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[
"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 mathematics cannot be 'solved', or that you will never be able to prove all statements that are true in any mathematical framework."
] |
[
"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 be proven to be true\" is utterly false in first order logic. If they cannot be proved nor disproved, then they are neither true nor false; in some cases they are true, and in some cases they are false.",
"One way to look at the first Gödel's incompleteness theorem, which already answers in some sense OP's question, is that ",
"."
] |
[
"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 close to even knowing what all the ",
" are."
] |
[
"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, which breaks down starches.",
"https://www.ncbi.nlm.nih.gov/pubmed/12108756"
] |
[
"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 the bandwidth-delay product), the unacknowledged data can then be retransmitted and the amount of data sent between acknowledgements fixed appropriately.",
"If you look up \"slow start algorithm\" you can find more details. There are also various other algorithms to try to optimize performance, but the use of acknowledgements to determine when data is lost is basically key to the design of TCP."
] |
[
"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, you will get what you're given\"",
"This is dependent on what protocol is being used, I assumed TCP here"
] |
[
"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 due to contention."
] |
[
"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 the \"large-scale\" structure of this system could consider it very ordered -- everything is very, very uniform (density of particle positions, temperature, etc.), and any deviations in the symmetry are very, very small. But, someone looking at the \"small-scale\" structure would consider it very disordered -- everything is influenced by everything else nearby in complicated ways that make it extremely hard to predict; you can't easily find nice equations to describe where something will be after a certain amount of time, etc.",
"Now consider the opposite kind of system: consider a universe filled with a few sparse black holes of different sizes, with the rest of space being empty. For ",
" system, someone studying the \"large-scale\" symmetries will consider the system very disordered: there is no uniformity and likely no pattern in the distribution of black holes, and the average deviation from a symmetric (empty) universe is a really, really big deviation (a black hole). But someone studying the system on the \"small-scale\" will see a very ordered, predictable universe: you could fairly easily calculate (or at least approximate) how the black holes would interact with and orbit eachother, and make reliable predictions on the long-term behaviour of parts of the system.",
"So really, either type of system could be considered ordered, or disordered. It really is in the eye of the beholder.",
"Instead of order and disorder, think of entropy in terms of microstates and macrostates. This is easier to illustrate with an example:",
"Consider two fair, six-sided dice. Rolling either die gives you a number from 1-6. If you roll both die, there are 6",
" = 36 possible combinations: {(1, 1), (1, 2), (1, 3) ... (6, 5), (6, 6)}. These 36 possible combinations are the \"microstates\" of the system of both dice.",
"Now consider the ",
" of both dice: there are only 11 possibilities, the numbers from 2-12: {2, 3, 4, ... 11, 12}. These 11 possibilities are the \"macrostates\" of the system.",
"Notice that, if you roll both dice, ",
": you have an equal probability of getting either a (2, 3) or a (6, 4) or a (1, 1).",
"However, for the sum of both dice, the macrostates are ",
" equally likely: Some macrostates are more likely than others. Specifically, getting a \"7\" is more likely than anything else, and getting a \"2\" or a \"12\" is the least likely. This is because there is only 1 way to roll a \"2\" or a \"12\" -- (1, 1) and (6, 6) respectively -- however, there are many ways to roll a \"7\": (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), and (6, 1).",
"So, we say that the macrostate 7 is \"entropically favoured\" -- the sum of 7 has a higher \"entropy\" because there are more ways to rearrange the system without changing the overall macrostate. Whereas the sums 2 and 12 have a lower entropy because there is only 1 way to rearrange the system and have it be in the same macrostate.",
"You can use anything other than dice -- for example, an ideal gas in a box. There are about a zillion ways to rearrange molecules in the gas, but keep the box filled uniformly. But, if you move all of the molecules into the left half of the box so that the right half is empty, there are fewer arrangements which keep the box half-full.",
"If you have a system that is in a rare macrostate (a state that is entropically ",
"favored, like two dice reading \"1\" and \"1\"), and you rearrange it (roll the dice), you will probably have a more common macrostate. But the opposite is not true -- if you are in a common macrostate and rearrange the system, you will still probably have a common macrostate afterwards. This provides the basis for the laws of thermodynamics -- systems that go through random (or even pseudorandom) rearrangements will tend to settle into entropically-favored macrostates, and those macrostates are generally the ones that are in thermodynamic equilibrium.",
"So when we talk about the universe as a whole increasing in entropy, what we mean is that the universe is settling into macrostates where the internal microstates can be rearranged in many ways, and the macrostate would stay the same.",
"So then the early universe is not necessarily more \"ordered\" but is in a rarer, entropically-disfavoured macrostate (one where the density is very high and systems are not bound together or stable, and there are few degrees of freedom), and over time it settles into a more common, entropically-favoured macrostate (one where the density is much lower, and there are many more bound, stable systems with more degrees of freedom). As you can see, the earlier state can easily be seen as more \"random/disordered\" and the later state as more \"ordered\".",
"Hope that helps!"
] |
[
"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 yesterday having even lower entropy than today. This is in clear violation of the second law and the reasonable explanation for this is that the day before yesterday had even lower entropy. And so goes the argument all the way back to the big bang. The only way we can explain entropy being lower in the past is by setting up a boundary condition at the big bang where the entropy is extremely low. We have no good explanation for this boundary condition, but at least the problem has been swept under the rug of the big bang. "
] |
[
"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. Still low order. Now let it bake in the sun and the win erode it. The new pile of sand is in \"high\" entropy because there are many more ways to disorder the sand all over the ground then organize it in a tight clump.",
"The very start of the big bang began with everything that is and ever will be in a single state ... \"being\" that's the lowest amount of entropy possible. From there space expanded and there was room available for things to interact and do their thing [higher entropy]."
] |
[
"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 if consumed or even touched due to illness and disease. ",
"So it would be beneficial for early man to have a negative reaction to such objects through smell and those who avoided them would be more likely to survive and pass on their genes which has continued to today while the people who enjoyed the foul smells were eliminated by natural selection."
] |
[
"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 sometimes a harmless or even beneficial substance will smell disgusting because we respond to it similarly to a noxious one."
] |
[
"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 that is living cells. Most of the \"wood\" is actually dead cells that are now used for transport, storage and structure. Only a smattering of cell specialized for repair exist in the woody part of a tree. These cells would not be used as a metric for death. ",
"The living system of a tree is near the bark. It is the center of new growth and vital to the transportation of materials. Furthermore, it is critical for tree that this network of cells (known as the cambium) is uninterrupted. Roots require things that the leaves produce and vise-versa. Because of this, the cells from the ",
" that is completely severed by felling it are going to die eventually; the amount of time depends on the species and local conditions. That cambial death would be the equivalent of a flat line IMO. However, the roots complicate things. ",
"Some trees will sprout from their roots when the main stem dies, leading to the question; \"Did this tree really die?\". The roots never stopped living and the new stem is functionally and genetically identical to the one just felled. The cambial tissue in these tree doesn't die after felling; it would be comparable to a starfish regenerating a limb. "
] |
[
"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 probability of being wrong similar to an alpha value. alpha may be <0.05 when the tree falls (depending on the species), but it could still regrow roots in some cases. Maybe alpha is <0.001 when all the leaves on a fallen tree dry up, but even so it could still leaf out again. Several years later I could imagine alpha <0.000001 since the tree could have been using stored carbon to build roots the whole time and might just still pop new buds.",
"So you sort of have to pick your significant alpha."
] |
[
"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 various changes which ",
"limit the ability to focus on near objects",
". ",
"The Sphincter pupillae and dilator pupillae muscles become less responsive, limiting the ability of the pupil to dilate and so limiting the amount of light that can be focused on the retina. ",
"The actual structure of the eye loses fatty tissue and undergoes other changes such as liquefaction of the vitreous humour which can not only change its shape (and so directly alter the necessary focusing power) but also create physical disturbances in vision.",
"Conversely, wearing the wrong (or no) prescription, squinting, reading in the dark etc will only strain your eyes - this can cause a headache and a sense of tiredness as you overexert the small muscles involved, but it doesn't actually cause permanent damage.",
"I suspect your friends were told to warn their friends about possible vision damage if they shared their glasses since they're comparatively delicate and passing them around everyone who wants a go trying them on is an excellent way to get them broken - it's a convenient lie for a parent to tell their child in order to discourage that sort of thing."
] |
[
"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 demonstrated deterioration beyond what everyone experiences anyway as a consequence of ageing. "
] |
[
"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 demonstrated deterioration beyond what everyone experiences anyway as a consequence of ageing. "
] |
[
"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 amplitude of the wave, but requires frequency information to transform into Power per unit area.",
"This would be equivalent to tracking the photon flux per unit area ( in counts ) as you would for XRays or Gamma Rays and multiplying by planks constant * Frequency."
] |
[
"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 middle of that range and least sensitive to the lowest and highest frequencies, and lots of people have hearing loss. Virtually everyone older than mid-20s has some degree of hearing loss--it's a normal part of aging--and lots of people have worse-than-normal hearing loss due to exposure to loud noise or medical issues.",
"Anyway, here are some example pressure amplitudes for infrasound:",
"For most waves in physics, amplitude can be measured in multiple ways. For example, a sound wave will be associated with a pressure, but also with a density and particle velocity. All three quantities are proportional to each other, but we traditionally measure pressure amplitude in sound waves in air and water because pressure is easiest to measure in those settings. However, \"sound\" waves in the earth (seismic waves) are traditionally measured by the velocity of ground motion because that's easier to measure in solids. It doesn't really matter because they're all interchangeable.",
"Finally, you mentioned power or energy. In general, power flux (Watts per meter^2) and energy density (Joules per meter^3) are both proportional to amplitude squared."
] |
[
"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 work this way, which is why the commercials always talk about asking your doctor about specific infections."
] |
[
"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 shot while on the drug.",
"The idea may be to provide it short term, promote death or tolerance of the currently activated T cells (so ideally you aren't sick with an infection and this is primarily just your pancreas-specific T cells) and then to remove the drug and hopefully maintain the lack of self-specific T cell response. But certainly while the antibody is present and likely for some time thereafter any/all T cells will be affected, including those that would be protective against pathogens."
