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[
"Why was I told to decelerate before turns and accelerate through turns?"
] |
[
false
] |
[deleted]
|
[
"Come on Mr engineer!! You don't remember any of your physics courses? :P",
"But seriously, its simply centripetal force. Fc = m*v",
"/r. The centripetal force is directed outwards from the circle that you would make if you continued turning. This outwards force could flip the car over or cause it to lose traction."
] |
[
"In line with the question itself, most driving instructors will tell you to decelerate ",
" the turn, not decelerate during the turn until you hit the midpoint."
] |
[
"You want to transfer weight on a motorcycle too. For one thing, the rear tire usually has a much bigger contact patch (it's thicker), so you want most weight on it. For another, slight acceleration in a turn will place both suspensions at middle point, i.e. at optimum point to provide stability."
] |
[
"when asteroids/comets pass near the earth, why don't we send stuff over for science?"
] |
[
false
] | null |
[
"Pretty much, everything we have in space is in some kind of orbit. Of course, satellites orbiting the Earth are in orbit (which is obvious), but even when we send satellites (or people) to the Moon (or Mars) they are still in orbit- an orbit called a transfer orbit. They are only under powered flight for a short time, and that powered flight puts them into an orbit they want to be in. ",
"So even if the comet is close to Earth, it still takes a bunch of energy to observe it, because the satellite still has to get into the same orbit as the comet. If it wasn't in the same orbit as the comet, and instead just tried to intercept the comet, the comet would only be nearby for a couple of seconds before zooming by. And regardless of how close the comet is to Earth, it still takes about the same amount of energy to get into the comet's orbit. "
] |
[
"Because being near the earth don't make it significantly easier to land stuff there. ",
"If we want to send payload to asteroid, we must match the orbits. It's much easier to match orbits if they are similar even if the asteroid is nowhere near the earth, than try to catch random asteroid that passes the earth 50 km/s to different direction. ",
"Nasa has already landed probe to an asteroid in 2001: ",
"https://en.wikipedia.org/wiki/NEAR_Shoemaker"
] |
[
"\"",
"Yes, this is generally correct."
] |
[
"Are there other problems like random/drunk walk and cross-product which have significantly different solutions depending on the number of dimensions?"
] |
[
false
] |
A random walk (drunkard's walk) in or dimension will 100%* at some point return to its starting point. In three or more dimensions, a random walk is not guaranteed to return to its starting point. Another example is the cross product, which is only defined in three and seven dimensions. There is no two-dimensional cross product. Are there other problems whose solutions (or lack thereof) differ dramatically depending on how many dimensions the problem has? *100% meaning " " C.f. and
|
[
"How many ways are there \"to do calculus\" on Euclidean space? For dimensions 1,2,3,5,6,7,8,9,10,11,12,... there is only one way. For four dimensions, there are infinitely many ways to do so. These are called ",
"Exotic R",
" spaces.",
"Somewhat relatedly, the ",
"Poincare Conjecture",
" (proved by Perelman) says that if a 4D object \"looks like\" a sphere, then it is a sphere. This was relatively easy to prove in every dimension, except 4D. Proving it in four dimensions was a longstanding open problem and was made one of the Millennium Prize Problems, worth $1million for a solution (which Perelman turned down). Perelman had to invent radical new math to solve this problem in four dimensions."
] |
[
"The ",
"wave equation",
" which is used to model (among other things) the propagation of sound waves behaves differently in odd and even numbers of dimensions. ",
"In odd numbered dimensions (except 1d) the wave propagates radially from a point source with a sharp wave front only supported at one point. If there were a loud bang then the sound would travel toward you, you would hear it and then it would pass you and you would not hear it anymore. ",
"In even numbered dimensions the wave propagates radially from a point source and once the wave front has caught up to you would would hear the sound. However, as the wave front passed you you could still hear the sound as the solution to the wave is supported everywhere behind the wave front. It would be noisy to live in 4 dimensions. "
] |
[
"In physics, ",
"stable orbits",
" between two bodies can only exist in three dimensions (where the force of gravity is proportional to the inverse of the square of distance).",
" ",
"In graph theory, graphs embedded into the (Euclidean) plane can always be properly colored by ",
"four colors",
". Graphs embedded into a line are always 2-colorable, but graphs embedded into 3 or more dimensions can require an arbitrarily large number of colors.",
"Perhaps related, only some graphs can be ",
"drawn in the plane",
" without any edges crossing. Meanwhile any graph can be embedded into 3D space without any crossings.",
" ",
"In geometry, in the 2D plane, there are infinitely many ",
"regular polygons",
". In 3D space, there are five ",
"platonic solids",
". In 4D, there are six ",
"regular 4-polytypes",
" (a 4D analog). In all higher dimensions, there are always exactly three ",
"regular polytypes",
".",
" ",
"[Edit] One more: The ",
"hypersphere packing",
" and ",
"kissing number",
" problems have known solutions only for 1, 2, 3, 4 (kissing number only), 8, and 24 dimensions. (Of course a solution for any number of dimensions exists, but it is not known yet.)"
] |
[
"If the farthest known object is observed as 13.1 billion light years away, how far is it really?"
] |
[
false
] |
since it is 13.1 billion light years ago as well. how far is it really? light took 13 billion years to get here, so 13.1 billion light years away 13 billion years ago.
|
[
"About 45 billion light years if the Hubble Expansion Constant has acted as currently predicted. Sorry I didn't throw that in my first answer."
] |
[
"So if space wasn't expanding a stationary (with respect to us) object that emitted a photon 10ly ago which just reached us today would be 10ly away. Since space is expanding how far away an (stationary before metric expansion) object is when a photon that it emitted reaches us after a certain amount of time depends on the expansion of the space that the photon that was emitted had to travel through. Hubble's constant is currently believed to be about 70(km/s)/Mpc so the farther something is away the faster it is moving away and the more space a photon would have to travel through even if it were moving at the speed of light."
] |
[
"understood, but how far away is the farthest object, if it appears 13.1 billion light years away?"
] |
[
"What is the covid19 mortality rate among healthcare workers?"
] |
[
false
] |
Hi redditors. Do any of you know of any official data on covid19 mortality rate of healthcare workers (by country, preferably)? I would be very interrested to learn more about this.
|
[
"I don’t know where the official data is, but it seems like mortality rate may be higher than the general public.",
"This may be due to health care workers being exposed to higher amounts of virus. The more virus you start with, the further the infection has progressed before your immune system starts to work.",
"https://keleefitness.com/why-are-so-many-young-doctors-dying-of-covid19-in-wuhan-it-may-be-because-they-are-exposed-to-a-high-viral-load-upon-infection/"
] |
[
"Thanks for the ref. Interresting that it seems like it's theoretically plausible at least, that virus load might increase mortality among healthcare workers, although some early data I have seen from wuhan seem to indicate a mortality rate equal to the healthy population"
] |
[
"I cant see any reason why it would be any different than the same age and health groups in other professions. Infection rates will likely be different, (balancing much higher exposure with higher ppe use) but mortality rates are calculated off the underlying infextions rate, so there is no reason they would vary by occupation"
] |
[
"Is there any scientific truth to the idea that you shouldn't sit too close to the TV?"
] |
[
false
] |
[deleted]
|
[
"No. However focusing on one spot for a long period of time can cause eyestrain, however that is only temporary.",
"You may find this interesting.\n",
"http://tlc.howstuffworks.com/family/tv-bad-for-eyes.htm"
] |
[
"Yes, and modern flat screen LCD and plasma TVs are much more dangerous that older ones.",
"Their higher centre of gravity and narrower base means that they can, ",
"and sometimes do",
", fall on children sitting too close."
] |
[
"Color CRTs put out EM radiation in the form of X-rays, from the electron beam slamming into the metal shadow mask. See ",
"Bremsstrahlung",
"."
] |
[
"What are the conditions for annihilation?"
] |
[
false
] |
Sadly I don't have a physics tutor to ask questions to, my understandings comes solely from self-study, so I apologise if my assumptions are incorrect or if the question seems outright stupid. I used to believe that most every-day interactions were physical. That is to say that if I push a chair, the atoms in my hand were in direct contact with those of the chair, and this caused the force when I pushed. Now however, I believe that these interactions are electrical, and that atomic and subatomic particles don't come into physical contact in such circumstances, instead the electrons in orbit about the atoms in my hand repel those in orbit about the atoms in the chair. My reason for this thought process is the Rutherford experiment and the fact that most Neutrinos can pass through large bodies (such as the Earth) with no interaction at all, presumably because they lack charge. Onto my question. I have read that annihilation occurs when a particle... Does something with its antiparticle. The phrases I've heard for that something are "interact"," collide", "come into contact with", etc. Taking the example of positrons from beta+ radiation, I've read that these annihilate almost immediately to produce gamma rays. What interaction between a positron and electron is necessary for annihilation to occur? These particles are tiny and have opposite charge, so surely it's unlikely for them to actually experience contact so quickly? Is there a certain range a particle must be within of its antiparticle to annihilate? If so, what determines this range (e.g. mass)? If not, what condition must be met for annihilation to occur?
|
[
"What interaction between a positron and electron is necessary for annihilation to occur?",
"Electron-positron annihilation is electromagnetic.",
"These particles are tiny and have opposite charge, so surely it's unlikely for them to actually experience contact so quickly?",
"They don’t have well-defined positions in space. “Contact” doesn’t really have meaning in quantum mechanics."
] |
[
"Are you saying that it's caused by an electric force then?",
"The electromagnetic force, yes.",
"Is there a specific magnitude of force that must be experienced between them then? If so, what determines this value?",
"There's no threshold energy for electron-positron annihilation to photons. It can happen if the electron and positron have zero relative kinetic energy, and that's actually where it's most likely to happen."
] |
[
"Sadly I don't have a physics tutor to ask questions to, my understandings comes solely from self-study, so I apologise if my assumptions are incorrect or if the question seems outright stupid.",
"I used to believe that most every-day interactions were physical. That is to say that if I push a chair, the atoms in my hand were in direct contact with those of the chair, and this caused the force when I pushed. Now however, I believe that these interactions are electrical, and that atomic and subatomic particles don't come into physical contact in such circumstances, instead the electrons in orbit about the atoms in my hand repel those in orbit about the atoms in the chair. My reason for this thought process is the Rutherford experiment and the fact that most Neutrinos can pass through large bodies (such as the Earth) with no interaction at all, presumably because they lack charge.",
"Since atoms aren't little hard balls there is really a lack of definability of what you call \"come into contact physically\". There's only forces keeping them apart. Surfaces are something macroscopic. ",
"Onto my question. I have read that annihilation occurs when a particle... Does something with its antiparticle. The phrases I've heard for that something are \"interact\",\" collide\", \"come into contact with\", etc.",
"How exactly they do it isn't relevant in QFT. Particles just get close and undergo some process which is allowed in the weak, strong or electromagnetic interaction. We can accurately calculate the likelihood of them interacting to give various outcomes (the cross section). ",
"Taking the example of positrons from beta+ radiation, I've read that these annihilate almost immediately to produce gamma rays. What interaction between a positron and electron is necessary for annihilation to occur?",
"The electromagnetic interaction allows for a charge and is anti particle to annihilate into a photon. If you have composite particles like protons annihilation encompasses other processes than producing photons as well. (This is also why describing annihilation as producing light from matter and anti matter isn't correct and also light isn't \"pure energy\" etc). ",
"These particles are tiny and have opposite charge, so surely it's unlikely for them to actually experience contact so quickly? Is there a certain range a particle must be within of its antiparticle to annihilate? If so, what determines this range (e.g. mass)? If not, what condition must be met for annihilation to occur?"
] |
[
"How long would it take to send an unmanned probe to Kepler-22b and for it to send observational data back."
] |
[
false
] |
and what kind message would you send. (in the assumption there may be intelligence life)
|
[
"Voyager has travelled ten billion miles in thirty years.",
"http://voyager.jpl.nasa.gov/",
"One light year is about six trillion miles, which means that for Voyager to travel one light year it would take it about twenty thousand years. Keppler 22 b is six hundred light years away, so a probe to go there would take about 12 million years."
] |
[
"Well to be fair Voyager was designed to interact with the planets not fly out of the solar system. It is conceivable that we could alter the use of gravity assisted slingshots to increase its escape velocity. But regardless, the shortest amount of time it would take would be 1200 years(600 years at light speed and then 600 years for the data to return). "
] |
[
"Perhaps another offshoot of this question would be.. how far would a man made probe have to travel to get close enough to identify radio waves or other signs of intelligent life? Can we do that from Earth or would the evidence simply be to far to detect at measurable levels?"
] |
[
"Why Do We Have Different Blood Types?"
] |
[
false
] | null |
[
"Short answer: Mutations.",
"Long answer: We consider type A blood \"normal\". The gene that encodes the glycosyltransferase enzyme (the part that differs in blood types) for B blood has 4 point-mutations compared to A (that means somewhere along our history, a cell replicated the gene with 4 mistakes).",
"So, B type blood as 4 different amino acids in the glycosyltransferase enzyme sequence than A blood.",
"O is a different type of mutation: One of the DNA base pairs is missing. The gene is one \"letter\" shorter than it should be.",
"Now, this causes a much bigger difference. Since DNA is read 3 base pairs at a time, if one is missing it pushes the entire sequence off. (Instead of cat-dog-bat-end, if G was missing you'd have cat-dob-ate-nd {terrible example, but I don't know a quick way to explain how DNA/RNA become protein})."
] |
[
"There's a theory that having a mix of blood types in a population helps with virus resistance.",
"When viruses kill a cell and burst out they often have small pieces of cell stuck to them. The viruses then go out and try to infect other people.",
"If you're blood type A and get a virus from someone with type B blood, your body can have an easier time recognizing it as an invader and mounting its defense."
] |
[
"Most mutations get corrected (and don't end up getting expressed or passed on at all), so having a significant mutation develop is somewhat rare.",
"In terms of dominance/advantage, only O is \"defective\" (and it is genetically recessive). A and B will both be expressed in people with both gene (they're functionally identical, but immune systems of A type will attack B type and vica-versa).",
"The blood types don't make a big enough difference for them to die-out (just like black hair, or ear lobes). O+ type can cause problems, if both parents are O+ (has to do with immune response, I believe. I'm not good at pregnancy topics)."
] |
[
"Is `wave function collapse' time reversible?"
] |
[
false
] |
It seems like it is not, but this is very strange to me since all of the other laws of nature are manifestly invariant under time reversal. The same is also true for the evolution of a quantum mechanical system in the absence of any observer. And if wave function collapse is indeed time irreversible, wouldn't that imply a violation of the assumptions underlying the second law of thermodynamics (whose proof assumes that the fundamental laws of nature possess a time-reversal symmetry)? Of course you can just avoid these inconsistencies if you pretend that wave function collapse does not occur, since the mathematics doesn't really require it; but doing this seems to lead to the many-worlds interpretation which is not a widely accepted point of view.
|
[
"How silly to think that the equations we use to describe the world might actually describe the world!"
] |
[
"No, the wave function describing that system changes over time as described by its Hamiltonian and the Schrodinger equation which are time dependent. In general, the probability distribution for the outcome you observe could change if you measure it 5 minutes from now or 10 minutes from now."
] |
[
"No one really knows the mechanism that causes a wave-function to collapse. What we know from decoherence is that a QM system coupled to a macroscopic system will eventually evolve in such a way that the \"total wave function of the system\" will have bumps with completely disjoint supports. But nothing can tell you which one of these bumps you will actually observe.",
"The fact that we never observe the collapse implies, disregarding many-worlds, that the evolution is non-unitary. There are non-unitary extensions of Schroedinger evolution that address the problem, like ",
"GRW",
". In Bohmian mechanics this is solved by looking at the wave-function as a hidden variable and doing statistical physics over the configuration space generated by the hamiltonian.",
"And if wave function collapse is indeed time irreversible, wouldn't that imply a violation of the assumptions underlying the second law of thermodynamics (whose proof assumes that the fundamental laws of nature possess a time-reversal symmetry)?",
"Maybe someone who actually does QI can answer better, but what I believe is that you can get over that by defining entropy over the density matrix, instead of quantum states. See ",
"http://en.wikipedia.org/wiki/Von_Neumann_entropy",
" "
] |
[
"Why the sun’s gravity doesn’t attract the Earth toward the sun vertically?"
] |
[
false
] |
If I drop an apple in the Earth the apple goes directly toward the center of the Earth because of the gravity. Why the Earth doesn't fall directly toward the center of the sun but it orbits around the sun?
|
[
"Imagine that you throw the apple horizontally - it'll move around the Earth for a bit before hitting the ground, right? Then you throw it again, but faster, and the apple travels a much longer distance before hitting the Earth.",
"What would happen if you threw your apple so fast that by the time it falls, the Earth's surface has curved away from the apple, meaning it's actually still in the air? It would keep falling! Assuming that there's never any hills or mountains in the way, and the apple keeps its initial speed, it would keep trying to fall towards the ground, but the Earth is too curved for the apple to ever hit it.",
"The Earth and Sun are similar - the Earth is falling towards the Sun, but it's rate of motion around the Sun is too fast to ever fall in. If the Earth lost some of its kinetic energy, and hence slowed down, its orbit would start to fall towards the Sun."
] |
[
"If you throw an apple, it will go a ways before falling to the Earth. If you throw it hard enough, around 18,000 mph, it will orbit the Earth, or would if there wasn't any atmosphere. The Earth is moving at around 67,500 mph in its orbit around the Sun, so that's why it doesn't fall in."
] |
[
"Because the earth is hurtling sideways at over 66,000mph. This is fast enough to make us miss the sun while at the same time falling toward it.",
"If there were no air, you would be able to throw an apple straight out at 17,650mph and it would be going sideways so fast that it would be far enough away by the time it should have hit the ground that it would miss the earth entirely and come round the planet, smacking you in the back of the head in about an hour and a half.",
"Try this: ",
"http://waowen.screaming.net/revision/force&motion/ncananim.htm"
] |
[
"Is there a known mechanism that gives rise to fundamental electric charge?"
] |
[
false
] | null |
[
"I'm not sure if this answers your question, but there is a important theorem in physics called Noether's theorem. ",
"Noether's theorem (kind of) states that any time the behavior of your system doesn't change ( ",
"), when you change something about your system, there is a corresponding function of the system that doesn't ever change ( is conserved).",
"Common examples are: Spatial translation. If you can change ",
" your system is in space, and it still behaves the same then the momentum of the system will always be the same, the momentum is conserved.",
"Temporal translation. If your system behaves the same at different times, then there will be a mathematical equation who's value is always the same, we call that the energy.",
"In some sense you can think of \"momentum\" as that which is conserved due to translational invariance, and \"energy\" as that which is conserved due to \"temporal\" invariance. ",
"One of the other ways a system can be different, yet still behave the same is ",
", gauge invariance is when a system only cares about the ",
" between two values, not the values themselves.",
"In some sense you can think of electric charge as that which is conserved due to the gauge invariance."
] |
[
"To be clear, electrons do not get charge from quarks."
] |
[
"Electrons are not made of quarks, they are a fundamental point-like particle. Things which are made of quarks are called hadrons. An electron is not a hadron. A proton, on the other hand, is an example of a hadron. Protons are made of three quarks. Neutrons are also hadrons, but they do not have any charge because the charges of the different quarks they are made of happen to exactly cancel out."
] |
[
"Why isn't Dark Matter attracted by Gravity to form more dense objects?"
] |
[
false
] | null |
[
"Dark matter ",
" attracted by gravity, like all matter is.",
"The reason dark matter doesn't form more dense objects is because dark matter doesn't interact (significantly, at least) with anything -- even other dark matter -- so there is nothing to slow it down and keep it near the center of a gravitational potential.",
"Consider a dark matter particle falling towards the center of a star. It picks up speed as it falls (conversion of gravitational potential energy to kinetic energy). But it doesn't really interact with anything in the star, so when it gets to the center of the star, it has maximum kinetic energy, and goes flying right out the back end of the star, which slows it down as it gets farther away from the star (conversion of kinetic energy back into gravitational potential energy). So dark matter always ends up in an orbit-like trajectory, spending most of its time away from the center of a potential.",
"Make sense?"
] |
[
"Dark matter is attracted by gravity, but it does not form dense objects because it passes right through itself and other matter (at least that is one of the simplest possible types of dark matter, there are other possibilities as well). Without some form of interaction, it will never \"clump\". Clumping requires that the relative velocity of a group of dark matter particles goes to zero. The only way for this to happen is through some dissipative force (or by random chance)."
] |
[
"It depends how you define \"dense objects\" and on what scale. Non-self-interacting dark matter forms \"dense objects\" in the same sense that our solar system is a \"dense object,\" but not in the same sense that planets or stars are dense objects (which is what the OP obviously means)."
] |
[
"Could subjects in a study being aware of the placebo effect lead to a potentially useful drug/treatment's being rendered ineffective?"
] |
[
false
] |
[deleted]
|
[
"A placebo is used as an experimental control, so it is intended to deal with a range of possible problems that might come up experimentally.",
"If the people getting the real drug show significantly fewer symptoms of depression than the ones on the placebo, then experiment would indicate that the drug is having a beneficial effect.",
"One can imagine a drug that interacts significantly with a person's belief that they were on a real drug. Such a drug might work much better than a placebo if the person knows they are on the drug, but wouldn't differ from placebo if the person doesn't know whether they are on a real drug. A typical placebo trial would have a difficulties dealing with such an interaction, but it is extremely unlikely that such a drug exists.",
"Be careful not to read too much into the placebo effect. It is much greater in conditions where experiments rely on self-reporting or where reversion-to-the-mean would be expected. ",
"In a very interesting study of Asthma",
", researchers found that although a placebo was almost as effective as real medicine based on patient self-reports, it was almost an ineffective as no-treatment-or-placebo based on measures of actual lung capacity.",
"Fundamentally, a placebo is just an experimental control. One of the things you need to control for is the unreliability of self-reports."
] |
[
"Yes. The negative aspects of a placebo effect are known as the ",
"Nocebo",
" effect."
] |
[
"Couldn’t that issue be avoided by ",
" the subjects that they are not getting the placebo? (even if they are)"
] |
[
"Would a nebula looks as pretty from the inside?"
