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[
"How much does diet as a young person affect someone's health later in life?"
] |
[
false
] |
Like many college students, I don't always pay attention to what I eat. I consume a lot of pizza, fried food, soft drinks, etc. It doesn't seem to affect my health much right now, since my body fat percentage, blood pressure and cholesterol levels are all very good. But could I be quietly doing damage that will later lead to health trouble? For example, is heart disease related to diet and exercise in a person's later years only, or the product of an entire lifetime? I'm not asking about the habit of eating junk food, by the way. I only mean the long term biological effects of that junk food.
|
[
"Regarding cholesterol specifically, there is evidence that suggests that a lifetime's exposure to cholesterol influences heart attacks. Some people in the Dallas Heart Study have particular PCSK9 mutations that cause them to have low LDL-cholesterol for their entire lives. These people have a lower risk of developing heart attacks -- much lower than what one would expect based on similar levels of reduction for a couple of years late in life with drug therapy. Thus, this provides a hint (but is not conclusive) that lifetime lipid levels are important.",
"http://www.nejm.org/doi/full/10.1056/NEJMoa054013"
] |
[
"not an expert, but an example might be that certain nutrients such as vitamins and minerals are required for correct dna function, that would be an explanation as to why diet would caude you problems later on, with dna damage or errors being cumulative not really being noticeable until middle age and onwards perhaps.",
"This article",
" suggests that dna damage may be repaired by diet also."
] |
[
"There was a ",
"recent study",
" published that has linked poor diet to lower IQ.",
"A predominantly processed-food diet at the age of three is directly associated with a lower IQ at the age of eight and a half.."
] |
[
"Leap Years and time difference"
] |
[
false
] |
If every year is about 365.2425 days... how come after a year passes the time still matches the sunlight? Shouldn't it be behind six hours? And after two years we would be 12 hours behind and have opposite night/day?
|
[
"Here, check out this ",
"previous discussion",
" "
] |
[
"Thanks. And sorry, didn't realize this was a repost"
] |
[
"No. This is two different mechanisms. The day/night cycles is simply the day revolving around itself once. This takes 24 hours, and is what we call a day. ",
"A year is the earth moving once around the sun. This isn't perfectly dividable into days, so we need leap years to make sure we don't lose days. If we lost days the seasons would become out of sync after a some years.",
"In a way the year starts at midnight and end at 6 in the morning. Next year it ends at 12 in the morning. This don't affect the days at all, as they are separate, and we can't be arsed to wait to celebrate the new year until the extra 6 hours have passed so we just add the extra day."
] |
[
"What is the probability of a couple having identical non-twins?"
] |
[
false
] |
Scenario: A couple plans on having 2 children which are not twins. What is the probability that the two children will have the exact same genetics?
|
[
"Here's ",
"my answer",
" to this question from about a month ago. The figures I give are for the probability of being unrelated (or rather of being substantially less related than the expectation), but the calculation is symmetric, so those probabilities are the same for the other half of the distribution.",
"It's not explicitly impossible, but the probability is so low that it basically won't even happen."
] |
[
"Thanks for the reply!"
] |
[
"Looking at this from a basic biological perspective:",
"If you ignore crossover, each parent can form 2",
" different gametes, resulting in 2",
" (70 368 744 177 664) different zygotes. The odds of forming two identical zygotes in a row is 1/2",
" which is 2.0 x 10",
" .",
"It's obviously not that simple, there are factors that will make it more or less likely. Once you take the average of 2-3 crossover events per chromosome into account though, I don't see this realistically happening."
] |
[
"Instead of the universe expanding at an increasing rate which is accounted for with the term dark energy, could there be an outside force pulling the universe and as the galaxies get closer the pull gets stronger, causing them to speed up?"
] |
[
false
] | null |
[
"Yes. You can imagine that by chance we are just living in an underdense region, which would expand faster than the rest of the Universe.",
"The problem is that the expansion seems to be isotropic (=the same in all the directions). So it would mean we are almost at the center of this bubble. It's highly unlikely and cosmologists don't like to assume our position is special. But it's a possibility we should consider and try to rule out from the observations."
] |
[
"Is expansion uniform and does it expand at the same rate in all direction?"
] |
[
"As far as we can observe, it seems to be."
] |
[
"How strong would an induction coil have to be to heat up the iron in your blood significantly, if that is possible?"
] |
[
false
] | null |
[
"Inductive heating only operates on conductors, and the ionic iron in your blood is a completely different form of the element than the metallic form that you find in a hunk of metal. "
] |
[
"Your blood is salty though.",
"Iron is a fraction of a percent of your body by weight and bound to proteins. Salts are free to disassociate and make you very slightly electrically conductive..."
] |
[
"An alternating magnetic field doesn't heat materials via magnetism but via the eddy current. So any conducting material will do; it doesn't have to be magnetic. Since the fluids in the body are conducting it is possible to heat them up in an alternating magnetic field. But I can't give you numbers."
] |
[
"Does Protandim do anything? If so, how does it work?"
] |
[
false
] |
My Dad keeps going on and on about it. It just seems like a scam to me. Is it better than eating fruits and vegetables?
|
[
"Your body has evolved in an environment where it processes natural foods. Dietary supplements can be useful if you're lacking some specific substance, but I'd say that in general, you're better off eating the original source of the vitamins, minerals, antioxidants, etc."
] |
[
"Why? Please provide support for your claims and explain how this works."
] |
[
"Humans developed in a world without artificially-produced substances. Your body is used to certain ratios of nutrients. There are well-known facts (like ",
"calcium inhibits absorption of iron",
" ) that supplement companies will ignore so they can have both iron and calcium on their bottle.",
"Read the ",
"Protandim website",
". They make a number of claims with generalizations like \"Scientists agree\", catchphrases like \"clinically proven\". A lot of their points are followed by an asterisk, which points to this very light-grey text at the bottom of the screen: \"*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.\"",
"I'm not saying that supplements in general, or this one in particular, can't help. I'm just saying that it hasn't been studied by a regulated clinic. Their results ",
" be valid, but my assumption is that their \"clinical proof\" is provided by a clinic that their company runs.",
"The FDA regulates dietary supplements ",
"in the U.S.",
". They guarantee that they contain known-safe ingredients, but there's no guarantee that the supplement actually does anything. There's some degree of manufacturing oversight, but the FDA's fairly understaffed in that area.",
"Basically, my point is that I'm skeptical. Protandim does, in fact, \"do something\". They've got two ",
"peer-reviewed papers",
" published, ",
"one of which",
"(PDF) they actually link to. But if your father's skipping out on fruits and veggies, those provide a ",
" of substances that this supplement doesn't. I can say that I don't think that this stuff will actually ",
" anyone, but it's no replacement for actual food."
] |
[
"What is the probability of my cards adding up to a prime number. I stick my hand into a full deck and pull out a stack (could be 1 card, could be all 52)."
] |
[
false
] |
Pulling a random # of cards out of a deck, what is the probabilty of these cards adding up to a prime number?
|
[
"I assumed that all possibilities to draw a stack of cards had the same probability, including the empty stack of cards. A Jack counts for 11, a Queen for 12, and a King for 13. I found a (roughly) 18,4% probability for the sum to be prime.",
"I don't think there is any good theory which would give the answer right away, so brute force it is. But you have to do it cleverly, because if you want to test all the 2",
" possibilities, your program is not going to finish soon. Working by deck sizes is not a good idea. The way to go is to:",
"1) Take the empty deck",
"2) Compute the possible ways to get each given number between 0 and 364 (initially, there is only the empty deck, so you have one way to get 0 and 0 ways to get anything else). If you have all the cards, finish; otherwise, go to 3).",
"3) Add a card that you can possibly choose in your deck. Go to 2).",
"Here is the code (Fortran):",
"PROGRAM Cards\nIMPLICIT NONE\n\nINTEGER :: i, j, k\nINTEGER*8 :: FinalSum\nINTEGER*8, DIMENSION(0:364) :: ScardsSum\nLOGICAL, DIMENSION(2:364) :: IsPrime\n\n! The array ScardsSum gives the number of ways for the sum of the cards in a stack to be k, for k between 0 and 364\nScardsSum(:) = 0\nScardsSum(0) = 1\nDO i = 1, 4\n DO j = 1, 13\n DO k = 364, j, -1\n ScardsSum(k) = ScardsSum(k)+ScardsSum(k-j)\n END DO\n END DO\nEND DO\n\n! Next: A sieve of Eratosthenes to get all the primes between 0 and 364. \nIsPrime(:) = .True.\nDO i = 2, 19\n IF (IsPrime(i)) THEN\n DO j = 2*i, 364, i\n IsPrime(j) = .False.\n END DO\n END IF\nEND DO\n\n! I sum all the possibilities corresponding to prime sums\nFinalSum = 0\nDO i = 2, 364\n IF (IsPrime(i)) THEN\n FinalSum = FinalSum+ScardsSum(i)\n END IF\nEND DO\n\nWrite(*,*) FinalSum\n\nEND PROGRAM Card\n",
"It could be optimized, we could use the symmetries of the problem, but since the program already runs in the blink of an eye...",
"Finally, you get 830014923665902 ways to get a prime number, against 2",
" = 4503599627370496 ways to pull out a stack of cards, so a (roughly) 0.18430033580727522846 probability to get a prime number."
] |
[
"The number of all k-combinations for all k: 0 <= k <= n is n",
" . (EDIT: REALLY TIRED THIS PROBABLY ISN'T TRUE IN DECK OF CARDS CASE BUT IT'S PROBABLY STILL HUGE",
"EDIT: JUST KIDDING THIS IS STILL CORRECT) So, if we're looking to brute force this approach and assume that checking a combination takes a millisecond, we'll be waiting about 142,000 years for our results. So, we need to be a bit smarter.",
"The max number we have to deal with is 364, which is what you get if you take the whole deck (13+12+...+1) * 4. So, we have to deal with the following primes:",
"2 3 5 7 11 13 17 19 23 29 \n 31 37 41 43 47 53 59 61 67 71 \n 73 79 83 89 97 101 103 107 109 113 \n 127 131 137 139 149 151 157 163 167 173 \n 179 181 191 193 197 199 211 223 227 229 \n 233 239 241 251 257 263 269 271 277 281 \n 283 293 307 311 313 317 331 337 347 349 \n 353 359",
"Now, it's nearly 2am here and I can't justify staying up all night to try to work this out. However, I'm thinking for each possible stack size you pull out you could calculate the probability of it landing on each possible number. Then you could figure out which are prime, get the probability of stack size k being prime, and then combine all those results in an overall probability.",
"For example, for k = 1: We have equal probability of it landing on any number from 1 to 13. As 6 of those numbers are prime, we have a 6/13 chance that upon drawing one card from a deck it is prime - 0.462",
"For k = 2: It can land anywhere from 2 to 26. Doing some math you can come up with the following expressions (from combinations of two n sided dice):",
"P(k) = (k - 1)/169 , for 2 ≤ k ≤ 14",
"P(k) = (27 - k)/169 , for 14 < k ≤ 26",
"P(2): 0.005917159763313609",
"P(3): 0.011834319526627219",
"P(4): 0.01775147928994083",
"P(5): 0.023668639053254437",
"P(6): 0.029585798816568046",
"P(7): 0.03550295857988166",
"P(8): 0.04142011834319527",
"P(9): 0.047337278106508875",
"P(10): 0.05325443786982249",
"P(11): 0.05917159763313609",
"P(12): 0.0650887573964497",
"P(13): 0.07100591715976332",
"P(14): 0.07692307692307693",
"P(15): 0.07100591715976332",
"P(16): 0.0650887573964497",
"P(17): 0.05917159763313609",
"P(18): 0.05325443786982249",
"P(19): 0.047337278106508875",
"P(20): 0.04142011834319527",
"P(21): 0.03550295857988166",
"P(22): 0.029585798816568046",
"P(23): 0.023668639053254437",
"P(24): 0.01775147928994083",
"P(25): 0.011834319526627219",
"P(26): 0.005917159763313609",
"Pulling out the values we care about, we get:",
"P(2): 0.005917159763313609",
"P(3): 0.011834319526627219",
"P(5): 0.023668639053254437",
"P(7): 0.03550295857988166",
"P(11): 0.05917159763313609",
"P(13): 0.07100591715976332",
"P(17): 0.05917159763313609",
"P(19): 0.047337278106508875",
"P(23): 0.023668639053254437",
"So, adding these up we get 0.337.",
"By calculating that probability value for each stack size, you can figure out the total probability of getting a prime number.",
"As you get more cards drawn from the deck this calculation becomes more and more difficult, but I'm wondering if the results can be charted out as some sort of probability curve and then estimated from that. If it was pick n random numbers from 1-52 we'd approach a normal distribution and the calculation would be pretty straightforward, but as we only have 4 of each number available to pick I'm not sure how that messes with the curve.",
"Anyhow, apologies for the incoherence of all this, I'll get back to it tomorrow. Maybe this will just be some food for thought"
] |
[
"I'll check back in a year to see if you're done yet ;)"
] |
[
"What sort of negative consequences could result from a desert ecosystem suddenly receiving an exorbitantly large increase in rainfall?"
] |
[
false
] |
By this I mean say, frequent small showers, perhaps the occasional storm. Weather patterns in wetter parts of the world. EDIT: 11 comments, but only 3 are displayed. What gives?
|
[
"Desert dirt is usually VERY hard and has a hard time absorbing moisture. When there is suddenly water, it mostly just flows creating large flooded areas and mudslides. I live in a desert area and any time it rains we get flood warnings and roads close because they get flooded. When I was a kid, there was a time when my neighborhood was flooded and people were boating in the streets."
] |
[
"Desert soil can be impermeable (leading to flash floods as you say) but it doesn't have to be. Sand, for example, is quite permeable. "
] |
[
"In general systems always tend to assume a form of equilibrium. The moisture in air and ground is one example of this. However if it suddenly starts rainning too much the ground will become oversaturated and can't take up any more water. The water will then stay on the surface flowing towards lower ground. This will create lots of heavy erosion. "
] |
[
"I am an astronaut. Part of my ship/station spins to create artificial gravity, part of it does not. What happens when I move from non-spinning portion of the ship to the spinning portion (and vice versa)?"
] |
[
false
] |
[deleted]
|
[
"You'd have to do more than jump. You'd have to run fast enough to counteract the motion of the spinning portion. If you could do that, though, then yes."
] |
[
"Not until you came in contact with the floor. Well, the air there is likely moving very slowly towards the outer wall of the spinning portion, so you'd very slowly drift. But without some way to transmit the force you would experience from the spin, you wouldn't experience the force, and thus wouldn't fall."
] |
[
"That's not true. Check out the formula. Coriolis force is cross product of vector of angular speed and vector of your speed. Both vectors are perpendicular in the situation I've described earlier so there has to be coriolis force."
] |
[
"How does aging work? Did people age the same way 100 or 1000 years ago?"
] |
[
false
] | null |
[
"Aging was pretty much the same 100 and 1000 years ago. It's not exactly true that people didn't live as long hundreds of years ago. What's true is that the life expectancy was lower, but that was mainly due to much higher rates of death during infancy and childhood, and the lack of medicine to prevent people from dying from certain diseases. Someone in their 40s or 50s wouldn't have been thought of as elderly back then, and they would have looked pretty much the same."
] |
[
"Biologically people would age the same way. But the less advanced medicine would also mean that non life threatening injuries and illnesses would not heal as well as they do now. Many people would be left with bad scarring, there'd be more people with stiff or crippled limbs from earloer injuries, all these things would give the impression of age.",
"So while someone who was healthy their whole life at 50 would look the same as 50 now, that generally wouldnt be the case"
] |
[
"I think the fact that we now have a vastly improved diet has certainly altered the way we age. If you eat things which have oils or nutrients which are good for the skin then physically I imagine you would look younger."
] |
[
"What exactly detracts humans and other animals from cannibalism?"
] |
[
false
] | null |
[
"Well, from one evolutionary standpoint, it's more likely for disease to jump from human to human than from an animal to a human. "
] |
[
"This. Members of the same species share almost identical immune systems so a disease that is capable of surviving in the victim is more likely to find the cannibals immune system hospitable than a prey with a dissimilar immune system."
] |
[
"In addition to what others have said, you can look at it like this: ",
"It is more beneficial to a community to increase its population than decrease it. More members means more work, more food, and more protection. Cannibalism would decrease population, not to mention it would limit trust, which is generally essential to a community.",
"Now, when it comes to ",
", we have laws which protect our right to life. Unless some factor such as religion supersedes law, cannibalism is out of the question."
] |
[
"I saw a dead wasp being picked up by another wasp who flew away with it. Why would a wasp do this? Is this typical behavior?"
] |
[
false
] | null |
[
"Food. Most wasps are carnivorous, meat is meat.",
"Edit: Since people are asking, I was giving a vague but accurate answer to a vague question. I don't know what kind of wasp he saw, but I assume it's a standard yellowjacket (",
"http://en.wikipedia.org/wiki/Yellow_jacket",
") which will eat... well lots of things but they are predators. It's totally normal for a such a wasp to consume a dead comrade. As many of the people replying to this have pointed out, there are so, so many species of wasps which fill tons of niches. "
] |
[
"Insectologist here,",
"While adult wasps don't eat much meat based product (though some have been known to from time to time) their young do need meat which the adults obviously have to find.",
"Depending on where you saw the dead wasp it was either picked up to be taken and used as food or alternatively taken further away from the nest, the corpse of an insect near their nest comes with the inerhent risk of danger by way of attracting ants.",
"Hope that helped."
] |
[
"carnivorous ants are a threat to all other insects (and a few invertebrates) except for the very, very few that prey on or parasitize them.",
"the 'Zerg Rush' is an extremely effective strategy in the insect world."
] |
[
"What is the most probable physical distance between you and a random person on the internet?"
] |
[
false
] |
[deleted]
|
[
"I imagine you'll need to provide a specific starting point before anybody can answer that question.",
"Simplest answer would be total land area divided by population: per Google, 510.1m/7.442b = 0.0685 people per sq. km.",
"EDIT: Ah, that's not quite right, that'd be average distance to nearest person at all. You'd need to multiply that by the percentage of people online at any given moment (best answer I could find after a brief search: ",
"https://webmasters.stackexchange.com/questions/18392/how-much-percentage-of-total-internet-users-are-online-at-any-given-moment",
"). If we go with an even larger number to improve the odds, we'll say 80 million online at any one time. That accounts for 1.07% of the population, so we multiply 0.0685 by 0.0107 to get 0.00073295 people per sq. km. Inverting that gives us the total area, and circularizing that area means at some point within roughly 21km of your location will be another internet user.",
"Of course, that's not accounting for areas that have zero effective population. Unfortunately, someone else will have to help with such a calculation, as the first four articles I read gave me 1%, 10%, 40%, and 83% of the surface is occupied by humans, which will all give vastly different answers.",
"It also does not account for time zones or dates, where people on the day side are more likely to be online, although during weekdays it'll be before or after work with highest population densities.",
"And of course, it also does not account for the local standard of living: third world countries are going to have a smaller percentage of people with access to the internet, much less actively online."
] |
[
"As the crow flies? Or as the neutrino travels?",
"Simplifying the earth somewhat as a sphere 6378 km in radius...",
"As a crow flies -- Maximum distance traveling along a great circle geodesic would be pi*6378 km. Or about 20,000 kilometers. So somewhere between zero and twenty thousand kilometers. My WAG is ten thousand kilometers.",
"As a neutrino travels -- Maximum chord between two points on a sphere is a diameter. So maximum distance would be 2*6378 kilometers or about 12756 kilometers. Zero kilometers would be minimum distance. In this case I believe average chord length would be 2/pi * 12756 kilometers or about 8,120 kilometers.",
"It also depends on where on earth the person is. Someone in the middle of the north Atlantic would be closer to many internet users than someone in the middle of the southern Pacific ocean."
] |
[
"Interestingly, every non-uniform distribution will lead to a smaller average distance than a uniform distribution. And the internet users have an extremely nonuniform distribution - nearly all of them are in the northern hemisphere, for example."
] |
[
"What is the root cause of odd phobias?"
] |
[
false
] |
Like fear of clowns or cotton. What makes a small percentage of people scream in terror from these harmless things?
|
[
"Phobias are caused by operant conditioning and heuristics. In other words, humans experience a stimuli and then coincidentally the circumstances are such that it surprises them and induces a fear response. This then is paired and develops into what we call a phobia. For example, a toddler is sitting enjoying the circus. Suddenly a clown appears out of nowhere and squirts the toddler with a flower. This catches the toddler off guard and the toddler is frightened, and begins to cry. From then on whenever the toddler sees a clown, his brain expects to be surprised negatively speaking and there is a chance that that individual will pair clowns with fear from then on. Phobias are fairly common and there is a cure for them known as systematic desensitization.",
"Between 8 and 18 percent of Americans have some sort of phobia.",
"http://en.wikipedia.org/wiki/Systematic_desensitization",
"http://en.wikipedia.org/wiki/Phobias#Etiology",
" "
] |
[
"maybe...but why do people have such perfect matching reasons for it.",
"Like cotton phobia almost everyone with it hates the smell, the sound it makes when moved and the way i works. If that theory is correct wouldn't the hate it for different reasons?"
] |
[
"For it to be a genuine phobia the person has to fear and hate the stimuli. For example, wincing at the sound of fingernails on a chalk board is not really a phobia, so much as it is an annoying stimuli. ",
"If someone has a phobia to the sound of something, it's rooted in fear and anxiety to that particular sound. And stimuli don't have to just be visual. For example, a child who is beaten every time chicken is frying or mozart is being played could develop aversive reactions to these non-visual stimuli."
] |
[
"Why do thunder and lightning not occur during a snowstorm?"
] |
[
false
] | null |
[
"It happens. I've experienced it during a blizzard in the 90's. "
] |
[
"http://en.wikipedia.org/wiki/Thundersnow"
] |
[
"I don't know why bitternIdontcare got downvoted. It ",
"does happen",
", and I've seen it several times."
] |
[
"How do we know what the inside of the Earth is like?"
