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[
"How do astronomers both find things so far away that aren't objects, like the KBC Void or Boötes Void, and identify objects' properties like atmosphere, temperature, and whether there's water and such on or in the object?"
] |
[
false
] |
I understand we have VERY powerful telescopes and fairly advanced technology, but if you look at any photo of the night sky, no matter how high the quality or magnification, the sky is so densely packed with objects that it seems totally impossible to identify certain 'Voids' that are basically just gaps in between stars if we use the naked eye. Also, I understand that this isn't really a single question but I have a few that kind of overlap (and I don't see the point in making a separate post(s)). When we find out what a planet and its atmosphere is made of, is it always the result of us sending things like probes to physically examine it, or can it be done from here on Earth? Sorry for making such a long post.
|
[
"For voids, we essentially look at how far away all the objects in a given part of the sky are, this can be done using redshift (See ",
"here",
"). When a survey was done by Robert Kirshner, Augustus Oemler Jr, Paul Schechter and Stephen Shectman of Galactic redshifts in 1980 they discovered that there was an area in the direction of Boötes with a very low galactic density. When we look at it we see that almost all the galaxies in that direction are closer to or further away from us than the void."
] |
[
"Here's how we work out what a distant planet's atmosphere is made of. When light passes through the planet's atmosphere, some wavelengths of it are absorbed by the gasses and then re-emitted. However, the direction these wavelengths are emitted are essentially random, so when someone on Earth looks at the light coming from that planet, there'll be a dip in the number of photons of those wavelengths being detected. Then we compare which wavelengths are not being detected as much to tests done here on Earth and from that can work out what gasses make up that atmosphere."
] |
[
"Note that for this technique to work, we need the planet to have an orbit that takes it between Earth and the star it is orbiting. Which is not that common. That's why we have only analysed a few atmospheres (a few hundreds to my knowledge). This is also one of the techniques used to detect those planets. "
] |
[
"If a 1000 kg cube impervious to all heat/pressure/radiation was dropped into our sun, how far would it sink before reaching equilibrium with the gravity of the sun and outward force of fusion?"
] |
[
false
] |
Considering the photosphere as the "edge" for measuring how far the object has descended. Edit: The hypothetical object is as dense as the sun's core.
|
[
"It would sink until it reached a depth where it was the same average density as the gas around it. This is essentially the same as what happens in the ocean: your buoyancy force (the force holding up a submarine or fish) is equal to the weight of the water you're displacing. If you weigh more than the water you're displacing, then you sink. If you weigh less, than you float. The differences in the Sun is that you're dealing with a superhot plasma instead of water, and because the density of the sun's plasma gets a lot thicker as you get deeper, whereas the ocean's floor is not very much more dense than the ocean's surface.",
"Here's a graph of density with distance from the centre of the Sun",
". Note that gold is marked on the graph: if you dropped an indestructible incompressible chunk of gold into the Sun then it would drop quite far in: it would only start floating once it had fallen about 70% of the way to the centre."
] |
[
"Don't forget radiation pressure!",
"Yeah, that's the tricky bit - it's going to depend on how transparent your material is. hmm...",
"On another note, is there a functional parameterization of that curve?",
"Well, it depends on how accurate you want to be! It's usually just done numerically (like this is here), but there are dozens of analytic approximations you could pick from, the simplest being a ",
"polytrope",
"."
] |
[
"Don't forget radiation pressure!",
"On another note, is there a functional parameterization of that curve?"
] |
[
"What are some interesting examples of humans influencing the evolution of a species?"
] |
[
false
] |
Most people who've taken a basic course in biology know about the speckled moths that turned black during the industrial revolution due to pollution. I want to know what other examples there are of humans influencing the evolution of other species. The more interesting or unexpected the better.
|
[
"Elephants are evolving to lose their tusks",
" because poachers selectively kill elephants with the largest tusks. What had been a rare trait is now advantageous for elephants, because no poacher is going to kill an elephant without tusks. In some places over 50% of elephants have no tusks. Those that do have tusks have smaller ones on average.",
"Antibiotic resistance",
" and ",
"pesticide resistance",
" are well documented and cause serious problems. They are caused by the overuse and/or misuse of antibiotics and pesticides. A small number of bugs randomly happen to have some degree of resistence to the chemical. Application of the chemical kills all the nonresistant members of the population but leaves the resistant ones. When the survivors repopulate, the new population will all be resistant and therefore much harder to kill."
] |
[
"I responded to a ",
"similar question",
" in ",
"r/AskScienceDiscussion",
" a few days ago, so I'll repost it here (assuming that's allowed). I actually used the exact same example with elephant tusks as the ",
"u/dromio05",
"'s comment! (And resistance to drugs is also a great example).",
"Artificial selection in the many species of plants and animals we've domesticated is definitely the most obvious answer, as other comments allude to. If you're talking about something less \"intentional\" though, there are several examples where hunting by humans has caused evolution in wild populations, like ",
"elephants evolving smaller tusks",
", ",
"bighorn sheep evolving smaller horns",
", and ",
"cod evolving smaller everything",
" (and also reproducing at a younger age). ",
"These are just some examples of clear directional selection exerted by humans, but of course we also cause evolution in many other ways. By changing existing ecosystems, introducing species to environments they've never seen before, and creating entirely new environments like urban landscapes, humans cause lots of species to change, and this leads to greatly increased extinction rates, but can also result in the formation of new species (",
"source",
"). Though that's not to say that this has a net positive effect on biodiversity.",
"Since none of those examples is necessarily very \"unexpected\", I'll add another one. Though I did touch on how humans shape habitats in many ways, I didn't actually directly discuss any of the effects of climate change, which are already quite noticeable in many species. One good example of this is that increasingly mild winters have selected for ",
"changing colours in tawny owls",
", with ",
"brown morphs",
" becoming much more common at the expense of grey ones (at least in Finland).",
"Though this is in some ways similar to the classic peppered moth study, the evolution of camouflage here is occurring on a much broader scale as a direct response to changes in seasonality, rather than more locally-dependent pollution levels, and will likely be a much more permanent change (since ",
"white peppered moths have become much more common",
" again after clean air legislation became common, but climate change looks like it's here to stay pretty much)."
] |
[
"I responded too some days ago similar question. I bring it to you: ",
"Just to add a very interesting example. ",
". ",
"In short: They developed samurai faces in their shells because people in the area avoid to take the ones who has a face-like pattern. This human behavior leads to a high face-like poblation of crabs passing their genes. ",
"Long (and very interesting): ",
"https://en.wikipedia.org/wiki/Heikegani",
" ",
"And by Carl Sagan in Cosmos: ",
"https://www.youtube.com/watch?v=dIeYPHCJ1B8",
"Original post here: ",
"https://www.reddit.com/r/askscience/comments/b25lvd/what_effects_are_humans_having_on_evolution_of/"
] |
[
"How (by natural processes) are nutrients added and changes made in an area of soil over time to make it fertile?"
] |
[
false
] | null |
[
"This highly depends on the geology of the area.",
"One example is coral atolls. In tropical, but shallow seas, coral reefs build up and up until they break the surface to create a small baren island. Seafaring birds tend to be the first visitors. The birds eat fish and leave deposits on the island. Some times their feces contains seeds from other places, or a coconut washes up on shore. Eventually some plants start to grow, which attracts more birds, more plants, more feces for nutrients. Feces and falling leaves create more soil for more plants to take root.",
"There are plants like legumes, some species of trees, and clovers that \"fix\" nitrogen from the air and self-fertilize the soil around them as well. ",
"You might be interested in learning more about the Nitrogen cycle: ",
"https://www.britannica.com/science/nitrogen-cycle"
] |
[
"The nutrients in soil are released by the breakdown of rock forming minerals. Rocks weather into mineral grains, which slowly react with water and dissolved gases to convert into things like clay and silica, while also releasing potassium, phosphorus, magnesium, calcium, and other necessary elements. Nitrogen is also needed, but while it's abundant in the atmosphere it's impossible for plants to directly access (it's a triple bonded molecule of two nitrogen atoms, which plants can't break). Instead it's typically added to soil by some microbes living in the soil that manage to convert gaseous nitrogen into a usable form that the plants can then uptake."
] |
[
"So the nutrients in soil are these ions: K",
" Ca",
" Mg",
" Na",
" NH4",
" Fe",
" Zn",
" Cu",
" Mn",
" as cat ions and NO3",
" PO4",
" (normaly as H2PO4",
" or HPO4",
" SO4",
" MoO4",
" BO3",
" as an ions",
"This is what we in agriculture talk about as soil nutrients. Very long ago rock contained minerals that were ground down by erosion and blown into area's or rocks where dissolved by acids produced by plants or fungi to absorb them. What was left where soils made of a combination of Silicon oxides, Aluminium oxides and carbon. We call these soils sand, loam, clay and peat soils with all mixed soils having special names.",
"Soil we call \"fertile\" (it is a very broad term) in terms of nutrients are soils that have the right amounts and ratio's for the crop you want to grow on it. To little and the plant growth is slowed or stopped because they all play some part in the metabolism of plants. To much of them and they can become toxic to the plant.",
"When we started harvesting plants and shipping them (think 3000 BC) we started taking the nutrients out of the ecosystem our ancestors where farming in. Rivers brought silt and dissolved minerals form upstream and flooded farmland to replenish farmland. soil that was not flooded by rivers would eventualy become infertile and be left to nature and slowly become fertile again through dust blowing in, rocks dissolving under the forest and animals moving nutrients between ecosystems. ",
"During the middle ages people started getting the hang of how to make soil fertile. Manure from animals and people where used to make small areas of very fertile land while the animals produced manure form large pastures. Nitrogen binding crops started to be used like clover in Europe. Producing nitrogen for itself and then being fed to animals to release its nitrogen in the manure. (you need to destroy a nitrogen binding crop to have it release the nitrogen it bound).",
"During the 1800 Great shit deposits where found. (",
"https://en.wikipedia.org/wiki/Guano",
") This became the first mined/artificial fertilizer. The work of Liebig then made fertilizing into a science. Discovering that crops needed nutrients and what those nutrients where. After this other rocks started to get used as fertilizers. Potasium,Sodium,Magnesium Chlorides combined with groundup limestone, Apatite treated with sulfuric acid and Chilisalpeter became the basis for the synthetic fertilizers we know today. In the 1900 the haber bosch process made mining NO3- unnecessary, potasium sulfate and magnesium sulfate replaced the chlorides, fosfates where further refined into Ca(H2PO4)2, Gipsum was used for soils with good pH but that needed calcium and Ammonium nitrate and urea replaced sodium nitrate. Special compound where made for the trace elements. In the early days they where present in the minerals with the macro elements.",
"Carbon has to be either added or held constant in the soil so it can buffer nutrients and water. Modern practices like cover crops and no till agriculture allow us to use a intensive crop cycle while retaining carbon in the past half the crops grown would have low yields but add carbon back to the soil. Better methods can reduce the carbon lost by working and natural loss and increase the carbon added each growing season.",
"This post is mainly about Europe. I don't know much about the agricultural practices in afrika, azia or america before modern agriculture."
] |
[
"Something I've always wondered is why have we never landed a rover on Venus?"
] |
[
false
] | null |
[
"'We' have - the russians did."
] |
[
"The russians landed probes that collected atmospheric data and stuff like that. Nothing like the stuff they're doing on Mars right now."
] |
[
"Venusian surface conditions are kind of extreme. The Venera probes only survived for 23 to 120 minutes each."
] |
[
"Why do positrons only have positive spin?"
] |
[
false
] |
[deleted]
|
[
"I'm not sure where you heard positions only have positive spin, but you're misinformed. By positive and negative spin, I'm assuming you mean spin +/- 1/2. Positrons have the same spin as electrons. They are identical to electrons in every way except they have the opposite charge."
] |
[
"Should I delete the question?",
"I'd say not to. If you delete it, no one else can glean any knowledge from it, and (in theory) if you leave it, people also won't have to ask it again."
] |
[
"Should I delete the question?",
"I'd say not to. If you delete it, no one else can glean any knowledge from it, and (in theory) if you leave it, people also won't have to ask it again."
] |
[
"Question about the Ask Science guidelines... Observer != Conscious person?"
] |
[
false
] |
I noticed the following in the guidelines section, under the Philosophy of Science/Logic heading. Why is that an important distinction? Sorry, if this has been asked before.
|
[
"It's pointed out in the FAQ because it's common to confuse the jargon term ",
" with the common English term ",
" (i.e.: a conscious person/animal who observes something), which can lead to many questions based on this faulty premise.",
"Here are a few previous discussions on this kind of subject:",
"http://www.reddit.com/r/askscience/comments/kau6y/what_does_observer_mean_on_a_quantum_level/",
"http://www.reddit.com/r/askscience/comments/ggnjl/a_question_about_the_observer_in_the_double_slit/",
"http://www.reddit.com/r/askscience/comments/hckp8/why_isnt_the_cat_an_observer_in_schrodingers/",
"http://www.reddit.com/r/askscience/comments/kaok9/quantum_consciousness/",
"Feel free to read these then ask any follow-up questions!"
] |
[
"Hello: Your question is stuck in the spam filter, and I think that you need to resubmit with a different title. If you rephrased your title to something like \" Why, in quantum mechanics, is the observer specifically specified as not a conscious person\", it would garner more attention, and wouldn't look like a discussion about the AskScience guidelines. Thanks!"
] |
[
"Hmm, very interesting... Thanks for the reply!"
] |
[
"Is tungsten carbide-coated D2 steel susceptible to corrosion?"
] |
[
false
] | null |
[
"Without really specific description of requirements, standards, and environment, it can't be said absolutely but...no, it's not.",
"In open-air at room temperature, Tungsten Carbide offers very good corrosion resistance (does depend slightly on the binder being used). In combination with D-grade steels which also offer mild-to-stainless resistance to corrosion I'd say your piece is not really susceptible to corrosion. "
] |
[
"As a fellow materials scientist (who took a shot in the dark) I agree with this...mostly. I just think it's worth noting that tungsten carbide and D-grade steel are both pretty good in most (reasonable) environments",
"Also, we all know Face Centered Cubic is what's up. /unnecessaryfeelingoflatticesuperiority"
] |
[
"As a fellow materials scientist (who took a shot in the dark) I agree with this...mostly. I just think it's worth noting that tungsten carbide and D-grade steel are both pretty good in most (reasonable) environments",
"Also, we all know Face Centered Cubic is what's up. /unnecessaryfeelingoflatticesuperiority"
] |
[
"Why is neutron emission so harmful?"
] |
[
false
] | null |
[
"Unbound neutrons can collide with nuclei in a target materials and result in a chain reaction of potentially harmful effects.",
"The neutron will impart a large amount of kinetic energy to a nucleus it collides with causing it recoil and become ionized. This heavy charged ion (HCI) can then collide with other atoms creating a branching cascade of collisions that continues until all the energy is dissipated. So for every nucleus a neutron collides with, you get a shower of HCIs that are very effective at breaking molecular bonds, either damaging DNA directly or by creating free radicals that later attack DNA. Depending on its energy and the mass of the initial recoil nucleus, a neutron may still have enough kinetic energy to create additional cascades.",
"If a neutron is absorb by a nucleus, that nucleus may be transmuted into a radioactive isotope that may decay by alpha, beta, or gamma emission.",
"Neutrons are extremely penetrating as they are not subject to the electric force and will only react with nuclei (much smaller than atoms) and most nuclei have very small neutron collision cross-sections. Hydrogen doesn't have a big cross-section, but it has a high number density to weight ratio for water and hydrocarbons, so neutrons are more likely to dump their energy in them. Lead in contrast has a tiny cross section and few nuclei per unit mass and is almost transparent to neutrons.",
"Points 2 and 3 are actually why the neutron bomb was developed. The radii at which the blast, heat, or radiation from a tactical nuclear weapon are sufficient to knock out a tank, armored vehicle, or bunker are actually not that large. A neutron bomb is a nuclear weapon optimized to maximize neutron flux, which goes right through the metal and composites used to make a tank's armor and doses its water laden crew. Some of the nuclei in the vehicle will also become activated and add to the dose. The crew will succumb to acute radiation poisoning and the vehicle will become a hazard until the activated nuclei decay."
] |
[
"It's not the neutron itself that is really dangerous, it's the nucleus that it hit that do emit high energy photons to lose the energy acquired in the process. It makes neutron emissions extremely dangerous.",
"Those high energy particles can then go around and damage chemical bonds, break molecules (including DNA, thus possibly causing cancer) and create highly reactive elements from the break which can further damage other molecules."
] |
[
"It can basically disrupt chemical bonds in the body through the ionization of hydrogen in molecules. Read more ",
"here",
"."
] |
[
"Is Magnetism Simply Angular Momentum at the Atomic Level?"
] |
[
false
] |
(As I understand it, and probably way off) Imagine electrons that exist in the metallic cloud of valence electrons contained within a bar magnet. This magnet has a lot of free flowing electrons within the iron. At the North pole the electrons are spinning in one direction, who knows, maybe similar to a vortex. At the South pole, the electrons are spinning in the opposite direction. Is the force that leaks out - what we call magnetism - simply just angular momentum from electrons spinning within the bar magnet? Your views are appreciated as always,
|
[
"I'm not sure whether your question is why spins would line up in a ferromagnetic material, or why lined-up spins would cause a magnetic field -- I'll try and give a quick answer to both.",
"For the first, ferromagnetism is basically a result of the Pauli Exclusion principle (what isn't, right?). As fermions, any two electrons want to be antisymmetric. As charged particles, they also want to be far away from each other. In larger atomic orbitals (think unfilled d orbitals like those in iron, nickel, or cobalt) there is some considerable overlap between where one electron wants to be and where it's neighbors are hanging out. Since they are not friendly neighbors they want to see as little of each other as they can -- they want to spread out, and that favors a ",
" antisymmetric wavefunction (i.e. they spend as little time as possible in the same place). To remain antisymmetric overall, this requires a ",
" of the wavefunction.",
"As for why this creates a magnetic field, it's because this quantum mechanical property of spin causes particles to have an intrinsic magnetic moment. While it's analogous to a spinning sphere of charge, It's not ",
" this or that. It doesn't make much sense, I think, to ask ",
" particles have electric charge -- it's just a property of particles. Same with their spin and associated magnetic moment -- it might result in crazy stuff but hey, whatya know, they have spin and a magnetic moment. But since they have these magnetic moments, if they all align they can cause a very sizable magnetic field, which can be seen by anything with electric charge nearby.",
"Also, to pick one nit, in the \"perfect\" bar magnet we're talking about here the spins at both ends are aligned in the ",
" direction. We have one direction picked out and there is an \"in\" side and an \"out\" side, no flipping of directions for the spins within."
] |
[
"Fundamentally, a magnetic field is a relativistically transformed electric field. In other words, when charged particles are moving, there's a magnetic field around them.",
"I still don't really understand ferromagnetism, though. I mean, I understand that it comes from the \"spin\" of the electron, but then I'm told that this spin really doesn't exist at the quantum level, so you just have to accept that it's a quality of valence electrons that creates a magnetic field just like you'd expect from an actual spinning electron. But I'm probably missing something there."
] |
[
"This",
" may help. I believe the spin of all the electrons adds up in the magnet and amplifies. I don't completely understand it myself, but that article helped clear some things up for me."
] |
[
"This might sound like a stupid question, but was the sky pitch black eons ago?"
