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[
"So on the front page is a post about oil being able to completely cover an area of water with a one molecule thick layer. For large industrial oil spills, how does this layer affect the absorption of carbon from the atmosphere?"
] |
[
false
] |
I've got to imagine that a large oil spill would literally cover hundreds of square miles if the oil is distributed as a one-molecule layer. Considering how often this happens, does it contribute to climate change, or is the effect relatively neutral?
|
[
"I don't know the answer to your question, but here's a related and interesting issue:",
"I know someone working on a mine pond reclamation project for his master's thesis. The \"lake\" that he studies has a (more-or-less) permanent oil layer on the surface, which (as shown in the YouTube videos) severely dampens certain categories of waves. When you look at pictures the effect is quite dramatic. The lake also has a much lower than average oxygen content - due in part to some of the material at the bottom of the lake and also the source water - but my colleague believes that the lack of oxygen is also tied to the lack of waves. Wave breaking mixes oxygen into the water column. With the oil, you severely inhibit wave breaking so you likely inhibit this oxygen transfer. At this point, how much of the oxygen reduction can be attributed to the oil is unknown."
] |
[
"Even a large oil spill can only cover a fraction of a fraction of the ocean surface, so the effect of any spills on the global carbon cycle is neglible. It is definitely a bigger problem in enclosed water bodies, as ",
"u/maedhros11",
" mentioned. Oil spills cannot cover the entire ocean surface as a one-molecule layer because even the slightest disturbance due to wind for example, would disrupt that layer. The oil molecules also get degraded by oxidation and other chemical changes, so a very thin layer would be broken up before it can spread over the whole surface."
] |
[
"This is completely tangential to the original question, but in the days of yore, one of the techniques for dealing with heavy seas when in a small boat was to release oil into the water on the windward side of the vessel. This would dramatically dampen the waves, thus increasing the likelihood of survival for the boat and her crew. Of course, in the modern era, this is strictly against the law, and shouldn't really be necessary any more."
] |
[
"How portable can we build CO2 scrubbers to be?"
] |
[
false
] |
I encountered in (which, admittedly, I only glanced through) and I began thinking of how portable can CO2 scrubbers become. Having worked aboard a submarine for a few years, I only have a passing familiarity with scrubbers. But would it be possible to equip them aboard automobiles and other vehicles? Now I don't only mean equipping them on purely petroleum-powered vehicles to negate their own emissions, but also installing them in hybrids and electric-powered vehicles to counteract the carbon problem. If it were possible, they could even be installed in tractors, airplanes, and other farming equipment to counteract cattle and other natural emissions. Is any of this feasible, or am I just blowing more smoke? Edit: Needed grammar checking after I submitted this in my half-asleep state. I did little looking up and, apparently, a detail I had forgotten about submarine ventilation and atmospherics was the additional CO/CO2 burner. Would this have any effect on carbon emissions? Or could this only be used to discharge gases into the ocean?
|
[
"I found a diagram of the scrubbers found aboard subs. ",
"http://www93.homepage.villanova.edu/michael.b.walsh/CO2Scrubber.htm",
" ",
"Now I have also been reminded that we used, in addition to the scrubbers, CO/CO2 burners. Would these have any adverse effects to emissions, if they were manufactured for portability? "
] |
[
"I found a diagram of the scrubbers found aboard subs. ",
"http://www93.homepage.villanova.edu/michael.b.walsh/CO2Scrubber.htm",
" ",
"Now I have also been reminded that we used, in addition to the scrubbers, CO/CO2 burners. Would these have any adverse effects to emissions, if they were manufactured for portability? "
] |
[
"They can be very portable, for example, ",
"Closed-circuit rebreather",
" diving systems all contain a CO2 scrubber. These systems allow divers to stay underwater for extended periods. ",
"However, using them for the purposes you are mentioning isn't likely because there will always be a cost to build them, and refill the scrubber, etc... that will negate the gain you get from trapping the gas, especially since these applications produce orders of magnitude more CO2 than simple human respiration. "
] |
[
"How close does the energy of a photon have to be to the energy jump of an electron for it to absorb the photon?"
] |
[
false
] |
If an electron can only absorb all or none of a photon and can only jump up to specific energy levels, the energy of the photon would have to be equal to the energy level of the electron. But, I am assuming that there can be some error, otherwise it would rarely happen. What is this error and why is there one?
|
[
"The answer is if you are going to transition between two bound states (energy levels) the energy of the photon and energy of the transition must match ",
" for non-scattering interactions.",
"That being said its not \"rare\" because we are typically measuring ensembles of many many atoms. These ensembles have statistical broadening effects, as well as uncertainty effects in the light field that make them more probable. For example the precision something can measure a frequency of light is going to be inversely proportional to the time it can interact with that light field. Meaning most systems can only interact for a set amount of time before the light field is turned off. This innately gives the light field some uncertainty in frequency.",
"These uncertainty effects give both the atom/molecule and the light field a distribution of available frequencies. Now the probability that the light will interact (be absorbed) but the object will be proportional to the overlapping area of the two frequency distribution functions. There are more factors at play here but thats the basic point.",
"Additionally you can have scattering events where only part of the photos energy is absorbed due to induced fields."
] |
[
"I think they may have a misconception about the photo electric effect. Like dirac said, the probability is a distribution such that probability that a specific photon with energy E will undergo this interaction with a nuclei of an element with Z protons is proportional to Z",
" It is much more prevalent with high Z nuclei in a low E intensity. No specific discrete value is necessary for each photon. The closer the photon energy to the electron binding energy the higher the probability. As the energy surpasses the binding energy of that electron, the chances decrease with E"
] |
[
"They weren't talking about the photoelectric effect at all. The OP discretely mentioned transitioning energy levels (i.e. bound state absorption), while the photoelectric effect operates [roughly] in a continuum when above the disassociation energy. When you see someone mention jumping to an energy level, 99.99999999% of the time they are not going to be talking about the photoelectric effect.",
"That being said you seem to be a little confused on the p.e. effect yourself. The correct formatting of your equation is: Z",
" / E",
" (its meant to say that at very high photon energies the likely hood of an electron being emitted actually drops because of scattering effects). ",
"Second E in this equation is photon energy not electric field (intensity). These two quantities are completely independent of one another. The probability of a P.E. interaction should always go linearly with E field.",
"Intensity is never ever ever ever a word used to describe energy so you shouldn't have mixed it up."
] |
[
"If weightlessness in orbit is due to free fall and not lack of Earth's gravity, then is there weight in space on trajectories? I.E. traveling to the moon?"
] |
[
false
] | null |
[
"It's not an \"orbit\". It's an orbit. It's highly eccentric, but it's not like it's going to escape orbit or something. It's not called the Hohmann Transfer ",
" for nothing."
] |
[
"Yes. A spacecraft in a Trans-lunar trajectory will be ascending in Earth's gravitational field, gaining potential energy. While it does so its speed will gradually decrease due to the gravitational pull. So gravity is still pulling from the spacecraft.",
"I understand if you want to choose a different name for this force since it won't show up in a scale, but in textbooks you'll still see it as \"weight\". And it is still mass times the acceleration of gravity, the only difference is that the acceleration will decrease with altitude."
] |
[
"There would be, if the space ship got to the Moon by pointing itself at the Moon and going in a straight line. Then, until you were really quite far from the Earth you would feel quite a bit of pull towards the Earth. But, as you might have guessed, that isn't how we send things to the Moon. ",
"When we travel from planet to planet, we travel in what is called a ",
"Hohmann Transfer Orbit",
"- which is a much lower energy requirement than going \"straight\" there. Thus, the entire time (other than when they are burning their rocket to pick up speed) the space ship is still in an \"orbit\" of sorts, thus still in free-fall. "
] |
[
"Why is 0! equal to 1?"
] |
[
false
] | null |
[
"If you are running a restaurant and during the entire day one person (call them A) comes in for a meal, there is only way your day can play out: \"A came in\". 1! = 1",
"If you are running a restaurant and during the entire day two people (call them A and B) come in for a meal, there are two ways your day can play out: \"A came in, then B came in\", or \"B came in, then A came in\". 2! = 2",
"If you are running a restaurant and during the entire day nobody comes in for a meal, there is only way your day can play out: \"Nobody came in\". 0! = 1"
] |
[
"The answers talking about bijections or convention are correct but I feel that you miss a more general phenomenon :",
"What do I mean by an empty product ? Let's take a concrete example of a product of products :",
"(4x5x9)x(5x123x47)",
"By associativity of multiplication, we can rewrite",
"(4x5x9)x(5x123x47) = (4x5x9x5)x(123x47) = (4x5x9x5x123)x(47) = (4x5x9x5x123x47)x(∅)",
"I deliberately wrote (∅) and not (1) to make a point. (It's not a meaningful notation). What is left in the right parenthesis at the end is not 1, it is an empty product. It is a product of 0 numbers. But that empty product behaves exactly like the number 1. So it makes sense to say that the empty product is equal to 1.",
"So now, what is n! ? It is the product of all natural numbers 1<= k <= n",
"If n = 0, there is no such natural number, and hence 0! is an empty product. By our previous discussion, 0!=1",
"Actually, this phenomenon is much much general than for just multiplication. An empty sum is equal to 0, an empty composition is equal to the identity, an empty union is equal to the empty set. Each time you want to apply an operation to 0 terms, you get the identity element corresponding to this operation."
] |
[
"Perhaps the analogy wasn't perfect, but it corresponds very well to a mathematical reason why 0! =1 , namely k! is the number of ways the elements of a set with k elements can be arranged and the elements of the empty set can only be arranged in 1 way. ",
"A lot of the time the use of 0! boils down to whether or not we can extend a theorem that works on a nonempty set to include the empty set as well (that way we can say a set of k elements instead of adding more restrictions). Saying the elements of the empty set can be arranged in exactly 1 way is both intuitive, and it makes some things easier, even if it is just playing with semantics."
] |
[
"If you slowed down the cooling of glass to a solid, could it form a crystalline structure?"
] |
[
false
] |
From reading it seems that glass is an amorphous solid because it cools too quickly for the molecules to line up. If you were to slow down the cooling process enough, could it form a crystalline structure? If so, would the properties of the glass change in any noticeable way?
|
[
"I have done some glassworking in my past and seen what you are imagining. You sometimes see ",
"crystal-like flakes and roughness",
" on the surface of handmade glassware. That's glass's crystalline phase. It is brittle, rough and considered a defect.",
"Usually this is caused by overheating of the surface during the firing process; glass becomes doughy and workable before it stops being glass, and can be recooled into a finished piece without ever losing its vitreousness. If you heat it too much then it has the opportunity to recool as a crystal instead."
] |
[
"That sounds very very cool. You don't have any pictures of it do you?"
] |
[
"Not quite. Tempered vs annealed glass relates to the amount of internal strain, not whether it is crystalline."
] |
[
"Can lightning be used as a source of energy?"
] |
[
false
] |
would it be possible to create some sort of massive negative charge between the earth and its atmosphere where lighting happened very frequently? then outfit these "lightning fields" with some sort of device or structure that could gather the energy that the lightning produces?
|
[
"You're trying to violate the first law of thermodynamics. Lightning doesn't \"produce\" energy. It is a transfer of energy. The energy you could get from the lightning is less than the energy it woulld take to 'create some sort of massive negative charge' in the first place."
] |
[
"Triggered lightning has actually has been done with ",
"rockets",
" (turn down volume) but as a reliable energy source is a different issue. You have to store the energy in a bolt that has an electrical potential of millions of volts at kiloamps of current that lasts for tens of microseconds."
] |
[
"And also, one single bolt doens't even have that much energy, its just that it goes al at once"
] |
[
"Could you Destroy a Black Hole by feeding it a whole bunch of Anti-Matter"
] |
[
false
] | null |
[
"No. Adding antimatter or matter to a black hole increases the black hole's mass. In fact, there is no difference between a black hole assembled from a bunch of matter or a bunch of antimatter.",
"The Hawking calculation of black hole radiation does NOT suggest that antimatter going into a black hole decreases the size of the black hole. Rather, the calculation involves virtual particles -- a ",
", not actual objects -- of negative energy (not specifically matter or antimatter) as an intermediate state, leading to a quantum effect of black hole radiation. Matter vs. antimatter plays no role here."
] |
[
"Once inside the black hole, the particle's origin as matter or anti-matter is irrelevant. What the black hole keeps track of is the mass, the spin, and the charge, and that's it.",
"Note that even if you imagine a particle/antiparticle collision inside the event horizon, all you are imagining is energy that stays stuck inside the black hole, where you can't see or measure it."
] |
[
"Wut.... Quarks are not anti quarks"
] |
[
"Theoretically, can deserts be turned into arable lands?"
] |
[
false
] |
The question might come off as one better suited for yahoo answers. Nonetheless, I'm assuming that the process of arable lands turning into deserts involves several chemical reactions; if those reactions were to be reversed, can we regain or expand our arable lands? Furthermore, if certain types of bacteria and invertebrates die as a land turns into a desert, can they be reintroduced into the desert environment as it turns arable?
|
[
"Climate has a lot to do with why a desert is a desert, as most (all?) deserts don't receive adequate moisture from prevailing wind patterns, and that's probably what initiates desertification of a previously non-desert area. Once that has happened though, the biomass, primarily soil, of the area tends to dry up and blow or wash away. Once that happens, the area is pretty much stuck as a desert regardless of changes in moisture availability until something major happens, like flooding with an inland sea that deposits more biomass, or perhaps the development of a large river that brings soil from some other area."
] |
[
"It is possible to reverse desertification, but a lot of it has to do with why it became desert in the first place. A great deal of desertification in modern times has to do with climate change and that no one is routing water into those areas. With enough water and proper soil, you could create arable land nearly anywhere. The idea of irrigation is basically the foundation of this argument. Irrigation turns land that was previously unsuitable for farming into farmable land. Basically, with enough care, you could grow crops anywhere.",
"As for turning deserts into forests or the like, that's a lot more difficult. The use of trees and whatnot to prevent soil from blowing away is well documented. Whether that can be used to gradually reclaim a desert is beyond my level of expertise."
] |
[
"Don't underestimate the power of plants to alter the microclimate at ground level. They help to moderate temperature, slow the wind, and raise humidity - making the area much more amenable to life. With time, they also add organic carbon to the substrate, the beginnings of fertile soil. And where going out and planting trees isn't feasible, we can alter microclimate by making amendments like laying out grids of straw bales to add organic matter, reduce surface wind speed, and reduce moisture loss from the substrate. Add a seed bank and plenty of time... and you can, in many cases, at least generate enough plant life to hold the soil in place and prevent further erosion.",
"This said, I doubt most deserts could become \"arable\" in the traditional sense (of allowing ploughing of the soil, etc), without drastic geological change. What ",
" possible is to set up perennial agricultural systems using trees, especially in areas that were once somewhat productive have become desertified as a result of human meddling (ongoing overgrazing with livestock, and overharvesting of firewood are big problems).",
"Google \"desert reclamation\" for more info."
] |
[
"Dumb Question: How do Lakes and Ponds become populated with Fish?"
] |
[
false
] |
Have they been there for centuries as the lake got smaller and the water sources stopped flowing? Does evolution in fish happen in these ponds / lakes over the many years?
|
[
"i remember seeing a similar question - but it was how big puddles of water on mountain tops have fishes. The answer to that was - birds carry them there, some eggs stick to their legs and it fell on these puddles when they fly by and created a small system."
] |
[
"\"Evolution\" or at least genetic segregation does occur within lakes. This has been documented with fish in lakes on and near Vancouver island. ",
"Lakes also usually have river outlets so they are connected to ocean. "
] |
[
"I don't get why I'm being downvoted for this. It's not a scientific answer, but that doesn't mean it's not true. If it weren't for fisheries restocking them, some lakes would have way less fish, if any. Ask a \"dumb\" question, be prepared for a \"dumb\" but technically right answer."
] |
[
"How do multiple members of the same siphonophore species have the same shape if they are just colonies of individual animals?"
] |
[
false
] | null |
[
"The same reason you and other animals have the same shape even though you are just colonies of individual cells (after a manner of speaking). The colonies grow from each other in a defined pattern, producing a similar final outcome. ",
"Don't imagine that a bunch of individuals clump together in a random mass and then sort themselves out somehow. Instead, individuals bud off each other to produce the final form. The colony always grows certain types in certain places."
] |
[
"What determines the body plan ? Do they have something similar hox genes ?"
] |
[
"Animal colonies are made up of multiple physiologically integrated and genetically identical units called zooids that are each homologous to solitary, free-living animals. Siphonophores, a group of pelagic hydrozoans (Cnidaria), have the most complex colony-level organization of all animals. Here the colony-level development of five siphonophore species, strategically sampled across the siphonophore phylogeny, is described from specimens collected using deep-sea submersibles and by self-contained underwater breathing apparatus diving. These species include three cystonects, Bathyphysa sibogae, Rhizophysa filiformis, and Rhizophysa eysenhardti, and two “physonects”, Agalma elegans and Nanomia bijuga. These data, together with previous findings, are analyzed in a phylogenetic framework to reconstruct key features of the history of colony-level organization and development in the Siphonophora. It is shown that gonodendra and gastrozooids of the examined cystonects arise as independent buds directly on the stem, whereas probud subdivision (the origin of feeding, reproductive, and other zooids from a single bud) is a synapomorphy of the Codonophora. The origin of probud subdivision is associated with the origin of cormidia as integrated units of colony organization, and may have allowed for greater morphological and ecological diversification in the Codonophora relative to the Cystonectae. It is also found that symmetry is labile in siphonophores, with multiple gains and/or losses of directional asymmetry in the group. This descriptive work will enable future mechanistic and molecular studies of colony-level development in the siphonophores.",
"Src: ",
"http://link.springer.com/article/10.1007/s00427-006-0101-8",
"Might be an interessting read"
] |
[
"Why doesnt the iron in red blood cells rust when it binds with oxygen molecules? And how do red blood cells deposite the oxygen molucules if its binded with the iron in the red blood cell?"
] |
[
false
] |
Be nice. I have the low end high-school understanding of chemistry and biology. I know why blood cells are able to "carry" oxygen to different parts of the body I just don't understand how they get rid of it or where it goes and how it's used on a molecular bases... But you don't have to answer that last part, I'll learn it in college eventually.. :D
|
[
"Well, red blood cells have the protein hemoglobin in them, which in turn contains ",
"heme",
" groups, which is a big organic molecule with an Fe(II) atom in the middle. So it's not free or metallic iron, it's already formed an iron compound and the iron is already oxidized a bit, and won't react with the oxygen, as it's already bound to the nitrogen atoms of this big ring structure. ",
"So no oxidation takes place, the oxygen molecule just binds (weakly, as a 'ligand' rather than a proper covalent bond) to the metal atom there. There's no big change in the chemical state of the oxygen or iron here, although the ",
" state of the iron changes. ",
"Under certain circumstances the iron in hemoglobin can be further oxidized to Fe(III) and reduced back to Fe(II) though. ",
"The binding and dissociation of O2 to hemoglobin is 'controlled' by a number of factors, among others the CO2 concentrations and pH, which differ between your lungs and cells. So you have the result that it 'wants' to pick up O2 in your lungs and 'drop' it in your cells. "
] |
[
"I find the control of oxygen-binding by carbon dioxide (i.e., the ",
"Bohr effect",
") pretty amazing. Basically, carbon dioxide binds to hemoglobin and changes the shape of the protein, which in turn makes it easier to release the bound oxygen."
] |
[
"Not only that, but heme complexe's actually look like red blood cells, and the entire binding site becomes concave, to literally catch oxygen, and convex once it's bound. It's a truly fascinating little feature of our bodies."
] |
[
"Do animals have a biological way to \"tell time\"?"