] |
[
"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 tissue, because while the individual molecules that made up the cells may be long gone, they are constantly being replaced by new ones such that the structure of the cell is effectively the same one you have always had. This can be said of many (not all) of your nervous system cells, heart cells, and bone cells.",
"EDIT: As far as the replacement rate goes, it varies a lot depending on tissue. Skin may be the fastest, replacing itself within a month. Full red blood cells turnover takes 4 months. Some (like the ones above) never fully turnover. I believe the heart on average turns over 40% of its cells in your lifetime. These rates tend to reflect the function of the particular tissue.",
"EDIT2: Forgot GI epithelial cells, they are the fastest, replacing themselves in days."
] |
[
"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 the solvent first.",
"Im not a Dr. or so but i would be astonished if its possible to make a gaseous ferrofluid."
] |
[
"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 magnetic nanoparticles from sticking together? I will ask tommorow if I remember."
] |
[
"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. ",
"Opinions should be recognized by strong facts and strong arguments, not by the person giving them. What your education has given you is the means to build strong arguments. You don't know all the answers and nor should you feel expected to. What you can do is address a specialized problem, put together information and make a case for sound course of action. "
] |
[
"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 training me to understand the reasoning are poor communicators...",
"Honestly I think most people in the job force have no idea what they are doing and fake it until they make it. "
] |
[
"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 limited to only travel away from the sun."
] |
[
"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 high speeds."
] |
[
"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 it in place. Since there's no fixed axis that it rotates on, putting a solar sail on one side would just wind up knocking it kind of off-center.",
"If you have the capability for that kind of orbital construction, you're probably better off just building solar panels in space. More electricity for your buck."
] |
[
"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, heating it.",
"In any case, the differences would be pretty small."
] |
[
"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). If it has, the trial can be stopped early, and all the controls switched to the new med (or conversely if the test is significantly ",
" they can be switched back to standard treatment). ",
"That way, you first ensure that everyone in your trial is getting ",
" the current best treatment, and are able to switch over as fast as possible. ",
"It’s pretty unusual for new treatments to be that significantly better; incremental improvement is the norm (but like compound interest, small improvements every year for 50 years can lead to the dramatic improvement in, say, many cancer treatments that we see).",
"If you’re wondering why we even bother with clinical trials when we ",
" something is going to be da bomb, we are really good at “knowing” wrong - even scientists deep in the field often have incorrect expectations. It’s probably much more common to ",
" trials early because the test med is worse than standard of care, than because they’re even better than expected."
] |
[
"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 spectrum of the ",
"Cosmic Microwave Background Radiation",
", which permeates the entire universe. "
] |
[
"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 minimum equilibrium temperature that a mass can get down to in space. In other words, if we sent an object to the blackest part of the universe, it would drop to a temperature of 2.7K. The reason it won't go down any further is due to background radiation which is ",
" in the universe."
] |
[
"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 personalities are the product of one integrated brain, not each hemisphere independently. It is misleading to the point of being wrong to describe people as either “left brain” or “right brain” in terms of their personality or how they process or learn information, and not just because it is a simplistic false dichotomy."
] |
[
"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 processing (i.e., it happens on both hemispheres, instead of mostly just one side). What this means? No idea."
] |
[
"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 processing (i.e., it happens on both hemispheres, instead of mostly just one side). What this means? No idea."
] |
[
"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 able to sense when we touched something, rather than just us seeing it?"
] |
[
"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 molecule looks like, not just what it's composed of.",
"https://en.m.wikipedia.org/wiki/Glucose",
"https://en.m.wikipedia.org/wiki/Formaldehyde"
] |
[
"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 empirical formula is CH2O; however, it's ",
" formula is C6H12O6.",
"Explained another way, a molecular formula like A6B6 can be simplified to AB only if it's ",
" into 6 different AB molecules. E.g. you never call NaCl as Na2Cl2 since you can physically separate the 2 NaCl molecules in the latter formula. On the other hand, you CANNOT ",
" separate the CH2O units in glucose (though you can do so chemically)."
] |
[
"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 fossils are around that old. If you want to be more specific - when did the genus ",
" evolve - that would be around 2.3 million years ago with ",
". ",
" is usually defined by its bipedalism and the beginnings of the use of tools and fire.",
"I studied all this for a few months at Uni, so I could go on and on and on, but I'll just point you over ",
"here",
" and suggest you read the whole page - or at least ",
"this",
" table.",
"In case you can't be bothered to read all that, the most important quote would be \"According to the Recent African Ancestry theory, modern humans evolved in Africa possibly from ",
", ",
" or ",
" and migrated out of the continent some 50,000 to 100,000 years ago, replacing local populations of ",
", ",
", ",
" and ",
".\" There's an important caveat here - the word \"replaced\" doesn't neccessarily mean out-competed or overran. Recent genetic evidence suggests interbreeding and cooperation.",
"EDIT: Edited for tone."
] |
[
"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 generally consistent with non-African populations being derived from African populations via a population bottleneck on the order of 50-80 thousand years ago",
"3",
" (that reference says 50,000, but I've seen other estimates that are higher; it's something that's inherently difficult to estimate exactly, but we can do a reasonably good job putting upper and lower bounds on), whereas Europeans and Asians split from one another a bit later, maybe 30-40 thousand years ago.",
"It is true however that there were other humans living in the rest of the world before our ",
" ",
" ventured out of Africa. Neandertals are known to have been living in Eurasia for hundreds of thousands of years before our ancestors ventured out, and in one of the coolest discoveries of the 21",
" century, in my opinion, we now have very good evidence that the ancestors of modern non-Africans interbred with Neandertals",
"4",
" resulting in approximately 2-4% of their genomes being derived from Neandertal DNA. It also turns out that some Melanesian populations can trace some of their ancestry (~2-6%) to an archaic human group known as Denisovans",
"5",
" (intriguingly, the only evidence we have for the Denisovan's existence is a pinky bone found in a cave in Siberia, and a full genome sequence obtained from it).",
"So it's not disputed that there ",
" human populations living in much of the world for the last few hundred thousand years, nor that some of those populations did make a contribution to the ancestry of modern day humans, but the ",
" majority of modern non-African ancestry can be traced back into Africa within the last 100,000 years, and multiple analyses have concluded that the signature of introgression in from Neandertals could have been left by a surprisingly small number of successful interbreeding events",
"6",
"7",
" , perhaps as infrequently as once per 50 years over a period of about 10,000 years.",
"The whole \"Out of Africa\" vs. \"Multiregional\" debate has largely played out in the field of Anthropology, as far as I can tell. To me, the above suggests that the truth is best captured by what has been referred to as \"Out of Africa\", but I imagine some would look at the above and call it \"Multiregional\". As long as we can agree on the facts (most human ancestry traces to Africa within the last 100,000 years) I don't think it much matters."
] |
[
"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 individual spectral components that contribute to the stars' total spectra. Thus, the answer is no."
] |
[
"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 were getting at with the \"vice versa\" at the end of your question. But we don't consider these to be stars. That is because part of the definition of a star is that it is luminous. So the boring answer to your question is that there are no dark stars because of how we define what it means to be a star."
] |
[
"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 works depends on many things. There's not one way to do it. Are you matching pre-programmed \"memories\" or matching images previously captured? Object recognition involves complicated algorithms we take for granted. Think about how electrical impulses from your eyes generate signals that our brains can match to stored data, even though the object may be under different lighting conditions and viewed from a different perspective - maybe even different colors.",
"I believe what our brain does with different objects is to separate them into different categories and use different image recognition techniques to match them (e.g. noticing something is a face will use different factors to recognize than realizing something is a car, then trying to recognize it). Generic techniques would be trying to map boundaries on the object and comparing the shape of the boundaries, or the colors inside them, or even a pattern in the pixel data both color and grayscale. Motion tracking can also use the objects pattern of movement or speed to help in recognition. Face recognition specifically looks for anchor points (eyes, nose, mouth, etc.) and looks at their shape and relative spacing. I've seen some demos that line-trace the mouth and eye region to estimate the subject's mood.",
"If you are really interested, I would google line following robots to get a basic understanding of some of the concepts of vision tracking. It is a popular, basic project. AI is much more complicated and there are many books (of varying quality) on the subject. They range from the software engineering side to the philosophical, so I wouldn't blindly grab one off the shelf."
] |
[
"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 HAL 9000). Instead, AI is split into many smaller subfields, each solving a specific problem in a way often unlike a human.",
"What you've described could accurately be framed as a ",
"Computer Vision",
" problem, a ",
"Pattern Recognition",
" problem, a general ",
"Machine Learning",
" problem, or several other overlapping domains. Again, there are many algorithms that could be at work here.",
"How you frame the problem is also important. Some algorithms are ",
", meaning they require some a priori knowledge to \"train\" the algorithm before it can recognize something. In this case, the robot would need several examples where it's told when it's looking at a red ball, and examples where it isn't. ",
"Conversely, some algorithms are ",
", classifying something without having seen it before. For example, the robot might be programmed to detect moving objects with some level of object memory if the ball rolls behind another object. Again, there are many ways to solve this problem too, each with their own limitations and strengths.",
"For your example, a robot might recognize a red ball by searching for a spherical-shaped boundary where the color gradient of the image data transitions to red. It might have to look at several \"patches\" in the data randomly before it detects anything. Once it detects the ball, the robot can store the position it last saw the ball and start searching from that location in the next video frame.",
"Another approach might be to feed the image data into a pattern classifier like a ",
"neural net",
". After showing the robot a lot of red ball examples and non-red ball samples, the algorithm builds a connected network of \"neurons\" that may \"fire\" if the each neuron's input crosses a learned threshold. The big difference here is the network connections might not make sense to anyone who looks at them."
] |
[
"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 it rained last night, the grass is probably wet.\" Since the conclusion here is the same as the information given, it can abductively reason that it might have rained last night, and say so.",
"In general, all of artificial intelligence comes down to rule-rewriting, proof solving, pattern-matching, and similar processes."
