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[
"What is the smallest weight difference perceivable by the human hand?"
] |
[
false
] |
What is the smallest weight difference between two objects that I would be able to notice just by picking the objects up?
|
[
"Its called Differential threshold or 'Just Noticeable Difference' and theres too many factors to give it a value"
] |
[
"There's a law in my medical physiology textbook (which I can't recall currently but will update when I find, but it might be \"Differential Threshold\" mentioned before) that stated humans can detect about 10% change in sensory stimulus.\nFor example, if you are holding 10g, you can detect a 1g increase. However if you are holding 100g, it will be very hard to detect a 1g increase but a 10g increase will be noticeable (to the same extent that the 1g change was previously).\nAs for the absolute minimum that we can detect, I'd assume it would have to do with the touch (which is essentially a pressure change) receptors on your skin, which vary depending on the region you are talking about. But free nerve endings are the ones which detect even the slightest touch (like the touch of a feather). For example, a slight cotton wisp touch on your cornea causes you to blink (corneal reflex) and free nerve endings on your eye are responsible for detecting the force exerted by the cotton wisp.\nIf you are talking about the actual weight that we can estimate accurately, I'll let an expert physiologist answer that.",
"Source: Guyton Medical Physiology 12th edition"
] |
[
"Exactly, There might be an average out there, but there are varying levels of sensitivity involved. "
] |
[
"What is the significance of the c^2 term in Einstein's famous equation (E=mc^2)? Does it reflect some sort of radial symmetry?"
] |
[
false
] | null |
[
"If you take the length of something and square it, you get an area, not another length. If you take a speed and square it, you get distance",
"/time",
", not another speed.",
"Saying c",
" is faster than the speed of light doesn't make any more sense than saying an acre is longer than a mile."
] |
[
"The best way to think of it is as a conversion factor. When we look at the mathematics of relativity, it's all much simpler and much more symmetric if we choose units such that c=1, a unitless value. These units are therefore called natural units, and in using these units, we find that for an object at rest E=m. Of course, if we're not working in natural units, then we need the appropriate conversion factor, since energy and mass don't have the same units in, say, the metric system. Therefore, we find that E=mc",
".",
"A consequence of this is that, since c is very large when expressed in units which are closer to human experience, such as meters and seconds, the c",
" factor is even larger in these same units. That means that if we convert mass into usable energy, it takes a very small amount of mass (to us) to produce a very large amount of usable energy (to us)."
] |
[
"A co-worker of mine ridiculously claims that since nothing moves faster than then the speed of light, the speed of light squared doesn't mean anything",
"Did you point out that c+1 = c+1 just means c = c but represented differently, and nothing breaks the speed of light there?",
"e = m * c",
"is also",
"m = e / c",
"is also",
"c = √(E/m)",
"is also ",
"c = (E/m)",
"et cetera, et cetera."
] |
[
"Is there a more technical name for when something 'settles'?"
] |
[
false
] |
The only two things I can think of is nail polish and mustard. If you leave them for a long time the water/liquid moves to the top. Shaking/stirring it up put it back to rights.
|
[
"An emulsion is a type of colloid in which one liquid is dispersed through another (immiscible) liquid. Colloids are basically mixtures of materials where one is dispersed through another. ",
"http://en.wikipedia.org/wiki/Colloid",
"In actual fact I think both nail varnish and mustard are probably sols - a type of colloid in which a solid is dispersed through a liquid.",
"The process of the dispersed phase coming together is known as aggregating, segregating, or flocculating, and it can then settle out. There's nothing wrong with using the word 'settle'."
] |
[
"I believe the term is ",
"Emulsion",
". Segregation is when it seperates out."
] |
[
"There's also sedimentation."
] |
[
"How does total pressure (as supposed to partial pressure) affect the diffusion of components in a mixture?"
] |
[
false
] |
Scenario A: You have a tube with a permeable membrane in the center. On one side 50/50 water and alcohol on the other pure water. Pressure between the sides are equal. Scenario B: it's exactly the same as scenario A except that at time 0 you inject an amount of water into the 50/50 side (making it no longer 50/50). So Volume, molarity of alcohol, and temperature haven't changed but pressure has. How does the diffusion of alcohol compare between the two scenarios?
|
[
"I'm having some trouble parsing this. If you add water into one side then volume and molarity of alcohol both change. Volume changes because liquids aren't compressible. By \"molarity\" do you mean the amount of alcohol? Because molarity means molar concentration."
] |
[
"A simpler version of this would just be \"pressure is applied to the 50/50 solution side of the membrane\". Like ",
"u/Twink_Ass_Bitch",
" said, what happens depends on how permeable the membrane is. If it's permeable to both, the solution from ethanol side will move to the water side until pressures are equal. If it's only permeable to water, the water will move from the ethanol side to the pure water side until the pressure is equal to the osmotic pressure forcing water back to the ethanol side (bearing in mind that the osmotic pressure will increase in the process, because the ethanol side will contain less and less water)."
] |
[
"Tell me if I'm off base here but it was my understanding that liquids are only mostly non compressible. That liquids being non compressible was a rule of thumb because for most things they are. But in reality they simply have very large changes in pressure for small changes in volume.\nMolarity is moles/Liter. And in the scenario I changed neither volume or moles of alcohol."
] |
[
"As humans what fears are we born with and which do we learn?"
] |
[
false
] |
I always presumed we were born with the fears of falling and loud noises. The rest to me was picked up from our adult peers. Is this assumption correct or are new borns hardwired with other survival instincts?
|
[
"According to psychologists James Kalat and Michelle Shiota in their book ",
", \"Sudden, loud noises frighten virtually everyone, from birth through old age. That fear is also present in virtually all other animal species, except those without hearing.\" They next suggest that separation from loved ones may be another innate fear, citing the work of Shair et al. (2003) who found that many mammalian infants share a similar distress response in reaction to separation from their mother.",
"Although we do not have a innate fear for snakes and spiders, the fact that humans can learn this fear so quickly suggests a \"built-in predisposition to learn them (Öhman, Eriksson & Olofsson, 1975; Seligman, 1971)\". The authors expand on evolutionary research and monkey studies. Most importantly, it is noted that studies have found that (in monkeys) this predisposition is unique only to snakes. \"Ordinarily, laboratory-reared monkeys show inhibition and withdrawal from snakes the very first time they see one.\" Mineka (1987) found that \"if a monkey watches a movie of another monkey running away from a snake, it develops a fear of snakes, but if it watches an edited movie showing a monkey running away from flowers, it develops no fear of flowers.\" ",
"Evidence for this predisposition in humans is weaker, but still suggestive. Humans who get shocks paired with pictures of snakes show a conditioned physiological response (increased breathing and hear rates) very quickly, as opposed to those who got shocks paired with pictures of houses who developed weaker responses (Öhman, Eriksson & Olofsson, 1975).",
"The authors note other that other explanations for this do exist, though. \"For example, unpredictable, uncontrollable events are more stressful that ones we think we can control. Snakes and spiders pokes unpredictable dangers, whereas hammers are unlikely to attack you by surprise.\"",
"Source: Kalat, JW & Shiota, MN. (2012). ",
". Belmont, California: Wadsworth Publishing. (Pages 158-160)."
] |
[
"Falling, loud noises, and any experience that causes pain are the only natural fears."
] |
[
"Interesting stuff.... thanks for the responses:)"
] |
[
"How realistic is the cancer \"vaccine\" talked about recently?"
] |
[
false
] |
A recent post to is talking about a cancer "vaccine" talked about in this . All sorts of claims have been made about cancer in the post. So, how realistic is this?
|
[
"So, immunotherapy has long been seen as a holy grail for cancer treatment. The immune system is naturally programmed to attack cells that have gone a bit weird (to use the scientific term). The problem tends to be that the cancer cells can also alter themselves so that they are disguised from the immune system, or in fact inhibit any immune cells that come into contact with them. This stops the immune system from seeing them as dangerous, allowing the cancer to grow. So the balance of the immune response is in favour of leaving the cancer alone.",
"What this treatment does is inject the tumour with molecules that tell the immune cells in the vicinity of the tumour to wake up and start doing their job, overcoming the inhibition that the cancer cells have put in place. This means that the balance of the immune response is now to attack the tumour, which seems to work very well.",
"The really cool thing is that now that the immune system is trained to see the tumour as bad, and will attack similar cells in different sites. This is why it behaves in some fashion like a vaccine.",
"It's perfectly viable, and very exciting. As always, there is always the question of how well it translates into human biology but it is still very promising. I think one problem is going to be how specific the immune response is. In the paper, they see the immune cells are trained to attack cells with protein markers unique to the tumour cells, which is a good sign. One concern might be that if you accidentally trigger the immune response to normal cell markers, it could cause your immune system to attack healthy cells which would obviously be a very bad consequence. Another would be how readily a tumour can evolve to overcome the immune system attack. If the immune system only ends up going for certain markers, it could miss tumour cells that don't have the same ones. These could then continue to grow and cause the cancer to return.",
"ETA: thank you kind, golden stranger!",
"...strangers!"
] |
[
"Frankly, in a field where even the possibility of inching forward is worth celebrating, it's very nice to think we may be able to take a full stride."
] |
[
"Ah, I see. Thanks for the information.",
"So, in summary it is very promising, however there are still some concerns that need to be further looked at."
] |
[
"I've always wondered: What is the evolutionary advantage of acne?"
] |
[
false
] |
Well, there probably isn't any, but what's the advantage of the increase in oil production that causes it? Before you hit puberty, your skin is clear and seems perfectly healthy. During and after puberty, your pores go haywire for no apparent reason, the only noticeable effect of which is a proclivity for infection and swelling. Why on earth do they do this?
|
[
"For a trait to be retained, it doesn't necessarily have to be evolutionarily advantageous - just not disadvantageous.",
": Please see ",
"this comment below",
" for a more complete answer to OP's question."
] |
[
"Subem is that oil, from the sebaceous gland, that P. acnes, the anaerobic bacteria that causes acne, likes to live in. Subem would normally waterproof hair or fur in other animals, but humans don't have enough for this to be effective. ",
"The trait is probably neutral, but since it does cause acne it may even be deleterious and selected against. Human concepts of time are too short however for us to notice any change if that were the case."
] |
[
"This means that people with acne have, at least in the past, been able to procreate at some time. Fear not!"
] |
[
"Somebody please explain how sidewalks and roads crack?"
] |
[
false
] | null |
[
"Most often from the material expanding (heat from sun) and contracting (cooling at night). The never ending cycle cracks the material. Once cracked, water can get into the structure and freeze. This accelerates the deterioration.",
"Secondarily, the sub-base can settle if not properly compacted. It can also bulge when the soil underneath expands due to moisture (look up expansive soil).",
"Earthquakes, erosion, excessive heavy traffic all can contribute.",
"Lastly, tree or plant roots can raise or crack these materials."
] |
[
"Metals rust and therefore become weaker and unattractive. It would be costly to change or take care of them. Also, the fact that metals are typically good conductors and therefore not so safe. However, rust is an insulator so that problem is solved when metal rusts(I'm not sure how good of an insulator it is though) "
] |
[
"Would a metal road peform better with respect to these issues? What are the disadvantages of a road made of metal?"
] |
[
"Should I throw a apple core when in the outdoors or just keep it and throw it to the garbage later?"
] |
[
false
] |
So I was eating an apple at the beach the other day and it got me thinking. Is it less harmful for the environment if I just throw the core or any organic waste right in the outdoors or keep it and throw to the rubbish instead, where it will be together with a ton of non organic materials that will not decompose? And what do YOU do?
|
[
"In the Environmental Science class I TA'd for in grad school, each semester we had a guest lecturer from the local landfill come to talk about what a landfill is, how it is constructed, how it works, etc. etc. etc.\nShe actually made a point of saying that due to conditions in the landfill (compression and anoxia were mentioned, off the top of my head), an apple core will take significantly longer (on the order of tens of years) to decompose in a landfill than it would otherwise.",
"Tossing it on the ground isn't always the best. As others have said already, there's the issue of seeds to consider. Plus, it will still take time to decompose, and some people may not take too kindly to a rotten apple core laying about on the beach/hiking trail/suburban lawn/side of the highway/wherever. Be considerate. Think about where you would be tossing it. The best option may be to save it and compost it later."
] |
[
"As a back packer, I can say that you should be careful what you do with organic waste that may contain seeds. There's almost zero chance that your apple core will result in an apple tree that disrupts the ecosystem of your suburb. However, if you are in a national park or some other delicate ecosystem, just pack it out."
] |
[
"I don't meed in the streets. I mean when you are in the mountain/beach/forest."
] |
[
"How does the electromagnetic theory of light explain intensity?"
] |
[
false
] |
Before Einstein introduced the quantum theory of light, what was the explanation given for different intensities of light of the same frequency? Because intensity is amount of photons per area per second but that means you had to consider light as quanta which the em theory didn't do. Is there any fault in my thought process? Thank you!
|
[
"Photons are not necessary to understand the intensity of a classical light wave. The explanation you mention is just how the quantum description of light is reconciled with the classical theory.",
"The classical case of electric dipole radiation is worked out ",
"here",
". You can see that the field strengths have an amplitude proportional to the dipole moment, and then the calculation is carried through to the Poynting vector and the radiated power. There’s no mention of photons anywhere, because it’s a classical treatment."
] |
[
"Electric and magnetic fields can have about any strength you want. If you set up a giant capacitor, you can crank it up to generate an electric field inside as strong as your equipment can handle.",
"In an electromagnetic wave, you have an oscillating electric field that generates an oscillating magnetic field that generates an oscillating electric field and so on, propagating on and on until something external makes it stop. A strong electric field makes a strong magnetic field, which makes a strong electric field, and so on. And vice versa.",
"The intensity of the light just comes from the intensity of the electric and magnetic fields. You can plug either into the equation because they're both proportional to each other. It comes out to the square of the peak strength of either the electric or magnetic field, multiplied by a constant (a different constant depending on if you're using the electric or magnetic field strength).",
"This wave is propagating in a direction, which means you can definitely define a ",
" - i.e. what quantity of energy is flowing through some surface - which is the same as the intensity of light hitting a surface."
] |
[
"Thanks! I found a similar explanation on stack exchange some time after making this post, thanks for confirming!"
] |
[
"As the Sun loses it's mass does this mean that it is also losing it's gravitational pull on the Earth causing the Earth to move further away from the Sun?"
] |
[
false
] |
[deleted]
|
[
"Yes.",
"The sun is slowly losing mass, which implies that the orbital radii of the planets is gradually increasing (though this is very insignificant). Also, when the sun begins to transition to a red giant, it will shed about 1/3 of it's mass, causing a significant change in orbits."
] |
[
"So we're doublefucked. Sun is dying and we're getting farther away. And the sun gets to swell up until it nearly engulfs earth, before it dies. The future feels depressing. We run out of resources, our Sun dies, and the entire universe expands until rips itself apart. Does it have to be that sad? "
] |
[
"It's so far away we will likely have moved to another planet/solar system/galaxy or exterminated ourselves by then. Also consider that homo sapiens as we know them have only been around for about 200,000 years, so it's also likely that we won't be the same species. A lot can and will happen in the next 5 billion years.",
"If you want to get philosophic, consider that in a millennium, nothing you did will be remembered, and none of it will have any significant effect on the future anyway, aside from procreating."
] |
[
"What are our realistic alternatives for a smooth transition from fossil fuels?"
] |
[
false
] |
With world oil production being at a plateau since 2005 with an expected terminal decline within 1-4 years, it's past time we found a way to retrofit our current infrastructure. Are there any viable sustainable alternatives?
|
[
"I'd be interested to see where you got those numbers. The oil companies have found significant new reserves in the last few years, and the increasing oil price is making formerly uneconomic reserves economic again.",
"Either way, to be frank the only other power source we have which can produce anything like the levels we need in a reliable manner across the world is nuclear. We will still rely on petrochemicals where high energy densities are required, such as in aviation. However, electric cars have come on leaps and bounds in the last decade, and would be a feasible technology for a nuclear-electric economy."
] |
[
"Only nuclear, by at least an order of magnitude."
] |
[
"It would almost certainly be through biofuels. There's been quite a lot of work in developing 'drop-in' biofuels, that is biofuels that behave similarly enough to traditional jet fuel that the plane does not have to be modified.",
"EDIT: Oh, and for the OP, you should enjoy reading this blog. ",
"http://physics.ucsd.edu/do-the-math/post-index/",
"\nIt's pretty blunt about the challenges we face transitioning from fossil fuels."
] |
[
"Is the Copenhagen interpretation still the leading interpretation of QM, or have others like the hidden variable interpretation made any ground?"
] |
[
false
] | null |
[
"People usually choose to drop locality because no-one has a good way to understand what dropping realism means.",
"No way, most people drops realism, this is why non-local theories with hidden variables (eg Bohmian mechanics etc.) are not that popular. Dropping locality leads to huge troubles with relativity.",
"Dropping realism is also not that hard to understand: it \"just\" means that things you do not measure do not have assigned values and you can't really speak about them. So, using your ball in a box example, dropping realism means that just because you found a blue ball in one box, you cannot from this say that the other ball is red. Well, you can say it, but its not really a meaningful statement, until after you've opened that box and checked. This is in technical terms called not having counterfactual definiteness. And sure, it's weird and not very intuitive, but this is what one does in the Copenhagen interpretation and its relatives. "
] |
[
"As an Everettian, I'd like to claim that the Everett (many-worlds) interpretation has gained some ground, but I feel like I'm going to get some pushback on that.",
"In any case, I'd say regardless of whether anything else has been gaining much ground, Copenhagen has probably lost a fair amount of ground - for example, David Mermin calling it ",
"shut up and calculate",
" and Asher Peres saying - ",
"in an article",
" that seems to support Copenhagen, but deny it standing as an interpretation in the philosophical sense - that \"There seems to be at least as many different Copenhagen\ninterpretations as people who use that term, probably there are more.\"",
"Psi-epistemology - the idea that the wavefunction isn't \"real\", so most hidden-variable theories except pilot-wave - has also lost ground recently, thanks to the ",
"PBR theorem",
", which says that under a modestly broad set of assumptions you can't have a hidden-variable theory. Though I should say there are still a number of people who believe those assumptions are wrong."
] |
[
"Just for fun I will talk about Popper's interpretation (related to the ensemble formulation) since it isn't much discussed among physicists. ",
"In this interpretation we take quantum mechanics as a statistical theory from the start, after all we cannot reason from non-statistical premises to statistical conclusions. The key here is that we take the wave-function as a real object (it can be \"kicked\" and it \"kicks\" back). We also talk in terms of propensities: probability as a singular statement that resolves into long-run frequencies on repetition (this is an indeterminist theory). Crucially we deny that the wave-function is a property of individual particles, it is a property of of the experimental (or natural) set up and attendant boundary conditions as well as the particles. So we immediately remove the wave-particle duality as a result of this without losing explanatory power. States in Hilbert space correspond to statistical assertions of the theory, we can measure the position and momentum of an individual particle to arbitrary precision together (often through retro-dictive techniques but EPR has his back here) but we cannot predict average outcomes of these measurements at the same time due to the statistical scatter entailed by the uncertainty principle. Popper argues further that without being able to make these precise measurements we could never test the uncertainty relations in the first place (statistical scatter test requires a finer resolution than the scatter to hope to be accurate). This brings up the role of the Heisenberg uncertainty relations, they are a statistical scatter relation, and respond to our experimental set-up as a result of this. Rather neatly we explain the double-slit experiment in terms of the way the number of slits \"kick\" the probability distribution of the experiment, there is no messing around with \"how does the electron know which slits are open?\".",
"An indeterministic and objective formulation of quantum mechanics without the messy subjective-objective switching that goes on in Copenhagen or the untouchable/untestable metaphysics of many-worlds.",
"The weak points? Well we might run into trouble when considering mixed states (but this doesn't seem overly difficult because of the distinct probability types being employed). We might also wonder about whether the interference of our propensities makes sense in the double slit, should individual slit propensities both appear when both slits are open? Some authors have argued that there is no reason to suppose they should (I find this interesting but a bit weak as refutation attempts go). A more serious one is about the nature of propensities as valid probabilities, Popper himself wasn't bothered by this, viewing them as \"explaining quantum behaviour\" rather than giving a general account of all abstract probability.",
"On the whole I would say its flaws are less serious than Copenhagen (not saying much here), which tends to dodge criticism by being vague or simply by switching between objective and subjective language on a whim."
] |
[
"How are telescopes and space observatories arranged at the L2 Lagrangian point so they do not interfere with each other?"
] |
[
false
] | null |
[
"Spacecraft placed at a Lagrangian point are not literally parked at that singular point in space. In reality, they are placed in orbits with the L-point at their center. ",
"For example, the JWST will orbit L2 at a distance of about 800000 km (500000 mi). There is plenty of room. The L2 region is essentially empty space."
] |
[
"There's actually only one spacecraft currently located at the Sun-Earth L2 point - ",
"the ESA Gaia probe",
". Previous missions to L2 were moved to heliocentric orbits after the conclusion of the mission to avoid interference with future missions.",
"Because L2 is unstable, spacecraft located there have propulsion systems that allow them to make adjustments and stay at the Lagrangian point. As long as the different projects are aware of the positions of the various different L2 missions, I don't think it would be likely to have any collisions. And of course, the spacecraft themselves aren't massive enough to exert any non-negligible gravitational interactions on each other."
] |
[
"Spacecraft there typically avoid the shadow of Earth, to do that they go in a wide (pseudo-)orbit around L2. But even if they would not: A few thousand kilometers don't matter there. For practical purposes L2 is actually a region of space orders of magnitude larger than low Earth orbit, where thousands of satellites fly around at high relative velocities. We can't launch enough satellites to make L2 crowded enough to worry about interference."
] |
[
"It is very difficult to find unbiased information about GM crops."
