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[
"Why does water make a buzzing sound right before it begins to boil?"
] |
[
false
] |
[deleted]
|
[
"Could you elaborate? I've never noticed this. It may be coming from the pot that you are boiling the water in, since the metal in the pot is expanding a bit as it heats up."
] |
[
"Agreed. Boiling water over a bunsen burner in a glass beaker makes no such sound."
] |
[
"Are you sure it's the water and not the heating apparatus, especially if it's electrical. "
] |
[
"What particles emitted by the Sun pass directly through the Earth as if it (Earth) wasn't there?"
] |
[
false
] | null |
[
"Neutrinos."
] |
[
"I guess you win the award for most accurate and succinct answer to any question in this sub.",
"Fun facts about ",
"neutrinos",
". They come in 3 tasty flavors (electron, muon, tau) and each has a different but immeasurably small mass (meaning we still don't know what they are), which means they're almost always moving very near the speed of light.",
"They're formed in the Sun as a byproduct of the nuclear reactions. They have such a tiny cross-section for interaction that they're ",
" impossible to detect (i.e. having to travel through several light years of solid lead before there's a 50% chance of one scattering off any of the atoms).",
"If you build a careful enough detector, you can measure some of them though. The first time they did this, they only measured 1/3 as many neutrinos as the theory was predicting: called the ",
"solar neutrino problem",
" which stumped people for a couple decades. The current solution is known as ",
"neutrino oscillation",
", which lets the neutrinos change flavors. Because the early experiments were set up to only detect the electron neutrinos, if by the time they reach Earth they had changed into the other two flavors, the number of electron neutrinos would be 1/3 of the expected number without allowing flavor changes."
] |
[
"they're almost impossible to detect ",
"Because they're not impossible to detect! ",
"/u/astrocubs",
" even gave the example of the experiment that first detected them. The key is that even though they are incredibly unlikely to interact with anything, there are also a ",
" of them. Roughly 100 trillion pass through your body every single second!"
] |
[
"The atomic bombs that were dropped on Japan in WW2 were huge. How small could modern science make bombs of the same yield?"
] |
[
false
] | null |
[
"Modern designs are probably highly classified."
] |
[
"Im sure they are. But what is theoretically possible is what I am asking. What limited the bombs to the size they were and how small could we make those components now? "
] |
[
"/u/RobusEtCeleritas",
" is correct that designs and often even the shape of weapons components are classified to prevent giving away how the weapons work. ",
"However, we can set a lower bound: If you are a nation with an advanced nuclear weapons program, sufficient infrastructure and are interested in building the absolute smallest weapon possible, then you need at a minimum, around five kilograms of plutonium-239. This equates to about the size of an American baseball.",
"Keep in mind you'd still need conventional explosives, reflectors and other physics package components to successfully initiate your miniature weapon, so your actual size is somewhat larger than just the baseball-sized sphere of plutonium.",
"Also, just because you have the absolute minimum sized device, doesn't mean that it is suitable for your particular needs, only that it is the epitome of nuclear miniaturization.",
"The USA developed some small nuclear weapons to defend the ",
"Fulda Gap",
" in Germany and potentially some sites in Asia during the Cold War.",
"Davy Crockett, tactical nuclear gun",
"Nuclear land mines"
] |
[
"Is there such a thing \"oversleeping?\" Is there really a perfect number for hour-to-sleep?"
] |
[
false
] |
What's the science behind statements like "too much sleep is bad for you?" Is there really such a thing as "oversleeping" Also, there seems to be a lot of studies suggesting that there is a perfect number of hours to sleep (usually suggesting its somewhere between 6 and 9). What's the deal with that, and why do people think that such a number even exists? There seems to be a lot of pseudoscience around sleep, so I'm hoping the experts here can clear things up :)
|
[
"I am not an expert but I have a family friend who is. I have tried to find the research papers that he has described to me, but failed, so you should believe any responses that have research papers to back them up instead of mine. According to this sleep researcher, you cannot sleep too much unless you are clinically depressed. Sleep studies found that people who were forced to stay in their bed for up to 13 hours a night with the lights off and no distractions would sleep several extra hours, then eventually sleep around 8 and 1/2 hours and be happier, healthier people. They have validated this study a number of times and found that people cannot sleep too much and they are simply catching up from lost sleep (again, unless they are clinically depressed).",
"Sleep studies have consistently found that people sleep on average around 8 and 1/4 to 8 and 1/2 hours a night when they made up for any sleep deprivation. They also found that when people weren't allowed to sleep this much, their abilities in mental activities or activities involving reactions got worse for every night that they lost sleep (I believe that as little as 1/2 hour of sleep can make a statistically significant difference). The only problem with this research might be a selection bias in the people who are willing to participate in sleep research and sleep in a research lab."
] |
[
" The abstract conclusion states",
":)"
] |
[
"There are multiple papers that I've seen that shows that sleeping more than 8 hours a night is ",
"detrimental to your health",
". Just googling something like 'average sleep death rate' turns up other corroborating sources. "
] |
[
"Where is energy stored in the human body for short term use?"
] |
[
false
] |
As I was finishing a jog the other day, I was wondering where all the energy to do intense physical activity is stored. Is it mostly in the blood in the form of glucose? That seems like a lot of energy for just blood sugar. I remember that the liver stores glucose but it's been a long time since I've taken a biology class and I can't remember much. Also I know that fat buildup is energy reserved over a long period of time, but ultra-marathoners and the like are all very skinny looking so I get the feeling that that isn't it.
|
[
"The body stores a polymerized form of glucose called ",
"glycogen",
" in the liver and the muscles. When the blood glucose level drops, the glycogen can be broken down into glucose and used."
] |
[
"Glycogen is not doing all the work when you jog. There is a misconception that when you do low level activity, you only burn one fuel source and when you start doing intensity activity you switch to another fuel source. All sources are being used (fat, protein, carbs) it's the proportions that are different during various activities."
] |
[
"Individual cells produce ATP (usable energy for our bodies) from glucose (obviously from what we ingest) in the mitochondria. My understanding is that this is a continual process, and the difference between running for 45 minutes at a constant jog and standing still for 45 minutes isn't that enormous for our bodies to dip into any type of stored energy (unless you're malnutritioned, in which case it begins to burn calories stored in fat and muscle).",
"This is just a guess, so don't take my word for it (haven't taken biology in many years, but have a basic understanding of biological functions)"
] |
[
"Why supermassive black holes have low density?"
] |
[
false
] |
From a Wikipedia article about the Shwartzchild radius: supermassive black holes have low densities. The average density of a supermassive black hole can be less than the density of water This is very surprising to me, my idea of a black hole reguardless of its mass is that it is a dense thing. Can anyone explain where I'm wrong?
|
[
"Here the density is defined as the mass of the black hole divided by the volume contained within the Schwarzschild radius. The radius increases in proportion with the mass, so the volume increases as the cube of the mass, so the density goes as mass over mass cubed, which is the negative-two power of mass.",
"However, it's not clear whether this average density is a meaningful physical concept.",
"White dwarves are even weirder: the heavier they get, the smaller their radius gets. "
] |
[
"The size of a black hole is defined by the mass, and by the diameter of its event horizon which, for supermassive holes, is very large, and encompasses a lot of empty space. So, if you take the total mass, and divide by the total volume to get density, it is quite low. However, this is misleading (and confusing). It's like getting the average density of a 2-liter pop bottle that is mostly empty, but has a little bit of lead in the bottom."
] |
[
"As an extreme example, if you compressed all the mass in the observable universe into a point, the Schwarzschild radius would be very nearly the size of the observable universe.",
"It is ",
"unclear if that is significant or not",
" but it certainly ",
" profound."
] |
[
"[Biology] Why do human babies take so long to become capable of many activities, while animals do it very quickly?"
] |
[
false
] | null |
[
"\"Animals\" don't really \"do it quickly\". In fact there is quite a vast gradient. If you imagine two main ways of being born.",
"\n1. You develop quickly we will call this precocious",
"\n2. You are useless. We will call this altricial. ",
"In both ways there are many driving evolutionary factors that impact whether an animal is precocious or altricial: phylogeny, resources, predators, sociality, age of sexual maturation and other life history factors. Hoofstock are good examples of precocious animals. They are readily preyed upon and are often on their feet, sometimes within a day or two. Birds are an example of an altricial animal in that they are usually fairly useless at birth and they mother for a longer period of time. This is grossly over simplified as there is much variation, but you get the point. ",
"You'll find on this gradient the more altricial the animal the more parental investment that takes place. If animal mothers for a longer period of time it takes immense resources to do so. It gets quite complicated when we look at all animals because there is a huge gradient among species. Within birds reasons for altricial vs precociousness varies. Within mammals the ",
" trend is that larger animals are more precocious as they are larger bodied, are longer lived and less preyed upon. But, once again this varies depending upon the animals niche. ",
"The rabbit hole is actually deeper if you consider R/K selection:",
"I just pulled this from Wikipedia-",
"\nmature rapidly and have an early age of first reproduction",
"\nhave a relatively short lifespan",
"\nhave a large number of offspring at a time, and few reproductive events",
"\nhave a high mortality rate and a low offspring survival rate",
"\nhave minimal parental care/investment ",
"\nmature more slowly and have a later age of first reproduction",
"\nhave a longer lifespan",
"\nhave few offspring at a time and more reproductive events spread out over a longer span of time",
"\nhave a low mortality rate and a high offspring survival rate",
"\nhave high parental investment ",
"The reason I bring this up is because it is another way to examine the answer to your question. \nSo if you were to examine what I've told you so far you would come up with the solution that humans are K -Selected Altricial. This is an important frame of reference. Among the primate order most primates fit into a different category in that they are MORE precocious than us. They still have quite a bit of parental investment though. I could talk about the variation between primates, but I'm going to skip to apes. ",
"Humans are quite unique in that we have such large brains, and our babies are utterly useless. They can't even hold their heads up! Well, our brains are actually larger than any other animal in the animal kingdom relative to body size, yet our gestation is almost the same as other apes. For apes much of their neurological development happens outside the mother. We likely used to be as precocious as other apes, but we made a tradeoff in the name of an increased repertoire of flexible behaviors. It is also likely a result as a reduction in predators and a reduction in hair. Many young primates cling to their mother as a means of holding on. With our loss of hair this made it quite difficult for us to cling to our mothers. (Though I can't think of it now, I feel like I read a really good article about how a human baby's grip is still rather strong) There are many many other factors and this is a quite brief overview, but I hope this helps! ",
"Edit:fixed typos. I shouldn't post at 4 am. "
] |
[
"Bigger brain must be relative to size thats why whales and elephants have different skills than chimps"
] |
[
"Bigger brain must be relative to size thats why whales and elephants have different skills than chimps"
] |
[
"What does space-time bend respective to?"
] |
[
false
] |
I typically see models like but what about the space-time above? Or even the space-time outside the planet, if there is no matter in between to bend it into a bubble is it thought of as a 2d plane?
|
[
"Spacetime does not bend respective to anything. Curvature is an intrinsic property that can be measured from within a space without making any reference to an embedding of the space in something else.",
"In the most fundamental sense, curvature is a measurement of how much a vector moving around a closed loop will change when it comes back to its starting point. In flat space, it does not change at all (you can move an arrow around without turning in flat space and it will always point in the same direction). If you imagine a vector on a sphere, this is not true anymore: start with a vector pointing anywhere at the North pole, go down to the Equator, move along the equator and then back up to the North Pole and you'll see that your vector has turned compared to its original direction! In this sense, someone living in a 2D sphere does not need any 3D information to realize they live in a curved space. It's just a matter of moving arrow around."
] |
[
"This",
" is a better representation of the curvature of space-time; or to be more specific, the curvature of space. Space is 3-dimensional, to to see its curvature we need a 3D grid rather than a flat plane.",
"No no no no no no please stop.",
"Spacetime is 4-dimensional. It has 4-dimensional curvature. You cannot visualize this with a grid, it means nothing. Gravitation is the consequence not of the space-space components of curvature, but of the time-space curvature."
] |
[
"This",
" is a better representation of the curvature of space-time; or to be more specific, the curvature of space. Space is 3-dimensional, to to see its curvature we need a 3D grid rather than a flat plane.",
"Secondly, these visualizations are only analogous to the actual space-time curvature. We cannot draw the actual curvature of space-time, because we exist within it (and drawing time in a still image is difficult to imagine)! ",
"These sorts of images are only intended to give a conceptual idea of the phenomenon. They are not accurate representations of the true curvature of space-time."
] |
[
"Are electromagnic wavelengths limited ?"
] |
[
false
] |
Are there bounds ? Or is it theoretically possible to create waves at a frequency that we can currently not detect at all ?
|
[
"There is no known limit. Our current understanding is that photons can have arbitrarily long or short wavelengths. That said, it is suspected that there is probably some limit (far beyond our capability to produce them) for wavelengths approaching the ",
"Planck length",
", basically because if we ever try to measure a wavelength that small, it would require an energy density high enough to create a black hole. It is believed that space-time itself is probably pretty gooey at that distance scale because of quantum effects."
] |
[
"The only bound on electromagnetic radiation is whether there is enough energy to create one photon of light at the frequency specified. The energy content of one photon is given by E=hv, where h is Plank's constant (6.64x10",
" Js) and v is the frequency.",
"Whether we have the technology to produce high energy light however is a different issue, as most light from x-ray's and beyond are produced by nuclear processes."
] |
[
"Could there possible a way to transform the wavelength artificially ? I mean, maybe SETI just can't find anything because there are way more efficient ways of communication which we can not access yet. Or is that as unlikely as moving faster than light ?"
] |
[
"Can you approach a black hole from any dimension and experience the same result?"
] |
[
false
] |
I don't mean as a human, but as an observer that doesn't affect the stability of the black hole.
|
[
"What do you mean from any dimension? Do you mean from any direction?",
"If the black hole isn't spinning very fast then yes. If it's spinning fast enough it depends on your direction relative to its equator."
] |
[
"Yes, I suppose I mean direction. I think a common misconception is that a black hole is shaped like hole in the ground...a 2D surface with hole protruding normal to the surface. This is clearly incorrect, right?"
] |
[
"This would be correct in a 2D world. It's just much harder to draw in 3D.",
"A black hole is generally spherical. If it's rotating very fast, it can be a bit flattened but it's still 3D."
] |
[
"How do you measure what force is stronger?"
] |
[
false
] |
I've read about how electricity is a billion-billion-billion-billion times stronger than gravity. How can you make such a judgment when each is dependent on the amount of mass or charge and not some common factor?
|
[
"The charge/mass ratio of the proton is fixed, so if you take two protons, you can (in principle) measure both the gravitational and electromagnetic interactions, and when you do so, you'll find that electromagnetism is ~ 10",
" times stronger.",
"More practically, consider the fact that a refrigerator magnet that weighs perhaps an ounce can overcome the pull of gravity from all 6 million million million million kilograms of the earth."
] |
[
"This comes from dimensionless natural numbers known as coupling constants. In E&M this number is roughly 1/137, for gravity its something like 10"
] |
[
"You can illustrate this with an even more banal statement: Your arm does not fall off. Why is that? it's because the electrical forces in the chemical bonds that hold the atoms in your arm attached to the atoms in your body are so much stronger than gravity."
] |
[
"Since all our mitochondria (and therefore its DNA) comes from the mother, does that mean we are more genetically similar to our mothers than our fathers?"
] |
[
false
] | null |
[
"Yes, you could say that. However, as the mitochondrial genome is about 16,000 bases long compared to the about 3 billion you get from each of your parents, that's not going to be the deciding factor in which of your parents bestows you the most DNA. ",
"That will probably come down to whether you're a male (in which case you have been given a small Y-chromosome from your father and a big X-chromosome from your mother) and which small insertions, deletions and/or copy number variants each of your parents have."
] |
[
"Gobbedyret:",
"a small Y-chromosome from your father \nand \na big X-chromosome from your mother.",
"Warning: talking sex-determination, both come from father.\nBetter say: the father gives less genetic information to a boy than a girl because Y is smaller than X."
] |
[
"The difference is miniscule, and since the mitochondrial genome only codes for genes used within the mitochondria themselves, it's unlikely to have any noticeable effect on the final phenotypes. Unless you have an inherited mitochondrial disease, of course."
] |
[
"Why is expansion work by the gas in thermodynamics sometimes considered positive and sometimes negative?"
] |
[
false
] |
[deleted]
|
[
"The sign depends on who is getting the energy. In the expansion process, the energy of the piston is decreased and moved elsewhere, perhaps raising a weight or compressing a spring, thus the piston has a negative energy change. Conversely the expansion causes a positive energy change to the weight being lifted.",
"Different textbooks will use different sign conventions, so sometimes you'll see, ",
"dW = -PdV (+ 1st law)",
"or, ",
"dW = PdV (- 1st law)",
"It doesn't matter which you use as long as you are consistent and use don't change conventions. The important part is someone loses energy and somebody gains it as energy is conserved. If you're stuck and can't think of which sign convention is being used, draw a flow chart of where the energy is leaving and where is it going, then compare to the equations given and it should become obvious which convention is used. ",
"negative sign in that equation is in springs",
"This is also a convention, but it is a bit more layered (as F = -kx always holds true), forces are defined as the negative gradient (F = -dU/dx) of a potential energy. We could in principle defined them as the positive gradient, but then our potential energy would have to be defined as negative to compensate and keep the force opposing the compression or stretching. Ultimately it doesn't matter which convention is used (but ",
" uses the positive form) as long as springs don't loose energy if you compress them."
] |
[
"In regards to:",
"Different textbooks will use different sign conventions ... It doesn't matter which you use as long as you are consistent ",
"I believe the key phrasing is either work \"on the system\" or \"by the system.\"",
"The way its presented in texts is always confusing, I'd say. Clarity only comes from mastery of the concepts.",
"Advice for OP: ask yourself, is dQ, dW, as presented in this example, going to raise or lower U? Then treat signs so as to affect the appropriate change in U."
] |
[
"That looks correct. Where Q is positive heat supplied to the gas by the surroundings.",
"It is often required of you to decide the sign of dQ. If the surroundings have a lower T than the system, Q will flow out. If not, Q will flow in. "
] |
[
"What is the explanation for the fact that most cells are small and have cell membranes with many convolutions?"
] |
[
false
] |
I am not entirely sure if I can give anymore knowledge on the subject other than the semipermeable membrane may or may not have something to do with it. Thanks in advance for any help.
|
[
"Stuff moves in/out of the cell via the cell membrane. More cell membrane = more stuff able to move in/out. For cells of increasing size, the cell membrane size grows as the surface area (A = 4 pi r",
" but the cell volume grows faster (V = 4/3 pi r",
" "
] |
[
"In addition, various protein structures are often found outside the cell membrane (known as the extracellular matrix) in eukaryotic cells. Especially those in more complex, multi-cellular lifeforms, like people and fish. That means there needs to be enough surface area to echange water, food, wastes and still have room for those protruding protein structures, as well as any specialized structures a specific cell may have, such as ganglia or scilia."
] |
[
"To elaborate on this a little bit, more cell volume=more \"cell\" you have to feed. So, since volume grows faster than surface area, you reach a point where the surface area can't supply enough food to feed the volume of the cell. This limits cells to being pretty small."
] |
[
"How do cells know when to stop multiplying?"
] |
[
false
] |
As the first cells that make up an organ begin to multiply, and without a "director" telling the cells "enough is enough", how do they finally know when to stop?
|
[
"Typically during cell division, you also establish the fate of the resulting daughter cells. Typically what you'll have is one cell remains in a pluripotent (stem cell) state, whereas the other daughter cell differentiates into a cell type that will undergo a set differentiation and proliferation program that will produce a set number of differentiated cells. This is called \"asymmetrical cell division\" and is the result of either differential subcellular distribution of proteins and RNAs (e.g. PAR proteins or cadherins) or through competitive signal repression between daughter cells.",
"This gets even more complicated in that there sometimes ARE \"directors\" (we call them signaling centers or organizers) which are separate populations of cells that produce signaling molecules that spread through groups of cells and tell them to turn into specific sorts of tissues."
] |
[
"The complete answer is likely vastly complicated, since development is a time of many and complex intercellular and intracellular signalling. Even more confounding is that different cell types in different areas will be more sensitive, less sensitive, or completely insensitive to a particular stimulus. Thus, a sweeping generality is elusive.",
"However, I think that the generic ",
"formation of digits",
" is a sufficient example. The general rule for the behavior of cells in development: Location, location, location. In ",
"this case",
" apoptosis (cell death) is the default state, and the bone morphogenetic proteins (BMPs) responsible for beginning the signal cascade to cause cell death must be repressed in order to preserve the cell. If a cell receives a signal to upregulate (or more likely doesn't receive a signal to downregulate) BMP activity, which is almost certainly a location-dependent event, the cell will undergo programmed cell death.",
"tl;dr Cells are programmed to die by default, but the chemical signals unique to specific locations can repress that programming."
] |
[
"I'm going to look into the formation of digits. It seems like it may answer a lot of my questions. Thanks!"
