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[
"Is there a theoretical limit to the amount of energy a Battery can hold?"
] |
[
false
] |
I understand battery chemistry is complicated, and the watt hours/kilogram varies widely among different batteries. But all batteries are essentially stored chemical energy, right? Does this mean there is some kind of fundamental limit to the energy density of a battery?
|
[
"Yes, there is a fundamental limit to the amount of usable energy that can be concentrated in a region of spacetime. If you pack energy so densely that the storage mechanism becomes a black hole, then it will be impossible to retrieve any energy. Therefore the mass/energy (remember, there is a mass-energy equivalence) limit for any particular spherical region of spacetime is given by the Schwarzchild radius: r",
" = 2Gm",
" /c",
" where G is the gravitational constant, m is the mass (or equivalent mass), and c is the speed of light. Solve for m and you can get the maximum amount of mass/energy you can cram into any particular region of space and be able to get it back out again."
] |
[
"So that's the theoretical maximum. What is the current state of the art for batteries? And what is the expectedimprovement over the next decade?"
] |
[
"I'm not one of the people that designs the internals of a battery, but I do work with them daily. It comes down to the anode and cathode material, as well as the volume of each. Not only that, but how the cell is setup determines the storage capabilities and rate capabilities. Small changes in chemistry can lead to very different characteristics in possible discharge rates and overall capacity, not to mention cycle life and temperature ranges. ",
"As more research is done, more combinations of anode and cathodes can be found, as well as optimizing current technology. "
] |
[
"What's the reason that pigeons are extremely prevalent in cities, and not other species of bird?"
] |
[
false
] |
I'm not sure about other kinds of animals living in the sewers such as rats, but just walking around any city, you see pigeons everywhere. This might just be confirmation bias, but I also tend to never see pigeons outside of cities. What makes them attracted to cities, and why pigeons specifically? Have there been any major studies on pigeon populations inside and outside of cities?
|
[
"Pigeons are now city specialists. The original pigeons nested in rock cliffs and that plus a tolerance for human activity and an unspecialized diet made them very suited for living in cities (which are basically a bunch of cliffs). The ones you have seen have been living around humans for a long time, in fact, many are probably descended from feral pigeons--the birds were once widely kept and eaten (and still are, but not as widely)."
] |
[
"Rock Doves, also known as your typical city pigeon, are native to Europe and Asia. They are an introduced species in the New World. They were originally brought to the Americas as food, and as with so many introduced species they out-competed other birds to dominate cities."
] |
[
"I'd argue that in some sense pigeons are the native species of any human city, and whatever was living in, eg, the forest that was present there before is native to a different biome entirely. But that's more a matter of philosophy. But yeah, the name rock doves gives you a good picture of their original habitat. And their native range overlapped some of the earliest cities in the world, giving them a chance to \"get in on the ground floor\" as it were."
] |
[
"Why are bayesian statistics preferential to frequential statistics in drug design?"
] |
[
false
] |
Maths is not my strength, and I can't seem to get my head around the concept of why bayesian is better. If someone could describe the benefits of bayesian and why it should be used in laymans terms that'd help my understanding. The main difference from what I see is that bayesian uses the production of prior beliefs whereas frquential is adapted at the point of each test producing results.
|
[
"Because frequentist statistics works best when you have a theoretical \"infinite\" sample size. Typical example is, if you flipped a coin 5 times and it came up heads 4 times, a frequentist would assign a probability of 80% to heads. You'd need a coin flipping monkey that flips coins in a fair manner for the rest of eternity to get a probability of 50%.",
"You cannot have sample sizes that large in medical trials. That is why it is better to force a prior belief onto the experiment. They usually use Bayesian nets in medical trials because you can condition on the variables you choose, but the basic concept remains the same.",
"Of course, a hardcore mathematician will tell you that the selection of this prior belief if rather arbitrary. And it is! And the choice of your prior will affect your model. But it doesn't affect it by much. "
] |
[
"Yes. They're called mixture models."
] |
[
"Wouldn't choosing a range of plausible prior values and running several models rule in favor of one outcome more strongly?"
] |
[
"Why does mass 'bend' spacetime?"
] |
[
false
] |
I am Trying to find out what causes gravity.
|
[
"I am Trying to find out what causes gravity.",
"Well, nobody really knows."
] |
[
"And when a layman asks a \"why\" question, he generally means \"how\" and only a pedantic ass jumps on it rather than make an attempt to answer. "
] |
[
"Science generally deals with \"how\" rather than with \"why\"."
] |
[
"How does soap collect water from the air?"
] |
[
false
] |
I have noticed that on a number of occasions, when the air has moisture in it (like when has been raining for a good few days) the soap I have on the washer collects a multitude of small water bubbles on it. I have included which at least will show what I mean if the description hasn't already. I am assuming that the soap is acting as a catalyst to draw the moisture from the air, but I do wonder what the actual process is?
|
[
"Is it only the soap that has water on it? The only thing I can think of is condensation on the surface due to higher humidity (water content) in the air. I can't make a good argument as to why it would only be the soap that forms water beads, at the moment."
] |
[
"I was regretting that I didn't give additional details on the way into work this morning to answer your exact question :)",
"It is in fact ONLY the soap that ends up wet - and (at least to me) the weirder thing is that it will stay wet for days even after the humidity in the air has gone. There isn't a shower or bath in that room either, so it is purely picking up moisture from the outside air that comes in through a slightly ajar window."
] |
[
"Perhaps water that condenses on the soap ends up dissolving a finite amount of soap molecules into the droplet which proceed to act as a surfactant and aggregate on the water-air interface preventing evaporation?",
"I'm only guessing."
] |
[
"If I walk somewhere, I expend X calories to go Y miles. If I bike somewhere, I can expend the same X calories, but go 2-3Y miles. I know this intuitively, but I don't know why it is so. Where does the extra energy come from?"
] |
[
false
] | null |
[
"Having run 30 minutes and cycled 30 minutes last night I can help with this a bit. Running is a different motion to cycling, you lose energy through more means, swinging arms, impact with the ground ect. ",
"Essentially the answer is that the energy input is not 100% transferred into forward momentum."
] |
[
"It's not extra energy. You expend less energy per mile because of momentum. When you walk, every step propels you forward, step stepping and you stop going forward. On the other hand, stop peddling and you you are carried by momentum for a time. So when you get up to speed with a bike, you can peddle only to maintain speed, which takes less effort. "
] |
[
"Biking is much more efficient. "
] |
[
"Can you multiply units of measurement at will to create new ones?"
] |
[
false
] |
[deleted]
|
[
"Kilograms per second has plenty of uses - how much rocket fuel am I using, how much product can an industrial conveyor belt carry, how fast can I eat sushi etc.",
"It took me a minute to even picture Candela-meters. That would be a power output of light of one candela applied over the course of one meter. Those sneakers with the flashing lights could be measured in candela-meters; how many average candelas do the shoes apply over the course of a meter? It could be used to estimate how annoying and stupid a product they are and might give you a vague idea of how far the kid has to walk before the batteries burn out.",
"Almost everything will have a physical meaning, even if that meaning is really obscure or fanciful. "
] |
[
"This is a great question about dimensional analysis. You can combine units in any way you like, and with some creativity you can even give the result physical meaning.",
"For meter-candelas, say you're using a length of some material as a radiation source. The power requirement of this radiation increases linearly with both the length of the material and the intensity of the light. The dependence might be, say, 10 watts per candela of intensity, per meter of material. This quantity has units of ",
"W / m cd",
". We can give the denominator quantity of ",
"m cd",
" a fancy name like \"effective luminous size\", and then your desk, if made out of this material, would have an effective luminous size of ",
"2500 m cd",
". You can divide this by the light level in your room to get a unit of length. Mathematically that gives the ratio of \"the effective luminous size of your desk\" to \"the ambient luminous intensity\", which I might interpret physically as the desk size equivalent to the ambient luminous intensity. It has units of meters because, obviously, it's a length.",
"That's the same kind of construction that gives us ",
"\"man-hours\"",
" as a unit. We could duplicate it to produce a meaning for kilogram-seconds: you can borrow my truck to haul cargo, at a cost of $.01 per kilogram of material, per second of use. As another example, we might construct the same unit in another way. Say you hold 2 kg of gold bullion for 11 seconds, and I hold 3 kg for 5 seconds. We can invent a quantity called \"time-weighted mass\" having units of ",
"kg s",
", and our total time-weighted mass would be ",
"37 kg s",
". In total we spent 16 seconds holding those masses, so the average mass we possessed ",
" would be ",
"37 kg s / 16 s = 2.3 kg",
". This is physically reasonable: our average possession of gold over time should ",
" be 2.5 kg, because the lighter mass was held for much longer."
] |
[
"It's certainly possible to come across units that don't have physical meaning though. Proportionality constants in many equations can have really weird units (like square root meters or worse), especially in empirically-derived equations."
] |
[
"If the strength of the strong force doesn't decrease with distance, why doesn't every quark in the universe affect every other quark?"
] |
[
false
] |
[deleted]
|
[
"things that can't exist are weird like that"
] |
[
"From ",
"wiki",
": ",
"Every quark in the universe does not attract every other quark in the above distance independent manner, since color-confinement implies that the strong force acts without distance-diminishment only between pairs of single quarks, and that in collections of bound quarks (i.e., hadrons), the net color-charge of the quarks cancels out, as seen from far away. Collections of quarks (hadrons) therefore appear (nearly) without color-charge, and the strong force is therefore nearly absent between these hadrons (i.e., between baryons or mesons). However the cancellation is not quite perfect. A small residual force remains (described below) known as the residual strong force. This residual force does diminish rapidly with distance, and is thus very short-range (effectively a few femtometers). It manifests as a force between the \"colorless\" hadrons, and is therefore sometimes known as the strong nuclear force."
] |
[
"Yep, and that's exactly why they don't exist: since the attraction doesn't fall off with distance, the energy embodied in that attraction is enough to create some new matching quarks from the vacuum and voila, your attempted free quarks are now mesons or something."
] |
[
"If space and time are relative, and the universe is expanding, what is happening to time?"
] |
[
false
] | null |
[
"Interesting question! \nIn fact, nothing really happens to time! (given a frame of reference). In cosmology, we describe space-time using the ",
"FRW metric",
", notice that factor in the equation, a(t), only multiplies with the spatial coordinates. so the spatial coordinate changes according to a. And a changes according with time. In other words, t = t, but x --> a(t) x. (Sigma was the notation used in the wiki page linked). ",
"Now, there's more interesting stuff: the FRW metric comes from the assumption that the Universe is homogenous and isotropic. So the 'metric' written in the wikipedia page can be represented as a diagonal matrix, with only tt, xx, yy, zz components being non-zero. One can imagine a non-isotropic universe, there xy, yz, etc components are not zero. This means the universe expands ",
" in different direction, and there's a ",
"! One can also imagine that t mixes with spatial as well. In that case t \"expands\" or \"curves\" with spatial coordinate. But I don't know of a cosmological example. ",
"One good example that time mixes with space is inside a black hole. In there, physicists use a coordinate transformation, (u,v) plane, from (t,x). where (u,v) is a linear combination of (t,x). Statements like \"when something falls into a black hole, it can never escape\" can be interpreted as time mixes with space, and \"future\" is \"ahead\" now. and there's noway to escape the future, so it has to fall in. Pretty cool!"
] |
[
"Imagine a cube. It is expanding in all directions. Up, down, side to side, and left to right. These are the 3 dimensions we can perceive. Similar to how a 2Dimensional being would exist in an infinitely thin slice of the third dimension, we 3 dimensional beings exist in an infinitely thin slice of the 4th. The fourth dimension (time) is at a right angle to all other traditional 3 dimensional directions. Though seemingly impossible to perceive, you can measure the effects of its passing. ",
"If a 4 dimensional being were to watch us, I imagine we would look like ",
"this",
", existing only in on the hyper-plane of the present while expanding back (and forwards) 3-dimensionally through the 4th that we can't perceive. Time is basically 4th dimensional direction that the 3D universe is also expanding towards. "
] |
[
"While the universe is expanding all the main bits of it are experiencing the same rate of time. All the galaxies and stars are also in a universe 13.82 billion years old. Even though they're moving at high speed relative to us none are a bunch older. They were not accelerated relative to us. They were inflated away. This sorta makes sense. If they were accelerated that could only have happened at speed below the speed of light. As we're now seeing light from galaxies that formed the light 10 billion years ago we have to ask, \"how did those galaxies get 10 billion light years away from us in less than 3.82 billions years?\" ",
"The solution to that and a bunch of other problems is that there is a comoving reference frame. We're moving relative to that frame at a modest speed of 600 km/second, so we're aging a bit less than some things in the universe.",
"There are things that are moving so fast that they're experiencing great time dilation, but those are almost all hyper-accelerated cosmic ray particles, mostly protons and a few atomic nuclei. They've likely been ejected from active black holes and supernovae.",
"I'm not sure my answer hit exactly what you're getting at. Even though time is relative most of us are at relatively the same time, just separated in space by vast distances. If we jumped in similar space ships to meet in the middle we'd both be (or our descendants) of similar age when we met. We'd have very similar ideas about the age of the universe because we're in symmetric situations. We're not uniquely experiencing time at our rate. "
] |
[
"When exactly do people during the illness start producing antibodies for COVID-19?"
] |
[
false
] | null |
[
"Specific antibodies, if they're produced, are typically produced within ~5 days of infection (IgM), and continuously improve over the next few days along with a switch to IgG antibodies.",
"It's important to note that some people do not produce a significant level of antibodies to COVID-19 and other agents."
] |
[
"I think it all remains to be seen.",
"Your body has essentially two lines of \"learned\" pathogen recognition. 1) antibody-based immunity and 2) cell-based immunity. Thus, antibody levels (a marker for current vaccine studies) only tell part of the story. A person could have negligible antibody levels but a profound cellular response to a pathogen. ",
"The balance between these two arms/responses is partly the basis for someone having mild or no symptoms and getting intubated and receiving extra-corporeal oxygenation because your lungs are toast. That reaction more closely follows anaphylaxis than a \"healthy\" immune response. ",
"It may also turn out that some people just have no response whatsoever. The virus infects them, and the immune system is just like \"new phone, who dis?\" Not unheard of in the world of viruses. Some have asymptomatic infections in one host, but in others all hell breaks loose - this is seen even with cloned animals. Bizarre, and even our best science can't explain it very well. Suffice to say there's a lot more in that 99% of the genome we haven't deconstructed that is at work."
] |
[
"Thanks for your answer, but what do you mean, and what are the implications of, your last paragraph above?"
] |
[
"How does blood clotting work?"
] |
[
false
] |
I've tried reading around, but all I find is all sorts of whacky names for various substances in the human body and can't make head or tail of any of it! Two parts, really: Firstly, does blood always clot on contact with air? I was of the impression it did, but the things I have looked through have made no mention of what part of the atmosphere would cause clotting. If I left a blood sample out, having extracted it "non violently" (i.e. by not cutting the skin or whatnot), would it clot? Secondly, whatever the answer to the above is, what is the mechanism for clotting? If via the atmosphere, what triggers clotting but is prevented from doing it inside our body (as Nitrogen/Oxygen are both quite plentiful in our blood), and if otherwise, what's the process?
|
[
"Here is a simplistic video of the ",
"process",
", but there are 2 basic parts",
"the coagulation cascade which forms a mesh like structure called fibrin",
"Platelets which stick together with the fibrin to form a clot. ",
"It has really nothing to do with air to start a blood clot since these form in the body called a thrombus, but when a vessel is injured it releases tissue factor TF that starts the process. "
] |
[
"In the case of a large thrombus that ends up blocking a vessel, it's generally the result of a very slow thrombotic process that can build up over years. The condition is referred to as ",
"atherosclerosis",
", and is actually described extremely well by ",
"this diagram",
". Basically, an initial lesion can be formed by any number of traumas to a blood vessel, and if macrophages infiltrate the vascular wall it can begin the atherosclerotic process. Lipids begin to accumulate, coming out of blood and sticking to the macrophage affected area forming a 'fatty streak', which in turn acts to attract the depsoition of more lipids.",
"Eventually, the cell wall will 'heal' around the deposited lipids, narrowing the blood vessel and leaving a big deposit of fat/lipids under the cell wall. This deposition can grow for decades, until it reaches a point where it blocks the vessel completely, blocks it enough that a small clot passing through can entirely block the vessel, or it ruptures, releasing a number of small clots which can lodge in other vessels or organs, causing issue.",
"With regards to diseases of ",
"hyper-coaguability",
", they are broken into two groups, those caused by an ",
"over-abundance of platelets",
" and those caused by ",
"lack of anti-coagulants",
". However, these diseases tend to be treatable with synthetic anti-coagulants, and as such are not as life-threatening as haemophilia"
] |
[
"So, blood clotting is a really complex process for what appears initially to be reasonably simple. In the body, it's referred to as ",
"thrombogenesis",
". In short terms, when a surface in contact with blood is damaged, platelets are activated and bind to the site, activating a process known as the coagulation cascade, which in turn activates a couple of other processes etc. At the end of it all, you have a 'thrombus' or blood clot formed to cover the damage/block any hole.",
"Now, these processed generally occur within the body, and are regulated by chemicals in the blood that are constantly flowing past, generally to stop the formation of a large thrombus that can block a blood vessel (leading to things like strokes and heart attacks). However, when a sample of blood is removed from the body, it still contains large numbers of platelets and other chemicals that are part of the coagulation cascade etc, so clotting is often triggered. The 'violence' of the method of removal is irrelevant, as you are causing damage to a blood vessel in order to remove the blood, hence you are activating platelets. ",
"However, there are many chemicals that can act as anti-coagulants by blocking steps in one of the pathways involved in coagulation, and these are commonly used in places like blood banks to keep the blood from clotting as samples are taken.",
"If you're after a more detailed explanation of the clotting pathway I can give it a go, although I haven't looked at this topic for a few years now and I'm a little rusty"
] |
[
"If you had an oxygen tank and a hydrogen gas tank and you opened the valve pointing towards each other, would water vapor be produced?"
] |
[
false
] |
[deleted]
|
[
"Nope. If you mix hydrogen and oxygen, nothing happens. One spark, however, and the two will indeed combine, and create water. The reaction is exothermic, and in practice, this will create a nice explosion, as well as a bit of water vapor."
] |
[
"Just add a spark and your fire truck well it wasn't working originally, but I mean it is a \"real\" fire truck now"
] |
[
"Pressurized hydrogen and oxygen gas are extremely liable to explode when exposed to heat, so I don't think it's a good idea to drive a truckful of them to a fire.",
"Anyway, if you ignite hydrogen in the presence of oxygen, you will get water, yes. You may have done an experiment in high school chemistry where you did a reaction in a tube which made small amounts of hydrogen gas and then inserted a match into the mouth of the tube. You get a \"pop\" as the hydrogen reacts with the oxygen in the room, and when it's over you might notice that the walls of the tube are coated in water. ",
"Here's a demonstration.",
" (Edited for video)",
"Now, they had to introduce a flame to make the reaction happen in order to get over the activation energy. If they just mixed hydrogen and oxygen without fire or sparks, little would happen. Also, that \"pop\" comes from the fact that the reaction between hydrogen and oxygen releases a ",
" of energy. If you did that with enough hydrogen and oxygen to make sufficient water to fight a fire, you're going to have another emergency situation on your hands quite shortly. "
] |
[
"What's left of humanity for archaeologists 250 million years in the future to dig up?"
