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[
"As you get nearer to the center of the Earth, does gravity get stronger or weaker?"
] |
[
false
] |
This has bugged me for a while now. The reason that I can't figure it out is because on one hand, there is physically less mass below you to pull you down, but on the other, you are nearer to the central focus of the force. I've asked a few physics teachers, but they just shrugged.
|
[
"It most definitely gets weaker and if your physics teachers don't know this shame on them. Your comment \"central focus of the force\" is very incorrect and why you are having trouble figuring this out on your own. Gravity originates individually from every piece of matter in the planet. Pro figure out the force of gravity you need to sum up the force from every single piece. It turns out that as long as you are outside the sphere of the planet that mathematically it's ident cel to sum every bit at all the different distances as it is to assume all the matter is at the center of the planet. Once you are inside the sphere and that happy mathematical coincidence doesn't apply.",
"Imagine you are at the dead center of the earth you would in fact be weightless as all the matter is equally around you pulling in all directions."
] |
[
"Yes and no. The shortcut calculation of using the center point does need a certain amount of uniform distribution. ",
"However no matter what once you are inside the sphere of the planet you have some matter \"behind\" you pulling you in the opposite direction. As you get closer to the center you will have more and more matter \"behind\" you until you get the center when you have an equal amount of matter all around you."
] |
[
"Wouldn't the answer depend on the density difference of the matter at the core, the surface, and in-between?"
] |
[
"Just a quick physics problem"
] |
[
false
] |
I'm trying to get to grips with some basic mechanics and I encountered the following problem in a textbook. Sorry if it seems so trivial. A stone is thrown horizontally from a vertical cliff at a speed of 20 metres per second. The cliff is 30 metres above sea level and the stone hits the sea after 2.5 seconds. How far from the base of the cliff is the stone when it hits the sea? Take g as 10 m/s I understand that it is best to treat horizontal (x) and vertical (y) motion separately. Since it is distance I want to find, I'm looking to calculate the area under the velocity-time graph of x, which should be a simple line with negative gradient, v=20 at t=0 and u=0 at t=2.5. 20*2.5 = 50, 50/2 = 25m. I'm not sure what I've done wrong: the book produces an answer of 50m.
|
[
"50 metres.",
"20m/s thrown speed, it takes 2.5 seconds to fall. 20*2.5=50",
"The other information is irrelevant."
] |
[
"In typical projectile motion questions, you make an assumption that air resistance is negligible. This reasoning is why you assume the horizontal acceleration is 0 whereas the vertical is the familiar g.",
"You are correct in understanding that the motion along the x is independent of motion along the y. They are connected only through the time, t."
] |
[
"s = ut +1/2at",
"I take it you are using the equation above with a=0, reducing it to s=ut. Why is a=0? Won't air resistance will cause deceleration in the horizontal direction?"
] |
[
"Can an object that is on fire set another object on fire if the second object has a higher combustion point than the first?"
] |
[
false
] |
If this is a dumb question or doesn't belong here please excuse my ignorance. As I understand it wood has a ignition point of around 150 degrees. Does that mean the fire itself is burning at 150 and therefore could only light something with a similar ignition point?
|
[
"The ignition point is how hot it gets before it catches fire. The energy density tells you how much energy it produces, which you could use to figure out how hot it would burn. If objects could only set fire to things with lower ignition points, then you'd only burn the part of the wood that has a lower ignition point than it does where you light it."
] |
[
"Thank you scientist!"
] |
[
"A common method of lighting thermite involves lighting a magnesium ribbon with a butane lighter. The thermite then begins to burn from the magnesium ribbon, although you cannot light thermite using a butane torch directly."
] |
[
"I've always been told not to stand in front of a microwave when its on..."
] |
[
false
] |
I assumed it was because it emitted microwave radiation being spewed out of the microwave while it was being used, which would cause cancer or other mutations. I know DNA's absorption spectrum peaks in the UV range (260nm), so it is most prone to mutations then. However, I looked at the electromagnetic spectrum and noticed that microwave radiation has a larger wavelength (less energy) than UV radiation AND visible light. So my question to you, , is why should I not stand in front of a microwave if visible light has more energy than microwave radiation? Wouldn't visible light be more efficient at causing mutations than microwave radiation? EDIT: Thanks for your answers guys, can we focus on why microwaves seem to be more dangerous than visible light? (microwaves have less energy so shouldn't they be less dangerous?)
|
[
"There's no reason not to stand in front of the microwave. You'll notice a piece of metal with small holes in it in the window of your microwave, that's there to form a faraday cage around the microwave so that only a negligible amount of radiation leaks out."
] |
[
"They key is understanding how light interacts with molecules so here is a rough scale.",
"Radio/MW (sub 1THz ish)- Primarily causes molecular rotations, interaction with nuclei with spins or electron spins, phonon modes and low energy vibrational modes of large molecules",
"IR(micron range light)- Molecular vibrations",
"Visible/UV- electronic transitions",
"Far/UV to xray/gamma ray- enough energy to eject electrons or dissociate molecules.",
"To create a mutigenic reaction there has to be a chemical change. Now chemistry is actually all about electrons. So in reality anything below visible will (almost) never be dangerous in terms of DNA damage. Sure creating highly excited vibration states can cause weakened chemical bonds but its generally highly unlikely. Rotations will never cause damage from just their primary interaction alone and can only cause issues through secondary heating as they dissipate energy to surrounding molecules. In reality its only the electronic transitions of the visible/UV and higher that can cause weakened chemical bonds that are much more likely to react with low barriers. Further more, its the far UV and beyond that create free radicals, free electrons and ions that react readily with no barrier and can rapidly damage biological tissue faster than it can be repaired."
] |
[
"High power microwaves are indeed dangerous, and modified or faulty microwave ovens can cause serious injury. Microwave burns are pretty horrible, and (I am not a medical expert) I believe that microwave exposure can lead to cataracts.",
"Microwave ovens are carefully shielded for a good reason. At very least they can cook your flesh just as well as they cook your food."
] |
[
"How does time pass in a gravitational field."
] |
[
false
] | null |
[
"Inside a shell of mass, there is no gravity. You would have to be outside the sphere for these effects to occur."
] |
[
"The combined effects of all that pulling when inside a uniform spherical shell would be no net force."
] |
[
"The combined effects of all that pulling when inside a uniform spherical shell would be no net force."
] |
[
"Gamma function as a reliable (?) interpolation of the factorial (in relation to fractional calculus)"
] |
[
false
] |
Hello, I apologize in advance if I mess up some mathematical terms, English isn't my native language. I tried my best to look up the English equivalents of terms I'm about to use, but please do correct me if I made some mistakes. I'm not a mathematician by trade but I've always had a penchant for math and calculus (I had the more or less "standard" course of it in the university). I've recently stumbled onto an article about and it really interested me. While reading about it and calculating simple derivatives I came up with an interesting observation. Unfortunately there's no way to simply ask this question without showing how I came to it, so please bear with me for the next few paragraphs. Suppose we want to test that the 0.5th derivative of the 0.5th derivative of a function will give us the same result as the 1st derivative of the same function (that is, f0.5(f0.5(x)) = f1(x)). This statement makes sense since the powers of derivatives add up when we perform them one after another. For example, 2nd der. of the 3rd der. is the 5th der., etc. Using the fairly obvious idea from , we attempt to calculate the 0.5th derivative of . See image below: If we don't know anything about the , we have a problem here: this result has a factor of , which is not, to the best of our knowledge, a meaningful number. But we can decide to continue with our calculation. We can simply leave this factor in this original form ( of sorts) and see where it gets us. And so, we continue by calculating the 0.5th derivative of this result. See image below: The original idea that the property of the powers of the derivatives to add up is preserved with fractional derivatives stands true. Indeed, we got the result (= 1) which is the same as the result of the direct calculation of the 1st derivative. But what's more important is that the "bad", "unknown" number (the factorial of 0.5) and we got ourselves a result which is a number. I've tried to do the same thing with other fractional powers of the derivatives (calculating the 1/3rd der. 3 times in a row, calculating the 1/4th der. 4 times in a row) and it works successfully every time. I'm sure there is a simple enough proof that it works for all such cases but honestly I haven't bothered. The problem that is left is to find out the "real" value of the factorial of 0.5. Here one might argue that , since it "disappears" in the process of calculating the 0.5th der. two times. What I mean here is that we can imagine the factorial of 0.5 to be 432, 100500, 0.234 or any other arbitrary number - . Two 0.5th derivatives in a row would still give the correct result. But since we want to know the numerical value of the first calculation ("square root of x times ?"), we have found a way of calculating the factorial of 0.5 by introducing the . It "extends" the factorial function onto a set of real numbers; in particular, we can look up the value of Γ(0.5+1) ( ) and see that it's half of the square root of π. As a result, the 0.5th derivative of f(x) = x is approximately 1.129*sqrt(x). (which, unfortunately, I haven't found a way to express without showing you my thought process above). As shown above, - be it 1.772, 250 or -28 - the fundamental property of the derivative powers to add up would still hold true. If (hypothetically!) the process of calculating the 0.5th derivative two times in a row would give us something like this as a result (just as an example): ... then we would have something to work on. We would know that 0.5!/1.5! equals 1 (the real numerical value of the 1st der. of x), and from this proportion, we would derive some equations to find the numerical value of . But since all such "questionable" numbers disappear from the equations as soon as we get to an integer power of the derivative, . So, once again, this is the question that confuses me: why have we chosen to use Gamma function to calculate factorials of non-integers? Even the Wiki article on the factorial states ( ) that there are other ways to interpolate integer factorial values. And is there a way to know "for sure" which of these numerical results would be the actual correct one? The whole thing with "bad" numbers disappearing from the equations during the final act reminds me of cubic equations and how complex numbers can pop up and go away when you use the . Even if we know nothing about the numerical values of complex numbers, we can simply treat them as some constants and then they will simply go away in the end. However, we do have a way of calculating the numerical values of complex numbers from other mathematical fields. Here, however, it seems that , because . Is it true? We seemingly have no way of "testing" the values of the Gamma function for being proper representations of the factorials of non-integers, yet we use these values in fractional calculus. Why do we use Gamma function and not some other arbitrary function that happens to be equal to N! for integer N's?
|
[
"I don't 100% know the answer to your question, but I thought this huge post deserves an answer after 12 hours, so I will type one.",
"Speaking as a mathematician, the gamma function is essentially ",
" canonical generalization of the factorial function to reals. As you say, it's not unique, nor can it be (interpolation never is). The ",
"Bohr-Mollerup",
" theorem lends some credence to this claim, since any other factorial interpolating function that is not the gamma function must fail some other desirable property.",
"Of course that doesn't mean the gamma function is the canonical choice for fractional derivatives. On the other hand, we have a number of other ways to define fractional derivatives (Fourier transform is my favourite, when it works), so we can actually check these things. The gamma function fits other definitions, so it is right.",
"You will find that in every case you need a generalization of the factorial to reals, I daresay practically without any exceptions whatsoever, the gamma function is the correct choice.",
"we can look up the value of Γ(0.5) and see that it's the square root of π",
"Yes, but keep in mind that the gamma function is offset from the factorial by one. So Γ(",
") = (",
"–1)!, which means you actually want Γ(1.5) here.",
" Some details involving ignoring negative numbers is being skipped here."
] |
[
"The gamma function is the unique function that extends factorial that have this property for non-integers.",
"This isn't true. You can choose the values of ",
"(",
") arbitrarily for 0 < ",
" < 1 (of course, ",
"(",
") = 1), and the functional equation ",
"(",
"+1) = ",
"(",
") should determine ",
" for any ",
" > 0. This interpolates the factorial (because ",
"(",
") = 1) and it will satisfy your functional equation by design.",
"You need an extra condition. ",
"This theorem",
" suggests that it should be logarithmic convexity."
] |
[
"Wow, this is an incredibly elegant demonstration (and I suppose it's easy to generalize it for the 1st derivative of x to the power of anything, not just 0.5). Thank you!"
] |
[
"If a single radioactive Uranium atom was to pass through my digestive system, would any real damage be done?"
] |
[
false
] | null |
[
"One atom just isn't enough to do anything. A single banana is much more radioactive. In terms of toxicity allowances, they are on the order of micrograms per cubic meter in the air, which is much much much more than a single atom."
] |
[
"By the way, your body actually has quite a few uranium atoms in it, naturally.",
"From ",
"http://hps.org/publicinformation/ate/q3414.html",
":",
"\"The average person ingests about 2 µg (around 1/15,000 of an ounce) of uranium in food and water every day, but only a very small fraction—on the order of one or two percent—is absorbed into the body.\"",
"A simple arithmetic calculation can show you just how many atoms that is ...",
"Given: Molecular weight of uranium: ~238 g/mol",
"Given: Avogadro's number: ~6.022×10",
" mol",
"Given: 2 µg = 2×10",
" g",
"2×10",
" g × 1/238 mol/g = 8.403×10",
" mol",
"8.403×10",
" mol × 6.022×10",
" mol",
" = 5.06 × 10",
" atoms of uranium ingested daily",
"5.06 × 10",
" atoms of uranium ingested daily × 1% absorbed = ",
"So yeah. That's about fifty trillion atoms of uranium that you put into your body on a daily basis. That really ",
" a lot at all ... a completely miniscule amount, despite how much it sounds (we ",
" talking micrograms here ...). It's made even more miniscule when you consider that it is distributed throughout your entire body, which weighs many kilograms.",
"But yeah. Even 50 trillion atoms of uranium does no real damage. :) Atoms are such tiny, tiny, diminuitive things ... it's barely comprehensible ...",
"Edit:",
"Then there's also the fact that uranium is only dangerous when it ",
", and the most common isotope's half-life is quite long, at 4.5 × 10",
" years (that's about the age of the Earth). We can do another calculation to find out how many atoms of uranium in your body will decay in a single day ... but I've been drinking this evening and that calculation is a little more complex than I'm willing to do for you. :) Suffice it to say, it's the tiniest of the tiny amounts, even though it's actually many more atoms than you think. So even with all these uranium atoms decaying in your body and causing havoc, your body really doesn't even feel it."
] |
[
"I'd like to have a little more then just \"No.\" if all possible "
] |
[
"If quantum entanglement can't be used to transmit information, then how is this experiment (see description for link) possible?"
] |
[
false
] |
Been catching up on some reading, came across here. I've been told over and over again that entanglement can't be used to transmit information. So how the heck does this work? Aren't they extracting or inferring information about one photon's path from its entangled twin's behavior -- the exact sort of thing I've been told isn't possible?
|
[
"if you have an entangled pair, you cannot transmit information from one to the other without either having them interact again, or by sending a bit of classical information along.",
"In this case, the red light that passes through the image does interact with the yellow readout light through its interactions in the second nonlinear crystal NL2 and then on BS2. This ensures that no information is transmitted faster than the speed of light or anything. The clever design of the experiment ensures that the photons that are read out are different than the photons that interacted with the object, but the two modes still have to interfere again before readout to produce the image."
] |
[
"Quantum entanglement can't be used to transmit information faster ",
", but you can still do all sorts of things with it.\nThere isn't anything in the article implying that they transmitted information faster."
] |
[
"the two modes",
"The two modes, in this case, meaning the two entangled photons? Okay... so you're saying it's not just spooky interaction at a distance. The two photons interact with one another both before and after one half of the pair hits the object being imaged. Somehow, this results in information about the object or collision being passed to the readout light, even though it never interacted with the object itself. Is that accurate?",
" As a followup, this would mean that this technique couldn't be used to image, say, the interior of a black hole, since the pair must interact again and that's impossible once one of the photons has passed the event horizon. Is this also correct?"
] |
[
"Is it possible to add enough salt (or other solute) to water such that it is still an aqueous solution, but dense enough for a man to walk on?"
] |
[
false
] |
Pretty much the title. If you added too much solute, you'd be walking on a wet, mucky solid I would think. Is it possible to add so much solute that the aqueous solution is still liquid but dense enough to support a grown man (say 150 pounds over a surface area of 1ft
|
[
"Corn starch is suspended in water, it does not dissolve and would not be a solution. "
] |
[
"Corn starch, but only if you run. A supersaturated solution will become solid under sudden stress, but remain liquid otherwise."
] |
[
"Ah, cool. That would be so much fun to do. Is that an example of a non-newtonian fluid??"
] |
[
"Could electromagnetic radiation of a certain frequency be viewed as some base frequency photon being time dialated proportionally to its energy?"
] |
[
false
] |
If this is the case, does this perspective offer any interesting insights? If not, why so? Where in the mathematics does this idea break down?
|
[
"Time dilation is a really specific effect which requires either relative motion of emitters and observers or gravitational effects. Considering that photons are massless, there's not really a place to naturally decide on a \"base frequency,\" i.e you can always redshift or blueshift a photon more. You can decide on a \"base frequency\" (though physicists write it as a wavelength) for massive particles though, because you can write their mass in terms of wave properties,",
"E = hc/wavelength = mc",
"wavelength = h/mc",
"This is referred to as the Compton wavelength."
] |
[
"This doesn't offer a very useful perspective, because the frequency of electromagnetic radiation is frame-dependent (special theory of relativity) and so we can't point to a photon and say that it has an objective energy/frequency; it only has an energy/frequency relative to a given reference frame. In other words, in your idea, the \"base frequency\" would also have to be frame dependent, so you wouldn't have really gotten anywhere. Although maybe what you are advocating is the position that there really is a preferred reference frame and you want to call that the set of photon \"base frequencies\" or something. That idea died with the advent of special relativity in the early 20th century."
] |
[
"No, because photons do not have a rest frame; they travel at the speed of light. If you plug in the speed of light to the time dilation formula, you will see that you get an infinity. For this reason sometimes people say (somewhat sloppily) that photons are \"frozen in time.\""
] |
[
"I can't believe I'm asking this...but, why do men have nipples."
] |
[
false
] |
Just so you know, I honestly complemented making a throwaway for this question. So me and my friends have been smashing our brains together for an answer. It is just a vestigial structure? Does it even have a purpose? And if we evolved from a common ancestor did the male half of speices have nipples? WHY did they have them if they didn't need them anyways? So...
|
[
"The Queen's English is no more correct than American English. Your previous spelling was perfectly acceptable."
] |
[
"Because women have them.",
"All foetuses start off female. "
] |
[
"Basic answer would be that there is no evolutionary advantage to lose them. I'll leave it to the biologists to give a more in depth answer."
] |
[
"Why is the weather hot?"
] |
[
false
] |
What's the driving force behind heat waves? How can there be sustained hot air that isn't driven away by cooler air? Why am I sweating so much?
|
[
"During the local summer, whatever hemisphere you're in is tilted toward the sun, so the sun is in the sky longer, and the sun's light strikes the Earth at closer to a perpendicular angle. So the land and air around you get hotter than they do in the local winter."
] |
[
"That's just weather. You can think of the atmosphere as being like cotton balls being pushed around on a tabletop. Some of the cotton balls represent masses of relatively warmer air, while others represent masses of relatively cooler air. When a mass of relatively warmer air moves over where you are, the average temperature climbs."
] |
[
"Heat waves are local phenomena caused by unusual weather conditions. There is differential heating of the ground even at the same latitude because of various things like topography, vegetation (or the lack of it), urban centers, presence or absence of bodies of water, etc. Differential heating simply means that some areas get hotter than others for specific reasons, like the ones I mentioned above.",
"Now normally, there are many mechanisms for the localized high temperature areas to disperse their heat and equilibrate. For example, air rises over hot regions, creating low pressure. Cooler air may flow in from surrounding areas due to the pressure differentials.",
"Or thunderstorms may form. If there is intense heating over a period, a substantial mass of hot air may rapidly rise up into the atmosphere. At it rises, it cools down and the moisture condenses out, producing rain and hail. Again, the rain will cool the ground underneath, so this is another mechanism that keeps temperatures relatively \"normal\".",
"A heat wave happens occasionally because of some \"fluke\", that is, some relatively unusual circumstances which interfere with the normal dispersion of energy from hot spots to cooler areas. So what really happens in a heat wave is that the Sun keeps heating up the same spot day after day, but the normal mechanisms it has for losing that heat are temporarily compromised. If this continues for a few days, then enough heat builds up that we call it a heat wave.",
"There can be many reasons for such conditions. For example, the heat wave currently sweeping the midwest was because of something called a high pressure ridge. What happened was that an area of high pressure appeared in the ",
" above the region of the plains states. This interfered with the normal heat-losing mechanism. Normally, hot air rises, but the ridge of high pressure in the upper atmosphere prevented this from happening. If the hot air can't rise, it breaks the normal development of a low pressure system with winds blowing in from cooler areas. Instead, the low pressure area just grows at ground level and sort of sits there and stagnates. Thunderstorm development is also inhibited because of that high pressure ridge sitting on top - it doesn't allow the air from below to rise. So that sort of cooling is also reduced.",
"If this continues for a few days or weeks, the heat can really build up. Now you have a heat wave - a mass of superheated air which very slowly drifts eastwards, moving the heat wave eastwards along with the prevalent winds in our latitudes. Eventually it moves out over the sea or dissipates.",
"There can be many other reasons for such \"freak\" circumstances, but the mechanism is similar, in that it's something that interferes with the normal distribution of solar energy through winds."