] |
[
false
] |
I would really just like some suggestions of books or websites that offer solid, but not too technical, unbiased information about genetically modified crops/food. My goal is to come to my own conclusions about the pros and cons of GMO's and their effect on health and the environment from sources that aren't trying to persuade me one way or the other. I would prefer it to be from scientific, tested, and peer-reviewed sources that aren't written like a scientific, peer-reviewed journal articles, as I don't have a strong science background. Can anyone help?
|
[
"If I knew such a source and I pointed you to it, then how would you know ",
" was unbiased? Maybe I'm pointing you to a biased source which I think is unbiased because of my own biases...",
"Moreover, you're asking the wrong question. Asking whether GMO crops are bad for you is like asking whether \"plants\" are bad for you -- it really depends which plant you're eating. There's nothing that makes crops magically \"bad\" just because they've been genetically modified; on the other hand specific genetic modifications can potentially pose health or environmental problems (eg. if I modified my apples to produce rattlesnake venom).",
"Now, as for health problems caused by specific GM crops that actually ",
" rather than which are silly examples I just made up... I doubt there are any. The simple sorts of genetic modifications we've done so far are just to create an extra protein in a known substance (eg rice with extra Vitamin A) and the qualities of the novel protein should be well known. The ",
" for environmental problems, on the other hand, does exist -- for instance many crops are modified to be herbicide-resistant (encouraging farmers to use more herbicides) and there's also the possibility that having less genetic diversity in the world's crops (ie if all farmers are using genetically identical strains) could cause problems down the road making them particularly vulnerable to new viruses, et cetera."
] |
[
"You can't generalize risk and benefit assessments to all GM foods. You need to look at it one species and one gene at a time to really get a feel for things. For example, say you add a gene to make a tomato more frost-resistant, and you've already proven through clinical trials that the protein that gene expresses is completely safe for humans. In that case, there's very little risk of adding it to the tomato. Even if there's some gene transfer, weeds are generally very frost resistant anyway, so the added gene won't really increase their survival in any significant way. Also, the risk of gene transfer is lower than the critics commonly suggest.",
"When you get into adding BT toxin (which kills insects that eat the crops), the situation is more complicated. First of all, it's been shown to be safe for humans; If I remember correctly, it interferes in gas exchange systems that are only present in the insect respiratory system. But people don't believe that because (a) they believe it must be dangerous because it's got the word \"toxin\" in it, (b) Pesticides in the past have been unhealthy and misused and (c) they've seen too many movies and TV specials about how evil Monsanto is. Another often-cited danger of BT crops is that some insects will become immune to it if they're exposed to it, resulting in superstrains of pesticide resistant insects. I don't agree with this reasoning. The solution before having crops with BT built in was to spray the fields with BT solution. This resulted in the BT toxin being diluted by water in the environment, and having uneven coverage on the crops. In THIS situation there's a much better chance of an insect being exposed to only a low dose of the toxin, which is much more dangerous for superbug development. ",
"There was a case where a GM-soy developed for higher-quality animal feed ended up being allergenic for humans. In this case, it was caught by the careful safety checks the GM companies perform before it caused anybody harm, it was pulled from the market, and it was never intended for humans anyway. I think this makes an important point; If we are careful enough about screening and testing, we can make sure that GM strains that actually become a threat are removed quickly. Another important point is that the technology gets better and better all the time, so the risk of something unforseen happening gets smaller over time.",
"So like I said, you have to take it one gene at a time. It's very hard to get a straight answer because there's SO many people who are just afraid of them without understanding biology or science at all. ",
"Anyway, in my opinion, GM foods are quite safe, and the long-term benefit of feeding more people for less money will soon be the most important thing in the world. I'd rather eat a GM food that lasts longer on the shelf and is free of parasites than an organic food that's ridden with fungus and worms and is going to spoil quickly and costs twice as much money. Organic farms have about half the yield of GM farms, and that ratio is getting smaller all the time. If you replaced all the GM farms with organic, you would have major food shortages, the price of food would go through the roof, and people would literally starve, even in developed countries. Organic foods are cool for hippies and people that don't understand science, but seriously, fuck that."
] |
[
"Tell your friends that if they want to ignore science, then they can go ahead and believe in creationism too. Anyway, here's an actual ",
"scientifically peer-reviewed article about GM corn varieties.",
" This article makes a lot of the important points I made (I accidentally said that BT affects insect respiratory systems, but it's actually their digestive systems. Too much studying other systems lately...)",
"This article also makes another important point. When I was trying to find information about GMO yields, I found a lot of links suggesting that they in fact DON'T increase yields. There are a couple of issues about this:",
"BT-GMO's prevent insect infestations by particular pests. These pests won't be around every year, even on non-GMO farms, but it's a preventative measure",
"Farmers that excessively use pesticides are getting the same yield benefit at BT, but with a huge cost to the environment. From the article \"The numbers are particularly impressive for Bt cotton: the spraying of almost 2 million pounds of pesticides—roughly 50% of previous usage—has been spared since the large-scale adoption of Bt cotton.\"",
"Some modifications increase shelf life too; Yield on the farm and effective yield delivered to the customers are two different things.",
"Herbicide resistance (in \"round-up ready\" crops) save farmers a lot of money and are good for the long-term health of the farmland because it saves the farmers from having to constantly re-till their land to prevent weed growth. From the article: \"the increased planting of herbicide-resistant soybeans is an integral, but not sole, factor in the increased adoption of no-till farming— a strategy that reduces soil erosion.\"",
"This article also discusses the risks in a fair and realistic way, so your friends hopefully won't just view it as the opposite of their bullshit materials. ",
"If you do feel the need to argue with them, there's a lot of good points to make:",
"GMO's are some of the most thoroughly and rigorously tested things in the entire world, and I trust the expertise of the huge teams of scientists at the FDA more than I trust you (directed at the hippies)",
"I admit that big companies like Monsanto have a temporary monopoly and spend a lot of money protecting their product with lawyers. It costs them billions to develop these things, and they overcharge before their patent expires to make up the difference. It's the same thing as the pharmaceutical companies. Don't make the debate about business practices, make it about science.",
"People have been developing new genetic strains of crops ever since we were able to do farming. Using thousands of plants planted in thousands of farms over thousands of years, there have been a lot of random mutations, or mutations induced by viruses or other means. This leads to one crop standing out as growing faster, or producing bigger fruit, or tasting better, or being resistant to insects, etc etc. Then the farmer takes this stand-out strain and crosses it with another strain that has another trait he likes. This selective breeding introduces new foreign genes to the crop. Companies have been doing this for generations, and purposely inducing mutations to get new and better strains. This OK with everyone, but selectively choosing a good gene, screening it for years in safety tests, and then using it considered so dangerous by hippies because of a stigma, not because of a real danger. People don't understand genetics, and \"genetic modification\" has been used in too many horror movies, so that people are scared of it without understanding it.",
"Some people claim that GMO's are nutritionally deficient in some ways. Try to get your friends to explain exactly how that's supposed to work. The genes for the nutrients have not been removed. If the fruit grows bigger, than the concentration of certain nutrients may be diluted a bit, but the actual amount will be constant. Scientists aren't trying to remove the health value of crops. They'll also say that GMO's don't taste as good, but I'd wager that would never hold up to a blind taste test where they don't know which food is GM'ed. Try it out! Maybe there's some differences in that the non-GMO food has pesticides sprayed all over it, and is rotting faster.",
"The more food we get and the longer it lasts, the cheaper it is, and the more people you can feed with it. It's supply and demand, and demand for food is always going up. There are people starving to death in the world as we speak, and GMO's can help to feed them. Even if your friends argue that they're not good enough to do that right now, point out that this is very very early in the field of GM crops, and that in the future it's going to be good for everyone. Keep going back to that point. It's one that's not really arguable. They can bring up Monsanto, they can talk about \"frankenfoods\", whatever, it doesn't matter. GMO's will save more lives than anything else in the world."
] |
[
"why are the earliest sunsets not on the same day as the winter solstice?"
] |
[
false
] |
The winter solstice is December 21, but the earliest sunsets are December 5th through 10th. What's up with that?
|
[
"It has to do with the fact that the Earth is not only just spinning on its axis, but also orbiting the Sun. The Earth takes 23 hours and 56 minutes to rotate 360 degrees, but 24 hours to rotate so the same point on the ground is facing the Sun at the same angle. The ",
"Synodic day",
" and the ",
"Sidereal day",
" are the words used to describe these two apparent motions. ",
"To add another layer to that, the Earth's orbit is elliptical and it travels at different speeds depending on its proximity to the Sun. So we travel further on a given day in January than we do in June. This makes the Synodic day vary between 23h59m38s and 24h29s throughout the year. Since we want clocks that run the same speed all year round, we need to average the length of the day over the year (24h). This causes local noon to occur at times slightly off from solar noon; accordingly, sunrise and sunset are also offset."
] |
[
"No, this does not have to do with time zone. If you shift your time origin, you still find that earliest sunrise does not occur on the same date as solstice. It is an astronomical effect, not a horological effect. It is a real effect.",
"Both sunrise and sunset times vary periodically. Finding the minimum of sunset time (from any time origin) need not correspond to the minimum difference, that's all."
] |
[
"The solstice is the shortest day of the year, not the earliest sunrise of the year. Point of fact, it isn't even the earliest sunset of the year. The earliest sunrise may be around Dec. 5th and the earliest sunset is around the 9th-18th, but the days can still get shorter because the sunset is getting later and later at a faster rate than the sunset gets later and later. Here, have a ",
"look",
".",
"edit - I misquoted the original question, but the explanation is still holds."
] |
[
"We know that different hot temperatures kill bacteria and mold in food preparation, but can excrement from the organisms still cause health issues?"
] |
[
false
] |
Say for instance someone cooks ricotta cheese pie (baked for 1 hour at 350F) with moldy cheese or a potato chip manufacturer uses moldy potato in a batch. Most (if not all) bacteria and mold would die off. What about waste from the organisms (whether it be what is left after die off or excrement)? Could it cause health issues? Sensitivities? Is there a possibility of allergy?
|
[
"Yes, a lot of bacteria damage host tissue through toxins (called exotoxins), e.g. the bacteria that cause botulism and tetanus. A few of these toxins can be heat stable and still cause disease after the bacteria that produced them die.",
"Wiki on exotoxins"
] |
[
"This is absolutely correct. Some toxins can be inactivated by heat, but toxins can persist long after the organism is dead. A common problem in medicine is treating a systemic infection with antibiotics. Something few people see or understand(and frankly we doctors don't usually take time to explain) is that in a serious infection, when we attack bacteria with antibiotics the lysing organisms will release their contents and toxins into the body triggering a stronger immune response than had we just left the bacteria alone. In an emergent setting, we give patients steroids before or at the same time as the antibiotics. It seems counterintuitive as steroids will suppress the immune system, but it's really to prevent the dead bacteria from killing them."
] |
[
"Dead meat bacteria endotoxemia.",
"http://nutritionfacts.org/video/dead-meat-bacteria-endotoxemia/",
"The toxins in plant matter tend to be the kind that are intended for plants, while the ones that come from bacteria that is living in and living on flesh are understandably more virulent to your body, since they are intended for it."
] |
[
"Can what distinguishes human beings from other beings be defined \"scientifically\"? If so, how?"
] |
[
false
] | null |
[
"You'd need to determine what you consider a human.",
"In other words, you're asking \"what do we define as human.\" Biologically, a human is any living organism from the genus Homo.",
"However, you could define it to be whatever you like, really. Definitions are important only in that they are what we want them to be. Words and their definitions change all the time. We don't use language based on how dictionaries describe it, dictionaries describe how we use language."
] |
[
"Can you refine your question, and in such a way where it doesn't involve arguments in another subreddit?"
] |
[
"\"What distinguishes human beings from other beings\" is somewhat vague, but I see absolutely no reason why we wouldn't be able to make specific and falsifiable statements about particular properties that are true of human animals, yet not true of non-human animals.",
"Vague (and potentially false) examples might include \"Only human animals are capable of learning a language of sufficient complexity\", \"Only human animals are capable of reasoning using counterfactuals\", \"Only human animals are capable of making moral judgements\"..."
] |
[
"Why do different blood types \"attack each other\"?"
] |
[
false
] |
Obviously they would be clumping together because it's recognized as an "intruder" but why? Why do the human body specifically invovled anti-b/a proteins just for that (well maybe there is another reason why)
|
[
"The body is not specifically attacking non-type matched blood, but rather the body attacks everything that is not part of \"self\". A general mechanism by which the body fights off any kind of infection is by creating a very very very diverse set of antibodies which will bind all kinds of molecules. Some portion of this set will bind to molecules present in the body, such as those on red blood cells, but also on any other cell in the body. The body first screens out these antibodies and makes sure that they are never made again so that it will not attack itself. Misregulation of this process can lead to one of many ",
"autoimmune diseases",
". Once those antibodies are removed, all of the other antibodies are kept around, and if they bind anything, then the body will attack it. ",
"Humans have many markers on their cells, some that are identical across all humans, and some that have some variation. The typical blood type marker (O,A,B) are three different alleles present in the population that do not serve much of a purpose but happen to be different in different people. People with the O allele have a certain protein on the surface of the cell that has some set of sugar molecules attached. People with A or B allele have additional sugars attached to that same protein (different ones for A or B). Each person will likely have antibodies that can bind any of the sugar combinations that are not their own. So someone with O blood will have anti-A and anti-B antibodies, and someone with AB blood will not have any antibodies. Since no one has anti-O antibodies (O is part of A or B, so it's always present in all people), O is the universal donor. If you are AB and have no anti-A or anti-B antibodies, then you can receive any of the types since no matter which type you get, your body will not have anything that will attack the cells. There is more to type matching than just ABO blood type, but since red blood cells are so prevalent in donations, they are a major cause of incompatibility. Rh is another surface marker on red blood cells and that's where you get + or - blood (e.g. O+ or A-, etc.). Here + means you have the Rh marker and therefore will not have antibodies against it, and - means you don't have the marker and your blood will not induce a response in someone with - or +. Again, making O- the more universal of the donor.",
"When transplanting organs, there are more tissues than just RBCs that can induce an immune reaction, so other type matching is required. Hence it's harder to find good donor/recipient matches with organs and people that receive organ transplants will have to take medication to inhibit their immune system activity for the rest of their life."
] |
[
"Red blood cells have antigens on their surface, just like any cell in the body. Antigens can be protein, lipid, carbohydrate structures or a combination of these. Antigens are used by the body to determine self from non self. The body will make antibodies (proteins) to antigens that it determines are not \"self\". The ABO blood groups actually just refer to antigens on the cell surface, but they are also found on body tissues. Type B people have B and H antigens on their RBCs, type A have A and H antigens, Type AB have all three, and type O have H antigens on the surface. If you are Type B you will have naturally occurring Anti-A antibodies in your blood, these you are born with. Type A people will have naturally occurring anti-B antibodies. Type O will have anti-A, anti-B, and anti-A,B. Type AB do not have antibodies to ABO antigens. There are hundreds of antigens on your RBCs and many other blood groups, but ABO are the most important and the D antigen (Rh) is the second most important. ",
"Now, there are different types of antibodies but the ones in the ABO system are naturally occurring and IgM. Basically antibodies attach to the matching antigen. When this happens with ABO antibodies it causes a reaction with something called complement. This causes the red blood cell to burst (lyse). A person who has bursting RBCs will soon have anemia. With ABO antibodies this is almost immediate. With other antibodies to other antigens it is different and each has different characteristics.",
"I'm not sure your background on these subjects so if you need me to explain more I can do that. I'm an Immunohematologist (aka a blood banker)."
] |
[
"Beautiful answer, thank you!"
] |
[
"Gravity's speed limit is also the speed of light, but is it also slowed by a medium such as air or water?"
] |
[
false
] | null |
[
"To be clear, it's ",
" in either that travel at light speed.",
"Light is slowed down by being absorbed and then reëmitted a short time later (or we could talk about little antennas being driven slightly out of phase, again by absorption and reëmission, but this time everything is continuous). So the question is whether an analogous process happens with gravity. Unfortunately, we can't fully answer this, as we don't have a full theory of quantum gravity. GR does describe gravity waves being generated and being absorbed, but the amount absorbed is a tiny tiny fraction. Because this fraction is so tiny, it really shouldn't have any effect."
] |
[
"From the askscience guidelines: \"If you cannot clarify your answer in excruciating technical detail, don't answer at all. This is to reduce layman speculation, which is generally not helpful.\""
] |
[
"Not anymore, he isn't. Hah!"
] |
[
"what is the difference between a broken neck that causes death and one that causes paralysis?"
] |
[
false
] | null |
[
"It depends where the injury is and how severe it is. The nerves that control your body are aligned in a specific order, basically from the legs (near the bottom of the spinal cord) up to the head (near the top). If an injury occurs in your neck that completely severs the brain from communicating to the regions that control breathing for instance, you're dead. ",
"http://www.sci-recovery.org/sci.htm"
] |
[
"To summarize: the higher up on your neck the break is, the more likely you are to die."
] |
[
"so breaking a vertebra above approx. T2 could kill you, paralyze you in a number of different ways, or allow you to fully recover? ",
"why doesn't every vertebra above T2 have the same chance of killing me if broken?",
"*i'm using T2 b/c on the chart is looks like T2 is just above the heart and lungs."
] |
[
"What are the differences in the metabolisms of someone who can't get fat and someone who gains weight easily?"
] |
[
false
] |
[deleted]
|
[
"While this doesn't quite answer your question, perhaps it will give you some information that is part of the answer. ",
"Human microbiota (all the microbes in and on you) work has exploded in the last 10 years. One huge piece of research to come out of this is that ",
"lean people and obese",
" people harbor different profiles of bacteria (and different bacterial genes) in their gut. They took identical and non-identical twins, and their mothers, compared who was lean or obese, what microbes they had in their gut, and what the gene content of those microbes was. The idea of looking at twins is then you can control for the gene content of the host. What they found in short is that obese people had less diversity of bacteria (and their genes) in their gut along with a different assortment of bacteria. Some thoughts for why this might be is that the obese profile helps the host get more energy from their food.",
"However, at this point, it's kind of a chicken/egg discussion. We know what an obese microbiota looks like. Do people get inoculated with an obese microbiota and then become obese because of it? This could explain why we see obesity in families. Or is there something that individuals do that shift their microbiota towards that of an obese one, and it \"helps\" them become obese? ",
"I'm going to speculate now based on what I've read, and the people I've talked to about this (I've actually met and had a conversation with the lead author on that paper I linked to). I think this all might actually be a combination of things. Perhaps mom eats in a way that not only encourages weight gain, but also encourages an obese microbiota. She gets stuck in a cycle where her microbiota requires more food, so she eats more, maintaining her obesity. She then inoculates her kids with that profile, while maintaining the necessary external things that support their obese profile and that keeps them obese. And you can look at it from the flip side, lean people doing the things that maintain a lean profile AND inoculating their kids with it AND teaching them the habits that maintain that leanness. I have to wonder if part of the difficulty for some in losing weight isn't totally that it's \"hard\" to lose weight, but that it's hard to shift your microbiota back to that of a lean person."
] |
[
"People vary in their response to overfeeding: ",
"http://www.nejm.org/doi/full/10.1056/NEJM199005243222101",
"In this twin study, the subjects were overfed by 1000 calories/day, but their weight gain varied from 4.3kg to 13.3kg. The discrepancy appeared to be caused by genetic factors. A person who gained the least weight probably had a large increase in their metabolic rate, fidgeted more, and stored more of the excess energy as lean tissue rather than fat. A person who gained the most weight probably had only small increases in metabolic rate and stored most of the excess energy as fat.",
"In the real world, where it's easy to overshoot your daily calorie needs by a few hundred, having certain genetic factors would probably be of value in protecting you against weight gain."
] |
[
"Have any experiments been done with artificially influencing the microbiota population to see if weight loss results? (i.e. introducing desireable microbia, etc...)"
] |
[
"Can a polygraph distinguish between lies and normal nerves?"
] |
[
false
] |
First off, I apologize if this is the wrong flair, not really sure what filter it should be asked in. But I always thought if I was accused of murder and was asked to do a polygraph, just being accused and asked if I murdered someone would cause my pulse and nerves to go crazy. Can a person reading a polygraph test tell the difference between a lie and nervousness due to the pressure of the situation?
|
[
"Can a person reading a polygraph test tell the difference between a lie and nervousness due to the pressure of the situation?",
"Possibly. Have a quick skim of the Wikipedia article on ",
"lie detection",
". It'll be an important frame for this discussion because a big issue with all lie detection methods, polygraph and otherwise, is that they are not reliable. They will fail. Sometimes when someone is telling the truth (and the poly says they're lying), and other times when they're lying (and the poly says they're telling the truth).",
"The ",
"polygraph",
" is an old, and relatively cheap system. It measures a number of peripheral physiological markers, usually pulse, blood pressure, respiration and skin conductance. These measures are used because they are not fully under direct cognitive control (though you can do things to alter these, for example holding your breath will change skin conductance).",
"Can someone use these measures to tell if you're telling a lie versus if you're just nervous? They can, if they are able to reliable determine if you are lying. The difference between lying and being nervous is that being nervous is a state. It will be reflected in the peripheral indices throughout the testing session.",
"The way that a poly is typically done is to ask a series of simple questions. What happens to the peripheral markers in ",
" to these questions (event-related responses) is what the examiner will be evaluating. If you are nervous, this will be visible prior to the question being asked, but whether or not you're telling the truth/lying should still be visible in those peripheral markers above and beyond your baseline state. That is, if the test is doing it's job.",
"At the end of the day, the poly is not a great tool. It's prone to failure, it requires the person to be compliant, and it can be fooled, and quite easily. Also, galvanic skin response (measured via skin conductance), one of the canonical measures, can be completely absent in some people."
