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[
"What evolutionary pressures led to the differences of morphology among different human races?"
] |
[
false
] |
Question inspired by the Olympics. I use the term 'races' out of ignorance of a better way of classifying humans, but it seems as though people of African origin generally seem better suited for track races, people of European origin seem better suited for water sports, and people of East Asian descent seem to be better adapted for sports that require quick response times (like ping-pong and handball). Why are such skills so neatly divided among races? What was the evolutionary pressure behind the adaptation?
|
[
"My guess is that most of these apparent athletic advantages have far more to do with culture than they do with race. If you observe a human behavior, and you cannot think of a reason why it's adaptive, that's oftentimes a good clue that it's not adaptive after all.",
"Consider: track sports are a big cultural phenomenon among Africans (and, e.g., African-Americans). Not so much in Japan.",
"Also consider: countries that perform very well in weightlifting (including former Soviet republics and satellites, some Middle Eastern countries, and now China) often have very efficient feeder programs for recruiting young, genetically gifted athletes and prepping them from day one. The US used to have a good weightlifting program before the sport lost its cultural appeal. If barbell training ever gets big in Africa, I'm sure we'll see plenty of talented African weightlifters. Likewise, if lots of African nations start subsidizing their cities with swimming pools and clubs, maybe we'll see more high-placing African swimmers. Hard to say.",
"The preceding also contains another good example: Africans supposedly dominate in sprints, for which explosiveness (the power generated by individual motor units, as well as the ability to recruit motor units very quickly) is important, but they generally don't place high in weightlifting, even though ",
" is required.",
"I think the evidence is still (mostly) consistent with the old genetic observation by Lewontin, that variation within human groups is much larger than variation between human groups. Whatever variation does exist between human groups is probably not well represented by athletic competitions. Differences there are mostly due to contingent cultural factors, not genetic ones."
] |
[
"At least one study compared body types between whites and blacks. They found that blacks tend to have a higher center of gravity, which makes it easier to run fast, but harder to swim fast. ",
"Here",
" is an article about it. In the article they reference the study."
] |
[
"Even if genetics were the deciding factor, one would have to remember that the diversity among Africans dwarfs the diversity among other ethnic groups."
] |
[
"Anti-Photon"
] |
[
false
] |
Just something I have been wondering. Since Photons don't have charge, while they do have an antiparticle, it is completely indistinguishable from them? Right? So would this mean, that unlike other antiparticles, the two would not annihilate each other if they came into contact? Is this correct?
|
[
"The photon is it's own antiparticle and ",
" of this two photons can annihilate with each-other."
] |
[
"Under the usual conditions; when two photons collide, they annihilate.",
"In regular particle-antiparticle annihilation a particle and its antiparticle annihilate and produce two photons. Photon-photon annihilation is the time-reversal of this process, where two photons annihilate and produce an antiparticle/particle pair. In order for this to happen, the total energy of the photons must be sufficient to meet the rest-mass requirements for the particles produced in the reaction."
] |
[
"Pair production or creation of one electron and positron would be an example of two photons annihilating."
] |
[
"Which one is closer to the fossil records, the traditional view of evolution that it happened it gradual transitions, or the newer theory which is the punctuated equilibrium?"
] |
[
false
] | null |
[
"Both are consistent with the fossil record. Punctuated equilibrium is a form of gradualism. The Punctuated Equilibrium theory still allows for the incremental changes of gradualism during the \"stasis\" period of a species but states that genetic drift in large populations keeps the species relatively homogeneous. However, Gould et al theorized that when a population is separated into two groups unable to interbreed they rapidly formed distinct species.",
"Both of these theories are in contrast to Darwin's classical Theory of phyletic evolution, which states that changes occur at a constant and steady rate, gradually accumulating until one species turns into another."
] |
[
"Both are gradual, ok. I guess I wrote my question poorly.",
"\nThe traditional view is, evolution occurs in constant and steady rate. in punctuated equilibrium, it's like species stay pretty much the same until a \"punctuation\" or a big jump to evolve into a new specie occurs.",
"Okay. Which is closer to the fossil records, the big jump or the steady rate?"
] |
[
"It depends on which fossil lineages you look at. Some lineages, like many mollusks, are pretty well characterized by gradualism. Others, like vertebrates, seem to evolve in fits and starts, with species appearing very suddenly.",
"Why might this happen? Good question. Part of this is related to the old question about how speciation happens; is anagenesis (one species evolving into another, continuously) or cladogenesis (one species becoming split and evolving into two distinct species) more common? There's a joke among evolutionary theorists that just about everyone gets interested in speciation at some point, then dismisses it as an unsolvable problem.",
"It's worth noting that you've got to be careful distinguishing between punctuated equilibrium and gradualism. The cartoon picture of gradualism most of us have is morphological evolution at a constant rate. This is a caricature of Darwin and has pretty much nothing to do with evolution as it's ever been understood. Rather, gradualism allows for a variation of speeds of evolution; slow, fast, and everything in between (what Dawkins calls \"continuous variable speedism\"). Punctuated equilibrium, as Gould used it, refers to periods of ",
" (or near-total) morphological stasis interspersed with switches to very rapid evolution (what Dawkins calls \"discrete variable speedism\"). "
] |
[
"Why am I always tired throughout the day, but energetic at night while surfing reddit until 3AM? Shouldn't I just keep getting more and more tired until I fall asleep?"
] |
[
false
] | null |
[
"Your circadian rhythm is controlled by melatonin levels. Elevated melatonin causes drowsiness and melatonin should decrease to undetectable levels during the day.",
"Melatonin production is suppressed by shining blue light around 460 to 480 nm onto the retina. ",
"So perhaps you are not receiving enough blue light intensity early in the morning and it is only by late in the afternoon that your melatonin production is properly suppressed."
] |
[
"Sunlight would be the normal thing. ",
"According to some researchers the illumination intensity that excites the circadian system has to reach up to 1000 lux striking the retina for about an hour which is easily achieved by simply walking about in sunlight when you wake up.",
"Of course this doesn't help if it's dark when you wake up but can get blue-light boxes for the morning and there are also blue-light filtering glasses to be worn in the evening to allow melatonin production. ",
"The effect is not instantaneous and takes a week or so to entrain the circadian rhythm, this is why jet lag is more than just tiredness. \nThe following facts are known:"
] |
[
"What is meant by blue light intensity? Sunlight or what"
] |
[
"Is there a confirmed link between sleep deprivation and Alzheimers?"
] |
[
false
] |
Are there any current work, linking sleep deprivation to Alzheimers, or at least discussing it thoroughly(based on current research) (I'm new to this subreddit)
|
[
"It's still soon to determine that, but yes, sleep deprivation ",
" be a risk factor for Alzheimer's: there's a molecule that's produced in the brain called beta-amyloid. People with Alzheimer's have high levels of beta-amyloid in their brains, and sleep deprivation is one of the factors that influence the formation of deposits of this molecule in the brain (when you sleep, the levels of beta-amyloid decreases). Here's the ",
"full study",
".",
"Also, while we sleep our brain is preparing to give better responses during our waking hours: according to recent theories, sleeping is what enables brain plasticity. Here's ",
"a study on the subject",
" and here's ",
"an article",
" linking it (and a bunch of other studies) to Alzheimer's.",
"Again, those results aren't conclusive. We can't establish causation just based on these researches."
] |
[
"Agreed on all points. I just wanted to post another a 2013 article that talks about sleep and it's role in clearing things like amyloid through the brain using some sort of lymphatic system (termed glymphatic system). ",
"http://www.ncbi.nlm.nih.gov/pubmed/24136970",
"Again, you're right that there is no causative report. Furthermore, it's hard to even do a retrospective study on correlating long-term sleep deprivation and Alzheimer Disease. ",
"Bottom line is sleep is important, even though we don't quite understand it. "
] |
[
"Whilst you've made no claim on the contribution of ",
" to Alzheimer's disease, I feel one should note that a large portion of literature is now pointing towards ",
" as the primary cause of neurodegeneration in Alzheimer's disease. We sectioned many wild type healthy brains and found large deposits of ",
". Tauopathy is now where many treatments are aimed. "
] |
[
"If you bombard an iron-56 with neutrons, is there a limit to how many neutrons it can gobble?"
] |
[
false
] | null |
[
"You sure can't get past the neutron drip line, which I think is experimentally unknown but is somewhere after Iron-74. However, the process is nearly impossible because for instance, you have to pass through nuclides like Iron-72 which has a half life of 150ns, so it would be very hard to get another neutron added before it decays. In that regime, you also get oddball decays like beta- 2n, where the nucleus decays by converting a neutron into a proton+electron+neutrino, but also throws away two more neutrons in the process, so the result actually has 3 fewer neutrons.",
"Also, the neutron absorption cross section is going to start dropping by orders of magnitude as you approach the drip line. We don't even have neutron absorption cross section data beyond Iron-60, according to ",
"https://nds.iaea.org/relnsd/vcharthtml/VChartHTML.html",
" ",
"We have data on isotopes out near Iron-75 not by making them by adding neutrons, but by observing very-rare fission results from uranium. Basically, the uranium fissions while in a particle accelerator, and you can tell that one fraction was Iron-73 that then decayed a few hundred nanoseconds later."
] |
[
"It can keep capturing neutrons until it reaches a point where neutrons no longer remain bound to it. This is called the neutron dripline."
] |
[
"These are the kinds of questions quantum computers could answer, I take it."
] |
[
"How did dyslexia manifest itself before the rise of written language?"
] |
[
false
] | null |
[
"Well I'd hate to just link to wikipedia, but it does list ",
"many non-writing related characteristics of dyslexia",
"."
] |
[
"From the source for that line (a ",
"NY Times article",
"):",
"It has long been known that dyslexics are drawn to running their own businesses, where they can get around their weaknesses in reading and writing and play on their strengths. ",
"\"It has long been known\" is often akin to hand-waving, but they back it up with sources further into the article. This part tells you what they expected to find in the study.",
"The report, compiled by Julie Logan, a professor of entrepreneurship at the Cass Business School in London, found that more than a third of the entrepreneurs she had surveyed — 35 percent — ",
"The study also concluded that dyslexics were more likely than nondyslexics to delegate authority, to excel in oral communication and problem solving and were twice as likely to own two or more businesses.",
"That's more or less the meat of what you want to know. Take it with a grain of salt."
] |
[
"Dyslexia doesn't just affect written language. As a sufferer or it there are other symptoms that affect day to day life. Remembering names is a big one. Knowing directions and drawing dirt maps could have been challenging."
] |
[
"How robust is the paper from Steven Quay about the potential lab-based origin for Sars-CoV2, does it make a compelling argument and if so/not so, why?"
] |
[
false
] | null |
[
"So given that your background is virology/immunology, can you at least tell me if this guy Steven Quay is respected, considered a crank or what?"
] |
[
"Crank"
] |
[
"r/askscience",
" is not an appropriate place for ridiculous conspiracy theories."
] |
[
"I am sitting in a boat in a lake of superfluid helium. Can I use oars to propel myself? What about propeller? Also, am I in danger of sinking?"
] |
[
false
] | null |
[
"Assuming you mean liquid helium-4 at a temperature below the super fluid transition temperature, yes you are in danger of sinking. The liquid helium will creep up the side of the boat and the fill the inside. ",
"Propelling yourself would be hard as helium has essentially zero viscosity. However if you move the oars fast enough you can generate forward thrust anyway. I don't actually know off hand how fast this would have to be, but if you went faster than the speed of sound within the fluid it would be enough so the condensate faction couldn't just flow around the oar. "
] |
[
"The superfluid viscosity is very low, but not zero. Its possible to measure a finite viscosity in shear mode flow at all finite temperatures. There are contributions due to elementary excitations in the fluid, in the Landeau two-fluid model these excitations are referred to as 'normal' state fluid, whose bulk fraction decreases as temperature is lowered further below the lambda transition. The superfluid component does exhibit inviscid flow, but not the normal fluid component."
] |
[
"Helium-4 is a boson (has an integer nuclear spin) because it is made up of an even number of half-integer spin protons and neutrons. This means that it follows Bose-Einstein statistics that allow for the formation of the superfluid, which is Bose-Einstein condensate-like.",
"Helium-3 is a fermion (has a half-integer nuclear spin), so it can't natively form the superfluid. If you make it still colder, though, it can form pairs of nuclei (somewhat like how electrons do in superconductors) that collectively have integer spin and behave like a superfluid."
] |
[
"How does a bolt of lightning cause a current in an electric appliance even when the lightning does not strike the device?"
] |
[
false
] |
I'm also curious to know how a surge protector protects devices from the bolt.
|
[
"Lightning affects devices if it strikes a power line that supplies electricity to that device. That's how it usually happens. A surge protector detects an increase in current and cuts off the power to whatever is plugged in"
] |
[
"If a bolt strikes a power line that is connected to that device, there will be a very large and very rapid change in potential on the line. This causes a whole lot of charge to try to move. At its most basic, a surge protector reacts to this rapid change and breaks the circuit before the majority of the charge has a chance to flow through the connected devices.",
"Interestingly, lightning doesn't even have to strike the line feeding a device to cause a surge. Simply striking near the device can induce currents in either the device or the lines feeding it. This is because a bolt of lightning involves a very large amount of charge moving very rapidly, and for a very short time. Moving charges (i.e. current) generate a magnetic field, and a conductor placed within a varying magnetic field will experience an induced current (electromagnetism is a fascinating thing). This effect is extremely dependent on proximity, however, because the strength of the bolt's magnetic field drops off according to the square of the distance."
] |
[
"Unless the $3 \"surge protector\" you got at walmart is so shittly made it shorts and fries your gear anyways [been there done that]."
] |
[
"Why do people with down syndrome look similar to each other?"
] |
[
false
] |
Growing up, whenever I saw someone in my middle school or high school, whenever I saw someone with down syndrome I thought that they were in the same family and that it was a hereditary disease. I've come to realize that's not the case, when I was in college. So what is it about down syndrome that makes the person who has it look very similar to other people who have it as well.
|
[
"This is an evo-devo question + morphometrics question. I'm not great w/ evo devo, but I think I'm good enough to be able to give a coherent answer.",
"Developmentally, a whole host of genes work to define how your body grows. It turns out - when you average those genes together, based on how common they are in our species - you get an average face.",
"The difference between down syndrome and common people is much bigger than the differences within genes. Downs syndrome = 47 chromosomes, instead of the usual 46. This means that some of the genes that define development get double doses. This is bigger than the average differences within 46 chromosome individuals.",
"So, that means that the morphometric distance is also larger. Adding a whole chromosome is much bigger than adding in a random assortment of the genes in the pool, which is a continuous scale you are familiar with. In this case, the changes happen in a consistent direction as well! So, all those downs syndrome people are moved in a consistent direction away from the norm, which you can pick up on.",
"Cheers!"
] |
[
"No, OP is asking in ",
"/r/askscience",
" not ",
"/r/explainlikeimfive/",
"Although the link you provided is somewhat informative, ELIF is a different forum with a different readership, and more importantly, much different posting rules. It was perfectly valid for the OP to post here expecting a scientifically sourced and vetted answer ",
"If you're going to give a smug answer, please at least have the courtesy of giving one that is directly applicable to the OP's query, such as ",
"this one, from this very subreddit",
" The problem with doing so, however, is that it's less likely that anyone will check that old thread to answer any follow-up questions the OP might (most likely will) have.",
"Furthermore, the link you provided is archived and closed to further discussion."
] |
[
"I think there's another factor at play - how we distinguish faces.",
"A couple of studies have shown that babies can distinguish between different monkey faces incredibly well, but adults can not. After seeing potentially millions of humans but a tiny number of monkeys through our development stages, we hone our ability to distinguish faces only in those we actually come across frequently. This is the cause of the \"",
" people all look the same\" trope, where ",
" is whatever ethnicity is a minority where you are. (And as it relates to the topic at hand, people with down syndrome are a minority, and they are a minority everywhere.)",
"Can't link to sources (being productive at work as ever), but if you google for babies recognising monkey faces you should find quite a few articles pretty easily."
] |
[
"For beta decay: During positron emission a proton becomes a neutron and emits a positron (and neutrino). During electron emission a neutron becomes a proton, emitting an electron (and antineutrino). How is it possible that they can convert back and forth by continuously losing particles?"
] |
[
false
] |
I've had this question for a while. It doesn't make sense that they can convert into each other by losing particles each time. Can someone please explain.
|
[
"A proton is made of 2 up quarks and 1 down quark. A neutron is 2 down quarks and 1 up quark.",
"In beta- decay, an up quark converts to a down quark, and emits a W- boson. This boson decays to an electron and an antineutrino.",
"In beta+ decay, a down quark converts to an up quark and emits a W+ boson, which decays to a positron and a neutrino.",
"So at the nucleus level, what you see is a proton change to a neutron and vice-versa. But what is actually happening has to do with quarks flipping back and forth.",
"One other thing to note is that the neutron has more mass than the proton. As a result, a free neutron can beta- decay, but a free proton cannot beta+ decay. The reaction isn't reversible (in that sense). Beta+ decay can only occur in bound nuclear states, where some of the binding energy can go into the mass needed."
] |
[
"The W boson in neutron decay is a virtual particle: it's momentum and energy don't satisfy E",
"=m0",
"+p",
", as all real particles should (some folks call that \"off the mass shell\", as if we instead make mass the free parameter, the mass we would anticipate measuring doesn't match the mass of the W-boson). One way to think of virtual particles is that the Uncertainty principle, when framed in terms of energy and time, let's particles borrow energy for short periods of time. So, one of the down quarks of the up-down-down neutron borrows some energy from Nature, and has to return it within a specific time limit. The down quark uses that energy to convert itself into an up quark and a W- boson. The W- is still borrowing energy to make up for the huge amount of mass it has, so it returns the borrowed energy at the same time it decays into an electron and the electron antineutrino. States with \"borrowed\" energy aren't physical (energy wouldn't be conserved), so we can't measure them. A lot of energy needs to be borrowed, so it's a fairly rare process, hence the relative stability of the neutron compared to most baryons. A similar process is used for virtual pair production: an electron and a positron borrow energy from nature, pop into existing, and simply have to annihilate within the time frame to return the energy back to nature. You can't directly observe them, but they do have measurable effects (we think).",
"Not all bosons have mass. The gluon and photon are massless. The W+/-, Z0, and Higgs bosons all have mass."
] |
[
"In neither process do the protons or neutrons loose any particles. The electron/positron is created during the decay process and there is no sense in which it was inside the proton/neutron to begin with. Both forms of beta decay transform a parent nucleus into a product nucleus with less energy than the parent. The left over energy goes into creating the electron/positron and neutrino."
] |
[
"I just made some delicious instant chocolate pudding. How does it work?"
