title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"Why do we think black holes are infinitely dense?"
] |
[
false
] |
I've heard black holes explained as mass concentrated into a single point (a singularity), where the density is infinite. Could it be possible to have a black hole where density is high, but not infinite, such that its surface lies within its Schwarzschild radius.
|
[
"Why do we think black holes are infinitely dense?",
"Because there is no force we know of which can support matter beyond a certain density against gravitational collapse. But, we really have no idea whether black holes really ",
" infinitely dense or not. Most scientists expect they are not actually infinitely dense. But, absent a mechanism for keeping everything from collapsing to a single point, it is not known whether the singularity is actually avoided or not.",
"Could it be possible to have a black hole where density is high, but not infinite, such that its surface lies within its Schwarzschild radius.",
"It could be possible, yes. Some would even say it is likely. We would not be able to observe it however.",
"Different theories predict different things about black holes. General relativity predicts it collapses to a point, but some string theories predict the formation of what is called a ",
"fuzzball",
"; basically a big region of extreme strings that takes up most or all of the event horizon."
] |
[
"Different theories predict different things about black holes. General relativity predicts it collapses to a point, but string theories predict the formation of what is called a fuzzball;",
"There's a big difference between \"some string theorists predict\" and \"string theories predict.\" I'm not a string theorist, but I'm pretty sure it is not a general result in string theory that fuzzballs are the right description of a black hole."
] |
[
"Ooop. You're absolutely right -- thank you for correcting. I didn't realize my statement was worded so strongly; will correct!"
] |
[
"Would it be possible to attach food, O2, energy stores and rockets to the ISS and send it somewhere else to explore?"
] |
[
false
] |
[deleted]
|
[
"Maybe with really really slow acceleration, lest you snap off a section with too much torque. Or if you put the rockets at the points where sections meet up. But it's probably a horrible, horrible idea."
] |
[
"Engineering aside, I honestly think they'd all go completely batshit crazy before they even got out of the solar system"
] |
[
"Probably. I was even thinking Mars or moons of Jupiter or something."
] |
[
"Is Listerine's burning sensation indicative of actual cleaning, or is it just there to make you think \"Wow this must really be working\", when in fact the burning has no functional use?"
] |
[
false
] |
[deleted]
|
[
"The burning sensation is due to ethanol and other disinfectants that clean. However, in the past many companies have released mouthwashes that are just as effective as listerine but do not have the burning sensation. They all failed because people did not believe they worked as well. So, to answer your question... yes."
] |
[
"When determining the effectiveness of mouthwash you have to specify what it is you are trying to accomplish. Anti-plaque, anti-gingivitis etc. ADA (American Dental Association) only accepts a few ingredients as they have clinical proof that they are effective. Listerine is one of them. They use ethanol to dissolve their solvents. Listerine actually recently came out with a Listerine ZERO that does not burn since it does not have ethanol; however, this mouthwash also does not have any of the effective ingredients since the solvents won't stay dissolved. This isn't to say mouth wash that doesn't burn does not work just in the case of Listerine ZERO."
] |
[
"What makes listerine effective is the same thing that makes it burn. It is not necessary for a mouthwash to burn to be effective. Listerine uses disinfectants that burn specifically so that people believe its effective."
] |
[
"What causes objects in space to spin/rotate at the first place?"
] |
[
false
] |
Like planets or stars?
|
[
"Let's say you have two stars far away from each other, initially travelling parallel to each other in opposite directions. When they start getting attracted to each other, they start moving inwards towards each other. Because they initially have tangential motion with respect to each other, they start spiralling/rotating around each other."
] |
[
"No, I mean how the star or the planet itself revolves. Not spin.. Sorry if my question was unclear."
] |
[
"What do you mean? All the rotation is from the initial motion."
] |
[
"How would I find the percent composition of simple sugars in a fruit?"
] |
[
false
] | null |
[
"Have ",
" ever run a GC? What sample would you run it on? I don't understand your procedure. ",
"Also, most simple sugars ",
" between 100 and 300 C. Boiling them requires significantly higher temperatures, so I doubt even the oven is hot enough. Also, at such high temperatures you risk combustion of the sugar as well. And what do you mean by \"stick to the column?\" The stationary phase is liquid in GC. I'm shocked you still persist with GC for this. "
] |
[
"Using long fancy HPLC columns seems inefficient, expensive, and not very accurate for quantitatively determining relative composition. Even chiral affinity columns might be better.",
"Why would fractional solidification take forever? You boil off the water or any other volatile solvent; then heat the sugar mixture (to little over 200 C) till every component liquifies. Then slowly lower the temperature and collect the precipitate one by one. The timescale wouldn't be that different from simple distillation - of course, the slower you go, the more accurate. No fancy equipment needed - just a heat source, some containers, and an accurate balance."
] |
[
"Its still called a column, so I don't get your question. By stick to the column I mean retention times are determined by the partition coefficient between the mobile and stationary phase. In the U.K. this is colloquially referred to as 'sticking to the column'.",
"Anyway after a brief look around it seems most methods call for silylation of the sugars to increase their volatility enough for a decent GC trace. This would probably make my method impractical.",
"Good old HPLC it is. I went with GC first because I view it is easier to do quantitatively."
] |
[
"Is there a chance for a number to never be rolled in a random number generator if it is ran infinitely?"
] |
[
false
] |
I got into an argument with a friend of mine who is working for a random drop in a video game. He says that if he were to do the task that gives the drop infinitely he would eventually get it. I argued that since it is random and there is no pity timer that even if he rolled infinitely there is still a chance he would never get it no matter how unlikely. So who is right?
|
[
"Any \"random number generator\" you're likely to find will really be a ",
"random number generator (PRNG). In other words, it generates numbers according to some pre-determined algorithm. But if it's a good PRNG, it will have been shown a priori to generate numbers which very closely resemble a truly random sequence, as long as the period of the algorithm is not exceeded.",
"But that's the important point; any PRNG will have a finite (although potentially huge) ",
". Once the period is exceeded, it will start to repeat the same sequence.",
"So the problem of infinitely many trials can be reduced to a problem of one period-full of trials. Once you've generated every number in the sequence, there's no need to keep redoing it, you already know you'll just get the same sequence.",
"Now the question becomes \"Will the period cover every possible number in the sample space?\" and the answer is \"Hopefully, at least to some precision.\"",
"A very simple example of a PRNG is a ",
" (MLCG), which generates random natural numbers with the sequence:",
"n",
" = (a n",
") mod m,",
"where a is the ",
" and m is the ",
". You have to start out the sequence with an initial value n",
" called the ",
".",
"Statisticians have worked very hard to figure out \"optimal\" values of m and a such that the outputs of these particular PRNGs pretty well resemble uniform random integers between 0 and (m-1) with a very large period.",
"Using the transformation r",
" = n",
"/(m-1), you get \"random\" numbers uniformly-distributed between 0 and 1. And from this, you can make analytic transformations or use Monte Carlo methods to generate \"random\" numbers according to whatever PDF you want.",
"But clearly n",
"/(m-1) is a rational number. So already it's clear that r",
" cannot possibly be ",
" real number in the interval [0,1]. So there are infinitely many real numbers which will ",
" be generated using this algorithm, since you can never generate an irrational number. Typically (m-1) is extremely large so it's not a problem in practice, but the literal answer to the question is \"Yes\", this particular pseudorandom number generator will never generate any irrational number if you run it for an entire period. And since once the period is complete, you know how the sequence will go forever, you can say that one will ",
" be generated by this algorithm.",
"Now maybe you weren't asking about PRNGs but about actual random numbers. Take for example a totally fair, ideal coin. You can flip a coin arbitrarily many times and there's no guarantee you'd ever get heads. The probability of getting tails on every single flip for n independent flips in a row is (1/2)",
" = 2",
". This is an exponentially decreasing function of n, so taking the limit of this quantity as n goes to infinity clearly gives you zero."
] |
[
"This answer is not quite right. Assuming that there is a fixed probability p of the item drop, you're right that the probability of it not dropping is 1-p and that after infinitely many tries, the probability of it not dropping can be thought of as lim (1-p)",
" = 0. It would be correct to say that we will ",
"almost surely",
" get the drop after infinitely many tries.",
"However, a 0-probability event can still happen. Think about it like flipping a coin infinitely many times. In the end, you'll end up with some sequence like, say, S = (H, T, T, H, H, H, H, T, H, T, ...). Now, ex ante, what would the probability have been that you'd end up getting S? Well, you can think about it (handwaving alert) as 1/2 * 1/2 * 1/2 * ... = 0. So the probability of getting that sequence would have been 0. And in fact, the probability of getting any particular sequence at all is in fact 0. But you still end up with a sequence at the end.",
"This problem is exactly analogous to that. The probability of not getting the drop after infinitely many drops is like the probability of never flipping a heads after infinitely many flips, i.e. the probability of obtaining the sequence Q = (T, T, T, T, ...). That's just one sequence out of the infinitely many possible sequences that you might end up with, and has probability 0. But like all of the other sequences, you could still end up with it. "
] |
[
"Mathematically speaking, he is right. ",
"If the probability of the item dropping from of a given task (\"event\") is 0 < p < 1, then the probability of it ",
" dropping is (1 - p). The probability of it not dropping from doing the task twice is (1 - p)*(1 - p), or (1 - p)",
" and the probability of it not dropping from doing the task ",
" times is (1 - p)",
" ",
"As ",
" approaches infinity (i.e. grows larger), the probability of having at least 1 success approaches 1. Now, one might quibble that it never ",
" 1, but the rolling process also never stops if you're rolling \"infinitely\" - not the server shutting down, not the 2038 bug, not the heat death of the universe - and as long as there's \"1 more roll\", there's always still one more a chance to get it, and so you will never reach the point of \"never\". "
] |
[
"Why have the engineers at NASA outfitted their new manned exploration vehicle with rubber tires?"
] |
[
false
] |
The MMSEV (Multi Mission Space Exploration Vehicle) built at the Johnson Space Center seems to have rubber tires. Knowing how pedantic one has to be when designing equipment meant to go to the outer reaches of our solar system since you can't exactly pull up at a repair shop once you're on Mars, I was wondering why they'd run the risk of puncturing a tire? Granted, they can bring along spares but that would add to the payload you have to liftoff from earth . What I'm asking, basically, is why they didn't go with a design similar to where the tires are made from a hollow metal mesh in such a way that it can't be perforated.
|
[
"I would be surprised if that's the actual design. The various rovers have used ",
"tires that don't require inflation",
" and as you noted the Apollo landers used a more robust design. ",
"Best guess: They didn't want to ruin very expensive custom tires taking it for a joyride in Earth's gravity on asphalt.",
"Pretty much everywhere they would send a design like that will have much lower gravity (Mars: 38%, the Moon: 16%, Europa: 13%, Titan: 14%); all of which will be much less damaging to the tires. They may even have different tires for different environments. "
] |
[
"Yeah, I noticed the tires too, and this was my interpretation as well- they were a temporary modification for use in testing on earth. I'm sure the actual rover, when used on a foreign planetary body, would not have inflatable tires."
] |
[
"This is a 1-G mock-up test vehicle, clearly everything is not exactly near flight readiness (In fact for the MMSEV they are still a bit away from building flight-like). There is hardware you just can't use with gravity. This vehicle is mostly for cabin design and testing an independent wheel suspension system. "
] |
[
"Is a hot sauce only going to be as hot as the spiciest ingredient?"
] |
[
false
] |
[deleted]
|
[
"Yes. The spiciness will only be determined by capsaicin concentration. But people also like the consistency and taste of their hot sauce. Different peppers have different tastes. So blending certain peppers together will taste better than just a jar of pure capsaicin."
] |
[
"You will be diluting the ghost peppers though, so it would make it less spicy."
] |
[
"You will be diluting the ghost peppers though, so it would make it less spicy."
] |
[
"What exactly is going on when a \"shiver goes down my spine\"?"
] |
[
false
] |
And how does it relate to stimuli?
|
[
"It is not. ",
"NOT TO BE CONFUSED WITH MUSIC BASED TINGLES/SHIVERS\nThose are called frisson and can be discussed in ",
"/r/frisson",
" ",
"Please go there if you want that \"epic\" feeling."
] |
[
"They don't know for sure. Until then, explore this world:",
"/r/asmr"
] |
[
"I don't know if that's the type of phenomenon OP is referring to. We need more details.",
"ASMR is described as a pleasurable tingling sensation, often in response to calming stimuli like soft music or whispering; whereas the phrase \"shiver going down your spine\" is commonly used to describe a state of extreme excitement or fright."
] |
[
"How do we know that two photons are quantumly entangled?"
] |
[
false
] |
[deleted]
|
[
"Because we entangled them. There's no way to check if two specific particles are entangled; we have to make them entangled."
] |
[
"And how do we go about doing that?"
] |
[
"It's quite likely that we entangled them ourselves in the first place, but that doesn't mean we couldn't check random pairs of particles for entanglement. Whether you entangled them or not: you can still always measure their correlations and see whether they are stronger than allowed classically."
] |
[
"Does the Indian government has a protocol in place in case the Sentinelese decide to contact the rest of the world?"
] |
[
false
] | null |
[
"Not the right sub. Perhaps try a politics or law or some other kind of sub."
] |
[
"Would it not fall into anthopology? Pretty sure scientists would be the one helping the Sentinelese, not government officials."
] |
[
"The way the question is phrased it seems to be asking about what a current government policy/protocol is. That is not a science question."
] |
[
"Are we more well-rested when we use alarm clocks to wake us, or when we don't use alarm clocks?"
] |
[
false
] |
Setting alarms allows us to consistently wake up around the same time and develop a stable circadian rhythm. However, alarms do seem to be an abrupt disruption of our sleep, which can't be good, right? Conversely, not setting an alarm allows us to wake up in the most natural and gradual way, but is perhaps not very practical and results in an unstable rhythm. Which waking method would be better for getting optimal sleep?
|
[
"Alarm clocks disrupt sleep, and leave you more likely to feel tired. Using a clock to align (in circadian biology, we can it entrain) your natural rhythms can work, but if you're waking up to the alarm, you're not waking up with your biological clock. People are not infinitely flexible when it comes to sleep times, and you get many other entertaining cues during the day, like meals and exercise, so ultimately routine is best for establishing stable sleep that doesn't need to be disrupted by an alarm.\nSociety can make this hard though. For instance, puberty delays circadian rhythms, making highschool students want to sleep later. Some schools are changing to accommodate this, since it's natural and healthy, while most require you to use an alarm still, since they want you to entrain to a time pretty far from your natural rhythm."
] |
[
"Your body has two main phases NREM and REM, both these phases takes approximately 1,5 hour together before they start new cycle. To get a really good sufficient sleep you should cycle these phases at least 5-6 times throughout the night. If you interrupt the cycle before it's done it has actually negative impact. The more drastic your alarm is the worse the wake up - sometimes it might lead even to disorientation. \nNowadays ways of life are harsh on these natural body rythms. Take kids or teenagers for example, they have shifted circadian rhythm and need to go sleep later in the evening and need to wake up later in the morning, but schools are demanding them to wake up early in the morning disrupting natural rythms which might be the cause of some problems during the day, problems with focusing, being easily distracted, worse memory, etc. There's a lot about this topic, read book Why we sleep by Matthew Walker."
] |
[
"Why do schools still insist on early times? Is it really that more natural for adults to wake up early? Do they not also have hardships?"
] |
[
"If microprocessor manufactures are able to get more transistors on a processor why do they make them smaller?"
] |
[
false
] |
I understand that power and efficiency are factors they have to consider but if you're looking for all out performance why not make the processor bigger so that you can fit more transistors/cores/memory etc on it to make it faster?
|
[
"three things: propagation time, power consumption and (to some extent) price.",
"The first is that the electrical signal only goes so fast, slightly less than that of the speed of light. This seems fast until you realize that in one clock cycle at 3GHz light only travels 10 centimeters. Chips are usually less than this but once they get larger it can be a significant problem.",
"Secondly, the capacitance and hence power consumption of a transistor gate decreases with size. lower power consumption is a bonus by itself but it also directly relates to speed because it means you can run it faster before it starts dissipating too much heat for you to remove practically.",
"Also, although the smaller sizes are expensive to develop, ultimately you can produce more chips on one wafer than you could before, bringing down the price in the long run (this is more relevant on less extreme cases, such as embedded microprocessors)",
"Also, just adding more cores/transistors/memory doesn't immediatly make the computer faster for most workloads, especially games, since the software cannot effectively make use of increased parallism. Most of the increased transistor count on modern chips goes towards better branch prediction, more instructions, and better caching instead of increasing clock speed, for which you in fact want ",
" transistors."
] |
[
"The size of the transistor is connected to the electrical capacitance of it.",
"The smaller the less capacitance, and the higher frequency you can run it at without making it too hot."
] |
[
"in addition to the points raised by other comments -- don't forget that not only do the number of candidate chips from a wafer go down, but the increase in area means a higher fraction of the possible chips will overlap a flaw in the crystal, driving yields even lower. That is on top of the problem that a smaller feature size means that smaller flaws in the crystal, which would not have been a problem at a larger feature size, now break your chip.",
"So even if you manage to solve the problems noted elsewhere, you still end up with the larger chip being a lot more expensive than you might like.",
"It is a fine balancing act, cheap-but-small versus large-but-expensive.",
"As far as sequential versus parallel processing ... it is really really good that multi-core systems are getting more common. Perhaps we can start training software engineers earlier in the education cycle to think in terms of multithreading, and over the long haul end up with systems that do not waste so much time insisting on sequential processing where it is not really needed. But that goes to unrelated issues in education and programming language design ; )"
] |
[
"Rubbing alcohol is often use to sanitize skin (after an injury/before an injection), but I have never seen someone use it to clean their counters or other non-porous surfaces — is there a reason rubbing alcohol is not used on such surfaces but non-alcohol-based spray cleaners are?"
] |
[
false
] |
Edit: Whoa! This is now my most highly upvoted post and it was humbly inspired by the fact that I cleaned a toilet seat with rubbing alcohol in a pinch. Haha. I am so grateful for all of your thoughtful answers. So many things you all have taught me that I had not considered before (and so much about the different environments you work in). Thank you so much for all of your contributions.
|
[
"Alcohol used to be the antiseptic of choice for instruments and surfaces in healthcare settings. It remains so in some countries and settings. Alcohol was only replaced because it was ineffective against spores and some viruses."
] |
[
"It’s also highly flammable and sometimes using it over a broad area or enclosed space is a major fire hazard."
] |
[
"All the replies in here, and this is the first mention of the fact that alcohol is flammable. Probably a big reason it's not used for general household cleaning, ",
"unless you want to burn everything down. "
] |
[
"How is symmetry spontaneously broken in superconductors?"
] |
[
false
] |
I was reading about how spontaneous symmetry breaking occurs in superconductors and how Nambu proposed that by “breaking the symmetry” you give energy to break apart Cooper electron pairs resulting in giving them mass. I don’t really get how this occurs in superconductors.
|
[
"Without knowing your physics background this is difficult to answer, so let's take it one step at a time.",
"The symmetry which is broken is ",
". Usually, you cannot create or destroy electric charge. But a superconductor is a special state of matter, a ",
" of Cooper pairs. (Here condensate is in the sense of Bose-Einstein condensation). This means that you can take out a Cooper pair from the condensate \"for free\". In a rather precise sense, the condensate and the condensate plus or minus a Cooper pair is exactly the same quantum state.",
"Of course, overall electric charge must be conserved, and this is surely respected by a superconductor. But locally you can pull out a Cooper pair from the condensate at no cost."