] |
[
"Actually your mistaken, nervousness in not a factor since individuals are nervous when the \"test\" begins and when it ends.",
"That is what I am saying. The data is examined in an event-related manner, so any nervousness is going to be removed through baselining/normalising. At the end of the day, the poly is unreliable and should not be used as a lie detection method."
] |
[
"Actually your mistaken, nervousness in not a factor since individuals are nervous when the \"test\" begins and when it ends.",
"That is what I am saying. The data is examined in an event-related manner, so any nervousness is going to be removed through baselining/normalising. At the end of the day, the poly is unreliable and should not be used as a lie detection method."
] |
[
"Why can't dark matter just be neutrinos?"
] |
[
false
] |
It seems like an obvious sort of answer, so there must be a good reason it's not right
|
[
"From what we know about the masses of neutrinos, they can only have been part of hot dark matter at the time of structure formation, but we know from theory and simulations that a lot of cold dark matter was needed. ",
"Hot means that they're ultrarelativistic, that is kT >> mc",
", and cold is the opposite. Hot dark matter cannot collapse into halos, essentially, because a gas of particles moving at c or near c cannot clump together in a mass bound by gravity.",
"There's more here"
] |
[
"The term right-handed neutrinos is often used somewhat sloppy. It is often used for elementary neutrino-like fields that are not charged under the standard model gauge group (the \"right handed\" emphasises that they are not chagred under SU(2)_left ) . It is important to note that these particles are not to be confused with standard model neutrinos !",
"These new particles can in theory be used to explain a lot of different phenomena like dark matter, the lightness of the standard model neutrinos, baryogenesis and even more things. For pretty much all of these things they require to be heavier than SM neutrinos."
] |
[
"So about how massive would particles of dark matter have to be?"
] |
[
"I was taught that brown eyes are dominant but my father has brown eyes and mine are green, why?"
] |
[
false
] |
All of my high school science classes said that brown was the dominant trait, were they misinformed or am I just different?
|
[
"Dominance doesn't work like that. You can have a dominant gene mixed with a recessive, so the recessive gene would be masked. In that case, your mother probably had a recessive gene as well that ended up creating the recessive green you have. ",
"I'll give you an example. Let's say E is dominant (brown), and e is recessive (green)",
"Father = EE",
"Mother = Ee",
"The possible combinations in you would be as follows: EE, EE, Ee, Ee.",
"You simply make every combination of the two possible. In this case, you'd always end up with brown eyes as you always have a dominant E gene. However if your parents both carried a recessive, masked gene, this would be the situation:",
"Father = Ee",
"Mother = Ee",
"The resulting possible combinations would be EE, Ee, Ee, ee.",
"In three of those cases, you would end up with brown eyes. But the last ee would cause you to have green eyes. ",
"All of this is, of course, assuming that eye color is affected only by one gene with what is called complete dominance. Which it isn't. But that's more complicated genetics. For layman sake, I have made the answer less complicated.",
"Hope that answers your question!"
] |
[
"Brown is the dominant trait, but eye color isn't just coded for by one gene. It's coded for by a whole ton of different genes, just like skin color. ",
"Here's",
" a great explanation on this topic."
] |
[
"Eye color depends on three genes",
". Since autosomal genes (the ones that don't determine sex characteristics) come in pairs, if one gene is brown and the other is green, you'll get brown because brown is dominant. But if you pass your green gene to your offspring, and your mate passes their green gene also, then your offspring will have green eyes even if you and your mate both have brown eyes."
] |
[
"Why does ice break in a hexagonal pattern?"
] |
[
false
] |
Does it have anything to do with the molecular structure of H20 or is it purely coincidental?
|
[
"Google the crystal structure of ice and you'll see that it is in fact hexagonal. Same reason why snowflakes are usually hexagons too. It's due to the bond angles of water and how water molecules interact through hydrogen bonding. I wouldn't be surprised if there were planes of weakness in the ice due to the hexagonal crystal structure. I studied chem but I think a material scientist could better answer this. "
] |
[
"Ice as a crystalline solid is super bizarre stuff. For example, it's one of very few substances that are less dense as a solid than a liquid, which is why ice floats. The other crazy thing is how many crystalline structures ice can form. ",
"So far, we've observed 14 unique crystalline forms of ice,",
" which is more than any other known substance. Most of these are pretty rare and exotic, but it's possible that the ice in the video was one of these rare forms of ice and that contributed to the shape that it ended up in. Interestingly, the common form of ice ",
" have a hexagonal crystalline structure, but it of course doesn't reliably crack into perfect hexagons. So I think that some combination of perfect physical conditions (thickness of the ice, angle of the drop, etc) was probably the real deciding factor, but the crystalline structure could have had something to do with it."
] |
[
"I highly doubt that the whole ice on a lake is ",
"crystalline, so the crystalline structure of normal ice (hexagonal pattern) shouldn't affect the ice on a larger scale. If you look at the breaking pattern in the video, you can see that the angles between the different cracks are not all the same (as it would be in a hexagon), so I would rather guess the number of cracks formed has to to with the strength of the explosion (in this case), and I would expect it to be an even number of cracks coming from the center (which means: if three cracks intersect each other, you will see six \"lines\" coming from the central point)."
] |
[
"What are some possible reasons that some bands aren't showing up in my gel? (PCR)"
] |
[
false
] |
I took a picture of my gel and some bands are showing and some aren't. I'm guessing I didn't add enough DNA or I didn't add any DNA into my PCR tubes. Could there be any other reason why they won't show? Edit: or i didn't load the samples properly into the gel edit: i'm obviously a noob at research. and brb gotta go to lab meeting Edit. Thanks for the responses. I'm guessing i didn't pipette the DNA correctly... Going to try again. I love you guys . research is the best. TIL the small amount of cardiacmyoctes that the body creates are derived from other cardiacmyocotes
|
[
"The first question should be do you see your ladder/ molecular marker?"
] |
[
"Yeah, I just re did everything making sure that I put the DNA by staring at each tip and I got good results. ",
"Thank you sir!"
] |
[
"It's hard to mess up loading the DNA...you've got blue loading dye or something in your samples? If the blue goes in the well then it's loaded, even if you miss a little it's probably fine (just be careful that some sample doesn't spill over from one well to the next though)."
] |
[
"[Physics] Suppose I had a pound or so of pure protons, about how densely could they naturally be packed?"
] |
[
false
] | null |
[
"Naturally, they would just blow apart due to Coulomb repulsion."
] |
[
"Yes, but how far apart would they have to be such that the Coulomb repulsion is negligable?"
] |
[
"Coulomb repulsion has infinite range. So if you're imagining a totally empty universe, filled with some number of protons, they will repel each other forever. If you were to smash them together into a length scale where the strong force overwhelms the electromagnetic force, you may be tempted to say that the strong force could bind them. But actually, there are no bound states in this system. Even though the strong force is attractive at low relative momenta, it's not strong enough for a bound state to form, unless there are neutrons present."
] |
[
"Why can I reproduce sights and sounds in my head but not smells, tastes and \"touchs\"?"
] |
[
false
] | null |
[
"You might not have a very good sense of smell but really it just sounds like you don't pay as accurate attention to smell/taste/touch. Remembering/envisioning flavors is how cooks know that cacao and chilis will go together, but lamb and ice cream won't. Anyone who has ever tried to decide between perfumes has recalled scent. And as for remembering touch, I'd be willing to bet if you tried you could imagine the feel of rice and that of sand distinctly."
] |
[
"I suspect that you don't actually hallucinate the sights and sounds in your head either. They are vivid but (baring psychological disorder) you can probably tell the difference between a remembered image and an perceived one."
] |
[
"I suspect that you don't actually hallucinate the sights and sounds in your head either. They are vivid but (baring psychological disorder) you can probably tell the difference between a remembered image and an perceived one."
] |
[
"As an adult, is there any neurological difference between learning a new word in your first language and a new word in a second language?"
] |
[
false
] |
Learning a new word in your first language somehow feels different to learning a new word in your second language, even after the critical learning period. But why should it? Either way, you're learning to associate a new word with a particular meaning.
|
[
"Learning a language before puberty (12-13 y.o) is much easier, as the brain functions differently. Before puberty the brain could be imagined as a single unit, rather than two hemispheres that split different functions. However, after the puberty, the functions are split/ In terms of the language, the left hemisphere is responsible for naming the objects (i.e. the vocabulary) while the right hemisphere is responsible for the emotional understanding of the language. For the native language these are learnt all together, as the brain functions as a single unit. However, for adults these things are needed to be acquired separately and hence it is more complicated.",
"For more information I suggest reading about brain lateralization. These seem as a few good links: ",
"http://kccesl.tripod.com/readingmatrix/samplereadingfinal.html",
"\n",
"https://explorable.com/language-and-lateralization",
"\n",
"https://en.wikipedia.org/wiki/Lateralization_of_brain_function"
] |
[
"How are you getting your L2? Learning or acquisition? They feel different because they are different, but not because of L1 or L2 in this case. Comprehensible Input theory seems pretty applicable here.",
"FWIW, since we are discussing how new vocab feels, I completely learned my major L2 after any time that could be considered critical period, yet I don't ",
" like acquiring L1 or L2 vocabulary is any different."
] |
[
"I'd have to double check, though I am 90% sure they are two different brain areas. If you get a stroke in your native language area, you are supposed to be able to communicate in your second language. ",
"I believe the big difference between being multi-lingual and having a second language is just this. If you learned as a kid, you're multi-lingual and languages share a part of the brain. If you learn later, they don't.",
"I learned German, French, and Czech. To this day, I will throw in a German word when speaking French and vice versa, I will try to use Czech syntax with German words, etc. "
] |
[
"What methods exist or are being researched for non-intrusive neural interfaces?"
] |
[
false
] |
I'm very interested in possible applications of high-quality neural interfaces, especially given fMRI studies and neural prosthetics. However, I don't know much about potential technologies (and current technologies) for non-invasive (i.e. non-surgical) neural interfaces. What methods exist, and which are being developed but look reasonably hopeful?
|
[
"So I'm assuming something you can carry around with you, as opposed to fMRI. In that case you're looking at EEG or, maybe ",
"fNIR (functional near-infrared spectroscopy)",
" although neither is terribly portable at the moment. ",
"EEG has a notoriously crummy signal to noise ratio, so you really need to be able to grab onto some really strong signal. There are a couple that we can generate fairly reliably like the ",
"P300",
" which has been thought to occur when you detect something you're looking for. ",
"Of course, really what's happening with all of these BCI devices (most of the time) is ",
" signal decoding. Rather, they just need to be able to reliably detect a signal that the user can reliably produce and to distinguish it (classify it) from other signals. They can then pair a signal with some command, like ",
"selecting a letter on a screen",
", ",
"playing pong",
", or ",
"controlling a wheelchair",
". (",
"This",
" pong video isn't as long, but you can see that you can get much more sensitive and faster control. And ",
"this",
" is an older video of the letter selection).",
"Just search youtube or google for brain computer interface (BCI) and you'll find tons of stuff. If I recall, there was at least one video game company developing a cheap, wearable EEG cap for controlling things in games with maybe 3-12 electrodes?",
"If there's a more specific question you had in mind, I can try to answer it."
] |
[
"I like to draw people's attention to the spatial and temporal nature of signal processing in the brain, and that of the various methods used to measure it. Neurons in the cerebral cortex exist over its 250,000 mm",
" The signal changes on roughly a millisecond time scale every few tens of microns. HOWEVER, the signal in a cortical column had a lot of redundancy, so we could make a great neural interface if we could get a good sample every 500 microns in a grid, or with a million samples that operate on a millisecond time scale (I would actually prefer 0.1 msec, but make it 1 msec for argument's sake). That's about a million bits per millisecond, or a billion baud rate. ",
"Now, let's talk fMRI. The signal operates on roughly a 1 per mm",
" scale, which is awesome, for 250,000 samples in the cerebral cortex. However, the underlying signal, BOLD, is roughly 4-5 times less dense than that in its expression. We are actually measuring blood flow changes (and oxygenation), not neural activity. So now we are down to 1000 samples. And the blood flow changes every few seconds and has a nasty noise band called vasomotion at 0.1 Hz. So we have a few hundred samples per second. We can give them 4 bits each (being generous here) and we have about a thousand baud. But factor in vasomotion, and the need to load up the magnetic field to watch the decay, and the reality is fMRI is under 100 baud. ",
"EEG is another great technology. Awesome temporal resolution, but very crappy spatial resolution if performed extracranially. Maybe 16 spatial samples at 1 msec resolution, or 16 kbaud. However, factor in electrical noise from emg/eog signals, and you are again in the few hundred baud range. ",
"To get a \"matrix\" like interface, you are going to need a noninvasive interface that accesses a brain-dependent signal on a high temporal and spatial scale. I think we could do nice work in the several thousand baud range. It would not be matrix-like, but it could provide a reasonable proxy. ",
"The best brain machine interfaces today operate in the few dozen baud range. They are based on the \"good\" electrodes in a sample of several hundred implanted electrodes, and can do a nice job on simple tasks with 2-3 degrees of freedom. These interfaces have largely not improved since 1998 and are highly invasive. fMRI and EEG interfaces operate with an order of magnitude lower baud rate. The capabilities I outlined above are limited by noise sources that are troublesome. "
] |
[
"I'm not sure I'm following your question exactly, but yes, there certainly are limits. For EEG, the signal at a channel is the result of the firing of many thousands of neurons. So you are measuring an aggregate signal. You're also getting coverage for the outermost cortical layers. See ",
"/u/JohnShaft",
" 's response below. "
] |
[
"Why is plasma considered a different phase of matter than gas but metal isn't a different phase from solid?"
] |
[
false
] |
Plasma is basically a gas where the electrons aren't bound to the atoms, and the gas becomes chargeable and interacts with EM. A metal is a solid where the electrons float around in a "sea of electrons" and the solid becomes chargeable and interacts with EM.
|
[
"If you really want to go into defining phases in a rigorous way which applies in all cases, you need to go to a description that's too complicated for standard high school physics. IMO, the best way is using \"order parameters\" as described ",
"in this recent comment",
" by ",
"/u/IAmMe1",
". This includes all kinds of interesting phases like metals, magnets, and a lot of quantum phases. It also distinguishes plasma from an insulating solid from a metallic solid, effectively answering your question. Unfortunately, as I mention in another comment in that post, you can use this classification to argue that liquids and gases are really the same phase. ",
"So basically, the classification of phases that you learn in intro high school/college courses is intentionally simplified to help you out. People who work on phases of matter need a different method of evaluation.",
"EDIT: I should add that this comes from my bias from being a condensed matter physicist. I see concepts like ",
"allotropes",
" and ",
"polymorphs",
" on chemistry-related subjects which indicate that the terminology is probably different for other people. The way I define things is probably better for me because I work with quantum matter."
] |
[
"Metal is a phase of matter! It's a type of solid. A sub-group.",
"Here's an example with animals: Let Metal = Elephants, Solid = Mammals, Plasma = Lizards. Then elephants are a type of mammal, and mammals and lizards are both types of animals. It would be like asking, \"Why are mammals a different type of animal than lizards but elephants aren't a different type of animal than mammals?\" But I think you know the answer.",
"There are many types or phases of solids. There are also different phases of liquids, and perhaps gases and plasmas (I'm not sure). For example, graphite conducts electricity (it's a semimetal), but diamond does not. Graphite and diamond are both solids, and they're both made up of carbon atoms, but they're different phases of matter."
] |
[
"Hmm I wanted this to be easier to answer than I am finding it to be. ",
"The heart of the problem is, I think, that the definition of a \"state of matter\" (which I think you mean by \"phase\"",
" ) is somewhat arbitrary. I am having trouble finding a useful scientific definition of \"state of matter\" at the moment. Maybe someone actively teaching something like intro chemistry or physics could chime in. In high school in the US we generally learn that there are 4 states of matter: solid, liquid, gas, and plasma. In reality, there are many other states of matter but they occur under conditions that are usually achieved artificially in a laboratory or otherwise not observed in day-to-day life. Very broadly, a state of matter consists of a consistent set of physical properties over a range of thermodynamic conditions. You are right that a solid with metallic bonds has some very different properties than a solid with other types of bonds. Ionic liquids also behave differently than \"normal\" liquids. But we don't consider them to be a different state of matter. ",
"So you've actually got me a little stumped. I'm leaning toward it being arbitrary but if I had to guess at a truly scientific reason it may have something to do with the existence of transformation energies like e.g. the latent heat of melting etc. ",
" For a given state of matter (e.g. solid) materials can have many phases. Ice, for example, has many phases depending on the pressure and temperature that it is held at."
] |
[
"How do astronomers catalog and organize the locations of stars/planets/asteroids in the sky?"
] |
[
false
] |
[deleted]
|
[
"The celestial sphere can be thought of as two dimensional, and so stars are located on it using either right ascension, a description of their distance from the prime celestial meridian, and declination, their distance from the celestial equator, or using azimuth and altitude, which obviously changes as the stars seem to rise and set. Stars are so distant their relative motion is undetectable for the most part, but not entirely, so their relative locations are updated periodically, and about every 20 years new star catalogs come out. Observational astronomers don't generally worry about how far away a star is since you don't need that information to find it."
] |
[
"This is the first time I have seen it, but I think they use the ",
"Equatorial coordinate system",
". I'm basing this from that fact that star catalogues ",
"eg 1",
" use it as the input."
] |
[
"The bottom line is we don't actually know the distance to stars. We think we do, and we're probably right, but we can't be sure. We've decided that certain classes of variable stars and supernovae have intrinsic brightness, and that by measuring the perceived brightness of those stars as seen from Earth we then deduce they must be so far away. These stars are known as standard candles. How that data is stored for a computer simulation I couldn't tell you."
] |
[
"How do Computers manage Time so accurately?"
] |
[
false
] |
As I know so far, Computers have a system that increases a number by 1 every second and then convert that number into a format that we understand as a clock. How do computers know at what rate to increase this number. This is what I found when I looked for a definition of a second. How does a computer increase its time at the same rate as the defined second? Edit: thanks for downvoting
|
[
"A ",
"crystal oscillator",
" can be used to generate a very precise clock signal. The crystal naturally oscillates at a certain resonant frequency based on its material properties.",
"Since the frequency the crystal oscillates at is known, we can generate a clock from it. For example, if we know it's 16 MHz, we know that we should count off one second for every 16 million clock cycles.",
"Since the clock isn't perfect, the computer time may drift from the actual time by small amounts. Modern operating systems will periodically check in with a time service via the Internet and adjust the clock as necessary."
] |
[
"This guy pretty much nailed it on the head. ",
"To expand on this comment a bit:",
"crystal oscillators require electricity to work",
"the frequency of some oscillators are adjustable ",
"in order to keep time while the computer is unpowered, many computers have a small battery on the motherboard to help with this ",
"there are many ways a computer (remember that computers are everywhere) can receive a highly accurate time: crystal oscillators, GPS, IRIG, internet, other special synchronization protocols",
"if you dig into your Windows event logs, you will find that your computer is constantly adjusting its time by a few microseconds or milliseconds every day! Keeping timd accurately using only a single conventional source is pretty much impossible"
] |
[
"An interesting fact, most PCs and electronics use an oscillator clocked at 32,768 (2",
" Hertz or some other nice power of 2, so the timing circuitry is simpler. This way, the computer only needs a few stages of logic (flip-flops) that toggle every other clock cycle, and are linked so that every flip-flop is run by the output of the previous. Dividing like this is simpler than keeping track of an exact number of pulses."
] |
[
"If you get a face transplant, does it age?"
] |
[
false
] |
I debated asking this on , but I feel like there are more qualified people on here that can give me a good answer. I just watched video. A 41 year old got a 26 year old donor's face after an accident. Which made me wonder, would it ever age?
|
[
"Sure it would. Let's begin with normal aging which is usually a result of constant cell division decreasing the ends of chromosomes (telomeres). Once they get clipped enough, cells should stop dividing. Sometimes they do (senscence) sometimes they don't (cancer). There's also our frenemy oxygen! We need it to make energy, but it produces highly reactive chemical species called reactive oxygen species (ROS). These ROS if they aren't neutralized (antioxidants) attack DNA, cell membranes, etc., leading to, what we see as, aging (dysfunction). The same process occurs in every living thing, even transplanted faces! Simplistic, but you get the idea. Now the transplant question adds another layer of complexity: recipient's immune system will recognized donor's face as foreign and mount an immune reaction to it. Uncontrolled, this leads to rejection, which makes aging seem like nothing. I'd guess that at a cell/tissue level, transplanted organs 'age' faster. "
] |
[
"Is it really possible to live 15 years with no problem and then suddenly reject it ?"
] |
[
"I support all you have said",
"I would also add that scar tissue and extra cellular matrix (ECM) add to a lot of what we think of as ageing. In this case, the transplant would age normally if not faster due to donor-host interactions. "
] |
[
"How significant is the genetic difference between the Northern and the Southern White Rhino?"
] |
[
false
] |
With the last male Northern White Rhino dying today, and only two females left, chances for survival of the northern 'half' of this species is pretty much 0. Apperently they have enough sperm to keep the two remaining ladies getting pregnant, but it is not that straight forward of course. To my surprise however, I read that there are thousands of their Southern counterparts left. I don't have a clue about the differences between the two though. Although the reasons they are still around might be really interesting, I am more interested in the biological difference between north and south. Could 'we' rejuvinate the northern species by using their southern brethren? How different are they?
|
[
"The Northern and Southern once though of as subspecies (like different breeds of domestic dogs) are believed to be of different species entirely. DNA evaluation shows it is an evolutionary divergent lineage a million or so years ago. They are similar in that they both have wide mouths as they are both grazers (where their names came from). But other than that are as different to each other as they are to the black rhino, different morphology, different genetically. Like domestic dogs are similar species to ",
" foxes, coyotes etc NOT subspecies.",
"Edit: as others have pointed out, wolves and dogs ARE sub-species. But foxes and coyotes etc are not."