] |
[
false
] |
I was reading and got curious. If all humans were to die out (disease, climate change, etc.) relatively suddenly, what remnants of our civilization would still exist in 250 million years? How well would our remains be preserved/fossilized -- I understand that most of the fossils we have were saved in riverbeds and the like, but most humans aren't in those kinds of areas. What about earthquakes, tornadoes, and plate subduction? Would they help scatter/erase signs of our existence pretty thoroughly in the next 250 million years? tl;dr: 250 million years down the line, would another civilization be able to tell whether or not humanity had existed? What would they know?
|
[
"The longest figures I've heard for plastic degradability were around 1000 years -- several orders of magnitude less than 250 million."
] |
[
"The longest figures I've heard for plastic degradability were around 1000 years -- several orders of magnitude less than 250 million."
] |
[
"Bridges and nuclear stations have no chance of surviving that long. They require fairly frequent maintenance. Likely, they couldn't survive a thousand years, let alone 250 million."
] |
[
"Why does the pupil appear black, even when you hold a light up to it? Why can't you see inside the eye (easily)?"
] |
[
false
] |
[deleted]
|
[
"The retina is moderately absorbent of visible light (in humans) for what hopefully is an obvious reason. That and the round shape of the eye, plus the relatively small size of the pupil make it difficult to see into the eye, and make it appear black. There just isn't a lot of light that gets reflected out. And if you put your eye right in front of someone else's, your head will block a lot of the light that would be coming in the correct direction to help make things visible.",
"With that said, you ",
" look inside. My eye doctor will be doing that to me tomorrow. She'll first dilate my pupil to make it easier, then she'll use a ",
" bright light and two lenses, one near her eye and one near my eye. "
] |
[
"if you hold light up to your pupil, the eye lens illuminates a very small portion of the retina due to focusing, this is how the eye works. so to see this illuminated part of the eye you have to be lined up almost perfectly with light source to see any reflection. when this does occur we usually call it the \"red-eye affect\" the retina in the back of our eye is filled with blood vessels so the reflection is kind of reddish in color."
] |
[
"I fail to see the irony. How do you suggest she inspect my retina...a mammogram?"
] |
[
"How were atomic weights measured long ago?"
] |
[
false
] |
I recently read The Disappearing Spoon. I liked it quite a lot, but it left me with a few questions I can't seem to answer with internet research. When scientists were first seriously exploring the elements in a scientific way, the book mentions that they would estimate what they thought an element's atomic weight would be, and sometimes, after measuring it, they would have to reconcile their findings and unexpected things were discovered! What methods/equipment were they using to empirically determine atomic weights in the beginning? How was this done, and how does it differ from the way we do it now? I would assume that many of the original measurements were inaccurate to today's standards, but were there any that were very accurate for their time? thanks!
|
[
"This is very interesting question and one that occupied scientists throughout the 19th century. Atomic weights were first determined relative to each other. Hydrogen was initially set to be equal to 1. By ",
"Avagadro's Law",
" and the fact that two volumes of hydrogen combine with one part oxygen to form water, we can predict that oxygen weighs 16 times as much as hydrogen (assuming water is H2O). Once this is nailed down you can proceed to other elements. These relative weights are good enough for most chemistry.",
"The trickier part is figuring out the relationship between relative and absolute masses. Essentially you need to know ",
"Avogadro's Constant",
". If you look in that article you will see that it was not until the 20th century that people developed experimental techniques to measure this value. ",
"Perrin",
" used the phenomenon of Brownian motion (among others) to calculate Avogadro's constant. The basis of this calculation is that the mean random step size of a particle in suspension is inversely proportional to its mass/size."
] |
[
"Perhaps I'm misremembering, but I do think I recall that in the book, he said that elements that were thought to be one thing when discovered were actually others, and that this was figured out when they were weighed. Also, that some elements weights were different than expected... "
] |
[
"It seems like that would have been during the process of measuring relative atomic masses, not absolute masses. But I'm not familiar enough with the history of it to know what specific discoveries you might be referring to."
] |
[
"If a lightning bolt is around 5 times hotter than the sun (30,000 kelvins ) the sun (6,000 kelvins) , why are people that get struck not incinerated?"
] |
[
false
] | null |
[
"Temperature is a tricky concept.\nPeople can easily last 15 minutes in a 100C sauna, but putting your hand in 100C boiling water will cause major damage after mere seconds.\nIt is not only the temperature of a medium (a measure of the average speed of particles in that medium) that matters, but also how fast that medium can transfer its energy to you."
] |
[
"A quick google search for lightning burns shows that people get burned quite badly.",
"The reason they don't get incinerated completely is that lightning itself takes up only a small (relatively speaking) volume. The ionised channel itself is at most a few centimetres wide (I could be wrong here, not my field of expertise) and its heat dissipates into surrounding atmosphere, which is a very inefficient heat conductor."
] |
[
"Also alot of people who get struck by lightning are shocked through the ground (the gound's voltage potential can change over a significant area surrounding a strike, creating a current between a person and the ground). The severity of ground strikes can vary wildly, from just feeling a mild shock in your feet to electrocution."
] |
[
"During formation of a planet, what are the factors that contribute to whether that planet will become rocky or gaseous?"
] |
[
false
] | null |
[
"There are different theories/models how this might happen. ",
"Here's",
" an overview for starters.",
"One of the explanations is that when the protostar is forming it sucks in (due to gravitaion) almost all the gaseous material, leaving a very gas-depleted area around it, while the outer regions of the protoplanetary disk are rather gas-rich (see also ",
"Protostar",
" / ",
"Protostellar evolution",
").",
"So throughout the entire disk, the forming cores have similar composition, but the outer cores who are in the gas-rich medium start to attract the gaseous materials after a certain mass is reached.",
"Also, orbits are a factor. Inner planets won't have that much time to grow because they are closer to the star. They will have collected all matter a lot faster, respectively there is less matter available compared to outer regions of the disk. So while inner planet's growth is slowed down after a while due to lack of material, outer planets still continue to grow. In addition to this, it is assumed that orbits as we know them today are different compared to that time. So the protoplanets did not form at their current locations but somewhere else, then migrated into the stable orbits we can observe today.",
"But there are also other hypothesis, e.g. ",
"tidal downsizing",
". You can find lots of interesting stuff on ",
"arXiv",
" if you are interested in reading a few papers on that topic.",
"You might consider to check out related topics as well, e.g. ",
"super-Earths"
] |
[
"Gas giants form further away from the star of a solar system, as solar winds will blow the gas away. \nIf you took the rocky planets and put them in the area after the asteroid belt they may eventually form gas giants as they hold onto more and more gas, but close to the sun large atmospheres can't exist due to the solar winds."
] |
[
"but close to the sun large atmospheres can't exist due to the solar winds.",
"Wasn't most of the early extra-solar planets we found gas giants near their stars? Example - ",
"6.9 Jupiter masses at 1.33AU.",
"EDIT: Apparently there's a name for them: ",
"Hot Jupiters",
" - \"a class of exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital radii with semi-major axes from 0.015 to 0.5 astronomical units\""
] |
[
"What makes learning a language more difficult than just memorizing vocabulary and grammar rules?"
] |
[
false
] | null |
[
"Your brain does not process language the same way it processes random facts or skills. There are specialized areas of the brain for processing language. These parts of our brain become progressively more \"fixed\" as we get older. The more fixed they get, the harder it is to learn new languages.",
"There is something in neuroscience called a \"critical period\", which is a period during development over which a particular brain feature becomes fixed. Once that critical period is over, it becomes extremely hard to change that feature. ",
"Language actually has multiple overlapping critical periods related to different aspects of language. For example, there is a critical period for the sounds used in a language. Different languages have different collections of sounds, and as you get older you outright lose the ability to differentiate sounds not used in the languages you are exposed to. For example Hindi has two \"D\" sounds that sound completely different to native speakers but are indistinguishable to native English speakers.",
"By your mid-teens or so, your language critical periods are all over and it becomes very, very hard for your brain to add new languages."
] |
[
"im 18 years old. How difficult would it be for me to learn to speak spanish? I know the basics and I grew up listening to others speak it often. Would I still be able to learn?"
] |
[
"While it is difficult, it's not 'very, very hard'. It depends on exposure to the language and frequency of use.",
"If you live in a country with another language and try to speak/learn it daily, you will have a much higher probability of learning it than if you self learn for a few hours a week and never have conversation or interactions with the 2nd language."
] |
[
"Are there any examples of slavery or animal husbandry in species other than humans?"
] |
[
false
] | null |
[
"There are whole species of ants that do not produce workers form their queen. Insteads the queen makes soldiers that go ",
"enslave",
" other colonies and make their workers work for their queen.",
"Cuckoos do not raise their young but use involuntary service of other nesting brids to raise their young."
] |
[
"Even cooler than that, ants will corral aphids and milk them regularly like tiny green cows. "
] |
[
"Ants raise and protect aphids almost like pets (one of the more clever jokes in A Bug's Life). I'm sure there are others, try googling 'animals that keep pets' and you find some examples."
] |
[
"Why does a rope need to be massless for the tension to be the same throughout a rope?"
] |
[
false
] |
I thought that the mass of a rope (if it was completely stiff and unyielding) would just be factored into the mass of the box that is being towed. Why does it need to be massless?
|
[
"Consider a string with mass, hanging with no mass on the end. First, look at the very bottom of the string - how much mass is hanging from that? 0. So the tension there is 0. Now consider the top of the string - how much mass is hanging from that? The entire mass of the string.",
"You can also think about this in terms of a series of discrete masses joined by massless strings. Work out the tension for each string, then make the strings short and the masses small and you've effectively got a continuous massy string."
] |
[
"Consider a box hanging from a rope. The segment of the rope next to the box has mass and therefor contributes to the tension experienced near the top of the rope. The segment near the top also has mass, but does not contribute to the tension in the rope near the box.",
"This is even easier to see if you remove the box, and consider the graded tension that results from the rope alone."
] |
[
"Alright, so basically, if you are holding the rope at the top, you need to accelerate the mass of the rope. Then the force at the bottom of the rope is (Force at top) - (mass of rope)*(acceleration of rope)?"
] |
[
"What is the delay from opening your eyelids to your brain processing an image?"
] |
[
false
] | null |
[
"I am using A and B to just distinguish between the first and second thing/stimulus/input; they don't mean anything. ",
"\"Brain capacity\" is not a defined term. Normal humans have extremely similar brain structures. It takes less time to partially process a stimulus. For example, you can categorize a scene (e.g. indoor vs. outdoor vs. beach vs. forest) after ~100 ms. You can tell that something was there with even less time. The more you process the input, the longer it takes."
] |
[
"Depends on what you mean by process, but it's actually quite long -- on the order of ~150 ms. At least that's how long a static image must be presented for you to identify an object (with some caveats). As a result, there are \"post-dictive\" effects in perception so that if stimulus B is presented after stimulus A, it can affect the processing and therefore the subjective experience of stimulus A. "
] |
[
"So what you are saying is that the estimated delay should be roughly equal to around 150ms? I'm not all too familiar with stimulus A and B since I don't find biology the most interesting subject in the world. But I understand what you're saying. And are there anymore variables in the equation such as brain capacity, different kinds of structure inside the body to affect the traveling time from the back of the eye to the correct part of the brain?"
] |
[
"How do thermoreceptors in our body work?"
] |
[
false
] |
Normal thermometers work by measuring the height of a liquid, some electric thermometers work by measuring the resistance of an electric circuit; how do our ‘thermometers’ work?
|
[
"How do these thermo-neurons work? What is the mechanism that causes them to signal increased temperature?"
] |
[
"Thermoreceptors are a specialized type of neuron that can sense changes in temperature. The signals are then sent through the dorsal root ganglia into the spinal cord, where the signal crosses to the opposite side and travels up the lateral spinothalamic tract to the thalamus and the sensory homunculus of the cerebral cortex. \nHopefully that’s helpful to you! "
] |
[
"If you've got access to scholarly literature, here: ",
"https://www.degruyter.com/view/j/revneuro.2017.28.issue-1/revneuro-2016-0039/revneuro-2016-0039.xml",
".",
"In short, the neurons have a lot of different ion channels that are sensitive to temperature. When the temperature of the ion channel changes enough (depending if it is a \"hot\" sensor or \"cold\" sensor), its ion channel changes shape and allows the passage of ions into/out of the cell. This changes the cell's polarity (overall charge/direction). And polarity/electrical potential is how neurons get things done, so this change in potential causes them to \"fire off\" and signal that something is happening with temperature."
] |
[
"AskScience Panel of Scientists XXVIII"
] |
[
false
] |
This post is for new panelist recruitment! The previous one is . The panel is an informal group of Redditors who are . All panelists have at least a graduate-level familiarity within their declared field of expertise and answer questions from related areas of study. A panelist's expertise is summarized in a color-coded AskScience flair. Membership in the panel comes with access to a panelist subreddit. It is a place for panelists to interact with each other, voice concerns to the moderators, and where the moderators make announcements to the whole panel. It's a good place to network with people who share your interests! ------------------- ------------------- ------------------- Ideally, these comments should clearly indicate your fluency in the fundamentals of your discipline as well as your expertise. We favor comments that contain citations so we can assess its correctness without specific domain knowledge. Here's an example application: Please do not give us personally identifiable information and please follow the template. We're not going to do real-life background checks - we're just asking for reddit's best behavior. However, several moderators are tasked with monitoring panelist activity, and your credentials will be checked against the academic content of your posts on a continuing basis. You can submit your application by replying to this post.
|
[
"Username: ",
"/u/bwyazel",
"General field: Neuroscience",
"Specific field: Auditory Neuroscience, Neuroengineering, Research Pipeline Engineering",
"Particular areas of research include auditory neuroprostheses, the cognitive effects of hearing loss, and research infrastructure engineering",
"Education: PhD in Neuroscience, researcher for over a decade",
"Comments: ",
"1",
", ",
"2",
", ",
"3"
] |
[
"Username: ",
"/u/Ribbit-Genetics",
"General field: Biology",
"Specific field: Plant Evolutionary Genetics, mineralogy",
"Education: BA in biology, Ph.D. student in genetics & genomics. published research with UNC. Reseacher at Duke"
] |
[
"Hey,",
"I already have flair, but I was being extra ND and way too specific and young back then. Since, I've become quite multi-disciplined over the years. If I could just change my flair to \"Engineering\" or \"Engineering - Energy\" that would be less confusing for all. I won't abuse it and try to give answers about branches outside what I know, like Electrical engineering or such. Those folk believe in imaginary numbers! ;)",
"Username: ",
"/u/jade_crayon",
"General field: Engineering",
"Specific field: Energy",
"Particular areas of research include: Energy efficiency, HVAC, Ergonomics, climate statistics",
"Education: Doctorate in engineering",
"Comments: Same ones that got me my current flair so long ago. Can look those up I think, if needed.",
"Sorry for weird request."
] |
[
"How does an electric analog watch work?"
] |
[
false
] |
I can understand the concept behind a wind up watch- potential energy stored in a spring can turn gears calibrated to different ratios which will turn the hands. But how can a battery, nothing more than chemicals that react to produce energy, turn the gears at a consistent rate? Also, how do electric motors work? I apologize if these questions are at a lower level than most questions for this subreddit, but I feel at this age I should really know this by now.
|
[
"It's called the piezoelectric effect. There's a type of crystal that, when compressed, releases electricity. This is how a barbeque starter works. Conversely, if you apply electricity, the crystal deforms. The deformations are very regular, and thus can be used to keep accurate time.",
"Electric motors work differently; they rely on the fact that a current loop in a magnetic field experiences torque, and thus spins.",
"There are no stupid questions, only jerk answerers."
] |
[
"That's a really confused explanation. The piezoelectric effect is indeed used with a quartz crystal, but its function is to produce a fixed frequency signal used to keep time, not to move the hands. He's asking how the hands move, and that's done by a tiny electric motor that receives a pulse every second."
] |
[
"I think the weight of his question was on the \"consistent rate\" part, and the quartz crystal is indeed the answer to that."
] |
[
"What's happening when one gets \"butterflies?\""
] |
[
false
] | null |
[
"Butterflies? There's a wiki article for that: ",
"Some believe that this is caused by the release of adrenaline when one is nervous, which pulls blood away from the stomach and sends it to the muscles. This reduced blood flow, in turn, causes the stomach to temporarily shut down, and is possibly the reason for reduced appetite during love sickness.",
"\nI've always wondered, too. Now we know :)"
] |
[
"it is well known that askscience is not friendly toward jokes"
] |
[
"This is why we have upvotes."
] |
[
"Do insects do things that they consider funny?"
] |
[
false
] | null |
[
"We have no evidence that insects have a sense of humor"
] |
[
"Do you mean there is evidence to say that they don't, or that there is no evidence which says that they do?"
] |
[
"The latter."
] |
[
"Would it be possible to build a magnetic shield for earth to protect us from solar flares?"
] |
[
false
] |
Is it theoretically possible to build a "magnetic shield" that would protect us from an event like the ? If so, what would it take?
|
[
"Yes it is possible, and the earth already has one! The part of the earths atmosphere that protects us from radiation from the sun and other sources of radiation is called the ",
"magnetosphere",
". We could build an artificial magnetic shield by wrapping massive wires around the earth several times and inducing a missive current in the wires. Saying this is \"possible\" is not necessarily saying it's probable though. Building a global magnetic shield is far beyond our current engineering and resource capabilities. Other methods could be used such as an array of satellites all with massive magnetic fields, but these would face the same issues with availability of resources and modern engineering capabilities. "
] |
[
"I was thinking that the best way for this would be to put a satellite in the ",
"Langarian point L1",
" which is between earth and the sun.",
"I think that it would be a bad idea to build anything on earth that could temper with our own magnetic field. Rather I think it best to put a shield in between that only activates when needed. "
] |
[
"Also, how strong would such a field need to be If placed in space between earth and the sun? I don't understand enough about magnetic fields to make this calculation, but as I've understood it earth only has 25-65 microtesla at the surface and from what I can gather that isn't very much."
] |
[
"Besides the big bang, do the collisions which we create in our colliders occur naturally in our universe?"
] |
[
false
] |
Let's not make this a question about what is natural, haha. I just mean to ask, without the intervention of methodological minds, and besides the initial big bang, do the collisions/energies which we create also occur on their own? Thank you,
|
[
"The Earth is constantly being bombarded by cosmic rays, some of which have energies much greater than in the LHC. These interact with atoms in our atmosphere or on the planet itself. "
] |
[
"Yes. There are cosmic rays with energies that are magnitudes of order of energy above what we can manage to generate on earth. On the other end, you can also see hugely energetic events in the form of supernovas and hypernovas.",
"My guess is your question is more about cases where particle collisions convert energy into mass. In both of the above cases, energy is converted into particles. Colliders are nice because they eliminate many of the background processes that occur simultaneously to the particle interactions of cosmic rays or novas."
] |
[
"Depends on how optimistic you are! If we can one day manipulate superblackholes into colliding or the very fabric of spacetime, we might be able to engineer a situation that is more energetic than what occurs in nature. But nature has a pretty big lead on us, and I don't forsee us getting anywhere near the power scale of what's going on inside a star, let alone a nova, stellar collision, or black hole collision."
] |
[
"It's broadly accepted that all life on earth shares a common ancestor. does this mean the origin of life only happened once? or did life start multiple times and our current tree of life is a result of the one organism that outcompeted the rest?"