] |
[
"Does covering up the toilet seat with paper reduce contact with diseases/bacteria?"
] |
[
false
] |
Or have I been wasting 20 years of toilet paper? What about wiping the seat? Or should you just squat over it? So many questions
|
[
"In terms of disease, the pathogenic microbiota of a toilet seat, unless you are immunocompromised, is of no significant health risk--barring something foreign/sharp. Your skin is an excellent barrier to microorganisms. The reason we wash our hands is because we end up touching a lot of places that are not excellent barriers, such as mucous membranes like your nose, eyes, or mouth. Bacteria, viruses, helminths, protozoans, and fungi don't really have the mechanisms to penetrate your skin in most cases. In general you do not have to worry about disease contact when sitting on a toilet.",
"To your specific question about contact with bacteria, if you have a clean piece of paper and you put it in between your legs and the seat, then yeah, it will reduce contact of the surface bacteria on the seat. As others have said, however, bacteria are probably all over everything in a bathroom. Another consideration is that aerosolized bacteria are all over the place as well, since flushing has significant aerosolizing action. If you're worried about bacteria this much, you should wear a biohazard suit, because whether or not you use a paper toilet seat cover/toilet paper, you're being exposed to bacteria.",
"I, however, like how the toilet paper feels on my legs compared to the cold ceramic/plastic/wood that a seat is made of.",
"Source: Molecular Biologist, Biochemist, Microbiologist",
"Edit: Thanks for the gold, stranger! :D"
] |
[
"To add onto this post, the toilet seats themselves are relatively clean in respect to most other items in a bathroom. Provided that the toilet passes the sight test (no ones sprayed the seat with their feces and/or the toilet appears to be cleaned regularly). ",
"As ",
"/u/svenser",
" mentioned, flushing will aerosolize microbes regardless of matting with toilet paper. Also, your skin acts as a barrier against bacteria that you touch if you sat directly on the seat itself. Typically youll find ",
" and ",
" species of bacteria on these seats. Mainly these are common skin microbes that a lot of people carry as part of their natural flora and nothing to worry about unless you're immunocompromised. ",
"Personally, I'm more picky about using paper towels to open pull bathroom doors when I leave the bathroom as handles are usually riddled with microbes. One spends time washing and cleaning hands only for it all to be for naught because of people who don't clean their hands leave behind their bacteria on the handles for others to pick up. ",
"To answer the question, if it makes you feel better to line the seat, go for it, the difference in cleanliness is most likely negligible at best.",
"Source: also a microbiologist"
] |
[
"One spends time washing and cleaning hands only for it all to be for naught because of people who don't clean their hands leave behind their bacteria on the handles for others to pick up.",
"Those people also touch other doorknobs, elevator buttons, the coffee maker, railings, and other people's hands. It seems kind of silly to use a towel to open the bathroom door when the next thing you touch is going to be just as 'contaminated'. ",
"At the end of the day, if you wash your hands before touching your mouth, nose, eyes, etc, you'll be fine. ",
"Source: Building engineer. If just touching bacteria made you sick, I'd be dead. "
] |
[
"Why does failing to fully drain a laptop battery \"condition\" it to having a smaller lifespan?"
] |
[
false
] | null |
[
"Are you sure you're not confusing lithium ion (laptop) batteries with nickel metal hydride or nickel-cadmium batteries? Voltage depression (sometimes erroneously called a memory effect) from partial depletion is not really a concern with lithium ion batteries, though it was with NiMH and ",
" NiCd batteries. Draining a lithium ion battery entirely will help calibrate the battery sensor, but won't help the longevity of the battery itself (in fact quite the opposite)."
] |
[
"What? No, full discharge and charge cycles cause a smaller lifespan. ",
"A shorter lifespan is due to the volume change of the cathode material during charge and discharge cycles causing microstructure fracture. A standard laptop battery can only do about 300 cycles. The more complete cycles you perform, the faster it'll reach the end of its lifespan. "
] |
[
"The batteries don't benefit, but Apple does when you need to buy a new battery earlier than you otherwise would've. The user gets slightly more battery life per charge due to more accurate sensor reading, but the long term lifetime of the battery is less."
] |
[
"Why doesn't a device work if the batteries are inserted in reverse?"
] |
[
false
] |
I have with a battery that doesn't indicate polarity. I accidentally put it back in backwards after taking it out to remove the circuit-breaking plastic tab inserted between the contacts that it shipped with. Perhaps unsurprisingly, it didn't work properly. So, what is it about batteries (or, perhaps, electronic devices) that requires current to run in a particular direction? Why isn't the simple fact that electrons are moving through the circuit enough?
|
[
"This is not really a chemistry question, it is an electronics question. I'll answer for modern semiconductor electronics, but similar comments apply to older stuff as well.",
"Semiconductors come in various types but the easiest to explain are bipolar devices. The most basic bipolar device is a diode, and the nature of a diode is that electrons only flow in one direction through it, customarily from anode to cathode. So, if a circuit has a diode in it (as virtually all electronics do) and the battery is put in the correct way, electrons go in the right direction. If the voltage is reversed, no power flows. Bipolar transistors are similarly directional: current will flow from base to emitter in an NPN transistor, and not the other way around. Current will flow from collector to emitter, provided there is current flowing from base to emitter, etc..",
"Field effect transistors are a bit harder to explain, because they are bi-directional, but the relative voltage (gate being at a higher or lower voltage than source, for example) work on similar principles. Plus, many such devices include diodes which only work in one direction.",
"So, for anything more complicated than a lightbulb, those batteries have to go in only one way. Often, if there is a chance they get put in backwards, the circuit will have some degree of protection against this. With coin batteries, most holders simply don't make contact if reversed."
] |
[
"If it's a simple device like a single resistor (incandescent light bulb), the circuit will work properly whether \"pointing\" forwards or backwards. But most devices have components like diodes which only work properly if the current is flowing a certain way. A diode is like a one-way valve for current, so if you put the battery in the wrong way, the diode blocks the current flow, and the circuit doesn't work."
] |
[
"All makes sense, but I guess then it's a deeper question about why it's important that current flows in a particular direction. In the case of a semiconductor/processor I could see that it might be important for one logical operation to occur ahead of another, so that the second operation can react to the output of the first. But is there an inherent physical property of diodes that restricts them to operating in one direction (that we're forced to deal with, because that property exists), or is the directionality desirable because it allows for a certain type of operation/function (and the diode is specifically chosen/designed to only work in one direction).",
"(Edit - not sure if 'electronics' is an option. Would 'physics' or 'engineering' be better tags?)"
] |
[
"Is it possible to do blood tests using FTIR spectrometer?"
] |
[
false
] |
Hey guys, Im kind of lost and confused so i recently acquired a FTIR spectroscope and UV vis spectrometer as well. Basically im testing the water in my area daily. I was wondering what tests i could run on blood samples with these devices?
|
[
"I don’t think you could get much (if any) usable data from FTIR. The huge water peak at ~3500 would obscure a big part of the spectrum. Also, if there were anything besides water that the FT could pick up they would probably overlap and make the spectrum really hard to interpret. ",
"FTIR is definitely not a good instrument for aqueous solutions which blood obviously is."
] |
[
"Not really, at least id imagine raw blood wouldnt work. someone else mentioned how the water peak would be massive but even then theres enough junk in the blood that itneoild be kinda hard to differentiate. Even just small metabolites youll find over 100 of them in the blood and unless youre filtering things youll get everything which would make it way more messy. Proteins lipids and nucleic acids maybe. Not sure the exact range of IR or the exacg range of all metabolites (who would) lol).",
"If you did some sort of prep plasma you could maybe but its a strong maybe, and even then it may need other steps to process it."
] |
[
"You can get some useful info- I believe Bruker makes a specialized FTIR for aqueous protein analysis. There are some other methods available utilizing other FTIR techniques such as ATR-FTIR.",
"There are all sorts of methods for analyzing blood for specific proteins."
] |
[
"How does the Genetic Maternal Effect differ from Cytoplasmic Inheritance?"
] |
[
false
] |
And how do they differ from Genomic Imprinting? Edit: Thanks for clearing that up for me guys! Great responses!
|
[
"The Maternal Effect is when a zygote recieves mRNA, proteins and other molecules from the mother's eggs. These are gene products but not actual genes. Nevertheless, since this occurs right at the start of development it can have long lasting consequences.",
"Cytoplamic inheritance refers to the offspring recieving actual genes (DNA) from the mother that are not in the nucleus, mostly from the mitochondria, chloroplast and possibly from any viruses. This is actually part of the new zygotes genome and is inheiritable.",
"Source: Biology college classes, Wikipedia "
] |
[
"To build on this, these maternally-sourced gene products (mRNA etc.) can enact an effect on the phenotype of the offspring, through epigenetic modification, and thus produce a phenotype that might seem to ignore the underlying genotype (as described below)"
] |
[
"The genetic maternal effect refers to a case where an offspring inherits the maternal trait regardless of its own genes. So say you have a pink father (p) and a white mother (w). The offspring can inherit either the p gene from their father or w gene from their mother, but offspring with either the p gene or the w gene all look white.",
"As said by others, cytoplasmic inheritance simply refers to any genetic material that is passed onto the offspring, but is not in the nucleus. ",
"In many situations they can have the same outcome, wherein all the offspring have the maternal trait. The main difference being that cytoplasmic inheritance is a result from DNA that is only inherited only from the mother (at least in mammals), whereas genetic maternal effect is cause by other maternal factors (such as proteins or mRNA).",
"Genomic imprinting is a whole other complicated beast.\nThe parent's DNA will have tags on them. These tags can do many things, but the simplest way to think of them is just to turn the genes on and off. Since the offspring inherit their DNA from both parents, they will have both maternal tags and paternal tags. These tags can often be antagonistic. So a maternal tag may code to turn on a given gene, while the paternal tag may code to turn that same gene off. In a case where the maternal tag's code can \"override\" the paternal one, the gene in this example would be turned on. This does not mean that the offspring would inherit the maternal trait. It means it inherited the trait that the mother passed on to it. Since the tags on the DNA can change over the course of an organisms life, and even from cell to cell, the mother in theory could have been born with the tag to have the gene turned off, but passed on the tag to have it turned on."
] |
[
"What is the most basic form of life that still displays sleep-like behavior?"
] |
[
false
] | null |
[
"It seems to be the tiny roundworm C. elegans, not coincidentally one of the most intensely studied basic forms of life. It does something sleep-like called lethargus before each time it molts. This tends to suggest that sleep goes way back in our evolutionary history, for whatever reason."
] |
[
"Animals are basically all evolutionary traits. You'd be hard pressed to find something that wasn't."
] |
[
"Wow never even occurred to me (maybe most people for the matter) that sleep was an evolutionary trait. Makes me wonder if there are animals that never need sleep."
] |
[
"Why does our taste for different foods change as we age, and is there any evolutionary reason why this happens?"
] |
[
false
] | null |
[
"For the specific case of children tending to become more picky as they grow from a baby to a toddler, I've seen the argument made that this may be an evolutionary response to a child's new increased mobility. You wouldn't want a child starting to walk around eating anything and everything he can find. (I'm dubious about this, the way my kid will put pretty much anything in her mouth :/)",
"But if this is plausible, then as you grow older and wiser you would become less picky.",
"Aside from that, I'd imagine the primary cause of change in taste is simply changing nutritional and dietary ",
" as you grow older."
] |
[
"Well, underneath the post title (with 'comments', 'share', etc.) there is a 'save' option.",
"Click this.",
"When you want to view it later, go to the 'saved' tab on the Reddit main page (next to 'what's hot' and 'top')."
] |
[
"Toddlers do put stuff in their mouths, but they just spit it out if they don't like it."
] |
[
"Is there evidence for historic droughts affecting the Mesopotamian area/Euphrates-Tigris Rivers?"
] |
[
false
] |
Hello all! I read a paper in Nature about the 4.2 kya event in the Mesopotamian region and how scientists think a possible mega-drought contributed to the crises among several empires . I was wondering if there is other scientific evidence for droughts in the Euphrates-Tigris Rivers over the last 3000 years. I know there is a drought currently in the area, but have drought events occurred before? Any peer-review articles or evidence you all know of? Thank you!
|
[
"This factsheet",
" cites some geological papers that support a drought in that period. Also, some theories point to a drought contributing to the late bronze age collapse (around 1200 BC), which also hit in that region. ",
"Here's a paper",
" addressing it, and I am sure there will be more on that period."
] |
[
"There is a pretty extensive literature (which is not exactly hard to find) of climatic variability, drought, and influences of these on various societies in the Middle East / SW Asia at both long (e.g., ",
"Kaniewski et al., 2012",
", ",
"Xoplaki et al., 2016",
", ",
"Flohr et al., 2017",
", ",
"Jones et al., 2019",
", ",
"Fleitman et al., 2022",
") and short (e.g., ",
"Donat et al., 2013",
", ",
"Barlow et al., 2016",
") time scales. The general point is summed up nicely by the title of the Kaniewski et al., 2012 paper, i.e., ",
"."
] |
[
"Historically,\nWhen the roman empire and the Sasanian Empire went to war against eachother, they would always try to battle during periods of drought, in other to out manoeuvre eachother. The rivers stood as official boundaries between both empires, so anytine there was extended droughts one or the other usually tries to conquer the other."
] |
[
"Why don't I get a shock if I touch a railway track?"
] |
[
false
] |
I wanted to know how an electric locomotive runs since the pantograph only touches one wire. After some googling I found out that the return current is carried by the tracks themselves. So shouldn't I die of a 250kV shock if I touch the track?
|
[
"If the rail is Earth grounded, you are at the same potential as the rail. The potential difference between the wire and the rail may be 250 kV but the rail is at 0 V."
] |
[
"As ",
"/u/scratchx",
" wrote, the rails are grounded, so the potential between you and the rail should be very close to 0 volts.",
"Also, no rail road in the world uses 250 kV, 25 kV is the highest standardized voltage. "
] |
[
"There are a few rails on the line. ",
"Usually you have 2 guide rails and the 3rd one that carries the electricity (on the London Underground anyways) is called the ",
"Third Rail.",
"If you touch this you will be dead in microseconds."
] |
[
"Do all human beings share a common ancestor?"
] |
[
false
] | null |
[
"All living things on Earth share a common ancestor.",
"The last common ancestor to all life on Earth (",
"LUCA",
") lived ~3.5 billion years ago.",
"It's unknown when the most recent common ancestor of all humans today lived. Estimates are in the thousands of years. ",
"Wikipedia has an overview of studies",
"."
] |
[
"All humans on this earth share a common ancestor not only with every other form of life on earth, with our closest living relatives, and also with each another more recently in time. The last common ancestor (LCA) between modern humans and chimpanzees is thought to be a species existing prior to the emergence of ",
" at 4.4 million years ago (ma). Some paleoanthropologists believe that the LCA could have emerged as early as 7-5 ma; however, the fossil evidence of our ancestors are a very small sample size. ",
"More recently in time, all modern humans on earth today likely descend from a common ancestor leading to anatomically modern humans. This hypothetical shared ancestor should not be confused with mitochondrial eve, because mitochondrial eve only explains the mtDNA molecule (or the woman carrier of that molecule) from which all modern mtDNA molecules descend. Citations below. ",
"https://science.sciencemag.org/content/326/5949/73/F1",
"\n",
"https://www.jstor.org/stable/2888813"
] |
[
"Thank you for your reply. I meant whether all humans alive today share a single human as an ancestor, though."
] |
[
"If we found a mirror in space, pointed at Earth and 100 lightyears away, could we see what happened on Earth 100 years ago?"
] |
[
false
] |
Since it would take the light time to reach us, wouldn't a very reflective surface (like a mirror) that was facing Earth and was far away actually show us Earth's past? Also, would one that was 100 lightyears away show us 100 years ago, or 200 years ago (since the light has to first get to the mirror, then back to us)?
|
[
"It would be 200 years ago since the light has to travel twice the distance."
] |
[
"AsaChemicalEngineer is correct, 200 years, but its worth noting that since the earth is only reflecting light, not radiating it (visibly), we aren't very bright, so even if such a mirror was miraculously in place, we wouldn't be able to see much."
] |
[
"Not to mention the fact that a telescope would have to have a truly insane spatial resolution to show us anything useful or interesting."
] |
[
"What would happen to a nuclear power plant if it were to be hit by an EMP?"
] |
[
false
] | null |
[
"The first thing is the variances in electrical power would cause an rps (reactor protection system) actuation. The system is a fail safe system, and loss or interruption of electrical power causes the scram to happen. You would lose all offsite power. The steam driven cooling pumps would start. The electrical disruption would cause the plant to disconnect all power sources and start the diesel generators in emergency mode. After that it's a pretty standard loss of offsite power procedure. ",
"See the post here"
] |
[
"Existing plants have EDGs with governors which can operate either through a control system or just a mechanical component. Some EDGs only have mechanical governors. Additionally all plants have a steam driven cooling system which can run in blackout conditions if necessary.",
"In new designs, it is required to have a diverse actuation system ",
". Additionally the scram function is fail safe and loss of power causes the scram to happen.",
"For cooling, say in the AP1000 (which has a digital protection system) the passive core and containment cooling systems use shielded wires and DC power to activate would not be impacted. EMPs affect mainly large ac transformers, so DC shielded systems would be mostly unaffected. In an AP1000 plant once the initiation signal fires the plant is walk away safe for 72 hours minimum and with either a diesel pump or fire truck a minimum of 1 week which can be extended simply by drawing water in from a nearby water source and spraying it on the top of the containment. ",
"An example of Westinghouse's plant protection system, including diverse actuation:\n",
"Westinghouse Plant Protection System Architecture",
"For an example of diverse actuation systems see:\n",
"AP1000 Design Control Document Section 7.7 Control and Instrumentation Systems (see 7.7.1.11 Diverse Actuation System)",
"For more reading about diversity in protection systems see:\n",
"NRC Digital I&C Interim Staff Guidance 02, Diversity and Defense-in-Depth Issues ",
"Edit: Added references, cleaned up iphone autocorrect."
] |
[
"The ECCS pumps and the DGs are disconnected from the grid and have no electricity in them when they are offline. They are dumb systems which have no controllers and are either on or off. It would unlikely that an emp affect any of those things. ",
"Additionally see: ",
"http://www.reddit.com/r/askscience/comments/ubydh/what_would_happen_to_a_nuclear_power_plant_if_it/c4u7tyn",
" for the NRC's conclusions from a report on EMP near a nuclear power plant."
] |
[
"Why does canned air get really cold when I hold it upside down and spray it?"
] |
[
false
] |
I mean the type used to clean dust out of electronics. If you hold it upside and spray it it gets very cold. Also, most contents under pressure such as hairspray, cleaners, air fresheners and the like seem to feel colder after I pick them up and shake them. I assume the reasons are the same. PS don't actually test this indoors. The irritant they add to the stuff is strong and lingers for a half hour.
|
[
"Canned air isn't actually ",
". It's a mixture of nitrogen and other gases. When compressed into the can this mixture takes fluid form. Since some of the gases are heavier than air, when turned upside down the can will spray out the liquid mixture before it has had time to mix with the lighter gases. *When breathed in, these gases can displace the oxygen in your lungs. Be careful!",
"As for why it gets cold: ",
"adiabatic cooling",
"Basically it says when gases are compressed, and the pressure is released there will be a drop in temperature. "
] |
[
"When liquids evaporate, they ",
" heat."
] |
[
"PV=nRT (P=pressure, V=volume, n=number of moles of stuff, R=gas constant, T=temp in Kelvin)",
"When you spray stuff out of an aerosol can the pressure on the gas is dropping VERY drastically as it escapes form the highly pressured can into the atmosphere. In order for the gas law listed above to work, the temperature drops since the number of moles is not changing, nor is the universal gas constant, R. "
] |
[
"How do animals with eyes on either side of their head see?"
] |
[
false
] |
Do they have the ability to alternate which eye they use at a certain time? Or instead, is the image that their brain receives a combination of visual input of both eyes?
|
[
"Hunters = forward facing eyes = stereo vision = depth perception = prey in tummy ",
"Prey = eyes on side of head = panoramic 2D vision = see hunters = stay out of tummies "
] |
[
"Put the palm of your hand on the bridge of your nose, blocking out your central field of view. You now are viewing the world in a similar manner to an animal with a low binocular overlap. What is it like? You have no problem imaging the world as continuous, and you do not see the world as two completely separate images that are fighting in your brain.",
"There is no reason to think that animals with low binocular overlap experience the vision much different than you do, apart from the fact that they are probably bad at judging depths, and can see over a much broader horizontal space."