] |
[
"You may be confusing two things here: the breaking of the symmetry and the breaking up of a Cooper pair.",
"For the symmetry breaking, it is easier to look at charge-neutral superfluids (for instance Helium-4 below 2.17K). The condensation is the same: bosons can be put in or taken out of the condensate at will, and the number of bosons at any given point and time is not well defined. The same thing happens in a superconductor, but with two complications:",
"This last part means the Goldstone mode become gapped (this is called Anderson-Higgs mechanism), and also leads to the Meissner effect. This does however not pertain to your question.",
"In the presence of an (effective) attractive force, two fermions in a Fermi liquid can form a bound state (i.e. a state with energy lower than the Fermi energy). This is called the Cooper problem, and the bound state is called a Cooper pair. This relative energy of the bound state is called the ",
" Δ, because single fermions with an energy below this gap cannot enter Fermi liquid (now superconductor) anymore. However if you put in an energy higher than the gap, you make break up the Cooper pair. For instance, if the temperature is higher than (about) Δ/k_B, all the pairs break and superconductivity is gone (this is the Bardeen-Cooper-Schrieffer explanation of the critical temperature). Note however that by breaking up the pairs and destroying superconductivity, you ",
" the charge conservation symmetry.",
"In physics parlance, a relativistic particle without an energy gap is called ",
", while a relativistic particle with a gap is called ",
". In this sense the electrons become massive particles in a superconductor, even though there were not relativistic or massless from the beginning. This may what the book was referring to."
] |
[
"energy to separate the massless electrons from pairs into individual electrons, and this energy you have just put in can then be seen as mass",
"OP wrote:",
"energy to separate the massless electrons from pairs into individual electrons, and this energy you have just put in can then be seen as mass",
"So, it already regarded the electrons as massless. Of course, electrons (and Landau quasiparticles) have a sizeable rest mass, so taking them massless is an approximation. ",
"What I was talking about is the following. A non-relativistic free particle has Hamiltonian",
" = hbar/2",
" ",
"^2 + Δ",
"where ",
" is the particle mass, ",
" is the momentum operator and Δ is the energy gap (which could be zero).",
"But for relativistic particles (let's take them scalar for simplicity), the field-theoretic Lagrangian for the field ϕ is ",
" = ϕ(-",
"^2 + ",
"^2 + ",
"^2)ϕ",
"where ",
" is the energy; the dispersion relation is",
" = sqrt(",
"^2 + ",
"^2)",
"Here ",
" can be interpreted as the mass of the particle, but in condensed matter is more natural to think of this as the energy gap for a particle with otherwise linear dispersion. I had a the impression that OP's book was doing this: without the Cooper instability you have effectively free electrons, but the Cooper pairing induces a gap for single electrons, which in field-theory language can be interpreted as a mass."
] |
[
"How fast does an earthquake propagate?"
] |
[
false
] | null |
[
"The propagation of an earthquake would be equal to the speed of sound in the earth, which depends on the density, the shear modulus, and the compressibility of the material that the waves are passing through. This will be MUCH faster than the speed of sound through air, and a fairly tough calculation. Someone else can provide a better answer hopefully. Gonna have to give you the wiki link on this one.",
"http://en.m.wikipedia.org/wiki/Speed_of_sound",
"In the article is states the speed of sound through iron is 4 times that of air. So the propagation of an earthquake would be between 2-4 times the speed of sound in air. Rough estimate based on an unscientific source."
] |
[
"Are you asking about the speed of the seismic waves generated by an earthquake or the speed at which the actual earthquake rupture (so displacement on the fault surface) propagates? ",
"As for the first option, the speed of the primary waves (P-waves) would be the speed of sound in whatever material through which the wave is propagating. Secondary waves (S-waves) are slower, wikipedia says about ",
"60%",
" slower.",
"The speed of the rupture propagation itself gets REAL complicated. Suffice to say, it depends mostly on the material properties of the fault and is slower than the propagation of the seismic waves. That's about as much as I want to say since earthquake physics is not what I study and I don't feel like re-familiarizing myself with continuum mechanics for an AskScience answer.",
"Edit: I found a decent, simple discussion of this on ",
"wikipedia",
". Basically, rupture in most earthquakes occurs at a speed below the S-wave speed (the wiki article says ~90% slower). There are so-called \"Supershear\" earthquakes, which the article is about, during which rupture propagates faster than S-wave but slower than P-wave velocities. "
] |
[
"Here",
" is a plot of the seismic wave structure of the Earth. These wave speeds give the velocity that both shear waves (think holding both ends of a rope and moving your hands up and down) and compressional waves (pushing an accordion in and out) will travel through the Earth."
] |
[
"Are there any alternate explanations for the cosmic microwave background?"
] |
[
false
] |
When we talk about the decoupling of radiation from matter ~300,000 years after the big bang, what is actually occurring? I know the universe becomes "transparent" to its own radiation but by what mechanism is this happening? I'm an A-level physics student if that's of any help but I'm fairly familiar with some basic quantum theory. EDIT Thanks guys, so the opacity of the early universe is related to an equilibrium between protons and electrons and hydrogen atoms which is maintained by photons but this gets to a point whereby the photons no longer have sufficient energy to ionise the hydrogen, so the hydrogen becomes "transparent"? So where does Compton scattering factor into this as I've heard the CMB corresponding to a "surface of last scattering"?
|
[
"To talk about your second question, when we look at the edge of the known universe we are seeing a wall of hot plasma. The light is horrible at permeating this plasma because these unbound particles can absorb a near continiuum of light as thermal energy. Thus they couple very well and little light can escape. Eventually the universe expanded and cooled and allowed the particles to form neutral atoms and lowered its ability to absorb light thus rendering it transparent."
] |
[
"When the universe is young, hot, and dense (i.e. before about 300,000 years after the big bang), the distribution of photon energies is high enough that protons and electrons can't bond to form stable hydrogen. Thus, the universe is filled with a plasma, where photons, protons, and electrons interact at high rates and everything stays in thermal equilibrium. In that case, if an electron and proton try to bind to form hydrogen (a low energy state), a high-energy photon comes along and blasts it apart immediately, returning the electron and proton to independent, high energy states. All the low energy stuff can happen, it just doesn't last very long.",
"However, as the universe expands, the wavelengths of the photons in in the plasma \"stretch\" and their energies drop. Eventually, the number of photons with enough energy to break up hydrogen atoms drops below the threshold required to stay in thermal equilibrium with matter and all the electrons/protons join up to form hydrogen, which is essentially invisible to photons. ",
"This is a bit simplified, but the general answer to your question is that everything cools to below the point where photons readily interact with electrons and protons, so hydrogen forms, and that is even less eager to interact with electrons. Thus, the CMB travels relatively unmolested through space and to our telescopes."
] |
[
"When we talk about the decoupling of radiation from matter ~300,000 years after the big bang, what is actually occurring? ",
"We call it 'recombination.' It was when the universe had finally expanded enough to be cool enough that the (opaque) electron-proton plasma was able to 'freeze' into atomic matter. Basically, the electrons and protons combined to form neutral atomic hydrogen gas, and the universe became transparent, letting the light out, so to speak, or just letting the light have an immeasurably longer mean free path."
] |
[
"How do I hear music in white noise?"
] |
[
false
] |
I sleep with the ceiling fan and a loud stand-up fan to keep my noisy neighbors from waking me up. But as I'm falling asleep, I sometimes hear a faint, unrecognizable song. It wakes me up and then I can't hear it anymore. Is there any cause for this?
|
[
"White noise contains thousands of different frequencies. Your mind can subconsciously focus on certain frequencies, sometimes making up what you perceive as tunes. Also, take a look at ",
"auditory hallucination",
". "
] |
[
"This may sound nitpicky but I feel that is one of the tenets of this subreddit! What you are describing is not white noise. It is probably closer to pink or red noise (but more likely not \"noise\" at all. it's most likely more 'signal' than 'noise'). I only say this because if you start doing some personal research into the issue, it may lead you down the wrong path.",
"If it truly IS white noise, then you should do some science for us and try to sleep with actual white/pink noise playing in headphones and see if you hear the same 'song'"
] |
[
"Audiology graduate student here: Our auditory systems are able to perceive pitch and loudness due to a transduction process inside our cochlea (basically the nerve for hearing). After the sound signal has been changed into an electrical signal (inside the cochlea) that can be perceived by our central auditory nervous system (CANS), the CANS can recognize modulation of this auditory input. With little electrical knowledge, I would assume the fan is slowing down at some point in its cycle and then returning back its normal speed. Even though this is white noise, the brain can perceive that fluctuation.",
"tl;dr the brain can perceive fluctuations in an auditory signal, even if the signal itself is white noise",
"Edit: corrections"
] |
[
"Did any Predators regularly hunt our hominid ancestors?"
] |
[
false
] | null |
[
"Interesting discussion, however that is not true about Komodo Dragons, I recently found another discussion about it and here are a couple of links that describe it in detail. ",
"A quote from the article: \"But \"that whole bacteria stuff has been a scientific fairy tale,\" said Bryan Fry, a venom researcher at the University of Melbourne in Australia.\" The team found that the dragon's venom rapidly decreases blood pressure, expedites blood loss, and sends a victim into shock, rendering it too weak to fight.\" ",
"http://news.nationalgeographic.com/news/2009/05/090518-komodo-dragon-venom.html",
" ",
"http://phenomena.nationalgeographic.com/2013/06/27/the-myth-of-the-komodo-dragons-dirty-mouth/"
] |
[
"Homo floresiensis was a pygmy ancestor from Indonesia who were hunted by Komodo dragons. So not only are you half the size of humans today, but gigantic lizards tried to eat you.",
"http://humanorigins.si.edu/evidence/human-fossils/species/homo-floresiensis"
] |
[
"Haast's Eagle",
"\nVarious felids",
"\nVarious hominids",
"\nVarious crocodilians",
"\nMegalania",
"\nThylacoleo",
"\nHyenas",
"\nVarious others",
"Of course, odds are that in most cases these weren't ",
" ancestors, but humanity as a whole has had many predators. "
] |
[
"Wouldn’t cemeteries contaminate ground water like landfills do with lechate?"
] |
[
false
] | null |
[
"Yes. A quick Google scholar search can reveal several articles detailing the different contaminants and the risks that they pose. Contaminants range from heavy metals and organic solvents used in embalming to antibiotic resistant parasites. The potential is there. Natural attenuation can take care of some concerns, but not all.",
"For some references:\n",
"https://scholar.google.com/scholar?cites=14174838916457223178&as_sdt=80000005&sciodt=0,23&hl=en"
] |
[
"This is why sealable vaults are used. Vaults also prevent the divots that occurs when a coffin collapses underground. Earthquake can unseal the vaults though. ",
"I recommend natural burial if it is available in your area. This allows normal deterioration of the human body in a containment field."
] |
[
"Not true at all. Embalming chemicals are a major source of pollution."
] |
[
"What criteria are used to determine whether black hole is stationary or spinning, if black holes can't be observed?"
] |
[
false
] | null |
[
"We can \"observe\" a black hole's spin just as we can \"observe\" its gravity - by its effect on other things. I don't know if any black hole's angular momentum has been measured yet, but it would be expected to drag spacetime around with it (frame dragging) which would have an effect on how things orbit."
] |
[
"Also like to add that it's expected that all black holes have some spin anyways. Pretty much because it would be extremely unlikely to have the black hole have exactly 0 angular momentum. Additionally any actively accreting black hole will have angular momentum imparted on it from the infalling material."
] |
[
"Not just how objects orbit, but it's distortion of spacetime affects the red-/blue-shifting of light from the objects behind it. "
] |
[
"If it is common for moons to be tidally locked to their planets, why is the same not true of planets and their stars?"
] |
[
false
] | null |
[
"It's because the tidal stress on the planet from its star is generally smaller (the exception being the \"Hot Jupiters\" which ",
" in fact tidally locked). ",
"The tidal force depends on not only the strength of gravitational attraction, which is quite strong from planets/stars of course, but also on an additional term which is the size of the body compared to the size of the orbit, Δr/r. For moons around planets, this term Δr/r is much larger than, for example, Jupiter and the Sun. What this is capturing is how much ",
" gravity attracts one side of the planet compared to the other. For the tides of Earth's oceans, the gravitational force from the Moon changes much more moving from one side of the Earth to the other than that from the Sun does, so lunar tides are stronger than solar tides. The gravitational force from the Sun on the Earth is much stronger than the Moon's, but it doesn't change as much across the Earth as the Moon's does.",
"Some stars are in very close binaries with periods of hours or days, and have very large values of Δr/r. These stars are tidally locked to one another, which means they spin much faster than they otherwise would (the Sun spins around once a month). The fast spins mean they have strong magnetic fields, so ",
"these stars often have large star spots and coronal flares",
". "
] |
[
"It's in a 3:2 spin/orbital resonance, so tidal forces are strongly at play, though it's not the same thing as being tidally locked. It's no accident that Mercury is the only planet in our solar system to be so strongly affected by tidal forces since it's the closest to the Sun. The eccentricity of the orbit is to blame, but the eccentricity itself is also strongly influenced by Jupiter and is difficult to explore without computer modeling. "
] |
[
"Thank you, this was very helpful"
] |
[
"How can I measure the amount of arsenic in water?"
] |
[
false
] |
I'm trying to earn a small research grant for myself for the upcoming summer. My research idea is to measure arsenic levels in the water in and around a place called Rabbit Island. The island is in northern Michigan in Lake Superior. Long story short, there's lots of stamp sand, which contains arsenic, copper, and chromium, in the area from copper mining long ago. The deposits are getting into the rivers. While the levels are low, there aren't really many heath risks to humans or animals, but it could very well be rising. Only problem is, how do you measure arsenic levels in water?
|
[
"http://www.watertechonline.com/drinking-water/article/the-challenge-measure-arsenic-in-drinking-water-0807",
"Check the method IDs. Google isn't hard to use."
] |
[
"http://pac.iupac.org/publications/pac/pdf/1992/pdf/6404x0575.pdf",
"(Edited to put in the context of As determination as opposed to As containing compounds, which the paper is talking about)",
"... an ICP-AES detector offered the possibility of continuous\nmonitoring of arsenic. \n...",
"... an ICP spectrometer is simple and employs a short piece of\nTeflon tubing ...\nArsenic is monitored at the wavelength of the prominent arsenic lines; the emission line\nat 189.0nm is the strongest emission line but can only be used with vacuum or purge\ntype spectrometers. The emission line at 193.7nm has greater sensitivity than the\n197.2nm or 228.8nm lines but is affected by the carbon content in the solution because\nof the carbon emission line at 193.lnm. The 228.8nm line is the least sensitive\nbut is not affected by the carbon interference. The 197.2nm line is intermediate both in\nterms of sensitivity and carbon interference. Thus, the 193.7nm line or the 197.2nm\nline is used for aqueous phase... and the\n228.8nm or the 197.2nm line are used for... organic solvents.",
"...\n Selectivity may be defined as the number of moles of the interfering\nelement required to produce the same emission as a mole of arsenic. Selectivity\ndepends on the wavelength of the As emission line, the resolution of the\nspectrometer, the ICP operational parameters... Examples of the reported selectivity of the As 193.7 line were: more than 10",
"\nfor Ca, Cd, Cu, Hg, Zn, B, P, Se, and K ; 10",
" - 10",
" for Co, Mn, Fe, Si, Ni, Cr and Sn ; 500 for\nMo; 300 for Pb; 195 for Al and 51 for Ti. With the As 228.8nm line, Cd\ninterference (228.8nm) may be a serious problem if Cd species are present in the\neffluent. Interference by sodium chloride has been considered in terms of a\nchange in background emission. Appropriate interference correctors can probably\nreduce these spectrometric interferences.",
"http://en.wikipedia.org/wiki/Atomic_emission_spectroscopy",
"I don't know if that's out of the realm of possibility or not, it's just the first thing that came to my mind. "
] |
[
"There's a book called Standard Methods for water and wastewater that is exactly for this purpose. Given that the book is several hundred dollars, I don't have a copy lying around. However, I can almost guarantee there are several available methods...probably colorimetric, mass spec, etc. Check with EPA to see what methods they use and use that one if you want to get published."
] |
[
"Would sticking a conductive piece of metal in a USB port such that it bridges all the contacts fry the computer?"
] |
[
false
] |
What would likely happen? Would the USB controller be fried? I'm curious.
|
[
"It shouldn't, no. Generally, shorting out a voltage supply is a bad idea. However, the USB standard requires that there be some sort of protective mechanism in place. This normally takes the form of a PTC device - sort of an automatically resetting fuse.",
"PTC stands for positive temperature coefficient. When the device experiences high currents, it heats up (like any device). The 'PTC' part means that as it heats up, its resistance increases drastically. This intrinsically limits the amount of current which can flow through the circuit.",
"Worst case, you ",
" fry the USB controller, but that shouldn't damage the rest of the computer.",
"edit: This is all assuming that the computer and all USB devices adhere to the USB standards. I've seen some that don't."
] |
[
"Great answer, thanks!"
] |
[
"Bridging all contacts would not cause the power supply to fry the computer, however you would need to worry about your data pins. The data pins are the two in the center, and they're usually around 1V positive or negative. If the metal object we're shoving in there contacts the 5V+ and data pins it will blast 5V into those pins, and even for the brief fraction of a second before the metal object contacts the ground pin on the opposite side this could do some damage.",
" No sparks or smoke or dramatic stuff, it might heat up significantly before the power cuts out. Power will likely come back on again, but if plugged in wrong you might fry the data pins and cause it to be a \"charging only\" USB port."
] |
[
"How does gravity behave in the center of the earth(or any planet)?"
] |
[
false
] |
If somehow a straight hole was drilled from one side of the earth to the other and was sustained, how would gravity behave? I mean to say that if something(or someone) where to decend into the hole, and assuming the temperature in the center of the earth didn't kill/disintigrate it/them would it simply remain there? I say the hole would have to be sustained because you would literally have the entire world weighing you down and it would no doubt collapse unless some technology was implemented.
|
[
"As the other replies state, there is 0 net gravity in the center of the Earth. But for the mathematically inclined, I can add the following:",
"To see how this works mathematically, first observe that any spherically symmetric body can be thought of as a bunch of infinitely thin shells, all nested within one another. Then if we can find a way to characterize the gravitational pull of one such shell, we need only \"add up\" all the different shells. (If you're familiar with calculus, you may be getting flashbacks about now.)",
"The derivation is a little too hairy to draw out on reddit, but ",
"here's",
" a nice demonstration of it. To summarize the derivation, you use the differential form of ",
"newton's law of gravitation",
" to find the gravitational contribution of an infinitesimal mass element of the shell dM. You then need to integrate over all the dM's, the obvious choice for coordinates being polar as you integrate over the entire shell in a circular manner. ",
"After a little bit of trigonometry, you arrive at the ",
"following",
" antiderivative, which when solved for the indicated case of r=0 (i.e. the center of the shell of mass) gives a force of F=0.",
"Finally, you add up the contribution of all the infinitely thin shells. And since 0+0+0...=0, you arrive at the conclusion that the net gravitational force inside the Earth is zero."
] |
[
"Or more simply skipping the math, just assume that for every point in the perfectly symmetric shell which exerts a force, there is another exactly opposite which exerts the same force in the opposite direction.",
"They play tug of war with each other, and the center doesn't move. Now imagine that every part has an exact replica (same mass, same distance) in the exact opposite direction. ",
"This means that there is a lot of gravity, but it manages to perfectly balance out."
] |
[
"Yep, the derivation is for fun :)"
] |
[
"What part of the brain enables us to predict someone's sexual orientation?"