] |
[
false
] |
I’m new to this sub and I was curious, since I had nothing to answer this question with other than my own headcanon. So this might actually have a short answer than expected. So light takes a super long time to travel right? Since what we’re seeing up there (outside of the solar system) are dead or dying stars and the info hasn’t reached our eyes yet. So was there a time when no light from outside the solar system had reached the earth, making the sky pitch black at night save for the sun?
|
[
"Within the galaxy, the light travel times are actually quite short. The whole Milky Way is only about 100,000 light years across, and we're about 30,000 light years to the centre. But most of the stars you can see in the night sky are less than 1,000 light years away, and many are less than 100 light years away. It takes us about 200 million years to orbit the galaxy. The shortest lived massive stars live for millions of years, medium ones live for billions of years, and long-lived low-mass stars live for trillions of years. A molecular cloud will form collapse into stars, and then be blown away by those stars, over a period of 10s of millions of years or so.",
"Stars form and move so slowly compared to the light delay time that we're pretty much seeing every star in the night sky as it is now, except for small variations. Except for a few extreme objects, almost every star you see at night is still alive, and unchanged from what you see.",
"The Sun was also not the first star in the galaxy. There were a couple of generations of stars first. So once the Earth formed, the light from other stars was already all around, and the first night of the primordial Earth would have been a starry night (if the atmosphere was clear)."
] |
[
"To expand a little bit on this (unsurprisingly) excellent answer from ",
"u/Astrowiki",
", ",
"this table",
" lists the hundred or so brightest stars when viewed from the earth. Note that only six are more than 1,000 LY away and the most distant is just a bit over 2000 LY away (I believe this table mis-lists it at ~3,000 LY away, but either way the point stands).",
"There isn't exactly a firm line between what can and cannot be seen with the naked eye (if you know what to look for, how to look, and have exceptional eyes and dark skies you can see a lot more than a casual observer in the city), but ",
"even an exceptionally bright star will be marginally visible under good conditions if its 10,000 light years away",
". Collections of many stars (and individual stars that are temporarily ",
" bright, like ",
"supernovae",
") can be visible from much farther away, ",
"potentially up to ~10-15 million light-years under ideal circumstances for galaxies that are collections of billions of stars",
"."
] |
[
"As the sun wavers up and down in its orbit around the milky way, does it have to pass through any significant gas clouds on its way? And is it possible this may obscure a large number of stars in the sky at some point in the future?"
] |
[
"How do I derive a form of the Navier-Stokes Law which realistically reflects the vorticity surrounding complexly spinose Odontopleurid trilobites in conditions of incompressible steady flow?"
] |
[
false
] |
The recurring emergence of extreme spinosity in certain Trilobite lineages in the Paleozoic has been interpreted as adaptive specialisation to a planktonic lifestyle. However, Stokes Law merely demonstrates that a sphere of a given diameter may show suspension behavior in conditions of incompressible steady flow, for a given vorticity of ω = Ñ ₓ u. But spinescence directly affects vorticity in a chaotic fashion, and the resolution of Stokes law only covers the trivial scenario where y = -½ur² [1-3/2 (R/Ö r²+z²) + ½ (R/Ör²+z²)³]· … such a simplistic approximation won’t do….* I’m supposed to believe that the behavior of in freefall in the water column is the same as that of a sphere or equal volume … try that with a small pebble vs a dandelion seed and see where that gets you… This is the same approach taken by theoretical physicists who approximate the geometry of a cow by postulating it is spherical. Which is entirely inappropriate to my problem (not to mention rude to the cows, which are noble creatures of great chastity and virtue who deserve better). How do I solve Stokes law in such a manner as to take into account the actual shape of presumably planktonic complexly spinose trilobites such as Radiaspis radiata in a realistic fashion, “spherical cows” be-damned? Otherwise I’ll be stuck trying to figure out what to feed the spiny buggers if Stokes Law cannot account for their floating around with the rest of the plankton. It's a thorny problem.
|
[
"Well, you are on point with your observation that the approximation is too simplistic. One way to tackle your problem without approximating your odontopleurida as spherical is to describe their volume using ",
"spherical harmonics",
". By using this, you can treat them as spatially extended, non-spherical dust particles in a viscous fluid, but still maintain well-behaved properties like linear independence, orthogonality or symmetries for parity or rotations. Since spherical harmonics ",
"share a deep connection",
" with representation theory, you can find representations ℋ",
" so that there exists a trace-free tensor of rank l, further simplifying your problem, as this is completely isomorphic (and even diffeomorphic) to the strong/explicit diophantine inequality of Interuniversal-Teichmüller-theory (as discussed ",
"here",
" in corollary 2.3). And this may sound familliar to you, as this was extensively applied to describe spinose Lichida trilobites in strong shear stress divergence and deviatoric momentum flow (though only Devonian, not Tremadocian, but a generalization for this is active field of research).",
"I hope that helps."
] |
[
"Thank you for those insights. I'll admit I was initially tempted by the crude effectiveness of I-T-t, but refrained from investing my efforts in that direction in view of the general robustness of spinose ",
" taxa (Consider the loveliness of ",
" for instance",
" ... ",
" is the one on the right; I'm not too sure where the one on the left fits in the greater scheme of things, despite Todd from Micropaleontology giggling and yammering about ",
" ... shut up Todd). I was under the impression that a general consensus to the effects that ",
" occupied a benthic to necto-benthonic ecospace had been in place for quite some time, which would preclude extending the inherent variance of ℋl outside of Upper Flow regime conditions, given the ",
" of that quasi-meter size giant water cockroach.",
"Would you recommend beginning modelisation of the spherical harmonics from a stochastic perspective, or should I forge right ahead and tackle the Herglotz generating function for indeterminate non-linear geometries to take into account within-taxa ontogenic variations (keeping in mind that I'm using ",
" as a primary descriptor and silicified specimens of ",
" as a control group [see fig 4 of ",
", 1997, op.cit.]."
] |
[
"Try checking out ",
"this paper",
" and skimming through it's many citations. This sounds like a really interesting problem. Is this really how biological oceanographers parameterize all of their planktonic transport models? I'm happy to help you work through some of the Fluid Mechanics and mathematics if you have questions.",
"Love seeing hard questions like this on the subreddit!"
] |
[
"Would a cat living on a space station gain and shed it's winter coat?"
] |
[
false
] |
Assuming the the station used internal climate controls that remained steady all year. Would typical yearly (or monthly) cycles observed in the animal kingdom continue to exist when living in space?
|
[
"You win that bet: bird migration is almost certainly entirely triggered by changing daylight hours."
] |
[
"If you can adequately simulate the seasonal changes that normally trigger these events they would certainly occur. If not, I doubt anyone would be able to give you a straight answer right away, though I strongly suspect that cats wouldn't stop losing their fur. It might become a continuous process."
] |
[
"The thing that regulates seasonal shedding cycles in mammals is exposure to light. In higher latitudes days lengthen and shorten seasonally, alternately suppressing and stimulating melatonin production, which in turn regulates seasonal hair growth.",
"Temperature and humidity and all those other things apparently have no effect.",
"Bonus Question: I'd make an any-money bet that seasonal bird migrations are also related to seasonal changes in daylight hours, but that's a guess. Also for the birds, if you did want to stimulate migration you would have to simulate the earth's magnetic field so they'd know which way to go."
] |
[
"Air pressure \"below\"sea level"
] |
[
false
] |
If the oceans were to disappear and it were possible to stand at the bottom of the Mariana Trench, what effects would a person feel due to the increased air pressure?
|
[
"Interesting aside:",
"Volume of the oceans: ~1.3 billion km³ ",
"1",
"Volume of dry air in the atmosphere: ~ 4 billion km³ ",
"2",
"So, if you just completely removed the oceans, the air would have to expand to fill that space. Using the ideal gas law (PV = RT), assuming the total volume doesn't change and the temperature eventually comes back to ~20°C average,",
"P",
" * V",
" = P",
" * V",
"P",
" * 4 = P",
" * (4+1.3)",
"0.754 * P",
" = P",
"So, you would get roughly a 25% decrease in pressure at all points world-wide."
] |
[
"Except for the air would have to come from somewhere. So really, the question would be: how much air pressure would we have left up here where we normally are? I don't know the answer, but I bet this would cause some problems, especially considering most of the surface of the earth is water at present. "
] |
[
"that's a hole though, he's talkin' the entire volume of the ocean.. about 1.3 billion cubic kilometers. "
] |
[
"Does water become marginally more viscous as it approaches freezing?"
] |
[
false
] | null |
[
"Not just marginally, it's pretty significant. ",
"Here is a plot",
"."
] |
[
"You can actually tell there's a difference just by sound if you pour hot vs cold water from one container to another."
] |
[
"glass is amorphous but still a solid at room temp, not a super viscous fluid like that myth says"
] |
[
"How much worse could The Chernobyl Disaster have been?"
] |
[
false
] | null |
[
"Well, at one point the area below the reactor had to be drained because if it came into contact with the water there would be a massive explosion, so three engineers donned wet suits and a flashlight, which broke, and went into the radioactive water to drain it.",
"They lived too.",
"I suggest you check out Frederick Pohl's book Chernobyl"
] |
[
"So really only mildly worse. The local effects are somewhat significant, but \"radioactive dust around the globe\" Is about as dangerous as bananas. Considering how much \"radioactive dust around the globe\" was created during nuclear weapon tests, and how big the globe is. The exclusion zone would be larger in the downwind direction for the most part, not a circle radius."
] |
[
"Like a real global catastrophe or an equivalent to moving to denver for a year global catastrophe?"
] |
[
"How fast do I have to go to reach Alpha Centauri in 4.37 years (on my clock)?"
] |
[
false
] |
Alpha Centauri is 4.37 lightyears distant. If I go at 0.01 x , then it woult take me 437 years, because Lorentz contractions are not significant. If I go at 0.99999999 I would arrive in just a few days, since in my reference frame, the distance would shrink and I'd get there quicker. How fast do I go to get there in 4.37 years from my point of view? Hard mode: if I start at Earth and constantly accelerate until I get midway, then constantly decelerate until I get to Alpha Centauri. How hard would I have to accelerate/decelerate to arrive there 4.37 years later? Star problem: can somebody get me a Wolfram Alpha query that answers this question for any arbitrary distance? That is, "how hard would I need to accelerate in order to arrive at lightyears distance in years of subjective time?"
|
[
"This is a question about relativistic ",
"proper velocity",
".",
"For easy mode: assume you're using convenient units where speed is measured as a fraction of c, and time and distance use the same units (eg years and lightyears), then: γ=sqrt( 1 / 1-v",
" ), and Tp (proper time) = (d/v)/γ. You're trying to solve for Tp=d, or in other words, for vγ=1. You reach that for v=sqrt(1/2), in other words, about 71% the speed of light.",
"For hard mode, take a look at the \"Unidirectional acceleration via proper velocity\" section of the wikipedia article."
] |
[
"Something from that link that I never considered:",
"One major problem you would have to solve is the need for shielding. As you approach the speed of light you will be heading into an increasingly energetic and intense bombardment of cosmic rays and other particles. After only a few years of 1g acceleration even the cosmic background radiation is Doppler shifted into a lethal heat bath hot enough to melt all known materials.",
"One more reason interstellar travel isn't on the horizon anytime soon."
] |
[
"It's just a matter of setting the traversal time in years to the distance in light years, and finding the proper acceleration, I guess. Hard mode sounds simple when you look at it that way - thanks for the wiki link!"
] |
[
"What do we actually witness when we are shown an image of a 'sonic boom', and why does travelling at such a speed cause such an overt reaction in the air?"
] |
[
false
] | null |
[
"It's condensed water vapor."
] |
[
"Why does it condense? And in that case why does only a certain volume condense?"
] |
[
"Increased pressure turns water vapor into liquid water: ",
"http://serc.carleton.edu/images/research_education/equilibria/h2o_phase_diagram_-_color.v2.jpg"
] |
[
"How does squinting help you see?"
] |
[
false
] |
I happened to forget my glasses today so I had to squint to see the board. This led me to wonder why squinting helps you see things. Is it just a mental thing, or is there something to it?
|
[
"When you wear glasses you correct light refraction reaching your eyes. When you squint, you reduce the amount of light being refracted, therefore, making it easier to see. There is something called a pinhole occluder that does the same thing. You essentially look through a tiny hole and, if you wear a prescription, it makes your eyesight seem clear. Basically just poke a hole through an index card using a paper clip and look through the hole. You will be able to see perfectly."
] |
[
"Squinting hard can actually deform the eyeball ever-so-slightly, which in turn can have a small-but-noticeable effect no focal length."
] |
[
"When you squint, you're essentially reducing the aperture of your eye. As a result, you limit the light entering your eye to light rays that are essentially traveling straight toward your retina anyway. Rays that are already traveling toward your retina need not be refracted and bent toward it as much as light coming in farther from the center of your eye's lens.",
"If you think about a glass lens, the light entering the lens closer to its center (in line with the focus) continues travelling in a straight line. Light that enters the lens farther from the center of focus, at the edge, it needs to be bent quite a bit in order to be directed to the focal point.",
"This image gives a good example, though it's mainly showing another phenomenon called spherical aberration",
" Note how much more bent the lines at the edges are than the lines at the center."
] |
[
"Why doesn't an ant die when it falls from a very high place?"
] |
[
false
] | null |
[
"Surface area vs. volume. ",
"Small animals (anything smaller than a normal sized cat) have such high surface area compared to their volume that their terminal velocity is low enough for them to survive large falls.",
"That's why cats always land on their feet seemingly uninjured. ",
"When I learned this, it made the \"Person saves ducks falling from a high place\" youtube video seem a lot less... important. They would have survived regardless. ",
"So the answer is: They don't fall fast enough and don't have enough mass to get injured upon contact with the ground. Remember, when you are falling, you build up kinetic energy as 1/2mv",
" If your mass is small, you don't build up a lot of energy. If your surface area is large, your velocity is also slower. So small animals have very low kinetic energy as they fall."
] |
[
"I think the answer may be more physics than biology. Have you ever dropped feather? It falls slower than let's say a ball, even though both \"should\" experience a gravitational acceleration of 9.81 m/s",
" The feather is really light but has a high surface area, that's why it experiences lots of air resistance. It's terminal velocity is pretty low so the ant would not hit the floor as hard as a human jumping from a building. I think the structure and materials of the ant body might also help, a ant-size shrunken human would probably still die if we hit the ground hard enough to break our bones. ",
"Also, fun fact. When there is no air resistance (vacuum) a feather and hammer do actually fall at the same speed! Here is an awesome video of it being shown, on the moon! ",
"https://youtu.be/KDp1tiUsZw8"
] |
[
"Thanks, pal. "
] |
[
"Why are C and T typically the degenerate bases in the amino acid code?"
] |
[
false
] | null |
[
"Hydrolysis causes the Cytosine to trade its NH2 for an O, turning it into Uracil. This is a spontaneous reaction that is usually caught by the repair protein Uracil Glycosylase, but not always.",
"\nThe same thing happens to a slightly different form of Cytosine: 5-methylcytosine. In this case it trades NH2 for O and it turns to directly into Thymine.",
"\nIt just has to do with their very similar molecular structures. ",
"edit: typo"
] |
[
"Hydrolysis causes the Cytosine to trade its NH3 for an O",
"It's an NH2 not an NH3. ",
"This is a spontaneous reaction ",
"Definitely true, but also occurs a result of mutagens, ionizing radiation and UV."
] |
[
"D'oh, good catch!",
"\nI just meant it was a reaction that didn't need any energy to occur which is part of why it's so common; guess I should have elaborated for clarity :) "
] |
[
"Can we make laser pointers outside of visible wavelengths? (IR, UV, Microwave)?"
] |
[
false
] |
I have a laser pointer used for pointing at stars, and thought about laser pointers that are outside of the visible spectra. would microwave laser pointers be as dangerous as I'd imagine they are in terms of pointing them at people?
|
[
"Your green laser pointer? It's actually an IR laser. That IR laser passes through a crystal that takes 2 IR photons and converts them to 1 green photon."
] |
[
"That effect is actually a really big deal, because the cheaper green laser pointers actually produce more IR than green. Many of them even omit to send the output beam through an IR-absorbent filter (cost engineering, dontcha know) so the mixed IR/green beam can be powerful enough to damage eyes even if the green alone is not."
] |
[
"There are infrared, UV, and microwave lasers (called masers) but you might not find them in the handheld format you're familiar with. ",
"This one",
" for example is a $2000 IR handheld laser."
] |
[
"I just heard about the RH blood group system, but previously had only heard about the ABO blood group system. Do these exist concurrently, i.e. is everyone RH+/- and A/B etc. or are we all one or the other?"
] |
[
false
] |
I read the Wikipedia pages for these but it wasn't clear to me how it works. I'd also be interested to learn how blood groups actually differ and what that means in practical terms.
|
[
"The ABO and Rh+/- systems exist independently. If you've heard blood groups described as \"A negative\" or \"O positive\", the positive and negative refer to the Rh type.",
"Blood types are defined by antigens on the surface of red blood cells. These are proteins that hang out on the outside of the cell and act as markers (I actually don't know their purpose).",
"A and B refer to different antigens. If your red blood cells have antigen A, that's type A blood. Antigen B = type B.",
"There is no \"AB antigen\" — AB blood means the cells have both A and B antigens. There is no \"type O\" antigen — it's the absence of both A and B antigens.",
"There is only one antigen in this system, and you either have it, or you don't. If you have the Rh antigen, your blood is [AB, A, B or O] positive. If you don't have the Rh antigen, your blood is negative.",
"Use a person with type A negative (A-) blood as an example for blood transfusions. ",
"You can't accept red blood cells with different antigens to your own blood. E.g. if we gave our person AB blood, their immune system would attack the AB blood. The A antigen on the AB blood cells are fine, but the B antigen is unfamiliar and therefore triggers an immune response.",
"The same type of blood as your own is obviously safe. ",
"Less obviously, you can accept blood that lacks the antigens your blood has. E.g. our type A person can accept type O blood. Having the A antigen is not necessary. Type O blood is essentially invisible to the immune system, so people with all blood types can accept it.",
"AB blood, on the other hand, can only be given to people who have AB blood themselves. Types A, B and O will all attack AB blood because it has at least one unfamiliar antigen.",
"BUT WAIT. Our person is also Rh-, so they can't accept Rh+ blood. O- and A- are fine, but O+ or A+ would trigger an immune response, just like AB would.",
"The medical profession learned about ABO types before Rh type and it was tragically confusing there for a while.",
"(Compatibility is the other way around for plasma (the rest of the blood apart from red blood cells) for reasons that Wikipedia explains better than I can!)",
"Edit: meant to say there are other systems as well, as other commenters have pointed out."
] |
[
"They are independent things. Just like you can be left-handed and wear blue socks (or not) at the same time. There are a LOT of other blood group systems, but ABO and RH are the most important. Some of the others have names like MNS, P, Lutheran, Kell, and Duffy.",
"https://www.britannica.com/science/P-blood-group-system",
"If you get the wrong type of blood in a transfusion, or in a transplant, you could have a bad reaction and perhaps die."
] |
[
"Just as a correction, there are more than one antigen in the Rh system. The pos/neg is just Rh D, which you either have or don't. There's also C/c, E/e and a few others that aren't usually worth mentioning."
] |
[
"Is there anything in space we can see at two different times because of the bending of light on the way here? How much of a difference could be expected?"