] |
[
false
] |
I'm talking about U.S.'s pudding, the custard-like dessert ( ). It starts as a powder. Add cold milk and it gets that gelatin consistency. What's going on? Is it a dehydrated molecule that gets rehydrated? What are the delicious chemistry specifics.
|
[
"Alright, on the instant version, see where it says 'Modified Food Starch'? In this case, the modification is a process known as ",
", where the starch is partially cooked using steam and then rapidly dried. This means that the starch does not need to be heated to reach the thickening point, giving you delicious cold pudding in a fraction of the time.",
"Compare this to the cook-and-serve pudding which uses unmodified corn starch, which needs to be heated to close to boiling before it gels. The starch in wheat flour needs to reach boiling, which will damage the milk proteins as well and lead to a poorer-quality pudding."
] |
[
"No idea what that stuff is, but looking at the ingredients list, with cornflour / starch being the main ingredients, I assume it's to do with ",
"http://en.wikipedia.org/wiki/Starch_gelatinization",
".",
"Corn flour (corn starch in the US) is a thickening agent. Basically, to quote wikipedia: \"As the starch is heated, the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid\""
] |
[
"Pudding is not gelatin.",
"Ingredients in instant pudding:",
" Sugar, Modified Food Starch, Contains less than 2% of Natural and Artificial Flavor, Salt, Disodium Phosphate and Tetrasodium Pyrophosphate (For Thickening), Mono- and Diglycerides (Prevent Foaming), Artificial Color, Yellow 5, Yellow 6, Bha (Preservative).",
"Cook & Serve pudding isn't gelatin, either.",
"Ingredients in Cook & Serve pudding:",
" Sugar, Dextrose (From Corn), Cornstarch, Cornstarch Modified, Contains less than 2% of Natural Flavor, Artificial Flavor, Salt, Calcium Carrageenan (Thickener), Polysorbate 60 (Prevents Scorching), Butter, Yellow 5, Red 40, Blue 1."
] |
[
"What would happen if we built a giant smokestack that was tall enough to be in space, and started burning a bunch of stuff on the ground?"
] |
[
false
] |
Might be a silly question. Still curious just the same. What would happen to the smoke/pollution if we started burning a bunch of stuff here on earth but had all of the nastiness float up through a giant smokestack some distance off into space? Would it dissipate or just hang out there, ready to poison us at some later date? Thanks for any answers!
|
[
"Assuming you can build the stack in a way that it's stable. And then assuming that you could find a way to make sure everything goes all the way to the top and you could actually eject stuff into space...",
"Earth's gravity would just pull all that crap back into the upper atmosphere."
] |
[
"The official answer is that the risk of the rocket launch failing and exploding that \"nastiness\" (which, I assume, is nuclear waste, some pretty nasty stuff) all over the countryside."
] |
[
"so you'd have to build this huge hollow tube from the earth's surface out past the last layer of our atmosphere. Then you'd have to accelerate the smoke using a mechanical method past the escape velocity of the earth's gravitational pull. If you could do those things, chances are the smoke would dissipate, and be sucked back in to the earth's atmosphere over time. my two cents.",
"I always wondered why we didn't launch a rocket of nastiness into the sun to be converted into the raw elements again. I know the answers. Cost, risk."
] |
[
"Why did hominidae lose their tails in the evolutionary process?"
] |
[
false
] | null |
[
"To grow a tail takes energy. If a species that once had a tail stopped using the tail, it would be advantageous to not grow that tail and use that energy to do something else. ",
"This is called 'Reductive evolution'.",
"Of course, it's not as simple as a monkey having a kid, which ends up not having a tail. Evolution is a slow process. Even we as humans still have a vestigial tail. At one point when we are still embryos, one-sixth of all of our body is a tail."
] |
[
"Just a follow up question, would having a tail affect our bipedal efficiency?"
] |
[
"Tails were mostly used fr balance by creatures which require it. Apes did not."
] |
[
"Is there a temperature where water will never freeze or evaporate?"
] |
[
false
] |
To expand on that, say you had a ring of water left over on a table after a cup was sitting there for a period of time. In any 'normal' condition the water will evaporate off the table, and if it were especially cold it would freeze. Is there a situation where the water will remain in liquid state indefinitely due to its inability to change? edit: sorry for not looking at this in so long, but great answers! Thanks!
|
[
"It boils at 100 degrees Celsius it evaporates at much less. Thats how we get a water cycle on earth. ",
"Edit: at sea level , it can boil at lower temperature at higher altitudes"
] |
[
"It boils at 100 degrees Celsius it evaporates at much less. Thats how we get a water cycle on earth. ",
"Edit: at sea level , it can boil at lower temperature at higher altitudes"
] |
[
"Take an enclosed volume at 100% relative humidity, apply higher pressure and cool the air and the puddle would conceivably never evaporate. In fact, under those conditions additional condensation would form as the water vapor is 'squeezed out of the air', so to speak. "
] |
[
"Why do seismic waves (P waves and S waves) travel at curves through the Earth?"
] |
[
false
] |
I know how they refract when they reach structure boundaries because of the different density of the structures e.g. crust to mantle, but don't understand why they travel at curves through those structures.
|
[
"It's because refraction does not have to be an instantaneous process.",
"If the density changes suddenly, the wave will indeed just change the direction of its propagation.",
"But if the density changes gradually, the wave will follow a curved path. Think of it as the same change in direction, but over a certain distance."
] |
[
"Because the waves travel faster in denser mediums, and even within the layers themselves there is a density gradient. I visualise it as the 'outside' (deeper) part of the wave travels quicker and the 'inner' part of the wave travels slightly slower, resulting in a curve."
] |
[
"It's because even within the different layers of the Earth, like the mantle, there are small variations in temperature, density, seismic velocity and so on. These variations add up over distances so waves will continuously refract as they pass through areas with (slightly) different seismic velocities. Eventually the waves will refract to the point where they reach the critical angle and start moving back to the surface. ",
"This page",
" has some more info."
] |
[
"If a space ship is going 99% speed of light time is slower for them according to the earth (I think) but if the space ship is out reference point then the Earth is going 99% the speed of light. So wouldn't time be going slower on earth in relation to the ship?"
] |
[
false
] |
So 1 earth hour is only .5 hours on the ship (I am fully making numbers up here) because the ship is moving 99% the speed of light relative to the earth. But if you choose the ship as a reference point then the earth is the one moving so that would mean (as I understand) that 1 hour on the ship would only be .5 hours on the earth. And now 1 hour of thinking about this is causing a 3 hour headache!
|
[
"It is important to take into account the difference between the very nature of the two observers.",
"If you take the observer in the spaceship, what they see is the earth and all of space moving away from them, as if their ship is standing still. This means that we must also consider spacial contraction. This is the contraction of space in the direction of movement. It means that if, to take your example, a 1 meter ruler is moving at 99% the speed of light, the ruler will actually be .5 meters long when observed by a stationary person.",
"Now this means, in the reference frame of the dude in the spaceship, the distance of space that they are traveling through is actually shorter because, according to them, all of space is moving by at 99% the speed of light. ",
"Warning, the following is physics!",
"There is an interesting application in physics where scientists have observed muons that typically have a half life of 2.2 microseconds. These particles are created in the upper atmosphere and move toward the earth at very high (relativistic) speeds, something comparable to the speed of light. Using classical physics, we can easily determine that something like .05% of the muons will make it to the surface of the earth, however we experimentally observe something around 80%. ",
"It makes sense, if we use relativity, that in the reference frame of an on ground observer, the half life of a muon will actually be longer because of time dilation, this easily explains how 80% of the muons actually make it to the surface. But it is not so clear if we take the reference frame of the muon, and this frame is perfectly fine to use, so how do the muons survive with a half life of 2.2 microseconds, their half life cannot change because they are not moving relative to themselves. The answer is spacial contraction. Because they are moving so fast, they see the space that they travel through to be shorter. This means that, despite having a short half life, they don't have to travel as far to reach the surface of the earth and be detected.",
"It is weird to think that two different observers can explain the way something happens in two completely different ways, but physics tends to work like that."
] |
[
"Someone standing on the Earth will observe that time is moving more slowly on the ship, likewise someone on the ship will observe time moving more slowly on the Earth. This is just what is observed however, in reality since it is only the ship that has undergone acceleration, it is only the ship that will be moving more slowly through time."
] |
[
"I think I can explain some of the downvotes. Part of your answer is wrong. It is completely untrue that \"since it is only the ship that has undergone acceleration, it is only the ship that will be moving more slowly through time\". If this WERE true, then you have established sufficient criteria for a preferred reference frame, something that certainly doesn't exist in Special Relativity.",
"For as long as the distance between Earth and the Spaceship is changing (without acceleration, which is addressed by your verbage \"has accelerated\"), they will see eachother's clocks as ticking slower. The massive shifts that lead to the 'twin paradox' is due to the acceleration that the rocketship undergoes in turning around and coming back to earth, but ",
"."
] |
[
"If nuclear testing increased the Carbon-14 ratio of the atmosphere, would a comet or asteroid impact do the same?"
] |
[
false
] | null |
[
"No. The production of C14 was a direct result of interaction of energetic fission products - ",
"specifically neutrons",
". Those require nuclear events.",
"A meteorite or comet collision does not do this (it is simply a high energy collision), and does not produce the neutrons necessary to form C14 in the atmosphere."
] |
[
"Anything that can provide a neutron bombardment. Fusion or fission are basically the only two natural processes. "
] |
[
"Thank you!",
"Can any phenomenon other than nuclear fission produce excess C14?"
] |
[
"Why isn't the sky violet?"
] |
[
false
] |
[deleted]
|
[
"Edit: ",
"Better answer in the thread the Rupert's search link leads to"
] |
[
"Sunlight interacting with the Earth's atmosphere makes the sky blue. In outer space the astronauts see blackness because outer space has no atmosphere. \nSunlight consists of light waves of varying wavelengths, each of which is seen as a different color. The minute particles of matter and molecules of air in the atmosphere intercept and scatter the white light of the sun. A larger portion of the blue color in white light is scattered, more so than any other color because the blue wavelengths are the shortest. ",
"When the size of atmospheric particles are smaller than the wavelengths of the colors, selective scattering occurs-the particles only scatter one color and the atmosphere will appear to be that color. Blue wavelengths especially are affected, bouncing off the air particles to become visible. ",
"This is why the sun looks yellow from Earth (yellow equals white minus blue). In space, the sun appears white because there is nothing in between to scatter its white light. ",
"At sunset, the sky changes color because as the sun drops to the horizon, sunlight has more atmosphere to pass through and loses more of its blue wavelengths. The orange and red, having the longer wavelengths and making up more of sunlight at this distance, are most likely to be scattered by the air particles. ",
"The scattering of visible light by atmospheric gases is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering after Lord Rayleigh, who studied it in more detail a few years later. Rayleigh Scattering is where red, orange, yellow, and green are passed through and blue, indigo, and violet are \"scattered\" out creating the color. ",
"Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. The atmosphere acts as a color filter."
] |
[
"While it is true that a large portion of the sun's emmission spectrum is in the red-yellow band, and this can be detected using a ",
"spectrometer",
", the sun ",
" white to us in outer space because the human eye didn't evolve to differentiate between true white and the color of the sun."
] |
[
"Why is it that when I look in a mirror when I'm wearing glasses my eyes appear bigger but on video/photos they're smaller when I'm wearing the same pair. I have bad eyesight, full disclosure."
] |
[
false
] | null |
[
"because you are looking through the lens twice when looking at a mirror, and only once when seen directly"
] |
[
"This...changes everything."
] |
[
"Also, ever tried looking down a telescope through the wrong end? Same phenomenon."
] |
[
"Is it possible to create a human oocyte from male genetics to be fertilized by sperm?"
] |
[
false
] |
Seems like an odd question... Don't judge me. I'm just curious if there is enough genetic material in biological male DNA to create an egg, fertilize it, and have a surrogate carry.
|
[
"Yes – in fact, this is my PhD research project!",
"The basic idea is to convert pluripotent stem cells to egg cells. XY oogonia will undergo meiosis to form oocytes. Half of those will be non-viable since they'll lack an X chromosome, but half should be viable oocytes.",
"I'd be happy to answer any questions you might have about this. If you want more general information, you can look up \"in vitro gametogenesis.\""
] |
[
"theoretically you can take a sperm (that have to be an X carrying sperm) and pluck the nucleus from it and inject it into an egg that had its own genetics removed, Then fertilize it.",
"It won’t be a simple under taking however, even though the genetic material exist, it has be activated a certain way, and that is the difficult part. ",
"That is why gay couples still need an egg donor"
] |
[
"Cool! How do you deal with epigenetics and imprinting effects? I’m thinking of things like Angelman and Prader-Willi syndromes. Does the imprinting just reset?"
] |
[
"Do we already have an enormous database of naive B cells in our body, before even meeting the specific antigen?"
] |
[
false
] |
I can't wrap my head around how our body will make an antibody that fits the antigen during the first encounter. The VDJ recombinant genes are firstly random, and also they do not know how the antigen looks
|
[
"Yes, we do have a huge inventory of naive B cells normally present in our body. ",
"Antibody (and T cell receptor) development is something that seems really alien to our human eyes - it seems so wasteful and irrationally designed, and yet the end product is so efficient and elegant. The overall approach is simply to throw numbers at pathogens, making a vast oversupply of B cells, almost all of which are completely useless and will never do anything for us. ",
"That wasteful oversupply gets connected to a much more elegant system of amplifying and optimizing the tiny minority that are useful, so that the end result works very well. And the brute force oversupply kind of makes sense when you consider that the immune system has to be able to meet a functionally infinite universe of pathogen targets, which are actively trying to hide from it. ",
"But even though it works, and works well, it’s hard to imagine any human engineer designing this system."
] |
[
"In short yes,",
"This is because B-cells develop their B-cell receptor through VDJ recombination as pre-B cells prior to B-cell maturation. At maturation the B-cell leaves the bonemarrow to travel the body, and at this stage the B-cell is considered naive as it has not met a bindable antigen.",
"During the first infection many B-cells will possess the ability to bind the pathogens various antigens, this binding is a relatively week affinity. The immune system then has to decide upon the best binders which are selected for, this process is called clonal selection. Following clonal selection clonal expansion occurs, in which the singular B-cell proliferates and all progeny further diversify through somatic hyper mutation (amongst other methods). Of these mutations some will be beneficial and some will hinder antigen-antibody binding, but multiple rounds of clonal selection, clonal expansion and SHM occur improving binding ability each round. In the end the antibody produced is very specialised and many generations removed from the original naive B-cell that they would not appear related. Some animals such as sheep have very limited VDJ genetics as they rely upon somatic hyer mutation as their main source of antibody diversity.",
"I don't know if this helps but I can send you some good sources on B-cell development if you wanted."
] |
[
"I understand that rearrangements and shuffling of gene segments can result in a huge number and variety of B-cell receptors. I always wondered about how a finite number of genes could generate such a huge diversity of proteins and I got my answer, but where I'm not clear is how the immune system, upon infection with a previously unknown pathogen, identifies the \"winning\" B-cell and it's receptor (clonal selection), and then how the population of B-cells is enriched towards that winning receptor (clonal expansion). ",
"More specifically, how does the immune system detect the B-cell having the best affinity to the new pathogen? I'm assuming it's some kind of signaling or display on the B-cell surface? And then how is the receptor's amino acid and/or DNA sequence conveyed? If the immune system is to generate more of these winning receptors (and improve upon them through SHM) how is the information about that receptor transmitted and to what is it transmitted? ",
"Does my question make sense? (My area is not immunology. I have only a lowly bachelor's in biology where I focused on molecular/genetics)."
] |
[
"How do we know for sure that red-shift in distant galaxies / stars is because they are moving away and not because of some other unknown effect on light traveling for insanely long times / distances?"
] |
[
false
] |
I know that there is probably something very basic that I am missing but this question keeps coming back into my head after years of thinking about it, and I can't find anything online that explains it (from a google search anyway). I understand how the doppler effect works, and have no doubt that stars moving away WOULD be red shifted. But doesn't the fact that the farther away we look the more red shifted a light source is imply that there could be some effect on light that is due to the distance / time that light travels? As an analogy the farther I look in earth's atmosphere, the less color saturated the objects appear to be - that's not due to anything about the objects themselves, it's because of the journey the light has to travel to get to me and the effects of the atmosphere. The fact there is such a clear correlation between color saturation and distance would lead me to believe that the effect is because of the distance itself, not due to some other effect which causes objects that are further away to be less color saturated. I'm not saying that's a possible explanation for the effect, just an analogy of the way you would interpret the data and whether the effect is due to some property of the source itself or a property of the journey the information takes to get to you. Basically how have astrophysicists ruled out this possibility?
|
[
"This is basically the old 'Tired Light' theory, which was an earlier challenger to the explanation of expanding space:\n",
"https://en.wikipedia.org/wiki/Tired_light",
"Suffice it to say that a century of astronomical observations highly disfavor any model like this, but there are some good explicit examples in the wikipedia link."
] |
[
"This completely answers my question. Thank you!"
] |
[
"The analogy is insufficient as our atmosphere refracts light (bending) and different colours of light are refracted through different angles due to their different wavelengths, which is why we get a rainbow. Also photons of light will be absorbed by atoms/molecules in the atmosphere which is why objects appear fainter the further away from us they are. Water vapour is highly effective at this task. Given there is no \"atmosphere\" in space, refraction cannot happen and photons being absorbed doesn't happen to the same extent (there are still atoms in space to absorb the photons but waaaaayyyy fewer), so if you have two stars of equal brightness and one further from us than the other, the closer star will appear brighter. As you know, Doppler shift is a completely different effect to above. It's not bending light and it's nothing to do with photons being absorbed. ",
"How do we know for sure? Huge data sets covering millions/billions of galaxies show this to be a true effect plus the further away the object, the greater the red shift and this is consistent in every direction we look. Is it possible there is another explanation for this? Sure but there isn’t any evidence to support a different position at this time"
] |
[
"Would it be possible for an animal to have a mutation that would allow it to breed with humans?"
] |
[
false
] |
[deleted]
|
[
"No. Even primates have a different number of chromosomes."
] |
[
"Then again, so do those with downs."
] |
[
"Many individuals with Down Syndrome are either sterile or have significantly reduced fertility."
] |
[
"Can the Hubble telescope take a picture of the Webb telescope?"
] |
[
false
] |
Do their relative positions let them see each other?
|
[
"Hubble is in Low Earth Orbit, and spins around the Earth about once every hour and a half. So it quickly gets a view of almost everywhere in the sky.",
"But JWST is too small to be seen as more than a dot, even by Hubble. The sunshield is 22 metres across, but it's 1.5 million km away. This gives it an apparent angular size of 0.0027 arcseconds, but Hubble's best resolution is 0.04 arcseconds - anything smaller than that is a blur. An arcsecond is 1/60th of an arcminute, and an arcminute is 1/60th of a degree. The Full Moon is about 30 arcminutes (2160 arcseconds) across - half a degree. Jupiter at its closest is about 50 arcseconds across.",
"So yeah, you could hypothetically point Hubble at JWST and detect a point of light there, but it couldn't see it as anything other than a dot."