] |
[
false
] | null |
[
"There is no such single part of the brain"
] |
[
"The brains of homosexual men are in some ways more similar to those of women. See an earlier thread on this ",
"here",
" with a relevant link. ",
"There are differences in how certain parts of the brain may be active (i.e. the extent to which they respond) based on sexual orientation. The easiest example of this is how sexual preference affects response to pictures of people or faces of the same or opposite gender. ",
"You can find a little bit of a review ",
"here",
" <- pdf! ",
"Importantly, there is no single region or area. There are patterns of differences across many structures and there is no single \"feature\"."
] |
[
"The brains of homosexual men are in some ways more similar to those of women. See an earlier thread on this ",
"here",
" with a relevant link. ",
"There are differences in how certain parts of the brain may be active (i.e. the extent to which they respond) based on sexual orientation. The easiest example of this is how sexual preference affects response to pictures of people or faces of the same or opposite gender. ",
"You can find a little bit of a review ",
"here",
" <- pdf! ",
"Importantly, there is no single region or area. There are patterns of differences across many structures and there is no single \"feature\"."
] |
[
"3 Super volcanoes have been active this year all recording >4 magnitude earthquakes already. How big of a deal is this?"
] |
[
false
] |
Anyway, I'm wondering how often do these volcanos show activity. The other 16 supervolcanoes this site is tracking have shown no activity recently. Anyway, I was just wondering to what degree this is a threat. As far as I can understand, Supervolcanoes are labeled that because an explosion from them can impact the entire planet. Anyone want to clear up this information for me?
|
[
"Hey, you're from my home city!",
"But yeah, magnitude 4 is nothing, in Wellington we get a few of those a year. It's just the standard background rumbling - in fact, I've heard that it may be a good thing to have lots of little earthquakes to release the pressure, so when the \"big one\" happens it's not quite so big."
] |
[
"Hey, you're from my home city!",
"But yeah, magnitude 4 is nothing, in Wellington we get a few of those a year. It's just the standard background rumbling - in fact, I've heard that it may be a good thing to have lots of little earthquakes to release the pressure, so when the \"big one\" happens it's not quite so big."
] |
[
"If that's so, then why do seismologists hit the \"volcano panic\" button when they sense lots of little tremors in and around a volcano? Volcanic eruptions can be predicted, these days, but not earthquakes. Is the eruption of a supervolcano an earthquake?"
] |
[
"Venus is currently visible in the night sky in the US. Why is it going from super shiny big dot to almost not visible at all within 15 seconds?"
] |
[
false
] | null |
[
"Hi dizguc 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.",
" ",
" "
] |
[
"Planetary Sci"
] |
[
"‘Planetary Sci’"
] |
[
"Magnets: Energy from repelling poles?"
] |
[
false
] |
I'm new to all of this but I had an interesting thought. North and south poles attract each other, but north + north repels; is there an energy that could be harnessed by holding the magnets in place and running a coil between them?
|
[
"The short answer is no -- you can't get any more energy out of repelling magnetic poles than it costs to bring them together.",
"If you want an explanation of why your specific idea is wrong you'll need to explain it a bit better -- where does the coil go?"
] |
[
"An analogy that may be applicable is lifting a weight up to the ceiling and hanging it on a hook, the work you put in lifting the weight up is just stored as potential energy. There is no energy to harness until you unhook the weight and let it drop. ",
"Pushing the magnets together (or reversing the poles and pulling them apart) and then fixing them in place is like lifting the weight and hanging it there. "
] |
[
"Layman here but I took a grad-level class on Electromagnetics last term and stayed at a Holiday Inn Express last night.",
"The work you put in pushing the magnets towards each other is just exchanged with the potential energy of the field, which means no energy is created or destroyed, just stored.",
"There is no induced current in the coil in between until you start moving either the magnets or coil around."
] |
[
"Besides H20, would any other liquid be suitable to bathe in?"
] |
[
false
] |
Bit of a weird question but I'm curious. Is water the only safe compound humans can use to rinse off? Is there any other compound that: isn't absorbed by the skin; can mix with soap, skin oil, and common skin contaminants; is liquid at comfortable temperatures; nontoxic when ingested in small amounts; won't harm the eyes or other sensitive tissues; doesn't impart any smell to the body?
|
[
"Milk isn't the type of answer I'm looking for since it's mostly water anyway--same goes for buttermilk, juice, etc.",
"I thought about vegetable oils but it seems like those would just leave you really greasy. "
] |
[
"Supposedly people used to sometimes bathe in milk, because they thought that it was good for them and to show that they were rich enough to do that. ",
"Egypt's Cleopatara and Poppaea Sabina, a wife of Roman emperor Nero, took milk baths to improve their skin.",
"http://www.bbc.co.uk/news/uk-scotland-highlands-islands-18955103",
" ",
"It is said that Cleopatra, Queen of Ancient Egypt, took baths in ass milk to preserve the beauty and youth of her skin.[1] Legend has it that no less than 700 asses were needed to provide the quantity of milk necessary for her daily bath.[9][10]",
"This was also the case of Poppaea Sabina (30 – 65), second wife of Roman Emperor Nero, who is referred to in Pliny’s description of the ass milk virtues for the skin:",
"It is generally believed that ass milk effaces wrinkles in the face, renders the skin more delicate, and preserves its whiteness : and it is a well-known fact, that some women are in the habit of washing their face with it seven times daily, strictly observing that number. Poppaea, the wife of the Emperor Nero, was the first to practise this; indeed, she had sitting-baths, prepared solely with ass milk, for which purpose whole troops of she- asses used to attend her on her journeys.[11]",
"Pauline Bonaparte (1780–1825), Napoleon’s sister, is also reported to have used ass milk for her skin’s health care.[9]",
"(Cites in the article)",
"https://en.wikipedia.org/wiki/Donkey_milk#Cosmetic_use",
" ",
"Also in ancient Greek times soap hadn't been invented and they used to use olive oil to clean the skin. As far as I know nobody used to actually bathe in it, but you ",
". "
] |
[
"They would pour the (often scented) olive oil over their body and meticulously scrape it off."
] |
[
"Is the phenomenon of mixing certain foods and getting sick from that specific mix real? Or is it just in peoples' heads?"
] |
[
false
] | null |
[
"This has been removed because seeking ",
"medical advice",
" on ",
"/r/AskScience",
" is against our guidelines.",
"Please see our ",
"FAQ."
] |
[
"Wow. Asking if a combination of food can make someone sick is medical advice and not human biology? ",
"Maybe I worded the question poorly as I had been drinking a bit, but I don't think I was asking for medical advice. I was asking a true/false statement about how the body works. \"Can a combination of foods make one feel ill, as my wife claims.\"",
"If I word it that way instead of the long-winded way I wrote it last night, would it pass muster or would I still need to go to a different sub? "
] |
[
"Well definitely read ",
"this post",
" before you do anything. If you want help trying to rephrase the question to fit ",
"/r/askscience",
" after reading that, then ",
"message the moderator team",
" and we'll be glad to help you out!"
] |
[
"Is there any peculiarity about the places a supercontinent splits (e.g. the Atlantic coastlines of Africa and South America) or is it just about the subterranean magma flow?"
] |
[
false
] | null |
[
"There are a couple of things that (potentially) contribute to where the rift system that breaks up a supercontinent will localize, but all of them will generally lead to the rift system initiating broadly in the center of the supercontinent and roughly coincident with where the supercontinent was joined together in the first place. ",
"In detail, the presence of the supercontinent contributes to (1) an accumulation of heat beneath the supercontinent from insulation of the mantle by the thick continental crust, which will be greatest roughly near the center of the continental mass and (2) the development of a ",
"geoid",
" high within the supercontinent (and a corresponding geoid low in the surrounding ocean basin). In a very general sense, warmer earth materials mean weaker earth materials, so the first property would tend to make areas in the center of the supercontinent weaker. The geoid high represents an instability that likely drives (or at least contributes to) the breakup of the supercontinent. Once there is a force driving supercontinent breakup, the resulting rifts will localize where the continental crust is the weakest (i.e. if you start deforming any heterogeneous material, the weakest portion will start deforming first). As mentioned earlier, the center of the supercontinent may be warmer and weaker due to the insulation effect, but anything that contributes to a reduction in strength in a particular area may help to initiate a rift in that region. One of the primary sources of weakness are preexisting structures, meaning that the ",
"sutures",
" marking the locations where the constituent continental portions of plates were joined during supercontinent assembly likely are important 'guides' for the localization of rifts during breakup. Pangea is a good example, at least in the North America - Europe portion, as the rifting largely followed the location of the mountain ranges (e.g. the Appalachians, etc) that were formed during the assembly of Pangea. For those interested in more details, there are a variety of review papers about the supercontitent cycle which discuss the breakup and assembly processes (and the variety of ideas related to them) in great detail, e.g. these papers ",
"1",
", ",
"2",
", or ",
"3",
"."
] |
[
"Do plates fuse during the formation of a supercontinent? Is there any transverse motion creating faults? Are there hot spot volcanoes in the continental interior?"
] |
[
"Do plates fuse during the formation of a supercontinent?",
"Yes, this is generally what happens during continental collision, whether this is occurring as part of supercontinent assembly or more generally. A suture (as I linked to above) represents a former ocean basin and plate boundary that was consumed during collision.",
"Is there any transverse motion creating faults?",
"There may certainly be strike-slip / transform motion on faults within a supercontinent, it all depends on the details of the plate motion / dynamics at the time.",
"Are there hot spot volcanoes in the continental interior?",
"There may be, as with today, the location of most hotspots are semi-fixed with the plates moving over them, so if a supercontinent forms over or moves over an existing hotspot, there is nothing precluding hot spot volcanism from occurring. Really, there is nothing particularly special about a supercontinent condition other than all of the continental portions of plates are joined."
] |
[
"air conditioner heat removal rate"
] |
[
false
] |
Does the heat removal rate of a given air conditioner (heat removed per hour) depend on the temperature difference (Tout - T in) ?
|
[
"Yes. If it's not removing any heat then there's no heat being put out of the back. (In actual fact, that's not strictly true - there will be some additional heat produced due to the inefficiency inherent in the machine). If you're cooling a room, that heat is going to be put out the back of the machine."
] |
[
"followup. Since the energy required by the air conditioner to remove a given amount of heat depends on the outside temperature, at what outside temperature is the rating (Btu/ hour) measured?"
] |
[
"It really depends on the OUTSIDE temperature. As orbitalpete said, the heat is released from the back. Specifically, an air conditioner has two parts. If you think of a whole-house unit, you have an inside and outside unit. The outside unit (condenser) releases heat. If it is cold outside it is much easier to release that heat. Air conditioners work much better at moderate temperatures. If it is super hot outside the condenser may not be able to release much heat. ",
"In a through the wall, or through the window unit, the heat release is the part with the fins in the back.",
"In general, however, heat transfer of any kind does rely on the temperature difference."
] |
[
"Do the powerball numbers 01-02-03-04-05 have the same odds showing up as any other combination?"
] |
[
false
] |
Would I be anymore lucky picking random numbers than I would be if I picked 5 numbers that are next to each other?
|
[
"Every combination is exactly likely as any other (assuming the numbers are truly selected at random).",
"We humans tend to assign special significance to numbers with recognizable patterns like that, but they are only special in our minds. Every combination is equally likely."
] |
[
"You could use this \"special significance\" to your advantage. :-)\nYou'll be among fewer people who choose those numbers, so your percentage of the proceeds will be greater!"
] |
[
"The odds are exactly the same as you want a specific sequence to happen and each ball has the same chances to be picked.",
"For example, if you play with a coin, the odds are exactly the same between TTTT, TTHT, HHHH, HTHT, and any other combinations of head and tail. Here when you draw a ball, you don't put it back to be selected again, but the odds do not change between the next possibilities",
"Imagine you have 50 balls. The odds to get a specific ball is 1/50 (and you can say it's the ball n°1 if you want). Then you have 1/49 chances to get the second specific ball (and you can say it's the ball n°2 if you want) ect."
] |
[
"Why did my eyes change color from the time i was a baby?"
] |
[
false
] |
[deleted]
|
[
"Think that's odd? My birth certificate says I'm A- but my red cross blood donation says I'm O+..."
] |
[
"On a side note, I was born blonde, now my hair is brown....why!?"
] |
[
"As stated ",
"by wikipedia",
" and ",
"its citation"
] |
[
"How can meteorites be pure iron/nickel?"
] |
[
false
] |
I can't understand how some iron/nickel meteorites are pretty much pure iron/nickel. How did so much of these two metals condense from a gas phase to become a meteorite, or several meteorites, or asteroids? Did they used to be the core of a planet? Are they the nuclear ash splash from a nova? I'm OK with gases condensing into denser bodies, but it seems that there would be other materials around if there's iron. And why would it be able to solidify? Is it just condensing directly from gas to a giant crystal?
|
[
"With some exceptions, most iron meteorites are thought to have come from the cores of asteroids. The reason why they are so enriched in iron and nickel is due to ",
"differentiation",
", where the molten iron sinks to the center of the planetary body, leaving behind silicate materials floating on top. Nickel is one of the more abundant ",
"siderophiles",
", hence iron meteorites are also rich in nickel."
] |
[
"Oh man are asteroids blown - up planets? Why did that never occur to me "
] |
[
"Yeah one way I've sort of heard it explained in reverse is that we should actually expect to find huge asteroids that are more-or-less pure elemental stuff. So out there somewhere there's probably an asteroid of pure platinum, because long long ago some huge planet in its molten state had all the different molten metals sort out by density and solidify, then broke up for some reason and all the chunks that were held together by gravity should break up along the edges where two elements meet."
] |
[
"If we lived on a planet orbiting a sun (with similar characteristics of our Earth and solar system) closer to the center of our galaxy, could the light coming from the gas cloud surrounding a black hole outshine the sun?"
] |
[
false
] |
By a black hole I meant the black hole at the center of The Milky Way.
|
[
"In our galaxy, the SMBH at the center isn't accretiing, so it is completely dark. In active galaxies the accretion disk (and surrounding associated gas) is incredibly bright. The luminosity of the sun is ~4x10",
" erg/s. A typical AGN might have a luminosity of ~10",
" erg/s. That is 11 orders of magnitude brighter!",
"However, the question was whether the light would outshine our sun. So let's plonk our solar system in the center of an actve galaxy. Luminosity falls off as 1/r",
" so for the AGN to have the same brightness, it would have to be 158000 times further away. That works out to just 2.5 light years, which is ridiculously close on galactic scales! ",
"So the answer is no on two counts. Firstly our galaxy's SMBH doesn't have an accretion disk. And if it did then you would have to be very, very close indeed to outshine the sun."
] |
[
"The consensus is that most/all do. I'll just quote the first sentence of a 2009 review article (Turner & Miller):",
"Measurements of gas and stellar kinematics have shown that most galaxies harbor a black hole at their center (Kormendy and Richstone 1995; Magorrian et al. 1998; Ferrarese and Merritt 2000)"
] |
[
"sorry, off topic but, has it been confirmed that all galaxies have a super massive black hole at its center, or just most, or it's just random?"
] |
[
"What are the key differences between neural nets and hierarchical hidden markov models?"
] |
[
false
] | null |
[
"There is a great stack exchange answer for this question ",
"here",
".",
"For convenience I've pasted it below:",
"The thing that is hidden in a hidden markov model is the same as the thing that is hidden in a discrete mixture model so for clarity, forget about the hidden state's dynamics and stick with a finite mixture model as an example. The 'state' in this model is the identity of the component caused each observation. In this class of model such causes are never observed, so 'hidden cause' is translated statistically into the claim that the observed data has marginal dependencies which are removed when the source component is known. And the source components are estimated to be whatever makes this statistical relationship true.",
"The thing that is hidden in a feedforward multilayer neural network with sigmoid middle units is the states of those units, not the outputs which are the target of inference. When the output of the network is a classification, i.e. a probability distribution over possible output categories, these hidden units values define a space within which categories are separable. The trick in learning such a model is to make a hidden space (by adjusting the mapping out of the input units) within which the problem is linear. Consequently, non-linear decision boundaries are possible from the system as a whole.",
"The mixture model (and HMM) is a model of the data generating process, sometimes called a likelihood or 'forward model'. When coupled with some assumptions about the prior probabilities of each state you can infer a distribution over possible values of the hidden state using Bayes theorem (generative approach). Note that, while called a prior, both the prior and the parameters in the likelihood are usually learned from data.",
"In contrast to the mixture model (and HMM) the neural network learns a posterior distribution over the output categories directly (discriminative approach). This is possible because the output values were observed during estimation. And since they were observed, it is not necessary to construct a posterior distribution from a prior and a specific model for the likelihood such as a mixture. The posterior is learnt directly from data, which is more efficient and less model dependent.",
"To make things more confusing, these approaches can be mixed together, e.g. when mixture model (or HMM) state is sometimes actually observed. When that is true, and in some other circumstances not relevant here, it is possible to train discriminatively in an otherwise generative model. Similarly it is possible to replace the mixture model mapping of an HMM with a more flexible forward model, e.g. a neural network.",
"So it's not quite true that both models predict hidden state. HMMs can be used to predict hidden state, albeit only of the kind that the forward model is expecting. Neural networks can be used to predict not yet observed state, e.g. future states for which predictors are available. This sort of state is not hidden in principle, it just hasn't been observed yet.",
"When would you use one rather than the other? Well, neural networks make rather awkward time series models in my experience. They also assume you have observed output. HMMs don't but you don't really have any control of what the hidden state actually is. Nevertheless they are proper time series models."
] |
[
"I only have basic understanding of Graphical models, but one key difference is that HMMs are ",
"Generative",
" models, while Neural networks are ",
"Discriminative",
" models.",
"Perhaps other are more equipped to explain this in layman's terms."
] |
[
"Could you elaborate on what you mean by non-linear connectionistic approach? I think I understand the linear probabilistic method of HHMM"
] |
[
"Humidity makes it seem hotter when it's hot outside and colder when it's cold outside. Is there a medium temperature? (If it's above some certain degree the humidity makes it feel warmer but if it's below it that temperature it feels colder?)"
] |
[
false
] |
I've always wondered this and never got an answer. Say for example it's 80 degrees and humid, it will feel warmer than 80 degrees. OK, what if it's 75? Does the humidity still make it feel warmer? If I keep moving down at what temperature does the humidity stop making it feel warmer and actually make it feel colder? Assuming no wind and your a decently humid day with no rain
|
[
"Give this QA a read.. Very informative.. Here is a snip",
"In our training at Penn State, one of our professors declared that high humidity makes it seem colder when the temperature is below 53 degrees F and warmer when the temperature is above 53 degrees F. This makes sense if you extrapolate the heat index chart downward to cooler temperatures. I also can attest to the cooling effect of high humidity at cool temperatures from working outside in a wide variety of humidity conditions during cold weather (including Barrow, Alaska). Because of this experience, I have always said that the most uncomfortable conditions to work in outside are with the temperature right around freezing and the relative humidity at near 100%. However, this has always been a subjective thing and not scientifically well determined. ",
"AccuWeather has done us a great service by coming up with an index that determines the effect of humidity (as well as other parameters) for both cold and warm temperatures, called \"RealFeel\". It also takes into consideration other effects, such as cloudiness, radiation intensity, wind speed, etc. Unfortunately, because this is a patented product, RealFeel is only available by subscribing to AccuWeather's premier products service, which is well worth it if you need detailed information for planning purposes on a routine basis. ",
"http://www.newton.dep.anl.gov/askasci/wea00/wea00133.htm"
] |
[
"That's great! Thank you"
] |
[
"It's heavily dependent on the amount of wind and amount of humidity."