] |
[
false
] | null |
[
"You are right that life on Earth today has a ",
"Last Universal Common Ancestor",
". This is based on genetic evidence, which shows enough similarity across genomes to support common descent a single (hypothetical) ancestor. ",
"That is a separate question from the origin of life. We don’t know if life originated once. It could have originated, diversified, and then bottlenecked, leaving the LUCA of life as we know it. It could have originated multiple times but only descendants of the LUCA survived. This is very tough to explore because fossils that old are exceedingly rare – in fact, rocks that old are rare. Plus at that point, we’re talking microbes, so fossils we do have are tough to interpret. ",
"So while your question is a very good one, and extremely interesting, it’s not one we can answer – yet! Maybe someday."
] |
[
"It's also possible that there were multiple independent origins of evolving life that exchanged heritable information with each other as part of mixed communities and that's what gave rise to the universal common ancestor."
] |
[
"This is a very important point and is one reason why the diversity of life on earth being represented as a tree can be misleading! Horizontal gene transfer has absolutely allowed organisms to share genetic information despite their most recent common ancestor having existed in the very distant past."
] |
[
"Help with an odd sensation."
] |
[
false
] | null |
[
"Reddit's policies specifically forbid medical advice, please talk to your doctor if you are concerned."
] |
[
"I'm not sure exactly where in the post I was seeking medical advice. "
] |
[
"Your entire question relates to a medical condition had you are experiencing."
] |
[
"Does the volume increase if you have multiple speakers?"
] |
[
false
] |
Is the volume generated by a single speaker the same or less than the volume generated by two speakers which have each the same volume output? For example, is a single speaker with 50 db quieter than two speakers placed next to each other with 50 db each?
|
[
"Yes.",
"Two speakers will add their respective sound output (barring interference effects) and will be louder than 50dB.",
"I am too lazy to do the proper calculations for two speakers, so I'll do it for ten 50dB speakers.",
"If you have 10 50dB loudspeakers, they will have a volume equivalent to one 60 dB loudspeaker.",
"Edit: 2 loudspeakers with 50dB output are equivalent to one 53 dB speaker",
"Second edit: The answer might not always be yes if you rig multiple speakers up to the same output of an amplifier"
] |
[
"Amps generally generally give a certain wattage per channel, so adding a second speaker will most likely simply doubly the sound output. You can test it at home if you have speakers. Granted, it will be qualitative unless if you have some method of recording sound - come to think of it, a microphone and a copy of Audacity should do."
] |
[
"My rationale was that the output power might be split between speakers hooked up to the same channel. That way you'd reduce the output power of one speaker by adding another."
] |
[
"Do electrons have continuous motion, or do they jump around?"
] |
[
false
] |
One way to think of an electron orbiting an atom is a probability cloud, where it acts like a wave until it gets measured. Is it possible to ignore the wave and view it as a particle chaotically travelling around the nucleus? If it jumps to another energy level in a quantum leap, does it disappear and rematerialize at the next instant in a different place, or does it move through every space in between?
|
[
"The only thing we can know is what we measure. With macroscopic things like baseballs, we measure approximately continuously, and so we see \"smooth\" motion from point A to point B. But quantum mechanics we tend to be able to only measure ",
" points A and B. What happens between A and B is not (at present*) answerable by science. And there are many ways of interpreting philosophically what happens. One of the most useful mathematical techniques is to assume that the electron has taken ",
" between the points, and that these various paths interfere with each other mathematically. That seems to reflect the data best.",
"*: I say at present, but realistically, never. Science is in the game of predicting outcomes of experiments. If there's no experiment to predict it's not science. If we do somehow manage to measure the path between A and B (even weakly), then all we've done is make measures of A and C and B where C is some measurement or set of measurements between A and B. Right now it seems that any measurement C will destroy the effects of measurement B."
] |
[
"Neither.",
"You can't assign intuitive ideas about things existing and moving as you understand objects to do to quantum objects because they simply don't obey. Some of the behaviors are like the things you said, but this is resemblance, not a complete description."
] |
[
"To expand a little, electrons only exist as a probability wave until the moment their position is measured. The Copenhagen interpretation of Quantum Physics states, that said wave function collapses into one single position."
] |
[
"Is there any case where a=b, and b=c, but a does not equal c (transitive property)?"
] |
[
false
] | null |
[
"No. Equality has the transitive property."
] |
[
"Thanks, I was just wondering since I've seen this property in Physics, Math, and Logic, and I know that it's a foundational axiom in Algebra. So I was just wondering if there were any challenges to it, but I also kind of see how it is definitional in nature, therefore; if it is true, then it is true. But also I guess I have to wonder how true it is, if in application in the real-world there is actually any true equivalency between two discrete things. "
] |
[
"I guess simply positing here but since most things identity is perspective-dependent; under the idea that identity itself is relative to the perspective something is viewed from, or relatively defined, then the transitive property thus likely is only correct insomuch as the object(s) being defined are being defined from the same viewer-perspective, since theoretically the objects viewed from a different perspective could be defined differently, or relatively to the viewers perspective, but then I also guess that this would mean that they are different from that perspectice and no longer subject to the transitive property. ",
"Also, I suppose in the alternarive, two discrete objects that are different from each other and not subject to the transitive property from a single viewer-perspecrive could also be the same from two different perspectives, and thus transitive in that regard. But then we come to the same quandry again of whether there could be two different perspectives that view two discrete things as equivalent (the perspective itself being the transitive thing ",
" in this case), couldn't that only be true if the two perspectives were actually the same perspective, since in the real-world there are no two exactly equivalent different objects? ",
"I suppose this would be a property in itself that no two different object are exactly the same, which wouldn't seem exactly as logically intuitive as the transitive property, except that definitionally it would seem logical (and maybe through formal logic as well, but maybe not), because if two objects are different, then they cannot also be the same, at least definitionally. ",
"I suppose this analysis is assuming a property of universal parallax concerning identity, namely that; everything has a different identity from a different perspective. But I guess also through this analysis maybe if two things are viewed from the same perspective say an algebra or geometry framework-perspective then that would neutralize universal identity-parallax and thus allow transivity (and anti-transivity?) to exist, outside of which parallax would distort identity and thus comparisons and equivalencies, and disable transivity as a tool. "
] |
[
"Dolly the sheep was born in 1996. What, apart from law, is preventing cloning of humans?"
] |
[
false
] | null |
[
"I think OP wants to know scientifically what is stopping human clones. Obviously ethics and morals play into this. But from a scientific standpoint could this happen. I don't know, I would like to read the answer to this. I'm assuming it has something to do with our DNA being so complex."
] |
[
"The question should be: \"why should we attempt the cloning of humans\".",
"If there are no sensible reasons to do it, then it won't be done."
] |
[
"Why do the shortened telomeres not get passed on to offspring? Possibly a silly question..."
] |
[
"Why don't photons bounce off each other and distort our vision?"
] |
[
false
] |
I was sooooOOOooooo baked when I thought of this question. I would still like to know the answer though.
|
[
"Photons don't interact with each other, at least at low intensities."
] |
[
"Photons do not carry any charge, and in particular do not carry the U(1) charge of electromagnetic interaction, so in fact they cannot feel each other. On a classical level Maxwell's equations are linear, so (in the vacuum) a superposition of two fields that solves Maxwell's equations is still a solution, and the two solutions i.e. the two electromagnetic waves, do not interact but just superimpose. The gauge particle being boson has nothing to do with it, gluons are bosons and interact terribly strong. It has everything to do with the abelian nature of the gauge symmetry group. Photons can interact when you add matter e.g. charged fermions, to you universe. The phenomenon is called Delbruck scattering, but is extremely weak."
] |
[
"why not? and why does the intensity change things?"
] |
[
"How do paleontologists know what colour prehistoric animals were?"
] |
[
false
] | null |
[
"Many colors in current day birds, reptiles, fish, etc came from physical structures in their scales, feathers, etc, not pigments. The size and shape of these structures is what gives them a color, so if a fossil has a fine enough detail, one could see these structures and infer a color.",
"I am not sure about pigment based colors."
] |
[
"To add to this, in the case of feathers' pigments, pigment granules can be seen in fossilized feathers. They can tell what colour the extinct bird/dinosaur is by comparing the fossil pigment granules with modern day bird feather pigment granules. "
] |
[
"The truth is, they really don't. They use estimates based on the currently available fauna."
] |
[
"Did people with OCD wash their hands a lot before the germ theory was invented? What was the equivalent alternative?"
] |
[
false
] |
It's my understanding that OCD may manifest as a compulsive desire to wash hands and maintain a germ free environment. I'm assuming that people with OCD didn't wash their hands compulsively before hand washing was linked with preventing disease, so what did they do instead?
|
[
"Just to clarify, Obsessive Compulsive Disorder isn't necessarily about cleaning, washing or , as MyOtherAcctIsACar said perfectly, germaphobia.",
"Rather, it's about rituals, usually brought about by stress or stimuli. For example, someone with OCD might react to sneezing by touching a door handle or flicking the lights on and off a few times. ",
"Usually, the pattern begins early as a reaction to one stimuli or another, eventually becoming so ingrained by the time that they're adults, as with all psychological disorders [quirks or otherwise], that it hinders their day to day routine. There would be such a strong mental hurdle that you wouldn't be able to leave the house without tying and untying your shoes at least twice, for example.",
"In light cases, it's things like counting how many steps you take from one room to another and trying to do it in that many each time. In extreme cases, you wouldn't walk from one room to another without taking that exact number of steps and, if you were even half a step off, start over from the start.",
"A lot of people assume they have some form of OCD and, much like Aspergers, Anti-Social, Delirium, Dementia, etc, it's very misunderstood. This is because the terms for any psychological condition vary from \"tendencies\" which means you just have one or two traits that don't impede anything to a full blown syndrome, where it's practically textbook.",
"But, even professional diagnosis is vague and, in cases, overlaps enough so that there's a seemingly trivial difference between the two [i.e- dementia and delirium]. ",
"To sum it up, OCD could overlap with germaphobia in that one of the rituals was specifically washing hands, but over all, they are completely different things."
] |
[
"You are confusing OCD which is a diagnostic that describes a particular compulsive action, group of action or reaction repeated compulsively with germaphobia, an incontrolable fear of germs and often uncleanliness in general.",
"I don't know of reported described cases of germaphobia prior to the germ theory which itself predates modern psychiatry. Washing yourvhands however is a much more ancient act associated with the restoration of one's integrity (from germs or other forms of soiling) so I would expect that people have been developing such a comportements for a long time"
] |
[
"If you have read many stories and poems by Edgar Allen Poe, especially the short story \"The Tell-Tale Heart\", it becomes clear that due to stress or mental illness, people have always developed obsessive compulsive behaviours. But you cant obsess over things that you are unaware of."
] |
[
"Does the pilot-wave interpretation of quantum mechanics require an absolute reference frame that is incompatible with special relativity?"
] |
[
false
] |
Hidden variables may not be impossible, but if they require a field that guides particles deterministically, shouldn't we be able to measure our movement through that field (the same way we should have been able to measure our movement through the luminiferous aether, if it existed)? Wouldn't that provide an absolute reference frame? I don't see how pilot wave theory can be made compatible with special relativity. Am I missing something?
|
[
"It does require a preferred frame, which means there is only one foliation into spacelike hypersurfaces over which the particle trajectories are actually classically deterministic (which is the essential promise of the interpretation). Working in other frames, the Bohmian trajectories zig and zag in random, unpredictable ways. In particular, this can be understood via working out the pilot wave trajectories in EPR experiments. If one could observe these trajectories, one could use these random zigs to figure out (by process of elimination) which frame was preferred. But it is also a requirement of the interpretation that one can't ever access these trajectories at the level of granularity required to achieve this. So strictly speaking it is not consistent with SR, but the problem can be kept under the rug for practical purposes. Whether this is philosophically acceptable is up to you. And pilot wave adherents tend to be willing to abandon exact Lorentz symmetry as a guiding principle.",
"But preferred frame aside, remember that the pilot wave interpretation is also presented in terms of fundamental particle-like entities, while the union of quantum mechanics and special relativity produces quantum field theory, where particles are not really fundamental in this sense. To the extent particles exist at all in QFT, they instead are more like structured patterns in the fields. There is no broadly accepted or worked out pilot wave interpretation of quantum fields, and the idea is not particularly promising. The basic problem is that in QFT there is no analogue of QM's position operator. In QM, particle position can make sense as the defining hidden variable in all cases. In QFT, there is nothing that can perform this role. ",
"Additionally, there is no known way to do particle creation and annihilation in a classically deterministic way, even in a pilot wave interpretation. So when we demand this other important feature of QFT, the whole endeavor to save classical determinism fails anyway."
] |
[
"If you have absolute Newtonian time anyway, absolute simultaneity is ok. The issue here is really with violations of relativity of simultaneity, with how nonlocal HVs bring back a secret sort of absolute simultaneity in SR. With access to the HVs of spacelike EPR pairs, you can figure out ",
" hypersurface foliation, the unique definition of simultaneity in which the laws of physics are classically deterministic.",
"But maybe you're thinking of an application of Galilean relativity outside the Newtonian context which I'm not considering?"
] |
[
"It is just a generic feature of pilot wave interpretations that the exact position of the hidden variables is experimentally underdetermined, only determined up to the standard decoherence limit. The variables are just fundamentally hidden, even in a nonrelativistic version. Basically if you use a measurement device that tries to access the fine grained trajectory information, that changes the HV inputs for your subsequent EPR experiment, or undermines it completely."
] |
[
"Rotating doughnut shaped magnet.."
] |
[
false
] |
Does the magnetic field in the axis of a rotating doughnut shaped magnet become stronger at high RPM?
|
[
"If instead of magnetic (poorly defined) it was charged, the magnetic field would increase the faster it spun."
] |
[
"I think in general there needs to be a lot more clarification here. What way is the magnetic field oriented with respect to this \"doughnut\" in the first place?"
] |
[
"I meant natural magnet, like bicycle dynamo but inverted. On the other hand having a rotating conductor is another interesting question. What is the rate of rotating speed and increase in intensity of magnetic flux through the axis? "
] |
[
"Would it be possible to correct a malformed fovea?"
] |
[
false
] | null |
[
"Human Body"
] |
[
"Human Body"
] |
[
"What do you mean by malformed fovea?"
] |
[
"Dark Matter and LHC - how would we know if the LHC found dark matter?"
] |
[
false
] |
Some people think that dark matter is a different type of particle. Assuming it is, and that it can be created at cern using the energies available at LHC, how would we know if we found it? And would we be able to detect dark energy if we did create dark matter? And if we can have mirror energy why can't we have mirror forces, such as mirror gravity?
|
[
"If you imagine producing a dark matter particle at the LHC, just think about what would happen to it. The whole point of dark matter is that it interacts very very weakly with normal matter, so the particle would fly right out of the detector and we'd never see it. This shows up in the data analysis as missing energy, and is the telltale sign of such a dark matter particle.",
"With Re: to mirror energy, I have no idea what you're talking about. Such concepts as 'mirror forces' or 'mirror gravity' need a precise definition, and none exists in the scientific community. "
] |
[
"Not just missing energy, but crucially missing momentum. If they see a bunch of particles fly out in one direction, they know there must be a corresponding amount of momentum in the opposite direction, whether they see it or not."
] |
[
"Yeah, that's the jargon in HEP, but for the crowd here I wanted to emphasize the vector nature of momentum vs the scalar nature of energy."
] |
[
"Advantages of quantum computing outside of cryptography?"
] |
[
false
] |
[deleted]
|
[
"It only allows a very specific kind of parallelism, where you can only perform exactly the same operation on all the data and only get one result at the end (and it's only likely to get the right answer, you have to try a few times to be reliable). It's not as widely applicable as you might first think, but it's still quite useful in many situations.",
"Another answer is that it allows accurate simulation of quantum systems, which would be a great help for chemists and microbiologists."
] |
[
"Quantum computing isn't magic, but we do have some well understood situations where a quantum machine would dramatically outperform a traditional computer. The one that is most ubiquitous is probably ",
"Grover's Algorithm",
", which does a search of an unsorted database in time proportional to the square root of the size of the database. Classical computers cannot do any better than time proportional to the size of the database, so this would dramatically improve lookup times for massive databases. Granted, smart caching and other techniques can keep you from having to look through your entire data set whenever you need some data, but the principle is there. ",
"These sorts of algorithmic advantages are hugely important for fields that want to model complex systems. For example, our understanding of how proteins fold improves as our ability to model folding proteins improves. If better algorithms from quantum systems can allow us to fold larger proteins more quickly and at a better resolution then we can learn more about them. "
] |
[
"Many of our current protein folding algorithms actually rely heavily on heuristics to calculate the end result, simply because the computational power required to do a true low-energy state calculation is so high.",
"Would a quantum computer lift that kind of restriction, allowing us to apply full quantum mechanic calculations to protein folding, or would we still be limited to (much faster) heuristic algorithms?"
] |
[
"You can't get sunburned through a window, but do you still get the BENEFITS of sunlight through them?"
] |
[
false
] | null |
[
"No. Glass is (mostly/usually) opaque to the wavelengths of UV radiation that makes the skin produce vitamin D.",
"Not sure if there are any other advantages, except for the obvious ones (light in general makes you happier than darkness/rain etc.).",
"Edit: Not ",
" glass is ",
" opaque to UV-A/UV-B, of course. Most glass is mostly opaque to those wavelengths, though."
] |
[
"Um, I don't think that word means what you think it means. ;)",
"detrimental |ˌdetrəˈmentl|\nadjective | \ntending to cause harm",
"Anyway; AFAIK the wavelengths are the same. All forms of UV and lower wavelengths are prone to cause cancer."
] |
[
"I believe you can get sunburned through windows. I'm sure it's happened to me."
] |
[
"What are the cores of the Gas Giants in our solar system made of?"
] |
[
false
] |
And as a follow-up/piggy back, how do we know exactly whats beneath all the storms?
|
[
"Rules also dictate to be civil. To not act superior to those asking questions.",
"Just answer the question, vote and move on. People are interested to know of things, and will leave the forum knowing more than they did yesterday.",
"It also feels good to teach, as it is often the best way to learn. You'll gain a bit karma too, on reddit and metaphorically (charm). But undoing the good you could be doing, hurts your karma count and your charm; on the forums and in yourself."
] |
[
"Rules also dictate to be civil. To not act superior to those asking questions.",
"Just answer the question, vote and move on. People are interested to know of things, and will leave the forum knowing more than they did yesterday.",
"It also feels good to teach, as it is often the best way to learn. You'll gain a bit karma too, on reddit and metaphorically (charm). But undoing the good you could be doing, hurts your karma count and your charm; on the forums and in yourself."
] |
[
"Ninety percent of the questions on this sub could be researched by the one asking, haus. But sometimes asking out of laziness can provoke thought and conversation, as well as prompt other questions for other threads. Your sources are appreciated, either way- have a good day."
] |
[
"Do you think that we as humans are stopping evolution in our own species?"
