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[
"Is there an animal that primarily subsists on eating members of its own species/cannibalism?"
] |
[
false
] | null |
[
"This isn't viable due to ",
"trophic levels",
"/06%3A_Ecology/6.05%3A_Trophic_Levels). Each consumer needs a food source with roughly 10x the biomass of the consumer population to be sustainable, so a population of animals that subsisted on cannibalism would shrink rapidly."
] |
[
"No. If there was, it would run out of food and die. Different animals have varying degrees of willingness or ability to engage in cannibalism, but there's no species for which cannibalism is the ",
" source of food."
] |
[
"Cannibalism becomes more common when there is overpopulation but it will inevitably lead to a lower population and will never remain stable through cannibalism. The overpopulation phase is always fueled by an abundance of some other food source."
] |
[
"Do black holes cast a shadow?"
] |
[
false
] |
If I could place a black hole invetween the sun and the Earth (and presuming it wouldn't annihilate everything), would it cast a shadow on the Earth?
|
[
"This is not taking in effect gravitational lensing. ",
"If the original beam of light is wide enough and the position of the black hole relative to the surface and light source is correct, light bent by the black hole can light up the area were a shadow would be cast by a regular object. "
] |
[
"Some light will curve around the black hole but there will still be a part where light is blocked (",
"like this",
")."
] |
[
"So, depending on where you, the light source and the singularity are in relation to one another, you'll see more of a distortion than a shadow? "
] |
[
"I have some questions about something I read about: the habitable epoch of the early universe. Could you answer one or more of them for me?"
] |
[
false
] |
From this paper: I don't have much of a background in astronomy, physics or biology, I think I understand the gist of this theory, but I'd like a little more in-depth understanding. From what I gather, according to this astronomer, around 10-20 million years after the Big Bang, the background temperature of the universe was warm enough for liquid water to exist in a lot of places, so it's theoretically possible that primitive life could have appeared on rocky planets. What I'd love to know is: How certain are scientists that these conditions were actually present? Is it speculation or does it follow naturally from things we are pretty certain to be true? I imagine the universe was pretty different back then in terms of what kind of matter and structures were floating around. If I could hop on the Enterprise and explore back then, what would I see that's different from today? What level of diversity do we think evolved on earth during the first 10 million years of life here? All I know is that life was pretty basic. But did different organisms already inhabit particular niches and have specialized methods for survival, or was it just like warm algae soup? Is it reasonable to expect that life that might have appeared during this epoch might have evolved on a similar timeframe, or do we not have enough information to say? What happened? I understand that it's cooled down since then, I guess due to universe getting bigger and everything getting farther apart and cooling down. Is that basically right? (probably at least partially speculative) Were the changes that ended the habitable era gradual enough that life could have adapted? Is it possible that a planet on which life emerged in this era could happen to be in an orbit around its star in such a way as to shelter the life from the cosmic changes that were going on around it, or are there any other complicating factors I don't know about that would make that unlikely, like some kind of changes that would occur in the planet's atmosphere as the universe changed? If you know anything important or interesting that I'm not educated enough to even know to ask, please tell me that too :) Sorry if I'm stretching the rules by asking so many questions at once and being cheeky about the question mark in the title. I just found out about this and it seems so fascinating, so I'd like to know more.
|
[
"Oh boy. This paper is quite a stretch. Basically, it is saying that because we know the universe was very hot at the beginning, and is only 2.7K now, it must have been ~300K at some point in the past. This is true, and would have happened when the universe was 10-20 million years old. No one will debate that given our current model of the universe.",
"All this paper is pointing out is that ",
" rocky planet that existed in the universe would have been habitable (except the ones that were too close to their stars) since nothing can be cooler than the universe itself (or more specifically the cosmic background radiation). So yes, if any rocky planets existed, all water on their surface would've been liquid and could potentially foster life.",
"The question is how likely was it that any planets existed, and the answer is it's almost impossible. Even the author admits that most of the universe wouldn't even have stars at this young age, and any stars that did form so early would have to be 8+ standard deviation outliers (a 1 in 10",
" chance!!). Even in an infinite universe, that's exceptionally rare, so the author admits the distribution would have to be non-Gaussian and permit much larger tails.",
"But your problems don't end there. To form a rocky planet, you need rocks, which means you need elements heavier than H and He, which is all the universe had when it started. Thus, you need a star to go supernova to create your heavy elements, then you need those elements to cool and collapse into a second round of star formation, out of which a planet could then coalesce and form. This cycle itself is likely to take more than the 10-20 million year age of the universe, making planets by the time the universe was 20 million years old nearly impossible under our current models.",
"But I guess we can wait and see how our models of the universe change as we gather more data, figure out what dark matter and dark energy are, etc."
] |
[
"Yeah, the author (Avi Loeb) is a theorist who is pretty well known for doing this stuff sometimes. It's not 'crackpot', because the theories are usually logically sound, but they are often also extremely speculative bordering on impossible. Which can be extremely good for the field in pointing out new paths most people never even consider, but also produces lots of dead ends filed under \"just a bit too extreme\". Then again, who knows what we'll be saying about them in 50 years, maybe then some of them will resurface as \"way ahead of his time\"!"
] |
[
"From what I gather, according to this astronomer, around 10-20 million years after the Big Bang, the background temperature of the universe was warm enough for liquid water to exist in a lot of places, so it's theoretically possible that primitive life could have appeared on rocky planets",
"10 to 20 million years after the big bang is still more than 100 million years before the first stars could have possibly formed. The matter that formed out of the big bang was almost entirely made of hydrogen and helium with just a little bit of heavier stuff. There were no planets then, or any of the atoms that life as we know it needs to exist. Those atoms were formed in the death of the first stars. I think this answers your no. 2 and 6 questions, too.",
"For no 3, the fossil evidence is pretty rare. We know things like Stromatalites were some of the early life on Earth and they appeared about 1 billion years after the Earth formed. From there it took around 3 billion years for life to go from single celled to multicelled."
] |
[
"How significant are asymptomatic COVID-19 infections to the transmission of the disease?"
] |
[
false
] |
I know vaccines like Pfizer were shown in clinical trials to be quite effective at preventing symptomatic infections. What about asymptomatic infections, though? How big of a deal are they at this time, esp. with the rise of the Delta variant accompanied by waning vaccine effectiveness?
|
[
"There’s older data suggesting that anywhere from 30-50% of cases are transmitted from people who are asymptomatic ",
" Some of those people remain asymptomatic, but many of them were simply pre-symptomatic as you can transmit the virus up to 3 days before symptoms. ",
"Source: I had to write a medical assessment on asymptomatic transmission for work. I’ll try to add the scientific sources later when I have access to them.",
"Edit: These data were from before the Delta variant and vaccines. Vaccination likely improved the situation, but Delta is particularly nasty and has likely had an impact."
] |
[
"With the Delta variant, it is definitely unclear how significant asymptomatic transmission is. The CDC updated mask guidance a few weeks back after a study of an outbreak in Connecticut showed a few hundred positive cases resulted with vaccinated and unvaccinated patients having similar viral loads. Viral load has been correlated with transmissibility in other studies, so, theoretically, vaccinated people and unvaccinated people have similar risk of transmission. (Notably, there were less than 10 hospitalizations during this outbreak and no deaths). ",
"That being said, there are some limitations to this study, including that the outbreak occurred at a large event where people were likely in very close contact with one another. It’s unclear what the significance of this would be in everyday life. ",
"To answer your question about how big of a deal it is, it depends on what your goal is. If the goal is to prevent serious illness and/or death, the vaccines are so incredibly effective at doing this that it likely isn’t a big deal. Almost all of the deaths occurring during the current Delta spike are happening in unvaccinated individuals; if the vaccines were not effective against Delta, then the rate of breakthrough infections leading to hospitalization and death should be much higher. If the goal is to prevent all cases of COVID forever, this is an unfortunate development, because the Delta variant is far more transmissible and vaccines are less effective at preventing infection against Delta than against the original variant."
] |
[
"The CDC updated mask guidance a few weeks back after a study of an outbreak in Connecticut showed a few hundred positive cases resulted with vaccinated and unvaccinated patients having similar viral loads. Viral load has been correlated with transmissibility in other studies, ",
"I've seen this repeated ad nauseam since the Provincetown data went public. I want to be clear — despite the media headlines generated from this study, the bolded section does ",
" follow from the data. ",
"The data only showed that vaccinated and unvaccinated people ",
" carried similar viral loads. But we already know from other studies that vaccinated people are much less likely to develop symptomatic infections in the first place! So it's false to say that this study showed vaxxed and unvaxxed are equally likely to transmit the virus. ",
"The other potential confounder is that the study only measured viral load, not actual transmissibility. My (admittedly non-expert) understanding of this is that these tests can't differentiate live, infectious virus from viral particles that have been inactivated by antibodies/immune response, so there's good reason to think that viral load in these measurements is not a good proxy for transmissibility. More research needs to be done to clarify this point."
] |
[
"Why do you blow out different temperatures of air?"
] |
[
false
] | null |
[
"Human Body"
] |
[
"Human Body"
] |
[
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"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
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"our FAQ",
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"guidelines.",
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] |
[
"How do we measure the temperature of stars and quasars up to 100,000,000°? How do we know it's that hot?"
] |
[
false
] | null |
[
"The color of the light! I'm a material scientist not an astrophysicist so I eagerly await being told exactly why this is incomplete. The peak wavelength of a star indicates its surface temperature, it's called Wien's displacement law. The wavelength is inversely proportional to the temperature.",
"https://en.m.wikipedia.org/wiki/Wien%27s_displacement_law"
] |
[
"You're talking surface temperature of course, which is cooler than the zone where fusion is occurring, but we in a sense don't need to be able to measure this temperature directly because there is a requisite temperature to overcome the Coulomb barrier to create nuclear fusion within a star (or elsewhere). It's usually measured in MeV but you can convert to Kelvin readily enough - ",
"this link",
" also has a good discussion on why a direct MeV --> temperature is too high if you go with a direct conversion due to the distribution of energies (temperature is a measure of average kinetic energy)."
] |
[
"It's close enough for extremely hot objects that the OP asks about.",
"If you can use the spectrum to estimate the temperature to within even 10pc for such distant objects, that is a good enough result for astronomy."
] |
[
"Light Thrust?"
] |
[
false
] |
This is my first question in AskScience so forgive me if its been asked before. My question pertains to the properties of light, particularly its very special property of always finding the shortest travel distance. Why does this happen ? Also, I was just pondering ideas about how no object can attain the speed of light. However, is it possible to use light itself as mechanism of thrust? Realistically this doesn't seem possible to me because light is somewhat mass less and am unsure if it would even produce a force.
|
[
"Fermat's principle isn't that light rays ",
" the quickest path. It's not like light ray knows it will leave A end up to B and then optimizes to take the quickest path there. It's that the path that light rays that do reach B happen to ",
" is the quickest. \"Find\" and \"take\" are very different words. ",
"Consider sunlight. Light rays leave the sun and travel in a straight line to earth. That's Fermat's principle. They didn't take a zig-zag path, they didn't go past earth and then decide to turn around. They went straight. The quickest path. This doesn't mean all sunlight does this, after all some bounces off the moon and comes to earth, taking a longer path. It's that the light rays that do come directly to earth go straight. ",
"Now, in cases where it's not a vacuum, or any other constant media, it's a little different. But the same idea, it's not that light knows to go to B by the shortest path, it's that the light that does reach B has taken it. You can derive laws like the law of reflection or Snell's law from Maxwell's equation, and if you look at them you can see they follow Fermat's principle. ",
"If you need to go from point A to point B and have the requirement that you touch a mirror at one point, the shortest path happens to reflecting at the same angle as incident. If a light ray was to say go straight to the mirror hitting it at 0 degrees, and then bounce at off a new angle to go to B, this would be a longer path. Now of course this does not happen. It's not that a light ray that hits the mirror at another angle that is not the shortest path to B will take a longer path, it simply will not go to B at all. The light isn't finding the shortest path, the path that the behaviours of electromagnetic fields follow in hindsight will have been the shortest path. ",
"Same with Snell's law, to go from A to B through a medium interface, the light will have bent by a certain angle following Snell's law, which is ultimately following the boundary conditions that Maxwell's equations have at the interface. Now if you drew any other path with the two different velocities on each medium, like straight between with the shortest distance them for example, it would have taken more time. That's not that these light rays found the shortest path, lot's of other light rays left A at different angles, except they didn't take a longer path to B but instead didn't go to B. No optimal path was \"found\". ",
"As for thrust from light, you do not need mass, you need momentum. Introductory physics tells you momentum ins mass*velocity, but this is only right for large massive non-quantum objects at non-relativistic speeds. Light has momentum, even without mass. Whether you use the classical electromagnetic view or photon view, light leaving something is momentum leaving something. Due to conservation of momentum, this means the objects the light is leaving is gaining the opposite momentum, it has thrust. ",
"E",
" = (pc)",
" + (mc",
" )",
" is the full versions of E = mc",
" . A photon has energy (E) but no mass (m), so what it has is momentum (p). The momentum is p = h/λ, where h is Planck's constant and λ is the wavelength. The energy is E = pc or E = hf (f = frequency). Now, loosely speaking (technically should take the derivative), if we divide each side of E = pc by time we get E/t = cp/t. Now energy per time is power, and momentum per time is force. So we get P = Fc or F = P/c. You get a thrust force depending on the power of the light you put out (wavelength or frequency doesn't really matter), and it is scaled by the speed of light. Now c is a big number, so for even a megawatt of power (a fairly large generator) put out as radiowaves, light, x-rays, etc. directed in one direction you get 3 mN (0.0007 pounds) of thrust in the other direction. Not exactly a lot of force, but a force none the less. "
] |
[
"But this \"law\" annoys me. It isn't true, because mirrors obviously violate the principle (unless you specify that light must bounce off the mirror, but now you are adding extra rules).",
"Isn't that covered by the restriction that the rule only applies locally? The paths followed are the shortest in the sense that any path slightly different from them is longer.",
"Finally, the reflection and refraction rules can be derived with better grounding using Maxwell's equations or even conservation of momentum!",
"So it's not like light follows the path it does ",
" it's shorter, but rather that the path's shortness is a consequence (albeit a not immediately obvious one) of the \"rules\" light does follow. Right?"
] |
[
"The answer to your question on the distance light travels (optical path length) is a bit too hefty for me to get into at the moment, but I can answer your question about force.",
"Our most intuitive understanding of momentum comes from objects with mass - a truck is heavier than a car, so it has more momentum at the same speed (so don't cut off trucks). Collisions involve a transfer of momentum, which we easily and intuitively observe when the objects have mass. In the case of light, it clearly has energy - since it provides heat, for example - but where does its momentum come from?",
"The answer to that is its frequency. Where massive particles carry momentum respective to their mass and speed, light carries momentum related to the frequency of its oscillating electromagnetic field. When light is absorbed, it transfers that momentum. Incidentally, this frequency dependence is why visible light is nowhere near as harmful as ultraviolet light or X-rays. It doesn't have as high a frequency, so it carries less energy.",
"Hope that helps!"
] |
[
"What causes the crust to form 20-30 miles below the surface?"
] |
[
false
] |
Why isn't there molten lava everywhere just maybe 50 feet below the surface? What causes the crust to begin forming 20-30 miles below the surface?
|
[
"There's a lot of things right here, but there are also a couple clarifications I'd like to make...",
"While we don't get literal layers of molten rock anywhere, partial melting is extremely common in areas of mantle upwelling. It's not nearly as rare to have partial melt as I think you're implying.",
"The Mohorovičić discontinuity is a bit more distinct than you imply. While it's definitely not as perfect as a clean discontinuity like you'd see on a fault surface, it's definitely a measurable boundary phenomena (seismicity, viscosity, composition) that transitions on a scale of only about 500m (pretty thin in the grand scheme of things).",
"Most importantly, the 'smearing of ocean sediments and island chains onto continents' ",
" create new crust. If anything, it serves to destroy crust when some of the accreted province is subducted. As a generality, most new crust is created exclusively at MORs, where mantle upwelling creates basaltic crust. Most of the earth's continental crustal cores were formed billions of years ago, and are definitely not being formed at accretionary boundaries today (only accreted). You could make the argument that oceanic crust is being transfrmed into continental crust, but that's shaky at best and I don't think it would ever be called the 'creation of crust'. I know you know all this, but I just don't want anyone to be lead astray...",
"You're spot on about the formation of andesitic crust.",
"Cheers!"
] |
[
"Well, there isn't molten lava everywhere because except for the outer core of molten iron-nickle, almost the entire planet is solid. This includes the mantle - it is almost entirely just dense rock such as peridotite, with only a very tiny percentage of melt.",
"Secondly, the crust doesn't \"form\" 20-30 miles deep. The mantle-crust boundary has a lot of things going on, including the effective erosion of crustal material into the mantle through metamorphism which separates lighter and heavier rocks/minerals. The heavier ones, such as eclogite, can peel off and sink back into the mantle (e.g., eclogite delamination). This results in a net loss of crustal rock, but it also makes the remaining crust less dense, which serves to preserve what's left.",
"New crust is formed from the smearing of ocean sediments or island chains onto continents through plate tectonics. New crust is also formed when magma rises into existing continents, where it can either erupt from volcanoes as lava (new crust), or solidify within magma chambers as batholiths (which is basically where all the mountains of Yosemite, to name one region among countless, come from)."
] |
[
"Even including partial melting, most estimates for the fraction of the mantle that is liquid (that I've seen) at any given time is ~0.5% - 2%. There are certainly areas where molten rock is concentrated, and from what I understand most modern models predict a very tiny amount of melt to exist between many crystals in mantle rocks (allowing them to behave plastically, essentially), so melt definitely isn't rare per se, but I do believe it is still a very small amount in total volume. If you have more recent information I'd love to hear it though, it's been a few years since I've read any papers on this.",
"You are spot on about clarifying the other points. I didn't mean to imply the moho wasn't distinct, but it does come across that way in my post. And I did neglect to clarify that I was only talking about continental crust - that one hurts a little, I usually make a conscious effort to stick to technical definitions and terms when answering questions. Oops! Thanks for the input and explanations!"
] |
[
"How did we find out that 4% of the universe was the matter that we see?"
] |
[
false
] |
I'm not asking how we came to the theory of dark matter and energy, but how we came up with the measure of 4%
|
[
"The short answer is that the best results come from the ",
"Planck mission",
"'s measurements of the cosmic microwave background radiation. The results come from looking at the unevenness in that background, comparing that to the predictions of standard cosmology (predictions that depend on the relative amounts of ordinary matter, dark matter, and dark energy). ",
"Results are reported ",
"here",
" by NASA. To quote from this news release:",
"\"As that ancient light travels to us, matter acts like an obstacle course getting in its way and changing the patterns slightly,\" said Charles Lawrence, the U.S. project scientist for Planck at NASA's Jet Propulsion Laboratory in Pasadena, Calif. \"The Planck map reveals not only the very young universe, but also matter, including dark matter, everywhere in the universe.\""
] |
[
"Thank you, this was very helpful."
] |
[
"Glad to help."
] |
[
"Is the Heisenberg Uncertainty Principle derived or experimentally found?"
] |
[
false
] |
Title says it all
|
[
"It's basically a theorem about Fourier transforms. If you do a Fourier transform on the waveform representing the position of a particle, you get a waveform representing the momentum. If you do a Fourier transform on the air pressure, you get pitches of musical notes. The same principle applies in both. If a musical note isn't played for very long, it's pitch is less well-defined."
] |
[
"It is derived from the principles of quantum mechanics."
] |
[
"Those are good examples, but it's worth noting that the uncertainty principle is broader than applies for variables which are not canonical conjugates. For example, in the case of the hydrogen atom, position and energy share an uncertainty relation. See ",
"this",
"."
] |
[
"Is this sensationalist garbage? Or is Micho Kaku right when he says, \"We came close to losing Northern Japan\" ? (link in comments)"
] |
[
false
] |
I initially asked this in , but apparently you're not allowed to ask questions there.
|
[
"Sensationalist garbage. Micho Kaku has done very well for himself churning out vast swathes of bullshit. I don't know how he can look his academic colleagues in the eye."
] |
[
"He does not specifically say it was a bomb, he says that the area would have been rendered uninhabitable due to radioactive material. This is the case around Chernobyl and Pripyat, so given that amount of material in the reactors would it have been enough to create a similar type of exclusion zone in northern Japan?"
] |
[
"But it wouldn't have say... blown up?"
] |
[
"What is the difference between chaotic systems and stochastic systems?"