] |
[
"What proportion of total solar irradiance at sea level is within the UV spectrum ?"
] |
[
false
] |
I want to know what fraction of the average TSI 1361Wm is UV and what fraction reaches the ground.
|
[
"Do an estimate based on the image.",
"Your question is starting to sound more and more like homework help, which I am not willing to partake in."
] |
[
"I think this image will answer your question.",
"Really, you are looking for information on the solar spectrum, which will detail the amount of power at each frequency/wavelength. The nice thing about the image I linked to you is that it shows both the top of the atmosphere and the sea-level amount."
] |
[
"I was hoping for the integral of this between 200-380nm."
] |
[
"What happens when you are \"burned to death\""
] |
[
false
] |
What happen to the body when you are burned to death? Does your internal body temp. rise too high like a fever except faster? What stages does the body go through?
|
[
"The big thing is your lungs. The rest of your body is surprisingly resilient but when you inhale hot enough gas your lungs blister and you can't get oxygen."
] |
[
"Ok thanks"
] |
[
"Whats happening is a bunch of things. The heat from the fire is burning your skin causing huge amounts of pain enough to knock you out. It's burning by either denaturing proteins or using the fat reserves in your body as fuel. The smoke, fire and heat from the fire is also entering your lungs throat and esophagus as you try and breath again burning your throat as well as damaging the fluid layer in your lungs ",
"(side note: the only reason your lungs can transfer oxygen into you body is because there is a layer of liquid on your lungs.)",
"The heat is also boiling your blood, and internal fluids, causing massive homostatic shock. In other words, all the homostatic systems in your body that control temperature, blood pressure, CO2 content etc. etc. all go into overdrive. ",
"Basically fire really fucks you up."
] |
[
"Is it really harder to learn new things as we get older, or are we just making excuse?"
] |
[
false
] |
Does the human capacity for learning slow as we age? I feel like I'm making a lot of excuses as to why I'm not learning new things, or retaining things like I use to. Am I just making excuses, or is it really harder for me to learn new things?
|
[
"My personal experience is that plenty of older people learn rapidly and thoroughly. But this isn't the place for anecdotes or speculation, so let's go to the literature.",
"First, language. This may be a special case, but it is one much discussed; we often hear that when it comes to learning a new language, younger is better. ",
"That is not entirely true",
". Adults begin learning languages much more quickly than children, although children tend to reach a a higher level of fluency.",
"Second, computers. Here the old trope is true. ",
"Older people really are worse at learning to use computers",
".",
"But what about learning more generally? I found ",
"this article",
" from 1928 that tackled the issue. Their conclusions were interesting. They found that older people tend to have a little less innate learning ability than children, but that they make up for it with better study habits.",
"This more modern paper",
" paints a complicated picture. To quote: \"older adults are impaired on tasks which require conscious recollection but that memory which depends on automatic activation processes is relatively unaffected by age\"",
"Learning and memory and vast and complicated processes, so we shouldn't be surprised that there is no single, succinct answer. What you should take away from this is that young people tend to have some innate advantages, but they can easily be surmounted by the strengths and maturity of age."
] |
[
"I dont have a scientific explanation",
"Opening like this will get you downvoted every time."
] |
[
"As a Linguist, I would say there isn't enough cause to apply your citation about language to this particular question because it is extremely specific about what it means to say Adults learn certain aspects of language more quickly than children."
] |
[
"What nutrients, vitamins,etc. affect brain neuroplasticity the most?"
] |
[
false
] | null |
[
"So seratonin is the main decider for neuroplasticity to simplify it? What about Omega 3 and it's affects? That's another one I stumbled onto recently while researching this.",
"As for Seratonin, not exactly a nutrient, but what do you think about 5-HTP SAM-e effects? It's a pill that's really popular here in Serbia ",
" and as far as I understand, it's all about raising Seratonin, I doubt you'll understand much, but it says that it's from a african plant called Griffonia Simplicifolia ( ",
"https://www.hiper.rs/stress-and-mood-5-htp-same",
" )"
] |
[
"https://booksc.xyz/book/10659323/88340d"
] |
[
"https://booksc.xyz/book/10659323/88340d"
] |
[
"Is it possible to estimate Earth's total carrying capacity for Human Life? If so, what is it?"
] |
[
false
] |
As there are now around 7billion Humans alive on the planet (or will be soon, if not already), I was wondering if it was possible to estimate earth's carrying capacity for Human life. By carrying capacity I mean how many humans can earth support until some form of Malthusian catastrophe occurs. Will we reach a definitive number or will technology allow us to keep populating for billions of people yet?
|
[
"The idea of carrying capacity is ",
"indefinitely** i.e. without degrading the environment at all*.",
"To get a real understanding of this subject I highly recommend you read a book called \"Overshoot\" by William R. Catton. Or at least look up the terms \"population overshoot,\" \"carrying capacity,\" and \"drawdown.\" But I'll give you the cliff notes: Due to the drawdown of fossil fuels our current population has temporarily overshot the Earth's natural carrying capacity for humans by a huge margin. ",
"\"woaddude\" estimated ten trillion people as the Earth's natural carrying capacity. I don't know how to fully express how RIDICULOUSLY WRONG this number is. It's just... I don't even know. He used the sun's energy for his calculations. But the sun's energy is by no means the limiting factor of human growth. ",
"The point is that the Earth's carrying capacity for humans is way less than the number of humans we have now, and ",
" So a real estimate would be more like numbers seen before the industrial revolution, around one billion, maybe a little more. Technology is another factor, which is also addressed in the book, but I feel like most of so called \"renewable energy\" technologies are nothing more than band-aids that come with their own issues. ",
"Then again, I don't have any colored bars next to my name, so what do I know?"
] |
[
"turn solar energy into food at a 10% efficiency rate, which is pretty optimistic",
"That's ",
" optimistic! Currently, plants utilize solar energy at a rate of less than one percent. Some man-made solar panels, I believe, can get rates of up to 30-40% efficiency; however, converting this to food energy will result in some loss, of course."
] |
[
"I'll do a more optimistic, future-oriented estimate.",
"The average human needs about 2000 kcal/day. That translates into about 10",
" J/day. Energy on Earth comes from two main sources: solar and heat from radioactive decay. We'll consider this solar energy first (10",
" J) because its supply is infinite and we can easily capture 10% of this energy.",
"So 10",
" J x 10% / 10",
" = 10",
" people. This assumes that we can turn solar energy into food at a 10% efficiency rate, which is pretty optimistic. Let's knock it down an order of magnitude to account for non-usability of all of the sunlight's spectrum, diversion of solar energy to other sources, and other inefficiencies. ",
"With that, we can support 10",
" people, or 10,000,000,000,000...ten trillion people. That's a lot. It's easy to poke holes at this estimate, given that supporting such a population would require a lot of technology. It would also be a pretty crowded world, with a pop. density of 10",
" x 10",
" km",
" or 2 x 10",
" ppl/ km",
" This would be uncomfortable, so I'd advise future humans to limit their growth. ",
"Of course, the human living in this world would be very different from humans today. They would have to be biologically and chemically engineered to live sustainably on scarce resources. The main point of my comment is that there are still a great deal of untapped energy resources on Earth, and with intelligent utilization of these resources, it's easy to see how Earth can support a trillion humans, just as it supports trillions of ants, beetles, trees, fish, bacteria, and so on."
] |
[
"Why do we have our most nutritious meal at the end of the day, rather than at the beginning?"
] |
[
false
] |
In western society, most people have their most nutritious meal (and often the only warm food) at the end of the day, around 6pm. In other societies, such as in asia, it is often taken as lunch. But as far as I know there aren't any big populations that start of the day with a big, warm, meal. Why is this? Doesn't it make more sense to ingest calories, and thus energy, before you burn them in your day's activity? Does it have anything to do with metabolism? That we burn most of our calories while sleeping or something? But then it would seem that any sources of 'fast energy' (eg carbohydrates, I think) are going to waste.
|
[
"But as far as I know there aren't any big populations that start of the day with a big, warm, meal. ",
"Full English Breakfast - staple of the UK working class.",
"http://www.bbc.co.uk/food/recipes/stressfreefullenglis_67721",
"http://www.jamieoliver.com/recipes/pork-recipes/the-full-english"
] |
[
"In most Latin American countries, lunch is the large meal of the day "
] |
[
"Cultural reasons only.",
"Cultural and social. This I will agree with. I have seen it change for numbers of reasons. It's hugely important in determining meal times.",
"It doesn't really matter when you eat, not on body composition anyway. Carbs are just stored as glycogen until needed",
"This I am not sure on, and would like citations.",
"However, my point wasn't to nitpick this, but to agree that social and cultural factors are hugely important in determining when mealtimes are.",
"edit Typo"
] |
[
"Why do we refer to the aging of items in \"half life\", why not \"full life\" or the complete age of the item?"
] |
[
false
] |
For example, the half life of DNA is 521 years. Why don't we say the full life of DNA is 1,042 years?
|
[
"because in 1042 years, you'll still have 1/4 of the original sample left.",
"Moreover, suppose you want to describe something that changes at a rate proportional to how much of that stuff you have. I have 100 atoms of stuff, and each one of them has an equal probability to decay in some time x. So at first, with all those 100 atoms, there will be many decays. After 1 half life, 50 of them will have decayed. So now I have fewer atoms, and thus, fewer possibilities for decay to happen... so in the next half life, 25 remain. And in the half life after that 12 or 13 (let's say 12) and after that 6, then 3, then (let's say) 2, then 1... then each half life after that is a 50-50 chance that last atom will decay.",
"Do this for yourself... get 100 coins and flip them. Keep all the heads-up coins. Then flip them again, again keeping all the heads-up coins. Each atom, or DNA in your example, is like that... it always has some probability of \"flipping\" within some time. The half-life is just a convenient choice... how long should I wait until there's a 50-50 chance that one atom will have changed state?"
] |
[
"Let's be a little more specific with words. ",
"We don't know when ",
" any one part of our sample will decay. Each part is an entirely random process. So each atom in a sample of atoms is an independent random process. So ",
" to describe it, is when any one atom has had a 50/50 chance of decaying over time. We could, if we wished, use 1/e, or 1/3 or whatever. 50/50 is just easiest in an experimental standpoint. ",
"But when you have a big assembly of these atoms, then, on average, half of that assembly will have decayed in the half-life. (which is usually how we determine half-life to begin with). But for the remaining material, half life continues to describe, from moment to moment, how likely any one atom is to decay. ",
"The fundamental physics of the decay process \"sets\" the overall half-life for the element generally... but there's no exact prediction of when any one event will occur."
] |
[
"Different elements indeed have different decay rates because different atomic nuclei have different stabilities.",
"You don't have to use half life. You can use 1/4 life or 2/3 life if you want, but half life is simple and convenient"
] |
[
"How do the delta's in the Coordinate System which Leonard Susskind outlines at the start of his Cosmology lecture (up on Youtube) work?"
] |
[
false
] |
He says the physical distance between two lattice points on the cosmological grid is a(t) sqrt(delta x + delta y + delta z I can't really understand the delta's here. I get that they're not really physical distances, because they're supposed to scale with the movements of the galaxies so that they stay in the same points on the grid. The distance is what the a(t) scalar is for. But I don't then really understand what the delta's are for. Why can't the distance between the two particles simply be the a(t) itself? If Delta X isn't really a number, or a distance, how are we multiplying it? How is it interacting with other functions (like a(t))?
|
[
"a(t) does not depend on location. So why would we associate the same number for distance between a pair of galaxies and another pair, regardless of what pair we choose?",
"The best analogy for what's going on that I can come up with is this: sqrt(delta x",
" + delta y",
" + delta z",
" ) tells you \"how many of my standard-length measuring sticks fit between each point?\" Then a(t) tells you \"how long is my measuring stick compared to, say, last year?\" "
] |
[
"I think you're on the right track. Here's another possibly helpful analogy/example: You're measuring the distance across the surface between two points on a spherical balloon. You mark off three straight line segments of equal length that stretch straight between the two points. So you can declare that the distances are \"three lengths apart.\" Now you put some air in the balloon, so that a \"length\" is now twice as long as it was before. This corresponds to changing a(t) from, say, 1 to 2. The points haven't \"moved\" according to someone sitting on them, and they are still 3 lengths apart, but lengths have changed relative to what they were before. a(t) sets the overall scale for measuring distances. That's why a(t) is usually called the \"scale factor.\""
] |
[
"Sure, you can let the units of delta be as big as you want. If we set a(t) to 1 for a moment so it drops out of the distance equation, all you're doing with that equation is measuring the diagonal of a cube in some grid of coordinates via the Pythagorean theorem. The length itself does not depend on coordinates, but you can slice the grid as fine as you want. A meter is a meter whether you measure it with a meter stick or a thousand one-millimeter rulers. "
] |
[
"If there were more black holes than visible stars in our universe, could their mass and gravity account for that of dark matter?"
] |
[
false
] | null |
[
"The idea that massive objects could comprise the dark matter has long been pursued. We know any such stuff, if it were formed from normal matter, had to form before the epoch of nucleosynthesis, which started when the universe was only seconds old. That's why there's been a lot of investigation into \"primordial black holes\" (aka PBHs), ie black holes that formed before that time.",
"You can see ",
"here",
" that there's still debate about whether they could make up the dark matter. If you love details you can check out things like ",
"this paper",
", which concludes in the abstract that it's still possible to make up the dark matter out of PBH's \"if the mass function is extended\", which means \"if they come in a wide variety of sizes rather than all the same size\".",
"So, in answer to your question... the answer seems to be \"yes, it's possible\"."
] |
[
"You've got it backwards"
] |
[
"You've got it backwards"
] |
[
"How are desirable traits in Bonobos selected?"
] |
[
false
] |
From what I understand, they have indiscriminate sex with every bonobo of the opposite gender that they encounter. Wouldn't this eliminate natural selection for bonobos?
|
[
"Nope. It means that a bonobo that doesn't die early on and stays fertile will probably have more children than a dead bonobo.",
"This is enough for natural selection to work."
] |
[
"Without any selection, the bonobo population would increase exponentially. It clearly isn't (in fact, they're endangered), so there's still selection occurring. ",
"So, you're asking, selection for what? As DoorsofPerceptron pointed out, there's selection for survival, which is not trivial. And there still is plenty of room for sexual selection: all bonobo male-female sex won't result in offspring. I don't know about bonobos in particular, but in many other apes sperm will compete inside the reproductive tract -- ",
"this is the best open-access source i could find",
"Generalizations about inferior and mediocre genes are not that useful in evolutionary biology, since we often don't know what exactly makes a bonobo more or less fit. But it definitely is interesting to think about how different mating systems affect the way selection acts on a species or population."
] |
[
"I kind of understand but I still feel like there's something I'm missing. Aren't all the bonobos alive rather a large selection of phenotypes? There seems to be a lot of variation in the gene pool, and it seems like any male member of a group of bonobos is equally as likely to impregnate, as opposed to the most successful male. I realize the least successful males are selected against because they're dead, but it seems like mediocre genes are going to be the most commonly selected for. I'm not calling for bonobo eugenics or anything, but wouldn't this eventually result in an inferior great ape?"
] |
[
"Is there a way to consciously control the exact moment when we fall asleep?"
] |
[
false
] |
Recently, ive been able to hold myself in a wierd limbo between sleep and being awake. It feels like im hallucinating but i can control the direction the images and voices take as well as will myself awake and back into hallucinating. The only drug ive tried is marijuana, not recently, but being really high was similar to what i felt. I always thought sleep was something you could train your body to do at certain times, but ive never heard of anyone being able to decide they want to sleep, and just turn off. I cant replicate what i did regularly, am i just really tired? And on a related note, why do we have the symptoms we do of not enough sleep? (Red puffy eyes, blurred vision)
|
[
"This isn't science based but rather something I do to help myself fall asleep. Once I'm ready to fall asleep (I can't keep my eyes open while reading) I close my eyes and starting counting my breaths. When I lose count, I know I've slipped to a lower level of consciousness. By remembering the last number I was at I at least know when that happened. After a few slips of consciousness the big one usually happens."
] |
[
"and the weight in kg."
] |
[
"If you ",
" were a robot, the distance would have been measured in cm."
] |
[
"Question about brain tumor, in particular Glioblastoma?"
] |
[
false
] |
I just came across an article about the treatment of Glioblastoma and was wondering a) why is it that a Glioblastoma is so severe and other braintumors are not, even though they can be huge in size as well and b) what do people suffering from a Glioblastoma actually die of (for example, does the tumor eventually causes a stroke or bleedings in the brain)? I did a bit of googling, but didn't find much; a fellow scientist, who does research in cancer (not brain tumors though) wasn't really sure as well. So I hope anyone here might know. *(Since my question is a bit blunt on Glioblastoma and death, I phrased the title a bit vague and put my actual question in the text.)
|
[
"A) Glioblastoma is severe for a few reasons. First, it grows very quickly and has a tendency to appear \"out of nowhere\" already quite severe. Here's ",
"one month's growth",
", if you want to see an example. Second, it's hard to remove via surgery, since it can often have \"tendrils\" that are hard to find and reach into other areas of the brain. I don't think we know why exactly specific types of tumors grow quickly, although there's a lot of research into figuring out which genetic mutations give a better or worse chance of survival.",
"B) According to a ",
"couple",
" of ",
"studies",
" I found, the most common cause of death is ",
"brain herniation",
", which basically means your brain is under such high pressure that it gets squeezed out of the skull or into tight compartments, and blood supply gets cut off. People can also die from seizures or brain hemhorrages, or secondary complications like infections."
] |
[
"I can answer part a:",
"Glioblastoma cells are very ",
" and ",
", much more than the \"average\" cancer cell. The tumor cells move to other areas, so they physically spread around the brain. It only takes a few months for the cancer cells to spread and \"take over\" the brain.",
"Here's a ",
"review article",
" (I believe it's free to access) that explains (or at least talks about) the evasiveness of glioblastoma.",
"Here's a link to a ",
"biomedical engineering research lab",
" that's studying the cell migration of glioblastoma cells with efforts to find methods to treat the cancer by reducing the cell's migratory abilities.",
""
] |
[
"Thanks so much for your answers. Especially the second study seems quite on point to my second question. I‘ll have a closer look at it. Would it be okay if I come back to you with follow-up questions in case they arise? "
] |
[
"Why do humans die at body temperatures of 42°C, while the same temperature is normal for birds?"
] |
[
false
] |
[deleted]
|
[
"As you suggested, protein denaturation is the reason why humans become very unwell and eventually die with a core temp of 42ºC.",
"When it comes to protein stability and evolution, evolution typically does not select for stability, but rather function. So if being stable at 42ºC is required for function, evolution will select for it. Whilst not all human proteins will denature at 42ºC, some very important ones will. In the case of birds, evolution has selected for proteins that are stable at such a temperature.",
"In terms of stability, proteins are only marginally stable and are only stable to a threshold in which function is diminished. From experience, a single amino acid mutation in a protein structure can infer complete loss of structure or it could infer large increases in stability (~10ºC). So in general, bird proteins have a higher stability/function threshold than some important human proteins."
] |
[
"Surely their protein structure must be somehow superior to ours",
"Superiority can only really be judged in context. Humans typically inhabit an environment which allows them to efficiently radiate the heat from their bodies and maintain a contstant (low) body temperature irresepective of their level of physical activity. In such an environment there is no need to evolve proteins to cope with a higher body temp.",
"Birds on the other hand have a resting body temperature just a little higher than mammals but while active (in flight) it climbs to about 41-43°. Perhaps they could have evolved to cope with this by evolving a more efficient means of cooling, apparently they did not. Instead they evolved proteins which could withstand this temperature increase. Of course this comes with a trade off often proteins which are more heat stable are less efficient at cooler body temps"
] |
[
"I have had a temp of 42c measured orally...very unwell does not describe the sensation well."
