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[
"What is the biological explanation for why we often feel nausea in waves rather than one sustained reaction?"
] |
[
false
] | null |
[
"MD here. I don’t really like any of the answers here. Mine probably won’t be great either though because I don’t necessarily agree that nausea comes in waves. ",
"You can have what’s called a “colicky” pain in the abdomen, this is pain that comes in waves, which is due to peristalsis (the intestines basically contract in waves to help push food) and if there is an irritant in the tract, you will feel the pain on the contraction. ",
"Now, related to this is the fact that nausea is based on the gut brain axis. Your gut actually produces neurotransmitters, such as dopamine and serotonin, these communicate with the brain to tell it to vomit. For example, a common drug for nausea is metocloprimide which is a dopamine blocker. ",
"How these neurotransmitters interact from the gut and brain is very complicated and is based on our outside world (like our interpretation of possible anxiety causing scenarios) as well as what’s inside our body (something toxic). ",
"So, I think it is dependent on why you are feeling nausea in the first place. Spit balling now, in my experience, if I have something like food poisoning, I just slowly get more nauseous until a vomit response is trigger. If I’m feeling nauseous from anxiety, well, then likely my brain is trying to combat that nausea with other neurotransmitters or maybe by reducing neurotransmitter receptors in the brain as a way to try and balance the system, if that makes sense. The ladder, I suppose could be like a wave sensation."
] |
[
"Is this your theory or is it truly scientific?"
] |
[
"Is this your theory or is it truly scientific?"
] |
[
"Why is the binding energy within a nucleon positive?"
] |
[
false
] |
I posted this as part of another discussion, but it seems to have gotten largely lost in an excellent comment thread... First, my understanding of the basics. In nuclei, the binding energy nucleons is negative. We can tell because if you add up the mass of all of the protons and neutrons in a nucleus, the sum will come out higher than the mass of the nucleus itself. That is, there must be some "negative mass" as well, and that comes from the negative binding energy (negative because, for example, is lower at its equilibrium point than at infinity). Right. Here's the weird thing. If you consider, instead, a single nucleon and its quarks, then adding the mass of the quarks again gives a different number than the mass of the nucleon. This time, though, the mass of the quarks comes out dramatically than the mass of the nucleon. This suggests a positive binding energy. I understand that the strong force gets stronger with distance. That's going to mean that a graph like the one I linked above never actually reaches a limit as increases, which in turn means that the definition of binding energy becomes a little stranger (because you can't simply imagine bringing the particles to infinite separation). So how do we understand binding energy for a particle whose constituents be brought to infinite separation, even hypothetically (ie, neglecting the pesky quarks that tend to pop up in the intervening space)? And how does that energy come out positive even for a stable nucleon?
|
[
"Right. Here's the weird thing. If you consider, instead, a single nucleon and its quarks, then adding the mass of the quarks again gives a different number than the mass of the nucleon. This time, though, the mass of the quarks comes out dramatically less than the mass of the nucleon.",
"Not if you add up the ",
"constituent quark mass",
". That's the number that's comparable here. The 'bare quark' mass is significantly less, but that's basically a theoretical construct. In the formalism of quantum field theory, you basically treat things as 'bare' (non-interacting) and then add the interactions with the field back in to get the actual 'real' value (a method known as perturbation theory). ",
"For heavier things like protons and neutrons, which exist as free, observable particles, you can directly measure the mass. As you seem aware, it's not as simple for things like quarks though. "
] |
[
"I think the answer to this question is more one of definitions. Nuclear binding energy is the difference between the the sum of protons and neutrons in a free or unbound state vs the mass Protons and neutrons when clumped together in a nucleus. The sum of the masses of these particles when bound is less than their sum when they are unbound, so yes binding energy describes a loss (or negative) in the sense that it is the amount amount of mass lost when the particles are bound. However Binding Energy is the Value of this lost amount, and therefore given as a positive number. A simplified example would be say person goes on a diet and drops 5 pounds. We could say that the value of their weight was altered by -5 pounds , but the AMOUNT of weight that they lost was a positive number 5 pounds. "
] |
[
"I understand this. But the question was regarding the binding energy within a ",
", not ",
". My understanding is that the binding energy within a nucleon is positive because, unlike that within a nucleus, it comes from the kinetic energy of the constituents, which is positive.",
": Thanks for taking the time to post a reply, though -- especially so long after the question was originally asked! Who says the internet has a five second attention span?"
] |
[
"When using a spectroscope to analyze light from a far away star, how can we sure that the light the device sees is indeed from that star and that star only?"
] |
[
false
] |
Won't the light from different stars and galaxies reach the spectroscope in a "mangled" or mixed state? Sure, we can analyze this light and see what elements caused those wavelengths to be emitted, but we would be analyzing a "mixture" of photons from various galaxies and stars not the "pure" light from that particular star at which the spectroscope happens to be pointed at. Right? Can someone please explain this to me? I always found the explanation of pointing a spectroscope to a star to study its composition overly simplistic.
|
[
"You're kinda right, but it's something we take into account. The simplest way is to just make sure your target is by far the brightest object in the slit, so that the background stars and galaxies only contribute a tiny bit of noise. But often things are too close together to do that: the most striking example is when you're pointing at a galaxy, you are indeed getting the sum of loads of components: a mixture of billions of stars with different spectra, as well as all of the free gas, which all looks different because of its composition, temperature, velocity etc. A good chunk of the research is about disentangling this stuff, figuring out what mixture of gas and stars will produce the spectrum, and there is indeed room for misinterpretation - that's why it's a research topic."
] |
[
"Just to add to this: there are astronomers who devote their careers to the stuff lying in front of a bright object, and count on that stuff messing with the spectrum in a systematic way.",
"A common example is the study of \"quasar absorption lines\". So far as we can tell, galaxies extend significantly farther out than their luminous component - in addition to dark matter out on the rim of a galaxy, there are also clouds of gas and dust that are too cool to appreciably emit their own light. We know they're there, but we can't see them.",
"If you're very lucky, though, you may be able to find an extremely distant quasar (a bright galactic nucleus) that has a line-of-sight to Earth that cuts through the cold outlying clouds of a much nearer galaxy. Since the clouds of the nearby galaxy are so cold, rather than adding light, they'll actually subtract light from the spectrum of the much more distant background quasar by absorbing some of it. If we can precisely measure which wavelengths are subtracted, we can build up a map of how much gas there is, as well as its velocity relative to the parent galaxy.",
"It's a bit like trying to study the shape of shadow puppets, using the background illumination source as a guide."
] |
[
"Good point. This is also how we've found out about the atmospheres of exoplanets, by looking at how the star's spectrum changes when the planet goes in front of it."
] |
[
"Why do sodas fizz up if you shake them?"
] |
[
false
] | null |
[
"Sodas are over saturated with CO2, as you know. The fizz is from bubbles of CO2 coming out of solution. The rate at which the bubbles form has to to with nucleation sites and surface area for the gas to escape into.",
"When you shake a soda you create lots of tiny bubbles which allows the CO2 to come out of solution much faster, into each bubble, thus the greater fizz."
] |
[
"Follow-up question. How is the CO2 held inside of the liquid?"
] |
[
"It's dissolved in it and is constantly coming out and going into solution creating an equilibrium at the top of the bottle which is why if you leave it open it goes flat, when the gas comes out it just escapes instead of being able to redissolve"
] |
[
"How can Greenhouse gases affect so much the environment if their concentration is so low it has to be calculated in ppm?"
] |
[
false
] |
I've been casually reading about the greenhouse effect and I still don't manage to understand how can so little affect so much our planet.
|
[
"Carbon dioxide is at about 400 ppm. That's 0.04%. ",
"If you drink alcohol, 0.04% in your blood has an effect.",
"Paracetamol starts to be toxic at about 0.02% of body weight.",
"Lots of things can have a big effect in small amounts."
] |
[
"The greenhouse effect is one of the more misunderstood scientific phenomenon at the moment. The simplified explanation that we tend to hear a lot off is the blanket analogy, that the gases trap the heat in the atmosphere. While this is a perfectly good analogy, the more in depth explanation is as follows:",
"Energy from the Sun enters out atmosphere as shortwave radiation; things like UV rays and visible light",
"The earth absorbs a lot of this energy, but some is re-emitted back out as long wave radiation, which is further down the electromagnetic spectrum",
"This long wave radiation can be reabsorbed again by many greenhouse gases, for reasons to do with resonance, and is actually very similar to how your microwave works as well.",
"This energy can then be re-emitted a second time, back into our atmosphere, increasing the temperature and causing what we know as the greenhouse effect",
"However, what we refer to a lot nowadays is the human caused, or enhanced greenhouse effect. Greenhouse gas levels sat naturally at approximately 200-250ppm before the industrial revolution, and as ",
"/u/ausrandoman",
" said, now sits at about 400ppm. This is a huge jump in terms of energy absorption by those greenhouse gas particles, as there are nearly twice as many of them in the atmosphere. And because their effect is so profound (without all of them in our atmosphere the average global temperature would be around -18C) there is quite a hullabaloo about them today.",
"Hope that helped :) "
] |
[
"Nice work!",
"Also take into consideration that everything in our atmosphere happens in front af a huge, inactive nitrogen background. If you leave out the parts of our atmosphere that \"don't do anything\" you wouldn't be talking ppm anymore."
] |
[
"How is it possible for stars in a binary system be \"touching\" each other instead of the larger star gobbling up the smaller one?"
] |
[
false
] |
Got this question by reading the following news item:
|
[
"It's probably a good step here to stop considering stars as monolithic objects, but as blobs of gas/plasma held together by their own gravitational potential well. Imagine water pooling on an underinflated airbed, where the weight of the water is pushing down the same bowl that it's resting in.",
"The 'surface' of a star is thus somewhat fuzzily defined. Usually what we call the surface is the photosphere, which is the topmost layer/surface that's brightly emitting light. Above it, there's still gas, but it's too thin to be opaque. The density falloff is approximately exponential (cf. the thinning of Earth's atmosphere at altitude).",
"So what we have here is a case of a blob orbiting another blob, or I suppose two blobs co-orbiting since the smaller one is a significant fraction of the mass. The dense centers of the blobs are well separated enough that we can approximate the majority of the mass as single-point masses and put them in neat Keplerian orbits. It's old billiard-ball mechanics. The gauzy outer layers do intermingle, and the author says that their meeting is close together and at low enough an 'altitude' and dense enough to call it 'touching', deciding that yeah, that's part of the star rather than its solar wind. The idea of 'outer layer' of course gets weird since the density of an atmosphere (of a star or Earth) smoothly falls off all the way to infinity, essentially.",
"The author of the article helpfully links ",
"the Wikipedia page on Roche Lobes",
". So remember the bowl in the underinflated airbed? We can also use the old metaphor of the trampoline, I guess. Just imagine you standing one a trampoline next to a toddler. With two of them next to each other, you get a peanut shape in the gravity wells since when you add them to each other you can just linearly add together gravitational potentials. The bigger one of the two is also deeper. As the smaller star orbits, some of its outermost layers spill over the gravitational potential ridge between the two valleys, crossing the bridge of relatively low potential connecting the two parts of the peanuts, and flow into the deeper bowl, joining the larger star. But because the outer layers are really thin compared to the overall mass of the star, the orbits for now aren't really affected and it'll take a long time for a significant amount of the smaller star to be eaten."
] |
[
"It's also important to note that angular momentum must be conserved. With the two stars' cores orbiting out at a significant radius that's a lot of angular momentum, and if the stars ",
" merge, the new star would have a much smaller moment of inertia and have to be spinning faster than the original orbital speed to have the same angular momentum."
] |
[
"You've got some good answers already. Look up ",
"Roche lobe",
", ",
"contact binary",
", and especially ",
"common envelope",
".",
"http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Common_envelope.svg/500px-Common_envelope.svg.png",
"Contact binaries and common envelopes look about the same, to the untrained observer. The former are relatively stable; the latter devolve quickly and usually merge, blow up, or shed the envelope altogether."
] |
[
"If a blue giant star collapses into a neutron star and a medium sized yellow star collapses into a white dwarf; what does a small red dwarf star collapse and become?"
] |
[
false
] | null |
[
"Red dwarf stars have incredibly long life cycles(estimated to be 100 billion years long) - so long, in fact, that no red dwarf has yet reached it's final life cycle, because the universe in not old enough yet. However, according to star life cycle models, red dwarfs are expected to burn brighter and hotter as they age, until they eventually burn off all of their hydrogen fuel. When this happens, they will become low mass white dwarfs, and they will remain as such, until they eventually burn out and fade.",
"Edit: for clarity."
] |
[
"Good answer here."
] |
[
"Because of their convection currents which allow them to burn nearly all of their hydrogen and the low rate of fusion, it's likely that there would be only a small amount of material released as a planetary nebula. The star would likely expand a bit, before the majority of it slowly contracts and cools, eventually fading away into a ball of helium."
] |
[
"According to the 2013 Estimated Energy Use in the US report released recently, 59% of energy used in the US ends up as \"Rejected Energy\". What does this mean?"
] |
[
false
] |
I saw this diagram on and was curious about what is meant by "Rejected Energy" over on the right side. It's clearly very important! I figure it's just talking about energy lost to heat and inefficient engines/turbines, but is it really that much!? 59% is a lot...
|
[
"It's actually worse than that, the total energy usage for 2013 was 97.4 Quads, so over 60.5% of energy was rejected. ",
"The reason is because of the cycles we use to create energy. Most nuclear and coal plants use a ",
"Rankine cycle",
", where the heat that is created is used to boil water. That steam then turns a turbine (to create electricity), and the steam is then cooled down again into water so it can be boiled again. This process at maximum efficiency is about 36% efficient. So almost 2/3 of the heat created in those systems doesn't go towards making electricity. You can better with a Brayton cycle or a combined Brayton-Rankine (lots of new natural gas plants are combined cycle Brayton-Rankine plants), but even then you can only recover ~60% of the energy. "
] |
[
"Distribution losses",
" normally amount to around 7%. It is the ",
"carnot efficiency of thermal energy to mechanical energy",
" that is the major loss."
] |
[
"Many years ago, in ee college course, instructor said\n that of all the power generated at US power plants,\n more than half was lost to resistance in the high-voltage \npower lines (the huge towers), and that's subtracting from\nWhat the plant finally does produce."
] |
[
"It is said that electrons have spin. What does that mean?"
] |
[
false
] |
[deleted]
|
[
"Hawking's analogy (and a couple of similar others, I think there was one by Penrose) is really the only way to make sense of quantum mechanical spin in terms of anything familiar to us. Spin is, succinctly put, the intrinsic angular momentum of particles (like leptons and hadrons). It is ",
" a quantum mechanical phenomenon; particles with spin aren't really \"spinning\" in any sense of the word, and the property is best thought of as something that just happens to be ",
" spin.",
"I'm sorry if this isn't very enlightening, but quantum mechanics (and sometimes terminology) tends to have the amazing property of confusing everyone who tries to make sense of it in a classical framework."
] |
[
"So then what ",
" they doing? ",
"Or is the best way to describe it simply \"a thing that happens\"?"
] |
[
"Or is the best way to describe it simply \"a thing that happens\"?",
"That's about the extent of it. Electrons don't exactly \"do\" much insofar \"doing\" is classically understood. However, the effects of spin can be experimentally observed in dramatic ways, the most well-known of which is the ",
"Stern-Gerlach experiment",
".",
"As an historical aside, the existence of spin was hypothesised by Wolfgang Pauli before any of those experiments had been performed, and without much in the way of physical interpretation (he called it, if memory does not fail me, a \"two-valued quantum degree of freedom\"). Originally people did try to interpret it as a spinning electron, like ",
"/u/rMasculinity",
" was imagining, but quickly ran into violations of special relativity and abandoned the idea."
] |
[
"Could we have wifi in the visible spectrum of light?"
] |
[
false
] |
I know that wifi uses electromagnetic waves. Could you have wifi that sends signals in the visible range? Would our eyes receiving the light screw with it? I realize that it wouldn't work for actual use, because anything that we can see would block the signal, but is it theoretically possible?
|
[
"Yes, we already have this. It's called ",
"free-space optical communications",
". In the simplest example, if you stand on one mountain at night and your friend stands another mountain away from obstructions, you could communicate with your friend by pointing your flashlight at him and turning it on and off according to Morse code patterns. While simple, this method is very low bandwidth. Modern optical communications use electrically-modulated laser beams instead.",
"You are right that obstructions (trees, ground, people, dust, rain, clouds) make free space optical communications impractical in many settings."
] |
[
"My favorite example of this is attaching an audio signal to a laser diode and shooting it onto a photodiode."
] |
[
"There's a bunch of infra-red communication standards developed by ",
"IrDA",
" and actively used (though these days bluetooth is more popular). Plus there's low-bandwidth stuff used in various remote controls.",
"Naturally if you point your remote control at your eye (or any other black enough surface), it screws with it =) I mean, near-visible range of EM radiation is just light, that's it.",
"As for using actual visible light in an undirected fashion, you see, there's a lot of visible light around, so the transmitter should be powerful enough to allow the receiver to filter out the signal from the rest of the light, which would be pretty annoying. I mean, for the people around."
] |
[
"Is transportation of more than just a photon theoretically possible?"
] |
[
false
] |
I just read and found that in the book, the author claims that in 1993, a group of scientists used , defines as transmission and reconstruction over arbitrary distances ofthe state of a quantum system. The author explained the study, but I wanted to know: would it be possible to teleport bigger things? Like a molecule of sodium? The current problem is teleportation relies on quantum states to work, and a human has 10 atoms that a machine would have to pinpoint and analyse. Chrome doesn't recognize that word and changed it.
|
[
"http://xkcd.com/465/"
] |
[
"Quantum teleportation is not actual teleportation. Not at ",
". What's being teleported is only the state of a system; the ",
" still needs to be in both places. It is interesting only because it is not possible in general to make a perfect copy of a quantum state.",
"It has been done on atoms, though, and I actually think sodium atoms were used. Again though, completely unrelated to sci-fi teleportation."
] |
[
"It's not even that close to sci-fi teleportation. It's literally just copying data from one location to another; making it spontaneously rearrange raw materials into some object would require hardware capable of building that object. You wouldn't argue that copying data from your hard drive to RAM will help sci-fi teleportation happen, would you?"
] |
[
"Can we genetically engineer a creature to be smaller when fully grown?"
] |
[
false
] |
As in, have we worked out the genes for size? Or would this be a multitude of different genes? I ask, as Little People and Gigantism seem to have been scaled one way or another. So does that mean the end size would seem to be a certain scale? that all organs/bones follow? or would beings (Like Miniature horses) who are smaller than their otherwise identical species have all the organs of the body having the same genetic quirk. (Hope this makes sense.) *Edit: Also, Not using selective breeding, but actual genetic tampering via science. Similar to how GM Food is designed.
|
[
"Well some work has been done to identify the genes that affect sizes difference among dog breeds:\n",
"http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1000451",
"Basically, there are variations (SNPs) in only a few genes that can account in the size difference between, for example, a Chiwawa and a Grate Dane. These genes are well conserved in humans, and have been known to regulate body size in many other species. Some nice examples are genes in pathways that control insulin signalling (IGF1) and tissue architecture and growth (SMAD4). "
] |
[
"Are the SNPs found more often in the promoters/regulators of genes, leading to different levels of expression during development? or in the coding sequences?",
"I imagine both are true for different examples of genes involved, and if that is the case, how can SNPs in coding regions lead to differences in height/size?"
] |
[
"Typically these are SNP found in non-coding regulatory regions (promoters/enhancers) and typically affect robustness of gene expression and/or the tissues in which a gene is expressed. Often these non-coding SNPS accumulate at the higher rate, as they are mostly non-deleterious when compared to coding SNPs.",
"SNPs in coding regions could possible affect high/size several ways. One way would be to make an amino-acid change that would effect turn-over of the protein (the protein can no longer be modified pos-translationally, for example). This would result in either lower or higher levels of the gene product, and if this gene product was part of one of pathways I mentioned above this might lead to differences in hight/size. ",
"Additionally, some of these genes are often redundant with other genes and pathways converging on the same cellular process (i.e. signalling pathway affecting height/size), and if you knock out one gene/pathway the other(s) can compensate for the loss. However, there are some cases where both are required, and eliminating one through a coding SNP would result in not a loss of the signalling pathway, but a reduction. Thus, this outcome could also might leading to differences in hight/size. "
] |
[
"If a star falls into a black hole, can it still do nuclear fusion, and continue to combust?"
] |
[
false
] |
My intuition says no, but I'd like to know ?
|
[
"But what about the big black holes with huge event horizons. I once read that the largest of black holes wouldn't even tear a space ship apart but that you couldn't escape it once you fell through it.",
"Would a black hole at the centre of a large galaxy swallow a star whole before tearing it apart?"
] |
[
"At the event horizon, yes.",
"Source: ",
"http://en.wikipedia.org/wiki/Supermassive_black_hole"
] |
[
"I'm sorry I stole your thunder, I didn't even read further before I posted above. The density of stars varies from low to extremely high (depending on what depth you're looking at), so I'd like to see calculations for your statement (concerning black hole mass) before I agree with everything you said."
] |
[
"Are there mental benefits to lifting weights regularly?"
] |
[
false
] |
I've been lifting at home for a week now and I'm just curious.
|
[
"Yes, there are mental benefits. There are many studies on the positive effects of the many chemicals your body creates both during and after working out - take a look here ",
"https://cathe.com/5-brain-boosting-chemicals-released-during-exercise/#:~:text=Brain-Boosting%20Chemicals%3A%20Norepinephrine%20When%20you%20exercise%2C%20especially%20a,that%E2%80%99s%20both%20a%20hormone%20and%20a%20brain%20chemical.",
" ",
"There is also the fact that for 30-60 minutes - or however long you workout - you give your mind a break from the work it does all day long. For me, my workout is a break my brain enjoys."
] |
[
"Yes, sorry, I was thinking more exercise in general. I can't think of any mental benefits to lifting weights over other exercise."
] |
[
"My understanding is that these benefits come with basically any form of exercise, including but not limited to lifting weights. Is that right?"
] |
[
"AskScience AMA Series: My name is Franck Marchis, and I am a Senior Planetary Astronomer at the SETI Institute and Chief Scientific Officer at Unistellar. AMA!"
] |
[
false
] |
I am passionate about astronomy, and I have dedicated most of my research to the development of adaptive optics on large telescopes to study asteroids and search for exoplanets. I am proud to also work for Unistellar, a private company whose goal is to create the largest network of citizen astronomers around the world, capable of reconnecting with the dark sky with a digital, smart telescope and collecting scientific data for space agencies. I am pleased to announce new scientific results with the Unistellar network, where citizen astronomers helped derive the shape and size of an asteroid ( ). I recently did a SETI Live with citizen astronomers Rachel Knight and Brad Davis to talk about this project ( ). You can also confirm TESS exoplanet candidates and help astronomers to observe the sky 24/7. From your backyard, your balcony, your roof, or far away from cities you can join a network of 3,000 citizen astronomers and help us to explore the cosmos. The SETI Institute is the science partner of Unistellar. You can connect with me at @AllPlanets ( ) on Twitter, or on my page at Facebook. Links: I'm available at 10am PST (1 PM ET, 18 UT), AMA! Username:
|
[
"Amazing. Thank you for this. Obvious question: what it the most interesting or promising thing you have encountered thus far in the project?"
] |
[
"Have you found any aliens yet?"
] |
[
"Have recently read about phosphine on Venus that could be a bio marker. There has been a good amount of speculation as to how it got there. Do you have an opinion?"
] |
[
"I want to learn science...."
