) they can glint quite brightly and can actually be visible to the naked eye. Glint season ",
" ended earlier this week though...."
] |
[
"What animal is must abundant on earth by total mass?"
] | [
false
] | null | [
"I was down voted (lol) but ",
"http://www.antweb.org/antblog/2010/10/do-ants-really-have-the-largest-biomass-of-all-species-on-earth-laurie-usa.html"
] | [
"I was down voted (lol) but ",
"http://www.antweb.org/antblog/2010/10/do-ants-really-have-the-largest-biomass-of-all-species-on-earth-laurie-usa.html"
] | [
"So I was right? What the hell downvote machines. "
] |
[
"How loud would a sound have to be to be heard around the world?"
] | [
false
] | And as a follow up, besides destroying billions of eardrums, what effects would the sound have on the world? | [
"Krakatoa's last big explosion was heard 5000 km away and is estimated to have been 180 decibels.",
"http://en.wikipedia.org/wiki/Krakatoa",
"The sound of the eruption was so loud it was said that if one was within ten miles, they would go deaf."
] | [
"310dB at source apparently:\n",
"http://decibelcar.com/index.php/menugeneric/87"
] | [
"Forgive me for not being a scientist, but until a true expert comes along, I think these answers are misleading. Each medium has a maximum volume, above which sound will distort and be expressed as a pressure wave. Our atmosphere will allow 194 decibels. Given the size of the earth and the range of human hearing, ... |
[
"Let's say I walk into an elevator/lift while flying a remote control helicopter (I fly the helicopter in with me). The doors close and the lift moves down. What happens to the helicopter?"
] | [
false
] | null | [
"I agree, this is probably the best explanation. The helicoptor pushes air down in order to keep itself aloft. With the air moving slightly at first, it will slightly go up higher, but will stabilize itself once the air in the elevator is moving at the same rate.",
"Its almost like the ball in the car questions. ... | [
"I agree with this for the most part, but I don't think it's accurate to imply that the helicopter lifts itself by pushing air against the floor. It's a matter of momentum. The helicopter is forced up by accelerating air down. Period. A rocket in space accelerates by pushing fuel backwards. It doesn't matter that t... | [
"I agree with this for the most part, but I don't think it's accurate to imply that the helicopter lifts itself by pushing air against the floor. It's a matter of momentum. The helicopter is forced up by accelerating air down. Period. A rocket in space accelerates by pushing fuel backwards. It doesn't matter that t... |
[
"Our water is hard. If we want to minimize limescale deposits in our electric kettle, is it better to only boil the amount of water we need or to boil a kettle full every time?"
] | [
false
] | The kettle boils between .5L and 1.7L at a time. This is to settle a longstanding marital disagreement. | [
"It doesn't really matter. Higher temperature causes the dissolved solids to precipitate since they're actually less soluble at boiling temps. Counter-intuitive, but that's how it is.",
"So, less water means what's left will likely have more evaporation relative to the water volume (as most heat will be lost thro... | [
"Unrelated but if it has not been mentioned, putting a small ball of steel wool in the kettle helps keep scale off the boiler plate by using itself as a substrate. Just make sure it's pure steel wool and not a soaped or treated scrub pad."
] | [
"Yep. Carbon dioxide from the atmosphere dissolves into solution and lowers the ph of the water slightly by forming carbonic acid, allowing a bit more of the carbonates to dissolve. Bringing the liquid to a boil drives the carbon dioxide off, raising the ph, and causing those excess carbonates to precipitate."
] |
[
"What happens in a photon-photon colliding when each photon energy is 120 Mev?"
] | [
false
] | Hello, I am a 17 y.o stduent who is trying to fully understand photons colliding. We usually know that when two photons collide and each one's energy is 0.511 Mev they produce an electron and a postiron and this idea is the same for other particles. But what if two photons with an energy, which is not equivalent to any other particle, collide? What would they produce? Or would they even collide? Like for example 120 Mev. Thank you very much. | [
"They can pair-produce other particles, as long as the energy in the center-of-momentum frame exceeds twice the mass of the produced particle.",
"They can also scatter elastically without producing any particles."
] | [
"They can always scatter elastically, since there's no energy threshold for that. But the cross section is low, because photons don't directly couple to one another.",
"If the energy is below the threshold to produce any particle, they simply can't pair-produce anything."
] | [
"Yes, the extra energy just goes into the kinetic energies of the produced particles."
] |
[
"Why are atoms with full outermost shells more stable?"
] | [
false
] | It's always been a given that atoms which have their outermost shells fully occupied are the most stable- but why? What deters the electrons from being lost or gained or shared? | [
"Being lost: Those electrons are stabilised by the shell being full. The first ionization energy is quite high. Ionizing it would be to do so against a positive charge, and the additional energy lost by the shell being full would need to be put back in.",
"Being gained: Any new electron would need to go in the ne... | [
"The answer has to be considered in the context of other matter to be understood, I'll try as best I can.",
"Electrons can only orbit nuclei in set configurations, s,p,d and f orbitals (there are more but that's going to the edge of most chemistry). When electrons orbit in an atom they have to exist in a specific... | [
"You might be right, it's been a while since I've looked into what something like [Li]- would look like from an ionization energy perspective. Anyone want to chip in with what the first ionization energy of something like [Li]- [H]- or [He]- would be?",
"It's actually feeling wrong to denote lithium, hydrogen and... |
[
"Would a black hole have surface irregularities of mere atoms? How does it's gravity affect how smooth it's surface is?"
] | [
false
] | [deleted] | [
"In general relativity, black holes have no surface at all. The ",
" that people talk about is not a physical barrier, it's a mathematical point of no return. In the current understanding of gravity (though alternate theories exist) the mass of the black hole is concentrated into a single point with no volume, a... | [
"Event Horizon, what is the part. \"That people talk about\"? Isnt it it term?",
"Yes, event horizon is the correct term for the surface from which even light can't escape.",
"If light can't escape it, what else that is more relative actually can?",
"In general relativity, nothing can go faster than light - s... | [
"Event Horizon, what is the part. \"That people talk about\"? Isnt it it term?",
"Yes, event horizon is the correct term for the surface from which even light can't escape.",
"If light can't escape it, what else that is more relative actually can?",
"In general relativity, nothing can go faster than light - s... |
[
"Why is the 4th dimension publicly understood to be time?"
] | [
false
] | We have three spatial dimensions, and then all of a sudden, time? Aren't there more spatial dimensions? Why is time the 4th? If a square could express itself, wouldn't it declare itself to exist in the 2nd dimension, with time being the 3rd? | [
"The idea of time being a dimension long predates relativity, but in physics, relativity really skyrocketed the idea because explicitly in the mathematics, time was treated on the same footing as space and irrevocably you could discuss neither without the other, thus the unification now called ",
".",
"Mathemat... | [
"So saying that time is the 4th dimension is only accurate because we are in the third dimension, right? ",
"There's nothing wrong with having only two spatial dimentions and one time. In this case, if we lived in flatland, everyone would call time \"the third dimension.\" The listed value is just a title, the r... | [
"There is, in fact, a ",
"fourth spatial",
" dimension in which space itself ",
"is expanding",
" in.",
"What is this bullshit? Did you just make this up?"
] |
[
"What is the purpose of the inflammation response in humans?"
] | [
false
] | From regular NSAIDs to steroids, there seem to be a lot of medicines dedicated to lessening the inflammation response or halting it altogether. Does the inflammation response ever have a useful physiological purpose? | [
"Yup. Inflammation is the bodys response to damage or infection. If you step on a nail, the site of the puncture will swell as immune cells rush to the site to deal with the invading pathogens. Many things can trigger inflammatory responses and they play important roles in repair and defense. The problem is th... | [
"Do anti-inflammatories inhibit the immune response as they inhibit inflammation itself?"