] |
[
false
] |
I read something like this ages ago and it intrigues me. Can you really see the same thing in two places in the sky?
|
[
"Yes! Here you go: ",
"Astronomers Watch a Supernova and See Reruns",
"Very, very weird stuff - a combination of a supernova event and just the right alignment of Einsteinian gravitational lensing let astronomers view multiple different stages of a single supernova event.",
"EDIT: Yes, I can actually spell supernova..."
] |
[
"Sounds like you are describing gravitational lensing. Something as large as a galaxy can definitely bend light around itself in such a way that we can see multiple \"copies\" of whatever is behind it. The light may travel further around one side than it does around the other, so in theory yes we can see the same object as it appeared at two different times. Look up \"Einstein Cross\" for a great example. As for how large the difference is, I'm not 100% sure, it could vary pretty wildly based on the size and distance of the objects."
] |
[
"Check out the ",
"Einstein Cross",
". I think this is what you are asking about. It's an imagine of a quasar repeated 4 times by gravitational lensing around a closer galaxy. ",
"Also check out ",
"light echos",
". Sometimes we can see light reflected off of dust to see an event that happened earlier. "
] |
[
"Is there a significant difference of oxygen concentration in the air, during the daytime and night ?"
] |
[
false
] |
Since plants produce 02 in day and c02 in night , there's surely a difference but i want to know how much ? Does it affect human ? Does it affect the performance of an athlete for example ? Like is he more endurant when he runs during day than night
|
[
"following your logic, variations in the % oxygen should be about the same as variations in %CO2. CO2 concentration is about 0.04% (or 400 per million). So the variation in O2 concentration can only be ±0.04 percentage points a most. Even then, O2 concentration would only vary between 20.9-21.0%. Anyway, CO2 concentration don't vary nearly that much, less than ±0.01 percentage points (",
"https://www.nature.com/articles/s41598-021-82321-1",
") which gives, still assuming the two gases change in the same way, a variation of only 20.95±0.01 % for O2",
"this doesn't apply to indoor environments though, where there can be much larger variations, mostly because of people breathing a limited amount of air. O2 levels still won't change very much, since there's so much of it. But CO2 levels can increase a lot and become multiple times higher than the outdoor value, up to 0.50% (or 5,000 per million; ",
"https://www.nature.com/articles/s41893-019-0323-1",
") and since human respiration depends on both O2 and CO2 levels, this indeed has the effects you're thinking about. You can check the 2nd link for details"
] |
[
"Very clear \nThanks"
] |
[
"Don't plants respirate all the time but during the day they additionaly photosynthesis? Also because of gases diffusion in open space area without high pollution I think it's not as significiant. IMO your performance during the daytime jogging would be same as night session if the amount of oxygen in the air during day/night is the only condition."
] |
[
"At what mass of feces in your colon does your body feel the need to defecate?"
] |
[
false
] |
When does your brain receive the signal that causes you to feel this urge?
|
[
"It's more about volume rather than mass.",
" There are nerves that signal when the colon is stretching, causing the urge to defecate. But you can resist that urge (because, as discussed in another question, many animals prefer to defecate in a location not where they live and eat), and some water is reabsorbed, reducing the urge.",
"I couldn't find anything specific to the actual volume, but I'm certain that it is related to a lot of factors, like size of the person, variances in size of the colon, sensitivity to the urge nerve impulses. And some diseases, even some bad food can be involved in varying the volumes that might cause the urges.",
"I hope this partially answers your question."
] |
[
"Not exactly.",
"Intestinal physiology is built to conserve water, a surprisingly rare resource for evolving mammals. The colon attempts to remove as much water as possible, compacting the feces. More liquid feces usually indicates something's wrong, whether it's a viral or bacterial infection, some sort of toxin, or a disease. In that case, the volume is much larger, making the urge even more immediate. "
] |
[
"so that's why I always feel the poo shooting out when I enter the bathroom"
] |
[
"Can mosquitoes die if they bite someone with a high blood-alcohol level?"
] |
[
false
] | null |
[
"This is merely a speculation, as I could not find any information on mosquito's sensitivity to alcohol:\n A human can hardly go beyond the concentration of 0.50% (half of a percent) of blood alcohol and stay alive, and most drunken \"stupor\" cases exist around 0.06% - 0.15% (six percent of a percent to fifteen percent of a percent).\nSo it would be nigh impossible for a mosquito to get \"drunk\" from drinking a drunkards blood.",
"In addition, the blood does not go directly into the mosquito's nervous systems as it is ingested and digested within its stomach, and a mosquito's digestive system is known to break down even hardy viruses and bacteria ",
"(even HIV)",
".",
"Though, at the same time, mosquito's have been known to be especially ",
"attracted to people who have ingested alcohol",
".",
"Heck, this might not be a definitive answer, but it might help at least somehow."
] |
[
"Wile generally accepted as fact, the 0.5% BAC max is untrue. Depending on the level of alcoholism, many people can get up to 0.9% or even higher. I work as an EMT, and my personal best is a patient who ended up with a 0.86% after we dropped her off. Highest I have heard of was ~0.92% from another medic in my corp.",
"Just saying, it can go higher."
] |
[
"The LD50 means \"Lethal Dose median\" or \"Lethal Dose 50%\" that means that not everyone will die from the LD50 dose but it means that if you pick up a bunch of random people from the streets and give them a dose of alcohol that would be equal to .5% BAC (assuming that .5% BAC really is the LD50) then half of them would die and the other half would survive. So that means that the .5% BAC max is only half untrue."
] |
[
"Can one hear the way another person sounds to themselves by putting a speaker with a recording of their voice up to your throat?"
] |
[
false
] |
[deleted]
|
[
"Perhaps make a recording of your own voice then hold it up to your throat and see how it sounds."
] |
[
"From a sound engineering perspective there are strategies to mimic how the body alters sound. Not exactly the same but akin to ",
"dummy head recording",
". I'm not a neuroscientist but I would guess that there are other reasons we hear ourselves differently making things more difficult."
] |
[
"He means the other way around. He wants to hear what you sound like to you. "
] |
[
"Is obesity as much of an eating issue as we make it out to be, or is metabolism to blame?"
] |
[
false
] |
With my personal experience, I have been able to eat copius amounts of unhealthy foods and been able to maintain a relatively small and fit figure.
|
[
"It is mostly eating. Some suffer from disorders that cause them to put on weight but by far for most it is an overeating/eating poorly issue."
] |
[
"Certainly there are differences between people. Some can eat ten cupcakes and not gain weight and others seem to gain weight from looking at one.",
"That said it comes down to calories in and calories out. Some people may be more efficient (I am...I eat crap all the time and never gain a pound) and others less so.",
"There is a difference between being overweight and obese. Being a few pounds overweight is no big deal. Being obese is a big deal and in the US most obese people are so because they eat like shit, have little control over their food desires and do not exercise."
] |
[
"Certainly there are differences between people. Some can eat ten cupcakes and not gain weight and others seem to gain weight from looking at one.",
"That said it comes down to calories in and calories out. Some people may be more efficient (I am...I eat crap all the time and never gain a pound) and others less so.",
"There is a difference between being overweight and obese. Being a few pounds overweight is no big deal. Being obese is a big deal and in the US most obese people are so because they eat like shit, have little control over their food desires and do not exercise."
] |
[
"Are things in our peripheral vision distorted?"
] |
[
false
] |
I was wondering if there was any impact on our vision due to the curvature of our eyes, similar to how a map is distorted due to the projection of a 3D image on a 2D surface. Am I thinking this out correctly or does the curvature of our eyes contribute to us being able to see in three dimensions?
|
[
"I am by no means a total expert but: -",
"We see in 3 dimensions because of having 2 eyes. There is overlap between the two images each eye records. which is why we can see in 3 dimensions although more accurately it’s depth perception.",
"Secondly your brain does a lot of heavy lifting in terms of the image you see. ",
"But the curvature has a significant impact on clarity of the image,astigmatism is a condition where the cornea is a different shape which can cause an error in light refraction where the image doesn’t hit the correct point in your eye which causes distorted vision."
] |
[
"There is a neat self experiment that you can do to show that your vision is not a flat projective map. I got it from a YouTuber called Carykh.",
"Lie on your back in a smallish room near the center and close to the floor and look up at the corners of the ceiling. Depending on where exactly you are you should see that each corner of the ceiling makes an angle of more than 90° from your persepective. ",
"Intuitively you know the corners are square and your brain will correct a bit for the perspective, but in principle there are three straight lines going into the corner and if you aren't sitting with an offet towards one particular wall all the angles will be roughly equal and thus 120°. In practice you need to be a bit further from the ceiling then the walls to see everything at once so it'll be closer to 100° or something.",
"Now heres the second part. The lines connecting all of the corners should visually appear to be dead straight.",
"There is no shape you can draw on a flat plane, with four corners each greater than 90°, and straight lines connecting the corner. Either the angles must sum to no more than 360° or the lines need to curve. But visually you should see both so you can conclude your vision is not a flat plane. This is a problem because you cannot draw what your eye sees looking up at the cieling on a flat piece of paper.",
"This is before you even consider that you have two eyes and can see depth as well."
] |
[
"Amazing! The question that the OP asked is something that I have been asking myself for years, and I break my head trying to figure it out on my own! This question is difficult to find on the internet and I am happy to see that ",
"u/LockedLemming90",
" asked exactly the question in my head in the form of a question."
] |
[
"Is it possible for the speed of sound in a material to be greater than the speed of light in the material?"
] |
[
false
] | null |
[
"But if thе idеa of \"thе spееd of light in a matеrial\" doеsn't makе sеnsе, how do wе havе еffеcts likе rеfraction and Chеrеnkov radiation whеrе thе bеhavior sееms to dеpеnd on \"thе spееd of light in a matеrial\"? Is it simply that thе apparеnt photon travеl timе is influеntial, or is it scary stuff with thе wavе-particlе naturе of light intеracting with thе matеrial in quеstion?",
"Thanks"
] |
[
"The speed of light in a material should instead be replaced with the propagation of light in a material. I guess I was being facetious as a lot of askscience gets filled with \"speed of light\" discussions. My bad!",
"The wave-particle nature of light is also a little bit of conceptual stumbling block as a photon is not a wave, but the probability of where it is going to be is a wave, when it shows up at a location it is then treated as a particle.",
"Either way before I get too far off the point, when discussing propagation of light through a material you are talking about two things, phase velocity and group velocity. In the case of Cherenkov radiation you have something like an electron going faster than the phase velocity of light in a given material. This sets up a shock like a sonic boom and you get energy radiated. So someone may say the electron is going faster than the speed of light, but that is simply a misnomer. Indeed, the group velocity can exceed c in certain circumstances but in the end nothing is actually breaking the speed of light. Both of these velocities are just descriptions of where the light is going, not a determination of the speed of the light.",
"So yeah there is some scary stuff built right in =)."
] |
[
"The speed of light doesn't change in a material, just the apparent time it takes for a photon to be absorbed and re-emitted through the material. This is a different mechanism than a sound wave, which is a pressure wave. ",
"There isn't really a meaningful comparison here as I could say on the premises laid out the answer is a brick since it transmits sound but not light. If you are talking about the apparent time vs time taken for a pressure wave I would say no."
] |
[
"Reddit, one of my students asked an interesting physics question on string theory and matter decay. I have a physics background (engineer), but am having a hard time answering. Help me out?"
] |
[
false
] |
Below is the question: Is all matter slowly decaying into energy? According to the string theory, everything from matter to electromagnetic waves and forces is composed of the same fundamental building blocks: extremely small strings of energy (either open-ended or closed-ended). It also theorizes that the different properties (spin #, charge, mass, etc.) that arise in the different particles, forces, etc. are supposedly due to the different vibrations and shapes of the individual strings they are composed of. One thing that I’m wondering about is that this implication, that the four fundamental forces are composed of tiny strings of energy, might imply that these forces require some finite “fuel source” from which the energy in the form of forces can be radiated from. In other words, let’s say for example you have two bodies of mass free floating in space that are near each other and at rest. Eventually these bodies will begin to move toward each other due to gravitational attractions, which means they have both gained kinetic energy. So then where did this energy come from? Since energy cannot be created or destroyed, some form of energy had to have converted into kinetic energy to allow each body to have motion, so you could say that the gravitational potential energy was the source of this kinetic energy. But if energy is composed of tangible strings of energy, and the cause of one of the body’s motion is the other body’s presence, then wouldn’t that suggest that each body is radiating these energy strings in the form of gravitons (gravity’s “force-carrying particles”). If this is the case then there must be some source for this energy that is slowly depleting since gravitons are constantly being emitted in all directions. So the question here is what is this source of energy from which gravitons are emitted? Could it possibly be mass? We’ve seen in the case of the atomic bomb that small amounts of matter have the potential to convert into devastating amounts of energy due to Einstein’s equation: E=mc2. So could it be possible that all matter in the universe is slowly decaying into energy in the form of forces (gravity, electromagnetism, SNF, etc.) or other types of energy given off by some particles (photons, gamma radiation, etc.)? This would suggest that given the universe is stable long enough, all matter will eventually decay into pure energy. This also suggests that at an earlier time in the universe, the mass of a proton or a neutron could have been much higher than the mass we measure today. But this hypothesis would not be constricted just to the force of gravity; it implies that the forces of electromagnetism and the strong nuclear force, and the energy of photons and other forms of electromagnetic radiation require a depletion of this “fuel source.” If mass was not this fuel source, then possible there are already deposits of these types of energy strings that are residing inside of particles that are emitted in released in different ways and don’t have an effect on the particle’s mass. But then wouldn’t that suggest that the ability for a particle to have gravitational or electromagnetic effects on surrounding particles is only around until the source of it used up? Now, my first thought is that it's too hypothetical to answer. We don't know what forces cause Newton's Law of Universal Gravitation to hold true. Sure, it could be gravitons, but we don't even know if it exists. And even if it gravitons, they be being emitted by mass, but...again, we really don't know. But, your guys thoughts? Thanks.
|
[
"Energy isn't a substance, it's a quantity. Things don't turn into energy, they have energy."
] |
[
"It wasn't an accusation, it was a suggestion. I'm just saying, if he has the motivation to come on askscience and answer questions, it would help a lot of people if he could fix a blatantly false wikipedia article. Hell, that article probably leads a lot of people to come on here with false assumptions.",
"Seems reasonable. "
] |
[
"Not entirely correct. Photons are gauge bosons and they can be either real or virtual."
] |
[
"Would you be able to trace every living thing's family lineage back to the same singular original source of DNA, or is it not that simple?"
] |
[
false
] |
I understand that the answer to this, by necessity, needs to be theoretical, if not hypothetical. I have a general idea of how evolution went down, but is it really that simple? That it's thought we all originated from a single source? Are there any other viewpoints on the story of evolution that are a bit different?
|
[
"A single common ancestor is at least 10",
" times more probable than multiple ancestors."
] |
[
"Please explain further!"
] |
[
"The link really explains it much better than I ever could, but here's a magazine article that was written about the paper that's a bit more digestible.",
"http://www.wired.com/wiredscience/2010/05/origins-of-life-on-earth/"
] |
[
"Is the act of \"rolling your eyes\" a recent social trait?"
] |
[
false
] | null |
[
"Well, off the top of my head:",
"\"thumbs up\" used to mean \"seal the business transaction,\" and more recently meant \"good job/I approve/things are good,\" and now also means \"I want a ride.\" (and interestingly has been retconned incorrectly as the symbol ancient Romans used to signify that they wanted a gladiator to be allowed to live - we know the thumb was used, but we do not know if it was up, down, sideways, etc). -- of course, this is all western culture stuff - in Iran, it's obscene. And really, it's only USA/Europe western culture stuff. In Australia, while it now means \"good,\" it used to mean \"up yours.\"",
"Of course, hardly anyone realizes that the Vulcan salute from Star Trek is actually a derivative of a Jewish blessing gesture.",
"You might find ",
"A Cultural History of Gesture",
" interesting."
] |
[
"Quite recent, as it happens. It used to mean sexual excitation/flirtation. ",
"Shakespeare's Rape of Lucrece poem has a passage in which the main character is \"rolling his greedy eyeballs in his head\" at the thought of having sex with the woman he's pursuing. ",
"http://www.shakespeareswords.com/The-Rape-of-Lucrece",
" (line 368)"
] |
[
"In the course of human history, Shakespeare is fairly recent and certainly would suggest that eye rolling to express annoyance is not an evolutionary thing. ",
"But if you want a more recent example, in 1950 Hank Penny released a song called \"Bloodshot Eyes\" in which a former lover tries to woo the singer back by rolling her eyes at him:",
"http://lyricsplayground.com/alpha/songs/b/bloodshoteyes.shtml"
] |
[
"If 'warm air is able to hold more moisture' is a myth, how do you then define relative humidity?"
] |
[
false
] |
So I teach high school science. I mostly teach physics, but also teach Earth Science. I've seen it said that the idea that warm air is able to hold more water before becoming saturated is a myth. However, relative humidity is defined as the amount of water held by the air as a percentage of the amount it can hold at a given temperature. Experts please weigh in.
|
[
"The main misconception is the notion that \"air holds water\". It doesn't. The dynamics of evaporation and humidity would be very similar if the air was sucked out and replaced by a vacuum.",
"So what happens?",
"Water molecules in liquid form move around with varying kinetic energies and therefore varying speeds. Some will be slow, others will be faster. The average kinetic energy (speed) of the molecules is what we have defined as the temperature of the liquid. Put more energy into the liquid (by heating it for example) and the average speed of the molecules increases.",
"In the liquid, intermolecular forces generally prevent most molecules from escaping, but the fastest molecules are able to break free from the liquid if they get close to the surface between the liquid and the background medium (gas or vacuum). At this point, these molecules are no longer part of the liquid, but are now existing in the form of water vapour.",
"The molecules in the water vapour also has a wide variety of speeds and if the slower molecules strike the surface of the liquid (or any other sort of surface), they can be caught and transition from the gaseous phase to the liquid phase. Just like in the liquid, the average speed of the molecules in the water vapour depends on the temperature.",
"Now, in a closed room containing some body of liquid water, there'll be a constant exchange of water molecules leaving the liquid as water vapour and molecules of water vapour having too low energy to escape the liquid and becoming part of it. With no ventillation or other outside influence, eventually an equillibrium is reached between these two directions and the amount of water in each phase remains constant.",
"As with any gas, the water vapour in the room exerts a pressure. We use the term \"partial pressure\" to refer to the pressure that a (component of a) gas has if it were the only thing present in a volume. At constant temperature, according to the ideal gas law, this pressure is proportional to the amount of water vapour present. So the partial pressure of the water vapour is a measurement for how much water there is as vapour (per unit of volume).",
"Going back to the previous example of the sealed room: When the exchange between liquid and vapour phase is balanced out, we say that the situation has reached an equillibrium and the the partial pressure of the water vapour in this situation is called the equillibrium vapour pressure.",
"Now, it is hopefully understandable that this equillibrium vapour pressure depends on the temperature of the liquid and of the vapour. With higher temperatures, more molecules in the liquid will have the speed to break free from the liquid and enter the vapour phase and fewer molecules in the vapour will have an energy low enough to be absorbed into the liquid. And vice versa with lower temperatures.",
"So at higher temperatures, the partial pressure of water vapour can be higher. That means that the space can contain more water vapour. This same space is often also occupied by the air, but it is not the air or its properties that determine how much water vapour can hang out in the space.",
"Finally, we come to the relative humidity. The relative humidity is defined as the ratio of the current vapour pressure to the equillibrium vapour pressure. In our previous example of a sealed room, the relative humidty will eventually reach 100%.",
"If the relative humidity is less than 100%, then water in liquid form will evaporate at a higher rate than vapour will condense. If there is some form of ventillation, like in a house, this means that a volume of liquid water will completely evaporate given enough time. ",
"If the relative humidity is above 100%, we speak of supersaturation. The rate of condensation will exceed the rate of evaporation and water will start to condensate. This can happen on small airborne particles, allowing small droplets of water to form, for example like you have in fog.",
"The relative humidity depends on the temperature as well as the absolute amount of water present in vapour form, since the equillibrium vapour pressure depends on the temperature."
