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[
"I can equalize my ears at will, what muscle am I using to do this?"
] |
[
false
] | null |
[
"The OP doesn't appear to be using the Valsalva Maneuver. Many people, myself included, have voluntary control of opening the eustachian tubes without the need to use that technique. "
] |
[
"\"The eustachian tube joins the tympanic cavity with the nasal cavity (nasopharynx), allowing pressure to equalize between the middle ear and throat.\"",
"Yo Dawg, I heard you like popping your ears!"
] |
[
"There are four muscles associated with the function of the Eustachian tube:",
"Levator veli palatini (innervated by the vagus nerve)",
"Salpingopharyngeus (innervated by the vagus nerve)",
"Tensor tympani (innervated by the mandibular nerve of CN V)",
"Tensor veli palatini (innervated by the mandibular nerve of CN V)"
] |
[
"What exactly is the Doppler effect?"
] |
[
false
] |
I don't really understand it that well, correct me if im wrong but I'm assuming it's the way sound changes as it passes you.
|
[
"The Doppler effect is the change in frequency of a wave due to the fact that the source is moving relative to the observer."
] |
[
"Imagine a fire truck: When traveling towards you, the siren sounds are higher in frequency because it has a shorter in wavelength. ",
"Think about it because as the fire truck moves towards you, the wavelengths are squishing together and running out of room before it hits you. ",
"Once the fire truck passes you, the siren sounds lower and has a longer wavelength. ",
"Think if it like the fire truck is traveling away and the waves have more and more space from you."
] |
[
"Looks like you got some answers already but I always like to bring up that the same type of effect happens to light coming from distant moving objects like stars and galaxies. They will seem to be completely different colors because the light coming from then is moving towards us much faster than they are moving."
] |
[
"Do spiders actually consume flesh when they bite humans?"
] |
[
false
] |
This question stems from my girlfriend's fear of spiders and her uninformed assertion that they actually "eat" her when they bite--somewhat similar to the way that mosquito bites are the product of them actually deriving nutritional value from human blood. As such, I am less interested in whether a large spider like a tarantula would consume human flesh, but more whether or not the species of spiders that might be most likely to come into close contact with humans--the kind that leave bites on your arm when you wake up in the morning--actually leave said bites because they are consuming flesh for nutritional value. The answer to this question doesn't necessarily need to be region-specific, but just in case it factors into the answer, I am in the US. As such, my experience with these types of spiders is limited to species that live in North America.
|
[
"Are they eating you when they bite you? No.",
"When a spider bites you they do its to kill you. Its the same when they bite insects that get stuck in their web. The venom paralyses and/or kills the insect, they then wrap it up in silk and excrete digestive juices to break it down to eat.",
"Can spiders kill people? yes. Can they eat people? Its never been reported.",
"When they bite you they aren't trying to eat you.....they just want to kill you."
] |
[
"Spiders don't attack something that much bigger than them, their first instinct is to run away from us. Biting is a defensive mechanism, nothing else. As for the whole eating us, thing, they are physically incapable of eating anything, they don't have mouths."
] |
[
"they are physically incapable of eating anything, they don't have mouths.",
"ಠ_ಠ"
] |
[
"What would a Bubble do in zero gravity/space ?"
] |
[
false
] |
[deleted]
|
[
"In zero gravity bubbles won't have any weight, thus no buoyancy to counteract it. Diffusion should take occur if the bubbles are of sufficient size (micrometer order of magnitude), as long as there are other molecules around (such as air e.t.c). ",
"But in space, the pressure is much lower than atmospheric pressure. For a bubble to not explode, the outside pressure must be greater than the internal pressure (",
"see here for explanation",
"). Hence normal bubbles will probably explode in space "
] |
[
"The inside and outside pressures won't be the same, since the surface tension of the (spherical) bubble wall tends to pull the bubble smaller. The inside pressure needs to be slightly higher to counter that.",
"If the outside pressure is higher, the bubble will contract, but this increases the inside pressure until the inside pressure is higher by just enough to stop the bubble contracting further."
] |
[
"You couldn't have a vacuum, but (unless the bubble pops) there'll always be just enough pressure inside to overcome the surface tension -",
"So the bubble is self-regulating.",
"I couldn't find any videos of soap bubbles in low pressure, but marshmallows are made of zillions of tiny bubbles: ",
"https://youtu.be/OuHBzK-LK24"
] |
[
"Why are certain variables reused for different physical properties in Physics?"
] |
[
false
] |
I just got through with capacitance and charges section of my physics class (where sigma is the current density) and the current, resistance and emf section also has sigma, but it represents conductivity. I just thought of another one too: electric dipole moment and momentum are both denoted with a "p" as well. Are these related in some manner or did convention just get lazy and stop introducing new alphabets to describe different physical properties?
|
[
"Short answer: There's only so many letters out there."
] |
[
"And equations like:",
"⌂ = ₪",
" - ☺ (♫ / ╗)",
"would look kind of silly."
] |
[
"Occasionally other alphabets are introduced: ",
"Aleph number",
". But, in general, there's enough symbols in latin+greek for there to not be too much confusion, if we started using more alphabets we'd have to learn a lot more symbols and wouldn't really gain much from it."
] |
[
"Is it wrong to say that evolution is a FACT?"
] |
[
false
] | null |
[
"There is the fact of evolution, and then there is the theory of evolution.",
"The fact is that there exists (and is observable) change in allele frequencies in populations over time.",
"The modern theory of evolution is that all life on earth has come from a common ancestor through decent with variation, through selection by pressure presented via natural forces.",
"Similarly, there is the fact of gravity, as observed through the falling of objects on Earth and the orbits of planets;then there is the theory of gravity which hopes to explain ",
" objects attract each other through ideas like gravitons.",
"Evolution and gravity simply are, the theories are models that help us understand reality, and are subject to change as we learn more about how the universe works."
] |
[
"Technically nothing in science is fact. Some things are just closer than others; gravity, nuclear decay, evolution... If you want to be exacting you can say it is theory which is supported by an abundance of evidence, in fact there is no evidence that evolution is wrong (which would disprove the theory). Where people get confused are the different reasons why/how/through what mechanism evolution happens."
] |
[
"Technically yes; evolution is a theory that explains many facts we have observed in nature in the same sense that the theory of gravity explains the movement of celestial bodies. It isn't a fact because the idea can be subject to corrections, just like Newtonian gravity was \"replaced\" by general relativity, which reduces to Newtonian gravity again in the non-relativistic limit. For example, the theory of evolution was corrected to incorporate genes as the mechanism of inheritance when genes were discovered, and it undoubtedly will be modified further when more is known.",
"One of the biology dudes could probably give a more thorough, biology-oriented response."
] |
[
"I am teaching an Engineering Camp, need ideas!"
] |
[
false
] | null |
[
"The \"simple calculations\" part makes this tricky, but here are several vibration/resonance ideas:",
"Coupled Metronome Synchronisation",
"Pendulum Waves",
" - maybe simplify it to 4 or 5, and have them predict how long until they all line up again (least common multiple of each pendulum's period)",
"Different version of chladni patterns",
"Mass Spring Resonance",
" - maybe use a mechanical oscillator you can adjust and have them calculate the resonance. ",
"If you really want to \"stand out\" go for a ",
"Ruben's Tube"
] |
[
"Like that one Mythbusters episode, you can simulate the collapse of the Tacoma Narrows Bridge by tuning some resonator to the natural frequency of some model bridge. The kids can use simple beam equations to figure out the resonant frequency and then try to collapse the bridge."
] |
[
"You can show the different natural frequencies objects have, including adding a weight to show how it changes.",
"Small buildings to show how an earthquake would travel to the top floor.",
"Check out some of the towers in dubai. They have large pools or giant spheres in the building to dampen any earthquake or wind problems.",
"CHLADNI PLATES!",
" that make different designs with different fequencies "
] |
[
"Why are radioactive elements that only give off alpha radiation still dangerous, given that that's just a helium nucleus?"
] |
[
false
] |
[deleted]
|
[
"What I'd like to add here is that yes it's a nucleus, but a nucleus that will do almost ANYTHING to gain 2 electrons. This is what's so dangerous alpha radiation. They will rip electrons of any other molecule they come in contact with, and if that's your cell, it will do heavy damage."
] |
[
"What I'd like to add here is that yes it's a nucleus, but a nucleus that will do almost ANYTHING to gain 2 electrons. This is what's so dangerous alpha radiation. They will rip electrons of any other molecule they come in contact with, and if that's your cell, it will do heavy damage."
] |
[
"The problems begin when there is LOTS of alpha radiation.",
"Asking how many nuclei it takes to harm a cell is tricky. It depends what, where and when it gets hit... ",
"The relative biological effectiveness of alpha radiation is 20, compared to 1 for beta and gamma radiation. One alpha particle can be thought of 20 times more harmful to biological matter than a beta particle. ",
"Then it depends where it hits. Does the radiation hit red bone marrow? Really, really bad. The liver? Slightly better, but still to be avoided. The skin? Well, that's making the best of a bad situation. Interestingly the brain is also very unfazed by radiation... ",
"If you like numbers: radiation that hits red bone marrow is thought to be 12x as bad than the same dose hitting the skin. These are of course approximation values, used for example in radiation therapy."
] |
[
"Why does a small fire look so different?"
] |
[
false
] |
I just came across and asked myself why it's so obvious that this is a miniature camp fire. Shouldn't fire look the same in every size as it is just energy? Or has this to do with burning gas being twirled around in the air? Thanks!
|
[
"The heat of a fire causes convection, an upward flow of the surrounding air. A bigger fire generates more heat, so the velocity of the flow is higher. If the velocity is higher, the ",
"Reynolds number",
" is higher. When the Reynolds number becomes larger than a certain number, the flow becomes turbulent, which causes the flames to dance.",
"Edit: as rpebble pointed out, the Reynolds number also increases with the characteristic linear dimension. "
] |
[
"Pretty sure it's a similar reason to why water looks so different in small scale. The size/volume is important because different properties scale differently, e.g. mass scales according to volume (size",
" ), surface tension/interactions scale with surface area (size",
" ). Therefore you have optimal sizes for different droplets/flames."
] |
[
"I think what may be happening here, although I am no expert, is that when you have combustion, the products produced (C02,H2O and heat energy) in a small fire are in much smaller volume than that of their larger counterparts.",
"In effect, a large flame \"dances\" because there are substantially larger and more powerful volumes of gas fighting to occupy the same space. Also, the flame may appear to dance as it catches new pockets of oxygenated air to combust in. ",
"Also, you have to take into consideration that a larger body of flame can resist a wind buffet based upon its' pure energy alone-- if the flame is intense, any outside effects on the fire will react accordingly. It would take a lot of wind power to blow out a healthy camp fire (which is a lot more difficult to produce in nature than the about-to-be-mentioned). It only takes a tailwind of a walking person to blow out a matchstick.",
"Please correct me if I'm wrong. I'm no scientist."
] |
[
"Does putting ice on a burn help the actual wound or is that done just to numb the pain?"
] |
[
false
] |
Would the burn a couple of days later be worse if I didnt put ice on it?
|
[
"How would it damage the skin when its cooling down the burn area faster?"
] |
[
"I don't know the specifics, as i am not a doctor. But i would guess that it just \"kills the skin\" by cooling instead of heating. One could then argue that \"more cold for a shorter amount of time\" could allow for the use of ice, but you would still expose some of the skin to very cold temperatures, affecting that area more than if you used 10-15 degrees C water"
] |
[
"So what your saying is that it cool some skin fast then while its cooling more skin the all ready cool skin becomes too cold and becomes basically freezer burnt."
] |
[
"Why do turtles move so slow?"
] |
[
false
] | null |
[
"I always wonder what happens when we suddenly get things like 3 people in one week asking about turtle speeds, because another similar post came in. Did I miss a highly publicized turtle race? ",
"Let us know if you have any more questions! The panelist who wrote that response really likes turtles."
] |
[
"This question was actually ",
"just answered",
" a few days ago! Enjoy!"
] |
[
"Thank you!"
] |
[
"Why did Schrodinger put a cat in his hypothetical box?"
] |
[
false
] |
It's always troubled me, because surely the cat is itself an observer. The cat knows whether it's alive or dead so it seems it would only ever be in one state. Why not have a simple piece of machinery, like a clock? (Of course you'd need to replace the poison gas with some other means effective against clocks)
|
[
"The point of the thought experiment was \"",
" this theory of how quantum mechanics works were correct, ",
" my hypothetical cat would be both alive and dead at the same time. Since a cat cannot be both alive and dead at the same time, this theory of how quantum mechanics works is therefore not correct.\"",
"It was an argument as to why the ",
"Cophenhagen interpretation",
" of quantum mechanics was wrong, not a serious concept that could actually happen."
] |
[
"Considering whether something\"counts as an observer\" or not, is really another way of saying that brains are somehow special. To suggest that a waveform objectively is, or isn't, collapsed at a given moment, is not quite right. It all comes a little clearer if we only talk about physical states of affairs ",
" to a given observer.",
"Consider how this would all look if we double-nested the experiment. We have a man with a box with a cat in it, and the man ",
" the box are in another bigger box. I'm outside the bigger box.",
"First, the cat is either alive or dead. Relative to the man, the cat is in a dual state. Then the box is opened. Relative to the man, the cat's waveform is now collapsed.",
"But relative to me, the entire inner-system is now in a superposition: it either contains a happy man and a live cat, or a sad man and a dead cat.",
"But if 5 minutes later i open the bigger box and ask the man what he saw while the box was closed, he will have clear and coherent memories from that whole period, of finding just a dead cat or a live one; if the man is inside the closed-box system under consideration, then his memories are part of the superposition and they settle down to a coherent state(relative to me) when he's let out of the box.",
"This is offensive to many people's intuition because it doesn't ",
" like our minds are split and superimposed, in retrospect our memories tell a singular, coherent story. If i told the dude in the box that he spent five minutes ",
" rejoicing over a live cat and mourning a dead one, he'd tell me that's silly; relative to him, there was no indeterminacy."
] |
[
"The term \"observer\" in quantum physics does not imply or require consciousness. A clock is no more or less of an observer than a cat or a human."
] |
[
"Is it possible to medically erase memories from the human brain? Either a wholesale wipe or selectively?"
] |
[
false
] |
[deleted]
|
[
"\"Wholesale wipe\" - yes, it's better known as brain damage",
"\"Selectively\" - science fiction"
] |
[
"It's being looked into.",
"\nIt's a long read, though."
] |
[
"No. \"Eternal Sunshine of the Spotless Mind\" was a great movie, though. "
] |
[
"How do I become a scientist? Am I too late?"
] |
[
false
] | null |
[
"well first off your 19, not a '20something'",
"But I'm still willing to help, you've done a good job actually graduating from highschool. Now your next step into science should be to check your local university for the related course you want. Most likely you will need to either upgrade some classes or fulfill prerequisites. Then after those are met, you will be in the course"
] |
[
"A common path is:",
"Congratulations, you're a scientist! If academia turns out not to be for you, you can take your qualifications and do research in an industrial setting instead, such as people who research new medicines for pharmaceutical companies."
] |
[
"Talk to the university you want to go to. You may have to do some upgrading but people older than you have made the decision to improve themselves. Don't give up on this."
] |
[
"Why do humans have a want for material desires in relation to evolution."
] |
[
false
] |
Me and my friend have gotten into an argument, he claims that having a desire for something that you don't "need" to have (such as an ipad), doesn't fall under a characteristic of life. But I disagree, I say that having the desire of something that isn't needed, is simply humans using intellect, which (intellect) is humans way trying to survive and get ahead. I may be wrong, but I know it falls somewhere. So can you clarify this for me, ?
|
[
"Both of you would probably admit that you judge people by how they dress. Also, you would think of an iPad-owning person as richer than someone who does their work on an older laptop.",
"This is because by owning stuff, people signal their environment, and most want to signal that they are near the top and not the bottom of whatever hierarchy they deem most important. Buying an expensive but impractical luxury car does just that. People imitating signals used by those on top of your hierarchy is also a sign of that, think of the age old leopard pattern, labeling everything \"VIP\", etc. In areas where not money but criminal activity is prized, gang or prison signals are imitated instead.",
"All this behavior falls under ",
"Signalling theory",
" which is part of evolutionary biology. In non-social animals those signals are mostly whatever genes you were born with, but once a social hierarchy comes into play and it becomes as complex as in humans behavior and possessions come into play. The top of the hierarchy is associated with evolutionary success, and you want to judge your opponents position quickly and accurately and adjust your behavior accordingly. Deception is of course always present here, but eventually a stable pattern (",
"ESS",
") emerges."
] |
[
"Because our entire evolutionary purpose is to reproduce.\nTo reproduce we need a mate (and this is where fashion comes from/why it is \"important\") and material goods show wealth, so often wanting something material such as a ring is so we can show possible mates that we can provide or to show off to competitors that we are doing better than them. That is typical materialism in evolution :)\nSo yes you are completely right that when we want things it is to keep ourselves surviving or to reproduce. However it isn't really needed anymore, if you've read Gulliver's Travels there is a land in there which is basicly a satirical note on materialism (the horse people and the yahoos i think :D)",
"Has that helped at all? You are right yes, but perhaps your friend is saying it isn't necessary in life anymore?"
] |
[
"well, one thing to point out to people confused over evolution is to ask them if they understand it, because if they say they don't actually believe in it that is where the problem lies. If he does understand/believe then he must uderstand that anything and everything that exists is a result of evolution. Though not all evolved traits are 'good', and this is one that is no longer necessary the way I see it... but it WAS (ofcoarse) evolved. ",
"emotions aren't necessarily about intellect, I would say they are about socialising (and we can show the evolved aspects of socialising in animals/people) and the desires in search of happiness I suppose is right yes in that we want to be admired or part of a group and material goods are percieved to do this? I'm not 100% sure what you mean though so if im making no sense im sorry! (sorry its difficult to have a discussion like this without any face to face contact if you get me haha :) )"
] |
[
"Whats the usefulness of finding new bigger prime numbers?"
] |
[
false
] | null |
[
"Probably the most useful thing is the experience we gain in the hunt for the prime number. Writing programs to search for large primes is not trivial. Consider that the latest prime number is 23 million digits long. To store the number in its entirety takes about 10 Mb. People have to develop new algorithms to efficiently manipulate numbers this large. And once these algorithms have been developed they can be applied to other areas of research.",
"I'll also point out that the search for prime numbers helps generate interest in math. People can take part in the search at home. Some of these programs are run on home computers when they are idle. When people sign up for the programs they often do some self research to understand what their doing. This outreach aspect should not be underestimated in value.",
"Another point to make is the prime numbers are the building blocks of the integers. Every positive integer has a unique prime factorization. So studying the prime numbers is an important part of number theory. Every time we discover a new prime there's a chance that it will hint at something new pattern that we have yet recognized. ",
"At the same same time prime numbers have some interesting properties that were learning how to exploit. Encryption is often cited, but they can also be used for random number generation, and some other things. It's hard to imagine that a 23 million digit prime being useful today, but who knows what will happen in the future as computing continues to progress and people continue to test new ideas."
] |
[
"There's virtually no mathematical point to finding the actual primes. I say this as a number theorist. ",
"Finding new large primes is mostly a computer science pursuit. What may be of actual interest is any new methods for finding primes, new optimizations to existing algorithms, or just faster computer hardware. These may find other uses, but the actual prime numbers themselves are almost entirely useless.",
"From a mathematician's point of view the discovery of the latest largest prime is not really any kind of breakthrough. It doesn't add anything significant to our mathematical knowledge. It's the same with digits of pi, for instance.",
"I think such accomplishments get news coverage in lieu of actual mathematical discoveries because they are understandable by interested laymen. This is partly because, unlike in say theoretical physics, the important open questions of pure math are not really discussed outside academia."
] |
[
"I would add that new, bigger prime numbers are mostly useful because they are new, not because they are bigger. The smaller ones have just been easier to find."
] |
[
"What if someone put a modern cpu, running an algorithm to generate random (pseudo) 0's & 1's, into a huge magnetic field (~15 Tesla)? What would happen to the output? How does it relates to the design of the processor (like what specific area creates this sequence and how it would be affected)?"
] |
[
false
] |
[deleted]
|
[
"There is no \"randomness generator unit\" in the computer. The CPU is running a program, like any other program; the one you are talking about just happens to have an algorithm to generate a sequence of ",
" numbers, i.e., a deterministic sequence of numbers that will pass statistical tests for randomness over some time scale.",
"There are some physical systems that can be sampled to get sequences of random numbers, but that is not how computers generate pseudo-random sequences via an algorithm."
] |
[
"To be fair, there do exist \"randomness generator units\" for computers usually in high encryption applications."
] |
[
"It would error out and crash, ceasing the random number generation."
] |
[
"Will a cold can of soda(5°C) standing outside(30°C) reach exactly 30°C or less?"
] |
[
false
] |
[deleted]
|
[
"Entropy states that the thermal energy tends to flow to the colder region. In reality given enough time, the temperature of the can would fluctuate between hotter and colder than the surrounding air."
] |
[
"Entropy states that the thermal energy tends to flow to the colder region. In reality given enough time, the temperature of the can would fluctuate between hotter and colder than the surrounding air."
] |
[
"If you assume the air remains a steady temperature at 30C (with energy being put into the system to maintain the air at 30 C) then the can of soda will come to equilibrium at exactly 30C. ",
"If air at 30C and the soda at 5C are put into a small temperature shielding box, then the air and the soda will come to equilibrium at some temperature between the 2 starting points. "
] |
[
"How does string theory \"connect\" the differences between general relativity and quanum mechanics?"