] |
[
"Is it more effective to hold a door shut using your upper body pressed against a door, or using the static friction of your shoe against the floor at the bottom of it?"
] |
[
false
] |
[deleted]
|
[
"(note that the following assumes a rigid door - we all know that the possibility of the door bending is real, but that's ignored here) ",
"In either case, it's all friction. When you press your upper body, you are still holding yourself in place using friction of your feet against the floor. To open the door, the zombie (I assume this is research for zombie defense) must apply enough force to overcome this friction. ",
"When you wedge a shoe in front of the door, the force required to open the door is the force required to overcome that friction, or break your foot -it's that simple.",
"However, when you press against the door, you are adding multiple other ways to open the door, and adding another point of friction. So the zombie must do only one of these:",
"and so on. At the same time however, you are leaning in such a way as to increase the friction between you and the floor.",
"So the answer is dependent on many factors, but it comes down to this: you are adding additional \"minimums\" to the force required to open the door. If any of these are lower than the foot on the bottom of door, then you are less effective. If the minimums are higher (and you are increasing friction), then you are more effective. Personally, I can hold better (and with less fatigue) if I use the shoe on the bottom of the door in almost all cases."
] |
[
"I'd think leaning against the door, since you're using your feet to hold the door in place either way (your torso doesn't hold itself against the door), but when leaning against the door, you can push against it to increase the normal force of your shoes against the floor, thus increasing the frictional force resisting the door.",
"Just be sure to push on the side of the door opposite the hinge."
] |
[
"At the expense of bringing your muscles and ability to maintain your balance in to the equation.",
"From experience we all know the shoe is more effective."
] |
[
"Why is the common decent model accepted and the multi-ancestor model not?"
] |
[
false
] |
[deleted]
|
[
"Basically, only because our models say it is more likely to have one root than multiple to the tree of life. Here's more info on the ",
"Last Universal Ancestor",
" if interested.",
"However, you could still be right for reasons that the models do not take into account."
] |
[
"all extant organisms are just too similar to have multiple origins: we all store genetic information as DNA (except retroviruses but that's a whole different mess...), all use the same nucleotides in said DNA, all use the same combinations of nucleotides to code for the same amino acids, and all use remarkably similar cellular machinery to assemble these amino acids into proteins (many of which are remarkably similar in structure). "
] |
[
"source says: A universal common ancestor is at least 10",
" times more probable than having multiple ancestors…",
"Well that's a big number."
] |
[
"Do/can we use lightning rods to gather electricity?"
] |
[
false
] | null |
[
"Ohm's Law won't help you here :P You're looking for P = I * V.",
"1.21 GW sounds a little on the low side (my low-end numbers would give you ",
"30 GW",
") but it's within the same ballpark. Back To The Future at least got the whole \"there's no way in hell to store it\" part right."
] |
[
"I'm a mere EE student, so take this with a grain of salt.",
"I don't think there is such a system because a bolt of lightning is an extraordinary amount of power. My reference book says that an average bolt of lightning pushes a current of somewhere between 30,000 to 300,000 Amp at a respectable 1-100 MV, and that frankly scares me.",
"I can't think of a normal material that would survive that unscathed, and moreover I can't think of any realistic way to capture that energy to do useful work later on. An enormous bank of very high voltage capacitors is the only thing I can think of that even has a chance of not exploding immediately.",
"e: MV => mega volt, 1 MV = 1,000,000 V"
] |
[
"You can safely assume any very tall structure will be struck regularly, skyscrapers in particular get hit quite often.",
"Belltowers aren't quite high enough to qualify, but should still be equipped with a lightning rod as a protective measure."
] |
[
"What are June bugs and moths doing when they attach themselves to my window screen for hours?"
] |
[
false
] |
Are they really just lazy or is there a purpose to their lounging? They sit there forever.
|
[
"No, ",
"June bugs",
" are beetles in the ",
" genus. Though Wikipedia lists other north american beetles often called \"June Beetles\". (Not being condescending, genuinely curious, but Why didn't you just google it?)"
] |
[
"No, ",
"June bugs",
" are beetles in the ",
" genus. Though Wikipedia lists other north american beetles often called \"June Beetles\". (Not being condescending, genuinely curious, but Why didn't you just google it?)"
] |
[
"I am also interested in this but would like to clarify that I am specifically interested in what they are doing when they have not been drawn to a light source. In my case they tend to aggregate to the side of the house facing south to southwest and with lights on or off. There tends to be larger moths like ",
"antheraea polyphemus",
", ",
"actias luna",
", ",
"eacles imperialis",
"/",
"automeris io",
". I always assumed they were signaling mates with pheromones but would like to hear a more professional opinion."
] |
[
"With Entangled Cooper Pairs, can you resolve the \"which way\" quantum dilemma issue with the Lorentz Force?"
] |
[
false
] | null |
[
"Entanglement doesn't allow FTL communication."
] |
[
"It theoretically can? Hence the whole \"spooky action at a distance\" quote from Einstein.."
] |
[
"The no-communication theorem shows that it can’t."
] |
[
"If the LHC is the only thing powerful enough to do the experiments it does, how can science verify its results?"
] |
[
false
] | null |
[
"Here is an answer I gave in another ",
"thread",
" a couple of months ago:",
"Certainly, while it would be nice if there were two accelerators in the world that could perform to the level the LHC is capable of, there actually is independent confirmation of the result, both at the LHC and, to some extent, from Fermilab.",
"First, there are two independent experiments at the LHC that have detected the likely Higgs boson. These are the ",
"ATLAS",
" and ",
"CMS",
" collaborations. These experiments are looking at different events (the beam collisions, after all, that take place inside the ATLAS detector are different from the ones taking place inside the CMS detector), are using detectors with different designs (see the above links and ",
"this",
" from CERN and the links therein), and have different data analysis protocols.",
"Thus while the source of the colliding beams is the same for the two experiments, everything else is independent. (Perhaps it's not quite the same as two different solar neutrino experiments which have the same source for their neutrinos, but I would say the parallel is not entirely unfair.) Indeed, it was a deliberate choice to have two independent teams with independent detectors and data analysis teams:",
"Having two independently designed detectors is vital for cross-confirmation of any new discoveries made. ",
"source",
". ",
"In addition, although the Tevatron at Fermilab could not get to 5 sigma on this apparent Higgs particle, it was able to get data that is non-trivially consistent with the LHC data. They found results consistent with the LHC results at a level of about 2.9 sigma; you can see ",
"their preprint",
" or this ",
"journalistic account",
".",
"(Original answer ",
"here",
".)"
] |
[
"to simplify fishify's response, the LHC is an accelerator-collider, the \"engine\" that drives a number of different experiments stationed around it."
] |
[
"I'd like to point out that Fermi-Lab's ",
"Tevatron",
" was also capable of detecting the Higgs, and published a result on its detection there just before closing in september.",
"Because the LHC is higher energy, the number of possible higgs events expected in a time period is higher. The Tevatron, with collision energy of 1 TeV, is capable of producing the higgs, and most likely ",
" produce plenty of them during operations, if the higgs does in fact exist. The number of possible higgs events expected in the Tevatron is fewer than at the LHC, and so the Tevatron would not be able to resolve the data to conclude a result as precise as the LHC's. ",
"The Tevatron group's report on the higgs does not conflict or exclude the LHC's result, which is not confirmation, but still is an encouraging lack of ",
"."
] |
[
"To plant scientists: What are the most efficient plants to put inside a home for producing the most oxygen and cleaning up the air?"
] |
[
false
] |
[deleted]
|
[
"Back in the ‘80’s NASA studied exactly what you’re asking. ",
"You can find the quick chart here, or read the original study if you’d like. ",
"https://en.m.wikipedia.org/wiki/NASA_Clean_Air_Study"
] |
[
"Depends on who you talk to everyone will have a different list to give you. Aloe vera is one that always seems to make the list. Mums and dracaena are also on most house plant lists.",
"If you are fairly new to house plants I suggest a spider plant to be your choice. Very easy to take care of, and it takes care of some of your more common toxins and it's pet friendly. You can also repot the smaller spider plants that start growing very easily and spread them around your house, without having to worry about them. "
] |
[
"Sounds good. I live in Vegas, anything I should get in particular to keep bugs and stuff away?"
] |
[
"How does donating plasma help save lives exactly?"
] |
[
false
] |
Please be as detailed as possible!
|
[
"Blood plasma can treat hypovolemia (not enough blood). Plasma you donate can be put straight into another person (provided that the blood types are compatible.",
"If the plasma is processed, compounds like clotting factors, and immunoglobulins. These can be used to treat diseases like hemophilia. "
] |
[
"Plasma still has to be matched. ",
"Here's a chart"
] |
[
"I always think it's important to differentiate between donating plasma and selling plasma. When I say selling plasma, I'm referring to the plasma centers where you are paid for your plasma. You can also donate plasma, when you donate blood for a blood center like the Red Cross, the whole blood is separated into packed red blood cells, plasma, and platelets. Some blood centers also do plasma donation using plasmapheresis the same way that plasma centers do, but this isn't super common. Plasma for transfusion isn't in as high a demand as packed cells and platelets.",
"OK, so now that we have that terminology down, donated plasma is transfused into people who have coagulopathies, or clotting defects. It's sometimes used for volume expansion in people who are hypovolemic but it's technically not supposed to be indicated unless there is a coagulopathy which there often is if the hypovolemia is caused by rapid blood loss. When someone is bleeding out, they're not just losing blood cells but also the clotting factors and other proteins found in their plasma, so it's good to use plasma for volume replacement in that scenario. Someone who has a clotting factor deficiency for whatever reason, could theoretically be treated with plasma though it is more common now for people to be taking clotting factor concentrates which are also made from plasma. Plasma is also used to rapidly reverse the effects of the anticoagulant (\"blood thinner\") warfarin, which inhibits synthesis of several clotting factors in order to reduce stroke risk. In overdose situations this is a very handy aspect of plasma transfusion. Plasma is frozen almost immediately after it is separated from the cells. Its long shelf life (1 year, compared to about 35 days for red cells and 9 days for platelets) combined with its limited uses means it's not really in high demand. Many blood centers now ask for so-called double-red donations which return the plasma but allow you to donate twice as many red cells.",
"That's donated plasma. Now for sold plasma. Organ and blood donors cannot legally be compensated for their donation, so that should tell you right away that this is not plasma that's going to be transfused into a person, exactly. Incidentally, countries which pay blood donors have historically and currently had much higher rates of transfusion transmitted HIV. In any case, this plasma is used for a variety of other uses, primarily in the pharmaceutical, research, and clinical laboratory industries. They are used to develop and manufacture lots of medicines, for example. We use them in clinical laboratories as control materials- they are pooled and then assayed and assigned a known value, then we use them test our machines to make sure we're giving accurate results. One of my coworkers used to work in a pharmaceutical company and her job was to track down plasma donors who had recent infections of things like varicella because they were looking for control materials that had the right concentrations of antibodies throughout the different phases of illness and convalescence. They're also used to develop and sometimes manufacture the reagents we use to perform the actual testing. So while I honestly think it's a little bit of a stretch for plasma centers to say that you are saving lives with your donation, you are definitely helping people, albeit indirectly. The medicines we take and the tests we need to diagnose illness depend on this sold plasma. I have heard some pretty sketchy things about the practices and standards of plasma centers though.",
"Hopefully that's detailed enough!"
] |
[
"Can a given function be expressed as another unique function? If so how does one find these overlaps?"
] |
[
false
] |
I was wondering since there is an infinite amount of functions possible, there must be certain intervals in completely different functions that are almost identical. For example, are there polynomials (in terms of x) that are identical/similar to ln(x), e , sin(x), cos (x), etc.? How are these found...by chance? By the way, I am a high school student so consider that when explaining your responses. Thanks
|
[
"There are at least three answers to your question, depending on exactly what you are asking.",
"Fix some function f(x) on a closed interval [a,b]. If ",
" is continuous, then we can approximate ",
" arbitrarily close by a polynomial on that interval. This is actually a very strong statement since polynomials are very nice functions but continuous functions can be quite nasty.",
"This theorem is a special case of the Stone-Weierstrass theorem, and is itself often called the Weierstrass polynomial approximation theorem. What's even better about the theorem is that not only does it guarantee the existence of such polynomials, but it also gives a way to explicitly construct them. The so-called Bernstein polynomials offer a way to construct a polynomial that approximates a given continuous function arbitrarily closely.",
"This theorem (the special case, not the Stone-Weierstrass theorem) is taught in a first-semester course on real analysis.",
"If the function ",
" is C",
" (which means it can be differentiated at least ",
" times and all of those derivatives are continuous), then we can construct an approximating polynomial of degree ",
" given the derivatives at exactly one point in the interval. These are called Taylor polynomials. However, there are many more subtleties with this class of polynomials, since we may not be able to approximate the original function on the entire interval or even more than one point.",
"This theorem is typically taught in Calculus II, at least how to construct the polynomials, maybe not the precise statement of the theorem.",
"Finally, if ",
" is what is called ",
", then it turns out that its values in ",
" open interval ",
" determine the function everywhere else. (In fact, you don't even need an open interval. All you need are the values of the function on a set that has an accumulation point, e.g. the set {1, 1/2, 1/3, 1/4, ...}.) For instance, the function f(x) = e",
" is analytic. If you are given the values of e",
" on any open interval, then there is no other (analytic) function that has those same values in that same interval. So that partially answers your question of whether there can be a polynomial that is identical to something like ln(x), sin(x), etc. It turns out that all of those functions you listed are analytic, and so are polynomials. So there is ",
" polynomial that is equal to sin(x) or cos(x) or ln(x) or e",
" on any open interval."
] |
[
"You say there is no polynomial that is EQUAL to those \"analytic\" functions. What is the definition of equal?",
"The functions ",
" and ",
" are equal on a set ",
" if f(x) = g(x) for every ",
" in ",
".",
"For example is there a polynomial that is approximately those functions?",
"As I wrote, if you fix a closed interval and fix any ",
" function, then we can approximate the function as closely as we want with a polynomial. So, for instance, let f(x) = |x| (absolute value of ",
") on the closed interval [-1, 1]. Suppose our error threshold is 10",
". Then there exists a polynomial p(x) on the interval [-1, 1] such that the maximum difference between f(x) and p(x) is at most 10",
" on [-1, 1]. If the error threshold is 10",
", then there is also a polynomial q(x) such that maximum difference between f(x) and q(x) is at most 10",
" on [-1, 1]. The polynomials p(x) and q(x) are not necessarily the same polynomial.",
"That is what we mean when we say a polynomial can approximate a continuous function arbitrarily close. ",
"I feel like there must be another function that can define an analytic function.",
"You may think so, but you would be wrong. What I wrote about analytic functions is not meant to be obvious or even something that makes sense at first. It does seem bizarre that a function could be completely determined by only a \"few\" values. But it turns out that being analytic is a very strong condition to put on a function.",
"Generally speaking, analytic functions have global behavior determined by local behavior. Being able to deduce global properties from local properties is a very rare thing in mathematics.",
"Just to confirm is there a difference between a polynomial and a function.",
"A polynomial is a sum of non-negative integer powers of ",
". So x",
"+1, x",
"-4x",
"-7, etc. are polynomials.",
"Also... your questions are not exactly trivial to answer. As I said, the required math is not taught until a first or second semester course in real or complex analysis. Those are courses typically taken by a math major in college in their sophomore year. If you are only in high school and just starting calculus, even understanding what these theorem are saying may be difficult. You are asking good questions, but don't be discouraged if a lot of this goes over your head."
] |
[
"Yes. The coefficients can be any real number. In general, a polynomial is of the form",
"a",
"x",
"+a",
"x",
"+...+a",
"x",
"+a",
"x+a",
"where a",
" are any real numbers. If a",
" is not 0, then we say that this polynomial has degree ",
" (the highest power of ",
" that appears)."
] |
[
"Why does table salt applied to a wound cause pain?"
] |
[
false
] |
I know that sodium is involved in a neurotransmission, but I'm not sure if that is related. I also know that NaCl is essentially pH neutral, so I don't believe any acid-base reactions are going on.
|
[
"A quick Google search turned up this answer",
"Provided by Walter Sipe, M.D., clinical fellow of pediatric gastroenterology, hepatology, and nutrition, University of California, San Francisco (former HHMI medical fellow)\nBefore we get to the science part of your question, let me start by saying: Do not put salt on your cut. The single most important aspect of wound care in the backcountry is vigorous and copious irrigation with clean water (filtered or chemically treated so it is drinkable). You can generate a high-pressure stream by filling a zip-top plastic bag with water, poking a tiny hole in a bottom corner of it with a needle, and then squeezing the bag so water comes out through the hole. For dirty wounds, vigorous scrubbing to remove foreign bodies is also important. Exposing wounds to iodine, alcohol, peroxide, and pure salt is no more effective than water irrigation at preventing infection and can potentially damage tissues. The safest way to slow bleeding is to hold direct pressure on the wound until the bleeding stops.\nThe reason that salt stings a cut is that as the salt dissolves, it causes the fluid surrounding damaged tissues to become extremely hypertonic (which means that the concentration of salt and other electrolytes is higher than it is in normal body fluids).\nPain-sensing neurons have receptors on them that respond to a variety of stimuli. For example, there is a specific receptor that responds vigorously to capsaicin, which is the substance that gives jalapeño and habanero peppers their kick. So, quite literally, when you are adding hot pepper to food, you are (carefully, I hope!) inducing the sensation of pain to complement the other flavors of the meal.\nMore recently identified is a receptor that responds to changes in electrolyte concentration—such as the change that a large amount of salt induces. Thus, putting salt on a wound stimulates pain-sensing neurons in much the same way hot pepper does.\nWhen tissue is damaged, many pain receptors become sensitized—that is, they need a much lower level of stimulation to respond than they normally would. (For example, after you have burned your mouth, try eating some spicy food that you could normally handle—ouch!) Salt may then compound the pain by further damaging injured tissues and making them more sensitive in general.\n10/16/06"
] |
[
"It leeches fluid from the tissue surrounding the wound. Additionally, it may directly activate some pain receptors, but I can't find any support for that theory right now."
] |
[
"Thanks for saying \"this answer\" rather than \"the answer\". The thing about sodium is that it has a critical function in generating the most basic part of the nervous response, the action potential. Any time you mess with sodium concentrations, you're affecting the function of neurons at a deep level, not just activating specific receptor proteins. I'm guessing this explanation was, er, de-technicalized a bit for public consumption. "
] |
[
"If the stratum corneum is dead and covered in bacteria, why doesn't it decay?"
] |
[
false
] | null |
[
"It does. It constantly does. Think of your skin like shark teeth. Always having a new layer to push the old, dead layer out. Constantly being replaced. "
] |
[
"The stratified cells are tightly bound together, keratinized like fingernails, waterproof, and constantly shedding. The inhabiting bacteria lack enzymes to break down this cornified layer."
] |
[
"The stratum corneum has a high turnover rate and is constantly shed to avoid bacterial invasion."
] |
[
"Can you get drunk by inhaling alcohol vapors?"
] |
[
false
] | null |
[
"The danger here is that you can not vomit unabsored alcohol to prevent further intoxication if it is overdone."
] |
[
"The danger here is that you can not vomit unabsored alcohol to prevent further intoxication if it is overdone."