] |
[
"It honestly sounds like you are describing the mechanism for why 'warm air holds more water', not proving that statement wrong at all.",
"I think the central point is one of semantics. The air itself isn't holding the water. Rather, higher temperatures allow for a higher partial pressure of gaseous water to exist.",
"Playing with the other parameter (pressure) can also lead to interesting results (and might be something you can play with in your class). In my University days, I was a participant in an experiment that took place inside a Hyperbaric chamber. As part of the experiment, they took us down to 130 feet seawater equivalent (so just over 5 atmospheres). First, on the way down you could feel the compression heating, as you have in a diesel engine. We performed the experiment in a small pool that had been filled with warm water. Afterwards, we went through the protocols of decompression, and as they released the last of the pressure (going from about 2atm to ambient) the chamber clouded up as the water in the air condensed. ",
"In your class, you could probably achieve something similar with a clear vessel of some sort, some water in the bottom of it, and a bicycle pump. Bring the pressure up, let it sit for a while, then release the pressure. The inside should cloud up.",
"Edit: Hit save too early."
] |
[
"It honestly sounds like you are describing the mechanism for why 'warm air holds more water', not proving that statement wrong at all.",
"Well you first have to understand that water vapour isn't ",
". Water vapour exists in the same volume as air. The air itself has less to do with anything than the volume, pressure and temperature do. Air is just a mixture of gases that occupy a volume, and water vapour can certainly be one of these gases. However, the air doesn't hold the gas, the volume does. Saying air holds water is like saying that water vapour isn't a component of air, but then saying that it is when you do calculations. It's confusing and doesn't make sense to think of water vapour in this way.",
"You can see how air doesn't 'hold' water by having two flasks, one with pure water and the other with ocean water. If both flasks have the same temperature, liquid and headspace volume, and pressure, then they should have the same saturation vapour pressure. However this isn't the case because of the salt ions present, which in turn lowers the saturation vapour pressure above the ocean water, despite the exact 'same' air being above both liquids."
] |
[
"Can a shot of adrenaline to your heart (pulp fiction style) buy me a minute of consciousness when I'm bleeding to death?"
] |
[
false
] |
Say I'm a combat medic and I've just sustained multiple gunshot wounds. I know that my wounds are fatal and that I will die. However, I need a minute in order to complete my objective (say push a button that's twenty meters away). So before the darkness clouding around my vision turns into infinite night, I stab my heart with a hypodermic needle of epinephrine. Will this bring me back to consciousness for the minute that I need to complete my objective? Edit: Assume that there are 6 gunshot wounds but no vital organs or major arteries are hit.
|
[
"Assuming that the gunshots didn't hit anything major, I'd say yes.",
"But of course, the answer heavily depends on how many gunshots and where they are."
] |
[
"well, vital organs is vague, everything in your body is an organ..and its all pretty important.",
"But from my understanding a single gunshot is enough to take a limp out of commission, none of that movie shit where the protagonist can walk miles with 5 bullet holes (not to say this can't happen, generally speaking). This means that if one of your legs got shot, I'd be a sitting duck for someone to finish you off. If you got shot in the arm, I doubt you would be able to defend yourself. ",
"My best guess is that any more than 3 shots to your trunk would be enough to stop you from your objective."
] |
[
"Let's assume that there are 6 gunshot wounds but no vital organs or major arteries. "
] |
[
"Why don't we give many antibiotics at once to stop antibiotic resistance?"
] |
[
false
] |
[deleted]
|
[
"I think it is more about people not taking the antibiotics (or medication prescribed) seriously than it is about the bacterium being lucky. If you skip a dosage, you are possibly providing a sub-lethal dose of the antibiotic to the bacterium, giving a chance to the bacterium to develop defense tactics against the antibiotic. There are several other possible ways for the bacterium to gain resistance. On of them is of course random mutation but it is rare. That said, the problem with multiple antibiotics usage is that it is not only the harmful bacterium that we need to worry about. There are several much beneficial bacteria found on and inside our body (in the gastrointestinal tract) and they must survive the antibiotic treatment as they are absolutely necessary for normal functioning of the body. Minimum required medication seems to be our best resort IMO."
] |
[
"Antibiotic resistance is only sometimes due to a rare point mutation. More often it is a general anti-toxic mechnism, for example a pump getting rid of everything that could be potentially poisonous. What is more those mechanisms rarely occur one at a time - a resistant bacterium often carries a few of those.",
"The best antibiotics target things that are essential for and unique to the bacteria (like topoisomerases) to avoid resistance arising from point mutations. There are some compounds that target the more general resistance mechanisms, but I m not sure if they are actually on the market.",
"The problem with using antibiotics is that broad spectrum antibiotics are used for most infections at first and they put selective pressure on bacteria, causing resistance. You usually wouldn't get a narrow spectrum antibiotic that requires identifying the bacteria first unless you land in a hospital with sepsis. Fast and reliable diagnosis and applying narrow spectrum antibiotics would be a solution, but the methods and compounds don't seem to be there yet.",
"One last note: there are very few bacterial species that are resistant to all known antibiotics, so there is no reason to panic yet, but we need more novel antibiotics and ways to use them safer."
] |
[
"You are right saying that resistance is more of our fault than bacteria getting lucky. It was shown that bacteria exposed to sub-lethal doses of antibiotics gain resistance and become fitter, so in the end they are not killed by what is a lethal dose for a control group."
] |
[
"Seeing as it is Ramadan and all right now. I have always been curious are there any medical benefits to fasting?"
] |
[
false
] |
In case you didn't know. Fasting in Islam requires no food or water from sunrise to sunset.
|
[
"Can you explain the detoxing effect? I've heard that detox diets are a hoax."
] |
[
"Can you explain the detoxing effect? I've heard that detox diets are a hoax."
] |
[
"A very knowledgeable chemistry professor gave me this argument when I was an undergrad. I respect this professor, and he was enlightening in many ways, but I do not claim in anyway that the following statements and arguments are backed up by any science.",
"His argument was that when you fast, your body is forced to catabolize its own supply of fats, muscles, etc. Now, many cells in your body accumulate mutations and DNA methylations over the course of a lifetime. My professors argument was that your body, recognizing that it needs to catabolize the body to provide basic life support, would first catabolize the methylated and mutated cells first, leaving the healthy cells to grow and replace the catabolized cells. This was supposedly especially pronounced in muscle catabolism (or at least, his argument was based on muscle catabolism), in which mutated/methylated muscle cells which would not normally be destroyed and replaced would through this process be destroyed and the surrounding muscle cells could grow stronger to replace it.",
"Supposedly, this effect would also come into play if a person were to majorly tax their body in exercise, for example, running a marathon.",
"In other words, you have mutated cells in your body. Fasting kills them.",
"Now, this was a very knowledgable chemistry professor that was very enlightening in many ways, but I do not know if there is any research that substantiates this claim, so take this argument with a grain of salt.",
"If there is any nutritionist or biologist that knows better and can verify or debunk this, I would be grateful as well."
] |
[
"How efficient is chlorophyll in converting sunlight to energy compared to our best solar cells? If it is more efficient, why don't we copy what those cells do in designing new solar cells?"
] |
[
false
] |
Presumably we know how plants convert sunlight to energy, so I was wondering if they do so more efficiently than we do with solar cells. Then I got to wondering that if they do, why we don't have some type of artificial chlorophyll that we could use for solar energy.
|
[
"Presumably we know how plants convert sunlight to energy,",
"Plants convert solar energy into chemical energy with an efficiency around 3-6% depending on the species and other environment factors. Generally, our problem is that this chemical energy is not readily useful to us unless we first convert it into thermal energy (by burning it).",
"Solar photo-voltaic cells convert solar energy into electric energy with efficiency ranging from 6-45%. The high end of that scale are from experimental designs and may not be mass producible or cost effective. Solar cells in the 15-18% efficiency range are easily acquired on the market.",
"Solar thermal systems convert solar energy into steam which is then converted into electricity (typically with a steam turbine). A steam turbine in such a system is ~40% efficient but higher system efficiency can be achieved with multi-stage turbines. Environment factors like dust and mirror damage (which is used to focus solar energy) will reduce overall efficiency."
] |
[
"A problem here is that you're conflating two different processes. Simplistically, what is happening in the case of a solar cell is:",
"1) Photon hits optically active (in IR/visible/UV range) inorganic chemical compound leading to atomic/molecular excitation",
"2) Eventually this excitation leads to the liberation of an electron",
"Up to this point, plants are undoubtedly more efficient in harnessing solar energy. In photovoltaic cells, this liberated electron will then lose energy in such a manner as to generate a current. In photosynthetic systems, there is a third step:",
"3) The energy in the electron must be utilized towards the formation of glucose",
"Why do biological systems have this extra step? Because it is the chemical storage that enables organisms to access this energy when sunlight is no longer available. If we were to calculate the efficiency at this point, it would appear that photovoltaic cells are more efficient (see energy_engineer's comment).",
"So, can we mimic biology in the first two processes (as those seem to be what are relevant in photovoltaic cells)? It's not easy. It turns out that biology uses all sorts of quantum mechanical trickery (see pioneering work from the Fleming group at UC Berkeley, the Scholes group at U Toronto, and the Engel group at U Chicago) to make these processes as efficient as possible. This is at odds with the conventional understanding of quantum mechanics as in such a noisy environment, quantum features should quickly lose relevant, giving way to classical behavior. It turns out, however, that classical behavior fails to account for the efficiency of energy conversion.",
"At this stage, our understanding of how plants efficiently transfer energy from its initial capture to electron liberation is sufficiently inadequate such that trying to repurpose and engineer it would appear to not be feasable "
] |
[
"The most amazing part about chlorophyll - it's an organometallic complex nature came up with all on it's own! And it's easily reproducible by cells! Thousands of tons are produced every day. If only it were that easy for us to make solar cells. ",
"Plants can also bind carbon dioxide (albeit in a different process which does not use chlorophyll). Which is a feat that is ",
" for us to do repeatedly (even with current technology the best we have are chemical scrubbers and solid oxide fuel cells). ",
"So efficiency-wise, we can do much better than plants, but if we are talking about % of earth's surface used to gather energy- we are WAY behind. ",
"Plants cover 30% of the Earth's surface",
" and phytoplankton cover a large part of the world's oceans. Could we ever hope to achieve that kind of coverage with solar cells? Maybe. But not with current designs. ",
"The whole allure of chlorophyll is not its efficiency - it's the self-replicating nature of the material. "
] |
[
"Sun's rays question"
] |
[
false
] |
Well we all know the harmful effecrs of our own Sun's rays. (Ie. Radiation.) There are trillions of stars out there, a lot being bigger than our own. Do these stars have the same effect as ours on earth? Do they also create radiation for earth or are they too far to contribute anything other than the very distant light?
|
[
"Their radiation also hits us, but its nowhere near the magnitude of what we receive from the sun."
] |
[
"Not much. Look at how small and dim stars are. Whereas if you look at the sun, you could go blind. That shows just how much more intense the radiation from the sun is compared to stars. Light from other stars is minuscule at best."
] |
[
"I'd like to also ask, do these distant stars also contribute to say solar energy?"
] |
[
"What's going on with all of those sub-atomic particles?"
] |
[
false
] |
[deleted]
|
[
"I'll give you a bit of an overview.",
"The fundamental particles we know about are divided into two types: Fermions and bosons. Loosely speaking, fermions represent matter particles and bosons come from the forces between the fermions.",
"The bosons are:\n(Electroweak bosons):",
"W boson",
"Z boson",
"Photon (this particle is responsible for electricity and magnetism)",
"(Strong force boson):",
"Gluon",
"And the theorized Higgs Boson. This particle has been believed to exist for many decades, but not yet found. Hopefully (and most particle physicists likely) something fulfilling this role will be found at the LHC- the large hadron collider.",
"It is also expected there will be some kind of particle which mediates gravity, and this is usually referred to as the graviton. However, there is currently no completely satisfactory theory of quantum gravity, much less any experimental evidence about the subject.",
"Fermions are subdivided two ways. First off, there are three generations of fermions. Each generation appears more or less identical to the previous, except the particles have higher mass.\nSecondly, there are quarks and leptons in each generation.\nQuarks are subject to the strong force and the electroweak force, while leptons are only subject to the electroweak force.",
"The first generation of quarks is the up quark and the down quark.\nThe first generation of leptons is the electron and the electron neutrino.",
"The second generation of quarks is the charm quark and the strange quark.\nThe second generation of leptons is the muon and the muon neutrino.",
"The third generation of quarks is the top quark and the bottom quark.\nThe third generation of leptons is the tau lepton or tauon and the tau neutrino.",
"In addition to all these particles, there are anti-particles which have the same mass, but opposite charges.",
"Neutrinos are particles which only interact through the weak force (as far as we know), and hence are very difficult to detect. In fact, millions of neutrinos stream out of the sun and straight through the earth all the time without interacting with anything on the way through. ",
"Under ordinary conditions, the strong force binds quarks together very tightly, and hence they are not observed as individual particles. Rather, they are seen in clumps of usually two or three. A clump of two quarks is called a meson, and always consists of a quark and an anti-quark. A clump of three quarks is called a baryon. There are many kinds of mesons and baryons which have different properties based on which quarks make them up. The most common two baryons are the proton and the neutron. The proton is made of two up quarks and a down quark, and the neutron is made of one up quark and two down quarks.",
"A large part of the reason that ordinary matter consists of mostly electrons, protons, and neutrons is that heavy particles can decay into two or more lighter particles. Muons, for example, are often created when a cosmic ray strikes the earth's atmosphere- however, a muon at rest will decay very quickly (in about a microsecond) to an electron and two neutrinos.",
"In fact, even the neutron is unstable when it is not bound in a nucleus- the free neutron has a lifetime of around 15 minutes. (It decays into a proton, an electron, and a neutrino)",
"Standard model at wikipedia"
] |
[
"You are mixing apples and oranges. :) Some of those are particles, some are groups of particles.",
"To explain 99% of the universe, all you need is protons, neutrons, and electrons (plus photons). Everything else is detail and special cases.",
"But, the ones that you mentioned:",
"In fact, outside of protons, neutrons, and electrons, there are very few particles that live more than a few milliseconds."
] |
[
"There are six kinds of quark: top, bottom, strange, charm, top, bottom. Before they realized that a lot of particles are made out of quarks, they thought each new particle they discovered was a new fundamental one. Protons are made of three (up up down) as are neutrons (up down down). Strange and charm are way bigger than up and down, top and bottom even bigger.",
"A meson is made of two quarks, while a baryon is made of three. A certain kind of meson called the Pi meson is responsible for holding protons and neutrons together in a nucleus.",
"Electrons are electrons. A muon is like a bigger electron, and a tau is an even bigger one. These are called leptons (because they're light).",
"Each of the leptons has a neutrino that goes along with it. During weak interactions (including nuclear beta decay), a lepton and its corresponding neutrino (actually, one is an antiparticle) are released.",
"Then there are the W and Z bosons, which I like to think of as tennis balls that change whatever they hit. These carry the weak force.",
"Gluons carry the strong force, which I think of as springs holding quarks together. This may not be the proper way to think about it.",
"Photons are just quanta of electromagnetic radiation (you can think about them as carrying the electromagnetic force, but that's more complicated).",
"That should cover it."
] |
[
"Why are there spiral galaxies?"
] |
[
false
] |
Shouldn't they all be elliptical because objects orbiting closer to the center of the galaxy move faster and pass up the stars on the end of an arm.
|
[
"Most galaxies are formed as disks out of massive gas clouds. These gas clouds have some angular momentum (asking why they are endowed with some spin is a whole other question, one that is be happy to answer...). As the gas cools through a process called \"atomic line cooling\", the gas generally doesn't want to lose that angular momentum, even though it's being sucked in by gravity. As a result the spinning gas cloud ends up getting flatter. This flattening is a bit of a runaway process as it causes more gravitational pull towards the disk compared with towards the center. As the gas cools more and more the galaxy ends up as a rotating disc. ",
"The spiral arms (and sometimes a bar in the middle) form as a second step due to small density perturbations in the disk. The spiral arms are actually a density wave in the disk. Consider a highway with one lane in each direction. Now imagine a slowly moving truck on one lane (our density perturbation). Cars behind it will get stuck as they need to wait to over take it. As a result you get a higher density of cars behind the truck compared with ahead of it. That's basically what a spiral arm is - a build of stars and gas clouds trying to overtake a transient gravitational sink - and also incidentally why you have stars forming in the spiral arm. The increased density compresses galactic gas causing them to spawn stars. "
] |
[
"Yes they certainly will reconfigure. The stars in the galaxy are also bobbing up and down and bobbing inwards and outwards. Additionally the galaxy will suck in more material and grow; the addition of more material will also change the pattern speed and size of the spiral arms. "
] |
[
"The thickness (known as the scale height) of a disk Galaxy is a continuum from the thinnest flattest ones to fat ellipsoidal things that don't look much like disks at all. For the Milky Way we recently discovered that there are two disks superimposed if you divide the stars by age: a thin (young star) disk and a thicker one made of older Stars. Most states are in the thin disk though. So the full disk of the Milky Way is not so straight forward and a little complicated. But to put numbers on it, the thin disk is about 1000light years thick and the thick disk is about 3000 light years thick. The diameter of the Galaxy is around 100,000 light years. So the thickness to length is 1 to 100 about the same as a vinyl record. "
] |
[
"space radiation"
] |
[
false
] |
What kinds of advances have been made in absorbing space radiation in spacecraft and spacesuits? My understanding is that carbon is super useful for that. Does carbon fiber absorb radiation? How does this work?
|
[
"I'm not sure about what is done to prevent radiation harm to astronauts, but I design the electronics that go into spacecraft and all of the parts we use were designed to be radiation hardened, both in terms of architecture and fabrication. Everything undergoes rigorous analysis to show that the upset rates and latchup thresholds don't exceed the requirements for whatever radiation environment we will be facing. Some of the preventative measures include voting registers, parity bits, and resetting things on periodic signals."
] |
[
"how do you radiation harden your stuff? what's the material used?"
] |
[
"There is actually a good summary on the wikipedia page that says it better than I can: ",
"http://en.wikipedia.org/wiki/Radiation_hardening"
] |
[
"Can a moon have its own moon, or does the gravitational pull from the planet override the moons?"
] |
[
false
] |
title says it all.
|
[
"Sure. After all, the planets in the solar system all orbit the sun, but many of them have moons orbiting them without the gravity from the sun messing everything up. No reason you couldn't go another layer down and have something orbiting a moon."
] |
[
"Hasn't been observed yet, but not out of the realm of possibilities. If you think about it, the earth is one of the suns moons, saying that the sun is a moon of the galactic core might be a stretch though. ",
"First result on google search of \"moon of a moon\", says it better than I could."