] |
[
false
] |
From what I understand, chaotic systems are sort of a 'middle ground' between completely deterministic processes and stochastic ones because they're governed by deterministic equations, but because they're so sensitive to initial conditions it's impossible to predict exactly what's going to happen after a certain amount of time -whereas stochastic systems are completely random and therefore have to be analysed statistically. I'm not sure if this understanding is correct or not, hopefully one of you good men or women out there can clarify this.
|
[
"To put it pithily, stochastic processes are about ordered behaviors emerging from random systems, while chaos theory is about complex, random-seeming behaviors emerging from deterministic systems."
] |
[
"\"Emergent\" behaviors can occur in both stochastic and chaotic systems. The core distinction is that stochastic systems have a random component while chaotic systems do not—they're classical deterministic dynamical systems that exhibit surprisingly complicated behaviors."
] |
[
"this is more of how i understood it. you're describing emergent behavior, yes?"
] |
[
"Why does the body \"need\" 8 hours of sleep?"
] |
[
false
] |
The reason I put "need" in quotes is because not everyone needs 8 hours, but that's the recommendation. What I'm wondering is, why is it this long? Is there some process that our body is doing that takes hours to accomplish? Metabolizing something or storing memories perhaps? EDIT: I should probably clarify, the main point of this question is not "why do we sleep?" It's actually a more specific version (that I now realize, nobody really knows for sure): "what requires X hours to do in our sleeping bodies?" This latter question, of course, would probably be helped by an answer to the former.
|
[
"There has been a lot of questionable information posted about sleep recently on askscience, so I want to clarify using peer-reviewed, cited sources. I hope other comments will respect the askscience guidelines.",
"1) Why do humans sleep roughly 7-8 hours? Why do animals need sleep?",
"Sleep is a relatively young science, but there is a lot known. The amount of sleep (in hours), as well as the qualities of that sleep period (awakenings, etc.) are governed by a lot of factors, including body mass, brain mass, diet (carni/omnivores vs. herbivores), and intrinsic properties of ",
"neural organization",
". This breaks down for very short-lived species, but even they show periods of quiescence that are likely analogous to sleep.",
"What is getting \"made up\" by sleep is unknown, but one theory is that synapses are being ",
"pruned and adjusted",
" during that sleep period. What is known is that a certain frequency in the EEG, slow wave activity, dissipates ",
"across the night",
". This occurs during non-rapid eye movement (NREM) sleep, and is a good marker of built-up sleep pressure. REM sleep is also homeostatically regulated like NREM sleep, and many researchers think REM aids in ",
"long-term memory consolidation",
"2) Do we need to \"make up\" the time lost when we get only 4 hours or less? Can you function well for an extended period of time on small amounts of sleep?",
"Sleep is homeostatically regulated, just like body temperature. If the body gets too cold, there will be compensatory measure to heat the body. If the case that sleep is deprived, there will be compensatory sleep pressure. Sleep deprivation will negatively impact ",
"mood",
" and ",
"cognition",
", and one night recovery sleep after a large amount of sleep deprivation is usually ",
"not adequate",
". ",
"3) How do people with sleep disorders survive? / There's a region of the brain called the 'pons'...",
"Sleep deprivation will kill a mammal, ",
"period",
". In the early 20th century, there was an epidemic of a disease called ",
"encephalitis lethargica",
", in which people would initially have motor and insomnia symptoms but then enter a coma-like state. Anatomical follow-ups of this disorder implicated a region of the brainstem called the pons. We now know that specific neuron groups in the pons, acting with other neuron groups in other brain regions (like the hypothalamus, basal forebrain, and thalamus) interact to switch between wake, NREM, and REM. See ",
"figure 1",
".",
"edit: grammar, fixed encephalitis link"
] |
[
"Please read the ",
"AskScience guidelines",
" before posting. Top level comments are reserved for expert panelists or comments that provide factual evidence with appropriate sources. ",
"Thank you!"
] |
[
"Please read the ",
"AskScience guidelines",
" before posting. Top level comments are reserved for expert panelists or comments that provide factual evidence with appropriate sources. ",
"Thank you!"
] |
[
"How are the calories in beer counted?"
] |
[
false
] |
This is less of a scientific question... more of a procedural question. I was considering how beer, the best thing in the world, is marred by its high caloric content, and knowing the procedure typically used to measure calories, I wondered if these measurements are accurate. Foods are (precisely) tested for caloric content by placing them into a chamber within water, with the outer water tank heavily insulated. Resistive heaters are used to burn the food within the tank, which will increase the temperature of the water (both from the burning food, and the heat of the resistor). Measure the increase in temperature of the water, calculate the energy change, subtract out the heat added from the heater, bada bing, bada boom... Anyway, I was hoping someone could tell me how beer is handled, being that the ethanol in beer has a large energy capacity and is NOT metabolized as energy by the human body (and so, would not be a "calorie" that a dieter would be concerned about). So I did some math... Assuming a Belgian beer (the best kind of beer), a density of 1.062 g/ml can be expected in the final product. This translates to about 502.5 g/pint. Assuming 7% alcohol by volume (a fair middle of the road for beer) thats 35.17 g/pint of ethanol (the best kind of alcohol). The heat of combustion for ethanol is about 7.1 kCal/g (remembering, a nutritional/dietary calorie is 1 kCal). So therefore, the amount of ethanol calories is about 250 calories per pint. So, using this as a source of published caloric contents of popular beers: Sierra Nevada Pale ale has 218 cal/12oz, which translates to 283 cal/pint. I refuse to believe that the ingredients in the beer only add up to 33.4 calories, so can someone who knows the process say whether or not the alcohol energy is simply subtracted out from the final calorie measurement.
|
[
"we only net 215 kJ/mol of the 1325 kJ/mol, or about 16.2% of the energy",
"No, that's just a theoretical lower limit which assumes that all of the ingested ethanol is incompletely metabolized.",
"The standard energy density assigned to ethanol in nutrition information labels is ~7 kcal/g (not kCal, btw)."
] |
[
"It sounds like FlyingSaggittarius helped you make the link with the piece of information that you were missing, but since it sounded like there was also a calorimeter procedural question:",
"Beer labels (at least in the U.S.) aren't regulated by the same FDA rules that govern other foods and require nutrition labels. For this reason, no brewers are required to do any calorimeter testing (AFAIK).",
"If a brewer chooses to supply caloric information, it's usually calculated by an equation that incorporates the starting gravity of the wort and the final gravity. With these two numbers, the concentration of residual sugars and ABV can be calculated, and caloric content is established from these figures.",
"There are variations of the equations, but if needed, I can supply one equation that gives calories as a function of starting gravity and final gravity."
] |
[
"There is almost no chance that any acetic acid is excreted instead of metabolized or used in some acetylation reaction. From a cell biology perspective, that's some good shit. ",
"I argue that the acetate from ethanol metabolism should be counted as fats in calorie counting because its metabolism is more like FFA metabolism than CHO metabolism. "
] |
[
"What happen when an infected cell replicate itself ?"
] |
[
false
] |
Hi, So what i'd like to know is this, if a cell is infected by a virus or ""infected"" with mRNA from vaccine for example. What would happen if the cell replicate ? Would the new cells contain the virus or mRNA ? I'm thinking about this cause when you do workout you accelerate the replication process (I suppose since cells have to repair the part that you broke in your muscle during the workout). And since the vaccine is injected in the muscle I was questioning myself about that. Like, if it was the case, could it cause chain reaction, cells replicating with the virus again and again ? Maybe it's totally stupid tbh.
|
[
"The mRNA from the vaccines is gone within a few hours. mRNA is very unstable, and mostly has a half-life of a few minutes. That's one reason mRNA vaccines took a while to become practical. The current versions are generally modified to be more stable, but that only gives them a few hours of survival. (Obviously, that's one reason they're so safe -- they're completely eliminated from your body very quickly.) So there's no question of the vaccine persisting throughout a cell replication.",
"The protein produced by the mRNA translation is also unstable, like most proteins, though more stable than mRNA. I don't have a number for its half-life, but a day to a couple days is about right. So as soon as the mRNA is destroyed and new protein stops being made, the protein also begins to fade away and is gone within a week, probably less. If a cell containing the protein replicated, then each of the two new cells would have (on average) around half the original protein, and it would continue to half-life away.",
"Some viruses can persist through cell replications, but SARS-CoV-2 is a poor candidate for that. It's not incorporated into the genome and it disrupts cells so much after infection that they probably don't undergo replication. If they did, then you'd end up with two infected cells, each of which would rapidly be destroyed either by the virus directly, by the cell's response to the virus (cells typically commit suicide when they're infected, to prevent viral replication and amplification), or by the immune response to the infection (immunity also quickly destroys infected cells). ",
"So TL;DR, the mRNA vaccines are about as innocuous as you can imagine -- they last just as long as needed to kick-start immunity and then are gone within hours. The infected cells are much more damaging, but are rapidly destroyed or otherwise eliminated, almost always with no replication but if by chance a cell did replicate both progeny would be destroyed."
] |
[
"I would also like to add that muscle tissue, if that’s what you are worried about, doesn’t replicate. All the muscle cells you’re born with, you’ll carry around until your death (ish). \nWhen working out, the damage to parts of the muscle fiber is light, is mostly intracellular, and is repaired by hypertrophy, meaning that the cells repair the part required to create force and contract and add more contractile units. So technically even The Rock’s muscle have the same number of cells as mine, his cells are just muuuuch bigger"
] |
[
"Well there are 3 types of muscle tissue namely smooth, cardiac and skeletal. Smooth Muscle can replicate, however Skeletal Muscle And Cardiac Muscle can only do hypertrophy(increase the size)."
] |
[
"CDC and health departments are asserting \"Ebola patients are infectious when symptomatic, not before\"-- what data, evidence, science from virology, epidemiology or clinical or animal studies supports this assertion? How do we know this to be true?"
] |
[
false
] |
I've been a mod of for several months. We have a science issue coming up repeatedly, every day we cannot answer. Please help. All around the world we're hearing the same, repeated message: "Ebola patients are only infectious when they are symptomatic" A significant fraction of the controls, contact tracing, follow ups, health choices, -- in fact much of the whole response is being predicated on this understanding. We have one microbiologist and many commenters in the ebola sub saying this is premature, that really we don't know because we've never done human studies that lead to infections. My questions to -- Who are the experts who can answer this question? Do we really know this assertion is correct? Several people are arguing convincingly (as one example see here ) that the line being repeated by the CDC is a simplification and in reality inaccurate. Which is it? Are there any ways ethically to test this question or even gather relevant data to get us closer to a definitive answer? Thank you
|
[
"u/nallen",
" asked me to weigh in here, and I've been combing peer-reviewed articles and literature to see what we actually know about transmission while symptomatic. I have found a couple of sources, with the following caveat: 1) this kind of work has NOT been done in humans during a real-time infection. Everything I've found is based on post-outbreak reviews of cases, likely routes of transmission, etc.",
"tl:dr: The more symptomatic a person is, the more infectious they are. ",
" The more symptomatic a person is, the higher the risk of transmission. There is only 1 published case of infection by fomite, and the viral load of the patient who contaminated it was very, very high (the index patient died wrapped in a blanket, a sibling wrapped himself in the blanket immediately after, in grief, slept in said blanket, and contracted Ebola).",
"-One of the sources I found looked at transmission of Ebola and other hemorrhagic fevers on airplanes, in order to formulate a standard operating procedure (SOP) for cases where it is discovered that someone was on the plane while infected. This article uses both epidemiological data and literature review to form an opinion. As of 2012( ",
"one",
" ) there has not been a documented case of transmission on an airplane. The article further cites a number of relevant things; ",
"In the one documented case of repatriation by plane of a seriously ill, Ebola confirmed patient, none of the 4 health care workers in direct contact, nor any of the 74 secondary contacts contracted Ebola virus.",
"A case from the 'grey' literature (news, not data-driven) reported that a nurse who cared for a patient with \"presented with fever and jaundice, both not severe\" later died of Ebola virus infection. After she died, and Ebola was confirmed, they tracked the man down, and confirmed he had had Ebola. No one else on the flight was infected. The ",
"original",
" article (the news item) indicates the nurse who died cared for the sick man in hospital AND escorted him on the plane. This implies quite a bit of exposure, and prolonged exposure at that.",
"The literature review they did (current to 2012) indicated, ",
" However, risk of transmission may increase in later stages of the disease with increasing viral titres [19] and increased viral shedding. In a household study, secondary transmission only took place if direct physical contact occurred [20]; In an outbreak in 2000 in Uganda, the most important risk factor was direct and repeated contact with a sick person’s body fluids, as occurs during the provision of care. The risk was higher when the exposure took place during the late stage of the disease. However, one case was probably infected by contact with heavily contaminated fomites, and many persons who had had a simple physical contact with a sick person did not become infected. Therefore transmission through heavily contaminated fomites is apparently possible [21]. In summary, physical contact with body fluids seems necessary for transmission, especially in the early stages of disease (as is likely in passengers still able to travel on a plane), while in the later stages contact with heavily contaminated fomites might also be a risk for transmission.\"",
"ref 19",
" \\ ",
"ref 20",
" \\ ",
"ref 21",
"Further, statistically, caring for the sick person in the early stages of disease did not correlate well with contracting the disease- those present as the patient neared death had a significantly elevated chance of contracting Ebola. \"Among the post-primary case-patients, ",
" The risk was reduced when the patient stayed in a hospitals, probably because of the use of gloves, even before strict barrier nursing was implemented (6,7).",
"By contrast, simple physical contact with a sick person appears to be neither necessary nor sufficient for contracting EHF. \""
] |
[
"Great post. Thank you. This will help me in explaining to my friends and colleagues that there is no need to nuke Dallas."
] |
[
"Yeah, the idea of nuking Dallas gets categorized as \"landscaping improvements\" in most of Texas. "
] |
[
"How can QD help forensic scientist to determine the age of a fingerprint?"
] |
[
false
] |
Dutch scientist are busy with a technique to determine the age of a fingerprint with the use of quantum dots. I have tried to contact them, but they can't help me with anything since it's still a running project. I was hoping someone here could tell me more about how it is done. In short (and from my understanding) they want to connect QD to certain substances left over in a fingerprint. The more there are, the more it'll glow/or glow differently (?) The problem with this technique I found is that fingerprints can leave a different amount of substance depending on the surface/person/pressure/weather. Wouldn't that mean that if two persons left a fingerprint at the same moment, but one was set with more pressure and the donor just makes more oils in general, and the other one touched something lightly, it would seem like the first person was there more recent than the other one? Is that something that is true or do these fingerprint substances not only degrade but also change in construction/molecules. Does someone know more about this subject and is willing to shine more light on it?
|
[
"The researchers obviously didn't have definitive answers to that themselves when they wrote this:",
"In order to develop this technique we will first establish which biomarkers provide significant information about the time a fingerprint is deposit on a surface.",
"It's an ongoing research, so would we could little but speculate what exactly they are tracing. You could either ask the researches themselves (there's a contact form and many researchers are happy if someone shows interest). Or ask again in 2022 when the project has run its course and the results are published."
] |
[
"The premise of identifying the age of the fingerprint would be possible if a compound were used that degraded in air at a known rate into a different chemical. In the simplest scenario, the initial chemical may fluoresce a type of light that excites a nearby quantum dot and this emits visible light A. The chemical would then degrade into a different chemical that emits a different form of light, which could excite a different type of quantum dot and this could emit light B. The ratios of those two forms of light and knowing the kinetics of the degradation could tell you the time it has been degrading. Hard maybe on the practicality of that specific scenario, but I would not be surprised if something crudely like that is at play."
] |
[
"Damn, thanks this is exactly what I need."
] |
[
"What happens during near-death experiences?"
] |
[
false
] | null |
[
"The skeptic in me is coming out, so forewarning: I don't want to sound like an a-hole. ",
"I'd like to see a source about DMT. The only source I have been able to find on the internet is from a ",
"a book (warning PDF)",
" but not much of anything in peer-reviewed journals. Additionally, even on wikipedia, it gives some reason's as to threaten the credibility of this researcher's findings, such as: ",
"Only two of his test subjects reported NDE-like aural or visual hallucinations, although many reported feeling as though they had entered a state similar to the classical NDE. His explanation for this was the possible lack of panic involved in the clinical setting and possible dosage differences between those administered and those encountered in actual NDE cases. ",
"The \"typical experience\" you refer to can actually be better characterized by a temporal lobe seizure due to a lack of oxygen. The NYT actually has a pretty great overview ",
"temporal lobe seizures",
" where they discuss sensory hallucinations and feelings of an \"aura\" with reduced consciousness in the symptoms section. ",
"In any case, unless death is very sudden and unexpected, I would assume a lot of stress hormones are released before a near-death experience, with activation of the ",
"HPA axis",
". After the survival of the experience, there are probably tons of natural opiods and reward centers of the brain becoming active due to the positive experience of the actual survival. "
] |
[
"First off: there isn't all that much known about NDE's apart from anecdotal experience.\nChemically, it is often said that during an NDE, there is a release of certain neurotransmitters in your brain, including the powerful psychedelic compound DMT. This is often used as the explanation of the NDE, and the effects of DMT do often correlate with those reported to happen during NDE's.\nThe 'typical' experience often involves floating above your body and looking at yourself from above; possibly flying around and visiting relatives etc. If you want to experience similar things, try lucid dreaming, meditation and even DMT itself."
] |
[
"Strassman, the author of The Spirit Molecule himself said that there was no proof of DMT being released during death/sleep."
] |
[
"Do the air bubbles in boiling water get hotter than 100C?"
] |
[
false
] | null |
[
"They're actually water vapor bubbles instead of air, which is mostly nitrogen and oxygen. The water is at 100C and as the molecules gather more heat energy they turn to vapor, also at 100C. The temp is the same but the vapor just has more energy to be in the gaseous state. The only vapor that could reach a higher temperature would be at the walls of the pot if the pot was at a higher temperature. It's possible, but under most circumstances, no. The vapor will not exceed the temperature of the water. "
] |
[
"Gases are slightly dissolved in the water, but as you heat it up, more of the gases escape.",
"When you reach boiling, the majority of the bubbles you see in water will be water. That's why when the bubbles reach the surface and escape, they condense after meeting with the cool air and form a rising, misty column that people normally call steam."
] |
[
"From what I understand from your response: Heat from the pot (>100C) transfers energy to water vapor - by minute amounts - since the water can't heat it any higher. I have a hard time believe there no other molecules mixed around in the (distilled) water. Nitrogen and Oxygen molecules don't fit between H2O molecules? When the water is really boiling with bubbles the size of a quarter, that's all water vapor?"
] |
[
"Hypothetical Exoplanet Analysis"
] |
[
false
] |
What are some features of this artists conception of an exoplanet are scientifically inaccurate and/or impossible? Also, is there any truth to this picture? Source:
|
[
"Off the top of my head, the simplest example in that image of a mistake that I think would stand up is that it shows a star in the sky that is either very large or pretty close - and the brightness from it would certainly drown out the other stars in the black sky there.",
"Even the moon photos with their lack of atmosphere have the stars basically invisible as the brightness of the foreground totally overwhelms them.",
"Some of it seems plausible - the star is quite large or close, so it would be potentially possible to have some liquid water perhaps, the rocks and terrain, meh, why not.",
"It does look like the \"camera\" is sitting on a moon orbiting the gas giant. I could be wrong, but I think that if a gas giant was that close to a star, it would be quite warm indeed, which I think would then lead to a much faster moving atmosphere - meaning that the nice cloud bands wouldn't appear, but rather it would be more of a single color or smear at best, but I am happy to stand corrected if that is wrong."
] |
[
"The lack of an atmosphere would sort of ruin the chances of having liquid water i would think. What would the temperature be like without a prominent atmosphere and a sun at such a distance?"
] |
[
"I sort of assumed that there would be one which would allow for the liquid water, but left it at the sky being the wrong color :)",
"I don't know if there is a mix of gasses that could make an atmosphere which remained pretty dark/invisible even during a bright day (having such a large star nearby) but given the apparently clouds/fog on the surface of the planet, I let it be. Perhaps someone who knows more can state with certainty whether a dark/invisible atmosphere is possible like here? I would have assumed that the light would end up bouncing around so as to make a color depending on the gasses, but I could be wrong."
] |
[
"Would including more virus strains make influenza vaccine more likely to be effective in a particular year?"
] |
[
false
] |
Is there a biological limit on how many strains can be included in one vaccination? How about using a series of shots?
|
[
"\"Traditional flu vaccines (called “trivalent” vaccines) are made to protect against three flu viruses; an influenza A (H1N1) virus, an influenza A (H3N2) virus, and an influenza B virus. There are also flu vaccines made to protect against four flu viruses (called “quadrivalent” vaccines). These vaccines protect against the same viruses as the trivalent vaccine and an additional B virus.\"",
"https://www.cdc.gov/flu/protect/keyfacts.htm",
"Also the more strains, the more expensive it is to make."