] |
[
"After looking at various photos I am wondering; are there stars scattered around between galaxies, or is it completely empty in area between them?(in other words, are they all drawn in by gravity towards different galaxies)"
] |
[
false
] |
see here : it looks like there are a few stars in front of Messier 31, but they may be other smaller galaxies. And I think that the lights in the back are mostly other galaxies too. Far far away.
|
[
"Stars form",
" only in (relatively) high density regions that are not found outside of galaxies. So, more or less, all stars are inside galaxies.",
"However, sometimes because of the weird non-linear dynamics, stars can get flung out of the planes of ",
"spiral galaxies",
" (I don't know if this exists in ellipticals). These are refered to also as ",
" stars. But they are rare.",
"Finally, if you are looking at the sky, ",
" of the stars you see are inside the plane of the Milky Way galaxy. Also all the fuzzy blobs, being non-stellar objects are mostly within our galaxy. Only the following objects in the sky (as far as I remember) are actually outside the Milky Way (but they are close): the ",
"Magellanic Clouds",
" and ",
"Andromeda galaxy",
"."
] |
[
"rouge",
"rogue"
] |
[
"ivenoneoftheanswers's answer is pretty thorough and clear. There are some other ",
"stars in between galaxies, and there are some photos of them here",
". But they are very, very rare, and nearly all stars are found in galaxies."
] |
[
"A friend posted this \"fact\" about gravity on Facebook. Is this true?"
] |
[
true
] |
[deleted]
|
[
"Due to the fact that gravity travels the speed of light, and that the sun is in relative motion with the galaxy and everything, we don't actually orbit the sun. We orbit where the sun WAS 8 minutes ago.",
"This one is actually a lot of fun (or maybe not fun, depending on who you ask). ",
"No gravitational influence can propagate faster than the speed of light [1], ",
" the Earth orbits where the sun is ",
"!",
"The person who wrote what was on the facebook page was probably thinking of Newtonian gravity, like you learn in high school. In Newtonian gravity, you are pulled to where an object is exactly at that moment. So naively, you might think that with special relativity saying that nothing can exceed the speed of light, the way to correct Newtonian gravity might be to just introduce a delay and say that things are pulled to where the sun ",
" 8 minutes ago.",
"But this is not correct. Newtonian gravity does not work in special relativity. It is only an approximation that works when everything is moving very slow, and isn't exceptionally dense. ",
"Instead, Newton's Law of Gravitation is replaced by the demonically complicated Einstein Field Equations. These things are a horrible mess to solve.",
"One feature of the Einstein Field Equations is that they don't just depend on where a mass (or equivalently energy density) is, they also depend on the velocity of the object.",
"If you work out the effect of the velocity of the sun on the Einstein Field Equations (or actually a somewhat different but more calculable situation [2] ), you will find that the gravitational influence actually pulls the Earth to where the sun is going to be when the influence arrives at the Earth. So to a good approximation, the Earth orbits where the sun is at present.",
"[1] Assuming General Relativity is ",
", this is proven in ",
"http://arxiv.org/abs/gr-qc/9812067",
"[2] The \"photon rocket\" situation is used as a calculable metric for an accelerating source to show this effect of being pulled towards where a large object is headed rather than where it is. See ",
"http://lanl.arxiv.org/abs/gr-qc/9909087",
". I don't think anyone has calculated the metric of the solar system with the Sun, Jupiter, etc with enough accuracy in to calculate this effect explicitly."
] |
[
"Instantaneous as opposed to retarded."
] |
[
"Electrodynamics, which is also a relativistic theory, has this same property. The forces between charges point towards the instantaneous positions of charges. "
] |
[
"Are they any cases of animals using covering or \"clothes\" to protect themselves from the environment as humans have done?"
] |
[
false
] | null |
[
"Hermit crabs are an obvious example.",
"Pigs will slather themselves in mud to cool off. ",
"You could call a burrow a kind of \"clothing\" that animals \"put on\" to protect themselves from the environment.",
"The biggest problem is that the natural world doesn't present a lot of things which you can really use as a covering (which is why we need to do complicated things like weaving fibres or skinning animals). So without a high degree of intelligence and dexterity it's very hard to make \"clothes\". ",
"Heck, a lot of human tribes didn't have clothes. ",
"edit: Another thing is that we need clothes mostly because a lot of us live outside our natural habitat. If we still lived in Kenya then they would be less necessary."
] |
[
"Well, I'm not sure it's exactly what you're looking for, but it's pretty common for insects to use inorganic matter in their environments to cover themselves for protection.",
"\n",
"Caddisfly larvae",
" are a great example. They'll build a case for themselves out of anything around them. In that first pic the casemaker used rocks and gravel. In ",
"this example",
" the casemaker dressed itself in leaves that it's cut up and stuck together. ",
"This",
" is an interesting and somewhat unique casemaker. This species would usually use something whole like a hollowed out twig from its environment. But the individual pictured there happened to have come across and used the discarded case made by a completely different species of caddisfly casemaker. ",
"Another great example of this sort of dressing up from the insect world that people will often encounter is the ",
"bagworm moths.",
" This is actually the caterpillar of a moth that loves to dress itself up as things like ",
"pinecones.",
" ",
"Then there are the ",
"masked hunter nymphs",
" which will dress up like any kind of debris they find so they can more eaily ambush and kill their prey. Which is often bedbugs, so these mean little guys are your allies. ",
"And that just reminded me of the ",
"decorator crab",
" which will also adorn itself with basically anything it finds. Even if ",
"the thing it finds",
" might not necessarily agree with the arrangement. "
] |
[
"Its probably the same instinct that drives humans to do it. Need for shelter. I didn't really think of it till you asked this question but wouldn't ",
"this video",
" constitute an animal using its environment to cover itself? Granted the dog doesn't actually make the blanket or use any other materials but it seems to fit."
] |
[
"Would the insulin of the 1920s be acceptable for use in patients today?"
] |
[
false
] |
In the 1920s, insulin co-inventors James Collip and Charles Best sold the rights to the University of Toronto. Since that time I believe the formulations of insulin and its manufacturing method have changed quite a bit. My question: If you were able to transport the insulin from the 1920s to today's market, would it be approved by the FDA? Would doctors agree to prescribe it?
|
[
"The insulin back then was isolated from animals. Today’s insulin in recombinant humanized insulin manufactured in batch fermentation reactors. As a result, you are much less likely to have an immune response against today’s insulin. I think a side effect of the insulin back then is that you would gradually build up an antibody response to the animal derived insulin and develop a tolerance for it. So while it would still work, it would be an inferior product. ",
"As for FDA approval there are many animal derived products on the market today such as devices and formulations containing collagen, hyaluronic acid, albumin, etc. So yes I am sure there is a route to getting 1920’s animal derived insulin FDA approved. The technology to purify animal derived proteins has improved and so I am sure FDA would expect that technology would be used to ensure the purity of animal derived insulin."
] |
[
"You would not become tolerant of the porcine or bovine insulin but you could become allergic and that was a major issue. ",
"The FDA never rescinded the approvals of the older products. They were just abandoned. The companies which are interested in biosimilar insulins are going to make versions of the analogues because that is what is being prescribed. They aren't going to invest in products which are inferior and no longer being prescribed."
] |
[
"Today’s insulin in recombinant humanized insulin manufactured in batch fermentation reactors.",
"Significant correction. Recombinant human insulin is the 1980's insulin, it was approved for market in 1982. (it's fully human, not \"humanized\" which means an animal protein which has been modified to be more humanlike)",
"Modern insulins are modified to radically alter their biophysical properties compared to normal plano insulins.",
"Normal insulin takes 30-60 minutes to start working after injection, and only lasts for 3-6 hours.",
"Insulin Aspart is 2000's insulin, and starts working in 15 minutes.",
"Insulin Lispro is 2015's insulin, and starts working in under 5 minutes. This is your oh-shit button.",
"On the other end of the spectrum we have a series of insulins engineered to last much longer",
"insulin Glargine provides a steady level of insulin activity for about a day. This revolutionized the treatment paradigm by moving diabetics away from chasing their blood sugar around towards a once-daily regimen supported by short-acting stuff as nessecary. This was massive because previously only about a third of diabetics kept acceptable control of their blood sugar.",
"insulin Degludec which was approved in 2015 extends that window to about a day and a half, which is also a pretty big deal. It adds a much needed margin of error and it's Pharmacokinetic profile is smoother and more favorable for managing ideal blood sugar.",
"TLDR; none of these insulins are interchangeable with each other or normal human insulin. A fully dependent diabetic would literally kill themselves swapping out the bottle, or at least end up in a diabetic coma from either too low or too high blood sugar. All of the older insulins are still available, it's just no-one prescribes them because the health outcomes are a lot worse than the new stuff."
] |
[
"How do rocks like the lions rock form?"
] |
[
false
] |
Saw this picture on the frontpage and wondered how rocks like these form. Do they just pop op out of the ground?
|
[
"I believe this particular rock is a volcanic plug. It basically forms when magma solidifies in the vent of an active volcano. They become exposed when the surrounding, less resistant rock is eroded away.",
"This",
" diagram should be pretty helpful. The orange magma cools and solidifes, usually blocking off the main vent of the volcano, and the upper layers are eroded away."
] |
[
"Igneous rocks are usually a lot more resistant to weathering than the surrounding rocks, which can be from \"plugs\" or sills or dykes. One of the more famous examples would be Devils Tower in Wyoming. "
] |
[
"Interesting aswer didn't think of it that way. Thanks"
] |
[
"What Do You Think Of Marko Rodin?"
] |
[
false
] |
A friend of mine showed me some of his work. I've now read a lot of his stuff and find it interesting, but I'm not quite sure how much I believe of it. What really caught me off guard is when I tried to do research on him from sources not directly linked to him. For such an acclaimed genius with break through revolutionary ideas, I expected him to be a bit more famous. At the very least a wikipedia page or something. This is just weird.
|
[
"I made it through about 30 seconds before my BS detector went into overload. ",
"If you spend more time studying the fundamental fields of math and science (algebra, calculus, physics, chemistry, etc.) your intuition will develop as to what are and what are not solid ideas or theories. My personal intuition, which is far from perfect, says he isn't worth the time.",
"And in the spirit of building a good foundation I'd recommend the Feynman lectures here: ",
"http://research.microsoft.com/apps/tools/tuva/index.html",
"[edited for clarity]"
] |
[
"Woah, he claims to have found a way around the Heisenberg Uncertainty Principle, ",
"So he's claiming to violate a fundamental law of physics, among other things",
"He seems to be part of a big movement these days of people trying to mesh new age thought and quantum physics..."
] |
[
"Thanks.\nYea, I thought he sounded a bit crazy. What caught me was his graphs on the efficiency of his \"Rodin Coil\" versus a normal coil. If the graphs were true, his coil was absurdly more efficient. ",
"What is weird though is that I can't find any evidence of anyone using his coils industrially, nor any major break through articles on him.",
"I thought maybe I just didn't understand what he was talking about.\nGlad to see I'm not the only one who thinks he's crazy."
] |
[
"How does H. Pylori bacterium increases the amount of HCl produced? Or how does H. Pylori increases the activity of the proton pump?"
] |
[
false
] | null |
[
"I assume you're referring to why H. Pylori causes stomach ulcers. It doesn't increase HCL or change the activity of the proton pump at all. H. Pylori causes stomach ulcers by attacking and infecting the cells that line the stomach. With these cells damaged the acid within the stomach eats away at the tissue that's now unprotected causing stomach ulcers. ",
"The reason that th medication class \"proton pump inhibitors\" work in the treatment of stomach ulcers is that with less acid the stomach is better able to heal without the wound being constantly exposed to acid."
] |
[
"It is a bacteria, so antibiotics are used along with a PPI to allow the stomach to heal"
] |
[
"H Pylori is a bacteria that is very well adapted for infecting the stomach. It is a motile organism that releases a substance called “urease,” which converts a common substance urea into CO2 and ammonia. Ammonia is a base and HCl is an acid, so this will neutralize the local environment around the bacteria just enough to keep it alive. This is why the test we use for H Pylori is the “urease breath test.” Basically, you ingest some urea that has labeled carbon atoms in it. If H Pylori is in your stomach, then you can find those carbon atoms in the CO2 that you exhale during the test. Pretty nifty! We just have to have people not use proton pump inhibitors or antibiotics that could kill H Pylori for a bit before the test to make sure you don’t get a false negative. ",
"Back to your question—H Pylori can cause a few types of damage to the stomach wall depending on location. Once H Pylori erodes through the mucous layer in your stomach, it can set up shop there for a really long time, as it keeps neutralizing your stomach acid enough for it to survive but not enough to prevent damage to your own cells. If this happens in the main part of your stomach (the body), then you’ll get a local ulcer. However, if this happens in the “antrum” of your stomach, which is the exit just before the intestines, the cells there will sense that your stomach acid is less acidic, which releases a hormone called gastrin to correct this. However, your stomach acid actually was acidic enough already, so this increases HCl production even more and leads to problems, the main one being that you’ll actually start to get ulcers in the early small intestine (“duodenum”). ",
"So, long story short, H Pylori is well adapted to your stomach because it can neutralize the environment around itself to stay alive. Although it doesn’t directly increase HCl secretion, H Pylori can make your stomach think that there is not enough acid, which stimulates your stomach cells to secrete even more acid in the form of HCl."
] |
[
"If a tree were grown lit entirely from below, what might it look like?"
] |
[
false
] | null |
[
"It would depend partly upon the species of tree (and thus its usual growth patterns), and at what point in its development the uplighting as sole light source was introduced.",
"In general though, in the case of a tree, you would expect the main stem/trunk to grow upwards, but for the leaves to be angled so that their 'upper' surfaces were angled downwards towards the light.",
"A plant's direction of growth depends upon ",
" gravity and light: The parts of germinating seedlings destined to be above ground initially grow solely against the direction of gravity. Once above ground the growing tips tend to move towards the light, but the overall direction of growth is still also strongly influenced by gravity."
] |
[
"oops, I missed the \"grown\" in the title, thinking you were just wondering if the tree would look spooky or something like when people put a flashlight under their face"
] |
[
"I think you missed the point."
] |
[
"is Earth's helium really running out?"
] |
[
false
] | null |
[
"Yes its a finite resource. Its very expensive for that reason.",
"I used to be a commercial diver. Its used in certain diving gas mixtures, and because of how expensive it is, divers wear hats that reclaim what they exhale instead of letting it exhale into the ocean. Its collected back into a tank, and recycled. ",
"Its usually a pretty impressive recovery rate, something like 85% if i remember correctly."
] |
[
"While helium does escape earth's gravity, it's not just because it's lighter than air (otherwise it would just be a layer on top of our atmosphere).",
"Once helium rises high enough, it can be bumped into orbit and even into escape velocities by solar winds and other cosmological phenomenon (like cosmic rays). It's these phenomenon that actually make helium escape earth altogether."
] |
[
"Technically yes, helium is lighter than air, so as long as it can escape a pocket under the ground, it can escape gravity. But I have also heard this too. There are probably many pockets of helium humans aren't aware of, so in that way it's probably not running out any time soon unless someone has mapped all of the helium and knows this or uses it as a way to increase helium prices."
] |
[
"Is there rhyming in sign language, or a way to convey that two words rhyme in sign language?"
] |
[
false
] | null |
[
"There is indeed rhyming in sign language, although because sign language is visual rather than oral & aural, sign language rhyme is based on visual similarity between signs rather than aural similarity between sounds. This video has an overview of rhyming in English and in ASL.",
"Since the concept of rhyming exists in sign language, one could explain aural rhyming as analogous to visual rhyming, just as I have explained visual rhyming to you as analogous to aural rhyming."
] |
[
"This quotation from ",
"Pfau et al. (2012) ",
" might interest you:",
"One of the key elements of many signed poems is the repetition of sub-sign elements\nto create patterns that increase the poetic significance of the signs. Clearly, rhythm\ngenerated by timing of movements might be regarded as repetition of sub-sign elements.\nThe repetition of the elements at this level of the language may be seen as\nanalogous to patterns in spoken language such as rhyme, alliteration, and consonance,\nand is often loosely (and cautiously) termed “rhyme”. It is hard to treat it as a direct\ncorrelate of rhyme, however, because rhyme occurs as a result of sequences of sounds\nin spoken words, through repetition of word-final sounds, and the sign parameters do\nnot occur sequentially handshape, location, and movement path occur more simultaneously\nand cannot be isolated. There may be some argument for equating movement\nrepetition with “vowel” repetition, as movement is most easily manipulable through\ntime, and treating handshape with location more like “consonant” repetition, but still\nthe mode of the visual language does make signed “rhyme” different from that in\nspoken languages.",
"Signs may share varying numbers of parameters. They may simply have handshape\nor location in common, or they may be identical in both handshape and location but\ndiffer in movement (or share location and movement but differ in handshape, and so\non). The more parameters are shared, the tighter the “rhyme”, but some shared parameters\nmay be more salient than others. Certainly, due to the tradition of handshape\ngames in ASL folklore, many poets and audiences have come to appreciate poems in\nwhich the handshape is repeated (Klima/Bellugi 1979; Sutton-Spence 2001).",
"--Rachel Sutton-Spence. Ch. 41 \"Poetry\" "
] |
[
"Woah that's awesome! Thanks for posting!"
] |
[
"How does the chromosome number change over the course of evolution?"
] |
[
false
] |
This one has been bothering me for a while. I don't think even my high school bio teacher knew the answer. The way biology gets taught at the intro level it sounds like an organism usually won't be able to reproduce with other members of its species if it has a different number of chromosomes. Is chromosome number not as well-defined as we're taught initially?
|
[
"I think he might have been asking more along the lines of: \"Great apes have 24 chromosomes but humans have 23. It's not important the mechanism through which chromosomes can fuse so an offspring has have 23 chromosomes, but when it happens, how does this mutation pass to other members of the species (and eventually the entire species) when they cannot mate with other members of the same species because their chromosome pairs don't match.\" "
] |
[
"I think he might have been asking more along the lines of: \"Great apes have 24 chromosomes but humans have 23. It's not important the mechanism through which chromosomes can fuse so an offspring has have 23 chromosomes, but when it happens, how does this mutation pass to other members of the species (and eventually the entire species) when they cannot mate with other members of the same species because their chromosome pairs don't match.\" "
] |
[
"This can happen in one of two ways: an exiting chromosome is either duplicated or split. If it is duplicated (and the offspring don't die), the new species has extra copies of genes and therefore the copies can mutate to new genes without problems. If the chromosome is split, then the new organism doesn't have any extra genes but still has a different number of chromosomes.",
"For these to perpetuate and create a new species, the mutation has to occur in a way that does not prevent the affected organism from reproducing. If the chemicals on the egg and sperm match up close enough, they can fuse, but the offspring is rarely viable. Most people with down syndrome, which is caused by 3 copies of chromosome 21 (2 of each is normal), are ",
"infertile",
" so the effect would probably have to be less than that. I don't know about other polyploidies that survive, so having 3x chromosome 21 might be the only one. This is why humans have not budded off another species due to chromosome difference.",
"Chromosome number is indeed well defined, at least in eukaryotes. Most of the time in cells the chromosomes are unpacked and not distinguishable, but during mitosis and meiosis the chromosomes are packed up into distinctly visible chromosomes as seen in a ",
"karyotype",
". Organisms can reproduce with other organisms that don't have the same number of chromosomes, but the result usually doesn't make it past initial growth due to mismatched/conflicting genes and almost never is fertile."
] |
[
"Do Bones Get Stronger Through Constant Damage?"
] |
[
false
] |
I've seen Shaolin monks been stricken with sticks to strengthen their bones. Does this much damage actually promote bone growth when done multiple times a week, or does it do more harm than good? How much is overdoing it and does it work for muscles as well?
|
[
"The scar tissue that forms when broken bones knit back together (correctly, that is) is actually stronger than the original bone, but this only applies to particular kinds of breaks. I suppose deep-tissue trauma, repeated over a long time, will cause the bone to develop calluses just like skin, which will make it denser. ",
"To be honest, though, bones are quite a bit stronger than the average person is able to fully take advantage of. Pain limits the human body more than muscle mass or bone density, and the Shaolin discipline definitely involves raising pain tolerance beyond normal levels. ",
"So, ultimately, I don't think it's safe to say that constant damage strengthens bone. It has to be very specific, and it has to have time to heal. When bone breaks heal ",
", they can have lifelong and crippling consequences."
] |
[
"It becomes more interesting when describing the processes underlying bone remodeling. Remodeling results in laminar bone and development of Haversian systems (blood vessels surrounded by circumferential lamellae). Some amount of remodeling is driven by bone strain (ie deformation) but it's unclear exactly what strain magnitude, rate, energy density is necessary to cause remodeling. Remodeling decreases bone apparent density but increases strength. Repair of microdamage also increases strength locally.",
"That said, it's unclear whether the exercises of the monks is sufficient to have any meaningful effect on bone strength"
] |
[
"When a bone break heals the area around the break is thicker, like a scab almost, but not necessarily denser. Because of the extra thickness the bone is actually ",
" likely to break again either over or under the thicker part. After a year the bone goes back to normal because the body takes away the extra thicker bits of the bone."
] |
[
"Why are Gold and Silver relatively unreactive compared to other elements even though they only have one valence electron, like the alkali metals, which are extremely reactive?"
] |
[
false
] |
[deleted]
|
[
"I'd like to piggyback on this question:",
"Why are transition metals so chemically different? They only differ by d orbital elections, right?",
"I thought the d orbitals were not as... Exposed? As the outer s shell.",
"Now, this question is based on dim memories of chemistry, so I'm sorry if it's dumb."