] |
[
false
] |
[deleted]
|
[
"the colors are mostly false colors. Astronomers take a picture with one filter, say for UV light, and color that picture blue. Then they take another picture say for one specific visible frequency and color it green. Then another filter for IR, and color that red. They superimpose those pictures and get prettyness out. This is just an example of course; I guess in principle they could just take a picture in 3 different visible light spectra and appropriately color them, but that I don't think has as much useful science information in it."
] |
[
"While that is true for NASA's phots, have you seen long exposure shots by amateur astronomers? \nThey use normal digital cameras and get wonderful amounts of color. ",
"http://starizona.com/acb/ccd/introimagingama.aspx",
"But you're overall point is correct. Probably from inside, the nebula would look really write and bright and it would wash out the color."
] |
[
"I think it's hard to say, but I'm not an expert, maybe a real astrophysicist could help. ",
"Here's",
" an image of the eagle nebula the author claims is true color. ",
"Here's",
" a more standard three color composite on wiki. If you want, you could probably do some google or google image searches for \"true color nebula\" to get more points of data."
] |
[
"Can someone please explain dispersion to me? I don't understand the physics behind why light can be dispersed into ROYGBIV."
] |
[
false
] |
in particular, I don't see how this violates the wave rule that the velocity of a wave is only dependent on the medium it is in.
|
[
"Check out ",
"this",
". You're understanding me correctly, light's speed through a medium depends on both the medium ",
" the light's wavelength."
] |
[
"I'm not sure what you're talking about in particular, so let's start with a bottom's up approach.",
"Light is an electromagnetic wave that propagates through space ",
" a medium. A single \"bit\" of light, we'll call a photon, has three properties: wavelength, frequency and speed. They're all interrelated. The color you see has exactly to do with the wavelength of the light, nothing else.",
"If you put two photons together, you get a wave that is twice as strong (for the sake of avoiding pedantry, let's forget about observed intensities and 2 photons are not twice as bright as one photon). This is called the principle of ",
". Two, or in fact any number of photons can be placed on top of each other and you get a wave with some overall properties, but its still made up of the constituent photons.",
"So let's start with a bunch of photons whose wavelengths go anywhere from red to violet on the color spectrum and bunch them up. You end up with white light. Actually, the sun's light is very similar to this, coming mostly from blackbody radiation. If you take out bits of that light, you can separate it into its constituent photons of their corresponding color.",
"A prism does just this with diffraction. A white light, made up of all the colors, passes through it and different wavelengths bend differently, giving you the nice rainbow.",
"Clear some things up for you? I have no idea what you mean by breaking the wave rule. The velocity of a wave is only dependent on the medium is true to a first order - its also dependent on the wavelength (if and only if its in a medium), that's why a prism works."
] |
[
"according to rule #1 velocity depends on the medium, meaning a whistle vs a shout will travel at the same velocity in air. Dispersion violates this rule because each color travels at a different velocity despite them being in the same medium. is this correct? would that also mean other sources of Em waves travel at different velocities? For example, would this mean a radio wave would not travel at the same velocity as a gama wave?"
] |
[
"Is there any functional difference at either the hardware or software level between selecting 'restart' to restart your computer, or pressing shut down, and turning it back on?"
] |
[
false
] | null |
[
"At the OS level, no. The operating system will completely shut itself down either way. Likewise, all the hardware in your system ",
" have its state cleared during the restart. A reset signal is sent by the motherboard to all of the components in the computer on the restart. However, everything inside the computer remains powered on (hard drives, video card, and all of the various peripheral controllers, like the USB controller), unlike in the case of a shutdown, which kills power to (almost all*) the components. If those systems don't respect or improperly implement a reset procedure, the computer may not be returned to the same state as it would after a true power off/on.",
"I've actually experienced this problem in person. I had a PCI-E fiber interface card (which interfaced with a scientific system) that failed to properly reset during a soft restart. Wasted a good amount of time till I figured that out, because a restart and power off ",
" behave the same.",
"*For an example of one that isn't, a lot of modern systems will keep power to the USB devices so you can charge phones off the USB ports even with the computer off."
] |
[
"The 2 replies before this are misleading/wrong regarding the power button.",
"The easy part is that clicking or using a mouse on the start bar will cause a \"clean\" shutdown, where windows will send a signal to all running programs that they have to close now or be killed. This gives them time to close any open files like word process documents, so you don't corrupt your disk by leaving files open (basically making them 0-length) when the application closes. This is why after a power cut you may see word processors and similar having recovery options for the last used file.",
"The more complicated part is the power switch.",
"Before around 1996 the power switch handled full mains voltage (120 or 240v) and was the same as pulling the power cable out, or flicking the power switch on the wall socket. (note: these systems are still around today for some embedded stuff like milling machines or taxi booking systems, where companies won't upgrade for cost, business downtime or other reasons)",
"Since 1996 Microsoft and others introduced AC96 or ",
"ACPI",
" with hardware makers, to have more control over what happens when the power switch is pressed, which helps with file corruption and more, as I said above.",
"The action of the power switch is now low voltage (making it safer too) and sends a signal to the PC's hardware when pressed. The ",
"BIOS",
" in a PC now controls what that switch does, regardless of the operating system or version of Windows used (as was ignored in the 2 posts before this). This is controlled in the settings when you first power a PC on and press F1 or DEL or whatever it may be for your PC brand.",
"The technical details of how the CPU handles the power switch are ",
"here",
" but to break it down, it works in a few different modes as follows.",
"1) Pressing the power button and kill the power to the PC immediately, and work like the original power buttons or just pulling the power cord from the PC. (known as a dirty shutdown since it can leave files open and cause disk corruption)",
"2) The button sends a signal to the PC, which does exactly the same as clicking shutdown/poweroff on the start menu, and gives running applications time to ask you if you want to save any open files or not. Known as a clean shutdown.",
"3) The PC can dump its running state to a hibernation file on the hard disk, so that when its turned back on it'll resume from where it left off, but will have to load all its memory from this file once it gets power again.",
"4) The PC can do similar to #3 but saves it in RAM and goes into a low power usage mode and looks like its off even though it isn't. Sometimes you can tell because the fan(s) will carry on running in this mode to keep it col. This also means that if the power cable is unplugged, its basically the same as #1 and you may lose data, plus the PC will do a full normal boot once it gets power again.",
"What all this means to a normal user is what was already posted here, where the user won't know the difference between each BIOS setting, and will think the power button is the same as clicking shutdown with a mouse, and doing a clean shutdown. And this is the default setting for new PCs since its more user friendly. It's not always the case for older computers and ones used in bigger systems though.",
"A \"restart\" is basically a combination of the above 4 options, but normally means the same as power off then on, without actually cutting the power."
] |
[
"Because software is unreliable. There has to be a way to turn the power off for real if the OS is locked up or otherwise so unresponsive that it doesn't respond to a \"polite\" shutdown notification from the firmware. You could pull the plug, of course, but it's not always convenient."
] |
[
"Does the position of leaves affect the rate of transpiration?"
] |
[
false
] |
Like, for example, does the apical pair of leaves have a faster/slower rate of transpiration than the bottom pair of leaves and why?
|
[
"Yes and no. There are sun leaves, which are closer to the top of the tree, have thicker cuticles, are thick, and smaller. Shade leaves are typically found nearer to the bottom. Shade leaves are thinner, larger (more surface area to catch sun), and have more chlorophyll. Sun leaves (A) are ",
"more efficient",
" when sunlight is high, but after a certain amount of light is lost, shade leaves (B) become more efficient."
] |
[
"I'd also like to point out that the position of stomata matter as well, although to a much lesser degree because almost all plants have them usually on the bottom of the leaf. Stomata are holes used for gas echange in plants, although they have the unintentional consequence of water loss as water evaporates out of the stomata. Some plants such as lily pads have stomata on the top of the leaf, because the lower side is submerged in water. The top side of the lily pad will be exposed to more sunlight and therefore heat, evaporating more water. The position of the leaf affects position of stomata which somewhat affects transpiration."
] |
[
"In addition to change in position, leaves may also change shape. For example, Live Oak leaves will curl downward creating a \"moist\" micro climate around the stoma protecting them from wind and heat. "
] |
[
"Higgs and mass (hasn't been asked yet that I can tell)"
] |
[
false
] |
I've searched the archives and haven't seen this one come up yet, so I'll ask. If the Higgs is the conveyor of mass, presumably this means "inertial mass" and it has been asserted that inertial and gravitational mass are equivalent, then what's the relationship between Higgs and (quantum) gravity? It has also been stated that gravitation is only produced by rest mass, not relativistic mass, so does Higgs give particles rest mass?
|
[
"what's the relationship between Higgs and (quantum) gravity?",
"We don't know. We don't yet have a working model of quantum gravity, because mixing quantum field theory with general relativity leads to contradictions. Many people more brilliant than I are working on such theories, but it's safe to say that we probably won't be able to verify them anyway, at the energy scales we can probe at particle colliders. ",
"Sorry!",
"does Higgs give particles rest mass?",
"Yes."
] |
[
"Just a side point. The Higgs only gives mass to elementary particles. The mass of the proton, or other baryons, largely comes from the energy of quarks and gluons, not the Higgs mechanism. "
] |
[
"So they are intertwined... That's what I was wondering. No discussion I have read yet has talked about it in any way other than inertial. Wouldnt it be an even bigger discovery then, if finding it also found something about gravitons?",
"I mean, people talk about Higgs like it just adds some kind of viscosity to moving particles through space (inertia) and only seem to care about this aspect, but it seems to me rest mass is a whole lot mire important"
] |
[
"Questions about CME's"
] |
[
false
] |
Are Coronal Mass Ejections visible to humans from space in the light spectrum, and what would be the effects of being exposed to a CME in deep space?
|
[
"Coronal mass ejections are indeed visible in the optical spectrum, although they would be difficult to see unless you cover the main disk of the Sun with something, since the brightness of the Sun will overwhelm your vision.",
"It depends what you mean by \"exposed to\" a CME. They are associated with higher X-ray fluxes as well as dangerous cosmic rays, which are very harmful to humans. Cosmic rays are extremely difficult to effectively shield against, which is one of the limiting factors on the duration of human spaceflights."
] |
[
"CME's can be seen from space soon after their ejection from the Sun, provided the solar disk itself is occluded and other direct sunlight reflections are blocked from view as well.",
"Once the CME reaches the vicinity of any reasonably distant observer, however, it would be far too diffuse to be visible. An observer near Earth could, however, see its effects on ",
"aurorae",
" near the Earth's poles.",
"The primary effect of exposure in deep space would be irration by cosmic rays, which is potentially fatal."
] |
[
"That was extremely short and to the point. Thanks! "
] |
[
"Can you see time dialation ?"
] |
[
false
] |
I am gonna use the movie interstellar to explain my question. Specifically the water planet scene. If you dont know this movie, they want to land on a planet, which orbits around a black hole. Due to the gravity of the black hole, the time on this planet is severly dialated and supposedly every 1 hour on this planet means 7 years "earth time". So they land on the planet, but leave one crew member behind and when they come back he aged 23 years. So far so good, all this should be theoretically possible to my knowledge (if not correct me). Now to my question: If they guy left on the spaceship had a telescope or something and then observes the people on the planet, what would he see? Would he see them move in ultra slow motion? If not, he couldnt see them move normally, because he can observe them for 23 years, while they only "do actions" that take 3 hours. But seeing them moving in slow motion would also make no sense to me, because the light he sees would then have to move slower then the speed of light? Is there any conclusive answer to this?
|
[
"By time dilation, we ",
" that the light emitted by those on the water planet over 3 hours in their rest frame is received over 23 years by the spaceship in its rest frame. So the observer on the spaceshift sees them move in very slow motion. The images are also extremely redshifted and very difficult even to detect.",
"But seeing them moving in slow motion would also make no sense to me, because the light he sees would then have to move slower then the speed of light?",
"For a given observer, the speed of light is ",
" constant throughout all of space. A light signal right next to you will always have speed ",
". But distant light signals have different speeds. To an observer exterior to a black hole, light slows down as it approaches the event horizon. This is a consequence of the curvature of spacetime since we cannot generally have globally inertial coordinates, but rather only ",
" inertial coordinates.",
" There are a lot of follow-up questions about the non-constancy of ",
" and how that statement fits into relativity. It is true that in ",
" relativity, the speed of light is both invariant (all observers agree on the speed) and constant (the value is the same everywhere). That is known as the second postulate of special relativity. That's only true because we have the luxury of ",
" coordinates in special relativity, i.e., there is no spacetime curvature. Once you have curvature, general relativity takes over and ",
". We have to modify the postulate considerably.",
"The presence of curvature means that we can only have ",
" coordinates, which roughly means the following. At any point in spacetime, you can always adapt your coordinates so that spacetime \"looks flat\" ",
". (For the math inclined, this means you can choose coordinates so that at the point ",
", the metric has the form of the Minkowski metric with vanishing first derivatives.) Away from that single point, spacetime does not look flat. To capture this mathematical fact, we usually say things like \"special relativity holds in local experiments\" or \"you cannot perform a local experiment to distinguish between gravity and uniform acceleration\".",
"So how does the second postulate change then? Well, it's still true ",
". That is, if a light signal passes right next to you, you will ",
" measure it to have speed ",
", no matter how fast you are going and no matter where you are, as long as you are right next to it. So the speed of light is still ",
" but only ",
". But someone else very far away will ",
" measure the speed of that light signal to be ",
". In fact, suppose a light signal is traveling through space and we have a whole chain of observers, one after the other, camped out along the path of the light signal. For funsies, we don't even have to assume they are all at rest with respect to each other. As the light signal passes by each of them, they each measure its speed. Then some time later everyone reunites to compare their measurements. Guess what? They ",
" come back and say that the light signal had speed ",
".",
"However, suppose we picked out one specific observer and asked him to continuously measure the speed of the light signal. The moment the signal passed him, he would record a speed of ",
". But for all other points on the signal's path, he would record a value not necessarily equal to ",
". The speed could be less than ",
", the speed could exceed ",
", it may even be equal to ",
". But it's certainly not guaranteed to be ",
".",
"Now for all of the questions about the speed of light being a universal speed limit. ",
" is still true as long as you modify \"speed of light\" with the word \"local\". Go back to the previous example with the one observer measuring the speed of light along its path. Suppose that at some point he measures the light signal to have speed ",
"/2. That's fine. But that also means that ",
" he measures at that point can have a speed that exceeds ",
"/2. In other words, the local speed of light is ",
" the universal speed limit.",
"However, you should be careful that not everyone agrees on the local speed of light. That guy might say that light has speed ",
"/2 at that point, but someone else might say it has speed ",
"/4 or something. If the first guy measures some particle to be moving at ",
"/3 at that point, that does ",
" contradict the fact the second guy sees an upper speed limit of ",
"/4 at that point. Remember, they are using ",
" coordinates. Since both observers are not ",
" the light signal when they measure its speed, all they are doing is measuring a coordinate speed, which are generally not very physically meaningful. You ",
" unambiguously define the velocity of distant objects in general relativity.",
"If you are interested in more details, you can see ",
"this thread",
" and ",
"my follow-up post within that thread",
". If you are math- or physics-inclined, you can also check out an introductory GR textbook. I recommend Schutz for starting out, followed by Hobson. ",
"Sean Carroll's text",
" is freely available online, but is more appropriate for a graduate course in GR. Wald's text is classic but is for advanced graduate students."
] |
[
"Yup, the time dilation in that film was silly, 7 years per hour or something like that? That would mean everything in the sky would have been ",
" (hours in a year) x 7 times brighter than normal.",
"EDIT: not 2000 hours, no idea why I wrote that! ( Thanks ",
"u/jareds",
" )"
] |
[
"Would the people on the water planet see their astronaut friend and the stars (blue-shifted, I assume) whizzing around at high speed?"
] |
[
"Safe way to keep my goggles from fogging in lab?"
] |
[
false
] |
When I am in Biology lab my goggles fog up really fast and never let up. I tried taping a few small wads of paper towels on the inside thinking it would absorb the moisture, but that only yielded minimal results. I have Rain-X for my car, but question it's safety with it being in a closed system with my eyes. Is it safe if it dries adequately before using? Another thought I had was taping silica packets on the sides. (Like the small ones found in shoe boxes.) Any safe suggestions?
|
[
"Use cat crap. Seriously google it. That's what they use for ski goggles."
] |
[
"Yeah, my morning coffee made it even less pleasant though since I am in the lab at 8 AM."
] |
[
"ಠ_ಠ",
"Maybe that is how my lab partner got pink eye."
] |
[
"Are humans \"hardwired\" to divide the world into \"my group\"/\"others\"?"
] |
[
false
] | null |
[
"Yes we are. Humans evolved in tribal groups that required competition. As civilization developed this innate competitiveness never really went away. This is why humans can get so worked up about things like sports that we will kill each other (look up the soccer war, this legit happened). We are always finding an \"in\" crowd and an \"out\" crowd. This is also why politics can get so ugly. ",
"Scientific Review of the Subject"
] |
[
"Also try reading \"Us Against Them: How Tribalism Affects the Way We Think\" by Bruce Rozenblit. Again, there's a lot of overwhelming evidence of your question. That review and this book are just two examples I had fast access to but Google Scholar search anything about tribalism in humans and you'll get 100s of articles and empirical research studies."
] |
[
"Human beings are naturally categorical. It's not so much \"us vs. them\" as it is \"known vs. unknown\".",
"If you have knever seen, heard of, or experienced a couch and walked into a living room one day, on of the first things you're going to do is asses this huge unknown item.",
"Is it a bomb? Can I eat it?"
] |
[
"What is a mechanism of eyes getting tired by light?"
] |
[
false
] | null |
[
"Do you mean adaptation / afterimages? Or fatigue like you can get from staring at a computer screen for a long time?"
] |
[
"There are several factors that could contribute including the drying out of your eyes by not blinking frequently enough or the fact that you are focusing constantly at the same point in space (the ciliary muscle which controls the shape of your lens gets strained). You can find more information just by googling eye strain."
] |
[
"I mean fatigue cause by working in bright light in operation room as a surgeon or staring at computer screen for a long time."
] |
[
"I just watched a YouTube video where a phone battery exploded second after being stabbed with a knife. What exactly is happening to get that sort of reaction?"
] |
[
false
] |
[deleted]
|
[
"Many things happen at the same time. For instance, when you poke the battery with the knife, you create a short circuit (assuming the battery is charge). This will release a lot of heat, which will heat up the electrolyte in the battery. The electrolyte will become volatile and flames up if a spark is created. This is what you see. The lithium in the batteries doesnt really cause that much flame, its mostly the electrolyte. This is so because lithium is rarely in metal form in batteries (usually, its LiC6 on the anode, very rarely Li metal). "
] |
[
"Lithium is an alkali metal, like sodium and potassium. Alkali metals are highly reactive and flammable and so don't in nature in their pure forms. ",
"These metals have only one electron in their outer shell, and readily lose that electron in ionic bonding with other elements. This is the reason for their reactivity. ",
"soon it's shooting out fire like it thinks the men of Laketown are trying to steal its gold",
"It's interesting to note that lithium is actually the least reactive alkali metal."
] |
[
"Spot on. OP may be interested in ",
"this video",
" documenting the reactions of many alkali metals with water.",
"Don't try it, at home or otherwise."
] |
[
"Is there a kind of numbers more powerful than complex numbers or are those the most powerful among things that qualify as numbers?"