] |
[
false
] |
As far as I know, we've never drilled past the crust of the Earth right? So how exactly do we know what the mantle and core are like?
|
[
"You're absolutely correct - the deepest we've ever drilled is about ",
"12km",
".",
"So everything we know about the rest of the earth's internal structure has to be inferred from a variety of remote-sensing techniques, experiment, comparison to analogues, and then numerical models into which all this data is fed.",
"So, the first and perhaps most important is the use of seismic waves to understand the behaviour of the interior. EVery time an eathquake goes off it propagates P and S waves through the earth. Those waves travel at different speeds in different materials, depending on the shear and bulk modulus of the material (how fast it propagates a sideways deformation, and how fast it propagates a compressional deformation). We have a netowrk of seiosmometers around the globe, so when an earthquake goes off we can detect the arrival of those waves at different points. By knowing how far away the location are we can look at travel times of those waves to see how fast they propagated. Now do this for thousands of earthquakes all over the globe and you can begin to see patterns, where seismic paths which travel at certain depths have particular properties. What's also interesting is that it soon becomes apparent that the waves reflect and refract off certain boundaries. So, over time we can calculate ",
"different seismic ray paths which enable us to identify the main boundaries within the earth",
".",
"We can also calculate the seismic wave velocity at depth: ",
"http://upload.wikimedia.org/wikipedia/commons/b/be/Speeds_of_seismic_waves.PNG",
"By knowing those things we can start to make good inferences about what the material is like; we know how massive earth is, so we can begin to model pressure and temperature data with depth. Compbine that with experimnetal petrology (basically testing the behaviours of rocks and minerals at very high temperatures and pressures), we can infer what mineral phases are present at different depths. This is supported by observations of geological structures which have preserved parts of the lower crust and mantle, or in volcanics which sometimes bring up ",
"mantle xenoliths",
" - basically samples of upper mantle material.",
"Direct observations of these support the interpretation that asteroids formed in the early solar sytem (widely believed to have come from rocky protoplanets which became broken apart) can be used to understand the bulk chemistry of the earht better. The proportions of different stony, stony-iron and iron meteorites strongly suggest they are representative of early differentiation processes, forming iron cores within otherwise rocky planetoids.",
"Simple stellar physics tells us that there is a ",
"huge amount of iron",
" in the universe (it's the endpoint of fusion reactions), so it is reasonable to conclude that the magnetic field is produced by an iron-rich core. This is supported by the meteoritic evidence which supports the metallic centre being largely iron with a bit of nickel.",
"So that's bulk features kind of dealt with (bear in mind here that I have summarised decades of research by tens of thousands of individuals into a few paragraphs).",
"Where it's getting increasingly groovy is in our ability to detect small-scale variations. Having gathered ever more and better data from an increasing number of seismometers around the world, our understanding of the bulk structure is good enough that we have in the last couple of decades been able to start looking at spatial variations in these bulk layers, essentially using seismics as a very low frequency alternative of ultrasound on the earth. This field - known as seismic tomography - has enabled us to image things such as ",
"hot-spot mantle plumes",
", and ",
"subduction of plates",
" at destructive plate margins."
] |
[
"Hello there!",
"No-one has ever penetrated Earth's mantle to reach the core to investigate what it is made of, so much of what we \"know\" is theory based on intelligent deduction. Some deductions are based on good empirical (based on observation or experiment) data obtained by analyzing the seismic waves that are produced when earthquakes happen.",
"Seismic waves that travel through the deep interior of the Earth can sometimes be detected by seismographs in different parts of the world. Scientists observe where these waves reach the surface and how long it takes for them to get there. Comparing these observations with controlled experiments on the behavior of waves passing through different materials, scientists can then construct good theories about what materials deep in the Earth the seismic waves passed through on their way to the surface.",
"Cheers"
] |
[
"Additional detail: P-waves (primary or compressional waves) can propagate through both solid and liquid media, while ",
"S-waves",
" (secondary or shear waves) only propagate through solids because liquids don't have the shear strength to propagate them. We can tell that S-waves don't propagate through the outer core, which shows that it's liquid, and the solid inner core and the boundary between them produce additional reflections and refractions that were ",
"later detected",
"."
] |
[
"If I place two bowls of water in a freezer and one bowl is stagnant and the other is being stirred, will both bodies of water become frozen at same or different rates?"
] |
[
false
] |
Just curious to see if the friction of the water is enough to impact how water becomes ice.
|
[
"Mixing generally enhances crystal nucleation rates by increasing the number of critical concentration fluctuations. So I would say the stirred bowl will freeze quicker.",
"Why don't you try the experiment yourself and report back your findings."
] |
[
"Going back to my fluid mechanics days....",
"When water velocity goes up, the pressure goes down. Lower pressure means you need to be even colder to freeze water.",
"At the molecular level, there is additional kinetic energy which would require the temperature to be lower as well.",
"That being said, I dont know how significantly this affects freezing. I asked my Pchem teacher this question and my fluid dynamics teacher this question back in undergrad and they didnt know the answer.",
"so \"Why does the water at the edges of the river freeze?\""
] |
[
"In addition to what several others said, the turbulence of the stirring has the effect of keeping the liquid at an even temperature throughout. In stagnant water, the water near the edges can get colder than that in the middle of the bowl, which reduces the temperature delta between the liquid and bowl, which reduces the transfer of heat from the liquid to the bowl to the cold air of the freezer. The stirred water will keep the water warmer near the edges, increasing heat transfer, and reducing the freezing time.",
"Any time you are using a liquid or air across a surface to change the temperature of the surface, turbulence increases the heat transfer. "
] |
[
"Is there really a difference between adult and child medicine?"
] |
[
false
] | null |
[
"YES. There is a difference. Children are not just \"tiny adults\", and some medications have completely different effects in children vs adults. Similarly, many diseases are more common in particular age groups. This goes beyond a dosage phenomenon, there are many important differences in pediatric medicine. "
] |
[
"Having just covered this topic in anti-infectives. Many medicines will not be prescribed to children due to their indirect actions. A fascinating phenomena is metal chelation, where a molecule will chelate/sequester metal ions due to lone pair of electrons (in ketones, amides, acids etc) donating to polyvalent ions (Mg2+, Fe3+ etc.)",
"For example tetracyclines or quinolones (antibiotics, antivirals) will not be prescribed to children and you will be advised not to consume it with dairy as it will chelate calcium ions. Not only reducing the amount of Ca2+ you will absorb but also precipitating the medicine making it insoluble. "
] |
[
"Yes. The difference is also more than just size--children are not just small adults.",
"For example, the brains and bodies of children are, in some ways, more plastic and resilient than those of adults. They have a better chance of recovery from some types of injuries. An extreme example is the hemispherectomies that are sometimes used to treat rare, intractable epilepsy--an entire half of the brain is removed. This procedure is used almost exclusively in children, who have a better chance at recovering from such a dramatic procedure.",
"Children are also more vulnerable to some things than adults are. For example, their skin is more fragile and more vulnerable to burns (eg ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3038395/",
"). Children and adults differ in the way they break down some drugs and chemicals, so that dosage must be determined on a different scale depending on age, not just on height and weight (",
"http://www.sciencedirect.com/science/article/pii/S0273230002915588",
"). Children have more actively growing organs than adults, including brain, bones, etc., and their nutritional needs and response to stressors will differ because of that ongoing growth."
] |
[
"What is the actual mechanism behind the symptoms that are caused by trisomy?"
] |
[
false
] |
I’m not thinking of any specific chromosome but for example let’s say trisomy 21. What is about having a third 21st chromosome that affects the person in that particular way?
|
[
"Having an extra chromosome changes the balance of synthesized proteins. The different genes coding for one trait (say face shape) are not located on a single chromosome but one several different chromozomes.",
"Having an additional chromozomes adds genetic material that is processed by the cells. Phenotypes (manifestation of genes) depend on the genes a person has, and on the expression of those genes (amount, zone, time). If you change the amout of a certain gene you might change the phenotype.",
"That's my basic intuition, but adding an extra chromozome might also change zone a timing of gene manifestztion, and not only for the genes coded for on the extra chromozome. Then everything gets complicated and you have to dig into the specifics",
"TL DR Phenotypes (manifestation of genes) depend on the genes a person has, and on the expression of those genes (amount, zone, time). If you change the amout of a certain gene you might change the phenotype."
] |
[
"The general phenomenon is called gene dosage. This is also why we only observe trisomies from smaller chromosomes because the larger chromosomes have so many genes that the presence of an extra one is invariably embryonic lethal. ",
"https://www.weizmann.ac.il/molgen/Groner/research-activities/trisomy-21-gene-dosage-effect",
"With that said, polyploidy, where the number of chromosomes remains 2n, seems to be much less of a problem and is very common in plants. ",
"https://www.pnas.org/content/109/37/14746"
] |
[
"Trisomes for X, 13, and 18 are not \"invariably embryonic lethal\".",
"Those are not the larger chromosomes, they are smaller than average (except X). And the X chromosome is special because there's a mechanism to shut down all but one X chromosome in each cell. That's there specifically to correct the gene dosage imbalance between males and females."
] |
[
"Why are bright colors in nature associated with \"poisonous\" and how did poisonous animals develop these bright colors?"
] |
[
false
] | null |
[
"It is called conspicuous coloration. It is a means of communicating that you are poisonous. A brightly colored butterfly is eaten by a bird, that bird gets sick because it is a poisonous insect. The next time the bird sees a brightly colored insect, it won't eat it. ",
"What is interesting is that species will evolve to look like other poisonous species. For example, many butterflies have coloration that is similar to a monarch butterfly. Unfortunately, if there are too many \"fakers\" the effect is diminished. Then conspicuous coloration because a liability instead of an asset."
] |
[
"It is also called aposematic coloration. It is associated with animals that are poisonous (bad for you if you eat it) and venomous (bad for you if it bites you). Bright coloration with high contrast (frequently against black) warns predators not to mess with it. ",
"The coral snake has black, yellow and black bands, warning predators that it is venomous. The monarch butterfly has orange and black patterns, warning predators that it is poisonous. Bees and yellow jackets are yellow and black to warn about their sting. Most animals recognize these types of patterns and will stay away.",
"Müllerian mimicry is a type of aposematic coloration where different species of poisonous or venomous organisms will evolve to look similar to one another, maximizing the effectiveness of their warning signal. They will not just have bright colors with high contrast, but the same colors and the same patterns. ",
"Batesian mimicry is a type of false aposematic coloration where a harmless animal mimics one that is poisonous or venomous. Classic examples are the viceroy butterfly, which is not poisonous, looking a lot like the monarch butterfly.\nThe milk snake is a harmless snake with a very wide range across north america. In places were its range overlaps with the coral snake, it mimics the coral snake. In places where it overlaps with the copper head, it mimics the copper head. "
] |
[
"The other nonpoisonous species evolve to the poisonous color because the bird won't eat any nonpoisonous yellow ones either. Yellow accidentally becomes an advantage. "
] |
[
"How did Schrodinger come up with the wave equation, if he didn't derive it?"
] |
[
false
] |
I am from India and conservative people often boast about how Schrodinger got his wave equation from Hinduism. They say Schrodinger, because he used to study Hindu scriptures, got the equation inspired from Vedanta. Now, I know this is pseudoscience, so I tried to see how Schrodinger derived it. Google search says the equation can't be derived and is axiomatic. Then...how did he make this equation? Did his mind just produce this equation out of sheer intuition? I thought maybe its like how Newton got F=dp/dt, but again, this equation is far too complex to just come out of nothing. So...what's happening?
|
[
"axoimatic basically means he looked at what was measured and built an equation from what was observed. he knows he was right because his equation correctly predicts measurements, not because it is derived from other equations.",
"F=ma is kind of similar"
] |
[
"true experimentally",
"So Schrodinger put this all together and set out to find a wave equation description of the electronic states within the potential of the hydrogen atom. ",
"This wave equation correctly predicted the energies and intensities of spectral lines for the hydrogen atom.",
"See his ",
"personal review",
" of his contributions."
] |
[
"Hey thanks! That was a very detailed response. Also, thanks for showing me his own article. Didn't expect that as a citation"
] |
[
"What causes the appearance of pixelation in the spot emitted by a laser?"
] |
[
false
] |
has a decent drawing of what I'm talking about. I've long wondered about this, it appears to move with the laser not the surface when the beam is moved, so it must be a feature of the laser itself..
|
[
"It's called \"laser speckle,\" and the answer to your question is interference. ",
"Laser light is not like ordinary light; all the photons are in phase. Two photons in the laser, bouncing off two adjacent spots on your target, will travel slightly different distances before returning to your eye. This path length difference will cause them to be out of phase when the reach your eye, and thus to interefere with each other. ",
"In the dot of a laser, then, you'll get a bunch of spots, all right next to each other, some bright from constructive intereference and some dark from destructive intereference. This is exactly the pattern you're asking about.",
"Wikipedia has an article ",
"here",
"."
] |
[
"Another cool thing is using the speckle to do eye testing",
"http://en.wikipedia.org/wiki/Eye_testing_using_speckle"
] |
[
"Thank you for this one. I had played with the effect and determined that somehow the pattern is a property of my eye since the pattern moves with the eye and is not stationary."
] |
[
"In an AC, series LC circuit, how can the inductor voltage be higher than the supply?"
] |
[
false
] |
I understand how this is mathematically possible. Since the inductor and the capacitor voltage and impedence are in phase opposition, their combined impdence is the difference of the 2. Physically, I am having a hard time coming up with where the extra voltage comes from.
|
[
"KVL should hold true - the sum of the voltages around a loop should equal zero.",
"In an AC circuit, some voltages can be negative, that allows other voltages to be greater than the supply."
] |
[
"You can have a circuit where a component can have a higher voltage drop than the source. This is very common in split phase induction motors. In many cases, the start winding voltage will be greater than the supply. This is also why start and run capacitors are rated for such high voltage."
] |
[
"First off voltage isn't a conserved quantity, so don't freak out if you see circuits like that in the future. Recall that the voltage across an inductor is defined as:",
"\n",
"v(t) = L * di(t)/dt",
"\nIf you aren't operating in steady-state then it's very easy to see how the voltage can reach larger-then-supply voltages by creating a large change in the current.",
"But for steady-state AC I don't think you'll see that. Regardless of your choice of inductor or capacitor I don't think either will ever develop a voltage drop larger than the source. ....Right? "
] |
[
"Why do metal pots and pans (or even the occasional stranded fork or spoon) not short out kitchen electric burners? Shouldn't crossing several of the individual \"wires\" in the twisted element cause a short circuit?"
] |
[
false
] | null |
[
"The actual electrical conductors (resistors) in your stove aren't exposed. They're inside the heating element, enveloped in ceramic (non conducting), and then covered in the metal you see glow bright orange. They're totally insulated. Open up your stove and pull one out. Look at the plug and you can see the compositional layering. "
] |
[
"Electric stovetops are metal wire clad in ceramic insulator clad in an outer protective layer of metal. The ceramic keeps it from electrocuting you and the steel on the outside keeps you from accidentally damaging the ceramic."
] |
[
"Nope. Those toaster and radiant heater elements are often bare \nnichrome wire and depending on where you contact them can deliver \na substantial part of the voltage applied to them."
] |
[
"What is it that causes sweat to generally smell bad?"
] |
[
false
] |
[deleted]
|
[
"It's not actually the sweat that smells bad, it is the bacteria living around the sweat glands. You'll notice that not all sweat smells bad, either -- sweat that forms on your forehead is not stinky. ",
"The sweat that smells bad is sweat that comes from apocrine sweat glands, which are associated with hair follicles, and they are found mainly in the armpits, external genitals, and perianal area, but also in small amounts around the nipples, inside the nose, and in the eyelids. However, the armpits and crotch areas tend to sweat more due to the skin not being exposed, and so they smell worse. They secrete a more oily substance, and this oil is consumed by bacteria that live in those areas. It is the bacterial decomposition of the oils that causes the odor, not the sweat itself. ",
"Non-apocrine sweat glands don't cause significant odor because they secrete a more purely aqueous sweat that doesn't have much for bacteria to eat. "
] |
[
"Really not much. They're there because they can be. However, like anywhere on our body, a colonization of non-harmful bacteria do help to prevent pathogenic bacteria from finding a foothold, so they do provide that benefit. There is also a theory that some odors caused by these bacteria act as pheromones and may have played a role in our evolution - - ie, those with BO may have had an easier time reproducing, to the extent that apocrine glands became a universal trait. That, however, is just theory "
] |
[
"Really not much. They're there because they can be. However, like anywhere on our body, a colonization of non-harmful bacteria do help to prevent pathogenic bacteria from finding a foothold, so they do provide that benefit. There is also a theory that some odors caused by these bacteria act as pheromones and may have played a role in our evolution - - ie, those with BO may have had an easier time reproducing, to the extent that apocrine glands became a universal trait. That, however, is just theory "
] |
[
"Converting Magnetic Field Strengths - Ampere-Turns to Tesla"
] |
[
false
] |
A friend of mine wants to recharge a magnet in an old 1919 car engine. The internet has told him that he needs a field strength of 20,000 Ampere-Turns to do so. We have a magnetic field generator we think will work and even a measurement system in our lab. But we're going to take the measurement in Tesla (or Gauss). So how does one convert from this weird "Ampere-Turn" to Tesla? We googled the hell out of it, found only shady sources, and concluded that we need 40 TRILLION Telsa (which is patently ridiculous). So google has failed us. Does anyone know a good resource relating the plethora of magnetic field measurement systems? : an AT is a measure of magnetomotive force, but a Tesla is a measure of magnetic induction. The two must be related by something more complicated than a unit conversion.
|
[
" Holy smokes, I found a really cool Abstract to a paper that is likely talking about a magnet very similar to yours. Read ",
"On K.S. Magnet Steel",
" and check out one of the earliest scientific papers on the magnet. They used a ",
"-field of 0.13 Tesla for their hysteresis curve, which should have gone past magnetic saturation, which is fairly close to my 0.1T guess below. They likely go above and beyond saturation just as we do today. They also talk about how they heat treat the magnet in boiling water, which caught me by surprise at first. Anyone want to venture a guess as to why it's so low?",
"Alnico alloys were developed throughout the 1930s, so you're looking at a high carbon steel as your magnet for a 1919 car (if this is truly the case!). These alloys have a coercivity of approximately 20 kA/m, so at the very least, you're going to need a magnetic field strength that is three times greater than this. Four times to be safe (we go five times past the coercivity in the lab, more or less). You have a magnetometer that measures the field in Tesla? Great, your field must register ",
" 0.1T in order to saturate this magnet, but even greater to be safe. Make sure this field is parallel with the axis of the magnet. Despite another's comment, do not heat up your magnet. This will destroy its properties if you heat it up too much and is not necessary assuming it's still in good physical condition. If you think for some reason it's a more recent magnet, or just to be extra sure you fully magnetized it, take it up higher than 0.1T. The thing is, ",
". We take ours to a field of at least 5T even though our coercivities only require 1.2T. Can you please provide a picture of your magnet? I'm very interested.",
"The units for magnetism are extremely confusing, and there are multiple conventions which require different derivations. But in this case we're generally looking at ",
"Biot-Savart Law",
" (or the equivalent Ampere's Circuital Law in this case).",
"H = ",
" / (2",
"a), which can be integrated quite easily to give you the magnetic H field due to a coil, H = ",
"/2r where r is the radius of the coil. This is where the \"Ampere per meter\" or \"A-m\" unit gets its name. The A-m is the magnetic field strength, ",
", produced by a single coil of conductor wire that is 1 m in diameter carrying a current of 1 amp. But that's just math. Understand that ",
".",
"However, Tesla is the unit of magnetic induction, ",
". The magnetic induction is a material's ",
" to a magnetic field ",
". Iron respons to a magnetic field strongly. Even air does to an extent. So if you have a magnetic field generated in a certain location, the object in that vicinity will react to it and with magnetic induction. The two are related by a value called the permeability, μ. In a vacuum, it's μ_0 (\"mu naught\"). In air, it's close enough to μ_0. So if a material is in air, as in the case of your magnet, it's response to the magnetic field can be easily calculated.",
"The equation is simple with these SI units: ",
" = μ_0",
"Coercivity in this case is ",
" which is 20 kA/m for your sample. Since it will be in air, we're going to use the permeability of free space μ_0 = 4",
"10",
" . Plug it in to calculate ",
" in units of Tesla. The thing is, taking it to H_ci isn't good enough. We want to go above and beyond that. ",
" I now supplied a paper that talks about a steel magnet that I think might be yours, and it sounds like the scientists indeed used a field approximately 4 times greater than H_ci. Our magnets (Nd2Fe14B) have coercivities of about 12 kOe (1.2 T), so we take our machine to ~5T to saturate."
] |
[
"The internet has told him that he needs a field strength of 20,000 Ampere-Turns to do so. ",
"Is it possible that the source was indicating using a solenoid rated at 20,000 Ampere-Turn? Meaning, a solenoid with 20,000 loops coupled to a 1 Ampere source current?"
] |
[
"For an ideal ",
"solenoid",
", the relationship is ",
", where N is the number of loops, I is the current, L is the length of the solenoid, and µ is the ",
"magnetic permeability",
" of the core material. Your 20000 Ampere-turns would be the value of NI.",
"Note that (as some others have mentioned) 20000 Ampere-turns is not a measure of magnetic field strength. Based on the equation, you can't calculate a magnetic field strength from that value without also having the length of the solenoid it would be used in.",
"By the way:",
"a Tesla is a measure of magnetic induction",
"That would usually be called ",
"magnetic field",
" or magnetic flux density. I wouldn't call it ",
"magnetic induction",
", to avoid confusion with ",
"inductance"
] |
[
"Since the nervous system uses some form of electricity to transfer messages, is it possible to short it and what would happen if so?"