] |
[
false
] |
[deleted]
|
[
"As for books, I HIGHLY recommend ",
"The Demon Haunted World",
" by Carl Sagan. It will enlighten you on so many issues that have lead our society to where it is, and hopefully show you how to think clearly in this day and age. After reading this book (it is not quick read) I'm sure MANY idea's will spawn inside your head and let you think about what YOU want to do, not do what someone else tells you.",
" ready->read"
] |
[
"Bill Bryson's Brief History of Nearly Everything would also be a great place start. "
] |
[
"I recommend starting with a course of lectures on ",
"Academic Earth",
", if you're really committed to studying then watch one lecture a week and spend the rest of the week reading the books from the previous lecture's reading materials. ",
"Use ",
"The Khan Academy",
" to brush up on your mathematics as required.",
"I found ",
"this course on astrophysics",
" interesting, I've watched a couple of lectures and plan to do the entire course, but I'm currently casually watching Donald Kegan's ",
"Introduction to Ancient Greek History",
" on one monitor while I play X3 Terran Conflict on the other. I'm just watching the lectures rather than reading the books, but I only have a casual interest in the subject. It's better than watching TV, right?"
] |
[
"What does Math in Quantum Physics \"look like\"? Is it still much like applied math, or does it start to look more like doing proofs?"
] |
[
false
] |
[deleted]
|
[
"The two main ways of \"doing\" quantum mechanics are through the Schroedinger equation and through Heisenberg matrix mechanics. The path integral formulation is generally used in quantum field theory.",
"The Schroedinger equation is a second order differential equation, which is solved according to the boundary conditions giving a wavefunction describing a probability amplitude. The expectation values of various things (like the average position of a particle) is found by integrating the product of the wavefunction, the thing, and the adjoint of the wavefunction.",
"In matrix quantum mechanics, the vectors representing the state of a system are eigenvectors of the Hamiltonian matrix, with each eigenvalue being a discrete energy the system can take. Bra-ket notation is generally used here."
] |
[
"In general, quantum physics is very broad. ",
"There are people doing hard numerics, writing complicated code for high-performance computing on large grids. There are people designing models that match the results of such simulations and are intended to provide insight. And finally there are people who really think about the formal mathematical structures of the theory (they really write papers in a theorem-proof structure). The latter are certainly a minority.",
"Quantum physics is, mainly thanks to von Neumann, a very elegant theory from the mathematical perspective. This means that you can actually use extremely advanced mathematical structures (let's take von Neumann algebras as an example), although most of this work never really becomes \"mainstream\". Nevertheless, it is a fruitful playground, quite some modern mathematics was developed under impulse of quantum physics and regularly there are formal mathematical results which have serious implications for (quantum) physics.",
"Most theoretical quantum physicists, however, focus on more specific models. Simply stated, they try to understand/predict how some measurable quantities depend on various parameters. Usual this does not require you to really prove formal theorems, but rather to understand which approximations can and cannot be made. "
] |
[
"Quantum mechanics is mostly linear algebra. While there is a level of abstraction that can make linear algebra seem more \"theory-heavy\" than calculus and differential equations, linear algebra is actually ubiquitous in real world math applications, and if taught correctly should not feel much different than those classes. All of the 'vector spaces' useful to an introductory quantum class after all are sets of solutions of differential equations. The 'proofs' encountered in an introductory quantum mechanics class are of two types:\n1. Proofs designed to teach you how vector spaces work - they behave exactly like the vectors of classical mechanics - and that they are useful for solving (linear) differential equations.\n2. Calculations where you get to use the vector space structure to reason about general quantum mechanics problems without explicitly solving the differential equations. "
] |
[
"Is there one big, planetwide weather system, or does each country calculate their own? If so, what sort of communication exists between them?"
] |
[
false
] | null |
[
"Most countries have their own weather system, but that doesn’t mean they will only study their own country. For example, in Brazil they study the weather for most of South America, even if other countries have their own system"
] |
[
"to add to this: ",
"The basic of a weather forecast is always a global model (like GFS or ECMWF as mentioned above). With that as boundary conditions, weather services run regional models. The advantage of the regional models is the higher resolution, which is especially useful in mountainous regions. ",
"The world meteorological organization (WMO) coordinates that the observational data of the current weather from everywhere gets to the people who run the models."
] |
[
"There are several regional/country models, but there are some that do global models (though they may have a special focus for their country/region of origin). Probably the two most well known world models are the Global Forecast System (GFS) and the European Center of Medium-Range Weather Forecasts (ECMWF or just Euro). The ",
"GFS",
" is ran by an organization within NOAA. The ",
"ECMWF",
" is ran by a group of European member-countries. "
] |
[
"A catalyst lowers the activation energy for a reaction. Is there something that increases it, like an anti-catalyst?"
] |
[
false
] | null |
[
"Oh yeah, there are tons of things which can do this.",
"Some will object to this example, but I think ",
"protecting group chemistry",
" is a demonstration. You're basically adding something in solution that provides a barrier to a reaction you want to discourage. Another thing you could maybe call an anti-catalyst would be the lead in ",
"Lindlar's catalyst",
". You add the lead in to add an additional activation barrier against complete hydrogenation of alkynes."
] |
[
"This is maybe a bit of a tangent from the intention of the original question, but insofar as biological enzymes can be grouped as catalysts, a lot of things can be called \"anti-catalysts\". ",
"Enzymes employ conformation dynamics to catalyze reactions. In fact, an accepted theory for enzyme function is that enzyme active site conformation actually stabilizes the transition state of a given reaction, lowering the activation and affecting catalysis",
" That is, enzymes lower the activation energy barrier by poisitioning reactants in such a way that a given reaction is more energetically favored. ",
"This diagram",
" hopefully helps to visualize that. Therefore anything that messes with the appropriate conformation of an enzyme or its substrates/cofactors will affect changes in that enzyme's ability to catalyze a reaction. This can be anything from changing ion concentrations to employing konwn enyzme inhibitors. ",
"https://bio.libretexts.org/TextMaps/Map%3A_Biochemistry_Online_(Jakubowski)/07%3A_CATALYSIS/A._Methods_of_Catalysis/A5.__Transition_State_Stabilization",
"EDIT: Forgot to finish a senetence."
] |
[
"I'm going to say no. The reason a catalyst reduces the activation energy is because it provides an alternative pathway for the reaction to take place. For example, if C is the catalyst and A+B are your reactants, your full reaction would go from:",
"A + B > AB",
"to",
"A + C > AC, ",
"AC + B > AB + C ",
"The reactions with the catalyst would have a combined activation energy lower than the one without, in effect lowering the activation energy of the overall reaction. It is important to note, however, that this is a ",
" reaction. The result is the same, but it proceeds via a different pathway.",
"A reaction pathway which an overall higher activation energy than the simple A + B reaction wouldn't be favored at all, and would only reduce the reaction rate very slightly because it would consume some reactant, reducing the concentration. But this isn't behaving in any way like a catalyst, and the effect isn't nearly as profound.",
"The protecting group answer is probably the closest thing to what you describe. But IMO it doesn't behave like an \"anti-catalyst\"; once the group is removed by the reaction, it can't react again and regenerate in the same way."
] |
[
"How much energy does it cost to dry your hair with a towel vs a blow dryer?"
] |
[
false
] |
Considering you have normal should long hair and a modern blow dryer. Is it even possible to answer this?
|
[
"By and large, the two methods will consume close to the same amounts of energy, with the hair dryer wasting a noticeable deal more energy in the form of heat.",
"It may not seem like the towel is using that much energy to dry your hair, but that's because the work of evaporating the water is being done very slowly by the surrounding air. ",
"Thermodynamics dictates that there is a minimum amount of energy it takes to evaporate a given mass of water, and neither method is capable of expending less energy than that. Their difference lies in the efficiency of the process. The hair dryer is far less efficient than the towel because it is actively pumping heat into the water and wasting most of it as its deflected off of the hair. The towel basically transports the water from your hair into another medium where it can evaporate using the heat from the air as a source of energy."
] |
[
"I was actually thinking more of energy burned in my body when drying the hair with a towel. But I guess that depends on how intense I do it."
] |
[
"You know, google is awesome : )\n",
"http://answers.yahoo.com/question/index?qid=20081002115619AAQLZlR"
] |
[
"When an object at rest begins to move, does it experience infinite acceleration in the very first moment it begins movement?"
] |
[
false
] | null |
[
"No (in almost all cases) because it would require an infinite force or zero mass. Newton's second tells us F=ma and that sets the acceleration in classical systems."
] |
[
"I just wanted to add to JConXtsy response, that the equation you wrote should be dx2/dt2.. or d",
" x/d t"
] |
[
"This is AskScience, not 4chan. If you can't cite your information and present it civilly, don't post."
] |
[
"Can we expect a decisive answer about the existence of a ninth planet any time soon? Or is progress difficult and slow?"
] |
[
false
] | null |
[
"Experts in this field believe they've ",
" discovered all objects of Pluto size or larger in the plane of the solar system, out to about twice Pluto's distance. \"Probably\" because there's a small chance some may be very black and hard to see, or camouflaged in a few very starry regions of the sky.",
"There might be many objects smaller than Pluto, or really big ones that are much further away, but they will run into problems with the current definition of \"planet\". The definition requires that the object \"remove debris and small objects from the area around its orbit\", and this is difficult to do when the distances between objects are vast and the orbital times are very long.",
"https://www.universetoday.com/118118/it-looks-like-these-are-all-the-large-kuiper-belt-objects-well-ever-find/",
"https://www.space.com/25986-planet-definition.html"
] |
[
"Unless are you talking about the gravitational anomaly announced like 2 years ago? I think that that one is still up in the air for lack of visual detection",
"Yeah, I suspect he’s asking about the realistic odds of visual confirmation of a large planet way past Pluto. I’m curious too."
] |
[
"I think the only thing holding back right now is definitions. There are a couple we found that got disqualified back when they were debating Pluto's status. Unless are you talking about the gravitational anomaly announced like 2 years ago? I think that that one is still up in the air for lack of visual detection"
] |
[
"What happens to electrons during chemical reactions?"
] |
[
false
] |
I'm take organic chemistry and we are doing acid base reactions, but I'm wondering for all reactions in general. We have electrons transferring from species to another, but what actually happens to the electrons in a reaction. When the bond breaks, does the electron dissipate and a new pair come into existence when a new bond forms.
|
[
"When a bond breaks, the bonding electrons adopt one of the atoms. There are two types of bond cleavage: in heterolytic cleavage of a single bond, both electrons go to one of the atoms (if the original molecule was neutral, you now have a cation and an anion); in homolytic cleavage of a single bond one electron goes to each atom (and from a neutral starting molecule you now have two radicals). ",
"If you think about the atoms involved as planets and the electrons as spaceships orbiting the planets, then the bonding electrons are orbiting two different planets. To break the bond, you move the planets far enough apart that the spaceships have to pick a planet to orbit; under most conditions, they will pick the planet that wants them more. For planets, this is the more massive one. For atoms, the more electronegative atom wants the electrons more. In heterolytic cleavage, both spaceships pick the same planet; in homolytic, one spaceship goes to each planet.",
"Disclaimer: This is just a model to help you think about where the electrons go; it's not a great description of what's really happening."
] |
[
"This is how we were taught, but I'm wondering how accurate it is. It's like saying there are alternating single and double bonds in a benzine ring. All the carbon carbon bonds are the same length, not what you expect from alternating single and double bonds. It's all about resonance structures and the rings have multiple resonance structure and transforms into these different structures. The combo of all the structures is why all the carbon carbon bonds are the same length.",
"We are taught that electrons move to other molecules during bond formations. In reality, we can't track the electron migration from one bond to another. "
] |
[
"Electrons are real, and they really do move between atoms and molecules. They are not created or destroyed in reactions. In many ways chemistry is just the study of what electrons do in different situations. ",
"We have different theories to describe what the electrons do. I gave you an analogy that uses an essentially classical view of the orbital model of electrons (it seemed appropriate to the question you were asking). While a correct description of what the electrons are actually doing requires some form of quantum theory (they don't really orbit the nucleus the way a satellite orbits a planet, hence the disclaimer), the electrons really do move between fragments at all chemically useful levels of quantum theory.",
"In the case of benzene, the 3 pi electrons are delocalized around the six carbon atoms. Resonance forms are one way of describing this phenomenon, but it's not the only one; a little more discussion of resonance forms can be found ",
"here",
". Resonance structures are not real in the same way electrons are. ",
"We mostly can't track the electron migration in chemical reactions, but we can tell where the electrons are before and after they migrate. Take a very simple example, the reaction between dihydrogen and acetylene (HCCH) to make ethylene (HC=CH). Initially, there are two electrons shared between the H nuclei of H2, and six electrons shared between the C atoms (one sigma, two pi bonds). After the reaction, there are two new C-H bonds, one fewer C-C bonds, and no H-H bonds. We know exactly where the electrons were before and are now, even though we can't watch while they move from A to B. "
] |
[
"Do you think that paleolithic humans exhibited the same levels of nurturance to their young that we do today?"
] |
[
false
] |
[deleted]
|
[
"To be honest, I'd think that paleolithic humans care more about their children than people do today."
] |
[
"IIRC, there are ",
" fossils of old individuals with evidence of years of poor or no dentition. This indicates that probably some other member of the group was chewing or cutting their meat and nuts for them. ",
"They likely did develop faster than modern ",
", so the span of time for nurturing was much shorter-- Turkana boy is thought to have died at an age younger than he looks on superficial examination of his skeleton. He looks 12 or 13 and dental evidence suggests he was closer to 9 or 10, if not younger.",
"Attitudes about babies among the literate have changed enormously in the last 400 years. Many learned people in the 18th century treated their children like little more than pets."
] |
[
"seems like such behavior only evolved over the last 200 years or so",
"This change wouldn't be evolution, but a cultural shift; evolution can't operate on the time scale of just a few generations.",
"It seems to me that attitudes towards raising children in general are a highly cultural phenomenon, differing not just across time and countries, but even between you and your next door neighbor. ",
"Although there may have been cultural norms for any particular region and people in paleolithic times, I see no reason to think that different groups would have been any more homogenous than we are now; nor that even those within a group or region would necessarily all have adhered to its standards.",
"As for Homo erectus carrying her child around: that seems more likely than not to me. After all, other current living primates do this, as do a wide range of animals far less related to us."
] |
[
"Is there noticeable evolution taking place in humans today?"
] |
[
false
] | null |
[
"Yes.",
"This study",
" looked at multiple generations of women in Massachussets, comparing various medically relevant traits with the number of children each woman had. Because evolution occurs based on who has the most offspring, they were able to detect subtle but significant ongoing trends in human evolution.",
"The evolutionary trends they detected are: decreasing total cholesterol, decreasing blood sugar levels, decreasing blood pressure, increasing body weight, and delaying the age of menopause.",
"This means, for instance, that women with low blood pressure have more kids on average, so our population is slowly becoming biased toward lower blood pressures.",
"Another example is genetic immunity to diseases. ",
"This study",
" describes a gene that spread among cannibalistic tribes in Papua New Guinea in the recent past, which gives those who possess it total immunity to the deadly prion disease called kuru, which spreads through cannibalism of the infected."
] |
[
"The most recent example of evolution occurring in humans I can think of is the retaining of lactase, or the enzyme for breaking down lactose, even after weaning. Many people are saying that the ring and pinky fingers will be lost in the future, but I have yet to find evidence for this. Has a use for the appendix in humans been found, yet? If not, then we may be losing that vestigial organ, as well.",
"However, evolution is hard to measure in the present...or at least any noticeable evolution which is what your question is asking for."
] |
[
"Just because it's vestigial doesn't mean it's going to disappear. For that to happen the appendix would have to affect the ability for people to produce offspring, and a genetic anomaly that leads to appendix-less people, and said people being better at passing on said genes has got to be quite rare."
] |
[
"What is the etymology of the names of the nucleobases?"
] |
[
false
] |
I want to know how scientists came up with words like adenine, cytosine, guanine, thymine, or uracil. Also, if you know: where did the names of the twenty amino acids come from? I at least want to know if there is a general theme or way of going about naming these things. Ie, chemical groups, latin, greek... pure fancy? I'm sure there's a method and I want to know what it is. Thanks ever so!
|
[
"The names will have a variety of etymologies, but their suffixes are from their chemical classification as pyridines or pyrimidines.",
"Adenine: “Aden”, a Greek root, from the word for the Pancreatic gland. It was so named because the first isolated sample of Adenine by Albrecht Kossel was from the Pancreas.",
"Cytosine : “Cyto”, Greek root, meaning “cell”. Again, where Kossel isolated the sample from, because it was hydrolysed from the Thymus cells of a calf.",
"Guanine: my personal favourite, named by Julius Unger who extracted and isolated it from sea bird excreta, which is known as guano.",
"Thymine: as above with Cytosine, was named as such by Kossel because it was extracted from the Thymus gland.",
"Uracil: I’m not sure on this one, but would think it comes from uric acid? "
] |
[
"Fun question! Yes, pure fancy, actually, albeit with a tendency toward the circumstances of their discovery.",
"Since ",
"u/Gothic_Analogue",
" already did the DNA bases, I'll supply a few amino acids: asparagine was first isolated from asparagus; serine was first isolated from silk (l. ",
"); cysteine was first isolated from bladder tissue (gr. ",
"). Others are more down to chemical composition: proline is so named because it contains a pyrrolidine group, while methionine (as far as I can tell) is so named because it contains a methyl group.",
"It'd be cool if there was some kind of unified nomenclature, but at the time these compounds (both amino acids and DNA bases) were first being isolated, nobody knew that they were part of a particular set or system."
] |
[
"Extremely satisfying to learn, thank you."
] |
[
"Are black holes really infinitely dense?"
] |
[
false
] |
So I have heard several times that black holes are infinitely dense. But if gravity is connected to mass, that would imply that black holes have infinite gravity, which would mean that everything would be sucked together instantly. Is my thought process wrong somewhere? Are black holes really infinitely dense? Do we have solid evidense one way or the other? I find black holes to be extremely interesting, and deeply confusing.
|
[
"It means exactly what it says. A gravitational singularity is a mathematical construct that appears in black hole equations when you are essentially forced to do exactly as you've said - divide by zero. It basically says \"Either something is very wrong with your numbers or something we can't fathom is happening here\".",
"Maths relies on the laws of the universe applying consistently. 2 + 2 can be said to reliably add up to 4 provided the fundamental underpinning of that equation continues to exist. In a singularity, the laws of the universe go out the window. Maths can no longer be counted on to give a reliable answer. Space becomes timelike and time becomes spacelike.",
"That's why there's so little concrete information about black holes - with our current understanding of mathematics they are impossible objects. And yet when a sufficiently massive star collapses, with our current understanding of physics, the gravitational collapse can only lead to one conclusion."
] |
[
"Are black holes really infinitely dense? ",
"AFAIK, we don't really know. All we know is that in a black hole, currently accepted models don't really work. Hence the term \"singularity.\""
] |
[
"That's the problem with gravitational singularities. The math stops working at the point where one is formed."
] |
[
"What are some good science experiments to perform for my son?"
] |
[
false
] | null |
[
"This thread",
" is full of ideas and instructions. I'm sure some of them are good enough for your son."
] |
[
"How old is he, and what kind of material do you have access to? ",
"*Edit: Link to the pdf of ",
"The Golden Book of Chemistry Experiments",
"*EditEdit: This is in no way an endorsement of this book, as it is not exactly safe for your son to do alone. Be very careful when doing any of this, and fully research what you are doing before you do it."
] |
[
"Oh, that book is definitely too high level for a nine year old. If you have a university near you see if they have an outreach program though the chemistry or physics department. Ours puts on demonstrations for kids. Otherwise, ",
"Steve Spangler",
" has all kinds of neat stuff. "
] |
[
"would pure hydrogen gas in a sealed chamber burn?"
] |
[
false
] |
If you had a chamber of pure hydrogen gas, no other elements, especially oxygen, and tried to ignite said hydrogen, would it burn even though it has nothing to bond to?
|
[
"No. It could dissociate into hydrogen atoms but if there really is no oxygen, it can't burn."
] |
[
"Definition of Fire: Combustion or burning, in which substances combine chemically with oxygen from the air and typically give out bright light, heat, and smoke."
] |
[
"Fire has three principles, i.e. the triangle of fire",
"So the hydrogen would be the fuel, but without oxygen, or heat, it would not burn. To create fire, you'll need all three elements."
] |
[
"If I were to get enough viruses in a small space to be able to see them without a microscope, what would it look like?"
] |
[
false
] |
[deleted]
|
[
"White goo. Back in college we had to filter seawater for microbes and that's what we came up with. White goo which turned out to be billions of bacterium, single cell doo dads, and various microscopic muck all in a big giant coffee filter the size of a damn laundry basket. EDIT--NEVER DRINK OCEAN WATER Edit 2 -crabs actually start out microscopic, floating around as plankton, until they get fat enough for gravity to affect them and they sink down to the bottom. So when you see a big giant ass king crab? That is a damn microplankton that has become Godzilla sized over its age."
] |
[
"Awesomeness."
] |
[
"These membrane ribbon thingies",
" are actually made of thousands of viruses smooshed together. They are still too small to see with your eye, but they can give you a sense of what an aggregate of viruses looks like. "
] |
[
"If two balls filled with water hit each other, how do the shock/pressure waves propagate?"
] |
[
false
] |
[deleted]
|
[
"The wave front would be circular/spherical like ",
"these",
", and, as you suggested, would travel from the impact spot outward until the wave reached the opposite end of the ball, \"filling\" the ball."
] |
[
"video",
"Something like but not exactly like above. I couldn't find the actual experiment I was looking for. Apologies."
] |
[
"The experiment I posted involves cavitation so it is not exactly answering the same question. However, it does show how the pressure waves reflect around inside a sphere, which is part of what you are asking. The weirdness happening with the cavitation bubble moving around has to do with reflection from the surface of the bubble. The physics in this case are quite a bit more complicated than what you were asking. However, I think it does illustrate some interesting behavior related to the original question."
] |
[
"Are there any strange fears or mental disorders that exist only in specific cultures?"
] |
[
false
] | null |
[
"Fan death",
" would certainly be an example of the former.",
"Mental illness is hard because we don't, as yet, have a good objective idea of mental illnesses. There's a push towards a greater biological understanding and definition of common disorders, but our knowledge of the mind and brain is still too limited. The way we've defined mental illnesses has been a product of the dominant culture at the time. For example, you could have a look at how thinking about ",
"homosexuality has changed over time in the DSM",
". It's gone from being defined as a disturbance to being completely dropped from the manual (as a consequence of political pressure)."
] |
[
"https://en.wikipedia.org/wiki/Koro_(medicine)",
"\"Koro is a culture-specific syndrome delusional disorder in which an individual has an overpowering belief that one's genitalia are retracting and will disappear, despite the lack of any true longstanding changes to the genitals.\""
] |
[
"Because there are a number of things named Koro and this way it specifies which thing.",
"https://en.wikipedia.org/wiki/Koro",
"So it's Other:",
"Koro (band), a hardcore punk band from Knoxville, Tennessee",
"Koro (incense burner), a Japanese incense burner",
"Koro (medicine), the syndrome in which someone believes their external genitals are retracting"
] |
[
"What would it mean if we proved that P = NP, or P != NP ?"
] |
[
false
] |
What are the implications of proving one way or another? For example, proving that P = NP would it mean that cryptography is "useless"?
|
[
"A side remark: polynomial time is usually taken to be a short amount of time, and in the limit of large inputs it is much much ",
" smaller than exponential time. However, even if someone proved that P=NP, it could still be the case that the complexity of a problem scales as n",
" or something ridiculous like that. Talking about crypto for example, it means that there could be crypto protocols that although are broken in polynomial time, they take forever and a day to break for all practical purposes. So the possibility that they are secure wouldn't be completely ruled out.",
"P and NP, and the 'polynomial hierarchy' in general, are really coarse grained gauges of the complexity of a problem. P=NP would mean that we would have to go to 'finer grains' to distinguish the difficulty of problems."