] |
[
"Although your eyes are pointing forward, you get a very very wide viewing angle, almost 90 degrees either way. Animals with there eyes on the side have this ability too and therefore likely get a much more panoramic view of their full surrounding. "
] |
[
"Is there any correlation between LTR and RTL languages and the dominate handedness of that language's creator or culture?"
] |
[
false
] |
[deleted]
|
[
"Asian countries have the lowest percentage of left handedness of any developed country (2 to 5%, compared to on average 12% in western civilizations.) This would appear to belie reading preference and handedness. The negative corollary would appear to be significant, except the general consensus seems to be that pressure to conform to social norms is the prevailing factor in the dominance of right-handedness in Asian countries.",
"Edit: People keep pointing out how they were forced to use their right hands despite being left handed... and lo and behold I had already addressed this when I wrote the last sentence of the comment. If you're telling me your story because it feels good to say it out loud then I'm happy to serve and sincerely sympathize, please stop reading here and accept my salute, no human should have to fight their handedness on account of social stigma. There is a real possibility this is doing long term psychological damage. If you're telling me because you think I don't know or missed an important point... ",
" well, before this edit ",
" And yes that would include pressure from parent, teachers, extended family, peer pressure, etc."
] |
[
"Asian writing (i.e. Japanese, Chinese, and Korean) isn't truly RTL in the same way as Arabic or Hebrew though. It's top-to-bottom right-to-left in the traditional format - single lines written RTL can be thought of as multiple one-character columns of vertical writing.",
"http://www.jstor.org/pss/620771",
"There are decent sources on wikipedia:",
"http://en.wikipedia.org/wiki/Horizontal_and_vertical_writing_in_East_Asian_scripts"
] |
[
"Korean isn't RTL at all. Even in vertical writing each syllable is read left to right, and top to bottom. 닭 is an interesting example to use. It's the word for chicken, pronounced 'dalk' with a silent 'l'. \nㄷ - d, \nㅏ - a, \nㄹ - r/l, \nㄱ - g/k"
] |
[
"If motion is all relative to perspective, why would a rotating spacecraft (in space) simulate gravity."
] |
[
false
] |
I have a basic grasp of physics and understand centripetal force, but at some point all motion would be identical. Why would continued movement along a set path "simulate" gravity?
|
[
"Uniform motion and freefall are all equivalent. Acceleration and rotation are not."
] |
[
"If you (the OP) would like to know more about this, read about ",
"Fictitious Forces",
". I learned them as apparent forces, but as the first sentence in the link above points out there are many synonyms to the term.",
"Since the definitions of ",
"inertial",
" and ",
"non-inertial",
" reference frames can be somewhat confusing (as I know I first had issues with the distinction when first learning about them), an inertial reference frame is simply a frame of reference where no accelerations can be detected. In the case of a rotating space station, an inertial frame is how an outside observer floating in space would observe the spinning space station, and the non-inertial frame is how a person on the inside of the rotating craft would observe."
] |
[
"What's actually occurring in the rotating spacecraft question is a great example of Newton's first law of motion! Any object in motion wants to remain in motion unless acted on by an outside force. In this case, a mass wants to move in a straight line, however the wheel is the outside force acting on the object. ",
"Now the outside force (the wheel) can act on the object with the equation F=M*V",
"/R, so we can take a mass, and place it inside of a rotating wheel with a specific radius and velocity such that the force acting on the mass is -9.81 m/s."
] |
[
"Would glass from the Manhattan Project still be radioactive?"
] |
[
false
] |
So I recently visited a rock shop that had all sorts of glass, rocks, and minerals from various places. The prize possession of the owner was a chunk of thick yellow glass, maybe a foot tall and at least 6 inches thick. He said that this was glass that was used to view the testing of the bombs for the Manhattan Project, he had gotten a hold of it when someone was trying to dispose of it. If this guy is actually telling the truth, how much danger of radiation would someone be in if they visited the shop or the shop owner himself?
|
[
"Everything is radioactive naturally. A few thousand atoms decay in your body every second - mainly from potassium which is naturally a bit radioactive. A nuclear explosion nearby can increase the activity, but based on your description it is impossible to estimate by how much, apart from \"probably not relevant\". You can visit ground zero of the Trinity test today. While it can be measured that the radiation levels are higher than in the area around it there are inhabited places with higher natural radiation levels."
] |
[
"The wikipedia on Trinitite (",
"https://en.wikipedia.org/wiki/Trinitite",
") mentions that it is slightly radioactive, but safe to handle. Would it be too radioactive to wear as jewelry (or something else that is in constant contact with your skin)? It doesn't specify how radioactive or how much handling. "
] |
[
"If I get the conversion right, wearing ",
"these pieces",
" 24/7 would give you a radiation dose of about 10% the natural radiation dose for body tissue directly next to it, and negligible dose elsewhere. Compare this to living in Denver with much more than twice the sea-level radiation dose due to more cosmic rays at altitude."
] |
[
"Do animals abuse drugs?"
] |
[
false
] |
It is known that animals get drunk from over-ripe fruit. What about other natural high makers like shrooms, opium or coffee?
|
[
"Rats locked in small boring cages will self-medicate their depression with opiates if you offer it to them.",
"In a nice environment (enough space, privacy, companionship, good food, toys) they apparently won't.",
"Not sure if that counts as abusing drugs, or using them correctly.",
"http://sciencethatmatters.com/archives/6",
"He noticed that the rats in the experiments were stuffed alone in a boring cage with little else to do. “If I was strapped down alone in a cage,” he thought, “I’d probably want to get high too.”",
"So he built a rat park — a large, intricate, brightly-painted and heavily-padded structure to make the rats actually happy. He put half the rats in the normal cages and half in the park and gave both equal access to drugs.",
"The rats in the cage got addicted, while the rats in the park stayed away.",
"Then, even more strikingly, he took rats who’d had 57 days to get addicted to the drugs and took half of them out of the cages and put them in the park. The rats, even though they’d been addicted in the cage, suddenly stayed away from the drugs. They even voluntarily detoxed — trembling and shaking, but still staying off the drugs."
] |
[
"Catnip",
" is what first came to mind."
] |
[
"we could think of abuse as of \"use without the purpose of nutrition but to get high\"",
"Does my consumption of McDonald's constitute food abuse because I eat it for the taste and not the nutrition, or does the presence of any nutritional value whatsoever invalidate the idea of \"food abuse\"?"
] |
[
"I am interviewing a cosmonaut next week. I need your help coming up with some questions."
] |
[
false
] |
Next week I will be interviewing and I want to ask him some of the top voted questions. Aleksandr Lazutkin is a Russian cosmonaut who was awarded the Hero of the Russian Federation for bravery and heroism after he was on Mir when a supply ship collided with the station and as the on-board engineer help fixed an air leak and saved the lives of his crew. Currently he is the assistant director to Russian Cosmonaut Museum. Ask away, I have some of my own questions but I need Reddit's help. I will conduct the interview in Russian so I will post the translated transcripts next weekend. *Please note that is serious and I had to delete this post from AskReddit because people were posting really stupid questions
|
[
"I'd be curious to hear his opinion on the risks associated with space travel and exploration, especially in the context of recent discussions of having astronauts volunteer for one-way trips to Mars."
] |
[
"Questions:",
"It's hard to imagine working at a museum compares with space flight and the preparation for space flight, how did you adjust to not having these huge goals and responsibilities? I can imagine that shifting into the \"regular\" world was quite a transition.",
"Did the excitement of being in space ever wear off while you were in space? If so, how long did it take?",
"Do you consider yourself more of an explorer or a more a scientist?"
] |
[
"How long did it take to become acclimated to microgravity? What was most difficult when adjusting to this difference?"
] |
[
"Could someone explain this hawking radiation problem to me?"
] |
[
false
] |
Ok so as far as I understand, hawking radiation occurs thanks to the fact that in a vacuum, there are virtual particles and antiparticles constantly popping into existence and annihilating one another. Sometimes these particles appear just in the border of a black hole's event horizon, and, as I get it, one particle is absorbed by the black hole, so the other one must borrow mass from the black hole to cease being "virtual" and to become "real". My question is, given the fact that the black hole has absorbed one of the particles, hasn't it gained mass? and isn't that mass the only thing the other particle needs to borrow to exist? if this is so, why does a black hole lose mass in this process? or do I simply not understand it?
|
[
"The virtual particle picture is a description of the calculation Hawking used, but is a very poor way to think about what is going on physically. (One way to see it's a poor way to think about it physically is what you describe here.) ",
"What is going on is that an initial state (the black hole) evolves into a final state (slightly smaller black hole plus a particle flying away) due to quantum processes. You can think of it as a quantum tunneling process (see ",
"this",
" paper, for example)."
] |
[
"virtual particles appear in the vacuum of space and normally annihilate each other. at or very near the surface of a black hole one of the virtual particles can \"fall in\" the other particle cant annihilate thus the fallen particle, necessarily has a negative energy/mass, makes the black hole smaller, and the other particle is zips off away from the back hole. eventually over the eons the black hole should evaporate away... the smaller the black hole the faster this occurs. thus, black holes have a temperature even when they are not consuming normal matter."
] |
[
"why is it necessary that the fallen particle has a negative energy/mass? (thanks for the answer!)"
] |
[
"Feeding People Like Pets"
] |
[
false
] |
We seem to know a lot about what to feed pets because they get fed nearly the same meal every day for life and do quite well. So if vets can figure this out for animals, has anyone applied similar research for people? Is there a healthy set of meals that one can eat for their entire adult life? I've seen lots of reasons why optimal can't be done but surely we can come up something reasonably good, especially if we focus on the non-picky eaters. After all pets are good evidence that it can be done for many mammals, and birds.
|
[
"http://www.zupreem.com/our-food/primates/primate-diet-dry",
"They discourage people from buying this for personal use, though."
] |
[
"This guy tried living off monkey chow for a week, there's a video a day of his progress:",
"http://www.angryman.ca/monkey.html"
] |
[
"The answer is that yes, this is technically possible, but nobody wants to be the one to propose sucking all the joy out of life as a research project or health initiative."
] |
[
"What is the highest altitude we have ever found living organisms?"
] |
[
false
] |
[deleted]
|
[
"238 900 miles or 384 400 kilometers is the highest altitude we have ever found living organisms at. Its the distance to the Moon... Yes, I'm taking about humans.",
"All jokes aside, it depends on what exactly you want to know. Highest altitude non-human organism to be ",
" is the GRIFFON VULTURE who reached 37 000 feet or 11.3 kilometers - an altitude of a commercial airliner.",
"However, organisms can ",
" at higher altitudes if we decide to put them there. TARDIGRADES are the only non-human creatures capable of surviving in vacuum of space. Unlimited altitude."
] |
[
"Apollo 12 found bacteria living on Surveyor 3 on the moon a few years after the probe had landed."
] |
[
"It was a dormant colony, and it is still controversial if it actually survived on the moon or was introduced during transit or during analysis back on earth."
] |
[
"How do worker bees evolve if they aren't the ones reproducing?"
] |
[
false
] |
Just curious--how do worker bees develop positive adaptations for their survival when the drones are the ones that reproduce, and have a significantly different environment and life than a worker bee?
|
[
"This is interesting...",
"Since the reproducing bees don'thave the life the worker bees do, the evolutionary pressue is a different one.",
"Well I guess if the workers get a beneficial trait just by chance, the whole colony would prosper. The other way around, if the worker bees get a worse trait for their evolutionary niche, the colony will vanish.",
"So maybe it is more of an indirect-feedback-evolution.",
"The workers don't mate, but since they keep the colony alive, their fitness influences the survival or loss of a specific trait."
] |
[
"It's no more or less indirect than any other mutation on non-germ line cells in other organisms. A mutation that leads to the production of melanin in skin, for example, doesn't affect any of the reproductive cells - but we still treat it as fairly normal. That mutation affects the ",
", not the individual cells or organs independently of each other.",
"The key is looking at the ",
" as an organism."
] |
[
"The most important thing to remember is that in any living system, it isn't ",
" the individual which is under selection pressure, it is the genes themselves. It's therefore useful to think of how genes are passed along in bees.",
"Whilst not literally true, it might be a helpful analogy to think of the entire bee colony as a single reproducing organism. In this analogy, the queen is equivalent to the reproductive organs, and the workers are equivalent to the rest of the body. Just in the same way that genes for human organs are passed on through the sexual organs, the genes that code for specific traits in workers will be passed on through the queen. ",
"Perhaps the most important concept is that the queen has worker bee genes, it's just she doesn't use them.",
"Now consider that the workers' capacity to do their job effectively directly influences the reproductive fitness of the queen. Workers which have developed an adaptation will provide their queen with better reproductive fitness, and will be able to outcompete other colonies. Since this adaptation will have come from the genes which the queen carries, she will pass on these adaptive advantages to future colonies."
] |
[
"When We Feel Pain Why Do We \"Hold\" The Area Inflicted?"
] |
[
false
] |
Didn't know how to word the question so I'll try to elaborate here. If you stub your toe our reaction is to grab and hold our toe. If someone punches your arm the reaction is to grab your arm. If someone kicks a man in the balls he automatically puts his hands there and holds them. Is this some sort of instinctual act? Does doing that physically relieve pain? What are the reasons for doing this, whether instinctual, biological, physical, etc?
|
[
"http://bodyinmind.org/reducing-pain-through-touch/",
" -with references"
] |
[
"Right, that's what I'm saying. It's what I do almost automatically but I can't feel a tangible difference in pain that I feel. There has to be an explanation for why we do it."
] |
[
"Right, that's what I'm saying. It's what I do almost automatically but I can't feel a tangible difference in pain that I feel. There has to be an explanation for why we do it."
] |
[
"How is the success chance of Surgery calculated?"
] |
[
false
] | null |
[
"Its based on past experience, the success rate of any medical procedure is all about averages. \nPeople do studies and retrospective analyses on surgeries and break down things like survival rates, success rates post operatively and at different time points, and complications that may develop. \nFurther statistics may be done to look at breakdowns based on age, gender, concurrent disease, etc. "
] |
[
"More specifically, studies measure technical success (did the procedure work? i.e. did we get the appendix out), morbidity (complications), mortality (deaths), as well as various survival data. Survival data can be short term (30 days, etc), long term (5 years, etc). Survival data in cancer can also be measured in 'disease free survival' (how long has the patient been cancer free) and 'overall survival' (how long after cancer therapy has the patient remained alive regardless of if their cancer recurred). "
] |
[
"There is quite a lot of debate at the moment, at least in the UK, regarding how performance data should be presented.",
"There is a call for more data to be made available and surgeons are now expected to give success/failure rates that are specific to them where possible rather than just quoting general data from studies. Some specialities have endeavoured to make a lot of data available to the public for several years - especially ",
"heart surgeons",
".",
"Transparency obviously helps to improve outcomes and highlights problem areas but if not handled correctly runs the risk of being counterproductive. For example, surgeons who work in a high risk field or conduct very complex surgery may appear to be worse surgeons (higher death/failure rates) when really they may just be dealing with more severe cases.",
"Edit: ",
"Brief summary on the subject here from the English surgical body"
] |
[
"Considering a lot of deep space images are 'coloured in' what are the actual colours of the images released by NASA etc.?"
] |
[
false
] | null |
[
"It's not so much that they're just colored in as it is that different frequencies of non-visible light are given corresponding frequencies of visible light so that the image can be displayed visually. The pictures themselves are technically accurate, they're just from a viewpoint that humans don't typically have."
] |
[
"Not necessarily. Have you heard of the Hubble pallet? Essentially, for many Hubble images, certain wavelengths are assigned to be different colors, separately from how they appear to our eyes. For example, helium and hydrogen both primarily emit red light when excited in the way that they are in most nebula. Because this would lead to a fairly monochromatic picture, one is assigned to green, so that the images show the composition of the objects. This means that the pictures don't actually look how they would to our eyes, even when they only include visible light."
] |
[
"Well, that depends entirely upon the colour of the galaxy in question. But, by and large, you wouldn't see galaxies as much more than a pale smudge, as human eyes aren't very sensitive. There are many galaxies that have the same size in the the night sky as the full moon; however, we generally can't see them, as our eyes are rubbish."
] |
[
"What is it about metal that prevents it from getting \"soggy\" like fabric or sand, when in contact with water."
] |
[
false
] |
Just curious why, even a porous metal, won't get heavier, or retain ANY of the water when soaked.
|
[
"Metals form into crystals, or usually many crystalline ",
"grains",
". The atoms are tightly packed and there usually isn't any space for something as big as a water molecule to penetrate it. (The same is true of sand particles....they are impervious to water.) And metals don't generally form into a porous matrix, that is, one that is full of holes like a sponge. If they do, the holes can fill with water, but it won't go into the crystal grains themselves. ",
"A collection of metal particles, like sand particles, will hold water. Such a slurry does get heavier when the water is added, although the metal is so dense that it may not be as noticeable as with other particulates. ",
"If you make a fabric out of metal instead of cloth, it will also get heavier and retain some of the water, but not to the extent that cloth will. The water molecules cannot penetrate the metal crystals, but they can get in between cloth fibers. "
] |
[
"Think of the 3d shape of a quantity of sand or fabric, lots of space available for the water to get into and be attracted to as it is a polar molecule. In the sand's case I would guess that the attractions between fellow water molecules and the sand itself keep it together. ",
"Now atoms in a metal are ordered in tight crystal structures. In terms of relative space, the interfiber space of fabric is like flying to the sun, whereas the intermolecular space of a metal is like walking down the street. Due to actual repulsion or lack physical space the water molecules simply can not get \"inside\" of a metal in the way you are thinking.",
"I am by no means an expert, just what I surmise the answer to your question is."
] |
[
"Metal as porous as fabric or sand - it would have to be actual metal fabric, or metal \"sand\" (metal filings). Try with something like that first.",
"If it merely seems porous, but it's an actual chunk of metal, it's nowhere near as porous as the materials mentioned above."
] |
[
"What role does the Fat Content of food have in gaining or losing weight?"
] |
[
false
] |
I understand that eating High Calorie foods will cause you to gain weight if you don't burn off those consumed Calories, but I keep hearing ads for "Low Fat" or "No Fat" foods. Is this simply a marketing ploy, or does the Fat Content of food actually have an effect on Body Fat?
|
[
"It's not a marketing ploy in that the foods do actually have less/no fat in them, but you are correct in that Calories are the primary culprit. There is ongoing research to determine how what we eat effects our basal metabolic rate but but from what I know these effects are reasonably small."
] |
[
"Fat is one of three macronutrients in food (ie. the nutrients your body requires in significant quantities) - the other two being protein and carbohydrates.",
"The widely accepted and promoted notion that fat in food equals fat on your body is one you should be very careful about accepting on face value. Most nutritionists will tell you that calories are calories, regardless of how you get them - and if you eat more than you burn, your body will store the excess as fat."
] |
[
"It has some effect, but not too important. You will gain more fat eating 50 grams of sugars and not burning them than eating 20 grams of fat doing nothing. "
] |
[
"Is it possible to die of hypothermia in relatively warm water?"
] |
[
false
] |
Assuming you were to stay still in relatively warm water (lets say 80 degrese) could you die of hypothermia, since your body's heat would be dissapating into the cooler water? Or would your body not loose heat quicker than it could generate the same amount of heat?
|
[
"Damn, so given enough time, u could die of hypothermia in 90 degree water"
] |
[
"Yes. It will take longer than if the water is near freezing, but it can happen. ",
"Fatal hypothermia occurs when your core temperature drops below ",
"95 degrees F"
] |
[
"I think your body has enough internal friction to maintain a high enough temperature for survival in 90 degree water. I'm interested to know what the maximum temperature hypothermia could occur is, though. "
] |
[
"Facial expressions - surprise, fear, anger - nature or nurture?"
] |
[
false
] |
Is there something wired in our DNA that controls these facial expressions, or do we learn them by watching people as we develop?
|
[
"Dr. Paul Ekman",
" has published many articles regarding universal expressions and emotions.",
"The universality of the 6 basic emotions",
" suggest that there are some emotions that are expressed irregardless of environmental stimuli.",
"His writings suggest ",
"there are approx. 10,000 different possible expressions (3,000 of which are used for emotions) from 43 different facial muscles",
"."