] |
[
false
] |
[deleted]
|
[
"ok, first of all, let's talk about the common misconception that quantum mechanics refers to the \"very small\", or that there is a ",
" scale at which quantum mechanics holds. This isn't true and cannot be: quantum mechanics has only one fundamental constant, Planck's constant, and it just does not have units of length. It has units of action, or angular momentum.",
"Similarly, there isn't any large length scale at which general relativity starts being important. That's because the two dimensionful constant in GR, which are Newton's constant G and the speed of light c, do not have units of length and cannot be combined to make a length.",
"In general, each of these constants, which are all independent, can give different scales on which you can move independently. Ok, I know this makes very little sense, so let's make a super minimalist example, let's just use c and hbar and forget about G for a moment.",
"c fixes the scale of speeds for relativistic physics. If speeds are much less than c, it's nonrelativistic. If they are of order c (say, v/c = 1/2) then you are in the relativistic regime.",
"hbar fixes the scale of, for example, angular momenta for quantum physics. If ang mom is of order hbar, it's quantum. If it's much greater, it's classical (very roughly).",
"You can choose these two independently, because speed cannot be compared to ang momentum. You get four regimes:",
"v << c, L >> hbar, classical newtonian mechanics\nv ~ c, L >> hbar, classical relativistic mechanics\nv << c, L ~ hbar, nonrelativistic quantum mechanics\nv ~ c, L ~ c, relativistic quantum mechanics (aka quantum field theory)",
"Not sure if you see my point. There aren't two extremes at the end of a spectrum, they are two independent orthogonal directions in which you can move. You can add G back in to get a third axis, and then you're left with a graph like this:",
"cube of regimes",
"Ok, so given this cube, what string theory does is it provides a possible (and very appealing, if you ask me) piece of the puzzle to place in the \"Theory of Everything\" corner. You can get there from the General Relativity corner by moving in the quantum direction (quantizing gravity) or from the QFT corner by moving up in the G direction (adding gravity to QFT, which is essentially the same thing). That's what string theory is: a consistent quantum theory of relativistic gravitation (among many other beautiful things).",
"There isn't \"big things\", \"small things\". You can put yourself in the \"Theory of Everything\" corner, which is just the Planck scale. This does finally define a scale of lengths, namely the planck length, which is built out of G hbar and c as such:",
"l_P = sqrt( hbar G / c",
" )",
"So, if you look at things the size of the Planck length, both general relativity and quantum mechanics should apply, and so you need a theory of quantum gravity.",
"Now, the question of why do we need string theory to do that, that's another thing. "
] |
[
"This is why I chose to post here, thank you for the in-depth answer!",
"Be wary of ELI5. Lots of people reread \"explain to me like I'm 5\" as \"I'll explain to you like ",
" am 5\", in other words they make up shit. In my experience many physics answers in eli5 are just random wrong stuff. There is no quality control.",
"As for the last part, if you wouldn't mind, could you give some insight into why we need string theory for that? ",
"It's complex. If you try to implement GR as a quantum field theory you obtain a nonrenormalizable theory. A quantum field theory is generally a theory ridden with divergences (infinities); if these divergences are \"tameable\" by a certain procedure it's called renormalizable. An unrenormalizable theory becomes inconsistent around a certain energy scale - for GR this is the Planck scale.",
"From our previous experience with nonren theories we know it is strongly hinted that the theory wants a \"UV completion\", i.e. wants to be a smaller piece of a bigger theory with no such pathologies. String theory is an example of such a theory. It bypasses the problem of the divergences of QFTs (which are theories of quantum pointlike particles) by simply ",
" (strings are extended objects) and in particular it has the magical property of being finite, that is there are no divergences at all. It's more than renormalizable: there is nothing to renormalize. I cannot explain simply why strings have no divergences, but I can guarantee you it's beautiful.",
"So string theories are consistent, finite quantum theories of which have a classical limit that includes general relativity. There are no other known such examples as of today.",
"Also, as a side note, does the newfound detection of gravitational waves complicate our understanding of QFT? As far as my layman understanding goes, according to QFT spacetime is sort of a chaotic, sporadic mess, while according to GR spacetime is a static \"blanket\". Doesn't gravitational waves confirm that spacetime is a \"blanket\"?",
"You're confusing possibly the QFT corner of the cube with the quantum gravity corner (in the diagram, \"theory of everything\"). In QFT, spacetime is a fixed background. There is no curvature of spacetime or gravity because we are in the \"ignore G\" regime. QFT deals with relativistic* quantum particles on a fixed background spacetime.",
"In quantum gravity (Planck scale) instead, when both curvature AND quantum mechanics are there, we expect spacetime to be \"foamy\" in a certain sense; this is the quantum foam.",
"Gravitational waves instead have been measured in an absolutely classical regime. Spacetime is only foamy when you look at it around the Planck length. Over larger lengths it looks perfectly smooth. So GWs tell you absolutely nothing about anything quantum whatsoever. They are in the general relativity corner of the cube.",
"Again, thank you for taking the time to give such a well-explained answer :)",
"Thank you for the good questions."
] |
[
"This is why I chose to post here, thank you for the in-depth answer!",
"Be wary of ELI5. Lots of people reread \"explain to me like I'm 5\" as \"I'll explain to you like ",
" am 5\", in other words they make up shit. In my experience many physics answers in eli5 are just random wrong stuff. There is no quality control.",
"As for the last part, if you wouldn't mind, could you give some insight into why we need string theory for that? ",
"It's complex. If you try to implement GR as a quantum field theory you obtain a nonrenormalizable theory. A quantum field theory is generally a theory ridden with divergences (infinities); if these divergences are \"tameable\" by a certain procedure it's called renormalizable. An unrenormalizable theory becomes inconsistent around a certain energy scale - for GR this is the Planck scale.",
"From our previous experience with nonren theories we know it is strongly hinted that the theory wants a \"UV completion\", i.e. wants to be a smaller piece of a bigger theory with no such pathologies. String theory is an example of such a theory. It bypasses the problem of the divergences of QFTs (which are theories of quantum pointlike particles) by simply ",
" (strings are extended objects) and in particular it has the magical property of being finite, that is there are no divergences at all. It's more than renormalizable: there is nothing to renormalize. I cannot explain simply why strings have no divergences, but I can guarantee you it's beautiful.",
"So string theories are consistent, finite quantum theories of which have a classical limit that includes general relativity. There are no other known such examples as of today.",
"Also, as a side note, does the newfound detection of gravitational waves complicate our understanding of QFT? As far as my layman understanding goes, according to QFT spacetime is sort of a chaotic, sporadic mess, while according to GR spacetime is a static \"blanket\". Doesn't gravitational waves confirm that spacetime is a \"blanket\"?",
"You're confusing possibly the QFT corner of the cube with the quantum gravity corner (in the diagram, \"theory of everything\"). In QFT, spacetime is a fixed background. There is no curvature of spacetime or gravity because we are in the \"ignore G\" regime. QFT deals with relativistic* quantum particles on a fixed background spacetime.",
"In quantum gravity (Planck scale) instead, when both curvature AND quantum mechanics are there, we expect spacetime to be \"foamy\" in a certain sense; this is the quantum foam.",
"Gravitational waves instead have been measured in an absolutely classical regime. Spacetime is only foamy when you look at it around the Planck length. Over larger lengths it looks perfectly smooth. So GWs tell you absolutely nothing about anything quantum whatsoever. They are in the general relativity corner of the cube.",
"Again, thank you for taking the time to give such a well-explained answer :)",
"Thank you for the good questions."
] |
[
"There seems to be a small pocket of air inside chicken eggs. What gas or gases make up this air pocket?"
] |
[
false
] |
Also, I'm not sure what flair to tag this with.
|
[
"This is called the air cell. When an egg is laid the aircell is tiny or not present and as the egg cools and loses moisture the cell grows. This happens because eggshells are porous and air enters to make up the space from the lost volume of the egg contents.",
"It's mostly just air. So the gases are 78% nitrogen, 21% oxygen. "
] |
[
"Neato, I didn't even consider that the air came in externally. I imagined it as a biological byproduct of whatever goes on inside the shell while it's being formed."
] |
[
"Most people aren't aware of this type of transport mechanism. We tend to think (in common-sense terms) that solids are impermeable. In reality, even the densest of materials (metals) are permeable to other things on a large-time scale. If you put two pieces of any metal together, they will eventually exchange a significant (measurable) number of atoms. ",
"This is a uniquely different mechanism than something exchanging air molecules by \"leaking\" through a gap in a material. It is driven by the principal that a difference in fugacities/chemical potentials/relative amount of something in one place and another will drive the chemical from the place of higher \"amount\" to the place of lower \"amount\". People who study Chemical Engineering take an entire course on the exchange of atoms by this phenomenon known as Diffusion.",
"I'm ranting here, but this concept is widely relevant. Everything that happens in your body depends on this phenomenon occurring between the outside and inside of your cells. Nothing is really impermeable. No barrier is perfect. It's all a matter of the relativity of the transport of things across barriers."
] |
[
"How do I determine the amount of calories in an object? eg. a Boeing 747"
] |
[
false
] |
[deleted]
|
[
"An object like a Boeing 747 is more than just a loose collection of molecules -- it is a collection of atoms and molecules that are chemically bonded to each other. That means that, due to ",
"binding energy",
", their potential chemical energy as a whole is different from what you would get if you considered them separately and then summed the energies of each. In the case of something like a 747 you would probably want to know the total amount of each type of material, and then you could look up the potential chemical energy of each, and add that together, using some degree of common sense (for example if there are Li-ion batteries, you will want to add the chemical energy of battery, not the separate component parts of the battery). Of course by far most of the caloric energy in a 747 will be the fuel. After that, probably various plastics. Experimentally the way you find the amount of calories is to use a ",
"bomb calorimeter",
", that is, you burn the thing up, and measure how much extra heat is produced by the various chemical reactions you have triggered."
] |
[
"I don't think it's that hard. It's just a sum of the parts. If you want to make sure to get every single part, then it's a tedious process. But just using the big parts, you'll get a decent approximation.",
"If you know the plane is 20% fuel by weight, then you can just look up the calorific value of that much fuel, and you've already solved 20% of the problem.",
"Much of the weight of the plane would be aluminium, steel, etc. which would also be pretty easy to look up.",
"I think you'd very quickly have accounted for ",
" of the plane."
] |
[
"Generally to find the calories in a complex object you would have to burn all of it in an enclosed vessel, such as a bomb calorimeter. You then measure very precisely the changes in temperature etc. Calculating this theoretically would be very difficult as there are many different materials bonded together. "
] |
[
"A question in regards to the Grunenthal scandal from the 1950s and 60s..."
] |
[
false
] | null |
[
"This question is about science policy, not actual science. As such, I'd recommend you post on a subreddit better suited for that type of discussion. All the best!"
] |
[
"I see. Where would I find this sort of subreddit?"
] |
[
"Unfortunately this is where I'm probably going to be less than helpful. I suppose you could try ",
"/r/politics",
", ",
"/r/AskReddit",
", ",
"/r/scientists",
", ",
"/r/pharmacy",
", or ",
"/r/medicine",
"."
] |
[
"How does our body regenerate blood cells?"
] |
[
false
] |
[deleted]
|
[
"Blood cells, both red, and white are constantly being produced.",
"cells know as pluripotent hemepoietic stem cells divide (these are found in your bone marrow and to a lesser extent liver and kidney, and spleen), in the process they replenish their own populations as well as giving rise to the various progenitor cells; which type of progenitor cell is determined by various signalling molecules. these progenitors divide and in turn give rise eventually to the various different types of blood cells. ",
"http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Hematopoietic_growth_factors.png/350px-Hematopoietic_growth_factors.png",
" this flow chart shows a general idea of how it works.",
"Different conditions will affect what cells are produced at a certain time, say you have an infection, there will be release of IL-2 and IL-7, as a result the immune response, promoting the growth of lymphocytes. ",
"Say you have an allergic response you will have release of IL-5, as part of the allergic response and promote the growth of eosinophils and mast cells.",
"If you are hypoxic (not getting enough oxygen, say from emphysema or living in La Rinconada Peru) your kidney will produce erythropoietin and stimulate production of Red blood cells.",
"I should also point out that the processes that promote the growth of a type of blood cell are the same processes those blood cells are involved in.",
"Off course there is always some basal level of production, red blood cells usually have a lifetime of 120 days the spleen is responsible for clearing dead, dying, and dysfunctional blood cells from circulation; white blood cell populations are shorter lived and last 1-2 weeks unless they are activated.",
"http://en.wikipedia.org/wiki/Haematopoiesis",
" this wiki has some more information if that is unclear in any way... If you are still further interested each of these types of blood cells goes through a specific maturation process as well that you should be able to find.",
"edit: just to be more complete"
] |
[
"Layman version: The source of red blood cells is bone marrow (cells that occupy the inner cavity of bones), in adults the primary sites of blood cell generation are in the ",
" vertebrae, sternum, and ribs",
" In children, the marrow is more active in the long bones",
" There are many ways your body is able to regulate and maintain how many blood cells to produce as described above. You have cells in your bone marrow that are known as pluripotent hemopoietic stem cells, this just means that they are not in their mature state and have the ability to become any number of blood cells once given proper direction through various chemical signals, but unlike embryonic stem cells they are already in a state where they are matured to a point that they are destined to become some sort of blood cell. If your body detects that you need more RBC's (red blood cells) then the chemical signals will be sent to the these stem cells telling them to mature into a RBC. This process is constantly occurring to replace RBC's that have worn out and been removed primarily by the spleen (the typical life of an RBC is 120 days and your spleen has ways of detecting a worn out RBC and pulling them out of circulation and recycling some of the ingredients to make new RBCs), but production will also ramp up if you experience a rapid loss of blood cells (donating blood, traumatic bleeding) or if you go to a place of higher altitude where oxygen saturation becomes lower and your organs need more RBCs to deliver necessary oxygen levels.",
"Erythropoietin is a hormone that your body makes which triggers RBC production. It is also used as a drug to help people who have severe anemia and certain cancers to help them bump up RBC counts. It is also a drug abused by some athletes for performance enhancement.",
"edit: strikethrough above, correction per goodguy_asshole noted and amended.",
"Citation: 1- Wang S, Davoren JB. Chapter 6. Blood Disorders. In: Wang S, Davoren JB, eds. Pathophysiology of Disease: An Introduction to Clinical Medicine. 6th ed. New York: McGraw-Hill; 2010. ",
"http://www.accesspharmacy.com/content.aspx?aID=5367361",
". Accessed February 27, 2013."
] |
[
"actually in the adult most production of blood is in the pelvis, calvarium (skull (hence frontal bossing in the thalassemias)), the sternum, and then some minimal production in the diaphysis of some long bones... In children production is more in long bones, and in the fetus hematapoiesis takes place predominantly in the liver.",
"but other than that well said."
] |
[
"Do we know or have a estimate of the next system Voyager 1 will enter and how long it will take?"
] |
[
false
] |
Since plotting and projecting is so common in astronomy that someone would have taken the time to make the calculations.
|
[
"If Voyager were heading straight to the closest system, it wouldn't arrive for around 60,000 years. As it is now, it won't even get past the Oort Cloud, which is part of our Solar System, for 15,000 years or so. ",
"Voyager isn't headed to the nearest solar system, so it'll be much longer than that. ",
"Space is really, really big. "
] |
[
"Here is a nice article on Space.com",
" that answers this question better than I could!"
] |
[
"The term \"flyby\" doesn't really seem appropriate for something that only gets within 1.7 light years of a star. It'll hardly be 1.7 light years away from the sun by then. Real answer seems to be that voyager isn't going to enter any other systems."
] |
[
"Does the periodic table of elements go on forever? Is it possible to synthesize element 1,000,000?"
] |
[
false
] |
I understand that some elements have only been synthesized in a lab and last for mere fractions of a second, but is there anything keeping us from creating, for example, element 1,000,000 even if it only lasted for an incredibly short period of time?
|
[
"Most likely not. The IUPAC defines a chemical element as a nuclear species with a given atomic number which has at least one isotope with a lifetime exceeding around 10",
" seconds. This is the characteristic time scale of the \"motion\" of atomic electrons. So if the nucleus doesn't live at least this long, it cannot be said to meaningfully form bound atomic orbitals.",
"Given the trend of nuclear lifetimes at high mass numbers, it's reasonable to assume that eventually heavier and heavier nuclei will reach a point where there are no longer any nuclides which live long enough to be considered elements, by the IUPAC definition. Of course this is speculation, but we can't just assume that all elements are possible. We should instead assume that heavier elements ",
" possible until they are observed."
] |
[
"I certainly don't consider a neutron star to be an atom, or even a nucleus. It's closer to what we call \"infinite nuclear matter\". In reality it's a gravitationally bound system rather than a system bound by the nuclear force.",
"Maybe the IUPAC has a technical definition for \"atom\" as well, but I'd just say a nucleus with electrons (or substitutes, like muons) bound to it."
] |
[
"I'm aware of that, but that doesn't really answer the question. And furthermore these nuclides are unlikely to be stable; their half lives are probably on the order of milliseconds or so."
] |
[
"How is that plastic micro particles can enter the bloodstream? Aren’t they too large?"
] |
[
false
] |
Recently found micro plastics in the human bloodstream for the first time. I can understand finding plastic chemicals and compounds in blood, but aren’t actual particles too big to pass? We must ingest or breath all sorts of countless fine particles daily. Yet do those pass into our bloodstream too?
|
[
"Ingesting, eating and breathing in plastics are the initial step. ",
"Next steps could be localized or body wide. During digestion intestines absorb nutrients, this could be (and most likely is most common) way plastics build up in bodies. Secondly, lungs and really any body part that requires oxygen (all body parts) use red blood cells. This means then the red blood cells are ultimately the carrier and transporter. ",
"Summary: Red blood cells are assisting transport of micro plastics once they've entered the body."
] |
[
"Yes, that all makes sense, and explains how chemical compounds and molecules enter the bloodstream, but something as large as an actual particle which I would imagine are orders of magnitude times larger then oxygen molecules, and other nutrient molecules. I’m making a lot of assumptions, hence why I’m asking, but how could a particle—probably the size of or bigger than a blood cell pass the various cellular barriers to the bloodstream? Are the various articles misusing the term “particles” when they mean “compounds” or “molecules”. I read this as bits of plastic in the blood."
] |
[
"Red blood cells are 7-8 micrometers. Some of the smallest microplastics are 700nm. SIGNIFICANTLY smaller than RBC. ",
"Now to address the plastics question: all plastics are polymers, not all polymers are plastics.",
"What is a compound?",
"A compound consists of two or more elements that have a bond.",
"What is a polymer?",
"A polymer is a chain or endless link of macromolecules. There are synthetic (plastics) and natural (collagen, psyllium).",
"When researchers are saying they have found plastic in blood, what they mean is synthetic polymer compounds has been found in blood samples. ",
"Unknown Questions",
"Scientists are do not know whether it can pass blood barriers. Scientists do not know if a specific organ in the body will store the synthetic polymer chains \neternally or only for - short duration while your body excretes it.",
"Edit: altered 1st blurb on observed size"
] |
[
"Are there any living beings that can only be seen outside of our visible spectrum of light?"
] |
[
false
] |
[deleted]
|
[
"What a great answer. I would add that the entire field of ",
"contrast microscopy",
" has arisen to address the challenges of imaging transparent samples."
] |
[
"What a great answer. I would add that the entire field of ",
"contrast microscopy",
" has arisen to address the challenges of imaging transparent samples."
] |
[
"I'll chime in with some physics perspective, but remember that being completely invisible is extemely hard even for non living beings. Even if a material is transparent, as light is an electromagnetic wave, as it enters any material it interacts with the particles inside which results in a slowed velocity. Because of this, you see refraction effects, etc. The only things we regularly see be anything close to invisible in the real world is extremely smooth and flat planes which minimise these effects. ",
"To be very invisible, you'd need to be very transparent, while having a flat smooth shape that reduces those refraction effects, or be submerged in a material with similar indices in the visible frequency range. Being flat and smooth for animals is hard, and if you want to see in the visible range, you need to absorb some of the light (aka be partially visible at least at the eyes)."
] |
[
"According to an outside observer, does a beam of light shined directly at a black hole ever cross the event horizon?"
] |
[
false
] |
Or does it slow down as it approaches it, just like massive objects? If it does slow down, could someone please explain how this is consistent with the constancy of the speed of light?
|
[
"I'm trying to figure out how to translate this from maths to English for you.",
"The radial component of the line element, ",
" is a function of the gravitational field and of radial position, ",
" Specifically, it's (doing this from memory, so somebody correct me if I drop a sign or something) ",
" = ",
" √1–2",
"/",
" or something along those lines. Sorry for the approximate typesetting.",
"To put this in far less precise but more easily grasped terms, say we live in a universe of flat-out Harry-Potter magic, and you find yourself wanting to carry out this thought experiment for realsies. What you do is conjure up a non-rotating, uncharged, static black hole, a magic space satellite, a magic rope, a bunch of mirrors and a ruler.",
"You hang the magic satellite at a fixed point in space above the black hole, and lower yourself on the magic rope, fixing rulers in space as you go, measuring the distance between them with your ruler.",
"You stop long before you get to the event horizon — just because we're postulating Harry-Potter magic doesn't mean we're going to be stupid about this — and climb back up to your spaceship, then use a laser to bounce light off each mirror to check its position.",
"You find that the mirrors get farther and farther apart as they get closer to the black hole. That's because the metric is a function of radial position; the closer in to the black hole you are, the farther apart (in coordinate distance as measured by a distant observer) neighboring points are.",
"In other words, \"equally spaced out\" doesn't mean anything at all."