] | [
"Inflammation is like the body's response to any foreign body that has entered the blood stream. It works to eradicate those said foreign bodies. Sometimes the body isn't able to get rid of those bodies and the process is prolonged resulting in the redness, swelling, heat and pain. Hope that answers the question"
] |
[
"We are on the way to growing human organs, is making human blood feasible in a lab?"
] | [
false
] | [deleted] | [
"Blood products nowadays are practically risk free with respect to infections, so this is not an incentive. Donating blood is amazingly simple and cheap compared to in vitro production. Blood is a complex liquid!"
] | [
"It's not yet feasible. People have worked on it for years but can't get it done for one major reason: Oxygenation.",
"When talking about blood transfusion we usually mean the transfusion of erythrocytes, and I will only focus on them for simplicity. We transfuse erythrocytes because they are the carriers of oxyg... | [
"People are working on making blood from stem cells and reprogrammed stem cells. You can check out the work of Peter Zandstra for more information on this. Basically, you can take stem cells from cord blood and convince them using a controlled microenvironement to become the different cell types that make up blood,... |
[
"Could water clouds form on a planet with no/barely any liquid surface water?"
] | [
false
] | null | [
"Water ice clouds have been ",
"observed in the atmosphere of Mars",
", imaged directly from spacecraft on it surface."
] | [
"I'm not a scientist, but I do know that there is a star that routinely ejects jets of water from its magnetic poles.",
"Hypothetically speaking, a planet with water molecules on it, but with a temperature/pressure combination that would only allow for it to exist in a gas form, would have water \"clouds,\" thoug... | [
"Here you go"
] |
[
"Will a completely still objet emit radiation?"
] | [
false
] | null | [
"Yes. Anything with a temperature greater than absolute zero emits radiation."
] | [
"Lets say I have a stable state sphere made of some stable matter in a zero gravity/zero vaccum environment in an impermeable container somewhere in space away from gravitational effects to the point that the sphere if at placed at the center of the container does not move away to the sides. ",
"Okay now we have... | [
"Yes.",
"But what does \"completely still\" mean? In another, equally valid reference frame the object is moving. In yet another reference frame the object is moving at a different speed and in a different direction. ",
"A photon cannot be generated in one of these reference frames and not another, and for ever... |
[
"If platypi do not have stomachs, then how do they break down their food?"
] | [
false
] | null | [
"Species which lack a stomach & glands to secrete pepsin still have a digestive tract. Their diet renders a stomach superfluous and have literally lost the genes for it.",
"\"diets in which digestion via pepsins and acids was not likely or even possible. For instance, diets rich in chalky shells or bottom muck ca... | [
"I know that, but I don’t know how they break down the shellfish instead."
] | [
"You as a human technically do the same thing. If you eat like a pig and swallow your food without chewing your food does not have time to fully digest in your stomach. That's why you have a large intestine and a small one to finish the job.",
"The platypus technically just digests in the intestine."
] |
[
"Why do flames coming out of a rocket engine get narrower?"
] | [
false
] | Reference: The flames coming out of the rocket engine are clearly getting narrower as they move farther out. It's this effect due to fluid mechanics (Bernoulli's law?) or is it due to plasma dynamics (something counterintuitive happening because of moving free charges in the plasma)? A combination? Or something different? | [
"I’ve got a very long video all about expansion ratios and how an aerospike engine takes that squeezing effect at sea level and makes use of it! (Warning, it’s long, but I promise you’ll have all your questions answered!) - Are Aerospikes Better Than Bell Nozzles? ",
"https://youtu.be/D4SaofKCYwo",
"(EDIT) I sh... | [
"The atmosphere squeezes the exhaust plume. Those engines are calibrated to provide straight exhaust at a higher altitude. As you go higher up, ambient air pressure drops. So if you want a straight exhaust plume at higher altitude, that means the exhaust plume's pressure must be equal to the ambient air pressure. "... | [
"Atmospheric pressure is the correct answer. Towards the extremes of high pressure and low pressure some pretty weird stuff can happen, like the crazy plume of blue that the falcon 9 makes in the upper atmosphere."
] |
[
"How do cells know their 3D position, in order to make the correct shaped organism?"
] | [
false
] | null | [
"There are multiple mechanisms at play at different times in different tissues, and I'll just list a few.",
"One common mechanism is a gradient of a secreted factor. In the developing spinal cord, for example, the cells at the ventral side (bottom) secrete a signaling molecule called sonic hedgehog (shh). Shh dif... | [
"There is indeed a gene called 'sonic hedgehog'.",
"Fruit fly geneticists often give genes they discover goofy names like ",
" and ",
". When a pair of scientists discovered a gene that, when mutated, caused fly embryos to grow small hairs over their entire body. This caused the embryos to look like a hedgeho... | [
"There is indeed a gene called 'sonic hedgehog'.",
"Fruit fly geneticists often give genes they discover goofy names like ",
" and ",
". When a pair of scientists discovered a gene that, when mutated, caused fly embryos to grow small hairs over their entire body. This caused the embryos to look like a hedgeho... |
[
"Why don't magnets repelling each other glow?"
] | [
false
] | Allow me to explain my reasoning: I therefore assume that they repel each other through the use of photons, and we should therefore see them glow. Why am I wrong? | [
"Stationary magnets (or close to stationary magnets) repel each other through an exchange of virtual photons, not real photons. Virtual particles are not stable, quantized particles that can radiate away into space and into your eye. Virtual particles are simply one way to describe EM field configurations that are ... | [
"Visible light is comprised of photons with frequencies between, roughly, 400-800 terahertz.",
"The fastest spinning man made object spins at 600 million rpm, or roughly a million times too slow.",
"http://www.livescience.com/39275-fastest-manmade-spinning-object-made.html",
"Edit: To give you an idea how fas... | [
"Is it possible to spin a magnet at the right frequency to produce light, or will the photons produced always be low frequency?"
] |
[
"How does air become created in this situation?"
] | [
false
] | null | [
"There isn't more air being created. The air bubble stays the same size."
] | [
"Yes. I’m wondering what happens to the air in that space as you make it larger "
] | [
"It just floats to the top of the hole."
] |
[
"If oil is hydrophobic, how can it perform capillary action if capillary action requires hydrophilic bonds?"
] | [
false
] | null | [
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/HomeworkHelp",
"guidelines.",
"/r/AskMath",
"/r/AskPhysics",
"/r/PhysicsHelp",
"/r/chemhelp",
"If you disagree with this decision, please send a ",
"message to the mo... | [
"Your post was removed because of the reason stated. If you have a problem with this decision, then message the moderators (again, ",
"). Do not insult the moderators or otherwise be uncivil. We are not here to do your homework or your niece's homework."
] | [
"If you don’t know, just say you don’t know. "
] |
[
"How do lithium salts treat bipolar disorder and depression?"
] | [
false
] | I consider myself pretty smart, but the wikipedia article hasn't cleared much up about how it affects the physiology of the brain in a positive way. | [
"As I understand it, it really is a case of we have no clue, but it works. A researcher was testing them on rats for something unrelated, and noticed it kind of mellowed some of them out, so they ran trials and figured out it helped with bipolar for humans. "
] | [
"This is correct. Sometimes we just don't know by something works, but accept that it does and work around that fact. I asked yesterday how iodine works as an antiseptic, and it's the same thing: we don't know. There are also several pharmaceuticals whose mechanisms of action are unknown. "
] | [
"i believe current thinking is it substitutes for Na",
" ions in the axons, leading to different propagation of action potentials.",
"http://www.sciencedirect.com/science/article/pii/S0278584608002492",
" a link behind a paywall that i dont have "
] |
[
"How did/do wings evolve? Why are the in-between generations of \"not winged\" to \"winged\" creatures considered advantageous for evolution's criteria?"