] |
[
"Wikipedia's page on natural satellite",
" discusses this -- not yet observed, possible though unlikely, and maybe soon-to-be observed.",
"Also, further into the article is a short discussion on what natural satellites count as \"moons\", etc. "
] |
[
"How would you find the theoretical temperature of a system?"
] |
[
false
] | null |
[
"You can using thermodynamics and calorimetry, but some of the details are not straight-forward (at least to some). I would approach the problem like this in a mathematical sense:",
"-q(room air) = q(N2) + dHvap(N2) + dH(N2 for -200(deg)C to -195.8(deg)C)",
"This assumes energy is conserved and stays in the room, so all the energy from the air goes to heating the liquid nitrogen, hence the '-' on the left hand side (lost energy) that the right hand side gains.",
"where q = mC(Tf-Ti), you would solve for the equilibrium temperature, Tf as they would be the same for both terms of q.",
"Just a heads up though, the statement \"so the room is now 99 cubic meters air and 1 cubic meter liquid nitrogen\" misleading and also not needed to solve this kind of problem, as in the end, both the air and N2 will mix, as the temperature will most certainly be above the boiling point of N2.",
"Also note, there are several assumptions that are being made that would not be true of a real room as well. For example, no heat lost outside this system, and the room is sealed so no matter leaves the room. Another assumption I'm making is that you have some understanding in thermodynamics to work out the above equation. If not, I'll be happy to elaborate."
] |
[
"Alright I know this was a month ago, but I'm curios to see if there's a realistic way to find a theoretical temperature of the ",
"Nether",
" Using thermochem and calorimetry"
] |
[
"This is an interesting questions, considering I've played more Minecraft than I care to admit over the past few years. I'll give it some thought over the next little while and get back to you with what I come up with :)"
] |
[
"why does noise get quieter when we yawn?"
] |
[
false
] |
[deleted]
|
[
"Yawning activates a small muscle called the tensor tympani. This muscle is connected to your ear drum and increases the tension on it. With increased tension, the ear drum is less mobile and therefore less responsive to vibrations (sound). The end result being that sounds are perceived as dampened. Some people can activate this muscle at will, and they have found a home over at ",
"r/earrumblersassemble"
] |
[
"I didn’t know ear rumbling isn’t something everyone can do. Not that it matters.",
"edit: ear, duh"
] |
[
"Not me purposefully ear rumbling to test if it dampens sound and then realizing that not everyone could do that..."
] |
[
"Can animals be afraid of an item which represents a predator they have no point of reference for?"
] |
[
false
] |
[deleted]
|
[
"Trauma and fear have been demonstrated to be heritable. That whole archaic nature vs nurture division is looking rather blurry considering this, and epigenetics. ",
"https://www.washingtonpost.com/national/health-science/study-finds-that-fear-can-travel-quickly-through-generations-of-mice-dna/2013/12/07/94dc97f2-5e8e-11e3-bc56-c6ca94801fac_story.html?utm_term=.b0700c4043b4&noredirect=on"
] |
[
"I was a chicken farmer for a long time for Sanderson farms. Chickens raised in chicken houses are scared of flashlights because it produces a shadow that makes them think it's a hawk.. they will run away and pile up on each other.. sometimes suffocating one another... these chickens were hatched inside and raised inside. Never seen another type of animal besides other chickens their entire lives"
] |
[
"I’m not so sure the reason that the cats were afraid of the cucumbers was because they thought that it they were snakes but because it was something large that was not there a moment ago I think that the cucumber can be replaced with any item of equal size and the reaction would be the same. "
] |
[
"Were plants larger or smaller on earth two hundred million years ago as compared to today?"
] |
[
false
] |
I've heard a lot about how dinosaurs where able to grow very large due to the high oxygen levels at the time, did this mean that prehistoric plants were smaller back then from the lack of carbon dioxide? And how would the extinction event impact plant sizes?
|
[
"Just to correct a misconception: we do not have evidence that dinosaurs were larger because of higher oxygen levels. We have a ",
"number of posts in our FAQ",
" about this that go into details."
] |
[
"Excellent, then you're doing science right! I can try to answer them later today. I'm not an expert on fossil plants, unfortunately. I know we have some invertebrate paleontologists, and while inverts are also not plants, they may have a better baseline of knowledge on this subject than I.",
"Edit: I'd start with approaching things in the context of the geologic time scale. Check out plant evolution through time, because I think some of your questions will be cleared up by sorting out a sequence of events."
] |
[
"Thank you for the correction, but now I have even more questions."
] |
[
"When two protons collide and break apart, what force is actually causing them to break apart?"
] |
[
false
] |
So one of the shocking things I remember learning physics, is that solid matter never actually collides or touches. The electromagnetic force actually repels molecules from actually touching each other. So when one thing collides into another, its actually the electromagnetic force that rips it apart. But this got me thinking, about what's going on in a particle accelerator. The analogy we get is that two protons are smashed together. But what is actually happening? Is it the strong force, weak force? What is causing the protons to break apart?
|
[
"In a particle accelerator, we're giving these protons enough energy to get close enough together that their constituent particles (quarks and gluons) can interact via the strong and weak forces, which have very short ranges.",
"That being said, the EM force also plays a role in that.",
"When they interact, they produce new particles with momenta that make them careen in various directions away from the impact. "
] |
[
"Well, at this level, we don't even really think about binding energies or changes in mass anymore. You'll likely get a giant spray of particles coming out of the collision, not a couple discrete products, so thinking about things in those terms isn't that useful to us (while it is very useful for, say, nuclear physicists who operate at lower energies).",
"For example, we often produce things like W and Z bosons which are about 90 times heavier than a proton. We can do this because we've accelerated the protons to such high speeds, which gives the protons the energy to form heavier particles at the collision. These eventually decay into lighter particles, but talking about things in terms of mass changes and binding energies doesn't really capture what's going on.",
"Also, if you see a quark or a gluon zipping away from the collision, the peculiarities of the strong force will cause them to produce a huge jet of particles (mostly more quarks and gluons). It is this jet that we detect. We can't tease out individual particles from this huge spray."
] |
[
"Glukkake FTW.",
"But in all seriousness... Aren't even the various \"forces\" just shorthand for the weirdnesses of particle interaction? As I understand it, we represent the \"force carriers\" with so-called \"virtual particles\", basically meaning that \"It's ",
" a particle, just not\", and that it's only for modeling purposes because it's convenient to represent them as such.",
"So. Would it be accurate to think of the various forces that the particles exert simply as an extension of the properties of particles themselves, as opposed to an effect they have on some underlying, all-permeating field that they distort? Or does it really matter?"
] |
[
"Does Buoyancy Exist?"
] |
[
false
] | null |
[
"Your observations are astute. \"Buoyant force\" is indeed a fictitious force used to describe the difference in apparent weight of an object immersed in fluid. It does not exist without gravity. As for your second question about gases and surface tension, the answer is no."
] |
[
"Buoyant force is as real as centrifugal force! :)"
] |
[
"Just to add something to the discussion, here is a video about air bubbles in water in space! ",
"http://www.youtube.com/watch?v=cXsvy2tBJlU",
"The surface tension of the water keeps the bubble inside."
] |
[
"How are chip manufacturers getting around quantum tunneling in the manufacturing of smaller than 7nm sized chips?"
] |
[
false
] |
So we all know that quantum tunneling was going to be an issue down at the smallest transistor size levels, where 7nm was claimed to be the absolute limit. But now I'm seeing 7nm processes everywhere in my phone, in the CPU I'm using in my machine, and from what I'm reading Samsung and TSMC have manufactured 5nm process chips and are planning manufacturing of 3nm chips (the next size down). How are they getting around QT and how does this affect what is seen on screen?
|
[
"They're not getting around it. But also, they kind of are.",
"First though, \"5nm\", \"3nm\" and so on are just marketing names. There is nothing about \"5nm\" that makes it \"5nm\" other than the company in question saying it is. Some things are smaller than 5nm on a given 5nm node, and some are larger. I cannot recall exactly what node this started to be the case (there used to be an actual definition, one for DRAM, one for logic), but it was in the past two decades and got particularly ridiculous beginning around \"28nm\" up to now. ",
"The really concerning physical dimension for quantum tunneling to occur/not occur is \"gate length,\" and that's been basically sitting around ~16nm (",
"), plus or minus a few nanometers (depending on the manufacturer and process in question), since about \"45nm\" (mid-late 2000s). So that one critical dimension isn't getting smaller. And there isn't much they can do about it right now. ",
"They are still shrinking other dimensions though, and things don't work like they used to. Powered off transistors aren't really off, and leak power.",
"The workaround for this is that they just use bigger transistors in certain places for what's called \"power gating\". You get the benefits of having tons of small transistors, with a slight area penalty. ",
"In addition to power gating, they have made substantial improvements to the design of the transistors themselves. Gates now wrap around the channel on 3 sides, creating a device known as a Finfet. Silicon dioxide is no longer used as an insulator to the same extent -- hafnium dioxide preforms much better as an insulator. Gates are now metal instead of polysilicon. And there's an assortment of other changes that have occurred or are on the way. So performance has actually managed to improve somewhat, and things have still gotten smaller. The end is near... but not quite yet.",
"Gate length is not going to budge much unless some miracle occurs, though."
] |
[
"Well someone can explain this better but the names hardly refer to any feature size and hasn’t for awhile. They used to refer to the pitch or how I understand the space between two logic gates. Intels pitch was 70nm for 14nm and tsmc pitch was 80nm at 14nm.",
"Even then, they do face quantum tunneling and to fight that there’s more complex doping of the wafer to act as better barriers. I believe they have hit a pretty hard limit on actual gate width on FET designed transistor. Samsung had claimed at one point to be switching to a gate all around design to shrink further but not sure where that stands now."
] |
[
"The main leakage path for quantum tunneling is through the very thin layer of insulator separating the transistor channel and the gate contact (see ",
"this video",
" for a discussion of a lot of these issues). The insulating material we use for this was silicon dioxide because it was very easy to grow on a silicon wafer (it's basically just rusted silicon so you just apply heat in an oxygen rich environment). However, silicon dioxide is actually not a very GOOD insulator and thus this layer had to be very, very thin to allow the \"field effect\" to be felt in the channel for moderate voltages applied at the gate. This lead to increasing quantum tunneling through the insulator as it got thinner and thinner.",
"The solution to this has been to not use silicon dioxide but rather the much better insulator hafnium oxide. This allows the same \"field effect\" to be induced for the same applied voltage but with a thicker insulator layer (and thus less tunneling).",
"The second dominant leakage path is the quantum tunneling of electron in the source to the drain bypassing the channel (again see the video). The thinner the channel gets the more tunneling leakage there will be. This has been \"solved\" both by making ther barrier higher by moving to a \"fin\" structure and by not shrinking things anymore and instead allowing these \"node numbers\" to be largely meaningless marketing speak. So the \"solution\" has basically been to lie about how much you're actually shrinking things."
] |
[
"How does the security on a phone compare to the security on a computer, assuming both are using top-level technologies?"
] |
[
false
] | null |
[
"You know, I'm pretty close to just unsubscribing because of the mod team. Let people ask their questions, and leave the \"vagueness\" up to the reader. Stop filtering good questions. "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Your question does not refer to a single measurable quantity, as you seem to think security is, nor a use case, scenario, or threat model. It's not possible to answer such a query without either addressing all of them or making assumptions about what you wanted to ask, which is in both cases counterproductive and against our guidelines.",
"Please conduct some background research, narrow down your question and resubmit.",
"Thanks."
] |
[
"Looking for a citation web visualization tool (or something)"
] |
[
false
] |
So, let's say I have a bunch of articles, and I want to see how they interconnect, specifically what cites what. Is there some tool where I can plug in my citations, and it will look up the article on google scholar or some such, and make a web showing which articles cite what? Bonus points for showing relative distances in time. If all else fails, I'll use something like , but I'd like something specialized if it exists. Google has not been helpful; I'm not sure what to type in the search.
|
[
"One of my colleagues is working on creating an expert recommender system on a problem similar to this. He's working on creating a system that, given a set of articles, finds ",
" additional articles that are relevant and interesting to the articles provided, based currently on the citation network.",
"Based on the problems he was having finding good citation information (what, ",
", makes one citation equivalent to another?) and interacting with various citation databases, I'd wager that such a tool doesn't exist.",
"That's not to say you couldn't kludge something together. I just don't believe any tool of any great quality exists.",
"However, I would absolutely ",
" to be proven wrong, and I'm sure my colleague would enjoy someone proving me wrong.",
" I forgot to try to give advice on what to try to search for. The terms \"network\", \"graph\", and \"web\" would be relevant, since you are trying to extract a subset of the citation network. You could try additional terms similar to those. The words \"reference\", \"citation\", \"literature\", or something like that would probably be good. Additionally, the terms \"semantic\" or \"social computing\" ",
" show up since this sort of tool-building problem would probably fall into the computer science field of social computing.",
"Best of luck! And please tell me when you show me wrong, because I can't wait."
] |
[
"Cool, I will try those; but as for the semantic recommendation thing, I don't think I need anything as elaborate as that; really, I'm just looking for a good way to organize the articles I already have. I have a bunch loaded into Zotero, but keeping track of what cites what gets difficult once you hit 30 articles and counting.",
"Good luck with the recommendation service, though; it does sound like a cool idea!"
] |
[
"On a practical level, you could try manually tagging articles with the articles they cite. For instance, if you have an citation like the following:",
"[1] H. Benko, \"Beyond flat surface computing: challenges of depth-aware and curved interfaces\", ",
", 2009.",
"You could decide to give a tag to citing articles such as ",
". Then you could also tag the article, and that should make it easier to navigate your citation network. This doesn't help with the hideously monotonous task of adding these tags, but ideas are free, right?"
] |
[
"Is there any correlation between skin colour and body heat (and heat retention)?"
] |
[
false
] |
I'm convinced that there is! My girlfriend was born in England. She gets cold much quicker than I do and finds it hard to retain body heat. I on the other hand have a middle eastern background and am warm skinned most of the time (and don't get cold as easily as she does), I'm olive skinned and she is white skinned. Note: We currently live in Australia and have been for the majority of our lives. I know body hair comes into it, I guess genetically some ethnic groups are hairer than others (generally white skinned = not much hair). What other factors determine body heat retention (if any)?
|
[
"Early humans in the tropics probably developed dark skin to block out the sun and protect their body's folate reserves, which decreases with increased UV exposure. Early humans further from the equator probably developed fair skin to drink in the UV rays in order to make enough vitamin D to survive. As far as heat retention goes, it has to do more with surface area of the skin...as mass decreases, the relative surface area of the skin increases proportionately= less heat retention and more heat loss. The rest has to do with hair, sweat glands, and vasoconstriction"
] |
[
"The issue of skin surface area is related to body proportions, right?I read somewhere that people from warm climates tend to be more limb-y and less torso-y."
] |
[
"yep.. eskimos short and stocky, africans tall and lanky"
] |
[
"Why does my glass of water get a bunch of bubbles clinging to the glass after I leave it out for a few days?"
] |
[
false
] | null |
[
"It doesn't have to be days, 3-4 hours can be enough.\nMy understanding is the colder water from the faucet contains an amout of oxygen which comes out of solution as the temperature rises to room temp.\nGuess it could be tested with a bottle of tap water placed in a fridge."
] |
[
"Generally it is the gasses of the environment disolving in the water (see below). It can also be some of the hydrogen or oxygen coming out of solution due to an unbalanced state (equilibruim-wise).",
"Atmospheric gases such as nitrogen and oxygen can dissolve in water. The amount of gas dissolved depends on the temperature of the water and the atmospheric pressure at the air/water interface. Colder water and higher pressure allow more gas to dissolve; conversely, warmer water and lower pressure allow less gas to dissolve.",
"Source:",
"Scientific American"
] |
[
"That could be true, but most of the time it is not. I'm fairly certain to produce the amount of bubbles seen in the glass, your cultures would need to be visable to the human eye. <--100% assumption based"
] |
[
"Is it possible with unlimited fuel to reach the speed of light in space? Or is there a maximum speed that can be reached?"
] |
[
false
] | null |
[
"You can asymptotically approach c, but never reach it. With unlimited fuel, you can travel at 99.9999999999999999999% of c, but you’ll never reach c itself. You’ll also move into the realm of insane time dilation, so by the time you get back to Earth the Sun will probably have long since burned out. "
] |
[
"No massive object can travel at the speed of light. In principle, with enough fuel, any speed less than ",
" (with respect to Earth) is attainable."
] |
[
"You're already travelling close to c relative to a cosmic ray anyway. Speeds mean very little without frames of reference."
] |
[
"If a supernova from a star was racing toward us, would we know before it hit us?"
] |
[
false
] | null |
[
"Sun won't go supernova, it'll turn into a red giant, expel its atmosphere as a planetary nebula, and a white dwarf will remain."
] |
[
"It depends on the type of supernova. A type II supernova releases a burst of neutrinos a few hours before the light leaves the explosion so if you have a neutrino detector you would be alerted a few hours before you see the light from the supernova. In fact, there's a website that will send you an email if such a burst of neutrinos is detected."
] |
[
"Ah right, I'm sure I knew this.. Should really try finishing a thought before trying to be a 'smart-ass'. Going back to my hole now!"
] |
[
"How to generate electricity from scratch?"
] |
[
false
] |
Assume I wake up in pre-industrial civilization with only my clothes and everything I've got on myself. Past sucks, so I want to rebuild modern society as soon as possible. Unfortunately I'm just regular guy, I hardly know how any of the technology I use works, I could give locals some good ideas, but nothing radical. Luckily I have a smartphone/laptop with full wikipedia dump on it, possibly other technical information also. Alas batteries are far behind from other technology and I cant memorize everything important in just a couple hours. So I would need to do something to produce electricity to charge that device. How do I go about producing just enough electricity to charge that device, with no industry to support it?
|
[
"The most important thing to know is to be familiar with ",
"Lenz's law",
": The changing magnetic flux through a loop of wire is proportional to the amount of \"voltage\" produced in the wire. So you get yourself a coil of wire and a magnet, and maybe a water wheel, and you've got yourself a generator. Of course, the wire and magnet are non-trivial problems. Maybe someone here knows how to make a strong magnet on the cheap?",
"(Also there are other sources like DC batteries, but they generally require a society that has some basic chemical engineering in place)"
] |
[
"Yeah If I find myself dropped back into pre-industrial Hawaii.... I think I'm going to just let it be and enjoy myself."
] |
[
"You could also ",
"build a homemade solar cell"
] |
[
"Why does rain fall in drops and not as one mass of water?"
] |
[
false
] |
[deleted]
|
[
"Three main reasons:",
"1) Once a droplet reaches a certain size it starts falling, so there's limited time for a droplet to grow and merge with other droplets. There are some environmental properties which cause droplets to vary in size, but they can't grow indefinitely.",
"2) The water is spread across a large area. There is no mechanism to collect all the water into a small area.",
"3) If you dropped a large blob of water it won't stay as one blob, since it is dispersed by interacting with the air. The water in very tall waterfalls turns into very fine spray before it reaches the ground. Water from clouds would have even more time to get broken up."
] |
[
"When invisible water vapor condenses on particles of dust, it becomes visible as a cloud. When enough water vapor has condensed on a given particle to make it too heavy to float in the air, it will fall as a rain drop. Because these drops are formed individually, they act individually as rain drops."
] |
[
"This could also be related to Plateau-Rayleigh instability. The premise if that small perturbations are always present, and that the faster growing perturbations eventually cause the liquid to break apart in some situations.",
"http://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability"
] |
[
"What commodities are we going to run out of in the next x decades? What alternatives exist for these?"
