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[
"A question about Hepatitis C."
] |
[
false
] |
This is not asking for medical advice. I am pretty well educated in bloodborne pathogens, but can't find this answer anywhere. I know hep c normally takes 15-30 years for cirrhosis to develop, if it ever does. Have there ever been cases of extremly fast acting hep c, like cirrhosis in under 3 years? 5o follow that up, if it cannot progress that quickly, what are the other cost common causes of cirrhosis, other than alcohol?
|
[
"Studies have shown that the older you are when you acquire HCV, the more rapid your progression to liver injury.",
"Co-infection with HIV significantly speeds up the time to the development of fibrosis (cirrhosis).",
"Having a high BMI, or otherwise increased risk for hepatic steatosis (NAFLD) probably also increases risk/rate of development of cirrhosis.",
"Alcohol abuse in HCV infected patients speeds up the time as well.",
"Also, looks like peeps with HCV who smoke a lot of pot are at increased risk of developing cirrhosis (sorry Reddit) Here's a ref for this one:\n Influence of cannabis use on severity of hepatitis C disease.\n Ishida JH, Peters MG, Jin C, Louie K, Tan V, Bacchetti P, Terrault NA\n Clin Gastroenterol Hepatol. 2008;6(1):69."
] |
[
"Thanks for the info. Those are the factors I knew about except for the marijuana connection. That's really interesting and I will have to look into that study. Does it discuss the mechanism by which cannabis speeeds up formation of fibrosis? I never knew there was a connection. "
] |
[
"I am a drug and alcohol counselor, and unfortuantely I don't have access to Pubmed or any other database at my work. I searched as much as I can on google and everything gave me the 15-30 year timeline. I am looking for cases of statistical outliers where hep c moves particularly fast and what coinfections or other diseases can speed it up, or cause cirrhosis on their own. I can't find that info in any study I have read or anywhere on the CDC or NIH Hep C websites. Sorry for the confusion"
] |
[
"How can you tell if a solid ball of substance is uniformly dense?"
] |
[
false
] |
Supposing that any places of lesser density are exactly centered within it, like a perfectly spherical truffle with perfectly spherical chocolate filling, and assuming you don't know what material it is so you can't just try displacement.
|
[
"Measure its mass, radius, and moment of inertia. The moment of inertia about any axis passing through the center of mass should be 2MR",
"/5 for a uniform sphere."
] |
[
"This is a good way to get some insight of the density distribution, but it is not a sufficient to ensure it is uniform:",
"For example an infinitely thin hollow sphere with the same mass as a uniform sphere has a higher inertia. But now you can increase the mass of the hollow sphere without changing its inertia by adding some mass precisely in its center. So you can increase the mass until the total mass matches the mass of a uniform sphere with the same inertia, so that such a uniform sphere and the hollow sphere with weighted center have the same mass and the same inertia."
] |
[
"Look at how it oscillates when struck - there are solutions for the free oscillations of a radially varying sphere.",
"Not great for a truffle since vibrations don't propagate very well in chocolate, but it works for the earth."
] |
[
"Gravity pulling a sphere around the planet?"
] |
[
false
] |
Imagine an indestructible sphere around our planet, hovering 60,000 feet above us. Would it stay stationary over the planet, or would it fall? If so, which direction? Since gravity pulls from all sides, would it stay where it is and move with us? Edit: The earth is inside the sphere. Edit : Thanks everyone. Just a thought experiment, but interesting
|
[
"It's like balancing a big steel rod on end.",
"It's theoretically stable, but in practice, as soon as there's a slight perturbation (gravity of the Moon, say), the thing goes out of equilibrium and the Earth and sphere will collide.",
"(60,000 feet is basically touching already, on the scale that you're talking about.)"
] |
[
"Partly because they ",
" in orbit and your sphere is not. ",
"If you throw a ball up, it falls back down. That's what an orbit is, only bigger. ",
"If there's a big enough influence on something's orbit, it will definitely change the orbit or move the satellite or whatever we're talking about \"out of orbit\". ",
"You can theoretically put a zillion individual satellites in a \"sphere\" or \"cloud\" around a planet. But a solid sphere is not in orbit and moves in one piece. ",
"Representation of this - the satellites are shown greatly enlarged so that you can see them. - ",
"http://www.new-media.ca/wp-content/uploads/2009/02/space_debris_large.jpg",
" - "
] |
[
"Oh i see.",
"Answer: Inside the sphere you would feel no gravity at all. This is because inside a spherical shell, all the gravitational forces cancel out in every direction, ",
". So the earth and the shell would drift at whatever speed they started at. "
] |
[
"When I am trying extra hard to hear something quiet or far away, is my body doing anything different then normal, or am I just more focused on the sound?"
] |
[
false
] |
[deleted]
|
[
"When you're trying to listen to something quiet there are changes within your inner ear occurring. You have three little bones in your ear called ossicles, the malleus, incus and stapes which are flexed by sound waves coming into your ear. These sit against the oval window, which connects to a tube filled with fluid called the cochlea which is where your \"hearing\" receptors are. When you are trying to hear something quiet, the inner ear muscle around these ossicles move them closer to the oval window, making it essentially, more sensitive to sound as it will deflect the membrane more easily. ",
"There are also changes in your central nervous system where the brain causes your efferent nerve fibers which conduct the sounds you hear, to the brain, to hyperpolarize the bipolar cells which are responsible for recieving incoming messages from your receptor cells (the hair cells). When these are depolarized by the sound waves coming in (rather complicated system I'd rather not get into unless you want me to), you will hear noises. So the brain can raise the threshold for these cells to depolarize less easily when a noise is heard which will fire an action potential, and thus tell your brain you're hearing something. ",
"These two systems do the opposite when you are around loud noises to desensitize the systems too! Pretty neat :) ",
"Source: Neurophysiology PhD student. ",
"Edit: Made a few big mix ups in my response and wanted to clarify some! I'm embarrassed by how simple they were! Hope it helps :) "
] |
[
"I don't know too much about that. but I would assume that it can help to transmit sound a little. I know that your mouth/nasal cavity, and ears are connected via the eustachian tube. So it may help to amplify the sound in a way since they're all in a sense, connected to each other. But that was not discussed in my classes, sorry!"
] |
[
"is there any truth to the notion that opening your mouth slightly improves the ability to hear?",
"i read this somewhere, and they claimed it was due to the way the jaw and ear bones function, and that sound waves entering the mouth can help transmit sound through bones."
] |
[
"How long does it take Curiosity to transmit images back to earth"
] |
[
false
] | null |
[
"Right now, Mars is about ",
"1.6 AU from Earth",
", so it takes light (and radio signals) 14 minutes to reach us from Mars."
] |
[
"I believe I heard them say 14 minutes. So by the time it began the EDL sequence (the 7 minutes of terror) it had already been safely landed for about 7 minutes."
] |
[
"Please post ",
"in the official thread",
" in order to consolidate information."
] |
[
"If gravity acts via gravitational waves, is it possible to create an anti-gravitational to cancel out gravity? Sort of like noise-cancelling headphones?"
] |
[
false
] | null |
[
"Gravity does not act via gravitational waves. One theory to explain how gravity could work suggests that there should be waves (as a biproduct). Scientists believe they may have detected these waves, which in turn adds weight to the validity of the theory."
] |
[
"As far as I understand, gravitational waves are a result of two huge masses colliding and the result creates a rippling in space time called gravitational waves. No one knows what actually causes massive things to have gravity. "
] |
[
"But gravity waves still don't cause gravity right?"
] |
[
"What is instinct? How does it guide an animal's behavior?"
] |
[
false
] |
I was thinking about animals and their natural-born instincts. As I understand animals, they are born with a drive towards certain behavior, and we call this "instinct." For example, they know what their diet should be. I'd assume that if a baby lion that had never had contact with other lions were given a choice, it would know to choose to eat meat over vegetables. Is that true? If so, how is that information "programmed" into an animal without outside forces guiding the animal? If it wouldn't know instinctually, would it eat the vegetable, get sick and learn that way?
|
[
"I would respectfully disagree with the current top response. Our current understanding of animal behavior is such that each observed action is guided by a variety of factors and can have varying amounts of influence from genetics or ontogeny (learning). The nature vs. nurture argument is effectively null as no behavior is ever entirely controlled by genotype and neither does there exist one free of its influence.",
"My favorite example is birdsong. Our current understanding is that there is a genetic template that predisposes a bird to its species' song. However, there is a \"sensitive period\" during which it must cement and learn its song, the process of which is called crystallization, or else the result can be gibberish compared to song from birds allowed to develop normally. In fact, the learning and development of birdsong, which seems to have a solid genetic template, is theorized to even continue beyond crystallization and ",
"possibly rely on feedback from one's own song",
" or others just to maintain its integrity. On the complete end of the scale, birds with less complicated calls that we don't consider true birdsong ",
"don't seem to need the learning component at all",
", though this is still reliant on the development of the necessary brain structures for vocalization. ",
"This paper",
" gives a good review on birdsong. It is extremely like human language, which you may want to look up papers on as well if you want to see a good example of a human behavior that draws plentifully from \"innate\" vs. learned components.",
"Resdriden's citing of genetic influence on taste is entirely accurate - a well-known example in humans is the ability to taste a toxin in plants known as PTC, a reference to which can be found in ",
"this paper",
"'s introduction. Additionally, felines (as a rare exception in Mammalia) ",
"do not taste sweetness",
". The genetic influence of taste, then, for your example could easily help predispose lions to meat. But what about the effects of social enrichment on hunting, which are important for any animal with a CNS - even ",
"rats",
" and ",
"spiders",
"? We assume a lion know to eat meat if it never observed any other animal doing so, but to what degree can they really know their own diet and know what food to forage for? These are excellent questions to ask with complicated answers, and little if any behavior is truly \"hardwired\" in besides perhaps reflexes, which in another can of worms may themselves be learned - think of people you know who will vomit even today if they try to eat foods that coincided with them getting sick as children. "
] |
[
"You should read this article, if you can't get it free already, ask a librarian for help. ",
"http://www.nature.com/nature/journal/v434/n7030/full/nature03352.html"
] |
[
"Sure, I generally agree with what you wrote, but I think the OP was asking if there are complex behaviors that are truly genetic in origin. Or, at the very least, (s)he was asking if there are any complex behaviors which are not learned. There are several well documented examples of complex behaviors which are not learned. Thats not to say that most/all behaviors don't have a mixture of both, but rather there is some default behavior which is genetic in its template and that is modified by experience."
] |
[
"What is the absolute threshold for acceleration?"
] |
[
false
] |
Since we perceive acceleration rather than velocity, there must be a minimum amount of acceleration that our sensory mechanisms can pick up on. It's the same idea as the minimum number of photons/lumens to be able to see a light or a minimum number of decibels to hear a sound.
|
[
"Probably the best way to answer this question is to consult an aviation physiologist. They know a lot about this stuff.\nThere are small organs in our heads that amount to organic accelerometers. These are called otolithic organs. ",
"http://en.wikipedia.org/wiki/Otolithic_organs",
"\nI imagine that if one were to determine the bending strength of one of the cilia in these organs, the mass of the otolithic crystals that affect them, the viscosity of the crystal substrate, and the minimum cilia deflection required for detection, you could find your answer."
] |
[
"I was confused as well with donaldjohnston about the \"absolute\" part of your question. But we can at least throw up some numbers as a lower limit.",
"So far, no one feels queasy from the rotation of the earth, so we can probably be sure that this limit is bigger than the rotational acceleration of the earth",
"Knowing this we can set up a rotational acceleration as a_centrip = v",
" / R",
"v = (2 x pi x radius of earth / (length of day in seconds) =~ 463 m/s",
"R = 6378100 meters",
"a_centrip = .0337 m/s",
" or ~ 0.34% of 1G"
] |
[
"I meant more of a minimum acceleration that we can sense as humans with (I believe) our vestibular system, not a limit on acceleration based on the laws of physics. More of a psychological question than those answers, but that thread does look interesting.",
"edit: I didn't mean a maximum that we can sense either. I guess the term absolute threshold could be confusing; I learned it in psychology and was trying to sound smart. Basically for any sensory mechanism, there is a minimum value of stimulus that humans can pick up on. I'm curious as to what that minimum would be for our sensing of acceleration. As in the smallest change in velocity that we can perceive."
] |
[
"What is on the ISS live stream right now?"
] |
[
false
] |
It looks like they have a drop of water between 2 sensors of some sort. The camera might change before anyone sees and has an answer.
|
[
"I don't have an answer, but I made a screenshot for posterity.",
"http://imgur.com/A2T1OJh"
] |
[
"Thanks, The stream changed cameras so this is the best shot of what I was asking about. Its not possible to tell from a still but there seem to have been sediments floating around inside the ball of fluid."
] |
[
"That must be it. The sediment floating around in the fluid did start to create structure before they switched cameras. Thanks!"
] |
[
"What is the biggest misconception about your field?"
] |
[
false
] |
Either the most commonly held incorrect belief, or your favorite example of an encounter where someone was so confused that you didn't even know how to begin to communicate with him...
|
[
"Neuroscience: So very, very many things. Just a few/the most common I hear: ",
"\nIn neuroscience literature, plasticity is generally used to refer to changes in size/activity/response of a particular synapse. These kinds of changes occur all the time in every single one of the (estimated) hundreds of trillions of synapses in the adult brain, and is probably the main barrier to ever being able to \"map out\" the human brain.",
"\nEven if discussions of plasticity are limited to the laymen use of the term (ie. changes in brain function in a more large-scale or global sense), then it's also completely untrue. As a somewhat concrete example, if you cut off one of your fingers, the cortex previously used in sensation/motor control for that finger won't simply die, but will actually be taken over by the remaining digits on your hand. Your entire brain is subject to changes like this in the face of changing input or output demands. ",
"\nAt best, this is ",
" true. We have identified areas of the brain that, when excised/damaged, lead to specific losses of function (ie. Broca's region and language), and this causes people to make bold statements about localized function in the brain. However, it's very important to remember that most of our brain processes are extremely global in nature, and that true function often arises from reciprocal interaction of many different regions all at once, ",
"as I have discussed in more detail here",
". So, loss of an area may actually be cutting out one of many necessary stopover points in communication/processing pathways that are all making a contribution to function.",
"\nAs a great example of how loss-of-function is sometimes misleading is known as the Sprague Effect. Essentially, when an animal is given a unilateral lesion in it's primary visual cortex, it is expected to be (and will be observed to be) blind to the contralateral visual field and will not react to stimulus in that VF. Therefore, it is claimed, V1 is necessary for any perception of the visual fields. ",
", damaging the superior colliculus on the side of the brain contralateral to the V1 damage will restore the animal's ability to respond to stimulus in the field it is supposedly blind to! ",
"\nDon't get me wrong. The fMRI is an absolutely fantastic tool for monitoring and learning about brain function, and revolutionized how we study the brain. That being said, most people have a definite misunderstanding of how it works and what exactly we can glean from it.",
"\nFirst of all, the fMRI does not detect activity (ie. neural impulses) directly. Instead, it does so indirectly using the BOLD (Blood-Oxygen-Level-Dependent) signal, which, as its name implies, reflects changes in blood oxygen levels. To sum this up as quickly as I can, the fMRI machine measures the way the blood in your brain reacts to magnetic fields, and these reactions change based on oxygen content. When neurons become more active, they require more oxygen for metabolic activity, and your brain is able to provide it via hemodynamic responses that increase blood flow to specific area. So, it makes sense that monitoring where oxygen is being sent is the same as monitoring where the brain is more active.",
"\n",
" like all of neuroscience, it's really not that simple. The main reason is that the increase in oxygen is only a measure of presynaptic (input) activity, but not postsynaptic (output) activity. If that presynaptic neuron were inhibitory, then what looks to be an increase in local activity is actually a ",
" in output from that region! It could also be that an excitatory presynaptic neuron fires, but fails to activate its postsynaptic neuron and result in any meaningful output. There's no way to know what's happening in this sense. A further cause for confusion is that some regions of blood flow are co-regulated, so increased oxygen to an active area can lead to a misleading increase in a separate area still working at basal levels.",
"\nAdd all of this to the fact that fMRI images are heavily processed and averaged to cancel out the basal activity occurring everywhere in the brain and across many individuals, and you can see why they are not nearly as perfect as some think. ",
" At work and not getting any slacktime, so probably won't be adding anything else for awhile, if at all. Sorry! ",
"However, if anyone wants to tackle ",
", it would be awesome. This is something I should have mentioned when I first posted this, as it's one of the most pervasive misconceptions about the brain and memory out there. Patient HM had more than just his hippocampi removed, and it made all the difference!"
] |
[
"That physics is just an opinion."
] |
[
" There's not, and they don't. People who call themselves \"grammarians\" pass random judgments based on often-faulty reasoning and pretend they are explaining how language works. For linguists, language is what people say. We (synchronous linguists) essentially study how the brain processes language. So-called \"mistakes\" like \"I could care less\" or \"The thing is, is that...\" are not somehow less legitimate in our eyes than completely standard, grammarian-approved speech. If people say those things often, and are understood, then they follow the rules of natural human language ",
", since those rules can only sensibly be defined based on usage. ",
", i.e. ",
" Uhh... 2 fluently, and 2 reasonably well, but that has pretty much nothing to do with me being a linguist. ",
"philologists",
" ",
"*",
" (I mean, kids learn it in a couple of years, how complex can it be?) Take a look at Google translate's attempts to translate between unrelated languages, and you'll get an idea of how well we currently understand language. ",
"*",
" There is so, so much more to it than that. Seriously, you would be shocked to know how much of what comes out of your mouth is complex, subtle, and not mentioned in any traditional grammar book in the world (and probably only partially documented in linguistics literature).",
" See above. We are mostly taught prescriptive rules in high school--i.e. we are taught an artificial \"academic\" register that is actually not objectively any better than the way that \"uneducated\" people speak (obviously things like precise terminology ",
" better for academics, but that is not what I'm talking about. I mean teachers correcting kids who say \"Me and John went to the store yesterday.\"). "
] |
[
"Why is boiling point of perfluoropentane les than pentane?"
] |
[
false
] | null |
[
"The boiling point of a substance depends on the strength of the interactions between molecules. There are several different types of interactions that can contribute, but for hydrocarbons like pentane, the only type that matters is called \"dispersion.\" Essentially, due to random fluctuations, the electron cloud surrounding one pentane molecule briefly becomes uneven, creating a temporary dipole. The electrons in the neighboring molecules react to this dipole, creating a weak attraction.",
"The magnitude of this interaction depends on something called \"polarizability,\" which is a measure of how easily a molecule's electron cloud can become distorted. It turns out that carbon-fluorine bonds are much less polarizable than carbon-hydrogen bonds. Hence, replacing all of the C-H in pentane with C-F creates a molecule with much weaker dispersion forces, and thus a much lower boiling point."
] |
[
"C-F is poorly polarizable because fluorine is so electronegative. Electron density concentrates heavily around the fluorine, and because fluorine is also a very small atom, these electrons \"feel\" the fluorine nucleus quite strongly and are difficult to shift around ",
" polarize. Now, this effect would also create a strong permanent dipole (introducing a new type of attractive force), except that replacing ",
" of the C-H bonds with C-F makes the dipoles cancel out, leaving you with a molecule that's still non-polar. This is why fluorocarbons tend to have very low boiling points.",
"Chlorine is also very electronegative, but because it's further down the periodic table, it has more core electrons to shield its valence electrons from the nucleus, and hence it's much easier to polarize a C-Cl bond. As we keep going down to Br and I, atomic size increases and electronegativity decreases, both of which tend to make their bonds with carbon more polarizable as well.",
"On the other hand, C-H polarizes somewhat more easily despite a total lack of core electrons in H! This is due to carbon and hydrogen having roughly equal electronegativities, and therefore the bonding electrons sit almost exactly in between the atoms, rather than mostly located on one or the other. Therefore it's easier to tug them to one side or the other, because they were never partial to one particular direction to begin with."
] |
[
"-fluorine bonds are much less polarizable than carbon-hydrogen bonds.",
"Why??? I mean, wasn't there a linear relationship for C-H, C-F, C-Br, C-I"
] |
[
"As time progresses, does the perimeter of the visible universe recede because photons (albeit redshifted ones) from distant stars finally reach us, or does it get closer because inflation pushes stars at the edge of the visible universe away faster than their light can get to us?"