] |
[
false
] | null |
[
"Biology"
] |
[
"Biology"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not debunk or vet theories or offer peer review on ",
"/r/AskScience",
". For more information regarding this and similar issues, please see our ",
"guidelines",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Asteroid Detection"
] |
[
false
] |
I am working on a novel and a central piece of it is based around an impending asteroid collision with Earth. It is large enough that it will undoubtedly end all life on Earth, perhaps even breaking it apart. My questions are a.) what is a reasonable timetable for NASA (or some other space agency) to detect an asteroid of this magnitude? b.) at what point would it be visible by the naked eye? c.) how close would it be (distance and ETA) when it appears about 25-50% of the moon? I understand this is asking a lot but I can't stand when books or other media are scientifically inaccurate.
|
[
"first of all, give up the idea of \"breaking earth apart\" unless you want to be laughed at. you could not realistically separate any appreciable amount of earth mass with anything smaller than moon - even the moon was just a leftover of a collision of proto-earth with something of size of mars (probably). matter at that amount and that speed would become liquid and evaporate and then condensate and fall back to biggest clump. it's not like breaking little stone balls. there is nothing big enough for that in solar system.",
"a small asteroid coming from outside of solar system would be most likely not coming from the plane of earth orbit, where we look for these objects, and would be moving at enormous speed compared to what is possible in solar system (that is more than escape velocity from solar system, i.e. more than 3rd cosmic speed or cca 40km/s), which means, that we would most likely not notice it until it would be very close.",
"for the sake of argument, let's assume, that there is an orphan planet of the size of mars wandering through our galaxy and it's going to hit earth. given that mars brightness in opposition is about -3 mag and it is at the distance of about 1AU then, and assuming detection limit of about 19 mag (about the faintest asteroids that you can realistically find with current telescopes), we could see this planet at distance of more than ",
" 3000 AU, if we were looking directly at it. if it moves at speed of about 100km/s, it would take over ",
" 150 years for it to get to us from that distance. but we would not be able to determine it's trajectory accurately enough to say weather it will hit us or not until it would be much closer. it would be visible with naked eye on sky about 2 years before impact and as bright as the mars about 1 month before it. about ",
" 16 hours before impact it would be as bright as moon and about ",
" 4 h before it would be as big as moon on a blue sky. the impact would evaporate entire object and big part of earth mass and the rings of earth would take couple hundred million years to settle down."
] |
[
"i corrected the number to 150 years already (i forgot to account for dimmer sunlight at that distance the first time), but anyway, yes, mars is twice bigger than our moon and our moon is bigger than all asteroids in solar system together. our detection limits are so good, that we could see an object of size of space shuttle at about distance of pluto (i didn't calculate that figure, just remember reading it somewhere).",
"global killer is usually considered asteroid with size of about 10km, which would cause long term climate change. if such object hit earth, my bet is, that with our level technology some people would survive anyway. something bigger, say about 100km (impact like this probably happened some time during earth history, but it was very, very long time ago, when life was more about single cell organisms in sea) could be cataclysmic enough to wipe almost all life from earth, but i don't really have anything substantial to support my opinion with.",
"so let's go back to previous scenario. 100km asteroid at asteroid belt, like astraea is about 9 magnitudes bright. coming from depth of our galaxy, outside solar system, such asteroid 7 years before impact would be about 300AU away and it could be in theory detected, but 2 years before impact it would still be only about 17 mag, so it would be VERY unlikely that anyone notices it, especially if it had big inclination. about 2 weeks before impact you could see it with naked eye, couple of hours before impact it would be visible on day sky. i don't want to speculate what would happen during the impact, but the consequences would be literally geological (earth crust is about 100km thick, but again, it behaves like liquid at some point)."
] |
[
"So we would know about an asteroid of that size for 300 years? What size would fit the parameters of a) not being detectable until ~5 years before impact and b) global killer? 300 years would be far too long for what I'm working on. Thanks for the advice on breaking Earth apart, this is obviously not my field of expertise. "
] |
[
"Can we ever achieve a horizontal-launch into space?"
] |
[
false
] |
What I mean is, if you see the moon on the horizon and you want to fly straight for it instead of launching vertically upwards first into space. Is this ever possible?
|
[
"As ",
"/u/AsAChemicalEngineer",
" already mentioned, every orbital rocket launch propels itself both vertical and horizontal, in relation to the earth. In fact, most of the energy of conventional rockets is spent to increase horizontal speed.",
"The reason for this is that, contrary to popular belief, gravity is almost the same in low earth orbit (LEO) as it is on the ground. Weightlessness does not imply a lack of gravity. The reason astronauts experience weightlessness is because they are in constant free fall around the planet. If you look at ",
"this",
" picture of a cannon firing a cannonball at different velocities, you can understand how an orbital trajectory works then.",
"So why go up that high at all then? The real reason why most spacecraft start burning vertically is, as ",
"/u/AsAChecmicalEngineer",
" also mentioned, that our atmosphere is pretty thick, down on ground level. The higher you get, the thinner it is, thus reducing drag. What this means is that once you have a high enough velocity, and a low enough drag, you can continue 'falling' around the earth, without losing enough velocity to fall back down again. Thát is what an orbit is, but remember, gravity is still acting on every object in orbit.",
"Also, to take your question véry literally, some companies and agencies are actually trying to make space planes a thing. The most famous one at the moment is probably ",
"Space Ship Two",
", by Virgin Galactic. This is a small second stage spaceplane, carried from a bigger 'regular' plane. Once the big plane reaches a high enough altitude, the second stage is detached and propels itself into space (not into orbit though). The entire launch and landing sequence of the two-staged craft can be done with runways, as opposed to massive launch pads etc.",
"Another runway-launched space plane is the ",
"Skylon",
", which is still in early development. The most notable difference between Skylon and Space Ship Two is that Skylon is a single-stage-to-orbit spaceplane. What this means is that the plane is just one spacecraft. Nothing separates during the launch, and the entire thing gets up into LEO, and back again. And again, all this will be done with runways, as opposed to vertical launch pads.",
"Of course all this is just about getting into orbit, not getting to the moon, which is actually a lot more complicated. If you'd like to know more about the workings behind that, feel free to ask, or shoot me a PM or something, I'd be glad to explain more. :)"
] |
[
"Any launch that wants to get into orbit must do both horizontal and vertical. If you only propel yourself vertically, you only have your initial angular momentum from sitting on the rotating Earth to play with. This is insufficient, so launches must tilt horizontally to gain enough angular momentum to round out their orbit. ",
"You want to start vertically first though because your primary goal is to leave the atmosphere to reduce drag. Go up, then go sideways."
] |
[
"There's a game out which can help illustrate these concepts, even if the numbers and physics modeling aren't perfect. ",
"/r/KerbalSpaceProgram",
" allows people to build their own rockets and spaceplanes and launch them with full control. Admittedly it doesn't \"teach\" rocket science so much as it requires (at least a little) background in it, but my friend and Twitch streamer Das Valdez does a good job at that part."
] |
[
"What is a quantum mechanical explanation of how light is produced in an incandescent bulb?"
] |
[
false
] |
I have a basic understanding of how voltage is essentially electrical pressure (V=IR), the filament essentially acts as a resistor, and that photons are produced when electrons move from higher energy states to lower ones (with the frequency reflecting the energy of the gap). What I'm missing is a conception of how atoms of different types interact with the electrical current and voltage and how electrons are 'bumped' into higher energy states. Here are some questions, (please feel free to elaborate on them!) I apologize some of them are quite vague. Any clarifications, corrections of misconceptions, or helpful additional information would be welcomed.
|
[
"Great questions! A complete microscopic understanding of the illumination of a light bulb covers a huge amount of physics, as it's a fairly complicated system. Thankfully, it sounds like you are mostly on the right track. ",
"Essentially, there are two distinct processes happening when a light bulb begins to emit photons. The first process is the heating of the filament in the bulb through ",
"resistive heating",
". The second process is the ",
"thermal emission of photons",
" from the hot filament. I'll describe these two effects on the microscopic scale, and then I'll try and answer your remaining questions.",
"Whenever the tungsten filament is connected to a voltage source, the free electrons begin to accelerate towards the positive terminal. As they accelerate, they continually bounce off the lattice of fixed tungsten ions that compose the filament, much like how ball bearings are scattered off the lattice of pegs in the \"plinko\" game you see in arcades (in reality, many things scatter the valence electrons in addition to the ions, but scattering off the ion lattice is the part relevant to resistive heating). Whenever an electron collides with an ion, it transfers most of its kinetic energy to the ion, which then distributes that energy throughout the lattice as thermal vibrations. After the electron impacts one ion, it bounces off, picks up speed until it hits another ion, and so on. This \"plinko effect\" is the mechanism by which the current heats up the conductor. Different materials affect this process in various ways. In some materials, the atoms in the lattice may be further apart, which affects the scattering, or they may contribute more valence electrons per atom to the electron gas, for example. ",
"So, on to the second, more complicated phenomenon. Now that the filament is hot from the current (around 3000K or so...just shy of the temperature of the sun's surface), why does it emit light? The answer to this effectively requires cataloging the various processes by which photons can be produced. You mention one such process: the de-excitation of an electron in an atom from a higher energy level to a lower energy level. This is one mechanism by which a photon can be generated, but there are many, many more. In fact, electronic de-excitation is responsible for only a very small percentage of the photons produced by a light bulb. Most of the photons emitted by a tungsten filament are generated by three distinct phenomena: ",
"bremsstrahlung",
", ",
"dipole radiation",
", and lattice vibrational de-excitation (like an electronic de-excitation, only in this case it's the lattice transitioning from a higher vibrational energy state to a lower vibrational energy state, emitting an infrared photon in the process). Basically, photons are emitted whenever a charge accelerates, and hot metals, such as a tungsten filament, possess a huge variety of ways in which charges can be accelerated.",
"So, that is an overview of what is happening in a light bulb at the microscopic level. I believe the discussion above addresses your first three questions, though I'd be happy to elaborate further if need be. As to the fourth question, it depends on how broadly you want to study the spectrum. Studying the visible spectrum of light bulbs is easy...all you need is a prism or a diffraction grating like a CD. Studying non-visible parts of the spectrum are more difficult, as you'd need some means of detecting infrared radiation. For incandescent bulbs, most (over 90%) of the emitted photons are in the IR spectrum. As to the fifth question: yes, there are such materials. LEDs are a prime example, though they are made from semi-conductors, which behave entirely differently from conductors on a microscopic level, thus the description I gave above would not apply."
] |
[
"Question: How do the electrons accelerate after colliding with the ions? It seems like they would slow down after transferring energy to them. Or is it a wavelength thing? "
] |
[
"The electrons accelerate after hitting the ions because the electric field from the battery is constantly exerting a force on them. Going back to the analogy with plinko, the balls are falling under the influence of gravity, which is constantly pulling them downwards. When a ball hits a pin, it loses speed, but then gravity immediately begins to accelerate it downwards into the next pin. Current-carrying electrons act the same way, they are constantly accelerated towards the positive terminal of the battery. If they slow down after scattering off an ion, the electric field from the battery will immediately accelerate them back up to speed."
] |
[
"If human cells all contain the same genetic code and very only in the expression of genes, then why can researchers not take a dermal cell, change what genes it expresses, and \"create\" a different type of cell such as a stem cell?"
] |
[
false
] | null |
[
"To put it simply, they ",
"can and do",
". I should mention that the process isn't quite as simple as switching the expression profile of the cell from 'dermal' to 'stem' in one go. Our ability to fine-tune expression within cells is limited. Instead, a now-common way of changing differentiated cells into stem cells is by causing them to transiently express certain ",
"transcription factors",
", which causes them to revert to a more stem-like state. These induced cells are not the exact same as embryonic stem cells, though they share some important qualities."
] |
[
"The long and the short of it is that gene expression regulation is a younger field than understanding genes themselves (by definition if you think about it)..."
] |
[
"Thank you for the reply. You gave me more than my cell biology prof gave me."
] |
[
"Is energy actually momentum in the time dimension instead in one of the three space dimensions?"
] |
[
false
] |
The formula for work done on an object is dW = F dx. And F=dp/dt. And work done is energy E measured in joules. So this gives dE dt=dp dx. Doesnt relativity tell us that space and time are similar,( except for a conversionfactor c and a minussign in the invariant spacetime interval). So energy is simply momentum in the time direction.
|
[
"Actually kind of yes. In relativity, there's a quantity called 4-momentum, which is a 4D vector consisting of energy and the three components of momentum. Energy is the time-like component.",
"P",
" = (E/",
", p",
", p",
", p",
")",
"There's also four-position:",
"x",
" = (",
"t, x, y, z),",
"four-velocity:",
"u",
" = γ(",
", v",
", v",
", v",
") where γ = 1/sqrt(1-(v/c)",
") and v",
" = dx/dt etc.",
"and others",
"Four-vectors obey Lorentz transforms by construction. If you \"square\" them by multiplying them by themselves and the Minkowski metric matrix (ignoring GR here)",
"|A",
"|",
" = (A",
")",
" – (A",
")",
" – (A",
")",
" – (A",
")",
"you get a Lorentz-invariant quantity: something that's the same in all reference frames.",
"The (square root of) this quantity for 4-momentum is called invariant mass:",
"E",
" – p",
" = m"
] |
[
"Mathematics of relativity summarized perfectly. Please add this to the wiki"
] |
[
"Whoops. Fixed it, thanks."
] |
[
"How is it that dogs and wolves are still the same species? How much more do dogs need to change before they become a different species?"
] |
[
false
] | null |
[
"Dogs and wolves ",
" separate species, ",
" and ",
". There are many species of animals that can still interbreed but are still classified as separate species due to physical, behavioral, or temporal barriers that make it extremely unlikely for the animals to hybridize. Dogs and wolves are more physically distinct than some, so it seems more surprising. "
] |
[
"Try coming at it from a different angle. Imagine you are immortal and you've seen all species branch off from the first ones and expect to see more come and go. For you then, the idea of a species is very fluid, one species experiences transition phases that lead to it becoming two or five or fifty species. Instead of trying to categorize organisms into this species and that species, you simply accept the fluid nature of chromosomes passing from one generation to the next and getting mixed around and resorted. ",
"So to answer your questions:\n1. The multiple breeds of dogs and the multiple species of wolves are part of a transition phase in the Canis genus that will probably result in multiple easily distinguishable species but who knows, maybe they will merge back together or one will die out leaving only the other and rendering your question moot or the transitional amalgum of different varieties will persist as long as humans.\n2. Well if you dropped a bunch of great danes and a shih tzus in the woods together they probably wouldn't/couldn't interbreed so by some argument even different varieties of dogs are different species."
] |
[
"Dogs are Canus lupis familiaris though, not Canus familiaris. Dogs' species is Canus lupis, the same as wolves', and their subspecies is Canus lupis familiaris."
] |
[
"A question on conscious and subconscious processing"
] |
[
false
] |
[deleted]
|
[
"There is no metric by which we can actually measure \"conscious vs. subconscious\" processing; it is most certainly an arbitrary number that was (at best) derived by making loads of ridiculous assumptions."
] |
[
"Virtually any number boldly claiming what percentage of the brain does something is either a gross oversimplification or flat out wrong. Like the completely false claim that humans \"only use 10% of their brain.\"",
"I'm sure Crain knows a lot about marketing, but without any sort of study backing up his 8% claim, I am going to have to say he is talking out of his ass."
] |
[
"how can you quantify understanding of a message? That's ridiculous."
] |
[
"Have we put life on Mars?"
] |
[
false
] |
Unless the rovers that we sent to Mars were 100% Sterilized before they were launched, wouldn't they have carried with them lots of microorganisms, even ones that could eventually evolve into more advanced life forms?
|
[
"That is a serious possibility, and scientists have done everything they can to avoid it, but undoubtedly some bacteria have survived the trip. Mars is still extremely hostile to bacteria, so ones that survive the trip are just as likely to die on the surface, and even if they survive in hibernation on the surface, there's no water and little chance of them reviving.",
"So basically, there is a small amount that survives but it isn't very likely to thrive on Mars."
] |
[
"Excerpts from ",
" ",
"Mission Requirements",
" are below. For more detail, click the link.",
"NASA uses a variety of methods to measure, control, and reduce spacecraft microbial contamination for planetary protection purposes. Compliance with planetary protection is ",
" for solar system missions, as stipulated in the NASA Policy Directive (NPD) 8020.7G...",
"...Requirements for ",
" include limits on the probability of impact with Mars (and potential contamination of icy satellites), and may include limits on the probability of impact with the target body, and orbital lifetime constraints for orbiter missions. If the probability that the spacecraft will impact the surface of its target body is small, cleanliness requirements may be reduced....",
"For spacecraft ",
" on target bodies of biological interest, the planetary protection requirements also include limits on the spacecraft’s biological burden. The stringency of these limits depends upon the mission objectives, planned spacecraft operations, and specific target body...",
"A full-system approach, or partial ",
" of the entire spacecraft, may be required for landers and rovers with life detection experiments, and for those landing in or moving to a region where terrestrial microorganisms may survive and grow, or where indigenous life may be present. The current bioburden constraints for Category IVa-c missions to Mars are derived from quantitative studies performed on the surface, encapsulated, and mated materials of the Viking spacecraft...",
"Currently, the NASA-approved ",
" include dry heat microbial reduction (DHMR) and vapor phase hydrogen peroxide (VHP). The Mars Viking landers were subjected to DHMR at the sub-system and full-system levels, with the Viking-1 lander (as a terminal sterilization step) being heated at 111.7 ˚C (233.1 ˚F) for 30.23 h at a specified humidity of 1.3 mg/mL...",
"For icy satellites, the current limit on the probably [sic] of inadvertent contamination of a liquid water body is less than 1×10",
" [one chance in ten thousand], which will be refined in future years.",
"For all Category V ‘restricted’ sample return missions, several documents that detail the ",
" are also required."
] |
[
"What about tardigrades?"
] |
[
"Can the shape of a crossword puzzle be reconstructed if only the numbers are known?"
] |
[
false
] |
If so, I'd love to see you solve these two and tell me how you did it. Here's an asymmetrical one in a 13 by 13 field: And here's a symmetrical one in a slightly larger field: I do hope I didn't make any typing errors! ;)
|
[
"Not unless I've misunderstood something. What about this one?",
"Any of the following crosswords work:",
"1 x x x 1 x x x x x x\nx x\nx x\n x\n",
"So there's no way to tell how long those fields are. Even if you do know, say:",
"There is still more than one possibility:",
"1 x 2 x x x 1 x x x 2 x\nx x x x\nx x x x\n",
"This one is impossible even if you know the field size, it'll always be 6 × 3."
] |
[
"I understand what you're saying, but I'm giving you more information than that!",
"So, are you asking about the two specific problem instances you gave in the OP, or the general problem? Because I found a counterexample for the general problem, which answers the question in the title with a ",
": it is not possible, in general, to reconstruct a puzzle from the numbers (and the size).",
"Of course that doesn't mean that it's never possible to do this for ",
" of the problem. However, your example appears to have the following three solutions, of which yours is one.",
"1 × 2 3 × 4 1 × 2 3 × 4 1 × 2 3 × 4\n× 5 × × × 5 × × × 5 × ×\n6 × × 7 × 6 × 7 × 6 × 7 × ×\n",
"(Hope I didn't misunderstand any of the rules. And I prefer to use × to mark blank squares.)",
"But here's an instance that I think is uniquely solvable.",
"Giving:",
"1 2\n3 ×\n",
"Yes, symmetry will restrict the number of solutions, but it's possible to find ambiguous inputs then, too. I have no idea, though, whether the two instances you gave are unique. They're too large for me to check by hand.",
"I don't know whether the size of the problem will have an impact, either. The “number of numbers” will reduce the number of solutions, but the grid size will increase it."