] | [
false
] | null | [
"There are considered 4 separate evolutions of flight- insects, bats, birds and pterosaurs. I can't comment on 3 of the 4, but there are two common theories for how pre-avian theropods started evolving wings. They are wing-like front limbs to aid in gliding and to aid in ascending steep surfaces/aid in climbing. Fe... | [
"One modern but fairly primitive bird ",
" can use its wings for climbing:\n",
"http://en.wikipedia.org/wiki/Hoatzin#Breeding",
"(also check out the picture of climbing chick higher on the page)."
] | [
"But these limbs are on the back of birds now. So what pressures could there be for moving the position of these limbs? Wouldn't moving them make them useless for climbing?"
] |
[
"Would it be suitable to use canned air to extinguish a fire if turned upside down, or is what comes out flammable?"
] | [
false
] | null | [
"If you take a look at a bottle of duster, you may notice a myriad of warnings stating that the contents are flammable. Thus, not a good idea at all.",
"It doesn't matter if it's coming out very cold, it's still very flammable."
] | [
"actually, mine has no warnings aside from mentioning not to use it as an inhalant. "
] | [
"It is often extremely flammable, and you can easily ignite it with a lighter."
] |
[
"Is it true that almost everyone above a certain age has tiny tumors in their body, the lack of blood supply the only thing keeping them from growing further?"
] | [
false
] | Heard/read that somewhere (most likely in an article describing new cancer therapies that target the buildup of bloodvessels to the tumor). | [
"What do you mean by tumors?",
"Cancer is unregulated, invasive growth of one's own cells.",
"Tumors are unregulated growth of one's own cells. Note the difference: not all tumors are invasive. If it's not invasive, it's benign, for the most part.",
"Cancers: no.",
"Tumors: maybe. There are types of smal... | [
"There are several \"characteristics\" of tumor cells... the ability to grow its own blood supply is one of them. Some of the others include production of telomerase, insensitivity to cell suicide signals, endless cell growth, and insensitivity to signals that would suppress growth.",
"A group of cells could hav... | [
"Throw in immune surveillance and this is the best answer."
] |
[
"Why do we have so many variants of flu and COVID viruses, but we don't commonly hear of any HIV variants?"
] | [
false
] | null | [
"I wish we'd hear more about the diversity of HIV. It's a fascinating story. David Quammen tells it very well both in ",
"articles",
" and his book ",
"Spillover",
"). For instance (from the article):",
"Scientists think that each of those twelve groups (eight of HIV-2, four of HIV-1) reflects an indep... | [
"HIV mutates so fast each infected person might as well have their own strain. The traits of the virus are pretty stable. However to stop transmission you would need to have a vaccine developed for basically for each individual patient's particular strain. That's one reason there isn't a HIV vaccine."
] | [
"And, adding on to this, you can get infected by more than one, and if memory serves it indicates a more severe course for the disease (called co-infection). The wiki page on HIV subtypes is good for basic info. I thought I saw something once about the few had a small resistance to HIV-1 due to lacking one of the p... |
[
"As of today, the Dow Jones is at the highest level it's ever been and GDP Per Capita is the highest it's ever been. Why is inflation adjusted household income basically unchanged since the 1960's?"
] | [
false
] | null | [
"From eyeballing those charts, GDP per capita has gone up by ~$18k since 1999 while household income has gone up by about $10k for the middle quintile. Household income has gone up by about $35k for the top quintile during the same period. There are probably some other factors involved, specifically dealing with ho... | [
"Apple’s Pile Of Cash Is Still Growing, Up 6% To $145 Billion",
"Companies awash in cash, when will they spend it?",
"Seems they do sit on it"
] | [
"More money means more resources to try different things until something sticks. Less financially lucky entrepreneurs have to take a major risk if they want to start a business. Plus when you have money people naturally assume you deserve it and are more likely to purchase your product/service."
] |
[
"Why does my house shake when an airplane flies by?"
] | [
false
] | [deleted] | [
"It's the pressure (sound) waves coming from the airplanes engines. The sound waves are intense (loud) enough to actually feel the pressure shaking your house."
] | [
"Ok think about sound as compressed air. Because airplanes fly (somewhat) close to the speed of sound, rather than the sound going all over the place, it starts to build up at the front of the jet. This causes there to be a large and long (possibly a few feet as opposed to a tiny wave) area of high pressure air. ... | [
"Or is the house acting like a tuning fork? Also, why don't I vibrate when a plane flies overhead?",
"Bingo. Your walls are resonating to the tune of the sound wave coming off the plane. You don't vibrate [or feel it as much] because you're not resonating as much.",
"For instance, if you pluck a guitar string... |
[
"Is the incidence of lung cancer greater in countries where public smoking is allowed compared with countries where smoking is banned in public places?"
] | [
false
] | null | [
"Not sure about comparing countries but looking at US statistics is much easier, since there's the SEER data and state-by-state comparison is readily available.",
"CA: A Cancer Journal for Clinicians",
" is a great source for all kinds of cancer-related statistics in US. Table 12 (you have to scroll down quite ... | [
"Out of curiosity.. Access to health care and socioeconomic status would affect all types of cancer. Could you use overall cancer rate as a sort of a short hand for controlling for most other differences?",
"I guess if you can find appropriate data, you could also do a pre/post analysis on states with bans?"
] | [
"Exactly. I searched but didn't find any concrete evidence. There has to be something."
] |
[
"Can effect of gravity create energy from nothing?"
] | [
false
] | I'm a high school student so I hope I'm not putting a fool question here. I have two situation: One asteroid is in the outer space, away from any giant body. It contains little kinetic energy (is moving very low). So I imagine a "closed system" - considering the nonexistence of energy. A second asteroid (or rock body) is moving in the way of the first asteroid. This second one contains a lot of kinetic energy (maybe it was "spilled out" from a star orbit). Their orbit are so close they will attract and shock with each other. My question: where that energy of the "debacle" comes from? Considering they were destroyed and reduced to dust. It comes only from the moving body? Here's a draw: Instead of passing near the stopped body, the moving body would be somehow teletransported to the place where their gravity will make them collapse. Again: the energy that caused them to be destroyed comes only from the moving body? Is gravity "creating" energy from the simple fact that they exist (have mass)? edit: to complete it: The stopped body had no energy, but it could attract the moving body anyway. Where the energy came from? | [
"If we look at the reverse situation, work is done to separate two bodies (energy is transferred to gravitational potential energy that is proportional to the distance between them as they are moved apart). This gives them gravitational potential energy that is transferred back into kinetic energy if they are relea... | [
"Can you explain what's gravitational potential energy? The only potential energy I know is potential (mgh?)."
] | [
"Upon rereading it has become apparent that you were quoting the equation for GPE. You are right there, but there are other forms of potential energy when you get deeper into physics so the distinction is necessary."
] |
[
"Behind the veil of peer-review: Part 2 of our feature series on how science is conducted"
] | [
false
] | Welcome to week 2 of our feature series on the process of being a scientist! Last time we covered while working in research. The upcoming topics will include: writing up research/peer review, the good, the bad, and the ugly papers and discoveries that have impacted each field of science, and ethics in science. This week we'll be discussing the for publications. Our panelists will be answering questions related to papers and journals, including but not limited to: | [
"Also, I'd like to correct up front the misconception that peer review is some holy process that determines the validity of a study with absolute precision.",
"Peer review is more of a sanity filter. It's not there to determine whether or not the results are correct or to find fraud. It's just hoped that when s... | [
"For those who are unfamiliar with the process of scientific publishing and peer review, it tends to go like this:",
"A researcher submits a manuscript to a ",
"journal",
".",
"The journal assigns the submission to an associate editor, who determines at a general level whether or not the work is novel and i... | [
"Any number of ways. Mistakes can be made at all steps from project conception to the review process and it can be important to remember that the fault of publication of \"bad\" papers may lie with many people. Here are a few possible contributors, though certainly not an exhaustive list:",
"1) ",
" - At the en... |
[
"Is there any evidence to suggest that the subatomic particles we know of now are not made of smaller particles, which are made of smaller particles, which are made of smaller particles, etc?"