] |
[
false
] | null |
[
"Yes its possible. A neuron has a dendrite, a cell body and an axon. The dendrite takes the action potential of other neurons (through synapses) - it is a bit difficult because it often changes between a chemical signal and an electric signal - then the signal runs through the cell body (the middle part of the neuron with the nucleus in it) to the axon, where another action potential gets created, that will run to the synapse and there will most often cause the distribution of neurotransmitters. ",
"In your brain there may be some neurons that are \"short circuited\", meaning neuron 1 will stimulate neruon 2, which will stimulate neuron 3, which will then stimulate neuron 1. If this happens, and the neurons stimulate other neurons around them, you will get a seizure. (Thats often how epilepsy works. If a specific neuron gets stimulated - through a specific signal - it will \"short circuite\" and stimulate all those other nerves around it in a chaotic manner.)"
] |
[
"Well if you inject salt into the blood stream, that actually shorts the most muscles, because action potentials which are used to propagate the signal don't function anymore, because plus minus potential between cells outside and inside is no longer in balance. Salt contains positive ions and your system works by pumping those from inside to outside of the cell. But since you already have positime ions outside from salt, the system is broken. The end result is of course death due to heart (muscle) storage.",
"The opposite is also true. When you work out and sweat you can feelsometimes muscles just pulsing on their own, that's because sweat contains salts, and threshold for action potential decreases. That's why it inadvisable to not just drink water, but some kind of salty water."
] |
[
"As far as what happens, I think MS would be a good example."
] |
[
"How does a hypodermic needle versus a sewing needle pierce the skin differently from each other?"
] |
[
false
] |
I’m just wondering since I found out that sewing needles are apparently thinner. Why would a medical needle be less “sharp?” than a sewing needle?
|
[
"A sewing needle is a solid piece of metal that tapers to a point. It needs to be strong enough to pierce through whatever kind of fabric it's being used to sew, and hold its shape for a lot of hours of use. If you look at it under magnification, the point is centred over the shaft. ",
"A medical needle is hollow, and ideally it should have thin walls - because the thinner the walls are, the smaller the outer diameter of the needle (which determines the ouch factor) for a given inner diameter. Obviously, a metal tube with thin walls is less strong than a solid metal stick with the same diameter. Also, the point can't be centred over the shaft, because that's where the hole is. Instead, it has a bevel - imagine what it would look like if you cut a drinking straw at a 45 degree angle, and that's pretty close. Because medical needles are designed for single use only, they are actually sharper than sewing needles when new, but will get blunt very quickly if handled and passed around. ",
"Both sewing needles and medical needles come in lots of different sizes to suit different tasks. So it doesn't really make sense to say that either is thinner than the other."
] |
[
"Yep. Getting a blood sample taken uses a noticeably thinner needle than donating blood. I presume this is to increase flow to speed up the donation process."
] |
[
"That's part of it, but the main reason is shear forces on blood cells. The thinner the needle, the more blood cells get damaged by shear forces as they pass through. This is usually irrelevant when taking a blood sample for analysis, but it's important to minimise when you want the donated blood to last well in storage and be maximally effective for the recipient."
] |
[
"Are there any galaxies in the \"edge\" of the observable universe which we can't fully observe because part of it is unobservable?"
] |
[
false
] | null |
[
"It just doesn't work that way. Keep in mind that seeing farther away is equivalent to seeing farther into the past. And it is that phenomenon combined with the finite age of the universe which creates the limits to the observable Universe. For a very old/far away galaxy the image of the close side might be a hundred thousand years younger than the far side, but that's generally too short a time for there to be perceptable differences due to galaxy evolution or even formation.",
"We can see far enough back in time to see the period of time before galaxies existed and even to see beyond that into the period of time when the Universe was just an ultra high density plasma.",
"Galaxies are too small compared to the Universe's age when they formed to be able to see just half a galaxy. What we would see instead is an enormously red shifted proto-galaxy blob part and then progressively more redshifted light up to the boundary of the cosmic microwave background.",
"It's very difficult to wrap your brain around the concept, since there are boundaries between things we can see and things we can't, but they are not sharp boundaries. They are boundaries which fall away backwards in time."
] |
[
"None currently known. The furthest galaxy ever discovered (and just announced yesterday) is SXDF-NB1006-2 at 12.91 billion light years from earth.",
"Read more here"
] |
[
"I, and I believe the OP, were discussing the observational sphere - that is, as something moves from inside our observational sphere to outside... or something that is partially inside our observational sphere."
] |
[
"What about a bug bite makes skin swell / itch?"
] |
[
false
] | null |
[
"This occurs as part of your innate immune response. This means that it is short-term and non-specific. It is this non-specific response that will cause your initial swelling on site.",
"Basically something called cytokine proteins are made in response to the invasion of a recognized foreign body. Cytokines are secreted outside of the cell where they contact neighboring cells and recruit white blood cells through cell surface interactions.",
"Inflammatory response occurs when the called upon white blood cells flood the site. They will phagocytize pathogens or release granules which lyse (breakup) both pathogenic cells and your own cells.",
"Redness and heat occur as a result of the influx of blood cells while swelling results from fluids like plasma coming in from the bloodstream.",
"tl;dr cells recognize foreign particles which causes them to release chemical signals to other cells which say \"come fuck this shit up\". all that stuff coming in makes your shit swell."
] |
[
"As a followup, does that mean that if you use an anti histamine (or something similar) it is portentially makong your body more vulnerable to whatever foreign bodies caused the initial reaction? "
] |
[
"Thanks for the answer!"
] |
[
"What causes morning grogginess?"
] |
[
false
] |
I'm basically retarded when I wake up. What causes that? Does the brain wake up in a certain order, i.e. motor functions before language comprehension?
|
[
"You have a natural cycle of melatonin levels in your brain. Melatonin is a hormone that is made in the pineal organ (which responds to light through an array of different nuclei ultimately stemming from input from the retina). This is known as the circadian rhythm. It determines when you feel tired and when you feel awake (to an extent).",
"When you sleep, your body also cycles through different stages of sleep. If you wake up from stage 3 or 4 sleep, you are not going to be as alert as when you are awoken from stage 1, 2 or REM.",
"There's also evidence to suggest that endogenous opioids are released during sleep after a long period of sleep deprivation or sleeping for a long period of time, which could explain that \"nice, groggy\" feeling you get after sleeping like 16 hours.",
"Also, do you drink coffee? caffeine withdrawal can cause grogginess in the morning.",
"http://en.wikipedia.org/wiki/Circadian_rhythm#Biological_clock_in_mammals",
"http://en.wikipedia.org/wiki/Sleep#Physiology"
] |
[
"That doesn't quite make sense to me, wouldn't your brain be active before your body, in that case?",
"Interestingly enough, I used to be a very active sleeper, and did not have this issue. Now I sleep very still, and experience the grogginess a lot. However, I thrashed around a lot when I was like, 12. So there's that.",
"*Edit: by \"there's that\" I mean that it could be a product of maturing/puberty?"
] |
[
"I have the same problem when my alarm clock gets me up, but not so much on the weekend. I've always attributed it to waking mid REM cycle rather than naturally waking up when the cycle is complete. I've read that your brain releases paralytic neurochemicals during dreams to keep you from acting out you dreams. Before you wake up your body flushes them out, but if you wake up during this phase your brain has to fight the chemicals while trying to go through the normal process of waking. "
] |
[
"Does bees' honey concentrate or filter out toxins from the original flowers?"
] |
[
false
] |
I was thinking of this recently when reading an article on the main page about NYC beekeepers. In a pollution-heavy area, where flowers might be exposed to toxins in the ground/water/air, can those toxins concentrate into honey? Or is pollen and/or honey somehow insulated from toxins by some mechanism? Since I imagine it will be asked, we can break them out into earthly/local contaminants (heavy metals in the soil, agricultural runoff, etc) and air pollution from cars/trucks/smog/etc.
|
[
"I don't know about \"concentrate\" but toxins from the environment are certainly found in honey. Note this doesn't just relate to the bees' ability to filter toxins from nectar before producing honey - it also relates to the flowers' ability to filter toxins from water and soil before producing nectar.",
"Specifically, honey has been found to contain pesticides as well as heavy metal contaminants. In the case of pesticides, the concentrations have always been lower than stated safety limits, though heavy metal concentrations occasionally peak over recommended safety limits.",
"https://www.tandfonline.com/doi/pdf/10.1080/00218839.2007.11101407",
"http://science.sciencemag.org/content/358/6359/109.full",
"I'm not sure though, whether there is evidence of filtering vs. concentration vs. nothing with regard to honey or nectar production. That is, does the honey contain more or less of any toxin than the nectar did? Did the nectar contain more or less of the toxin than the ground water did? I dunno."
] |
[
"Yes honey ",
"can have toxins in it",
". This can be from the environment, a feature of the nectar itself as produced by the plant, or as a result of post extraction processing. From the environment the plants themselves do a lot of filtering before the bees collect the nectar or pollen so just because the plant is in a \"polluted\" environment doesn't mean there is any thing bad in the nectar. Research has been done ",
"specifically on heavy metals",
" in certain areas but most of the time its merely seen as a marker not so concentrated to be a human health hazard.",
"Bees can also be sensitive/picky as to what they collect. Honey bees are known to generally avoid rhododendron nectar, native bumble bees will collect it. This in part has to do with the design of the flowers but if a nectar has concentrations of something unappealing to bees they might simply not collect it. Likewise if its got something in it particularly toxic the worker might not even make it back to the hive. ",
"Certain pesticides",
" have been shown to cause disorientation and means workers collecting it might not make it back to the hive at all. It should also be noted that a pesticide that is deadly to honey bees and other insects might have little or no effect on mammals. Thats part of why we use the ones we use, so we don't poison ourselves.",
"Nectar collected by bees is stored in their honey stomach a chamber above the digestive stomach for transport. During this time enzymes are mixed with the nectar that start to make chemical changes. These can have an effect on the chemical composition of the nectar and start to break down some undesirables. ",
"Once back at the hive the worker will generally pass the nectar off to a younger worker. This younger worker will take the nectar and blow bubbles with it to increase its surface area and reduce the water content. Most nectar starts out around 80% water honey usually ends up around 18.5% or less. During this process more enzymes are effecting the nectar. Eventually its placed in a cell to further reduce in water content before being sealed with wax. This is the stage we identify it as honey. ",
"The worker who brought the nectar back to the hive might instead of passing it off recruit other workers to the nectar source. They will dance giving distance, direction and enthusiasm over the quality of the source. The worker will give tastes of the nectar to observing workers to demonstrate the quality as well. Bad tasting nectar won't generate many additional foragers. What this means is that even if a worker brings back something really nasty the rest of the hive won't necessarily flock to it, and even if they do it ends up getting mixed with all the other nectar brought in and diluted.",
"There are plants which produce nectars toxic to bees: ",
"purple brood",
" is a symptom of the collection from summer titi, and Carolina jessamine is also toxic to bees. Usually these aren't a problem as other plants bloom as the same time and the toxins are diluted to the point they won't matter even to the small larva and bees. On rare occasions however hive death can happen.",
"Pollen collection is different. Workers pick up pollen on the hairs of their body as they rub the stamens of flowers. They then take the pollen and place it in the pollen baskets on their legs by grooming themselves. Once back in the hive they will store the pollen in a cell, along with a little honey and some enzymes in order to start fermenting it. Most pollen is fed to larva, a little to young bees. Pollen is only incidentally found in the honey.",
"The difficulty with pollen collection is that first bees make mistakes. Honey bees are generalists when in comes to pollen. They seem to be aware all pollen isn't created equal (there are a number of proteins pollen might have and not all pollens have them all). They purposefully collect pollen from diverse sources to compensate. Honey bees placed in apple orchards have been observed purposefully collecting pollen from extreme distances outside the orchard bypassing nearby apple pollen so they have diversity. This trait also leads to them picking up things that are not pollen, but with grains of the same size. Honey bees have been observed collecting sawdust (they might be getting the fungus growing on the sawdust too, not just the dust itself), ",
"coal dust",
", powdered chicken and horse feed. Toxicity of pollen generally would not effect the worker, but it might cause the hive to collapse as the next generation fails to develop.",
"The human problem with pollen, assuming its pollen not coal dust, is that ",
"we collect the pollen at the entrance",
" before the bees even start to break it down. There is absolutely no filter like the enzyme breakdown of nectar, or even the internal transport leading to bee death or disorientation before we take it. Its straight from the source.",
"EDIT: Yes. Added some links."
] |
[
"though heavy metal concentrations occasionally peak over recommended safety limits.",
"Without reading anything about this, I'd question whether that's a big deal. Few people eat a teaspoon of honey a day, most likely, and most probably eat a teaspoon per month on average. ",
"So it's a far bigger issue to have a smaller concentration in potatoes, wheat, or other staples, than it is to have it in something few people eat regularly. "
] |
[
"If an object could absorb all light."
] |
[
false
] |
If I was holding a sphere, say the size of a tennis ball, that absorbed all the visible light that hit it, what would I see if I looked down at my hand ?
|
[
"An object that flawlessly absorbs all light, in contrast to reflecting it, is known in physics as a ",
"Black Body",
". An idealized black body will absorb any incident photon, regardless of energy level; however, this ",
" mean that the body will appear, as a black hole, to be completely pitch black. For a black body to be in thermal equilibrium, it instead will absorb the incident light, then ",
" it, maintaining balance with it's surroundings. ",
"This re-emission is very different from simply reflecting the light, however. A perfectly reflected photon would simply leave with the same energy it came in with, and the spectrum of light coming off of the body would exactly match the spectrum going in (aside: an object that does this perfectly is, in contrast, called a \"White Body\"). A perfect black body, however, will re-emit its absorbed energy over a specific spectrum ",
". This radiation, called (surprise) \"Black Body Radiation\" is described by ",
"Planck's Law",
", which quite excellently describes what we would expect to see.",
"So, getting to your actual question... what would we see? The spectrum given by Planck's Law is a smooth curve, extending over all frequencies, from radio up through gamma. However, the curve includes a peak, at which most radiation will occur; this usually falls somewhere in the infrared range, for objects at everyday temperatures. Thus, for an object at a temperature for which you could reasonably hold it in your hand, you would \"see\" infrared radiation being emitted, and would ",
" see a more-or-less pitch black object, although with some small amount of light still being emitted in the visible light range, and some other light being reflected in the visible range (since no ",
" perfect black bodies exist). ",
"Now, as the object in your hand began to heat up, the peak of the black body spectrum would shift into the visible light range, and the observed result would be something that everyone is familiar with, even if they don't understand the underlying cause: the object would begin to glow. At lower temperatures, it would glow a dull red (as the peak would be in the lower, redder frequencies); as it heated up, it would become yellower, before appearing to glow more-or-less yellowish-white as the peak reached the center of the visible range (again, this is a phenomenon that I'm sure you've encountered in life: hot things glow, very hot things glow white-hot). ",
"At this point, we can assume that you've gone ahead dropped the object, but it's worth noting that, as you heat up more, the peak will become sharper and sharper (see ",
"this photo",
"). At very high temperatures (think the surface of stars), the peak will be at a very well-defined, distinguishable frequency, in the yellower range for cooler stars, and reaching all the way into blue for extremely hot stars (at present, I don't believe there are any known stars hot enough to have a peak all the way in the UV range). ",
"This fact is utilized by astronomers to determined the \"",
"effective temperature",
"\" of stars - just by looking at the black body spectrum of a star, it's actually possible to predict the star's temperature within a reasonable degree of accuracy (although this isn't really part of your question, it's also interesting to note that, since certain atoms like to absorb certain frequencies of light, you can look at ",
" in the black body spectrum of a star to predict, again quite accurately, what elements are present in the outer layers of a star, as those elements will absorb the black body radiation leaving the more inner layers).",
"So then, ",
" - the object would look like a dull, unreflective black object at low temperatures, then start to glow at higher temperatures in much the same way everything else on the planet does. The reasons for this? Science!"
] |
[
"You would see a very deep black ball. Black is what we \"see\" when little to no visible light is present. "
] |
[
"The closest example that actually exists would be a black hole, as they come very close to a perfect black body. "
] |
[
"What makes common core so controversial?"
] |
[
false
] | null |
[
"Do we have any hard evidence that this seemingly complicated, and from most stand points unnecessary, alternative to traditional teaching has any merit?",
"I think you are confused. ",
"Common core is a set of standards.",
". It is not some alternative or un-necessary. It simply lays out the subjects children must learn at each grade level."
] |
[
"Then why are parents and faculty fighting it with such rigor? "
] |
[
"Because it controls when each subject is taught at the federal level.",
"Here is a good article.",
"It is the adoption of the new Common Core assessments that is giving teachers heartburn. Actually, it isn't even the assessments so much as the collision between the assessments and another, parallel initiative, which is to include student test scores in teacher evaluation -- a collision, by the way, that was predicted right here on The Huffington Post more than a year ago.\nAlthough many teachers weren't fully on board with the general idea, they have gone into full-scale revolt at the idea that their evaluations would be based on student results on brand-new tests built upon the relatively new Common Core State Standards."
] |
[
"Are the studies about the dog guilt response really based on good science?"
] |
[
false
] |
Over the last year or so, I've seen a lot of these studies saying that dogs don't really feel guilt, they are just responding to the owner's behavior and the so-called "guilty look" they get are either imagined or just a response to being scolded. Here's an example: It always seems like the studies are framed to produce this result. For example, in the one that I linked, the method is to have the owner leave a room and a dog is either given a "forbidden" treat or not. Then the owner comes back into the room and is told the dog took it or not, and they respond to that information, but it is typically wrong. Now first of all, there is no actual circumstance for the dog to feel real guilt in this situation because there is no instance of them actually taking the treat. Also, aren't humans similar in that they will also sometimes display irrational guilt, particularly as children, if they are innocent of an offense but are still scolded harshly? Does anyone know of a study of this nature with very good methods or would you consider one like the linked to be sufficient to make such a claim?
|
[
"Being told once not to do something is not the same as being told a thousand times not to do something.",
"Would dogs feel guilt if they did something, like sit on the couch, which they have been trained to not do?"
] |
[
"Firstly, there is a lot of anthropomorphizing that happens with the popular media and especially dog owners. Just because a dog 'looks guilty' doesn't mean that the dog actually ",
" guilt. It may just have a facial expression that humans interpret as such. That's just how humans are wired, and the wolves that could read and interact with humans got the food and eventually became domesticated.",
"This answer to this question will most likely vary a lot depending upon dog breed and training, which also influences the 'intelligence' that dogs have. There are different views of dog intelligence, and there are some great books out there on dog 'psychology' that delve into some of the research available. ",
" is one (Alexandra Horowitz), and ",
" (John Homans) is another. I've read the former, but only about half of the latter. "
] |
[
"That's sort of what I'm wondering too. ",
"I recall learning in psychology way back just from the textbook where there was some study where dogs were allowed to carry no basket, a basket, or a basket belonging to their owner, and they determined that dogs can feel pride when allowed to \"flaunt\" their owner in that way. No idea if it stood the test of time though. "
] |
[
"Would a mole of individually frozen water molecules which were then placed in a container together behave as a liquid?"
] |
[
false
] | null |
[
"\"Individually frozen water molecules\" doesn't make much sense, since phases are a property of bulk materials. However, you are essentially describing the process of making ",
"low-density amorphous ice",
", essentially a glassy solid made out of low-energy disordered water molecules."
] |
[
"I agree with what ",
"/u/xenneract",
" said. Asking about individually frozen water molecules doesn't really have any meaning; the freezing process of water deals with changes in the way that multiple molecules pack relative to each other. If you only have one water molecule, it isn't really a solid or a liquid or a gas because those terms only have meaning for a group of molecules.",
"If you had a bunch of individual molecules at a temperature below the freezing point of water and brought them together, they would most likely require some higher temperature in order to rearrange into some state where they can interact with each other."
] |
[
"You would probably end up with a super-cooled liquid that, when disturbed, rearranged into a solid. The state is defined by the amount of energy in the molecules and their orientation to one another. If you just set a bunch of low-energy molecules in a space together, they would have the energy of a solid, but the random orientation of a liquid. Then when you stir them around, they reorient into a solid."
] |
[
"Can we convert Hydrogen to Helium like scientists did with Nitrogen to Oxygen? if yes how do we do it? if no then why not?"
] |
[
false
] | null |
[
"Ah yes, that makes sense. If you can manage to produce ",
"N by bombarding ",
"N with neutrons it will undergo beta decay to produce ",
"O. The decay is rather quick, with a half life of ~ 7 s.",
"Something similar can happen in the case of hydrogen. The isotope ",
"H (tritium) undergoes beta decay to produce ",
"He. Tritium is rather scarce in nature, but is produced when ",
"H (deuterium) in heavy water absorbs a neutron. This happens in nuclear reactors using heavy water as a moderator, although not very often, as deuterium usually slows down neutrons rather than absorbing them. Some tritium is produced, which then decays to ",
"He. This decay is much slower than that of ",
"N, with a half life of ~12 years.",
"A nuclear reactor typically manages to produce a few kg of ",
"He each year. Party balloons would be rather expensive if this process was the only source of helium."
] |
[
"This conversion process happens in the sun all the time, and it is what people attempt to do in nuclear fusion reactors on earth. The problem is that you need incredibly hot plasma for the reaction to occur, which is difficult to contain without melting the reactor."
] |
[
"We can, just as with any other nuclear transformations. You can bombard nitrogen with protons and if a proton enters nucleus the atom will become oxygen. Rutherford was using alpha particles (helium nucleus) for this resulting in turning nitrogen into oxygen and hydrogen.",
"The general problem with this is that often you get a radioactive, unstable isotope. For example you could create gold this way, but it wouldn't be of much use :) Most of Nitrogen has 7 neutrons while stable oxygen isotopes has 8, 9 and 10. This means that producing an oxygen atom with 7 neutrons would result in unstable atom, radiating a beta particles."
] |
[
"What is antimatter?"