] |
[
"True, but context is critical. Ekman's research is based on showing pictures of actors assuming various facial expressions and asking the participants to describe the emotion exhibited in picture. This leads to quite a bit of wiggle as to the expression in question. ",
"For instance, it is more common to endorse a smiling face as happy, than a grimacing face as fearful...",
"unless the grimacing face is looking to the side",
", because we rarely see fearful faces looking at us head on (unless we are ax murderers). Contempt never quite makes the cut in the \"six basic emotions\" because it tends to be endorsed at a rate of about 50%, significantly lower than the top six. Embarrassment has a tremendously strong visual correlate (covering one's face, even congenitally blind children do this when embarrassed), but that's not a facial expression per se. Does this mean that a happy expression is a more \"natural\" than a fearful one? Or that contempt isn't \"universal?\" Or that embarrassment is learned? I suspect it just means that Ekman's method of assessing facial expressions is limited, and that his book shouldn't be seen as the final word in this debate. "
] |
[
"Ekman controlled for this in his study with the Fore people. You can read his book. "
] |
[
"Would a attempt to land people on mars using today’s technology be more dangerous then the first moon landing ?"
] |
[
false
] |
[deleted]
|
[
"Today's technology, in terms of propulsion, offers little more than it did in the '1960s. Most of the \"advanced\" propulsion technologies, such as ion thrusters or plasma thrusters, would be useless for landing since they are low thrust. In order to land a big mass on high gravity (okay, higher than the Moon) would require using chemical rockets to slow down. In terms of propellants, you'd have to use something that doesn't boil off, so liquid hydrogen/liquid oxygen are barred. Kerosene/liquid oxygen is still hard, most likely they would chose hydrazine variants (",
"MMH",
" or ",
"UDMH",
") oxidized with ",
"NTO",
" or ",
"nitric acid",
". This very similar to what they chose for the Moon landings (Aerozine 50/NTO).",
"Mars is the trickiest planet for landing on. On Earth, with a significant atmosphere, spacecraft coming back use a TPS (heat shield) to get rid of their orbital speed by shredding it aerodynamically upon reentry, and then when it's slow enough to parachute they do so until they touch down. Huygens also did this on Titan. On the Moon, with no atmosphere, they used retrorockets to slow down. On Mars ",
": has just enough atmosphere that you burn up if you don't have a heat shield, and just enough to use a parachute to slow down a bit, but not enough atmosphere to slow you down for a soft touchdown. You have to use retrorockets in the last moment.",
"Consider also ",
"martian dust",
", which can damage sensitive equipment such as bearings and cameras, and cause cancer or lung disease on humans. It's a bit less harmful than the Moon's because there is wind erosion, so the particles are rounded. However, also because of the presence of an atmosphere, dust won't settle down in a short time as it did on the Moon. This challenge forced engineers to come up with the crazy idea of the skycrane that landed Curiosity (this way they could keep the retrorocket exhaust far away from the ground). You could probably avoid the skycrane thing if the landing vehicle has some sort of protective shell or cover that stays closed for a long time after landing until the dust has settled.",
"But landing humans requires landing a much larger mass, not just for a vehicle that can support human life, but for one that can do so ",
". This means a ",
"life support system",
" with enough supplies of water, oxygen, food for a duration of one month in the case of a short-stay mission, or 2 years in case of a long-stay mission, or a regenerative life support system (which also always leaks a bit so it needs supplies anyway). Both supplies and regenerative life support translate into large masses, the latter being convenient for long missions.",
"Then you have to consider the larger gravity of Mars. This will not only require more retropropulsive force to land, but also require bringing more fuel for taking off later and achieving a high orbital speed.",
"So landing a large mass, on high gravity, with enough fuel for ascending later will require a big engine and a lot of fuel, which has to be launched from Earth, implying a high cost.",
"The only factor that plays in our favor is a smaller delta-v for landing since good part of the speed can be lost through aerodynamic means. Still, most of the challenges are physical, so modern technology does not help much."
] |
[
"In fact, it's probably too much involved to use a single-vehicle lander like they did for Apollo, because that would have to be absolutely humongous. What I think would be much more sensible would be something like the mission profile in the ",
" novel, and no doubt also similar real life plans exist/existed. You send several robotic precursor missions to the landing site, including prefabricated habitat modules and a return ship that starts synthesising fuel on Mars via ISRU - and then the actual crewed lander can be a lot lighter, because it only needs to land the crew and whatever equipment they need to survive until the hab is set up."
] |
[
"The propulsion concept is still similar, but we learned so much in all aspects of rocketry. In 1970 it was completely normal that 10% of the launches failed - crewed launches had a better ratio, but generally failures were very common. Safety standards have improved a lot everywhere. Today most launch failures are new rockets, especially from start-ups. The workhorses have a track record of tens of launches without failure.",
"A mission to Mars today is certainly much more risky than a mission to the Moon today, but I'm not sure about the comparison to the Apollo missions."
] |
[
"Can anybody explain the phenomena of a \"night rainbow\" to me? I just observed my first one. (details in text)"
] |
[
false
] |
is the weather report at the time of observation (includes moon phases, precipitation). The event occurred at about 11.30pm, Wednesday. I observed the rainbow for about three minutes before it disappeared. I'm calling it a rainbow, because it took on the same shape as the refracted light of a rainbow, the only difference being that what I observed was uniformly white and occurred just before midnight. I tried to take a photo, but I lack the photography skills and equipment to capture such a thing, so all I have is some black squares to show. I'm very curious to know what this is, as I'm usually very aware of the meteorological events that occur in my area, but I've never seen anything like this before.
|
[
"With the right conditions, a rainbow can occur at night as a result of refraction of moonlight. It seems monochrome, I guess because of the low light level. If the moon was out, and the bow was opposite of the moon, my guess would be that. I think it is called a moonbow."
] |
[
"Neat article that discusses this a bit:\n",
"http://www.space.com/12319-moonbows-yosemite-full-moon-lunar-rainbows.html",
"Happening in that article from waterfall spray, but could certainly happen from rain. "
] |
[
"Rainbows are formed by light refracting through and reflecting in rain droplets of the correct size and position with respect to the light source. The light enters the rain droplet and begins to spread out ",
"like shown here",
".",
"The light from the moon is similar to light directly from the sun. There are a few differences in the spectrum due to absorption by the moon's surface, but it is not monochromatic. So, in the case of light refracting through a water droplet, you will still get a multi colored rainbow.",
"I have two explanations for what you saw:",
"a quick source on rods and cones",
"Edit: Given your comment about it not being a \"halo\" I'm going to go with #2."
] |
[
"Is dopamine uptake lessened during higher temperatures/higher humidity?"
] |
[
false
] |
I'm a smoker and I've noticed that when it starts warming up for the summer I start smoking more cigarettes. I'd say I want to smoke about two or three times as much, and I'm wondering if this is a thing or I'm busy being an outlyer.
|
[
"To start with, you are not an outlier. People tend to smoke the least in February (in the Northern hemisphere) and the most in the summer. The current hypothesis is that people tend to smoke outside and that people hate going outside when it is cold. This trend has become more pronounced due to indoor smoking ban at many places.",
"I am not aware of any study that links smoking, dopamine, and temperature at once. However, there are some studies on the relationship between dopamine release and methamphetamine, and here too high temperature led to the ",
" of dopamine uptake. Dopamine also makes animals more sensitive to heat. Given this, I am somewhat doubtful that higher temperature would directly cause increased smoking."
] |
[
"Don't think about it in terms of dopamine. ",
"It is true that there is a particular network of circuits in the brain that has something to do with seeking rewards, and that one specific part of that network of circuits involves dopamine.",
"However, dopamine is used for a dozen other things in the brain that have nothing to do with reward. And the 'reward system' is by no means a 'dopamine-based' system. In case you're curious, ",
"here",
" is an image depicting the circuitry surrounding the mesolimbic pathway (sometimes called the 'reward system'). The neurons that release dopamine are the red arrows.\nKinda hard to see why you'd specifically call it a dopamine system, no?",
"Note also that that diagram is simplified, there are many other parts involved, using half dozen or so other neurotransmitters."
] |
[
"Hey, sorry about replying almost a whole month later. ",
"In the diagram you sent there are four colors representing neurotransmitters, what does each color represent?",
"\nIs the entire reward system affected by heat? The other answer on this post indicated that dopamine uptake is more effective as temperatures go up.",
"\nAre there more reward chemicals being released by cigarettes than just dopamine? If so, looping back to uptake efficiency, are those chemicals also taken in better in higher temperature?"
] |
[
"When we tag animals so they can be tracked and counted, do the tags affect the way their peers relate to them? Does it affect their mating chances?"
] |
[
false
] |
We often hear about how birds will select mates based on their plumage and I can imagine other animals noticing differences in fur color, quality, etc. Don't large colorful tags and bands get noticed too?
|
[
"It really depends on the species. Those species that depend more heavily on smaller color features are more likely to be affected by bands. It's an important consideration in the design of bird tracking studies! Here's an interesting study on zebra finches that found a preference in female individuals for males with red beaks or red identification tags: \n",
"https://www.google.com/url?sa=t&source=web&rct=j&ei=usM2U7axG_XesATtz4LICQ&url=http://www.researchgate.net/publication/51315807_Ultraviolet_vision_and_band-colour_preferences_in_female_zebra_finches_Taeniopygia_guttata/file/d912f512de0e932317.pdf&cd=9&ved=0CEEQFjAI&usg=AFQjCNHi1GSMYhshNsrrivSGYnit5fpOKQ&sig2=S10L3SAHhr5iqXE1TCChjQ"
] |
[
"Right. If we change their behaviour in any way, then the data we get from the tagged animals might not be representative of the rest of the population, so it might tell us incorrect things."
] |
[
"Ideally, though, scientists try to avoid influencing their mating chance, right?"
] |
[
"Physics/Static question: How can you tell which trig function to use when finding the coordinates of A here?"
] |
[
false
] |
I know that position A is (-10cos70sin30, 10cos70cos30, 10sin70) from looking at someone else's sheet. How do you figure out which trig function to use though?
|
[
"I think about projecting the line between the origin and A onto relevant planes/axes. If I project into the angle, use cosine. If I project away from the angle, use sine.",
"For example, to get the x-coordinate of A, I need to project into 70 and then away from 30. (It's negative, since it's pointing away from the x-axis.)",
"For y, project into 70, then into 30. (This time, it's in the same direction as the y-axis, so no negative sign.)",
"For z, project away from 70."
] |
[
"I think my issue is I have trouble visualizing the three dimensions. Is the 30 degree angle representing how far away from the Y axis A is and the 70 degree angle its incline into Z?"
] |
[
"Yes."
] |
[
"So how do programming languages work?"
] |
[
false
] |
How do programming languages work? We type text and then that text is interpreted into making something happen. But how?
|
[
"Modern programming languages are built on layers and layers of previous progress and the complexity behind them is truly incredible. There are many many millions of person-hours worth of work that have gone into the state of the art today.",
"Start from the bottom.",
"Processors execute \"machine code\", sequences of instructions and arguments that are encoded in binary and tell the processor what to do. Originally people \"wrote\" programs directly in machine code, encoding them on punch cards. Programmers pretty quickly gravitated towards a workflow where they would \"write\" programs long hand in notebooks using names of instructions, writing values of arguments in decimal, hex, or octal. Translating those programs into actual binary machine code was a fairly simple process, just consult a table that has translations between whatever the names of your instructions are and the actual op-codes, translate your arguments to binary (from whatever you represented them in) and then write down that list of machine code instructions. You can then load that into the computer in whatever method is available, such as toggling in code from a front panel or making punch cards. Over time that practice became formalized, the instructions were given standardized names, etc. It was further expanded with new conventions, elements that didn't correspond 1:1 with instructions but didn't require a lot of work to translate. For example, a jump (goto) a label instead of a specific, hardcoded address. As you go through the program \"assembling\" it into machine code you will know where you are so what address in memory the label corresponds to will become evident at the time, and can be easily filled in.",
"You can then go one step up from there by actually storing the \"assembly code\" on a computer in a text file. You could write a program, and a not terribly complex one at that, which would read that text file and produce machine code output, that could be executed by the processor directly. Mostly what is being done is going line by line through the assembly code, looking up the names of the instruction in a look up table then also translating numbers from, say, hex encoded ascii digits into a raw binary representation, then combining that into a single machine code instruction.",
"Now you have the beginning of programming languages as we know them. The basic idea is that you have some specification or set of rules for how a language is supposed to work, what a higher level instruction in that language is supposed to \"do\" and this is married to a program that takes as input text files that are written in that programming language and produce as output executable machine code. Or, a program which \"interprets\" the code \"live\" treating the text based code as executable and executing instructions as it reads the code (performing different functions dynamically based on the code in the program at each subsequent line). Both kinds of programming languages have been around for a very long time.",
"Once you have one symbolic programming language it becomes easier to create higher level languages. A language such as C is in many ways not terribly more complex than assembly. C adds a lot of specific \"control flow structures\" such as if/then/else, for loops, and so forth. These are things that had been built up as conventions by assembly programmers (\"boilerplate code\", essentially), and under the hood they are implemented entirely with simple operations and patterned sequences of jumps in a sort of \"fill in the blanks\" sort of way. A programming language like C merely implements such a template for you, for example, code like this:",
"if (x == y) {\n a = 100;\n} else {\n b = 5;\n}\n",
"Would then get compiled into this sequence of instructions (written out in more human readable form so I don't lose anyone):",
"You can see that this is just a simple template. You could see how you could take the C code above and process it using some very simple rules to create assembly code and then you could assemble ",
" into machine code. Indeed, some compilers have worked that way, but once you have gone that far it's not difficult to go all the way and roll even the assembler functionality into the compiler.",
"From there it's simply a matter of building more and more sophisticated compilers capable of executing more complex code. More rules, more functions, more templates, and so forth. Increment by increment new features get added to languages and new languages are born. Compilers are usually written in other higher level languages but once you have a compiler you can then usually write a compiler for a language in itself, as indeed has been done for many languages.",
"There's a whole theory on compiler and language design and it can be pretty heady stuff. In broad strokes compilation typically converts a stream of characters in a text file into a sequence of \"symbols\" that are stored in a data structure, that data structure is then analyzed and processed by the compiler through multiple steps, producing other intermediate data structures as a result, ultimately resulting in a sequence of low level machine instructions that can be written out as the \"compiled\" program. Modern operating systems require executable programs to have a \"header\" containing information on how the program is to be loaded into memory, etc. and that too is produced and written out to disk by the compiler."
] |
[
"That’s one of the best explanations I’ve ever heard. I wish that had been in my “Intro to programming using C++” class."
] |
[
"Great answer overall, and this is really good advice:",
"Start from the bottom.",
"I'd like to add to this answer by going even further down to the bottom.",
"Processors execute \"machine code\", sequences of instructions and arguments that are encoded in binary and tell the processor what to do. ",
"What does that mean? What are \"instructions and arguments in binary\", at the electricity level?",
"An early processor from the 1970s like the ",
"Motorola 6800",
" has 8 important wires coming in to control it -- it's an \"8-bit processor\". If you put 5 volts into the second, third, and eighth ones (corresponding to binary code 10000110, note the counting goes right to left), you switch on an ",
"electronic circuit",
" that will capture the next set of voltages you send. This capture circuit is called an \"accumulator\", and the code to activate it is just one of many \"instructions\" the chip can do. The human name for 10000110 is \"LDA\", which stands for \"Load into accumulator A\", but that's just for our convenience, all the chip cares about is changing voltages on wires. ",
"If you then put 5 volts onto the first and second wires, the circuit captures the value \"00000011\" (the binary version of the number 3) into the accumulator. Next, suppose you send 5 volts into the third, fourth, and seventh wires (binary code 0100110, which humans call \"INC A\", for \"Increment accumulator A\". This triggers a ",
"different circuit",
", which changes the stored voltages around from 00000011 to 00000100, which is equal to 4.",
"Congratulations! You've just made the computer do 3+1 = 4. ",
"My explanation uses the right binary codes for the 6800 chip, but it skips a lot of important details (like clocks and addressing). Today's computers are vastly more complicated -- and I mean ",
" -- but work on the same basic principle."
] |
[
"Are there genetic adaptations/mutations that humans underwent tens of thousands of years ago that were necessary for survival then, but not now? If so, what are they?"
] |
[
false
] |
[deleted]
|
[
"Wisdom teeth might have been useful if you'd already lost a bunch of teeth-- but if you've still got all your teeth when the wisdom teeth come in, they can cause all sorts of havoc."
] |
[
"Lactase persistence",
" is a recent one. It was necessary for survival in cattle herding peoples, but probably isn't under strong selective pressure today.",
"There are also a number of autosomal recessive IQ-boosting genes that are no longer helpful for survival. Some are under slight negative selection because they cause diseases like ",
"torsion dystonia",
" when inherited from both parents:",
"The Hereditary Torsion Dystonias (Dystonia Musculorum Deformans): Geographical Distribution and IQ in Dominant and Recessive Forms",
"Data obtained on a group of patients with the autosomal recessive form of TD and their siblings indicate that the gene for recessive TD increases intelligence.",
"Superior intelligence in recessively inherited torsion dystonia",
"The mean I.Q. of the patients was 121 (range 104-170) and that of their controls was 111 (range 76-147). This difference is significant (p<0.03). These data suggest that the gene for torsion dystonia enhances I.Q.",
"The 7 repeat version of the DRD4 allele can cause ADHD. It's more common in indigenous populations that are, or recently were, hunter gatherers:",
"Dopamine receptor D4 allele distribution in Amerindians: a reflection of past behavior differences?",
"Mirror",
"Common traits among hunter-gatherers such as novelty-seeking temperament, hyperactivity, and impulsivity could have been important and advantageous in new environments during America's prehistoric colonization.",
"DRD4 VNTR polymorphism in Oceanic populations",
"The DRD4 7R allele has been reported to be associated with behavioral and psychiatric phenotypes (e.g. novelty seeking (Benjamin et al., 1996; Ebstein et al., 1996) and attention-deficit hyperactivity disorder (LaHoste et al., 1996; Faraone et al., 2001))."
] |
[
"Good eyesight?"
] |
[
"Does an alcohol swab on a public toilet seat improve anything aside from piece of mind?"
] |
[
false
] |
[deleted]
|
[
"Assuming you apply sufficient sterilizing solution AND let it sit for the amount of time necessary for it to sufficiently sterilize the surface, you can feasibly end up with a pretty close to sterile surface. This is in fact how we sterilize surfaces in the lab. 70% ethanol is one of the standards for this. Now, an alcohol wipe used on a toilet seat is an attempt to replicate this, but the results will be less than stellar. It will be 'cleaner' than before, but not by much. First off, the alcohol wipe isn't going to have enough solution in it to sufficiently cover the surface of the toilet seat AND it will evaporate before it's really had a chance to sufficiently sterilize. If it helps you feel better. Go for it. But know that it isn't really doing much."
] |
[
"I remember reading somewhere that 70% alcohol is used in place of something more pure because you need the remaining water content to help absorb the alcohol through cell walls. Do you know anything more about this?"
] |
[
"It's been too long since I learned about the specific mode of action, that I don't even feel comfortable making an educated guess. Perhaps someone with a better memory for that stuff than I will chime in."
] |
[
"Why do Special Relativity and General Relativity time dilations take the same form when put in terms of energy? Is there a deeper reason for this?"
] |
[
false
] |
Special Relativity Time Dilation T = T_0/(1- v / c ) Replacing E = 1/2 mv T = T_0/(1 - 2E/mc ) General Relativity Time Dilation T = T_0/(1 - 2GM/Rc ) Replacing E = -U = GMm/R T = T_0/(1 - 2E/mc ) Which is of the exact same form. Is this some freaky coincidence or is there a deeper reason for this connection?
|
[
"Coincidence. K = mv",
"/2 is not valid in relativity."
] |
[
"No, because dimensionless factors don't necessarily have to be constants. For example, relativistic equations abound with the Lorentz factor (1 / (1 - v",
"/c",
"))."
] |
[
"Gravity is caused by a gradient in time dilation. If you change the metric to change the time dilation factor, you'll also change the kinetic energy",
"This entire comment is nonsense."
] |
[
"Given thalidomide's useful applications, if the only side-effect is found in pregnant women why is it not still prescribed for men or women not having children?"
] |
[
false
] |
There are studies showing thalidomide reducing angiogenesis in cancer and other applications. It has been used in treating leprosy in India, Africa and recently in Brazil but resulting in the associated birth defects in newborns. But why can't it be prescribed just for men and then used more widely?
|
[
"Thalidomide is indeed still prescribable in the US, with several indications. Prescribers have to be part of a special program, counsel women of childbearing age (WGA) on contraception and emergency contraception, and help monitor them for signs of pregnancy.",
"There are a number of drugs problematic enough that prescribing authority requires registry of a physician. ",
"Xyrem (sodium oxybate) is a form of GHB, widely demonized as a \"date rape drug.\" GHB was explicitly made schedule I (no accepted medical use) by Congress. But the drug proved to be awfully useful for narcolepsy, so now an exception is made for the specific formulation of Xyrem. Docs have to sign up for a registry.",
"Vigabatrin is an anti-epileptic drug which has irreversible peripheral vision loss as an adverse effect. For most patients, some peripheral vision loss is expected, not just possible. For that reason and others, approval in the US took much longer than elsewhere. But it's a very useful drug in the treatment of infantile spasms/West syndrome in infants, and in the border marches of the US docs were sending parents across the line into Canada to get it. Now it's approved but prescribing physicians have to sign up for a registry.",
"Also many others."