] |
[
"It's because of their ",
"d band structures",
". The Fermi level of a noble metal (+ absorbate) for instance is above the energy of the antibonding orbitals when an absorbate bonds to the surface. This isn't the case for Ni where the antibonding states of the bonded species are found as unoccupied states. Occupying antibonding states weakens the bond it's associated to.",
"Bulk metallic gold for instance is very unreactive, and so you typically wouldn't use it as a catalytic material. However, if you support it on a sufficient support material it's found to be a quite a good catalyst for certain oxidation reactions (",
"CO and water gas shift",
"). This is given to the existence of atomically dispersed species on the surface of the support material. These species don't have a band structure like bulk metallic gold so their chemistries are very different."
] |
[
"Chemical different in what ways? There are a few reasons depending on what phenomena your thinking of."
] |
[
"Does the temperature rise during a large fireworks display?"
] |
[
false
] |
We had a very overcast December 31st here in Copenhagen, Denmark but, of course, that did not stop anybody from launching TONS of fireworks during the course of the evening. This made me think about large, hour long firework displays (New Years, Chinese New Years, etc.) as to whether or not the ignition of the fireworks would give a noticeable rise in the local temperature? Would the mean daily temp in an urban location or city actually get warmer during that time period? of not, how many fireworks would it take before we would notice using regular methods of detection? Thank you all.
|
[
"I don't think it would make any difference really.",
"I could be wrong, but my logic tells me that if anything, fireworks would only briefly warm the air around them. \nThe warm air would rest on the cooler ground level air, and as warm air rises, it wouldn't really warm temperatures at ground level.",
"Reference for the warm air resting on cool air :\n",
"https://www.accuweather.com/en/outdoor-articles/outdoor-living/how-the-weather-affects-firewo-1/67310"
] |
[
"It wouldn't make any sort of difference in air temperature.",
"However it does make a HUGE difference in air quality, and some areas end up having absolutely atrocious air quality for quite a while after. I just read a read a really good write up about it, I'm on mobile right now but I'll link it later. It's quite surprising just how bad it gets"
] |
[
"Let's give everyone 1 kg worth of explosives (that is ",
" more than a typical person will use). That gives everyone something like 20 MJ or 5.6 kWh - the average per capita electricity consumption of 8 hours. Copenhagen has a population of 600,000 and an area of 86 km",
" (municipal population/area). 20 MJ * 600,000 = 12 TJ, distributed over maybe the first 100 meters of air, or 86 km",
" * 100 m * 1.3 kg/m",
" = 1.1 * 10",
" g. Nearly exactly 1 J/g, sufficient to heat the air by 1 K. The actual temperature change would be significantly lower as wind distributes the heat over a larger air mass. I also think I massively overestimated the amount of firework used but I didn't find actual numbers. Overall the effect on the temperature is negligible."
] |
[
"What would happen if you ate nothing but carrots?"
] |
[
false
] |
Just curious. Over any period of time, what would happen to your body?
|
[
"If you could somehow eat enough carrots to get 2000 calories, about 5 kilos, you'd also get about 45g nearly complete protein. That should be enough to avoid any protein deficiency disease."
] |
[
"If you could somehow eat enough carrots to get 2000 calories, about 5 kilos, you'd also get about 45g nearly complete protein. That should be enough to avoid any protein deficiency disease."
] |
[
"Color me skeptical* that the human digestive tract could handle 11 pounds of carrots daily. Eliding past GI tract capabilities though, the overload of other nutrients from that amount of carrots would have health problems, particularly vitamin/mineral toxicity.",
"*Orange, being the color of skepticism in this case."
] |
[
"Is there any correlation between certain names, and behavior? Are certain names more likely to succeed than other names? I imagine some names might cause bullying more than others. But I’m more curious if there are any names with a positive social correlation."
] |
[
false
] | null |
[
"Freakonomics did a thing on it. Basically if your name was more common and easy to say you are more likely to get picked. Also if your teacher called you up based on alphabetical order, people that got called last felt a negative psychological impact.",
"http://freakonomics.com/2013/04/08/how-much-does-your-name-matter-full-transcript/"
] |
[
"Woah, that alphabetical order thing is the exact type of thing I was wondering."
] |
[
"For men, there is a correlation between short, single syllable names, and senior/powerful positions in business. Even with different versions of the same name. I.e., \"Bob\" is more likely to have a higher title than \"Robert.\""
] |
[
"How was helium discovered?"
] |
[
false
] |
This question bridges history and chemistry but I'm wondering if anyone has better information about the history of Helium's discovery. Did Janssen and Lockyer work together to determine that the yellow line was proof of a new element? And how did Frankland factor in? Did Langlet and Cleve isolate Helium from Uranium ores or did Ramsay? Did two independent discoveries occur at roughly the same time? How controversial was the yellow line discovery? Did most or all of the scientific community accept that as proof of Helium's existence?
|
[
"The wikipedia ",
"article",
" seems quite conclusive and seems to fit with what I remember: First discovered as an emission line in the suns spectrum (hence the name \"Helium\" after greek ",
", sun) and later it was found (again by its emission line) on earth."
] |
[
"While I look forward to the kind of rigorous, informative, and accessible answers ",
"r/AskScience",
" does so well, I can only say that I've happily given hours of my free time reading and jumping-off from ",
"this Wikipedia entry",
". "
] |
[
"If you don't get an answer here, you can try ",
"/r/askhistorians",
", ",
"/r/historyofscience",
", or ",
"/r/philosophyofscience"
] |
[
"Does cold medicine actually help make you better, or does it just suppress your symptoms while your body heals itself?"
] |
[
false
] |
[deleted]
|
[
"Cold medicine is a broad group of pharmaceuticals that typically include a combination of cough-suppressants, decongestants, painkillers. There are no approved treatments that actually target any of the viruses that cause colds. And the only drugs that target influenza are prescription only. They're only for suppressing symptoms to keep you comfortable while your immune system deals with the actual infection."
] |
[
"Mostly they only suppress the symptoms (as always there are exceptions). And in the case of cough suppressant can actually make it worse. By not allowing the body to cough naturally and eliminate the mucus in the lungs, it can cause a build-up of mucus in the airways and prolong or worsen the illness. Some physicians will recommend cough suppressants at night to help sleep, but allow the cough to happen during the day to aid in recovery. \nSource: med school and shadowing docs. Probably literature to back it up but I'm too lazy to go find it rn."
] |
[
"There are no approved treatments that actually target any of the viruses that cause colds. ",
"There is some evidence that zinc (found in many nasal sprays) directly inhibits rhinovirus replication. Most research shows that zinc can slightly reduce the duration of a cold. See this Cochrane review: ",
"https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001364.pub4/full",
"."
] |
[
"Does cutting food decrease cooking time in microwave ovens?"
] |
[
false
] |
A microwave oven is said to cook food from the inside and out. I would think this nullifies the need for greater surface area. Am I wrong?
|
[
"I can't give you a clear answer but I can provide some relevant information.",
"Microwaves work by filling a chamber with high-energy, gigahertz-frequency electromagnetic radiation. A 1 gHz microwave is a time-varying electric field: at any given point in space, the electric field will change polarity (positive to negative and back again) 1 billion times per second. When the wave encounters a polarized (charged) molecule, the field exerts a force on the charged molecule, aligning it with the electric field. The field is continuously changing, so it continuously exerts force on the molecule. This movement causes the molecules to bang into each other, creating heat.",
"Because water is so polar, it absorbs a lot of energy from the incoming wave in very little space. In electrical terminology: water is very conductive and therefore has a low skin depth. So stuff with a lot of water in it definitely heats from the outside in. ",
"A lot of other molecules in food (fat and sugar) are much less polar, so they do not heat as efficiently. They also have a bigger skin depth, so microwaves can penetrate deeper into these materials. Not exactly cooking from the inside out, but definitely distributing heat more deeply into the food.",
"Based off that, you might think fatty stuff cooks more evenly. But fats and sugars are poor thermal conductors, while water is an excellent thermal conductor. So creamy soup will require a lot of stirring to heat evenly, while a cup of water will heat very evenly without any stirring, despite water's thin skin depth.",
"Water vapor also helps disperse heat even if there are air pockets in the food. Air is a terrible conductor of heat.",
"Also worth noting: water has a very high specific heat: it takes more energy to heat water by a certain temperature than it does to heat fat. So watery stuff heats efficiently and evenly, but takes more energy to do so. ",
"tl;dr: If you cut up/stir fatty stuff, it will heat more evenly. Not sure if it will cook faster though. If you want something to cook slowly, put a cup of cold water in there with it.",
"I'm a professional electromagnetic engineer, but I do not have a PhD in this stuff, so clarifications/criticisms are welcome."
] |
[
"That sounds accurate... But considering if you cut the food, you now have greater surface area for the waves to hit, wouldn't that speed up the heating process?",
"Wouldn't a spread out mm thick pancake heat faster than a fat inch thick pancake of the same mass for the same reason?"
] |
[
"Possibly, based on what the \"food\" is. If you are referring to slicing it into thin pieces, (as opposed to random cuts into the meat) it should. Microwave ovens operate via dielectric heating, so the microwaves exert work on the polarized molecules (like water) because they attempt to align with the rapidly changing electric field. Since heat is nothing more than molecular kinetic energy, this causes the food to heat up.",
"Cooking time is based on the exposure of the waves to the polarized molecules in the food and the convection of heat throughout the food. A glass of water may be heated almost entirely on the outer layer, but has excellent convection of the outer hot water to the inner cool water. A steak, on the other hand, can develop hot and cold spots because the transfer of heat to cold areas is limited, and can only come from the incident microwaves. ",
"Think of a thick piece of food as being composed of many concentric layers, like a gobstopper. Each layer acts as a shield; which means some of the incident wave will be reflected, part will be absorbed, and part will be allowed to pass through to the next layer within. Since water is NOT conductive (although the impurities in it commonly are), there's little reflection. Each internal layer only receives the energy that is not absorbed by the layer above it. ",
"Edit: There's some talk about conservation of energy. This is correct that the same power is going into the food. However, thicker food with poor internal heat distribution would heat around the outside, without allowing energy into the cool center. When we talk about \"cook time\", I would say that food that's hot on the outside, but not the inside, is not cooked. EndEdit.",
"Spreading food out thin, as most microwave dinners do, allows even exposure to the incident microwaves, reducing cook times. "
] |
[
"Why do the world's governments and media EXCLUSIVELY talk about COVID19 vaccination rates, when studies have shown that natural immunity is far superior?"
] |
[
false
] | null |
[
"Everything you say is wrong."
] |
[
"Sorry how is it wrong?"
] |
[
"It doesn’t match reality. They do talk about infection immunity, and infection immunity isn’t “far better” than vaccine immunity (both of which are “natural”)."
] |
[
"Does modern sedentary lifestyle contribute to the rising amount of depression?"
] |
[
false
] |
Hello ! Nowadays people are less physically active, and the rate of depression has been rising. Physical exercise is regularly advised as a remedy for depression and other mental health issues. Could it therefore be, that normal mental health requires a "homeostatic" amount of physical activity? Does sedentary lifestyle play a part in the grand scheme of more people becoming depressed? Thanks for the answers :)
|
[
"A gigantic meta-analysis from the British Journal of Sports Medicine says yes.",
"Thirteen cross-sectional studies with 110,152 participants and 11 longitudinal studies with 83,014 participants were included in this meta-analysis. The summary RR of depression for the highest versus non-occasional/occasional sedentary behaviour was 1.25 (95% CI 1.16 to 1.35, I2=50.7%) for all included studies. The pooled RRs of depression for sedentary behaviour were 1.31 (95% CI 1.16 to 1.48) in cross-sectional studies and 1.14 (95% CI 1.06 to 1.21) in longitudinal studies. In subgroup analysis by different types of sedentary behaviour, the pooled RRs of depression were 1.13 (95% CI 1.06 to 1.21) for long-time TV viewing and 1.22 (95% CI 1.10 to 1.34) for prolonged computer or internet use.",
"https://bjsm.bmj.com/content/49/11/705.share",
"It is also important to understand the more complex role that exercise plays for our body as a whole. One of the most interesting longitudinal studies, and one that anyone in almost any medical or research field comes across eventually is called the Framingham Heart Study. It has been going on since 1948 with the children and then the grandchildren of the original participants, and contributed more to our understanding of Cardiovascular Disease than almost any other study. ",
"There have been tens of thousands of write-ups on the data from this study, but I'm going to link one of the early analysis. ",
"https://www.ncbi.nlm.nih.gov/pubmed/23474622",
"Estimating the effect of long-term physical activity on cardiovascular disease and mortality: evidence from the Framingham Heart Study ",
"One of the things Framingham shows is the role of exercise in all-cause-mortality (ANY cause of death from cancer to heart attacks and suicide.)",
"Of the variables they controlled for - regular vigorous exercise was shown to be one of the most important factors in not only reducing deaths from Cardiovascular Disease, but also reducing all cause mortality. ",
" "
] |
[
"Many of the brain's core functions--balance, peripheral vision, proprioperception, heat regulation, &c--are only fully engaged during physical activity. Just walking down a flight of stairs requires a lot of mental processing. ",
"When you're sedentary, big elements of your brain's capacity are idling, even if you're consciously engaged in reading / writing / watching the screen. ",
"It's pure conjecture to say this has any bearing on mood. But it's interesting to think about. It could also be why low-intensity exertion, like yoga & walking, seems to yield similar mental benefits as higher intensity sports like running and cycling. ",
"EDIT: ",
", obvs."
] |
[
"I think you make an interesting point. Of course getting active isn't a cure all for people suffering from depression but I do wonder if someone \"didn't have time\" to get caught in the cycle of depression by being stimulated in a variety of ways if it would be as prominent a problem.",
"So many people (myself included) get caught in this cycle of going to work all day, coming home and trying to feel like yourself for 2 or 3 hours before you crash, just to wake up and go back to work. By the time you hit the weekend (if you're lucky enough to get those) you might feel like you \"deserve\" a weekend off from the hustle and bustle and you just become a hermit.",
"Many people are devoid of sunlight as well. Spending all your time under and looking at artificial light and not being active is unhealthy in so many ways, not least of all, mentally. I am aware that people are encouraged to be more open and involved in the mental health discussion and that we see more numbers for this reason.",
"edit: I mean we see the numbers rising because we talk about it now, and that being a farmer or something, working the land does not exempt you from mental health issues. We are more aware now and without data it's hard to know the difference electric light and office jobs made"
] |
[
"Why does the center of the earth never cool down?"
] |
[
false
] |
It must be constantly losing heat, why doesn't it level off?
|
[
"First, a clarification, the core of the Earth (and the Earth as a whole) is losing heat, but it is relatively slow. The reason it is slow is a combination of four main factors: (1) The core (and more broadly the Earth as whole) started off with a lot of heat, i.e. enough for the entire planet to be ",
"a liquid initially",
"; (2) Radioactive decay of uranium, thorium, and potassium in the mantle and crust continue to contribute significant amounts of heat, and probably ~50% of current heat flux is from ",
"radiogenic heat",
" (plus there were even greater rates of radiogenic heat production early on from short lived isotopes like ",
"Al); (3) Rocks are not great heat conductors, compare the thermal conductivity of ",
"rocks (0.5-5 W/(m x K))",
" to the thermal conductivity of efficient conductors like ",
"metals (e.g. copper, ~400 W/(m x k))",
", though this is partially overcome by convection in the mantle being the primary process by which heat from the core is moved toward the surface, but rate of heat conduction through the crust is still limiting; and (4) air is an even worse conductor so the rate of heat loss from the crust, to the atmosphere, and eventually space is not efficient and serves as an insulator to a certain extent (again here though, heat in the atmosphere can be more efficiently transported through convection than just conduction).",
"EDIT: Just to expand on point 2 a bit, because radiogenic heat production is tied to the amount of radiogenic isotopes, this means that even without considering extinct isotopes, ",
"heat production was greater in the past",
" (because there was a larger concentration of isotopes which have since decayed away) and the amount of radiogenic heat production will continue to decrease (as the concentration continues to decrease). This reduction in radiogenic heat production through time is slow though given that the half lives of the relevant elements are 100s of millions to billions of years."
] |
[
"Tidal heating of Earth from the Sun (or Moon) is negligible compared to primoridal heat and radiogenic heat. ",
"This paper",
" on the possiblity of tidal heating of Earth like exoplanents might be useful for thinking about why this is not a significant source of heat for the Earth."
] |
[
"Pressure does not generate heat, pressurising (the process of increasing pressure) does."
] |
[
"Is rinsing your mouth with water after drinking coffee good enough to prevent staining your teeth?"
] |
[
false
] |
Or do you need to brush your teeth every time you have coffee? And how safe is sprinkling baking soda on your toothpaste when you brush your teeth? How does teeth staining occur? Is it instant or does it take a while to sink in? So for example, if you have a cup of coffee and you go to bed..I presume that would be pretty bad for your teeth right?
|
[
"Correct, the acid in food and drink softens your enamel, so brushing after eating or drinking is ",
"harmful to your teeth"
] |
[
"I was under the impression that brushing your teeth after eating or drinking something acidic you end up with added abrasiveness, I'm not sure how acidic coffee is (and I guess it varies depending on milk quantity and how sweet you have it), but brushing right away might even be damage to your teeth. My understanding is that flossing will remove plaque from the edges of your teeth without this abrasive action so that might help reduce the staining."
] |
[
"coffee stains just like any other stain/ dye does.......the longer and more frequent the exposure...the deeper the stain(typically).......",
"so theoretically, yes, wasshing your mouth out with water should help (kind of like hosing off a piece of wood you just applied stain to....but im not sure its going to have a noticeable effect.....because the coffee has already come into contact with your teeth.",
"as for baking soda.......check the ingrediants on your next tube of toothpaste........baking soda is one of them........so no harm will come from using it in your toothpaste (within reason.....it is an abrasive after all)",
"as for general tooth health, im no dentist......but from what i have heard, the staining is only cosmetic, and has no actual bearing on the health of the teeth."
] |
[
"What causes hair to \"get used to\" being combed or done a certain way after awhile?"
] |
[
false
] | null |
[
"Oils will slowly accumulate and solidify on your scalp. This preserves the general position of your hair at its base, forming a kind of grain that the rest of your hair follows. If you have longer hair, you'll notice that when you wash your hair with shampoo, it falls in random directions. This is because you've freshly cleaned this layer of solidified oil off. "
] |
[
"I am a Master Licensed Barber in the state of Minnesota. Not to be confused with a Masters DEGREE which I certainly do not have."
] |
[
"Is there any evidence for this lasting longer than until you shower? Like an actual permanent change in the way your hair falls?"
] |
[
"Do we know how much your mental or physical condition at conception effects the outcome of a fetus?"
] |
[
false
] |
Say the woman is an alcoholic at the time of conception, or the man is on a week long LSD trip, or either are in the throes of a clinical depression at the moment, would the fetus be more predisposed to addiction or mental health issues as opposed to if they had been conceived prior to these events? Or if this makes more sense, would a baby born to teenage parents who have never smoked, drank, done drugs, or experienced any major life problems or mental illness yet have a better genetic predisposition than a baby born to the same couple 20 years later after heavy drinking and drug use had occurred and the development of a mental health issue or two? I'd imagine it would be hard if not impossible to research, but if I, the least knowledgeable (of science) person I know, am wondering about it; there must be someone out there who's thought about the same sort of thing and found the answer, right? Any and all answers are welcome. Thank you in advance!!!
|
[
"So the parents' past experience or current condition won't generally affect the ",
" the offspring inherits, but it can affect the individual's traits/phenotype.",
"The most important factor is going to be the mother's state during pregnancy, as she provides the developmental environment, which, for example, ",
"accounts for on the order of 60-75% of the variation in birth weight",
". There are a lot of other things you could want to measure besides birth weight, and I don't have references for them off the top of my head, but I would suspect a lot of other traits measured at birth would show relatively strong contributions from the fetal environment.",
"As for working out what specifically the causes are, that's a little more difficult (and not really my area). One example is currently/recently on the front page of ",
"/r/science",
":",
"Antidepressant Use in Pregnancy Linked to Anxiety in Offspring",
"[journal article]",
"Another example would be ",
"fetal alcohol syndrome",
".",
"And google scholar has lot's more",
"The other main way I can think of would be via ",
"epigenetic effects",
". Basically this refers to any piece of information which is inherited but is not transmitted via the DNA sequence, and whereas the fetal environment can only have effects up until birth, the impact of epigenetic factors can continue afterwards, as they can effect the way that genes are expressed throughout development in the offspring. This epigenetic information is usually inherited in the form of ",
"methylation marks on the DNA",
". In some cases, the parental experience/condition can impact which epigenetic marks the offspring inherits, such as ",
"as may have occurred in a few known cases in humans",
" (yeah, I'm citing io9, but Epstein knows his stuff).",
"Exactly how important these effects are is not entirely known. There's only a handful of concrete examples at this point, and prevailing evidence probably points toward their being not insignificant, but probably less important than genetic and external environmental effects."
] |
[
"Yeah, the whole business is badly overhyped. Some neat results, but no basis for all this \"rewriting our understanding of biology\" nonsense."
] |
[
"Yeah, the whole business is badly overhyped. Some neat results, but no basis for all this \"rewriting our understanding of biology\" nonsense."
] |
[
"Why is smell so tightly linked to memory?"