] |
[
false
] |
I've heard it thrown around in science fiction, and seen a couple of posts talking about it. What exactly is it?
|
[
"Antimatter is a type of material composed of particles that, while having the same mass as normal matter particles, have opposite charge and other physical properities.",
"To explain, consider first the normal sort of matter we encounter everyday; it is composed of atoms, which, in turn, are made up of three types of particles; Protons, neutrons, and electrons. Each of these has a specific charge and other properities; Protons, for example, carry a positive charge, have mass, where as neutrons have no charge, and mass, and electrons have a negative charge and very little mass.",
"In Antimatter particles, we have particles with opposite charges; rather than having a positive charge, the antiproton has a negative charge, where as the antielectron (called a positron) has a postive charge. Antineutrons, similarly, have opposite properties from their ordinary matter brothers (primarly, because it has no charge, the fact that it's composed of antiquarks and has a baryon number of -1 rather than a neutron's +1)",
"Like normal matter, antimatter can and does form atoms, like antihydrogen or antihelium. ",
"Antimatter is really difficult to produce in a lab because (as you note) the reason it tends to show up in science fiction; annihilation reactions. When a particle and it's anti-particle meet (Such as a proton and an antiproton) the two 'annihilate' one another, releasing significant amounts of energy in the form of gamma rays. Despite the name, annilhilation reactions are probably better thought of as transformations of particles, since energy can't be destroyed. ",
"Obviously, this just touches on antimatter, but hopefully it'll help you understand what it is."
] |
[
"I've heard antimatter can be thought of as going backwards in time. What does this mean?"
] |
[
"There's a symmetry in physics called CPT symmetry (the acronym stands for charge conjugation, parity inversion, and time reversal). In short, it says that if you replace all particles with antiparticles (charge conjugation), flip the sign on all of your spatial coordinates (parity inversion e.g. x -> -x), and run time backwards (time-reversal, a well defined mathematical operation even if it seems fantastical) then you end up with a picture where the physics you started with looks exactly the same. ",
"So, in a sense you can think of normal matter as antimatter moving backwards in time in a spatially inverted universe. However, thinking about it like that is, in my opinion, more confusing than illuminating. ",
"There is also a deep connection between CPT symmetry, antimatter, and something called Lorentz symmetry. There's a difficult to prove theorem in physics called the CPT theorem which states that CPT symmetry and Lorentz symmetry are essentially the same thing. Lorentz symmetry is a bedrock of modern physics which comes from Einstein's theory of special relativity. If you don't remember, the special theory of relativity forbids things with rest mass (e.g. you, the earth, but not photons) from moving at the speed of light or faster. ",
"What does this have to do with antimatter? Well when thinking in particle physics you often talk about probabilities. If I have some massive particle initially at position point x1 and time t1, what's the probability of finding it at position x2 and time t2? If the distance* between these two space-time points is something called space-like the probability better be zero (space-like means that if I tried to send a beam of light between the two locations x1 and x2 it would take a time longer than t2 - t1). Having a massive particle (e.g. electron, proton or something more massive like you or me) be able to move through a space-like interval, which again is moving through a spatial distance in a time shorter than that of light, leads to big problems (e.g. violating causality). The technical terminology would be saying that you're violating Lorentz symmetry which is a big no no in physics. ",
"Yet, if you follow the math out, you find that the probability for your massive particle to propagate through a space-like interval is non-zero! How do we fix this? The clever trick here is to say that antimatter propagating between the same two points gives a contribution that exactly cancels this troublesome term. So we say that there must exist an antiparticle for every particle so we pick up this important cancellation and preserve Lorentz symmetry and casualty.",
"*Note that the distance I'm referring to here is a ",
"spacetime interval",
". This is different from the colloquial meaning of distance which only involves intervals in space. "
] |
[
"Does COVID viruses stay dormant in your body after you recover?"
] |
[
false
] |
Hi all, just wondering can COVID viruses stay dormant in your body even after you have recovered from it? I know cold sores & chickenpox can stay in the body for long periods of time without being activated, and I was wondering since all of these are all categorized as a viral infection, could this apply to COVID as well? Thanks in advance guys, genuinely curious about this.
|
[
"Not in the same way. SARS-CoV-2 is an RNA virus. It has to keep replicating to stick around. So it's not dormant. Chicken pox and wart virus can splice their genome into our genome and just wait. Later the virus genome is activated and starts replicating again."
] |
[
"This sounds a lot like an theory designed to avoid experimental validation.",
"No matter how much you test, if you don't find it is either too small to be detected and/or somewhere else. ",
"This would mean that there virus is in a location where the immune system cannot reach. Not impossible, but unusual."
] |
[
"I think that Herpesviruses don't actually splice their genomes into ours. Their DNA is indeed present in the nucleus, but actually integrating int our own linear DNA would interfere with their replication and DNA packaging. ",
"They are not like HBV (which does it sometimes) or HIV (which does it routinely). Those two viruses utilise cellular RNA transcriptase and their own reverse transcriptase. Their DNA intermediate is transcribed into linear RNA. ",
"Herpesviruses, from what I know, rely on their genomes being circular to undergo rolling cycle replication or replicate like bacteria do. True, they can sometimes integrate into our genomes (because DNA sometimes undergoes recombination and we can't help it), but it's unlikely that the functional virus can recover from that."
] |
[
"How do we determine where a sound is coming from?"
] |
[
false
] |
I was sitting on the bus and realized that I knew pretty much exactly where a girl behind me was sitting, just because I could hear her talk. How do we do that? Edit: Thanks for the answers, guys. Damn, nature's awesome.
|
[
"Sound localization",
" happens because our brains are able to interpret the differences in sound coming from both of our ears and use it to locate the source of the sound."
] |
[
"Just wanted to quibble because the answers have been slightly vague (not wrong, just vague) so far. ",
"There are a few animals (humans not usually listed among them), that use a neural ",
"tap-delay-line",
" in their midbrain structures to very precisely time when sounds arrive at different ears. This system must be extremely precise because there is only a millisecond difference between sound arriving at ears (ears ~10cm apart, sound in air ~340m/s delay between ears <1ms). These animals are typically things like owls that need to do extremely precise sound localization (within a few cm at a distance of several m). In mathematical terms, this is deriving the location of a sound from a phase delay between the ears.",
"Most organisms (including humans) do a different calculation. Because of the presence of the skull, which distorts sound waves as they travel through it, and the geometry of the ears with respect to the sound source (i.e., the ears are at different angles relative to the noise), the ",
" of the sound will differ slightly between the ears. It is much, much easier to derive sound location from this frequency difference and that is what most organisms do (though the uncertainty will be higher, frequency differences tell you the angle of the ears relative to the sound integrated across a longer time window. Phase gives you an instantaneous observation of the angle).",
"Note that the owls are right up against the boundary of neural sensitivity. Neurons can only depolarize about twice/ms, and that's about how fast they need to go to detect that phase difference in sound arrival. By coding frequency instead, they can get decent localization at firing rates more reasonable for their biophysics."
] |
[
"Which leads to really cool things, like ",
"holophonic sounds",
"."
] |
[
"What makes a star grow from white to yellow, then red, then blue?"
] |
[
false
] |
Sorry if I got the order wrong. More specifically, why do stars grow bigger and start to fuse helium into heavier elements over time?
|
[
"Wow ok, I was wayyy off. I was under the impression that a star stages from dwarf up to hypergiant and follows a sequence of colors because of the fact that when our star will eventually run out of fuel, it will start to expand and become red. I thought that when a star ran out of hydrogen it started fusing the helium it's been making, but I guess that was a silly assumption. Thank you for your very detailed answer, you're very good at explaining this concept. "
] |
[
"Wow ok, I was wayyy off. ",
"I think, i didn't explain it very well, because you are more or less correct. You said: ",
"I was under the impression that a star stages from dwarf up to hypergiant ",
"Dwarf stars, which are basically the same like main sequence stars, do evolve to giant stars. But as i said, not all stars start as main sequence stars. The most massive ones can start as hypergiants. Some of these stars may change their color, but not all do it in the visible spectrum, when they are massive and therefore hot enough to make their transition completely at the blue end of the spectrum. ",
"For all dwarf stars you are correct however: They shift color when they leave the main sequence to the giant, bright giant, supergiant or hypergiant branch. ",
"...it will start to expand and become red. ",
"I thought that when a star ran out of hydrogen it started fusing the helium it's been making, but I guess that was a silly assumption. ",
"That's not silly at all, that's what is actually happening: ",
" ",
"When a star has enough mass, the helium fusion starts and expands the star indeed, as the helium fusion releases so much more energy than the hydrogen fusion. However, most of the stars simply don't have enough mass. ",
"Because of the greatly increased radiation flux, the hull of the star expands. It is also more luminous for exactly the same reason. However, with the increased surface size, the temperature on the surface is ",
" so it becomes more reddish. ",
"I think you can better visualize this when looking at a normal ",
"HRD",
" ",
"and one that shows ",
"stellar evolution",
". ",
"Unfortunately in none of them are blue hypergiants visible. Anyways, i think this gives an better idea how it works. "
] |
[
"Ok, the pictures do help a lot. Sorry for my lack of understanding. So I'm curious, what causes a star to begin to evolve? From your explanation, I know that a star begins to fuse Helium when it becomes massive enough, but what causes the star to become more massive? "
] |
[
"Linguists of Reddit: do any written languages (real or fictional) take into account pitch? Length? Volume?"
] |
[
false
] |
In other words, is it feasible to have a written language that conveys emotions as they are spoken? How ridiculously complex would this language be?
|
[
"Many Chinese languages, including Mandarin and Cantonese, are tonal."
] |
[
"Many Chinese languages, including Mandarin and Cantonese, are tonal."
] |
[
"I guess I was trying to explain how speech combines so many different things to create wholes that can be drastically different from one another, even if they're simple. For example, saying \"That's nice.\" It can sound sincere, insincere, enthusiastic, apathetic, depressed, sarcastic. As far as I can tell, unless it's contextual, written English can't convey that emotion. An exclamation point can help, but not entirely.",
"As for volume, stress accents deal with part of the word, yes, but not the entire word, and not precisely. Do any written languages account for volume as dB? Aside from TYPING ALL IN CAPS!!!!",
"Same with length. The best example for what I'm asking is sheet music. The notes have a clear and defined length. Any languages give syllables that specificity?"
] |
[
"How is it possible to detect where the impact between particles occurs inside of an accelerator?"
] |
[
false
] |
If my understanding is correct, the uncertainty principle limits our ability to know the exact position of a particle in space. If that is the case, how are we able to detect their position inside of accelerators accurately enough to get them to smash into each other as well as detect the position of the impact to record the results?
|
[
"I think you are overthinking a bit too much. Simply, we don't detect every particle position.",
"To answer your title question- when people use accelerators, we use magnets to guide the particles. Why? Because protons are charged particles and react to an EM field. To crash these atoms, places like the LHC have points where the lines of protons intersect. Most of the times, the protons will just pass by each other. Run your experiment long enough and you get a collision. Imagine this collision like two missiles colliding with other. The collision spits out a lot of elementary particles and the LHC has detectors to pick up these particles. They then have computers to take the data and map it out. ",
"I don't know how accurate these particle maps are but I'm sure their error is larger than what the Heisenberg uncertainty allows for (like you stated the Heisenberg principle only limits the knowledge about position and momentum, not completely obscures). "
] |
[
"Imagine this collision like two missiles colliding with other.",
"Actually, it's like shooting two needles across the atlantic ocean and hoping that they collide. But if you shoot 100 billion needles at once a collision becomes fairly likely."
] |
[
"Can you be more specific? Are you talking about physics experiment- crashing protons together for elementary particle studies- or new element synthesis-crashing heavy ions together?"
] |
[
"What is \"gimbal lock\" as it pertains to spacecraft, and why is it such a big deal?"
] |
[
false
] |
I've tried reading but probably need an easier to understand explanation. I recall watching the movie Apollo 13 and they were always afraid of gimbal lock, but I never understood why, and why it was such a bad thing. Is it still an issue in today's spacecraft? Thanks! I read up on and think I understand what's going on: the gyroscopes provide information about orientation much like how if you close your eyes in a car you can feel the car turning right or left, and if you know your orientation when you started, you can know which way the car is facing based on this. Thus if the gimbals "lock" together, you no longer have the ability to tell your orientation and thus your ability to navigate is ruined.
|
[
"Gyroscopes make use of nested gimbals and a flywheel, which allow a craft to measure its orientation in 3D space because the gyroscope remains in a fixed position because of its angular momentum. However, when using a 3 gimbal system (one rotating about the x, y, and z axes) there is a problem where the rings can line up and become stuck there, again because of the conservation of angular momentum. So if the gimbals \"lock\" like this you would lose the ability to measure your direction in one of the axes. To solve this problem, a motor keeps a fourth outer gimbal spinning constantly to counteract the tendency of the 3 ring system to lock. If power is lost (like in Apollo 13) this motor stops and gimbal lock can become a real problem for navigation. "
] |
[
"Gimbal lock is actually a much deeper phenomenon than you described",
"Modern gyroscopes don't actually use spinning flywheels or gimbals. Common ones (like the ones you might find in a cell phone or quad rotor) use microscopic vibrating bits to measure the coriolis force and really fancy ones (like in military missiles) measure the interference of two laser beams going opposite directions in a circular path. There are probably others, but those are the ones I'm familiar with.",
"Despite the upgrade in technology gimbal lock can still happen because Euler angles (pitch, yaw, roll) are not a mathematically complete description of the orientation of an object. Basically at certain points (which correspond visually to gimbals in the old kind of gyro lining up) the degrees of freedom of Euler angles can drop below 3. The problem can be solved completely by using a system with 4 degrees of freedom to represent rotations (this is the mathematical equivalent of adding a fourth gimbal to the gyro).",
"The most popular choice these days is quaternions since they have other properties that make them useful for computations. Namely its possible to compute rotations using a few less operations than rotation matrices (important for speedy graphics processing) and because its relatively easy to subdivide one big rotation into many smaller ones (important for nice smooth looking movements in computer graphics)."
] |
[
"thing of note to easily understand gimbal lock: imagine you are playing a first person shooter and you point your gun vertically at 90°: you are no longer able to point the gun left and right, moving the mouse sideways only rotates alongside the gun's axis. You have two axes locked in the same attitude providing the same rotation."
] |
[
"Why is there no layer that distributes instructions to CPU cores equally?"
] |
[
false
] |
Right now, the program's gotta make sure all cores are utilized evenly. Why is there no layer that does this as default?
|
[
"Because this would not be beneficial at all. On the contrary really. If your program is using threads then the operating system will distribute computations between the cores, but if your program is monolithic it would be very difficult to make this work. ",
"Some data would have to be constantly passed between the cores, which would slow things down much more then the benefits of this parallel instruction execution. Same goes for data and instruction caches that CPUs use. They would become useless and thus the program would slow down significantly."
] |
[
"This is already done to an extent. Modern processors are generally superscalar, meaning they can executive multiple instructions at once, and feature out of order execution. However, there's a limit to how much this can help. ",
"Most programs have code that depends on the results of other sections of code. It's not possible to have this code run in parallel just like it not possible to have somebody do your taxes before knowing how much you made.",
"Processors also contain memory that is only accessible to each core. In particular, registers are small amounts of memory that a core can access directly. Current processors cannot do much of anything without using their registers. Attempting to divide code at a very fine level runs into the problem that the code will need access to the registers. But if the code is running on separate cores then it won't have access to the same registers. You can get around this by writing data to RAM. But accessing RAM is slow and your code would run slower.",
"You also have to make sure that the cores aren't stepping on each other. Imagine if you have a block of memory that two cores are working on. How do you ensure that they aren't working on it at the same time and don't interfere with each other? How can you tell that this block of memory is special?",
"A lot of work is being done in this area, but it's hard."
] |
[
"A program's basically a linear list of instructions presented to the CPU. Later instructions often depend on the results of earlier instructions. If you ran the instructions on multiple cores, say an earlier part running on core #1 and a later part running on core #2, then core #2 would have to wait until core #1 has computed all its inputs, and sent it to core #2. The sending takes a while (compared to the speed at which a core executes instructions on data that's already \"hot\" in the core's registers or L1 cache).",
"And worse yet, if the sequence running on core #1 doesn't figure out all the outputs #2 needs until near the very end of its computation, then it'll be finished and start to idle before #2 even gets the data to begin. So you'll ",
" have only one CPU active.",
"So the answer to your question is there's no way to turn an inherently serial workload (where each thing that's computed has lots of dependencies on other things which were recently computed) into a parallel workload. And if you claim to your system (OS, CPU, whatever) that what you have is a serial workload, it's hard for the system to (1) \"figure out\" that it's actually a parallel workload in disguise, and (2) distribute the workload to the different cores in a way that doesn't waste most of your time on stalls and communication overhead.",
"It's much easier from a systems point of view to make hardware / OS / programming languages so that when the user has a parallel workload, they tell the system it's a parallel workload, these are the pieces and how they communicate with each other.",
"Which means it's up to the designer of each program to figure out how to do that. Which is harder than you might think.",
"There is some progress -- the fairly new Go programming language tries to make it easy to express parallel workloads by the way they communicate messages. Rust, another fairly new language, takes a different approach, trying to have the language itself carefully keep track of who's allowed to modify and access each piece of data, which is a common source of programming bugs."
] |
[
"Would more salt dissolve in hotter water heated under higher pressure? what's the limiting factor stopping more salt from being dissolved at greater and greater temperatures and pressures?"
] |
[
false
] | null |
[
"Based on the trend linked, one can reasonably expect NaCl solubility to increase at over 100°C. So while pressure should not directly effect solubility, raising it is the only way to get water past 100°C."
] |
[
"Based on the trend linked, one can reasonably expect NaCl solubility to increase at over 100°C. So while pressure should not directly effect solubility, raising it is the only way to get water past 100°C."
] |
[
"Water can become supercritical in deep sea hydrothermal vent systems and we actually use the brine separation from the super critical fluid enriched in dissolved gasses as a proxy for understanding the sub-seafloor temperature."
] |
[
"I have a cold. Why is there a \"threshold\" for sneezes?"
] |
[
false
] |
[deleted]
|
[
"It's this type of thinking which leads one to believe ",
"webbed feet are normal.",
"is an autosomal dominant hereditary trait which causes sneezing, possibly many times consecutively (due to naso-ocular reflex [3]) when suddenly exposed to bright light. The condition affects 18-35% of the human population."
] |
[
"Now you know how it feels to be a chick during sex. "
] |
[
"Look up into a bright light when you have this problem, it will never trouble you again."
] |
[
"How can a car's breaks work if the engine is still running without either the engine breaking or the break pads wearing down?"
] |
[
false
] |
Break pads use friction to stop the wheels from turning, but if the engine is still running, the spark plugs are firing, the gears are turning, which are trying to turn the wheels. So, it seems like if this is the case, something should break. What am I missing?
|
[
"Picture a turning shaft coming from the engine with a flat disk attached to the end. Now picture a second shaft coming from the rear axle, and also ending with a flat disk attached to the end.",
"The two flat disks are very close together, facing each other.",
"Press the two disks together, and the engine is connected to the rear wheels. Pull the two disks apart, and the engine isn't connected to the rear wheels.",
"That leaves out quite a few of the mechanical components of a car's clutch but it's effectively what is going on."
] |
[
"The use of the phrase \"internal clutching devices\" was intended as an oversimplified means of explaining....The torque converter performs the function of a slip clutch....but explaining the specifics of that mechanism would only cloud the explanation where simplifying it to \"clutching devices\" allows the easier comparison to a manual transmission. ",
"BUT by all means anyone who reads this....Ravioli is more correct than I was. "
] |
[
"It appears that you are missing the clutch.",
"The clutch acts as a dynamic disconnect point between the drive shaft and the axles. There are some other things involved, like the transmission and differential(s), but for the sake of simplicity let's just reduce the the system to the driving shaft and the driven shaft. ",
"The driving shaft connects directly to the engine and turns when the engine is running. The faster the engine is running, the faster the driving shaft is turning.",
"The driven shaft connects directly to the wheels and turns when the wheels are turning. The faster the vehicle is traveling, the faster the driven shaft is turning.",
"Now we hit the question you are asking - how do we turn the driving shaft and the driven shaft at different speeds? If the engine is idling and you are stopped at a red light, the driving shaft still needs to move, but the driven shaft needs to be stationary.",
"And here is where the clutch comes in. The clutch is a device that allows the driving shaft and the driven shaft to disconnect and reconnect. But if it was just an \"on/off\" situation, then there would be some problems!",
"If the engine is idling and you are stopped and the clutch instantly connects the driving shaft and driven shaft, you'll lurch forward suddenly (driven shaft suddenly starts rotating) and the engine will die (driving shaft suddenly stops rotating). Anyone who has learned to drive a manual has done this accidentally.",
"So the clutch has to be able to vary the amount of connection between the driving shaft and the driven shaft. The exact methodology of this varies car to car and goes into some details where I get hazy.",
"But the concept remains - the clutch serves as a dynamic disconnect point between the engine and the wheels."
] |
[
"Can muons be used to \"boost\" hot fusion reactors?"
] |
[
false
] | null |
[
"The temperature of the plasma in fusion reactors is on the same order of magnitude or greater than the binding energies of muons in muonic atoms, so many of them likely won't even occupy bound states."
] |
[
"Could you create muonic atoms first and then do magnetic compression while the muonic atoms are still fusing to boost the muonic fusion?"
] |
[
"Maybe, but an idea like this can't be fully fleshed-out in Reddit comments."
] |
[
"What criteria allows a polygon to tessellate on a sphere?"
] |
[
false
] |
I roughly know the criteria for tessellating a polygon on a plane. Follow-up: Can a polygon tessellate on a paraboloid or hyperboloid? If so, how?
|
[
"Do you mean to ask about regular polygons?",
"It seems to me that if you were able to tile a sphere with regular polygons (that is, shapes on the surface of the sphere whose edges are composed of segments of great circles), that you'd be able to fairly easily project inwards and obtain some sort of polygonal solid, which in turn makes me think you'd only be able to tile the sphere with triangles, squares, pentagons and hexagons. I would think higher degree polygonal tilings would imply the existence of regular polygonal solids which don't exist.",
"I might be wrong though.",
"EDIT: Not hexagons."