] |
[
"Actually each strain added reduces the chance of developing a successful immunity. ",
"Source, the vaccine website. "
] |
[
"Yes, and the time to grow and produce several hundred million doses, so it has to be done well before flu season, and the strains active are apparent.",
"And the expense of producing hundreds of millions of doses extra in case of a major outbreak, and panic, many of these most years will simply be thrown away."
] |
[
"On paper, wavelengths in the electromagnetic spectrum are often represented as looking like sine waves, is this actually how they are structured, or is it just a decent 2D approximation?"
] |
[
false
] |
Are they really 2-dimensional constructs like they are represented on paper, or is that just a rough cross section or something? What would a more accurate image look like, if there is one?
|
[
"sine/cosine functions are perfectly good, exact solutions to Maxwell's wave equations. One thing i will note though is that the 2D representations you are describing are a special case known as \"plane\" polarisation. In general light is elliptically polarised, and the more commonly known \"plane\" and \"circular\" polarisations are just special cases of this.",
"EDIT: Im only describing one component of the EM wave, for example the electric field. There is also a magnetic feild perpendicular to this which follows the same rules."
] |
[
"Well they have two perpendicular components: the electric and the magnetic field. So ",
"this",
" is a bit more accurate. However, those fields don't actually extend into space: the arrows represent the strength of the magnetic or electric field, not how far they extend."
] |
[
"Something I've never understood about these figures is what's going on just to the right or left of that axis. Or above the axis for that matter. I guess I'm not explaining this too clearly. The wave in this figure is one dimensional, so what's going on a foot above that line, for example? Do the electric and magnetic fields have the same magnitudes and directions as they do on the line shown?"
] |
[
"How come the skin of people that lift heavy objects with weird parts of their body doesn't rip out?"
] |
[
false
] |
So I was watching episode of GMM and I was wondering. How can you lift so much weight with your tongue \ eye lids?
|
[
"Well, not that I know the answer, but to clarify your question a bit... "
] |
[
"Skin and muscle good tensile strength. Muscle fibers split along the direction of contraction, but the tongue has fibers running multiple directions, so it's less likely to tear. Skin is generally stretchy to a point, then resists further stretch. As long as the hole is made by a round point and the weight applied slowly, the fibers are pushed apart instead of cut, and the skin can support more than you'd think without tearing. The main issue for most of us would be pain. These activities are going to be very painful."
] |
[
"Not a biologist or medical expert but I know that skin has pretty good tensile strength. But it's not just the skin, when people pull stuff using random body parts (say, their ear lobes) the force is distributed to the tissue underneath too. Muscle tissue also has good tensile strength."
] |
[
"What are the health detriments of LSD or magic Mushrooms? (Long term and short term)"
] |
[
false
] | null |
[
"Sources?"
] |
[
"One of the dangers of hallucinogens is becoming agitated by the hallucinations and hurting yourself or others."
] |
[
"Pfff thats a tall order, even though it does happen, it's usually due to underlying mental illness that exacerbates the drugs effects. Now, short term? Memory loss, depression, anxiety, aftershocks or \" flashbacks \" of the trip, sweats, paranoia and a few more. Long term: HPPS (hallucinogenic persistent perceptive syndrome) - where you may see \"trails\" or streaks from lights/objects months even years after cessation of hallucinogenics. Schizophrenia, bi-polar disorder, major depressive disorder, depersonalization, derealization are just some of the possible short and long term effects from these types of drugs."
] |
[
"Why is magnetic attraction more powerful than gravity? Also, is there such things as \"magnetic waves\"?"
] |
[
false
] | null |
[
"The answer is nobody has any idea ",
"http://en.wikipedia.org/wiki/Hierarchy_problem"
] |
[
"To my knowledge it is not well understood why the electromagnetic force is stronger than gravity. I'm sure there are hundreds of theories, but there's no compelling evidence for any of them. Right now, it should just be taken as a fact.",
"Magnetism and electricity are coupled together such that a magnetic wave always produces an electric wave. This is light."
] |
[
"Can somebody tell me why the above comment is being downvoted? It is correct, and nearly identical to the other two."
] |
[
"[[Medicine]] How do tests for viruses works?"
] |
[
false
] |
[deleted]
|
[
"There are a lot of possible techniques, but one of the easiest test to produce is done through a technique call quantitative polymerase chain reaction or qPCR. In terms of protocol, the DNA and/or RNA of the sample is first extracted. If it's RNA it gets reverse transcribed back in to DNA. We'll then add two things to the sample. First is a dye that fluoresces when bound to DNA and second is a set of primers. Primers themselves are short pieces of DNA that selectively bind to what we want them to (in this case, the viral DNA).",
"During qPCR, 2 things happen. First, through the primers that are used, we can selectively double a specific portion of DNA so 1 strand of DNA becomes 2, 2 becomes 4, and so on, and second, we check the fluorescence of the sample so we can see how much DNA is in the sample. This happens 35-40 times.",
"If even one strand of viral DNA is present, it is quickly duplicated",
"\nmany time to a huge amount (over a trillion strands) and the fluorescence signal shows an exponential curve. If there isn't viral DNA there is no increase in the fluorescence signal.",
"In terms of positives, the test is relatively fast. It only takes one day to complete the test and it can be performed in a somewhat large scale. Most microbiology labs could perform 96 independent tests in one experiment. It's also highly sensitive."
] |
[
"A really simple way of explaining is...",
"Swab your nostril",
"Get the viruses genes from the swab (it’s RNA, not DNA)",
"Turn that RNA to DNA",
"Make a shit ton more copies of that DNA",
"Stick a bunch of sticky light up things that will stick to the DNA. ",
"These sticky things will only light up if they are complimentary to Viral DNA",
"If you see it lit up, you have the corona"
] |
[
"Those letters are DNA bases, think of them like binary code in a computer (except there’s 4 not 2). They code for information which codes for the organism, in this case the virus. What the test does is it looks for a piece of that code which only this virus has. It would be like looking for the part of the code that says “blond hair” to see if someone with blond hair is present, but this is way more specific. ",
"DNA looks like a ladder where there are 2 strands attached to each other, and a strand will only bind to a complementary strand (like puzzle pieces). So the “primers” listed are small fragments that can fit in like puzzle pieces to a specific spot in the DNA that is only on the virus. They’re used to make bigger strands and they can copy many times to exponentially increase a small fragment of the virus’s DNA (if present). ",
"Copying many times is important because samples from patients contain more than just the virus, so there is actually a lot of random DNA in the sample, you want to make it so there is so much viral DNA that the other DNA is insignificant. ",
"So it’s more like you photocopy something a bunch of times, and if it’s there now you have a bunch of glowing. If its not there then you photocopied nothing and there is nothing to glow."
] |
[
"how can we test string theory?"
] |
[
false
] |
everything I've heard about string theory sounds like an interesting idea. IDEA. not a theory. how can we test the postulates of string theory in order to confirm that it is a viable ?
|
[
"It seems to me like you're hitting the standard \"but wait\" after learning about string theory and its limitations. It seems to me that a lot of people learn about it and go \"aw that sounds really cool.\" Many stop here. Then some people say \"but wait it can't be tested, why does it have all this press, isn't it just so much pseudoscience?\" (kind of the other extreme) When in reality it's just stuck in this nebulous space in science we haven't invented a word for.",
"You see, string theory is a reasonably sound mathematical theory that explains observed phenomenon. But it postulates additional assumptions about the universe that haven't been confirmed by experiment, so it isn't a 'good' scientific theory yet. But the fact that there exists ",
" to make these measurements, even if we don't have the technology at present, seems to suggest that it's better than just a nice bit of math. So it's just in this grey area between overdeveloped hypothesis and untested theory.",
"There are some upcoming measurements we expect to be ",
" for string theory to be true, but not ",
" to show that it must be ",
" description of reality. Finding supersymmetric partners of standard model particles at the LHC is one of these necessary, but insufficient findings. If we don't find supersymmetry, that's going to rock string theory's foundation. If we do, then it just eliminates a few of the less popular non-string-theory extensions to the standard model."
] |
[
"Absence of evidence isn't evidence of absence. It is, however, a good argument for not spending much time worrying about string theory."
] |
[
"We can't, yet."
] |
[
"Is Tobacco on its own actually harmful or is it just the chemicals used by Companies in their Cigarettes?"
] |
[
false
] |
[deleted]
|
[
"According to available scientific literature, it looks like both tobacco on its own as well as the additional chemicals inhaled by smoking a cigarrette are considered to be carcinogenic.",
"Non-smoked things like chewing tobacco and snuff are associated with cancer risk, especialy oral cancers",
". While it has not been determined experimentally what chemical (or combination of chemicals) is responsible for this association, most of the articles I've come across guess that the culprits are either nitrosamines or radioactive polonium/lead that can be enriched in tobacco plants using certain fertilizers (in my opinion, the nitrosamines link appears to be much more credible).",
"While it depends on the material and method of combustion, I think smoke from burning any organic material is going to produce some carcinogens like ",
"PAHs",
". Though I think there are some carcinogens found in cigarette smoke that are not found in regular tobacco. ",
"Cigarette smoke is also associated with cancer, particularly lung cancer",
", for reasons similar to those for using non-smoked tobacco (nitrosamines and Po/Pb 210).",
"Edit: both types (smoked and non-smoked) of tobacco contain nicotine."
] |
[
"Inhaling smoke is bad for you, regardless of the plant being burned.",
"The additives do make it worse."
] |
[
"Indoor air pollution is major health risk in developing countries WHO: ",
"Indoor air pollution and health",
". Paraffin candles, gel wax candles and scented candles also release carcinogens to the air. ",
"It should not be surprising that Inhaling smoke directly to your lungs is bad. "
] |
[
"What happens to the reaction mass from a rocket firing (prograde) in orbit?"
] |
[
false
] |
Presumably, it loses enough velocity that it ends up on a suborbital trajectory. But what then? Does it dissipate into space? Does it stay in an elliptical orbit and threaten other spacecraft that might pass through it? Does it fall through the atmosphere and burn up? Does it fall through the atmosphere and burn up? Where does it go?
|
[
"If a rocket is burning in a low enough orbit then what you presumed is correct, the exhaust gas ends up in a suborbital trajectory. (An exception would probably be thrusters with a very high specific impulse, which means an exhaust speed much faster than escape speed, or rockets in very high orbits).",
"But when the gas falls back it doesn't burn up because it doesn't behave like a solid body. It is in an environment where atmospheric pressure is negligible, so it expands indefinitely. By the moment when it reaches the atmosphere it can be treated as a rarified gas, i.e. like a lot of separate molecules with no relation between them. Each of them will collide with another molecule in the atmosphere and the gases will mix - that's it. There might be some heating but it will be spread over a very large volume of air, therefore not a high temperature.",
"When a solid reenters the atmosphere it's different because it doesn't expand. All its molecules are forced to move together, compressing the air in a very small area, which in turn causes shockwaves and heating."
] |
[
"I think you're using prograde in the wrong sense. Burning prograde (towards the direction you're going) will increase your velocity. Burning retrograde (opposite prograde) will reduce your velocity. Orbit velocity differs at different altitudes. ",
"For an example, let's use the ISS. The ISS currently orbits between 417 and 426km. The lower number is your apapsis, and the higher number is your periapsis. If you burn prograde at your periapsis, you raise your apapsis, and burning long enough will switch them around, so you are no longer the highest point in your orbit. For the apapsis, the same concept applies. If you burn retrograde at an apsis, you lower the opposite apsis.",
"If you lower your apapsis low enough to where the trajectory intercepts the atmosphere, it can possibly hit things, but it would be very rare, as they are spaced apart by a huge distance. We currently try to place unusable objects into the Graveyard orbit if we can, but there will still be debris that can still hit it as it goes down. If the entry angle is not managed, the ship can rip apart as it enters the atmosphere (See ",
"The Columbia Disaster",
"). When entering the atmosphere, ",
"aerobraking",
" occurs, in which the ship will slow down to a significantly lower speed, and will stop almost all horizontal velocity (to where it is falling straight down). It goes where ever the trajectory takes it."
] |
[
"I'm curious about the spent reaction material though. If the ship is burning prograde, then it stands to reason that the reaction mass is being ejected on a retrograde vector at high velocity. The ap",
"apsis of the ship would increase, but the periapsis of the spent material should come down a long ways, especially considering the delta-v imparted by being blasted out the exhaust nozzle of a rocket engine.",
"(By the way, the apoapsis is the high point in the orbit, and the periapsis is the low point. You had that backwards in your comment.)"
] |
[
"How important is social interaction in our everyday mental health?"
] |
[
false
] | null |
[
"In social psychology we talk about a concept called the ",
". This is the desire to form and maintain close relationships with some other individuals and we call it a need because when we lack belongingness then we suffer more than just an unhappiness. People who are lonely in addition to mental health problems are often shown to have low cardiovascular output and high ",
"TPR",
" and have more physical health problems including higher risk of early death. ",
"Hawkley, L. C., Burleson, M. H., Berntson, G. G., & Cacioppo, J. T. (2003). Loneliness in everyday life: Cardiovascular activity, psychosocial context, and health behaviors. Journal Of Personality And Social Psychology, 85(1), 105-120. doi:10.1037/0022-3514.85.1.105",
"So it's not ",
" mental health that we're concerned with when talking about social isolation and rejection.",
"The effect of not belonging is linked to low self-esteem. ",
"Williams writes",
"...",
"Instead they self-ostracize, perhaps avoiding further rejection by pre-empting the possibility of acceptance. Furthermore they report a substantial rate of depression, suicidal ideation, suicide attempts, eating disorders, and short-term promiscuity. They feel little ability to change\ntheir situation, and have resigned\nthemselves to feeling unworthy of\nattention at all. Clearly, the repeated\nthemes emerging from these letters\nand interviews must be treated with ca\nution: there is no way to determine\ncause and effect. It is just as plausible that ostracism leads to depression\nas depression leads to ostracism. It is likely that both co-occur, resulting\nin a vicious cycle.",
"... as the long term effects of ostracism and rejection.",
"It's called a need to belong, and not a want. This quote from Warren Jones explains why - \"In two decades of studying loneliness, I have met many people who say they have no friends. I have never met anyone who honestly said to me they didn't want to have any friends.\""
] |
[
"The way to investigate this is to read up on the effects of social isolation ",
"http://www.livescience.com/18800-loneliness-health-problems.html"
] |
[
"not as important as an indivudual might think. this fights in to Maslow's Hierarchy of Needs where (in order of importance) it is, food and water, safety, love and belongingness, gaining the respect of others, self actualization. so in more simple terms, social interaction is more important to us (according to maslow) than graduating college or sharing the same hobbies as our parents, but if we dont feel safe or we are hungry, social interaction isnt as important to a human."
] |
[
"If a human body was cut in half by a long blade that is of 1 atom thickness, would he/she die shortly after?"
] |
[
false
] |
[deleted]
|
[
"Forcing atoms apart by 1 atom would cause cell death in the vast majority, or at least a signifigant number of the affected cells. The splitting of proteins, lipids, membranes, and nucleic acids by a single atom is still a substantial change, and these molecules would not spontaneously self-heal.",
"However, even given the assumption that each affected cell died, this would represent a tiny proportion of the cells that make up the body. The death of this number of cells would not in itself lead to death. ",
"I can see two ways in which such an incision or gap could lead to the death of the organism: 1) The disruption of a substantial amount of vascular tissue - ie blood vessels, while not necessarily causing hemorrhaging, may cause massive clotting leading to stroke, heart attack, or pulmonary embolism; 2) The simultaneous disruption of nervous function on such a large scale, especially within the brain, could cause seizure or other large-scale disruption of essential nervous function. I don't have nearly the knowledge of medical science to speculate on the probability of any of these results, but they I think are at the very least within the realm of possibility.",
"Which of the three axes was cut in half could also change the prognosis. I suspect a cut seperating the dorsal half from the ventral would be by far the most threatening of the three."
] |
[
"Forcing atoms apart by 1 atom would cause cell death in the vast majority, or at least a signifigant number of the affected cells. The splitting of proteins, lipids, membranes, and nucleic acids by a single atom is still a substantial change, and these molecules would not spontaneously self-heal.",
"However, even given the assumption that each affected cell died, this would represent a tiny proportion of the cells that make up the body. The death of this number of cells would not in itself lead to death. ",
"I can see two ways in which such an incision or gap could lead to the death of the organism: 1) The disruption of a substantial amount of vascular tissue - ie blood vessels, while not necessarily causing hemorrhaging, may cause massive clotting leading to stroke, heart attack, or pulmonary embolism; 2) The simultaneous disruption of nervous function on such a large scale, especially within the brain, could cause seizure or other large-scale disruption of essential nervous function. I don't have nearly the knowledge of medical science to speculate on the probability of any of these results, but they I think are at the very least within the realm of possibility.",
"Which of the three axes was cut in half could also change the prognosis. I suspect a cut seperating the dorsal half from the ventral would be by far the most threatening of the three."
] |
[
"I'm not so sure about this. Molecules larger than a single atom pass through cell membranes all the time without significant damage, so I don't think that cell membranes would be compromised; another lipid would just slide into its place. I think that the majority of the damage from the atom cutter would occur to like DNA, which would be cut in half in a very small number of cells. Proteins are abundant and would remain unaffected, those being cut in half would simply be recycled into amino acids by the cell. The odds of a single atom cutter actually hitting the nucleus of cells is low-- the nucleus is small and cells are not as densely packed in the body as you would imagine. Most of the space in the body is fluid filled or dominated by connective tissue. Cells also can repair double-stranded breaks in DNA, so even the cut cells may survive. In my opinion, neurons and blood vessels would remain unaffected because they most likely already have gaps in the tissues larger than 1 atom big. The crosslinked fibers that make up these structures certainly have gaps between them-- it's a mesh, not a sheet of metal or anything. ",
"All this said, I think that the individual would become very sick due to the need to repair some DNA, and synthesize and recycle tons protein. However, I don't believe it would cause death. Feel free to convince me that I'm wrong!"
] |
[
"We generally count in base 10, computers use base 2 and hexadecimal, is there some orderly relationship among the various constants of physics that suggests nature has a preferred \"base\"?"
] |
[
false
] |
Part of the motivation for this is the question "Are we living in a simulation?" If so, we might expect some indication of the physics engine's architecture to show up in our physics.
|
[
"No. The base used to represent a number is just an arbitrary choice. The number itself has its own meaning, independent of how you choose to represent it. If you'd like an imperfect analogy, it is like writing a word in one typeface or another; the choice of typeface does not change the word."
] |
[
"Base e has the lowest radix economy",
"Where \"radix economy\" is a term that the author of that Wikipedia article made up and which nobody takes seriously."
] |
[
"There is no interesting and useful property of numbers that depends on the number base. The base is just a way to write down numbers. It doesn't change the number in any way. ",
"Edit: Apparently many people don't like my blanket statement. The truth is these types of questions pop up on this sub fairly often because I think many non-experts think base representation is something fundamental or something that hinders our understanding of math or anything like that.",
"The answer to these questions is always the same: all of the important and useful properties of numbers have absolutely nothing to do with the base. The base is just a way to write down the number; it doesn't change the number in any way. So rationality, primality, being a power of 7, transcendentalness, etc. all have absolutely nothing to do with the base. ",
"Sure, you can come up with some property that depends on the base. For instance, an integer is even if and only if its base-2 reprentation ends in 0. But who cares? That's not really too important and if you're going to reference the base specifically in your property, then you're just cheating the intent of my blanket ststament that bases don't matter. Because they really don't when it comes to the myriad of questions similar to that of the OP. ",
"(Does base matter for some applications? I suppose it matters in how floating point arithmetic is performed. But, again, that's just so far from what OP is asking or what the myriad of similar questions ask. But I suppose part of one's expertise is knowing that stuff like floating point arithmetic is just irrelevant to the OP's question, and so I apologize for any confusion there.)"
] |
[
"Why Do We All Generally Agree On What Creatures Are Cute or Grotesque?"
] |
[
false
] |
[deleted]
|
[
"This might interest you.",
"TL;DR: Things that have large eyes and round, soft bodies are more likely to elicit the response because they remind us of our own babies and make us release certain hormones. Even inanimate objects can be seen as cute if they have the types of features we look for. It then becomes a learned response as we try to replicate the dopamine/oxytosin high.",
"Edit: But I think there is more variation in what people perceive as cute than you think. You might be using a confirmation bias just because there do seem to be a few that most people would agree on. However, I know of plenty of people (myself included) that find some very unconventional animals as cute. This most likely relates back to the \"conditioned cuteness\". Different life experiences cause people to have those chemical highs from different criteria."