] |
[
false
] |
I'm not asking about the absolute size of the visible universe; I'm asking if the number of stars inside the boundary line is increasing or decreasing (stellar lifecycles aside!)
|
[
"It does both.",
"It's best to think of this in terms of \"co-moving volume\". This is where you imagine a volume that expands naturally with the universe. If the density of the universe is basically constant, the amount of stuff within a \"co-moving volume\" is constant throughout the age of the universe.",
"The reason it's good to think of things in these terms is that we can answer the core of your question without dealing with stellar lifetimes etc. The density of stars changes a lot over the history of the universe, but I don't think that's what you're talking about.",
"But in terms of co-moving volume, what happens is the observable universe expands as the light from more stars starts to reach us, but then the accelerating expansion of the universe starts to dominate, and the co-moving volume of the observable starts to go down again as stars and galaxies are start to move out of view.",
"This is plotted in ",
"this figure",
" which I took from ",
"this paper",
". The \"Hubble Sphere\" is the key part here. It expands, reaches a maximum, and then contracts again. We're in the part where it has started contracting again.",
"Just to be clear: this is the ",
" volume of the observable universe. The ",
" volume of the observable universe is always expanding. But the ",
" within the observable universe has reached a peak, and will continue to decrease as distant galaxies disappear over the \"horizon\"."
] |
[
"The observable universe radius also increases in comoving coordinates. So I'm not sure what you mean when you say the amount of stuff in the observable universe has reached a peak. It seems you're actually talking about the event horizon. But I wouldn't really say the stuff inside the horizon has reached its peak. The amount of stuff just asymptotically decreases to 0. The observable universe is always taken to mean \"the region inside the particle horizon\", and this region grows in co-moving volume. That means as time goes on, there are ",
" galaxies entering it. It's incorrect to say the \"amount of stuff inside the observable universe\" has reached a peak. This is why I really think you're confusing the particle horizon with the event horizon.",
"The Hubble sphere is not really meaningful either (since it's the surface for which the recessional speed is 1), so I'm confused why you bring it up at all. There's nothing physically meaningful about it. It's the event horizon that determines with which galaxies we can communicate."
] |
[
"The Hubble Sphere grows to a peak and then shrinks. The Event Horizon grows, but asymptotes towards a maximum.",
"You're mixing up two coordinate systems here. The Hubble sphere grows to a peak and then shrinks, ",
". The event horizon grows but asymptotes to a maximum, ",
".",
"That might be a better definition fire the observable universe yeah",
"I've never heard/read anyone use anything other than the particle horizon to define the observable universe. It's also what a layman thinks of as the observable universe too because that's what we mean when we talk about, say, the size of the observable universe. We mean the distance to the particle horizon."
] |
[
"(anthropology/bio question) Allergies"
] |
[
false
] | null |
[
"That is probably the wrong way to look at it. You can't just look at an evolved trait and assume that it is beneficial. It might be there at random, or because it is hard to separate it from other, beneficial traits.",
"In the case of allergies, it is probably a case of tuning the activity of the immune system. Too low activity, and you get infected constantly. Too high activity, and you get immune responses to non harmful external or internal molecules, leading to allergies and autoimmune diseases, respectively. As infections are really bad, while most allergies are, at most, a nuance, the balance is struck out with some people having mild allergies, and very few people having too low immune response.",
"By the way, this is also why claims of \"boosting the immune system\" is bullshit. You definitely don't want your immune system to be too active, and if a product actually did boost the immune system, it would be extremely dangerous to consume.",
"As another side note, there is a different theory as to why we have allergies. We have co-evolved with a lot of parasites. It is in the interest of these parasites to slightly deactivate our immune system. If were evolved in a setting where out immune system was always being slightly deactivated, it would be in our interest to have it set a bit to active by default, so that it would have the right level of activity after slight deactivation. Now, we have removed all of those parasites, leaving us with a slightly over-active immune system, leading to more allergies and autoimmune diseases. I am not sure what the level of evidence for this hypothesis is, so take it for what it is."
] |
[
"That last bit, ELI5:",
"Imagine you are living with a friend. You do the shopping, he does the cooking. He likes quite spicy food, while you like the food less spicy. In order to get the food more like you like, you start buying milder chili. This works for a while, until your friend adapts, and starts to put more chili in his dishes. You start buying even milder chili, and your friend puts even more chili in the food. This goes on for quite a while, until the food is mostly bell peppers. Now you move out, and your friend starts buying the ingredients, and buys ordinary chili, but still puts in the same amount. His meal is now far to hot for him."
] |
[
"summon redditanalytics subreddit=askscience search=allergies"
] |
[
"If combustion/fire needs oxygen to keep going, then why would a strong wind (meaning one bringing a lot of oxygen toward you) tend to put a light out or make it hard to start one?"
] |
[
false
] | null |
[
"Think about when you light a candle, you hold a match to it to supply heat until it catches fire. This is essentially the same thing the flame does for itself to stay lit - transfer energy to the unburned fuel to get it hot enough to burn. When you blow the flame away from the candle, that is like moving the match away before the fire has caught.",
"You're right to think increased oxygen flow could help a fire burn, though. It's a case of competing factors. If the flow is too fast it will carry the flame away, but if it is not too fast then the extra oxygen can help the fuel burn."
] |
[
"In the case of a conventional flame, say, a camp fire or a candle, the breaking of bonds in the fuel (wood, wax, oil, etc.) releases more energy than the breaking consumes. This energy is released in the form of light and heat. Much of the heat escapes the system while some is absorbed by other molecules, breaking bonds, and continuing the reaction. If you blow on a candle or a large gust of wind puts out a small fire, convection removes too much heat for the reaction to sustain itself. If you have a freshly lit fire or a candle, the combustion reaction is taking place mostly on the surface and this is easy to achieve. In the case of burning coals, however, the reaction is occurring deeper in the material. In this case, you may temporarily halt the reaction at the surface, but the layers below are not subjected to the convection. As a result, the surface is quickly supplied with heat from the interior and a fresh supply of oxygen from the atmospheric interface. With a greater concentration of oxygen available, the combustion reaction rate increases, and the rate at which heat is released is greater. Heat also increases the rate of reaction through the material. This is why blowing on coals causes them to burn hotter and faster while a candle will be extinguished."
] |
[
"The ratio of oxygen to nitrogen does not change with the speed of the air. So no, you're not changing the equilibrium, nor do you smother a fire by blowing on it. "
] |
[
"What is Neosporin actually doing when I apply it to a cut?"
] |
[
false
] |
[deleted]
|
[
"Neosporin works as an antibiotic and also claims that it speeds the healing process. A couple studies in the past have shown that Neosporin does not have any increased efficacy in wound healing than a basic petroleum jelly. So pretty much it just protects the wound from any outside bacteria by placing a gel 'shield' over the cut/scrape.",
"Source"
] |
[
"In particular, Neosporin contains bacitracin, polymixin B, and neomycin which are effective against a range of both Gram positive and negative organisms. "
] |
[
"No. It prevents infection. Healing happens on its own through normal physiological processes. By preventing bacterial infection and the resulting inflammation,tissue damage etc., healing can proceed normally"
] |
[
"What causes light and heavy sleepers?"
] |
[
false
] |
I am a really heavy sleeper. It takes two regular alarm clocks and one alarm clocks on wheels to wake me up. Why is this different for different people?
|
[
"Differences in \"heavy\" versus \"light\" sleepers has to do with a type of brain activity called ",
"sleep spindles",
". Within the past ~2 years, research has started identifying genetic markers that influence sleep spindles."
] |
[
"Are brain waves just a visual measurement for electric or chemical activity in the brain? For example, when someone sees a sleeper spindle show up on a readout, does that indicate that some chemical or electric process is happening? "
] |
[
"Great questions, although I can only respond with current theories/hypotheses because we don't have clear definitive answers yet. Sleep spindles represent (thalamocortical) brain activity that we believe may be a signal of the brain \"managing\" information from the sensory systems during sleep. So if someone is sleeping and there is noise around them, sleep spindles are a sign that the body is managing that noise but keeping the person asleep. We think that these sleep spindles are a sign that the brain is able to somehow process and ignore (or just ignore) the sensory information and still maintain sleep. ",
"People who show less sleep spindles are more easily awakened by noise. "
] |
[
"Can a linear accelerator be re-configured and used as a 'decelerator'?"
] |
[
false
] |
Let's say one had a beam of charged particles moving at some speed, could they be slowed using a linear accelerator that is reconfigured to decelerate the particles? If it's simpler to think about this with defined 'packets' of charged particles, or particles that penetrate the 'decelerator' one at a time, then so be it.
|
[
"In principle, yes. But this is not the most efficient way to slow down a beam of particles. To ",
"slow down a charged particle beam",
", you just shoot it at some material. Charged particles lose energy and slow down as they interact with matter."
] |
[
"Actually, yes! There are a few rf-cavity based linear accelerators that recirculate the beam back 180-degrees out of phase to decelerate the beam and recapture beam energy. This allows for extremely efficient operation with very high average beam currents.",
"For an example see the ",
"Jefferson Lab energy recovery linac",
"."
] |
[
"I thought something like a linear decelerator was used for the cold antimatter experiments? "
] |
[
"Is light that is being \"pulled in\" by a black hole moving faster than regular light?"
] |
[
false
] |
If light can not move fast enough to escape a black hole, does it move faster towards it because it is "sucked" in? I doubt it is possible, but what really happens as light approaches it? Edit: Thanks guys!
|
[
"Light is still moving at light speed. It is space itself that is entering the black hole faster than light speed. Think of the light as a fish swimming against a stream. The fish might be moving at a regular pace but if the water flows too fast to anybody on the side of the rive the fish looks to be going backwards."
] |
[
"Light as ",
"/u/CatalyticDragon",
" said always moves as at the speed of light. But due to black holes' intense gravity they stretch out space time- meaning what you call 1 meter might be increased to 100 meter so apparently it wont seem to move at the speed of light. Light doesnt really get \"sucked in\" after one point it is absorbed. Its momentum and energy are sucked in by the black hole."
] |
[
"If light can not move fast enough to escape a black hole",
"The reason, under general relativity, why light can't escape is because all directions inside a black hole point towards the singularity, due to the warped nature of space.",
"Once you are inside the event horizon, you could point yourself in any direction, and it won't matter. No matter what direction light goes, and no matter how fast it goes, it doesn't matter, because it will always be heading towards the singularity. There is no direction it could go to escape. "
] |
[
"What do you get when you take multiple integrals? Derivatives? What is their application?"
] |
[
false
] |
Hey . So I just finished up a calculus 1 course and was left with a few questions about taking multiple derivatives/integrals. From the calculus course combined with the physics course i was taking i learned that differentiating a position function will give you velocity. Differentiating that gives you acceleration. Differentiating that gives you jerk. But what happens when you differentiate jerk? It's going to give you the fourth derivative of the function, but are there any practical applications at such high-order derivatives outside of constructing polynomial approximations of functions? (I only have a brief introduction to this subject so my knowledge of it is limited). Similarly, integrating a function gives you area under a curve. Integrating that will give you volume. But what do you get when you integrate volume? What is the applications of this?
|
[
"There are some physical models that use fourth order derivatives. Anything over that is extremely rare. Higher order derivatives are mostly useful in mathematics.",
"Actually, your brain is a highly specialised solver of second order differential equations. It has to be, to control your body in a universe where the governing mechanics is second order (Newton's law). You can experiment with this by asking people to play a game where they control a vehicle by adjusting its ",
" order derivative. It will be very easy for ",
" < 3 and extremely difficult for higher ",
".",
"I heard once that the only time fourth order derivatives were used in politics was when a president said in a speech that \"the rate of increase of inflation is decreasing.\" I don't know if that's true.",
"Multiple integrals can be used for just about anything, and the interpretation doesn't have to be volume at all. For example, we integrate over probability spaces to get probability. These spaces can have any dimension you care to study, and nowhere does volume have to come into play.",
"Nevertheless, there are higher dimensional analogues of volume, just like volume is a third dimensional analogue of area. Usually it's called hypervolume, ",
"-volume (in ",
" dimensions), content or measure."
] |
[
"Derivative just represents how quickly something is changing. Velocity represents how quickly position is changing, and acceleration is how quickly velocity is changing. You can keep taking derivatives past that to see how quickly acceleration is changing, then again to see how quickly that is changing, etc. We just don't have names for them. ",
"It's similar for integration. The integral of acceleration is how much velocity has changed. The integral of velocity is how far you've traveled. The integral of position doesn't mean anything in particular, though. For other physical quantities, there is a meaning. The integral of force with respect to distance is equal to work, etc."
] |
[
"You can experiment with this by asking people to play a game where they control a vehicle by adjusting its nth order derivative. It will be very easy for n < 3 and extremely difficult for higher n.",
"Interesting idea!"
] |
[
"Why does our skin get numb when we're cold?"
] |
[
false
] | null |
[
"So your sensation comes from neurons that brings information from your skin to your brain. When it's cold, you can imagine that reactions needed to send that information slows down, and then when numb, most of that signal can't move out of that area towards your brain simply because the nerves can't fire effectively any more. "
] |
[
"Blood flow to exterior arteries is restricted to keep the internal organs warm. "
] |
[
"\"Veins carry oxygen-poor blood cells back to the heart and lungs to be re-oxygenated, so it is reduced blood flow in the arteries that can cause a drop in sensation in the legs, arms, hands, etc. Arteries contain freshly oxygenated blood and carry it throughout the body. As you mentioned, it is the capillaries that directly provide the nutrients to nerve cells which in turn allows for signal transduction to occur, but it is the arteries that supply the capillaries with fresh blood. ",
"Nerve cells require a continuous flow of nutrients, especially Ca2+ and Na+ ions in order to properly function. As you may recall, nerve signal transduction depends on the nerve cell being able to route a wave of depolarization across the length of the axon. Without the vital nutrients and oxygen that fresh blood supplies, the electrical gradient can't be produced, resulting in no signal being sent to the brain. Your body interprets this lack of signal as numbness. You can try this out on your own by pressing against the large artery on the inside of your upper arm. After a few minutes you'll notice a drop in the sensation of your entire limb, which is due to your nerve cells not having fresh nutrients. ",
"As for veins, blocking a vein will only lower the amount of blood that is being re-oxygenated, but there are hundreds of veins in your body that can compensate for a single vein being blocked, so it is very unlikely that blocking a single vein will have any effect. The only way that vein blockage could cause problem is if it is completely blocked off, resulting in a buildup of oxygen-poor blood not being able to leave a site, at which point numbness will be the least of your worries, and gas gangrene and swelling will become more pressing issues.\"",
"Not mine, but a more than thorough explanation I found ",
"here",
".",
"Edit: I also wanted to add that in case you are not familiar with it, the Na+ ions are the driving mechanism in neuron synapses (near the skin surface at least, it gets more complicated the deeper you go). Sodium receptors send a chain of response from the area to your brain. Thus, to draw a comparison, this is why numbing agents such as novacain work. Novacain inhibits the sodium receptors from talking to one another which means the signals from the area where the novacain is placed are not produced and the brain has no way of feeling anything in that region. Same mechanism as numbness from cold but brought about in a different way. "
] |
[
"What is happening (physically and chemically) inside of an atomic bomb at its detonation?"
] |
[
false
] | null |
[
"The HowStuffWorks article is pretty good. If you have any questions after reading it feel free to ask.",
"http://science.howstuffworks.com/nuclear-bomb.htm"
] |
[
"Colloquially speaking, an atomic bomb, as opposed to a hydrogen bomb, is a fission device. This means its energy depends on breaking atomic nuclei apart. A relatively easy way to do that is to start off with a slightly unstable, large nucleus and throw a neutron at it. The Plutonium isotope Pu-239 is large and easy to break, and when it breaks it also emits some neutrons.",
"Since Pu-239 decay yields neutrons, you can't have too big a piece of it, because if it's too big the neutrons from spontaneous decay, and from fission because of neutrons will cause a runaway nuclear reaction, and the whole thing will go up before you're ready. So to make a bomb you start with a non-critical mass, and then make it go critical somehow.",
"Modern bombs make it go critical by compressing it. That way when it's at normal density, it won't explode, but then when you compress it, its density will make it have a runaway nuclear chain reaction.",
"To do this you start off with a sphere of Pu-239, then surround it with a shell of styrofoam, and then another shell of U-238, and then another shell of some kind of chemical explosive. This last shell is made of elements of explosive like the panels of a soccer ball, so that you can detonate each one precisely, since the explosive shell has to explode as symmetrically as possible.",
"At the center of the plutonium sphere, there's also a small core of some element that produces a lot of neutrons when it's squeezed. When you detonate the explosive soccer ball, the shockwave of the explosion forces the uranium tamper toward the plutonium sphere. The styrofoam is there to let it gain some momentum from the expanding gasses of the initial explosion.",
"When the uranium hits the plutonium, it squeezes it down from all sides and increases its density to critical density. Aided by supplemental neutrons from the core, atoms of plutonium break apart and release more neutrons, which cause more plutonium to break apart and release more neutrons, and then you have a nuclear explosion on your hands."
] |
[
"Yes. I've done plenty of my own research. In the end I just felt confused and mixed up between the myriad of facts thrown at me. I guess my reason for coming to reddit with this question was to have a more 'to the point' answer, rather than having to examine intricately written articles. "
] |
[
"What happens at the end of a mapping satellites lifecycle?"
] |
[
false
] |
I am using the following assumption, correct me if I am wrong: A Satellite that is mapping the Earth, as I understand, it would have to burn fuel in order to change its inclination in order to map the entire surface of the earth. What happens once the fuel is gone or near gone? Does ground control put the satellite into a parked orbit, leave it as it is, or de-orbit it? Is there any public data on mapping satellites and how much fuel they have left for orbital maneuvering?
|
[
"A Satellite that is mapping the Earth, as I understand, it would have to burn fuel in order to change its inclination in order to map the entire surface of the earth.",
"That doesn't really happen. Any satellite will have to use some amount of fuel to make small adjustments to its orbit, but making large changes in inclination is pretty much out of the question - it would be grossly inefficient.",
"Mapping satellites like the ones used for Google Maps are put into what's known as a sun-synchronous orbit. The orbit is highly inclined (right around 98 degrees) and uses the equatorial bulge of the Earth to move the orbit of the satellite just enough so that, at any point in the satellite's orbit, the sun is in the same relative position (or, more practically, the shadows on the ground are always the same length and direction). The 98 degree inclination also has the benefit of covering almost the entire globe - there's only a gap of 8 degrees at the poles where imaging isn't possible. These satellites then map the Earth almost completely once every 16 days or so.",
"You may be interested in reading up about the recently-launched Landsat 8 (and, in fact, the entire 40 year history of Landsat) for some information about mapping from space."
] |
[
"No, not really from further away. They're just at a higher inclination to begin with. A higher inclination means more latitudes are covered (in fact, the inclination also tells you the highest latitude achieved by the satellite - that's equal to the inclination or to 180 minus the inclination; e.g., a 51.6 degree inclination will have you traveling between 51.6 degrees North and South latitude; a 98 degree inclination will have you traveling between 82 degrees North and South latitude). Since more latitudes are covered, it's just a matter of time before the orbit puts you over almost the entire surface of the Earth. In the case of Landsat, it takes about 16 days for the satellite to map the same swath of Earth.",
"Heck, the Space Shuttle did something similar from a comparatively low inclination with the Shuttle Radar Topography Mission. It just happens to be that the most interesting parts of the Earth are between about +/- 60 degrees latitude."
] |
[
"So the inclination is not changed really after it is put in place",
"Correct. There might be a few tenths to one degree of change, but not anything drastic.",
"98° for the Earth's most intersting parts",
"98 degrees is useful for two reason. One, it allows coverage of almost all the Earth. If you look at a map, you can see that huge portions of the Earth's landmasses fall between 82 degrees North and South, which is the maximum latitude achieved for a 98 degree inclination.",
"Two, it allows the satellite to be in a Sun synchronous orbit, which gives you constant lighting. This makes two images taken days, weeks, or even years apart a lot easier to analyze. If, in one image, the shadows faced east and were very long, while in another, they faced west and were very short, it would be difficult to see what actual differences happened on the surface of the Earth. The Sun synchronous orbit makes this a non-issue, thanks to the way the Earth's oblate gravity interacts with an orbit at that inclination.",
"...and then Landsat 8 is basically able to see the entire Earth in a 16 day orbit from around 700km up?",
"The orbit doesn't take 16 days. It takes about 100 minutes. But Landsat only passes over the same points on the surface of the Earth in daylight once every 16 days or so. So for about half of the orbit (the half that's in sunlight) Landsat takes pictures of the Earth - let's say over Central Europe. It does that continuously; on the next orbit (100 minutes later), it will cover Western Europe, after that it'll be over the Atlantic, then North America, etc. After sixteen days, it'll be back over Central Europe during daylight, and it'll start the mapping cycle all over again. All this without expending any fuel.",
"Also, do you have any idea what happens to these Satellites once they reach their planned/extended mission duration?",
"It depends on the satellite. I think satellites in Low Earth Orbit are deorbited if possible; if not, they're put in an orbit that will decay as soon as possible. Geostationary satellites (usually communications satellites) are put into what's known as a graveyard orbit, where they're put into in an economically useless orbit that won't interfere with active satellites. Up until recently, however, disposal plans weren't really high priority. Now, I think there's a requirement for considering the end of a satellite's life before launching, at least with American satellites."