] |
[
"This is a fairly famous thought experiment involving a convergent series of partially silvered mirrors strung along a radial vector.",
"The short version of the answer is that as the light scatters off each mirror, what comes back to the distant observer is more and more red-shifted, tending toward infinite redshift at the horizon."
] |
[
"TL; DR: No. Also remember that both time and space change in sync.",
"No, an observer away from the black hole never observes it cross the event horizon. Of course, you never ",
" see a light ray cross any given point either. But that's not what you mean. To usefully talk about this we have to go quite a bit deeper. Unfortunately, how you set things up may change what you think about the answer.",
"We have to make a couple of distinctions here: there's what a given observer will ",
", which is the actual pattern of data he or she receives, and what is ",
", which is what inferences are draw by the observer to explain what is seen. This latter depends on what theory they use, of course, so may not be really unique. ",
"If you want to know when a light ray crosses some point, you need something at that point to signal this back to you (such as a mirror to reflect it), and some method to calculate back to when the light you see now must have been leaving that point (which can be rather arbitrarily involved). Your choices for both of these really can affect the answers. When you place a mirror somewhere, how do you know it stays there? \"It's stationary\" you may say, but even in Newtonian physical models, stationary according to one observer is moving according to another, and each point of view is equally valid. Okay, so you mean stationary according to you. But you're not there, and in General Relativity there is no unique answer as to whether something is moving with respect to you. Still, the Schwarzschild geometry is relatively nice, and doesn't fluctuate between you and the horizon. You can try tying the mirror to a rod that's connected to you. Unfortunately, when you try to place that mirror at the horizon, the rod must break -- it needs to apply an infinite acceleration to keep the mirror there, and your rod is just not strong enough. This does give us a limiting process though. If you had an arbitrarily strong rod, you can place the mirror arbitrarily close to the horizon. For any finite time, you can place the mirror close enough to ensure the light's reflection doesn't return until after that point. But this doesn't tell you when the light hit the mirror, only when it returns to the observer.",
"At this point you have to make some inferences and/or decisions about what this \"should\" mean to an outside observer. The standard answer using special relativity (i.e. away from black holes) is to define distance in terms of half the round-trip time for light, depending on the speed of light being consistent. We can follow this prescription and set up a \"coordinate chart\" around the black hole, giving a time and distance to every event. This makes the horizon infinitely far away in some sense. But someone falling in to the black hole rather than staying at a fixed distance can do the same thing. They will report very different observations than you, but you will of course hear their reporting as being slowed down, and won't see them finish falling through the horizon. Even as they fall through they will continue to insist that the reason your (not actually infinitely strong) rod broke is that you were pulling on it (you were, to keep it from falling in), and this produced a differential acceleration along it. Are they right? Are you right? Yes, you both are."
] |
[
"What would happen to an astronaut if one of his limbs was exposed in space?"
] |
[
false
] |
[deleted]
|
[
"He would get a terrible, terrible sunburn. If he left the arm exposed longer, the high energy radiation would probably give him skin cancer in that area later in life, along with enhancing the possibility of other forms of cancer elsewhere in his body. It is a common misconception that space is so cold it would cause any exposed skin to instantly freeze. Yes, space can be very cold, but it is also a near-vacuum, so there isn't enough matter around the astronaut's arm to suck heat away at any significant rate. All heat loss would be through the arm's radiation of energy...not exactly a hurried process for something so relatively cool, and that's IF the astronaut isn't absorbing heat energy from the sun (again, sunburn), or is at least a fair distance from Earth to avoid our planet's radiation. The aforementioned sunburn of all sunburns would be in full effect before he started seeing his skin cells freezing.",
"On another note, people also often tend to think that if an astronaut's helmet were to be removed in space, a whole plethora of gruesome things like his eyes popping or his lungs getting turned inside out would occur from sudden lack of pressure. Yes, there would be a lack of pressure, and the change would be sudden, but the difference is essentially from one atmosphere inside the space suit to 0 atmospheres in the near-vacuum. No dramatic popping would occur. The lack of pressure would cause any moisture in his mouth or nose to boil away, and the air in his lungs would be pulled out by diffusion. Death would occur rapidly, but our astronaut would remain intact. ",
"Bottom line: space is a dangerous place. But it's not a horror movie. "
] |
[
"Wouldn't the gasses in his blood and cells start to boil? Kind of like the bends but more extreme?"
] |
[
"No, the blood wouldn't boil."
] |
[
"Quantum tunneling, and conservation of energy"
] |
[
false
] |
Say we have a particle of energy E that is bound in a finite square well of depth V. Say E < V (it's a bound state). There's a small, non-zero probability of finding the particle outside the finite square well. Any particle outside the well would have energy V > E. How does QM conserve energy if the total energy of the system clearly increases to V from E?
|
[
"The Schrodinger equation is just a ",
"conservation of energy equation",
". So, any wave function that satisfies Schrodinger's equation must necessarily conserve energy. The wave function for the finite square well most certainly conserve energy, as we find the wave function by solving Schrodinger's equation.",
"In the solution to the finite square well we stitch together multiple functions to get a continuous and continuously differentiable wave function. In the region where the particle is actually in the barrier, it is a different equation than in the region where there is not potential.",
"Being flippant with multiplicative constants:\nIn the barrier: \\psi ~= e ^ (-\\kappa x)\nOutside the barrier: \\psi ~={ sin(k x)\n { cos(k x)",
"Where \\kappa",
" is ~= (V-E), while k",
" is ~= E.",
"Because \\kappa",
" > 0, the kinetic energy of the particle in the barrier is negative. This means that the total energy of the particle, kinetic plus potential, is the same.",
"This also leads to imaginary momentum eigenvalues. {\\hat p = i \\hbar d/dx, \\psi ~= e ^ (-\\kappa x) => \\hat p\\psi ~= i \\hbar (-\\kappa) \\psi} These are much more problematic than negative kinetic energy, believe it or not. This is because ",
"axiomatic quantum mechanics",
" specifies that observables are hermitian operators, and ",
"hermitian operators have real eigenvalues",
"Overall, the answer to your question is that energy is conserved because we force it to be conserved by requiring that wave functions satisfy Schrodinger's equation. However, this introduces a number of philosophical questions.",
"Edit: Fix a formatting issue.",
"Edit: I also wanted to add ",
"this paper",
", which covers this question really well."
] |
[
"The particle doesn't gain any energy when it tunnels. What we mean by quantum tunneling is when a particle surpasses a barrier that it could not surpass classically. ",
"If I am bound in a finite square well of depth V<E, ",
", I don't have anything to tunnel through. If, on the other hand, there is \"room\" outside the well, I can tunnel through the well barrier to a state that still has energy E<V. I don't gain any energy moving through the barrier, I just move to the other side."
] |
[
"The uncertainty principle guarentees that if you are found within the barrier (thus a delta x given by the barrier width) that the uncertainty in you energy is large enough that you cannot ensure that it was lower than the barrier height. Thus, the uncertainty principle prevents you from \"catching\" a particle somewhere were it should not be able to recide."
] |
[
"How do you describe refraction through quantum mechanics?"
] |
[
false
] |
Also, I've heard of the experiments in UC Berkeley in which they slowed down the speed of light to 9.7km/s. Was this 'slowing down' the speed at which the light travelled, or only the speed?
|
[
"They didn't slow down the ",
", if that's what you're wondering. They used tricks to slow down the transmission of light in a semiconductor. Wikipedia's article on slow light will tell you so ;)",
"But yes, the light actually traveled at 9.7 km/s. ",
"At Harvard, researchers managed to actually ",
" a light beam for 1.5 seconds in a cloud of very cold rubidium atoms. Neat!"
] |
[
"Richard Feynman on Quantum Mechanics",
"Part 1: Photons: Corpuscles of light (1h17m)",
"Part 2: Reflection and quantum behavior (1h38m)",
"They are long, and really worth it. It's Feynman. Refraction can be explained with the box with a mirror in it, which is in part2 around 28 minutes in."
] |
[
"Well, in a sense, it's a question that's impossible to answer. Once you get down to the quantum scale, it's literally impossible to know what a single photon is doing between interactions.",
"But if you zoom out, so to speak, and stop thinking about photons but rather the whole beam of light as a wave phenomenon, you find that when light travels through a medium, interference in the wave between the different frequencies of light making up the beam results in a ",
" — that is, the speed of the overall wave itself, as opposed to the individual components that make up the wave — that's slower than the speed of light in a vacuum.",
"So it's not a hijink, really. It's a consequence of the way light — being an electromagnetic phenomenon — interacts with the electric field generated by the charged particles that make up the medium through which it's propagating. It'd be possible to do the math for single photons and add it up — and I imagine these calculations have been done — but it would be hellishly complex, and modeling a beam of light as a composite wave made up of smaller waves all of which interact with the electric field makes the math simpler, and yields predictions that are just as useful."
] |
[
"How long would it take for a running faucet to erode through a ceramic sink?"
] |
[
false
] |
Let's say it's running at full blast and it's a regular-sized sink (and ceramic because it's a usual bathroom material). Would it be something like a couple years of continuous running, or on the order of hundreds of years?
|
[
"Depends on the water. If it has a high calcium or silicon content and is hotter than ambient, then mineral deposition could actually achieve the exact opposite - filling in the entire basin with hard mineral deposits known as ",
"calcareous or siliceous sinter",
". This often happens around hot springs, for example. ",
"If the water carries particulate matter of sufficient hardness to scratch ceramic, then it might eventually erode the sink, in much the same way that flowing rivers carve canyons. But even then it would take centuries at least. Most water-carved canyons were formed across millions of years. ",
"But pure water that does not freeze in the sink would be unlikely to have any real effect against ceramic, even across centuries."
] |
[
"I don't know if you intended your question to be slightly demeaning, but I can totally see why the guy might think the sink would break in half like that:",
"Both of those situations beg application of the scientific method, and these types of questions are smart ones because it demonstrates curiosity and desire to understand the world and are the focus of this subreddit. If you intended your post to be tone neutral you can disregard this, but if not these are the kinds of questions we want people to ask - something you obviously do care about because you did give him the correct answer and more.",
"tl;dr - We need to turn hintss into ",
"a scientist",
"."
] |
[
"Erosion at Niagara Falls is in no way comparable. ",
"Erosion at waterfalls",
" mainly occurs by undercutting and resulting headward erosion. The water preferentially erodes weak layers at the base of the falls and the overlying layers, lacking support, collapse and the broken material is removed."
] |
[
"What parts of the human body that we are born with are never lost/replaced?"
] |
[
false
] |
I'm thinking at the cellular/structural level. Cells on the epidermis die and are sloughed off, thus being recycled, but what parts of the body are opposite to this, i.e. never being recycled?
|
[
"Nerve cells,Cartilage, and eggs cells in females"
] |
[
"Even in non-proliferating tissues such as the ones you pointed out there still is biochemical turnover. With mutations and repair even the DNA in those cells would undergo changes. The lower you dive into structural levels the harder it is to find actual constants."
] |
[
"By that definition, there will never be a cell that doesn't 100% ever get modified or get lost. I was talking about cells that aren't replaced mostly. All cells will eventually die."
] |
[
"In simple terms, how did Einstein prove relativity and that time experienced by body would be less if it travels near the speed of light?"
] |
[
false
] | null |
[
"Here's what happened historically:",
"First, we have \"classical\" physics. Thanks to Newton and his successors, we have some equations of motion that describe reality extremely well. One interesting thing about these equations is that if you give all of your objects the same velocity boost, it all cancels out and you end up with the same system. This is called ",
". It means that you can't determine if there is some universal standard velocity, because the physics of the universe doesn't change if you give it a boost. So this is the standard situation up to the modern era.",
"Then, in the 18th and 19th centuries, a lot of people were doing experiments with electromagnetism, learning how electric and magnetic fields behave and interact with each other. One dude called Maxwell put these equations together (into Maxwell's Equations) and found out that if an electric field generates a magnetic field, and a magnetic field generates an electric field, you can keep that process going on forever to generate an ",
", that just so happened to move at the speed of light. So, now it looks like light is an electromagnetic wave, which is cool.",
" these equations don't work the same as the classical equations of motion. If you give everything a velocity boost in Maxwell's equations, you end up with little bits left over! This means that electromagnetism (and therefore light) changes depending on how fast you're going!",
"This was a major problem. It means that, contrary to what everybody had thought, the physics of the universe apparently ",
" depend on your velocity, which means that is some fixed special velocity, which is the only velocity that Maxwell's equations are accurate in. People invented something called the Ether, and it was the velocity of the Ether that was was thought to be the one special velocity. However, experiments showed that the Ether idea didn't really work, unless you keep on modifying the Ether to fit each experiment, which isn't very convincing.",
"However, Einstein came up with another idea. Maxwell's Equations change when you boost everything by the same velocity, ",
" you assume that time and distance to be universal. If you allow time and distance to ",
" be universal, then Maxwell's Equations can still work if you give everything a velocity boost, it's just that time and distance have to change instead. And if you go through the mathematics of that, that's how you get time dilation, length contraction, and all that stuff."
] |
[
"You mean muons, right? "
] |
[
"It's all correct, but you don't mention any proofs, which was OPs question.",
"Einstein didn't prove it himself. But the first proof is myons. Myons decay after while. Cosmic radiation produces myons in the upper atmosphere. But at the speed they are travelling, they shouldn't be able to reach the ground. Or at least not as many as we actually observe should reach the ground. The reason why so many reach the ground is that they actually experience time at a slower rate.",
"Later on they actually put atomic clocks on planes, flew them around the world and compared them afterwards. The time difference they showed matched exactly Einsteins predictions."
] |
[
"Can you effectively wash your hands with cold water and old-fashioned (not antibacterial) soap?"
] |
[
false
] |
Just curious whether cold or lukewarm water negatively affects the effectiveness of hand-washing in the absence of antibacterial soap. If so, what temperature is required for maximum efficiency while remaining tolerable for your skin?
|
[
"Yes, and in fact traditional hand-washing with normal soap is actually seen as ideal by modern public health officials. As far as I know, temperature has a negligible effect on handwashing, as the time that the water has contact with your skin is negligible, if you're thinking about it in terms of killing the bacteria through heat. ",
"The idea of washing the hands is to simply wipe the oils/dead skin layers that harbor dirt or bacteria, not to do anything to the dirt or bacteria itself.",
"Finally, you may already know this, but the reason public health officials recommend traditional soap now is that antibacterial soaps can promote strains of antibacterial resistant bacteria."
] |
[
"Source, which cites reputable sources:\n",
"http://health.howstuffworks.com/skin-care/cleansing/basics/hand-washing2.htm",
"google search that led to above link: Water temperature and hand washing",
"Yes, you can effectively wash hands with cold water and normal soap. The positive effects of handwashing come from physically removing the disease-causing cells/viruses from the hands. Soaps are manufactured to work best (i.e. lather) in warm temperatures, but remain effective with liquid water of ANY temperature."
] |
[
"The fats and dry matter that you want to remove, reacts with the caustic effects of the soap. This means that the base negative charged hydroxide ions of the soap attracts the positively charged oxonium ions of the dirt, and thus breaks the bonds that has formed and makes the structure of the dirt. The water acts as a powerful solvent, since water has the properties of both a base and an acid.\nIn the chemical reaction of cleaning, and in most other chemical reactions in general, temperature serves to speed up the process, since higher temperature means that molecules moves/vibrates faster. In conclusion, the effect will be the same no matter the temperature, but cooler water will take longer time. ",
"Added: To address the antibacterial question, besides the physical removal of dirt, and therefore also bacteria, normal luke warm water will have no antibacterial effect. Most bacteria in our daily life will easily tolerate any temperature we willingly will expose ourselves to. Many soaps that claim antibacterial effect will therefore have an added chemical that counter bacterial growth, such as chloric compounds or quaternary ammonium compounds. "
] |
[
"If you had a chamber with propane at 2000 deg F, and you introduced table salt, would you get any Na2O?"
] |
[
false
] |
Reference for salt reactions in a carbon combustion environment:
|
[
"Given that the combustion of propane produces water vapour, it seems entirely reasonable to assume so. As the wikipedia article says, the NaCl gas reacts with water in the air to form sodium hydroxide and decomposes to give sodium oxide.",
"Something to bare in mind is that on exposure to air with moisture in it (i.e almost any air at all) Na2O will return to being caustic sodium hydroxide."
] |
[
"What if there is almost no air, and very little combustion, as in pyrolysis conditions?",
"To clarify, I'm going to hook up a propane tank to an electric kiln and flood it as I heat it up to 2000F. Then I am going to let some air in and throw in table salt. It makes gorgeous pottery finishes."
] |
[
"Assuming no air, only propane and salt (assuming pure sodium) you would get no sodium oxide as there are no oxygen molecules present. As soon as you add air, you have oxygen molecules that changes the game. Then you get H20, C02, CO, Na2O, NaOH all as products plus other trace molecules. I'd have to run the simulation to tell you concentrations. "
] |
[
"Why can't we make an artificial heart that lasts a very long time?"
] |
[
false
] |
I know there are artificial hearts, but why are they only a temporary solution? Shouldn't the technology be there to make a very good, maybe even better heart?
|
[
"Shouldn't the technology be there to make a very good, maybe even better heart?",
"Well, the answer is simply no. There's no rule that technology should be that good.",
"To fully replace a heart, you need a small, extremely durable machine capable of repeatedly performing a fairly energetic task for many years without being difficult or dangerous to keep powered. It also has to interface with the body safely, and react appropriately to the body's many chemical signals. All of these things together are an immense task."
] |
[
"Along with this, the artificial heart has to be able to react appropriately to different requirements, such as beating faster when the person is phtsiy active to provide enough oxygen to the body. "
] |
[
"Also blood clots. This isn't a problem with your heart since it's designed to prevent blood clotting. But with an artificial heart, any points of stagnation or grooves etc is going to create an embolism. That is a very bad thing.",
"Our biomaterials and pump designs just aren't quite good enough yet either."
] |
[
"How close are we to finding a cure to the Common Cold? What's the 'official' steps in finding/confirming a cure?"
] |
[
false
] |
[deleted]
|
[
"I'm going to be pessimistic and say, not very close. The common cold is not the result of one virus. There are hundreds of different viruses that can cause it. So if you want to cure it, you need to find a way to stop every one of those viruses.",
"In general, there are two strategies that are used to find cures. One is to create a vaccine containing an attenuated or killed strain of your microbe of interest or with just components from those organisms which will help prime your immune system to fight it off when it does actually see it. This doesn't always work because the live organism might have other tricks up its metaphorical sleeve to bypass recognition by the immune cells.",
"Another strategy is to find some kind of chemical that stops the virus from reproducing or bacteria from growing. You could take the everything and the kitchen sink approach where you screen a humongous chemical library and hope something works. Or you can figure out what protein is essential for microbial survival and find something to stop that protein from working. For example, an antiviral may target a receptor to prevent a virus from infecting the host cell or an antibiotic might target an enzyme essential in contributing to bacterial cell wall integrity. These chemicals are fairly specific, so it wouldn't be any use demanding an antibiotic to treat a viral infection if the only thing it targets is a bacterial disease."
] |
[
"The problem is that there's no such thing as 'the common cold,' that's just what we call any low-level infection which doesn't kill you and gets cleared in a reasonable time frame. ",
"We could eventually work up a vaccine to any one particular virus, but there are so many of them mutating so quickly that it wouldn't make a dent. To truly 'cure' the common cold, we'd need a treatment that was universally effective against ",
" viruses, and we're really nowhere near something like that."
] |
[
"In terms of ever finding a cure for the \"common cold\"....",
"Hahaha not even close (though this last winter was pretty good to us) ",
"There are just too many viruses that can cause the common cold (over 200). Sometimes we have a better guess at what the kid has based on other symptoms, GI problems we think Enterovirus, asthma like we think RSV, Croupy cough we think PIV, etc etc. We have fancy new ($$$$) viral assays that we can send out to determine what a kid may have gotten sick with (the really sick ones) but many times the kid is feeling better by the time the results come back . This past year there we had a lot of kids that had Metapneumoviruses, but that's my own experience. Rarely do these viral assays come back as something like orthomyxovirus (Influenza). ",
" covered what it takes to prevent a known virus, but the sad thing is that these viruses mutate every year ( This is why certain vaccines are updated every year) ",
"Get well !"
] |
[
"Is there a Super Massive Black Hole at the center of EVERY galaxy?"
] |
[
false
] |
I have read several obscure science articles describing the probability but none state it definitively. I know scientist say their is a super massive at the center of the milky way. I have been wondering if true why.
|
[
"Probably not.",
"Small irregular galaxies may not have central black holes, though they could just have relatively low mass ones we haven't detected.",
"A2261-BCG is a (very) large galaxy that appears to lack a central SMBH. It's theorised the black hole formed but was later ejected in a galactic merger.",
"EDIT: ",
"https://phys.org/news/2007-05-galaxies-black-holes-uncommon.html",
" briefly discusses the theory behind black hole ejection. When two black holes merge asymmetric gravitational wave emission can kick the resulting black hole out fast enough to escape the galaxy. Realise the black hole is only a few percent of the galaxy's total mass, so the rest of the galaxy doesn't follow the runaway supermassive black hole. The 2007 work suggests this kicking effect is unlikely but not impossible."