] |
[
"Also many others.",
"Please post, this is interesting."
] |
[
"If I remember correctly, there was an issue with it switching isomer whilst in the body. I have no source for this though. Any one else?"
] |
[
"Is the coefficient of friction we use in the equation F=μN just a heuristic device of lower-level physics? There seems to be no practical way to predict the fricative force that will act on an object without already KNOWING it's μ. Can it be determined by its physical/chemical traits?"
] |
[
false
] |
So say you've got a simple situation with a block on an inclined plain. Is there a way to determine the force of friction that will be opposing the gravitational force both without measuring it and without knowing μ beforehand?
|
[
"You can derive the coefficient of friction by simulating the interactions of many individual atoms, like they've done in this paper: ",
"http://physics.aalto.fi/~asf/publications/10.1007_s40544-013-0021-3.pdf"
] |
[
"The coefficient of friction is dependent on area of contact and material properties like surface roughness and elastic modulus [and many others]. While you in theory could use the sum of all relevant properties to calculate the friction coefficient, it's much easier/simpler/faster to just measure it. There are also tables of already-measured values for common surfaces, which generally work well enough for most practical use.",
"Outside of getting a more accurate [albeit not very useful] coefficient value, I'm not sure what you hope to gain by this. What's the point of calculating it when it's faster/easier/simpler and less prone to mistakes?"
] |
[
"this is exactly what it is, but its on an even more complex level. Think about the interface of the components, on the nano scale these textural gradients are as mountains in proportion to the relative size of the molecules. We are able to approximate it much like trigonometry, functions at increasingly, arbitrarily high polynomial degrees tend to have only minor variances. A summation of the forces can be batch approximated much like you would calculate a mole of substance, collectively averaging out. For all intents and purposes of the abilities of our scientific measuring equipment we can end up with collective values of a similar and corresponding amount of certainty. This leaves our measurements accurate to their degree of capability to increasingly approximate systems of interaction at an increasingly more complex degree. Much like how your calculator screen ends after a certain number of digits. These decimal places are known. Like when you integrate and you end up with a C, constant value. Constants are only an approximation of complexity unmeasurable to our degree of certainty without knowing all dimensions of the initial conditions.",
"Do five year olds have a basic grounding in the calculus method? Maybe some of these here fancy mathematicians will come up with a better way..."
] |
[
"Is our sun orbiting something?"
] |
[
false
] |
As a follow up question I was wondering about G-Force. How come we don't experience it the same way if we are hurdling thru space at astronomical speed?
|
[
"Yes, we orbit the center of the Milky Way Galaxy. ",
"As for G-forces, these are caused by ",
" not by speed. For a test you can do at home, accelerate in your car really fast. You'll feel yourself be \"pushed\" into your seat. Then stay at whatever speed you are at. No matter how fast you are going you won't experience that force anymore. "
] |
[
"It's worth noting the sun (and almost all other stars in the galaxy) does not orbit the supermassive black hole. We orbit around the center of mass of the 500-700 million stars within our radius around the Milky Way, not the 1 million solar mass black hole which makes up a tiny percent of the total mass. ",
"Only a handful of stars, very close to the black hole, orbit it directly."
] |
[
"Hey thank you."
] |
[
"What do tumors and cancers actually do thats so deadly?"
] |
[
false
] |
What is different from like a cyst growing in the same place?
|
[
"A cyst is like a little sac of fluid. If it gets very large it might push on the tissues near it, but that's unlikely. In any case it's just a single, well-contained thing. If necessary it can be drained or surgically removed. ",
"Some cancers are benign, and act similarly. They stay in one spot. At worst they cause some problems in the immediate area. ",
"Malignant cancer is very different, in two ways. ",
"First, a malignant cancer tends to grow without limit. This causes major problems in most of your organs. A tumor in your lung can displace healthy lung tissue, impairing breathing. A tumor in your colon can grow into the internal space and obstruct your bowels. A tumor in your brain can slowly squash the rest of your brain against the sides of your skull.",
"The second major difference is that malignant cancer does not just stay in one spot. Cancer cells split off and drift through the bloodstream, eventually settling into some other organ, where they begin to multiply and grow new cancer. This is called ",
".",
"That's one of the things that causes danger even from cancers that may sound harmless. For example, melanoma is a kind of skin cancer. You may think that a growth on the skin isn't likely to interfere with anything life threatening. But if melanoma isn't treated early, its cells are likely to spread to places like the liver, lungs, or brain, causing new cancerous disease there. ",
"Metastasis is also one of the things that makes cancer so hard to treat. Even if you cut out all the cancer you can find in the original spot, there may be a few cells that have spread outside that region. You need to use more widespread treatments like chemotherapy or radiation to eliminate the stragglers, and if you don't get them all, there's always the chance for one to land in a favorable spot and start the problem over again."
] |
[
"Your cells die a while after they are created, this is a deliberate process that goes on constantly at different rates throughout your body. Cells have a sort of lifespan in which they are useful and will basically replace themselves and shut down, then be removed.\nCancer occurs when a cell stops functioning properly, usually due to DNA changes and no longer dies after it’s reached the end of its normal lifespan. It’s effectively a separate entity living inside your body.\nIf its DNA is damaged the right way, it will continue replicating without the earlier cells being removed and will grow and grow, with each cell drawing on the resources it needs to survive and replicate, competing with the normal body cells for resources at a greater and greater rate as it expands.\nEventually, it starts taking resources away from cells critical to bodily function, or consuming so much your body can’t feed the tumour as well as run itself, this is when your body begins to fail. Either wasting away or losing the function of vital organs.",
"A cyst can be thought of more in terms of pimples or boils, they’re a sort of bubble or sac of fluid that fill up, usually caused by infection. They’re a single bubble and, while they can lead to spreading infections or press on vital organs, they can just be lanced and drained in most cases. They’re not alive, they grow because fluid is added and they don’t spread like cancer.",
"Once lanced, cysts usually are just gone. If you remove a tumour, even if a few cells remain they can continue replicating and growing. Worst case, cells sort of come loose, get carried to other parts of your body and grow new tumours, the more tumours the worse the situation gets. Tumours also aren’t always little balls like cysts mostly are, they often follow the paths of easiest growth or most nutrients and can end up like long spiderweb looking tendrils, worming through lots of cells and organs that you need to survive, making them extremely hard to remove.",
"Since we don’t really understand the triggers cells use to self destruct, or the mechanisms by which these fail or are turned on, we currently don’t have a definite way to simply cure cancer, so we resort to aggressively killing the tumours with chemicals or radiation, both of which do a lot of damage to the whole body and often treatments are ended when the impact of treatment is bad enough that you’ll likely die either way, with cancer being the less strain."
] |
[
"Cancer cells do not have longer telomeres. They do not follow the normal processes of self-regulation, and that's what makes them cancerous in the first place. In many cases they have shorter telomeres than healthy cells, but even that is not always true."
] |
[
"[Human Body] What caused the sores on Mark Watney's body at the end of The Martian?"
] |
[
false
] | null |
[
"Hi CatatonicTaterTot 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.",
" ",
" "
] |
[
"Human Body "
] |
[
"'Human Body'"
] |
[
"What is the science behind CDC reducing quarantine to 5 days for covid?"
] |
[
false
] |
The CDC recently reduced quarantine guidelines stating: “The change is motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after. “. Sounds good but they don’t provide references. What is the actual evidence?
|
[
"Here is the science behind the decision:",
"\n",
"https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/scientific-brief-options-to-reduce-quarantine.html",
"In particular -",
"\n\"Wells et al (6) (preprint pending peer review) estimated the post-quarantine transmission risk (PQTR) for persons who have remained asymptomatic during quarantine based on RT-PCR testing performed within 24 hours prior to the date quarantine was discontinued. With average incubation periods of 5.2 days and 8.3 days, the PQTR fell below 1% after a 5-day or 7-day quarantine, respectively.\"",
"Additionally -",
"\n\"Reducing the length of quarantine will reduce the burden and may increase community compliance. This document lays out evidence to support two options to shorten the quarantine period. Shortening quarantine may increase willingness to adhere to public health recommendations but will require evaluation; not only in terms of compliance with quarantine and contact tracing activities, but also for any potential negative impacts such as post-quarantine transmission. Any option to shorten quarantine risks being less effective than the currently recommended 14-day quarantine. The variability of SARS-CoV-2 transmission observed to-date indicates that while a shorter quarantine substantially reduces secondary transmission risk, there may be settings (e.g., with high contact rates) where even a small risk of post-quarantine transmission could still result in substantial secondary clusters.\"",
"It seems like a combination of unlikely transmission for those who are asymptomatic (after 5 days) and decreasing the overall burden on people who have to quarantine or isolate. A lot of public health policy revolves around the principle - \"it is better to have a little than nothing at all\" IE people are more likely to quarantine if it's 5 days rather than forgo it completely if it's 10+."
] |
[
"The key is symptom free.",
"Much like when they said vaccinated could take off masks and the unvaccinated said they said no more masks.",
"Sadly they won't read the actual point of this...at least the people who don't want to anyway."
] |
[
"The key word ",
" is so vital but is being left off all the news article titles. It seems disingenuous and dangerous to me."
] |
[
"Why does fashion change?"
] |
[
false
] |
Why is it that certain fashions from the 70's and 80's are no longer in style today? Why do people stop seeing bell bottoms as the "cool thing" and now see them as tacky and quaint? Why is it when I look at pictures from the past I go what the hell where people thinking when it came to clothes?
|
[
"The (really famous) french sociologist ",
"Pierre Bourdie",
"u has a really interesting theory which applies on this subject but also far beyond.",
"His main idea is that every choice that we make as an individual is driven by our social environment. He drew this ",
"diagram",
" that exemplifies well this idea. Unfortunately that diagram is in French, i couldn't find an english version despie my best efforts. But you get the general idea.",
"So how does exactly your social environment influence your taste? According to Bourdieu, the main factor is the people's will to distinguish themselves from other people, to show that they are unique individuals with their own tastes and that those tastes are sophisticated. Your choices as a consumer reflect a symbolic hierarchy that is determined and maintained by the socially dominant in order to enforce their distance or distinction from other classes of society.",
"Now let's apply this to fashion. The socially dominant group (which is defined by the appropriation and monopolization of cultural, financial and social capital) starts to wear some type of clothes (let's say skinny jeans), listen to a certain kind of music, etc. They start to dress differently and listen to other groups of music than most people because they want to distinguish themselves form them. Then, other less socially dominant groups try to mimic their tastes in ordre to show to themselves and other groups that they're part of the socially dominant group. This goes on until a vast part of the society shares the taste for skinny jeans. So the socially dominant group has to switch his tastes in order to continue to show to everybody (including themselves) that they have more sophisticated and distinguished tastes than the rest of the society.",
".",
"For a qucik overview of Bourdieu's work on individual taste, check this ",
"article"
] |
[
"To be sure, the earliest punks in London (1975, before the term 'punk' was even known there) were seen as nothing but a bunch of bohemian weirdos. Rotten and his gang of street kids looked like recently released mental patients to most people. Nobody wanted to mimic them, not even the bourgeoisie that normally look to the artists for the raw material of distinction (as Bourdieu notes). Even several notable individuals from the New York scene (who viewed themselves as legitimate bohemes) who ventured over to London were put off by what they saw as a bunch of nasty, nihilistic little teenage ghouls.",
"It was the Londoners who ended up making a mass media spectacle out of it (starting with the Grundy Incident). It was seen as a threat in Britain (a classic moral panic, in fact) and as a joke in America, especially once the Sex Pistols fizzled out in San Francisco. Then a short while later you had 'New Wave', which was much more photogenic and amenable to the runway (and to High Street). At that point, bell bottoms, wide-collar paisley shirts, and coiffed 70s helmet hair were put to rest. ",
"The line between artists/hipsters who influence elite groups who then influence everyone else isn't always so straightforward."
] |
[
"Fashion usually is the way to look different and better than the average. When the average becomes like you, you have to move forward, as in different animal species."
] |
[
"How can lighting safely hit an airplane?"
] |
[
false
] |
There are many YouTube videos of airplanes being struck by lightning. I was wondering how that is possible without causing serious damage to the plane or the people on it?
|
[
"Lightening \"tries\" to find the easiest path to the ground. It is much easier for electricity to flow through metal than through air, so, when the lightening hits the plane, the current travels through the outer casing of the fuselage not through the air inside."
] |
[
"As you can see in ",
"this video",
", the lightning doesn't actually end at the plane, so the energy of the lightning doesn't dissipate into the plane. The electrical charge just moves trough the plane, in it's search for the route of least resistance. ",
"The amount of energy that is dissipated in an object depends on the resistance of the object. A tree has a high resistance, so if lightning strikes a tree, the tree absorbs a lot of the energy, leaving it exploded and burned. An outer shell of an airplane, however, is made out of metal, which has a low resistance. The airplane therefor absorbs just a small amount of energy (which is probably converted to heat), but most of the charge is just conducted."
] |
[
"According to Gauss' Law of electromagnetism, an electric field cannot penetrate a completely enclosing (perfect) conductor. And although the aluminum skin of an airplane is not an ideal conductor, it is pretty good. ",
"Any charge which might remain on the airplane (which doesn't continue to travel on with the lightning bolt) will become distributed evenly on the conductive surface, trying to maximize the distance between charges. "
] |
[
"What happens at the exact middle point between two black holes that are of equal strength?"
] |
[
false
] |
Is there a theory that explains this question? I was watching a video about black holes that orbit each other and started to wonder what would happen at the middle point of two equal mass/strength black holes?
|
[
"That depends on how close you are to either black hole, and how massive they are.",
"Tidal forces close to a black hole (and any particularly massive body) would cause an object near it to stretch because the gravitational field strength at the bottom of the object would be noticeably stronger than the strength at the top, so the bottom would accelerate quicker than the top (I'm sure it would be quite unpleasant). But for this to be noticeable across the width of a human (let alone the distance between two atoms), you'd either have to be very close or it would have to be very massive.",
"In the case you mentioned it really depends on how close the black holes are together and how massive each one is, but I think it would be possible for atoms to be pulled either side in certain circumstances."
] |
[
"A second grader asked Neil DeGrasse Tyson this question.",
"Video Here"
] |
[
"That doesn't answer my exact question but that was interesting to listen to."
] |
[
"Can Someone Explain 'Efficient' Burning to Me?"
] |
[
false
] |
I was talking to a friend of my brothers who works with polymers and to simplify the discussion completely, I asked what we should do with excess plastic and he said to efficiently burn it. He sort of explained that it means supplying more oxygen to bound with carbon but I'm still confused. What is left over after efficient burning? Since the carbon is taken out of a compound what is the ash? He also said that if you efficiently burn it, you can burn anything without producing harmful gases othe than co2. Why is this?
|
[
"The basic end product of combustion of organic material is nearly always carbon dioxide, but this relies on there being enough oxygen available. Gases like CO can form after incomplete combustion, or some kind of solid residue can be left behind. These compounds are often toxic, which is why burning plastic can be nasty if you don't know what you're doing. If you completely burn organic material, there will nearly always be no solid residue at all."
] |
[
"The ",
" PVC contains only carbon, hydrogen and chlorine. Complete combustion with oxygen will form carbon dioxide, water and hydrogen chloride (HCl gas)."
] |
[
"With efficient burning we mean that all the material is burned sp that one does not end up with unwanted chemicals.",
"For example if one was to burn Hydrogen gas(H2) EFFECTIVELY what happens is that the hydrogen reacts with the oxygen molecules(O2) in the air and forms water(HO2). Simply water, nothing else.\nThis will under normal circumstances never happen though, as you would have some material which will pollute the burning process.",
"When burning plastic which is basically semi random long strand molecules consisting of mainly hydrogen, carbon and oxygen.\nAs you see from the materials an efficient burning might preferably result in CO2 and water.\nBut in plastics(For example, PVC, or polyvinyl chloride) you also have small amounts of Chlorine which can form Chlorine gas, which is bas! Sulfur can lead to highly acidic compounds. Nitrogen reacting with the carbon can form CN gas which is or is part of Cyanide which is very toxic. CO or carbon monoxide, which is toxic, forms i there is not enough oxygen. And the list goes on!",
"Ash is the materials which aren´t reactive with air at 'normal' burning temperatures. Like heavy metals for example.",
"Pardon my english. I'm drunk.",
"Edit. CO"
] |
[
"Scientists: Do you have shaky hands? What do you do about it?"
] |
[
false
] |
This has been an issue for me for the past few years. I feel like my hands are much shakier than your average person. This is very scary, since my career is to basically work with very small components. I don't want to hit 35 years old and be unable to continue hands on research because of my hands. Does anyone else suffer from this problem. Am I just overreacting? Should I exercise my hands more? Is the problem just exaggerated since I work with tiny objects and tweezers all day? I would really like to know others experiences with shaky hands. edit: my grandmother, and great aunt both have an essential tremor.
|
[
"Where I'm from, P.I. in an academic setting means \"primary investigator\". We generally talk about P.I.s in the context of government grants, as in \"she is the P.I./primary on that grant\". "
] |
[
"Where I'm from, P.I. in an academic setting means \"primary investigator\". We generally talk about P.I.s in the context of government grants, as in \"she is the P.I./primary on that grant\". "
] |
[
"Yes, it's actually been a problem in my field of work. Nanotechnology does not go well with shaky gorilla hands.",
"You just have to move slowly and deliberately and be very, very careful. If it's really bad, maybe some occupational therapy."
] |
[
"Prosthetics: Can someone born without a limb (rather than losing it after birth) use advanced prosthetics controlled by nerves and neural pathways?"
] |
[
false
] |
I understand (or at least, I think I do to some degree) that if someone loses an arm, for example, cutting-edge prosthetics can utilize nerves and existing neural pathways to control the prosthetics. Let's say instead, however, that someone is born with an arm that stops short of the elbow due to a birth defect/genetic condition. At no point have they had an elbow, or forearm, hand... If he are she is born this way I presume that there is no neural pathways/nerves to dock onto. I am sure that technology will continue to advance so I guess I am not asking if it likely will ever be possible but rather if it is possible with existing tech and approaches. The inspiration for this question is the video that has made more than a few circulations around the internet: a video where a little boy (maybe a few years old) with arms that stopped just short of the elbow who was interacting with his newborn sibling. He utilizes his arms and mouth to pick up his sibling's pacifier and put it in her mouth. A very heart warming video. Many of the responses commented how jealous they were that he would grow up to have awesome android arms. But one comment asked whether it would be possible to have these and cited concerns that there might not be neural pathways to use them. Any thoughts? Thanks so much for the response everybody! This is my very first post to reddit after years of lurking... First, let me say that I was totally overselling my confidence when it comes to how much I understood about this subject at a base level. To clarify the question, I believe what I was picturing in my question was what is referred to as a myoelectric prosthetic. That seems to be the system of prosthesis that is most commonly featured in videos and articles. I will briefly read up on the basics of myoelectric systems before trying to read any more responses. While I am definitely interested in the use of neurons with prosthetics, the question is probably more appropriately: Can someone born without a limb as opposed to losing a limb later in life use myoelectric prosthetics? Why or Why not?
|
[
"This is a amazing question and one I cannot fully anwer. The sheer complexity of the nervous system is mind boggling. From my understanding you phrasing however is somewhat flawed. Prosthetics don't 'interface', for lack of a better word, with nerves. They instead use the output of said systems. You're nerves send a signal to your muscles and the muscle responds in a way it's biologically designed to. We can read that response and use it as input.",
"What is mystifying to a certain degree is that even though you would expect our nerves and muscles to be hard wired from brain to muscle this is actually not the case. Even though the nerves or wires run from A to B they don't seem to be hardset into performing a single function. The human body has adopted to be more flexible. ",
"In essence a baby is a prime example. They will hit themselves in the face trying to get their arm movements right. It's like a robot running through calibration to asses their range of freedom. Given enough time a adult could rework their nervous system into signaling a appendage to respond to their desires.",
"But to boil it down. Do people born without a arm lack the nerves to control a prosthetic? Biologically yes. Could they adapt to using a prosthetic arm? Yes, but it becomes harder with age.",
"Don't have the time to provide sources atm but I hope others will do so as well and challenge my views on this topic. It's interesting to think about."
