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[
"Could quark color confinement limit the accelerated expansion of the universe?"
] |
[
false
] |
When quarks are pulled apart there is a point where the gluon field "snaps" to create a new quark/antiquark pair, wouldn't the expansion of the universe some day supply enough energy to cause massive creation of mesons, thus slowing expansion down or at least stabilize it's rate?
|
[
"Here's a similar question from earlier: ",
"http://www.reddit.com/r/askscience/comments/grcna/big_rip_question/"
] |
[
"I remember someone showing that this could only happen if the accelerated expansion was more than accelerated (or w < -1 in physics lingo).",
"But suppose that this could happen and you can go around creating quarks. Essentially you change nothing, since most of the mass of the pair comes from the gluon potential energy, actually. But anyway, while you are increasing the potential energy linearly in a, the whole thing dilutes as something in between 1/a",
" and 1/a"
] |
[
"this is way over my head.. explain it to me like i'm 5;) "
] |
[
"What's going on the brain of a psychopath? Scientifically, why can't they feel emotions?"
] |
[
false
] | null |
[
"Psychopaths feel emotions. They do not feel empathy.\n",
"http://en.wikipedia.org/wiki/Psychopathy",
"Psychopathy (/saɪˈkɒpəθi/[1][2]) is a personality disorder characterized primarily by a lack of empathy and remorse, shallow emotions, egocentricity, and deception.",
"That means, just for an example, you see a little kid holding a wad of cash on a bridge. You won't toss the kid over the bridge no matter how the circumstances make it appealing i.e. no is watching, no one would find the body, odds of being caught are minimal. I mean, this cash is basically sitting there, all you gotta do is toss the kid over the bridge.",
"But you won't do it because you feel empathy, and you don't want the kid to feel the terror because you sympathetically feel his terror as well.",
"A psychopath would toss the kid over the bridge and take the cash, because he does not feel empathy. But he certainly feels emotions. He'd be pretty pleased with himself. "
] |
[
"The first paragraph of the shallow emotions section says ",
"Psychopaths do not feel emotions as deeply as an average person. Though they are not completely unemotional, their emotions are so shallow that some clinicians have described them as mere \"proto-emotions: primitive responses to immediate needs.\"",
"And the last",
"Researchers have conducted brain scans on psychopaths while exposing them to emotionally-charged words such as \"rape\", \"murder\", and \"love\". In a normal person, these words will provoke activity in the limbic system, which governs emotions. Psychopaths showed no such activity. They react to emotionally-charged words as if they were neutral words (e.g. \"tree\", \"chair\", \"spoon\"). They do, however, show activity in the brain areas associated with language processing, suggesting that their response is more cognitive than emotional",
"Narrowing it to just empathy seems a bit strict."
] |
[
"From what I read -from The Psychopath Test - they don't have a functioning amygdala. So they basically don't have fear, guilt or remorse. Bob Hare did crazy tests in the 70s where he would tell his test subjects (prisoners- both psychopaths and non) that they were going to get a painful shock at the end of a count down. He'd then count down from 10 and shock them. The nonpsychopaths would sweat and stress out in anticipation. The psychopaths would not. Then he did it a second time. So the prisoners knew exactly how bad the shock hurt. The psychopaths still didn't break a sweat. It really is a great read (The Pyschopath Test by Jon Ronson)."
] |
[
"Do elevators use regenerative breaking? (reposting)"
] |
[
false
] |
I've posted this question a few times now and it just seems to disappear from the timeline. It never shows up in the New tab either. =/ Here's hoping it works. During a single ascent and descent the energy expended to raise the elevator from the first floor to somewhere higher is equal to the difference in potential energy at those two positions. Then that same energy can be gained on the descent and stored in a battery similarly to how hybrids do it. Then the net expenditure in energy can be reduced only to the loss due to friction and the conversion between electricity and motion, both of which can be trimmed considerably if I'm not mistaken. So do elevators do this? If not, why not? Edit: Thanks to everyone who answered!
|
[
"I repair elevators. The elevator is usually setup so the counter weight equals the mass of the elevator plus forty percent of the rated elevator capacity. An elevator generally only draws a decent amount of power while starting and stopping. The power saved by using a regenerative drive is so minimal that you'd never recoup the added cost in electricity savings."
] |
[
"Keep in mind that elevators have gigantic counterweights with masses about equal to that of the elevator, so as long as they don't accelerate quickly, they aren't doing as much work as you may think they are. For fun, compare to the ",
"Atwood machine",
"."
] |
[
"I think this is the key point. I was talking with the elevator repairman in my building (mostly to make sure I wasn't going to end up trapped in one of them, because how many times have you actually seen an elevator repairman?) and he said something in passing that lead me to believe that the weight limits on elevators are not because of limitations in what they can support but because of limits in what the motors can move. Because of the balancing, they can get by with such underpowered motors that throwing off the balance substantially can burn one out easily."
] |
[
"What causes the feeling of you 'falling' out of your sleep?"
] |
[
false
] | null |
[
"fast and short answer: the brain confuses your body relaxing with weightlessness, freaks out and tries to deal with falling. "
] |
[
"Radiolab did a segment about the hypnic jerk. ",
"http://www.radiolab.org/2010/sep/20/still-hanging/"
] |
[
"Radiolab did a segment about the hypnic jerk. ",
"http://www.radiolab.org/2010/sep/20/still-hanging/"
] |
[
"Why are so many common pain relievers also fever reducers?"
] |
[
false
] |
Acetaminophen, Ibuprofen, and Aspirin seem to be the most common over-the-counter pain relievers, but they also work as fever reducers. Why does fever reduction seem to go hand-in-hand with pain relief? Is it a trait of the drug itself, or does soothing pain and inflammation in the body reduce fever?
|
[
"But acetaminophen isn't an NSAID, correct? Does it still affect the COX enzymes? It doesn't typically do much for inflammation, AFAIK.",
"P.S. Thank you for digging up the info on the NSAIDs, that does make a lot of sense!"
] |
[
"But acetaminophen isn't an NSAID, correct? Does it still affect the COX enzymes? It doesn't typically do much for inflammation, AFAIK.",
"P.S. Thank you for digging up the info on the NSAIDs, that does make a lot of sense!"
] |
[
"What do you mean by \"responsible for\" in tour first sentence? "
] |
[
"How do spacecraft like Cassini avoid being ripped to shreds by space dust?"
] |
[
false
] | null |
[
"There's simply so little of it. A couple of dust impacts over a whole mission, maybe.",
"I'd be interested in seeing what happens to voyager in a billion years, maybe it would run into some occasional bits in interstellar space and become a cloud of dust heading in one direction. More likely it won't run into much and will eventually get stuck in a huge orbit around a black hole after being swung around a few it was too fast for. Maybe align close enough to something like a star or black hole and get sucked in. A couple billion years from now. Would love to see the condition of it before that happens, though. "
] |
[
"When Cassini first flew between the rings and Saturn (couple months ago), they actually turned the spacecraft to use the radio dish as a shield since they didn't really know what to expect. It actually encountered so little dust, that they opted not to use the \"shield\" in later dives."
] |
[
"Get out. Now that's cool. I'm glad I asked! It was the rings specifically that made me think of the hazard"
] |
[
"Can your eyeballs freeze?"
] |
[
false
] | null |
[
"Eyeballs contain two types of liquid",
"If you had a set of eyeballs, detached from the human or animal body (for example cow eyeballs used for dissection purposes) they would freeze at 32 degrees F or 0 degrees Celsius- or perhaps a few degrees below due to the tissues surrounding the eye.",
"Eyeballs attached to a living human/animal will not freeze unless the entire body is lethally frostbitten-\nWhen the eye is attached to the human body there is a constant supply of warm blood circulating throughout the eye, regardless of the temperature outside. There is also a massive amount of muscle and tissue surrounding the socket to keep the eye warm. So unless the actual body is dying from cold, your eyes will be fine."
] |
[
"Thank you as well."
] |
[
"Can you elaborate please."
] |
[
"Labeling a Protein with GFP?"
] |
[
false
] |
[deleted]
|
[
"Yeah, to echo what rupert1920 said, I'm gonna have to recommend finding a lab that does it and having someone teach you. I was in the unfortunate position once of being the guy in a genetics lab who had to learn some biochemical techniques that no one in my lab was familiar with, and the ",
" way I even got close to figuring it out was by going to a biochemistry lab and having them show me how it was done.",
"DNA cloning isn't ",
" hard really, but it's complex enough that if you just follow some written protocol, and it doesn't work the first time (which it probably won't), you won't even have a clue as to how to troubleshoot it without outside help."
] |
[
"I know this is unhelpful, but in a pure Material lab this is not gonna happen. Aside from the protocol itself (which isn't terribly complicated but can be temperamental), there's just so much ",
" I don't think you have. I recommend outsourcing to another lab or company.",
"Also, what are you mapping exactly? What are you measuring and how do you plan to measure it?"
] |
[
"Thank you. "
] |
[
"Provided you didn't burn, would you float or sink in molten lava?"
] |
[
false
] | null |
[
"You would float. Lava is about 3 times as dense as water, while people are approximately as dense as water. Thus, just as wood floats in water (wood is less dense than water, so it floats), a person would float in molten lava.",
"You can a whole discussion of this ",
"here",
"."
] |
[
"But, the burning is an important thing to consider. Even if a liquid is denser than you, you won't be able to stand in it, you'll end up horizontal and how much you float depends on your buoyancy. You're made mostly of water, and lots of stuff that releases other gases, like co2, when they burn. Now, the part of you that's going to release gasses the fastest is the part of you that is the hottest, so your body injects gases into the lava it is contacting. This is going to create a violently active lava foam, and you are denser than the foam. Pumice floats on water. So the foam will engulf you and your whole body will begin to release gasses, which travel upwards, preventing you from rising through them. But if you sunk beyond a certain depth, the greater volume of lava above you wouldn't contain such a high percent of the gases released by you. So while you will not sink below a shallow depth, you'll still sink until you're ash. ",
"Edit: Guess someone didn't like my explanation, well, ",
"here's a video of garbage being thrown into a volcano. ",
" Does it float?"
] |
[
"That video is incredible. Do you know if the turbulence in the lava is from gasses leaving the trash box and rapidly expanding?"
] |
[
"Is it possible that a mountain taller than the everest existed in Pangaea or even before?"
] |
[
false
] |
And why?
|
[
"The tallest mountain of all time is probably around the height of Mount Everest because mountains hit something called the ",
"isostatic limit",
" whereby they cause the earth's crust to compress from sheer mass. Olympus Mons is another mountain that reaches the isostatic limit, but is significantly higher because of Mars' reduced gravity and less active plate tectonics. The field of paleoaltimetry deals with this and similar questions.",
"EDIT: Damn, this blew up. Lots of questions here I don't know the answer to. I'm not a geologist, just a nerd who remembered a tidbit from an undergrad geology class I took 8 years ago, then confirmed it with Google. =/",
"EDIT 2: ",
"Just found this!"
] |
[
"Probably a lost cause given the number of upvotes the top comment has received, but I feel the need to point out that while ",
"it",
" is correct in the sense that Everest probably represents about the highest mountain we'd get on Earth, the explanation provided along with that is a gross (and largely wrong) over simplification. There are many physical limits on the height of mountain ranges, which include:",
" This is probably the one that gets closest to what is being described in that top comment (",
"\"whereby they cause the earth's crust to compress from sheer mass\"",
"), but has less to do with isostasy and more to do with work (in the energy sense) involved in building topography. For mountain ranges like the Himalaya that are built through the collision of continents, this collision represents the energy input. At a certain point, the amount of work required to continuing to increase elevations exceeds the input and it is \"easier\" to simply expand the mountain range laterally. For those interested in a technical treatment of this, check out ",
"this paper",
". ",
" Isostasy is an important factor, but within that, the really important point is the nature of the lithosphere that the mountain range is sitting on. While thinking of topography on the Earth from a purely isostatic standpoint (i.e. blocks floating in water) works to some extent, the better description is in terms of flexure (i.e. blocks sitting on a taut sheet of elastic). The height of a mountain range (the height of your block measured relative to some reference) will depend on the density and size of the block and the strength, essentially the thickness of the elastic sheet. You could imagine the same exact block having very different heights depending on whether the sheet is very thin (sinks down a lot, block is not very high) or very thick (doesn't sink much, block is much higher). In terms of mountain ranges, this basically depends on the type of material in the mountain range, the shape of that mountain range, and the nature of the lithosphere it forms on. This is largely why Olympus Mons on Mars is as high as it is, not the gravity, but rather because the thickness and the rigidity of the Martian lithosphere is much much greater than Earth's and thus can support larger loads. Coupled with the lack of active tectonics and a fixed source for magma from a hotspot leads to a giant volcano.",
" Probably one of the most important aspects for collisional mountain belts, like the Himalaya are the fact that they have reached the height they are by crustal thickening, basically the crust being deformed and stacked on top of itself. Because of the isostatic/flexural response, as the crust thickens, elevations increase but the depths (and thus the pressures and temperatures) that the bottom, or root, of your mountain range is experiencing also increase. At a certain point, the temperature and pressure conditions reach a point where the material making up the mountain range will change into a very dense rock called ",
"eclogite",
". The eclogite will be denser than the mantle rocks against which it is juxtaposed, which is gravitationally unstable, leading to a process called ",
"delamination",
", where this dense elcogitic root detaches and sinks into the mantle. Going back to the isostasy discussion, there is now a reduced thickness of crust which on the long term will lead to a reduction in elevations of the range.",
" Another huge factor is the effect of climate and erosional processes on the height of mountain ranges. There is a relatively popular idea referred to as the \"glacial buzzsaw\" which predicts (and has been largely born out by data in many of the Earth's active mountain ranges) that mountain ranges generally will not exceed a certain height because of the actions of glaciers, check out this ",
"video that describes the \"buzzsaw\" in a simple way",
". Glaciers are incredibly efficient erosional agents, so once a mountain range reaches heights sufficient to start forming glaciers, the glaciers in turn buzz down the peaks of that range. The height limit imposed by glaciers would obviously depend on latitude (higher latitudes can support glaciers at lower elevations), general climate, and the precipitation patterns in the mountain range (still need precipitation to form glaciers). "
] |
[
"Thank you for the great and clear answer!"
] |
[
"Has science determined the most effective way to study while in school?"
] |
[
false
] |
I know there's a lot of dimensions to the act of studying, i.e duration, intensity, specific study strategy ( e.g outlining, making note cards, etc). I've heard people talk about the Pareto method as the best duration and my teachers have always brought up things like outlining, etc. Is there any one combination that is the best across subjects? Conversely, is there any method that works best when studying mathematics?
|
[
"Not sure if this is what you had in mind, but here are a few thoughts. Also, this isn't my main area of study, so if someone has new thoughts to add, please do.",
"Spacing is better for retention than blocked studying. Adaptive spacing is even better. Most people do this naturally when they have something like flashcards: if you get an answer correct, you put the flashcard at the end of the stack or further back; if you get an answer wrong, you put it only a little bit deep in the stack to have it reappear again soon. This method is better than blocking (studying only one item at a time for a long time). I believe this research has been going on for a long time, all the way to the beginning of the 20th century if not sooner. For example, see ",
"Perkins (1914)",
" or ",
"Edwards (1917)",
". See ",
"Melton (1970)",
" for something a little more recent. And ",
"here",
" is an article (from 1988!) wondering why spacing effect literature has had little effect on classroom/teaching methods. See also ",
"Richland et al. 2005",
" for some more recent thoughts on the matter and ",
"Kornell and Bjork (2008)",
" for applications to category learning.",
"Testing is a memory enhancer. So testing yourself actually improves long-term retention. This is sometimes called the testing effect (e.g., ",
"Roediger and Karpicke, 2006",
"). ",
"There's some work on \"desirable difficulties\" (the part of the Malcolm Gladwell's new book that is under some criticism) that suggest that making study more effortful will increase retention (Bjork, 1994 <- book chapter, so I don't have a link). Similar ideas have been mentioned with respect to difficulty of retrieval as opposed to encoding, e.g., ",
"Pyc and Rawson (2009)",
"."
] |
[
"In the original paper, I believe they simply made the font of the study material more difficult to read (small or blurry). I think the idea was that this required greater effort / concentration to retrieve the material and that this benefited encoding. I'd look for papers by Bjork or Oppenheimer; both are mentioned in the Gladwell book which might be more accessible (although many are a little upset about the conclusions he draws from this desirable difficulty literature re dyslexia).",
"It's not obvious to me how this can be adapted to actual studying when you are by yourself. ",
"A broader takeaway might simply be that greater attention = better encoding. If you are one of those people who study with the TV on in the background, maybe you will actually encode better without the TV even if you feel otherwise. There are a couple of papers out on metacognitive judgments of memory that show that people often feel that they would remember better in certain situations, but actually remember better in others. In other words, we're pretty bad at assessing what conditions are actually beneficial or harmful for learning and whether we've learned / memorized something or not."
] |
[
"Thank you answering my question. Can you talk a little more about what it means to make something \"effortful?\""
] |
[
"When I lift something is my brain continously sending signals to the muscle to contract or does it send one signal to contract and one to relax?"
] |
[
false
] | null |
[
"Continuous signal for continuous muscle work. The signal stops when you will your muscle to relax. The signal itself is in action potentials per second. The neurons firing action potentials on muscle cells telling them to contract can fire more rapidly or slowly, leading to different contractions."
] |
[
"There are more AP/s overall lifting something heavy but not for each muscle fiber as each muscle fiber works in an all or nothing fashion. As in if you're using only your bicep to lift something then as soon as you begin lifting it your body will tell a certain amount of muscle fibers, a motor unit, in your bicep to contract and they will contract to their max potential. When something is heavy to lift it means that the muscle fibers already contracting are unable to lift the object on their own, so the brain begins to recruit more muscle fibers within the muscle to contract, it may also recruit other muscle groups to aid with the lift. When it does this the overall AP/s increases simply due to the increased amount of muscle fibers in use rather than more AP/s being sent to tell a singular muscle fiber to contract stronger as it is already contracted to its limit"
] |
[
"Interesting, and does the AP/s change depending on how much strain there is? Ie is it more AP/s to lift something heavy than something light?"
] |
[
"Why do planes fly?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"https://www.reddit.com/r/askscience/comments/7nlsuf/which_explanation_for_aerodynamic_lift_is_correct/"
] |
[
"https://www.reddit.com/r/askscience/comments/7nlsuf/which_explanation_for_aerodynamic_lift_is_correct/"
] |
[
"What's the science of drinking while pregnant? There is a lot of conflicting information out there."
] |
[
false
] |
I am not a scientist (which is probably apparent by the way I am asking my question). Everything I can seem to find about drinking during pregnancy simply says "We don't really know what's going on, so how about you don't drink, eh?" I am not really satisfied with this answer and have a hard time believing there is not more, uh, science that could be used to explain the matter. I've read that a woman should not drink from the second of conception. But, it seems that most people will end up drinking some time after conception because it's impossible to know that one is pregnant until several weeks into a pregnancy. I've also read that a baby does not begin receiving nutrition from the mother's bloodstream until the fourth or fifth week after conception. So, how would earlier pregnancy drinking even matter? Or, is it just a matter of professionals being worried about the woman's nutrition while carrying the fetus (a concern that if she is consuming alcohol, she may not be consuming enough nutritious food)? Additionally, wouldn't any alcohol that is consumed get filtered out before it reaches the fetus? I have a feeling a lot of the warnings out there about drinking during pregnancy are advising women to be overly cautious and paranoid. This has been asked here before, but there was no satisfying answer given or reply beyond "It's just easier to tell women to not drink at all, rather than to drink in moderation, because you can't trust those who tend to binge drink to know the difference."
|
[
"There's a good amount of data out there on the topic (though of course it is hard to do a real randomized control trial of any sort). Unfortunately, I have yet to see a definitive study that clearly answers all of the questions we have on the topic (partly due to the ethical difficulties in this field).",
"This ",
"systematic review",
" found that a threshold of more than 4 drinks per day was associated with motor deficits in childhood, while a threshold of less than 10 drinks per week was not associated with motor deficits.",
"This ",
"review paper",
" cites 30-40g per occasion and 70g per week as key thresholds for 'child behavior problems'. ",
"This ",
"older meta-analysis",
" found that there was no significant difference in incidence of fetal malformations with moderate alcohol consumption (defined as 24g - 168g of alcohol per week). However, a later study (",
"referenced in this review",
") found a significantly increased relative risk (35% more) for miscarriage with the same level of alcohol use. ",
"This ",
"systematic review",
" found that low levels of alcohol (defined as < 83g per week) was not associated with miscarriage, stillbirth, intrauterine growth restriction, prematurity, birthweight, small for gestational age at birth and birth defects including fetal alcohol syndrome, but notes that caution is warranted with this interpretation due to weaknesses in the studies they analyzed. ",
"This ",
"meta-analysis",
" found that there were no effects on low birth weight and small-for-gestational-age infants up to 10g of alcohol per day (about 1 drink), while preterm birth rates were not affected until 18g per day. After these thresholds, there is a dose-response relationship between alcohol consumption and adverse effects.",
"This ",
"meta-analysis",
" found a significantly lower degree of mental development (assessed using the MDI, a standardized measure) for 12-13 month old babies with any level of alcohol exposure. However, they did not find significant differences for 6-8 month olds or 18-26 month olds.",
"As you can see, the data out there is fairly diverse, with many studies indicating a lower threshold for harm. Unfortunately, the data so far is definitely not conclusive, since many findings are drawn from studies limited by methodologic flaws. Because of this uncertainty, ",
"ACOG guidelines",
" still emphasize that there is no definitive threshold for safe alcohol consumption during pregnancy, but also agree with the above studies that a threshold of about 7 drinks per week puts a woman into a higher risk category. "
] |
[
"Alcohol can absolutely cross the placenta and enter the fetal blood stream. This can cause fetal alcohol syndrome, as alcohol acts as a teratogen after crossing the fetal blood/brain barrier, and can produce substantial central nervous system defects and brain abnormalities. The exact mechanisms by which this happens are debated and likely varied, but it is unquestionable that alcohol produces these effects in the developing fetus. There is evidence that alcohol shows a dose-response relationship (i.e., risk increases with consumption), with effects clearly seen at one drink per day.",
"As for timing, the brain is forming throughout development, so ethanol can always have an influence. The maximal effect of ethanol consumption seems to occur between seven and twelve weeks.",
"I.e., due caution is appropriate. Don't drink during pregnancy."
