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|---|---|---|---|---|---|
[
"Does the earth continually produce new oil?"
] |
[
false
] | null |
[
"Several people have noted that oil is still being produced, albeit slowly. \nIt is interesting to note that coal is essentially not being produced at all. Coal formed from early wood that could not be decomposed, but since fungi have since evolved the ability to digest wood, undigested wood no longer occurs in large enough quantities to form coal, except in exceptional circumstances."
] |
[
"Yes, but extremely slowly compared to the rate that we use it. The process from living organism to oil takes milions of years and some of the oil we drill up is hundreds of milions of years old.",
"In comparison, oil has only been used by humanity for the last 2 centuries and we've already used up a large part of our known oil reserves."
] |
[
"I've seen estimates in the 25 - 50 barrels per day range for global oil creation. (Our usage is somewhere about 93 millions barrels a day)"
] |
[
"Why is a neutron-neutron (or even greater) configuration impossible?"
] |
[
false
] |
It seems a neutron-neutron configuration would be more stable than, say a proton-proton configuration where the Coulomb forces are present. Yet the latter may exist (albeit extremely unstable), but I see no mention of the former as even a possibility. Why is this?
|
[
"/u/RobusEtCeleritas",
" has a pretty good answer but it may be hard to understand without previous knowledge of nuclear structure, I'll try to explain what's going on more simply.",
"In a nucleus you have nucleons which exist in different energy levels just as electrons exist in orbitals. If you have two nucleons in the lowest energy level in a nucleus then if they are the same particle they are constrained to have opposite spins (just as with electrons in orbitals) due to the Pauli exclusion principle. However, the attractive force from the strong nuclear force is significantly stronger between particles with aligned spins. This is why the di-proton and di-neutron aren't stable, the nuclear binding forces are too weak because of spin-spin interactions. However, if you have nucleons that are different they can both occupy the lowest energy level in a nucleus with the same spin, which significantly increases their strength of attraction by the strong force. This is why deuterium (with a net spin of +1) is so much more stable than a diproton or dineutron."
] |
[
"You are correct that the diproton is more unstable than the dineutron due to Coulomb effects. However both of them are unbound, even neglecting Coulomb effects. Ignoring isospin symmetry breaking (due to EM forces and the proton-neutron mass difference), the diproton and dineutron are the same system as far as the nuclear interaction is concerned. They are also the same as the unbound \"first excited\" resonance of the deuteron.",
"They don't form bound states because the nucleon-nucleon interaction is not strong enough to bind them."
] |
[
"Ah, so the nuclear force is dependent on spin. Thanks!"
] |
[
"Smart people of reddit, in a perfect scenario--what would be the fastest a human could possibly travel on a bike with only leg power?"
] |
[
false
] |
[deleted]
|
[
"Around 130 km/h: ",
"http://en.wikipedia.org/wiki/Cycling_records#Speed_record_on_a_bicycle"
] |
[
"Totally flat smooth surface with no wind and high tech aerodynamic helmet and suit."
] |
[
"Totally flat smooth surface with no wind and high tech aerodynamic helmet and suit."
] |
[
"Why do nuclear fission and fusion give off energy?"
] |
[
false
] | null |
[
"Hello,",
"This is addressed in our FAQ.",
"Cheers."
] |
[
"How do I get to the FAQ?"
] |
[
"It's ",
"here",
"."
] |
[
"Is there a known algorithm used to define how difficult a word is to type?"
] |
[
false
] |
I've looked around and didn't find anything on the subject. Please excuse me if I just didn't google hard enough. But the current factors of word difficulty that I have thought about are: So my own rather unscientific definition of how difficult a word is, is: WordLength + HandChanges + (L1L2_distance + L2L3_distance*L1L3_distance + R4R5_distance + ...)
|
[
"Not an answer, but this seems like a question related to Information Theory similar to the ",
"Levenshtein Distance",
", which measures the minimum number of edits required to turn one word into another word. You may find something similar to what you're describing in the same field of Information Theory."
] |
[
"I would measure the maximum number of times the same finger needs to press a different key. If each finger only needs to press one or fewer keys, then the whole word could be typed in a single well timed mashing motion. It's also easier to roll your fingers from the pinkies towards index fingers. ",
" is easier than "
] |
[
"It depends... How big are your hands?"
] |
[
"Are climate change and global warming interchangeable terms?"
] |
[
false
] | null |
[
"Correct, they are not interchangeable. "
] |
[
"No. The climate can change in lots of ways including more extreme weather patterns."
] |
[
"Sorry, do you mean, no they aren't interchangeable terms?"
] |
[
"What is dark energy?"
] |
[
false
] |
I recently read an astronomy book that mentioned it, but I am still confused. Sorry if the question is a bit broad.
|
[
"Basically it's a density that space has, even when there's seemingly nothing there. This drives the accelerating expansion of the universe. We know that the universe is accelerating from various cosmological measurements (like the recession speed of distant supernovae), but the actual nature of dark energy is unknown. One proposed explanation, that it's due to the energy of the electromagnetic vacuum, gives a hilariously wrong predicted value when compared to the actual measurement."
] |
[
"To add more detail/context to the question itself:",
"Dark energy is mentioned in articles and magazines and books for the scientifically literate (but not at all experts or even physics majors or minors) in keeping with the answers I've already read in this thread, but it still seems a bit... mysterious? I'm sure there's some jokes in there somewhere.",
"What happens when I read these answers, or something like the Dark Energy article on Wikipedia, is that it all sounds nice and mysterious, but I don't get the sense the writers of the articles have a good understanding of what it really IS. This red flag goes up in my head and makes me wonder if all we have going for us in this understanding are vague interpretations of the mathematics (crunched with whatever numbers telescopes and spacecraft are transmitting back). I'm sorry if this comes off as reading really dumb. When I read about dark energy it's often written as though \"yeah, dark energy, no big deal 73% of everything woop\" but the conversation stops shortly thereafter aside from methodology of measurement.",
"But are there alternate theories or considerations, though, given how mysterious or frontier our understanding of dark energy is? Important parts of cosmological models being wrong, or off? Not measuring the right things, or the right places, or the right times? Do we know dark energy isn't some kind of mass because it's not exerting a gravitational field? Could it be wathes of particles we don't even know exist yet, with properties we don't yet understand?",
"The whole subject reminds me of that luminiferious aether I read about once, like it's this all-encompassing medium that seems real swell but I don't think it'll survive the next scientific leaps, but we're in the middle of it with incomplete understanding all like \"dark energy, legit.\" Am I totally off base?"
] |
[
"Dark Energy is the term applied to the ~73% of the matter-energy density in the Universe.",
"Using observations of the CMB, we can determine the total mass concentration, the ratio of regular matter to dark matter, and the total concentration of energy + mass, i.e. regular matter, dark matter, and dark energy.",
"When we look at how much matter, regular + dark, we see we get ~27%. And the ratio is approximately 7:1 dark to regular. ",
"Then we see that there must be somethign else to take up the rest of the 73%. That is what we call Dark Energy.",
"We call it \"dark\" because it doesn't interact with the electromagnetic force, so it can't emit or absorb light. We call it \"energy\" because it's not mass, and measurements differ from what we would expect if there were extra mass-energy density in the form of matter instead of energy.",
"We believe dark energy is driving the accelerated expansion of the Universe. If you calculate approximately how much momentum the Universe has from the Big Bang, and remember that momentum and energy are conserved, then we don't ever expect the acceleration of the expansion of the Universe. We'd expect it to coast or slow down over time. But it's speeding up. This energy must come from somewhere, and it's believed to be from Dark energy. ",
"Dark energy is weird. It's got \"negative pressure\" associated with it. I.e. the larger volume it takes up, the MORE it pushes outward. This is opposite of what we encounter in everything else. Most of the time if you have a fluid container and you make the container larger, the pressure goes down, not up. "
] |
[
"What is the reason that men and women are athletically different?"
] |
[
false
] |
I'm not trying to be sexist, but I find it to be fact that the average man is more athletic than the average women. I've grown up with a sister, and she has never been able to throw a ball gracefully. Is it because the culture of being a boy, generally, focuses on developing athletic talent? Or is it more of physical reason? Does a man's higher muscle:weight ratio allow for more athleticism? or, lastly, does a man's brain have more developed motor control? I'm leaning toward the brain thing. I just figure that a man's motor control is more fine tuned. Something possibly to do with the cerebellum? I'm shooting in the dark here
|
[
"Men's genetics have been fined-tuned over the last couple million years to by more physically apt to overcome and meet the demands of hunter-gathers, followed by the relience on those same athletic requirements even once we became sedentary. The difference is also reinforced by types of things that young boys and girls do -- although even if you raised a boy and a girl oppositely for the first 15 years, the boy would still be able to outpace the girl.",
"This is how I understan it. It'd be cool to have a panelist chime \nin."
] |
[
"My wife has said it's not sexist if its a fact."
] |
[
"Butts and Nuts."
] |
[
"Why do transformers explode so spectacularly in severe storms?"
] |
[
false
] |
One just blew up outside of my house last night in the severe thunderstorms we've been having. Bzzzzzt! Bzzzzzzt! BANG BANG, jets of blue flame spurting out. When power transformers blow, their death throes are pretty spectacular. What causes all the fireworks? And what about downed power lines causes them to fail in this manner?
|
[
"They run at very high voltages to facilitate more efficient transport of electricity, so what you are seeing is probably a combination of electrical arching and metal components melting and vaporizing. Squirrels routinely blow them up too.",
"Either that or it's those pesky Decepticons at it again!"
] |
[
"Most pole transformers are filled with a non-electrically conductive oil to help facilitate cooling, some of this probably vapourizes and ignites when the transformer overloads, the pressure from this vapour probably also helps with the loud noises as it bursts out of its container."
] |
[
"<layman>",
"Very large ",
"capacitors",
" shorting out would cause a heck of a show, but I don't actually know if that is what is going on. A tremendous amount of energy can build up and be stored in a capacitor, and if it shorts and discharges all at once, you'd see that energy released as light and heat and sound (BOOM). ",
"</layman>"
] |
[
"Why, on a evolutionary and biological basis, are we repulsed by each others body odor?"
] |
[
false
] | null |
[
"There was an experiment on TV once -- they took four or five guys, gave them shirts, had them work out, then took the shirts back and labeled them. They gave the shirts to four or five girls without telling them who the guys that had worn them were, had them smell the shirts, and then rank them for preference. Each girl had one or two they liked (a couple girls fought over one shirt, IIRC), but for each girl there was a shirt they clearly defined as the WORST smelling one. Each girl had chosen a DIFFERENT \"loser\" -- even the shirt that was fought over was someone else's \"worst\".",
"They then brought out the guys and placed them in front of the girl who had chosen them as smelling the worst. It turned out that each girl had chosen her BROTHER'S shirt as the worst smelling to herself. Was it some sort of anti-incest pheromones or simply growing up together and subconsciously associating the odor?"
] |
[
"This sounds interesting but the sample size is quite horrible."
] |
[
"As a public transport using resident of New Delhi, I can confirm this.",
"Smell like piss? We won't mind."
] |
[
"Speed of light and quantum entanglement"
] |
[
false
] |
As I understand special relativity, as something approaches the speed of light, time, from its perspective slows down. Therefore, would it be true to suppose that a photon, traveling at the speed of light, does not experience time? Further, because no time is experienced by the photon, does it exist at both it's start and end point simultaneously? Is this or could this be the cause of or the effect we perceive as quantum entanglement?
|
[
"As I understand special relativity, as something approaches the speed of light, time, from its perspective slows down.",
"As evanwestwood already pointed out, this is not correct. In your own rest frame, your clock will tick at its normal rate. Other moving observers, however, will measure your clock ticking at a slower rate. According to special relativity, both descriptions are correct.",
"Therefore, would it be true to suppose that a photon, traveling at the speed of light, does not experience time?",
"No, this would not be true, and here is why: Photons cannot have a rest frame of reference. Special relativity demands that massless particles move at exactly the speed of light ",
". But if a photon is in a rest frame, then it is not moving at the speed of light. There are only two ways to resolve this contradicton -- either we must abandon special relativity, or we must abandon the idea that photons have a rest reference frame. Special relativity has an absurd amount of evidence confirming its accuracy, but no measurement has ever been made \"from a photon's reference frame,\" so it is natural to abandon the latter to preserve the former.",
"I know that the above may seem counter-intuitive, but there are ",
" problems with your reasoning too. You are correctly seeing that the mathematical limit of a ",
" particle's rate of time tends to zero as the speed tends to c. However, this mathematical limit is ",
" the correct limit for ",
" particles. Consider: As a massive particle's speed tends toward c, its energy/momentum tends toward infinity. Photons, however, have an energy/momentum that is finite and extremely small, despite travelling at exactly c. Thus, we must conclude that massless particles and massive particles are quantitatively different somehow, and do not obey the same mathematical limits.",
"Technically speaking, in general relativity, massive particles follow timelike geodesics, and the norm of their tangent vector is -1 (and this value does not change with the mass or speed, it is always -1). However, massless particles follow null geodesics, and the norm of their tangent vector is 0 (this also does not change with its relativistic mass).",
"Edit: Missed a question. :)",
"Is this or could this be the cause of or the effect we perceive as quantum entanglement?",
"No, because massive particles can also be entangled. We have observed entanglement not only in electrons, but also in entire atoms (and I believe very recently, even in large molecules such as fullerenes)."
] |
[
"According to its frame of reference, the photon \"experiences\" no time",
"This cannot be true. It is not possible for a photon to have a rest reference frame in special relativity, because special relativity requires massless particles to move at c in ",
" reference frames. Please see my post here for a more detailed explaination:",
"http://www.reddit.com/r/askscience/comments/wtpfr/speed_of_light_and_quantum_entanglement/c5gf1ez",
"(The rest of your post is correct. :)"
] |
[
"as something approaches the speed of light, time, from its perspective slows down.",
"This is not correct. ",
"Lets say that you are on Earth and can watch a clock on a spaceship that is flying by. If the spaceship is travelling at a sufficiently large fraction of the speed of light, you would see its clock tick slower than your own and your own clock will appear to keep ticking at the same rate. The spaceship would not notice its own clock ticking at any other rate, and would in fact, say that your clock is ticking slower."
] |
[
"What would happen to light shined into a perfect box of mirrors?"
] |
[
false
] | null |
[
"Hi ImperialStarDestroyr thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics"
] |
[
"'Physics'"
] |
[
"How fast would I have to tear paper for it to burst into flames?"
] |
[
false
] | null |
[
"I don't believe you would ever (even in some idealized case) be able to ignite paper by tearing it. Do you have a specific source for why this might be possible?",
"Activities like metal cutting do cause ",
"potentially large temperature increases",
". This is because there is a lot of plastic deformation happening during metal cutting. That is to say, during cutting the metal is deforming and tearing in a way that dissipates energy from the cutting process into the metal. ",
"In paper tearing, this doesn't really happen. If you take a piece of paper and rip it in half the edges will pretty much match up without any extra permanent deformation having taken place. There is some energy released during tearing, the noise you hear is part of it, but even if you assume all that energy is dissipated into the paper itself the paper has such a high surface area relative to its volume that it will lose that heat to the atmosphere very quickly. ",
" To make some simple calculations (which are very much simplified and not at all rigorous), paper has a toughness of around ",
"20 Jm/kg",
", a density of say ",
"0.8 g/cm",
", and a specific heat of ",
"1.3 J/g/K",
". So lets say our paper has a thickness of 0.1mm = 0.01cm. Our paper releases 2 Jcm/g * 0.8 g/cm",
" * 0.001 cm = 1.6E-3 J/cm. So 1.6 mJ for every 1 cm of tearing. Lets assume all that energy is deposited uniformly into the 1 mm = 0.1 cm around the tear. For the specific heat, C*rho*t*w = 1.3 J/g/K * 0.8 g/cm",
" * 0.01cm * 0.1 cm = 1.04E-3 J/cm/K. Comparing this to the energy release per tear length we see a temperature increase of 1.6E-3 J/cm / 1.04E-3 J/cm/K = 1.5 K. ",
"So, TLDR, you would get approximately 1.5 deg C temperature increase in the 1 mm closest to tear line. Even with all our approximations, that is along way from ignition."
] |
[
"The more paper you have, the more paper there is to burn. Tearing more paper does not concentrate the heat at all."
] |
[
"There is nothing sophisticated going on with my example calculation. I was just going by the units and the knowledge that a fracture (or in this case tear) releases energy uniformly per unit length of the tear. ",
"But because energy is released per length of tear, tearing more paper doesn't mean more temperature, it just means a longer line of slightly warm torn edges. To increase the temperature change by the factor of 100 or so you would need for ignition, you would need to increase the energy by the same factor. So maybe if you made over 100 parallel tears within 1 mm of paper and did it quickly enough that the energy didn't dissipate, ",
" you could cause ignition. But your tears would have to be closer together than the the thickness of the paper, which doesn't seem realistic. "
] |
[
"Why do patterns form with a laser and diffraction grate?"
] |
[
false
] |
[deleted]
|
[
"I'm pretty sure what you have here is two 2D diffraction gratings stacked upon each other. When the dots go in and out of focus, the person is only rotating one grating relative to another. That's how the person produces the different diffraction patterns. If you want to learn how diffraction works/diffraction gratings work, I'd recommend checking out a physics textbook or doing some web research. I've attached a few links for your reading pleasures.",
"Wiki",
"Diffraction - Hyperphysics"
] |
[
"No, it looks like he is rotating ",
"one of two diffraction gratings",
"."
] |
[
"Looks like he uses a kaleidoscope and not a refraction grate."
] |
[
"Why haven't we been able to analyze samples of different foods to find out exactly what the ingredients are and the percent of each ingredient in the food? You know, to unlock the mysteries of Coca-Cola, Big Mac sauce, etc."
] |
[
false
] |
Or does this technology already exist? If so, how can these "top secret" recipes still remain secret?
|
[
"We can do this. We can tell you exactly what chemicals are in any particular food. The problem is, if you're attempting to replicate a \"secret recipe\" is that most of these chemicals will be complicated organic molecules, so we can't exactly reconstruct from scratch by adding chemicals to a vat because it'd be prohibitively time consuming and expensive. ",
"Knowing what's in something doesn't tell us the method of creation."
] |
[
"We'd need to get someone who's an expert in organic chemistry to give a definitive answer, but I'll try to give an example:",
"Let's look at beer. Let's say we wanted to figure out how to make beer, and we decide to do this by using mass spectrometry (which'll let us see the exact chemical makeup of the beer). The chemical results we'd get out of this analysis will contain things like water, ethanol, betaglucanase, ammonia caramel, rhoiso-alpha acids, sulphur dioxide, protease, amyloglucosidase, propylene glycol alginate and a big long list of other organic chemicals with very long names.",
"Having this list still tells us nothing about how the beer was MADE though, it just tells us what's IN it. The people who made the beer didn't go through this list and put all these chemicals in a vat to produce beer. They used a brewing process that took much simpler ingredients, and that process produced all these chemicals. Mass spectrometry can't tell us the process used to make the food, and food is mostly about the process."
] |
[
"You must also consider marketing when talking about why these \"top secret\" recipes exist. Is McDonald's going to be dethroned by some random mom and pop burger joint if they suddenly figure out how to make Big Mac sauce? Probably not. Does the allure of a secret sauce, that no one else can create, give more reason for people to eat Bic Macs or continue to eat them because of their perceived tastiness. Yes.",
"Just as Coca-Cola or KFC chicken isn't really any different from a regular coke soda or fried chicken. It's mostly psychological."
] |
[
"Would a helium filled drumset sound higher in pitch or just not work?"