] |
[
"The blur is the \"point-spread function\", which depends on the optics of Hubble rather than the shape of the object. If you cancel it out, it turns a blurring spot into a sharp point, but doesn't give you any shape information."
] |
[
"Yes, although that would still be effectively a single pixel. If you want a 4 pixel wide image, which is still extremely low resolution, then it'd need to be about 60 times larger.",
"But yeah, HST has high resolution, and JWST isn't that far away on an astronomical scale, and is pretty big as far as artificial satellites go."
] |
[
"[Biology] Why can't we use transgenic polyDNAviruses from parasitoid wasps to introduce beneficial metabolites straight into our own DNA?"
] |
[
false
] |
If we can identify the genes responsible for the production of beneficial proteins and the like why can't we take the polyDNAvirus venom from parasitic wasps and splice them in to create a vaccine that would allow our bodies to produce cures for stuff like Parkinsons that are caused by running out of them?
|
[
"These are viruses that originally infected one insect and adapted to infect a different insect so that would be a tricky part as far as using it for humans is concerned. The basic premise of what you are saying is \"gene therapy\" and there are people working on adapting various viruses for that. "
] |
[
"We are trying - this technique is known as gene therapy, and has made great strides recently (as in within the past month or so).",
"Viruses are stripped of their DNA, and a new piece is added, to be inserted in specific tissue type. Adenoviruses are more common, as their DNA can hang out in the nucleus without the need to insert itself into the cell's DNA and possibly break an existing gene.",
"The problem nearly everyone overlooks is that these viruses do not replicate - they simply deliver DNA to their hosts. Therefore, we can not target the whole body, only a small subset of certain organs. ",
"Currently a gene therapy method to cure Huntingtons is in clinical trials, with very promising preliminary results. ",
"For Parkinson's disease, stem cell methods are the most sought after, as promising work is being done is mouse models that show we don't need to mess with our genomes, simply create the right type of stem cells and inject them in the right places."
] |
[
"Gene delivery is a very real thing we're working on. I think what you're talking about is a retrovirus; a type of virus that basically rewrites our DNA with its own. ",
"The most popularly known kind of retrovirus is HIV, the AIDS virus. While retroviruses like HIV retool our DNA for its own nefarious purposes, we're working on doing exactly what you're saying; to deliver genes that would be beneficial for us."
] |
[
"How do I get melted plastic off my cast iron?"
] |
[
false
] | null |
[
"If it's just this are of the pan, take some steel wool to it, or some mechanism to grind off the metal, like metal polish. It's probably going to be easier to remove mechanically now that you've baked it on that chemically. "
] |
[
"How localized is this plastic residue? All over the inside of this skillet in a thin layer, or in a single glob?"
] |
[
"Get the pan really cold. The plastic might be able to peel off then.",
"Acetone probably won't much but melt the plastic further. ",
"I would go nuts with a wire brush on it. Then reseason the pan. "
] |
[
"How many fundamental constants are there?"
] |
[
false
] |
I am pretty sure the speed of light is a constant (Or maybe it's just equal to 1 and not considered a constant?) But what are the fundamental constants relevant to our universe that can't be derived by an equation but simply had to be measured?
|
[
"One of the rare questions that can be simply answered with a link to an article: ",
"http://math.ucr.edu/home/baez/constants.html",
"tl;dr: 26"
] |
[
"you can derive the number of constants from all the other constants."
] |
[
"Not to be rude or whatever, but this isn't the sort of thing that requires \"proof.\" It's just definition. It's customary in some branches of physics to convert all physical quantities to units of length before doing any calculation. When you do, all physical quantities end up being expressed either as units of length — mass, duration and energy — or per-units of length — acceleration, angular velocity — or per-units of area — energy density, mass density and pressure. Once you've done this, ",
" and ",
" all drop out, because they're all exactly one once you've done your conversions.",
"There's ",
" about units, or constants that relate units. They're all totally arbitrary. It's just as meaningful to measure mass in terms of length as it is to measure it in terms of kilograms. More so, really, since length is an intrinsic property of the geometry of the universe, while the kilogram is a lump of metal in France."
] |
[
"Why are there two formulas for half-life?"
] |
[
false
] | null |
[
"What formulas are you referring to?"
] |
[
"Remaining Sample = me",
"\nand\nRemaining Sample = m÷2",
"Where\nm = initial sample size,\ne = the natural constant of e,\nr = (ln2)/h,\nh = length of one half-life (in years),\nt = elapsed time since beginning of decay (in years)"
] |
[
"These equations are equivalent."
] |
[
"Why was earth bombarded with meteorites so much throughout its history, but not now?"
] |
[
false
] |
[deleted]
|
[
"During the ",
"late heavy bombardment",
" the Earth was pummeled with meteors much more often than it is now. It's unknown exactly why the heavy bombardment happened, but it may have to do with changing orbital patterns of the gas giants. The late heavy bombardment ended about 3.8 billion years ago.",
"In the time since then, there's no evidence to suggest that the earth was bombarded with meteors at a rate much greater than it is today. Small meteors hit the earth every day, but burn up in the atmosphere before they hit the ground. Meteors with diameter 5-10m hit the earth about once a year. Objects with diameters over 50m strike the Earth approximately once every thousand years. (",
"source",
").",
"To give some perspective, we would only expect to have seen about 10 such meteorites in all of recorded history. Statistically, we should not expect to have seen any strikes much larger than that in recorded history, even given that the rate of large meteor strikes has remained constant over the past several billion years."
] |
[
"Great answer, thanks. Kudos for the sources also :-)"
] |
[
"Additionally, Jupiter does a great job of hoovering most incoming debris from the Oort Cloud."
] |
[
"Former creationist here: with so few pre-human fossils over millions of years, how do we extrapolate data of past human evolution?"
] |
[
false
] |
21 years old and for the first time I'm getting a science education at my local community college. But I'm just confused at this area of human evolution. We have a small amount of our ancestor's fossils, and usually they're spread across millennia and vast geographic distances, how does science form connections between these fossils? I'm not trying to ask this as a "gotcha" question or anything, I'm genuinely confused about how we are able to relate fossils that are so far apart in geography and time.
|
[
"Actually there are more than just a few fossils. Here's ",
"a list of just a few of the thousands of them",
". I remember seeing a video about forensic paleontology once, but of course I can't find a link to it. It was pretty interesting, the idea is that bones can only grow and wear in certain ways, and the ways they grow and wear can tell you a lot about the animal that owned them.",
"The process of putting fossils in order and ascribing them to an ancestral line is complex. There are various means of dating fossils remains. Often different ways of dating are used on the same piece, for cross checking.",
"Certain telltale signs of anatomy are revealing. Humans have a mutation compared to chimpanzees, that makes the ",
"jaw muscles smaller and weaker",
", which enabled the cranium to enlarge and the zygomatic arch to diminish. So if you find a skull with a small zygomatic arch and a large cranium, you know at least that it has that mutation, so it's more along the human line than a skull that doesn't have those features.",
"Similarly it's possible to tell just from a femur the type of animal and whether it was walking upright or not, and so place it more along the human line than other primate femurs.",
"Once you get good at reading the signs, it's less difficult to tell the differences, though they can still have intramural disagreements about certain fossils, and where they belong in the family tree."
] |
[
"Hi, I am actually a grad student studying paleoanthropology, and I'm happy to answer any questions that you might have about human evolution. I mutatron answer some of the basics, and I just wanted to chime in with some more details. ",
"Depending on who you ask, there are either a lot of human fossils, or not very many. Obviously as a paleontologist you always want more. Heres a cool map that shows many human fossil bearing sites around the world. Its several years old, so by now there are many more dots that could be added (",
"http://www.handprint.com/LS/ANC/disp.html",
"). The number of fossils (actual specimens, not necessarily species) also depends on what time period you're looking at. Humans and chimpanzees last shared a common ancestor somewhere around 7-6 mya, and for the several million years following this splitting, there are very few fossils. Once we get to about 4.5 million years ago, we start seeing more, and then once we get to around 2 million years ago we start seeing even more.",
"So what happens when someone finds a human fossil (lets say a skull, which is rare to find)? As mutatron mentioned, hopefully we have a pretty good idea of how old it is if we're lucky enough to have found it between two layers of date-able volcanic ash. If we cant peg down the date of a fossil very well, then things get much more complicated (as with some caves sites in South Africa). The person who finds the skull, who presumable has spent a lot of time studying comparative anatomy of apes, monkeys, and other fossil humans, will determine if this a new species or not. If there are other fossil humans known from the same area or time period, and the new skull looks like others from the same place/time, it will usually be assumed that the new fossil belongs to one of the existing species. Also keep in mind, when I say \"looks like\" this is actually a judgement based on qualitative features and quantitative measurements of the fossil and comparisons with others. If the new fossil is sufficiently different than others, then it will probably be classified as a new species, and potentially even a new genus. When this happens, the other will publish a description of the fossil, as well as the diagnostic features (in this case of the skull) which separate from other known fossils. ",
"Ok, so now, getting back to your question, how do we know the patterns of relationships between the fossils we find, and living humans and apes? For this we resort to a method called cladistics. (Here is a more in depth summary then im about to give: ",
"http://www.ucmp.berkeley.edu/clad/clad1.html",
"). The basic assumption is that species that are more closely related, tend to share features that animals more distantly related do not possess. For example apes (humans, chimpanzees, gibbons, orangutans, and gorillas), do not have a tail. All other monkey species do. Therefore, we can use this piece of information to assume that the loss of a tail is a feature that unites apes together as a group, to the exclusion of monkeys. And in fact this is one of many shared features which unites apes as a group of individuals more closely related to each other than to any monkeys. We use this same method within a group that includes humans and things more closely related to humans than chimpanzees (members of this group are called hominins), and using lots of different pieces of anatomical information, we can generate hypotheses of patterns of relationships, in the form of phylogenetic trees (heres a simple one that I would tend to agree with but its also missing several species: ",
"http://tolweb.org/onlinecontributors/app?service=external/ViewImageData&sp=20939",
"). In this tree, humans, (Homo) are more closely related to the genus paranthropus than either are to Australopithecus afarensis for example. Using this method we can deduce relationships among all the fossil hominins that we find. ",
"Also keep in mind, that when a lot of people get into human evolution, we all tend to assume that its linear. For example, Australopithecus afarensis (~3.3 mya) begat Homo habilis (~2.3 mya) begat Homo erectus (1.8 mya), but these kind of direct relationships are super hard to establish, and many people try to stay clear of that, at least now-a-days. In addition, from what we see in the fossil record, there are generally several hominin species roaming around at the same time. For example 100,000 years ago there were Homo erectus, Homo sapiens, Homo neanderthalensis, and Homo floresiensis, some of which were in the same place at the same time!",
"So I meant to say more too, but I feel like this post is sufficiently long. If you want any more info just ask!"
] |
[
"It also helps that many of these fossils are located in the East African Rift system, which helps us document the age of the fossils. Lots of sediment is available to bury bones before they're destroyed by the elements because of the deep valleys created by the rifting. Volcanic eruptions in the area produce ash and lava, which allow us to radiometrically date those beds. Fossils found in sediments sandwiched between ash beds can thus be assigned to a date range, the oldest possible age being that of the ash bed below, and the youngest possible age being the ash bed above. The result is that our assumptions of the order of morphological changes in the line of human ancestors can be double-checked by radiometric dating. Once we have a \"feel\" for the morphological changes that human ancestor species underwent in one area, we can keep an eye out for possible in-between stages elsewhere. ",
"This is edging towards circular reasoning territory, an argument that creationists like to deploy against geologists/anthropologists. However, we don't classify fossils on just morphological data alone - other evidence, like the absolute age of the sediment and location of the find, is used in conjunction to suport the assignment of a fossil to a specific pre-human lineage. ",
"See here for a better explanation as to why this ",
" circular reasoning."
] |
[
"What are some dyes that stain human skin, and how do they work?"
] |
[
false
] | null |
[
"We don't offer advice or recommend products on this sub."
] |
[
"what if I rephrase the question what dyes penetrate the cell wall or something? Where can I ask"
] |
[
"You could try some bio related sub. You could try posting to ",
"/r/findasubreddit",
" to see if someone can suggest a specific sub"
] |
[
"Why is carbon so rare compared to oxygen in the inner solar system? Why don't we have tons of carbide minerals on earth?"
] |
[
false
] | null |
[
"Largely because of the quantities of the elements in the universe. The Milky Way, which seems to be a generally good indicator of the broader universe, has much more oxygen than carbon. 10,400 PPM are oxygen, while only 4,600 are carbon.",
"Source: Croswell, Ken (February 1996). Alchemy of the Heavens. Anchor. ISBN 0-385-47214-5."
] |
[
"But by that logic, there should be more carbon than oxygen as you lose oxygen along with the carbon. Twice as much oxygen in the case of carbon dioxide. "
] |
[
"But by that logic, there should be more carbon than oxygen as you lose oxygen along with the carbon. Twice as much oxygen in the case of carbon dioxide. "
] |
[
"Assume that there's a body in a perfect vacuum with some kinetic energy. If the entropy always increases, does the body somehow lose its kinetic energy?"
] |
[
false
] |
...Assuming that its gravity vectors compensated. Or does it only lose its thermal energy by emitting progressively colder and colder light?
|
[
"Its motion alone does not increase the entropy, nor decrease it.",
"If it is a blackbody, it will radiate energy and increase entropy. But if you ignore blackbody effects, its motion alone does not change the entropy. Giving the body some kinetic energy will be an act that increases the entropy of the system (remember - to consider entropy increasing, you need to consider the full system), but once that energy has been imparted there is no change in entropy as that object remains in a static frame of reference."
] |
[
"I think this is the best answer, but to clarify for the OP (since she/he seemed to be implying a radiating body), a blackbody in motion ",
" lose kinetic energy as it radiates heat. This kinetic energy loss is due to the loss in mass (the object will not lose velocity if the radiation is isotropic). For an energy amount E radiated, it will have E/c",
" less mass.",
"This thought experiment is precisely how Einstein derived E=mc",
" in his original paper."
] |
[
"Actually, this is the answer I wanted. In fact, I had the idea that the radiated energy is converted from the mass of an object, but, in that case, I wonder how this conversion mechanism works. But then I also thought that the radiation would consume the object's thermal energy hyperbolically (so that the temperature never reaches 0K), and it should, right? Or not? Or are they somehow related? So, could you please expand on how the mechanism you described works, or perhaps link some literature I could read."
] |
[
"How did the Earth's mantle and core become so hot?"
] |
[
false
] |
Were the materials already hot when the solar system was forming, or did it happen later?
|
[
"Scientific American said it best \"There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements.\" "
] |
[
"The most recent paper I've seen has radioactivity at about half the Earth's heat budget:",
"http://www.nature.com/ngeo/journal/v4/n9/abs/ngeo1205.html"
] |
[
"People can only measure the temperature of the surface of the Earth. Convection moves heat to the surface. It actually cools the Earth down faster, but for a while it will feel hotter than it would without convection."
] |
[
"Does an integer n exist such that e^n is also an integer? If so, what does n equal? If not, why not?"
] |
[
false
] |
[deleted]
|
[
"Yes. e",
"=1, so n=0 is such an integer. ",
"But aside from this, there does not exist such an integer. This can be seen using the ",
"Lindemann-Weierstrass Theorem",
". A consequence of this theorem is that if r is any nonzero algebraic number (ie: a root to a polynomial with rational coefficients), then e",
" is transcendental (ie: not algebraic). In other words: e",
"=Transcendental.",
"If n is any nonzero integer, then it is a root to the polynomial p(x)=x-n, which means that e",
" is transcendental, so it cannot be an integer. Note that the n=1 case shows that e itself is transcendental. We can also prove that pi is transcendental like this. If pi were algebraic, then i*pi would also be algebraic, and then this theorem would say that e",
" is transcendental. But e",
"=-1, which is not transcendental, so it must be the case that i*pi, and therefore pi, is transcendental."
] |
[
"This is correct, but it seems sort of like overkill to invoke the Lindemann-Weierstrass Theorem, since it suffices to note that the existence of any positive n such that e",
" is an integer would imply immediately that e is algebraic, when it is known to be transcendental. Of course, you can play the same game for negative exponents as well."
] |
[
"If e",
" is irrational but not transcendental, then e",
" is ",
" - that is, p(e",
")=0 for some polynomial p(x) with rational coefficients. But then e would be a root of the polynomial p(x",
"), contradicting the fact that e is transcendental."
] |
[
"If gravity bends light particles, is it possible we see some stars twice ?"
] |
[
false
] |
For example: Is it possible that light made 360 around some mass and then travelled back and one of small stars on the sky is Sun? How can we be sure about distance and location of stars on night sky?
|
[
"This does happen, but only for very strong sources of gravity. It happens around black holes, but we're only just this year getting enough resolution to see that happen. It's more common to see this happen around huge galaxy clusters. These clusters are very distant, and the background object they are ",
" is even more distant. So we can't see this happen with individual stars - but we do see multiple images of bright distant quasars. This also magnifies the quasar, and this is how we get the best views of the very distant universe.",
"One fun thing here is that quasars actually vary in brightness over time. As the light is travelling in different paths for the different images, we see one image go through a peak of brightness, and then the other image follow a little while later. So we get a snapshot of the same quasar at different times, which gives us an extra insight.",
"Some nice pictures ",
"here",
" but there's loads around the web.",
"Lensing that doesn't produce clear double images is also quite common. When two stars happen to line up exactly for a moment, we get a ",
" event, and the background star will get brighter for a bit. The exact pattern of how it gets brighter tells us about the sources of gravity in the lensing system, and can even help us find planets. There's also ",
", where any galaxy ",
" distorts the shape of background galaxies behind it. And in galaxy clusters, you can often see galaxies apparently bent into circles and arcs by the cluster's lensing effect. Some nice pics here: ",
"https://upload.wikimedia.org/wikipedia/commons/b/b9/HST-Smiling-GalaxyClusterSDSS-J1038%2B4849-20150210.jpg",
"But, this is a small effect within our own galaxy, and can be modelled and subtracted when necessary. For distant galaxies, the effect can be dramatic, but only in some circumstances, and even then we have enough information to cancel out the effect if we need to. In fact, rather than making the night sky more confusing, gravitational lensing gives us a zoomed-in view of small bits of the cosmos, and gives us hints about how gravity works and where the mass of the universe is hiding out."
] |
[
"Gravity lensing was used to watch Supernova Refsdal happen four times. The light didn’t make a 360 around an object, but it did follow four separate paths around a galaxy to reach us four times, weeks apart.",
"https://www.scientificamerican.com/article/scientists-see-same-star-explode-4-times/",
"[Edit] I realized that gravity doesn't \"lend\", so corrected the word to \"lensing\" as it should have been in the first place! That will teach me to post from my phone."