] |
[
"r/AskScience",
"As always, please refrain from anecdotes, speculation, jokes, and off topic discussion. ",
"Thanks!"
] |
[
"Why do we use mouse fibroblasts and bovine serume to culture embryonic stem cells?"
] |
[
false
] |
I was just reading up on some stuff on the NIH website about stem cells, and they had that bit about their culturing. I don't understand why they need the fibroblast cells (for structure or support?) or the bovine serum. Just general curiosity. If anyone has links or answers that would be great Thanks!
|
[
"The fibroblast cells are usually mouse embryonic friboblasts. These cells release several key factors, including leukemia inhibitory factor, that promote the proliferation of human ESCs. In addition, fetal bovine serum contains many factors that support ESC self-renewal and proliferation. ",
"Over the years there have been many successful attempts to remove animal products from human ESC culture for two major reasons: 1) Contamination of ESCs and their derivatives with animal products is undesirable for a commercial/ clinical product due to possible allergic reactions among patients. 2) The factors secreted are many times unknown so researchers want to understand the complex interactions that support ESC proliferation, self-renewal and differentiation. Towards this end, there are many protocols that use a \"defined\" media replacing serum with Knockout Serum Replacement and adding LIF and/or BMP to human ESC cultures. There are several cell lines now that grow well without the fibroblast feeder layer or serum. The idea is that these lines are more attractive for translational research because there is no contamination with animal products and their media components are defined."
] |
[
"Ah thanks, I got my information from this website, ",
"http://stemcells.nih.gov/info/2006report/2006Chapter1.htm",
", and they never really told me why they used fibroblast cells for culturing. Also, that article stated that LIF, in the presence of serum, was not sufficient to promote self-renewal of human ES cells. Rather, it works for mouse ES cells. Thanks for the help!"
] |
[
"There are several cell lines now that grow well without the fibroblast feeder layer or serum.",
"This. We just started doing this with our human ESCs. So far the morphological differences are minor to none, but we have noticed they differentiate slower. But we definitely want to move off of using the MEFs (mouse embryonic fibroblasts) because it's hard to perfectly replicate experiments."
] |
[
"When is the next time humans will evolve?"
] |
[
false
] | null |
[
"Evolution is a continuous process."
] |
[
"then everyone will be differently evolved, but i dont see it"
] |
[
"Everyone looks different and we all have inherited traits from our parents. Perhaps you mean something else by \"evolution\" than how the word is typically used."
] |
[
"Where does body heat come from?"
] |
[
false
] |
I understand that blood is warm and the cardiovascular system distributes blood/oxygen/heat throughout the body, but how does the blood get hot in the first place?
|
[
"The catabolism of sugar, fat, and protein with oxygen to make ATP (basically transferring energy from chemical bonds to a different type of bond that is used by the body's cells as fuel) is not 100% efficient. This produces heat and thus warms our blood. The blood circulates to your core and warms your body. ",
"Heat and sound are types of energy leaving a system. An engine, for example, is not efficient and loses a lot of energy from combustion of fuel to heat and sound. "
] |
[
"Have you ever stethoscoped yourself? There's a lot of weird noises that your brain ignores"
] |
[
"That is correct, but the amount of acoustic energy is negligible for humans and engines. When screaming you lose far more energy from exhaling warm air than from producing sound waves. "
] |
[
"Is there any genetic or other benefit for tree leaves to get so brightly colored in the fall?"
] |
[
false
] |
I know part of it is just the conversion of the remaining sugars and chlorophyll loss. But it seams to me the trees must get something out of it? Bright colors in nature are usually for mating or spreading of seeds. Neither one appears to be the case with dead leaves. I'm wondering if perhaps the bright colored leaves on the forest floor, reflect more light than dull brown leaves, and therefore help keep the branches/trunks warmer and chemical processes going in the day time? Edit: Found this, "The evolutionary theorist W.D. Hamilton and Samuel P. Brown of the University of Montpelier speculated in a recent paper that the healthiest trees might put on the flashiest fall displays of (anthocyanin) red leaves. They further speculated that this leaf signal might give fall-feeding insects, such as aphids, a warning to avoid trees that are healthy and have the best defenses. This is an intriguing possibility for yet another role of anthocyanin in tree protection." near the end of this paper,
|
[
"The reflected light of the dead green leaves on the forest floor cannot be used by the surrounding living trees whose leaves are the same colour. The green colour that we see is the wavelength of light that the chlorophyll(and supplementary light-absorbing molecules) cannot use. The white light they receive has all the wavelengths, they \"break down\" what they can and reflect what they cannot(that being the wavelengths that look green to us). ",
"Here is a disgusting analogy: You know that you get all your energy from food. Say your food is the photon of white light the plant receives from the sun. Your body digests the food similar to how a plant digests sunlight. Whatever you cannot digest you \"emit\", likewise, whatever wavelength the plant's leaf cannot absorb, it \"emits\". ",
"So, following along with this analogy, theorizing that plants use the reflected light of other leaves for energy, would be like saying... well, I don't really have to say it."
] |
[
"Yes, that part is fairly obvious about the green light, But I was asking if there was any benefit of them changing to the bright colors. I would imagine its a teeny one if at all. "
] |
[
"There is no advantage to the colour itself. They are brightly coloured as they are because the tree is producing more chlorophyll than xantophyll, carotene and other pigments that typically reflect other colours. Chlorophylls absorb more energy than other pigments, so the plant produces much more of it than it does other pigments. In the fall, when there is less sunlight, plants stop producing chlorophyll and the other pigments become visible. The other pigments were always there, but the plant needed chlorophyll so much more that the amount of chlorophyll prevented the other pigments from showing their colour."
] |
[
"How strong does a drink have to be to dehydrate you?"
] |
[
false
] |
Alcohol inhibits ADH secretion which leads to the old "one drink in two drinks out." Do drinks below a certain percent alcohol by volume hydrate you while drinks over that point dehydrate you?
|
[
"This is not an actual answer to the question. Please read the ",
"r/askscience",
" posting guidelines."
] |
[
"In the past, people would brew beer/wine at the same strength that we do now, but they would water it down significantly before consumption (3-4 parts water to one part beer). A weakly alcoholic drink is enough to kill most pesky water-bourne pathogens. This is why children in medieval times were able to consume beer and wine without being intoxicated all the time."
] |
[
"Question: Do you have a source for your 2 in 1 out info? I've never been able to find one. "
] |
[
"Do the languages we speak affect how we perceive (not reproduce) sounds?"
] |
[
false
] |
EDIT: I appreciate the responses so far, thank you! Are there experiments where the same sound (a linguistic sound) was heard by two people with different native languages?
|
[
"Yes, absolutely. We build a phonological model in our head that is trained to recognize a subset of all possible phonetic segments. This allows us to error-correct in our native language more easily.",
"For instance, in my dialect of English, I have the vowel /u/. This is a high back rounded vowel, the one in the word \"boo\". I do not have the vowel /ɯ/, which is the unrounded version. (This vowel exists in Japanese, FYI.)",
"If I hear [ɯ], I'm going to analyze it as /u/, not /ɯ/. This means we can be a bit sloppy when talking and people aren't going to be terribly confused that I pronounced a different vowel, because anything \"close enough\" gets analyzed as the familiar phoneme.",
"Edit: also not sure why this is flaired neuroscience when this is in the clear purview of linguistics."
] |
[
"also not sure why this is flaired neuroscience when this is in the clear purview of linguistics.",
"Well he does speak about perception which would go under neuroscience.",
"And also in that sense the answer is absolutely. We actually hear different sounds differently depending on our language proficiency. Two sounds that sound exactly the same to me can sound very different to someone else speaking different language. So it's not just that we bundle \"close enough\" phonemes together in conscious level. It's also that we bundle them together in the \"preprocessing\" stage. ",
"In general our hearing is much more convoluted than just analyzing frequencies and amplitudes of sound. For example what we see actually affects what we hear. Different lip movement combined with same sound actually changes the perception of the sound, not just our interpretation of it. "
] |
[
"There's a higher rate of perfect pitch among native speakers of tonal language like Mandarin, Cantonese, and Korean. In English for example we use pitch to adjust inflection, for instance when asking a question you'll raise the pitch of your voice at the end of the sentence. In tonal languages pitch inflection is used to actually change the meaning of individual words and are a part of their phonemes. The suggestion here is that perfect pitch may be an innate trait of many people but only exhibits itself if the skill is developed, as tonal languages use more pitch changes it's suggested that plays into how likely a child is to develop the skill. ",
"That said if you think of music as a language, musical training has a huge impact on our perception of sound and much more so than language. Musicians for example have better sound localization (identifying where a sound comes from), they're better at isolating a sound from background noise, and have better pitch perception (perfect pitch almost exclusively is seen in people who play music from an early age)."
] |
[
"Do dogs actually have no concept of time? do any animals?"
] |
[
false
] | null |
[
"I don't believe your premise is correct. There is an obvious difference in the way my dogs react after not seeing me for a week versus a few hours. ",
"I recall a documentary I saw that analyzed a dog's ability to seemingly know when it's owner was home before the owner was within eyesight of the front door. ",
"The dog knew approximately what time the owner came home and what type of car sounds to listen for. The dog would be fooled if similar car sounds were made around the same time, but not react if the correct sounds were made outside of the normal window of time the owner came home. To me, this would indicate they have a sense of time."
] |
[
"Thank you. I changed the wording of the question"
] |
[
"There's no way of definitively knowing how other animals perceive time, and research on how dogs perceive time is rather limited.",
"There's a good article at discovery here:",
"http://animal.discovery.com/pets/dogs-perceive-time.htm",
"Also note that things like circadian rhythms, knowledge of daily feeding times, etc., show that dogs do have some level of understanding of time."
] |
[
"Just like in supersonic motion, the object that creates the sound can move faster than the waves it produces, is it possible for the E-field or B-field that make up light to move faster than the light?"
] |
[
false
] | null |
[
"The light (i.e., the electromagnetic wave) ",
" the E- and B-fields. So the answer to your question is trivially \"no\"; something cannot travel faster than itself.",
"But perhaps you mean to ask whether a source of light can travel faster than the speed of that light ",
". So, for instance, can an underwater light source travel faster than ",
". Yes. That's perfectly fine. That particular question is commonly asked and a common example of this phenomenon (called ",
") is seen in the typical blue-ish glow of underwater nuclear reactors."
] |
[
"Yes. ",
"Sort of.",
" The mechanisms for the production of sound and light waves are different, so obviously the analogy should not be taken too literally. "
] |
[
"So is Cherenkov Radiation a sort of 'superluminal flash', analogous to supersonic booms? "
] |
[
"How many calories do you lose when donating blood?"
] |
[
false
] | null |
[
"most people die if they donate too much\nprobably"
] |
[
"Anything over a pint every 56 days. Not to mention it's dangerous to do much exercise for a number of hours after. It'd be an extremely dangerous or inefficient way to lose weight. Just watch your caloric intake and exercise regularly."
] |
[
"This guy calculates it at about 450 calories.",
" He took into account blood glucose, sugar, fat, and red blood cells."
] |
[
"What will be the effects to Europe/the rest of the World if the Bardarbunga volcano erupts?"
] |
[
false
] |
Or should it be a matter of 'when', not 'if'. And if I may add - could this eruption trigger the other Icelandic volcanoes on the same 'chain'?
|
[
"This depends on a number of things, but chiefly a) what kind of magma is down there and b) what the weather patterns are like at the time.",
"Bárðarbunga is particularly well known for its lava flows, which generally require low gas contents in the magma. That means the eruptions will generally be effusive - so rather than big clouds of ash you tend to get a much lower ash discharge. That is in contrast to the Eyjafjal and Grímsvötn eruptions in the last few years, which produced significant ash plumes, due to a high gas content.",
"Now, Bárðarbunga is beneath a glacier, and that can provide enough fluids through melting to make the initial phases of even a low-gas eruption form large ash plumes. however, that would likely only be the case for a few hours.",
"As far as the weather patterns go, if there ",
" an ash cloud, it is very much at the whims of the variable high and low weather systems in the North Atlantic. It's not unlikely that a large ash discharge would shut down much of North European airspace again though. That's about the extent of the hazard though.",
"As far as triggering other volcanoes, the geology of iceland is very complicated, and there are certainly volcanoes which seem to share some aspects of their plumbing system. However, this is far from the norm, and in even in those cases where it is true, the high-level magma chambers are generally not related. So while a particular magma supply may result in some volcanoes showing similar behaviour, there is ",
" little evidence to suggest activity at one volcano influences activity at any other."
] |
[
"Possibly, but it depends on the plumbing system and where each feeds off from. "
] |
[
"Thank you for replying! I appreciate the explanations. "
] |
[
"Is the vacuum of outer space fundamentally the same as the empty space between particles like electrons and proton? Or are they different somehow?"
] |
[
false
] |
To be clear I'm not suggesting that planets and stars are equivalent to protons and elections. I'm just curious about the empty space. I've heard that the vacuum of space is actually supposed to be an energetic place because of virtual particles, how does this compare to the mostly empty space of an atom?
|
[
"An atom is not mostly empty space. This is a common misconception. The electrons, protons, and neutrons that make up an atom are not little solid balls separated by vast expanses of empty space. They are quantum objects that act somewhat like waves and somewhat like particles. In an atom, the electrons act mostly like waves and are spread through-out the entire atom into shapes called \"orbitals\". An atom is therefore not empty, but filled with electrons spread out into wave states. ",
"Although outer space contains fewer atoms than Earth's surface, it does contain some. Perhaps you mean the regions in outer space between atoms? This is not that much different than the regions of space inside atoms, although the mass and charge density are much lower. The key concept is that electron wavefunctions are not completely contained in a rigid sphere you would call the atom. The electrons in an atom spread out diffusely far beyond the atom. The electron wavefunctions will be very small in a region of space a few meters away from all the nearest atoms, but in principle it will not be zero. So, the region between atoms is not fundamentally different than the region within atoms. Both have wavefunctions and fields.",
"Both the space between atoms and the space within atoms contain vacuum fluctuations. In an atom, the electric fields are stronger because you are closer to particles, and this stronger field has more of an effect on the vacuum fluctuations. But fundamentally there is no difference."
] |
[
"Here's the problem: in quantum mechanics, there's a clear division between what you see and what is actually there.",
"The truth is that there is a wavefunction, which governs the probability of what you see at any given time. Imagine the universe as a giant spinner, and every time you take a measurement and make an observation, you see the results of the spinner. However, you never see the spinner itself, merely the results of the spinner. Also, we will never see the actual spinner, because the act of observing it is what causes the spinner to spin. The good news is that we can calculate the spinner. Sorry if this is confusing to you.",
"Part of the problem is that you want to see the wavefunction; you want to see the whole reality. But you can never see the wavefunction, you can only see what it spits out when you measure it. Trying to visualize it is impossible because the instant a photon hits the wavefunction, it collapses (or becomes entangled). The wavefunction is all math, it's not a reality with which you can familiarize yourself."
] |
[
"I've heard this wave/particle explanation before and I know it has something to do with observance, but I've always had difficulty trying to visualize what a subatomic particle would actually LOOK like, say, if you magnified it to size of your palm. Is trying to visualize it just an exercise in futility?"
] |
[
"When was there a 'cosmic visible light' background?"
] |
[
false
] |
Since the expansion of space causes the wavelength of cosmic microwave background to lengthen, presumably it would have covered other parts of the electromagnetic spectrum in which wavelengths are shorter. We also seem to have a pretty good idea of the rate (and rate of acceleration) at which space expands. So at what point in the history of the universe could I look around me and see blue everywhere? Is there an equation for this? I'm not afraid of math.
|
[
"Shortly after the Recombination era - the era from which cosmic background radiation originates - the cmb was bright orange. ",
"To understand what exactly happened, let's backtrack a bit.\nUntil 380 000 years after the big bang, the universe was too hot to form neutral atoms. Electrons and protons whizzed through space which such high speeds, that electromagnetic attraction wasn't strong enough to bind them together. Thus, space was filled with a hot plasma, that gave off thermal radiation. During this time, the universe was opaque to photons. Photons would bump into electrons frequently. This scattering of photons results in a mostly in-transparent universe with a visibility of a few thousand lightyears at most. (Which sounds a lot but is very small at cosmic scales)",
"Due to the expansion of the universe, this plasma finally cooled down to around 3000K. Which is cool enough to form neutral atoms around 400 000 years after the big bang. Since neutral atoms don't interact with photons that willingly, the universe became transparent. Thus, the thermal radiation of the plasma in the recombination era was emitted into all directions and from all points in space. And since the plasma was around 3000K at that time, and the black body radiation at that temperature is orangy, the hole universe was filled with orange light for a few million years.",
"The universe during the first few million years after the big bang saw the first stars being formed, but during this time, the only radiation emitted was the hydrogen line.",
"Over time, as the universe continued to expand, the cmb got redshifted. Now, ~13 billion years later, the cmb is redshifted down to around 2.7K, which is in the microwave part of the spectrum. "
] |
[
"By the time planets (solid objects you could stand on) had formed, the background radiation had already expanded and cooled below the visible range of the electromagnetic spectrum. Space was already \"dark\" before the first planets formed. "
] |
[
"Just to make sure I'm following. There was no point in time where there was a solid surface to stand on and the night sky did not appear black with spots in it correct? "
] |
[
"Does milk spoil inside of female mammals?"
] |
[
false
] |
If a female, let's say cow, isn't milked for a while, does her milk spoil in the same way milk spoils if left out in a similarly temperatured container?
|
[
"It’s possible. Mastitis is an infection of the breast or udder, due to pathogenic bacteria gaining access to the breast milk. However, under normal conditions the environment that the milk is in is highly controlled, sterile condition. "
] |
[
"This is just nonsense, and dangerous misinformation. Natural milk absolutely spoils and raw milk is far more hazardous to health, it has a higher bacterial content and spoils quicker. There is more to producing yoghurt than just leaving milk out to spoil, as anyone who has left out milk (yes even 'natural' milk) will know.",
"One ",
"Source",
", but there are many more out there."
] |
[
"This is just nonsense, and dangerous misinformation. Natural milk absolutely spoils and raw milk is far more hazardous to health, it has a higher bacterial content and spoils quicker. There is more to producing yoghurt than just leaving milk out to spoil, as anyone who has left out milk (yes even 'natural' milk) will know.",
"One ",
"Source",
", but there are many more out there."
] |
[
"If I was in intergalactic space such that a nearby galaxy filled up my entire field of view, would I be able to see it clearly? Or would it still be as dim as the milky way is in the sky here on earth?"
] |
[
false
] |
[deleted]
|
[
" This is why you need about the same darkness of sky to see both the Andromeda Galaxy as well as the Milky Way.",
"As you approach an object, the brightness of an object increases as the distance squared, but the total amount of area in your field of view will ",
" increases as the distance squared. The result is that while you get a lot more photons, it's spread over a lot more area, and the total amount of \"surface brightness\" - brightness per square degree - remains constant.",
"Note that this only works for resolved objects like galaxies and nebulae, when the entire object is already large enough to resolve as more than a point. For point objects like distant stars, it actually will get brighter; if you get twice as close to a distant star you'll get 4 times as many photons but it will still appear as a point, and thus appear brighter.",
"For nearby stars such as the Sun, though, this constant surface brightness ",
" work. The total sky area the Sun takes up is about twice as large at Venus, so you'd get a total of about twice as many photons as we do here on Earth. However, if you cut a 1/4 degree x 1/4 degree hole in a black piece of paper and held it up to the Sun in both places, that tiny patch would be just as bright."
] |
[
"This is one of those extremely disappointing facts about reality. Even if we get magic spaceships and zip around nebulae and dart from galaxy to galaxy without a care in the world, to our eyes, it would be mostly pitchblack, with faint smudges of gray. ",
"Those romantic images of space stations suspended in pink mist, surrounded by blue wisps of ionized gas, are reserved for our robot children."
] |
[
"You know whats truly amazing? You don't even need to be a professional astronomer to be able to get to see the beautiful colors out there. ",
"I've just started to get into astrophotography, so I'm not that good... But for somewhere between $500 to $3000 and a bit of patience you can see the beauty of the universe from your own backyard! ",
"/r/astrophotography",
" is quickly becoming my favorite sub... For the past few months I've been in love with it, but now, I was finally able to get my own telescope and photography setup... If you (this Is directed anyone, not just YOU) get a chance to see the universe through a good telescope, take it. Because it will truly change your life.",
"Hubble images are beautiful... But to see a nebulae with your own eyes, even if the quality isn't that great... Well that's a whole new experience. It's like you're really a part of the universe in that moment. Like it isn't 100,000 light years a way."