] |
[
"If you have enough oxygen but too much carbon dioxide, Why would too much carbon dioxide kill anyone when carbon dioxide is nontoxic?"
] |
[
false
] |
I was watching Apollo 13 when they explain at one point in their voyage that they had enough oxygen but too much carbon dioxide.
|
[
"Too much carbon dioxide is called ",
"hypercapnia",
". If it gets bad enough that the acidity of the CO2 lowers the blood pH, the condition is called ",
"respiratory acidosis",
".",
"CO2 directly causes problems because it is a ",
"vasodilator",
", which means it causes blood vessels to expand. In severe cases, too much expanding of vessels inside the skull can put too much pressure on the brain, leading progressively to headache, dizziness, panic, convulsions, unconsciousness, and eventually death.",
"Acidosis is a problem because it changes the electrolyte balance in the bloodstream. Most importantly, pH causes an increase in the level of circulating potassium. Potassium plays an important role in regulating the heart's natural pacemaker, and too much of it (",
"hyperkalemia",
") tends to cause irregularities in the heart rhythm. If the irregularities get too bad and are untreated, the heart rhythm can become disorganized and unable to circulate blood, which of course will be deadly.",
"The movie is correct that these states are independent of oxygen availability. It's quite possible to have plenty of oxygen in your bloodstream, and still die of an overload of CO2."
] |
[
"Hemoglobin has an affinity for both O2 and CO2, though these affinities are not equal. ",
"When it's carrying CO2, it has less affinity for O2",
", so if there's a mixture of CO2 and O2, and there's too much CO2, you won't be able to get enough O2 onto the hemoglobin to transport to where it's needed in the body. So you suffer from hypoxia and eventually suffocate."
] |
[
"It acidifies the blood. C02 + H2O -> H2CO3, carbonic acid."
] |
[
"Where does a human's digestive acid come from?"
] |
[
false
] | null |
[
"Where does the creation of stomach acid occur? ",
"Do we naturally take in enough Hydrogen and Chlorine to keep creating HCl in our stomachs?",
"Could I produce less stomach acid if I simply stopped eating NaCl?"
] |
[
"Cl- and Na+ ions are used in enough vital bodily functions that you would die long before stomach acid production was ever affected. ",
"Gastric acid is produced in the gastric glands lining your stomach. It's a bit of a complex process, but this video explains it nicely:\n",
"http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter48/hydrochloric_acid_production____of_the_stomach.html"
] |
[
"I understand the digestive system. What I was curious about was where the acid comes from. Does our digestive acid(meaning HCl) form within a certain section of our body like the gall bladder or the spleen. Also part of this question was to find out if we recycle our HCl or does it just exit as waste. I am sorry if my original question was a little vague. "
] |
[
"Ununoctium is the largest element in the periodic table (#118). Is it theoretically possible that there could be elements with more electrons (that haven't yet been discovered), or is Ununoctium the theoretical \"largest\" element?"
] |
[
false
] |
As far as I'm aware, an element gets its number in the periodic table based on the number of electrons. Ununoctium has 118 electrons (with 8 electrons in the outermost "ring"). Is it possible that there may be elements with more than 8 electrons in this outermost ring, or even with more electrons in a new "ring" (pardon my lack of scientific language, I am but a mere layman)? For example, the structure of Ununoctium is 2, 8, 18, 32, 32, 18, 8, could a new element perhaps have a structure of 2, 8, 18, 32, 32, 18, 9, or even 2, 8, 18, 32, 32, 18, 8, 1? I imagine this will be ridiculously unstable, given how unstable the final few elements actually are, but is it a possibility?
|
[
"I imagine this will be ridiculously unstable",
"Actually, element 120 (unbinilium) is right in the middle of the ",
"island of stability",
", so, it might be more stable than you'd think.",
"Even unbihexium (element 126) ",
"\"is predicted to be near the centre of the hypothesized island of stability, and thus may have a very long half-life\"",
"."
] |
[
"Sure, the electronic structures have been calculated up to 172, ",
"by Pyykkö",
". There's no known definite limit to the number of electrons in an atom. It's the ",
" that's unstable."
] |
[
"This is inaccurate. Basic chemistry teaches that elements are defined by the number of protons in it's respective atom. An element with more electrons could have a greater width, because it might have more shells, and therefore be \"larger\". The elements on teh periodic table, though, are not organized by physical size."
] |
[
"Many of us would have anecdotes of pets attempting to comfort us when we're sad or sick, but are there any scientific studies on animals knowing when people are unhappy and showing empathy towards us?"
] |
[
false
] |
Obligatory edit: Oh cool, went to bed and this got front paged! Thanks for all the responses everyone. It'll take me a while to read through everything, but I'm sure there's a lot of good stuff here.
|
[
"A recent TED talk on the subject was just posted: ",
"TED",
"The talk is about the idea of empathy, morality, and fairness in various primates. The talk is very entertaining to watch, but here's the break-down.",
"Yes, the ability to empathize is an evolutionary trait that is not limited to humans. Being social and caring for others allows many populations to survive and thrive. Many animals have even shown to ability to comfort somebody and other animals when they are sad, hurt, or otherwise in need of comfort. ",
"Pets are particularly adept at showing empathy, which is why, in many cases, they became pets in the first place. It's a dog's ability to share our emotions that makes him man's best friend. Even going back to when dogs were first domesticated, it's this emotional capacity that has been one of their greatest strengths."
] |
[
"I don't disagree with anything you'd said, but I cannot find a source for:",
"Many animals have even shown to ability to comfort somebody and other animals when they are sad, hurt, or otherwise in need of comfort.",
"short of Washoe, who I linked to already. Do you have anymore? I find those stories heartwarmingly awesome, if anyone knows of more."
] |
[
"Animal Therapy",
" is becoming more accepted, and the wiki sources are more than valid. Some of the suggested animals (usually aquatic ones) are actually less suitable than most believe, and horses are often very good for this.",
"There are measureable personal benefits to having pets in our lives as well.",
"See here.",
" Yes, it's a slideshow, but I peeked through the sources, and they also all, are things I've read before and am comfortable saying were well studied and reported.",
"Another",
" study that shows consistently that they are good for our health.",
"Washoe",
" the chimpanzee was able to empathize with a keeper whose baby had died by miming crying and offering a hug upon hearing that her baby had died."
] |
[
"Is there any factual basis to the phrase \"red sky at night, sailor's delight, red sky at morning, sailors take warning\"? What meteorological phenomena, if any, are responsible for this occurring?"
] |
[
false
] | null |
[
"The origin of the saying is unknown, although a form of it appears in the bible (Matthew 16:2-3). It has some basis in science and is a fairly good predictor of-though no guarantee-of weather at the mid latitudes in the Northern Hemisphere, where storm systems generally follow the jet stream from west to east. A red sky in the morning indicates a sun rising in clear eastern skies casting its rays on storm clouds approaching from the west. At night the clear sight of the red setting sun would tell a sailor that no storms are to the west.",
"Source"
] |
[
"http://www.reddit.com/r/askscience/comments/hwt8a/what_is_the_explanation_behind_pink_in_the_night/"
] |
[
"I would say it's something to do with air pressure.",
"I would say..."
] |
[
"Can someone explain causal fermion systems and the Dirac Sea to me in \"smart layman's terms\"?"
] |
[
false
] |
Because Wikipedia's article on them are all grad student-level gobbledegook. I need something more on the level of A Brief History of Time or Cosmos.
|
[
"The Dirac sea was an attempt to make sense of the problems when one tries to relativistic quantum mechanics. These problems go away when you use quantum field theory instead and so the Dirac sea is not really relevant.",
"That said, it is an interesting idea. Basically the Dirac equation has positive and negative energy solutions. The negative energy modes can have arbitrarily negative energy and this causes a problem where you'd expect to be constantly showered with positive and negative energy particles which can spontaneously form from nothing.",
"The idea of the Dirac sea is to get around this by positing (thanks to the pauli exclusion principle) that all of the negative energy states are full. This means that the runaway process I described before can't happen. But what happens if you give enough energy to one of these negative energy states such that its energy becomes positive. Well now you have a positive energy particle (usually though of as an electron in this example) and a \"hole\" in the sea of negative energy particles. It turns out that such a hole behaves exactly like a positron (if the positive energy particle is an electron)."
] |
[
"I understand that the Dirac Sea isn't needed in the Standard Model. However, causal fermion systems (an alternative to the SM) apparently use it."
] |
[
"Sorry, I'd never heard of causal fermion systems and it seems like almost nobody has if you look at the number of citations the papers have. Good luck",
"Just a fun aside: beware of things which are called \"casual such and such\" the word causal is almost always attempting to make people think causality makes sense in whatever the thing is. c.f Causal sets."
] |
[
"I live in the midwest. Let's pretend it's just me, in my backyard, with a shovel, and nothing but time on my hands. How far can I dig before the shovel just can't go any deeper?"
] |
[
false
] |
For the sake of argument, let's say that I have a magical way of tossing the dirt I shovel out of the hole so it doesn't fill itself back up, but I can only dig with the shovel. I can take breaks, sleep, eat, and weather won't affect it. I'm just curious how deep I can go before the dirt is too compact, or I hit a huge layer of rock, or something like that. EDIT: I flagged this as earth science, but....that might not be right
|
[
"Geotechnical engineer here. Here is the scenario I think you are imagining: there is you, a shovel, and your backyard. You start digging a hole just wide enough for you to stand on the bottom and perform the \"digging\" motion and throw the dirt out of the whole (lets say 6 foot diameter). The way I see it there are three things that would stop you:",
"1: Personally, I would not get in a 6-foot diameter hole deeper that 4 feet deep, but lets say you don't know any better and keep digging deeper. Depending on exact soil type I give you any where from 5 to 15 feet deep before your hole collapses and you are crushed/suffocated to death.",
"If it was me, or you did know better, you would have to start digging a hole that looks like an inverted cone, with",
"\n about 45 degree slopes. Not a real problem for your scenario, but you sure just added a ton of extra digging.",
"2: The next limitation would be groundwater. Your scenario didn't include buckets, pumps, or scuba gear, so you would be screwed as soon as you hit groundwater. Depth to groundwater is quite variable depending on exact location, but could be anyway from 15 to 500 feet deep. I would say groundwater is usually 15-50 feet deep.",
"3: The third limitation, and the one you were thinking about is bedrock. Almost any soil type can be dug with a shovel, with varying levels of difficulty, but bedrock is bedrock. So no digging to china with a shovel for you. Depth to bedrock is also highly variable. Up towards Colorado and Montana, the bedrock can be 40-100 feet deep (or at the ground surface). Down towards Mississippi, bedrock can be over 300-500 feet deep (I think)."
] |
[
"inverted cone, with about 45 degree slope",
"Just adding: use slope < soil's "
] |
[
"Foundations for large structures can get pretty complicated but usually will involve piling into bedrock and some sort of pad or raft foundation anchoring the load bearing columns in the soil at a stable depth.",
"For a look into how complicated they can be here's the foundation system for the Grand Lisboa Hotel in Macau:",
"http://imgur.com/Sz9EF5w"
] |
[
"Why do some parts of a download take longer than others to download?"
] |
[
false
] | null |
[
"What kind of downloads? ",
"You wouldn't be talking about P2P ( torrents ) download per chance?"
] |
[
"In what context? Without some more info I can say:",
"In general, some ISP give you a \"boost\" for the first part of each download.",
"If you are talking torrents/P2P file transfer, in this type of file sharing information is broken down in pieces and pieces that are more \"available\" (more people have them) get downloaded faster. It is also affected by the upload speed of the peer who's sharing that piece."
] |
[
"During the course of a download, your speed can vary. With a traditional direct download, you're sharing computer and network resources with other people around the world, so your download speeds will go down if there's network congestion.",
"In a peer-to-peer situation, other people are sending you the file. Sometimes, other people drop in and out of the available sources for the download, and that can impact your speeds."
] |
[
"How are astronomers able to take such clear images of celestial bodies?"
] |
[
false
] |
Our planet is constantly spinning and in orbit around the sun at extremely high speeds. And so is whatever they want to take an image of. How can they still come up with clear images of things so many light years away?
|
[
"Large telescopes will automatically track (i.e. rotate with) the position of interest in the sky while taking long-exposure photographs. Space telescopes do the same thing. Your handheld camera or phone has a very short exposure time of (at a guess) a few milliseconds. Space telescopes take exposures lasting hours, and will sometimes take the same photograph at multiple different times and stack the images later. Because the objects are so faint, it takes that long to gather enough light to make a decent image.",
"EDIT: If anyone is bothered by the fact that I didn't include any precise information or sources - for some reason I thought I was in ELI5. I'll leave it, though."
] |
[
"I don't think we have anything that tracks individual planets. The movements would be too small. We can track individual stars",
", and the differences we see between separate images of the same star enable us to infer something about the star and any planets that might be around it.",
"These things all conspire to make it hard to detect small planets; the dimming as the planet passes in front of the star will be very little, and the wobble of the star will be very slight. This is why all the planets we know of are quite large. Small planets are probably just as common, but they are much harder to find.",
"[1] At BEST we might track individual stars. More usually we would scan a particular section of the sky and trust that the star doesn't move enough within that patch for it to be an issue."
] |
[
"The adjustment of the telescope is to compensate for earth's movement and rotation, not the movement of what it's looking at. Unless it's something in our solar system, it's unlikely the photographed object would move even one pixel, even for long exposures. "
] |
[
"Are there any AI programs out there that have the ability to modify and recompile their own code?"
] |
[
false
] | null |
[
"Self modifying code exists, but it is not done by intelligent programs. Back in the 1950s and 60s, programmers had very little memory availiable, so they wrote programs, that rewrote parts of themselves to change functionality approriately (i.e. your disk driver was temporarily rewirtten to serve a different device, so you only had to store one program and a small one that contained orcalculated the differences.).",
"Today we have computer viruses (or virii), that modify themselves in order to evade antivirus software. These are called ",
". However the changes that are made are not \"intelligent\". Statements are replaced by equivalent instructions or parts are inserted that don't do anything useful.",
"It's pretty difficult to find friendly sites that offer such viruses for study purposes. VX Heavens used to be great but it was taken down by law enforcement. However mirrors supposedly exist, if you want to dive deeper into metamorph viruses."
] |
[
"You're talking about recent Jeff Dean and Andrew Ng work, article here",
"http://www.extremetech.com/extreme/131717-google-and-stanford-create-a-digital-brain-that-like-an-infant-learns-to-identify-a-human-face-from-scratch",
"If you read the paper their object recognition accuracy is 15.8%; hardly a solution to the problem. It's very unlikely that there is a hard/complete solution to a the kind of learning task they are attempting. They say it's \"like how infants learn\" but infants are never faced with a world full of completely unlabelled data."
] |
[
"How specific are you being with \"AI\"? If you mean programs in general, see ",
"Self-modifying code",
"."
] |
[
"If gravitational paths such as orbits are conic sections, what is the cone?"
] |
[
false
] |
I'm curious as to why a gravitationally determined trajectory, or any trajectory influenced by an inverse square law force, follows conic sections. How can I understand this? Bouncing off of that question, is there any known relation between Dandelin spheres and Kepler's first law?
|
[
"Conic sections are special because no matter where you are on the orbit, certain relationships and distances between you and the foci (or directrix) remain constant. This is precisely the behavior required for angular momentum to be preserved which makes sense as angular momentum by definition tells you about the relationship between a point on the orbit and the relevant focus.",
"is there any known relation between Dandelin spheres and Kepler's first law?",
"Yes! The foci will be on the shared tangent plane of two spheres both flush with the cone. As you can see in this picture, ",
"https://upload.wikimedia.org/wikipedia/commons/2/21/Dandelin1.png",
"The point P in the image will then maintain the same combined distance to both foci—which is the definition of the ellipse.",
"Greg Egan's website goes over all the gory details of this here,",
"\n",
"http://www.gregegan.net/SCIENCE/ConicSectionOrbits/ConicSectionOrbits.html",
" "
] |
[
"Conic sections are special because no matter where you are on the orbit, certain relationships and distances between you and the foci (or directrix) remain constant. This is precisely the behavior required for angular momentum to be preserved which makes sense as angular momentum by definition tells you about the relationship between a point on the orbit and the relevant focus.",
"This is a bit misleading though since you suggest that inverse-square force laws give rise to conic orbits ",
" of conservation of angular momentum. But angular momentum is conserved for ",
" central force fields."
] |
[
"Sure, but angular momentum is constrained differently depending on the shape involved. Different shapes with angular momentum conservation let you produce different U(r). Essentially the ",
"Binet equation",
"."
] |
[
"As spacetime expansion accelerates, does this mean that the force due to dark energy is increasing?"
] |
[
false
] |
Or is it a constant force (if it even really is considered a "force")? And if so, will this force ever become big enough to overcome the force of gravity within galaxies, and pull their individual stars apart from each other? And eventually even individual molecules or atoms might be pulled apart?
|
[
"You can reason the first part of this out with basic mechanics: force=mass*acceleration; thus a constant force yields constant acceleration. AFAIK, we don't know enough to determine whether the force itself is increasing or remaining constant, and if it's not constant, what trajectory it will follow. If, for example, the force is increasing exponentially, then it would eventually rip apart everything (see ",
"this",
" wiki article). But if it's a gentler trajectory, the current state of affairs, where things that are gravitationally bound stay together but things that are, for the most part, gravitationally separated, will eventually be pulled apart, could be continued. Expansion would have to be orders of magnitude of orders of magnitude faster for it to rival the electromagnetic or strong force."
] |
[
"I am glad you ask. Look, since we don't know, what exactly dark energy is, we characterize with the help of a bunch of numbers. One of those is the ratio of energy density and pressure, called w. For regular matter, dark or not, it is 0, for radiation, w is 1/3. We know w for dark energy must be smaller than -1/3 so that it accelerates the universe.",
"Now if dark energy happens to be a cosmological constant or vacuum energy, then the force is constant, which is implied by w=-1. Vacuum energy density would stay constant over expansion. Unfortunately, current measurements point to w=-1 with a error margin of .2 or so. So it could very well be -1.2 or -0.8. This is crucial, since a w<-1 would mean that the energy density is actually increasing while spacetime expands and the acceleration would get faster and faster, ultimately leading to a \"big rip\", where galaxies, solar systems, planets, and eventually atoms and possibly even baryons would get ripped apart. Read more about it on Wikipedia.",
"In interesting fact in that case is also that some advanced civilization similar to us in a couple billion years would not perceive anything else than their own galaxy, they would never be able to figure out the big bang theory.",
"Ok I am going to bed now."
] |
[
"In interesting fact in that case is also that some advanced civilization similar to us in a couple billion years would not perceive anything else than their own galaxy, they would never be able to figure out the big bang theory.",
"I always wonder, and maybe this is more philosophical than scientific, if we aren't limited to what we can see when we look up at the cosmos in some similar way to this, and we'll never know about it."
] |
[
"Does a Tesla Coil affect your smartphone in any way?"
] |
[
false
] |
I was toying around with a little Tesla Coil and I was taking some pictures of it. I noticed that my phone was spasming out, as if someone pressed stuff randomly on the screen. This stopped as soon as I turned it off. Why does this happen?
|
[
"This is called EMI, electromagnetic interference. It is a common problem with electronics and subject to a lot of testing. Devices have to meet standards of resistance to this interference, But if you exceed the limits, it gets spazed.",
"https://en.wikipedia.org/wiki/Electromagnetic_interference",
"You just applied an interference level beyond what the phone was designed to resist."
] |
[
"Thanks! Can this damage your phone or it just affects it during the high interference?"
] |
[
"Depending on the field strength, it can just interfere, or at stronger field levels actually damage the electronics. I wouldn't risk my phone exploring this level."