] |
[
false
] |
Every morning without fail my cat will wake me up minutes before my alarm. Is an animal's sense of routine strong enough to know when to do something down to the minute?
|
[
"Sure they do. I'll answer your question more generally, and not worry about just your cat. Most animals have different priorities at different times of the day. For example, female crickets will hide in burrows during the day, and only move around after dusk when it is safe to search for mates. Male crickets will also, unsurprisingly, begin to chirp during this time. These are behaviors that are governed by clock mechanisms.",
"Let's first talk about the 2 basic kinds of clock mechanisms.",
"There are two major ways animals can track time, and they use both or just one. The first way is that they behave according to a built in biological clock, an internal timing mechanism with a set schedule that isn't affected by the environment. Of course our sense of timing is partially removed from the environment-- when we fly across several time zones, we see this first hand. Our internal feelings-- like when we feel tired, or hungry-- are tuned to the environment we just left, not to the one where we just landed. Eventually though, we do shake off the jetlag and adjust, but this takes time. The second way organisms can track time is that the relationship between central nodes in an animal's nervous system is largely determined by feedback information that is gathered through environmental stimuli. These mechanisms allow individuals to modulate their behavior in response to environmental changes, like a decrease in light intensity as nightfall approaches.",
"Let's look at these two ideas in the context of cricket calling cycles. Maybe each day the crickets call at about the same time because they have a sort of internal timer that tracks how long its been since they last called. Crickets might use this environment-independent system to begin chirping each evening. Alternatively, maybe cricket's just begin chirping once the light intensity falls below a set level, regardless of timing. If this is correct, then crickets should never chirp if you keep them in a bright room, regardless of how long they are in there. It turns out though that if you keep crickets in a room with constant temperature and bright lights 24 hours a day, they'll still chirp for around 3-4 hours each day. If crickets are kept in constant light, then they'll initiate a round of chirping every 25-26 hours. A cycle of activity like this devoid of meaningful environmental cues is called a free-running cycle. Note that this free-running cycle lasts longer than a standard 24 hour day. This means that we can conclude that the cyclical pattern of calling in crickets is at least partly due to an environment-independent circadian rhythm.",
"But what happens if you keep these crickets in a room with 12 hours of light and 12 hours of dark? The lights-on lights-off cycle can give crickets an environmental cue to time their chirping cycles around. Do they use it? It turns out that they do, just like other species like monarch butterflies or pigeons can reset their clocks when you change their light-dark cycle, or like the way we can when we fly across time zones. After a few days, the male cricket begins to chirp about 2 hours before lights out, anticipating \"nightfall\", and keep chirping until about 2.5 hours before the lights go on in the \"morning\". So consistent with the idea that clocks are based on environmental stimuli, this calling cycle matches ones you see in nature, which is synchronized with dusk. However, unlike the previous free-running cycle, this cycle doesn't slowly deviate from the 24 hour day, but is reset each day to begin at the same time in relation to \"lights-out\" This was discovered by Werner Loher in 1972. From these results, we can see that the complete control for a cricket's clock has both an environment independent component, the biological clock, which cycles once every 25-26 hours, but hey also have an environment activated reset device that synchronizes the clock with the environmental light-dark cycle. Basically, crickets have both an internal and external clock, since they have a biological clock that can be adjusted with environmental cues.",
"What about species that have multiple types of behavior at a given time? We can look at the sand cricket for this idea. The sand cricket comes in 2 forms-- a long-winged nocturnal form and a short-winged diurnal form. The long-winged form can fly, so it's active at night, when it's safest to leave the burrow and search for mates, but the short-winged form can't fly, so it stays in the safety of vegetation on the ground during the day (discovered by Derek Roff and Daphne Fairbairne in 2007). How do the circadian rhythms of these crickets differ? Anthony Zera took blood samples from both types of these crickets over a 24 hour period. It turns out that a molecule called juvenile hormone (JH), which regulates lots of insect behavior, didn't really change much in short-winged crickets throughout the day. However in long-winged crickets, you see a large rise in JH concentrations in the late afternoon or evening. A correlation of a rise in JH which an increase in activity suggests that a timed surge in JH helps the long-winged crickets prepare to fly. I'll go into more detail later, but the idea here is that hormones play a key role in animal's ability to \"tell time\".",
"I have to go do some stuff now, but I'll edit in more information later if you like. This is just a quick intro about these two ideas on how an animal can \"tell time\"-- either through internal timing mechanisms, or through perception of external factors. However, what actually goes on in the animal? There are 3 major factors you can think about-- neurobiology, genetics, or physiology. I'll talk about each in turn in a future edit.",
"Now that I've established a general framework of the mechanisms, I'll get into more specifics.",
"So in addition to the role that hormones play in regulating circadian rhythms, we can also look at other mechanisms of circadian behavior, like the interaction between neural circuits and genes. For example, even though the daily cyclical release of JH probably affects the behavior of long-winged sand crickets, other aspects of the circadian function of these insects involve the optic lobes of their brains. If you cut the nerves carrying sensory information from the eyes of male crickets to its optic lobes, you put the insect into a free running cycle. This suggests that visual signals of some kind are needed to reset the daily rhythm to local conditions, but even without this information, they still show some kind of rhythm. If you cut the connections between both optic lobes and the rest of the brain though, the calling cycle completely breaks down and they call at random times during the day. This suggests that crickets have a master clock mechanisms in their optic lobes, which sends messages to other regions of the nervous system, and receive hormonal signals generated by the animal's endocrine system (refer to Johnson and Hasting's 1986 textbook for more info)",
"As I said in my previous post, circadian rhythms aren't just in insects, but you see them in lots of vertebrates as well, including humans. If you're interested in the control of circadian rhythms in mammals, then you probably will study the hypothalamus, specifically the suprachiasmatic nucleus, a pair of neural clusters that receive information from the retina. The SCN is thus a prime candidate for the mechanism that processes information about day and night length, which is information that can be used to adjust a master biological clock. If the SCN is a master clock or pacemaker that is needed to maintain a circadian rhythm, then neurons in this region should change their activity cyclically over a 24 hour period. It turns out that they do, with some groups of SCN cells being inactive at night, but activating at dawn and firing through the day (Robert Colwell 2012) Another thing that should happen is interference with circadian rhythms if the SCN is damaged. It turns out that if you destroy the SCN of hamsters and rats, they lose their circadian rhythm of hormones, locomotion, and feeding. If you take these arrhythmic hamsters and transplant SCN tissue from fetal hamsters, they sometimes regain their circadian rhythm, but this doesn't work with transplants from any part of the brain (DeCoursey and Buggy, 1989). Additionally, if an arrhythmic hamster gets a SCN transplant from a mutant hamster with a circadian period that is much shorter than 24 hours, then the previously arrythmic hamster will get the new, shorter circadian rhythm, which is evidence supporting that the SCN controls circadian rhythm in hamsters."
] |
[
"Basically, crickets have both an internal and external clock, since they have a biological clock that can be adjusted with environmental cues.",
"Awesome information! Can animals adjust their biological clocks without any environmental cues based on the schedules of other creatures? Example being being able to change their biological clock based on local predators. (Normally nocturnal creatures coming out during the day to avoid nocturnal predators)",
"Also is it possible that my cat got on a schedule of waking me up minutes before my alarm because he doesn't like the high-pitched sound of it?",
"Again, thanks for the reply - super informative! I'd love to read any other information you have."
] |
[
"I've editid in a bit about the neurobiology of circadian rhythms. I'll add more as I get some breaks lol"
] |
[
"Where can I see the entire human genome?"
] |
[
false
] |
I remember a poster in school which showed the entire sequence in the black/white lines (I'm sorry, I don't have a clue about the actual name of the methods or anything). Is there anywhere that I can see the entire sequence in this format and is there anywhere that would give some more information on our genetic make-up in simple terms? (Even if it was in a way that showed it in the "letter" format - ATCGGCAT etc)
|
[
"The poster didn't have the full sequence. The Venter group sequenced 2.91 billion base-pairs, and you can see ",
"here",
" a whole bookcase of books with the sequence, each chromosome being several books. And ",
"here",
" you can find ",
" paper about the sequencing."
] |
[
"How about ",
"this",
"?"
] |
[
"The entire genome is browseable with NCBI map viewer. ",
"http://www.ncbi.nlm.nih.gov/mapview/map_search.cgi?chr=hum_chr.inf&query"
] |
[
"Can insects “heal” from injury like animals do?"
] |
[
false
] |
If I try to smush a spider, and mostly miss but still manage to cause a little bit of damage, will the spider be able to heal from said damage? (I’m being ambiguous about what the damage is... I didn’t want to restrict what the answers might be!)
|
[
"Though importantly, most insects (unlike spiders) have determinate growth and do not molt any more once they reach adulthood, so they can't really do much at that point."
] |
[
"Though importantly, most insects (unlike spiders) have determinate growth and do not molt any more once they reach adulthood, so they can't really do much at that point."
] |
[
"Depends on the kind of injury, and whether we're talking about insects or spiders. Spiders can heal exterior injuries quite well, up to and including regrowing lost legs; they molt (shed their skin) regularly, and with each molt, any lost parts of the exoskeleton (including entire legs) can be replaced, although they're smaller than usual to start with, needing a few molts to get back up to size. ",
"This Australian spider celebrity",
" regrew the full set starting from just two legs.",
"Insects can also replace limbs when molting, but unlike spiders, they only molt while they're growing. Once an insect has gained its wings and reproductive bits, it's a non-growing, non-molting adult, and any limbs it loses beyond that point are lost forever. Insects can still heal minor cuts, though, by essentially plugging the hole with melanin (the same compound that acts as the main pigment in human skin). This melanin is produced by specialized cells in the insect immune system.",
"Also, as an ecologist, can I just say I appreciate your username, ",
"u/redfieldsratio",
"? :)"
] |
[
"Asteroid A/2017 U1 may be the first interstellar object to be observed to pass through our solar system. If we had had more warning of its arrival, could we have sent a probe to it? How much warning would we have needed?"
] |
[
false
] |
I'm curious if such a mission is possible using current technology, given the object's unusual trajectory and high velocity.
|
[
"It's very small, and going really ",
" fast. It came close enough to Earth's orbit that sending a \"flyby\" probe would be conceivable: basically you could send a probe out to where it's going to be, and let it zip right past you. But as ",
"/u/katinla",
" says, matching orbits for a rendezvous would be impossible.",
"Also it's really unlikely we'd have detected it any earlier than we did. It's ",
" small (a couple hundred meters across) that only a really good telescope could see it. A year ago, it was roughly 100 times further away, and probably a million times harder to spot. And even a desperate crash program to build a space probe to visit it would need a year or more to build, launch, and travel to the intercept point."
] |
[
"Sending a probe to an asteroid is no longer a utopia since Rosetta successfully did a Rendez-Vous with comet 67P. But it was relatively easy because it was in a low speed orbit around the Sun that doesn't get too far away.",
"We would need years of warning, which we didn't have for A2017 U1 and we're unlikely to have for any further interstellar objects. It was just 400m across, not easy to be seen util it got close enough.",
"Its hyperbolic excess velocity was 25 km/s, that's high. It must have been moving at 48 km/s when at 1 AU from the Sun (escape speed from the Solar System at 1 AU is 42 km/s, Earth's orbit speed is 30 km/s). This delta-v may be much higher than it seems because it's not coplanar with the orbit of our planet, and plane change manoeuvres require a lot of delta-v.",
"For a Rosetta-like spacecraft of 3 tons of mass, the optimistic delta-v neglecting plane change (18 km/s) would require 164 tons of liquid hydrogen and liquid oxygen. This doesn't fit in any launcher we currently have or is planned (NASA's SLS will only be able to take 130 tons to LEO), so it would require multiple launches and in-orbit Rendez-Vous and docking. Hydrogen as fuel is too optimistic for this because it would boil-off before we can assemble it for the Earth-escape burn. Storable propellants are less efficient, so the above figure would be exponentially larger. And anyway it is too optimistic because I neglected staging.",
"Advanced propulsion techniques such as ion engines are useless when you only have one chance and a limited time to reach it.",
"So... it doesn't sound feasible with current propulsion technologies. At least not at a realistic cost.",
"Edit: seems like in the above figures I confused Rosetta's dry mass and wet mass. It was only 1.23 tons, so the total would be like 67 tons. Probably doable in a single SLS launch if we're lucky enough to have a nearly coplanar alien rock.",
"Edit 2: Out of curiosity I looked up the inclination of this asteroid and it turned out to be 122°. That's retrograde. Don't even have to do the math to say reaching it is completely unrealistic. May the next one have a nearly-zero inclination..."
] |
[
"If you were just going to do a flyby, no plane changes, where your probe meets a/2017 u1 at the probes apogee, you could do it with a Rosetta or less mission. The object came within 60 times the distance of the moon to the earth (roughly 23064000 km), and the delta v for the transfer part of a Hohmann transfer from 200km to this target apogee is about 3.2 km/s or a total whopping 11km/s if you consider your leo velocity as well (7.78 km/s). An earth escape velocity is 11.186 and we know that Rosetta had to escape earth so for sure, you could do a Rosetta type mission which used an Arian 5 rocket. Bear in mind that your probe would be observing some object 400m across zing by it at a high relative velocity.",
"Hmm.. If we did a mission like it, I would be curious if we could intercept it for a kinetic impact, if so, maybe just send an impactor and observe the spectrum of the explosion kind of like the LCROSS mission. I bet you could get a science mission like that within a year, you just have to be able to bump somebody's payload going up to GEO(appx 4.2km/s delta v from LEO to GEO parking orbits). But if a/2017 u1 was a space probe, it might start an interstellar war lol."
] |
[
"Arsenic in food. What's the real story?"
] |
[
false
] |
[deleted]
|
[
"The CDC's Chemical Profile page for ",
"Arsenic",
" is a really good place to start.",
"In the US the only exposure levels that have been set are for occupational exposure, by OSHA, and the EPA has set a standard for arsenic in drinking water (0.01 ppm).",
"In general, you probably won't ingest enough arsenic from food to give you cancer, but a chronic low level exposure to arsenic will cause other health effects (nausea, vomiting, skin discolouration, ...) ",
"It also depends on the type of arsenic and type of exposure. Inorganic arsenic is more readily absorbed through the skin, and has been found to be more harmful than organic arsenic compounds. Organic arsenic is found in pesticides, so that's more likely the type you would ingest."
] |
[
"You are thinking of cyanide."
] |
[
"He most likely meant elemental arsenic vs soluble inorganic arsenic. The only studies done on organic arsenic have been on animals.",
"One caveat I have of making such a distinction, is most of the time, we don't know what form of arsenic we're being exposed to because it so readily transforms in the environment (either oxidizes, binds, etc) - so unless you're drinking arsenic straight out of a labelled vial, knowing if its elemental/inorganic/organic is tough.",
"But yes, drinking copious amounts of arsenic, as in greater than 2 mg-As/kg - which is the low end of the \"lethal dose\" (so a 70 kg (~160lbs) person would have to ingest ~140 mg of Arsenic in a single go) would kill you. There are a few other factors that need to be taken into consideration when determining lethal dose though - gender, age, physical activity, diet...",
"The chances of this happening accidentally though is pretty low - unless, of course, you're trying to kill yourself. Or someone is trying to kill you."
] |
[
"What is a wrinkle? How do wrinkles look different at cellular level compared to smooth skin?"
] |
[
false
] |
[deleted]
|
[
"People get wrinkles as they get older due to a decrease in collagen production in the dermis layer of skin. In addition, collagen is also broken down faster by the body. This leaves the person with a lack of volume in the dermis, and epidermis will sink and wrinkle as a result. Dermal fillers, used in plastic surgery, focus on filling that volume back up and and emphasizing collagen production."
] |
[
"Well that's one way, however generally supplements are mainly cons. However having added potassium can help. A big factor can be to try and keep out of the sun, and drink water! Fluids help lots with the skin."
] |
[
"Skin is extremely flexible and has enormous tensile strength. This is due to proteins and the cellular composition of skin. However skin cells need a good blood supply and therefore minerals and water- achieved through active transportation, diffusion and osmosis.Also skin contains elasticin and collagen which protect it drom damage and give a snooth texture.When you get older or a foreign substance is added often oils can be broken down leaving the skin dry and unsaturated giving an appearance of a wrinkle as it loses its flexibility. Where they differ at a cellular level- definitively they are the same cells. However it is difficult to say, mainly they differ due to lack of minerals and oils- giving rigidity and inflexibility with more than one cell/fibres. Overall adding to a fold in the skin described as a wrinkle."
] |
[
"Can humans die due to being in water for too long?"
] |
[
false
] |
Discussing ways a human could die, my friend asks me if a person could die for staying in water too long. Could a human stay in a body of water(oceans, rivers, pools) for too long for it to become fatal? What if they were to receive constant food and water?
|
[
"I seem to recall a study finding that pruning was actually the result of our epidermis responding to the wet environment to gain more traction... I'm on mobile or I'd track it down, sorry :/"
] |
[
"I seem to recall a study finding that pruning was actually the result of our epidermis responding to the wet environment to gain more traction... I'm on mobile or I'd track it down, sorry :/"
] |
[
"Human bodies just aren't made for prolonged submersion in water. I don't know exactly how long it would take to impact your health but ",
"this gentleman",
" apparently spent over 50 hours straight underwater, although granted he was wearing dive equipment. Besides any ill effects that you might experience from osmosis as Eletrophorus mentioned, there's also the matter of sleep. It may not be a very big deal in a pool environment where one can float on their back comfortably, but if this is an ocean environment where waves can knock you around a lot it wouldn't take very long for you to simply become too exhausted to tread water anymore."
] |
[
"Why have we evolved to have compassion at the levels we have?"
] |
[
false
] |
As humans have matured, it seems that compassion has become more and more prevalent in our species. This to my mind seems to go against the "survival of the fittest" principle of evolution I imagine it increases the chances of survival (and therefore procreation) of the not-fittest. Now I am not condoning neither am I for an elitist situation where people who aren't considered the fittest are not allowed to reproduce (or worse, killed), but I am wondering why evolution might have put this mechanism in place.
|
[
"Compassion is a feeling that falls under empathy - empathy, or putting yourself in the shoes of others - can be very helpful evolutionary speaking. If compassion leads you to care for others (sick, wounded, poor...) you may increase their chances of survival. If they are close kin this falls under the kin selection theory - where in helping others who are closely related to you increases your inclusive fitness (you share genes with your closest relatives, by helping them survive and reproduce, you in turn pass on a part of your own genes to the next generation). If you help someone who is more distantly related to you, or not related to you at all, you may see a return of the generosity at a later point in time when you need help. This is called reciprocal altruism.",
"Humans have an interesting ability to consider non-blood relatives as close kin - family friends, in-laws, bonds through marriage. Also, our long-term memories allow us to remember good and bad acts that people preform to us. Thus we associate ourselves with helpful people, compassionate people, nice people, empathetic people and we dislike cheaters and aggressors. Helpful people in the long-term are more beneficial to our own personal survival - by getting us through not just the good times, but most importantly the bad times - they help insure our own survival. By associating ourselves with as many nice, helpful people as possible through blood relations, marriages, communities... we insure that an ever growing network of people are looking out for us (and us in turn them).",
"http://en.wikipedia.org/wiki/Reciprocal_altruism",
"http://en.wikipedia.org/wiki/Kin_selection",
"evolution might have put this mechanism in place.",
"I know you probably just wrote really fast but just FYI- Evolution does not create the behaviour/traits, the traits/behaviours must be there already (for example arising through mutation), natural selection acts on these traits/behaviours and they change over time resulting in evolution. "
] |
[
"From a purely game theoretical standpoint, it can be argued that compassion arises from the prevalence of ",
"cooperative games",
". Individuals that are better able to cooperate when \"playing\" such games are often more fit.",
"You may be interested in exploring the relevant field, ",
"Evolutionary Game Theory",
"."
] |
[
"Ironically my degree was in Artificial Intelligence and Computer Science and one of my courses was evolutionary computing :)",
"What you say is certainly true for a certain level of compassion, but I should think that if the compassion gets past some threshold, to the point that it is reducing the ratio of fit to not-fit procreators, then it would guess it reduces the effectiveness of the survival of the fittest model? (The same could be said for medical advance, or rather applied use, specifically in the field of genetics)"
] |
[
"How much ice would we have to mine from the moon to make cargo missions to resupply water to the ISS economically viable?"
] |
[
false
] |
[deleted]
|
[
"It's actually simpler than you think. ",
"Gerry O'Neill",
", an early proponent of space colonization (see ",
"this",
") realized that you don't need rockets to launch material from the Moon. He proposed to use magnetic launchers. The big expense of lunar mining is the need to maintain a presence at the mine."
] |
[
"This might work. However, trying to run an industrial operation with minimal cost is not the same as running a scientific experiment. Mining is dirty, and equipment requires maintenance and repair."
] |
[
"This might work. However, trying to run an industrial operation with minimal cost is not the same as running a scientific experiment. Mining is dirty, and equipment requires maintenance and repair."
] |
[
"When putting her to bed last night, my daughter (7) asked me to get her \"a science book, and a book about space!\" Any recommendations to nurture a budding 7-year old scientist, reddit?"
] |
[
false
] | null |
[
"When I was that age (and as I got older), I loved looking at books with lots of pictures and little blurbs covering a variety of topics and using that as a jumping off point when something in particular struck my fancy. I would suggest going to a local book store and looking at some of those big, glossy coffee table books and how-things-work books or anything similar that is in the kids section. I would avoid getting too focused a book until she expresses a more focused interest."
] |
[
"Is eyewitness still around?"
] |
[
"+1\nI had one of those hard cover A3 sized books with plenty of pictures and covered a variety of topics from space to precipitation to light to electricity etc. All explained in a page or two then next subject. Kept my young wandering mind focused and curious"
] |
[
"Did National Socialists' program of euthanizing the mentally ill have lasting impact on mental retardation rates in Germany?"