] |
[
"Proving P=NP would have vast consequences beyond cryptography assuming that the algorithm for reducing an NP problem to a P problem is efficient. For instance, it would put mathematicians out of a job. Checking that a mathematical proof is correct is a problem that is in P. If P=NP, then if a proof is of reasonable length a computer can find the proof as easily as it could be checked. Thus, assuming we are only interested in proofs of propositions that are reasonably short, mathematics would become completely mechanical.",
"Philosophically, P=NP would defy many of our intuitions - it effectively implies that brilliance can be made mechanical. \nTo illustrate by analogy: if P=NP a computer that can appreciate one of Bach's masterpieces (verify that it is a Great Work) can write a masterpiece of equivalent quality (create a Great Work). ",
"For more on this topic see Scott Aaronson's ",
"essay",
" on philosophy and computational complexity."
] |
[
"Almost everyone thinks P=/=NP, for the intuitive reasons stated above. But no one has any idea how to prove it one way or the other - in fact, it has been proven that two promising avenues which have been used to prove other things in computer science will not work for the P vs. NP problem."
] |
[
"Can you help explain this Mythbusters result?"
] |
[
false
] |
Mythbusters examined whether you can save gas by only making right turns. In their final experiment they drove a delivery truck around various locations - once with left and right turns, once with only right turns. The path with right turns only: Was longer Took more time Consumed less fuel Why would this be the case? Link to video (it's a mini-myth, so only 2 minutes long): The top response says it's "because you're not stuck idling". But, to reiterate, the of the right-hand-only trip was . So either they spent even time idling (not less), or they converted idle time to drive time. There has to be something else at play. I think these comments are the most convincing arguments so far (Currently not at the top, but will likely be there soon):
|
[
"I'll give my best explanation here for you. I've logged more than a half million kilometers driving almost any vehicle imaginable over nearly any terrain you can think of. I have a firm grasp of what affects fuel consumption in vehicles.",
"A trip using right hand turns in of itself does not, and cannot change the fuel consumption of a vehicle. A turn is a turn, your vehicle does not care which direction it is turning. It still requires the same amount of fuel to propel the vehicle forward.",
"However, the turns they were making were in the city. This changes things, because it is almost guaranteed that you will have to stop for a left hand turn. Right hand turns can be rolled through if you time them correctly. This is a key difference, because the most fuel is used by a vehicle's engine when accelerating. The more you speed up and slow down, the more fuel you will use. This is why highway fuel consumption is almost always less than city consumption, even though you are traveling at faster speeds. ",
"The second point that I want to address is their test location. It looks to my unfamiliar eye to be San Fransisco; a city notorious for it's hills. Of course, driving up a hill requires more fuel than coasting down one. Driving a different route to the same stops will certainly ensure that the topography you encounter will not be identical, which could lead to skewed results.",
"Furthermore, I'd like to address the point about the shipping company programming their GPS units to calculate a route that takes only right turns when possible. There are several reasons for which you would want to do this when running a delivery service. ",
"First, right turns are inherently safer. I'm certain that a company operating a fleet of vehicles would see a decrease in liability exposure from collisions due to left turns.",
"Secondly, because the road system in North America is designed for left hand drive vehicles, by making right turns only it is easier to ensure that you arrive in front of the building you intend to stop at, instead of across the street. This strategic planning can save minutes at every stop, which is crucial when your day consists of potentially hundreds of stops."
] |
[
"I can't believe I had to scroll almost to the bottom before anyone mentioning acceleration. The only reason you need to burn fuel when not accelerating is because of air/ground resistance. Every time you break you essentially throw away all your kinetic energy and convert it to heat and earth momentum because normal cars does not have power regenerative breaking like electric cars does. To regain that kinetic energy when accelerating you need to burn the corresponding amount of fuel. If you must choose between stopping completely when making a left turn and preserving some of the speed in a right turn, that should make a world of difference."
] |
[
"They also did the myth completely wrong. The way they did it, they took 3 rights instead of a left, the way UPS does it is they have an algorithm that creates routes with maximum rights and minimum lefts. with a fleet of trucks, they reach every destination."
] |
[
"Could Venus one day become what Earth is now?"
] |
[
false
] |
Scientists have found that Mars used to store water millions of years ago, until it's atmosphere was swept away and became what it is now. That lead many to speculate that Earth could one day become Mars. But could Venus terraform into a sister Earth? After all, Earth used to be highly volcanic and full of CO2 like Venus is now.
|
[
"Consider for a moment the proximity of Venus to Sol. Earth is perfectly far enough away to avoid being scorched to a relatively barren wasteland. While Venus has a thick layer of insulating cloud cover that protects it from the majority of solar radiation and blasting heat, that same effect traps greenhouse gasses and insulates the planet. For Venus to become remotely earth like, both of those processes would need to be reversed or stopped completely. And were that to occur, the planet would be roasted with solar radiation. So no, it's unlikely that Venus would become more earth like. ",
"Now that's not to say that at some point in the distant past when the sun was smaller that Venus didn't resemble earth to an extent."
] |
[
"This leaves out magnetosphere, rotation period, and a satellite relationship like that which our planet has with the sun and the moon, and the possibility of increased water content. For starter, the lack of magnetosphere allows lighter gases such as helium, hydrogen and oxygen to be \"burned off\" by radiation and solar winds.\nNot really disagreeing with your assessment of current conditions, and granted it would require an astronomical event to change things to more terran norms, but we do live in a universe of astronomical events. I think a more thorough assessment and explanation of differences and what would be needed from a scientific perspective is in order. "
] |
[
"Oh, by all means, go in to further detail. I was just giving a very basic assessment of what I know. I'm not much of an astronomer or anything, just studied a bit about these things. :)"
] |
[
"Can we say which molecules are more likely to occur in a soup of elements?"
] |
[
false
] |
Is it possible to estimate which molecules are more likely to occur in a mix of elements under a specified temperature?
|
[
"Using thermodynamics, it is possible to estimate, to some extent at least, which molecules will predominate at equilibrium. One would need to know the entropy and enthalpy of formation for every possible compound. However, since it can take an exceedingly long time to reach equilibrium, this approach is limited in it's practical utility. ",
"Away form equilibrium, kinetics are important, and these are much harder to model accurately. Additionally, since some materials can act as catalysts and vastly alter the activation energy of certain reactions, determining the non-equilibrium concentration for a mix of elements can become impossibly complex. In fact, even simple kinetic equations can be impossible to solve without approximations."
] |
[
"This is a major concern in aquatic chemistry.",
"We gibbs free energy and other thermodynamic properties to calculate equilibrium coefficients that describe the distribution and speciation of compounds at equilibrium. Because there are so many possible compounds that can form, and if all compounds are assumed to be in equilibrium there will be a set thermodynamic equilibrium constant for each set of possible reactions, you are going to have a massive matrix of unknowns to solve. On top of that, compounds in solution have an activity coefficient, which is a parameter that if affected by the concentration and charge of other ions in solution. The math becomes very tedious and even in relatively simple solutions you can end up with many equations and many unknowns. Often assumptions are used to simply the calculations and arrive at an approximate solution. This can then be checked against known thermodynamic values to determine accuracy.",
"But to answer your question, yes."
] |
[
"Welcome to the field of astrochemistry. In fact this is exactly what we [try] to do. From reasonably simple kinetic models, we can start with the basic atoms (C, O, H blahblah) and the build up which and how many molecules will be made from these at the interstellar temperatures (typically CO, OHCH3, H2CO, NH3 etc). From there you have to keep branching that out and you can predict the environment over billions of years as these are created, destroyed, and build up into larger systems.",
"That being said, the results aren't exactly spectacularly accurate and the models are still being refined. This is largely because space is a pretty darn complicated system, a lot more complicated than a beaker in a lab."
] |
[
"Can earthen or concrete houses sustain damage from fire?"
] |
[
false
] |
I am specifically thinking of brushfires and wildfires, and if concrete or earthen structures would be shelters if surrounded by fires, or they would still either get too hot or sustain some short of damage. Is the answer different if the structure is above the height of the surrounding ground, or build into the ground to be at the same height? Does the presence of even small amounts of vegetation on the structure effect the result?
|
[
"Regardless of what happens to the structure in a wildfire, the air itself will become hot and be a problem for any life on the inside of the structure.",
"That being said, concrete is far from invulnerable from damage from extreme heat. Heat above 700F can cause significant damage to concrete, and heating of metallic reinforcement bars can cause them to lose strength. "
] |
[
"If a structure is built into the ground I would imagine it would barely be affected due to the fact it wouldn't really feel the heat. Dirt a decent enough insulator that it wouldn't be affected. Stone and brick should be fine but concrete can crack and break in extreme heat. The big problem is still smoke though if you could keep smoke out and "
] |
[
"Bush fires and wildfires do not usually burn that hot but if it gets hot enough any type of wrong heat treatment could make the steel inside the walls (even the concrete)loose some of its strength as you can see in ",
"this",
"\n diagram any temperature above ~750deg C could entirely change the crystal lattice of structural steel (that means every single atom moving from its original position). But as long as the temperature doesn't get too high a paint job should make it as good as new. You should definitely get get the walls inspected in the case of a fire though."
] |
[
"Is there a way to speed up radioactive decay by \"proactively\" harnessing energy instead of passively harnessing the decay emission? If so, can you shorten the time frame of that element becoming inert?"
] |
[
false
] | null |
[
"It is possible to produce fission or fusion on demand. Fission can be produced by bombarding atoms with high energy particles, as happens in a nuclear reactor, nuclear bomb. Note that both reactors and bombs use a chain reaction wherein fission produces the very particles which cause fission. Fusion requires only heat and pressure enough to overcome the atomic cores' natural repulsion. The Sun and research reactors built for the purpose provide this. (Don't confuse these reactors with fusion ",
" reactors. Current reactors are for research purposes only, and do not produce more power than they consume.)",
"More to the point, I think you are referring instead to the third way that an atomic number may change: radioactive decay. It is not possible to increase this process by harnessing the energy (photons) emitted during decay. The reason for this is that each atom decays independently, not due to proximity or interaction with its peers. The decay of each particle is a simple first order Bernoulli process, with the combination of a large enough sample acting like a Poisson process. Each particle has a given (and constant) probability density of decaying at every given moment until if finally does. The \"half life\" is given by the time over which that integrated flat probability density is equal to half (0.5). In that time, approximately half of a given sample of such a particle will be expected to have decayed. For example, a particle with a half life of 50 years will have a decay probability density of 0.5 / 50 years = ~3.17 x 10",
" 1/sec or 0.317 nHz.",
"If, hypothetically, we could remove each atom just after it decayed, leaving a constantly pure block of non-decayed radioactive element, this would not actually accelerate the process. The rate of radioactive decay is proportional to the number of ",
" radioactive atoms, not their density. So while the pure block will decay at a greater rate measured as a percent, it's rate of decay measured in number of decaying atoms will be the same as a block twice as large with only 50% radioactive (non-decayed) atoms."
] |
[
"Relativity is a very good asterisk to add to the above. Since time itself is effected by relativistic considerations, so is radioactive decay. However, time moves slower for bodies undergoing relative motion. E.g. radioactive waste blasted at near the speed of light and then blasted back to Earth at similar speed would come back somewhat less aged than radioactive waste which had stayed put at a lower velocity here on Earth. Having undergone less time, it will have decayed less as well.\nIf instead, you wanted to maintain a high concentration of radioactive elements for a long time, you could keep them in a near-light-speed loop, having the effect of greatly slowing their decay. This is one of the facets of relativity confirmed in experiments with cyclotron particle accelerators, which do just that. Particles with decay times much too fast to be observed by modern detection methods at normal time rates can be observed because they decay much more slowly when judging from our reference plane as they cycle around at relativistic speeds."
] |
[
"This is a great answer, thank you. ",
"Would the half-life decay be increased by moving at relativistic speeds? If we launched a large block of nuclear waste into space and accelerated it, would it decay faster than an equal sized block on earth, or does relativity not apply to half-life decay?"
] |
[
"How is the “habitable zone” of a star calculated?"
] |
[
false
] | null |
[
"It's based on sunlight available, but more specifically it depends on the feedback cycle that keeps Earth's climate stable, the carbon-silicate cycle. Volcanoes continuously produce both CO2 and fresh rock, and that rock reacts with CO2 to pull it out of the air and sequester it as carbonate minerals, which are then washed downstream and end up in the ocean floor, where they enter subduction zones, melt, and rise back up through the crust to complete the cycle.",
"The important point is that the rate at which these reactions pull CO2 out of the atmosphere depends on temperature, and of course CO2 controls the temperature. If there is excess CO2, the temperature rises, and the rate of reactions increases to pull that CO2 out. If there is a shortfall of CO2, the temperature drops, and the rate of reactions decreases, allowing volcanic activity to replenish the CO2. As it happens, the balance is achieved at about where liquid water exists on the surface (this isn't entirely coincidental; water plays an important role in the reaction as well, which is why a waterless world like Venus has so much CO2).",
"So it's assumed that any planet with some volcanic activity, water, and exposed land will tend to balance out to the appropriate level of CO2 for habitability, and the limits of the habitable zone are set where incoming sunlight is so great or small that the cycle breaks down.",
"At the inner limit, even without CO2 surface temperature is so high that much of the oceans evaporate into the upper atmosphere, where they cause a strong greenhouse effect, raising the temperature by hundreds of degrees and causing further evaporation. The water in the upper atmosphere is split by sunlight into hydrogen, which escapes to space, and oxygen, which reacts with surface materials, and over time the oceans are lost completely. Venus appears to have gone through this process at least a billion years ago (stars brighten as they age, so the habitable zone moves outwards).",
"At the outer limit, so much CO2 is required to keep the surface warm that it begins forming clouds, which reflect away more light than they retain. Eventually adding more CO2 causes more energy loss due to cloud formation than energy retention by the greenhouse effect, and so the planet ultimately freezes over.",
"Based on these limits, the \"classical\" HZ runs from about 95% to 170% of Earth's distance from the sun, or equivalent light from other stars (roughly--the different spectra of light from different stars has a slight effect). But there are various ways a planet might \"cheat\" its way around these limits--a slow-rotating planet might form permanent cloud formations that cool it significantly, allowing it to be habitable far inside the inner limit; and hydrogen can act as a greenhouse gas that won't form clouds as readily as CO2, allowing a planet with much of it in its atmosphere to be habitable far outside the outer limit."
] |
[
"Radiation as a form of heat transfer is an inverse square relation with regards to distance as it is just another form of electro-magnetic radiation (like light, radio waves etc). Find the source radiation, and with known values for min and max temp for life, calculate distance. ",
"I’m not sure if it only depends on temperature :/"
] |
[
"Well, from what little I’ve read I understand the basic requirement is that planets be allowed have liquid water, so it would make sense that it be based on temperature... then again I understand there are factors such a as tidal friction that affect the surface temperature of a planet, so, idk..."
] |
[
"What happened to Thermal Depolymerization?"
] |
[
false
] |
Remember this thing that was going to turn all our trash and organic wastes into tasty methane and a kind of light crude? What happened? Here's the If memory serves, the idea is to use heat and pressure manipulations to crack hydrocarbon chains in the feedstocks in a close, anaerobic system. It sounded good but we haven't heard about it recently. Anyone know why?
|
[
"Oh it (and related waste-to-fuel technologies) are still quite a hot topic within chemical engineering and research. Nothing's really stopped. ",
"What happened Carthage pilot plant specifically, seem to be what often happens with new technologies - some guys are so eager to be first-to-market that, rather than wait for the technology to mature, get there with overly-optimistic economic projections and then fail. (see for instance the whole dot-com boom)",
"There are various other waste-to-fuel technologies that are (arguably) farther along though. "
] |
[
"It's still alive and kicking. I was at the Plastics Recycling Conference back in March and they had a whole afternoon session about it. "
] |
[
"Looking over my notes, it seems lik Polyflow has a pilot plant, Agilyx has a demo pland and JBI is fully operational in Niagara Falls. You end up with a very sweet crude that is taken to the local refineries, as they already have in place the distribution/sales/... structures.",
"The speakers all seemed to push the idea that this would work best for materials that do not have an efficient recycling operation in place, or for \"undesired\" materials that someone sticks on you. i.e., you want the waste PP from a converter, but they will only give it to you if you also take the PC/PMMA blend that you don't want."
] |
[
"Is there an area of effect for radiation?"
] |
[
false
] |
There were experiments on the demon core which took several lives due to radiation exposure. If the incident hadn't been quickly stopped, would the core have just remained in a critical state until it eventually decayed or would it over heat and melt or would it explode? Also, what sort of area would be consider lethal due to radiation?
|
[
"Yeah I probably shouldn’t have said it would explode. I do know there have been cores that wreck themselves in (non-nuclear) explosions, but completely forgot that those are all based on the water turning into steam REALLY fast.",
"The reactor probably would melt itself though. I do know that those small, bare metal core test reactors need to be carefully controlled because it the melt risk. They can generate more heat than the reactor can absorb over the pulse time.\n",
"https://en.m.wikipedia.org/wiki/Godiva_device",
" "
] |
[
"According to ",
"this article",
", the reaction stopped itself due to thermal expansion. ",
"Here is a quote from Schreiber, who witnessed the incident:",
"“But the screwdriver slipped. The thing dropped completely closed, and that made it super critical, prompt critical. It was stopped by the expansion of the core and beryllium, but it was enough to put out a lethal shot of radioactivity. ” Slotin flipped the assembly open with his bare hands. “It stopped it from sitting there and cooking, which would have been a pretty sad mess,” Schreiber said.",
"So, if i'm understanding that correctly, it wouldn't have exploded. Im not sure what he means by \"cooking\" and \"pretty sad mess\", but i guess it would have restarted the reaction after cooling off and maybe melt.",
""
] |
[
"The core would undergo “rapid unplanned disassembly” which is nuclear engineer speak for turn into a bunch of little pieces. That thing had no cooling or any of the other pieces needed to let it operate indefinitely. In addition, neutron poisons would build up over time and slowly kill the reaction. This would happen far faster (think days to months) than the radioactive decay of plutonium.",
"Also the radiation falls over 1/r",
" So if you are twice as far, the radiation is four times less. You could probably safely be within 100 feet of that thing, although you would start to hit your legal dose limits pretty quickly."
] |
[
"What's with the Tapir continental distribution?"
] |
[
false
] |
I understand there are four species of Tapir, three in South and Central America (the mountain, lowland, and Baird's) and one in Southeast Asia (the Malayan). How did this happen? Do we know on which continent they first evolved?Are they an example of convergent evolution? If not how did a rouge Tapir get to a whole different continent? We're there more widespread populations at one point and these two islands are all that remain? I just want to know how these weirdos got where they are. Thanks!
|
[
"According to the source I found, fossils of relatives of modern tapirs are found in not only Asia and South America, but also North America. They likely first evolved into what we know as tapirs in Asia, then crossed the Bering Land Bridge into North America. From there they continued on to South America as well.",
"With the submerging of the Bering Land Bridge and the extinction of North American tapirs, we get the large gap between the two populations of tapirs we have today.",
"This is just what I gathered from the source though, if anyone here is a tapir expert please correct me.",
"Source: ",
"http://digimorph.org/resources/tapirs.phtml"
] |
[
"This is mostly correct, but to add on to/clarify it, tapirs are also known from Europe and it's not exactly certain where they first evolved. Also, the land bridge they crossed isn't the famous Pleistocene Bering land bridge, but an older connection between the two continents that occurred in the Miocene...still basically the same place, but the climate was rather different. ",
"https://blogs.scientificamerican.com/tetrapod-zoology/on-world-tapir-day-a-quick-look-at-part-of-tapir-history/"
] |
[
"The first tapir-like animals evolved in North America about 30 million years ago.",
" From there, they spread rapidly into Asia; the tapirids in Asia and in the Americas (North America only for most of tapirid history) diverged ",
"20-30 million years ago",
". At that time the Earth was about 4 - 6 degrees C (7 - 11 degrees F) warmer than a 1960 - 1990 baseline and the Bering Land Bridge existed, so tapirids were able to travel from North America to Asia via land. Interestingly enough, even though tapirs are now mostly in South and Central America, the land bridge between North and South America wasn't formed until about 3 million years ago - so in relative terms, tapirs have been in Asia much longer than South America even though there are now more tapir species in Central/South America. Tapirs used to be far more widespread across the Americas and Asia."
] |
[
"Compared to the strong interaction, to what degree does gravity contribute to holding particles together?"
] |
[
false
] |
Given that the closer two objects get, the stronger the gravitational pull, I am wondering how physicists proved that it isn't gravity holding nuclei and particles together. Is the idea of "really close and therefore really strong" just bogus? Or is gravity just demonstrably not that strong?
|
[
"No. Gravity is so negligible on the quantum level that we can completely ignore it and get effectively identical results in our experiments. "
] |
[
"Gravity is demonstrably not that strong. Even using our equations, placing particles that close together wouldn't even cause a force close to that of the strong force. ",
"Besides, we have evidence of a non-gravitational strong force in the form of particle reactions and decays. "
] |
[
"The really big difference is that the strong force gets stronger with increasing distance. It behaves somewhat like an elastic band. The more you try to pull it apart the harder it gets. It is mediated by gluons. They are passed back and forth in what is known as a flux tube. Eventually the force becomes so great that it is more energetically favourable to create a new pair of particles than to stretch the tube any further and it will snap resulting in a quark-anti quark pair.",
"Gravity on the other hand has infinite range but gets weaker the further apart things are. "
] |
[
"Can anyone explain the Risch λ and threshold of Risch?"
] |
[
false
] |
I came across this reviewing an article on a meta-analysis of GWAS for Crohn's Disease. I had never seen this statistic before, and I am having a hard time finding a good description of it. Anyone familiar with this?
|
[
"Link to article?"
] |
[
"It is behind a paywall, ",
"http://www.nature.com/ng/journal/v42/n12/full/ng.717.html",
"The PMID is ",
"http://www.ncbi.nlm.nih.gov/pubmed/21102463"
] |
[
"Kind of a ",
"random place to find it",
", but:",
"Risch's lambda (λ) is defined as the risk to a relative of an affected individual divided by the population risk."
] |
[
"How much radiation am I exposing myself to when I reach into a microwave after it's finished heating my food?"
] |
[
false
] | null |
[
"As ",
"/u/rupert1920",
" said, microwaves dissipates very quickly, as quickly as visible light. By the time the \"pling\" or \"beep\" indicating that the microwave oven is done reaches your ears, the energy in the microwaves will have dissipated. ",
"If you by radiation mean \"nasty radioactive stuff\", the answer is simply \"none\". A microwave oven use radio waves of the same frequency that WiFi uses, 2.5 GHz. This frequency is far from energetic enough to be ionizing, neither does it contain free neutrons. So there is nothing nuclear going on in a microwave oven. "
] |
[
"NMR (nuclear magnetic resonance) was not renamed to MRI (magnetic resonance imaging). We scientists still say we have NMR labs and perform many experiments that have nothing to do with imaging whatsoever. Imaging is a very specific subset of NMR techniques that is actually mostly used in medicine and associated research, but rarely in physics or chemistry.",
"You are correct, however, that the people who named the technique - or the PR of the first commercial manufacturer - dropped the \"nuclear\" to avoid negative connotations of the word, which most people associate with fission (\"nuclear energy\")."
] |
[
"None. Microwaves are not ionizing, so they are not \"radiation\" as it is popularly thought of.",
"Science has multiple definitions for radiation, so you might be confused because of that. Usually, when scientists talk about radiation they mean electromagnetic radiation, which is usually non-ionizing.",
"Scientists will always say ionizing radiation if they are referring to alpha, beta, or gamma rays, which are what the popular term \"radiation\" refers to."
] |
[
"Some planes from WW2 were designed in such a way that the bullets they fired had to go between the propeller blades. How did the designers make sure they won't hit a blade and was the fire rate affected?"
] |
[
false
] | null |
[
"How did the designers make sure they won't hit a blade",
"As far as I know the trigger mechanism to fire each bullet was coupled via a ",
"cam",
" to the shaft of the propeller. As the propeller shaft turned to a particular position the cam would trigger the gun to fire the bullet. This would mean that the bullet would fire and leave the barrel of the gun and pass through the rotating propeller blades only when the blades were in a position out of the firing line no matter what the rotational speed of the propellers."