] |
[
"How would a spherical, non-rotating galaxy maintain it's shape? Shouldn't gravity cause it to collapse inward if it isn't spinning?"
] |
[
"How would a spherical, non-rotating galaxy maintain it's shape? Shouldn't gravity cause it to collapse inward if it isn't spinning?"
] |
[
"What happening when/why do we 'zone out'?"
] |
[
false
] |
I don't really know how to explain 'zoning out' if you don't know what I mean--probably the best example is when you're and somebody who sees that will probably wave their hand in front of you. Anyway, is it just us acting stupid for a minute or is there some kind of neurological 'hiccup' going on?
|
[
"Your brain devotes huge amounts of energy to \"filtering out\" information that it finds irrelevant. For example, at any given time you usually don't feel the clothes on your skin, you don't pay attention to all the sounds around you etc. If you did you would go crazy dealing with sensory overload. ",
"My guess is that when you're focusing on something mentally, daydreaming or whatever, your brain \"pulls down the blinds\" in a manner of speaking and blocks a lot of sensory information from your environment from reaching your consciousness. "
] |
[
"Well, as a kid with ADD, I frequently zone out when I'm bored. ",
"http://discovermagazine.com/2009/jul-aug/15-brain-stop-paying-attention-zoning-out-crucial-mental-state",
" implies that it's related to daydreaming. But still, there is some difference between the two"
] |
[
"Microsleep"
] |
[
"If a living organism, say a cell for example, is composed of a combination of tinier living compounds, which is then made up of smaller non-living matter--Would it be possible to re-create that same living organism using a combination of non-living matter?"
] |
[
false
] | null |
[
"I'm not quite sure what the paragraph is trying to say, but it is certainly possible to create life from \"dead\" components. Life is but a series of (complex!) chemical reactions.",
"One way of looking at it is human reproduction. How is babby formed?! Literally, the mum is eating the building blocks for that baby. Nothing she eats has to be alive, it simply has to have the right nutritional value. Yes, the initial zygote is alive... but that's simply a system of chemical reactions inside a very small bag.",
"I think you might appreciate this example more: Craig Venter and his team of biologists created new life, using sophisticated but ultimately not magical techniques. There was NO life when they started. All the components they put together, if left \"sitting on the shelf\" undisturbed, would never amount to anything. The cellular membrane is just a layer of fat molecules organized by hydrophobicity. The genetic code is just another (incredibly complex) chain of nucleotides.",
"The point is, while Craig Venter and Co. did put bits of other cells together to create new life, the raw material was in no way alive. Complex? Yes. Derived from living sources? Yes. The key point is that we CAN make the things they pulled from other cells, it just takes lots of time and effort. Craig Venter's Frankensteinian cell could have been created from scratch using raw amino acids and nucleotides, given sufficient time. We HAVE the raw coding sequence to make ribosomes etc, it just takes a LOT of time and effort to put together so corners were cut by snipping useful bits from existing lifeforms.",
"Here is a link. ",
"http://www.theguardian.com/science/2010/may/20/craig-venter-synthetic-life-form"
] |
[
"By and large the smallest organisational unit which can be said to be alive is a cell (putting the virus argument aside for a moment). Cells are composed of a wide variety of compoments, almost all of which are complex organic molecules, these include lipids (fats), proteins and enzymes, DNA and many more...",
"It's is moderately easy to extract and purify any one of these components and they will have some manner of biochemical activity (i.e. as a catalyst in the case of enzymes). However we don't consider these activities, taken on their own, to be living.",
"At the smaller scale again, organic molecules are composed of atoms. Which are just atoms. They too are not individually alive.",
"recreating that, even if it means making a gigantic being following the same structure, would it be possible?",
"I think the answer to this question is fundamentally yes. If we can create a (v.large) \"machine\" which can replicate, sense, respire etc... Then it ought to be classed as living. However I don't believe that we are neccessarily constrained to having to replicate these processes the way cells do them. And people have already hypothesised nano-bots and Von neumann replicators which could likely be classed as living structures"
] |
[
"This is a philosophical question, IMO. For arguments sake, if we had perfect knowledge of how individual atoms come together to yield the emergent phenomena we call consciousness, in addition to the requisite bodily functions needed for life, then the answer to your question is maybe?"
] |
[
"How do we determine sea level?"
] |
[
false
] |
Do we base it off of some point on land, and then depending on if it raises or lowers from that point we know if the sea is rising? And if that is how we do it, do we measure that point at high or low tide? Also, how often do we change topography maps with the new sea level?
|
[
"There are two main ways to determine sea level. \nFirst, is to do the whole geoid math that ",
"/u/ToasterFanclub",
" mentioned. The other way is to take an hourly, 19-year average of tide levels and use that mega-average as sea level. This second way is used in aviation, atmospheric sciences, and land surveying. So i think this is the more respected data for determining sea level."
] |
[
"Yes, over water that would be the better, and rereading the OP, this would be the better answer"
] |
[
"Short answer. It would be based on the geoid. It would be the height of where the water would be if that pesky land wasn't in the way. ",
"Longer answer explaining the geoid and how it affects what level the water would be:",
"Start off with a stationary ideal planet. Gravity would pull everything in and make a perfect sphere",
"But earth isn't stationary, it's spinning, so the middle bulges out a bit in what's called an oblate spheroid. ",
"On top of that, the mass on earth isn't uniform. land masses are heavier, water is lighter, etc. Than means if the water could flow freely, more water would flow to those more massive places raising where sea level would be. ",
"Another way to think of it would be where acceleration due to gravity matches that of sea level (gravity gets weaker as you get higher, it gets stronger as you go lower), but gravity is hard to measure that accurately. ",
"You could also look at whether the average pressure matched the average pressure at sea level, but pressure fluctuates too much for this to give you good data in a reasonable about of time. "
] |
[
"James Webb Space Telescope question."
] |
[
false
] |
Someone told me that this telescope, when deployed, will actually be able to observe exoplanets; not just their gravitational pull on stars, or dark spots, but it will be able to take images of planets in other solar systems. Is this true? I haven't been able to scrape up any information on this claim.
|
[
"We have already taken pictures of planets around other stars, most notably this star: ",
"http://en.wikipedia.org/wiki/HR_8799",
" "
] |
[
"http://en.wikipedia.org/wiki/New_Worlds_Mission#Starshade"
] |
[
"So will the JW be able to produce better photos than this? Does anyone know by what order of magnitude better?"
] |
[
"Does Epsom salt actually do anything?"
] |
[
false
] |
[deleted]
|
[
"Chemistry student with a dash of pharmacology education here:",
"Your skin is capable of absorbing compounds, but the actual ",
" is likely to be low. High enough for therapeutic effects? I don't know.",
"Drugs are introduced into a cell via a number of routes: passive diffusion, facilitated diffusion, or active transport. Because your cells compose of a phospholipid bilayer, ions (such as magnesium sulfate in water) do not cross the membrane well. However, non-polar compounds, such as steroids (e.g., hydrocortisone) are readily absorbed, and is commonly used to treat skin rashes. These are much larger molecules, but can cross the membrane because it is not charged, and has low polarity. Even bigger molecules would require active transport - the cell expends some energy to ship these molecules in.",
"Now, regarding the size of magnesium sulfate - seeing that the salt is only about 120 g/mol, I'd say it's not too big to pass via aquaporins - small special pores in the membrane designed to let ions pass. However, I can see the amount passing through as being very small. As to its therapeutic effects... I tried to do a literature search, but all I've seen so far are case studies of magnesium overdoses from people either doing epsom salt ingestions or enemas."
] |
[
"Both of those studies are highly biased, don't you think?"
] |
[
"The second one may be. Although the first one is on a site promoting the benefits of magnesium, the study is produced independently by the University of Birmingham. "
] |
[
"Do scale-prevention devices based on quartz crystals work? If so, what is the scientific basis?"
] |
[
false
] |
I've come across this product called that claims to prevent scale buildup, using nothing but quartz crystals. Electricity is not provided, the quartz just sits there. Quartz crystals, allegedly, "emit low end frequencies" which break up scale and prevent it from forming. It sounds like pseudoscientific nonsense to me, am I wrong?
|
[
"quartz is piezoelectric, but it won't oscillate unless there is oscillating voltage applied or it is part of an oscillator circuit. The amplitude of motion for a tiny crystal is very tiny. The frequency of the crystal goes up with decreasing size, so tiny crystals oscillate at very high frequencies, not low. In fact, typically megahertz frequencies, not acoustic frequencies, so its not \"sound waves\"",
"There shouldn't be any significant voltage differences in your pipes unless they are actively corroding, in which case you've got a very different water problem.",
"quartz crystals are nothing more than beach sand. It's abrasive, like sandpaper, which could dislodge thin flakes of scale. However, it appears the device contains the crystals and they are not being washed through the plumbing.",
"quartz is hydrophillic, it produces a concave meniscus when contacting water, because the surface is capable of hydrogen bonding. This could be the source of the claim that water reorganizes itself around the crystal, and may have some surfactant property. This is a similar claim to some of those plastic soapless laundry soap balls that have been debunked. Any \"water restructuring\" that occurs only pertains to molecules in immediate contact with the crystals, and is lost when they flow away. There is no \"permanent restructuring\" as the site claims. Otherwise, beaches on the ocean would have already changed all the water in the world forever.",
"Because the surface of quartz is terminated with hydrogens, it does have a pKa value, so it could be considered slightly acidic compared to hard water. It could be claimed that it buffers the water, somewhat like the ion exchange resin in a water softener. I do not know what the buffer capacity would be or if it is enough to have an impact on the pH or the redissolution of lime scale. Water softener exchangers need to be regenerated frequently since the active surface sites are consumed. And they are rather large appliances. It is unlikely there is enough pH buffering capacity in this small device to last very long. The surface will adjust its hydrogen concentration to be in equilibrium with the pH of the water.",
"Reading more carefully, it says \"a plumber is not required for installation\" it just clamps on the OUTSIDE of the pipes, therefore it isn't even in contact with the water. It claims that \"without radiation\" just being in the vicinity of water it can physically alter it, permanently.",
"\"Once the Scalehound is installed on your home if it is an older tank 3 years or older, blow down your hot water tank once a week until no visible scale exits in the tank.\"",
"Quite simply, 100% of their claims of scale reduction is due to the instruction to descale your water heater manually every week. Paying them for the useless little blue clamp on thing is just the cost of that piece of advice.",
"If I was that unscrupulous, I would be rich too."
] |
[
"In fact, typically megahertz frequencies, not acoustic frequencies, so its not \"sound waves\"",
"Just want to correct this. Even if the frequencies are high above the maximum frequency of human hearing they are still \"Sound Waves\" according to the acoustics definition. Acousticians do categorize sound waves as being Infrasonic and Ultrasonic based on frequency, but all of these are still considered sound waves."
] |
[
"Unfortunately, getting a voltage from dissimilar metals only works if there is a temperature gradient - gotta love the Seebeck effect. Columbium is right, quartz crystals (when voltages are applied) operate at relatively high frequencies - I've never seen one below about 20KHz. Looking at their website, I find myself highly skeptical - in their FAQs, this is what they have to say about quartz:",
"\"Quartz is an abundant material which has the ability to enhance energy by absorbing, storing, amplifying, balancing, focusing and transmitting. Quartz is a natural occurring element that has not been analyzed fully by the scientific community, yet we have discovered the secret to harnessing this magnificent resource for the benefit of civilization.\"",
"Call me cynical, but that sentence sets off more than a few warning bells in my head. From a thermodynamics standpoint, the act of suspending calcium in the water requires energy, and that energy has to come from somewhere - I'm not seeing a clear way for that to happen."
] |
[
"What is the relationship between gravity and magnetism?"
] |
[
false
] | null |
[
"This is a totally unanswered question in physics, and an extremely important one too.",
"Right now, the consensus in physics is that there are four fundamental forces: electromagnetism, weak nuclear force, strong nuclear force, and gravity. The standard model of particle physics accounts for only the first three and leaves out gravity entirely. While Einstein's theory of general relativity accounts for gravity quite well, it currently is not at all connected to the theory of the other three forces.",
"A theory that explained all four forces perfectly (and thus could articulate the relationships between them) would be a theory of everything and, potentially, the fundamental endpoint of human understanding of the natural world.",
"So you have (perhaps unknowingly) asked THE QUESTION, and, unfortunately, science has nothing to tell you."
] |
[
"thanks. I was just about to ask if there was any progress on the topic"
] |
[
"thanks. I was just about to ask if there was any progress on the topic"
] |
[
"What are the main differences/similarities between Gram positive and Gram negative bacteria?"
] |
[
false
] |
First time poster long time lurker. I recently went on a bit of a Wiki dive when looking at Petrichor, and found out about actinobacteria and the Gram test, but I can't quite discern from looking at the two wikis the differences and similarities of what Gram Positive and Negative bacteria have. I am not a scientist in any regard, but I find this fascinating regardless. Especially the study of Petrichor and Human evolution/sensitivity to the smell (like 5 parts to a trillion or something? idk, I'm an archaeologist.) and the ability to find food after a drought. It's just cool, but yeah I was wondering what, if any, are the main differences and/or similarities there are between Gram Positive and Gram negative bacteria are and if the test is as important as it sounds?
|
[
"The main difference is their cell wall/cell envelope structure. Both gram positive and negative have an internal cytoplasmic membrane surrounded by a peptidoglycan layer (cell wall). The peptidoglycan is much thicker in gram positive bacteria, but gram negative bacteria also have an outer membrane surrounding the peptidoglycan that is not present on gram positive bacteria. Lipopolysaccharide (lps/endotoxin) is a major component of the outer membrane and during an infection is sometimes able to over activate the immune system causing septic shock. There are many other differences but the membrane/peptidoglycan layer is the major difference used to classify.\nEdit-MSc candidate in microbiology and immunology. Feel free to PM any other bacteria questions and I'll do my best to answer"
] |
[
"Another difference between them is that the membrane of gram negative bacteria is generally more complex than that of gram positive. "
] |
[
"I believe so, I remember reading it, im not a biologist by any means, but I took A.P bio and learned a decent amount. "
] |
[
"Why do lines come out of light sources when you squint?"
] |
[
false
] |
My best guess is that it is coming from something about my eye-lens shape being changed.
|
[
"I'm trying to remember the exact term for this, but it's the same effect that you see in cameras. Essentially, when you squint, you are changing the shape of the \"aperture\" for your eye, and the number of streaks and the shape of the streaks depends on the shape of the aperture.\nFor cameras, you have an octagonal or such shape, and when you squint you make a slit shaped aperture. \n",
"http://gallowayphoto.wordpress.com/2010/04/17/high-f-stop-with-bright-lights-in-the-frame/"
] |
[
"I've always kind of thought it might just be how the light shows through your eyelashes, but I'm glad you asked because I've been really curious too."
] |
[
"By closing your eyelids just until the lashes mesh without completely closing the lids."
] |
[
"Question about an alien spaceship travelling to earth"
] |
[
false
] |
I had a discussion about it and now am rather confused. Following situation: An alien planet is 10'000 lightyears (LY) from earth. So at our year 0, they receive the radiowaves from year -10'000. An alien ship launches and travels to earth with lightspeed (if this is a problem, let's say 99.9%) just as the radiowave from year -10'000 hits the planet. The ship itself can receive the waves as well. Now as the ship travels the 10'000 years to earth, does it receive 20'000 years worth of radiowaves? How? Because as soon as the ship reached the planet, the year there is 10'000, and thus the ship crossed every wave of the last 20'000 years.
|
[
"Now as the ship travels the 10'000 years to earth, does it receive 20'000 years worth of radiowaves? How?",
"Yes. It will be doppler shifted, though. So not only are the frequencies higher, everything is played in fast forward, so to say. Time dilation also comes into play. The closer the aliens get to the speed of light, the closer the travel time will approach zero. So it could take them only 1 second from their perspective for the whole trip (still 10'000 years from the outside), and then they will receive the entire radio history of the last 20'000 years within one second (in super fast forward)."
] |
[
"It might actually heat up the spaceship quite a bit, yes. "
] |
[
"The ship spends 10000 years in transit but at the same time it is crossing radio waves going the other way. It crosses 20000 years of radio waves."
] |
[
"What would happen if the Sun suddenly disappeared...?"
] |
[
false
] |
(The Sun disappear suddenly and instead there is only space). Specially interested in: How long would be until the temperatures on Earth made human living impossible? Could some living beings (like extremophyles on hydrothermal vent) survive? What would happen to the orbits of the planets?
|
[
"We would have about 8 more minutes of light.",
"But way more interesting to me is that we would have about 8 more minutes of gravitational attraction before we began to float off in a straight line. Gravity operates at the speed of light."
] |
[
"For 8 minutes, nothing at all. We'd keep on orbiting and we'd still see the sun. Then... it gets bad. (speculating:) Presumably we'd fly out of the solar system on a straight path along some vector tangential to our orbit, as would all the other planets. We could quite possibly live underground, there was a thread on that a few days ago but I can't find it."
] |
[
"No, for eight minutes it would be like nothing has happened at all because, at that distance from the Sun ",
"."
] |
[
"The Human Genome Project cost $2.7 billion. 20 years later, it costs <$1000 to sequence the genome. Was the cost of the project fundamentally necessary for subsequent progress, or could we have \"waited\" for the technology to become cheaper?"
] |
[
false
] |
I'm very much a clueless layman, but I'm learning about genetics for the first time. I don't mean this in any sort of combative way–the Human Genome Project had countless benefits that we can't possibly track, and I'd imagine $2.7 billion is a trifle compared to its broader impact. My question is just narrowly about the way that genome sequencing has dropped rapidly in cost. Was it fundamentally necessary to first use these exorbitantly pricey methods, which provided the foundation for the future research which would make it affordable? Or are the two questions inherently separate: the Human Genome Project gave us a first, initial glimpse at our mapped out genome, and then a decade later separate technological developments would make that same task much cheaper (as is commonly the case in science and technology). The "could we have waited" in the title is probably misleading–I really don't mean any sort of value judgment (the project sounds enormously important), I purely mean "could" in a narrow hypothetical (not, "would it have been a good idea to wait", which I highly doubt).
|
[
"The cost of gene sequencing has dropped dramatically, but these two numbers are apples and oranges. The Human Genome Project \"mapped the genome\". Meaning it created a \"reference genome\" that is roughly accurate for every human being on earth. It's like a scaffold upon which you can place any individual sequence you might read. ",
"Today, you can take short reads of roughly a human genome-worth of DNA for less than $1000. That sequencing can tell you if the person has any small mutations. But without the reference genome, all that information would be worthless because you couldn't place all the little fragments of DNA where they sit on the larger genome.",
"Think of it like having a big jumble of small phrases that you know belong in a big epic novel. Your job is to tell us what page the phrase belongs on. HGP pieced together the whole novel for the first time, so now your job is much easier because you can just do a CRTL+F. ",
"Today, people continue to assemble new reference genomes (e.g., new species) and reassemble the human genome to look for larger variations that don't agree with the original reference genomes created by the HGP and others. You typically can't do that for <$1000. It could cost you tens or hundreds of thousands of dollars, depending on what tools you use and what accuracy you desire. ",
"Tl;Dr: creating a new reference genome is much cheaper than it used to be and has certainly enabled by technology created in the course of the HGP and others. But still very very expensive."
] |
[
"We did go through a bunch of technological leaps though. The HGP was done with Sanger sequencing and the nanopore and similar we've got today are hundreds of times cheaper per base."
] |
[
"Short answer is no. Basically the people working on the Human genome project developed and advanced the technology while also proving that it was even possible! ",
"A good analogy would be that it cost about $2.27 Billion for the Sputnik mission to get the first person into space and SpaceX rockets cost about 57 million to get into space. But without the basis for going to space SpaceX would seem impossible. ",
"Basically, it’s always going to be more expensive to do something the first time because, well it’s the first time. But all the subsequent attempts get better as things get more mainstream. And things likely will only get cheaper, we can now analyze thousands of genes at once for extremely cheap using MicroArrays, look those up on YouTube they’re very good.",
"Random story about DNA sequencing (not sure how accurate this is but one of my college professors told me this). Evidently the guy who developed a way to speed up PCR (what let’s us sequence DNA really fast) did it while he was high looking at the 2 yellow lines in the middle of the road. And in his brain they were going together and separating and so he had the idea to, rather than have 1 copy of a sequence of DNA and trying to read it, just make a ton of copies so it’s easier to analyze."
] |
[
"I want to create a contained \"atmosphere.\" Is this possible?"
] |
[
false
] | null |
[
"All of that depends on the type of experiment you are preforming, what kind of data you need, what kind of model you are making, etc.",
"Building an airtight vessel that has a gas composition of our atmosphere or close to it is pretty simple, but things get complicated pretty fast. Do you need to analyze the gas composition? Now you need access to a GC. Need to recreate our sun on a small scale? Now you need a very precise lamp and calibration equipment. Measuring some kind of equilibrium? Now you need to include all the intricate pieces (our planet is pretty damn complex).",
"If you define your question better we might also be able to point you in the right direction. There are quite a lot of people working on understanding our atmosphere and all its intricacies, I'm sure there are panelists in this subreddit that can point you to relevent information or confirm whether or not that info exists yet."
