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[
"If E=MC^2 and we've converted mass into energy, have scientists turned energy into mass yet?"
] |
[
false
] | null |
[
"The equation E = mc",
" is frequently misunderstood. It doesn't mean \"mass can be converted into energy\" or \"energy can be converted into mass\" it's telling you how much mass energy has. ",
"A scenario to explain what this means:",
"We often think of a nuclear bomb, for instance, as \"converting mass into energy\" because the mass of the products weigh less than the mass of the reactants. But imagine a nuclear bomb enclosed in a perfectly thermally insulated and mirrored box. It's on a scale and it weighs exactly 100 kg. The bomb goes off. If mass were converted into energy, we would expect the scale to now weigh less. But it doesn't. As long as the energy is trapped inside of this mythical box that is perfectly insulated and perfectly mirrored, the scale will still read 100 kg. Mass isn't converted to energy- energy ",
" mass, and as long as that energy is held inside, the mass remains the same. It's only after we open the box, and allow the energy to carry away some mass, via heat, light, sound, etc. ",
"So, with nuclear bombs (but really, those aren't the only ones. Every reaction obeys E= mc",
" even chemical reactions like burning. It's just that nuclear was the first one that released enough energy that the mass deficit was measurable) bound energy, which adds measured mass to an atom, is released as free energy (coming out as light, heat, etc). But, any time to add energy to a system, and it stays bound to that system, that system will have a higher effective mass. For instance, the fact that the Earth is rotating adds about ",
"3E12 kg",
" to the effective mass of the Earth."
] |
[
"The short answer is yes: this happens at particle accelerators all the time, e.g. the Large Hadron Collider. You let particles collide at high energy and they’re able to convert that energy to create new particles with mass.",
"Source: I’m an astro particle physicist."
] |
[
"A better question to ask is have scientists been able to turn energy into matter yet to which the answer is a definite yes."
] |
[
"How will melting polar caps raise sea levels, if melting ice in a cup doesn't raise that water level?"
] |
[
false
] |
If the mass of the ice is already displacing that amount of water, how will that ice melting effect the sea level?
|
[
"Much of the ice is locked up on land and not free floating. The Greenland Ice Sheet for instance:",
"\n",
"http://en.wikipedia.org/wiki/Greenland_ice_sheet"
] |
[
"In addition to the melting ice transferring water from land to oceans, also recall that water itself expands as it warms up. Warmer oceans require more volume"
] |
[
"Antarctica is a continent, most of the ice there is on land. Currently 30 cubic miles of ice are melting off of Antarctica per year. Greenland is an island, currently 90 cubic miles per year are melting off of Greenland. The Arctic Ocean is an ocean. You are correct that none of the ice melting in the Arctic Ocean will affect sea levels. "
] |
[
"RNase trouble"
] |
[
false
] |
This is directed to some fellow lab workers. Do any of you have a recipe for a non-commercial RNase cleaning solution? Would appreciate if it would be as nontoxic as possible. It would help me tons since im working almost exclusively with RNA and want to save time and money.
|
[
"You mean for benchtops & the like? We used to use ~0.1N NaOH. Bleach works, too. "
] |
[
"No. I mean bleach, sodium hypochlorite. ",
"H2O2 is hydrogen peroxide. Not the same thing, but it might work. Bleach is cheaper & more shelf stable, though."
] |
[
"My old lab always used ethanol which seemingly worked well."
] |
[
"What causes someone's brain to not make serotonin?"
] |
[
false
] |
[deleted]
|
[
"Short answer: they are probably just wrong. But if they're right, it's probably genetic.",
"TPH2 is the gene encoding tryptophan hydroxylase in the CNS, the enzyme synthesizing serotonin from tryptophan. Somewhat surprisingly, the lack of it doesn't outright kill you. ",
"Mice bred with ablated TPH2 genes made it to adulthood",
". But they were ... different. Mothers often cannibalized her litter. The mice fought to death quite often, even the females. They were, in a sense, extremely antisocial.",
"A deficiency in serotonin has been suggested as a ",
"biomarker of antisocial personality disorder",
". There's even been court cases where it has been argued that murderers can't have intended to kill their victims, because their serotonin deficiency made them unable to form proper intentions.",
"It's quite common to hear that depression has something to do with low serotonin levels. The research is inconclusive. On the other hand, low serotonin levels are ",
"definitely associated with impulse control and aggression",
".",
"Serotonin is also needed to synthesize melatonin, so low serotonin levels would cause serious sleep problems. This is via TPH1, though. But I don't think your friend has an actual lack of the TPH2 gene. So. There was a ",
"case report",
" of a man with a condition that left with a lack of dopamine and serotonin. The dopamine deficiency was recognized in his childhood, and he was treated with levodopa. The serotonin deficiency, however, went unnoticed. This man became extreme obese. This is probably because of the lack of impulse control. His social life was seemingly non-existant, judging from this sentence from the report: \"",
".\" He slept for about 12 hours a day, with a very irregular rhythm.",
"So if your friend is correct, they would have little to no impulse control and extreme sleep problems. Which I'm sure you would have noticed. On the other hand, they could be on medications.",
"If their brain actually can't synthesize serotonin, it's most likely a genetic condition.",
"There is another enzyme that's often brought up in this context, MAO-A, but that's not involved in the production of serotonin. It's involved in the degradation of it. I mention it because ",
"this enzyme has been shown to be affected by environmental stress",
". And it can lead to impulsitivity and aggression.",
"The reason why I say that they could be wrong is that serotonin has been implicated in a lot of weird new age ideas. For instance, there's this idea that negative ions in the air can affect your serotonin levels. Which is stupid and wrong. And there are some psychiatrists who take the easy way out and tell their patients that the reason why they need to take SSRIs is because their brain can't produce enough serotonin. Which is also stupid and wrong. Genetic conditions that prevent the brain from synthesizing serotonin are very rare. Since they mentioned it without mentioning a specific disorder, I think it's more likely that they are just mistaken."
] |
[
"As far as I know, it doesn't run in the family or anything. Also I know he was put into a child clinic/ward for a few days and then the classified it as clinical depression (I don't know if they figured it out the actual cause or not).",
"If you still think it's a mistake, what could they have mistaken it for?",
"Edit: thanks, this is really informative"
] |
[
"Low serotonin levels and polymorphisms in the TPH2 gene have been linked to various psychiatric disorders including depression, bipolar disorder, and schizophrenia. However, that doesn't mean his brain is incapable of producing serotonin. That would be pretty catastrophic, and I'm unaware of a disorder in which a person completely does not synthesize serotonin (if I'm wrong someone correct me...that would be incredibly interesting). I would say it's 99.99% likely he's wrong or misunderstood his physician. "
] |
[
"Would an electromagnet inside a chamber provide thrust?"
] |
[
false
] | null |
[
"Any forces due to the magnetic on the chamber would be internal to the magnet-chamber system, so there can be no net acceleration of the center of mass of the system, by Newton's second law."
] |
[
"But the magnet would be attached to the vessel. So wouldn't the vessel be part of the system? If you were to fire a bullet into a closed cone in space, wouldn't the bullet push the cone forward?"
] |
[
"Yes, but the center of mass of the system wouldn't change."
] |
[
"Possibilities of chess moves"
] |
[
false
] |
How would one calculate how many different possible openings there are for a chess match up to the tenth move?
|
[
"The process is rather straightforward. You reinterpret the rules of chess into a set of grid based mathematical formula and logic dictating possible \"legal\" moves. From there, you move to combinatorial mathematics. Conceptually, for the first two moves, the only pieces that CAN be moved are pawns (each of the 8 moves either one or two spaces) and the two knights (which have two possible options in the first move). So after the first two moves, there are exactly 400 possible outcomes (20 moves for white times 20 for black). ",
"By the fourth piece, things are rather more complicated, so that instead of actually extrapolating moves into an endgame, most chess computers focus on strategy evaluation and eliminate moves that are mathematically disadvantageous from their calculations. "
] |
[
"most chess computers focus on strategy evaluation and eliminate moves that are mathematically disadvantageous from their calculations.",
"So in fact, they wouldn't calculate all scenarios?"
] |
[
"No, there are far more move combinations than can possibly be calculated. They use heuristics, which are kind of like guidelines. Moves that make you more in control of the center of the board, for example, probably get +points, while moves that put a piece in immediate jeopardy likely get -points.",
"I know next to nothing about chess, so I might be wrong in the specifics. But you get the idea."
] |
[
"Could 1.21 gigawatts really be harnessed from a bolt of lightning?"
] |
[
false
] | null |
[
"Actually, I think it was \"jiggawatts\" in the movie that Doc was referring to. ",
"According to Wikipedia, the peak output of an average lightning strike is more on the order of a terawatt, however a rare positive bolt is upwards of hundreds of terawatts. A Terawatt is a thousand gigawatts, so Doc was underestimating by an order of magnitude. It should be pointed out that wattage is overrated, though--wattage is your power per unit of time. So the shorter of a time period that energy is released, the higher the power. Lightning has high power over a short time, so it only releases a relatively moderate amount of energy. ",
"The Z machine internal confinement fusion reactor supplies almost 300 terawatts. Well, that sounds like like an insane amount of energy, but it's only for 70 nanoseconds. Let's see here, 70 nanoseconds times 300 terawatts per second, um that's 21 million joules. Still sound big? Well that's 5 million calories, which is only 5 thousand Calories (food Calories with a capital C are kilocalories). And 5000 calories is equivalent a couple big macs, a supersize fry and a large milkshake. I told that to my physicist cousin once (who worked on the Z machine) and she got really mad because I made her hundreds of terawatts sound like not very much energy. And it really is not a lot of energy, it's just very compacted into a small period of time. ",
"Same thing with lightning. A few gigajoules of electricity in a lightning bolt sounds like a lot until you realize that it's just equivalent to a few hundred hamburgers. Not a mind boggling amount of total energy, but certainly a lot. Enough to make you fat, and certainly enough to power the flux capacitor of a DeLorean for a couple microseconds.",
"Source(s):",
"http://en.wikipedia.org/wiki/Lightning",
" ",
"http://en.wikipedia.org/wiki/Z_machine",
" "
] |
[
"It is a ",
"valid pronunciation",
" of \"giga\" to use a soft g sound at the start like Doc Brown did. It has the same root as the word \"giant\"."
] |
[
"The core problem here is that gigawatt is a unit of power, not of energy. A gigawatt is a lot of power, equivalent to that produced by a large electric power plant, but without knowing how much total energy is also required it's somewhat of a useless figure. Since 1.21 gigawatts over, say, a nanosecond isn't much total energy.",
"If we hypothesize that the time machine doesn't require much total energy and merely has some unusual requirement for a very short high power pulse then potentially lightning could be used as a source of power.",
"However, it's overstating things to say that generating 1.21 gigawatts is difficult, if all you need is a short pulse then it's not that hard to do with a bank of capacitors or with a tesla coil.",
"In short, it's a bit of tech babble that doesn't make much sense though is still technically correct."
] |
[
"Why is it that we can die of sleep deprivation?"
] |
[
false
] | null |
[
"die, apparently from the insomnia",
"This is not correct. Patients with FFI typically die of infection, like aspiration pneumonia from dysphagia."
] |
[
"The ones who die from not infection presumably die from insomnia...",
"That is not what that source is saying. That source simply says that some patients remain conscious (although this is debatable, as they are not very responsive) and others are in a full coma when they die. But they typically die of infection.",
"There is no known \"death from insomnia.\" These patients have spectacular, widespread, catastrophic neurodegeneration. They also have insomnia, and they die. That does ",
" mean they die ",
" of the insomnia. These patients also have profuse sweating, but they don't die ",
" profuse sweating either."
] |
[
"sleep deprivation itself in a single incident cannot kill you",
"Not so. See, for instance, ",
"Fatal Familial Insomnia",
". People with this disorder gradually lose the ability to sleep and eventually die, apparently from the insomnia, not accidents secondary to sleep deprivation."
] |
[
"Are the number of bytes output from a compression algorithm directly proportionate to the number of input bytes?"
] |
[
false
] |
Hello AskScience, For both lossless and lossy compression algorithms, is the size of the compressed data directly proportional to the size of the input data? For example, let’s say I’m using algorithm A on data d1, and the compressed output is size s1. If I run algorithm A on d2, and size(d2)==2*size(d1), will s2 == 2(s1)? I understand there are many different compression algorithms so this may be hard to answer truly in the general case, just want to get a basic understanding.
|
[
"No, in general it is not. Compression algorithms are more effective when there's more structure in the data. Exactly what type of structure leads itself to be more compressible will depend on the algorithm.",
"A simple test you can do is to take a photo file, open it in Paint and save it as Bitmap (.bmp). Then, create an empty image of the same pixel dimensions, but completely blank. Save it ti a new file using the same .bmp file type. Compare the file sizes and note that they are the same. Bitmap files are uncompressed (by default, in theory the file format does allow for some forms of compression).",
"Now, compress both files to their own .zip file and compare the file sizes. You'll note that the blank image compresses to a much smaller size than the image containing a photo, despite both input files being the same size.",
"The very simple structure of the blank file (\"everything is white\") is much easier to compress than a detailed picture."
] |
[
"The case I've always heard as an extreme example of data structure is a file format that could contain one of two things. Either it contains the complete works of Shakespeare (estimated to be around 5,600,000 bytes) or nothing. In that situation you can theoretically make a compression algorithm which compresses everything down into 1 bit. Where a 1 results in the complete works of Shakespeare and a 0 is an empty file. In that example your compression ratio would obviously be enormous.",
"Stepping down from the Shakespeare example consider a file that could contain a random mix of two words. \"Hello\" and \"Goodbye\". In the same way a compression algorithm for that file could encode each word as a 1 or a 0. 1 is hello, 0 is goodbye. ",
"Generally speaking the more structure your data has and the better able to identify patterns in that structure the compression algorithm is the more it can be compressed. It's not really based on the number of input bits at all."
] |
[
"That makes a lot of sense, thank you!"
] |
[
"The universe is said to be around 23% dark matter, 72% dark energy and 5% ordinary matter. If we don't know what dark matter and dark energy are, where do the percentages come from?"
] |
[
false
] |
Edit: I just want to clarify, I'm aware of what dark matter and dark energy are. I'm by no means an expert, but I do have a basic idea. I'm wondering specifically how we got those particular numbers for them.
|
[
"We can calculate things like gravity and energy density of the universe base on how the galaxies behave on a cosmic scale. We can also calculate how much stuff is out there by direct observation. When we look at the cosmos and look at how the galaxies behave, there is not enough material to generate the gravity (even when accounting for all the gas and dust that may obscuring it). So there's some matter that doesn't emit light but still generates that gravity we see. We call it dark matter, because that's what it is: dark.",
"There's also an expansion to the universe that suggests that the energy density is not what we can directly measure. There's a bunch of stuff out there causing the universe to expand at an accelerated rate. We call it dark energy, because, hey, we have dark matter already--why not call it \"Dark Energy\"; that way it sounds cool.",
"So there's like 5 times as much matter as what we can see, and like 3 times as much energy density as what can be explained by that matter. So that's where the percentages come from: just add up all the stuff we know about that makes up the universe even if we don't yet know what that stuff is."
] |
[
"Could these phenomena just be (but probably not likely) an incomplete understanding of how physical laws, which are already discovered, work?"
] |
[
"In layman's terms: dark matter is ",
".",
"We can calculate the gravitational forces that impact everything we can see - stars, planets, black holes, dust, etc. We can calculate how much gravity the things we observe is generating. The problem is, they don't add up. There's way more gravity affecting everything than what is being generated. All of that unexplained gravity is just generalized as dark matter until a better explanation comes along. Same kinda deal with dark energy."
] |
[
"Where does water come from?"
] |
[
false
] |
Hydrogen formed shortly after the big bang, oxygen forms through stellar fusion, right? What causes them to bond together? Is it just that they bump into each other in gas clouds?
|
[
"While I don't know the process of planetary formation or what not that could form water, water is more energetically favorable and stable than a mixture of elemental hydrogen and oxygen so it presumably would spontaneously form under the right conditions."
] |
[
"In addition to the other comments, something that's interesting to note is the process of fusion in stars. The process that you're often most familiar with is to keep sticking hydrogen ions (protons) together until 2 of them decay into neutrons and 2 remain protons and form a helium nucleus. But there's another cycle in stars called the ",
"C-N-O cycle",
" where Carbon, Nitrogen, and Oxygen nuclei act as almost a fusion catalyst. If I'm not mistaken, and I may well be, it's part of why there are a lot of carbon, nitrogen, and oxygen atoms in the universe. And if there's a lot of hydrogen and a lot of oxygen, water's pretty much inevitable.",
"Edit: never mind. I was mistaken."
] |
[
"If you mix hydrogen and oxygen together and then set the mixture on fire, you get water vapour.",
"edit: hence the name 'hydro'gen."
] |
[
"Why do we sometimes keep strong memories of mundane or unimportant events in our lives? Is there a specific reason why we do so?"