] | [
false
] | I may be completely off-base because my grasp of QM isn't the best, but it seems that every time we find a fundamental particle, we eventually discover an even-more-fundamental particle. What do the theories say and what does the evidence point to about finding the last particle/particles? Or are we already there? If we are, why do we think that? | [
"If one assumes quarks/leptons are themselves composite, made of preons, you get very stringent experimental bounds on the structural size of quarks/leptons, on the order of 10 ^ -18 m.",
"This means that preons have gigantic masses compared to the quarks and leptons they compose. So the masses must accurately ca... | [
"Meters, yes, corrected."
] | [
"Just for clarification: 10",
" what? Meters?"
] |
[
"Exactly how many fundamental 'fields' are there?"
] | [
false
] | Besides the electromagnetic field, how many other fields are there at a given point in space, what are they called, and how are their values represented? Also, can we measure all of them, theoretically or practically? | [
"You probably know that there is a particle associated with the electromagnetic field, the photon. It turns out that all fields have particles associated with them, and all particles are associated with fields. Thus, if you want to know how many fields we know of, you just need to look at the list of known elementa... | [
"I think even among physicists we would refer to the \"gluon field\" rather than all of the components as separate fields. I think ",
" is the appropriate number to quote for a laymen. ",
"However ",
" is a number I have also seen for the standard model. This is form counting each charged particle twice (e.g.... | [
"200 is based on all of the vector and spinor components, and both the SU(2) and SU(3) representations. So some particles have as many as 24 components.",
"EDIT: spinal -> spinor. Stupid autocorrect."
] |
[
"What is \"dark saturation current\" in diodes?"
] | [
false
] | I got the idea that it must occur in the dark/no light conditions. I think it is a current. But, I really don't know what it is.... I could use a superclear explanation if you can provide one. Thank you! | [
"It's the current in a photodiode in the dark when you reverse-bias it, but not to the point of breakdown. You can see why that is from the ",
"equation",
" for current through a photodiode in the dark. As V becomes more negative, the exponential term will go to zero, and the result of the expression will go to... | [
"Oh, OK. I did not know that it was the current that was produced under reverse bias. ",
"When you say \"when V becomes more negative\" do you mean \"when V becomes larger\"? My impression was that voltage can only be positive or negative. So, the Voltage is working against the direction of the photodiode would b... | [
"Yeah, I meant larger in magnitude, but with a negative sign- as you reverse-bias the diode more. If you forward-bias the diode, you'll have exponential growth in current (well, at least until you blow the diode). If you reverse-bias the diode, you have exponential decay towards saturation (again, until you achieve... |
[
"Does a sunburn increase your chances for skin cancer only in the area that was burned?"
] | [
false
] | null | [
"In general, yes. Cancer results from mutations in the DNA. The UV radiation from the sun can make breaks in the DNA in cells, which make it more prone to mutations and thus cancer. So technically, only the cells that are exposed to the UV radiation are at greater risk of cancer."
] | [
"So when a burn happens and mutations occur in the DNA of the cells were burned, those cells don't replicate and pass on those mutations to all other areas of the skin? Those mutations that occurred basically give rise to new cells with those mutations only in the area that was burned? ",
"Meaning a burn that hap... | [
"Somatic cells such as your skin cells replicate via mitosis and result in daughter cells with genome identical to the parent cell. If the parent cell had a mutation, hopefully it would undergo apoptosis (basically self destruct), or hopefully it would be caught by the immune system. If not, that mutated parent cel... |
[
"Do we have evidence that all life today originated from a single organism, or is it possible that life started multiple times in our history?"
] | [
false
] | null | [
"Similar questions have been asked before. You might want to check them and the wikipedia entries on abiogenesis, last universal common ancestor, and cell. (Can't link because I'm on mobile, sorry)",
"The current assumption (by no means definite) is that, at the very least, earliest life forms interacted to such ... | [
"Both are possible, those statements don't contradict each other in any way. Because all life that currently exists on Earth is similar in its fundamental characteristics, it's overwhelmingly likely that all current life shares a single common ancestor. But that doesn't mean that life didn't get started before that... | [
"Is it also possible that life started multiple times and didnt die out? Like theres only one way for life to evolve until it reaches multicellular levels? And that two or more distinct populations with out any contact debeloped into this one common ancestor?"
] |
[
"Where does the energy go when the interference between two rays of light is destructive?"
] | [
false
] | I know that if you have two rays of monochromatic light and make the phase difference between these enough so that the interference will be destructive there will be a dark spot on the wall where the beam should have hit. But then this must mean that the energy gets lost somewhere? Wouldn't it? Will the energy be lost along the way somehow or will all the energy be transferred to the spot anyway just without showing the light? | [
"You can't arrange it so as to obtain ",
" destructive interference. It will always have some neighboring regions of constructive interference as well. If your ",
" are wide, this is easy to see why this happens. If your rays are narrow, light will spread out by diffraction. You can't really have rays of lights... | [
"Does the same apply to noise-cancelling headphones (i.e. is there a zone where the sound is twice as loud)? Or do sound waves work differently than light waves in such a case?"
] | [
"Kind of, yes. With noise cancelling headphones, you usually have one region of low energy (around your ears), but potentially higher energy elsewhere."
] |
[
"How do I explain the origin and nature of time to an 8 year old?"
] | [
false
] | Honestly, Reddit, I'm stunned that an eight year old is able to simply understand the concept. Last week, he asked me where the universe came from. BAM! Big Bang. Where did people come from? KAPOW! Monkeys, little man. What's more, I know my explanations stuck. In stumbling for a response, his mom, my girlfriend asked him, "well, um, how do you think the earth got here? Was it god or the Big Bang?" "You mean, like, little rocks that turned into bigger rocks that turned into bigger rocks? That way, the Big Bang." I have no idea how to explain time, as my understanding is vague and esoteric as it is. The extent of my understanding is that time is a product of gravity, and that it is relative to speed. As a man with a background in history, I'm pretty proud of this limited knowledge, but know it's missing almost everything, and have no way of relaying it to a kid. Besides, this will be a good exercise for anybody interested in educating people on science. If you can explain it accurately in terms that a second grader can understand, you understand it well enough to explain it to just about anybody. Just channel your inner Neil deGrasse Tyson. | [
"Your best bet is probably time is just a way of measuring change. Explain to a kid how watching a movie is just a lot of pictures moving really fast (you can make a flip book or something as well). Time is just the difference from one frame to the next, but it is continuous.",
"For the rest of science get him ... | [
"Time is a dimension. In our universe, there are three and half dimensions. You can go up and down, side to side, or in and out. But in the time dimension, you can only go one way. You can't go backwards in time. This is why, if you break something, you can't undo it. Time only goes one direction. But even t... | [
"I guess I'll throw in something kid related instead of science related.",
"In my opinion, one of the best things you can do to encourage the scientific spirit is to encourage the attitude \"I don't know, so let's find out.\" Science is an acknowledgement that we don't have all the answers, and that we have to c... |
[
"How do electrons and things and people have mass and be physical, if electrons are made from massless particles?"
] | [
false
] | null | [
"Electrons are not made of massless particles."
] | [
"Thanks for your reply! So that image is wrong? I had someone else tell me it was technically correct in another thread! ",
"And what about the rest of my question, have any insights or answers? Again thanks my friend"
] | [
"Yes, that image is wrong. Electrons are elementary particles, they're not \"made of\" anything else.",
"As for the parts about \"touching\", it's hard to define \"touching\" something quantum-mechanically. And ultimately all matter is quantum-mechanical. Atoms and molecules don't have surfaces that can \"touch\"... |
[
"They've found evidence for liquid water on mars a dozen times, and journalists allude that it may be habitable. But what are they leaving out that makes living there impossible?"