] |
[
"As you describe it no, but as the others have pointed out a mass in between a source and us can bend the light enough to make the source bend, as two images, four or even as a ",
"ring",
", depending on the alignment between the three participants.",
"The above example is two galaxies acting as lens and source, the same effect happens for stars too, but the separations are too small to pick apart the individual objects so we only see a the star get brighter instead.",
"Distances for the galaxies are determined via redshift, ie how much their spectrum is shifted to the red side, where more distant objects are redder then closer ones. For the lensed galaxies the images have the same redshift while while the central lens galaxy looks bluer. That said I have no idea how the do it in detail with microlensing, but I assume it's along some geometric reasoning since microlensing events are not really long lived and you'd have to be lucky to capture a spectrum while you catch it."
] |
[
"If a pregnant woman eats very little, will the baby take nutrients from the mother's muscles or fat stores? Or will the baby be malnurished?"
] |
[
false
] |
And the other way around. If the mother eats a lot will the baby be born larger?
|
[
"The human body is greedy, even a mother's. Eventually the mother's body will begin taking steps to save the MOTHER vice the BABY. So the baby will not be \"saved\" per se, but rather the fat and glycogen stores will still be shared in the body."
] |
[
"I would just add that if the mother has gestational diabetes the baby can be born very big, which I guess you can compare to overeating. Women can get gestational diabetes regardless of diet but still essentially has the effect of causing the baby to put on weight due to the high levels of glucose they're exposed to in the womb. Extreme malnourishment can result in miscarriage of the baby but probably depends when in the pregnancy the malnourishment occurs\n Chronic malnourishment can prevent women from getting pregnant to begin with as they stop getting periods etc, it's seen fairly commonly in anorexia."
] |
[
"I would just add that if the mother has gestational diabetes the baby can be born very big, which I guess you can compare to overeating. Women can get gestational diabetes regardless of diet but still essentially has the effect of causing the baby to put on weight due to the high levels of glucose they're exposed to in the womb. Extreme malnourishment can result in miscarriage of the baby but probably depends when in the pregnancy the malnourishment occurs\n Chronic malnourishment can prevent women from getting pregnant to begin with as they stop getting periods etc, it's seen fairly commonly in anorexia."
] |
[
"Why are subatomic particles so small?"
] |
[
false
] | null |
[
"They are subatomic... What's the alternative?"
] |
[
"Superatomic"
] |
[
"I don't understand... That's the definition of the term, smaller than an atom... They are what make up the atom... They can't be larger than the atom"
] |
[
"If someone was completely submerged in mercury how long would it take for that person to die after being removed?"
] |
[
false
] | null |
[
"It ",
" be toxic if handled incorrectly, but the ",
"liquid form",
" doesn't absorb quickly through skin. It's the inhalation of gaseous mercury vapor that tends to cause problems."
] |
[
"What would you expect them to die from? A person can ",
" mercury and usually show no negative effects. I also would raise the question whether it would be safe for a person to be submerged in ",
" liquid with the density of a heavy metal."
] |
[
"Well I heard that mercury caused disease....did i science wrong?"
] |
[
"Do Planets 'die' of old age?"
] |
[
false
] |
I misread the 'Do Plants die of old age' question, and now really want to know if planets 'die?' I suppose 'dying' would constitute no longer being geothermically and tectonically active. Thanks in advance!
|
[
"Rock planets like Mercury, Venus and Earth will become insert over time. As their cores cool the magnetic fields they emit will lessen which will allow the atmosphere escape. This is one reason why Mars is considered a dead planet."
] |
[
"I'm not sure if they \"die\". Mercury/Venus/Earth will die as they will be absorbed by the sun.",
"As for the other planets, they may just float around in darkness for eternityas the sun's gravity will have weakened. I wonder if Jupiter and the other gas giants will look the same without the sun's energy."
] |
[
"DOH! I forgot about those magnetic fields."
] |
[
"Would a massive object, moving near the speed of light, create a \"wake\" of effects behind it?"
] |
[
false
] |
If an object with a great amount of mass were to zip past our solar system at nearly the speed of light, what would it's effect be? Would it's brief gravitational presence affect our solar system in a notable way? Would it's effect be made-less by the fact it is only around for a brief moment? Is gravity the only concern to have, or would space "ripple" behind it causing further problems?
|
[
"General relativity is very complicated. That is no understatement. Even if you specified exactly the parameters you mean here, like the exact rest mass of the object whizzing by our solar system, it's speed, and an initial trajectory at some time t, solving einsteins equations would still probably be impossible. ",
"Gravitation couples to itself, and by this I mean the effects of such an event in turn affect themselves. There could absolutely be a slew of latent affects of such an event - long after the massive projectile is long gone - due to its momentary gravitational influence. ",
"I will point out that it is not often useful to think of a fast moving object as being more massive - and not useful here if we want to imagine this situation with our usual notions of gravitation. In such extreme relativistic situations, the energy density and momentum are relevant quantities to consider.",
"In such extreme examples, the affects of GR can be alarming and very unintuitive. There is a notion of pressure in GR that can cause bodies to repel one another in certain circumstances. That is not to say that gravity as we know it is repulsive, but is a recognition that gravitation is a result of the greater phenomenon that is the metric responding to energy and momentum.",
"A massive object moving at a relativistic speed by itself does NOT \"appear\" ",
" heavier as others have pointed out. However, if it is massive and moving quickly, it may induce accelerations in the massive bodies in our solar system. Acceleration does transform the metric and imply curvature - another example of gravity coupling with itself.",
"Ripples indeed.",
"It is cosmologically extremely unlikely that anything very massive and fast moving would approach our system. Massive and fast moving things are almost guaranteed to be very far away, and stay far away."
] |
[
"Thanks for that explanation.",
"\nI find it really difficult to find 'rules of thumb' associated with GR effects. I hadn't heard before that pressure gives a repulsive component."
] |
[
"This Book is awesome.",
"Nobody likes tensor calculus all that much, but in chapter 4, the author does give some examples to build intuition, and discusses some of the counter-intuitive affects that are possible. "
] |
[
"Does \"shaking off\" an injury actually do anything?"
] |
[
false
] |
Like when you hit your finger with a hammer, knock your hand against a wall, stub your toe, or something that results in you sporadically shaking that body part, does it lessen the pain we feel? Or is it just a human reaction to try and "remove" what caused the pain?
|
[
"It is a learned reflex. Obviously, pain receptors are activated when you hurt yourself. By shaking your limb, or rubbing the injured area, you activate other receptors in the skin that 'interfere' with the pain signal and essentially divert the brains attention away from the pain. Hope this helps!"
] |
[
"Distraction. Distraction takes your focus off the pain. "
] |
[
"Well injured things get inflamed, which is basically a swelling to promote bloodflow, and thus healing. Centrifugal force it could help jumpstart this process of increased blood flow.",
"Also when you've been cut, the damaged endothelium collagen (inside-ish of blood vessel) coming into contact with the platelets starts the extrinsic coagulation cascade. I've read that rubbing the cut (sounded relevant lol) would further damage the endothelium, and thus causing more surface platelets to attach to, causing fibrin clot to better form. ",
"Someone able to confirm or deny the second one through? "
] |
[
"What would the Earth be like if it didn't have plate tectonics?"
] |
[
false
] |
For example, if the core were just solid room temperature iron instead of being hot, what major geographical differences would you predict as a result? I'm not 100% certain whether this would even stop plate tectonics altogether or not.
|
[
"Hard and dead. The geothermal energy that drives the plates also creates the magnetic fields that protect us from solar wind that would strip away our atmosphere. That would be bad."
] |
[
"This isn't quite correct. The magnetic field results from currents in the outer core driven by solidification of the inner core; the ",
"plates are driven",
" largely by density differences in the lithosphere, the outermost layer of the Earth. Two separate processes. Additionally, there is a lot of debate whether a magnetic field is required to retain an atmosphere. Venus, for example has no internal magnetic field."
] |
[
"A slightly less drastic change (sorry for answering a different question!) would to be ask: what would the Earth be like if it still had a hot core, but didn't have the specific arrangement of tectonic plate motion that it currently does?",
"The main features of current earth that depend on our specific system of plate tectonics are the plate boundaries (ridges, mountain chains, etc.), and the existence of thick continental shields \"floating\" amidst much thinner oceanic crust, a system kept stable by the oceanic crust's \"conveyor belt\" motion, where crust forms in mid-ocean seafloor spreading, and then subducts at convergent plate boundaries.",
"The comparison is somewhat controversial, but some geologists point to Venus as an example of \"Earth without plate tectonics\" (though it's also \"Earth with a 500-C surface temperature\"). Here's an extended quote from ",
" (1998, p. 206) making that comparison:",
"Imagine taking hold of Earth in the mid-Archean and stopping once and for all whatever primitive plate tectonics were occurring on the surface. Perhaps a few protocontinents have reached respectable size ... sodium-rich granite or granodioritic material is beginning to accumulate within the continental cores. Other protocontinents are present, but haven't yet reached the state at which such felsic materials ensure buoyancy; instead, they are rather unsteady basaltic rafts floundering at near-neutral buoyancy in a basaltic crust. In the ocean basins, most of the area of the planet, small-scale subduction zones have been established at the edges of some of the protocontinents, carrying hydrated rocks down to shallow depths where partial melting occurs. As these cease to function (by our imagined interdiction), felsic products of basaltic partial melting stop being produced.",
"The interrupted planet must still rid itself of heat, and so, basaltic protocontinents continue to form; as they get bigger, they eventually founder in the crust. Other hot spots pop up elsewhere and produce new sites of volcanism and growth of plateaus destined eventually to sink. The ocean floor never becomes part of a conveyor belt recycling crust and volatiles; it therefore ages with time along with the rest of the planet. Over billions of years, this ocean floor records the scars of hot-spot formation, foundering of plateaus, abortive attempts at subduction, and asteroid impacts. [...]",
"To find a planet whose surface seems to record such a story, we need look no further than Venus. Venus illustrates what happens to an Earth-size and Earth-composition planet on which plate tectonics fails to take hold beyond the early formation of protocontinents. [...] Venus lacks the bimodal ages of continent and ocean floor that Earth possesses. It also lacks the accompanying bimodal height distribution of Earth ... in which the mean elevation of continental crust is well separated from that of oceanic. Instead, a broad range of heights exists on Venus, consistent with: (i) no continuously-renewing ocean floor; and (ii) no large-scale production of buoyant granites from the basaltic crust, hence no mechanism to create large continental shields.",
"[I'm not a geologist, but the above is pretty much directly taken from stuff written by people who are.]"
] |
[
"how much would i weigh if the earth was not rotating?"
] |
[
false
] |
or alternately, how much effect does the centrifugal force of the earth spinning have on diminishing our weight? would objects fall faster?
|
[
"Yes there is an effect, depending on your latitude. ",
"Here is the ",
"formula",
", with the ",
"chart",
". ",
"Sometimes you have to take this gravity variation into consideration in international trade (so your buyer near the equator won't complain that the shipment weighs 0.1% less than expected on his spring scale). ",
"And if the earth was not rotating, your apparent weight is the same as your weight at 90 degrees latitude now -- if we ignore the fact that earth is not perfectly symmetric. ",
"P.S.\nAnd ISO wisely pointed out in their definition of weight (ISO-80000):\n\"...It should be noted that, when the reference frame is Earth, this quantity comprises not only the local gravitational force, but also the local centrifugal force due to the rotation of the Earth, a force which varies with latitude.\""
] |
[
"Why any market would use weight instead of mass as a measure is beyond me."
] |
[
"So, in what we call \"inertial\" reference frames, the perspectives of observers that aren't accelerating, and the laws of physics hold good, there is no such thing as a centrifugal force. In order to have a circular motion you need a ",
" force, some force that is pushing/pulling you inward to the center of the circle. In the case of a car going around a tight turn, it's the tires pushing on the road that push on the car that push on the door to push ",
" around in a circle around the turn. But you of course just feel the door pushing on you and you pushing on the door because of the whole equal-and-opposite reaction thing. In the case of a spinning planet, it's gravity that pulls you toward the center of the planet. So since the centripetal force ",
" your weight, I'm going to say no change at all in your weight. ",
"the total acceleration felt toward the earth = g-(radius of the earth*sin(latitude)*angular velocity of the earth",
" ). ",
"radius of the earth*angular velocity of the earth",
" =.03386 m/s",
" So, the total correction from rotation = .03386*sin(lattitude) less than the standard gravitational acceleration ~9.806 m/s"
] |
[
"What causes rivers to snake?"
] |
[
false
] |
While checking out Northern Canada on Google Maps, I noticed some rivers were snaking much more than what I usually see. What causes this and what influences some rivers to snake more than others?
|
[
"In a curve the water is \"pushed\" towards the outer side from the flow, that leads to more erosion there and makes the curve even deeper. On the inside the eroded material can be deposited again. Eventually the curves get so deep that the river makes connections between them. Over time you can get what you see in the image. Curved sections everywhere, some still connected to the river, some not. This is called ",
"meander",
" after a Turkish river."
] |
[
"From what I remember from high school Earth science, a young river is relatively straight, a middle aged river meanders (snake) an old river develops oxbow lakes, where the meandering has gone to such extremes, that at certain places, the river will have sections that have been cut off from the main stream creating a small lake, or pond.",
"If I remember correctly, this is part of the natural life cycle of a river."
] |
[
"Well, old very snakey streams eventually cut through and leave you with small pools/ponds of water",
"Generally I think snakey streams come from the geology. If the land curves the stream does. If a stream hits a hill it bends. If the hill is soft it and the stream is strong it may cut through. If the stream is weak and the hill is hard rock then the stream will curve around it. If a stream is strong band the hill is hard rock the stream may eventually cut through the rock.",
"I think the wider the initial river, the more meandering the final slower stream ends up."
] |
[
"Are the orbital planes of other solar systems parallel to ours?"
] |
[
false
] |
I know that we can observe exoplanets when they pass in front of their star and we can get a peek at the atmosphere because photons are able to pass through it and then reach us. However, it seems like such an event is very unlikely. Why is it that all of these exoplanets seem to be going directly in between their host star and earth in order for us to be able to view them so consistently? What are the chances of that? Are the orbital planes of different solar systems parallel with each other? This is the only explanation I can think of.
|
[
"You're right that it's unlikely - we can only observe a small fraction of exoplanets using the transit method. So we have to survey huge numbers of stars to find the few that are lined up right at the right time. These are ongoing surveys that continually take pictures of large amounts of sky to see when stars get dimmer. The Kepler satellite in particular can see 116 square degrees of sky, which is almost 600 times the apparent area of a full moon.",
"There is obviously a bias here, but it's a well known bias that's easy to understand. Orbital inclinations seem to be random, so we can reasonably accurately say that some x% of planetary orbits should be inclined correctly for us to see them, and use that to estimate the total number of planets we should expect. We can also take into account the sensitivity limits - i.e. what fraction of correctly aligned orbits might have planets too small to be seen etc."
] |
[
"Why is it that all of these exoplanets seem to be going directly in between their host star and earth in order for us to be able to view them so consistently?",
"Because those are the only ones we can detect.",
"Any exosolar planes that aren't perfectly lined up edge-on between us and their star make planets in those planes quite invisible to us, because the way we detect exoplanets is by searching for regular dips in stellar brightness as they pass exactly between their star and earth.",
"We've ",
"catalogued millions of stars",
", but spotted only ",
"a handful of exoplanets",
" (bit over 4000) despite the fact that current thinking is that ",
" stars may have multiple planets.",
"Are the orbital planes of different solar systems parallel with each other?",
"Nope, they're (probably) pointing in all sorts of random directions so we can't see their planets from here.",
"As an example that we do know about, ",
"our solar plane is some 60° offset from the Milky Way's plane",
", and all the galaxies we can see are pointing in random directions.",
"This is the only explanation I can think of.",
"Nope, you've got cognitive bias because you haven't compared the number of stars with confirmed exoplanets against the number of stars around which we're theoretically capable of detecting exoplanets if they were orbiting just right.",
"If you do that comparison, you'll find that we've only detected an infinitesimal fraction of the expected number of exoplanets that could be observed if their orbital plane somehow became irrelevant.",
"If most solar systems had the same orbital plane, we would expect to observe lots of exoplanets near stars that lie on our orbital plane, and none on stars that aren't near our orbital plane.",
"As far as I know, the current data disagrees with that hypothesis ;)"
] |
[
"Yes, the star always wobbles, and when the orbital axis aligns correctly the wobble is parallel to our line of sight and the Doppler shift can be used to deduce the presence of exoplanets. It's called the radial velocity method and is common alongside the transiting method as a means of detection.",
"To \"notice\" the wobble depends on the resolution of your spectrograph and a lower limit on the velocity is set. The ELT is planned to drastically improve this limit."
] |
[
"I understand that space is huge, but if we're able to spot and locate stars 13 billion light years away, why can't we easily locate a suspected planet in our own solar system in today's age?"
] |
[
false
] |
Inspired by article about a potential 9th planet.
|
[
"I wrote about part of the problem ",
"here",
". However, we don't see stars billions of lightyears away. We see collections of stars billions of lightyears away. The light from all of the stars will add together into something that we can pick up with our specific telescopes.",
"Additionally, we're not looking for specific galaxies that far out. We look in a patch of sky and galaxies are everywhere, so finding them is \"easy\" in that sense. Instead, you're trying to point a telescope to look for an extremely faint object that has to be in one exact position on the sky, and that's another reason why it's so difficult."
] |
[
"Finding \"Planet Nine\" will be no easy feat, just as it took thousands of years after the beginnings of astronomy, until the invention of the telescope for Uranus and Neptune to be discovered. Now we have very great telescopes and even a good number of them in space! These telescopes are good at taking in lots of light over long amounts of time. The ",
"Hubble Deep Field",
", one of the first images of galaxies over 10 billion light years away, was taken by combining a bunch of observations. Each observation was at a particular wavelength for about 35-40 hours (nearly two days of taking in light at each wavelength), so it was no simple feat to find these far away stars. Additionally, at these distances, it is impossible to see individual stars; rather we are seeing whole galaxies that appear as tiny smears in the sky! These galaxies are immensely bright because they are made of billions of stars. Some galaxies have an absolute magnitude of -22, which is insanely bright. For comparison, our Sun's absolute magnitude is about 5, meaning those galaxies are 27 magnitudes brighter, or over 60 billion times intrinsically brighter than our Sun (magnitude is not linear). Additionally, the Universe is isotropic, meaning it's basically the same everywhere on big scales, so the Hubble Deep Field or something like it could be found anywhere we look.",
"In contrast, \"Planet Nine\" doesn't even make its own light, but has to rely on the Sun's light. Brightness falls off as distance squared, so since it hits the planet and then reflects back to us, it is actually squared twice, or to the fourth power! Imagine how faint Pluto is (to be fair, Pluto is much smaller, so let's increase its area by about 25 times). The apparent magnitude of Pluto is about 15, but a larger planet reflects much more light, so maybe we could have a magnitude of about 11.5. Now, the planet is supposedly about 30 times as far as Pluto, and remember distance is squared twice, so we receive about 0.0001% as much light as Pluto, or nearly 15 magnitudes dimmer. This is really dim! However, the worse part is that there is only one planet, so we can't look everywhere. It takes a very long time to look at big swaths of sky because we need to zoom in a lot to see this planet, plus it will move very slowly so we need to differentiate it from stars by taking many pictures. Hope that helps!"