] |
[
false
] |
We can recall very insignificant things like a statement, joke, image, or object from a particular moment even if we sometimes forget everything else about it. These memories can also feel very lucid, kind of like the popular statement, "I remember like it happened yesterday". Do we know the process behind it?
|
[
"There might be something behind that memory that effects you today, or you keep being reminded of that moment and after a while it becomes a normal memory that pops up at random times. The human mind is one of the most complicated things on earth (also gravity). It’s weird how some of the things that we ALL are in contact with every day are the things we know the least about. "
] |
[
"Well this is a possible answer, but I don't know wether it will work for all cases. Studies have shown you are more likely to remember emotionally responsive events rather than \"boring\" ones. For example you might remember getting a toy as a child because at the time it happened you were overwhelmed with joy telling your brain to store and cherish that memory. So it may seem random or irrelevant now but the brain remembers it as a highly important event. While something boring like studying is generally harder so you won't remember it for a long time. So if per say you had to remember a school concept you might not be able too since it was a long time ago when you studied, but if you did an interactive lab you both have a better understanding and an emotional response of fun or excitement which you might remember for a significantly longer time. "
] |
[
"does this mean that i would do better on my tests/exams if i wasn't getting so bored and actually tried to enjoy it?"
] |
[
"Do photons create some sort of friction when they hit on a moving object? And, if so, does the color of the object have any effect on it?"
] |
[
false
] |
I know that it is assumed for photons to have no mass. What we know, however, is, that an object absorbs different wavelengths depending on its color. A black car standing in direct sunlight for example becomes warm faster than a white one in the same position because it absorbs more light. This in further consequence means, that the car receives energy from the light. Now let's picture an object moving in a vacuum. When I now point a flashlight to this object, the object receives energy from it. Does this somehow make an impact on the movement of the object, and if so, does the color of the object matter as it does with the cars in the sun?
|
[
"Photons have momentum, despite having zero mass, given by p = E/c, where E = hf (h = Planck's constant, f = frequency). Since momentum is conserved, photons impacting an object do indeed exert a force on it (though it doesn't have anything to do with friction). ",
"Reflectiveness does make a difference - if a photon with momentum p impacts an object and is absorbed, then the object must have momentum p. If, however, it is perfectly reflected, then the photon is left with momentum -p (it's actually slightly less than this, as it gives a bit of energy to the object, but fairly close), meaning that the object must have momentum 2p. If the reflection is diffuse (which in the visible spectrum would be a white rather than mirrored object), the momentum gain and direction from the object will depend on the scattering angle, but will be at least p for a flat surface normal to the incoming radiation."
] |
[
"The heat in this example isn't caused by friction it's caused by an energy transfer as the photon interacts with the surface. Black surfaces are more absorbent and less likely to reflect a photon causing them to heat up quicker where as white objects are reflective causing photons to be more more likely to rebound and so imparting less energy . "
] |
[
"As others have said, the radiation pressure is less \"friction\" but rather a momentum transfer or kick in the direction of the light.\nSomewhat tangentially, doppler cooling of atoms works in this way, by absorbing light doppler shifted into resonance of an atomic transition the atom is pushed in the opposing direction to the light source. See ",
"this link",
" for more info. In this case, it is the color of the light, not the color of the object (atoms don't really have \"color\" in the sense you mean) that is important"
] |
[
"Is it possible to construct a non-trivial self-similar structure with integer Hausdorf dimension?"
] |
[
false
] | null |
[
"The ",
"3D version of the Sierpinski triangle",
" has Hausdorff dimension 2."
] |
[
"Sure, the boundary of ",
"the Mandelbrot Set has Hausdorf dimension 2",
"."
] |
[
"Sure, make a non-planar piecewise-linear path in 3 dimensions so that the Hausdorff dimension of the fractal you get by replacing each segment with scaled down version of the path etc. is 2. Actually do this in a program and show us for extra credit."
] |
[
"Allele question in regards to Paternity test (9 of 15 do not match)"
] |
[
false
] | null |
[
"Genetic tests are based on ",
"Short Tandem Repeat Analysis",
".",
"The test splits DNA into areas of interest (the loci), and those areas are \"amplified\" (that is, another process is used to make a bunch of copies of each locus).",
"STR analysis works like this: The loci are chosen because they're interesting areas; they're areas where a few bases are repeated a bunch of times over and over, and the number of repeats varies greatly between different people. Of course, the child has 2 sets of each locus (one from the mother, one from the father). For each locus, you'd expect that at least 1 of the 2 repeat lengths would be the same (if you're testing a child and a parent, I mean).",
"These",
" are the length variations for one locus, in 6 different people.",
"My understanding is this: The STR length at a location has about a 1 time per 1000 replication generations probability to change, due to \"replication slippage\". That means that for each locus, there is a ",
" chance that some \"slippage\" occurred, and the repeat-count could be off (usually by 1). But there's zero chance (realistically) that a child's STR would vary from a parent's at 9 out of 15 sites."
] |
[
"Thanks so very much! ",
"That really puts it into perspective. There IS room for \"slippage\", but not on the scale that he has experienced. ",
"Unfortunately, the woman that he chose to sleep with, has already taken a paternity test with who she thought was the father. With that partner (testing was done at a doctor's office), there wasn't any type of replication slippage, and he had 0 common Loci. He's been trying to convince her of what you just described, but she is looking at the results as a percentage, without any type of actual comprehension as it pertains to DNA. She's thinking that the other guy didn't have ANY matches, so since my friend has matched %40, he has to be the dad. ",
"Anywho, hopefully this will help her to understand better. My friend has given consent to another test with a doctor, more for her peace of mind than anything. I'm hoping (for her sake), that she'll finally come to an understanding.",
"Thanks again for the help, and the explanation that my friend can understand and try to convey.",
"Cheers"
] |
[
"The important part is \"0% match\", and in your friend's case, it would've been better if they weren't provided with more detail than that.",
"For all I know, most people that share your friend's racial makeup might hit 40% of the child's genetic markers, haha."
] |
[
"How is it that I can see my retinal blood vessels when my eyes are subjected to bright light?"
] |
[
false
] |
Every time I go to the eye doctor, their apparatuses shine light into my eyes and I see flashes of my blood vessels that I assume are on my retina. How is the light being refracted/absorbed by them in order that I can see them?
|
[
"this happens to me as well. i wonder if we're weird. i'd also like an answer to this question."
] |
[
"Well, I am relatively certain that this is common. I've thought a lot about this and the only thing that I can speculate is that it may have something to do with the red eye effect in flash photography. "
] |
[
"Red-eye is caused by the light going into the pupil and reflecting off the blood inside, or so I was told..."
] |
[
"Why don't I feel pain in my sleep?"
] |
[
false
] |
[deleted]
|
[
"\"Pain\" has two components: nocioception and conscious awareness. The prior occurs during sleep, but not the latter.",
"Nocioception is the physical or chemical stimulation of the pain receptor neurons (\"nocioceptors\") due to an aversive stimulus and the transducing and encoding of these signals. These signals from the receptors are relayed to a second neuron that brings the signal from the spinal cord to the ",
"thalamus",
" and then a third neuron, which brings the signal from the thalamus to the neurons in the \"primary receiving area\" of your ",
"somatosensory cortex",
", which is in the parietal lobe. This receiving area also reacts to the neurons that encode signals generated by touch, temperature, and proprioception (where your body is in space) and helps you mentally integrate and become aware of these signals. ",
"During sleep, the signals do not really reach your cortex due to a \"gating\" effect by the thalamus, which is a part of the brain that functions like a major relay and integration center for many sensory pathways. It is hyperpolarized in this state, making it much harder to excite (depolarize) and thus harder for the signal to transmit. There may be other gating mechanisms as well, but this is the one I'm most familiar with. In short, the signals from the painful stimulus thus have trouble reaching your conscious brain centers. ",
"I'm sure there are neurologists or anesthesiologists here that can give a more thorough/accurate answer, but that's the best I have.",
"EDIT: I'll find something peer-reviewed for you in a moment, but ",
"this",
" looks relatively accurate to start off.",
"EDIT2:",
" Peer-reviewed",
", nice quick summary."
] |
[
"Ah sorry, I might have added an edit after you posted. Signals are reduced, not completely absent. Some signals get through, signals which the gating systems of your brain recognize as necessary. Different stages of sleep show different levels of inhibition. For more detail than that, you'll need to ask a neuro expert."
] |
[
"How come we wake up if pinched, poked, or nudged, then?"
] |
[
"Is it possible to create 100% vacuum?"
] |
[
false
] |
Is it at all possible to create 100% vacuum here on earth, if yes. then how?
|
[
"Heh, finally my job is useful. I design vacuum chambers for a living. The short answer is no, we cannot achieve a perfect vacuum. Even the best pumps, like cryopumps, which actually condense gas molecules onto the pump surface, cannot get every single molecule. Even if you could capture all molecules all materials outgas slightly, meaning they emit gas particles. So you will constantly have molecules entering the chamber. We use special cleaning methods, low outgas materials, and even bake hardware to try and reduce this but it still happens. We cannot even create a vacuum equal to that in outer space. Hope this helps. "
] |
[
"Hmm, 30 mm mercury is 30 torr. The lowest vacuum I have heard of is in the 10",
" torr range using capture pumps. "
] |
[
"Hmm, 30 mm mercury is 30 torr. The lowest vacuum I have heard of is in the 10",
" torr range using capture pumps. "
] |
[
"Could Black Holes be responsible for the Matter/Antimatter Imbalance?"
] |
[
false
] |
I just read an article on astronomy.com about black holes forming without a star. For some reason my first thought went to the very early universe. I remember a documentary, maybe the new cosmos, saying there was an equal pair of matter and antimatter in the universe, but due to something, there became more matter than antimatter... My question: could one of these primordial black holes have been responsible for the imbalance of matter and antimatter in the early universe?
|
[
"For a theory to explain the matter and anti matter asymmetry in the universe, it needs to satisfy three conditions, called the Sakharov conditions. The theory must have baryon number violation, C and CP violation (this ensures that processes involving matter and antimatter won't cancel each other out), and an out of equilibrium process. If you don't have all three then it cannot explain the matter antimatter asymmetry in the universe. ",
"While a black hole can violate baryon number, and an evaporating black hole isn't in thermal equilibrium, gravity treats matter and antimatter in the same way, which means it cannot violate C and CP symmetry, hence the matter anti matter asymmetry cannot be due to Hawking radiation. "
] |
[
"The point is that a black hole could form in the early universe when their was an equal amount of matter and antimatter, and it could create or destroy matter. However, it will also create or destroy the equal and opposite amount of antimatter, and the rate at which it does both of these processes will be equal, hence it will never create more matter then antimatter. ",
"To make this more concrete, let's consider the early universe with an equal amount of matter and antimatter and assume a black hole formed there. This black hole will consume matter particles, but it also will consume antimatter particles at the exact same rate, which means there will still be the same amount of matter as there is antimatter. And when this black hole emits Hawking radiation, it will emit matter particles, but it will also enjoy the exact same amount of antimatter particles. So the total amount of antimatter will still be the same as the total amount of matter in the universe. ",
"For a process to create more matter then antimatter, we need this process to distinguish between matter and antimatter and treat them differently (this is the C and CP violation I mentioned on my first response), however gravity treats matter and antimatter in the exact same way, hence it could not have created the matter antimatter asymmetry we see in the universe today. "
] |
[
"I wasn't aware Black Holes were made of anything",
"They are not, ",
"/u/whippleball",
" is incorrect. Whatever the matter (or antimatter) was before becoming a black hole is irrelevant to the black hole after formation. All roads lead to Rome—at least in classical general relativity—which is also the source of the black hole information paradox that still befuddles physicists."
] |
[
"How accurate is our perception of time across space?"
] |
[
false
] | null |
[
"I doubt national geographic printed that because it's not true: The universe will not \"end\" in 5 billion years. In fact our current understanding of cosmology leads us to believe that we most likely live in a (\"flat\") universe that will go on expanding forever. ",
"You might refer to the ",
"heat death",
" but that's a matter of time scales far, far larger than billions of years."
] |
[
"here is the link: ",
"http://news.nationalgeographic.com/news/2010/10/101027-science-space-universe-end-of-time-multiverse-inflation/#.VcowjHSsCb8.facebook"
] |
[
"Eventually there will be no hydrogen left and star formation will stop. This happens in about ",
"100 trillion years in the future",
", and a few trillion years after that the last red dwarf will burn out and the universe will be rather cold and dark.",
"I had absolutely no idea what you were talking about with time shutting off in five billion years. I ",
"found what I think you're talking about",
" and this looks like bullshit with a very sketchy line of reasoning and one paper on Arvix. "
] |
[
"Why does a bobsled travel faster when it has more mass?"
] |
[
false
] |
I've read that its because the higher momentum allows it to overcome the drag and friction. However, wouldn't the added mass increase the friction to begin with? I've also read that the thin metal runners somehow decrease the friction which doesn't make sense considering friction has no relation to surface area. If someone could correct me or clarify this that would be great. Thanks.
|
[
"Because the heavier bobsled is still the same size, which means it's got the same drag but more gravitational force. More force + same drag = higher terminal velocity. ",
"Basically, imagine a bowling ball and a similarly sized beach ball being dropped from a building. The bowling ball will end up going much faster because it has the same drag but way more weight. ",
"I doubt the friction of the runners has much of anything to do with it. Aerodynamics almost certainly plays the largest role in determining the max speed of the bobsled (human variables aside). "
] |
[
"Since we've all been trained to believe that weight does not actually effect the rate at which we fall, let me try and explain this. ",
"The truth is that in a vacuum with no air friction, the bowling ball, and beach ball will fall at the same rate. However since we do have air resistance on earth we get what I like to call for simplicities sake the parachute effect. Imagine a person falling in a parachute, then take a look at a vehicle being dropped via parachute. Even though gravity, and air resistance are the major players. The weight of the object in question ",
" pull harder or lighter on the source of the resistance. ",
"To see this look at military drops. Soldiers will jump with small chutes, but vehicles, and supplies will have multiple chutes or larger ones."
] |
[
"F=ma",
"Acceleration (the rate we fall) is constant. The force depends on mass. The parachutes provide a resisting force to gravity. Thats why a heavier obiect needs more parachutes."
] |
[
"Would a large garden of photosynthetic microorganisms south of the equator have a significant effect on the ecosystem, and would it be sustainable?"
] |
[
false
] |
[deleted]
|
[
"Such a farm already exists pretty much. Most oxygen is produced by algae and plankton in the oceans. They are mostly microscopic. ",
"Edit: these are not farms per se but exist naturally. "
] |
[
"Not a dumb question at all. There has been very serious research into ",
"fertilizing specific parts of oceans to produce algae blooms",
", which will hopefully sink and sequester carbon. Some experiments have been done, so far it looks like it could do more harm than good. ",
"But years of research and some multimillion dollar experiments have been done to explore your \"dumb question\", and something of the sort may be done in the future."
] |
[
"I did not mean to imply that was a dumb question. I was just very brief as posting comments from my phone is a bit annoying. "
] |
[
"Does gas under high pressure conduct heat better than gas under atmospheric pressure?"
] |
[
false
] |
My thought is that gas isn't very thermally conductive due to the extra space between particles compared to liquids and solids. So, if you squished a bunch of particles in a small area the distance would increase, would this also increase thermal conductivity? Thanks!
|
[
"Not by much. Thermal conductivity in gases happens by molecules gaining thermal energy and moving to a colder place. Adding more molecules gives you more energy carriers, but they can’t move as far before bumping in to each other. So the thermal conductivity of most gases increases only slightly with pressure.",
"If you get near the boiling point, or the pressure is so low the molecules fly the length of your chamber without bumping into anything, the situation is different.",
"https://www.electronics-cooling.com/1998/09/the-thermal-conductivity-of-gases/",
"https://www.engineeringtoolbox.com/amp/air-properties-viscosity-conductivity-heat-capacity-d_1509.html",
"https://www.engineeringtoolbox.com/amp/methane-thermal-conductivity-temperature-pressure-d_2021.html"
] |
[
"But each time they bump into each other they bounce apart with shared energy. So the energy is still conducted but not by the original molecule which began with it."
] |
[
"Well, gas has a hard time sitting still to \"conduct\" heat - convection and advection is inevitable.",
"And you have to be additionally precise in your setup.",
"More pressure means more gas matter or less gas volume, or somewhere in between.",
"But take it to its logical extremes: Almost 0 matter means a vacuum and not heat transfer from \"conduction,\" and infinite pressure means infinite matter needs to be heated up, thus no \"conduction.\"",
"But if convection is permitted, then generally higher pressure makes it easier to transfer heat between molecules"
] |
[
"Why did trees not \"take over\" the prairies like they did the rest of Canada?"