] |
[
"My friend doesn't believe I have experienced rapid solidification in my house"
] |
[
false
] |
This is what happened: When I got home I put a few coronas in the freezer. Later in the evening I remember I had actually put them there. I open the freezer and take a bottle, it is cold but not frozen (all liquid), I take my bottle opener and open it, I took a big sip and it was pretty cool but not too cold to drink. At this point I still have the bottle in my hand and suddenly I see white flakes appearing inside the bottle, feeling confused I just stare at the bottle until many more flakes continue to appear and in less then 10 seconds the whole beer is frozen! Yes the same bottle I just opened and took a sip out of just froze while I had it in my hands! I keep telling my friends the story but they refuse to believe it actually happened, so tell me askscience, this CAN happen right?
|
[
"Yes"
] |
[
"Congratulations, you ",
"supercooled",
" your beer. When you took the first drink you agitated the beer, resulting bubbles acted as sites of nucleation for crystal formation."
] |
[
"It is possible, and it is called supercooling:\n",
"http://en.wikipedia.org/wiki/Supercooling",
"The basic premise is that you cool a liquid down below it's freezing temperature, without it freezing. It's easier to do when you cool a liquid rapidly: aka putting it in your freezer. Disturbing any of the liquid while it is supercooled causes crystallization to form, rapidly.",
"As such, I believe part of your story. Supercooled beer does happen, although taking a sip of the beer should have sufficiently disturbed it to the point of rapidly freezing, but I'm not a super expert on thermal physics, just an undergrad.",
"Also, relevant: ",
"http://www.youtube.com/watch?v=H0YvkbJhWxk"
] |
[
"I learned in my Geology class last week that all the galaxies regardless of direction around Earth are exhibiting blue shifts. Since they're all moving away, how exactly are we supposed to collide with Andromeda?"
] |
[
false
] | null |
[
"I see a few erroneous/ambiguous comments so just for clarity (with some basic sources) ...",
"In general, all galaxies regardless of direction or distance from Earth exhibit redshift, not blueshift. The amount of redshift is proportional to the distance from us. This is known as ",
"Hubble's law",
", and it's due to the fact that these galaxies are moving away from Earth; the ",
"metric expansion of space",
" causes them to accelerate away from us according to the distance between them and our galaxy; farther distances result in greater accelerations and thus greater velocities.",
"That said, the ",
"Andromeda Galaxy",
" actually exhibits a blueshift, not a redshift, because it is moving towards us. There are other galaxies in the ",
"local group",
" that also have blueshifts. These galaxies are moving towards us because the local group is gravitationally bound, and the gravitational force between them can be greater than the acceleration due to the expansion of space.",
"Hope that clarifies! :)",
"At distances larger than our local group, gravity of the galaxies alone is not enough to keep them gravitationally bound. The next \"scale\" up is that of a galaxy cluster, which is not too much larger. These are also gravitationally bound, but are only so because of the presence of dark matter, which increases the amount of gravity to several times more than the galaxies themselves exhibit. Beyond the scale of clusters, gravity is not strong enough even with dark matter to keep galaxies bound to eachother."
] |
[
"Actually most galaxies are redshifted as they move away from us.",
"Since Andromeda is moving towards us it is one of the few blueshifted galaxies."
] |
[
"Actually most galaxies are redshifted as they move away from us.",
"Since Andromeda is moving towards us it is one of the few blueshifted galaxies."
] |
[
"What differs in the brain/body when moving, say a finger, compared to just thinking about moving it?"
] |
[
false
] | null |
[
"There isn’t actually a consensus on this. Everyone will agree that assuming that the action is voluntary, you’ve got some executive function stuff going on either way. Then there is something called motor programming, which can be thought of as a file cabinet of motor actions from which your brain draws. The selected motor program is “sent” to the motor cortex, and then activity there proceeds down some things called corticospinal tracts and goes to the body part you want to move. Answering your question is where it gets fuzzy. It also depends on in what way you are thinking about moving your finger. If you’re imagining it, then a lot of people would argue that that motor program is pulled from the file cabinet and sent to the motor cortex, but some inhibitory activity prevents the motor cortex from asking anything of your finger. The interplay between motor programming and motor activity is still not well understood, and there is a lot less distinction than how I’m making it seem."
] |
[
"I once heard (watched a video) that imagining moving causes a really tiny subtle movement, and this is how ouija boards work. everyone's ",
" that the piece is moving, and since their hand is on it they imagine their hand moving which causes them to push it the way it seems to be going. since everyone is doing it, eventually they agree on which way its moving and involuntarily push it together.",
"Apparently a way to demonstrate this effect is to hang an earbud or something on a cord (maybe 1-2ft long) from your hand, and then imagine swinging it back and forth. if you do it right the earbud should seem to start swinging all on its own because of the subtle movements created by you THINKING about swinging it.",
"Perhaps this effect could be related to the question in some way?"
] |
[
"Something similar also happens",
" during internal monologue, with the muscles of the larynx and tongue executing tiny, usually imperceptible movements that match those that would occur to speak those thoughts out loud. This has lead to proposals that sensors to pick up this movement, combined with a cochlear implant at the receiving end, could be used to create synthetic telepathy."
] |
[
"Is DID (or multiple personality disorder) recognised as genuine by the medical community? What do we know about it and its causes?"
] |
[
false
] |
A recent post had a brief conversation about whether it's 'real' or not - what's the scientific/medical community's consensus, if there is one? On a basic level is it just a matter of self-delusion, or does the brain literally close parts of itself off from itself? Is it possible for the other personalities to have distinct memories of a different childhood or anything like that? What's the best way of dealing with them? Any links to reputable studies or reports would be fascinating! Thanks!
|
[
"There was a recent Science Friday on this topic. They had a psychologist and psychiatrist that were on different sides of the debate. The discussion got rather heated, and was quite fascinating. The short answer is that it's very controversial.",
"http://www.sciencefriday.com/segment/10/21/2011/exploring-multiple-personalities-in-sybil-exposed.html"
] |
[
"Dissociative identity disorder is recognized by the DSM which is the holy bible of mental diagnostics. Like all mental disorders there is debates as to it's defining characteristics, so there's always controversy which way the debate seems to sway in terms of consensus is never to easy to gage. Anyway here's a relevant article, I'd recommend you read;",
"http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0039279"
] |
[
"Don't think of multiple personality disorder as multiple people living inside of one brain.",
"Think about how you behave in front of your parents vs how you behave with your friends. Not the conscious choices you make, but the subconscious or unconscious differences in behavior. You might be more anxious in one situation, more bold in another, and more relaxed in a third, etc. Those are all different \"personalities\" in some very real senses, specifically things like behavior types.",
"In DID, that is just more severe and is partitioned with selective memory loss. So in certain situations, the person with DID will go from, say, their stndard day to day personality to the personality that is good at handling that specific set of emotions or specific experience. This is especially the case for \"triggering\" experiences, that is, situations that are directly related to the event or events that originally caused that. For example, if a person develops DID as a result of sexual abuse by a teacher, they may switch over to an alter that exists solely to deal with that stress when in a situation that reminds them of that trauma. That alter might, for example, be the kind of good submissive student that the teacher told them to be and may act sexually different, because the entire point of that alter is to be able to handle that shitty situation they were in back in the day. That alter doesn't have an internal life and doesn't really exist for any purpose except to protect the person from having to go through and remember that abuse. ",
"If that makes any sense.",
"I'm not a psych professional, but this is my understanding of the disorder from having been in a relationship with and now maintaining a friendship with someone who is coping with DID. It is a real thing but it doesn't really follow the media portrayal of the disorder particularly closely."
] |
[
"New Intel Chip on Front Page: Does this differ quantum mechanically from other methods of storage?"
] |
[
false
] |
Front Page article: After learning about semiconductors and band gaps in quantum, I'm just wondering if there is any progress for physics with this announcement.
|
[
"I don't think, after looking at the paper in ieee, that they used QM at any step in the development (though its a trade secret so maybe...). At any rate the important part of this tech is the phase transition that occurs when you apply a current. Phase transitions do not require QM to understand, see ",
"landau theory",
" of second order phase transitions. You might even view this as a step back since conventional hard disks leverage spin valves that increase the resistance in the head and tell you what bit you are reading. "
] |
[
"It seems that it's intended to be a replacement for RAM and not disks."
] |
[
"It says its flash, which is normally reserved for non-volatile memory which means it can be used for storage."
] |
[
"Are there any two stars that we know are extremely (or unusually) close to each other?"
] |
[
false
] |
If so, how close are they and how do we know that? I use the term "extremely" loosely. How far apart do stars need to be to form? Also, if this does happen, what sorts of problems does it present if any?
|
[
"There are two pulsars (neutron stars) that are 60,000 km from each other. That's much closer than the Earth is to the moon.",
"The system is called PSR J1744-3922."
] |
[
"Both are a bit heavier than the sun, about 30% heavier. However, because they're so dense, they're only a few miles in diameter."
] |
[
"As for what problems close stars cause, each star in a binary system has a region around it called a ",
"Roche lobe",
", inside which matter will remain bound to that star. If a star is larger than its own Roche lobe, it will gradually lose matter to the other star. This often happens in binary systems in which one of the stars is a neutron star or a black hole, especially if the partner star is a red giant."
] |
[
"Why is bare, non-insulated wires still the norm for electric transmission lines?"
] |
[
false
] |
Is it just cost? I live in an area that's fairly forested and there are fairly frequent power failures due to trees falling onto the power lines. I notice that some streets have insulated, twisted power lines instead - even the (edit: transmission/medium voltage), 3 conductor lines are insulted and the twisted cables seem really thick. Is seems that this has benefits for safety and for reliability in case something falls on the line. Is it just cost that makes this the exception and not the norm?
|
[
"Firstly, the voltage is really high - a simple layer of plastic isn't going to cut it. insulation to keep 10,000, 100,000 or 1 million volts is not trivial.",
"If a tree falls on a wire, the insulation and wires are likely to be damaged anyway.",
"The wires are out in the sun all day. Most plastics will last only a few years under those conditions.",
"Those wires carry enough current to get warm. A plastic wrap will stop them loosing that heat, which means they will get hotter and sag more.",
"Because of this, only low voltage and low current wires use insulated wires in a bundle - like feeds to a single street. For anything more serious than that, bare cables with large glass insulator stacks are used."
] |
[
"First, technically they are insulated since air is an insulator, but I'll assume you mean coated with an insulator material.",
"If memory serves, and I'm about half a decade removed from power systems studies, it's largely due to the added weight on the lines because of the required thickness to be effective, which would require reduced spacing between poles, as well as having to replace the entire lines frequently as most insulators would degrade substantially being exposed to both the elements and UV light from the sun. ",
"You'd probably be looking at at least doubling to tripling electricity bills to account for the substantially higher O&M costs this would require."
] |
[
"The insulted wires in urban areas on overhead lines are almost always end user low voltage (<1000 V) or telecommunication wires/fibre. Not distribution medium voltage (1,000 - 50,000 V) or transmission high voltage (50,000 - 1,000,000 V). ",
"We do insulate distribution conductors in urban areas. This is almost always done underground though. You don't see overhead power lines in a lot of newer, and more expansive, neighborhoods anymore. We sometimes do insulate transmission conductors too. This is done in very dense urban areas (downtown of major cities) and for other scenarios that necessitate it like under sea transmission lines. ",
"The problems with overhead insulated medium or high voltage cables:",
"More expensive",
"Much heavier. Both from the insulation, but also more metal required as it can't run as hot or the insulation will melt. ",
"Harder to install",
"Still going to be damaged if a tree falls on the line",
"Exposed to the elements, sun light, and frequent temperature changes which cause expansion and contraction. The insulation isn't going to last very long.",
"If you have high voltage transmission lines, you clear the trees and put the conductors on very high on steel towers. If you need cheap, economical, long distance distribution, you put the conductors on wood poles. If you are in a dense urban area, for rather short distances, are worried about line contact, and have the the money, you put insulted conductors underground."
] |
[
"Newton's 1st Law"
] |
[
false
] |
[deleted]
|
[
"Your error is here:",
"That implies that there's a force keeping it in motion",
"No force is required to keep an object in motion if it already is. That's the point of the first law."
] |
[
"\"",
"\"",
"No, there's no force keeping it moving. It is the object's momentum that is keeping it moving at a constant speed. In the absence of external forces (friction, etc.), it will keep moving at a constant speed and direction."
] |
[
"Forces cause acceleration, not speed. You initially apply a force for a small amount of time, producing acceleration on the ball and changing its velocity from zero to something. Once you stop applying the force, the acceleration disappears too, and the ball keeps moving at constant velocity. "
] |
[
"Do \"higher thinking mammals\" like primates and dolphins have names, like we do, for each other?"
] |
[
false
] |
A few more (tangentially) related questions: Where does this sense of identity come from? Is it the same as sentience? How does the human brain almost seemingly hardwire recognizing our own names (which happens even in incredibly noisy situations)? Is it true that we can recognize our name much easier aurally than visually? (It seems harder to pick out one's own name in a lot of text) At what age do all the above begin to manifest in infants?
|
[
"Birds do:",
"http://blogs.discovermagazine.com/80beats/2011/07/13/baby-parrots-learn-their-names-from-their-parents/",
"... each bird has its own signature call that others use when addressing it and that the bird uses itself in avian “conversation.” Scientists have long wondered where these calls come from. Now, a new study of wild parrots shows that even before chicks can “talk,” their parents have provided them with a moniker, which they will tweak and then use throughout their lives.",
"More here:",
"http://www.geekosystem.com/parrot-parents-name-babies/"
] |
[
"Yes. Many other mammals have names for each other. (or at least distinct responses to individuals they recognise)",
"Most animals are sentient, sentience is just the ability to feel. I suspect you mean sapient, which means the ability to reason. Sapience is a bit of a tricky thing to categorise and it's too fuzzy a word to actually apply this question.",
"We recognise our names through practice, it isn't hard-wired because we mostly have different names.",
"Most people recognise things better verbally. Writing is a system that has evolved to mimic the way we speak. ",
"I'm not sure when this starts to manifest in children. Infants start to recognise different individuals around six months but that is mostly because their eyes don't develop well enough until then, probably earlier. "
] |
[
"I'm no expert on psychology (animal or otherwise), but it seems to me that assumes he is conditioned to hearing his name at both positive and negative things, which muddies up the idea that he is just reacting to a a sound that he thinks will be followed by a positive experience. He hears his name just as often after he does something bad as when he does something good. Of course, the tone of my voice changes depending on whether I'm happy with him or not. Also, he certainly realizes that his name refers to him and him alone (that is, he recognizes that if someone says his name, nobody is happy or mad at another dog, or another animal; its him). To me, that is an essential part of what a name is."
] |
[
"where does the energy for the movement of electrons around a nucleus come from?"
] |
[
false
] | null |
[
"The simple answer is that it does not require energy to move around the nucleus. The more complicated answer is that this is a major problem with the \"",
"orbital model",
"\" of the atom, as orbiting electrons would be accelerating and therefore give of electromagnetic energy.",
"It is actually one of the problems that ",
"quantum mechanics",
" explains."
] |
[
"I'm not sure what you're asking here. Are you imagining a scenario where there is a constant input of energy required to maintain an orbit? Because that isn't the case.",
"Furthermore, thinking of the electrons as existing in a moving orbit analogous to that of planets is erroneous. The electron is described by a 'probability cloud' around the nucleus, informing us of the probability for it to be located at a particular location in the orbital."
] |
[
"To which the cop replies \"you were doing 56 miles per hour\". Heisenberg then cries \"fuck you! Now I'm lost!!!\""
] |
[
"What causes Cheerios (and other cereals) to link up into little rafts?"
] |
[
false
] |
When there are just a few cheerios left floating in milk, they don't float around independently from one another. They instead tend to link up into little groups. It doesn't feel like they're sticky. What gives?
|
[
"You may have noticed the effect that, if you fill up a glass of water, the water is not flat, but has a rim at the edge. This is because, due to the surface tension, water is 'sticky', so clings onto things. If you were to put a cork in said water, it would float to the side, as it is less dense than the water and so naturally wishes to be at the highest point. This is called the meniscus.",
"It is the same with Cheerios- water sticks to the side of the Cheerio, forming a meniscus on the side of the Cheerio. Other Cheerios (being less dense than water) move towards their counterparts as they wish to be at the highest point. However, if more than a few Cheerios clump together, the combined weight of them pulls them downwards, so the other cereal does not wish to go there, and so floats away. This is why, when eating, you do not get much clumping if the bowl is full, but if it is empty you do."
] |
[
"See ",
"Cheerios effect",
"."
] |
[
"Think of the surface tension of water as a thin layer of saran wrap. The weight of the Cheerio depresses the surface of the water, creating a little dip in the surface. Gravity will cause adjacent Cheerios will slide along the side of the depression and they push up against each other, dipping the surface a bit more, etc."
] |
[
"What are the most advanced computers in the world being used for?"
] |
[
false
] | null |
[
"There are numerous applications of supercomputers. I'll describe my own usage as an example.",
"The Navier-Stokes equations are nonlinear partial differential equations that describe the motion of viscous fluids. Other than extremely simplified situations, they can not be solved analytically so we use numerical methods to approximate solutions. These solutions give us various flow data throughout a flowfield described by geometric surfaces and boundary conditions. Because flowfields can be so complex, with tiny turbulent length scales, it can take a ",
" of computing power to approximate these solutions.",
"Supercomputers are used to approximate these equations for the aerodynamic design of rockets, aircraft, jet engines, submarines, and many other vehicles or objects. These equations are also used to study the weather. Right now I'm running a simulation of a supersonic aircraft using more than 2000 processors."
] |
[
"I can confirm this. We use Navier-Stokes for analysing fluids as well and one calculation on a very high end PC can take up to 20 days, and that is after reducing the number of tets in the model. I can easily imagine a run taking orders of magnitude longer."
] |
[
"It depends on what you mean by \"advanced.\" There are lots of computer applications today with demanding constraints. Some computationally expensive problems might go to supercomputers, but programs that intelligently control cars and planes have demanding real-time and reliability constraints, while other applications require extreme power efficiency, low latency, data throughput, etc. ",
"If you mean supercomputers, and by advanced you mean fastest computation rate, you can find a monthly updated list of such machines online:",
"https://www.top500.org/lists/2019/06/",
"Look at the organizations that operate these machines and Google them if you'd like. For example, some relevant pages I found for the top 3 sites in June 2019:",
"Oak Ridge National Laboratory",
"Lawrence Livermore National Laboratory",
"National Supercomputing Center in Wuxi (China)",
"The short answer is that these machines are being used to tackle important scientific problems in domains that require tremendous amounts of computation. One of the biggest applications is climate modelling, both because of the pressing need of the climate emergency, and because planet-scale simulation necessarily requires a lot of computational power and a lot of memory. But, any application domain can become computationally challenging the closer you look: there are projects that simulate materials at the atomic or molecular level, and there are projects that simulate fusion energy reactions at the subatomic level.",
"It's important to note that the kinds of problems that supercomputers solve are not necessarily mathematically difficult to solve, but rather the number of \"co-moving pieces\" that must be considered is just very large. You could model the local climate around a city with maybe a hundred or a thousand individual points just fine on a powerful desktop computer. But, if you want to divide the entire Earth's atmosphere into one mile by one mile by one mile volumes you're looking at approximately two billion points of data, and disturbances at any one of those points could potentially affect all of the others. ",
"Also, it's important to note that there are probably a number of very powerful supercomputers that are not represented on that list because they are being used for military or national defense purposes. For example, the ",
"National Security Agency is believed to have the most computing resources of any one organization on Earth",
", but they're not telling anyone what they do with that. They're probably decrypting, cataloging, and analyzing the world's digital communications, but that's just a guess based on their historical mission. ",
"But, supercomputers are only one definition of \"advanced\" computing. You might instead consider what the most specialized computer architectures are doing. For example, GPU (graphics processing) technology has come a long way, and these days GPUs are used to highly accelerate not just graphics computations, but also scientific and machine learning applications. For example, you can't fit a supercomputer inside a car, but if you want to build a self-driving car then you need a reliable, local computational platform that can scan the road ahead, pick out other cars, people, and obstacles, and then decide how to react. In fact, ",
"GPU leader NVIDIA builds hardware and software",
" that is specially designed to handle these tasks. The total computational power in this system is much lower than a supercomputer, greater than your average home computer, and these systems have demanding real-time constraints that are not a part of traditional computing. ",
"There are also ",
"Application-Specific Integrated Circuits",
", or ASICs. These are single-purpose computers designed to do exactly one task, but do it extremely fast and efficiently. These are used either when blazing fast speed on a single task is important, like bitcoin mining, when extreme energy efficiency and reliability are important, like in satellite and space applications, or when extremely low reaction times are necessary, like controlling the power grid."