] |
[
false
] |
I'm afraid I have to explain where I'm coming from, exactly. We start with natural numbers: 0, 1, 2, 3, ... They obey several important rules regarding addition and multiplication: both are commutative, for starters: . Then we notice that the inverse of our addition operation sometimes is undefined, is not a natural number. So we extend the natural numbers with negative numbers, yielding integers. Our addition and multiplication operations still work exactly the same for the integers that happen to be natural numbers and they still obey those rules. Then we notice that the inverse of multiplication sometimes is undefined, and define it, giving us rational numbers. Then we notice that the squaring operation, multiplying a number with itself, has an inverse operation of taking the square root, which is undefined for some numbers (like 2, for example), and we invent real numbers*. Then the same goes for the taking a square root of a negative number, we add a whole bunch of numbers represented as , living on the complex plane, of which real numbers form the X axis with , and invent the rules for addition and multiplication that are compatible with addition and multiplication of real numbers and that still obey the commutativity rules for all numbers. Is that the end? Or are there operations on complex numbers that are undefined for some of them, allowing us to extend those with some extra numbers that still obey the commutativity of multiplication and addition? : strictly speaking, noticing that sqrt(2) is not a rational number would prompt us to invent algebraic numbers. Real numbers seem to come from an operation of taking a limit of a converging rational sequence, which is not the same as finding an operation that has an inverse that is undefined and extending our set of numbers to make it defined. Is there an operation that would give us real numbers in the way of noticing that its inverse produces a real number for a rational argument? Also, I know about quaternions and octonions, they aren't commutative regarding multiplication and therefore are not proper extensions of complex numbers, as far as our notion of a number goes.
|
[
"We need to talk a little about ",
"Fields",
". These are arithmetic objects where you can add, subtract, multiply and divide in a nice, commutative way. We can think of a \"Number System\" as being a field that we can construct in natural ways starting from the Natural Numbers. ",
"It's not hard to show that whatever field we construct from the Natural Numbers must also contain the Rational Numbers. The Rational Numbers are sort of like the base/starting point for Number Systems. So we can ask: How do you get larger fields from the Rational Numbers, using natural constructions? There are exactly two ways to do this.",
"The first way is to take a polynomial with rational coefficients, p(x), and create a new field by adding the fewest number of numbers needed to get a field that contains all the roots to p(x). So if p(x)=x",
"+1, we can create the field of all numbers of the form A+iB where A and B are ",
" numbers and we declare that i satisfies i",
"+1=0. This is related to the ",
"Gaussian Integers",
" in the same way the rational number are related to the normal integers. If we look at p(x)=x",
"-2, then we can look at all number of the form A+sqrt(2)B, where A and B are ",
" and we declare that sqrt(2) satisfies (sqrt(2))",
"-2=0. In this case, rationalizing a denominator is the same division in this new field. These are two different fields that extend the rational numbers, but we don't have all the Real Numbers when we add the roots of x",
"-2=0 and we don't have all the Complex Numbers when we include the roots of x",
"+1=0. We can do this for any polynomial to get bigger and bigger fields. ",
"These kinds of fields are called ",
"Algebraic Number Fields",
", because we can construct them starting from the rational number and using only the algebraic structure of polynomials. In general, these can be thought of as higher dimensional objects over the Rational Numbers. The two fields I mention have dimension 2, but the field given by p(x)=x",
"+x",
"+x",
"+x",
"+x",
"+x+1 has dimension 6 over the Rational Numbers, and the field given by p(x)=x",
"+x+3 has dimension 60. If d is the degree of the polynomial whose roots your adding, the dimension will be between d and d!. There are infinitely many Algebraic Number Fields for every possible finite dimension, and a huge open problem in Number Theory is to be able to systematically describe the structure of the collection of all Algebraic Number Fields. But the important thing is that these are field constructed from the Rational Numbers using purely algebraic means. It is also important to see sqrt(2) and sqrt(-1) on the exact same page, because their constructions follow identical methods, we just use different polynomials. Sqrt(2) is not the reason we make the Real Number and sqrt(-1) is not the reason we make the Complex Numbers!",
"It is impossible to construct the Real Numbers or the Complex Numbers as an Algebraic Number Field. Algebraic Number Fields are completely apathetic to any kind of geometry that we might usually assign to the Rational Numbers, so we usually pretend that there is no geometry or order when working with them. This is not true for the Real Numbers, they are a Geometric and Analytic (Calculus) construction. So what we do is we look at the Rational Numbers and impose the geometry on them that we're familiar with. In this geometry there are holes that can be filled and we can fill them using limits. This results in the Real Number that we're familiar with. It is only a coincidence that it contains versions of the algebraic things from before like sqrt(2), the motivation is to fill in the holes of the geometry to get a \"complete\" object. ",
"Something great that happens is that if impose this geometry on the Rational Numbers, and we create an Algebraic Number Field using some polynomial, then we can extend this geometry to the Algebraic Number Field! This new geometry on this new field will have it's own holes and so we can use limits to fill these in to get ",
" completed field. In general, there is no reason for these to give us the Real Numbers again, and if you do this with the field generated by sqrt(-1), you will obtain the Complex Numbers. The question can then be \"If I complete a really huge Algebraic Number Field, can I get something bigger than the Complex Numbers? This is what the ",
"Fundamental Theorem of Algebra",
" answers. It turns out that completing an Algebraic Number Field is the same thing as adding whatever roots we were using to the Real Numbers, but the Fundamental Theorem of Algebra says that the Complex Numbers contain ",
" the roots of any polynomial, so the highest that we can get is the Complex Numbers. Even if we complete the 60-dimensional object over the rationals associated to x",
"+x+3, we'll still only get a 2-dimensional object over the Reals. This is because the Reals and Complex Numbers have an uncountably infinite dimension over the rational numbers, so extending something from 1 or 2 dimensions is basically the same as extending something from 60 or 100",
" dimensions.",
"So to answer your question \"Is there anything ",
" than the Complex Numbers that we can still call a number system\" is \"No, due to the Fundamental Theorem of Algebra\". But the story isn't over...",
"A question we can then ask is \"Is the typical geometry on the Rational Numbers the only ",
" geometry?\" And the answer is a resounding \"No!\" It turns out that for every prime number of the integers, we can define a completely ",
" geometry on the Rational Numbers. Essentially we encode the arithmetic information about a prime number P into this new geometry by saying that the \"size\" of a number is small if P divides it a lot, and large if it does not (this is because 0 divides it infinitely many times, and it must have zero size.) In general, if I have a rational number R=P",
"(A/B) where n is any integer (positive or negative) and P does not divide A or B, then we say that the P-adic size of R is P",
". So the 2-adic size of 24 is 1/8, of 13 is 1, of 1/32 is 32 etc. It is impossible to draw this geometry, so it is a little unintuitive, but it's structure turns out to be really nice and is similar to the ",
"Cantor Set",
". These new geometries are why it is important not to always impose the geometry we're familiar with, because that restricts our story. This new geometry will have new holes in it, different than the ones from before, and we can use the limits associated to this geometry to fill them in, and these completed fields are called ",
"p-adic Fields",
".",
"Some p-adic Fields contain sqrt(2), others have sqrt(-1), some have both but it depends on the prime we use. Just like we could complete Algebraic Number Fields using the typical geometry, we can also complete them using these p-adic geometries and get finite dimensional extensions of the ordinary p-adic fields. But unlike the Real Numbers, the p-adic fields have extensions of any dimension! The Fundamental Theorem of Algebra does not restrict ",
" dimensions. ",
"To recap: Field generated over the rational numbers using roots to polynomials are all in the same class called Algebraic Number Fields, and should thought to be on the same ideological level. There's not much difference between adding sqrt(2) and sqrt(-1). We can also construct fields through geometric means, most generally called \"Local Fields\", these contain exactly the p-adic Fields, and their extensions, and the Real Numbers plus it's only extension, the Complex Numbers. Because we can lump in the Real Numbers in a category where everything else has an associated prime number, we typically refer to the Real Numbers as the field completed by the \"Prime at Infinity\" (this has geometric analogs that make this language make more sense). It turns out that a lot of formulas that involve primes are always missing a little correction term before they make sense, but if we include the \"Prime at Infinity\" and do to it what we did for the ordinary primes, these formulas become complete. So it's fundamental to not see the Real Number or Complex Numbers as being particularly stand-out, but as just part of the smaller category of fields generated by the geometry of prime numbers.",
"Each of these local fields has only the information about one prime, hence why we call them local (they only look \"near\" a single prime). A question we like to ask is \"If I know something is true in every p-adic field and the real numbers, is it also true for the Rational Numbers?\" The answer to ",
" is \"Sometimes\". If you have a, say, two variable quadratic equation, like 3x",
"+5xy-3",
"=0, then if this equation has a solution in ",
" the p-adic fields + the real numbers, then it will have a solution in the Rational Numbers. This is ",
" true if we look at cubic equations, there are some that have solutions in all the local fields, but not in the Rational Numbers. Measuring how big this discrepancy is when we look at ",
"Elliptic Curves",
" is something that the ",
"Millennium Prize Problem",
" known as the ",
"Birch and Swinnerton-Dyer Conjecture",
" talks about.",
"Also, I know about quaternions and octonions, they aren't commutative regarding multiplication and therefore are not proper extensions of complex numbers, as far as our notion of a number goes.",
"I 100% agree. People usually talk about these as the natural extensions of these ideas, but they're wrong. Algebraic Number Fields and p-adic Fields are the natural objects when looking for more number systems."
] |
[
"There are other ways to construct fields that extend the Complex Number, but the Fundamental Theorem of Algebra says that it can't be finite dimensional and the fact that the Complex Numbers are complete says that it can't be geometric/topological in nature. For instance, I can look at the collection of all rational functions on the Complex Plane, which will give me the Field of Rational Functions over C. This is a field that contains C, but it is infinite dimensional and isn't arithmetically motivated. The elements of it are functions of the form p(x)/q(x), where p and q are polynomials, so it wouldn't make sense to call these \"Numbers\". The information here is more related to the analytic structure of the Complex Numbers or the geometry of the Complex Plane. ",
"We can actually construct many different kinds of surfaces using the Complex Plane, such as the ",
"Riemann Sphere",
" or a Torus (which is actually an Elliptic Curve), all of which are called ",
"Riemann Surfaces",
". And to every Riemann Surface, S, we can look at the collection of all functions on this surface so that when we zoom in far enough, this function looks like a rational function on the plane. We call this collection C(S) and it is a field called the \"Field of Rational Functions on the surface S\", and these fields are different for each surface so there are many fields that contain C as a subfield. Knowing the structure of these fields can help us tell them apart. These are geometric constructions on which the functions defined on them result in fields. These are fields of functions, and they tell us about the underlying geometry of the object, so they are not fields of numbers.",
"However there are similarities between Algebraic Number Fields, Local Fields and these Geometric Constructions. One of the most important mathematicians of the 20th Century, ",
"Alexander Grothendieck",
", found a way to view Algebraic Number Fields as the function fields of a weird kind of geometry associated to prime numbers. He essentially defined a geometry on something related to the collection of prime numbers, and found that the function fields of flat surfaces over these geometries were exactly the Algebraic Number Fields. There is now a huge field called Arithmetic Geometry that studies different geometric objects that we can construct from Number Fields, of which a subset are the Number Fields, in a way that mimics the objects created from the Complex Plane.",
"But even in this field, there are clear things that distinguish the purely geometric constructions of Riemann Surfaces from the construction of new number systems via Number Fields and Local Fields. Over Number Fields, no matter how large we get, the collection of remainders after division is always ",
". But for things created from the Complex Numbers, this is not the case, and we lose a significant amount of properties key to studying thing that could be thought of as \"numbers\". At most there are \"parallels\" between these two things, but they are fundamentally different enough for us not to consider them the same.",
" Maybe this was a little cryptic, but there are larger fields we can create that mimic the construction of Algebraic Number Fields using very abstract concepts. I wouldn't call these methods \"unnatural\" by any means, but they end up distancing themselves too far from the integers to be considered \"Number Systems\"."
] |
[
"If I have the rational numbers, and consider all the logarithms of rational numbers at every rational base, I have the set log_r(s) where r and s are positive rational numbers. I can look at the smallest field that contains all these elements and this field will have a ",
" basis over the rational numbers. This means that this field has countably infinite dimension, but the reals have ",
"countably infinite dimension, so they are not the same. ",
"Unfortunately, logs do not have nice enough arithmetic properties to make a nice and clean number system. It exists, but it isn't an algebraic number field and is not pretty. I've actually sat down and tried to see when this field looks like and I did not enjoy myself."
] |
[
"Fermi Paradox: How can a truly multi-stellar civilization die? (Looking for scientific perspectives or book recommendations.)"
] |
[
false
] | null |
[
"Astronomy"
] |
[
"Hello,",
"Open-ended questions like this would be more appropriate for ",
"/r/AskScienceDiscussion",
". You might also be interested in ",
"/r/AskScienceFiction",
"."
] |
[
"Maybe I shouldn't have classified it as astronomy. It's really a population dynamics question, but in the context of a galactic ecosystem. I want to know whether a causally disconnected expanding sphere of colonization can be universally disrupted by purely local influences"
] |
[
"Can you get all of the energy out of a battery at once?"
] |
[
false
] |
Say you needed all of the electricity out of a battery in a very short amount of time, can that be achieved?
|
[
"No, there is a physical limit to how fast you can extract power from a battery. Here is a case example: take a lithium ion battery. How does the energy get stored in this case? You are storing charge, which can become mobile on-demand and then be a current that does work. In a Li-ion battery lithium ions (surprise) migrate from the cathode to the anode (explanations of how this happen are not important here) and this is called charging. When you want to discharge the battery, you migrate them back to the cathode, and in doing so move electrons through the circuit and do your useful work. Okay; now, say you wanted to get it all out at once: you would have to move ALL of those Li-ions not only out of the lattice of the anode where they exist, but through the electrolyte and into the cathode lattice INSTANTLY. They have there own speed at which they go, sure you could in theory make them move through the lattice quicker, but move them to quick and they will just smash into the lattice of the anode/cathode instead of moving into position all nice-like. Different materials will have a different discharge time based on what ions your using, how much space (size of vacancies in the lattice) the ions have to move through, and other factors that are difficult to determine other than experimentally. So, no, you cannot get all the power out instantly.",
"If you want to extract all the energy as fast as possible (instantaneously is impossible), you really want to use a capacitor. Where the energy is stored in the electric field itself, that way there are fewer physical limitations to consider and your discharge rate comes from the field collapsing, which is very fast.",
"Hope this helps, comment for further explanation of anything."
] |
[
"I would argue that short circuiting the battery would get all the energy out of the battery faster than a capacitor. Place a wire with the least resistance across the terminals. (Obviously don't do this, as it may cause a fire or until the wire across the terminals melts.)",
"A capacitor based discharge would slow as the capacitor charges up."
] |
[
"In the case of short circuiting, where does the energy go? Into the wire and than lost as heat?"
] |
[
"What (if any) physiological changes do men experience when their partner is pregnant?"
] |
[
false
] |
As a follow up, what drives these changes? Pheromones released by the woman? Just seeing a pregnant belly? The conscious brain trying to process and prepare for the future?
|
[
" Make sure you distinguish between research on father's-to-be vs. fathers. The findings are better understood for fathers, whereas there is far more dispute regarding changes in expecting fathers."
] |
[
"There are cases, I think just slightly over 10%, where men have been known to experience increases in ",
" depression, often linked to increases in stress and cortisol. It hasn't been sorted out if that's because of having to live with stresses of pregnancy, or actual hormonal responses to being around a pregnant woman (specifically ",
" future child). ",
"Some semi-inconclusive studies have shown that men experience an increase in estrogen and prolactin around the same time a pregnant woman does. ",
"I don't know why or how, though. Personally, I'd also be interested in hormonal responses of men being around pregnant women that aren't bearing their child. ",
"http://www.scientificamerican.com/article.cfm?id=fathers-postpartum-depression&page=3",
" Bit of a mix up with depression and stress. Fixed now. "
] |
[
"I know that the question was specifically asking about what happens when their partner becomes preganant, but I thought it was worth drawing your attention to ",
"this",
" article about what happens when to the fathers brain shortly after he becomes a dad. ",
"Shortly after a monkey becomes a father there is an increase in the density of dendritic spines in the prefrontal cortex (PFC). This increase is thought reflect an increase in the total synapse number and therefore increase in connectivity. The ",
"PFC",
" is thought to be involve in complex planning and emotion regulation and is the part of the brain that is most expanded in humans (and to a lesser extent, non-human primates).",
"The other interesting finding in this paper is that there is an increase in PFC vasopressin receptors (V1R). V1R are thought to enable social attachment in several species and can roughly be thought of as a the the male counterpart to oxytocin (though this should not be thought of as strictly dicotomous). In woman, oxytocin is released during childbirth and breast feeding and this release is thought to facilitate attachment to the child. The fact that we see an increase in V1R in the male brain suggest that it is priming itself for attachment as well. ",
"I hope that helps answer your question",
"I thinks its also worth pointing out that these changes could be happening during pregnancy, but these researchers chose to focus on the period short after fatherhood begins. "
] |
[
"Why is cancer so prevalent, considering the complex factors needed to initiate such growth?"
] |
[
false
] |
(Disclaimer: I hope I'm not simply showing my ignorance here by asking this question and that it's worthy of being asked) After reading , and taking note of its laundry list of needs for cancerous growth: Circumvent DNA Repair Overcome Apoptosis Recruit blood vessels to supply nutrients Make growth signals/ignore inhibitors Attack the body it suddenly seems like a big leap for a cancer cell to come into being, over and over again, independently in millions and millions of patients. So what am I missing here? How can cells meet these requirements with such relative ease?
|
[
"It's probability. If you live long enough you WILL get cancer. It is inevitable. ",
"Consider this: the error rate of DNA polymerase is approximate 1/10",
" which means in the course of copying the 3 billion base pair genome, every time, you can expect it to make 300 errors each time. Wow. Considering your body has trillions of cells, you would expect an extreme amount of mutations to be found before you would even be born. This doesn't happen because of excellent DNA repair mechanisms, but the risk is there. ",
"So you have a mechanism (and this doesn't include oxidative damage, radiodamage, viruses, etc), in the cell that will spontaneously generate mutations at a known rate. This gives you a basis of forming cancers.",
"So while you have all of those items, not all of them are necessary for cancers to form, and they don't all have to be formed at the same time. Cancers evolve just like organisms, so the first trait that it might evolve might be activating an oncogene. It can now proliferate. But that doesn't mean that it doesn't have DNA repair mechanisms. For example, seminomas are radiosensitive, which means when you irradiate them, their DNA repair mechanisms tell the cell to kill itself.\nA tumor can grow for a long time before mutations arise in the tumor that secrete angiogenic factors. It is very common to see necrosis in the center of tumors, because they will grow regardless of the amount of oxygen they are receiving. ",
"It is very typical on autopsy to find multiple adenomas, or tumors that tried, but just couldn't make it to become a metastatic cancer. ",
"A good wikipedia article on the subject."
] |
[
"Actually it is a miracle that it doesn't happen more often, given:"
] |
[
"This is not true of all cancers. The classic example is testicular cancer, which has a peak incidence at about 30 years of age and declines. You are less likely to get testicular cancer at 40 than 30 and less likely to get it at 50 than 40.",
"Certainly that is true of certain kinds of cancer, but for the majority of cancers (breast, colon, prostate, skin, brain, uterine) one of the larger risk factors is age. But my point stands. If you don't die of heart disease, kidney disease, COPD, if you live long enough, you will get cancer. ",
"What do you mean \"we don't know how cancers start\"? There are dozens of models out there for how cancers start, or how someone can be predisposed to cancer. Check out the genetics behind ",
"retinoblastomas",
", or ",
"Li-Fraumeni",
", where you are missing a copy of p53. You could check out ",
"Lynch syndrome",
", or ",
"APC",
".",
"All of these tumor syndromes give a very good idea of how cancer starts. A regulatory mechanism (e.g. p53) is knocked out, then another is knocked out. Suddenly you have no checks on cell cycle, you get unchecked mutations, activation of oncogenes->cancer. ",
"So while we can't necessarily predict who will get cancer and who won't, we have a pretty good understanding of what is required to transform a normal cell into a cancerous one."
] |
[
"I can type without looking at the keyboard, but when asked to draw a keyboard, I am completely unable to correctly label half of the letter keys. How is this possible?"
] |
[
false
] | null |
[
"Exactly, just try it yourself. I get this more often with video games- if someone asks me what button to press to do something, I have to pick up a controller to figure out what to tell them."
] |
[
"Can't you just pretend to type a word and figure out where the letters are? I know where the letters are in reference to my fingers. So \"i\" is right middle finger up. I could easily use that to draw a keyboard. It is much easier to pretend to write out a word while paying attention to where the fingers want to go. "
] |
[
"So if someone wanted to draw a keyboard, they would have to pretend to type and draw each letter key they tried using?"
] |
[
"If supposedly solid objects are mostly empty space, why does it seem that no light penetrates solid objects?"
] |
[
false
] |
If I hold a laser pointer up to a thin piece of solid plastic, then with my naked eye I can't see any "laser light" coming out the backside. Since supposedly solid objects are mostly empty space why is it that (it seems) absolutely zero light penetrates solid objects?
|
[
"Not all solid objects are opaque. Opacity is a bulk material property that depends on ",
" the material, and the color of light you shine through it. A color filter is a great example of a solid that will be clear to only some colors of light, while blocking others. You can have something like carbon, which in one state (soot) is very opaque and doesn't let visible light through, but in another state (diamond) is extremely transparent.",
"Opacity has more to do with the material than the state of matter."
] |
[
"The \"empty space\" are the electron clouds within the atoms. Since the hard-shell size of the electron is very small, it is often awkwardly stated that an atom is mostly empty space. But \"size\" is really dependent on how fast an object is travelling. Edit: \"fast\" in a classical sense. In other words, how much kinetic energy the object has.",
"For example, let's say a very slow asteroid is headed towards Earth. Obviously if it is headed straight at it, it is going to hit. But if it is headed even a moderate distance away, it can get caught in the gravity of the Earth and eventually spiral in and hit the Earth. So the effective size of the Earth is larger than the physical size. But if the asteroid is going very fast, it is just going to blow right past the Earth unless it is on a very direct course.",
"The same kind of thing happens with the atoms in a material. In many cases, the photons of light are low energy energy that they interact with the material rather than passing through.",
"The gravity analogy isn't exact, since we aren't talking about orbits, but I think that it should be a sufficient explanation to understand that the electric field (like the gravitational field) can have an effect/effective size larger than any physical size of the objects emitting the field. Maybe someone can expand upon it or think of another analogy to help explain."
] |
[
"Thanks for the well-drafted response. I think it all makes sense--the asteroid analogy really helps to visualize things."
] |
[
"Has the weight or mass of Earth changed overtime?"
] |
[
false
] |
For example if everything were even, all the resources on Earth have always been here and the contributed to the weight or mass of earth. We take those resources and make things. Sometimes the things we make emit gases or substances that upon leaving the atmosphere don’t weigh on the Earth anymore. Then all the space debris we’ve sent into outer space. So, is the Earth lighter than say 25,000 years ago? 1,000,000 years ago?
|
[
"Y'all are weird for talking about the mass of rockets. They weigh very little compared to 40 kilotons of dust falling into the atmosphere every year, and that is eclipsed by 100kt of hydrogen that bounces out of the atmosphere annually. ",
"BBC News - Who, What, Why: Is the Earth getting lighter?\n",
"http://www.bbc.co.uk/news/magazine-16787636"
] |
[
"“Population growth and new buildings are not a factor, he says, because both of these are actually made up of existing matter on the planet.” ",
"Woah. So earth’s 7 billion people didn’t actually add anything new in terms of total matter? For some reason I can’t get my head around the idea that all the way from being sperm and egg, you are just the sum of all the food and drink you’ve consumed, minus your waste. And that the food and drink you consume, regardless of what it is, was already here in some form of matter or another. ",
"Also, the earth is just yeeting hydrogen into space at this point."
] |
[
"Also, the sun shines on Earth and photosynthesis occurs making green leaves that then falls to earth and makes soil. So that technically adds mass.",
"I'm not sure just how tongue-in-cheek that last bit was. But for the record, while the sun emits various types of radiation, photons are massless."
] |
[
"If you sleep in a colder environment, will you burn more calories?"