] |
[
"I understand what you're saying, but I'm giving you more information than that!",
"Suppose these are the numbers:",
"And suppose you know the size is 6 × 3.",
"How many other solutions are there than the one below? (blanks are blank squares, x's are black squares)",
"1 2 3 4\n x 5 x\n6 x 7\n",
"The x's in the second row could move a few spots and so could the one in the third row. But wouldn't there be fewer solutions if the size of the puzzle was bigger and/or if the puzzle has to be symmetrical?"
] |
[
"My jacket was producing static-electricity as I was listening to music. My head phones rubbed against my jacket as I took it off, and distortion to the music was heard. What causes this?"
] |
[
false
] |
[deleted]
|
[
"Does the distortion remain? If so, your device has been permanently damaged by electrostatic discharge. ",
"If you just heard some crackling, and it sounds fine now, then the electrostatic discharge did no permanent harm. ",
"The magnets didn't cause this, they just helped play the sound. "
] |
[
"Headphones acting like an antenna maybe?"
] |
[
"Headphones acting like an antenna maybe?"
] |
[
"Does increased vegetable and fruit intake help prevent/reduce cancer in individuals?"
] |
[
false
] | null |
[
"This is controversial, it's often thought to be true but looking at some of the literature it seems like the effect might be small or might only be for certain types of cancer. "
] |
[
"People whose diets are rich in plant foods such as fruits and vegetables have a lower risk of getting cancers of the mouth, pharynx, larynx, esophagus, stomach, and lung, and there is some suggested evidence that such individuals also have a lower risk of cancers of the colon, pancreas, and prostate.",
"source",
"It's also not clear whether the vegetables are directly beneficial or whether it's correlated to other lifestyle factors, or whether it means you're replacing foods that increase cancer risk with vegetables.",
"Fruits and vegetables, however, are strongly associated with a decrease in heart disease risk (see the source above) and heart disease kills more people than cancer ",
"source",
". ",
"So...uh...don't stop eating them?"
] |
[
"Posting from my phone so my only reference is based on what I've learned in my medical pathology class- vegetables are an excellent source of fiber and increasing your dietary fiber intake will increase the bulk of stool and make that shit slide out easier, literally. Not enough fiber in your diet increases your risk of diverticuli and subsequently colorectal carcinoma. Therefore, eating more veggies should lower your chances of getting that type of cancer. Possibly others too, but that's the one I remember off the top of my head."
] |
[
"Is there a way we can see microwaves?"
] |
[
false
] |
[deleted]
|
[
"Yes, microwave radiation can be captured by a camera and converted into a visible image. For example, here is a handheld device that lets you peer into the microwave spectrum: ",
"http://www.fastcompany.com/1139317/walleyes-microwave-camera-brings-x-ray-vision-home"
] |
[
"John_Johnson2 answered the main question, but it should also be noted that microwave ovens are usually fairly well shielded so you shouldn't be seeing much in the way of escaping microwaves."
] |
[
"This is the best way to do it. However keep in mind that you have to take the rotating plate out. The chocolate should not rotate. If you have an oven without a rotating plate it will not work, because the microwaves are scattered around the oven by different means and do not form a standing wave. ",
"The distance between melted parts is one half of the wavelength. "
] |
[
"Is it possible for any type of memories to be passed genetically?"
] |
[
false
] |
I'm not sure if memory is the correct word for this. It's more of an "intuition" or "feeling" when I am around something that has been related to my family for generations. Is it possible for people to pass on low-level memories to their offspring? Perhaps some type of social memory?
|
[
"No memory specifically related to the parent: Skills everyone is born with (breathing, walking, etc.) are technically genetic, but no specific experience that either parent has could be passes on. The nervous systems are never in contact with each other."
] |
[
"I wouldn't think so - the purpose of the genetic code is to code for different proteins and their biochemical properties. Perhaps there are certain inclinations that can be passed genetically through hormonal regulation, aversions and preferences based on enzyme reactions - but not any sensory memories."
] |
[
"I would say no, because there is no way that's been discovered for something like a memory, which is essentially just certain neurons in the brain firing in a certain way, to be encoded genetically. Not only in the sense that genes code for proteins so there's no way for them to be expressed, but also because our genes are mostly conserved, with the exceptions of a few mutations, throughout our life. For a memory to go from just a cognitive one to a genetic one, our genes would need to be modified somehow, which as far as we know at the moment is not possible."
] |
[
"If I have 1 fully functional 3D printer, can I make another fully functional 3D printer from it?"
] |
[
false
] | null |
[
"Currently, no. None of the existing 3D printers are fully capable of this.",
"Self-replication is, however, a primary goal of the RepRap project, an open-source collection of 3D printers. They print most of their main parts, but still require \"vitamins\" - motors, nuts, bolts, lead screws, etc. Also, electronics to control the printer must be purchased.",
"Individually, nearly all of the parts could be made on separate 3D printing processes, but even then, things like nuts and bolts, where high strength and close tolerances are required, are better suited for large-scale manufacturing. (It's just cheaper and easier to buy a bolt than try to print one with good \"bolt\" qualities.)",
"It is theoretically possible to do what you're asking, and I think there are still people working on it, but there's just not one single 3D printer technology that's fully capable of this."
] |
[
"Yes, just to reiterate, that is essentially the primary goal of the ",
"RepRap project",
". The concept is hundreds of years old and is discussed on the aforementioned website's ",
"self-replicating machine page",
"."
] |
[
"Some of the hobbyist printers exclusively use plastics, however larger-scale industrial printers can print using metals or ceramics."
] |
[
"Why is red meat \"red\" and white meat \"white\"?"
] |
[
false
] |
I'm assuming it has something to do with different types of muscles across species?
|
[
"Pasting from a thread yesterday.",
"It has to do with different proportions of proteins. White meat chicken breasts have mostly fast-twitch type muscle fibers (high in glycogen), fast but low endurance, which give the characteristic white meat flavor. But the legs are used far more often in a chicken, so they have more slow-twitch type darker fibers, which have higher endurance at the loss of power. This is why duck breast is darker and more gamey, ducks need the endurance fibers in the flight muscles for cruising. Once you move into \"red meat\" animals it is mostly slow-twitch fibers (rich in myoglobin), giving that red meat flavor. Additionally, different animals have different circulatory systems, making some meat harder to drain of blood, giving the metallic taste and darkness of a lot of game animals. At the darkest end of the spectrum is seal/whale meat. Their systems hold lots of blood in the muscles to aid in diving, and can't be bled-out as effectively.",
"TL:DR Different proportions of proteins."
] |
[
"Myoglobin in red meat gives the red pigmentation."
] |
[
"and white meat doesn't have much myoglobin in it. boom, question answered"
] |
[
"How new is the science used to make covid vaccines, could they have been made 5, 10 or 20 years ago?"
] |
[
false
] | null |
[
"\"Five years ago we simply could not have gone from sequence to vaccine inside of a year. \"",
"Quote from Derek Lowe ",
"Myths of vaccine Manufacturing",
" . An easily readable article",
"",
"His blog also contains the popular \" Things I Won't Work With\" found ",
"Here"
] |
[
"There are several vaccines utilizing several different technologies. Some of these technologies have been around for decades, while others like Pfizers mrna vaccine is pretty much a brand new technology. ",
"Another thing to note is the speed at which these vaccines have been developed. Everything from genome sequencing to drug development to data analysis and even drug approval and manufacturing get better year after year, accelerating the rate at which we were able to respond to and produce vaccines to address the covid pandemic. If this had occured 20 years ago, the response could have taken years as opposed to just a year or two.",
"Just as an extra little note, one cool thing that came out of this horrible situation was the amount of money that was pumped into vaccine research, like mrna, which is thought to be able to treat a large variety of diseases. This pandemic inadvertently accelerated that research and could lead to cures for things like cancer sooner than they would have otherwise."
] |
[
"Thanks for this, \"things i wont work with\" cracked me up. Never working with HF again in my life."
] |
[
"Do psychologists value anecdotal evidence more than other scientific fields? If not, why is so much of the data about mental illness seem to be based on the patient's accounts?"
] |
[
false
] | null |
[
"If you ask someone about their political opinions, you get anecdotal evidence. If you ask the exactly same questions from hundreds people, that's data you can work on and use to create scientific results. ",
"Same applies to social sciences, medicine and psychology among other things. "
] |
[
"30-40 is enough of a sample size to approach a normal distribution for a variable, but says nothing about finding meaningful relationships. The word you're looking for is Statistical Power (Cohen, 1988). "
] |
[
"I don't think they value anecdotes more, but they are more dependent on them because evidence is harder to come by in psychology than in other fields. The reason is that it's difficult to experiment on people. You can't just take 100 people with mental illness, lock them up and say: half of you don't get any social interaction for the next month, we'll see if that makes you worse. In other areas of medicine, they make these kinds of experiments with rats, which are astonishingly similar to humans in about everything except their mental facilities."
] |
[
"What is atmospheric pressure and density at the point above Jupiter where gravity is equal to that on Earth surface?"
] |
[
false
] |
I was wondering if it would be possible to establish an aerostat-based station on Jupiter, but computing this is somewhat over my head. I know there probably would be other serious problems with that (like weather?), but curious if it's possible at least in theory.
|
[
"The pressure and density would be near zero, because that point is about 44,000 km above Jupiter's surface"
] |
[
"I am referring to the outer extent of its atmosphere.",
"The earth equivalent gravity point is 44,000 km beyond that, or about 110,000 km from its center."
] |
[
"Saturn, on the other hand, has a \"surface\" gravity of 1.065g at the 1-atmosphere level ",
"according to NASA",
". The temperature at that level is -139 Celsius, which is only about 50 degrees colder than Antarctica in winter.",
"The biggest problem with your idea is that since Saturn's atmosphere is 96% hydrogen, it would be extremely hard to get enough buoyancy to lift a significant amount of weight. But that hasn't stopped it from being used in ",
"science fiction",
".",
"EDIT: Upon further reflection, Venus might be an even better candidate for this kind of mission. Its atmosphere is denser since it's mostly CO2, which means you get much more lift with the same sized balloon. And its gravity well is much, much shallower than any of the gas giants."
] |
[
"Why does the skin on the outside of fruit not oxidise?"
] |
[
false
] | null |
[
"The cell walls in the skin are tightly packed together, slowing the diffusion of oxygen. They skin is basically acting like cling-wrap that you might put over a bowl of fruit salad. Also, often fruits (apples are good example) will have a waxy coating on their surface as well. This prevents oxidation but it also prevents the apple from drying out from evaporation (dessication) and probably helps to protect it against pests."
] |
[
"The cellular structure of the skin slows the oxidation process. ",
"More info here: ",
"http://www.scientificamerican.com/article.cfm?id=why-does-bruised-fruit-tu"
] |
[
"Thank you! Is it possible to give me a simple explanation of the technical 2nd half? Also why do the cell walls stop oxidation?"
] |
[
"How much more computational power will it take for modern video games to play in 8k HD?"
] |
[
false
] |
I would like to get a sense of scale for how far we'd have to take hardware to play on extreme resolutions. 8k Resolution is 7680 × 4320 (33.1 megapixels) which is 16, 1920 x 1080 screens in a grid. I'm not familiar with the math of a modern game. I understand drawing triangles, texturing them, then lighting them, then post process. However, I have no idea what this means in computational power required. So assuming you had a computer that could play something modern like Crysis 3 (or whatever 3d engine you know about) at 1080p at 30 fps, could you put that into math per second terms? How much faster would everything have to be to play the same game at 16 times the resolution (if it isn't linear scaling)? Is it feasible with currently available hardware (8-way sli or something)? If you took a guess, how long until a single cpu/gpu combo be able to play 8k games? Thank you to anyone who cares to answer.
|
[
"Theoretically it is actually a linear progression as you would assume: calculating 16 times as many pixels requires 16 times the computing power. Technically there are limitations that make it not exactly 16 times, but it's pretty close. For example, if you can play Crysis 3 at 30fps in HD, you should expect to play it in 8K at almost 2fps.",
"If you wanted to push it back to 30fps, you'd probably need multiple computers running multiple cards in SLI (more than 16 in all, because of losses due to technical constraints)."
] |
[
"The complexity in rendering the 3D scene won't change. Games like Crysis simply send the list of triangles/textures to the video card, and tell it to render them - but it will take a lot of bandwidth.",
"It takes 16 times the effort to render a scene at 7680x4320 then it does at 1920x1080. Assuming 6 bytes per pixel (3 for color, 1 for byte-aligned padding, 2 for depth) and two screens, you need 200MB on the video card to contain such a screen. For rendering something at 60 fps (which is at the refresh rate), your video card must handle at least 12GB/s. (The current high-end graphics card are around 200GB/s.) ",
"The weakest point is the video cable, which will need to handle 2GB/s; HDMI only handles 1.3GB/s, meaning that you will need two of them just for a single display if you want to maintain full quality - or you could get multiple monitors and instead have four 3840x2160 displays. ",
"Also, these calculations don't factor secondary aspects for rendering. It may need 12 GB/s, but the video card may need to read/write to its memory multiple times. There's also optimizations that make some of these read/writes unnecessary. Some cards may decide to just use 24 color bits per pixel to help save memory (and thus increase throughput), ",
"In summary, if you can render something at 1920x1080 at 16x FSAA, your videocard can handle rendering one frame at 7680x4320. Again, there may be optimizations for FSAA that might not appear in the non-super sampled render. "
] |
[
"You aren't actually rendering it at that high of a resolution, there are much less computationally intense ways of anti-aliasing."
] |
[
"If Earth was in Mars' orbit would our atmosphere still be able to support life through greenhouse warming?"
] |
[
false
] | null |
[
"I think your question needs some clarifying. Do you mean, 'would we be warm enough to sustain life?' "
] |
[
"There are two hurtles to terriforming Mars. "
] |
[
"If you were to magically plop and atmosphere on Mars that had Earth-like pressure at the mean ground level, it ",
" erode into space, but the timescale is still several million years. So compared to human timescales, it's pretty much stable. Robert Zubrin's book \"The Case For Mars\" goes into much more detail."
] |
[
"How is nature able to keep a relatively even number of sexes in births?"
] |
[
false
] |
I often find myself wondering how it is that my Brother has three boys, and a good friend has three girls, and that as far as I know, the ratio of male/female on the planet is relatively even? Actually, the more I think about this, the more it seems that no one is really going to know.
|
[
"For humans, the sex of the offspring is determined by the sperm having an X or a Y chromosome. These are produced in roughly even quantities as a product of the 50/50 genetic distribution of the male. It's basically a repeated set of coin flips over a very long period of time. The longer the coin is flipped, the closer to an even 50/50 distribution your results will be.",
"After this, there are various things that affect survival by sex, and other factors that can play a role in real world distribution. For other species of animals sex can be determined in different ways, like for ants. But unless there are significant differences in means of producing the gametes, a species varies enough by sex that survival into adulthood is significantly different, or the animal can change sex, the real world distribution is going to be roughly 50/50."
] |
[
"Your sample size is small!",
"Your father is always XY and your mother is always XX. You get one sex chromosome from each parent. Mom always contributes an X, and 50% of the time dad contributes a Y. I could go into more detail if you like. It is always 50:50. Even in herd animals where males are surplus, it is still very close to 50:50. ",
"Some studies",
" have found that other mammals can \"choose\" the gender of their offspring tactically in response to the environment. The mechanism is unknown and I am not entirely convinced."
] |
[
"I'm not sure if this is what you're asking but I'll explain the evolutionary basis for a 1:1 sex ratio (but note that this is not true of all species).",
"We'll use an example population of 100 individuals and we need to start at some unbalanced sex ratio. Let's use 70 males and 30 females (you'll see by the end that it doesn't matter what our starting point is). Think of yourself as a parent with children born into this population. Your son is able to mate with 30% of the population and your daughter can mate with 70% of the population. You can easily see that its better to be female in this situation because they can find a mates more quickly (and then have more time/energy for other things). Here's the tricky bit: PARENTS that have more daughters will have their genetic code favored in this situation because female children do better than male children. Those successful children will also be predisposed to have more daughters than the base population. In this way, the sex ratio of the population will begin to favor females. You may see some overcompensation where females begin to outnumber males but the same process will direct the sex ratio back towards 1:1 where neither sex has a mating advantage over the other.",
"source/more details",
" "
] |
[
"Could we send an object to another galaxy cheaply?"
] |
[
false
] |
More specifically If I was going to die in 5 years and I have a sum of money (350-500 million USD) , would it be feasible to have my body frozen (or preserved in another way), sealed in a protective container and launched to a distant galaxy? Are we even able to model space well enough for it to even have a chance of making it? Would it me more reasonable to try to place it in orbit around another object in our galaxy? If this doesn't belong here I will delete it. I just figured I would have a better chance of getting a trustworthy answer here.
|
[
"I'm dead doesn't matter to me."
] |
[
"What numbers are off? I guess I should have specified that I meant escape velocity relative to the galaxy, but I assumed it was understood from context. ",
"NASA says the sun moves ~230 km/s about the galactic center",
" , Wikipedia said about 220. "
] |
[
"Sure, all that could be done (but it might cost a lot more than $500 million).",
"So long as you could get the correct course and sufficient speed to overcome various drag factors from all the local bodies and many others you'll pass on the way, plus the small but cumulative friction with stuff like gas and dust particles, your body could well ultimately get to another galaxy. But the Earth would probably be consumed by the Sun's swelling into a red giant before your body arrived there (five billion years or more)."
] |
[
"I recently learned in physics about how every action has equal opposite reaction. On the topic of gravitational force the opposite is normal force. Where does this force originate from?"
] |
[
false
] |
[deleted]
|
[
"The reaction force is on the other body. For example: when you're on a chair with wheels and push against a wall. The wall \"pushes\" you back and you roll away. In general the rule is this:",
"If you push something, it pushes back on you. If you pull on something, it also pulls on you.",
"There is always a reaction force. Imagine you are falling. Gravity is pulling on you, but there is no normal force. That would break the rule. The normal force is not the reactionary force to gravity, but it is a result of gravity.\nWhen the earth pulls you down, you also pull the earth up, a tiny bit. You move much more than the earth, because you are much lighter, but it still happens.",
"The normal force is a force that happens because you push down on the floor, because of gravity. It's essentially the same force you get if you were leaning against a wall, gravity is not especially important. The origin of the force is quantum mechanical. Some particles are not allowed to be in the same state as other particles. For example electrons. You cannot have two electrons in identical situations. Because you are pushing on the floor, you're forcing the electrons between you and the floor to be closer. They don't want that, so they push back. This is called the Pauli exclusion principle and gives a force of you push (specific) particles together. If you want to read more on it, here's a Wikipedia article:",
"https://en.m.wikipedia.org/wiki/Pauli_exclusion_principle"
] |
[
"The normal contact force of (for example) the floor on you forms an action-reaction pair with the normal contact force of you on the floor. The normal force does not form an action reaction pair with gravity."
] |
[
"There's an easy way to keep track of reaction forces: reaction force B is always ",
" as initial force A, and never acts on the same object. ",
"The reaction force for the earth pulling down on you with gravity is a gravitational force. In this case, it's you pulling up on the earth with gravity. If you're standing on something, then there's a contact force pushing up on you, exactly canceling the gravitational force on you. The reaction force to that contact force is another contact force: the contact force from your feet pushing down on the earth. Neither you nor the earth experiences any acceleration because the net force on both of you is zero. ",
"Jump up in the air, and while you're in the air, there isn't any contact force any more. The gravitational forces are still there, and they still satisfy Newton's Second Law. The gravitational force on you accelerates you toward the earth, and the gravitational force on the earth accelerates it toward you (remember the third law: F = ma, which rearranges to a = F/m. m(earth) is very big but it's not infinite, so a > 0)"
] |
[
"What is with eyes?"