] |
[
"The best way to fix this problem is to create a mechanical linkage between the engine and the trigger mechanism of the gun. The gun is triggered only when the prop is known to be out of the way.",
"This requires several things: ",
"a gun that fires exactly when you tell it to (within hundredths of a second), not even a quarter of a second later, which was a problem for some types of guns;",
"a way to know where the propeller is at any given time; this one is relatively easy, as you can just attach a cam to the prop shaft; ",
"and a way to connect the propeller to the trigger - this is a bit sticky as well because if this linkage isn't stiff and strong enough to resist distortion at any allowed speed, your timing will be off substantially.",
"This synchronization does affect the fire rate, in principle - you can't fire any more often than when you have \"holes\"; if you fire once per hole for a two-bladed prop, that means you can only fire at a rate of 2x the prop speed in RPM. In practice, this wasn't really a problem because the props moved fast enough.",
"Wikipedia has an extensive article on the subject."
] |
[
"Synchronization was a big enough problem that later designs went away with it and just placed guns on the wings, even if it meant difficulty in placing the ammo, and gun convergence limiting effective targeting range and other details.",
"Germans instead just fired one big cannon through the center of the propeller. That needed no synchronization, and it also had no convergence issues.",
"Of course, there was nothing wrong with synchronization in theory, but it was increasingly not worth it, it was an additional mechanism that could break and had to be maintained; also, planes got faster, the time window available to fire on an enemy decreased a lot, and unsynchronized guns could fire at a much higher rate."
] |
[
"A deck of cards is split in two. I only choose from one pile. Does it affect the probability of choosing x card?"
] |
[
false
] |
[deleted]
|
[
"No. Probability is the same; the size of the two splits don't even have to be the same size. ",
"An example; let's say you want the probability of choosing the ace of spades. One split has 30 cards, the other 22.",
"\nThe prob that the ace is in the first split is 30/52; and 22/52 in the second split. \nThe probability that it is chosen if drawn from the first split is 1/30; if from the 2nd it's 1/22. \nWe assign any probability p, as the probability of choosing to draw from the first split (it doesn't matter what p is).",
"So, the probability of drawing our ace of spades is:\n30/52 x 1/30 x p + 22/52 x 1/22 x (1-p)\n=p/52+(1-p)/52\n= 1/52"
] |
[
"Yes, that's exactly right. \nIn the extreme case lets say the split is 51 and 1 cards. In that case, if the ace is in the small stack it's 100% that you'll draw the ace. On the other hand, there is only a 1 in 52 chance of it being there. "
] |
[
"I get a normal shuffled deck of 52 cards. You name a card. I split the deck in into two piles, one with N cards and the other with 52-N cards. You pick a card at random from one of the piles. Call it Jack of Spades (JS).",
"Suppose you pick which pile you will choose from at random. You have 1/2 chance to pick N card pile. Let's say you do so. JS has N/52 probability to be in that pile and ",
" and ",
" You have 1/N chance to randomly pick JS. Therefore your probability to get JS ",
" is",
"(1/2) (N/52) (1/N) = 1/104",
"Now suppose JS is in the other pile. You have (1/2) chance to pick that pile, and JS has probability (52-N)/52 to be in that pile. ",
" and ",
" you have 1/(52-N) probability to draw JS. Therefore, your probability to randomly get JS ",
" is",
"(1/2)(52-N)/52 1/(52-N) = 1/104",
"This value 1/104 can easily be understood. Each of the probabilities we computed corresponds to a specific chain of events: JS ends up in a specific pile and you then choose that pile and randomly draw JS from that pile. We computed it that way to answer your specific question. Now let's ask \"what is the probability that I get JS ",
"?\". Whether you get JS from one pile or the other doesn't matter if we're asking that question so we add the probabilities together: 1/104 + 1/104 = 1/52. This is the same as the probability of drawing JS from a single un-split deck. This makes sense. splitting the deck doesn't change anything because you chose which pile you would draw from at random.",
"Now you might think if you choose a pile ahead of time that will change things. ",
" This turns out to not be the case and you can probably work out why.",
"Extensively edited for clarity and correctness."
] |
[
"[Math] Why is 1/x continous?"
] |
[
false
] | null |
[
"When we say a function is continuous we mean \"continuous on its domain\", unless otherwise specified.The function f(x) = 1/x has domain D = (-∞, 0) U (0, ∞), and ",
" is continuous on that domain, being the quotient of two continuous functions whose denominator is never 0.",
"(This may seem like an odd convention, but it makes perfect sense in higher mathematics. When you say a function is continuous, this has a precise meaning in terms of topologies. The set D is implicitly taken to have the subspace topology induced by the topology of the real numbers. We don't want to keep saying \"on its domain\" when it's obvious that's what we mean.)",
"The function g(x) = (x",
"-4)/(x-2) is also continuous for the same reason. However, the difference between these two functions is that ",
" cannot be defined at x = 0 to make ",
" continuous for all real numbers. But ",
" can be so defined. In this type of problem, we would want to distinguish between a function continuous on its domain and a function continuous for all real numbers.",
"Any not piecewise defined function I can think of is \"not continous\" only in the points that don't belong to the domain so then if I follow the \"1/x is continous\" thinking these functions are continous too.",
"All of the common functions you encounter in introductory calculus that are not \"piecewise defined\" (this is an ambiguous term by the way) are all continuous on their domain. This is why in introductory calculus, students often get the impression that the only way a function can be discontinuous on its domain if the example is contrived to be so, e.g., let h(x) = 1 if x > 0 and let h(x) = 0 otherwise.",
"The problem with this way of thinking is that functions are not the same as formulas. A function is a map from one set to another. Strictly speaking, a function is really a set of ordered pairs. \"Formulas\" have absolutely nothing to do with that, and the same goes for continuity. But in introductory calculus, we can't really talk about functions in that abstract way because you typically do not even cover the precise definition of a limit, let alone the definition of continuity."
] |
[
"I have taught Calculus I for many years, and I can confidently say \"no\". (But obviously I don't teach your course, so you should not take that as definite answer.)",
"That's also not to say that you should think \"if I see a single explicit formula for a function, it must be continuous\". And you should certainly not forget that asking whether a function is continuous on the entire real line is different from asking whether the function is continuous (no qualification).",
"You should ",
" why a function is continuous at a particular point rather than just memorize what the answer should be."
] |
[
"The definition you gave is perfectly fine and correct. The function f(x) is continuous at x = a if lim",
"f(x) = f(a). (This one condition is enough since the validity of this equation implies that f(a) exists, i.e., that x = a is in the domain of ",
", and that the appropriate limit exists. For some reason, calculus textbooks tend to write the existence of each quantity as separate conditions.) We then say a function is continuous if it is continuous at each point of its domain. You can then prove that sums, differences, products, quotients, and compositions of continuous functions are always continuous.",
"There is a difference between asking whether ",
" is continuous and asking whether ",
" is continuous at x = a. If f(x) = 1/x, then ",
" is continuous but ",
" is not continuous at x = 0. It's very important that you clearly understand the conventions used here.",
"Of course |x| is a piecewise defined function.",
"Why \"of course\"? What about the function f(x) = sin(x) if x > 0 and f(x) = -sin(-x) otherwise? Is that also piecewise-defined? Again, ",
" functions can be made to be piecewise-defined. What about the function g(x) = sin(x)? Is that piecewise-defined? Is it defined by a \"formula\"? If you are going to answer \"yes\" to the latter question, I challenge you to come up with a formula that defines ",
" that is not a tautology. (In Calculus II, you would learn a good way to define ",
". In a sense, the only functions we actually know to calculate with formulas are polynomials and roots.)",
"This is a very subtle point that is lost on almost all calculus students. It takes a while for students to start to understand functions not in terms of formulas. Just keep reminding yourself that there is no such thing as a \"non piecewise-defined function\"."
] |
[
"How big would a volcano blast need to be to have the same effect as greenhouse gasses released by human activity in six months?"
] |
[
false
] | null |
[
"A large volcano blast typically throws a huge cloud of soot high into the atmosphere. The soot blocks a significant fraction of incoming solar energy (by absorbing it and re-radiating it to space), and can stay aloft for several years. Except in the immediate vicinity of the volcano, the net effect is to cool Earth's surface.",
"The same phenomenon is called 'nuclear winter' when it is caused by nuclear bombs incinerating entire cities. If most of the major cities were burned, it could put enough soot into the atmosphere to block out the Sun to the point of causing widespread crop failure and starvation."
] |
[
"Humans are putting about 26 billion tonnes of CO2 into the atmosphere per year. That's over 130 times more than ",
". A moderately large eruption, such as the Eyjafjall or Mt St Helens eruptions might be expected to put up to 300,000 tonnes of CO2 into the atmosphere per day. So, lets say it's erupting for 100 days (3 months), it would still need to be 870 times bigger than either of those eruptions. ",
"Mt St helens ejected about 1 cubic kilometer in a day To be anything like comparable to human emissions this volcano would need to be many many times bigger than Yellowstone (which erupted about 1000 cubic kilometers of material over several days or weeks - we need it to erupt that volume in a day, every day, for 3 months).",
"To put this in perspective, you would need to erupt 100,000 cubic kilometers of material. That's is a sphere 60 km across. It's enough material to bury the entirety of Hawaii's Big island under over 10 km of solid rock. Except volcanoes inflate that volume by injecting it the gas bubbles. That means the 100,000 cubic kilometers of what we call 'dense rock equivalent' would actually be in the form of more like 200,000 - 300,000 cubic kilometers of pyroclastic sediment. That's 25 times the volume of Lake Superior.",
"For your 6 month value, you need an eruption that big to occur for 50 days, producing 100,000 - 150,000 cubic kilometers of sediment.",
"And that is all based off a very high estimate of how much CO2 those volcanoes were producing in a day the number may well be half that, which obviously doubles all our subsequent estimates..",
"Either way, that kind of ash input into the atmosphere will have very drastic global climate implications immediately - Krakatoa which erupted less than 9 cubic kilometers of dense rock equivalent back in 1883 caused a global 1.2 degrees C cooling."
] |
[
"Wow ty for such a great answer. "
] |
[
"Is the angle a photon can travel quantized?"
] |
[
false
] |
Is the angle a photon can travel quantized? If not, then is the information capacity of a single photon essentially infinite, since there are an infinite number of angles it can travel and all we have to do is position a mirror to whatever angle we need to designate an arbitrarily long mantissa? (Okay, steering or measuring a photon angle to infinite precision requires equipment from the same place that supplies ideal gasses and such, but that's just a problem for the engineers, right?)
|
[
"No it's not, it can go at any angle you want it to.",
"The information capacity is then still limited by angular resolution, which is governed by beam diffraction, the size of your detector and so on."
] |
[
"No it isn't. The ultimate capacity limit would be the Heisenberg uncertainty in the mirror's angular position (assuming you're bouncing the photon off a mirror)."
] |
[
"Ah, yes, you are very correct.",
"I was thrown off by your mention of angular resolution which I mistook immediately as simply an engineering problem."
] |
[
"Can someone please explain the String Theory as simply as possible?"
] |
[
false
] |
Pretend that you are describing the String Theory to a(n) 4 year old. Thank you! EDIT: Thanks for all of the answers!
|
[
"It says that at the smallest level, fundamental particles can be described by a vibrating string. Just as a guitar string plays a different note depending on the type of vibration, a string would be a different particle depending on how it was vibrating."
] |
[
"If you're looking for a good book that can give you a general understanding of string theory, The Elegant Universe and/or The Fabric of the Cosmos by Brian Greene do an excellent job of providing a layman's understanding"
] |
[
"In utter seriousness, this is the best layman explanation I have seen:",
"http://xkcd.com/171/"
] |
[
"Why do things get darker when wet?"
] |
[
false
] | null |
[
" of a material is the ratio between speed of light in vacuum and speed of light in that material. Light tends to bounce back when encountered with a sharp change in refractive index. Being wet means that there's a water film covering the material, mediating the change in refractive index, resulting in reduced reflection.",
"Part 2 of the story",
"Apart from index mediation, the water film does something else. For rough/fibrous surfaces, the reflection will be ",
", i.e. visible from all directions. When a water film is present, the surface becomes smooth, and the reflection will be ",
", and only visible in one direction. So in most directions, the material will appear darker.",
"Conductors are a completely different beast. The reflection off of metals are not solely dictated by the refractive index."
] |
[
"Layman's example!",
"Your shirt is a fabric, but zoom in and there are many tiny broken pieces of thread sticking out. Each of these catch and refract light, making the fabric appear a bit lighter. This is also part of why clothes 'lose color' in the wash as more threads break, and wear begins to become more noticeable. When you apply water, these non-uniform fibers get pressed down or are completely glossed over by said water (like OP said), which means the fibers are no longer able to refract and diffuse light to the degree they were doing so beforehand, making them appear darker. It hasn't actually changed colors, it's simply unable to reflect as much light overall through the water as it could without the water."
] |
[
"This is the simplest explanation I can make.",
"A layer of water sits on top of the fibres. \nThis re-refracts the light that’s bouncing off the fibres back onto the fibres, instead of a single refraction like what would normally happen when the material is dry.",
"This allows the material to absorb more light, making it appear darker. "
] |
[
"I still have trouble understanding how two objects can have differing weight, and yet fall at the exact same speed in vacuum. And why do spinning gyroscopes fall slightly slower than non-rotating objects in vacuum?"
] |
[
false
] |
And if you had a solid gold bowling ball and a solid aluminum bowling ball of the same size, the gold would outweigh the aluminum bowling ball yet fall at the same rate... How is this even possible? Does gravity interact on an atomic level with individual atoms and creates "inertia" in the process due to heavier elements having more protons, neutrons, and electrons or do heavier elements just have more atoms for any given volume than lighter ones which gravity exerts its force upon... On top of that why do objects spinning on an axis of rotation fall slower than objects without in a vacuum? I still can't help get the feeling that some of these classical physicists were wrong. Very few had precise instrumentation for measurements. Do I even make any kind of sense or am I just a blabbering idiot? Please feel free to tear me a new one.
|
[
"Somebody ",
" explained what causes gravity. That question was conclusively answered nearly a hundred years ago. It's just not a simple answer.",
"The first thing you have to accept is that space and time are related. Changing the way you move through space changes the way you move through time … ",
"The second thing you have to accept is that spacetime has a geometry. What's more, it's not the Euclidean geometry we all learned about in high school. It's more complex than that. It has rules, and the rules are straightforward and simple enough, but it's just ",
" from what we all visualize when we think of things like the Euclidean plane.",
"Now that we have these two facts, we can put them together and fully explain gravitation. There's a ",
" of math involved, which I will skip in full here, so we can focus on the core concepts.",
"Every particle in the universe is in motion all the time. This motion includes components of motion through space — which may be zero — ",
" As you sit there, right now, at rest, you are moving in the futureward direction through time.",
"Now, how we measure motion in spacetime depends on where we stand. If you and I are at rest relative to each other — standing still in the same room, for instance — then I will measure your motion to be entirely directed in the futureward direction. In technical terms, the space components of your motion will be zero, from my perspective.",
"But if we're moving relative to each other, I will measure your motion to have some space component as well as your intrinsic time component.",
"But here's where the non-Euclidean geometry of spacetime comes in. If you consider a particle moving through space, that particle can move in any direction ",
" at any speed. It can move up, or down, left or right, and it can move quickly or slowly. A physicist would say that the ",
" of that particle's velocity is non-constant. That is, it can speed up and slow down.",
"But motion through spacetime is different. The ",
" of your velocity through spacetime is constant, regardless of how you're moving. What this means is that motion through spacetime can be visualized as a ",
" of your ",
" When you're at rest relative to me, I see your four-velocity vector point straight toward the future. But when you move relative to me, your four-velocity vector — as measured by me — rotates, so it points ",
" in the futureward direction, but also in some space direction.",
"That's special relativity in a nutshell. If something is moving relative to me, I will observe that its rate of futureward progress through time — as measured by a clock moving along with whatever I'm observing — to be less than my own. In other words, the moving thing's clock will tick more slowly than mine.",
"Now, remember that before I said your motion through space affects your motion through time … ",
" In regions of curved spacetime, such as around a planet, the geometry of the universe causes your four-velocity vector to tilt. As a result, your rate of futureward progress through time (as measured by me, a distant observer at rest relative to the gravitating body) will be less than my own, ",
"But from your ",
" perspective, you won't observe yourself moving at all. You will be at rest ",
" You will measure your own four-velocity as being pointed entirely in the futureward direction, with no space component at all, just as it would be if you were at rest in empty space, far from any other matter.",
"This is general relativity in a nutshell: in regions of curved spacetime, four-velocity vectors become tilted in such a way that a distant, non-falling observer will see you move in the direction of the gravitating body. Because your motion takes you from an area of lesser spacetime curvature to an area of more spacetime curvature, you will appear — again, from the point of view of a non-falling observer — to accelerate toward the ground at a constant rate.",
"But from your own perspective, you will experience no acceleration. You will simply sit there, at rest, while the planet ",
"And that's why different bodies fall toward the ground with the same observed acceleration. Because how you move relative to a non-falling observer doesn't depend ",
" on your mass, or any other physical characteristic. It only depends on the curvature of spacetime where you are at a given instant, and that's a function of the Earth's mass, not your own.",
"Now, what causes spacetime to curve? That's an excellent question, and one that's not entirely resolved yet. We know for a fact that mass causes spacetime to curve; the curvature of spacetime around the Earth has been directly measured by the Gravity Probe B experiment. But we also know that ",
" contribute to spacetime curvature. The sum of all these contributions is represented in the Einstein field equation by a mathematical object called a ",
" and the total quantity is referred to as ",
" It includes energy density, energy flux, momentum density and momentum flux. Some of these things combine to create physical quantities that we recognize as pressure, or as shear stress. But in real life, the contribution to spacetime curvature from something like pressure is so much smaller than the contribution from mass alone that we have a hard time measuring it. Technically, a hot oven gravitates more than an otherwise identical cold oven, but the difference is extremely, extremely small under ordinary conditions.",
"It's also believed that there's at least one other contribution to spacetime curvature that we haven't yet been able to isolate, directly measure or even partially describe: dark energy. Dark energy is a hypothetical but extremely likely quantity that causes spacetime to change even in the absence of matter and energy. It's this still-mysterious quantity that we think is responsible for the metric expansion of spacetime, which got a ",
" of discussion in this subreddit last week.",
"So long story short, we understand extremely well ",
" gravity works. The underlying mechanism that causes it has been modeled, the models have been tested, and the observations match the predictions of the theory to a very fine degree. What we don't yet understand is what all the things in the universe are that contribute to gravitation. We know what the big ones are, but there are little ones that are yet to be well understood.",
"We also don't yet understand how ",
" behave in the presence of extreme gravitation. In ordinary space, like between galaxies or near the Earth, gravitation is so insignificant that other interactions are basically free to go on about their business as if there were no gravity at all. But in regions of ",
" spacetime curvature, like around the center of the galaxy or far back in time near the beginning of the universe, it's not clear how these other interactions behave. We don't know, for instance, how electromagnetism works in regions of extreme spacetime curvature. So there's quite a bit of work being done today trying to figure those things out. It's an understandably hard problem to solve, since we're talking about environments that can't be reproduced, or even simulated approximately, in the laboratory. So we're stuck with things like astronomical observations to give us a clue about what's going on in those far-off, hard-to-observe places and times.",
"But on the whole, gravitation is ",
" a solved problem. We basically understand it as well as it can be understood. It's just not an easy theory to teach to, say, high-school students, which is why we stick with Newton's approximation of gravitation when we talk about the basic principles involved."
] |
[
"You know that old saying about how sharks have to keep moving or else they'll die? Sharks — so the legend goes — lack the power to draw water over their gills, so they have to keep swimming in order to get oxygen. So a shark — according to myth — must always swim to stay alive.",
"Imagine a shark that works by these rules, but with an extra constraint: It can only swim at one speed. It can't speed up, it can't slow down. It always swims at exactly (let's just make up something here) one foot per second.",
"But it can swim in any direction you like: up, down, sideways, whatever. Its ",
" is unconstrained, but its ",
" is constant.",
"Got that mental picture in your head?",
"Okay, now imagine we're watching a shark swim around its tank. At any given moment, we know exactly what the shark's ",
" is: It's one foot per second. At least, it better be, or else the shark is dead!",
"But we do not know, without sitting down and measuring it, what the shark's ",
" is. Because velocity is a directed quantity: You have to describe it in terms of a magnitude ",
" a direction. \"One foot per second\" is a speed. \"One foot per second due east\" is a velocity.",
"So the shark's ",
" is constant, but its ",
" varies, because it can change direction.",
"Let's say we want to get an idea of how the shark is moving at any given time. In order to describe its motion, we have to establish some frame of reference. We could do this in any number of ways; the most obvious would probably be to use spherical coordinates. Since we know the shark's speed is constant, and we're only concerned about the direction in which it's moving, we should be able to fully describe its motion in terms of two angles, right?",
"Well … we're not going to do that. Because we're not ",
" watch a shark swim here; instead, we're ",
" thinking about particles moving through spacetime. So in concession to that fact, instead of using spherical coordinates like a sane person would, we're going to use Cartesian coordinates.",
"A little review, just for funzies: Imagine a sheet of graph paper. Any point on that paper can be described in terms of some-number-of-squares to the right and some-numbers-squares up from an arbitrarily chosen origin point. We call these two numbers ",
" We can give them names: ",
" and ",
" for instance. But the names are just labels we apply for convenience. We could just as easily call them ",
" and ",
" which physicists usually do.",
"Extend the system of coordinates from two dimensions to three, and you can describe any point in space. Now in addition to ",
" and ",
" we have ",
" — sometimes also called ",
" but we're calling it ",
" because it's just plain cooler.",
"The direction of our shark's motion at any instant in time can be described with just three numbers: ",
" ",
" and ",
" To save on typing, we can generally refer to these things as ",
" where ",
" is 1, 2 or 3. This is all just notational shorthand.",
"Now, say we arbitrarily decide that due north is the ",
" direction, the ",
" direction is due east, and the ",
" direction is straight up. If the shark is swimming at one foot per second due north (we know it's one foot per second because the shark's speed through the water is constant, remember), we can say its velocity is (1,0,0). That is, its ",
" component of velocity is 1, and its ",
" and ",
" components of velocity are zero.",
"If we look at it at some later time and find the shark swimming due ",
" we'd say its velocity is (0,1,0). That is, no ",
" or ",
" components, and its ",
" component is 1.",
"But what if it's not swimming straight in any of the cardinal directions? What if it's swimming ",
" Well, we could say that its velocity is (1,1,0) … but we'd be wrong. Because remember, ",
" It can't speed up or slow down; it can only change direction. If it's swimming northeast, its velocity is not (1,1,0), but rather (⎷2/2,⎷2/2,0).",
"If we watch the shark for a while, we'll see that as its direction changes, the components of its velocity change in a complex way. If one component of velocity increases, at least one other component of velocity ",
" decrease.",
"Now, all of this is predicated on the notion that the shark's speed through the water is a constant: it never changes. There's an analogous concept in relativity called ",
" If a quantity is ",
" that doesn't just mean it never changes. It means it's always the same regardless of who does the measuring.",
"Just as our imaginary shark always swims through the water at a constant speed but varying direction, every particle in the universe always moves through ",
" at a constant speed but varying direction. The constant speed at which we move through spacetime is — fun trivia here — the speed of light. But your ",
" through spacetime can change. And the way it changes is analogous to how the shark's direction changed while its speed remained constant: if one component of the shark's velocity increased, at least one other component had to decrease.",
"Now, when we talked about the shark in the tank, we used three coordinates to define its velocity at any given moment: ",
" ",
" and ",
" When we talk about particles in spacetime, we have to introduce a fourth coordinate: ",
" which is the ",
" of ",
" You need three components to describe a velocity in space; you need four components to describe a four-velocity in spacetime.",
"If you actually work through the math — which I'm not going to do here, because there are vulgar fractions and radical symbols and all sorts of stuff that's hard to type — you'll find that the components of four-velocity are interrelated. Specifically, the time component of four-velocity — which we can interpret as your instantaneous rate of futureward progress through time — is related to the ",
"Translated into English: The more you move in space, the slower the rate at which you progress toward the future through time.",
"Now, it's important to remember at this point that your motion through space is not absolute. It's only meaningful when considered in relation to some other object. And if I compare your motion to a variety of other objects, I'll get different numerical values for your space components of motion. If you're in a spaceship moving fast relative to the Earth, I (sitting here) will find that your velocity has such-and-such components. But if I'm also in a spaceship moving relative both to the Earth and to your spaceship, I'll find that your velocity has ",
" components. The components of your velocity are not absolute, and there's no objective way to say that these components are ",
" and these ones are ",
"What that means is that ",
" But — and again, I'm leaving the maths of this as an exercise — your clock will never run faster than mine. It will only run at the same rate as mine (if we are at rest relative to each other), or more slowly than mine (if you're moving at all relative to me). The greater I observe your velocity through space to be, the less I will observe your rate of futureward progress through time to be. Just like if the shark is swimming northeast, he's swimming more slowly northward than he would've been if he were swimming due north.",
"Now, the natural question to ask next is whether my clock or yours is ",
" running more slowly. I mean, they can't ",
" be running more slowly than the other, right? Well, it turns out that's a more tricky problem than it might seem at first glance. When we think about comparing clocks to see which one is faster, we have to carry with us some notion of simultaneity: We wait for both clocks to tick at the exact same moment, and then we wait to see which of the two will tick again sooner; that's the clock that's running faster, and the other clock is running more slowly.",
"But it turns out that if we're not at rest relative to each other ",
" If I observe both your clock and mine to strike noon at the same moment, you — moving differently from me — will observe those two events happening at different times; either your clock will strike noon first and mine will be slow, or vice versa, depending on how we're moving relative to each other. But if we're moving ",
" relative to each other, we will not agree on simultaneity.",
"So the truth is it's impossible for us to say which of the two clocks is ",
" faster and which is ",
" slower, because we will never see both witness any two events occurring simultaneously. If two events appear simultaneous to you they won't to me, and vice versa. So we'll never have a basis with which to compare our two clocks. All we can do is conclude — correctly! — that yours is running more slowly than mine from my perspective, and that mine is running more slowly than yours from your perspective.",
"This is not an optical illusion or a trick of perspective. It's intrinsic to the geometry of the universe."