] |
[
"Yes because the vomiting reflex in regards to over consumption of alcohol is due to the fluid in the semicircular sacs in your head by the ears (basically motion sickness). Fun fact: if you drink heavy water at a particular ratio to alcohol, you won’t feel dizzy and won’t vomit if you over consume. ",
"EDIT: ",
"source - ",
"http://www.newsweek.com/meet-astronaut-who-discovered-why-you-throw-after-drinking-too-much-442880",
"source if you’re skeptical about Ken Money’s discoveries - ",
"http://www.asc-csa.gc.ca/eng/astronauts/canadian/former/bio-ken-money.asp"
] |
[
"Is the Delta variant a result of COVID evolving against the vaccine or would we still have the Delta variant if we never created the vaccine?"
] |
[
false
] | null |
[
"Delta arose in India when vaccination levels there were extremely low. Delta has only slightly increased vaccine resistance relative to the earlier strains of SARS-CoV-2. And delta has greatly increased transmission capacity. ",
"So delta arose in the absence of vaccination, doesn’t do much to avoid immunization, and has obvious selective advantages unrelated to vaccination. So yes, the delta variant would still be here if there was no vaccination. In fact, if vaccination had been rolled out fast enough, delta (and other variants) would have been prevented, because the simplest way to reduce variation is to reduce the pool from which variants can be selected - that is, vaccinate to make far fewer viruses, making fewer variants. ",
"For all the huge push anti-vax liars are currently making for the meme that vaccination drives mutation, it’s obviously not true, just from common sense. A moment’s thought will tell you that this isn’t the first vaccine that’s been made - we have hundreds of years experience with vaccination — and vaccines haven’t driven mutations in the past. Measles vaccination is over 50 years old, and measles didn’t evolve vaccine resistance. Polio vaccination is around 60 years old, no vaccine resistance. Yellow fever vaccine has been used for over 90 years, no vaccine-induced mutations. Mumps, rubella, smallpox. No vaccine driven mutations."
] |
[
"I think there's a common misconception that needs to be addressed here- something that makes a lot of people believe that vaccines can cause mutations in viruses. Since antibiotics can cause resistant bacteria to evolve over time, it's easy to think that something similar can occur with viruses and vaccines. However, this is a fallacy. Unlike antibiotics, vaccines don't create selective pressure for resistant strains of a virus. At least no more-so than naturally acquired immunity does. ",
"This requires some explanation. Bacteria are living organisms that reproduce on their own. Bacteria that can cause infection in humans can also exist and grow in any suitable environment. Antibiotics are chemicals which can kill certain species of bacteria but which are not harmful to human cells. As enough bacteria are exposed to an antibiotic, occasionally one might have a mutation which gives them a resistance to it, and this resistance allows that bacterium to outcompete their sisters which do not have that gene, and eventually become dominant, thus making an antibiotic less useful over time. ",
"On the other hand, viruses are not living cells. They cannot reproduce on their own. Instead, they reproduce by attaching themselves to another cell and injecting genetic material into it. This material hijacks the cell's protein and RNA or DNA making machinery and turns it into a \"virus factory\", and preventing it from doing its normal job. The cell then releases the viruses into the host's body and then viruses can infect other cells. In the human body, your immune system identifies infected cells and kills them. It also creates antibodies which can bind to virus particles and destroy them. But it takes time for your immune system to \"learn\" how to make the proper antibodies for a given strain of virus. During this time, many cells become infected, creating more viruses and damaging tissue. And as viruses are created, occasionally your cell's machinery leaves a transcription error, or \"mutation\", which can change the way the virus attacks the body. Usually the mutations are irrelevant or cause the virus to be unable to infect a cell. However, very rarely a mutation can cause a virus to be able to do something very different than previously possible- like infect new types of cells or even jump species. Or, in some cases, to evade antibodies which were effective against prior strains of the virus. ",
"A vaccine gives your body a chance to recognize proteins in a certain virus and make antibodies without actually infecting you with the virus. This way, if you actually are exposed to the virus, you will fight it off without it having as many chances to reproduce. Fewer reproduction events means fewer chances to create a mutation which will evade the vaccine. Vaccine derived immunity is very similar to \"natural\" immunity. It's not doing anything to the viruses that your immune system wouldn't have done anyway, but gives it fewer chances to mutate.",
"Lastly, I want to highlight the fact that vaccines kill viruses in the exact same way as your immune system already does, so there's nothing special for them to develop resistance to versus natural immunity. Antibiotics are a completely separate mechanism. You can kill a petri dish full of streptococcus with some penicillin, and the bacteria can also evolve resistance in said petri dish. If you take a vaccine and mix it with a vial of virus particles, it will have no effect on it. In fact, some types of vaccines are designed to PRESERVE virus particles so that they can be put in your body without being destroyed.",
"Edit: Please don't treat this post as authoritative in any way. I am not a virologist, and this explanation is based on mostly general knowledge, and may have errors. This comment was inspired by a now deleted comment that suggested that the existence of vaccine-derived variants is propaganda and misinformation. I was trying to point out a logical fallacy explaining why antibiotics are not analogous to vaccines at all. I didn't expect to get so much attention, and some of the responses correctly pointed out that vaccines actually can and do create selective pressure on viruses in certain circumstances. However, for various reasons, from a public health perspective, it's better for everyone to get vaccinated while it's better to limit antibiotic usage as much as possible. There has been a lot of great discussion generated from this post, including from actual virologists who you should all take with more confidence than what I've said."
] |
[
"Excellent answer. One quibble: using the term 'attaching themselves'. \nI think it is better to say that the virus 'becomes attached'. ",
"I know this is a nuance, but I read variations of 'attaching themselves' a lot and it gives the impression that a virus is acting in some deliberate manner as though it was self-directed. It isn't."
] |
[
"Why could a pebble made of neutron star material slice right through the Earth?"
] |
[
false
] |
During episode 3 of Wonders of the Universe a couple of weeks ago, Brian Cox makes the statement that a pebble made of neutron star material would weigh more than Mt Everest and, if dropped, "it would slice straight through the Earth like a knife through butter." How could this happen? When a normal object is dropped, the object accelerated towards the ground due to the Earth's gravitational pull, correct? So if the pebble slices through to the centre of the Earth, how does it continue to accelerate and slice through the remainder (and what would happen after that?)
|
[
"The density of neutron star material is so high that even the ordinary force of gravity would create tremendous pressures if a small pebble were to rest on the Earth. The entire weight of Mt. Everest weighing on a spot only a square centimeter or so in area would generate pressures far in excess of those any ordinary material would be capable of withstanding. As the neutron star fell deeper into the Earth it would accelerate, then fall through the center of the Earth, it would fall back and forth within the Earth slowly losing speed until it ultimately came to rest at the Earth's core.",
"However, that's a bit academic as a pebble sized mass of neutron star material would not be stable, it would rapidly degenerate into ordinary matter (releasing a lot of energy in the process)."
] |
[
"presuming of course that it was at rest on the surface to start and the earth was a perfect sphere and whatnot. If perhaps it was the situation I imagined in my head when I first read OP's question, a pebble of neutron star flying in from space, it would accelerate down, cut through the earth, decelerate on the way out, and exit with its speed minus whatever speed it lost from say, friction and energy losses to its collision with the earth."
] |
[
"ëh, figurë a nëutron's on thë ordër of 10",
" fm, and ëach has on thë ordër of 1 GëV of ënërgy. Thërë's 10",
" fm",
" in 1 cm",
" so 10",
" GëV of ënërgy? that's likë 10",
" Joulës which is thë samë as thë rotational ënërgy of thë ëarth's rotation says wiki (ordërs of magnitudë articlë, I can't link)"
] |
[
"How do T-cells know which cells they've already inspected?"
] |
[
false
] |
From what I understand, T-cells are constantly traveling in the body, inspecting cells by looking for antigens. If they're self antigens, then the T-cell doesn't attack, whereas if they're non-self, they attack. My question is how does a T-cell know when it just inspected a cell? Does the T-cell leave something behind on the cell to mark it as checked or does the cell itself present something on its surface to indicate that it has just been checked? If there is no such system, then what prevents the T-cells from being stuck in a loop, and just inspecting the same cell over and over?
|
[
"It doesn't know. And it doesn't loop because it's not like the T-cell specifically waits until the current cell under investigation has \"passed inspection\" before moving on. The T-cell just moves around, continuously coming into contact with other cells in the neighboring environment, and if it happens to brush shoulders with bad antigens then it triggers an attack. But if no attack is triggered, it'll just keep on happily moving about. The key is that the time it takes to trigger an attack is much less than the time it takes a T-cell to \"move over\" any given cell."
] |
[
"It might help to see ",
"this video",
", to get a sense for the amount of movement even in a fairly calm environment, the lymph node. Once T cells dissociate from their scanned target, just the random jiggling about in the node means that it almost certainly will find a new target rather than just re-attaching to the same one. (Probably there is a certain amount of re-attachment, but not enough to cause constant loops.) ",
"The video (and several other ",
"equally interesting ones",
") are from ",
"Imaging the Single Cell Dynamics of CD4+ T Cell Activation by Dendritic Cells in Lymph Nodes",
", which explains:",
"T cells approach DCs randomly and, in the absence of cognate antigen, make exploratory contacts with DC dendrites lasting only minutes (19). If a T cell fails to detect the appropriate MHC–peptide complex, it quickly departs to make room for another T cell to interact, thereby enabling each DC to contact thousands of T cells per hour in a process of stochastic T cell repertoire scanning (19–21). Because DCs localize near HEV (28), contacts with newly homed T cells would be favored, further enhancing the efficiency of stochastic scanning."
] |
[
"T-cells have long processes that they use for palpating/probing MHC (the cell-surface molecule that presents antigen). If they find a matching antigen they are activated, if not, they move on (diffusion or what-not).",
"Much of this probing/activation will happen in lymph nodes, where there's plenty of cells jostling for attention to present antigen, so there's no need to \"mark\" a searched cell.",
"In any case, since each T-cell recognizes a specific antigen, \"marking\" it would be useless, since the antigen must be tested over and over until (if ever) the matching T-cell finds it."
] |
[
"What's going on chemically when acid melts through stuff?"
] |
[
false
] |
Does it cause some sort of chemical reaction that destroys some chemical bonds or something?
|
[
"At low concentrations, H+ ions react with X (often a metal) to make H2 and X+. So hydrogen takes electrions from whatever is reacting with the acid. This produces hydrogen gas, and the the ion of the reactant. This reaction will still happen for most acids that become concentrated.",
"Some acids, when concentrated, bevhave differently. For example, concentrated ",
"sulfuric acid",
" (H2SO4) is a very strong dehydrating agent. Its ability to dissolve things often results from it pulling water out of whatever it is reacting with. For example, sucrose (C12H22O11) will react with sulfuric acid to form pure carbon as it makes 11 water mollecules out of the H22O11 in each sucrose mollecule.",
"Another one is ",
"nitric acid",
". Because of its structure, it can oxidize many metals which are more electronegative than hydrogen. In this case, the NO3- ion reacts with H+ and X to make NO2 (or NO), H2O, and X+. Basically NO3- donates oxygen atoms (which are stronger oxidizers than H+), and this is what oxidizes X. Similar acids are listed under the ",
"oxidizing acids",
" wiki page.",
"Lastly, there is one special case acid I want to mention, and that is ",
"aqua regia",
". It is a mixture of nitric acid and hydrochloric acid. It is known to be able to dissolve gold, platinum, and almost all metals. It works by having the nitric acid disolve a tiny bit of the metal (so for gold, Au becomes Au3+). But nitric acid can only put so much Au3+ into solution before the reaction stops (equilibrium is reached). The HCl reacts with Au3+ to make AuCL4-, which removes Au3+ from solution, so more Au can be disolved by nitric acid."
] |
[
"Do you a particular example you have in mind?",
"One that I can think of is the reaction between hydrofluoric acid and glass (which is mostly silicon dioxide). This weak acid will eat through the glass no problem. It's used as an etchant.",
"The fluorine in the acid reacts with the silicon in the glass to produce SiF4. It's a gas that just escapes away. It also makes water. Exposure of glass to HF completely changes the structure of the glass.",
"Does this example help?"
] |
[
"Yes, it does. Thanks!"
] |
[
"Why does gene damage & mutation eventually end up with cancerous cells but not with something else?"
] |
[
false
] |
For example why doesn't it end up with absurd but harmless features? Like, say, you have serious gene damage & mutation in the cells of your breast. Why do those cells become rapidly growing & reproducing cells, instead of, idk, growing weird red hairs on your breast? It might sound dumb and sci-fi but I hope you get the point.
|
[
"Sometimes random mutation does result in such things! However, because the human body has an incredible amount of cells, a single mutation will rarely be very perceptible (especially because many cells are part of large systems that will compensate if it stops performing a certain function).",
"Single-cell mutations only become apparent if the cell in question proceeds to split a large amount of times. This can happen if it's become a cancer cell (which is why we notice those but not all the other mutations), but also occurs if the mutation occurred in a sperm or egg cell. The last bit is how we get organisms with all-new genes, rather than just the parents' genes reshuffled."
] |
[
"it doesn't! you know how older people often have weird pigmentation spots on their skin? also skin tags, and hairs growing out of strange places and so on? that's exactly what you're describing",
"we have trillions of cells in our bodies, a lot of which continue to divide for the rest of your life. mutations happen all the damn time. literally all the damn time. including mutations that can be cancerous, single cells with such mutations arise in your body basically every day but your immune system usually destroys them. you also get strange harmless mutations all the time, most of which either get repaired, or also get destroyed, or die on their own eventually. only a small portion of random mutations in somatic (=not reproductive) cells have the potential to become cancer"
] |
[
"Also, in most cases, the genetic mutations initiate the cell’s “self destruct” mechanism, causing it to die."
] |
[
"Are the rings of Saturn really so fine or is it some due to lack of photographic resolution?"
] |
[
false
] |
In nearly all the photos of Saturn the rings show up as vivid and almost smooth in texture. Are the photos true to nature and the rings are made up of very fine/small rocks/debris? Or is this some kind of photo effect? Things in space are pretty dark so perhaps the exposure might have to be pretty long in order to take a picture with enough light, but in turn blurring the rings to make them look smooth. Thanks
|
[
"Saturn rings are formed from ices and rocks ranging in size from millimeter to meters max (not so common) so in comparison to the huge Saturn, and since they are mostly in the same plane , they seem fine.",
"http://en.wikipedia.org/wiki/Rings_of_Saturn",
" "
] |
[
"It's sort of like taking a picture of the beach - it's made of sand with some larger rocks mixed in, but from any distance (like an airplane to take the example closer to the relative distances of spacecraft from the rings) they all blend into a relatively smooth color."
] |
[
"Exactly. It's worth remembering the scales involved here. Just the B-ring (the inner of the two brightest rings) is twice as wide as the diameter of the earth - with a maximum particle size of a few meters, it is even finer than sand on a beach."
] |
[
"If photons are massless, why are they affected by gravity?"
] |
[
false
] | null |
[
"Because - contrary to what your physics teacher may have taught you in high school - gravity isn't a mysterious force-at-a-distance proportional to the masses of the two objects. In other words, you don't need to have mass to feel gravity (or to gravitate yourself).",
"The picture of gravity you're thinking of is Newton's, and it's quite outdated: it was replaced nearly a century ago by Einstein. In the modern picture of gravity, what looks like a particle moving under gravity is really just the fact that spacetime is curved, and things moving on straight lines (or the closest equivalent) in a curved space look curved. Think about a simple example on the surface of the Earth, which is also curved: if you look at a plane's flight path, it looks highly curved, even though it's taking the shortest route between its departure and destination!",
"Of course, photons and other massless particles live in spacetime, so they'll feel gravity just as well as any other particle. And on the flip side, because photons have energy, and energy is the other side of the coin of mass (think E=mc",
" ), photons can have a gravitational effect of their own. In fact, during the earliest days of the Universe, most of the gravity in the cosmos was caused by photons rather than matter.",
"Einstein's theory reduces, mathematically, to Newton's in the special case where particles are travelling very slow and gravitational fields are weak and unchanging. But as you can see they're very different conceptually, and the gravitational bending of light is one of the most dramatic consequences of the differences between these two pictures."
] |
[
"Please please please look in ",
"r/sciencefaqs",
" before posting. You'll find ",
"the answer",
" there. A ",
"search",
" of previous questions yield ",
"many results",
" as well."
] |
[
"Only massive objects create gravitational fields",
"This isn't true at all! Spacetime curves in response to both energy ",
" mass, and since massless particles like photons still have energy, they'll curve spacetime. As I mention in my top-level post, this isn't just a pedantic concern. Photons were ",
" dominant source of gravity in the very early Universe, causing it to expand in a qualitatively different way than it did later, when matter became dominant. We can test this quite precisely by measuring the ",
"abundances of light elements",
" formed during that radiation-dominated era."
] |
[
"What is actually happening when you whistle?"
] |
[
false
] | null |
[
"The air spaces either between your tongue and teeth or tongue and the roof of your mouth create a resonant chamber that vibrates when you blow air through it. You can change the size of the chamber by moving your mouth/tongue to create different pitches. ",
"edit: grammar"
] |
[
"Usually the faster you get the air to pass over the resonant chamber the harder it vibrates and thus the louder the whistle gets. I believe using your fingers makes a more stable resonant chamber that you can blow harder on and thus produce a louder sound."
] |
[
"Why does rolling my tongue over with my fingers allow me to whistle 50x as loud?"
] |
[
"If you wear less clothes than comfortable in the winter. Would you a) lose weight due to increased metabolism burning fat to keep warm, or b) trigger the body to go into hibernation mode and store fat?"
] |
[
false
] |
Just curious
|
[
"...humans dont hibernate.",
"You'd probably c) be cold, and d) eat more to make up for the extra energy youd need to stay warm."
] |
[
"I typically lose weight in the winter and I by some people's terms don't ware enough layers. Also I will shovel snow in a pair of shorts and a t-shirt because I get really hot and feel like I'm over heating. But I prefer a colder climate any ways. So my story might not be any help to you. "
] |
[
"I .. can't tell if you're trolling me"
] |
[
"Humans need oxygen, but what other gases can replace the other elements in air? More specifically can argon replace nitrogen and would it be safe to breathe?"
] |
[
false
] |
I was recently watching and in the episode it was mentioned that the planet's air is 20% oxygen and 80% argon (or something like that, it's not mentioned in wiki). I was curious about this and dug up about the exact same thing. Then I found . The argon section is lacking. Can we safely breathe an argon-based atmosphere? And on a side note would our voices be lower?
|
[
"You can breathe it. It just doesn't offer significant advantages over nitrogen for regular uses. They use breathing gas mixes to avoid nitrogen narcosis at high pressures mainly. Argon doesn't improve upon nitrogen in this respect (it's actually 2x worse according to sources I found), so there's no reason to use an argon/oxygen mixture. It's more expensive and worse performing. It will make your voice deeper to replace nitrogen with it."
] |
[
"Semi-related"
] |
[
"Actually, argon could be neuorprotective over nitrogen....",
"Here",
"It's important to add that I can find evidence that ",
"xenon",
" can be used as an anesthetic, so we can expect argon to have greater narcotic effects than nitrogen. This could be an issue if we're talking about %'s reflecting our atmospheric composition."
] |
[
"A question about Jupiter and the other gas giants?"