] |
[
"In addition to what has already been said, consider this: you can easily point out a distant star with your naked eye, but can you spot pluto? ",
"The problem with discovering a planet nine is similar. Although it is much closer than a distant galaxy, it is much dimmer and thus harder to find, especially without knowing which region of the sky it might be in."
] |
[
"Since the surface pressure of Saturn's moon Titan is comparable to Earth, couldn't an astronaut explore it with nothing other than a respirator and arctic clothing? No space suit required."
] |
[
false
] | null |
[
"It is far too cold...a hundred degrees colder than the coldest temperature recorded on Earth."
] |
[
"Chill being the pertinent verb here "
] |
[
"Forgive my ignorance, but how?"
] |
[
"Does an egg get heavier, lighter, or stay the same weight while the baby chicken is growing inside?"
] |
[
false
] |
the time period is from when the egg is completely formed to when it hatches.
|
[
"Chickens are animals, which means they need oxygen to live. The egg shell is gas permeable to allow for respiration to occur. Just like any other cell, the embryo is taking in oxygen and emitting carbon dioxide. This process combined with a slow loss of water vapor would serve to make the egg lighter as time goes on."
] |
[
"Not unless there's enough energy to generate matter-antimatter pairs. I feel like this is probably not the case."
] |
[
"The key word there is ",
". As atoms/molecules/etc in the yolk are converted into chicken parts, like muscles/nerves/etc, the total amount of matter present doesn't change. Of course, the entrance and exit of oxygen and water vapor, and other things that can pass through the shell, can change the total amount of matter inside the egg."
] |
[
"If I sat in a computer chair with a freely rotating seat on the north or south pole, after 12 hours would I be looking the exact oppsite direction as I started?"
] |
[
false
] |
[deleted]
|
[
"At the moment you put the chair there, you are already rotating (because you stand steadfastly on the rotating earth) and thus the chair in your hands is already rotating. Similarly, when you sit down your body is already rotating and the chair's seat plane is already rotating. So even if the is no further friction between you and the ground, you will keep rotating in perfect synchronicity with the earth due to conservation of momentum. Thus you will always look in the same direction (relative to the earth, that is - relative to the stars, you will of course have turned 180 degrees like everything else on earth).",
"There might be other effects from the way the surrounding air moves (basically wind, etc.) that I am not sure about right now, though."
] |
[
"Can you please explain why a Foucault pendulum works then? "
] |
[
"I've got to admit I've never seen that before... nice toy! ;)",
"I think such a pendulum is subject to the ",
"Coriolis effect",
", because it moves (at least in part) in longitudinal direction (i.e. along the north/south axis). Objects that are closer to the equator need to be faster to keep up with the earths rotation than objects closer to the north pole. So even if the pendulum starts in synch with the earths rotation, when it moves the earth's rotation keeps going a tiny bit faster or slower than what it started out with. Compare this with the chair: even though different particles of the chair rotate at different absolute velocities depending on whether they are closer or further away from the exact pole, they do not change their distance to the pole, so each particle can keep the rotation in synch with the speed it started out with.",
"Taking this line of thought further, I would speculate that if it were possible to start the pendulum in a perfect east/west orientation, it should not show the effect (but then again, it moves up and down too which would also change the speed of synchronous rotation...)."
] |
[
"Looking for D2 (molecular deuterium) phase diagram"
] |
[
false
] |
I need a diagram of the equation of state for molecular deuterium with temperature and pressure ranges from 0-300K and 0-1 MPa, or something near those ranges for an experiment I'm doing at work, and Google has only been able to provide me with diagrams in the GPa range or temperatures >1000K, which is not possible with the apparatus I have. Does anyone have access to any papers which characterize the equation of state for D2 or would be able to point me in the right direction?
|
[
"I don't know one offhand.. looking at scholar/scifinder it seems most studies are aimed at high pressure/temperature scenarios, as you say. ",
"Here's one",
" that might be useful, though.",
"Excuse the presumption, but are you sure you ",
" one? The intermolecular forces which govern the phases/equation of state should be near-identical for H2 and D2. The only significant differences in their thermodynamic properties would stem from the differences in vibrational states and zero-point vibrational energy, which would probably result in rather small contributions at the \"ordinary\" temperature/pressure ranges you're talking about. (If you're willing and good with statistical thermodynamics, you could probably derive some simple corrections.)"
] |
[
"Just on a whim I'd image the extra mass begins to contribute quite a bit as you approach O degK or as KT starts to approach the energy of your lowest modes. Aside from that, I'd tend to agree."
] |
[
"Well, the ZPE is part of the enthalpy. But as you go to 0 K, the \"non-classical\" contributions to what's going on aren't negligble anymore, and you really have to start thinking about stuff acting quantum-mechanically, and weird quantum-mechanical phases and stuff. And the mass certainly would matter there, since hydrogen tunnels easier. If he'd said 30-300K it'd be a lot easier than 0-300K, because a lot of weird stuff can start happening under 30 K.. ",
"BTW, questioner.. I forgot I ",
" know another reference offhand. The ",
"NIST chemistry webbook",
", which has a ",
"bunch of thermo data for D2",
"."
] |
[
"Why isn't the sky completely white at night?"
] |
[
false
] |
Shouldnt it - from earths perspective - be filled with stars, which are far from each other, but "lines up" from our view? Does the light reflections from these not reach earth?
|
[
"You've hit upon a very old question called ",
"\"Olbers' Paradox\"",
".",
"The solution relies on the fact that the universe is not infinitely old, so only finitely many stars and galaxies are observable and they collectively subtend an angle on the sky much smaller than the full sky."
] |
[
"The solution relies on the fact that the universe is not infinitely old",
"To others, also keep in mind that even if the universe was infinitely old, we would not see any stars in the night sky besides our own galaxy's, since if the Universe was remotely that close of age, we would have been isolated from the rest of matter by the rapid expansion of time-space."
] |
[
"First off you need to take into account the fact that these stars are extremely far away and that their intensity (power per unit solid angle) drops off at a 1/d2 relation where d is the distance away from the source. So when the light gets to earth it is extremely dim. ",
"This is actually at the heart of Olber's Paradox, and doesn't by itself solve anything. The reason being is quite simple: If you assume that stars are evenly distributed throughout the universe, then if you look at any particular \"shell\" of some finite thickness surrounding the earth, you'll find that the volume (and thus number of stars) of the shell scales with r",
" exactly canceling the 1/r",
" dimming of the light from the individual stars, and thus each concentric shell contributes a constant additional brightness, leading to an infinitely bright sky for a classical universe which is both infinite in extent and age."
] |
[
"What does /askscience think about the legitimacy of Near Death Experiences?"
] |
[
false
] |
That is, that they're legitimate evidence of anything asides from the fact that someone thinks they remember something strange happening. I've read stories of people who come back from having been dead for a few minutes and recounting stories of where they went and am curious if the scientific community thinks this is a legitimate topic of debate, or psuedo-science.
|
[
"I've yet to find an ethics board who will approve my proposed experiments on the subject..."
] |
[
"Here",
" is a short article on what happens near death. ",
"It's likely just the brain having hallucinations as it goes hypoxic and people are thinking that means something, because some people desperately want to believe that this isn't all there is to it. "
] |
[
"If by legitimate you mean \"do they happen\", the answer is yes! If you mean \"does this make it evidence of an afterlife/soul/etc\", the answer is no.",
"I think it's a fascinating topic to look into, especially when we don't know yet exactly ",
" they occur, but suspect DMT is involved."
] |
[
"What is this strange circle around the sun?"
] |
[
false
] |
Hi, is from few minutes ago. What's this perfect circle around the sun?
|
[
"It's called a 'halo,' and it's caused by sunlight passing through finely spread ice particles in a high altitude cloud layer.",
"A Huffington Post article about halos",
"The Wikipedia page on halos",
"(edited to fix the wikipedia link)"
] |
[
"Here's a painting",
" of the same phenomenon observed over Stockholm on April 20, 1535."
] |
[
"Thank you"
] |
[
"When we look into the night sky what exactly are the bright lights?"
] |
[
false
] |
[deleted]
|
[
"The Hubble Deep Field is a tiny area chose specifically for the lack of nearby stars that are easily visible. The area is roughly the size of a 10th of the full moon. ",
"The vast majority of what you see with your naked eye are stars which are local to our galaxy. There are about 10,000 naked eye visible stars. There are 5 easily naked eye visible planets. They are bright and obvious but easily confused with stars. There are a handful of naked eye galaxies; the Magellanic clouds if you are in the Southern Hemisphere, the Andromeda Galaxy for the Northern and a reasonable dark locale. There are a few naked eye nebula like M42 in Orion. In addition there is the globular cluster Omega Centauri which is really s collection of thousands of stars close together (there may be another glob visible to the naked eye but I can't think of one). They tend to appear as fuzzy objects rather than distinct stars if they are apparent to the naked eye. But overall what you see are stars local to our galaxy. "
] |
[
"Our galaxy is 100,000 lightyears across. On a clear summer day you can see 7000-10000 points of light. 99.99% of those are from a sphere around Earth with a radius of about 4000 light years, no more."
] |
[
"All of the above.\nGalaxies, stars, planets, we can see them 'all' with our naked eye. However, most of the stars we can see from Earth un-assisted by telescopes, will be in our local galaxy, and the galaxies we can see are still in our local cluster. The local cluster is like your town. Your yard is the galaxy. You can see a lot of the houses and yards near by. Except in space we are talking a few thousand light years away. \nIf you look west around dusk this time of year, the extremely bright object you see is most likely our closest planetary neighbor, Venus. In the early morning to the south, you can catch a glimpse of Jupiter. In fact, they are so bright you can easily take a picture with a plain cellphone camera. ",
"Venus taken with an unassisted cellphone from my back deck on a hazy cloudy night on Monday:\n",
"https://imgur.com/a/VxKBR",
"Jupiter is the white dot above the trees. Again, cellphone camera with no magnification. \n",
"https://i.imgur.com/m2A7Pmt.jpg",
"If you spot Orion in a very dark night, his belt looks a bit cloudy because there is a nebula there. "
] |
[
"[META] Monday Lab Meeting!"
] |
[
false
] |
[deleted]
|
[
"I've begun writing that pesky little dissertation thing"
] |
[
"This week I'm on my own as everyone else has flown off to the states to visit our other site. Someone has to man the fort I guess...",
"Alllll byyy myyysellffff "
] |
[
"Busy.",
"Got my experimental equipment finally set up after 3 months of prep ( 3.5m long flume tank to run simulated pyroclastic flows into), so have been carrying out the first tests in it. Mostly a case of finding the leaks, fixing them up, and getting a feel for how it all behaves. Been getting through prodigious amounts of masking tape and paper towels, as well as gaining a reasonable amount of experience in plumbing high pressure gas systems. Stinking cold over the weekend, but still managed to feel guilty for not getting in yesterday to get some more done on it.",
"Also been making a lot of headway with a project I've spent a year trying to get set up collaborating between some guys at the National Oceanography Centre in the UK, and some other researchers scattered at universities around the world. It's a pilot project to see if some software I was working on the development of in my last postdoc (which was designed to model submarine turbidity currents) can be used to investigate what happens when a pyroclastic flow enters the ocean. I've generated the first sets of data and we're now hammering through the process of trying to work out what variables we can constrain, what we can't, and how to get the information we need from the data we have - the dataset I'm testing has a lot of cores extracted from the seafloor in the area. We're now seeing if the guys who did the original analyses on these have measured the things I need to get the model to accept the information, or if there is a clever way we can estimate those numbers from other measurements they've made. Lots of stuff to do with particle size distributions, grain sorting, that kind of thing. Because it's a pilot project there's no funding attached, so it's all very dependant on the goodwill of people helping out and getting stuck in to the development discussion while I tweak and progress the modelling in my spare time (done remotely on a dedicated workstation at my old place of work which sits unused in the evenings). Managed to get some very well respected and competent colleagues on board, and everyone seems to agree that progress looks promising. Extremely relieved.",
"So two pretty big sets of progress, just in time for me to try and get some abstracts together for a big conference in July, for which I need the proposed papers submitted by the end of this month. The age-old joy of submitting abstracts for work you haven't actually finished yet.",
"Fiance is coming out to visit on Thursday for 4 days, so I lose a couple of days work but maintain my sanity for a bit longer. Need to get a few runs done today to make up for the time, but sat twiddling my thumbs (or more accurately - writing this) while waiting for 15 kg of tiny little 0.05 mm diameter beads to dry out in the lab oven."
] |
[
"During a workout, how long does it take for the human body to use fat directly?"
] |
[
false
] |
[deleted]
|
[
"It's not so much time related as it is intensity related. Intensity here is defined as percent of max heart rate, so high intensity would be close to max heart rate.",
"In order to contract, your muscles need a high energy molecule called ATP. ATP basically gives energy to things to allow them to work. In order to synthesize ATP, your body uses food. Protein, fat, and carbohydrates can all be used to create ATP.",
"A single molecule of the basic carbohydrate that your body uses for ATP production, glucose, can create about 30 molecules of ATP. A single fatty acid, however, can create upwards of hundreds of molecules of ATP. Therefore, fat is a much more efficient energy source than glucose, and your body prefers to use fat as much as possible.",
"However, fat takes longer to make into ATP than glucose. There is a transportation limit, and once your muscles need more ATP than the fat that can be transported can provide, it starts using glucose. Glucose is fast, so when exercise becomes more intense, you start shifting away from fat usage to glucose usage. What this means is that at lower intensities, you use a higher percentage of fat. When you're sitting around doing nothing or just walking, you're using almost solely fat for ATP production.",
"However, because there is a higher total energy requirement for more intense activities, you actually end up using more fat until about 60% of max heart rate. You're using a lower percentage because glucose has stepped in, but the actual amount is higher.",
"Edit for source: ",
"http://www.textbooks.com/ISBN/9780078022531/Scott-Powers/Exercise-Physiology_-_0078022533.php"
] |
[
"Do you mean 5/30/65? Why would adding more carbs and cutting fat cause you to burn fat?"
] |
[
"If I understand you correctly, you confirm what I've read in a few sources I found credible. What I read is that you start burning fat. As your activity level increases, fat burning increases, but its max rate is limited. To expend more energy than the max fat burn rate supports, you start burning glucose. This does not decrease the fat burn rate, which remains at its maximum, but does provide more total energy, allowing a more vigorous workout than fat burning alone would allow.",
"I see an effect that fits with the above description when I ride my bicycle for more than 25 miles or so. After 90 minutes to 2 hours, I've burned through whatever glucose my muscles and liver can provide and I'm reduced to fat burning. I can go at only about half the effort and its not nearly as much fun as when I have glucose available. For those long rides to be fun and not slow to a crawl, it's eat early, eat often to keep the glucose level off the floor.",
"So long as I don't overdo the carbs, I get to have carbs and still burn fat at the same rate as if I weren't eating carbs at all.",
"Does that fit with your understanding?"
] |
[
"What happens to the cells in our body when we die?"
] |
[
false
] |
Do all cells cease function and die simultaneously when Brain activity ceases, or is it more gradual as oxygen and respiratory substrates being to run out after Brain function stops?
|
[
"It's more gradual. The medical definition of death is fairly arbitrary, especially since we can, to an extent, artificially extend metabolism beyond the endpoint of a lot of things you might call \"death\" (e.g. cessation of brain activity, cessation of natural heartbeat). Individual cells will die as they starve for nutrients due to lack of nutrient-laden blood flow."
] |
[
"It actually occurs pretty rapidly once oxygen is no longer brought in. "
] |
[
"Apoptosis (programmed cell death) occurs after our bodies die as no more oxygen is brought in. The biochemical reaction inside the mitochondria of the cell (cellular organelle basically the power plant) which creates energy cannot happen. ",
"Without ATP ( the energy that drives the cell), factors such as tumor necrosis factor from inside the cell are released and breakdown occurs. These factors cause a \"domino effect\" were rapid apoptosis occurs throughout an organs cells."
] |
[
"An esteemed director of our institute has recently retired, I am looking for an interesting/unusual scientific gift for him, suggestions?"
] |
[
false
] | null |
[
"Maybe you could get him an early edition of Principles of Geology or some other significant work."
] |
[
"I used a rubics cube, glued it to fix and labled the sides accordingly to make an epsilon tensor. Did it for a birthday gift to a physics nerd, he was amused.",
"Dunno if your prof would like it aswell or if he even recognizes it. :)",
"Budget ~10$"
] |
[
"Maybe it's the Waterboy fan in me.. but I always thought a sample of dirt/water/etc from all over the world would be neat."
] |
[
"Is it true that there are certain frequencies that cause fear in humans?"
] |
[
false
] | null |
[
"Would be nice with some sources."
] |
[
"Yes. Certain frequencies of infrasound can produce that effect. These are below our range of hearing but can still be perceived, usually the result is something along the lines of feeling your skin crawl or feeling like you're being watched (increases in anxiety, unease, and fear).",
"Infrasound due to issues with airflow (from hallways or rooms that result in standing waves, or HVAC equipment) are a common cause of people feeling like some particular place is \"haunted\". Since people find they have the same response when they are in a particular part of a building but they don't see any obvious reasons to feel that way so they reach for a word like \"haunted\" (either seriously or playfully).",
"Several experiments have confirmed this relationship between infrasound and anxiety/fear, but there's still a lot of research that hasn't been done in the area yet."
] |
[
"At high intensity, various low frequency sounds will resonate with your internal organs. You can be made to lose control of your bowels and bladder. Systems like this have been used for crowd control, but the last time I heard of them they were used for repelling pirates off the coast of Africa. Those ship-mounted systems were said to burst eardrums, amongst other things."
] |
[
"Why doesn't the brain fry up in an EMP blast?"
] |
[
false
] |
If the neurons communicate using electrical and chemical impulse wouldn't the brain fry up if it is caught within a blast radius of an EMP. I haven't heard this happening , so what stops the mechanism that happens within an electric circuit that doesn't happen in Brain.
|
[
"Ions of sodium, potassium, calcium, and chloride react within the neuron to generate an electrical signal."
] |
[
"I think he was being rhetorical. ",
"Transcranial Magnetic Stimulation (TMS)",
" is real."
] |
[
"Our brains are not made of metal wire and gating semi-conductors. As such, changing magnetic fields passing through us do not generate electrical fields the way they do in metals and such."
] |
[
"Will a makeshift Faraday cage protect you from a Taser?"