] |
[
false
] | null |
[
"Sometimes 'stupid' questions are the best questions! ",
"It would depend on the pressure of the helium in the drumset. When something like a guitar string or a drum-skin oscillate, there's a restoring force pushing/pulling it back. The ",
"speed of the wave",
" depends on this restoring force. If you changed the pressure in the drum you could change the wave-speed on the drum-skin. Since the drum can only oscillate with certain wavelengths (called ",
"harmonics",
" ) if you change the wave-speed, you change the frequency (in sound it's also called the pitch).",
"Now, if you didn't change the pressure (i.e the helium was at room pressure). The wave-speed of the drum would be the same and you would hear the same frequency.",
"I imagine you're thinking of when people inhale a little helium and their voice goes up in pitch. The difference here is that the sound you hear is travelling ",
" the helium in your vocal chords. ",
"For the drum, the main sound you hear is coming from the drum-skin through the air to your ear. You could hear some effect from the sounds ",
" the drum as they would change pitch. ",
"So in short, you might hear a small difference, but it wouldn't change the sound coming from the drumhead.",
"It would be interesting to see though, you should (safely) try it out!",
"EDIT: Just realised I may not have been clear. The ",
" restoring force for a string or drum is the tension, but you could change the total force by changing the pressure."
] |
[
"Yes, in this case (again assuming no differences in pressure), the wavelength of the oscillation is the same, but the speed of sound in helium is faster than in air. Since:",
"c = λ x f\n",
"An increase in the wavespeed, for a constant wavelength, results in an increased frequency.",
"This would be a lot harder to test though, we'd need some proper breathing apparatus and a lot of pocket money to buy that much helium! "
] |
[
"Silicone sealant may seem scary to use in this situation, but it could work well to seal the head and the rim, and it's not bad to remove on polished surfaces and metals (caveats - time consuming because of the little bits that get left behind, and some silicone sealants release acetic acid - possibly corrosive). ",
"To seal the threads for the hardware you could use wax for a temporary seal (melt it into the threads and tighten - heat and tissue will let you remove it and it'll not be harmful if some is left behind). ",
"If your kit has vents, you could use them to fill the drum by means of a Schrader valve or a Presta valve (the common types of valves used to fill inner tubes / tyres on bikes) for convenience. ",
"Most of the drum volume is down to resonance. Changing pressure or the gaseous state will have a profound effect on the tone / volume / pitch of the drum, still, fun idea. "
] |
[
"Why do bats make such good reservoirs for zoonotic viruses?"
] |
[
false
] | null |
[
"The main factor is that they are extremely social, living in colonies with millions of individuals while also traveling long distances and interacting with other colonies. They move back forth between colonies picking up and passing around diseases giving them a lot of opportunity to evolve. ",
"Pig pathogens are far more likely to be able to infect people but pigs don't get around nearly as much as bats, if a new pathogen infects one pig farm it will take a lot less time for it burn through the population."
] |
[
"A big part is their body temp, I recall. They may display fewer symptoms, and thus incubate better, because of their higher body temp.",
"\"Bats—the only flying mammal—display several additional features that are unique among mammals, such as a long lifespan relative to body size, a low rate of tumorigenesis and an exceptional ability to host viruses without presenting clinical disease.\"",
"https://www.nature.com/articles/s41586-020-03128-0",
"Here's a long article that is detailed and not paywalled.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7123318/",
"At least one place referenced a STING protein that helps them not have an immune response, but that article was locked, so I don't have any other details."
] |
[
"Bats are the only powered-flight mammal and as consequence their muscles are in a constant state of damage. That muscle damage would provoke a constant state of inflammation however bats have evolved an immune system that has a much more toned toned inflammation response (as compared to ours) and a heightened innate immunity antiviral response.",
"It's thought that this balance of immunity allows some virus to replicate but not enough to harm the bat and not enough to trigger a massive immune response to all the broken down muscle cells.",
"Unfortunately, when there's spillover to humans, our sensitive and slower immune system goes crazy and we see diseases like hemorrhagic fevers.",
"Bats are a great reservoir because their are so many, second only to rodents who also carry plenty of spillover disease."
] |
[
"When an electron and a proton come together, the electron orbits the proton forming a hydrogen atom. What prevents the electron and proton from just sticking together? Why is an orbit formed?"
] |
[
false
] |
Thanks in advance.
|
[
"The radius of the proton is ~10",
" meters, so having the electron stick together with the proton requires it be localized to that volume. If you try to confine an electron to that much space, by the Heisenberg Uncertainty Principle, the RMS spread in its momentum is on the order of 100 MeV and it would quickly escape, since the binding energy for two unit charges with 10",
" meters in between is only ~1 MeV",
"You can use the uncertainty principle along with the classical expression for the total energy of an electron in a 1/r potential and you find that the stable state is when the electron is at the Bhor radius. It's common to call this as an \"orbit\" but it's not: the ground state of hydrogen has no angular momentum, it's like a spherically symmetric cloud of electron-ness around the proton, occupying all the space down to r=0. In a sense it is almost like they are \"just stuck together\", it's just that the electron being so much lighter than the proton means that it is much more spread out in space."
] |
[
"Yes, RMS is root mean square, sorry.",
"The wikipedia article you want to see is the one on the ",
"Heisenberg Uncertainty Principle",
"Also helpful would be ",
"http://en.wikipedia.org/wiki/Bohr_model",
"\nand ",
"http://en.wikipedia.org/wiki/Basic_concepts_of_quantum_mechanics",
"Your question is actually very deep, and historically it was this concern (or more specifically a related one: that classical theory predicts an electron orbiting a nucleus will radiate light and fall into the nucleus) that motivated much of quantum mechanics in the first place. I only scratched the surface conceptually with my answer"
] |
[
"No, that Wiki article is completely unrelated. Read up on Heisenberg's uncertainty principle:",
"http://en.wikipedia.org/wiki/Uncertainty_principle",
"The basic idea is that on very small scales, where quantum mechanics comes into play, you can't know a particle's momentum and position exactly. If you say the particle is definitely in some tiny radius, then you have to have a large uncertainty in its momentum to compensate. Mathematically, the product of the uncertainty in a particle's position and the uncertainty in its momentum has to be greater than some constant, so reducing the uncertainty in one means increasing the uncertainty in another."
] |
[
"What do the other 3% of peer reviewed studies on Climate change say?"
] |
[
false
] |
I'm familiar with the stat that 97% of peer reviewed studies say humans contribute to climate change. What do the other 3% say? Is there anything to them? Always thought it would be valuable to read the other side, but I honestly can't track down the studies
|
[
"Most of them are objectively wrong in some way or another. There was a paper from a few years ago that went through a selection of the 2-3% (38 different papers to be precise) in an attempt to replicate their results and found that they suffer from a variety of flaws. ",
"Here is the paper",
" in question, and here is one (of many) ",
"write-ups",
" about that paper, which might be more readable for some. (Also, important to note that the Benestad et al paper itself seems a bit brief, but ",
"the 81 page supplement",
" walks through the methods in detail and provides a full catalogue of flaws in the examined papers).",
"Some of the common themes identified in the 'contrarian' papers were (1) cherrypicking, i.e. they got to their conclusion by ignoring large portions / aspects of their datasets, (2) bad curve fitting, which is some mixture of shoddy statistics and or odd examples of correlation being assumed to equal causation (e.g. just because the temperature record also correlates with some other natural phenomena that has no demonstrable physical link with temperature, does not mean that global warming is caused by that phenomena), and (3) sort of related to that last one, proposing causes for global warming that had no basis in physics, etc. ",
"The full list of flaws (from the linked supplement) is pretty telling in of itself, including: questionable analytical set-ups, selective use of data, curve-fitting, biased analytical design, ignoring negative tests, questionable presumptions, questionable representation in data, looking at irrelevant aspects, false dichotomies, circular reasoning, statistical errors, misrepresentation of statistical intervals, failure to account for the actual degrees of freedom, misconceived mathematics, incorrect interpretation of mathematics, implausible physics, lack of plausible physics, incomplete account of the physics, irrelevant analogies, and finally misrepresentation of publications. You could almost present this as a list of pretty much everything we're trained not to do when performing and reporting experiments and/or observations (of course, I don't think any of these papers did ALL of these at once, though that would be almost impressive in a perverse way)."
] |
[
"Or to put it another way, that 3% is more about the imperfections of peer review than about real errors in climate change science."
] |
[
"Sorta disagree. It's not the reviewers' job to fact-check and confirm the paper's data and results, but it absolutely is their job to point out the sort of serious procedural errors and invalid methodology that ",
"/u/CrustalTrudger",
" refers to."
] |
[
"In a random question of random number predictions (i.e. lottery drawing), is a set of consecutive numbers any less likely to occur than any other combination of numbers?"
] |
[
false
] | null |
[
"The set of possible outcomes in a choose k numbers from n possibilities lottery, is the set of subsets of size k from the set of n possibilities, i.e. n!/((n-k)!*k)!.",
"The set 1,2,3,4,5,6 is just as likely to be drawn as 12,32,33,40,49,52 for example.",
"However there are only a very small number of consecutive sets versus a much larger set of other combinations, so it will take a very long time before any real lottery will draw a set of consecutive numbers."
] |
[
"A ",
" set of numbers, say consecutive, is no less likely to randomly occur than any other particular number set.",
"Although in the lottery, it is less likely for ",
" consecutive set to occur, versus any nonconsecutive set. "
] |
[
"But if you are picking lottery numbers, I think it's worth remembering that if 1,2,3,4,5,6 wins, the pot would be split between a huge number of smartasses."
] |
[
"What happens to food as you cook it?"
] |
[
false
] |
I know the answer is very different depending on what we're cooking. I'd like to ask about two different things, starches and meats. So let's say we pop bread into a toaster oven at 500F. In the beginning we'll get evaporation of water, then the browning reaction, then it turns black. What is the composition of the black stuff? If you let it go on long enough, will it become elemental carbon (with metal impurities)? Next, we're going to grill a steak. So we pop it on and the meat starts to sizzle. We have the Malliard reaction going on the outside of the meat and proteins breaking down and coagulating on the inside. Then it will start to char as well. I would believe that since the composition of meat is much heavier on amino acids, that the blackened end product would be completely different than the bread if you leave it on the grill till it's crispy black. What exactly would it be?
|
[
"I would like to recommend ",
"On Food and Cooking: The Science and Lore of the Kitchen",
" by Harold McGee to anyone interested in these type of questions or cooking in general. It describes in detail almost everything you'd want to know about the science behind various cooking processes. There's even a whole chapter on various browning reactions. The writing is understandable enough that you don't need to know much above high school level of chemistry and it will change the way you look at food forever. ",
"After reading this book you feel like a scientist every time you're in your kitchen because you're not simply cooking, you're experimenting with your food. The book teaches you to ",
" how something will taste and which ingredients will work together and why others will ruin your appetite.",
"PS: If you're going to read this, don't get the Kindle version, the formatting is terrible and you really need a physical copy as you'll be flipping 10 - 300 pages forward to look at an appendix or a reference picture. I was lucky enough to get this book at my local library. ",
"edit: ",
"Here",
"'s a relevant passage about the browning of meat( google books)",
"and ",
"Maillard reactions",
", including ",
"health effects",
"."
] |
[
"Much appreciated. So the blackened carbon, will it be a mass of network bonds like graphite or a mishmash of long chain molecules, polymers, and polyaromatics? I.E. will the stuff be relatively biologically inert or cancerous?"
] |
[
"The real black stuff would be inert.",
"The stuff right below it could be nasty, it's hard to say, but generally stated, it's fine."
] |
[
"As photosynthesis requires light, why aren't plants black to absorb the full spectrum of light, instead of green which doesn't?"
] |
[
false
] |
I know that plants at the shrub layer in forests and jungles tend to be a darker green to make up for the fact that they receive less light, so how comes every plant doesn't do this then so that they could produce more food? Edit: Holy crap this is a lot of responses. Thanks so much! And yes I know that plants are green because they reflect green light, sorry for the confusing wording.
|
[
"A Black equivalent of Chlorophyll does exist - usually within Seaweed.",
"This is because most plant life would overheat and their enzymes would denature if they were to absorb all spectra of light - therefore green is the commonly used colour as it reflects mid-energy photons and absorbs high energy (blue) light and lower energy (red) light"
] |
[
"Also plants are generally limited more by CO2 availability then light, at least under full sun anyway. Thats why plants grow just fine in greenhouses with sun shades drawn to block a portion of the light, still getting all that they need."
] |
[
"Generally limited by CO2 availability from the air. Still air will rapidly be depleted of CO2 around plants. This is why increasing CO2 in greenhouses under otherwise unlimited conditions (lots of light/lots of water) causes increased growth and can also increase plant heat tolerance.",
"Edit: Also why fans and wind are so good for rapidly growing plants and part of the reason why greenhouse ventilation is such a big deal.",
"Edit the 2nd: The \"unlimited conditions\" in the greenhouse would also need to include full access to nutrients such as nitrogen, phosphorus, potassium, magnesium, etc."
] |
[
"What traits we have from some of our ancestors; Neanderthals?"
] |
[
false
] |
[deleted]
|
[
"Neanderthals are not our ancestors. They share a common ancestor, and were contemporaneous with modern humans. ",
"(Now to go out of my field a little: Non-African modern human DNA may contain a small amount of \"pure\" Neanderthal DNA, but this research is too recent for speculation about noticeable shared traits.)"
] |
[
"Well, it depends what you mean by \"ancestor\". The Neanderthal population does not comprise the majority ancestry of modern humans. But every living non-African human has individual ancestors that were Neanderthals."
] |
[
"The way in which genotypes map to phenotypes (\"traits\") is really quite complex, and we're only just beginning to really work out how that all works. You may have learned in high school biology about ",
"Gregor Mendel an his pea plants",
", where one gene coded for one trait, but what we've been learning in the last 20+ years or so is that most genes do not map to traits in such a simple one to one manner. Many genes are ",
"pleiotropic",
", meaning that they influence multiple different traits, and many traits are ",
"polygenic",
", which means that the expression of a single trait in a particular individual is influenced by many genes (e.g. 200+ and counting for human height, with some predictions that the number may be as high as 600 or more).",
"What this means for your question is that unfortunately, we can't really say anything about how specific traits may have been influenced, because we don't know enough about how the genes influence the traits."
] |
[
"Does the body send signals to fat and muscle cells?"
] |
[
false
] |
How does a fat cell 'know' when to give up its stored energy? How does a muscle cell know when to grow? Does the body tell it with hormones or some such thing, or do the fat and muscle cells just follow some kind of rule set? Are there any drugs designed to instruct the cells to behave in desirable ways?
|
[
"Welcome to the wonderful world of Physiology my friend! Physiology is the study of how organisms function. Cells communicate in several different ways, most of which are chemical. There's a few ways that the body communicates with itself. ",
"Autocrine signals cause the cell secreting the chemical to undergo a change. This is seen in immune cells like T-cells.",
"Paracrine signals cause cells near the secreting cell to respond in some way. This is seen in neurons that secrete neurotransmitters.",
"Hormones are signals that affect cells in a different area of the body. This is seen in sex steroids like estrogens and testosterone.",
"Electrical impulses. Exactly what it sounds like. This is seen in the heart with gap junctions.",
"The body produces these signals to convey that something has changed. This causes the body to respond to try and get the bodily process back to a baseline level. This is called homeostasis. For example, when your body runs out of glycogen in the liver, blood sugar levels drop. This drop in glucose signals the body to undergo gluconeogenesis, or making glucose out of a lipid (fat) or amino acids. It's the drop in blood glucose levels that signal the body to start this."
] |
[
"There have and several have been successful. Obviously, you know about steroids. There have been some studies on leptin (it's the hormone that reduces the feeling of hunger), but nothing came of it. There really is no hormone that burns fat. Lipolysis Is stimulated by low blood sugar. I guess you could give someone thyroxine (a hormone from the thyroid gland in the neck) which would increase metabolism, but it's really bad for you. Substances like cocaine and methamphetamine impact dopamine release in the brain. They also tend to lead to bad decision making. "
] |
[
"So has any research been done in making drugs mimic some of those signals, say to lose fat or build muscle. I guess steroids would be a muscle building hormone... but is there anything else?"
] |
[
"Is there a way to get an electrode connected to your nerves without tons of money?"
] |
[
false
] |
I'm very interested in implants and exploring possibilities of human nervous system, and I was wondering if it was possible to connect something to your nerves without specialized lab equipment and thousands of dollars or euros.
|
[
"I feel like you shouldn't be doing anything with anyone's nerves if you can't answer this question yourself...",
"That aside, elaborate on what the electrodes are meant to do? You can affect the nervous system by applying an electric shock, like in nerve conduction tests - and this doesn't require breaking the skin or real \"expensive\" equipment. But again, the equipment is there for a reason - voltage and current are carefully controlled, etc."
] |
[
"Your intuition is correct. I know a tiny bit about the design of such devices. ",
"The reason why it's ordinarily quite hard to electrocute yourself with a car battery is that dry skin acts as a pretty good insulator. But if you attach an electrode with conductive gel to it, then a car battery can kill you quite easily.",
"One important guiding principle in the design of something like an EEG device is to ensure that no part of the internal circuitry is ever directly connected via a conductor to the human. Because if is, then a short circuit in the device can supply more than enough current to stop your heart. ",
"Internally, the electrodes only connect with the rest of the device via optoisolators or inductive coupling."
] |
[
"Without tons of funding you want to go with an uninvasive system (such as EEG for cortical or EMG for afferent and neuro-muscular signals).",
"I am actually building a system from scratch for use in brain-computer interface application and would highly recommend it. I am merely a bachelor in cognitive neuroscience and a hobby solderer.",
"Start out with simple chips like the TL84 for texas instrument and the INA114 is great. You can actually google INA114 (its made by texas instrument) and download the data sheet pdf. Scroll down the page a little and you will see a basic EKG system they suggest (which you can easily modify the gain for cortical or neuromuscular EMG).",
"For the next step up in difficulty and awesomeness look into AVR micro-controllers. If you can program very basic commands in C (or are good at copy/paste of others online code) you can make a simple analog to digital converter [but shhhh... don't tell anyone bc labs and private companies charge hundreds of thousands for these simple devices that can be so easily made in someone bedroom]\nI got into this because I was upset with my univerisities lack of sharing equipment for fringe science by undergrads and am now inventing and sharing my designs with everyone. \nI have a google sites page /jeradacosta if you would like to see [still in the works] and I am new to reedit so I don't know if I am allowed to plug a website so its just google dot com /sites/jeradacosta\nplease hit me back with feedback as I love collaboration and interesting ideas"
] |
[
"To what extent did sexual selection and self domestication contribute to the wide variety of human pigmentation?"
] |
[
false
] |
It seems like there is a lot of consensus that differences in skin pigmentation largely emerged as different groups of humans adapted to different climates with varying degrees of exposure to ultraviolet radiation. , for example, Nina Jablonski makes the connection between darker skin and more exposure to UV radiation. On the other hand, I've noticed that both domesticated dogs and cats also have a large variance in pigmentation (very notably, in eye color: ; ; ). And as anthropologists like to say, humans are also a domesticated species, having domesticated ourselves using culture and civilization over the last few thousand years. That makes three very interesting examples of domesticated animals with very notable variance in pigmentation. As far as I know, there are no other examples of large mammals where such a dramatic variance exists. Aside from this very interesting correlation, is there any evidence that suggests that domesticating factors like sexual selection played a role in the wide divergence in human appearance? Conversely, is this type of physical variance potentially a sign of domestication, and does the existence of such variance in humans give sway to the idea that humans are "domesticated"?
|
[
"http://www.sciencedirect.com/science/article/pii/S0047248400904032",
"This abstract suggests we have established a very obvious correlation between latitude/ sun exposure and the skin pigmentation of the local population of humans. It also suggests that such pigmentations are quite mutable and respond well to changes in sun exposure.",
"Historically, no, domestication hasn't had an impact on the pigmentation of human skin, and also suggests that skin pigmentation is not a sign of domestication in the human population, but rather a very real example of the process of natural selection/ evolution at work. ",
"Whether a case can be made for this today is an interesting thought. I believe historically, only one group has practiced 'domestication' of humanity on a practical level: Nazi Germany and its Aryan master race agenda. Since WW2 we have put in place laws to prevent this type of conscious domestication occurring again."