] |
[
"Just wanted to mention to those interested that San Diego Zoo institute for conservation research has large ongoing research projects regarding northern white rhinos. There are sperm and eggs banked in their frozen zoo from previous northern whites, plans to use southern whites potentially as surrogates for implanted pure northern white embryos, all using reproductive sciences, genetics, and stem cell biology. Really interesting stuff. ",
"http://institute.sandiegozoo.org/species/white-rhino"
] |
[
"Thus far, attempts to cross-breed them have been unsuccessful. To be fair, Sudan was too elderly to survive mating pretty soon after his transplant to Ol Pejeta, and one of the female northern whites has a bad hip and the other has ovarian cysts, so the opportunities to event attempt natural crosses were slim. (I study botany and entomology, not animal physiology, so I’m just relaying what colleagues at OPC have told me. No idea if it’s pre- or post-zygotic problems.)"
] |
[
"Can diverged species converge once again and breed if given enough generations?"
] |
[
false
] |
Could a group of organisms from the same species be isolated so they diverged and formed a new species (and thus no longer be able to breed with one another), then be reintroduced and reproduce once again? Given an unlimited number of generations and resources. Also is there any cases of this in history? Or is it more likely that once you split on the old family tree there's no going back?
|
[
"Theoretically speaking, no. By definition, species are populations that have diverged to the point where they can no longer interbreed (as your question suggested). This is due to the evolution of reproductive barriers, either prezygotic (meaning the two species no longer recognize each other as potential mates, don't reproduce at the same time, have incompatible sperm and eggs, etc.) or postzygotic (hybrids between the two species are sterile or inviable=dead). ",
"In practice, things are much more complicated and interesting. First, we do not describe species based on their reproductive isolation from all other species (impractical to test directly) but based on their morphology, behavior, and more recently, the extent to which they share similar DNA sequences. Thus, we may call two populations 'species' when in fact they are perfectly capable of hybridizing, and maybe even do regularly. Second, there are many examples of species pairs where reproductive isolation is incomplete. It is common for young species pairs to produce hybrids where only one of the sexes is sterile or inviable, but the other sex is fertile and (relatively) healthy. This can allow genes to flow between the species via the fertile hybrids. There is no rule for exactly how much gene flow between populations would disqualify them as separate species, highlighting the disconnect between the theoretical definition and practical application of the species label. See ",
"this paper",
" as an example of how gene flow can vary across the genome between mouse species.",
"I do not think that humans and neanderthals constitute a good example of this phenomenon, since we have no evidence that modern humans and neanderthals were ever reproductively isolated."
] |
[
"Theoretically it IS possible but practically its impossible. Technically, a set of step-wise changes (i.e. one mutation event followed by another) connects any two divergent species. The same set of mutations in reverse will bring any two species back into the zone of genetic compatibility.",
"In reality (nature) its highly improbable that two species that have diverged to the point of reproductive isolation through physiological/developmental/genetic changes might naturally accrue the necessary mutations to viably interbreed again. However if the divergence is say 1 fixed mutation past some hypothetical threshold of compatibility (maybe a change in the structure of an enzyme in the sperm's acrosome or a receptor on the egg's envelope), then a mutation undoing that one would allow them to interbreed again. ",
"Edit: You're definitely right on about the way species are defined in practice. We know that Grey Wolves in North America interbreed with Coyotes at an appreciable rate. Yet we consider them both separate species. We also define populations elsewhere in the world such as Eurasia as the same species, Grey Wolf, in spite of there being literally no gene flow between them and their North American counterparts."
] |
[
"This is probably relevant: ",
"Ring species"
] |
[
"What exactly causes particles to produce a magnetic field?"
] |
[
false
] |
I know what a magnetic field is, and how magnetic fields interact with each other, but I'm not sure on what actually causes them in the first place.
|
[
"You naturally get magnetic fields in two ways:",
"You have current, e.g moving charges.",
"You have a fundamental magnetic dipole, e.g charged particles with spin (otherwise known as fundamental angular momentum).",
"You can make also make dipoles out of current loops (method 1.) but these are distinct from fundamental dipoles."
] |
[
"(since i don't see that you mentioned it): time-dependent electric fields also produce magnetic fields."
] |
[
"My bad! This is essential for the magnetic field produced by light. In my head I was just thinking about charged sources!"
] |
[
"Why do we have a single, globally standard system for time but not other units of measurement?"
] |
[
false
] |
I was wondering where to ask this as I would like an answer. I mean, I know that time is linked to the movement of the earth around the sun but at the same time it's weird to think that it developed differently than temperature or weight or what have you.
|
[
"There is far more pressure for a standardized time than for standardized length or volume (and so on) measurements.",
"First, measurement of time is a bit less arbitrary than measurements of other things. A day is a day for everyone on earth. How you divide up a day is arbitrary but you still have a benchmark everyone agrees on. There is no particular reason to pick a liter or mile and so on as the measurements for those things. They are even more arbitrary.",
"As communications and travel became simpler and more common it became increasingly necessary for everyone to get on the same page with what the time it was (railroads really moved this forward...before that it was kind of a mess).",
"Further, accurate timekeeping became critical in navigation at sea. Latitude could be determined by star measurements with a sextant but longitude calculations required accurate clocks. Once the first accurate clocks were made that sufficed for navigation everyone who could got one and the standard spread.",
"There is far less necessity in agreeing on what to call a given volume or weight of stuff.",
"EDIT to add: Even with all that we still screw around with what time it is a bit. Daylight savings time is observed some places and not others and the time lines where we denote an hour difference zig and zag rather than following the latitude lines perfectly...sometimes by a lot (as you can see ",
"here",
"...looks like ALL of China is on one timezone where it seems it should cross five of them and Iceland is on GMT although it should be an hour off...and so on)."
] |
[
"First, there are plenty of other units of measurements that are globally standard. For example, electric potential is always measured in volts, everywhere in the world.",
"Second, I think a large part of it is because time measurement leaves very few tangible artifacts (other than clocks). Once you spec a physical object, survey a plot of land or write down a recipe you are potentially creating a very lasting record that is locked to a particular measurement system. Time, not so much. "
] |
[
"That wasn't the question. I think he wants to ask why the standard measurement of time is universally accepted. There are plenty of other nations that had their own standard systems of other measurements prior to this last century."
] |
[
"Can something burn totally outside the visible spectrum?"
] |
[
false
] |
I'm wondering if there could be, for example, a fire that primarily radiates microwaves, or radio waves, or something of that nature. Most fire (or all, as far as I know) radiates in the infrared and visible spectrums. Could a fire exist entirely outside of those?
|
[
"Sure. And it is actually not that exceptional. Methanol is a highly desirable fuel for automobiles, but it has a major drawback that methanol flames are more or less completely invisible.",
"Here's a video of a methanol fire demonstrating the difficulty: ",
"https://www.youtube.com/watch?v=MnDX4FpDAzQ"
] |
[
"Blackbody radiation can make UV rays easily. That chart shows what the radiation ",
" like, but that says nothing about the components of the radiation that are outside the visible spectrum, only the distribution within it. By Wien's displacement law you can make the frequency distribution peak at arbitrarily high frequencies just by raising the temperature enough. Some stars can reach 3 billion degrees, which corresponds to a peak emission of low-energy gamma rays."
] |
[
"They used and still use pure methanol in racing. But there are better fuels then methanol (nitromethan/ethanol) and it's hard to optimize engines on pure methanol, that's why in most of the cases blends are used. And not seeing the flame just seems not to be a problem.",
"Burning methanol isn't the big concern, it burns with lower temperature than normal gasoline, is harder to set on fire and you can extinguish it with water. Methanol is safer than normal fuels in this regard.",
"One big problem is the high toxiticity and that it's not even the best fuel. Tehanol for example is a much better alternative."
] |
[
"How come we humans can recognize a face from caricature drawings?"
] |
[
false
] |
As per the title, why can we recognize faces from caricature drawings with wildly exaggerated features? Takes this caricature drawing for instance: Even with the elongated bottom half of the face, with deformed lips and, stretched eyes and nose, we can tell who the the person in the drawing is. (I guess provided we've seen the actual real face before). Even with caricatures that exaggerates different features, we can still recognize it as the same person, as shown in these other caricature drawings: I wonder why is that, and thanks.
|
[
"As you could imagine, recognizing faces is a really important part of being a human. It's so important that we have a whole area of the brain dedicated to recognizing faces. It's called the fusiform face area and it's located on the ventral portion of the frontal cortex. To add to this, it's generally better to recognize something that isn't there than not to see something that is. This bias combined with the huge amount of resources is what allows us to recognize caricatures, and even see faces where there are non, such as in the bumpers of cars. "
] |
[
"All the features of the face you recognize are there, just distorted. Some part of the face might be made bigger or smaller or flatter but all the parts have the same or similar layout color and form. The artist makes sure that is the case."
] |
[
"Human memory is associative, meaning that we don't recall things in isolation but rather based on relationships with other items. The brains stores relationships between items as synaptic connections between neurons, which allow us to reconstruct patterns even when they are distorted by \"noise\" (in your example, anything which is not part of the original face or image). Each time we see a pattern such as a face, these connections are strengthened. The pattern eventually becomes an \"attractor,\" a pattern stored in the brain towards which similar patterns will converge. In addition to caricatures, another example of this is the fact that we can often recognize ",
"extremely pixelated images of famous people",
".",
"There are very simple models of this, such as the Hopfield network, which uses only a few artificial neurons. If you have a math background, you might like to read more about the ",
"Hopfield network",
" and how it stores stable patterns."
] |
[
"Why are there no other Earth-like planets in our solar System?"
] |
[
false
] | null |
[
"It depends what you define as \"Earth-like\".",
"Mars, Mercury and Venus are \"terrestrial\" planets.",
"(What actually renders calling Martians extra-terrestrials pretty stupid...)"
] |
[
"All of the planets in our solar system are essentially pretty unique, almost no two of them are quite alike. Venus and Mars aren't that different from earth though aside from the liquid water oceans that they lack. "
] |
[
"Well Mars is a lot smaller than the earth, and I was wondering why it has no magnetic field to shield it?"
] |
[
"Could chemoautotrophic bacteria live in the hostile environments of another planet?"
] |
[
false
] |
Not entirely sure if this is the place to ask this question, but I was recently watching on Vimeo, and got curious. Bacteria have been known to thrive in some of the most hostile places on earth. Places where we don't think life could possibly exist because of lack of oxygen, light, and other things deemed necessary for life, yet they still do. So I was wondering, if it would be possible for bacteria that use nitrogen as an energy source to survive in other planets with high levels of radiation and toxic gases.
|
[
"The discovery of extremophile organisms like bacteria has certainly broadened our understanding of life, and the sheer strangeness and lengths it can go and survive.",
"So, the answer is yes. There definitely ",
" be organisms on other planets, even those that we might have traditionally thought of as being too hostile to life to support it. ",
"The discovery of such extreme organisms has led some scientists and more than a few science fiction authors to speculate about the possibility of life on Europa, one of Jupiter's moons, or on Titan, one of Saturn's moons. Both are rather extreme compared to earth, but it might just be possible. "
] |
[
"'Survive' is too weak a term. A number of extremophiles don't just survive, they thrive and live in these environments. ",
"It's true that we might not have evidence that abiogenesis could occur in harsher environments--but then, we don't really have that great of grasp of how it might occur under what we consider ideal conditions. "
] |
[
"We discovered some organisms CAN survive, not that abiogenesis can occur in such hostile enviroments."
] |
[
"Are there any moons we know of that rotate the planet at the same rate that the planet spins?"
] |
[
false
] |
If the rotation of the moon/rotating object matched the planet's rotation in terms of degrees, it would always be visible. Similar to how one side of the moon is always pointing towards earth. I was wondering if there is a planet where one spot on the planet always sees the moon at the same point in the sky?
|
[
"There is no planet like this, but ",
"Pluto",
" and its moon ",
"Charon",
" have this property. They are mutually ",
"tidally locked",
"."
] |
[
"The term you're looking for is geosynchronous orbit. I don't know of any moons in such an orbit."
] |
[
"As another commenter said, Pluto and Charon are mutually locked.",
"The important thing to note with this question - all planets with one moon will eventually end up in this situation given enough time. The Earth's rotation is continually slowing and eventually it's rotation will match the orbital period of the moon.",
"However in Earth's case the sun will become a red giant and destroy the Earth long before Earth and moon have a chance to reach this state."
] |
[
"Why is it hard to create tests for Covid19?"
] |
[
false
] | null |
[
"It's all three of those things. Various reagents have been in shortage at different points during this pandemic, and global demand is astronomic compared to the baseline. Many of the reagents are made in places that have been hard-hit (e.g. China) so it's required a retooling of the entire supply chain, not just scaling production up.",
"Instrumentation is important as well. These instruments used for RT-PCR are expensive, and once installed need to be validated before use, which takes time. After the pandemic, it's unlikely that this increased throughput will be needed, so there's reluctance to invest so much time and money for a temporary thing.",
"Finally, labor is a problem. While retraining technologists to run RT-PCR isn't a big problem, getting all the extra coverage without emptying all the other sections of the clinical lab is a big problem. There's a pretty large shortage of clinical laboratory personnel in the US (did you know that national laboratory professionals week was at the end of April?) and so redeploying staff can quickly mess up a hospital's workflow. Where I am, we relied on furloughed research scientists to run the tests, who have plenty of experience with PCR but almost none with the clinical aspects, and so there were a lot of logistics that had to be figured out before we could unleash the kraken.",
"To add to all that, any time something new is added (be it new reagent, new method, instrument, personnel, transport media, swab type, etc) we want to make sure it works before going live. So there's a good amount of testing ",
" the testing. We can only cut so many corners."
] |
[
"RT-PCR instruments are reasonably expensive, in the 60K-80K region for the one's we buy depending if we get the diagnostic model or not. It's expensive enough that you only buy what you need. New ones were in very short supply, it took us a couple of months to get additional PCR instruments."
] |
[
"The short answer is you need way more than just primers for a PCR test.",
"The early shortages were actually the enzymes, most assays use a single reaction to go from RNA to cDNA to PCR amplification. These are fairly specialized master mixes, and a lot of labs all use the same brand of this master mix which ran short.",
"RNA extraction reagents were also in short supply from various vendors. In a clinical lab the different brands aren’t interchangeable until proven to be so. Automated equipment also is specialized to a single workflow and can’t tolerate any changes. That means if your RNA extraction kit goes on backorder, RNA testing shuts down.",
"Equipment is also an issue, if the RNA extraction instruments and PCR thermocyclers are already heavily utilized for other tests there aren’t just a bunch of unused equipment sitting around. These instruments are expensive, and in general it takes 4-6 weeks to get in, even outside of a pandemic.",
"The final point is labor, all of these tests take time to do in the lab. Each sample has to be checked in and verified. RNA extraction and the PCR steps take time to do. Staff have to be very careful because false results and swapped samples are a huge concern. I’d estimate a lab spends more labor time on each sample doing non-lab work than actual lab work for this test."
] |
[
"What will happen to our solar system during the years when the Milky Way & Andromeda galaxies collide?"
] |
[
false
] |
After watching several different simulations of the two when they collide, I can’t help but notice that some of the stars on the outer edges of their disk shape look like they get thrown out into deep space. Since our solar system is close to the outer edges of the Milky Way, will we be one of those unfortunate few that get launched out into deep space? Due to the massive distance till the next Galaxy at that point will we eventually be pulled back in? Or will we stay safely nestled within the colliding forces? Obviously we all will be long dead when this happens, but it’s our planet and I’m curious about its future.
|
[
"The odds of anything physically hitting us are very low. We could potentially lose some stars that we see now, and we would gain new visible (to the eye) stars as well. Even with the new stars, the chances of a supernova affecting us are pretty low as well."
] |
[
"i'd venture to guess that our perspective of stars and constellations would be completely different... except for any bright galaxies."
] |
[
"Yes, even a million years from now the stars in our sky will be different. The collision with the Andromeda Galaxy will start about 4000 million years from now.",
"To answer the OP, during the collision the Sun will swallow Mercury, Venus, and possibly Earth, and then collapse into a white dwarf. But this is only because the Sun will happen to run out of fuel and die around that time, and the collision with Andromeda has nothing to do with it. The Sun's orbit around the galaxy will change: it will probably end up in a somewhat wider orbit around the merging galaxies, but there's a small chance it will end up near the center."
] |
[
"How the hell do siphonophores work?"
] |
[
false
] |
In Siphonophores the organism is said to be composed of several distinct zooids. How are these zooids differentiated from a single genetically uniform zygote? How are they organised into distinct parts of the organism, do cells migrate or are all the zooids in different parts of the organism with no hybrid tissue? These fuckers blow my mind like what the heck are they doing with this outrageous multi-species shitshow that invariably ends up looking super cool, examples of or just the Portuguese man of war. How the frick do their embryos develop to form distinct zooids and how do these differ enough to be considered unique organisms rather than cell types. Is it just spooky epigenetic shit that merits then being classified into groups of zooids? Also side note on a specific siphonophore, how in the hell does Glaucus marginatus consume cnidocytes without being affected by the compounds released when they burst. Sorry for the overload of questions I am really enjoying these ocean lads rn. Any answers to anything is appreciated
|
[
"Siphonophores are a type of hydrozoan. Probably the best known hydrozoan is a ",
"hydra",
", a small freshwater animal that's similar to a sea anemone. I'm going to start off talking about hydras to explain the basics, since they are like a highly simplified siphonophore, and then move on to the real thing.",
"Take a look at pictures of hydra, and they will tell you a couple of important things. The first is the body plan of the hydra. Body plan is the basic shape of an animal...for example, the land-vertebrate body plan includes a head, four limbs, and a gut running through the body. A hydra is simpler, it's basically a bag with tentacles around the open end. ",
"The second thing to note is that most hydras you see in pictures have a bud or two coming off of them. Basically, the hydra has a smaller hydra sticking off the side. This will eventually grow big enough, drop off, and become a new independent hydra. This is one way hydras reproduce.",
"Fundamentally, a siphonophore is not that different from a hydra where the buds do not fall off, but instead remain attached to the body. The different buds develop into different, specialized shapes that may be used for movement, defense, feeding, or reproduction, but they all share the same basic \"bag shape\" body plan of the hydra. This is why they are zooids and not organs...each individual zooid is a copy of the basic hydra body plan...imagine if your arm, for example, had its own tiny mouth and gut and limbs.",
"Siphonophore colonies are basically a string of zooids, usually hanging from a float. ",
"This page",
" explains the body plan. The float is at the top, then there's usually a chain of specialized zooids that propel the colony, finally there's a chain of feeding and reproductive polyps. You can see this well in ",
"this pic",
", there's a nub at the top, that'd be the float, the pneumatophore. Immediately following this is a chain of propulsive zooids, the nectophores, and then down below is an orange, stringy clump of feeding and reproductive polyps. There's a growth zone where these zooids are budded off.",
"Really, all this is explained beautifully in ",
"this video",
" I just found. ",
". ",
"Some other notes: ",
"these things aren't actually multispecies, despite the zooids being very different from each other. ",
"You know how I said siphonophores usually have three parts: float, propulsive polyps, and then the feeding/reproduction polyps? Portuguese man of war have a huge float but no propulsive polyps, and the feeding/reproductive polyps stay more in a clump rather than extending into a chain.",
"Glaucus marginatus isn't actually a siphonophore, it's a mollusk. It ",
" siphonophores though, and steals their stinging pneumaticysts for its own defense. They are tolerant to the stinging poison but also have a slime that helps keep the pneumaticysts from firing. They eat the unfired ones and transport them through branches in their gut to the those frills that stick out of their body, and can shoot them out to defend themselves from there. ",
"here's a link",
" with a good explanation."
] |
[
"Siphonophores belong to class ",
"Hydrozoa",
", and are probably best understood by comparison to more \"typical\" hydroid colonies, such as ",
". Most hydrozoans have two main life stages: a stationary polyp stage and a swimming medusa (jellyfish) stage. Polyps feed and grow on the ocean floor like coral or sea anemones, and they can reproduce in two ways: sexually or asexually. Sexual reproduction in most hydrozoans involved creating little medusas that swim off and mate with each other to form offspring, which plant themselves somewhere to become new polyps. (Interestingly, one polyp can produce a whole bunch of medusas while it continues to live as a sedentary polyp!)",
"Asexual reproduction of is simpler. A new clone polyp starts to bud off of the side of the parent polyp. In non-colonial hydroids, like ",
", the bud pops off eventually and begins to live independently. However, in colonial hydroids, they can stay attached and create branching structures of inter-connected individuals. This is the case for ",
". Importantly, the colony members (zooids) are not just physically stuck together, they share a common digestive system. This means that certain zooids can focus entirely on producing medusae while they are fed through the work of their siblings. These reproductive zooids are the bulb-shaped structures on ",
"this image",
".",
"Siphonophores follow the same basic principle, except they swim instead of being attached to the ocean floor. A siphonophore begins as a single floating protozooid, which ",
"buds off",
" more individuals who stay connected and specialize into ",
"various jobs",
". Some zooids feed, some reproduce, some protect the other zooids, and some swim.",
"I hope that clears things up!"
] |
[
"Thanks so much for your answer, I apologise for calling Glaucus marginatus as a siphonophore - this was the result of me misinterpreting the phrase “cryptic species complex” on the Glaucus Atlanticus Wikipedia page. Loved the video, thanks again for the help. "
] |
[
"What's the minimum size necessary a thing has to be to be seen from the ISS?"