] |
[
"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 where they lived... someone else can take point from here.",
"I'd suggest searching ",
"r/documentaries",
" for free things to watch . The BBC have produced several excellent documentaries as well and they're now on youtube. "
] |
[
"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). It's on youtube and might answer some of your questions. Also a BBC series called \"the incredible human journey\". It's a 5 part documentary and again it must answer some questions... or just provoke new ones!"
] |
[
"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 hands to interact with a plethora of surfaces since birth, the skin is less sensitive as it has become tougher over time. ",
"In addition to that, our face and other parts of our body that contain hair follicles are prone to acne because of sebum production. Sebum is a oily substance that is produced in the sebaceous glands and secreted through pores. Dirt and other substances get mixed with sebum in our pores and block the pores, causing acne! ",
"So really, our face is sensitive due of the large number of nerve endings and the lack of friction that comes into contact with our face. Our face is prone to problems like acne because of sebum production. ",
"http://health.howstuffworks.com/skin-care/information/skin-types/oily-skin.htm",
"http://www.medicalnewstoday.com/articles/107146.php"
] |
[
"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 multicellular eukaryotes with millions of cells. ",
"It's thought that multicellular life evolved when conditions forced unicellular organisms to \"huddle together\" due to lack of food, like in ",
"slime mold",
". It really depends on your definition of \"organism,\" but yes, they do exist."
] |
[
"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 halfway point between us and the edge of the observable universe, then light would take ",
".",
"This would cause an interesting effect. Say the mirror is one year beyond the halfway point (~6.9bn light-years), and there is a galaxy halfway between us and the mirror (3.45bn light years). We cannot see ourselves because Earth would not have been hit by any photons making the round trip. However, if we observed the reflection of the galaxy, we would see it as it was 10.35bn years ago, while the actual galaxy when observed directly would be as it was 3.45bn years ago.",
"The further the mirror gets beyond the halfway point, the more of the space between us and the mirror becomes unobservable. What we can see in the mirror, would essentially look identical to what we see when we look out into the universe, with galaxies getting younger and more primitive the further away they are. Except, instead of looking at far away alien galaxies, we would be looking right back at ourselves billions and billions of years ago.",
"This is of course impossible, because unless the mirror always existed there, putting one there would not have this effect. Still, I find the thought of looking at an ancient Milky Way kind of creepy for some reason.",
"EDIT: In regards to seeing \"through\" it. If you mean it is translucent, then we would just see all the above images superimposed over the normal backdrop."
] |
[
"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 you started, though you'd be facing the same direction. In that case, looking at the edge of the universe with the assumption you had a clear path with nothing obstructing your view, you'd see the back of your own head! Although what that looked like 20 some billion years ago might not be so recognizable. "
] |
[
"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 atmospheric shock wave that was rendered visible at that point in the expansion (though I don't know precisely why)."
] |
[
"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 \"In the first few microseconds after detonation, the bomb casing and shot cab are destroyed and vaporized. These vapors are accelerated to very high velocities, several tens of kilometers per second, faster than the shock front. However, this acceleration happens in a short period, so the material is trapped behind the shock front even though it eventually travels faster than the shock front. The various light and dark patches are caused by the varying vapor density of the material splashing against the back of the shock front. The irregular variations in mass distribution around the bomb core creates the mottled blob-like appearance.\"",
"Another interesting thing which is visible in these videos is the \"double flash\" effect. There is a first fireball (formed from radiation heating of the air), then it fades and you can see another fireball (formed from the shockwave) which is expanding inside the first, and which eventually becomes bigger."
] |
[
"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 sky."
] |
[
"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 hundreds of them (if you know where to look). Various websites track satellites and make predictions for their visibility, e.g. ",
"http://calsky.com/",
"If you have a dark sky and equipment for a long-term exposure you can see the ring of geostationary satellites. ",
"They appear as dots",
" in a long-term exposure while everything else makes streaks."
] |
[
"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, an explosion localized to one spot can't be heard as such by people on the opposite side of the planet."
] |
[
"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. Where the ball moves forward with the car, saying almost stationary with the car, but to observers its moving."
] |
[
"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 the fuel has nothing to push against.",
"The air enclosed by the elevator is forced upward by the ground. Because the helicopter lifts by pushing the air, it moves relative to the air. So, it maintains its altitude relative to the floor of the elevator.",
"Depending how fast the elevator accelerates (and how fast goes) at first there might be a jolt and a slight drop in altitude. It takes time for the air to accelerate, so unless the changes are subtle it might take a moment for equilibrium to be resettled."
] |
[
"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 the fuel has nothing to push against.",
"The air enclosed by the elevator is forced upward by the ground. Because the helicopter lifts by pushing the air, it moves relative to the air. So, it maintains its altitude relative to the floor of the elevator.",
"Depending how fast the elevator accelerates (and how fast goes) at first there might be a jolt and a slight drop in altitude. It takes time for the air to accelerate, so unless the changes are subtle it might take a moment for equilibrium to be resettled."
] |
[
"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 through conduction via the walls of the kettle) thus concentrating the minerals more, but more water means more dissolved minerals to begin with wanting to precipitate out when the temp rises to boiling.",
"Overall less water would be better as it would reduce the amount of minerals available to deposit, however if you only used the bare minimum and left just a few cc's of hot water in the kettle the evaporation would likely cause more deposits to form.",
"Your best bet is actually to use just a bit more water than you need (which reduces energy use too as you're not heating water only to let it cool to room temp again) and then immediately refill it to 0.5 liters (or whatever the minimum is) with cold water."
] |
[
"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 next shell out. The first ionization energy would be extremely low or even negative - It'd be energetically favourable for the electron to spontaneously wander away. This is often called the screening effect.",
"Being shared: An electron would have to come the other way, and there's no room for it. Only very strongly electronegative elements (e.g. oxygen, fluorine) can reliably share with something that has a full shell, such as xenon."
] |
[
"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 shell (the principal quantum number, n, being a positive integer: 1,2,3...) and in a specific orbital as shown here (",
"https://chemistryonline.guru/wp-content/uploads/2016/07/fea.jpg",
"). These orbitals are defined by the azimuthal quantum number, l with s = 0, p = 1... Two electrons maximum can exist within each orbital. ",
"Now for the old 8 electron rule. This refers to electrons in the northern part of the periodic table where principal quantum number is low, and so the outer shell contains only an s and 3 p orbitals, for a potential total of 8 electrons (2 in each orbital). Now say we wanted to add an electron to a noble gas, in order for that electron to exist on the noble gas atom it must be in an orbital of a much higher potential energy. In order for this to occur the electron would have to be much more stable as a result of being in this orbital as opposed to its original source (remembering here the principal that all things tend towards the state of lowest potential energy i.e. most stable state) and this is hardly ever the case.",
"Atoms such as an Na 'lose' electrons because the potential energy for the electron in that orbital was at a higher potential energy than the orbital to where it is going, such as the p orbital of a Cl. This is orbital is not that much higher in energy to that of the other electrons because it does not require a jump to a higher energy level (n) Overall an Na and a Cl exist in a lower energy state as Na+ and Cl-. The potential energy of the orbitals in question is determined by the nuclear charge, among a few other things.",
"tl;dr Full shells are at a tipping point where adding any more electrons requires a big jump in the potential energy of that electron, and where the the electrons currently in orbit are of a fairly low relative potential energy and so they'd have to be going somewhere ",
" stable for it to be energetically favourable for them to leave."
] |
[
"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 helium as negative ions! Although hydrogen does look like it might be reasonably stable."
] |
[
"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, and consequently no surface, called the singularity. Regardless of the theory, certainly there is no longer any atomic structure at all. The most compact objects (with surfaces) that we know about are neutron stars, which have envelopes and crusts of atomic species where the pressure is less, but which break down into a material that is even denser than the nucleus of an atom. Atoms certainly are not the structure of material deep inside of neutron stars. ",
"Since neutron stars are the densest objects we know of with surfaces, we can answer your question in regards to them instead of black holes. The outer crust of a neutron star can have small \"mountains\" on it, and a quick back-of-the-envelope calculation shows that they can't be reasonably be larger than ~1 cm because the gravity is so strong that it will pull down anything higher than that (similar to how there's a maximum height for mountains on Earth or Mars or any other planet based on the strength of gravity at the surface). As the neutron star spins, these \"mountains\" create an asymmetric moment of inertia and should emit gravitational waves. Instruments like LIGO are currently trying to detect these gravitational waves (in addition to much louder-but-shorter ones like merging neutron stars). "
] |
[
"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 - so if light can't escape, nothing can. ",
"Steven Hawkings has been trying to convince physicist for some time that the point of no return does not exist.",
"I am assuming that you are referring to ",
"this recent article",
". This has been discussed in the media as Hawking saying that black hole don't exist, while he is discussing a more technical point. To understand the point of view that he is defending, you have to know the difference between an event horizon and an apparent horizon (and I'm going to simplify the actual mathematical definitions). \nAn event horizon is a surface from which no light can escape to infinity, from now and until the end of times. \nAn apparent horizon is a surface existing at a given time, which surrounds a region from which light rays can't expand outward at that given time (but the rays can do whatever they want at earlier or later times).",
"What Hawking is defending (I think) is that when a star collapses to a black hole, you can get very long-lived \"apparent horizons\", from which light doesn't escape, and which have the expected properties of a black hole from the point of view of an outside observer. But you don't get an event horizon, because as the black hole evaporates (through Hawking radiation) the information that went into the hole during collapse is somehow released.",
"What happens to the information going into a black hole is a hotly debated issue in astrophysics though. Hawking's view is just one interpretation. Practically, however, evaporation takes a very long time (for the black holes that we see, it takes onger that the age of the universe). And by observing the universe at a given time, we can't really see the difference between an \"apparent horizon\" and an \"event horizon\", because the event horizon requires us to know what the universe looks like at all times, while we only observe it at the current time. So from the point of view of an astronomer looking at the universe, an apparent horizon has all the properties that you would expect from a black hole."