] |
[
false
] |
If you sleep at a lower temperature will your body burn more calories to keep you heated? Is it a negligible amount? Does anyone know what would be the peak temperature for this (at some point your body must be heating at 100% capacity I imagine and lowering the temperature anymore wouldn't help). Just a curious thought I had last night as I was going to sleep and I was wondering if anyone here would know! Thanks!
|
[
"Yes, your body works very hard to maintain your body temperature in a narrow range, and any time spent in cold weather will mean more energy spent to stay warm. I don't have specific numbers for you, but someone can probably give you a back-of-the-envelope calculation.",
"The problem with this strategy is that your body responds to being cold by adding more body fat. I'm not an expert on this, but generally, people in cold environments have very large appetites and tend to put on weight."
] |
[
"Wouldn't running or exercising create considerable heat to keep you warm?",
"EDIT: can someone tell me why i'm being downvoted?"
] |
[
"You're probably being downvoted because someone else wanted their comment higher."
] |
[
"What new subreddits would you like to see?"
] |
[
false
] | null |
[
"Haha, it happens. Have a good one!"
] |
[
"First off, your post is not appropriate for AskScience, this is an AskReddit question. Secondly, your suggestion of ",
"r/askmedicine",
" can't exist as that would violate Reddit's terms of service. Not to mention that those of us who are physicians would be legally liable for any answers we give and could be sued, fired, and otherwise disciplined for answering medical questions about an individual over the Internet. "
] |
[
"Holy crap. I could have sworn I submitted this to askreddit. "
] |
[
"How are the cells in a fern gametophyte able to reproduce and grow with only one set of chromosomes?"
] |
[
false
] | null |
[
"They multiply by mitosis like cells with two sets of chromosomes, they simply couldn't undergo meiosi because they can't reduce their chromosomes. ",
"Having one set of chromosomes doesn't affect meiosis, it just makes organisms more likely to suffer from mutations, since, if there's a mutation in a gene that isn't corrected, the other copy of that gene isn't there to continue making the protein. That's why plants and other organisms that are constantly exposed to the Sun are haploid for a short period of their cycle or are never haploid at all. In ferns, the gametophyte is as reduced as it is precisely for that reason."
] |
[
"I see. So if they differentiate tissues, they do it by just reading the one set of genes they have rather than the to sets we have?"
] |
[
"Yeah, I don't have a lot of knowledge on gene regulation and expression but they'd have to be able to differentiate and grow normally with just one copy."
] |
[
"What's under the Canadian Shield? [geology]"
] |
[
false
] |
I know the Canadian shield is a rich source of minerals but for the life of me can't find any information as to what the layers underneath the Canadian Shield are.
|
[
"The shield isn't just one rock type. It consists of multiple volcanic arcs, ophiolites, and even sedimentary rocks that have been smashed together over millions of years. So generally when talking about the shield it would be correct to say the mantle is underneath it. Also, the mantle is very much solid - not a \"molten sea of rock\" (unless you're talking about the outer core, but that's quite a ways down)."
] |
[
"We have samples of the mantle brought up through tectonic and volcanic activity. We haven't yet managed to drill down and directly sample the mantle."
] |
[
"As I understand it, once you got through the craton you would be encountering the upper mantle."
] |
[
"Is there a limit to how many people can view an object?"
] |
[
false
] |
[deleted]
|
[
"If you've ever seen a group of people crowded around an object, but you were unable to see the object yourself because they were in the way, you have experienced this phenomenon. So yes, the limit is based on the distance from the object to the inner layer of the crowd, and the packing density of the people. Very small hexagonal people forming a sphere at a great distance from the target object would yield the largest number of possible observers. This would also be hilarious."
] |
[
"Well yes, at the maximum limit (which would increase with r ) the photons would be blocked. The same way you turn a light on in a room with no windows, and close the door. No one outside can observe the light as its being blocked by the wall. Then imagine that the walls/floor/ceiling are people, and the atoms that make it up are individual observers. ",
"As for reflection, yes ",
" light would be reflected, but a lot of it is being absorbed. "
] |
[
"Would not very small equilateral triangular people get more people into the same 'area' - since a hexagon is just 6 equilateral triangles"
] |
[
"Can you have a reference frame moving at the speed of light?"
] |
[
false
] |
Is a reference frame traveling at c valid (say a reference frame centered around a photon)? I understand that any (almost any?) inertial reference frame is valid; however, does this break down as velocity approaches the speed of light? Can you use a Lorentz Transformation to convert to a photon's reference frame and still arrive at sensible answers? Thanks! Background: Entering 4th year undergrad physics, i.e. I've gone over special relativity, haven't touched general relativity.
|
[
"Yes and no. There are situations in which it's useful to boost a system to infinite momentum in order to reduce the number of degrees of freedom, and the corresponding mathematical complexity of the problem. But that's a mathematical trick, not a valid description of a real phenomenon. And it only works if you colour within the lines. If you just boost the universe to infinite momentum and start asking arbitrary questions, you get nonsensical results back.",
"So yes, you can construct an infinite-momentum frame. But in all but the most specific circumstances, you "
] |
[
"No.",
"I mean, you can take the limit as the relative velocity approaches c, and you get ",
" answer. The problem is that you get something meaningless; all spacetime intervals in the reference frame have zero length. What are you going to do with that?"
] |
[
"Write a science fiction novel, of course. Or maybe a quantum self-help mysticism manual."
] |
[
"Was there life on Earth when the asteroid hit that tore off our moon?"
] |
[
false
] |
If so, are there potentially fossils on the moon, or are elements of the fossilization process not present over there?
|
[
"As far as we know, no. The moon was formed roughly ",
"4.5 billion years",
" ago, and our oldest records of life date back roughly ",
"3.6 billion years",
". The earth was most likely a dead planet when it was struck."
] |
[
"Thank you. "
] |
[
"The Earth would have been a mostly-molten ball of rock without any stable atmosphere and certainly without any liquid water. And just to clarify for OP, it was a roughly Mars-sized body (referred to as Theia) which would have hit the Earth, not just any old asteroid."
] |
[
"After inserting a donor, how do surgeons \"restart\" a heart after a transplant?"
] |
[
false
] | null |
[
"Yes, most eletrical pulses are created in the brain, which controls the whole body. The heart is the only organ that is autonomous in eletrical pulse, it controls itself. Fun fact: A heart can still beat seconds, or even minutes outside the body before stopping because of oxygen starvation! Usually a simple massage applied direct to the heart can stimulate it to start beating again. Sometimes it is needed small eletrical shocks."
] |
[
"You forgot about the enteric nervous system, which is completely independent from the brain as well. "
] |
[
"That is incredibly interesting. I never knew we had cells that just create electricity"
] |
[
"How does the Hubble Telescope take pictures?"
] |
[
false
] |
I know in photography to take pictures you need to be standing still to not blur the image, you also need to (depending on your exposure and a bunch of other factors) also keep it still for that factor. So how does it take clear photos?
|
[
"The HST is an active tracking telescope. It maintains a specific orientation relative to the stars when it takes an exposure. It does this by using sensors to lock onto \"guide stars\" and then using its attitude adjustment systems (reaction wheels) to keep those guide stars on the same position on the sensor (covering the same pixels).",
"Of course, because the HST is in orbit that leaves unfortunate possibilities such as the telescope pointing at an object and then during its orbit the Earth coming into the frame. Scenarios like that are figured out during the planning stages and simply excluded.",
"As for blurring, the side to side and forward and back movement of the telescope through an orbit (much like the motion around the Sun due to following Earth's orbit) isn't enough to cause any distortion in the photos. As mentioned above the telescope is basically \"motion stabilized\" to keep it on the same patch of the sky to sub-pixel precision and the parallax due to the tiny amount of orbital motion is much too small to show up."
] |
[
"[ENCRYPTED]\nU2FsdGVkX1/47spXJ5vdqqPTLu//0X7vPmHW0KN0hNuxBcv9LCstScsbLGU0th6IvfAPWycX/3JgJjdmmx6fxE7/4C1ApnBNmWYInldWQAts0yrVcg55jVOcI9xWkMStkOH60WQfa0Oh5I74XQAmNVjMb8cug2t/r9/gdjKdBonFkmbuheAks/u5Y2/e+xeHltioBwJ0RSKvluSenuB0fuW5Ijn4seMQTNDMG17KbRYmCJpr316DFA0ZPJzVcDly0+E5UN+SfXSPwB5r1kipoougZm/mzI1P/Z9Uq9VVk+5/im97odO+KIVyLJ9D/7KJRiqB16zhw2hn7jageQcf/WWCuzrOL7KnIXzDINTA8LqUebTFnI0n5maVbNa4HyEa"
] |
[
"Hubble orbits the Earth at about 7 km/s. The Earth orbits the Sun at about 30 km/s. How can we get clear pictures from the Earth?",
"The answer is the same in both cases, the objects pictured (or the resolution of the telescopes) are so large that the motion of the telescope is negligible."
] |
[
"Could satellite take picture of street as if you were to take it standing in middle of street by looking at side of planet?"
] |
[
false
] | null |
[
"To add to this, the optical issues of reaching through that much more atmosphere would not be insignificant.",
"And perhaps most of all - a lot of what is thought of as satellite imagery by the general public (google maps for example) is actually aerial photography."
] |
[
"Yes, that's technically possible. A view angle that's near-tangential can allow for views that might seem more natural for humans. But it's not particularly practical -- much of the value of satellite imagery is being able to avoid obstructions.",
"Getting the satellite to just skim the earth's surface would also be difficult. Imagery at high off-nadir angles of 70° or so (what you're suggesting is closer to 90°) exist and maybe higher, but the fine control given elevational differences on the globe would be an engineering challenge.",
"There are also other technical problems with the processing and analysis of high off-nadir imagery. Accurately geo-locating the data, that is, positioning it on the globe would be difficult and might not even make sense depending on how high the angle is. Another issue is that the image is acquired through a much thicker column of atmosphere than when looking straight down. This means images are more likely to be obscured by clouds or 'dense atmospheres' if acquired using visible or IR, so a better bet may be to use radar. If using existing satellites and just tilting them, the angle also introduces exaggerated pixel distortions, misregistration of bands, and color skews -- things that are 'easy' to fix, but would require a new calibration.",
"Here are some examples from the folks at Digital Globe: ",
"http://blog.tomnod.com/high-angle-satellite-images",
"\n",
"http://blog.digitalglobe.com/geospatial/real-technology-real-benefits-part-1-pointing-agility/"
] |
[
"Sorry, let me clarify. All of the global and regional imagery is satellite. once you're down at the level of seeing individual buildings it is mostly now aerial photography. Very remote areas are still satellite but with a corresponding loss of fine detail"
] |
[
"What would be observed in the Large Hadron Collider to indicate that a new particle might exist, for example, a supersymmetric particle counterpart?"
] |
[
false
] | null |
[
"It depends on the specific particle and analysis."
] |
[
"At the relevant energies the effective collisions are between partons, i.e. quarks or gluons. The rest of the protons doesn't participate in the main collision. They just make things messy afterwards (hadronization).",
"It would be difficult to tell if a new particle is fundamental, but the study would depend on the particle. ",
" you expect to see a substructure if you have an energy similar to the particle mass. Which you have by definition if you create the particle newly. So generally we would expect to see the constituents instead of a composite particle."
] |
[
"If the supersymmetric particles form composite particles like, for example a proton is formed from quarks, the structure of which was probed by deep inelastic scattering experiments, would LHC be able to detect the signatures of this, because the LHC uses comparatively large particles such as protons and not small pointlike (in so far as we know) electrons? ",
"Someone asked me how we know if particles are fundamental particles (for example the electron), and others that seem to have \"structure\" such as the proton from deep inelastic scattering experiments, and my answer probably wasn't very convincing how it would be known that unknown particles, such as supersymmetric particles, would be fundamental."
] |
[
"Do bland-tasting strawberries have less nutritional value?"
] |
[
false
] |
Wild strawberries and home-grown strawberries usually have a ton of flavor, while store-bought strawberries taste like water -- is there a nutritional difference between them? Are there more vitamins in the more flavorful ones, or just more sugar?
|
[
"Kind of a strange one here, the background will depend upon your region to a degree.",
"Strawberries have, for a long time in some circles, been regarded as ",
"non-climacteric",
":",
"because its ripening process is not governed by ethylene.",
"Fruits like tomato are typically harvested when they are very immature, they are packed tightly into trucks where the hardness of the unripened fruit allows it to be shipped more effectively. Once the unripened tomato reaches its destination the tightly packed truck is pumped full of ",
"ethylene gas",
". There are other post-harvest ripening methods, but this is a very common one.",
"Now, some studies have shown a link between ethylene production and strawberry ripening, but it is not common to use truck ripening methods with the fruit because historical factors led to alternative methods. Instead of being treated like other delicate fruit, commercial strawberry varieties have been bred for traits that are not typically desirable in fruits.",
"Compared to your specialized, potentially locally bred, home garden variety of strawberry the common commercial strawberry plant is very hardy, the fruits are particularly large, and they ripen particularly quickly. The high ",
" of ripening contributes to the particularly bland flavor. Berries in commercial varieties have been shown to produce full redness in ",
"20 days",
", I have observed faster ripening in the field, on the order of two weeks, but I cannot locate a source to support the regular viability of that speed. Berries ripened this quickly are very bland, but do not rot on the vine for weeks, and can be further ripened and softened before harvest. The ripened state of these strawberries is determined by their size, their color, sometimes their fragrance, and the condition of the connection between the fruit and the plant - not by their flavor.",
"One effect of this high rate of ripening is that, while color develops to present the appearance of a ripened fruit, the actual physiological process of ripening does not progress as far. The cart has been bred to proceed the horse, so to speak. ",
"Does this actually affect the ",
" of the fruit? Well, that is a difficult one. ",
"Studies of ripened vs unripened fruit pulp",
" in other fruit types shows that there is difference, but that difference is primarily in the relative composition of carbohydrates. I am aware of no evidence to suggest that vitamin content, for example, changes appreciably during this process."
] |
[
"The effects of ethylene are myriad, ",
"climacteric ripening is extremely complex",
". Evolution of ethylene ",
" is emulated by creating high external concentrations of ethylene gas, it is proposed that the mechanism for climacteric ripening results from gene regulation which occurs in the presence of the ethylene. In this sense, the post-harvest ripening process should be activating the same genes and facilitating the same sequence of biological synthesis reactions similar to how they occur in the field. However, this is only one component of the ripening process, which involves several other regulating compounds. ",
"Anecdote would tell us that the post-harvest ripened fruit does not taste as good, we can attribute this to the ",
"relatively rapid intake of solutes during ripening",
", the majority of which are carbohydrates. That particular article is about legumes, whose seeds store a relatively large amount of nitrogenous compounds and fats, apples and tomatoes have a much lower concentration of these relative to their carbohydrate content.",
"As to nutritional value, this is harder to assess without a clear definition. ",
"Do post-harvest ripened fruit contain fewer carbohydrates? Yes, in most cases, because fruit undergo a net intake of solutes during ripening with a relatively high portion of this intake being of carbohydrates. ",
"Do they contain less protein and fat? Yes, in many cases, as these are imported into the fruit in order to build reserves for seeds some fruit varieties will increase their nitrogen and fat content over the course of ripening, the impact will vary greatly between different fruit varieties. ",
"Do they contain less vitamins, minerals, and trace elements? This is unlikely, based on our understanding of the action of fruit growth it is unlikely that trace element or vitamin content would have a high dependence on ripening, as fruits are not undergoing rapid cellular division once they have entered the ripening stage, and the chemical gradient for intake of trace elements is relatively small. in limited cases fruits will lose trace element concentration as they become more ripe, the plant will harvest water soluble compounds like chlorophyll in order to recycle the desirable trace elements like magnesium that they contain. For example, in ",
"tomatoes",
":",
"The results show that chlorophyll and tomatine concentrations decrease rapidly during the growth of the tomatoes",
"While post-harvest ripening emulates the effects of field ripening, it does not allow for the exchange of water-soluble compounds. Post-harvest ripened tomatoes do not break down their chlorophyll in the same way as vine ripened varieties, as the typical mechanism for breaking down these molecules is dependent upon gene regulation related to the parent plant. So, if your diet is lacking magnesium, you want unripened tomatoes, they are therefor more nutritious in limited contexts. You can see the difficulty in using the word nutritions in a general physiological context."
] |
[
"Correct, although flavor will be subjective, the ethylene actually has the effect of making many fruits, like tomato and banana, sweeter as they ripen. This is because part of the change which occurs is that the ethylene regulates gene expression which causes stored starches (stable, long lasting, less quickly digested) to become other complex carbohydrates like sucrose, fructose, etc (less stable, more easily digested, more prone to bacterial growth).",
"The truck ripened fruits, were they to ripen 'on the vine', would be simultaneously receiving inputs of carbohydrates from the vascular system of the plant. These carbohydrates would be subject to the same ripening mechanisms as those stored within the fruit, but the vine ripened fruit has a larger supply of them available (depending on the condition of the plant, of course). ",
"It is odd to think, but the ethylene doesn't effect the taste - that is to say, you cannot ",
". However, in the presence of ethylene the taste of the fruit changes (based on ripening condition), because ethylene causes non-taste-related changes which subsequently impact taste-related compounds."
] |
[
"How do we remember and mentally reconstruct tastes and smells?"
] |
[
false
] |
I was typing up a cookbook entry about cumin and it mentioned mixing cumin, cinnamon, and saffron. Instantly I knew exactly what all three taste like and what they'd taste like together. Visual information retention I can understand, as that image is crafted by the brain from light received by your eyes. It never really left your head because it never really entered it, you're just putting lego bricks together and calling the final product a boat. But taste, taste is weird. A taste, as I see it, is a chemical signature of something. It's completely external with no interpretation on your part. Visual representation changes depending on how much of the light spectrum you perceive and how fine-tuned your brain is (a schizophrenic, a colour-blind person, and you will see the same thing in three very different ways), but taste is completely foreign and contained only in the molecular structure of that object with no need for your brain to reconstruct data into some sort of picture (preference and association aside, as those are both behavioural). So why is it, with absolutely none of that unique chemical composition behind saffron or cinnamon inside of or reproducible by my body, that I can mentally taste both just as clearly as if I had them in my hand? It isn't just some vague association either, I can taste all the complexity of a vanilla bean, the tartness of Spanish marmalade, and smell both lavender fields and my favourite spice houses even though I'm nowhere near any of that. If taste and smell are completely foreign chemical signatures, how do I go about mentally reconstructing them?
|
[
"the brain retrieves the stored information of that taste in a relatively same manner as when you retrieve visual memory.",
"Definitely need to see a source for that."
] |
[
"the brain retrieves the stored information of that taste in a relatively same manner as when you retrieve visual memory.",
"Definitely need to see a source for that."
] |
[
"Right, so you're thinking about this all wrong.\nLight is emitted by something. Light hits retina. And activates certain retinal cells. Activated Retinal cells sends signal into the brain. The spatial pattern of cells activated in the retina activates a certain collection of neurons in the brain. Is is this pattern that allows you to receive the light emitted off a red boat and know that you are looking at <a red boat>. If you looked a a green boat from a different angle, potentially completely different retinal cells would be active, but the pattern of neurons activated in the brain would somewhat overlap, those that coded for <boat>.",
"Taste/Smell is analogous. Something emits chemicals (Rather than photons of light). These enter your nose and activate a certain pattern of olfactory epithelial cells. These then send signals to the brain, which activates a certain pattern of neurons in the brain. It is this pattern that represents <Lemon>. If you were to smell Lemon Grass a different (though in this case, probably partially overlapping) pattern of cells would be activated in the olfactory epithelium, which would activate a different pattern of neurons in the brain.",
"Just like when you remember an image, your retina does not become active; when you remember a smell, your olfactory epithelium does not become active. What is activated are higher level areas, further down the pathway. The areas responsible for coding the nature of the sense to begin with."
] |
[
"Why does the Earth's gravity (or gravity in general, for that matter) pull with a constant acceleration rather than a constant force?"
] |
[
false
] |
I'm in Physics II, so I know of Newton's Law of Universal Gravitation, F=(mgG)/r , so I know that the force between two masses only depends on the distance between them, but ? Do we know why? Why is it that a 10kg object will be pulled with a force of 98N while a 1 kg object will be 9.8N, yet are accelerating at 9.8m/s ? Why is it that two objects, like in Galileo's experiment, fall at the same rate? I would normally assume that an object (like the Earth for example) would always pull with a constant force rather than acceleration?
|
[
"Why does the Earth's gravity (or gravity in general, for that matter) pull with a constant acceleration rather than a constant force?",
"Okay basically it works like this: the ",
" of gravity is stronger for heavier objects, proportionally to their masses.",
"But in accordance with the idea of ",
", heavier objects require ",
" to accelerate at the same speed.",
"Both of these effects are proportional to the mass of the body, so they cancel eachother out. It's like dividing \"m\" by \"m\" -- you get 1.",
"Does that help?",
"By the way:",
"I know of Newton's Law of Universal Gravitation, F=(mgG)/r",
"This is incorrect -- Newton's Law of Universal Gravitation is F= G(mM)/r",
"(There are two masses, not two \"g\"s.)",
"We know that F = ma, so the acceleration due to gravity is:",
"a = F/m = GM/r",
"Thus the acceleration only depends on (1) the distance to the other massive body, and (2) the mass of the body."
] |
[
"Each kilogram of mass experiences the same pull. So a 1kilo mass experiences ",
" the pull of a 2kilo mass. Why then does it not go at half the speed it has half the pull?",
"Because it also has half the mass. Imagine two bowling balls - one 1kg and the other 2kg. Which is harder to push along the floor? The heavier one right? Because of inertia. By the same principle the greater mass and greater inertia for the heavier mass ",
". So all things accelerate at the same speed (neglecting air resistance)."
] |
[
"Let's start with the last question: The force is proprtional to the mass of the object being pulled (so double the mass means double the force.) When you think about it, it has to be this way:",
"Imagine if the force was constant, say 98N, regardless of mass. An object of 10kg would be pulled by 98N. But split the object in two, now suddenly you have TWO objects being pulled with a total of 2*98N = 196N, just from a \"cosmetic\" splitting of the object. In fact what constitutes a splitting? Why wouldn't every atom of the object be considered a single object that gets 98N each?",
"As to why they fall at a constant acceleration: The force is proportional to m, but the acceleration comes from F=ma, which means a=F/m and the mass cancels out.",
"For a more conceptual explanation, do the same thought experiment as above: Imagine \"cosmetically\" splitting a heavy object into two lighter objects. Does it make sense that they would suddenly start falling slower just because you split them up? Or in reverse, does it make sense that two light objects should start falling faster just because you bind them together into one object?"