] |
[
"Thank you, this is helpful.\nI definitely would want to \"recreate\" the sun, I didn't realize it would require that much precision. Now that I think of it though, maybe it could work without it? I had the idea of essentially getting this \"atmosphere\" together, rising the temperature to global averages with, and measuring the fall of temperature with the insulation of the atmosphere alone. I thought I may need a \"sun,\" but perhaps it could be done by applying external heat to a scaled down equivalent?"
] |
[
"I think it really depends on what exactly you are trying to measure. If you want to measure just the raw insulation of a certain mixture of gasses then you don't necessarily need a fake sun, though you can also find this data or calculate it from known properties without running an experiment.",
"Faking the sun itself isn't incredibly hard, researchers have been making fake suns for evaluating solar cells and other things for quite awhile. It isn't the easiest thing either, as you need to make sure your light has the appropriate emission spectrum and that the irradiance on your surface is correct. Put the light a little too close or a little too far away and you completely skew your data.",
"It might help if I/we knew your exact question a little better. What exactly is the hypothesis or the question that you are trying to answer here?"
] |
[
"How do energy saving light bulbs work?"
] |
[
false
] | null |
[
"I am assuming you mean CFL's vs incandescent. ",
"In this case incandescent bulbs heat a filament enough that its blackbody radiation shifts into the visible range. Now a lot of this electricity that goes into heating dosen't make it out as visible light but instead as heat and is essentially wasted since we cant see this far IR light.",
"CFL's however create a plasma that emits mostly invisible photons as electrons pop in and out of bonding with an atom. These photons then hit a phosphor coating (if you have ever broken a fluorescent light this is the white powdery stuff on the inside) the inside of the glass and that then emits visible light. This process produced very little heat and the phosphor has a fairly high quantum yield thus very little of the input energy is wasted compared to the incandescent bulb."
] |
[
"Now kids, don't go out and break flourescent bulbs to observe this coating firsthand.",
"These bulbs contain mercury.",
"Mercury's bad, mmmmmkay?"
] |
[
"yes I get the reference....but newer bulbs are mercury free ;D Yay"
] |
[
"What would space battles realistically look like in the near future?"
] |
[
false
] | null |
[
"Over large distances, lasers would be almost necessary. Space is really big, and lasers obviously move faster than any other weapons available."
] |
[
"Depends on what you mean by \"near-future\". But I'd recommend reading about The Outer Space Treaty: via Wikipedia,",
"The Outer Space Treaty represents the basic legal framework of international space law. Among its principles, it bars States Parties to the Treaty from placing nuclear weapons or any other weapons of mass destruction in orbit of Earth, installing them on the Moon or any other celestial body, or to otherwise station them in outer space. It exclusively limits the use of the Moon and other celestial bodies to peaceful purposes and expressly prohibits their use for testing weapons of any kind, conducting military maneuvers, or establishing military bases, installations, and fortifications (Art.IV). However, the Treaty does not prohibit the placement of conventional weapons in orbit. The treaty also states that the exploration of outer space shall be done to benefit all countries and shall be free for exploration and use by all the States.",
"Of course, countries only pay attention to such treaties as long as it benefits them. It's almost certainly just a matter of time until space is a context for military positioning and conflict. But at least there's a barrier to entry.",
"The ",
"Chinese 2007 test of a 'killsat' missile",
" is a pretty important landmark. It's unknown what countermeasures each nation has developed (largely depending on how the missile is guided).",
"For more theoretical/hypothetical stuff, I'd recommend ",
"this",
". Some pretty scary stuff.",
"Really, your questions are valid but there aren't answers yet, since the form space warfare will take will depend upon the strategic and tech choices of the actors involved. Nobody wants to show their hand to give others' a leg up on countering their strategy."
] |
[
"While that's true, the 2007 Chinese killsat test is particularly important in the context of space warfare, since China's the sort of country that might actually put this tech into use (as evidenced by their ambition, lack of stake in the current space status quo, behavior in other contexts, etc)."
] |
[
"Is a radio station's transmitter power approximately equivalent to how much power a light bulb would need to have to be visible everywhere in the radio station's listening area?"
] |
[
false
] |
Obviously what type of bulb and what time of day would matter a lot, but my basic question is whether a radio transmitter is essentially a giant light bulb that just generates light outside of the visible spectrum.
|
[
"I think that this slightly misses the point of the question, which I believe is more along the lines of \"How does a radio station's broadcast range compare to the range over which a visible light source of the same power would be visible?\""
] |
[
"radio waves have a much (MUCH) ",
" frequency than light.",
"Typical visible frequency is about 5*10",
" Hz . Typical VHF 10",
" Hz which means that it has a roughly 1 million times lower frequency (and lower energy).",
"However, transmission depends on the frequency/wavelength, but it is more complicated than higher energy--> more transmission \n",
"http://www.udel.edu/Geography/DeLiberty/Geog474/spectrum.jpg"
] |
[
"radio waves have a much (MUCH) ",
" frequency than light.",
"Typical visible frequency is about 5*10",
" Hz . Typical VHF 10",
" Hz which means that it has a roughly 1 million times lower frequency (and lower energy).",
"However, transmission depends on the frequency/wavelength, but it is more complicated than higher energy--> more transmission \n",
"http://www.udel.edu/Geography/DeLiberty/Geog474/spectrum.jpg"
] |
[
"Is the frequency range of human hearing limited by the biology of the ear, or brain capability/processing?"
] |
[
false
] |
Suppose technology were advanced enough to create a bionic ear implant, capable of interpreting frequency ranges wider than 20Hz-20kHz. Could the human brain interpret the signals and give us super hearing abilities?
|
[
"You can hear ultrasonics quite well by using frequency division or heterodyning systems, which are the basis of bat detectors. The basic technique is to divide the ultrasonic frequnecy by some constant to remap it onto your normal hearing range or to convert high frequencies detected into clicks to let you know that there is sound at that frequency. And there are a few wearable bat detectors, so I guess that would qualify as bionic, although the better ones are much larger.",
"Without using bat detector type circuits, there are still some ways some humans can detect ultrasonics. Very young children can hear up to 22 kHz; older people can sometimes hear this range and beyond with specific types of ear damage (happened to me - thickened tympani due to chicken pox) - the thickened ear drum is less responsive to lower frequencies (I really can't hear anything below about 70 Hz) but is more responsive to higher frequencies. The problem is that your ability to detect pitch of a signal is more limited at higher frequencies due to broader critical bands (which is why the musical range really stops at about 4 khz, although harmonics are important up to 16 kHz), so you can not discriminate individual pitches any better. Perceptually, higher frequencies end up just being detection events (clicks at onset, odd almost tactile feeling) or heard as lower frequency sounds. This remapping is similare to what happens to hearing due to presbycusis (age related upper frequency hearing loss). You think you're hearing high frequencies but what has happened is that your brain stretches lower frequencies from the ear into the region of the brain that used to detect higher frequencies. As a musician friend of mine said, \"I thought I could hear high frequencies until somebody played some for me.\""
] |
[
"This is in fact a combination of both. The human ear works because of sound waves will make hair cells in the cochlea move. Thus generating an electric current, which is sent to the brain where it gets \"decoded\". The cochlea wouldn't be capable of catching waves outside the 20Hz - 20kHz. That's why humans can't hear infra- or ultrasones, simply put: the brain simply doesn't get neural response from the colchea.",
"on another note. I think creating a bionic ear implant and putting it in ones ear is a very tricky subject. I presume you mean that the whole inner ear compartment gets changed by the implant. Not only it's tricky to put a microscopic device in ones ear, but how on earth is it going to generate a neural response, decodable by a human brain?\nAnd let's hypothesize it IS possible, the brain still wouldn't be able to decode information from the implant from ranges outside the 20Hz - 20kHz for it has NEVER encountered those in any natural way.",
"tl;dr : a) it's almost impossible to create such a device\nb) if it IS possible, the brain wouldn't be able to decode the \"information\" sent from the implant."
] |
[
"Thanks for your responses! I've learned something here. However I'm a little surprised by the conclusion from Mallasun. I suppose I jumped to the conclusion that the brain might be capable of decoding wider frequencies—given better equipment—in a similar way to how eye mutations or defects allow some people to see UV."
] |
[
"Is there a widely-accepted theory as to the characteristics of randomness?"
] |
[
false
] | null |
[
"The lottery is not going to be affected by quantum physics, and that's the only source of true randomness there is. The lottery numbers that are picked don't care who's buying them. The butterfly effect, and all of chaos theory, can (and usually does) occur in perfectly deterministic systems; it's just that they're not predictable in any realistic sense."
] |
[
"So all of what we know as 'randomness' or chance on a macroscopic scale is only considered as such because we have no way of predicting it with perfect accuracy (or, often, with any accuracy at all), but the outcome of a given 'random' event (e.g. the rolling of a die) is essentially predetermined as soon as the action is undertaken?"
] |
[
"Sure. Think about what happens when you're rolling a die: you give it some velocity in some direction, and it falls, hits the table, rolls and bounces around, all following perfectly ordinary laws of physics. Given complete knowledge of the entire system, you could predict the outcome, unrealistic though that is in practice. After all, there isn't any room for randomness; there isn't some point at which the laws of physics say \"insert random input here.\""
] |
[
"Why can't we as a planet completely switch over to nuclear energy and shoot the radioactive waste into the Sun?"
] |
[
false
] | null |
[
"The two most common reasons we cant dispose of the waste in space are: ",
"Expense. Right not it's just too damn expensive to launch stuff into space, let alone to the sun. But this will come down soon.",
"Risk. If that rocket carrying it to the sun blows up in our atmosphere, well, we'd all be having a very bad time. You couldn't risk that happening even just once. There are fairly indestructible canister that are used for radioactive transport, and designed to stay water and air tight in a catastrophic train crash, but are they enough to survive a rocket explosion?"
] |
[
"Reasons for not switching to nuclear:",
"Public fear. Also from the lawmakers who implement it. People just don't trust the safety enough. Especially since the Japanese tsunami incident recently. That incident prompted a massive inspection of all reactors in Europe. Cant remember exact stats, but that majority of them had recommendations of improvements due to not meeting current standards. Some in Russia are completely unsafe, but won't be improved because they're being shut down soon. ",
"Cost. Those things are expensive.",
"They're not clean. There is still a LOT of waste produce by nuclear reactors. There's the radioactive side, but also regular carbon from many of the support services they require. "
] |
[
"So right now, we're limited by technology of space travel and the social stigma of nuclear safety. Say both of these issues are solved over time, it would, in theory, be safe to dispose of nuclear waste by shooting it at the Sun? Could all waste produced by humans be disposed of this way? "
] |
[
"If we our sun was a different type of star, emitting different types of radiation or light, would our plants be a different color?"
] |
[
false
] |
Just as the title reads.
|
[
"Well we actually evolved to see certain wavelengths of electromagnetic radiation, roughly .4-.7 micrometers. This is because the light that gets to our eyes has the highest concentration of light in that spectrum. To address your question, ALL colors would be different because we would not be seeing the same way, even though it theoretically could look the same? ",
"But I think to answer your question more directly, for example, if the sun were to suddenly emit a vastly different wavelengths of EMR, then yea, colors would be different. "
] |
[
"I'm going to assume you mean \"would plants have evolved to use different wavelengths of light and therefore would not be green if our sun emitted different wavelengths of light than it does now\".",
"Obviously, if you went to some other planet, or \"restarted\" evolution of this planet, plants (and animals) could end up being vastly different. but in the end, I suspect the answer is \"no\". See this link: ",
"http://hyperphysics.phy-astr.gsu.edu/hbase/biology/ligabs.html#c2",
"In theory, no matter what spectrum of light a star emits, to be as efficient as possible, a leaf should be black (absorbing all the light). According to the link above, terrestrial leaves are not good at absorbing green wavelengths of light because there was a bacteria that existed early in plants' evolution that was good at absorbing green light. Apparently betacarotene \"helps\" plants absorb some green spectrum light.",
"So, even if our sun gave off different wavelengths of light, providing the same early bacteria were present, plants would still be (mostly) green. And, no matter what spectrum is emitted, a plant would ",
" be black to absorb all the light."
] |
[
"Yes, thank you! I couldn't figure out how to word this question. That's very interesting. Thanks for the clarification!"
] |
[
"What Would Happen if the Forces Holding the Molecules in your Body Together Disappeared?"
] |
[
false
] | null |
[
"Hi j0nr thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics"
] |
[
"Physics "
] |
[
"How do we know genetically modified foods are safe for human consumption?"
] |
[
false
] |
Taking BT corn for example. Assuming the necessary animal and human trials have been conducted to demonstrate the cry1Ac protein is safe for human consumption: This protein is 1178 AA in length, yet the gene it is encoded in is 75 Kb. That would suggest only 4.7% of this gene codes for the cry1Ac protein. How thoroughly do we understand the structure and function of the other 95.3% of the gene? Are all the other coding, non-coding, promoter, etc sequences thoroughly studied to make sure no unexpected effects could occur? And what about epigenetic factors? In my graduate biotechnology course I was told we did not fully understand how most non-coding DNA operated, and we were just beginning to get a grasp on epigenetic mechanisms. If we do not fully understand what these non-coding genes do, how can we say it is absolutely safe for human consumption? edit:
|
[
"You are asking the wrong question: ",
"First the GM crops",
"The only mechanism by which DNA can harm us is by the proteins that it encodes. DNA itself can do nothing, it just gets digested. DNA is DNA no matter it's source.",
"The proteins that we want a GE organism to express are very well understood. That is the point of selecting them. ",
"The plants then are tested extensively for allergens and if there is even the slightest chance somebody could be allergic to the protein, then it doesn't get approved.",
"For non-GM crops",
"No testing is done with non-GM crops and some of these are lethal to some people, such as peanuts.",
"There is no guarantee that a traditionally bred plant isn't poisonous, after all 1000s of genes are being modified, and none of these are tested.",
"Many hybrid plants are mutagens, that is they were created by radiation, chemical or other type of mutating agents. Again 100s of genes can be altered in random ways. These are also untested and many are grown as \"organic\"."
] |
[
"You said yourself that we do not fully understand how genes and the epigenome function. This is true. Because of this, we cannot absolutely predict the effects of a given gene based on our knowledge of genetics. However, that is true for every organism. If you examined the entire genome for Bt corn, it would be equally impossible to determine if any of the other genes might have unexpected effects. Based on this approach, it's impossible to say if anything is, to borrow your phrase, absolutely safe for human consumption. Thankfully, the FDA does not use this methodology, or we'd all be quite hungry.",
"The process works just the same as with any food (though certainly more stringent with GMOs)- check if it has any known toxins, carcinogens, etc., test if it is noticeably harmful to animals or people, and if no red flags get raised, then it's probably safe to eat. There's no absolute certainties, but it's close enough."
] |
[
"The testing applied to GM crops is no different than the testing applied to any other food product that comes on the market - arguably stricter for GM, actually."
] |
[
"Would a comet in a binary star system have two tails?"
] |
[
false
] |
It's my understanding that a comets tail is caused by solar winds, so I'm wondering if a comet interacting with solar winds from multiple stars would have multiple tails?
|
[
"The tails ",
" caused by solar winds, but having two star would ",
" cause there to be two tails.",
"When you have one star, the force acting on the comet's dust is basically in one direction (unless you go across vast distances), and grows weaker with distance.",
"When you have two stars, you just get two forces, you add them up to get the result, and the tail would fly in that direction with that push."
] |
[
"Vectors!"
] |
[
"The two tails you are seeing there are the gas (ion) tail and dust tail (larger particles), both caused by a single source.",
"Read more at Wikipedia"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Where does the music in my head come from? Why does it happen?"
] |
[
"The fast growth of bamboo mostly doesn't come from specific genes, but rather from the structure of the plant itself and the environment it is growing in. Bamboo is a grass, and grows entirely from the tip of the shoot. Since all the growth of the plant happens at one point, it grows fast. Something like an oak tree grows from the tips of hundreds of branches at once, so no branch grows nearly as fast. ",
"Additionally, bamboo only grows that fast in optimum environments where there is plenty of water and nutrients and sun."
] |
[
"The fast growth of bamboo mostly doesn't come from specific genes, but rather from the structure of the plant itself and the environment it is growing in. Bamboo is a grass, and grows entirely from the tip of the shoot. Since all the growth of the plant happens at one point, it grows fast. Something like an oak tree grows from the tips of hundreds of branches at once, so no branch grows nearly as fast. ",
"Additionally, bamboo only grows that fast in optimum environments where there is plenty of water and nutrients and sun."
] |
[
"Where did Earth's water come from?"
] |
[
false
] |
[deleted]
|
[
"The same reason that it's the only planet with life on it. We're the perfect distance away from the sun for the elements of life to latch on and grow! Hydrogen, oxygen, nitrogen, carbon, and other life essential elements were cooked up for billions of years in the core of a star before exploding in every direction. Some landed here :)"
] |
[
"Earth is not the only planet with an abundance of water. There's ice on mars and moons like Europa. It has been hypothesized that there is a subsurface ocean underneath Europa due to water vapor plumes.",
"I can't say for certain what other planets have or do not have water, because I am nowhere near this field of study, but I can say that your statement seems very likely to be false."
] |
[
"Different planets have different masses and different distances from the sun. Mercury is so close that most of it's atmosphere has been blasted away by the Solar wind. Saturn and Jupiter also have huge amounts of water, but they are diffused throughout a vast planetary atmoshpere so they only take up a small percentage of the total volume.",
"It's worth remembering too that the water on earth is only a tiny proportion of the total volume and mass of the planet. But because the earth has a rocks core that is more dense the water stays on the surface and is much more visible. Further unlike a lot of other planets( eg Mars), the earth has a strong magnetic field that protects the atmosphere from the solar wind and stops it being blow out into space.",
"However the mass of the earth isn't sufficient to keep all gases here - Helium is too light to be captured and if it is in the atmosphere it rises to the top and then slowly leaks into space.",
"Remember also that the elements that make up water - Hydrogen and Oxygen are common throughout the universe. This is because they have relatively stable nuclei.",
"It just happens that some planets have different masses, different magnetic fields, and different distributions of elements that cause different proportions of water on the surface."
] |
[
"AskScience AMA Series: I am Tom Talbot MD MPH, an infectious diseases physician and infection prevention expert/vaccine advocate who's been working on the frontlines during the COVID pandemic. AMA!"
] |
[
false
] |
I am an infectious diseases physician (for almost 2 decades) working at Vanderbilt University Medical Center (VUMC - views expressed are my own and don't represent formal VUMC guidance). Much of my professional career has focused on infection prevention as the VUMC Chief Hospital Epidemiologist (a fancy word for medical director of the institution's infection prevention program). I work to reduce the risks of patients and healthcare workers catching an infection related to healthcare. This could be infections after surgery, infections due to medical devices, and infections related to emerging pathogens, like COVID. I'm also a recognized expert in and advocate of vaccinations as a way to protect individuals, other patients, and healthcare workers from harm (such as spread of viruses like influenza and now COVID). Now that several effective COVID vaccines are available, these will be the tools that help get us to the other side of this pandemic. However, vaccination efforts have been hampered by supply/logistic issues, confusion over eligibility, and hesitancy. Happy to chat with everyone today at noon (ET, 17 UT) about COVID and the vaccines! Twitter: Username:
|
[
"Thanks for the AMA. Two questions.",
"Has there ever been a vaccine in the past that was safe in adults but unsafe in children? I am aware of the formalin inactivated RSV vaccine from the 60s that killed a few young kids, but not sure if they were trialed in adults first to test safety. I can't find much literature from the 60s.",
"Why do you think cases have dropped globally in recent weeks? Even in areas that don't celebrate Thanksgiving/Christmas (like India)."
] |
[
"Great question -- we need to have the vaccine trials being performed in children completed (and hopefully show a similar benefit as we've seen in adults); even if not as protective, if we get more adults immune to the virus, then spread can still be slowed markedly. It's likely that the COVID virus will be with us for good, but the hope is it becomes more like our usual respiratory viruses where most are protected. Mutation is still an issue but we've got to see how big. The virus does not seem to mutate as readily as influenza, but we may need more frequent vaccine boosters if it does show ability to mutate more frequently."
] |
[
"Great questions -",
"Off the top of my head, other than just having vaccines that have not been tested in kids, I cannot think of such a vaccine. Maybe the early pertussis vaccines that caused febrile seizures, but that was just that the infants had less tolerance for fevers vs. an adult.",
"Honestly, one of the best answers to the reason for declines question I have heard is that we've been thinking of everyone as part of a single herd when really we have several herds -- simplistically, one that has stayed home, masked, not traveled, not gone to restaurants/bars and another who has. It is possible that the latter herd has a higher immunity as they've gotten infected and exposed their usual contacts?? If so, the worry is if the former group starts to relax, will they join the other herd and get exposed/see cases rise? It's also possible that the messages of the strain on the healthcare system finally was heard and people followed guidance more broadly, but I am not sure that has happened (I'm a bit cynical on that)."
] |
[
"Do the physical properties of ice change at different temperatures?"