] |
[
"No, you basically have it right.",
"Let's go through it step-by-step. Let's imagine first that you and I both possess ideal clocks. What I mean by that is that these clocks are ",
" in a way no real clock could ever be. They tick off once per second ",
" and nothing in the universe can change that. Bump them, jostle them, set them on fire and they'll still keep perfect time. Okay? With me so far?",
"Now, let's further assume that these clocks are moving along with us, me with mine and you with yours. Okay?",
"So each one of us has a perfectly precise and perfectly accurate way to measure the passage of time. All we have to do is look over at our respective clocks.",
"Let's further assume that we're also equipped with magical ideal telescopes. They can see anything, at any distance no matter how it's moving, and with perfect clarity. (If you want to really get into it, we will also assume that these telescopes magically correct for the frequency shift of incoming light, but that's a phenomenon we're explicitly choosing to ignore here.)",
"So the upshot is that I can measure the passage of time by looking at my clock, and I can also look though my telescope at your clock no matter where you are or how we're moving. And vice versa.",
"Okay?",
"Now, let's start out by imagining that we're at rest relative to each other. If I look at your clock, I'll see that it agrees with mine. Say I start marking time at some arbitrary moment, and continue to do so until ten seconds have elapsed on my clock. At the end of that time, I'll see that your clock also says ten seconds have elapsed.",
"We cut, now, to a later time, at which you are moving at a very great speed relative to me. We're specifically ignoring ",
" for reasons I'll explain shortly. It's like in a movie; we were at rest, and then the film cut and now it's later and you're moving really fast at a constant speed relative to me. Okay? Just to put a number on it, let's say that speed is about 260,000 kilometers per second. So really extremely fast.",
"I do the same little experiment I did before. At one moment, I note the time that my clock reads and the time that your clock reads, and start counting seconds. When my clock says ten seconds have elapsed, I stop counting. I look at your clock and discover to my amazement that it insists that only ",
" seconds have elapsed. Since I know, with the certainty of a monk, that your clock is just as ideal as mine, my only possible conclusion is that time is ",
" Since the only thing that's different between now and before is that you're moving relative to me, it must be because of your motion that your time is running more slowly.",
"Now, let's flip it around. You're moving past me at a high speed — again, about 260,000 kilometers per second. But from your moving reference frame, you look down at my clock and do the same experiment … and discover that when your clock says ten seconds have elapsed, ",
"This is clearly impossible! It cannot be so that both clocks are running ",
" One clock ",
" be right, and the other clock ",
" be wrong! ",
"Well, not really. You see, it's all down to just one little fact that has all these consequences: the speed of light is the same in all reference frames.",
"Let me explain that a bit more completely. To keep things simple, I'm not going to bother describing an experimental apparatus for measuring the speed of light. It's not hard to do, freshmen in college do it all the time. Let's just assume that we each have a magical speed-of-light measuring machine in our possession.",
"Let's imagine there's a third person in our little imaginary universe, a person equipped with a laser. This person is going to shoot her laser at us. (If you like, you can imagine she's your ex-wife. It works for me.)",
"This third person shoots her laser first at me. I'm at rest relative to her, so when I measure the speed of the laser light coming at me, I get a certain result: about 300,000 kilometers per second.",
"Now she shoots the laser at you. You're moving toward her at 260,000 kilometers per second, so since the laser light is coming toward you at 300,000 kilometers per second, your ",
" must be the sum of those two numbers, or 540,000 kilometers per second. Right?",
"Well, no. See, when you measure the speed of the laser light, you find that it's about 300,000 kilometers per second: ",
" the same result I got. Even though you're moving very fast relative to the light, and I'm standing still relative to the light.",
"There's no easy way to explain ",
" this is true in simple terms. It's best if, at this point, you just accept it as an experimentally verified fact: No matter how you're moving relative to anything else, you will always see light as moving at the same speed. It's difficult to accept intuitively, but it's just a fact of nature.",
"From this fact of nature, alllll these other phenomena emerge. If you're moving relative to me, our clocks will not agree. In fact, you will see mine running more slowly than yours, and I will see yours running more slowly than mine. It's not got anything to do with the clocks, either; time ",
" moving more slowly for you than it is for me … ",
"This is possible because, when you're moving relative to me, we can no longer agree on simultaneity. From your perspective, you wait for your clock to read 12:00 noon, and then you look at my clock to see what it says at that exact same moment. Let's just imagine that when yours says 12:00 noon, you see that mine says 12:30 for instance.",
"One might assume that if we looked at the experiment from the other way around, when my clock says 12:30 I'd look through my telescope and see that yours says 12:00 noon. But that's not so. Due to our relative motion, we no longer agree on what events in the universe are simultaneous. Two events that you see as being simultaneous, I see as happening at different times.",
"We also cannot agree on the lengths of things. Remember the ex-wife with the laser? Say her laser puts out light of exactly 550 nanometers, measured at the laser aperture. When I look at that light, I'll see it has a wavelength of 550 nanometers, because I'm at rest relative to the light. But when you look at the light — from your perspective of moving toward it at 260,000 kilometers a second — you'll see that its only 225 nanometers! Instead of a pleasant green, the light is deep in the ultraviolet, invisible to your eyes. That's because from your reference frame, you see the 550 nanometer wavelength of the incoming light contracted to half of what it is in a reference frame that's at rest relative to the laser.",
"Basically all the \"weird\" things that come up in special relativity — time dilation, length contraction, the relativity of simultaneity — are consequences of the fact that the speed of light must be the same in all reference frames, without exception. This is just an inherent fact of nature, and so the geometry of spacetime has to be non-Euclidean in order to accommodate that fact of nature.",
"Now, as to your question about the twin paradox … special relativity (which is what we're talking about here) ",
" applies only to inertial reference frames — that is, reference frames that are moving relative to each other only at a constant velocity, not accelerating. When you talk about accelerated reference frames, you have to change your mathematics a bit. You can no longer apply the algebraic Lorentz transformation to convert lengths and time intervals in one reference frame to lengths and time intervals in the other reference frame. Instead, you have to use a different mathematical formulation — and there are a couple, one involving hyperbolic trigonometry and one involving differential geometry. The math is more complex, in a way, but more importantly you get different results.",
"The twin paradox is called a paradox because applying the Lorentz transformation naively tells you that the twins should disagree about which one is younger, and yet when they get together at the end of the story one of them is objectively younger and one is objectively older. The reason for this is because the Lorentz transformation only works in inertial reference frames; it does not work in accelerated reference frames. And in order for the twins to get back together at the end of the story, at least one of them ",
" accelerate ",
" three times: once when he leaves Earth and gets up to a high relative speed, once when he turns around and heads back toward Earth again, and once when he slows down to land. During the \"coasting\" parts of the experiment, the astronaut twin sees time back on Earth running more slowly than his own time. But during those three acceleration phases, he sees time on Earth run ",
" than his own time. It all adds up to more time in total elapsing on Earth than in the spaceship. So it's not really a paradox at all, just an illustration of how you have to treat inertial and accelerated reference frames differently."
] |
[
"How do astronomers store and access data about stars, galaxies, etc.?"
] |
[
false
] |
Does all research in astronomy require new observations? I'm guessing no, but that leads me to wonder how astronomical information is stored. I'm interested in how it is logically organized and stored for analysis and study, as in a database/datawarehouse, etc., not in physical storage. Is there a recognized standard that information is converted into? Can astronomers run pattern-matching queries across giant data warehouses of information from telescope observations, looking for clues that might suggest a certain type of pulsar; a gas cloud of a certain composition; a galaxy whose redshift and position make it a likely member of a certain cluster, etc.? Aren't most current instruments connected to telescopes capturing data digitally? I guess what I'm wondering is whether there's a standard way to format that data, and whether or not it's made broadly accessible to all professional researchers in a usable way. Is it the kind of thing that there's enough data available to researchers that they can run queries against coarse grained data looking for interesting targets, and then they can go get time on a big scope to observe the target in much higher resolution, or with specialized kinds of instruments, to get the much finer grained information about the target that they need to answer their questions?
|
[
"There's a lot of questions in there...",
"At the most basic level, optical and infrared astronomers have a data format called .fits (flexible image transport system) that is pretty much a recognised standard in terms of data storage. It's basically horrible, but it works, and it's hard to shift such an entrenched standard. I have the feeling that hdf5 has a chance to become the standard in the next few years, but it's not there yet.",
"Beyond that, there are not really good standards. Just about every telescope has its own peculiar data conventions. For instance, there is general agreement about the way to encode critical basic information like how to map pixel coordinates to sky or wavelength coordinates, but each telescope might use a different keyword to store that information. Which makes it hard to collate data from many telescopes into a central repository. ",
"But then, what makes it virtually impossible is that the process of going from raw data off the telescope to a fully calibrated, science grade, combined dataset is a very long and delicate process. I'm not sure that anyone really believes that it is reasonable or possible for a one-size-fits all approach to this problem.",
"That said, people have been actively working on these kinds of things, under the banner of 'the virtual observatory'. (See ",
"IVOA",
"). ",
"In lieu of a really good and useful virtual observatory, the current status quo is that most telescopes make their archives open and freely available in one way or another. Typically, the data are only available in their raw form, and not super well documented. And in my experience, the searchability of most archives is pretty basic. So while useful data may well exist, there are pragmatic hurdles to making those data immediately accessible.",
"At the same time, most large-scale 'legacy' surveys will make their final catalogues and dataproducts available in a reasonably timely manner. People have figured out that this gets their datasets used, which gives them profile, and thus citations. The best example of this is Sloan, but it is truly exceptional in this regard. A more typical example would be something like 2MASS (google it, and try to figure out what you can access!). In the in between, there are projects like the Hubble Deep Fields, where maybe the images will be available, but not the catalogues; or the catalogues might be available, but not the redshifts. And so on.",
"I guess the short answer is that data access is managed in a very ad hoc way. People do think about how to do this better, but it's not a priority for the vast majority of professional astronomers.",
"Last thought: have a look at the Theoretical Astronomical Observatory (",
"TAO",
"). I think that, in the quest towards better and more transparent data access, this project is trying to lead by example."
] |
[
"A lot of it is done through sky surveys, where the results of telescope observation is accessed from a database. An example is the ",
"Sloane Digital Sky Survey",
", which you can use to get ",
"pictures from the telescope",
", or more technical information like spectra."
] |
[
"The ",
"VAO",
" is the US organization responsible for coordinating the efforts of the IVOA. The VAO directory is a repository for astronomical data and service providers. You can search the directory by keywords to find the type of data you are interested in. \nAnother interesing tool is VAO SkyQuery, which can combine queries across multiple data providers. This is possible because the data providers in the VAO directory have agreed to be complaint with the IVOA standards.",
"Having said that, I have to admit that I haven't check the directory for a while. So I don't how current it is.",
"Now the data. Most of the modern telescopes nowadays use CCDs; therefore they produce digital data. This is called raw data. Depending on the project contractual requirements, the raw data may or may not be released to the public immediately. Medium and large public funded projects these days often have a public outreach clause that specifies the timing and the amount of data to be released. \nHowever, only a very small number of people in entire world is capable to process the raw data and produce something useful. To reduce the raw, one needs the detailed knowledge of the telescope, the instrument, the science targets, and the observing program. While all these may be included in the raw data archive, this is such a cryptic information that only the initiated can make sense of. Note that we are not talking about pretty pictures. In astronomy, 99% of the data consists of spectra.",
"All this is too big a topic for just one short answer. Stopping here."
] |
[
"Can plants form addictions?"
] |
[
false
] | null |
[
"No. OP is asking if a plant can be an addict, not that if you can be addict to that plant."
] |
[
"Dependence can be both physical and psychological. We can rule out psychology in plants but physical dependence or formation of tolerance might occur in plants. And you would only need basic nervous system like that of plants for this to happen. "
] |
[
"Yes, thanks for reminding me. Plants do not have a nervous system, so they cannot obtain an addiction."
] |
[
"What type of porcelain glaze reduces surface tension?"
] |
[
false
] |
[deleted]
|
[
"You're dealing with an extremely complicated set of physics: Wetting and contact angles.",
"There are no easy generalizations that can be made. ",
". There is ",
" a set of equations that can be used to calculate the wettability of a specific material, with a specific fluid.",
"Every fluid will behave differently. Every surface will behave differently.",
"Glass CAN make water bead on its surface. It can also make it wet the surface. Porcelain CAN make water bead on its surface. It can also make it wet the surface. Even intuitively absorbent materials, like a sponge, or fabric, can make a fluid bead up. We've all had clothing that spills will bead on, until we move the slightest bit, and its absorbs. Conversely, intuitively \"slick\" surfaces like a car's paint, or a piece of polished metal, can be wetted. ",
"This phenomenon is not a simple matter of surface tension, even though surface tension is one variable in the set of equations that govern it. There are many other factors: what is the composition of the ",
" surrounding you? What is the chemical composition of the pigments you have dissolved in the water?",
"All you can do is test different materials, to find which ones work best for you. Trying to predict this is essentially impossible."
] |
[
"All you can do is test different materials",
"To this excellent answer I'd only add: \"...and different surface treatments and coatings.\" As you note, there are a very large number of knobs that one can turn to adjust wetting."
] |
[
"The surface isn't reducing the surface tension of the water. What defines whether the water beads up, is a competition between the surface energy of the solid, the surface energy of the liquid and the interfacial energy between the solid and the liquid (as well as a few other things). Have a look at ",
"this wiki",
".",
"However, it's not straightforward to predict if the water will bead up. Though you can simplify it slightly. Generally speaking, a solid with a lower surface energy will cause the water to bead up, as forming exposed solid surface isn't as costly compared to a surface with higher energy.",
"But surface roughness also plays a big role in defining how wetting a liquid is. The rougher the surface, generally, the more the liquid will bead up.",
"So to more directly answer your question: it looks like the dinner plates are made from smoother and lower surface energy materials than the porcelain. Though this is a massive simplification and a true analysis of this would also include a discussion of the interfacial energy between the liquid and the solid (as well as any effects due to dirt)."
] |
[
"How big/fast would an asteroid have to be to split the earth in half or shatter it completely?"
] |
[
false
] |
I mean... scientists are always taking about asteroids wiping out LIFE on earth... but what about wiping out the planet entirely?
|
[
"According to ",
"this table",
", you'd need 2.9*10",
" J of energy to break the Earth up into small pieces (remaining in the same orbit). Any object orbiting the Sun won't be traveling more than about 40 km/s in the vicinity of the Earth, or it would escape the solar system entirely.",
"Using those numbers, your asteroid would have to be at least 3.6*10",
" kg. That's about half as massive as the moon.",
"edit: Actually, if the asteroid happened to be traveling opposite to the direction of the Earth's orbit, you could achieve a relative velocity of around 70 km/s, and get away with a 1.2*10",
" kg asteroid. So only a sixth as massive as the moon."
] |
[
"Of course, if they remain in the same orbit, I imagine they will one day fall back together and Earth will be back... with a vengeance!"
] |
[
"You want to ",
" the Earth? As in, make is so there's no planet here?",
"You can get a good first-order approximation of that by calculating the gravitational binding energy of the Earth. That's two hundred and forty thousand billion billion billion joules, or the kinetic energy of the moon accelerated to 180,000 miles an hour."
] |
[
"Why does taking Accutane cause so many problems during pregnancy?"
] |
[
false
] |
My brother was recently prescribed Accutane and there are warning labels all over the packaging telling women to not take it while pregnant. I am aware of the birth defects it creates, I am just interested in the science about why it is so dangerous.
|
[
"Firstly, a lot of drugs cannot cross the placenta because of solubility or other physical factors, but accutane is fat soluble and a derivative of vitamin A, so the placenta has a natural proclivity to uptake it for fetus building purposes. Most of the teratogenic effects it causes such as vision abnormality, mental retardation, and facial deformity can be explained by its similarity to vitamin A (ie the body thinks its vit A, but its not so it doesnt work as such, and shit goes awry) For instance, normally vitamin A plays a pivotal role in the function of vision. When a photon hits 11 cis retinal (vit A) it is 'unsprung' into the straighter all trans isomer. This change in shape of the molecule is necessary for transmitting the signal of that photon to the brain. If a baby incorporates accutane which is 13-cis retinoic acid (slightly different) its not gunna work as a signal transducer in the vision cascade. "
] |
[
"Accutane, also known as isotretinoin, has a close resemblance to retinoid acid which is the active form of vitamin A.",
"Retinoic acid functions as a central signal molecule during the embryonic development by mediating correct development of posterior part of the embryon through interaction with Hox genes. This development is a very delicate balance as the concentration gradient from the different embryonic tissues producing retinoid acid to the target area may regulate what specifically is being developed.",
"Retinoic acid is therefore crucial in the establishment and correct development of the anterior/posterior axis and its structures. By introducing Accutane in the system of a pregnant mother, this delicate balance is skewed because Accutane may act in the same manner as the \"native\" retinoic acid. ",
"This results in a functional surplus of retinoic acid during the embryonic development which leads to serious birth defects because some of fundamental steps in human (as well as other chordates) development has been seriously altered by Accutane and its ability to act like retinoic acid."
] |
[
"Wow, thanks for the response. Thats more thorough than I could have asked for, thank you!"
] |
[
"Why do I get different values for the molar mass of a mixture depending on how the moles are counted?"
] |
[
false
] |
I was looking on a few different websites on how to calculate the molar mass of dry air. They all give roughly the same answer - multiply the molar mass of each constituent by its percentage concentration, and add everything up. This gives about 28 g/mol for dry air. However, I noticed that oxygen was counted as 32 g/mol. This is correct, as oxygen gas is more or less always in the form of O2. But let's imagine for a minute that the air is full of monatomic oxygen, with a molar mass of 16 instead, and that the same number of oxygen atoms are present. The concentration in the air would be the same, by mass at least, so the mass of the air should remain the same. When I calculate the molar mass using monatomic oxygen, though, the lower molar mass of the monatomic causes the overall molar mass of dry air to be lower, even though the number of oxygen atoms has not changed! How can this be? Is it because a mole of air with monatomic oxygen would be less dense, or something?
|
[
"Diatomic oxygen (O2) constitutes 20.95% of the molecules in a volume of air. Let's say we're talking about a 22.4-liter volume at standard temperature (0°C) and pressure (1 atm), which contains 1 mole of molecules, of which 0.2095 mol will be O2 molecules.",
"If, in your hypothetical scenario, each O2 molecule was split into two monatomic O atoms, you would have 2×0.2095 mol = 0.4190 mol of oxygen atoms.",
"Thus, the contribution to the effective molar mass of the air would be the same:",
"(0.2095 mol)×(32.00 g/mol) = 6.704 g of O2",
"(0.4190 mol)×(16.00 g/mol) = 6.704 g of O",
"*",
"If the above is not the explanation you are looking for, then please post your calculations, so that we can check your work.",
"*",
" I misunderstood your question, and have amended my answer ",
"below",
"."
] |
[
"Here's an even simpler explanation:",
"Calculating the effective molar mass of the molecules that make up a gas mixture (air) is equivalent to determining the average size (mass) of the parts (molecules) that make up a whole thing (the air). As an analogy, consider a whole pie (the air), that has been sliced into many slices (molecules). The slices may have different sizes (like different molecules may have different mass), but you're interested in the ",
" size of a pie slice (which is analogous to the average molar mass of the gas molecules). Because the mass of the whole pie remains fixed, the average mass of a slice is just the whole pie mass, divided by the total number of slices.",
"Now, assume you start with a subset of slices that each have a mass of 32 g (these are analogous to the O2 molecules). If you slice each of the \"O2\" slices in half (yielding 16-gram slices), then what happens to the average size? Of course, the ",
" pie slice is now smaller, because there are more slices overall.",
"Since we're just playing mind games, you could hypothetically do the opposite: instead of just splitting the O2, take all of the oxygen atoms and join them with two nitrogens each to make nitrous oxide (which has a molar mass of 44 g/mol). Now you will have a smaller number of pie slices overall, so the average size of a slice will be ",
" ",
". If you do the calculation, the effective molar mass for this hypothetical gas mixture will be ",
" ",
" than the result for air.",
"*Edit: Fixed typos: lower-->higher, smaller --> larger"
] |
[
"I think I understand where you are coming from: more molecules, more objects for the total mass to be distributed amongst. The only thing is: if you have a smaller number of pie slices, shouldn't the average size of a slice be ",
"?"
] |
[
"What specifically about ginger/menthol/wasabi causes one's sinuses to open?"
] |
[
false
] |
Is there some chemical component that each plant shares, or do we just react this way to certain concentrated flavours?
|
[
"It actually doesn’t open the sinuses, It gives the feeling that your sinuses are opening from a cooling effect. It’s a trick on the receptors in your nose even if you can’t smell. \nActual nasal decongestants have active chemicals and can have added menthol but it’s not required."
] |
[
"I'd like to add to this with: subjective feeling of decongestion is related to perception of airflow, and substances OP mentioned provide an additional \"cooling effect\" by chemically stimulating the cold receptors. This is interpreted as increased airflow - similarly to how after using a cooling spray on your skin it's suddenly way easier to feel even a slight breeze. There was even a ",
"study",
" done on that effect, that proved that menthol alone can increase the subjective feeling of decongestion on par with some actual decongestant with zero increase in nasal flow.",
"Drugs such as xylometazoline and adrenaline delivered topically will actually affect the size of nasal conchae (turbinates) - with mid concha hanging directly over the maxilary sinus entrance."
] |
[
"Wasabi contains allyl isothiocyanate which is an irritant. Your body increases mucus production and secretion in an attempt to protect the nasal tissue and flush the chemical from your nose. Horseradish contains the same chemical."