] |
[
false
] |
I'm wondering where I can find data on this. Cross-country analysis on mental retardation rates would be particularly interesting.
|
[
"I don't know the statistics, but from what I do know about mental retardation, I would have to say it is unlikely to have had a huge impact. Some developmental disabilities can be hereditary, but for the most part they are random genetic anomalies (like down syndrome can be) or injuries to the brain (from prenatal drug/alcohol abuse, abuse after birth, seizures, lack of oxygen after birth or choking sometime in childhood, etc...). It is usually not passed down to offspring from those who are disabled because those people don't frequently reproduce (not that it never happens, just less often than those other causes) so euthanizing the disabled wouldn't lessen the number of kids born with disabilities much."
] |
[
"Just to add to the excellent observations from others:",
"If mental disability has a genetic cause (and it's not due to, say, nondisjunction), it's likely to be recessive. This is an oversimplification; for example, mutations in the same part of chromosome 15 can cause either Prader-Willi or Angelman syndrome depending on whether they're on the maternal or paternal chromosome. But we'll run with it.",
"Suppose a form of mental retardation is caused by a recessive allele with a frequency of 1%; suppose this locus begins in Hardy-Weinberg equilibrium, so the population consists of 98.01% homozygotes for the \"normal\" allele, 0.01% homozygotes for the mutant allele (these people will be mentally retarded and therefore euthanized), and 1.98% heterozygotes (normal phenotype).",
"Now suppose you remove all the mentally retarded individuals. In effect, since ",
" copies of the mutant allele in the population are carried by heterozygotes, this will have almost no effect on the frequency of that allele. You've effectively taken the frequency of that allele from 1% to about .98%. In the next generation, therefore, the frequencies will be almost exactly the same; you'll have about 98.05% homozygotes for the normal allele, 1.94% heterozygotes, and .0094% homozygotes for the mutant allele. All that work, and all you did was permanently remove about 6% of the mentally retarded individuals from the population.",
"You can repeat this over a few generations and even consider forms of mental retardation that are slightly more frequent in the population. It won't help in any readily observable way. Negative eugenics on recessive traits, to a first approximation, simply doesn't work."
] |
[
"hmm, to me it seems like grandtheftautumn just doesn't have any statistics to cite and instead contributed some useful, valid observations."
] |
[
"I met a man denying that we ever went to the moon. His main argument was that the astronauts would have died passing through the Van Allen belts. Does this claim have any truth?"
] |
[
false
] |
I know we dont know how much about the Van Allen belts but from some reading I found that a satellite in that region is exposed to 25 Sv in a year which is about 3 mSv an hour which if i remember correctly is pretty high, but not enough to kill, maybe increase risk of cancer. He also claimed that solar/gamma rays would kill astronauts. Surely that was the purpose of the gold foil on the lunar lander, to act as a Faraday cage?
|
[
"Correlation is evidence."
] |
[
"Correlation is evidence."
] |
[
"No one is interested. Please stop entertaining idiots like the one you've met."
] |
[
"Is it possible that we as a species of this planet are missing out on a sensation because of our environment and/or anatomy?"
] |
[
false
] |
For example, imagine an alien race that doesn't have the ability to hear anything (for whatever reason), yet we know that under the right conditions, sound exists.
|
[
"Absolutely, there are many things that humans can't sense that other animals can (and we don't even have to leave earth to find them). For instance, some animals can sense magnetic fields (some birds and insects) and some can sense electric fields (many fish) ",
"(Source)",
". ",
"In addition, you can also consider that there are plenty of animals that can hear ",
"higher or lower frequency sounds than we can",
". Many animals can also see beyond the visible spectrum of light (into the ",
"infrared",
" or ",
"ultra violet",
"). Not to mention all of the chemicals that we cannot smell or taste.",
"There are signals all around us that we can't perceive. Many of them can be perceived by other animals."
] |
[
"Just to add to this. ",
"There are also lots of senses that humans have that we don't necessarily realise. The 'five senses' we are taught about in school are a grand oversimplification. Touch, for example, is not just one sense; we have multiple pain senses, both hot and cold temperature, fine, deep and vibration sensation. Proprioception is one that many people do not realise we have - this is the ability to tell what position our body is in without looking or feeling. If we did not have this, our ability to balance and coordinate our movements would be diminished greatly. Sight is of course split into seperate senses; black and white, and colour. We are able to sense many more things about our environment than we realise."
] |
[
"This is a bit of an oversimplification. A lot of creatures would be MORE successful and more able to survive as a species with other adaptations that they don't have now, without potentially endangering the entire species through resulting overpopulation. ",
"One example is the ability to swim or fly longer distances. This would allow many more creatures to move to islands or different land masses and establish threshold populations there, increasing the odds that 'survival as a species' would continue in the event of a cataclysm or other massive localized change to an environment. "
] |
[
"How can I interpret c^2 or v^2?"
] |
[
false
] |
It is hard for me to visualize this concept. I can visualize velocity and I can visualize acceleration. However, I cannot visualize a squared velocity. What does that even mean? When you consider the formula F = ma, this makes perfect sense to me because that just means mass at an acceleration. But e=mc means mass at a what? I know if you rearrange the formula, it can be e=F*d (constant force through a distance). Is this the only way to interpret the formula? Someone had mentioned that c is just a constant and does not mean anything. I don't see how that can be true. If it was just a coefficient sure, but I don't see how a constant means nothing. : To clarify my question, I'm not asking about what c is or how e=mc was derived. That was just an example. I'm wondering how to interpret velocity * velocity in general.
|
[
"e=mc2 means mass at a what?",
"E=mc",
" means the energy of mass at rest. The ",
" in this equation is the square of the speed of light, but ",
" is much more than just that. What Einstein really discovered in Special Relativity was that the universe does not exhibit what is known as ",
" in which there are no preferred positions or speeds in the universe. Instead, there is in fact one special speed in the universe, ",
", which is ",
", meaning that all observers everywhere agree on its value. Anything traveling at ",
" in one reference frame also travels at ",
" in all other (inertial) reference frames. All the \"weird\" consequences of SR are a result of applying this axiom. ",
"The fact that light happens to travel at this speed is almost an afterthought. Nothing would have to actually travel at ",
" in order for it to still be a fundamental quantity describing, not the speed of any accidental phenomenon, but something fundamental about the structure of the universe.",
"Hence ",
" in E=mc",
" is not the mere \"speed of light,\" but rather \"the Lorentz invariant speed of the Universe,\" a fundamental universal constant, like ",
" or ℏ, both of which, by the way, also carry units.",
"if you rearrange the formula, it can be e=F*d",
"No, E=mc",
" and E=Fd describe two totally different things. E=mc",
" describes the energy contained in mass at rest, whereas E=Fd describes the ",
" to a body when acted upon by a classical force, and is always zero when the mass is at rest (since at rest, the distance traveled must be zero)."
] |
[
"I don't think that the general concept of \"velocity squared\" really means much. You never solve for it, for instance. In K=1/2 mv",
" , it just means that doubling the velocity quadruples the energy and so on.",
"I think it would be better to think in terms of W=Fd and Joule = Newton ⨉ meter, if you want a more fundamental understanding of the units of energy. It just so happens that a Joule is also a kg ⨉ (m/s)",
" , but the two meters in that m",
" are two ",
" meters: one is the meter in the speed inside the Newton, and the other is the component of displacement in the direction of applied force. So although the units look like a squared velocity, and sometimes you calculate energies with squared velocities, fundamentally that's not really the unit."
] |
[
"I'm not physicist, but I can give a quick answer, and maybe someone else will come along and give a better one.",
"First thing, e=mc",
" wasnt just written down out of no where, it was derived from other equations. Indeed, it is a result that can be derived in all sorts of ways, including one of my favorites just ",
"imagining a photon in a box",
".",
"However, another way, comes from using \"Lorentz Transformations\". A simplified version of this comes from simply imagining what would happen if a beam of light bounced between two mirrors, ",
"the two mirrors were moving",
". The light beam then moves in the shape of a triangle. Everyone knows that when it comes to triangles, the square of the hypotenuse is equal to the square of the other two sides. And as one of the sides is proportional to 1/c, we end up with a c",
" in our equation.",
"So enough with the derivation. What does unit's squared mean? Well, I think you need to ask yourself, why do you have no problem with a unit of force times a unit of distance, but a yet a unit of velocity times a unit of velocity seems unnatural to you. Does acceleration freak you out because it is proportional to 1 over seconds divided by seconds? And I hope you don't have an issue with area or volume, because if you do, you're head might explode of you find out that the definition of a volt is kg ⋅ m",
" ⋅ s",
" ⋅ A",
"What I'm getting at, is I can multiply anything by anything, and if I do, then the units are multiplied. Sometimes those results have obvious real work, tangible significance, and sometimes they don't.",
"To answer the volt thing, one can see how the units come about. A voltage = How many Joules of energy per Coloumb of charge do particles have: v = J/C. Joules = Energy = 1/2",
"v",
" = kg * (m/s)",
" = kg . m",
" . s",
" . A Coulomb is how much charge flows past a point during an amp of current, hence C = A . s . So v = (kg . m",
" . s",
" / (A . s) = kg . m",
" . s",
" . A"
] |
[
"What is the physiological basis for crying after being presented with emotional stimuli and is it shared by other species?"
] |
[
false
] | null |
[
"To the first question, there are two answers. The first is that the tears released when crying* contain manganese and the hormone prolactin, lowering the quantities of these chemicals in your body. Since these are the chemicals that are responsible for our emotional stress, lowering getting rid of them can make you feel better. ",
"The other reason you cry may be to alert others around you that you are in distress and need help. Basically other people see you crying and know that they should come and help you. ",
"I don't know if these traits are shared among species, but i assume they are.",
"*there are multiple types of tears that our bodies can release, each with different chemicals in them"
] |
[
"Here are some articles about this",
"http://www.independent.co.uk/life-style/health-and-families/features/how-crying-can-make-you-healthier-1009169.html",
"http://www.healthylifect.com/mind/article/The-science-behind-your-tears-582550.php",
"http://lifestyle.iloveindia.com/lounge/why-does-crying-feel-good-2372.html"
] |
[
"Cite this please."
] |
[
"[CS] Developers, how is \"corrupted\" text (e.g. i̶̶̪̦̼͇͇̞̯͉͡ŕ̭̰͕͘ ̳̦̀͟h̀͏̧̮͔̼̠̗̫̯̭̲̜̺̬̗ ̴̷̡̫͎̟̦̠̞͡f̶̝͕̞͇̳͚̩̹̖̦̭̙͜͡) created and displayed?"
] |
[
false
] |
[deleted]
|
[
"Those ",
" unicode symbols. Unicode includes all sorts of complicated things beyond ASCII's simple assumptions that one symbol follows another from left-to-right. It supports ligatures (combinations of characters), scripts written in both horizontal and vertical directions, character rotation, characters whose appearance ",
" on which direction you're writing in, and a host of other things.",
"Because it supports English (left-to-right), Hebrew (right-to-left), Japanese (sometimes vertical), Arabic (ligatures) and other languages with very different writing styles all at once, it of course has to include the ability to do all of those things. As well as each writing system's equivalents or alternatives to things like superscripts and emphasis. Which means you can make some epic insanity with combinations.",
"You can paste your example text ",
"into a converter",
" to see the unicode codes for each character to help tease out what's happening."
] |
[
"In Unicode, there's a class of characters called \"combining characters\" which mark over multiple letters. An unlimited number of these can be used to mark certain letters or letter combinations.",
"The way these things work is by taking a few letters and then adding a shit ton of combining characters until the whole thing is a total mess. For science, I wrote a python script:",
"import unicodedata #Python!\na = \" i̶̶̪̦̼͇͇̞̯͉͡ŕ̭̰͕͘ ̳̦̀͟h̀͏̧̮͔̼̠̗̫̯̭̲̜̺̬̗ ̴̷̡̫͎̟̦̠̞͡f̶̝͕̞͇̳͚̩̹̖̦̭̙͜͡)\"\nfor char in a:\n print(unicodedata.name(char))\n",
"which shows the name of each of the 68 Unicode characters in that string.",
"Here's",
" the full list.",
"And ",
"here's",
" the list for \"▒̵̧̭̲̲̈́̀͂̔▒̴̨̣͙̪̏͋͗̾░̸͓̙͔̺͗̔̅̚░̵͉͈̖̼̾̀̓͂.\" as well.",
"As to how they're created: usually by a website that generates them automatically by randomly mixing combining characters, but sometimes by somebody just going crazy in CharMap.",
"Why are they allowed? Well, they're as valid a Unicode string as any other. Some languages use diacritics in that way, although not to the ridiculous degree you see here.",
"Edit: Added import statement to the code fragment."
] |
[
"They are allowed to exist because they are technically valid. If you put spaces between the letters and zoom in or start deleting them character by character with backspace, you can see that the first example is just regular text with too many diacritics, while the second are some special characters, also with many diacritics on top of them. The text looks nonsensical to us, but there is nothing wrong with it from the computer's perspective. Multiple diacritics are needed for some langauges or phonetic transcriptions."
] |
[
"There seems to be a disagreement between magnetic north as indicated by three compasses and maps that depict my house"
] |
[
false
] |
I was looting my closet today and found a couple of magnetic needle compasses and when I checked the first it seemed to be off by about 10° I figured it was just old. But then I started looking at a few other magnetic compasses (two more) and they All pointed 10° to the right of North. According to satellite pictures of my house from Apple maps and Google maps one wall faces perfectly north I tried taking compass readings at several points in the house near walls and in the center of the largest room. Where is this discrepancy coming from?
|
[
"Magnetic North and Geographic North are two different directions. The higher in latitude you are, the more extreme the deviation will be according to a compass.",
"The magnetic pole ",
"wanders about somewhat",
" (at the moment it's heading NE at about 55km per year). If you have a decent quality navigational map (e.g. Ordnance Survey type) you should find in the key or at the bottom of the map it tells you how far magnetic north is declined from grid north at the publication date for that map grid, and what the expected drift is per year from then and in what direction. Any decent compass will be able to change the declination so that you can allign the compass accurately with grid North."
] |
[
"Magnetic North",
" and true geographic north are not the same. The exact location of the Earth's north magnetic pole wanders somewhat over time, and is currently some seven or so degrees south of the North Pole, located somewhere in northern Canada."
] |
[
"There is a difference between true north and magnetic north. True north is the direction from you to the geographic north pole (that is, the point where the axis of rotation of the Earth \"pokes through\" the top of the Earth). ",
"Magnetic north",
" is in the direction where the pole of the magnetic field of the Earth extends through the top of the Earth. Right now, it is about 9 degrees away from the geographic North pole, so your estimate is about dead on. "
] |
[
"Are all liquids incompressible and all gasses compressable?"
] |
[
false
] |
I've always heard about water specifically being incompressible, eg water hammer. Are all liquids incompressible or is there something specific about water? Are there any compressible liquids? Or is it that liquid is an state of matter that is incompressible and if it is compressible then it's a gas? I could imagine there is a point that you can't compress a gas any further, does that correspond with a phase change to liquid? Edit: thank you all for the wonderful answers and input. Nothing is ever cut and dry (no pun intended) :)
|
[
"Liquids are ‘incompressible’ in that they are only slightly compressible.",
"If we set ‘z’=1 where a fluid density doubles for a doubling of absolute pressure at constant temperature, liquids have a ‘z’ between about 0.001 and 0.05.",
"Gasses/vapors typically range from 0.4-1.6.",
"Z is compressibility."
] |
[
"All liquids are compressible. You just need much more pressure for a much smaller effect compared to typical gases.",
"If you compress a gas enough (and maybe heat it, depending on the gas) you reach the critical point, a point where the difference between gas and liquid disappears. The clear separation of the two phases only exists at \"low\" temperatures and pressures."
] |
[
"It's worth stating that the elementary approach to water flow using incompressible equations is because it's a ",
" good approximation. The difference is nearly immeasurable in most setups."
] |
[
"If I was in a truck that drove of a bridge and managed to jump from the cab, would I initially be descending at the same rate as the truck or would I have started a new rate of descent?"
] |
[
false
] |
I don't even know if this is the right sub for this, I'm bored in traffic and had this random thought. Edit: if the mods see this and could whack a physics tag on this that would be great, I didn't know how to on mobile.
|
[
"Since a truck has a lot more surface area than you do, you'd fall faster than the truck as you have less surface area for air to slow your descent.",
"Except, a truck has a lot more gravitational force acting on it to counteract any force due to friction.",
"So, it would depend on the truck.",
"I would imagine for a typical truck you may be falling slower."
] |
[
"It has an effect on the gravitational ",
" itself. If there are no other forces, the mass of the object just cancels out when you calculate the acceleration, so it doesn't matter.",
"However, when you're dealing with a real world situation where things like air resistance are a factor, the mass of the falling object absolutely does matter."
] |
[
"Technically, you're both right and wrong in your own special ways. At first, yes, the person and the truck will have the same initial velocity, but only for a moment. As they continue to fall, they both feel an acceleration due to gravity of roughly 9.81 m/s",
" however, they do not actually accelerate at this rate. Their actual acceleration is ",
", where acceleration due to drag is equal to the force of drag divided by the objects mass. While mass is definitely a factor of drag, it is not the only one, and it is incorrect to state that one object will travel faster purely because it is more massive. Drag is also dependent on the shape, surface area, surface texture (how smooth it is), orientation, yadda yadda yadda, of the object; as well as the external conditions, such as temperature, humidity, and altitude. All that being said, you can qualify an earlier statement by saying the the more massive object will most likely ",
" reach a higher velocity than the less massive object, once it reaches terminal velocity. This is because the force of gravity on the more massive object, the truck in this case, is significantly larger than the force of gravity on the human. This means that the truck will have to obtain a much higher velocity (I don't want to look up the average mass of a truck right now and give you a real number, sorry :P ) before the force of drag is equal to the force of gravity, resulting in terminal velocity. But this can also be incorrect in some cases, such as if the truck is acted upon by an external force, such as a parachute, while the human was buck naked, hairless (to be as smooth as possible) and in a very aerodynamic position (such as a straight dive). In this case, it's possible that even though the truck has a much higher force of gravity acting on it, the human is still able to move faster, due to the truck producing such high drag, while the human is producing very little drag."
] |
[
"Does Platanus orientalis (looks like a maple tree) provide a sweet syrup like \"Maple Syrup\" as produced by \"Acer Saccharum\"?"
] |
[
false
] |
The scientific names are in the question but in case I got them wrong, do the maple trees that grow in Kashmir (referred to as Chinar) produce maple syrup like their look alikes in Canada?
|
[
"The genus ",
" is only very distantly related to the maples- they're both eudicots, but that is an enormous group of extremely diverse plants; for example, ",
" is more closely related to ",
"water lilies",
" than it is to maples, and maples are more closely related to ",
"poinsettias",
" than to ",
"Interestingly, the sap from at least some members of the genus ",
" can be used to make syrup. Euell Gibbons experimented with making syrup from the American sycamore, ",
" and reported that it tasted like poor quality molasses. It certainly won't taste anything like maple syrup, apart from being sweet. A much more common alternative to maples are the birches, genus ",
" but there are likely many different types of tree that can be used in this way; all that is really necessary is lots of sap with a fairly high sugar concentration. And no nasty flavors when its concentrated, of course."
] |
[
"Platanus species are not maple trees and aren't even that closely related. That said, blacksheep998 is pretty much correct. You could probably get and distill the sap from them but and it would be sugary, but it probably wouldn't taste the same because the other compounds present would be different. ",
"According to wikipedia, ",
" is preferred for sap collection because of the very high sugar content with consistent production in the spring and the clarity of the sap (few lignins and other molecules clogging it up). It also has the traditional \"maple syrup\" flavor whereas syrups made from other trees have a different flavor. "
] |
[
"Maple syrup is simply a concentrate of the sugary sap found in sugar maple trees. All trees transport sugars in their sap, so any tree should be able to produce syrup if you extracted and distilled the sap.",
"The problem is the other chemicals present in the sap. Many, probably most, would taste terrible. And some would even be toxic."
] |
[
"Why can't we use capacitor as batteries?"
] |
[
false
] |
Instead of chemical batteries?
|
[
"Batteries have much higher energy densities than capacitors, so they are used where you need to store a lot of energy. On the other hand, capacitors can be charged and discharged much faster than batteries, so they are used where high power is needed."
] |
[
"Chemistry mostly. One is based on storing energy in an electrical field in a dielectric. Batteries are based on electronegativity. ",
"There are designs and products on the market that have both in them. Super capacitors."
] |
[
"Batteries are designed so that two chemical plates (electrodes, + and -) create an environment that enables the travel of electrons in one direction and ions (the atoms the electrons separated from) travel in the opposite direction. The good thing is you store a lot of energy, the bad things are your speed of energy release is limited to how fast the ions travel and destructive chemical reactions that kill the batteries performance after many uses.",
"With capacitors you apply a charge that forces electrons to the edge of a gap they cant cross, but they really want to cross, so they get stuck stored in an uncomfortable place, think of rubbing a balloon against your hair and generating a static electricity field. When you draw charge from a capacitor, your speed of drawing current mainly depends on electrons traveling, which is a shit ton faster than the batteries ions can travel. You are also less likely to have any rogue chemical reactions with a capacitor with many uses.",
"So batteries are for when you need a little bit of power over a long period. Capacitors are for high instantaneous power which can be charged and discharged over and over."