] |
[
false
] |
Are the planets just pure gas? Can I drive a spacecraft straight through the center or will I eventually hit something? What holds all the gas together in a planetary shape?
|
[
"Well, we know its size, and we know its gravity. What we actually don't know is it's composition. :) Not entirely. We have guesses and approximations, that are probably really, really close, but we don't know it ",
". And that's kind of the hold up. ",
"And, because of the extreme pressures, temperatures, and gravitational effects close to the center, we don't exactly know how some materials will react. There is a speculation, that at the center of jupiter, hydrogen in a metallic form might exist .... which doesn't exist naturally anywhere we have looked (so far), and really can't, by our current understandings of the laws of physics. ",
"But, honestly, we don't know all that much for sure about these either, and just about the time we think we have some of them figured out, along comes an exception, or something that doesn't fit the models. ",
"What it boils down to is that there is a ",
" in the universe that falls under the category of \"We don't know that for sure\" -- more than a lot of scientists like to admit, and way more than most ordinary people suspect or belive."
] |
[
"/u/seek3r_red",
" has answered pretty well, I'd just like to share this link: ",
"http://en.wikipedia.org/wiki/Jupiter#Internal_structure",
"...and focus on this particular point:",
"Can I drive a spacecraft straight through the center or will I eventually hit something?",
"Definitely not. Even if there were no solid core, eventually temperatures and pressures will be so high that your spacecraft will be completely destroyed and it may even vaporize.",
"http://en.wikipedia.org/wiki/Galileo_(spacecraft)#Galileo_Probe"
] |
[
"We only know its composition at the surface, because that's all we can see. We know its mass, but we don't know if there's a solid mass of rock and metal in the center or a mass of ice or the gas just gets progressively denser. Its average density is 1.33g/cm",
" but that doesn't really tell us anything about what the core is like. The density of the Earth is 5.52g/cm",
" but the core is much denser. We had to use seismology to figure out what the internal structure is like, which isn't an option for the gas giants at the present."
] |
[
"Question regarding light and how cameras/eyes see images"
] |
[
false
] |
[deleted]
|
[
"What do you mean by 'ordered fashion'?"
] |
[
"I imagine that it wouldn't attain that configuration; I imagine light travelling in many directions and very chaotic so it doesn't make sense to me that we see images."
] |
[
"I believe OP refers to",
"When you see a diagram of how a lens works, it shows light entering in parallel lines and then focused. ",
"and imagines that light coming in from objects somehow attains this configuration before entering the lens."
] |
[
"Chemical trails?"
] |
[
false
] | null |
[
"It's a common optical effect: it's the shadow of a thin straight aircraft contrail. Such shadows are three-dimensional dark slots hovering in the air.",
"To look for these on a sunny day with many contrails, just wait for one contrail to cut across the sun, or wait for it to drift until it crosses the sun. Then at the same time the slot-shadow will be crossing your location, so you can gaze up into it.",
"Why don't we see these constantly? Contrail shadows won't be noticed unless you are positioned within the shadow-slot yourself. In that case, if you gaze along the slot, you'll see darkness against the sky. The blue color of the sky is created by sunlight illuminating air from the side, and within the shadow-slot this isn't happening.",
"Observers outside the slot won't see much. The dark slot is still there, but the sky-darkening effect is then spread across a much wider patch of the sky.",
"It's a bit like gazing through a pane of glass (invisible), versus looking into the edge of the same glass pane (opaque blue-green)."
] |
[
"Wow. Thank you so much. I was kind of freaked out when I saw it :P I really appreciate it. "
] |
[
"Much weirder is when the sun is trailing the plane from your perspective, so ",
"the shadow-slot juts out in front."
] |
[
"Has there ever been a comprehensive pain scale established."
] |
[
false
] |
The reason I ask this is because the age olde argument, of what hurts worse, came up with my girlfriend. We decided to turn to you for answers. Nut shot Vs. Birth. Go.
|
[
"I pass hundreds of kidney stones a year, here is my rating scale:",
"Noticeable pain",
"Annoying/nagging pain (when you start complaining) ",
"Painful pain (when you start taking stuff, applying heat/ice) ",
"Excruciating pain (when you start screaming, crying, rolling on the floor, puking, etc.) ",
"Immobilizing pain (when the body starts shutting down) ",
"A long time ago I thought excruciating pain would get worse and worse but then I discovered number 5 where your body starts the heavy chemicals and begins to shut things down to save you from the pain. ",
"Right now I am passing a kidney stone plus I have a toothache that is making my whole head throb and it's a weekend so I can't do anything about it. Unfortunately it is still only excruciating pain, but I wish it would just get worse so my body would let me sleep. ",
"Also a big factor is your fear of the pain. I have had so many stones and I know I just have to wait it out which actually makes it more bearable. So in nut shot vs child birth (which happens a hospital surrounded by doctors) I say nut shot is way scarier and therefore way more painful. "
] |
[
"Or, you're a soldier and both your legs have just been blown off, but you're in shock and numb and give only a \"3\" because you don't really know what's going on. "
] |
[
"I'd imagine because it's completely relative among a group of humans who all have different thresholds for pain. In emergency medicine, we always ask, \"On a scale of 1 to 10, 1 being no pain at all and 10 being the absolute worst pain in your life, how bad is your _________.\"",
"The problem is that most people will say 8-9-10 and not be in tears. C'mon, you called an ambulance for this broken ankle and you're calling it a 10 yet you're not screaming like a madman or crying your eyes out.",
"It's relative. Some people handle pain extremely well. Some are crybabies. You can't get a consistent answer."
] |
[
"Questions about the Placebo Effect"
] |
[
false
] |
I got a few questions I always wondered about the placebo effect or things I have heard about it and didn't know where true, hopefully I can get some answers here :D I heard if you know something is a placebo it still works? Does the method of placebo matter? (pill, injection ect) 2b. Does it matter if you gave the patient anything or can you simply tell them they are cured. Can you administer the placebo yourself? As in can I have a cold and say to myself time for a placebo, and go mix up some sugar water and have it help? Does the placebo effect imply that positive thinking on its own helps beat medical problems? If someone thinks they will beat cancer or similar do they have a better chance then if they think they will die? Is there a noticeable difference in strengths between nocebo effects and placebo effects? If someone gets a nocebo that causes headaches and they get a placebo that fights off headaches what wins out? Is there any connections real connections between placebo effects and negative and positive reinforcement? I know that was a lot of questions but thank you in advance for answering what you can help with.
|
[
"Yes, this is true.",
"The method does matter. 2 Sugar pills are a more effective placebo than 1 sugar pill. A saline injection is a more effective placebo than a sugar pill. More dramatic 'fake' treatments are more effective placebos, so simply saying 'you're cured' is not very effective.",
" Actually I have no idea.",
"I'm not sure about 3-6. "
] |
[
"I haven't downvoted them but the reasons for downvoting would include:",
"(1) it is true that being told you are receiving a placebo can result in a placebo effect: ",
"Placebos without Deception: A Randomized Controlled Trial in Irritable Bowel Syndrome",
".",
"(3) Administering yourself a placebo should work, according to the results of the study linked above. ",
"(5) They've defined \"nocebo\" wrong. A nocebo is not when a placebo doesn't work. A nocebo is when you get the negative effects from a drug without taking an active drug; for example, if you believe that you are taking a drug that commonly produces headaches, then taking an inert substance can produce headaches.",
"(6) Positive/negative reinforcement doesn't apply to the placebo effect but classical conditioning does. Because classical conditioning is a major component of how placebos work, there doesn't need to be a conscious expectation of something occurring. That is, even if you know you're taking a placebo, it won't stop it from working in some cases - in the same way that even if Pavlov's dogs know that food isn't coming, they will still salivate when they hear the sound of the bell.",
"There's a good review on these issues here: ",
"The Placebo Effect: Dissolving the Expectancy Versus Conditioning Debate",
"."
] |
[
"Beg to differ on 3). Being involved in a clinical trial where you are given a placebo by a physician is substantially different from giving yourself a placebo."
] |
[
"What special procedures are involved in whole cell imaging by SEM or optical microscopes?"
] |
[
false
] |
I know it is more difficult to capture images of whole cells by optical or electron microscope. What exactly must be done to reveal a cell's morphology and microstructures?
|
[
"I'm actually midway through studying a couple lectures on microscopy in molecular and cellular biology!",
"Optical microscopes are pretty straight-forward when it comes to preparation. This is mostly because optical microscopes can't see things that are too small. The maximum ideal resolution for a standard brightfield microscopes, and confocal laser-scanning microscopes (CLSM) are about 200nm. This means that any two points that are closer than 200nm will just appear as one point with optical microscopes. This is enough to observe larger organelles, like nuclei, mitochondria, or chloroplasts. ",
"There are a number of stains you can use for optical microscopy. Different stains can stain different parts of the cell. Different stains bind to different things (like lipids in the cell wall).",
"Electron microscopes are a whole other ballgame. They require a whole lot of preparation, as what they look at is incredibly small and fragile. Right now, I'm just going to talk about transmission electron microscopy (TEM) which is mainly used to look at a cell's internal structures. Scanning electron microscopy (SEM) is what is normally used to generate 3D images of the surface of a microscopic object. TEM has a maximum theoretical resolution of 40 picometres, or 0.04nm. In practice, recent breakthroughs have allowed resolutions of 50pm, or 0.05nm. ",
"Sample preparation for TEM is a tricky business. As cells are living and dynamic, you first must stop all movement in the cell. You can chemically fix, with something like glutaraldehyde. This method takes about 30 seconds to full kill and immobilize the cell. Within that time, artifacts form, and can lead to misshapen images. A better (but more expensive) method is cryofixation. This is the use of liquid nitrogen and high pressures to immobilize the cell in milliseconds, which leads to much cleaner images.",
"After fixation, the sample must be stained. Usually, this is done with osmium tetraoxide which reacts selectively with lipids in all cellular membranes, and makes them electron dense. The more electron dense an object is, the more electrons it scatters, the darker that portion of the image will be in the final result.",
"Next, the sample is dehydrated with ethanol, or acetone (in the case of cryofixation). If a sample has any water in it, the electrons in the electron microscope will cause the water to heat up rapidly, and ruin your sample. After dehydration, the sample is embedded in a plastic epoxy resin, which provides structural support. ",
"Finally, the sample is sliced ridiculously thin (100nm) with an 'ultra-microtome', which isn't too different from a deli-meat-slicer that you find in a deli. It just has a glass, or diamond knife which allows it to cut really thin. ",
"Heavy metals can be added to further stain the sample. Lead, for example, binds to cellular macromolecules leading to increased contrast.",
"Feel free to ask me about any specific details of this. I wasn't sure how much detail to give for each steps. "
] |
[
"Obviously TEM preparation for something like a ceramic or polymer wouldn't be as difficult, but, other than actually cutting the ideal size and de-ionizing the surface, would you have to take any extra procedures?"
] |
[
"Hmmm... I'm really not sure about microscopy of things outside my own field of molecular and cell biology. ",
"Feel free to have a read through ",
"Wikipedia's bit on TEM sample prep",
"."
] |
[
"We’re conducting research focused on modifying bacteria to make them slurp up heavy metal pollution. Mutating organisms for our benefit: Yay or nay? Why?"
] |
[
false
] | null |
[
"Have you tested it out on real copper spills? Perhaps you could find some and take them to your lab. It would be annoying for you if they couldn't survive other toxic conditions in the environment and essentially became rather expensive fertilizer."
] |
[
"The copper contamination that we simulated in the lab was more concentrated than most that would be found outside.",
"You're exactly right; the next phase of research involves going out and getting real samples and working with the bacteria in them."
] |
[
"Can you explain what the purpose of these bacteria is? What are you trying to achieve by adding these bacteria to a copper spill? "
] |
[
"How would an anti-matter black hole interact with a matter black hole?"
] |
[
false
] |
What would happen if a black hole from a matter star collided with a black hole made from an antimatter star? Would they explode normally? Would there be odd gravitational fluctuations? Could it warp space-time so drastically that it would create a wormhole?
|
[
"There is no difference between a black hole that arises from a matter star or a black hole that arises from an antimatter star. If two black holes collide, they just become one larger black hole and, in the process of coalescing, emit a whole lot of gravitational radiation."
] |
[
"A black hole isn't composed of antimatter, or regular matter, for that matter... It doesn't matter what kind of star the black hole formed from, once it has become a black hole, it isn't matter anymore. ",
"The no-hair theorem states that a black hole can only be described by three externally observable characteristics; mass, electric charge, and angular momentum (or spin). Any other information about how the black hole formed, or what has fallen into it, disappears behind the event-horizon. ",
"Basically, besides those three characteristics, black holes are all the same. So when black holes collide, they don't annihilate each other, they merge into one larger black hole while releasing a large amount of radiation in the form of gravitational waves. "
] |
[
"While we have not yet directly observed anti-matter falling towards the ground, there is no serious model in which anti-matter has \"anti-gravity,\" and here's a good way to see this.",
"Let's consider light. Light is made of photons, and photons are their own anti-particle. So if matter and anti-matter were influenced in opposite ways by gravity, we would expect that a photon not be influenced gravitationally, since it is its own anti-particle. But, in fact, we know observationally (and also as predicted in general relativity) that light ",
" deflected by gravity."
] |
[
"How did certain animals evolve from breathing underwater to breathing air?"
] |
[
false
] |
[deleted]
|
[
"The earliest air breathing fish lived in water all the time and had working gills. But they lived in swamps and stagnant ponds and places like that. Like most fish today, they probably swam up to the surface and gulped at air when the oxygen content of the swampy water decreased. This circulates water at the aerated surface over the gills. At some point, some fish started swallowing air, which passed into the gut. The gut is highly vascularized to aid in absorption of nutrients, so the air could be absorbed into the bloodstream there. Over time, a certain outpocket of the gut became specialized for absorbing oxygen, and bam! lungs! Incidentally, the swimbladder found in many fish is evolved from a lung, not the other way 'round. ",
"The key thing is that lungs evolved looong before fish went onto land."
] |
[
"I did a pulmonary physiology seminar a few years ago and read quite a bit about swim bladders. If I remember, teleosts evolved a pneumatic duct and eventually swim bladders, with a branch at some point between lungs and swim bladders. No organisms have both swim bladders and lungs. So I don't know if we can really say if lungs -> swim bladders or pneumatic ducts to lungs or swim bladders. Correct me if I'm wrong.",
"Interestingly, after the evolutionary step of developing these types of lungs, reptiles (and birds) went a completely different way than mammals (faveolar versus alveolar lung). Proves that the modern bird lung is a complete marvel and outperforms the mammal lung in almost every respect. Bar-headed goose migrating over the Himalayas, baby."
] |
[
"Bird lungs are indeed amazing. Did you know that bird-style lungs are believed to be one reason sauropods could have such long necks? Circular breathing really helps reduce the \"dead space\" problem and also provides better efficiency for giant bodies.",
"It would appear that the bony fish ancestral to both lobe-finned fish and ray finned fish had an outpocket of the digestive tract consisting of a pneumatic duct to the gut and a sack. Since both lobe finned fish and \"primitive\" ray finned fish use this sack for gas exchange, it is thought that use as a lung--or at least, as a proto-lung, preceded the use as a buoyancy device, which is mostly found among the more \"advanced\" ray finned fishes. Though it's true that lungs in terrestrial vertebrates and swim-bladders in teleosts represent two branches developing from the ancestral organ."
] |
[
"How bright is the inside of the Earth?"
] |
[
false
] |
If there were a hypothetical transparent tunnel that passed through the diameter of the Earth, how bright would it be? Is there any particular part that would be brighter than the rest?
|
[
"How much light something gives depends on its temperature. This is called ",
"blackbody radiation",
" and is the reason why all hot objects give light (lightbulbs, hot iron, magma, the sun). The center of the earth is about the same temperature as the surface of the sun, so it would give of approximately the same amount of light per square meter."
] |
[
"This didn't sound right, but I checked, and yoenit is right - the center of the Earth is theorized to be about 7000K, and the surface (photosphere) of the sun is 5800K. Note that the corona ",
" the photosphere is 5x10",
" K"
] |
[
"The inside of the Earth isn't lava/magma, nor is it cold rock (which are the two things that a volcano is composed of). ",
"The vast majority of the inside of the planet is just heated rock (solid, not liquid - at least until you reach the outer core). I'm not going to speculate how much light might be released by said rock, but it's definitely a very different situation than what you get out of a volcano."
] |
[
"If I pour a line of flammable liquid on the ground and light it, can you calculate the speed at which the flame will propagate?"
] |
[
false
] | null |
[
"The speed at which the flammable liquid propagates is essentially the speed at which the chain reaction occurs, which depends on many different factors that can be difficult to account for, but we know the gist of how certain individual variables will affect the speed of propagation of the flame. These three are important:",
" This is basically the temperature at which the liquid will spontaneously combust without any external source like a spark or flame. The uncombusted liquid must first absorb the thermal energy released from the already combusted liquid before the uncombusted liquid can combust. The higher the temperature threshold for the spontaneous combustion of the liquid, the longer it will take for the uncombusted liquid to absorb enough thermal energy from the already combusted liquid to reach its autoignition temperature to combust, and therefore the slower the flame will propagate. So, a lower autoignition temperature corresponds to a faster propagating flame.",
" This is how much heat energy a given amount of flammable/combustible matter will give off when it combusts. A high heat of combustion means that, for a given amount of flammable liquid, the amount of heat energy given off is high, which correlates with high reaction temperatures. The higher the temperature, the faster the reaction rate. Therefore, a high heat of combustion corresponds to a faster propagating flame.",
" This dictates how quickly an applied heat will travel through a medium. Matter with a high thermal conductivity will distribute heat through itself faster than that of a low thermal conductivity. In the case of the flammable liquid, a high thermal conductivity will allow the heat energy released from already combusted liquid to quickly transfer to the uncombusted liquid to allow the uncombusted liquid to ignite. Therefore, a high thermal conductivity corresponds to a faster propagating flame.",
"Edit: I am aware that there are many more variables that determine the speed at which the flame propagates. I chose these three because they are properties inherent to the fluid itself, rather than external influences such as wind and/or atmospheric conditions. There are a few others that I haven't mentioned, such as specific heat capacity and volatility, both of which would affect the speed of propagation, but the three I listed above are the first factors that came into mind."
] |
[
"My focus was mainly on the intrinsic properties of the liquid itself, but yes, there are a myriad of other influences, such as variations in oxygen levels, ambient temperature, wind, introduced impurities, exposed surface area to volume ratio, flow of the liquid, etc. that can be chaotic in nature or otherwise make it nigh impossible to calculate the speed of propagation of the flame with a simple formula."
] |
[
"I can probably make a weak-ass concept of a mathematical/computational model, based on ",
"/u/silberklinge",
"'s comment ",
"here",
".",
"Summary of what I'm trying to do: subdivide that line of flamable liquid (now known as \"petrol\") on the ground into many tiny segments, each one being a control volume of it's own. Calculate when each segment will ignite, then calculate how the heat transfer from this segment to the neighbouring segment. Then calculate how long it takes for that segment to heat up to ignition temperature.",
"Example:",
"At t=0:",
"At each next step, eg t=0.05",
"You can see that each of the calculations requires massive amounts of assumptions and simplifications for the maths to work. It's probably better to do some empirical studies in \"standard environments\"."
] |
[
"How do attractive forces work?"
] |
[
false
] |
I understand (at least I think I do) how repulsive forces function at the quantum level, but I cannot find any explanation for attractive forces. Let's take the electromagnetic force, mediated by the photon. When two similarly charged particles come near each other, they exchange photons with each other and repel because of the change in momentum. How does this work for attractive forces? For oppositely charged particles the light cannot impart a negative momentum on them so what is happening here?
|
[
"Virtual photons are no billiard balls that charged particles throw at each other but are just mathematical relics that you get from solving the underlying process perturbatively.",
"edit: The ",
"posts",
" that ",
"u/Lagrangsch",
" linked contains a very good, more detailed explanation."