] |
[
false
] |
[deleted]
|
[
"The southern part of the prairies is almost devoid of trees, but the north half is all forest. In ",
"this",
" picture, the dark blue represents the taiga and boreal forests. The yellow indicates grasslands. ",
"As for the actual cause of this happening, it can partially be attributed to the presence of the Rocky Mountains. Saturated air from the Pacific Ocean moves eastward, dumping its contents over BC. Once the air moves to mountains, the air cools (with the gain in elevation). This is called adiabatic cooling. The cooling causes the water vapour to condense and form droplets, which become too heavy to be suspended in the air, and fall as rain. ",
"Most of the moisture in the air parcel is lost over the Rockies, so most of Alberta and Saskatchewan (and parts of Manitoba) get mostly dry air. Due to evaporation and partially transpiration, the air over the prairies will eventually gain more moisture, but it isn't as substantial as the air in B.C. ",
"This can be attributed to the lack of moisture in the grasslands, which in turn will affect the amount of foliage.",
"EDIT: For those of you wanting some sources:\n",
"Here",
" is one describing adiabatic cooling and moisture loss over mountains. ",
"Here",
" is a lengthy description of the processes. Essentially, it can be summarized by ",
"this",
" photo. ",
"To paraphrase, the warm air rises over the mountain, cooling as it gains altitude (it cools at the dry adiabatic lapse rate). Once the temperature of the air reaches the dewpoint, which is based on initial pressure and saturation of the air parcel, precipitation occurs. The elevation at where the air temperature is equal to the dewpoint is called the lifting condensation level. This is when the air is fully saturated. The air now cools at the wet adiabatic laps rate. Eventually, the air will empty its moisture over the mountain and become \"dry\" again (not fully saturated). Here, it will warm at the dry adiabatic lapse rate as it drops down the other side of the mountain. The dewpoint will also rise, but not as quickly as the air temperature. "
] |
[
"The current reason for the lack of trees in the southern \"Prairie\" provinces is that most land is under cultivation. ",
"However, the reality is that several species of trees can grow quite well without irrigation even in the Palliser Triangle which is one of the more severe prairie environments. This has been demonstrated by a number of forestry test plots (the one that pops to mind is near Caron, SK).",
"Historically, though (and here I can't provide you with a reference), the fire cycle didn't permit forests from being established in the area since it is semi-arid (as noted in A_1337's response). So, I think it is important to note rainfall is sufficient to establish forests but other environmental factors (high wind, lack of natural fire breaks, high temperature in summer) contribute to a fire cycle frequency which favours grassland ecology over forest ecology. "
] |
[
"This is all purely speculative. Please back this up with some real documentation on whether or not saline soil deposits or glacial till have anything to do with lack of forests over the great plains. Most of the southern extent of the current US on that map which were supposedly underwater are now covered by extensive hardwood forests."
] |
[
"If gravity is caused by a curvature in space time, what is the idea behind the graviton?"
] |
[
false
] |
I'm very, very layman, and just starting to try to understand some of the theoretical physics developed over the last century. One of my main points of confusion is in fields and how their excitations are particles and the exchange of particles manifest the fields' forces...and that gravity is unique(?) among the forces - we haven't confirmed the existence of the graviton, I don't think. But if gravity is caused by curvatures in space-time, where exactly does the graviton fit in? Is gravity actually a field w/excitations? I'm a bit confused.
|
[
"You're probably tempted to think of it this way: a large object sends out gravitons, which each exert a slight pull on anything they encounter. Correctly, you've determined that such a vision would be inconsistent with general relativity's vision of gravity as spacetime curvature, and hit a contradiction.",
"Instead, gravitons wouldn't interact with other objects directly, they'd be the particle which caused spacetime to curve. Generally speaking, anyway. There are still enough problems with this model that we do not have a great theory reconciling general relativity and quantum mechanics.",
"Note also, that even the electromagnetic force doesn't work with charged objects emitting photons, which bounce off other objects and cause them to move. Instead, the photons represent changes in the electromagnetic field, and charged objects move based on their interactions with the field."
] |
[
"One of my main points of confusion is in fields and how their excitations are particles and the exchange of particles manifest the fields' forces...",
"virtual particles aren't real. no actual particles are exchanged in an interaction. ",
"in general you get particles (or sometimes quasi particles) when you have some field with quantized vibrations. in a crystalline solid you have vibrational modes in the lattice which are quantized so you have things behaving like particles (these are quasi particles called phonons). ",
"and that gravity is unique(?) among the forces - we haven't confirmed the existence of the graviton, I don't think.",
"physics is currently working on a theory of quantum gravity. ",
"But if gravity is caused by curvatures in space-time, where exactly does the graviton fit in? Is gravity actually a field w/excitations? I'm a bit confused.",
"general relativity is a classical theory, the classical limit of a theory with gravitons maybe. maybe like classical electromagnetism has electric and magnetic fields and when you quantize it you get photons. the field in general relativity is the metric g, which encodes the curvature of spacetime. and potentially if you quantize that you'd get quanta called gravitons. but there's experts on here who know more about this. ",
"in any case it's difficult to get an idea of quantum field theory without prerequisite knowledge. it's a graduate topic with a lot of technical jargon. "
] |
[
"It's certainly not correct to liken \"virtual particles\" to \"quasiparticles\" the way you do, if only for the fact that you can have virtual quasiparticles, too, much like virtual photons (nevermind that \"are emergent phenomena\" isn't saying much). You have quantised excitations of a field (maybe displacement of the lattice) that behave like particles and can be measured. They are not \"as 'not real' as virtual particles\". They aren't elementary particles, though.",
"Further reading",
"https://physics.stackexchange.com/questions/189302/has-a-phonon-a-formal-quasi-particle-ever-been-observed-as-a-point-particle",
"http://nvlpubs.nist.gov/nistpubs/jres/74A/jresv74An4p537_A1b.pdf",
" historic paper by nobel prize winner schrieffer (S in BCS)",
"Edit: I recall now, that we've had such a discussion recently, where you've already confused quasi and virtual particles, while also calling virtual particles \"very real\" (and saying they have real effects - which they don't, they are one possible mathematical tool to calculate real effects), (and misquoting Griffiths, who in his particle physics book says (paraphrasing) 'technically real particles are a subclass of virtual particles if you consider a large enough diagram, say one of two interactions where a photon is an outgoing particle of the first and an incoming for the second' rather than 'virtual particles are real').",
"I’ve read Intro to QM, and if I remember correctly, David most certainly treats Virtual Particles as a very real thing, classifying them as short lived particles rather than long lived, and said that its philosophically possible to consider a photon being absorbed by ones eye as a virtual particle.",
"I understand it’s popular here to treat Virtual Particles as as a type of perturbation quasiparticles, but I think that is significantly more of a philosophical call than a scientific one. We see real, tangible effects caused by Virtual Particles, so I’m not sure why that differs from something like a gluon, which we can’t observe directly but know it’s real because of how Particles form."
] |
[
"What kind of an experiment could prove String Theory to be false?"
] |
[
false
] |
I do understand that technology limits us in what we can physically do. I'm interested in what kind of an experiment would we need to do to disprove it.
|
[
"String theory makes three main \"large-scale general predictions\" that it won't budge on, regardless of the model under consideration:",
"-large-scale gravity follows GR exactly; the various modifications and extensions in the literature are false.",
"-Lorentz invariance is exact; other theories often predict some violation on small scales",
"-All particles ever found (including whatever dark matter is made of) must be described by QFTs of the generic type that the Standard Model is. Compared to any arbitrary QFT, string theory is very specific about the types of low-energy effective theory it can reduce to.",
"To a certain point though, this is the 'wrong question'. QFT is not even close to falsifiable: there are some QFTs that ",
" (but have extensive dynamics; it's not a trivial vacuum). Really I don't think we know remotely enough about QFT in general to even propose what a falsifying experiment would look like (that didn't violate established prior results on QM and SR). A huge number of things that behave nothing like any particle we've ever seen are possible with QFT, but that doesn't mean that searching for the standard model within it was a poor choice. Similarly string theory 'as a whole' only has relatively few falsifiable predictions, but what people are actually trying to do is build models ",
" string theory (like the Minimally Supersymmetric Standard Model) that are ",
" more testable and conform to many of the specific details that make up the standard model."
] |
[
"\"If you manage to find one idea that’s not obviously wrong, it’s a big accomplishment. Now, that’s not to say it’s right. But not obviously being wrong is already a huge accomplishment in this field.\"",
"-Nima Arkani-Hamed"
] |
[
"Basically, colliding particles together with 100 trillion times as much energy as the LHC would show whether they have a stringy substructure or not."
] |
[
"How much does the earth need to move to/from the sun in order for life to end?"
] |
[
false
] |
Asked by my 8 year old daughter.
|
[
"There are various estimates",
" but we're probably closer to the \"too hot\" edge than the \"too cold\" edge. About 5-25% closer to the sun, the greenhouse effect is strong enough to cause much of the oceans to evaporate, which causes a stronger greenhouse effect, and eventually all Earth's surface water is blown off into space. We end up like Venus.",
"Around 20-100% further out and the greenhouse effect no longer functions properly because CO2 forms clouds that reflect out more heat than they trap. The planet cools and some of the CO2 ends up forming surface ice--along with all the water. We end up sort of like Mars but with more ice.",
"The sun is gradually warming up over its lifetime, so in about a billion years the habitable zone will move past Earth and the former outcome will happen."
] |
[
"The habitable zone is where liquid water can typically occur due to radiation from the star (as opposed to, say tidal forces like some moons). As far as we know, liquid water is required for life. However, the habitable zone is quite large - if Earth was the size of a marble, the habitable zone would be the width of a semi-truck with trailer, so not very miraculous for a planet to fit in it. Earth is so close to the inner edge of that zone, we'd be on the hood of the semi, which is something life would have adapted to compared to if we were near the center like Mars is or the outer edge like the asteroid belt. "
] |
[
"Just to add to this, Mars is about as close to the \"outside\" of the habitable zone as Earth is to the \"inside\"."
] |
[
"What advances or changes in design have made modern engines so much smaller and more powerful than their older counterparts?"
] |
[
false
] |
I have always been pretty confused at the power discrepancy between modern engines and older engines. weighs 22 tons and only produces only 110 HP. Shouldn't the 22 ton engine have enormous displacement? I understand that, as a hit and miss, it fires only when it "needs to", but under maximum load such as when testing its maximum horsepower shouldn't it fire every time like a modern engine? If so what is the difference between it and a tiny outboard motor that produces 200 HP? Another question along the same vein: I was watching the trying to find an answer to this. "Otto's engines were much too large and clumsy for a car, but one of his employees called Gottlieb Daimler developed a much smaller engine" that "produced nearly as much power" as its larger counterpart. I thought "I've found the missing link!", but I haven't been able to find much information on Daimler's high speed engine. What exactly did he do to go from hulking behemoth to compact machine with nearly no loss in power?
|
[
"This is a pretty loaded question, and there are a couple different major factors at play here (with a slew of secondary supporting factors).",
"First and foremost, your example is not just comparing engines of different vintages, it's comparing two engines with extremely different designs. Among many things, the hit-or-miss engine generally doesn't have control over valve timing, the intake valve is run based on engine vacuum alone. This is a very different mechanism from cam-driven-valves.",
"Comparing more similar engines from different vintages, there are a variety of factors, but the biggest driver by far are the (myriad) aspects of the design that determine the speed that the engine runs at. The two primary factors that determine an engine's power is how much air/fuel is can pump (per unit time), and how efficiently that fuel is converted into mechanical energy. I would suggest that the former is the bigger driver, in the grand scheme of engine development, although the latter is important too. With improvements in engine layout (such as overhead valves and better understanding of fluid dynamics), we can get much more air in and out of an engine. With improvements in design, materials, dynamics, manufacturing, and other factors, we can run the engine much faster. And, with improved design, metallurgy, controls, and manufacturing, we can get more efficiency out of an engine (higher compression ratios, less energy wasted as heat, and other types of improvements).",
"Finally, I would point out that output per size is not, by itself, a great measure of how \"advanced\" an engine is. For example, a modern diesel truck engine is probably much more advanced than a motorcycle engine from the 80s, even though the latter has much higher specific output (power per displacement). For a variety of reasons (power delivery and longevity being the main ones), larger engines are often better suited for the application."
] |
[
"Dude, sorry, but you don't seem to be qualified to answer questions on this topic.",
"The short answer is that if Engine A is huge and outputs 100HP, and Engine B is small and outputs 100 HP; Engine B is more efficient.",
"This is incorrect, or at the very least extremely vague and not in keeping with the standard definition of \"efficiency.\" Generally, efficiency refers to energy output relative to energy input, or some similar metric. Based on the information you posted, you cannot say which engine is more efficient. There are many reasons to build a larger engine for the same power output (lower stress, longevity, reliability, possible cost savings). The larger engine could have the same or better (fuel) efficiency, depending on the design of the two engines.",
"If you're using \"efficiency\" in some non-standard way, like \"size vs. power efficiency\" or something, sure, you're right, but that wouldn't make a lot of sense to phrase it that way.",
"Efficiency in outputs can be gained via better fuel (gasoline vs. steam)",
"Um, steam isn't a fuel, buddy. Steam is just a working fluid, used in external combustion engines. These engines still use a fuel, which could be wood, or coal, or gasoline, or uranium, or solar energy."
] |
[
"There are several factors that are combined to make the modern engine. First things first, the kind of engine is every important, for example electric engines have a lot of HP for their size thanks to fact that the shaft is the only moving part, so it's really only limited to current and keeping it cool.",
"Specifically for internal combustion engines, like what I think you want to talk about, the most important parts are the compression ratios (how compressed the fuel is before combustion vs how far is pushes the cylinder down, more is better) and how well you burn your fuel. The compression ratios are improved by better and harder metallurgy techniques. Harder metals can have better tolerances and higher pressures without losing pressure. The second part is how well you're burning your fuel. You want this as close to 100% as possible. In the old days, they were more concerned about being able run an engine on stuff that wasn't clean enough to clean your house with, keeping it running was more important than keeping it efficient. Now a days, fuel and oxygen mixtures are careful and constantly monitored by special systems to keep it as efficient as possible.",
"Tl;Dr",
"We just make out engines out of better stuff, and the stuff making them run it much much better than back then.",
"Edit: Just watched your video. I think you're 'missing link' is the replacement of the flywheel with the cam shaft"
] |
[
"How do they make quartz vibrate at an exact number of gigahertz for chips? Is there a special way to size or cut them? What is involved?"
] |
[
false
] | null |
[
"In watches, Quartz crystals are the norm now. Basically the Piezo-electric effect. When you apply a force on the crystal, it will release a voltage, so if you apply a small voltage, it will oscillate. Most quartz crystals in watches mainly use 32.768kHz frequencies, and so this is the amount of counts to advance by 1 second on the watch. ",
"The frequency for this comes out from the cut and shape of the quartz used (it is a natural frequency), as the electric pressure from the applied voltage is shape and material dependant (for the piezoelectric material). ",
"To add this up to computer GHz ranges, frequency multipliers can then be used from the stable quartz frequency."
] |
[
"First of all, you shouldn't post this as a comment but in the text field in your actual question.",
"You have mixed up CPUs with crystal oscillators. A crystal oscillator contains a crystal that does indeed vibrate at a very precise frequency. Processors, however, does not \"vibrate\" in the same way. A computer processor is being driven at that specific frequency. There is an oscillator circuit that creates a clock signal at the frequency the CPU is working at (or rather, a significantly lower frequency that is then multiplied up to the wanted frequency.",
"The frequency of a CPU does not indicate that it's vibrating at that frequency, it's indicating that the CPU is running calculations at that frequency. "
] |
[
"There are no quarz-oscillators that vibrate at frequencys beyond 50Mhz. \nFor most digital circuits a PLL is used. This uses a slow quartz oscillator at some MHz as reference, to generate a clock signal at some GHz.",
"For RF stuff you also find osciallotors based on GUNN-Elements, YIG and other fun and interesting structures."
] |
[
"Why do dogs tilt their heads sideways when trying to process something mentally?"
] |
[
false
] |
[deleted]
|
[
"i've always seen it as a visual que of \" say that again, or come back again\" somewhat a partial understanding and interest"
] |
[
"I don't think they do for the processing itself, rather for information gathering. IIRC, that's a visual aid--shifting one eye enhances depth processing by adding a new point of reference."
] |
[
"It could also act as a social mechanism, showing a sort of inquisitive-curiosity body language might bring other members of the pack in to observe "
] |
[
"At what points on or above the Earth does a GPS stop functioning?"
] |
[
false
] |
I know in tunnels or in city areas it can be troublesome at times, but do GPS work in all places on the surface of the Earth generally speaking? Also, at what altitude would they stop working? If I were to go to space and be next to a GPS unit would it give me valid information?
|
[
"GPS units have ",
"been used in space",
" to track to position of satellites that are above the GPS satellites.",
"A GPS works based on information about where the satellites are (which is included in the signal), and the distance from the satellites (really the precise timing of how long it took to reach the receiver). So as long as you have a good signal, it should be possible to figure out where you are. There are a few limitations:",
"You need a signal from at least three satellites to find your location. the GPS satellites aren't stuck at the equator in a geosynchronous orbit, so their orbits can cover the entire globe.",
"GPS signals are very weak so a tunnel, a tree canopy, or even heavy rain can block them. A better antenna can help with this.",
"If a GPS signal reflects off a building or cliff, then the timing gets messed up and it gets your position wrong.",
"The accuracy depends on where the satellites are. As the angle between satellites decreases, so does accuracy perpendicular to them. This is one of the reasons that GPS precision vertically isn't as good as horizontally."