] |
[
"Why did the pages of my book wrinkle as they dried after I dropped it in the toilet?"
] |
[
false
] | null |
[
"You know how napkins/toilet paper/tissues tend to completely disintegrate when you let them soak in water for a while? That's what's happening, but on a smaller scale.",
"The presence of water in paper disrupts the intermolecular forces that hold individual cellulose molecules together. So instead of staying in place, the cellulose molecules can start to move around. As the paper dries out, the intermolecular forces come into play again, but now all the cellulose molecules are in a different position from before. This leads to the wrinkly or wavy look of water-damaged paper.",
"In the future, you can minimize the waviness by compressing the book (or just the affected pages) with a heavy object until you're sure that it's completely dry. This will minimize how much the cellulose fibers move around."
] |
[
"I've actually got SEM images of paper towel before wetting and after wetting from a middle school science fair project last year and let me tell you they look ",
" different when they've dried after wetting. If anyone's interested, ",
"here's the science fair poster",
"."
] |
[
"I didn't get to play with electron microscopes until I got into grad school. No fair!"
] |
[
"What is the difference between an island and a continent?"
] |
[
false
] |
What is the cutoff? Why is Greenland an island but Australia is a continent?
|
[
"So then why don't we call the Arabian Peninsula or India continents? Or perhaps more accurately, is it appropriate to call them continents if you're not specifically referring to the tectonic plates?"
] |
[
"There really is no easy answer to this question, it depends on who you ask. Australia is considered by some to be an island-continent and a continent by others. ",
"India was once very much like Australia before it collided with Asia (or Eurasia) and is now considered part of Asia, even if it is tectonically distinct. ",
"Also, ",
"Greenland isn't as big as the Mercator projection would have you believe",
". Moreover, Greenland never fully rifted away from North America. Rifting started when Pangea was breaking up but then stopped, ",
"resulting in an aulacogen (failed rift) between Southwestern Greenland and Labrador",
". "
] |
[
"It depends on if you are trying to answer \"why is Australia defined as a continent and why is Greenland not, geologically\" or \"why do they have different words in the lexicon\". ",
"Also, North and South America are on separate tectonic plates, so they definitely have a reason to be two separate continents, however the difference between Russia and Europe is more of a political boundary than a crustal boundary (although some consider the Ural mountains to be the 'geologic' boundary between the two, even though they are on the same tectonic plate)"
] |
[
"Are there any other body parts that are able to pick up oxygen besides my lungs?"
] |
[
false
] |
[deleted]
|
[
"All parts of your body utilize oxygen. Your lungs just get the oxygen into your body, from there the oxygen is absorbed into the blood and distributed to your entire body. So to answer your question; Yes, your whole body is capable of picking up oxygen, however only the lungs are able to convert atmospheric oxygen into a form usable by your cells."
] |
[
"The cornea is, afaik, the only organ that is oxygenated independently of the cardiovascular system. Owing to its position and its lack of blood vessels, the cornea is able to meet its needs via oxygen naturally dissolved in tears. ",
"http://www.aclm.org.uk/index.php?url=04_FAQs/default.php&Q=3"
] |
[
"There are several requirements for ",
"gas exchange",
" to occur, such as a moist environment and a short distance to diffuse across. Ideally there would also be a large surface area for the exchange to take place.",
"In humans, the only organ that meets these requirements are the lungs. So short answer is that only the lungs are capable of significant gas exchange from air to blood.",
"Amphibians are capable of considerable gas exchange across their skin as their skin is thin, permeable to water, and vascular. ",
"Humans",
" would have close to no oxygen transfer due to thicker, impermeable skin.",
"However, if we were to cut someone open and bypass the water-proof skin barrier, oxygen exchange may occur to some extent. "
] |
[
"Does literature support subconscious competitiveness while driving?"
] |
[
false
] |
Often, while attempting to pass another car on a highway, the other car will increase their acceleration before I am able to overtake them. Is this a subconscious impulse on behalf of the other driver?
|
[
"I am actually doing research on this sort of thing now, but kind of a different explanation.",
"Based on what vehicle we drive and what situations we are put in, we can be primed with aggression. People driving a sports car or truck are typically moreso primed this way than other vehicles. We have to attribute that aggression to something. That something can be ourselves, other vehicles, other drivers, stoplights, anything. A lot of the time, it is other drivers. ",
"Now, what you are talking about is the other person having small man syndrome, or an inferiority complex, which makes them feel weak when someone passes them. Essentially, the person views themselves as aggressive, manly, whatever, and someone passing them (driving faster than them) contradicts that view. This causes a self-discrepancy and cognitive dissonance.",
"A self-discrepancy is the difference between who you view yourself as an who you think you should be or want to be. If you want to be the person who drives fast and someone passes you, you now have a discrepancy, so you prevent/fill that discrepancy by speeding up.",
"Cognitive dissonance is a conflict between belief and action. It causes an uncomfortable feeling that must be alleviated by changing your belief or changing your action. Chances are, they aren't going to change the belief that they are the person driving fast enough, so they change their action by driving faster."
] |
[
"In terms of you not realizing what is going on, yes. Unless you've been taught about the two things, you probably won't figure out the process you're going through."
] |
[
"Thanks so much for answering! I didnt think anyone would. Question though, is cognitive dissonance and self-discrepancy subconscious in this situation? Is it usually?"
] |
[
"How come chemists never consider whether their compounds are interacting with the silicon in glass test tubes?"
] |
[
false
] |
There's lost of experiments where chemists create vacuums because they are worried about interactions with air, but they never seem to account for the silica in glass. Is it because it's pretty stable? But shouldn't it still be considered as possibly a variable in chemistry experiments?
|
[
"Yes, it's pretty stable. It is considered though. For instance, if you're working with hydrofluoric acid then you can't use glass and must use plastics or certain ceramics that don't include silicon."
] |
[
"Air contains oxygen, which is a decent oxidizing agent and reacts with a lot of things. Borosilicate glass, which is what most laboratory glassware is made of, is pretty inert, and therefore, unless dealing with certain extreme chemicals, it's not an issue."
] |
[
"On the contrary, there is a great deal of research looking into passivation of silicon or silica walls with boundary layers, because at short distance it has a significant role. ",
"See for example section 7"
] |
[
"When we hurt something like our wrist we either wrap it up to make it warmer or put ice to make it stop swelling. Whats wrong with just the regular body temperature?"
] |
[
false
] | null |
[
"Not a bad question. The point of an ice or warm wrap isn't to control the body's temperature. Rather, it's using temperature as a tool to illicit a response from the body that could assist healing or manage pain. Ice, for example, can help reduce swelling in a broken wrist. Heat can relax injured muscles and increase blood flow. ",
"You could ask \"how come our body can't do this without help?\" Well, the human body is pretty good at healing itself, but it's not perfect. This is why we need doctors, medicine and sometimes a icewrap. "
] |
[
"Ice: ",
"Numbing the pain. The nerve endings in the area can't function very well when cold, and thus the amount of pain signals from this area is reduced. ",
"cool the area down, thus decreasing blood flow to the area, thus limiting the amount of swelling or the amount of bruising in the area. Less bruising = less time needed for healing later and less pain. Less swelling = mainly less pain, but maybe also less repair needed later. ",
"Pressure:",
"Stabilize the area which helps prevent pain if you have to move this area of your body. ",
"Prevents swelling (although be careful that sometimes putting too much pressure on may make matters worse : there always will be some swelling, and if there is nowhere for the swelling to go because the bandage is too tight, valuable tissue may get err squished... like arteries or nerves... not good). ",
"Something hot: I wouldn't apply heat first to an area where you expect bruising or swelling to occur. You can apply it later (after a couple of hours), when the bleeding (bruising) has stopped and the tendency of the area to swell has become much less, too. Heat increases the speed of enzyme reactions, and these are needed to heal the injury. Heat probably",
" also increases blood flow to the area, and again this is needed to heal the injury (get nutrients, oxygen and immune cells to the area to assist in repairing, transport waste products away from the area).",
"For both heat and cold goes, that you should not injure the skin while applying heat or cold. Making the skin blister from the cold or the heat is not going to be helpful in recovering from the injury.",
".",
" Probably because I am not sure... maybe someone else can clarify?"
] |
[
"This is right.",
"Also, if you're just wrapping something in tape or an Ace bandage, that's not intended for warmth. It's to stabilize the area and prevent further injury. When we want extra heat in an area we provide it from outside, such as with heat packs, hot compresses, or a hot water bottle."
] |
[
"Why doesn't air unmix?"
] |
[
false
] |
If "air" is a mixture of light and heavy gasses, why doesn't air unmix? (I am sorry for not knowing a better word to use here) Why exactly don't lighter gasses like oxygen float above a layer of heavier gasses like carbon dioxide, like some fluids would?
|
[
"The real reason air doesn't separate into layers is entropy. There is an enthalpic component to mixing that would favor the heavier gases being on the bottom (that depends on the strength of gravity), but the dominant factor at room temperature is the favorable (positive) entropy of mixing. ",
"It's not a question of giving air enough time to settle; it's just straight thermodynamics saying that it's more favorable for the gases to be mixed.",
"For certain extreme cases (H2 mixed with Xe), they might separate, but I have a hard time believing that air would separate at room temperature (I don't feel like doing the calculation)."
] |
[
"This is the best answer here.",
"To elaborate: while it is true that there is an enormous amount of mixing in the atmosphere, as another poster mentioned, a sealed container of air at a uniform temperature ",
" (under normal conditions; the behavior starts changing when nearing the condensation point of a gas, e.g. very high pressure or low temperature). This is because the density of a gas is only determined by the volume of its containment. Gases have both a very high particle velocity (at room temperature it's on ",
"the order of 500+ m/s, or 1000+ mph",
", as well as a long mean free path of each molecule (the mean free path indicates the average distance between particles) . The mean free path for most gases at standard conditions is on the order of 100 nanometers or more. A gas molecule is on the order of 100 picometers (1000 times smaller). This results in the there being a large amount of empty space for a gas molecule to travel through before interacting with another, leading to each gas in a mixture expanding to homogeneously fill a container, as the gas is only bound by an interface it cannot diffuse through, e.g. the wall of the container (we can assume that the solid container is non-porous and the gas has negligible solubility and diffusive properties in said solid). ",
"There is no inherent density for a single molecule of a given gas (or any substance for that matter). Because the gas molecules do not bind to each other, and only interact in what are effectively elastic collisions, combined with the large mean free path and particle velocity, the mixture of gasses will always remain mixed."
] |
[
"That's because the cold CO2 hasn't had a chance to warm up and mix with air yet, not because it naturally separates."
] |
[
"I have a porcine and now bovine heart valve. Are there any other human replacement parts taken from animals?"
] |
[
false
] | null |
[
"I know in the 60's they looked into transplanting chimp kidneys, but it didn't take. Apparently you want the donor parts to be genetically unrelated enough to prevent diseases from the original species popping up in the recipient, but not so different that you can't use them.",
"Like, monkey livers are too close, but ostrich livers are too different.",
"Only successful example of this sort of operation I can think of, aside from heart valves, is somebody replaced my boss with a horse's ass."
] |
[
"Do only body parts count ? Cause insulin used to be from pigs and if I recall correctly, anti tetanic immunoglobulins were taken from immunised horses. \nThere are also temporary skin grafts from fish skin, which are used to cover and protect a big burn for which it is difficult to have enough skin to graft directly from the host."
] |
[
"You could and you do implant mechanical valves that are made of metal and plastic (Vs biological valves which are of animal origin). They have the benefit of being very long lasting, so no need for further surgery, because the valves won't degrade. However they have some inconveniences (like anticoagulants for life)."
] |
[
"How do other animals display similar or better coordination of limbs with such smaller cerebellums?"
] |
[
false
] |
[deleted]
|
[
"First, notice that the best predictor of brain size in general is body size, not behavioral complexity. Other anatomical features can be more revealing. In the case of the cerebellum, you can start with the ratio of its size with respect to that of the rest of the brain. Animals with particularly enlarged cerebella include some rodents (like squirrels), primates, some birds (parrots, crows), and bony fishes. ",
"Also consider that the cerebellum is not only only involved in balance and general motor coordination, it's also involved in motor learning. Although cats can be nimbler than a typical human, their repertoire of behaviors and their ability to learn new ones are smaller. For example, a cat's ability to turn mid-air is impressive, but it's likely a fixed action pattern that requires relatively simple wiring. Compare that to a human's ability to play the piano, which involves extremely fine tuning of motor coordination that is learned and not pre-wired. The same can be said about the gait of centipedes (which by the way don't have a cerebellum): it surely is amazingly coordinated, but it's also largely automatic. Compare that to a human's ability to say a tongue-twister, which requires a great deal of learned muscle coordination. ",
"Anatomically, the learning aspect might be related to the fact that, compared to that of other animals, the primates cerebellum has relatively larger lateral lobes, which are mainly connected to the neocortex. I hope you find this answer helpful. "
] |
[
"One thing to keep in mind about the cerebellum: it is not motor function only. ",
"Probably only 10-20% of human cerebellum is motor-related, the vast majority projects to and receives projections from association cortex.",
" A more interesting comparative anatomy question is why does human cerebellum have so little motor representation?"
] |
[
"Thank you! I have a BA in Neuroscience and am starting a PhD program this year :)"
] |
[
"How do you measure the strength of a magnet?"
] |
[
false
] |
I guess I would measure it in Newtons by using a graduated cylinder full of distilled water of known height, the magnet, a metal ball of known masse, and a stop watch. I would measure the time the ball reaches the bottom of the cylinder from where it is dropped at water level (0 acceleration) and calculate from there since I know the density of the water, the value of the gravitational pull, the height of the cylinder, the masse of ball, and the two different times. What is the official way to calculate this? Bonus: lets say the height is 50.0 cm, the ball of 10.0 grams is dropped at 0.00cm and there is a 2.00 second difference what is the force of the magnet in newtons? I'm bored and just randomly asked myself this question which is now intriguing me. Edits: density of water:1kg/m G=9.800m/s Viscosity of water at 20°C = 1.002 Edit 2: I guess you would first need to calculate the time the ball takes to fall, then add/remove(?) 2 seconds and go backwards and take G off the resulting amount of newtons.
|
[
"I'm sure there are many ways to measure the strength of a magnet. As a person who has done some experiments with an accelerometer, I would try setting up an experiment using the magnet in question on a ferrous material at a prescribed distance that is hanging on a wire. If the wire is taut enough, gravity shouldn't even be considered (except for the friction). Determine the frictional coefficient of the weight on the wire, the mass of the ferrous material (with the accelerometer), and run some simple trials. ",
"Using established equations and taking into account the non-conservative friction you should be able to determine the \"strength\" of the magnet after a few trials with a decent ruler and stopwatch.",
"Your setup requires a lot more factors like viscosity, density, gravity, etc. As a person who has had to design their own experiments I offer this advice: whenever possible, make the experiment simpler.",
"p.s. use better constants if you are looking for better results. g = 9.80665 ms"
] |
[
"Normally you use a ",
"magnetometer",
", although that's not particularly descriptive, given that the name means \"thing you measure magnets with\". The article discusses a variety of possible techniques. "
] |
[
"What you described is somewhat functionally similar to a crude ",
"Gouy balance.",
" Magnetic balances are an old and time-tested method but they aren't really used much anymore.",
"Magnetic properties are measured with different things depending on the information you want.",
"SQUID",
" (",
"uperconducting ",
"antum ",
"nterference ",
"evice.) is the modern workhorse instrument for magnetic measurements. It measures magnetic fields with extreme accuracy by using a superconducting junction known as a ",
"Josephson Junction",
". Its good for measuring the ",
"magnetic moment",
" of a substance as well as its hysteresis.",
"EPR/ESR (Electron Paramagnetic/Spin Resonance) is used for more fine investigations. Its primary use is to determine how the magnetic fields are situated and coupled in a substance (By determining values such as D, E, g-factor and hyperfine coupling.)",
"Some more exotic techniques are ",
"neutron diffraction",
" and Evan's method. In neutron diffraction the interaction of the spin of the neutron and the electrons around the nucleus provides additional diffraction which can be measured and related to the magnetic moment of that atom. Evan's method is a modified form of ",
"paramagnetic NMR",
", in normal NMR (Nuclear Magnetic Resonance) you measure how the magnetic moments of the nuclei couple, with Evan's method you measure how much your paramagnetic sample shifts these values. This can be directly related to the magnetic moment of your sample.",
"There are other methods as well, these are just ones I'm somewhat familiar with. Its an incredibly rich and intricate field!"
] |
[
"Are the animals living in the city of Pripyat (the city that was devistated by the Cherynobil disaster) deformed from radiation?"
] |
[
false
] | null |
[
"Oh boy, my favourite topic! ",
"While the Chernobyl wildlife do have large degrees of deformities, they largely manifest in their internal organs, immune systems, and reproductive sucess-- no three-headed deer, just birds with smaller brains, fewer eggs, and fewer babies that are born alive and make it to adulthood. A lot of the animals there appear to be abundant, but actually don't have enough surviving offspring to replace their own numbers; the population is maintained through immigration from the surrounding areas. ",
"Timothy Mousseau",
" is the leading English-language scientist in the field and has spent over ten years publishing findings on Chernobyl's wildlife, check his papers out."
] |
[
"please don't upvote comments like these that don't contribute to the discussion. There are countless other reddits for that, keep this one for science."
] |
[
"Go to Detroit and find buildings that were abandoned in the mid-80s. I'd be willing to bet they look at least similarly decayed inside."
] |
[
"Can someone explain the Frank-Starling mechanism to me, and how it relates to circulatory shock?"
] |
[
false
] |
[deleted]
|
[
"The Frank-Starling mechanism describes how stroke volume increases to match end diastolic volume of the heart. This means that the heart will eject the amount of blood returned to it with each beat. It helps to keep arterial supply in line with venous return.",
"Shock has many many causes, and I'm not certain how or why you're relating it to the Frank-Starling mechanism. Is this in regards to a specific question or at least a specific type of shock?"
] |
[
"Here is a diagram to supplement Teedy's definition",
"Just to tack on a further definition, Frank Starling refers to the fact that there is an \"optimal length\" of stretch of the muscle fibers of the heart. This is the point at which the most cross-bridges are formed in the sarcomere (muscle unit) so the greatest amount of contractile force can be created. Once you get past that point (fluid overload, heart failure, etc) then the sarcomeres are stretched too far and cross-bridges are lost, creating a weaker contraction. The Frank Starling effect is an inherent property of muscle fibers.",
"This is NOT the same as increasing contractility, which has to do with increased sympathetic input to the heart during, for instance, exercise."
] |
[
"Bang on correct.",
"I'd guess that he's thinking of either cardiogenic or hypovolemic shock, but I want to be sure before getting into those as they get in depth fairly quickly, and I'd rather not spend all night typing an essay."
] |
[
"Could a magnetic field kill a human being ?"
] |
[
false
] |
[deleted]
|
[
"At the very far extreme in terms of magnetic field strength is the ",
"magnetar",
", which produces magnetic field strengths so strong that it'll begin to affect water in your tissue due to diamagnetism. So... it'll tear you to pieces.",
"Things like ",
"transcranial magnetic stimulation",
" affects the firing of your neurons using magnetic fields comparable to those found in MRI. Using stronger fields for a far longer period of time can definitely affect brain function."
] |
[
"MRIs use static magnetic fields to generate the Larmor precession in the first place, not to mention a static gradient field along the Z-axis is required in order to obtain slices. That field is somewhere along the strength of 1.5 T, if I remember correctly.",
"Edit: Grammar"
] |
[
"Yes, but but aren't we talking about fractions of a picosecond?"
] |
[
"Why does hair change as you age? ie in colour, curly to straight..."
] |
[
false
] |
When I was younger I had straight blond hair. Now I have completely different curly ginger hair with the opposite texture. I have heard of hair going straight to curly, but not so much the other way round. Why is this? Edit: Front page! Thanks for all your insightful responses, I've enjoyed reading them.
|
[
"Part of this is due to the changes in hormonal balance and the length you keep your hair. As you age the hormone levels in your body will change impacting your hair texture and sometimes the color. There are other environmental effect other than length as well. For example, humidity will increase the curl potential of your hair as it increases, etc. "
] |
[
"Is there a way to make pubes grow really, really long? Since they tend to stop growing at a certain length. Like, trick it into thinking it was just shaved? ",
"Edit: I want monster pubes"
] |
[
"Every hair on your body has a terminal length -- a length beyond which it just won't grow. That length is different for different hairs and different for different people. So, if you've never cut those hairs, then whatever length they are now is probably already at the terminal length and they won't grow any further.",
"This is also why most people can't grow their head hair down to their ankles -- most people's terminal length isn't that long."
] |
[
"What is a computer doing in the ~ 60 seconds it takes to start up? That's billions and billions of instructions correct?"
] |
[
false
] |
Also, how is data stored in memory when there's no power?
|
[
"When there's no power, data can only be saved in persistent memory - magnetic storage (HDD) or flash memory storage are the most common. These don't require power to hold data. \nData in RAM or cache isn't persistent, but it's much much quicker than persistent storage for reads and writes. (This is effectively the computer's working memory/area).",
"When you boot a computer it has to read a lot of information from persistent storage into RAM, as well as ensure that it knows what hardware is available and configured (Power On Self Tests etc)."
] |
[
"It does a ",
" of testing..",
"It was about a year ago when I covered this in college and I havent really looked at it since, but from memory it goes something like:",
"1) The power supply does its own test- it checks all the different components and makes sure everything is in order. Once thats done it sends a 'power good' signal to the CPU",
"2) CPU checks the various hardware to make sure everything functions right and checks if theres any DIP switches or jumper settings that need to be applied it happens here.",
"3) At this stage the individual bits hardware will do its own tests. Like some harddrives for example can do a self test and make sure there is no imminent failure about to happen.",
"4) Next it figures out where to boot from (CD/HD/USB/Network etc)",
"5) The BIOS has to go looking on the HD (or wherever) for the MBC/MBR and then find the active partition. Which finds the ntldr which then finds the boot.ini",
"6) At this point if you are dual booting, say windows and linux you will be offered the choice of which OS you want to load.",
"7) Then it starts loading the OS into RAM.",
"8) Next it goes to the Registry and looks for the hardware profile and starts loading the drivers.",
"9) Lastly it loads up winlogon which then loads up the LSASS which loads the login screen...."
] |
[
"Yup, a lot of it is just copying everything the operating system needs into the RAM, which is why replacing your Hard Drive with an SSD can bring startup time down from over a minute to around 15 seconds. "
] |
[
"How does digital information degrade or become corrupted?"
] |
[
false
] | null |
[
"A very vague question, but here is one example: A digital signal is a stream of 1s and 0s. So if you want to send a digital signal over a wire you must use low and high voltages to represent the signal. But as the cable becomes longer and longer, the differences between the low and high voltages become less. This is because of electrical resistance in the cable as well as noise and interference which can alter the signal. Eventually there is a point where the receiver will not be able to distinguish whether a voltage is supposed to be a 1 or 0 and then you have a signal corruption. ",
"To add to this, digital signals do not really 'degrade' as most signals are error checked, meaning that the receiver or reader of the information can detect if some of the data has been altered, and treat the data as corrupted (and ask for it to be re sent)"
] |
[
"To add to this: most digital media storage and transfer formats have extra data embedded in them that allows a limited number of bit failures to be corrected ",
".",
"This is why (small) scratches in a CD surface have no effect on the audio quality; the effect of these errors can literally be calculated away perfectly. Up to a point, at which point digital media tends to fail quite noticeably. This contrasts nicely with analog media, that exhibit ",
".",
"OP may be interested to read the ",
"Wikipedia article on error correcting codes",
" to see how perfect error correction is achieved in digital media."