] |
[
"Could the event horizon of one black hole be deformed by the gravity of another close black hole?"
] |
[
false
] |
Or are event horizons usually spherical?
|
[
"Yes, when they are extremely near each other, the event horizons of two black holes can deform. They can grow \"fingers\" towards each other until they merge. "
] |
[
"Once their horizons intersect, there is a process of \"ringdown\" in which the newly formed merger remnant BH event horizon oscillates down to its final form. The solutions interior to the horizon are chaotic and not very friendly. It's unfortunately not as simple as \"we have two singularities and a point of equilibrium between them.\""
] |
[
"If their event horizons intersect would there be a locus between the singularities with 0 net gravity between them?"
] |
[
"My cats have eaten the same dry cat food, everyday, for years... Do they mind??"
] |
[
false
] | null |
[
"Cats have very few taste buds (fewer than 500, compared to over 1500 for dogs, and over 9000 for humans), so I don't think they care all that much. The smell is likely more important to them. "
] |
[
"Don't worry evolution will take it's place and fix it. We shall see one more taste bud here soon\nEvolution is science right?\n(downvotes to the left)"
] |
[
"Don't worry evolution will take it's place and fix it. We shall see one more taste bud here soon\nEvolution is science right?\n(downvotes to the left)"
] |
[
"Does the ISS need to constantly make micro course corrections to compensate for the crew's activity in cabin to stay in orbit?"
] |
[
false
] |
I know the crew can't make the ISS plummet to earth by bouncing around, but do they affect its trajectory enough with their day to day business that the station has to account for their movements?
|
[
"Momentum is conserved in a closed system. People in the ISS can't permanently change its trajectory by moving around. They push off one wall, sending it in the opposite direction but then they must necessarily then hit the other wall, undoing what they did. The center of mass momentum of the station+occupants is fixed."
] |
[
"Why would a spinning space station experience more drag? Isn't drag the result of atmospheric particles hitting the space station? Wouldn't those particles hit whether the space station is spinning or not?"
] |
[
"A different orientation could lead to a larger cross section of the station.",
"The effect of humans on the orientation is completely negligible, however. The ISS orientation is unstable on its own and needs gyroscopes to stay as it is anyway.",
"Edited for clarity."
] |
[
"How is space research done?"
] |
[
false
] |
I understand the basic principle of an orbiting telescope, using some series of lenses making an slr look like tinker-toys, but how are things like the temperature of the sun, the size and distance of planets, and the shape of galaxy's figured out?
|
[
"The shapes of distant galaxies are figured out simply by looking at them. They're very far away, but they're ",
" so it's not that challenging to take photographs of various sorts. The resulting pictures are informative, but they're also quite pretty.",
"The shape of ",
" galaxy is inference and speculation, and unsurprisingly, it evolves quite dramatically over time. It's known not to be elliptical or irregular, because we can see that much with the naked eye on a clear night in the countryside. But beyond that, it's best guess piled atop best guess.",
"A few decades ago, it was assumed that the Milky Way was a spiral galaxy with as many as twelve (!) distinct arms. Then for a while it was believed that ours was actually a barred spiral with just two arms.",
"Now the prevailing model is a sort of compromise, a barred spiral with two well-defined arms (Perseus and Centaurus, they're called) and a number of \"spurs,\" including the one that we're in, all surrounded by the distant and enormous Monoceros Ring. It helps not at all, of course, that the arms of a spiral galaxy aren't actual structures in any meaningful sense, but rather variations in stellar density of as-yet-unknown cause.",
"I imagine most people would be amazed by just how little we know of our own galaxy, compared to depictions of same in fiction. For instance, it was discovered just a few years ago that our galaxy contains within it ",
" some thirty thousand light-years in diameter. Whether this galaxy — called Virgo after the area of the sky in which it appears — is just passing through the plane of the Milky Way or being torn apart and \"eaten\" by our galaxy is an open question."
] |
[
"The temperature of the sun can be inferred in a variety of ways. One way is to look at the radiation we receive from it and compare it to the spectrum of what's called a ",
"black body",
".",
"The distance of a planet (from the Sun) can be figured out by looking at how it moves across the sky, and comparing it with the known ",
"laws of planetary motion",
". ",
"I don't know the answers to your other questions, but you might also be interested in the fact that the chemical composition of the upper layers of stars can be figured out using a certain type of ",
"spectroscopy",
". "
] |
[
"In case anyone else is trying to find more information on the mentioned Virgo galaxy, which is rather hard to find because it shares its name with the Virgo supercluster of galaxies, here's a link: ",
"http://en.wikipedia.org/wiki/Virgo_Stellar_Stream"
] |
[
"Why does placing a wooden spoon over the top of a pot of water stop it from boiling over?"
] |
[
false
] |
.
|
[
"When the bubbles hit the spoon they go 'POP'"
] |
[
"Does this really work, do you have any reference our just personal experience? I guess I will have to conduct some tests.",
"A trick I know work is putting a metal spoon in the pot. This reduces the entropy gradient since it conducts heat. Having a lower entropy gradient means less convection. It doesn't completely stop boiling but makes it less violent."
] |
[
"It doesnt work with steel or metal things"
] |
[
"A bullet is shot and is travelling at 2,500 FPS. As the bullet travels, is the space directly behind it (let’s say an inch) filled with air? Or does the bullet push it aside and there is ‘nothing’ behind it?"
] |
[
false
] | null |
[
"The nose of the supersonic bullet creates a shock wave pushing the air out of the way, but the tail of the bullet creates an \"expansion wave\" -- basically the opposite of a shock wave -- that allows the air to flow in behind the bullet again. The pressure behind the bullet will be low, but not zero.",
"Here's a photo",
" of a bullet in flight at about the speed you're talking about. The expansion wave I mentioned isn't very obvious, but you can see that there's turbulent air right behind the bullet."
] |
[
"Stability of the bullet is due to the spin of the bullet along the long axis. This stability can be calculated via an empirical formula called the Greenhill formula.",
"Neat fact - you can reduce drag on a bullet with a flat base by bleeding air into the turbulent region directly at the base of the bullet in the photo provided by agate_, allowing the airflow to remain laminar. This is called Base Bleed, and can extend the range of some artillery shells by 30% \nsource: ",
"https://en.m.wikipedia.org/wiki/Base_bleed"
] |
[
"Here",
" is a similar question asked by someone on stack exchange. The answer given was about 3x higher velocity but still in an idealized sense. In reality you can’t create a full vacuum but the air pressure behind a bullet would be significantly lowered. ",
"The bullet pushes the air out of the way but as soon as the bullet passes the air will cram back in. In order to create a pure vacuum you would need to fire a bullet that travels significantly faster than the average speed of the molecules in the air. "
] |
[
"Where did the bacteria in our digestive system come from in the first place?"
] |
[
false
] | null |
[
"Well, for one, in a minor way, from whatever touches our mouth or gets far into our nose. You can think of the body as doughnut shaped. The dough is where all the organs are, and is bounded by epithelial tissue. On the outside, that's skin, and on the inside it's the esophagus, stomach, intestine tissue, etc. When you eat any food, if the bacteria are able to survive the stomach, which many are, they can settle nicely in your digestive track, in the doughnut hole.",
"However, the actual initial colonization happens during birth. The majority of our bacteria (both on skin and in our guts) comes from the bacterial in the vagina and from the bacteria on the skin of the first few people that touch us. Once those cultures are established, they kind of run the place and keep other bacteria out fairly well. This is one of the reasons why doctors recommend that newborns have skin-to-skin with the mother (and father) as soon as possible after birth."
] |
[
"As the womb isn't actually as sterile as everybody previously thought, the first bacteria a human encounters is in the womb. Bacteria have been found in amniotic fluid, in blood the umbilical cord, the membrane around the fetus, etc. "
] |
[
"It's ironic that pandas do that. They have the guts of a carnivorous animal\n They're one of the most inefficient animals there is."
] |
[
"How much of the planet was covered in forest before humans, and how much is covered in forest now?"
] |
[
false
] |
[deleted]
|
[
"Lots of speculation in this thread, but no actual answers.",
"The best data ",
"from the UN",
" shows that about 3.9 billion hectares of forest are around today, and ~6 billion were before human civilization. We've cut down about a third of the total forest on Earth."
] |
[
"It's worth noting that in some places human activity is causing the reappearance of forests. Much of the Eastern U.S. was cleared for agriculture in the 18th and 19th centuries, but now that so much farming has moved to the Midwest a lot of the old farmlands are reverting to forest. Human activity, especially fire suppression, has also given rise to novel kinds of forests. In Texas you have sizable groves of mesquite, the result of overgrazing by cattle who eagerly eat the mesquite's seedpods, while on the former grasslands of the Gulf Coast there are forests of ",
"chinese tallow tree",
", an ornamental that has become naturalized."
] |
[
"Forestry management dates back to somewhere between the 5th and 13th centuries depending on how you define it. If you are harvesting trees heavily you immediately grasp the importance if being able to harvest them within a reasonable distance of where they are needed for the transportation you have available at the time, so you start treating them as a crop. ",
"Humans that do not do this are not the humans harvesting them heavily, those humans are still slash & burn farming or trying to clear an area for livestock."
] |
[
"Is ADHD over diagnosed?"
] |
[
false
] |
I just saw a report on NBC Nightly News about how so many children are being diagnosed with ADHD. I also commonly hear the layperson saying "It's just kids being kids, the don't need any medicine." Is the rise in diagnoses just from heightened awareness (like I've heard about autism)? Also, 20 years ago my sister was diagnosed with ADD. what's the difference between that and ADHD?
|
[
"Most studies suggest that 5-7% of children have ADHD. This comes from studies that take, for example, 1,000 children and do comprehensive assessments to determine whether or not they meet criteria for ADHD. However, in the real world about 10-20% of children are diagnosed or treated for ADHD (in the US. The numbers are different in the UK for example). So, either the studies are wrong (pretty unlikely), or ADHD is over diagnosed. As a psychiatrist, I assure you that I see it misdiagnosed ALL THE TIME by primary physicians. There a lot of issues that play into why, and the problem is that there are a lot of medical conditions that can lead to symptoms of ADHD, and making the distinction really requires an in depth assessment and a trained expert.",
"ADD = ADHD Primary Inattentive Type. They used to have two separate names, ADD, and ADHD. Now, they've lumped them all into ADHD, with three subtypes 1.) Primary Inattentive 2.) Primary Hyperactive 3.) Combined."
] |
[
"Of course. Pay close attention to the methodologies used in each study, and how it correlates with the results.",
"http://journals.lww.com/co-psychiatry/Abstract/2007/07000/Epidemiology_of_attention_deficit_hyperactivity.13.aspx",
"http://www.ncbi.nlm.nih.gov/pubmed/18998276",
"http://www.ncbi.nlm.nih.gov/pubmed/10944656",
"http://onlinelibrary.wiley.com/doi/10.1002/mrdd.10036/full",
"http://mbldownloads.com/0808PP_CNS_ERT_ADHD.pdf",
"http://ww1.cpa-apc.org:8080/publications/archives/cjp/2001/december/study.asp"
] |
[
"Do the prescribed medicines have side effects?",
"Yes. Hypertension, appetite suppression, weight loss, agitation, anxiety, sweating, headaches, dizziness, insomnia... among other things. ",
"If a child is misdiagnosed, can giving them the medicine mask their undiagnosed mental issues that you allude to in your answer, giving them further problems?",
"I was alluding to medical, not mental disorders (however anxiety disorders are frequently confused with ADHD). For example, sleep apnea is far more common in children than was once thought, and the symptoms of untreated apnea can be very similar to ADHD. Treating with psychostimulants will often reduce the problematic symptoms, but leaving the apnea untreated can lead to severe cardiac, vascular, and neurological problems. There are a host of other medical disorders that are similar, which is why a trained expert conducting an evaluation is so crucial in order to not miss these things. "
] |
[
"How dark is outer space?"
] |
[
false
] |
If you got far enough into space, away from the sun or another star, would you still be able to see your hand in front of your face, or would it be too dark?
|
[
"You don't even need to leave Earth for it to be that dark. On a moonless night in the wilderness, fifty miles from the nearest streetlights, you can only see your hand by the black hand-shaped void where it blocks out the stars."
] |
[
"But this would be due to the earth blocking the sun's light. Out in space far away from anything you wouldn't have this massive rock blocking light from hitting at all angles, even with how minimal light there would be I would feel you could still see your hand"
] |
[
"I think the question here is: if you were in interstellar space, would the stars provide enough light for you to be able to see anything? "
] |
[
"Why were stations like Mir or Skylab put in orbits that decayed over time?"
] |
[
false
] |
[deleted]
|
[
"It takes more energy to get to a higher orbit. (And because of ",
"the tyranny of the rocket equation",
", what might seem like a small difference in energy requirements can translate into a substantial difference in fuel requirements.) That's a cost that has to be paid not just when you launch the station into orbit, but for every future mission that rendezvouses with it.",
"If you're already sending supplies and crew members up every few months, then the additional expense to give your station a little boost once in a while is small in comparison."
] |
[
"The ISS does need regular boosts.",
"Attach a rocket engine at its center of mass and boost, would be my guess as to \"how\"."
] |
[
"The ISS does need regular boosts.",
"Attach a rocket engine at its center of mass and boost, would be my guess as to \"how\"."
] |
[
"Oumuamua was spinning end on end. It is possible the acceleration observed as it rounded the sun was due to some form of boomerang effect?"
] |
[
false
] | null |
[
"Space is very nearly a perfect vacuum, better than most artificial vacuums on Earth and often measured in atoms per cubic centimeter. The aerodynamics that make a boomerang work don't apply here. Light pressure is much stronger - and still incredibly weak.",
"It's not often that a paper makes my hair stand up but ",
"this did.",
" That's going to bother me in the back of my mind until I'm sure it's wrong. The object moved like it was being subjected to light pressure, but it allegedly moved too fast to be rock and probably wouldn't have survived if it were being pushed by comet outgassing.",
"Lightsail is a bad guess given the flight characteristics. For the mass it might be sheet metal. The only other information available is that it's red, not traveling that fast for an interstellar object, longer than it is wide, and slowly tumbling end over end.",
"The gods must be crazy and we've found a giant empty can of Coca Cola. Or somebody's dropped fuel tank. That's a bit concerning - aliens should exist, but finding such an object really should be unlikely."
] |
[
"So the basic idea is that, after tracking the motion of 'Oumuamua, it was found that its acceleration didn't ",
" match what we'd expect from gravity alone. The Sun's gravity pulls stuff towards it, but it looks like there was also a weak force pushing 'Oumuamua away from the Sun too. The effect is small, but the tracking of 'Oumuamua is so precise that it's very significant. It looks like this effect is related to the distance from the Sun, and is proportional to 1/distance",
"A \"boomerang\" or drag effect is unlikely, because that would depend on the speed of 'Oumuamua rather than its distance. The low density of gas in the solar system would also make this effect too weak.",
"The simplest explanation is that it's out-grassing. Like a comet, as it gets close to the Sun it warms up, some of its solid material turns into gas and flies out in little jets. However, this is a bit tricky because we haven't seen any gas coming out of the object, and its spin hasn't changed over time, which is what you'd expect if you're blowing gas out.",
"Radiation pressure was another possibility, but it's not really strong enough to work. The only way it would work is if the 'Oumuamua was incredibly light or incredibly thin, which seems unlikely. Some people have got a bit over-excited about this in a \"ooh what if aliens?\" way, but that's a bit dodgy.",
"The other possibility is gravitational effects - maybe there are two gravitating bodies that look like one? But again, this is a bit tricky because we should be able to see them drift apart a bit, and we don't see that.",
"Another possibility is that there is simply an error in the original work. Gravity is also proportional to 1/distance",
", and so if their value for the gravity from the sun (GM) was too high by 0.1%, then that would give the exact same answer. However, I haven't gone through the work in detail to see if such a mistake is likely."
] |
[
"If it ever was a probe it would take 11,000 years for it to travel one lightyear at 26 km/s. This has been out there for some time. It's also tumbling which suggests the attitude control system is offline, and might have been offline since before humans invented fire. ",
"So derelict, garbage, or natural object. "
] |
[
"When an F-22 raptor lands on the runway, because of the stealth plating can ATC(Air Traffic Controll) see it on their radars?"
] |
[
false
] | null |
[
"The F-22, like most planes, will have a ",
" - a radio transmitter that broadcasts information about the plane. When taking off or landing at a friendly airport, an F-22 would have its transponder on, and thus ATC can track it no problem. The transponder will be turned off when stealth is required.",
"Should the transponder fail, the F-22 pilot will rely on radio contact with air traffic control."
] |
[
"Should the transponder fail, the F-22 pilot will rely on radio contact with air traffic control. ",
"Stealth aircraft on non-combat missions usually carry a radar reflector. This 'breaks' their stealth so they can be tracked by radar."
] |
[
"The F-22 is not a \"stealth\" aircraft, and is detectable by ground-based radar, although the radar return appears to be a smaller object. Additionally, when the craft begins approach, flaps and landing gear increase the radar cross-section."
] |
[
"Deep space probes that are in \"sleep\" mode while traveling. Do we just gamble and hope it doest hit anything like an asteroid?"
] |
[
false
] |
Just saw an article on the US space probe set to explore pluto that just "woke". So made me think if its on stand by mode, how do we know if it crashes? Or does it have a feature constantly active, like a laser, to detect objects and move it self?
|
[
"It is sent in a trajectory that doesn't intersect any known asteroids. This is not wicked, they are separated by hundreds of millions of km, so in most cases the simplest trajectory that works to intercept the planet is already safe enough.",
"Smaller objects that cannot be seen from Earth, i.e. micrometeoroids might be a more realistic concern, though not much.",
"a feature constantly active, like a laser, to detect objects and move it self?",
"This would be completely useless. Satellites in orbit around the Earth are moving at over 7 km/s (to understand how big this speed is, a racing car can barely get close to 0.1 km/s). Interplanetary probes are significantly faster. Even if you could \"see\" a small obstacle at those speeds, the probe wouldn't have enough time to do anything before a mess happens.",
"In cases in which the probe is expected to have a higher probability of hitting small meteoroids it can be protected by a double-layer MMOD shield. Those things work by letting the incident object crash against the first layer, effectively breaking up into lots of smaller sand grains, so they hit the second layer in a much larger area that makes it easier to absorb the impact. This is regularly used in some Earth orbits where debris is abundant. In the case of interplanetary probes it'd make little sense, but I can conceive some rare cases in which it could be needed, e.g. intersecting the tail of a comet."
] |
[
"An asteroid hitting the Earth is a different matter - the Earth is a large gravity source and is actively pulling things towards itself. Asteroids in the area will, over time, tend to gravitate to us.",
"Asteroids hit the Earth all the time. Most of them are small and inconsequential, some are larger, like the Russia ones. They still do no harm. The premise of an Earth-killer asteroid is a pretty rare thing."
] |
[
"Space is so mind boggling empty, that we ignore the chance of collision and just send probes on their paths without any security measures. The chance of collision is basically non existant for any prictical purpose and pictures of dense rock clouds are vastly exaggerated."
] |
[
"How, or why, do refraction and dispersion occur?"
] |
[
false
] |
I'm an A-level physics student and we've just covered refraction and dispersion. Our teachers have said we don't need to know why and how they happen but I'd like to know because it'll help me understand everything. They tried to explain but they've told me so many things that contrast that I don't know what's what any more. Here's what they've said to me about dispersion: "It's because frequency is variable." "Frequency is constant and cannot change so it's the wavelength." "It's because the different wavelengths of EM waves travel at different speeds." "Speed is always constant for all EM radiation because it always travels at the speed of light." "It's because the wavelength is variable" - then didn't explain how this affected it. Here's what I've currently done some research to find: Refractive index is different for each different 'colour' of visible light due to the frequency difference so each colour refracts by different amounts. If this is the case, how come we don't get a rainbow in every refraction? Now refraction, which I probably should have started with. I've been told it happens due to the absorption and re-emission of the photons and that this is similiar to what we learned in the photoelectric effect when electrons absorb photons but I've also been told it's due to the oscillating electric field interacting with the greater number of electrons in the denser material causing interference or resistance but I don't understand how this resistance occurs, if this is correct of course. I've been told absorption and emission is both correct and incorrect on different occasions by the same teacher. Many premature thanks,
|
[
"Speed of light is constant in a vacuum, but not as it passes through matter. "
] |
[
"See this animation and page for a good description. \n",
"http://physics.ucdavis.edu/Classes/Physics9B_Animations/ReflRefr.html",
"\n(Sorry I'm on mobile, you may have to copy/paste)",
"The frequency of light is constant, but it's speed is not. Light will slow down when it enters some medium such as glass or water. If a beam of light hits the surface of some medium, say water, at an angle, the light will refract due to interference with itself. The easiest way to look at this is by applying Huygen's Principle (shown in the link I provided). "
] |
[
"To add, different frequencies of light (colors) are slowed differently in materials. Look up 'index of refraction vs frequency' plots on Google. \nThis means that light beams of different colors will bend differently if shot into some medium at an angle. This leads to the formation of rainbows (like the Dark Side of the Moon album cover). "
] |
[
"Is there a reason why 8 bits make up 1 byte?"