] |
[
"that sounds right - if you simply retain the vertices of the sphere tiling and replace all the great circle arcs by straight lines in euclidean space, you have a solid all of whose faces are identical polygons. i am not sure if there are any solids other than the five platonic solids that have all their faces identical and all their vertices on a sphere - i suspect the answer is no, but i do not know how to prove it."
] |
[
"There are not, indeed. There are many ways to prove it, but I don't know any ways I can quickly type out here on my phone. They're easy to look up, or I can respond later if you prefer. "
] |
[
"So multiple galaxies colliding create quasars, what do multiple collisions of quasars create?"
] |
[
false
] |
[deleted]
|
[
"(Astrophysicist here)",
"Quasars aren't formed by galaxies colliding. When galaxies collide it triggers intense star formation (look at ",
"Arp 220",
", for example) which is extended over a region many thousands of light years across.",
"Conversely, a quasar is a point source; this means that it is small, and we can't resolve it even with the best telescopes we have. Quasars (the name comes from 'quasi-stellar object', due to being point-like sources) come from the huge energy you get pouring out when material (gas, dust, stars) falls onto the supermassive black hole at the centre of a galaxy. ",
"So, you can't really get colliding quasars. Even if two galaxies hosting quasars collided, the chance of getting the two supermassive black holes to crash into each other is essentially zero."
] |
[
"Couldn't you get two quasars to be formed in the same galaxy? and then have them (over time) attract each-other and collide?",
"I thought there were models for colliding black holes, but maybe I'm mistaken."
] |
[
"Quasars are basically the vomit of giant blacks holes, and nobody knows for sure what happens when two black holes collide. You'll probably get one hell of a show though."
] |
[
"Does gravity have a speed?"
] |
[
false
] |
[deleted]
|
[
"Yes gravity propagates at the same speed as light.",
"This leads to ",
"http://en.wikipedia.org/wiki/Gravitational_wave",
" (s)"
] |
[
"Not an expert. But I think it travels at the speed of light. Can we even test that?"
] |
[
"According to general relativity, gravitational deformations in space-time propagate at the speed of light (they must in order to preserve causality). Therefore, to the best of our knowledge, it would take at least 8 minutes until after the sun dissapeared for us to notice, electromagnetically ",
" gravitationally."
] |
[
"What would happen if it was possible to split a proton using a quark?"
] |
[
false
] |
I’d like to preface by saying I’m extremely new to splitting atoms and the technology behind it. I’ve been doing some research into nuclear energy and I think I understand the very basic concept of a neutron is fired at an atom which causes a chain reaction of the atom continuously splitting which creates energy. I know that inside protons are quarks, not too familiar with those but I’m learning. My question is if we could capture quarks and fire them at a proton would that create the same amount of energy, or any energy at all?
|
[
"Quarks are subject to confinement, so there's no way to produce a beam of individual quarks, only bound hadrons.",
"But anyway, we already ",
" \"split apart\" protons. For example, the LHC, which collides two proton beams."
] |
[
"The force that holds quarks together works the opposite of most forces, like gravity or electromagnetism gets weaker the farther apart things are. The strong nuclear force that holds quarks together gets stronger the more you move the parts apart, so you need more and more energy to get them apart. ",
"Worse because dumping a large amount of energy into them and them being made of so little the end result is instead of breaking them apart you just end up generating a bunch more quarks that are also bound to the one you are pulling on. So you will never finish pulling it off, you will simply always found it stuck to other quarks no matter how hard you pull. "
] |
[
"Sort of, with the added detail that as you pull the two quarks apart you add energy to the bond between them, and because the force pulling them together has a minimum value (around the weight of ten tons, as I recall!) the potential energy in the bond quickly exceeds the mass-energy needed to create two more quarks. So the rubber band quickly snaps apart into two new rubber bands holding two pairs of quarks together. ",
"Wikipedia has some illustrations sketching out the process.",
"This is all unlike the electromagnetic bond between an electron and a proton, for instance: in that case, the force between them rapidly approaches 0 as they grow further apart, and the potential energy in the bond never gets anywhere near the mass-energy of creating new charged particles."
] |
[
"How fast would you have to drive west to keep the sun at the same spot on the horizon?"
] |
[
false
] | null |
[
"Take the cosine of your latitude, multiply by the mean circumference of the Earth, which is 24,874 miles, and divide by 24 hours."
] |
[
"It depends on your latitude. At the equator you would need to circle the Earth in 24h so about 1,500km/h. At the North pole you would pretty much just need to keep facing the Sun so pretty much zero.",
"edit: multiplied by 3"
] |
[
"Boom",
"."
] |
[
"At what point can we definitively say that a moving object has left our solar system?"
] |
[
false
] |
What is the boundary of our solar system and how do we determine it? Is there a gray area and if there is, how large is it? Or have we assigned a distinct boundary to our solar system and if you go one meter beyond it, then you've left the solar system?
|
[
"The recent articles about the Voyager stated clearly that it is defined based on not being able to detect either the solar wind or the magnetic field of our solar system, and that the amount of gray area is basically unknown, and will only be known after Voyager goes much further and no longer detects any solar wind and none of the magnetic field from our solar system that we will then know the boundary is behind Voyager. They said that the ship was kind of in a gray area already, so it seems not to be an all or nothing deal. ",
"http://www.space.com/16167-voyager1-spacecraft-interstellar-space.html",
" "
] |
[
"the amount of gray area ... will only be known after Voyager ... no longer detects any solar wind and none of the magnetic field from our solar system ...",
"Wouldn't this distance be affected by how powerful the spacecraft's on board detectors are?"
] |
[
"The decay of the strength of a radiation source decreases as a square of the distance from the source. From this, and from the rate of decay it is possible to observe the data converging towards a final value representing essentially the background radiation from interstellar space. Usually criteria can be set which will detect the convergence of the strength of the signal and assume a value of zero once it reaches 99.9% of the steady state interstellar value. While technically it will continue to decay indefinitely, there's a point at which it is just accepted as \"close enough\""
] |
[
"How do genes \"encodes\" the geometry of the body of a specie ?"
] |
[
false
] |
All species have different shapes, proportions of their limbs and bodies. Also, we know how to read genes and how ATGC codes enable other proteins to produce some kinds of other cells or molecular structures. I can understand it can change over time because of evolution, but how will the fetus begin to build some embryonic shapes like the spinal cord, the organs, the bones ? What dictates or rules cells or proteins to say "spawn a stomach here" or "spawn 3 fingers with 3 phalanx" or "make sure this body have those proportions" or "make sure this bat's arms have wings" ? Pardon my logic, because I'm more fond of maths and programming, but if geneticists mapped a genome, can't they make an elephant with 6 legs, make human have horns or wings ? Again sorry for the ignorance, but I know X-men is plain fictional and non-sense to me, but what do we know about the geometry of life being and the relation with their genes ?
|
[
"How DNA encodes the geometry of an organism is the central problem of ",
"Developmental Biology",
".",
"One key part that isn't completely understood yet is the transcriptional regulatory system. Certain DNA sequences, which do not encode amino acid sequences, act as on/off switches for producing these amino acid sequences. These types of DNA sequences are known to be important in encoding geometry. They turn on or off based on whether proteins in the cell bind to them or not.",
"The most famous example is probably a gene called ",
" found in the fruit fly. It encodes a protein that binds to different parts of the DNA leading to production of a set of proteins that can produce an eye. ",
"This has been artificially induced to produce flies with eyes on their legs."
] |
[
"I'll try and give you a short, but broad outline of how development works. When you get down to it, the cells of your body grow the way they do because they are told to by specific signals. ",
"Signals are transmitted through the interaction of proteins with DNA, RNA, or other proteins. The most important kind of protein for development is transcription factors, which are able to turn on or off ",
" genes. ",
"I was going to go through from the formation of the zygote, but it was getting too long and complicated. You can sort of think of development as dominoes. Knocking the first one over, knocks another over, which might then knock two over. Now you've got two lines of dominoes that continue on, etc. Each time a line splits, that represents cells 'differentiating' or specializing, for example a ",
"hematopoietic stem cell",
" turning into a erythrocyte (red blood cell) or a macrophage (white blood cell).",
"As the body develops, cells release and absorb certain signals that tell them where they are. For example, in the early embryo cells at one pole will excrete signal A and cells at the other will excrete signal B. Thus, cells that sense only signal A know that they are at one pole; cells that sense only signal B know that they are at the other; and cells that sense a little of both know that they are in the middle. Sensing these signals tells these cells to turn on/off different genes so that they can be the kind of cell that is needed in the place they are.",
"A cool example of this is how your hand develops. Your hand starts out more or less as a blob of cells. Then at the spot of the blob that will one day be your thumb, a signal reaches the cells to start making a hand. The small cluster of cells on that other part of your hand then start to produce a hormone. The hormone then diffuses out along your hand. The cells nearest to the signal get a high dose, which tells them to turn into your index finger. As you move further away from the hormone producing cells, the hormone dose gets lower. Cells that get a slightly lower dose have been signaled to be your middle finger, cells that get a low dose have been signaled to be your ring finger, and cells that get a very low dose have been signaled to be your pinkie finger.",
"If you want to understand all of development, and how all the body plan stuff works hox genes and homeoboxes (as ilovedruglol points out) are a great place to read up, but this is the basic 'logic' of how bodies develop.",
"To specifically answer your X-men question. These things may all be possible, but some are easier than others. A 6 legged elephant should be pretty easy. By copying a hox gene, you can essentially tell the middle of the elephant that it should pretend to be legs, and it will grow legs. Adding a structure that exists in one animal to another is more difficult. It tends to be that lots of these transcription factors are conserved between species, but do different things. So if I gave you a hormone that tells the backs of flies to make wings, it might just cause you to grow hair, or bone, or god knows what. It's possible, but it would probably involve giving you an impractically large number of genes to make it happen."
] |
[
"but if geneticists mapped a genome, can't they make an elephant with 6 legs, make human have horns or wings ?",
"Depending on how exactly you define \"mapping a genome\", geneticists really haven't mapped genomes, they've sequenced them. We can tell you the sequence of all 3 billion bases (A's, T's, G's and C's) in the human genome, but we don't really know what most of those do. You could consider mapping to be finding all the genes, but even then, you have to figure out what all the genes (about 25,000 in humans) do, and how they work together to make something, like a leg."
] |
[
"Why do infinity mirror tunnels appear to curve off in the distance as opposed to keeping in a straight line?"
] |
[
false
] |
[deleted]
|
[
"It's very hard to align mirrors to be perfectly parallel and any deviation, no matter how minor, will be multiplied over and over. The net result is that almost any hall of mirrors will always appear to bend off in one direction or another.",
"(Edited for autocorrect mess)"
] |
[
"Because the mirror aren't perfectly parallel so the light doesn't bounce straight back and forth. It is possible to get straight or nearly straight tunnels but no one puts in the time or effort to make a perfect one."
] |
[
"Though, because the bending tells you exactly what direction the mirrors are off, it's pretty easy to align them until the bending is almost totally gone... ",
" they can be adjusted at all, most mirrors just aren't built to be adjustable. "
] |
[
"is it possible to boil a pot of water simply by the act of stirring?"
] |
[
false
] |
my understanding is that heat is the random movement of atoms and that the faster the movement the hotter they are. so my question is, it possible to boil a pot of water simply by the act of stirring? and if so how much stirring would it take to boil a liter of water?
|
[
"Yes. You have to add the heat faster than it can dissipate (by evaporation or radiation), so you'll need to stir it very quickly. A stirring machine can accomplish this for you. Science joking aside, top-tier blenders can boil water."
] |
[
"I wanted to call BS on the blender thing, but it appears you are right. I would have thought the speeds would need to be a lot higher."
] |
[
"If the motor is generating that much heat, it would be a really shitty motor."
] |
[
"How can a storm which packs 60+ mph winds only be moving at 25 mph?"
] |
[
false
] | null |
[
"Like swinging a rope in a circle overhead at 20 km/h while walking at 5 km/h."
] |
[
"The wind is going 60 mph in a circular tornado. The eye of the tornado is moving 25 mph, but the winds creating the tornado itself are 60 mph."
] |
[
"Great analogy!"
] |
[
"How do bugs hibernate for so long if they have a short lifespan?"
] |
[
false
] |
I always wondered how bugs come back every year and I kind of assumed they migrated. Apparently some do but also some hibernate, like mosquitoes. But I only see them during the summer. How do bugs with short lifespans not go extinct every winter?
|
[
"I'll address mosquitoes specifically, they do one of three things:",
"Mosquito females lay eggs in late fall. They lay them in moist ground, which promptly freezes at the start of winter. This freezing renders the egg dormant, and little to no biological activity happens at this stage. In the spring, when conditions are more favorable, the eggs become active again and proceed to develop into larvae.",
"They hibernate...ok not quite but they do live through winter in a very inactive state. Only female mosquitoes are alive in the winter (males die after mating). Metabolism drops and they hide in things like dead logs or in that hole in the tree your local squirrel hangs out in during the winter. When it warms back up, they first look for blood (convenient if they're living with an animal) and then lay their eggs in the freshly thawed pounds, pools and puddles abundant in the spring. ",
"For some species of mosquito they enter diapause, which suspends development and essentially halts metabolism. When the weather warms up, metabolism starts again and eventually so does development."
] |
[
"Some insects do migrate, but most species living in temperate climates overwinter. How they overwinter depends on the species; some as eggs, some as immature stages (nymphs, larvae, or pupae), and some as adults. Insects can live for longer than many people realize. Species with only 1 generation per year live for about a year (or a few individuals at least do). Species with multiple generations per year may have short-lived cohorts during the summer, but the generation that overwinters will be relatively long-lived and may have specific behavioural and physiological adaptations for overwintering. Some species even have multi-year life spans, such as periodic cicadas (13 or 17 years, mostly as nymphs hidden underground), and various butterflies, dragonflies, beetles, etc. that spend several years feeding as immatures before turning into adults, reproducing, and dying soon after."
] |
[
"Ok, I work in aging research so I'll give this a shot. There are animals that can enter a seemingly non-aging diapause stage. By non-aging I mean that no matter how long they are in this stage, their post-diapause lifespan remains the same. How they do this is completely unknown, but really, this reflects the fact that we actuallly do not really understand what causes organisms to age in the first place. So not only don't we know how aging is delayed, but we don't know where to start looking. "
] |
[
"Not sure where to categorize this: Is information infinite?"
] |
[
false
] |
Bear with me here, this is not a philosophical question. And I'm not high or otherwise mentally altered. People think of information and the potential body for all information as something that is infinite. But if information is stored in digital bits, written texts and synapses between neurons, then it is finite as it exists in matter in energy. . Does this mean that there is a potential limit for the universe's capacity for information? Could we exceed 10 bits of information? If so, in what medium could it exist? Have we already exceeded that amount, rendering my question moot (if so, fair enough, just ELI5 because I'm obviously dumb). Or is information finite, and if so, what is the universe's potential capacity for information?
|
[
"The computational capacity of the universe is finite, and you can relate it to the number of particles in the universe and their individual degrees of freedom. ",
"Here is a paper which estimates there to be around 10",
" bits available in the universe",
"."
] |
[
"Information in the observable universe is finite. ",
"Seth Loyd: Computational capacity of the universe, Physical Review Letters 88 (23):237901.",
"\n",
"http://arxiv.org/abs/quant-ph/0110141",
" "
] |
[
"You can get the paper from arxiv. Another poster was kind enough to post the link.",
"http://www.reddit.com/r/askscience/comments/16e4xl/not_sure_where_to_categorize_this_is_information/c7v6kyy"
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"The laws of physics don't change as things get small. The same laws of physics apply on all scales. You just typically only notice quantum effects in \"small\" systems."
] |
[
"Is there any way for a planet to have a gas moon?"
] |
[
"Natural climate change happens over extremely long periods of time giving Earth and it's various life forms time to adapt. The climate change caused by humans in the last 100yrs would take thousands of years to occur naturally. Plus we should be in a cooling phase if humans hadn't caused warming.",
"Source: ",
"http://www.cnn.com/2015/11/06/world/two-degrees-question-ice-ages/index.html"
] |
[
"How does information transmission via circuit and/or airwaves work?"
] |
[
false
] |
When it comes to our computers, radios, etc. there is information of particular formats that is transferred by a particular means between two or more points. I'm having a tough time picturing waves of some sort or impulses or 1s and 0s being shot across wires at lightning speed. I always think of it as a very complicated light switch. Things going on and off and somehow enough on and offs create an operating system. Or enough ups and downs recorded correctly are your voice which can be translated to some sort of data. I'd like to get this all cleared up. It seems to be a mix of electrical engineering and physics or something like that. I imagine transmitting information via circuit or airwave is very different for each, but it does seem to be a variation of somewhat the same thing. Thanks! Edit: A lot of reading/research to do. You guys are posting some amazing relies that are definitely answering the question well so bravo to the brains of reddit
|
[
"It's a ",
"huge tower of abstractions",
". I'm just going to talk about wires to simplify, and I'm going to leave off a bunch of essential but distracting bits. Let's imagine you've got a couple of computers and your network cable is that lightswitch and light bulb.",
"First off, agree on what ",
" and ",
" are. (e.g.: Don't confuse the issue by using dimmer switches. Don't use a blacklight. That sort of thing.) And agree on a ",
"signalling scheme",
" and bit-rate. One ",
"common scheme for slower connections",
" is: let's say I want to send a byte (8 bits). I start a metronome. I turn on the light for one ",
" (just to let the receiver know somethig is incoming). For the next eight ticks I turn the light on or off depending on whether I'm sending a 1 or 0. And at the end of the byte I make sure to leave it off for a couple ticks so that the receiver has time to write stuff down. The receiver, when they see the light go on the first time, starts their metronome and each time it ticks they record a 1 or 0 depending on whether the light is on or not. After eight ticks they have a byte.",
"So you can see I've built a tiny slice of that tower. I started with \"I can flip a switch back and forth\" and now I have \"I can send bytes\". Next up I'll want to build something more sophisticated, but I can forget about light switches and just think in terms of bytes. For example, maybe I come up with the idea of a network packet / datagram, and I define something like \"I send a special value to start, then the sender and receiver addresses, then a count of the number of bytes in the contents, then the contents, then an end-marker or error-checking-code or something\". Now I'm one step closer: I can send ",
" around, I can build networks (computers can look at those sender and receiver addresses and forward packets along if they know where they go next), I can use the wire for multiple things by sending to different addresses.",
"Next I might define a way to do a request-response exchange — we exchange some packets to establish that we're talking, I send as many packets as I need to tell you what I want from you, you respond with as many packets as you need to reply. Now I can request webpages from you. And so on."
] |
[
"A cool thing about that idea of asynchronous serial signalling using start and stop bits is that it is much older than you'd expect - it was in commercial use by 1919, for teleprinters sending typed text over telegraph lines. Exactly as described above, except using only five bits for each character instead of eight. (Not counting start and stop)"
] |
[
"Encoding binary information in circuits is simple - you vary the voltage between two levels. Low voltage represents the digit 'zero', slightly higher voltage (5 volts, for example) represents the digit 'one'.",
"With digital signals over radio, things can get much more complicated since there are concerns about efficiency, interference, etc. But it's not hard to imagine simple schemes that work just like regular AM or FM audio transmission (over radio). Pick a frequency to represent 'zero' and a different frequency to represent 'one', and transmit a carrier wave that varies between the two."
] |
[
"Was the development team of the first atomic bomb surprised by the size of the explosion or had they calculated how much energy would be released before the first explosion?"
] |
[
false
] | null |
[
"The size of the explosion of a nuclear fission bomb is directly a result of the efficiency of the fission reaction. Will you fission 5% of the total fissile material, or 10%, or 20%, or what? In the case of the Trinity \"Gadget,\" this efficiency was related largely to the amount and symmetry of the compression of the implosion lenses, and prior to the Trinity shot they had no real way to know how well they would likely behave. They had done various non-nuclear tests, but these were highly variable and inconclusive. So there was a very large set of unknowns. ",
"(The complete fissioning of 1 kg of fissile material releases on average about 18,000 tons of TNT worth of energy. The fissile material in the Trinity gadget was 6.2 kg. So you can get a quick estimate of the efficiency by dividing whatever yield you are asking about by the maximum possible fission yield, 18 x 6.2 = 112 kt. So a yield of 10 kt would be 10/(18 x 6.2) = 8.9% efficient. There are some other factors involved — a ",
"not insubstantial",
" part of the yield apparently came from fissioning in the natural uranium tamper — but this is a good rough way to do it.)",
"On the eve of the test, the committee which was in charge of the final test estimates thought it was most probable that the weapon would release between 4,000 and 5,000 tons of TNT equivalent (4-5 kt). In other words, they estimated that the efficiency would be about 4% or so. There were other estimates made as well, including a set of bets by physicists who had designed the bomb. Of the scientists whose bets we know:",
"J. Robert Oppenheimer, head of the project, bet it would be only 300 tons of TNT (.3 kt) — a very low-confidence bet!",
"Nuclear physicist Edward Teller, ever the explosive optimist, thought it would be 45 kt — a whopping 40% efficiency.",
"George Kistiakowsky, the chemist in charge of the explosive lens system, thought it would be 1.4 kt — low confidence, again.",
"Nuclear physicist Hans Bethe, who was in charge of many of the efficiency calculations, thought 8 kt was a solid bet. Which is reasonably optimistic.",
"And future Nobel Prize winning physicist Norman Ramsey, who was later in charge of assembling the bombs on Tinian, put his money on 0 kt, a fizzle. As low-confidence as it gets. (Unlike the others above, Ramsey had close experience with the firing system, and was potentially betting on it failing in some way.)",
"The physicist I.I. Rabi arrived to the pool late and the only value left, supposedly, was 18 kt, which he bet. Which turned out to be the winning choice — but (so the story goes) it wasn't because Rabi was optimistic or pessimistic, it was because no one else wanted this number.",
"The actual Trinity detonation was determined to be about 20,000 tons of TNT (20 kt), and so was about 18% efficient, which is to say, 5X more efficient than the most probable calculation on the eve of the test, and better than most of the people who were close to the weapon's production estimated. ",
"So there was certainly some room for surprise in there. Even had they known exactly what it would have been, those in attendance were awed by its power — it was one thing to know it would be a big explosion, it was another to actually see it, to feel that new sun coming up in the middle of the night, to experience the searing brightness. All who were there were deeply impressed by the test, and it performed, as we can see, quite excellently compared to what they had expected. I am particularly fond of the eye-witness account by General Thomas P. Farrell, which ended with the following paragraph: ",
"For more on Trinity, I thought ",
"this article I wrote a few years back",
" came off particularly well."