] |
[
false
] |
Why do we feel a "connection" with somebody when looking at their eyes? We don't feel a connection when smelling someone's nose? why is sight different than the other senses. (I think touch/connection makes sense because it actually does connect people physically)
|
[
"There is a decent wikipedia article on ",
"Eye contact",
". It goes over some social implications, but doesn't really delve into the meat of the issue. Fortunately, there does seem to be a good amount of research on the issue. ",
"This study",
" postulates that, since eyes are a good feedback indicator, eye contact is linked to affiliative motivation (an unconscious desire to maintain relationships). ",
"This study",
" investigates the importance of eye contact during infancy. It seems that eye contact plays an important role in developing many relationships, including flirting. Another study, thrillingly entitled ",
" tackles that beast, but arrives to the unsatisfying conclusion that it's good to be attractive, but eye contact certainly doesn't hurt when flirting.",
"But ",
" you ask? What really causes that connection? This is where it gets tricky, and where some speculation comes in. David Sloan Wilson wrote a wonderful book entitled ",
", and in it he tackles a few topics of human evolution. He describes how important (and overlooked) human social structure has been on human evolution. A good part of this (along with why rock throwing is important) is devoted to our body language and how we communicate our feelings in a way that we can't control. This helped prohibit individuals trying to take advantage of others; their real intentions were displayed with out them knowing. Now, to speculate, eye contact could be some sort of challenge. Initiating eye contact shows a desire to know what that person is thinking and what their intent is. Also, by initiating eye contact, you are opening yourself up to them for investigation, putting your intentions on display. I feel like ",
"this study",
", which documents how people felt that individuals avoiding eye contact were being deceptive, vindicates that speculation.",
"Edit: forgot a word."
] |
[
"Speculation: \nIt's rooted in evolutionary psychology, and eyes being identified as living things. ",
"Numerous animals",
" evolve \"eye spot\" patterns to ward off predators. An eye is an image we pick up on and pay attention to as a symbol of attentiveness and the presence of another being."
] |
[
"I remember reading somewhere (a long time ago, so sorry if I misremember something) as well that when we stare at someone's face we non-psychopaths for a fraction of a second mimic their facial response, and it illicits an empathy reaction. ",
"I know it's been covered a decent amount that being in the presence of someone happy is more likely to be happy, and the same holds true for people who are sad.",
"Feeding off that there's also the fact that we use our eyes (and foreheads) for visual cues of mood. We've also evolved many mechanisms for quick detection of certain visual stimuli, and a lot of it centers around the eyes. ",
" and all that stuff...",
"For example, a fear response in someone causes the eyes to open wider than usual, and seeing this facial expression causes a cascade of reaction which results in heightened attentiveness. It's a very base impulse reaction mediated by activation of the amygdala when we see a fear reaction.",
"I think something similar holds true for disgust (which is also brow mediated), but I don't really remember it. I think we evolved this response due to putrefaction/bacteria and such. Obviously smell plays a bigger role in that, but even when we smell something bad we have a response with our eyes (furrowed brows and raised cheeks -> squinting)",
"Things like happiness and sadness actually don't illicit as quick a response. There are of course methods for detecting real/fake smiles as well which involve the eyes. Crinkling of the eyes during a smile = real smile, only movement in the lower half of the face = fake smile.",
"A lot of these mechanisms are ",
" evolutionarily evolved/conserved too. Our ability to detect very small changes/disparities in the face is ridiculous. Imagine if we had that much visual acuity for feet, or something. ",
"It's like with other animals as well, we have can a very difficult time telling two animals of the same breed apart, but animals of that species would have no such problem. Obviously with some animals this is less face (or even visual) based and based more on other visual factors (or scent), but still.",
"Now, I don't remember the exact mechanisms behind a lot of this stuff, would you possibly care to elaborate more? I'm actually really interested in all this, but I sold all my undergrad psych books so I'm a little out of my depth here."
] |
[
"Do dogs understand pictures of their owners?"
] |
[
false
] | null |
[
"From this article I found, the answer is ",
"sometimes",
". They're kind of bad at it, as dogs rely much more heavily on smell/hearing than sight, so they may or may not recognize ",
" photos. Some are easily confused by things like haircuts and camera angles.",
"The study was pretty small with only 12 dogs and 12 cats. When given the option of a handler picture vs. non-handler picture. The dogs chose their handler 88% of the time, while cats choose their handler only 54% of the time.",
"The most interesting thing though, is when they tested animals' abilities to recognize other animals in photos. Dogs were able to identify familiar dogs 85% of the time, while cats chose familiar cats a whopping 91% of times.",
"EDIT: Dropped the part where I referred to sight as a \"tertiary sense\", I picked that up from elsewhere on reddit, so I can't define the term and shouldn't use it."
] |
[
"That's exactly what humans are like. Its easier to tell one human being from another than tell two similar animals apart."
] |
[
"Except that dogs are better at telling humans apart than telling dogs apart? That's so wholesome. "
] |
[
"When i catch a drop of rain on my tongue, is it safe to assume that that water has been anywhere, or even everywhere in the world?"
] |
[
false
] |
I could be completely wrong here (which is why I'm asking), but my understanding of the water cycle is that all the water in the world has basically been here for hundreds/thousands/millions of years, and it all goes round the same cycle of evaporating up into clouds and then precipitating back down over and over again. So if that is the case, does that mean that when i catch a drop of rain on my tongue, that drop of rain could've at some point been part of the pacific ocean, or the snow on the peak of mount everest, or any other place in the world? I think it would be pretty cool to be able to think that. TL;DR Where has rain water been?
|
[
"All the matter that makes up our planet, including the atoms comprising water, were formed by nuclear fusion in the center of now-extinct stars. Earth was formed about 4 billion years ago, so that means that every atom on the planet, though unimaginably older than 4Gy itself, has been circulating in some way for 4 billion years. ",
"Not every water molecule has always been a water molecule, though. Lots of biotic and abiotic processes, like lightning, sunlight and metabolic processes (just for example) can split and/or form water. Thus, the atoms within any specific water molecule could have been in that arrangement since Earth's formation, or for a few hours. Because of the sheer volumes of water existing on earth, however, the rate of turnover is extremely slow -- that is, most water is staying water, because the processes that mediate hydrolysis or water formation act very slowly on a human timescale. ",
"So, your raindrop could be composed of water molecules that have been all over the world (in polar icecaps, in dinosaur pee, you name it) on their 4 billion year old journey to your tongue. Even better, just think about how every oxygen atom in the raindrop was formed in the center of a long-extinct star somewhere else in the universe and has now arrived on the tip of your tongue, your tongue made also of atoms formed in the center of also-extinct stars light-years away. ",
"As Carl Sagan said, we are \"star-stuff.\" "
] |
[
"Im no specialist but considering earth is generally a closed system, with little water escaping into space or being added from space, ~4.5 billion years being a long time for water to run amok around earth, and with a drop of water made of thousands/millions/billions(?) of molecules then yes some of those molecules have been just about everywhere that they could have on earth"
] |
[
"awesome answer, thanks. Its cool to think that i probably just drank t-rex piss"
] |
[
"If you hold your finger over a garden hose the water comes out in a faster, more controlled burst. Is the average water use per second or minute actually higher or does it just appear to be?"
] |
[
false
] | null |
[
"The rate of flow of the hose remains the same (meaning the volume of water coming out of the hose per second). However, since you are restricting the opening size, to get that same volume of water per second through that smaller hole it must come out at a faster speed. But you aren't getting a greater volume of water per second."
] |
[
"Sorry I was giving the simplified freshman physics explanation that we give to our students when they're first studying fluid flow. We usually just have them assume constant flow rate to make it easier. I didn't think I'd need to get so detailed as to include changes in fluid flow rate."
] |
[
"the amount of water that leaves the hose is drift velocity * cross section area. ",
"the smaller the hole, the faster the velocity, to keep the amount of water per second constant. ",
"this only works for large holes, if i make a very tiny hole, only very little water will come out. but in a garden hose the amount of water per second will only be a little smaller. ",
"i propose you fill a bucket once with and once without thumb and see that it will take roughly the same time, but slightly (maybe unmeasurable) longer with the thumb."
] |
[
"If I amplitude modulate a 10k Hz audio signal at 15 Hz, what frequency would my mind perceive?"
] |
[
false
] | null |
[
"You will hear 10 kHz. ",
"You can listen here",
".",
"The above sound was created with the following code in matlab",
">> Fs = 44100; %Sampling Rate\n>> dt = 1/Fs; %Intersample time\n>> x = 0:dt:5; %Time vector\n>> y = sin(2*pi*x*10000); %Create the base 10kHz Frequency\n>> ymod = sin(2*pi*x*15); %Create the modulating 15Hz signal\n>> y = y.*ymod; %Elementwise multiplication between the two\n>> audiowrite('10khzmod15hz.wav', y, Fs); %Save the file\n",
"I might also add, this effect is not at all surprising, as the modulating signal isn't really there. If you look at at the frequency components of the modulated signal, you find that there is no 15Hz signal, but two signals, one at 10kHz + 15Hz, and one at 10kHz - 15 Hz, like ",
"this",
"."
] |
[
"cos(a)cos(b) = ((cos(a)cos(b) + sin(a)sin(b)) + (cos(a)cos(b) - sin(a)sin(b)))/2",
"Which by trig identities,",
"= (cos(a-b) + cos(a+b))/2",
"So let's set a = 15t and b = 10000t.",
"cos(10000t)cos(15t) = (cos(10000t - 15t) + cos(10000t + 15t))/2",
"= (cos(99985t) + cos(10015t))/2",
"So modulating a 10 kHz signal at 15 Hz is the same as playing a 99985 Hz signal and a 10015 Hz signal at the same time.",
"If you're off by like one hertz, then the ",
"beats",
" are really obvious, and you just hear one signal being modulated. If you're off by a lot, you just hear two different notes. With this, it would probably pretty much just sound like a 10 kHz signal."
] |
[
"I can definitely hear the modulation, though, as a rapid pulsing of the sound. Is this because of nonlinearity in the ear leading to intermodulation products, recovering the 15 Hz tone?"
] |
[
"What properties of water make it such an efficient radiation shield?"
] |
[
false
] |
I've seen pictures of nuclear plants using pools of water as a radiation shield, why is that? Ex.
|
[
"Water is very important in shielding against neutrons, and the reason is that water has lots of hydrogen in it.",
"Neutrons have no electric charge, so unlike every other kind of ionizing radiation, they don't interact significantly with atomic electrons. This means that neutrons only interact with nuclei. And you are probably aware that nuclei are geometrically much smaller than atoms. So from purely geometric arguments, you would think that the probability of a neutron interacting in some material is very small compared to other common forms of radiation. And that turns out to be correct.",
"Neutrons are highly penetrating radiation, and they penetrate further when their energies are higher.",
"So when a neutron ",
" interact with a nucleus, what happens? Well, it can either scatter elastically, or cause a more complicated nuclear reaction. (The latter is what leads to ",
"neutron activation",
".) Elastic scattering is generally the dominant process over inelastic scattering or other reaction channels, so I'll just consider elastic scattering here.",
"What happens when a neutron scatters elastically off of another nucleus. Imagine throwing a billiard ball against other balls of various masses. You throw the billiard ball agains a bowling ball, what happens? The bowling ball recoils a little bit, but the billiard ball retains the lion's share of the kinetic energy. Take the limit where the mass of the bowling ball is infinite; you're throwing the billiard ball against a brick wall. Now the billiard ball essentially loses no kinetic energy.",
"But now imagine throwing a billiard ball against another billiard ball. If you hit it dead-on, the first billiard ball will essentially come to rest, and the ",
" one will get all of the kinetic energy.",
"So what if you can get the neutron to hit something of the same mass, which interacts more strongly with matter, and can be stopped more easily by the surrounding atoms? Are there any particles that meet that description? Of course: protons. Protons have electric charge, so they are much easier to stop in matter, because they interact very much with atomic electrons.",
"A proton is just a hydrogen-1 nucleus, and since we're talking about chemically stable materials rather than ions, we want a material with lots of hydrogen in it. The goal is to get the neutrons to scatter off of hydrogen nuclei, and take kinetic energy away from the neutrons as quickly as possible. Once the kinetic energy has been given to charged particles, they're much easier to stop within the shielding."
] |
[
"Some qualitative things: Water is cheap, it can’t crack and has no holes or gaps (it is uniform). It can be purified. The only activated products from pure water is deuterium or tritium, and only if impacted by neutron radiation. Tritium is fairly benign as far as radioisotopes go. ",
"Water can be flushed/cleaned. It can be drained if needed for maintenance with relative ease (and refilled). Water acts as a good buffer for radioactive gases and can hold up a number of radioisotopes if they do escape. ",
"Water is also an effective cooling medium, so when you are dealing with decay heat it can multi function as a coolant, shield, and moderator. "
] |
[
"I like your explanation very much, it's very intuitive. Reminds me of Richard Feynman explaining water phases, fire or rubber bands in similar manner."
] |
[
"If I wanted to sail in a straight line for as long as possible without hitting land, where should I shove off/where would I land?"
] |
[
false
] | null |
[
"Across the surface of a sphere (although the earth is not really a true sphere), the shortest distances between two points lies on the ",
"great circle",
" that connects them. Typically in non-euclidean geometry (such as for geometry on the surface of a sphere) we define a \"straight line\" in this way. Wikipedia seems to indicate that the longest path on a great circle over water is:",
"From the south coast of Balochistan province somewhere near Port of Karachi, Pakistan (25°25′N 66°25′E) across the Arabian Sea, south-west through Indian Ocean, near Comoros, passing Namaete Canyon, near the South Africa coastline, across the South Atlantic Ocean, then west across Cape Horn, then north-west across the Pacific Ocean, near Easter Island, passing the antipodal point, near Amlia island, through the South Bering Sea and ending somewhere on the east-north coast of Kamchatka, near Ossora (59°38′N 163°24′E). ",
"Here is a ",
"link to the article",
" and a ",
"map of the route",
". I don't know if we know that this is this the absolute longest, but it is the longest I could find. Neat question!"
] |
[
"A \"straight line\" on a sphere is a segment of a ",
". If I start out going along a given latitude and go straight, I will continue along the great circle that is tangent to that point. So if I start along 60 south, I'll end up moving north, graze the 60 north line, then go back south and end up where I started on the 60 south line.",
"Here's more intuitive feel: Imaging drawing a circle exactly the same size as the 60 S. circle on the earth, tangent to the equator. Now imagine I start at the point where that circle touches the equator, moving straight west. I will of course continue along the equator, not along the circle. To stay on that circle, I will have to continuously turn. The equator is a ",
".",
"The path you showed only ",
" special because we chose to draw the lines of latitude and longitude where we did. In principle we could have drawn one of the poles anywhere on earth."
] |
[
"That would not be a straight line. You would have to continually turn slightly toward the south to prevent moving north."
] |
[
"Is there acceleration for data transfers? ie (5MB/second)/second?"
] |
[
false
] |
I know acceleration is velocity over time, with velocity being change in position over time. Well, data transfer, would be bytes of data over time. (The velocity of the data itself could be a completely different question). My question is, can you apply the same idea of acceleration to bytes over time over time?
|
[
"here's a rough idea of how it works: the transfer rate increases linearly",
"There are several modes. There's also an exponential phase when a connection is opened; if you only did it linearly, it would be hard to saturate fast clients (i.e. your 110 megabit cable modem) in a reasonable time without DoSing slow clients (i.e. your 2g cellphone).",
"Also, it's worth noting that various internet companies have been known to \"cheat\", i.e. ramping speed faster than the RFC technically says to, in order to improve site performance."
] |
[
"Thanks for pointing this out, didn't know this. Any source I can read up for details?",
"http://blog.benstrong.com/2010/11/google-and-microsoft-cheat-on-slow.html",
"http://research.google.com/pubs/pub36640.html"
] |
[
"Yes, TCP is a protocol that automatically adapts the rate of data transfer based on the extent of congestion on the network path. Without going into the details, here's a rough idea of how it works: the transfer rate increases linearly (i.e. with a constant \"acceleration\" in mechanical terms) until it encounters data loss (which is used as an indicator of congestion), and it adapts to this by halving the transfer rate.",
"So the linear phase of TCP does conform closely to the notion of acceleration."
] |
[
"A question of neutrinos and Anti-matter?"
] |
[
false
] |
if antmatter is matter with the opposite charge, and photons(haveing neutral charge) are their own ant-matter, how can there be ant-neutrinos?
|
[
"There's more to charge than just electric charge. There's also colour charge and weak isospin.",
"Neutrinos have spin-1/2 and are therefore fermions (particles with half-integer spin).",
"The weak force couples to (interacts with) left-handed fermions and right-handed antifermions. Here, \"handedness\" refers to ",
"chirality",
".",
"It is actually an open question as to whether neutrinos and antineutrinos are distinct particles (Dirac fermions) or just the same particle with opposite chirality (Majorana fermions).",
"It would be nice if they were Majorana, because the Higgs interaction requires both left-handed and right-handed versions in order to give mass to fermions, and it is known from neutrino oscillation that neutrinos have non-zero mass.",
"Some experimental efforts towards answering this question involve ",
"neutrinoless double beta decay",
" and ",
"lepton number violating decays"
] |
[
"Antineutrinos have opposing ",
"chirality",
" to their \"normal\" counterparts."
] |
[
"thanks for immediately correcting on the spin part, it is chirality.",
"As for the nomenclature, i meant more as saying if dirac or majorana picture is used to describe."
] |
[
"How far can a typical bug see?"