] |
[
"The only point I would make in this, is that I think it partially depends on why they don’t have a limb, which could effect how the nerves form. That being said, I would guess there is a good chance the nerves would get pruned if they don’t have one at all, or even if born with a limb, but lose it very quickly "
] |
[
"The original answer is not correct. Modern prosthesis don't connect the nerves which are lost to the robotic mechanism. What is typically used is targeted muscle re-innervation which remaps a different area or nerve to control the robot. For instance, it can remap squeeze a muscle on your back to close fist. Most of the research I've read into that seems fairly easy to learn as long as you have any motor function in the area that you're remapping to. ",
"Sauce"
] |
[
"Does pregnancy affect lifespan in any mammalian species?"
] |
[
false
] |
Excluding mortality due to birth complications, does pregnancy itself affect lifespan? Have such effects been noted in mice or other mammals?
|
[
"Don't have any information on mammals, but if you remove the ovaries from anoles they survive much better. This may be due to the resources which would have gone to reproduction being available to maintain the lizards in higher condition.",
"EDIT: Source, a paper I read last week. The anoles were brown anoles, living in the wild."
] |
[
"I came across ",
"this",
" which addresses your question with humans (skip to the \"UPDATE\" about 1 screen in), though the answer seems to be: \"it depends\". ",
"If you have access to the American Journal of Human Biology, you can read more ",
"here",
".",
"In human females allocation of resources to support reproduction may cause their insufficient supply to other metabolic functions, resulting in compromised physiology, increased risks of diseases and, consequently, reduced lifespan. ",
" ",
"Reduced lifespan in women with high fertility may be undetectable due to methodological weaknesses of research or it may be truly absent, and its absence may be explained from biological principles. I will discuss the following reasons for a lack of the negative relationship, described in some demographic studies, between the number of children and lifespan in women: (1) Number of children is only a proxy of the total costs of reproduction and the cost of breastfeeding is often higher than the pregnancy cost but is often not taken into account. (2) Costs of reproduction can be interpreted in a meaningful way only when they are analyzed in relation to the overall energy budget of the woman. (3) Trade-offs between risks of different diseases due to reproduction yield different mortality predictions depending on the socio-economic status of the studied populations. (4) Costs of reproduction are related not only to having children but also to having grandchildren. Such intergenerational costs should be included in analysis of trade-offs between costs of reproduction and longevity."
] |
[
"interesting question...but can be logically reasoned out. The longer the pregnancy, the greater the amount of energy the parent must spend on the offspring in embryonic development. Longer pregnancy also means the size of the offspring will be larger, leading of course to a larger adult organism. Larger organisms in general have a lower metabolic rate than smaller animals due to surface area vs volume. Thus, in order to get the most return from the initial reproductive investment and pregnancy, it would be the most beneficial to prolong the lifespan of the offspring as long as possible, so that there can be a maximized time to continue the propagation of genes. "
] |
[
"Why does blowing at a candle/wind extinguish the flame?"
] |
[
false
] |
Shouldn't blowing increase the volume of oxygen that passes through the flame allowing it to burn brighter?
|
[
"You are removing the fuel. A candle flame consists of a pocket of vaporized fuel (wax) whose surface burns, fed by oxygen. When you blow out a candle you are blowing away that pocket of vaporized fuel before it has a chance to be replenished. You have blown out the candle. The candle remains hot enough for a while to continue issuing fuel vapor, but you have blown away the burning surface that previously provided enough heat to ignite the vapor. "
] |
[
"Depends on how hot, depends on how much, depends on how fast. If the air was as hot as the average temperature in the area surrounding the flame and slow enough that weird hydrodynamic effects don't become important, it would continue to burn. But at this point you're probably melting the candle itself with your magic air beam, and it's a moot point. "
] |
[
"So what if you blew hot sir onto it?"
] |
[
"I have electrical outlets in my tiny bathroom, how does the steam from every shower I take not create an \"electric mist\" and electrocute me?"
] |
[
false
] | null |
[
"Water vapor is pure water, which is actually an insulator. Water itself is not a conductor at all, but when it has impurities inside of it the impurities are what conducts the electricity.",
"Even if the water vapor did somehow have conductive properties it would take the path of least resistance, which is directly to ground, not through a human with very high resistive qualities. In addition to this it's now standard code that any electrical outlets near running water must be GFCI outlets instead of normal outlets. So even in the rare occasion that water did condense on the outlet or it came in contact with conductive steam, it would simply trigger the GFCI's safety precautions and short to ground.",
"Edit: I made some mistakes in my answer, read the guys below please."
] |
[
"You missed the point that water vapor/mist exists in the air as small 'droplets' that are separated by air. There is no unbroken path of water vapor from the socket through the air."
] |
[
"If I am not completely mistaken, the \"measuring\" in this case is not so much a fancy electronic device, as it is a coil wrapped around the live and neutral wires. Because the current is AC, this would induce a current in the coil unless the current in the two wires is precisely equal in magnitude (thus inducing currents in opposite direction that cancel). The coil wire is usually hooked up in such a way that even a small current will trip the breaker. ",
"Many devices also include a fuse or bimetallic strip to protect against excessive currents, but it is far less sensitive. "
] |
[
"Can black holes be accelerated by a gravitational field?"
] |
[
false
] |
I'm wondering if the mass inside a black hole can be attracted to another body, and so by extension if we theoretically have two black holes somewhat close to each other, is it possible for them to orbit each other?
|
[
"While not observed yet, this idea of binary black holes is definitely possible! There's nothing special about black holes disallowing them from being able to orbit one another. They're just large masses like other celestial objects that happen to have their mass contained in an infinitely small space. Binary black hole systems are theorized to be the sources of the largest gravitational waves. Due to these waves decaying their orbital energies, binary black holes eventually collide and merge into a larger black hole.",
"source ",
"1",
" ",
"2"
] |
[
"Yes on all counts - it's even possible for two black holes to merge.",
"At this point, I'd usually quote some examples of known objects, but hopefully you'll appreciate that it's actually quite difficult to find a black hole binary system! However, a similar class of objects are x-ray binaries, where we can see matter falling from a star onto a compact object, sometimes a black hole. The most famous example of those is probably ",
"Cygnus X-1",
", where a supergiant star and a black hole are orbiting each other - at a stretch, you might even say that the black hole orbits the star, as the star is actually the heavier object in the system!"
] |
[
"That's actually so cool! I realized that the answer to my other question was really obvious because if a black hole cannot be accelerated then it'd break Newton's Third Law, but it turns out that my additional question was more interesting. Thanks!"
] |
[
"Would it be possible to create an aerogel like substance out of caesin?"
] |
[
false
] |
You could follow to make the protein fluff. Then take the protein fluff and put it under a vacuum in a freezer to sublimate out the water.
|
[
"It would not have the structural properties of a aerogel, it would likely crumble."
] |
[
"No answer to your question, but I'm curious why you would want to. Any uses in mind for a substance like that?"
] |
[
"Low(ish) calorie protein bars."
] |
[
"Does the color of light affect plant growth?"
] |
[
false
] |
My wife and I were hiking and chatting the other day and both of us noticed how a weeping willow we'd passed appeared entirely yellow because of the yellow reflecting from the new spring buds. The branches, the trunk, and of course the buds all appeared to be in almost sepia tones. Chatting led to pondering, and now I'm wondering if the color of the light hitting a plant will have an effect on the plant's growth and, if so, whether variations in the color of flowers, buds, and leaves may in part be a method through which a plant can regulate the colors of light reflected and absorbed. I'm a lawyer, not a biologist, so I apologize if this question is idiotic. I have almost zero science background.
|
[
"Yes it does. Plants contain a chlorophyll which absorb all colors but mostly red and blue. Green is reflected thus we perceive the plant as green. This means that plants will not grow as much in green light but will in all other colors. That's about the extent of my knowledge of plant physiology though. I'm not sure exactly how red petals of a rose affect a plant. ",
"I think another interesting question is why do plants not take advantage of the green rays of sunlight but do take others. Anyone know this? Other than the answer \"evolution did it\""
] |
[
"There are different types of stars in the universe. Our star gives off lots of red light. Plants evolved on this planet, so naturally, they evolved to take advantage of the most numerous types of photons of light available to them. (You can think of a photon as a packet of light energy.) But blue photons are higher in energy than red ones. Therefore, if the plant can also absorbe blue photons, it will be able to do photosynthesis more efficiently. Green photons are not as numerous as red ones, nor as high energy as blue ones, so they have been \"ignored\" by plants.",
"\nI'm a retired AP Biology teacher. Scientific American published a great article: The Color of Plants on Other Worlds."
] |
[
"what? the spectrum of the sun peaks at a greenish wavelength."
] |
[
"Is light pure energy? Is there even any meaning to the phrase \"pure energy\"? Can energy ever exist by itself?"
] |
[
false
] |
I've heard people talk about photons as being little packets of "pure energy." I was under the impression that energy was simply a quantification of something's ability to do work. If this is the case, how could "the ability" to do something ever exist all by itself? Is it more accurate to say that energy can only ever be a property of something, and never a separate entity in and of itself?
|
[
" ",
" Light does have the advantage of being energy that is only in the form of momentum. E",
" - p",
" c",
" = m",
" c",
" . When you have no mass, then E=pc. But for everything else, its energy is both the energy of its motion (momentum) and the energy of its mass.",
"edit: Strikethrough, new text italicized."
] |
[
"Everything that exists is energy, in one sense or another."
] |
[
"Energy is not a physical construction of any kind. So it doesn't make sense to 'be' energy. Objects in the universe have a property that we call energy. Much like an apple can have the property of being red. "
] |
[
"How long would it take a closed, undisturbed Nalgene bottle with tap water to be 'in stasis' for eternity?"
] |
[
false
] |
I've started drinking water from an old-school nalgene bottle (original white and blue, not the fancy ones) lately and started wondering about how long it would take (cap screwed on) for the tap water to turn into something undrinkable and what that would turn into over a longer period of time. We started thinking of variables, such as the tap water source, the size of the bottle mouth, whether it was completely sealed, etc. and realized that AskScience might be better at thinking about the factors involved. I'm curious to see how long it would take for all of the organisms contained in the bottle to run out of a food source, die, be broken down by RNases and DNases, and for those -ases to stop working also. Will the bottle ever reach a state of stasis where it will stay that way (if still closed and undisturbed) for eternity? Will it take 50 years? 1000 years? What will the water be like then, in stasis? Will it become consumable again?
|
[
"I can't comment on the biological aspects of this, but as far as I know Nalgene bottles are made of polyethylene, which degrades over time. I would expect that on geological timescales your bottle will unseal, releasing all the water, and eventually become a puddle of smaller hydrocarbons."
] |
[
"That's not something I even considered. Thanks!"
] |
[
"That's not something I even considered. Thanks!"
] |
[
"Does magnitude of smell have a unit? Would the quantity be a vector, or would it be scalar?"
] |
[
false
] |
[deleted]
|
[
"The number of particles would affect potency, so maybe parts per billion or parts per trillion. However, concentration only helps compare identical compounds. A low cocentration of sulfur has a \"more powerful\" smell than a high concentration of nitrogen."
] |
[
"Sensitivity would also be extremely varied among species, even among individuals. Parts Per X seems to be the only objective form of measurement."
] |
[
"This is completely inappropriate for ",
"/r/AskScience",
"."
] |
[
"If a \"spaceship\" like one found in sci-fi movies were to actually be blown up in outer space, would it resemble anything at all like we see in movies?"
] |
[
false
] |
Often in movies, we see fireballs or flame and smoke. I'm pretty sure there would be no sound, as that is simple science. But the explosions... are they possible because of the oxygen that escapes at demolition? How would it look?
|
[
"Not for long!"
] |
[
"Not for long!"
] |
[
"We're a long way from militarized spaceships, so any discussion of this in detail is going to be tentative.",
"That said, if there are human crews on a ship and the ship gets exposed to vacuum (whether from rail gun fire or some more prosaic form of chemically powered artillery), the air will rush out and that will be the end without any spectacular results. ",
"The are some circumstances where it might be possible to have something more visually interesting happen. For example, it is possible that a ship could be using some ",
"hydrazine",
" compound for rocket fuel, in which case if something pierced the oxidizer tank and the hydrazine tank, some reaction between the two might occur. (This would work most likely for unsymmetrical dimethylhydrazine and nitrogen tetroxide which react on contact. However, for exactly their dangerous nature, they aren't used that frequently for rockets and are becoming less common. I suspect that a ship that would be regularly be shot at would use a less dangerous combination). ",
"Most plausible more exotic power sources would actually be safer. For example, a fusion reactor when damaged will simply shut down. This is a small part of why fusion power is considered to be much safer than fission power."
] |
[
"Since the Earth is not a perfect sphere is gravity different on different places? If so, would that mean time passes differently in those places as well?"
] |
[
false
] | null |
[
"Yes, on both counts. The effect has been measured, but it is tiny; see this ",
"newspaper article",
"."
] |
[
"Also, to be clear, the article is slightly misleading when it implies that you'd notice time passing at a different speed (if it wasn't different by trillionths of a second of course). Even if you spent a year somewhere where time passed half as fast (like on an extremely-fast-moving spaceship) it would still feel like a year anywhere else, since your brain would be moving through time more slowly as well. You'd just notice that two years had passed on Earth when you got back, and if you could somehow observe Earth from the spaceship everything would look like it was moving twice as fast."
] |
[
"The speed of the beam is necessarily measured from all inertial reference frames to be c, the same. If there seems like there'd be a difference in the speed of light to reconcile with this fact, what you'd find is the wavelength of the light contracts or expands. It propagates at c, though."
] |
[
"Why do our planets orbit without drifting closer to the sun?"
] |
[
false
] |
Did we just get really lucky with the way they lined up when caught in the sun’s orbit?
|
[
"There's a couple things at play here. ",
"First, planets weren't really captured by our Sun. The Sun and the planets all came from the same rotating disk of particles called a ",
"protoplanetary disk",
". Random, small clumps which happened to stick together, and over millions of years, those small clumps grew and grew into a star and the planets. That disk was already stable, and the gravitational potential of the final system (Sun + Planets + Asteroids) has a very similar distribution to the potential of that disk- so it makes sense that the final distribution is also stable. ",
"Secondly, orbits are relatively stable. Add a little energy to an orbit, or take a little away, and it changes the shape of the orbit, but it will stay in orbit."
] |
[
"The distance from the sun for all the planets does vary by a few million miles. But for the average distance to decrease the velocity of the planet would need to be decreased. And there's not a lot out in space to slow down a giant planet."
] |
[
"With only gravity and constant masses the orbits stay the same.",
"Satellites in low Earth orbit decrease their height over time because Earth's atmosphere provides a little bit of drag, but that doesn't apply to planets orbiting the Sun (the solar wind is completely negligible).",
"The Sun is losing mass, which makes the orbits increase their radius slightly over time. ",
"For Mercury this has been measured",
"."
] |
[
"How much pollution did nuclear weapon testing cause?"
] |
[
false
] |
There has been 2482 nuclear test bombs detonated, how much pollution has this caused, and how much of an impact has it had on the climate and atmosphere?
|
[
"Nuclear testing above ground spread radioactive fallout all over the world.",
"For the average individual, whether that individual is a plant or an animal or a person, the effects have been negligible.",
"At the population level however, ",
"it has become apparent that the radioactive fallout from nuclear testing has travelled up the food chain and ended up in people's bones and teeth, increasing the risk of cancer.",
" Not by much per individual, but when you are looking at millions and millions of people we're still talking about a large number of deaths.",
"Other studies have also been done",
" on \"Downwinders\", people who lived downwind from nuclear test sites in Nevada. Again, these studies have revealed a large number of cancer cases and quite a lot of cancer deaths and again, spread over a very large population meaning that the individual risk is low."
] |
[
"The 50s and 60s have been posited as a potential start to the potential Anthropocene epoch, partly due to the fact there is now a sedimental record of when nuclear testing began. 1952 is approximately the time this record became global rather han concentrated around test sites "
] |
[
"Wow, so if humans become extinct and in the distant future visiting aliens were to do earth samples they could see that someone developed nukes?"
] |
[
"Has there been any known examples of non-valence electrons being used in a chemical bond?"
] |
[
false
] | null |
[
"This doesn't really answer OP's question. In no case are carbon's inner shell electrons (those two in the 1s orbital) used in hybridisation or bonding. All four in the 2s and 2p orbitals (hybridise as appropriate) are the valence electrons.",
"OP: None that I'm aware of. The energy difference between valence and inner shell electrons tends to be quite massive, because you would have to break open a completed electron shell in order to get non-valence electrons involved in bonding. After all, one way to look at bonding is as a poor substitute for those valence electrons being in a filled shell.",
"These distinctions get a little hazy in heavy elements, so it's possible that such an example might be found there, but I doubt it."
] |
[
"To be a little pedantic, any electron involved in a chemical bond is by definition a valence electron, so in that sense your question doesn't really make sense - you can't have a non-valence electron in a bond. However, I think you're really asking whether there are examples of bonds formed using electrons not from the s or p orbitals, in which case the d orbitals can certainly be used, depending on the energetics."
] |
[
"I believe sulfur and phosphorus can form bonds using their d orbital electrons, this allows them to form five bonds simultaneously. I believe some halogens can also form 5 coordinate systems which implies that they're using their d orbitals as well. Thats it i think for organic atoms.\nAs for inorganic materials i believe that transition metals regularly react using their d orbitals, and can all kinds of interesting covalent bond structures. I think vanadium can have 11 or 12 bonds at once which definitely suggests its using something other than valence electrons."
] |
[
"Do people with advanced HIV have no allergies?"
] |
[
false
] |
[deleted]
|
[
"I would made an initial conjecture that by the time they lack sufficient CD4+ T cells to generate new IgE producing B cells that they are probably not long for this world anyway.",
"They'd have the same allergies that they've had prior to that point of course. Losing CD4+ T cells doesn't make your memory B cells that have already been selected, etc, etc disappear. Low helper T cell number would just make acquiring a new allergy difficult, but like I said, at that point they have more important things to worry about."
] |
[
"I don't understand what you are saying... I'm not a doctor"
] |
[
"I don't understand what you are saying... I'm not a doctor"
] |
[
"[Astrophysics] Can a black hole be ripped apart by going between two other black holes?"
] |
[
false
] |
Consider 3 black holes, or a black hole and 2 sufficiently massive bodies. Imagine two of the black holes are in some form of paired orbit, perhaps they were paired as a double star during their earlier lifetimes. The third black hole passes through what you might consider L1(Lagrangian 1). Half our wandering black hole will be closer to one of the paired black holes, and the other half of our wanderer will be closer to the other. If the pair of massive bodies has a sufficiently small distance between them, could the third wandering black hole be ripped apart when passing through the exact center. If it does get ripped apart, would gravitational forces distort space sufficiently for the contained matter to spill out? Or would the singularity become two black holes which each move toward their respective closer massive body? Or perhaps some other action would occur? Bonus points if you show your math. Thanks!
|
[
"Half our wandering black hole will be closer to one of the paired black holes, and the other half of our wanderer will be closer to the other. If the pair of massive bodies has a sufficiently small distance between them, could the third wandering black hole be ripped apart when passing through the exact center. If it does get ripped apart, would gravitational forces distort space sufficiently for the contained matter to spill out? Or would the singularity become two black holes which each move toward their respective closer massive body?",
"First off, you can't break apart a black hole.",
"Second, you're making some mistakes here-- if you put a point mass (a black hole is pretty much a perfect point mass) precisely between two equal point masses, it will feel no force. Black holes don't have halves, all the mass is at the center.",
"If you ",
" have two equal-mass black holes orbiting each other with a third in the center of their orbit, they would inspiral and all the black holes would merge into one (although if there were the right perturbations to the system, one of the black holes could get kicked out of the system in 3-body interaction)."
] |
[
"Our current understanding of black holes forbids them breaking apart again once they have formed. Imagine that you could, and a singularity has just split apart into two singularities that are currently a very short distance from each other. Both singularities are almost certainly well within each others' event horizons, which means they must necessarily move towards each other. There's no way you can get them far enough apart to have two distinct event horizons."
] |
[
"Yeah, the point mass problem is a major issue. Thanks for the solid analysis. I suppose this does set up a potential experiment to see if a black hole truly acts as a point mass. Thanks for the solid analysis. "
] |
[
"What determined the size and shape of the tectonic plates?"