] |
[
"EDIT: My post is currently at the top, but you should skip straight to ",
"/u/restricteddata",
"'s much better one: ",
"https://www.reddit.com/r/askscience/comments/9zrl1q/was_the_development_team_of_the_first_atomic_bomb/eabstj1/?utm_content=permalink&utm_medium=front&utm_source=reddit&utm_name=askscience",
"I can't speak to their surprise, but the predicted yield was 5-10 kt and the actual yield was about 20 kt.",
"Source: ",
"http://www.lahdra.org/pubs/reports/In%20Pieces/Chapter%2010-%20Trinity%20Test.pdf",
"Search for \"predict\" in that document.",
"Wikipedia mentions that in Rhodes' Making of the Atomic Bomb (which everyone who's interested should read!), that there was a betting pool and Edward Teller said 45 kt."
] |
[
"The effects could well be called unprecedented, magnificent, beautiful, stupendous and terrifying. No man-made phenomenon of such tremendous power had ever occurred before. The lighting effects beggared description. The whole country was lighted by a searing light with the intensity many times that of the midday sun. It was golden, purple, violet, gray and blue. It lighted every peak, crevasse and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined. It was that beauty the great poets dream about but describe most poorly and inadequately. Thirty seconds after the explosion came first, the air blast pressing hard against the people and things, to be followed almost immediately by the strong, sustained, awesome roar which warned of doomsday and made us feel that we puny things were blasphemous to dare tamper with the forces heretofore reserved to The Almighty. Words are inadequate tools for the job of acquainting those not present with the physical, mental and psychological effects. It had to be witnessed to be realized.",
"Wow... I can't believe I've never heard this before. I've been totally enamored by nuclear bombs since I was really young. I've also been obsessed with space travel. All these years, I thought I wanted to go to space the most. Now, I think I want to see a nuclear explosion even more."
] |
[
"Why do I get headaches if I concentrate too hard? How can I prevent this?"
] |
[
false
] | null |
[
"Sorry, this is definitely heading tdown the ,no medical advice' rule on reddit. A medical professional is the only appropriate person to ask this kind of question."
] |
[
"Hmm. I guess I was focusing more on the first question than on the second, but I see where that would be in violation of Reddit's ToS. Honest mistake; my apologies. I will rethink these kinds of questions in the future before I post them."
] |
[
"There's certainly a question in there you could repost. Something along the lines of 'Can concentration cause headaches? If so, how?'"
] |
[
"How do Na+ and Cl- ions conduct electricity in salty water?"
] |
[
false
] |
So when two electrodes are placed in a salty solution, on becomes a cathode (+) and the other an anode (-). The Na+ ions are attracted to the anode and Cl- to the cathode. How does this form a closed circuit? I don't understand. I also found that when the ions are at the electrode, they lose/gain an electron, but I still don't see how that forms an electric current
|
[
"You almost said it yourself. Electricity is defined as the constant flow of electrons or electrically charged particles through a substance. Since sodium chloride is soluble in water, you get those two ions with differing charges, in the same ratio. Sodium ions flow to the anode and chloride to the cathode, like you said. You can imagine these ions forming a bridge of sorts, from one electrode to the other. When electricity hits this solution, it is effectively adding electrons to the solution. These new electrons want to get to a positively charged area, so they move across the bridge of ions in order to give their electrons to the ion that prefers to be negative (in this case, chloride), therefore reducing the chloride. ",
"I couldn't find any sources that provided help which was strange, but in my gen chemistry class we studied electrochemistry and made batteries, much like ",
"this one",
". \nNote: someone with better knowledge of electrochemistry would be much more of a help as I didn't have much time to write this and probably did not include a step or two. "
] |
[
"so they move across the bridge of ions",
"How is this done? I'm pretty sure this was the question OP asked.",
"give their electrons to the ion that prefers to be negative (in this case, chloride), therefore reducing the chloride. ",
"Chloride is already negatively charged. How can you reduce chloride (-1) if it was already reduced from chlorine (0)?"
] |
[
"This post",
" has a good, detailed way of describing the process (including pictures, yay!), as it isn't as simple as how I stated it. There are a few intermediate steps happening along the way, like production of H2 gas at the anode, leaving behind an OH- (the \"electron\" I referred to). This OH- wants to travel to the cathode, since opposites attract. When NaCl was deposited in the solution, the Cl- actually forms a gas, C2, and since it is a diatomic, 2 e- are produced. These two electrons with the OH- all move towards the cathode, which is how the current flows through.",
"So you can think of it like this:",
"At the anode, this is happening (remember! The 2 electrons in the reactants side come from an electrical source, whether it be via lightning, live wires, etc):",
"2 H2O(l) + 2e- -> H2 (g) + 2 OH-(aq)",
"H2 has no charge and we now have a negative charge near the anode, which is already negative - OH- wants to move itself far away from the anode. This step is the reduction step.",
"At the cathode, the process is:",
"2 Cl-(aq) -> Cl2(g) + 2e-",
"Once again we're creating more of a negative charge in the solution. This step is the Oxidation step.",
"Thus we have a negative charged 2OH- and 2e- moving towards the cathode, which is positively charged, creating that \"bridge\".",
"I hope that made some sense. Like I said before, Electrochem isn't my strong points and if anyone sees an error let me know to correct it."
] |
[
"are there any animals that cannot swim?"
] |
[
false
] | null |
[
"\" I called the mammal curator of the Rio Grande Zoo in Albuquerque, New Mexico, Tom Silva (you remember him from my \"Can elephants jump\" column). According to Tom, most large primates such as gorillas and orangutans cannot swim, partly because their centers of gravity are in their necks and sternums. \"They sink like stones,\" says Tom. He says he has seen chimpanzees swim, though.\"",
"http://www.straightdope.com/columns/read/1838/is-the-camel-the-only-animal-that-cant-swim"
] |
[
"Plenty of people are unable to swim."
] |
[
"butterfly comes to mind",
"heavy/dense birds maybe, ostrich?"
] |
[
"AskScience AMA Series: I am a forensic anthropologist at the University of Florida who will be excavating for human remains in Tulsa, Oklahoma during the 100th anniversary of the Tulsa Race Massacre. AMA!"
] |
[
false
] |
Hi Reddit, my name is Phoebe Stubblefield! I am a forensic anthropologist, a research assistant scientist and interim director of the C. A. Pound Human Identification Lab at the University of Florida. During the centennial of the Tulsa Race Massacre, I will continue to excavate with the Physical Investigation Team at the Oaklawn Cemetery in Tulsa, Oklahoma to identify victims from the violence in 1921. I'm here to answer your questions about the intersection of cultural anthropology with forensic sciences and our work in uncovering some of the history behind the Tulsa Race Massacre, a devastating attack on what was once known as Tulsa's thriving Black Community. My research interests at the University of Florida are: More about me: In 2002, I received my Ph.D. in Anthropology from the University of Florida where I was the last graduate student of Dr. William R. Maples, founder of the C.A. Pound Human ID Lab. As an associate professor at the University of North Dakota for 12 years, I directed the Forensic Science Program, created a trace evidence teaching laboratory and helped undergraduate students learn more about careers in forensic science. I have also served as forensic consultant for the North Dakota State Historical Society, the North Dakota Bureau of Criminal Investigation, the Minnesota Bureau of Criminal Apprehension and with different medical examiner districts throughout Florida. I will be on at 2p.m. ET (18 UT) to answer your questions, AMA! Username:
|
[
"I have a more personal question - how does this work impact you emotionally? I mean from the the actual human moment you have when interacting with a deceased person? Do you have support when you need it? Does your profession have things in place to prepare you for that? Are you expected to just toughen up? Do you get mad at people who did things in the history you’re discovering?"
] |
[
"Thanks for joining us here in AskScience! How do you go about identifying particular victims in a setting like this? Is it context + the general info you can get from the skeleton like gender, height, and age range? Or is there more detailed info you can get from individual skeletons that narrow down the identity of the remains to a specific person who we know was murdered in this event?"
] |
[
"Thanks for asking a question! My contract is to do all I can to achieve identity, indicate context (associated with the race massacre/not associated/not determinable), and document the cause of death, traumatic or otherwise. I'm being cautious about the prospects of publication. Academia has a long history of using Black bodies for science, without the least representation of the deceased as a stakeholder, let alone their relatives. I am a student of that tradition, but I hope to let the next of kin have a voice. I do suspect cultural context will figure highly, I suspect in the patterning of trauma, but it's a hypothesis waiting for testing."
] |
[
"Why can we not reach absolute zero?"
] |
[
false
] |
I understand we can get to within billionths of a degree of it, but what stops us being able to actually achieve absolute zero?
|
[
"No, they did not achieve at temperature of T=0! They realized negative temperatures, which is an effect unique to quantum systems, but it is not the absolute zero. ",
"Also, there are some theorists that actually dispute the fact that there can be negative temperatures and attribute this to mathematical inaccuracies when defining temperature. "
] |
[
"No. At absolute zero a quantum system is in its ground state. The ground state of a free particle is simply uniform everywhere. That's pretty unrealistic since there are always potential wells which would create bound states, but there's no logical problem."
] |
[
"We cannot achieve absolute zero because there is no place in the universe that is absolute zero, therefore heat will be transferred into any object that has such a low temperature. For example, imagine you have a steal box and within it you have some sort of gadget that is trying to bring the temperature down to absolute zero. The box would have to be placed somewhere (e.g. on a table), and the tables heat would transfer to the box, thus not allowing it to reach absolute zero. "
] |
[
"Why are chemical and nutrition tests always performed on rats?"
] |
[
false
] |
When we want to know how something applies to us humans, wouldn't it make more sense to test other primates, like chimpanzees? Is is just the cost difference between a rat and a monkey that has determined this?
|
[
"The brain chemistry between rats and humans is very similar in the way it reacts and deals with new substances making it suitable to run preliminary tests. Another benefit is the growth cycle of a rat to maturity is a lot faster than that of a chimp or monkey allowing studies to be performed on the effects of chemicals on the brain during adolescence. In addition I assume that there is a lot less opposition form animal protection groups about caging and testing rats that on primates."
] |
[
"Rats are mammals, so a lot of their physiology is similar to humans. It is not exact by any means (or even all that close). But rats are cheap to house in large numbers, easy to breed, and simple to take care of. Legally, there are many exceptions for rats and mice that do not apply to animal testing on dogs, cats, pigs, horses, and non-human primates (which are all models used after testing on rats). Since rats are so abundant, it's not a huge deal if a bunch are killed from whatever testing is done on them. ",
"That being said, ALL animal testing is first approved by an IRB (institutional review board) and IACUC (institutional animal care and use committee) to ensure the most ethical practices. Additionally, animals that are used in experiments are kept in a vivarium with in-house veterinarians that monitor animal health and ensure compliance. ",
"I work with rats everyday, some of my colleagues use other animals, but rats are the best for basic science research. Once an idea is vetted and properly investigated for long-term potential in humans, further animal testing in more physiologically similar animals will proceed. This is why medical science takes so long to progress (among other things)."
] |
[
"Yay, a topic that is totally up my alley! I'm actually currently studying veterinary medicine with a goal of working on an IACUC and have worked with mice/rats/others for about 10 years in various capacities.",
"First, I want to say that ",
"/u/baloo_the_bear",
" is right on the money, but I'd like to add my two cents on top of his answer.",
"When is comes to choosing animals to do research, especially basic, new research, one of your main goals is conservation of money. Rats, and to a bigger extent, mice, are great for that. As ",
"/u/baloo_the_bear",
" said, they are very cheap and take up very little real estate in an animal facility. Most facilities allow 5 mice per cage. A cage rack can hold around 108 cages, which means around 540 mice in a 3ft x 7ft x 7ft space (147 cubic feet). Less space needed = less money to invest.",
"Why do we need so many animals? Lots of times the animals that are being studied are ",
"transgenic",
" or otherwise genetically modified, and there are times when multiple experimental genes need to be bred selectively into one mouse. For this to happen, you sometimes have to breed lots of mice in order to get the combination of genes that you need. This can take lots of time and lots of animals, which can amount to lots of money. Using a cheap animal model (if possible) is a great way to get a lot of bang for your buck. This is necessary at a time when federal research funding has been ",
"harder to come by",
".",
"Once that research is done, you can definitely work with animals that are of closer relation to humans. But before you would want to invest that kind of time and money, you want to make sure that you have solid, scientifically-supported reasoning to back you up.",
"You also have to address the ethical concerns when using primates in research. One of the big questions is \"if these animals are so closely related to humans that experimenting on them would be ideal, ",
" we use those animals?\" It really depends on how closely related you think they are socially, emotionally, and with regards to intelligence.",
"Recently, this has become a hot-button issue, and the NIH has issued guidelines and rules as to ",
"when you can chimpanzees in research",
" and when you use them, under what conditions they must be kept. Even this move toward conservation of an endangered species is controversial because it means that certain diseases that we can ",
" learn more about through chimp research (like AIDS, Hep C, Ebola, etc) will be stifled. Very important research might have to wait.",
"Even if using chimps for medical research weren't being restricted, keeping those animals under ideal conditions poses problems. First, keeping a controlled environment is difficult (as you can't keep them in little aerated cages or ",
"isolators",
" like you can mice). Then you have to account for keeping their envirnoment as healthy for them as possible which means:",
"problem solving behavior",
"And as you can imagine, every one of those things cost lots of money. So if you're going to use chimps you have to have a great idea, have great science to support it, and have lots of money to spend (which means making it very appealing to human medical research).",
"Sometimes other animal models are better than chips or mice or rats, too. It all depends on what you're studying and how that question relates to the animal's biology. For example, you wouldn't want to do gallbladder research on a rat. Why? Because the rat ",
"doesn't have a gallbladder",
". Now take that idea and imagine how many other differences there are between animals and between animals and humans, and you have an idea of what being the veterinarian on an IACUC is like. That being said, there are a ",
" of similarities between species."
] |
[
"If the collision of antimatter and matter results in lots of energy. Would creating matter out of energy also create antimatter?"
] |
[
false
] |
I know I'm severely simplifying a complex situation, but that's the best way I could think of phrasing it.
|
[
"Yes. ",
"Pair Production",
" creates both a particle and an anti-particle from energy, but it requires very high energy photons and typically happens in a heavy nucleus."
] |
[
"Yes, creating matter out of photons, etc also creates an equal amount of antimatter. This is because there's a symmetry in the standard model associated with lepton number and baryon number, which means that the total number of baryons (leptons) minus antibaryons (antileptons) will not change. I.e. if you create a baryon, you also create an antibaryon. If you create a lepton, you must also create an antilepton. ",
"This actually isn't the entire story though. The symmetry which I mentioned is actually anomolous, which means that quantum effects can actually violate this symmetry. Today, these quantum effects are so unlikely to occur, that we can treat it as if they never happen, however in the early universe, we did have particles being created without an equal number of antiparticles being created. "
] |
[
"If by \"energy\" you mean \"photons\", then yes:",
"http://en.wikipedia.org/wiki/Pair_production"
] |
[
"Would a larger cerebellum give you greater self control?"
] |
[
false
] |
I remember going over it in class and the cerebellum is responsible for most voluntary actions. So would a larger cerebellum give you more self control whether it be over things like motor skills, or impulsive behavior?
|
[
"Although the cerebellum is important in motor control, it is not the region of the brain that initiates movement (The direct motor control comes from the Motor Cortex region in the Cerebral Cortex). The cerebellum is responsible for coordination, precision and timing. It receives sensory inputs, processes the information, and sends the information out to fine-tune motor activity. Because of that, injury of the cerebellum doesn't cause paralysis, but produces disorders in fine movement, balancing, posture, motor learning etc. e.g. if your cerebellum is injured, you may still move your arm to swing a tennis racquet, but you may have trouble hitting a moving ball.",
"The cerebellum also plays a role in some cognitive functions and language.",
"Hence, the cerebellum is not quite responsible for self-control either. Well, it could play some roles in self-control, but no one discovered it, but chances are that it's not a major role of the cerebellum. ",
"Self-control is more about \"free will\". No one knows for sure whether cerebellum contributes to free will (probably not, but not sure). Obviously, animals like mice have a cerebellum, but arguably having any free will. It's difficult to conclude on this matter. ",
"The myth that a larger region of the brain would give rise to better functions for that region is also not confirmed. You could potentially have a very large Broca area, but not very good with speeches. This is because many things can give rise to a larger region of a brain, but not necessarily better functions. e.g. more neurons there doesn't mean they would coordinate into a proper network, larger cells in there also probably won't contribute to better functions etc."
] |
[
"So from what I remember from my course in neurophysiology that I took several years back, the \"control\" the cerebellum gives is non-concious corrections. Ie: your brain decides to move the tip of your finger somewhere, and it knows how to roughly control the muscles to do so. The cerebellum takes these rough commands and smooths them so that the action is not jittery. Thing's such as self control and the suppression of impulsive behaviour occurs in the frontal lobes.",
"So a larger cerebellum probably won't give you better impulse control or self control, but may have some impact on your motor skills."
] |
[
"the cerebellum is basically the brain's ",
"transmission",
". it doesn't do a lot on its own - the cerebrum is largely responsible for your volition."
] |
[
"Why does grapefruit change the way a persons body metabolizes medicine/drugs?"
] |
[
false
] |
What is in it that does this? Do other fruits and foods do this?
|
[
"http://en.wikipedia.org/wiki/Grapefruit_drug_interactions"
] |
[
"Your body releases enzymes from the liver called cytochrome p450 enzymes. These are responsible for breaking down drugs. Some drugs (or foods) cause an increase or inhibition of these enzymes. In the case of grapefruit, there is an inhibition. Less breaking down of meds occurs and so more chance for side effects to occur. "
] |
[
"Can this also be clinically used to increase the good effects of a drug? Could they combine a small dose of an expensive drug with grapefruit enzymes to effectively imitate a larger dose?"
] |
[
"Why doesn't cancer lead to the creation of another organ?"
] |
[
false
] |
From what i get, cancer is when a cell reproduces crazily, but if there are different types of cells(heart, liver,lung) why does it make a tumor instead of whatever that type of cell is supposed to be part of?
|
[
"For example if some lung tissue became cancerous, it isn't lung cells that are proliferating, it's cancer cells. The DNA mutations completely change the cell and makes it no longer work for the host.",
"\nIt's really just a mush of cells that do nothing apart from use your body's resources to divide. "
] |
[
"Thanks!!!!!!!!!! You made it really clear! "
] |
[
"You have a lot of different types of cells in each organ, which are organized in a specific way to do their jobs properly. One of the main requirements for cells to become cancerous is that they stop responding to the signals that are supposed to regulate where/when/how they grow.",
"So if you get lung cancer, and, say, some of the cells that are supposed to be the inner surface of the lung start growing and proliferating unchecked, they are never going to grow into a new lung because 1) They are only one of the many types of cells that makes up a whole lung, and 2) They have stopped \"listening\" to the instructions of how to grow/organize a lung. They are just growing into an unorganized mass: a tumor."
] |
[
"When we talk about previous ice ages, how widespread was the cold? Did it cover the whole planet?"
] |
[
false
] | null |
[
"Aren't we still technically on an ice age by some definitions?"
] |
[
"There is a distinction to be made between global or near global glaciations in the deep geological past vs. periods of permanent ice at the poles vs. the advance of said polar ice due to orbital variation. ",
": In the past there have been instances (Sturtian, Marinoan, and possibly Ediacaran) of near-global glaciation which are popularly referred to as Snowball Earth states. Although the initial hypothesized state of the planet was that of a \"hard\" freeze (i.e. total glaciation encompassing the global ocean), this has been IMO fairly conclusively refuted in favor of a \"soft\" freeze or \"Slushball\" state with open ocean near the equator (see e.g. ",
"Rieu et al., 2007",
"; ",
"Allen and Etienne, 2008",
"; ",
"Le Heron, 2011",
"). Solar luminosity, continental configurations, GHG concentrations, and a number of factors were vastly different then compared to the present. Using modern topography, a Snowball state can be reached with a 10-15% reduction in solar irradiance and preindustrial GHG levels (",
"Yang e tal., 2012",
"). The average global temperature would be several tens of °C colder, but a precise value would depend a lot on your assumptions. ",
": Some people argue that technically, any time during which there exists substantial ice at the poles can be referred to as an \"ice age\" or \"ice house\". I don't have a source handy but this was something that could be found in museums like the National Museum of Natural History, as an example. ",
"However, this is not what most people think of when they hear \"ice age\". If you use this definition, we are currently in an \"ice age\". ",
": Periodic variations in the Earth's position relative to the sun results in changes in the intensity, duration, and distribution of insolation, which drives climatic variation on millennial timescales. These orbitally-driven changes cause increases and decreases of glaciation but stop well short of Snowball states. The Last Glacial Maximum is what people commonly think of when they think of the \"ice age\". This is simply the most recent maximum, ",
"which occur ~100 ka during the Pleistocene",
". Orbital increases in glacial extent can be seen throughout many periods in the geologic/paleoclimatic record, although not always in the eccentricity/100ka spectrum. ",
"The Last Glacial Maximum is believed to have been ~4-7°C colder than present, depending on the proxies and modeling assumptions used (",
"IPCC AR4",
"; ",
"Schneider von Deimling et al., 2006",
"; ",
"Annan and Hargreaves, 2013",
"). ",
"In terms of maximum ice sheet extent, the LGM reached its fullest extent ~26 kya, with significant latitudinal variation (",
"Clark et al., 2009",
").",
"The ice sheet and alpine glacial advance was extensive but was nowhere near global, reaching down to the upper portion of the present US, but certainly not the subtropics or equator: ",
"http://i.imgur.com/Tbh6yNK.jpg"
] |
[
"There have been a number of \"Ice Ages\" of varying severity. ",
"probably the most severe [\"Ice Age\"] of the last billion years, occurred from 850 to 630 million years ago (the Cryogenian period) [before there was complex multicellular life or life on land] and may have produced a ",
"Snowball Earth",
" in which glacial ice sheets reached the equator",
"http://en.wikipedia.org/wiki/Ice_age#Major_ice_ages",
" ",
"During the recent \"Ice Age\" (with mammoths and people hunting them with spears, etc), the areas covered with snow and ice were very roughly similar to the areas that get snow and ice now, but it accumulated to great depths rather than melting off every spring and summer. ",
"The ice on both North America and Europe was about 3,000 m (9,800 ft) thick near the centers of maximum accumulation [close to two miles, or higher than the Appalachian Mountains, though not as high as the Rockies], but it tapered toward the glacier margins.",
"http://en.wikipedia.org/wiki/Quaternary_glaciation"
] |
[
"Why are cancer survivors more likely to 'relapse' (get cancer again) than someone who has never had it? Are their surviving cells more susceptible to damage?"