] |
[
"How does WiFi go through walls?"
] |
[
false
] |
So to my understanding, WiFi is Bluetooth; which is infrared light. Infrared light waves are less intense then electromagnetic light (the visible light). So how can my wireless router a few walls away from my computer send light information to it if I can't see it Line Of Sight? Does it act as a wave ? Does it go through the wall? Do the atoms that make up the wall, hold and then release the light wave? And if infrared red light can travel through or around walls why can't we see around or though walls? TL;DR How does WiFi travel where normal light doesn't?
|
[
"WiFi isn't bluetooth and neither is infrared light. Your basic WiFi is ",
"radio waves",
" in the 2.4, 3.6 and 5 GHz frequency bands, ",
"from standards definition IEEE 802.11",
". ",
"Bluetooth uses ",
"short wavelength radio transmissions in the ISM band from 2400-2480 MHz",
". ",
"So both use radio waves, neither is infrared light."
] |
[
"First: Intensity and Frequency are two independent properties of light. Infrared is lower frequency than visible light, but can be both more or less intense (think power).",
"Second: Light of all frequencies penetrate most materials, but the attenuation experienced is generally inversely related to frequency. That is, higher frequencies get blocked easier than low frequencies, so it's easier for lower frequencies like radio to pass through walls that are typically opaque to visible light. Higher attenuation factors can be overcome with more intensity (higher power), although it can be very impractical in most cases. ",
"To answer your question, WiFi isn't Bluetooth, but it transfers information via modulating an EM wave in the radio frequency band. It's basically like a fancier, low-power version of FM radio. "
] |
[
"Radio waves are also lower in frequency than the visible spectrum... so the same way that radio waves do it :D"
] |
[
"When your body responds to changes in temperature by doing things like sweating or shivering, is it our minds’ perception of the temperature that causes this or does the temperature somehow directly do this?"
] |
[
false
] |
Since that was probably a confusing title, here’s an example: if you were sitting in the snow and it was below freezing out, yet somehow in your mind you were completely convinced that it was warm out and that you weren’t cold at all, despite your internal temperature dropping, would you still start shivering?
|
[
"It's all regulated by your brain, but it's not a conscious thing. As an interesting example of this the reason you feel chills when you have a fever is because there are chemicals being released in your body in response to an infection which increases your body's \"thermostat\" to a higher level. In the time between your body raising the \"set point\" (a rapid change) and actually increasing the temperature to the new \"set point\" (a slower change), your body thinks it is colder than it should be, inducing the chills in spite of an actually elevated temperature. So manipulation of the brain via medications such as antipyretics can also change how the body interprets its thermodynamic state to some degree. That being said, this is not a conscious decision, so you wouldn't be able to run around outside in the cold and not shiver, in the same way you can't will yourself to not feel pain or hunger."
] |
[
"Unrelated but the dudes who walk on coals aren't actually nearly as impressive as they first appear. By stepping quickly you don't give the coals much of a chance to actually transfer the heat into your feet and there's water on the ground before and after, so their first few steps are just producing steam and they're cooled off immediately after the walk. It's mostly an illusion with the rare exception of the ones who actually ",
" burn themselves with them slowly in a ",
"\" feat but they're pretty rare."
] |
[
"Unrelated but the dudes who walk on coals aren't actually nearly as impressive as they first appear. By stepping quickly you don't give the coals much of a chance to actually transfer the heat into your feet and there's water on the ground before and after, so their first few steps are just producing steam and they're cooled off immediately after the walk. It's mostly an illusion with the rare exception of the ones who actually ",
" burn themselves with them slowly in a ",
"\" feat but they're pretty rare."
] |
[
"Is there always a set number of atoms in the universe?"
] |
[
false
] |
I mean like is/will there be/was there always the same amount? Ofcourse we won't know the amount if so I just really need to know this. Always bothered me since I was young.
|
[
"No. Nuclear fusion and fission will change that number."
] |
[
"Mass doesn't. It changes in nuclear processes.",
"Locally, energy is constant, but not cosmologically."
] |
[
"True.",
"It should be said though that the total mass/energy of the universe remains constant (remembering that energy and mass are equivalent with E=MC"
] |
[
"How factually correct is Haldeman's depiction of time dilation in the Forever War?"
] |
[
false
] |
I was recently finished The Forever War by Joe Haldeman and I was curious as to how accurate his representation of relativity and the flow of time is throughout the novel.
|
[
"Can you describe it for people who haven't read it?"
] |
[
"Yeah, no problem. This if from the first section of the novel. Essentially humanity is engaged in a war that branches out across the galaxy. Humanity has near light speed travel technology and their ships can reach speeds up up to ninety percent the speed of light and uses this technology to travel between Collapsars, which the book describes as wormhole like phenomenon that allow ships to travel thousands of light years in a very brief amount of time (mere seconds to minutes). In the first battle with the enemy they travel at maximum speed from a base planet, enter a collapsar, fight the battle, and return through the collapsar. While this encounter occurred over only two years to those involved, back on Earth over 25 years have passed. "
] |
[
"I happens to be in the middle of reading it right now. It's not mathematically correct. At 0.9c, it would only slow down by a factor about 2.3, so 2 years would be 4.6 years, not 25.",
"Edit: to have 25 years pass on earth, it needed to be traveling at about 0.9968c."
] |
[
"Can anyone give a comprehensive explanation of sunglass lenses?"
] |
[
false
] |
Reading up on sunglasses is confusing as heck, especially for anyone hoping to save a bit of money. There's a lot of science here, and I'm having a lot of trouble finding a proper comprehensive rundown of everything that's involved, and what it all winds up meaning for consumers. First you need to decide wether you want CR-39, Polycarbonate, Trivex, or Glass lenses. Does it even matter? Well, it might. If you're buying cheap and the glasses don't come with much (or any) reliable info, at least you'll know they're relatively UV resistant if they're Polycarbonate or Trivex, because that's a natural quality of those two solutions. Even still, they're not naturally UV400 compliant, so additional treatment/layers/coatings are needed to achieve that. Speaking of which, what the heck is UV400 and how does it differ from the other standards? Which is best? How much does it matter if you get a pair of sunglasses that doesn't explicitly comply. Are there various levels of compliance? What about how UV and Polarization are even achieved? There are different methods, but what are they, and which are the most effective/desirable? Again, how much does it really matter? I know if it's a coating that easily wears off, that's bad, but how common is that? I've read that some Polarization is incorporated right into the lens itself, some are layered into the middle of the lense between sheets of glass, and some are just a film that's applied to the outside. What are the differences? There's no Polarization standard as far as I know, so how do you know what you're getting? Which is best? I've heard lens clarity and uniformity can be a big deal, but aren't always easily perceptible. I've heard ones with lower clarity/uniformity can stress eyes and eventually cause notable eye problems. Is that accurate? How does one identify good lenses in this regard? I'm sure I'm missing quite a bit, but I hope someone who knows more about this topic can give a lot more information. Thanks!
|
[
"Whatever you get, you ",
" want polarized lenses. Sunlight reflecting off of surfaces tends to be strongly polarized in the horizontal plane while polarized lenses are polarized in the vertical plane (fun experiment--try rotating a polarized lens held between you and any horizontal surface with a light reflecting off of it; you'll see the reflected light \"turn on and off.\" This even works with store lighting reflecting off of a shiny floor). This works for sunlight reflecting off of pavement, cars (windows, bodies, chrome, etc.) water, buildings--you name it. I never drive without my polarized sunglasses."
] |
[
"Second that, polarized lenses is a very good feature. Good for drivibg and also very good anywhere near water. I use my polarized sunglasses on boat vacation, It helps a lot with eyestrain from reflections and makes it easier to see reefs right beneath the surface."
] |
[
"Even more fun - put the first two sunglasses at right angles to each other so they are blocking light, then put a ",
" pair between them at 45°. Light gets through again!"
] |
[
"Why/how does resetting a router fix so many connection issues?"
] |
[
false
] | null |
[
"Longtime computer tech here. ",
"This is a very wide open question! The rebooting of the router can resolve DNS resolution issues on both the WAN side and the LAN side. Your modem may require authentication between the router and the modem and that has failed, thus rebooting the router allows the modem to resync with it. ",
"It goes on and on: ",
"Routers, like any computer system, has software on it that may be in a glitched cycle that it cant get out of. ",
"Every time a router boots up it goes through a form of POST (just like the first few images you see on your computer, the Power On Self Test) that can detect and remedy several issues. ",
"Sometimes the problem is on your computer and rebooting the router fixes it because the connection is shut down for a moment allowing the OS to resolve its issues. ",
"It goes on and on. It mainly has to do with what the problem was that interfered with your internet connection to determine ",
" the rebooting of the router resolved it. "
] |
[
"On a very simplified level, a router is a ",
"finite state machine",
" - a software construct that is designed to operate in a fixed number of states and can transition between these states based on predefined rules.",
"For example, the states might be:",
"And the rules might be something like:",
"This type of state machine is a very common construct in computer science, though it is often a gross oversimplification of what really goes along behind the scenes - it is more true to think of a router as a complex system of hundreds (probably thousands) of interconnected state machines, each with its own area of responsibility.",
"As you can imagine, creating a set of rules that can fully cover all the situations that a state machine can be in get very tricky very fast once you have pieces that depend on other pieces. This is why modern electronics often fail - a situation develops that was not properly accounted for in the states and rules that make up the product or some of its components.",
"For example, the rules I made up above contain a flaw. There is no rule that ever takes this imaginary router out of the Not Connecting state! This means that after configuring the router, you need to restart it, causing it to pass through the Starting state once more.",
"The same happens with many cheap routers, since the environment they are tested in is bound to be simpler that real world scenarios, causing many shortcomings to not appear during product development. For example, a large spike in data sustained over half a minute might cause the component that manages data input/output buffers to mess up its internal accounting, so it forever thinks there is no place to put the data that is coming from the Internet. You can try this out with consumer-grade \"Gigabit\" network gear - if you saturate the connection and really give it a gigabit per second of data, some such devices will stop functioning until a restart.",
"This is, of course, only one possible explanation, though a rather fundamental one. Much of everyday troubleshooting done by IT personnel revolves around trial-and-error experiments to try to determine the conditions that cause such failures and to find workarounds for them (e.g. configure the devices so that the problematic situation is not encountered)."
] |
[
"To add another one, most cheap residential routers have a very limited supply of RAM. Depending on how the router is configured, many open connections could cause the router to refuse new connections, thus leading it to effectively shit the bed. I used to see this with my old router all the time whenever I had a bittorrent client open: half an hour in, the router would crap out and it would have to be reset to clear its RAM and allow it to start fresh."
] |
[
"If I write a program that generates every possible version of a 50KB jpeg file, do I then have a picture of everything that exists in the universe?"
] |
[
false
] |
This kept me awake tonight: So if I generate every possible jpeg image I should have a picture of everything that exists, has existed or will exist in the future. And also pictures of everything that doesn't exist.
|
[
"The amount of combinations how you can fill 50KB is limited.",
"It's finite, yeah, but it is BIG. I just calculated an approximation and tried to post it, but reddit literally won't let me make a post long enough to contain the number. In fact to post the entire number of 50KB binary files in decimal I would need to post 12 comments, each the maximum length of 10,000 characters long. Not all of those will be valid JPEG files, but you get the idea.",
"The number of possibile 50KB jpegs is big on a scale that's pretty much impossible to imagine. It's so big that there's really no way you could actually do this.",
"To go further, the absolute shortest length of time which makes sense in physics is called the Planck Time. The fastest any computer could ever do anything in our universe even in principle is a big multiple of this. Our universe is expected to last perhaps 1E1000 years total. If you started at the big bang and calculated as fast as any computer can in principle (in fact much faster), and generated one 50KB binary file per planck time, by the time the universe ended completely you would have generated 6E-119360% of the possible combinations. That's 0.0000<about a hundred thousand zeros>0006%. Never mind the storage space. It's fair to say that \"every 50KB file\" is a thing that simply cannot exist in our universe.",
"Edit: Due to complicated physics things specified in replies to this post, the planck time stuff isn't quite right. Generating all those images is still not going to happen though."
] |
[
"I remember being 12 years old when I just figured out how to render sprites on my ZX Spectrum. I had the exact same thought as the OP and actually wrote a program to generate all possible sprites of 16x16 pixels. I thought I was going to sit back and watch every porn picture imaginable unfold before my eyes.",
"1 hour after typing RUN I was looking at a couple of lines of what looked like morse-code wiggling about and I realized I had greatly greatly underestimated how big a space 2",
" really was."
] |
[
"To go further, the absolute shortest length of time which makes sense in physics is called the Planck Time.",
"This doesn't affect the correctness of your answer, but I thought you might like to know that the above statement isn't quite true. The Planck length (and accordingly, the Planck time, which is a measure of temporal length, also called duration) is the scale at which we know quantum corrections to general relativity become significant. That does not mean it is the shortest length of time, or even the shortest length of time that makes sense -- it's the shortest length of time we can theoretically probe accurately without a quantum theory of gravity. However, even quantum mechanics treats space and time as perfectly continuous (in QM it is the ",
" that are quantized, not spacetime), so there is no reason to believe a quantum theory of gravity must have a minimum distance/time scale.",
"There ",
" models of spacetime such as loop quantum gravity that treat spacetime as discrete, and use the Planck scale as the scale for quantization of spacetime, but (a) none of these models have evidence supporting them as of right now, and (b) many of these models predict that photons travelling very long distances would experience some diffusion due to interaction with quantum fluctuations on the order of the Planck scale, but images from the Hubble telescope have failed to show the calculated blurring. There is still plenty of debate over whether or not the blurring was calculated correctly, though."
] |
[
"If the energy:mass ratio changed, would gravity change?"
] |
[
false
] |
Is the amount of energy-stuff that matter is equal at all relevant to the amount of gravity it pulls off?
|
[
"Are you asking about the equivalence principle?"
] |
[
"Yes, it would change. A good example is the expansion history of the universe, as the expansion rate is governed by gravity. In the early times, the universe was filled with particles that moved nearly at the speed of light, so most of their energy was kinetic. As the universe expands, this particle soup cools down, and they lose their kinetic energy. After some thousands of years pass, the particles move slower and slower, until finally their speed is essentially zero (what we have today).",
"Now, it's not very difficult to show that the expansion law the universe follows is different in these cases. For the first (radiation dominated) case, the universe expands like t",
" . In the second (matter dominated) case, it expands like t"
] |
[
"The transition between the two is smooth (but reasonably quick, cosmologically thinking)"
] |
[
"How is a species declared extinct?"
] |
[
false
] |
Pretty much the title. Who declares it officially and how is it determined with any certainty that's it's gone and not just difficult to find, especially smaller species in large ranges?
|
[
"It used to be easy. The convention was that if a species hadn't been sighted in 50 years it was considered extinct, but as of the 90's, according to the International Union for Conservation of Nature:",
"\"A taxon is Extinct when there is no reasonable doubt that the last individual has died. A taxon is presumed Extinct when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form.\"*",
"Hth",
"*",
"http://www.iucnredlist.org/static/categories_criteria_3_1"
] |
[
"That makes sense, thank you"
] |
[
"How does this apply to species which only exist in captivity e.g. axolotls? Are they considered extinct?"
] |
[
"Why did physicians historically administer vaccines into patients buttocks as opposed to the Arms/thighs?"
] |
[
false
] | null |
[
"Are you sure you mean vaccines and not antibiotics? Many vaccines are delivered to the arm/thigh, including mmr and smallpox.",
"More fat/muscle to hold the shot. Penicillin is administered to the buttocks, and it's a large injection. Add in the fact that it's often fresh from the cooler so it feels like peanut butter. All together this means that you can't give someone a full dose in the arm, especially if they're skinny or a child/baby."
] |
[
"There's a maximum injection volume depending on the intramuscular injection site, i.e. Deltoid 0.5-2 mL vs. Dorsogluteal 4 mL. This ",
"article",
" touches on the rationale/history a bit."
] |
[
"Add to that higher vascularization. A muscle as big as the gluteus maximus has way more blood going through it compared to a small muscle such as the deltoids."
] |
[
"Why do we hate waiting so much? What is the factor which separates waiting from resting and relaxing??"
] |
[
false
] | null |
[
"Waiting combines two unpleasant things: frustrated (blocked) progress and loss of control. The frustration-aggression hypothesis has good support, though I don't know as much about scientific support for negative reactions to loss of control."
] |
[
"The frustration-aggression hypothesis has good support",
"This is a theory of aggression, not of frustration. Frustration alone is a negative reaction to waiting (via goal obstruction).",
"Edit: To be clear, by invoking the frustration-aggression hypothesis, sleepbot is suggesting that waiting leads us to aggress. This seems unlikely (or at least, I'm unaware of any research suggesting this). On the other hand, we can more straightforwardly say that waiting makes us feel frustrated (the negatively valenced, low arousal form of anger), since waiting prevents us from immediately proceeding toward our goals. Whether this frustration causes us to aggress depends on a lot of factors (see Baron & Richardson, 2004)."
] |
[
"Dude this is why I want to be a psychologist. It's so interesting learning about what fuels human behavior."
] |
[
"Realistically, not like in movies, how much force does it take to knock someone out?"
] |
[
false
] |
[deleted]
|
[
"Knock outs are less about absolute force from the punch and more about the forces acting on different parts of the brain. Specifically, a strike that causes the head to twist either down up or side to side can place sufficient stress on the brain stem leading to loss of consciousness. Not surprisingly, variables associated with loosing consciousness are related to neck length, and neck muscle strength which can absorb some of the twisting forces. "
] |
[
"It is certainly possible"
] |
[
"As an aside, the way people are knocked out in movies where they lose consciousness for several minutes (or however long the plot requires) is very, very unrealistic. If someone is out for more than a few seconds it means they have a very serious, possibly life threatening injury and will show very obvious symptoms when and if they regain consciousness. ",
" is a good example of a show that treated concussions as an on/off switch for the brain (they aren't)."
] |
[
"If the moon had seas, how would the tidal forces compare to Earth seas?"
] |
[
false
] |
Would there be tides at all? Would they be stronger, weaker, act any differently etc?
|
[
"The moon is tidally locked to earth (the same side is always facing us) so ignoring the sun and the moon's elliptical orbit and axial wobble, there would be no tides at all.",
"In reality the solar tides are still important, so the moon would still have tides with a period of 14.75 (earth) days, half the ",
"synodic month",
". I don't think the effects of the elliptical orbit and axial wobble would be significant compared to that.",
"It's hard to say how high the tides would be, since tides are very dependent on topography. On earth the tides range from zero in assorted places, to the Bay of Fundy where the sea level changes by 16 meters in 6 hours.",
"That tidal wave in Interstellar is artistic license, a planet with a deep global ocean wouldn't have noticeable tides."
] |
[
"What are you even saying?",
"That was a planet revolving around a black hole.",
"Ok. But that has nothing to do with what I said. I mentioned that there were at least some shallow areas on the planet (in response to the 'deep global ocean' line)",
"We revolve around the sun",
"I won't argue with that, but again this has nothing to do with anything. I wasn't talking about ",
". I was talking about a movie.",
"Which is nothing in comparison",
"You can't know that. How far was the planet from the black hole? The Moon is nothing compared to the Sun. Why does the Moon have a larger effect on our tides? (Don't answer that)",
"In fact, they should have felt a lot more weightless",
"You can't know that. If they were on the side facing the black hole or facing away from it, yeah they should have felt a little less weight. But this would not be the case near the black hole's \"terminator\" on the planet (for lack of a better term)."
] |
[
"That tidal wave in Interstellar is artistic license, a planet with a deep global ocean wouldn't have noticeable tides.",
"This doesn't change your point, but the water is actually quite shallow, at least in that area. ",
"Still"
] |
[
"Why is homebrew considered safe to drink, but distillates from said homebrew considered unsafe due to methanol?"
] |
[
false
] |
Or rather why do people claim this? shouldnt there be a similar quantity of methanol predistillation as post? does methanol interact with the body differently at different saturations? it just seems odd that drinking 4 beers is safe but 2 shots from the same product minus a bit of h2o is methanol poisoning blindness country. is there any truth to this? tossing the heads from the start of the run isnt a bad idea, because it'll make the hangover less intense, but is it really as dangerous as people say?
|
[
"Be very careful here!",
"A still is a device that is designed to separate ethanol and water. Is takes advantage of the fact that ethanol has a lower boiling temperature than water. ",
"The danger is that methanol has a lower boiling point than ethanol. So the same process that separates the ethanol from the water, also separates the methanol from the ethanol. ",
"So you are correct, before distillation the methanol is very dilute. But after distillation, the initial product to come out a still has a dangerously high concentration of methanol. ",
"This is the danger. Even if you use all natural ingredients, the distillation process makes a small amount of toxic spirits. ",
"Its a simple fix. Simply throw away the first alcohol to condense. But if you don't know what your doing and don't do this, you run the risk of poisoning yourself or worse a friend that you shared you spirits with. "
] |
[
"I'm not sure how much of this is from prohibition-era stills that used industrial methylated spirits, and if it's even really a concern any more. There are a few things to consider:",
"Methanol has an LD50 of 5g/kg I think, but it's really only present in your product at around 3ppm, which is about 0.003g/kg. So the ethanol would kill you first.",
"An improperly distilled product would have more methanol in it, but sufficient quantities of ethanol will compete with the methanol for metabolism, and ethanol always wins this fight, so as long as there is at least as much ethanol in your distilled product as methanol, you would be fine, since the metabolism of methanol into the harmful formaldehyde will be much, much slower.",
"With modern stills, people strive for purity as opposed to prohibition times when they wanted quantity. It would be quite difficult to distill a large amount of methanol into your end product, plus even if you did it would stink considerably.",
"Basically you should be fine, so long as you operate the still properly with the correct ingredients. This warning is a leftover from times when bootlegged alcohol wasn't safe and moonshine stills that don't use proper ingredients/distill properly."