] |
[
false
] |
[deleted]
|
[
"Compound eyes, as seen in insects, have relatively poor resolution because of the ",
"diffraction limit",
". Each facet in the compound eye suffers from this limit individually, so while the total compound eye can be quite large, its vision is limited by the much smaller facet size.",
"For example, for a dragonfly with an eye diameter of 5 mm the diffraction limit for the whole eye (what it would get if it had a single lens like we do) would be 0.24 arcminutes at the ultraviolet wavelengths dragonflies can see at (their ultraviolet sensitivity ",
"peaks at 350 nm",
", which I used here, but goes all the way down below 300 nm.",
"0.24 angular resolution would be great - that's 2-4 times as good as humans. But as I said, a compound eye is limited by the diameter of its individual facets, not the total eye size. The eye of a big dragonfly like the one we're considering here can have 30,000 facets, giving each one a typical diameter 170 times smaller, or about 30 µm. The angular resolution is also 170 times smaller, resulting in an angular resolution of about 40 arcminutes. In practice, the facet size is not constant across the eye, though. The forward looking part is optimized for higher resolution at the expense of the rearward-looking parts (this variable-resolution property is something our eyes have too - we only have sharp vision in a tiny part of our visual field - we just don't notice much because we move that sharp region around as needed). Therefore, dragonfly eye resolution can get a bit better than my back of the envelope caculation, and ",
"14 arcminute resolution is possible",
".",
"Theoretically it would be possible to get around the limitation of individual facet size in compound eyes if the facets were to form an ",
"interferometer",
" together, but as far as I know there is no evidence that this is happening, and ",
"the facet spacing in the compound eye matches the what one would expect from diffraction limit calculations for individual facets pretty well",
".",
"So, how good is 14 arcminute vision? It's 14 times worse than a typical human, but that's far from useless. ",
"This image",
" has an angular resolution of 14 arcminutes: Its field of view is 69.4 degrees = 4164 arcminutes, resulting in 297 horizontal pixels at 14 arcmin resolution. I think it's pretty clear to see what's going on here, even at decent distance. (Note that dragonflies can see in almost every direction at once, so this image does not give a good impression about their field of view.)",
"Dragonflies probably have the best vision among insects, so what about more typical ones, like flies, butterflies, wasps and beetles? Typical resolutions are around 60-180 arcmin or so, with even worse numbers for very tiny insects (you can't have large facets if your whole body is tiny). For example, the popular fruit fly (Drosophilia megalogaster) has an angular resolution of roughly 300 arcminutes, about 300 times worse than a human. At that resolution my image example from above would be only 14 pixels across. That's starting to be a bit limiting.",
"Spiders use a different system than insects. Instead of huge compound eyes, they have a smaller number of larger eyes (so more similar to us). This should make it easier for them to achieve high resolution. Jumping spiders can have a resolution of ",
"15 arcminutes",
", which is very similar to dragonflies. Jumping spiders are among the spiders with the best eyesight, but I don't know if 15 arcmin is their limit, nor if other spider types like ogre-faced spiders do better. It wouldn't surprise me if they do.",
"So, what does all this have to do with how ",
" the bugs can see? Compound eyes have almost infinite focal depth, so they don't have to trade off between focusing at the distance and focusing nearby (we handle that issue by changing the focus of our eyes instead, so we aren't really limited by that either), so this does not limit their ability to see far. Ultraviolet light, which insects rely on to reach their highest resolution, is attenuated by the atmosphere, but that's not much of an issue at the near-visual wavelengths involved here. So I think the angular resolution discussed above is the only real limitation for how far they can see.",
"In that case there is no real limit to how far they can see, just that the further away an object is, the smaller it will look, and hence the fewer details will be visible. That's just the same thing we experience when we look at distant objects - you can see lots of detail on a cow standing next to you, but a km away you can see that it's a cow, but not much more, and even further away the cow will just be a dot. A dragonfly will experience the same thing, just 14 times closer.",
"As an example of how there's no arbitrary distance limit on insect vision, a dragonfly can see the Sun just fine, even though its 150 million kilometers away, and dung beetles use the Milky Way to navigate at night, even though most of it is 30,000 light years away."
] |
[
"Bugs don't process visual information like we do. They detect motion and distance, that's why they typically have two eye \"pods\"",
"It's tough to generalize the vision of multiple bugs, but they basically see movement and react to how far away that movement is occurring. Their other senses besides vision are much more useful, especially when detecting prey."
] |
[
"It is the remote light source that has to do the hard work of making itself visible, not the observer. Obviously, an insect is able to see the sun, at a distance of ~10^8 km. However, i guess the insect is unable, unlike the human naked eye, to distinguish the Andromeda Galaxy, which is at 2 million light-years."
] |
[
"How does natural selection and evolution explain mimicry?"
] |
[
false
] |
From when I took biology, I've wondered how some organisms can almost perfectly mimic something that originally looked nothing like it. I think I understand how the process of would work- where a mutation causes an organism to appear similar to another species, making that organism more successful in reproducing and surviving. However my confusion arises when I see species like the that look almost indistinguishable to their respective model. Wouldn't it take multiple steps for a dramatic change in appearance to develop. In the first steps of the process, when the mantis isn't camouflaged well enough to be 'fitter' than others in its species, how does mimicry, or that mutation, survive. Also if instead, the intermediate step is actually suitable for avoiding predators, then why would the mantis continue to evolve and improve its disguise. Thanks.
|
[
"This is a very good question and addresses evolution in a broad sense, not just mimicry. ",
"A common misunderstanding about evolution is that intermediates are not effective, and from that misunderstanding people wonder how forms which we think of as \"finished,\" your flower mantis for example, could come to exist at all.",
"In order for a mutation to be beneficial, it only must be slightly so in order to become dominant over time. Say the original non-flowerlike, flower mantis ancestor developed some trait that made it and its offspring only slightly better at catching prey. Maybe the mantis hatched from its egg a white color instead of green and matched the petals of the flowers in its habitat. From there, any small change that made its descendants more like that flower would be a beneficial mutation. Since any mutation in this direction aids in fitness, even if only barely, over time the mantis species could evolve into what we see today.",
"The key is to realize that new traits don't have to be far better than older ones. They only have to be a little better. If you want more details, I would recommend The Blind Watchmaker by Richard Dawkins."
] |
[
"With a single insect, no it wouldn't make much of a difference. I haven't seen Blind Watchmaker, but I would assume it meant that across a population and over a period of time, the insects with 96% would eventually out-compete those which were 95% (assuming all other things are equal).",
"Edit: Gave it a watch, that's exactly what me meant."
] |
[
"I also wonder about this a lot and have a related concern; in ",
", Dawkins suggests that an insect that looks 96% like a leaf has an advantage over one that looks 95% like a leaf, but is this really true? It seems like if the difference isn't major enough, there isn't enough of a selective advantage for there to be differential survivorship, especially after you consider all the stochastic factors too. It seems to me like changes have to be quite significant for selection to be effective. Can you comment on this?"
] |
[
"when talking about climate change, why do we never talk about the heat that everything produces as a byproduct. Burning coal,nuclear power plants even the electrical grid gives off a ton of heat.Is the heat from the sun trapped in our atmosphere so much worse than the heat we create on earth itself?"
] |
[
false
] | null |
[
"Because it (waste heat) is small compared to radiative forcing driven by greenhouse gases. ",
"Flanner, 2009",
" estimated that globally waste heat contributed about 0.028 W/m",
". The forcing from greenhouse gases is ",
"3.0 W/m",
" (Figure 4)",
", or a bit over 100 times more. The Flanner paper does project that waste heat could start contributing measurably to warming by 2100, but of course this depends on how/if we change our modes of energy production as different ones produce different amounts of waste heat, along with projections of population growth, energy consumption, etc."
] |
[
"The excess greenhouse gasses produced since the start of the industrial revolution are currently adding 100 times more heat to the atmosphere than the waste heat of civilization."
] |
[
"It isn't mentioned because it isn't a controversial contributor. Water vapor is a known greenhouse gas and is taken into account in models. I believe the reason it's not discussed as often as something to reduce is it stays relatively low in the atmosphere and has a short life time relative to carbon dioxide."
] |
[
"There is 2 twins born equal. One has a bad lifestyle and becomes fat, the other works out everyday. Will the strong one's offspring be born with higher physical development potential than the fat one?"
] |
[
false
] |
Secondary question. Assuming the parent is not there anymore after birth. How much does how you live your daily life will benefit your offsprings if you compare an average healthy dad to an athlete healthy dad?
|
[
"According to traditional theories of inheritance, it won't make any difference. Any benefits you get from exercise won't be passed down to your children, because they only affect you. Just like breaking your leg or cutting your hair won't cause your children to be born with a weak leg or short hair. Having a parent or parents who promote healthy eating and physical activity is likely to have beneficial effects on a child's health for obvious reasons, but that's behavioural, not genetic. ",
"However, there's a lot of new research in a field called \"epigenetics\", which is about how what we do in our lives affects our genes. There's strong evidence that ",
"exercise affects how our genes are expressed within ourselves",
" by doing things like reducing the amount of inflammatory proteins that are produced, but I haven't been able to find much research showing that you can pass on these effects to your offspring. There is some research showing that being obese or eating a ",
"high-fat diet during pregnancy increases your risk of having an obese child",
", but I couldn't find anything specifically on exercise tolerance or strength."
] |
[
"How about if 2 people have 10 children, take the fittest one and the least fit one. Do the offsprings of each of those 2 share the same chance to having fit offsprings?",
"From the way you've asked the question, it sounds like inbreeding is a serious issue. I assume you're asking about two couples who each have 10 kids, and how different matchups of their various children, sorted by fitness, have implications on the fitness of the children? Keep in mind your question has abandoned the original premise of controlling variables related to genes."
] |
[
"The fitter children would likely have fitter children themselves and vice versa, because we're now dealing with genetic factors--we're taking kids that are BORN more or less fit, rather than those who worked out more or less during their lives.",
"Rather than fitness, which is a kind of murky concept and really complex, let's look at something that's more easy to think about, like height.",
"If you had a pair of twins, and one cut off part of her legs to make herself shorter and the other didn't, and they both had kids, would the one with the cut-off legs have shorter kids? No, that wouldn't make any sense. This is analogous (if we forget epigenetic) to your first example.",
"But if you had a couple that had 2 sons, and one was 6'2\" and the other was 5'5\", the 6'2 child would be more likely to have taller children. This is because the reason that person is 6'2\" is because they inherited more of the \"tallness\" genes.",
"This is in fact exactly how animal and plant breeders do their thing. This is somewhat simplified, but if you want a bigger breed of dog you can literally just breed the biggest puppies from each litter with eachother and over time each generation will get slightly bigger on average.",
"This is also how evolution works in the simplest sense, although it doesn't require a \"breeder\" guiding it--it just requires pressure from the environment. If an animal lived in an environment where the offspring who were bigger tended to live longer and have more babies themselves, the average size of the animals in that environment would increase."
] |
[
"You fill a glass with ice cubes, then fill the remaining volume with lukewarm water. At what point between the start (100% ice) and finish (0% ice) does the water achieve its coldest temperature?"
] |
[
false
] |
[deleted]
|
[
"Why do you think it must ever reach 0% ice? It might not. If the shape of the ice pieces were such that, say, 80% of the volume were ice, you'd have a glass filled with ice and water. I've seen this with crushed ice. The smaller the ice pieces, the less room there is for water.",
"Whenever the ice stops melting, that's when the combination is at its coldest."
] |
[
"That's all true but Be careful when throwing around words like 'coldness' since here it implies energy flows from the ice to the water which is definitely not true and in fact is never true. "
] |
[
"That's all true but Be careful when throwing around words like 'coldness' since here it implies energy flows from the ice to the water which is definitely not true and in fact is never true. "
] |
[
"If many symptoms of an illness are the body's response to a bacteria/virus/etc, what would something like the common cold do if we didn't have these responses?"
] |
[
false
] |
Things like fever, swelling, and fatigue are natural immune responses, so what bodily harm would the actual illness do? Sorry if the question wasn't clear enough. I'm asking what, specifically, the illnesses would manifest as, and what damage would be caused by a virus such as the common cold.
|
[
"Rhinovirus",
" is the main cause of the common cold. It's lytic in nature, which means in order to spread from cell to cell it bursts open the cells it has infected, effectively killing them. If you didn't have your immune response, the virus would enter your respiratory tract and slowly, but surely, destroy your lungs. ",
"Not all viruses are lytic in nature, but most hijack your cells' machinery for their own reproductive purposes, impairing the ability of those cells to function properly. So even if the virus doesn't directly kill your cells, it will still affect the normal functioning of whichever organ it infected.",
"As a side note, calling the people who are offering their help smart asses for not understanding your question is counterproductive. You can rephrase something without offending others."
] |
[
"Fever and swelling are part of your bodies way of fighting off infections. I am not sure with viruses, but many bacteria's proteins are only stable in a certain temperature range so when you get a fever, your body is trying to stop these proteins from functioning properly. Your bodies cells have a higher tolerance to temperature (to a certain degree) and can survive while invading cells may not. (not true for all infections)",
"Swelling is your immune response to get more white blood cells to the site of infection to help fight it off. ",
"So not having these responses would mean the infection would be able to get a better hold on your body, and eventually probably kill you, not too different to having AIDS.",
"Here is some material that talks about the immune response to infection that may answer some of your questions better!",
"http://www.nlm.nih.gov/medlineplus/ency/article/000821.htm"
] |
[
"Well, actually if you really wanted to know what would happen take AIDS out of the situation and go right for SCIDS. AIDS, doesn't eradicate your entire immune responses it only greatly depresses it, hindering any response futile in normal innate or adaptive immune response. SCIDS, or Severe Combined ImmunoDeficiency Syndrome (alymphocytosis) ",
"http://en.wikipedia.org/wiki/Severe_combined_immunodeficiency",
" is the body never develops an immune system (aka T and B cells) which is what you would need to fight a Viral infection, because the NKt cells, or the cells that phagocytose the pathogen would not be present. However the body would be able to mount an innate (inborn) response aka Macrophages, heamatopoietic cells (white blood cells eosonphils granulcytes etc etc) This would cause a pyretic response (fever) and release of TGF beta, interferon gamma. The down side to this would be systemic (whole body inflammation) Along with High fever. The death would be quite agonizing from such simple infections due to high fevers, which would cause delusions, tremors, seizures, neurological deficits from brain swelling (cerebral edema) So in summation the bodily harm would be catastrophic if you did not have an immune system, each infection could mean death.",
"Hopefully this is helpful! Cheers"
] |
[
"Since the air is over 70% nitrogen and humans require oxygen but only breathe out carbon dioxide, what happens to all the nitrogen that we inhale?"
] |
[
false
] | null |
[
"Nothing. We breath it in and out unchanged. Molecular nitrogen is very inert chemically, because the bond in it is extremely strong - that's incidentally the reason why almost all practical explosives are rich in nitrogen: the nitrogens in them can't wait to reorganize themselves into N2 molecules, liberating a lot of energy in the process.",
"A part of the nitrogen we breathe gets dissolved in our blood, but that still does not change it from N2. As the amount of dissolved nitrogen in the blood is pretty constant unless the pressure changes, there is not much happening - this is only important for divers, because breathing gas under high pressure deep underwater makes more N2 dissolve in the blood and its release when you climb back up is what causes the \"bends\" in divers, which can be fatal if proper decompression is not followed."
] |
[
"but only breathe out carbon dioxide, ",
"This isn't really right. ",
"The air we breathe out is slightly depleted in oxygen and slightly rich in CO2, but it's still pretty close to normal air, with about 70% nitrogen."
] |
[
"Breathing is primarily pumping nitrogen gas in and out of our lungs for no reason and with no effect. That's why nitrogen gas is so deadly. There are incidents if leaks in plants which use nitrogen gas industrially, and when the issue is discovered, there have some times been piles of dead bodies. ",
"One doesn't know they're suffocating when they breathe pure nitrogen. They just starve of oxygen and pass out. Someone sees the body, goes to see if they're alright, and the same thing happens again. Over and over."
] |
[
"Is it safe to eat uncooked bugs? Also, what type of bacteria and parasites live on other bugs?"
] |
[
false
] |
This summer has been pretty hot and I've been leaving the windows open. Consequently, it's been filling up with flies, bees, spiders, moths, and occasionally other things. On a whim I ate a spider, and this got me thinking about the safety of eating insects I catch, and I had a number of questions relating to this. Do bugs have bacteria,worms, or other parasites on/in them that makes them unsafe to eat? If bug carries a dangerous disease/parasite such as malaria or sleeping sickness, does the transmission of the disease mainly depend on one path (biting?/fluid exchange) or can it be transmitted through other methods? What about flies and other animals that live off raw guts or dung? Do the bacteria in the poop/guts rub off onto the bugs, making the bugs unsafe to eat? Regarding raw guts, roadkill, and poop, is it the bacteria and resulting infection that make you sick when you eat them, or is it toxins that are in the poop/guts? When the bacteria are inside of you do they multiply and secrete toxins? I ask that because I'm wondering how much volume matters. I would be eating moths and spiders I snatch for kicks, not trying to make meals. This also relates to the '5 second rule' and whether food that has touched the ground is safe.
|
[
"I don't have an answer for you, but more of a suggestion.",
"Keep munching on all the creepy-crawlies and keep us updated with a diary of how your body reacts.",
"What I do know however, is that you can normally ingest something venomous without feeling the effects of the venom, but eating something with a poison mechanism wouldn't be a good idea. Poison needs to be ingested for it to show its true effect, while venom needs to enter the body through other means, such as a bite."
] |
[
"My hunch is most of the parasites that are on bugs are specific to those bugs, and cannot do much to you. That said, parasites are crazy; they might use your stomach lining just as well as they used a beetles, for example. I wouldn't do it uncooked, since a lot of diseases are transmitted by bugs.",
"Spiders specifically, mind you, are eaten in some places. "
] |
[
"Bacteria are known to be ubiquitous, meaning, they're EVERYWHERE, even on us and other animals. But only a small percentage of known species are pathogens (disease-causing). As with parasites, most of them are microscopic, especially their ova/eggs which are carried by vectors like mosquitoes. ",
"Based from what I've learned, it's not safe to eat raw snails because they serve as intermediate hosts for a lot of parasites like the Schistosoma species. However, they're still not mature when they're inside the snails. Most of them are still in their egg form and are released outside when they reach cercariae stage. Humans and other vertebrates serve as their final host. They can't cause diseases to the intermediate hosts but they can cause dangerous ones to the final hosts. I'm guessing you're already familiar with Schistosomiasis. :)"
] |
[
"How does the gut microbiome recover after a very strong antibiotic course?"
] |
[
false
] |
Let us assume that a person takes a very strong antibiotic for over a month. I presume that this will impact the gut microbiome in a bad way. Now, how will the gut microbiome recover if most of it gets affected?
|
[
"This is in fact a problem.",
"The gut microbiome will usually slowly grow back, as you normally keep ingesting all kinds of bacteria which normally a part of it. But after strong antibiotic therapy it can happen that the composition of the microbiome changes in undesired ways. This can lead to chronic conditions, including food intolerances and certain types of colitis. ",
"In bad cases, it might require a ",
"fecal transplant",
" to restore the microbiome."
] |
[
"It can, and the transplanted microbiome has to be carefully chosen. If I recall correctly, the gut microbiome of close familar members is usually well compatible in general."
] |
[
"It doesn't have to be family members. The ",
"/r/HumanMicrobiome",
" wiki covers this in depth. ",
"/u/paradoxonium"
] |
[
"A few questions regarding the asteroid orbiting Earth NASA just announced..?"
] |
[
false
] |
So, I have lots of questions regarding this, many probably unanswerable. Could it collide with the moon? How could this affect things like our tides? How long has it been there? Could this arise in a matter of decades, or has it probably been there for centuries, millennia, or longer? Could we land our own satellites on it and take advantage of its apparently rather stable orbit? Would it be affecting our tides or weather at all? Could we see it with the naked eye, or with any at-home tech, any time soon? I presume it's unlikely to hit Earth anytime soon, looking at the article. How unlikely? Could it be mined for minerals? If anyone educated or experienced in anything related to this has any information, or even any guesswork, related to these questions, or even any more interesting info, I'd love to hear it :) I'm not used to being unable to google something and read pages of information on it, haha! Feel free to answer just one question, or even provide more info completely unrelated to my questions. Edit: RIP inbox. My mother always said I ask too many questions for my own good. Who needs Google, anyway?
|
[
"It isn't really \"orbiting\" in the traditional sense of a closed orbit with a definite period IIRC. It is a near-Earth object with a relatively stable orbit around the Sun. The earth's gravity tugs on it and affects its orbit, but it is outside of the Earth's \"Sphere of Influence\" (~0.01 AU or 1.5 million km), where Earth's gravity dominates. The moon on the other hand has a well-defined Earth-centered orbit (~384000km from surface) and lies well within the Earth's SOI. ",
"I am assuming this is the object you are talking about -> ",
"https://en.wikipedia.org/wiki/2016_HO3",
"As for your questions:",
"\n1. It is highly unlikely that it collides with the moon as it doesn't even come inside Earth's SOI. It's too far away and too small to affect the tides.",
"\n2. Orbital calculations indicate it has been a \"quasi-satellite\" for almost a century.",
"\n3. Well, technically you can send a spacecraft there. It is a matter of figuring out the trajectory for whatever type of mission you want. Depending on it's mass, the \"Landing\" may be more of a \"docking\" due to extremely low gravity.",
"\n4. The Wikipedia page says the object has an \"absolute magnitude (H)\" of 24. Magnitude is a way of defining brightness and the smaller the number, the brighter it is. For comparison, the moon full has an H value of +0.25. I think a difference of 1 in absolute magnitude translates to a 2.5x decrease in brightness (I may be wrong with the exact figure). So +24 is extremely dim. You would probably need a huge telescope to see it.",
"\n5. No idea really. I would think because it is in a relatively stable orbit w.r.t the Earth, we are safe.",
"\n6. Depends on what is on there. We really don't know much about it at this point. It is way too small and very far away. "
] |
[
"And would result in an unstable orbit, because the moon would continue to \"gravity assist\" the asteroid until it's ejected from earth orbit or hits something.",
"Here's a gif that demonstrates the idea. ",
"https://i.imgur.com/b6e3S0a.gif"
] |
[
"So it doesn't seem like it could collide with the moon, the article there states that our gravity keeps it within 38-100 times the distance of our moon at all times, so its far to distent to do that. ",
"it isn't big enough to effect our tides in any way",
"it is also fairly small, so with the naked eye id doubt, but wih star gazing binocs or a telescope you could, assumeing you could zero in on it (again its rather quite small)",
"based on the article it doesn't seem like it could impact earth. "
] |
[
"Do galaxies provide environments for certain types of stars to form within them?"