] |
[
false
] | null |
[
"The human eye has an angular resolution of phi =1'=1/60° and the ISS has an average orbit altitude of z= 400 km. So the length l of the object in question is calculated as follows:\ntan(phi/2) = l/z so l=400km*tan(0.5')= 58 m. So theoretically, astronauts should be able to see football fields (as a dot). Note that this calculation works only if the astronaut is looking at the object in an 90°-angle."
] |
[
"That's a lower bound. Atmospheric distortion will probably increase that. "
] |
[
"That is awesome. Thanks for calculating it it looks complicated. For some reason I though you'd have to be way bigger to be seen. Huh. That's astounding thanks :)"
] |
[
"Can you compress a single molecule of a substance?"
] |
[
false
] |
[deleted]
|
[
"This is basically what happens in neutron stars. If you compress atoms hard enough, you can get them to the point where the orbital electrons are \"close\" enough to the nucleus to substantially increase the probability of electron capture. At this point, the electrons are able to combine with protons in the nucleus, which changes them to neutrons. ",
"Now, if this compression can happen to atoms, it's reasonable to assume that it can happen for molecules too. However I should note that the compression must be ",
" powerful. It's not something you can do easily."
] |
[
"The chemical bonds that hold a molecule together are deformable. If you have a lone molecule that is flying towards a solid wall, with sufficient speed the molecule will fall apart and the fragments might undergo some chemical reaction with other molecules nearby.",
"A key part of chemical reactions involves breaking old chemical bonds to make new ones. In fact, the details and consequences of how methane falls apart is an ",
"active research topic",
"."
] |
[
" //",
"Whither the Pauli Exclusion Principle then?"
] |
[
"[All Fields] We (non-scientists) like to think of science as, well as an exact science. What is something that is contested in your field, and where do you stand on it?"
] |
[
false
] |
I guess pretty much what the headline implies: In your field of study, are there any points (even better if they're widely accepted, but still fiercely debated) that there still isn't a solid general consensus on? I don't so much mean "Evolution vs Intelligent Design", but more just "We're really not sure how $THING works, but this is what I think based on $EVIDENCE"
|
[
"In computer vision and machine learning absolutely everything is up for debate. We're not actually trying to describe something that already exists, but to build something new. This means that the only right answer is one which works today.",
"The Bayesians(probability represents prior knowledge of a model) finally beat the Frequentists(no it doesn't), as outside of a very few domains it's incredibly obvious that prior knowledge about the world is clearly needed. So now the split is between Bayesians, and structured learning.",
"For people outside the debate, Bayesians believe everything is a probability, and the best way to estimate the location or type of an object is to pick its most probable state. Structured learning agrees with all of this, and then follows up with the comment \"Your models are so bad that treating their outputs as probabilities makes things worse, we need to do something different.\"",
"Then there's MAP vs. marginal estimation i.e. should we pick the coherent solution that is most likely to be completely right, or the incoherent solution which is more likely to be partially correct on average.",
"Then there is discrete vs continuous optimisation, i.e which one is right for any task you can think of. ",
"Then there is top down verses bottom up verses holistic reasoning. Should vision be done by driving scene knowledge from the top down to the little fiddly details, or should it be emergent, and driving from the smallest details up to global understanding. The third school of thought insists that everyone else is wrong.",
"Then there is the big split between wanting things done working, and wanting things done right.",
"After this, there's the little technical battles that people keep fighting that won't mean anything to most people in the field, never mind outsiders."
] |
[
"Tissue Engineering. Not really any debates there, but many people both inside and outside the field call it a \"voodoo science\". There aren't too many underlying principles, and its really just a bunch of labs trying to throw stuff at the wall to see what sticks. We take the principles of cell biology, and try to make an organ or a tissue out of it. Sometimes we get lucky, most of the times, we don't. Sometimes we discover something new that relates to actual cell biology along the way. Fun stuff all the same."
] |
[
"There aren't too many underlying principles, and its really just a bunch of labs trying to throw stuff at the wall to see what sticks.",
"..Sounds like engineering alright :)"
] |
[
"Why do healing wounds itch?"
] |
[
false
] |
[deleted]
|
[
"There are two answers here that are each half of the whole answer. Healing causes itching in part because of some of the hormones that are signaled in the wound-healing pathway, and also because of mechanical deficiencies in scar tissue vs. normal tissue. ",
"Wound healing is a complex process, so I'm just gonna go with a high-level explanation, since in order to get down in the weeds would take literally months. ",
"The first stage of wound healing is blood clotting and vessels constricting - your body is trying to seal the wound and stop you from bleeding out (your body, on a basic level, doesn't know the difference between a paper cut and getting stabbed with a sword). After this, the next step in the wound healing process is inflammation. A variety of hormones are released by damaged cells and immune cells that cause inflammation (such as hystamine) and attract more immune cells. The immune cells consume and destroy foreign invaders (bacteria) and particles (everything else) as well as destroy and consume your damaged cells. This inflammatory stage can cause itching, as the various hormones that cause the inflammation also cause you to be itchy. This is the hormone-induced itchiness another poster referred to. ",
"After and during the inflammatory phase, cells begin to proliferate to take the space of the damage tissue. To give them a scaffolding to build on, the body puts down collagen fibers as a sort of temporary \"skeleton\" (scaffolding is a better word, but I already used it). The cells of the damaged tissue then use that \"skelo\"-scaffold (which, except in pathological conditions, is never actually ossified) to help reform the tissue. However, collagen laid down for that scaffolding is poorly organized - the fibers point every direction, which means that the collagenous \"scaffold\" is very non-elastic. So instead of stretching under tension, it just pulls on all the tissues it's attached to. That causes the surrounding tissues to be pulled on, which can cause irritation and cause that itchy feeling. This is the mechanical aspect another poster referred to.",
"These processes are not discrete either. ",
"Wound healing is a ",
" complex process, so like I said, that is a very high level overview. If you'd like to dive into it more, the wikipedia page on wound healing is a good very-slightly-less-high-level overview. "
] |
[
"Itch receptors are present in the skin. They are all thought to be sensitive to histamine, which is present during healing. The itch receptors are poorly studied, in part because they are C fibers (narrow axons) and are therefore difficult to isolate in electrophysiological experiments. ",
"See Torebjork et al in the Journal of Neuroscience, 1997. "
] |
[
"IIRC from my physiology classes, it’s because scar tissue is tighter than regular tissue, and your skin has a lot of touch receptors. The stretching “tickles” them a bit. ",
"Secondly, especially with skin, the healing process is very dehydrating, and dry skin is also itchy. ",
"I could be wrong, but that’s how I understand it. "
] |
[
"When water/sweat is on our bodies, what property of water reacts with the air to cool us faster?"
] |
[
false
] | null |
[
"The water molecules have a distribution of energies, and the ones that are most energetic evaporate away, lowering the average energy of the molecules and thus the temperature."
] |
[
"It's not reacting so much as evaporating. To evaporate it has to be at a higher temperature, which means it has to have more energy - that energy comes from your skin and since you then have less energy (in the form of heat) you cool down."
] |
[
"You're asking about something called \"evaporative cooling\" which isn't unique to water (think of rubbing alcohol - much better at cooling the skin, but anyway...)",
"Water has ",
"a lot of special properties",
" and the relevant ones here are unusually high thermal conductivity and heat of vaporization.",
"When your skin is wet, there is a thin layer of water sitting on top of it. High thermal conductivity means that the water can suck heat from your skin very quickly. It does this until your skin and the water have reached the same temperature",
"See iorgfeflkd's comment for why evaporation causes the temperature of the remaining liquid to drop. Roughly speaking, the heat of vaporization determines how large that temperature drop will be. In all, you could think of it like this:",
"1) heat passes from skin to water until temperature of skin and water are equal\n2) evaporation happens, dropping the temperature of the water. Go to step (1)"
] |
[
"When a beta minus decay process turns a neutron into a proton and an electron, why does the electron get expelled from the nucleus?"
] |
[
false
] |
I know that Electrons are not found in the atomic nucleus, but why does it have to leave it, if it has been produced there? And a second one: can the newly formed electron be taken up by the electron shell of the same atom?
|
[
"Momentum conservation. ",
"A neutron at rest, decays into a proton, an electron and an anti-neutrino(electron variant). ",
"Since the anti-neutrino is ",
" massless, it carries away some percentage of energy off, and carries huge momentum. The proton and the electron soak up that momentum in the opposite direction, and their total momentum must sum to 0, because the original neutron had no momentum, it was at rest. Usually, that means that the electron is given a huge kick, so huge, it ejects the electron out of the nuclei to the continuum. ",
"Electron energy distribution"
] |
[
"You're most likely looking at plots of the radial probability distribution, which is the density at radius r, summed over the surface of a sphere of radius r; i.e. it's been multiplied by 4πr",
" , so it's naturally zero if r=0. That plot tells you which radius the electron is most likely to be at, rather than which point (or infintesimal volume of space) it's most likely to be in. The actual density for a 1s orbital for instance is (disregarding constants) e",
" , which obviously has its maximum at r=0. ",
"While many orbitals do have a node at r=0, the total electron density for a ground-state atom always has a large, sharp peak at r=0 with a cusp (the slope of which is ",
"proportional to the charge of the nucleus",
"). ",
"Here, for instance",
" is a plot of the electron density of water in the H-O-H plane, which gives you an idea of what densities look like (pretty boring actually). In that particular plot the density peak at the oxygen nucleus is cut off to fit the graph. "
] |
[
"So in principle, a slow beta electron might end up the shell of the atom where it has just been produced? "
] |
[
"How does melatonin work in the body, and what does it do?"
] |
[
false
] |
I'm particularly interested in the research being done on how melatonin prevents or treats cancer.
|
[
"Generally, melatonin works as an antioxidant. On the topic on preventing cancer, there was a study in 2001 that showed melatonin was able to prevent DNA damage in hamster kidneys. The article was focusing on a very specific type of DNA damage and then related these results to carcinogens.",
"Source",
"Edit: Formatting"
] |
[
"Hamster kidneys! Thanks, that actually gives me a place to start. :-)"
] |
[
"what did i miss? when did melatonin stop being used solely as a sleep aid?"
] |
[
"What does CO2 actually do to the ozone layer?"
] |
[
false
] |
I have been doing some research and get varying answers so I figured I would try to ask some people smarter than me. So does CO2 help or hurt the ozone layer? Most mainstream articles talk about how it’s the “most dangerous greenhouse gas” and such, but yet I’ve also seen articles saying it is helping close the hole in the ozone by keeping nitrogen oxides from reacting with the O3. So which is true? Does it actually help or hurt
|
[
"CO2 has no effect on the ozone layer. The ozone layer is a layer of O3. The problem with CFC is the cloro. As in chlorine. A single chlorine atom can break down as many as 100,000 O3 molecules. CO2 is greenhouse gas. That means it allows visible light and UV to pass thru but reflects radiated heat. Like the glass in a greenhouse, it let's in light to warm the inside but holds in the heat. gases are rated as GWP. global warming potential. This is a rating relative to how much greenhouse effect is had relative to CO2. So CO2 has a GWP of 1. Some refrigerants that replaced R22 freon, have GWP over 1000. So 1000x more greenhouse effect than CO2. but those new refrigerants don't have chlorine so they don't harm the ozone layer. Some natural gases like methane also have EXTREMELY high GWP. if climate change cause frozen methane pockets to thaw out, it could cause a runaway greenhouse effect.\n-source: 609 certified HVAC tech",
"Edit: forgive my grammar. I'm swipe typing on mobile. Just trying to get the info in before someone shows up with wrong info.",
"Edit: i think where you are confused is you think greenhouse gas is the same as \"harm ozone layer\" those are 2 separate functions a gas can have on the environment.",
"Edit: so to answer your question directly, CO2 has no DIRECT effect on ozone layer. It probably does help prevent other nox from harming it but id say that's an indirect effect."
] |
[
"Ozone ",
" 'help keep in heat' - as ",
"/u/Captain_Trips_Tx",
" said, ozone is a greenhouse gas like CO2. We quantify the amount of heat a greenhouse gas 'keeps in' through a metric called the ",
", and the radiative forcing of ozone in the present atmosphere is ~0.35 W/m",
" compared to ~1.8 W/m",
" for CO2 (note that these figures are slightly out of date as they are from the ",
"2011 IPCC AR5 report",
"). In other words, CO2 is currently causing around 5x more warming than ozone is."
] |
[
"I gotcha. Thanks for explaining!"
] |
[
"How does gravity affect light?"
] |
[
false
] | null |
[
"The source of gravity isn't just mass, it's the stress-energy tensor, which contains things like mass, energy, and momentum."
] |
[
"What exactly is this \"stress-energy tensor\" if I may ask?"
] |
[
"You can think of it as a 4x4 matrix which contains things like mass, energy, and momentum. And it has certain transformation properties under Lorentz transformations."
] |
[
"What's the fastest possible speed a human can potentially reach?"
] |
[
false
] |
We all know that world records get set every now and then, but is there eventually going to be a world record that can literally never be broken ever in a race? Will a human being under the perfect conditions ever be able to hit a speed that is the fastest possible ever?
|
[
"It depends very much on the limitations of the race. Are you talking fastest speed over, say, 100 meters on foot? A mile on a bicycle? Or strapped to whatever contraption someone can dream of to go fast?"
] |
[
"Well I suppose it would be interesting to see what the predicted maximum would be for each event. But The article already posted seems to explain most of what I was wondering :)"
] |
[
"The record for fastest speed ever achieved by a person is apparently held by the guys on Apollo 10. Figured it had to be something like that."
] |
[
"Once the Earth was formed into a planet, has the North Pole ever not been covered in ice?"
] |
[
false
] |
[deleted]
|
[
"Yes. In the beginning, pre-atmosphere, Earth had a very hot surface. It was essentially the fiery leftovers from the creation of the Earth. Even much later, when Earth was a more recognizable water-covered, atmospheric, life-harboring planet, there were still periods when the polar ice caps did not exist. According to ",
"this article from NOAA",
":",
"\"Geologists and paleontologists think that during much of the Paleocene and early Eocene, the poles were free of ice caps, and palm trees and crocodiles lived above the Arctic Circle\"",
"So yes, there was a time when the ice caps didn't exist."
] |
[
"Also note that the continents we know didn't always have their current shape and position. There have been numerous supercontinents over the millions of years since Earth cooled enough for ice to form. There have been many times when there just wasn't any land AT the north pole to get covered in ice. ",
"There is no land surface as such under the current North Pole, but it is hemmed in for most of its circumference by Europe, Greenland and North America. It is unknown of such a large and stable (comparatively) expanse of ice could have formed and remained at the pole during one of the many supercontinent cycles. "
] |
[
"For much of Earth's history the poles were not covered in ice. We happen to be in an ",
"ice age now that began about 30 million years ago",
", but before that the poles were generally ice-free since the end of the last ice age, 260 million years ago.",
"https://en.wikipedia.org/wiki/Timeline_of_glaciation"
] |
[
"If the eye is opened during sleep will the brain still process the visual information?"
] |
[
false
] | null |
[
"No, and maybe!",
"OK. During sleep, particularly REM sleep, the ascending sensory pathways are shut down by strong inhibition. On the other hand, visual input provides a very strong drive to inhibit sleep. Enough light in the eyes, and you stand a good chance of waking up. However, lower amplitude visual inputs should be shut off. "
] |
[
"Yes. The pathways involve the PPT/LDT, reticular thalamus, and LGN. Yes, a coma involves shutting down these same pathways. So does persistent vegetative state (now politically correctly called unresponsive wakefulness syndrome). "
] |
[
"the ascending sensory pathways are shut down by strong inhibition",
"Physically, what's happening when the visual pathway is \"shut down\"? Is there some spot where the optic nerve connects that gets a dump of some chemical that suppresses the neuron actions? I would imagine it needs to be fairly early in the visual chain.",
"Another question that just occurred to me: If someone is in a coma, are the visual sensory pathways shut down in a similar way?"
] |
[
"My dad has early onset Alzheimer's, 23andme gives me a 2.0x risk of Alzheimer's. I'm 24, what's my game plan?"
] |
[
false
] | null |
[
"Lots of curry and spicy foods.",
"Alzheimer's is all but unheard of in India."
] |
[
"Eh I'll stick with awesome food. If it's the water, you can move?"
] |
[
"It wasnt about the water. I just took an example which was near to that food thing. I just wanted to show that you cant break down the whole cultural and medical environment of a counter/culture to food. It would be too easy :D \nBut anyway great food i can agree to that (but thats not on topic anymore)",
"Back on topic: I'm not that familiar with Altzheimer, but as I remember its not that researched at the moment. So reasons etc. arent that clear as they would be needed to make an decision. Maybe you should live every that as it would be the best (eh, well you wouldnt remember I think...). Hard question OP. Eating lots of curry and spicy foods could be helpful. It also could never happen that the Altzheimer desease emerges..."
] |
[
"If I mix rubbing alcohol and water to lower the freezing point of water, will it take longer to thaw?"
] |
[
false
] |
I am about to make some ice packs for the cooler. I was going to use a mixture of water and rubbing alcohol to lower the freezing point and make colder/flexible ice packs that do not freeze completely. Will these ice packs stay colder longer that a straight frozen water ice pack will? If not, am I better off using straight water or another mixture?
|
[
"My intuition says yes, because adding alcohol lowers the freezing point of water, and the specific heat of liquid water (4.187 J/gK) is higher than that of solid ice (2.108 J/gK)."
] |
[
"You should keep in mind however that the specific heat of isopropanol is much lower than that of water (2.604 J/gK). Perhaps more importantly though, the heat of fusion of water is 333 J/g, so by decreasing the amount of frozen water, you're decreasing the amount of energy that needs to go into phase change before energy can go into raising the temp of the ice pack."
] |
[
"You're absolutely right - the phase transition dominates the energy transfer, so it's better to use a substance with the highest possible heat of fusion, such as pure water. The wikipedia page on ",
"ice packs",
" claims that the substance used in ice packs is typically water or a water gel with additives to prevent bacterial growth. "
] |
[
"Why does the far side of the moon have so many small craters while the near side has several very large ones?"
] |
[
false
] |
When I look at images of the moon, the side which always faces the earth has several very large craters but the side that faces away from us is pockmarked with much smaller ones. This leads me to think that the far side of the moon has suffered many tiny impacts while the near side has suffered fewer but much larger impacts. Is that the case? If so, why? Is the Earth's gravity affecting the way that meteors strike the moon? Or this an illusion, because the far side getting struck by large impacts but these large craters are getting erased by many smaller impacts (While they do not as commonly strike the near side, thanks to Earth's protection). These are just a couple of rough guesses, clearly I don't have a lot of knowledge about this.
|
[
"This is a function of the difference in the thickness of the crust between the farside and nearside of the Moon.",
"The frequency and size of impacts on the Moon is actually roughly equal between the two sides. In fact, the largest impact basin on the Moon is on the far side, ",
"Aitken Basin",
", the huge dark area in the southern hemisphere. It's a bit difficult to see since it's been heavily eroded by smaller impact craters, though it's much easier to spot in a ",
"topographic map",
".",
"However, Aitken Basin doesn't look at all like the large impacts on the near side, such as ",
"Mare Crisium",
". The difference is that the crust on the near side is much thinner than on the farside. ",
"Back when the Moon was still young, its interior was still molten and large impacts were much more common. Keep in mind that the Moon was also fairly volcanically active for the first billion years or so, during which most of those impacts would have occurred. It would have been much easier for a rising mantle plume of magma to break through the thin near side crust, particularly where it was even thinner in the large impact basins.",
"As a result, the big impact basins on the near side were filled and resurfaced by lava, erasing most of the craters there. By the time the lava finally cooled ~3.5 billion years ago, impacts were much less frequent, so only a few more recent ones can be spotted on the otherwise smooth surface of the solidified lava - that's what gives Mare Crisium its much more pristine appearance.",
"Now, exactly why the nearside crust is thinner than the far side remains a controversial topic of debate in planetary science. Some folks claim that this can be done with differential tidal heating, while other say that's impossible.",
": It's an illusion. Both sides are hit with roughly the same frequency, but the large near side impacts got filled in with lava because the crust is thinner on that side, thereby erasing the evidence of the first ~1 billion years of impacts in those locations."
] |
[
"You have to think of it in terms of ",
" pull. ",
"The whole Earth is being pulled by the Moon, determining its orbit in space. The near side is being pulled a little more than average so there's a bulge on that side as it tries to be in a nearer, faster orbit. On the other hand, the far side is being pulled a little less than average so there's a another bulge on that side as it tries to be in a farther, slower orbit."
] |
[
"Again, ",
"that's incorrect",
". The tidal force would pull the lava to both the nearside and farside of the moon, for the same reason that there are two \"high tides\" at any moment on Earth."
] |
[
"Is it theoretically possible to assemble fused subatomic particles into macro-scale 3-dimensional objects?"
] |
[
false
] |
I know a little bit about some of the concepts of quantum physics - enough to know that the strong nuclear force is really strong. I was reading an article about nuclear fusion when it dawned on me that if it were possible to fuse protons or neutrons of the like into chains or rings, creating a new element with spatial structure instead of just chemical differentiation from the other elements, that element could be used as a new rigid material, the strength of which would be unparalleled by anything humans have created thus far. I just want to know if it's possible or not based on current theories in the field.
|
[
"I love this question, as it is basically trying to get organic chemistry in nucleii. Complex molecules that are not simply as compact as they can get like a crystal depend on delicately balanced attractive and repulsive forces. Neutral atoms tend to generally repel one another when the electron shells overlap, but attract each other by dipole moments when a short distance apart. Some are ionised and attract each other strongly, others form covalent bonds. This allows complicated shapes to form. But nucleons ought to just attract one another with the strong force, and protons repel one another.",
"I like the idea of a structure that is a long chain of neutrons with attached protons to repel sections and keep it from collapsing into a sphere. But these things are not hard balls, they are waves and will just rearrange themselves to the lowest energy level, even if it means beta decay and reverse beta decay happening.",
"Imagine building a tower of Jenga bricks end on end. Then remember that neutrons do not even have a flat side to balance them on"
] |
[
"The simple problems are that firstly neutrons are so strongly attracted to each other they would clump rather than form rings.",
"Secondly neutrons weigh and therefore have more energy than a free proton and electron. So any clump of neutrons will begin to decay into protons until the repulsive force of the protons would reduce the energy more than the conversion of a neutron . Protons repel one another because of electrostatic force, and it works out that any clump of mixed protons and neutrons greater than about 88 protons becomes unstable and can lower its energy by emitting a helium nucleus.",
"Extreme gravity can overcome this limit, in for example ",
"neutron stars"
] |
[
"If you're talking only using protons and neutrons, wouldn't you also be creating something amazingly dense like a neutron star? Your material would be too heavy to move."