] |
[
false
] | null |
[
"A byte hasn't always consisted of 8 bits, it is hardware dependent, and so there have been implementations 4,5,6 and 7 bits in a byte. It was just how those implementers decided to represent that information. For example, ASCII is transmitted at 7 bits to the byte and hardware that made use of ASCII would have to follow this standard. It was when AT&T started using 8 bits that it became popular, because that infrastructure was everywhere.",
"Soon, everyone started using it, and now you see almost all hardware using 8 bits to the byte. There isn't a standard that says how many bits there should be to the byte, it's just the most commonly used one. "
] |
[
"The 8th bit was used quite often as a parity bit, 7 bits gave 128 characters enough for the full latin alphabet plus common punctuation plus 1 bit for parity.",
"It was fairly common in the early days of computing, there is a funny story about Cray and Parity bits.",
"For a contrary view, Seymour Cray, premier designer of supercomputers, held parity designs in contempt. He felt it showed poor design—if you designed your transmission paths to be reliable, you would not have to waste resources on parity. His famous quote on this (circa 1963) was \"Parity is for farmers\" (after the use of the term \"parity\" in the New Deal). After he later included parity bits on the CDC 7600, Cray reputedly said that \"I learned that a lot of farmers buy computers.\" ",
"http://en.wikipedia.org/wiki/Parity_bit#History"
] |
[
"As powerful as it would be, I would still overcluck it"
] |
[
"Are there any plants/animals that have absolutely no elements in them heavier iron? ie life that doesn't require the explosion of a supernova to exist."
] |
[
false
] |
So I know that most stars only fuse up to iron so these are the most common elements in the universe, and that the human body needs some elements heavier than iron, like iodine, but is there anything on this lovely planet of ours that doesn't require elements heavier than iron to work? edit: thanks!
|
[
"Nope. There might've been at some early stage in evolution, but all single- or multi-cellular life that's around now requires (among other things), zinc, copper and molybdenum. ",
"Just to mention one example, there's copper in Cytochrome c Oxidase, and that one enzyme alone is present in all eukaryotic life and most bacteria as well."
] |
[
"I gotta point out a very common misconception in your title. It's true that supernovae might produce many of the heavy elements in the universe through the ",
"r process",
", but about half of the heavy elements are produced in the ",
"s process",
", which happens in some giant stars. There are also some additional minor processes.",
"Now that I've answered a question you didn't ask, I'm looking forward to seeing the answer to the question you ",
" ask.",
"Edit: since zinc, copper, and molybdenum were mentioned, all of these are produced in the ",
"rp process",
" which occurs in ",
"explosions on the surface of neutron stars",
" (though neutron stars are made in supernovae so...)"
] |
[
"haha thanks, me too!",
"EDIT to ask a question, so the s process is just a bunch of neutron capture yeah? is it the case that this is not energetically favourable but just happens anyways cos there's loads of neutrons flying around with enough kinetic energy?"
] |
[
"How does an hydropower plant in a river affect the river?"
] |
[
false
] |
The water is running through Turbines, which should kill most fish. Is that not a big problem for wandering fishpopulations?
|
[
"Dams (whether they are hydroelectric or serve another purpose) fundamentally alter a lot of the underlying characteristics of a river and thus have very large impacts on a variety of life, mostly downstream of the dam, but also in the area immediately upstream that is inundated. In terms of the dam being a physical barrier and/or a direct cause of death for fish when interacting with turbines, in many respects this is one of the more easily addressed issues. Structures like ",
"fish ladders",
" or other mechanisms of transporting migratory and economically valuable fish (e.g. salmon) past dams are regularly implemented, e.g. ",
"more examples described here",
". ",
"However, simply making sure the fish can get where they are going ignores the fact that the presence of the dam often changes the river environment to the point where it may no longer be conducive to those particular fish species (and other plant and animal species). Some important examples:",
" Dams change the temperature of the water, as the impounded reservoir will often stratify with abnormally warm water on the top and abnormally cold water on the bottom. Release of these cold bottom waters will then reduce the temperature of the water downstream of the dam, which can have negative impacts on fish populations, ",
"e.g. Clarkson & Childs, 2000",
". This is the most common example, but generally dams wreak havoc on the natural diurnal and seasonal temperature structure of rivers, which is problematic for species adapted to particular temperature ranges.",
" The dam also doesn't just impound water, it traps sediment. Starvation of sediment downstream of the dam will often cause incision, bank erosion, lack of floodplain inundation (depriving the floodplain of nutrients, etc), abandonment of channels, etc , ",
"e.g. Ligon et al, 1995",
". With specific reference to the sediment and fish, sediment on the bed of rivers is often important in the spawning cycle of various fish, so removal of the upstream sediment source can impact the ability of these fish to reproduce. ",
" Finally (and maybe most obviously), dams dramatically change the hydrology of rivers downstream of dams, e.g. ",
"Graf, 1999",
" or ",
"Graf, 2006",
". This means that there may be extremely low flows at times (when water is being preferentially retained in the reservoir) or extremely high flows at times, but regardless, the flow in the river will be very different than the normal flow in that river. This will impact the amount of water in the river, but will also change how sediment moves, etc (which feeds back to some of the changes in the river environment described in the sediment paragraph above).",
"These are just a few of the big ones and ignores changes in the chemistry of the water, accumulation of material upstream of the dam, etc. If you're interested in this topic, there are lots of books (in addition to journal articles) written on the effect of dams on river habitat / ecology / geomorphology.",
" There are strategies/structures employed at dams that can reduce the direct interaction of fish with the dam and make sure they can move around it, but the fundamental changes that a dam imposes on a variety of river characteristics (sediment transport, temperature, etc) can still make them incredibly destructive with respect to all sort of animal and plant species that live in or near the river."
] |
[
"Just to add to your as usual excellent write-up: the flood control coming with damming rivers often reduces the spring flooding of adjacent vegetation. While that is of course a desired effect from a civil engineering perspective, many fish species use those flood zones for reproduction and are badly affected by the dam."
] |
[
"I will add that these impacts go beyond fish using flood zones to a whole variety of cascading effects. Example: spring floods create sandbars that are a specialized environment for both plant and animal species. Some tree species only sprout on the newly exposed post-flood bars. When the floods are eliminated these bars don't form. The establishment of these new groves stabilizes the newly created bar, inducing flow changes in the rivers path. Without these new bars and vegetation patterns, the river become increasingly channelized with high banks, eliminating still other microenviroments that other species depend on for their habitats"
] |
[
"Is there a formula to calculate the average range of a photon (emitted as gamma radiation from a decaying radioisotope) with a particular energy in a particular material?"
] |
[
false
] |
I'd like to be able to calculate the average range of gamma emissions from radioactive nuclides in air, given the energy of the emission. I know the linear attenuation coefficient comes into it - and that the linear attenuation coefficient of a material depends on its Z and the energy of the photon, but I can't actually find a formula anywhere. Or is there not technically an average range because the number of photons decreases exponentially with depth in the material?
|
[
"If one exists, it's probably some obscure empirical relation in old textbooks. In practice, you would usually just look up a value for the attenuation coefficient rather than trying to calculate it."
] |
[
"The reason you aren't finding a formula is because it's fairly complicated and there are lots of different processes going on and they all have to be added up. There's ",
"the photoelectric effect",
" which depends on the energy level of every electron in every element in the material, ",
"Compton scattering",
" which is described by the fairly complicated ",
"Klein-Nishina equation",
", and for high-energies also ",
"pair production",
".",
"In practice ",
"compilations like this one",
" are made by computer programs which calculate all of the effects and then people who need them just look them up, or they're measured directly."
] |
[
"Are you after a formula for the attenuation coefficient, or how to use the attenuation coefficient to work out what you need?"
] |
[
"How do we know the second law of thermodynamics is a law and not merely something we've never seen broken?"
] |
[
false
] | null |
[
"Keep in mind that the second law is an inherently statistical statement. There's always a non-zero probability that some process won't obey the second law. It's just that when you have macroscopic numbers of particles (on the order of Avogadro's number, say, 10",
" the probability that heat flows backwards is effectively zero (like, 10",
" or less). We'd have to wait a very very long time (several times the age of the universe) to be able to observe such a thing happen spontaneously.",
"(Then, right after it happened, the system would go back to thermal equilibrium and no one would ever believe you.)"
] |
[
"Aren't all laws of nature like this? Couldn't the most fundamental laws be \"merely something we've never seen broken\"? ",
"Why should the sun rise tomorrow? We've seen a pattern in that it rises each day, but we can't be 100% certain that it would next day.",
"Truth is, there are no \"laws\". All science and uniformity of nature is based on inductive reasoning and recognition of patterns; we attempt to predict utilizing past experiences. One could argue that uniformity of nature is not true, but we're much better off assuming it is. You could assume that the second law of thermal dynamics could be broken anytime, but that's like assuming that your next meal is going to poison you. We've seen the pattern holding true for so many times, might as well say it would in the future.",
"Check out this wikipedia article on inductive reasoning ",
"http://en.wikipedia.org/wiki/Problem_of_induction",
" "
] |
[
"No, it's a law because of your second sentence, not your first."
] |
[
"If Humans Had Never Evolved: Top Animal Candidates for Sentience and Technology?"
] |
[
false
] |
Say the most 'advanced' of the Great Apes were the chimpanzees or bonobos or some kind of fairly stupid Lucyish creature, still kickin' it in Africa. Climate or circumstance made sure that hominids with big brains, a penchant for weaponry and an upright stance just didn't show up. Fast-forward however many millions of years, and there is a globe-spanning civilization or collection of civilizations of tool-using, self-aware entities. Which animal root did they evolve from? I think I'm going for bears, but some kind of octopi are a close second. Bears just seem uncannily intelligent, they use tools occasionally, they show evidence of fairly complex planning, they can walk upright if they need to, allowing the use of their front paws for carrying items, and they get high on magic mushrooms (I'm fairly convinced that getting high as shit on psychadelics was responsible for a lot of very early culture and religion). As for our many-tentacled friends, some octopi are smart as fuck, imagine if they figured out how to make nets and spears.
|
[
"I don't think there's ever much benefit in speculating about future evolutionary directions, but the current non-primate leaders in tool use are probably ",
"birds of the crow family",
". Birds are also pretty good with language. "
] |
[
"Peer review of comments came back negative, posts were redacted."
] |
[
"Peer review of comments came back negative, posts were redacted."
] |
[
"I keep hearing that Voyager will take 10,000 years or 100,000 years to reach the closest star. Is it actually aimed towards a star or is it just going in a random direction?"
] |
[
false
] | null |
[
"Voyager 1 will pass within 1.6 light years from some nameless star in Camelopardalis. Voyager 2 will pass within 1.7 light years from 248 then in 300,000 years pass 4.3 light years from Sirius. So really, they're not aimed at anything.",
"Here is my source at JPL",
"."
] |
[
"This doesn't directly answer your question, but I think it's still interesting: ",
"Voyager 1 travels at about ",
"17 km/s",
" or 61,200 km/h. ",
"Alpha Centauri is the closest star system to our solar system. That system is about ",
"4.37 light years",
", or about 41.5 trillion kilometers away. ",
"If Voyager 1 ",
" headed toward the closest star it would take roughly 675 million hours or 77,000 years to arrive. ",
"Alternately, the Helios probes are the ",
"fastest spacecraft ever built",
", traveling at about 253,000 km/h. If Helios were headed to Alpha Centauri it would take approximately 163 million hours, or 18,000 years to arrive. ",
"The Neolithic or Agricultural Revolution is usually considered to be the beginning of human civilization, and that happened somewhere around 10,000 BCE.",
"Basically, in the time it would take our fastest spaceship to reach our closest neighbors the entire story of humanity as we know it, from the beginnings of civilization to the present, could play out one and a half times.",
"Space is pretty big, guys. "
] |
[
"Voyager 2 will pass within 1.7 light years from 248",
"For the record, the name of the star is ",
" 248. It's currently a little over 10 light-years away, but ",
"will be the closest star to our Sun 35,000 years in the future",
"."
] |
[
"Why do trash cans smell even after they've been washed?"
] |
[
false
] |
My plastic kitchen trash can smelled bad. Really bad. So I took out the trash, and washed it with soap and hot water. That didn't remove the odor. So I bleached it -- I sprayed it with a bleach solution, making sure to let it sit for 10 minutes before I rinsed it. Still have smell remaining. I washed it again. Still there. I've asked around, and this seems to be a pretty common phenomenon (anecdotal, of course). So what's going on? Is soap and water just not good enough for the kinds of decay processes going on in trash cans? Or is there some kind of residual odor in the can?
|
[
"I can only speak in generalities -- but I think it's pretty reasonable that those smell molecules have simply diffused into the plastic. At the molecular level, the plastic will be quite porous."
] |
[
"My first thought was actually a metal trash can. But I honestly don't know the answer to this question. I don't expect the polymers in mass produced trash cans to be as good quality as specialty ones that are found in a research setting."
] |
[
"Are there certain plastics that are more or less susceptible to this? In other words, is there a trash can I can buy that won't have this kind of problem?"
] |
[
"Einstein said vegetarianism will improve health and increase chances of survival of life on Earth, how much more beneficial is a vegetarian diet?"
] |
[
false
] | null |
[
"Einstein was not a famous nutritionist. I can find no evidence that he ever made any scientific claims about the benefits vegetarianism."
] |
[
"Given that Einstein was a physicist I don't think we should listen to his claims about nutrition, even if he actually said that (he didn't)."
] |
[
"If you consider the fact that energy/mass is lost in every stage in a food chain due to the waste products that animal produce, or simply because energy is lost as heat as a result of the animal using it's muscle, then if everyone just ate plants we would have more than enough food for everyone.",
"tl;dr Adding more things inside the food chain means more energy is lost, therefore eating plants would be able to provide the whole world with food."
] |
[
"space time and earthtime"
] |
[
false
] |
I don't know if i'm saying this right but if time in space is different to time on earth, is the possibilty of being in space and having time move much quicker then on earth at all likely. By which i mean; say we were on earth and a star was going supernova in 1000 years earthtime (at the point of the star and not by which we view it here) but if i was somewhere else in the universe and was still calculating time as earthtime would it be possible for it to go alot quicker. By that i mean it actually is 1000 years but because time is different the 1000 years goes past in what feels like the time of 500. I really don't know how to explain but any parts that you do not understand just ask and i'll do my best to explain in further detail The reason i ask this question is because the thought that to us the universe is over 13b years old by our time but what if the time is different to the point that it moves exceptionally faster but time for us is just slower.
|
[
"There is no preferred universal inertial reference frame. However, there is a reference frame that has a unique property that the cosmic microwave background doesn't look hotter in one direction and colder in the opposite. We are moving about 600 km/s relative to this reference frame. This is too slow for relativistic effects to become important. However, for a neutrino emitted from a supernova and flying towards Earth, the whole trip can seem like a few seconds."
] |
[
"This is not meant as an attack, but you are very confused about how relativity works. ",
"This article",
" is an excellent summary, and I would recommend reading it. If afterwards you have questions, come back here and ask. The problem is from where your apparent level of understanding is, it would take a lot of effort to answer your question. "
] |
[
"The difference between time on earth and in space is incredibly small.",
"\"In 1976 the Smithsonian Astrophysical Observatory sent aloft a Scout rocket to a height of 10,000 km. At this height, a clock should run 4.5 parts in 10",
" faster than one on the Earth.\"",
"That's not far enough to be called \"outer space\" but it's pretty far. And that's 4.5 parts in 10,000,000,000 btw. So the clock would be 0.000000045% faster at 10,000km."
] |
[
"Time Machine Question (More about how accurately we can calculate our place in time and space)"
] |
[
false
] |
[deleted]
|
[
"Well, ignoring the obvious problems with time travel, the position of the earth could be calculated fairly well for a couple million of years. You might want to check out works of Jacques Laskar, who simulated the behaviour of our solar system over 100 Million Years. He has also found indication for chaotic behaviour in a time frame within 4 or 5 millions years which means that predictions over say 10 million years are not accurately possible. This was confirmed by Jack Wisdom and Gerald Jay Sussman in 1992. Further the rotational velocity of the earth varies and the tilt undergoes a so called nutation every 18.6 years. For a couple of millenia this should imho be possible, given very precise measurements and calculations. I wouldn't bet my ass on it though. But I could send myself a message if I popped up somewhere else, right ? : )"
] |
[
"I hear this brought up a lot- and I'm not saying this about you OP, but as a trend- and a lot of people say it thinking it makes them super clever, but I believe asking this shows a lack of understanding of the laws of physics. ",
"All inertial reference frames are identical, and if you are travelling \"through time\" then you must actually mean \"travelling through the time of an inertial reference frame\" (because all time is local, there is no such thing as 'travelling through the universe's time) which it seems what you want to do is travel through \"Earth's\" time, and thus you might as well travel through the Earth's inertial frame. "
] |
[
"The Earth is in free fall so it is in an inertial frame."
] |
[
"AI: How would it function without motivation?"
] |
[
false
] |
I keep hearing these opinions and predictions from the smartest people of the world like Musk and Hawking that AI will take over our planet in the future. I'm confused (well, duh!) We, as humans, are driven by motivation and emotions. Everything we do has a REASON for it. We don't go and kill someone - there's always some internal thought process that goes on in a person's mind, no matter how screwed up it is. : Why would Artificial Intelligence ever care about "taking control of the humans"? Or is everybody implying that the advanced AI will have emotions and motivation, and evil thoughts? Because if that's the case, why would someone create such a thing? Right now, there are millions of things which scientists can develop and produce that can ultimate kill us (now or later), but they don't do it because they understand the repercussion. How is "motivated AI with potentially evil thoughts" any different?
|
[
"This isn't a complete answer to your question, but consider the ",
"Paperclip Maximizer",
". It's a thought experiment that shows that an AI does not have to have \"evil\" intentions to be dangerous. Basically the idea is that someone makes an AI whose goal it is to make as many paperclips as possible. But without human notions of emotions or ethics, a paperclip maximizer with sufficient intelligence and capabilities could destroy our civilization as it turns us all into paperclips.",
"The point being, without careful consideration of many future paths that an AI could take, we could inadvertently create a very dangerous being as a side effect."