] |
[
false
] | null |
[
"I am looking for research based answers from research based people in their respective fields.",
"How is this not relevant?"
] |
[
"To be fair, this is a very specific question. Finite commodities. Nothing complex. ",
"I want to maximise the best chances at getting good answer. Please reconsider letting my question through. Suppressing questions doesn't help anyone, especially when they are good ones like mine. This question has never been brought up before here, I searched first."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"How can we measure the universe's age in years?"
] |
[
false
] |
If years are a measurement of earth's revolution around the sun, and we (I guess "we" here can be extended to complex life) have only been "aware" of time for ~2 billion years (taking half the , how can we possibly measure the age of the universe in the same way that we measure earth time? For that matter, since we humans have only been around for ~100,000 years (and have only been doing science for what? 10,000 tops?), how do we know "time" acted the same in the first 5 billion years as it did in the previous 8? Doesn't our 100,000 year window seem like an extremely small sample size given the 13.7 billion "years" before? (In Krauss' A Universe from Nothing, he mentions that time acted almost as a large spacial dimension for a short period of time after the Big Bang, but I can't remember if that lasted all the way through the first 300,000 year "plasma" phase of the universe)
|
[
"If years are a measurement of earth's revolution around the sun, and we (I guess \"we\" here can be extended to complex life) have only been \"aware\" of time for ~2 billion years (taking half the , how can we possibly measure the age of the universe in the same way that we measure earth time?",
"A year can also be broken down into 3.15569e7 seconds, which are not dependent upon the earth at all. ",
"Nothing prevents you from extrapolating this backwards beyond the formation of the earth. ",
"We simply describe the age of things in earth years because it is convenient for us to grasp/understand, rather than saying the universe is 4.1024e17 seconds old, which tells me very little.",
"To understand what 4.1024e17 means, I'd probably have to put it in terms of something more familiar... Like years."
] |
[
"For any observer who is at rest relative to the cosmic microwave background, the age of the universe will appear the same. And no, time is not altered by the density of the universe, since gravitational time dilation happens from the ",
" of spacetime rather than merely the density. So it's more about how uneven the distribution of matter is than about how dense it is."
] |
[
"When we say \"rest frame of the CMB,\" we mean a frame in which it looks as isotropic as possible. If you just look at it standing on Earth, you'll get a large extraneous asymmetric Doppler shift signal due to the motion and rotation of the Earth, Sun, and Milky Way relative to this frame. The CMB maps you see from WMAP and Planck have all that stuff subtracted off, along with foreground Milky Way and extragalactic emission."
] |
[
"How did eukaryotes evolve?"
] |
[
false
] |
Or at least, what are the prevailing hypotheses?
|
[
"The ",
"endosymbiont theory",
" is the one that gets the most traction, and is probably correct. ",
"Basically, some early prokaryote took on a parasitic lifestyle; living inside and off of another, larger prokaryote. Over time, this developed in to a symbiotic relationship, the former parasite not just living off the host but also benefiting the host in some way. Over time, this became an obligate lifestyle; the host gradually became dependent on the symbiont and vice-versa."
] |
[
"On a related note, the ",
"Hatena arenicola",
" is an example of how chloroplasts probably evolved in eukaryotes through endosymbiosis. Hatena actually starts out as a heterotroph and eventually injests an algae cell but instead of completely breaking down the algae cell, Hatena retains the chloroplast organelle to produce its own energy through photosynthesis living the rest of its life as an autotroph."
] |
[
"Awesome, thank you. "
] |
[
"Does water evaporate faster if it is mixed with alcohol?"
] |
[
false
] |
Title is pretty self-explanatory. Was wondering if a mixture of alcohol and water were to evaporate (I am aware that the alcohol will evaporate much faster), but would this have any effect on the evaporation rate of the water itself as well? Reason is because I made a cheesecake and accidentally got the crust soggy. I flipped it upside down and put it back in the oven to try to evaporate as much moisture as possible. Had the idea of putting some everclear in a spray bottle and misting it down a bit to speed up evaporation. Would this hypothetically work? Thanks fellow scientists, I love you all :)
|
[
"Alcohol-water mixtures do evaporate faster than pure water. That said, spraying alcohol on food will likely cause other problems -- for example, the alcohol may partially dissolve some oils or fats and change the texture of the food."
] |
[
"Technically, yes. This is done all the time, especially when cleaning things with small crevices, such as toys or electronics. ",
"However. ",
"Everclear also has other things in it, such as sugar. I know nothing about baking and I have no idea what kind of side effects you might have. ",
"But yes, alcohol will mix with water and help it evaporate quicker."
] |
[
"Thanks for the reply man, you've confirmed my intuition. It did end up turning out just fine by the way, no alcohol needed"
] |
[
"What did Carl Sagan mean when he said, \"If you wish to make an apple pie from scratch you must first invent the universe\"?"
] |
[
false
] | null |
[
"In any creation project, you have to get something from someone else. A pie needs flour. If you want to make your own flour, you'll need wheat, and milling equipment. To get that, you'll need farms and metal, which needs soil and minerals. To truly say you made it, you'd have to make the dirt and minerals. To make iron you'll need a star to form iron out of lighter elements. And to make a star... all the way back to the big bang."
] |
[
"I understand it as a particular perspective on what \"from scratch\" means. Sort of a reductio ad absurdum, but it's less of an argument and more of an observation. Basically, if you take \"from scratch\" to enough of an extreme you can take it all the way back to the Big Bang. "
] |
[
"This will get downvoted, but you're an asshole along with the 9 people who (at the moment) have upvoted you. The strict posting rules should be to prevent the influx of jokes and immaturities, not to eradicate kind behavior. It's a harmless comment (inexplicably downvoted) which doesn't detract from the conversation. Ugh."
] |
[
"Does gravity still 'work' when scaled down?"
] |
[
false
] |
[deleted]
|
[
"Small, yes, but theoretically possible.\nGiven an orbital radius, of 1m, the above calculated gravitational attraction force of 7.5x10-15 N, we can calculate the required speed for this orbit to be viable (ie no decay or orbital enlargement) from the equation for centripetal acceleration, a=v",
"/r, and Newton's second law, F=ma.",
"Mass(ant) = 1.6x10",
"kg,\nF(gravity) = 7.5x10",
"N",
"a(centripetal) = F/m = 4.69x10",
" m.s",
"v = sqrt(r.a) = 6.85x10",
" m.s",
"Or roughly 0.25 meters per an hour",
"Edit, formatting, not used to reddit comment format..."
] |
[
"Small, yes, but theoretically possible.\nGiven an orbital radius, of 1m, the above calculated gravitational attraction force of 7.5x10-15 N, we can calculate the required speed for this orbit to be viable (ie no decay or orbital enlargement) from the equation for centripetal acceleration, a=v",
"/r, and Newton's second law, F=ma.",
"Mass(ant) = 1.6x10",
"kg,\nF(gravity) = 7.5x10",
"N",
"a(centripetal) = F/m = 4.69x10",
" m.s",
"v = sqrt(r.a) = 6.85x10",
" m.s",
"Or roughly 0.25 meters per an hour",
"Edit, formatting, not used to reddit comment format..."
] |
[
"Small, yes, but theoretically possible.\nGiven an orbital radius, of 1m, the above calculated gravitational attraction force of 7.5x10-15 N, we can calculate the required speed for this orbit to be viable (ie no decay or orbital enlargement) from the equation for centripetal acceleration, a=v",
"/r, and Newton's second law, F=ma.",
"Mass(ant) = 1.6x10",
"kg,\nF(gravity) = 7.5x10",
"N",
"a(centripetal) = F/m = 4.69x10",
" m.s",
"v = sqrt(r.a) = 6.85x10",
" m.s",
"Or roughly 0.25 meters per an hour",
"Edit, formatting, not used to reddit comment format..."
] |
[
"How do small birds survive sub zero temperatures with such little body mass?"
] |
[
false
] |
I understand the concept of hollow, thus insulating, feathers, but it just amazes me that these little creatures are still flying about. It's been below zero for several days where I live. Their bodies are so small, they cannot possibly produce much heat.
|
[
"MS in biology here...not sure about that specific species of bird, but usually keeping warm is going to involve a few things, 1) maintaining body heat through the expenditure of energy, so metabolism needs to be supported by adequate food consumption, and 2) preserving that body heat through insulation such as fat and feathers. They may/will also have behavioral adaptations such as huddling together, or being able to find the warmest places in their immediate environment to find shelter."
] |
[
"Very good explanation. Birds need to find a lot of food during the winter (which is why bird feeders are so busy) to keep their temperatures up. I band birds in my spare time, and we're not allowed to use mist nets (fine nets that catch birds in flight) for catching in the winter because it restricts their movements and disrupts their feathery insulation; they can freeze to death in minutes."
] |
[
"Don't forget about ",
"torpor",
"! Hummingbirds are the most well known for going into a torpid state overnight, but many other birds can do it too. And some can do it for even longer, the longest known being the Common Poorwill (88 days!)."
] |
[
"Why are some illnesses more (or less) serious to adults than to children?"
] |
[
false
] |
Chickenpox, mumps ect. Why are they less serious in kids, but potentially fatal in adults. Equally why are some things trivial to adults, but serious in children?
|
[
"Sometimes it is the immune response itself, being stronger in adults, that can cause fatality. An apposite example is \"cytokine storm\" with respect to influenza outbreaks - it is the case that the young are more susceptible to having a stronger immune response (positive feedback loop where cells are stimulated to synthesize MORE cytokines) which leads to an intense over reaction (fever for example). However, the elderly will have a less intensive immune reaction - yet enough to fight the infectious agents."
] |
[
"It is because Children and adults have fundamentally different biological systems at play. Children are not small adult s but unique in their own right, they have weaker immune systems at a very early age which makes them susceptible to infection but less susceptible to immune mediated damage e.g. Hepatitis B (no acute infection, jaundice but keep the virus chronically). Kids also have an enhanced ability to repair, regenerate amongst other things which makes them more resilient to cellular injury, but more susceptible to genetic cancerous conditions due rapid turnover of cells. Overall it is a double edged sword, but the key is that children are distinct from adults in many respects."
] |
[
"Complications make some illnesses more serious to adults than to children. Adult chickenpox can lead to serious complications if pneumonia (which is more serious with adults) occurs and mumps in adults is often associated with meningitis and encephalitis, which isn't as common with mumps in children. Some illnesses, like the flu, are more serious in children because of complications as well."
] |
[
"How much damage would a sudden reversal of the magnetic poles do?"
] |
[
false
] |
My (somewhat paranoid) sister says that the 2012 apocalypse will happen when the solar system lines up with the galactic core and reverse Earth's magnetic poles. I was wondering how much damage a sudden reversal of the poles would do.
|
[
"There is an easy experiment you can do at home to assuage your concerns about what impact a magnetic pole reversal may have on modern-day technology:",
"1) Take a laptop or smartphone or other piece of tech and place it in front of you. ",
"2) Next, pick it up and rotate it 180°. ",
"Congratulations, your tech has survived a magnetic pole reversal! Yes, this is seriously all it is."
] |
[
"That was literally the best explanation for anything I've ever heard."
] |
[
"Polar reversals are not really sudden the way most people would think of them. They happen over the course of anywhere from 1,000 to 10,000 years, so they just seem instantaneous on a geological time scale. It is actually quite possible that one is occurring now, as the poles have moved a fairly significant distance (about 10 miles) in the last few years, and it looks like they may be accelerating. So basically the chances of a sudden magnetic reversal on dec. 21 is essentially nil.",
"With that being said, as to the damage a reversal would do: very little. There have been thousands of pole reversals in earth's history, and none seems to have caused much of a problem to the life around at the time. There was some speculation that the P/T boundary was partially caused by a magnetic reversal, but that idea has pretty much been scrapped."
] |
[
"Are there any \"one-way\" membranes?"
] |
[
false
] |
Basically I'm just curious if there are any materials that will allow liquids through, but only in one direction.
|
[
"Cells have membranes that only allow things to pass one way. This could be something as small as protons passing through a pump or something as large as kilobases of mRNA going through the nuclear pore complex. But active transport across these membranes requires a source of free energy (like GTP or sunlight), because otherwise you would violate thermodynamics. A passive membrane must be bi-directional."
] |
[
"Such a membrane would violate the second law of thermodynamics, unless it was externally powered or needed a pressure differential to work (like a valve).",
"Thought experiment: take a pool of water and divide it in two with a wall of this membrane. The water will flow through random motion all to one side, decreasing entropy."
] |
[
"So, no chance for the Gungan city to exist?"
] |
[
"Why does all garbage smell roughly the same?"
] |
[
false
] |
[deleted]
|
[
"This doesn't really answer OP's question. If garbage all smells the same because it's harboring the same disease, that just raises the question of why does it all harbor the same disease?"
] |
[
"And why doesnt garbage composed of different material smell wildly different? "
] |
[
"The reason our nose is located above our mouth is presumably so that we don't ingest things which our body can't process as food, or which eventually kill us. One of the things that kill humans is disease. Our sense of smell has evolved to associate things harboring disease with a very bad smell (e.g. excrement). One of the things that harbors disease is garbage. The types of disease that garbage harbors is why garbage smells like garbage."
] |
[
"Does tectonic activity contribute to sea level changes?"
] |
[
false
] |
There is an article on front page right now about how Antarctica is actually gaining ice(more specifically increasing in elevation) more than it is shedding ice. When we try to quantify sea level fluctuations, is tectonic activity taken into account?
|
[
"Tectonic activity can certainly affect sea level. It depends mostly on the speed at which the plates move, which in turn affects the age of the material on the plates. Consider that at a divergent plate boundary, material is being added to the plate. This fresh material is hotter and less dense. Because the plate is then on average less dense, it \"floats\" higher on the asthenosphere. So, as the rate at which material is added to a plate (which is related to how fast plates are moving apart at a divergent boundary) changes, so does the rate of change of the plate's density. The changes in where the plate \"floats\" on the asthenosphere affects how much water is displaced. I hope this answers the question. I only have some college intro level geology and oceanography experience."
] |
[
"I doubt it. Tectonic movement is generally a very slow process, and the change in rate is likely even slower. Sea level changes with tectonic sources are processes that take millions of years. Actually, tectonic activity isn't part of climate, so by definition, it would not be factored in, I should think."
] |
[
"The two principle factors that control eustatic (global) sea level are tectonics and glaciations. Tectonics are not entirely independent of climate, although climate change activists fear the melting of glaciers and the resultant sea-level rise mostly. As glaciers melt from the continents, however, a process known as isostatic rebound occurs that results in uplift of previously depressed crust. On a more local scale, this can have effects on relative sea level (rise). The uplift of Everest the OP references is due to a convergent plate boundary (continent to continent), but this sort of tectonic activity does not drastically effect sea level, which is what climate changists truly fear."
] |
[
"What is the time uncertainty in the energy time uncertainty principle? How can we derive this from position and momentum uncertainty? How to calculate it since we do not have an operator for time?"
] |
[
false
] | null |
[
"This",
" is my favorite explanation of the time-energy uncertainty relation. The gist of it is:",
"the \"uncertainty\" in time is expressed as the average time taken, starting in state ψ, for the expectation of some arbitrary operator A to change by its standard deviation.",
"You're not using t since, as you know, there is no time operator, but rather using a measure of how quickly your wavefunction changing.",
"Note that this is not derived from the position-momentum uncertainty relation. Position-momentum uncertainty is just a specific case of the general uncertainty relation:",
"∆a∆b >= 1/2 | < [a,b] > |"
] |
[
"The time uncertainty is the lifetime of an unstable state, and the energy uncertainty is the intrinsic linewidth (full width at half maximum) of the state.",
"This is independent of the position-momentum uncertainty relation."
] |
[
"By that logic there is no space because the only way an observer knows if space extends is if something is where the observer is not. He can only know that however if something moves from there to here."
] |
[
"Which of a nuclear explosion's effects are unique to it being nuclear?"
] |
[
false
] |
Radiation and fallout are obviously due to the radioactive fuel source, but what about things like the flash or mushroom cloud? How many of, say, Little Boy's effects could be replicated with 12,000 tons of conventional explosives?
|
[
"Mushroom clouds are not unique to nuclear explosions, it’s just a result of fluid-dynamical instabilities (Rayleigh-Taylor, and subsequently Kelvin-Helmholtz). If you put a denser fluid above a less dense fluid (including fluids of the same composition, but with a downward temperature gradient) buoyancy drives any perturbation on the interface to grow. That’s Rayleigh-Taylor, which drives the stem of the mushroom cloud upward. Then if you have two fluids in contact moving with different velocities at the interface, that causes perturbations at their interface to grow. That’s Kelvin-Helmholtz, and it creates the swirl at the top of the stem, giving a mushroom shape. So this is just the behavior of air when you make it very hot, and a nuclear explosion is just one way to make a region of air very hot.",
"Like you said, ionizing radiation and residual radioactivity are due to the nuclear reactions that occur, or decays of radionuclides that were present in the nuclear weapon itself. So that’s unique to some kind of nuclear device.",
"But also the thermal effects, including thermal radiation (not all of which is ionizing). The temperatures reached by a nuclear detonation are many orders of magnitude higher than what would be reached with conventional HE."
] |
[
"The specific feature unique to nuclear explosions in atmosphere is the double flash - essentially the explosion generates a bright flash which is briefly dimmed by the shockwave passing through it, before brightening up again... this does not happen with conventional explosives, so much so that detecting the double flash is how a ",
"Bhangmeter",
" detects a nuclear explosion in atmosphere."
] |
[
"The time it takes for the detonation wave to propagate across a volume of 20 kt of conventional HE is maybe ~ milliseconds, while the energy release of a nuclear weapon happens on a faster timescale.",
"But what's more important is the temperature produced, because that determines the thermal radiation (and energy which is released as radiation is ",
" released via the blast wave).",
"A detonation of conventional HE might produce temperatures on the order of thousands of degrees, while a nuclear detonation will produce temperatures on the order of ",
" of degrees."
] |
[
"Would the Hubble be able to take a picture of the James Webb and Vice Versa?"
] |
[
false
] |
Question...
|
[
"JWST (James Webb Space Telescope) will be all the way out at the L2 Lagrange point, which is about 1.5 million km from Earth. HST (Hubble Space Telescope) is in low earth orbit, only like 500 km up, so from anywhere in HST's orbit, JWST will still be about 1.5 million km away.",
"The L2 Lagrange point is permanently \"behind\" the Earth, as seen from the Sun. These is so that both the Earth and the Sun are in the same direction from JWST, and JWST can block out both of these bright sources more easily. As an infrared telescope, JWST is particularly sensitive to heat, so it's designed to not point towards Earth at all. So they wouldn't even want to point it at HST at all.",
"In terms of resolution, both HST and JWST have about the same resolution - about 0.05 arcseconds. An arcsecond is 1/3600th of a degree. The Moon is about 1800 arcseconds across. At a distance of 1.5 million km, 0.05 arcseconds is a resolution of over 300 m. So the resolution isn't nearly enough to take a proper picture of either, as each telescope is well under 300 m in size.",
"In theory, HST could maybe image JWST as a blurry point if you aimed it right though. It wouldn't be an actual picture showing any detail other than that it's a point of light though."
] |
[
"Without Earth, at that distance to the Sun an orbit would need to take longer than one year because it's a bit farther away from the Sun. Earth provides the necessary additional gravity to keep a spacecraft in a one-year orbit at L2."