] |
[
"Unless there is methanol present in the homebrew, there will be none in the distillate. Wine will have more methanol, a sugar wash will have almost none. Besides that, a typical distillation goes through three stages:",
"1) foreshots & heads collection. Since methanol boils at a lower temperature than ethanol, the first stuff out of the still will contain the lions share of the methanol. It can also contain various nasties like acetone and other low boiling point fluids. \nThe rule of thumb is to throw out the first 100ml out of the still to get rid of the junk. Sometimes people keep this to use as lighter fluid or to clean up ink stains. Sometimes you end up with a big jar of it collected over many distillations. This is the poisonous stuff that could hurt you, it will at least give you the worst hangover of your life. Dont confuse this with your drinking spirit.",
"2) hearts collection. This is the good stuff, dillute to desired strength and drink.",
"3) Tails. This is the stinky stuff with a higher boiling point, mostly water. You can add it to your next run to squeeze out a bit more hearts next time."
] |
[
"Is there a Doppler effect for quantum mechanical wave functions?"
] |
[
false
] |
Essentially they are also linear waves, right?
|
[
"Yeah. If an object is emitting particles with the same energy in its rest frame then (as energy and frequency of the wave are basically the same thing) as it moves towards you, you will see them blue-shifted, and as it moves away they will be red-shifted. In this case it's basically just velocity addition, except for massless particles (of course)."
] |
[
"To an outside observer the box will appear shorter, so the wavelengths of the wavefunctions will also appear shorter."
] |
[
"What about a particle in a box, where the boundaries move at a certain speed ? "
] |
[
"Does the sun make a noise?"
] |
[
false
] |
After looking at amazing photos of the sun, I wondered if there was any sound coming from the sun. I understand that when I hear a campfire for instance, I'm hearing the sound of air and wood being consumed by the fire. I know in space no one can hear you scream but can you hear our local giant furnace roar?
|
[
"Sound the way we hear it on Earth is impossible in space since you need some kind of medium for sound waves to travel through. However, the sun, like everything else in the Universe, emits radio waves. We can intercept those radio waves and turn them into sound, just like when you turn on the radio in your car. ",
"Here's what it sounds like.",
"Also here's ",
"Neptune",
", ",
"Jupiter",
" and the ",
"Earth",
". (The Jupiter one has a bit more of an explanation, though it's kind of poorly written.)"
] |
[
"Fun fact: if you could hear through space as you can through air, you could indeed hear the sun, and it would so loud it would be the ",
". To see this, note that sound intensity decreases by the inverse square of the distance, same as apparent size does; so the sound the sun makes would be essentially equivalent to a \"large-marble-sized nuclear explosion held at arm’s length.\"",
"Source: ",
"http://www.askamathematician.com/2011/10/q-if-you-could-hear-through-space-as-though-it-were-filled-with-air-what-would-you-hear/"
] |
[
"RAAAAAAAAAAAAAAAAAAAAAAAAWR"
] |
[
"Does blending fruits and vegetables in a high speed blender destroy a lot nutrients?"
] |
[
false
] |
So I have gotten into the green smoothie craze and purchased a vitamix blender a couple weeks ago. Unless I'm eating out, nearly all my fruit and vegetable consumption comes from the random fruits and vegetables that are thrown in my blender. My consumption of fruits and vegetables have increased a lot due to the speed and convenience of just blending everything together. I'm pretty sure you lose something when your turn whole fruits and vegetables into liquefied mush. Just wonder how much and what you lose in that process.
|
[
"As long as you're consuming everything that went into the blender, you're getting all of the nutrients. Physical forces can disrupt cells and denature some proteins (it's how meringues are formed, for example) but they really can't destroy nutrients; the molecules are simply too small.",
"All bets are off if you're using a juicer, though. The pulp that gets left behind is composed mainly of the very valuable insoluble fiber and a number of nutrients get trapped and left behind as well."
] |
[
"Denatured proteins are still perfectly viable sources of nutrition."
] |
[
"Browning is the action of polyphenoloxidase enzymes on, as you might expect, polyphenols. Some polyphenolic compounds have health benefits, but they also tend to be in fruits without high levels of polyphenoloxidase and the you can easily prevent the action of polyphenoloxidase by lowering the pH. So if you're mixing high-polyphenolic fruits (like berries) with polyphenoloxidase-containing fruits (like apples) then throw in some citrus as well and you're fine."
] |
[
"Why does grafting apple trees result in an edible apple?"
] |
[
false
] |
My understanding of apples and apple trees is lacking.... If an apple tree is left alone to grow naturally it will produce crabapples, correct? So who figured out that connecting the root stock of one tree to the shaft of another will produce flowers that when pollinated yield an edible apple? I would have never thought to do something like this in a million years if someone else hadnt first figured it out. So, what is happening within a grafted tree (on the chemicaly/biological level) that changes the edibility of an apple?
|
[
"If an apple tree is left alone to grow naturally it will produce crabapples, correct?",
"No. A macintosh tree will produce macintosh apples without a graft. A Mac might be grafted to a hardy root stuck to improve survival in harsh conditions, or it might be grafted onto a dwarf rootstock to force it to be smaller for more economical picking/pruning."
] |
[
"Do you know if they breed true, or if they just have good enough root systems to be made from cuttings?"
] |
[
"When a tree is grafted you basically end up with a clone of the original tree growing off of the root stock you put it on. ",
"You take a piece of a type of apple tree that makes good apples and you put it on a type that makes better roots.",
"If you plant the seeds from most apples you will not get something that resembles the parents. You will get a new combination of genes that has a low probability of being good for eating."
] |
[
"Can the human body have too much blood?"
] |
[
false
] | null |
[
"In addition to polycythaemia, which is mentioned above, you can also be given too much blood! If you give too much blood [product] via transfusion to someone they can get Transfusion Associated Circulatory Overload (TACO). "
] |
[
"In the case of the genetic mutation (Polycythemia vera), blood letting is a correct course of action, iron supplementation is a grave error though. The whole point of blood letting is to deplete the body's iron stores to stop it from producing red blood cells. ",
"Please don't try to explain things that you do not know enough about. "
] |
[
"In the case of the genetic mutation (Polycythemia vera), blood letting is a correct course of action, iron supplementation is a grave error though. The whole point of blood letting is to deplete the body's iron stores to stop it from producing red blood cells. ",
"Please don't try to explain things that you do not know enough about. "
] |
[
"Is looking at a TV or computer screen in the dark worse for your eyes than in a well lit room?"
] |
[
false
] |
[deleted]
|
[
"It only causes short-term issues, nothing permanent.",
"Lightness/darkness changes (when as minimal as turning the lights on) only cause pupil dilation, not retina damage. "
] |
[
"I think there is also concern that in a dark room the pupils will dilate. A small bright patch in the dark will still result in a dark environment (on average), so the pupils remain dilated. In this case, the portions of the retina exposed to the TV light will be getting more light than normal. Is this a problem?",
"My eyes feel tired very quickly when I use my smartphone in the dark."
] |
[
"It just causes short term eye strain which can be pretty severe in some cases, it's a good idea to have the wall behind the screen at a similar brightness as the monitor is when displaying white",
"Most screens come 2-5 times too bright for the average room, so most need to be turned down to around 20-30% brightness"
] |
[
"How do scientists know the size of the universe?"
] |
[
false
] | null |
[
"For reasons I don't fully understand",
"Here, I'll attempt to clear it up. You are correct, the guy you replied to is wrong.",
"Space can expand faster than light. We can measure how fast space is expanding, and that's called the Hubble constant, which is 70 km/s/Mparsec, but it's always changing",
"On phone, so I can't go into too much detail.",
"Edit: When I get to my laptop I'll add more."
] |
[
"When scientist talk about the size of the universe, what they mean is the size of the observable universe...\nsince the universe is 13.47 billion years old and light has a maximum speed, the speed of light, the size of the observable universe is c*t (in each direction)",
"Concerning the size of the \"whole\" universe: The universe is all there is, so you can't compare the size of the universe to another reference frame...\nThere is no \"outside the universe\", Time and Space are part of the Universe."
] |
[
"the size of the observable universe is c*t",
"For reasons I don't fully understand, this is wrong, it's much bigger.\n",
"More info",
"We can't really ",
" anything about what's beyond the observable universe.\nIt could be infinite, it could be about an inch larger than what we can see.\nUnder fairly reasonable assumptions, it's probably much much larger than what we can see."
] |
[
"Discussion: Kurzgesagt's newest YouTube video on the Information Paradox!"
] |
[
false
] |
Hi everyone! Today on AskScience we're going to learn about the information paradox and why black holes could delete the Universe, with the help of Kurzgesagt's . Check it out and come ask your questions!
|
[
"Trillions of years doesn't do it justice. A supermassive black hole with 10",
" solar masses would take ",
"about 10",
" years to evaporate",
". We don't really know how the universe will evolve on such long timescales (we don't even know if protons are stable on these timescales, for example), but it certainly won't be in any configuration like it is now or has been previously, unless you subscribe to the Big Bounce theory, which afaik fell out of scientific favor a while ago. This question basically reduces to \"how will the universe end\", which we don't have a definite answer to yet."
] |
[
"I saw this video earlier and it was the first time that I've actually had a brief explanation about what information actually is. However, AskScience, it would be great if someone could go into further detail as to what information is. "
] |
[
"Black holes lose a small part of their mass over the billions (potentially trillions) of years that they exist.",
"In time, when the last black hole finally dwindles its last bit of mass, would the universe be in a position like it had been at its beginning? I.E. pockets of matter spread out in an uneven array, allowing gravity to take over and for stars to form once again.",
"Or does entropy ensure that this won't happen?"
] |
[
"If I travel fast enough to red or blue shift radio waves, what would happen to the sound coming from a radio program?"
] |
[
false
] |
I realize that I would have to adjust my station to the new frequencies, but would the radio beat or tone shift up or down as well?
|
[
"The Doppler effect works on electromagnetic waves."
] |
[
"Well, it would change the station first of all... So if you tuned in at 98.5 MHz you might instead tune in at 98.6 MHz. ",
"After that I think things should be slowed down, regardless of if it is ",
"AM",
" or ",
"FM",
". If we had a 10% elongation of the wave, we should also have a 10% slow down in modulation of the wave, so a 100Hz tone lasting for a second would instead be ~90Hz lasting for 1.1 seconds. "
] |
[
"You could almost say that traveling at a certain rate is the same thing as single-sideband FM modulation, if you wanted to get esoteric.",
"TIL! That's a nifty way to look at it. So in both AM & FM cases, you'd hear lower pitches but stretched out signals with a red shift and higher pitches and a sped up signal with a blue shift. Is that right?"
] |
[
"Are Galaxies still being born?"
] |
[
false
] |
If there was a period of time in the Universe's ancient history when galaxy clusters were being formed, is that period over forever? Is the Universe now uniformly consisting of Galaxy Clusters and Groups? And, in the future, will these galaxy clusters (and groups) be uniformly spread out? Finally, if so, is this the way the universe will remain until it is over, or will galaxies begin interacting and colliding with one another as we near the end of the Universe? Or will each galaxy's stars simply break down into systems of spread-out black holes?
|
[
"I'm going to disagree with the comment by cofwjz. While stars are still forming, galaxies are no longer being 'born'. To be honest, it's even rather hard to define what being 'born' means for a galaxy. ",
"First you need to understand what a galaxy truly is. Sure, it's a collection of gas, dust and stars. But, from a whole-universe perspective, it is best understood as a collection of baryons (i.e. normal matter, like protons and neutrons) existing within a 'gravitational well' created by dark matter. ",
"The Universe is full of Dark Matter, which is distributed something like ",
"this",
". At the dense spots (called 'halos'), the dark matter has enough gravitational attraction to attract other matter -- mainly gas, which then turns into stars, eventually forming a galaxy. So, at each of the bright yellow spots in this dark matter 'web' there is a galaxy.",
"So, what would it mean for a new galaxy to be 'born'? This is hard to answer. From one point of view, the slight dark matter overdensity, which acted like the 'seed' of the galaxy, is the baby galaxy. And this existed right back near the big bang, before normal matter had even condensed out of the raging energy maelstrom. ",
"To say a 'new' galaxy was forming now, I guess you'd be talking about a concentration of dark matter (which currently has no gas or stars mixed in), which is accreting gas, and forming stars, for the first time. And this is almost impossible. Any dark matter halo massive enough to attract significant quantities of gas would have already done so. The Universe is actually winding down from its galaxy formation period. The intense epoch of galaxy formation was about 7-10 billion years ago, and we've been on the downward slope ever since. There's not much 'new' forming now. "
] |
[
"Yes, galaxies and stars are still being born, but the rate at which they form has diminished considerably due to the effects of ",
"dark energy",
", which suppresses the growth of structure in the universe. For objects like galaxies to form, their self-gravity has to overcome the expansion of the universe, and dark energy is causing that expansion to accelerate over time.",
"We don't know how dark energy will behave in the future, but if it continues to accelerate the universe's expansion, then it will continue to gradually suppress the formation of galaxies, until eventually the galaxy formation rate effectively vanishes. In that case, objects that are gravitationally bound to each other (like our Galaxy and the Andromeda galaxy) could still merge, but more distant objects will recede from us increasingly quickly. They will eventually recede past our causal horizon, meaning that we will become unable to see the light they emit.",
"The galaxies themselves are not expected to dissipate, because they are bond together by gravity from their dark matter. But eventually, all the stars in the galaxies will burn out, becoming cold remnants like white dwarfs, neutron stars, or (in some cases) black holes. The distant future could be very bleak..."
] |
[
"In response to seladore, I agree that it is nontrivial to define what exactly we mean by a galaxy being \"born\" today. The only sensible way to quantify the rate of galaxy formation is ",
"rate = dn(M)/dt ",
"where n(M) dM is the number density of galaxies in some narrow mass bin dM centered on mass M. And I assure you that this derivative is nonzero and positive across all observable galaxy masses M. That is, if I count all the galaxies in the universe of mass M at some time in the past, and then count the number of galaxies of mass M today, that number has increased. That is the sense in which galaxy formation is going on today.",
"The definition you propose is tantamount to defining galaxy formation as the time when the very first star forms inside of a newly formed dark matter halo. That definition is useless as a measure of the abundance of galaxies. In contrast, the definition of the galaxy formation rate I gave above exactly quantifies how the abundance of galaxies changes over time, and that rate is nonzero."
] |
[
"If men have XY and women have XX what would happen if scientists created a YY human or if it is impossible, why?"
] |
[
false
] |
I already somewhat understand how reproduction works. with a mother passing on one of her X and the father passing on either an X or a Y, which would decide the sex. so would this mean that XX are very feminine, XY half feminine and half masculine, and YY some sort of super manly being? I assume a YY human wouldnt have nipples...
|
[
"During Metaphase I of meiosis, the sperm or unfertilized egg can incorrectly separate the duplicated chromosomes and have additional copies of sex chromosomes in one egg or sperm, and then no copies in another egg or sperm. Most of the time it causes a spontaneous abortion (miscarriage), or the sperm/egg will not continue with fertilization (undergo apoptosis), but rarely the fertilization will occur with a defective gene count, and fertilized fetus will be viable. Here's a brief but not all-encompassing list of the conditions:",
"XY male, normal (included as a reference)\nXX female, normal (included as a reference)",
"X0 Turner Syndrome:\nAffected persons are phenotypically female, but smaller and may or may not undergo sexual maturation; even at sexual maturity sterility is common. Cognitive ability and other capabilities usually are normal, but some mental impairment is possible. ",
"XYY: Double Y karyotype, usually taller than normal, may have slight cognitive impairment, but are otherwise normal, sterility is common. Behavior, mood, and criminal tendencies are not higher than others in the population.",
"XXY: Klinefelter syndrome, pheontypically male, usually tall, but do not undergo sexual maturity, however may have large breasts, nearly always sterile. Also usually have mild-moderate cognitive impairment.",
"XXXY: Normally not viable, but in extremely rare cases when an individual survives pregnancy they are similar to Kilnefelter syndrome.",
"XXX: Trisomy X, phenotypically female, symptoms vary from completely normal to moderate behavioral and cognitive dysfunction.",
"XY (Female): Defective SRY gene, so genetically male but a defective SRY gene in fetal development blocks development of the testes (and male physical features). Otherwise normal.",
"YY: Not viable, the X chromosome is required. If an ovum were to somehow still survive the mitotic [meiotic] checkpoints and be present for fertilization, the fetus would abort spontaneously.",
"Source: <cough cough sneeze> dusted off my old genetics textbook"
] |
[
"Well, the short answer is that the X chromosome has a lot of important genes on it that males require for living. Our system is sort of a \"default female\" system; meaning that we only develop into males if the proteins from the Y chromosome are present and get expressed. If there is no Y chromosome, we just continue development as female. Both boys and girls use the genes from the X because they are essential, and the Y carries mostly \"male\" development signals. Girls actually have to deactivate one of their two X chromosomes to avoid over expression of those genes (google search Barr body if you're interested). So, a YY baby would be missing a lot of functional genes and would not survive long past zygote or whatever means were used to create it. ",
"Now, since you're probably interested, plenty of XYY humans exist (as well as XXX or just X). It's interesting to see what effects that has on the carrier. XYY males have actually theorized to be more aggressive by nature, and I think someone actually did a study on a bunch of death-row murderers to find a connection, but I can't remember what they found."
] |
[
"There are also conditions where you can have XX males and XY females.",
"De la Chapelle Syndrome and CAIS or Complete Androgen Insensitivity Syndrome, respectively."
] |
[
"Is Peak Oil frowned upon in the scientific community?"
] |
[
false
] | null |
[
"I understand 'peak oil' to be the time that oil production begins to decline as a result of lack of supply. Given this definition and the fact that there is a limited amount of oil available, I don't see how peak oil could possibly be a myth. Do you consider my definition to be incorrect, or am I missing something else?"