] |
[
"How did early humans clean themselves?"
] |
[
false
] | null |
[
"Also, did they wipe their butts after pooping? Or just poop and go?"
] |
[
"Well, it's not really hard to do. Block one nostril and exhale very forcefully. Basically what you do when blowing your nose with a handkerchief but without that and a bit more forcefully because it gets messy otherwise."
] |
[
"When out on patrol, Roman soldiers would just go to the toilet wherever they were. Back at the fort, they shared communal toilet spaces, such as can be found at Hadrian's Wall. The toilets had their own plumbing and sewers, sometimes using water from bath houses to flush them.",
"http://www.bbc.co.uk/learningzone/clips/how-did-the-romans-go-to-the-toilet/5409.html"
] |
[
"Why do my calculator and Wolfram Alpha disagree on a negative number with a fractional exponent?"
] |
[
false
] |
When calculating something like (-2) my TI calculator gives a (real) value of about -1.515, but when I ask Wolfram Alpha for the it gives an imaginary number, but with the same magnitude as what the calculator gives. Why is there a difference, and is one of them wrong?
|
[
"The answer is right in the page. Over the complex numbers a complex number (note real numbers are complex numbers with 0 imaginary part) has n n",
" roots.",
"http://i.imgur.com/6NgioRk.png"
] |
[
"Yes. That's basically it. There are deeper reasons, but in essence it's because (-1)",
" doesn't have a real solution. ",
"The slightly deeper reason you can see by looking at the roots of (-2)",
" plotted in the complex plane: ",
"http://imgur.com/HmngYU8",
"As you can see they are 4 symmetric points across the plane. If the denominator is even you will have an even number of symmetric points in the complex plane. That means that you will either have 2 real roots (for example how x",
" = 1 has both +/-1 as a root) or none (how x",
" =-1 has no real roots)."
] |
[
"It seems you have a satisfactory answer to your question already, but I just want to point out on the three TI calculators I tried out (-2)",
" will be interpreted by the machine as (-2",
" )/5. The parenthesis really need to go around the exponent, but it's never a bad idea to just put them around everything that it makes sense to."
] |
[
"How can V8 vegetable juice go a year without expiring?"
] |
[
false
] |
I have a bottle of V8 that says it expires Jan 2014. I've actually had it for about two months and just finished it. What is it that allows it to last so long?
|
[
"What's this totally incorrect and potentially-hazardous nonsense? ",
" of 'bad things' can grow in food under anaerobic conditions - not least ",
", which causes botulism. V8 juice holds because it's been pasteurized, which is when you heat up sealed containers of food to kill the bacteria in them. ",
"See the sidebar where it says no 'layman speculation'? "
] |
[
"What's this totally incorrect and potentially-hazardous nonsense? ",
" of 'bad things' can grow in food under anaerobic conditions - not least ",
", which causes botulism. V8 juice holds because it's been pasteurized, which is when you heat up sealed containers of food to kill the bacteria in them. ",
"See the sidebar where it says no 'layman speculation'? "
] |
[
"Usually if the expiration date is affected by breaking the seal, they list the second date, right? ",
"Not necessarily, no. It ",
" doesn't hold as long once it's been opened. It depends entirely on the product but it's typically days to a few weeks. Two ",
" sounds like a very long time, it's possible the V8 has some preservatives in it to keep it longer after opening. At least most juices wouldn't normally keep that long. "
] |
[
"How would our trajectories differ between interplanetary travel and interstellar travel?"
] |
[
false
] |
I understand the basics of changing a space crafts orbit to reach "nearby" destinations, such as the moon or Mars, or any body in our solar system. But across the enormous distances between star systems, how would the trajectory of a spacecraft look? Would it be relatively straight-lined point-to-point, or adjusting our orbit the exact same we currently do, but on a galactic scale? This is of course assuming that we use spacecraft that work like those we have today, nothing futuristic using warp or FTL or anything like that
|
[
"One thing others didn't mention is how the navigation requirements for the spacecraft are going to change.",
"Currently, if something is in orbit around the earth, we can use GPS or ground based optical measurements of the object to determine its current orbit. If we're near some other celestial body (such as OSIRIS-REx at Bennu, or a mars vehicle coming in for landing), we use terrain relative navigation where we build maps of the surface, and use images/LiDAR to determine where we are relative to known features.",
"In \"deep\" interplanetary space though, where you aren't close to anything, we primarily use the Deep Space Network (DSN). The DSN is a series of ground stations on Earth that use Two-way Range, Doppler, and Delta-DOR to measure the current position/velocity of a spacecraft. There are also some other options such as celestial navigation where we can image other planets/solar system bodies, and by knowing where they are in space at the time of the image, we can back out where we must be to observe their relative positions.",
"However, in interstellar space, none of these techniques would work. The DSN (as it currently stands) would not be able to obtain measurements that far out. For a mission like that, something like ",
"SEXTANT",
" (Station Explorer for X-ray Timing and Navigation Technology). These are new techniques whereby we detect the pulsars emitted by pulsars in the milkyway and use their regular pulses as something akin to GPS, but that would work anywhere in the galaxy.",
"Another option is the use of abberation. As you move faster and faster, your field of view somewhat expands, causing the apparent positions of other stars to contract and get closer together. By measuring this abberation, you can back out how fast you might be going. This would be coarse, but could provide another useful datapoint in addition to an x-ray pulsar based technique for estimating your trajectory."
] |
[
"If you want to reach Proxima Centauri, the nearest star, in less than 10,000 years then you need to have a speed of at least ~100 km/s (both relative to us and Proxima Centauri, doesn't make a big difference).",
"During that time the rest of the galaxy accelerates the spacecraft by ~100 m/s, so that's already a tiny effect, but it also accelerates the Sun and Proxima Centauri by almost the same amount. The difference in acceleration is far less than a meter per second - it's completely negligible. If you want to go faster (e.g. to reach more distant stars) the effect gets even smaller.",
"Your interstellar spacecraft might have some non-trivial course within our Solar System while it's speeding up, and it might do some maneuvers at the target star, but in between it's just a straight line for all practical purposes."
] |
[
"Ok, so, low earth orbit ('LEO') is typically 7.8 km/s. We typically have a delta-V of +4.2km/s to throw something at Mars from LEO, then -1.4km/s to circularize/slow down to Mars orbit on arrival, for (4.2 + 1.4 = ) 5.6 km/s of delta-V total from LEO. That gets you to Mars in ",
" btw.",
"Meanwhile, Mars is orbiting the Sun at 26 km/s. Earth is 30ish. In an imaginary frame of reference, you're going maybe 35 km/s relative to the Sun, then, back-of-envelope, to get from Earth to Mars on a Hohmann Transfer that takes 259 days.",
"Alpha Centauri is moving towards us at around 22 km/s, give or take, so, at a very basic level, stars are moving at similar relative velocities as our inner planets' orbital velocities, meteors, and interplanetary travel with chemical rockets.",
"If you're talking cryobarge/generation ship, the relative velocities are such that ",
" once you're more than a few days from the last planet/star you're in circular orbit of, you're pretty much going in a straight line lookin' leg of a hyperbolic orbit, e.g. a Sol Escape trajectory.",
"Much faster than that? Leave orbit, aim at destination, fire Star Drive for X hours at Y gees of acceleration, turn around at midpoint, start slowing down. Like, nothing outside of the galactic core is moving above the tens of km/s in relative velocity at a 'to the next star' scale. All bets are off for actually getting in and out of orbit around planets/moons with small orbits around their parent..."
] |
[
"Is there ever anything going on that is not a chemical reaction?"
] |
[
false
] |
Force maybe?
|
[
"Yeah, seeing as a chemical reaction is defined as \"a process that involves rearrangement of the molecular or ionic structure of a substance\" everything that doesn't do that is not a chemical reaction. E.g. boiling water and melting ice involve rearrangement of the spacing between water molecules yet the water molecule does not react chemically. So you could think of a million things that aren't chemical reactions. "
] |
[
"I am presuming here you mean bond breaking or bond formation as a chemical reaction. All nuclear reactions, like radioactivity, do not qualify as chemical reactions. Sound waves are not a chemical reaction, they are gas molecules undergoing pressure waves, no bond formation or breaking involved at all. Phase transitions from solid to liquid to vapor, these involve the transfer of energy into or out of the material, again no chemical reaction necessary."
] |
[
"Phase transitions involve breaking/forming of intermolecular bonds, nuclear bonds are broken/formed during nuclear events. Just to clarify. "
] |
[
"If fire goes from red to yellow to blue to white, matching with the frequency of light why do we not (or very rarely see) green natural fire?"
] |
[
false
] |
I’ve seen multiple fire colours from natural heat and not copper, strontium or others. So why is it that we rarely (or don’t) see green fire?
|
[
"This is an excellent question! ",
"The short explanation is: it's just the way the universe works. ",
"The medium explanation is: ",
"Planks' law",
" governs the spectral density of electromagnetic radiation emitted from a ",
"black body",
". As the temperature of a body increases from absolute zero, it emits radiation with a peak wavelength starting in the microwave range (i.e. ",
"CMB radiation",
"), increasing into the ",
"far infrared",
" around room temperature, and entering the visible around 1000K. As the temperature increases the peak narrows as the intensity increases. But (due to the nature of cosmological constant, and many other factors), when the blackbody temperature is around 5100K and the peak is at ~500nm (what should be green), the width of the peak is so large as to encompass the entire visible spectrum. So it appears white instead of green to our eyes. The reason we can distinguish the red and blue shades is because those are the highest and lowest colors our eyes can see, so when the peak wavelength is in the infrared we see mostly red and when the peak wavelength is above the violet range, we see blue/white (due to the shape of the ",
"spectral emissivity curve",
")",
"The long explanation is: I'm not a physicist, but I'm sure a real physicist could go much more in depth about this phenomenon. (Insert physics here)"
] |
[
"Actually a very good explanation. It’s why we don’t see green stars, too"
] |
[
"/u/Farnswirth",
"'s answer refers exclusively to the blackbody radiation of a medium, which accounts for the vast majority of the flame colors we are familiar with, however the flame can also assume a specific color through the bright emission of spectrum lines from excitable atoms, which can happen at any frequency of the spectrum.",
"Borax and copper sulfate are the most common compounds that produce a green flame."
] |
[
"Is it possible to have an \"opaque\" laser?"
] |
[
false
] |
[deleted]
|
[
"Photons are uncharged bosons. As such, they can occupy the same state and can pass through each other without interacting. In order for a light beam to be opaque, another light beam propagating through the same space as the original light beam would have to scatter off or be absorbed by the original beam. This does not happen.",
"Although photons do not directly scatter off each other, they can theoretically indirectly scatter off each other by decaying into matter-antimatter pairs which interact and then recombine to make photons. But the energies involved are so high and probabilities are so low, that I don't believe that indirect photon-photon scattering has been conclusively observed in the lab yet. In any event, particle accelerators are needed to get the energies required for photon-photon scattering. A regular optical laser won't suffice.",
"Also, in theory, if the photon density gets high enough, it could form a black hole, which would be opaque. But that is an exotic prediction at extreme energies that are inaccessible to earthlings. ",
"Note that if a material is present in the volume of space where two light beams are intersecting, all sorts of interesting things can happen. The initial beam can indeed render the material opaque."
] |
[
"Based on photons alone, not for reasonable lasers. If you focus enough light in one place, it's theoretically possible to create a ",
"kugelblitz.",
" However, it is possible, within an atmosphere, to create a laser that ionizes the air into plasma, which is generally opaque to electromagnetic radiation below it's plasma frequency. Generally this is accomplished with ",
"a focused laser and very short pulses",
", because it requires tons of power. But ",
"electrolasers",
", using a laser induced plasma channel to conduct electricity can produce opacity over longer distances. "
] |
[
"Also, in theory, if the photon density gets high enough, it could form a black hole.",
"I don't see how that would work. The energy in the beam has to come from the laser medium, which would have been a black hole already. Even if you try to get this effect by firing multiple lasers at one point, I still don't see why that would create a black hole. You cannot just add up the energy, pretend that the momentum doesn't exist, and apply the Schwarzschild limit. Maybe it does create a black hole, but the metric would have to be dynamic in time and account for the formation. I'm not even sure that problem has been solved yet."
] |
[
"Which is heavier, ice or water?"
] |
[
false
] | null |
[
"Assuming \"amount\" means either mass or # of molecules then they are the same weight. If you freeze a certain amount of water it will have exactly the same mass in both states but more volume in the ice state (lower density). Both samples would have an identical number of water molecules as you don't form or destroy molecules by changing states of matter."
] |
[
"So changing states doesn't effect the weight, because the matter doesn't physically change? Does this extend to gasses as well? Would boiling a kettle of water but \"catching\" the steam result in the same amount of moisture, just displaced differently then?"
] |
[
"Careful with the terminology. A phase change is a physical change but not a chemical one. If there is no chemical change then all the molecules on one side are exactly the same as the other, just with some different energy or state.",
"Also, even with a chemical change mass is always conserved, so as long as you have a closed system then the mass will never change even though physical properties like phase, density and such can change.",
"If you caught all the steam that came off a boiling kettle it would weigh just as much as the \"missing\" mass of the water."
] |
[
"Does the shape of a lightning bolt have an effect on the sound of the thunder?"
] |
[
false
] |
Primarily if we were to graph a bolt of lightning and compare it the the levels recorded to that associated roll of thunder, would we see a correlation? What if the sound were graphed in a 3D space? How different is a forked lighting bolts' thunder VS the thunder from a bolt with no forks? Does this make sense?
|
[
"I have issue with your perfectly straight lightning bolt. Certainly if it were close to you and straight, the sound would be one big boom, but given the size of lightning bolts, the closest part of the \"line\" would reach your ears perceptibly sooner than the furthest.",
"To get a single BOOM you'd need a circular arc with your head as the center."
] |
[
"I have issue with your perfectly straight lightning bolt. Certainly if it were close to you and straight, the sound would be one big boom, but given the size of lightning bolts, the closest part of the \"line\" would reach your ears perceptibly sooner than the furthest.",
"To get a single BOOM you'd need a circular arc with your head as the center."
] |
[
"Resoning",
" \nFork lightning is the actual lightning. Sheet lightning is actually layers of clouds illuminated by hidden fork lightning. ",
"This is the closest I could get between the difference between the sound of forked and sheet lightning. I think they maybe a muffling effect due to the clouds, however, there isn't a significant difference."
] |
[
"Why don't airliners pre-rotate their wheels prior to landing?"
] |
[
false
] |
It would seem to me that landings would be a lot smoother if the plane's wheel were already turning at a speed that roughly matches the aircraft's landing speed, rather than the wheels having to go from 0 to 200 kmph at the instant of making contact with the ground. Or do they already do this?
|
[
"I work in the aircraft wheel and brake industry. First, a landing doesn't leave kgs of rubber on the runway... only a few grams. Second, aircraft are very weight conscious, and anything not necessary costs a lot of money in fuel. Spinning up the tires before landing would require some mechanism (motors, fins, gerbil wheel, etc.), which would add weight to the aircraft with minimal returns. Summary: it's not worth it."
] |
[
"Also, aircaft almost never land perfectly straight due to crosswinds - this means that some sliding is necessary at touchdown; pre-rotating wheels would reduce this initial slip on the runway and add unwanted lateral forces to the undercarriage."
] |
[
"Okay. Looked it up and it seems I exagerated a little from my memory. BUT this site ",
"link",
" says that it is half a kg per landing. ",
"Specialized rubber-removing machines are actually operating regularly, although maybe not daily. Source: I work at an airport.",
"This article explains it too: ",
"link"
] |
[
"Why haven't we weaponized lasers to a point that they could just blast a hole in any human from a long distance?"
] |
[
false
] |
I know there are extremely powerful lasers used in surgery or industry. Why hasn't the DoD created some weapon that would allow a novice shooter to blow a hole in someone from two football fields away? No gun shot. No gravity or wind carrying the bullet away from the target. Drone killings would be simpler and cause little to no collateral damage. Assassinations would be as easy as just having line of sight.
|
[
"There's two physical reasons for the difficulty. One is the power source and the other one is diffraction/scattering. The surgery (and machining) lasers have a very significant power supply and close to the target. In order to get much of an effect, you need a lot of optical energy in a small location (i.e. a high intensity).",
"The surgery and machining lasers are able to draw a lot of electrical power from their power supply, which is good because high-powered lasers are generally not very efficient from electrical to optical output (i.e. how much optical power the laser outputs vs. how much electrical power it consumes). 10% is an extremely high number for a high-powered laser. So, a soldier would have difficulty carrying a power source for the laser.",
"The other problem is a problem of having all of the energy produced by the laser focus to a small spot, so as to concentrate all of the energy that the laser does produce. The laser beam does not propagate in a straight line because of diffraction. The equation for the spot size (assuming that the beam is merely propagating) at the target is size~1.22(wavelength)(distance)/(Diameter of laser aperture). So, given fairly realistic numbers of a 1 micron wavelength, 200 meters (~two football fields) and say a 3 mm diameter laser aperture, we have a spot size of ~80 mm, which about 750 times less intense than the beam leaving the laser. It doesn't get any better when we put a lens there, because diffraction is worse than the lens. Even if we make the beam diameter 12.7 mm (same size as a .50 cal bullet), we still get greater than a factor of two reduction in intensity at the target, and that laser has just become a lot more difficult to make.",
"As such, we're very far away from a man-portable laser (if it's even possible) and the vehicle-mounted ones are expensive for the simple reason that those physical problems mean the laser is very expensive to make and maintain. Advances are happening, but so far we're pretty far away from having general laser weapons deployed all over battlefields."
] |
[
"Herrsmith laid out the technical limitations very well, but here's the reason why this isn't even a very feasible idea:",
"Cauterizing a 12.7mm/.50cal hole in someone's body is no where near as catastrophic as having a 50g piece of metal tear through your body at 3000 ft/s. Many of the reasons why lasers are used in surgery are the precise reasons why they make a terrible weapons.",
"Bullet wounds are brutal and nasty. There's blood loss; there's the acute nature of the wound which has the potential to damage critical areas; then there's the fragmentation of the bullet, your armor, and yourself (i.e. your own bone) that can cause additional trauma and blood loss; and then there's ",
"hydrostatic shock",
".",
"The terminal ballistics of a laser are essentially non-existent. You are assaulting the human body with focused radiative energy, instead of imparting kinetic energy into a medium. I assume a laser would essentially cauterize the wound as a byproduct of its action. In other words, photons about about the nicest thing you can throw at someone. Even if you could create one powerful and small enough, it still wouldn't be a very effective weapons system.",
"Furthermore, lasers still have to deal with the biggest problem that bullets have, they've got to get through the atmosphere. (Gravity is predictable) The atmosphere can be some powerful armor if your using lasers to kill people."
] |
[
"The answer is simple. Converting stored electrical energy into light energy is extremely inefficient. An 11 watt IR laser could take several hundred watts of power to operate. That's a lot of wasted energy, usually in the form of heat."
] |
[
"Can quantum entanglement / other phenomena of QM be explained by a higher dimension?"
] |
[
false
] |
Hey guys, excuse my science speak as I am a layman, I was just wondering, if there was indeed a dimension that encapsulates/ is parallel to our space time, that is not restricted to space/time, could that dimension explain spooky action at a distance? Like the particles would be 'connected' through that higher dimension.
|
[
"I would say it ",
" spooky action at a distance, and it's not well understood at all. But I agree that higher dimensions wouldn't solve any of the remaining questions."
] |
[
"Quantum entanglement is not a \"spooky action at a distance.\" It's very well understood and doesn't require higher dimensions, nor would the addition of higher dimensions actually help explain it."
] |
[
"Quantum mechanics is local.",
"It might be. We have no conclusive proof either way. But nobody actually working in this field believes that QM is really local. ",
"Your example wouldn't change that in any way even if it was correct. But it's not, because the correlation will be there even if you don't compare the two measurement outcomes. "
] |
[
"How far across a genus or species do allergies go?"
] |
[
false
] |
Such as a person being allergic to a dog. How far from canis lupus familiaris is would you need to go (if at all) to not be allergic to one?
|
[
"As ",
"/u/ketralnis",
" says, the allergy is to a specific substance (usually a protein) produced by the source of your allergy. If any other organism (including ",
"!) produces a protein with similar structure to the one you are allergic to then you will also have an allergic response when exposed to it. Look up antibody cross reactivity for more info."
] |
[
"And so is that how people can have multiple allergies to seemingly different organisms? Because they happen to contain some type of protein of similar structure that their body rejects or reacts to?"
] |
[
"That is a possible factor, however it is more likely that those individuals are predisposed to allergic responses and are actually making antibodies to different proteins produced by each of the organisms they are allergic to. Genetic or environmental factors can result in a tendency to produce IgE antibodies (associated with allergies) instead of other antibody types which mediate response to infections in different parts of the body."
] |
[
"Why are transistors so crucial to modern technology?"