] |
[
"Well, legally you can't own a GPS receiver that operates above 11 miles due to weaponization concerns. That's a human law though, lets assume you had one that bypassed the restrictions.",
"I can't think of any reason they wouldn't work even if the receiver was right next to another GPS satellite. There are functioning ones on the International Space Station which orbits at around 200 miles. Ballistic missiles are tracked using GPS as well, and they frequently get up around 700 to 800 miles. In fact, the satellites themselves communicate with each other using the GPS system and they orbit at 12,000 miles or so. "
] |
[
"You need a signal from at least three satellites to find your location.",
"Four, technically. With three, you still have two valid solutions to the set of time/distance equations - one where you actually are and one at the \"mirrored\" position with respect to the plane spanned by the three satellites."
] |
[
"Does centripetal force cause the same time dilating effects as surface gravity (i.e gravity generated from mass)?"
] |
[
false
] |
Hi All, I work in a stem cell lab and use centrifuges daily to spin cells to the bottom of flasks and what not. We measure the force generated from the centrifuge in RCF, which to my misinformed understanding kind of translates to G. Does the RCF or G experienced by my cells inside to centrifuge cause time to pass more slowly for these cells relative to me, standing outside the centrifuge? I wanted to put a timer inside the centrifuge (or two to balance it) and have another with me to try measure the effects, but thought I should ask first to limit to possibility of me breaking stuff. Thanks
|
[
"Last time I asked this question I got \"No\" as an answer, because the principle only holds locally. For example gravity results in tidal forces, acceleration does not. I'm a layman and on a cellphone, but if you're inclined you can scour my message history from when I asked this same thing here before.",
"EDIT: I.e, gravity and acceleration are not equal.",
"EDIT2: Back on computer again, searched through my history, ",
"this post",
" is a response to a series of questions of mine involving time-dilation induced by an accelerated frame of reference as a substitute for gravity.",
"Courtesy of ",
"/u/mofo69extreme",
":",
"While it's technically correct in that you can mimic accelerated frames by introducing equivalent gravitational fields into special relativity, a gravitational field that is generated by a physical distribution of matter can never be equivalent to SR + an accelerated frame. This is why Einstein was careful in his wording of the equivalence principle, which only holds locally (for small enough regions)."
] |
[
"The centrifuge would slow down time for your cells as it gets faster, thus increasing the Gravity in that location. I imagine space-time like blanket and when something has a high mass in comparison to other areas it possesses more gravity in comparison as well. The higher gravity \"weighs down\" the blanket. In these weighed down areas time moves at a slower rate than that of a spot with less gravity/mass. A good example is if you're near a black hole, which has a lot of mass and thus gravity, your perception of a few minutes or hours there could be, in comparison, years on Earth.\nSadly, I don't believe a lab centrifuge could create any measurable time differences but it's great that you want to experiment! "
] |
[
"When I first asked the question I did some research on Wiki, for example on the LHC. While you there have special relativity due to the relative high velocity you also have (what I can guess is) high acceleration in a circular path. This acceleration, according to what I could find, did not result in the same effects as gravity of the same strength would have. I don't have a source for this at the moment as I'm off to school but I'll edit one in when I get back home. Just thought I'd post if you wanted to dig around for yourself.",
"EDIT: True to my word, here it is. ",
"Wiki on Time dilation of moving particles, Section Clock hypothesis",
".",
"The clock hypothesis states that the extent of acceleration doesn't influence the value of time dilation. In most of the former experiments mentioned above, the decaying particles were in an inertial frame, i.e. unaccelerated. However, in Bailey et al. (1977) the particles were subject to a transverse acceleration of up to ∼10",
" g. Since the result was the same, it was shown that acceleration has no impact on time dilation.",
"Source",
" that the Wiki refers to."
] |
[
"If you flash freeze water, will it still expand in the same way as 'normal', gradual freezing?"
] |
[
false
] |
One of the main issues for cryogenic freezing is that the water is the blood expands. The blood vessels housed in the haversian and volkman canals in turn expand and cause microfractures throughout the osteons. It is often quoted that flash freezing is a way to overcome this, but is that entirely true? Would it not be more effective to find a way to safely introduce an antifreeze chemical like that seen in some Arctic fish species?
|
[
"Water will expand regardless of how it is frozen; however, what changes is the size of the average ice crystal. When you slow freeze water it tends to build one giant crystal over time since water can slowly collect and arrange itself to form a unified solid. When you flash freeze each water molecule basically has to grab the nearest neighbor and as a result the average ice crystal tends to be significantly smaller since they don't have enough time to diffuse and order itself. ",
"Now as far as the biological side of this I remember hearing about it a long time ago because my sister did her master's work on this topic, but I sorta tuned it out since I lean towards the physics side of the science spectrum instead of the bio side. Not enough math for my interest. :)",
"It could have something to do with the formation of large ice crystal can also cause sharp ice to form which can tear tissues. But this is just conjecture so I'll defer to someone who is a little more knowledgeable on the subject. "
] |
[
"From a physics perspective, do you think it would be possible to near instantaneously freeze blood to the point where the crystals are small enough not to expand beyond the capacity of the Haversian canal? How would you go about doing this?",
"No. When ice crystals form, the space occupied by ",
" expands, so you cannot avoid the overall expansion. Regardless of how small or large the crystals are, expansion is unavoidable.",
"One of the alternatives is to make ",
"\"amorphous ice\"",
", that is, to freeze water so fast and under intense pressure that water ",
", and instead simply freeze in their position as if it was a liquid. Unfortunately, we haven't found a method that generates amorphous ice at 1.00g/mL, and all the amorphous ice requires extremely high pressures (~GPa) that our biological structures cannot survive.",
"Would it not be more effective to find a way to safely introduce an antifreeze chemical like that seen in some Arctic fish species?",
"The \"antifreeze chemical\" in these fish species are different to the antifreeze we use in cars. Antifreeze in cars are typically some alcohol mixture that lowers the freezing point of water (think: storing vodka in freezer). This kind of antifreeze will destroy biological structures such as cell walls and proteins by upsetting hydrophobic interactions.",
"The antifreeze chemicals in these fish species are actually complex proteins that have an ice-like surface (AntiFreeze Proteins/AFPs). The best picture I can find is a thumbnail ",
"here",
". AFPs bind to small, nucleating ice crystals, and stop them from growing further. This does not remove small ice crystals, but it effectively stops their growth, and so avoid microfractures.",
"Since AFPs do not re-dissolve ice crystals, the reaction is not reversible, and so we must replenish the AFPs regularly. It will reach a certain point where no more AFPs can be added, and so this method cannot be used to preserve something indefinitely.",
"Alternatively, we need a method to redissolve ice nuclei which are bound by AFPs ",
". Some kind of advanced MRI/NMR to pick out ice nuclei, and targeted laser heating, perhaps?",
"To read more about AFPs:",
"http://www.nature.com/nature/journal/v308/n5956/abs/308295a0.html",
"http://www.nature.com/nature/journal/v375/n6530/abs/375427a0.html",
"http://www.nature.com/nature/journal/v429/n6988/abs/429153a.html"
] |
[
"Thanks, that's really interesting. From a physics perspective, do you think it would be possible to near instantaneously freeze blood to the point where the crystals are small enough not to expand beyond the capacity of the Haversian canal? How would you go about doing this?"
] |
[
"What does this answer for the integration of sqrt{1+x^3} mean?"
] |
[
false
] |
So I'm using the sympy library in Python, and I wanted to see the result for the integration of sqrt{1+x^3}. The answer I got was . I only recognize the Gamma Function notation in this expression, but I don't know how I can evaluate this. What does the F_1( ) represent? Some observations: I tried using limits as (0,3) in this integral, and got a real valued . The intergration for sqrt{1+x^k} is , which is pretty neat!
|
[
"The function 2F1 is the ordinary ",
"hypergeometric function",
", here expressed with a = -1/2, b = 1/3, c = 4/3 and z = -x",
". You can check the documentation for ",
"sympy.hyper",
".",
"It's a power series type expression that can express a large family of parametrized functions with different choices of parameters a, b and c, which I suppose is what makes it appealing for a tool like sympy.",
"As you can see the wikipedia page has some integral results involving it, but exactly which formulas go into integrating sqrt(1+x",
") I don't know."
] |
[
"One of the better references for the hypergeometric function(and a whole lot more) is ",
"Abramowitz and Stegun",
" if anyone wants to look deeper.",
"It was written in the 50s for the US government so it's very nicely in the public domain and you can find in many places online."
] |
[
"I can't break down this integration for you, because I simply don't know how it happens. But I can say that it's not at all difficult to find simple elementary functions whose integrals (antiderivatives) aren't elementary. Symbolic integration is just a really tricky problem.",
"The Gamma function is maybe even the least surprising part. It's true that you don't see it a lot in undergrad calculus, but it's a function that's both closely related to factorials, which play a role in many power series, including the hypergeometric function, and also is defined using a definite integral."
] |
[
"How much does metabolism factor into alcohol tolerance?"
] |
[
false
] |
[deleted]
|
[
"When people refer to metabolism they usually mean basal metabolic rate which is the amount of energy burned at rest. This doesn't really come into play with alcohol tolerance as alcohol breakdown is determined by alcohol dehydrogenase concentration in the liver and body composition. Regardless it only really varies at most 10% between individuals. ",
"As for the differences between women and men; women tend to have lower body mass and less water in the body and thus will have a higher concentration of alcohol in the blood given a similar amount consumed. Women also typically have lower amounts of alcohol dehydrogenase and thus can't break down alcohol as quickly as men. Of course men and women lie on a bell curve of alcohol tolerance with overlapping tails and some women will have a higher tolerance than some men."
] |
[
"That might be tricky problem to solve, because I'm sure some of it is perception as well. ",
"Have access to a breathalyzer? That'd be a fun experiment, take readings from each in the am and see if there's really a difference in metabolism or if the difference is mostly perception based. "
] |
[
"maybe your friend and you could go halfsies...for science! \nstill a bit much, but if you ever decide to go through with some experimentation, come back to the thread and let me know!"
] |
[
"Would a sharpie work in zero gravity?"
] |
[
false
] | null |
[
"If you were correct, then you wouldn't be able to write with a sharpie for an extended period of time on the ceiling. Sharpies feed ink primarily based on ",
"Capillary Action",
". Try it."
] |
[
"If you were correct, then you wouldn't be able to write with a sharpie for an extended period of time on the ceiling. Sharpies feed ink primarily based on ",
"Capillary Action",
". Try it."
] |
[
"In the context of this discussion, positive Gs would pull ink towards tip when tip is oriented Down. Zero G would have no pull. Negative Gs would pull the ink in the opposite direction, i.e. towards the rear of the marker as it was pointed up towards the ceiling. A sharpie will work through ",
"Capillary Action",
" regardless of the direction of gravity, at least for Earthly gravity magnitudes."
] |
[
"How/why do high-elevation limestone formations exist?"
] |
[
false
] |
[deleted]
|
[
"Tectonics / deformation. Most limestones are marine and form at / very near sea level (there are lake carbonates, which can form in high elevation lakes, but the vast majority of carbonates are marine). Deformation of rocks, driven ultimately by motion of the tectonic plates, can exhume or bury rocks depending on the details of that deformation. At its simplest, imagine the behavior of a single ",
"reverse or thrust fault",
" driven by compression. One side of this fault will be displaced upwards relative to the other (i.e. the hanging wall), effectively increasing the elevation of the rocks on this side of the fault. Mountain ranges are built through series of thrust faults which will ultimately push up and exhume large packages of rocks."
] |
[
"Portions of the rocks which make up the Himalaya are marine rocks, yes. This is pretty common in collisional mountain ranges (i.e. the Himalaya are not unique in this respect in any way) because the formation of a collisional mountain range is usually preceded by consumption of an ocean basin by subduction and then, finally, collision. Some portion of the sediments in that intervening ocean basin will be \"scraped\" off and accreted into the mountain range as it grows."
] |
[
"For an even more dramatic example of this, the rocks at the summit of Mount Everest are composed of fossil-bearing ",
"marine limestones",
"."
] |
[
"After the nuclear explosion at Hiroshima, the shadows of some victims were left on the ground, and some are even etched in stone to this day. What causes this to happen?"
] |
[
false
] |
I would however like it explained very, very simply if possible. I'm a fairly simple man myself.
|
[
"As I understand it:",
"Light and/or heat from atomic bomb explosion bleached the concrete sidewalks. If someone was standing there, the light didn't hit the sidewalk to bleach it, so the shadows are the unbleached parts."
] |
[
"Nuclear weapons are incredibly bright, so much so that a large portion of the blast energy and almost all of the heat comes from the light. Everything around the object is burnt/bleached when the flash occurs. It is such a quick effect(about 10 seconds), however, that even being out of direct line of sight will mean the difference between a third degree burn, and just feeling like you are in an oven from hot air.",
"Take a look at this video.",
"See that cloudy stuff coming off of the buildings before the blast wave arrives? That is actually paint, frying off the side of the building from the light."
] |
[
"I noticed how that featureless cinderblock house took the blast way better than any of the other buildings, I wonder if that has anything to do with why they were such a popular design back then."
] |
[
"How do water-soluable ingredients, like sugar, affect the volume of a system?"
] |
[
false
] |
My fiancee and I were curious when we were measuring out ingredients for dinner tonight. If I have 1/4 cup of sugar and mix it with 3/4 cup of water, is the total volume of the system 1 cup, or because sugar is water-soluable, is the total volume less than that?
|
[
"Good question. It actually varies a bit, depending on the way that the molecules are solvated. Any solute going into water is going to disrupt the natural state of liquid water's structure. And that can go either way. Some salts will actually make the overall structure more compact than it was before, and you'll get a contraction of volume, while other solutes can expand it. Figuring this out from first principles is extremely hard, actually, as is figuring how how soluble a given substance will be in water in the first place. (It all depends on hydrogen bonds and the balance of polar/nonpolar interactions, crucial things that we struggle to model computationally).",
"The physical chemistry term for the volume effect is \"partial molar volume\" (",
"http://en.wikipedia.org/wiki/Partial_molar_property",
"). That page, for example, has a graph of the volumes of water/ethanol mixtures. It's always less than either of the pure substances, and it bottoms out at about 40% ethanol. That was all determined experimentally, though - all these things have to be."
] |
[
"So then the question that follows from my fiancee would be, if I measured them in the same cup (in this case, measured out 1/4 cup of sugar and then filled it with water until it hit the 1 cup mark), would it be \"accurate\" or should we not be lazy with the measuring?"
] |
[
"I'd say that you shouldn't be lazy, unfortunately. You're going to be off by a significant amount compared to measuring the dry ingredients (sugar) and the liquids in separate containers.",
"Here's an article on making nectar solutions for hummingbirds that goes into this exact problem:",
"http://www.museum.lsu.edu/~Remsen/HUMNETf/sucrose_article.html",
"Note that (for example) four cups of water and one cup of table sugar (sucrose) gives you a final volume of 4.54 cups!"
] |
[
"[Chemistry] How does a bond store energy?"
] |
[
false
] |
Hi! I'm currently studying Biochemistry and one of the fundamental molecules for all biochemical reactions is of course ATP. I still cannot grasp the concept however, how ATP stores energy. There is hydrolysis of bonds that releases phosphate groups and is I understand, forming a bond releases energy whereas destroying it needs energy. In the case of ATP you break a anhydride bond making it ADP and Phosphate - with a release of energy. Where does the energy stored in those bonds come from? I get that the Phosphate in the body is never actually used up - its just split off and then later reused. And when regenerating the ATP you have a proton gradient that drives the ATP Synthase. but how is a bond actually storing energy ? I'm really confused about that...
|
[
"I will try to give you a super simple answer to your question using an analogy.",
"So, imagine a ball on a hill, this ball is on the top of the hill in a small divot and isn't moving, but clearly would fall and release potential energy if it wasn't held in place. This ball is in a \"high\" potential energy state, where the bottom of the hill is \"low\" potential energy state. Now imagine this ball represents your bond, it is currently stable, but has the ability with a small push or interaction to fall far down. The process of getting over the first bump is breaking your first bond, and the bottom of the hill is the new bond. The new bond is \"stronger\" than the first one in the same way that falling down a hill means if you want to launch into space you need more energy than if you launched off the top of the hill. With the earth representing what your atom/molecule/electron is bonded to. In other words, your ball after falling down is more strongly \"bound\" to the earth.",
"The long story short here is, the first bond is a high potential energy state, and when you cause that state to fail and you end up in a lower energy bond, the difference in energy between the bonds is released as most often kinetic energy/movement/heat in the system. Your chemical bonds are perfectly analogous (but on a significantly smaller scale) to an object in the gravity well of a planet. ATP is a man standing on the top of Mt. Everest, and ADP + Phosphate is that man splattered at the base after falling off (with his falling energy used for something.)",
"I may have rambled a bit, but I hope I helped."
] |
[
"In the case of ATP, from what I understand, the ATP is rather unstable. It takes a lot of energy to force three bulky phosphate groups into such a small area, so ATP easily hydrolyses to ADP+Pi. This reaction can be coupled to other ones to drive it. ",
"I.e. you take the weak ATP bonds with high energy electrons in them which are easy to break apart (just requiring some energy and an enzyme to speed along the process) and you can use the hydrolysis to form species which would be energetically unfavorable to form but can be made more easy to form if you give them the additional energy of forming a bond with the phosphate group.",
"The energy comes from the strong bonds formed between the very reactive and unstable orthophosphate and the new molecule. I believe hydration shells also play a part, from what I remember- they are quite favorable for the ADP and the Pi, with strong hydrogen bonds that are better than those for ATP."