] |
[
"Perhaps a good way to answer your question is to look at what people say who claim peak oil is not a real concern. Robin Mills' ",
" seems to me to be a pretty fair treatment (well, much more fair than the whole \"peak oil is a liberal plot!\" screeching you often see). Here's the main points from his book (in bold), with a little background and commentary from me. I took this from a larger article I helped write elsewhere - sorry for the cut-and-paste, but the article is hosted on Squidoo, and Reddit doesn't allow links to Squidoo. ",
"Disclaimer: I'm not a petroleum engineer or whatever; I've just tried to educate myself about peak oil. Also, FWIW, I disagree with Mills' assessment)",
"Reserves estimation is both an art and a science. Peak oil proponents tend to cite the lower range of such estimates. For example, the peak oil theorist Colin Campbell estimates that the total endowment of world's oil (past production + known reserves + expected new finds) is about 2100 billion barrels (2.1 trillion). A 2003 Shell oil estimate was about 3.3 trillion barrels. The USGS figure was 4.7 trillion and some estimates are as high as 6 trillion. OPEC numbers are a particular source of contention, primarily due to a lack of independent verification of reserve figures published by the state apparatus in these countries. Furthermore, the two camps don't even agree on what constitutes a new discovery. If additional oil is found in a mature field (say, in a deeper rock strata) peak oil critics count this as a new discovery. Peak oil proponents count this as part of the original find, a practice known as \"backdating.\" This tends to skew plots of discovery history, and is one reason peak oil critics dismiss the discovery peak that alarms the peak oil camp.",
"A major difference - perhaps the major difference - in the worldview of peak oil proponents and critics is that the former tend to view oil in terms of society or the environment whereas the latter view oil as a business. An oil company doesn't produce oil because it's necessary or because it's the right thing to do; they produce oil because it's profitable. Conversely, they don't produce oil if it's not profitable, regardless of other considerations.",
"These worldviews clash in the interpretation of falling world production. Both sides agree that falling production is an inevitable consequence of falling discovery. But peak oil critics claim that oil prices have simply not been high enough to make exploration profitable. These days, with oil prices reaching record highs, such a claim may seem hard to believe. However, it is necessary to consider the long-term price history because exploration and development of new finds has a substantial lead time. Over the last 30 years, oil prices - for better or for worse - have been relatively low. Perhaps even more problematic are price shocks that plague the industry, such as the price collapse that followed the 1974 OPEC embargo. Prices that are low and/or unpredictable, peak oil critics claim, discourage investments in exploration or development of new production capability. Declines in discovery and production are consequences of economics not geology.",
"Critics claim that the peak oil camp lives in a vacuum, viewing rising demand and decreasing supply marching inexorably lockstep over the cliff. In contrast, peak oil critics have faith in market forces - specifically price - to control this process. A higher price immediately reduces demand by encouraging people to drive less or use public transportation. In the medium-term, high prices will result in more aggressive efforts to curb demand such as higher CAFE standards, conversion of fleet vehicles to natural gas, and increased sales of hybrid cars. If conventional oil prices remain high in the long-term, non-conventional oil such as tar sand and oil shale become competitive. World reserves of oil shale alone is estimated to be in excess of 20 trillion barrels - a sufficient quantity, peak oil critics claim, to meet oil demand for decades. This will buy enough time for a smooth transition to renewable alternatives such as hydrogen fuel cells or next-generation electric vehicles.",
"While peak oil proponents have a lot of faith in technology when it comes to alternative energy, their faith in petroleum engineers is indeed decidedly lacking. The late economist Matt Simmons stated there is \"no new technology on the blackboard\" as recently as 2006. There may be a grain of truth in his assessment. Although the last decade has seen significant advances in the use of 3D seismic imaging, most oil technologies are quite old. The first off-shore well was drilled in 1938, and the first deep-water well in 1947. Satellite-assisted exploration goes back at far as Landsat and the first commercial oil found using a seismic survey was in 1924, On the other hand, new technologies are almost certainly proprietary, so what is and is not on the blackboard may be impossible for an outsider to determine.",
"The distinction between non-OPEC and OPEC peak production raises concerns about increasing reliance on oil from unstable regions of the world. Peak oil critics claim such fears are unfounded. To date there has been no significant interruption of supply caused by terrorism. Furthermore, while a a disruption resulting from a hostile \"regime change\" or an embargo could indeed cause shortages in importing nations, it would be catastrophic to any OPEC country involved. Oil exports make up almost half of the GDP of Persian Gulf countries; a loss of oil revenue is simply unthinkable.",
"The peak oil + climate change argument goes as follows: since oil looks like it's running out, and continued use of fossil fuels will lead to catastrophic climate change anyway, why make any effort to prevent a peak? The sooner it happens, the better.\nContrary to what many believe, there are peak oil critics who fully accept climate change as a real and pressing danger (Robin Mills, for example). However, these critics argue that climate change is not cause to eliminate fossil fuel use - which is impossible anyway - but rather it is reason to maximize the use of cleaner-burning fossil fuels such as natural gas and aggressively implement technologies that reduce CO2 emissions. The greatest gains to be realized are in power generation. Peak oil critics tend to dismiss alternative energies in the power-generation sector and for good reason: it is likely many countries will satisfy their immediate needs with coal. For example, China is building hundreds of coal-fired power plants to generate electricity, even though high-speed natural gas turbines exist that are more environmentally friendly (and more efficient). However, coal is cheaper than natural gas, and China has a lot of it. The irony is that peak oil might correlate with an increase rather than a decrease in global CO2 emissions.",
"Clearly, the petroleum industry employs some very smart people, and there are always improvements to be made in exploration and recovery methodology. Remember: total reserves > total discovered oil > accessible oil > recovered oil > refinable oil. Ingenuity can be applied to any of these inequalities to increase reserves. The critical questions are how much, how soon, and for how long."
] |
[
"Can you explain what you mean, so that I know what you are exactly talking about?",
"This is important, because if you categorically claim that the Peak OIl is myth, you are actually claiming that oil extraction capacity can increase until oil resources are completely depleted. "
] |
[
"Do cravings for specific kinds of food mean anything about the nutrients my body needs?"
] |
[
false
] | null |
[
"I think what you're getting at is akin to, does someone with an iron deficiency crave iron-rich foods (for example).",
"As some of the others stated, deficiencies sometimes correlate with cravings, but the foods craved don't necessarily have anything to do with the deficiency. Your satiety hormones don't know that spinach is high in calcium, so they can't be that specific in cravings."
] |
[
"I don't know if this is entirely the case. A biological need for a particular nutrient can indeed be tied to a craving for a particular food. Your body, on some level, probably knows something of the nutrients it is ingesting and associates these with what it is eating. In elephants, the correlation between craving and nutritional need has also been show to also exist beyond the acquisition of caloric or protein needs. ",
"Due to their size and plant based diet, elephants are often lacking in the necessary sodium their bodies need, as well as other minerals. To compensate for this, elephants have commonly been found to dine on dirt or mud from the bottoms of the lakes as well as dirt from the ground. They do this to obtain the minerals they need, particularly sodium. The mud elephants eat has been found to be higher in sodium and other minerals than the average for the soils in the areas they live. It is therefore unlikely that the dirt/mud elephants ingest is ingested just because elephants like eating dirt. ",
"More importantly, there is a correlation to elephants' periods of eating high-mineral mud and the periods in which their bodies are most deficient in the nutrients it contains. Female elephants eat more of the mud then males, as their nutritional requirements are generally higher. Elephants with actual deficiencies also eat more until their nutritional needs are met or sated. ",
";TL/DR elephants, and possibly other mammals/animals, seem to eat undesirable foods solely for their nutritional value during times of nutritional, but not caloric deficiency. ",
"http://scienceblog.com/983/elephants-eat-dirt-to-supplement-sodium/"
] |
[
"I get spinach cravings. Maybe you're not eating well prepared spinach?",
"I feel like I frequently crave vegetables after, say, a long weekend of junk food and beer, but it's probably just confirmation bias."
] |
[
"can EDTA change the oxidation state of an ion or atom?"
] |
[
false
] | null |
[
"Can you give a more specific circumstance?",
"Assuming you are excluding acid-base reactions (which it certainly could since it has both acid and base groups), then no, it is rather unlikely to directly alter the oxidation state of metal ions. ",
"There could be rare cases in which the coordination of EDTA activates the metal ion to be oxidized or reduced by a different species, but that's not a direct action of EDTA.",
"Edit: Also, EDTA can be reduced by strong reduction agents, trivial answer would be something like sodium metal, but also formally sodium borohydride (the boron), dysprosium diiodide, but I suspect this isn't what you mean."
] |
[
"Really having fun with this AAS/ICP analysis aren't you? Is this lipstick again? ",
"Well, first off, it probably isn't Pb, the conditions are pretty darn oxidizing, and ICP/AAS doesn't typically tell you oxidation state anyway. (I can't off hand think of a case in which it would.)",
"So what's going on in this sample? You say:",
"\"a known amount of lead nitrate and nitric acid were added to a sol'n and wasn't detectable\"",
"This seems strange. I would imagine it's pretty difficult to get below the detection limit on either instrument. ",
"The answer may be here:",
"\"sol'n with lots of dissolved organic compounds\"",
"The organic compounds may be keeping the Pb from dissolving, or being sampled properly. The EDTA, as a strong chelating agent, may free the Pb ions from the sample, allowing for them to be detected."
] |
[
"it's in an acid peroxide sol'n with lots of dissolved organic compounds; a known amount of lead nitrate and nitric acid were added to a sol'n and wasn't detectable by ICP-OES or AAS. When EDTA was added, it increased the amount of lead present by a lot. I first thought it was the matrix effects inhibiting the reading, but maybe it's Pb-->Pb2+ which absorbs and emits at a different wavelength?\nI'm not really sure what else would cause this effect."
] |
[
"Can hydrofluric acid be used to quicken lens grinding?"
] |
[
false
] | null |
[
"I will say no for two reasons.",
"First, if referring to eyeglass lenses, I don't think glass is used anymore, or perhaps very rarely.",
"Second, if glass, the precision milling needed could not be easily controlled (if at all) chemically. Also, the quantity of material to be removed would probably make the usage of a chemical totally impracticable.",
"The mass production of lenses has been extremely automated and is very exact. There really wouldn't be any point in attempting to handle such a hazardous material."
] |
[
"To add, etching glass with HF would most likely make the surface more rough. The etching process produces porous surfaces. ",
"Here is a paper where they studied the surface roughness on glass slides etched with HF. ",
"Paper",
"\nEdit: see pg 9 of the pdf "
] |
[
"Could be a number of reasons you need glass instead. Maybe you need something that doesn't scratch as easily. "
] |
[
"Why does steam sometimes rise from cold water?"
] |
[
false
] | null |
[
"Steam or water vapor is invisible, the \"steam\" we see is really the water vapor condensing into small water droplets which scatter the light giving them their cloud like appearance.",
"This happens when the warm water vapor enters a region of cooler air. A tea kettle going into the room produces these clouds of steam.",
"Now back to your question. These clouds of steam you see rising from cold water happen in the winter. Generally a lake or a river is still unfrozen but a very cold air mass has moved in with temperatures in the 20s F (below zero C) or lower. The water has vapor pressure, so it is continuously evaporating, however when it enters the colder air, the air can't hold that much water so you see the clouds of steam (and probably some ice crystals) above cold water in the even colder air."
] |
[
"Essentially yes. If you watch the weather reports, you may hear the meteorologist mention the \"dew point.\" This is the temperature at which water vapor starts condensing. So when the air temperature reaches the dew point, the water vapor starts forming little water droplets which is a cloud near the ground.",
"Since this is the summer right now, this can happen if a warm humid mass of air passes over a colder body of water. The air near the water is cooler, so the humidity condenses forming fog."
] |
[
"Is this how fog forms?"
] |
[
"How does freezing sperm not destroy or damage it?"
] |
[
false
] | null |
[
"Your assumption is correct. When you freeze cells willy-nilly, the cells will burst as ice crystals form. Thus, they will be dead when you try to thaw them. Methods for preventing this have been developed over the last few decades, including: rate of freezing, thawing procedure, and the inclusion of cryoprotectants. Cryoprotectants are compounds which have the ability to prevent the formation of large intracellular ice crystals. The most common one used in the lab is DMSO, but it looks like glycerol is the most popular for freezing clinical specimens. ",
"Here is an in-depth peer-reviewed article describing the different aspects of sperm crypreservation.",
"https://www.hindawi.com/journals/au/2012/854837/"
] |
[
"Donated sperm has to be stored for six months before it can be used in treatment, in order to screen the donor for infections. Sperm cells have been frozen, thawed and successfully used in treatment for more than 40 years, although not all sperm survive the freezing process.",
"Frozen sperm must be stored in extremely cold temperatures (-196 F), but in order to ensure that the fewest possible sperm are damaged, the freezing must be gradual.",
"After a minimum of 48 hours have elapsed from the time of the initial freezing, an initial \"test sample\" is thawed and tested again to ascertain from each specimen how well the sperm survived the freezing. "
] |
[
"Yeah, but brains, being more complex and more vulnerable than sperm, are much harder. ",
"With sperm, if you kill half the cells, you're still ok, because you don't need all the cells, just most of them. ",
"With the brain, if you don't kill any cells, but they lose their connective structure, you're done for. If you kill a quarter of the cells, you're probably done for. ",
"The brain has to be preserved as a whole tissue, where the whole thing has to maintain its structure and where every cell that dies represents an unknown and possibly massive loss. Our current techniques do some pretty decent damage to the brain tissue. ",
"So the hope isn't to preserve the brain ",
", but to preserve it ",
" that some future society, with better understanding of the brain, can either repair the damage, or, by inspection of the damaged tissue, produce some representation (digital or biological) which copies your brain function. That part is kinda hand wavy, because we have no idea how much damage it's possible to repair or ignore even in theory, so the best we can do is do as little damage as we can and cross our fingers. "
] |
[
"How are two photons quantum entangled?"
] |
[
false
] |
As in, when the Chinese scientists "teleported" a photon by entangling it with another, how did they do that?
|
[
"You get a pair of entangled photons basically by creating it, rather than taking two photons and somehow \"entangle\" them.",
"There are many ways to do this, but a very common technique is to use birefringent crystals like barium borate. Classically speaking, this crystal acts as a beam-splitter, as it has two different refraction indices for two orthogonal polarizations of incoming light.",
"On a quantum level, a process called \"spontaneous parametric down conversion\" can occur, where a single photon is converted to a pair of two photons. The resulting two photons together have the same energy and total momentum as the original photon, but may travel in different directions. The polarizations of these two photons are correlated, hence they are entangled.",
"The process is super tedious, as the SPDC is a very rare event, but using a very high powered laser beam you can get a decent amount of photon pairs out of it."
] |
[
"The process is super tedious, as the SPDC is a very rare event, but using a very high powered laser beam you can get a decent amount of photon pairs out of it.",
"With the by now very common ",
"periodically poled",
" crystals and periodically poled waveguides you can get decent down-conversion rates even at moderate intensities.",
"In my setup for example I get millions of entangled photons per second with a laser pump of 1 mW - that's intensity of a moderately strong laser pointer."
] |
[
"There is no principle limit on how long/far away photons can be entangled. De facto we can only make use of the entanglement for a very short time: The photons leave with the speed of light and our current methods for confining the entanglement of the photons are very inefficient and lossy.",
"Storing the entanglement of photons efficiently is one of the problems that current many quantum information groups are currently working on, as it is an requirement for some interesting applications like the ",
"quantum repeater",
" or scalable quantum computation with photons."
] |
[
"How are if then statements translated into their fundamental logic constructs (logic gates)?"
] |
[
false
] |
In higher level programming languages you have if then statements for conditional control. In the study of logic you have antecedent and the consequences with implications. I don't understand how these implications are implemented into CPU designs. Although it probably is very basic knowledge, I'm missing some kind of detail. I hoping someone here could help. I would like to know how they constructed using only logic gates such as and/or/not. Thanks
|
[
"The comparative operators are implemented in the CPU with subtraction. For example in all comparisons of A==B, A>B, etc. the subtraction A-B is calculated and the result's value sets CPU Flags such as the Zero Flag which indicates A==B, or the Negative Flag which indicates the result of A-B was less than zero and so B>A.",
"So from one subtraction the CPU knows the results of all comparisons. Then, the if(A==B) { becomes a conditional jump. If the Zero Flag isn't set, it jumps to the code past the body of the if-statement.",
"That conditional jump is really a conditional data move whereby the numeric value of the memory address of the code after the if-statement is conditionally moved into the CPU's Instruction Pointer (which holds the memory address of the next executing instruction), depending on whether (in the case of A==B) the Zero Bit was set after the subtraction (or other bit depending on the user's actual comparison). To accomplish && and || conjunction and disjunction the CPU just AND's or OR's the composite results before continuing.",
"Accomplishing a conditional move on condition of the Zero Flag can be accomplished by using the Zero Flag's value as the write-enable bit of the move-value-into-IP-Register operation.",
"Also the logic you are studying is mathematical logic and has nothing to do with the creation of the computer. For analysis of computational logic you should explore the work of George Boole, John Vincent Atanasoff, Clifford Berry, Charles Babbage, Alan Turing, and Charles Peirce.",
"After George Boole et. al. produced the foundation for computational logic, few people recognized its significance and still continued developing their own wacky theoretical logics which unfortunately are a distraction to the true advance of human progression. However the same is said of all human endeavor as we cannot truly recognize the merit of the various approaches until the validity manifests in the creation of something significant like the computer. And at the same time we cannot fully rule the approaches out either because they may (and have at various times) prove significant in various areas."
] |
[
"Then, the if(A==B) { becomes a conditional jump.",
"Unless it's running on an architecture that uses ",
"predicated execution",
", in which case the instructions in the ",
" and ",
" blocks are annotated with a flag saying \"do this only when the condition flag is set/not set\". ",
"(Note: some architectures support both methods)."
] |
[
"First off, computer programs aren't really translated into actual logic gates. Rather, they are translated into lists of machine instructions, describing a sequence of manipulations to carry out.",
"The exact format of the instructions is defined by the electronics in the processor. Some processors like x86 have many. Others like ARM have relatively few.",
"The processor loads the program into memory and starts running down the list of instructions. Some instructions tell the processor to jump to another part of the program.",
"If-then constructs are implemented with a couple of different kinds of instructions.",
"For example, in a hypothetical processor this C program could be translated like so:",
"\nif(x < 3) {",
"\n// x is less than 3",
"\n} else {",
"\n// x is more than 3",
"\n} ",
"----becomes----"
] |
[
"Questions about the compression of fissile material in a nuclear bomb."
] |
[
false
] |
[deleted]
|
[
"If I tell you, will you promise not to build one?"
] |
[
"According to ",
"this article",
" you can compress plutonium to three times its normal density, and the more you compress it the higher the yield.",
"I think these devices usually have a uranium tamper that not only provides a good deal of momentum for the compression but also decreases the the amount of plutonium required by reflecting neutrons back into the core."
] |
[
"For a typical nuclear weapon these days, it's on the order of inches. While the designs of the weapons are of course closely guarded secrets, the basic parameters aren't. The subcritical core in the first stage of a fission-fusion weapon can't be much bigger than a football."
] |
[
"Is all energy consumed by a computer turned to heat, or is some amount wrapped up in \"information\"?"
] |
[
false
] |
So, w/r/t conservation of energy: If you have a system with a machine that lifts a weight, and you put X amount of energy into the machine, the heat energy of the system goes up, but not by all of X, because some of that energy is bound up in the gravitational potential energy in the weight. When you drop the weight back down, then all of X energy eventually ends up as heat energy... Right? My question is: If you dump X energy into a computational device to calculate a complicated math problem, does the heat energy of that system go up by all of X? Or is some of that energy bound up in... the information from the result of the calculation(?) or something else? Like, if your computer's memory starts as a random jumble of 1's and 0's and then you spend some energy to calculate and store the first million prime numbers or something, is there energy bound up in that calculated information the way that there is energy stored in the gravitational potential energy of a raised weight, that turns back into heat when you erase the information or drop the weight? (Assume it takes the same amount of energy to store a 1 or a 0 in memory; or that the number of 0s and 1s in memory are roughly the same whether or not there is useful information in there).
|
[
"Essentially all of the energy you put in a computer will be converted into heat. There are some obvious conversions: heat from electrical resistance (the largest output), heat from the friction of moving parts, and sound and air flow from the system getting dissipated as heat in the surrounding environment.",
"There are a few less obvious conversions though. The first is EM emissions, the strongest of which come from the power supply. If your case is metal and doesn't have any windows, it'll act like a Faraday cage and catch them, turning them into heat or passing them through the ground line where they will still be turned into heat. If your case is partially plastic or windowed, these emissions will escape into the environment, likely to be converted into heat there.",
"As for storing data, this can be an exception, but it's a very negligible one. Flash memory, both the volatile kind used in RAM and the non-volatile kind used in SSDs, stores 1s and 0s in capacitors. Charged capacitors, pumped full of electrons, correspond to 0, and uncharged capacitors correspond to 1. Electrons and a lack of electrons can both be used to perform work depending on the neutral level, so there is some raw energy potential stored up there. Since electrons have non-zero weight, memory containing an excessive number of them is also going to be heavier, tying up some gravitational potential energy. These energy stores are negligible compared to everything else though.",
"Magnetic storage just changes particle orientation, so there is no net change in energy storage going on there."
] |
[
"Electrical engineering ",
" here:",
"Depending on the type of memory, the data may be stored in a capacitor (DRAM) or a flip flop (SRAM). Both of these store the energy in the forms of voltage, which is a potential difference in energy between two points.",
"The actual calculations are electrical energy which will be dissipated into heat energy by resistance within the circuits."
] |
[
"I'm not sure if it applies in this case, but much of our electrical notation is \"backwards.\" If Benjamin Franklin had labeled the electron as positive, making the positive flow of electricity the same direction as the flow of particles, we'd have some tidier math today. As it stands, positive flow is opposite the direction of particle flow, and a \"positively charged\" capacitor (1) is actually the one without electrons. In the case of data storage, we could arbitrarily decide to flip that back around and make 0 be positive (uncharged) and 1 be negative (charged), but since positives and negatives are equally easy to store, there'd be no benefit to it."
] |
[
"How exactly do animals think (if at all)?"
] |
[
false
] |
I've always wondered how animals process their thoughts. As a fairly average human, I filter my conscious thoughts through language - that is, everything I see, feel, desire, etc. comes across as a thought in my head, and those thoughts occur via language. So how would an animal with no spoken/written language go about processing thoughts? Or a human raised in isolation who was never taught a language? What about apes who are taught sign language, or parrots that have a vocabulary in the hundreds of words? I guess the TL;DR version of my question is when I see my cat's bowl, I think of the word "bowl". What goes through the cat's mind?
|
[
"After several minutes of rigorous experimentation, one black eye and a colleague who will not stop laughing, I'd like to respectfully inform you that your hypothesis sucks."
] |
[
"Depends on the animal. A lot of animals don't really think, they just do. That is, they're driven almost purely by instinct. ",
"Other animals, such as monkeys, dolphins, dogs, rats, and so on, you can watch them 'think' and see the proverbial wheels turning in their head while they figure something out. I can't prove that they're thinking in the same way that we do, but I don't know what else you would call it. It's a bit different than when they're in a Skinner box."
] |
[
"I have no expertise on this matter.",
"What I've noticed is that my thinking happens in at least two steps. First I have a thought, which is a quick impulse and triggers the next step. The next step is to put that thought into words. The second step takes much longer. As an experiment, I sometimes attempt to skip putting the thought into words at all, but I've had no luck in being able to do useful thinking without making use of language. My personal feeling is that language is a uniquely powerful tool for organizing thoughts logically and making them specific. "
] |
[
"Can non-highlighted posters please post any credentials you have related to science when you post?"
] |
[
false
] |
What about suggesting/requesting this on the right side column?
|
[
"It shouldn't be necessary. Incorrect answers tend to be accurately downvoted already."
] |
[
"It's kind of a pain to type this every time I respond. Plus it always sounds like I'm bragging or something along those lines."