] |
[
"When you play a chord on a guitar, do all the sound waves from the different strings lump into a single wave?"
] |
[
false
] |
I'm pretty sure mathematically they can be described as such but does this actually happen? Do the air molecule vibrations get added together perfectly? Does your brain interpret each wave individually or as a single sound wave?
|
[
"Sound is nothing but a variation in air pressure. When multiple sound waves combine all that is really happening is the pressure of the air in any one location becomes the average pressure of all the waves affecting that location. Any sound wave is just a plot of the air pressure at that specified point over time. As each point has only one air pressure at a time there is only one wave.",
"Your ear then uses mechanical sympathetic resonance sense to detect which frequencies are variously abundant in the resulting air pressure changes. ",
"TL;DR: YES"
] |
[
"Yes, but you can separate them again with Fourier analysis, which is pretty much what the brain does with the signal, and is why we hear the chord as a chord and not a complete mess. In fact, the sound from a ",
" string is already a superposition of sin waves in a harmonic series. Typically (but depending on how the string is plucked) every second harmonic will be attenuated, and if you look at the signal in the time domain, it will be roughly a triangular wave."
] |
[
"Actually the \"Fourier analysis\" is done mechanically in the cochlea of the inner ear, rather than in the brain itself. The proximal portion is is stiff and resonates with high frequencies, and the distal portion is floppy and resonates with low frequencies. The neurons of the auditory nerve respond to the vibrations along the cochlea, and are arranged tonotopically. So the input to the brain (the auditory nerve) is already a \"Fourier transform\" of the sound wave."
] |
[
"How do ocean animals \"drink\"?"
] |
[
false
] | null |
[
"They filter out the salt. Saying they don’t drink is misleading, as lots of water is ingested while eating and just while going about their life. But they all have ways of filtering it that land animals just don’t need. So we don’t have."
] |
[
"Not every sea creature, only mammals lack this ability to filter out the salt from sea water, saltwater fish filter out the impurities from the water and basically pee them out in highly concentrated yrine"
] |
[
"But if every sea creature gets its water through eating other sea creatures, where does the original water come from? "
] |
[
"What would the crust of a neutron start look like?"
] |
[
false
] |
If two neutron stars collided, and a portion of ones crust was flung off, what would that crust look like? Given the huge decrease in pressure / temperature, how would it act (rapid expansion? Fragmentation? Stay intact?)? Edit: apologies for this misspelled word in the title. Start = star
|
[
"The crust is made up of iron bathed in a sea of free electrons. It's not made of \"neutronium\", i.e. pure neutrons, until below that. It's surface temperature will be of order one million Kelvin, so while it's still on the neutron star, I'm not sure it would look like anything except blinding (relativistically too!).",
"If two neutron stars collide, you're almost certainly going to end up with a black hole. Some stuff would get ejected (see ",
"image",
" of the process) and would be mostly a gas of neutrons, electrons, and other particles. A lot of these will end up combining in various ways (this is the ",
"r-process",
"). I don't think a chunk of crust would remain intact.",
"I guess if you want to ignore all of these effects, it's an iron crust. I'd guess it probably looks something like that. On a neutron star though, it'd be very smooth, not like ice crusts (see ",
"Europa",
"). Current estimates limit the size of \"mountains\" on neutron stars to meters on some to smaller than microns on others. So, very smooth!"
] |
[
"Without sufficient pressure, the ejecta would decay in an massive explosion, as the half life of free neutrons is only about 15 minutes or so. I have no idea what neutronium would look like to be honest, if it came from an ordinary hot neutron star it would probabely be brightly shining, like any other hot material. I can't say how it would look like on an cold neutron star. "
] |
[
"Neutronium, assuming it didn't decay like the previous comment would suggest, would be impossibly spherical compared to anything we're used to. While we don't yet know what color it would be if the star was cold, it would be completely uniform due to there being little to no deviations in the structure of a neutron star. Lastly, the remains would simply fall apart, releasing large amounts of particles as they did so."
] |
[
"Would it be hypothetically possible to build a device that jams a single radio frequency so we'd always have a convenient \"dead station\" for our iPods in the car?"
] |
[
false
] |
And if so, how difficult would it be to make?
|
[
"Wouldn't that also jam the iPod radio transmitter?"
] |
[
"No, jamming the station would also jam your iPod and I also believe that intentionally jamming a licensed frequency is a very illegal.",
"If you're in the USA, Wikipedia says:",
"Blocking radio communications in public can carry fines of up to $11,000 or imprisonment of up to one year."
] |
[
"All you can do is transmit another signal. You can't grab a signal and pull it out of the air. "
] |
[
"moments after the big bang, if all matter was inside the swarzchild radius, why didn't gigantic black hole form?"
] |
[
false
] | null |
[
"The reason that a black hole normally forms is because there is a lot of matter in a small space that's all being pulled gravitationally toward the center of mass. This means that you need a mass differential: you need a very strong gravitational force pulling each particle in a single direction (i.e. toward the center of mass) compared to a much weaker gravitational force in all other directions (i.e. toward empty space).",
"With the universe just after the Big Bang, that latter condition didn't exist. Yes there was a lot of mass...but it was incredibly uniform in its distribution, such that each individual particle was being pulled by gravity in all directions equally. As such, the gravitational forces all canceled out and no black hole could form."
] |
[
"The big bang was not like an explosion outward from a point. It was more like an infinite sponge starting in a squeezed state and relaxing, causing an expansion similar to an inflation. Assuming the universe is infinite, then it was still infinite (and uniform) during the big bang. Even if the universe is finite, it would have still been uniform -- so the same density of matter everywhere, which means it can't collapse into a black hole as there are no regions which are overdense.",
"Hope that helps."
] |
[
"A simple way to think about it is that to form a black hole, you need mass-energy to be concentrated in a small area compared to space.",
"But the big bang happened everywhere, so immediately after the big bang the region where the mass-energy was concentrated was the same size as all of space."
] |
[
"Aerogel as a CPU cooler?"
] |
[
false
] |
Thinkgeek.com sells aerogel pieces for about 35 bucks. Would it be possible for me to use aerogel in a case mod, or put it on my CPU like a heatsink? This might not work at all, but it would be really cool if it could!
|
[
"It is really good at ",
" heat, meaning it will trap the heat on the cpu rather than moving it away. Kind of the opposite of what you want."
] |
[
"diamonds, carbon nanotubes and graphene are the best conductors of heat. obviously none of them are even close to practical at the moment. the most practical heat conductor that you could use is pure silver, as it is around 45 times better at conducting heat than thermal paste. in general, pure metals like copper, gold, aluminum, steel, etc have good thermal conductivities. the problem with these metals is that the surface of the metal and the surface of the CPU are not perfectly flat, so you need something like thermal paste to fill in the air bubbles (air is a good insulator)."
] |
[
"We have an aerogel detector in our experiment actually."
] |
[
"If I tried to \"swim\" through outer space, would I be able to?"
] |
[
false
] |
If so, what swim stroke would be the most effective? If not, why?
|
[
"No. Based on conservation of momentum, in a perfect vacuum, you wouldn't go anywhere because you'd need some momentum to go in the other direction. ",
"Space isn't a perfect vacuum but for the intents of this question, it's a pretty good approximaton."
] |
[
"Plenty! Lot of people, myself included, study what's called the ",
"interstellar medium",
", the gas and dust and particles that exist out between stars. Space is actually really really active and dynamic and not a vacuum at all, it's just that relative to Earth, it is. A \"typical\" number density is about one particle per cubic centimeter. Compare that with one ",
"mol",
" of gas on the Earth, which then leads you to about ",
"10",
" particles",
" per cubic centimeter.",
"Anyway, even though the number density is so small, there's a lot of stuff to learn about because space is so big, so there's a lot of particles to deal with."
] |
[
"Basically, there is nothing to push against, so you would not move."
] |
[
"Optimal probability strategy for drawing numbers?"
] |
[
false
] |
Let's say that you and 9 other people have to draw numbers (1-10) from hat. The numbers drawn are random; however, you get to control when you draw a number from the hat. Is there an optimal strategy if you want a certain number? Or a number within a range?
|
[
"There is no difference when to draw. Lets replace numbers with colors and lets say there are 9 white and one blue ball, and you want blue ball.",
"If You draw first, probability to get blue ball is 1/10",
"If you draw second, probability is 9/10*1/9=1/10 (probability first did not get blue ball times probability to draw blue of 9 remaining)",
"If you draw third, probability is 8/10*1/8=1/10 (probability first and second did not get blue ball (1-1/10-1/10=8/10) times probability to draw blue of 8 remaining)",
".....",
"And if you draw last probability is still same: 1/10*10/10 = 1/10"
] |
[
"Thanks, I understood what you found wrong in my proposed solution. I used this formula:",
"1 - P(A∪B)=1 - (P(A) + P(B) - P(A∩B))",
"When there is only one blue ball P(A∩B)=0, since both first and second cannot draw blue ball at same time (I probably should have added 0 earlier to avoid some confusion).",
"When there are 2 blue balls I would get: \n1 - P(first got blue ball) - P(second got blue ball) + P(both got blue ball) = 1 - 2/10 -2/10 + 2/10*1/9 = 56/90",
"It is more messy, but also gets job done (and it gets even messier when you draw 4-th). When there are more than 1 blue ball your proposed method is much simpler and straightforward",
"Off topic: ",
"Thanks for teaching me new word :)"
] |
[
"Oh my god, while it is correct, this formula isn't intended to be use with a lot of subset. ",
"It is totally right, but it gets so messy so quickly, it wouldn't have cross my mind to use it."
] |
[
"Does b-lactamase exist naturally? Did all enzymes and/or modifiers that provide antibiotic resistance exist in nature at one time?"
] |
[
false
] | null |
[
"In some ways - yes. Evolution can't produce anything ",
", it can only modify existing structures. For example, B-lactamase is a mutated version of normally occurring digestive enzyme. It could be even enzyme with a very restricted mode of action against antibiotic. But any resistance is better than none, and it will suffice to be selected by evolutionary pressure."
] |
[
"I wasn't able to find an exact reference for this, but I'm reasonably certain b-lactamases existed prior to the discovery of antibiotics by humans. Most antibiotics we have today are either based on or similar to the bactericidal compounds produced by other microbes which includes penicillin. These compounds were not new within their communities (often soil) but rather tools of a long-standing evolutionary battle between species. Initially penicillin was highly effective for humans because only those bacteria which lived with Penicillium fungi were resistant. But as we used it more and more, we created an enormousness selective pressure for pathogens to pick up the gene as well.",
"The short answer is that every antibiotic isolated from nature most likely already had a gene or pathway which would make bacteria resistant to it as well."
] |
[
"I was going to state that b-lactamases would certainly exist naturally because b-lactam containing antibiotics also exist naturally. You already had it covered.."
] |
[
"What is the context of the geometric mean when the 50 ohm compromise for impedance matching was determined?"
] |
[
false
] |
I had wished to understand why transmission lines and other electrical systems typically use 50ohm loads for impedance. Everywhere I look online, websites just repeat the facts that this is derived from taking the values that provide highest power transfer (30 ohms), lowest power loss (77 ohms), finding the arithmetic mean (53.5) and geometric mean (48), and 50 is a compromise between them. There’s a lot of other history and data on various other values, but I’m hung up on why geometric mean was considered. I understand the arithmetic mean more intuitively as a midway point between these two ideals, but I can’t wrap my head around the purpose of the latter. I have only seen the GM used in basic geometry for triangle side ratios or for certain statistical growth scenarios so I don’t have a good image of its use in this real world application; is there a connection with the trigonometry of RF waves and reactive components, or something simpler?
|
[
"Let's say you had two solutions of equal volume, one with a strong acid in it and a pH of 6, the other with a strong base and a pH of 8. Let's say you add these two solutions, what is the resulting pH?",
"If you took the arithmetic mean of the 6 and 8, then you correctly get a pH of 7. However, if you took the arithmetic mean of the concentration of hydrogen ions (1.0x10-6 and 1.0x10-8) then you incorrectly get 5.05x10-7, (a pH of roughly 6.3). To correctly average the ion concentrations you need to take their geometric mean: ",
"Which gives you the correct pH of 7.",
"What this demonstrates is that the geometric mean is simply the arithmetic mean of a bunch of log-transformed values. What this means is, whenever your values are logarithmically distributed then you should take their geometric mean, or take their logs and then take their arithmetic means. ",
"I could only speculate as to why they take the average of the GM and AM for loads for impedance, so I won't. But I hope this gives you an intuition for when to use GM and why it crops up in scenarios involving growth."
] |
[
"Just a small correction to your example: The arithmetic mean of 10",
" and 10",
" is 5.05x10",
", or pH of roughly 6.3. AM of two values will always lie between those values, in your calculation it didn't."
] |
[
"50 is sort of in the middle between the two and is a nice round number, that is why it was chosen. I think some source just looked at both means and justified the choice as \"the average between both means\" and other sources you read copied them.",
"A standard is just that: a standard. As long as everyone agrees about transmission lines having a 50 ohm impedance the whole system works with minimum power loss. It being 50 means it's probably easy to remember and that is why it's chosen.",
"Neither geometric nor arithmetic would actually be the optimal mean for this. The standard was chosen to balance out optimal power handling and lowest signal loss, to get the optimal point (and thus sort of a mean) you'd need to know the relative weighting of each of the two. Then, in the case this is both 1, you would calculate the percentage loss (from optimal) and look for the point where the squared sum of these quantities is lowest. Since neither functions are purely linear or purely logarithmic, neither mean will give this point.",
"(Or you could be an engineer about it and call it about \"fiddy\" and work with that)"
] |
[
"Why do we expect Lake Vostok to show early earth life forms?"
] |
[
false
] |
It seems to me that something that has been isolated for so long would show us more about evolution in harsh climates and less about early earth bacteria. We have discovered relatively mild isolated systems before(I think of life on deep sea volcanoes, and in isolated underwater caves) but we learn more about how life adapts than what we learn about early life. So why should we expect different if we find life forms in Antarctica's deep lake "Vostok"?
|
[
"I have no definitive answers, mostly because I am a high school student, but I believe it is because of how ridiculously harsh conditions were on early earth. It is believed that before complex life evolved on earth, the planet went through many cycles of heating and cooling. The earth went from too hot to support life, to too cold for liquid water, etc. Early earth may have resembled lake Vostok at one or more point(s) in prehistory."
] |
[
"You would need a source of energy to have life, no matter how hardy. Since light obvious doesnt make it down there, there would have to be some source of geothermal energy to anything to live. "
] |
[
"Not necessarily. Just look at the chemosynthetic bacteria that function as primary producers in deep-sea vent communities. While there is plenty of heat for them to use, their energy comes from chemical reactions within the bacteria, not the volcanic heat. While the lack of heat and light is not ideal for life, it does not make it impossible."
] |
[
"How catastrophic is a supernova is terms relative to a nuclear explosion?"
] |
[
false
] | null |
[
"According to the NOAA, an average hurricane releases 1.5x10",
" Watts of energy from windspeed.",
"\n",
"http://www.aoml.noaa.gov/hrd/tcfaq/D7.html",
"\nAn ant is about 3mg, and a human is roughly 100kg. From ",
"http://www.reddit.com/r/AskReddit/comments/iphci/if_you_could_compress_a_lifetime_worth_of_farts/",
" let's assume that the human has a fart of 250mL. Doing the math, I'm getting the power of an ant's fart to be 7.6x10-6 Watts. ",
"A hurricane, therefore, is about 2x10",
" times stronger than an ant's fart. The supernova is 5.8x10",
" times more powerful than the most powerful nuclear weapon ever detonated. "
] |
[
"A small supernova will release more energy than the sun will produce in its entire life. Wikipedia suggests the sun releases the equivielnt of 9.192×10",
" megatons of TNT per second. The atomic bomb dropped on Hiroshima was about 15 kilotons. This means the sun is producing just over six trillion times the amount the energy of an atomic bomb ",
". ",
"Now take into account the main sequence of the sun lasts approximately 10 billion years. ",
"This is some pretty sloppy maths, but the best estimate i can find is that a supernova releases more energy than 10 trillion of the most powerful nuclear bombs ever produced. (bear in mind these bombs would be about 3000 more powerful than the Hiroshima bomb too!)"
] |
[
"This is why I love reddit."
] |
[
"Will the cores of the gas giants ever cool? If they will, what will become of the rest of the planet?"
] |
[
false
] |
They say that Mars lost most of it's atmosphere due to its core cooling, and no longer having a magnetic field to protect itself from solar radiation. Since planets like Jupiter and Saturn are pretty much entirely atmosphere, will they end up as small blocks of frozen hydrogen?
|
[
"The cores are balls of assorted ices ........ so they are already and have always been cold. ",
"This is completely wrong.",
"The core of Jupiter is believed to be a mixture of rock and ice somewhere around 24,000 Kelvin. We have an earthly observation bias that ice needs to be cold, but it does not. At the extreme pressures found inside Jupiter, you can have very, very hot ice.",
"The gas giants are not solid so the reacted mass of floating chemicals will remain that a reacted mass of floating chemicals an electro-magnetic field would not matter.",
"I research giant planets for a living, and I have no idea what this means."
] |
[
"The cores are balls of assorted ices ........ so they are already and have always been cold. ",
"This is completely wrong.",
"The core of Jupiter is believed to be a mixture of rock and ice somewhere around 24,000 Kelvin. We have an earthly observation bias that ice needs to be cold, but it does not. At the extreme pressures found inside Jupiter, you can have very, very hot ice.",
"The gas giants are not solid so the reacted mass of floating chemicals will remain that a reacted mass of floating chemicals an electro-magnetic field would not matter.",
"I research giant planets for a living, and I have no idea what this means."
] |
[
"First we need to understand the current structure of Jupiter. ",
"At the top we have the atmosphere, made mostly of cold hydrogen gas. As we dive deeper, the pressure and temperature starts rising. Eventually once hot and dense enough we hit a layer where hydrogen has transitioned to a \"supercritical fluid\", a state that shares properties with both solids and gases. Going even deeper, the pressures increase further so that hydrogen is forced into a solid state, in spite of warm temperatures.",
"Somewhere around ~30% of the way down, the pressure is so great the electrons from hydrogen atoms are forced into higher and higher energy states so as not to violate the Pauli Exclusion Principle. Electrons can start moving freely, conducting between atoms, and so the hydrogen becomes metallic. At the temperatures we expect at these depths, it is in a liquid metallic state.",
"Finally, deep, deep down, there is some kind of solid core of rock and ice, although exactly how large it is remains a subject of vigorous debate. Hopefully we'll know more about this puzzle when the Juno spacecraft arrives at Jupiter in 2016 and starts probing the deep interior.",
"Now, as for the cooling bit: it turns out to be quite difficult for metallic hydrogen to cool, as electrons must drop down to lower energy states...but it's at such high pressure that most of those states are all already occupied. It can still happen by conducting/diffusing heat into non-metallic layers, but that's an incredible slow process, very similar to white dwarf stars cooling into \"black dwarfs\" after considerable time.",
"Over many billions of years, the liquid metallic interior, will likely cool enough to become a solid metallic interior. This isn't quite certain, as the phase diagram for hydrogen at such extreme pressures is not well known - it may be that metallic hydrogen can remain a liquid even at low temperatures for a specific range of high pressures. ",
"Once most of this heat has escaped to space, the overlying gaseous atmosphere will eventually collapse, becoming a solid ice. This process may be somewhat similar to how part of Mars' CO2 atmosphere collapses into CO2 ice caps during each winter.",
": Yes, they will cool after many, many billions of years, and will leave a mixture of solid hydrogen ice in the outer layers, and most likely solid metallic hydrogen deep down."
] |
[
"What is a potential height for a tsunami generated by a large earthquake on the Cascadia Subduction Zone? How far would this wave travel and what regions would be underwater from it?"
] |
[
false
] | null |
[
"This is the type of thing that is the mandate of state and national geologic surveys and associated agencies. For WA state, the ",
"Department of Natural Resources",
" deals with producing hazard maps of this type. Specifically, they have produced ",
"tsunami inundation",
" maps for a variety of areas throughout WA state. Not all of these scenarios are specifically for a Cascadia quake, for example the ",
"Seattle map (large PDF warning)",
" considers a tsunami generated by movement of the Seattle Fault (because of the nature of the sound, significant inundation of Seattle from a Cascadia event is unlikely). OR has a similar set of ",
"maps",
", produced in this case by the Department of Geology and Mineral Industries.",
"Finally, for a more visual look, we can consider a ",
"simulation of a past major tsunami, specifically from the 1700, estimated M 9.2 earthquake",
". You can see that in the Pacific NW (and other areas), the tsunami wave height exceeds 3 m. There are similar types of simulations for hypothetical earthquakes, which might be a bit more readable than the maps, e.g. this ",
"one for WA",
" (again, from DNR)."