] |
[
"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 - so if light can't escape, nothing can. ",
"Steven Hawkings has been trying to convince physicist for some time that the point of no return does not exist.",
"I am assuming that you are referring to ",
"this recent article",
". This has been discussed in the media as Hawking saying that black hole don't exist, while he is discussing a more technical point. To understand the point of view that he is defending, you have to know the difference between an event horizon and an apparent horizon (and I'm going to simplify the actual mathematical definitions). \nAn event horizon is a surface from which no light can escape to infinity, from now and until the end of times. \nAn apparent horizon is a surface existing at a given time, which surrounds a region from which light rays can't expand outward at that given time (but the rays can do whatever they want at earlier or later times).",
"What Hawking is defending (I think) is that when a star collapses to a black hole, you can get very long-lived \"apparent horizons\", from which light doesn't escape, and which have the expected properties of a black hole from the point of view of an outside observer. But you don't get an event horizon, because as the black hole evaporates (through Hawking radiation) the information that went into the hole during collapse is somehow released.",
"What happens to the information going into a black hole is a hotly debated issue in astrophysics though. Hawking's view is just one interpretation. Practically, however, evaporation takes a very long time (for the black holes that we see, it takes onger that the age of the universe). And by observing the universe at a given time, we can't really see the difference between an \"apparent horizon\" and an \"event horizon\", because the event horizon requires us to know what the universe looks like at all times, while we only observe it at the current time. So from the point of view of an astronomer looking at the universe, an apparent horizon has all the properties that you would expect from a black hole."
] |
[
"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 ",
".",
"Mathematically, the argument is quite simple. To specify a unique location in a geometric space, a point, there is a minimum amount of information you need. In our universe this seems to be four numbers, how up or down, how left of right, how forward or backward, and when."
] |
[
"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 result of counting, a human invention. We could call time \"the second dimension\" and make ",
" our fourth dimension. The ordering doesn't matter, neither philosophically nor mathematically. ",
"Time is one of the four dimensions in our universe we know about. How we order those dimensions doesn't matter. ",
"Edit: We can also consider geometries with no time dimensions. Euclidean geometry is an example of this, just three spatial dimensions, no time. We can also consider having ",
" time dimensions. What about a universe with 2 time dimensions and 6 spatial ones! That'd be something huh?"
] |
[
"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 that inflammation can be chronic, and inflammation hurts. If your joints are just inflamed all the time your body will ache and it will be incredibly unpleasant. Anti-inflammatories are targeted towards chronic inflammation."
] |
[
"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 oxygen in our blood and thus do the most important job blood has: Getting oxygen from the lungs to the rest of the body. In cases of massive bleeding, when there's not enough blood left the first and biggest problem is the lack of oxygen in the peripheral body, especially the brain.",
"Now erythrocytes move oxygen from the lungs to the body with the help of a protein called hemoglobin. Hemoglobin is a protein consisting of four sub units with a iron ion in the middle. With this sub units it can bind four oxygen molecules. The great thing about hemoglobin is that it's affinity to oxygen (how strongly it holds onto it) changes with the amount of oxygen and other factors (CO2, pH ) in the surrounding tissue. ",
"In the lungs there is obviously a lot of oxygen. Here hemoglobin has a very strong affinity to oxygen. It's grabbing it and doesn't let go. When the o oxygenated blood reaches the heart and gets distributed to the body it will sooner or later reach the capillaries and be surrounded by tissue with low oxygen. Here the hemoglobin changes the way it behaves: The affinity for oxygen drops so the oxygen floats away from the erythrocyte into the tissue.",
"The problem for lab created blood is: We cant fake this behavior. When we create oxygen carriers they either hold onto oxygen too strongly (so the oxygen doesn't reach the peripheral tissue, but gets carried back to the lungs instead) or not strongly enough, so the oxygen never leaves the lungs in the first place.",
"Creating a carrier which can do that would probably result in a Nobel price."
] |
[
"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, then expand them to get large(r) volumes relevant to therapeutics. The major hurdles to translating this technology are: the fact that cord blood is hard to get, and there's a lot of (necessary) regulatory burden around accessing and using it; and the technical challenges associated with expanding relative fragile cells in vitro. The first hurdle has likely been handled because we now know that stem cells created from adult cells are equivalent to embryonic stem cells, which means a lot of the risks associated with using them are significantly reduced. The second hurdle is one that time will solve. I would say that we can expect these blood products to hit the market in the next decade. The process will involve taking adult cells from a patient, transforming them into stem cells, differentiating those cells into blood cells, growing large volumes of them, and then injecting them back into the patient. This is already done with CAR T cells in some cancer therapies. "
] |
[
"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,\" though they would most likely not look anything like clouds here on Earth."
] |
[
"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 established the container is still at the dead center or seems to be to the smallest detectable level. ",
"How do i know ( i am inside (like a ghost ofc with all my gost detectors and instruments) the container and can observe the sphere but not know anything outside) when the sphere starts moving to the sides, away from center ... if ",
"The container is spinning OR the Universe is spinning around the container?"
] |
[
"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 every non-accelerating object there's some reference frame where it's at rest. From that you can deduce that if any non-accelerating object can emit a photon then one can emit photons while at rest. "
] |
[
"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 can neutralize stomach acids\" ",
"https://www.livescience.com/41661-why-platypus-wont-regain-stomach.html"
] |
[
"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 should take a second to point out this image is the wonderful John Kraus’!! ",
"Be sure and follow him for more incredible images."
] |
[
"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. ",
"What this results in is that in lower altitudes, the exhaust plume gets squeezed as it is lower pressure than the surrounding air"
] |
[
"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 diffuses away from the cells that secrete it, so the area closest to the ventral side has the highest concentration of shh, and the area farthest from the ventral side has the lowest concentration. A developing cell just needs to sense how much shh is in its environment to identify its position. As you can imagine, if there were multiple gradients along different axes, a cell would be able to define its 3D location with more precision, and this happens in other parts of the nervous system.",
"Another common mechanism is through cell-cell contact, where cells migrate to be with other cells that express complementary proteins on their surfaces. It's as if some cells have the sticky part of velcro and some have the fuzzy part, and the sticky cells find the fuzzy cells and stick to them.",
"A third mechanism might be considered the \"just keep swimming\" mechanism. In the developing cerebral cortex of the brain, newborn cells migrate out past their earlier-born cousins until they reach the outer limits of the previously-born cells, and then they stop. They don't \"know\" that they're supposed to be at any particular level, but they keep migrating until they see a \"stop\" signal (which is provided by another layer of cells on the surface of the brain)."
] |
[
"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 hedgehog to a scientist spending hours looking at them through a microscope, inspire the name ",
"Later, another group of scientists discovered that the ",
" gene was not unique to flies, but was found in nearly every animal they had looked in. They named the human version ",
", after the video game character."
] |
[
"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 hedgehog to a scientist spending hours looking at them through a microscope, inspire the name ",
"Later, another group of scientists discovered that the ",
" gene was not unique to flies, but was found in nearly every animal they had looked in. They named the human version ",
", after the video game character."
] |
[
"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 not stable, self-propagating fluctuations (i.e. real photons). The word \"virtual\" is unfortunate because stationary magnetic fields are real enough, they are just not really stable particles that can radiate away and take on an independent existence. Magnets don't glow visible light because visible light consists of visible-frequency real photons, and stationary magnetic fields consists of virtual photons.",
"Although human eyes are not sensitive to stationary magnetic fields, there are machines and other creatures that are. To a homing pigeon, a magnet does \"glow\" in some sense of the word since they are able to detect magnetic fields (aka virtual photons). A human can indirectly \"see\" the virtual photons that constitute a magnetic field using a small compass.",
"Also, if you wave a permanent magnet about, the magnetic field is no longer stationary, and you create real photons in addition to the virtual photons. However, these real photons are very low frequency - far too low to see with your eye. But you could pick it up with a suitable radio antenna."
] |
[
"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 fast you would have to spin a magnet to get visible light at 400 terahertz, the magnet must be no bigger than about a micron, otherwise the outer parts of it would be going faster than the speed of light.",
"Additionally we don't have any materials which would withstand being spun any where near this fast."
] |
[
"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 moderators."
] |
[
"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. Feathers appeared before any of this and are thought to have evolved for temperature regulation. ",
"Edit- spelling"
] |
[
"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 small, benign tumors that a healthy person could have. For instance, most middle aged men have some degree of hyperplasia in their prostate. Some sun spots are tumors. You might have some polyps in your colon.",
"So why don't these tumors grow? Most of them do grow, but slowly, not because of blood supply, but because their growth retains some regulation. Some of these tumors are pre-cancerous, meaning that if they have some extra genetic damage, they could eventually become cancers.",
"So while a person may be carrying some benign tumors with them, most of these tumors are unlikely to need treatment.",
"Some cancers are treated with anti-VEGF medications which limit the growth of blood vessels. But with what we currently know, it would be absurd to treat everyone with these."
] |
[
"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 have undergone a series of mutations that may have added several characteristics from that list, but may NOT have gained the ability to grow a blood supply. That would fit your criteria. But is it cancer? Not really - this would be classified as some type of pre-cancerous growth.",
"This touches on an important fact - the number 1 risk factor for cancer is ",
". Over your lifetime, cancer is always developing. Usually it takes the form of these pre-cancerous clumps. "
] |
[
"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 independent instance of cross-species transmission. Twelve spillovers."
] |
[
"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 proteins it uses for entry, HIV-2 bypasses it, but it was so long ago that I am not sure if that was refuted or not. But yeah there is a LOT of HIV variability that the general public doesn't know about. It doesn't make the news like flu strains or COVID strains, though it really should've.",
"EDIT: It's not that HIV doesn't have many strains like the flu and COVID. But it did suffer (and in many ways still does) bias - there is not news coverage on it (and this can be traced back to malicious policies during the 80s, 90s, 00s) and so info was generally suppressed and so it's not common knowledge like flu and COVID."
] |
[
"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 how these numbers are calculated, but the trend is pretty clear: the pie is getting bigger, but the rich are taking a larger and larger cut of it every year."
] |
[
"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. However, because it is sound waves building up, we must remember that the high pressure air is not a solid brick but many tightly packed waves. As these hit your house, they start to hit it many times with strong force with apparently a good resonance causing the shaking. "
] |
[
"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 it makes a sound, but equally if you make that sound the string can vibrate, but the neighbouring strings might not [depending on how loud the tone is]. Same idea."