] |
[
"Does the temperature of the water in a glass of ice water change as the ice melts?"
] |
[
false
] | null |
[
"When pure ice reaches 0 degs C it starts to turn into water. The water/ice mixture will stay at 0 degs C until all the ice is turned into water. Then the water will rise above 0. The same is also true for reverse. Also this is the ideal case. Statistically speaking there is always the probability for fluctuations. "
] |
[
"When ice melts the temperature does not change. The energy goes in to the melting process rather than increasing the temperature."
] |
[
"While the other comments are true, a better answer would be that the nearby water remains at a nearly constant temperature while the water, say, at the bottom of the glass warms up and rises to the top, causing a convective current to form within the glass"
] |
[
"Why does high blood sugar damage the kidney's filters?"
] |
[
false
] |
[deleted]
|
[
"I'm trying to work out how diabetes can cause diabetic nephropathy.",
"This is a complex topic and the exact mechanisms are unknown. Here are some of the contributing factors: ",
"Glomerular hyperfiltration - filtering more glucose, fats, and proteins leads to inflammatory reactions and fibrosis (controversial) ",
"Advanced glycation end products (AGEs = proteins/AA with covalently bonded sugar moledulce) accumulate and interrupt normal protein function ",
"Increase oxygen free radicals due to hyperglycemia",
"Increased inflammation means signaling molecules (cytokines) which can have negative effects on the kidney are released",
"In what way are the filters damaged? ",
"And why does that cause the release of renin?",
"In general? Check ",
"here",
". In diabetes specifically, it may have to do with increased prorenin. It may be because of other blood vessel effects. It may just be that those with high blood pressure and diabetes are just more likely to have nephropathy. The big take away is that Angiotensin Converting Enzyme Inhibitors (ACE Inhibitors) like lisinopril and Angiotensin Receptor Blockers (ARBs) like losartan which interrupt the renin-angiotensin alodsterone system play a major role in the treatment of diabetic nephropathy by reducing blood pressure and decreasing the fibrotic effects of angiotensin. ",
"Here are some sources for further reading: ",
"Mechanisms 1",
" ",
"Mechanisms 2"
] |
[
"I work in dialysis and have taken anat & phys, emt paramedic classes and I was under the impression that high blood sugars cause damage to capillaries such as those in the kidneys, eyes, toes and fingers. Please correct me if I'm wrong or if my assumption is too general. Didn't get to read the sources but will as soon as I get a free second."
] |
[
"Diabetes can manifest with a variety of vascular complications. In general you can look at these in two categories: ",
"Microvascular, includes: retinopathy (eye problems), neuropathy (nerve problems), ulceration, and nephropathy (kidney problems) ",
"Macrovascular, includes: heart attack, claudication (pain in legs), and stroke/TIA (mini-stroke)",
"The question is why does high glucose lead to these problems. To just say that it damages the capillaries doesn't address the question. Especially when you consider that the glomerulus is essentially a tuft of capillaries. ",
"edit: shortened"
] |
[
"Is it safe to watch the sun with the naked eye during a sunrise or a sunset?"
] |
[
false
] |
Why?
|
[
"It is safe to watch because of an effect known as Rayleigh scattering. When the sun is at a greater angle, it has to travel through more of the atmosphere to reach us, meaning the higher frequency light has a higher chance of \"bouncing\" off of the gas particles in the atmosphere. This is also why the sun changes colors while setting. "
] |
[
"The amount of dimming and colour changing depends on atmospheric conditions. On a humid summer day sunset, the sun turns totally red, and it might even fade out a bit above the horizon. On a clear cold day, the sun might have colour between yellow and orange and feel too bright too look at. I have difficulty believing that it is always safe to watch sunrises and sunsets. This question requires experts."
] |
[
"the sunlight during sunrise and sunset is much more attenuated (dispersed) due to scattering attributed to the long passage the sunlight takes through the atmosphere when it is just over the horizon. "
] |
[
"Do pronghorns have velvet?"
] |
[
false
] |
have what's basically a hybrid between ) and ; permanent bone cores that grow and shed a layer yearly. , does anyone on here know whether they have - blood vessel-rich skin that supplies nutrients to growing antlers?
|
[
"When I think of velvet, I think of a thin layer of haired skin-type tissue, vascular like you said, that antlered ruminants eventually rub off to reveal the underlying bony antler that persists for several months until it too falls off. ",
"North American antelope don't have that. It's more like a thicker layer of compacted keratin over epithelial tissue with the bone core supporting it all - somewhere between a toenail or sheep/goat horn and hair.",
"You can think of the horn sheath that's shed kinda like velvet, but it's not heavily vascular like velvet; it gets nutrients from the underlying bone core. To me it's more like the keratin part of a hoof or toenail than an antler.",
"E: here's a review that goes into the tissue types a bit, comparing between various ruminants:",
"https://royalsocietypublishing.org/doi/10.1098/rspb.2011.0938"
] |
[
"North America antelope are one of a kind, yes :)"
] |
[
"No problem. The other thing I thought to mention - antelope horn shedding is a bit like how you lose a fingernail after hitting it with a hammer. Sometimes it hangs on for months until the new fingernail pushes underneath of it, causing it to fall off."
] |
[
"Why can't I cut a solid, and then stick the two pieces back together again?"
] |
[
false
] |
If I take a solid iron rod, and saw it in half, what is actually happening on an atomic level? And why I can't I stick the two solid pieces back together, unless I convert one of the pieces to liquid first?
|
[
"You can. In fact, it's known as cold welding and commonly used in space. ",
"Under normal conditions, the moment you cut it, contaminants stick to the surface and the metal reacts with the atmosphere to form an oxide layer. This prevents the previous metallic bonds from reforming. ",
"For other objects, they tend to have crystalline structures which have to be perfectly aligned to reform the bonds. "
] |
[
"Why don't two piece of glass stick together?",
"The surface of glass is very \"bumpy\" on an atomic level. The pieces \"touch\" each other only on a very small area. They do \"stick\" together there, but the force holding them is too small to carry their weight.",
"You can do 2 things to make 2 pieces of glass stick together:",
"Polish their surfaces. But they will never become a continuous piece of glass as you will still have considerable gaps. You can't polish them fine enough and contaminants will also pollute the gap.",
"Sprinkle some water on them. The water will fill the gaps and push and sublime the remaining air in the gaps. This will stick the 2 pieces togther because outside air pressure will push them together. Note that you can easily break this formation if you just slide the pieces along another, as the water doesn't actually put up any resistence."
] |
[
"Why don't two piece of glass stick together?"
] |
[
"Did the sun's recent explosion cause the sun to move even a hair?"
] |
[
false
] |
Theoretically it should have right? Action-reaction and with no other forces on it (gravity)? Since action-reaction forces are ideal in space does that mean the sun moved just a hair? What could this mean for the future?
|
[
"The sun is moving through the solar system all the time, mostly around the center of mass of the Jupiter's orbit with some perturbations from Saturn and the other planets. Momentum would be conserved when the sun burped out its gas, but that wouldn't have much effect on its path."
] |
[
"thanks for your reply!"
] |
[
"Solar ejections are equally likely to occur in any direction.",
"Over the course of time, this tends to average out. The movement by a hair in on direction will be offset if the next explosion is from the other direction.",
"EDIT: By any direction, I mean any radial direction. They are more likely to be ejected near the equator, but no particular direction is preferred. "
] |
[
"Is water necessary for tectonic activity to take place? if so, why?"
] |
[
false
] |
So i seen this mentioned on a youtube video about Venus. It mentioned that Venus has no tectonic activity because its water evaporated millions of years ago. What effect does water have on tectonic activity?
|
[
"The surface temperature is extremely high on Venus, which is a big reason why the average surface temperature there is 460 Celsius, where it is about 14 Celsius here on Earth. Sure there is still convection still going on Venus, however the difference in Surface temperature and Core temperature is not far enough apart. Also lava on Earth is normally in between the 650 and 1200 Celsius, so with this we can see that Venus has a much more liquid like state in terms of its lithosphere so there is less stress that builds up to develop tectonic activity."
] |
[
"No it is not needed, you need convection from the core outwards to drive tectonic activity. What cools it on the surface doesn't matter as long as the surface is cooler than the core so that convection will continue to occur."
] |
[
"Is the problem with Venus that there is no significant cooling on the surface for convection to take place?\nSide question: does Venus have any levels of convection taking place?",
"Thank you for your answer"
] |
[
"Why do some forms of birth control (pills specifically) limit their starting dates?"
] |
[
false
] | null |
[
"Most hormone pills have a biphasic or triphasic combo of progesterone and estrogen. This is done to mimic\n the natural hormones of the body but ultimately the levels of the estrogen and progesterone are titrated to a level that mimics pregnancy and prevents ovulation and also thickens cervical mucus to prevent sperm from entering the uterus.",
"Now for these to be effective they must be taken a) before you ovulate and b) in a part of the cycle where it won't screw your hormones already in circulation. ",
"The first day of your period is actually the first day of your cycle in medical eyes. It should last 3-7 days. Next, You the have 7 days of increasing hormones followed by ovulation at 14 days past your first day of your period. You have to fertilize the egg within 3 days of ovulation to become pregnant or it is useless and is shed. It takes the egg 7 days to travel down the Fallopian tube and an additional 3 days to implant (if fertile). That leaves 4 days before your next cycle starts.",
"Therefore to recap, you have to take the BC before you ovulate and at a time when it can override your hormones and prevent ovulation that ultimately won't extend your cycle too much otherwise your body will have all sorts of weird things going on and will take a long time to adjust."
] |
[
"The pill essentially stops the egg from being released. If you take the pill too late you will already be ovulating and be able to get pregnant. Each pill is different and has different hormones. It isn't \"unsafe\" but it ensures your taking the hormones during the correct times. Side note it is best to wait a month after you start the pill before you start going at it. That is the only way to be sure your egg hasn't already been released before the pill took effect. "
] |
[
"The reason isn't one to worry about so much for most basic estradiol contraceptives. The reason you're told to do that, is because if you start then, you will be protected from pregnancy by the time your menstruation ends. Because, generally oral contraceptives like this and ortho take a week to properly give you the prevention you are looking for. If you start in the middle of the month, you likewise aren't protected until a week after taking it properly. So, essentially, there is no real reason other than to get better results. Some women may start taking it and then have sex the next day, get pregnant and wonder why it didn't work. Basically telling you to do it the way you state eliminates a lot of human error."
] |
[
"At what altitude does the sky cease to be blue?"
] |
[
false
] |
Is it always blue until you leave the atmosphere?
|
[
"I will answer your question with a question.",
"At what point does the red become blue in the following image?",
"http://d2o0t5hpnwv4c1.cloudfront.net/612_gradients/webkit.jpg"
] |
[
"Sorry, I guess the point I was trying to make was that as you move outwards from the atmosphere, the blue will eventually become darker and darker, until it is totally black. You could arbitrarily pick a point where you say \"There, it's black now, not blue\" - but it would probably be different for each person.",
"So yeah, a gradual transition - just like how in that image I posted you could probably pick a point and say \"it's blue now\" if you wanted, but really, it's a gradient so... yeah :)",
"Hope that makes sense!"
] |
[
"Sky gets dark at around 30 kilometers. You can see stars during the day at these heights."
] |
[
"I can throw a baseball a lot further than a ping pong ball. I cannot throw a bowling ball nearly as far as a baseball. Is there an \"optimal\" mass or mass to diameter ratio for a ball to throw it as far as possible?"
] |
[
false
] |
I'm assuming a perfect sphere here, so you can ignore modifiers like dimples on a golf ball.
|
[
"There are a lot of details which this answer will not contain, but this will give you the tools to start thinking about the question. ",
"The reason you can't throw a ping pong ball very far is that it is that the force of the air resistance causes a large acceleration on the object. The force on the object due to air resistance is a function of the speed of the object and the size/shape of the object. So, a ping pong ball and a solid lead ball the same size/shape as the ping pong ball thrown at the same speed will have the same force of air resistance on it- this will lead to the same change in momentum on both. However, that change in momentum is a much larger acceleration on the ping pong ball. ",
"In some mathematics, we say dp/dt = F (change in momentum as a function of time is equal to the force applied). Since momentum is m*v, if they leave with the same velocity (v), since the lead ball has a larger mass it has a larger momentum. So, working it out, say both balls are thrown at a velocity of 1000 m/s, and the ping pong ball has a mass of 0.001 kg and the lead ball a mass of 1 kg, and a force of 1 N is applied to the two balls for 1 second. Then, the ping pong ball starts with 1 Ns of momentum, and the lead ball starts with 1000 Ns of momentum. After the 1 N force is applied for a second, the ping pong ball is now has a momentum of 0 (so, it has stopped) while the lead ball has a momentum of 999 Ns, so still has a speed of 999 m/s. Thus, the same change in momentum has lead to a much larger change of velocity in the ping pong ball. So, by looking at this, given a velocity, the more massive the object the further it will fly. ",
"Now, we have to look at \"given a velocity.\" The object you're throwing will leave your hand at the speed your hand is moving when you let go of it. Even holding nothing, there is a finite speed you can move your hand. Putting a ping pong ball in there might not decrease your arm movement at all. Putting a bowling ball there decreases it a lot. Any time you throw a ball, you have to move the mass of your arm + the mass of the ball. The final speed of your arm will be governed (to an easy approximation) by the formula:",
"Iw",
" = T*theta",
"Where I is the moment of inertial (we'll come back to this) w is your rotational velocity (from which you can get velocity you let go by with the simple formula v = w*r where r is the length of your rotation), T is the torque you can provide your arm (this comes from your rotating torso, shoulder and elbow) and theta is how much you rotate your arm by. The amount of Torque you can provide is basically a constant, based on how strong you are. Theta is determined by your throwing motion, which we'll also consider constant. So really, to get the highest w possible, you want as small of an I as you can. Well, I comes from the amount of mass you're trying to rotate. However, the mass of your arm means you'll always have some I, and it will increase as the mass of the object you're throwing increases. However, by adding something light, the percentage increase in I is small, so the change in w will be small. As the mass increases, the percent change increases as well. And the more massive the arm is that is doing the throwing, the less adding something like a baseball to it causes a percentage increase, so the more massive your arm is, the heavier of an object you could throw and still get a large velocity. So, the optimal velocity will depend on that as well. ",
"So, at the end of the day- what's the answer. And it's going to depend. It's going to be a balance between how powerful your air resistance is, and how much adding weight to your arm slows down your arm, and then you're going to have to solve a nasty differential equation, and it will pop out the optimal mass. But, basically you'll be trading off these two things the entire time. "
] |
[
"So something extremely dense and aerodynamic but not very big would be best, right?"
] |
[
"well when you throw a ping pong ball it has very little momentum compared to a baseball. momentum is p=mv so if you throw the balls at the same velocity then momentum=mass. Less mass = less momentum so it wont go as far. As for the bowling ball its just so heavy that you have a hard time getting it to the velocity that you throw a baseball at"
] |
[
"Is the temperature of a black hole absolute zero?"
] |
[
false
] |
Since matter keeps getting denser and denser, and moves less and less to the point of absolute zero where nothing is moving or vibrating, and it is giving off no black body radiation, would a black hole be absolute zero? It fits the characteristics of what something would be like at absolute zero.
|
[
"This was thought to be the case before the 1970s, but Bekenstein and Hawking showed that black holes actually emit blackbody radiation, albeit at a very low temperature for realistic-sized black holes. The temperature is inverse proportional to the mass, and for a solar mass black hole, the temperature is about 60 nanokelvin. In practice this is effectively zero, because the cosmic microwave background is a scorching 2.7 kelvin in comparison."
] |
[
"It happens due to quantum effects on the even horizon. If a black hole cannot \"eat\" anything, then eventually it shrinks and \"dies.\" Of course it's not like its shooting out stuff at a huge rate, it's very little matter that escapes for every unit of time."
] |
[
"Yes, a solar mass black hole is definitely still way colder than the CMB. But if you had a small enough black hole, the temperature could get quite hot. Hawking has been hoping for a while that evidence for small black holes (perhaps created in the early universe) could be detected, which would be the best hope for experimentally verifying Hawking radiation."
] |
[
"[physics] Why doesn't Helium freeze at 0K?"
] |
[
false
] |
I know reaching 0k is actually impossible. But from my understanding, all predictions indicate that helium would remain a liquid at 0k
|
[
"The interactions among Helium atoms are too weak, at atmospheric pressure, to condense Helium to a solid even at absolute zero. Note that, at absolute zero, the atoms still possess a positive amount of kinetic energy. (I.e. they do not slow down to zero speed at zero Kelvin.) An increase in pressure is required to freeze Helium.",
"edit: For more information see ",
"Zero Point Energy",
"."
] |
[
"At 0K, atoms have the minimum amount of kinetic energy. If the potential energy of a flat sheet of atoms looked like an egg carton - a lattice or grid of wells - then imagine each atom is wobbling back and forth inside the well. However, because of \"quantum\", the lowest possible energy state of each well, or simplified ",
"quantum harmonic oscillator",
", still requires that each atom is wobbling. ",
"The most intuitive reason is the Heisenberg uncertainty principle. If every atom were perfectly still, you'd know both its position and momentum exactly, which isn't possible."
] |
[
"I thought the definition of temperature was based on kinetic energy. How do atoms retain kinetic energy at a theoretically perfect and absolute 0K?"
] |
[
"Why does old coffee stick only to the highest level in a cup?"
] |
[
false
] |
I've noticed that whenever a cup of coffee or hot chocolate is left out and cools, it always leaves behind a ring where the highest level was. Why does this happen to drinks and soups when hot but not when cold?
|
[
"Good question! The physics of coffee rings is pretty interesting and was worked out in the 90's - see ",
"this paper in Nature",
", and if you don't have access you can find a non-paywalled copy ",
"here",
". Coffee is a colloidal suspension of solid particles in a liquid. At the \"corners\" of the liquid body that are exposed to air (i.e the edge of the cup), evaporation creates a flow of fluid towards the edge. This drags more of the suspended solids to that region and bumps up their concentration. Eventually evaporation lowers the liquid level in the cup but a ring is left behind because the concentration of solids was so high in the \"corner\".",
"The hot drinks are evaporating faster than cold drinks, so the flow will be stronger there. But you can see the same effect with wine so it isn't limited to hot liquids."
] |
[
"Why do anything? "
] |
[
"Why do anything? "
] |
[
"What is the (engineerical) knowledge concerning the longevity of Batteries in relation to their performance?"
] |
[
false
] |
For example a lithium ion battery (48v / 29 Ah). Does the performance of either 1 kwh, 2 kwh or 3 kwh influence the longevity, if so in which way?
|
[
"It's not entirely clear what you're asking here. Please correct me if I'm wrong, but what I think you're asking is: do we know how long batteries last (either runtime or lifetime) given a certain power usage?",
"If that's the case, we do. Check the data sheet for your favorite battery. You'll notice the nominal runtime in 0.05C usually (20 hour runtime), and various curves for cycle lifetime given depth of discharge (DoD is more important for lifetime than current draw, not that current draw isn't important either)."
] |
[
"Ah, I see now! I wish I could give you a better answer right now; all I can say is your general suspicion of the battery exhibiting lower longevity is what I have experienced in my projects. I will allow others to share whether there has been any extensive testing done on this. Great topic and I don't think I've seen it asked here before!"
] |
[
"Hi there,\nFirst: Thank you for your reply. Second: Please bear with me as english is not my first language. I am interested in the experience through testing results by engineers versus the theoretical supposed outcome. For example when named batteries are build in devices/or vehicles. Further example: let´s say a electro-scooter. The more power the faster the scooter accelerates from 0 to 25 miles/h. Is the longevity of a Battery with 1 kwh better or worse as the one with 3 kwh? Does more power strain the Batteries more, or not? Maybe there is no difference at all. In short what are the experiences of the engineers?"
] |
[
"Space Telescopes: Since they are _somehow_ moving, relative to the Earth or Sun (which are both moving), what is the longest exposure time they can use without getting motion blur? How does this affect clarity and detection?"
] |
[
false
] |
Since the observer is moving, a long exposure time will produce motion blur of the target, but long exposures also allow for increased sensitivity to weak light. I'm curious how space telescopes are hypothetically limited since they are always in motion (not to mention their targets).
|
[
"You can read about the Hubble's pointing systems ",
"here",
".",
"The simplest mechanism is the use of gyroscopes: these keep the Hubble pointed in the same direction in space even as it orbits the Earth, so you don't get immediate blurring. The Hubble ",
"ultra deep field",
" image was made with numerous 20 minute exposures."
] |
[
"a long exposure time will produce motion blur of the target",
"Not really no. Telescopes in space and on the ground have autoguiders called fine guidance sensors on space missions which track objects in the field of view. They sense tiny errors in the pointing of the telescope and actively correct for this by feeding back information into the pointing system. There are limits to these systems and errors but you don't see anything like motion blur unless something has gone wrong. "
] |
[
"Cool. ",
"Do you know if 20 minutes is the maximum time for an exposure? Or what kind of distortion we get with a 20 minute exposure (minimal, but certainly not zero...)?"
] |
[
"What is the most humane method of execution?"
] |
[
false
] |
By humane, I mean which method involves the least amount of suffering for the person who is being executed. Conforming with this definition, which method is most humane? The gulliotine, hanging, the electric chair, lethal injection or something else I have not listed here? Also, if the most humane method is not the one used for executions in the United States today, why not - does it have a medical justification?
|
[
"In 2005, University of Miami researchers, in cooperation with an attorney representing death row inmates, published a research letter in the medical journal The Lancet. The article presented protocol information from Texas and Virginia which showed that executioners had no anesthesia training, drugs were administered remotely with no monitoring for anesthesia, data were not recorded and no peer-review was done. Their analysis of toxicology reports from Arizona, Georgia, North Carolina, and South Carolina showed that post-mortem concentrations of thiopental in the blood were lower than that required for surgery in 43 of 49 executed inmates(88%).",
"21 (43%) inmates had concentrations consistent with awareness.[5] This led the authors to conclude that there was a substantial probability that some of the inmates were aware and suffered extreme pain and distress during execution. "
] |
[
"There was a good ",
"BBC Horizons",
" episode about \"humane killing\", from what I remember of it, they ended up advocating death by hypoxia caused by a noble gas as being the best method. See the ",
"wikipedia article"
] |
[
"Wow, your argument didn't seem that hard pressed... I stand corrected! I had no idea the injections weren't administered by a physician; I made a poor assumption. That's too bad as if administered correctly lethal injection should be painless. Thanks for posting this!"