] |
[
"Side tangent since you seem like a smart person able to explain things: I do not understand how the L2 point works. How is there gravitational equilibrium there when it's not between the Earth and the Sun?"
] |
[
"Climate Change"
] |
[
false
] |
Can some explain in detail how the increase in CO2 leads to climate change? I've always understood it on the surface, but not the details. I want to be able to counter argue opposite talking points such as found here Thanks
|
[
"The Wikipedia article on the ",
"greenhouse effect",
" is a good starting point. ",
"The basic idea is that the hotter an object is, the faster it loses heat through thermal radiation. The earth is in a state of equilibrium where it loses heat at the same average rate at which it receives energy from the sun. Greenhouse gases trap some of the escaping radiation, shifting the equilibrium to a warmer temperature.",
"When a photon scatters off a gas molecule, it does in a mostly random direction. What this guy doesn't understand is that gases like CO2 only absorb radiation in certain (very well measured) wavelength bands. Because the earth is much cooler than the sun, the outgoing radiation is much more biased toward the far-IR part of the spectrum. So more radiation is prevented from going out than from coming in."
] |
[
"Follow the energy:",
"The Sun radiates like a blackbody with a 6000 Kelvin effective temperature, so it's peak wavelength is ~ 500 nm (i.e green light). Some of this radiation gets radiated in the direction of Earth. It so happens that there's not much in the Earth's atmosphere which absorbs at these wavelengths, so the light goes straight through to the ground. Some of it gets reflected and goes back into space, but most of it is absorbed by the Earth causing the surface to get warmer.",
"The Earth, like the Sun, radiates like a blackbody to shed energy/heat. The wavelength at which most of the energy is radiated is inversely proportional to the temperature of the body (Wien's law), so the Earth radiates mostly in the infrared. Unlike for visible light, there is a lot of stuff in the Earth's atmosphere that absorbs infrared light (like CO2 and water). So, the infrared light emitted by the Earth likely gets absorbed somewhere in the atmosphere. The molecule that absorbed this energy will eventually re-emit it, in some random direction (so it has an equal chance to be heading towards the Earth as heading towards space). Effectively what this means is that the energy hangs around for a while, which means that there's generally more energy in the atmosphere than there would otherwise be. It's like placing an obstacle on a freeway: the density of cars in that area will increase because it's harder for them to get through. Eventually, the energy gets radiated out to space, so at any time there's as much energy coming from the Sun as is getting radiated to space.",
"Without the greenhouse effect the Earth's surface would be a bit colder than the freezing point of water.",
"Increased CO2 (and other greenhouse gasses) in the atmosphere means that the heat (i.e. the energy in the form of infrared light) will on average hang around longer before it escapes to space. This translates to an increased temperature (more energy -> higher temperature)."
] |
[
"Thank You.",
"This does a great job of explaining the effect."
] |
[
"Since all life shares a common ancestor at some point, how 'related' might I be to a chimpanzee, in the traditional sense? (Could a chimp be my ten thousandth cousin? My hundred thousandth?)"
] |
[
false
] |
I was thinking about how the tree of life is like a really big family tree and it brought me to this question.
|
[
"The last common ancestor of humans and chimpanzees is estimated at ",
"5-10 million years ago",
" and ",
"average generation length",
" = 15-30 years",
"Using those numbers ~166666 to 666666 generations back...",
"So nth cousins share a n+1 common ancestor.",
"Somewhere between 166665th cousins and 666665th cousins. ",
"Give or take. a lot. "
] |
[
"The most recent common ancestor between humans and chimpanzees is estimated to have been around 6 million years ago. Assuming a generation time of 20 years (may be off somewhat but it's good enough for Fermi), that would be about 300,000 generations ago. I think that means that chimps are our 300,000th cousins, give or take."
] |
[
"Once two branches have diverged, any inbreeding within either branch doesn't matter for the most recent common ancestor."
] |
[
"How does Shotgun sequencing work?"
] |
[
false
] |
If the genome is broken by restriction enzymes, how can they be computationally put in order? The way I was thinking about it was "they are broken into puzzle pieces and reassembled by the computer" . However, this doesn't make sense to me for two reasons: 1) Wouldn't they have the same ends, so it would be impossible to put back into order and 2) How does this help with sequencing? you're breaking them into bite sized peices and putting them back into order?
|
[
"With shotgun, what you get out is just contigs, not chromosomes.",
"Contigs vary from a few kilobase to millions of kb, depending on genome architecture. ",
"Assembly algorithms are based on homology, so as long there is sufficient variation to uniquely map individual 20-200bp reads (length depending on the tech used) you can create longer and longer contigs.",
"Problems arise with genomes that don't have a lot of variation. Stuff like repetitive elements and polyploidy gunk up the works really badly. This is where you would use a more traditional approach by sequencing long stretches of known regions to bridge the gap between repetitive regions.",
"How does this help with sequencing? you're breaking them into bite sized peices and putting them back into order?",
"The main advantage of shotgun over more classic techniques such as chromosome walking is speed and cost, at the expense of accuracy. ",
"Shotgun is by far the cheapest option, because it just homogenizes the genome. This makes it ideal for reference-guided assembly experiments. ",
"Usually, for new genomes, you use a mix of different read lengths, with very very long reads used to bridge gaps in coverage between the shotgun sequenced regions. ",
"1) Wouldn't they have the same ends, so it would be impossible to put back into order",
"A lot of people thought this when Venter first tried the shotgun approach. but in the end the concerns turned out to be unfounded.",
"The ability assemble reads into a denovo genome depends on three things."
] |
[
"Going to try and use layman's terms here.",
"You go to the store and buy 100,000 of the same 1,000-piece puzzle of a ship on the sea. You complete each of the puzzles, and randomly smear glue over parts of each completed puzzle. Then you shuffle everything up, breaking apart any pieces that aren't glued together.",
"Now your goal is to figure out the design of the puzzle. They are all the same puzzle, but the glued-together fragments are all a little bit different. Some chains of pieces look like sky, some look like the ship's mast, others look like the ocean. You start to group together similar pieces - ocean with ocean, sky with sky, ship with ship. Eventually you have a huge pile of ship-only pieces, and ocean-only pieces, etc. Since they are all the same puzzle, some fragments contain the port side and the mast - others have the starboard side and a bit of port - others have the mast and some of the stern - others still have where the stern meets the sea. Spend enough time overlaying the puzzle fragments and a whole ship is borne.",
"Does that make sense? By breaking apart many, many copies of the same whole sequence (",
"), you end up with a whole bunch of overlapping pieces which a computer program can stitch together."
] |
[
"Well, to get the draft of a genome, sequencing is just the first step of the process. ",
"What you get with shotgun sequencing is a lot of fragments of some genome. These are called \"reads\", and their size may vary according to the technology used (454, Illumina, etc.). ",
"The next step is \"assembly\", and I think that this is what your question is about. Depending on the genome, two types could be done:",
"Reference assembly",
"De-novo assembly",
"With \"Reference assembly\", you map the reads obtained during the first step to a known genome of a similar organism, whereas, with de-novo assembly, you join those reads based more or less in how their extremes are alike. For example, if some read, let's say, read A ends with \"CGT\" and another read, let's say, read B starts with \"GT\", then both reads would be joined, and so on.",
"Obviously, this is a highly simplified version of what is done, but I hope you can get the big picture of the process."
] |
[
"Can a spaceship descend slow enough to Earth that it wouldn’t encounter the intense heat generated upon reentry?"
] |
[
false
] |
If a craft was able to decelerate to a slow enough speed, could it gently fall back to earth using vector rockets (or something) and main thrust to keep the descent slow enough or would it be unable to punch through the Earth’s atmosphere? Less heat and constant radio communication are cool, right? (Pun intended).
|
[
"Yes it could. But that would require about as much propellant as what is used to launch the rocket in the first place so it's not really practical. "
] |
[
"In principle, yes. The reason we don't do this is that it means that we get the deceleration \"for free\". Instead of having to use a huge amount of fuel to slow yourself down and gently land, you can use the atmosphere to aerobrake.",
"You would need to slow your speed down to zero, which means you need a rocket as big as the one that would bring you up to that speed. So, you would need an entire multi-stage rocket system to be lifted into space to get that much acceleration. But of course you now need to lift that huge multi-stage rocket into space using an even bigger multi-stage rocket. You end up with something so huge that it becomes incredibly expensive, and more difficult (and more dangerous!) to design and launch.",
"So instead, we use the Earth's atmosphere to slow down, which means we can launch rockets without an absurd budget. There is a danger in such a dramatic re-entry, but there would also be a danger in having a larger and more complex series of rockets anyway."
] |
[
"Any way of reducing the tangential velocity would work. A highly spiraled entry (with fixed wings and a careful entry velocity) would work as well, but would be incredibly difficult and take a long time."
] |
[
"If an object reaches absolute zero does it lose all mass?"
] |
[
false
] | null |
[
"No, it still has its mass. Absolute zero doesn't imply an absence of energy, it just implies that they system has its ",
" energy. The minimum is not necessarily zero."
] |
[
"A free particle can't have zero energy. A massive particle has a minimum energy of mc",
", and a massless particle must move at c in all frames of reference, so it must have nonzero momentum (p), and an energy E = pc."
] |
[
"If something had zero energy would it then have zero mass?"
] |
[
"Why do we get the urge to throw up when we smell something bad?"
] |
[
false
] | null |
[
"I have no sources to back this up, but basically, if you eat something bad, you should throw it up, yes? So if you smell something bad, your body is reacting as if it might have contaminated anything you recently ate, and wants to get rid of it. "
] |
[
"I figured something along those lines myself actually lol, just wasn't sure."
] |
[
"I do not get this urge. "
] |
[
"How do kinetochore microtubuli take chromatides with them when depolymerising?"
] |
[
false
] |
So I know THAT it happens: kinetochore microtubuli bind to the kinetochores on the chromosome, then they start depolymerising and they take the chromatides with them. I can find all of this on the internet, what I can't find, however, is how it happens. Why does the chromatide go along with the depolymerising microtubulus? What sort of attraction is there? I'd think that as soon as the microtubulus starts depolymerising, the bond with the chromatide would break and the chromatide would get left behind, but that isn't the case. So why?
|
[
"If you can ",
"see this figure",
" I think it might help you understand. The kinetochore of the chromatid is not attached to the ",
" of the microtubule. It is attached a little further 'in', on the side of the microtubule. ",
"Imagine a rope with a ring loosely fitted ",
" one end, but not directly on the end. If you start unwinding the rope on that nearby end, you sort of 'push' the ring along toward the other end. Now, factor in the fact that the ring (Dam1 complex) is associated with kinesins that can walk (instead of being passive, like the ring in my analogy), and you can see how the problem you bring up in the OP is not really an issue anymore.",
"Edit: Another caveat to my analogy -- I don't want you to get the wrong idea. When you're pulling apart the strands of the rope, you're using energy to pull. That isn't really analogous to microtubules depolymerizing. The analogy is just to help you visualize what it sort of looks like."
] |
[
"There are motor proteins pulling on them called kinesin-related proteins (KRPs). There are many different types of KRPs with many different shapes. The simplest example I can think of is kinesin-5. It looks like ",
"two kinesins attached by their tail ends",
". For each pair of microtubules (MT), there'll be many KRPs working in tandem, pulling on the MTs like a piece of rope. As the MTs are being pulled, they'll take the chromatids along with them. Depolymerization plays no role in the movement itself.",
"Edit: ",
"Better pic of kinesin-5",
"."
] |
[
"The kinetochores shorten at the plus end (the end attached to the chromatid) by depolymerization of the tubulin dimers that make up the microtubule (MT).",
"Due to the interactions of various microtubule associated proteins (MAPs), the microtubule stays attached to the kinetochore on the chromosome as the microtubule depolymerizes. Other MAPs slide along the microtubule back towards minus end (towards the microtubule organizing center), dragging the chromosome along with it."
] |
[
"A quick question on information transfer speed within cables?"
] |
[
false
] |
I was having a quick browse on cnet today when I read that Singapore had released broadband out there with a 100Gb/s transfer speed, this got me thinking, with my broadband at home perhaps a short part of my connection is fibre optic but the majority of it is made from what I assume is copper cable? I'm studying theoretical physics at university but we aren't covering information transfer until next year so forgive my limited knowledge on the topic if I sound a little silly! So when I send data from my computer this is transferred along the cable by electrons, but I know that electrons have a very slow drift speed , so how do the electrons that leave my computer transfer information so quickly? Do they somehow transfer the information between electrons and how come this speed can be increased or decreased? Sorry if this question seems a little silly to those of you who know more on this topic and thanks for any responses I appreciate it!
|
[
"One electron \"pushes\" the next electron through the electromagnetic field, without needing to be right on top of it. The next electron then pushes another electron farther down in the same way. An electrical signal is not really carried by individual electrons. It is carried by the electromagnetic field, and supported by the electrons. The information of the signal is contained in the waving pattern of these \"pushes\". Since propagating electromagnetic field fluctuations are essentially light (although not necessarily at visible frequencies or in a free-space propagation configuration), electrical signals travel at speeds that are on the order of the speed of light in vacuum c, which is very fast. Electrical signals go slower than c because the material tends to get in the way. In fact, you don't even need the electrons for an electromagnetic signal to propagate. A signal in an optical fiber is an electromagnetic signal that does not rely on being coupled to conduction electrons, and can therefore travel faster, and at higher frequencies and bandwidths.",
"Now, don't confuse physical signal speed in a wire with data transfer \"speed\". The physical signal speed is how fast a fluctuation in the electromagnetic field travels down the wire, and is therefore constant for a given wire at a given frequency. The data transfer \"speed\" is not really a physical speed at all. It is an information transfer \"rate\". It can change based on how many different independent frequencies you are using at the same time to send a signal down the wire. It also depends largely on the processing speed of the computers at each end of the wire, i.e. their receive and transmit speeds, as well as the latency in the rest of the network. When you upgrade the data transfer rate of your internet connection, you are usually not changing anything about the wire to your house (unless you do literally install a new wire). Instead, you are paying your internet provider to dedicate to you more of their computer processing power and down-network bandwidth."
] |
[
"If the cable is capable of transfering higher frequencies, then the cable can support faster data transfer. But cables work as a damper for high frequencies and therefor the data transfer is limited. On the internet the data transfer rate is mostly limited by the switches and routers between two computers and other data which is traveling on the internet."
] |
[
"Really well explained thank you! So are higher frequency electrical signs capable of transferring more information, or is it the rate at which the frequency can be changed that determines the amount of information transferred? "
] |
[
"What are the effects of spontaneous decay of carbon-14 in genes?"
] |
[
false
] |
Carbon-14 spontaneously decay into Nitrogen-14 via beta radiation. As our genes contains carbon atoms, some of them should be carbon-14 isotopes and they would naturally decay into Nitrogen-14. So I was wondering what are the effects of replacing a carbon atom into a nitrogen atom in genes, and what might the beta particle do to a gene if it hit it.
|
[
"Well, carbon is chemically different from nitrogen, so in most situations you couldn't swap out a carbon atom in a molecule for a nitrogen and have the bonds remain the same. Depending on its position, the nitrogen atom might pop out of the molecule, or eject one of the atoms beside it, or the molecule might break apart. If this happens in the center of the DNA molecule (where the \"letters\" are), you might get left with a slightly wonky \"letter\" that might lead to a mutation - essentially a spelling error - when the DNA was next read or copied. If it happens in the sugar-phosphate backbone on the outside of the DNA, it might cause a break in the DNA molecule on that side.",
"Thing is, in either case, this probably won't even register. Your full genome exists in billions of copies throughout your body - one for each cell, with some exceptions - and a single DNA break in a single cell is either fixed shortly by the cell's DNA repair machinery, or the cell dies and is replaced. If the decay occurred in a cell destined to become a gamete (egg or sperm), it could cause one of the handful of unique new mutations (relative to our parents' DNA) that each of us starts our life with. For one of those mutations to even be located within a gene is unlikely, but if it is, it may or may not have some effect that will be very situationally dependent, as are all mutations.",
"Maybe a boring answer, but the fact is that DNA lives a very rough-and-tumble life in our cells! It's constantly being bombarded by radiation (including, yes, beta particles) and pelted and torn by the cell's own chemicals, all of which causes the occasional mistake, 99.9% of which are found and fixed by repair systems, and the remainder of which mostly have no effect anyway. (When they do, that's where new genetic variation - for good or bad - come from.) Carbon-14 decay is just another drop in the bucket of constant background mutations."
] |
[
"Oh OK. So the body will probably repair it, or it won't spread through the body.",
"There goes my hope of an X-men mutation!",
"THX for the answer ☺️"
] |
[
"Well, put it this way, if a mutation does occur that gives you* a cool new ability - this is extremely unlikely, but it does happen occasionally, which is how evolution gets its raw material, as it were - carbon-14 decay ",
" one way this mutation can happen. I was primarily trying to explain that a carbon-14-induced mutation shouldn't be qualitatively different from any other of the many mutations, due to all kinds of factors, your body faces every day. :)",
"*"
] |
[
"Could this be a form of synesthesia?"
] |
[
false
] |
came up in DAE a few days ago, and I thought I'd pose it to the experts.... If I hear a sharp, sudden noise when I'm half-asleep (car door slamming, door banging, one of our fatass cats belly-flopping off the windowsill, etc), I get a quick flash of brightness/static behind closed eyes to "accompany" it. Would this be considered a form of synesthesia? I know that this term is incredibly broad....
|
[
"I get the same thing, and it appears to be a somewhat common byproduct of ",
"hypnagogia",
".",
"Sometimes there is synesthesia; many people report seeing a flash of light or some other visual image in response to a real sound. "
] |
[
"Good to know! I totally got this when my TV used to give a little \"bang\" from discharging itself."
] |
[
"To be synesthesia, I believe it must be consistent."
] |
[
"Has there been any actual research into the claim that shaving accelerates hair growth?"
] |
[
false
] |
This belief seems to be quite prevalent. I've even had MDs tell me this. And I've heard the reason why women with wispy mustaches don't shave is because they're afraid it'll start growing even faster and darker. It would probably be quite easy to test scientifically, even for an average redditor. For example, shave one leg (chosen randomly) every week for a year and don't shave the other one. Then shave both, wait two weeks, and measure hair growth, strength, color, and rigidity. If there's any truth to the myth, then we should see a real difference between the legs. So has there been any research into this claim? Any truth to it?
|
[
"The reason that this belief is held onto is likely because, in a sense, it ",
" true that shaving will make the hair grow back thicker than if you pluck or otherwise pull it out, or even leave it alone, because you're only chopping it off mid growth so that the thick part of the hair pops up instantly, and now with an extra hard edge, rather than a new hair growing slowly, and coming out with a wispy, soft little top part. ",
"So, compared to pulling hair out, or leaving it alone, shaving does make the hair that grows back thicker and more hard (rigid from the cross-cut).",
"But some people take that to mean that the hair itself is growing differently when you cut it, when it's actually just a mechanical change to the shape of the hair.",
"So it's more of an issue of semantics here than anything else."
] |
[
"AFAIR it is an urban myth, classic confusion of cause and effect. I'm sure this has been tested (after all hair growth is a HUGE commercial buisness). Hair growth depends on testosterone levels and genetics primarily. "
] |
[
"BMJ says shaving has no effect",
"* (scroll a bit down), and there's a nice ",
"WikiAnswers page",
" on why that is so.",
"*) They mention a study from as early as 1928. I found one by a certain M. Trotter, but it is not available online. Take ",
"this one",
" instead."