] |
[
"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 a bit) shows incidence rates by state. Look at the column for \"Lung & Bronchus\" and go down each row to compare among states. Then, refer to ",
"this wiki article",
" for information on state-by-state smoking laws.",
"Just a quick example: lung cancer incidence in Alabama with no state-wide ban is 89% for males, 51.6% for females. In California, a state that adopted smoking ban early on, incidence rate is 49.2% for males, 39.0% for females. There are many factors to consider of course. Access to primary health care, socioeconomic status all play into cancer incidence and death rates. So, we can't draw direct conclusion about the relationship between smoking ban and lung cancer this way, but it is a quick way to just glance at the numbers and get some ideas about it.",
"CORRECTION: I mistakenly put % for the numbers, but they're actually ",
", not percent. (That would be awful numbers!!)"
] |
[
"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 released and allowed to return together. This must mean, therefore, that any two objects must have gravitational potential energy between the two of them that becomes kinetic energy as they are attracted and accelerate towards each other."
] |
[
"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 some outside experts look at a paper they will be able to find some errors or shortcomings the authors missed, and judge the importance of the paper.",
"To quote ",
"from the policies of ",
",",
" the top general physics journal:",
"Referees are requested to comment critically on the validity and importance of the paper, and they are asked their opinion concerning the degree of interest of the paper for the readers of Physical Review Letters. Referees submitting favorable reports are asked to provide positive reasons for recommending publication. The editors also appreciate any suggestions of the referees directed toward improvements in style, grammar, completeness of references, etc. Advice received from referees concerning the scientific merits of a paper are considered very seriously; ordinarily, no paper which receives important scientific criticism from a referee will be accepted without further review. Although advice from referees concerning the suitability of the paper for the journal in terms of importance, broad interest, and accessibility is solicited and is vital, the editors do not consider such counsel definitive and will weigh their own perceptions of the paper and of the journal, and their understanding of the opinions of the readers of the journal, in reaching their conclusions on these aspects of acceptability.",
"It's simply not possible for referees to determine positively that a result is correct, short of redoing the study themselves."
] |
[
"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 important enough to be published. There is a general hierarchy among journals in different fields, and the most well respective journals are much more selective in which papers they accept.",
"If the manuscript passes this test, it is sent to 2-5 independent reviewers, who are scientists working in the same field. It is usually a one-way blind process; the reviewers know the identity of the authors, but the authors do not know who the reviewers are. Sometimes it is two-way blind. They read the draft and make comments as to the validity of the methods and results in the paper. They may also propose additional experiments for the authors to perform in order to make the study complete.",
"The editor compiles the comments, and decides whether to accept the paper as is, accept with revisions, or deny acceptance.",
"If accepted, the journal does all the necessary typesetting to prepare the paper in publication format. The journal usually publishes a paper copy semi-regularly containing the accepted papers, and releases PDF copies to online academic publishers."
] |
[
"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 end of the day, being a reviewer is a large responsibility that some scientists do not fully appreciate. In theory, associate editors and editors also bear some of this burden, but depending on the journal and the manuscript influx, AEs and editors may not have the time to critically read a manuscript, so it is really the job of the reviewers to dig in and look for failures in logic, methods, analysis, etc. Sometimes reviewers do awesome jobs and really vet things fairly, sometimes they do a hatchet job because they don't like the conclusions (independent of the quality of the science), and sometimes they're just lazy. That last one is a big potential contributor to \"bad\" papers. A quick read of a submitted paper is probably just not sufficient to really dig deeply into the work and its implications, but often this is all that someone chooses to do, for many reasons.",
"2) ",
" - On the other end of the spectrum, you can get reviewers who seem to want to do nothing but inject meaningless crap into your paper. Ultimately, you do not need to address everything your reviewers suggest and if you can make a good case why what they are suggesting is wrong or a bad idea, you can often ignore it, but you are expected to take their reviews seriously, even if they are ridiculous. I personally have admitted defeat a few times and just accepted some change a reviewer suggested even though I didn't think it was particularly relevant. I have drawn the line when I think it makes the wrong interpretation, but I'm sure there are a few lines in my papers that seem like total one-offs thanks to some reviewer comment.",
"3) ",
" - Science is collaborative, which is generally a good thing. However, sometimes you and your co-authors don't agree, actually, most of the time you and your co-authors don't agree it's just a question of whether that disagreement is on whether that line in figure 1 should be red or blue versus the main conclusion of the paper. Researchers also subscribe to different levels of conservatism (in the true sense of the word, not the political leaning) so some may want to include every possible explanation for a dataset and others may only want to present the preferred one, even if that preference is based on something non-scientific. Ultimately, what goes into the paper will be some compromise and should mostly reflect the first few authors wishes (this is written from the perspective of geology where author order equals level of contribution, generally), but sometimes bigger appeasements can be made. Sometimes, things are lost. Handwaving gets added to keep someone happy. Etc.",
"4) ",
" - This kind of falls into two categories. On one hand, you can argue that more obscure journals tend to have less rigorous review processes and thus may be a backdoor for \"bad\" work. Another important one is article length. Publishing in really short format, high impact journals (Science, Nature or discipline specific equivalents) means you have VERY little space to make your point. So, if you have a dataset that can be interpreted 3 different ways, you probably only have space to discuss 1 way and chances are you're going to pick the \"sexy\" way as opposed to the 2 other ways that mean your story isn't cool enough for Science or Nature. Bias alert - this is potentially an unfair view based on experiences with said high-impact journals.",
"5) ",
" - Sometimes people do stupid things. Scientists are people, ergo we do stupid things too. Sometimes we make assumptions that aren't really supported, sometimes we take a shortcut in the lab that doesn't seem like it should matter, sometimes we just make a mistake. If that mistake isn't caught, it might find its way into a paper. Remember, that a single paper may represent years of work from many different people. If one person makes a mistake 4 years ago, that could screw up everything and produce a result that is ultimately wrong. I tend to have a positive view of other scientists so I like to think that for the most part these are unintentional errors or omissions, but you do see stories which suggest sometime they are intentional. Generally, for a mistake, real or fabricated, to make a big impact something else in the review process will have to fail, but depending on how deep down in the process it is, it may not be apparent to a reviewer, even if they are doing everything they should."
] |
[
"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 cancel with the negative binding energy to yield a much lower total mass, which is unlikely. This is a fine-tuning problem that makes the preon hypothesis unfavoured."
] |
[
"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 elementary particles.",
"It does get a little more complicated, however, if you actually want to ",
" the fields. We generally think of the electromagnetic field as a single field, but it actually consists of six independent values at any point in spacetime. What's more, the photon isn't really associated with the electromagnetic ",
", but the electromagnetic ",
", the electric potential and vector potential considered together. It turns out that we can consider this potential as a single vector field, with four components corresponding to four directions, three in space one in time. The vector potential forms the spatial part of this, the electric potential the time part. The reason we call it a vector field is because of how it transforms when we change to a different frame of reference, either by rotating or changing our velocity. Thus, it makes sense to consider these four values as a single field.",
"Classifying all of the particles in the Standard Model in terms of how they transform under rotations and \"boosts\" (changes in velocity), the four force carriers (photons, gluons, W and Z bosons) are all vectors, the Higgs boson is a scalar, and all of the remaining particles are called \"spinors\". This means that they transform in a way that is somewhat similar to vectors, except that they end up with an overall sign change when you rotate 360 degrees.",
"That's not the end of the story, though, because there are other things we can do with the fields besides rotate our frame of reference. It turns out that in some cases we have we can add or subtract two or more fields in a very particular way to get new fields, and these new fields behave in the same way as the originals. For example, if we have two scalar fields, g and h, but all of the math that governs their behavior is expressed in terms of g",
" + h",
", then we can do a rotation in the g-h plane without changing the physics any. It's generally impossible to tell the difference between g and h experimentally, so we consider them two parts of the same field as well.",
"Returning to the Standard Model, this is what gives rise to the idea of \"color charge\" of quarks and gluons. For each of the named quarks there are actually three different fields, which transform into one another according to a group of complex matrices called ",
"SU(3)",
". This is on top of the fact that each of those three fields is a spinor, and is, in fact, actually two spinors, because they transform under SU(2) as well.",
"So you see, depending on how you count them, there are anywhere from 17 fields to around 200."
] |
[
"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. electron and positron) and quarks and gluons according to their SU(3) representation (3 colors of quarks, 8 for gluons)",
"This is what is given on the ",
"wikipedia page for the standard model",
"How do you get 200?"
] |
[
"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 -(dark saturation current).",
"Basically, it determines the base current your device will have through it when it's being operated in photoconductive mode."
] |
[
"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 be negative, I guess?",
"So, as the reverse bias Voltage increases, the exponential term will go to zero. Can you explain why this is? I thought it would go to zero when the when the factor is 1.... (Not very good at math, not too clear here..)",
"But, OK, so the exponential term goes to zero, that leaves -1 which is multiplied by the dark saturation current and you get -(dark saturation current). OK. Does this mean that the DSC is negative, ie working against the current generated by the light?",
"Can you explain in more detail about how it determines the base current?",
"Also, why is it \"saturation current\"? What is saturated by what?",
"I am sorry to ask so many questions but I really want to understand this and I don't have any background in engineering/math. Thank you very much!",
"I am trying to read the book \"Solar Electricity\" by Markvart, but it is tough going....",
"Thanks again!"
] |
[
"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 breakdown and blow the diode).",
"The exponential term will go to zero because the exponent becomes relatively large with a negative sign. Look at a graph of ",
"exp(x)",
", and you'll see that it is close to zero in the negative domain.",
"The negative sign in front of the current means that it is flowing the direction opposite what it would be if you forward-biased it. The photocurrent is also negative in this sense- the graph for the I-V characteristic will be pushed down as light is applied to the photodiode.",
"The photocurrent and the dark current add up, see ",
"this model",
" of a photodiode. If you operate the diode in photoconductive mode, the dark current will be close to the dark saturation current, so any photocurrent will be added on top of the dark saturation current.",
"It's called the \"saturation current\" because the device essentially gets saturated at that current- reverse biasing the device more will not yield any additional current (well, at least until you get into breakdown).",
"No problem!"