] |
[
"There’s one group of animals not everyone agrees on: insects. Most people in advanced societies are repulsed by the idea of touching bugs, but in areas with low access to food, insects can be a delicacy, and they’re an excellent source of protein (grasshoppers are becoming more popular for consumption in the west). One theory is that insects were demonized by ancient civilizations during the infancy of agriculture. Their capacity the destroy crops might be interpreted as the wrath of deities."
] |
[
"There's a lot of spiders that ",
"a fair amount of westerner's find cute.",
" Mostly ones with big ole eyes. The depiction is also important. Most people find snails in real life to be gross, but animated ones like the ",
"den den mushi from One Piece",
" or snails from Spongebob like Gary can be found to be cute. Notably these snails also have large eyes."
] |
[
"Do we have any idea of how to make \"artificial gravity\"?"
] |
[
false
] |
[deleted]
|
[
"Any form of acceleration is indistinguishable from gravity. So a spinning ship causes an acceleration pointing \"inward\" (ie you don't keep traveling in a straight line, you keep getting pushed toward the center). There are some limits here as to how fast to rotate it and whatnot so as not to make people sick. If you were doing some sort of long distance trip under constant acceleration (a fairly tough trick to pull off I should say), then you could just define the floor to be the wall opposite the direction of travel. ",
"as for just \"creating\" a gravity field, that remains firmly entrenched in science fiction for now."
] |
[
"Any form of acceleration is ",
" indistinguishable from gravity. I make that nitpick only to observe that that nicely explains away the fact that spinning drums must be of a certain minimum size. Too small, and the \"locally\" part of \"locally indistinguishable\" is smaller than your ",
" Which is a problem."
] |
[
"Please, always feel free to nitpick away. I think I was referring to the nausea from rotating around too quickly, but I guess that would also fall under the jurisdiction of this local indistinguishability? (ie the acceleration on your inner ear doesn't exactly point toward the \"floor\" or something)"
] |
[
"If differences in human phenotypes such as skin colour, hair colour, etc. are due to clinal adaptation, what clines lead to the development of East-Asian slanted eyes?"
] |
[
false
] |
Since there is good evidence to suggest we radiated from Africa, I presume that primitive humans did not have slanted eyes, but I guess a possibility is that primitive humans did in fact have slanted eyes, and the change to non-slanted eyes is actually an adaptation. In either case, why/how did this happen? EDIT: Also, I'm running on the assumption that eye shape is a product of clinal adaptation, when it may very well not be. However, I would expect that it is based on the fact that we have many forms of slanted and non-slanted eyes as you move East-West, and this smooth variation is expected with clines.
|
[
"The explantation for epicanthus is that Central Asian steppes, the area where proto-Mongoloids origated, were very dusty with common dust storms and the epicanthus helped them to protect their vision. But it's also possible that it was a random mutation and an example of the founder effect.",
"Because epicanthus doesn't occur only in Mongoloid-descended populations, but also in some tribes in Africa, like the Sudanese Dinkas and some Bushmen. But the Malagasy people on Madagascar have it from Mongoloids, since the first settlers there were Austronesians who originally came from Taiwan."
] |
[
"http://www.nytimes.com/2013/02/15/science/studying-recent-human-evolution-at-the-genetic-level.html?_r=0",
"The gene that controls for it, also does for other asian physcal traits (teeth shape, less breast tissue etc...) Several of these would seem to reduce energy requirements as well.",
"Edit; misremembered article without rereading, added trait by acident which was not there, apologies"
] |
[
"The trait you are speaking of is called the ",
"Epicanthic fold",
" and the evolutionary basis for it is not well understood, but it is often attributed to acting as ",
"a sun visor protecting the eyes from overexposure to ultraviolet radiation or as a blanket insulating them from the cold.",
". "
] |
[
"Is there a mathematical object analogous to a matrix with more than two dimensions?"
] |
[
false
] |
I guess it would resemble a stack of matrices. What would such a thing be used for?
|
[
"A multidimensional array with rank (or order or degree) greater than 2. ",
"Tensors",
" are an example."
] |
[
"Tensors are actually a subset of what was asked about. In general any n-dimensional array would generalize a matrix; a tensor, however, is an object that ",
" In other words, a tensor is invariant under coordinate transformations. So if I have a (0,2) tensor, it would take two vectors and give me a number. If I rotate my coordinate system, the components of the vectors and tensor would change, but the action of the tensor on the vectors would remain the same. If the object didn't have these properties it could possibly still be represented as a matrix, but it would not be a tensor."
] |
[
"A tensor.",
"What you're referring to as \"dimension\" is actually called ",
".",
"The rank of a tensor describes how many indices you need to specify an element of the tensor.",
"A scalar is a rank 0 tensor.",
"A vector is a rank 1 tensor.",
"A matrix is a rank 2 tensor.",
"As far as I know, there are no names for tensors of higher rank, but you can have as many indices as you want."
] |
[
"Is there an exact number of atoms in the Universe?"
] |
[
false
] |
And if yes, then do we know roughly how many?
|
[
"That's by the way the number of atoms in the observable universe. The universe is much bigger than the observable universe, and evidence indicates that it's actually infinite. Unless the Copernican principle in really, really wrong, the density of the universe is approximately constant, so the number of atoms should be infinite too."
] |
[
"At any given time the number of atoms is changing. For instance, in stars you have four hydrogens becoming one helium.",
"However, you can assume that the vast majority of atoms are hydrogen, and use this to calculate approximately how many atoms are in the universe, and it's about 10",
" ."
] |
[
"evidence indicates that it's actually infinite.",
"I find that fascinating. I don't understand how it could have a beginning if it's infinite in size. Could you explain?"
] |
[
"Would it be possible to see the Earth in the sky from a different location millions of years ago?"
] |
[
false
] | null |
[
"But the stars don't stay in the same spot for all that time right? What we see now is the light of stars a million years ago, wouldn't they have moved since then? "
] |
[
"Fair enough. At some point in the distant future, is this scenario possible? "
] |
[
"Can you rephrase the question? What do you mean by seeing the Earth in the sky? ",
"I think you may be talking about going 1 million light years away and looking back at what the Earth looked like 1 million years ago. If you were 1 million light years away and had a telescope powerful enough to pick out the details on the surface of the Earth, then yes, you could see what the Earth looked like 1 million years prior. However, we can not look at the Earth 1 million years ago because we would first have to travel 1 million light years away. Because we can't travel faster than the speed of light, it would take us at least 1 million years to get there. Assuming we could instantly assemble our telescope, the earliest we could see the Earth is 1 million years before we arrived (ignoring any relativistic effects) which is the same time we left! So, we could at most see all the things that happend on Earth since we left. "
] |
[
"How are photons created/emitted?"
] |
[
false
] |
I know they're related to the electron, i'm just not sure how...
|
[
"I know this question doesn't make sense because of relativistic principles/Heisenberg, but if you could imagine watching an electron release a photon what would it look like? Or what would we imagine it to be visualized as? A radial propagation of an EM wave from the spherical electron?"
] |
[
"Specifically to do with electrons, it is when they transition from the conduction band to the valence band through a loss of energy (the energy difference between the bands known as the band gap). This energy loss can happen in a non-optical fashion, for example as a wave through a crystal lattice (phonons), or optically as a photon. ",
"The energy of the photon is exactly equal to the energy difference in the band gap. This is because a photon is just a packet of energy, with energy relating to wavelength by E=hc/wavelength where h and c are Planck's constant and the speed of light respectively. This is what causes the photon to appear in the electromagnetic spectrum, as its wavelength will correspond to a \"colour\". Approximately 2-3eV produces the spectrum of visible light, while lower energy transitions are the infrared, microwave and radio and higher energy transitions go into the ultraviolet, X-Ray and gamma regions.",
"Under normal circumstances these transitions will not occur as a molecule will tend to its most stable state, the one with all its electrons in their lowest possible energies (Pauli exclusion prevents them all having the ground state energy), so the electrons must be excited by some means. Heat is one way to excite an electron to a higher energy level but they can also be elevated with other incoming electrons being absorbed by the electron (this is how lasers work in part). However, due to the molecule wanting to be in its most stable state, the electron will decay quickly to a lower energy and must lose this energy, either as a photon or in some non-optical way."
] |
[
"Photons are emitted when there discrete changes in electric (or magnetic fields). The most common example is an electron moving from one energy level around an atom to a lower one."
] |
[
"What radio signals would travel into space?"
] |
[
false
] |
I am mainly asking if our radio signals from earth would theoretically be detectable from other places in space. Would our TV or internet signals leave earth?
|
[
"true but there is still a very low change for earth catching any other signal, it would be like trowing a single sand spec at another single sand spec yes there out there but them both hitting each other is not likely"
] |
[
"true but there is still a very low change for earth catching any other signal, it would be like trowing a single sand spec at another single sand spec yes there out there but them both hitting each other is not likely"
] |
[
"Following the laws of physics, any wave will travel as farther they can. So yeah, all waves we have produced, either it's radio waves, gamma rays or microwaves, all have travelled to space and will continue to do go farther. However, the intensity of the wave will decrease exponentially as it flees away from you.",
"The intensity of a wave is inversely proportional to the distance travelled from you squared. Also, it is directly proportional to the net power radiated by the wave. As you can see, the intensity of the wave will, of course, decrease drastically with the distance travelled."
] |
[
"if the earth is constantly rotating AND orbiting the sun then HOW is the north star always due north?"
] |
[
false
] | null |
[
"Technically, the north star (",
"Polaris",
") is not ",
" due north: it's current angle is about 0.5 degrees away from the true celestial north pole. If you take ",
"a long enough time lapse",
", you can see that over the course of the night Polaris does make a very small circle around true celestial north. But for rough navigational purposes it is close enough to say it is the \"north star\".",
"Because earth is spinning in space with no* friction, its axis of spin is roughly constant: always pointing in the same direction. So over the course of the year, ",
"the axis of spin always points in the same direction in space",
", even as Earth rotates around the sun. Since the stars are ",
" far away compared to Earth's orbital size, the change in position of the stars is negligible. To give you an idea of how small this change in angle is: the closest star (Proxima Centauri), is 4.243 light years away, or 268,000 times further away from us than the sun. This means over the course of the year, the position of even the closest star only changes by ",
"about 0.0004 degrees",
": completely imperceptible to human eyes. In fact, for all but the closest stars, this \"",
"parallax",
"\", or change in apparent position as the Earth revolves around the sun, is ",
"!",
"Now that I've said all that, I need to backtrack just a tiny bit to give you the whole picture. In an ideal world where the Earth was the only thing in the universe and just sat there spinning away, its rotational axis would never change, and north would always be the same direction. But there are external influences on the Earth: primarily gravitational effects from the moon, sun, and other planets. These effects cause Earth's rotational axis to \"",
"precess",
"\", or ",
"change in a circular pattern over time",
", exactly like a spinning top. Earth's main precession cycle takes about 26,000 years, and so \"north\" changes quite drastically over the course of thousands of years! Celestial north will be closest to Polaris (about 0.45 degrees separation) in the year 2100. However, in the time of the Ancient Greeks and Romans, ",
"Polaris wasn't even considered the \"north star\"",
": it was too far away!",
"I hope this answers your question, let me know if you have any follow-up."
] |
[
"Incredible answer. Thanks!"
] |
[
"Hi PaddyAtomic 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 ",
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", 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.",
" ",
" "
] |
[
"Can cement be liquified after setting?"
] |
[
false
] |
[deleted]
|
[
"Not through any approach that you would think of as common. As the cement component of concrete (which is cement plus aggregate materials) hardens, calcium silicate forms. The solubility of calcium silicate in almost every solvent is very poor, so you can't dissolve it again without a large amount of acid. Its melting point is also very high, so it's unlikely that you could heat it enough to melt it. You could grind the material back to a very fine powder and suspend it in water, but that wouldn't really be a liquid—just a suspension. (",
"Source",
")"
] |
[
"Is disposing of used/old concrete a problem then?"
] |
[
"Old concrete can be crushed and introduced as aggregate for subsequent concrete mixtures."
] |
[
"How is it that we can determine the size, velocity, distance, AND chemical makeup of distant stars?"
] |
[
false
] |
It seems like one would need to know at least one of these variables to derive the others, given that distant stars only show up as a point of light. I understand the concepts of red and blue shift, and I would think that it would complicate the determination of velocity and chemical makeup. i.e. Is the star red because it is highly metallic or it's moving away from us? Does the star appear big because it's close to us, or because it's big?
|
[
"And from the chemical make up of a star we can determine its age (or period of a star's life cycle) which gives information on size, temperature distribution and many other physical properties."
] |
[
"Red/Blue shift isn't used in determining star's makeup. Elements emit light in very narrow, specific spectral bands; so every chemical/compound has a distinct signature. Starlight can be analyzed for its wavelength makeup, based on that data scientist can then start assigning dominant species present. "
] |
[
"So for example, a young star would still have lots of hydrogen and not much heavy elements. An older star would have more heavier elements and less hydrogen. Luminosity tells us its size and with those two things, we can determine age. With all that we can determine how much red/blue shift there is that is making the colors off of what they would normally be."
] |
[
"In mathematics, is it ever possible to prove that you can't prove something?"
] |
[
false
] | null |
[
"In ",
"mathematical logic",
" such proofs are routine. Some examples:",
"Gentzen's consistency proof of Peano arithmetic",
"non-Euclidean geometries",
"Cantor's continuum hypothesis",
"Closely related to this there are also ",
" proofs, which can refer to two different kinds of thing:",
"Gödel's completeness theorem for first order logic",
"Tarski's proof of the completeness of elementary geometry",
"Gödel's very famous incompleteness theorems"
] |
[
"Not quite. The incompleteness theorem (a version of it) states that you cannot prove Con(T) from the theory T (under certain assumptions on T). This is an example of a proof that something is not proveable. ",
"There are many more examples: having the mild assumption that predicate logic is consistent, every false statement is proveably not proveable. ",
"Also, google \"independent formulas\""
] |
[
"There are. One is Gödel's incompletness theorem\n",
"http://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_theorems"
] |
[
"What do + and - mean when talking about the metric of spacetime?"
] |
[
false
] |
[deleted]
|
[
"As ReverendBizarre said, it's a convention to tell you whether you put a minus sign on the time coordinate (in the metric) and a plus sign on the spatial coordinates, or vice versa. Generally people working in relativity like -+++, and particle physicists like +---, because they're weird. I suppose it's because if you have -+++ then the metric becomes the usual Pythagorean theorem on constant-time surfaces (dt=0), so geometrically minded folks use that, but then particle physicists don't like it because your energies come out negative (since they're associated with time rather than space).",
"You need to specify which one you're working in, as it does affect your calculations, but anything you observe has to be independent of the signature, so it really is just a convention."
] |
[
"I really can't see a way to explain this in a non-mathy way without losing a lot of the meaning... so here goes some basic definitions with a follow up example. The + and - refer to the 'characteristics' of the four dimensions. The metric of spacetime is expressed as a scalar product of characteristic 1 (or 3 anti-isometrically as is common in field theories). This means at every point in spacetime, if we look at any two 4-dimensional vectors situated at that point, their scalar product (this is sort of like an inner product, except inner products can't be negative) expressed as <v, w> is real. If we demand it is symmetric, that is <v, w> = <w, v>, and not degenerate, which means there is no v such that <v,w> = 0 for all w, then we can show 2 things. First is that there exists an orthonormal basis, v_1, v_2, v_3 and v_4 such that |<v_i, v_j>| = 1 if i = j and 0 otherwise. Second is that the number of <v_i, v_i> = -1 is constant for all orthonormal bases. The number of vectors that have this negative characteristic is the characteristic of our scalar product. In particular, our metric obeys the symmetry and non-degeneracy at every point. Since the metric is smooth, the characteristic is constant throughout spacetime, since to transition to a different characteristic scalar product, we would need the metric to become degenerate at some point first.",
"Our spacetime has characteristic 1, and the corresponding negative dimension of any orthogonal basis is then the time dimension. This is why vectors with negative scalar product are called timelike and the others spacelike. To illustrate how the negativity affects things, first imagine a cylinder in normal 3D euclidean space, which is dimension 3 and characteristic 0, since the dot product is as usual (and this defines the metric of euclidean space). If we take a 2 dimensional slice through it at an angle, notice it creates an ellipse. As we angle the plane more and more, the ellipse becomes longer and longer. Notice the 2 dimensional plane is defined by 2 orthonormal vectors. Now suppose we did the same thing in spacetime, except we took 3 orthonormal spacelike vectors, so the 4th one is timelike. These 3 vectors define our space of simultaneity. If we had a circle standing still in our space, this corresponds to a cylinder in spacetime (the circle is constant along the time dimension). If we then change our velocity relative to the circle, we are basically changing our space of simultaneity to be at a greater and greater angle, which corresponds to a more and more angled slice of the cylinder. But because our time dimension is negative, instead of the circle becoming longer, it shrinks along the direction of our motion. This precisely corresponds to what one observes as length contraction.",
"e: typo, inner products are generally regarded to be positive-definite"
] |
[
"That's usually called the signature, sometimes written as (-+++) or (+---). What this means is that the line element of the spacetime is written as (let's use flat space as an example),",
"ds",
" = -dt",
" + dx",
" + dy",
" + dz",
"or",
"ds",
" = dt",
" - dx",
" - dy",
" - dz",
"This difference in sign on the time and space parts of the metric makes the geometry of the spacetime Lorentzian rather than Euclidian.",
"Both (-+++) and (+---) are equivalent.",
"The line element, ds",
" is used to measure distances in the spacetime."
] |
[
"Is there actual evidence that essential oils such as rosemary acts as insect repellants?"
] |
[
false
] |
I'm concerned about household pests, namely bedbugs, and I'm looking for cost-effective preventative methods. I've found anecdotal references to essential oils like rosemary, lavender, and peppermint being used to repel insects. Is there evidence that these are actually effective?
|
[
"A line of marching pharoh ants will absolutely turn and run from lavender oil. I see it every time summer rain drives them inside my front door. But the concentration of lavender oil vapor that works would be hard for a human to tolerate, and expensive. You can't bomb your whole house with enough lavender to work.",
"I don't know anything about bedbugs, but they will probably approach an essential oil they find irritating rather than starve to death.",
"Look into diatomaceous earth. It is sharp on a microscale, so it damages insect exoskeletons, but mostly harmless to humans. (It dries the skin, and you don't want to inhale much either) It is approved as an additive to stored grain, including organic grain, and can be used on organic crops as well.",
"Diatomaceous earth only kills with direct contact, and it works best on soft bodied insects. It is reasonably effective on adult fleas, but it works like a neutron bomb on the squishy larvae."
] |
[
"http://www.animal-fences.com/downloads/COMPARATIVE%20EFFICACY%20OF%20INSECT%20REPELLENTS%20AGAINST%20MOSQUITO%20BITES.PDF"
] |
[
"I actually did a small research project on this in Rutgers University's Department of Entomology -- \"The Essential Oils of Plants as Mosquito Toxicants\". Well, it's not terribly relevant to repellents, but I can confirm that ",
" essential oils non-trivially kill second enstar mosquito larvae (while others, like sage and rosemary, do not)."
] |
[
"How do we know that all of the continents were once all connected?"
] |
[
false
] |
[deleted]
|
[
"Lots and lots of corroborating evidence. Palaeomagnetism and oceanic crustal dating are two of the most important.",
"When some rocks form they preserve a record of the magnetic field present at the time. THis can happen in igneous rocks, as iron-rich mineral crystals grow in allignment, or even sedimentary rocks deposited in low energy environments where iron-rich mineral crystals deposit in allignment. Because the magnetic field is 3D, this allows us to understand not only which way was North, but also what latitude the rock was at. So by dating these rocks (and doing it for lots of different aged rocks on each continent) we can understand how the continents rotated and migrated through time. Do a google search for polar wader curves for more information on this.",
"Furthermore, because the ocean basins are formed at mid ocean ridges, we can date the different sections of the ocean floor and understand how fast they grew, and how (for example, the atlantic ocean has no subduction zones along its margins, and we know it started opening in the South before 'unzipping' toward the North).",
"This information is further supported by stratigraphy which matches up across continents (for example volcanic sequences in North America which tie up geochemically as being identical to stuff in Northern Europe), and palaeontological evidence (e.g. fossil species found in South America and Africa but nowhere else).",
"The shape of the previous supercontinent is really quite well understood. The further back in time we go, the poorer the record becomes, but we know the supercontinent cycle has occurred several times. ",
"http://en.wikipedia.org/wiki/Supercontinent_cycle"
] |
[
"Rock samples from the edge of each continent match up with each other. ",
"Edit: Plants, soil, etc. Anything else of merit you can think of too, but rocks are the most obvious and intact evidence."