] | [
false
] | Mars doesn't have an atmosphere, right? Thus no air to breathe. And it doesn't have an atmosphere because there's no magnetic field to protect it from solar flares, right? Thus anyone on the planet would be killed by radiation? What are the real problems we'd have to overcome to live on Mars today? | [
"First, Mars has an atmosphere, it's just a lot thinner than Earth's. Also, as it has a grand total of zero plants, it has no way to repopulate the oxygen supply, which makes even the even-minimal atmosphere even less breathable.",
"Second, it's 2.536e8 km [on average] away from Earth. This makes 'technical' ma... | [
"You're leaving out the biggest issue: radiation. Mars has no planetary engine to generate a protective magnetic shield. It once had one but it has since solidified and everything on mars is bathed in radiation"
] | [
"But no/little water",
"No -- this is false. There is plenty of water ice -- more than we could think of using up. And that is a key to surviving there."
] |
[
"How does gravity affect entropy?"
] | [
false
] | So I was reading about Boltzman and his ideas on entropy ...and i was wondering if while it's true that the disordered state is most probable on certain scales, wouldn't gravity, that acts on all particles, tend to draw things back into an ordered state over long time or on a larger system level? How does the tendency of gravity to create lumps and more ordered (1/f, power law distributions, etc) square which the second law of thermodynamics? | [
"Let me start off by saying that there is no known process which is capable of globally reducing entropy. So even with gravity pulling particles together, the entropy of the system must remain constant, or increase with time. In the case of a gas cloud compressing itself (like in the formation of a star), energy ... | [
"right but i guess i'm thinking more on systems levels, which then is defined by where the boundaries of the system are drawn. so you could take a gaussian field of disordered particles and change the magnitude of your observation and see that the field is part of a more ordered system (say a nebula following an at... | [
"In thermodynamic systems, there is a quantity called the Helmholtz free energy, which is the difference between the internal energy of the system, and the energetic contribution of entropy. To write it out, it's H=U-TS where H is Helmholtz free energy, U is internal energy, T is temperature, and S is entropy. Ther... |
[
"Can a planet rotate on its major axis WHILE simultaneously rotating on its minor axis?"
] | [
false
] | If it is possible, are there known examples? Does it happen naturally during the course of planetary evolution? If not, what kind of catastrophic event would trigger it? Also, if it were to happen to a place like Earth, how would it affect the climates, seasons, magnetosphere, atmosphere (composition and such), time keeping, etc.? Sorry, I know this is a loaded question, but answering any portion of the above would suffice. I've been really curious about this for months! Thanks | [
"What iorgfeflkd is talking about is called \"precession\", all planets have it to some extent, and it is exactly what you're talking about."
] | [
"Rotations always happen in a plane, so since we live in 3D space then anything (not only spheres) can only rotate about a single axis. If you try to combine two rotations of a single object around two axes then you end up with a rotation around a new axis, but it's still a simple, single-axis rotation."
] | [
"It's not clear to me what sort of motion you're describing. Are you talking about rotation (spinning), or orbital motion around the Sun? Which axes do you mean when you refer to the \"major\" and \"minor\" axes?"
] |
[
"What is the currently-accepted theory for how the moon was formed?"
] | [
false
] | In 1976, the "Big Whack" model was proposed that combined aspects of three other incomplete models (intact capture, co-accretion, and fission). The Big Whack model proposed that a planetoid impacted the Earth while still in a semi-molten phase, scattering particles into Earth's orbit. These particles then coalesce into a body that is now the moon. Is this still the currently-accepted theory, and has any new evidence been revealed since then to prove/modify it? | [
"Geologist here...yep, the impact theory is still the accepted theory on the formation of the moon. ",
"Since the 70s, better computer modeling, improved geophysical studies of the earth and moon and isotopic evidence have added pretty convincing evidence in support of the impact hypothesis.",
"The wikipedia ar... | [
"The moon is slowing migrating away from Earth, not towards it. And, to be pedantic, stars like the sun don't explode. They swell, puff off outer layers and then shrink into a white dwarf."
] | [
"It should be noted that despite it being the well accepted theory there are still many unknowns around the exact details of the process (",
"Cattaneo and Hughes 2022",
")."
] |
[
"Why do stars and planets rotate around a single axis? Why don't any \"tumble\", rotating around 2 axes?"
] | [
false
] | Also, are there any objects that do "tumble", like asteroids? What about exo-planets, which are out in space by themselves? ED: To clear up what I mean by "tumbling", I'm referring to a dual-axis spin; for example, Earth rotating as it does, around a N-S axis, while that axis in turn rotates around another. | [
"Short answer: because they are (approximately) spheres. Smaller objects like some asteroids with more irregular shape generally ",
" \"tumble.\"",
"Longer answer: Some answers here suggest that this is simply a matter of being able to represent a composition of several rotations as a ",
" rotation about a s... | [
"Nothing rotates around 2 axes. All three dimensional rotations, however \"complex\", ",
"can be simplified to rotation around a single axis (Euler's rotation theorem",
". The composition of two (or more) rotations is a (single) rotation. ",
"EDITED: Still learning something new every day. Although Euler's th... | [
"While true, when we (planetary scientists) refer to asteroids as \"Tumbling\" what we mean is that they are in non-principal axis rotation - meaning that they aren't rotating around one of their principal axes (the solid lines in ",
"this diagram",
" of an ellipsoid). Perturbations from the Sun and other plan... |
[
"Why does light blend differently than pigments?"
] | [
false
] | I get that light is additive while pigments absorb light, but wouldn't a wave of blue light reflected off a pigment in the end be the same thing as a blue light source? EDIT: It may be better to think about my question in wavelengths instead of colors, since colors really don't exist and are just illusions of our brains. So are primary colors. | [
"To your eye it's the same, but a green wavelength of light can be very, very different than a mixture of blue and yellow light sources. From a science point of view, one is a single pure frequency while the other is a combination of several frequencies which ",
" to the one you see.",
"Adding lights together i... | [
"The part that trips me up is why colors use the primary (RGB) while pigments use the secondary (CYM).",
"Because of the additive and subractive factors you have mentioned. Cyan, magenta and yellow are are the respective complements of red, green and blue; ie, W - R, M = W - G and Y = W - B, where W is white. For... | [
"The primary colors really have no basis in fundamental science, but rather how our brains/eyes interpret colors."
] |
[
"Did the Big Bang start time or does it just mark the start of time?"
] | [
false
] | null | [
"Time, as it is understood in General Relativity, is simply a dimension through which things travel within the universe (although not one of the three spacial dimensions, it can be easily pictured as being simply another axis through which things travel). In this way it is best to think of time as being part of spa... | [
"It's also worthwhile to repeat here the oft-quoted statement, \"It may be like asking what's north of the north pole; it's a meaningless question.\"",
"...Question: If time is a dimension much like the three spatial dimensions, why are the rules different? I can travel back and forth in the x, y, and z axes bu... | [
"The view of time being an equivalent axis to the three spacial dimensions on a graph makes it easy to visualize, however the actual math is not the same. The time axis does follow somewhat different rules than the others, but nonetheless directly influences and is influenced by changes in momentum along any of the... |
[
"Effects of glyphosate on rhizosphere?"