] |
[
"This is generally true for a Cascadia earthquake (e.g. this ",
"tsunami simulation for a M9",
"), but there is still a risk for a tsunami for a rupture of the Seattle fault, e.g. ",
"this page, and specifically the Elliott Bay map",
"."
] |
[
"While there are folks at UW studying a variety of things related to Cascadia, for most hazards related questions, you're usually going to be better off looking for what is on offer from state or local agencies (i.e. geologic surveys, department of natural resources, department of mineral resources, etc, every state has a slightly different name). While many of us in academia do work on hazards related questions / issues (and often provide a lot of the data critical to various hazards products), but it's really the state / federal agencies which spend the time to compile all of this and produce true hazard assessments / maps / visualizations for public consumption."
] |
[
"How did scientists (or geologists?) determine that the Earth was 4.5 billion years old?"
] |
[
false
] |
I know it has something to do with measuring the amount of uranium left in a lead rock, or vice versa maybe. I'm just having trouble understanding the methods and reasoning that lead (ha) to the conclusion!
|
[
"Most elements decay into other elements over time at a known rate. ",
"For example ",
"U has a half life of 4.5 billion years and decays through a chain of other isotopes into a stable isotope of lead.",
"http://en.wikipedia.org/wiki/Uranium-238#Radium_series_.28or_uranium_series.29",
"Because they have different densities (or are sometimes gasses, etc.) if a uranium heavy mineral was melted, the decay products would separate out and float away, so by measuring the amount of decay products, scientists can find out the amount of time which has passed since a rock solidified if it had the appropriate initial composition. Very simply, uranium and lead have much different densities, so if you find them in a rock together it means the lead came from decay of the uranium. Find the ratio of the two elements in the rock and you find it's age (with a little math).",
"http://en.wikipedia.org/wiki/Age_of_the_Earth#Radiometric_dating"
] |
[
"The age of the earth conclusion is indeed more complex and robust than that one measurement, but it's a basic start to understanding. Your hypothesis has reasonable merit, but isn't the case. Verifying evidence includes dating meteorites fallen to earth, moon rocks, and the sun itself.",
"I highly suggest reading the article which provides much more information than can reasonably be contained in a reddit post.",
"http://en.wikipedia.org/wiki/Age_of_the_Earth"
] |
[
"Floating in space doesn't stop elements from decaying, but it does stop (or at least impede) them ending up in the same place as their decay products. To use the uranium example, when uranium decays in space, prior to forming a planet, you get a planet with uranium deposits and lead deposits, for the same reasons you have concentrated deposits of anything. When uranium already in a planet decays, though, the lead can't go anywhere, so the uranium deposit turns into a mixed lead-and-uranium deposit. You can use the proportions of the two to figure out how long it's been since planet formation stopped and the uranium deposit was formed. "
] |
[
"If some big disaster occured and wiped out almost all of humanity, how many people would be needed to keep our species alive and why?"
] |
[
false
] | null |
[
"According to the genetic bottleneck theory, between 50,000 and 100,000 years ago, human populations sharply decreased to 3,000–10,000 surviving individuals.",
"[31]",
"[32]",
" It is supported by some genetic evidence suggesting that today's humans are descended from a very small population of between 1,000 and 10,000 breeding pairs that existed about 70,000 years ago.",
"[33]",
"[34]",
" ",
"https://en.wikipedia.org/wiki/Toba_catastrophe_theory"
] |
[
"To clarify, genetic bottlenecking refers to the loss of variety in a gene pool due to low population numbers, not an event specific to human history. Cheetahs have also gone through a genetic bottleneck which explains why they're all very genetically similar, and any currently endangered species which used to have a larger population is going through one now, assuming it recovers rather than becoming extinct. This is a major problem, as members which may have had adaptive traits that would be advantageous in the future if not absolutely necessary for survival can no longer help to prevent extinction should a rapid environmental change occur."
] |
[
"Basically you need 50 breeding individuals to avoid inbreeding depression and 500 in order to adapt,” he says. It’s a rule still used today – though it’s been upped to 500-5,000 to account for random losses when genes are passed from one generation to the next",
"https://www.bbc.com/future/article/20160113-could-just-two-people-repopulate-earth#:~:text=Anthropologist%20John%20Moore's%20estimate%2C%20which,of%20potentially%20dangerous%20recessive%20genes",
".",
"Good article explaining a lot about inbreeding"
] |
[
"Where does the calcium come from during aortic calcification / stenosis?"
] |
[
false
] |
I only learned calcium ions playing a role in the nervous system, and since the cardiovascular nerves are independent (mostly) during heart beat (synapse from SA to AV node), and the cardiovascular nerves are not nearly as extensive as the muscles of the heart, where does the calcium physically come from during calcification of heart valves? Is there a small amount in our blood? Any journal or research references would be greatly appreciated!
|
[
"Without citing any research articles or journals, I can confidently say that calcium is present in the blood. It is simply impossible for calcium to get anywhere in the body without at least some being in the blood. Even in neurons, muscles etc, there will always be some calcium lost with every cycle of whatever process requires the movement of Ca2+. This loss will be replenished by the body's solute and metabolite transport system; blood. ",
"In your studies into neurons using calcium ions for action potential propogation, you may have come across the table that states the concentrations of Ca2+ inside the cell and in the intersitium, with the concentration being higher outside the cell. The interstitium is in close equilibrium with the blood when it comes to small solutes, so there is roughly the same concentration of Ca2+ in the blood as would have been shown to you in that table.",
"As is commonly known, calcium is stored in bones. The inorganic compound it exists as helps keep our bones resistant to compression and, with the help of collagen fibres, torsion. Calcium deficits in the blood are replenished by stores in the bone, but after a certain age bone calcium itself cannot be replenished - even when excess is present in the blood/diet, leading to brittle bones in later life.",
"A bit off topic, but still quite interesting. "
] |
[
"Thank you soo much. Great starting point into looking to journal articles. I am now going to try to find any information I can regarding the equilibrium/ calcium contraption in intestinal fluid and blood. "
] |
[
"There is calcium in the blood. Most of it is bound to protein in the blood, mostly albumin, but some of it is as free ions. "
] |
[
"Why does mass bend space-time?"
] |
[
false
] | null |
[
"Because it has a rest energy E = m c",
" and energy-momentum curves spacetime.",
"As to why energy-momentum curves spacetime, and what exactly this means, that's quite a question.",
"Assuming the equivalence principle, we know that ",
" spacetime can be \"bent\" by something, it ",
" to be energy-momentum, either in the way General Relativity prescribes or in a slightly different form. So barring a few details we know we must have Einstein's field equations",
"Einstein tensor = constant * stress-energy tensor",
"Where the Einstein tensor is a function of curvature, and the stress-energy tensor is composed of the densities and fluxes of energy and momentum. There is almost no other possible form for this equation. In particular the source of curvature can only be energy-momentum and not, say, some other form of charge.",
"The reasoning to deduce the above result is sadly very technical. I'd basically be paraphrasing all of Einstein's work if I tried to explain the proof.",
"We have reduced ourselves to the above with an unknown constant. The constant can in principle be zero. There is no reason in known theoretical physics for it not to be. However, empirically we observe gravity. Rewriting the constant as such",
"constant =: 8 π G/c",
"(that's a definition of G) and studying a special limit of the above equation we find, of course, that the above implies the existence of Newtonian gravity, where Newton's constant is G. Since we experimentally know since the 1600s that G is nonzero, because, well, gravity exists, we know that constant also isn't and therefore stress-energy ",
" curve spacetime.",
"That's where universally accepted physics ends; a real answer to the ",
" question, that is why is G nonzero in the first place, would be a theory of quantum gravity. My favourite is of course string theory, in which a spacetime where Einstein's equations hold blossoms in a very neat way. However it gets way too mathy very fast and I also cannot guarantee this is actually what happens in the real world, so I'm omitting an explanation."
] |
[
"im pretty sure E(rest)=mc",
" is only rest energy, since c is a constant and m is (rest)mass"
] |
[
"I recommend Hobson's intro to GR as a first textbook, and then Carroll."
] |
[
"How was the island in the Manicouagan crater formed?"
] |
[
false
] |
[deleted]
|
[
"Above a certain size, the stress re-equilibration of a major impact has a rebound effect which produces a central uplift (see fig 10, here: ",
"http://www.lpi.usra.edu/publications/books/CB-954/chapter3.pdf",
").",
"However, in the case of Manic, since the impact is Triassic, the crater is FAR from fresh. In particular the last few glaciations have brutally ground down pre-existing topography and overlain what was left with glacial landforms. Remember there was a continental glacier about 3 km thick sanding down this part of the world not so long ago. Those depressions as they currently stand are the result of preferential glacial erosion in fractures and weathered rocks along the rim of the crater.",
"Also worth mentioning, there was no island there before the construction of the Daniel Johnson dam on the Manicouagan river in 1959: the current lake around that island is in fact an artificial hydro-electric reservoir. Consequently, René Levasseur \"island\" is artificial as well, the water from the reservoir just enhances the outline of the crater which becomes much more visible that way.",
"Québec is rife with great craters. Among the favorite are Pingaluit (",
"http://en.wikipedia.org/wiki/Pingualuit_crater",
") and the Lac-à-l'Eau-Claire double impact (",
"http://fr.wikipedia.org/wiki/Lac_%C3%A0_l'Eau_Claire",
")!"
] |
[
"Many ",
"impact craters",
" have a bump in the middle. These are know as ",
"Complex Craters",
". You can see numerous examples in those articles.",
"The reason for the formation is:",
"Above a certain threshold size, which varies with planetary gravity, the collapse and modification of the transient cavity is much more extensive, and the resulting structure is called a complex crater. The collapse of the transient cavity is driven by gravity, and involves both the uplift of the central region and the inward collapse of the rim. The central uplift is not the result of elastic rebound which is a process in which a material with elastic strength attempts to return to its original geometry; rather the uplift is a process in which a material with little or no strength attempts to return to a state of gravitational equilibrium.",
"In other words, the material is displaced from the cavity, then rushes back in. In the same way that water spurts upward after a droplet hits, the pressure of inrushing material from all sides pushes the center back up again."
] |
[
"Vaguely recalling something I read once, I believe that the uplift in the centre of craters is due to the shockwaves from the impact rebounding off lower levels of rock - this will happen most powerfully at the centre of the crater, which is closest to the reflecting layers of rock. I've tried finding some information to back this up online, but not had much luck.",
"(However, I may well have remembered parts of this incorrectly!)"
] |
[
"If macromolecules are the building blocks of life, why do macro diets usually only focus on proteins, carbohydrates, and lipids (fats/oils), but exclude nucleic acids?"
] |
[
false
] | null |
[
"DNA is indeed one massive macromolecule. But DNA (aka a nucleic acid) cannot be metabolized in the way fats/sugars/proteins are. DNA is made up of nucleotides which can act as the skeleton for other things like healthy cholesterols and hormones, but eating DNA really doesn't provide any source of energy for our bodies. \nSource: medical student "
] |
[
"Thanks! I kind of understand this-but I was curious as to if we could be missing something. Many of the foods cited as being good for people for other reasons such as protein and oil also have high concentrations of nucleic acid: fish, spirulina, vegetables. I thought that maybe nucleic acids have a benefit, but we've not been able to study (or realize) it."
] |
[
"its more of a correlation vs causation thing. Most healthy things are \"alive\" and thus have nucleic acids (plants, fish, turkey, fruits). "
] |
[
"Is there any practical use for laminar flow in liquids, or is it purely a neat aesthetic phenomenon?"
] |
[
false
] | null |
[
"In grease bearings and the like, you select a viscosity to avoid turbulence and make a set amount of friction to avoid over heating.",
"In pipe flow you avoid turbulence to avoid flow induced vibration fatigue in metal and excessive pressure drop along the line. ",
"In food prep, you apply chocolate or whatever in a controlled fashion, rather than spray it all over the factory floor and you have to lick it up.",
"I'm sure there might be medical and pharmaceutical uses, but that's outside my wheelhouse. Maybe even fluid-robotics. Again, not my wheelhouse."
] |
[
"As far as medical stuff goes, anything that deals with blood (dialysis, heart lung machines, LVADs etc) pretty much needs to be laminar. Blood cells are not happy when things are turbulent, and if you start lysing (breaking) blood cells, things become a problem fast. ",
"In general I would say that laminar flow is the preferred situation for most fluid flow. Turbulent flow by its nature is difficult to account for. The engineering math is so, so much easier when flow is laminar."
] |
[
"There are MANY applications for laminar flow."
] |
[
"Does neuroscience discount the whole discipline of psychology?"
] |
[
false
] | null |
[
"they are very tightly interwoven and cannot be separated, so it can't be that either one discounts the other.",
"at the margins, there are neuroscience studies that seem to have little to do with psychological science - e.g. a study of how exactly how a neurotransmitter binds to a receptor; or psychological studies that make no reference to neuroscience, like a study of word memory.",
"but in between there are tens of thousands of studies that either involve both domains simultaneously - like a study of how neurons in monkey cortex respond when the monkey is doing a memory task developed by experimental psychologists - or which make strong reference in one or another direction (with psychologists interpreting their data in terms of a model of brain function, or neuroscientists studying a particular phenomenon because of its psychological significance, like the increasing number of receptors on some class of neuron after learning).",
"even apparently independent topics (e.g. neurotransmitters, word memory), if you look closely, will turn out to have deep connections to the broader science that includes both cognitive and physiological facts.",
"so no, one does not discount the other. they seem to me (a psychologist who studies brains) to be two sides of the same coin."
] |
[
"I do not think that external v. internal properties of a human is a helpful distinction between the two, as neuroscience is very interested in describing in terms of brain anatomy and function the mechanisms of identity synthesis, feelings and emotional states, the emergence of consciousness by means of synchrony over various frequency bands of oscillation, etc."
] |
[
"I do not think that external v. internal properties of a human is a helpful distinction between the two, as neuroscience is very interested in describing in terms of brain anatomy and function the mechanisms of identity synthesis, feelings and emotional states, the emergence of consciousness by means of synchrony over various frequency bands of oscillation, etc."
] |
[
"Are there any studies showing how many Covid-19 cases are asymptomatic vs pre-symptomatic, and is there a difference in the infection rate or viral load?"
] |
[
false
] |
When the pandemic started, most of the attention was on "asymptomatic" infectees, but I've seen more people saying many of them may have instead been pre-symptomatic. What is the number of asymptomatic people that never get symptoms, and is there any differences between pre- and a- symptomatic people?
|
[
"This ",
"study in Indiana",
" found 44% of patients with an active infection were asymptomatic. I've seen estimates of 20-80% of cases being asymptomatic, our understanding of the prevelance of asymptomatic cases could definitely be improved. ",
"There was a ",
"very recent JAMA study",
" comparing viral load between asymptomatic vs symptomatic patients...there was no significant difference.",
"We don't fully understand why some people are asymptomatic and some people get very severe disease. ",
"One theory",
" is the amount of virus one is exposed to impacts severity. Another factor could be ",
"ABO blood type",
": people with type A blood are more likely to experience severe symptoms, while patients with type O blood experience milder symptoms. Another factor could be the ",
"types of immune responses",
" elicited by your body, but we don't know what drives those differences. There could be many other factors we don't know about though."
] |
[
"Not exactly what you're asking about, but Radiolab recently had a very interesting podcast episode about how a large percentage of homeless seem to be coming down with COVID-19 but remain asymptomatic, possible due to having higher Vitamin D than the average population. ",
"https://www.wnycstudios.org/podcasts/radiolab/articles/invisible-allies"
] |
[
"Thank you for sharing that, it makes me feel better. \nSincerely, someone with blood type A"
] |
[
"Out of all the spacecraft we have landed on planets, is it possible some may of contained bacteria that has stayed on that planet? And possibly even spread?"
] |
[
false
] |
[deleted]
|
[
"Concern about contamination is the reason why Cassini was thrown into Saturn. Originally the plan was to just let it keep going after it ran out of fuel, but discovery of geysers on Enceladus made scientists realize that if it crashed there, any microbes missed by the sanitation process could survive and multiply. They decided it wasn't worth the risk and decided to destroy Cassini instead of putting it in a semi stable orbit. "
] |
[
"This is actually a huge concern for any space agency, since if there is any life on another planet and we bring our bacteria we risk killing that life. NASA has strict sanitation policies for spacecraft and personal, usually requiring them to spray down the aircraft with chemicals and having workers wear full body suits. Some bacteria still gets through of course, and a more recent concern is that some bacteria have begun consuming the chemicals NASA uses for sanitation."
] |
[
"For a long time, it was thought that this had actually happened with Moon probes. Parts of one of the early unmanned probes (Surveyor 3) were brought back by Apollo 12, and upon analysis they thought that there were some still-viable bacteria in it. However, as I understand it, they now think that the Surveyor parts were contaminated with bacteria after they were brought back."
] |
[
"What is the evolutionary advantage of desensitization?"
] |
[
false
] |
By desensitization, I mean the down-regulation of receptors to repeated stimuli. Is there an advantage to such phenomenon?
|
[
"Our sensory systems are built to detect change in the environment. If there is some continuous signal that is irrelevant, we want to ignore it and prioritize processing on things that might affect us (e.g. threats, targets etc.). The classic example is that soon after putting on your clothes, you stop feeling them. If you focus, you can again for a bit, but it's not an important sensation that we want to be experiencing all the time."
] |
[
"To expand on that, the evolutionary advantage comes from the reduction of energy used to detect, send, and process the signals that are irrelevant."
] |
[
"if you want a big theory, you could read about the ",
"free energy principle",
", the basic idea is that any living system, including a neural system, should always be striving to minimize its activity; reducing response to a constant stimulus is an instance demonstrating the principle."
] |
[
"If a container filled with gas was left alone for a very long time will the gas eventually run out of kinetic energy?"
] |
[
false
] |
Assuming the container was isolated from any form of external force and energy.
|
[
"There are two possibilities here.",
"If your container is perfectly insulated, then it is a closed system and no energy can leave or enter. In that case, the gas can't run out of kinetic energy because, basically, there is no other place for that energy to go.",
"If your container is not perfectly insulated, then it will communicate with its surroundings, and what will happen is that it will equilibrate with the environment it's in. Eventually, its temperature will become the same as the surrounding temperature. When this happens, then its molecules will still be moving — unless the surrounding temperature is absolute zero — because temperature is nothing more than a measure of the average kinetic energy of particles of some material.",
"So: insulated = remains at its present temperature; not insulated = equilibrates temperature to environment; either way, temperature above absolute zero = molecules are still moving."
] |
[
"No. That is what \"perfectly insulated\" means (and this isn't something you can ever achieve in practice, of course)."
] |
[
"So you are assuming that the container is pressurized, doesn't leak, and is completely isolated from outside sources of energy, such as heat.",
"Is this correct?",
"If so, your question is, if given enough time, the tank, with the pressurized gas, will \"loose\" its kinetic energy (which I think you mean the potential energy) of the compressed gas? ",
"No. The energy from the bottle is from the potential energy from storing the gas in pressure. Until the gas is release, the energy will remain inside the bottle. ",
"Source- wicked hung over mechanical engineer..."
] |
[
"Does quantum entanglement allow us to study some of the paradoxes associated with time travel?"
] |
[
false
] |
I recently came across this fascinating video of the where a single photon passes through a double-slitted barrier and is subsequently split by a prism into two entangled photons. The first photon always goes to the same detector, D0. The second photon goes on a different path to meet a number of possible detectors. D0 doesn't give any way to determine which slit the original photon went through. However, the other detectors may or may not give that information, depending on their position. Since the two particles are entangled, D0 will show either an interference pattern or a clumped pattern based on which detector the second photon hits. These results are always 100% correlated. Based on the detector the second photon hits, you will always know the pattern at D0. Also, based on the pattern at D0, you will know which of the possible detectors the second particle must have hit. If the path to D0 is shorter than the paths to the other detectors, doesn't that mean we can predict the future with 100% certainty? If we make the paths of the other detectors long, couldn't this give us time to attempt to change the results that we see at D0? In my mind this is analogous to the grandfather paradox - where the future is known, but somehow we are prevented from changing it. This experiment seems awfully simple to set up. And it would appear to be simple to change the results after seeing D0. Has this been done before or is there something I don't understand? Thanks!!!!
|
[
"I'm not going to address specifically your question about the delayed choice quantum eraser, because it's been a while since I've read up on it. I will tell you about another experiment that used quantum information to probe the grandfather paradox.",
"http://arxiv.org/abs/1005.2219",
"Basically, they said, if time travel works according to certain rules (as posited by earlier research), they can do an experiment and post-select photons are already in a state that is consistent with having travelled back according to those rules and study what happens. They concluded that if time travel worked that way, and you tried to kill your grandfather with a quantum gun (one whose firing is probabilistic), it will always collapse to the state where it did not fire, and avoid the paradox. But there was no actual time travel in the experiment."