] |
[
false
] |
[deleted]
|
[
"Three main reasons.",
"That person could have had a genetic mutation that causes them to be more likely to get certain cancers. ",
"The treatment could have been incomplete. In theory, even if one cancer cell survives treatment or is missed by surgery the tumor could regrow.",
"the cancer may have already undergone metastasis, where cells enter the bloodstream and end up in other organs. Once the primary cancer site is treated, the secondary, distant sites may go undetected for a really long time as the cancer re-grows in other organs. This would lead to a recurrence of cancer."
] |
[
"When some cancer cells aren't killed by treatment methods, they can resume division. This creates a new tumor, which, if you've taken away all the cancerous tissue you can find, looks like getting cancer again."
] |
[
"http://xkcd.com/931/"
] |
[
"In a deck of playing cards, drawing 1 card at a time, how do you calculate the probability of drawing the King of Diamonds before the Two of Spades?"
] |
[
false
] |
You do NOT replace the cards you take. Also, what if you had a deck of 21 cards with 10s and up (aces high) plus a Joker, and you were calculating the odds of drawing the King of Diamonds before the Joker? What if it was of drawing all four kings before the Joker?
|
[
"This is a lot easier than you think, I guess.",
"The probability of any permutation of cards is equal. Due to symmetry, half of them will have the king of diamonds before the two of spades, and the other half of them will have the two cards the other order around. So for the question in the title, the probability is 50%.",
"The same goes for the question with the joker.",
"For the one involving the four kings and the joker, you are looking at five cards. The probability that the joker is last is ⅕.",
"All the other cards are just noise. What you're doing is picking a permutation of the cards you're interested in.",
"Edit: I hope I didn't just do your homework for you."
] |
[
"To lay out what TheBB said more simply:",
"All of the other cards have nothing to do with the problem. Each draw of an irrelevant card is like you might as well have never drawn the card. Just pretend all of the other cards aren't there, because they don't matter.",
"For the first problem there are two possible outcomes. The King of Diamonds comes first or the Two of Spades comes first. Two possible outcomes. So the probability of getting a single certain outcome (in this case, King first) is 1/2.",
"For the second question, how many outcomes are there? Again, all of the other cards and details are just fluff. It doesn't matter what order the kings come in so we'll refer to all of them as simply K, and the Joker is J. You could get: JKKKK, KJKKK, KKJKK, KKKJK, KKKKJ. There are 5 possible outcomes. And you want the probability of getting one of them (in this case, KKKKJ). So the probability is 1/5."
] |
[
"Thanks, it seemed so much harder. I was thinking \"okay, 1 in 21 chance of king right away, 1 in 21 of joker. If you don't get either, try again with 1 in 20 odds of both, etc. This seems hard, let's ask some people. My friends don't know, let's google it. I can't find what I'm looking for, let's ask someone else.\" I was using this for a school project on probability where you needed to make a gambling game for \"Casino School Name Here\". (also taught you how bad the odds in casinos are.) I had come up with my idea, all I needed was to balance the payout based on how many cards you betted on. So I could have done fine without this, but my players might lose a lot of \"money\" fast and quit. Thanks again!"
] |
[
"If you measure how much smaller an object is in a reflection, is it possible to calculate the distance to the mirror?"
] |
[
false
] | null |
[
"Absolutely, if you know the size of the object in real life.",
"Edit: The simplest way to do this is via trigonometry, based on the basic principle that angle of incidence is the same as angle of reflection.",
"With a flat mirror, the object appears the same size as if it were at a distance equal to its distance from the mirror + your distance from the mirror. (By distance I refer to the distance the ray of light travels)",
"For example - if an object is one meter away from the mirror, and you are one meter away from the mirror, then the size of the object you see on the mirror is the same as if you viewed the object 2 meters away. It is also the same as viewing an object half its size at half the distance. This concept can be summed up by ",
"this image",
".",
"Read up on ",
"virtual image",
" for a cursory introduction to optics."
] |
[
"Well, if you know the curvature of the mirror it can be done as well!"
] |
[
"You would also need to be sure the mirror was not curved."
] |
[
"What is the mechanism of quantum entanglement?"
] |
[
false
] |
I know the basics, tickle quantum widget A, and over there, instantly, quantum widget B laughs. I know it can't be used for communications since we can't know the original state, so we can't measure a change. My question is what force or phenomenon is transmitting state change between from A to B? Is it anything that is even describable?
|
[
"It's describable since it's a prediction from quantum mechanics. The basic idea is that if A and B are entangled then they are only one object. Entanglement means you can't consider AB as two different objects A and B. So that's why tickling the A part of the object AB can make the B part laugh."
] |
[
"If by \"mechanism\" you mean \"intuitive picture that doesn't involve mathematics\" and if by \"physically\" you mean \"something I can understand with my mind which is designed for classical physics\", then yes, nobody understands quantum physics. But we do have a good description of it."
] |
[
"No, it can't be described. That's why Einstein called it \"spooky action at a distance\". It's also important to note that nothing is being \"transmitted\" - the \"spooky action\" is instantaneous."
] |
[
"Since Neptune and Pluto have intersecting orbits, will they ever collide? If not, what's the closest they will ever be to each other?"
] |
[
false
] | null |
[
"These questions are answered by ",
"http://en.wikipedia.org/wiki/Pluto#Relationship_with_Neptune"
] |
[
"Wow, I think it's even more interesting that even over millions of years, they will never collide due to how stable their orbits are. Thank you"
] |
[
"No prob!"
] |
[
"I have a Brita filter that leaks, which I catch in a small container on the shelf below. The water in that container freezes, but nothing else in the refrigerator does. Why?"
] |
[
false
] | null |
[
"Wind chill can speed cooling and result in the perception of lower temperatures, but it cannot actually cool below its intrinsic temperature."
] |
[
"Cold air would apply windchill I presume, and that would lower the temperature just below the freezing point? "
] |
[
"Remember that salt water lowers the freezing point of water; other minerals behave similarly. If the filter removes minerals in your water it could make it freeze at a slightly lower temperature.",
"The location probably plays a large part as well, if it is in a thin layer and falls through cold air it would freeze much more readily."
] |
[
"How can the universe be 150 billion light-years across and only 13.7 billion years old?"
] |
[
false
] |
A coworkers and I had this discussion Friday and we may very well have confused ourselves into missing something obvious. Taking the fact that the universe is 150 billion light-years across and estimated to be 13.7 billion light-years old how is this possible? Knowing that a light-year is the distance traveled over a year it should just be a 1:1 ratio correct? Couldn't the max radius of the universe be 13.7 billion light-years while the full universe would be 27.4 billion lightyears? We spent a half an hour in passionate debate about this and I went as far as to convert distances, calculate the speed of light in miles/year and find out how many actual miles light would travel during the age of the universe. The more we discussed the topic the more we were stumped...it seems so straight forward and yet so illogical, we could very well just both be missing something obvious. This all started with this article, and my coworker asking the age of the the universe then stating "how can anything be 18 billion light-years away if there have only been 14 billion years of expansion?". So what obvious conversion or explanation did we miss? Sources:
|
[
"Light rays can reach us from a distance greater than 13.7 billion light-years because the universe has been expanding while the light ray has been travelling. While the ray of light itself can't have travelled further than 13.7 billion light-years, the universe is still expanding ",
" it, so by the time it reaches us, the distance between us and the object it came from is greater than 13.7 billion light-years."
] |
[
"\"While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be expanding away from each other at a speed greater than the speed of light.\" ",
"--Wikipedia : ",
"Metric Expansion of Space",
" "
] |
[
"because space is expanding everywhere, not just at an \"edge\" which is how you may be invisioning it. "
] |
[
"Does food need to constantly rotate in microwaves ? If so ,why ?"
] |
[
false
] |
I know this might be a stupid question ,but why does food need to rotate in a microwave ? If the principle is to use radiation to heat the food shouldn't it work while the object is stationary ?
|
[
"Microwaves are resonant cavities, so you get standing waves in them. This means that the energy apported to whatever you have inside is not spatially homogeneous, not even averaging over time, and as the radiation for microwaves is in the cm range (if it were in the sub-mm range it wouldn't be noticeable for practical terms) this could become quite noticeable. To avoid this problem, you rotate your food: You are now crossing minimums and maximums, so you do average over time and get a more homogeneous heating.",
"You can test this taking out the piece that rotates in your microwave and putting something susceptible to deform when heated, like liquorice: ",
"http://imgur.com/EFCLB6f"
] |
[
"No, but it helps to cook it more evenly.",
"Early microwaves didn't have turntables. We had to open the door part way through cooking and rotate it manually. If we didn't, it wasn't unusual to pull out a TV dinner that was really hot in some spots, and cool in others. ",
"The turntable just automates the procedure."
] |
[
"Um. The source you provided says the exact opposite. From that source:",
"When microwaves pass through water the water molecules absorb some of the microwave energy and as a result they twist and turn, writhing around, as the radiation passes by. However after the microwaves have gone the molecules stop moving again, remitting the energy as more microwaves. In free water molecules this does not result in a heating.",
"In a liquid things are rather different. The water molecules are close to reach other and so there is \"friction\" between them. It is the rubbing of one molecule against another as in liquid water that allows the energy to be retained and prevents it being reemitted as microwaves. The \"friction\" between the writhing water molecules and other molecules in a solid also heats up the solid.",
"Microwave ovens operate at a frequency of 2.45 GHz (2.45x109 Hz) and this is NOT the resonant frequency of a water molecule.",
"However microwave radiation of any frequency will affect them although they may not resonate.",
"I didn't say the water moecules ",
", I said they ",
". Though that microwaves of any frequency will cause them to vibrate is news to me, so thanks for pointing that out."
] |
[
"Why are adverse reactions to vaccines more common in younger people than older people?"
] |
[
false
] |
I was looking through the adverse reactions to the COVID vaccines, and I found it interesting that the CDC report that younger people are more likely to experience (or at the very least report) an adverse reaction to the COVID vaccines than if you were older. I would have thought it would be the opposite (due to older people having weaker immune systems)? Can someone explain this phenomenon? Is this something of all vaccines? What's the biological mechanism here? Refer to table 1 of : 64.9% of 18 to 49 report an adverse reaction. I thought perhaps it was to do with unequal category sizes (18 to 49, versus say 50 to 64), but I don't think it is as this represents 2/3 of the total. P.S. I really don't want to get into a debate about whether or not people should take the vaccine or not (I think people at risk, definitely should). I simply want to understand why vaccines effect different age groups in different ways. (For some reason moderators removed this post... This is a legitimate medicinal question, but for some reason I'm not even allowed to ask it)
|
[
"Keep in mind that the data that you're looking at is collected by VAERS, which is a voluntary self-reporting online tool. Looking at this table, you can see that 64.9% of people who reported an adverse reaction to VAERS are ages 18 to 49. The survey pool here is limited to those who reported, it's not indicative of everyone that received a vaccine.",
"Naturally, the data is going to be biased toward those that actually go through the effort of going online and reporting, which, statistically speaking, is going to be a younger crowd. Additionally, this is data that was collected as of January 13th, which is long before any state opened up vaccines to the general population for people under 65 years of age. The younger respondents on this survey are most likely those working in the healthcare industry (who had early access to the vaccines), who would have a greater awareness of the VAERS tool."
] |
[
"Keep in mind that the data that you're looking at is collected by VAERS, which is a voluntary self-reporting online tool.",
"On this note, here's a guy who successfully submitted a report to VAERS that the Flu vaccine transformed him into The Hulk: ",
"The chief problem with the VAERS data is that reports can be entered by anyone and are not routinely verified. To demonstrate this, a few years ago I entered a report that an influenza vaccine had turned me into The Hulk. The report was accepted and entered into the database.",
"Because the reported adverse event was so… unusual, a representative of VAERS contacted me. After a discussion of the VAERS database and its limitations, they asked for my permission to delete the record, which I granted. If I had not agreed, the record would be there still, showing that any claim can become part of the database, no matter how outrageous or improbable."
] |
[
"Extremely rare and serious adverse reactions aside, most \"side effects\" from a vaccine are generally just due to your own immune response. ",
"It's a well established fact that with almost all vaccines, older people will have a less severe reaction, because they have a weaker immune system. Which also means they will have less effective protection.",
"So gettings some side effects from a vaccine, such as feeling slightly sick for a day or two, is actually a good sign. It means it's working."
] |
[
"The liver is the only Human organ capable of regeneration. Is it possible to donate your liver multiple times?"
] |
[
false
] | null |
[
"No, it's not possible. The liver can regrow but doesn't create the proper structure required. In other words, you're growing more cells, but they're not able to function as well as the original liver because the cells are not structured into lobules the way they originally were. We are not able to duplicate organogenesis in an adult human."
] |
[
"Not an expert on this; but its probably possible but not ideal. The criteria never mention anything about not being a past donor.",
"However, every surgery is risky (~0.5-1% risk of death) and the liver may not regrow to full size after each surgery. I wouldn't be surprised if the regrown liver still has scars from each surgery; but can't find any info on that. The donor is typically hospitalized for a week after the surgery and typically three weeks recuperating after that."
] |
[
"IIRC, you can live on half of your liver because after the donation it will eventually be able to function at the same level it did before. Not growing back to normal size."
] |
[
"Why aren't planets positioned from greatest mass to least mass in relation to the sun?"
] |
[
false
] |
I was talking to someone religious (nothing crazy) and something they said caught my attention. They said that how come Earth's positioning and our solar system in general is positioned so perfect to sustain life for millions of years. Furthermore, they said that planets technically should form in order of greatest mass to least mass and our solar system isn't like that, thus there have to be some kind of divine intervention.
|
[
"There's really no reason they should be. Planet formation is a complex process, but if anything it should be the opposite because the stellar wind can inhibit the formation of gas envelopes around protoplanets. ",
"If we look at the known stellar systems with more than six planets",
", none of them have the ordering your friend suggests they \"technically\" should have, and the sizes are generally independent of their orbital position."
] |
[
"but if anything it should be the opposite because the stellar wind can inhibit the formation of gas envelopes around protoplanets",
"What we should be observing is actually an increase in mass as the planets move away from the star, and then a decrease again as we get towards the outer edge of the system, where the protoplanetary disc would have been much more diffuse (causing planets to form slower, and making it hard for them to accrete so much mass). And lo and behold, this pattern is actually present in the Solar System, with two exceptions:",
"Mercury: 0.0553 Earth masses",
"Venus: 0.815 Earth masses",
"Earth: 1 Earth mass",
"Jupiter: 317.8 Earth masses",
"Saturn: 95.2 Earth masses",
"Uranus: 14.5 Earth masses",
"Many theories and models of the early Solar System's formation indicate that Jupiter moved around a lot in its youth, starving Mars (and possibly also Saturn) of material. Also, it seems likely that the two ice giants switched orbits at some point, and that both probably formed a fair bit closer to the Sun, seeing as how other objects around and beyond Neptune's orbital zone (i.e. the Kuiper belt and scattered disc objects, like Pluto) were never able to accrete enough mass to become true planets.",
"Your basic idea about the solar wind affecting the accretion process is correct though. It seems likely that it can strip heavier material away as well, if a planet's close enough. Solar wind interactions are thought to be why Mercury's rocky mantle is so thin compared to the other terrestrials - it was probably bulkier at some point, but had a lot of that silicate material blown off by bombardment from the early (and more magnetically active) Sun before its surface solidified."
] |
[
"Earth: 1 Earth mass",
"I DEMAND to know where you are getting these figures. This sounds preposterous! "
] |
[
"Where would I have to stand on the earth the next coming midnight GMT to be able to look directly upwards and see the galactic core of the Milky Way?"
] |
[
false
] |
Question arose after reading a chapter in Carl Sagans 'Cosmos' and spending a few weeks in the Ukrainian countryside where I was able to take photos like this: Any relevant maths appreciated.
|
[
"Based on the fact it's ",
"near Sagittarius",
", playing around with this ",
"http://neave.com/planetarium/",
" puts you somewhere in the Atlantic ocean off the NW coast of Africa."
] |
[
"http://upload.wikimedia.org/wikipedia/commons/6/62/SagittariusCC.jpg"
] |
[
"Do you really want to tie the time to GMT? if you're GMT midnight and the galactic core isn't above that time zone you could be asking for day-lit sky. I think you may be wanting to ask \"where is the next place I could stand to have the galactic core at 90° elevation at local midnight?\""
] |
[
"Aren't the statistical methods used in medical research lead to a loss of lots of useful data ?"
] |
[
false
] |
Usually most medical studies and certainly high quality ones(like systematic reviews and cochrane) , use some statistical method to generalize an answer over a group of people. But in the process , don't we lose information about specific sub group who have a different reaction(sometimes much better) from the average, to said treatment ? And what does medicine and medical interpretation do to still extract that data and not lose it ?
|
[
"Science works like this; You make a hypothesis, then you test it. If you collect data, then look for a pattern that makes that data work, that can be useful- but you need to test that newly hypothesized pattern on different data.",
"This is because the likelihood of data having SOMEthing that appears like a pattern is high, simply because of the number of possible things that could be a pattern. For example, if you have some treatment and you test it on school age children, you might find that it does not invalidate the null hypothesis - that is, it doesn't work.",
"However, if you then look at the same data, except bucketed by the first letter of the last name, you have 26 times as many opportunities to produce a data set that appears to show a correlation. If you have some reason to believe that there is a causal flow there, you can run those tests on other data- but you don't get any additional information, really.",
"(If you plan in advance, you can do something like Bonferroni correction, but you still need to plan your methodology and state your hypothesis before looking at the data.)"
] |
[
"1) When any mathematical operation is performed on any data, there is a loss. To keep it to a simple, a mean does not have the value of the original dataset. Adding an SD may help, or it may not. While many consider the segment of the data set of the mean +/- 1 sigma to include 68% of the population as cant, it is really given by Tchebycheff's inequality, Depending on the shape of the dataset the area of the mean +- 2 sigma can include anywhere from 75% to 100% of the data. Too many people abuse high power tools like SAS, SPSS, etc without knowing how to interpret the data. Of course as the ananlysis become more complicated, they become less reliable.",
"2) Multiple metastudies have claimed that more than half of all conclusions reached in medical research studies are wrong, including medical metastudies. Given a lifelong career in Public Health my inclination is to believe this to be likely.",
"3) When studies are done on humans, they are almost always subject to an inability to keep the subjects to the standardized conditions of the test. Through ignorance or mendacity people fail to adhere to the conditions required. ",
"4) There are enormous numbers of unknowns that can affect results. Even in environmentally controlled animal studies there is much room for error (as opposed to blunder), where unknowns conflate to produce wrong results.",
"5) So how does the system work. It depends on the repetition of results. Sometimes, depending on what is being tested can take decades or longer to determine that literally dozens, and perhaps hundreds, of previous studies were wrong. As an example consider the promulgation of margarine for the prevention of heart disease. It is just about within the last decade or so that the trans-fatty acids in the original margarine were as bad or worse than the lipids found in butter. ",
"In the late '70s I published a method for improving the precision of a lipid test. About a hundred other labs tried it, and roughly half found a statically significant improvement, the other half did not. Clearly there was something there, and there was also at least one unknown that affected results. Unfortunately I had become involved in an all consuming project that left no spare time to try and isolate the issue.",
"Or consider PSAs. The guy who invented the test states that it is only to be used for testing men with known prostatic malignancies. Yet it is considered a gold standard test. Physicians who are aware of its failures, and the mental and physical damage high results can inflict on a patient and his family, do not have the 15 minutes or so to explain the pros and cons of having the test done. They have it done automatically because it has become the standard of care, not because it is necessarily the best thing for the patient.",
"The question I put to you OP, is how do you know when you are keeping bad data, or throwing out good data?",
"Modified area under curve to +/- 2 sigma"
] |
[
"If you plan in advance, you can do something like Bonferroni correction, but you still need to plan your methodology and state your hypothesis before looking at the data.)",
"Isn't the idea of post hoc tests that you can do them without having planned to do them beforehand? If they take into account the higher probability of type I errors then why not?"
] |
[
"Is there a clear definition of what distinguishes sentient creatures from non-sentient creatures?"
] |
[
false
] | null |
[
"Interestingly, I recently attended a seminar on this topic.",
"Most scientists argue a lot about this topic. Generally, from the literature, vertebrate animals (those with a backbone) and some invertebrates (octopi & squid) are considered to have a certain level of consciousness.",
"The 'mirror test' has long been used as a way to identify self awareness in many animals (",
"1",
"). A mirror is placed in front of the animal and if it responds in all 3 following ways (in order) it is deemed to be sentient.",
"However, this is just one way to know if an animal is sentient or not and it is not perfect either.",
"A recent article by Kohda ",
" (",
"2",
") shows that fish (",
"), which are widely considered to not be self conscious, can emit behaviours that could be interepreted as having 'passed' the mark test.",
"This highlights the inconsistencies with the mirror/mark test and that it might not be the most appropriate method in determining an animal's self awareness."