] |
[
"What does computer data look like physically? What makes certain hard drives hold more data than others?"
] |
[
false
] |
Thanks for all the responses everybody!
|
[
"This kind of breaks it down",
"guy's brilliant"
] |
[
"There's various different forms of computer data.",
"In RAM, and while the CPU is working on it, it's simply electricity; often +3.3 volts of electricity means \"1\", while 0 volts means \"0\". All data is made out of 1s and 0s stringed together; for example, the letter A can be represented as 01000001.",
"On the hard disk, it's stored as magnetic fields on something called a \"platter\". The platter is a thin disk that spins really really fast, and a bunch of \"heads\" will read the magnetic fields off tiny sections of it - again, certain fields mean \"1\", and others mean \"0\" - and when you write data to the disk, other heads will change the magnetic field of a tiny section of the platter.",
"When data is read off a hard disk, usually it's then written into RAM, so that the CPU can do something useful with it; convert it into a bunch of pixel data that can be displayed on your screen, then send it off to the graphics card, for example.",
"Certain hard drives hold more data than others either because they have more platters to store the data on, or the heads can read/write to even tinier sections of the disk than other hard disks, so they can fit more data onto the same size of platter.",
"There's also a few other ways that data can be stored, however I'm not sure how they work."
] |
[
"Every electron in a metal has a spin and as a result acts like a tiny tiny magnet. Now normally all these magnets are oriented randomly, so the effects of one are canceled by another. But in certain materials, quantum mechanics (many hairy details that you probably don't want to know) results in neighboring spins wanting to be aligned together. Hence aligning large part of spins in the material, hence giving you a kitchen magnet!",
"Now as an aside a very common way to explain this is to say that material is made of tiny magnets (spins), which just like ordinary magnets will align due to the magnetic interaction. This is not completely right! It's quantum mechanics that is the main driving force in making kitchen magnets work!"
] |
[
"Can the body use alcohol as fuel?"
] |
[
false
] |
You often hear that alcohol is fattening or contains a lot of calories. It's said that alcohol contains 7 calories per gram. But can ethanol itself be used by the body as a fuel source? By what mechanism? Does it ever get converted into glucose that the brain and muscles can use? Does it get converted into fat and stored subcutaneously or viscerally? Assuming that you got vitamins and minerals from supplements and enough amino acids and essential fats, could you survive on alcohol as a fuel source? I don't understand why that would have evolved. My understanding is alcohol is basically a toxin that the liver has to remove. I found another question on it here but the answers seemed more about causing fatty liver rather than the specifics I'm interested in. I think a lot of the advice is down to sugars and carbohydrates in the drinks, e.g. in beer/cider/wine or in the mixers e.g. coke. What about if you just drank vodka, which apart from a few impurities mainly contains ethanol and water. Is it as fattening as all the advice warns us? Would 100ml of 40% vodka be like 40g of ethanol or 280 calories (for simplicity I have assumed ethanol has the same density as water)? It seems like a lot of calories. There are only about 36 calories in 100ml of coke. If it does contain that many calories, is the effect on weight gain the equivalent to the same number of calories of sugar?
|
[
"The article ",
"Relationships Between Nutrition, Alcohol Use, and Liver Disease",
" has some information about this:",
"\"",
"\"",
"The article ",
"Alcohol and Nutrition",
" observes that:",
"\"",
"\"",
"Back to your questions:",
"Assuming that you got vitamins and minerals from supplements and enough amino acids and essential fats, could you survive on alcohol as a fuel source?",
"Given the damaging effects on metabolism described in the above articles, including absorption of certain vitamins, and given that \"",
",\" your health would begin to measurably deteriorate immediately. Another important factor here has to do with blood glucose levels:",
"\"",
"\"",
"Back to you again:",
"I think a lot of the advice is down to sugars and carbohydrates in the drinks, e.g. in beer/cider/wine or in the mixers e.g. coke.",
"That's correct. The article ",
"How Long Can You Survive On Beer Alone",
" describes someone who lived on a beer and water diet for 46 days. But beer contains sugars which provide a less problematic energy source than ethanol. I'll risk a little speculation and say that without those sugars, your survival would likely be severely compromised. As you mentioned, you'd basically be trying to survive by getting energy from a toxin.",
"I don't understand why that would have evolved. My understanding is alcohol is basically a toxin that the liver has to remove.",
"Alcohols including ethanol are produced naturally in animals including humans - this is known as \"endogenous ethanol production\". \"",
"\" (",
"source",
"). Since ethanol is toxic, being able to metabolize it is evolutionarily important.",
"However, the human ability to handle ethanol in relatively large quantities likely goes beyond this. There's evidence that \"",
"10 million years ago, a common ancestor of gorillas, chimps and humans emerged with an enzyme that could digest alcohol 50 times more efficiently than earlier incarnations",
",\" which is hypothesized to be related to diets involving fermented fruit harvested from the forest floor.",
"Of course, more recently in human history, many societies have relied heavily on alcohol consumption, which has apparently resulted in adaptations:",
"\"",
"\" (",
"Nutritional Adaptation",
")"
] |
[
"Yes ethanol does contain ~7kcal/gram. Ethanol itself isn't a fuel source, but is converted into \"fuel\". ",
"Ethanol is detoxified in the liver by this process:",
"\nEthanol -> Ethanal (",
") -> Ethanoic acid (",
")",
"Acetic acid can be converted into ",
" which is used in ",
". ",
"Ethanol is 0.789 times as dense as water so 100ml of 40%abv vodka, would contain about 221kcal. (= 31.56g of ethanol). ",
"I'm not sure if it's effect on weight gain is similar to that of sugar, though. "
] |
[
"That's very interesting. Thanks."
] |
[
"How is surface tension related to droplet formation?"
] |
[
false
] |
Say you're trying to form a drop of water by letting it out of a small tube. Using the same tube, after adding soap to the water, will the drops formed in this process be bigger or smaller compared to pure water drops?
|
[
"This is actually used to determine liquid surface tensions",
" (or ",
"this",
"). The pendant drop technique uses changes in the shape of a suspended liquid drop to determine a liquids surface tension. All suspended drops of liquid will deviate from a spherical shape as gravity pulls the drop down. The greater the deviation from a perfect sphere, the lower the surface tension - only an infinitely large surface tension will produce a perfect suspended sphere."
] |
[
"Depends how much liquid you put through the needle. The maximum volume of the drop for a given liquid and given needle geometry is a constant though and is directly proportional to the surface tension. So soapy water would produce smaller maximal volume drops of liquid."
] |
[
"Thanks for your answers! Have a nice day"
] |
[
"Why do storms on our solar systems outer planets last so long?"
] |
[
false
] |
Title. Earth's toughest storms seem to only last a few weeks. But storms on the outer most planets have storms which have lasted for years or decades. What is so different about Earth?
|
[
"This is half remembered from a planetary science class a few years ago, so it may not be entirely accurate, but I think it’s related to the lack of land masses/analogous features to break up the storm. Hurricanes/typhoons on Earth form and strengthen over the ocean, then dissipate once they make landfall. There isn’t an equivalent for gas planets like Jupiter, so the storm eventually reaches some quasi-equilibrium and stays that way for much longer than on Earth. "
] |
[
"Both water and land absorb energy from wind through friction. The reason storms normally form and grow over the ocean is that the ocean supplies it with water vapor, which is the fuel the storm needs to grow and maintain itself. I guess the gaseous nature of the outer planets means less fiction for the driving force(s) of the storm to overcome. "
] |
[
"This is a wild guess, but could it be slowed down because the outer planets are much colder, leading to slower reactions.",
"Also, storms on earth more or less always involve water or water vapour, whereas the atmospheres of other planets contain different compounds. Different materials behave differently.."
] |
[
"How are neutrinos formed?"
] |
[
false
] |
And I mean, not where they are formed, but how, and from what are they created from? Thanks in advanced!
|
[
"Kind of. When ",
" themselves decay (like muons or tau leptons) they produce a neutrino of their same flavour, and then a W boson that decays as iorg points out. So a muon decays to a mu neutrino, and a W",
" boson that decays to an electron and an electron anti-neutrino. It turns out that electron or muon or tau neutrinos aren't the \"stable\" state of neutrinos, and they actually oscillate among flavours, but that's another story for another time."
] |
[
"During beta decay, a W boson decays into a lepton and an antineutrino, or an antilepton and a neutrino."
] |
[
"Is that the only way they can be created?"
] |
[
"Noether's Theorem - does the Principle of Relativity result in a conservation law?"
] |
[
false
] |
First, let me preface this by saying that I don't fully understand the math behind Noether's Theorem - I'm mostly hoping for a qualitative explanation (but math is good too :) As I understand it, , broadly stated, says that for any symmetry in physical laws, there is some corresponding conserved quantity - a conservation law. Given that the states that a moving observer cannot experimentally determine their motion relative to an outside source, would this count as a type of velocity symmetry? And if so, what conservation law results from this?
|
[
"I think it's a case where the math is at some level necessary. When we express physics in terms of say, a Lagrangian description, we can perform certain transformations on that description. For instance I can add +x, some arbitrary distance to all of the distances in the Lagrangian, and when I crank through the math, I'll find that the momentum in the x direction stays the same. Similarly, adding time will show a conserved quantity known as energy.",
"I think where you'll see relativity appear is that observers will disagree about who's moving and how fast and just how long distances are and how fast time is ticking by. But the conservation results of momentum and energy will end up balancing out in a conserved 4-vector of Energy-Momentum (often called the 4-momentum). And guess what that relationship ends up being. ",
"E",
" - ",
" c",
" = m",
" c",
" ."
] |
[
"It's sort of like this. Say you started from absolutely nothing and wanted to derive all of modern physics. Obviously you'd have to make some observations along the way, but a lot of physics consists not of equations derived directly from observation but rather equations that follow inevitably and logically from other equations. So it'd be a process of observe-infer-deduce-repeat.",
"The thing is, though, that there are multiple ways to derive all of modern physics. For example, you could start with notions like work and force and derive simple equations of motion from them … or you could skip all that and just work in phase space and go straight to Lagrangian or Hamiltonian mechanics, then derive equations of motion ",
"Modern physics isn't a direct linear succession of idea-to-idea. There are closed loops of implication. Take Noether's theorem for example. It says that for every continuous symmetry there's a conservation law … but it ",
" says that for every conserved quantity there's a corresponding symmetry. You can get to the central idea by approaching it from either side."
] |
[
"Recall, if you please, that Noether's theorem applies only to ",
" symmetries. What you're thinking of there would be a ",
" symmetry.",
"Consider a point on a circle. If you translate the point a little bit along the circle, you're effecting a symmetry of rotation about the center of the circle; you're not in the same place, but you're in a place that's sufficiently \"same\" for there to exist a conserved quantity. But if you translate the point along the circle by a distance equal to an integer multiple of 2",
" times the circle's radius, then you're right back where you started from. That's a symmetry, but it's not a ",
" symmetry. It's a ",
" symmetry, because it breaks if you translate by 2",
" plus a little bit.",
"The universe is reflection-symmetric as well as being rotation-symmetric, but there's no general conservation law associated with that symmetry, because it's discrete rather than continuous."
] |
[
"Why is the Higgs Boson listed separately from the other Gauge Bosons in the Standard Model?"
] |
[
false
] |
[deleted]
|
[
"Because the Higgs boson is not a gauge boson.",
"Gauge bosons are spin 1 particles that are needed to ensure that a local symmetry holds.",
"The Higgs boson is a spin 0 particle and it does not serve to ensure the existence of a local symmetry."
] |
[
"No, it doesn't have to be spin 1. In part, I was keeping things simple since OP seemed to be referring to diagrams of the Standard Model, but it's also the case that if I simply said \"gauge boson,\" in most contexts I would implicitly mean a vector field. But you're right to raise this.",
"Just to spell things out a little:",
"If you've got an internal symmetry that is gauged, then the associated gauge particle will be a vector.",
"If you've got a local symmetry that also deforms spacetime, then you can get a higher index gauge boson. If gravity could be quantized, the graviton would be a tensor gauge field.",
"Of course, in Kaluza-Klein theory, you take a higher dimensional rank-2 tensor gauge field (higher dimensional graviton) and decompose it into several lower dimensional objects -- e.g., in going from 5 to 4 spacetime dimensions, the 5-dimensional rank-2 tensor gauge field decomposes into a 4-dimensional rank-2 tensor gauge field, a 4-dimensional vector gauge field, and a 4-dimensional scalar. So in this case, how you think of the Lorentz properties of the fields depends on whether you take the 5 or 4 dimensional point of view.",
"Edit: Typo fixed (\"that\" --> \"the\")"
] |
[
"Does a gauge boson need to be spin-1? I thought any boson with a gauge symmetry counted. (Of course, all the ones that appear in the standard model are spin-1 anyway.)"
] |
[
"How are the routes of blood vessels determined?"
] |
[
false
] |
One day I was looking at my hand and started wondering about my blood vessels. How are their routes determined? I would imagine they take the shortest and thus most economical route possible — as it seems to be everywhere in nature — to deliver oxygen etc. to the cells. How do they find that route? Is it possible to simulate this process anyway?
|
[
"many MANY things in nature follow a similar fractal branching pattern. Your blood vessels, a tree's branches, your brain cells, the roots of many plants, etc. Even more, fractal patterns like this are found in tons of things outside of the biological sphere: ocean wave patterns, lightening bolts, earthquakes. So to answer your question, no, the mechanisms behind a tree's branching and the formation of a network of blood vessels are almost certainly unrelated, but they both follow a very similar pattern of diffusion, one that is pretty ubiquitous throughout the universe. "
] |
[
"Blood vessels are a physical approximation of a kind of ",
"space-filling curve",
" (actually they are a not a \"curve\" in the mathematical sense but never mind). This is because every cell in your body needs oxygen, so needs to be close to a blood vessel, so on the large scale it looks like blood vessels fill the entire volume of your body. Obviously there needs to be room left over for the rest of you, but this is the reason why many similar structures - leaf veins, root systems, for instance - exist."
] |
[
"Follow up question: I've noticed before that the patterns in tree branches looks similar to the branching of a network of blood vessels. Is this just a coincidence, or is there some similar mechanism driving the patterns?"
] |
[
"How come we know so little on the whale shark?"
] |
[
false
] |
It's the biggest fish in the ocean, we know where to find them, where they nest(nest?) and exactly what they look like. Yet, no one really knows what's their life span(60-100 is no where near precise) or how they reproduce. Why don't we just track them?
|
[
"Because they only hang out near the surface to eat - After that, they dive up to ",
", where they do most of their living. We can't easily go that deeply, so as a result, we don't really know what they do down there (though we know by inference they mate and give birth down there, because they don't do it near the surface).",
"So, we really only know their dining habits. Everything else about them (even how long they live, we don't know for sure) remains a mystery."
] |
[
"Sharks actually avoid the limitations of air bladders by regulating their buoancy with their livers which contains large quantities of lightweight fluid lipids."
] |
[
"That's really interesting and brings a bit of a followup question to my mind. ",
"Would animals that live so deep and then need to rise so far to eat not be at the risk of something like the bends from the sudden change in pressure?"
] |
[
"Are there materials that are good at conducting heat but not electricity or vice versa?"
] |
[
false
] | null |
[
"Actually there are materials that are designed to do exactly this for use in thermoelectric generators - they're called 'phonon glass electron crystals' or PGECs.",
"Other guy isn't wrong they are very much intrinsically related (it's called the wiedemann-franz law). Overall THERMAL conductivity is the sum of contributions from the vibrations within the material (phonons) and the motion of electrons. But what you can do is minimise the former without really affecting the latter, for example by having lots of layers of different material (therefore introducing interfaces that scatter phonons) as a kind of composite. You've then significantly reduced thermal conductivity without sacrificing electrical. "
] |
[
"Diamond.",
"It has a thermal conductivity five times better than copper, with synthetic diamonds having the highest thermal conductivity of almost any substance known. Diamonds are also generally a very good electrical insulator, although some colors of diamond occur because of impurities that also make them a good semiconductor.",
"EDIT: Adding some graphs here:",
"Diamond's thermal conductivity",
" is well above all metals, challenged only by graphene.",
"Diamond's electrical conductivity",
", meanwhile, is very low, on par with quartz (SiO",
") and plastic (PET)."
] |
[
"Not sure if there's materials where this mechanism is enough for them to be \"good\" heat conductors, but phonons (collective excitation of a crystal, where the atoms are moving relatively to each other) can also transfer heat within a solid. ",
"Edit : A ",
"link",
" where you can read something about how phonons play a role in heat conduction processes."
] |
[
"Do planetary bodies in a \"stable\" orbit gradually move any closer to the body they orbit?"
] |
[
false
] |
[deleted]
|
[
"In the Newtonian approximation, it does not move closer. General relativity does it have it emitting gravitational waves, taking away this kinetic energy, and moving closer. However, this effect is incredibly tiny. We don't have to worry about spiraling into the sun, even on timescales of billions of years."
] |
[
"There's discussion of how the effects scale at ",
"http://en.wikipedia.org/wiki/Gravitational_radiation#Power_radiated_by_orbiting_bodies",
"For some of these we can indeed measure as the orbital periods decrease. ",
"http://en.wikipedia.org/wiki/PSR_B1913%2B16"
] |
[
"There's discussion of how the effects scale at ",
"http://en.wikipedia.org/wiki/Gravitational_radiation#Power_radiated_by_orbiting_bodies",
"For some of these we can indeed measure as the orbital periods decrease. ",
"http://en.wikipedia.org/wiki/PSR_B1913%2B16"
] |
[
"How do antidepressants make you gain weight?"
] |
[
false
] |
[deleted]
|
[
"Potentially, in a variety a variety of ways ",
"(taken from this recent consensus report on the subject)",
", although the unsatisfactory answer is that exact causes aren't really defined.",
"The mechanisms are related to both direct drug effects on appetite stimulation, or on normal resumption of appetite when patients begin to feel better, or both. ",
"These drugs directly influence appetite and cravings for food because the compounds are not really selective in the neurones they target or the effects they produce, and their beneficial effects in neurones involved in mood and behaviour may not be beneficial (with regards to weight gain) in areas of the brain concerned with regulating appetite. Having said that, antidepressants may not have quite the same impacts on weight gain as other psychoactive drugs.",
"Postulated mechanisms for different antidepressant drug classes, from the above review:",
". Tricyclic drugs have been implicated in weight gain. Anticholinergic activity has been considered a possible mechanism for weight gain in that it causes dry mouth, which can lead to excessive consumption of high-calorie beverages. A craving for sweets has been reported among patients taking amitriptyline, nortriptyline, and imipramine.",
". Selective serotonin reuptake inhibitors (SSRIs) selectively block the reuptake of serotonin into presynaptic nerve terminals. Because they enhance serotonin, it is possible that use of SSRIs results in a lower intake of carbohydrates. Minimal weight gain and decreases in appetite have been associated with the use of SSRIs.",
" has been associated with an increase in appetite and weight and with dry mouth. The mechanism of this effect is not well understood."
] |
[
"Various drugs have actions at different receptors. There appears to be at least a rough correlation between weight gain and blockade of specific dopamine (D2), histamine (H1), and serotonin (5-HT2C) receptors. Older tricyclics like amitriptyline, as well as the atypical drug mirtazapine, are the serious weight-gainers. ",
"Many newer antidepressants have no such effect; of the SSRIs, only paroxetine is associated with significant weight gain. SNRIs are similarly neutral, and bupropion can even promote weight loss. It's also worth remembering that loss of appetite can be a symptom of major depression, in which case weight gain could simply mean a good response to the drug.",
"http://www.consultant360.com/article/psychotropic-induced-weight-gain-review-management-strategies"
] |
[
"But from what I know most antidepressents make it much harder to work out due to less motivation, fatigue, among other side effects.",
"Why would antidepressants ",
" motivation? Increased motivation should be the whole point, no?"
] |
[
"Question about dissimilar metal corrosion..."
] |
[
false
] |
[deleted]
|
[
"The oxide finishes on both the aluminum and the fastener should prevent the formation of a galvanic cell. Even if galvanic corrosion occurs, the less-noble aluminum piece is much larger than the SS component, so the corrosion will be very slow.",
"Cheers."
] |
[
"The general term for this is \"galvanic corrosion.\" ",
"Black oxide may react with the aluminum, but I can't find a definite answer. I'd repost to ",
"/r/engineering",
"."
] |
[
"From what I can tell the black oxide coating should prevent corrosion between the two metals."
] |
[
"Why is there atomic motion? i.e. why do atoms move?"
] |
[
false
] | null |
[
"Because other atoms bump into them! The universe began at a nonzero temperature, which means that it began with some energy available for motion. Atoms have been jostling into each other ever since!"
] |
[
"Yep! In each bump between atoms, energy is conserved. This means that what you started with is still the same amount of energy you'd have now (ignoring some important things like expansion of the universe that we can get into if you want, but it's a bit more complicated)."
] |
[
"Sorry to continue to ask, Why?? ",
"You are saying that from the time of the big bang enough energy was imparted into the atoms of the universe to maintain constant motion?"
] |
[
"Would someone mind walking me through how they calculate the the time it took for light from a type 1a supernova to get to our planet?"
] |
[
false
] |
Just so you know what I know: I know what a standard candle is and why we need that to figure out how far away it is. What I don't know is the equation(s) that is used or how to use it.
|
[
"A number of methods",
" are used for determining distance."