] |
[
false
] |
I think I understand why, from a physiological standpoint, smell is so tightly linked to memory in comparison to the other senses. I remember reading something in a psychology class about how the olfactory system was closely linked to the amygdala and hippocampus, which control emotion and associative learning. This means that whenever we encounter a new smell we tend to associate it with the emotions and surroundings at that moment, and when we encounter it again those memories are immediately brought back. So this I understand. My question, is why did the human olfactory system evolve this way? Why was it advantageous from an evolutionary standpoint to have olfactory perception so tightly linked to emotions and memories, but not our other forms of sensory perception?
|
[
"Think of it from another angle - is sense of smell really that much more related to memory than the other senses?",
"Sure, you can open up an old suitcase from your attic and get a whiff of some smell that makes you think of some vacation you took 15 years ago. Sure thats amazing. But what about the other senses? Theyre also pretty amazing.",
"You can see the face of someone you havn't seen in 20 years, and instantly recall their name, likes, dislikes, and all your experiences you shared together.",
"You can taste a piece of candy that you havnt enjoyed since your childhood and suddenly be brought back to some experience from way back like it was yesterday.",
"Same goes for hearing. Someone can say \"Hey remember in grade 4 when Jonny pissed his pants in class?\" And you instantly remember that whole day and everything that happened.",
"TLDR: Sense of smell has some amazing connections into our brains, but then again so do all the other senses. The brain as a whole is an amazing pile of goo, regardless of which input mode its using :)"
] |
[
"A lot of people don't know this, but it's actually the nose that is the part of the body directly responsible for memory. Take elephants: big nose, good memory.",
"You shouldn't feel bad though. Just a short time ago people didn't know that sex led to babies."
] |
[
"I saw you didnt have any comments, so ill give you one :) And a interesting read good job! "
] |
[
"If you point your phone camera at an IR LED (like in a TV remote) it is visible but why does it show up as blue/purple rather than red?"
] |
[
false
] | null |
[
"The explanation has to do with how digital cameras try to determine the color of an object. Cameras usually use a sheet of silicon sensors to detect the intensity of incoming light. However all the intensity tells you is how much total light falls on a given pixel (weighted by how responsive the sensor is in that spectral region). In other words, the best you could do at this point was to build up a grayscale image. In order to get information about the color, you need some way to separate light by wavelength. One way to do this is by adding a grid with color filters, e.g. a ",
"Bayer filter",
" on top of the sensor layer, ",
"as shown here",
".",
"Now this set of filters is the only know the camera can distinguish between different colors. Because there are only three color filters, there is only so much spectral information you can get. However, that is fine, since our eyes also only have three types of biological censors, called cone cells, ",
"that can distinguish colors",
". As a result, a camera can detect more or less as much spectral information as our eyes can see. A display can then use three color sources (e.g. RGB or red, green, and blue lights) to mimic the same color our eyes can see. ",
"That intro was a bit long, but we finally we can get to the heart of the question. The actual efficiency of the red, green and blue pixels of a camera is shown in ",
"this graph",
". Notice that above 650nm, a filter is said to block off most of the near infrared (IR) light. Of course, a bit of it will leak in. In the case of things like an IR remote, the light will usually have a wavelength of ~900nm. In that wavelength range, the green, red, and blue detectors are triggered about equally strongly. Now when the camera tries to map this response on the RGB color space, it looks for the closest mixture of visible colors that would have given the same reading. It turns out that you can mimic a similar response by shining white light with a bit of extra blue/violet light mixed in. As a result, the camera decides that this was the light that must have hit it and records the infrared light as having a violet hue. "
] |
[
"Thanks for such a detailed answer :)"
] |
[
"Thank you for taking the time to properly explain that! "
] |
[
"What did we leave behind on the moon?"
] |
[
false
] |
Is it correct to assume they left a bunch of junk/equipment on the lunar surface? Or did they just leave a plaque and footprints? What manmade objects are sitting up there right now?
|
[
"Link with out the let me google that for you:",
"http://en.wikipedia.org/wiki/List_of_man-made_objects_on_the_Moon"
] |
[
"Link with out the let me google that for you:",
"http://en.wikipedia.org/wiki/List_of_man-made_objects_on_the_Moon"
] |
[
"Wait, so you're telling me it's possible to pass along information ",
" being a dick? Fascinating..."
] |
[
"Does light speed up as it moves away from a sun and its gravity?"
] |
[
false
] |
I know that light travels at c in a vacuum, but it is also affected by gravity, and can bend around planets, stars etc. As light is emitted from a star, does it travel (relatively) slower ah first and then speed up as it moves away and becomes less and less affected by the star's gravity?
|
[
"Depends on who you ask. An observer watching the photon pass closely by them will always see it moving at c.",
"But a far-away observer won't necessarily see the photon traveling at c.",
"Let's work it out for a photon moving radially outward in the Schwarzschild metric. So this would describe the outside region of any spherically symmetric mass, including a non-rotating planet or star.",
"The Schwarzschild metric is",
"ds",
" = -(1 - 2GM/(rc",
"))c",
" dt",
" + (1 - 2GM/(rc",
"))",
" dr",
" + r",
" dΩ",
".",
"For anything moving purely radially, dΩ = 0. And for a photon, ds = 0. So that simplifies to",
"0 = -(1 - 2GM/(rc",
"))c",
" dt",
" + (1 - 2GM/(rc",
"))",
" dr",
"which can be solved for dr/dt",
"dr/dt = (1 - 2GM/(rc",
")c = c - 2GM/(rc).",
"So if the mass of the object is just zero, you get back the flat Minkowski space where the photon moves at c for all observers. But with the mass nonzero, the space is curved. So while a local observer still sees the photon moving at c, a far-away observer sees the photon moving with some position-dependent speed.",
"If the planet/star has a radius R and the photon is shot directly upwards from the surface, an observer at infinity will see its initial speed as c - 2GM/(Rc), and as it moves upwards, the photon will appear to speed up, its speed approaching c from below. However that doesn't mean that the photon is gaining energy. The energy of the photon is a function of its frequency, not its speed as measured by some far-away observer. The photon will redshift, losing energy as it climbs out of the gravity well of the star/planet."
] |
[
"I didnt understand all that you wrote here. Just wanted you to know i enjoyed reading it!"
] |
[
"In more simplified terms. An observer near the photon will see it travelling at c. An observer far away will see it travelling initially at a fraction of c and then speeding up. The discrepancy is due to the fact that space is different where one observer ia standing vs the other.",
"Space near the first observer is stretched but he doesn't notice that. The second observer does. ",
"Now, as far as the photon goes. It loses energy as it escapes the gravity well, which does not affect its speed, which is always c locally, but rather it causes it to shift towards red."
] |
[
"Why is it that L'Hospital's rule only works when the limit is to an answer that is in indeterminate form?"
] |
[
false
] | null |
[
"The proof uses the fact that it is indeterminate. The special case ",
"here",
" is fairly simple to go through if you'd like."
] |
[
"You can actually call it l'Hospital or l'Hôpital. Both come from french. The os has been transformed to an ô. So, while old, the \"Hospital\" term isn't inherently false."
] |
[
"Yeah, it's silent in both cases"
] |
[
"Zero Gravity and Fire"
] |
[
false
] |
If you were to strike a match in Zero Gravity which way would the flame burn? Because heat rises in gravity I have a hard time wrapping my head around how a flame would look in zero gravity.
|
[
"Here's a short video of a flame being lit in a microgravity environment, ",
"http://www.youtube.com/watch?v=Q58-la_yAB4",
" and an article that provides some insight into fire in microgravity ",
"http://www.smithsonianmag.com/science-nature/In-Space-Flames-Behave-in-Ways-Nobody-Thought-Possible-179731321.html",
" . Unfortunately I have a very limited understanding of physics and can't explain anything in greater detail, I hope this helped. "
] |
[
"Archimedes principle doesn't exist in zero gravity. That means that Cold air doesn't flow below the hot air. ",
"On earth: \nWhen a candle is on fire, oxygen is turned into other chemicals which are evacuated upward by Archimedes principle because they're hot.",
"In zero gravity :\nthe candle would create a cloud of non flammable gas around it. And for the same reason that putting a lid on top of a candle kills the flame, the candle will use all surrounding oxygen and then die.",
"Let me link you a video: \n",
"https://www.youtube.com/watch?v=DKxAs_f1SP8&feature=youtube_gdata_player"
] |
[
"As the video you linked explains the candle or fuel won't die but will instead burn at a much slower rate through the diffusion of oxygen molecules which enter into the flame allowing it to continue burning."
] |
[
"Is there a fundamental constant that all other constants are based on?"
] |
[
false
] |
I'm curious to know if there is single constant that all other constants can really be derived from. A) If so, is that constant always the same no matter what? For example, if it is measured in a vacuum vs. in a black hole. B) If no, how many basic constants are there? And why is it that we cannot derive one constant from another?
|
[
"No, that is not the case. There are many physical constants, and you have to make the distinction between dimensionless constants (like the fine structure constant), and constants whose numerical value depends on what units you are using, like the gravitational constant.",
"John Baez discusses about 25 dimensionless constants ",
"here",
". (Well, that's what he says, but he talks about quark masses)."
] |
[
"As ",
"u/iorgfeflkd",
" noted, there are about 26 dimensionless constants that determine how physics works. We would like to reduce that number by finding a theory that could predict some of their values, but for now they are all determined empirically.",
"But to address your secondary question:",
"A) If so, is that constant always the same no matter what? ",
"We don't know if these constants are the same everywhere or not. There was an interesting observation a few years ago that ",
"the fine structure constant might be higher on one side of the universe and lower on the other",
". As far as I know, there is still some debate on whether the results are significant or not but if true it might mean that the fine structure constant and other dimensionless constants are set arbitrarily by our position in the universe."
] |
[
"(Well, that's what he says, but he talks about quark masses)",
"What matters is the mass ratios, not the value of the mass in one particular set of units. As long as you express each of those masses as multiples of the Planck mass you will still have dimensionless constants."
] |
[
"How do ants navigate while holding food?"
] |
[
false
] |
I was watching ants carrying things around today and the ones that weren't on a defined path or were carrying a heavy load would walk backwards. My question is, how do they know where they're going if they can't use their eyes or antennae?
|
[
"For some ants (perhaps all?) this can be due to chemical trails. As they go out to forage, they'll lay down a chemical trail that they can follow back AND that others can follow out to also find food. One nifty trick I learned from an entomologist was that ammonia based windex can be great to help get rid of ants, both because it will kill the ants themselves, but also because it will disrupt the chemical trail making it more difficult for other ants from the same colony to return to the same area."
] |
[
"They lay one trail to find their way back. If they find food they lay a different one on the way. This prevents ants from following the same trail as someone else with no payoff. Once an ant comes back with the food trail, the rest jump on it."
] |
[
"You are quite correct, and that's what I get for rushing through writing my answer."
] |
[
"If Mars has around 1% the atmosphere of Earth, would the windstorms actually feel that strong, or would they be like a gentle breeze?"
] |
[
false
] |
[deleted]
|
[
"This is actually pretty easy to estimate. The extra pressure you would feel can be estimated from the ram pressure formula, P = rho v",
" where rho is the mass density of air on the martian surface and v is the wind velocity. ",
"We can find rho by using the ideal gas law, P = (rho / (mu*mH)) * k * T. The Mars rovers measure an air pressure of 600 Pascals. Assuming a CO2 atmosphere (mu ~ 28) and a temperature of 200 K, I find rho ~ .01 kg m",
"The Mars rovers measure v to be about 500 kph in very strong dust storms, so the wind exerts a ram pressure of about",
"P ~ rho * v",
" = .02 PSI",
"A 30 mph wind on Earth exerts a similar pressure. So I guess a really strong dust storm on Mars would feel really strong, but that's only because the wind pressure scales as the wind velocity squared. Most of the time you would never notice Martian wind."
] |
[
"do you really call that easy? I envy your innocence."
] |
[
"The scaling of the wind to do work (such as turning a wind turbine, or how you feel it) is a function of its kinetic energy, which goes as mass times the velocity",
"As you mentioned, the density of the atmosphere at the surface is quite a bit lower than here on Earth, about 1/100th that of Earth's. That 1/100 goes into the mass term, so for an equivalent wind speed, Mars' winds will feel 100 times weaker.",
"However, sustained winds can be fairly fast - during dust storms there are regularly sustained winds of 30 meters per second (about 67 mph or 108 kph). That goes into the velocity",
" term, and that squared term means a little bit of increase in speed leads to a large increase in kinetic energy. To put this in another way, a 60 mph wind on Mars will feel like a 6 mph wind on Earth, because 10",
" = 100.",
": Yes, the 1/100th density will make the winds feel 100 times weaker...but you'd only need 10x faster winds to make up for the difference."
] |
[
"Are there convection currents in boiling water?"
] |
[
false
] |
And where do the bubbles in boiling water come from? The bottom or from the middle?
|
[
"The bubbles are steam and they form at nucleation points on the surface of the pan in the case of a pan being heated from the outside. The water absorbs enough heat and changes from liquid to gas. The churning that you see in boiling water is not a convection current. It is caused by the phase change rapidly increasing the volume of the water as it changes to steam. Buoyant forces then force the steam bubble to rise to the top where it bursts and the steam exits the system"
] |
[
"There are, they're just minor compared to bubble buoyancy if you have a rolling boil."
] |
[
"Unless it's a perfectly insulated sphere, heated uniformly, a single isotope, in space, etc. it's going to have a thermal gradient and density differences/buoyancy."
] |
[
"Would pulling planets into the sun extend it's life."
] |
[
false
] |
In Invader Zim, there is a race of "planet jackers" who pull planets from other star systems into their on star. The idea is that it's like stoking a furnace and that it will extend the life of their own star. My question is: Is that what would happen?
|
[
"Leaving aside how adding mass to the sun would change its lifetime (big stars usually burn out quicker, not slower) it is important to point out that the sun contains 99,85% of the mass in the solar system. ",
"So even by throwing ALL the planets into the sun plus all the asteroids and comets you would not even increase the suns mass by 1 %.....",
"Therefore, even if you could extend the lifetime of a star by adding mass, planets are a poor source as they are basically crumbs thrown in a lake."
] |
[
"Adding an earth-like planet to the sun would do almost nothing. The earth is not nearly massive enough to have an effect. It also doesn't have the materials you'd want. ",
"You want high hydrogen and helium content, low metal planets like Jupiter or the gad giants, but even at that you're increasing the mass of the star, and therefore it's gravity, so you're going to get diminishing returns (since the increase in size would make it burn fuel faster). On top of which, as you add mass you are going to start messing the orbits of the planets up, they'll get sucked into the star as you add mass to it. ",
"This, of course, ignores the absolute infeasibility of the act itself, for every reason from actually moving a planet without it ripping apart to getting the planet to impact with the star without causing significant gravitational perturbations with the orbits of the planets around that star. "
] |
[
"Wouldn't you shorten the life if a star by introducing iron to its core?"
] |
[
"Why must we postulate a Higgs field?"
] |
[
false
] |
I understand that the question of why stuff has mass requires there to be some mechanism that imparts mass to objects. However, doesn't the same apply to charge? In other words, why do we need a Higgs field for mass but not for charge? Or is it the electric field that is imparting charge to charged objects?
|
[
"(Hyper)Charge like mass is one of the properties of the elementary particles in the Standard Model of Physics (SM).",
"Charge is mediated by the exchange boson that we call photon and that part of the SM becomes quantumelectrodynamics and simplied even more the classic Maxwell equations.\nSo as you see, we do have such a bosonic field concept for charge, in fact that's where our attempts for using a similiar formalism for mass come from.",
"The \"best\" and theoretical most researched attempt to introduce mass into SM in a gauge invariant way (a very important symmetry which a trivial mass term would violate) is the Higgs mechanism, but it's not the only way to generate mass, infact in the SM the Higgs only generates fermionic masses, bosonic masses come from a Yukawa term."
] |
[
"You could say that interacting with the Higgs field is what gives things mass, and interacting with the photon field is what gives them charge. That's a bit of a simplification but it avoids math."
] |
[
"When you say \"photon field\", is that different from the electric and/or magnetic field? "
] |
[
"What would Earth be like if it was tidally locked with the sun (earth only faced sun on one side). How would life evolve?"
] |
[
false
] |
How would life evolve to cope with living on a planet like this? What would the weather patterns be like with one side basically a desert and the other an arctic waste? What kind of challenges would be faced living in a slim temperate zone in between the two?
|
[
"I can comment on this, as I do research on planetary dynamos.",
"So this is a big misconception regarding magnetic fields, especially among scientists who know only a bit about dynamos.",
"Yes dynamos as we know them require the planets to be a fast rotator, but the key word here is \"fast\", which is a relative term. When we call something a fast rotator we really mean that it is fast relative to the velocity that the fluid moves at and the distance it has to cover.",
"As it turns out, the core is really really big (the liquid gap is 2300km across) and the fluid moves very slowly (~1mm/second). We can get a number from this which quantifies how important rotation is relative to inertia. It's called the Rossby number and it is U/(L*Omega) where U is a characteristic velocity, L is a length scale, and Omega is the rotation rate. ",
"If the Rossby number is much less than one, then rotation is dominant, if it is much greater than one, then rotation is not important. Another way to look at it would be to compare the time for one rotation of the planet, to the time of one core crossing by a fluid parcel (that would give you Ro=1). As long as the rotation time is faster than the core crossing time (Ro<1), rotation is dominant.",
"Lets say that the earths orbit remains the same and it is somehow tidally locked, making its rotation period one year (2",
"24",
"60)=2*10",
" plugging in our length scale and velocities we get a Rossby number of .002 meaning that even if the Earth was tidally locked and somehow accomplished this at its current orbital distance (which isn't possible to begin with) it is still in the \"fast rotating\" regime.",
"A common misconception among scientists who don't study dynamos is that venus doesn't have a magnetic field because its rotation rate is too slow (~240 days), it is actually for other, complicated reasons involving the mantle."
] |
[
"I'm not a scientist and can't comment on the evolution aspects. However I am most certain that life probably wouldn't exist at all on Earth, due to the fact that without the Earth rotating as fast as it does, there wouldn't be a magnetic field. Without a magnetic field, the effects of photodissociation would be much more apparent and possibly occur more rapidly. Basically, water(and other molecules) would be broken up into oxygen and hydrogen compounds that would either fall to earth as solids or be blown into space as gasses over millions of years due to the strong effects of the solar wind to the point where there wouldn't be much of an atmosphere left, either that, or we turn into Venus, which is fairly identical to Earth in size and mass, and has an active(possibly) geology, but spins far too slowly to have a magnetic field. More recent evidence has implied that Venus may have had oceans at some point, but due to the lack of a magnetic field, the water was lost to space. With a still active mantle, Venus continued to create volcanoes, without any water to absorb it, the planet built up the massive CO2 atmosphere it has today. ",
"http://www.sciencedaily.com/releases/2008/12/081218094605.htm",
"\n",
"http://en.wikipedia.org/wiki/Photodissociation",
"\n",
"http://en.wikipedia.org/wiki/Magnetic_field_of_celestial_bodies",
"Edit- Cornell University study:",
"Atmospheric dynamics of Earth-like tidally locked aquaplanets",
"http://xxx.lanl.gov/abs/1001.5117"
] |
[
"It's questionable whether significant non-ocean-bottom life would exist at all, and that's assuming all the water isn't energetically 'boiled' off the planet.",
"The slowing of rotation would change the distribution of the oceans, which would be an important consideration - the constant sunlight on the Pacific ocean, for example, would likely cover much of the planet in heavy clouds, and larger macroscopic life might evolve underneath those clouds. A meteorologist would be better equipped to answer how much weather would transfer heat from the hot side to the cold side of the planet. ",
"This is ignoring the points brought up by endeavour3d, about whether the atmosphere would even be able to stay on Earth in such conditions."
] |
[
"What would happen if I swallowed a ball bearing and went for an MRI scan?"
] |
[
false
] |
[deleted]
|
[
"Its fairly likely that as you enter the MRI room that the metal detector would go off, and you wouldn't get anywhere near the magnet. (At the ~10 MRI machine rooms I've been to, all have had a metal detector surrounding the door that will go off if you are wearing any metal it detects -- usually they are very sensitive).",
"Now, the response of the metal ball bearing to the magnetic field will depend on what the ball bearing is made of -- specifically its magnetic susceptibility. If its made of Iron/Nickel/Cobalt/Manganese or a ferro/ferrimagnetic material, they'll be a very strong response, if its made of something that's only paramagnetic/diamagnetic like aluminum or titanium its will likely have next to no response to have a minimal response to the field. (The force on an iron ball is roughly 100 million times stronger than on an aluminum ball due to the difference in susceptibility.) ",
"Now the F = gradient (M . B) -- where M is the magnetization (the magnetic field induced in the material which is basically dependent on the magnetic susceptibility and the field it is in), B is the B field, and gradient basically points in the direction of maximum change and is greatest when things are changing the fastest. That is the greatest force will not be when the ball is in the center of the magnet (there the B field will be pretty uniform so the force will be almost zero, until you try moving it out), but when the ball is entering/leaving the magnet. Again, modern MRI machines work with a superconducting electromagnet that is always on (except the very rare shutdown when the magnet is quenched and the current turned off).",
"Finally, while the response to entering the MRI's magnetic field is the main danger (with the metal ball getting ripped through your body), there is also the danger of the metal absorbing the radio frequency (RF) pulses during the actual scan. (Roughly, an MRI works by sending RF pulses to excite the nuclei's magnetization to decay at different rates based on the tissue its in.) You know how its bad to put metal in a microwave as it heats rapidly and can cause arcing, because it absorbs electromagnetic waves so well? Its similar for the RF pulses of an MRI -- it absorbs the energy very well and can cause severe burning of the surrounding tissue. So even if you swallowed a non-magnetic ball that's still a decent conductor, your stomach could get severely burned during the MRI scan."