] |
[
"Yeah I was 17 too once. Dear lord would I smack that kid around some now. That being said, I think shadydentist is right that a lot of these posts get well moderated by up/down votes. I personally have only gotten active in this forum for the last few weeks, but I've been watching a lot of threads. The unscientific or incorrect posts do tend to just filter down and good threads up. There are exceptions, but I think it's alright. ",
"Plus sometimes the panel members don't always have the full or correct answers either ;-)"
] |
[
"Is there anything in nature that is sweet and poisonous?"
] |
[
false
] |
I heard recently that evolutionally, humans have a predisposition to sweets because there is nothing in nature that is sweet and poisonous. Is there any merit to this? Is there anything in nature that is sweet and poisonous? Are we drawn to sweets because of evolutionary traits?
|
[
"Lead tastes sweet. In fact,it has been used to sweeten wine by the Romans. It wasn't a good idea. "
] |
[
"Ethylene glycol (common antifreeze) is sweet and poisonous, but I am unsure whether it occurs in nature. One thing that both occurs in nature and is sweet is one of the lead salts called \"sugar of lead.\" ",
"The broad truth is that all substances are toxic if taken in large enough amounts. Water, when taken in large enough amounts in a short while, will kill you. I'm talking about drinking, not drowning.",
"Think of it this way. Every substance probably has a safe range, but when that range is exceeded, it becomes poisonous by overwhelming the bodily defenses. You could even regard any common food as a poison, because eating too much of it for too long will cause the chronic poisoning we know as \"obesity.\"",
"I don't know if anybody cares, but I do have a PhD in chemistry."
] |
[
"Right, of course everything in moderation. I mean more like in plants and animals. ",
"But lead is a really good answer, thanks. I kind of want to go lick some now. "
] |
[
"Is the plane of our solar system within the plane of the Milky Way? If so, do they spin in the same direction?"
] |
[
false
] |
If so, why is. . .those things? Edit: when I say "within the plane" I mean "on the same plane".
|
[
"No. They are offset by about 60",
" from each other.",
"The sun and planets trace a path through the sky called the ecliptic. This represents the plane that our solar system orbits on. In reality it's not a completely flat plane, but it's close. If you watch the path of the sun during the day you can get a rough idea of where the ecliptic is in your location.",
"The Milky Way is visible on a good night from my house. I live about 12 kms outside a small city. If you can't see the hazy glow of the milky way, you should be able to consult a star chart and find some of the major constellations that coincide with its location. Taurus, Perseus, Cassiopiea, Lacerta, Cygnus, Vulpecula, Aquila, Scutum, Saggitarius, Norma, Circinus, Crux and Carina are some of the relevant ones.",
"Edit: If you don't live in an area where stargazing is possible, I suggest you download a program called ",
"stellarium",
". It allows you to see what the sky looks like from anywhere on Earth, or even from Mars."
] |
[
"There is no reason why it should be on the same plane. The 60",
" offset is just the way things happened when our solar system was born in a cloud of interstellar gas. It could have been any angle, and in other stellar systems it happens to be other angles.",
"Try to think of it as being kind of like the atmosphere of Earth. There are numerous air currents all blowing in different speeds and different directions, up, down, North, South, East and West. The overall effect is that the atmosphere still revolves around the Earth roughly once every 24 hours though.",
"Yet another example is in our own solar system, the planets orbit the sun in an almost flat plane, yet the tilt of the axis of each planet is different. Earth and Mars are very similar in this respect but that is merely a coincidence."
] |
[
"Our solar system also moves \"up and down\" along a sinusoidal wave relative to the plane of the Milky Way."
] |
[
"Are neonicotinoids 'bee killing' pesticides?"
] |
[
false
] |
The EU is talking about banning neonicotinoids, and everybody is raving about how this is evidence based policy. I can see there is some evidence that neonicotinoids kill bees, but it's not obviously conclusive (from my very quick scan of the literature). These kinds of questions have been asked a few years ago, but I believe significant new evidence has come out since, so I think it's worth asking again. Edit: thanks for all the answers so far. I just wanted to clarify: I suppose the point in the question is - if they ban neonicotinoids, would that have a significant positive effect on bee populations? Of course, many of the answers have addressed that, and answers to the unclarified question are still appreciated.
|
[
"\"Neonics\" are insecticidal chemicals that will kill pretty much any insect including bees. The problem is with application. No one is spraying bees with insecticide (maybe some peoole are idk) but their use leaves large residual ammounts in the environment which eventually get back to the bees since they tend to get around. Neonics are used to protect crops from crop pests but guess who is pollinating thise same crops? Its the bees. So even without targeting bees with insecticides they still get adequate contact and dosage to have an effect on their health.",
"Source: Im an entomology grad student that works on how to kill social insects (ants)."
] |
[
"Neonics are very persistent in the environment. Some pesticides stick around a long time, some are gone very quickly. That's part of the problem; neonics stick around and become an issue for non-target species. I deal with pesticides daily in my career and these are indeed a problem. I support a ban, because we have many other effective and less harmful products we can use. "
] |
[
"Neonicotinoids are pesticides similar to nicotine, a natural insecticide in tobacco. Like most pesticides, they are categorized based on their application. In this case, they are a general insecticide that will target any insect that comes in contact with it, affecting their nervous system. Bees are natural pollinators so they will become in contact with residual insecticides. The problem with pesticides is that even though they are meant to target specific pests, they can have an unintentional effect on other species such as organochlorines.",
"Source: Undergraduate Toxicology student"
] |
[
"How do bacteriophages have the energy to inject their DNA into cells?"
] |
[
false
] |
I've been curious for a long time about how viruses, specifically bacteriophages, are able to move, seemingly on their own, once they are attached to a cell. I am talking about the plunging that they do in order to inject their DNA into a cell. This seems like much more focused movement than what they do until they come around to the right kind of receptor, right? After some Wikipedia reading, I came across this paragraph: However, I do not understand reversible nor irreversible binding, and I'm hoping someone here might be able to explain this in slightly less technical terms. Here's the question as succinctly as I can pose it: How to bacteriophages summon the energy to plunge into a cell? Thanks for considering this question!
|
[
"Antiviral biologist here, not a biochemist though. It's a series of chemical reactions similar to the way proteins can change their conformation as a result of a single binding. In the simplest terms, when the phage connects to the membrane, the difference in polarities at the binding site creates a cascade of changes into what is the most ideal organization of atoms in the structural protein sheathing. These changes eventually lead to the expulsion of the DNA from the structural protein and into the cell.",
"The reversible vs irreversible, in this case, just correspond to different phases of binding. Reversible is before the 'hypodermic needle' section has made contact, where as irreversible is after, as the cell's membrane has been penetrated."
] |
[
"To put what crackadillicus said a little more simply; There are proteins that can also \"snap outwards\" to the same effect, I imagine that it is probably just a larger mechanism of one of these. Hemagglutinin in Influenza is one of the cooler examples of this :) ",
"http://www.pnas.org/content/94/26/14306/F1.expansion.html",
"As a side note, I find wild protein actions like that absolutely fascinating, structural biology is awesome."
] |
[
"Then you will love this one about production of hemoglobin. I do not think it is actually a simulation, but it has a strangely realistic touch. Might be the sound effects.",
"http://www.youtube.com/watch?v=GkdRdik73kU"
] |
[
"Energy Production Area Usage Question"
] |
[
false
] |
Hello people of , I have been reading about different energy production methods and have become more and more interested in nuclear energy, the LFTR especially makes me interested. And I started to think of space usage. Obviously, wind and solar farms need to take up a lot of space. But how much space is that? So what I am asking for is a comparison between how much area is needed to produce the same amount of energy for each energy production type (Wind, solar, nuclear (both today's current reactors and LFTR). Thanks!
|
[
"I would recommend watching the TED talk by David MacKay, ",
"TEDxWarwick - David MacKay - How the Laws of Physics Constrain Our Sustainable Energy Options",
".",
"He's the author of the book ",
"Sustainable Energy - without the hot air",
", which is an amazing book for examining sustainability with electricity for the long term of the earth, and is the chief scientific advisor to the UK Department of Climate Change.",
"In his TED talk he specifically discusses the land mass use and unit energy per unit land area as a way to compare various energy sources, and I think that will give you the answer your looking for. LFTR will use the same land area as a conventional nuclear plant FYI."
] |
[
"Awesome! Thank you very much, I shall watch this right away"
] |
[
"There's a thread over at the ",
"EnergyFromThorium forums",
" that tries to visualize the energy density of different sources of energy.",
"This post",
" have a very nice graph that shows how many % of earths land mass is required to produce all the worlds energy demand 2010 using different energy sources."
] |
[
"Do we know why those with Autism/Aspergers/ASD tend to fixate and obsess intensely over certain perhaps unusual things?"
] |
[
false
] |
I have ASD and I've always wondered this. I was thinking that in a similar way to the proposed model of Aberrant Salience for psychosis (which says that psychotic symptoms first emerge when excess dopamine leads to the attribution of significance to stimuli that would normally be considered irrelevant), a similar thing happens in ASD. Am I on the right track or am I completely off?
|
[
"The neurolobiokogy behind autism is way more complicated than that behind schizophrenia. We simply don’t know currently. That’s why there’s no FDA approved drug to treat autism, unlike ADHD, Schizophrenia, or depression. ",
"The FDA does approve some antipsychotics to use in autism but only for autistic agitation (rage) . "
] |
[
"Treat and cure have slightly different meanings in English. When we treat a disease, we're just making it better, but when we cure a disease, we make it go away. Some treatments lead to cures, but not all."
] |
[
"A lot of a misinformation here so I thought I’d pipe in.",
"So far what we think could be the cause of ASD, or at least connected to ASD, is failed apoptosis in the cerebral cortex. Apoptosis is planned cell suicide, and failures in apoptosis are implicated in various diseases, most notably cancers, tumours, and some others.",
"Considering the symptoms, and the volume of the brain increasing more rapidly than it should, it’s likely that the language, communication, and other areas/centers of the brain are compressed, leading to inhibited growth, development, and activity. The cranium has a likited space, anything in excess will lead to the detriment of another structure. Unfortunately we still aren’t certain of what occurs, but we do have various leads and various associated symptoms for ASD that could eventually lead us to an answer.",
"A decent read: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4688328/"
] |
[
"Quantum Diffraction of a Macroscopic Object"
] |
[
false
] |
In Chad Orzel's book 'How to Teach Physics to your Dog,' he explains that a 20 kg object (dog, in this case) has a wavelength of 10 meters. To diffract around a ten centimeter barrier, the object's speed would need to be 10 m/s. Am I wrong in thinking these speeds could be achieved by cooling to near absolute zero? Would it be possible to diffract a macroscopic object if cooled enough?
|
[
"lambda (wavelength) = h/p = h/(mv)",
"To diffract around a 10 cm (.1m) barrier: .1 = h/(20kg * v) -> v = h/2 m/s",
"That's around 10",
" m/s. T = mv",
" /(3 k_B ) where k_B = 1.38e-23",
"that's around 10",
" degrees K... The lowest temperature ever attained with a few atoms is 10",
" K. I don't think it's gonna happen."
] |
[
"No, to my knowledge bucky balls which are predictable, have been shown to have a DB wavelength and show quantum behavior under certain circumstances.",
"The point of this was simple; it's unknown. We can't test those systems, so we can't say anything about them except what they would probably do."
] |
[
"Would it be possible to diffract a macroscopic object if cooled enough?",
"I would hazard a guess: probably not. The state of a macroscopic object is coupled to the state of its environment in a thermodynamically irreversible manner. This results in quantum decoherence, which is one of the reasons macroscopic objects don't exhibit quantum behaviour. Even a very cool object is still coupled to the environment, so it's still quantum decoherent."
] |
[
"How does vaccinating trees work?"
] |
[
false
] |
I was walking on the street when I saw two guys in high Vis coats injecting a tree with something. When I asked them, they told me they were vaccinating the tree. I never realised that plants could be vaccinated or that they had something like an immune system. Could someone knowledgeable on this explain how the vaccine works, what kind of vaccines are available and for what plants and what they can protect against, and how long they last?
|
[
"I think he over simplified what he was doing, but it was most likely some sort of fungicide or bactericide. The only case I know where it is commonly use is for ash dieback, a fungus transmitted by the emerald ash borer. It's a good way to make sure it is transmitted through all the tree's system."
] |
[
"I am unaware of any adaptive immune responses in plants (ie what a vaccine would work on). There are some attempts to prime the innate immune responses in order to illicit a stronger response, but that is not a vaccine.",
"[",
"source",
"]"
] |
[
"Ah that makes sense. It's still interesting that you have to inject a bactericide or fungicide for it to spread well.",
"I found this article and assumed that it was a vaccine, but actually reading it, it seems more like what you described. ",
"https://www.newscientist.com/article/mg16021641-100-a-jab-for-trees/",
"So compared to vaccines where your body would generate the antibodies. This is kinda like just placing antibodies everywhere inside the tree, with the tree being passive in all this?"
] |
[
"Theoretically, what would happen to a mother and child if the umbilical cord was never cut?"
] |
[
false
] |
Professor did not have an exact answer. Just a question, what would happen if up to say, age 20, the cord just wasn't cut? (all this is in theor, of course.)
|
[
"Well, considering that the umbilical cord is connected to the placenta, and the placenta is \"delivered\" by the mother within hours after childbirth, not much would happen if you leave it attached. Some people actually do leave the umbilical cord connected -- it will dry up and eventually fall off after a few days. "
] |
[
"Well, nothing happens to the mother because the placenta gets comes out very shortly after the baby is delivered - it gets detached from the her...as for the baby, I can't imagine much happens - it'll just just be a gross, stinky mess having to lug a baby and placenta around."
] |
[
"Thank you. Didn't know what to expect for answer but thank you for such a straightforward one."
] |
[
"Why would the food industry use embryonic human cells in the production of \"flavor enhancers?\""
] |
[
false
] |
It's a link to an anti-abortion group American Life League, so don't click if you don't want to give them hits. The gist of the article is Senomyx Biotechnology produces flavor enhancers for food giants—Nestle, PepsiCo, Cadbury Adams LLC* (a Kraft company) and Solae—using aborted fetal cells HEK-293 (human embryonic kidney), which were taken from an elective abortion in the 1970s. What do food companies use human cells for? Is this something worth getting upset about?
|
[
"Senomyx used that cell line to ",
"test how receptors respond to taste",
". They ",
" \"produce\" flavor enhancers using those cells - that's at best misleading reporting, and at worst complete libel, to further ALL's agenda."
] |
[
"HEK 293 cells are a very widely used cell line. Damn near every biology research institution in the US and Europe has a vial or two of them frozen down somewhere. I think I have a few in my storage tank. ",
"Yes, they originally came from an aborted fetus, but they are a stable transformed cell line. This means that they can be grown essentially forever, much like the famed HeLa cells. ",
"They are not killing babies to make soft drinks, test soft drinks, or whatever. ",
"People often use HEKs for transient transfections; you make them temporarily express a specific gene of interest to try to analyze how the gene product works. ",
"In this case, the are expressing receptors known to respond to certain taste signals and then exposing them to certain signals to see if they can get a response. "
] |
[
"I was looking for information from knowledgeable sources. I'm not exactly sure what you're implying, but I definitely was skeptical of the article, especially considering the organization that posted it. "
] |
[
"Is there a \"complexity threshold\" at which a sound wave becomes unintelligible to our brains?"
] |
[
false
] |
One of the special features on a DVD I own has all of the episodes from the disc play at the same time (more like "annoying feature," amiright?). As an experiment, I tried to pick up any of the dialog from one of the 12 or so scenes but really wasn't able to. With so much language being spoken, my brain couldn't follow any of it. Is there a known complexity level, so to speak, at which our brain can't distinguish individual sound sources? And, does it vary for language vs. environmental sounds? For example, is this "confusion" threshold lower for language patterns than it is for picking up non-language sounds against a crowded non-language noise field?
|
[
"There isn't really such a known level. In fact, there isn't even a reliable way to measure the complexity of speech in noisy environments.",
"There are a lot of factors that contribute to how well we can understand the speech (the \"speech intelligibility) of a given speaker (the \"target\") when other conflicting sounds (called \"maskers\") are present. We know many, but not all, of the general rules involved. Some of those rules are:",
"However, algorithms meant to actually rate the intelligibility of one target/masker situation relative to another don't do very well when compared to real human listeners in realistic situations, even if we eliminate higher-level factors like context. It is a complex interplay of many factors, and although we have a pretty good idea what those factors are, we don't have as good a handle on how they interact with each other in complex, real-world situations."
] |
[
"This is a really great response. Thank you. My understanding of hearing is that the brain is basically doing a Fourier transform. Do you know if anyone has looked at the signal complexity itself to see if there are anything approaching objective measurements? "
] |
[
"It is more complicated than an ordinary Fourier transform. And it isn't the brain doing it, it is the inner ear itself. Different parts of the inner ear respond to different ranges of frequency. This means the sound is broken up into overlapping, asymmetric, roughly logarithmically spaced frequency bands. Further, there is an active feedback component that can alter these frequency bands on-the-fly. And the frequency bands change width depending on the loudness of the sound.",
"Looking at various measures of complexity was one of the first things they tried. It is just a very, very poor predictor of intelligibility except in very artificial situations."
] |
[
"Electrons and Double Slits"
] |
[
false
] |
I keep hearing how observing Electrons passing through a "double slit" produces a pattern like a particle, but not observing produces a wave [interference] pattern. Is this as literal as it sounds? For example, when you power on the observing machine it flips to a particle pattern and when you power it off it abruptly changes back to an interference pattern? That sounds crazy, but I understand the whole concept is crazy anyway. Have any of you science Redditors actually observed [or not observed] this?
|
[
"Is this as literal as it sounds? For example, when you power on the observing machine it flips to a particle pattern and when you power it off it abruptly changes back to an interference pattern?",
"As long as you understand that the \"observing machine\" is not independent of the system. It makes as much of an impact as one ",
" a pitch to test if a pitch has been thrown - it changes the system."
] |
[
"I hate this video, not only because it's an excerpt from a video promoting a cult, but also because it's implications are totally false. The video implies (and the aforementioned cult hinges on this implication) that the electron is aware it's being watched ",
" any sort of interaction.",
"This is wrong because in order to observe the electron you must interact with it. This interaction is what causes the wavefunction to collapse, and although still very bizarre, knowing this makes the experiment a whole lot less \"magical\"."
] |
[
"I hate this video, not only because it's an excerpt from a video promoting a cult, but also because it's implications are totally false. The video implies (and the aforementioned cult hinges on this implication) that the electron is aware it's being watched ",
" any sort of interaction.",
"This is wrong because in order to observe the electron you must interact with it. This interaction is what causes the wavefunction to collapse, and although still very bizarre, knowing this makes the experiment a whole lot less \"magical\"."
] |
[
"What about the other 99% of electrons NOT in the outer shell? Do electrons in complete inner electron shells do anything interesting?"
] |
[
false
] | null |
[
"You are correct in the second sentence: Because electrons are indistinguishable there is no meaning behind saying that they swap orbitals. ",
"To put it another way, if two electrons swap spots it's exactly the same as if nothing happened"
] |
[
"I can't answer for what they do chemically, BUT they definitely are still important physically.",
"For example:",
"Most X-ray generating tubes work by bombarding a material with electrons, seeking to knock out inner shell electrons. When these inner shell electrons get knocked out the electrons in higher levels replace them (since the inner shell is more stable) releasing photons as characteristic X-rays. Because the exact wavelength of the X-ray light is determined by the energy difference between the bands these X-rays can be used to identify elements (Energy Dispersive X-ray Spectroscopy).",
"Also, the non-valance electrons still have a charge and so the Van der Waals interaction will be stronger in heavier (i.e. more electrons) elements."
] |
[
"The inner electrons play a role in certain nuclear decays, like ",
"electron capture and internal conversion",
"."
] |
[
"Classical explanation of radiation pressure?"
] |
[
false
] |
I understand Maxwell's prediction, that the oscillating electric component of the wave will oscillate a charge perpendicularly to the wavefront, and the magnetic component will then give a net force in the same direction of the wavefront. This only explains the phenomenon for a charged particle though, and from this explanation, a neutral particle would not experience a force, and hence should not experience radiation pressure. But experiment shows that even neutral surfaces will experience radiation pressure. So, from a classical em wave point of view, what is happening?
|
[
"I don't really know of any acceptable answer other than to say that it is a property of the E (electric) and B (magnetic) fields to carry momentum, because if they did not then conservation of momentum would not be satisfied. A bunch of math can be done to show this is the case. And from that more math can be done to derive an expression for the pressure generated from an oscillating E and B field. I suppose the key idea comes from the Poynting Theorem and the poynting vector. "
] |
[
"I understand arguments for why the wave must carry momentum, but how does it transfer this momentum classically?"
] |
[
"If you understand that the fields carry momentum then I'm not quite sure what your problem with E+M waves in particular is. If a wave has momentum then clearly when it hits something momentum will be transferred (based on the properties of the object that it is hitting), since the light momentum is no different than your car's momentum. ",
"Perhaps you might like Griffiths explanation:",
"The electric field drives charges [the electrons/protons] in the x direction, and the magnetic field then exerts on them a force in the z direction. The net force on all the charges in the surface produces the pressure."
] |
[
"Does the use of microwave ovens distort chemical structures in foods resulting in toxic or otherwise unhealthy chemicals?"