] |
[
false
] |
If we look at photos of different galaxies, we see that they come in different sizes, shapes, and color. Many galaxies have certain color schemes so that a given galaxy is mostly of that color (like some galaxies being predominantly yellow, some pink, some purple, etc). I understand that these colors come from stars at different temperatures, and this would mean that the majority of the stars in the said galaxy would be in a similar temperature range. Does this mean galaxies provide an environment of a sort, that promotes the formation of stars within that temperature range? Or is it simply pure coincidence when the majority of a galaxy is comprised of stars at similar temperatures?
|
[
"In terms of stars in a galaxy there's really two main things going on.",
"High-mass hot blue stars put out the most light, and live the shortest lives. Low-mass cold red stars put out the least light, but live the longest lives.",
"If a galaxy has active, ongoing star formation, then it will keep making blue stars, and the galaxy will look blue. If a galaxy does not have active star formation, then all the blue stars will be dead, and the red stars will be the dominant source of light from the galaxy.",
"Spiral shaped galaxies generally have active star formation and are thus bluer, especially in the spiral arms, while elliptical shaped galaxies generally do not have active star formation and thus are redder."
] |
[
"Another effect of ongoing star formation: the high-mass stars are luminous enough to ionise the surrounding Hydrogen, causing it to glow red when it recombines. It's called an ",
"H II region",
", and they can be quite prominent in ",
"some galaxies"
] |
[
"That's really cool! I see that the H II regions in the bottom picture are more or less punctuated. I'm assuming a single star isn't big enough to make such a large H II region. In this case, does this mean there are large \"hot spots\" within a galaxy where stars form more actively, like Pillars of Creation?"
] |
[
"If two objects collide on Earth, their kinetic energy is converted to other forms such as light and sound. But in space, it can't be converted into sound energy, so what would it get converted into? And would it be more destructive for the objects in question? Or am I completely misguided?"
] |
[
false
] | null |
[
"Heat. ",
"Depending on size and composition the objects would vibrate, undulate, or temporarily rearrange themselves for a little longer in space if their environment didn't easily remove their excess energy. Basically, they'd get warmer. Eventually they would radiate the excess thermal energy."
] |
[
"Isn't sound still a kinetic energy? In my understanding that collision would still cause a vibration of both objects, whether in space on not, with vacuum only disabling it from being \"heard\" anywhere. Assuming there is no medium to carry it through space, you could for example pick up the sound via laser microphone, amiright?"
] |
[
"yes the two objects would start to resonate. The effects of the collision i guess would be a bit more pronounced, when compared to the same collision happening in an air filled environment, because a fraction of the energy would be lost in making the air molecules vibrate. But i woulld guess the amount of energy lost that way is extremely small."
] |
[
"Do magnets have a shelf life?"
] |
[
false
] |
To be more specific, to rare earth magnets lose their power over time? If not, why do we not use this as a source for energy? Also would electro-magnets become less powerful over repeated uses? I know my terminology is way off but I'm not well versed in magnets and how they work.
|
[
"Check out this thread",
".",
"...rare earth magnets lose their power over time?",
"Yes, permanent magnets can lose their magnetism over time. Impact, heat, and strong magnetic fields (or combinations thereof) can shorten the life of a permanent magnet.",
"If not, why do we not use this as a source for energy?",
"Let's take the example of things that ",
" lose their \"power\": electrostatic interactions. An electron and a proton won't lose their charge, and therefore will always exert a force towards each other. Does that allow for a continual source of energy?",
"Let's take another example. You have a book on a shelf. You know it can fall, thus it has the potential for kinetic energy. Can you use it as a source of continual energy?",
"Just because some potential energy isn't lost over time doesn't mean it ",
" be used as a continuous source of energy. Magnetism, electrostatics, and gravity all have ",
", which is used up as soon as you transform it into another form of energy to be harvested. So two magnets stuck together, two charges stuck together, or your book on the ground is the final states in that system. In order to return to the original state, energy must be provided into the system: you must pull the magnets/charges apart, and you have to lift the book back up.",
"Also would electro-magnets become less powerful over repeated uses?",
"They do, but I do not know the precise mechanism. An electrical engineer or a physicist can tell you more about wear from high currents."
] |
[
"A magnet is, well magnetic, because the magnetic spins of all [most] of the atoms in the system are aligned. Their individual fields then add to make a macroscopic magnet.",
"Yet this alignment is most often not a favorable energy state. Often the disordered random spin orientations should be preferred.",
"So why doesn't it just change into disorder? They key here is that there is a barrier between ordered and disordered. In order to transition between the two each atom has to have enough energy to overcome that barrier. ",
"Imagine a guy standing with a bucket of baseballs with a wall in front of him. On the other side of the wall there is a big hill leading down to another guy. If that wall is really tall hes going to have to try really hard to get a ball over and most of the time he won't. It will just bounce off and land back where it started. However, every so often he will get a ball over, though that is rare.",
"Thus, every so often some of the atoms will indeed randomize their spin and hop over that barrier but it would take a long time for the entire magnet to randomize at room temperature. The atoms are effectively frozen, like water ice, in their macroscopic magnetic form.",
"Now when you apply heat, current or other magnetic fields to the system you are adding energy. This energy can give the atoms enough energy to hop over this barrier and randomize. Thus if you took a rare earth magnet and stuck it in a flame it would no longer be magnetic once its cooled."
] |
[
"Do these spontaneous randomization's happen more often at a preferred location (i.e. near the outer surface of the magnet)? Or are they randomly distributed over the material? Is the rate of decay influenced by the overall strength of the magnet?"
] |
[
"Why are the bars in bar-galaxies not immediately sheared by differing rotational velocities?"
] |
[
false
] |
We live in a bar galaxy, and we've observed many others. I don't understand why that's a stable formation. (I wanted to edit out of the subject, but I cant. By that I mean on galactic timescales.)
|
[
"Bars, and indeed spiral galaxies in general, are formed by density waves - that is, the structures are stable, but the placement of a given star within the structure varies. Mutual interactions between the stars keep the structure stable.",
"This is hard to get your head around, so here are a couple of animations - ",
"https://en.wikipedia.org/wiki/File:Spiral_arms.ogv",
" ",
"https://en.wikipedia.org/wiki/File:Galaxy_rotation_wave.ogv",
" These don't show bars, unfortunately, but the same general theory applies (as described in the paper linked in one of the other comments)."
] |
[
"The reason is that differential rotation does not occur in bars: it largely rotates as though it's a solid object. This is due to the orbits of stars in the bar. Rather than having circular orbits around the galactic centre they instead have either u-shaped or figure-of-eight-shaped orbits through the bar. ",
"Figure 8 in this paper",
" shows what such orbits look like."
] |
[
"That's a clear explanation, and the animation definitely helps. Thank you."
] |
[
"Why do people have nightmares?"
] |
[
false
] |
[deleted]
|
[
"This is a little difficult to answer, but I'll try my best, with the limited knowledge that I do know of sleep and one prevailing theory that one of my professors explained.",
"In Hobson et al.,",
", they propose that sleep has many functions, but one of them particularly involves our consciousness and how we perceive the world. They state that the brain is equipped with a virtual model of the world that generates predictions of its sensation, and that dreaming lays the foundations of waking perception. Basically, when asleep, our mind is trying to analyze our environment and come up with potential, probable situations that we may encounter. The premise of their hypothesis was that the waking brain engages with the world to predict the causes of sensations, while in sleep the brain's generative model is actively refined so that it generates more efficient predictions during waking. ",
"So, what the hell does that mean? Very briefly and simply put, our brain is trying to make sense of our environment and interactions that we have, and the outcomes for them. Then, during sleep, the brain organizes this material in order to predict future situations and their outcomes. It is important to note that they go on to state that the content of dreams is ",
" a prediction of what will happen, but an exploration of what could, or could not, happen that is necessary to minimize model complexity - making it a more efficient model of the experienced world on waking. ",
"So how to nightmares come in to this? Well, using the study above, you might conclude that nightmares are our brains telling us this situation ",
" happen, and thus we should be prepared for something like it; it is similar to bayesian probability in which our mind assigns probabilities to potential events, compares it to what is \"known\", and then spits out a probability for that certain thing from happening/appearing. ",
"In short though, we are not exactly sure, though there are some other theories out there (unfortunately, I am not well versed in any of them), but it seems to be that nightmares are our brain's way of reminding us that there is a chance, however small, that that situation may come up, and it needs to be ready to perceive the threat, and correctly predict the most common outcome and then take action. Sorry if this is all over the place, cognitive neuroscience is not one of my strong points and the \"whys\" of consciousness can get very complicated very quickly, and require some abstract thinking. Hope this helps. "
] |
[
"Oh don't worry, you're fine! And to be honest, I don't have an answer for you about that specifically. If you look at ",
"this post",
", you'll see that a guy literally lived another life while unconscious after being knocked out. It's a very interesting read simply from a cognitive neuroscience point of view; anyways, anything is simply possible. \"Heightened brain function\" can refer to a plethora of different things, and yes, you very well be right that certain people can predict future events better than others. It's a bold claim, ",
" also may have some validity. But like I said before, I have no idea. Maybe someone else can answer this question better than I can. But neuroscience, and cognition, leads to many theories - and we don't know exactly the hows and whys just yet. "
] |
[
"Does this mean (and I may sound completely stupid or ridiculous here) that people who claim to 'see' the future and future events may just have heightened brain function while asleep. So their brains are better at making sense of their environments as well as being better at organising and predicting future situations and their outcomes.",
"Sorry if this doesn't make sense it was just a thought when reading this thread, very intriguing. I'm sort of new to the whole reddit thing, especially ",
"/r/askscience",
", so again apologies "
] |
[
"Sustainability question regarding using the sun's energy to convert water to H and O2."
] |
[
false
] |
In the scenario, solar energy is used to produce electricity which is used for electrolysis of water. The hydrogen could be used to power just about anything (cars, trains, buses, generators, etc...) and the byproduct would be water vapor. Knowing that this could never be a 100% efficient process, is it feasible to produce enough solar electricity to make money on selling the hydrogen?
|
[
"Just be warned that this is without doing any mathematical calculations and just looking at second law of thermodynamics. Since there will be energy lost in using electrical energy to get hydrogen, why not just directly use electrical energy generated? ",
"Converting to hydrogen will be same as storing energy but will require massive infrastructure. Doesn't really help much. "
] |
[
"because it can be faster to fill a tank of hydrogen than recharge a battery in a car."
] |
[
"Upvoted.",
"I can see why that would make sense."
] |
[
"US Solar Industry"
] |
[
false
] |
Hey , I've been looking for information on this subject for a while. I was wondering what everyone knows about the solar industry in the US. I've always been interested in working in cleantech/alternative energy and I was hoping someone could tell me more about the state of that industry in the US (especially with the economy as it is and the reduced manufacturing costs in China). If not solar, what else looks promising in the US, or even Europe? PS: I'm studying Industrial/Processes Engineering.
|
[
"I install solar in Hawai'i and the it's just to cost prohibitive for most people even though we pay some of the highest electrical rates in the nation.\nI keep on hearing about all these great new developments i.e. spray nano panels and nanogel batteries, but I've yet to see them for sale or installed any. I would say that panel cost reduction and battery improvements are a must before the mainstream is able to go solar.\nhope that makes sense and helps\nAloha"
] |
[
"From your perspective, besides bringing down the cost of the panels and inverters themselves, what else can be done to reduce your installation costs? I'm thinking along the lines of: what can be done to help you do your job quicker and cheaper (and more profitably)?",
"Also, can you recommend any online communities or other resources where solar industry professionals congregate? On reddit, ",
"r/energy",
", ",
"r/solar",
", ",
"r/renewable",
", ",
"r/renewableenergy",
" seem to be more about shouting down the opposition than actually talking about the industry."
] |
[
"The only way is bring down the cost of energy systems and create fair financing options for homeowners. As far as making my job easier, it's already pretty easy. \nI don't know of any industry sites, I just walked up my local windmill installer and told them I have my own tools, truck and I learn fast and work hard... put me in coach! And I was on the working on the site the next day.\nDon't know if that helps but thats how I got into the industry."
] |
[
"[Computer Science] Why do torrents slow down as you're reaching the very end?"
] |
[
false
] |
followup question: Are there any clients that intentionally employ "bad torrent practices" to ensure the best download speed for the individual at the expense of the swarm?
|
[
"Because you need a specific bit.",
"The more specific a bit you need, the less likely it is that people who are not done with the torrent have that bit",
"Since the people who share the most, are the people still getting the torrent (most people stop sharing after done) the fewer bits are left, the smaller the chance that a lot of people have that bit to share with you"
] |
[
"The answers so far are no more than partly correct. There ",
" a real effect caused by a lack of 100% seeders, but it's not the main effect in play here. You don't mean a gradual slowdown, like in the last 10-20%, but rather your DL rate cutting to almost nothing in the last 0.25-0.50%, right? I know what you mean. ",
"Usually, when you're downloading, you're getting chunks from peers at a ",
" of different speeds. One peer might be sending you chunks at 2mbps, one at 500kbps, and 3 at 10kbps each. Now suppose you're in the last 1% of a download, and you're downloading all the remaining chunks at once from these peers. The chunks from the fast peers finish quickly, and you're left with just a couple of chunks from the slow peers - and so your download rate slows dramatically. ",
"In theory, a client could just drop the chunk from a slow peer, and download it again from one of the fast ones, but I don't think any of them do this and it's considered a bad practice - I could see it messing up the ratio tracking a lot of trackers do. "
] |
[
"It's called \"endgame mode\" in uTorrent. When all chunks yet to be downloaded has been requested from somewhere, it will start making duplicate requests for those chunks to all connected peers."
] |
[
"Why do some organisms age faster than others? What determines how fast an organism ages?"
] |
[
false
] | null |
[
"The rate at which an organism ages has all to do with the natural selection of its life strategy. This means: organisms that are at a higher risk of dying early on in life, evolve to mature quicker so that they can reproduce sooner. "
] |
[
"But on a more micro scale, what pressures would lead to a longer lifespan? How could longer-living people be selected for if by the time they get old, they are either dead or not suitable for mating. ",
"Hopefully my question is clear."
] |
[
"Life history strategies. Organisms that are easy pretty and likely to get killed often have fast life history and will reach reproductive age very quickly and produce many offspring at a time with relatively little parental care for those offspring. Animals with slow LHS, like humans and elephants, mature slowly, have long gestation periods, produce fewer young at a time, and their young require more parental care after being born. These are the organisms that are less likely to get gobbled up early on in their lives. Natural selection most likely selects for these traits that cause animals to have fast or slow life history strategies. If mice did not reproduce quickly, they would get eaten and never get a chance to produce offspring. Thus, natural selection will select for those traits that allow the organisms to reproduce successfully."
] |
[
"What is the highest level of antibody in the body when healthy?"
] |
[
false
] | null |
[
"Which antibody?"
] |
[
"thats my question. Is it antibody A, G, D, M, or E that is highest in a normal, non-sick, person"
] |
[
"Oh I see. Then the question should be \"which antibody...\" Please make a new post."
] |
[
"How and why does lactose intolerance suddenly happen in adults?"
] |
[
false
] | null |
[
"So in most people, lactase, the enzyme that breaks down lactose, stops being expressed (made by your body) after childhood (when you would no longer be drinking your mothers milk back when we lived out in the wild) Making the enzyme costs your body energy it could be using elsewhere and so we have evolved to stop making the protein after childhood. However, in some Northern European and African populations, people have had mutations to the pieces of dna that dictate when lactase is made which in turn results in what is called “lactase persistence” or lactase being made your whole life. "
] |
[
"To add to this, the switch to lactose tolerance was evolutionary, which caused the gene to persist after the random mutations. Those populations that show lactose tolerance where those who lived with domesticated cattle to produce milk. Being lactose tolerant was an advantage, allowing individuals to consume more nutrition directly from raw milk, as opposed to those who were lactose intolerant who would have to process the milk to lower lactose cheese before being able to gain nutrition from it. Over the generations, those who were lactose tolerant were stronger more apt to live longer and breed more; therefor propagating the lactase creating genes. If there was no evolutionary pressure, lactose tolerance would be a random distribution that would change from generation to generation, instead of the geographical and cultural clusters that we see it as today. "
] |
[
"Let’s also not cook our food and live without shelter and not use technology. Like all other mammals."
] |
[
"If you painted a room with 5 gallons of paint would the rooms volume decrease by 5 gallons?"
] |
[
false
] | null |
[
"A ",
"significant fraction",
" (around 60%) of the mass of the paint in the can is solvent, which will evaporate and not add to the volume occupied by the dried paint.",
"Also, it would be a fairly big room to need 5 gallons of paint!"
] |
[
"The interior volume of the room would decrease, but almost certainly not by the total volume of the cans of paint.",
"Aside from incidental losses (like paint drips on the floor and the painter, plus paint left on the brush or roller) the applied paint would also soak into the wall to some degree. Most importantly, however, would be the water or other volatile compounds that would evaporate away as the paint dried. This ",
"industry page",
" indicates that actual solids in a can of latex paint only account for 33% of the total paint contents. ",
"Total decrease of the room's volume could be significant, particularly for small spaces - see ",
"this picture",
" of the thickness of multiple layers of paint. However, the ",
" of the paint is probably more frequently an issue - as has been the experience of NASA with the ",
"space shuttle.",
"(This is a good question!)"
] |
[
"According to Lowe's, one gallon of paint covers 350 sq. ft. ",
"source",
". I'm assuming that that figure takes into consideration the evaporation of the solvents and the absorption by the wall. I don't know how thick a typical coat of latex is, but let's say it's 2 mil. So the volume of an imaginary rectangle on a 35' x 10' wall painted 2 mil thick would be 420 inches x 120 inches x .002 inches = 100.8 cubic inches, or just under 0.5 gallon (1 gal = 231 ci). So, the case you asked about would be 5x this, or just over 2 gallons loss of space."
] |
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