] |
[
"There are multiple proofs for that. As far as I know, the main point is certain fossils, which were found on two different continents far away from the other. These fossils 1. couldn't just fly over that huge distance and 2. were that similar, it was nearly impossible for them to have developped by their own.",
"In addition to that, there are a lot of geological proofs, like certain minerals which are totally identical to such on another continent. Also different kinds of glacial marks from glaciers of other continents show that these once was one only continent."
] |
[
"Why does nicotine take away hunger momentarily, but when the effect stops the sense of hunger is even stronger?"
] |
[
false
] | null |
[
"Hi kemmuli 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.",
" ",
" "
] |
[
"Chemistry"
] |
[
"'Chemistry'"
] |
[
"What is the origin of Ebola?"
] |
[
false
] | null |
[
"Likely transfer from fruit bats in or around the Kitum Cave region in then-Zaire (which gives its name to the most dangerous case-death strain) and modern Congo/Gabon. High monkey populations around this area function as a reservoir for Ebola Zaire."
] |
[
"Ebola (or ebola hemorrhagic fever) is a zoonotic viral disease which has resurfaced multiple times in separate \"spillover\" events from its animal reservoir species, which likely includes bats and nonhuman primates. There's more than one ebolavirus, and multiple strains have been implicated in outbreaks, with the Zaire ebolavirus thus far being the most deadly.",
"Even though ebola can be transmitted from one human to another, humans are not a reservoir species for ebolavirus due to the fact that it a) does not remain indefinitely latent in the human body b) is relatively hard to transmit in that it requires direct physical exposure to infected material and c) it is very frequently fatal. This is why outbreaks have been relatively sporadic with no global spread."
] |
[
"More terrifying. Ebola Zaire had a 90% case fatality rate when discovered."
] |
[
"How do \"veins\" of precious metals occur?"
] |
[
false
] |
Since elements like gold, silver, etc. cannot be formed within the planet, whatever is in the planet has existed since the planet's formation, plus the occasional meteorite. While densities would surely come into play during planetary formation, it seems that those elements would be fairly evenly distributed throughout the planet. However, they are (to my understanding) often found concentrated in certain areas or in "veins" running through said areas. What accounts for the concentrations/distributions of heavy metals on Earth?
|
[
"Not an economic geologist but I have a geological background, so I'll welcome any corrections by a real expert. Veins of metals, ore minerals, or even plain quartz and mica can form by hydrothermal deposition in an already-existing crack. ",
"This means that you have some mineral source--a magma body, say--with hot water flowing around it. Some elements \"want\" to escape the magma more than others because of their chemical properties. These are preferentially drawn into the hot water and carried away from the magma. Hot water flows through cracks, cooling as it flows away from the magma. As it cools, it becomes supersaturated and deposits minerals along the crack walls. ",
"Because the chemistry of interactions between water and those elements is so different from the normal behavior of those elements in a silicate melt (magma), a very different set of minerals gets deposited in those veins. There is some overlap--quartz and micas are common in veins, for example--but you'd be hard-pressed to find much pyrite, chalcopyrite, galena, or gold (to name a few) in a typical body of igneous rock. Similarly, you probably won't find much pyroxene (for example) in a vein.",
"So, ultimately, it's because gold tends to get pulled out of magma (where it's very spread out) by hot water, and as the hot water cools, it deposits it along the crack walls (thereby concentrating it)."
] |
[
"Finite. Atoms of heavy elements (including gold, silver, platinum, and all other precious metals) are created by nuclear fusion in the hearts of dying stars. (Traditionally this meant supernovae, but more recent studies suggest ",
"colliding neutron stars",
" are to blame.) When the interstellar dust cloud surrounding our newborn Sun condensed into planets, that stardust included those heavy elements. Barring random asteroid impacts, the Earth has all the gold and silver it ever will have.",
"However, even though you can't create gold with chemistry, and no chemical reaction can change one element into another, precious metals can be ",
"synthesized in nuclear reactors",
" or harvested as byproducts of certain nuclear fuels, but that tends to be uneconomical."
] |
[
"I wonder; do you know if these precious metals are finite? Or can they be chemically created?"
] |
[
"How can a whole galaxy form within the first 600 million years of the universe?"
] |
[
false
] |
This is in response to a recent link today on . This galaxy is thought to have formed within the first few hundred million years from the big bang. A question I've always had regarding this is - how can a whole galaxy form in such a short time. We may not, at first, think of 600 million years as a short time span, but in the realm of galaxies, that is not long at all. It takes our solar system roughly in our own galaxy... galaxies need to coalesce from matter, and matter can only travel at significantly less than the speed of light, so it takes a great deal of time for galaxies to move. For instance, the are a pair of galaxies in the midst of a 1.2 billion year collision. They started approaching each other about 1.2 billion years ago, and about 600 million years ago they passed through each other. Seriously, it took them more than a billion years to just bump into each other - . Is it just me, or does the theory of early galactic formation seem a little rushed to you? Are there answers, or is this just something we take for granted so we can fit it into the big bang model?
|
[
"A question I've always had regarding this is - how can a whole galaxy form in such a short time.",
"The answer is that 600 million years is more than enough time to spontaneously concentrate mass, trigger thermonuclear fusion in individual stars and create spiral formations out of those stars.",
"The fact that it might require more time than this to collide two galaxies, isn't by itself an argument against the formation of a galaxy in the same time frame."
] |
[
"One explanation is that the mass density in the early universe was such that the time scale for galaxy formation was radically different.",
"Remember that, for spacetime to have the flatness it appears to, the cosmological expansion rate would have to stay at or near escape velocity, which implies a much greater mass density at 0.6 BY than 13.7 BY.",
"Obviously with a greater mass density, there are more mass interactions and higher gravitational forces than at present.",
"I discuss these issues in depth in ",
"this article",
"."
] |
[
"As ",
" said, rotations and collisions have nothing to do with it. You could just as easily say \"our galaxy hasn't even rotated 60 times since it supposedly formed, so there's no way it can be 13 billion years old\". The two aren't related. Also, one would hope that the currently held theory of early galaxy formation would be a good descriptor of \"how this all can happen in such a short time span\". If not, well, it's not a very good theory.",
"That being said, your question is still a good one. There's a ",
"Wikipedia article on galaxy formation and evolution",
", but hopefully one of the astronomy/cosmology panelists will chime in and provide more details and answer follow-up questions. I'm interested to learn more myself."
] |
[
"If a venomous snake bites it's self is it immune to its own venom?"
] |
[
false
] | null |
[
"It varies snake to snake but is ",
"not definite",
". The venom needs to enter the bloodstream to be effective. Snakes that fight within their species tend not to bite each other so there isn't much pressure to develop protection against their own venom. There are snakes that are immune to the effects of other snake venom that they hunt."
] |
[
"I'm sure this came of question from the .gif of a snake head biting it's dismembered body.",
"Someone mentioned difference of injection versus ingestion. Ingestion wouldn't cause any complications unless it had a wound inside itself for it to enter the bloodstream.",
"Also I think someone said snakes tend to \"accidently\" bite themselves during an attack of a prey, don't remember if they said they're unaffected by it due to the need to inject venom or not."
] |
[
"But doesnt any ingested food eneter the bloodstream anyway after it is broken down? Why would the venom not enter the bloodstream like normal food molecules?"
] |
[
"What is the ticking that you hear after a car has been turned off?"
] |
[
false
] | null |
[
"Nope, look up Antimony cooling instead. There seem to be very few videos of the phenomenon, but even the wiki page states that Antimony makes more pronounced versions of that sound."
] |
[
"Additionally, different alloys will shrink at different rates as they cool. If they're bolted together you'll get that ticking sound. "
] |
[
"Additionally, different alloys will shrink at different rates as they cool. If they're bolted together you'll get that ticking sound. "
] |
[
"Can anyone simply explain the mechanisms that protect the small intestine from the digestive juices released by the biliary system and pancreas?"
] |
[
false
] |
[deleted]
|
[
"I will assume that you are talking about the acidic chyme that comes out of the stomach after its digested all of the food. In this case there is a small tube that is between the stomach and the actual beginning of the intestine, it is called the duodenum. When the chyme (The mixture of the acid, food and the other digestive enzymes from the stomach) enter this tube, the pancreas releases NaCO3, this is basically baking soda and is a base so it neutralises the chyme to a PH of about 8. From here it is safe for it to enter the small intestine where the nutrients will be absorbed into the bloodstream. Here's a visual: ",
"https://sites.google.com/site/isami16/22_13Duodenum_L.jpg"
] |
[
"Ok but thats the mechanism that neutralizes the acidic mix coming out of the stomach. You asked specifically about protection from the digestive substances from the pancreas and biliary tract... "
] |
[
"Ok but thats the mechanism that neutralizes the acidic mix coming out of the stomach. You asked specifically about protection from the digestive substances from the pancreas and biliary tract... "
] |
[
"Why is gravitational force so weak?"
] |
[
false
] | null |
[
"This is a difficult question to answer. I assume you're referring to the fact that gravity is the weakest of the four fundamental forces. Is your question why it is weakest? If that's your question the answer is basically \"because it is.\" One of the forces had to be the weakest and it happens to be gravity.",
"If your question is \"why is it referred to as weak, when it seems so strong.\" The answer to that is more fun. You're probably sitting in a chair right now. You're held to the chair by gravity, but the electromagnetic forces of the bonds in the chair (and your butt) keep you from falling through the chair. So yes, gravity is the weakest, and that weakness allows objects to be stacked, and for your butt to stay above the chair seat. Here's some more info on the fundamental forces:",
"https://en.wikipedia.org/wiki/Fundamental_interaction",
"Perhaps you can clarify your question? Or the motives for your question?"
] |
[
"The fact that gravity is weakest of all the four forces is the statement of the gravitational coupling constant in the 4 dimensions that we perceive, G_4, being much much smaller than the coupling constants of other forces. This discrepancy is usually termed as hierarchy problem in physics.",
"There are multiple proposed solutions to the issue. One such solution can be argued from the point of view of any theory that allows higher dimension such as string theory.",
"The gravitational constant is inversely proportional to the planck mass and it can be showed that the relation between the planck mass in 4 dimensions, M is related to the Planck mass in higher(4+d) dimensions, Mh as ",
"M",
" ~ Mh",
" l",
"where l is the size of the extra dimensions which are much smaller than the 4 dimensions which we can observe.",
"One can adjust the parameters l and d in such a fashion that the Mh is actually very small or in other words, the gravity in the full 4+d dimension is strong and comparable to other forces. One way to interpret the above equation is that the gravitational force loses its strength as it seeps through the extra dimensions."
] |
[
"As Victor Stenger points out, the gravitational force is no weaker than the electrostatic force. That is, 1 N of gravity is just as strong as 1 N of coulomb force.",
"Anyone reading this post probably knows that in the particular example of an electron and a proton spaced a certain distance apart, the gravitational force is ",
" (intentionally avoiding the phrase ",
") the electrostatic force between them, but the relative strength of the two forces has to do with the properties of the electron and proton, not the properties of forces between them, ",
". If particle physicists were to discover a particle whose mass to charge ratio were sqrt(",
"/",
"), then their attractive gravitational force and repulsive electrostatic force would be the same strength at any distance.",
"Edit: oops."
] |
[
"Why can we freeze embryos for IVF but not adult humans? What makes it possible for embryos?"
] |
[
false
] | null |
[
"Hello! Not an expert in freezing and thawing live specimen but well practiced in freezing and thawing dead specimen while keeping organs and microstructures intact. The major concern with freezing biological matter is the formation of ice crystals. Water forms crystals and expands when frozen and can result in burst cells and organelles. To avoid this, we introduce cryoprotectants. These are basically antifreeze that diffuse into the cells and around it to avoid formation of crystals. It's very easy to diffuse these new compounds into microscopic specimen because the surface area to volume ratio is very high compared to humans. Very rapid freezing with liquid nitrogen, also known as flash freezing, also helps in avoiding formation of large crystals (slow freezing means more time for the molecules to align). So the simple answer is size. We can't introduce cryoprotectants into every part of a human being fast enough nor can we flash freeze a human body fast enough."
] |
[
"Speed and perfusion. Big problems both during freezing and thawing:",
", water is the enemy. It expands and forms crystals as it freezes, which together rupture cell membranes and effectively ravage tissues. If you just drop someone into a cryonic vat as-is, the brick of icy cellular mush you get will be far too damaged to ever be viable again. If you're familiar with freezer-burned meat, imagine that happening to everything in your body, including your heart and brain. Not pretty.",
"The workaround for that is antifreeze. Yes, seriously. Get all the water out of a person that you can and replace it with something that won't crystallize and thaws early enough to allow replacement during resuscitation. But that's where speed and perfusion are nightmares: every minute you're waiting to freeze someone while you replace water is a minute that tissues are dying from anoxia. This is the worst with the brain: it dies really, really fast without oxygen and yet the blood-brain barrier makes it one of the hardest places to achieve non-water perfusion with.",
"That said, there have been advancements with this where cooling the body to ",
" freezing to slow neuronal cellular death combined with better antifreezes and techniques might get us close to reaching \"frozen\" with something that's still viable. A rabbit brain was successfully frozen and thawed using some of these -- though, notably, not yet ",
": ",
"https://www.newscientist.com/article/2077140-mammal-brain-frozen-and-thawed-out-perfectly-for-first-time/",
"So we might be kinda-sorta close to getting cryonically frozen humans that are damaged lightly enough bring back. Very doubtful anyone frozen today is, but we might be there within a few decades.",
" is even harder, though. Even in the best-case scenario, you have a bunch of critically oxygen-starved tissue frozen; every ",
" of anoxia counts once things unfreeze, and the brain in particular really needs to go from frozen to \"warm and oxygen-perfused\" very, very quickly. Human brains are really dense and, as mentioned, really hard to permeate -- we don't currently have much of any clue about how we'd warm a brain out of cryonic suspension enough to restore blood and oxygen without having orders of magnitude more anoxic duration than those brains can take. Exotic ideas abound about blood replacements that can achieve oxygen transport while still perfusing a very cold brain, but it's all total conjecture at this point.",
"And that aside, the dance when you restart everything ",
" in the body is hard, too. You need to swap all of the liquid in the entirety of very complex human vasculature -- including at least ",
" of what exists intercellular media and the like -- and restore circulation with oxygen very, very quickly and very, very consistently. Simplifying a bit, but if you hand reaches 1C while your arm is still -2C, you're going to have a bunch of things in your hand die while your arm is waiting.",
"We don't have any real line of sight on how to achieve this super-fast, super-consistent, super-precise reoxygenation of a big, complex organism with all of the systemic coordination that's necessary. There's nothing to say it shouldn't be achievable someday, but let's just say we have no reason to believe it'll come sooner than commercial fusion.",
" Because they're small and easy to perfuse! You can get all of the damaging water out of embryonic structures and flash freeze it way before the lighter anoxic time constraints kick in, and it's not (comparatively) hard to warm and reoxygenate them quickly and consistently enough to have them in a good, healthy state years and years later. Smaller organisms -- especially ones that evolved resilient structures -- can already be revived that way, too: tardigrades and other similar animals have been thawed after tens of thousands of years: ",
"https://www.smithsonianmag.com/smart-news/scientists-revive-tiny-animals-spent-24000-years-ice-180977928/"
] |
[
"There are multiple types cryoprotectants and while they are generally supposed to be non-toxic it is only to a certain extent of concentration and exposure time. Extended exposure will interfere with daily bodily functions and metabolism. So unfortunately impossible to walk around with it indefinitely. The wolverine question is interesting because some animals have evolved to have cryoprotectants for living in the arctic or surviving winters! I don't know of any mammal that can do it but I know of at least 1 frog and 1 fish species. Info may not be updated but last I checked both are being studied to study how to preserve human organs!"
] |
[
"High Tides vs Low Tides"
] |
[
false
] |
I am going on a trip to the Gulf of Mexico sometime in August and to prepare properly I need to know what the pros and cons of high tides and low tides are.. I have already looked up a but of course I am having trouble understanding it. To my understanding if I go to the beach during low tides, there will be more 'stuff' on the beach since the water is further out like seaweed, shells, things like that. But if I go during high tides then the water will be more chaotic and harder to swim in, is this correct? Sorry if I have posted in the wrong subreddit, but I am truely having trouble finding answers to this. All google gives me is Bob Marley lyrics. Thanks in advance!
|
[
"Should I take it this is your first time at the sea side?",
"High and low tides will have different behaviours at different places, depending on the seafloor topography and coastline shape at that point. There's no golden rule.",
"All that chart is telling you is what level the tide is at at any given time of a particular day. ",
"My advice? Go to the beach. While it's useful information to know (",
"particularly in some places",
"), don't get too caught up in it."
] |
[
"Indeed this is my first time, I guess I will just go and have a good time. I was just trying to get the most out of my vacation. Thanks for replying!"
] |
[
"If it's a rocky beach below a cliff, you don't want to be there when the waves are crashing into the rocks/cliff. If there's sand as far as the eye can see (the most likely case for the gulf of mexico), you don't have to worry about it except riptides and things.",
"Low tide can be lovely and super cool to explore."
] |
[
"Realistically, When will we run out of oil?"
] |
[
false
] | null |
[
"Never. As oil gets rarer and harder to extract, it will get more expensive until almost nobody uses it anymore, but we won't ever run out."
] |
[
"basically this. A lot of the reservoirs that are deemed 'dry' and have stopped production, can have as much at 50% of the petroleum left, it just became much more costly to extract it. There's a really good business opportunity for an engineer somewhere. ",
"We are also working on getting new, unconventional resources such as more offshore material, tarsands (a terrible option), tight gas, and shale gas (also a terrible option due to the hydrofracking). So we will technically never run out of oil, we'll just run out of easy oil. "
] |
[
"We won't, technically. What'll happen is that as scarcity increases, the price will rise, and eventually it'll be priced out of range of practicality. We'll never actually squeeze the last drop of oil out of the planet.",
"Predicting a date for that \"practicality\" point is pretty much impossible, as new developments in extraction technology make the picture awfully blurry."
] |
[
"Why do some animals eat their own young?"
] |
[
false
] |
Seems counter-intuitive from an evolutionary perspective, yet several species will eat their own young, or the young of other parents (which I can understand slightly more -- trying to protect THEIR specific genes rather than the species as a whole). Either way though, I find it hard to understand why an animal would evolve with this characteristic. It seems to harm their chances of continuing the species in any context.
|
[
"There several scenarios, most having to do with bet-hedging and resources allocation, consider the following:",
"Female mice will reabsorb their embryos when the dominant male has been replaced. This is believed to be aimed at limiting female investment in offspring which will be destroyed at birth by the new dominant male. It will also maximise the speed at which the female is available for re-impregnation by the boss-mouse. A similar process is noted in lions, but the young are put down at birth or soon after."
] |
[
"Wonderful response, thank you :)",
"Edit - Very interesting question as I have asked this myself in the past. It's almost an accepted view of cannibalism. I assume it's natural selection taking effect in it's unusual ways. The weaker mouse's DNA is literally eaten alive whilst the new stronger dominant mouse spreads his own."
] |
[
"Yep - while putting those resources unto constructive use. It is highly adaptive behavior."
] |
[
"What do physicists mean when they say \"information\"?"
] |
[
false
] |
My physics professor was once telling us in passing (was not the subject of the lecture) about the holographic principle, where the amount of information that a black hole can consume is dependent on the surface area of the black hole rather than the volume. He never said matter or anything like that and I felt like since everyone else seemed to get it I didn't want to sound like an idiot by asking what he meant by information.
|
[
"The holographic principle itself is something more general, but what your professor was talking about is a closely related concept called the ",
"Bekenstein entropy bound",
". This is the idea that the entropy in a certain region of space is limited to a certain value, which you can calculate using the size of the region and the amount of energy in the region. And the entropy of a system is the logarithm of the number of possible independent quantum states the system can be in, given its energy content, times a constant. Information is defined as the same thing, with a different constant.",
"General relativity tells us that a region of space can only hold a certain amount of energy (at which point it is a black hole), and given that maximum amount of energy, you can use the Bekenstein bound to compute an absolute maximum amount of entropy (or information) that can exist within the region. You could think of this as the \"worst-case\" maximum amount of information needed to specify the quantum state of the region.",
"Information itself is a lot like information in the classical sense; it's a number of bits. For example, if you have some system that can be in 1000 different states, that represents just under 10 bits of information, because with 10 binary digits you can make 1024 different binary labels, enough to assign one to each state and have a few left over."