] |
[
"Thanks but that doesn't actually answer my question. Knowing the frequency will tell you how fast its traveling away from you, but not the distance. My question is how (what equations and how do you do the math with those equations) do we know how distant it is from us?"
] |
[
"Thanks but that doesn't actually answer my question. Knowing the frequency will tell you how fast its traveling away from you, but not the distance. My question is how (what equations and how do you do the math with those equations) do we know how distant it is from us?"
] |
[
"Why do some LEDs remain on for seconds after they've been switched off?"
] |
[
false
] | null |
[
"It is really down to how the circuit is designed. Sometimes capacitors in the circuit (or more accurately the power supply) will continue to provide power after supply voltage is cut off. It doesn’t inherently have anything to do with the LEDs behaviour. The LED just glows when you apply voltage across it and will go out immediately once voltage is no longer being applied. "
] |
[
"Some white light LED's will exhibit ",
"phosphorescence",
" after they are turned off. This is because virtually all general illumination white LED's are a Blue, Violet, or UV LED with a phosphor painted on the chip. It is this phosphor that after glows. But, the ones I have seen do this are very faint. So if they delay at a fairly bright level, it is the capacitors as you pointed out.",
"There are some white LED sources were they use a red, green, blue combined chip. This is actually an inefficient way to do white light. Has to do with poor quantum efficiency of the green and red LED's. It is done this way were you want an adjustable color lamp. Like in theater work."
] |
[
"LEDs usually require a very small of current to operate.",
"This means that if there are any energy storing components in the circuit (capacitors or inductors) they can sustain the LED for a while after the power source has been turned off."
] |
[
"If you suddenly eat a lot more than you normally do in one meal, does your body process the extra calories normally?"
] |
[
false
] | null |
[
"While I'm not a metabolic or GI expert, perhaps I can shed some light.",
"The several segments of the GI system are specialized in specific things depending on which segment of the GI you're looking at. Example: stomach, mechanical, acidic and enzymatic digestion of large segments of food.",
"The segment you have to really be concerned with are teh jejunum through the small instesti. These segments are specialized of water and nutrient absorption and I cannot emphasize the TREMENDOUS amount of surface area in these tissues that specialize in nutrient absorption. These tissuse are compressed, have vili on the folds that are compressed and then have microvili on the vili which are on those folds. All this contributes to surface area which absorption/diffusion can take place. (",
"Jejunum",
")(",
"Sm Intesti EM",
")",
"That paired with the immense blood supply to the gut make this system extremely efficient. However, I feel it is not impossible to overload the system. First, absorption of each type of nutrient is a process independent of others (Fat and Carb uptake are mediated through different cellular processes). ",
"There can be individual differences with the efficiency of each of these with the most variance in fat absorption. It is possible to overload this system by simply loading too many nutrients into the system for DIGESTION to efficiently take place. This can be because of too much material or difficult to digest material. If anyone has ever eaten too many protein shakes in one sitting knows the result: Loose Stool. This is primarily because there is too much nutrient content in the lumen of the large intestine as the content passes through the Lg Intestine is not able to absorb water and dehydrate the stool. ",
"As far as exact calorie count at which this happens, it's not that simple. Calories come into the diet in different forms and this mix along with individual differences is what dictates the amount absorbed. If you eat 1500 calories from a carb heavy source like potato chips I doubt your GI would have trouble dealing with it. However, 1500 calories of bacon or lard may not do so well and you'll spend the next 2 hours on the toilet. ",
"Sources: Alberts Mol Bio of the Cell 5th",
"Edit, put wrong source initially, whoops."
] |
[
"I can't speak to the ketogenic diet's efficacy, some people with IBD disorders do well on it but as far as weight loss its probably the sheer lack of carbs that does it. High protein, low carb content diets work basically all the same. The Adkins diet by nature was a ketogenic diet. It just didn't have it in the name. ",
"Diets get a lot of media attention and hype by the public... It's not always accurate information that's being circulated among the fitness community. "
] |
[
"as a dietician...your body is very much capable of absorbing more than 4000 calories per day. The most I have seen a patient report consuming was nearly 7500 calories. This person had severe metabolic diseases. The 'extra calories' cannot simply pass though your system. If you start to eat more than you are capable of digesting your stomach will begin to refuse the food that you are trying to put into it. Then you start to get stomach acid up and into the oesophagus."
] |
[
"\"Black hole erupting for first time in 26 years\" - CNN.com Can someone tell me what it is that is actually being studied, and why it is interesting?"
] |
[
false
] |
I love that more and more science based news stories are being run in today's popular press, but I came across on the cnn front page this morning, and I honestly couldn't make heads or tails of what is actually going on. Has a particularly dense part of the accretion disk made it to the horizon and the radiation jets are gaining in intensity? How does a black hole "wake up" or "erupt"?
|
[
"there is another star orbiting the black hole, and gas from the star is accreting onto its surface and igniting a fusion reaction",
"Just to clarify – NASA's terminology here was confusing, but what you described is a ",
"cataclysmic variable",
", in which accretion from a binary companion onto a white dwarf ignites fusion reactions on the surface of the white dwarf. This system instead is a ",
"low-mass X-ray binary",
", in which the liberation of ",
" of material entering a black hole leads to heating and emission of blackbody radiation. The emission is this system is unikely to be due to fusion reactions, since accretion disks rarely achieve sufficiently high densities to ignite fusion reactions.",
"More information about this outburst may be found ",
"here",
". "
] |
[
"Yes, in a reference frame where both us and the black hole are slow. And it's a nuclear reaction, not a chemical one."
] |
[
"Well this is all the information they give so you can't really tell anything:",
"A NASA satellite detected the first sign of a black hole 8,000 light years away from Earth on Jun 15, 2015. Astronomers around the world are studying the event.",
"Googling that phrase reveals that V404 Cygni is emitting more x-rays than usual. This system is a nova (not a supernova): there is another star orbiting the black hole, and gas from the star is accreting onto its surface and igniting a fusion reaction."
] |
[
"Is it possible to create an optical filter that polarizes a narrow band of frequencies, but lets the rest of the light bandwidth to pass through unchanged?"
] |
[
false
] | null |
[
"If you're talking explcitly about the visible/nearvisible soectrum I don't know of one singular optical component that could be used to do this but I am willing to be corrected. I think you could do this if you have two polarizing beamsplitter cubes and some notch filters of the appropriate wavelength though. Will happily explain the setup if this would be useful. If you're thinking of light outside the visible range though i don't think i can help."
] |
[
"Once I have done an experement with a simple linear polarizing photo lenses: i have used them as glasses with the angle between left polarizing axis being turned -45° while the right one +45°. The result was interesting, when looking thru these glasses a lot of surfaces appeared flickering (which makes sense considering they were for one eye and bright for another).",
"Then I have read about the color-blindness correction glasses EnChroma, and I was thinking how was the effect implemented. So the first idea was - to provide different polarisation filters for, say, green for the left and right eyes."
] |
[
"I think you could do this if you have two polarizing beamsplitter cubes and some notch filters of the appropriate wavelength though.",
"Ha! That's actualy very smart! That was exactly what I was interested in. Ideally I would like to have a sort of a film though :) ",
"Thanks!"
] |
[
"Do chickens have a limited supply of eggs throughout their life, or can they produce eggs as long as they have a functioning reproductive systema?"
] |
[
false
] | null |
[
"Birds, like humans, have a limited number of primary oocytes in their ovaries. But most of them don't live long enough to run out. ",
"This Slate article",
" that addresses your question says that some macaws, which are very long-lived, can run out of eggs, but the ",
"study they cite",
" is on humans, and I can't find the macaw fact anywhere else. Still, biologically it makes sense that if a bird lived long enough, it would be unable to continue producing eggs."
] |
[
"Thanks man, exactly what I was looking for"
] |
[
"They make pretty good pets. They eat leftovers, bugs, and make fertilizer for gardens. Also, if you snuggle them when they are little, they will snuggle you when they are older. It's a tiny fluffy dinosaur that likes you and that's pretty cool."
] |
[
"How much DNA do we share with our maternal grandfather?"
] |
[
false
] |
How much DNA do we share with our maternal grandfather? EDIT! As a MALE, how much DNA do I share with my maternal grandfather.
|
[
"On average, an individual inherits 1/4 of their autosomal genome from a given grandparent. Each of your parents inherited exactly 1/2 of their genome from each of their parents, and you in turn inherited 1/2 of your genome from each of them.",
"However, due to the fact that genetic recombination during meiosis occurs in large blocks, instead of freely between each pair of bases, there is actually substantial variation around that number. My advisor actually wrote up ",
"a blog post",
" about his exact question not that long ago. ",
"For example, ",
"here",
" are two histograms showing the fraction of a particular grandparent's genome present in a given parent which is transmitted to their offspring (in other words, if you divide the scale on the x axis by 2, then that gives you the distribution on the fraction of your genome that you would have inherited from a maternal and paternal grandparent respectively). ",
"Here",
" are the same figures, but for chromosome 1 (the largest) and 22 (the smallest) alone.",
"One thing you'll note is that at the genome wide scale, and also when you look at individual chromosomes, the distribution is more tightly centered around 1/4 for maternal grandparents than for paternal grandparents. This is because, ",
"for reasons that aren't entirely understood",
", females have higher rates of recombination than males, meaning that they do a better job of giving an even mix of their parents DNA to their children than males, who have lower recombination rates, and therefore are more likely to pass on large blocks of DNA from one parent or the other, which results in the child having more or less DNA from one of their grandparents.",
"So on average, 1/4 of your autosomal DNA comes from each grandparent, but on the maternal side you are likely to be closer to 1/4 from each grandparent than on the paternal side, where the likelihood of a larger imbalance (potentially as extreme as 10:40) between the two grandparents is greater.",
"The above discussion also ignores a few other pieces of DNA that have different inheritance patterns. These are the X and Y chromosomes, and the mitochondria. For all individual, one of their X chromosomes is a mixture of the Xs that your maternal grandparents carried (just as described above for the autosomal DNA). If you are male, you have a Y chromosome that you inherited from your paternal grandfather via your father, while if you are female you inherited your second X chromosome from your paternal grand",
", via your father. Lastly, mitochondrial are inherited via the maternal line only, so your mitochondrial DNA comes only from you maternal grandmother."
] |
[
"In humans, DNA is comprised of 46 chromosomes. X and Y are the two special chromosomes that determine gender, but they only represent a tiny portion (~5%?) of your total DNA. So in general, when talking about your DNA in total, gender makes no difference. You should, ",
" inherit 1/4 of your DNA from each of your four grandparents. But, if you are a male, then yes you can be 100% certain that you have the same Y as your father, and your father's father, and your father's grandfather, etc."
] |
[
"Sorry, see my edit.",
"How much DNA does a male share with his maternal grandfather?"
] |
[
"How were the very first computer languages/operating systems coded?"
] |
[
false
] |
Without any basis with which to code such complex programs, did they have to write everything in binary? Machine code?
|
[
"Assembly languages are just a step above binary. Assembly code is basically just CPU instructions expressed in human-readable text. Assembly \"compiler\" (actually ",
") is almost a 1:1 converter between text representation and binary. (It may also have some macros and other conveniences). People used to write everything in assembly before the advent of higher-level languages.",
"Of course you still need to write that first assembler, but as you can imagine it's not a very complicated program. And once you have it you can use ",
" program to implement a more complicated assembler. That technique remains common when developing higher-level languages as well: you start with a rudimentary compiler, then you use ",
" compiler to implement a more complete compiler (so, in effect, the compiler compiles itself). For instance, gcc is itself written in C."
] |
[
"The original way to program the oldest computers was to develop the instructions by hand and then wiring that in with ",
"wires into a plug board",
".",
"But later computers were initially programmed one byte at a time through front panel switches where you could usually set each bit of some structure such as a byte, word, etc. and deposit that binary value into a memory location.",
"You would literally program every bit with switches. ",
"Video here:",
"https://www.youtube.com/watch?v=XV-7J5y1TQc",
"and",
"https://www.youtube.com/watch?v=NtAF-WfWyGU",
"The first is a bit goofy, but it gets the concept across.",
"Edit: better video here: ",
"https://www.youtube.com/watch?v=EV1ki6LiEmg"
] |
[
"Of course you still need to write that first assembler, but as you can imagine it's not a very complicated program. And once you have it you can use that program to implement a more complicated assembler.",
"Ah, I never considered that possibility! It's fascinating to hear how coders worked around technical limitations back then."
] |
[
"What is the difference in mental stimulation between reading and watching TV?"
] |
[
false
] |
I've noticed that I get sleepy when reading, even when I'm really enjoying the book - but within a minute of putting the book down and turning on the TV I'm suddenly wide awake and alert, even when I don't really care to watch TV. I'm curious what areas of the brain are stimulated in reading vs TV and why the latter jolts me awake. I assume it's something to do with light & noise but would love to hear it explained by someone knowledgeable in that area.
|
[
"Not a top level answer here, but no one else has posted yet, so...",
"I'd say it's more likely that you're experiencing conditioning. For me, it's the opposite effect. I can read all night and not fall asleep, but I have grown accustomed to watching things when I go to bed, so I easily fall asleep watching TV. In fact, I can't sleep easily without it.",
"All of that means that I doubt it's a difference in mental stimulation and more a reaction of what you expect to happen. If you read, get sleepy, and turn to the TV to stay awake, you're conditioning yourself to respond to the TV with alertness."
] |
[
"Good point - I've known people who would get droopy eyed five minutes into a movie and by an hour would be fast asleep, regardless of how loud or fast-paced the movie was. Maybe they're falling asleep to TV every night."
] |
[
"This is not my field of expertise, but there are some observations I can pass along.\nReading is more active than watching TV. In reading your eyes take in visual stimuli that are first interpreted as characters / words, then integrated into sentences / images / concepts. It requires reference to the earlier parts read for continuity, including resolution of erroneous assumptions. (As imagining the room is brightly lit with big windows, to later learn that the room has heavy curtains hiding the windows, etc.) Yet you fill in many details that are not specifically mentioned for the sake of continuity. TV is more passive in that more is given and less is created internally.\nBut reading is also self-paced, while the images of TV come at you at their own pace. There are many TV shows that have scenes that go so fast it is not possible to see a lot of the detail that goes blurring past.\nDifferent parts of the brain will be used and to different degrees with the two mediums. I cannot give more detail, as this is not my field."
] |
[
"How do we calculate current world population? Also, how accurate is that count?"
] |
[
false
] |
Burning question on my mind for awhile now. How do scientists calculate the current number of people on the planet? Is it some massive database, clever , or something else?
|
[
"Censuses, surveys and estimation. Most (all?) countries have some sort of census, literally asking everyone in them how many people are there. This can be validated by taking smaller populations and checking the numbers (like census data says 100 people live in this district, lets go door to door and physically count them and see how much the census was off). Sometimes people from outside (like another international organization) will do these checks.",
"Then other people might do their own independent estimates, find X buildings in a city, Y apartments per building, and Z people per apartment. Multiply it out and see what you get. And then extrapolate those numbers to similar areas.",
"There are also records for stuff like new housing, death records and birth records, it gives you an idea of where people are moving and how the population is growing. Current numbers are estimated with the best known numbers plus estimated growth rates.",
"This is generally done from the lower level up, and each country gets their own population count, and experts figure out how accurate it is and get that best estimate. Add up all countries and you get a very good estimate of population."
] |
[
"This is not the type of question that a mathematician usually thinks about. Our work isn't about estimation, though it is relevant to statistics. I'm not saying this to be rude, just to point out that a different flair will get more relevant users seeing your question. I would suggest 'social science' as a more appropriate flair."
] |
[
"Perhaps more like good than very good, although I suppose there's always the realistic enough hope that all the errors from individual countries roughly cancel each other out at a global level.",
"There's that old quote I can't remember about the English census in India - all the high level workings were really reliable but ultimately it was relying on reports filtering up from the villages and....",
"Probably better than that these days but they're still a really quite hard thing to be fully accurate about."
] |
[
"If neutrons have no charge, what force causes them to stay in the nucleus of an atom? And do electrons ever come into contact with nuclei?"
] |
[
false
] | null |
[
"There is a nuclear force that bounds protons and neutrons together in a nucleus. You may have heard of the strong nuclear force that holds quarks together inside of protons and neutrons, and the nuclear force is a manifestation of that. It's similar to how van der Walls forces that keep atoms near each other are a manifestation of electrostatic forces that keep electrons bound to atoms.",
"Electrons sometimes come into contact with the nucleus, which can induce radioactive decay. This is called electron capture."
] |
[
"To go a little further, this idea drives nuclear reactions like fission and fusion. In a nucleus, you have two main competing forces; the nuclear force pulling in and the electric force pushing out. The nuclear force only acts over tiny tiny distances, about the width of an atom at maximum; neutrons contribute to the nuclear force. The electric force acts over large distances, centimeters or meters; neutrons do not contribute to this force.",
"In fusion, you start with two separate small nuclei. It is very hard to push the two nuclei together initially because of the electric repulsion between the protons. But, once you get them close enough for the nuclear force to be relevant, they pull together and fuse.",
"In fission, you start with a very large single nucleus. So large, the nuclear force from one side does not have much effect on the opposite side. This means it is just on the brink of the electric force ripping it apart. This is basically what happens when something like uranium naturally decays."
] |
[
"Yeah that's not really accurate.",
"http://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/"
] |
[
"Do cats that get into a lot of fights learn 'combat moves' or is a cat's fighting style instinctual?"
] |
[
false
] |
Do cats that get into a lot of fights with other cats learn more lethal and effective tactics and styles, or is this all innate and genetic?
|
[
"What can be said for sure is they get used to it. That's what repetition training to harden soldiers is about. Take one guy who has stabbed a dozen guys and one guy who has only used a knife on steak. The action of plunging a knife into another human's body will be a more comfortable action for the former, just like a cat who has gotten into a dozen rolling battles will more quickly get into the proper mode the next time another cat plows into them.",
"Obviously other factors come into play in fights, but as far as cats learning specific techniques, that's hard to determine. They're going to naturally execute movements most efficient with their body and muscle structure to some degree. Humans honing their own movements, practicing them (this is key, as the only actual practice cats get is fighting and playing), and sharing and collecting information about them is a product of human psychology more than anything. Cats would have to routinely figure out the more precise efficient movements and practice them outside of a fighting environment like a martial artist for this to work. ",
"More than likely, the naturally toughest and most experienced cat as far as past fights will be the toughest cat. He will have the best chance of executing the most effective moves, and some may even be typical of its individual style or behavior, but I don't imagine you'd see any results of a conscious effort to train particular techniques. The fundamentals of cat fighting are likely instinctual, combined with the physical traits of the cat and enhanced by actual experience in fights. "
] |
[
"Do you really honk so ? "
] |
[
"Do you really honk so ? "
] |
[
"What causes differences in virus longevity outside of the body?"
] |
[
false
] |
Herpes virus is said to only survive a few seconds outside of the body but the influenza virus can survive up to 24 hours and cold viruses survive for a week. What are the mechanisms and factors that both lead to the virus destruction and cause the difference in survival time? "It is highly unlikely that HSV will be passed on to other people by the sharing of towels or toilet seats. Outside the body the herpes virus cannot survive for more than a few seconds." "Cold viruses have been shown to survive on indoor surfaces for approximately seven days. Flu viruses, however, are active for only 24 hours."
|
[
"Actually HSV can survive longer than a few seconds outside the body. What's debatable is how long can a sufficient amount of the virus exists outside of the body, enough that can infect. That's also the question with other pathogens. Yes there are trace amounts hours or days later, but ate those amounts enough to infect. "
] |
[
"Virus is a pretty broad term, and different types have very different structures and survival strategies. ",
"Viruses can encode their genetic information as either DNA or RNA, which can be either single stranded or double stranded, and if it's single stranded, it can be either the sense or antisense strand. Viruses also vary greatly in their capsid make up, they can have very different shapes and they can be made of different types of proteins. Many viruses also have a lipid envelope surrounding the capsid, this can also vary greatly between types, and some don't have one at all.",
"I can't speak to the specific viruses you listed, but with such diversity, it stands to reason that they could vary greatly in their ability to survive outside of a host. For example, it would make sense that a double stranded DNA virus with a large capsid and an envelope would have very different survival requirements compared to a single stranded RNA virus with a small capsid and no envelope."
] |
[
"I think this answer has a lot of merit, but HSV is an enveloped double-stranded DNA virus and has a short lifespan outside the body, while rhinoviruses (the cause of most colds) are single stranded, non-enveloped RNA viruses. I would suspect the major factor influencing viral lifespan may be the stability of the outer viral capsid proteins. Some may be stable over a range of temperatures, humidity levels and ionic conditions, while others may disintegrate if not present in the temperature and humidity/ionic conditions of the mammalian host."
] |
[
"If the universe is expanding, does that mean that new space is being created?"
] |
[
false
] |
If not, then what do we mean when we say the universe is expanding? What is actually happening?
|
[
"When we say the universe is expanding we mean that, if you were to go out into space, where there was nothing else around and place two beacons (which somehow didn't have any gravitational attraction to on another), one meter apart, and make sure they weren't moving relative to one another. Then later come back and measure the distance betweem them, you'd find that they were futher apart than before. The space had expanded and the beacons had been carried along with the expansion. ",
"Asking how space is 'created' is a question its difficult to make sense of. What's space made of in the first place? It might not be made of anything. If it's not made of anything in what sense is it being created? If we want to know if there's more of it, we'd have to know how much there was in the first place. So if you'd like to define space by talking about distances between things, and say if the distace increases then there's more space, then I think that's ok. But I think it's much better to not talk about the creation or destruction of space at all, but to talk about what's happening directly. That is, that the distances between things are increasing, and we call that the expansion of space."
] |
[
"hmm does the PE lost between two bodies (say the 2 beacons) balance with the KE of the apparent velocity?"
] |
[
"hmm does the PE lost between two bodies (say the 2 beacons) balance with the KE of the apparent velocity?"
] |
[
"My mind was blown after reading this article. Can someone tell me about your fascination with cellular automata?"