] |
[
"The triphosphate groups store a lot of electronegativity (P is fairly electronegative, O is very electronegative) and the individual phosphate groups sterically hinder each other. Getting rid of a phosphate can help that and release a lot of energy.",
"Also, any energy required to make a bond is what you get when you release it (enthalpy will return to its standard state), except for some entropy."
] |
[
"How is it possible that scars remain visible after decades?"
] |
[
false
] |
Doesn't the regeneration of cells in the skin eventually make the scar disappear?
|
[
"Asked three days ago",
". Please use the search function."
] |
[
"A quick search will tell you when the cut goes past the skin cells scaring occurs, it is a connective-like tissue, not made of living cells "
] |
[
"Pravusmentis was correct, it is not made of living cells. Scar tissue is the result of our blood-clotting response to cuts. We evolved the ability to stop bleeding within minutes/hours by compromising the regeneration of normal dermal layers in that area. Without normal dermal layers the area will not regenerate normal skin for the rest of your life. It may sound weird but it is true. There are scar-removal gels which are mainly holistic remedies. I've heard good results from people who have used them. I do not think there is considerable evidence based science/medicine on these."
] |
[
"Why don't satellites fall into an equatorial orbit around planets?"
] |
[
false
] |
The planets roughly orbit the sun's equator, right? Why can we send satellites in any directional orbit around a planet that we want? Why don't they eventually fall into an equatorial orbit?
|
[
"It's not that the planets have fallen on to the sun's equator, so much as that their creation shared a common angular momentum. The sun rotates in the same plane as the planets orbit because as these particles collapsed they preserved the net angular momentum.",
"But satellites are launched into orbit and then have their angular momentum changed to a new orbit. Now maybe, after enough collisions and interactions the satellites would fall into an orbit that shares the same net angular momentum, but I kind of doubt it."
] |
[
"I don't think there's any reason for satellites if the Earth to \"naturally\" change from their current orbit to an equatorial orbit. In fact, near earth orbits along the equator are subject to more perturbations of their orbit than satellites in stable orbits at about 65 and 115 degrees IIRC.",
"Plus, Pluto isn't in an orbit around the Sun's equator, it's significantly more inclined than the planets."
] |
[
"Satellites actually do do that, to some extend. Nearly all satellites have some sort of stationkeeping capabilities to maintain their orbits from various perturbations. The thing is, those perturbations are usually extremely minor, and it would generally take tens or hundreds of years at the minimum to make really significant orbit changes.",
"Planetary rings are a good example of orbiting debris reaching an equilibrium. But that happens over millions of years."
] |
[
"Why are drinks carbonated with carbon dioxide instead of another gas?"
] |
[
false
] | null |
[
"Another important reason is solubility. CO2 is about 200 times more soluble in water than nitrogen and oxygen, 100 times more than argon or helium, etc. That means a soft drink that's been pressurized with one of those gasses will go flat faster than a co2 drink.",
"There are gasses more soluble than CO2, like SO2 and NH3, but they're not exactly safe to consume."
] |
[
"CO2 was the first form of gas dissolved in soft drinks. When you make root beer from scratch the yeast will consume the sugar to produce CO2 as a waste product. When in a sealed container, the gas will dissolve into solution. It made for a nice effect, you open the container and the gas release would create a fizz. When soft drinks moved to the soda fountain it made sense to recreate the fizz. CO2 was the logical gas of choice because the additional 'bite' created by the carbonic acid formed from the dissolved gas in the soft drink. This kept everything the same as individually made soft drinks and resulted in the continued popularity of soft drinks. "
] |
[
"Thank you! This is the best answer of them all. CO2 is highly soluble in water, hence why it is found so often in nature."
] |
[
"Why do White Blood Cells not form clots in capillary beds?"
] |
[
false
] |
[deleted]
|
[
"It isn't the size of sickle cells that's the problem. It's their shape. Their distorted shape causes them to not move through the capillaries as smoothly. These blockages accumulate and can lead to organ damage due to hypoxia.",
"It isn't the cells that clot; it's clotting factors (certain proteins) in the blood that clot. These clotting factors are activated when the linings of blood vessels are damaged by high blood pressure or hypoxia. This causes blood clots to form more easily all over the body. There is also widespread vascular inflammation.",
"Another problem is the misshapen hemoglobin in the RBC. This mutated hemoglobin damages the cell membranes and is less efficient at carrying oxygen.(Edit to clarify: it's the damage to the membrane that creates the sickle shape.) It makes them quite fragile and short-lived. The bone marrow compensates by making more sickle RBCs, which leads to more blockages. The hemoglobin floating free in the blood places additional strain on the liver and kidneys. They have to do more with less oxygen, further contributing to organ damage.",
"Edit to add: WBCs are too large to enter the lumina of capillaries so they don't get stuck like sickle RBCs."
] |
[
"Thank you for bringing up the rigidity. That is another aspect of the pathophysiology I hadn't thought to mention. I barely scratched the surface, just enough to answer OP's questions and correct some misconceptions. The pathophysiology is very complex and entire textbooks have been written about it.",
"But you're incorrect about clotting. The damage to the endothelia of blood vessels activates the intrinsic pathway, leading to hypercoagulopathy. This is why sickle cell patients are prone to strokes and heart attacks.",
"Here",
" is where I went to verify my answer to OP was correct, though by no means comprehensive."
] |
[
"It isn't the size of sickle cells that's the problem. It's their shape",
"I think it's more about rigidity/elasticity. Normal hemoglobin has charged amino acid residues which repel each other. In sickle-cell disease, they are substituted for valine, which is neutral. Rather than repelling, they stick to each other. This causes red blood cells to become rigid, and they get stuck in capillaries, leading to hemolysis.",
"I don't think blood clots are part of the pathophysiology, but correct me if I'm wrong."
] |
[
"How does shingles cause a rash when the infection is located all the way in the dorsal ganglia?"
] |
[
false
] | null |
[
"The varicella zoster virus (VZV) can lie dormant in the dorsal root ganglia for decades after the immune system has cleared the virus from the rest of the body (from an initial chickenpox infection). ",
"However, once reactivated, the VZV resumes replication and virions are transported through neural cells from the ganglia into the associated skin area. The subsequent immune response produces localized inflammation, blistering, and pain."
] |
[
"I see thank you"
] |
[
"As a followup, how do we know that the cells are lying dormant in the dorsal root ganglia?"
] |
[
"What would happen if a drug addict was hit with amnesia?"
] |
[
false
] |
Would he lose his addiction?
|
[
"It's a fair question, because it's hard to imagine an addict who doesn't know their addiction.",
"A more polite answer would point out that they would suffer withdrawal symptoms and either stumble across something that \"fixes\"them, or seek medical treatment, or recover from them, or die."
] |
[
"But would they know the source and solution to their pain?"
] |
[
"There doesn't have to be dependence or tolerance for there to be an addiction. For opioids and alcohol and some other substances, yes that is the case, but the notion that there has to be tolerance and dependence to classify a it as an addiction or substance use disorder is a big misconception. ",
"Morphine does not mimic dopamine, it is not a dopamine receptor agonist, a dopaminergic agent or a dopamine mimetic. An example for that would be drugs like cabergoline or bromocriptine. Morphine acts on the CNS opioid receptors (Primarily the mu, kappa and delta subtypes). "
] |
[
"Is there a definitive moment where you transition from \"awake\" to \"asleep\"? What happens at that time, if it exists?"
] |
[
false
] |
[deleted]
|
[
"There is not a precise moment when the transition occurs. In simple terms, this is because different parts of the brain can \"fall asleep\" at different times.",
"The way the onset of sleep is usually defined is in terms of ",
" brain activity, as measured using the electroencephalogram (EEG), i.e., electrodes on the scalp. There are characteristic changes in brain activity between wakefulness and sleep.",
"Using a set of rules, technicians are trained to \"score\" sleep in 30 second blocks, based on what is the primary mode of brain activity in that 30 seconds. (Mathematical algorithms can do it too). Brain activity is scored as wake, rapid eye movement (REM) sleep, or non-REM (NREM) sleep, with NREM sleep divided somewhat arbitrarily into 3 stages: stage 1, stage 2, and stage 3. Sleep onset can be defined as when somebody first moves from wake to stage 1 sleep (lightest stage of sleep). This just means the first 30 second block that is primarily stage 1 sleep.",
"Across the transition from wake to sleep, there is a gradual lessening of awareness, a gradual change in brain activity, and a gradual reduction in muscle tone. There is not a single discrete moment where the brain suddenly switches into sleep.",
"The thalamus actually \"falls asleep\" before the cortex by ",
"several minutes",
". We also know now that it is possible for part of the cortex to be asleep while other regions are awake. Sleep isn't just a global brain phenomenon. ",
"It can occur ",
" within neuronal assemblies",
". When we are asleep, most of our neuronal assemblies are \"asleep\", but they may not all make the transition from wake to sleep at the same precise moment. It is also probably possible for some neuronal assemblies to transiently awaken while others are still asleep -- this is now thought to be the basis for some parasomnias, like sleep-walking."
] |
[
"Sleep onset has associated amnesia that is normal as you transition to sleep. The amount of amnesia though, is variable. This is why you never remember when you fall asleep. Although generally sleep and wake is considered mutually exclusive, that is not always the case. So sometimes there is some bleeding of one into the other (which sometimes lead to things like hypnogagic hallucinations as you fall asleep, or sleep paralysis as you wake-- google them). But to keep it basic as you start to fall asleep, you go into transitional sleep (N1) which (hopefully) transitions you to a deeper sleep (N2). People's perception of sleep in N1 seems fairly variable (i.e. some think they are awake, some think they are asleep), N2 and other stages are for the most part experience by most as clear sleep.",
"With the exception of dreams in REM, most of sleep also seems to have some level of amnesia/timelessness associated with it. Whereas in REM dreams time is experienced one-to-one (as opposed to what the Movie \"Inception\" will have you believe), in other states there seems to be less clarity from the sleeper."
] |
[
"There seems to be a window of tiredness for falling asleep, and if sleep doesn't occur within that window the person feels more awake and has trouble falling asleep.",
"There are many reasons that this can occur. A common reason among people in modern society is light-induced delay of the circadian rhythm.",
"Sleep is regulated by two processes:",
"There is an increasing drive to sleep with increasing time spent awake. This is usually called the ",
"sleep homeostatic process",
".",
"There is a circadian rhythm in sleepiness and alertness.",
"The circadian rhythm increasingly promotes wakefulness across the day, with a peak that normally occurs a few hours before bedtime. ",
"This serves to offset the increasingly sleepiness that would otherwise occur across the day due to increasing time spent awake",
".",
"The peak in circadian alertness is sometimes called the \"forbidden zone\", because it is very difficult to initiate sleep at this time (sleep onset is forbidden). This is why it's typically very difficult for people to initiate sleep a few hours earlier than normal.",
"If the circadian rhythm is delayed, this peak in alertness arises around bedtime, meaning you get a second wind right when you are trying to fall asleep. The circadian rhythm is mostly responsive to light, and we know that even relatively low levels of artificial light delivered after sunset cause delay of the circadian rhythm."
] |
[
"How can you melt styrofoam to remove the air and then reuse the raw material for remolding into something else."
] |
[
false
] |
I've seen how they recycle syrofoam by heating and melting it but it's used for hard plastics like windowframes and whatnot. What I'd like to know is, is it possible to use the dense material and remake/ mold it back into styrofoam? I've seen the machines in China do this but they all use a base powderlike material that expands 50 times its size when heated with steam and fuses into it's shape. Reason I'm asking is there's many environmental uses and applications for styrofoam. (insulation, building etc) getting hold of it is easy but meling it down and then reshaping back is proving difficult to find information on. Help !
|
[
"Acetone will melt it, then it gets hard again after the acetone evaporates. Doesn't resemble Styrofoam anymore though, more like regular hard plastic."
] |
[
"I was at a talk by Phil ",
"Jessop",
" not too long ago when he was talking about this. ",
"Recycling styrofoam is non-trivial to do (cheaply) because the air bubbles (and most of styrofoam is air) messes up extrusion and other large scale processes. It's simply cheaper to make new stuff from scratch. One of the things the Jessop group do at Queens was exploring using CO2 for recycling the material - check out their website/papers for more info."
] |
[
"Instead of just a question about the science, it sounds like you're actually trying to do ",
" with it (i.e., have an application in mind). What is it that you're trying to do? What does \"no chemical\" mean? What facilities do you have available? Where are you getting your scraps from? How are you getting the air out from it? Melted polystyrene is a viscous liquid, which is why getting rid of the bubbles are difficult."
] |
[
"How does gravity work? How is it that something, just because it has mass, pulls everything towards it?"
] |
[
false
] |
Why is this big dead rock pulling on me just because it's a big dead rock?
|
[
"Well, at some level the answer to every \"how\" question just leads to more \"how\" questions.",
"Right now, our best understanding of gravity is that it's the curvature of spacetime, and that \"time\" bit is important.",
"Let's start with flat spacetime. In everyday, uncurved, flat spacetime (which is really anything ",
" the spacetime we actually experience everyday, but that's language for you), if you and I are initially at rest relative to one another then we remain at rest relative to one another. But what does that really mean? It means that, taking my reference frame to be the one in which we're working, if I measure the distance to you when my clock tells me it's one time and then measure the distance to you when my clock tells me it's some other time, I will get the same answer both times. Of course, we're both moving into the ",
"; that's how we get from my clock telling me one time to my clock telling me another time. But we're not moving ",
". So if we were to draw a picture of spacetime, we might put time vertically and space horizontally, and then our paths would just be two vertical lines, like ",
"this",
".",
"Ok, but what if spacetime is ",
". Then, depending on how it curves, our paths in the above diagram will no longer be straight, vertical lines. Not because there's some force moving us around, but just because the \"straightest possible line\" in a curved space isn't the vertical line of the above diagram. It turns out that if we work through the math, they will in fact bend toward one another and meet at some point, kind of like ",
"this",
" (note I didn't actually work out the exact curvature here; this is just representative of what our curved path through spacetime ",
" look like), where I've assumed that we get stuck together once we collide.",
"Now, the next question is how does the presence of mass (really energy) cause spacetime to curve. We have no answer to that question; it appears to just be a property of our universe that the local curvature of spacetime is determined entirely by the local stress-energy-momentum density."
] |
[
"If you find out, you can go get your nobel prize in Stockholm "
] |
[
"Think of space-time as a fabric with a giant massive ball on it as your massive object. That ball depresses the fabric and other masses will roll down into it if they come too close. Time is also slower because space-time are linked. If the RATE of time depended on the smoothness of this fabric, an indentation would create a little pool where the flow of time moved a bit slower. "
] |
[
"How does neutral odor-neutralizers work?"
] |
[
false
] |
I just got to thinking about this. I remember in "Police Academy" (Movie), one of the guys used an air freshener to remove the gas (did not work ofcourse). Got me thinking, those neutral ones, how do they remove smell? I guess the same can be applied to deodorants too.
|
[
"Some of them contains a molecule that's donut-shaped, with the donut-hole having affinity to smelly molecules; an example of this pairing is ",
"cyclodextrin",
" (as host), and ",
"thiols",
" as guest. As the smelly molecules are now sequestered, they are no longer available for your odor receptors, thus \"neutralized\" (nothing related to neutralization in the acid-base chemistry sense).",
"As to ",
" these hosts bind to an unknown guests: it mostly relies on non-specific, weak interactions. This is the subject of a field called \"",
"supramolecular chemistry",
"\", or, chemistry beyond the molecule, for which the 1987 Nobel prize was awarded.",
": bonus fun fact. The reverse application is also possible: there were Japanese underwear that have \"plugged donuts\", specifically, plugged with shark-liver-oils. The idea is that these oils will now only be released slowly, keeping your bottom smooth for a prolonged period. "
] |
[
"He's asking about products that ",
" use a masking scent, but rather neutralize the smell completely."
] |
[
"Thank you! Good fun fact too :)"
] |
[
"How small is the smallest possible rocket that can reach space?"
] |
[
false
] |
To make it simple: A regular cigar-shaped solid-fuel rocket. It can be multi-staged if necessary, but stages are sitting on top of each other (i.e. no strapped-on boosters). Space is defined as begining at 100km above sea-level. Launched from equator. Propellant, can be any solid propellant (not sure what is the best). I am not sure how to do the math. I am looking for diameter and length of the rocket as well as amount of propellant on board. I am sure someone must have calculated this before. Can anybody point to some references?
|
[
"Data point: ",
"this amateur rocket",
" reached an altitude of 115 km and it is 21 feet long, 10 inch diameter with a launch weight of 724 lbs."
] |
[
"That's pretty awesome."
] |
[
"Nice find! thank you."
] |
[
"What state of matter do soap bubbles fall into?"