] |
[
"The guy you're thinking of is ",
"Claude Shannon",
". But this doesn't answer OP's question. I will leave it to an actual physicist to talk about the information content of black holes."
] |
[
"These bits have on and off, occurance and non occurrance, conformations that flip depending whatever the thing is.",
"Quantum bits have more than just on and off -- they can take any linear superposition of on and off. So for example they can be (loosely speaking) half on and half off, or one quarter on and three quarters off. That is what makes them a quantum bit, as opposed to a classical bit, which can ",
" be either on or off."
] |
[
"How do stains work on the molecular level?"
] |
[
false
] |
How are the particles that become stuck on clothing so difficult to remove? And as a follow up question, how do stain removers work?
|
[
"I can tell you how bleach works on some types of stains. So some Compounds have color because of the molecule is a conjugated system. Meaning that more than 8 groups of alternating double then single bonds in a row all share electrons. When light hits this conjugated system it absorbs then releases energy that we see in the visible spectrum. Bleach comes in and breaks double bond(s) in this system making them single bonds. This breaks the conjugated system up either completely or into smaller conjugated systems. So for example, where you had 8 groups of alternating double then single bonds you now have 2 conjugated systems of 4 groups which emit light in the ultraviolet spectrum and it’s not visible, BUT the stain is still there, you just can’t see it.\nI suspect the stains are hard to remove because intermolecular forces between the stain maker to the fabric. "
] |
[
"So my washed clothes are still dirty? "
] |
[
"It's a matter of what the stain likes more: water or cloth? Stains usually are made up by fatty molecules (oils, fats, etc) that don't mix up with water (think oil and water, they don't mix together and form an emulsion). This means the stain likes to stick on cloth, rather than getting dissolved into water...unless you help the stain in the trip! And to help the stain, you need surfactants! (",
"https://en.wikipedia.org/wiki/Surfactant",
")",
"\nSurfactants are molecules made by up a \"fatty\" lipophilic part, and a \"watery\" hydrophilic part: these molecules bind the fatty part in the stain, then when you rinse the cloth with water the watery part brings them from the cloth to the water side. Easy isn't it?",
"\nDisclaimer: I hold a master's degree in chemistry. Not exactly surfactant chemistry, but I got to study the subject."
] |
[
"If one were able to stand on a planet the size of Jupiter, what would the horizon look like?"
] |
[
false
] |
I've been asking myself this today and I can't quite visualize it. On Earth, the curvature of the horizon is always less than five miles distant on the surface, but Jupiter is many times larger.
|
[
"This can be calculated with some geometry. The equation is that ",
"distance=sqrt(height(height+2Radius)).",
"The answer to this for jupiter is about 16.7 km. It would look ",
" flat to you. It would also seem to take up a little bit more of your field of view because your angle to the horizon would be a little bit less. "
] |
[
"Why would it ever look like a bowl?"
] |
[
"Sort of like standing in a bowl, then. That would be a really weird optical illusion."
] |
[
"Why can we determine the lifetime of short-living particles up to femtoseconds and less, but for the neutron we are unsure on the order of seconds?"
] |
[
false
] |
I just read , and in the last paragraph it says And the team is already designing its next-generation experiment, which aims to nail the neutron lifetime within 0.3 seconds. Compared to the lifetime of the Higgs, which is on the order of 10e-22s, this is a pretty large error. How come there is such a huge difference? Do our measurements scale like that? Or is it something like when measuring something like the length of a car we make a bigger error than when doing scattering experiments with nuclear particles?
|
[
"The way that you measure the lifetime of the neutron and of extremely short-lived particles like the Higgs is totally different. There are different systematic uncertainties involved.",
"You don't directly measure lifetimes of things that live for 10",
" seconds; instead you look for resonances in scattering or reaction cross sections. The resonance will show up at an invariant mass corresponding to the mass of the particle you're looking for, and the resonance will have some energy width (full width at half maximum). The time-energy uncertainty principle says that the resonance width is inversely proportional to the mean lifetime of the particle.",
"So if you identify some exotic particle as a resonance in your spectrum, you can extract its mass and lifetime from the position and shape of the \"bump\" you see."
] |
[
"The intrinsic linewidth of something that lives for 10 minutes is on the order of 10",
" eV, which is far below the energy resolution of any experiment. These kind of indirect measurements are really only amenable to things with very short lifetimes. Direct measurements of the lifetime are preferred when possible, but for something that lives for 10",
" seconds, direct measurements are not feasible."
] |
[
"That makes a lot of sense, thank you. In the article, they talk about a \"bottle\" method, where you put a certain amount of neutrons into some kind of container, wait some time, and then look how much neutrons are left. The other method is detecting the protons the neutrons are decaying into. Using the principle you just described, would it be possible to establish a third method for measuring the neutron lifetime, or are these kinds of measurements only suited for those very short lived particles?"
] |
[
"Is there an instance in recorded history of an infection going from first outbreak to an endemic disease?"
] |
[
false
] |
If so, when did people decide to just give up on containing it?
|
[
"People do, but they don't really understand what's happened since the media stopped reporting on it at some point.",
"I consider myself pretty science literate, but I wasn't sure off the top of my head what ultimately ended up happening with H1N1. When I read your response I realized I personally have no idea if it died out, was contained, or spread throughout the population.",
"I checked Wikipedia ",
"here",
" and the Wikipedia article really doesn't provide any update on what's happened since then.",
"The top Google result for h1n1 is ",
"this CDC page",
" which ends by saying \"On August 10, 2010, WHO declared an end to the global 2009 H1N1 influenza pandemic. However, (H1N1)pdm09 virus continues to circulate as a seasonal flu virus, and cause illness, hospitalization, and deaths worldwide every year.\"",
"So I guess it's still going strong, but it's sort of blended into all the other things we call \"the flu,\" and the government doesn't describe it with the word \"pandemic\" any more.",
"I think, unless you work in the medical field, you're likely to assume that H1N1 died out or was fully contained. People think \"few cases = huge story\" implies \"affects whole population = becomes main topic of the 24 hour news cycle.\" When reporters aren't shoving it in people's faces, they just stop paying attention to these events.",
"Security expert Bruce Schneier says people shouldn't be afraid of anything that's in the news. You should be a lot more worried about dying in a car accident than a mass shooting. Inversely to what the relative news coverage response to those two kinds of events suggests."
] |
[
"“",
"” ",
"It’s only been in the last 20-30 years or so that “containing it” became an actual option. Before that, surveillance was not advanced enough to identify a disease before it was widespread. ",
"Compare HIV in the 1980s to SARS in 2003. HIV was already globally widespread before it was recognized as a syndrome, let alone before the virus was identified. SARS was recognized early enough that containment was actually possible (though just barely; I don’t think people appreciate just how close that was to causing a pandemic). ",
"Legionnaires’ Disease, identified in 1976 might be a partial counterexample, though it is at best only partially contained - it still causes thousands of cases each year but with a known cause it is limited and preventable.",
"Even in 2009/10, the H1N1 pandemic originating in Mexico circulated undetected long enough and widely enough that containment wasn’t effective, in spite of extensive attempts (not quite as extensive as the current travel restrictions on COVID 19, but at least part of that was because it was more obviously futile earlier). ",
"Before HIV, disease spread and pandemics were mostly things that people recognized after the fact, when it was in the peak of disease spread. For example, the 1968 H3N2 influenza pandemic, which killed about a million people in a year, was recognized relatively early but long after it had spread internationally. (It became endemic and is now a seasonal influenza virus.)",
"Or for milder diseases, they might be recognized only long after the fact. We know, for example, that all four human coronaviruses that are now endemic all originated as bat coronaviruses that jumped into humans in the past 100 or so years. As far as I know, we have no record of the actual disease they caused, even though presumably they were causing a mild but distinct pandemic when they did so. ",
"So if we think about diseases that have been recognized early enough to think abut containment, we have (off the top of my head)",
"Probably a bunch more that I am forgetting. ",
"But that’s the point. Look at these global outbreaks of potential pandemics that have all occurred in the ",
", that no one remembers. Why do people have to ask about them on Reddit? Why aren’t they daily topics of conversation? Why aren’t people demanding more and better public health and surveillance to identify them? Why do people tolerate cuts to the CDC budget? ",
"People will say it’s because the media don’t cover these things, but that’s not an answer. The media cover things that people want to hear about. They don’t cover epidemics because people don’t care. People don’t care because the public health system has worked well enough to protect them. Because the public health system worked, they think it’s not doing anything, and don’t care when people try to dismantle it. ",
"And that’s how we find ourselves trying to hire firefighters when our house is already on fire."
] |
[
"Do people really not remember the H1N1 pandemic of 2009/2010? It was literally ten years ago."
] |
[
"Can you implant the nuclear genome of any cell into a sperm and have it fertilize an egg?"
] |
[
false
] |
If yes, is technology like that even in practice?
|
[
"the DNA in sperm is haploid, i.e. it has one set of chromosomes, while the DNA in a \"normal\" cell is diploid"
] |
[
"http://en.wikipedia.org/wiki/Haploid#Haploidisation",
"Thanks for pointing me in the right direction."
] |
[
"Let me clarify that with an example: Subject A wants a child, yet lacks functional gonads, could he use a donor's sperm cell?"
] |
[
"How come blood vessels and nerves are not pinched when we bend our elbows/knees and other bend parts?"
] |
[
false
] |
*Bendy parts. Sorry for title typo.
|
[
"Well, depends on how you define pinched. They aren't really pinched because they aren't in the joint barring major trauma. They can, however, have slight pressure on them at maximal flexion (particularly if you are a bit big) that you would experience as \"pins and needles\" and eventually pain over time. That would be those in front of the joint. Those passing behind could be put on slight stretch with the same symptoms. Other neurovascular structures pass beside the joints and don't care that much about flexion usually. "
] |
[
"To add to this, it's useful to consider that limbs do not completely compress when bent. If you imagine a garden hose, when you bend it , a crease forms which compresses the water stream. The hose construction is relatively stiff compared to the 'body'. The 'body' of the hose is only water, which deforms easily under pressure from the hose construction.",
"Bending a limb does not result in the same deformation. The outer construction (skin) does not exert a large pressure on internal tissue, which in turn is not compressed to a large degree. It is still possible for vessels and nerve structures to become pinched, but it is not a wholesale phenomenon."
] |
[
"Blood vessels definitely can be partially or completely pinched off as joints flex. Veins operate at lower pressures than arteries so they are more likely to be occluded. Our body gets around this by forking arteries/veins to create collateral paths which may eventually join up again. ",
"Here is the arterial circulation ",
"around the knee",
", and here ",
"the elbow",
". "
] |
[
"What did people feed babies before mushed up store bough food in jars? Did mothers used to chew the food and then give it to their babies like birds do?"
] |
[
false
] | null |
[
"Complete speculation here, but they probably also breast fed for significantly longer than most modern societies. In modern poorer cultures, some mothers breast feed children at 5 or 6 years old."
] |
[
"Unlike birds, humans don't need to chew food to mash it up. We have hands and tools such a mortar and pestle. Softer foods were cooked and pureed or mashed into a paste-like consistency, much like what you find in bottles today."
] |
[
"People use mashing tools to mash up food for babies, and sometimes for themselves - mashed potatoes for example. Probably most people now living do not buy baby food in jars at the store."
] |
[
"Does angiogenesis really help against cancer? And what are the newest results about what food does help?"
] |
[
false
] | null |
[
"I think what you are looking for is anti-angiogenesis, the inhibition of the growth of new blood vessels. These studies (",
"Study 1",
", ",
"Study 2",
", ",
"Study 3",
" show that anti-angiogenesis can be useful in reducing the size of tumors in patients. However, this is effect is not uniform across all patients. Different ages and different types of tumors respond differently to this treatment. The studies also say that more research is needed to fully understand anti-angiogenesis treatments."
] |
[
"Also ProTip:"
] |
[
"Thank you for the help. As far as I've understand the conclusions is that further research is needed and there can't be made any definite statements about it yet - just like you already said in your first comment.",
"The TED talk is kinda missleading or seems to be more promising while what they're actually doing is teasing in order to get some more funds for further research..."
] |
[
"If C02 is heavier than air then how is it causing global warming?"
] |
[
false
] |
I understand that CO2 isn't much heavier than air so a slight breeze would move it around pretty good but wouldn't the wind cause a pretty even distribution of the gas at all altitudes? I don't see how CO2 is holding in excess heat when its evenly distributed.
|
[
"CO2's ability to trap heat has nothing to do with its distribution. CO2 absorbs solar energy and turns it into heat more efficiently than, say, the nitrogen that makes up most of our atmosphere."
] |
[
"Yes. However CO2 is not the only factor. In fact, methane traps heat ",
" 72 TIMES better than carbon dioxide. Also, it must be realized that the Greenhouse Effect is not a bad thing, it actually has been a main component in the survival of the organisms on this planet. Although, too much CO2 can accelerate the effect, causing rises in temperature etc.",
" Thanks to benjamin_kyle for the information about methane and its ability to trap heat, I was completely unaware of the awesome potential methane had to change our planet!"
] |
[
"This is called the Greenhouse Effect, right?"
] |
[
"Can someone explain this madness?"
] |
[
false
] |
Just found this pair in my pensil pouch. Its like the Bic pen had melted around the Boxy eraser. I live in Iceland so the chance of leaving the pouch in a car during summer time and getting the pen hot is almost impossible. After removing the eraser, the material left behind was soft to the touch but definetly not ink. After removing the soft blue material there was a clear grove left behind.
|
[
"Solvent in the eraser dissolved the plastic in the pen. "
] |
[
"Acetone?"
] |
[
"I would guess hexane but that is just a guess."
] |
[
"Does quality of sleep differ significantly if induced with a sleep aid (i.e. melatonin or an antihistamine) compared with sleep that occurs naturally?"
] |
[
false
] | null |
[
"Sleep induced via melatonin should be the same size melatonin is produced endogenously any time you sleep, and the way you get it (probably) doesn't matter. Sleep induced by a antihistamine or sedative is of a lesser quality, though I can't remember the titles of the papers I read on it. IIRC, these drugs tend to interfere with the REM cycle and the cycle just before it (I believe they shorten their duration and also make them \"weaker\"). Lastly, if a sedative or antihistamine has a long enough duration/half-life, it will be present in large enough quantities when you wake up to make you feel groggy in the morning. This is distinct from getting a good sleep, but is still important in it's own way.",
"Actually, I just remembered that MIT or Harvard (can't remember which) did a study on melatonin showing that it had a similar effect to the sedatives and histamines' next-day grogginess because the average doses in commercially available melatonin tablets (3mg) is roughly 10x higher than the minimum effective dose.",
"Ironically this was written late at night when I should be asleep, so please forgive any typos/confusing sentence structure."
] |
[
"Good post, thanks!"
] |
[
"So those are very different ",
"Melatonin doesn't make you sleepy, it regulates your body clock - specifically it increases at night. It can help you sleep properly, especially if you have poor sleep hygiene, because it can help overcome other \"zeitgebers\" or time cues (like light and stimulation) that are telling you it isn't night yet.",
"Antihistamines make you sleepy by blocking histamine receptors in the brain and these ",
"decrease REM sleep and increase Non REM sleep",
". So that can affect sleep quality.",
"Most other sleep aids activate GABA-A receptors (these inhibit nerve cell firing) and they are usually either imidazopyridines (like ambien) or benzodiazepines (like klonipin or valium). These also affect the architecture of sleep",
"So melatonin is your best bet - or doing 20 min or so of exercise every morning and not using your phone in bed. (you can also try getting old, I can't stay awake past 9:30 now)",
"edit- spelling of ambien "
] |
[
"Is comet 67P's gravitational pull strong enough for me to remain standing on it without floating away?"
] |
[
false
] |
[deleted]
|
[
"Comet 67P/Churyumov-Gerasimenko is so small that its gravitational pull is several hundred thousand times weaker than on Earth. For this reason, the Rosetta lander had to touch down at no more than a walking pace. It also needed a harpoon to safely anchor it to the comet’s surface and prevent it from bouncing back into space. So to answer your question if you jump at full force you would fly away."
] |
[
"Even though it touched down at a walking pace, it still bounced several hundred meters. It's quite weak. "
] |
[
"Thank you!"
] |
[
"How is Ballistics Gelatin an Accurate Representation of the Human Flesh?"
] |
[
false
] |
I know that Ballistics Gel is the same density as human flesh is, therefore allowing a somewhat accurate representation. However, I also noticed that when using ballistics gel dummies/torsos, the gelatin is significantly thicker than human flesh would be. Wouldn't the thickness, despite being the same density, affect the accuracy of the results?
|
[
"Before ballistics gel, pigs were used, as they were found to be similar density to human flesh, and are pretty much the same size and weight, for repeat testing. Not completely sure, but I think ballistics gel is mixed to the same density as pig flesh still, but that's one of the main reasons to use ballistics gel, is that you can control the density.",
"Ballistics gel tests are already approximations, so the ",
" of what you are testing for is going to vary anyway, as it doesn't simulate skin, bone, clothing, etc.",
"The main reason for using ballistics gel in the first place, is to see what the bullet is doing, and not so much the damage to the target; to see whether the bullet rolls, fragments, penetrates, or cause cavitation, etc. Slight variations in density isn't going to change the bullet behavior much."
] |
[
"I wouldn't say \"rather than\" damage, since the behavior of the bullet is what indicates what type of damage it may cause when fired into a living person.",
"For example, what you think of as a \"standard\" (full metal jacket- lead interior with copper alloy jacket) bullet such as 8mm Mauser is a comparatively large bullet. When entering soft flesh like a human abdomen the bullet will carry through the target in a straightforward manner. Newer, smaller, rounds like the 5.56x45mm instead have a propensity to tumble, causing a wider path of destruction. Although the smaller, faster bullet has lower muzzle energy than the older, larger \"battle rifle\" rounds like 8mm Mauser, 30-06, and 7.62x54r and therefore doesn't convey the same kinetic effect, the internal wounds are quite serious.",
"Another example are hollow points, which utilize a different mechanism to achieve similar results. These bullets have an unjacketed tip, so when the bullet enters soft flesh the bullet will expand (the sides peel back), causing more tissue damage.",
"From a military standpoint it is also important to remember that you aren't only shooting at soft targets. Things like armor or cover will stop expanding bullets much easier than an FMJ bullet. For these reasons FMJ might be preferred by the military, whereas something with less penetration might be preferred by police to limit collateral damage."
] |
[
"At the extreme loading rates imposed by bullets, the depth of gelatin blocks doesn't really matter. The dynamics of a cue ball falling onto a chunk of gelatin are significantly influenced by the thickness of the gelatin because stress transmitted through the gelatin can find it's way to the other side and push back depending on the boundary condition (against a table or open air). The stiffness and strength of the gelatin also affect the slow impact behavior, governing how much deflection and tearing will occur.",
"With the extremely sudden loading rate of a bullet impact, the density of the gelatin becomes a far stronger influence on the behavior of the gelatin. I get the feeling that the strength and stiffness of the gelatin also barely matters at the loading rates and forces at hand. The gelatin is quite weak compared to a lead bullet. I suspect that the effects which rip a bullet apart, causing it to fragment or mushroom are mostly hydrodynamic forces predominantly caused by the inertia of the gelatin. Basically the gelatin behaves like a tank of water except it more or less holds its shape so all of the little bullet bits are held where they finally lost momentum. Since flesh has roughly the same density of gelatin, it doesn't matter much that there's sinew, muscle, and organs which probably behave similarly to gelatin. Bones are another story. ",
"Bones can deflect lower velocity rounds or high velocity bullet fragments. I think they don't bother casting bones into gelatin to keep the test idealized and easily repeatable. Anyways, a major bone strike is far more devastating than a through and through unfragmented round in a combat scenario most of the time.",
"Gelatin blocks are cast to be thicker than the human torso so as to capture particles which would have gone through. Having a sense of how much further they flew is useful to get a sense of the damage potential of the bits which would have continued through a target of lesser thickness. "
] |
[
"Is it possible to destroy the sun?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Half the questions on here are hypothetical... we have info on the sun and info on nukes. Are you suggesting someone can't work something out about this? "
] |
[
"This question would be better suited for our other subreddit: ",
"/r/asksciencediscussion"
] |
[
"In the night sky, why do the stars twinkle/shimmer, but the planets do not?"
] |
[
false
] |
[deleted]
|
[
"Stars are nearly points of light in the sky. They hardly have any dimensions, due to their sheer distance from earth. Planets, on the other hand, have a visible width from earth. Even when looking through a reasonably good backyard telescope, stars still are simply points of light in the sky, while planets have a much more defined shape.",
"Our atmosphere is not a perfectly smooth sphere that encompasses the earth. It has different densities, and different thicknessess all the way through it. This turbulence can cause distortions in the way light passes through the atmosphere. Tiny points of light are affected far more than larger, more defined planets. ",
"Here's a nice overview on ",
"'Astronomical seeing'",
", the effect you are describing."