] |
[
"I'm not exactly sure what the clinical protocols (I tend to stay on the research rather than clinical side of things), but I believe they wouldn't MRI an unconscious person (without medical history or someone vouching for metal not being in their body) for fear they had metal in their body/pacemaker etc. So you'd get Xray (or CT) if imaging was required. Before every research scan I've done, the subject being scanned has to sign a lengthy disclosure form saying they don't have metal in their body, list any prior reaction to gad contrast, etc."
] |
[
"This is why Magneto kicks ass."
] |
[
"Chimp Feet versus Human Feet"
] |
[
false
] |
Chimps appear to have "hand-feet" with "toe-thumbs" which I assume would give them greater dexterity and grabbing ability. Humans lost this feature in the transition from ape to human. I am curious about the following: Is there a biomechanical advantage to the human foot? For example, does it make us faster? Does it make it easier to walk/run for extended distances?
|
[
"The human foot is often described as a rigid lever during human walking and running. This is in contrast to what we see in apes, which is an opposable big toe, which resides on a foot that is much more loose (the foot joints are generally more mobile). ",
"A rigid foot is definite a benefit when you're constant walking on flat ground, and no longer need a grasping big toe during movement in the trees. This is because when we propel ourselves during walking or running, you're calf muscles contract and in turn some of that forward force is transmitted through the foot to the ground. A rigid foot resists deformation, and more efficiently transmits that force. ",
"One of the other big things that has changed is that the big toe is much more robust compared to the other toes in humans. This is because at the end of each step, the big toe is transmitting a lot of force to the ground, and a big, robust toe is more able to deal with the stress. "
] |
[
"Ah very cool, I expected an answer like this but I am very glad to have it confirmed. Thank you for taking the time to type it up."
] |
[
"Would you say the condition seen in humans represents a change from a chimp-like foot, or are chimp feet and human feet derived from a common ancestor who looked like neither/both? I think the OP is assuming the former."
] |
[
"AskScience AMA Series: Summer is tick season. We are experts on the science of Lyme disease (and other tickborne illnesses), and we are here to answer your questions. AUA!"
] |
[
false
] |
Lyme disease, an infection caused by the bacterium Borrelia burgdorferi that is primarily transmitted by Ixodes scapularis (also known as blacklegged or deer ticks), . Beyond the characteristic erythema migrans ("bullseye") rash, symptoms range from arthritis to damaging nervous and cardiac systems. With so many cases every year, it is imperative that everyone learn what steps can be taken to minimize and prevent Lyme disease infections while also getting up to date on the current scientific and medical interventions being used to treat and cure Lyme disease in infected individuals. Join us today at 2 PM ET (18 UT) for a discussion, organized by the American Society for Microbiology, about all aspects of Lyme disease (and other tickborne diseases). We'll take your questions and discuss what people can do to prevent Lyme disease, how Lyme disease is best diagnosed and treated, and what to do if you suspect that you have Lyme disease. Ask us anything! With us today are: Links: Please note that we will NOT be making medical diagnoses or recommending any medical treatments or procedures for individuals.
|
[
"Why are lymes disease vaccines readily available and recommended for pets, but not for humans?"
] |
[
"Yes, there have been different Lyme disease vaccines available for pets, mainly dogs, for many years. One type, based on the OspA protein of the Lyme disease bacterium, is essentially identical to a human Lyme disease vaccine that underwent a large clinical trial and was approved by the FDA for human use. It was available from 1998 to 2002 but was withdrawn from the market by the manufacturer. It's a complicated history but here are a couple open access sources that cover it well from a social as well as medical perspective: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3460208/",
" and ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870557/.",
"\nMy own view is that two events in particular helped tipped the scales against acceptance of the vaccine. One was a lukewarm recommendation of the vaccine advisory panel to the Centers for Disease Control and Prevention (CDC) and the other was a scientific paper that suggested that the arthritis some Lyme disease patients suffered with was the result of a damaging autoimmune reaction to the OspA protein during infection. That conclusion was subsequently refuted and no longer promoted, but by that time the vaccine was off the market. But there has been renewed interest by pharmaceutical companies in a human vaccine, as people recognize the continuing spread of Lyme disease, the disabilities it causes, and the limited means to prevent it. One new vaccine based on the OspA protein is undergoing clinical trials and others are in the works."
] |
[
"After contracting Lyme Disease, at what point is it actually incurable? As in, what is the timeline after being that it is considered permanent?"
] |
[
"How do pulsed neutron sources work and when are they utilized?"
] |
[
false
] |
I know that the pulsed sources have been used in particle accelerators, but don’t most of them use proton beams?
|
[
"You can produce a beam of protons using a proton accelerator. To reach high enough energies in a reasonably-sized accelerator, you will need some kind of RF or induction accelerator as opposed to an electrostatic one. ",
"Using an RF accelerator necessitates that the proton beam be bunched longitudinally.",
"The protons should have energies on the order of 100 MeV to GeV. Then you can just shoot the pulsed, high-energy proton beam onto a thick, solid or liquid target, made of something like tungsten or mercury. Spallation reactions will occur in the target, which smashes the target nuclei to pieces, resulting in the emission of multiple neutrons. The neutron kinetic energies follow a continuous spectrum ranging from zero up to the proton beam energy. Because the proton beam has a pulsed time structure due to the accelerator RF, the neutrons will also have a pulsed time structure. In order to spread out the neutron pulses in time, the proton beam may be injected into a secondary \"accumulator ring\", where multiple proton bunches are collected and manipulated before finally being sent to the target.",
"So now you have a neutron source with many different neutron energies, and pulsed in time, to do with as you please. These kinds of machines are used for experiments in nuclear physics, materials science, etc.",
"Some examples are ",
"SNS",
" at Oak Ridge and ",
"LANSCE",
" at Los Alamos."
] |
[
"You can also use a 'chopper' to turn a continuous neutron beam into a pulsed one, which is essentially a rotating disk or drum made of neutron absorbant material with slits/holes. One big advantage of pulsed neutron sources is that it is generally difficult to measure the energy of a neutron at the detector, but if your neutrons are in pulses and you know both when it set off and how far it has travelled, you can determine the velocity from the 'time of flight'."
] |
[
"Interesting! Is the only way to create a pulsed neutron source from a proton beam?"
] |
[
"If I get bitten by a snake, does it matter how many times I am bitten?"
] |
[
false
] |
For example: I have been bitten by a snake whose venom will kill me. I obviously need to get to the hospital for anti venom. Should I try to grab the little fecker who bit me for identification? As I have been bitten anyway, am I immune to extra bitings?
|
[
"It depends on where you are in the world, as different snakes have different venoms and different countries have different procedures to deal with those venoms.",
"No, being bitten once does not make you immune from being bitten a second time. The amount of venom plays a role, and multiple bites usually means you've been envenomated with more venom (not always, though-- some snakes can inject an awful lot with a single bite, and some may give \"dry\" bites without any venom). There's a local story about a guy who was bitten by a king brown snake and decided to put it in a bag for ID, only to be bitten ",
" more times in the process. His outcome was not so good.",
"The importance of accurate identification varies according to country. In Australia we have a swab test that identifies the antivenom type needed from venom residue left on the skin, making visual ID unimportant. I'm not so familiar with snakebite procedures in other countries, so reading up on your local snakebite procedures is a pretty handy thing to do."
] |
[
"If you're in Aus, you don't really even need to worry about polyvalent antivenoms now that we have the venom detection kit. It's why it's super important to not wash the bite site."
] |
[
"That would cause huge problems. Antivenom has ",
"a variety of side-effects",
"-- the more vials of it you need, the more problems can occur.",
"Antivenom isn't a single \"magic bullet\" injection, by the way. It's given through IV in hospital slowly over half an hour or so, with adrenaline standing by in case of anaphylaxis. If handled incorrectly, antivenom can kill you even faster than the venom can."
] |
[
"Why does the shower curtain pull inward when I turn the shower on?"
] |
[
false
] | null |
[
"\"Bernoulli effect theory:",
"The most popular explanation given for the shower-curtain effect is the Bernoulli's principle.[1] Bernoulli's principle states that an increase in velocity results in a decrease in pressure. This theory presumes that the water flowing out of a shower head causes the air through which the water moves to start flowing in the same direction as the water. This movement would be parallel to the plane of the shower curtain. If air is moving across the inside surface of the shower curtain, Bernoulli's principle says the air pressure there will drop. This would result in a pressure differential between the inside and outside, causing the curtain to move inward. It would be strongest when the gap between the bather and the curtain is smallest - resulting in the curtain attaching to the bather\"",
"I've always heard this explanation as fact...",
"Edit: Thanks for the downvote douchebag, apparently you've downvoted everyone else who responded to this thread. "
] |
[
"The other responses here are saying 'hot water', which probably has some affect, but does not explain the 'shower-curtain effect' given it still occurs when the water is cold. ",
"This is actually a well discussed phenomena with no definite conclusion. ",
"Have a read",
"."
] |
[
"A physicist by the name of David Schmidt won a sort of joke Nobel prize for his research in this area. He ran a simulation of the fluid dynamics within a bath with a shower curtain and found that a \"horizontal vortex\" formed inside.",
"Basically, the running water causes the air in the bath to rotate on a plane parallel to the shower curtain, forming a vortex. The middle of a vortex is a low pressure zone, which sucks the shower curtain inward.",
"The other theories probably contribute to the effect as well, it's most likely that it's produced by a combination of mechanisms rather than just one.",
"Article on Wikipedia"
] |
[
"Is sweating an indication of burning calories?"
] |
[
false
] |
If I'm laying completely still in the sun, and sweating profusely, am I burning calories?
|
[
"Everything your body does requires energy. Sweating is more an indication of overheating since evaporating sweat is a cooling mechanism. Although people can also sweat because they are nervous. The act of sweating requires energy as water is excreted from the skin but it is not a direct indication of high energy use. "
] |
[
"Sweating is primarily about heat regulation as ",
"/u/applemonkeyman",
" says. Evaporating sweat cools you down, so you sweat when your internal temperature goes beyond a certain point. Sweating can also be a response to stress/anxiety. Some people have been known to sweat after eating spicy food.",
"There are other oddball conditions, such as gustatory sweating (you sweat when you eat, or when you see/think of food) caused by mixed-up connections between the parotid gland that produces saliva, and the nerves that innervate the skin on your face."
] |
[
"I think so, sweating is the body's way of regulating temperature and any process such as this requires energy. The amount of sweat released depends on a lot of factors, for example, if the person is overweight, they will sweat more as the body needs to exert more energy to cool down. So use of energy = burning of calories surely?"
] |
[
"In math, are there any proofs that can only be completed by contradiction? If so, how would someone go about proving that?"
] |
[
false
] | null |
[
"(in this post I'm using ",
"~",
", ",
"V",
", ",
"^",
", and ",
"->",
" for negation, logical OR, logical AND and implication, respectively)",
"It depends on what you call by \"proof by contradiction\". If you are trying to prove a negation the only way to do that is by contradiction (if P being true leads to a contradiction then (not P) is true). On the other hand, proving a positive by contradiction (not P being leads to a contradiction therefore P must be true) is something more controversial that you can try to see if its possible to do without.",
"Intuitionistic logic",
" is what happens when you do that. It is essentially the traditional classical logic but without the rule for (~~p -> p) or, equivalently, without the rule saying that (p V ~p) holds for every p.",
"Proving that something is impossible to prove without these rules is kind of tricky. The traditional way involves a theorem showing that any proof you can write could be simplified into a special \"normal\" form if you wanted to. You can then use exhaustive case analysis to show that this special normal proof does not exist for your statement and therefore, no proofs at all can exist for it.",
"Anyway, for some examples, my textbook gives the following examples as things that cannot be proven in intuitionistic logic (and therefore require proof by contradiction or case analysis):",
"((p -> q) -> p) -> p",
"p V ~p",
"~~p -> p",
"(~q -> ~p) -> (p -> q)",
"~(p ^ q) <-> (~p V ~q)",
"(p -> q) <-> (~p V q)",
"And since I'm feeling like writing a lot today, I would like to add two interesting points.",
"The first one is that intuitionistic logic is not only useful as a mathematical curiosity. It has many applications in computer science, since it turns out that the kinds of statements you can prove in intuitionistic logic correspond very closely with what sort of things you can have a computer compute. Computers must also constructively calculate every value they use - they can't get a value out of thin air from a double contradiction.",
"Secondly, I would like to link to this neat example of a ",
"nonconstructive proof",
" that is only possible in classical logic but is forbidden in intuitionistic logic."
] |
[
"As a computer Science major, proof by contradiction is the most popular method for proving the Acceptance Problem for Turing Machines is undecidable."
] |
[
"Sure, proving that something can't exist (a negation) is precisely what you need proofs by contradiction for."
] |
[
"If Alternating Current changes the direction of current periodically then how do we have positive wires at our home?"
] |
[
false
] | null |
[
"Its not actually positive. It's hot. One wire sends power out to the switch, which interrupts the hot, then from the switch to the device. Imagine the electricity surging back and forth by the smallest increment of distance that you can at that switch 60 times per second waiting to jump through it and complete the circuit.",
"Neutral is the return leg, and comes from the device back to the panel. ",
"Once the switch is closed and you complete the circuit through the device, both wires will appear to be hot, having voltage and current. However, only the black or red will have electricity when either a device is not plugged in, or the switch to a permanent device (light fixture) is off. ",
"This excludes 240v devices, where both wires are always hot."
] |
[
"This excludes 240v devices, where both wires are always hot. ",
"This is only true in the US/North America, correct?"
] |
[
"Yes, according to Google, European 240v is 1 hot, 1 neutral and a ground as opposed to NA where its 2 hots at 120v a neutral and a ground.",
"I learned something today, thankyou."
] |
[
"When was Darwinian natural selection accepted over other theories of evolution such as Lamarckism?"
] |
[
false
] |
I suspect the discovery of DNA and genetics provided the evidence the theory needed but I'm not sure.
|
[
"It was a pretty gradual process. First off, it's worth noting that most of the time when we talk about Lamarck we don't fully appreciate to what degree he ascribed agency to nature. He believed not just that acquired traits were inherited, but also that organisms evolved because they were responding to a sort of innate drive to better themselves, that everything in nature was constantly advancing up a kind of ladder of being, and that new, \"lower\" organisms were constantly appearing out of nowhere to fill in the gaps as beings \"above\" them evolved upward. As far as I'm aware, this kind of teleological thinking was becoming unpopular already in Darwin's day, and wasn't heard much after the close of the 19th century.",
"If we use \"Lamarckism\" loosely as meaning \"inheritance of acquired traits\", then even Darwin himself was actually a Lamarckian to some extent. He thought that active use and disuse of organs and limbs during an animal's life would result in growth or atrophy that could then be inherited. What set Darwin apart was that he proposed natural selection (a phrase he also coined, although he wasn't the first to think of the concept) as the ",
" driver of evolution. Darwin became the face of evolution pretty much as soon as ",
" was published, but his model of evolution wasn't universally accepted as the best one until after his death, partly because there were bits missing from it.",
"The most important things happened in the early 1900s, during what we call the ",
"Modern Synthesis",
". At that time, Darwin's missing pieces - Mendelian inheritance (which solves the problem of novel traits blending into the noise of the gene pool through mixing), and mutation (which explains where new traits come from in the first place, a problem that Darwin failed to solve satisfactorily) - were woven together with natural selection into something that finally made sense. Mutations were already known in the 1800s (Darwin calls them \"sports\" in his writing), but ",
"Morgan's work on fruit flies",
" demonstrated that they actually produce novel Mendelian alleles (gene versions), making them feasible as a source of genetic variation. Furthermore, the advent of population genetics meant that selection and evolution could actually be quantified, calculated and measured in theoretical or actual gene pools.",
"DNA was ",
"discovered in the late 1800s",
" - around the same time that Mendel was discovering the principles of genetics, in fact - but it wasn't until the 1950s that DNA was ",
"demonstrated to be the carrier",
" of genetic material, and shortly thereafter, ",
"had its molecular structure figured out",
".",
"Studies of DNA in the 1950s and onward showed ",
" genetic information is encoded, mutates and is passed on on a cellular and molecular level. In this way DNA science did clarify the mechanisms and help solidify evolutionary theory, but really, at the start of the 20th century we already knew enough on a black-box level to conclude that ",
" natural selection makes sense and can indeed produce and adapt new variants and species, and ",
" acquired traits aren't usually inherited, so Lamarckism doesn't really work. A few decades into the 20th century, natural selection had definitely become the mainstream in evolutionary science. Mind you, Lamarckism ",
" wasn't truly dead, and in the 1920s there were still some researchers who tried to demonstrate inheritance of acquired traits - google Paul Kammerer's work on midwife toads if you want an interesting story of controversy, scientific fraud and (possibly) Nazi conspiracy.",
"Finally, of course, later developments in DNA science have also added the corollary that ",
" some acquired information really ",
" inherited, albeit not in the way Lamarck envisioned. These processes, and the study of them, are referred to as epigenetics.",
": Added a couple of links and notes."
] |
[
"Great summary, we really do treat Lamarck as a caricature today. He wasn't totally giraffe-neck crazy, he was just wrong.",
"The process of epigenetic inheritance, where information not written in the DNA code can be passed on to the next generation, is far from settled. It definitely occurs in plants, but it's not known how significant the changes are in animals or if they can persist long enough in populations to affect natural selection. "
] |
[
"Honestly, I feel almost the opposite about Lamarck - the contemporary conversation about him ",
" just how crazy his views were by modern biological standards. That said, it probably said more about his time than it did about him as a thinker. Teleological reasoning didn't leave evolutionary science until well after Darwin, and you still find it lingering in how people talk about evolution today."
] |
[
"pros and cons of popular disinfectants?"
] |
[
false
] | null |
[
"We don't offer any form of medical or safety advice on this sub including product evaluations. Please see the guidelines. "
] |
[
"I am not deciding on which one to use and i am in no need of using one i’m just asking why doctors use them in those situations (sorry for any troubles but i do truly believe it fits within the guidelines)"
] |
[
"Oh I see. In that case, I recommend making a new post with a different phrasing; perhaps something like: why are different kinds of disenfenctants used in different situations? "
] |
[
"Given a closed small closed system that doesn't expand, would baking soda and vinegar create enough pressure to where some of the reaction would not occur?"
] |
[
false
] |
If given a closed container with infinite strength, what would happen if baking soda and vinegar were introduced? Would it eventually create enough pressure that they don't react with eachother?
|
[
"According to the parameters you have laid out (and assuming this experiment was taking place at room temperature): No.",
"Vinegar is an aqueous solution of acetic acid, typically at a concentration of 4-12%. That leaves the remaining 88-96% water.",
"The reaction acid-base reaction in this system is:\nCH",
"COOH ",
" + NaHCO",
" ",
" --> CH",
"COO",
" ",
" + Na",
" ",
" + CO",
" ",
" + H",
"O ",
"We see that the CO",
" formed will be in the gas phase, which could potentially build up in pressure and cause some sort of equilibrium halting the completion of the acid-base reaction. ",
", CO",
" gas is moderately soluble in water. Any headspace pressure built up from the CO",
" production would be mediated by the abundant reservoir of water before halting the acid-base reaction.",
"On the other hand, scenarios where I could imagine such an equilibrium ",
" or ",
" develop would include conducting the experiment with glacial acetic acid (i.e. anhydrous or water-free acetic acid) or in a system not at room temperature but nearer to the boiling point of water, where CO",
" is minimally soluble in water.",
"edit: damned subscripts!"
] |
[
"I didn't even know Reddit had subscript formatting. You have enlightened me.",
"For those wondering, it's ",
"*_subscripttext_*",
" to get ",
" (hooray for RES's Source feature). "
] |
[
"Yes, because LeChatlier's Principle and the change in pressure due to closed boundary conditions (e.g., fixed volume). ",
"A change in one of the variables that describe a system at equilibrium produces a shift in the position of the equilibrium that counteracts the effect of this change.",
"At some point the reaction stops, and reaches equilibrium (delta G = 0). ",
"Not ",
" the exact same scenario, but this type of thing ",
"occurs on nature in caves",
" ",
"Except in a closed system, perhaps even ",
"adiabatic or isothermal",
" in this case (you said \"infinite strength\"), nothing is introduced, and nothing leaves, not even energy. So the system MUST reach equilibrium at some time T. That doesn't infer the system will be at equilibrium at time t (where time t is some arbitrary time value) but will return to equilibrium assuming no outside influence to T, P, etc. ",
"Another good reference system to look at is the human body. Hopefully you don't put one in a vacuum. That would be bad!"
] |
[
"Is it possible to solidify a pure noble gas?"
] |
[
false
] | null |
[
"Yes it is. Even though the Noble gases don't have large IMF (inter-molecular forces) they still have London dispersion forces which if you take enough energy out of it in theory it could be a solid around absolute zero"
] |
[
"Yep - for instance Radon, which is admittedly one of the easiest has a melting point of - 71 C, which isn't even that cold (you can get that cold with a dry ice/acetone bath)."
] |
[
"Actually it's way lower. The average temp of the universe is only a little more than 2 K, the lowest number I'm seeing is 100 picokelvins, just 0.0000000001K. They have all sorts of fancy equipment they use to do this like the ",
"dilution fridge",
". ",
"Here's",
" a pretty cool video where someone describes how they work."
] |
[
"Burning question: how does Magma emit light?"