] |
[
false
] | null |
[
"the bubble part is liquid, the air inside is gas"
] |
[
"At the interface between the air and the water, there will be a layer of ",
"surfactant",
" molecules (the soap). Part of the surfactant molecule is hydrophilic, and part is hydrophobic. The molecules arrange themselves along the surface so that the hydrophilic part is facing the water and the hydrophobic part is facing the air. This reduces the surface energy of the interface, stabilizing the bubble shape. ",
"A field of bubbles has vastly more surface area in contact with air than a flat layer of water. Normally the surface area of the air/water interface tends to be minimized to reduce the energy of the system, which means that bubbles would be unstable, but with the surfactant molecules reducing the surface energy at the interface the energetic \"cost\" of the increased surface area is very low. ",
"None of this changes the phase of the materials; the air is still a gas, and the water is still liquid, and the surfactant molecules are still (technically) dissolved in the liquid, although they have preferentially adsorbed to the air/water interface. "
] |
[
"Byron690 has it exactly right. Something interesting to note is that if it was a bubble of just a pure liquid and gas, it probably wouldn't be stable. You need what is known as a surfactant, in this case soap, to lower the surface tension. This effect helps stabilize the bubble. "
] |
[
"How strongly does the IQ bell curve correlate with achievement?"
] |
[
false
] |
[deleted]
|
[
"Here's",
" a paper that attempts to relate Piaget IQ tests to standardized test scores for school achievement, and finds little overlap.",
"This",
" study states >When success measures were regressed against intelligence and personality scales or factors, intelligence did not account for variance beyond that explained by personality.",
"However, ",
"this one",
" seems to indicate that it can be predictive of success, but only in very specific circumstances and that life outcomes (getting a job, getting a career, rate of pay), when controlled for other promotional factors that influence/are influenced by IQ, aren't largely dependent on IQ."
] |
[
"They do answer your question. The answer is \"less than the majority\". Especially that 3rd paper I referenced. I realize you probably don't have access to the full article, but allow me to pull out some key points.",
"Under the section: Employment Prospects and Wealth Generation ",
"To what extent do IQ scores, obtained before individuals enter the labor force, predict such indicators of social status as employment and wealth? ... IQs themselves predict about 25% of the variance in SES and about 15% of the variance in income. Controlling for parental SES results in a reduction of about 25% in the predictive power of IQ. Jencks (1979) observed that if two brothers who grew up in the same family were compared on their SES as adults, the brother who had the higher IQ in adolescence would tend to have the higher adult social status and income. This path, however, is mediated by amount of education. The higher-IQ brother would be more likely to get more education and, correspondingly, to have a better chance of succeeding socioeconomically.",
"This is stating that IQ scores predict about 25% of the differences in socioeconomic status that you see, and about 15% of the differences in income that you see. When you control for factors that influence IQ and factors unrelated to IQ that influence individual outcomes (eg. the socioeconomic status of the parents.)",
"IQ seems to be predictive of the reaching of all steps of career life in a stable society, where Western schooling is valued and rewarded, income is scaled in rough correspondence to years of education, and highly skilled labor is needed. What happens, however, in societies passing through a stage of turmoil, where the social value of education is not high, income does not correlate well or at all with amount of schooling, and there is little demand for highly skilled employees? Very little research evidence is available that can help answer this question. Various writings on cultural psychology, discussed later, suggest that, in most developing societies, there is a conflict between the kinds of intelligence valued by schooling and the kinds of intelligence valued by local communities.",
"This further modified the previous percentages by stating they only hold up when you have a society that values and rewards schooling. Currently, the economic (in?)stability and job potentials in the United States, for example, are cause less of a correlation with success for those graduating with a Bachelors degree than they did previously.",
"Under the section: IQ and Career Outcome",
"There are statistically significant correlations between \"general intelligence\" composites and performance within a job (for reviews, see Hunt, 1995; Wagner, 1997). Hunter and Hunter (1984) reviewed a large number of studies and found that, when corrected for sample biases, the correlations between intelligence and job performance ranged from .27 to .61 (see also Schmidt & Hunter, 1998). When supervisor ratings were [End Page 9] used as a criterion, the mean population validity coefficient was .53; it was higher for more intellectually demanding jobs (e.g., the validity estimate for \"manager\" was .53) and lower for less intellectually demanding jobs (e.g., the estimate for \"clerk\" was .27). Hunter (1983) reported that differences in intelligence accounted for as much as 29% of the variance in job-performance ratings after the ratings were adjusted for error variance. The author found that IQ was more powerful as a predictor of success on the job than was any other variable considered. ... In sum, cognitive ability predicts anywhere from 4% to 30% of the variance in job performance.",
"This is saying that for highly skilled jobs (they cite \"manager\"), IQ plays a larger role in job performance than with lower-skilled jobs (they cite \"clerk\")."
] |
[
"Define success. "
] |
[
"What is the reason for goosebumps?"
] |
[
false
] | null |
[
"Yup! Here's some copy pasta: \nGoosebumps are a physiological phenomenon inherited from our animal ancestors, which was useful to them but are not of much help to us. Goosebumps are tiny elevations of the skin that resemble the skin of poultry after the feathers have been plucked. (Therefore we could as well call them \"turkeybumps\" or \"duckbumps.\") These bumps are caused by a contraction of miniature muscles that are attached to each hair. Each contracting muscle creates a shallow depression on the skin surface, which causes the surrounding area to protrude. The contraction also causes the hair to stand up whenever the body feels cold. In animals with a thick hair coat this rising of hair expands the layer of air that serves as insulation. The thicker the hair layer, the more heat is retained. In people this reaction is useless because we do not have a hair coat, but goosebumps persist nevertheless. "
] |
[
"If were as hairy as our ancestors, goosebumps would fluff our coat to make us look bigger and scare off attackers. ",
"At least that is what my 10th grade biology teacher told me back in 1979. If science has come up with a better answer since then, I apologize. "
] |
[
"By erecting hairs in animals that haven't lost their fur, more air is trapped in the fur, keeping the animal warmer. "
] |
[
"Why don't they power comet landers like the Philae with small, reliable nuclear generators like they did with Voyager II (which is still generating power now 37 years later)?"
] |
[
false
] |
Philae has been with very low power levels since it set down on the comet a few weeks ago, because its solar cells are not receiving enough direct sunlight (press says it's likely in a shadowy area of the comet). Why did mission designers subject such an important aspect of the mission (power!) to the variability of sunlight coupled with the highly variable landing conditions and terrain? Aren't reliable, small, tested and tried radioisotope thermoelectric generators readily available? Haven't they been successfully used in space exploration for many decades?
|
[
"Aren't reliable, small, tested and tried radioisotope thermoelectric generators readily available?",
"No, they're rare and very expensive. The United States stopped producing plutonium ",
"238",
" (the kind used in Voyager) in 1988, and starting purchasing it from Russia. ",
"Now even Russia is running out. More can be produced, but it's an expensive process. I'm not sure any European nation has the capability, so ESA would have had to purchase it from Russia (if they were willing to sell). ",
"According to this",
" it would cost roughly $5.5 million per pound to create if production was restarted. Curiosity used 11 pounds of plutonium 238. ",
"Haven't they been successfully used in space exploration for many decades?",
"Yes: Voyagers 1 & 2, Curiosity, Cassini–Huygens and New Horizons."
] |
[
"It's not a nuclear reactor per say. It's a radioisotope thermal generator, which takes heat and converts it to electricity using the thermoelectric effect. RTGs use radioactive material but they do not utilize fission or fusion and are not reactors. ",
"RTGs have a lot of mass for their power output. If you put an RTG on Philae, you would now need Philae to have more fuel, larger components, sturdier components, bigger engines, which in turn would require Rosetta to be bigger, have bigger engines, more fuel, which means the original launcher would need to be bigger. If the cost and mission objectives do not outweigh the added complexity and weight of having an RTG, then it's not really worth it. In this case, I think putting an RTG in would drastically increase cost and complexity and may have been prohibitive to even doing the mission in the first place. "
] |
[
"Pity Philae was sent by the Europeans then?"
] |
[
"If our intestines are filled with other living creatures, how did THEY get there?"
] |
[
false
] |
Its said that the majority of our digestion is owed to a staggering host of bacteria that preside within our flesh-guts. Its the reason we can process grains and such, but how did they get there? Is a fetus in a womb containing the same bacteria we are? Are they getting them from their mother, or what?
|
[
"Initially, the microbiota in the guts is seeded by the mother during birth. There are bacterial populations in the birth canal that essentially get smeared on the baby's face during birth, and these are the first species that get into the gut. These are really important too, and not just for digestion. The gut microbiota interact with and instruct the immune system. The importance of this initial seeding of bacteria is demonstrated by the fact that ",
"children born by Caesarean section have a higher risk of allergies than those delivered vaginally",
"."
] |
[
"In theory it's possible, but I don't think elective C-section is ever a good idea, because it's still pretty major surgery. I also don't think it's necessary, as having 'poor' microbiota is due more to absence of good species than presence of bad. If there are concerns about the quality of microbiota, a ",
"fecal transplant",
" should be able to take care of the problem."
] |
[
"During a vaginal birth, the doctors/nurses don't need to take any care to ensure the bacteria colonize. Bacteria are hearty fellows, and if they get on the baby's nose/mouth (which they will), they will assuredly find their way to the digestive tract.",
"As for babies born via C-section, I can't speak as to the current practice in delivery rooms, but I wouldn't be surprised if they do. From the link I originally posted:",
"A more radical idea is now being tested by researchers in Puerto Rico. In the study a number of pregnant women have their vaginal microbiota screened before their planned Caesarean. After the birth the midwife takes a compress with secretions from the mother’s vagina and smears it over the baby’s face. The theory is that in this way the important bacteria may be transferred to the child. A similar study in Sweden is being planned.",
"This is a fairly new area of understanding in human biology, but I wouldn't be surprised if the practice of inoculating all babies born became standard in the next decade."
] |
[
"Why do we care about the heavy elements like 119 and 120 that decay in like .00002 seconds? What could we possibly use it for?"
] |
[
false
] |
why do we care tho? to prove we can?
|
[
"Producing and studying them allows us to constrain theoretical models of nuclear structure, and possibly atomic structure as well.",
"There are around 3000 known nuclear species and about 7000 predicted to exist. Many of these 4000 undiscovered nuclides are either producible using existing technology, or will be within the next few years.",
"Why ",
" we study them?"
] |
[
"We want to confirm the laws of physics as we understand them. Say we are looking for 119. Our models will give us an idea of that that nuclei will look like. The geometry of the nuclei is very important in understanding and calculating the energy of an emitted particle. So we make predictions about the alpha decay energy and we hope that the alpha particle from a decaying 119 will actually have that energy. If it does, or model is confirmed and hurray, if not it's back to the drawing board. Often somewhere in the middle. "
] |
[
"ANY information we can gather is good for the overall model. If it exists someone will be studying it."
] |
[
"Does the average person think s/he is smarter than the average person?"
] |
[
false
] |
...much like the average person thinks s/he is more attractive than they actually are (from a study I've read on here before). Seems like the more people I meet, the more I realize how many ignorant fools think that they're more informed/intelligent/cultured than the great majority, when they usually aren't.
|
[
"Yes! It's called the ",
"Dunning-Kruger effect",
"."
] |
[
"Im on the phone right now, so I can't look up the article. But they once held a study in which people were asked to rate their intelligence and whether or not they were above average. Afterwards they were told almost everyone claimed to be above average and explained how this was impossible. Then, they offered subjects the opportunity to change their answers. Surprisingly, close to none actually thought they were at fault, just the rest of the study.",
"I'll see if i can dig up a link later"
] |
[
"Damnit. I guess I overestimated my ability to post this first."
] |
[
"What causes nightmares?"
] |
[
false
] | null |
[
"According",
" to Dr. Antti Revonsuo nightmares are rehearsals (training) for the daily struggle to survive. I.e. they are simulations which allow us to act accordingly in real situations. For example, a wolf pack is chasing you, you run and keep running no matter what. ",
"In modern days it is not very likely that a wolf pack is going to hunt you down, therefore modern day nightmares are often also different. They have adapted to modern day threats. "
] |
[
"They did a study, and sorry askscience im on my phone so i cant link it, but basically they took mice and stuck them in cages filled with water at the bottom and a doughnut shaped object in the middle of the cage. The mice would attempt to sleep by climbing on top the doughnut but as soon as they fell into the deeper stages of sleep their muscles would relax and they would fall through the center into the water, waking them up. In this way they could never get the necessary rem sleep where we dream. They then took these mice and put them in a mock up of their natural habitat. When they presented one of their natural preditors to the habitat, the mice were completely uneffected. They did not know to run or flee from it even when it got close. They made sure it wasnt just sleeplessness that caused this by giving them amphetamines. When this was done with mice who got normal sleep they knew to run from the preditor. ",
"Basically our brains are always searching for the monsters that used to terrorize us as cavemen. Since we generally dont have to worry about wolves or bears waking us from our sleep, we have to seek out things to dream about to 'keep us on our toes'. Our bears and wolves nowadays tend to be social terrors. If you havent had any particularly traumatic experiences your brain will just sort of run with whatever nonsense frightens you, even if its just going to class in your underwear or being embarassed.",
"Now the minute you experience anything truely lifethreatening or traumatic that goes out the window. Your brain is going to make sure you reherse that event over and over again probably till you die so that youre ready should it happen again. I recently talked to a vietnam vet who had lost a young soldier who was serving on his pt boat. He said even now he goes to sleep and almost every night he relives his death. It almost brought him to tears just talking about it. Anyone who has had life threatening experiences can tell you that theres a real good chance you are going to dream about it and often.",
"Heres the interesting thing i read in that article about the mice. They suggested that immediately following such a traumatic event, you should do something incredibly mundane and boring for hours, i.e. play tetris. If you can focus on this for long enough theres a chance it might overwrite your brains data storage and prevent such horrific things from turning into PTSD. Im sure its completely a long shot but maybe it would work."
] |
[
"I think this goes a little too far in assuming that dreams and nightmares are a purposeful action by the mind. It would be just as valid to suppose that with the necessary reduction of sensory input that occurs during sleep, the brain is free to continue cycling through memories and predictions.",
"If this does occur then it would be logical to infer that since none of the output to the motor neurons is generating sensory responses as a result of ",
"REM atonia",
", the brain must rely entirely on its own predicted input for those actions; a cycle that could easily move beyond the realm of predictability and generate the bizarre experiences of dreams and nightmares.",
"It would also neatly explain why sometimes we have perfectly normal dreams in which we live out everyday experiences with little to no strange 'dream occurrences'."
] |
[
"Based on order of magnitude, are humans closer in size to the Planck length or the diameter entire observable universe?"
] |
[
false
] |
[deleted]
|
[
"Human: 1 m. Plank Length: 10",
" m. Observable universe diameter: 10",
" m."
] |
[
"http://en.wikipedia.org/wiki/Observable_universe"
] |
[
"http://en.wikipedia.org/wiki/Observable_universe"
] |
[
"Why does your throat get sore?"
] |
[
false
] |
This might be a really silly question, sorry. When you get a cold, why does your throat get sore? I understand why your nose might run or get blocked and why you might have a cough or a headache etc, but I can't think of why your throat gets sore. What immune purpose does it serve?
|
[
"The confusion here seems to stem from “purpose” of immune reactions. While the other symptoms you mentioned do serve a function (like coughing to get the pathogen out), not all immune reactions are for the same reason. A sore throat (a sore anything, really) is cause by inflammation in the area, which really just means a combo of dilated blood vessels and a bunch of white blood cells that have been summoned by distress signals from damaged tissue. Chemicals released by damaged cells and by WBC presence (things like histamine, serotonin, too much extracellular Potassium and calcium, substance P) can directly trigger pain nerves. Some of those substances, and others (interleukins and other cytokines), continue the cycle and bring more WBCs and vessel dilation, which makes more of those chemicals, which makes more pain, etc etc etc. ",
"The swelling of the epithelial and surrounding tissue in the throat, in addition to a lowered threshold for pain caused by those pesky cell damage associated chemicals, makes it hurt to swallow and things like that. If you have a really bad sore throat, you might see a white, lacy appearance to the tissue at the back of your throat—that’s MALT, or mucosa associated lymphoid tissue, activating and developing all those white blood cells to fight the infection locally."
] |
[
"This is perfect because I woke up with a sore throat today. The covid test was negative so just some other annoying virus."
] |
[
"This is perfect because I woke up with a sore throat today. The covid test was negative so just some other annoying virus."
] |
[
"If everyone started driving electric cars tomorrow, how would it effect our power requirements? Would there be a significant increase in power draw?"
] |
[
false
] | null |
[
"There are about 254 million vehicles in use in the U.S., and they're driven about 3 trillion total miles.",
"If all of those miles were driven in EVs, and those EVs averaged about 3 miles per kwh (at the power plant), then that would require about 1 trillion kwh.",
"The U.S. produces about 4 trillion kwh / year",
", so that'd be about a 25% increase in the total electric production.",
"BUT, while that simple answer might be of interest, that's not really what you asked. That's the total change we'd see in ",
" demand, while the change in ",
" demand is much different.",
"Power demand peaks",
" in the afternoon hours, and is much lower in the middle of the night, when most EVs charge. If we can ensure that most EVs continue to charge overnight (e.g., with time-based pricing), ",
"studies have shown",
" that about 70% of the fleet could be charged using existing idle capacity."
] |
[
"Very interesting. I suppose the increase of EVs could wind up balancing out the reduction on power use being noticed by power companies due to solar panels.",
"Thanks"
] |
[
"Perhaps, except EVs don't typically charge when solar is producing. Rather, a concurrent increase in both solar and EVs might mean a leveling out of the load profile curve.",
"Other forms of generation will be needed less during the day and needed more overnight, so plants can be operated in a more continuous fashion, which could lead to increased efficiency and reduced emissions per fuel unit."