] |
[
"AI/Machine Learning PhD student checking in here.",
"The problem with your question, and similarly with the sensationalist articles surrounding the opinions of ",
"Hawking and Musk",
" is that at this point we don't know and can't really make this kind of prediction. Let me explain. I'll try and answer your question whilst addressing the Hawking/Musk \"we should be scared of AI\" angle as well.",
"Currently, AI really is in its infancy. As someone who works in the field and occasionally has to tell people what I do, its always very interesting to see people's faces light up: sci fi has given the general public this very skewed (and exciting) vision of how AI works. Now I'm not saying AI is not exciting - if it wasn't, I would probably be working in another field. What I am saying is that the public perception of AI and the current state of AI don't line up very well and there needs to be some management of expectations here.",
"So firstly, and perhaps someone from Neuroscience will correct me here, we don't know how consciousness and personality work very well. There are a huge number of theories: the school of reductionism think that consciousness can be mapped directly to specific parts of the brain[1]. Non-reductionists think that consciousness does not directly map to the physical brain and that there is some sort of \"explanatory gap\" that, once discovered, would tell us where consciousness comes from [2]. Either way, science is kind of stuck there at the moment. So given that the general scientific community can't agree upon how consciousness works and we have no way to tell beyond simple empirical observation of other conscious beings: how do we even begin to model it accurately in a computer system?",
"Well there isn't much work going in to fully functioning \"thinking\" computers these days (that said, work does go into modelling personalities for AIs/NPCs in games etc[3]) but we can and do model \"motivation\" using a concept called a heuristic. A heuristic is essentially a fancy way of saying \"something to aim for\" to a computer. AIs are often programmed to use a fitness function (literally a function that determines how 'fit' or 'good' something is) to aim for a heuristic. I'm talking in annoyingly abstract concepts here so lets take on an example.",
"A chess playing AI is given the heuristic \"only make moves that improve the state of the game for you\" and the fitness function \"is the state of the chess board better or worse after doing this move?\" The chess playing AI will search through all the possible moves it could make against the human player and evaluate them with the fitness function - \"moving this knight here would mean the other player could take it next round so this is bad\" or \"moving the bishop here means I can take the other player's queen, this is good\". It will evaluate possible moves and try to take one with the best outcome in accordance to its heuristic - eventually winning the game. You could say that the AI's motivation - its heuristic - is to win the game of chess. (if you're interested this is a technique called heuristic search [4]). ",
"A few posts talk about the paperclip maximiser which is an extreme example of a heuristic search gone wrong - the machine's heuristic is to maximise the number of paper clips[5] but the problem was not well defined so the machine turns everything - including humans - into paper clips. The problem here is not the AI per se, it is giving an optimising algorithm with a loosely defined heuristic too much control over the physical environment without at least providing safe guards/exception conditions - think Asimov's laws of robotics - hard coded rules that prevent the AI from turning people or food sources into paper clips would prevent a catastrophe here. ",
"/u/GregHullender",
"So in terms of Evil AIs ",
" to kill us, I don't see that happening in my career. AIs with human motives and feelings and desires are just too far beyond our capability. Badly defined AI problems/heuristics are about as close to the Hawking/Musk nightmare as the current state of AI really gets currently. Hence \"we can't answer that question\". Maybe once we know more about the mind and how it works and are able to model full personalities that \"think\" then this conversation would be worth having again.",
"Final note: In the late 30s and early 40s a nice physicist called Robert Oppenheimer came up with this idea of creating huge amounts of energy by fusing materials together on a nuclear level - what a wonderful way to power cities cleanly and efficiently. He didn't really consider how well the same technique could be used to level cities. After Japan was nuked he (lifted a quote from a Hindi scripture) saying \"Now I am become Death, the destroyer of worlds.\" ",
"I think Hawking and Musk are right to remind us, especially those of us working in AI, that as well as considering the good that could come out of a technological advance, it is our duty to consider bad side effects too and do all that we can to prevent them from coming to fruition.",
"[1] ",
"http://books.google.co.uk/books?id=q2xDfZ_TC-gC&lpg=PR7&ots=PaSPMPzpCm&dq=consciousness%20reductionist&lr&pg=PR7#v=onepage&q=consciousness%20reductionist&f=false",
"\n[2] ",
"http://link.springer.com/chapter/10.1007/978-94-010-2557-7_9#page-1",
"\n[3] ",
"http://books.google.co.uk/books?id=IoPg7QEyDgAC&lpg=PA1&ots=ve9c0FAAB9&dq=artificial%20intelligence%20personality&lr&pg=PA1#v=onepage&q=artificial%20intelligence%20personality&f=false",
"\n[4] ",
"http://intelligence.worldofcomputing.net/ai-search/heuristic-search.html",
"\n[5]",
"http://wiki.lesswrong.com/wiki/Paperclip_maximizer",
" added a thing, thanks GregHullender"
] |
[
"The paperclip maximizer is a great example of the \"newsy\" uses of computers that raise questions like this. Why doesn't anybody ask \"Could a human with unchecked powers cause lots of problems?\" A computer with unchecked powers would be a dangerous thing, but it's not because of some deep flaw in our understanding of AI. Engineering is all about balancing alternatives while maintaining diversity. That's why we grow many kinds of plants as food, doing just one thing would be unsafe. Just because a computer is able to play chess or Jeopardy well doesn't mean it's smart, much less smarter than all the humans on Earth.",
"Allowing anyone/anything to \"take over the planet\" is stupid and dangerous. Just because it's a novel computer doesn't make it safer. Nobody is going to do that, because we've known since the rule of Julius Caesar that it's not a good idea. If humanity gets dumb enough to do this, it's dead already."
] |
[
"Can someone explain the implications of amino acid imbalances, and specifically how they link to l-tyrosine and phenylalanine?"
] |
[
false
] | null |
[
"L-tyrosine (Y) and phenylalanine (F) are usually discussed in regard to a condition called phenylketonuria (PKU). There are 20 different amino acids, all of which the body needs to make proteins. The body can make some of these on its own (these are called non-essential), but others you must get from the diet (essential). Normally, F gets Y is not essential as long as you have adequate F from the diet. People with PKU cannot convert F to Y. They get a buildup of F, which is toxic, and a deficiency of Y. So people with PKU need to watch they eat/drink and make sure it is low in F. ",
"BCAA's also have a disorder associated with them - Maple syrup urine disease. Patients cannot break down BCAAs, and the urine becomes a little thicker, darker, and smells like maple syrup. These patients should avoid BCAAs as much as possible. For a normal healthy person, the amino acid content in 5 hour energy should not be a concern. "
] |
[
"Ah gotcha, that makes sense. Is there a connection between Y/F and none of the other essential amino acids (other than each other). Basically, my sister was claiming that ALL amino acids are dangerous because they cause other essentials to fall by the wayside during catabolism causing said imbalance. Is there any truth to this? Or are there only certain 'combinations' to be weary of?"
] |
[
"Amino acid \"imbalance\" really means amino acid deficiency. Amino acids are the building blocks of all proteins, so I don't understand what your sister means when she says they're \"dangerous\". As long as you have the amino acids you need, your body will be fine. Excess amino acids can't be stored, so you body will break them down, and excrete the nitrogenous waste in the urine. "
] |
[
"How does iron exist IN the earth without rusting?"
] |
[
false
] |
Better yet, how do we have it in our blood without it out oxidizing? There's water and oxygen in our blood.
|
[
"For the record: ",
"so yes, pure Fe2+ iron is not found in your blood or in the earth.",
"I think you mean that Fe",
" is not found in your blood or in the earth, because (one of) the ionic forms (Fe",
" and Fe",
" ",
" found in your blood and in the earth. Hemoglobin for example, as you mention in your text, has bound Fe2+.",
"Magnetite is Fe2O3, \"rust\" is a hydrated form of FeO2",
"Fe2O3 is ",
" a hydrated form of iron. Fe(OH)2 and Fe(OH)3 are. Fe2O3 contains no OH-groups and therefore, it is not an hydrated form."
] |
[
"For the record: ",
"so yes, pure Fe2+ iron is not found in your blood or in the earth.",
"I think you mean that Fe",
" is not found in your blood or in the earth, because (one of) the ionic forms (Fe",
" and Fe",
" ",
" found in your blood and in the earth. Hemoglobin for example, as you mention in your text, has bound Fe2+.",
"Magnetite is Fe2O3, \"rust\" is a hydrated form of FeO2",
"Fe2O3 is ",
" a hydrated form of iron. Fe(OH)2 and Fe(OH)3 are. Fe2O3 contains no OH-groups and therefore, it is not an hydrated form."
] |
[
"It's very hot in the Earth's core, hot enough to break down Iron oxides (Iron oxide decomposes at under 1600 Celsius, Earth's core is over 5000 deg. Celsius). Also, Iron Oxide is less dense than Iron, so the metallic Iron sinks to the core while rust would float higher up.",
"Also, Iron in our blood ",
" oxidize, that's why we have it in our blood in the first place. Iron in Hemoglobin is bound in a molecule which makes it easy to reversably oxidize. When blood passes through the alveoli in your lungs it gets exposed to air where it releases bound CO2 and takes up O2, becoming oxidized (it does this because there is much, much more O2 in the air than CO2, even though it binds to CO2 stronger). Then your hemoglobin transports those little bits of rust to your cells where the relative lack of O2 causes another exchange, and the Iron deoxidizes and releases the O2 into the blood and surrounding tissue where it can then be used for metabolic chemical reactions."
] |
[
"Why, with a sinus infection, does pressure in your sinuses/head build up whether you blow mucus put or suck it in?"
] |
[
false
] | null |
[
"The paranasal sinuses are poorly innervated - pain tends to be vague and poorly localizable in the sinuses because the brain has a difficult time precisely interpreting what little sensory input it receives from the sinuses.",
"When an acute bacterial sinusitis occurs, with all the inflammation and mucus production that accompanies it, inflammatory cytokines (signaling molecules) sensitize nervous tissue which innervates the sinus mucosa. Instead of the typical sensation of pain that you'd normally get from inflamed tissue, most will describe fullness or pressure, or just vague discomfort over the cheekbones, above the eyes, or near the bridge of the nose. ",
"This \"pressure\" sensation can be present even when no blockage exists to allow pressure buildup",
".",
"This can be thought of as analogous to myocardial ischemia (i.e., a heart attack) - pain due to ischemic heart disease is classically described as a dull \"pressure\" sensation (\"an elephant sitting on my chest,\" e.g.). The heart and other visceral organs are poorly innervated by sensory nerves as well, which is why internal pain can present as poorly localizable or with dull or vague discomfort, akin to sinus pain and pressure. "
] |
[
"But why would it seem to build pressure if you blow out or suck in? The same reason aggitating a sore limb would hurt?"
] |
[
"The pressure you are feeling has extremely little to do with the mucus in your nose. The pressure is due to swelling and inflammation of the irritated mucosa in the nasal passages.",
"If you look at decongestants that treat sinus pressure and pain, they do not alter mucus secretions at all. All approved decongestants (pseudoepedrine, phenylephrine, and topical drugs such as oxymetozelone) are sympathomimetics, meaning they mimic the sympathetic nervous system. In layman's terms these drugs act to cause the blood vessels in the nasal passages to contract, allowing less fluid into the nasal tissues. By letting less blood and fluid in, but still allowing the existing fluid to exit, the total amount of swelling in the nasal sinuses decreases, decreasing pressure, pain, and usually reopening nasal passages to allow nasal breathing.",
"While we do have drugs that thins mucus these are rarely used in treating sinus pressure. The one exception is the OTC drug Mucinex (guifenisin) which often is combined with decongestants and marketed in the hopes that people will assume it is better, when in reality it has no better efficacy then the decongestant alone."
] |
[
"Why do you sometimes randomly get that loud ringing noise in your ear for no apparent reason?"
] |
[
false
] |
[deleted]
|
[
"I responded to a similar ",
"thread",
" about about how tinnitus is thought to occur, and this thread was suggested. So for those interested: ",
"Tinnitus is defined psychologically as the spontaneous perception of sound in the absence of external stimuli, and neurophysiologically as aberrant activity within the acoustic system which elicits said psychological effects. ",
"There are two forms of the disorder: ",
"Objective and subjective tinnitus",
". The former of which is mainly due to vascular issues, but the latter, the one everyone knows, is because of otological issues (or ear issues). The pathophysiology of tinnitus is massive, and it remains very complex and not well understood. Many ",
"medications",
" may cause it, and some individuals -like myself- suffer from ideopathic tinnitus, which occurs when no observable issues are identified within the inner-ear. ",
"This ",
"paper",
" reviews some of the proposed mechanisms. What is understood is that although cochlear damage can lead to tinnitus, the ",
"cochlea",
" itself is not solely responsible for its generation. This is because the spontaneous cochlear activity - that is information being sent from the cochlea to the brain randomly- once thought to be generating tinnitus can be adequately attenuated with aspirin, whereas the manifestation is still sustained ",
"cite",
".",
"What is currently being investigated is the phenomenon of spontaneous hyperactivity across the auditory system, elicited by loud noise ",
"example",
". One explanation now for how cochlear damage may elicit but not cause tinnitus is best put in the reference I just mentioned: \"*Neural degeneration in the adult central auditory system is a potentially important mechanism by which injury to the inner ear can cause hyperactivity in the DCN, since it directly affects the relative strengths of excitatory and inhibitory inputs to DCN neurons *. The \"",
"DCN",
"\" here is just one in a long line of pit-stops in the brain, auditory information takes before arriving at the auditory cortex.",
"The mechanism is very complex, and researchers do not yet quite understand the precise neurophysiology behind it, but we know there is normally damage to the inner ear resulting in downstream shifts in activity, due to either excitotoxicity/degradation, leading to a synaptic shift away from homeostasis. Some have suggested the effects are more ",
"widespread",
", causing more changes throughout the auditory cortex. So we have a mechanism right now that spans virtually the entire auditory pathway. As for folks like me with spontaneous idiopathic tinnitus, I won't hold my breath.",
"Edit: I should add that if you suffer, or think you suffer from tinnitus, see a doctor. There are a battery of tests they can perform to help determine if it is because of vascular or cochlear damage. With that said, even if they don't find anything, there is simple treatment. White noise generators also help in dampening the ringing when you need to sleep. "
] |
[
"Great answer on general tinnitus...but you missed that he was specifically asking about transitory tinnitus: The type that starts out of apparently nowhere quite loudly with a nearly pure tone, persists for several seconds and then fades away completely. Often associated (at least in my experience) with a temporary 'fading' of other sounds.",
"Edit: The specific term is Transient Spontaneous Tinnitus.",
"Edit2: From a paper published by NCRAR ",
"Tinitus Definitions and Background",
" (pdf):",
"It seems that almost everyone experiences “transient\near noise,” which typically is described as a\nsudden whistling sound accompanied by the perception\nof hearing loss (Kiang, Moxon, & Levine,\n1970). ",
"\nThe transient auditory event is unilateral and\nseems to occur completely at random without anything\nprecipitating the sudden onset of symptoms.\nOften the ear feels blocked during the episode. The\nsymptoms generally dissipate within a period of\nabout a minute. Although transient ear noise has\nbeen described as “brief spontaneous tinnitus” (Dobie, 2004b),\n any reference to tinnitus in this book\ndoes not include this auditory phenomenon.",
"(emphasis added by me):",
"The short and long of it: It happens to almost everyone, we don't really know what causes it (there is ",
" that it may be caused by a single dying hair cell), it doesn't appear to do any measurable harm."
] |
[
"Seeing how he says randomly, then I'd assume it's acute. I get it once or twice a month."
] |
[
"How do different immunosuppressants like Avonex and Imuran differ in their biological function?"
] |
[
false
] | null |
[
"Please, do not ask for medical advice here. Thanks."
] |
[
"I'm not. I'm curious as to why 2 drugs, both labelled as immunosupressants, treat 2 separate illnesses. What is the biological mechanism behind immunosuppressants and how do their functions differ across drugs?"
] |
[
"Ok thanks. I'll try again, and delete this one."
] |
[
"What is the fastest human sense?"
] |
[
false
] |
I've read a few blogs and articles that say that hearing is the fastest human sense. I've done searches in Google and Google Scholar with little success. However, I don't see many that cite very credible sources in Google and Google Scholar hasn't yielded anything pointed towards the question. I found this medical blog about hearing: It talks about the actual process of hearing, but doesn't point to any experiments or papers. It simply states that the brain registers sounds in .05s while touch and sight are about .2s. It's also geared to talk about hearing aids which doesn't sound like the most impartial thing. I also found this piece: But the results don't include taste or smell (not that I would expect those to be the fastest). Furthermore, the two sight experiments aren't very helpful in that one is slower than hearing while the other is faster. Can anyone point me towards a more definitive source that at the very least gives me a solid answer on the speed of hearing against sight? Thanks so much!
|
[
"Smell is actually a little part of your brain sticking its tendrils through the cribiform plate in your skull. You smell with a part of your brain, not a sense connected to your brain through a nerve or nerves. ",
"What? I thought that olfactory stimuli are transmitted through the olfactory nerve. And I don't know whether that is directly related to your argument, but I know that retina, however, is considered part of the central nervous system."
] |
[
"Smell is actually a little part of your brain sticking its tendrils through the cribiform plate in your skull. You smell with a part of your brain, not a sense connected to your brain through a nerve or nerves. ",
"What? I thought that olfactory stimuli are transmitted through the olfactory nerve. And I don't know whether that is directly related to your argument, but I know that retina, however, is considered part of the central nervous system."
] |
[
"Like three marijuanas? "
] |
[
"Difference Between Pain Medicines"
] |
[
false
] | null |
[
"First off, patient experience with various pain killers is highly variable for their specific painkiller aspect. ",
"While you may like ibuprofen for headaches and aspirin for muscle aches and naproxen for that trick shoulder, it may be very different for someone else. AFAIK, the reasons for this are not fully known. My personal opinion is that it's due to highly diverse factors and/or a variant of placebo. That is, I think naproxen works better than aspirin, therefore it does. This is ONLY looking at how well one works for you, not how long it works of how quickly it kicks in.",
"You have two classes there: the NSAIDs (ibrprofen, aspirin, and naproxen) and acetominophen. First, the NSAIDs. ",
"These inhibit two different but related enzymes, COX-1 and COX-2. They inhibit both because the enzymes are very similar physically. COX-2 makes things that are pain and inflammation signals. COX-1 makes things you need to keep your body running smoothly under normal conditions. The side effects from the different NSAIDs are largely rooted in the ratio of inhibition. They all inhibit COX-2 more strongly than COX-1, but the ones that inhibit COX-1 less will have less severe side effects. Some of these side effects are useful, though, like taking aspirin as a \"blood thinner\".",
"There are also differences in how long they take to kick in (this has to do with absorption and specific mechanisms if inhibition) and how long they take to wear off (same, plus resistance to metabolism)",
"Acetaminophen....we're not sure how it works. WTF, yeah. It's been around forever, but we don't have a clue. Well, maybe clues....Maybe it's a COX-2 specific blocker, maybe it blocks a proposed COX-3, maybe it's full of elves*. We do know it doesn't hit COX-1, which is why it is generally considered one of the safest painkillers....just don't ever, ever drink when you're taking it.",
"*It's not elves. "
] |
[
"Great question! Let's keep this on topic without a lot of anecdotes kids! "
] |
[
"Could you give me some grievous statistic or figure to convince me to never ever drink while on acetaminophen.... (I have a few times)?"
] |
[
"What does a wave function look like?"
] |
[
false
] |
[deleted]
|
[
"It is possible to see, using scanning microscopy, the interference pattern of delocalized electrons on a surface inside a ring of atoms, which you could interpret as a visualization of a wavefunction.",
"pic",
".",
"The \"height\" is related to the electron density."
] |
[
"one of the postulates of QM is that the wavefunction itself is physically meaningless. Ψ(x,y,z,t) = ψ(x,y,z)e",
" is a general solution to the time dependent Schrodinger wave equation. Note the presence of i, why does the solution contain an imaginary number? well, you'll have to consult mother nature for that one, but in broad strokes, it is required to satisfy boundary conditions.",
"Now, this is simply a wave function. To gain physical meaning from it, it must be integrated with its complex conjugate over the region of space you are interesting in. This will provide you with the probability of finding the particle within that region of space. Interestingly enough, multiplying by the complex conjugate negates the effect of the imaginary term i, so you then have only really solutions.",
"So in short, you cannot see a wave function...ever, it does not exist. But you can use a wave function to determine the probability of observing what that wave function describes"
] |
[
"The problem is that the image you posted is actually not the 'wavefunction', but the mod-square probability density (psi-star times psi). There is no way to visualise the wavefunction itself - a good reason why is to look at the units of psi - inverse cubic meters square rooted. This has literally no real life analogy or basis to measure."
] |
[
"If the flu kills approximately 36,000 people in the US every year, why aren't we doing more to prevent it like we are doing for ebola?"
] |
[
false
] |
The flu travels much quicker and more easily yet people seem to brush it off.
|
[
"There is a lot of research being done for influenza. The NIH is spending approx $312 million ",
"this year",
" in research. Then there are multiple other companies doing private, independent research. The problem with seasonal influenza is that it mutates every year. There needs to be a lot of research to predict the strain of influenza each year. Then the appropriate vaccines need to be made and distributed.",
"Why aren't we trying to prevent it like Ebola? The flu season comes every year and there is nothing to prevent it from spreading besides constant vaccination and hygiene. Ebola is new to the US and sells easily in the media."
] |
[
"From what I know, the deaths due to the flu are usually due to confounding factors, such as existing sever health issues.",
"And I think the death rates for each disease is quite significant. If you did not take serious steps against ebola you could potentially get a large population decimated."
] |
[
"That's a common misconception.",
"Although elderly, sick, immunocompromised, young etc are more vulnerable to the flu. A significant number of healthy adults develop ARDS and die from the flu each year"
] |
[
"Why can i see the outline of the whole moon right now, even though only a sliver is lit up?"
] |
[
false
] | null |
[
"Reflected Earthlight: In the same way the dark surface of the Earth is lit by moonlight, the dark surface of the moon in turn is lit by the light reflected from the Earth."
] |
[
"It even has a beautiful name: earthshine."
] |
[
"Wikipedia link: ",
"earthshine"
] |
[
"[Mathematics] Probability Question - Do we treat coin flips as a set or individual flips?"
] |
[
false
] |
is having a debate on the gamblers fallacy, and I was hoping could help me understand better. Here's the scenario. A coin has been flipped 10 times and landed on heads every time. You have an opportunity to bet on the next flip. I say you bet on tails, the chances of 11 heads in a row is 4%. Others say you can disregard this as the individual flip chance is 50% making heads just as likely as tails. Assuming this is a brand new (non-defective) coin that hasn't been flipped before — which do you bet? Wow this got a lot bigger than I expected, I want to thank everyone for all the great answers.
|
[
"I've always summarized it as such: ",
"People basically confuse two distinct scenarios.",
"In one scenario you are sitting at time 0 (there have been no flips) and someone asks you: \"What is the chance that I flip the coin heads eleven times in a row?\"",
"In the second scenario you are sitting at time 10 (there have been 10 flips) and someone asks you: \"What is the chance my next flip is heads?\"",
"The first is a game you bet once on a series of outcomes, the second is game where you bet on only one outcome. ",
"Edited: ever so slightly due to ",
"/u/BabyLeopardsonEbay",
"'s comment."