] |
[
"It mostly has to do with the storage medium. Hard drives, SSD's, DVD's, etc have a very small life span. The problem is that in a lot of cases, if a segment of the file goes missing for some reason, the rest of the file is typically unreadable. This can happen because of the storage medium, but it can also happen because of something that might have happened during writing or reading. This is one reason we shouldn't just unplug our external drives without unmounting or \"safely removing\" them or by not shutting down our computers properly. If there is any activity on the drives when you pull the plug like that, you risk leaving a file that ends abruptly or even causing physical harm to the disk itself.",
"Quick tidbit:",
"I work in film preservation. We preserve both on physical film and digital mediums. The digital mediums fail so often that archives that use them have to be constantly backing them up and swapping out drives, while the film mediums just sit there and last a thousand years with little to no maintenance."
] |
[
"[Physics] Why do charges flow from positive to negative?"
] |
[
false
] | null |
[
"They don't. Or rather: the abstract definition of charge flowing from the positive electrode to the negative is inaccurate.",
"In reality, a current can consist of a various species of particles: electrons, positive ions, negative ions. Since electrons are by far the lightest, in most situations the current is mostly determined by the flow of electrons. In a regular metal wire, the ions are part of the metal and are thus fixed, while electrons can move freely, but from negative to positive, opposite to the direction of the reference current. However, in a semiconductor material, current is carried by both positive and negative charges.",
"The convention that current flows from positive to negative is an arbitrary choice. You could easily define it the other way around and nothing would change. For historical reasons, we use positive-to-negative and while in many cases the dominant flow of charge carriers is in the opposite direction, it's not really worth the hassle to change the definition."
] |
[
"Thank you so much man. Your explanation agreed to ",
"this",
". I just wanted to find out if this was still accurate since it's not recent. "
] |
[
"Yep, it's just an arbitrary choice that was made long ago that we stick with.",
"Similar to rotational motion having \"counter-clockwise\" as the positive direction. I believe that was also 100% arbitrarily chosen."
] |
[
"What is the world's strongest acid?"
] |
[
false
] |
I've come to learn that there is no such thing as the "strongest" acid. But what acid is generally considered more powerful than the other well-known acids, for example sulphuric acid?
|
[
"Perhaps ",
"superacids",
" interest you?"
] |
[
"The strongest known acid (according to the chemical definition) is ",
"fluoroantimonic acid",
", with a pKa of -25."
] |
[
"I have a feeling by \"strongest\" you mean \"most corrosive\" rather than \"dissociates the most hydrogen ions.\" It depends what you're dissolving. If you're trying to dissolve organic material, then piranha (a mixture of sulfuric acid and hydrogen peroxide) is up there. If you want to dissolve metals like gold, then aqua regia (a mixture of hydrochloric and nitric acid) is the tool of choice, and if you want to dissolve glass then hydrofluoric acid does the trick.",
"Hydrofluoric acid will probably kill you before piranha even if it doesn't dissolve as fast, because the fluorine gets into your bloodstream and you die.",
"I'm not a chemist, but my research involves methods of etching materials using clean-room procedures which generally involve the above mentioned acids."
] |
[
"The Kepler Space Telescope is discovers planets when their orbit crosses the light of the star. Doesn't this limit our discovery of planets to planets with short orbit periods?"
] |
[
false
] |
[deleted]
|
[
"Yes it does. It also limits us to planets whose orbits are angled towards us. It's remarkable that it still detects so many planets, which hints at how common planets are.",
"Clarification: I'm just talking about Kepler, not every exoplanet search method."
] |
[
"Here's the ",
"Kepler planet candidate period distribution",
" as of right now.",
"Notice how the number of planets drops off toward periods of 100+ days. This is because",
"It's less likely a planet that far away is going to pass directly between the Kepler telescope and its star to block the light. So even if there were equal amounts at 100 days as at 10 days, we'd expect to see ~5x fewer of the 100 day planets transit just because of geometry.",
"It's harder to find planets with 100+ day periods. Kepler only operated for 1400 days. Finding planets with less than 10 transits limits you to only the deeper ones. The more transits you have, the more you can dig into the noise and find smaller planets.",
"Edit: These two effects combine to tell you why no one from the Kepler team has announced the confirmation of a 1 Earth-radius planet in a 1 year period around a Sun-like star yet EVEN THOUGH all the studies seem to be saying there are probably a handful of them transiting in the Kepler data set. I'd be willing to bet it will happen, but it's going to take a lot of work digging into the data and proving you're actually seeing a real signal."
] |
[
"And that's not to mention that it was only looking at a sliver of our galaxy.",
"http://en.wikipedia.org/wiki/Kepler_(spacecraft)#mediaviewer/File:LombergA1024.jpg"
] |
[
"Since gravitational waves are real, does that mean all gravitational orbits are decaying?"
] |
[
false
] |
As the waves would use up energy
|
[
"Yes. Even for a simple binary system like the Earth-Sun system, gravitational waves are constantly being produced. The reason is that such orbits cause a change in the so-called ",
"quadrupole moment",
" of the total mass distribution of the system. This change is the key requirement for shooting off gravitational waves. And yes, you are right, if the system is losing energy in this way, then the ",
"orbits will decay over time",
". In fact, this exact effect provided one of the earliest bits of indirect evidence for gravitational waves. When astronomers looked at a certain ",
"pulsar-neutron star binary",
", they saw that the period of the pulses was changing in a systematic way. The best explanation for this change is that the binary was experiencing orbital decay by losing energy through gravitational waves. ",
"Now, it's worth pointing out that in most cases this effect is very, ",
" weak. For example the Sun-Earth system loses about 200W due to gravitational waves. This is roughly the power of a couple of old incandescent light bulbs, which as you might guess is nothing on an astronomical scale. This energy loss causes the orbit to shrink by a measly 1*10",
"m per day, or about the size of an atomic nucleus. If you waited for the Earth and Sun to ",
"spiral inwards through this process",
" and crash together, you would have to wait more than 10",
" times the age of the current universe! "
] |
[
"If you waited for the Earth and Sun to spiral inwards through this process and crash together, you would have to wait more than 1013 times the age of the current universe! ",
"And obviously that's ignoring other effects, such as the Sun losing mass and the Earth's orbit therefore moving outwards."
] |
[
"I just added that in, it would take about 10",
" years, which is roughly 10",
" times the current age of the universe. Needless to say, we are at least safe on this front :D. "
] |
[
"Would it be possible to create a spacesuit or device that could help astronauts resist Io's intense radiation environment so a manned mission to this exotic and amazing world would be possible?"
] |
[
false
] |
Granted its an inhospitable hellhole, probably even more so than Venus, but its such a beautiful, dynamic, and bizarre world, one would just love to get a glimpse of what it looks like to walk around on that surface. Will the radiation, however, make this a total pipe dream or will we ever devise a method to shield ourselves from the torrent of high energy particles?
|
[
"You're right to assume that radiation can be tricky. If you walked unprotected on the Jovian moons you'd absorb a lethal dose of radiation in a matter of hours, develop radiation sickness and probably die a few days later.",
"But whether we can protect you from that is a bit harder to answer. We have two main aspects to consider:",
"Unlike Earth's, which has an inner radiation belt with protons and an outer one with electrons, Jupiter's radiation belts are mixed. Electrons are generally easy to shield, even at energies of 100s of MeV they won't penetrate very deep. But protons can traverse suits and thin spacecraft walls even at just 10 MeV.",
"Io is in a favorable position in the middle of the two proton belts, where the flux of protons is reduced to a minimum. Still, if the data I have is correct, the dose could still be high enough to be lethal. There's a significant flux of >15MeV protons in the order of 10",
" particles per cm",
" and per second.",
"Shielding a spacecraft against protons of 10s of MeV is feasible. The ISS is shielded against them in fact. As the energies of particles increase, the flux decreases significantly, and when you reach the territory of >100 MeV protons, which are too energetic to shield against, fortunately the flux on IO is orders of magnitude lower.",
"So I can answer yes to your question if you accept exploring Io inside a vehicle (which could be a surface vehicle with wheels, just make sure you don't drive close to any volcanoes). You'd be protected against electrons of all energies and against protons in the order of 10s of MeV. You'd still receive a low dose of radiation from protons of >100 MeV, but I can let you go as long as you don't stay there for long (few hours, a day at most).",
"But a suit, shielding against protons of such energies, would be too thick and probably too heavy. Lower gravity helps, but still, I doubt you'd be able to walk with that.",
"I like the fact that your question allows me to be open minded as you said \"device\". Then we can get into the field of technologies under development and discuss ",
", which basically means a magnetic field. Since we're talking about relatively low energies, the magnetic field that would be required to protect you isn't that strong. Little concern for human health, though the effects aren't thoroughly studied, and little concern that superconductor coils will produce crushing forces on each other. You could carry it like on a cart with wheels, you'd be safe as long as you stay next to it. And then you'd be able to walk just with a spacesuit.",
"But the biggest concern would be ",
" in the first place. Galactic Cosmic Rays have very high energies, the spectrum peaks at 300 MeV but is still significant at >1GeV. They can't produce a lethal dose due to the low flux, but they can cause a cancer. On Io you'd be relatively protected by Jupiter's strong magnetosphere, but during your trip in deep space you'd be fully exposed. We cannot realistically shield against them, the shield would have to be too thick and massive to be launched with any realistic budget. The fact that the trip is so long makes things worse - getting to Mars is already hard enough, getting to Jupiter I dare to say it's just unfeasible. And active radiation shields would have the concerns I raised above, unknown effects on human health as they are so strong an probably crushing forces on the spacecraft structure. GCR are still an open problem in human space exploration."
] |
[
"Enough shielding for Jupiter's radiation? Sure.",
"Enough shielding for GCR? No, not even nearly enough.",
"But anyway the point of my comment was \"too thick and massive to be launched with any realistic budget\". If you do the math, shielding the equivalent volume of 1 ISS module would be more massive than the entire ISS. Now if you're talking about an interplanetary spacecraft, not only you need all that mass for the shield, but also a lot of propellant to move that mass into another planet. Not realistic in terms of launch costs."
] |
[
"For low level radiation, low enough to not cause acute radiation sickness, the solution could just as well come from medicine as from physics. If cancers can be easily treated in future getting one will be no big deal.",
"Of course such a cancer treatment is far from easy to develop."
] |
[
"Does a person with XYY syndrome require both Y chromosomes to contain affected genes to have a Y-Linked recessive condition?"
] |
[
false
] | null |
[
"To my knowledge, there are no Y-linked recessive diseases."
] |
[
"Dominance and recessive requires the assumption that the person inherits one copy of a gene from each of their parents. In the case of the Y chromosome, if a person inherits a Y chromosome, it is always from the father. If the person happens to inherit two Y chromosomes, it is due to nondisjunction during meiosis in the father, and so both Y chromosomes will be identical. As such, it is impossible to determine whether or not a Y-linked disease is dominant or recessive because there is only ever going to be the same one Y chromosome. This is unlike the X chromosome, where a female can inherit one from each parent. ",
"Edit: This is ignoring the potential for epigentic modification of the genes on the Y chromosome, which could potentially lead to differences in gene expression, regulation, etc."
] |
[
"Is that because there aren't any, or because they don't need to figure that out? It could well be that there is a recessive Y-linked disease, but since (allmost) every male has 1 Y chromosome it may seem like they're all dominant and therefore noone has ever researched it. It could also be because no male with XYY syndrome ever had a Y-linked disease, but that could be coïncidences. I'm actually pretty curious about this now."
] |
[
"Question About Genetic Modification In Human Fetuses"
] |
[
false
] |
I've been asked to do a basic science based lecture based on genetic modifications. I'm having some trouble finding specific answers. Has this been done successfully yet, and to what extent? How do they go about doing it, as in a basic step by step process? What laws (in the UK or US) are in place about this? What are the risks? Many thanks
|
[
"Try \"gene therapy\" there have been a few attempts in infants for diseases such as severe combined immune deficiency. It's very preliminary and there are many ethical and practical issues. "
] |
[
"I'm almost certain that this is not being done in human fetuses.",
"Gene therapy stumbled a bit after initial success with treating SCID [1] with a later consequence of blood cancer. SCID is an immune disease in which an important gene is totally non-functional, so in these trials the researchers removed marrow from the patients, infected the cells with a retrovirus that contained a functional copy of the important gene, and put the marrow back.",
"That idea is still what gene therapy can do, but now we have better tools (in trials). Retroviruses (HIV is an example) were initially used because they efficiently add DNA to a host genome and cells taken from a human body don't do well for very long. So whatever we do has to be fast. The problem is that retroviruses stick their DNA randomly (though not uniformly randomly [3]) into the host genome. Add to that the fact that millions of cells are infected at a time, each cell ending up with the virus landing in a different part of the genome. And so the chances are not too shabby that the virus will land close to genes that promote cell growth and division. This is what happened in the SCID cases mentioned above. The virus landed in front of and then turned on \"oncogenes\" that, when activated inappropriately, allow cells to replicate unchecked. And so many of the children ended up developing cancer (though they were cured of SCID).",
"These days people are trying thinks like Zinc Finger Nucleases and TALENS that can be engineered in the lab and targeted to specific spots in the genome. These have the additional benefit that, not only can you add genetic material (like with retroviruses) but you can also edit the genome directly. These things are in various clinical trials around the world. The main problem now is getting those modifying reagents into the target cells. It is a very hard problem (for reasons I won't go into since this is already super long).",
"In direct answer to your questions:",
"(1) It has been done successfully, though mostly in animal models (mice, zebrafish, cattle).",
"(2) (This is simplified tremendously) With retroviruses, the virus is modified to have some of its genes replaced with whatever you want to add to the target genome. Virus is then made in one set of cells, harvested, and used to treat other cells. That virus then inserts its genome (and your gene along with it) into the target cells' genomes, and those target cells can be somehow put back into a patient. With targeted (e.g. ZFNs and TALENS) approaches, a series of proteins have to be engineered to bind specifically to one spot in the genome and cut the DNA there. Then those proteins have be somehow put into the cell (there are many ways, and this step is the biggest hurdle). Finally the cells need be put back into the patient (unless you somehow find a way to get the ZFNs to the cells within the patient, which is the eventual goal).",
"(3) No idea, but the technology is outpacing the law so probably there isn't much.",
"(4) The risks are: off-target integrations (like in the SCID case), that cells taken out of the body will have change in undesirable ways before being put back, and that we might not understand the biology enough to predict consequences of any particular change to the genome. In principle the targeted approach is very safe, it's just that we don't know how to get the reagents to target cells in the human body.",
"Hope that helps!",
"[1] ",
"http://www.ncbi.nlm.nih.gov/pubmed/10784449",
"[2] ",
"http://www.ncbi.nlm.nih.gov/pubmed/12529469",
"[3] ",
"http://www.ncbi.nlm.nih.gov/pubmed/20864581"
] |
[
"i did a research paper on SCID. i think the therapy adds 2 years with almost 75 % survival, but after 10 years it drops to about 33% survival"
] |
[
"Why do we shake when we're nervous or scared?"
] |
[
false
] | null |
[
"While I appreciate everything paramedics do (they are a vital and necessary part of the medical system) I feel compelled to point out the following about this response:",
"Paramedics are not Doctors",
"Paramedics are not scientists",
"The article does not provide links to actual science",
"The article is anectode heavy"
] |
[
"adrenaline",
"http://www.emergencymedicalparamedic.com/hand-tremors/"
] |
[
"Yes it is anecdotal, no paramedics are not doctors, no they are not scientists. Still, it gives an example of what you would be experiencing with your hands shaking.",
"The answer is still adrenaline. It doesn't require hard science showing how the brain triggers the release, etc. etc. There is no point in using $5 words to answer a $2 question.",
"I would argue that an experienced paramedic, soldier, or police officer could give a much better account of how adrenaline causes your hands to shake than a scientist."
] |
[
"If the sun were to disappear right now, how would the planets arrange themselves ? Will we obtain some funky configuration where the planets orbit Jupiter and Saturn or will the planets simply be flung out into space ?"
] |
[
false
] |
[deleted]
|
[
"If the sun were to disappear right now, all the planets would fling off of their orbit in a manner roughly similar to the shape of the letter J (without the serif at the top). There might be slight deviation from the pull of other planets but it would be virtually insignificant. Collision would be possible but unlikely - imagine shooting an earth-sized bullet at jupiter; it's an incredibly small window only slightly aided by their pull to one another, and compensating for the other planet's current trajectory leaves us with an even less likely chance for collision.",
"tl;dr No, we'd fling off into space, with very little chance of collision."
] |
[
"By a larger factor, most of the mass of the solar system is in the Sun. Without the Sun, the planets would basically just keep going in straight lines, with only tiny deviations due to each other's gravity. If two planets happen to cross very close to each other, then they'll have a stronger deflection, but most likely the planets will completely miss each other and just drift off around the galaxy."
] |
[
"you could always buy the game Universe Sandbox off steam, take out the sun and find out yourself in a realtime simulation."
] |
[
"By what process do we increase neuron activity through attention?"
] |
[
false
] |
When we "pay attention" to an area in our visual field, the neurons fire more rapidly and the surrounding off center neurons are somewhat stifled. Through what process does this happen? Is there an originating signal that comes from somewhere?
|
[
"Attending to a given area in our visual field is more evident in areas V4 and FEF, in the latest studies at least ",
"(Georgia et al 2009)",
".",
"V1 neurons fire more rapidly in response to input from the Lateral Geniculate Nucleus, which in turn receives input from the retina; this is simply because you are actually visualizing something.",
"The higher order rapid firing occurs first in the FEF and then in V4. What we speculate here is that the subject \"decides\" to pay attention and the prefrontal cortex signals FEF to look at a given area. The oscillations between FEF and V4 then synchronize slightly out of phase (out of phase enough to accommodate for the time needed for synaptic transmission from one area to the other).",
"What happens is trough of these synchronized oscillations seem to correlate with increased firing rates associated with the visual stimuli being attending to; so we hypothesize that the attenuation is priming these areas of the brain for more clean, consistent, regularly spaced input.",
"more sources: ",
"Fries et al 2008",
" and ",
"Han et al 2009"
] |
[
"It seems biased because that's the sensory modality that we know the most about, so the other senses just haven't been experimented with in as much depth. There have been some experiments that have touched upon audition that suggest the patterns of oscillations may translate well to other sensory modalities.",
"EDIT: Source: ",
"(P. Lakatos et a 2008)"
] |
[
"A lot of this literature seems to be biased towards the visual sense. Do similar processes occur when you pay attention to an auditory or olfactory cue? Is it the same top-down regions effecting increased firing rates?"
] |
[
"What is real world example of a fourth order control system?"
] |
[
false
] |
In my Mechatronics class, we're going over some basic control systems and we were given examples of first, second, and third order control systems. We were told that a Cruise control is a good first order example, a Spring-mass damper is a good second, and a PID controller is an example of a third order control system. Are there any real world examples of a Fourth Order control system? or any system for that matter? Side note: Our final project is a line follower, for which I have implemented a pretty successful PID controller. Would it be improved by adding higher orders of control? (ie Second derivative, second integral etc.)
|
[
"I didn't know off-hand of any applications but a quick Google search found that it is frequently of concern in robotics and mechatronics with respect to motion and vibration control. Conceptually, if you have mass-spring-damper (or even just mass-spring) systems connected to each other in series, you will end up with higher order equations to work with."
] |
[
"Because you're forgetting the mass term in the total force equation. Spring force is proportional to displacement, damper force is proportional to velocity, and mass force is proportional to acceleration, which is second derivative, thus second order."
] |
[
"When talking about \"order\" as the OP means it, it's only referring to the order of the equation that you're working with, not necessarily what you're trying to control. You can end up with a fourth order equation by having two mass-spring-damper systems connected in series.",
"To put it another way, it doesn't make sense to think of the system order in terms of \"controlling displacement,\" because by controlling displacement, you're also controlling velocity, acceleration, etc."
] |
[
"Could you Skype at Relativistic Velocities?"
] |
[
false
] |
If I'm on a ship traveling at relativistic velocities and I attempt to Skype with someone back on Earth (assuming Wi-Fi reached that far and the receivers were tuned to account for the red/blueshift), what would it look like to the people on either end? If they could connect, would either one be able to notice the time dilation?
|
[
"As long as the ship is traveling at velocities below the speed of light (c), communication is possible.",
"But as the velocity increases, all communication signals get shifted towards longer wavelengths. This means that the \"bandwidth\" of the signal decreases, and you can't pass as much information through it as before. It's like having an internet connection that gets slower and slower.",
"At the speed of light, communication with the ship flying away from you is obviously impossible, and the bandwidth becomes zero.",
"Both parties will observe that the time on the other end runs more slowly.This will be independent of whether they are moving towards each other or away from each other, or even past each other.",
"However, there will also be a Doppler effect on top of it that will slow the stream down when the ship is flying away, and will speed things up when it is flying towards the Earth. You can only calculate time dilation after you make corrections for the Doppler effect.",
"Also, as the ship gets further and further away, there will be large delays between the time you say something and the time you hear their response. Even trying to talk to someone on the Moon is hard, because you need to wait for two seconds to hear back from them."
] |
[
"Accelerations are indeed the key here. If you fly very fast to Alpha Centauri and back, you will be younger than your twin that stayed on Earth.",
"If you fly to A. Centauri and stay there, you will be younger than your twin because you were the one who experienced the acceleration. If he flies to join you later, you will both be the same age again (provided he flies at the same speed as you)."
] |
[
"Both parties will observe that the time on the other end runs more slowly.This will be independent of whether they are moving towards each other or away from each other, or even past each other.",
"This is a consequence of special relativity. I fully understand that. Two observers who are in motion relative to each other both observe the other's clock running slow.",
"OK so why is it often said that, if I get in a rocket ship and travel away from Earth very fast, then turn around and come back, I will have aged less than people on Earth? Is it because the rocket was accelerating and the Earth was not? If so, why?",
"And let's say I accelerate to 0.5c from Earth's perspective, then I coast for a few lightyears, then I decelerate to moving back toward Earth at 0.5c, coast, and then I decelerate to land on Earth. In each of those phases, what would be my perspective of clocks on Earth?"
] |
[
"Will plasma from vaccine recipients be as effective of a therapeutic as plasma from those previously-infected?"
] |
[
false
] |
I’ve heard (anecdotally) that giving critical patients plasma from someone who has recovered from COVID-19 seems to be a very helpful treatment. Presumably, this plasma is in short supply. Should vaccine-recipients be similarly encouraged to donate plasma? Would the plasma from the vaccinated be as effective or more effective of a treatment?
|
[
"Convalescent plasma, though it has been talked up a lot, really hasn't shown efficacy in randomized clinical trials. Here is a large one published recently in ",
"NEJM",
".",
"No significant differences were observed in clinical status or overall mortality between patients treated with convalescent plasma and those who received placebo. ",
"Additional RCTs also have not shown a statistically significant benefit of covalescent plasma: ",
"JAMA",
" (this one was quite small) and ",
"medRxiv (preprint)"
] |
[
"Thanks. Those studies seem to be pretty conclusive thus far. Anecdotally, I know two people who turned a corner after receiving convalescent plasma, but I acknowledge that doesn’t override real studies in the topic. I’m surprised to see it having such poor outcomes given what I thought I knew."
] |
[
"I would note that the immune reaction after a vaccine - even different types of vaccine - is different to the immune reaction after infection. The actual virus is trying to hide from our immune system, while the vaccines we're using are actively trying to agitate our immune system. Especially the RNA vaccines which are being developed - they're engineered to activate the immune system. Thus plasma from vaccinated individuals may behave differently to blood from recovered patients."
] |
[
"Why are there two individual hybrids between horses and donkeys?"