] |
[
false
] |
Does ice change at all at different temperatures (below 0°c obviously), for example does it become in any way harder the colder it is?
|
[
"Under the right conditions, ice can take on different crystalline forms called \"solid phases.\" Parameters like ",
"temperature, pressure, and volume",
" govern these varying morphological regimes (image from ",
"Wikipedia:Ice/Phases",
", which features an excellent summary table). ",
"This University page",
" is another good resource for learning about solid phases of ice.",
"With respect to your example, 'hardness' describes resistance to plastic deformation (and it doesn't look like much research has been done to characterize the hardness of different solid phases of ice at comparable conditions). ",
"This AskScience answer",
" cites ",
"Nesje and Dahl (2000)",
", which claims that ice hardness (for naturally occurring hexagonal ice) increases from 1.5 to 6 on the Mohs scale as it cools from 0 to -70°C. ",
"A different AskScience thread",
" contains a similar discussion on ice hardness at different temperatures and references ",
"this 1958 article on single-crystal ice hardness",
"."
] |
[
"Wouldn't that suggest it does harden? Generally breaking a material involves breaking bonds, which break by absorbing too much eneegy. If there's less vibration at -70 as opposed to -10, the ice must absorb more energy overall to reach the point where bonded molecules will separate? "
] |
[
"Yes it does. At least on an atomic level. Generally, atoms vibrate a little bit. They do when water is frozen at -10°C and they do when it's frozen at -100°C. The difference is that at lower temperatures, atoms vibrate a little bit less than they do at higher temperatures. At one point, they stop vibrating at all. This is called the 'absolute zero' or 0 Kelvin. It is aproximately -273°C and is the coldest anything can be on this planet. So it doesn't harden per se, but something does change when it gets colder."
] |
[
"If the earth spins at 1000mph, how does a rocket fly back into the atomsphere and adjust to the spin?"
] |
[
false
] |
So if a rocket flies head on to the earth which is rotating at 1000mph, how does it align with the rotation of the earth so that it's at at a suitable position to land?
|
[
"Rockets don't come straight down to land. They come in at only a few degrees of inclination away from the surface of the planet/atmosphere, moving in the same general direction as the Earth's rotation. Friction with the atmosphere then reduces their velocity until they're moving at nearly the same horizontal speed as the atmosphere."
] |
[
"We actually usually have sort of the opposite problem. It's rare for a spacecraft to return to Earth head on. Typically they return from orbit, and getting into orbit is not merely a matter of getting above the atmosphere but of gaining velocity. The basic concept of an orbit is that you are moving horizontally so fast that by the time you've dropped vertically 1 foot, the surface of the Earth has curved 1 foot away.",
"To achieve this near Earth a spacecraft has to reach about 17,000 mph. We usually launch spacecraft such that their orbital speed is in the same direction as Earth's spin--because it's a free 1,000 mph head start--so a spacecraft typically has a speed of 16,000 mph relative to the surface. Thus the issue is not catching up to Earth's spin, but slowing down to match it. The usual solution is to lose just enough orbital velocity to cause the spacecraft to drop into the atmosphere, and then let the atmosphere's drag do the rest of the work--it's spinning with the surface, so it will eventually slow the spacecraft to that speed--and to time this descent to land the spacecraft roughly at the desired destination."
] |
[
"There's definitely more to it, but part of it has to do with the fact that when approaching earth, it's not like there's a discrete line where the atmosphere starts and that is going at 1000 mph relative to the space just outside it. The atmosphere gradually gets more and more dense as you get closer to earth, so anything approaching would kind of ease into it to some degree. Also, down at ground level, the atmosphere is rotating right along with the surface of the earth, but presumably this speed of rotation doesn't stay the same as the atmosphere gets less and less dense and further and further from earth. I'm sure space agencies have very detailed models of how all this works so they can plan in detail, but at a basic level, the rocket would ease into the atmosphere very gradually and encounter/adjust to the density/resistance/motion of the atmosphere over the time of the approach. "
] |
[
"If systems move toward entropy, why do atoms tend to bond toward non-reactivity?"
] |
[
false
] |
[deleted]
|
[
"You're missing something about ",
". They lose energy when they bond, meaning that energy is given off as heat, which creates more entropy than is lost by forming a bond. The entropy of the atoms and their surroundings as a whole increases. ",
"An ",
" system moves towards greater entropy. If you bring a bunch of unbonded Cl atoms (for instance) together in a hypothetical scenario where they can't dissipate the energy from forming Cl2, then most of them won't be bonding at any given moment."
] |
[
"I got the first part, but the second got me intrigued....\nCould you add ti that explanation, why would a clorine care about being in a closed or open system?"
] |
[
"It doesn't 'care'. Here, ",
"see this graph",
", it's a typical representation of what the energy (vertical axis) looks like for two atoms, separated by a distance r (horizontal axis). There's a minimum, which is the bonding distance, and there's a maximal dissociation energy (D0) required to pull apart the two, as seen by how the curve flattens off to the right.",
"The red lines in that diagram represent the vibrational states of the atoms. (BTW, the lowest red line/vibrational state is not at the bottom, which is the lowest energy if it was classical. Hence things are still vibrating when in their lowest energy state, that's a quantum 'zero-point vibration energy', the difference between De and D0)",
"As you can see, the topmost vibrational state is the same as the dissociation energy, so when the two atoms come together, the electrons lose energy when forming a bond, and that energy is transferred into the vibrational energy of the molecule. And the vibrational energy is enough for the atoms to fly apart again. ",
"If the relative kinetic energy of the two atoms is above De, they will fly into each other, R getting smaller) and hit the 'wall' represented by the energy increase at small R, where the atoms are well closer than bonding distance and now into the region where their electrons repel them. In simple terms, if they're moving too fast, the two atoms will just bounce off each other rather than bond. (Which is indeed what starts to happen when a gas starts to become a plasma)",
"So the Cl atoms will only stick together for a longer period of time if the molecule can dissipate some of its vibrational energy and move some 'rungs' down that ladder of vibrational energy states. ",
"But: If you've got an isolated system of separated Cl atoms, they all start forming bonds, but these bonds can break as easily as they're formed, because the fresh pairs are staying in their highest-energy vibrational state. Since it's an isolated system, that energy can't be lost to the surroundings. Which means it can only be transferred to other chlorine atoms. And then that atom (provided it's not lost any energy) will be moving faster, and now have enough energy to simply bounce rather than bond.",
"So from a starting point of every atom being unbound, every atom has the energy of De. For every well-bound atom (energy < De) there must be at least one that's free (energy > De). Entropy/probability dictates here that you will have more free atoms than bound ones though, because there are more free-atom states than molecule states for a given amount of energy. Some of them will be bound though, as it'd be a higher entropy state to have all atoms unbound as well."
] |
[
"Why is the magnetic force vector perpendicular to the magnetic field?"
] |
[
false
] |
[deleted]
|
[
"We can explain this by symmetry arguments! The force acting on a charge due to a magnetic field is a vector (like all forces) but the magnetic field is a pseudovector. Vectors change sign under a reflection transformation and pseudovectors do not. ",
"Here's an intuitive way of thinking about it. Imagine we place a mirror on the floor and drop a baseball onto it. We know the force due to gravity will pull the ball down towards the mirror, but the mirror image of the ball looks like it is accelerating upwards toward the mirror surface. Thus the mirror image of vectors like force and velocity has the opposite sign of the original. ",
"Now, place a current loop in front of the mirror that generates a magnetic field pointing towards its surface (like the \"vertical mirror\" in ",
"this image",
"). The magnetic field direction depends only on the current direction in the loop, which is NOT changed in the mirror image. Therefore, the magnetic field in the reflection of the current loop points in the same direction as the original current loop. ",
"Now launch a test particle into the field generated by the current loop. Because force is a vector (odd under reflection) and magnetic field is unchanged in the reflection, the magnetic force cannot have any components parallel to the magnetic field because these components would not flip sign in the mirror image as a force must. "
] |
[
"The force acting on a charge due to a magnetic field is a vector (like all forces) but the magnetic field is a pseudovector.",
"Isn't that a bit of a chicken-and-egg sort of thing? Given that explanation, aren't I going to ask, \"Well then how do you know it's a pseudovector?\"",
"We didn't find out how magnets worked by creating a mirror universe and seeing what was flipped around what axis. Aren't you describing a mathematical formalism as though it's empirical evidence?"
] |
[
"Magnetic fields in a different reference frame are just electric fields.",
" ",
"Consider a frame with a positive test particle moving to the left and below it, a line of positive charge moving to the right. In this frame, you can say that the test particle is deflected upwards by the combined forces of the electric repulsion from the line of charge and the magnetic field generated from the motion of the line. ",
"In another frame where the particle is stationary and the line of charge is moving faster to the right, the test particle isn't moving with respect to the magnetic field, but it has to be deflected by the same amount to behave the same in all frames. In this frame, the test particle sees a Lorentz-contracted line of charge, increasing the effective charge density. The magnetic field has transformed into an electric field by changing reference frames."
] |
[
"What can you do with a synchrotron that you can’t do with an electron microprobe?"
] |
[
false
] |
I have done some synchrotron stuff, but never use an electron microscope and am wondering more about it. I am a soil chemist and focus a lot on redox chemistry. Would it be the EXAFS are only with synchrotron but XANES can be done on a microprobe? Is it the fluorescence stuff microprobes can’t analyze? Is it a different range in energy levels? Just curious, thanks!
|
[
"Do you mean an electron microscope? The electron microprobe was developed to analyze compositions of unknown samples using wavlength dispersive xray spectrometry and an array of standard samples.",
"In a transmission electron microscope you have access to similar features in the X-ray data of a light source in the form of an electron energy loss spectrum (EELS) . Energy resolution is the main difference, but new systems are approacing < 0.03 eV. Look up EELS analysis if youre interested, particulary extended energy loss fine structure (EXELFS) . Gatan's website has a pretty decent primer on EELS.",
"",
"Edit:",
"Here is the Gatan educational site I was talking about ",
"www.eels.info"
] |
[
"I believe I was, thanks for the clarification! ",
"And gotcha yeah I’ll check that out, thanks!"
] |
[
"To piggyback off of this, electron microscopes are ideal when you have small samples, or need to probe specific features of a sample.",
"The wavelength of an electron is 2 (if i remember correctly) orders of magnitude smaller than an xray. This means it is easier to beat diffraction limited resolution. Additionally, hecause electrons are charged particles, it is a but easier to refine spotsize."
] |
[
"Why is General Theory of Relatively needed to explain the orbit of Mercury?"
] |
[
false
] |
[deleted]
|
[
"GR is more important for Mercury than the other planets because it's much closer to the Sun, deeper in the gravitational potential where GR effects are stronger. ",
"Mercury's orbit, like the orbit of all the planets, is not circular but is eccentric. One part of it's orbit is closest to the Sun (perihelion), the opposite part of it's orbit is furthest (aphelion). Further, the perihelion of Mercury drifts, or precesses, around the Sun so that it's orbit isn't quite closed, but instead traces a rosette, like in ",
"this image",
".",
"Now, things precess in classical physics, too, so why do we need GR? Well, the ",
" of precession can't be fully explained with just Newtonian gravity. Of the total 574 arcseconds per century that it drifts, 531 arcseconds per century can be explained by Newtonian gravity through tidal interactions with Jupiter and the other planets. Hey, that's not bad! But for a long time no one could work out where the rest of it came from. General Relativity explains the extra 43 arcseconds per century. That's a small effect, but it's noticeable. This wasn't a prediction of GR since the discrepancy had already been noticed, but it was a strong explanation of a hitherto unexplained problem."
] |
[
"Pluto was discovered in the same way sort-of. Neptune didn't totally account for the orbit of Uranus, so some additional calculations were performed and led to the discovery of Pluto.",
"However as it turns out, the calculations were in error, making Pluto's discovery mostly a lucky fluke. They just happened to be looking in the right place when Pluto was going thru."
] |
[
"If I remember correctly, precession does not occur for the point mass two body problem with an inverse square law. I would imagine that whatever approximation is being used by the simulation has a significant enough error so that the effective force is noticeably not inverse square law. Of course, if the simulation is also modeling other phenomena than just Newtonian gravity, that could be the explanation."
] |
[
"[chemistry] Why is sunlight a mixture of all the other lights?"
] |
[
false
] |
So i was reading my chemistry textbook yesterday. And i came across the "Radiant Energy Spectrum". I think Neils Bohr used this to prove his atomic model theory. In the textbook it said that all elements give off a unique set colors that are part of the Light spectrum. Simply because when electrons are charged and go back to its normal orbital they give off photon particles (Light units?) that are equal to the energy they once revived to be excited. I hope I've got this all right but if all (gaseous?) atoms give off a unique set of the lights when charged, Then why does the suns light give off all the colors in the light spectrum, or in other words have all the colors in them?, I'm very curious as to why this is i hope someone can answer.
|
[
"Everything you talked about is regarding atomic (or molecular) absorption and emission - and you're correct in that there are only specific allowed electronic transitions.",
"The sun, in addition to atomic emission, gives off a huge amount of ",
"black-body radiation",
", which is a different phenomenon that gives rise to a continuous emission spectrum. The black body radiation is so overwhelming that atomic emission spectra is often not observable (the lines for helium was only observed during an eclipse)."
] |
[
"I think im gonna need a masters degree in chem to understand black-body radiation :("
] |
[
"naw, you'll need one in physics :P"
] |
[
"Why are there no stars in pictures of earth taken from space?"
] |
[
false
] |
I was having a debate about the validity of the space program with one of my coworkers. He is a moon landing denier and asked me this question to which I was stumped.
|
[
"Just to clarify, it has nothing to do with \"focus\" necessarily, and everything to do with exposure.",
"Quite simply, both film and digital cameras have a very limited range of exposure. You can expose for the deepest shadows by letting a lot of light through the lens, but then you end up with blown-out highlights (too much white for the brighter areas, which eventually become solid white).",
"OR you can expose for these highlights by letting a lot less light through the lens, but then you don't have enough light to \"see\" the shadows -- they end up pitch black.",
"The sun is so bright relative to the ambient light (which is almost nothing if you're going by starlight) that in order to get a well-exposed picture of the earth during daylight we need to let in an extremely small amount of light whose range makes the sun-lit parts of the earth look well-exposed.",
"In doing so, of course, we're basically ignoring any ambient light there may be, which -- you guessed it -- is coming from the stars.",
"We ",
" expose for the stars so that they appear as tiny solid dots (similar to what you do when exposing for them at night with 20+ second exposures), but once again this means you'll end up with a super bright solid-white earth."
] |
[
"It's because cameras have to focus on a light source. The amount of light earth reflects back into the camera is so intense, focusing it causes the much dimmer stars I'm the distance to disappear. \nIf they held up a piece of paper and blocked the earth from view when they snapped the picture, the stars would come back into focus. \nYour friend is wrong. You can zoom in on the landing site with modern technology. We brought rocks back. We left mirrors on the surface that we regularly shoot lasers at to measure the distance between earth and the moon. Its because of this that we now know the moon is slowly drifting away from earth."
] |
[
"The premise is false. There are photos of earth from space with stars. Its just a matter of finding the right photo that has the right exposure.\nFor example here: A long exposure taken with a UV camera.",
"http://en.wikipedia.org/wiki/File:Apollo16EarthID.gif",
"The same reason you cant see stars during the day. Camera's and film have a limited dynamic range. Essentially if you expose for a bright scene, light sources that are faint will not be captured as the exposure time is to brief. If you expose for a low light scene then objects that are bright will be over saturated and washed out."
] |
[
"How do astronomers pick up signals from the early universe?"
] |
[
false
] |
I understand they travel at the speed of light and are from far away, hence they are from billions of years ago , but if matter expands at less of the speed of light then shouldn't those signals have gone past us long ago ?
|
[
"matter expands at less than the speed of light",
"That's where you're confused. Matter doesn't expand. Space does, and matter is pretty much fixed in space (at super ginormous scales where galaxy clusters form filaments). Whatever the actual rate of expansion is, as long as it expands at all, then there is a radius around you beyond which matter that in fixed in space recedes faster than light from your point of view. Note that matter doesn't move faster than light in space, it's space itself that inflates, which leads to far away sources receding faster than light. That's our horizon, we can't see farther than that. And since space is still expanding, more and more sources are disappearing behind the horizon."
] |
[
"Thanks!"
] |
[
"Also OP needs to know that in the case of the ",
"cosmic microwave background",
", the EM radiation IS traveling at the SOL. But even that presents a problem. How did the CMB become so perfectly uniform? There was not enough time for thermal equilibrium to have happened. So theories on how this happened have been proposed.",
"The high degree of uniformity throughout the observable universe and its faint but measured anisotropy lend strong support for the Big Bang model in general and the ΛCDM (\"Lambda Cold Dark Matter\") model in particular. Moreover, the fluctuations are coherent on angular scales that are larger than the apparent cosmological horizon at recombination. Either such coherence is acausally fine-tuned, or ",
"cosmic inflation",
") occurred.[5][6]",
"Also a ",
"variable speed of light",
" theory was proposed."
] |
[
"Does electrical current have something similar to a water hammer?"
] |
[
false
] |
I understand that electrical current is the flow of electrons through a conductor. It is often compared the water flowing through a pipe. When water is rapidly shut off it can cause a water hammer. Does something similar happen when electrical current is rapidly stopped?
|
[
"Yes. If there is inductance in the circuit which is sort of like momentum then when you have a sudden change in current (closing a switch) you get a spike in voltage. Given we manage lots of power these days by turning transistors (elctonic switches) on and off very fast this is an important phenomenon. The solution is to add capacitance (sort of like expansion tanks I guess) to smooth the spikes."
] |
[
"While it is a good analogy it does lead to some really bad ideas. ",
"Things that directly lead to a large water hammer, like a long straight pipe, have nearly no impact in a circuit. Nearly none of the steps I would use to reduce water hammer would have an application in circuits. Things that increase the impedance of a circuit, like a coil, would have no impact on a pipe circuit!",
"Water hammer is due to the momentum of the moving water. The total mass of water in motion is critically important. ",
"In an electrical circuit the momentum of the current is a physical thing, but is unimportant. I can double the number of electrons in motion with nearly zero impact on the circuit impedance. The drift current is so slow, and the mass of the electrons is crazy small. The momentum of a electrical circuit can be ignored.",
"However what people relate to is the inductance of the circuit, which is a property of electromagnetism. A flowing electrical current creates a magnetic field. If the current is in a steady state ( DC ) the magnetic field is also constant. A constant magnetic field does not induce a current in other circuits.",
"However when you change the circuit, such as creating a break, the current can suddenly begin to change. This rapid change in the current will cause the magnetic field to collapse. A changing magnetic field induces a voltage in conductors. ",
"There is a reason that Fluid Dynamics and Circuit design are not taught in the same class."
] |
[
"This effect can be also used in boost converters for generating a higher voltage from a lower one."
] |
[
"Why doesn't a star's gravity disturb its planets' moons?"
] |
[
false
] | null |
[
"There's the concept of the ",
"sphere of influence",
" where the gravity of a planet, despite being weaker than the star, is locally dominant due to the short distance. Therefore a moon or an artificial satellite can still be in orbit around a planet despite the presence of a much larger attractor.",
"The star is still attracting the moon and the moon is still orbiting the star. But the planet-moon system is still attracted as a whole, so in a reference frame centered on the planet you can still see the moon orbiting the planet.",
"Earth's sphere of influence is more than twice the distance to the Moon. If you place an artificial satellite at this distance it will be too unstable to orbit the Earth."
] |
[
"The star is still attracting the moon and the moon is still orbiting the star. But the planet-moon system is still attracted as a whole, so in a reference frame centered on the planet you can still see the moon orbiting the planet.",
"I think this is the most important point if you want an intuitive grasp of it. The Moon ",
" orbiting the Sun, the same way the Earth is. In a reference frame centered on the sun, the moon's orbit ",
" is just a slightly wobbly ellipse. People might have a mental picture of it doing loop-di-loops, but its path is actually always concave towards the sun."
] |
[
"If you place an artificial satellite at this distance it will be too unstable to orbit the Earth.",
"You mean no artificial satellities can have stable orbit at same altitude as where the moon is? Is this because of the moon, or because of the sun? ",
"Or did you mean at twise the moons altitude?",
"And what do you mean by unstable? It will be there for months? Years? Tens of years? Millions of years?"
] |
[
"Why is it that in some areas, the western side of a mountain range is desert and the eastern side is lush, but in other (sometimes nearby) regions, the opposite is true?"
] |
[
false
] |
I noticed this looking at the satellite view of , where there appears to be a flip to the north of Santiago. What accounts for this?
|
[
"For the Andes, in addition to the orographic effects described in the other answers, because the mountain range spans such a huge range of latitudes, you are also seeing some influence of global scale atmospheric effects, like the ",
"Hadley Cell",
". There's a nice discussion of the interaction of local and global climate and topography by Manfred Strecker and others, titled \"Tectonics and Climate of the Southern Central Andes\" in Annual Review of Earth and Planetary Sciences that talks about this for the Andes. "
] |
[
"The Rain Shadow effect is well covered here, but the \"flip\" of the Andes is also due largely to the Hadley Cell effect, in which latitude determines general wind direction. ",
"This image",
" shows the South American situation nicely- the wind coming directly from the ocean is wet, and that same wind becomes dry after crossing the Andes."
] |
[
"The cells themselves are due to the coriolis effect, which has more to do with the fundamental physics of our orbit and planet shape than temperature or chemical makeup of the atmosphere. So, the fundamental driver of the wind cells won't change.",
"That's not to say that there can't be local effects from climate change that might effect rainfall on a mountain range, though."
] |
[
"Will water cool faster, slower, or at the same rate at higher vs. lower temperatures?"