] |
[
false
] | null |
[
"Yes, microwave ovens distort chemical structures in foods. The heat from the microwave energy causes proteins to uncoil and change their shape, causing their texture and flavor to change. This phenomenon is known as \"cooking\", and is the same whether you microwave, boil, bake, or fry food."
] |
[
"Piggybacking the top comment, microwaves actually create ",
" harmful chemicals than most other cooking methods. Any cooking method that creates char or browning (grilling, frying, searing, and even baking) creates carcinogens. Microwaving has a hard time creating char because it primarily boils the water in the food and boiling water tends to top out at a relatively cool 212F."
] |
[
"Way too late to the party but I literally did my human nutrition MSc dissertation on how cooking methods alter nutrient content so figured I'd contribute anyway, especially since that info hasn't been of much use anywhere else up to now! Microwaves don't radiate your food, as many believe, they simply excite water molecules which then transfer that energy (in the form of heat) to the rest of your food. This is therefore a fairly innocuous cooking method, and other than warming it up / denaturing proteins it isn't going to do an awful lot to your food. It's also pretty good for preserving micronutrient content for this reason.",
"EDIT: Some people had further questions, so I've uploaded my literature review ",
"here",
" if anyone else is interested."
] |
[
"How are eyeglass lenses made and cut? How are existing lenses tested for prescription?"
] |
[
false
] | null |
[
"Episode of ",
"How It's Made",
" may shed some insight."
] |
[
"Lenses start as \"semi-finished\" blanks, that look like hockey pucks. They are cut or \"surfaced\" by a diamond or carbide blade in a computer controlled machine called a \"generator.\"",
"Lenses are measured or \"neutralized\" in a machine called a lensometer, or vertometer.",
"Prescriptions are measured mainly in Diopters, which is semi-related to metric units of distance. "
] |
[
"In terms of measuring the prescription, a piece of equipment called a focimeter is used. It looks a lot like a microscope.",
"With the manual type, the lens is gripped on a table, and you view through an eyepiece a lit 'grid' which is projected through the lens. There is a dial on the side of the focimeter, and as you turn it, different aspects of the light grid become clear.",
"The majority of prescription lenses have 3 basic components - known as sphere, cylinder and axis. The sphere and cylinder refer to curves which cross each other at 90 degrees to one another - these curves give the lens it's 'power' measured in diopters. Power being how much it will bend light. The axis refers to how that cross is positioned on the surface of the lens.",
"As you turn the dial and get part of the grid in focus, what you have basically done is move components in the focimeter to 'cancel out' the power of the lens. There are markings on the dial from which you can read off the lens power at that point.",
"Then, you just need to keep turning until you get the other section of the grid in focus, this will give you the power of the other curve in the lens.",
"The axis is determined by rotating a graticule to line up with the clear parts.",
"Some lenses only have a sphere component - those are the easy ones to read! ",
"There are automatic machines these days, but it's way more fun doing it manually!",
"Edit: this picture shows both the unit, and the view when you look though: ",
"focimeter"
] |
[
"Do Most Comets Orbit in the Same Plane as the Planets?"
] |
[
false
] | null |
[
"There are three(ish) types of comets. Inner solar system short period comets, outer solar system short period comets, and long period comets. A typical inner system short-period comet might be something like ",
"9P/Tempel 1",
", which orbits the Sun every 5.6 years, and has an orbital inclination of 10.5 deg. A typical outer solar system short-period comet might be something like ",
"Halley's Comet",
" which orbits the Sun every 75 years and has an inclination of 162 degrees (making it effectively retrograde). A typical long-period comet might be ",
"Hyakutake",
" with a period of about 70,000 years (and an aphelion of about 3400 AU) and an inclination of 124 degrees.",
" comets are likely undiscovered, and exist in the Kuiper belt out through the Oort cloud, having never gotten close enough to the Earth during human civilization to be visible as a stereotypical comet with a tail. Those comets have a pretty big spread of inclinations, they aren't precisely spherically distributed but they have a larger range of inclinations than the planets."
] |
[
"No, that's still not right - Earth's axial tilt is 23.5°."
] |
[
"Not sure where you got that 29.29° figure, but the orbital inclination of Earth is 0° by definition. The other planets are ± a few degrees from that."
] |
[
"What would it take to alter the earth's rotation?"
] |
[
false
] |
I thought this would be a simple "I'll Google that" but it was not. What I mean is, what would it take to speed up or slow down our rotation? has some pretty interesting stuff, but not what I'm looking for. Anyone out there know where I should go to look for this?
|
[
"This can be calculated via energy equations. Basically you are going to need something that has a significant mass compared to the mass of the Earth...which you can't really get from on the Earth. Your best bet would be to make use of some extraterrestrial energy source, like an rogue small exoplanet heading somewhat near Earth, and try to deflect it early on to collide with us."
] |
[
"To make that kind of change in the moment of inertia you would need to have a huge change in the geometry of the planet, or add a hell of a lot of energy from somewhere. The first is impossible. The second would require a asteroid/planetary impact of such magnitude that changing the length of the day is the least of your worries."
] |
[
"I'm not sure what you mean. Even if you just sit down (move your center of mass closer to the Earth's) you'll speed up it's rotation slightly. Everything that interacts with the Earth has an effect on it's rotation. Perhaps a notable one is as the Moon moves farther away the Earth slows down. In about 2-3 billion years you can expect days to be twice as long if the current rate continues."
] |
[
"What is the biochemical origin of caffeine dependence?"
] |
[
false
] |
There's a joke that if you've been drinking coffee for a long time, when you wake up you'll need a coffee to get you back to the point where you were before you started regularly drinking coffee. But, if you stop for a week or two, your baseline goes back up. What happens to regular coffee drinkers to lower their baseline wakefullness, and is it chiefly neurological or psychological?
|
[
"Caffeine is a nonselective adenosine receptor antagonist, acting at A1, A2a, A2b, and A3 receptors (it also binds to a few other receptors, but we’ll ignore those for simplicity’s sake). From knockout studies in mice, it appears A2a is critical for the stimulating effect of caffeine. In the brain, Adenosine levels fluctuate as the day passes with the highest levels at night. Higher levels of adenosine produce a drowsiness effect. When you consistently apply an antagonist to a cell, a common response is the cell will upregulate the particular receptor that is being antagonized. As such, consistent caffeine intake can result in an upregulation of adenosine receptors [1]. When you do not intake caffeine, you thus experience a heightened response, or a sensitization, to adenosine, and thus feel an increase in drowsiness. "
] |
[
"Antagonist meaning that caffeine binds to the adenosine receptor and blocks adenosine from binding. Importantly, caffeine binding to the receptor produces no effect. Conversely, adenosine binding to the same receptor would cause an effect (adenosine is an agonist).",
"\nUpregulate simply meaning the cell increases the number of adenosine receptors on its cellular membrane. "
] |
[
"Can you define antagonist and upregulate in this context? Thanks!"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Why is it that SSRIs treat so many things? Is it that depression, bipolar disorder, anxiety etc. are all related in some way, or is it that serotonin modulation just happens to alleviate each of them through different mechanisms?"
] |
[
"Bisphenol A is still a topic of discussion among health agencies; however, many of the bans in place today are purely to allay growing public concerns. In 2011 the EPA listed BPA as a non health concern. BPA is a naturally occurring hormone that is incorporated into products such as the lining of food cans, water bottles, plastic products, etc. ",
"Here is a report from 1985 where BPA was addressed as a low to moderate toxin with low potential for bioaccumulation:",
"http://www.sciencedirect.com/science/article/pii/S0045653597101333",
"Here is another report on current BPA levels and human toxicity:",
"http://www.tandfonline.com/doi/abs/10.1080/10590500600936482#/doi/abs/10.1080/10590500600936482",
"The report concludes by saying that Bisphenol A is not a carcinogen and is rapidly excreted through urine (as stated in the abstract).",
"Some more educated concern about BPA is that is can mimic estrogen or more specifically estradiol, causing the chemical to be an endocrine disrupter. Most concern from researchers I found revolved around infant and toddler exposure to BPA. At the very least BPA should be limited in young children. The general consensus is that current levels of BPA are not significant enough to cause harm in humans or animals. Although laboratory tests have been shown to have ill effects: ",
"http://m.toxsci.oxfordjournals.org/content/54/1/154.short",
"TL;DR - As with most things BPA can be dangerous in large amounts. Current BPA exposure is quickly excreted from the body. Don't swim in hand sanitizer (for multiple reasons). Companies have largely banned BPA to placate growing public concerns. Public concern, while not completely unfounded, is not justified due to current research. "
] |
[
"Serotonin is involved in many aspects of mood regulation and anxiety, but it's not entirely clear why serotonin agonists alleviate symptoms. That said, it's generally not advised to treat bipolar disorder with SSRI medications, as research has indicated that they are correlated with hypomanic or manic episodes, though, again, we're not 100% sure why.",
"Personally, I prefer these medications be used as scaffolds so that patients can do the cognitive and behavioral work necessary to make more substantive and lasting change."
] |
[
"How does melatonin exactly work in regard to sleep? What are the physiological mechanisms that are implicated?"
] |
[
false
] |
I can't seem to find anything on how it exactly works.
|
[
"Hey there. This is a biochemistry question, with an answer that will (essentially) be gobbledygook if you aren't a biochemist.",
"A short example of what im talking about here:",
"\"Melatonin is a derivative of tryptophan. It binds to melatonin receptor type 1A, which then acts on adenylate cylcase and the inhibition of a cAMP signal transduction pathway. Melatonin not only inhibits adenylate cyclase, but it also activates phosphilpase C. This potentiates the release of arachidonate. By binding to melatonin receptors 1 and 2, the downstream signallling cascades have various effects in the body. The melatonin receptors are G protein-coupled receptors and are expressed in various tissues of the body\"",
"This is an exerpt from here:",
"https://go.drugbank.com/drugs/DB01065",
"The short answer- it's complex, biochemically speaking, and not actually fully understood yet. But it affects things like adenosine pathways (I think? Adenylate cyclase, from memory , is part of this pathway. Adenosine mediates alertness, and is blocked by caffeine, which is why caffeine keeps you awake, and why when you adjust to caffeine you are sleepy/less alert without it- because adenosine receptors up-regulate in order to compensate. This means that you then have an over abundance of adenosine receptors and you ",
" caffeine just to feel normal) . But i degress. The point is this is just one pathway that melatonin plays a role in.",
"I have studied biochemistry (a lot of which I have forgotten lol) but mostly I am familiar with some of this because I have autism (this is mentioned in the link provided) and people with autism produce less melatonin. I take it regularly for this reason.",
"Hope that helps at all?"
] |
[
"This helps immensely so thank you very much. Ive read in a few articles that the mechanism is still relatively unknown but i wasn’t sure if that was an isolated fact or not. But yes thank you a lot"
] |
[
"serotonin is converted to melatonin",
" in the pineal gland, a small endocrine gland located in the brain near the hypothalamus.",
"When there is light, the eyes receive this light and send signals via the retinohypothalamic tract to the hypothalamus (specifically, the suprachiasmatic nucleus). This in turn signals the nearby pineal gland to stop producing melatonin, by blocking the enzymes that convert serotonin to melatonin. ",
"When it's dark, there's no input to the hypothalamus and the pineal gland begins producing melatonin. This is what is referred to as the circadian rhythm. Melatonin then goes on to bind to MT1 and MT2 receptors which, among other things, inhibits neuronal input of the suprachiasmatic nucleus (SCN) and promotes the 'sleep' phase of the sleep cycle. MT_1 decreases the frequency of the SCN electric activity via inhibition of adenylyl cyclase, whereas MT_2 shifts the phase of circadian rhythm. This is why melatonin and other melatonergic drugs are effective at treating sleep disorders brought about by disrupted circadian rhythm, like jetlag or night-shift workers. Melatonin also has long-term effects through gene transcription via CREB, where it contributes to memory retention and early brain development. ",
"FURTHER READING:",
"https://pubmed.ncbi.nlm.nih.gov/27314810/",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5091650/"
] |
[
"[physics] How does gravity differ across a planet?"
] |
[
false
] |
There is a post in about a gravity map of the moon. It varies. How does this occur? My limited understanding is that gravity is determined by mass, the more mass the greater the gravity. This is also affected by the density of the mass, with both mass and density playing together to make gravity. So is the variation in gravity across the moon (or another planet) due to pockets of more dense elements? Is it just averaged out? How does the fluctuation in gravity across the earth affect the orbit of say, the It's?
|
[
"This is the image",
" you're referring to? Which annoyingly doesn't have a legend to tell you the values. They do say that red corresponds to high mass values and blue are low values.",
"It's important to note that when you learn about calculating gravity in your physics 101 class you are treating them as point masses. You are concerned with the mass of 2 objects and the distance between them. Planetary bodies are not point masses and have heterogeneity when it comes to the distribution of the mass. ",
"These values you are seeing are gravity anomalies. They are the difference from what you expect to measure there. Gravity as an exploration tool is notoriously difficult but it is used extensively in mineral exploration or looking for sinkholes. There are ",
"a lot",
" of corrections you have to make to insure that the measurement is correct. Also, gravity anomalies aren't measured using g. They are measured using Gal (more often mGal). 1 g = 980 Gal. You can look at this ",
"gravity anomaly",
" map of the earth and see that there is only about 100 mGal of difference. This is only 1.02x10",
" g of variance. It's so small that it would be averaged out in rounding.",
"Effectively, when you look at these maps, you should look at them as distribution of mass/density. It's used in mineral exploration since the metals are more dense and you'll get large anomalies. Sink hole exploration would give you values that were lower than you expected (since there a big hole underneath you)."
] |
[
"The ISS has about 90 percent the gravity of the earth. That's ~100 Gal (100,000 mGal). That's a huge difference when doing calculating anomalies compared to the ~100 mGal difference on earth. This difference is included when they do their corrections (free air). Again, without knowing the actual values I can't really compare the two. You're effectively measuring very very small differences in density."
] |
[
"They're on a linear scale. The measurements are just really small. "
] |
[
"If you drop something made of glass and it doesn't break, does it weaken the glass at all in case you drop it again?"
] |
[
false
] |
[deleted]
|
[
"I'm sorry, but the unhelpful (but true) answer is: it depends. ",
"If you dropped just plain glass that has not been toughened or coated, yes, it will weaken. This is because you would introduce microcracks in the glass which would then act as stress concentrators that amplify future stresses.",
"If you dropped a toughened/coated glass, it depends on how much impact there was and whether there were existing defects in the glass. If there were, you'd probably have propagated a crack, making it weaker. If the impact was mild enough or the glass strong enough, nothing will happen. ",
"tl;dr: Cracks are stress concentrators. If you grow them or create them, you've weakened your glass object. "
] |
[
"This guy knows what he's talking about. Most glass is very brittle, meaning that when you subject it to loading it only deforms elastically. Elastic deformation is completely reversable and is the result of the bonds between atoms stretching like rubber bands, once the force is removed the bonds return to their original length and the material is in the exact same state it started.",
"Of course cracks are a different story. Obviously if a crack forms (or propagates) in the material, it doesn't go away when you remove the force exerted on the glass. As j3thro said, these cracks will act as points of stress concentration, making it more likely that damage will occur in that area when a stress is applied on the material again.",
"I don't know how much detail I should go into things, since fracture mechanics is a very broad and complicated subject, but I'll try to paint a very broad picture of what can happen. Let's consider three different cases where we drop a block of glass from different heights:",
"The first block is dropped only a short distance, when it hits the ground it has a force exterted on it which results in stresses being applied throughout the material. However, since the force upon landing is small, the stress is within the elastic limit and results only in elastic loading as I described above and no permanent damage is done to the glass.",
"The second block we drop from a very large height. The force acting on the block results in incredibly high stresses that are concentrated by tiny microscopic flaws that exist in the material. Enough energy is involved in these stress fields to cause these tiny microcracks to propagate unstably, shattering the block as thousands of cracks form and propagate, merging with one another and splitting the block into thousands of tiny shards.",
"The third block we drop from some intermediate height. The force of landing results in stresses that exceed the elastic limit, but are not quite large enough for the cracks to grow unstably or merge with one another. Therefore, we get the formation of some new cracks and the growth of existing cracks. These cracks act as stress concentrators that have stress fields surrounding them. If we kept repeatedly dropping the block from this height, we would grow the cracks a little more each time. Eventually, the cracks throughout the material would grow enough that their stress fields start to overlap, these stress fields are additive, so once cracks get close to each other they concentrate stresses even more effectively and it becomes very easy for the cracks to merge. Of course when enough cracks merge, the block of glass will simply start falling apart.",
"Keep in mind that this is a very simplified model, but it should give you a general idea of how things work. "
] |
[
"Pyrex is a brand name.",
"In the USA it used to be made of ",
"borosilicate glass",
", however now uses ",
"soda-lime glass",
" (with regard to kitchenware, lab equipment under the Pyrex brand is still all borosilicate in the USA). Any US Pyrex pre-1998 is borosilicate."
] |
[
"What would happen to the structure of a radioactive diamond as it decays?"
] |
[
false
] |
For a diamond made entirely of carbon-14, which I understand undergoes beta minus decay into nitrogen-14, what will happen to its tetrahedrally bonded structure as individual carbon atoms decay, and are replaced by nitrogen atoms? One idea I had was that the nitrogen escaped the structure leaving gaps in the lattice. If this occurs, would the diamond then conduct electricity, (given a significant proportion of the carbon had decayed) since some carbon atoms will be only bonded to 3 others, and will therefore have free electrons, similar to graphite? Also, if the nitrogen were to escape, would it have to form nitrogen molecules as it does so (and therefore two adjacent carbon atoms would have to had decayed?), or would it leave the structure as singular nitrogen atoms? Finally, could the nitrogen remain tetrahedrally bonded in the structure (forming four bonds to adjacent atoms rather than the usual three)? If so, after all of the atoms have decayed, what would you be left with? Bonus question: would a diamond made of carbon-14 look any different to a regular diamond, i.e. refract light any differently? Sorry this question is so long, but I'd be interested to find out what occurs, or if I have misunderstood the idea completely.
|
[
"I'll take a naive stab at it: diamond is basically silicon in many, many ways. They are both group IV atoms that form diamond lattices that result in semiconductors. The real difference is that the bonding is stronger in diamond which is why silicon, as a semiconductor, has a bandgap of Si is 1.1 eV where diamond has one 5 times larger (5.5 eV). Nitrogen, like phosphorous and arsenic, is an n-type dopant for a group-IV semiconductor. Thus, initially the diamond would behave just like a diamond that is becoming more and more n-type. Electrical conductivity would increase exponentially with doping (i.e. conversion of C to N) but optical properties, to first order, would remain largely unaffected as the bandgap narrowing would be minimal.",
"However, there's a catch. We don't actually use nitrogen as a dopant in silicon because of its very low solubility in Si. What solubility means is that below the solubility limit, you basically have N playing nice with Si and basically it just takes the spot of an Si atom in the lattice but you still have an Si diamond lattice, just with the occasional N atom. Beyond this solubility limit, the nitrogen begins to form its own separate phase. So you no longer have N taking the place of Si, but rather separate regions of some nitrogen compound and silicon. They separate. At this point the material would start to behave like undoped diamond again with large defect grains whose average size increase as the average size of N precipitate grows. However, I don't actually no the solubility of nitrogen in CARBON. So that picture may change a lot, but regardless at SOME point you'll be past the solubility limit.",
"Beyond that I can't help you, as I'm a physicist not a chemist and things become more about chemistry at that point. I don't know what precipitate nitrogen would form in diamond and I don't know if/when the material would crack or deform as the grain size of the N \"islands\" grew.",
"EDIT: The chemical symbol for nitrogen is N, not Ni, you think I would've remembered that...."
] |
[
"There is a thing called ",
"Nitrogen Vacancy Center",
" which is a Nitrogen atom replacing a C atom in a diamond next to a vacancy (missing C atom), so energy from the radioactive decay might promote the formation of such a vacancy (I don't know about the energies involved, so I cannot say how often this will happen).",
"With a half life of 5,730 years, C-14 will decay rather slowly, so any structural change is taken quite some time. So in the beginning the newly formed N will act as an dopant in diamond as ",
"/u/cantgetno197/",
" already explained, maybe also some N-V centers like I explained above. With higher and higher concentrations of N you would lose the \"diamond\"-character of your specimen, your C atoms would probably go towards the thermodynamically favored graphite structure. For the Nitrogen it is more favorable to be N2 (like in the air) compared to retaining the tetrahedal bonding of the diamond, but also the formation of some organic molecules like ",
"amines",
" is possible (with enough H coming from the surrounding)."
] |
[
"It's not an easy question to answer as atomic diffusion rates can vary by something like 10 orders of magnitude. Substitutional diffusion (i.e. jumping from a crystal lattice site to another crystal lattice site) is understandably slower, all other things being equal, than interstitial diffusion (an impurity atom just sitting in a gap in the lattice and jumping to another gap) for example. Here's a page with some neat little animations if the many types of diffusion that can occur:",
"https://www.tf.uni-kiel.de/matwis/amat/def_en/kap_3/backbone/guidedtour_r3_2_1.html",
"Size of the diffusing atom relative to the lattice constant (average distance between crystal unit cells) is obviously hugely important as well. For example, the diffusion constant for hydrogen (the smallest atom) to diffuse in iron is like 0.5 mm",
" /s, but the diffusion constant for iron to diffuse in iron is 400 mm",
" /s. Which is a 1,000x different.",
"But to throw down a number, some quick googling says that the self-diffusion of aluminum (i.e. aluminum atoms diffusing through an aluminum crystal structure) happens at a time scale of about 0.4 millionths of a second. Which is to say, I suppose, that an average aluminum atom may make about 2 million jumps a second. (honestly the source isn't that clear, I'm not sure if that's per atom or unit cell or what).",
"That may seem crazy fast, but to give some context, an electron in silicon will scatter off of acoustic phonons about a trillion times a second, so about a million times more often. "
] |
[
"Are memory techniques bunk? Is it actually possible to develop better memory?"