] |
[
"Your question reminded me of this ",
"study",
" which made the ",
"news",
" a few years back. Xasrai is certainly right about the evolutionary advantages of light/dark skin in the regions they developed. However, this study suggest that sexual selection coupled with environmental factors(*which gave this selection greater influence) gave rise to the divergent hair and eye colors of Europeans. Cavemen apparently prefer blonds.",
"This view is certainly not proven or universally excepted and your term of self-domestication does imply some end goal which is probably not appropriate. Still it is a safe bet that sexual selection has played a role in human evolution. In cases like hair and eye color where natural selection would seemingly not be as strong, sexual selection could be the deciding factor."
] |
[
"What about cultural preference to a certain race? Africans only marrying Africans and Japanese only marrying Japanese, for example. These are still prevalent and were even more so back in time. Couldn't you consider such practices a positive pressure to maintain the light (or dark) skin? ",
"In Europe, for example, if darker sin was frowned upon and made it more difficult to find a mate."
] |
[
"Do different types of cells become what they are by turning on and off certain areas of a person's genetic code to therefore alter protein production?"
] |
[
false
] |
Is the difference between cells found only in the fact that they make different proteins?
|
[
"See ",
"Gene regulatory network",
".",
"Pretty god explanation there:",
"In multicellular animals the same principle has been put in the service of gene cascades that control body-shape.[2] Each time a cell divides, two cells result which, although they contain the same genome in full, can differ in which genes are turned on and making proteins. Sometimes a 'self-sustaining feedback loop' ensures that a cell maintains its identity and passes it on. Less understood is the mechanism of epigenetics by which chromatin modification may provide cellular memory by blocking or allowing transcription. A major feature of multicellular animals is the use of morphogen gradients, which in effect provide a positioning system that tells a cell where in the body it is, and hence what sort of cell to become. A gene that is turned on in one cell may make a product that leaves the cell and diffuses through adjacent cells, entering them and turning on genes only when it is present above a certain threshold level. These cells are thus induced into a new fate, and may even generate other morphogens that signal back to the original cell. Over longer distances morphogens may use the active process of signal transduction. Such signalling controls embryogenesis, the building of a body plan from scratch through a series of sequential steps. They also control maintain adult bodies through feedback processes, and the loss of such feedback because of a mutation can be responsible for the cell proliferation that is seen in cancer. In parallel with this process of building structure, the gene cascade turns on genes that make structural proteins that give each cell the physical properties it needs. It has been suggested that, because biological molecular interactions are intrinsically stochastic, gene networks are the result of cellular processes and not their cause (i.e. Cellular Darwinism). However, recent experimental evidence has favored the attractor view of cell fates",
"Gene Regulatory Network resembles state machine, or higher order recurrent neural network if you look closer. Interesting stuff. "
] |
[
"The breakthroughs in metabolic engineering usually come from biological discoveries and development of techniques. As far as achievements go, large portion of pharmaceuticals use at least one bioprocess, as they create enatiomerically pure products, which are required in drugs. Newer technologies include butanol producing strains of yeast and bacteria. Older developments include bioplastics, which are biodegradable, and antibiotics.",
"Limitations are bascially caused by lack of knowledge of the biology or techniques. One of the biggest hurdles is that the species that perform a certain reaction or metabolism best are often ill suited for industrial processes but the ones suited for industrial processes may not be the best, even when engineered, at that particular metabolism.",
"I think right now, the biggest goal of most metabolic engineers, is to supplant fossil fuels in some way, be it liquid fuels or pure long chain polymers. It's all about the money."
] |
[
"Thanks that's really helpful."
] |
[
"How and why does high blood volume/pressure pose a risk to health?"
] |
[
false
] |
Hi there. I am looking to understand how high blood pressure or high blood volume alone (with no atherosclerosis or other signs of CVD) can damage health. I am interested in the specific physiological mechanisms (if any) through which chronic high blood pressure damages any part of the human body. Thank you!
|
[
"There isn't one specific answer to this, but from the hearts perspective: High blood pressure increases what we refer to as afterload, which is essentially the force that must be overcome by the heart to open the aortic valve and eject the blood from the ventricle. ",
"In simplified terms: Higher afterload means the heart has to work harder. Like any muscle it remodels to accommodate this workload. Eventually though, this remodeling becomes pathological and the heart can't pump efficiently so cardiac output suffers, this activates a system that conserves blood volume and increases blood pressure, making the problem worse, and it can eventually lead to death by congestive heart failure if not managed well.",
"It can also damage the kidneys as mentioned, increase shear stress in blood vessels that promotes atherosclerotic plaque formation (fyi everyone has some amount atherosclerosis, it's not only unhealthy people) and much more."
] |
[
"Full understanding of this topic probably requires you to do some reading. See ",
"http://cvphysiology.com/",
" if you're interested. In short: it's not a desirable state long term but under physiological conditions your blood pressure spikes as a consequence of increased cardiac output in an attempt to increase blood flow (due to high metabolic demand etc). Factors that cause vasoconstriction such as cold weather or stress will also increase your BP.",
"The relationship between pressure and flow can be explained by poiseuille's law and ohms law but the simplified version is that higher pressure differences (between two ends of a tube - for example a blood vessel, or between a capillary and the surrounding tissue), lower resistance, and wider diameter of the tube lead to increased flow. Wider diameter has the added effect of dropping the pressure though so you may need to increase cardiac output to ensure enough of the good stuff is actually making it out into the tissue.",
"Im cutting this down a bit so apologies: if for example you want lots of blood somewhere (exercising muscle) you can vasodilate the blood vessels in that area, but this drops the pressure in the local area and might compromise the pressure required to drive that blood out into the tissue where its needed, but you also increase cardiac output so it's all good. However, you aren't dilating everywhere (as this could cause shock, see below) so your systemic blood pressure will rise as a consequence. If you're otherwise healthy then this isn't really an issue. A few hours after you stop exercising or whatever, it will go back to normal. The problem arises when \"something\" is causing your BP to be elevated all the time. Particularly so that it doesn't dip a bit while you're asleep.",
"For background: There are baroreceptors that detect your blood pressure and this ends up signalling your heart, vasculature, and kidneys to act in ways to try to bring that back into normal range. The normal range is important as if it's too low then things don't get enough blood flow and cells start to die. Poor systemic perfusion is known as shock. We name it based on what causes it. Bleeding too much? Haemorrhagic shock. Heart can't pump properly? Cardiogenic shock, something triggers systemic vasodilation? Distributive shock, etc ... but I digress.",
"Anyway, chronic elevation of your blood pressure can desensitize these receptors and they begin to treat the elevated pressure as normal and so stop trying to fix it when it's actually too high. This strains the heart, kidney's, etc as mentioned. ",
"Apologies for any errors, written on my phone etc."
] |
[
"High blood pressure is a relatively recent phenomenon in humans. Mechanisms that maintain lower limits of blood pressure have been well conserved through evolution and it’s easy to understand why. Loss of blood, sudden and short bursts of high intensity activity, and other events that occur in nature require dynamic increases in blood pressure. The causes of hypertension did not exist before modern humans and therefore were never a pressure selected against in nature where as mechanisms to maintain lower limits of blood pressure helped survival. "
] |
[
"Why is it that I can safely eat a rare steak but eating undercooked chicken, fish, or pork could land me in the hospital?"
] |
[
false
] | null |
[
"Actually fish can be eaten raw, ever heard of sushi?",
"Pork can also can now be eaten undercooked but it doesn't taste that much better. The main problem used to be a parasite (",
"http://en.wikipedia.org/wiki/Trichinosis",
") which has been pretty much eradicated.",
"The only bad one is chicken, which can contain salmonella. The reason it does is because salmonella is a pretty resistant bacteria which can make us pretty sick but doesn't affect the chicken (or most birds/reptiles for that matter)."
] |
[
"Only in the US. All eggs are processed in such a way as to remove the outer membrane, allowing bacteria (salmonella?) to penetrate the shell, which is actually semi-permeable. ",
"Raw eggs in other countries are much safer.",
"A Forbes article on the topic",
"efraim lower down in the thread."
] |
[
"Eggs are edible raw, but the eggshell has plenty of bacteria on it. If the shell comes in contact with the insides while cracking, it will need to be fully cooked."
] |
[
"How is 'sea level' measured?"
] |
[
false
] |
Also, why am I able to drive on a highway and have my GPS say I am 7 or 8 meters below sea level? Shouldn't that be covered by water? For what it's worth, I am located and drive throughout New Brunswick Canada, very near the coast.
|
[
"That makes sense. The areas I'm referring to being below sea level are directly on the coast. ",
"This area",
" for instance reads as -7m below sea level from my truck's dash. It's directly on the coast so the sea water wouldn't have to climb over top of anything to fill this area in. ",
"I suspect that my understanding of 'average' level of water doesn't mean what I think it means though. "
] |
[
"That makes sense. The areas I'm referring to being below sea level are directly on the coast. ",
"This area",
" for instance reads as -7m below sea level from my truck's dash. It's directly on the coast so the sea water wouldn't have to climb over top of anything to fill this area in. ",
"I suspect that my understanding of 'average' level of water doesn't mean what I think it means though. "
] |
[
"GPS altitudes are in reference to the ",
"World Geodetic System",
", which is an oblate spheroid (squished sphere) centered at the Earth's center of mass. Its measure of sea level incorporates corrections for variations in the Earths gravitational field, but still doesn't always line up with the actual mean level of the sea."
] |
[
"Are women emotional and men rational ?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"We do not debunk or vet theories or offer peer review on ",
"/r/AskScience",
". For more information regarding this and similar issues, please see our ",
"guidelines",
"\"Hysteria\" and similar arguments (e.g. \"excitable delirium\") are not scientific. They have been used to discredit people that were justifiably unhappy with their oppression.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I was citing hysteria as an example of how psychologists can be wrong. Hence I wanted to know if there was a biological consensus on the stereotype"
] |
[
"As I pointed out, we don't address such stereotypes or try to debunk baseless sexist ideas"
] |
[
"Additions to Highschool curriculum in the last 10 years?"
] |
[
false
] | null |
[
"Physics"
] |
[
"Physics"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Is laughing instinctual for humans, are animals capable of laughing too?"
] |
[
false
] |
Why, physiologically and psychologically, do humans sometimes have the overwhelming urge to laugh? What is happening in our brains? Why do we all do it in the same way (roughly). And are animals capable of laughing, or synthesizing humor (or whatever is the external force causing us to laugh)?
|
[
"The results of this study indicated that chimpanzees produce ",
" that is distinct in form and occurrence from their ",
". These findings provide the first empirical evidence that nonhuman primates have the ability to replicate the expressions of others by producing expressions that differ in their underlying emotions and social implications. The data further showed that the ",
" Notably, some chimpanzee groups of this study responded more with laughter than others, an outcome that provides empirical support of a socialization of expressions in great apes similar to that of humans.",
"source",
"A number of the acoustic features of these tickle-induced sounds were subjected to phylogenetic analysis, and they found that, as has been previously noted [2] and [7], human laughter was acoustically distinct from the tickle-induced calls of the other apes. Nevertheless, there were enough ",
", across species, to reproduce the hominid family tree, which has been well-established based on biomolecular (DNA sequence, for example) and morphometric traits. The central significance of this finding is that, despite considerable differences in the manners and contexts in which humans and other apes laugh, ",
"source",
"Acoustic outcomes revealed both important similarities and differences among the five species. Furthermore, phylogenetic trees reconstructed from the acoustic data matched the well-established trees based on comparative genetics. Taken together, the results provide strong evidence that ",
" Findings also show that distinctively human laughter characteristics such as predominantly regular, stable voicing and consistently egressive airflow are nonetheless traceable to characteristics of shared ancestors with great apes.",
"source"
] |
[
"Rats laugh when you tickle them"
] |
[
"Rats giggle when tickled!!",
"http://www.youtube.com/watch?v=j-admRGFVNM&feature=youtube_gdata_player"
] |
[
"Is the event horizon of a black hole a 3D globe, or a 2D ring?"
] |
[
false
] |
I understand all black holes shown in publications are just simple examples, there are no real pictures. But saying that, what do the leading theories say about the real shape? Is it a black ball or more like a whirlpool vortex? Is it more like an ice cream , the pointy end is the singularity and the open end the event horizon?
|
[
"The black hole event horizon is a spherical surface surrounding the matter inside of the black hole. The radius of the sphere is given by the ",
"Schwarzschild radius",
", or the radius within which the ",
"escape velocity",
" is equivalent to the ",
"speed of light",
"."
] |
[
"The event horizon is perfectly spherical for a non-rotating black hole, but for a rotating black hole it will be somewhat oblate."
] |
[
"I'd imagine most black holes are rotating? Or is rotation rare?"
] |
[
"Once a rocket reaches space and goes in to free fall, how do they get fuel/oxidant to flow downward towards the nozzle without thrust or gravity pulling it downward?"
] |
[
false
] |
There has to be some simple mechanism that pushes the fuel and oxidant out of the fuel tanks once they've cut their initial thrust. What is it?
|
[
"In the simplest tank design, the propellant is at the bottom, separated by a diaphragm from an ullage volume where a pressurizing gas pushes the diaphragm.",
"Pros: very simple and cheap design",
"Cons: you lose pressure as the propellant is consumed and the gas expands on an every time larger volume. This can be mitigated if the ullage volume is initially very large, so the gas won't have expanded a lot, but then you'll have the problem that big tanks are massive (in space, you want things to be as light as possible so they can be accelerated easily with little propellant).",
"A better design is to keep the gas in a separate small container at high pressure, with a pressure regulator feeding the gas gradually into the tank. Then as the propellant is consumed, more gas flows into the ullage volume and pressure is kept nearly constant without the need for a very large tank.",
"Pros: less massive, nearly constant pressure",
"Cons: more complex and expensive",
"In simple rocket engines (e.g. for attitude control), sometimes these approaches suffice. But when high thrust is required (i.e. high mass flow rate), then the pressure from the gas and diaphragm may not enough to ensure a good flow into the combustion chamber. Then you need turbopumps. They can be powered by the same fuel and oxidizer with a pre-burner."
] |
[
"You can either use an inert gas to pressurize your tank and push the propellant towards the engines or you can bump the rocket with something like a cold gas thruster or a small ullage motor to get all the propellant to flow to the bottom just prior to ignition."
] |
[
"The third stage of the Saturn V used ullage rockets. It only had to relight once, so it had four small solid rocket motors that would give it a kick forward to force the propellants to the \"bottom\" of their tanks so that they could properly feed the turbopumps. Once the engine's lit, you're good to go.",
"After the third stage of the launch vehicle was jettisoned, The Command/Service Module and the Lunar Module had much less mass and were able to just use their reaction control system to provide the thrust to accomplish the same thing.",
"In addition, many rockets use separate high pressure helium tanks in addition to some sort of ullage kick to provide a blanket of pressurized gas \"above\" the propellants that provides the motive force to actually get the liquid propellants into the combustion chamber. Helium is generally used because it remains a gas at the same temperature any cryogenic propellants are liquid at, so it won't condense out and get ingested by the engine with likely catastrophic consequences. In non-cryogenic applications it's still a good choice because it remains a gas at lower temperatures than any other gas, thus reducing the heating required to make sure it vaporizes properly when introduced into the propellant tanks. Similarly, it requires less heat to keep it from freezing solid than any other viable choice. In fact, it can't even exist as a solid below something ridiculous like 350 psia, so if you don't exceed that pressure, keeping it from freezing isn't even something you have to worry about.",
"So, the kick from the ullage motors or RCS sends the propellant to the bottom, the high pressure gas gets it to flow to the combustion chamber adequately to get a start on the engine, then engine thrust takes it from there."
] |
[
"We are scientists from the Society of Vertebrate Paleontology coming to you from our annual meeting in Toronto, Canada! We study fossils. Ask Us Anything!"
] |
[
false
] |
We are scientists from the Society of Vertebrate Paleontology coming to you from our annual meeting in Toronto, Canada! We study fossils. Ask Us Anything! Hi ! We are members of the , here for our 9th annual AMA. We study fossil fish, mammals, amphibians, and reptiles — anything with a backbone! Our research includes how these organisms lived, how they were affected by environmental change like a changing climate, how they're related, and much more. You can . Joining us today are: ( ) is the Curator of Palaeontology at the Royal BC Museum in Victoria, BC. Her primary area of research is on the dinosaur group Ankylosauria, including their evolutionary relationships (phylogenetics) and the biomechanics of their tail clubs. You can read more on Dr. Arbour’s website at ( ) is the Curator of Fossils at the at Duke University in Durham, NC. His research focuses on the evolution of carnivorous mammals and primates, especially in Africa and North America. He is also part of several teams working to network natural history collections. Dr. Borths co-produced the paleontology podcast series Past Time ( ). ( ) is the Curator of the North Dakota State Fossil Collection and the Paleontology Program Manager for the North Dakota Geological Survey. His research focuses on the evolutionary history of ornithischian dinosaurs and studying Eocene and Oligocene faunae from the Great Plains region of North America. Find him on twitter @boydpaleo. ( ) is a paleontologist at the University of Tennessee whose research focuses on the processes of fossilization, evolution, and biology, of crocodiles and their relatives, including identifying bite marks on fossils. Find her on Twitter @UglyFossils. ( ) is a fossil preparator with the State Historical Society of North Dakota. She has cleaned and repaired many fossil specimens for public museums and institutions over the past 18 years. Some well known specimens she worked on include “Jane” the juvenile Tyrannosaurus rex and “Dakota” the Edmontosaurus sp. fossilized natural mummy. ( ) is a paleoecologist and Assistant Professor at the University of Cincinnati. His research focuses on Pleistocene paleoecology, taphonomy, and using fossil and subfossil records to help conserve and manage modern ecosystems (Conservation Paleobiology). Find out more at JoshuaHMiller.com. ( ) is an ecologist who works on landscape-level modeling of coastal and wetland ecosystems. She also studies the morphology and ecology of fossil and modern crocodylians, and uses quantitative methods to inform conservation decisions. ( ) is an early career paleontologist and Assistant Curator of Geology at the Illinois State Museum in Springfield, IL USA. Her research focus is paleoecology of Quaternary mammals, including their diets and geographic distributions. ( ) is the Assistant Curator of Paleontology at the Virginia Museum of Natural History in Martinsville, VA. His research focuses on the evolution of reptiles during the Permian and Triassic periods, a time of great change that saw the rise of the dinosaurs. Please check out the Virginia Museum of Natural History at vmnh.net. Dr. Pritchard has also co-produced the paleontology podcast series Past Time, available at . ( ) is the Director of Visitor Engagement and Education at the Raymond M. Alf Museum of Paleontology in Los Angeles, California. His previous work focused on the paleontology of Southern California, particularly the evolution of marine mammals. Today, his research has shifted to education and DEI in STEM as a National Geographic certified educator and cofounder of the Cosplay for Science Initiative. He was recently named a Grosvenor Teacher Fellow with National Geographic and Lindblad Expeditions. You can find him online as @paleoparadox.
|
[
"There have been so many really incredibly preserved fossils out there, ranging from single cells preserved in the act of division to mummies of whole mammoths (like this ",
"recently discovered baby",
"). And while it is awe-inspiring and exciting to be able to study the ",
"mother's milk",
" from the stomach of a baby mammoth, even more poorly preserved specimens have lots to offer. In fact, it is often those less dramatic specimens that may preserve things like bite marks, which tell us about species interactions from long ago."
] |
[
"Which is the best preserved fossil ever discovered that gave a lot of information? More than any other fossil of it's kind has."
] |
[
"Usually, we start by just walking around and looking for fossils coming out of the ground. After finding something interesting, we work to carefully remove the rock around a particular fossil. If there seems to be a lot of material still buried under the rock, that may be a good place to start setting up a formal excavation (to start digging!)."
] |
[
"If chronically high cortisol levels can eventually lead to cancer, and cannabis raises cortisol, can marijuana actually contribute to cancer risk?"