] |
[
false
] |
How ~ does ~ magma emit light? And - in the hypothetical scenario that we have access to a heat-resistant camera that could survive a submersion in a magma pool or stream - what would we see? Would there just be darkness? Or would we still see the radiant light that we see at surface? Thanks in advance!
|
[
"All objects in the universe emit so-called ",
"thermal radiation",
". This radiation is electromagnetic radiation (just like radio, visible light, etc.) and it is emitted across a wide range of frequencies. The frequencies that are emitted, and how ",
" of each frequency, depends on the temperature of the object: ",
"hotter objects emit more radiation",
", and at higher, more energetic frequencies.",
"The sun, at a blazing-hot 5,778 K (5,505 °C, 9,941 °F), emits a ton of visible light, as well as other frequencies from radio waves all the way up to X rays. Somewhat less hot objects, like a steel-forging furnace, will emit some visible light, but ",
"mostly at the longer, less energetic frequencies at the red end of the spectrum",
". Humans, around 310 K (37˚C, 98˚F) ",
"emit a lot less light, and mostly at far-infrared frequencies",
". Side note: ",
"this is how infrared goggles work",
", detecting the IR light being emitted by different objects and determining what temperature those objects are.",
"You may see where I'm going with this. Magma (technically called ",
"lava",
" when it's above ground and visible), is kind of hot. Not as hot as the sun's surface, but way hotter than your skin or mine. Probably pretty close to the steel forging temperatures I mentioned above. Due to this fact, it emits a significant amount of thermal radiation as visible light, though most of it is longer, less energetic wavelengths, closer to the red end of the spectrum. This is why we see lava as glowing red or orange.",
"As for the second part, that's pretty easy: assuming you could make such a camera, it would see the same orange-red light that we see at the surface, though it might be a little yellower and brighter the deeper you go, since the temperatures get hotter when you go deeper."
] |
[
"Just so you're clear, visible light isn't the only 'light' out there. It's a small chunk of the ",
"electromagnetic spectrum",
".",
"The radio waves we use to communicate, that's light. The microwaves that heat your food, that's light. Just because it's not visible doesn't make it not light.",
"The common thing between all of them is that they're all electromagnetic waves, AKA photons, AKA ",
"electromagnetic radiation",
". They have different properties when at different wavelengths/frequencies.",
"Low frequency/long wavelength light, like radio waves doesn't carry much energy.",
"As you increase the frequency, the wavelength gets shorter, and the energy increases.",
"High frequency/short wavelength light like gamma rays carry enough energy to be harmful to humans. Remember the word radiation from earlier? This is the kind of light you'd worry about if there's a 'radiation hazard' around.",
"In the middle there's the kind of light that our eyes have evolved to see.",
"Everything with a temperature above absolute zero radiates some form of light. Really cold things radiate in radio, or microwave light. The hottest stars and supernova events give off gamma waves. The hotter something is, the more energetic the light it gives off.",
"As you're reading this you're radiating infrared light. Infrared is the type of light right below the visible spectrum.",
"Have you ever seen a piece of iron or steel being forged? They heat it up and at first you can't see anything, but as the metal gets hot it starts to glow with a red light. That means it's hot enough to radiate the lowest energy visible light, red.",
"That's exactly what lava and magma are doing. They're molten rock that's hot enough to radiate visible light. If you stuck a camera in lava it would pick up that light."
] |
[
"Yes, the light is moving between every little bit of rock under the surface, as well. Your camera would see light down there (then melt, even if made of magical force fields, because the very same light it needs to image anything cannot be dumped back out again, so every photo you take must heat it up... but I digress)",
"The core is also hot enough that things would become blue-hot not just red hot like surface lava."
] |
[
"How good are we at identifying sexual dimorphism in extinct animals?"
] |
[
false
] |
Sexual dimorphism can run a huge gamut between simple size/coloring changes to things like the angler fish that look completely unrelated. The differences between species in the fossil record is often extremely small, sometimes involving tiny distinctions in certain bones. Is there a reasonable chance some of these species are really just different sexes of the same species and how do paleontologists approach that?
|
[
"Obviously this depends a lot on the particular type of animal in question, but the point you raise is certainly an important one.",
"Firstly, for many extinct animals it is non-trivial to identify sex ",
", let alone start to build a picture of sexual dimorphism. In the case of dinosaurs, for example, it is sometimes possible to positively identify a female by the presence of medullary bone, a type of tissue that is only formed during egg-laying. This was first done by ",
"Schweitzer et al. 2005",
" with a ",
" specimen, but this technique is rarely applicable, and of course cannot identify males or females during other stages of life. Others have used context clues to infer that dinosaurs found near clutches of eggs are female, but these are just biased assumptions - and indeed, more rigorous work comparing clutch sizes with those of modern birds suggests that at least some dinosaurs had paternal care (",
"Varricchio et al., 2008",
"). Ultimately, it is quite hard to definitively say that a specific fossil is male or female, a fact which recently led to Sue the ",
" officially changing to ",
"they/them pronouns on Twitter",
".",
"Even in some cases where we can identify features that are almost certainly secondary sexual characteristics of one sort or another, there are still potential issues. ",
"Lambeosaurine hadrosaurs",
", with their diverse array of head ornamentation, are a prime example. In at least one case, two groups of specimens that had previously been thought to represent males and females were found, on closer inspection, to have no temporal overlap, and were separated by at least half a million years (see ",
"Stokstad 2006",
" and ",
"Evans and Reisz 2006",
"27%5B373:AAROLM%5D2.0.CO;2)).",
"There is the possibility of using a purely statistical approach to try to find distinct morphological groupings within a species that may be sex-associated, such as ",
"Larson 1994",
"'s \"robust\" and \"gracile\" ",
" specimens, but small sample sizes (15 in that case, which is more than most dinosaur species have available!) and difficulties due to different developmental stages will always present potential issues with such studies. That said though, there are definitely some which present pretty convincing arguments for the presence of two identifiable sex-associated groups, such as ",
"Bennett 1991",
"'s examination of over 1000 specimens of ",
"/",
". Of course, it helps that these individuals are both numerous and also ",
"quite highly sexually dimorphic",
" in the first place.",
"So in summary, I would say that we are not very good at accurately characterizing sexual dimorphism in the fossil record. As you suggest, there have indeed been at least some cases where what we now think of as different species were once considered different sexes of a single species, and its very possible that the reverse also occurs. I'll leave you with a review by ",
"Mallon 2017",
", which investigates sexual dimorphism in dinosaurs more thoroughly than I ever could, and in fact fails to find statistically significant evidence for such a pattern in any of the nine species examined."
] |
[
"As you suggest, there have indeed been at least some cases where what we now think of as different species were once considered different sexes of a single species, and its very possible that the reverse also occurs.",
"Wasn't Triceratops found to be the juvenile/young adult form of Torosaurus?"
] |
[
"That's a whole other can of worms, but yes, that idea was proposed by ",
"Scannella and Horner 2010",
". However, there has been a fair bit of pushback from other researchers on this (e.g. ",
"Longrich and Field 2012",
", ",
"Maiorino et al. 2013",
"), and so in general I believe the majority consensus is that ",
" is still valid."
] |
[
"How accurate is the notion that all human embryos start out on a female path of development?"
] |
[
false
] |
I've seen it claimed before that all human embryos start out on a female path of development and that male development kicks in due to the SRY gene, while female embryos continue on the default plan of development. How true is this? Is it more accurate to call male development the variation and female development the default, or is it more accurate to call embryos undifferentiated initially? Is female embryonic development influenced by sex specific genes in a manner similar to male embryonic development?
|
[
"Short answer: yes and no, depending on how you want to phrase the question.",
"Long answer: So genetically, X is the basic plan and the Y chromosome changes things up. This makes sense, considering that you can't live without at least one X chromosome while the Y is a very stripped down chromosome with SIGNIFIGANTLY fewer genes on it than the X. (This is the case in humans and closely related species. There are different ways of sex differentiation but that don't matter here.)",
"Developmentally, the gonads of both sexes (the ovaries for woman and testes for men) come from the same initial tissue structure which I have seen called the primordial gonads, which is a cool name. The gonad does not start as an ovary then change, it comes from a blank slate which is specialized for its future role. In both cases the gonads descend to some extend with the hwlp of the gubernaculum, but males, the gonads descend and become external as the testes while the ovaries remain internal. There is a loooot more to the differentiation clearly but that involves describing the Genesis of different cell lines and other cool but long winded stuff.",
"There can be dysfunction in the development of the gonads (and sexual organs in general) due to flukes, chromosome nondysjunction and similar issues giving you more X or Y than you should or the disbalance of certain hormones during development. These disorders can ranger from the gonads failing to properly descend (especially prominent in boys) or a very undifferentiated genital structure."
] |
[
"Essentially, if you're walking on a path that forks to the left and the right, you weren't on the left path the whole time, nor the right. You're on ",
" path. did I get that right?"
] |
[
"Yes. But you can only go down one of those paths unless you have a key for the door of the second one."
] |
[
"Why do computers use base 2 instead of base 10?"
] |
[
false
] | null |
[
"You ask",
"Wouldn't a computer that uses base 10 natively process calculations in those disciplines faster than a computer that has to translate everything to base 2 and then back?",
"There's two aspects to an answer:",
"Radix 10 computers did exist. Babbage's engine and the \"Witch\", for instance. They were costly and inefficient. A binary circuit is easier by design; a single voltage threshold suffices, no analog precision to take care of, and that also makes it smaller & cheaper.",
"There are very few algorithms which are influenced by the choice of radix (e.g. radix sort on a specific domain). Even then, the gains (which are not complexity gains, but constant) can not justify changing the entire infrastructure (runtime, language(s), OS, drivers, and so on) of the execution environment.",
"Questions like this often come up in introductory computer architecture classes. There are quite a few quality online courses nowadays by top universities. I would suggest you choose one and follow along if you want to know more!",
"Cheers!"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"thats fine. just curious would you mind steering me in the right direction so i can learn why it's fundamentally flawed? i dont mind googling it, but if you know off hand that would be helpful. thanks"
] |
[
"Is it possible for a brown dwarf to emit enough light that a human on an orbiting planet would be able to see (to some extent)?"
] |
[
false
] |
I'm working on a science fiction setting in which a small planet orbits a brown dwarf. A group of crash survivors live in a crater at the north pole. The climate is temperate but dark, akin to a summer's evening. The warmth comes partially from the planet itself (for reasons that can't be revealed quite yet). The sun stays low against the horizon, visible perhaps due to refraction in the atmosphere or from the permanent rain/fog at the crater's lip. I've done some basic research but I'd love to hear whether thinks this is feasible. If it's not entirely plausible, do you feel you could maintain a suspension of disbelief in such a setting?
|
[
"I love astronomy. IIRC, your planet will have to be very near the brown dwarf to provide a livable temperature and it will be ",
"tide locked",
" with one side permanently facing the sun.",
"Survivors living in a crater on the sun-facing side with a huge, dim sun the color of dried blood hanging overhead like some baleful eye would be much more believable. ",
"edit: Imagine a dim sun covering half the sky and you have the idea. Also, don't brown dwarfs have a problem with occasional flares?",
"more editing: from wiki",
"the actual appearance of T dwarfs to human visual perception is estimated to be not brown, but the color of [magenta coal tar dye] ",
"http://en.wikipedia.org/wiki/Magenta_(color)#Magenta_dye_.281860.29",
"). [6][7]"
] |
[
"A typical brown dwarf will have a luminosity of 10",
" - 10",
" Watts. Some have temperatures above 3000K, meaning there would be plenty of emission in the visible spectrum, even down to the coolest stars at several hundred degrees. ",
"The light you see decreases with the square of the distance from the star. So for example, I'm sitting 3 feet from a 60W light bulb, and it's plenty bright. If I were 3 feet from a 10",
" W brown dwarf star, it would be a whole different story. ",
"At earth distance, a brown dwarf would be 0.1-0.01% as bright as the sun. But this would still 10-100 times brighter than the full moon."
] |
[
"Thank you! Could (something like) constant volcanic activity be enough to keep the planet warm at further distances from the sun?"
] |
[
"Why is recovering data from a failed external hard-drive so complicated?"
] |
[
false
] |
This has happened to me twice now. Brought my failed drive to a computer store only for them to tell me it needed to be sent off to some specialist, costing upwards of $1500, to recover the data. The tech at the store said the process is quite complicated. I'm definitely ignorant of how data storage works but it seems like it should be a relatively straightforward process. Is bad design of these drives the problem or is the nature of data storage much more complicated than I'm giving it credit?
|
[
"I wouldn't be able to give you any details, but I can give you a high level idea with what it likely involves.",
"Hard drives having moving parts in them (the disk is spinning, an arm is moving back and forth, etc), if those mechanical things fail, or if there's a more detailed problem with reading it apart from the disk being damaged, then the only way to recover the data is to either open the drive up and fix those parts, or take out the disk and read it with different equipment; and either way that has to be done very carefully so as not to scratch or damage the disk.",
"If it's a problem with the disk itself (scratched, or otherwise) then you'd need take the disk out still, and either attempt to repair the surface of the disk or use more sophisticated equipment to try to read it directly.",
"But I'd love to see a more detailed and technical explanation for how you actually do those things.",
"Moral of the story: back things up on separate drives."
] |
[
"Also, it would need to take place in a clean room (not cheap) to avoid the smallest particles of dust. The data density on modern disks is amazing, so a single bit of dust on a disk can cause havoc. ",
"Sometimes, it's as easy as swapping the heads and/or platters (to a similar HDD donor drive). Other times, it's replacing the electronics. Once you get there, you have to copy the data to a new drive straight away. "
] |
[
"Thanks for your reply"
] |
[
"Why do we still use conventional current?"
] |
[
false
] |
We now know that electrons move in a circuit not the positive charge. If we consider Physics as the model of our reality, why do we still use conventional current. Doesn't it get annoying if you think about the situation practically? Are there any situations where using electron current is a better option than conventional current model?
|
[
"Currents don’t always consist of negative charges. It makes more sense to have the current density point in the direction of motion of positive charges. If you’re dealing with currents that are made by the motion of negative charges, it’s not that hard to remember that the direction of the current density should be opposite to the velocity of the charge carriers."
] |
[
"The problem is the process of switching over.",
"Say tomorrow Congress instructs the US government to reverse the definition of charge. The next day, every company who sells an electrical device in the US has a panicked staff meeting. Every battery maker needs to come out with a new line of batteries with the + and - labels reversed. (And what about the ones like AA that have a bump on one end? Is that still going to be the + side, or is it - now?) Everyone who makes anything with a battery, from remote controls to cars, needs to throw out all their old stock and make new widgets with the + and - reversed in the battery compartment. Everyone who makes a device that measures voltages or currents needs to reverse the scale on their meters. (And what about red vs black wires? Is red negative now, or not?) And what about semiconductor devices? Is a PNP transistor now an NPN? What about every computer chip in the world? They'll still work, of course, but all the blueprints are wrong now. And what about magnetic devices? The magnetic field depends on the current and a right-hand rule. Are we going to say the magnetic field now points the other way, so every device with a magnetic field arrow needs to be redesigned, or are we going to use a left-hand rule from now on? And who makes sure everybody makes these decisions the same way?",
"Oh, and every textbook in physics, chemistry, and electrical engineering needs to be rewritten too. (You might not have thought of chemistry, but that's where it gets ",
" ugly.)",
"Anyway, after trillions of dollars of product redesign, a new array of batteries and devices are manufactured that have the new reversed charge convention, and start to be sold in stores. And that's where the ",
" trouble starts. People buy new batteries for their old cars, connect them up positive to positive, negative to negative, and the cars are destroyed. Parents use some old batteries for new kids' toys, and the toys run backwards or don't work at all, causing mass confusion. An electrical engineer specifies PNP transistors in a circuit, but someone uses the ",
" ones instead of the new ones, and a whole product run is scrapped. A chemistry student uses chemical data from last year's textbook, and gets all her homework wrong -- or worse, if she's doing a lab. Some amateur electrician hears about the changeover, mistakenly assumes it applies to alternating current as well, flips the black wire with the white wire while fixing his vacuum cleaner and electrocutes his wife. ",
"After more trillions of dollars are spent throwing out all the old electrical stuff and replacing it with all new equipment, there's a knock on the door, and hey, it's an ambassador from the European Union, who wants to remind the US that other countries exist, that nobody can rewrite the rules on electricity for the whole globe, and given the disastrous rollout in the US, the EU would like to keep electrons negative please. So now and forever more, every US device needs to be cross-wired positive to negative to connect it with an EU device. Hope you remember that when you're jump-starting your Audi, but the real trouble is Boeing, whose new Dreamliner is made with a cockpit built in the US, batteries from Japan, landing gear from France, and engines from either the UK or the US, depending, every part with a hundred wires labeled positive and negative. Or maybe negative and positive.",
"You get the picture: often, the changeover from a bad system to a good one is so awful it's better to stick with the bad one."
] |
[
"Another way to put OP's question is: why not consider that the electron charge is the positive one?"
] |
[
"Did the Hanford B reactor generate steam?"
] |
[
false
] |
I know they piped in huge amounts of cold water from the Columbia river to keep cool. I was wondering if this river water was heated enough to boil in the reactor.
|
[
"Cripes, my apologies - I hadn't even thought to check whether the Hanford reactors were research ones, rather than standard power generation one.",
"I can find spurious references to the water pumps being able to run on steam power (e.g. ",
"page 12 of this document",
" (pdf)), but can't see anything definite about what the source of that steam might be."
] |
[
"Edit: I really need to learn to read first."
] |
[
"The reactor was a graphite moderated, water cooled reactor. The water was taken from the river and it flowed in tubes within the reactor. Here is an interesting paper on the reactor. It talks about the water flow. The water would not boil within the reactor. That would reduce its ability to absorb heat.",
"http://files.asme.org/ASMEORG/Communities/History/Landmarks/5564.pdf"
] |
[
"Does the legality of virtual child pornography affect the number of incidences of sex offending against children?"
] |
[
false
] |
[deleted]
|
[
"There is approximately zero research into this area. Obviously, you can't change one of a region's laws for the sake of a control group. If you replace \"legality\" with \"availability\" then it becomes slightly easier to research, but still nearly impossible.",
"There are various ways it could possibly be researched. One is to investigate offending and non-offending pedophiles and compare the rates of how much they look at virtual child pornography. However, this is effectively impossible because of the social taboos - you can't FIND non-offending pedophiles. They hide because they don't want to be stoned to death in the streets. Nearly any other method of research will run into the same problem.",
"One method of research that won't run into this problem is to investigate known child molesters who have served their time, been released from prison, and have been out of prison long enough that their parole has ended (since looking at any form of pornography is typically illegal for a sex offender on parole). Such people, if living in a country where virtual child pornography is legal, could potentially be divided into two groups for an A-B study. There aren't many of these people though, they tend to either relapse into sex crimes or get murdered in prison. Even if you can somehow find enough, good luck getting funding for that study; you're more likely to get your office burned down by an angry mob. Not many sociologists are keen to study a topic that has a high chance of getting them branded a pedophile and/or murdered.",
"I will point out that virtual child pornography is absolutely 100% illegal in the US though. The Ashcroft vs Free Speech Coalition case you're citing was made irrelevant a year later due to the ",
"PROTECT act of 2003.",
" That link includes a mention of a federal case that was appealed multiple times and the guilty verdict was upheld repeatedly. To date however, unless a case I'm not aware of has slipped under the radar, this law has seemingly never been enforced except in situations where there was also actual child pornography or child abuse. It's apparently being used to help make convictions on child molesters stick, not to go after people who only download hentai. However I'm sure if you email your ",
" DVDs to the FBI they will be more than happy to put you in prison.",
"I'm not any kind of legal, psychiatric or sociological expert. I'm just someone with... a vested interest. I've had this discussion a lot of times before."