] |
[
false
] |
I have a bunch of formulas I need to memorize for school: is it really possible to become a person with great memory for abstract numbers/equations if you have never had mind for memorization before?
|
[
"Well, from the cognitive psych I can remember, the short term memory uses something called ",
"\"chunking\"",
" (~mnemonics when people do it actively) to store information for quick recall, so if you broke your formulas down to simpler chunks, you could potentially remember them more effectively. The problem is that the whole \"magic number 7\" thing is actually quite well supported, and while more nuanced in its specifics, 7±2 is pretty accurate. So if your formulas are very long it may not be easy even with chunking/mnemonics to remember it all. But I'd say within limits it is possible to train your memory so that you encode things more efficiently so they can be retrieved more easily."
] |
[
"I definitely think this is true, but it's a skill that needs to be developed and takes an investment of time and effort to get results. Our brains are wired to be good at remembering some types of information (e.g. unusual things, emotional moments, stories, music) but not so good at others (strings of data like a phone number). Many memory techniques are a way of encoding information from one of these difficult formats into something more suitable. ",
"I have done a little experimenting myself when I wanted to remember a lot of rather boring information. A strategy I used was to turn individual pieces of information into a funny picture in my head, then I would create a story that linked these pieces of information together. The power of this approach is that if you can manage to remember any single part of the story then it prompts you to remember the rest of the story. It's also pretty obvious if there's a hole in the story which helps you realise when you're forgetting something. ",
"Just look at ",
"this guy",
". There's nothing really special about him -- no offense!! -- but he can remember the order of 3,068 cards. What I mean is that he's not some kind of abnormal freak or genius that ordinary people like us could never hope to be. He seems like a pretty normal dude who has worked hard to teach himself techniques for memorising things and practiced until he got really good at it."
] |
[
"Memory techniques aren't really about \"developing\" your memory. An analogy could be that of a man using a lever to lift an object. Has he developed his strength? No. He has learned a trick that exploits the laws of physics.",
"In much the same way, mnemonics exploit how your mind works rather than boost your memory.",
"Here are some simple principles of memory:",
"We remember absurd details better than those that are as expected. This is because the brain is biased toward new information (wanting to integrate it as part of your knowledge base).",
"One piece of information helps you remember another. This is because our brains are biased toward processing sequences.",
"When you combine a new piece of information with an old one, you are more likely to remember the new. This is because the old piece of information is stored in your long-term memory, and through association they get connected.",
"How can we exploit the three in one method? We can use the method of loci.",
"You take a familiar route (most people start off with their house/apartment) and place the information you want to remember at different locations (e.g. different rooms). It is important to make the mental images of the information absurd.",
"Take a simple grocery list with five items:",
"Then take a route with at least five points:",
"And combine them with an absurd twist:",
"I ",
"wrote an article on Medium",
" where I tried explaining how this works in terms of structures in the brain."
] |
[
"More prime numbers: Why can't we make a formula to determine every prime number, or \"predict\" which numbers will be prime?"
] |
[
false
] |
Why can't we make a formula to determine every prime number, or "predict" which numbers will be prime? I know there are certain numbers that have a non-negligible chance of being prime before you actually evaluate them for primality (such as Mersenne Primes), but why can't we actually develop a rule that lets us easily determine what all the prime numbers are? Thank you!
|
[
"What do you mean \"determine every prime number\"? We do have all of the following:",
"The problems are: (a) there's infinitely many of them, so if you try to make a list they never run out, (b) the algorithms for determining that a number is prime are very computationally intensive: it takes a lot of time, relative to the size of the number, to determine whether it's prime.",
"The tests for pseudoprimes (numbers that, if they pass the test, have a high chance of being prime) exist because of the cost of determining whether larger numbers are prime, not because we can't do it."
] |
[
"Yes, but he is asking for a \"formula\" that can predict the primes. I can't really answer because I don't know anything about number theory. But, the closest we have I think is riemann hypothesis. "
] |
[
"There are ",
"explicit formulas",
" for the nth prime, but they're not efficient."
] |
[
"How did extremely large dinosaurs with tails, e.g., amphicoelias fragillimus, mate?"
] |
[
false
] | null |
[
"Someone has wondered this before",
"This is at a museum in Spain."
] |
[
"This is a great demonstration but the OP is asking about much larger creatures. The Amphicoelias is a sauropod, and was an herbivore. The T-Rex or similar was much much smaller by comparison. ",
"Obviously these animals reproduced successfully, but I think the answer of how may come to speculation at this point, unless someone has a good reference to a study. "
] |
[
"Although there is no fossilised evidence of any Dinosaur with a penis we can look at animals today to answer this question. ",
"Modern Birds are a living members of the Dinosaur clade, by looking at the earliest bird species, the Ratites, we find reproductive appendages in the males that we can call penises. So we can infer that Dinosaurs were likely to have had penises as well. ",
"Ostrich penis",
"So to answer the question about how such a large animal reproduces we can look at modern large animals. Whales are the best example. Large baleen whales employ an enormous flexible penis to fertilise females movement of which they have almost complete controle over. Therefore sauropods like Argentinasaurus may well have come up with a convergent solution to the problems of large size and fertilisation. ",
"TL;DR... Sauropods probably had huge flexible penises to impregnate females. "
] |
[
"If I were traveling at the same speed as an electron, would I observe it generating a magnetic field?"
] |
[
false
] |
In other words, I know that a moving electric charge produces a magnetic field. So assuming there was a lone electron flying through empty space and I could match speeds with it and observe it while travelling parallel to it. Since, from my frame of reference, neither of us are moving, is it generating a magnetic field? If not? Intuitively I would think someone traveling slightly slower WOULD observe a magnetic field. I know this is somehow deeply tied to the questions which sparked Special Relativity, I can never find a good answer as to WHY though. It's been bugging me since I first started learning about Maxwell's Equations. Thanks!
|
[
"Your idea is correct, but in reality you see a magnetic field no matter what.",
"If the electron were a point charge ",
", the magnetic field it produces would be zero in any frame where it's not moving. And in any frame where the electron ",
" moving (no matter how slowly), the magnetic field would be nonzero.",
"But in reality, electrons have spin. And since they have spin and charge, they have an intrinsic magnetic moment. You cannot perform a Lorentz transformation to remove this magnetic moment, so it's present in all inertial frames.",
"So even when the electron is perfectly still, it has a magnetic dipole moment and thus generates a weak magnetic dipole field."
] |
[
"Still scratching my head about how the \"non-intrinsic\" field can be zero for one observer and non-zero for another. In possibly a naïve point of view, it seems like that indicates it both exists and doesn't exist at the same time.",
"The same can be said of a lot of things. Kinetic energy, for example. In a frame where an object is moving, it has kinetic energy. In a frame where it's stationary, it doesn't have any kinetic energy."
] |
[
"I thought that was a \"different\" phenomenon than the magnetic field generated by the moving charge?",
"Classically, they are exactly the same. If you have a charged object and you rotate it, it has a magnetic dipole moment because there is moving charge.",
"But quantum-mechanically, you can't really associate the spin of an electron with \"motion\", yet the magnetic dipole moment persists.",
"The problem here is not in your understanding, it's in your choice of an electron as the example. If you had a perfect point charge with no intrinsic dipole moment, then its magnetic field would be exactly zero in any frame where it's stationary.",
"But if instead of thinking about this idealized particle, you think about a physical electron instead, you cannot do away with its intrinsic dipole moment.",
"Would the non intrinsic magnetic field be absent for the viewer travelling at the same speed as a moving electron?",
"The \"non-intrinsic\" field is zero in any frame where the electron is stationary.",
"You said that even if an electron was perfectly still, Are you saying literally ALL movement including any intrinsic movement on the quantum scale? If so, How is the magnetic dipole moment generated?",
"The intrinsic dipole moment exists because the electron has charge and spin. You can never do away with the charge nor spin of the electron, so the dipole moment cannot be removed either.",
"Would that mean that the magnetic field actually has nothing to do with any kind of momentum/movement/velocity?",
"The problem is that \"movement\" and \"velocity\" are not concepts which have much meaning in quantum mechanics. But nevertheless, you can come up with situations where you wouldn't consider the electron to be \"moving\" at all, but it will still carry its intrinsic dipole moment, always."
] |
[
"If PI has an infinite, non-recurring amount of numbers, can I just name any sequence of numbers of any size and will occur in PI?"
] |
[
false
] |
So for example, I say the numbers 1503909325092358656, will that sequence of numbers be somewhere in PI? If so, does that also mean that PI will eventually repeat itself for a while because I could choose "all previous numbers of PI" as my "random sequence of numbers"?(ie: if I'm at 3.14159265359 my sequence would be 14159265359)(of course, there will be numbers after that repetition).
|
[
"\"As it turns out, mathematicians do not yet know whether the digits of pi contains every single finite sequence of numbers. That being said, many mathematicians suspect that this is the case\"",
"http://www.askamathematician.com/2009/11/since-pi-is-infinite-can-i-draw-any-random-number-sequence-and-be-certain-that-it-exists-somewhere-in-the-digits-of-pi/"
] |
[
" In addition to this, is that mathematicians don't know whether pi is a normal number or not, that is, whether every digit occurs equally often. It's suspected that pi is a normal number, though."
] |
[
"Yes, that's why it's ",
". Not proven."
] |
[
"Relativity and mass - how is it that matter gets more massive with increasing velocity if mass is imparted to matter by particles?"
] |
[
false
] |
I'll admit, I'm a bit baffled by all this. After a sci-fi movie binge, I got thinking about space travel. I stumbled upon travel through constant acceleration. I further read that the reason why traveling faster than the speed of light would not be possible under these conditions is because a spaceship would get more and more massive as velocity approaches c. I tried and made sense of it through different sites, but I couldn't find answers. Firstly, is it true that a spaceship approaching the speed of light would get too massive and therefore require too much energy to accelerate further? Secondly, I was under the impression that mass was imparted to matter by particles (perhaps the Higgs?). If that's so, how can objects get more massive with increasing velocity?
|
[
"Things don't actually get more massive as they approach the speed of light. That's a persistent myth about relativity.",
"However, mass isn't just the sum of individual particle masses: it's the total energy the objects have at rest. That's why nuclear fusion and fission can release energy: because the daughter products have slightly less mass than the mother products."
] |
[
"The amount of matter in the system does not change with speed.",
"The amount of energy the system has does change with speed.",
"The myth is that since an object takes more energy to accelerate to faster speeds, then its mass has increased, because a heavier object would also require more energy to accelerate to faster speeds.",
"This however is not true. The object does not gain any mass, just energy."
] |
[
"There is indeed a quantity called the invariant resting mass of the whole system, that gets bigger, if you increase the particles' speed.",
"In special relativity you form the so called four-momentum of a particle by combining its energy and momentum: (E/c, p) where p is a three-dimensional vector. From this objekt you can calculate the mass of the particle as the difference of the squares of the first (timelike) and the following three (spacelike) components:",
"m",
" c",
" = E",
" /c",
" - p",
" ",
"You can easily see that this is just an alternative expression of the relativistic energy formula.",
"\nSo this is an invariant property of a single particle, which means, that it has the same value no matter how fast you are moving relative to the particle.",
"\nBut it gets even better: if this particle is the only object in the world, then some easy assumptions about space itself make this four-momentum a quantity that doesn't change with time, making the \"mass\" a conserved quantity too.",
"If you look at a system with more particles, the same assumptions about space lead not to the conservation of every single particles momentum but only of their complete sum.",
"So for example in a 2-particle system the quantity",
"M",
" c",
" = (E1 + E2)",
" /c",
" - (p1 + p2)",
" ",
"is both, conserved and invariant which means that it stays the same over time and that every observer agrees about its numerical value and is therefore sometimes called the system's \"invariant restmass\" or its \"center of mass energy\".",
"Note that this can be seen as an explanation of particle collisions where new particles are created and therefore the sum of the masses is not constant: indeed it's only this invariant mass that needs to be conserved, not the mass of the respective colliding particles on their own. (Otherwise massless particles like photons could not create massive particles in a collision, which is indeed a regular process.)",
"Edit: well, now i forgot the most important point: if you look at the formula of the invariant mass again, it first seems as if bigger velocities made the mass smaller (because p1, p2 contribute with a minus) but you need to keep the constraint of the masses of the single particles in mind. When you increase One particle's momentum its energy will rise to. Well, there is one easy case of this equation you can directly analyze: you go to the center of mass system, where p1 = -p2.",
"\nThe equation reads then like:",
"M",
" c",
" = (E1+E2)",
" /c",
"Now it is easy to understand, that the mass will rise as the single energies increase and therefore as the particles get faster."
] |
[
"Can electricity wear down conducting media, like wires?"
] |
[
false
] |
I know transistors can be worn down by flowing current, but can wires/cables too?
|
[
"Yes, it can!",
"We typically think of electronics failures as a mystery, just throw it away and replace it if it fails. But electronic failure mechanisms is a growing research field, and the physics behind many electronics failures is quite fascinating. There are many different phenomenon that cause electronics to fail. Your question in particular - the flow of current wearing down the metal that carries it - is known as electromigration.",
"We think of current flowing as a constant, continuous thing. But at an atomic level, it is really countless discrete electrons moving from a cathode to an anode, being pressured to move by a potential difference. Well the electrons dont move in a straight line - there are atomic nuclei in the way ",
"Electrons are tiny, but they do have some finite mass. Millions and billions of them keep bumping int atomic nuclei as they make their way across a wire - and they can cause some of those atomic nuclei to move (think of it as momentum transfer - the electrons bumpo into a nucleus and transfer momentum to it). Eventually if enough electrons bump into enough ions, a crack (or area of poor contact) can form in the wire, rendering it useless. This happens on a tiny, tiny scale.",
"You may be thinking: The force of electrons hitting an ion is too small to break the metals atomic lattice! (Okay, maybe not) But its true. However, metals are not perfect lattices, they are a bunch of lattices (each alone is strong) that are bonded together in shapes known as grains. These grains are weak at their boundaries - and this is where electromigration typically takes place."
] |
[
"It's a growing problem in new designs for computer chips that have 3D integration. 3D integration meaning that, since we're basically at the limit for how many MOSFETs (the transistors that drive modern computer chips) can be crammed per area, there is a push to essentially have multiple layers of these things. I.e. if you can't put more transistors per centimeter square, than you can still fit a bunch in a centimeter cubed.",
"It also is a problem in power electronics I believe",
"Electrons flow from minus to plus; does that mean that they also push nuclei out the negative terminal",
"No, in no way are nuclei ever flowing in a conductor in the sense of \"current\". We are talking about, basically, the formation of and propagation of atoms that are out of their spot (atomic defects) in the regular crystal lattice, especially at grain boundaries. It's a story of the growth and propagation of the amount of defects."
] |
[
"If this is real, why don't we have copper flowing out of wires and into the next adjacent circuit element?",
"He's talking about the wire breaking down, not a flow of the metal at a macro scale.",
"Basically, you can see this with the wires becoming brittle, cracking internally or the resistance in the wires building up because of micro-gaps in the wire. Think of a light bulb burning out after being in use for a long time - what often happens is that the filament became brittle and cracked due to vibration or other stress.",
"Electrons flow from minus to plus; does that mean that they also push nuclei out the negative terminal?",
"No. Remember that the atomic nucleus has a positive charge, electrons aren't going to push a nucleus, they're attracted to it. It also weighs far more than the electrons do. "
] |
[
"Is it better to inhale bad fumes through the mouth or the nose?"
] |
[
false
] |
if you absolutely have to breath in bad fumes, is it better for your health to go through the nose hair filters (but through the olfactory receptors which worry me as it's a short path to neurons) or directly to the lungs? If it depends on the type of fumes, what are the general guidelines and why?
|
[
"Not an expert, but nose has hair and secretes mucous to help with some things. Olfactory receptors slowly regenerate because they are exposed to caustic materials."
] |
[
"Wouldn't it be throat and esophagus versus throat, esophagus and nasal passages?",
"Or do the nasal passages absorb a significant part before it goes to the pharynx?"
] |
[
"(Neuroscience undergrad here!) ",
"The olfactory bulb is one of two places in the human brain that holds neural stem cells, the other area being in the hippocampus where memories are formed throughout life. Here are a few papers on the subject:",
"Pagano et al., 2000",
"Gritti et al., 2002",
"Gage, 2000",
"Johannsen et al., 1999",
"Like normal stem cells, they can proliferate and differentiate if exposed to the proper growth factors / mitogens etc. "
] |
[
"How is it that it can be so light outside in the middle of the night in winter, in particular when snowing?"
] |
[
false
] |
It's nearly midnight and the sky has a very orange glow with everything outside easily visible.
|
[
"I guess if you live in a very light poluted area, and it snows, the snow scatters the light all over the place as it is crystals of frozen water. The have a refraction index and can redirect light so it might appear brighter. The same reason the winters with snow are usually brighter than the ones without. Asphalt absorbs most of the light, snow reflects most of the light."
] |
[
"You must live in a light-polluted area. The color you describe sounds like the sky I had when I lived in northern New Jersey - it's the sum of a zillion streetlights and signs. In a less populated area, you will not have an orange glow, believe me (telescope owners travel just to experience that)."
] |
[
"As the others have said, you must be in an area with high light pollution for what you are seeing to be emphasized when it is snowing (ie, when it is cloudy). Light from streetlights and such reflects off clouds and somewhat illuminates everything on the ground even if there are not streetlights immediately nearby. This happens summer or winter but the effect is magnified in winter since the ground is covered in white snow rather than dark colored grass and dirt. Same reason why a white room appears brighter when lit with a small lamp than a dark brown painted room. The white color simply reflects more light than the dark color.",
"That being said, even without light pollution, a full moon on a clear night can provide enough light to produce distinct shadows. With snow, a clear night with a full moon can appear almost like day. It is light enough to read by (with maybe a little eye strain) and dark things like a tree or house will stand out in a snow covered field for at least a half mile (probably more, it is hilly in my area so a half mile is a big field)."
] |
[
"Do superconductors conduct heat with no resistance?"
] |
[
false
] |
Since electrons encounter no resistance, I was wondering if a superconducting material would transfer heat with little to no resistance meaning it could stay in the material indefinitely. So for further context imagine cooling a solid chuck of superconductor and throwing it into the vacuum of space. If nothing acts upon the superconductor to heat it, would it stay cold forever, or would it eventually normalize? If the vacuum of space is throwing the experiment off with radiation, etc. then what about a perfect earthly vacuum. Would it always be cool, much like a superconductor would always retain electric current?
|
[
"No, superconductors actually have lower (electronic) thermal conductivity than a normal metal. This is sort of expected because superconductivity arises at low temperatures from a large amount of coherence between electrons, while heat is (very loosely) a measure of disorder, and superconductivity is killed at high temperatures. ",
"Superconductors are weird because the electric current is carried by the ground state (Cooper pairs) rather than the excitations (broken pairs). Thermal transport and specific heat get suppressed because they're still carried by excitations, which are very high energy since you need to break a Cooper pair. "
] |
[
"In addition, superfluids, which could be pictured as electrically neutral superconductors, are very good thermal conductors. The reason is that heat is transported by convection, which is very easy in superfluids, rather than diffusion.",
"For instance, the magnets used at LHC are cooled by not simply liquid helium, which is very cold, but by superfluid helium, which can get rid of excess heat much better."
] |
[
"heat is transported by convection, which is very easy in superfluids, rather than diffusion.",
"Do you mean the second sound?"
] |
[
"Does drinking coffee, or consuming other diuretics, result in a net loss of water from your body?"
] |
[
false
] |
I know diuretics cause increased urination, but since coffee and tea are mostly water, does my body wind up with more or less water than if I had not consumed any liquid?
|
[
"It's still a net gain. If you drink 100 ml of coffee, you'll pee slightly more than if you had drunk the same amount of water, but you're not going to pee away all 100 ml of that fluid.",
"You can survive just fine if the only liquid you consume is in the form of caffeinated drinks. You might have symptoms of mild dehydration, but the body can compensate. More significant risks would be heart palpitations (if you had ",
" of caffeine), or diabetes and weight gain if your chosen drink was sugary soda."
] |
[
"Caffeine has generally been thought to be a diuretic, ",
"though the extent to which that claim is true",
" ",
"has been called into question as well",
". At any rate, the amount of water you would consume from drinking tea or coffee would more than compensate for any diuretic effect."
] |
[
"If this were not the case, I would have shriveled up long ago.\nFrom a New York Times article March 4, 2008",
"Investigations comparing caffeine with water or placebo seldom found a statistical difference in urine volume, the author wrote. “In the 10 studies reviewed, consumption of a caffeinated beverage resulted in 0 to 84 percent retention of the initial volume ingested, whereas consumption of water resulted in 0 to 81 percent retention.”"
] |
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