] |
[
false
] |
[deleted]
|
[
"Our current best theory for the mechanics of plate tectonics is that it's driven by convection cells within the mantle: Hot rock and magma rises up through the mantle to the boundary of the crust, where some of it breaks through to form new oceanic crust in mid-ocean rifts, but much also moves along the bottom of the crust, and the force from friction helps the plate move. Eventually this rock cools and falls back into the mantle, and this helps pull down subducting ocean crust. This massive, slow-moving convection cell works well enough until continents collide. Continental crust does not subduct and can only be compressed so far, so eventually the plate stops moving and the convection cell breaks down. But the heat from the Earth's interior has to get out somehow, so eventually it breaks through even the thick continental crust and forms a rift zone. The continent is broken apart and a new ocean is formed with a rift running down it's center, previously-formed oceanic crust subducts on the other side of the splitting plates, and a new convection cell is formed. Why these rifts form exactly where they do is probably due to the specific fluid dynamics of the mantle at the time, which are hard to reconstruct or predict."
] |
[
"If I understand you correctly, the boundaries between different continental plates are formed due to many different variables (temperature, fluid dynamics, heat and pressure resistance of the rock and magma, preexisting motion, etc), and that's why they are unpredictable and inexplainable?",
"Follow up questions: in the past (geological time, of course) there used to be different plate boundaries? Like, the african plate didn't exist, instead different plates in the area it's currently in with different boundaries?",
"For example, Hawaii is created by a hotspot. Is it possible that there could have been a large schism in the now-Pacific plate (creating two smaller plates) that fused together over millions of years into the plate we know and love today?"
] |
[
"Plates change all the time (by geological standards) but the modern-day continents have pretty long histories. The continents are formed around cratons, billions-years old sections of tough crust. North America is formed around a particular large one so has existed in a more-or-less recognizable form for at least 600 million years, but the other continents have multiple cratons with independent histories.",
"The same can't be said of Ocean plates; it's rare to find oceanic crust over 100 million years old, because when ocean plates collide (or when ocean hits a continent) one plate subducts until it's eaten up. So no, the Pacific was never split; the Hawaii hotspot is just a random fluke."
] |
[
"How can NaALO2 (Sodium Aluminate) possibly exist?"
] |
[
false
] |
Metals have a tendency to always loose electrons, right? they have less electrons in their outermost shells than there are needed to fill it's outermost shell completely. How the hell is Aluminum borrowing electrons from Sodium? It's a metal. It makes it highly unstable. And if not, then what is going on? Please explain in detail. It even seems to be forming a covalent bond but metals don't form covalent bonds. P.S.: I am a 10th grade student and am struggling to learn about science. Please don't shout at me.
|
[
"The aluminum is in a positive oxidation state (+3) here as well. As a simplification, think of the compound as a salt of the positive sodium ion (Na+) and the negative aluminate ion (AlO2-), in which there are basically covalent bonds between Al and the two Os. (In practice, the chemistry of Al is super-complicated and \"NaAlO2\" is probably a bunch of structures that average out to that formula.)",
"Similarly with other salts of metal-based ions, including common ones like KMnO4, Na2Cr2O7, K3Fe(CN)6, Na2WO4, etc. The anions here consist of a central metal ion effectively covalently bonded to other atoms. "
] |
[
"so Al is forming a covalent bond? Is this possible? and if it is, then whom is Na bonded with?"
] |
[
"It doesn't really answer your question, but bonding is more of a spectrum with ionic at one end and covalent at the other. Aluminium is a strange element as it kind of lies in the middle, it's bonding could be classed as covalent (in AlCl3 for example) or ionic (like in alumina)."
] |
[
"Has light always been present in the universe? If not, when did the first light emitting object form?"
] |
[
false
] | null |
[
"Light has been present since at least a small fraction of a second after the Big Bang. However, for the first 380,000 years thereafter, light would bounce around from atom to atom, never travelling very far before hitting the next one, so it wasn't for 380,000 years that the Universe became transparent and light could travel through. That primordial light is what we now see as the cosmic microwave background."
] |
[
"Jesus. That's the second dumb mistake I made in that post. Yes, I meant transparent (and have edited it). Thanks. I posted that literally right after waking up, which I guess is telling me I should have a cup of coffee before posting here :)"
] |
[
"Yep. Typo corrected. Thanks."
] |
[
"At what percentage of alcohol, would the hydrating effects of water and the dehydrating effects of alcohol cancel each other out?"
] |
[
false
] |
Say I have a drink that is ethanol and water, like a watered down vodka. Presumably, the water in the drink would hydrate me, and the alcohol from the drink would dehydrate me. At which ratio would the hydrating/dehydrating effects cancel each other out? Was the wine/beer of the past weak enough so that people didn't need to supplement it with water when wine/beer was the standard drink?
|
[
"This is going to be a pretty difficult question to out and out answer, as many things beyond just what % alcohol the H2O/EtOH mixture you are drinking happens to be. Your kidneys are dealing with a lot of filtration of various electrolytes and metabolic byproducts, and the whole process is affected by a complex neuroendocrine balance on top of that. So the degree to which your kidneys are excreting Na",
" for example, will affect its ability to hold on to free water. The diuretic effect of alcohol, I believe, is a Loop of Henle effect (LoH is where much of the free water excretion/reabsorption happens). EtOH also affects things like vasopressin levels which tells the kidney to hang on to more free water. The overall balance of effect will get pretty complicated, and I doubt there is a \"break point\" where you will become dehydrated if you only drank 2.3% ABV beer, for example.",
"EDIT: Another \"for example\" thought I just had...Let's say you only drank good old fashion water and no alcohol. This wreaks havoc on the body (for a bit different reasons) as well, as your kidneys eventually lose the ability to keep up with the free water excretion. The dangerous result is that your blood's sodium concentration goes down. This disease is called psychogenic polydipsia, and it's not exactly a dehydration state per say. The other related disease is called beer potomania, but this also is essentially a malnourished state and not really a dehydration state. Rather your kidneys don't have enough \"stuff\" to excrete to get rid of free water."
] |
[
"People have died from drinking as little as 1-1.5 gallons in ~1 hour. It's actually not too difficult to die from upsetting the electrolyte balance in your brain."
] |
[
"So how much water is too much, on average?"
] |
[
"If observing a quantum particle causes its wave function collapse, how is it possible for us to know what the wave function is?"
] |
[
false
] |
So my last question asked about how the function f(x) changes before and after observing a quantum particle, but that brought me to wonder how we even formulate the equation for what the initial wave function of a given particle looks like if we can never observe it in its natural state. I'm guessing it's some sort of derivation/integration of the resulting dirac delta function?
|
[
"If you just have a single copy of the system in question, then in general it is impossible to reconstruct the wavefunction that it is currently in. ",
"If you have several copies, then you can make several measurements. In quantum mechanics a measurement corresponds to a projection in the sense that the expectation value of a binary measurement corresponds is equal to the projection of the original state onto the state for which you measuring.",
"Just as you use several projections in a tomography to reconstruct a 3D distribution, you can use the projections that correspond to your measurements to reconstruct the original state of the quantum system, which lives in a (potentially high-dimensional) complex vector space instead of a real 3D space, but mathematically there is no fundamental difference between these two cases.",
"The process of reconstructing the original state from several measurements is known as ",
"quantum state tomography",
" because of this analogy. How the reconstruction will actually look like depends a lot of the quantum system in question, especially which kind of degree of freedom you are interested in and even for a given system there are different techniques with different advantages and disadvantages.",
"edit: It's easy to see in the simplest case of a two-dimensional quantum system (an example would be a spin 1/2 particle). It's state lives in a 2D complex vector space, but can also be visualized in a 3D real space as in ",
"this picture",
". You cannot measure the state directly, but you can measure the projections onto x, y and z axis which correspond to the expectation value for three different measurements. If you know all the projections, than of course you can reconstruct what the original state was."
] |
[
"take a look at this for instance ",
"http://physicsworld.com/cws/article/news/2013/may/23/quantum-microscope-peers-into-the-hydrogen-atom",
" "
] |
[
"You're right that we can't really know the initial state before measurement, except if we had many copies of the same state. But you do know the resulting state once you've measured it, and then you can plug that state into the Schrödinger equation to see how it will change over time to predict subsequent measurement results. There are also thermodynamic reasons for expecting most systems to be near their ground state at low temperature, so often it's assumed that the initial state before interacting will be the ground state. "
] |
[
"Is there an upper bound to the EM spectrum?"
] |
[
true
] |
[deleted]
|
[
"Current theories normally allow for photons with arbitariliy high energies. Issues such as pair production of massive particles as mentioned in other responces will limit the energy of photons we ever see. Since very high energy photons will very likely produce massive particles. However as far as current theories go, I am unware of any upperbound on photon energy but you would need to come up with some sort of process which could produce such energies.",
"However at some scale our current theory probably won't work anymore. We don't know what physics looks like at extremely high energy. For example you can not really use quantum mechanics to say things about stuff smaller than the planck length, so a photon whose wavelength was smaller than the planck lenght might not make any sense. ",
"So a photon with more than 10 Gigajoules may not be possible, but we don't have any idea what physics will look like at that scale."
] |
[
"Essentially no. Photons can have arbitarilly small energies. At least with current theories. This actually causes lots of calculational difficulties for certain problems.",
"There may be some argument that if the universe has a finite size, then the lowest possible energy a photon could have would be one with wavelenght equal to the size of the universe. I am not sure that would even need to be true, but even if it were it would be so increadibly small it could not have any noticible effect and would never be able to be detected."
] |
[
"No, this isn't correct. Pair production can occur, but only in the presence of an electric field. Photons are perfectly capable of existing at energies greater than 2 x electron mass (the threshold for pair production) if there is nothing to interact with. And pair production itself is a stochastic interaction, and isn't guaranteed to occur even if the photon passes through an object."
] |
[
"How can Burning wood (carbon) generate UV radiation?"
] |
[
false
] | null |
[
"Note that your blackbody radiation plot is log scale and therefore has to be cut off at some place on the y-axis. ",
" temperature blackbody will emit ",
" UV radiation. "
] |
[
"Do you expect a lot of UV for some reason?",
"The thermal emission will contain tiny amounts of UV. In principle chemical reactions can directly lead to UV emissions as well but I'm not aware of specific reactions that would occur in a wood fire."
] |
[
"The hydrogen part of the burning wood emits UV. Some ",
"fire sensors",
" specifically detect this UV.",
"Edit for the neg rater:",
"http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Analytical%20Documents/FGD_MAN_UVS-H2_Hydrogen_Flame_Detector.pdf",
"The UVS-H2 is a smart, stand alone fire detector. The detector is specially designed to respond to UV radiation emitted by Hydrogen (H2) fires as well as range of fires including ",
" and metal based fires. ",
"Wood: ",
"https://en.wikipedia.org/wiki/Wood#Structure",
" ",
"Cellulose: ",
"https://en.wikipedia.org/wiki/Cellulose",
"Cellulose is an organic compound with the formula (C6H10O5)n",
"Lots of hydrogen in it."
] |
[
"Who is moving compared to who based on inertial frames and time dilation?"
] |
[
false
] | null |
[
"Each twin observes the other twin to be aging slower, because each twin is at rest in their own rest frame and it's the other twin that is moving - hence the \"paradox\" part of the twin paradox. If you change the speed of one twin or the other, you're introducing acceleration which breaks the symmetry in order to match the rate of time passing between the two. You will observe identical results in that the twin being accelerated will have experienced less time - key word being ",
".",
"That's also the reason there will be no such thing as \"slowest moving matter\", because all movement is relative."
] |
[
"Thanks for the response. According to what I have read in literature, the accelerated twin will age slower, and upon return and slow down to his siblings frame he will still stay physically younger as time did tick past slower in the accelerated frame. \nThe difference being is that if we accelerate the twin at rest to the frame of the already accelerated twin, he would start aging slower as opposed to if we slow down the accelerated twin, who will age faster compared to how he was while travelling at high speed. So in other words there seems to be a difference in the end result depending which one is accelerated/decelerated compared to the other. From this I still feel that further conclusions can be derived."
] |
[
"The difference being is that if we accelerate the twin at rest to the frame of the already accelerated twin, he would start aging slower as opposed to if we slow down the accelerated twin, who will age faster compared to how he was while travelling at high speed.",
"No no. As I said before, movement is relative. There is no absolute, objective measure of speed, and therefore no absolute measure of time dilation. In other words, there isn't a speed you can point to and declare one twin to be aging faster than the other.",
"As you stated before, let's say Twin A is on Earth, and Twin B is on a rocket. In the reference frame of Twin A, Twin B is the only one in motion. Twin A observes Twin B to be aging slower. Likewise, in the reference frame of Twin B, Twin A is the one moving, therefore Twin B observes Twin A to be aging slower. Hence the paradox.",
"You seem to be making a distinction between \"slowing down\" and \"speeding up\" - there is no difference. If neither twin is accelerated, both of their observations are correct - they each see the other age slower. If any one is accelerated, ",
".",
"All you need to do is look at this from the two reference frames - especially in your proposal of having the two twins being the only things in the universe. How do you distinguish \"speeding up\" and \"slowing down\"? You simply cannot. Acceleration is acceleration."
] |
[
"AskScience AMA Series: We study neutrinos made on earth and in space, hoping to discover brand-new particles and learn more about the mysteries of dark matter, dark radiation, and the evolution of the universe. Ask us anything!"
] |
[
false
] |
Neutrinos are one of the most exciting topics in particle physics—but also among the least understood. They are the most abundant particle of matter in the universe, but have vanishingly small masses and rarely cause a change in anything they pass through. They spontaneously change from one type to another as they travel, a phenomenon whose discovery was awarded the 2015 Nobel Prize for Physics. Their properties could hold the key to solving some of the greatest mysteries in physics, and scientists around the world are racing to pin them down. During a , scientists will discuss the hunt for a “sterile” neutrino beyond the three types that are known. The hunt is on using neutrinos from nuclear reactors, neutrinos from cosmic accelerators, and neutrinos from man-made particle accelerators such as the Fermilab complex in Batavia, Ill. Finding this long-theorized particle could shed light on the existence of mysterious dark matter and dark radiation and how they affect the formation of the cosmos, and show us where gaps exist in our current understanding of the particles and forces that compose our world. This AMA is facilitated by the American Association for the Advancement of Science ( ) as part of their , IFIC/CSIC and University of Valencia, Paterna, Spain , scientist at Fermilab, Batavia, Ill. , scientist at Lawrence Berkeley National Laboratory, professor of physics at the University of California, Berkeley, and co-spokesperson for the Daya Bay neutrino experiment in China , Communications Director, Fermilab
|
[
"How exactly can neutrinos shed light on the nature of dark matter? Is there any hypothesis that scientists want to test regarding the connection between the two, or is the research more exploratory at this stage? "
] |
[
"Olga Mena Requejo (OMR) and Katie Yurkewicz (KY): Thanks for your question! It turns out that all neutrinos are a form of dark matter. The three neutrinos we know exist and have been already discovered are hot dark matter particles. We call it hot dark matter because they have tiny masses. On the other hand, sterile neutrinos (a fourth theorized type we haven't yet discovered) may be an additional component of dark matter. There are many other proposed components of dark matter, which are being searched for in many other ways. "
] |
[
"KY: Great question, and one that we are all asked whenever we venture outside the scientific world. I like to answer this in three parts.",
"1) We are making these measurements, and hopefully these breakthroughs, nor for ourselves but for our grandchildren's grandchildren. We have no idea right now what we could eventually use a sterile neutrino (or a Higgs boson, or a gravitational wave) for. But based on the last hundred-plus years of scientific investigation, it has been shown over and over again that discoveries that were initially thought to be useless turned out to have a huge effect on technological and societal development. The discovery of the electron, of electromagnetism, of relativity, all had completely unknown uses at the time but now power our lives.",
"To put it another way, asking us in 2015 what we could do with sterile neutrinos would be like asking someone in the late 1800s (when the electron was discovered) to predict iPhones.",
"2) Pushing the boundaries of scientific discovery forces us to push the boundaries of technology, and these advances often make their way into other areas of society. Particle accelerators were pioneered in the 20th century for nuclear and particle physics. Today more than 30,000 particle accelerators are at work all around the world, and the vast majority are not used for scientific discovery. They are used in industrial processes like ink coatings, heat-shrink tubing and electron-beam welding, and for medicine for sterilization and cancer treatment.",
"3) The quest for discoveries about the fundamental underpinnings of our universe inspire many young (and older!) people to learn more about science and become scientifically literate. This not only helps build the technologically advanced workforce we will need for the next century, but also helps educate everyone about the process of science and how science works. Our society has become so dependent on science and technology that I believe it's absolutely imperative that everyone know enough about the scientific process to be able to make sound decisions to leave the best possible world for future generations."
] |
[
"Just found out there is an ongoing lawsuit in my town because of Benzene pollution. Many people attributing it to their illnesses/cancer. What is the radius and exposure time to be seriously affected by this? (Links enclosed)"
] |
[
false
] |
Here is a link to the map showing the pollution (Zip code 14150): Here is a link to the article about the pollution: I don't really want to reveal where exactly I live on the internet, but if anyone can shed some light on what areas are unsafe to live in and for how long a period of time. My girlfriend and I have lived in Tonawanda for the past year and plan to for one more year at least for financial reasons...but our lease is up in February and we will move if we are in danger of experiencing negative affects of this pollution. Thanks for the help
|
[
"Benzene toxicity usually occurs through inhalation. You would need to know the levels of benzene are in your local area to make any estimate of toxic effects. Just as a general rule, you would be better off higher up (upper levels of a multi-story building, or living on a hill) than lower. Since benzene is heavier than air.",
"Just for reference, typical levels are about 2-3 parts per billion inside a house. In high vehicle traffic areas, you get levels of like 10-15 parts per billion. These numbers are from the ",
"NIEHS Report on Carcinogens",
"."
] |
[
"Very helpful, thank you. Who would I contact to find out Benzene levels in my particular neighborhood? Or I might look into that bucket test the people in that article conducted."
] |
[
"I spent a little time digging, and am having trouble finding any legitimate concentration values for benzene in your area. But based on restrictions put on coke manufacturers in the past few decades, and an already large dip in monitored benzene levels from even 2007, you should be fine. ",
"If you feel comfortable, you could PM me a bit more specific area (e.g. East of 64, west of Kenmore Dr.), and I'll do my best to give you some quantitative estimates. But assuming you two are healthy adults, and you do not have any daily, direct contact with benzene, (like working at the coke factory), I would not worry. "
] |
[
"Why do some people get headaches after drinking draught beer?"
] |
[
false
] |
I work in a restaurant and often people order a bottle over a draught that's on special and claim the reason is that draught beer gives them a headache. I've been surprised by how often I've heard this. Is there any scientific reasoning behind why this would happen?
|
[
"Cheese has never been demonstrated to cause, trigger, or promote headache:",
"Holzhammer J, Wöber C. Schmerz. Alimentary trigger factors that provoke migraine and tension-type headache. 2006 Apr;20(2):151-9.",
"\"Controlled trials suggest that alcohol and caffeine withdrawal are the most important nutritional precipitating factors of migraine and TTH. ... A selective sensitivity to red wine has been shown in some patients, ...scientific evidence for cheese as a precipitating factor is lacking.\"",
"[me again] One theory was that tyramine in red wine is the culprit. But red wine contains hundreds of other substances. The results of this 1988 study are not consistent with the theory that tyramine is the constituent of red wine that promotes migraines:",
"Littlewood JT, et al. Red wine as a cause of migraine. Lancet. 1988 Mar 12;1(8585):558-9.",
"This study serendipitously discovered that grape juice induces CYP1A2:",
"Xiao Dong S, et al. Possible enhancement of the first-pass metabolism of phenacetin by ingestion of grape juice in Chinese subjects. Br J Clin Pharmacol. 1999 Oct;48(4):638-40.",
"[me] So there's a possible mechanism by which red wine promotes headache: an unidentified constituent of the grape juice in red wine induces CYP1A2, thereby increasing the rate of caffeine metabolism, thereby making caffeine withdrawal headache more likely to occur.",
"(CYP1A2 is short for cytochrome P-450, the gene that expresses phenacetin O-dealkylase, often referred to as CYP1A2 or the CYP1A2 enzyme, an hepatic [liver] enzyme that dismantles many substances including caffeine.)"
] |
[
"Cheese has never been demonstrated to cause, trigger, or promote headache:",
"Holzhammer J, Wöber C. Schmerz. Alimentary trigger factors that provoke migraine and tension-type headache. 2006 Apr;20(2):151-9.",
"\"Controlled trials suggest that alcohol and caffeine withdrawal are the most important nutritional precipitating factors of migraine and TTH. ... A selective sensitivity to red wine has been shown in some patients, ...scientific evidence for cheese as a precipitating factor is lacking.\"",
"[me again] One theory was that tyramine in red wine is the culprit. But red wine contains hundreds of other substances. The results of this 1988 study are not consistent with the theory that tyramine is the constituent of red wine that promotes migraines:",
"Littlewood JT, et al. Red wine as a cause of migraine. Lancet. 1988 Mar 12;1(8585):558-9.",
"This study serendipitously discovered that grape juice induces CYP1A2:",
"Xiao Dong S, et al. Possible enhancement of the first-pass metabolism of phenacetin by ingestion of grape juice in Chinese subjects. Br J Clin Pharmacol. 1999 Oct;48(4):638-40.",
"[me] So there's a possible mechanism by which red wine promotes headache: an unidentified constituent of the grape juice in red wine induces CYP1A2, thereby increasing the rate of caffeine metabolism, thereby making caffeine withdrawal headache more likely to occur.",
"(CYP1A2 is short for cytochrome P-450, the gene that expresses phenacetin O-dealkylase, often referred to as CYP1A2 or the CYP1A2 enzyme, an hepatic [liver] enzyme that dismantles many substances including caffeine.)"