] |
[
"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 happens on my shoulders and causes a mutation will not result in all of my skin cells having that exact mutation in the years ahead?"
] |
[
"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 cell will pass it’s mutated genome to its daughter cells. And those daughter cells would pass the mutated genome they received on to their daughter cells when they eventually undergo mitosis. Thus, the cancer grows in size. The tumor can spread by invading nearby tissues or by metastasis (some cancer cells leave the primary site and travel to new areas of the body where they continue to grow). ",
"But if you received sunburn and eventually developed cancer in one area of your skin, that exact mutation will not spread to all of your skin cells. That mutation will only be seen in the cells arising from the original mutated cell."
] |
[
"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 a degree that all organisms can eventually be traced to one ancient species, if we can call it that. (Even if multiple life forms had arisen independently, they must have converged at one point.) So all current organisms orginated probably not from single cell (may or may not be true), but very likely from a single community of primitive life forms.",
"The supporting evidence are:",
"1) all three domains of life have similar gene coding systems and mechanisms. (Genetic codes are considered \"universal\"; also, plural for \"systems\" because minor variations do exist.)",
"2) There are many genes, protein folds and even entire subcelllular machineries that are shared by most organisms. (Select few might have lost them during evolution.) For example, ATP synthases feature in most organisms, and their structures have been pretty well conserved over the millions (billions?) of years.",
"Hopefully this answered the question."
] |
[
"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 ancestor lived, and then quickly died out in the cataclysms of our planet.",
"However life hasn't started multiple times \"in our history\". History refers to the period of time when humans have recorded the occurrence of events."
] |
[
"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; it is either a wide ",
" or a spreading ",
".",
"So the answer to your question is that the energy goes into the regions of constructive interference; those regions receive more energy than just the sum of what they would have had from each light source on their own. ",
"In the case of two coherent light sources, light amplitude oscillates from 0 (destructive) to 2x (constructive). Since energy is amplitude squared, that oscillates from 0 to 4x. So the math all works out."
] |
[
"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 the complete Magic School Bus series. Seriously. You would probably enjoy it yourself as it still came in helpful well into university."
] |
[
"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 though you can only go one dimension in time, you can change how fast you're going through it. You can do this by moving really fast in one of the other dimensions that you can go both ways in. But you have to go ",
" fast, as fast as light. Then you will slow down in the time dimension, which will make it look like the rest of the world is speeding up.",
"I'm really proud of that by the way. :)"
] |
[
"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 carefully go find them.",
"So I reckon you should sometimes respond \"I don't know, let's find out,\" then go on to reddit with him, or go to the library and get a book, or w/e."
] |
[
"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\" each other. But that's a technical point, macroscopically, it's easy to say when two things are touching and when they aren't."
] |
[
"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' malfunctions and the related that much more serious. It's hard to ship out a maintenance crew, which means that the people who live on Mars must either build everything they need or take it with them. And taking a lot of stuff with you on a multi-year trip makes it take longer and be more expensive.",
"Thirdly, there aren't a lot of natural resources [compared to what we expect on Earth]. Yes, there's plenty of rock. But no/little water, no trees/wood, no openly-visible mining deposits [for things like iron, coal, etc]. The Earth is relatively rich in natural and practical resources, Mars is not.",
"Fourth, it's expensive. It'll probably cost literally hundreds of billions of dollars to send any decently-sizable crew to Mars. And most 'investments' by corporations are much better spent buying a congressman or police force. More practical ROI, anyways.",
"So I don't see it happening anytime soon. We'll need to run into some serious overpopulation issues, or a war that threatens to eradicate all human life [not that improbable, actually]. But I doubt that expanding to Mars will really change that, it'll just add additional layers of segregation. I for one would love the opportunity to explore/expand, but my faith in humanity's motivations is lacking."
] |
[
"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 must be conserved. So as the particles collapse in on each other, the fall into a gravitational potential well. Gravitational potential energy is reduced, so this energy must go somewhere else... and it goes into heating the gas. Higher temperatures open up more possible modes which can contain energy, and thus increase the total number of microstates.",
"So overall, as gravity pulls particles together, the gravitational potential energy causes them to heat up. This heating must (at a minimum) keep the overall entropy constant."
] |
[
"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 attractor) which is gradually drawing gasses into a much more ordered system. ",
"not sure what you mean here. What is meant by Gaussian field of disorder particles and what is meant by changing the magnitude of your observation?",
"i guess the point of the question is if, as you say the overall entropy is constant, why do we have the idea that entropy is always increasing? does local entropic reversals like the formation of stars, or ecological processes start at some point to suggest perhaps these local reversals might be part of a larger cycling of entropy rather than a strictly one way process? ",
"The best case scenario is that entropy is constant (adiabatic and perfectly reversible). In reality, increasing entropy is what gives thermodynamic systems the \"push\" they need for a change to happen. For example, the only way you can have reversible heat transfer is if both thermal reservoirs are at the same temperature. But if two reservoirs are at identical temperatures, there will be no heat transfer. If they are at different temperatures, then the hotter reservoir's entropy will decrease by Q/T_hot and the cold reservoir's entropy will increase by Q/T_cold. The Q's must be the same (conservation of energy), and so the overall entropy must globally increase (T_hot>T_cold). This is the case for any process... no process can occur unless entropy increases globally (a perfectly reversible and adiabatic thermodynamic process cannot truly exist... you'd wait infinitely long to see any net change).",
"i guess another way to consider it is if the big bang created a large cloud of disordered particles why do we see more a more ordered universe? wouldn't constantly increasing entropy suggest that the early state of the universe would remain constant and disordered?",
"Which condition is more ordered: ",
"A cloud of particles at uniform temperature, which is macroscopically homogenous. ",
"A universe where there are (seemingly random) hot spots surrounded by cold vacuum, where the hot spots are orbiting each other, colliding with each other, and radiating energy (heat transfer) to the vacuum.",
"Certainly one could make the argument that our current universe is more disordered than a homogenous cloud."
] |
[
"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. Thermodynamics systems evolve in such a way that H is as small as possible (minimized). This means that at constant T, U wants to decrease, and S wants to increase to make H smaller. But sometimes, reducing the internal energy will decrease the entropy: this is the case for magnets, where aligning the molecules decreases internal energy but reduces entropy. If the temperature is low enough, this can happen (it's also why magnets fail at higher temperatures), because U is bigger than TS.",
"Anyway, that's my long winded explanation of why thermodynamic systems can sometimes behave in a way that appears to decrease entropy.",
"There was also a more exotic proposal recently that gravity is an emergent effect ",
" entropy."
] |
[
"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 article is pretty good."
] |
[
"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 single axis. Although this is true, I think it misses an important point, namely, conservation of ",
"angular momentum",
".",
"The key observation, I think, is that angular momentum-- a vector quantity that is conserved in an isolated system-- and angular ",
"-- the \"spin axis\"-- are not the same thing. Angular momentum is a product of moment of inertia and angular velocity.",
"For a sphere (e.g., a planet), the angular momentum and angular velocity are generally proportional; i.e., they point in the same direction, and thus the sphere spins around a fixed axis. The mathematical reason for this is that the moment of inertia (basically a matrix of values) does not depend on a particular spin axis.",
"But for a more irregularly-shaped object such as a small asteroid, this is not necessarily the case. For only a very precise initial \"spin\" of the asteroid does its angular momentum and angular velocity point in the same direction. For \"most\" initial conditions, they don't line up, and so for momentum to remain unchanged, angular velocity (i.e., the spin axis) ",
" to change. The result is \"tumbling.\""
] |
[
"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 theorem is of course true, it seems that \"tumbling\" is recognized by planetary scientists as referring to non-principal-axis rotation. Though the stated assumption in OP's question (that things can rotate about 2 axes) was incorrect, if you look at it as a question about non-principal-axis rotation then it makes sense. Thanks ",
"/u/conamara_chaos",
" and ",
"/u/possiblywrong",
" !",
"NEXT EDIT: OP has now clarified what he meant, rendering this answer less than useful. Y'all can stop upvoting me and upvote ",
"/u/jimbelk",
", ",
"/u/conamara_chaos",
", and ",
"/u/possiblywrong",
" instead. "
] |
[
"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 planets will cause this non-principal rotation vector to precess with time - hence the \"tumbling.\" (I recommend looking at some ",
"papers by D. J. Scheeres",
" if you want to learn more about tumbling asteroids.)",
"So why are stars and planets usually in principal axis rotation? My guess (I'm still learning more about rotational dynamics), is that it is because you can think about them as being fluid bodies, in (roughly) hydrostatic equilibrium. The rotation of the planet itself will deform the body, forming a tidal bulge which sets the principal axes. This differs from small bodies, like asteroids, which are (usually) thought of as rigid objects."
] |
[
"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 is ",
"additive",
" - that is, the baseline is black and as you add lights, the colors approach white.",
"Mixing paints together is ",
"subtractive",
" - that is, the baseline is white and as you add ink, the colors approach black.",
"This seems strange, but is actually quite logical. Look for similarities - in both color wheels, the rainbow follows its' usual order. The part that trips me up is why colors use the primary (RGB) while pigments use the secondary (CYM). Anyone have a good explanation for that part? (Edit for formatting)"
] |
[
"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 example, red is made as M + Y, which subtracts both green and blue from white, leaving red. This makes it easy for your laser printer to convert from the colours on your RGB monitor to similar-looking colours on paper."
] |
[
"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 space-time, rather than being a completely separate entity--it is as much a part of the universe you travel in as space is.",
"Thus, since space-time, which makes up all of the universe which we can interact with, was created in the big bang, time as we understand it would have come into existence along with it. That's not to say there was nothing \"before\" the big bang (we don't know for sure yet), but however you might try and understand that period, it was not likely \"time.\" We are, unfortunately, forced to describe the \"before\" using time-like terminology simply because that is how humans think and understand, given we exist in a universe with time."
] |
[
"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 but I seem to only be able to travel in one direction along my time axis.",
"Hang on, let me try again.",
"Nope, still going forward.",
"Why is that?"