] |
[
"Short answer is no. You can't predict where the other particle will land by observing D0 alone. The sum total of the interference patterns at D0 created by the other detectors is always a bell curve type probability pattern. They never actually see an interference pattern at D0. It is only after the measurements are taken at D1-D3 that the data at D0 can be sorted and we see a correlation.",
"Yet, these experiments are set up for the purpose of violating realism. Realism is locality and noncontextuality. Entanglement tests locality and erasure tests noncontextuality. DCQE is a combination of both entanglement and erasure that tests both locality and contextuality in one experiment but in a limited way.",
"Your question boils down to this: Is it possible to have the outcome at D0 change after we measure it, depending on what we do to its entangled partner on the other path(s)? This seems possible, because time stamps indicate the pattern we see at D0 is a result of where the other photon landed 8ns later at D1-D3. Somehow (even if we can only determine it after the fact), one particle seems to be affecting its entangled partner at D0. ",
"The question becomes: Is it possible to violate one aspect of realism without violating the other? Can Bob have a measurement at his detector, but that measurement somehow changes based on what we do to Alice's particle? Can I have a measured particle here and its entangled twin over there in a superposition at the same time? To test this, you would either have to extend the path greatly(greatly to the point of impracticality...a photon would travel the diameter of the earth in less than half a second), or find another way to modify one path to violate noncontextuality.",
"Turns out that experiment has been done: ",
"http://phys.org/news/2016-03-features-quantum-mechanics.html",
"You will see in the experimental setup that it's basically a DCQE, but they modified it to have Alice's path test noncontextuality multiple times (by bringing her particle in and out of 'superposition'), while Bob's particle tests locality (by virtue of entanglement with Alice's particle).",
"They determined it is not possible to measurably violate locality without violating noncontextuality at the same time, and vice versa. By violating one, you automatically violate both. This implies some \"higher\" resource that is controlling both locality and noncontextuality. "
] |
[
"Thank you, I read the abstract and it sounds interesting. I like that term, \"retrodiction\" (versus \"prediction\")."
] |
[
"Is north pole shift really gonna happen?"
] |
[
false
] |
[deleted]
|
[
"I'll assume you're referring to a flip of the polarity of the Earth's geomagnetic field. Two points and then we'll get to the meat of your question.",
"(1) A pedantic point, but kind of important, it's not really meaningful to ask if the \"pole shift will happen\" as the geomagnetic pole is constantly shifting and drifting, e.g. ",
"this map of movement of the North pole over the last few hundred years",
". ",
"(2) ",
"Geomagnetic reversals",
", i.e., the flip of the magentic poles, have happened 100 to 1000s of times in Earth's history. In short, ",
"they happen all the time (geologically speaking)",
". So the most basic answer to the question is yes, of course, a reversal will happen sometime in the future.",
" The answer is nobody knows. The strength of the dipole (i.e., the portion of the magnetic field that behaves kind of like a bar magnet with two oppositely oriented poles) has been ",
"decreasing since ~1700",
". A decreasing strength of the dipole field would be expected as part of a reversal, but it also happens during ",
"excursions",
" and in general the intensity of the field is expected to ",
"vary through time",
". The official position of the ",
"USGS",
" is that we are likely not approaching a reversal. As discussed on that page, there is really no way to know whether a change in the intensity of the field is actually a reversal until we're well into the reversal, i.e, it's not a predictable thing based on the observations we can make."
] |
[
"Great answer! What would be the reproductions of the reversal?"
] |
[
"One thing to add:",
"\"the time that it takes for a reversal to complete is on average around 7000 years for the four most recent reversals.",
"\n Clement (2004) suggests that this duration is dependent on latitude,",
"\nwith shorter durations at low latitudes, and longer durations at mid and",
"\n high latitudes.Although variable, the duration of a full reversal is typically between 2000 and 12000 years.\"",
"Link",
"So even if that would start to happen it takes ages and wont be sudden at all like some believe"
] |
[
"Why do many various neurotransmitters exist if nerve signals are binary?"
] |
[
false
] |
As far as I know neurotransmitters are only released, bound to receptors and reuptaken in the synpatic cleft. I that is the case, then what's the point of multiple neurotransmitter types if chemical signal is going to only be translated into a binary electric signal that is 1 (excitation of the membrane), while none is 0 (resting membrane potential)? For me, in my limited knowledge, it appears as if their existance is useless since electrical signals alone or just a single neutrotransmitter type would suffice, unless neurotransmitters were released into the intracellural space and all neurons in an area of the brain with specific receptors would pick them up, which isn't a case in models I can find on the internet or in books. I know I am wrong but having asked many highschool teachers noone was able to answer this question to me years ago. Can anyone explain this to me in best detail possible?
|
[
"The first signal isn't binary. At the dendritic spine, neurotransmitters open different ion channels. Glutamate opens Ca-channels, GABA opens Cl-channels, etc. This creates graded membrane potentials called PSP (post-synaptic potential). All the PSP's from different dendrites travel to the soma, where summation occurs. This means that all potentials are added together. Some are negative (IPSP), some are positive (EPSP). If the end result reaches a certain threshold, the neuron is depolarized. This creates an action potential, which is binary.",
"Having several different intracellular cascades is also useful for regulation, like synaptic plasticity. The more neurotransmitters and receptors the brain has, the better it can regulate itself. It allows for a larger resolution of local regulation.",
"unless neurotransmitters were released into the intracellural space and all neurons in an area of the brain with specific receptors would pick them up",
"This is exactly what happens, it's called ",
"neuromodulation",
"."
] |
[
"Neurons are relatively specialized for certain types of incoming signals. The presence of specific receptor proteins determines what type of chemical signal will cause a given response (excitatory, inhibitory, modulatory, etc).",
"The average number of synaptic inputs onto a given neuron is like TEN THOUSAND. This means that each of your ~one hundred billion neurons each have a specific signal type hard wired AND a terribly complex job of integrating all of those signals. ",
"Add to that: over a dozen chemical signal types exist as networked pathways in the mammalian brain, each with distinct effects depending on brain location, and ultimately behavior. ",
"TL;DR: chemical signalling in the human brain evolved to be much richer than binary electronics allows."
] |
[
"This. ",
"The analogy of a nerve impulse I would use would be an insanely complicated chain of analog bias circuits.",
"Not a whole lot in nature is binary"
] |
[
"I read that there are high concentrations of interstellar dust and gas near the center of the galaxy that make it difficult to resolve stars. If Earth were orbiting a planet very near to the galactic center, would space appear “hazy” instead of clear and black?"
] |
[
false
] |
Likewise, would the same apply to a planet within a nebula? If the affect wouldn’t be enough to make a difference visible to the naked eye, are we inside a nebula or some gas “cloud” ourselves?
|
[
"Some minor pedantery first: There are high concentrations of dust and gas towards the center of the galaxy. The actual galactic core is pretty devoid of dust and gas compared to the arms. When looking towards the galactic center, our view of the core is obscured by the nebulae in the arms between us and it.",
"On to the question: It depends on the nebula. For some, it would appear very noticeably hazy, or even completely opauqe in places, while for a lot of sparser molecular clouds there would only be a slight haze everywhere.",
"Although there is dust everywhere in the Milky Way, the Sun is in an unusually sparse area. Our 'local bubble' is a region about 300 light years across created by the supernova shell from massive past stars that formed with the Pleiades. In this region, there's 10x less dust than the Milky Way's average. Very locally, the Sun and a couple other nearby star systems are going through the slightly denser Local Interstellar Cloud, which has around 2x less dust than the average (and 6x more than the surrounding local bubble)",
"But this is a very small region, so combined with still being less than the average Milky Way dust density, it really is not a very significant cloud."
] |
[
"Excellent answer. Thank you!"
] |
[
"Well that's just untrue. Even in interstellar space there's quite a few atoms of hydrogen and helium in any given cubic meter, and I think hydrogen atoms count as 'anything'. (the amount is a few hundred thousand to millions of atoms)",
"In terms of more substantial stuff, there's an estimated number of about 0.2 'oumuamua-sized interstellar objects per cubic AU, which is admittedly very sparse, but definitely not something you could avoid forever.",
"in Earth's orbital region, there's enough meteoroids regularly falling through space to deposit 500 grams *every second*. Earth is admittedly huge, but 500 grams is still a lot. Space is certainly empty, but nowhere near as empty as you're suggesting."
] |
[
"Anyone have suggestions for darkening tungsten?"
] |
[
false
] |
I have some Tungsten that I want to make dark and, if possible, more rough. Does anyone have suggestions for doing this? It can be a reaction on the tungsten surface or some sort of coating.
|
[
"Yes, more information please. What kind of equipment do you have available? Is this in a lab or a garage or a kitchen?"
] |
[
"You can oxidize the surface to a black oxide color"
] |
[
"Does the surface have to remain tungsten? There are lots of ways of applying coatings or changing the surface of materials, but you'll need to be more specific for people to select some to share."
] |
[
"What are some of the simplified lies we are taught that doesn't accurately describe what's really happening?"
] |
[
false
] | null |
[
"This question is too broad, and not actually a question that can be answered by science since it's an argumentative premise (meaning that it is subject to debate, not that you are being argumentative.)",
"I'd like to let this question through, but in reality, it would likely turn in to an absolute shit-fest, with people chiming in about what they were taught not being accurate later on etc... Some teachers do a better job than others, some journalists do a better job than others, some scientists do a better job than others, it's a statistical thing."
] |
[
"Very well. Thanks for the reply."
] |
[
"We are considering this question as a \"Discussion\" thread put on by the Panelists, so it's a good question, we just really would need to be far more prepared."
] |
[
"What is the fastest form of space travel?"
] |
[
false
] |
Not warp drive, light speed, or anything like that. If we were to build a ship right now, what would be the fastest engine possible? Rockets? Solar sail? Ion boosters? Nuclear explosion for propulsion?
|
[
"Full link here",
" - need to backslash the brackets in order to include them."
] |
[
"\"Fastest\" depends on how far you want to go. Chemical rockets are pretty good for getting you to the moon. They're probably not the best bet for getting you to alpha centauri. How far do you want to go?"
] |
[
"let's say extra solar."
] |
[
"How did menstruation evolve in humans?"
] |
[
false
] | null |
[
"Hi pianopolo9 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Hi pianopolo9 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Hi pianopolo9 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"How do birds 'know' how to build their complex nests?"
] |
[
false
] |
I've seen a lot of bird nests, some of them somewhat complex. Humans build things much more complicated than bird nests but how do non-self-aware birds 'know' how to build their still somewhat complex nests?
|
[
"Here's an article",
" that discusses the neural aspect of programmed animal behavior. Serotonergic signaling (i.e. with the neurotransmitter serotonin) was found to play a major role in the maternal behaviors of mice, including nest building, pup retrieval, cleaning, and nursing. This is regulated through transcriptional programming, e.g. the presence, absence, or level of various cofactors influences which genes get expressed. There is also evidence that the ",
"some aspects of programmed maternal behavior are regulated epigenetically",
".",
"I'm not sure if any of this work has been done with birds specifically, as it's a lot easier to study rodents (and do things like raise a strain with specific genes knocked out)."
] |
[
"The question is though, what mechanism is responsible for storing and conferring this information over generational gaps? Where in the DNA of a parent bird is it stored that they prefer stick type A over stick type B etc"
] |
[
"Do you know if we find any programmed maternal behaviour with humans?"
] |
[
"What do we know about an individual's ratio of X sperm to Y sperm? Specifically, what things contribute to that ratio?"
] |
[
false
] |
What started as a philosophical discussion on the morality of gender selection turned into an argument in my house this evening. I made the statement that in the future, gender selection technology would likely advance to a point where a male could take a pill for a few weeks leading up to conception that would ensure his body only produced one type of sperm; X or Y. I suggested that this would theoretically be possible with some form of hormone or chemical that temporarily produces an environment that inhibits the creation of a certain type of sperm. I was told that this was "messing with nature" and shouldn't be done, and I made the mistake of saying that my theoretical pill was exactly the same as the contraceptive pill, in that it changes the conditions within the body and prevents or promotes a certain bodily behaviour through hormones. I guess this is ultimately a two part question: 1) How accurate was my understanding of how the contraceptive pill works, and 2) Is there any research on what factors contribute to sperm ratio? The only things I could find on google regarding #2 was a whole bunch of Yahoo answers that suggested if you conceive on the even days in a month, you will have a blah blah blah... I stopped reading. Any takers?
|
[
"Sperm can be sexed in a lab.",
"The ratio in humans is indistinguishable from unity.",
"Some animals alter the sex ratio of their gametes. Theoretically, a substance could be made that preferentially targets one sex of sperm. ",
"The oral contraceptive pill contains generally contains two hormones, estrogen and progesterone to inhibit gonodotropin hormone release to inhibit follicle development and ovulation in the female."
] |
[
"Hormones aren't impacting if sperm have an X or Y chromosome, it is a completely random event during meiosis and has a pretty much equal chance of happening. Therefore, it would be very difficult to target that process by some sort of pill intervention. "
] |
[
"I'm pretty certain that due to the fundamentals of ",
"meiosis",
", each parent cell will produce 2 Y sperm and 2 X sperm, so the ratio should be 50:50."
] |
[
"What \"generation\" star is our Sun?"
] |
[
false
] |
I understand that a certain number of elements are created when a star goes supernova. What is left over then becomes another star that goes supernova and creates the next level of elements, rinse and repeat. How many of these cycles have we been through to create the natural elements that exist on Earth? On reflection, I assume that some of the ancestors on the stars family tree will be from more recent generations at the same level of ancestry. Can we make any educated guesses as to how many ancestors our sun has? (Not just number of generations but actual number of stars.) How old is the oldest ancestor star on our tree? And when/if our sun goes supernova, which elements will it create that are not naturally occurring now?
|
[
"The Sun is a Population I star, meaning it contains metals from previous generations of stars. By measuring the spectral characteristics of stars, we can observe the ratios of metals to hydrogen or helium, and from this, we can determine how many generations of \"ancestors\" the star has had.",
"Stars may be classified by their heavy element abundance, which correlates with their age and the type of galaxy in which they are found.",
"Population I stars include the sun and tend to be luminous, hot and young, concentrated in the disks of spiral galaxies. They are particularly found in the spiral arms. With the model of heavy element formation in supernovae, this suggests that the gas from which they formed had been seeded with the heavy elements formed from previous giant stars. About 2% of the total belong to Population I.",
"Population II stars tend to be found in globular clusters and the nucleus of a galaxy. They tend to be older, less luminous and cooler than Population I stars. They have fewer heavy elements, either by being older or being in regions where no heavy-element producing predecessors would be found. Astronomers often describe this condition by saying that they are \"metal poor\", and the \"metallicity\" is used as an indication of age. ",
"http://hyperphysics.phy-astr.gsu.edu/hbase/starlog/pop12.html",
"Astronomers also theorize that there was a generation of very old stars with extremely low metallicity. These are Population III stars. Recently, some astronomers have found evidence there may be Population III stars in a very bright, distant galaxy.",
"As a side note, the sun will not go supernova. It will become a red giant, shedding its outer layers, and making it very easy to roast hot dogs on Earth.",
"edit: red giant"
] |
[
"The sun would become a red giant and then a white dwarf. Red dwarf stars are small main sequence stars; class K or M."
] |
[
"Our star the 'Sun' is composed of about; 70% Hydrogen; 28% Helium; 2% metals, and has a diameter of 1,390,000 kilometers making it one of the larger stars in the galaxy as it is larger than most stars in our galaxy.",
"As for our star's origins, the asteroids in our solar system are leftovers that originated from the solar nebula which is believed to have collapsed to form our star, and the planets about 4.5 billion years ago. ",
"No, our star won't go nova, it does not have enough mass to do so, only very massive stars can end their lifetime as either a supernova which resaults in either a nebula, or a pulsar, or end their lifetimes by collapsing under their massive gravity as either black holes or become nuetron stars.",
"Our star can end it's lifetime as either hypergiant, or a white dwarf."
] |
[
"Are tumors edible?"
] |
[
false
] |
IE, would anyone notice if a cow developed cancerous growths (in its muscles or I guess organs) before it was butchered?
|
[
"If you've ever eaten any sort of meat from a processing plant, chances are good you've eaten some tumor."
] |
[
"And feces. Don't forget about the feces."
] |
[
"Tumors are generally only harmful to the specific individual they came from (with a handful of ",
"notable exceptions",
") - if they enter the body of another individual (or another species), the immune system recognizes it as foreign and rejects it. This doesn't work if it's your own tumor, as said tumor displays the same (unique to the individual) ",
"biochemical markers",
" as normal tissue. Indeed, this inability for the immune system to recognize and reject cancerous cells is the very reason cancerous cells are so harmful - in all other respects, they're less hazardous than many bacteria that your body fends off every day.",
"As such, eating the tumor of another species (or another individual) would likely do you no harm - your digestive system would kill most of it, and anything that's left would be rejected by your immune system, just as any other foreign organism would be."
] |
[
"If I apply a force to an object not through its center of gravity such that it accelerates both linearly and angularly, is its linear acceleration less than if I applied a force to it through its center of gravity so it only accelerated linearly?"
] |
[
false
] |
If so, how does that fit in with F=ma? If not, doesn't that violate conservation of energy? (I'm assuming something rotating has more energy than something equivalent not rotating).
|
[
"Be careful about trying to talk about F=ma when talking about a force at the end of a rod (or other object where you're not pushing through the center of mass) in a particular direction. It makes sense only for the first infinitesimal instant, after which the contact point has moved, and not in a simple linear way as if you'd pushed the center of mass. I mean consider what happens once the rod has taken a quarter turn. Which direction is your force in now? The problem isn't that F=ma doesn't work. The problem is that your scenario is way underspecified. But conservation laws are great because you can look at initial and final states of the system without really caring what happened in between, so when in doubt, trust them."
] |
[
"It's linear acceleration is identical. ",
"/u/uh_no_",
" is wrong, or, more charitably, answering a question you didn't ask. And the reason is exactly what you say: F = ma. If the net force on the object is the same then the acceleration will be the same. ",
"Energy conservation looks like this: dE = W. The change in energy is the work done on the object. If you are pushing on an object off center while it is rotating, you will need to apply your force over a longer ",
" than if you were pushing on center. Since work is force dot displacement, that can mean that you are doing more work, and so more energy gained, the excess of which explains the rotational kinetic energy. "
] |
[
"You are talking about motion of a rigid body. F=ma is strictly true for only a point source, where there is no rotation.",
"A complete description of motion is given by F=ma (where F and a are vectors) and M=dH/dt (where M and H are vectors). M is the moments and H is the angular momentum.",
"For simplicity, when teaching beginning physics, we usually stick with problems where H is zero.",
"Another way to express this is with ",
"Euler's equations",
" in the center of mass frame. You would then add F=ma for the center of mass motion."
] |
[
"How does the tension in a lift cable decrease as it accelerates downwards?"
] |
[
false
] |
Shouldn't the upward tension increase since mg and ma act along the same direction?
|
[
"You're thinking about it the wrong way. When the lift is stationary, the forces are balanced. The tension in the cable provides an upward force, equal and opposite to the force of the lift's weight. Mathematically, T - mg = 0",
"If the lift is accelerating downwards, that means the net force is in the downward direction. The weight of the lift doesn't change. The only way for the net force to change is if the tension in the cable decreases. This is done by having some mechanism like a motor which provides slack to the cable.",
"Mathematically, T - mg = -ma"
] |
[
"Hmm I still don't get it. I did it mathematically and got what you got. But it doesn't make sense to me spatially (I hope that's the right word)."