] |
[
false
] | null |
[
"Cortisol may lead to cancer because it's an immunosuppresant on T cell, which (among other thing) survey your body for precancerous cells. It can also lead to central obesity (back hump, etc) because cortisol is one way for your body to regulate fat accumulation.\nI'm not sure how cannabis might raise cortisol levels, but there are cannabanoid receptors in the lower brain that also controls energy homeostasis (hunger, for one, and fat accumulation through cortisol release, for another -they are related in the part of the brain called the hypothalamus).\nAlso, if you're unsure about one study done in one lab at one university, I strongly encourage you to do follow up reading in peer reviewed journals (I cannot stress this enough) that try to pinpoint this effect that you're trying to answer."
] |
[
"Here",
" is a study (full free article) you may have come across before, but it states this as the results in the abstract: \"At socially relevant doses, Delta-9-THC raised plasma cortisol levels in a dose-dependent manner but frequent users showed blunted increases relative to healthy controls.\" It is interesting that there would be a development of neruoendocrine tolerance. Just a jump off study if you are interested in delving into it. "
] |
[
"Can you cite where you read that cannabis increases cortisol levels?"
] |
[
"Aerodynamics Application"
] |
[
false
] |
If dimples help golf balls fly better, why don't we put dimples on our cars' exteriors? Are there any motor companies that have researched this? The MythBusters tried it a while ago and reported an 11% increase in efficiency. Needless to say, their testing is less than rigorous.
|
[
"Golf balls are spherical; and with dimples on them, they are begging to be spun in the air. The dimples increase the range of flight for the golf ball because of lift (and low air drag because of no flow separation). A car with dimples on it would be similar to a car with a spoiler on the back end. A spoiler serves to \"spoil\" unfavorable air travel across the car (that is, decrease lift to increase traction and stability).",
"The necessary velocities for a spoiler to have any affect on a car is outside the realm of most people's driving habits. It becomes necessary for race cars however (which have spoilers and diffusers to help with air flow).",
"FastSkinz",
", a company that sells a dimple-covered vinyl vehicle wrap claims that their product would keep the boundary layer across the top of the vehicle with flow separation only occurring at the trailing edge (thereby reducing drag). Their claim is an 18-20% increase in fuel economy. ",
"Contrary to their belief, the drag caused by the top of your car isn't nearly worth that much and may only be a couple percent. ",
"Here is a picture",
" from their ad about flow separation, and ",
"here is the air flow across a similarly shaped vehicle",
".",
"Popular Mechanics did a little study",
" on this some time ago and determined that FastSkinz results were a little dubious.",
"Here is a picture of a dimpled Lexus LS 460L",
" from the 2009 US Open. I think it was more of a gimmick than anything. Lexus has also has dimpled undercarriages for some of their LS 430 series but I don't know any relative benefits on that."
] |
[
"As an example of why spoilers are (in some cases) necessary, you can take a look at ",
" testing the Koenigsegg CCX",
"."
] |
[
"thank you, that is very interesting. ",
"I particularly liked the flow visualization around the vehicle."
] |
[
"How do central banks determine exchange rate targets?"
] |
[
false
] |
[deleted]
|
[
"Hi there,",
"This is somehow out of my area of study, but I see it non the less as an interesting one. I would however suggest that you narrow it down as it is very broad now. I'd suggest that you break out the questions into separate ones as, as it is now it is in my opinion to wide to properly be answered here.",
"Regarding if it is a political or an economic one. It is both, depending on the country to be honest. Most central banks are \"neutral\" from government policy, but in many countries government can still set inflation targets etc. that the central bank has to aim for. But I'd argue that it mainly is an economic question.",
"Anyhow, I think you'd get better answers if you break the questions to separate ones as follows:",
"How would a central bank decide what the 'right' exchange rate is when devising monetary policy?",
"How do Central Banks weigh the relative importance of employment vs growth vs consumption and how do exchange rates really affect each?",
"What are some of the prevailing schools of thought on exchange rate targets?"
] |
[
"So first of all most central banks do not have explicit targets - the US government does not for example nor the British though they will view the currency as being over/under valued at certain levels.",
"So the exchange rate is actually set by the markets - by where trades actually happen and there is a feedback loop here from central banks though it is not the only force in action.",
"Most central banks have a mandate to target say inflation or unemployment and this reflects public sentiment - eg the FED is very cautious of deflation but the ECB more cautious of inflation. ",
"As for is this politics or economics in most major economies the central bank is independent of (direct) political control. ",
"Let's take an example of the Swiss government who have declared that the USDCHF (swiss Franc) rate will not go beneath 1.2000. Done to control inflation in the country. As this number goes down it means one USD is worth less and less CHF - that is the CHF becomes more valuable. ",
"So what actually happens is that when the rate moves to 1.20000 the Swiss central bank is there buying USD and selling CHF. Now this is important because they are acquiring USD (which they can't manufacture) and selling CHF (which they can print off) so they can maintain this rate as long as they like. Now in practice everyone in the market knows they are buying at this level so it self corrects.",
"Imagine it were the reverse - they wanted to cap the exchange rate; they could only do this so long as they had USD to sell and the market can over run them - see black Wednesday when the British government were essentially bankrupted by a hedge fund.",
"So this is how they directly can control exchange rates - but there are a series of controls they have using interest rates, bond repos, QE a vast set of evolving tools!"
] |
[
"Well I understand that most currencies float (or like RMB partial float), but like you said \"they will view the currency as being over/under valued at certain levels.\" What makes them think one way or another? Does it really come down to \"public sentiment\"? Do they not have their own thoughts on what is 'good' for the economy in the long run?",
"Also on the more mechanical level, if you choose to let your currency float, why would you build foreign exchange reserves at all? (i.e. the US still does have some forex reserves even if they're much less than China's) The point of reserves is to manipulate exchange rates right?"
] |
[
"How does the International Space Station regulate its temperature?"
] |
[
false
] |
If there were one or two people on the ISS, their bodies would generate a lot of heat. Given that the ISS is surrounded by a (near) vacuum, how does it get rid of this heat so that the temperature on the ISS is comfortable?
|
[
"Hey I worked on the ISS thermal control systems. The station is essentially cooled by a water cooler like you see in high end PCs. All of the computers and systems are on cold plates where heat is transferred into water. This is necessary because without gravity air cooling doesn’t work well. The warmed water is pumped to heat exchangers where the energy is transferred into ammonia. The ammonia is pumped through several large radiators where the heat is “shined” into space via infrared. The radiators can be moved to optimize the heat rejection capability. The reason the radiators are so large is that this is a really inefficient method but it’s the only way that works in space. ",
"The reason we use water first and then ammonia is that ammonia is deadly to people. The ammonia loop is separate from the water loop and located outside the station. However if there were to be a heat exchanger breach high pressure ammonia would get into the water loops and into the cabin. That would be the end of the station essentially. We had a false alarm in 2015, scary day. ",
"Just realized that I didn’t answer the question completely. Any heat generated by the astronauts themselves would be removed from the air via the ECLSS. It’s not really an issue though. "
] |
[
"Water would freeze if it was pumped through the space-side radiators. Ammonia can stay liquid down to -107F (-77C) and so can be pumped through the radiators without freezing and blocking them. "
] |
[
"It is honestly an awful potato of a photo to show the panels. Here's a better view (the white fold-out panels): ",
"https://i.stack.imgur.com/cpIBo.jpg"
] |
[
"When under anaesthetic for surgery or else, if a doctor holds open your eyelid, is the brain still registering sight or have your eyes 'shut down'?"
] |
[
false
] |
Edit: Just to clarify, I had this thought today because I wondered what it would be like if I ever had to have surgery on one of my eyes. I'll be damned if I'm letting them anyway near either of them when I'm conscious or aware, but then I thought 'well they're going to be holding my eye open anyway, how much of that will register?'
|
[
"Yes your brain would respond. There is a great deal of literature on perception and visual perception in particular. The cells of the early visual cortex will respond to any signal coming from the retina. Including when the subject is unconscious. They have done this exact experiment with single-unit recording in animals and found an equivalent response to a behaving animal.",
"Source: I am a vision scientist."
] |
[
"There's a little more to the story. Many studies of visual function (e.g. Hubel and Wiesel) were/are done in ",
" animals. Yes, they were prepped under anesthesia, but anesthesia was discontinued prior to recording (whether such experiments are ethical is a question for another time).",
"As a rule, anesthesia tends to clobber the CNS (if it didn't, it wouldn't be anesthesia). Barbiturates do, urethane does, chloroform does, volatiles like Halothane do. About the only ones that don't are the disassociatives like ketamine. ",
"So the complete answer to OPs question is: ",
".",
"Source: sensory scientist who had my results in an anesthetized prep sneered at by pompous jackasses who did analogous recordings in an awake animal."
] |
[
"There are lots of classes of anesthetics. I'm speaking in regards to barbiturates, like Amytal. These drugs depress central nervous system response. So in a sense, the eyes are not \"shut off\", in the sense that your eyes are getting input, its just that the brain isn't being stimulated nearly as much, if at all.",
"It's like sleeping. When you're asleep, you can hear, but it won't wake you (which is kind of analogous to your \"brain registering hearing\") unless it crosses a higher threshold."
] |
[
"Why are most opera singer's a bit overweight? Is there a correlation between body volume and vocal abilities?"
] |
[
false
] | null |
[
"Her costume is also the reason Vikings are depicted with horned helmets these days. That originated with one production of the Ring Cycle or other."
] |
[
"Her costume is also the reason Vikings are depicted with horned helmets these days. That originated with one production of the Ring Cycle or other."
] |
[
"What about Pavorratti (sp), or Placido Domingo? Both are large guys, did their body size correspond to their ability to reverberate?"
] |
[
"Can bacteria orbit a bowling ball ?"
] |
[
false
] |
Can somthing really small but still not in the subatomical scale like say bacteria orbit around somthing big like a bowling ball or a 10 meter diameter steel ball ?
|
[
"Strictly speaking, anything can orbit around anything. If M is the mass of the central object, and r is the radius of the orbit then the orbital speed must be sqrt(GM/r) where G is the gravitational constant, which is about 10",
" in SI units. So you can see that the only way to really achieve an orbit in humanly observable terms (speed and radius 'near one' in SI units) is with a very massive object (about a ",
" trillion kilograms at least). In practical terms you need much more than that because there's no ordinary materials that can fit such a mass within a 1 meter orbital radius, so you have to not only go with more massive objects, but also larger ones. ",
"You can expect an orbit around a bowling ball to be in the order of micrometers per second. Such speeds are not really stable for very light objects in atmospheric conditions, but in a pure vaccuum outside the influence of external forces there's nothing that prevents such an orbit."
] |
[
"If all that's in the universe is the bacterium and the bowling ball, then the bacterium will orbit the ball.",
"In reality though there's other stuff. The bowling ball is itself orbiting something. The ball will have a sphere of influence, a region of space around it in which small objects will orbit the ball. Objects outside that will orbit the bowling ball's parent body (a planet, for example) directly.",
"Now in some situations an object's sphere of influence will be smaller than the object itself! This means nothing can orbit it.",
"An approximation is given by the formula for the Hill sphere. In practice, over long timescales orbits close to the size of the Hill sphere are unstable.",
"https://en.wikipedia.org/wiki/Hill_sphere",
"For example a bowling ball in low Earth orbit couldn't have anything orbiting it. But raise it to geostationary orbit, and it could, at least in the short term. For small things like bacteria non-gravitational forces such as solar radiation pressure become significant."
] |
[
"In 1827, Robert Brown notice, through his microscope, pollen grains in water jumping randomly around. This is called [Brownian motion]",
"https://en.m.wikipedia.org/wiki/Brownian_motion",
"). Albert Einstein won a Nobel Prize by showing this movement is caused by water molecules hitting the pollen. ",
"Bacteria's orbit around bowling balls ",
"would likely be disturbed by Brownian motion caused by molecules in the atmosphere. "
] |
[
"Does dark matter and dark energy also exist on Earth or only in space?"
] |
[
false
] |
Is there dark matter in our atmosphere surrounding us right now? If not, where is it found? As close as our orbit or way farther out in space?
|
[
"Dark energy is associated with space itself, so it is literally everywhere, with the same amount being found at each point. However, within galaxies there is enough matter that gravity wins out over the expansion caused by dark energy, so while it's still there, we don't notice its effects.",
"Dark matter is instead composed of discrete particles, which have some density distribution that varies with position in the galaxy. So there is dark matter anywhere within the solar system, but the particles are just passing through on their own orbits around the galaxy. Because dark matter doesn't interact with normal matter, if any happen to actually \"collide\" with the Earth, they just pass straight through. Depending on what the mass of the dark matter particles is, there could be thousands or even millions passing through you each second. ",
"The solar system is so small on galactic scales that the dark matter density is basically constant everywhere within it, so again, again, we don't see any local effects due to dark matter. There's one exception to this, which is that it might possible for dark matter particles to get \"trapped\" at the bottom of deep gravitational wells i.e. at the core of the Earth or Sun, or more realistically, around the black hole at the centre of the galaxy. If this happens often enough, its density could build up enough that we might be able to detect it, via a specific type of gamma ray signal. There's been various attempts to look for this, but none have had any success yet."
] |
[
"It relies on the statement that dark and luminous matter don't interact being almost, but not quite true. If rare interactions can occur, a collision within the Sun could take away energy from the dark matter particle and allow it to get trapped.",
"There's also attempts to directly detect dark matter passing through the Earth that rely on a similar interaction happening - they look for the transfer of momentum from a dark matter particle that collides with a heavy atomic nucleus within the experiment.",
"There's theoretical grounds to expect dark matter to have this interaction - if it does, then the abundance of dark matter works out to be what's required to explain a lot of astronomical and cosmological observations. Somewhat unfortunately, it was expected (or hoped, at least) that the LHC would find evidence of dark matter if it did behave this way, and that hasn't happened."
] |
[
"That doesn't mean we can't accurately constrain what their properties need to be, thanks to the huge amount of indirect evidence we have. Rather than rehash it, I'll point you to ",
"this excellent comment",
" which summarises why dark matter remains the leading hypothesis.",
"Many laypeople seem to want to believe that astrophysicists are part of some conspiracy to discredit alternatives to dark matter, but as one of them I can say that (a) there is no evidence that that's the case, and (b) even if it was, it's unclear what we'd be gaining from doing so. There's no commercial/financial incentive; collectively we're in it for the pursuit of knowledge. So we'd have no reason to knowingly advance an incorrect theory."
] |
[
"Do hair products \"kill\" your hair?"
] |
[
false
] | null |
[
"Hair is already dead, so what exactly do you mean by kill? Do you mean cause baldness, cause breakage, etc? Repost this question with your definition of kill. :)"
] |
[
"Ah, I see how I mislead people. Sorry for that. Well this one type of pomade was thining out my hair. My relatives and some friends said if I keep using it my hairline would start to receed and soon become bald. Is that true?"
] |
[
"Post a new question that asks just that. We can't definitively tell you that is what is occurring, but if you asked a ",
" question you may get some answers. A good way to ask would be, \"Is it possible that a hair product such a pomade made with x, y, and z could cause balding / hair loss?\" ",
"Just keep any personal info out of it (so we don't get in trouble for medical advice)."
] |
[
"Pet question, details inside! (sorry if this is in the wrong subreddit, I tried looking for a more suitable one)"
] |
[
false
] | null |
[
"This isn't a place for veterinary advice..."
] |
[
"I disagree ಠ_ಠ",
"That's why I'm here.",
"OK edit not this type of question. I'll leave the post removed and answer it personally."
] |
[
"I'm really sorry but I tend to agree with bobtentpeg that this isn't the right subreddit for this type of question as it's not about science but more asking for personal veterinary advice. Unfortunately I'm not sure I have a good recommendation for another subreddit, however one of our other mods is a vet and they may be able to point you to a better subreddit. I'll make sure they see your post, but I've removed it from AskScience. All the best! "
] |
[
"Can the heart actually \"skip a beat\"?"
] |
[
false
] |
When people get surprised or scared, a lot of them will say, "My heart just skipped a beat!" Is there any truth to this, or is it just an expression?
|
[
"So there's actually two parts to this question: 1) are there sometimes heart rhythms where there is beat missing? and 2) what happens you are startled?",
"1) Are there sometimes heart rhythms where there is beat missing? ",
"Yes! There are many types of arrhythmias that involve a dropped beat. The most inoccuous perhaps are what are called compensatory pauses, usually following a premature atrial or ventricular beat. Premature beats are not necessarily pathological, but may be the result of sinus node irratability or other ongoing problems. What happens is that a beat comes too early, and, as the name implies, there is a pause where the normal beat should follow. Typically the beat after that is normal, and returns to regular rhythm. ",
"More dangerous dropped beats are in pathologic processes like Mobitz I or Mobitz II Type 2 AV blocks, in which the AV node that allows the atria to electrically communicate with the ventricles, either creates prolonged blocks to where a beat is dropped (Mobitz I) or where suddenly a beat drops out (Mobitz II). More rarely and more dangerous is a High Degree 2nd degree AV block, where multiple beats are dropped in a row. There are other times beats may be dropped, but these are the most common. In general, though, ",
", and are only detected on physical exam or ECG.",
"2) What happens when you are startled?",
"So we talked about types of dropped beats, but an important thing to realize is that those beats are not normally felt. So what happens when you are startled? What are you feeling then?",
"Well, when you're startled there is a sudden surge of catecholamines such as epinephrine. This increases both the rate and contractility of the heart. The transition from a resting rate to an accelerated rate and contractility often is perceived as \"missed beat,\" or a \"lump in the chest.\" However, this represents the physiologic changes as the heart accelerates and becomes more sympathetically activated, not actually a dropped beat. In some people who also experience some pain with this, there is also an element of coronary insufficiency, in which the coronary arteries of the heart are slower to respond to the epinephrine than the rest of the heart is, creating a transient cardiac hypoxia."
] |
[
"What about anxiety-related palpitations? They seem to fall partially in both categories, based on this description."
] |
[
"Wow! I didn't realize that there was quite that much going on. Great answer, thank you!"
] |
[
"Why can't we take pills that deliver all the needed nutrition to our bodies instead of consuming food?"
] |
[
false
] |
This may be a rather obvious question, but I was thinking the other day: Is there something preventing a person to stop eating food all together and just consume pills that contain all the needed nutrients to fuel the body for a single day (or even longer)? Would there be drawbacks from doing something like this?
|
[
"Assuming you package the most dense food source (fat) into pills, you would need to swallow about 250 large pills per day to meet your energy requirements, if you add an adequate amount of protein to your diet, that number increases to around 400 pills."
] |
[
"Sorry if this is not scientific enough as an answer, but it's basically because nutritional science is shaky at best. For a very long time, Fats in all forms were vilified, until we figured out that some fats were good. We found a new bad guy in carbs, but that is proving to be less and less true as well. I suggest reading 'In defense of Food' by Michael Pollan. He explains how a large part of how food affects our body is actually the delivery system. We figured micronutrients out years ago, and have been try to jam as many of them into processed foods as we can (I'm looking at you \"Vitamin-C enriched white bread), but all studies have found that the nutrient enriched processed food is no better (and typically much worse) for you than their natural counterparts. We don't have the answer to our nutritional needs, despite what people try to tell you."
] |
[
"The largest capsule size on the market designed for human consumption is size \"000\", which holds 1.37 ml. If you fill them with pure oil, that is 11 calories per pill, a pill of equal size full of protein would have 5 calories at most. \nAssuming a 2000 calorie daily energy requirement, and 56 grams of protein, you would need to swallow 45 pills full of protein, and 162 pills full of oil to meet your energy requirements. The lowest price for bulk \"000\" capsules I found was about $0.03 each, the cost of that many capsules would exceed the cost of the food in them."
] |
[
"Why do Africans have the hair they do? And why does almost everyone else have straighter hair?"