] | [
false
] | I recently got into an argument where I was defending GMO's, and while following up with evidence and sources, I thought to myself - since anti-GMO arguments tend to feed a lot on pathos than reality - what actual empirical evidence does the anti-GMO crowd have to draw on? In the process, I came across from 2013 about the detrimental effects of glyphosate on soil (and yes, I know that GMO != glyphosate), which draws its empirical evidence largely entirely from Robert Kremer's work on glyphosate. His paper seems to capture the substance of his work well: Current crop production relies heavily on transgenic, glyphosate-resistant (GR) cultivars. Widespread cultivation of transgenic crops has received considerable attention. Impacts of glyphosate on rhizosphere microorganisms and activities are reviewed based on published and new data from long-term field projects documenting effects of glyphosate applied to GR soybean and maize. Field studies conducted in Missouri, U.S.A. during 1997–2007 assessed effects of glyphosate applied to GR soybean and maize on root colonization and soil populations of and selected rhizosphere bacteria. Frequency of root-colonizing increased significantly after glyphosate application during growing seasons in each year at all sites. Roots of GR soybean and maize treated with glyphosate were heavily colonized by compared to non-GR or GR cultivars not treated with glyphosate. Microbial groups and functions affected by glyphosate included Mn transformation and plant availability; phytopathogen–antagonistic bacterial interactions; and reduction in nodulation. Root-exuded glyphosate may serve as a nutrient source for fungi and stimulate propagule germination. The specific microbial indicator groups and processes were sensitive to impacts of GR crops and are part of an evolving framework in developing polyphasic microbial analyses for complete assessment of GR technology that is more reliable than single techniques or general microbial assays. Wikipedia seems to describe as a benign, commonplace fungus (and of course, too much of something can still be a bad thing; also, it was a strain of that almost wiped out bananas in the 1800's, if I'm not mistaken), and the paper's introduction notes increased susceptibility to , which Wikipedia tells me is significantly more dangerous, but honestly, if I've learned anything during my time at university so far, it's that if I have to Wikipedia stuff even just once while reading a paper, then I don't know enough to fully understand it. Moreover, I couldn't really find anything to Kremer's work (the USDA work referenced in the NYT article sort of sidesteps the issue - understandable given the sizeable literature). Hence my question: how significant are these findings, really? Is glyphosate actually as threatening of an ecological risk as Kremer , and how much actual support does his work offer to ? | [
"Absolute terrible science, and exactly the answer I was ",
" looking for. There are ",
" risks, and then there are the fabricated lies that anti-GMO fearmongers spew, and this is the latter.",
"From the ",
"Genetic Literacy Project",
":",
"Glyphosate controls weed growth by interfering with the metabol... | [
"Absolute terrible science, and exactly the answer I was ",
" looking for. There are ",
" risks, and then there are the fabricated lies that anti-GMO fearmongers spew, and this is the latter.",
"From the ",
"Genetic Literacy Project",
":",
"Glyphosate controls weed growth by interfering with the metabol... | [
"I wouldn't be too concerned. As stated in his paper \"further study is required.\"",
"A quick survey of the literature finds that other studies ",
" been done on the effects of glyphosate on soil bacteria, and most of the studies that have been done find that at high levels of glyphosate (10-100x the recommend... |
[
"Is physical hunger onset by a lack of nutrient intake / absorption, or simply by an empty stomach?"
] | [
false
] | I always wondered how folks, such as military personnel, who eat high-caloric meals that are relatively small portions and are still able to operate throughout the day with constant hunger, as I had assumed that it was based on what is physically inside of the stomach. It certainly feels that way. Some context on this question: I have gone on a low-calorie diet. Very low-calorie, in fact, simply because the portions that I decided to have over the past week seemed to keep me satiated and I haven't experienced any sort of headaches or dizziness as a result. However, I do notice that I'm starting to feel a little queasy throughout the day, mixed with hunger... but I can't tell if it's because the small portions throughout the day do not fill my stomach up very much, or if it's because it's truly not enough sustenance for my body. | [
"Hunger and satiation are controlled in a manner much more complex than simply relying on presence/absence of food in the stomach. ",
"Ghrelin",
" and ",
"leptin",
" are two hormones discovered in the mid-90's that play a role in the extremely complex hormonal regulation involved in appetite. There is still... | [
"Short answer: Yes. ",
"Longer answer: Hunger is no easy subject. We don't know all about it, but we do know some factors that contributes to satiety. ",
"Chewing",
" reduces hunger. The stomach content, of course. There is a strong habitual connection, so if you eat at 10 each day you will feel hungry at 10.... | [
"Ghrelin and leptin",
" control hunger."
] |
[
"How are space agencies able to find out what caused a malfunction like the weak strut that caused the Space X rocket to explode shortly after liftoff especially when the entire vehicle is destroyed?"
] | [
false
] | Title | [
"In the case of this ship, there were over 3,000 channels of telemetry data being sent back to the ground. Analysis of this data showed overpressure in the upper stage, and a drop in pressure in the helium tank.",
"Piecing the data together, the best guess is that the strut constraining the helium tank failed."
] | [
"Also they used high precision accelerometers throughout the launch vehicle. These accelerometers are precise enough that they're really just very complex microphones. They use the signals from these to triangulate the initial failure point much like how geologists analyse the interior of the earth using seismograp... | [
"A 3rd thing is that once they suspected the strut in question they were able to take one in storage and demonstrate that it had a flaw that would cause it to fail under similar conditions."
] |
[
"How seriously is the fractal holographic unified field theory taken?"
] | [
false
] | null | [
"It is complete bullshit and enjoys zero respect from the physics community."
] | [
"It's not really not viable, it is completely nonsensical. It might seem at a superficial level (for example, if you don't have a formal education in physics) that it all kind of makes some kind sense, but the single sentences are random sequences of words which don't go anywhere.",
"The \"predictions\" are actua... | [
"yes."
] |
[
"If the big bang was not an explosion but rather space itself expanding, why are other galaxies redshifting?"
] | [
false
] | null | [
"This has been removed because it’s a commonly occurring question on ",
"/r/AskScience",
" or a question that can be answered easily through a single Google or Wikipedia search. To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
"... | [
"but, i was not able to find an answer to this by searching through ask science, in fact my question caomes from seeing scientists answer question like this the same way so many times on ask science. this is actually a question about the way scientists answer these questions. yes there are plenty of questions about... | [
"We appreciate that some misconceptions commonly arise and we do tolerate repeat questions ",
". However, there are many many previous threads on this topic, as well as good descriptions of the phenomenon on wikipedia.",
"In brief, light is always traveling at a speed of ",
". Suppose light is being emitted i... |
[
"Why is the very early universe not described as a black hole?"
] | [
false
] | I tend to think of the time in and around the Big Bang in a physical, knowable sense, because I am not a physicist. Thus, it is difficult for me to think of the Big Bang as much more than a big explosion that leaves behind a big ball of elementary particles. Keeping this is mind... Moments after the big bang, when all the matter in the universe was contained within a fairly small amount of space, it seems to me that a black hole must have formed. Now, I would define a black hole as a concentration of matter with enough gravitational pull to overcome light. It doesn't seem that light randomly entering the event horizon of a black hole is actually necessary for a black hole to exist, so I do not make this constraint. My question, then, is why these moments (more likely quite a while) after the Big Bang are not described as one large black hole. Was the matter ripped apart and scattered by the Big Bang? It seems it must have been, because otherwise the universe would be one large black hole, a lot of space, and limited in its gain of entropy through Hawking radiation. I'm almost certain that this question is entirely too simplistic because of my limited understanding of physics, so please have patience. | [
"This is a common misconception:",
"when all the matter in the universe was contained within a fairly small amount of space,",
"That isn't the case, all the energy and matter in the universe was infinite in size, with uniform density.",
"Just because space has been expanding, doesn't mean that it started at a... | [
"Your question was answered ",
"here",
".",
"edit: there's a link there to ",
"this comment",
", reading that will help you visualize the whole expansion thing."
] | [
"Why can't it be infinite?"
] |
[
"Before the phonograph, did human beings know that their voices did not sound the same to others?"
] | [
false
] | null | [
"I do not believe you understand what he is asking.",
"The voice you hear in your head while talking sounds very different than the voice of a recording of yourself.",
"JohnnyMox wants to know if there is another way of finding this out.",
"Regarding his question... Echos may have given people a hint."
] | [
"Short of an echo, probably not. "
] | [
"Gotcha.",
"In that case any sort of horn shape would give you a fairly clear idea of what you would sound like if you could speak in to one and and hear out the other with minimal reverberation. Even sticking you head into a small hole (say on a pot of some sort) would aid."