] |
[
"I've always summarized it as such: ",
"People basically confuse two distinct scenarios.",
"In one scenario you are sitting at time 0 (there have been no flips) and someone asks you: \"What is the chance that I flip the coin heads eleven times in a row?\"",
"In the second scenario you are sitting at time 10 (there have been 10 flips) and someone asks you: \"What is the chance my next flip is heads?\"",
"The first is a game you bet once on a series of outcomes, the second is game where you bet on only one outcome. ",
"Edited: ever so slightly due to ",
"/u/BabyLeopardsonEbay",
"'s comment."
] |
[
"You sir have answered a question that's bothered me since childhood and elegantly too. Props."
] |
[
"If the vacuum of space is such a great insulator why did the Apollo 13 astronauts nearly freeze?"
] |
[
false
] |
I didn't want to hijack the computer in space thread but the first answer made me think about this. Why is there any concern for heat loss in such a near perfect vacuum?
|
[
"Insulators function to inhibit the physical transfer of heat. (Conduction)",
"Heat is lost through space quite fast because the heat is radiating away faster than is coming in. (Radiation)"
] |
[
"I'd be hesitant to say \"quite fast\" just because radiative cooling can be substantially slower than other forms. As noted, space does make a decent insulator, but certainly not a perfect one. For that matter, depending on the situation (for instance, how much sunlight you are receiving) the process could actually be reversed. "
] |
[
"Imagine you're the designer of a spacecraft. Since there's no conduction or convection in a vacuum, you have only two tools for controlling temperature:",
"Radiative heat transfer physics tells us that warm objects emit energy in the from of photons (light). The rate of energy emission (power) is proportional to e*T",
" T is absolute temperature (Kelvin scale), and e is emissivity, a parameter describing the surface properties. A perfect mirror has an emissivity of 0, meaning it absorbs nothing and emits nothing. A perfect blackbody has an emissivity of 1, meaning it absorbs everything and emits the maximum possible amount of thermal radiation.",
"Things get tricky when you have a material with a different emissivity at difference wavelengths of light. Most of sunlight's energy comes in the form of visible light. However, a room-temperature object emits most strongly in infrared. This can be used to advantage when designing a spacecraft. Titanium dioxide paint has a low emissivity for visible light (making it appear white), but a high emissivity for infrared. That means it doesn't absorb much visible light, but readily emits (and absorbs) infrared light. Because an object near the Earth is subject to direct sunlight, this white paint is very handy for preventing the spacecraft from overheating.",
"As a spacecraft designer, you can't fine-tune our paint job perfectly, and your analysis may not account for everything in the space environment. Furthermore, the spacecraft spends some time in close proximity to Earth, which also radiates infrared strongly, raising the temperature of our spacecraft, then moves away from Earth. If you overheat, you have no options for cooling the spacecraft, and the astronauts may be endangered. So it's safer to aim for a low equilibrium temperature, and make up the difference using a heating element (the combined heat generation of all electrical systems).",
"When Apollo 13's oxygen tank exploded, they were forced to minimize electricity usage, which means much less internal heat generation. Therefore, the equilibrium temperature dropped."
] |
[
"Probably another stupid Higgs question,"
] |
[
false
] | null |
[
"Where did my question go? ",
"edit: that wasn't the question, I just want to know"
] |
[
"What was the question?"
] |
[
"What was the question?"
] |
[
"When happens from the perspective of a photon when you shoot it towards the edge of the universe?"
] |
[
false
] |
So as I've learned from AskScience, when you shoot a beam of light towards an object, lets say a wall, it travels from the flashlight to the wall at the speed of light from the perspective of a stationary observer. But apparently, from the perspective of the photon, time is dilated so much that it gets there basically instantly. So I'm wondering what happens to this photon when its shot into outer space with nothing to block its path. Do we lose this energy forever? Or its nothing extra ordinary and the photon just happily travels forever ?
|
[
"Really, it just makes no sense to talk about the perspective of a photon. They don't experience time, so they don't have a perspective."
] |
[
"Neil deGrasse Tyson answered ",
"this",
" on his first AMA here on reddit."
] |
[
"It would simply watch the universe age in reverse, and watch the universe fizzle out of existance as the light had not yet reached there."
] |
[
"Why can't scientist come up with a method to highlight the resistant proteins on cells?"
] |
[
false
] | null |
[
"Hi Chemrxt thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"What does this mean? Resistant proteins? Highlight?"
] |
[
"So when a human is giving a cancer drug, the cancer drugs helps the immune system technically destroy the cancerous cells; any cancerous cells that are left adapt (proteins in the outside of cells change, mutation, become resistant to that certain med). So why isn't there a method to hit cancerous cells with a functional group that would enable the immune system to be able to highlight them vs the healthy cells?"
] |
[
"Why is iron so abundant in the universe"
] |
[
false
] |
I understand Iron comes from the end result of fusion processes in very massive stars. However, looking at this article: raises a question: Iron is generated last in big stars. Why then is there so much more iron present in the universe than other elements which are generated before iron in the fusion cycle in large stars?
|
[
"It's got to do with nuclear binding energy. The heaviest nucleus that can be created in a star is, if I remember correctly, nickel-56. So as a massive star ages, it accumulates a lot of nickel-56 nuclei in its core. When that star turns into a type Ia supernova, the nickel-56 nuclei are scattered into space.",
"But nickel-56 isn't stable. It decays via electron capture into iron-56, which ",
" stable.",
"So we end up with a lot of iron-56 in the universe. This observed fact — that there's a spike in the abundance of iron relative to the elements immediately before and after it in the sequence — is called the "
] |
[
"DISCLAIMER: Not a scientist, have no sources. Please someone with credentials confirm or deny the following. ",
"I read somewhere that Iron has the lowest \"energy potential\" (not correct phrasing). ",
"That is to say, when you fusion two hydrogen atoms together it takes a lot of energy but you get more energy out. ",
"Likewise when you fission uranium it takes a lot of energy but you get more out. ",
"But with iron you can neither fusion or fission iron and get more energy out than you put in."
] |
[
"Yes, when you try to fuse Iron (or heavier) the reaction requires more energy than you get out.",
"http://hyperphysics.phy-astr.gsu.edu/hbase/astro/nucsyn.html#c1"
] |
[
"A quick question about S-Waves"
] |
[
false
] |
Last night I was watching BBC's Horizon, talking about the center of the earth. One scientist was saying how S-Waves can only travel through solid rock, hence were fundamental in proving the inner core of the earth is solid. What I don't understand is if S-Waves can only travel through solid rock, how do they pass through the inner core having passed through the liquid outter core on the way?
|
[
"They don't pass through the liquid core. It's called the ",
"S-wave shadow zone",
". Only the P-waves go through the liquid outercore, but only with significant refraction. It's the P-waves that allow us to understand the solid inner-core. "
] |
[
"True, but there is also mode conversion where the P wave that travels through the liquid outer core become s-waves at the inner outer core boundary, they then mode convert back to p waves at the next inner outer core boundary. The modelling work for the mode conversions led to the hunt for these weaker mode converted waves and they were then found to show the model worked. See slide 6 of ",
"this",
" presentation."
] |
[
"The original S-waves that are propagated by a seismic event do not go through the core, and the P-waves are most certainly not totally converted into S-waves, probably only a portion. We can't measure the effect of the S-waves in the inner core, because they exist only in the inner core, which means that S-waves can't be used to measure the existence of an inner core, only how the S-waves interact with the P-waves in the inner core. ",
"Probably the person on the tv show just didn't explain it well enough to say that there can be newly formed S-waves in the core from the propagation of P-waves. "
] |
[
"If a sociopath loses his/her memory (amnesia, etc), is he/she still a sociopath?"
] |
[
false
] | null |
[
"You really need to clarify the question.",
"A sociopath is someone without empathy. According to the DSM-IV, a sociopath has 'antisocial personality disorder.' ",
"They are unable to relate to the feelings of others. This is associated with violence towards others, since they are unable to empathize.",
"It appears to be independent of memory."
] |
[
"So you cannot create a sociopath, i.e Dexter would be one no matter what his past was?"
] |
[
"They would have no qualms about turning on you though, it would be hard to control an army of psychopaths"
] |
[
"Will the earth ever revert to Pangaea or a similar land congregation?"
] |
[
false
] | null |
[
"Earth has had several supercontinent cycles, taking somewhere between 250 to 500 million years to go from supercontinent to many continents to supercontinent again. Pangea was only the most recent, with Gondwana before that, Rodinia before that, Nuna (or Columbia) before that, Nena before that, and several before that, taking us all the way to about 3.5 billion years ago. "
] |
[
"To further this point, there are several hypothetical models predicting the future movement of the continents. Pangaea Ultima is one of the proposed names for a supercontinent that may form in about 250 MA, with the close of the Atlantic Ocean. "
] |
[
"Wikipedia has a pretty good page on the ",
"Supercontinent Cycle",
"."
] |
[
"Is it possible to have damage in the brain so that you can remember something without ever seeing it?"
] |
[
false
] |
[deleted]
|
[
"It doesn't require brain damage to have or cause false memories."
] |
[
"I think what OP is asking is if you can recall an event or object without visualizing it."
] |
[
"Not what I meant. I meant that if event A happens, your eyes record it, and then send it to the part of the brain that records it, but don't send it to the part of the brain that lets you see it. So you wouldn't actually be able to see Event A happening, but you will be able to remember it."
] |
[
"Physics: Forward momentum with a headwind"
] |
[
false
] |
On the other thread I saw , and I have no idea how forward movement is achieved with a headwind.
|
[
"I am going to make the observation that the guy is standing (in the glider) at the top of a hill. The wind isn't just coming in horizontally, but it is actually coming ",
" as well because once it hits the hill it doesn't just stop, but kind of follows the hill. This will be relevant later.",
"Consider now a glider in free-flight in open air. As it falls air hits its wings and the wings redirect the air backward. This creates an equal and opposite force in the wing. The direction of this force is based on the angle and shape of the wing, but it amounts to an upward and forward force on the plane. Upward as the wings push down on the are and forward as the wings push the air backward because of the angle of the wings. This forward force is what gives the glider it's forward moment in free atmosphere. If the forward force is not enough to fight the air resistance, then the glider stalls. Adjusting the angle of the wings will affect the balance of these forces and will affect how much of the reactionary forces go towards forward and upward.",
"Now consider that it is not the speed or direction of the aircraft that matters, but the ",
" speed and direction of the wind ",
" the aircraft. As the guy stands there the wind is moving toward him and upward, just as it would if he were falling and moving forward in free-atmosphere. All he has to do is adjust the balance of the forces to increase his forward speed relative to the wind which makes it appear as though he just starts moving forward. If you look close, as he starts moving forward he starts to lose some altitude. This is because less of the reactionary forces are exerted upward."
] |
[
"A quick shitty drawing",
"The roughly wing-shaped object is the wing. The four arrows starting at the word 'wind' represent the wind. When they hit the bottom of the wing, the wing experiences a force in the direction of the long arrow pointing at a right angle from the base of the wing. It is perpendicular to the wing because of the nature of how simple forces are applied. Friction can work at a parallel to a surface, but a push force has to be perpendicular to a surface.that creates the arrow that is perpendicular to the wing and represents the actual force applied. The direct upward arrow and the direct leftward arrow represent the two vectors that represent the reactionary force vector, on providing lift and the other providing thrust. As the wind goes upward past the aircraft, the glider can use that to push it forward. Generally this is accomplished as the aircraft falls downward. In the case of the video you represent here, the wind is traveling ",
" so lift and forward thrust is generated in the exact same way as if the craft were falling downward. The only difference is the glider is stationary as the wind moves instead of the glider moving and the air being stationary."
] |
[
"As it falls air hits its wings and the wings redirect the air backward.",
"This is the part I am confused on. How does it creat thrust?"
] |
[
"Is there any reason why Earth's orbit wouldn't be in the style of a Möbius strip?"
] |
[
false
] | null |
[
"The way gravity works all orbits have to be in the shape of a ",
"conic section",
". This means they can either be circles, ellipses, parabolas or hyperbolas."
] |
[
"Not sure what you mean there. But yeah this is the only possible shapes for a single body orbiting around a more massive star or planet."
] |
[
"So it already is in that style?"
] |
[
"Are we any closer to a functional and practical early diagnosis/screening for alzheimers disease? Are we any closer to reliable, safe treatments?"
] |
[
false
] |
Forgive me, . It has been years since I picked up the textbooks. Namenda is nice and all, but it's overpriced and isn't very effective unless Dementia is diagnosed early on. Oh and diagnosing AD is still only accurate after an autopsy. What are some of the recent advances?!? What exciting discoveries have been made?
|
[
"The aetiology of Alzheimer's is still large unknown and the subject of much discussion, conjecture, theorisation and experimentation. There are currently no known cures, and no treatments that substantially slow the progress of the disease once it becomes apparent."
] |
[
"Thanks for the reply. ",
"I refuse to believe the fatalistic viewpoint, however. I'm willing to bet that advances have been made in early screening, and that there are promising drugs that haven't made it to human testing yet."
] |
[
"There are drugs being tested",
" but the success rate so far has been zero, mainly because we still do not know the how, why and what of the disease. There are plenty of theories, and some of those have led to millions being spent on development and trials, but so far, no cigar."
] |
[
"Do our pupils dilate when we dream about light?"
] |
[
false
] |
Last night I dreamt about being in a very dark room for a long time. Eventually I walked outside and was met by this very bright daylight. It hurt my eyes, but the pain eventually disappeared, as it would in a real life situation, because of our pupils adjusting. I found this very fascinating, because it's probably all imaginary, but it felt so real. Do our eyes react to imaginery impulses, like in this case, (bright) light in a dream? PS: I don't know the antonym of dilating in the context of pupils, so I stuck with it in the title.
|
[
"Vivid dreams like the one you described typically occur during REM sleep. Interestingly enough, the pupils are generally constricted (the antonym you were looking for) during REM sleep, though they do dilate periodically during this time. This intermittent dilation occurs in conjunction with other physiological changes, such as predictable changes in heart rate and blood pressure. While the exact source of these physiological features is unclear, their consistency and resemblance to other information processing activity/patterns in the brain suggest that dreams about light are probably ",
" the actual cause. ",
"This paper",
" expands upon the process and contains decent citations if you're interested in reading the research publications.",
"That being said, it's worth mentioning that the pupillary response can be ",
"conditioned",
" in response to stimuli under certain circumstances, so it might be theoretically possible to produce a Pavlovian response in which the pupils dilate in the presence of dream light source, though such an experiment seems very technically challenging to me. "
] |
[
"I am going to preface this by saying that I'm probably not qualified to answer this question. That being said, something I learned in my high school psychology class seemed relevant, so I did some googling...",
"I didn't find a definitive answer, but I found enough information that I would fairly confidently answer your question with yes, the pupils do dilate and undilate during sleep. Studies have shown that dreaming about doing something like running will activate the regions in your brain and the nerves responsible for running. But you don't run in your sleep. This is because while you're asleep, your body paralyzes itself. Chemicals are released into your nerves which prevent your nerves from actually firing (side note: sleep paralysis is caused by these chemicals remaining in your body after you wake up). The exception to this is the autonomic nervous system, which is the section of the nervous system that is responsible for unconscious actions; things like your heart beat, digestion, and pupil dilation.",
"Based on this, I think it's reasonable to conclude that the pupils are not paralyzed during sleep. After all, other autonomic nervous system functions aren't paralyzed when we sleep; we don't stop breathing, and our hearts don't stop pumping blood.",
"But again, I'm by no means an expert in this subject. Hopefully someone who knows more than what I found on Google will show up and provide a more complete answer, but in the meantime, I hope my comment at least helps you do a bit more searching around online"
] |
[
"Tangentially related: There was ",
"an intriguing study",
" done 50 years ago experimentally testing the opposite direction of what you suggest, whether (real) pupil dilation and visual stimulus during sleep impacts reports of visual stimulus during dreams. They found no association, though add the usual caveats about relying on a single 50-year-old study."
] |
[
"What exactly is happening when a body part 'falls asleep' and why does it hurt so much when it wakes up?"
] |
[
false
] | null |
[
"Almost correct (it's not a direct mechanical process for your normal dead leg) - the term for the short-circuit of nerves you're describing is ",
"paresthesia",
".",
"There are a number of causes (",
"see this excellent review",
"), but when you get a dead leg normally it's probably driven by ",
"ischemia",
". From the abstract:",
"The alkaline shift produced\nby hyperventilation selectively increases the persistent Na+ conductance,\nwhile ",
". Postischemic and posttetanic paresthesias\noccur when hyperpolarization by the Na+/K+ pump is transiently prevented\nby raised extracellular K+. The electrochemical gradient for K+ is\nreversed, and inward K+ currents trigger regenerative depolarization.",
"That is, you block the blood flow, which depolarises the axons via transient and persistent sodium channel activation (the 'gates' Raelifin is referring to are mostly voltage-dependant sodium channels). The influx of positive Na",
" ions (and buildup of K",
" outside the cell) into the axon causes the activation of the nerve (action potential propagation) and prevents deactivation. And voila, you get a dead leg and pins and needles - the sensation of nerve activation in the absence of outside stimulus.",
"Really, check out the review, it's nice and as far as I can tell free to access (PM me if you want a copy).",
"Edit: basic chemistry (thanks chamois). Also, it has been pointed out by AnatomyGuy that direct pressure on the nerve can indeed cause problems (such as carpal tunnel and nerve pinching between bones)."
] |
[
"I study brains, not body nerves, so take what I say with salt.",
"Signals are transmitted along nerves by way of axons -- long tubes with gates in their sides (membrane). When the potential difference across the membrane goes past a certain threshold, the gates open and let ions into the cell. These ions spread out from the entry point and cause the potential difference further along to become more positive, opening up more gates. The whole thing is a chain reaction caused by the ions and gates.",
"I imagine that if sufficient pressure was applied to the axon, it would restrict the ability for ions to flow down its length, thus stopping the chain reaction and essentially killing the signal.",
"Again, I am a student, not an expert."
] |
[
"from howstuffworks -",
"Nerve impulses carry sensation information from nerve endings in the body to the brain, as well as instructions from the brain to the parts of the body. When you interfere with this transfer by squeezing the nerve pathways, you don't have full feeling in that body part",
"I was just wondering about a related question - what 'flow' is actually impeded? I can understand a compressed blood vessel no longer able to conduct blood. But what is the mechanism where squeezing a nerve impedes its ability to conduct electrochemical impulses?"
] |
[
"What is the smallest 'thing' that can have a temperature?"
] |
[
false
] |
This is a question in the same spirit as: "What give's an electron its negative charge." Is there a fundamental thing that carries temperature (sort of like ye olde Caloric theory of heat transfer)? Is there any sort of quantum heat particle - like a phonon - for heat energy? If we follow the mechanical theory of heat, is there a fundamental scale akin to the Planck length that heat exists within?
|
[
"The smallest \"thing\" that can have a temperature is a single particle that carries with it a kinetic energy. To see this imagine that we have a one particle system where the particle is at a high kinetic energy (equal to its average kinetic energy since there is only one particle in our system), and we place it in contact with a second system of N particles where N is on the order of ~10",
" and the average kinetic energy per particle is lower than that in our single particle system. ",
"What will happen is that the single particle will transfer it's energy to the second system (and absorb energy from the second system) until on average the single particle system has the same average kinetic energy as any particle in the second particle system when the two systems reach equilibrium with each other. This is a heat transfer and we say that at the beginning the single particle was at a higher temperature than the particles in the N particle system, but that after the heat transfer both systems have reached equilibrium they are now at the same temperature with the save average kinetic energy per particle. ",
"You can certainly define things this way, but when you are dealing with one particle systems it is sort of like what's the point? The average and the actual kinetic energy are the same in the case of a one particle system, so we don't need to use statistical ideas like temperature to describe it. Where temperature is handy is in systems with many particles where the actual kinetic energy of a particle may vary considerably at any moment, but the average kinetic energy of that particle over a long period of time is a constant. Temperature is a way of characterizing this average kinetic energy of one particle or several particles.",
"Is there a fundamental thermal scale akin to the Planck length? In one sense yes, a scale that incorporates a special constant for heat energy exists using kT where k is the Boltzmann constant of 1.38x10",
" J/K. This constant serves to convert the temperature to energy units in the same way that Planck's constant h serves to scale the frequency of radiation or a particle to units of energy. ",
"However, Plancks constant brings with it a special meaning (as some minimum volume in p and q phase space or some such thing that prohibits certain quantities from reaching zero), and to my knowledge the Boltzmann constant carries with it no such limiting meaning. For example, quantities that contain it such as S = klnW can become zero with no difficulties (as for example in perfectly ordered systems where W=1). In contrast, some systems in quantum mechanics cannot reach zero due to the uncertainty principle that incorporates Planck's constant h. In this sense the thermal constant and Planck's constant are different in that the former sets no apparent limit on quantities reaching zero whereas the latter does.",
"EDIT: Typo patrol as usual."