] |
[
false
] |
Mules are from a male donkey and a female horse. Hinnies are from a female donkey and a male horse. If either are still the offspring between a horse and a donkey, why is there a difference? (Same question applies to Ligers and Tigons)
|
[
"Sperm and eggs aren't created equal. In addition to DNA there are many cellular factors transmitted from ova to offspring. This results in differences in the new hybrids based on what the mother species was. "
] |
[
"they aren't all sterile, most are though. or more like, its harder for them to conceive due to chromosome issues. "
] |
[
"Ligers and Tigons",
"This has some sexy tangential biology to it. ",
"Male ligers are the largest living cats.Two factors play in here through imprinting (explained beautifully above) and another effect.",
"Maternal size impacts offspring birth weight impressively. A comfier womb with less restrictions lets a fetal cat grow larger. So it makes a lot of sense for the tiger-mothered offspring to be larger.",
"Male lions are dramatically bigger than females and this seems to be because of genomic imprinting from the lion's sperm. ",
"So a male liger is doubly huge: it is big because the maternal womb permits greater growth and big because the paternal genome directs the body to grow like crazy."
] |
[
"What, other than their intended use, are the differences between a CPU and a GPU?"
] |
[
false
] |
I've often read that with graphic cards, it is a lot easier to decrypt passwords. Physics simulation is also apparently easier on a gpu than on a cpu. I've tried googling the subject, but I only find articles explaining how to use a GPU for various tasks, or explaining the GPU/CPU difference in way too technical terms for me. Could anyone explain to me like I'm five what the technical differences actually are; why is a GPU better suited to do graphics and decryption, and what is a CPU actually better at? (I.e. why do we use CPUs at all?)
|
[
"They differ greatly in architecture. In the context of CUDA (NVIDIA's GPU programming offering) the GPU runs a single program (the kernel) many times over a dataset and a great many of those copies execute at the same time in parallel. You can have dozens of threads of execution all happening simultaneously.",
"Basically, if you can phrase your problem in such a way that you can have a single program that runs over a range of input and the individual problems can be considered independently a GPU-based implementation will rip through it orders of magnitude faster than a CPU can because you can run a whole bunch of them at once.*",
"It's not the the GPU is intrinsically better than a CPU at graphics or cryptographic maths; it's all about getting dozens and dozens of operations all happening at once whereas a classic single-core CPU has to take them one at a time. This gets tricky when you start talking about advanced computational techniques that may swing the problem back towards favoring a CPU if you need a large amount of cross-talk between the individual runs of the program but that's something you'd have to grab a few books on GPU-based software development to get into.",
"*: I should note that this kind of \"do the same thing a million times over a dataset\" is ",
" what games do when they implement a graphics rendering solution. Programs called shaders are run on each pixel (or subset thereof) and they all run independently at the same time to complete the task in the allotted time. If you're running a game at 1024x768 that's 786432 pixels and 786432 instances of the program have to run in (assuming 30fps) less than 1/30th of a second! A single-threaded CPU simply can't compete against dedicated hardware with the ability to run that kind of program in parallel."
] |
[
"(or are there extra cores?) ",
"They aren't 'cores' as you'd traditionally think of them, but they act the same. You can think of it like a whole bunch of cores all packed together and sharing some hardware but having to execute the same program on different bits of memory. You can't branch off into different programs or functions as a traditional CPU can. Many such concessions were made in the name of simplifying hardware development and maximizing performance and just wouldn't fly on a commercial CPU.",
"Also, why isn't the same architecture used for CPUs?",
"Most programs can't take advantage of the kinds of capabilities a GPU-like CPU would offer and it'd end up largely being dead weight. Because the 'cores' of the GPU are bound together into tight groupings that all have to do the same thing trying to execute normal code has massive performance implications.",
"The CPU and GPU are just meant for two different kinds of problems. Companies have been trying to shoehorn GPU-like structures into a CPU for years but never quite make it in the consumer space."
] |
[
"As a crude analogy, compare a very small team of highly skilled employees against a large group of minimum wage temps. ",
"Certain tasks are done much better by the skilled team with more access to company resources and who know how to best approach the problem and to prepare so that no one is idle because a detail isn't ready yet. This guys are the CPU equivalent. They are easier to give tasks to (program) and can carry out the task in a smart sequence without being told (instruction reordering).",
"On the other hand if your task is easy to express in a checklist, the sheer manpower of all the temps can get certain work done fast. These are the GPU. These temps are not given the best tools and may work slower. They also have little freedom when there is a bottleneck (certain machines are occupied).",
"The tradeoff becomes how you spend the fixed budget (silicon area). One answer is to pick one focus but only end up able to compete on certain bids.",
"If you have a managerial genius or just a simply an easy to explain task, the team of temps can get things done faster or with a smaller budget."
] |
[
"Why are song tunes much more easily remembered than the lyrics?"
] |
[
false
] |
It's always easier to recall a tune than the lyrics to that tune, and I find this intriguing as words can be paired with physical objects and experiences, unlike notes.
|
[
"While those assumptions may not apply to everyone and my answer may not be as 'sciency' but the instrumentals to music with lyrics are extremely repetitive, more so than any of the lyrics. Try playing a more classical song in your head and see if you can make it through the entire thing, I think you'll find words are easier to remember correctly."
] |
[
"The brain is hardwired to operate on patterns. See here: ",
"https://en.wikipedia.org/wiki/Pattern_recognition_%28psychology%29",
"Your brain operates almost entirely based on patterns. Think of the way you read. You don't actually recognize the order of the letters in a word. Your brain recognizes the first and last letters, then looks at the letters in between. The brain then determines what the word is based on it's memory of what words begin and end with those letters and contain the letters in between. ",
"Music is entirely based on patterns of frequency. Music is prolific because it is entirely based on patterns. Think of a melody; the same notes played over and over again in sequence. Your brain latches onto this because this is how your brain learns. ",
"See here: ",
"http://arxiv.org/pdf/0907.4509.pdf",
"This article has some great sources as well: ",
"https://www.brainpickings.org/2012/09/04/the-ravenous-brain-daniel-bor/",
"Lyrics can contain patterns. A Chorus, for example, is a pattern. That's why it's easier to remember a chorius than a verse.",
"Mind you, I'm not a scientist or researcher, just someone who is interested in the subject."
] |
[
"Late to the party, but I'll add my two cents:",
"A lot of neuroscientists are waking up to the idea that the brain is, essentially, a prediction organ. Its main function is to extract patterns from its environment and to use these to predict what is likely to occur next.",
"Even the most simple form for learning, classical conditioning, is about prediction. A tone rings, and you receive an unpleasant shock. You learn that the tone can be used to predict the shock. You found the pattern.",
"This is also true for music. It's probably the reason why music is enjoyable at all--we enjoy cracking patterns. ",
"A lot of researchers agree on this",
". Music is interesting to us because we love being able to anticipate what comes next. Complex music is harder to predict. It takes more effort. But the experience that follows is greater for it. We want it to be slightly unpredictable. Or else it would be boring.",
"Dopamine is known as a \"pleasure chemical\". This interpretation has neuroscientists all over the world rolling their eyes. A more accurate view is that dopamine is used to predict what will happen next. Accurate predictions are satisfying. ",
" unpredictable predictions are more interesting, though. Why are jokes funny? Because we think we're able to predict what comes next, but something else comes instead. And that \"something else\" is something that ",
" have been predicted. And thus we are entertained. It's the exact same with tv-shows. And books.",
"There's something about simple melodies that makes everyone engaged. We are all familiar with what to expect. What fulfills the pattern we are presented. And so we are satisfied when we hear that chorus: we can anticipate what comes next.",
"Did you know that Outkast's \"Hey Ya\" was really disliked when it first appeared on radio? People changed the channel when that song came on. It was too unpredictable. Then something happened. An interesting strategy was used: the song was sandwiched between top hits. And so people stuck around, heard the song a few times without digging it, and then it happened. People found themselves able to predict the melody. And they loved it.",
"Lyrics are different because they aren't easily predicted. Often, musicians get around this issue by having super simple refrains. Nirvana decided before writing their spectacular hit-album Nevermind that they would have choruses that sounded almost like nursery rhymes: they were to be as simple to sing along to as possible. In In Bloom you have two verses and the chorus is repeated six times: \"He's the one, he likes all our pretty songs, and he likes to sing along,\" Cobain sings, making fun of the people he knew would love their music solely because it was catchy."
] |
[
"With many devices today using Lithium to power them, how much Li is left in the earth?"
] |
[
false
] | null |
[
"In 2015 the USGS predicted that we have over 365 years of lithium left at current production rates, and that doesn't take into account recycling. It's also with noting that there are a number of emerging battery techs that will replace lithium ion given time. ",
"https://www.greentechmedia.com/articles/read/Is-There-Enough-Lithium-to-Maintain-the-Growth-of-the-Lithium-Ion-Battery-M",
"The mining and production stats start a little ways down"
] |
[
"I'd like to add that if this works anything like oil, you're talking about proven deposits and the current possible production output. The amount of estimated resources left can change as new deposits are discovered, or even as existing sources are found to have more or less capacity than previously estimated."
] |
[
"A small but important thing that many people don't know: The resource constraint for Lithium-ion battery power is not actually the Li, but the metal used for the other electrode, which nowadays is mostly cobalt."
] |
[
"With an estimated 1,000,000 nematode species, what distinguishes them all?"
] |
[
false
] |
I was on a Wikipedia safari, and read that there are 25,000 known nematode species, and 1,000,000 estimated total species. I'm wondering what could possibly distinguish between 1,000,000 variations of a little worm. Could someone explain the minimal distinguishing characteristics of a species of nematode?
|
[
"Many of the distinctions are on the genetic level. Two worms may look the same to the unaided eye and even live in the same habitat, but be vastly different genetically and totally unable to crossbreed."
] |
[
"How do they know who to breed with and who not to breed with? Smell? Pheromones? Or is there some other way in which they can distinguish between members of the same species?"
] |
[
"Nematodes are found everywhere on the planet, literally everywhere. Each type of environment is going to require a different strategy for optimal survival. Then you have to think about how many types on environments there are. Just considering a blanket term of the ocean floor is not enough. Different depths will require different strategies as much as if a different region has a different water chemistry and the same depth.",
"What also needs to be considered is the evolutionary history. As an example, imagine that a single nematode species living on the coast of North America split so some worms began to move further north and some moved further south. Eventually, we have a species living on the equator and a species living in the arctic. They have different methods of adapting to their environment. Now imagine that fir some reason, each slowly moved to the same location somewhere in the Atlantic. They may live in the same environment now, but because they each had different \"machinery\" from their adaptations to the equator/arctic, the way they adapt to this new environment may \"repurpose\" that machinery. This leads to 2 distinct species with different strategies of survival living in the exact same place. ",
"Just apply this to the entire planet and it isn't hard to see how 1,000,000 different nematode species could exist."
] |
[
"Can Ice X or other phases of ice be stable at atmospheric pressures?"
] |
[
false
] |
[deleted]
|
[
"Phase changes are reversible. If taking ice above ~65 GPa changes it from ice VII to ice X, taking it below 65 GPa will send it right back to ice VII. It's the same way as taking water at 1 atm below 273 K and then back above 273 K. It'll freeze then melt again. There's no magic way you can have a material undergo a phase change in one direction only. ",
"That's thermodynamically speaking, though. Kinetics are a different game. This is why you can have diamonds appear to be stable at ambient conditions when graphite is the preferred state of carbon under those conditions. Whether or not the phase transition kinetics of ice X are sufficiently slow to let you heat it to 800 K without a phase change is something that Wikipedia unfortunately does not have the data for. "
] |
[
"My problem exactly, which is why I was asking honestly, some phase changes are stable, some reverse. So I basically wanted to know if ice X XI XII XV etc are stable at 1 atm :/.",
"Though looking like they might not be but do you have a source for reversibility of ice phase changes due to pressure?"
] |
[
"Your best bet would be to look up kinetic studies of condensed phase water. The source for reversibility of ice phase changes due to pressure is any thermodynamic PT diagram of water, or those found on google - thermodynamically, as ",
"/u/staus",
" said, ice X is unstable at 1 atmosphere, and will revert to the proper phase at whatever temperature the substance is held at. Whether it happens fast or not is a kinetic study. But, as far as thermodynamics is concerned, ice X is not stable at 1 atmosphere. "
] |
[
"Will a solar panel generate more electricity when moving towards the sun?"
] |
[
false
] |
For a real-world example, if the ISS's solar panels were maintaining the same angle relative to the sun while orbiting the earth would the energy collected be greater during the portion of its orbit where it moves towards the sun than when it's moving away?
|
[
"I can't give you a full answer, but there are two main effects that have to be taken into account. As the panels move towards the source, the energy of the photons gets blue-shifted, so the panels would be receiving a greater energy flux overall. However, solar panels are optimized to collect a specific frequency of light. If the light gets shifted above the optimal range, the overall energy collected could decrease."
] |
[
"Excellent answer. Ive heard this question asked before and it got out of hand before the idea of designed wavelength was mentioned that I don't know if the OP ever noticed or considered it as an important consideration. "
] |
[
"Not really, at 70 km/s the frequency would shift by like 0.02%."
] |
[
"Can you or can you not see stars out of the space station windows, or for that matter, on the surface of the moon?"
] |
[
false
] |
I answered my own question.
|
[
"You can.",
"However, stars are so faint that they don't show up in the background on most pictures from the moon/the space station, because the exposure settings are mostly set to illuminate some object(s) in the foreground."
] |
[
"I had heard an interview with Armstrong saying otherwise, but I cannot recall for certain. So if the exposure was corrected, would you see a wonderful vista, more so than the best location on earth?\nAlso, if you have any links on the subject I would be grateful. Not easy to search this on Google. Thanks."
] |
[
"Yes, you could probably see more stars from space as there are no ",
"light pollution",
" or other atmospheric noise.",
"Some links about the moon pictures and why they don't have stars in them:",
"http://en.wikipedia.org/wiki/Examination_of_Apollo_Moon_photographs#Absence_of_stars",
"http://earthobservatory.nasa.gov/blogs/earthmatters/2011/09/28/where-are-the-stars/",
"http://www.badastronomy.com/bad/tv/foxapollo.html#stars",
"About Armstrongs supposed interview:",
"http://www.clavius.org/bibsibrel.html"
] |
[
"How do scientists calculate the age of planets, stars, and galaxies?"
] |
[
false
] |
I was trying to search on Google about this, including the age of the Universe, and the sources kept saying we can tell from the age of the stars and galaxies around us. How do astronomer's figure out how old stars and galaxies are though? Also, kind of related, I also read that our Milky Way galaxy is 100,000 light years around and 1000 light years thick. How can scientist figure that out too?
|
[
"I assume you read the wikipedia entry on \"age of the universe.\" which is a good starting point. From that you should at least gather that the age is based on how fast the universe is expanding. If we know how far everything is from us, and how fast it is moving (including its accelerating) then we go backwards to figure out how much time that took for those galaxies to get there. Presto! 13.8 billion years. ",
"To add to your knowledge of how science got to that point, you might want to start with several more wikipedia entries: cepheid variable stars, type IA supernova; Shapely Curtis debate and island universe debate. ",
"By the early 1920s scientists were arguing about how large our galaxy was, and a lot of them thought our galaxy was the same as the universe. All the stars and nebulae were all inside our galaxy and maybe it is 10,000 light years across. Included in all this stuff were so called 'spiral nebula.\" Which most thought were the same as the regular nebula, e.g. Horsehead nebula, Orion nebula, Eagle nebula etc. Those are basically gas/dust clouds several thousand light years (ly) from us. ",
"But eventually Hubbel could measure the light from cepheid variable stars within those spiral nebulas that suggested they were much further away than 10,000 ly. this has to do with the island universe debate and the Shapely Curtis debate, which you can google. Hubbel and Curtis supported the idea that these spiral nebulas were really outside our galaxy. Shapely said that made no sense because they would have to be like 100 million light years away and no one believed that. And also that the nova stars inside them would have to be super bright for us to see them this far (they are that bright, they are supernovas). you can google the rest. (Shapely did figure out the position of our sun in the galaxy so he was a pretty smart guy too) ",
"Cepheid variable stars were categorized by a lady named Henrietta Swan Leavitt who worked at Harvard. she figured out that basically the longer they take to brighten and dim (the \"period\") the brighter they are. Not just how bright they look to us, but their absolute brightness or Luminosity. ",
"To figure that out she studied all the cepheids that were within the Magellanic clouds. Some sort of nebula back then but we know them as irregular galaxies, the closest galaxies to us. Because they were all in the same cloud, they were all about the same distance to us (again maybe 10,000 ly they thought). So they were all about the same distance and the bright one had longer period and the dimmer ones had shorter period. So she constructed a graph of how bright such a variable was based on how long its period was.",
"This became a kind of ruler to measure distances; say you find a Cepheid in another galaxy, and it brightens and dims every month. You look it up on the graph and you see it is supposed to be 4 candles in brightness (assuming it is the same distance as the Cepheid variables in Henriettas graph). But instead it is only 1 candle bright. It must be twice the distance as that standard, because the brightness drop as the squared value of the distance (so at twice the distance it's 1/4 the brightness). ",
"That is the basic concept in most of these yardsticks for measuring. ",
"Now eventually the shapely-Curtis debate ended by determining that these \"spiral nebulas\" were really other galaxies. They used the cepheid variables to measure the distance. Later in 1943, Walter Baade was the first to actually see a star outside our own galaxy. Hubbel had apparently picked up the light from the variable stars in Andromeda etc. 20 years earlier w/o actually seeing the star itself, as I understand it. Of course this just confirmed the theory of galaxies. ",
"Cepheid variables I think can be used up to 50 million ly; now they use the brightness of Type IA supernova to determine distances greater than that. this time they used to math to understand just what a supernova is, and what it is made of, and how bright it should be and its period or how its brightness will change over time. Then when they see one go off they measure its brightness/period and that tells how far away it is because its further away it will be dimmer. ",
"So the supernova method is a way to measure distances I think about up to 1 Billion ly. ",
"So first they figured out cepheid variables have period/luminosity relationship; they studied spiral galaxies to determine they were outside our galaxy; they used Cepheid variables to measure the local galaxies and supernova to measure the more distant ones. "
] |
[
"I'm at the University of Manchester and we use noble gases to find out how old certain rocks are such as moon rocks, mars pieces and meteorites. Noble gases tend to not react with other elements, cause they're too \"noble\", and so act as great tracers. This brought about certain dating techniques like Ar-Ar dating etc. You can also irradiate a sample that has halogens in it (Cl, Br, I) to convert them into noble gases and then analyse the noble gases that way. ",
"Edit: Thought I'd clarify that the noble gases are He, Ne, Ar, Kr etc"
] |
[
"as a follow up, here is a really good summary of the above methods as well as quite few more that have been developed in recent years. there is a good diagram at the top that summarizes all these methods and what distances they are used for. ",
"http://en.wikipedia.org/wiki/Standard_candle#Standard_candles"
] |
[
"Between Eusthenopteron and Panderichthys what happened to the anal fin?"
] |
[
false
] |
Looking at the charts of evolution of land animals the anal fin disappears between Eusthenopteron and Panderichthys. Do they become part of the pelvis? Do the bones of the anal fin simply stop being being created? Some combination or do they change in some other way all together?
|
[
"The dorsal and anal fins are unpaired fins, and form separately from the pelvic girdle from which the paired pelvic fins are attached. In the Elpistostegalia, the dorsal and anal fin are lost and don’t reappear in any later tetrapods. The tail (caudal) fin is retained in some forms, and still observed in some larval amphibians. The loss of the unpaired fins was a developmental (genetic) event during the evolution of the lineage."
] |
[
"Seconding what meat_popsicle13 said. Just in general, midline fins like the anal and dorsal seem to be more labile than the paired fins. There are widespread losses, gains, and subdivisions of the dorsal(s) in particular, but the anal is also lost in all kinds of lineages, even some sharks. It's probably easier to switch the midline fins off, developmentally speaking, because they don't have as many attachments to other elements as the pectoral and pelvic girdles."
] |
[
"Depends on what you mean by homologous. All fins, both paired and unpaired, share a “deep homology”, meaning they share a set of conserve genetic and developmental mechanisms that regulate their formation. This deep homology may be “redeployed” as appendages reappear in lineages."
] |
[
"Can petroleum extraction cause tremors/earthquakes?"
] |
[
false
] |
Petroleum is being extracted from the subsoil and years of continuous extraction could leave the cavity where petroleum used to be empty. Could this cause the ground above the cavity to collapse, possibly leading to a tremor/earthquake?
|
[
"Let's break your question up a bit, first:",
"Petroleum is being extracted from the subsoil and years of continuous extraction could leave the cavity where petroleum used to be empty. Could this cause the ground above the cavity to collapse",
"There are some misconceptions about the nature of oil/gas deposits embedded here, I'll refer you to my ",
"answer to a related question",
", but here is the most relevant bit from this post:",
"There are not large chasms filled with oil/gas (or groundwater) that we tap into when we extract these resources. A much better visual is wet sand, i.e. the oil or water we extract occupies spaces between grains within the reservoir rock, this is why 'porosity' (amount of space between grains) and 'permeability' (how connected those spaces are to each other) are extremely important for reservoir rocks. So what happens when we extract oil/gas or water from a reservoir rock? Well, what we call the 'pore fluid pressure' decreases (basically the force exerted on the grains by the presence of a fluid between them that is trapped) as the material filling the pores is extracted. This can lead to compaction (i.e. a decrease in porosity), which causes a bulk volume reduction (i.e. density increases), which means the ground surface lowers (i.e. subsidence).",
"So, what you can and do get in areas of oil extraction is a lowering of the land surface, but not via collapse.",
"Now for the more general question:",
"Can petroleum extraction cause tremors/earthquakes?",
"Yes, and we typically refer to that as ",
"induced seismicity",
" (though as you can see in that link, oil / gas extraction is not the only cause of induced seismicity). Generally, induced seismicity results because some human activity changes the state of stress in a region in such a way that a fault that previously did not have enough stress (or enough stress in the right orientation) on it to fail, now does. At present, the most common (or at least most discussed) form of induced seismicity related to oil and gas production comes from the injection of waste water. ",
"The USGS",
" has a nice set of resources discussing the induced seismicity problem within the central US.",
"Returning back to the problem of subsidence (land lowering) caused by reservoir compaction after extraction of oil/gas (or groundwater), this also can change the state of stress in the local area and thus also induce seismicity. It's a little harder to find discussions of this, but ",
"this paper (pdf)",
" documents induced seismicity in the Netherlands that seems to be driven by differential compaction of the reservoir after petroleum extraction. To emphasize though, the earthquakes here are being caused by changes in the stress field as different areas compact more or less, not via catastrophic collapse of large voids."
] |
[
"I don't know if followup questions are allowed, but I'll try... Can the induced seismic activity be compared (in gravity, frequency and consequences) to the normal seismic activity? Is there any basis for fear mongering about oil and/or gas extraction through \"fracking\"?"
] |
[
"First off, most of the worries regarding induced seismicity are not from fracking, but rather waste water injection (you end up with large amounts of waste water whether you've fracked or not, it's more about the local geology than the technique). In the case of Oklahoma, a lot of the wastewater that's being injected is produced in wells that are being fracked, but these regions have a lot of 'formation water' i.e. fluids along with oil and gas, so the fracking has little to do with the waste water. ",
"With that out of the way, it really depends on what you mean by 'normal seismic activity'. The earthquakes generally produced in induced seismicity are small (lots of magnitude 2's and 3's) and frequent. Largest ones are in the mid to low 5's. Comparing rates of seismicity pre and during periods of injection in places like Oklohama pretty clearly indicate that the increase in occurrence of earthquakes is ",
"substantial to say the least (check out the graph)",
". Now, this rate of low magnitude earthquakes and occasional 5's wouldn't really be problematic in a place where buildings, infrastructure, etc were designed for it (e.g. California), but a magnitude 5 in a place with little to no thought in building design given to earthquake shaking (e.g. Oklahoma) is not great. Another worrisome aspect is that we don't necessarily have an idea of what the upper bounds on potential induced earthquakes are, will depend on nature of faults in the region, background stress state, and how the injection changes the stress state (all things that are pretty challenging to measure). So I wouldn't characterize it as 'fear mongering about oil and/or gas extraction through \"fracking\"', I'd say it's realistic concern about the potential implications of massive amounts of waste water injection and seismic ramifications of that in a place without the infrastructural preparation for earthquakes."
] |
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