] |
[
"Tyramine indirectly causes a pressor response when it's taken into nerve terminals and causes the release of catecholamines. In most situations, 1) monoamine oxidase can metabolize tyramine relatively quickly before this sympathomimetic action can occur, and 2) the amount of tyramine in food is not nearly enough to trigger significant dopamine/norepinephrine release.",
"However, when you're on a MAO inhibitor, and you eat foods high in tyramine (like aged Stilton cheese, for example), you can trigger a hypertensive crisis with resulting severe headache. This was in fact the reason tyramine's sympathomimetic effects were discovered - a neurologist's wife was on a MAOI and got headaches whenever she ate cheese. So tyramine can promote headaches in this specific setting.",
"Whether tyramine triggers chronic or acute migraines in the general population is not well established. It's entirely possible that you have a subset of the population who have lower MAO activity, or lesser expression, or different kinetics for MAOs. This specific population could develop hypertensive crises from too much tyramine. I agree with you that eating cheese is highly unlikely to be the cause of all or even most migraines or headaches.",
"A third explanation for headaches after alcohol consumption is the ",
"alcohol flush reaction",
", due to a defect in acetaldehyde dehydrogenase."
] |
[
"What does it mean when science articles say super high-frequency graphene CPU's do not have the \"required on/off ratio\" for discrete calculations? Link to article in post."
] |
[
false
] |
I was reading when I came across this interesting but jargon-filled article: The part that was very interesting to me was the 7th paragraph, Graphene transistors may be able compute faster than conventional transistors, but are not ideal for PCs yet, Lin said. Because of the lack of energy gap in natural graphene, graphene transistors do not possess the on-off ratio required for digital switching operations, which makes conventional processors better at processing discrete digital signals. And I became very curious as to exactly what that meant and why it was so! I interpreted it to mean the transistors used could not "isolate" charge very well, so for a given cycle the CPU required some kind of majority of transistors to be one charge, and some minority to be the other, and that if not some kind of capacitance would take effect between them and cause malfunctions. I know there must be some physicists, EEs, or material science types in here who can help me better understand the what and why of this! Thanks guys!
|
[
"I'm sure the guy who made the comment knew what he was trying to say but maybe the journalist 'simplified'. First, IBM developed an experimental transistor which sets a speed record (this is probably a better article ",
"http://physicsworld.com/cws/article/news/2011/apr/07/graphene-transistor-shines-on-diamond-like-substrate",
" ) This particular development refers to a single transistor - not an Integrated Circuit and not a computer of any kind. They almost certainly tested the transistor by making an oscillator, which is an analog circuit.",
"Transistors can be optimized as 'signal' (good for analog) or 'switching' (good for digital). If I recall correctly, signal transistors have better linear characteristics while switching transistors tend to be better switching 'on' and 'off'. So, this particular transistor is not a good switch and they would likely have to modify its characteristics to improve its switching function before applying it to computing uses.",
"That being said, they have a transistor, not an IC nor a CPU. You can make a CPU from individual switching (or even signal) transistors but because of wiring and parasitic effective, even with these new transistors it would probably run slower than a $3 Atom processor. ",
"IBM has been working on Graphine ICs, but even these are very simple and we are years away from seeing a Graphine CPU of any type."
] |
[
"Very interesting, thanks! I've studied some basic computer engineering stuff, but never did I come across an analog transistor before, kind of a weird idea to me because I have no idea how they're used. But you've basically answered my question! Now I have a lot of stuff to google."
] |
[
"I did not articulate the concept of signal vs switching transistor well but it is worth noting that the world is, essentially, analog. If I could insert a graph, I'd show that the input/output ramp of a signal transistor tends to be a gentle ramp while the same graph for a switching transistor tends to be a steep ramp. Think of a 'twitchy' volume control (switching) or a nice smooth volume one (signal)."
] |
[
"If general relativity, or the physics of the Big, and quantum theory, or the physics of the Small, cannot be reconciled - where's the line between them?"
] |
[
false
] |
Shouldn't there be some point at which they overlap? Or is there a gap between them? Does general relativity apply, for example, to the cellular level? Or the molecular level?
|
[
"In answering a question like this, it is crucial to distinguish between the formalism of the theory (the equations and how they are used to make predictions) and the behavior of the universe that we model with the theory. We believe that the universe, at all scales, follows all the laws all the time. We believe gravity as described by GR affects everything, and we believe that all matter behaves as described by quantum theory.",
"The conflict between the two is in the realm of the mathematical tools we use to model and make predictions. If you are searching for an exact \"point of conflict\" it might be said to exist at the point at which physical systems contain enough mass-energy to cause observable gravitational effects. Because quantum mechanics does not include the gravitational force, it would not predict the aspects of the system's behavior which are due to gravity. An example of something that might be called a conflict which exists on the macroscale rather than the micro is that a naive calculation of the vacuum energy of space using quantum field theory predicts that the cosmological constant should be much larger than what we actually observe."
] |
[
"Q: Can GR and QM be reconciled?",
"A: At first glance this question seems to suggest that quantum theory and GR are inconsistent. But they aren't inconsistent.",
"Q: Then what needs to be reconciled?",
"A: In modern theoretical physics you write down a classical Lagrangian. IE an equation that describes the classical behavior of the fields you want to describe. Doesn't matter if you want to study gravity, E&M, or the nuclear interactions. The starting point is always a classical theory. Then we apply quantization procedures. Over the years we have figured out how to successfully do this E&M and the nuclear interactions. However when we try to do this with gravity, our best efforts fail.",
"Q: Doesn't that mean they have irreconcilable differences?",
"A: Not in the way you mean. There is no place where gravity stops working and quantum begins working. ",
"Q: But what about the physics of the small vs big?",
"A: As 2x4b says it just turns out that gravitational corrections for a quantum system are so small they don't matter, and the opposite is true. You have to look at the system and determine which effects are most important. This is essential all of modern physics. Almost nothing being done in research today is exact, and therefore we have to make assumptions based on which effects are most important to our system. Effective field theories in condensed matter systems are rich with examples where this is the case.",
"Q: But what about a quantum theory of gravity?",
"A: Who says we need one? No one knows if we do, certainly any corrections to current observations that would be predicted by quantum gravity would be so insignificant that they wouldn't matter. I would rather not even begin to discuss whether there is a graviton or not.",
"Finally we know that you can actually marry gravity and QFT and it has been done. The most famous example of this is the original calculation for Hawking Radiation. Technically what the calculation does is instead of working with QFT with Special Relativity as its background, the calculations are done on the curved manifold that exists outside a black hole. While doing QFT on curved manifolds (which themselves obey GR) is certainly doable and completely consistent, it isn't something that is done often. ",
"I hope this has answered any and all questions you may have."
] |
[
"Even when you do QM + GR you still get quantum fluctuations, this is what leads to Hawking Radiation. After all, QM + a specific solution of GR gives you QFT. That solution to GR is a smooth manifold, it gives you SR.",
"The issue becomes \"what does it mean to quantize gravity?\" We do not currently have a satisfactory answer to that question. This still doesn't change the fact that GR and QM seem to live to gather quite nicely."
] |
[
"What would a monomolecular sword (or wire) really do?"
] |
[
false
] |
The concept is well know from SF (William Gibson, Shadow Run, Warhammer 40k). I guess my question consists of two parts: 1) Is it, theoretically, possible to construct something that consists of a long "string" of single atoms or molecules (I'm naively thinking of a sort atomic pearl necklace, I guess), and 2) assuming we could construct a monomolecular sword/wire, what would it do when it comes into contact with solid matter (I can't quite see how a chain of single atoms could "cut" something in half, as those things do in SF)
|
[
"Ell975 makes a good point. If you tried to cut something with a monomolecular wire (like an atomically thin cheese-slice I guess?) the Van der Waals forces would cause the two separated surfaces to re-join. ",
"There have been a ",
"number",
" of ",
"syntheses",
" of atomically-thin wires, mostly made of gold. Gold has big fat atoms so it's relatively easy to manipulate compared to other metals. ",
"Similar work",
" has been done with silver.",
"However... trying to make a sword out of a wire seems like a silly thing to do, so perhaps you are referring to a blade with an atomically thin cutting edge? There are many applications where atomically thin blades are routinely used, for example good ",
"AFM",
" tips commonly have only a single atom on the end. Often when preparing samples for electron microscopy by ",
"ultramicrotomy",
" either a ",
"glass",
" or ",
"diamond",
" knife is used, both of which are atomically sharp due to their preparation by fracture through two intersecting crystallographic planes. While both of these things are particularly sharp, they are extremely delicate. This would be the problem with constructing a sword with such a blade; unless you were cutting marshmallows and fairy dust it would buckle and deform extremely quickly."
] |
[
"That's not wholly accurate. It while van der wals forces would cause the object to rejoin to itself, it would do so with numerous defects.",
"For example, if you cut through a strand of DNA it's going to have a very hard time joining back together without defects.",
"If you cut through a polymer it may well break the covalent bonds permanently due to reorientation of the structure.",
"If you cut through a piece of steel like this you will introduce dislocations into the lattice, which may make the plane of cutting much weaker and assist in fracture.",
"So the object may not totally separate, but it will introduce a signifigant of local randomization where the object has been \"cut\", which may weaken it substantially or cause it to become defective."
] |
[
"A line of atoms would be useless for cutting. This is because a regular sword splits an object apart and the two pieces are too far away from each other to rejoin. However, by using an atom thick blade, the molecules of the material being cut would still be close enough to attract each other."
] |
[
"My friend told me he thinks microwaved water kills plants. I call on you all to help me convince him that microwaves are perfectly safe."
] |
[
false
] |
[deleted]
|
[
"It's complete hogwash. Nothing happens when you microwave (pure) water other than it gets warmer. There's no way of telling, even in theory, whether or not some quantity of water has been microwaved in the past or not. ",
"I'm afraid you won't find any articles in Scientific American, because they don't usually bother to run articles debunking things at this level of absurdity. "
] |
[
"snopes.com/science/microwave/plants.asp",
"Here. Snopes is legit. And they give reasons for their answers. Hope it helps. "
] |
[
"Tell your friend that microwaves are machines that use light in the microwave region to induce rotations and vibrations in water molecules that increase the overall kinetic (and thermal) energy of the sample. Microwaves are just slightly higher in energy than radio waves (",
"http://upload.wikimedia.org/wikipedia/commons/c/cf/EM_Spectrum_Properties_edit.svg",
"), and thus mostly harmless if they pass through you. Anyway, that doesn't matter - once the water cools down to room temperature, the energy that the microwaves provided has left. ",
"In other words, there is NO reason AT ALL for this to be true. Microwaving water causes the molecules to bend and rotate, nothing more. Molecules of water are bending and rotating all the time anyway, so there's no way water that has been microwaved is any different from, you know, water that hasn't."
] |
[
"Is it true that meteorites could have created life on earth ?"
] |
[
false
] |
[deleted]
|
[
"All life that we have studied thus far has shared similar genetic strategies, using nucleic acids to store information and pass that information on to subsequent generations. If there were a form of life that originated elsewhere in the galaxy and arrived here we might reasonably expect that it would use a different \"biochemical alphabet\". At the moment, it appears that all life on earth descended from a single primordial cell. A number of meteorites may have landed here a few billion years ago, bringing some of the material that later became life. But once life got started here, it doesn't appear that we have received outside competition."
] |
[
"Lab tests have shown various organic compounds could survive extremely long durations in space, including reentry. If, for example, Mars or Venus or Europa (or any body for that matter) were once teeming with life and a meteorite impact propelled surviving organic compounds to Earth. The primordial cell you're talking about could very well have been from another planet. And right now, it appears to be a valid hypothesis, as all experience done show that it is feasible... provided there was life on another planet/moon. ",
"Though, I'm more inclined to believe the enzyme originated from inorganic compounds, naturally. Only within the last 3 months were we able to do that in lab tests... enzymes being created from inorganic compounds only through the process of evolution. It's a much more simple hypothesis, and therefore, more likely. "
] |
[
"It sounds like what you're talking about is ",
"panspermia",
". Everything that I'm going to say about it you can find in the wiki article as I am no expert in the subject but anyway, it's the idea that life is able to survive in asteroids or other similar things and when these objects crash into a suitable environment, the organism would be able to then thrive and be the origin of life on that planet.",
"There's the hypothesis involving this idea that life on Earth may have arisen in such a way. As far as I know there's no direct evidence of that at all but there have been experiments testing to see if this is possible. The most common proposed way that this could happen is through bacterial spores, as we've found incredibly hardy and viable spores that have survived for millions of years. I also remember from an astrobio course I took there was some experiment done where bacteria/bacterial spores were essentially shot in a bullet to see if they could theoretically survive being in a meteorite impact. I don't remember the names of the experimenters but after a google search I found this ",
"paper abstract",
".",
"As far as panspermia and the origin of life on Earth goes, the most likely source of a seeded asteroid would be Mars because its close to us. As far as I understand it basically it would work something like this: some sort of meteorite would hit an area that contained bacterial life or something similar and cause spellation of the surrounding area flinging the organisms into space. If these organisms formed bacterial spores they could possibly survive the extreme conditions of space, especially if they were encased in a protective shell of rock. Then after some period of time, the rock encasing the spores would hit Earth and some of the spores would be able to survive and then be able to germinate.",
"One important note is that this doesn't attempt to explain at the origin of life, but just the origin of life on a specific planet. Life would still need to form somehow on the original planet. As far as how serious this hypothesis is, I'm not sure. It's not very well supported in terms of direct evidence of such an event, but there is evidence that it is possible. An additional thing to consider is that if this process of flinging bacterial spores into space after meteorite impacts is possible and not too unlikely, life from Earth may spread to other celestial bodies in our solar system. Something I thought was an interesting idea anyway."
] |
[
"[Astronomy] The sun's magnetic poles swap every 11 years. Does this have any effect on the earth?"
] |
[
false
] |
It says that The solar magnetic field extends well beyond the Sun itself And is more about the "heliospheric current sheet". My question is, is earth effected by these magnetic changes at all?
|
[
"Firstly, we should note here that the sun's magnetic poles don't swap every 11 years, as the sun does not have magnetic poles like Earth. Instead, it has multiple norths and souths all over it because it's a plasma. This is why that article you cited has a lot about north/south sunspot pairs in it.",
"The 11 year solar cycle is primarily noteworthy because you see a lot more sunspots at solar maximum. And yes, this does get noticed on Earth, as you get a ",
" more coronal mass ejections (CMEs- basically, giant explosions of solar matter) during solar maximum, as they're usually from complex sunspot regions on the Sun (which may not even exist on the sun during a minimum). If you've read about crazy aurorae reaching as far down south as Florida, or radio blackouts from solar flares, or the time there was a giant power blackout in Quebec... well, they all took place during a solar maximum!",
"Beyond that, no, the magnetic field of the sun doesn't really affect us on Earth at all."
] |
[
"The first part is not quite true I don't think. While the magnetic poles and field lines of the Sun aren't like the Earth's, the solar hemispheres do have a reasonably well defined polarity. ",
"This",
" shows it quite nicely. In one cycle, for the northern hemisphere, the south polarized sunspots always occur on the left of the north ones, while this is reversed for the southern hemisphere. Then, 11 years later it flips, so there is a pretty well defined magnetic cycle every ~22 years, on top of the solar activity cycle every ~11 years. There was a wonderful .gif I tried finding which showed exactly this happening, but unfortunately I can't find it."
] |
[
"Beyond that, no, the magnetic field of the sun doesn't really affect us on Earth at all",
"Actually, (It's a pretty subtle phenomenon, noticed only by those in the shortwave radio community I'm guessing) but the height of solar activity that occurs every 11 years can actually boost signals and enable longer distance transmissions. I think it has to do with the signals being more able to bounce off the ionosphere.",
"Anyone with more knowledge about this, please feel free to elaborate. I just remember learning about this when I was super into shortwave radio at the same time the sun was doing its 11 year flippy-do."
] |
[
"What happens if you break the sound barrier under water?"
] |
[
false
] | null |
[
"There would be a sonic boom, just like in air. ",
"Cavitation",
" and ",
"sonoluminescence",
" would probably be the main differences you'd notice, and there would be tremendous amounts of heat produced (much more than in air).",
"I think you'd run into a lot of issues trying to do it in reality, though, since the amount of heat being produced by the absolutely colossal force you'd need to get up to that speed would be boiling the surrounding water off like crazy."
] |
[
"The Glock has a muzzle velocity of ~375m/s. The speed of sound in water is ~1500m/s . The only thing that video is showing is the release of gasses from the round."
] |
[
"Interesting! I didn't know that. Maybe they have a video of a supersonic gun firing underwater? I can't imagine it would look too different though.."
] |
[
"If the Earth was flat, would rainbows be straight lines?"
] |
[
false
] | null |
[
"Rainbows have nothing to do with the shape of the Earth, only to do with the refraction of light through (roughly) spherical raindrops. The refracted light spreads out in a cone and the part-circle we see is a cross-section through that cone. (If you are ever fortunate enough to experience a rainbow while flying in a plane, you may get to see the complete circle.)"
] |
[
"No, because the prisms are still more or less randomly oriented.",
"There actually ",
" prisms in the air, in the form of ice crystals. There are several optical phenomena related to refraction with these, namely ",
"parhelia",
", various ",
"arcs",
" or the ",
"22° halo",
". The prism structure defines certain viewing angles under which reflection of the sunlight can occur, leading to the localized phenomena."
] |
[
"If raindrops were prism-shaped, would rainbows be straight lines?"
] |
[
"How large does building has to be so the curvature of the earth has to be considered in its design?"
] |
[
false
] |
I know that for small things like a house we can just consider the earth flat and it is all good. But how the curvature of the earth influences bigger things like stadiums, roads and so on?
|
[
"Definitely for the Large Hadron Collider and similar insanely large particle accelerators or that laser-bouncing tunnel for detecting gravity waves. Not just because they are huge but because their operation relies on incredible precision.",
"IIRC the LHC had to account for how the moon's gravitational pull moves Switzerland/France and if the bedrock under the east side moves slightly more than the bedrock under the west side then the beam will be out of alignment."
] |
[
"The Humber suspension bridge has a main span a little less then a mile long (4,626 ft). Due to the Earth's curvature the two main supporting towers (510 feet tall) are 1.4 inches further apart at the top than the bottom.",
"https://en.wikipedia.org/wiki/Humber_Bridge"
] |
[
"I love this information. I had not considered research facilities. I'm sitting here thinking about enormous warehouses and indoor football fields and crap. ",
"However, I'm not sure they sculpted the building's structure specifically to the curvature of the earth for the precision required. That seems like more a \"we have this really cool laser that has the most stable legs, and most motion dampening arms, so we know exactly where it's supposed to go.\"",
"Just seems like if the moon's gravity DID shifte one side more than the other, an alarm should go off, and the collider should not fire, until the correction has been made (either mechanically, or manually). I imagine it probably runs this safety check every time it asked to fire."
] |
[
"Steady eyes"
] |
[
false
] |
How exactly do we keep our eyes fixed on an object when we move our head around? For example, if I'm looking at a lamp across the room, I can move my head around while my eyes stay locked on the lamp. While still looking at the lamp, I can keep my head still then move my eyes around, obviously using muscles to do this. Why don't I feel the muscles keeping my eyes steady in the first scenario and how is it done?
|
[
"This thread",
" explains why quite nicely. Basically, you have two sets of eye muscles, one of which is specifically designed for movement tracking."
] |
[
"Your vestibular system is in charge of figuring out the position of your head. Your ear has tubes called the semicircular canals, which are oriented along various axes and filled with fluid. They work just like a level tool to sense the angle and position of your head. There are nerves that are constantly sending signals from this system to your eyes so that changes in your position are compensated by the position of your eyes. It isn't a conscious process, so you don't notice it or have input over it, whereas you can consciously choose to move your eyes to follow something so you are aware of it. They are two different and somewhat parallel systems, one that takes orders from the vestibular system and one that takes orders from higher-order brain systems."
] |
[
"Thanks for the information, that helps to clear it up a bit :)"
] |
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