] |
[
false
] | null |
[
"Most sources I've found suggest it helps keep the head (importantly, the brain) cool and protected from the sun.",
"Straight from ",
"Wikipedia",
":",
"Jablonski[36] asserts that it was evolutionarily advantageous for pre-humans to retain the hair on their heads in order to protect the scalp as they walked upright in the intense African (equatorial) UV light.",
"...",
"By contrast, some believe that tightly coiled hair that grows into a typical Afro-like formation would have greatly reduced the ability of the head and brain to cool. They reason that although hair density in African peoples is much less than their European counterparts, in the intense sun the effective 'woolly hat' produced would have been a disadvantage. However, anthropologists such as Nina Jablonski make the opposite argument with regards to this hair texture. Specifically, Jablonski's assertions [36] suggest that the adjective \"woolly\" in reference to Afro-hair is a misnomer to the extent that it connotes the high heat insulation derivable from the true wool of sheep. Instead, the relatively sparse density of Afro-hair, combined with its springy coils actually results in an airy, almost sponge-like effect. This, in turn, Jablonski argues,[36] more likely facilitates an increase in the circulation of cool air onto the scalp.",
"Hope that helps."
] |
[
"So you're saying there are two conflicting schools of thought on this issue?"
] |
[
"There are assertions like Jablonski's and critiques of those assertions. I haven't found any other suggestions."
] |
[
"How is it determined which direction objects in space will spin?"
] |
[
false
] |
Thought about this while watching the toilet water go down the bowl and remembered how in the southern hemisphere he goes counterclockwise. Is there anything that determines which direction things like galaxies, black holes and planets turn ?
|
[
"water in your toilet does not spin the other direction in the southern hemisphere. ",
"The direction your toilet flushes is 100% defined by the way it was designed. ",
"Coriolis force only acts appreciably on large areas or high velocities while \"on\" the surface of a spinning object (planet, merrry-go-round, etc)",
"everything in the universe which has a spin got that spin based on whichever direction the angular momentum of initial conditions dictates. ",
"There is no rule of rotation out in the universe. "
] |
[
"More or less at random. Take a star, for example. It forms from a cloud of gas floating out in the galaxy, when that cloud collapses under its own gravity. But all the different parts of the cloud have slightly different velocities, so the velocities that they have relative to the center of mass will induce some spin as the cloud collapses down, and suddenly you have a spinning ball of gas. Similarly for galaxies which form in a similar way."
] |
[
"Though toilets typically have jets that determine their direction, the coriolis force can matter if you have a large pool of water that contracts inward without other rotational forces. If you take a motionless meter wide pool of water and let it drain through a small hole, it will eventually start spinning in the direction you'd expect because of coriolis forces (as long as it is far enough away from the equator)."
] |
[
"Why is fuel on space vehicles often stored in spherical vessels?"
] |
[
false
] |
A good example: I realize that this probably does not hold true for all types of fuel, but what types of fuel stored like this, and why? Why not use cylinders, or other shapes that better fit the form of the space in which the vessel is located? Wouldn't it be a more efficient use of space? Also, I realize that a number of the vessels pictured may be compressed gases for life support or verniers, but my question in these cases still stands.
|
[
"Here's",
" a better picture of the tanks.",
"I wasn't a design engineer on the program, so I can't say for certain, but I think these are used because they are the most efficient use of weight, which is much, much more precious a commodity than volume when we're talking about putting something into LEO.",
"A sphere is the shape with the least surface area to volume ratio, so a sphere would give the largest volume for a given mass of tank. Additionally, a cylindrical (or any other) shape for a pressure vessel would have more stress concentrations - I don't think this would be a deciding factor, but it may have been considered as a design feature.",
"Edit: Also, interestingly, one of these tanks from Columbia was ",
"found in a lake",
", mostly undamaged. "
] |
[
"The stresses in the wall of a spherical pressure vessel are lower than in (for example) a cylindrical vessel, by a factor of two. There is a discussion ",
"here",
". So the walls of the spherical vessel can be half as thick as those of a cylinder, for the same pressure, for the same material."
] |
[
"Yeah, I'd say it's likely entirely because of weight, with the added bonus that's it's also the strongest, and least surface area to worry about insulation issues.",
"I believe those are cryogenic tanks too, meaning they're probably at very high pressure, and need to be kept well insulated."
] |
[
"How much of the temperature on earth can be attributed to geothermal heat from the mantle and core etc?"
] |
[
false
] | null |
[
"Essentially none, unless you're sitting on a hot spring or fumarole over a tectonic rift or hot spot. Check out figure 1 here--extreme values of mantle heat flow are around 0.5 Watts per meter squared. By contrast, solar radiation is on the order of 1000 W/m",
" (depending on season and latitude). That means that if you magically put a perfect thermal insulator below the crust, surface temperature would be almost completely unaffected."
] |
[
"Check out figure 1 here",
"...you didn't link anything."
] |
[
"Not quite none. More like 40 K. So solid nitrogen and solid oxygen and dry ice, liquid hydrogen, and still gaseous helium. And while the surface of the oceans would obviously freeze over, they'd serve as a pretty good insulator to keep much it the rest liquid underneath."
] |
[
"When it is crazy cold in the U.S. does that mean that the globe is likely colder overall at the moment, or is the distribution of cold and warm on the planet just distributed differently?"
] |
[
false
] | null |
[
"You basically can't infer anything that specific from a single event. That's the whole essence of the difference between weather and climate; at any single moment the weather in one place doesn't tell you a whole lot that is useful about the weather somewhere else. Only over time can you identify any kind of pattern.",
"If you are asking about the recent cold-snap in North America? Yes, it was definitely the case that cold and warm were just distributed differently. Several articles recently had great world-map visuals of that, like ",
"this one",
"."
] |
[
"For convenience"
] |
[
"No, Antarctica is warmer than the average for Antarctica this time of year. Ohio is colder than the average for Ohio this time of year. ",
"Those maps are about deviation from the average, not absolute temperatures. "
] |
[
"How does sickle cell anemia grant resistance against malaria?"
] |
[
false
] |
I know it does, but it didn't come up during a recent series of lectures in my parasite biology class. I know about the life cycle of and PfEMP1 if that makes it easier to explain.
|
[
"Sickle cells have a lower oxygen carrying capacity. This causes the malaria parasites to suffocate in the blood. But a side effect of Sickle cell anemia is shortness of breath because your blood can't carry quite enough oxygen "
] |
[
"You see it a lot in Africans because malaria is a big problem over there. Sickle cell anemia is actually an evolutionary defense mechanism "
] |
[
"I didn't expect it to be so simple. Thank you for answering."
] |
[
"I have a question about the James Webb Space Telescope"
] |
[
false
] |
More specifically on it's ability to see 13.4 billion years into the past. I understand the principle ( light particles travel fast but not infinitely fast, and the further the object the longer it would have taken the particle to reach us, thus the what we see is actually the "past version" of the object) But I have trouble representing myself this, and the theory that the universe is ever expanding together. How can we see something that dates from an "epoch" where the entire universe was smaller? I'm sorry I can't phrase this better.
|
[
"This is actually a very subtle question you've asked here.",
"How do we define \"distance?\" Oh, well, that's easy. It's that thing you measure with a ruler.",
"But there's an unspoken assumption beneath that: that the two things you want to measure the distance between are ",
"Say a bird lands a branch of a tree outside your window, stays there for a moment, then flies away. \"Gosh, that bird was really close,\" you might say. \"I wonder how far away it was?\" So you get out your ruler and you measure it. Not to the point where the bird is ",
" obviously; the bird flew away a long time ago. But to the point where the bird ",
"When we talk about large scales — or even everyday scales but at high precision — we have to be careful to distinguish where things ",
" from where they ",
" And on the scale of the observable universe, when light might take billions of years to get here from there, we can't even take words like \"are\" and \"were\" for granted; we have to rigorously define ",
" as well.",
"Out of that emerges the realization that there's really no single objectively-true definition of the word \"distance.\" We can't imagine going out to a distant galaxy with a very long ruler and measuring the gap, because it takes ",
" to make the trip, and distances ",
" over time! We can't even just default to using a ray of light, because even though light's effectively instantaneous to us over short distances, it still takes aeons to cross the radius of the observable universe.",
"So we're left with three ideas of \"distance.\" One is what you normally think of as distance: the distance you'd measure with a ruler, if it were possible to ",
" and measure it. Another is light-travel distance; if photons had tiny mileometers on them, the light-travel distance is what the mileometer would say. It's how much distance a ray of light ",
" in our frame of reference between the time is was emitted and the time it was absorbed. Finally there's the idea of ",
" which is essentially the proper distance ",
" as opposed to at any other time.",
"When you look up at the sky, whether with your eye or with a telescope, what you're seeing is an ",
" of how the thing you're seeing looked at the time its light was emitted. When we look at the surface of last scattering — the most distance thing we'll ever be able to see — we're seeing light that was emitted from certain point in space a certain time ago: about thirteen and a half billion years, and about thirteen and a half billion light-years away ",
" That's how much distance in our reference frame would be indicated on the photons' mileometers, if they had them.",
"Does that mean the surface was thirteen and a half billion light-years of proper distance away when the light we're now seeing was emitted? No. It was closer to us than that, by a significant fraction. But in the intervening time, the metric has expanded such that the light had farther to go to reach us than the proper distance separating where we are now and where it was then at the moment it was emitted. Exactly how much closer is something that's hard to estimate, because there are a great many variables involved, but a factor of about a thousand is a good estimate. So somewhere on the order of ten million light-years.",
"Still very far away!",
"But where is that surface ",
" Those points from which that light was emitted thirteen and a half billion years ago: how far away from us are they in proper distance right now? Obviously we can't magically freeze time and measure the distance with a ruler. But we can compute, based on how the scale factor of the universe has changed over those thirteen and a half billion years, what the instantaneous proper distance to that surface would be ",
" if we had both the ability to magically freeze time and a very long ruler. That answer depends on a lot of variables, but a good estimate is around forty-five billion light-years.",
"Really though? It's all academic. It's interesting in a sense to contemplate how much distance separates two points in space at some instant in time, but remember that nothing can traverse space in less time than it takes a ray of light to make the trip. In practice, things are as far away from us as the time it takes light to get from there to here. Which means those points out on the surface of last scattering, the ones that are some forty-five billion light-years away from us ",
" are really ",
" farther away than that. If something interesting happened at one of those points right now, this moment, we will literally never know about it. Our sun will have left the main sequence and our planet will have ceased to exist hundreds of billions of years before any information about events happening right now on that surface could reach us.",
"So in effect, to distinguish between past and present, over cosmological scales, is pretty pointless. We can say that events out there are simultaneous with this moment right now, but any knowledge of them lies so far in our future that our species will be reduced to molecular dust hundreds of billions of years before we have any chance of learning about them."
] |
[
"All* the protons, neutrons, and electrons in your body come from an epoch when the universe was smaller (much, much smaller). What's so crazy about finding photons that have done the same?",
"*Basically all, at any rate."
] |
[
"I don't think this was the question the OP had - photons are going to stick around for a while if they don't interact with anything. Rather, I think OP was asking, \"\"If photons come from a time when the universe was smaller, why haven't they arrived yet?\" I think that there are several incorrect hypotheses the OP is making.",
"First, two things are happening. ",
" observable universe is expanding. I say ",
" in italics because if you're anywhere else in space your observable universe looks a bit different at the edges. Our observable universe is expanding because the universe is getting older, giving more distant objects the time to send us light. Our observable universe is pretty much a sphere, and is expanding at the speed of light.",
"The other thing that is happening is that the entire universe (which is much, much bigger than our observable universe - the current best guess is that it's infinite) is being stretched apart. To use a common analogy, think about drawing two dots on a deflated balloon. Now inflate the balloon. The dots don't stretch, but the distance between them does. ",
" ",
"Now what's happening with the objects that we can just barely see - the ones that are at the limit of our telescopes' power? Well, those objects -- as we see them -- represent objects that lived very early in the life of our universe -- if I recall correctly, no more than a billion years after the Big Bang. So it's useful to observe them, because some things in our universe were very different back then - for example, the populations of stars.",
"Now you might ask, \"If we see something 13.4 billion light-years away, are we seeing it as it was 13.4 billion years ago?\" The answer to that is ",
" - we'll see it as it was ",
". This is because as that lonely little photon was making its way through all the space between that object and us, the space in between was expanding! So (and I'm making up numbers here) something 13.4 billion light years away might appear to us as it was 13 billion years ago, because the photons that would be arriving now (if space weren't expanding) are delayed because they have to travel farther.",
"Now what's interesting is that the expansion of the universe is accelerating, so that at a certain point (I think rather far in the future) any light coming towards us from very distant objects will encounter space between us that is stretching so fast that it never makes any headway towards us at all! So we'll never be able to observe the entire universe, even if we wait around for billions and billions of years."
] |
[
"Is there a chemical reason why elements change properties when forming compounds? (ex. sodium and chloride losing explosive and poisonous properties when forming table salt.)"
] |
[
false
] |
Something I have always wondered and just discovered this wonderful subreddit to ask it in. A quick google search did not offer me anything, I'd appreciate any help!
|
[
"It's all about electrons...atoms with incomplete shells react with others in a way that allows it to complete the outer shell. Atoms react to give up, receive, or share electrons to produce a completed outer shell.",
"Atoms with a complete outer shell do not react with other atoms. ",
"See diagrams at:\n ",
"http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%20101%20lectures/chemistry/chemistr.htm"
] |
[
"Atoms love to have completed electron shells. The inert gases? The outer electron shell is complete, so they are almost totally unreactive. They are at peace. ",
"In the periodic table, sodium is one further along than neon, an inert gas. Therefore, it has one lonely electron in the next shell, and it's very reactive. ",
"Chlorine has one less electron than argon, so its outer shell is one short. It is also very reactive. ",
"When they combine into the NaCl structure, the extra electron of the sodium effectively fills the remaining slot in the outer shell of the chlorine atom, and the result is very stable. "
] |
[
"A lot of chemistry and physical properties come from the way electrons are arranged in molecules. Electrons can be shared or exchanged to form bonds, electron clouds may be denser around different parts of the molecule, they could be moving between states of high or low energy. When a reaction happens, the configuration of these electrons changes, resulting in new chemical and physical properties for the resulting compound. "
] |
[
"Orientation in space?"
] |
[
false
] |
Might be a stupid question but planets in space don't neatly align horizontally do they? Are some planets higher or lower then others? Do you go up or down to get to other planets, how does it work?
|
[
"The planets in our solar system are all approximately on the same horizontal plane. The ",
"wikipedia page",
" provides a table of the different orbital angles/inclinations of planets.",
"Other planetary systems are aligned on different planes, there is nothing special about our orbital plane."
] |
[
"What you are asking about is called \"inclination\". Some planets have more inclined orbits than earth and in order to go there you need to perform an inclination change, which in layman's terms might be considered \"going up or down\".",
"http://en.wikipedia.org/wiki/Orbital_inclination_change"
] |
[
"Yes, the planets do not neatly align in space. Here's why:\nConsider the equator of our sun. The plane of this (sun's) equator is called the ecliptic plane. \nNow consider the planetary orbits around the sun. Each planet's orbit can be tilted in any orientation from any point (think of a plate that you're balancing on a fingertip in the middle of the plate -- the plate will \"tilt\"). \nThe earth's orbit is similarly tilted to the sun's equatorial plane. Same thing with all the other planets, though some are more tilted than others. Hence, depending on where the earth is with respect to where the other planets are in their orbits, the planets will appear either \"higher\" or \"lower\" to us as we view them.",
"As for whether to go \"up\" or \"down\" to get to other planets, there is no up or down in space. What you need is to get from the edge of your planet's \"plate\" to the edge of some other planet's plate, both of which may be tilted with respect to one another. Hence, a plane change is required.\nThis \"tilt\" of the place is spoken of as the inclination of a body' orbit."
] |
[
"ALTERNATE REALITY: Could Modern Scientific/Medical Understandings Have Been Discovered In The Past?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I understand, can you suggest a thread under which I may post this?"
] |
[
"r/asksciencediscussion",
" could be a good fit."
] |
[
"Can Brownian motion be considered an application of chaos theory ?"
] |
[
false
] |
Chaos theory applies to systems highly sensitive to initial conditions. In the (highly unlikely) situation where we know everything about every particle (for exemple, in the case of a computer simulation), can Brownian motion, a typical stochastic process, be considered an application of chaos theory ?
|
[
"Semantically no, but practically yes.",
"The distinction between chaotic systems and stochastic systems is that the latter is assumed to depend on variables that cannot in principle be known. Brownian motion is usually considered to be stochastic, and if we know the initial conditions it's probably not proper to call it Brownian motion.",
"Semantics aside, your example of a computer simulation is precisely the ",
"n-body problem",
", and in fact was one of the problems that led to the development of chaos theory. So practically speaking, Brownian motion with known initial states is chaotic."
] |
[
"I don't see how it would be very useful to think of Brownian motion in that way. At the fundamental level, Brownian motion is an example or 'application' of the ",
"Fluctuation-Dissipation Theorem",
". Its only necessary to have a system with many degrees of freedom in thermal equilibrium, and most often restricted to systems with linear response. In contrast, Chaos is something observed in systems with inherently non-linear interactions, such as non-linear force coupling or large amplitudes, with typically just a few degrees of freedom, and there are no restrictions on thermal equilibrium. There may be other theories that describe the Brownian motion of non-linear systems, and those theories may have connections to Chaos, but its not necessary to invoke those complications to understand ordinary Brownian motion."
] |
[
"Really clear and concise answer ! Thank you very much !"
] |
[
"Some questions about airloy aerogel, a strong ultralight nanoporous material with remarkable insulating properties."
] |
[
false
] |
How much heat can it withstand? Could you build pottery kilns out of it? Is it toxic? Does it decay or fall apart over time? It seems to me that this is a wonder-material. Why is it not manufactured on a mass scale for common use (in house insulation, in ovens and other appliances and machines, in battery casings, etc)? Is the cost of manufacture especially prohibitive? Is it simply not as useful as I imagine it is?
|
[
"How much heat can it withstand? Could you build pottery kilns out of it?",
"less than bulk silica, the high surface area makes it start to soften and deform relatively easy. You could use it as insulation but it would not be a good first wall material as it would melt and deform.",
"Is it toxic? ",
"No it is usually just pure silica, there is silica in food products.",
"Does it decay or fall apart over time?",
"Yes it can absorb water and degrade over time, it is also physically weak.",
"It is very expensive to produce on the industrial scale, requiring supercritical solvent extraction to form the aerogel structure. Spun fiberglass on the other hand is cheap to produce in enormous quantities. It is very useful but only in specialized applications where the performance outweighs the cost. ",
"http://www.cabot-corp.com/Aerogel/Apparel"
] |
[
"Primarily silica based gels as those are the most common.",
"Any material with that high of a surface area will be pretty unstable at high temperature. Fine grained structured have an extra inherent energy because of their small size, high surface areas and highly defective structures. This energy reduces temperatures when things start moving around upon heating."
] |
[
"Aerogels are pretty expensive to manufacture, so that limits them to applications where the thermal performance justifies the cost. If you go to the website mentioned in the YouTube comment, they sell a 50x75x7mm slice of this stuff for $90. That's about 1,000,000 times as expensive as styrofoam."
] |
[
"If Earth was a perfect sphere, how deep would the water be?"
] |
[
false
] |
I'm asking because theoretically a perfect sphere would mean Earths water would be spread evenly everywhere. I guess I'm also curious about how much water is on Earth? Is there a guess as to how much water is held in the atmosphere and on the polar caps?
|
[
"Wolfram|Alpha",
" gives the volume of water as 1.386x10",
" km",
" . I'm working on an integral using the ",
"radius",
" of the earth (given by Google) now to solve the depth, but I feel like I won't have enough time.",
"Here are my results: I didn't need the integral except to think about it, but the depth would be 2.71 km for a sphere. Equation ",
"here",
" giving the radius of the water to be 6380.81km, ",
" greater than the radius of 6378.1 km "
] |
[
"For such small depths compared to the size of the Earth you'll only need the surface area of the Earth and the total volume of water for a very good estimate. Indeed, my calculations agree with yours (given that the estimate from WolframAlpha is right)."