] |
[
"While this post is accurate in some ways it also presents an incorrect narrative that there is no research being done into pedophiles or treatments for pedophiles. ",
"Germany proved providing free of cost therapy works to treat those sexually attracted to children: ",
"http://www.spiegel.de/international/spiegel/therapy-for-pedophilia-i-hate-my-desires-they-make-me-sick-a-441199.html",
"Regardless of what disorder you call the attraction to children the treatments the Germans pioneered works ",
"http://www.ncbi.nlm.nih.gov/pubmed/25471337",
" \nAnd has been studied for over ten years. ",
"As for sexualized toons this is the most indepth article I ever read: ",
"http://scholarship.shu.edu/cgi/viewcontent.cgi?article=1040&context=student_scholarship",
"An argument often made on reddit is that having the will to abuse children is OK as long as you don't act on real children.",
"They argue cartoons and dolls are totally different except they are training themselves to take it to the next level.",
"Those that say they aren't hurting anyone by talking about abusing children, thinking about it all the time, simulating it with cartooms are just training themselves to become a pedophile instead of explaining that process not only goes against societial norms but encourages endangering children instead of seeking treatable without harming anyone. ",
"Mental illness can he difficult to diagnosis. A proper diagnoses from a qualified psychologist is important to determine not only why someone feels and thinks the way they do, but to recommend treatment options. ",
"There are neurological issues at play that could be different from anything you imagine: ",
"http://usatoday30.usatoday.com/news/health/2003-07-28-pedophile-tumor_x.htm",
"\nThis is the line screamed at schizophrenics yet we are to believe that everyone attracted to a child is also a psychologist?",
"Anyone could misdiagnose anything. Professional help is important. ",
"If we have a look at DSM 5\nRef. 1, p 698",
"\"Use of pornography depicting prepubescent children is a useful diagnostic indicator of a Pedophilic Disorder” ",
"DSM-5 states that an indicator of a Pedophilic Disorder would be that an individual has “acted on” his sexual urges (Ref. 1, p 697). “Acted on” could mean that he has actually molested a child. On the other hand, it could also mean that he has masturbated to pedophilic fantasies or that he has viewed child pornography. The current criteria for diagnosing a Pedophilic Disorder place some persons who have never molested a child into the same diagnostic category as those who have done so\"",
"No scientific study or psychological treatment will suggest indulgence of fantasy as healthy, even virtual fantasy. ",
"10% of the population is pedophiles if the German studies hold true.",
"That's not the problem, ",
"Or the very common myth propagated that the DSM doesn't say pedophile is a disorder, when in fact it does.",
"The DSM literary reads “pedophilic disorder\". Classed as a paraphilia.",
"Then somone will say pedophilic disorder is different from pedophile except that is not what the DSM or law says. That's just another myth from /pedofriends",
"A paraphilia is not an orientation and is classed in the DSM as a disorder.",
"Other DSM-5 paraphilias are exhibitionistic disorder, fetishistic disorder, frotteuristic disorder, sexual masochism disorder, sexual sadism disorder, transvestic disorder, voyeuristic disorder and pedophilic disorder. Despite all these things being labeled a “disorder” in DSMs for years, the actions some of them result in — for example, flashing, assault and battery, and “peeping Tom” behavior — are all uncontroversially illegal.",
"Now let's consider who is really paranoid those that claim the cops will lock them up forever or kill them for seeking treatment, a lie, if they seek treatment there will never be a report made unless there is a specific child under threat ",
"Or the entire psychological academia saying only a qualified psychologist can identify a mental ilnness and recommend treatment?",
"People have fantasy and don't define themselves by it. Some fantasy is safe to explore, others are incredibly dangerous. ",
"Pedophiles apply unhealthy sexual addictions and exploitation fantasy to children rather then seeking mental help. ",
"Functional magnetic resonance imaging (fMRIs) and positron emission tomography scans (PET) has revealed that the abnormalities of pedophiles exhibit appear in the frontal and central regions of the brain. In particular, there is a decreased volume of gray brain matter in the ventral striatum. As a result, the nucleus accumbens, orbital frontal cortex, and the cerebellum are all affected\nThe accumbens is the central mediator of reward signaling and expectation. The striatum and orbito frontal cortex control this reward system. As a result, this contributes to the etiology of pedophilia because a reward deficiency complication disturbs the neurotransmission of dopamine involved in compulsive and addictive behaviors.",
"Structural Brain Abnormalities in the Frontostriatal System and Cerebellum in Pedophilia.” Journal of psychiatric research 41.9 (2007): 753-62. Cite:\n",
"http://www.ncbi.nlm.nih.gov/pubmed/16876824",
"Untreated obsession about sexual fantasy can establish feedback loops, habit, eventually addiction to unhealthy fantasy, and eventually self abuse or worse abuse children instead of getting help.",
"People hate child molesters is because they pick on low hanging fruit while knowing damn well the pain and sorrow they cause. The argument is made that someone would take abusive action against someone else that didn't ask for it, doesn't deserve it, has entirely to do with lack of self control. ",
" These impulsive disorders include pathological gambling, kleptomania, and even Tourettes syndrome. There is substantial evidence for the existence of physiological and genetic overlaps. In particular, studies have shown that alterations in the frontostriatal circuitry are a major abnormality leading to obsessive-compulsive behavior. Pedophiles tend to act inappropriately and exhibit poor judgment because they lack the ability to control their impulses:\n",
"http://neuroanthropology.net/2010/05/10/inside-the-mind-of-a-pedophile/",
"However, with therapy and treatment as we've seen from the Germany therapy results and the cultural shift to pushing mentally ill to access free of cost therapy they can live normal lives without letting obsessions and mental illness control them. They can be rehabilitated.",
"Those that have thoughts of abusing others may indeed have a mental illness but that mental illness doesn't make them instantly into a child molester. That is a choice they make themselves. To even allow those thoughts to continue, to explore them, to not immediately seek mental help and use CBT and therapy to figure out why they have the thoughts is inexcusable.",
"Mental healthcare is too important to be left to armchair psychologists"
] |
[
"This article",
" describes sex crimes against both adults and children in several countries before and after online access to porn in general and child porn.",
"In multiple countries they saw a large drop in assaults with the timing correlated to the availability of pornography.",
"The findings support the theory that potential sexual offenders use child pornography as a substitute for sex crimes against children. While the authors do not approve of the use of real children in the production or distribution of child pornography, they say that artificially produced materials might serve a purpose.",
"Now of course virtual porn isn't the same and it might not work as well. On the otherhand, it seems reasonable to at least consider it and potentially study it. Perhaps even allow a trial - say former abusers are randomozed to either usual care vs. Access to virtual child porn?"
] |
[
"If dark matter has no electromagnetic interaction, what would touching it feel like?"
] |
[
false
] |
I understand that the vast majority of forces we encounter in everyday are due to the electromagnetic force. So if dark matter does not interact electromagnetically, what would it feel like to submerse your hand in a bucket of dark matter? Do we even have an inkling of an idea?
|
[
"Yes."
] |
[
"It would feel a lot like being in a bath of neutrinos. This would probably be a good time to point out that we are in fact in a bath of neutrinos, with 65 billion per square centimeter or thereabouts.",
"So yeah, it'll just fly right through you without you noticing. Which kinda puts a damper on the whole bucket thing."
] |
[
"Neutrinos are what's called ",
" yes."
] |
[
"To my understanding, things don't have a choice, why are living beings different, if at all?"
] |
[
false
] | null |
[
"Perhaps I didn't explain well what I meant. ",
"Consider the atoms and molecules that make us up. Those molecules form muscles and other tissues that work thanks to energy that we assimilate. So far so good.",
"A muscle simply moves because an electric signal that comes from the brain tells it to move, then the muscle uses the energy that was stored and performs the actions that we consider movement, but without the brain's signal it can't do that.",
"So this means that, in order to have a choice, we'd have to be able to control when and how to send these signals, right?",
"But as I understad, these signals are sent only as a result of the molecules composing the brain, obeying the laws of physics. When a certain condition is met (we feel pain for example) we (our brain) performs an action (sends an electrical signal, for example move away from the pain).",
"This is fairly simple, but if we go a few levels deeper, to send any signal, a certain condition must be met, it may even be other brain signals.",
"What I wondered is if we have any choice at all over those signals, or they are just results of conditions that we experience. I think it's still not clear, but I don't know how to phrase it better."
] |
[
"Personally, I believe that the result of dice thrown is only deemed random for lack of sufficient information.",
"This would be true classically, but if quantum effect truly randomize the result of each action, then it becomes impossible to predict the result (Given that you try the action in the exact same conditions in different parallel universes).",
"If there was indeed a ",
"hidden variable",
" that lets us determine the result of quantum effects, then it would be really a deterministic universe.",
"Anyway, for the rest I agree with you. There is no reason to know if we tuly have free will anyway. It's just curiosity."
] |
[
"Only answering because it is unanswered. I have to technical info to offer but thoughts. We are a product of \"random\" mutations. I use quotes because of new studies showing that environment perhaps has more of an impact on mutations than previously thought. Anyways, the adult human body is made up of about 37 trillion cells. Big number. Each cell is made up of about the same number of atoms. These numbers could be way off but it doesn't matter because the point is self evident that the body and brain are made up of LOTS of tiny bits. Perhaps 7x10",
" atoms in the body or 7,000,000,000,000,000,000,000,000,000. These atoms are tiny magnets with different sizes and charges leading to different clusters (molecules) forming, that interact in different ways. Every bit of our existence is logical... is an odd thought but seemingly true. Free will and a soul are merely ideas that make our existence more palatable. (I have to admit I can't fully accept this notion, I will never completely rule out the possibility of a higher power) \nAnyways, the process of \"life\" by this point in time where we have gotten this incredibly complex (7x10",
" also has innumerable outside influences that affect us from the moment we are conceived. From the noises we may hear and things we may feel while in the womb to the weather every day of our lives, no two lifeforms have the same experience and therefore do not mutate/change in the same way. Reproducing propagates these differences while introducing more mutations and setting up the next generation to be even more varied.",
"Tl;Dr We would be the same if we were all born in purgatory and had no interaction... And were born identical..."
] |
[
"If there was an ideal environment (such as no predators and unlimited food/habitat resources), would evolution still take place?"
] |
[
false
] |
[deleted]
|
[
"I disagree. Competition is an important factor in evolution, but not a necessary one. Even assuming infinite food/resources/space etc., no competition and no predation, allele frequencies would still change over time. Some genotypes would lead to higher fecundity than others, and they would gradually become more common in the (exponentially growing) population. ",
"Surely, the nature of the genotypes that will rise in frequency will be different than in a real, competitive environment. As a simple example, in the real world individuals that have less offspring may still have higher fitness, because they take better care of their offspring and ensure their survival to adulthood. In this hypothetical \"infinite food\" world, a higher number of offspring would probably have higher fitness even without good parental care. But this is still evolution, just in a slightly different direction.",
"By the way, humans are constantly evolving even today."
] |
[
"For hypothetical purposes, evolution would not be necessary, but it could happen through a mutation that “ups the game” and makes one of the animals more attractive to a mate. ",
"I imagine a good example would be a cockroach. They can survive in what feels like anything, and they really haven’t changed much relatively speaking."
] |
[
"Humans are continuing to evolve. Recent and ongoing changes include the ability to digest lactose as adults, loss of wisdom teeth, malaria resistance, and many more."
] |
[
"[Psychology] Can a healthy and mentally sound adult develop Anti-Social Personality Disorder?"
] |
[
false
] |
I know that ASPD is usually considered hereditary and appears to be expressed at a very young age, but could someone in a healthy environment and in good health develop it?
|
[
"ASPD (and other personality disorders) are theorized to be caused by a combination of genetic, social, and environmental factors. ASPD is entirely possible despite a \"good\" life. You can have a healthy social environment, for example, but if you have a large number of genetic/biological or environmental vulnerabilities, the balance can tip. The problem is that good life or safe life or healthy life are sunjective to the person experiencing it. A minor issue for one could be very traumatic for someone else.",
"It's true that the strict DSM citeria for ASPD specifies evidence of conduct disorder before age 15, but someone who fit all other criteria could be diagnosed with something like 'personality disorder NOS' under DSM IV and ICD-10, or 'unspecified disorder' under DSM 5. A clinician could also diagnose ASPD regardless, if they had solid reason to do so. Conduct disorder is one of those things that some clinicians avoid in some cases, and recollections of childhood are not always as accurate as others would like. Clinicians have to use their best judgement."
] |
[
"Well put and well written. Thank you!"
] |
[
"Thank you!"
] |
[
"When the moon is in the sky during daytime, does it increase brightness on earth due to reflecting light, even if just by a fraction?"
] |
[
false
] |
Or does the brightness of the sun overwhelm it too much to measure?
|
[
"Yes. The moon contributes 400,000 times less light, which is too small to measure (from the ground, anyway).",
"https://en.wikipedia.org/wiki/Apparent_magnitude#Example:_Sun_and_Moon"
] |
[
"The short answer is yes. Anything that you can see is reflecting light at you. However there is a massive difference between a full moon at night and broad daylight. I would be surprised if the increase in brightness from the moon is more than 1%. I would guess it's a fraction of a percent. You would need some very high tec equipment to measure it.",
"Also the moon won't be at full brightness, because a full moon can't happen if the moon and sun are on the same 'side' of the earth."
] |
[
"It would increase the amount of light hitting the Earth by some amount. I don't know how much, but I would guess it would be measurable. The closer the Moon is to full, the more light it would reflect to the Earth."
] |
[
"If the Graviton is discovered, could we use it to create artificial gravity in an other way than centripetal force?"
] |
[
false
] |
I have been searching the Internet lately for artificial gravity, but the only way right now to create that is a rotating rigid body. If we could somehow manage to detect the graviton and use it (just like we can use electrons), could we create artificial gravity with it?
|
[
"Not really. The graviton would allow us to unify quantum mechanics with gravity, but we still expect the macroscopic behavior of gravity to be exactly what general relativity predicts. It is similar to the way QED still gives rise to Maxwell's equations."
] |
[
"Two things:",
"1) there is basically zero chance the graviton will be discovered in the lifetime of anybody alive today (we haven't even found classical gravitational waves yet).",
"2) if you use gravitons to produce a gravitational effect that is a real gravitational field- not something which mimics it."
] |
[
"Thanks. I may have been wrong in the choice of the word 'artificial'. By that I meant gravity that isn't 'created' by an attracting mass, but a man-made gravitational field."
] |
[
"How far \"back through time\" can we see using telescopes?"
] |
[
false
] |
Assuming we had a telescope of infinite resolution (eg we could see molecules on Mars), and we focussed it as far away as possible (past early galaxies ect), what would we see? Would we see anything special, or is it just darkness all the way to infinity?
|
[
"The furthest back we can see with photons would be right after the ",
"recombination",
". That's what the cosmic microwave background is, the light given off by as the Universe cooled (albeit highly red shifted, which is why it is made of microwaves). This happened about 380,000 years after the Big Bang."
] |
[
"how much further if we can eventually build good neutrino telescopes? Is there anyway to see further than that?"
] |
[
"That is an interesting question. What would you be seeing? We are essentially able to see the light from the big bang cloud. We can not see any further because photos could not travel through the cloud. My understanding of the event would mean that there would not be any neutrinos. But even if there were there may be some other problems. Neutrinos do not travel at the speed of light. I do not have the calculation but something traveling even a fraction slower than the speed of light would have a huge gap form over the 14 billion years. Also even if there were neutrinos you would not be seeing any further back, I doubt that there would be a high enough concentration of them to be able to from an image. But that is an interesting thought question. "
] |
[
"Would repeated exposure to varying scary experiences desensitize one to the feeling of fear (conditioning) or would it cause long term psychological harm?"
] |
[
false
] | null |
[
"The ",
"Little Albert experiment",
" would seem to indicate that, at least at a young age, this can cause long term harm. On the other hand, a lot of training occurs for people who need to deal with dangerous situations (firefighting, police, soldiers), which to me (I am no expert) would suggest that there is a spectrum with a number of variables to consider."
] |
[
"Don't know much about PTSD, but is it a fear response paired with \"turning on\" of previous combat training/experience? If that's the case, then is it possible for a civilian, for example, to continuously watch/read/play horror stories which may elicit an initial fear response but, after a while, they may become harder to frighten because they know that they are experiencing fiction. Bringing that (possibly flawed) logic further, would their brain have a longer \"hold on a minute while I process this fear source\" until fight or flight kicks in? Perhaps a bit longer than someone who doesn't expose themselves to fearful stimuli?"
] |
[
"Don't know much about PTSD, but is it a fear response paired with \"turning on\" of previous combat training/experience? If that's the case, then is it possible for a civilian, for example, to continuously watch/read/play horror stories which may elicit an initial fear response but, after a while, they may become harder to frighten because they know that they are experiencing fiction. Bringing that (possibly flawed) logic further, would their brain have a longer \"hold on a minute while I process this fear source\" until fight or flight kicks in? Perhaps a bit longer than someone who doesn't expose themselves to fearful stimuli?"
] |
[
"If a valve is broken in the left ventricle of the human heart, what impact does it have on the blood moving around the body?"
] |
[
false
] | null |
[
"The left ventricle is the larger of the two, and has the less enviable job of ejecting blood into the systemic circulation (brain, little toe, taint, etc). It interacts with two valves, the Mitral (named after a bishop's hat for its shape) which interfaces with the left atrium, and the aortic, which separates the ventricle and the aorta.",
"It's a great deal more complicated than this but for the sake of brevity and because I'm not exactly an expert, we'll say there are two ways a valve can 'break'. It can regurgitate, which is basically a way of saying the leaflets of the valve fail to close and it fails in its job of maintaining one-way flow, or it can stenose, or narrow, which gives the heart a hard time pushing the blood through.",
"Mitral Stenosis: In short, the left atrium has to work a shedload harder to get blood to the left ventricle. Blood will back up here like a traffic jam and eventually make its way back to the lungs, where the backlog interferes with blood oxygenation. In really nasty cases, the red cells will haemolyse (burst) and immune cells will start eating the pieces, which gives you iron depositions in the lung. Not a great place to have it.",
"Mitral Regurgitation: Here, some of the blood that's supposed to go through the aortic valve will instead blast right through the hole the incompetent mitral valve has left open. This gives you grief in a few important ways. First, you'll get regular bursts of ridiculously high pressure blood shooting up through the mitral valve, into the pulmonary veins and into the lungs' vasculature, noted above as a Bad Thing. Secondly, during the filling phase the left ventricle will be inundated with blood volume without a mitral valve to moderate it. Over time, the heart will dilate to compensate (known as eccentric hypertrophy), which if left long enough will manifest as congestive heart failure.",
"Aortic Regurgitation: As with the mitral regurgitation above, you'll have a volume-loaded left ventricle, so expect all the good congestive dilatory symptoms. In addition, the blood leaking back through the aorta into the left ventricle will severely hamper your diastolic pressure (aortic pressure during the heart's filling phase), which will manifest as a 'bounding pulse', or a pathologically wide gap between systolic and diastolic (someone I saw just today had a BP of 130/50).",
"Aortic Stenosis: Don't get this. The left ventricle, in spite of its best efforts, will have trouble maintaining blood flow through the narrowed valve, and hence to the rest of the body. You'll wind up with decreased levels of oxygenated blood in the systemic circulation, and eventually the metabolic needs of your tissues will outstrip what the heart can provide. Hypoxic encephalitis, fainting, and ischaemia to the periphery will result, especially during exercise. To make up for the ridiculous pressures resulting from squeezing your body's worth of blood through a tiny hole, the left ventricle will swell to add more contractile force to its output (known as concentric hypertrophy). This will help to a point but eventually the increased size of the ventricular walls will allow for less blood volume, and you'll end up with an outsized heart that can barely hold any blood within its walls.",
"These conditions are by no means the only ones, and they often coincide with each other (the guy I mentioned earlier had both AS and AR, basically a tiny opening that never closes), but it's a start. If you don't want these conditions, avoid rheumatic fever.",
"Source: underachieving medical student."
] |
[
"You just clarified something I didn't realize was important. Thanks.",
"Didn't know about the iron depostion in the lungs.",
"Knew about pressure effects on Monday he lungs ans the effects f regurgitation though. Bernoulli applied to echos and calculating pressure deltas is a neat application. But the iron scares me a bit.",
"Can you explian a bit more about its effects?",
"Sorce: parent of a truncus patient currently doing well on a Melody valve"
] |
[
"To expand a little on what you said:",
"MS: A rare disease in the developed world these days. The majority of MS results as a post-infectious complications from streptococcal infection (rheumatic fever). With reasonable access to antibiotics this disease becomes very rare. It is still seen fairly commonly in the developing world.",
"MR: More common mitral valve disease in the developed world.",
"AR: Much less common that AS. Various causes",
"AS: More common aortic valve disease. Most AS is senial degenerative in nature (i.e., wear and tear, disease of advancing age).",
"TL;DR - MR >> MS in the developed world. AS >> AR"
] |
[
"I read somewhere that the engine noise on airplanes diminishes our sense of taste, making food seem less salty. Biologically, what's going on that makes this so?"
] |
[
false
] | null |
[
"I understood that it was changes in cabin pressure and humidity that had a greater impact on our sense of taste than the noise."
] |
[
"The lower air pressure affects our sense of smell, which is much more important to our ability to taste than most people realize. Humidity can act as a transport for some chemicals, but not for others."
] |
[
"This is the only thing I've found with that suggestion",
", but it cites a 48 person \"study\" that seemed pretty far from scientific."
] |
[
"How do humans get accustomed to the temperatures of the places they live?"
] |
[
false
] |
For example Eskimos can handle the cold very well and Aborigines do well in the heat. Also as simple as someone from Minnesota will be wearing shorts when it's 30 degrees but someone from Miami will be shivering while bundled up in layers.
|
[
"The body has a temperature regulation system controlled by the hypothalamus. When in colder weather, it signals the pituitary gland to produce more thyroid stimulating hormone to increase metabolism and create more heat. It doesn't happen as much today due to air conditioning and heat, but in older times people's hypothalami would reset each summer and winter due to the seasonal temperature changes as well."
] |
[
"People who live in cold climates DO acclimate to the winter via increased thyroid hormones, just nowhere near the extent that we would if we were exposed to the elements. For example, in the winter, people commonly wear very different clothes around the house (fleece pants/sweatpants vs a t-shirt and shorts in the summer). This is because the house is actually colder, just not that much colder. During the winter, we're often just a little bit too cold and in the summer, often just a little too hot. Our brain and body responds to this, and that increase in thyroxin is what raises our metabolism as well as our appetites in the winter time.",
"It's worth noting that our circadian rhythms also change due to decreased sunlight meaning more melatonin productions, though I'm unsure of the effects that melatonin levels have on appetite, if any."
] |
[
"So I have a follow up some question:",
"Since our we don't need to increase our metabolisms in the winter time due to heating, does our bodies know we don't have to eat as much too? That is, is winter weight gain is biological or just a cultural phenomenon due to fall and winter holidays (Thanksgiving and Christmas). "
] |
[
"What is coefficient of friction on Velcro?"