] |
[
"Stars are essentially point sources of light and planets are small discs. Atmospheric disturbances are refracting the point sources more noticeably than the larger planetary discs, where the twinkling gets averaged out over a larger area of the sky."
] |
[
"Short answer: it's a wave-interference phenomenon. Starlight is coherent, but light from planets is not. With an incoherent light source, any interference fringes get washed out. (Light from a point source is always spatially coherent.)",
"The fast twinkle is actually a ",
"Fresnel Biprism",
" effect, where different temperatures of air cause beams of starlight to slightly refract and cross each other. Where the beams are superposed, interference fringes resembling \"",
"laser speckle",
"\" appear. Slow air motions causes the speckle interference pattern to travel across your face.",
"Quick experiment: watch a twinkling star at night, and cross your eyes. You'll notice that each of the doubled images twinkles differently. They're not in sync. The moving interference fringes are narrow, so your two eyes cannot fit inside a single fringe.",
"Light from an 'extended source' such as a visible planetary disk is not spatially coherent, so for planets all you'll see is the atmospheric lensing effects, but without the travelling ",
"interference fringes",
"What if a single star was bright enough to cast shadows? In that case you'd see the interference stripe-patterns on your face and spread all over the ground. There's one case where this actually happens. During a total eclipse, just as the sun vanishes behind the moon (or just as it reappears,) the remaining visible sun forms an extremely narrow line. It's like a single-slit optics experiment. In this situation the eyewitnesses often report that grey bands or stripes are racing across the ground. This is star twinkle patterns made visible!"
] |
[
"Due to the constant expansion of space, is it possible at some point in the future that stars would cease to be visible in the night sky? If so, how long would that take?"
] |
[
false
] | null |
[
"No, because the expansion is irrelevant on the scales of collapsed structures like galaxies and galaxy clusters. Our solar system isn't expanding, the stars in our neighborhood aren't expanding away from us, and don't let anyone tell you otherwise!"
] |
[
"I might be wrong, but I always understood it that because of the accelerating rate of expansion eventually the rate of expansion will be strong enough to overcome gravitational bonds within galaxies, and eventually even to overcome the strong/weak nuclear forces and electromagnetic attraction. I always understood that eventually every single particle in the Universe will be causally disconnected from every other particle due to the acceleration."
] |
[
"Sorry, I ignored several complications here. The stars in the night sky will never leave due to the expansion of the Universe. However, at some point in the future we ",
" expect the night sky to become empty. Eventually - after about 100 trillion years - stars will cease forming, and all that will be left will be brown dwarfs and stellar remnants. These will, over time, all be either flung out of the galaxy or sucked into black holes. The night sky will be quite lonely by then."
] |
[
"Can animals get STDs too?"
] |
[
false
] | null |
[
"YES. ",
"A particularly interesting one is 'canine transmissible venereal tumour' aka dog's bollocks cancer. It's a cancer that's passed on by cancer cells colonising individuals other than their original host through close contact. ",
"The only other cases of these transmissible cancers are Devil facial tumour disease, which affects Tasmanian Devils and Contagious reticulum cell sarcoma of the Syrian hamster, which is a cancer of the digestive system. ",
"The dog's bollocks cancer is the only one of these that is specifically spread through sexual contact. ",
"http://en.wikipedia.org/wiki/Canine_transmissible_venereal_tumor",
" "
] |
[
"Yes. Here is an article on it. ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1045078/pdf/brjvendis00066-0022.pdf"
] |
[
"It's a cancer that's passed on by cancer cells colonising individuals other than their original host through close contact.",
"Well that's terrifying and interesting. There's no such thing in humans... right?"
] |
[
"'Chemistry' How does one speed up the oxidation of iron?"
] |
[
false
] |
I am trying to make an artsy rust pattern in some iron, however I was hoping that I could speed up the process that iron turns to rust. I assume this is done through oxidizing agents, is there a household one that works quickly? I've been trying hydrogen peroxide, however leaving a piece of iron in a tray of peroxide all day long yielded nothing.
|
[
"Salty water will do it. As explained ",
"here",
", salt in water boosts the rusting process.",
"\nAlternatively you can heat it up to around 600 C or more fo the oxidation to occur faster."
] |
[
"This sounds like a good idea. To a lesser degree than aluminum (but similar), iron can have a passivation layer of iron oxide that protects the bulk of the underlying metal from being oxidized. Getting rid of it allows the oxidizing agent to come into contact with fresh iron, greatly speeding up the oxidation process.",
"Interesting side note - aluminum is a very active metal, oxidizing almost immediately upon contact with air. We don't see it crumble instantly into dust because that outer layer of aluminum oxide (once formed) protects the metal underneath. Like iron."
] |
[
"Wrapping it in copper tubing/wire would speed up galvanic corrosion enormously in salt water."
] |
[
"What are the effects of rising atmospheric CO2 other than warming the planet?"
] |
[
false
] |
I was just reading this article: In it i states:> NASA said the planet was warming because of greater levels of carbon dioxide in the atmosphere as a result of human activity, mainly the increased combustion of fossil fuels. In 1880, the first year of the temperature record, “the carbon dioxide level in the atmosphere was about 285 parts per million,” NASA said. “By 1960, the atmospheric carbon dioxide concentration, measured at NOAA's Mauna Loa Observatory, was about 315 parts per million. Today, that measurement exceeds 390 parts per million. So my question is, other than warming the planet through the greenhouse effect, what other changes take place with the ever increasing levels of CO2 in the atmosphere? For example does it increase growth in plant life? Is there any direct effect on humans?
|
[
"One major effect is that it increases ocean acidity due to a shift in the equilibrium point of ",
"this reaction",
". One of the most immediate effects of this is on ",
"Coral",
", which are already almost gone in many parts of the world. Coral are being hit by many factors (temperature, pollution, eventually water level rise... they're incredibly fragile), but pH is a big part of it."
] |
[
"Davecasa's is absolutely correct in pointing out the ocean acidification. Here's a few time series of ocean pH taken from some subtropical locations: ",
"Ocean carbon dioxide and acidity",
"In regards to plants if we ignore the effects of higher CO2 on the climate, a number of experiments have been done in controlled settings where plants are grown in an atmosphere with much higher CO2 concentrations. Some have shown that if the plants are provided with sufficient nutrients, increased CO2 leads to greater growth; however, when the plants are in a nutrient-limited environment, growth rate is affected only slightly. Others summarized in this Nature Education article by ",
"Taub 2010",
" basically conclude that the benefit depends on the plant itself. For instance some plants like corn and sugarcane (all member of the C4 classification of plants) are relatively insensitive to enhanced CO2. As a broad generalization though, higher CO2 does lead to higher plant growth (with some evidence to the contrary e.g. ",
"Shaw et al. 2002",
". ",
"Edit (forgot to address effect on humans)\nI don't think humans are affected significantly by the higher CO2 emissions. As it stands right now, CO2 only forms (by volume) ~0.04% ~400 parts per million (ppm) of the air that we breathe compared to oxygen's ~21%. The CDC lists the \"immediately dangerous to life or health\" concentration of CO2 to be 40000ppm, or approximately 100 times what's currently in the air and OSHA has an upper limit on CO2 concentration to be 5000ppm (~10 times the amount CO2 in the atmosphere)."
] |
[
"I hope you don't mind this correction/clarification. The only estimate of the amount of net primary productivity (i.e. photosynthesis and accordingly O2 produced) that I know of is from ",
"Field et al. 1998",
" which pegs the proportion of O2 produced in the ocean at about about 46.2% with land being 53.8%.",
"Ocean acidification primarily affects all organisms (including corals and a type of phytoplankton called a coccolithophore) which use calcium carbonate (CaCO3) to make their shells or bodies. Due to chemical equilibrium reactions, these shells dissolve at much shallower depths when the pH of the ocean is lower. As such, other organisms which don't rely on CaCO3 shells for protection may outcompete them. It remains an open (and an ongoing area of research) how the composition and diversity of plankton (and indeed the entire marine ecosystem) is adjusting and will change under ocean acidification."
] |
[
"Can we ever reach 0 degress Kelvin?"
] |
[
false
] |
I was watching a video on Linus Tech Tips showing a quantum computer. He said that the unit gets down to .015 Kelvin. What ways could we achieve 0 degress Kelvin, and if it's not possible why? Also, why does a quantum computer need to operate at such a low temperature?
|
[
"The third law of thermodynamics disallows cooling a system to absolute zero."
] |
[
"An ELI5 statement of the third law is just \"You can't cool something to absolute zero.\""
] |
[
"Technically, no. Practically - we can approach it incredibly close. In fact, cooling something becomes progressively easier as you approach zero, because heat capacity drops as T",
" around 0K.",
"A deeper question is, what you consider a good enough approximation for 0 K? Is 10",
" K good enough? Then we are already there, there are adiabatic demagnetization systems that will take you to picokelvins."
] |
[
"What do electrons do with/to an atom when they're not bonded to anything?"
] |
[
false
] | null |
[
"Remember that electrons aren't just particles, they also have wave properties (they are sort of complicated wavy/particly things that are best described with math and metaphors which rely on human experience tend to fall short). When an electron is bound to an atom it is basically in a standing wave on top of that atom. There are a great many different standing electron waves in 3-dimensional space around a given atomic nuclei and these end up having different energy levels, so naturally the electrons tend to fall into the lowest energy configurations. These standing waves take the shape (to a first order approximation) of ",
"spherical harmonics",
" in 3D space. We call these standing waves ",
"\"orbitals\"",
" (you'll notice the close relationship between the shapes of the spherical harmonics and of orbitals, because they are closely related), and they are how electrons nestle as close as possible (well, with as little energy as possible) around a nucleus.",
"A covalent bond formed by electrons between two or more atoms is essentially a \"molecular orbital\" wherein an electron exists in a standing wave pattern that encompases two (or more) nuclei."
] |
[
"Can you clarify your question?"
] |
[
"My main idea for the question came from the fact that (last time I checked,) alpha particles are basically helium without the electrons, which made me wonder, what are the electrons actually doing besides bonding to other elements?",
"Tl;DR, what do electrons do when they're not used in bonding with other elements? do they just sit (or rather, orbit) there doing nothing?"
] |
[
"How genuine are Dr. Mehran Keshe's claims that the Earth will soon be hit by mega earthquakes which will claim around 40 million lives and will divide the continents?"
] |
[
false
] | null |
[
"As Das_Mime pointed out, this is complete nonsense. Let's ignore the fact the author is a fraud and look at the article:",
"He said: \"The South American continent is the starting point of the weakness. There will be earthquakes of 10 to 16 here and in one location 20 to 24.\"",
"I don't know what he means exactly, but if he's suggesting earthquakes of a magnitude of 20-24 that's beyond even an amusing level of ridiculousness. EQ magnitude, these days calculated as 'Moment Magnitude' works on a log scale- an increase of 1 in magnitude is equivilent to an increase in moment of 10x (a function of rupture area, average displacement of the rupture area and the shear modulus, an inherent property of the rocks), or a total energy increase of about 32x. ",
"To put into perspective how ridiculous this is when taking into account, and using the formula",
"log E = 5.24 + 1.44* (Magnitude)",
"to convert from magnitude to energy, a magnitude 24 earthquake would release around 3.6*10",
" joules of energy.",
"To put that into perspective, the sun releases around 4x10",
" joules of energy a second. To release as much energy as one earthquake this big it'd take as much energy as the sun puts out in around 3 million years. Or looking at it another way, that's about 10",
" megatons of Tnt worth. The Earth only weighs 5.9x10",
" tons - or 5x10",
" megatons. So a magnitude 24 earthquake would release as much energy as if you had ",
" and blew them all up at once. That would be quite the earthquake indeed.",
"But really, the explanation why it's impossible is much more simple. Remember how magnitude is a function of area and average displacement- it's considered impossible for an earthquake to exceed Magnitude 12 because that would require the entire earth to rupture, which is obviously impossible. ",
"Source",
"Even a magnitude 10 earthquake has never been observed or felt. There are no known faults that could possibly rupture severely enough to produce such a big earthquake. I'm not really a seismology expert, but I guess it might be theoretically possible to get a magnitude 10, though simply not possible with Earth's current tectonic structure.",
"So yeah, I wouldn't lose any sleep over it!"
] |
[
"To use a technical term, it's horseshit. ",
"Such earthquakes would be totally unprecedented, and there's no reason to even think that they're possible, much less that they're likely. ",
"The very article you linked admits that there is absolutely zero evidence backing up such a claim, and that Dr. Keshe has no qualifications in geology whatsoever. If you bother to look up his website (which I won't link because it's garbage), you'll see that he claims to have solved all the problems of space travel, free energy, and just about everything else. ",
"Nobody knows how to precisely predict earthquakes. Geologists can certainly assess risk factors and map out areas where quakes are more likely, but this guy is a complete fraud. "
] |
[
"Run the formula given above on those two numbers and subtract the result. "
] |
[
"How does salt preserve food?"
] |
[
false
] | null |
[
"To my understanding it causes an environment that isn't as easily habitable for microorganisms. Some bacteria can actually live in a high salt environment, ones that can cause foodborne illness at least. Not 100% sure on that but I learned something like that in a food safety and sanitation class. The same would go for organisms that can decrease the shelf life of a food.",
"EDIT: Found something else that just popped into my mind. It also dehydrates the food. Water content promotes growth of microorganisms. Water activity of 85% or more promotes growth, along those lines, a pH of above 4.6 does the same. "
] |
[
"High salt concentrations kill most bacteria through osmotic pressure, the same way salt kills slugs. Since the concentration of salt outside the bacteria is higher than inside, water rushes out to equalize the concentration. This dehydrates and kills the bacteria."
] |
[
"The main thing is that it dehydrates the food. Sugar will have the same effect (i.e. dried fruit). In any form of food preservation, the goal is to remove or freeze the water from the product."
] |
[
"What do we actually sense when we feel that something is wet?"
] |
[
false
] |
As far as i know there aren't any specific receptors for 'wetness' and sometimes it feels like something is wet but as soon as you enter a warmer environment the sensation is gone. I also heard that mercury doesn't feel wet although it's liquid. How does that work?
|
[
"The typical sensation of wetness is related to the coolness of the evaporative effect. When we are wet, either from sweat or an external source, the water is immediately drawing heat from our skin as it evaporates. Hot or warm water splashed on us feels different at first because it's actually adding heat. It feels wet and uncomfortable as soon as its temperature drops below our body temperature.",
"Mercury does not evaporate. It and other non evaporating liquids may give a sensation of its presence, but won't feel cold like water or alcohol."
] |
[
"I believe the precise answer to this question is an area of active research, but I'll do my best.",
"I would disagree with Hagenaar that the coolness that we sense is related only to the evaporative effect. Instead, I would point to differences in ",
" that would likely explain part of the sensing that is going on when we interact with liquids. Instead of having to produce enough thermal energy to evoporate the liquid -- or a thin enough layer of liquid that it would evaporate under normal thermal conditions -- the body would use existing thermal sensors in the skin to sense the relative direction and amplitude of heat exchange. This is why metals feel cool to the touch, the metal is pulling away body heat at a fast rate. Wood, on the other hand, does not feel as cold because heat is not exchanged as quickly.",
"It is well known that the hand has thermal receptors, in addition to the various pressure and vibration sensors. These are the rapidly-adapting (RA) and slowly-adapting (SA) receptors, and sometimes known by their specific names: ruffini endings, pacinian corpuscles, etc. These receptors continue on as afferent nerves, where they insert into the brain via the gracile and cuneate fasiculi in the medulla. From there, the signal moves to the thalamus and then various areas of the cortex, where it is processed.",
"The ",
" \"sense\" of wetness is probably a combination of the thermal senses, as well as pressure and vibration senses, and would need to be processed. Certainly pressure has a role, as hydrostatic pressure can be perceived when the hand is submerged. Vibrotactile senses would also come into play as we interact with objects that are wet. Dry objects would elicit higher amplitude vibrations in the skin as we run our fingers over them. Wet fingers would see these vibrations dampened. There is some interesting work being done that investigates the role of fingertip ridges and oils in the mechanics of hand grip. ",
"Please see this great seminar",
" by haptics researcher Vincent Hayward where he goes into the mechanics of the fingertip and his work trying to tease everything apart. He discusses specifically the controversy in the haptics community as to the purpose and effect of fingertip ridges and the sweat/oils that we produce.",
"Sources:",
"[1] CE Sherrick and RW Cholewiak. Chapter 12 -- Cutaneous Sensitivity. In: Handbook of Perception and Human Performance, Vol. I. (1986) Eds. Hoff, Kaufman, Thomas. ",
"[2] JM Loomis and SJ Lederman. Chapter 31 -- Tactual Perception. In: Handbook of Perception and Human Performance, Vol II. (1986) Eds. Hoff, Kaufman, Thomas. "
] |
[
"Liquids also have the effect of reducing friction. So when your finger feels cool and when you touch something that feels slippery, you know it's wet. "
] |
[
"Why are string theory dimensions smaller and not larger? (more in description)"
] |
[
false
] |
Why couldn't another dimension in our universe be too big to observe? At one point (in a TED talk) it was stated by Brian Greene that the remaining dimensions yet to be discovered in our universe are smaller and smaller in size. He also provided the idea that these smaller dimensions are the avenue for interaction with other smaller entities in our universe, like energy. This left me with a question about the direction in which different dimensions are being investigated. Why can our 3 observable dimensions be excluded from the possibility that they do not help to comprise something bigger? Has this already been dismissed or does no one know how to approach investigating it? **I know these TED talks are older but from what I could find they haven't changed much in their simplified forms of explanation.
|
[
"It loops back around itself on a small lengthscale. The universe in an Asteroids game has a finite size; you could leave one end of a rope somewhere, fly across the edge with the other end, tie the ends together, and pull it tight: it's not wrapping ",
" anything, but it still can't shrink past a certain point; the length of the rope is the circumference of your universe in that direction. An Asteroidsian would be able to determine that they were living in a \"wrap-around\" rectangle, and they'd be able to measure the size of the screen (i.e. their universe).",
"By saying a dimension is small we literally mean that the length along it, in the above sense, is a very small length."
] |
[
"If I'm understanding your question correctly..",
"One of the main reasons any higher dimensions must by necessity be \"small\" rather than \"large\" is that we observe the intensity of gravitation, electromagnetism, sound etc all obeying an ",
"inverse square law",
" when you move away from the source - because they're being spread across a 3d sphere. In general, if something is radiating in ",
" spatial dimensions, its intensity varies proportional to 1/distance",
" so if we were living in 9-large-dimensions space, you'd expect the intensity of the sunlight reaching us to vary as 1/distance",
" for example, which we don't see.",
"If those higher-order dimensions are very tiny (and \"rolled up\"), their effects will only be noticeable at very tiny distances, where a force could \"leak\" into them and not obey inverse-square at those distances.. which could help explain some physics phenomena we ",
" see, like the ",
"hierarchy problem",
" where the strength of gravity compared to the weak force doesn't seem to make sense."
] |
[
"Because larger dimensions are obvious, like our 3 dimensions (which may be infinite in size), because you can move around in them. "
] |
[
"Why do painkillers work for specific kind of pain?"
] |
[
false
] |
[deleted]
|
[
"Aspirin and ibuprofen are both anti-inflammatory analgesics, which work by inhibiting production of prostaglandins, a group of lipid compounds which produce soreness and inflammation. They do not target specific pain, but rather circulate until they encounter a location which is producing prostaglandins, where they act as antagonists.",
"Therefore, any benefit that either of these two drugs possess in regards to targeting specific pain is likely a result of the placebo effect."
] |
[
"work by inhibiting production of prostaglandins, a group of lipid compounds which produce soreness...",
"and yet...",
"targeting specific pain is likely a result of the placebo effect",
"Could you elaborate?"
] |
[
"I'm sorry, I should have been more specific.",
"The first segment that you've highlighted is an explanation of why exactly these drugs cannot target specific pain - their pharmacological mechanism simply cannot allow this to happen. Aspirin cannot be better at dealing with back pain than headache, for example. Given that aspirin and ibuprofen share the same mechanism, individuals should not experience a differing level of relief between the two drugs, especially in regards to relieving particular types of pain.",
"As for the placebo effect, this would allow these otherwise indistinct mechanisms to have distinct effects. If you, as a person, believe that aspirin is better than ibuprofen for treating headache, then it will be better for treating headache. There are a wide variety of explanations for this, such as your past experience with either drug (having taken one in the past for less severe pain, resulting in a perceived increase in efficacy when compared to other drugs, for example), or the size and colour of the pill capsules themselves."