] |
[
"Imagine it's a tug rope instead, you against someone else, currently in equilibrium where both of you are pulling equally. If you want to win by accelerating the rope towards yourself, you have to pull harder than your opponent; if the elevator wants to move upwards, the tension force has to be greater than the gravity force is. If you pull less hard, you and the rope will get accelerated towards your opponent; if the tension force decreases, the elevator will move downwards.",
"If you let go of the rope, there's nothing to oppose your opponent's tug on the rope, which is accelerated towards them at whatever rate dictated by their pulling strength. Similarly, if you release all tension eg. cut the elevator cable, then the elevator falls and bad things happen."
] |
[
"Why did some social mammals evolve into patriarchal groups and others into matriarchal groups?"
] |
[
false
] |
Specifically looking for an answer outside of the context of human culture. For example, elephants, meerkats, lions, and killer whales all live in matriarchies - why did they evolve this way while many other mammals evolved in patriarchies?
|
[
"Excellent question! And not an easy one to answer.",
"Mark Van Vugt and Brian R. Spisak did research on this in human societies. Their findings showed a strong preference for female leaders during intragroup competition (fighting within your own group) and male leaders during intergroup (fighting with a rival group) competition. ",
"Here is the journal article",
".",
"If we extrapolate this for all social animals we can sum it up to:",
"Matriarchal - Unlikely to be in direct conflict/competition with neighbors of your same species. Or large predators. Managing conflict within your tribe.",
"Patriarchal - Likely to be in direct conflict/competition with neighbors of your same species. Or large predators. Managing conflict outside of your tribe.",
"We see this in our closest relatives the chimpanzee, who often have territory disputes between tribes.",
"Hyenas, however, are matriarchal and spend more time in competition with lions than they do their own species.",
"It also seems that food availability may have something to do with it, which works well with the competition theory.",
"We see in insects matriarchal societies run by queens (ants, bees, wasps) and the same in the Naked Mole Rat. ",
"I'll try to get more exampless up in a few, I'm on mobile and walking to an appointment."
] |
[
"Food availability seems to work well with competition theory. No need for aggressive males running the show. The differences between the Common chimp and Bonobos are pretty incredible. The Max Planck Institute has a great chart ",
"here",
"."
] |
[
"I'm not sure if Bonobos are a matriarchal species but I found it really interesting the contrast in their culture compared to chimpanzees. Isn't it due to more access to food with less competition with other large predators and apes? "
] |
[
"Since sound travels at different speeds depending on the medium, what's the fastest speed it could possibly reach?"
] |
[
false
] | null |
[
"In certain types of plasma and degenerate matter (like inside a neutron star) it can sizeable fractions of light speed. I believe the speed of sound through plasma is the speed of light divided by the square root of 3."
] |
[
"Plasmas can be as dense or as rarefied as you like, given certain other conditions. To some approximation, metals can be thought of as plasmas. Likewise, the interstellar medium, with less than one particle per cubic metre, is also a plasma.",
"The speed of sound in a plasma goes like (ZT_e/m_i)",
" , where Z is the charge on the ions, T_e is the electron temperature and m_i is the ion mass.",
"This means that the speed of sound depends on how hot the electrons are and how heavy the ions are. The reason for this is that sound waves in plasmas have two competing influences: the light electrons want to go as fast as they can, but as soon as they start moving away from the ions, they create an electric field which pulls them back. They overshoot the ions and then oscillate back and forth - this creates a plasma wave. So you can see why it depends on the electron temperature - hotter electrons means they move faster, so they can travel further before the electric field pulls them back. Heavier ions means that the wave gets damped faster, slowing down the wave.",
"I've massively simplified what actually goes on, as plasmas are pretty complex beasts, with dozens of waves, all with different speeds and dispersion relations."
] |
[
"So is plasma extremely dense? I thought sound moved through denser material faster, but my impression of plasma is that it isn't very dense at all? ",
"Sorry for the stupid question. "
] |
[
"Is it possible to siphon energy from lightning?"
] |
[
false
] |
Its energy, right?
|
[
"Yes, it would be possible to harvest lightning energy, it just isn't terribly practical. You certainly could build devices that lightning would tend to strike (rather than the ground, buildings, or trees) and route that electrical power. But you'd also need to store the power, and distribute it to places where it could be used by humans. ",
"Since lightning doesn't tend to be concentrated in just one place, those systems would have to be replicated many, many times. And if the strikes were not close to places where the power would be used, distribution losses would use up much of the power. These factors, along with the undependable nature of lighting, make such a system economically unattractive as a significant source of power. "
] |
[
"Storage is really the problem. There's a lot of energy in a lightning bolt, but it comes in very quickly. You need a system that can absorb that much energy, then provide it back at a much slower rate. Such things exist (large capacitors), but it wouldn't be cheap to do. Putting in a system like that would probably cost enough to pay your electric bill for the next couple of centuries. ",
"The only way I can imagine it making sense would be if we were already using large banks of capacitors for something else. For example, if everyone drove an electric car containing a large capacitor, maybe it would make sense to have neighborhood lightning rods that would funnel electrical strikes to everyone's car. You'd still need to invest in special infrastructure to make it work, but it is (very slightly) possible that it might make sense. "
] |
[
"Ahh, makes sense, but what about a more home friendly use, like on the roof of your house to be stored somewhere. Could that ever become practical?"
] |
[
"Can light orbit a black hole?"
] |
[
false
] |
[deleted]
|
[
"It is physically possible. However, the orbit has extremely tight tolerances. Off slightly in one direction and the light’s trajectory will be merely bent instead of orbiting. Off the other direction and it spirals into the black hole. "
] |
[
"The tolerance is zero. Every deviation from the perfect path will lead to the photon quickly escaping or falling in.",
"Every photon energy has the same orbit. They follow straight lines in spacetime and they don't depend on the photon energy."
] |
[
"It's actually significantly outside the event horizon. Specifically, photons would orbit at 1.5 times the Swartzchild radius. At the event horizon, light can only escape the black hole if it is travelling directly away from the singularity."
] |
[
"How do homonyms form across languages? For example, \"Right\" means \"correct\", \"law\", and the direction. In Spanish \"derecho\" means the same three things. How do these parallels happen?"
] |
[
false
] |
I'm sure there are other examples, but Right/Derecho seems to stand out (three identical definitions!). I know English has a lot of Romance language roots, and so it shares plenty of words with Spanish (more than it shares with most languages). But... "Right" is Germanic in origin. So how did two independent languages form the same homonyms in parallel? I know it can't be a coincidence...
|
[
"You have to go further back than Latin. (PS: English is not a Romance language, although there are bits and pieces of Romance stolen and/or shoehorned into it) There is a ",
"Proto-Indo-European",
" language (PIE) that is the theoretical ancestor of many languages.",
"Many times, with languages, you have to look at cultural and lexical connections as well as phonic connections. ",
" and ",
" are theorized to come from a PIE root ",
"reg",
", meaning ",
". So it is possible that the words come from a king—",
"—who leads—",
"—and their leadership is unquestionable and the law, leading to ",
" meaning both. Similar cultural forces may maintain the associations, while local dialects reshape the word (Latin ",
" meaning ",
" meaning ",
" ends up eventually with ",
")."
] |
[
"This is interesting because even in Finnish, which descends from Proto-Uralic and not from Proto-Indo-European, the words for correct, right (direction) and right (legal) are the same* word:",
": correct, right (direction)",
"\n",
": justice, legal right",
"They are also related to \"oikoa\" (to straighten) and a large number of compound words starting with \"oiko-\" usually relating somehow to straightening; for example \"oikosulku\" (short circuit), \"oikotie\" (shortcut), \"oikopäätä\" (straightaway).",
"* "
] |
[
"To add another language related to English: In German \"rechts\" is the direction, \"Recht\" is law, and \"recht\" can be used for \"[done] in the correct way\" (although you'll rarely hear it, \"richtig\" is more common)."
] |
[
"Why would a bird repeat a whole scale of notes in succession?"
] |
[
false
] |
[deleted]
|
[
"Basically birds don't do vocal warmups, so what you heard was most likely the actual song(s). We'd have to hear a recording to know for sure what species you were listening to, but my guess is that you were hearing one of the species that (a) has a song that is a simple trill or whistle, and (b) has individual repertoires, such that each male knows several different possible songs of different pitches, (technically, different song types) and (c) mixes up the sequence of the song types when singing. In most of these species males don't do a pitch sequence like what you're describing, but you might have heard a male who just happened to put his song types into a pitch sequence that morning.",
"If you're in the eastern US by any chance and you heard this recently, my immediate guess is Northern Cardinal. There's a lot of other birds that do trills, but few sing in winter and most are migrants; but cardinals are nonmigrants, stay on territory year-round and do sing in winter occasionally (on sunny days usually) and they do have a variety of trills on different pitches. (Also, female cardinals sing too, which is quite unusual.) Dark-eyed Junco also comes to mind, though I can't recall if they ever sing in winter or where they are at this time of year. If you're outside N America, I don't know. Give us a date & location and we can narrow it down. ",
"Sorry for lack of cites, am not on my laptop..."
] |
[
"Thanks for the response. I'm in Phoenix, and though I can't remember precisely what time of year it was, I believe it was a cold crisp morning, so early spring probably. ",
"What the bird sang was clearly a pattern of repeating one note four times, then moving on to the next note which he repeated the same number of times, on up the scale like this, and then going back down. It was just like - do do do do - ray ray ray ray - mi mi mi mi - on up like that, and then back down again. It may not have been a whole scale, but it was certainly five notes worth at least.",
"EDIT: to give an idea of cadence, I'd say something like 170 bpm with a three or four beat pause between each set of notes.",
"But it stood out because it sounded so odd, and made no sense to me at all, as far as any experience I'd had with bird noises."
] |
[
"bird songs are fairly plastic, they have been shown to shift frequencies to avoid traffic noise, for example. Birds are odd, lots of weird noises."
] |
[
"Question about Atomic Orbitals and Scale"
] |
[
false
] |
If there were an atom with an S orbital the size of the Earth, what would be the size of the subsequent P, D, and F orbitals?
|
[
"If you had an orbital the size of earth its physics would no longer be dictated by quantum mechanics, and its position would no longer be defined by a probability density. But, if you are willing to ignore reason, check out this ",
"picture",
". This is for n=3 shells. You would just take the max of the biggest hump for the s orbital in picomters (about 70pm) and get the ratio of that to the ratio of the radius of the earth. Then you multiply the position of the biggest hump in the p orbital to the conversion factor. ",
"Also worth noting, wavefuctions extend forever. Sure there are regions at which the probability is virtually zero, but there is still finite probability. That means all s,p,and d orbitals are the size of earth."
] |
[
"Interesting plot element! (pun intended)",
"f orbitals get pretty tricky -- they can do weird things sometimes in certain elements and compounds, depending on temperature, carrier density, and a bunch of other electronic structure properties. "
] |
[
"Thank you, very interesting, I just wanted a rough idea of relative scales. I thought the P and D orbitals would extend outside the S orbital, but I suppose not. EDIT: And in case you were wondering why I would ask about such an unreasonable situation, I'm in the research phase for a science fiction story. It takes place at an indeterminate time in the future where gravity is understood well enough that gravitational orbitals have been discovered. And a mad scientist is trying to destroy the world by altering the Earth's gravitational field from an S orbital shape to a P."
] |
[
"What's happening when you crease or roll up paper? Why does it stay that way?"
] |
[
false
] | null |
[
"Got all this info from ",
"this",
" article. ",
"Paper is made up of vegetable fibres, which are felted together. They felt together because the fibres are somewhat rough, although other agents, such as size are often added to encourage the fibres to stick together. But the fibres are brittle and when you crease paper the fibres along the line of the crease they are permanently fractured. It is this permanent line of tiny fractures that forms the crease. Because it is indelible, the paper is said to \"remember\" the crease\". Even ironing with a hot ironing will not get rid of the crease.",
"Basically, what's happening is that the paper is breaking its physical bond with the fibers along side it(but not necessarily with the ones that aren't directly where you folded it). It doesn't occur with all the fibers, however, so the paper still sticks together. They stay this way because they are brittle, like glass, and, just like when glass breaks, it can't be put back together.",
"Hope this helped."
] |
[
"This also explains why if you want to tear a piece of paper in a nice, even, straight line, it helps to crease it before you tear - the fibers that were fractured by the folding process represent a weak point in the chain, and so they break first, preventing the tear from proceeding irregularly."
] |
[
"I'll explain it in a structural/materials sense. Have you ever taken a piece of metal and been able to bend it, and it comes back to its original position? When it can go back to its original position, we say that we are within the elastic (yield) limit of the material. ",
"When you apply enough strain to a certain material, such as when you crease paper or even bend a piece of metal too far, you are taking the material past its elastic limit, and into the plastic range. When you enter the plastic range of a material, deformations become permanent on the material. When deformations become permanent, then the material cannot physically go back to its original state. The elastic limit of a material is generally defined as failure criteria for most structural applicatons.",
"Futhermore, if you keep taking a material past its elastic limit, it will deform even more, and eventually, fracture, which is the ultimate strength of the material. Materials such steel have a very large plastic region, where you can bend it in the plastic region for a very large strains before it will rupture.",
"This is a very general description of how materials work on a macro scale, but I hope you get the picture. Creasing paper is putting the material along the crease in the plastic region of the material, whereas rolling up a piece of paper mostly keeps the paper in the elastic region. When you roll it up, there is some plastic deformation, which explains why it sometimes retains that shape."
] |
[
"How is the reactivity of alkali metals with water measured and how do they compare?"
] |
[
false
] |
First, some background, I'm an art student making an animation installation about the groups of the periodic table. When making group 1, I thought of this video I'd seen on youtube So I showed caesium as an blowhard boasting about being the "emperor of the alkali's." He then gets corrected by the host, mendelevium. But as I was fact checking this, everything I found said that caesium IS the most reactive. Am I misunderstanding this video or is the video just wrong? But also, for a chart in my animation I do need to understand how the reactions of all of the alkalis are measured and how they compare.
|
[
"Sort of but you didn't address the issue raised in the video that I posted. Thunderfoot claims that when cesium reacts with water it actually releases less energy than lithium does."
] |
[
"Sort of but you didn't address the issue raised in the video that I posted. Thunderfoot claims that when cesium reacts with water it actually releases less energy than lithium does."
] |
[
"So for the purposes of my video, I shouldn't say that caesium is less reactive, but I could say that the reaction of caesium with water releases less energy?"
] |
[
"When two things are placed in the microwave, one gets hotter than the other. Why is this?"
] |
[
false
] |
Why is it that when two objects are put in a microwave, one of them comes out hotter or more properly cooked than the other? This happens in different microwaves, so I'm pretty sure it's not isolated.
|
[
"The microwaves aren't even across the entire bottom. That's why they have time rotisseries to help counteract the problem. "
] |
[
"Water content is key. As well as metal (calcium in bones). The more of either of these the food has, the faster it heats relative to its mass. "
] |
[
"What are these objects? Microwave oven doesn't heat all materials the same way. For example you can heat water in the microwave very well but it's not so good at melting ice. "
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"hello to the medical doctors,",
"has any homeopathic remedy ever been proven to actually work? have any even been clinically trialed?"
] |
[
"I'm assuming you're using homeopathy as a synonym for alternative medicine rather than referring specifically to homeopathic medicine which is a distinct subfield. Homeopathy is based on extreme dilution of the targeted \"toxin\" to be ingested. The dilutions commonly specified in homeopathy are well beyond concentrations where a detectable amount would be present and in many cases to the point where it's unlikely there's even a single molecule of the target in the administered dose (",
"Wiki",
").",
"Other alternative medicines, specifically those based on traditional herbal medical practices have yielded some drugs on market or derivative medications. The best example is Asprin, which is a derivative of a compound found in willow bark. Willow bark tea and other preparations are recorded medicines as far back as Ancient Egypt (",
"Wiki",
")."
] |
[
"Not that I can think of -- it's not uncommon for elements to have both 2+ and 4+ states (manganese comes first to mind, but there are others too).",
"There is nothing special about the 8th period or the S-block in terms of properties either except as an \"isn't that neat\" factor.",
"Of course the chances of being able to experimentally determine the oxidation states of such short-lived isotopes are pretty slim."
] |
[
"How big or small was the universe at the time of the big bang?"
] |
[
false
] |
Compared to a common household object.
|
[
"We have no idea how big the whole Universe is or was at any time. The simplest assumption for calculations is that it is homogeneous and isotropic at all higher scales, that it is spatially flat, and simply connected; these assumptions imply it's infinite at all time.",
"What we know is: given a region of size R today, we know of big it was at all times. We codify this in a scale factor a(t), such that the ratio a(t)/a(t_0) is equal to R(t)/R(t_0) for any region.",
"Then, studying the evolution of a(t), it is found that (in the classical theory) it becomes zero at a finite time in the past t_BB. This is the Big Bang singularity. Again, assuming classical general relativity holds, the size of any given region at time t_BB is 0."
] |
[
"Let's say a(t_0) is 1. It isn't necessarily, depending on conventions, but let's just say it is 1 today. It doesn't matter.",
"Now, consider the first combination of hydrogen, when the CMBR was emitted. This happened around t_r = 400 thousand years after the BB. I tell you that a(t_r) is around 1/1000.",
"Here's what you can infer from that. Take a region of space right now that is one metre across. Then at that time t_r it was a millimetre across (one-thousandth). If you take a region that is 10 metres across now, it was 1 cm across then (still one-thousandth). And so on.",
"Basically a(t)/a(t_0) is how big any region of space was at time t compared by how big it is now. (t_0 is now).",
"Then, the answer to your original question is that a(t_BB) at the big bang singularity was zero."
] |
[
"You might want to imagine a 2D universe that is mapped onto the surface of an inflating balloon. If you draw some galaxies on it, then for an observer standing on any one galaxy all the other galaxies appear to be moving away. The balloon is inflating at a fixed rate now, so using general relativity we can map what is looked like in the past. This is a \"perfect\" balloon, so our equations imply that the whole thing would start off as a point.",
"But here is the problem. We can only see a limited circle of the balloon because of the finite speed of light. Our circle is small enough that we can't detect that the balloon is curved at all. So it could be a really big balloon. In fact, it could be an infinitely big balloon, in which case no matter how far back in time we went it should still be infinitely big.",
"So, we can say for sure that the small circle around us we can see, called the visible universe, used to be very small. But we can't say how small the entire universe was because we don't know how big it is today.",
"One last wrinkle is that while we think the visible universe started out very small (smaller than a proton), we can't extrapolate the size at the earliest times, called the ",
"Planck epoch",
", because we don't have a quantum theory of gravity. Even though the visible universe was incredibly small during this time, if the entire universe in infinite now then even during the Planck epoch it was infinitely big (but very dense in energy)."
] |
[
"If we had a convenient black hole available to observe, what questions could we answer about them that we can't already calculate?"
] |
[
false
] |
Like if we had a moon-mass black hole orbiting us at the distance of the moon, and could launch any space probe with our current technology, what sort of questions about black holes could we answer? (I'm not sure if a moon-mass black hole at moon-orbit is safe, if it isn't, just readjust the black hole to be a safe one at a safe distance) We seem to calculate out so much of their properties. I'm curious as to what we DON'T know but would love to directly observe.
|
[
"It's not about our ability to calculate their properties, but about our ability to verify those calculations. Strictly speaking, we can't say that a solution is physically valid, unless we observe the corresponding behaviour in nature.",
"p.s.: Am I the only one finding the idea of 0.11 mm big black hole orbiting our planet funny?"
] |
[
"It would be so trolly. It would have taken people centuries or even millennia to find this massive and almost invisible mass that caused the tides. I guess gravitational lensing would show its location.",
"Plus it would actually take about 10",
" years to evaporate which is a lot longer than I was expecting."
] |
[
"Well, for one, it would pretty much confirm that they exist in nature. As much as we love our black holes, just about all the observational evidence for them can probably be explained by other forms of exotic stars. So it would be nice to confirm they exist.",
"That being said, I'm not even SURE we could tell much about it. There are alternative black hole models where event horizons don't really exist, where time is frozen and where there is no singularity and no true event horizon. Even Stephen hawking has recently come to believe true event horizons do not exist.",
"We would be unable to settle this question though. From the outside a black hole with an event horizon would probably look identical to some other exotic object that gets asymptotically close to having an event horizon...",
"Aside from that, no one really knows what happens near the event horizon of a black hole. It would be interesting to send a probe there that radios back data \"in real time\" as it approaches the event horizon. Some say there may be a firewall and/or \"frozen\" matter.",
"The probe would of course experience massive time dilation as it got close to the point where we'd get 1 data packet per century and the light would be so low-energy we'd need massive detectors to detect it...",
"Also if the black hole were rotating quickly enough as it revolved around the earth I think we'd finally be able to detect gravity waves.. Which would be nice."
] |
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