] |
[
"It all depends on interpretation. As I wrote above, ",
" was able to \"pass\" the mark test but they are not considered to be sentient .",
"It really depends on who is interpreting the behaviours that they are seeing the animal perform. Some might say the behaviours they witness indicate self consciousness, while others may disagree.",
"This method for testing animal self awareness is not perfect. I'm not sure how it could be improved as it's not my niche area of research."
] |
[
"Ants have passed the mirror test, so can they be considered sentient?"
] |
[
"What is actually happening when soap \"lathers\", and why is water so crucial for a good lather?"
] |
[
false
] |
Also, why do some soaps lather more easily, with less water, than others? I was just in the shower, and my body wash wasn't lathering as much as I wanted it to on my loofah. So I stuck it under the water for a second, and then of course it did a much better job of lathering. And I started wondering why some soaps need more water than others to lather well, why (liquid) soaps need water to lather at all, and what lathering actually . The only example I could think of, for a soap that doesn't need water added to lather well, is chlorhexidine. (I'm a veterinary technician, and we use chlorhex as a surgical scrub. Not sure what is commonly used in human medicine). Anyway, you can lather up a gauze sponge with chlorhexidine scrub really well, without adding any water at all. Why is this? Edit: I know this is really stupid, but hopefully I categorized this acceptably. I was (am) trying to decide if it belongs in Physics or Chemistry...
|
[
"As the other user posted. Lather is just a gimmick. Studies have been done with market groups to determine how individuals FEEL about lather and what is the right amount. Chemists are constantly manipulating contents of conditioners, soaps and shampoos depending on their target market's feelings about the physical nature of products. "
] |
[
"Shampoos and such usually contain sodium laureth/lauryl sulfate, ",
".",
"No. ",
"Sodium laureth is an extremely effective foaming agent by in addition to being an anionic surfactant."
] |
[
"Is it the same with shaving soap? I was under the impression that the density of the lather was important to keep the hair standing up or something."
] |
[
"How are complex instinctual behaviors (like how beavers know how to build dams) encoded into DNA?"
] |
[
false
] |
It seems like many animal behaviors (mating rituals, beavers/birds building nest, ants creating colonies etc) would be things that are so complex that they would have to be learned through example or observation, and yet somehow most of these skills are hardwired into their DNA. I don't understand how DNA, which I think of as the blueprints for the physical construction of living things, can also contain such incredibly specific behavioral routines. I hope I am explaining this question clearly, because I would be fascinated to hear the answer. Thanks in advance!
|
[
"Well, it's not 100% of the mechanics behind dam construction, but a major component appears to be that beavers have a compulsion to pile sticks on the sound of flowing water until they can't hear it any more. If you stick a speaker playing the sounds of running water in the middle of a field, they will pile sticks on it. ",
"In practice, this results in beaverdams. Water in a stream is noisiest at the shallow riffles. Beavers pile sticks on this point. water gets channeled around. Beavers pile sticks on that, and so on until there's a full dam with water just seeping through.",
"Now, there's good evidence that more than just this goes into dam building, because beavers do some more advanced engineering tricks if needed....but it does go to show that complex behaviors can originate from relatively simple underlying causes. In most cases there's not a hardwired \"final plan\" there's just a series of a few \"if X, do Y\" instructions that result in the final product."
] |
[
"That is amazing. I think this may be the single coolest fact that I've learned from askscience. Can you provide a link/citation to back that up?"
] |
[
"Mentioned on page 43, without a citation to back the claim up in this thesis.",
"After extensive google-scholar-fu I found the following passage:",
"It has been shown that beavers do not plan their dam. Young beavers were reared in isolation from adults, and were never exposed to a beavers' dam. Nevertheless they built dams. In one experiment, the young beavers were exposed to the recorded sound of running water. With this stimulus they built dams even in a still tank of water (Wilson, 1968, 1971). These experiments show that dam building is the result not of purposeful action but of instinctive behavior.",
"Which cites ",
"this book",
" and \"Observations and Experiments on the Ethology of the European Beaver\", both by the same author.\nThese works are also cited by the Wikipedia article on beaver dams when talking about instinctual cues; I don't have access to these books so I can't say for sure what the contents are.",
"The Wikipedia article on beaver dams provides an additional citation: Richard, P.B. 1983. Mechanisms and adaptation in the constructive behaviour of the beaver (C. fiber L.). Acta Zoologica Fennica 174:105-108.\nUnfortunately I can't find the article online."
] |
[
"What is stopping us from creating a physical test to determine a person's age?"
] |
[
false
] |
Most cells in your body have a limited lifespan and they are replaced over a particular period of time. Some of the cells are not changed but it is probably extremely difficult at this point to take any information regarding age from them. I guess these are the main reasons for the lack of a such test. I know there are some tests that can give a rough estimation. How accurate can they be? Will we ever be able to come up with a completely accurate test?
|
[
"I'm not knowledgeable on this topic, but I do remember reading about this paper a couple years ago. The paper is about a method the authors claim can accurately age people using DNA: ",
"http://www.cell.com/current-biology/abstract/S0960-9822(10)01286-8",
"In the present study, we demonstrate that human individual age can be estimated accurately and reliably from blood using T-cell DNA rearrangements, and we provide a robust and sensitive real-time quantitative PCR protocol for application in various areas of bioscience."
] |
[
"The rate of \"damage\" would vary depending on the person's genetics, environmental exposure, diet, etc."
] |
[
"The rate of \"damage\" would vary depending on the person's genetics, environmental exposure, diet, etc."
] |
[
"If a man or woman didn't go through puberty due to medical/genetic causes, is there a cutoff age when it can no longer be induced?"
] |
[
false
] | null |
[
"Nope! Ask any trans* person who's undergone hormone replacement therapy as an adult - the process is virtually identical to puberty. They develop all the secondary sex characteristics of the gender they're taking hormones to match (including breast tissue - a lot of transwomen who go on HRT develop sufficient breast tissue just from HRT that they don't need to get any surgical additions). So, transmen experience voice breaking and grow facial hair, and transwomen lose their facial hair and grow breasts. They also experience mood swings, acne, and redistributions of fat and muscle tissue that more typically match those of their gender. The only major differences are that they won't have any growth spurts, and of course their gonads and genitalia won't change without surgery.",
"This is common knowledge within the trans* and allied community.",
"Edit: sources. If you scroll down to the \"Effects of Hormones\" section, this guide from the Stanford student medical center explains how HRT affects transwomen: ",
"http://vaden.stanford.edu/health_library/TranswomenHealthConcerns.html",
"and transmen: ",
"http://vaden.stanford.edu/health_library/TransmenHealthConcerns.html",
"Edit 2: Correction, hormone therapy will not eliminate facial hair in transwomen. It will probably thin and lighten it, but not remove it. Transwomen who can afford it will often get laser hair removal to eliminate their facial hair. For additional clarification, when I said \"no growth spurts,\" that refers to the fact that upon reaching adulthood, bones harden and lose the ability to become longer or shift. Adolescents going through puberty will experience lengthening bones and (for women) realignment of the hips to make a wider pelvis; adults undergoing HRT will not be able to have these changes just via HRT."
] |
[
"One thing that can't occur later in life is bone development - for example the hip bones are shaped quite differently between ",
"males",
" and ",
"females",
"."
] |
[
"Just a correction, trans women will not lose their facial hair from HRT alone. There may be some lightening of colour at best, and body hair will grow in thinner and lighter as well, but facial hair usually has to be removed via laser or electrolysis, or both."
] |
[
"Reddit, why do archaeologists still have to dig? Why don't we have \"ground scanners\" that can peer into a site and tell us what's there?"
] |
[
false
] |
I realize it's not that easy or straightforward, but...
|
[
"Hello, archaeologist here.",
"There are a few reasons.",
"1) There are multiple layers of things. If a ground scanner can see something, it would block whatever's behind it.",
"2) Differentiation. How could you tell the difference between a rock and earthenware, or a rock and worked rock? Or even tougher: piece of tree root vs. carved tree root?",
"3) Subtlety. How can you see minute soil changes on a non-contact scanner?",
"4) Resolution. To replace digging, a scanner would have to be able to read inscriptions on bottles, resolve mortar on bricks, and show us colors on polychrome pottery. That's a tough task. Further, many details that help with interpretation are ",
". A little chip here, a gnaw mark on a bone there.",
"5) Cleaning/conservation. Many features only become apparent after conservation and cleaning.",
"6) Human interpretation. There's a lot of interpretation, pattern recognition, and a \"way of seeing\" that archaeologists do. There's no replacement for a trained eye just ",
" at the site.",
"That said, remote sensing has gotten much better, and it has helped us immensely, especially in maritime sites. If it's got relief above the bottom, we can find it acoustically. If it's got ferrous metal, we can find it magnetically. Unfortunately, non-magnetic sites under mud or sand are still invisible, and will likely remain so for some time. This means that a lot of submerged prehistoric sites may never be found.",
"Did that tome answer your question?"
] |
[
"There's also an issue of funding. Archaeologists frequently don't get nice toys because they are expensive, and we are poor. It's amazing how tiny-budget a lot of these digs are.",
"Power also becomes an issue sometimes."
] |
[
"There's also an issue of funding. Archaeologists frequently don't get nice toys because they are expensive, and we are poor. It's amazing how tiny-budget a lot of these digs are.",
"Power also becomes an issue sometimes."
] |
[
"Do wolves or wild dogs wag their tails? What is tail-wagging for?"
] |
[
false
] |
[deleted]
|
[
"Tail wagging is one of many forms of non-verbal communication dogs engage in. Wolves, like dogs, also wag their tails. ",
"Source",
" ",
"Source2"
] |
[
"Dogs and wolves also wag their tales to disperse hormones and odors throughout a territory."
] |
[
"Of course. All dogs wag their tails as a form of communication. Just like all birds chirp as a form of communication (or maybe not all of them idk-there are a shit ton of really fuckin' weird birds)."
] |
[
"[biology] what do jellyfish eat?"
] |
[
false
] | null |
[
"From Wikipedia:\nJellies are carnivorous, feeding on plankton, crustaceans, fish eggs, small fish and other jellyfish, ingesting and voiding through the same hole in the middle of the bell. Jellies hunt passively using their tentacles as drift nets. Their swimming technique also helps them to capture prey; when their body expands it displace more water which brings more potential prey within the reach of their tentacles.",
"Make me wonder how they digest it."
] |
[
"Jellyfish are pretty primitive animals, they have an opening underneath the \"umbrella\" which is their \"mouth\" and leads to a cavity (\"stomach\") covered by cell layer named gastrodermis. Water + living things in it such as plankton are ingested into this cavity and degraded there, after which nutrients are \"absorbed\" in the jellyfish body. And to the next most likely question to arise - waste is released through the same opening, so unlike most animals there's only one hole."
] |
[
"Jellyfish are cnidarians and cnidarians are classified by a specialized cell know as the cnidocyte which are located on the jellyfish's tentacles (Medusa and Polyp phase). Cnidocytes are pretty much coiled \"harpoons\" which when prey (plankton, small crustaceans) are close my they shoot out and inject a toxin, this is why it burns when you get \"stung\" by a jellyfish. Some can actually kill you or do some really nasty damage (check out the Portuguese Man-Of-War). Jellyfish do have a mouth though but no anus, no stomach and certainly not a digestive system. Excretion is facilitated through simple diffusion.",
"Jellyfish are actually pretty bad-ass. Look up some videos on youtube and you'll see what I mean."
] |
[
"Could you perfectly preserve a human body by bombarding it with gamma rays to destroy the bacteria?"
] |
[
false
] |
Killing the bacteria that decomposes your body should preserve your body.... (assuming you could keep it in a perfectly sterile environment) Right?
|
[
"I presume you mean preserve a dead body, for intense radiation will certainly kill you.",
"Firstly, even in the absence of other living organisms to decompose you, your body will break down after death. When you are alive the cells in your body continually work to maintain themselves. Once your heart stops all the cells in your body are deprived of the oxygen and nutrients they need to function, so they begin to die. Stuff that is meant to be kept inside the cells leaks in and stuff that is meant to be kept inside the cells leaks out. Enzymes within the cell begin to operate out of control and the cells break apart, spilling their contents everywhere and damaging other cells. As the cells that make them up break down, tissues lose their structure and function. This process is called necrosis.",
"Moreover, parts of your body, such as your pancreas, contain enzymes specifically designed to break things down (in order to digest food). These enzymes are carefully managed in life, but once you are dead they run out of control and begin to digest your own body!",
"So, even a body without any fungi or bacteria will spontaneously break itself down due to the process of necrosis. The only way to slow necrosis is to either lower the temperature or completely remove all water from the body. This is why thousand-year-old bodies are preserved frozen in ice or buried in sand. I don't think this would match your definition of \"perfect preservation\", however. It is not necessary to sterilize a body under these conditions since cooling down or drying out halts both the progression of necrosis and also the progression of life (of the bacteria).",
"The only way to preserve a body in any sort of condition that resembled life that I know of is via cryogenics. "
] |
[
"There have been freeze-drying services for dead pets for decades now. The results are pretty startling:",
"http://www.livescience.com/18784-gallery-freeze-dried-pets.html"
] |
[
"Pretty much what lopel said, but with the addition of thinking of what happens to people who get radiation therapy for their cancer. This uses a weaker type of radiation, but is still capable of ionizing stuff to radical species (free radical damage). The end result is cellular damage caused by chemicals (protein, DNA) reacting with the radiation itself. If you're blasted with gamma rays trying to kill bacteria, you're going to do more damage to yourself trying to get the bacteria. ",
"So, in short, no you can't perfectly preserve a body with gamma radiation. Like lopel said, you're best bet is to freeze it."
] |
[
"Is human response to music cultural? All societies have some form of rhythm, but if I were to find some previously uncontacted Papua New Guinean tribe and play them Adagio For Strings would they feel sad?"
] |
[
false
] |
Would Ode To Joy make them feel happy? Would Approaching Menace make them feel tense?
|
[
"Yes. Uncontacted tribes have been shown clips of music usually associated with fear like the shrieking strings from the Psycho murder scene and they only experience joy because music is a joyous occasion in their culture."
] |
[
"There are sonorous aspects to music that are more natural than cultural. Music that is \"tense\" may contain many dissonances, whereas consonance is prevalent in \"uplifting\" songs. Both of these relate to natural sound production: consonance achieved with sonorities that jive with superparticular ratios, dissonance when they don't. Only a small contributor to the depths of OPs question.",
"To that end, I grew up with western music, and hearing Adagio for Strings makes me quite happy! "
] |
[
"I think this is a complex subject. Human beings in general do have an innate appreciation for music. I think even throughout all animals a certain vibe of emotion can be experienced through music, especially through consonance and dissonance. ",
"But rhythm seems to be more specific to human beings. I've never seen another animal ",
" groove to music the way some people do. I've seen them mimic dancing though. ",
"But not all humans have this either.",
"I think there is a cultural side of it for sure \"fashion\" of music, absolutely, and that on its own would influence cultures that never heard a music before. This can often be very powerful and cause people to hate or dislike something that if they approached it objectively, they would naturally subjectively enjoy the music. That even happens in our societies where some people will say \"That music sucks!\" and then 10 minutes later they are singing the melody and tapping their foot, but if it doesn't fit with their social image, they denounce it. ",
"Aside from that though, I think harmonically and rhythmically in a general sense, most lost tribes would appreciate music the same way. Even cats and dogs and things like that will show an appreciation for music. But they will never dance. However, a toddler will dance, even if it's not something they are copying that they've seen. "
] |
[
"What is the right way to think about particles in quantum field theory?"
] |
[
false
] |
[deleted]
|
[
"So theres a complex relationship between the classical fields and the \"Hilbert space\" which represents the quantum particles. ",
"This is an EXTREMELY subtle concept that students who pass two semesters of QFT don't always comprehend. And it's also incredibly abstract. Also, it's not particularly going to satisfy what you're actually asking since quantum don't really exist in the classical fields.",
"So far, the most developed theory we have says the classical fields are just a means to generate the operators that the quantum mechanical \"Hilbert space\" uses. ",
"(Quick definition: A Hilbert space is just the mathematical term for mathematical space of eigenvectors that quantum mechanics exists in. I'm assuming you took linear algebra as an engineer. Let's say we we have an abstract two dimensional vector space. These vectors have a row vector * column vector inner product, they can be transformed by linear matrices, they can be added to other vectors etc. Our Hilbert space is like this but infinite dimensional and a few more properties to make the probabilistic interpretations nicer.)",
"We model particles as classical fields. Let's just work with a basic real scalar field right now. Your picture is accurate (though nobody ever actually looks at the classical behavior of the fields in QFT). Every point of the four dimensional spacetime has a value. We have a function φ(t,x,y,z) that takes as input the position in spacetime and yields as output a scalar value. This is our quantum field. I'll write φ(x) for simplicity where x is the 4-vector holding (t,x,y,z).",
"These fields satisfy the classical four dimensional wave equation: ∂",
" φ = 0 where ∂",
" = ∂t",
" - grad",
". So these fields, classically at least, are exactly analogous to any standard field that you're familiar with that satisfies the wave equation. As of now, there are no particles. Nothing but classical fields. ",
"Great. But now this is where quantum mechanics happens. We now assume a mathematical feature. These fields φ(x) are promoted to operators on our Hilbert space. (Think linear, unitary matrix with determinant 1) These operators φ(x) act on our quantum mechanical states (think vectors). The simple rule we assume is that [φ(x),π(y)] = φ(x)π(y) - π(x)φ(y) = iδ(x - y) where π(x) is the momentum of the field and δ is the Dirac delta distribution. Remember, φ and π are now (representable) as matrices at this point. And now, particles start to exist. ",
"To be honest, this relationship really insightful or easy to understand. I'm just saying it since it's one of the fundamental postulates of QM. We just postulate that the fields are subject to this commutation relation and are operators on our Hilbert space and BOOM... quantum mechanics. You just need to understand that we promote these classical fields to operators on a Hilbert space.",
"So, now we have a field operator φ(x). We write our vectors in quantum mechanics as |φ⟩. The vacuum state with 0 particles is |0⟩. So φ(x)|0⟩ = |x⟩ where |x⟩ is a state with a particle isolated at the position x = (t,x,y,z). φ(x) is the operator that creates a particle isolated at the point x. ",
"The classical fields never really take the shape of a single particle propagating. They just create single particles in the Hilbert space. The Hilbert space contains the information about the particles. ",
"We can take the inner product of this state |x⟩ with it's dual (column vector version) ⟨x| to find the probability of measuring the particle at that point in spacetime. |⟨x|x⟩|",
" = 1. This is another postulate of QM. All we can really derive out of these states is probability. The inner product of the state with another state yields the probability of finding the state in the second state. |⟨state2|state1⟩|",
" = Probability(1->2). ",
"In QFT, we study scattering events. We look at φ_1 + φ_2 -> φ_3 + φ_4. We take |⟨φ_4, φ_3|φ_1,φ_2⟩|",
" and we try to find this probability and then we measure the situation in a particle collider. This is the probability to find the initial state with two particles φ_1 and φ_2 and for them to scatter in the collider and then to find the particles φ_3 and φ_4 in the detector afterwards. We massage various relationships like [φ,π] to get other mathematical relationships until we have enough things to calculate this.",
"SO. As I said, subtle, abstract and not that enlightening and not that clarifying as to what your question was. We don't view the particles as bubbles in the fields. We view them as Hilbert space states. The fields are just tools to analyze the states. ",
"All that being said, a useful intuitive model (and it is absolutely nothing more than that) is to just simple think of little pebble like bubbles moving around in the fields. When I think of the φ + φ -> φ + φ scattering, I think of two bubbles traveling along a scalar field and colliding and turning into two other bubbles flying away. This is certainly not 100% accurate to the rules of QFT, but it is a nice little visual to have. "
] |
[
"Yes, exactly. The momentum is derived from the Lagrangian using the definition of the momentum from the Hamiltonian formulation. π(x) = ∂ℒ/∂(∂φ(x)/∂t) where ℒ = 1/2 (∂φ)",
". It turns out to be ∂φ/∂t. ",
"Also note, that the field momentum is not quantum mechanical. Fields have momentum classically and this momentum is derived the same way you'd find the momentum if you were studying a normal classical field."
] |
[
"This is more or less the right way to think about it, with a few caveats. One is that everything is quantum, so the picture of a field vibrating like water waves is just that, a picture. In reality the field does not have a definite value. ",
"Another is that what we usually call \"particles\" in QFT are momentum eigenstates, i.e. plane waves. They are completely delocalized; you should think of them as being an infinite wave with a definite wavelength, not a localized vibration. If you take superpositions of such states you can get a localized wave like you're picturing.",
"I recommend reading ",
"this article",
", it's pretty great. It definitely is the best layman/\"intuitive\" description of particles that I've seen."
] |
[
"Do CPUs make noise?"
] |
[
false
] |
I've always wondered what's the noise (something like crunching nuts) that PCs make during heavy load. That's particularly evident during Windows boot, but totally absent in OS X. I'm pretty sure that's not HD vibrations because I heard this sound coming from SSD PCs.
|
[
"All those high-pitched whines you hear coming from electronics come from the vibrating cores of transformers and inductors. There is a name for this phenomenon that I always forget. Basically though, the changing magnetic field of the current passing through the inductor/transformer causes its core to rapidly vibrate. ",
"Electricity on it's own can only indirectly make noise \n(well maybe except for arcing)."
] |
[
"Nothing that you can hear from the actually CPU chip.",
"There are fans on the CPU and case fans that can be noisy, especially if the bearings are bad. Some power supplies can make noise as well. The power supply on the laptop I'm using sounds like someone eating cereal.",
"I'm guessing you are hearing something out of the power supply. "
] |
[
"http://en.wikipedia.org/wiki/Electrostriction",
" ",
"and",
"http://en.wikipedia.org/wiki/Magnetostriction",
"This is what you are talking about. I've made parts that make this noise while switching voltages. Surprises you at first!"
] |
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