] |
[
false
] |
I was off this last week and decided to refresh my AI knowledge. I was looking for information on autonomous agents and stumbled upon cellular automata. I researched the topic in the past but not much in detail. For the past week, I really got into it and my mind is completely blown. Basically, cellular automata consists of applying simple rules (programs as Stephen Wolfram calls them) to a on/off cell grid. You start with some initial state and then run the program. Over time, patterns start to emerge. In one speech, Stephen Wolfram claims to have modeled space and time with some of his experiments. It is fascinating stuff. Also, I want to write some applications with real world examples. Could you also help me build some practical? Right now, I was thinking of building a visual turing machine demo. Article: Example Application:
|
[
"I can't read any of Wolfram's stuff without thinking that he's a complete blowhard. Yeah, he's found some interesting stuff, but he crouches it all in this \"mind-blowing\" pseudo-philosophical speech that often has little to do with what he's actually describing. For instance, the discussion of \"purpose\" in the article you linked to, which completely begs the question of whether purpose is something that exists in the universe or whether it's something we ascribe to things. This after he just talks about the cultural contingency of meaning. He also completely mixes up the two meanings of the word purpose---that of end result, and that of intention---as though because the same word is used for both they must be tied together in the same concept. Or his Principle of Computational Equivalence, which even in his book he admits comes purely from his own intuition and is only supported within the framework he's developed. It's like, what is he getting at, what is he trying to prove? How smart and world-changing he is? Because that's what all his stuff comes down to: \"look at this world-changing stuff that ",
" done.\" And who is the one who is calling it world-changing? He is.",
"OK, so I know I've just made a bunch of ad hominem attacks and not actually discussed cellular automata. I only bother because of the language you use of having your \"mind blown\". What really is so impressive to you about all this, I ask? Does it come down to the actual ideas, or the language used to encapsulate those ideas? I mean, what the fuck does \"modeled space and time\" even mean? Don't you think that if he actually had a more useful computational model than general relativity, that we'd have heard something about that by now?",
"My take on this whole thing is that he's found a useful way of creating a specific kind of patterned data using iterative techniques. Which isn't that difficult, in the end. However, it will be useful once we can go the other way, and recognize patterned data using iterative techniques. That's what will allow our von Neuman computers to begin acting more like us, \"intelligent\" in a way that we understand. How poorly Wolfram|Alpha works for most tasks involving more than one or two concepts shows just how he hasn't managed to do that. Even Google's Bayesian statistical approach to language parses it better than his approach does.",
"edit: I am very curious what those who are smarter and better educated in regards to computer science take away from Wolfram's work, because I recognize I may be missing something. Most of my critique centers around him and how his own hubris turns me off from his work (and I think he makes a terrible philosopher of science). But that there is something fundamentally world-changing about cellular automata is something I'd be willing to believe. I just have never heard it from anyone other than Wolfram."
] |
[
"From what little I understand, there's a school of thought in mathematical physics that holds that a (hitherto unspecified) cellular automaton is sufficient to simulate the universe. A corollary of this is that the fundamental operations of the universe are very simple, indeed. ",
"FWIW, it's a neat thought and I wouldn't mind it being true, but I'll believe it when someone's written a cellular automaton that produces the Standard Model and General Relativity. But just think of running a program that's actually equivalent to a bit of universe like our own :) "
] |
[
"If you convert the digits of pi to binary, somewhere in that massive string of bits is a quicktime movie of your entire life, from birth to death. ",
"Now, if you only knew where to find it, we'd "
] |
[
"Why are there two spring tides per lunar month?"
] |
[
false
] |
I understand that a spring tide produced the highest high tides and the lowest low tides because the Moon and Sun are aligned. This makes sense when the Moon and Sun are both on the same side of Earth. However, I don't understand why a spring tide happens when the Moon is on the side opposite of the Earth from the Sun. It seems like these should cancel each other out and produce a lower tide? Can someone explain this? Here is a page with a diagram for reference:
|
[
"Go back to the reason tides occur. The moon's force of gravity on the Earth is stronger on the side closest to it, and weaker on the side opposite. So while the solid Earth is pulled as a unit, the oceans are pulled more on the near side and less on the far side. That is why there are two tidal bulges, one on each side of the Earth. ",
"That rather oversimplifies the situation, but that's the gist."
] |
[
"Extending on this to more directly answer OP's questions, the two bulges from the moon align with the two bulges from the sun twice per lunar month, and roughly add (spring). Between those two times (7 days before/after), they're opposed, making the tides smaller (neap).",
"Although the sun is of course much more massive, the fact that the moon is so much closer dominates the tidal forcing (gravity falls off as 1/r",
" and although tides are caused by a gravity gradient rather than gravity so this isn't quite as straightforward, you can see why being close is important). As a result we observe only lunar tides, and the solar tides just modify the tidal range throughout the month."
] |
[
"This image (may) help to explain the forces at work.",
"http://www.lhup.edu/~dsimanek/scenario/tides02.gif",
"Because the centre of mass of the Earth-Moon system is not at the centre of the Earth, all the particles on and in the Earth experience an inertial force whose direction is opposite to the direction of the Moon from the centre of mass and whose magnitude is equal to that of the force exerted by the Moon's gravity at the distance of the centre of the Earth.",
"On the side of the Earth nearer the Moon, the Moon's gravity exceeds this inertial force, pulling the oceans in a bulge toward the Moon. On the far side of the Earth, the inertia of Earth's movement around the centre of mass of the Earth-Moon system is greater than the force of the Moon's gravity, pulling the oceans into a second bulge away from the Moon.",
"Further, these forces resolve in the same way for all the mass involved, which produces the force on the Moon which has slowed its rotation until it became tidally locked."
] |
[
"What is going on in my brain that prevents my thoughts from flowing normally when I am nervous?"
] |
[
false
] |
Yesterday I had a job interview. I drove to the interview pretty confident. When I got there and sat down to three people asking me questions, I froze. My thoughts were no longer fluid. I forgot to tell them key elements of my work experience. I felt like I wanted to leave mid-interview. Afterwards, while driving home, I was no longer nervous and my thoughts flowed normally. I feel like I sacrificed my chances of a job there because of my nerves. What is going on in my brain that prevents my thoughts from flowing normally when I am nervous? Are there any drugs I can take that will help? Specifically, a drug that will not interfere with any other aspect of my body, just my jumbled nervous brain.
|
[
"Hey good for you, you just discovered the difference between an alcoholic and most people. This is actually huge because people judge (like you were) based on their own experience and as such don't understand why an addict can't just stop. I mean, when I drink I can stop after one or two no proble, and so can everyone I know, so why can't an addict just stop,,,it must be a problem with self control, they just need to learn how to limit themselves. That is a very very common view of addiction, even from people that know addicts or claim to understand addiction. The problem is that it couldn't possibly be more wrong.",
"The brain chemistry and physiology of an addict is completely different from that of a normal brain. There are differences both in size and shape of different brain structures, functional differences in regions of the brain, and different neurochemical levels present throughout the brain as well as hormone levels throughout the body. Some of these differences are genetic and present prior to the first use of a chemical substance, some are a result of the use. This all boils down to the fact that the way an addict thinks and experiences the world is vastly different than most people, it cannot be explained or fully understood by non-addicts (for the record I am not an addict, I have just interviewed thousands of them about this subject). An alcoholic quite literally cannot have two drinks without losing full control over their decision making and behavior, at that point it is almost as if they have a seperate personality that takes over. Often they can only watch from another place in the brain begging themselves to stop drinking/using but unable to do anything about it. ",
"I am hopeful that you will consider this and perhaps gain some level of insight about th experience of an addict and how it cannot be judged through your eyes and experiences. If you are interested I could try to put together some into resources for you to gain a better understanding of what an addicts life is like, and the physical and chemical reasons for the differences in behavior."
] |
[
"That's your amygdala's fight or flight kicking in. Your reptilian brain wanting you to get the fuck out of a stressful situation. I don't know what drugs would help, but as someone who gets anxious, shy, and stressed out in similar situations, learning to de-stress through breathing exercises has been crucial. I want to know why some people never have problems like this."
] |
[
"All of it applies to pot. It is actually a total misconception that marijuana is not that physically addicting. It has a clearly identified and diagnosable withdrawal syndrome that often makes it very difficult to quit for heavy users. It is not a highly addictive drug, but it does absolutely cause physical addiction. To put it in perspective, 30% of people that ever try heroin become dependent, with marijuana that number is estimated to be around 3-5%. The withdrawal symptons are somwhat relatable to nicotine withdrawal but with less agitation and more nausea and insomnia. ",
"The physical and chemical effects of marijuana are not very well understood. There is barely anything resembling a scientific consensus of what the brain chemical actions of marijuana are, due to lack of study b/c of politics and the fact that there are so many psychoactive components. Again, in perspective cocaine has a a single chemical component that is psychoactive (more if combined with alcohol) where as marijuana has a minimum of 50 psychoactive components (and that is just the cannabinols and not the other 400+ chemical compunds that are less understood). The only compunds we have any significant information about is THC and canabidiol (CBD), so what actually occurs in the brain is not well understood. What this means is that the addictive process is not understood at a neurochemical level unlike other addictive drugs. ",
"What we do know is that there is an addictive process involved. Most people that would be diagnosable as marijuana dependent are smoking multiple times a day, every day of the week. When they attempt to quit they experience a withdrawal with onset around day 4-6, a peak around day 7-10 and a cessation around day 14-18. The symptoms involve hot and cold chills, sweating, anxiety (severe), agitation, irritibility, insomnia, nausea, cognitive and memory difficulties, and fine motor disruption. For most these symptoms are reletively mild, although because of the popular belief that there is no withdrawal from marijuana people often attribute these symptoms to another source and start smoking again to gain relief. There are likely more withdrawal effects that are longer lasting but due to lack of understanding of the full effects of the drug, and the fact that the withdrawal syndrome wasn't fully accepted by the scientific community until just a few years ago, there have not been significant studies done on this line of inquiry. ",
"In short, yes the same addictive processes are involved with marijuana use as with any other drug of abuse. The exact way the brain is effected is not known fully, but the basics are known. If you want to know about the basics, which is a much longer disscussion, wikipedia has a great article that will give a basic understanding of what occurs in the brain when addiction is present, at least those changes that are consistent through all addictions. Look up \"disease concept of addiction\", \"mesolimbic dopaminergic reward pathway\" and \"locus coeruleus\" to get a really good basis of what areas of the brain are generally involved, there are many more but those only need to b discussed for a much higher level of understanding. ",
"If you want to quit smoking marijuana and are having problems with it there are some good resources out there that are really helpful. Self-help books get a bad rap for being hokey but they can help. If you search \"quitting marijuana\" on amazon you will find many good resources. The thing to remember is that 1 in 5 treatment admissions in the US in 2007 were for marijuana addiction. People often need professional support to quit. You can also look into medical help in quitting, anti-anxiety medications for withdrawal or underlying anxiety problems, anti-emetics for nausea, sleep aids during withdrawal can all be helpful in the early stages of quitting as well as for treating any underlying problems that were self medicated by the marijuana. Good luck."
] |
[
"How do smoking/cancer probabilities work? If you smoke 40 cigarette a day from 16-50 are you 40x more likely to get lung cancer?"
] |
[
false
] |
I'm curious exactly how the advice plays out? If you are smoking 50 a day are you increasing your risks by 10% by going to 60 a day or is it diminishing returns? If there is a diminshing returns fator then is it an even line from 1 or does it curve in some way? Is smoking 5 a day only a little bit bitter than smoking 20 a day or is it hugely better? Is the person who smokes 1 a day for 30 years highly unlikely to get lung cancer? Thanks
|
[
"We measure smoking impact in terms of pack-years (packs/day * # of years). This accounts for the total amount of smoke exposure for the lung, but doesn't take into account time frame over which it occurs. Conceivably, a 20 pack-year history with of 20 packs/day over 1 year would be worse than 1pack/day over 20 years, due to the temporal concentration of carcinogen exposure. However, I have not seen any literature that demonstrates this, and all of the lung cancer specialists/pathologists I've spoken to on the topic say there's no significant difference. ",
"Some modeling below: note that it is only looking at lung cancers; smoking is associated with a lot of other non-pulmonary cancers as well.",
"Overall, smoking ",
" (OR=8.2, 95% CI 6.0-11.4). A dose-response relationship was observed as a function of duration, intensity and pack-years. Using restricted splines cubic models, we have shown that ",
" while the ",
". The following characteristics were associated with a higher relative risk: smoke inhalation, smoking non-filter cigarettes, smoking dark tobacco cigarettes and starting at a young age. In addition, duration, intensity and time since cessation was significantly related with histological type. This was not the case for characteristics such as the use of a filter or not, the inhalation pattern, or the type of tobacco smoked. The proportion of lung cancer cases attributable to cigarette smoking was 55% (95% CI: [47-63%]).",
"source"
] |
[
"Thanks for this and doing the research for me, it's really nice of you. With that said can you do me a favour and sum up what the quote is saying in total layman's terms? I know that sounds stupid but I'm still having trouble following it as it relates to my question. Is giving up one cigarette a day very beneficial or statistically not much difference from not smoking as compared to smoking a whole pack a day?"
] |
[
"How do smoking/cancer probabilities work?",
"They are primarily based on coincidental evidence.",
"If you smoke 40 cigarette a day from 16-50 are you 40x more likely to get lung cancer?",
"More likely to get lung cancer than whom?"
] |
[
"By how much is the Earth's magnetic field decaying yearly?"
] |
[
false
] | null |
[
"Saying that Earth's magnetic field is \"decaying\" is a bit misleading, since that sort of implies that it's currently decreasing and will never recover. The fact is that the strength of Earth's magnetic field ",
"changes all the time",
", sometimes getting stronger, sometimes weaker, and in a very unpredictable way.",
"With that said, currently Earth's magnetic field has been weakening for at least the past thousand years - or at least its dipole moment is weakening. Unlike a lot of ",
"cartoon diagrams",
", Earth's actual magnetic field is actually pretty ",
"complex and patchy",
", and not just made of a single north and south magnetic pole.",
"However, we can extrapolate what just the big north-south component is - the so-called \"virtual axial dipole moment\" (VADM) - and measure how that's changing over time. The results depend a bit on how you decide to do this, but since about 500 AD most methods generally agree that the ",
"VADM is weakening quickly",
", by roughly 0.07 percent per year.",
"This is one of the main reasons folks think we're headed for a geomagnetic reversal sometime soon. Reversals are notoriously difficult to predict, but a general guideline seems to be that if our dipole magnetic field gets below 0.4 Gauss, a reversal is imminent. We're currently at about 0.6 Gauss and decreasing. ",
"Bear in mind that even during the middle of the reversal, there's still a magnetic field, just none of the big north-south component we're used to. Instead, we'll have lots of smaller north/south magnetic field patches spread over the planet - and a cool side effect is that aurorae will be visible from a lot more places.",
": About -0.07% per year."
] |
[
"That offcenter magma curling creates our magnetic field.",
"Magma is semi-molten rock found in the mantle. Magma does not create a magnetic field since it's not electrically conductive.",
"It's the convection and rotation of the liquid iron in Earth's outer core that generates our magnetic field through the dynamo process."
] |
[
"That offcenter magma curling creates our magnetic field.",
"Magma is semi-molten rock found in the mantle. Magma does not create a magnetic field since it's not electrically conductive.",
"It's the convection and rotation of the liquid iron in Earth's outer core that generates our magnetic field through the dynamo process."
] |
[
"How I can I picture a radio wave in 3d space?"
] |
[
false
] |
I only ever see them depicted as sine waves online, but my guess would be that 'sine waves' are to radio waves as what '12' is to a carton of eggs. Is it possible to picture how they are around me in my environment?
|
[
"a good simple way is to imagine concentric spheres, where the surface of each sphere represents the positive waveform peak. then you can imagine an EM source in front of you that is more or less creating expanding bubbles, where each new bubble, \"wave,\" (sine wave positive peak) begins at the center of the previous bubble, and the distance between spheres would be the peak to peak distance of the sine wave. that's probably what I first did in college at least, but obviously theres more to it and that was just a personal tool. field strength heat maps are good at representing them.",
"maybe in simpler terms even you could just imagine the blastwave of an explosion, but in the electric field instead of in the air, and repeating every period.",
"also a critical first step that I found many people overlooked is fundamentally understanding that there is indeed an elecromagietic field around us in all of space by default in which waves travel, and just being able to visualize that domain at all is key."
] |
[
"They do mess with the radio signal, definitely. They are both EM waves, and if two waves are in the same place, they interfere. UV is on the order of nanometers while FM radio is more like feet, so it is a million times smaller and very weak comparatively if all the way from the sun. But the real reason is that your radio is specifically designed to filter out any electromagnetic waves it is not interested in. When you are tuning a radio you are moving a physical filter and deciding which electromagnetic frequencies to let into your speakers. ",
"Also what ",
"/u/YouHaveToGoHome",
" is technically correct in that the emission doesn't look exactly spherical. I googled and found this ",
"https://gigazine.net/gsc_news/en/20170529-3d-printed-radiation-pattern/",
" website where a guy 3d printed a radiation pattern, I think it's really good! "
] |
[
"The idea is that when projected into a single plane, the electric field component of a radio wave emitted by a source looks like a sine wave. But depending on which plane around the source you project into, you can get very different looking sine waves. This is the idea of a Fourier decomposition: a radio wave might be composed of a bunch of small sine waves, but its overall shape can look nothing like that when you add up all the sine waves. One example of how a radio wave might look is dipole radiation [1], which kinda looks like pulsating toruses (donuts) when rotated into 3D. This pattern is what a very simple antennae might use. Another example is a plane wave [2] which would be akin to a laser.",
"More-technical (in case you were wondering):",
"Some commenters are asking you to imagine pulsating spheres spreading out in space, but that isn't technically correct. The only way to create a spherically symmetric system is to have all your charges sit still because any translation or rotation would \"break\" the spherical symmetry of the system, but stationary charges can't create radiation due to some physics laws. Essentially, radiation only comes from dipole and higher order sources (a positive charge sitting by itself can't create radiation; to create a magnetic field you need to charge to accelerate). ",
"Alternatively for the topologists out there, EM radiation can't be spherically symmetric due to the hairy ball theorem, which says that there is no continuous tangent vector field over a sphere which doesn't become zero at some point (the magnetic field vector over any given sphere of radiation is a tangent vector field that would be continuous and non-zero everywhere). ",
"[1] ",
"http://juluribk.com/2010/01/14/radiation-from-dipole/",
"[2] ",
"https://upload.wikimedia.org/wikipedia/commons/4/44/Plane_Wave_3D_Animation_300x216_255Colors.gif"
] |
[
"How long could you survive being in space unprotected?"
] |
[
false
] |
Sci fi movies have shown people surviving being in space for various amounts of time, from being killed instantly to being able to survive for a fairly long time. How quickly would being in space with just regular clothing actually kill you?
|
[
"You won’t explode, our bodies are pretty closed systems. You won’t freeze, heat transfer is far slower. If you had air in your lungs they’d explode due to gas expansion in low pressure. So I guess the answer is: how long can you stay conscious after completely exhaling? You’d just asphyxiate, so a minute or so. Maybe longer with tissue (read:brain) damage. "
] |
[
"Humans can survive a vacuum for more than a second. ",
"We even have a video of it",
".",
"Ionizing radiation within a second is completely negligible in space. It would only matter if you are next to a nuclear explosion, inside a star or in the core of a nuclear reactor - in all these cases you have other problems anyway."
] |
[
"Humans can survive a vacuum for more than a second. ",
"We even have a video of it",
".",
"Ionizing radiation within a second is completely negligible in space. It would only matter if you are next to a nuclear explosion, inside a star or in the core of a nuclear reactor - in all these cases you have other problems anyway."
] |
[
"Do genetic diseases that don't show up until later in life get passed on more frequently?"
] |
[
false
] |
It seems like they would. Because if a diseases that showed up earlier in life, say while you were still fertile, then there's more of a chance of you dying/becoming incapacitated and not being able to reproduce and therefore not able to pass on the disease.
|
[
"Yes. Huntington's ~",
"~ disease usually starts after 30, which is a major factor in its continuing existence. You've already reproduced by the time it starts. When it starts before 20 (juvenile HD), there's much more strictly limited reproduction."
] |
[
"HD positive here. Fwiw, I don’t like the name Huntington’s Chorea. We generally call it Huntington’s Disease. I know it seems nitpicky. Because it’s an orphan disease and the largest problem to research and quality of life is awareness it means more. The chorea name is from an era that had a much more limited understanding of the illness."
] |
[
"Likewise, genetic diseases that kill the person before they reach puberty are very rare because they can only enter the gene pool through random mutation (or carriers for recessive disorders)."
] |
[
"When obese people lose weight, one of the things they always say is how much more energy they have. How much of this energy is due to the loss of fat and how much is due to better exercise/diet?"
] |
[
false
] |
I'm basically wondering if the energy gain is because your body doesn't have the fat anymore or if it's because people are eating better/exercising more and not necessarily due to the fat loss. I'm also wondering how one would go about studying this. I was thinking giving some people minimal amounts of food to lose and others exercise/diet, but I think the results will be tainted. I can't think of a good control group either. Maybe people who just got liposuction?
|
[
"It depends. Given they lost weight through dieting and exercising - it's a combination of both. ",
"Primarily through weight-loss - To experience what they go through, put on a weighted vest, and play basketball in it for a few minutes. Then take it off and try to play basketball, it'll feel a lot easier to run around (you'll have more energy). Bodies don't become more efficient at creating energy due primarily to fat loss (although there are some studies that may hint towards a correlation). It's that their muscles aren't carrying a tire around their waist all the time, and can expel the same amount of energy on a more rigorous tasks, and less on the similar ones."
] |
[
"Both. Jus carrying around less weight helps, eating healthier and exercise helps, but another thing to consider is the fat. Adipose tissue is a very active and dynamic organ, it is an endocrine organ in that it can release or downregulate many hormones and other chemical signals and can contribute to systemic inflammation. Injecting the plasma of obese rats into blood type matched normal rats induces cytokines response and inflammation"
] |
[
"Either way, it's like a car. Old engine, full of gunk - low performance. Clean up the engine and tune it up - high performance."
] |
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