] |
[
"Most of this is good, but you can define temperature to be one particle as for example using the kinetic theory where the average KE = 3/2(kT) for a single particle. For a system of N particles, the total KE is then 3/2(NkT). ",
"Where temperature becomes useful is in many particle systems, but you can use it to describe single particle systems if you like (and it is done this way in derivations all the time)."
] |
[
"Most of this is good, but you can define temperature to be one particle as for example using the kinetic theory where the average KE = 3/2(kT) for a single particle. For a system of N particles, the total KE is then 3/2(NkT). ",
"Where temperature becomes useful is in many particle systems, but you can use it to describe single particle systems if you like (and it is done this way in derivations all the time)."
] |
[
"If an object keeps accelerating, will it eventually turn into a black hole?"
] |
[
false
] |
Since mass increases as speed increases, and mass goes to infinity as speed approaches c.
|
[
"No, also mass doesn't increase with speed.",
"It cannot become a black hole: there are coordinates in which it is stationary and thus obviously doesn't become a black hole. So it cannot become a black hole in any frame"
] |
[
"but doesnt energy have an effect on the gravitational field according to general relativity?"
] |
[
"but doesnt energy have an effect on the gravitational field according to general relativity?"
] |
[
"Why don't we sneeze in our sleep?"
] |
[
false
] | null |
[
"the trigeminal motoneuron pools that mediate the sneeze reflex are inhibited during NREM sleep and are actively suppressed during REM sleep as part of atonia. Which means it is much more difficult to sneeze during NREM sleep and nearly impossible in REM (without also causing waking).",
"http://www.reddit.com/r/askscience/comments/natrc/do_you_sneeze_when_you_sleep/c37rj3d",
"edit: I clarify in a comment below:",
"The distinction is that you can wake up to sneeze, but you can't sneeze in your sleep. You may be sleeping, wake up to sneeze, and immediately fall back asleep without remembering that you sneezed. It's a bit of a silly distinction I'm afraid.",
"There is no \"evolutionary trade-off\" between sleeping and sneezing. If something is irritating your nasal mucosa during sleep, you will wake up and sneeze."
] |
[
"Because there is more value in sleeping.",
"Sleep also inhibits other normal bodily functions, like hunger (shouldn't it be important to know when one is hungry?) and, more importantly, consciousness (what if there are predators nearby?)."
] |
[
"But why is it beneficial when we are awake but not while sleeping? "
] |
[
"Why does it require more energy to accelerate a mass faster, as it approaches the speed of light?"
] |
[
false
] |
Does it have something to do with the higgs field? Assuming it exists?
|
[
"Well, the most intuitive, if you don't know much of the math, would be to say that the speed of light has to have the same value in every reference frame. You can take that as a principle, derive it from electromagnetism, or just do what Einstein did and note that experiment suggests pretty strongly that it's true. The rest of the funny properties of relativity follow from there. Time and space have to be relative because if they were absolute, then c couldn't have the same value to observers moving at different velocities. In order to compensate for this, length and time have to be fluid, contracting and dilating with motion so that the speed of light is maintained for all observers."
] |
[
"Nothing to do with the Higgs field - this was understood more than a half century before we even realized we needed a Higgs field.",
"The reason is that force isn't ",
" just the product of mass and acceleration as you might have learned in high school. Without getting into too much ",
"mathematical detail",
", suffice it to say that the usual equation F=ma actually looks like F=γ",
" ma, where the relativistic factor γ is nearly 1 for speeds much less than the speed of light, and gets infinitely large for speeds approaching the speed of light. So if you're applying a constant force F to an object, then its acceleration goes as 1/γ",
" which gets smaller and smaller as its velocity gets closer to the speed of light. The mathematics conspire so that you could never, applying a finite force, ever accelerate a massive object to the speed of light!",
"(If you do like mathematical detail, what's happening here is that instead of F=ma, the fundamental equation for force is F=dp/dt, the time derivative of momentum, and momentum isn't actually mv but rather γmv.)"
] |
[
"Pretty much yes. You have to accelerate the energy as well."
] |
[
"Is a covalent bond the strongest bond known?"
] |
[
false
] |
If so, why? If not, what is stronger?
|
[
"The answer is not so black and white, though. Yes, inorganic compounds can have lattice energies that are anywhere from ",
"600 to a few thousand kj/mol",
". The carbon monoxide bond energy and the N-N triple bond both have energies around 1000 kj/mol, making them stronger than some ionic compounds. Also, keep in mind that NaCl has a rock salt structure with coordination number of 6. So to determine how each electrostatic interaction is contribution to the lattice energy is difficult.",
"Another thing to consider is that the line between ionic and covalent is extremely blurred. Everything has a percent ionic character and even the classical ionic example NaCl is only about 75%. So, all things considered, it is difficult to say. However, most ionic compounds have structures that are harder to disrupt than covalent bonding."
] |
[
"No. Ionic bonds are much stronger. It doesn't seem like it at first, since ionic compounds easily dissolve in water, but you have to think about bonds in terms of the energy needed to break them. ",
"The melting temperature of NaCl is 1474 F (801 C), this is an ionic bond.",
"Compare that to the covalent bonds between, say, the atoms in glucose or wood which take much less energy to break.",
"The reason ionic bonds dissolve in water with seemingly so little energy is because the water is able to surround and gently separate the atoms because of its polar nature."
] |
[
"All true. The guy didn't seem like he needed this much info. Its like, \"How does division work?\"",
"\"Well, integrals...\""
] |
[
"I just did something amazing. Can someone help me settle my disagreement with my wife iver just how amazing it was?"
] |
[
false
] |
My wife and I were pulling M&Ms out of a two pound bag of M&Ms and trying to guess what color we had pulled out before looking at it. This quickly escalated to guessing pairs and then triplets. So, I would say, "blue, red, and red," and reach into the bag and pull out three. Neither of us got the triplet but my wife guessed the pair three different times. She was getting braggy, so I declared, "I'm about to win the lottery!" I then called six colors (brown, brown, red, blue, green, and yellow). I closed my eyes and pulled six candies and Holy Mother of Shat and Fortune I pulled those six colors out. Obviously, we both freaked out. Now, I want to know what the probability is of doing this. My wife thinks it's 1/6 X 1/6 X 1/6 X 1/6 X 1/6 X 1/6, because there are six colors in the bag so each pull is a 1/6 chance to guess right assuming even distribution of colors. This puts it at about 1/46,656. I feel like it must be lower, because if I pulled six times, I might have pulled wrong one, but corrected it with the next pull. Like the first pull could have been blue, not brown as I was guessed first, then the second pull could have been brown to "fix" the first one. Since I'm drawing six, wouldn't it increase the chances of getting each one right? Right? Maybe? Help!
|
[
"You're not accounting for reordering. For a given string of six colors, there is a 1/46656 chance that you'll pull them ",
". But if you're just seeing if you match the colors that you say, you need to make each reordering of the same six to count as one. To do this, you need to compute 6!/6",
". This is 5/324, which is about 1.5%. Your wife got lucky, but not ",
" lucky. ",
"Also, ",
"M&M colors are not uniformly distributed",
"."
] |
[
"Why does that image use 26 M&M's to represent 25 M&Ms' worth of data?"
] |
[
"Since he wants \"brown, brown, red, blue, green, and yellow\" in any order, the probability would be C(6,2)*4!/6",
" assuming equal distribution of the six colors. The binomial coefficient C(6,2)=(6*5)/(2*1) accounts for the two positions of the browns in the sequence; the 4! is there to count the different ways the other 4 colors can appear in the sequence; 6",
" is the total number of different and equally likely sequences of 6 M&M colors.",
"If the colors are not equally distributed, say p",
", p",
", p",
", p",
" and p",
" are the probabilities of brown, red, blue, green and yellows, respectively, and we assume there are enough M&M's that pulling out one color does not appreciably change the probability of the others, then the overall probability of the outcome \"brown, brown, red, blue, green, and yellow in any order\" would be p",
"*p",
"*p",
"*p",
"*p",
"*C(6,2)*4!/6",
" since each of the sequences counted above has probability p",
"*p",
"*p",
"*p",
"*p",
"."
] |
[
"Would it be a good idea to diversify a newborn child's microbiome as much as possible?"
] |
[
false
] |
When a new child is born, im to understand that both parents should hold the child with their bare chest or at least get good skin to skin contact as to populate their microbiome with the parents bacteria and such. Would it be a wise idea to have another two or three people who exhibit good health get in there just for the diversity it would offer? In particular, people who are not related to the parents, seeing as a parent or sibling of the parents would have a very similar biome. Thanks for your help!
|
[
"The skin microbiome is actually not what you are going for here. It’s important but you don’t really want the skin flora to be the source of gut diversity (I think the microbiome you are interested in). The main seed of the gut comes from the mother during passage through the birth canal - largely the GI flora of the mother. The compression of passing through the small area forces some suction in the infant to get the flora where it needs to go. \nRegardless the seeding is critical for the gut microbiome to establish, but a diverse diet <3. Years is what is gonna get the diversity more established - probiotic fibers are key, as are sources of environmental microorganisms. ",
"Source - I’m a professor in the US who does research on the microbiome and it’s impacts on health."
] |
[
"Thank you! ",
"Im actually interested in all biomes. Thats really interesting on the establishing of the gut biome. And im glad im aware of the diet role. It seems to make sense thinking about it, but im glad you brought it to words. ",
"I was in fact though asking about the skin biome in particular, haha. I was discussing it with my girlfriend and i just was wondering if there would be an advantage to having a wide array of species setting up shop on the skin at birth. And what would an advantage of that external biome look like? ",
"I can see how my addition of \"people who exhibit good health\" is a bit misleading. Just speculation on a more diverse profile on that external biome species list."
] |
[
"Gotcha. There isn’t much work in the skin area right now (I have a grant at the moment to study it though!). I think the skin to skin is more for attachment though it wouldn’t surprise me if that is mediated by some microbiome sharing we don’t understand yet. The goal would be to not get the skin flora in the gut right away, particularly if you are dealing with a C section. You don’t want to establish skin bacteria in the gut right away - at least that’s the thought right now. Do we really understand understand this though? Not really!"
] |
[
"Is the speed limit of light only determined experimentally?"
] |
[
false
] |
Or is there some theoretical calculation/simulation/model that tells us precisely what that value is and that doesn't rely on any experimentally determined values at all, during the course of that derivation? I think the answer is No. Still, what would the implications be if we could formulate a theory based only on axioms and compute this limit? Would other fundamental constants also rapidly follow? Are there simulations that determines this value stochastically? (for the concluding question) - Is there some purely theoretical (axiomatic?) computation for the speed of light? Or some simulation which would show, for instance (I'm visualizing a result), a range of possible values for the vacuum speed of light, but very high probability for one value?
|
[
"To generalize your question: \"Can the numerical values of physical constants be predicted theoretically?\"",
"This is actually a more important question than at first glance. First if all, the absolute numerical value of a constant depends entirely on your choice of units, so it is not very fundamental. Instead, ratios of physical constants are more fundamental, as they have the same physical value in all unit systems. For instance, the mass of an electron in kilograms mostly just tells us what a kilogram is defined by humans to be. But the ratio of the mass of an electron to the mass of a proton is fundamental (or the ration of the electron mass to the Plank mass). Can such a number be predicted theoretically? Although there is not complete proof that all such numbers can be predicted theoretically at this point, that is really the end goal of science: to be able to predict ",
". With this in mind, if a physical constant must be inserted manually into a theory, it is a sign that the theory is incomplete. ",
"Now let's look at the speed of light in vacuum, c. It is indeed constant in all frames, but that does not tell us anything about its numerical value. In natural units, c = 1, but this really dodges the issue by punting the problem to other constants. First we have to make c dimensionless by comparing it to some other fundamental speed. For instance, let us choose the reference speed v = k e",
" /hbar which just includes the other fundamental constants (k is the Coulomb constant, e is the electric charge, hbar is the reduced Plank constant). This speed v is the speed of an electron in an atom according to the Bohr model. Then c/v = 137.036... which is a dimensionless number called the inverse fine structure constant. The fine structure constant describes the strength of the electromagnetic interaction, which makes sense because light is an electromagnetic wave.",
"To my knowledge, no current theory predicts the value of the fine structure constant, and therefore the dimensionless speed of light. But it is hoped that future theories will be able to predict this."
] |
[
"Even if there was, the computation or simulation would be based on the properties of the universe. It would basically just be a really, really inefficient way of measuring it.",
"Something along the lines of what you're talking about comes from atomic physics. The fact that integer-spin particles can occupy the same state as each other but half-integer-spin particles cannot is something that occurs at effectively zero velocity, but can only be understood in terms of relativistic transformations. If you were to do a bunch of experiments measuring Fermi-Dirac and Bose-Einstein statistics, you could perhaps figure out the speed of light based on this (edit: consensus is that you could figure out that there is a speed, but not the speed itself). To bring it even closer to what you're asking about, if you were to set up a quantum computer based on bosons or fermions perhaps you could figure out the speed of light from its behaviour, but I'm not really a quantum computing guy.",
"The short of it is that no, you can't get information about the universe without studying it."
] |
[
"Although there is not complete proof that all such numbers can be predicted theoretically at this point, that is really the end goal of science: to be able to predict everything.",
"If we are to take the idea of no free variables seriously, we'd need a theory saying that the universe is the way it is because that's the only way the universe could be. If we had several ways of making a universe that choice would be a free variable. In an odd way it would transition from an emperical question to a mathemical proof. "
] |
[
"Can a virus infect a bacterium?"
] |
[
false
] | null |
[
"Yes viruses that infect bacteria are known as bacteriophages or simply as phages. ",
"Generally phages are can be categorised in to two groups; lysogenic and lytic, this refers to the the life cycle of the phage. Lytic phages insert their DNA into the cell which stays separate from the bacterial DNA and in most cases after the phage has replicated a sufficient amount of times the cell will lyse and die, allowing the phages to infect other cells.",
"Lysogenic phages integrate their DNA with the bacterial DNA and the replication of the phage DNA is undertaken by the bacterial cell as it replicates. ",
"Lytic phages can be used to treat bacterial infections this is known as phage therapy and although not currently used in most country's it has the possibility to treat certain infections that may not be treatable by antibiotics. ",
"Some bacteria have special adaptations to defend against phages such as producing a polysaccharide layer known as a capsule that can stop some phages entering the cell."
] |
[
"That was an amazing answer. Thank you for taking the time and giving the effort. "
] |
[
"Lol thanks, did some research involving phages a few years ago and found it pretty interesting."
] |
[
"What is the physical meaning of the velocity of electronic information transmission?"
] |
[
false
] |
I am studying electric circuits and the book explains that there is a difference between electronic transmission of information and transport of electrons through conducting wires, pointing out that the former occurs at a rate 12 orders of magnitude higher than that of the latter. While I understand what is physically meant by the transport velocity of electrons, I can't figure out what is meant by the electronic transmission of information. Could someone explain what this is, and why it should be so much faster than the actual motion of electrons?
|
[
"Think about it this way, when you put water through a hose, it takes a while for the water to come out the other end, right? The speed of water in the hose is analogous to the velocity of electrons in a wire.",
"Now think about the hose again: this time, the hose is already full of water. When you turn the water on, water comes out the other end almost instantly. The water isn't travelling at that speed, but forcing water into one end of the pipe forces water out of the other end of the pipe very quickly.",
"Going back to the electron/wire analogy, wires are already full of electrons. When you push more electrons into one end of the wire, you force electrons out of the other end very quickly, even though the electrons themselves aren't going that fast."
] |
[
"In a circuit electrons are just carrying the charge, but there is also an ",
" around them. When you move a charged particle, it changes a field around it and those changes propagate in the field with a speed that can be different from the speed of the particle that caused those. A very rough analogy - you hear a moving car when it disturbs the air well before it drives close to you. Changing electromagnetic field also affects charged particles when it encounters them, influencing their motion. So when electrons start travelling at the beginning of the circuit, the change that causes in the EM field propagate very fast along the circuit and lead to other electrons following the similar motion much much faster, that the time it would take for the original electrons to complete the circuit. ",
"The changes in the EM field can propagate fast. F.e. the light can be though of as EM waves, and the speed of EM waves in vacuum is the speed of light ",
" (299792458 m/s). In electronic circuits electrons also excite EM waves that have different parameters and depending on circuit may mostly stay inside the wires. Those travel a bit slower (2/3 ",
" in communication cables f.e.), but still much much faster than individual electrons. ",
"To summarise: moving electrons excite changing EM field in which those changes propagate extremely fast and then can affect other electrons further away."
] |
[
"This is transport of electrons through conducting wires",
"As you can see, this is VERY slow, but like shadydentist said, electronic transmission of information is different in that it works by essentially one electron pushing into another and so on, like a set of dominoes."
] |
[
"Does gravity cause heavier isotopes in gasses/liquids to tend towards the bottom of their container?"
] |
[
false
] |
[deleted]
|
[
"Yes.",
"But it's a pretty subtle effect, and in natural systems is going to be masked by much more dominant fractionation and mixing effects. "
] |
[
"I'm not sure if just gravity would be enough, but centrifuges are used to separate isotopes."
] |
[
"What this man said, however I imagine Brownian Motion would overpower it in our regular gravitational field."
] |
[
"If you are past the sound barrier in a plane do you still hear the sounds you create?"
] |
[
false
] |
[deleted]
|
[
"Sound is a transversal wave that needs a carrier medium. In most cases, this carrier medium is air. The maximum speed of sound waves in air is somewhere around 343 metres per second which equals 1235 km/h. \nIf you are faster than this, the sound waves you produce aren't faster than you anymore, which means you can't hear them. Inside a plane the air stands still. Relative to the plane you don't move. This means that you can hear the sounds you create. "
] |
[
"If you are in a closed cabin, the air around you is moving with you and sound will propagate normally through that air.",
"If you were describing a scenario where you were moving in a stream of air faster than the speed of sound, then no, sound cannot travel \"upstream\" through the air fast enough to reach your ears.",
"There's also the consideration of structure, which will transmit sound (and much more quickly than in air, which is relatively slow). So if there were, say, engine noise, that noise could be transmitted through any physical connections and reach you as sound, but again it depends on the configuration of the question with regards to cabin air."
] |
[
"Yes, you would, because the metal that the plane is made of is not moving with respect to you or the engine making the noise (and neither is the air inside the cabin)."
] |
[
"If 98F is my inner temperature, why does it feel so hot when the ambient temperature is 97F?"
] |
[
false
] |
Why does my body feels the need to cool itself at that temperature?
|
[
"Because your body is constantly generating more and more heat you'll only feel comfortable when your body is able to shed heat at the right rate. ",
"At 97F the air around you is barely conducting any heat from your body, but down at 70F it feels just right.",
"But then water at 70F will feel pretty chilly, because water is more conductive than air at equal temperature. "
] |
[
"A good point to be made about perceived temperature is that we do not sense temperature, we sense the rate at which heat is conducted and whether it is conducted away from or towards the body. ",
"This is the reason your bathroom floor feels colder than the bathmat next to the tub does. The tile or vinyl conducts heat away from you much more rapidly than the bath mat. It's the same reason you can roast a hot dog on on a metal prong over the fire and eat the hotdog right away but can't touch the prong for fear of burning yourself. ",
"::edit::\nThe video that taught me about this. ",
"http://youtu.be/vqDbMEdLiCs"
] |
[
"Yes, two objects in the same environment are typically the same temperature the only reason one feels cold or warm is its conductivity of heat. "
] |
[
"Do the particles within an atom gravitationally attract each other?"
] |
[
false
] | null |
[
"Yes, but gravity is much weaker than all other forces on that scale."
] |
[
"How do we know? Has it been confirmed experimentally?"
] |
[
"Well it’s essy to calculate using Newton’s law of gravity and Coulomb’s law if electrostatics."
] |
[
"Where would you have to be standing on Earth such that you were furthest away from the Earths centre?"
] |
[
false
] |
[deleted]
|
[
"The summit of ",
"Chimborazo",
", Ecuador."
] |
[
"its location along the ",
"equatorial bulge",
" makes its summit the farthest point on the Earth's surface from the ",
"Earth's center",
"."
] |
[
"The Equator bulges an average of 43km (27mi) farther than the poles. Everest being much farther from the equator means it isn't the highest point from the core, just the highest above the surface."
] |
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