] |
[
"Regarding amounts ",
"here are the numbers",
"... almost all is in the oceans (97.5%), very little in the atmosphere (0.001%). The ",
"water on land is mainly in the ice caps of Antarctica and Greenland, the rest in the ground",
"."
] |
[
"Would replacing a transmission with an electric generator, and placing electric motors at each wheel be more efficient than current vehicles?"
] |
[
false
] | null |
[
"But without needing a variable about of torque you can use a turbine engine that is upto 60% efficient",
"so it's actually 0.6*.8 *.885 = 0.4248",
"and 0.4248 is more then .34",
"This is the main advantage of why serial hybrids are so promising. "
] |
[
"Efficiency of Internal combustion engine 37%(1)\nEfficiency of Vehicle Mounted Electric Generator 80%(2)\nEfficeincy of electric motor 88.5 (3) (I chose the 20-49 HP motor as you would have one on each wheel giving you upto 196HP for your car).",
".37 *.8 *.88.5 = 0.262.",
"37% down to 26% is approximately a third of your output lost due to transformations so you would have to be losing about a third of your energy in the transmission to make it worth while.",
"Drivetrain losses are only about 5%-6% (4)",
"Edit as promised:",
"So whole system comparisons:",
"Gas engine and traditional drivetrain: .37 * .94 = 34.78% efficient",
"Gas Engine + electric transformative: .37 *.8 *.885 = 26.2% efficient ",
"Or Ignoring the gas engine efficiency:",
"Drivetrain losses at 6% (4) you get 94% left over.",
"Trans-formative efficiency 0.8*0.885 = you get 70.1% left over.",
"So I say no, not worth it.",
"(1) ",
"http://en.wikipedia.org/wiki/Internal_combustion_engine#Energy_efficiency",
"(2) ",
"http://en.wikipedia.org/wiki/Electric_generator#Vehicle-mounted_generators",
"(3) ",
"http://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html",
"(4) ",
"http://www.fueleconomy.gov/feg/atv.shtml"
] |
[
"A car converts chemical potential energy of the fuel directly into rotational motion of the wheels. A gas/electric generator converts chemical potential into rotational motion, into electricity, and then you would convert this electricity back to rotational energy in the wheels. I don't know how exactly how efficient you could make each of these processes, but it is very likely that you can't make 3 conversion steps more efficient than 1."
] |
[
"Any mycologists here? What is growing on my lawn?"
] |
[
false
] |
While mowing the lawn this morning, I noticed what I thought were multiple presents from a neighbor's sick dog. However, when I picked up the substance with a plastic bag, it disintegrated into a fine dark powder. Since I probably inhaled some of it, I thought I'd take it to my pathology lab and see if I could figure out what it is. (It's just a wet mount without stains. Best I can do with the equipment I have.) I live in the desert southwest, by the way, so is a concern. A Google search for what these fungi look like in nature was not fruitful, but the size of these elements isn't too dissimilar from the spherules and endospores that I see in coccidioidomycosis in the lungs.
|
[
"That looks like ",
"Fuligo septica",
", AKA the dog vomit slime mold. That's it's real common name, which probably doesn't surprise you much. :D"
] |
[
"I would recommend cross posting this to ",
"r/mycology",
" as well, they have a fairly active community. "
] |
[
"Thanks for the heads up. I should have figured there would be an ",
"/r/mycology",
". :)"
] |
[
"Are blood bags usually sealed (in a vacuum)?"
] |
[
false
] |
I didn't know exactly where to post this, but I was calculating the pressure of blood coming from a blood bag for a physics problem and was curious to know if blood is normally stored in a vacuum (so no additional pressure from air). EDIT: Just to be clear, I don't mean a perfect vacuum of course, just enough that the increase in pressure is negligible.
|
[
"Being sealed and being in a vacuum have nothing to do with each other. A pure vacuum is an area in space with no matter. For practical applications, it's an area with almost no matter, meaning it has extremely low pressure. Blood in a sealed bag has a pressure, and that pressure is a sum of atmospheric pressure and pressure from any blood on top of the spot being observed.",
"But yes, it is sealed in a bag that is impermeable to air. Just because it's impermeable to air doesn't mean that air pressure doesn't act on it. That pressure is just ignored in most simple physics problems because it is accounted for on both sides of a pressure or mass balance equation."
] |
[
"If you did put blood in a vacuum, it would boil (cold boiling) and loose water rapidly. Probably killing the blood cells from the ice forming from heat loss."
] |
[
"I suppose they are not in fact vacuum sealed as you readily need to insert vacuum tubes into the bags to draw out the blood for use. If there was already and existing vacuum in the bags the blood would not be pulled out through the tubes. However, it is important that the inside of the bags remain closed systems. That meaning that they cannot be affected by contaminatnts from outside the bag, but they can however be affected by heat from outside the system.\nSource: CandMed, and here is one manufacturers list of features for their bloodbag: ",
"http://www.macopharma.com/category/transfusion/blood-collection/blood-bags-and-accessories/"
] |
[
"If you boil down peroxide enough will you eventually get pure H2O2?"
] |
[
false
] |
If no, then why not?
|
[
"The decomposition of hydrogen peroxide is accelerated by heat. There are no conditions where its decomposition ",
" thermodynamically favourable."
] |
[
"You may have a hard time getting hydrogen peroxide to persist long through boiling, but it can be concentrated through other means.",
"It's an incredibly dangerous material to attempt to concentrate though, it is highly reactive and will give off explosive and corrosive vapors.",
"Many peroxides are exceedingly dangerous at high concentrations, they're very strong oxidizers and are often explosive."
] |
[
"Just in case you are considering trying to make or acquire high purity hydrogen peroxide, you should know that in high concentrations it can be extremely dangerous. Among other things it is a poison, will bleach skin, and if improperly handled or disposed of can easily mix with things that will form an explosive mixture."
] |
[
"On USGS DYFI maps, how plausible is it that people are feeling M4.3 earthquakes almost a thousand miles away?"
] |
[
false
] |
Often times I’ll be looking at an earthquake report and reading the Did You Feel It responses. For the , some people report feeling it in Santa Rosa, or even in Salt Lake City, which are all 400-600* miles away. Is this plausible scientifically?
|
[
"Relatively unlikely given the details, though we'll return to this below. Given that it's a public system, it's expected there will be both intentional and unintentional misreported data to the Did You Feel It (DYFI) system. In response, the USGS does a variety of filtering to try to remove outlier reports for downstream usage of the DYFI data (e.g., ",
"Wald et al., 2011",
", ",
"Quitoriano & Wald, 2020",
"). Anecdotally, I've seen a fair number of earthquake geologists and seismologists discuss the \"internet\" or \"social media effect\", i.e. someone sees that there's been an earthquake somewhere distant on twitter/facebook and then recalls a weird noise in their house at the same time and so they report it as being felt, even though this is likely not related to the earthquake if they are really far away and the magnitude is low. Outliers aside, the data from DYFI reports is surprisingly good, typically showing pretty good reproducibility, i.e., reports of shaking intensity from the same are are similar (e.g., ",
"Worden et al., 2012",
") and it compares quite well with instrumentally recorded estimates of the shaking intensity (e.g., ",
"Atkinson & Wald, 2007",
", ",
"White et al., 2018",
").",
"Now, the obvious caveat to the original statement about the likelihood that some of those distant felt reports are real, is that there are a variety of details that dictate how far away a given earthquake will be felt. Some of the primary details are (1) magnitude of the event, because the total energy released will provide some bounds on the intensity of shaking, (2) depth of the event, because the shaking intensity drops with distance from the source, so shallow events will be generally be felt further away at the surface, and (3) the nature of the rocks through which the earthquake waves are passing, because generally more fractured rocks and loose sediments will attenuate seismic waves quicker than intact rocks. This last one can lead to pretty major differences in distances over which an earthquake is felt. The classic example is the disparity the size of the area that experienced shaking from the ",
"M5.8 Mineral, Virginia earthquake compared to a comparable event on the west coast",
". This is largely because the west coast has more fractured rocks and more loose sediments compared to the east coast. For the event you're asking about, given that it's on the west coast, people feeling this relatively small earthquake all the way in Salt Lake is very unlikely. If this same event had happened on the east coast of the US though, feeling shaking at larger distances may not be as unlikely (depending on some of the other details as well)."
] |
[
"This is the kind of detail that will lead to some of the variance they observe in a given location, but the fundamental idea is that things like the DYFI maps are spatially aggregating responses so if the response rate is high enough, details like that will tend to average out. The questionnaire does ask whether you were in a building or another location, but does not ask specifically what floor your on (and how this would influence the felt effects would depend a lot on the engineering details of the building). While being in a tall building vs ground level will influence the estimated intensity, it's not going to change the intensity estimate that dramatically."
] |
[
"What about being on the ground floor vs the top of a high rise?"
] |
[
"If water must be boiled to be sterilized, why do I only have to heat my chicken to 165 degrees F?"
] |
[
false
] | null |
[
"Boiling doesn't completely sterilize water. It is however convenient and easy to do, and drastically reduces the numbers of pathogens in contaminated water.",
"Likewise, you don't ever completely sterilize food by heating, you do however reduce bacterial numbers to an acceptable number. The reason that you cannot take a rancid piece of meat and simply cook it to \"kill\" the bacteria, is that removing the bacteria does not remove the toxins they have already produced."
] |
[
"Yeah, dealing with bacteria is a numbers game, you rarely ever kill all of the bacteria. You only have to heat chicken to 165F if you just got it from the store, and it doesn't have a funny smell. Then 165F is enough to kill most of the bacteria one expects to find in fresh chicken. If it's rancid, there could be still enough bacteria in it to make you sick if you cooked it past 212F. No matter what you do, there are still going to be some bacteria, but your body is equipped to easily handle small invasions.",
"With water you're also looking at parasites, from protozoans to worms, which oftentimes cause more problems than bacteria.",
"edit: Actually, there are ",
"some bacteria which require heating to 250F",
"."
] |
[
"I'm taking a foods 101 class in high school, and the answer I got was vague; The bacteria and pathogens normally found in chicken are different than the ones in water, so they require a higher temp to be killed. I believe it is the same for all types of meat meaning that they all have to be cooked at certain temps for the pathogens usually found on the corresponding meats."
] |
[
"Does Guaifenesin affect all mucous secretion?"
] |
[
false
] |
Including secretions in the digestive tract?
|
[
"This is weird, because it runs completely counter to my own experience. I had asthma and quite a few bouts of bronchitis as a kid, and now whenever I get a cold I will get a cough that descends into my chest and requires me to cough very hard, very often, to keep my airways from building up firm mucus. Taking guaifenesin will, within half an hour, result in a cough that produces ",
" more, and more easily, than anything else I've ever done."
] |
[
"Fun little tid bit is that guaifenesin really isn't that great for thinning airway mucous. There is a 2004 article in American Family Physician that said that the only difference was a reduction in coughing.",
"Truthfully the whole glass of water you're recommended to take with the drug works just as well if not better at thinning secretions, including those in the GI.",
"So the answer is no."
] |
[
"If you want cough suppressant, dextromethorphan is the only way to go. If you want to thin secretions, pseudoephedrine works for most people but you'll have to ask the pharmacy counter for it because you can only get a limited supply each month due to one of its ingredients being used to make meth."
] |
[
"What molecular signal initiates the physiological process of muscular hypertrophy?"
] |
[
false
] |
[deleted]
|
[
"Exercise induces",
" ",
"growth hormone",
" expression. Growth hormone ",
"acts in the liver to stimulate IGF-1 release",
". ",
"IGF-1 acts in the muscles",
" to stimulate ",
"calcineurin",
" and the ",
"AKT-mTOR pathway",
". Calcineurin stimulates the transcriptional (RNA) program to repair the damaged muscle through ",
"NFATc1",
". mTOR directly increases protein synthesis and causes hypertrophy. ",
"Various cytokines",
" produced by immune cells invading the torn sites are also active in inducing repair pathways, turning over proteins, and producing hypertrophy through inflammation."
] |
[
"No its pretty different. Smooth muscle cells are in the intestine, vasculature, and bronchioles. Smooth muscle is very different from skeletal muscle (though clearly they are both still muscle). ",
"A quick glance suggests a lot of different factors can cause smooth muscle hyperplasia but EGF and serotonin seem to stand out. The mTOR pathway is really more of a protein synthesis pathway, though there is lots of cross talk in the pathways so it induces proliferation too."
] |
[
"No its pretty different. Smooth muscle cells are in the intestine, vasculature, and bronchioles. Smooth muscle is very different from skeletal muscle (though clearly they are both still muscle). ",
"A quick glance suggests a lot of different factors can cause smooth muscle hyperplasia but EGF and serotonin seem to stand out. The mTOR pathway is really more of a protein synthesis pathway, though there is lots of cross talk in the pathways so it induces proliferation too."
] |
[
"What are the raw ingredients of birth control pills?"
] |
[
false
] | null |
[
"Birth control pills are made with synthetic hormones, usually estrogen and progestin. ",
"The ",
"wikipedia article on Progestin",
" has a brief description of the synthesis.",
"For a much more detailed story, check out this article:",
"http://www.med.nyu.edu/content?ChunkIID=21816",
"Yams and soybeans provide some raw materials that are then synthesized into the hormones used in the pill."
] |
[
"The Active Pharmaceutical Ingridient in birth control pills is progesterone-like hormone. It can be synthesised from saponins from wild yam plants. Saponins contain the steroid structure which is needed for the synthesis of steroidal hormones. You can compare theese to molecular structures and see the similarities ",
"http://en.wikipedia.org/wiki/Progesterone",
" ",
"http://en.wikipedia.org/wiki/Diosgenin",
". "
] |
[
"I couldn't find anywhere the actual precursors they still use, but I suspect it's still very similar to in the 50s. Yams are a very economical precursor source for progesterone synthesis. You can make pounds of progesterone for a few dollars, which would be enough to dose thousands of patients."
] |
[
"Can a photon at λ=0 exist, despite the infinite energy required by E=hc/λ?"
] |
[
false
] | null |
[
"No. You can't have a wavelength of zero. If there's zero distance from one peak to the next, and half that distance from peak to valley, then the peak and valley are going to have to be in the same place, so it has to have both the maximum and minimum electromagnetic field. That makes no sense."
] |
[
"Hey, this is a great answer. I do, however, wonder still about this, leading from your answer. What does this mean for a photon in superposition?"
] |
[
"Superposition just means adding them together. If you superimpose a photon with a peak at one point with one with a valley at that point, you'll get a photon with a node at that point.",
"If you have a photon entangled with another particle you can have the photon be at a peak with the particle at one place and a valley with the particle at another, but you're really dealing with the configuration space. You have a peak where the photon is at one place and the particle is at another, and a valley where the photon is in the same place and the particle is in a third place."
] |
[
"Is the earth's atmosphere perfectly spherical?"
] |
[
false
] |
I know that it gradually fades away, but is it more dense/bumps over land and sort of drops over water?
|
[
"I'm going to go through with you on this in order of most significant to least significant",
"Firstly it's more or less oblong and is thicker at the equator due to earths rotation.",
"Secondly, the moon pulls on the atmosphere similar to ocean tides",
"Thirdly, convection would cause the atmosphere to be shallower on ocean, but this is hardly noticeable because of how we define what is atmosphere and what isn't."
] |
[
"The atmosphere also fluxes with temperature. There was even an idea to use the HAARP antenna in Alaska to heat and swell the ionosphere. This would increase the atmospheric drag on low-orbit space debris and help them re-enter sooner. "
] |
[
"Gravity isn't uniform over the Earth's surface and I assume it affects atmospheric 'level' in a manner similar to how it affects sea level. If you haven't seen it, here's a great Minute Physics video that explains how the difference in gravity can cause changes in sea level of +/-70 meters:",
"https://www.youtube.com/watch?v=q65O3qA0-n4",
"/u/Idtotallytapthat",
" mentions a bunch of other factors that affect atmospheric density/thickness."
] |
[
"What, if any, advantages do beech and oak trees gain by holding on to their dead leaves months longer than other deciduous species?"
] |
[
false
] |
[deleted]
|
[
"My thought is that it relates to the location of the root system and the cost-benefit between hydration and damage. Most trees concentrate their roots around the ",
"drip line",
". \"A tree’s dripline is a ring around the tree canopy on the ground level that receives most of the\nrainwater shed from the tree canopy.\""
] |
[
"I was taught that the leaves remain in place to protect to buds that haven't developed yet"
] |
[
"The retention of dead leaves that are normally dropped is called ",
"marcescence",
". That wiki link connects to some papers describing the potential benefits."
] |
[
"How do scientists capture the movement of subatomic particles as an image?"
] |
[
false
] |
When ever i see an article about neutrinos, quarks, or atomic physics in general i tend to see accompanying images of What's going on here?
|
[
"There are many different types of particle detectors, they can be split in to two generic types, tracking detectors and calorimeters.\nType 1) Tracking detectors:\nThese can only detect charged particles, as they traverse the detector.\nExamples of these are bubble chambers [1], cloud chambers [2] and more recently silicon detectors [3].\nThe basic premise of a cloud chamber is: take some substance, for example pure alcohol and vaporize, then cool it in a clean, non dusty environment. \nThe alcohol doesn't have anything to condense around, so can not transform back into a liquid, so when a charged particle travels though the vapor\nit ionizes the particles of the vapor that it interacts with causing a trail of condensation to form, this is what we observe as the particle track.\nThe process is very similar in a bubble chamber.",
"If we want to be able to measure some of the properties of the particle eg mass, velocity, charge, then we apply a magnetic field across the detector, in which the particles trajectory is changed.\nThis gives us the spirals that we observe in the picture from the link you posted.",
"Type 2) Calorimeters.\nThese measure the energy of a particle, they absorb all the energy of the moving particle, and convert it to something we can read out.",
"Most modern particle physics detectors use a combination of tracking detectors and calorimeters. For example here is an event display from the CMS experiment at cern.\nThe coloured blocks show energy deposits in the calorimeter, whilst the yellow lines are the tracks. We have moved away from taking photo's of bubble chambers, which than have to be inspected by 100's of people looking at photographic plates, to reading everything out electronically and putting 100's of PHD students and post docs in front of computers, to do the same job, but on a much larger scale.\n",
"http://cms-tracker.web.cern.ch/cms-tracker/TKpictures/7TeV_event.jpg",
"I hope that was clear enough, it not just ask more questions.",
"[1] ",
"http://en.wikipedia.org/wiki/Bubble_chamber",
"\n[2] ",
"http://en.wikipedia.org/wiki/Cloud_chamber",
"\n[3] ",
"http://en.wikipedia.org/wiki/Compact_Muon_Solenoid#Layer_1_.E2.80.93_The_tracker"
] |
[
"Great explanation! I loved that cms image link."
] |
[
"I chose CMS as its what i work on ;)"
] |
[
"When cycling, how much drag can hair actually cause?"
] |
[
false
] |
I cycle to and from work, in my spare time, etc. I'm curious if there has ever been an in-depth look into how much drag your hair can actually cause. I've got fairly thick hair, I push it to the side and slightly up; the wind catches it. I see that professional cyclists have tight caps they wear. Have there been any controlled experiments on the matter? Does it make a night and day difference? Thanks.
|
[
"Specialized did some tests regarding this earlier this year: \n",
"http://www.stickybottle.com/coaching/are-you-more-aero-and-faster-with-shaved-legs-these-wind-tunnel-results-are-staggering/",
"These were of course wind tunnel tests but quite many seconds over a rather short distance. But for the average commuter it seems hardly worth the effort :)"
] |
[
"Lemond also had aerobars/time-trial bars, which likely made a much larger difference than his helmet."
] |
[
"I don't know how scientific you would consider it, but pro and semi-pro cyclists mostly agree that shaving your legs saves you several seconds over each hour of riding. ",
"Shaving arms and faces has a smaller effect, as the legs move faster with respect to the air (all that forward and backward motion)."