] |
[
false
] |
If I put a glass of water, that is at 60°, in a room that is 65°, would the water get to room temperature faster than a glass of water at 35°, in a room that is at 40°?
|
[
"Okay, so the traditional thermodynamics answer is that the cold one gets to room temperature first. It takes a certain amount of energy to cool the water per unit temperature and the atmosphere can only supply that energy at an (approximately) constant rate.",
"Now if you put the glasses in a freezer, counter-intuitively the hot one can in some cases freeze first. No-one really knows why, and it seems to be a complicated fluid mechanics question.",
"Have a look at\n",
"http://en.wikipedia.org/wiki/Mpemba_effect"
] |
[
"Semantics.",
"The definition of cool is 'A fairly low temperature.'. If the temperature drops then it is, by definition, 'a fairly low temperature' relative to it's previous temperature.",
"It's not a scientific term, but there's not reason to be so nit picky. There are plenty of questions that don't use scientific terms that get the point across, and it doesn't sound like he's writing a scientific paper to be reviewed by his peers."
] |
[
"It all depends on the accuracy that you desire in your answer. To a first approximation, they both will reach their new temperature at the same time.",
"But if you dig in enough and get picky enough, you will start to find some differences. The heat capacity of water will show small changes with temperature, as will the convective heat transfer coefficients. (For instance, the air in the 65 C room is more viscous than that of the 40 C room and this will alter the rate at which the convective cells flow.) I'm not going to make a guess as to what the outcome will be."
] |
[
"Why doesn't water ever get 'red hot' or emit light when heated or vaporized?"
] |
[
false
] |
Even glass does this.
|
[
"The underlying principle here is blackbody radiation. The simple answer is that water never gets hot enough to emit blackbody radiation before vaporizing, at which point it is dispersed into the air and cools very rapidly. ",
"Wien's law",
" tells us how hot a blackbody (or to decent approximation, any common object) has to be in order to emit light at a particular wavelength. You'll see that \"red hot\" is quite a high temperature compared to the boiling point of water. However, you would find that hot water emits quite a lot of infrared light!"
] |
[
"Glass, iron etc glow when heated because the atoms in the structure vibrate rapidly without actually leaving the structure. It's called incandescence. Solid/liquid water doesn't do this (at 1 atm) because it becomes a gas before reaching incandescent temperatures. Well, it does emit, but not in the visible spectrum. Once your water vaporizes, each molecule gains degrees of freedom beyond vibration (translation, rotation). The thermal energy is distributed among the molecule's degrees of freedom. Steam won't glow because water molecules won't get enough energy in their vibrational degrees of freedom."
] |
[
"Considering there are ways to increase the boiling temperature considerably, could it be possible then? What about visible light?"
] |
[
"If hot water cleans more effectively, then why do we brush our teeth with cold water?"
] |
[
false
] | null |
[
"Put a toothbrush in your mouth for 5 seconds and it will heat up (or cool down) to the temperature of the inside of your mouth. It wouldn't matter if you wet the brush with cold or hot water, you're brushing at body temperature in the end."
] |
[
"Many people thinks its the detergent in the toothpaste that does the cleaning but this isn't the case. Many companies add sodium lauryl sulfate to the tooth paste to the provide the foam that everyone associates with cleanliness, using a toothpaste that does not foam just isn't satisfying. It's actually the abbrasiveness of the toothpaste and the toothbrush that actually works to brush plaque/food particles away.",
"So hot water/cold water doesn't really matter."
] |
[
"This was why i didnt use warm water, my grandmother always used to tell me it would poison me haha\nAll i know is that everyone i've asked outside brushes their teeth with cold water."
] |
[
"Does taking medication for cold symptoms delay your body's ability to fight the illness?"
] |
[
false
] | null |
[
"Here's an evidence-based answer from a review done in January of 2004 from the Journal of Family Practice.",
"Generally, the use of acetaminophen/paracetamol (brand name Tylenol) did not affect the course of of rhinovirus (common cold), varicella (chicken pox), and may even prolong the course of shigellosis (bacillary dysentry, more common in India or Africa) and influenza A. It may also prolong the infectious window for both common cold and influenza A.",
"A level A recommendation is usually based on strong, consistent evidence from randomized clinical trials, the highest standard of clinical trials. A level B recommendation is also based on evidence from clinical trials, but there is no guarantee of quality, or the study may be very limited in scope. A level C recommendation is based on expert opinion, case studies, and conjecture based on knowledge of disease pathogenesis, or even just usual practice.",
" (evidence level: A-)",
" (evidence level: A)",
" (evidence level: C)",
" (evidence level: B-)",
"Source",
"Edit: I don't mean any disrespect to the other answers, but they are mostly deductive answers based on what we know about fever and its relation to some diseases. As far as I know, there have not been any detailed biochemical studies into the mechanism of interaction between fever, antipyretics, and course of most illnesses. Unless they can provide a link to such a study, I would advise taking the other answers as educated conjecture and not as science-based answers."
] |
[
"Cold medications consist (usually) of many different ingredients such as diphenhydramine for sneezing/runny nose, acetaminophen for pain/fever, a decongestant such as pseudoephedrine or phenylephrine, and sometimes and anti-cough or expectorant. ",
"The important thing to remember is that all of these medications only treat the symptoms of a cold, not the cause (which is a rhinovirus). They have only a small effect on your immune system and therefore should not increase or decrease the time it takes to recover. ",
"To answer your other question, it is very unlikely that you are hurting your body by taking these medications. Colds in general are very mild illnesses (unless you have certain autoimmune disorders) and have no lasting harm. ",
"Source: pharmacist",
"EDIT: as some have pointed out I might have been unclear about fever reducers. From one of my comments: \"Actually, the whole purpose of fever is to kill the invading bacteria quicker. This is why normally people should let a fever run its course because even though it's unpleasant, it is helping you. The exception is when a fever gets high enough to cause damage (around 103 F and up).\""
] |
[
"Hi Clessa, great response. ",
"The one issue I have with this response is that \"prolongs the course of illness\" is rather imprecise. Are we talking hours, days or weeks? What's the margin of error?",
"Edit: I'm clearly blind."
] |
[
"Say that I weigh myself just before bed: 150lbs. I weigh myself immediately after waking: 148lbs. What processes happen while I sleep that cause this overall loss of mass overnight?"
] |
[
false
] |
[deleted]
|
[
"The weight loss would be due to breathing, mainly in the form of expelled carbon dioxide with some water vapor as well. You intake oxygen, but expel carbon dioxide (basically just an oxygen molecule plus a carbon atom), with that extra carbon coming from the food you ate. All the carbon adds up. You also lose some water vapor out of your cells into your lungs, and from there into the air."
] |
[
"There are some nice answers in this thread involving respiration. First you should calibrate your scale at those two times of the day; it is likely that the temperature is different in the morning and evening, and if you're using an inexpensive scale temperature may be important. You can do this by taking a heavy object (say, a gallon of water) and weighing it by itself at night and in the morning and see if the two measurements agree. You may need something pretty heavy to see the change, though. If you have some freeweights around that could be good."
] |
[
"I'd also expect this to be a measurement error of some sort. There is no way you could exhale two pounds of carbon dioxide in a night, although you might exhale a detectable amount of mass as water vapor."
] |
[
"Is there a \"deeper,\" physical explanation for QM uncertainty or complementarity in particle-spin measurements?"
] |
[
false
] |
I gather that spin about orthogonal axes is subject to uncertainty in that (roughly speaking) if we know x-spin at 100% confidence, then we can only guess y-spin at 50%, and vice-versa. I also gather that the mathematical formalism requires this. But is there a known or hypothesized (physical) explanation for why spin would be subject to uncertainty in this way? (Do competing "interpretations" suggest their own answers? E.g., is there a Many-Worlds explanation of orthogonal-spin-uncertainty, in terms of a route through universe-branches? Is there a different (?), DeBroglie-Bohm explanation of orthogonal-spin-uncertainty, in terms of the workings of a pilot wave? And so on.) Thanks for any help you can provide.
|
[
"The act of treating \"quantum uncertainty\" as a literal uncertainty is to treat a quantum particle as a literal particle. But that is not the current mainstream interpretation of quantum particles. Rather, a quantum particle such as an electron is a wave-like fluctuation in a quantum field. So, \"uncertainty\" is more properly understood as \"a wave state spread over many values\". For instance, an electron's position has uncertainty. In the modern, mainstream interpretation, this does not mean that the electron is a solid little ball with a definite location that we simply don't know. Rather, it means that the electron is a wavefunction that is spread over many locations. The same concept applies to other observables with uncertainty. For instance, the uncertainty in momentum can be understood as the the wavefunction being spread over many values in momentum space.",
"All of the observables about a quantum object, including spin, are described by its wavefunction. \"Uncertainty\" (e.g. wavefunction spreading) arises from the fact that a wavefunction cannot be simultaneously collapsed in two dimensions/variables that form a conjugate pair. If you want a rough, conceptual picture behind the uncertainty relations, it would therefore be \"waves just need to be spread out to some extent in some dimension to still be waves\"."
] |
[
"Okay, this is pretty helpful; thanks again!"
] |
[
"Any \"deeper\" physical understanding is entirely dependent on your interpretation, so there really is no one clear cut answer, sorry."
] |
[
"Lottery lightning strikes twice?"
] |
[
false
] |
Hypothetical: I buy a lottery ticket from a convenience store in California and win the jackpot. The chances were 20 million to one -- 20 million tickets sold in the state of California. The next week I buy another lottery ticket from the same location. The chances of winning are the same -- 20 million to one. I argue that my chances of winning are the same as the week that I won. My friend says that it not the same because "lightning does not strike twice at the same location. The chances of consecutive winning tickets bought at the same location are higher." This explanation does not make sense to me. For me, if all things are equal (the lottery is not rigged), then it doesn't matter where I buy the ticket if every location has the same chances of selling the winning ticket. The only explanation I can think of that my friend might be right would be if a SINGLE location sold thousands of tickets AND a winning ticket MUST BE SOLD. Who is right? A steak dinner is riding on this. Here is a link to California's MEGA millions lottery game for reference.
|
[
"You're absolutely right - the chances of you winning the lottery the second week are the same as they were the first week (1 in 176 million).",
"Where the odds get longer is if you ask the question 'what are the chances of someone winning the lottery two weeks in a row'. In that case you multiply the probability of event A by the probability of event B. That gives you odds of somewhere in the region of 1 in 30,000,000,000,000,000",
"If you've ",
" won the lottery in week one, however, the odds of winning the next week will be unaffected by the outcome and so remain the same as for any other individual event (1 in 176 million).",
"NOTE - I've simplified the probability calculations here, as the lottery happens every week so there are also calculations that might take into account the probability of it occurring in any subsequent week. The answer above, however, is of the correct order.",
"Finally - lightning does very much strike multiple times in the same place. some infor here, but plenty more available ",
"http://www.weatherimagery.com/blog/lightning-strike-twice/"
] |
[
"\"The lottery is not lightning. Your chances of winning are not affected by the results of previous lotteries.\"",
"Of course, lightning isn't affected by the results of previous lightning strikes either."
] |
[
"except lightning isn't random. if lightning hits somewhere twice for example, there's a good chance theres a reason and it's more likely to hit there again. if lightning never hit twice, there would be no use for lightning rods on tall buildings. i don't know the physics behind lightning, but on flat ground it may be true that lightning hitting the same place twice in one thunderstorm is less likely since the charge in that area has been discharged etc."
] |
[
"Is there a stable solution of n-body orbits in 3D where one body is significantly smaller than the rest?"
] |
[
false
] |
This question was brought on by the recent question about 6 blackholes arranged in a cube, which had some obvious problems, but it got me thinking about wether you could have a stable multibody orbit like a stable Plummer sphere as shown here: with all the bodies bar 1 being blackholes, and the final body being a human or a spaceship. If the Plummer sphere problem has too much abstraction to be accurate, what about a 3 body solution? or a 4? and so on? I've found what appear to be stable 3 body solutions, including the famous figure 8: . But i would not be able to approach finding a solution with the parameters i'm asking for. Edit: It’s been pointed out that I’ve conflated the meaning of periodic and stable. In terms of this question a periodic solution would satiate me, a stable solution or any comment on the possibility of one would be worth gold
|
[
"If you meant in 3D, as in, non-trival solutions, I don't have a response. However, there is a stable but trivial n-body system of the masses arranged in any collinear orientation, and with rotation around the center of mass."
] |
[
"No? I said no such thing. I said I have no response for general systems, as I'm not an expert. I only have enough knowledge to suggest that there is a specific construction of n-bodies (for all n) that is stable (in relation to each other).",
"I don't know enough about orbital systems and the math behind them to suggest the existence or non-existence of other systems. My particular solution is a generalization of three (L1 L2 & L3) of the Lagrange Point constructions, but for any given number. I don't know if L4 or L5 are expandable to higher orders.",
"Edit: also, iirc, L4 and L5 might rely on trivial mass for the small body, which means they wouldn't be technically stable. However, Cunningham's law might kick in for this last tidbit."
] |
[
"You might want to read about lagrange points, where objects can hold their relative position in relation to two other more massive objects. Of the 5 lagrange points in a 2 body system, 2 are stable.",
"https://en.m.wikipedia.org/wiki/Lagrangian_point",
"In addition to the lagrange points made by the sun earth system, the earth moon system also has it's own lagrange points, thus allowing for stable orbits of small objects in 2 of those lagrange points."
] |
[
"Can light polarization be explained as an emergent property of a photon? (quantum mechanically)"
] |
[
false
] |
I'm familiar with the classical description of light polarization ) and I'm familiar with basic quantum mechanics... but how does polarization emerge from a photon's properties? Does a photon have an orientation? If so, how?
|
[
"Polarization is an intrinsic property of photons. Polarization with which you're familiar actually arises from the spin of the photons.",
"Because photons are massless and spin 1 particles, we can describe any state by breaking it down into states that have spin 1 aligned along the direction of motion or spin 1 aligned exactly opposite the direction of motion. These states correspond in the particle language to states of opposite ",
" or, in the language you're used to, clockwise or counterclockwise circular polarizations.",
"Of course, linear combinations of circular polarizations can produced linear or elliptical polarizations."
] |
[
"Great answer, thanks!",
"Polarization is an intrinsic property of photons. Polarization with which you're familiar actually arises from the spin of the photons.",
"I was wondering if that was the case, since spin is the only property I know of with some \"direction\" to it.",
"Because photons are massless and spin 1 particles, we can describe any state by breaking it down into states that have spin 1 aligned along the direction of motion or spin 1 aligned exactly opposite the direction of motion. These states correspond in the particle language to states of opposite helicity or, in the language you're used to, clockwise or counterclockwise circular polarizations.",
"So a single photon is circularly polarized?",
"Of course, linear combinations of circular polarizations can produced linear or elliptical polarizations.",
"I really didn't expect this. I had assumed that a circularly polarized beam was the \"noise\" state, a superposition of all types of conceptually-simple linear polarization -- in analogy to collimated light. You are saying that a single photon is circularly polarized, and to obtain the conceptually-simple linear polarization one needs a relatively complex superposition of photons to have linear polarization emerge?"
] |
[
"To my knowledge it A good rule of thumb is that ",
". This means that any interaction with matter - absorption and emission - must occur in discrete chunks of ",
" which we chose to name \"photons\". Another way to think of this is that \"photon\" is the name we give to a unit of ",
", not the EM field.",
"I don't particularly like the photon model because it leads to questions such as yours that show why the particle model doesn't ",
" make sense in many contexts. You could also ask the question \"what is the wavelength of a photon\" or \"what is the phase of a photon\" - these are all equally confusing questions to ask about a ",
". ",
"I have, of course, heard of polarization described in terms of the ",
" quantities, but I've never heard of polarization described as any physical property of a ",
". I've always heard of it referred to simply as some property it has."
] |
[
"After the COVID vaccine is out will we still need to social distance and wear masks?"
] |
[
false
] |
Oxford said that by the end of 2020 there will be millions of doses of the vaccine available to the public. With all of those doses out and millions more coming in the following months, when will all of the restrictions be lifted and we can return to normal life? Edit: Wow, I was not expecting this to blow up like it did. Thank you mysterious redditor for the gold!
|
[
"Yes. It will take a long time for the vaccine to deploy, especially to countries that have poorer economies and inadequate healthcare systems. In addition, if travel is less restricted, community transmission will continue to be a risk. Nobody really knows when the right time to open up will be."
] |
[
"First thing to note is that while we have phase 1 and 2 data for several of the early vaccine candidates we have no phase 3 data, which is where vaccines shows how effective they are. Some of the ones we hope will work may not prove to work or they could show bad adverse events in a larger population. Phase 1 and 2 have had less than 1000 people in most cases and in many cases less than 100. A vaccine that hurts 1:10,000 people is not going to be used in all probability. We won't know that until phase 3. ",
"When you can relax some restrictions within a population depends on 5 main factors: R0 of the pathogen, the length of immunity from natural infection, the population that has had it naturally, the effectiveness of the vaccine, the fraction of people who take it. ",
"Your goal is to get the total number of people in your population over the so called herd immunity threshold. That depends on R0 of the pathogen and also on the heterogeneity of your population (do old people only hang out with old people, or do people mix). From that society movement you can get an effective R0 which would tell you the basic effective level of immunity you need in the population to get R0_effective < 1 which would prevent epidemics but not people getting sick still.",
"Let's say the effective R0 requires 60% of the population to be immune to get under 1 for R0_effective. Let's say you live in the US where in a lot of places about 10% of the population has already had COVID and let's assume that natural immunity is long-ish lasting based on T-Cell results from SARS-COV-1. In that case we need 50% more immune people. Let's say we get a vaccine with 80% effectiveness then we need about 62% of the population to take such a vaccine to get to the level we are targeting. (0.62*0.8 ~= 0.5). For the US in total that means we would need 217 million doses. ",
"80% effective is rosy for how effective this vaccine might be. The FDA has indicated it would give a EUA for 50% effective. Clearly you can't get to 60% immune with a 50% effective vaccine. ",
"Don't get too too sad though, even if you don't get to R0_effective < 1 everyone who does it a vaccine reduces the rate of spread. ",
"Ball park you will need 75% of your population to get a vaccine to really go back to normal. That will happen if the current candidates make it through phase 3 sometime in the middle of 2021 in rich western democracies. It will happen by 2022 for everyone. If every candidate works then maybe you get there by very late 2021, but I'm skeptical, you need 5-6 billion doses. If you thought testing for COVID was hard..."
] |
[
"It helps to understand the scale involved. If vaccine development successfully finishes on October 1 and they can make a million doses a day (which may be optimistic, but they’re trying to get a jump on production before trials finish), then there will be 92 million doses manufactured by New Years. If every single batch meets quality control standards (seems unlikely to be that perfect), every single one goes to a member of the public in need (which assumes that the distribution is efficient), every dose works and creates an immunity (doubtful), and none of those people get sick before the vaccine immunity is in place (risky), the 92 million people will be vaccinated.",
"Using US numbers as an example, that still leaves 240 million people unvaccinated, who will be at risk if we push to reopen faster. Further, that assumes that all doses go to Americans, which is extraordinarily selfish and will absolutely burn critical international bridges.",
"At a million doses produced, QCed, delivered a day, it will take another 240 days (end of August 2021) to cover everyone else in the country. To reach decent herd immunity levels, maybe we only need 90% of the population (maybe 300 million total), which gets us to late July 2021 instead (this year’s 92 mill and 208 mill next year).",
"To cover the world as a whole with that level of herd immunity will require 7 ",
" doses (~90% of 7.8 billion). At a million a day, that’s 7000 days, or 19 years. 100% coverage adds another 2 1/2 years.",
"Now, in reality, things aren’t going to go that smoothly. But in our favor, we can expect massive increases over early production numbers as new plants in multiple countries come online and the process grows more efficient. But we also probably won’t start at a million a day, either.",
"My point is that it’s going to take considerable time for any novel vaccine to be produced and rolled out in sufficient numbers to cover a material percentage of the public, and you can bet that nearly every nation on the planet will be squabbling to get their fair share (or more). That will make it difficult for any one nation to quickly reach sufficient herd immunity, let alone 100% coverage. And that doesn’t account for setbacks like issues during trials or production, espionage (corporate or otherwise), sabotage (do you really think agents from our enemies won’t attempt to prolong this crisis), politics, antivaxxers and 5G conspiracy theorists, and so on. I mean, with the way this year has gone, I could totally see someone bombing the factory because of Bill Gates RFID chip tracking crazy.",
"Depending on how the vaccine is rolled out, some areas may be able to open quickly. For example, if hard-hit cities get enough early on (to stem the tide), maybe that will help stall the pandemic and we can reopen those cities. If everyone was to start wearing their masks and keeping distance, we could open before the vaccine’s ready. If first responders and critical personnel get it first, then we can’t reopen, but we’ll stop hemorrhaging those lives at least, and it will help the rest of survive. But let’s be honest...in the US, the wealthy and mega wealthy will get two doses each...",
"Edit: Holy moly!! Thank you all for the awards. I’m stunned, flattered, and grateful! I’m glad I could post something you found of such value - thank you!"
] |
[
"Why don't moths fly toward the sun?"