] |
[
"Why is turbulence less dangerous than it seems, and when should we actually be worried while on a flight?"
] |
[
false
] | null |
[
"When you hit a bump in the road at high speed, it feels far more impressive than it actually was. It's similar with turbulence. Just like a sudden pothole, you probably don't anticipate it, it may cause discomfort, but it's not actually harmful as long as you're strapped in.",
"What's refered to as turbulence when flying is typically just one or more unexpected gusts of wind. And while such a gust can push the aircraft up, or down, or sideways, the primary motion of \"going forward really fast\" remains unchanged. Airplanes travel through the air at speeds of >500 km/hour for jets at cruise speed.",
"And as long as an aircraft has wings and is going foward really fast, the lift force that keeps the aircraft in the air will still be there, regardless of whether the aircraft is in clear skies or shaking in various directions.",
"So you should become worried when the aircraft loses one or more wings (necessary for lift-forces) or loses all engine power (necessary for going forward really fast). Note the \"all\" in the previous sentence, since airplanes are designed and pilots are trained for flying with reduced power (such as the loss of one engine)."
] |
[
"Turbulence usually isn't a problem because modern aircraft are equipped with control systems that stabilize it during flight. Most turbulence only occurs for a brief period of time before the airstream returns to a fairly laminar flow or is compensated for by the flight controls.",
"Turbulence becomes a dangerous issue when a few different modes occur, generally in concert with each other:\n1) If the turbulence is too high, then the aircraft will encounter numerous regions of low and ambient pressure. The aircraft will repeatedly gain and lose lift which places stress on the aircraft. Any structurally weakened sections subjected to these forces may be prone to breaking in air. \n2) If the turbulence is too rapid or synchronous with the flight controls, then resonant modes can occur in the system impeding stability.\n3) If the aircraft does not have an automated flight control system (i.e. most pre-WW2 aircraft or RC planes), then the pilot is forced to compensate for any turbulence manually and may not have sufficient sensory data to do so.\n4) Lastly, most turbulence is due to adverse weather conditions that cause sensory degradation such as aircraft icing and extremely low visibility."
] |
[
"Yeah I would imagine T/L turb is deadly. I always feel the least comfortable about 100-200 meters in the air when the aircraft performs its first 20 degree bank."
] |
[
"At what point does attraction to youthfulness become counterproductive?"
] |
[
false
] |
[deleted]
|
[
"Interestingly, male chimps prefer to mate with older females, presumably because the older females have shown they can survive long term and have lots of experience raising offspring. So the human approach isn't the default.",
"Oh, and about blonds. I can't guarantee it's the case here, but there's a phenomenon known as preexisting bias. It's been documented in several animal species. Basically, the attraction to a particular trait can exist in a species which does not actually express that trait. So, for instance, you could artificially give a male fish an elongated swordtail and females of his species, who had never seen a fish like this before, would find him more attractive than unmodified males. So theoretically gentlemen could have preferred blondes long before any existed."
] |
[
"hmm, on a side-track, why are certain people sexually attracted to prepubescent child given that this confers no reproductive advantage ?"
] |
[
"hmm, on a side-track, why are certain people sexually attracted to prepubescent child given that this confers no reproductive advantage ?"
] |
[
"Multi-part Question: Fans vs Air Conditioner. Relative Humidity and Self Cooling. Overall Cost/Benefit."
] |
[
false
] |
It's that time of year, and the housemates and I are having "disagreements" about cooling and humidity. help us settle the argument. Fans & AC list Does it take more energy to run JUST the AC or 5 fans? What about with [2] more 8" single fans? The argument often shifts between the cost of the AC, but then the "it's too humid". Obviously, it is a subjective feeling, but I'd like to put some numbers behind it, so we can equivocally agree "YEP, it's OK to turn on the AC now." Since humans cool through moisture loss, and humidity plays a part in how cool we feel, how can I use fans to find an approximation to an air conditioner. Am I going to get a cooler feeling using the AC or the fans?
|
[
"I'd guess your A/C unit uses as much electricity as 12 box fans. 11,500 BTU A/C unit uses about 1200 Watts. A box fan uses around 100 watts. But thats only the amount of electricity it uses when the compressor is running. The exact amount of energy used by your A/C unit will depend heavily on what temp you set it at and how hot it is outside (plus the effect of the sun on your building). The best solution would be setting the A/C unit at a high temp and using the fans to supplement it. This way your A/C acts as an emergency reserve to prevent the temperature from going above the temperature at which the fans are effective."
] |
[
"It's an older AC, early/mid 90s. The dial goes only to 10. It is set at a low cooling instead of high cooling. It is supplemented with fans. ",
"The flat doesn't stay cool long due to it being in the SW Corner of one of the higher floors. It does get a nice breeze when the windows are open. "
] |
[
"Well then I would ",
"get one of these",
" and run an experiment to settle the debate. I'm pretty sure you'll find that not using the A/C will be the cheaper solution but A/C the quality of life that A/C can bring you is often worth the expense. "
] |
[
"If I lit a candle in space on a spaceship then what would the flame shape look like since there is no gravity?"
] |
[
false
] | null |
[
"Round"
] |
[
"Here's the picture (it's a bit far down)"
] |
[
"The reason that flames are ",
"tear-drop shaped",
" is because heated air is lighter density and rises, while convection draws cooler air into the flame, feeding it with oxygen.",
"In space, there is no \"up\", so the flame maintains a spherical shape. Incidentally, without the convection necessary to draw more oxygen into the flame and dispel the CO2 that is produced, fires in space will simply put themselves out. The only way to maintain a flame is to wave it around."
] |
[
"How do machines produce randomly generated numbers from a distribution?"
] |
[
false
] |
I was lamenting about how much I had to mark this weekend, and jokingly proclaimed I should produce random grades according to a distribution. But how do machines do that? Suppose I wanted to generate a series of numbers that were distributed exponentially, or normally. What is the process for creating such an algorithm?
|
[
"As long as you can produce random numbers from a uniform distribution you can transform them to whichever distribution you want by using the cumulative probability distribution of the desired distribution. ",
"https://en.wikipedia.org/wiki/Inverse_transform_sampling"
] |
[
"That is really neat. Thanks for the post."
] |
[
"This would be hardware technique. While an algorithm of some sort would be needed to turn this randomness source into something useful, the randomness itself does not come from the algorithm. No purely algorithmic (i.e. deterministic) process can produce true randomness."
] |
[
"Can anyone r/AskScience identify the strange creature currently residing in my bathroom sink?"
] |
[
false
] |
and of the beast in question. Saw it on my shirt in the mirror when I entered the washroom. I think it must have fallen on me while I was outside. Relevant information: Edit: I just noted the grammar fail in the title. My bad...
|
[
"In the future, if you have any insect ID questions, definitely check out ",
"/r/whatsthisbug",
". "
] |
[
"It's an 'inch worm'- the caterpillar phase of the ",
"geometer moth."
] |
[
"Yep. \"Inch worm\" caterpillar. They are abundant in the midwest of the US. I guess in Canada too. "
] |
[
"Why do photons impinging on a CCD camera exhibit poisson noise?"
] |
[
false
] |
I've never gotten a straight answer to this question. I know that this is true, but I don't understand why it is so.
|
[
"not every kind of light exhibits poissonian statistics and so it really depends upon what generated the light and how you are detecting it. ",
"There is also a big distinction between saying the light has poisson noise and the current coming out of the detector has poisson noise. ",
"So if you take the cleanest most perfect continuous source of light you can buy, i.e. a laser, the light that comes out has a constant amount of energy per unit area per unit time. when you then focus that light down onto a ccd detector, there is a constant can continuous rate of energy flowing onto each pixel of the CCD. ",
"Now where the poissonian statistics comes from is that the probability for exciting an electron and then multiplying that electron into an observable signal is a constant and fixed rate which is completely independent from one time to another. ",
"When you have a random process which has a constant probability for exciting discrete events in a unit time bin, you get poisson statistics for the total number of counts you see after integrating from some time.",
"So what makes the poisson noise is not really the light but how the ccd responds to the that light."
] |
[
"I'm not really sure if poisson noise was an issue in film-based images or not. it depends upon what you were doing with it I guess.",
"\nBut yes, for a constant light source the moment you 'convert' to discrete things, that's when you get poisson noise. ",
"(however when you start moving away from a small mean to a larger mean a poisson distribution rapidly starts to look like a normal distribution.) ",
"as for film, in principle, there was poisson noise (this molecule changed color vs. this one didn't.) but you couldn't really see it because you weren't counting molecules anyway. ",
"now clearly if you have a source of single photons then they won't have poisson statistics. you will get one count and one count only (with a prefect detector.)"
] |
[
"With film, the poisson effect shows up as ",
"grain",
"."
] |
[
"What would happen if I shot a photon orthogonally from a black hole?"
] |
[
false
] |
As in orthogonal to the event horizon. would it have to stop and turn around? Thanks
|
[
"A photon always travels in a straight line, but space itself may be curved such that this straight line doesn't look straight to someone somewhere else.",
"In a black hole (within the event horizon, and to the extent that it even makes sense to say this), space is so warped that there are no paths out of the black hole. The photon doesn't turn around, it just keeps going and never gets out.",
"Outside the black hole (even a tiny distance from the event horizon), the photon would go in a straight line until it hit something, but would lose energy escaping the gravitational well, manifesting as a redshift."
] |
[
"From the inside of the black hole or from the surface of the event horizon?\nIf from the surface, it would escape to infinity with \"infinite red shift\" - it's energy would be zero in infinity.",
"Behind the event horizon, the only permissible movement is towards the centre. No matter how you shoot it will fall towards the centre. ",
"Well, at least in Schwarzschild metric, I don't know about the rest, I only had intro course to general relativity."
] |
[
"So the space its warped in a way that erik make it end up in the middle. That's crazy..."
] |
[
"How much energy could you produce by solar panneling the entire sahara desert?"
] |
[
false
] |
output with the technology we have now, and with near distant technology?
|
[
"2.8 quadrillion watts",
" with current technology. ",
"4.3 quadrillion watts",
" with the theoretical maximum of current technology.",
"Impurity band semiconductors could possibly get higher, as much as ",
"9.8 quadrillion watts",
".",
"Of course this is completely ignoring the difficulty of getting the energy anywhere, ignores that it only produces this power during the day, ignores clouds, and honestly overestimates the solar irradiance by a bit (in my opinion). ",
"But it works for a order of magnitude calculation I suppose."
] |
[
"its just hypothetical, not practical at all, i know. "
] |
[
"To put that in perspective, world energy consumption is about ",
"142 quadrillion-Wh",
", so we need about 50 hours of sunshine."
] |
[
"Are there any animals that eat mushrooms or plants that are psychedelic?"
] |
[
false
] | null |
[
"Reindeer are known ",
"to eat fly agaric",
". The author of Shroom claims that the stories about ",
"humans consuming reindeer urine",
" after the animals have eaten the mushrooms to get high are true."
] |
[
"I've heard the opposite to be true: Reindeer would actually crowd around snow that humans have urinated in after consuming psychedelics, jostling each other to get a piece of the action"
] |
[
"Plants are not inherently psychedelic, but rather psychedelic to humans (because of how they interact with our species' specific brain chemistry).",
"However, monkeys, elephants and cats (just off the top of my head) have been observed to imbibe alcohol or substances that are psychoactive to them for apparently recreational reasons."
] |
[
"What's the maximum height a fly or a mosquito can reach?"
] |
[
false
] |
I mean flying of course! Is there a limit? How high is that? Why?
|
[
"National Geographic Article about bumble bees",
"\nI mention bumble bees because they were studied a lot by scientists. Some people thought bumble bees shouldn't be able to fly because they are too heavy, so they ran a lot of tests on them!",
"Helicopters have an upper limit of height in which they can safely fly because as you go higher, the atmosphere thins. Less air, means less lift. The same goes for insects!",
"To answer your question directly, there is no absolute value at which insects can reach, but bumble bees can fly higher than Mt Everest. Flies, and other fast flying swift insects could reach those heights as well, but they have no need to. They have extra power, so they can carry pollen, nectar, eggs, fly quickly and efficiently at low altitudes."
] |
[
"I think it's quite obvious that there isn't really much science going into how high insects can fly, so there is no direct answer to the highest flying insect. The only insect that was tested was bumble bees, and they were found to be able to fly higher than the highest land on Earth. So the answer that is known is AT LEAST Mt Everest height. Likely much higher. What's so confusing about that?"
] |
[
"Found a link that goes into detail",
"https://www.livescience.com/55454-how-high-can-insects-fly.html",
"The highest altitude where insects (butterflies and flies) have been found is 6000m. However, they tested bumblebees in a pressure chamber and they were able to fly at 9000m! (for reference, Everest is at 8848m).",
"It's not explicitly spelled out in the article, but based on that and reading elsewhere on the internet it seems the observed altitude limit has more to do with temperature than pressure. Bumblebees were able to fly at higher simulated altitudes than insects are actually found...but at high altitudes temperatures are low and insects generally have trouble flying at low temperatures due to the difficulty of keeping their muscles warm enough. ",
"However, I suspect the actual maximum height insects reach is actually rather higher than any of the numbers listed above. Supercell thunderstorms have strong updrafts and can reach higher than 22000 meters. You can be certain that insects get caught in these updrafts and lifted very high. Some probably even survive the experience."
] |
[
"Where do fish in high altitude/mountain streams and ponds come from?"
] |
[
false
] |
I've been hiking in Europe and Asia and have seen fish even in tiny puddles at very high altitudes, close to the ice cap source of the river. How the hell do they get here? Surely both migration and reproduction is incredibly difficult against a current and in such isolated bodies of water
|
[
"You always hear about birds transporting eggs, but I've never seen documented evidence of this (please, if anyone has a paper on this send it my way!). I have seen it documented for plants and aquatic invertebrates, however.",
"What ",
" definitely happen is that humans will introduce fish into every body of water they come across. I live in the mountains right now, and I know that many of the fish in various bodies of water around here have been added by people. This is definitely the case with manmade bodies of water. Through most of the USA it's pretty much a given that a mix of bluegill and bass will be added to any farm pond, both for fishing and to keep mosquito populations down. Mosquitofish are added to everything up to and including old pools for the latter reason.",
"You know you are looking at human introductions if you see fish like rainbow (pacific coast NA) or brown trout (Europe), largemouth bass (East NA), bluegill (East NA), goldfish (East Asia), mosquito fish (Southern NA), or various minnows outside their native ranges (in parentheses). ",
"Aside from that, there are mountain fish species that are quite capable of working their way up into the headwaters of streams. Even an intermittent stream connection between a pond and downstream waters can be enough to allow fish to swim up and colonize it. Montane fish can tolerate and often require very cold waters for survival."
] |
[
"Dont forget that fish are very resourceful, and that seeing a puddle at one moment in time does not give you a complete picture of how it is related to other bodies of water. Water systems can be connected at different times and fish can migrate up them, then they become isolated stranding the fish in funny places. Also they could be placed there, either by natural (bird, bear, etc) or by human ",
"https://www.reddit.com/r/gifs/comments/49vmj8/populating_a_lake_with_fish_by_dropping_them_from/",
" or ",
"http://www.fieldandstream.com/photos/gallery/fishing/2009/10/stocking-rocky-mountain-cutthroat-trout-planes-colorado/?image=0"
] |
[
"It's so interesting that you posted this here OP, I came to ask the same question almost exactly -- if X and Y lakes were frozen 10,000 years ago or not carved by the glaciers or formed by the melt water yet, then how could there possibly be fish in them? It's not like they could \"evolve\" there in 10,000 years, based on the presently accepted theories, so how did they get there? Fish picked up by birds and transported from other fresh water bodies on earth? Aliens put them there? Magically the fish eggs were taken up into the clouds and dropped into another lake? what? how did they get there?!"
] |
[
"How are quantum tunneling in stars and their weight associated with each other?"
] |
[
false
] | null |
[
"So is my answer widely false or just inaccurate?",
"It's inaccurate to imply that tunneling is ",
" crucial for the sun to sustain fusion at its current temperature and density.",
"If you take the core temperature of the sun and convert it to an energy (kT, on the order of the average kinetic energy of the particles in the sun), it's on the order of keV. The Coulomb barrier for two protons is about 0.6 MeV.",
"So the typical relative energy of two protons is well below the energy that would be needed to classically overcome the barrier.",
"Is there just a correlation between the sun's mass and quantum tunneling (i.e. lots of protons necessary for quantum tunneling having the effect you can observe every day = lots of protons to make up all that mass) or is there a bit of causation as well (i.e. the mass is helping quantum tunneling to Some extent)?",
"There is an indirect relationship between the mass of the star and the rate of tunneling, in that the mass of the star influences its temperature, which influences the kinetic energies of the particles, and the probability of tunneling depends on the relative energy of the particles.",
"When you convolve the tunneling probability with the Maxwellian energy distribution, you get a ",
"window",
" where stellar fusion most often occurs."
] |
[
"It's inaccurate to imply that tunneling is not crucial for the sun to sustain fusion at its current temperature and density.\nIf you take the core temperature of the sun and convert it to an energy (kT, on the order of the average kinetic energy of the particles in the sun), it's on the order of keV. The Coulomb barrier for two protons is about 0.6 MeV.",
"Wouldn't you expect the average energy to be well below the required energy for fusion to occur. If the average proton had all the energy to fuse with another proton, or just a sizeable portion, wouldn't you end up with a star that burned almost 'instantly', on the scale of star lifetimes?"
] |
[
"The fusion cross section would certainly be higher if the average relative energy were above the Coulomb barrier. I don't know what astrophysical implications that would have."
] |
[
"Is there any documentation of how much or what type of bacteria there are on the surface of the eyes?"
] |
[
false
] |
They say the mouth is where most of the bacteria are on your body, so I wondered how the bacteria on your eyes would compare. I am talking about the actual wet eye surface. Also in case anyone knows, if this bacteria is somehow destroyed for an extended period of time, will the eyes be harmed?
|
[
"I found one scholarly article:\n",
"http://www.ncbi.nlm.nih.gov/pubmed/19620859",
"\nDoes it help? Its probably not exactly what you're looking for.."
] |
[
"your eyes are protected with enzymes, one of these is lysozyme which can disturb the reproduction of gram-positive bacteria but the article posted by thermalphysics seems to be a good point to start."
] |
[
"Not exactly but that does help, thank you."
] |
[
"What is the correlation between brain size and intelligence? Is it possible for a large-brained animal to be unintelligent or a small-brained animal to be highly intelligent?"
] |
[
false
] | null |
[
"Sure. Rats have tiny brains, but they're quite intelligent. The ratio of brain size to body size matters a bit more than just overall brain size, but there's still not much of a proven correlation. There are just too many factors. ",
"It's probably down to evolutionary pressures in the end. Rats benefit from being very intelligent, but lions can survive just fine without being very clever."
] |
[
"Another thing to note is that birds have higher neural density than mammals, hence they can pack the same number of neurons in their smaller brains as a bigger mammalian one. Macaws for example are considered highly intelligent animals, some compare them to a 2/3y old human in that regard"
] |
[
"To add on- there’s also the correlation of “how much energy is available” for brain power. Humans divert a proportionally huge amount of energy to our brains, whereas other animals do less so. Even so, among the animal kingdom there are varying levels of energy availability"
] |
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