] |
[
false
] |
Learning about the effects of friction between one object and another. I would like to know what the approximate static and kinetic friction between a marble and a strip of Velcro would be. Note that its the soft part of Velcro, not the hooks. Also it is nylon Velcro, and I do understand that there is very little information given. The marble is an average glass marble. The information doesn't have to be super accurate, just ballpark.
|
[
"Wouldn't the better question be: \"How would I calculate ",
" on velcro? Or, perhaps, if you feel more physically inclined, \"how would I ",
" coefficient of friction on velcro\"? ",
"In this way, we encourage a reader to perform an experiment. "
] |
[
"Could one consider velcro a meta-material with a coefficient of friction greater than 1?"
] |
[
"One way might be, to adhere velcro on a tiltable plane, and try to slide stationary objects along it by precisely manipulating the tilt. Friction coefficient could be measured by the degree of tilt between different materials."
] |
[
"is the Pythagorean theorem appropriate for figuring out how far apart two stars are?"
] |
[
false
] | null |
[
"It's not appropriate to apply the Pythagorean theorem there, since you don't have a right triangle."
] |
[
"Do you know what is?"
] |
[
"The ",
"law of cosines",
", but you additionally need to know the angle between the two stars."
] |
[
"If you traveled underwater faster than the speed of sound (in water), would you get a sonic boom?"
] |
[
false
] |
And if so, how would it manifest? Would there be a bubble of air or something like that? I assume it would be quite a bit different from how sonic booms work in air.
|
[
"There are a few problems with this. The speed of sound in water is much higher than in air: 343 m/s in air, and 1481 m/s in water",
"1",
" Technically, the friction at work here depends on the shape of the object we're talking about- but at these speeds, I bet there would be ",
"problems",
" with any shape. The speed of the object would super-pressurize water in front of it that would spontaneously vaporize, creating a pocket of gas that surrounds it.",
"Edit: by problems I didn't mean to imply it isn't possible, just a lot harder than the same feat in air."
] |
[
"According to ",
"this",
" page, creating a large enough cavitation bubble to encompass the object in question would lead to reduced drag in comparison to a small or non-existent bubble. "
] |
[
"The speed of the object would super-pressurize water in front of it",
"Um.. how would it do this? Pressure waves cannot travel faster than the speed of sound...",
"Does anyone have a tank (the kind with a giant gun on it), a tank (the kind that holds water), and a really really fast camera? :-)",
"https://en.wikipedia.org/wiki/Muzzle_velocity"
] |
[
"What is the smallest object we can see with our naked eye without the aid of any instruments?"
] |
[
false
] |
I've recently read Ergroilnin's thread on what is the smallest object we can see with the aid of instruments. That got me think what about the smallest object without instruments?
|
[
"This is an extremely interesting question, which deserves a full answer. Unfortunately, I have to run, so will just say a few words and release it from the modqueue.",
"The two key points to kick off with are that both 'smallest object' and 'see' are surprisingly malleable terms. In terms of smallest object, we can detect offsets in a straight line (vernier acuity) that are far smaller than the smallest pixel we can distinguish from those surrounding it (resolution acuity), which does not always correlate with our ability to identify an image (recognition acuity). In terms of 'see', this may depend on where on the visual field we are talking. So the limiting factor may be different in the fovea (where photoreceptors are very tightly spaced), versus the periphery (where photoreceptors are more sparse). In general:",
"Quantitative comparison of the data with retinal anatomy and physiology suggests that pattern resolution is limited by the spacing of primate beta (midget) retinal ganglion cells, whereas pattern detection is limited by the size of individual cones. ",
"Thibos et al, 1987",
"The limiting factor also varies with age. Thus, Colin Blakemore has some interesting data looking at how information is progressively lost as one ascends up the visual processing hierarchy in the young monkey.",
"In terms of a simple tl/dr answer, in the medical world 'adult-like' central-recognition-acuity is considered to be about 30 cycles per degree [cpd] when the stimulus is at high contrast (black vs. white), though this number decreases with contrast (dark grey vs. light grey). If you think that the width of your thumb nail at arms length is probably about 2 cpd, divide that by 15. Plenty of adults exceed this ability, so assuming you are a healthy adult, your recognition acuity may be more like 40 to 50 cpd.",
"Hope that helps get the ball rolling"
] |
[
"Thanks for your comment, it was an interesting read. How about we standardize it to an average young adult with a 20/20 eyesight. And for the object, it should be something that we can instantly recognize when we see it at high magnification."
] |
[
"degrees-visual-angle is a distant-invariant metric of size. It describes the size of the image in terms of its size on the retina. It is is computed as:",
"y_deg = rad2deg(2*atan(x_cm/(viewingDist_cm*2)));\n",
"so if x_cm is the width of a single white stripe, and a cycle is made up of one white and one black stripe, then cycles-per-degree equals:",
"cpd = 1/(y_deg*2)\n",
"The contrast of the stripes (white vs. black) strongly affects acuity, yes. The contrast of the grey surround probably does have some effect too, but this would be more subtle/complicated."
] |
[
"Can an object be accelerated to (almost) the speed of light arbitrarily fast?"
] |
[
false
] |
Or is there a physical limit to acceleration as well as speed? Thank you.
|
[
"There’s no fundamental limit to the acceleration as there is for the speed. But there are “engineering limits” to how fast people or things can accelerate without being killed/damaged."
] |
[
"It's interesting to note that the only reason such limitations exist is because most forces are surface forces. This means they are applied to the surface of the object only (your chair transfers the force of acceleration from the car to your body). Because of this the loads must be transferred through the structure of the object. This creates stress in the object. If the stress exceeds the breaking stress of some part of the object, permanent damage can occur. For humans, the concerns also include things like blood pressure and ability to expand the lungs. However, such concerns do NOT apply to what are called body forces. These forces (including gravity, and electromagnetic forces) apply equally to all parts of the object simultaneously. This means that internal stresses are not necessarily generated. So theoretically, if we could accelerate a human with body forces, there would be no limit to the magnitude of the acceleration."
] |
[
"Excellent point. Just to illustrate, when you free fall, you are being accelerated but you don't feel that acceleration."
] |
[
"Watching Cosmos...questions about light...brain hurts!"
] |
[
false
] |
[deleted]
|
[
"I can elaborate on 1). I'm going to lay a small amount of groundwork, so bear with me if you know this already.",
"First: Visible light is one tiny part of the ",
"electromagnetic spectrum",
". The only way it differs from the other parts of that diagram (x-ray, infrared, etc.) is in its wavelength. Gamma rays have a wavelength smaller than that of an atomic nucleus, radio waves can have a wavelength larger than that of a building, and visible light has a wavelength in between.",
"\"But why can we see visible light and nothing else?\" This has everything to do with how our eyes work, and nothing to do with some special divide between visible and invisible radiation. The sensors in our eyes are only tripped by a small range of radiation. Everything within that range we call \"visible light\" or \"visible radiation.\"",
"Okay. Groundwork laid. Still with me?",
"This will seem off-topic, but bear with me. Think of sound waves: a static object will emit sound waves at a constant wavelength. The speed of sound is constant, so the only way we can make higher- or lower-pitched sounds is by changing the wavelength of the sound. Think of it like a pistol vs a machine gun: the bullets will move at the same speed but more will pass through the area in front of the machine gun in ten seconds than will pass in front of the pistol.",
"Light works the same way. It has a constant speed, but its wavelength varies, which gives us radio waves (a low sound or slow-firing pistol) to gamma rays (a high-pitched sound or fast-firing machine gun).",
"Ok. Let's take a break before getting into redshift and blueshift and let that information sink in. Here's a kitten: ",
"http://imgur.com/TtOlm",
"We're back. I'm going to assume you know about the Doppler Effect. In short, a wave-emitting moving object (like a rocket-powered flashlight or a loud car) will emit those waves closer together. The waves will have a constant speed, but will be compressed in front of the object as the objects motion means it releases each wave closer to the previous one. It works ",
" the same way with light. The waves from that flashlight will compress in front of it, shortening the wavelength. This is blueshift. The radiation will now appear further right on the above diagram than they would if the flashlight were still. It's that simple.",
"If you get blueshift, redshift is a snap. What if that flashlight is moving away from you? Each light wave emitted would be farther than the one in front , as the emitting object moves backward while emitting waves of constant speed. This increases the wavelength moving it farther down the red side of the spectrum. This is redshift.",
"Here's a rather funnily-animated video that gives a visual representation of the Doppler effect: ",
"http://www.youtube.com/watch?v=76X1LtWkUE8&feature=related",
"Also, as a thank you for reading this tower of text, ",
"here's another kitten.",
"-An object doesn't have to be red or blue to redshift or blueshift. A radio wave could blueshift and still be a radio wave- just one a little closer to being a microwave. But if we moved that radio fast enough towards you, the waves it emits would shift into visible range! Isn't that awesome? You could ",
" your radio work!",
"-You probably know from Cosmos that we can measure the speed of distant galaxies from redshift and blueshift. But how? How do we know what the original wavelength was anyway? The answer: spectrometry. We know what wavelengths common elements give off. Hydrogen, when it gets hot, gives off ",
"this.",
" This means that hydrogen gives off a combination of four wavelengths of radiation. Getting into the how of that goes into quantum mechanics, so I'll avoid it here. But a redshifted or blueshifted hydrogen star will show up like ",
"this.",
"\nYou can see how the emission lines have shifted. The speed of the object determines just how much that shift is.",
"I am really sorry for the obscene length of this post- I just get excited about this sort of thing.\nFinally, here's one last kitten: ",
"http://i.imgur.com/HAgja.jpg"
] |
[
"You only perceive the light that hits your eyes. You can't see the other trajectories because they aren't hitting your eyes, and they aren't bouncing off anything. For instance, if you look at a person in front of you and a tree to their left, you can see light from them and light from the tree, and you know that they can see the tree, but you can't see the light that they are taking in."
] |
[
"You only perceive the light that hits your eyes. You can't see the other trajectories because they aren't hitting your eyes, and they aren't bouncing off anything. For instance, if you look at a person in front of you and a tree to their left, you can see light from them and light from the tree, and you know that they can see the tree, but you can't see the light that they are taking in."
] |
[
"How do electrons never collide with the nuclei of atoms?"
] |
[
false
] |
I am aware of the concept of centripetal acceleration and orbit and all that, but it seems statistically impossible that no electron, after being manipulated by another electron or proton, would ever wobble out of orbit and strike the nucleus of an atom. If there is such attractive force between protons and electrons, why are there not vast quantities of electrons stuck to nuclei everywhere? And what would be the consequence of an electron/proton collision?
|
[
"That'd be the planetary model of the atom, which is incorrect. Actual electrons don't 'orbit' at a fixed distance from the nuclei. They 'move' quantum-mechanically, which means they don't have a definite position and velocity; all we can say is the probability of finding the electron(s) at various points surrounding the atoms. (called ",
", rather than orbits) ",
"There's usually a non-zero probability of finding the electron at most points. For an electron in a 1s orbital (the 'innermost' one), there's a non-zero probability of the electron being at the nucleus. ",
"So electrons do, in fact, scatter off the nucleus on a regular basis. But the effect of this on the overall 'motion' of the electrons is very small. Mostly, very little happens. But if the nucleus has an over-abundance of protons, a proton in the nucleus can occasionally '",
"capture",
"' an electron and form a neutron (plus a neutrino). ",
"Electrons don't 'stick' to the nucleus because of how quantum mechanics works (it's 'wave-like' behavior, if you want). In QM, a particle that's confined to a smaller region of space has higher kinetic energy. It's not centripetal force that keeps the electron in orbit, but this 'force'. ",
"On one hand you have the electrical attraction of the positively charged nucleus, so the electron will lower its potential energy if it's (probability distribution) is closer to the nucleus. On the other hand, you have the kinetic energy, which increases when the electron is localized to a smaller region of space. When these two 'forces' balance out, you have a stationary state - an orbital. (I'm basically stating the Schrödinger equation for a hydrogen atom, here)"
] |
[
"Electrons exist in certain orbitals because it is at those positions that the wavelength of the electron forms a standing wave. If you take a rope that is connected to a wall, and oscillate it with your hand to form a standing wave, you will notice that you can only form a standing wave at certain frequencies and distances from the wall. If you have a fixed frequency, then you will only be able to form a standing wave at certain distances from the wall. The electron has a fixed frequency, so it is only able to form a standing wave at certain distances from the nucleus, these are the orbitals. "
] |
[
"They do, ",
"sometimes",
"."
] |
[
"Question about traveling at light speed."
] |
[
false
] |
I read this : "It is interesting to observe that a real particle, in our universe, subject to all the laws of physics we understand, is a rather better interstellar voyager than the best fielded in the 24th century by the United Federation of Planets. Their much-vaunted Galaxy Class starships are capable of speeds slightly in excess of Warp Factor 9, an apparent velocity of 1516 cochranes (or 1516 times the speed of light).[4] At a velocity of 1516 c, traveling to the centre of the galaxy would take, as perceived by the life forms on board, a little more than 21 years. By contrast, an observer on board the Oh-My-God particle would arrive at the nucleus of the Milky Way, according to his clock, just about 3 seconds after leaving Starbase Terra. That's more than 9,700,000 times faster than the starship. In the time the starship spends vacuum-whooshing and rumbling its way to the nearby star Aldebaran, the particle could travel to the edge of the visible universe." on this website: " " Maybe I'm not getting something, but wouldn't a starship traveling at 1500+ times the speed of light get somewhere much faster than a particle travelling at 0.99999... times the speed of light? Thanks for your help!
|
[
"Star Trek warp speeds ignore relativity."
] |
[
"And everything occurs in the same reference frame."
] |
[
"Basically the speed of light is the speed limit of the universe (as far as we know) so travelling faster than c doesn't make physical sense (sorry to be mean.) ",
"The reason the OMG particle takes 3 seconds is due to a relativistic phenomena called time dilation. For someone observing the particle who is for all intents and purposes stationary, as the particle approaches c the particle (relative to the observer) 'experiences' time at a slower rate. the time dilation experienced by the particle relative to the observe approaches infinity as the particles speed approaches c.",
"Therefore for the particle hurtling towards the centre of the galaxy even though the trip appears (to the outside observer) to take t = (distance to galactic centre)/(speed of light), the particles self-perceived travel time is, in this case 3 seconds. ",
"If you read the article for the link you posted it explains it ok.",
"Additionally ",
"http://en.wikipedia.org/wiki/Twin_paradox",
" "
] |
[
"TIL ISS gradually loses altitude while it's orbiting earth. Why doesn't this happen to the moon?"
] |
[
false
] | null |
[
"The ISS is losing altitude because it gets slowed down by the atmosphere.",
"The moon is much farther away than the ISS and doesn't have this problem."
] |
[
"The migration of the Moon away from the Earth is mainly due to the action of the Earth's tides.",
"The Moon is kept in orbit by the gravitational force that the Earth exerts on it, but the Moon also exerts a gravitational force on our planet and this causes the movement of the Earth's oceans to form a tidal bulge.",
"Due to the rotation of the Earth, this tidal bulge actually sits slightly ahead of the Moon. Some of the energy of the spinning Earth gets transferred to the tidal bulge via friction.",
"This drives the bulge forward, keeping it ahead of the Moon. The tidal bulge feeds a small amount of energy into the Moon, pushing it into a higher orbit like the faster, outside lanes of a test track.",
"This phenomenon is similar to the experience one feels on a children's roundabout. The faster the roundabout spins the stronger the feeling of being slung outwards.",
"Source",
"Edit: I fail at links"
] |
[
"Contrary to what common sense would dictate, the moon is actually GAINING altitude as its orbit decays. It is a very slow rate, however the reason it is gaining is that it is taking the angular momentum of the earth's rotation. As the earth spins, it transfers a small amount of its momentum to the moon. Back when the earth was still young a day was roughly 8 hours, and over the billions of years, the length of a day has slowly has gotten longer and longer. "
] |
[
"Why can we breathe out more air than we breathe in?"
] |
[
false
] | null |
[
"Because you don't empty your lungs all the way during a normal breathing cycle. We call the amount you can breathe out beyond what is breathed out during a normal respiratory cycle the expiratory reserve volume. "
] |
[
"In terms of weight, you do breathe out \"more\" air. As for volume, I have no idea what the density for CO2 is at these temperatures."
] |
[
"What makes you think you can breathe more out??"
] |
[
"Can a rotating non-expanding universe explain Hubble's red-shift data?"
] |
[
false
] |
Could the angular velocity/acceleration be perceived as velocity "away" from us?
|
[
"No. Rotation has poles. The redshift data do not. "
] |
[
"It's an interesting idea. It doesn't work but it's fun to imagine. The issue is that the Hubble velocity field is isotropic: wherever you look, galaxies are moving away faster as they are far away. If the universe was somehow behaving as a sphere rotating around an axis you could see the direction of the axis as galaxies there would not appear to move at all, whether from or towards us. Furthermore, assuming we are not on the axis, we would see weird blueshift happen to galaxies closer to the axis."
] |
[
"What if it was rotating on an axis through a higher dimension?"
] |
[
"Is it possible for a virus to infect a bacteria or a parasite?"
] |
[
false
] | null |
[
"Yes, absolutely.",
"While I can't say concretely that there is not a single cell in the world that cannot be infected by a virus, it's very likely.",
"There are known examples of viruses capable of infecting bacteria, archaea and eukaryotes (plants, animals, fungi and protozoans).",
"Viruses that specifically infect bacteria are referred to as bacteriophages, and are some of the best studied examples of viruses.",
"Your question is ",
" vague, and I get the impression you're asking something along the lines of \"can a bacteria get HIV?\" or something like that. Well, no, viruses that infect humans do not infect bacteria or vice versa (to our present knowledge). ",
"Viruses gain entry to cells by interacting with specific protein receptors on cell surfaces. Very distantly related organisms like bacteria and animal cells are enormously unlikely to be targeted by the same virus simply because they don't have the same receptors expressed on their cell surfaces.",
"When you say parasites I'll assume you mean something like a tapeworm? Or possibly... A protozoan like Plasmodium (a few species of which are the causative agents of malaria)? Yes, there are viruses that infect both of these broad categories."
] |
[
"There is phage therapy.\nBut human testing isn't allowed in many countries. "
] |
[
"Are there any studies on using bacteriophages to fight bacterial infections in humans or animals? "
] |
[
"How many more \"new\" stars become visible each year?"
] |
[
false
] |
In other words, how many stars join the observable universe each year?
|
[
"The edge of the visible universe is where we see light from 380,000 years after the big bang, when the universe became transparent. If there were stars back then (and we had telescopes orders of magnitude more powerful) we'd see them emerge. But there weren't any, so all we see is empty space emerging. Stars didn't form until about 200 million years after the big bang, so we can see them where the light was emitted when the universe was 200 million years old. We don't watch stars enter the visible universe. We watch them form."
] |
[
"I'm going to start with a disclaimer that I'm not exactly an expert on this but I think I can help find some kind of an answer for you. Someone please correct me if anything is inaccurate below.",
"Pretty much every individual star visible from Earth is astronomically very close to us in our galaxy. The average distance I believe is just in the hundreds of light years away. Very close considering the galaxy is like 100,000 light years across.",
"So I did some searching and I found ",
"this",
" article from nasa giving us a number of 7 new stars within the galaxy every year. Considering the estimates for total stars in the galaxy being around 400 billion, it would be incredible if we were able to able to catch a specific one forming in real time. ",
"Also if our visual neighborhood is 1000 light years in diameter that gives us an area one 10,000th the size of the milky way. So assuming star generation is random, which it probably isn't, every year would give us a 1/1400 chance of a star even being close enough to see from earth, at least with the naked eye."
] |
[
"This is right. Also, we can only resolve galaxies (not individual stars) at that distance and they are very strongly red shifted, making detection difficult. The current record holder is ",
"GN-z11",
", and that is 32 billion light years away from us and we are seeing it as it appeared when the universe was 400 million years old. There are a few candidates for older objects from Hubble deep field images, but we need better images to confirm them. ",
"The James Webb Space Telescope will be able to collect much better images (it has better sensitivity in the IR, which you need because of the huge redshifts). After it comes online, we should be able to see many more distant galaxies and get a better idea of how quickly they formed after the big bang. We then can put together a much better estimate of how many stars are at the edge of the visible universe."
] |
[
"How can a black hole, which can't have light escape, emit the more light than anything else when it gamma ray bursts or forms into a quasar?"
] |
[
false
] |
Basically, how can a black hole, which nothing can escape from emit so much? Also can multiple gamma ray bursts occur, or does it only happen soon after a hypernova?
|
[
"hmmm...I think what we're seeing (via satellites and telescopes) are the effects of a black hole on matter adjacent to it. Gravity attracts gas, gas is compressed and heats up. If the gas gets hot enough it is ionized and becomes a plasma. Plasma interacts with local magnetic fields and all kinds of crazy phenomena occur. Most of these effects occur close to a black hole, but not so close to the event horizon that radiation - which includes visible light - that it gets trapped there. Most radiation is free to wend its way across empty space, which we eventually see."
] |
[
"Yep. ",
"What we're seeing",
" is either the matter in the accretion disk, heating up and emitting light as it spirals in; or matter flung out along the poles before it quite reached the black hole. (Or neutron star or other really dense object; black holes aren't the only things that generate accretion disks.)"
] |
[
"Tests of the constancy of the fundamental constants are a continuing enterprise. So far, there is no significant evidence for their variation at the 10",
" level. See ",
"this",
". I can provide more references, if you're interested."
] |
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