] |
[
"How and why does matter (gravity) bend space-time?"
] | [
false
] | [deleted] | [
"Well the how is described mathematically with the Einstein field equations, which, wile looking fairly simple to the untrained eye, are actually quite complex. Understanding the how requires training in differential geometry which is basically graduate level mathematics.",
"The why is more of a philosophical que... | [
"I think at this point all we know for sure is that it does. We know that in free space we can imagine there's this 3D grid, each line of the grid can be called a geodesic. Normally all these grid lines would be straight, forming a lattice of cubes. If an object were set in motion along one of those lines it would ... | [
"It's not really a question that can be answered. You could flip it around and say: if spacetime \"bends\", the net effects resulting from this have been given the name \"gravity\""
] |
[
"Why does background noise sound amplified and resonate when your own voice matches its tone?"
] | [
false
] | For example, humming while an industrial machine in the distance is at a steady noise makes it sound louder and fuller inside your head. There's a bit of a "warble" to it like when you tune two guitar strings to the same note and play them at the same time. Sorry if this is hard to understand. I've done it to pass time while working near running machines and ventilators. | [
"I typed up a nice, long reply and it wouldn't submit :(",
"It's a phenomenon called 'constructive interference'. When two waves (in this case, sound waves) meet they interfere with one another, creating a new wave that's the sum of the two. When the waves have similar frequencies and the right phase, they 'add... | [
"I was reading that and was thinking about the electronic mufflers they make. I have seen ones that vary the pitch to make cars sound different. as in making a 4 cyl sound like a v12"
] | [
"Definitely sounds like something that's possible.",
"Not sure how big of a market there is for that sort of thing, but once they have the hardware in place to do electronic noise cancellation something like altering the noise characteristics shouldn't be that big of a challenge. It'd take someone much smarter t... |
[
"Do night shift workers produce the sleep hormone melatonin during the day?"
] | [
false
] | Or are we all biologically wired to produce it only at night? Is their quality of sleep subsequently worse? | [
"The pineal gland only releases melatonin when two conditions are satisfied:",
"It is the \"biological night\".",
"Light levels are low.",
"Theoretically, night-shift workers can satisfy both of these conditions during the daytime, leading to normal release of melatonin during the daytime. In practice this is... | [
"Less than 3% of permanent night workers show complete adaptation of their circadian system to their imposed work schedule, and less than 25% adjust to a point that some benefit would be derived from the adaptive shift that they have made.\nPartial re-entrainment to a permanent night shift schedule, with the follow... | [
"First, it's important to note that melatonin is not a prerequisite for falling asleep. It certainly can help people fall asleep, but there are many other factors that regulate sleep and sleepiness besides melatonin. People can of course also nap during the day when they are not releasing melatonin.",
"In fact, i... |
[
"What actually happens when you microwave metal?"
] | [
false
] | I just want to know what is happening when metal is microwaved. Here is my background in science, I am in my second semester of organic chemistry. Anything will help! | [
"The metal acts as an antenna. The powerful electromagnetic field in the microwave induces an electric potential in the metal, which may be sufficient, depending on the geometry of the metal (points arc much more easily, and thin films are also vulnerable) and other factors, to induce arcing (when a sufficiently hi... | [
"Sharp points, like the prongs on a fork or something, are much more likely to induce arcing, which is when current jumps through the air (which is usually non-conductive), producing the sparks you see if you microwave metal. This is because electric charge tends to build up more easily on points. Crumpled aluminiu... | [
"It's mostly dangerous because it can set fire to things. It can also damage the microwave."
] |
[
"If a meteorite of a similar size to the one the wiped out the dinosaurs hit an ocean instead of solid ground would it be better, worse or no different for us?"
] | [
false
] | edit: So pleased this question has given rise to so many great answers and subsequent questions. Thank you all so much! A great read. | [
"You've left out the latent heat of vaporization for water, which is 539 calories per gram, so you're off by roughly a factor of six.",
"Doesn't really change the outcome here, but it's generally valuable to understand the significant amounts of energy in phase changes."
] | [
"You've left out the latent heat of vaporization for water, which is 539 calories per gram, so you're off by roughly a factor of six.",
"Doesn't really change the outcome here, but it's generally valuable to understand the significant amounts of energy in phase changes."
] | [
"You've left out the latent heat of vaporization for water, which is 539 calories per gram, so you're off by roughly a factor of six.",
"Doesn't really change the outcome here, but it's generally valuable to understand the significant amounts of energy in phase changes."
] |
[
"Are there any parasites that exclusively live on/in humans?"
] | [
false
] | With the extinction of a few years back, I wonder if there are any parasites that are fully dependent on/in humans like was fully dependent on the California Condor. Furthermore, if there is/are any, are they damaging to us? | [
"Many. Malaria plasmodium parasites, for example, have two stages to their life cycle one that occurs in mosquitos (sexual reproduction) and one that occurs in the bloodstream of humans (asexual reproduction and maturation). Without either stage, without entering either host, the parasite will not reproduce. If a m... | [
"The bedbug (Cimex lectularius) can feed on other animals but is adapted to feed on humans, you basically have to deprive it of humans for it to feed on other things. So not truely obligate, but probably good enough for your question. There isn't much evidence of disease transmission in these guys, they are more of... | [
"Pathogens of the type you describe are prime targets for eradication due to the fact that once human transmission cycles are broken, they are effectively extinct because there are no natural reservoirs from which they can re-emerge. The best example right now is ",
"Guinea Worm",
". The Carter Foundation has... |
[
"Firewood cracking?"
] | [
false
] | Well, sitted infront of my fireplace and watched it burn lively i realised i have only a theory why wood "jumps" and cracks. My theory is that it has something to do either with trapped oxygen released or places in the wood that was bent(branches, etc) are popping under pressure... So, what really makes it crack, throw coal and move? | [
"expanding gasses and water vapors trapped within the burning wood. your first assumption is correct. "
] | [
"More likely to be sap than water in aged firewood. Happens a lot with pine for me. "
] | [
"Probably water vapor from water trapped in the wood boiling"
] |
[
"Is the term \"Non-renewable resource\" a really poorly coined term?"
] | [
false
] | I was recently reading in my Biology textbook that all chemical reactions are reversible, and from common knowledge I know that most physical reactions are also reversible. Plus, with the law of conservation of matter, no matter actually ever disappears. Therefore, when we use materials like gas to power our cars, wouldn't it be possible to harvest all of the products and recreate the gas we just used? Consequently, doesn't that make every resource renewable? | [
"...all chemical reactions are reversible...",
"That means ",
" is reversed though - including the energy released in a reaction. So there is no way to reverse the reaction ",
" harvest the released energy at the same time.",
"And this is disregarding the ",
"irreversibility of some processes",
"."
] | [
"I would say that it's inaccurate in the sense that ALMOST every resource is in some shape or form renewable BUT I would say that it is NOT a \"poorly coined term\" because when exhaust is released in the air it has gone through chemical changes and it is, for all practical intentions, not recoverable. although nat... | [
"There's a lot of question about reversability, because may processes are theoretically but not practically reversible. You'll never be able to unscramble an egg, and you'll never be able to unburn gasoline. The problem is roughly that you have to spend more energy determining how to reverse a given process than ... |
[
"Newly discovered potential planet (object of interest) KOI-172.02 was announced on the 7th as a \"Super Earth.\" Where is it located?"