] |
[
false
] |
If you were to weave copper wire into a shirt in a tight enough pattern, would it successfully redistribute a Taser charge?
|
[
"The OP doesn't actually need a faraday cage. He just needs something which will bypass the human component of the circuit between two taser darts."
] |
[
"For a taser the current will flow from one dart (terminal) to the other. Conductive clothing provides a path of lesser resistance for the current, outside the body. The current is dissipated inside the taser, possibly damaging it because it is not pushing against such a large resistance."
] |
[
"Anything conductive will do it. Chainmail will do nicely."
] |
[
"Does the Christmas tree I cut down still photosynthesize in my living room?"
] |
[
false
] | null |
[
"IRGA = infrared gas analyzer if anyone else couldn't quite get it from the context. "
] |
[
"If cut and put in water relatively quickly (within a day), with the bottom part cut off so that it can pull up water, it probably is photosynthesizing. As long as it's 'drinking' (the stomata are open and it's pulling up water) and the cells are alive, I can't think of much reason to think it's not. I'll bring the IRGA home next year and try it!",
"Semi-related, we know that shoots from conifers will continue to photosynthesize for about 5-6 minutes after being cut. That's handy because it gives us a window to measure photosynthesis rates without needing to get heavy equipment up to the top of the tree."
] |
[
"Thank you :) Doesn't everyone know obscure lab equipment abbreviations?"
] |
[
"How is a cold virus able to target specific areas of the body, ie the throat?"
] |
[
false
] | null |
[
"There are many, very different types of cold viruses, and each of them bind to different receptors found on cells in various locations (including the throat).",
"For example rhinoviruses bind ICAM1, adenoviruses bind CAR, coronaviruses bind ACE2, infuenza viruses bind sialic acid, etc.",
"Different cells will have different levels of those receptors (and they are not only found in the respiratory tract) as they have actual functions in the body, the viruses are just hijacking them. But a cell lacking those receptors or another species with different enough receptors cant be infected."
] |
[
"You've made this curious, stoned redittor very happy"
] |
[
"To add to the previous post, this is the very reason why specific viruses vary in their pathogenicity. Retrograde viruses like HTLV or HIV are only able to bind with the receptors on specific leukocytes, thus making it statistically improbable to contract it from airborne or droplet particles since those leukocytes typically reside in lymphatic tissue or the blood stream."
] |
[
"Why are breasts so attractive? After all, they're just fat and mammary tissue. Is it a psychological thing to do with breastfeeding as infants?"
] |
[
false
] | null |
[
"The two main running theories are ",
"a) Breasts are made of fat, and so good sized ones show a woman has had plenty to eat (implies good health and good skill at staying alive) and will be able to produce plenty of milk to feed her offspring. ",
"b) Humans are pretty neotenic (we look in some ways like juveniles of other apes). This is especially true of females when compared to males. Breasts are only present on sexually mature females, and serve as a signal to males indicating maturity.",
"These explanations are not mutually exclusive, and presumably other contributing factors may occur as well.",
"It's probably not psychological thing to do with breastfeeding, considering the number of people who were bottle-fed don't seem to show any less interest.",
"EDIT: I got to thinking biology here, but ",
" culture has a strong role in shaping whatever underlying biological tendencies that people have. "
] |
[
"First off, I'd like to point out that as a primarily psychological topic that it is difficult, if not impossible, to differentiate whether or not breasts are attractive based on evolutionary biological impulses or cultural, sociological constructs. At this point no one in the primary literature (that I know of) agrees that breasts ",
" ",
" universally attractive among humans.",
"From a biological perspective:",
"Men spent more time looking at breasts than any other portion of female bodies in a University of Wellington eye fixation test.",
" ",
", this does ",
" provide unambiguous proof for the theory that breasts are indicative of fertility because, as the researchers themselves state, \"Men may be looking more often at the breasts because they are\nsimply aesthetically pleasing, regardless of the size.\"",
"Other studies, however, have failed to show ",
" preference for breast size and instead point to Waist-to-Hip ratio as a better indicator",
".",
"From a sociological perspective:",
"Men who tend to engage in short-term, low-commitment relationships are more attracted to large breast sizes than men who tend to engage in long-term relationships with high emotional commitment",
". If the evolutionary psychologists in this thread are correct (i.e. large breasts are intrinsically attractive), then in light of this study, shouldn't large breast sizes been selected ",
"?",
"Attraction to breasts is varied across cultures, with some preferring small, pointed breasts, some preferring larger breasts, and some where breasts are not seen as secondary sexual characteristics at all (Namibia amongst them, if I recall correctly).",
". (I own the book, can't find an online version, sorry). Breast fetishim has been called an exclusively American/Western modern phenomenon, not a biological fact."
] |
[
"Does it have anything to do with \"These are forbidden, so I want them more\"?",
"Are breasts a lesser deal in societies that are less modest about nudity?"
] |
[
"How are multiple signals passed over wires (phone lines, fiber optics, etc...) without interference?"
] |
[
false
] |
I was thinking about the old days especially when most communication was over the phone lines which I know to be multiple individual strands of wire spanning thousands of miles with various interconnections. But, if my neighbor and I are making a phone call at the same time, how do the lines keep those 2 signals entirely separate when its on the same line for at least a part of the transmission?
|
[
"There are three basic ways. Either you send the signals at different times and then reassemble at the receiver (time division multiplexing), or you send different frequencies or colors (frequency division multiplexing) and separate at the receiver, or you encode the different signals digitally such that they all appear like noise to each other but you can descramble them at the receiver (code division multiplexing). The latter is very common in cell phones."
] |
[
"If you're talking about internet signals then it kind of works like the post office. Your computer takes the message you want to send and wraps it in a digital \"envelope\" which has the source and destination address in it. The computer talks to the modem, which talks to the ISP modem. Then the ISP routing computers (called routers) look at what the address is and use information to figure out how to get a little closer to there. It then sends it to the next router in the chain that does the same thing until it reaches the destination.",
"On each step the receiving router sends a short message back saying \"i got it\". Your computer also expects an \"I got it\" message back called an ACK (Acknowledgement) packet. If your computer never receives the ACK from the other end it tries to send the message again. The internet is based around a self-healing message passing network which is designed to survive large chunks being knocked out by nuclear bombs (it was originally a military project). It does this by having many different paths to any one place and dynamically routing around outages.",
"As to how you know there isn't something blocking your way. When you start a connection you send something called a SYN (Synchronize) packet. SYN is a request to start a conversation. The destination sends an ACK packet, and the other end sends back a SYN+ACK packet in one. That way you know you can get there in principle. If something happens to the network during the conversation then the message's ACK is never received. Your computer tries again, and again but eventually gives up (3 tries I think generally). I'm mostly describing a method of communicating called TCP/IP, but it represents the majority of traffic on the internet."
] |
[
"Maybe I misunderstood your question. Are you asking how the receiver knows which multiplexing scheme is encoding the data? If that’s your question then the answer is it doesn’t have too. Every communication system has to be designed around one scheme or another as all the hardware and software would be different. ",
"The answer to your second question is absolutely yes. This is the key performance metric and design challenging of a communication system. Generally you want to be able to send as much data as possible per unit time (in other words your bandwidth) and you are limited by various characteristics of your system, your communication scheme, and the physical channel you are using to communicate."
] |
[
"What explains the optical distortions in Jacques-Henri Lartigue's famous 1913 \"Car Trip\" photo?"
] |
[
false
] |
The photo in question shows This predates Photoshop obviously. The crowd is skewed to the left and the rear tire appears ovoid.
|
[
"There is a nice explanation with animations here:",
"http://www.largeformatphotography.info/forum/showthread.php?31903-Jacques-Henri-Lartigue-and-his-camera",
"The effect can still occurs in modern cameras. Most digital SLRs have mechanical shutters and many video cameras use rolling-shutter image sensors which give the same result. The effect is usually not as pronounced though, because modern shutters are faster."
] |
[
"I took a photo while dropping my cell phone, and the result looked somewhat similar:",
"http://imgur.com/fwumC4x"
] |
[
"Here is a nice video of a propeller. There you can see what trippy forms the rolling shutter effect can produce: ",
"https://www.youtube.com/watch?v=LVwmtwZLG88",
" Basically it's the same effect as on the car, only in a video and with a much faster object."
] |
[
"Why does hyperventilation not produce alkalosis in the dog?"
] |
[
false
] |
Good morning askscience guys, I have a question that I've been thinking about for years. To the point, physiologically the human being has mechanisms to regulate acid-base control, and among them is pulmonary ventilation, in case the blood turns to a more acidic pH, the body generates hyperventilation to regulate the pH. Otherwise, hyperventilation produces alkalosis. So here is my question, dogs in hot weather or extreme exercise hyperventilate and do so a lot. How is it that dogs regulate blood pH quickly without suffering alkalosis when they start hyperventilating? I appreciate your response in advance, thank you very much.
|
[
"DVM here.",
"\nDogs do have the same acid/base compensation mechanisms as humans do, and you're right that a dog breathing too much will cause alkalosis. This is actually something we look for when trying to interpret bloodwork.",
"There are two reasons why dogs aren't getting clinically significant alkalosis while panting to cool off. ",
"One is the idea of \"dead space\" in the airway. Dogs take shallow breaths, or \"pant\", to move air over their mucosa, using evaporation of the water there to carry away the heat. Because they're not taking full breaths only just a tiny amount of air goes into and out of the lungs. The rest is just moving up and down the trachea and mouth. These tissues don't exchange gas, they're 'dead space' from a respiratory perspective.",
"The other reason is that (if they're otherwise healthy) they compensate for the alkalosis through metabolic activity."
] |
[
"I’m case a vet doesn’t jump in with a more detailed highly sourced answer, vet tech here jumping in to say you are making a flawed assumption that normal panting counts as “hyperventilation” for healthy dogs. Dogs CAN get respiratory-related acid/base imbalances, especially if they are on a ventilator with incorrect settings, are deeply sedated, have brachycephalic airway issues, or are otherwise in situations that are not normal for them as a species, and in hospital we would monitor ETCO2 and blood gases/pH regularly in those cases. But a dog just panting isn’t “hyperventilating” like a panting human would be."
] |
[
"Hyperventilating only causes alkalosis if you have increased ",
". You can, however, have a high respiratory rate without increasing alveolar ventilation by taking small breaths.",
"Example: let’s say we have a human with a normal breath of about 400 mL. 150 mL of that never reaches the alveoli. Only 250 mL does. If you breath 12 times a minute, that’s a total minute ventilation of 4.8 L and an alveolar ventilation of 3 L. If you now start breathing faster, say 20 times a minute, but decrease tidal volume to 300 mL, now you have a total ventilation of 6 L/min but the alveolar ventilation stays 3 L/min. Do that again, say 40 times a minute, 225 mL per breath, 9 L/min total, 3 L/min alveolar ventilation.",
"While only using a small amount of that breath to replace air in the alveoli, ",
" the minute ventilation can be used for cooling. So it’s easy to change the amount minute ventilation without changing the amount of alveolar ventilation.",
"Note: I took some liberties like assuming there’s no air admixture in the airways and uniform pathways for air to your alveoli. In reality, it’s a bit messier than this.",
"Second note: although I think this is a large part of the reason dogs can hyperventilate without issues, I don’t actually know for sure. They might use other pathways (metabolic compensation of alkalosis, for example)."
] |
[
"Which country will leave it’s continent first?"
] |
[
false
] |
Obvs this will take millions of years but which country will be the first to leave its continent? India is pushing into Asia which is continuing to raise the Himalayas, it stands to reason somewhere else is doing the opposite and will one day cease to be in its original continent. I wonder where is moving fastest and if there are any predictions of what the globe will look like in the future.
|
[
"Probably the countries on the east side of the ",
"East African Rift",
", so portions of Ethiopia, Kenya, Tanzania, and Mozambique and all of Somalia (presumably Djibouti would sink into the ocean if spreading of the EARS continues and progresses to complete continental rupture and ocean basin formation). These are already on another plate (i.e., the ",
"Somali plate",
") compared to the rest of the African continent. Projections suggest that this Somalian plate will fully separate from the rest of Africa, with an ocean basin forming between them, within 25 million years in the future (",
"van Hinsbergen & Schouten, 2021",
"). As discussed in this paper, this is highly speculative and depends on one possible future outcome for plate motions, but if correct, further in the future, this Somali plate would collide with India, forming a new mountain range between them. This hypothetical future collision is animated in this ",
"video",
" (that was produced in conjunction with the aforementioned paper)."
] |
[
"What an absolutely brilliant answer, exactly what I was looking for. Amazing"
] |
[
"That's the nature of plate motion projections, i.e., they are inherently uncertain. Whether lithospheric rupture will occur in the EARS and when it will if it does is a relatively small uncertainty in these types of projections compared to deciding whether we'll see extroversion (i.e., the pacific ocean basin closes) or introversion (i.e., the atlantic ocean basin closes) as we move toward the next supercontinent assembly."
] |
[
"Can an electromagnetic chain/coil gun be used to launch spacecraft to orbit?"
] |
[
false
] | null |
[
"Aren’t all Reddit questions answerable on google "
] |
[
"This question has already been asked a lot on ",
"/r/askscience",
" :",
"https://www.reddit.com/r/askscience/comments/58baxy/why_are_electromagnetic_railguns_not_used_to/",
"https://www.reddit.com/r/askscience/comments/76chjw/could_we_catapult_eg_satellites_with_a_large_and/"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"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."
] |
[
"IS it possible to break down atoms into their separate parts and re-arrange them how you like?"
] |
[
false
] |
[deleted]
|
[
"Nope, we can't do that.",
"It is possible to transmute certain smaller elements into certain bigger ones, but that just means smacking the atoms together at very high speed. For instance, to experimentally create element 118 (",
"ununoctium",
"), scientists put some Californium atoms at the end of a particle accelerator, and smacked them with high-speed calcium ions. This is very expensive, not entirely reliable, and it's a whole lot more crude than if we could rearrange the parts like Lego bricks."
] |
[
"Breaking stuff is ",
" easy. Rearranging subatomic particles isn't really a meaningful concept because ",
"Quite apart from the ",
"uncertainty principle",
", you face the extreme difficulty that the sort of forces available to you for the purpose of manipulating your sub-atomic particles are going to be the same as the forces which tend to assemble them into atoms. ",
"It's a bit like trying to build an ",
"Airfix",
" model with nothing apart from a sledgehammer and a paint roller covered in (already tacky) glue, both of which tools you are manipulating with the grabber arm of a ",
"JCB",
". "
] |
[
"Are you asking - can we break down the atoms into their individual electrons, protons, neutrons and bring them back together as a different element?",
"Like a matter compiler (from SciFi)?"
] |
[
"Why doesn't Cerenkov Radiation violate causality?"
] |
[
false
] |
When charged particles travel faster than the speed of light in a certain medium (usually water), they emit blue light in an analogous situation to an sonic boom. That's a really cool effect, but I'm stumped as to why something has to travel faster than the speed of light in a vacuum to violate relativity/physics in general. If the universe were filled with water or sometime else with a high refractive index, would "time" progress in the same way?
|
[
"When scientists refer to the speed of light related to causality ( c ), what they are actually talking about is the speed of a massless particle (usually the photon). When you hear about the speed of light in a medium slowing down, what you are hearing about is the macro level appearance of moving light. The reason it slows down is because as photon move through the medium, they are periodically absorbed and re-emitted by atoms in the substance. This absorption takes time, so the light seems to take longer to move through it. Between atoms though, photons are always moving at c.",
"In my opinion, 'speed of light in a substance' should always instead be called the speed of propagation of light in the substance instead, because they are two different things, and this does tend to confuse new people.",
"Hope this helps!"
] |
[
"The light photons are moving at the speed of light, but the density of the fluids slow down the ",
" since the light bounces back and forth.",
"So some particles move faster ",
" than light, since light are more likely to collide with the fluids."
] |
[
"Thanks for the helpful responses, HalfCent and Natanael_L! Anyway, I realized that of course the photons themselves must still move at c -- otherwise they would never outrun their fields, and there would be no radiation at all."
] |
[
"Sometimes after I sweat a lot I can brush any part of my body and salt will fall off. Why?"
] |
[
false
] |
And I mean like a lot of salt. I know it's salt because I've tasted it and it's extremely salty.
|
[
"A little off topic but have you ever had that checked out? It makes me think about you potentially having cystic fibrosis. One form is due to mutations in salt transporters that cause people to lose a lot of it. One of the old ways doctors would test children for it was to lick their hand and if it was super salty, they were tested further.",
"Having actual chunks of salt forming on your skin from sweating seems like there might be an underlying issue."
] |
[
"Sweat is a way of cooling down. When you sport or when it's hot outside your body temperature rises, this increased temperature is not good for your body (our body/proteïns are optimized to work best around 37.5°C). So we need to cool down by sweating. Sweat is actually just water with ammonia/urea and salts (Na, Cl, K, etc). The water evaporates on the skin, this creates the cooling effect, so only the dissolved materials stay on your skin = the salt! If you sweat alot there will be alot of salt left, so you can actually taste it. And often your dog will also like it ;)!"
] |
[
"That's not off topic. And I dunno. Would this kill me? Because I've been doing this for years. "
] |
[
"Why do many animals have a \"rare\" type that is either solid white or black? Also why are they not any other color."
] |
[
false
] |
[deleted]
|
[
"Its a lack of pigmentation expressed in animals, caused by genetic mutation. Since all animals have genes related to pigmentation, all animals can have mutations in those genes. There are a few basic types: ",
" animals do not produce melanin. ",
" animals lack yellow pigmentation.",
" animals lack red pigmentation.",
"An animal who has all three of these mutations is ",
" and will be pure white.",
"In addition, they can also have a ",
" form. An animal can be ",
" (which produces animals such as the black panther), ",
", or ",
". These will cause an excess of the coloration previously mentioned. "
] |
[
"I don't know the answer to your first question other than it's to do with genetics, but animals are usually not other more exotic colours because those colours are usually not effective for their purpose. A crimson red lion wouldn't be a better hunter than a beige one in an African savanna."
] |
[
"I don't really know the answer to your broader question, bu tin the case of the squirrel pic, I'm pretty sure the white one is an ",
"albino",
". Black and grey and sorta brown squirrels are common in my experience, but I've never seen an all-white one."
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"sending information virtually instantaneously over long distances",
"It's not how this works. There can be no superluminal information transfer and quantum entanglement doesn't affect it at all. It's true, at least for now, that it seems there is no delay in setting the particles state, but it has little to do with any information transfer.",
"Imagine I gave you a box with white or black ball, and identical box to your friend. Now both of you get very far away from each other. Now when you open your box and find a white ball, you know that your friend has a black ball. In a way your observation sets the state of his box instantaneously, but I think you can see that there is no information transfer here... The whole trick is that you can't actually \"force\" the state (and thus also force the state of entangled pair). You can only measure the state.",
"The real advantage of quantum communication, which was tested a while ago, is the fact that you can't eavesdrop on a quantum channel because it would automatically modify the data stream. See ",
"https://en.wikipedia.org/wiki/BB84",
"As for the practical problem of keeping the system in entangled state, there is no silver bullet solution. In fact this is one of the main problems with building big quantum annealers / quantum computers right now."