] |
[
"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 other axes.",
"The most important thing to remember is that the speed of light is absolute in the universe in ",
" reference frames, regardless of your momentum, and is the ultimate speed limit in the universe (it takes infinite energy to accelerate anything with mass which is not already at the speed of light to the speed of light). It's possible to get really, really close to the speed of light, but really hard to get beyond that.",
"Now, accelerating through space causes time around you to pass slower (the line becomes longer to reach the same point on the time axis of the graph, if you will, because it is drawing a less direct line or curve). As you approach the speed of light, you are now moving at the maximum possible velocity in the universe, which corresponds to time passage being right around zero on the graph. In order to pass into the negative side of that axis on the graph (backwards in time), you would require velocity greater than the speed of light. Since you lack the impossible amount of energy necessary, you are unable to transcend that speed barrier, and are thus stuck moving forward along the positive side of the time axis."
] |
[
"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 metabolism of plants; it has no effect on the metabolism of humans and animals and therefore has a very strong safety profile, documented over the past 40 years and confirmed by multiple independent international agencies.",
"Ignoring all literature by Seralini, the Andrew Wakefield of GMO's, there is absolutely no empirical evidence substantiating your claims.",
"From ",
":",
"Reviews on the safety of glyphosate and Roundup herbicide that have been conducted by several regulatory agencies and scientific institutions worldwide have concluded that there is no indication of any human health concern. Nevertheless, questions regarding their safety are periodically raised. This review was undertaken to produce a current and comprehensive safety evaluation and risk assessment for humans. It includes assessments of glyphosate, its major breakdown product [aminomethylphosphonic acid (AMPA)], its Roundup formulations, and the predominant surfactant [polyethoxylated tallow amine (POEA)] used in Roundup formulations worldwide. The studies evaluated in this review included those performed for regulatory purposes as well as published research reports. The oral absorption of glyphosate and AMPA is low, and both materials are eliminated essentially unmetabolized. Dermal penetration studies with Roundup showed very low absorption. Experimental evidence has shown that neither glyphosate nor AMPA bioaccumulates in any animal tissue. No significant toxicity occurred in acute, subchronic, and chronic studies. Direct ocular exposure to the concentrated Roundup formulation can result in transient irritation, while normal spray dilutions cause, at most, only minimal effects. The genotoxicity data for glyphosate and Roundup were assessed using a weight-of-evidence approach and standard evaluation criteria. There was no convincing evidence for direct DNA damage in vitro or in vivo, and it was concluded that Roundup and its components do not pose a risk for the production of heritable/somatic mutations in humans. Multiple lifetime feeding studies have failed to demonstrate any tumorigenic potential for glyphosate. Accordingly, it was concluded that glyphosate is noncarcinogenic. Glyphosate, AMPA, and POEA were not teratogenic or developmentally toxic. There were no effects on fertility or reproductive parameters in two multigeneration reproduction studies with glyphosate. Likewise there were no adverse effects in reproductive tissues from animals treated with glyphosate, AMPA, or POEA in chronic and/or subchronic studies. Results from standard studies with these materials also failed to show any effects indicative of endocrine modulation. Therefore, it is concluded that the use of Roundup herbicide does not result in adverse effects on development, reproduction, or endocrine systems in humans and other mammals. For purposes of risk assessment, no-observed-adverse-effect levels (NOAELs) were identified for all subchronic, chronic, developmental, and reproduction studies with glyphosate, AMPA, and POEA. Margins-of-exposure for chronic risk were calculated for each compound by dividing the lowest applicable NOAEL by worst-case estimates of chronic exposure. Acute risks were assessed by comparison of oral LD50 values to estimated maximum acute human exposure. It was concluded that, under present and expected conditions of use, Roundup herbicide does not pose a health risk to humans."
] |
[
"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 metabolism of plants; it has no effect on the metabolism of humans and animals and therefore has a very strong safety profile, documented over the past 40 years and confirmed by multiple independent international agencies.",
"Ignoring all literature by Seralini, the Andrew Wakefield of GMO's, there is absolutely no empirical evidence substantiating your claims.",
"From ",
":",
"Reviews on the safety of glyphosate and Roundup herbicide that have been conducted by several regulatory agencies and scientific institutions worldwide have concluded that there is no indication of any human health concern. Nevertheless, questions regarding their safety are periodically raised. This review was undertaken to produce a current and comprehensive safety evaluation and risk assessment for humans. It includes assessments of glyphosate, its major breakdown product [aminomethylphosphonic acid (AMPA)], its Roundup formulations, and the predominant surfactant [polyethoxylated tallow amine (POEA)] used in Roundup formulations worldwide. The studies evaluated in this review included those performed for regulatory purposes as well as published research reports. The oral absorption of glyphosate and AMPA is low, and both materials are eliminated essentially unmetabolized. Dermal penetration studies with Roundup showed very low absorption. Experimental evidence has shown that neither glyphosate nor AMPA bioaccumulates in any animal tissue. No significant toxicity occurred in acute, subchronic, and chronic studies. Direct ocular exposure to the concentrated Roundup formulation can result in transient irritation, while normal spray dilutions cause, at most, only minimal effects. The genotoxicity data for glyphosate and Roundup were assessed using a weight-of-evidence approach and standard evaluation criteria. There was no convincing evidence for direct DNA damage in vitro or in vivo, and it was concluded that Roundup and its components do not pose a risk for the production of heritable/somatic mutations in humans. Multiple lifetime feeding studies have failed to demonstrate any tumorigenic potential for glyphosate. Accordingly, it was concluded that glyphosate is noncarcinogenic. Glyphosate, AMPA, and POEA were not teratogenic or developmentally toxic. There were no effects on fertility or reproductive parameters in two multigeneration reproduction studies with glyphosate. Likewise there were no adverse effects in reproductive tissues from animals treated with glyphosate, AMPA, or POEA in chronic and/or subchronic studies. Results from standard studies with these materials also failed to show any effects indicative of endocrine modulation. Therefore, it is concluded that the use of Roundup herbicide does not result in adverse effects on development, reproduction, or endocrine systems in humans and other mammals. For purposes of risk assessment, no-observed-adverse-effect levels (NOAELs) were identified for all subchronic, chronic, developmental, and reproduction studies with glyphosate, AMPA, and POEA. Margins-of-exposure for chronic risk were calculated for each compound by dividing the lowest applicable NOAEL by worst-case estimates of chronic exposure. Acute risks were assessed by comparison of oral LD50 values to estimated maximum acute human exposure. It was concluded that, under present and expected conditions of use, Roundup herbicide does not pose a health risk to humans."
] |
[
"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 recommended application) there is a slight but significant increase in some bacteria and fungal populations, but the effect is rather short-lived.",
"http://www.wssajournals.org/doi/abs/10.1614/0043-1745%282000%29048%5B0089%3AEOGOSM%5D2.0.CO%3B2",
"http://onlinelibrary.wiley.com/doi/10.1002/tox.2530070303/abstract",
"As far as the article from food integrity- well, they don't provide sources for their claims (at least not anywhere where it's easy to find them) which reminds me of the adage \"That which is claimed without evidence can be dismissed without evidence.\"",
"If you have any specific questions about the food integrity claims, I can dig around a bit and see what I can find."
] |
[
"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 much to be learned in the areas of the gut-brain and hormonal regulation of appetite. "
] |
[
"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.",
"Now for your question, you stop feeling hunger after a while without food. Try it yourself, if you don't eat for a day it's not that bad. ",
"James Cracknell ran Marathon Des Sables. In that race you have to carry all your food. He decided to eat only powder. After a few weeks on this he found out that he couldn't function on it, even if he consumed enough calories. In the end he had to change his plan."
] |
[
"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 seismographs. "
] |
[
"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 actually mostly circular and empty. Occasionally they manage to be actually wrong.",
"It is very important to emphasize that those who \"study\" this are not real physicists and that their titles are fakes appointed by the Resonance Institute itself, making this a full-fledged scam. This includes Haramein personally."
] |
[
"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",
" ",
"For more information regarding this and similar issues, please see the ",
"FAQ."
] |
[
"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 the big bang but it'd take hours of scrolling through specific things to find an answer to this specific question... and i'm sure there are plenty of bored physicists looking for a question like this to answer, and it would take like 3 minutes, so would it really hurt to let someone answer it? or for these automatic responses to at least offer some insight? there's plenty to read about the big bang within ask science, so many in fact that searching the keywords i would need to search makes it like finding a needle in a haystack. ",
"just seems like the whole point of ask science is for people to get immediate answers to curiosities and for scientists who enjoy helping the layman, so the layman doesn't have to read a textbook to figure it out. not everything is going to be some groundbreaking unheard-of question. "
] |
[
"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 in periodic waves from a source and traveling to a receiver, a distance ",
" away. If there is no relative motion and no expansion of space, then the time it takes a wave to travel from the source to the receiver is the distance divided by the speed, ",
". Each wave takes the same time to reach the receiver, so waves arrive at the same rate that they are emitted.",
"However, if the space in between the source and the receiver is expanding with time, then the distance each wave must travel to reach the receiver is continually increasing. The first wave will have to travel less distance than the second wave, which will have to travel less distance than the third wave, and so on. Consequently, each wave will take a little longer to cover the distance from the source to the receiver than the previous wave. This means the waves will arrive with a greater spacing in time than the spacing with which they were emitted. In a classical interpretation, the wavelength has increased and the frequency has decreased. In a quantum interpretation, the energy of each photon is reduced. In other words, red-shift has occurred.",
"On very large scales (e.g., between galaxies), this red-shift is large enough to be detectable, because the distance between galaxies is increasing the whole time the light is traveling."
] |
[
"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 \"small\" point. If you keep shrinking infinite space down smaller and smaller, it is still infinite just tightly packed.... it never reaches a \"point\" or defined area.",
"The big bang happened \"everywhere\" at once."
] |
[
"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 question. Science is concerned with building useful and effective models of reality, not so much with trying to reason out why these models are the way they are."