] |
[
false
] |
[deleted]
|
[
"Solid state devices was not my favorite class, but this what I remember. They can hold a charge, being on/off or 0/1, which is what computers understand. They also amplify voltage fairly linearly in a certain input range. Being a lot smaller than old vacuum tubes, so we can have more \"brains\" in a computer that is bit the size of your entire house like back in the day. \"Moore's Law\" says that the number of transistors that fit on a chip doubles every 2 years. Heat is still an issue, though, so I have heard that we will eventually get to where heat overcomes any size problems of fitting more transistors on a chip, so that our technology will dead end. They are trying to do quantum computers now, which I know nothing about, but I remember a link here recently where scientists say they made a quantum computer that is faster than a universe-sized normal computer. Sounds pretty crazy, huh?"
] |
[
"Transistors don't generally hold a charge. A controlling voltage must be maintained. Flash memory transistors do use a second gate to hold a charge but that is something extra."
] |
[
"I thought that was a bad way to word it, so I googled, and other people used it so I thought it was okay. Curse you, internet. I remember ram having to refresh every .000000001 seconds or something. That class was not my favorite, and it was many moons ago."
] |
[
"For the universe, if the Big Bang were 12:00:00 on Jan 1, and the theorized Heat Death were 11:59:59 on Dec 31, what day/time is it now?"
] |
[
false
] |
[deleted]
|
[
"So the \"heat death\" isn't a sudden event - it's a gradual process of everything drifting away from each other. But we can look at some of the events that will happen along the way that could mark the \"end\" or ",
". For comparison, the universe is about 13 billion years old right now.",
"After about 100 billion years, the expansion of the universe will have caused every galaxy outside the Local Group to have disappeared over the \"horizon\". This is well after the merger between Andromeda and the Milky Way, so there's just one massive galaxy, plus a few dwarfs hanging out.",
"By about 500 billion years, all of the smaller galaxies will have merged too, so the entire \"observable\" universe is a single galaxy of stars.",
"After about 100 ",
" years, star formation will have stopped a long time ago, and every star in the galaxy will have run out of fuel and turned into a white dwarf, neutron star, or black hole. We still have a galaxy, it just doesn't really have any \"normal\" stars left. However, there is still plenty of radiation coming out of neutron stars etc, and advanced life could survive off \"solar\" power.",
"We could define the \"heat death\" as the point where the white dwarfs and neutron stars have cooled enough that the universe is dark and it's almost impossible to power life. For white dwarfs, this might be another 1,000 trillion years (a ",
" years) after they form. I'm not actually sure about neutron stars because they're more complex.",
"But let's take ~1,000 trillion years as the end of the \"warm\" universe. If we are 13 billion years into it, then that's about one hundred-thousandth of your calendar year. This comes out to about 400 seconds. So we could say that it's about 12:07 am on Jan 1st."
] |
[
"Keep in mind that recorded history only goes back 0.1 milliseconds on this scale, and anatomically modern Homo Sapiens only emerged ~.01 seconds before that. The dinosaurs went extinct 2 seconds ago.",
"Human civilization has only been around for the tiniest fraction of the age of our universe, and our universe has only been around for a tiny fraction of its liveable age. We tend to think of ourselves as the \"end\" of human history - that all the interesting stuff has happened and things have kind of settled down now. But really, we've barely even started to see what humanity is going to do."
] |
[
"Keep in mind that recorded history only goes back 0.1 milliseconds on this scale, and anatomically modern Homo Sapiens only emerged ~.01 seconds before that. The dinosaurs went extinct 2 seconds ago.",
"Human civilization has only been around for the tiniest fraction of the age of our universe, and our universe has only been around for a tiny fraction of its liveable age. We tend to think of ourselves as the \"end\" of human history - that all the interesting stuff has happened and things have kind of settled down now. But really, we've barely even started to see what humanity is going to do."
] |
[
"How does the new idea of a cyclical universe fit into thermodynamics?"
] |
[
false
] |
I can only assume that the recent idea of cyclical universe has been thought through much more than I could ever dream of doing. I have a grasp of thermodynamics, namely that entropy is always decreasing, but the idea of a cyclical universe doesn't seem to fit into this. How can the universe end with complete disorder, so much so that there is effectively nothing in it, and then "reset" back to a "zero" entropy and begin again? Like I said, I have a grasp on thermodynamics, but I am probably way off base on a couple of my premises above. The bottom line is that I'd like a better understanding of what the new idea of the universe says that probably can't be described in a short internet article that spends time talking about the old theory.
|
[
"This does not conflict with thermodynamics. Entropy is only a measure of probability, which is to say that higher entropy states are more probable than others. The second law is \"almost always\" true in that the universe is more likely to transition to a more probable state than a less probable state. It turns out that for all practical purposes \"almost always\" is good enough for us since very small increases in entropy lead to huge increases in probability. As an example, let's say that some spontaneous process generates 1 calorie of heat (enough to heat a milliliter of water 1 degree Kelvin). At room temperature, that would correspond to an entropy increase (dq/T) of about 3.3 millicalories / K. That corresponds to a probability increase by a factor of e",
" = 10",
", which is astronomically large. So you can see why for all practical purposes the second law is true.",
"But it's important to point out that the second law doesn't say the universe MUST transition to a more probably state; it merely states that if you know nothing else about how the universe works then you must assume that the universe is more likely to transition to a probable state than an improbable state. Thus the chance of entropy going down is just improbable (by large orders of magnitude like the one I mentioned above).",
"Also, note that there is actually more to it than I just described. Entropy is nothing more than an anthropomorphic measure that represents a measure of our knowledge of probability of different states of the system, given the variables that we measure about that system. That is important, because as we learn more about the universe and make new types of measurements on it, the measured entropy changes (since entropy is nothing more than a measure of the probability of a configuration given constraints, and as we add new constraints then those probabilities change). The second law says that if we make no new observations on a system, then, that it will gradually progress to the most probable configuration that is consistent with those observations.",
"If this is a subject that interests you, then I highly recommend you read:",
"http://www.mdpi.org/lin/entropy/cgibbs.pdf",
"This is an excellent paper by E. T. Jaynes that does an amazing job of explaining entropy, certainly a much better job than I can, short of just copy/pasting his paper."
] |
[
"An interesting thing to consider: a black hole is actually the highest entropy state possible in the universe, because from the perspective of someone looking at the hole, all of the microscopic states of the matter that fell in can only be described by three macroscopic parameters (mass, rotation and charge). So, if entropy keeps increasing in the universe, one is left to wonder if that would mean that all matter must eventually end up in one giant black hole. A black hole of course is characterized by having a single infinitely-dense singularity in the center of its event horizon. So at what other point was all the matter in the universe concentrated in a singularity? Hmm.....",
"Note the above should not be taken too seriously, it's only speculation by someone who isn't too familiar with this subject matter. Also, this is all complicated somewhat by things such as Hawking radiation, the possibility that the universe will expand faster than gravity can pull it together indefinitely, as well as the fact that we don't know whether information in black holes is truly \"lost\" forever or not."
] |
[
"Also, this is all complicated somewhat by things such as Hawking radiation, the possibility that the universe will expand faster than gravity can pull it together indefinitely, as well as the fact that we don't know whether information in black holes is truly \"lost\" forever or not.",
"As t -> infinite black holes evaporate away to nothing.",
"Remember, a time period of 10",
" years is still nothing compared to t=infinity.",
"At t=10",
" years, all the black holes in the universe will have evaporated away, and all particles will have decayed to photons, and all photons would be at their lowest energy, or decayed themselves. (I'm not really clear on what the final fate of the photons would be. Still trying to find out if anyone has a good theory on that.)",
"Read the chapter on \"Deep Time\" in Phil Plaits \"Death from the Skies\". One of my favorite descriptions of the eventual fate of the universe."
] |
[
"Why are saline solution injections used as a placebo in vaccine trials?"
] |
[
false
] |
I’ve been reading up on how vaccine testing works recently, and I noticed that trials that use placebos often choose saline solution. Why is saline solution the most common choice instead of pure water or another alternative?
|
[
"It mostly resembles the osmolarity of human fluid and is therefore the most 'neutral' for the human body. This is exactly what you need from a placebo, something that does next to nothing when injected in the body, where as pure water would activate different mechanisms in the body to compensate for the loss of osmolarity (because it lowers the concentration of salt in the body)."
] |
[
"Edit: 0.9% Sodium Chloride or “normal saline” is what they refer to as an “isotonic crystalloid.” That means that the osmolarity most closely matches a healthy human body and therefore does less cell damage. Hypotonic solutions and hypertonic solutions move to areas of higher and lower concentrations (respectively) and cause shifts in electrolytes and cell damage to healthy cells. (Those solutions are beneficial in other conditions). ",
"In short - saline is chosen because it does the least amount of damage. ",
"https://biologydictionary.net/isotonic-vs-hypotonic-vs-hypertonic-solution/#hypotonic-solution",
"Sorry for an error in a post purely replied to on a mobile device. 🙄"
] |
[
"0.9% Sodium Chloride or “normal saline” is what they refer to as an “isotonic crystalloid.”",
"As a materials scientist, I was interested in the origin of \"crystalloid\". The solution itself is not crystalline. The correctly complete term \"crystalloid fluid\" is apparently intended to draw a distinction from \"colloid fluid\"; the former (typically containing salts) crystallizes when dried, whereas the latter (typically containing larger molecules such as proteins and peptides, including possibly particles, droplets, vesicles and cells) does not, although large molecules can crystallize under certain conditions."
] |
[
"Would it be effective to remove all nonfunctional junk DNA from human/animal genome?"
] |
[
false
] |
Well, apart from making it incompatible with his own species. According to several articles I've read, big part of human genome is not relevant to any proteins or any other mechanism in our organism.
|
[
"There's no such thing as junk DNA, that term has fallen out of favor. ",
"There is coding DNA and non-coding DNA (formerly \"junk\"). We're learning that much non-coding DNA may have a structural or regulatory role that we are unaware of.",
"That being said, there's a lot of DNA that can be done away with, but doing so wouldn't make any cellular process that much more efficient. The only process that would really be affected would be replication, and the enzymes that polymerize DNA are so mind-blowingly effective already that a couple million extra base pairs between friends isn't too much of a problem."
] |
[
"There are people more qualified to answer this, but here is one answer.",
"First, the term \"junk DNA\" is becoming a bit of a lesson for biologists. It's a poor term. More and more functions are being found all the time. We can describe regions of DNA as one of the following: gene, gene regulator (non-coding but important - like promoters), transcribed but not gene coding (microRNAs, etc.), and lastly structurally important (telomeres and potentially \"junk DNA\"). ",
"The key point is that people used to think if it wasn't a gene, it wasn't relevant. But now people are realizing that even non-gene parts of the genome (most of it!) have functions. Telomeres protect the ends of chromosomes, for example, and have impact on things like aging. ",
"Your question is mostly targeted toward the last way I mention to classify DNA: structurally important. Let's keep genes, promoters and every part of the genome we know does something (transcribed but not gene coding) and let's even keep telomeres because we know they have a function. There still might be several consequences to having a genome that consisted only of the bare essentials. ",
"Even regions of DNA that we think do absolutely nothing to regulate genes are probably important for the structure of chromosomes (the packages of DNA we all have). In technical terms, this could be important for the way chromosomes are condensed, the way the chromosome axis is formed (cell division stuff), and the way chromosomes pair up for homologous recombination. Think about structural functions of DNA as the difference between a small car and a pickup truck. The pickup truck has the same engine and parts of a small car, but the added bed has a purely structural function. ",
"There could always be something we don't yet know about in so called \"junk DNA\"",
"[EDIT] * It is ",
" that having less DNA to soak up potentially harmful mutations could be deterimental. ",
", but you can get the essence of the argument by realizing that if you have more DNA, there is less chance of a mutation affecting something super important important (like a gene). ",
"Source",
"That being said, we can remove parts of the genome without really seeing negative effects, but exactly how much we don't know. I don't think anyone would say having a \"optimized genome\" free of any nonfunctional DNA (in the traditional sense) is a good idea."
] |
[
"To be clear in all of this, there is a fundamental lack to terminological consistency among biologists/geneticists when it comes to talking about genomes and about the role of DNA within those genomes.",
"DNA is never ",
" \"coding\". DNA servs as a ",
" for RNA (which itself can code) but DNA never ",
" for protein in the way that RNA does. In fact, most of the large so-called \"coding regions\" of eukaryotic DNA are actually comprised of many nucleotides that contain ",
" peptide-coding information (eg, UTRs and introns).",
"A better way to think about DNA is in terms of ",
"--is a region of DNA transcribed or not? If it is transcribed call it \"transcribed\" and if not, call it un-transcribed. If you want to delve deeper and look for biologic meaning in the transcribed RNA, then you can consider what the RNA is doing here and is the ",
" ",
" or ",
"?",
"Finally, the structural contribution of DNA is very important (if poorly understood) But again, the role that a region of DNA may play in genome structure is ",
" of whether or that region may be transcribed as well. Structural roles and transcriptionally-important regions are not necessarially exclusive of one another.",
"And if all this hasn't made the point: \"junk DNA\" is a bad term if, for no other reason, it over simplifies and dismisses the very complex roles that DNA plays. Yes, there is bound to be some redundancy and waste in the genome but it is by no means ovbious where that surplus may reside. "
] |
[
"Is the heat generated by an internal combustion engine mainly from the actual burning of the fuel or from friction within the engine?"
] |
[
false
] |
I am thinking about your average car, and how the heat is generated. Bored driving one day looking at the temperature dial the question came to mind.
|
[
"Much of the engine's high temperature comes from simply burning that gasoline. The reaction takes place at a high temperature and of course it heats up various engine parts.",
"Then, some fuel energy is transformed into mechanical energy and moves various parts of the motor. Due to friction, some of this mechanical energy is then transformed into heat. But originally it's the same thing - the energy resulting from burning the fuel, it just takes a longer route to become heat.",
"But in any case, ",
" energy, both thermal and mechanical, in a motor comes from burning the fuel one way or another. It may just take different routes and transformations to become what it is."
] |
[
"I think the question is really, how hot would the engine get if it was being powered by another engine, not fuel?"
] |
[
"It wouldn't get hot. Friction in the engine is very minimal. There is proper oil lubrication everywhere to ensure this."
] |
[
"Hydrochloric Acid and Tin Foil?"
] |
[
false
] |
I have been acid washing sediment samples with a 10% HCl solution and accidentally used 100% HCl on a few of them, which isn't a big deal, it's just to wash away the carbonates. However, to speed up the process we put them into a hot water bath, upon coming back 3 hours later, I found the tin foil over the samples with the 100% HCl eroded, with yellowish scum over top of the samples My question is, if this new substance, which I think is AlCl3?, gets into my sample, will it just disolve into the solution and get washed out when I rinse my sample with DI water until it is no longer acidic? or will there be extra aluminum in my sample, I need to test for %Corg and %N so I dont want my readings messed, thank you to anyone who can help me with this
|
[
"100 percent hydrogen chloride is a gas, I am guessing you mean some 30-36 percent solution diluted by a 1/9 factor. The 30-36 percent stuff is common because this is the amount that can reasonably be dissolved in water without significant off-gassing. Heating it drove hydrogen chloride gas off the solution, along with some water vapor, which reacted with the foil.",
"The color you are seeing isn't actually the AlCl3, which is colorless, but rather the chlorides of iron which comprise about 1-2 percent of commercial aluminum foils. As for carbon content being off, it may be: the process used to manufacture aluminum foil uses hydrocarbons based lubricants which are deemed food safe and are washed off before use, but are still present in trace quantities: depending on what kind of accuracy you need contact might skew readings, but only with an extraordinarily sensitive device."
] |
[
"You did indeed form AlCl3. Luckily, it's fully soluble in water. (Only Ag",
" , Pb",
" , Cu",
" , and Hg2",
" are insoluble). If you wash it thoroughly, you should be fine."
] |
[
"Thank you! I will rinse them about 20x just to be certain"
] |
[
"What did Americans sound like in the 1700s/ early 1800s?"
] |
[
false
] |
Is this even possible to figure out ?
|
[
"Linguist chiming in here. These sort of questions are fraught with problems from the get go. First you have to isolate what area of the USA your are referring to. Within the original colonies you would have had more than one linguistic group, but there is usually a dominant one. In Labrador there are people currently studying this same thing among the Innu (related to Cree, not at all related to Inuit), in communities like Sheshatshit (yes I know how that sounds, go look it up) we see that because of forced relocation of two dialects the more \"prestigious\" variety, the one of the more upper class, is becoming the dominant dialect among those speakers who speak other dialects.",
"Now imagine this on a much larger scale, and also add in various political boundaries and lack of movement between groups. There is really no way to tell, as English was never one contiguous dialect. Even today there is what is called the ",
"Northern Cities Vowel Shift",
" so even now there is great change in American English.",
"You guys should consider adding a linguistics section in here to get rid of the laymen speculation and links to youtube and random news sources that are far from scholarly.",
"Edit. Just want to further clarify a point about dialects I linked, if anything American English is becoming more diverse, with more clearly distinct dialects. This is contrary to layman speculation that people are losing their linguistic identity or vernacular. Even in your less diverse neighbour to the north, some old dialects are making a resurgence (St. John's English among those born after the 70's), others changing like the gen x vowel shift in southern Ontario."
] |
[
"Mark Liberman and Geoff Pullum of ",
"Language Log",
" have mentioned on multiple occasions that linguistics seems more vulnerable than other fields to baseless speculation and urban legend being taken as fact (see the case of the ",
"\"nasal drawl\"",
", or the ",
"\"Obama pronouns\"",
" meme which circulates in the mainstream press). Like you, I'm rather disappointed in the quality of the comments in linguistics-related threads here."
] |
[
"Sadly the morpheme breakup is shes-hat-shit, for those who do not know the IPA it sounds like \"shay-hat-shoe\""
] |
[
"When I disinfect a cut with alcohol am I killing \"good\" bacteria that would speed the healing process?"
] |
[
false
] |
Assume the cut has a relatively low risk of infection.
|
[
"As far as I have seen there are no bacteria that help to speed wound healing. However you are killing the fibroblasts that are trying to heal the wound and thereby topical antiseptics slow wound healing. The data is fairly poor but the only topical antiseptic that can be diluted to a point that it kills bacteria but not fibroblasts is Dakins Solution (Sodium Hypochlorite). I'll try to find the article.",
"Here it is. ",
"https://www.evernote.com/l/ABDJk4NErqxO_LK1UxMh0eydY3jtC9UlxTY"
] |
[
"This touches upon a common misconception.",
"We are frequently told that our body is swarming with bacteria - \"good\" bacteria, which is true but the misconception is that they are everywhere in our body. In reality our body, once you go under its surface, in normal circumstances is sterile. Our gastrointestinal tract is an unbroken tunnel through our body that extends from our mouth to our anus essentially making us into cylinders or \"donuts\". It is in this passage, and on the outside of our body (eg the skin) that all this bacteria lives (along with other micro-organisms like fungi). But the walls of this passage prevent bacteria entering the \"inside\" of the body as much as the skin on the outside of our body does.",
"That's why the bacteria that lives in our gut is not referred to as an \"infection\" - it's allowed to live there and contained by, for example, the stomach and intestinal lining. If it broke that barrier and entered our body then it would be an infection."
] |
[
"While many species of bacteria live in your body that are beneficial to you, none live inside the sterile environment below your skin. Billions of bacterial cells live on the outside of your skin and have several functions, i.e. outcompeting non-native bacteria, or replenishing your gut biome, but are actually quite pathogenic when they gain access to areas they are not supposed to be. Your body is technically in a constant balance with the bacteria in your body.",
"So, when you get a break in the skin, species gain access to areas where they can cause destruction and the immune system responds. When antiseptics are introduced to an infection site, it is a nuclear bomb of sorts, killing most things it contacts. The difference is that, depending on the species, the bacteria may require anywhere from 4-24 hours to propagate, while the body can continue to send fibroblasts and macrophages from elsewhere in the body much faster. Eventually, with constant use of soap & water, or antiseptics, the bacteria are \"out-competed\" for the infection site by the body's immune defenses, which are faster, better designed for specific purposes, and in greater numbers. ",
"Again, this is a simplified example using a fairly common skin species like staphylococcus epidermidis. Other species can be very destructive or difficult to contain. Clostridium perfringens, when introduced to an anaerobic environment under the skin will produce toxic gasses that suffocate and necrotize all living tissue around it, rendering any localized immunse response ineffective, often necessitating amputation. Staphylococcus aureus, another common epidermal species, when introduced to the dermal or subdermal layer is also quite destructive but is generally contained in what we call an abcess. "
] |
[
"How can you detect details of a distant planet like Kepler 22?"