] |
[
"Why do our voices age and how? (Why do old people sound different than say a 40 year old, etc)"
] |
[
false
] | null |
[
"Speech/Lang student here! As you grow from a child to an adult, you vocal folds lengthen and strengthen (hence why your vocal range is larger and deeper than that of a child). But as you grow old, your vocal folds weaken. Vocal folds are like any other muscle in your body, they get stronger until a certain age and then weaken in old age. "
] |
[
"will they start to weaken if you don't use them much?"
] |
[
"To a lesser degree. Your vocal folds will still weaken with just age, but if you learn good vocal fold usage they won't be nearly as damaged / compromised when you're older. No smoking, very little throat clearing, soft onsets of sounds, speaking at a reasonable volume. All of these things not only help vocal health but also prevent vocal nodules. Illness is the biggest reason many older people have compromised voice quality, but when that happens just have a good SLP on call and they should be able to ease the deterioration. "
] |
[
"How effective is washing your fruit and vegetables in removing pesticides?"
] |
[
false
] |
I always rinse fruit and veggies with water before cooking/eating them thinking that it removes most of the pesticides, but my roommate says this is pretty useless in terms of removing pesticides.
|
[
"A three-year study showed that rinsing under tap water significantly reduced residues of nine of the twelve pesticides examined across fourteen commodities. Four fruit and vegetable wash products were found to be no more effective at removing eight of nine pesticide residues from produce than either a 1% solution of dishwashing liquid or rinsing under tap water alone for three commodities studied.. ",
"More info: ",
"http://www.ct.gov/caes/cwp/view.asp?a=2815&q=376676"
] |
[
"It depends.",
"What is the dose? What is the frequency of ingestion? What is the specific pesticide being used? All of these questions will drastically effect the answer. Also, some of our answers are still being researched and formed.",
"It's hard for me to answer because I do not know what are the most popular commercial pesticides, herbicides, fungicides, etc. for the large variety of produce used in the US. That is made even trickier by the fact that some produce comes from outside of the country, where pesticide regulations are potentially different.",
"Glyphosate",
" (Round-Up), as one example, is considered relatively safe in low-dose chronic exposures. However, ",
"there is debate",
" that it may disrupt the endocrine system.",
"Looking at other common pesticides may yield different findings. ",
"Parathion",
", which is an organophosphate insecticide, is currently regulated throughout much of the world because it produces rather severe chronic and acute toxicity. Organophosphates work by irreversibly inactivating the important enzyme acetylcholinesterase. For this reason, some organophosphates had previously been used in war time as nerve gas."
] |
[
"Follow-up question: Is it necessary to wash fruit or veg before cooking? Would the heat and moisture remove the pesticides anyway? "
] |
[
"Are there waves of air on top of our atmosphere like waves of water on the surface of the ocean?"
] |
[
false
] | null |
[
"Well, sort of.",
"There's no real top to our atmosphere the way there is a surface of the ocean - it just sort of gradually thins out.",
"With that said, though, both experience the same kind of ",
"gravity waves",
". Note these are not at all the same as ",
" waves you'd see around a black hole - similar name, very different phenomena. Gravity waves are essentially waves driven by a buoyancy force. In the ocean, you see them manifest as surface waves; in the atmosphere, they can sometimes be seen as undulations in clouds.",
"Gravity waves in the ocean break when they hit the beach. In the atmosphere, they tend to propagate upwards, breaking when the air gets so thin that it can't really carry them any more. There's good evidence to show that quite a few upper atmospheres are warmer than expected due to gravity waves breaking and depositing their energy at those locations."
] |
[
"Kelvin-Helmholtz wave clouds are formed when there are two parallel layers of air that are usually moving at different speeds and in opposite directions. The upper layer of air usually moves faster than the lower layer because there is less friction. In order for us to see this shear layer, there must be enough water vapor in the air for a cloud to form. Even if clouds are not present to reveal the shear layer, pilots need to be aware of invisible atmospheric phenomenon.",
"http://www.siskiyous.edu/shasta/env/clouds/bm1s.jpg"
] |
[
"There is a phenomenon known as stratospheric mountain waves which are loosely akin to this. Extremely powerful updrafts that reach into the stratosphere. Recent projects have sought to build sailplanes that could surf these mountain waves to get instrumentation to those high altitudes. ",
"https://en.wikipedia.org/wiki/Perlan_Project"
] |
[
"Could you actually fall into a black hole ?"
] |
[
false
] |
As I understand it, time goes faster and faster (in your reference frame) as you approach the speed of light (in the black hole's reference frame) when falling into a black hole, until it eventually gets infinitely fast. But thanks to Hawkins radiation black holes have finite lifespans, so woudn't the black hole die before you reach its event horizon ?
|
[
"If you jump into a black hole, you will pass the event horizon and reach the singularity within a finite amount of time. For most stellar sized black holes, this takes a small fraction of a second from your point of view though as you're shredded by tidal forces so you won't be alive for it. For super-massive black holes the time spend inside might be on the order of hours. (Corrected from seconds)",
"You also won't witness the lifespan of the universe or anything on your doomed journey. There will be some final light signal which reaches you before you reach the singularity. In other words if you were watching a distant clock, there would be a final time you would read if tidal forces hadn't yet killed you.",
"Mass loss due to Hawking radiation is an incredibly slow process. And you as an in-falling observer won't notice anything strange falling in, like excessive temperatures. The black hole will only appear \"hot\" if you accelerate away from it, like with a rocket.",
"Now... here's an interesting question, what if you jumped into a tiny black hole who is massively radiating energy? Presumably the singularity might wink-out or vanish before you reach it. I don't quite know the details of this question, but I suspect that infalling observers will always be able to reach the singularity before the black hole vanishes to avoid weird pesky non-physical paradoxes. The radiation pressure would also be significant preventing real matter from entering."
] |
[
"In General Relativity the concept of a gravitational force like F ~ r",
" is done away with all together. You’ll never actually calculate any forces in GR like you would do with classical physics. ",
"This might answer some of your questions "
] |
[
"It appears you have the idea of the singularity and the event horizon slightly muddled. ",
"Time from your reference frame essentially always goes at the same speed. But in order for you to witness the universe ending etc., you would have to reach the singularity.",
"The singularity is far inside the event horizon of course.",
"The event horizon is often mistaken as the point in which gravity over comes light BECAUSE it’s faster/stronger than light. But that isn’t fully accurate. Anything beyond the event horizon still moves at speeds and time explainable by physics but all future points of that things position is not able to travel outside of the event horizon or interact with observers outside the horizon. ",
"E.G. seeing objects requires light to hit the object then bounce back into our eyes. But if that light never makes it back into our eyes then we see nothing. ",
"This is why black holes appear black.",
"Space itself beyond the event horizon would appear to be somewhat normal even as an observer transitions into the event horizon. However the further inside one falls the more light from other angles can travel from a point to the observer. ",
"This happens because gravity bends the light around and back To the observer. This stretches the observers field of view to the point at which the observer will eventually be able to see themselves. Even the back of their own head."
] |
[
"Why is the oxygen to hydrogen mass ratio on the shuttle's external tank 6:1 instead of 8:1?"
] |
[
false
] |
Wouldn't a mass ratio of 8:1 be optimal?
|
[
"An optimal reaction is indeed a 1:8 ratio, but having unburnt hydrogen in the exhaust produces a higher specific impulse.",
"That is to say the fuel is more efficient in producing thrust when in a 1:6 ratio, even though energetically it is more efficient at 1:8."
] |
[
"Very interesting. Can you give us the very simple Newtonian mechanics explanation of why that is the case? Clearly it is due to the lighter hydrogen atoms/molecules. But in an ",
"ion thruster",
", in contrast, they use the heavy Xe atoms."
] |
[
"This is exactly right. A rocket exhaust's efficiency is purely a function of the velocity of the exhaust gas. The Hydrogen will move at a much higher speed per given energy than the water, so it is more efficient.",
"As a side note, this is exactly how you'd create high efficiency propulsion with a thermo electric thruster in space, but it's using the combustion of the exhaust gases for energy production rather than an electric (nuclear or solar) generator.",
": Thanks for the gold!"
] |
[
"Where does the electron get its charge from?"
] |
[
false
] | null |
[
"It is a fundamental property of the electron. It is not believed to result from interactions with other particles the way mass is."
] |
[
"There is no answer beyond the fact that electrons have charge."
] |
[
"No, as they consist of quarks. This is true of the constituent quarks, however."
] |
[
"Can Anti-Matter Elements Exist?"
] |
[
false
] | null |
[
"Yes, and we've created some of them."
] |
[
"Could you list the ones that have been created? I’m interested in this topic. Thank you!"
] |
[
"Here",
" is some info about it, I don't know how up-to-date it is."
] |
[
"Does the tar from smoking really cause lungs to turn black?"
] |
[
false
] |
I have seen the pictures and know conventional wisdom states that the lungs of smokers turn black due to smoke, however I came across which refutes the claim. I know it's from a biased smoker blog, however the cited references seem reasonable. The basic idea is that it's emphysema which causes black lungs and not tar, and while emphysema incidence is higher among smokers that doesn't mean that all smoker's lungs turn black. is what an image search for emphysema turns up. One of the most striking claims I think is that smoker's lungs are routinely used for transplants. Would blackened lungs really be transplanted? About 13 percent of double-lung transplants in the U.S. came from donors with a heavy smoking history, according to Taghavi’s new study, presented Tuesday at the annual meeting of the Society of Thoracic Surgeons In the end, after all other variables were accounted for, people who got lungs from heavy smokers lived as long and as well as those who got lungs from the tobacco-free, Taghavi found. There was no significant difference in cancers, though the study didn’t specifically look at lung cancer.
|
[
"Emphysema is a disease that causes damage to the lung tissue so that the tiny air spaces grow into relatively huge air spaces. You need a high surface area to transfer oxygen from the air into the blood, so when the tissue separating the tiny air spaces is destroyed to make bigger ones, you lose surface area and can't take in oxygen as efficiently. You also lose a lot of the 'support' tissue which holds the airways open, so people with emphysema can't exhale fully and get the old, stale air out of their lungs. ",
"As far as I'm aware, the disease process of emphysema wouldn't turn the lungs black (I've never seen that, or heard that claim before now), but the larger spaces may make the tissue seem darker, as it's got bigger holes - much like a new bathroom sponge with tiny holes looks lighter than an older bathroom sponge with big gaping holes.",
"Emphysema happens because the body's own immune systems and cell regulation systems goes wrong and lung tissue is broken down but not replaced. Generally, this is an inflammatory reaction to an irritant. Say you breathed in a really fine dust, the dust would settle in your lungs and irritate the tissue. So your body send immune cells to eat up the particles. Unfortunately, these immune cells can't break down non-biological particles, so they can't remove the source of the problem so they tend to keep on sending signals for more immune cells to come and help them. ",
"All these immune cells (which are designed to break down proteins from pathogens like bacteria) are recruited to the area and they start to break down the proteins around them - even though these are healthy lung proteins! Now the lung becomes damaged, so the body calls in more immune cells to try to get rid of what's causing the damage, and you end up with a cycle of damage that just gets progressively worse. ",
"Emphysema can be cause by a genetic problem (alpha1 antitrypsin deficiency), but this is rare. In the vast majority of cases (a ballpark figure is 80-90%) there is some degree of prolonged smoking history or very fine particulate exposure ",
". As most dusts will make you cough or feel unpleasant, there aren't many situations where you purposefully draw particles into your lungs - apart from smoking. ",
"I want to emphasise that",
" or any lung damage. And not all people with emphysema are or were smokers. HOWEVER, the link is very very clear. Drawing particles into your lungs over and over again several times a day for years or decades will provide the irritant trigger for pre-disposed people to develop the inflammatory response that leads to emphysema. ",
"The other side of the smoking coin is chronic bronchitis. This is when the airways themselves become inflamed (due to being irritated by particles) and swell a bit, narrowing the airways and making it harder to breathe. To protect themselves, the lungs secrete lots of sticky mucus to trap the particles; the idea being that you can cough up the mucus and get rid of the particles. Unfortunately, the prolonged 'attack' of smoking every day means that you can never clear the particles, no matter how much mucus your lungs make and you're left with a hacking cough and shortness of breath. Worse, this mucus is perfect for bacteria to grow in, so you may suffer frequent chest infections. ",
"Like I said, the mucus traps particles, including smoke and tar, so the airways can often seem darkened and sticky because of all the smoke stuck in the mucus. If you have emphysema as well as chronic bronchitis, the large air spaces can fill up with blackened mucus which can give you that horrifying scary picture so often used to frighten people who smoke. ",
", most transplanted organs are from relatively young/healthy people. You wouldn't give a diseased liver to someone who needs a liver due to having a diseased liver! As said above, not all smokers develop lung disease. Lung disease also tends to develop very very slowly, it can take 50 years of smoking 20 a day before any impairment is noticed. If you HAVE smoked, but you quit, then your lungs may still be relatively healthy. ",
"Finally, if someone is about to die in the next 6 months from lung disease, and you offer them the choice of waiting for an unknown length of time (probably years) for a non-smoking, matching donor, or having a transplant done NOW from someone who smoked for 20 years, they'd probably go for the smokers lungs now. I mean, if they were healthy enough to be up for donation, you'd probably get several years of use out of them, and that's way better than dying in 6 months, right?"
] |
[
"The problem is that it's virtually impossible to know if you're susceptible to lung disease from smoking unless - yanno - you smoke for 50 years. The damage builds up so slowly. ",
"I've had patients come in and say they've smoked 60 a day for 60 years, and their lung function is perfectly normal. I've had patients come in and say they've never smoked, but they lived with a smoking partner for 5 years, 20 years ago, and they've got classic 'smoking' patterns in their lung tests. ",
"You can be absolutely healthy as a smoker in your 20s, quit in your 30s, but it might not be til your 60s that the damage is revealed - by which time it's FAR too late to do anything about it. Smoking one at a party when you're 32 may cause that one additional mutation that will eventually lead to your cancer at 55. Or it may not. You just don't know. ",
"My point is that yeah, there are a hell of a lot of really outrageous scare tactics out there, and a lot of it goes to an extreme which can be a bit ethically dubious; but I think the 'anti-smoking lobby' is trying to get people to realise that they're gambling today against tomorrow's health. It's all fine for you now, but will you regret it when you're unable to even stand up out of a chair without having a rest and some oxygen to recover?",
"Also, like I mentioned above, smokers don't just put their own health in danger. Sure, risk yourself, I really don't care. But smoking around your kids, your colleagues, your neighbours? Perhaps someday a kid will sue their parents for the lung disease that took root in their childhood - when they had no choice and couldn't escape it. YOU might not be susceptible to lung disease, but are you gonna gamble with your kids' health too?"
] |
[
"For the kids and partners of smokers, the effects can be similar to if they'd smoked themselves. Again, returning to \"in genetically predisposed people\", so it'll vary VASTLY from person to person. ",
"But like I said: they won't know if being around smoke is gonna make them sick until YEARS after they were around the smoke that made them sick.",
"You're absolutely right about vehicle emissions, but just because something else is bad - or worse - doesn't make this thing good or irrelevant. "
] |
[
"Why is it that strong negative emotion can give someone a sick feeling in their gut?"
] |
[
false
] |
It's a weird sensation, just wondering why it happens and how it works...
|
[
"In fact, about 95% of the body's serotonin is found in the gut, not in the brain! ",
"http://www.scientificamerican.com/article.cfm?id=gut-second-brain"
] |
[
"I have generalized anxiety disorder so I know this feeling well. I have read before that it's due to serotonin receptors in your stomach, and also that it's due to the release of epinephrine, as your body is priming it's fight-or-flight reaction."
] |
[
"That's crazy when you think about people trusting their gut, or 'gut feeling'... go figure, maybe it's not such a bad idea sometimes"
] |
[
"Biology question: Will 192 degree water kill bacteria in one cup coffee maker?"
] |
[
false
] |
[deleted]
|
[
"Your temperature is fine, but you seem to have seven times as much DNA as a normal person."
] |
[
"Laboratory-grade sterilization requires 15 minutes at 121 degrees celsius, however for your purposes you should be fine. I know from experience that at 95 C that 5 minutes is enough to reduce bacteria to less than 1 part in 10",
" and your machine is at 88 C, so you will probably kill most bacteria."
] |
[
"This comment was hilarious."
] |
[
"Does our brain process the image our eyes see all at once, or does it start at one point and move from there (like starting in the centre and moving outwards, or from one side to the other)?"
] |
[
false
] |
Idk if this is something that we have the technology to test, but I just wonder if this is a known thing or are there some working theories or something? Also, knowing this could be used for things like marketing and creating illusions, right?
|
[
"Primary processing of different areas of a visual field will happen simultaneously, as the cells doing the processing are actually topographically organized. However, because there is greater detail in the fovea (dead center) of your visual field, there's simply going to be more raw information to speed up downstream feature extraction. This is pretty intuitive, as if we see a big brown fuzzy object somewhere in our visual field, we will recognize we are looking at a bear much quicker if we are staring at it than we would if it were on the periphery of our vision."
] |
[
"Depends on what you mean by “process”. All the light from a scene in our field of view hits our retinas near-simultaneously, and so we form a visual representation of it all at once. After that, certain things are attached saliency by the associated brain networks, but it’s not always location dependent."
] |
[
"However, because there is greater detail in the fovea (dead center) of your visual field,",
"And to be clear, it is ",
" greater detail. The fovea is essentially the only place we have clear vision. We don't notice this because we can move our eyes very quickly to focus on different areas, and our brains are very good at filling in the missing details everywhere else."
] |
[
"Is it true that 40% of all domestic violence victims are men?"
] |
[
false
] |
Is it true that an astounding 40% of domestic violence is against men? I knew that domestic violence VS men was under reported, but this seems unreal.
|
[
"Counting victims who have experienced domestic violence at least once in the previous year, that is correct (recent British Crime Survey result). Counting incidents, 90% are committed against women.",
"Data on perpetrators are not routinely collected. DV is defined as violence against any family member over the age of 16, so we don't know how many perpetrators are fathers, brothers or sons (or mothers, sisters or daughters) rather than lovers. We do know that gay men experience violence from their partners more often than lesbians.",
"This is a study on perpetrators, IIRC the only one a recent UK government report on DV could cite: ",
"www.nr-foundation.org.uk/downloads/Who-Does-What-to-Whom.pdf"
] |
[
"That is either journalistic rephrasing, or the study failed to describe the data accurately. The definition of domestic violence, as used by the BCS, is given on page 4 here: ",
"http://collection.europarchive.org/tna/20090120202659/homeoffice.gov.uk/rds/pdfs04/rdsolr1804.pdf"
] |
[
"I'm confused, how can 40% of the victims be men if 90% of incidents are committed against women?"
] |
[
"Is the periodic table of elements valid in everywhere in this universe?"
] |
[
false
] | null |
[
"Yes, as the laws of physics are the same everywhere - at least within the (very small) current measurement uncertainties and within the observable universe."
] |
[
"Yes*, the periodic table is valid everywhere.",
"*The atomic weights listed on the table are not. The atomic weights are an average of all the different isotopes that are commonly found on Earth. How much of each isotope there is depends very much on where you are in the universe. The relative abundance of different isotopes is very important for nucleosynthesis, which is an important part of astronomy, and nuclear technology."
] |
[
"It's a natural assumption that the laws with its constants are the same everywhere but we check, of course. If the fine-structure constant would be significantly different elsewhere then many heavier elements would behave differently. People checked: It is not. Similarly, a different proton to electron ratio would influence chemical properties, but the ratio is the same everywhere we checked - again within measurement uncertainties, as measurements never produce an exact value."
] |
[
"How is Zero Gravity simulated?"