] |
[
"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 continue moving in that direction at that speed forever (one of Newton's laws). Entities with enough mass have this ability to warp those geodesic lines toward themselves, essentially directing anything traveling along the line towards themselves as well. The capacity of the mass to force these lines to bend towards itself is called it's gravity. For the visual thinkers, imagine one of the cubes of the lattice had a star in the middle of it. This star's mass/gravity would cause the \"walls\" and edges of the cube around it (space-time fabric) to all bow inward kinda like a square trampoline with a bowling ball in the middle. Anything traveling along one of those edges would be directed toward the star, if not at the the star, and at an accelerating rate proportional to the mass of that star and the object's distance from it (assuming the object is relatively small, else we'd also have to factor in its mass's influence on the star). Hope this helps a little."
] |
[
"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 up' to a wave that sounds louder than the individuals that it was made from. The 'warble' you hear is caused by you not being perfectly in sync with the machine sound, you can modulate the 'warble' by slightly raising or lowering your own pitch.",
"The opposite is called 'destructive interference', when two waves of similar frequency and opposite phase meet. The resulting wave is quieter than either of the individuals that made it up, and is the basis for noise-canceling headsets and some car mufflers.",
"A good example is when two people sing the same note. The resulting sound is louder than either individual, and 'richer' because the characteristics of their voices combine into something we interpret as better sounding than either alone.",
"e: spelling"
] |
[
"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 than me to implement though :D"
] |
[
"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 difficult to achieve, because it is difficult to shift circadian rhythms to align with night-shift work and difficult to avoid light exposure during the daytime.",
"The pineal gland receives signals from the brain's circadian pacemaker (the suprachiasmatic nucleus), which itself receives signals from the retina. When the circadian pacemaker enters its biological night phase, it tells the pineal gland to start releasing melatonin. This signal is terminated if the circadian pacemaker starts receiving light signals from the retina. For example, if you switch on a light during the night, ",
"you will temporarily suppress melatonin release",
", which will then ramp back up again once you turn off the light.",
"Note that even in total darkness, the pineal gland does ",
" release melatonin during the biological day. Both the above two conditions must be satisfied.",
"Now what do I mean by the \"biological night\" exactly? I mean when your circadian pacemaker perceives that it is time for your to be asleep. The timing of the circadian pacemaker's rhythm is determined largely by your daily sleep/wake and associated light/dark schedule, although there are also significant inter-individual differences and changes with age. ",
"In an individual who is regularly sleeping at the same time at night and working a day-shift, the biological night and the actual night will coincide. This is good in terms of melatonin release, because it's naturally dark during the biological night, although of course we can still mess with this using artificial light.",
"Individuals who work night-shifts are exposed to a very different light pattern, which affects circadian timing. However, most night-shift workers do not fully adapt their circadian rhythm, because it requires ",
"very careful avoidance of the natural light/dark cycle",
" (which is a strong synchronizer of the circadian rhythm) and maintaining shift-work schedules even on days off.",
"In individuals who are able to fully shift their circadian rhythms to align with their night-shift schedules and block out natural and artificial light during their own biological night (during the daytime), melatonin release occurs as normal during the daytime, helping to promote sleep during the daytime.",
"But for most shift-workers, there is only partial shifting of circadian rhythms and significant exposure to light during the biological night, due either to the biological night partially overlapping the work schedule or due to receiving exposure to natural light during the daytime.",
"source"
] |
[
"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 following activities, is associated with greatly reduced impairment of the circadian rhythm during night shifts:[12] .",
"Intermittent bright light pulses during night shifts",
"In one study of rotating shift-work female nurses suffering from clinical insomnia, higher intensity and briefer duration of bright light exposure during the first half of their evening/night shift, with a daytime darkness procedure, improved their insomnia, anxiety and depression.[12] \nCircadian realignment has not yet been associated with a reduction in the long-term effects of shift work. ",
"source"
] |
[
"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, in individuals who are tetraplegic, the connection between the suprachiasmatic nucleus and the pineal gland is severed, so the pineal gland never receives the signal to release melatonin. In these individuals, melatonin levels are ",
" low, yet they sleep a normal amount; sleep quality is slightly lower, but that could be as much to do with the injury as melatonin.",
"Second, the amount of melatonin suppression depends on the brightness and the color of the light. Typical room light suppresses up to about 50% of melatonin release. When you are sleeping, only a fraction of this light will reach the retina due to filtering by the eyelids or due to orienting your body to face a darker part of the room."
] |
[
"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 high potential induces dielectric breakdown in the air) or currents sufficient to cause flash heating.",
"It's possible to create metal objects which can be microwaved safely; you'll see inserts in some combination microwave/grills, for example. It depends on the geometry of the object and the particular characteristics of the individual microwave. Experimenting is probably not a good idea."
] |
[
"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 aluminium foil or similar causes the same effect.",
"Meanwhile, very thin metal films (a common demonstration uses an optical disk) are very vulnerable to having eddy currents induced and heating up dramatically, since the electrical resistance is fairly high due to the thinness. Aluminium foil is usually too thick for this effect, and as long as it isn't crumpled or folded can actually be microwaved fairly safely."
] |
[
"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 malaria infected mosquito feeds off of a pig or a cow instead of a human the mosquito will be fine, but the parasite won't reproduce in the host. The trypanosomes responsible for sleeping sickness are similarly restricted to human hosts, so it seems."
] |
[
"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 a nuisance pest.",
"Human lice (Pediculus humanus) / Pubic lice (Pthirus pubis) are both obligate human parasites. Lice in general are very specialized and tend to evolve along with their hosts, their phylogeny tends to mirror the phylogeny of their host. The body louse can transmit disease but as far as I know the Pubic louse is just a nuisance."
] |
[
"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 put substantial effort into a global eradication campaign that is on the verge of declaring success. President Carter himself made light of his own health problem due to cancer by expressing a desire to outlive this disease. "
] |
[
"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 natural gas is constantly being created deep underground, the rate is far too slow to be renewed within the shortness of a human lifetime. So really what is meant by nonrenewable resource is something that can't be grown and regenerated regularly such as fossil fuels, diamonds, lithium, etc"
] |
[
"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 you would ultimately gain by doing so. Look up Maxwell's demon - it's a fascinating topic. There's still quite a bit of debate as to where the asymmetry comes from - we're not quite sure why given laws of physics that ought to be time reversible, we end up with an arrow of time. But the fact of the matter is, entropy is always increasing.",
"There's a sense in which the problem is actually the other way around: no resource is truly renewable (though some can be renewed for longer than others)."
] |
[
"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 oscillations you can track the passage of time. Commercial quartz oscillators have an error of at most a second every few days. This isn't nearly as accurate as the cesium-based atomic clocks, but it's sufficient.",
"In computers, the RTC remains powered when the computer is turned off or even when the computer is disconnected from power. There's a small battery on the motherboard that provides power to the RTC to allow it operate continuously. Modern computers can use internet time servers to synchronize their clocks, mitigating the small deviations in the RTC.",
"Computer software can read the value of the RTC to obtain the time. Usually the operating system throws in an abstraction layer so applications don't directly communicate with the RTC, but instead with the operating system, which means that the software developer doesn't need to know the implementation details of the RTC, but can rely on the operating system to handle this."
] |
[
"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 energy of its own. If you catch the liquid right when it hits the freezing point, but before it accumulated that little bit if extra energy, a little movement will fuel the process."
] |
[
"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-ocean ridges or subduction zones."
] |
[
"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 C, C++, and Fortran, and things like CUDA/OpenCL on GPUs. There's lots of reasons assembly isn't used.",
"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.",
"Scientific software can be rather complex. As an example from my work, I typically run on somewhere between 10 to 1000 CPU cores, but similar work scales as large as the largest HPC resources available. The codes I write typically consist of around 10,000 to 100,000 lines of C++. This means the software itself is really pretty damn complex, and managing that level of software complexity is extraordinarily difficult, meaning that doing it in assembly is a pretty crazy undertaking. Making sure everything works is difficult in high level code, let alone assembly.",
"Raw optimal performance in terms of code efficiency almost always is less important than algorithmic performance. I can write a better algorithm in python that solves a problem faster than the most efficient assembly code that's using a worse algorithm.",
"I'm a scientist by trade and education, but only a software engineer by necessity. You're operating under the assumption that people like me could actually write assembly code that is more efficient than what an optimizing compiler can produce from higher level code. It's highly unlikely that I would actually produce faster code using assembly than my compiler produces, while also being able to accomplish all the complex tasks it needs to. It's also highly unlikely I can write resource management utilities for thousands of nodes that is superior to what is available, and even less likely that I can craft the network communication routines necessary for parallel computing.",
"I should add that it is very common to use libraries for computationally-intensive tasks such as linear algebra, and these libraries have been optimized by vendors using low level code (see Intel MKL, for example). But for computational scientists, these things are basically black boxes."
] |
[
"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 performance can be significantly improved by careful refactoring of the code. "
] |
[
"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 is been released in the small amount of time when it hits the planet.",
"I believe some more modern weapons are kinetic. They contain no explosive payload. Just enough mass and velocity to destroy the target."
] |
[
"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 is hundreds of kilometers -- it has about the same opacity as Earth's atmosphere. ",
"The material at the photosphere scatters light through all the other processes that work everywhere else in the cosmos -- Rayleigh scattering (scattering of light by electric polarization of molecules, atoms, or ions), Thomson scattering (direct scattering of light by electrons that are jiggled by the incoming wave's electric field), and absorption/re-emission of spectral lines by atoms. It's certainly possible to illuminate the photosphere with a bright external beam - but the scattered light would have to be comparably bright to the Sun itself, which is no mean feat. ",
"That very project (illuminating the Sun) has been done in the radio band -- people have bounced radar pulses off the Sun itself. Coherent emission is very easy in radio: if you happen to be inside the beam of the NORAD radar curtain, and looking in its particularly narrow frequency band, Earth is the brightest known object in the galaxy.",
"The universal \"rays\" in renderings of the Sun are not actually meant to represent (as some say) the solar corona, or anything else happening on or around the Sun itself. They represent stray light in the viewer's eye, just like the \"halo\" around a lit candle is stray light in the human eye."
] |
[
"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 do not do stellar physics however so it is not exactly my area of expertise. Maybe someone in the field could fill in with some information on ongoing research?"
] |
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