] |
[
false
] |
How do we know Kepler 22 is Earth like? How can we detect anything about a planet that is 600 light years away? There's no way we could detect life on a distant planet with our current technology right?
|
[
"Since this is where the top link goes to, here are a few other questions that have been posted.",
"Could humans live on a planet with gravity 2.4x (potentially Kepler 22b) Earth's?",
"If kepler 22b is 2.5 times the size of Earth would theoretical humans living on the planet have to be 2.5 times the size of Earth humans due to gravity?",
"Is Kepler 22B close enough to see in any significant detail with the James Webb Space Telescope?",
"How would the gravity feel?",
"How far is Kepler-22b from earth? and How long would it take to get there?",
"My answer to this specific question. ",
"For such a distant object, we have no details about it in terms of spatial resolution. As I answered ",
"here",
", we do not have the technology available to resolve any sort of features that far away. \nSo what can we see? We have light coming from there so we can measure a few things:",
"The intensity of light, and how it changes with time, will be the light from the neighboring star. We detect these planets because we notice that this intensity drops for a little bit of time, then picks back up later, (and then there is even another small drop when the planet is on the opposite side of the star). this measurement allows us to get estimates for size, distance from the star, etc. (essentially the info we have seen so far) \n",
"This picture",
" is data that shows what a planet rotating around a star shows up as. Notice the two dips. And here is a link to other various ",
"light curves from the Kepler project",
" that don't show planets. ",
"Next, there is the the spectrum of the light. I suspect we wont be able to use this to tell much information about the planet, because we would have to compare the spectrum as a function of time from when the planet is blocking sun, reflecting sun light, and when its on the oposite side and not visible. Possibly, from this, if we can get sufficient data we can extract information about the chemical composition atmosphere, although i suspect its unlikely. (I know that we do do this for other planets in our solar system, but I'm not sure on the accuracy, or difficulty of such a measurement, and for something so far away, i would expect it to be very difficult). ",
" : Quick google search showed ",
"this article",
" which details exactly what i suspected, apparently its been done, so i suspect it will be possible to do the same on this planet... not sure what results it will yield though, we'll just have to wait and see. "
] |
[
"The planet reflects its star's light like our moon reflects the sun's light. When the planet goes behind the sun, its reflected light is hidden behind the sun and so it is removed from the sum of light that is directed towards us."
] |
[
"Transits (planets crossing in front of their parent star) are detected by observing dimming of the light emitted from the star. By noting the magnitude and duration of the dimming in comparison to the mass of the star, you can deduce both the planet's size and orbit, and consequently know how much solar radiation it is subject to, and accordingly, whether it is possible for liquid water to exist on the planet's surface."
] |
[
"What would happen if you took a laxative and an anti-diarrheal at the same time?"
] |
[
false
] |
[deleted]
|
[
"I'm not versed on the subject; I'm merely providing guidance based on intuition and relevant Wikipedia knowledge.",
"Laxatives fall into several categories, of which I'll list just a few examples:",
"Bulking agents (those dietary fibers you hear about, among other things) allow your stool to bulk up and retain more water, which makes them more slick, among other things.",
"Stool softeners allow added water and fats to be incorporated, which again, make your stool slick or mushy.",
"Stimulants actually act directly on the muscles and nerves controlling peristaltic action (the uncontrollable act of moving food along in your digestive tract).",
"Now, barring the stimulants, all the others act directly on the stool itself. This is important, because antidiarrhoel substances are similarly differentiated. Examples:",
"Bulking agents. Hey look, they've been mentioned twice! If your stool is too hard/dense, these allow it to soften up. If you're having diarrhea problems, these let your stool actually form as solid mass by giving your stool the opportunity to coagulate.",
"Anti-inflammatory drugs (e.g. Bismuth Subsalicylate) aim to reduce irritation of the bowels and limit how much water your system dumps back into your digestive system.",
"Opioids have a direct impact on the nervous system underlying your bowel movements.",
"Okay, so based on these examples, here's what we're looking at. Bear with me, this is where I'm starting to apply logic without actually knowing much medicine.",
"Bulking agents are like the magic cure to any irregularities, hence why doctors tell you to eat your fiber. It'll regulate you in ",
" way, be it by possibly helping to correct constipation or diarrhea. This depends on the cause of the problem.",
"If you have a ton of stool softeners and a ton of anti-inflammatory drugs, you're probably still going to have diarrhea as your stool will end up soft without the aid of your digestive tract emptying more water into it.",
"Pair stimulants such as Phenolphthalein with bulking agents, and odds are you'll be moving normal crap more frequently. Pair opioids with bulking agents, and odds are you won't be moving crap nearly as frequently. Your crap will be normal, but you may start to bloat as it builds up.",
"Pair stimulants with opiates and you'll probably do some serious damage beyond just your digestive tract.",
"Points sourced from:",
"http://en.wikipedia.org/wiki/Laxative",
"http://en.wikipedia.org/wiki/Antidiarrhoeal"
] |
[
"Why don't you try it yourself and report back the results. For science."
] |
[
"One of them will win. "
] |
[
"how do the laws of of physics break down in a black hole"
] |
[
false
] | null |
[
"Why does that happen?"
] |
[
"Why does that happen?"
] |
[
"So we just dont know?"
] |
[
"How does shampoo/conditioner work?"
] |
[
false
] |
It's just one of those things that everyone uses but nobody understands how it works. Thoughts?
|
[
"The purpose of shampoo is to wash and remove dirt, oil buildup and other adsorbed compounds (e.g. smoke) that you don't want in your hair. Conditioner is used to change the properties of your hair, usually in some favorable way. They are separate products, because in some cases they counter each other in purpose. That is to say that conditioner wouldn't work properly in the presence of shampoo and vice versa. All-in-one products are a compromise of the two processes. I think of shampoo as stripping away compounds from hair and conditioner as building it back up, but that's a little simplistic.",
"Shampoo has a pretty good definition on wikipedia:",
"Shampoo",
" is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair. The goal is to remove the unwanted build-up without stripping out so much sebum as to make hair unmanageable.",
"The list of ",
"conditioner",
" ingredients on the wiki page describes some of the ways that conditioner can modify your hair (copied directly from the conditioner link):"
] |
[
"Take a look at the ingredients on your shampoo bottle. Most likely you will see Sodium Dodecyl Sulfate or Sodium Laureth Sulfate or one of their derivatives. ",
"These compounds are surfactants. Surfactants have heads that are attracted to polar subtances like water and tails that are attracted to nonpolar substances like oils.",
"When you rub shampoo on your hair, the hydrophobic tails grab onto the excess oil in your hair and orient themselves into little spheres with the hydrophilic heads pointing outwards and the hydrophilic tails, and the oils that they can mix with, on this inside of the sphere. This structure is called a micelle, and it gets washed away when it comes into contact with water.",
"Most of the other ingredients in your shampoo are fragrances.",
"Some surfactants are too zealous in their removal of oils and end up making your hair brittle and weak, however."
] |
[
"So it's essentially the same principle as soap acting on hydrophobic compounds, except on my head. Interesting!"
] |
[
"Why is it favorable to have a dominant hand or 'side' over ambidexterity?"
] |
[
false
] | null |
[
"It's a reasonable story, but is there any specific evidence that that explanation accounts for handedness? One could wave their arms and offer such an explanation for a lot of human behavior."
] |
[
"It's a reasonable story, but is there any specific evidence that that explanation accounts for handedness? One could wave their arms and offer such an explanation for a lot of human behavior."
] |
[
"I think this is a topic up for debate! ",
"\"More than 90% of the human population is right-handed, and biased hand use is also observed in non-human primates and other mammals. But whether there is a dominant preference for one hand at a population level is still debatable. What has made most humans right-handed during evolution is still unknown.\" ",
"Sun & Walsh, 2006",
"One idea could be that having skills lateralised to one side of the brain is advantageous basically because it means you leave space for more skills! The left side of the brain controls the right side of the body and vice versa; so if you are right handed, the left side of your brain controls your right hand and encodes more of the memories required for dexterity. \nThe above paper looks interesting!"
] |
[
"why does a liquid always have an equal amount of positively and negatively charged molecules?"
] |
[
false
] |
also, is the same true for a plasma?
|
[
"They don't always. But a charge imbalance implies a voltage difference and thus an electrical field, so it's not easy to keep charged particles from moving in response."
] |
[
"Not just theoretically, it happens all the time. In your body for instance. Nerve cells 'fire' by building up a ",
"charge difference",
" in the form of calcium or potassium ions, which are then released. The ",
"mitochondria",
" in your cells produce ATP molecules by 'pumping' H",
" ions across a membrane. They're then forced to flow back through ",
"ATP synthase",
", forming ATP in the process."
] |
[
"so does this mean that, theoretically, there is a way to create a positively charged liquid, if you have the right amount of power(via electrical fields or,...) and are able to apply it in a sense that would separate the positive from the negative molecules?"
] |
[
"What is it that makes our brains like sponges when we're children that gradually goes away?"
] |
[
false
] |
Until we'd rather ask what's wrong with our brains than force it to do the revision that used to be .
|
[
"When you're young, your brain is still making millions of neural connections and is the most plastic, or changeable. You brain doesn't fully develop until your mid 20s but the most drastic changes occur younger than that, mostly before puberty. If you think about it, your brain has to learn so much--language, fine motor skills, societal cues, interpersonal skills, etc. in your early years. That is done through these neural connections. That's why, for example, children tend to pick up language a lot easier than most adults--their brain is a lot more accommodating to new, unfamiliar information. In contrast, the adult brain is more set in its ways, as synapses undergo pruning--this means that the unused connections are largely not functional because they're not being used. That's why the adult brain is significantly less plastic. However, it is important to note that your brain remains capable of incredible neuroplasticity throughout your life, as can be seen sometimes in brain damage patients who essentially rewire connections in their brain. This is just one example of the capacity of neuroplasticity following traumatic brain injuries. However, it's still not to the same level as that of a child. "
] |
[
"Thank you"
] |
[
"Expanding on this. Is there any research or information showing a prolonging of this plasticity? Ie, besides being a healthy person are there ways to prolong the brain's \"spongy state\"? Obviously you never stop learning, but it seems like an attractive idea to learn a language as fast a child."
] |
[
"Is \"burn in time\" for headphones real or a myth?"
] |
[
false
] |
Burning in is usually referred to the time it takes for headphones to reach optimal quality after being taken out straight out of the box. My question is if burning in is real or a psychological affect.
|
[
"Piston rings, cylinder walls, valve guides. Engines have tons of metal parts sliding on other metal parts, and in the first few hundred miles they wear into each other at a level that's not economically feasible to do before assembly. That's why you should change your oil after ~1000 miles or less, because there is metal in it now.",
"On a historical note, old Soviet tanks would 'break in' to the tune of >500g of metal being caught by the oil filter."
] |
[
"Is there a measurable effect? Yes. Is it a noticeable effect? Probably not. I'm not sure how headphones would compare to regular speakers, but the physical improvement amount is usually around 5-10% for regular speakers. I would imagine that the shorter throw/smaller cones on headphones would have less percentage improvement.",
"Break-in test charts.",
"Second test on the same headphones",
"Math for floor-speaker break-in",
"In all cases, the break-in measurements are less than +/- 1 dB. "
] |
[
"Although i don't have evidence that burn in time is something measurable, or distinguishable by human ears, i don't think it's an unreasonable hypothesis. ",
"All moving parts change their characteristics after use. Just like how a car manufacturer recommends that you drive a car gently for a few hundred miles. And headphone designers would account for the change in friction, stiffness etc, so their product would sound the best over it's lifetime, not necessarily on the first day. "
] |
[
"Why is it that with things like video games, the user can't see the source code, but with html pages, the user can?"
] |
[
false
] | null |
[
"Video games are usually written in a language that makes use of something called a compiler. A compiler takes the source code of the software, analyzes it, and produces machine code that will perform the activities designated by the source code. This output will look nothing like the original source code, but it will run.",
"HTML is a document format that is meant to be consumed as text. There's no reason that you could not have an \"HTML Compiler\" (In fact, I think Adobe has things like this), but the web has standardized on a mostly-open clear-text standard. This standard is why you can view the source code of web pages."
] |
[
"HTML isn't a programming language, it's a \"mark-up\" language. Keep that in mind.",
"Computers don't understand programming languages. A computer is a CPU unit, it only knows voltages at its pins corresponding to 0s and 1s. Your CPU doesn't understand C++ or Java. What it does understand is Assembly or Machine Code. In Assembly, tasks are accomplished by one-by-one feeding \"instructions\" which amount to some set number of 0s and 1s (something like 64) into the CPU one by one. The instructions are incredibly simple: take the bits in this CPU register, add them to the bits in the register and put them in this register; swap this and this register and so on. That is the sum total of the actual functionality a CPU has. If you have ever had to write code in assembly you would know that it is the most god-awful, frustrating experience ever constructed by mankind. So programmers don't do it. So that brings us to the question of what is a programming language? A programming language, as I\"ve said, means nothing to computer, but rather it is a series of agreed definitions and specifications that a bunch of computer geeks sat down at a meeting and agreed on what functionality should result. In C++ it was agreed that if someone write something like: int myVariable;, that 32 bits of space should be allocated for some variable which within the code can be referenced by the tag \"myVariable\". The crucial thing is that all of this has nothing to do with a computer and how it ACTUALLY does things. It's just a bunch of people drawing diagrams and making specification documents. But once the specification of a programming language is made, then what? Well then people write algorithm using it but, again, the computer has nothing to do with those algorithms, the CPU makes no distinction between a file that contains \"C++ code\" and a file that contains your best amateur poetry. The crucial ingredient is what is called a COMPILER. A bunch of guys/girls coming up with a specification doesn't make a program, the ACTUAL work gets done when someone makes a program that translates C++ code INTO assembly code. That's where the real magic happens. Thus C++ is just an agreed upon set of definition and specification that a translator program can rely on when automating the conversion of this \"human-readable commands\" to Assembly Op-code (what a CPU understand). Thus a CPU never has access to the much more sensible and human comprehensible \"script\" that was translated to machine code, it only has access to a black box of query and response that is the final executable. Thus that information is considered \"secret\", like a recipe.",
"Conversely, HTML isn't a programming language but a mark-up language. Again, a bunch of dude/dudettes sat down and diagrammed and debated over a specification but this time, rather than there being a compiler, it is intended to specify how a browser should represent things on the screen. Thus the idea is that the browser receives the very human readable set of mark-up instruction and then depending on the browser it is its responsibility to make what shows on the screen agree with what those CS nerds agreed each mark-up instruction should do. "
] |
[
"JavaScript is a programming language and can be delivered to browsers in a human readable format (though it is often minified) and then interpreted in that format. \"Programming language vs markup language\" is not the distinction here. \"Compiled vs interpreted\" is the correct distinction."
] |
[
"Is 5 hour energy bad for your body?"
] |
[
false
] |
If it is, what about it makes it bad for your body.
|
[
"Make sure you don't have ",
"too much",
" of a good thing & you should be alright."
] |
[
"Wouldn't this depend on the vitamin and it's solubility?"
] |
[
"It would. Any vitamin that you ingest has to be handled by your body. Obviously if these drinks were fortified with fat soluble vitamins then there would be a lot higher chance for toxicity. With water soluble vitamins though they are excreted through the urinary tract, and with some B complexes the feces. This means that our body must process these and excrete them. Excess doses in the thousands of percent tax our bodies ability to handle this \"waste\" and in some cases may make it a priority over other normally produced waste allowing it to accumulate or continue flowing through our blood stream. "
] |
[
"Hey scientists...why is it, do you think, that animals like my dog and cat, don't seem to respond at all to music....?"
] |
[
false
] |
it's so weird, a drop of a spoon and they perk up, but death metal or chopin seems to have NO affect at all....and ideas?
|
[
"This is not a scientific answer but in the absence of a true response...",
"Animals are very accustomed to ignoring human produced sounds: in particular, anything focussed on the human hearing range around 80Hz-8kHz (this includes most musical instruments regular range except cymbals, triangles and some woodwinds).",
"Animals will certainly respond to human voices, particularly words they know, but when those voices are recorded, they'll ignore them. Pretty much all recorded sound begins losing clarity much higher than 12kHz, whereas cats and dogs are particularly sensitive to sound in the 20-25kHz range. Additionally pets are generally used to ignoring TV and stereo speakers as sources of interesting sounds – even when you're playing a sound that they'll normally respond to.",
"An interesting related question: why do humans respond to music at all?"
] |
[
"The same mental pathways that allow us to understand complex language are active when we appreciate music.",
"Dogs and cats lack these pathways. They can understand sounds, even simple commands, but cannot combine sounds together into sentences. The same is true for music, they are unable to combine individual noises into a musical thread."
] |
[
"They can understand sounds, even simple commands, but cannot combine sounds together into sentences.",
"Not true. Some breeds of dog can understand nouns and verbs, I own such a dog and she very clearly understands sentences. She also seems to like Classical Music and hate the sound an acoustic guitar makes. (Particularly when I am trying to play one.)"
] |
[
"Ways to escape heat death of universe?"
] |
[
false
] | null |
[
"Is the following possible: Using a large initial investment of energy, we accelerate everything we have (our planet(s), flotilla etc) to relavistic speeds relative to CMB and blueshift it appreciably so we have a 'CMB sun'. Ignoring collisions with interstellar and intergalactic media (which would be disastrous at relativistic speeds, but it's an engineering problem so we'll assume it's fine), this will achieve the following:",
"1) limitless useful energy, which can be stored as matter (assuming we have the technology to convert photons into matter for energy storage).\n2) relativity causes the rest of the universe to effectively cease aging - CMB intensity remains constant practically indefinitely due to large Lorentz factor\n3) effectively this setup is self sustaining forever - even if protons decay, we can always make new matter from the constant 'CMB sun'. The only downside is such a civilisation can no longer meaningfully interact with the rest of the universe."
] |
[
"Non scientist here, but hopefully by replying naively to you, it will generate better responses! ",
"If we accelerated earth close to c, I don't think this causes the rest of the universe to effectively cease aging, rather, it causes ",
" and the earth to effectively cease aging while the rest of the universe appears to age very fast. E.g. for every 10 beats of \"Earth-clock\" the \"Outside-clock\" would beat a million times. We'd be in a frozen time bubble while the universe aged and died, and then our bubble would also suffer from a heat death.",
"Even though the rest of the universe would appear - and be - long dead, from our perspective we would not have prolonged anything - our local clock still appeared to us to beat at one beat per second. All we would have done is time travel to the \"end of the universe\". "
] |
[
"Thanks but I'm pretty sure the rest of the universe will slow down relative to observers on a fast moving frame."
] |
[
"Is there any relationship between an organism's number of chromosomes and it's complexity or features?"
] |
[
false
] |
I was reading the Wikipedia article on humans and learned that all the other apes have 24 rather than 23 chromosomes. This made me interested in how many chromosomes other species have, and the list I found seems to be all over the place. Daisies have 2, rice has 24, hegehogs have a few hundred, a lot of mammals seem to have around 40, what exactly is going on here? I don't see any kind of pattern aside from the difference between hominids with 24 and 23 chromosomes. Plants, mammals, birds, and insects all seem to have all sorts of chromosome counts, so what's the deal here? Why is there such a massive diversity of chromosomal numbers? Why do things with such different numbers of chromosomes look so similar? Why does it take 24 chromosomes to make rice but only 2 to make daisies? Is rice incredibly compliated? Inefficiently structured? Is a lot of it just redundant junk? I have to say I'm absolutely mystified. This is something I'd never given the slightest thought to in the past but it seems significant.
|
[
"The relationship is not linear or simple. Complexity is very difficult to define and subjective, so this is a stumbling block in the discussion, but I will take it to mean something subjective, like structural intricacy. First of all, chromosomes are not a good indicator of genome size. In your example, in human evolution two of the ancestral ape chromosomes actually fused to create chromosome 2. Chromosomes can fuse and separate, be lost, or get mixed up without really \"changing\" the informational content of genome. Nor does there seem to be a linear relationship between genome size and complexity, since amoebas have genomes far in larger than any vertebrate genome. "
] |
[
"There is little to no relationship between genome size and organism complexity. The difference in chromosoome numbers is related to the amount of non-coding DNA present. Some organisms like viruses have none and therefore have very small and uncomplicated genomes while others have a lot of it ( human have ~80% repetitive sequences). Organisms with different number of chromosomes can loo similar if the parts that code for functional products ( both RNA and protein) are similar or related (It is more complex than this but this is the gist)"
] |
[
"since humans evolved from apes.",
"This is a common misconception. Humans are apes. The lineage that leads to modern chimpanzees have existed for as long as the lineage that leads to modern human. The only reason why humans have one fewer chromosome pair is due to a chromosome fusion event that occurred on the human lineage after the split between chimpanzee and human.",
"As far as I know, there is no connection between \"complexity\" and chromosome number, whatever \"complexity\" means. Chromosomes are just a way of packaging DNA, their number does not directly translate to genome size (i.e. number of genes). And even the connection between \"complexity\" and genome size is debatable (although it has been shown that obligate parasites have reduced genomes)."
] |
[
"When pouring a liquid from a cup, why will it sometimes run along the bottom of the cup and then drip instead of coming out the top as expected?"
] |
[
false
] | null |
[
"Just speculating because nobody is here but I feel it is due to ",
"cohesion",
" of the liquid and ",
"adhesion",
". ",
"For example, water likes to stick to water and charged surfaces, so say that the cup is slightly charged for whatever reason, the water will prefer to go to it rather than air, even though it is a longer path. And since now there is a slight stream of water on the side of the cup, water will continue to stick to water and flow that way. Thats why if you pour water onto a surface, the stream might not be straight but water will try to flow in the same path as previous."
] |
[
"There was an article on this in New Scientist magazine some years back but I cannot remember which one, and cannot access their archives from here. However, anyone who has a subscription should be able to search their back issues via the WWW, for an article about a scientific paper on pouring tea from a teapot by a professor at a British university, and 'perfect angle' (or perfec shape of pot?) at which it poured, rather than run down the side of the pot."
] |
[
"While the coanda effect probably contributes, cohesion/adhesion makes a big difference. I discovered while taking organic chemistry that different liquids have ",
" different pouring characteristics. For instance, it's basically impossible to transfer isoamyl acetate to a different container without making a mess (and making everything smell like bananas). I suspect mercury would pretty much never run down the cup"
] |
[
"What's the best way to treat a scrape, cut and minor lacerations?"
] |
[
false
] | null |
[
"Clean any debris from the wound, disinfect, dry the area and then bandage with a sterile dressing.\n",
"http://www.sja.org.uk/sja/first-aid-advice/wounds-and-bleeding/bleeding.aspx"
] |
[
"Moist wound healing",
". ",
"See also",
"."
] |
[
"Tea Tree Oil is amazing for minor cuts etc.\n",
"http://en.m.wikipedia.org/wiki/Tea_tree_oil"
] |
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