] |
[
"Does calcium stop being stored in human bones after a certain age? If so, when?"
] |
[
false
] |
[deleted]
|
[
"Bone resorption beats out bone formation depending on more than one factor though age is an important one. For women their chances of this happening and leading to osteoporosis increase dramatically after menopause or around 50+. This doesn't mean that bone formation isn't happening just that bone resorption is higher. Bone remodeling is a constant process with Osteoblasts forming bone and osteoclasts \"eating\" or resorbing bone."
] |
[
"No, hydroxyapatite (bone) is made up of calcium phosphate and a few other minerals/elements. Osteoclasts are cells that \"eat\" bone releasing these factors into the bloodstream. Osteoblasts(different type of cells) secrete these factors into a matrix that makes bone. Lacking calcium would result in no bone formation and would be present more in starvation/malnourishment. Age related bone loss is due to a decrease in factors that promote osteoblast activity, for women undergoing menopause estrogen decrease is usually considered the culprit and there are multiple medications that attempt to correct for it. Calcium levels are mostly dependent on your dietary habits."
] |
[
"No, hydroxyapatite (bone) is made up of calcium phosphate and a few other minerals/elements. Osteoclasts are cells that \"eat\" bone releasing these factors into the bloodstream. Osteoblasts(different type of cells) secrete these factors into a matrix that makes bone. Lacking calcium would result in no bone formation and would be present more in starvation/malnourishment. Age related bone loss is due to a decrease in factors that promote osteoblast activity, for women undergoing menopause estrogen decrease is usually considered the culprit and there are multiple medications that attempt to correct for it. Calcium levels are mostly dependent on your dietary habits."
] |
[
"Can anyone help explain to me Ultracentrifugation"
] |
[
false
] |
[deleted]
|
[
"I think you are asking about density gradient centrifugation rather than ultracentrifugation.",
"Ultracentrifugation is just spinning very, very fast. Using this ",
"technique",
" you can pellet down specific cellular components by spinning at different speeds. For example, spin at 21,000g to pellet large organelles and cell membranes. Then spin the supernatant (soluble fraction) at 100,000g to pellet vesicles.",
"This is different from ",
"density gradient centrifugation",
", a technique in which ultracentrifugation is often used. First, you build a density gradient using something like cesium chloride (old school, for DNA preps, hazardous) or sucrose (newer, less hazardous, more general applications). You can carefully layer sucrose solutions of different percentages in the tube to make a gradient. Then, when you add the sample and spin very fast, the sample will separate out with things stopping their movement down the tube when they reach the layer of the same density.",
"This is then analyzed by carefully drawing off layers and looking at what stopped where. Different cellular components with different densities will be separated. For a DNA prep, the plasmid DNA (small and circular) will be physically separated from the genomic DNA of the bacteria (larger and circular). I know people who use that technique to separate out DNA based on the relative GC content, where some DNA has more of some kinds of bases."
] |
[
"You got the separation of materials based on size/density correct. That is important because it can be used as a method to separate out substances and therefore purify whatever substance you are trying to collect--usually DNA or proteins. For instance, in research this summer, I used an ultracentrifuge to purify plasmid DNA. The spin separated the sample that I had put into the centrifuge by density, so that the plasmid DNA collected as distinct bands (visible with UV light). I could then collect the DNA and leave all other impurities, such as proteins,RNAses, etc. behind. Ultracentrifugation could also be used to pellet cellular organelles. Essentially, it separates what you want to collect for further research from other particles in your sample. That is the best way I can think to explain it at least, hope it helps!"
] |
[
"[Feel free to correct me if I'm wrong!]",
"OK, so you have the whole centrifugation thing down I think. You spin a tube with stuff in it super fast and all the components separate out into layers. Thing is, plain old centrifugation isn't able to separate as well as ultracentrifugation. You can get blood to separate out into plasma, red blood cells, but the platelets and the white blood cells don't separate out individually, they're stuck in one layer together. With ultracentrifugation you could set up a tube in a certain way to get everything to separate out into their own bands."
] |
[
"Is boric powder a useful substance to get rid of German Cockroaches?"
] |
[
false
] |
My house has been crawling with German cockroaches and I heard online that boric powder would work. I need a scientific explanation for this.
|
[
"Not in my exp. Those little fkrs can breed so fast. ",
"I stopped an infestation from happening by going to my local DIY Pest Control place. Spent $50 on two products. A spray that kills the egg sacks that stay attached to the mothers. The other product was a poisonous gel that the roaches eat. The females who drop the dead egg sacks will immediately look for food and eat the gel. ",
"Worked great in like 4seeks. "
] |
[
"Disclaimer: source involves close up of a roach, and is therefore quite gross.",
"I think they're quite beautiful actually.",
"And the video is extremely interesting! Not so much because of the grooming, what I find far more interesting is the re-attempts the cockroach makes at grooming the restrained antennae. I wonder if this is because the cockroach \"knows\" whether a task finished or was interrupted (the interruption being the antennae slipping out of it's grip due to the restrictor), or if there's stimulus from dirt on the antennae re-triggering the grooming behaviour?"
] |
[
"Disclaimer: source involves close up of a roach, and is therefore quite gross.",
"I think they're quite beautiful actually.",
"And the video is extremely interesting! Not so much because of the grooming, what I find far more interesting is the re-attempts the cockroach makes at grooming the restrained antennae. I wonder if this is because the cockroach \"knows\" whether a task finished or was interrupted (the interruption being the antennae slipping out of it's grip due to the restrictor), or if there's stimulus from dirt on the antennae re-triggering the grooming behaviour?"
] |
[
"Why does the color black attract more heat than other colors?"
] |
[
false
] | null |
[
"i would turn that explanation around; it's not that black things absorb more light - blackness is a perceptual property, not a property of a physical surface. a material ",
" black ",
" it absorbs so much of a broad (visible) spectrum of incident light."
] |
[
"i would turn that explanation around; it's not that black things absorb more light - blackness is a perceptual property, not a property of a physical surface. a material ",
" black ",
" it absorbs so much of a broad (visible) spectrum of incident light."
] |
[
"This is one of the clearest explanations I've heard, thanks"
] |
[
"How do we account for the gain/loss of time in a day due to earthquakes and tectonic activity?"
] |
[
false
] |
I'm aware of how earthquakes, such as that last big one in Japan, can cause the earth to spin faster, but I'm wondering how we can account for these moments in time.
|
[
"Through ",
"leap seconds",
". They are added every few years to account for the slowing of the Earth's rotation from the moon's tidal friction and internal tectonic processes."
] |
[
"Yes. The minute takes its name from the Latin ",
", meaning \"small part\". The second is the ",
", the \"second small part\", and the minute can then be called more fully ",
", the \"first small part\". I don't know if it comes from court something something; ",
"Wikipedia",
" mentions medieval scientists."
] |
[
"Sometimes, yes. ",
"On occasion, a very massive earthquake can bring a whole bunch of Earth's mass closer to the core",
", which has the impact of slightly increasing the speed of Earth's rotation. To use the most common analogy: it's exactly the same as when an ice skater brings their arms inwards, increasing the speed of their spin."
] |
[
"Why are things like vanilla extract advised NOT to be stored in the fridge, and away from light?"
] |
[
false
] |
[deleted]
|
[
"With regards to Vanillin, I do work with it and can attest to the fact that it can crystallize and drop out of solution at refrigerator temperatures. "
] |
[
"Recrystallization, a basic concept for those working with organic chemistry :P it's true for every compound, i'd say. Any solvent dissolves better when it's hotter, and when it's colder, certain compounds will precipitate and crystallize.\nIt's beautiful :D"
] |
[
"For some reason I can't see 3 of the 4 comments there seem to be here so i'll give my view anyways.",
"It makes absolutely no sense that a molecule will decompose faster at lower temperatures, that much is obvious I would say. ",
"So the question is if by \"vanilla extract\" you mean vanillin, or if you really mean just generally vanilla extract. In the case of vanilla extract it would be many different molecules. \nThe only reasons I could come up with off the top of my mind for it to get spoiled at lower temperatures are either increased unwanted moisture (in which case you should just make sure it's dry and sealed before storing it as cold as you want), or if the formation of ice crystals would somehow damage the extract (deep freezing can potentially damage tissue, for example, and sometimes makes food spoil faster, or it can result in \"splitting\", such as when a beer freezes, or when butter splits, etc).\nLight can of course cause photochemistry to happen."
] |
[
"Why don't we shoot atomic waste into the sun?"
] |
[
false
] |
The question may be a bit silly, but I was talking to some friends and some of us said the reason is purely financial, because nobody would pay the millions necessary to shoot tons of waste into the sun. Other said it may be certain effects that the radioactive waste would have. What is true? Why don't we do it and get rid of all this debate?
|
[
"Your friend who said the reason was purely financial is right … but may have failed to make the point strongly enough.",
"The Earth is in ",
" around the sun. That means the Earth, and everything on it, is moving through space at about seventy thousand miles an hour. In order to drop something into the sun, you'd have to bring it to what is effectively a dead stop in space, which means accelerating it from rest to seventy thousand miles an hour going in the direction opposite the Earth's orbital motion.",
"That's twice the velocity necessary to fling something ",
" Now, we have launched a rocket to solar escape velocity before, about 35,000 miles an hour … but only ",
" in all of human history, and doing so required a custom-assembled rocket and more than two hundred million US dollars, and the total payload was still only about a thousand pounds. And that's ",
" of what we'd have to do, in terms of total velocity, to fire a payload of the same size into the sun … and rockets don't scale linearly with final velocity but rather ",
" meaning the cost of putting a thousand-pound payload into the sun would probably be on the order of a billion US dollars, not counting the up-front R&D costs.",
"And did I mention that spent nuclear fuel is among the densest stuff on our planet? A ",
" of the stuff weights more than a thousand pounds — 1,189 pounds, to be precise.",
"\"Purely financial\" doesn't even begin to cover it. To put any ",
" of the stuff into the sun would literally cost more than the total amount of money in the whole world."
] |
[
"To begin with, ",
"this",
" is one reason."
] |
[
"That's like making a chainsaw out of wood!"
] |
[
"How do invertebrates, like the octopus, protect their vital organs?"
] |
[
false
] |
[deleted]
|
[
"The octopus brain is behind its eyes, and yes it is fairly small. Octopi have a very developed intelligence, and as we refine methodologies for studying octopus behaviour and intelligence their intellect is becoming very apparent. They can change the shape of their bodies quite dramatically, with the ",
"Indonesian Mimic octopus",
" being one of the best examples. Their problem-solving skills are quite advanced, as they will test openings with one to several arms to determine the size of the opening before attempting to pass through it. They will not even attempt to exit the opening if it is smaller than the distance between their eyes, because although they can change shape and move interior organs around a bit, there are limits. ",
"Due to their invertebrate nature, you're correct that their organs aren't as protected as a vertebrates, but there aren't too many situations in their habitat that will force them through very small openings. Basically though, their organs aren't very protected, but this allows for much more flexibility and defense of a different nature than structural. Their organs can be squeezed, but mostly they are just moved around inside.",
"Octopi can also learn by watching each other, and even after ",
"watching another",
" open a box once, an octopus figures out very quickly how to copy the behaviour. Not really relevant to your question but I find it fascinating."
] |
[
"Eg, I could imagine, if I was designing an organism, it might make sense to have an \"arm brain\" for each arm that could control the arm, respond to impulses",
"Funny, you just described....an octopus! 2/3 of an octopus' neurons are in its arms, and the ",
"nonsomatotopic organization",
" of its nervous system allows for a wider dispersal of organization and processing that allows many lower level functions to be carried out autonomously without necessary input from the brain proper."
] |
[
"Do any invertebrates have a \"decentralised\" nervous system (for lack of a better phrase)? Like could an organism distribute smaller \"computing clusters\" (again, lack of good phrase; ganglia/nodes) that pre-process sensation or post-process commands for action? ",
"Eg, I could imagine, if I was designing an organism, it might make sense to have an \"arm brain\" for each arm that could control the arm, respond to impulses (reflex-esque behaviour) and do a lot of the lower-level stuff, then report a simplified data stream back up to some \"self-brain\" that organizes all the smaller brain behaviours. "
] |
[
"A fundamental property of bosons and fermions is that their wavefunctions are symmetric and antisymmetric respectively in terms of exchange of particals. Why is this so, and how do we know it?"
] |
[
false
] | null |
[
"Why spin works/transforms the way it does? I'm not sure anybody really understands spin. ",
"I do not think that spin is so mysterious. In terms of the representations of the lorentz group it is pretty clear what spin is (a very good explaination is in Weinbergs QFT books) "
] |
[
"A common (but somewhat bogus) argument is that since particles are indistinguishable, then exchanging two particles can only make the wave function differ at most by a phase factor (e",
"), as changing the overall phase of the wave function is the only change you can make that will not change any observable properties. Second, you have the condition that exchanging the same two particles twice must of course give you back the same function as you had from the start. ",
"So, Ψ(x1,x2) = Ψ(x2,x1)e",
" = Ψ(x1,x2)e",
"So e",
" = 1, which means that the phase change theta is either π or 0, meaning either the sign of the wave function changes on exchange or it doesn't. The former particles are fermions and the latter bosons, by definition. ",
"The more proper proof of all this is the spin-statistics theorem, which links it to the spin of the particle (fermions being half-integer spin particles and bosons integer-spin). Why spin works/transforms the way it does? I'm not sure anybody ",
" understands spin. "
] |
[
"So spin statistics theorem shows that integer spins are symmetric and half integer spins are antisymmetric...",
"Yes.",
"also shows that bosons are integer spin and fermions are half integer spin",
"I'm not sure what you mean by that. How do you define bosons and fermions? You can either define them by the symmetry or their spin, and then the spin statistics theorem tells you that they are related. So it's doesn't \"also\" show that bosons are integer spin and fermions are half integer spin, because that's either the definition or the result of the theorem that \"integer spins are symmetric and half integer spins are antisymmetric\""
] |
[
"Question about Carl Sagan Quote and Carbon atoms."
] |
[
false
] |
So I've always heard that "This is something carbon atoms do after 13 billion years"... I'm sure I got the quote a little wrong, but that's beside the point. My question is: what kind of atoms decay into carbon atoms? Can the quote be taken literally? Wouldn't most carbon atoms have decayed into something else by now? I am sadly uneducated when it comes to chemistry, so please keep your answers as accessible as possible.
|
[
"To summarize the science part of it, the big bang basically only created hydrogen with a little helium (and trace amounts of Li, Be). All the heavier elements (up until Fe) are made by fusion in stars, and all the elements heavier than Iron were made from supernovae of dying stars.",
"Now as others carbon isn't usually formed by something decay into it. Carbon is produced in stars via nuclear fusion, of say two helium-4 nuclei forming beryllium-8, and which meets up with another helium nucleus to fuse into carbon-12. ",
"[1]",
"Obligatory comic from today"
] |
[
"The actual quote is:",
"\"These are some of the things that hydrogen atoms do given fifteen billion years of cosmic evolution.\"",
"It's from the last episode of Cosmos. It refers to evolution, in that hydrogen atoms formed stars, which created all other elements (including carbon), which formed self-replicating molecules, which evolved into humans, etc.",
"So, yes, the (original) quote can be taken quite literally. The full essay (link below) is very accessible to non-scientists, and I highly recommend it.",
"source"
] |
[
"Oh, cool! Thanks for the info, guys, including the essay and the comic. ",
"So, next quick question: when an atom decays, doesn't it create a different atom? ",
"If so, is carbon never one of those atoms?"
] |
[
"Are young men more likely than young women to die of heart disease?"
] |
[
false
] |
A close family member recently lost a young nephew aged 19 to an undiagnosed heart condition. My mother and I had a conversation where we realised how prevalent it seemed to be - we could think of several instances of our seemingly-healthy male acquaintances who passed away suddenly where the cause of death was undiagnosed heart disease, but no female acquaintances. These were all healthy young men, what gives?
|
[
"This is not saying that heart attacks are becoming more common in younger people. It is saying that there are more ",
" of young people with heart attacks, especially young women. This could be related to increased surveillance, better understanding of heart attack signs/symptoms especially in women, healthcare workers taking heart attack like symptoms in the young more seriously, our ability to actually intervene in heart attacks which leads to more people staying in the hospital rather than be discharged home from the ER, better public awareness of signs and symptoms of heart attacks, and stricter guidelines on acute coronary syndrome. It could also be related to the obesity epidemic, rising levels of diabetes and hypertension, and rising female smoking rates.",
"",
"I suspect the former plays a bigger role but regardless you cannot definitively say that there are more heart attacks in younger people now than 20 years ago from this study alone."
] |
[
"EDIT: Ignore this post for now. The numbers I gave you are percentages, not absolute numbers so it is not going to accurately answer your question",
"",
"I'm not sure you are asking the question you want to ask. The answer to the question in your title is simple: the CDC reports causes of death by gender and age every few years. Here is the link to causes of death by age ",
"for girls",
" and ",
"for guys",
". Essentially the numbers show that from age 15-35, the percentage of female deaths from \"heart disease\" is ever so slightly higher than the percentage of male deaths from \"heart disease\". After 35, this reverses. Now, I caution you - ",
". You would need to do a statistical analysis before saying such a controversial statement.",
"",
"With that said, \"heart disease\" is quite a vague term. Most young people (up to age 30) who die of \"heart disease\" aren't dying from the classic heart attack (about 2% of them do). Rather, they die from structural heart disease or arrhythmias. Sudden cardiac death in the young is a huge topic in cardiology and these aren't easy to spot. It is extremely rare (but it does happen). Because of how rare they are, it is not worth checking every single person for these diseases (because that would take hundreds of billions of healthcare dollars). Even the screening tests that are common like ECGs in young athletes are absolutely abysmal in picking up these abnormalities."
] |
[
"Actually in general heart attacks are becoming more common in younger people, especially women — source:",
"\n",
"https://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.118.037137",
" "
] |
[
"Would the Bat-Signal work in reality?"
] |
[
false
] |
Could a projection system such as a spot light produce a clear enough image on a cloud landscape similar to how the Bat-Signal works? Why hasn't anyone tried it?
|
[
"Yes it works and is done from time to time. ",
"http://i.imgur.com/1TPkP.jpg"
] |
[
"That looks more like a laser than a spotlight."
] |
[
"Pirateparty logo Arrrrr =)"
] |
[
"What would happen if we can completely modify our DNA?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScienceDiscussion",
"Please see our ",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"If it is impossible to go the speed of light, couldn't we figure out that \"stopped\" is in our universe?"
] |
[
false
] |
If we somehow, theoretically, went fast enough that we started to see noticeable, recordable effects from approaching the speed of light, then went the other way and did the same, couldn't we figure out what the speed of light is relative to? I've always wondered this because while we can't go the speed of light, it probably wouldn't be relative to our own star, or the center of our galaxy, so what would it be relative to?
|
[
"This is actually the core problem that special relativity answers.",
"You can't go faster than the speed of light relative to ",
" frame of reference. At the same time, the speed of light is always the speed of light relative to everyone.",
"This works because the classic velocity addition formulae you learn at school turns out to only be a low-speed approximation. So, if a car is driving at 100 kph, and it turns on its headlights, you don't see the light moving at c+100kph, you see it moving at c. You can't just add the velocities and get the right answer. The full formula is:",
"v = (v1 + v2)/(1+ v1*v2/c",
" )",
"That (1+ v1*v2/c",
" ) factor is the special relativistic correction, which is small enough to ignore if v1 and v2 are much smaller than c. If you plug in v1=c or v2=c, you always get v=c."
] |
[
"That is ",
" what Michelson and Morley tried in 1887, to pinpoint the direction of motion of the ",
"luminiferous aether",
". To their dismay, they found no preferential direction of motion, which in turn led to the founding principle of special relativity: the speed of light is the same in any inertial frame of reference."
] |
[
"We routinely accelerate things to over 99.99% the speed of light relative to Earth. Just tiny particles, not spacecraft, but the concept is the same. Let's say you would be in a spacecraft that moves at 99.99% the speed of light relative to Earth. Now what? For you Earth moves at 99.99% the speed of light while you do not move. Everything that moves at the speed of light as seen by Earth also moves at the speed of light as seen by you, and vice versa. The situation is perfectly symmetric. Well, if we ignore that you'll get bombarded by dust particles moving at ~99.99% the speed of light relative to you... but the physics is exactly the same for you and for Earth. There is nothing that would make one reference frame different from others."
] |
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