] |
[
false
] |
[deleted]
|
[
"Insects often use the sun for navigation purposes. Imagine that it's daytime, and you want to travel in a straight line. As long as you're not traveling for hours and hours, you can get a pretty good approximation of a straight line by keeping the sun in the same position in the sky (say, to your left). Since the sun is so far away, it appears not to change position as your travel.",
"However, if you tried to use this technique at night acting as if your porch light were the sun, you'd find yourself \"orbiting\" the light. A few random variation in your course (i.e. not traveling in a perfect circle) and you can easily start spiraling in toward the light.",
"That is why many insects seem attracted to lights at night. They're simply misapplying their simple navigation rules, treating the light as if it were the sun."
] |
[
"I managed to find some quotes from a book called ",
"Ecological Consequences of Artificial Night Lighting",
":",
"Several theories try to explain the behavior of moths around artificial sources of light, but none accounts for the diversity of observed behaviors. The light-compass theory postulates that moths navigate by flying at a constant angle to a distant light source such as the moon. When near a lamp, they mistake the lamp for the distant light source and fly at a constant angle to it. This directs them along fliht paths that spiral in toward the lamp, or circle around it (Baker and Sadovy 1978; see Chapter 14, figure 14.7, this volume). Experimental evidence supports the hypothesis that moths navigate by establishing a visual fix on the moon (Sotthibandhu and Baker 1979). The mach band theory posatulates that artifical light produces visual artifacts of apparent darkness next to the light source. The moth flies toward the apparent darkness, which directs it into a path around the light (Hsiao 1972). Other theories postulate that moths fly to artificial sources because the light dazzles them (Robinson and Robinson 1950), temporarily blinds them (Hamdorf and Höglund 1981), or signifies open space (McGeachie 1988).",
"So it sounds like there are several hypotheses, and the moon-navigation one is one of the more popular ones. But this research seems pretty old, and I'm not sure if there's anything more recent."
] |
[
"I managed to find some quotes from a book called ",
"Ecological Consequences of Artificial Night Lighting",
":",
"Several theories try to explain the behavior of moths around artificial sources of light, but none accounts for the diversity of observed behaviors. The light-compass theory postulates that moths navigate by flying at a constant angle to a distant light source such as the moon. When near a lamp, they mistake the lamp for the distant light source and fly at a constant angle to it. This directs them along fliht paths that spiral in toward the lamp, or circle around it (Baker and Sadovy 1978; see Chapter 14, figure 14.7, this volume). Experimental evidence supports the hypothesis that moths navigate by establishing a visual fix on the moon (Sotthibandhu and Baker 1979). The mach band theory posatulates that artifical light produces visual artifacts of apparent darkness next to the light source. The moth flies toward the apparent darkness, which directs it into a path around the light (Hsiao 1972). Other theories postulate that moths fly to artificial sources because the light dazzles them (Robinson and Robinson 1950), temporarily blinds them (Hamdorf and Höglund 1981), or signifies open space (McGeachie 1988).",
"So it sounds like there are several hypotheses, and the moon-navigation one is one of the more popular ones. But this research seems pretty old, and I'm not sure if there's anything more recent."
] |
[
"Can forces act across time as well as across space?"
] |
[
false
] |
If time is just another dimension of space (equivalent to l, w, h), then do gravity and electromagnetism (and the other two forces) act on objects in the past and/or future?
|
[
"If time is just another dimension of space (equivalent to l, w, h)",
"Time is different from space. In general (or even special) relativity, time is considered one dimension of space-time (hence the name), because you can't study space and time separately.",
"Electromagnetism and (AFAIK) gravitation propagate at the speed of light. So, if you do something on Earth, it can't have any effect on the Moon with less than 1 second of delay. So, in a way, you can only act on the Moon's future (by one second), but you have no way of choosing that delay: it's linked to the distance between you and the object you try to act on.",
"If the object in question is moving at relativistic speed relative to you, or with a different acceleration, it's even more complicated, since you can't agree on what time it is."
] |
[
"The universe is not isotropic in the time direction. You might be interested in ",
"maximally symmetric spacetimes",
", one example of which I've linked. ",
"I guess, broadly, the pattern over time seems to have been that energy density has been decreasing, while always being homogeneously and isotropically distributed in space, from the perspective of an observer in the frame from which the CMB looks maximally isotropic. (Maybe an expert can check that last sentence for accuracy; that's my understanding, but I'm not a cosmologist by any means.)"
] |
[
"Related question:",
"We know that matter/energy in the universe have homogenous distribution on the large scales.",
"Can we name any pattern regarding the distribution of events over the history of the universe?"
] |
[
"Why do people have different blood types?"
] |
[
false
] |
[deleted]
|
[
"Same reason we have different eye colours and different hair colours. Arbitrary differences mean that there were random mutations somewhere along the line.",
"Also, the differences may be arbitrary, but what if a disease came along that only killed people with, say, B type blood? Or a disease that only A types could withstand, and quickly killed everyone else. That's macro-evolution, baby!"
] |
[
"Use the search function, question has been asked twice:",
"http://www.reddit.com/r/askscience/comments/f19p4/how_or_why_did_blood_types_evolve_is_there_any/",
"http://www.reddit.com/r/askscience/comments/iepiv/why_did_we_evolve_with_different_blood_types/"
] |
[
"Its cool that you don't want to see repetition too often but what I don't like is the discouraging of discussion. Just because a question has been answered does not mean there isn't more to talk about. ",
"The idea of \"Just use the search function\" is the same as saying \"Just Google it\", pretty much making ",
"/r/askscience",
" obsolete "
] |
[
"How does my body form antibodies against the antigens of other blood types eventhough i have never been exposed to them? ( for eg how did a person with O blood group form anti-a and anti-b?)"
] |
[
false
] | null |
[
"Contrary to how it may be presented in general discussions, your body does not \"form\" antibodies in response to antigens. Rather, when antibody producing cells differentiate (become antibody producing cells from more general precursor cells) the portion of the genome that is responsible for producing the antibodies undergoes ",
"dramatic and random rearrangement",
"J_recombination). So everyone has a large number of B-cells each of which has a (more or less) unique and different antibody sequence. This repertoire of antibodies is not the same across people because of this randomness.",
"In the process, cells that produce antibodies that bind your own cells are removed. What remains are a collection of cells that produce some large but limited set of antibodies. When an antigen is present one or more of these antibodies may bind weakly to the antigen. Through a complex system of interactions between various immune cells, the B-cells that make that antibody undergo expansion and further mutation. This leads to a process called ",
"affinity maturation",
". Here the cells mutate their already somewhat working antibodies to be more specific and bind tighter to the antigen, and those that do the best job are kept around and form memory cells. This is the process that takes ~2 weeks from the time the antigen is present to become immune.",
"Specifically for blood groups, the different blood groups correspond to different sugars that coat a protein on the surface of red blood cells. Glycosylation (addition of sugars) is very species specific (many proteins are glycosylated differently across species even if the proteins themselves are very similar), thus there are generally many sugar-specific antibodies floating around as they had been selected from previous antigen exposures. This means that it is very very likely for a person that was never exposed to A or B antigen to have at least moderately binding anti-A/anti-B antibodies.",
"TL;DR Antibodies are created through random mutagenesis first and then are selected for activity only after the antigen is seen. This pattern - introduce variation, chose the best variant after selective pressure - is just how evolution works on almost every scale."
] |
[
"Blood Bank Guy is a pretty well known resource for students on the subject, and he has a good ",
"primer on ABO",
" testing. The straight forward, low-level answer:",
"When humans are born, we have no ABO antibodies of our own (we may have a few floating around from our mom, but we haven’t made any yet). As we start to live, within the first few months we are exposed to a multitude of bacteria both in the environment and in our digestive system. Some of those bacteria contain antigens that look “just like” human A and B antigens. As a result, by the time babies get to 3-6 months of age, they generally start making their own ABO antibodies"
] |
[
"I just took an immunohematology course and this is the way we learned it. The bacteria in our environment are responsible for a person acquiring anti-a and anti-b seemingly without any exposure."
] |
[
"If aliens were to look at earth through a telescope from 65 million lightyears away, would they see dinosaurs?"
] |
[
false
] |
[deleted]
|
[
"So I should add like two more ",
"'s?"
] |
[
"Yes.*",
"*But this telescope would have to be very, very, very large to have the proper resolution to see Earth, let alone individual objects on Earth."
] |
[
"very, very, very large ",
"Read: impossibly large. To resolve the earth as a single pixel at a distance of 65 million light years a lens would be large enough to fill most of the inside of Mercury's orbit. "
] |
[
"What is the hottest object in the known universe?"
] |
[
false
] |
I know this is a stupid question, but I am interested in knowing
|
[
"It's actually the quark-gluon plasmas produced in the Large Hadron Collider and and Relativistic Heavy Ion Collider. They can reach trillions of degrees."
] |
[
"It's within a very small volume...like the size of atomic nucleus."
] |
[
"Not only is this intense heat in a very small volume, but it is also only that hot for an extremely short amount of time"
] |
[
"Why don't we snore while awake? What changes in our breathing when we fall asleep?"
] |
[
false
] | null |
[
"Respiratory therapy student checking in. There are a few factors which may compound with eachother causing symptoms ranging from simple snoring, to severe sleep apnea. As mentioned earlier, the snoring sound comes from a closing airway in the back of your mouth/throat. ",
"While we sleep we have different stages of sleep we cycle through every 90 minutes or so. The last of these is called REM sleep. During REM sleep our body is at its most relaxed and muscles that normally support the throat and tongue relax as well and collapse the airway. As air is forced past these now flappy tissues, they make sound we hear as snoring. ",
"Other factors which we look at are usually related to things that would cause the mouth and throat to be small. A small or recessed jaw doesnt allow for as much space to begin with. Obesity fills the neck area with fat pushing in on that space. ",
"To fix this we can use specialized mouth guards which pull the jaw forward, pulling the tongue forward with it, opening that space. CPAP machines use constant air pressure to force the airway open from the inside, enough to allow for adequate breathing. "
] |
[
"Some people do snore while awake! This is called stertor. It is usually associated with airway narrowing or loss of muscular tone. \nThe true question then becomes: Why do people snore more often when asleep? This is because our muscular tone is lower while sleeping. \nIn short, snoring/stertor comes from vibrations of the throat, palate or tongue. The Bernouilli effect causes tissue collapse and vibration (sound). This is most likely to happen with air flowing past narrowed, flaccid tissue. Our muscular tone decreases while sleeping which may lead to snoring or frank obstruction (obstructive apnea).\nsource: im a snoring surgeon"
] |
[
"I'm a sleep tech. People that come in snoring while they're awake....its like a neon sign that says severe sleep apnea. "
] |
[
"Can an airplane traveling along magnetic field lines become magnetized?"
] |
[
false
] |
This stems from my knowledge that in order to magnetize something like a screwdriver, you physically move the object through a magnetic field ALONG the magnetic field lines. The earth has a natural magnetic field running basically longitudinally. If an airplane were to leave from the magnetic south pole due directly magnetic north or vice-versa, would the airplane, or any of the objects onboard become magnetized? Also, how does this not affect data/credit cards?
|
[
"So, as has been stated, Aluminum is not ",
"ferromagnetic",
", and cannot be magnetized even if you tried.",
"Basically, magnetization occurs when the atoms making up the material have a dipole moment because of a lone electron orbiting. When the dipole is subject to a magnetic field, it tends to align with said field. In certain cases, this alignment can be retained and the object can remain magnetized.",
"Yes, if one were to follow a field line in a plane with perfectly still (relative to the plane) ferromagnetic objects, there is a good chance they will become magnetized. This isn't too far off from how we get natural magnets, in that they can be formed due to the Earth's magnetic field.",
"You don't have to worry about this in a commonplace environment because the field lines of Earth's magnetic field aren't so easy, or convenient, to follow in a plane. On top of this, the objects in your bag are moving in other random directions pretty frequently (turbulence or maybe you want your iron rod in your hand to fiddle with), which help deter the magnetization process. Furthermore, any other ferromagnetic material will interfere with field lines and make them all sorts of random directions.",
"You certainly don't have to worry about credit cards or data, because as I recall, in order to damage it you have to have enough energy to flip a magnet 180 degrees, and the Earth's magnetic field isn't actually that strong (you only see it when you suspend a magnetic material in water to reduce friction to a minimum, whereas you can fully PICK UP said magnetic materials with a refrigerator magnet). It's only gradual changes from prolonged, proper exposure which can create/alter magnets from the Earth's field."
] |
[
"Earths magnetic field is too weak to have any noticeable effect and aircraft are usually made of aluminum which cannot be magnetized."
] |
[
"Maybe you were thinking of this already but steel ships can become magnetized. The Navy has a facility to degauss them ",
"http://en.wikipedia.org/wiki/Deperming"
] |
[
"Where can I find information/charts about efficiency of vaccines?"
] |
[
false
] |
I have tried to find a char with 3 variables for several illnesses, i am specially interested in infections where the vaccine is not very effective and with a long incubation period. I am trying to make an interactive page where you see an scenario for example a classroom or a zoo visit with an X% of kids who are not vaccinated and one kid infected then make a simulation on how many kids will get infected in a day or before the first symptoms appear on the first kid. The idea came in with the video of the whipping cough baby. I was thinking on doing something similar, like 'how will the classroom sound after 3 days' for example. so i would like to find 3 variables. 1) How likely a person is to get infected without vaccination 2) How likely a person is to get infected with vaccination 3) How long it takes for the first symptons to appear Thanks for reading
|
[
"Truthfully I don't know of many places that would give all this information so succinctly to you. You would have to do a bit of research. Here is a link to the CDC list of curent vaccines available in the US ",
"http://www.cdc.gov/vaccines/vpd-vac/vaccines-list.htm",
". You can just google them 1 by 1 to get the specifics on it. Shouldn't take more than an hour to do the majority of them. ",
"To find the infection rate without vaccine look up \"incidence of...\" That will give you the number of new cases per year. For the incubation period of an infection just google \"incubation period of... \" It may be harder to find infection rates with vaccine though."
] |
[
"why wouldn't that be public information?"
] |
[
"Efficacy rates of the vaccine and infection rates in vaccinated individuals are fairly complicated.",
"For example, the tuberculosis vaccine most commonly used (BCG) varies in efficacy in different regions. Part of this is that different regions have different strains of the vaccine (and different strains of tuberculosis), but there are also some confounding factors that scientists have different theories on. Vaccine failure can be linked to a lot of different conditions, such as effective cold storage, that can be hard to track properly. ",
"In a lot of cases, exposure of vaccinated individuals can be hard to track. If I get the flu vaccine, but don't get flu, is that because the vaccine protected me, or I never ran across that particular strain? If I do get the flu, is it a strain that I was infected with, or a different strain that I wasn't protected against? ",
"Because it's not ethical to just experiment on people, all this data (in people) comes through epidemiological studies, which include many factors. You can extrapolate a bit from the literature and by looking at lots of reviews, but it's not going to be as simple as \"vaccine X has a 10% failure rate\". You might look for papers looking at antibody titer over time, but even that's not going to be completely accurate; some people have low or undetectable antibody but are protected, others will be vulnerable to disease causes that dodge their antibody or are exposed to very high levels and so still risk disease. "
] |
[
"Is it actually possible to suffer a heart attack from being scared or startled?"
] |
[
false
] |
I just read another Reddit post about a woman who was presumed dead, only to wake up at her funeral, then dying of a heart attack because she was so shocked at the fact that she woke up at her funeral. Is this actually possible? I assume that if you already have a weak heart it's likely, but what if you have a healthy heart? Can you be startled/scared so badly that it can cause a heart attack?
|
[
"As ",
"/u/eosha",
" said, if there is some underlying ",
"coronary artery disease",
", a sudden elevation of blood pressure or heart rate triggered by a ",
"sympathetic surge",
" could be enough to cause a plaque to rupture and cause ",
"infarction",
".",
"This is also a condition triggered by stress (physiologic or emotional) called ",
"Takotsubo cardiomyopathy",
", and it was first described in Japan. It's named after traditional octopus traps there because the left ventricle dilates and ",
"looks like those pots",
" when you do a ",
"ventriculogram",
". These patients present like an acute coronary syndrome and therefore often undergo angiography, and the apex of the heart is usually akinetic (doesn't move properly) with a dilated left ventricle. ",
"Normal left ventricular function",
": Left image is diastole (filling of the ventricle), right image is systole (the \"squeeze\"). Notice how in the normal LV, there is symmetric contraction of the ventricle.",
"Takotsubo cardiomyopathy",
": Again, left side is diastole (normal appearing), but on the right you have ballooning and akenesis of the ventricular apex."
] |
[
"Yes. Fear can activate the body's sympathetic nervous system, which controls heart rate and blood pressure, among other things. In extreme cases, or if the circulatory system is already damaged/weak this can cause stroke, heart attack, etc.",
"http://www.scientificamerican.com/article.cfm?id=scared-to-death-heart-attack"
] |
[
"This is good info. Thank you."
] |
[
"Why are heavy duty wires not made of one solid wire?"
] |
[
false
] |
What's the reason for this? Is it to increase flexibility or strength? Or one Solid Wire is never invented in the first place?
|
[
"Higher strength, way better flexibility (thick wire is technically a rod).",
"\nAlso - the ",
"skin effect",
" which makes the AC electricity run on the outer shell of the wire, which makes more wires - more surface."
] |
[
"the skin effect which makes the AC electricity run on the outer shell of the wire, which makes more wires - more surface.",
"If the strands of a stranded cable are not insulated, then there isn't much difference in skin effect between a solid wire and a stranded one. If you are concerned about skin effect, you either use something like a Litz cable (braided, insulated conductors) or a hollow-core conductor.",
"It isn't exactly about strength or flexibility, either, although flexibility is close. The real reason for stranded wires is basically metal fatigue.",
"Because the single piece of metal is much thicker in a solid wire than the many thin strands in a stranded wire, bending a solid wire a certain amount results in much higher stresses than bending a stranded wire the same amount.",
"Every time you bend a piece of metal past its yield point (the point past which the metal stays at least a little bent or deformed after you let go of it), you have damaged the structure of the material, and that damage builds up over time as metal fatigue. Eventually, after long enough, the piece of metal breaks. Solid wire is much easier to bend past its yield point than stranded wire.",
"So, basically, any time a wire moves, you use a stranded wire to prevent metal fatigue from eventually breaking the wire. The more movement the wire is expected to be subject to, the finer the strands you use.",
"Note that it doesn't take a lot of movement, either - a solid wire clamped or connected to something at the end and allowed to vibrate even a little bit (i.e., the whole wire isn't tied down) will eventually break right at the connection point."
] |
[
"Mostly flexibility and ease of handling. But also for strength; drawing a wire down in diameter (pulling it through a hole in a plate to make it thinner) aligns the metal crystals similar to how forging does. Depending on what equipment is used, there's a limit to how thick a wire you can practically draw through a die, so even for very large cables that don't need to flex much (such as on suspension bridges), the individual strands will be below that size."
] |
[
"How far would a bullet have to travel for it to be affected by the Coriolis effect?"
] |
[
false
] |
[deleted]
|
[
"Not a scientific answer, but when I was a scout in the army our sniper section guys told me they compensate for it on north/south shots over 1000 meters."
] |
[
"Here's a very simplified and completely hypothetical/theoretical approach to determine whether or not Coriolis would affect it:",
"Imagine you shoot the bullet from the North Pole due South. You are aiming towards, say, China. If the bullet instantaneously got to its destination, you would hit China. If it took, say, 4 hours, you might hit somewhere in Eastern Europe. Eight hours, and you hit the Atlantic. Twelve? Somewhere in the USA. ",
"Coriolis \"force\" arises due to the fact that the Earth is a rotating reference frame and you are using a topographic reference frame (non-rotating with respect to the Earth) to describe your bullet's trajectory and has ",
" ",
"As for your question, the bullet would have to have a significantly low (~1) ",
"Rossby number",
" to be \"affected.\" To get a rough calculation, say the velocity of a hypothetical bullet at midlatitude (45 deg, say) is 1700 m/s and is unchanging. In order to get a Rossby number that implies the Coriolis force is significant, you would need a characteristic length of about 15000 km."
] |
[
"What is your threshold for defining something as being \"affected\"? Your answer depends entirely on that."
] |
[
"What is the maximum length of a peptide and minimum length of a protein?"
] |
[
false
] |
Also, linking to an article would be nice, I know what wikipedia says.
|
[
"Interesting question. A peptide is technically any two or more amino acids linked by a peptide bond, so there is no maximum size. All proteins are peptide chains, the largest one in humans is titin, a spring-like muscle protein comprised of 34350 amino acids. Its virtually impossible to work with biochemically as a whole. Probably, there are bigger peptides out there. ",
"Protein can also be used to refer to any peptide chain and in nutrition I believe it refers simply to amino acid content. There is no strictly delineated minimal size.",
"In terms of usage, protein generally refers to a complete gene product, whatever its size. Protein fragment is used to refer to incomplete gene products greater than 30-40 amino acids in length, and peptide is used to refer to everything smaller. "
] |
[
"it's an arbitrary distinction, which is what Wikipedia says. So why are you asking for a definition? For what it's worth, the ",
"IUPAC",
" says proteins have \"molecular weights greater than about 10000 (the limit is not precise).\"",
"It's like asking \"What's the maximum length of stubble and the minimum length of hair?\""
] |
[
"Actually, scratch that. I just remembered that there are so called Anti-Microbial Peptides - gene products involved in innate host response to pathogens. They are termed peptides despite being complete gene products I suppose because they are so small. But, again, there is no strict rule about it. You could call them proteins and no one would call you out on it. "
] |
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