] |
[
"There's been much publicity lately about using quantum entanglement as a means of sending information virtually instantaneously over long distances. ",
"But one thing I don't understand: How do you keep the quantum systems (the ones which contain the entangled particles) from decohering prematurely — before your information is transmitted or even encoded? That's necessary for quantum computing, right?"
] |
[
"The theorem does hold. It has been proven."
] |
[
"Why can we effectively fight off bacteria but it seems like modern medicine can't help at all against viruses. Why are we still helpless against viruses?"
] |
[
false
] | null |
[
"Viruses and bacteria are inherently different things. Bacteria are simple prokaryotic organisms and with that come with a variety of ways you can destroy them (based on their cell wall type, etc.). Viruses are a little bit more tricky because they aren't \"alive\" in the traditional sense. They are a bundle of DNA/RNA in a protein capsid that utilize a host to propagate themselves. Depending on the type of virus, it can either be lytic and explode the cell with newly formed viruses (it utilizes the mechanisms that a cell would normally replicate itself while inherently destroying the cell) or be lysogenic and incorporate itself into the host genome for generations until it is ready to become lytic.",
"With this in mind, you can't simply destroy a virus in the same way you can bacteria because they are very different in composition. A lot of things that would destroy a virus would also destroy the proper functioning of a cell, so you'd have to find other mechanisms to fight it off (such as using an inactivated virus to teach your immune cells to recognize it and fight it off i.e. a vaccine)."
] |
[
"Antiviral drugs do exist. Just that they don't have virucidal activity (i.e. they don't directly kill the virus). You see, viruses are simply protein and genetic material, and coming up with a drug that selectively destroys these structures in the virus while maintaining all other proteic structures in our body intact is currently beyond the reach of our technology.",
"So, how do antiviral drugs act? There are basically two approaches: interfering with their reproductive cycle or stimulating our immune system to destroy the viruses.",
"The first method is the basis of HIV treatment, in which the patient usually takes three drugs that interfere with the reproductory cycle of the virus in two or three different ways. By doing this you stop the production of new virus copies and allow the immune system to destroy the ones that are left. Only that some HIV copies are still stored inside some immune cells such as macrophages and Langerhans cells and thus are \"out of reach\" and can escape being destroyed, so we can't completely eradicate the virus copies. Besides the drugs used in HIV treatment, this approach is also the mechanism of action of Aciclovir (used in herpes treatment), Oseltamivir (used to treat flu) and Ribavirin (used to treat viral hepatitis), among others.",
"The second way is more recent and much more expensive. Interferons are proteins that are a natural part of our immune system modulation. By applying injections of \"cloned\" interferon molecules to some patients we can now cure chronic hepatits C. Besides the cost, interferon therapy also has ",
"a LOT of potential side effects",
", so don't expect to use it to treat minor viral infections anytime soon. Another possible way to treat viral infection is to use monoclonal or polyclonal antibodies that identify the virus and bind to it to prevent them from attacking other cells and allow immune system cells to capture the viruses and destroy them. It's currently used to prevent some serious acute viral infections and has been recently introduced as a ",
"therapy for respiratory syncytial virus infections",
" in children.",
"So yeah, basically we ",
" treat viral infections with drugs, but we can't directly kill them and it's not very safe or cost effective to use some of these drugs in minor viral infections."
] |
[
"A bit simplified: Viruses are mostly internalized using membrane receptor interactions. Should those receptors be missing, they are suddenly without a way to enter our cells. ",
"HIV-1 utilizes CCR5 (=CD195) and CXCR, originally chemokine receptors on Th lymfocytes. And HIV-1 resistant people (at least the type that I know off) are homozygous carriers of CCR5-delta32 mutation which results in a non-functioning and thus unexploitable receptor.",
"Source: I'm med student"
] |
[
"Regarding the current news of the FDA revoking the approval of Avastin, why is VEGF a target for cancer treatment?"
] |
[
false
] |
So, today, the FDA revoked the approval of Avastin for use in the treatment of breast cancer. Apparently, Avastin (bevacizumab) targets vascular endothelial growth factor-A. From my limited knowledge, it seems like VEGF is utilized in the human body for the growth of vasculature as a normal function of the human body as well as in malignant tumors. So why would VEGF be considered a target when its inhibition could affect normal bodily function?
|
[
"Any cancer treatment will almost certainly affect your normal tissue as well - remember that cancer is ",
" gone haywire.",
"VEGF is an attractive target for cancer therapy because it is often overexpressed in cancer cells. This allows the tumor to recruit a massive blood supply, allowing it to grow and spread. But if cancer cells have, say, 1,000 times the number of VEGF receptors as normal cells, the treatment will preferentially target the tumor.",
"edit: also note that we have come a ",
" way from the original drugs for cancer treatment. These new antibody-based treatments can target very specific broken processes in the cancer cells. The first successful chemotherapy drug was an antagonist for folic acid, which is needed in every cell for division. In other words, the drug just targeted ",
" because of the fact that cancer cells divide more often."
] |
[
"To elaborate: the new blood vessels which grow info a tumor are often far from perfect and leaky. This causes elevated oncotic pressure within the tumor, which in turn diminishes uptake of chemotherapeutic agents in the tumor. VEGF receptor blockers thus make other therapy more effective. Moreover, the tumor itself recruits new bloodflow to meet elevated metabolic demand causes by rapidly dividing cells. Lack of sufficient oxygen and accumulation of waste products causes timofeeff cellen to die. ",
"I cannot provide references right now as I am typing this on my phone, but I will try to get some and post them here.",
"Edit: Damn auto'correct'"
] |
[
"Typically VEGF is most active in tissue remodeling, most often from wound healing or cancer. I suppose for growing kids, there would be systemic tissue remodeling throughout the body, or possibly body builders who are building muscle.",
"Anyways, if the tissue is not in the process of remodeling (either muscle building, growth, wound healing, cancer, etc), the tissue will already have a matured vasculature. There would be no real need to grow a new vasculature, and VEGF inhibiting drugs would do very little to these tissues.",
"In cancer, the tissue is constantly growing. This means constant remodeling as well, and as a result, the cancerous tissue is extremely metabolically active (cell division and remodeling of extracellular matrix takes energy). As a result, the cancer secretes VEGF to recruit blood vessels to supply oxygen and nutrients.",
"If we apply an anti-VEGF drug, basically, all blood vessel growth is suppressed. This kills the tumor (in theory), and does not interfere with normal tissues in the human body.",
"Hope this helps."
] |
[
"How can acids with a different pH level have the same concentration?"
] |
[
false
] | null |
[
"Some acids are more likely to donate a proton than others. So an acid, that donates protons easily, will have a lower pH level than another acid, which hardly gives away its protons, although they both have the same concentration. "
] |
[
"And since ",
"pH is a measure of the dissociated proton, H",
" , concentration",
", not the total dissolved material concentration, it is only the same for two acids if both acids dissociate in solution to exactly the same extent.",
"So for instance, if a 0.1 molar solution of a strong acid like HCl is made up, it will dissociate essentially completely to 0.1 molar H",
" and 0.1 molar Cl",
" and have a pH of 1 (the negative log of 0.1). But a 0.1 molar solution of a ",
" (acetic acid, for instance) may only dissociate to the extent of 0.1%, so you get a solution 0.001 molar in H",
" and 0.001 molar in CH2COO",
" with 0.999 molar CH3COOH remaining in solution. So this solution has a pH of 3"
] |
[
"Concentration is not a measure of potency.",
"It's purely a measure of how many acid ions are dissolved into a solvent, as a ratio.",
"It's a pure ratio of solvent to solute.",
"Strength is a measure of how many dissociated ions are formed when the acid is dissolved into an aqueous solution.",
"A string acid, such as hydrochloric acid dissolves completely in water (leaving only h+ and cl- ions behind)",
"Citric acid is a weak acid that dissolves only partially in water.leaving some ions, and some nuetral particles.",
"pH is a measure of the molar concentration of free hydrogren (H+), and is a specific property of aqueous solutions.",
"Adding hydrochloric acid to a solution increases it's pH (because it releases the hydrogen from the chlorine), but it only ends with 1 H+ molecule per chlorine particle added.",
"Adding a weak acid will change the oh less because only some of the weak acid will dissociate and firm free H+ particles.",
"You would need a smaller concentration of a strong acid to get to the same ph as a larger concentration of a weak one because the weak acid dissociated less free hydrogen (H+) assuming the same original number of particles of acid."
] |
[
"If Mars once had complex multicellular life, would there be any evidence leftover on the surface today?"
] |
[
false
] |
[deleted]
|
[
"The earth is about 4.5 billion years old. Up until 600 million years ago there was no multi-cellular life. So 3.9 billion years of no life or single cell life.",
"More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago. ",
"https://astrobiology.nasa.gov/news/how-did-multicellular-life-evolve/",
"It's believed that Mars only had water and an atmosphere for about the first billion years of it's existence, which is about how long it took for single cell organisms to develop on Earth.",
"So, assuming Mars and Earth's development of life had roughly the same timelines then Mars became barren about 3 billion years too early for multi-cellular life to develop."
] |
[
"It's highly doubtful that Mars ever had complex multicellular life; even Earth with it's fairly ideal conditions only developed complex mulicellular life somewhat recently, within the past billion years, when Mars had already become inhospitable to surface life. However, simple unicellular life can leave traces too, and it's possible that we've already discovered fossilised traces of these organisms on Mars; ",
"structures have been found there which bear an exciting similarity to microbial mats on Earth",
", and may be the remains of ancient microbial communities. Our current tools on the ground aren't sufficient to determine if they really are microbial fossils or just oddly shaped rocks."
] |
[
"Yes unlikely unless Eukaryotes cells managed to hitch a ride from Earth to Mars via some like a recent (i.e. 600 million year old or less) meteor strike, but even then if it landed on Mars it would find an environment that would be extremely hostile to life...so no there is/was no multi-cellular life on Mars.",
"The most exciting possibilities are the potential microbial mats found by MSL"
] |
[
"If Mars is a candidate for terraformation, could the same process be done for Venus?"
] |
[
false
] |
I understand very small basics of the process of terraforming but my curiosity essentially stems from the similarities in size of Venus to Earth. I know that Venus is much hotter and has atmospheric pressures that would crush us but are there viable techniques that could significantly alter the planet in order for there to be human visitation one day? What other worlds could theoretically be candidates?
|
[
"Venus is very close to the sun, making it very hot and the radiation levels very high. \nIt would be a lot harder to live there than Mars."
] |
[
"Venus has a size roughly like Earth's and a nice and thick atmosphere to work with in terraforming imaginary ideas. The main problem of Venus though is that its day last to long, about 243 earthly days, and that makes it a difficult planet to terraform even for a longterm project. We would have to engineer life (plants but also the rest) to withstand months of light (and heat) and then months of darkness (and coldness). Or we would have to find a way to shorten the Venusian day. If you like the idea try to calculate how much energy would it be needed to ",
" acelerate the planet to an earthly day length, it makes up for a nice physics problems.",
"Mars is a much better candidate, probably the best in our system, because its day and year are not too far of Earth's, the planet has an atmosphere even if thin, the size and therefore gravity are less than Earth's but within life probable limits for adaptation, and the planet has significant amounts of water. ",
"Both planets have a difficult to solve problem however with their lack of magnetosphere compared to Earht. The magnetosphere is a magnetic field created by the rotating inner mass of the planet, that shields the planet from solar radiation and wind and prevents largely the loss of atmospheric water to space.",
"With our current knowledge and technology I believe Mars could be terraformed, although the cost would be astronomical :) Maybe some time in the future. Venus would need a project spanning many several thousand of years unless an unknown and aboundant source of energy is found."
] |
[
"So Venus would essentially require its 'spin' to increase before Earth-like plants could be grown there? That's one thing I hadn't considered actually despite knowing it was longer than its year, one of the factlets I took in as a kid. While there are active volcanoes on Venus would this be a likely problem too?"
] |
[
"When building like the Empire State Building (or taller) get too old and need to be brought down, how will they do it safely?"
] |
[
false
] | null |
[
"A Japanese construction company demolishes buildings a floor at a time. ",
"Link with video and explanation",
". Seems like it would be useful to tear down a building like the ESB when it has reached end of life. "
] |
[
"From the article: ",
"Basically, construction workers build a hermetic structure covering the top floors of a tower that is supported by powerful jacks. Inside the structure are the heavy machines and demolition crews, who take apart the walls and cut the floors into concrete slabs that they lower to the ground via interior cranes. ",
"The hermetic seal of the structure ensures that no contaminants are leaked. Generally, these seals prevent air from getting into or out of the sealed area and so you wouldn't see dust leak out. These seals also prevent any physical debris from falling outward; that being said, there is not as much \"in-your-face\" debris (like normal demolition jobs) because the physical debris is disassembled and removed via the inside. "
] |
[
"How long can we expect a building like ESB to last?"
] |
[
"Lightning storm while white water rafting; which is safer?"
] |
[
false
] |
So we just had a cubicle debate when a coworker informed us that he went white water rafting this weekend. If you're out on the river, and a lightning storm rolls in, are you any safer in the water in a rubber raft or on the ground? Consensus here was that as long as you're in the rubber raft, being insulated from ground, you should be OK. This doesn't sound right to me, but all my Google searches are turning up is advertisements to go white water rafting.
|
[
"I think google is encouraging you to do this... for science.",
"Seriously though, during any thunderstorm, your first priority is to get off the water. Water is a pretty good conductor of electricity, so even if a strike occurs at a fair distance away, you could still be electrocuted. Also, chances are that your rubber raft is soaking wet on the outside, providing a nice conductive shell... ",
"Always get off the water, stay low to the ground ( i would get on the shore, and cover with the raft). Lighting is attracted to locally tall pointy objects, especially conductive ones, so the lower/flatter you are, the safer you are froma direct strike. This is also why you never take cover under trees during a thinderstorm. Trees have a tendency to attract lightning ",
" explode when they are struck. If the lightning doesn't kill you, shrapnel might."
] |
[
"The rubber raft does not make you safer. Air is highly resistive. It's more resistive than rubber. The bolt has already travelled through a couple miles of air. A few mils of rubber will make no difference. Same goes for your car tires. Its the skin ofthe car (hopefully a metal) which will save you. Not the tires. I'd say that your coworker is dangerously wrong."
] |
[
"I reckon because you're in a river which is presumably surrounded by higher banks, even cliffs, and trees, then you're less likely to be struck by lightning, as it'd tend to hit something higher. In terms of in the river or on land, I'm not sure."
] |
[
"Can you die from a magnet? How strong does it have to be?"
] |
[
false
] |
Is it possible to kill a human with a strong enough magnetic field? If so how strong does this magnetic field have to be? And is is even possible to generate such a strong field?
|
[
"A 16 tesla field is enough to levitate a frog. As I recall, the magnetic field of a magnetar is enough to shred a human, but it's in the gigateslas. "
] |
[
"Actually, as I understand it, extreme magnetism will break molecular bonds. Extreme magnetic fields distort the behavior of electrons. Given enough distortion, it is possible to turn normally reactive elements into chemically inert substances. Just splitting enough internal water into pure hydrogen and oxygen would kill a person, though it may well be that much more complex molecules, like neurotransmitters and DNA, would break down much earlier as a starship of doomed people approached a magnetar.",
"P.S. Sorry for the weird phrasing. Initially I read another response as \"rip your atoms apart,\" and I started out objecting to that, then later realized that claim hadn't actually been made."
] |
[
"What will actually kill a person in those circumstances? "
] |
[
"If whale pods tend to stick together through generations, how do they prevent inbreeding?"
] |
[
false
] |
Pods I've heard are gigantic families of whales. Mothers, fathers, children, grandparents, uncles, etc. With this I've heard they tend to stick together and the kids tend to hang around their mothers even in adulthood. If this is the case, how do these younger generations get mates to bring calves into the world that are not inbred? Or is inbreeding something that happens a fair bit?
|
[
"According to ",
"this paper",
", killer whale pods will temporarily associate with each other and mating will occur between whales of different pods. This helps reduce inbreeding even though the whales don't disperse from their natal pods.",
"In other species, like the ",
"sperm whale",
", one sex will disperse from its natal pod to join other pods, either permanently or temporarily. For sperm whales, its the males that disperse, which tends to be true of most social mammals."
] |
[
"One of the main theories I've heard is that orcas will only mate with those that have a different regional 'dialect' than they do. Since all their relatives have the same dialect as they do, this functions to prevent inbreeding. ",
"Here's a basic summary of orca 'culture' and mating behaviors."
] |
[
"They also follow annual migration routes -- colder waters for better hunting and warmer waters for breeding and rearing calves. They will frequently wind up in the same mating grounds at the same time of the year. Humpback whales will even actively compete for mates, not unlike dolphins. It's kinda' cool.",
"(BBC - Planet Earth series)"
] |
[
"Electrons and elemental properties"
] |
[
false
] | null |
[
"Different elements by definition have a different number of protons in their nucleus, and different nuclear charges, which in turn determines how many electrons they're likely to attract. All chemical and material properties depend on what the electrons are doing. (And in terms of the total electronic energy, it's actually a relatively small part of what they're doing)",
"Electrons are attracted to the nucleus since they have opposite charges, and they repel each other since they have the same electrical charge. In short, that's where all chemical/material properties come from. So obviously, changing the nuclear charges and/or the number of electrons will have a big impact on those properties. Changing other things (such as the mass of the nucleus or its magnetic moment) doesn't do as much, which is why isotopes of the same element have largely the same chemical properties."
] |
[
"You're right about the electrons, it's a large part of chemistry. Each atom has a different ",
"electron configuration",
". Some electron configurations are strongly correlated with certain chemical properties. For example, noble gas configurations correspond to very high stability and inertness."
] |
[
"You're adding protons ",
" electrons. Again, opposite charges attract. It takes energy to separate them, so you don't have many things in nature that just sit there with a net positive or electric charge on the larger scale. So you do not just have 79 protons but 79 electrons as well in a gold atom. ",
"I can not make sense of how the addition of protons causes so much variation in the properties of all the elements",
"Well, why not? If I were to increase the gravitational pull of the Sun 79 times, wouldn't the planets change orbits dramatically?"
] |
[
"Is the speed of light defined by special relativity or assumed by it?"
] |
[
false
] | null |
[
"my question is whether all observers agreeing on the speed of light is an assumption of SR",
"Yes, that is a postulate (an assumption).",
"I guess what I'm asking is, did Einstein figure out that the difficulties people were having with electromagnetic field theory could be resolved by assuming that the speed of light is constant for all observers, and therefore take the constancy of the speed of light as an axiom?",
"Yes."