] | [
false
] | I've searched high and low for this answer and can't seem to find it anywhere. was announced by the NASA Kepler team earlier this week but every article I've read just mentions it's "orbiting a G-type star." stars are basically within 80% to 120% the size of our own Sun. There are a bunch of them out there (Alpha Centauri A and Tau Ceti to name a couple.) I also tried searching and and this closest thing I could find was . I was wondering if that object might be orbiting the same star, hence the similar designation? Why are there no names anywhere?! Edit: I think I've found that the stars and that its Right Ascension is 19 33 02.626, and its declination is +44 52 08.00. Is there somewhere I can plug this in to see what it points to? Edit 2: I just found as well, but still no distance from us listed. Edit 3: I emailed Wm. Robert Johnston, author of the I could find as to where his sources were and if he had any insight into how to find the distance. His reply: Most of the Kepler stars do not have measured distances. However, assumptions about the distances are folded into the calculations that extract putative planet detections. So I've calculated distance estimates based on the reported data; in the case of KOI-172 = KID 8692861, . He continues: Basically I take reported stellar temperature and diameter to get absolute luminosity and bolometric correction, then I apply an empirical correction for the dimming from interstellar dust (this I derived based on the sample of KOI stars with measured distances), then I can back out the distance. A caveat: the Kepler team comes up with stellar diameter, temperature, and mass by fitting the observed stellar colors to model data, and this data enters in to the calculations that determine that the occulting object is a planet, and its characteristics. Among the assumptions involved is that the star is modeled correctly as (typically) a main sequence star. Since my distance estimates use their derived data, the estimates hinge on the same assumptions. Bob | [
"It's entirely possible that the distance to the star hasn't been measured; not all of them have."
] | [
"In case this partial answer is of value to someone, that's either in or near Cygnus. The closest constellation star (eyeballing) appears to be delta Cygnus."
] | [
"Seems to be 1040 ly away",
"You can search by Kepler ID 8692861\nOr by 2MASS ID J19330262+4452080",
"http://www.johnstonsarchive.net/astro/extrasolarplanets.html"
] |
[
"How do programming languages measure time?"
] | [
false
] | null | [
"Computers keep track of time by using a so-called real-time clock (RTC). The RTC is a separate component that often consists of a quartz crystal and some electronics to measure oscillations of this crystal and record them. The quartz crystal vibrates at a specific, constant frequency and by simply counting the osc... | [
"What is the lifespan of this small battery ? Could it provide power to the RTC during several years in an abandoned computer ?"
] | [
"From experience that's about the typical lifespan, yeah. It depends on the computer and the battery a bit. Some computers don't keep good time anyway."
] |
[
"Do small creatures hear noises louder than larger creatures?"
] | [
false
] | null | [
"Ants 'hear' through vibrations, so they would feel a vibration of sorts if a brick hit the ground near it. "
] | [
"This might not directly answer your question, but it is kind of related",
"Millions of years ago when dinosaurs lived, small animals began to arise. The animals show a change in skull shape that would imply they gained more sensitive ears as they got smaller. Probably was helpful in hearing other small animals."... | [
"You probably mean ",
", not ",
". I'm sure small animals arose long before the Mesozoic :P"
] |
[
"A question about freezing soda."
] | [
false
] | Today my brother bought a six pack of cream soda. He put it in the freezer to cool them down quickly. He then forgot about them. About an hour later, he remembered them and pulled them out. All were frozen except for one. He opened the unfrozen one to drink it, but after he opened it, it started freezing from the top down. After about a minute, it was completely frozen. What caused this? | [
"Basically, the soda was right around the freezing point, and the act of taking the soda out and disturbing it added the extra boost of energy to fuel to crystallization process necessary to turn the soda to ice.",
"While a liquid will turn solid at its freezing point, the act of crystallization requires some ene... | [
"A similar thing can happen with boiling liquids, which is why in lab we learn to use ",
"boiling chips",
" to avoid superheating well as why there are many videos on the internet of exploding intact eggs that have been in the microwave. (I recommend the former, but definitely not the latter, it's dangerous!)"
... | [
"I would think adding a disturbance (opening the soda) would add energy to the system and cause it to increase in temperature. The opening of the container should cause a cease in molecular relaxation which would increase the temperature (slightly). Just thinking out loud. I am very interested in this though."
] |
[
"Does the moon's gravity effect the Earth's mantle in a similar way that it effects the tides?"
] | [
false
] | The recent situation in Japan got me thinking... If the gravitational pull of the moon has the power to shift billions of cubic meters of water on the Earth's surface, what's it doing to the magma beneath the Earth's crust? Since the plates are essentially huge, overlapping islands floating on a sea of magma, what implications does the moon's gravitation have for seismic activity? | [
"The plates are not islands floating on a sea of magma at all, the mantle is solid. The plates are not floating on magma at all. The part of the mantle that isn't attached to the crust acts as a fluid, but it is most certainly still a solid. Only small amounts of magma are generated at the plate boundaries, mid-... | [
"http://en.wikipedia.org/wiki/Earth_tide"
] | [
"Can you explain how a solid acts as a fluid in the mantle?"
] |
[
"Are large scientific simulations written in low-level languages?"
] | [
false
] | I ask because I think that programming in low-level, optimizing the code for the specific hardware and managing system resources manually seems only logical for such intense tasks. Edit: I'm talking about Machine Code/Assembly code. | [
"Good question, this is right in my expertise wheelhouse.",
"Machine Code/Assembly level",
"Essentially never, outside of very niche projects. I'm actually not aware of ",
" significant use of such things in HPC. The vast majority of high performance (HPC) computational science simulation codes are written in... | [
"Usually not. That would make them hard to develop and maintain. Keep in mind that scientist who write these are not computer scientists or programmers. supercomputers they use usually provide optimized versions of scientific libraries, (linear algebra, fft, etc.) that are commonly used. still, it is common that pe... | [
"How low level are you talking? In my field (molecular dynamics), the big codes are written in C/C++. Older projects used FORTRAN. ",
"I know the GROMACS team have put a lot of effort into using SIMD instructions as well."
] |
[
"Why would a large enough asteroid explode when it hits Earth?"
] | [
false
] | I can't comprehend why a hot rock hitting into essentially another rock would cause Hiroshima or larger style explosions. | [
"Perhaps you are only considering chemical (nuclear or otherwise) releases of energy here. That is how the vast majority of human created explosions are made.",
"However any explosion is simply the release of a lot of energy of ANY type in a small amount of time. In this case the huge kinetic energy of the rock i... | [
"Yes, most rail gun's projectiles are non explosive, but then so are the projectiles from most guns. Large rail guns have a muzzle velocity of 6+km/s whilst a rifle may only have 1km/s, but there isn't any special difference other than velocity and mass."
] | [
"Yes, most rail gun's projectiles are non explosive, but then so are the projectiles from most guns. Large rail guns have a muzzle velocity of 6+km/s whilst a rifle may only have 1km/s, but there isn't any special difference other than velocity and mass."
] |
[
"What happens to a photon when it hits the surface of the sun?"
] | [
false
] | Hey askscience! I'm a web developer and I was working on a new weather-site, when I noticed that all the sun-icons had a small highlight/shine on them. Of course, this is just modern icon-design, but it got me thinking. So my question is this: What happens to a standard photon (let's even say it's a visual spectrum photon. Nothing high-energy or anything.) when it interacts with the surface of the(a) sun? Follow up: Would it be possible to shine a bright enough light to get a "reflection"/shine on a sun? Thanks in advance! | [
"The surface of the sun is a very good black body. This means that almost all photons that arrive at the surface will be absorbed. If you shine a lot of photons this absorption would heat up the surface and cause the sun to glow brighter, but you would need an extremely bright light source to achieve this."
] | [
"On the scales the photon cares about, there ",
" no surface to the Sun. The \"photosphere\" is the imaginary surface where the Sun becomes opaque - only about 1/3 of photons that arrive there from far away (say, Jupiter) penetrate any farther into the Sun. But the optical absorption length in the photosphere i... | [
"It would have to be a very tight binary, but it is not impossible to imagine. There are many interesting things happening in such tight binaries. Gas can pass between the stars and this will also lead to asymmetric effects. This is unfortunately very hard to study since it requires very high resolution images. I d... |
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