] |
[
"Due to the effects of time dilation, would a computer placed on Pluto outperform an identical computer placed on Earth over the same Earthly time period?"
] |
[
false
] |
Pluto has a lower equatorial surface gravity, equatorial rotation velocity and orbital speed. Relative to Earth, time should be faster, right? Would the Plutonian computer be able to accomplish more tasks in an Earth year than it's Earthly counterpart?
|
[
"Relativistic effects can be caused by gravity; blackholes, satellites, and Mercury are all impacted by this.",
"Why do you dismiss such effects as relevant for a computer on Pluto versus Earth?"
] |
[
"Your question is ambiguous because you don't specify how you measure time for the respective computers. ",
"If you have a clock next to each of the computers, and you measure how long it will take for the computer to perform a particular calculation, then you would get the same result on Pluto and Earth, because the clocks are affected by time dilation ever as much as the computer is ( and of course, your thought processes in your brain). ",
"However, if you are sitting on Pluto with a computer, watching the Earth computer through a telescope, then you will see your computer solving the problems quicker than the earth computer does. Somebody sitting on Earth watching Pluto, ",
" see the Pluto computer running slightly quicker. ",
"Note that this is very different from the ",
"twin paradox",
", because in the twin example they both travel at constant speed in constant directions. In contrast the Earth and Pluto orbit the sun in elliptical orbits, and hence undergo acceleration. The Earth also has a deeper gravity well than pluto, and as you noted a greater equatorial rotational velocity. ",
"Now, an interesting question is what happens if you start out with the two computers on earth, start them at the same time ( and same place ) , and then take one of them and fly it out to Pluto on a rocket. If the acceleration of the rocket is great enough, then its on-board computer will initially slow down more than the gain acquired from being brought further away from the sun. However, once you've gotten to Pluto and slowed down, the computer will slowly catch up to the earth computer, and eventually overtake it. If you leave it on Pluto long enough ( please don't ask me to calculate how long, it's a bit of a pain ) , and then bring it back, you will indeed find yourself with two computers sitting next to one another, on earth, with the one that went on a space trip to Pluto having performed more calculations than the one that stayed at home.",
"Note that this absolutely relies on the experiment being carried out inside a gravity well ( such as that of the Sun ). If you were to do the same experiment without a big gravity well then you end up with the original twin paradox, and then the computer that is on the accelerating rocket is the one that will have slowed down more.",
"Pheeeeew. That was a bit of a longer answer than I planned, but your question would also make an interesting exam question. \"Suppose two computers on earth, tasked with performing mathematical calculations, are started at the same time. One is then brought out to Pluto, left there for a while, and then brought back. How long does the computer have to stay on Pluto in order to perform more calculations overall than the computer on Earth? Does the rocket speed matter? What about acceleration?\"",
"I'm just happy the exam papers I had allowed me to assume spherical cows in empty space. "
] |
[
"the computer on Earth would say it is working faster than the one on Pluto.",
"No it would not. What general relativity says is you cannot tell the difference between uniform gravitation and uniform acceleration. It is however quite possible to tell the difference between being neither accelerated or affected by gravity on the one hand, and being in a state of strong gravity or acceleration on the other. ",
"The twin-paradox is resolved by this fact, because the postulates of general relativity ( with exception of the gravity/acceleration one ) speak of inertial frames. For accelerating frames you find that the clock that does the most accelerating ( or spends most time in a gravitational field depending on how you look at it ) is the slower one. ",
"The OP also forgot to mention that Earth is deeper inside the Sun's gravity well, and hence affected to a greater degree by gravitational time dilation. For the same reason an observatory put on Pluto would see a ",
" more red sun than we do, because the wavelength of the light has been stretched by gravity as it rises through the sun's gravity. "
] |
[
"Why does Saturn's belt always look extremely smooth in pictures?"
] |
[
false
] | null |
[
"Each rock that makes up Saturn’s rings is incredibly small when compared to the size of the planet and the ring itself. Most pictures are taken at a pretty big distance. ",
"Earth looks fully smooth when we see pictures of it in space, but we know from living here that it’s anything but."
] |
[
"The surface of the earth is basically as smooth as your skin.",
"There’s obviously some texture there, but fairly homogenous."
] |
[
"The surface of the earth is basically as smooth as your skin.",
"There’s obviously some texture there, but fairly homogenous."
] |
[
"What would the gravitational pull of earth be if it wasn't spinning?"
] |
[
false
] |
Or is the spin too slow to have a significant effect on gravity.
|
[
"About the same. The centripetal acceleration you feel is about 0.3% as strong as the gravitational."
] |
[
"3.5oz = ~100 grams",
"\nSeeing ounces in there with all the metric makes me uncomfortable."
] |
[
"If you weighed 60 kg and the earth stopped spinning you would weigh about 3.5 ounces more. your mass multiplied by velocity squared divided by the earths radius is equal to the centripetal force working against gravity.",
"Earth rotates at ~465m/s radius of the earth is ~6370 km plug in your weight do the math ;-)"
] |
[
"What is happening in your stomach when you hear it \"rumble\"?"
] |
[
false
] | null |
[
"From a Google search of 'stomach rumbling':",
"The \"rumble\" or \"growl\" sometimes heard from the stomach is a normal part of digestion. It originates in the stomach or upper part of the small intestine as muscles contract to move food and digestive juices down the gastrointestinal tract and functions as a sort of intestinal \"housecleaning\".",
"Properly known as ",
"borborygmus."
] |
[
"From an article in the citations of the Wiki:",
"Though stomach growling is commonly heard and associated with hunger and an absence of food in the stomach, it can occur at any time, on an empty or full stomach. Furthermore, growling doesn't only come from the stomach but, just as often, can be heard coming from the small intestines. Growling is more commonly associated with hunger because it is typically louder when the stomach and intestines are empty and so the organs' contents don't muffle the noise. ",
"source"
] |
[
"It's called the cephalic phase of digestion in which the gastrointestinal tract readies itself for food delivery in response to smelling or even thinking about food. There is a release of certain chemical messengers which cause the secretion of hydrochloric acid and enzymes, and also stimulate the muscular layers of the stomach to start contracting; this would constitute the feeling of a rumbling stomach, but the actual sounds would be due to gas, whether it be pockets of it being shifted or bubbles of it breaking the surface, both in your stomach and in your intestinal tract."
] |
[
"[Archaeology] Why is all the ancient stuff buried? Like wells, roman walls an such. Does the earth eat it?"
] |
[
false
] |
[deleted]
|
[
"Think about it this way: We find these archaeological sites thousands of years after they were inhabited. What happened in those thousands of years?",
"Well one scenario is that it was probably underground to begin with. Many archaeological sites consist of graves, garbage pits, wells, things that are built to be below the ground and abandoned and built over.",
"Then you have the big fact that these buildings get covered up by topsoil. Plants grow and die, wind blows sediment around, layer after layer of topsoil forms. Sometimes natural disasters/landslides will bury a building or a artifact. This is how over hundreds and hundreds of years, whole buildings are underground. ",
"Adding onto that, many buildings, notably in Rome/Middle East/ancient cities, will be fall apart or be abandoned, but the city will still be inhabited. So sometimes they will just get built right over with newer buildings. Hope this answers your questions."
] |
[
"I would also like to add, while not in all sites and the opposite can happen as well, in the majority of sites sinking and swallowing happening at differing rates.",
"Water, floods or rain water in general permeate the ground which allows solid structures to sink over time.",
"How much of a difference that makes depends on the area, in a desert subduction doesn't happen as often as say in tropical area. ",
"So in conclusion I wanted to add yes the earth does swallow up buildings, but it varies on how much it could be an inch or entirely cover the building, but yes as you state the majority of the reasons are sediment, mudslides over generations and rebuilding.",
"Hell even today we have to be careful. I live in an area where an entire condo complex is closed. Brand new, 600 people can't live there now. They built up the area prior and built a new building. Engineers were wrong and the building sunk in various places up to 10 feet. Parking lots collapsed in. The place was a very marshy place prior. Really sad to drive past it, it's all fenced in for protection now.",
"It's really sad to see stuff like that happen... With modern engineering mistakes. I hate to see what mistakes they made thousands of years ago."
] |
[
"Lots of good points here. It all depends on the environment. In southern Ontario, where I've done a lot of work, the typical topsoil is on average about 20-30cm thick, and that's where all the archaeological materials are. Below that is the strata that was deposited when the glaciers were still around, so that 30cm of topsoil represents about 13,000 years. That's very slow, and is mostly the result of leafs and plants dying every year and gradually accumulating and turning to soil. The people living there would have lived in houses made of wood, which rots, and then their artifacts are scattered everywhere around the site. In time, the new soil accumulates over top of it and after a long period of time, things get buried. But on a floodplain, soil accumulates a lot more quickly because a river carries a lot of sediment but when it floods the water is stagnant in the flooded areas and the sediment settles to the bottom and accumulates. And floods like this happen every few years, so after 1000 years you can get a few meters of soil on top of the site. ",
"The other place where I work is in the coastal deserts of Peru. The sites there are very much still above ground, but walls and parts of them are buried. The typical coastal site was probably built on a sand dune to begin with and eventually became a town or city with walls and large mounds and all sorts of things. But these dunes were formed by blowing sand and after the site was abandoned the sand kept blowing, so they're covered by sand that simply blew in. I've excavated a room, left it for a week as we moved onto another one, and that first room was almost entirely buried again just from the blowing sand, and that's in a desert where there is no organic soil accumulation, unlike what I described for Ontario. And when people were living there they knocked down walls to build new houses and leveled off the area by dumping sand, ash and bones from kitchen fires, etc. and this also buries things. And these are just two examples; there are all sorts of cultural and natural processes that bury things.",
"But a lot of archaeology is not buried at all. Machu Picchu did not have to be excavated; all the ruins sit above ground. They were covered with forest growth and that had to be cut away, but the site is not that old and there has not been enough time to cover everything. There are some excavations because things lying on the ground have become covered by what soil accumulation there is (in places) plus the cultural processes that lead to burial (e.g. graves, building things in different stages, etc.) But in places where there is little soil accumulation, like back in the coastal deserts of Peru, you actually find artifacts lying out on the surface of sites. Lots is buried too, but artifacts sit on the surface too."
] |
[
"if perpetual motion isnt possible, then how have things been moving for 16+ billion years? isnt that essentially perpetual motion?"
] |
[
false
] | null |
[
"What's referred to by a \"perpetual motion machine\" is something that does work for free. So for example you can have a pendulum that rocks back and forth in perpetual motion (though in reality friction will slow it down) but what is forbidden is extracting some ",
" energy out of it. So you can't use a pendulum to drive a generator to make electricity, and also expect the pendulum to keep going forever. Similarly there is nothing wrong with having particles bumping into each other in perpetual motion, as long as you can't extract that energy \"for free\"."
] |
[
"so why does the universe overall seem to have perpetual motion, but we cant make a perpetual motion machine without feeding it energy from outside?"
] |
[
"Inertia, conservation of energy, and conservation of momentum all keep things moving. "
] |
[
"How strong is the evidence for alternative hypotheses for the dinosaur extinction event?"
] |
[
false
] |
Meteorite strike: I get it. Big bump, irridium, dinos dead. But recently I ran into a geologist who is pointed out that there are other, bigger, craters that are not associated with mass extinctions, and who is convinced there story behind the K-Pg mass extinction event is more complicated. I'm not asking what happened per se, but if there any sense to these alternatives, scientifically speaking? Is this just crackpot pseudoscience or is there some merit? How can you tell?
|
[
"What caused the end Cretaceous, i.e., the K-Pg (or K-T in older publications) extinction remains a point of argument. The two important things workers quibble over, both for the impact hypothesis or others, are (1) timing (i.e., did the supposed event that caused the extinction occur coincident with the extinction) and (2) mechanism (i.e., just because X event happened coincident with the extinction doesn't mean it caused the extinction if there is no mechanism by which the event could cause an extinction).",
"The impact hypothesis (e.g., ",
"Alvarez et al., 1980",
") has always been provocative, compelling, and well marketed (e.g., Alvarez's pop-sci book popularizing the idea). From the peer reviewed literature, dating of impact related material mostly suggests that the timing of this impact is consistent, i.e., it is coincident with the extinction (e.g., ",
"Schulte et al., 2010",
"), but there has been other work to suggest it actually predates the extinction, i.e., the impact happened, some time passed and then the extinction happened (e.g., ",
"Keller et al., 2004",
"). The mechanism has also had some issues, with multiple suggestions of how the impact caused the extinction from shutdown of photosynthesis from dust injection to a \"thermal pulse\" of hot spherules (e.g., ",
"Fastovksy & Sheehan, 2005",
"), but some of these have been questioned, e.g., was there enough dust to actually shut down photosynthesis? (e.g., ",
"Pope, 2002",
"). ",
"Now, in detail, since the early days of the impact hypothesis being suggested there has been push back on whether it works as the sole cause of the extinction (e.g., ",
"Courtillo & Cisowski, 1987",
"). The alternative that is usually suggested, or at least pointed to, is the eruption of the ",
"Deccan Traps",
", a massive continental flood basalt province in India, which also occurred at about the right time (e.g., ",
"multiple comments on the Schulte article from above",
") and indeed has been suggested as the cause of the K-Pg for as almost long as the impact hypothesis has been around (e.g., ",
"McLean, 1985",
"). The main eruptive pulse of the Deccan Traps appears to be nearly synchronous (though maybe just a little before) the K-Pg extinction (e.g., ",
"Renne et al., 2013",
", ",
"Schoene et al, 2015",
"), though this too has been questioned and suggested that most of the Deccan Traps erupted after the K-Pg (e.g., ",
"Sprain et al, 2019",
") with even a suggestion that the impact itself influenced this post K-Pg eruptive activity (e.g., ",
"Renne et al., 2015",
"). For the Deccan Traps as the cause of the K-Pg extinction, the kill mechanism may have been global warming from pulses of greenhouse gases released by the volcanism (e.g., ",
"Tobin et al., 2012",
") or a combination of this along with ocean acidification and ocean warming (e.g., ",
"Keller et al., 2020",
"). ",
"While some proponents of the Deccan Traps as the primary cause of the K-Pg extinction discount really any influence from the bolide impact, gradually a more middle of the road view has started to emerge in the literature. Specifically, there is a growing idea that it was the combination of prolonged rapid environmental change driven by Deccan Traps volcanism for 10s of 1000s of years preceding the K-Pg, punctuated by the bolide impact (kind of the straw that broke the camels, or I suppose dinosaurs in this case, back) that was the joint cause of the K-Pg (e.g., ",
"Renne et al., 2013",
", ",
"Petersen et al., 2016",
", ",
"Schoene et al., 2019",
"). In this view, it is arguable whether either event alone would have caused the K-Pg extinction as we know it.",
" there is still a lot of debate as to whether a bolide impact or a massive and prolonged eruption of continental flood basalts were the primary kill mechanism for the K-Pg extinction, but there's seems to be some amount of growing consensus that it was actually the combination of the two. In this view, that would explain why \"there are other, bigger, craters that are not associated with mass extinctions\", i.e., the K-Pg impact alone probably would not have caused the extinction, but it was the final nail in the coffin after prolonged climate change and environmental disruption driven by the massive volcanic eruptions preceding the impact."
] |
[
"This is an excellent answer that puts it all very succinctly and has a couple of interesting references I’ve not come across before (it’s so easy to get fatigued of reading through people’s arguments against the ",
" cause than the one they’re researching, I think I kinda gave up on news about the K-Pg boundary). ",
"Anyway, I just wanted to say that perhaps it’s worth mentioning how those other craters that we have found which are larger than the Chicxulub one are from before the Phanerozoic so I’m not sure if you could even have a mass extinction. Not one that we’d be able to pick out in the rather ropey fossil record from that far back anyway."
] |
[
"That's a fair criticism to the \"there have been bigger impacts without mass extinctions\" point. You get sort of a similar issue with the Deccan Traps argument as well, i.e. \"We've had other continental flood basalts that didn't cause a mass extinction\". The poster child for continental flood basalts causing a mass extinction is really the Siberian Traps and the end-Permian extinction, but here it seems that this was caused by the context of the eruption, i.e., the eruption of the basalts through a large stack of organic and evaporite rich stratigraphy and the resulting liberation of a variety of compounds which did unpleasant things to the atmosphere and oceans (e.g., ",
"Visscher et al., 2004",
", ",
"Beerling et al., 2007",
", ",
"Reichow et al., 2009",
", ",
"Svensen et al., 2009",
", ",
"Burgess et al., 2017",
", ",
"Black et al., 2018",
"). Outside the context of the end-Permian, there is a general idea that these events could be related to mass extinctions, but there is a lot of nuance (e.g., ",
"Bond & Wignall, 2014",
")."
] |
[
"Why does blood testing make us feel lightheaded if we don't consume food beforehand?"
] |
[
false
] |
[deleted]
|
[
"A simple blood test does that to you?",
"I'd say that's more of a mental thing. The small amount of blood taken for blood tests (2 or 3 teaspoons) usually isn't enough to cause light-headedness, unless you're very tiny."