] |
[
"Thanks 👍"
] |
[
"It's a postulate of SR that there exists a finite upper limit to the speed at which physical signals can propagate. It's a ",
" of electromagnetic theory that light propagates at this speed."
] |
[
"Can human blood boil?"
] |
[
false
] |
If I had two cups of healthy human blood and placed it over a heat source, would it boil? At what temperature? Would all the water evaporate and leave a thick layer of dried blood?
|
[
"Yes, this very process is how the pigment ",
"Prussian blue",
" was historically synthesized - by boiling down blood in order to extract the iron.",
"Just like any other aqueous solution, you can boil it at approximately 100 degrees Celsius or above. The vapour profile of the solution depends on the vapour pressures of the constituents, and that's the basis of ",
"distillation",
". Blood has many constituents like red blood cells and proteins that don't vaporize easily, so boiling off the water will leave you with the non-vaporized portions of blood."
] |
[
"That's a common misconception though. Your body is very well capable of keeping the internal pressure in your blood vessels to not have blood boil."
] |
[
"Interestingly enough, one of the reasons Felix Baumgartner needed to wear an airtight pressurized protective suit for his space-jump was that the low pressure at that altitude would've caused his blood to start boiling."
] |
[
"Could graphyne potentially serve as a carrier of electrical current over extreme distances?"
] |
[
false
] |
[deleted]
|
[
"'As if they were massless' here is a very misleading if you don't know what it's referring to, which is ",
"effective mass",
". Which is something quite different from 'mass' in a proper sense. It's the 'mass' that they'd have defined by how they respond to an electrical field, if you pretend they act classically (which electrons don't). Effective mass is different in different directions, and it can even be negative. ",
"Anyway, neither graphene or graphyne are superconductors. "
] |
[
"Its actually pretty easy to make large sheet of graphene.",
"You can easily make a few cm",
" sheet with a CVD furnace and theroll to roll methods that Samsung uses can make huge areas of the stuff"
] |
[
"I haven't seen many. But science journalists are often wrong anyway. Graphene is not a superconductor. It can support a ",
" over short distances if you place it between two actual superconductors, due to the ",
"Josephson effect",
". Some people are just confused I suppose. "
] |
[
"How exactly does a large array of radio dishes spread across a field like ALMA in Chile create a 10 mile wide \"telescope?\""
] |
[
false
] |
I don't understand how you could get images from 66 radio dishes spread around a field. .
|
[
"Aha! This is my field, and I may be able to help you with this. Beware: we are going to go deep, deep down the rabbit hole into the land of aperture synthesis interferometry. Even those who've been doing it for years may still find it confusing at times, so if it seems totally incomprehensible, that's normal. ",
"This webpage",
" may help you.",
"In a telescope such as ALMA, the signals from each pair of dishes can be combined to form a ",
". For an interferometer the number of baselines is N(N-1)/2, where N is the number of dishes. So for ALMA there will be 2145 baselines total. Now, each baseline is basically a single example of a ",
"double slit experiment",
". A 2-dish interferometer will form an image that looks basically like what you get from passing a beam of light through a double slit, because it is essentially the same thing. ",
"The image of an interference pattern produced by a double-slit experiment basically looks like a bunch of parallel lines. Imagine that our interferometer is a set of detectors on a beach that detect when waves wash in. I wish I had a chalkboard, but oh well. Let's say I have detectors A, B, and C, which are equally space in a line along the shore. Detector A detects a wave, and a second later B detects that wave, and a second later C detects that wave. Based on the difference in timing, I can work out what angle the wave was coming in at. Now think about a line of 3 radio dishes-- they do basically the same thing, but with much much higher precision. Let's say this line of dishes is ranged east-west. During a short measurement, they could tell me about the precise position of sources in the east-west direction, but they can't tell me much about the source's position in the north-south direction (in astronomical terms, east-west is Right Ascension and north-south is declination, or for short, RA and dec). This is why the dishes are arranged in all sorts of different locations, so that we can get good angular resolution in each direction. ",
"For a single radio dish, the resolution is limited by the diameter of the dish-- the equation is ",
" where theta is the angular resolution in radians, lambda is the wavelength being observed, and d is the diameter of the dish. For an interferometer, d is the length of the longest baseline. So for example, the ",
"Very Large Array",
" in New Mexico has 25 meter wide dishes, but its maximum baseline is about 35 kilometers, so its actual maximum resolution is 1400 times better than a single dish.",
" the data is a more complicated question. In order to properly understand it, one needs to have a good understanding of ",
"Fourier transforms",
". In a very rough sense, though, waves which are hitting a telescope aperture are ",
" by the aperture (if you've done optical astronomy, you may have seen ",
"Airy rings",
", which are another example of the convolution which an aperture applies to a signal). Raw radio data come in the form of ",
", which are just data measurements along a particular baseline for a short period of time. In order to turn it into an image, a computer program runs an inverse Fourier transform on the visibilities, which can be thought of as de-convolving the signal.",
"I'm sure this has done as much to muddy the waters as to clear them, but feel free to ask me followup questions. I'm not really sure what, if any, your physics background, and this may have been a bit technical."
] |
[
"I really don't understand this but I got a jist. I guess the main technique is measuring waves at different locations and noticing the time delay and somehow overlapping them to make an image or.. un-overlapping them to make an image? Oh boy. I guess a good question to start is. What is a baseline? That would clear lots of things up. Also, is each dish receiving like one piece of information like one wave, or is it receiving a picture of an area of the sky? Or do my questions even make any sense?",
"(btw, I have year of highschool conceptual physics and half a year of highschool AP physics ><)"
] |
[
"A baseline is what you get when you combine the signals from two telescopes. Think of it as two telescopes tied together into a pair to form a double-slit experiment.",
"A single dish telescope will give you an image, albeit an extremely blurred image (because a single dish has poor resolution). "
] |
[
"Is it possible for nerves in the body to become intertwined or misconstrued? Would it be possible for a hair being pulled to be felt on another hair as if it happened to that one?"
] |
[
false
] | null |
[
"I'm not sure if this isn't something completely different, but isn't it quite common for pain to be \"moving around\" and be felt at locations different from the pain source?"
] |
[
"I have never heard of nerves getting mixed up or anything like that. As a general rule of thumb, all sensory nerve fibers refer back to a single spinal nerve called a dermatome (linked below is a dermatome map). Each spinal nerve supplies a certain area of the skin with sensory input. I have never heard of dermatomes being mixed up, nor seen anything on it on the internet through cursory research. Through dissection, I have seen nerves go through places they shouldn't normally go through, but they always innervate the things they should.",
"http://tlccrx.com/resources/printable-dermatome-chart/",
"Source: master's in human anatomy"
] |
[
"So whenever a patient walks into the doctor and says my knee hurts, there are many different things that could be wrong. In addition, how the patient communicates pain to the doctor and how the patient perceives pain is different for each person. This is why the doctor manipulates the patient and asks many different questions. Is the pain sharp or dull? Does the pain radiate? Which direction does it radiate? Did this pain have a sudden onset? All of these questions help point the doctor to the correct diagnosis. A torn meniscus is going to be a more dull pain only really present when the affected knee is carrying a load. This is going to feel much different than if you had a bruise on your knee. Linked below is an article on the sensors of the pain pathway. It's a dense read, but a good primer on nociceptors. ",
"All of this being said, neurons are neurons are neurons. They are very straight forward cells. When pain \"moves around\" there is usually a reason for that movement. Some underlying cause fires the neurons in a different part of the body making the pain \"move\". ",
"If you are still confused let me know, and I can try to give some more detailed examples.",
"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2964977/",
" "
] |
[
"Is our galaxy moving from momentum from the big bang or just from gravity-dark energy?"
] |
[
false
] |
So when I was younger my understanding of the big bang was that all matter blasted away from a center point and that the galaxies where all hurdling away due to this. I then learned how the big bang wasn't an explosion of matter but the creation/expansion of space time. So I just realized that we might actually be sitting still in the universe other than the momentum gained from gravity and dark energy. Its this right?
|
[
"So I just realized that we might actually be sitting still in the universe other than the momentum gained from gravity and dark energy",
"The universe has no frame of reference. A bullet train might be sitting still and the rest of the universe flying past it. Any frame of reference is correct.",
"Velocity, position, and distance are all relative. Acceleration is all that's absolute. That and the speed of light."
] |
[
"If you're in a box, and it's moving (or sitting still) you cannot tell how fast it is moving.",
"However, if a force is exerted on it (such as in an elevator), then you ",
" feel the force, as it moves relatively to ",
" which means ",
" move relative to ",
" While you could never determine its velocity, you could observe its change in velocity over time."
] |
[
"Galaxies are moving away from each other because of gravitation, not the initial momentum.",
"If you have an infinitely large space, and matter distributed in that space in a homogeneous manner, General Relativity predicts that the result would be a situation where 'space expands'. This is called the FLRW solution to Einstein's equations.",
"Look up things like expansion of universe/spacetime and you'll find your answers."
] |
[
"If light travels in a straight line, why aren't there gaps between rays of light if the source is far away?"
] |
[
false
] |
[deleted]
|
[
"Light isn't really rays, that's a simplified way to picture it that captures a lot of its behavior but fails in other ways. Light is a wavefront that spreads out as it travels, and the rays are defined to point perpendicular to the wavefront - in the direction the wave is moving at that point. So there are infinitely many 'rays', as the wave spreads out you just picture more rays to fill in the space between the ones that spread apart. They're a visualization tool and not a physical object so there's no conservation law or anything.",
"It's my understanding that as the wave spreads out it carries less energy flux in any given area, your eye/camera can only cover a certain area, the wave will eventually spread out to the point that there's not enough energy in that area to trigger the detector.",
"Sort of tangentially, it's my understanding that the photon view comes into play as the amount of energy that can be exchanged between the wavefront and your eye/camera is quantized into discrete units (the photons), but this has more to do with the interaction of the light and the detector and, though people (myself included) often talk about photons flying through space, it's not really an appropriate description and the light is better visualized as a wave as it travels."
] |
[
"There are, but you have to get really really far away. When looking at distant x-ray or gamma ray sources (like from other galaxies), the photons typically arrive one at a time instead of in a continuum."
] |
[
"Sort of tangentially, it's my understanding that the photon view comes into play as the amount of energy that can be exchanged between the wavefront and your eye/camera is quantized into discrete units (the photons), but this has more to do with the interaction of the light and the detector and, though people (myself included) often talk about photons flying through space, it's not really an appropriate description and the light is better visualized as a wave as it travels.",
"This is an absolutely excellent answer."
] |
[
"Question about the expanding universe and space ships."
] |
[
false
] |
This is something that has boggled my mind for a while, the universe is expanding, galaxies are flying the the universe at incredible speeds from what i read. Now how is it that when a space ship leaves our atmosphere the planet doesn't just fly away and leave the space ship in it's dust.
|
[
"Because metric expansion doesn't work ",
" like that. Whatever you've been reading, you should put it down.",
"The effects of metric expansion — which do ",
" involve \"galaxies flying [across] the universe at incredible speeds\" — are only really detectable on scales in excess of about a hundred million light-years."
] |
[
"\"space is expanding\" doesn't mean that space is expanding outward from a central location like an explosion. ",
"it means that the space between space is expanding much like if you consider baking a loaf of raisin bread. The raisins represents galaxies and the bread rising is an example of the universe expanding. as the Bread expands, the space between the individual raisins expands."
] |
[
"Ahh...now that makes more sense, thank you!"
] |
[
"What is the most interesting protein you know of?"
] |
[
false
] |
I once heard how influenza has a sort of knife--grappling hook protrusion made out of alpha helices that swings out and sticks into the cell wall when the pH changes. I don't know if that one is accurate. What else do you know about?
|
[
"My top three:",
"ATP Synthase",
"-This is literal rotary motor in your cells that turns a H",
" gradient into chemical energy by pushing bonds close to eachother. (And changing the binding environment)",
"Heat shock proteins",
"- These are little molecular barrels which collect mis-folded proteins and give them a chance to refold, they even have lids!",
"Myosin motors",
"- This class of proteins is how most large scale movement happens in your body. There is a lot of actin, myosin, and micro filaments in your body. Myosin motors (and similar proteins) use ATP energy to literally ",
" down these cytoskeleton elements to cause muscle contraction, deliver, compounds to the right areas in cells, and even to bend actin filaments to be cut during LTP."
] |
[
"PKM zeta",
"I guess I'm biased because I work on this one :)"
] |
[
"Myosin motors (and similar proteins) use ATP energy to literally ",
" down these cytoskeleton elements",
"I've shown the ",
"Inner Life of a Cell",
" video (a must-watch, if you haven't seen it already) to people from elementary school up to middle age, both scientists and the lay public, and when it gets to ~1:15 and the first violins kick in to the image of a myosin molecule dragging a vesicle across the cell, jaws drop virtually without exception."
] |
[
"Besides potentially causing hypothermia, what makes cool water enjoyable to drink, but horrible for swimming?"
] |
[
false
] | null |
[
"From an evolutionary standpoint, you drank water at whatever temperature the water source was. Once you start looking past the point where humans started inventing things, it's sometimes not possible to chalk up something humans do to strict evolution. We drink ice-cold colas because we like ice-cold colas, not because it imparts a survival advantage. In fact, many of the things we do specifically hinder survival - we smoke, we drink too much alcohol, we shoot heroin, etc. We do those things because we like them, not, for instance, because at some point in the distant past inhaling the smoke from burning leaves enhanced our ability to survive.."
] |
[
"According to this source (",
"http://www.sportsscientists.com/2008/01/exercise-in-cold-part-ii.html",
"),\nthe most dangerous factor isn't hypothermia but the so called Cold-shock response:",
"\"One of the first things you experience when submerging yourself in cold water is something called the \"cold-shock response.\" This is characterized by an uncontrollable gasp for air, followed by a prolonged period of hyperventilation - more rapid breathing. In fact, this response is one of the most likely causes of death in most cold-water immersions such as when one falls out of a boat into icy water. It's not difficult to see that if the timing of that \"gasp\" is slightly wrong, you'll take in a huge lungful of air, and one or two gasps while underwater is all it takes to drown.",
"The other big 'killer' is a heart attack, which can result when the temperature of the blood returning to the heart is suddenly cooled - this can affect the electrical conduction within the heart, causing fibrillation. So it is these two possibilities - drowning and cardiac arrest that are most likely the cause of death. However, as we said, most times, people blame hypothermia for death, when in fact the body temperature does not need to fall for an unlucky 'swimmer' to perish in the cold.\"",
"Plus, prolonged hyperventilation might lead to fainting or cramps (",
"http://en.wikipedia.org/wiki/Hyperventilation",
")."
] |
[
"Your questions assumes that humans prefer drinking cool or cold water. That may not be a universal preference among humans, just a cultural preference in the US and perhaps certain other countries. I grew up in Europe and never put ice in water or even other drinks...it just wasn't commonly done. I still drink liquids at room temp or maybe slightly below. My wife and kids grew up in the States and they curl their lips as the thought of drinking water that isn't cold. In England, beer is not served cold like in the US and while ice has become more common on the continent for drinks like Coke or Pepsi, it still is not used universally like here in the States.",
"People in Europe often drink warm/hot liquids (ie, tea) as they do here in the states (coffee) but I have to admit that such drinks are meant more for entertainment, social interaction (slow sipping) and as a source of caffein. Drinks meant to quench thirst are often at room temperature or cooler, depending upon the culture. "
] |
[
"Are gallbladders and lymph nodes actually green as they are always shown in diagrams?"
] |
[
false
] |
Neither bile nor lymph is actually green, so are gallbladders and lymph nodes always depicted as green just by convention or because they are actually green?
|
[
"For a gallbladder, yes but when it’s full. Bile tends to be a dark greenish color which makes the gallbladder appear green. However, the lymphatic system isn’t. Lymphatic vessels are more of a white color while lymph nodes are a pale brown. I believe the lymphatic system is usually drawn green in illustrations to give it contrast to the red and blue colors used to illustrate the cardiovascular system, since the two are often associated with each other."
] |
[
"Gallbladders color can range from tan, to pink-purple, to gray-green. The bile inside is usually consistent with the color of the overall gallbladder. Dark green bile tends to stain the mucosa, and if the gallbladder wall is thin enough, will change the color. ",
"Lymph nodes are almost always tan or tan-brown. ",
"Source: Pathology Grossing Assistant"
] |
[
"Well, the actually gallbladder when you're looking at it is not green. It's like any other viscera. But if you accidentally poke it or spring a leak in the cystic duct as you're taking it out, you'll see green coming out. Looks really gross on the laparoscopic camera."
] |
[
"How much has solar luminosity increased in the past billion years? Three hundred million years? It it significant?"
] |
[
false
] |
I am having difficulty finding a good answer to this question. Thank you.
|
[
"I found this in the footnotes of ",
"a 1972 paper by Carl Sagan and George Mullen",
" about the ",
"Faint young Sun paradox",
":",
"Estimated values of the increase in solar luminosity, AL, over geologic time are: 60 percent [M. Schwarzschild, R. Howard, R. Harm, Astrophys. J. 125, 233 (1957); (7)J; 30 percent [F. Hoyle, in Stellar Poprtlations, D. J. K. O'Connell, Ed. (Specola Vaticana, Vatican City, 1958), p. 223; C. B. Haselgrove and F. Hoyle, Mon. Not. Roy. Astron. Soc. 119, 112 (1959); D. Ezer and A. G. W. Cameron, Can. J. Plzys. 43, 1497 (1965)l; 50 percent [I. Iben, in Stellar Evolution, R. F. Stein and A. G. W. Cameron, Eds. (Plenum, New York, 19661, p. 2371; 35 percent [J. H. Bahcall and G. Shaviv, AstroplSs. J. 153, 113 (1968)l; 40 percent [I. Iben, Ann. Phys. New York 54, 164 (1969)l. A weighted mean of these values is 40 percent -C 10 percent.",
"So it looks as if the sun was about 70% as luminous as today in early geologic times, and has increased since then.",
"I'd love to hear more from an actual expert."
] |
[
"According to ",
"this paper",
", the solar luminosity a billion year ago was about 90% of what it is today. If you can not access the article, there is the arXiv preprint version that is basically the same."
] |
[
"It's saying it's up 40% from what it was originally, or in other words it used to be 70% of what it is now."
] |
[
"Why don't apes have facial hair but we do?"
] |
[
false
] |
What is the we came to have facial hair but our cousins don't? especially the region above the upper lips.
|
[
"They do!",
"Chimpanzees are the closest relations to us, and they most certainly have facial hair.",
"Example 1",
"Example 2",
"Many many more examples"
] |
[
"Layman here. They do have facial hair, but not in the same exact shapes/patterns we do. Facial hair is considered a secondary sexual characteristic, and as such, it's highly susceptible to selection. Basically, it's about what the females prefer."
] |
[
"Notice none of them have mustaches."
] |
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