] |
[
"It's an easy mistake to make when you see your first ",
"Feynmann diagram",
" to think \"Well that won't work for attractive forces\" but keep two things in mind:",
"First, the virtual photon can have negative energy and negative momentum. While that seems nonsensical to us in the macroscopic world, there's nothing that prohibits it with virtual photons because you can create any amount of energy so long as you do so for a sufficiently short period of time:",
"ΔE * Δt ≥ ħ/2",
"So what would happen if an electron emitted a negative-momentum photon? Well conserve momentum and the electron would move ",
" the direction of the emitted photon.",
"There's a second way of looking at this: Who's to say ",
" the photon was emitted ",
"? Why can't the electron on the left emit a photon ",
" the positron on the right, moving ",
" that positron? Now the electron's dragged toward the positron, and when the photon collides with the positron the positron is likewise dragged toward the electron. Attractive force, there ya go!",
"All this goes back to the larger issue, which is that the notion of \"exchanging a particle\" is merely a way of looking at the interaction, not necessarily a precise description of what's happening."
] |
[
"It works the same. The source of your confusion is that you think of a photon as some ball that the first electron throws away from the second one, but still hits it. It doesn't work this way. A single photon with a fixed momentum is a plane wave, and a plane wave isn't localized in any region of space, it is everywhere at once. Thus once the first attracting electron emits a photon, that photon can now interact with the second electron. The conservation of momentum is of course still true.",
"Any actual physical emitted photons would of course be spatially localized for causality reasons, which means that they will be composed not of a single plane wave but of an infinite collection of them. Since it is spatially localized and in particular zero at the place of the second electron (and moving away from it), it cannot interact with the second electron. In other words, on the level of actual physical measurable process the attraction via photon exchange is indeed impossible, but virtual photons can't be measured. Whether you think of them as a mathematical abstraction or as actual physical but unobservable weird particles is irrelevant at this point."
] |
[
"Calculate home water psi from the time taken to fill a container. Is it possible to do this without a gauge?"
] |
[
false
] |
My wife is redoing the bathroom. She finds a shower head that require a minimum of 23 psi to function correctly. So my question is can this be calculated? If I were to know the diameter of the pipe the water was coming out of and then measured the time it took to fill a gallon container would that be enough information to calculate the psi? It seems to me it would, but if I knew how I wouldn't be asking for help...
|
[
"I believe if you ring up your water supplier, they can just tell you.",
"23 PSI sounds very low, I believe the average household gets about 50-70, so you should be fine."
] |
[
"Sure you can, it's known as the bernoulli principle or bernoulli's equation, check it out on hyperphysics for a good explanation (and there's a calculator that should suffice for your needs):",
"Bernoulli & Pressure",
"Also a quick gander at the wikipedia page will help. If you can come back to us with figures I'm sure we'd have a go at working it out for you:",
"wikipedia article"
] |
[
"Thanks for your reply. I actually have a comp. sci. background so I'm sure I can handle the math, just didn't know what equations, rules would apply. I'll figure it out this weekend, thanks again!"
] |
[
"Does trying a knot in a string increase or decrease its entropy?"
] |
[
false
] |
Strings will naturally tie themselves into knots, but doesn't tying a knot yourself take work? Is the work decreasing entropy? Is there a point where tying another knot would have the opposite effect?
|
[
"It would increase the total entropy since the process of tying a knot is not ",
"reversible",
" due things such as friction. ",
"I found a paper on this topic here: ",
"http://arxiv.org/pdf/1003.5134v1.pdf",
"We estimate by Monte Carlo simulations the configurational entropy of N-steps polygons in the cubic lattice with fixed knot type. By collecting a rich statistics of configurations with very large values of N we are able to analyse the asymptotic behaviour of the partition function of the problem for different knot types. Our results confirm that, in the large N limit, each prime knot is localized in a small region of the polygon, regardless of the possible presence of other knots. Each prime knot component may slide along the unknotted region contributing to the overall configurational entropy with a term proportional to lnN. ",
" In the case of polygons with composite knots it turns out that the partition function can be simply factorized in terms that depend only on prime components with an additional combinatorial factor that takes into account the statistical property that by interchanging two identical prime knot components in the polygon the corresponding set of overall configuration remains unaltered. Finally, the above results allow to conjecture a sequence of inequalities for the connective constants of polygons whose topology varies within a given family of composite knot types."
] |
[
"An irreversible process can still have a net decrease in entropy, can't it? "
] |
[
"In a closed system no, if its open, sure locally, but overall entropy increases."
] |
[
"Is there a way to properly measure pain?"
] |
[
false
] | null |
[
"Admittedly those are all still subjective measurements. If the OP was interested in some kind of objective measurement, then the answer is no. ",
"There is a strong psychological component",
" to how we experience pain."
] |
[
"another prior thread"
] |
[
"The Pain Scale",
", ",
"the Dolorimeter",
", and often seen on ",
"r/TIL",
", the ",
"Schmidt Sting Pain Index",
". The man who developed this index subjected himself to stings from all manner of creatures. Brave, brave man. Not sure where a box jellyfish falls on this scale, but from all accounts, I would make a 5 for it and its cousins, whose stings are so painful they can shock your heart into arrest. "
] |
[
"Nat gas vs oil"
] |
[
false
] |
[deleted]
|
[
"Oil and natural gas are formed from the same ingredient: the decomposed remains of microscopic organisms that lived hundreds millions of years ago. Sediments built up on top of these organic materials after they were buried, increasing the pressure on them and pushing them deeper into the Earth where they were heated up. The heat and pressure both lasted for millions of years.",
"Oil and gas have different \"windows\" (",
"1",
", ",
"2",
") of temperature and pressure in which they will form. The oil window has lower temperature and pressure bounds than the gas window. Thus, if the oil is heated up too much it will turn into natural gas, an irreversable process. The organic material buried under Pennsylvania and New York was heated to higher temperatures than the material under the Middle East; as a result, the oil that existed in those states has turned to gas while."
] |
[
"I deliberately left that out because we don't know the regional histories well enough to say how long the oil/gas was heated or to exactly what temperature. In addition, there's a very good chance that the oil/gas is not in the same place it formed - it seeps upward and laterally due to its low density until trapped by cap rock, so we don't really know its true history."
] |
[
"I deliberately left that out because we don't know the regional histories well enough to say how long the oil/gas was heated or to exactly what temperature. In addition, there's a very good chance that the oil/gas is not in the same place it formed - it seeps upward and laterally due to its low density until trapped by cap rock, so we don't really know its true history."
] |
[
"How many different supernovae contributed the carbon on Earth?"
] |
[
false
] |
Is it possible that the carbon (for example) that ended up on Earth all (or mostly) came from the same supernova? If not, how many supernovae contributed to the molecular cloud that coalesced to form our solar system?
|
[
"There's a problem here with the initial question: interstellar carbon doesn't just come from supernovae. A very substantial percentage is produced from the mass loss of ",
"asymptotic giant branch stars",
".",
"Stars as small as half the mass of our Sun will undergo this phase near the end of their lives. Through a series of helium \"flashes\", where helium fusion initiates and then is later damped out, carbon that would normally be limited to areas near the core gets thoroughly mixed throughout the star. Combine that with strong stellar wind streaming off the surface of these stars (they can lose half their mass in the process), and you've suddenly got dying stars all over the galaxy seeding carbon into the interstellar environment. This generally takes the form of fine dust particles similar to soot.",
"As a result, just about any giant molecular cloud in our galaxy will have been seeded with carbon from a very large number of non-supernovae stars."
] |
[
"Just curious, stars half the mass of our Sun live a much longer time and can take more than 10 billion years to lose carbon in the way you described. Very massive stars on the other hand can become supernovae after just a few tens of million years.",
"Have there been enough generations of small and medium-sized stars to make \"a very substantial percentage\" of the interstellar carbon? Is the universe old enough for that at just 13.8 billion years of age?"
] |
[
"Oh, I don't doubt that the carbon COULD cone from one star. I just wonder how much mixing is going on."
] |
[
"Can someone tell me how to read this chart?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"It's not speculative, I'm just asking how to read a chart."
] |
[
"Sorry for the canned answer. It's a prewritten thing.",
"/r/AskScienceDiscussion",
" woudl be more appropriate for your question as you are asking about individual help understanding a paper. ",
"r/askscience",
" is more for general science questions. ",
"Btw your link is broken."
] |
[
"What would the timespan be for the majority of earth's population to be 'new' people?"
] |
[
false
] |
Here on Earth, a bunch of people die everyday and a bunch of people are born everyday. To explain my question in simple terms, if there were ten people on earth and one person died everyday and one new person was born everyday, it would take 6 days for the majority of the population to be new i.e. the majority of the population didn't exist 6 days before that. So applying this to the current situation we live in, what would be the timespan for this happening? I started to think about this after trying to figure out what percentage of the current population have lived the entire 21st century, and it just went from there.
|
[
"This is a sort of standard demographics/population biology question; I tried to answer it just now naively, assuming exponential mortality, but got a silly answer; you'd need to have the actual data from ",
"tables like these",
" along with a profile of current demographics and do some calculations on them.",
"A good undergraduate homework assignment to get it close, but maybe too long for a comment... apologies!",
"Edit: you got me interested, so I combined that table above with U.S. ",
"birth rates",
" and ",
"2010 census",
" in a spreadsheet. Answer: Drawing the \"line\" on Jan 1, 2010, and assuming rates stay the same for the next 100 years:",
"After 1 year, 1.4% of people in the U.S. will be \"new\".\nAfter 10 years: 14.2%\nAfter 20 years: 26.3%\nAfter 39 years: 49.7%\nAfter 40 years: 51.0%\nAfter 80 years: 94.3%\nAfter 100 years: 99.94%\nAfter 110 years: 100% [*]\n",
"[*] Technically, 120 years for the last person to die, in accordance with oldest known person."
] |
[
"The World Bank reports global life expectancy in 2010 to be 69.6 years."
] |
[
"Wow, that's great. I'm glad it peaked your interest. Over the course of the question being posted, I started to realise it might've been more relevant to simply ask:",
" ",
"Going off your 40 year calculation, do you think it's fair to say that by 2040 we will be close to that reality?"
] |
[
"electric potential question"
] |
[
false
] |
[deleted]
|
[
"You'd pretty much just be adding 100V to the field everywhere, and to all your calculations. Remember that the observable quantities (the electric and magnetic fields) depend on derivatives of the potentials, so adding a constant doesn't affect anything."
] |
[
"Ye. It doesn't even matter if you use \"affect\" or \"effect\"."
] |
[
"Nice."
] |
[
"How could vacuum energy cause the expansion of the universe?"
] |
[
false
] |
[deleted]
|
[
"Because it has negative pressure. As a matter of fact, not only it has negative pressure, as the pressure has the same magnitude as the energy density, which means that, once you do the calculations, you realize that no matter how you stretch the universe, the vacuum energy will still make it stretch even further.",
"To have an intuitive picture: imagine a balloon, the air inside makes pressure to expand the balloon, but there is a balance because the tension of the balloon surface tries to stop this expansion. In the universe, the gravity created by the energy density creates this inwards tension, while the pressure tries to make the universe expand. It turns out that if the magnitude of the pressure is above a certain threshold (1/3 of the energy density), the universe will keep on expanding, and the expansion will be accelerated. "
] |
[
"What is negative pressure?"
] |
[
"I believe it's everything explained in here (it's about inflation, but the idea is the same)",
"http://theory.physics.helsinki.fi/~cosmology/cosmo2012_09.pdf"
] |
[
"When looking at text through a wine-glass filled with water, why are the text both reversed AND upside down?"
] |
[
false
] |
I recently watched a video regarding , and the concept of the light refracting through the glass and water to flip the image/text behind it horizontally was easily understood. Last night I coincidentally saw this phenomenon when a friend's wine-glass was put in front of my pc's monitor with the digital-time showing behind the glass from where I sat. I thought "Yes! I'll try to sound smart by explaining to them why the time on my monitor were reversed and upside down when seen through the wine glass!". So I started explaining and got the the part of why it was flipped horizontally, but then I didn't know why the time was flipped upside down as well. Today I tried finding an answer online but only the typical horizontally flipped explanations were found. Then I thought about the shape of the glass itself; that the light entering the wine-glass from my point of view was being refracted both horizontally and vertically as opposed to only being flipped horizontally through a cylindrical-shaped glass as in the video. Is it correct to assume that this is because of the shape of the glass? Thanks!
|
[
"Is it correct to assume that this is because of the shape of the glass?",
"Yes, but more importantly, it's because of the shape of the ",
"When there is no water in the glass light basically passes straight through, almost regardless of the curvature of the glass because the glass is very thin. The image behind an empty glass isonly weakly distorted.",
"However, when you fill it with water, you now have a lens - it's a large volume where the index of refraction is different than air, so the light on the other side of the glass is more strongly refracted. ",
"This is because the index of refraction of water and glass are much higher than air. If you had a wine glass that was solid glass, or a floating sphere of water (with no glass holding it) you would see approximately the same thing - a flipped image. ",
"Ultimately, the glass is shaped like a magnifying glass, meaning that it's curved in both the vertical directions and the horizontal directions. Since the wine glass is round (not just cylindrical, but curved in both the horizontal and the vertical directions), ",
"it flips the image both horizontal and vertically.",
" Basically, light coming from the top gets switched with light from the bottom, and light from the left gets flipped with light from the right. ",
"The cup in the video is approximately cylindrical, so it only flips in the horizontal direection. If you took a blow torch too it and bent into a ",
"round shape",
" you could see the same thing with the cup in the video (Note: Do not try this at home). "
] |
[
"Thanks for the thorough reply!"
] |
[
"One more interesting thing, because the glass is acting as a lense it has a focal point. If you move the glass close enough to the screen, the text should flip back around to normal. "
] |
[
"Is it possible for a planet to have a sun orbiting it, rather than the other way around?"
] |
[
false
] |
Can a planet scale up, or a star scale down, to the degree that the relationship we experience on our planet, is reversed?
|
[
"All big planets we have found so far consist of a large fraction of hydrogen. This means that if you would grow to the size of a star it would simply ignite and become a star."
] |
[
"centowen's answer and ion_ion's follow up are essentially correct, but let me expand a little:",
"A celestial body's size depends on its mass and composition. If a planet were to simply be scaled to the mass of the sun, there is its composition to be considered. A star like the sun only has its size because of nuclear fusion in its core creating photons that exert pressure on the surrounding matter, otherwise gravity would simply collapse the whole thing into a black hole. To have fusion, you need to have elements lighter than iron, which is the cut-off point in exergonic (releasing energy) reactions. A planet like earth might not be comprised of enough light elements to have fusion at the necessary level to have a stable existence and might be crushed be gravity.",
"Also, it is important to be aware that a planet does not strictly 'orbit the star', but that both objects share a center of mass and both 'orbit' that, though it is strictly more correct to say that they rotate around this center while staying in a fixed relative position. For more than two objects, it is too complicated to solve (you might have heard of the three-body-problem) analytically, even though we can calculate numerical solutions to high precision. And with three bodies, there would be no stable 'center of mass' or a fixed position."
] |
[
"The Sun and the planets both orbit a place 'between' them. The caveat is that the Sun is so much more massive that this point is beneath its surface for all but Jupiter. ",
"In essence, the Sun also orbits the center of mass of this system, just as the planets do, it is just an extremely small orbit.",
"That being said, removing enough mass from a sun or adding enough mass to a planet to reverse their relative positions would rather calamitously change the nature of either body."
] |
[
"What is the tallest structure that can be built to have humans be transported to the top? Not a skyscraper. Just a tower with some kind of elevator to get as high as we can go without being in an aircraft."
] |
[
false
] |
I hope I'm explaining it right. If we wanted to make the tallest tower for humans to go up to, how high could we get? If I wanted to put elevators so that people could visit, would this be possible? What would be the major obstacles to go through?
|
[
"At the moment, the tallest structure in the world is the ",
"Burj Khalifa",
" building in Dubai, UAE. It stands as about 830 meters, though nearly two hundred meters of it isn't for human occupation. ",
"The answer to this questions is currently about a kilometer is as high as you can get with today's technology. Currently being built is the ",
"Kingdom Tower",
" in Saudi Arabia which aims to reach an even 1,000 meters. There are some others planned around this height as well. The problem with super-tall towers is you have to deal with the torque such a building will generate on itself--so you need to make sure the center of gravity isn't too high up the tower. This is why such super tall towers are wider at the base and thin out as you get higher, it's a more stable configuration. The ",
"Warsaw radio mast",
" is a good example of this, it was almost 650 meters tall and bent in half and collapsed back in 1991. ",
"There are proposed towers even taller than this--outside today's technology. One of the most massive is the ",
"X Seed 4000",
" at a whopping 4,000 meters. As you notice from the picture, the base is enormous. You can actually find completed design plans for it. More fantastic projects are also being discussed with the most famous being the ",
"Space Elevator",
" which would be go somewhere far past 36,000 km (geostationary orbit). The \"idea\" is a bit different here as it's be more like \"hanging down\" a tower than one traditionally supporting its own weight."
] |
[
"The idea predates Carl Sagan. Per wikipedia the idea of the ",
"space elevator",
" dates back to the 19th century and Konstantin Tsiolkovsky. I remember being introduced to the idea with Arthur C. Clarke's novel ",
"."
] |
[
"It's even simpler than that.",
"\nThe space elevator (cable + counterweight) is a mere satellite, whose center of mass is moving along the geostationary orbit. ",
"The fact that its lower part reaches the Earth ground doesn't change the way its center of mass moves along its orbit."
] |
[
"Isentropic compression in plain language?"
] |
[
false
] |
I've come across a passage in a memoir by a nuclear weapon designer which states: In August and September, Ron and I worked day and night to design an even more radical nuclear device. We further optimized the pulse shape to achieve practically isentropic fuel compression. It's the latter that I am just not 100% sure I grok in plain language, and looking up dictionary definitions of "isentropic" has not clarified it to me. The "pulse shape" is the initial radiation pulse from the fission primary; the compression in question is of the thermonuclear (fusion) secondary. Is he saying they compressed it equally from all sides, that it was completely compressed before the heat of the primary reached it, or what? Any insight would be appreciated. This does not need to be a totally basic answer (I am not new to the subject though I am not a physicist) but just something that puts this into plainer language than "isentropic."
|
[
"Isentropic means constant entropy. ",
"If the entropy of a working fluid doesn't change over the course of a process then the process is said to be isentropic. ",
"Reversible processes that are operated with zero heat transfer (q=0) are isentropic by definition."
] |
[
"Probably..."
] |
[
"Thanks. So is it likely correct to interpret the quote as saying that they managed to make a bomb design that resulted in compression of fuel with near zero heat transfer? "
] |
[
"Was the first second of the universe identical to a second passing just now?"
] |
[
false
] |
I remember Steven Hawking describing what the first second after the big bang was like and I just want to know, given the curvature of spacetime being so much less now, has time itself changed at all since it's beginning?
|
[
"time only runs at 1 speed. Time is relative, but it is fixed. ",
"the atomic decay rate of Cesium (on which a second is based), has not, and never will change. (though Cesium didnt exist in the first second, but if it had, it would have decayed the same rate as it does now)"
] |
[
"I don't think that last part is true, aren't the nuclear force coupling constants energy dependent?"
] |
[
"In the early universe it becomes useful to think of time in logarithmic units (so comparing 1 to .1 and .01 instead of 2 and 3). This is because a more useful measure is energy scale instead of time after the big bang. It seems a little weird to think that vastly different physics was happening a nano second after the big bang as opposed to miliseconds, how could so much happen in so little time? It makes sense if you think in terms of energies. "
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.