] |
[
false
] |
I'm trying to figure out how the "Vomit Comets" produce microgravity/zero gravity as well as a . I "Vomit Comets" produce microgravity as a result of angling the plane downwards to minimize drag as they free fall? Would you experience microgravity in a plane if you simply stalled it and fell tail first or belly first rather than nose down? I know that NASA utilizes "drop tubes" where they surround a payload with a drag shield, in a Vomit Comet, is the plane acting as the drag shield for the "human payload"? And can anyone explain how the rollercoaster produces zero go effects? There is no drag shield, so riders are experience friction with the air and they experience zero g while going UP as well as down? Thanks in advance, I'm quite tired so these questions are likely a large mess of words, my apologies.
|
[
"It has little to do with drag or other aerodynamic factors. ",
"Imagine throwing a ball into the air. It will travel in a parabolic arc.",
"Now imagine that ball is surrounded by an airplane, travelling in the same path, at the same velocity. To those in the airplane, the ball will appear float in the air for several seconds of microgravity, even though it is falling normally.",
"That is what a zero g dive does...throws people into the air, then follows the exact path they would if they were falling freely. The trick is not only to match their path, but also their velocity, accelerating downwards at 9.8 m/s",
" .",
"A roller coaster works the same way, although less precisely. If the roller coaster travels in the same direction, at the same velocity you would if you would be if you were falling, you get the sensation of microgravity. ",
"Note you can experience microgravity, even when travelling upwards, so long as the vehicle is travelling in the correct parabolic arc, and is accelerating downwards at 9.8 m/s",
" ."
] |
[
"If you have no net force exerted on you, other than gravity, you experience \"zero gravity\"."
] |
[
"The parabolic flights are necessary because they track the path that an object in a vacuum would fall.",
"When people talk about experiencing weightlessness on a roller coaster they are only talking about the main downhill drop segment. And I don't think anyone is claiming that it's true zero-G, just a similar sensation."
] |
[
"If we covered half the sun in a reflective mirror, how much thrust would all the reflected light and heat create?"
] |
[
false
] |
If a solar sail generates thrust, how much thrust would our sun make if we covered one hemisphere in a reflective mirror to direct everything backwards?
|
[
"So, given the mass of the sun is about 2 * 10",
" kg, that would mean you get about 3 * 10",
" m/s",
" acceleration. After about a million years the sun would get up to a velocity of 10 meters per second."
] |
[
"You have that the momentum associated with light is the energy over c. Therefore the force on a mirror is:",
"F = 2 L / c",
"where L is the power and the 2 is because the photon bounces.",
"The total power emitted by the sun is the solar luminosity L = 3.846×10",
" W.",
"Now, if we take the power emitted in one emisphere and divide by c we get:",
"2 * (L/(2c)) = L / c",
"but this is incorrect. Force is a vector quantity and all the forces acting on the little elements of mirror have different directions. A large part of them cancels (all the components orthogonal to the axis of the hemisphere). We need to correct for this by performing an integral; the relevant integral is",
"integral of sin(x) cos(x) dx from 0 to pi/2 = 1/2",
"and the final answer is ",
"L/(2c)",
"that's around 6.28 * 10",
" N."
] |
[
"What if we included the solar wind in this calculation? If we're somehow building megastructures with the intent of moving the sun, it seems we need to account for everything the sun puts out. ",
"Of course, this raises the question of why someone would want to move a star. If you have the magical-level of technology needed to create such structures, it would be easier to simply travel to another star that already exists near to wherever you're hoping to move the sun. "
] |
[
"Why does it seem that there’s more and more people allergic to more things?"
] |
[
false
] |
[deleted]
|
[
"Just to expand on this a bit more, most human parasites are known to produce molecules that inhibit our immune system. Many of them specifically inhibit our ability to mount allergy/anti-parasite responses. One theory then is that our immune system has evolved to react too strongly to parasites so as to overcome the effect of their immunomodulatory compounds. In the absence of these compounds, we may be more likely to develop allergies.",
"Recent studies have been looking at the use of parasitic worms to treat allergies. Overall it’s been pretty successful. When people with allergies or asthma are infected with hookworms, they exhibit reduced symptoms. So now they’re trying to isolate the compounds secreted by these parasites to be used as an allergy medication.",
"Some sources:",
"https://onlinelibrary.wiley.com/doi/full/10.1111/all.13944",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5682104/",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2814083/"
] |
[
"Just to expand on this a bit more, most human parasites are known to produce molecules that inhibit our immune system. Many of them specifically inhibit our ability to mount allergy/anti-parasite responses. One theory then is that our immune system has evolved to react too strongly to parasites so as to overcome the effect of their immunomodulatory compounds. In the absence of these compounds, we may be more likely to develop allergies.",
"Recent studies have been looking at the use of parasitic worms to treat allergies. Overall it’s been pretty successful. When people with allergies or asthma are infected with hookworms, they exhibit reduced symptoms. So now they’re trying to isolate the compounds secreted by these parasites to be used as an allergy medication.",
"Some sources:",
"https://onlinelibrary.wiley.com/doi/full/10.1111/all.13944",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5682104/",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2814083/"
] |
[
"Having difficulty agreeing with your argument. There seems to be more support for the hygiene hypothesis in the scientific community to explain the rise of allergies in developed countries, rather than them being undiagnosed.",
"An allergy and an intolerance are not the same. An allergy is driven by an immune response. An intolerance is not immunological driven, at least not in general.",
"In terms of likelihood, it seems challenging for a cohort of people to have simply lived their lives without encountering a peanut. Having something like an undiagnosed peanut allergy even after encountering peanuts almost seems like negligence from a health practitioner."
] |
[
"Does the energy of an alpha particle affect it's chance of capture?"
] |
[
false
] |
Hey . I've been learning about some nuclear physics/engineering lately, and recently learned about the (alpha, n) capture reaction with aluminum 27. With interest in spectroscopy, I ask: does the energy (MeV) of an alpha particle affect the chance that a light metal, in this case aluminum, will capture the alpha particle? (which happens normally when aluminum is bombared with alpha particles). I think I know the answer, but I just wanted to check here first. Thanks!
|
[
"So, would a difference of something like 300 KeV be a noticeable difference in capture chance, or is that an insignificant energy difference?"
] |
[
"So, would a difference of something like 300 KeV be a noticeable difference in capture chance, or is that an insignificant energy difference?"
] |
[
"Yes, especially near resonances. "
] |
[
"Which country has been most successful at combating pollution, and what did they do to be so successful?"
] |
[
false
] |
There are obviously a lot of outliers here with some countries being so abysmal initially almost anything they did would have a large impact. Looking to see which method(s) would be most successful in a country that doesn't have an abundance of low hanging fruit.
|
[
"I would say Bhutan. They restored large area of forests and even pledged to keep a percentage of area in the country reserved as forests.",
"They use hydroelectricity and their population is barely a million. So I assume they got all the power they need and more.",
"The forests are so connected and large that a tiger was tracked from the northern snowy mountains to the southern tropical-ish part of the country.",
"Bhutan is so green that it even absorbs more CO2 than it emits.",
"In my opinion, It's not easy to do what they did since bhutan is a small country and practically everyone is a tree hugger. Many countries won't achieve what buthan did due to geographic and economic reasons.",
"Source :\n",
"https://youtu.be/7Lc_dlVrg5M",
"\nWikipedia"
] |
[
"For anyone who have lived on both sides of the Atlantic, there are a number of contrasting things that highlight the disparity between US and Europe. It isn't necessarily any one single nations, but in many places in Europe, the sorting and separation of garbage is taken a lot more seriously than the states. Space is a premium in areas with large population densities and so there is a huge incentive to minimize the use of landfills. Of what can not be composted or recycled, Some are actually burned in special purpose incinerators for electricity. Sweden, for example, actually import trash to run their waste-to-energy plants. While superficially this puts CO2 into the atmosphere, it is actually a net loss in emissions because (1) if the trash was buried, organics and other decomposing parts of the trash generates CH4 which is many times more powerful as a greenhouse gas; and (2) burning fossil fuels instead to generate the same electricity releases new carbon into the environment that used to be underground rather than recycle the carbon in manufactured consumer goods back into circulation."
] |
[
"What a great story. Thanks for sharing."
] |
[
"Was there any species that lived both in the Old and in the New world?"
] |
[
false
] |
Apart form humans, was here any species whose area covered both the New world and the Old world before the discoveries?
|
[
"Brown and polar bears."
] |
[
"I'll add ",
"tapirs",
" to the list... technically they are separate species, however they are so unique in form and function that it is interesting that they are only found both in central and south america as well as the south pacific. And ",
"ospreys",
" although they are found globally (except Australia etc.) and not restricted to the two regions you mentioned. "
] |
[
"Species which live near the Arctic and Antarctic circles are more commonly spread out, since they have less distance to travel and are better adapted to travelling over the cold areas needed to take these shortcuts(as is the case with polar bears.) Aquatic species likewise are able to have a wide range because they can move from one place to another (like orcas). And birds with long flight ranges are also able to cover the distance (peregrine falcons)."
] |
[
"An impact crater has been recently discovered in Greenland that may have been caused by a 1-mile-wide asteroid. If an analogous asteroid were discovered heading towards Earth, would we be able to pinpoint in advance an exact impact location? How much time in advance?"
] |
[
false
] | null |
[
"We have several projects underway to use automated telescopes to find these objects, including the ",
"Catalina Sky Survey",
" and the ",
"Pan-STARRS",
" project. One of their biggest achievements is that they have probably found and tracked every asteroid that could impact the Earth that is 1 km across (0.6 miles) or larger, and confirmed that they're not going to hit the Earth in the next few centuries.",
"That's such a huge achievement for all of humanity, and it gets so little attention, that let me repeat it: after two decades of hard work, ",
".",
"You probably noticed I said \"pretty sure\". Some types of asteroids are difficult to detect, especially ones that spend most of their time closer to the sun than us, so we can't rule out some sneaky ones.",
"You might not have noticed I said \"asteroids\" only. Comets come from much farther away, they're almost impossible to detect until they fall into the inner solar system, and they move really damn fast. We have no hope of tracking all the comets in advance.",
"I also said \"planet-killers\", by which I mean objects big enough to cause a global disaster. There are still lots of undiscovered asteroids out there tens to hundreds of meters across, which could take out a city or small state.",
"Anyway, I didn't answer your question. If a dangerous asteroid has a \"near miss\", and flies close enough to the Earth that we can track it by radar, that gives us a precise enough position to tell us if it's going to hit us several years into the future, and pinpoint the impact location quite precisely. But if we're only tracking it by telescopes, the uncertainty is much greater. We can identify a \"stripe\" of locations across one side of the Earth where it ",
" hit, but that's about it.",
"To get a feel for what kind of uncertainty we can expect years in advance, the link below shows data used in a planetary defense ",
" done by JPL in 2017. To emphasize, ",
", but it's a realistic one.",
"https://cneos.jpl.nasa.gov/pd/cs/pdc17/"
] |
[
"\"probably found and tracked every asteroid that could impact the Earth that is 1 km across (0.6 miles) or larger\" does not mean \"They found them all\" ",
"They PROBABLY found the asteroids that are over 1km across. Smaller objects, non-asteroid objects and maybe some object we've missed (because it doesn't reflect as much light as we expect for something a kilometer across."
] |
[
"It is a pretty bold claim: it sure shocked me when I heard an asteroid expert make it! You're right to be skeptical, and nobody's suggesting we should stop looking. ",
"As we keep looking, we keep finding more and more small asteroids, but we've stopped finding more big ones. In 2000, early in the automated search process, 364 objects were discovered, of which 12 were bigger than 1 km and \"potentially hazardous\" -- on an orbit that comes really close to Earth. Later data showed that none of those will hit us.",
"In 2018, so far 1625 objects have been discovered, and ",
" are new potentially hazardous asteroids bigger than 1 km. In fact, we haven't seen a new 1-km PHA since mid-2016, and all the old ones are now known to be in safe orbits.",
"https://cneos.jpl.nasa.gov/stats/"
] |
[
"Is it possible to simulate evolution of a computer out of logic gates?"
] |
[
false
] |
Given modern computers in a simulation of NAND (or other ) logic gates and how they may be connected, is it possible to evolve a computer out of these primitives? I ask this because I have seen a clock evolving out of clock parts as per As I think more about this it seems to me that if it were true, the basic stages would be formation of half adders, adders, multiplexers and things like that and eventually a real computer that can do fetch-decode-execute cycle. Also, is it possible to evolve something more advanced than a computer? If we can simulate, how would one carry out constructing such a simulation? How could we select a fitness function for it?
|
[
"This sounds like it would be theoretically possible to do, if we had enough time.\nIn the clock video and in nature, evolution needs some form of determining what entity is most fit. In the clock video, a computer selected clocks based on their ability to tell time. In nature, a species ability to survive and procreate determines it's success. \nFor a system of logic gates to evolve, their must be a goal it is trying to achieve that determines its ability to reproduce. It is entirely feasible to simulate logic gates that perform small tasks such as arithmetic. \nThis could be simulate like the clocks were.",
"Simulating something more advanced than a computer using logic gates is currently unfeasible, as it took three weeks just to make a clock. ",
"It is physically possible for a processor to emulate a processor more powerful than itself, if the program could measure the goal of the simulation, but this would take an incredible amount of time.",
"You may be interested in something called artificial neural networks. These are simulations of biological neurons that adapt and change to meet a goal set by the simulator. They are not binary logic gates, instead, they are nodes with weighted connections, with the weights changing according to an algorithm to meet the goal. "
] |
[
"No, the speed of light in Life is 1 block per frame. That's the information propagation limit, and it's fairly trivial to construct a chain of some sort that disintegrates at light speed. You're getting it a bit confused with the fact that no known spaceships — cohesive independent self-translating figures — travel at greater than c/2.",
"I'm a bit intrigued by that fact. ",
" ",
"Proof, by John Conway himself, found. ",
"http://www.njohnston.ca/2009/10/spaceship-speed-limits-in-life-like-cellular-automata/"
] |
[
"It is not true that \"any Turing machine can emulate any other Turing machine.\" It is true that there exists such Turing machines; such a Turing machine is called a Universal Turing machine."
] |
[
"Is there any evolutionary benefits other than sexual selection in having blue or green eyes instead of brown?"
] |
[
false
] |
And other than Caucasian is there any examples known other than those of mixed race with Caucasian that have had the mutation that causes blue or green eyes?
|
[
"Like skin tone, lighter eye color is simply a reflection of lower pigmentation (less melanin). As with many genes, if those genes that influence eye color can mutate to less active forms without dicouraging the survival of a given organism, they may continue to mutate to less and less active forms. This means that if higher pigmentation isn't all that advantageous to some animal, lower pigmentation may result. ",
"There may be a selective factor at work, however: lighter skin tone was favored for north-dwelling human ancestors because it generates more vitamin D (which, closer to the equator, would have been supplied by the abundant sunlight). Because some of the genes that govern skin and eye pigmentation overlap, lighter eye color may have been coincident with lighter skin color."
] |
[
"Thus far no proven advantage but it is possible that the genes that contribute to blue & green eye color could be associated with other traits that confer advantage (such as lighter skin tones in northern latitudes).",
"Blue eyes in humans results from a single genetic mutation which probably spread through founder effect - meaning that all those with blue eyes can trace their ancestry back to the original mutant. ",
"I'm new here so I don't have a badge, but I am in my first year of grad school for biological anthropology. "
] |
[
"Since we know that skin and eye color segregate independently, it's doubtful that lighter eye color has anything to do with vitamin D production.",
"Not really true; the ",
" locus is associated with nearly all eye-color variation but also with some skin-color variation, and may be involved in melanin precursor transport. Nearly all blue-eyed people have a certain allele at the neighboring ",
" locus, which encodes a transcription factor that regulates ",
".",
"My guess is that it is the product of neoteny",
"Speculative, but so is any other hypothesis about this as far as I can see."
] |
[
"Is there evidence to suggest prehensile appendages on any dinosaurs?"
] |
[
false
] |
Are there any characteristics of bones in modern animals (elephant, rhinos monkey, etc) that suggest they have an ability to grasp with(monkey) or without(elephant) the bones themselves? If so, has paleontology found anything that would suggest so in dinosaurs?
|
[
"The only thing I am aware of is the relative sizes/amount of foramen in the skull for the additional/enlarged nerves needed to control prehensile lips/trunks etc. I remember reading that analysis of some dinosaur skulls had indicated that some species had prehensile lips like a modern rhinoceros."
] |
[
"Etymologically, prehensile means ",
" or ",
". With such a loose connotation, it's easy to suggest that many parts of the body could be considered prehensile. However, although definitions vary for different body parts (tails, tongues, feet, etc.), definitions almost all imply the ability to not just ",
" an object, but to ",
" it. We certainly can't manipulate objects with our lips with any sort of fine dexterity, but other animals such as manatees can.",
"Based on the definitions I'm familiar with, we wouldn't say \"humans have ",
" lips\", but we can say \"humans have lips that can be used for ",
"\". It comes down to definitions, but in this case, the definitions exclude human lips."
] |
[
"Do humans not have prehensile lips?"
] |
[
"Can bacteria die of old age?"
] |
[
false
] | null |
[
"Yes, over time bacteria accumulate damaged DNA, misfolded proteins, and old membrane/cell wall material. If it accumulates enough of these it will die.",
"When bacteria divide it groups all of these things into one side (called the old pole) before splitting in half. The daughter cell inheriting this old pole tends to perform worse than the other cell. ",
"Over time and after many divisions the cells with the oldest poles die."
] |
[
"That's actually a great question, I think it would be very tough to test in practice though. There are 'stem cells' that constantly replenish other cells that die off (like your skin and hair), and it would be interesting to know if protein aggregates and whatnot are concentrated in the differentiated cells more so than the undifferentiated cells, although this may just be limited by diffusion within the dividing cells. The thinking would be that any problems in the undifferentiated cells could be sluffed off and so wouldn't interfere with function of the progenitor cell as it still has to undergo many more divisions. Because division is considerably slower and the number of divisions cells undergo is so low in multicellular organisms compared to unicellular organisms (such as bacteria and yeast where this has been shown), this change may be negligible. Not sure it's ever been tested though and not sure how you could. (Outside of cell culture which I'm not sure people have tried with cells from multicellular organisms)",
"\nEdit: Speling"
] |
[
"Do multicellular organisms also push all the defects onto one of the daughter cells? At least to a small extent?"
] |
[
"If I had a 0.999... cm width chocolate cake, I can add some more chocolate and reach 1 cm. However, if I had the dimensionless/unitless number 0.999..., then it's equal to one. How?/why?"
] |
[
false
] | null |
[
"Well, if we're working with atoms, then 0.9999999cm and 1cm would have the same number of atoms, because atoms are only so big. The physical world is a ",
" bad place to try and understand the real line. But, for argument sake, if wood is continuous and you're cutting up wood to get 0.9cm, 0.99cm, 0.999cm, lengths then at some point you must stop. You will then only have 0.99999...99, not 0.9999.... because that would be the case when you make no cuts, because it equals 1cm.",
"But the fact that 0.9999...=1 directly implies that 0.999...cm and 1cm are the ",
" same length. 0.999... is not a process, it is a fixed value. A single, fixed number does not approach any number, it doesn't do anything except be a number. There are only two options: 0.999... and 1 are the same or they are different. And they are the same, there is literally absolutely positively no difference between 1 and 0.9999....",
"A way to discuss sameness is through the ",
"Leibniz Principle",
", which says that two things are the same thing exactly when all of their properties are the same. 0.999... and 1 share all the same mathematical properties, so they are equal. 0.99..cm not being 1cm would be a property that is ",
", but since 0.999...=1, we must have 0.99...cm = 1cm."
] |
[
"If you had 0.999...cm width of chocolate cake, then you would have 1 cm width of chocolate cake. 0.999... and 1 represent the exact same number, there's no difference. 0.999...cm = 1cm."
] |
[
"If you had 0.999...cm width of chocolate cake, then you would have 1 cm width of chocolate cake",
"Physically speaking, would 0.999...cm of, say, some wood, be different from 1cm of wood?",
"As in, would both be composed of the same number of atoms?",
"For example, ",
", ",
", and so on.",
"Now, given that we're talking in centimeters, a physical measurement, could I say that ",
"?",
"Would such an infinitely recurring decimal be a constructible number?"
] |
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