] |
[
"As others have said, this is not due to loss of blood glucose, blood pressure/blood volume, or any other mechanical process. This is caused by a process called vasovagal syncope. Certain stimulants (such as seeing blood, pain, needles, etc) cause a rapid increase in parasympathetic tone via the vagus nerve. This causes a rapid drop in heart rate and/or blood pressure, which results in dizziness or in more severe cases fainting."
] |
[
"What you describe has nothing to do with blood volume - it's a nervous response. The small volume of blood taken for testing is insignificant as far as your total blood volume goes, even if you are a small skinny person.",
"My wife has this as well - she often passes out during blood tests. She's not scared of needles or anything.. it's an uncontrollable thing.",
"Look up \"Vasovagal syncope\""
] |
[
"Why does sound from the TV sound fine when played back to us, but if it's recorded by another device, and then played back, it sounds horribly weird?"
] |
[
false
] |
You can always tell when someone doesn't have a digital PVR and are just recording shows with a camera pointed at the screen. One factor is the audio. Why is it that the TV can sound fine, but if you record that audio, it sounds horrible when played back?
|
[
"Mostly it'll be a combination of a low quality microphones being used, low quality speakers in the TV, and coloration of the sound from the room. This situation is analogous to a JPEG being recompressed over and over."
] |
[
"also lets say you are watching a movie. When they edit the movie they make sure to take out all ambient sounds out and digitally enhancing it so that you only hear what they want you to hear. When you record it most people don't bother to do this"
] |
[
"For the same reasoning if you took a digital picture of a painting, and then took a picture of your picture with your cellphone camera. Why doesn't the cellphone camera's picture look as good as the painting?"
] |
[
"Why do animals have a much shorter lifespan than humans?"
] |
[
false
] |
[deleted]
|
[
"We are animals. We've found cures and treatments to extend our lives. The average human life expectancy was ~26 in pre-agricultural times.",
"There are also plenty of animals that live longer than us, such as tortoises, lobsters, several species of birds, Sturgeons, Eels, Whales, Some sharks, mussels, clams, etc.",
"The Giant Sponge, which is an animal, lives for 2000 years.",
"Koi fish, have been documented at ages of 225+ years",
"Bowhead whales can live for over 200 years",
"Tuatora's live for 100+ years",
"So in fact, there are many animals that live much longer than us.",
"source 1",
"source 2",
"source 3",
"source 4",
"source 5",
"source 6"
] |
[
"The lifespan of an animal is going to the the one that has been selected by evolution as being optimal for passing the animal´s genes to the next generation. \nYou can have a species that has a long lifespan and has one/two offspring per year for 50 years. Or you produce 1000 offspring in one day and die afterward. Also, some species have evolved a system where the parent takes care of the offspring (for example we humans), in this case it is optimal for the adults to live a bit longer (a child growing up with as many parents/grandparents as possible will probably get better taken care of than an orphan). Other species opt for producing young that can take care of themselves straight away (this means investing more energy in producing more independent offspring).",
"None of the approaches is better or worse, I´d say, just different. "
] |
[
"Ah, so it's not about living longer, but simply living long enough to reproduce."
] |
[
"When lightning strikes the ocean, how far do the effects of the electricity go?"
] |
[
false
] |
It is well known that water is a good conductor of electricity. So when it gets struck, how far away from the original strike can the electricity be detected. Also, do the fish in the area feel it or have they evolved in such a way that they are "immune" to the electricity? Edit: So what actually inhibits the electricity from traveling an infinite distance. Also, when the lighting strikes and travels, does travel along a chain of positively charged Na ions or is there a field of ions created?
|
[
"Pure water is not a good conductor of electricity, but salts in the water can make good conductors. ",
"The lightning follows the path of least resistance, and does not enter the water immediately. Instead, it creates arc channels in a disk-shape on the surface of the water before entering the water. The voltage then drops off rapidly as the voltage spreads out in a half-sphere. Fish (and people) have a higher resistance than the salt water and so will experience less voltage than the water directly around them. An interesting ",
"paper",
" that touches on the topic.",
"A strike might not have dropped down to background levels (and still be detectable) as far as 1 km."
] |
[
"Yes he meant less current.",
"The lightning follows the path of least resistance,",
"Not true. Lightning, like all electricity, follows all paths, not just the least resistant one. However, the current that flows to each path, is based on its resistance. So the extreme majority of current travels through the path of least resistance. This is why lightning bolts are not a single line, but have many branches.",
"As a side note, Because the voltage is dissipating with distance, it is possible to have one part of an object at a much larger voltage difference in a lightning strike if that object covers enough distance, and the voltages involved are fairly large, like they are in lightning strikes; But since the salt water ocean is such a better conductor than earth, it takes much longer distances to achieve higher voltage differences. This is because the highly conductive salt water does not dissipate as much voltage per meter as earth, air, or other insulating materials do.",
"Source: I am an electronic technician."
] |
[
"will experience less voltage",
"You mean less current, right?"
] |
[
"Is there a way to see if condensation will form given a set of conditions?"
] |
[
false
] |
[deleted]
|
[
"the surface needs to be cooler than than the air otherwise the reverse reaction will happen and the water will evaporate"
] |
[
"what your looking for is dew point tables"
] |
[
"Ok, so why doesn't water condensate on me when I step outside if I'm 98F?"
] |
[
"What do we know about dinosaur agility?"
] |
[
false
] |
Were they quick and as mobile as their featherless representations in the Jurassic Park movies or slow and sedentary like modern reptiles? Does this have to do with the question of whether or not they were warm blooded?
|
[
"It's hard to give concrete estimates of speed from just fossils - certainly much harder than just measuring a living animal. Usually, some component of muscle reconstruction, range of motion analysis, and other facets of biomechanics go into estimates of speed. Different estimates have different advantages and disadvantages, and don't necessarily work on all animals.",
"Certainly, some dinosaurs were built more cursorially than others. The derived ornithomimids, with very elongate lower legs, were probably among the fastest non-avian dinosaurs; Thulborn 1982, for instance, places the top speeds of ",
" at about 56 km/h, while Christiansen 1998 found 51 km/h. The abelisaur ",
" was also very long-legged, and had hypertrophied thigh musculature after Persons & Currie 2011 - however, no estimates of its speed exist, and, while it was fast, it would probably not have been very good at turning. Although the dromaeosaur ",
" was not particularly cursorial among its relatives, it could still clock up to 42 km/h according to Thulborn 1982.",
"Even some of the not particularly cursorial-looking dinosaurs may have been capable of surprising speeds. Preuschoft ",
" 2011 suggested that the largest macronarian sauropods could have achieved speeds of 9 km/h alone on account of their size, although there have been contrary suggestions that they could not have exceeded 5 km/h. Hadrosaurs like ",
", running quadrupedally, may have reached up to 57 km/h after Sellers ",
", 2009. Christiansen & Paul 2001 furthermore hypothesized that the largest ceratopsians, like ",
", could have trotted along fairly comfortably at 35 km/h.",
"That being said, there are still instances in the Jurassic Park franchise where the dinosaurs are depicted as being ",
" flexible. The dromaeosaurs, for instance, are depicted as having fairly prehensile hands, which would have been prohibited in life by the presence of large, pennaceous wings, as well as the shape of the carpal bones. Likewise, their tails were vertically stiffened by highly extended vertebral processes, which means that some of the floppiness of dromaeosaur tails as depicted in JP is probably unwarranted."
] |
[
"There was a recent Scott Hartman blog post about the mobility of Dromaeosaur tails, called ",
"Tails of Woe",
". Essentially Hartman points out that while Dromaeosaurs did have some limited flexibility at the base of their tails, particularly the ability to angle it upwards away from their body at about 80 degrees, it didn't happen right at the base. It would have stuck straight back and curved upwards a few inches out from the hips."
] |
[
"There are fossilized footprints of dinosaurs, they were preserved as the mud petrified. From fossilized bones we know the length of the leg and the size of the dinosaur's body. Several clues are encoded behind this evidence. For instance, modern reptiles \"drag\" their bellies or keep them very close to the ground (that's what \"reptile\" means!), while their legs spread widely to both sides. When the first fossils were discovered, dinosaurs were thought to walk the same way, you can see this in the early depictions of the Iguanodon. But footprints tell us that dinosaurs did not spread their legs sideways, so they must have walked erect. This made them much faster.",
"Another important clue is the forward separation of footprints. By comparing this to the leg length, and especially in the case of bipedal dinosaurs like T Rex, it's possible to know that it couldn't have maintained balance as its center of mass was heavily tilted forward. This would put a time limit while standing in one leg until the second leg touched the ground ahead. From this time and the separation, paleontologists know that a T Rex could run at 40 km/h.",
"That's comparable to normal car speed (especially on a rough terrain!), so the Jurassic Park scene in which they have a narrow escape in their Jeep is realistic.",
"Edit: Here's Mantell's original drawing of an Iguanodon skeleton:",
"https://upload.wikimedia.org/wikipedia/commons/0/0a/Mantell%27s_Iguanodon_restoration.jpg",
"Note the curved legs like modern reptiles, and the historical mistake of confusing the long thumb claw with a horn. Today we know Iguanodon actually looked like this:",
"https://upload.wikimedia.org/wikipedia/commons/4/46/Dollodon_bampingi_Steveoc86.jpg"
] |
[
"Can I use quantum entanglement to keep synchronized timing information in different frames of reference?"
] |
[
false
] |
Quantum Entanglement is nifty. Let's assume I can mass produce entanglement such that I've got two big vats of entangled stuff and I get slowly dribble it out so that I know I'm looking at the 'same' particle on Mars as is being messed with on Earth. Could I transfer TIMING information? Say by setting value A during even seconds and value B during odd seconds but with EXACT precision, say by examining one particle per millisecond? The question came up by wondering if I could use entanglement to keep time and avoid all the relativistic error handling that seems to have led to the FTL neutrino conundrum?
|
[
"I am totally not at all experienced in the quantum arts, but measuring an entangled particle in vat A wouldn't make its corresponding particle in vat B known to the Martians. The only thing that would happen is that if the Martians measured that particle in vat B and told us Earthians with conventional communication methods what the measurement was, we would be able to reply with a pithy \"Yeah, we know\""
] |
[
"What some others have said here is only partly correct, because you can indeed use entanglement to improve clock synchronization, just not the way you suggested.",
"This paper (and related papers by the same authors) explains how: ",
"http://arxiv.org/abs/quant-ph/0103006",
"That wouldn't solve the problem with the FTL neutrinos though because it still means light has to actually travel between two clocks and then synchronization will always be a question of the exact gravity potential they encountered on the way (which might not have been properly accounted for in the neutrino experiment).",
"This problem cannot be solved with anything we know about entanglement because even if you had your \"vats of entangled stuff\"---let's call them quantum memories---at two remote locations, that would still mean that some initial signal must have travelled between them to entangle them in the first place."
] |
[
"If you have particles X and Y in an entangled state, observing either of them will destroy the entanglement.",
"What you are proposing is X being on Earth and Y being on Mars, and both X and Y can take values A and B. When you switch X from one state to the other, the people on Mars will have no idea of what has happened will they make measurements on their particle. You can't have a situation where the people on Mars are constantly staring at their particle and it twitches all of a sudden because the particle on Earth is twitching. Looking at the particle once will destroy entanglement.",
"That said, even entanglement will not allow you to send useful signals FTL. The best clock synchro we can accomplish using signals is at light speed, and then using calculations for whatever relativistic effects might have been at play while the light travelled from Earth to Mars.",
"All entanglement can do is make your information harder to eavesdrop on or hack, or make it more robust so something like a stray magnetic field from a solar flare doesn't disturb it. You can't use it for send info FTL."
] |
[
"Does cancer evolve?"
] |
[
false
] |
So, i'm asking this partly based on some recent events in my life, though i'd prefer not to get into too many details. I know someone who was diagnosed with malignant melanoma, but they were lucky enough to qualify for a drug trial that specialized in late stage melanoma patients. The drug in question was only for patients whose cancer fit a particular genetic profile. Additionally the drug's effectiveness is known to decrease over time, partly because the cancer adapts around what the drug is inhibiting. This got me thinking however... Do cancers evolve similar to natural selection in more traditional organisms? Does this mean the likelihood of finding 'cures' for types of cancer would be tempered with a shelf life on how long that cure remains viable? It seems fascinating because on one level you have cancers which survive and adapt inside the ecosystem of their host, but on another level you have humans who are (sometimes) genetically predisposed to certain cancers. Successful treatment options presumably gives them an opportunity to spread those genes back into the greater population, giving those cancers more chances to be treated and (presumably) mutate around existing treatment methods on a long enough time line. Am I radically incorrect here? Is it possible, on a long enough time line, successful treatment of cancer will lead to more treatment resistant forms of cancer?
|
[
"Cancer is a clonal process, i.e. a single mutated cell starts dividing and progressively mutating further,and acquiring new characteristics over time, like losing the proteins necessary for attaching to other cells (and thus invading other places) or metastasizing. It is a Darwinian process. ",
"Nature paper on it",
". ",
"On the side of resistance to chemotherapy, some cancer cells do develop specific mechanisms, kind of parallel to those bacteria have for antibiotic (e.g. overexpression of the target protein, efflux pumps, etc.)... still, remember these mutations occur randomly, but the mutant clones are selected by treatment. That's why you usually don't limit yourself to only one way of treatment. (e.g. you combine surgery, chemo and radiation, since using only one will likely lead to selecting the resistant cancer cells)"
] |
[
"Are you familiar with the difference between somatic cells and germ-line cells? Germ-line cells are the cells that pass genetic information to offspring; human germ-line cells are sperm or eggs. Somatic cells are everything else. Cancer typically develops from somatic cells, and even if sperm or eggs became cancerous I would assume they can't function normally. So, colonies of cancerous cells can evolve within an individual as Ich_bin_surreal explained, but any adaptations to treatment would not be passed to offspring because sperm/eggs are not part of the colony of cancerous cells."
] |
[
"That makes total sense. I think my question is slightly different, however. ",
"For the part of the question relating to an increase in less-treatable cancers, I'm more curious if the fact that people can reproduce more and more frequently because of more successful cancer treatments will lead to a net increase in those cancers in the general population (because of the ability to reintroduce genetic predispositions to specific cancers). If so, and there is a small chance that a particular type of cancer is not treatable with known therapies, does that mean that successfully treating cancers will lead to more and more occurrences of cancers with resistance to known therapies? ",
"In effect does this become a selection mechanic that undermines cancer treatments in the human population? If that is the case, this seems to be a situation that favors the selection of treatable cancers even in the absence of them having the ability to reproduce via direct cell lines."
] |
[
"What is the coolest Astronomy fact that you know?"
] |
[
false
] | null |
[
"The \"luminosity\" (i.e., energy produced per unit time) in gravitational waves as two black holes merge is greater than the luminosity of all the stars in the observable universe."
] |
[
"That every atom in our bodies came from stars that exploded and died sending those building blocks out.",
"If you want it in Christian terms \"the sun died so we could live\" "
] |
[
"Actually Christians think \"If the sun is a star, then how come it is a circle?\""
] |
[
"What would be the short and long term ramifications of being on an all-liquid diet vs a traditional solid food diet?"
] |
[
false
] | null |
[
"I did it after a surgery. I can tell you my symptoms:",
"Diarrhea.. Assuming you're taking in the correct amount of calories and nutrients.. this will subside as your system adjusts. You will need to increase the amount of salts, or \"electrolytes\" to compensate for the high water intake.",
"An heavy increase in gas, which will eventually return to normal within a few weeks. Doubling up on gas-reducing meds like Beano offer some relief.",
"Chew gum, or you will lose muscle tone in your jaw. This really isn't that important, as it will come back, but in the long term.. you will lose the aesthetic quality of your jaw muscles. I don't know if it's because of the surgery, or what.. but mine still hasn't fully recovered. \\=",
"Some nutrients aren't water soluble... a pure liquid diet is not possible. Shakes and slurries are as close as you can get.",
"I didn't see much difference in a positive light. Although... I did see a massive boost in my health that came from drinking exceptional amounts of water, which i still enjoy today. I only went without solids for two months.. but I learned water in almost any form goes a long way. "
] |
[
"I've just recently started drinking a LOT more water, for health reasons. Could you elaborate on the health benefits you've experienced with the increased water consumption? :)"
] |
[
"Almost noone is going to see this comment because it wasn't a very popular post, but it's a good question, and I'd advocate water any day. Probably going to go a little overboard on it, though.",
"I drink a bare minimum of 64oz of water per day. That's two xlarge gas station soda-fountain cups.",
"A few basics that are unique to my situation:",
"I have an on-going vitamin D deficiency. It's genetic and requires me to adjust my diet accordingly.",
"I have long hair paired with a natural aversion to the heat. Luckily I don't have any body odor condition.. but I do experience excessive sweating.",
"Also, the positive effects I attribute to the high water intake may be magnified due for the following reasons:",
"I'm on a low-carb diet. This means high protein, fiber, and raw foods. ",
"I have well water, and don't buy bottled water unless I'm out.",
"I spend a lot of my time outside, performing elective low-exertion physical labor.",
"Also, all of this is considering you don't have any pre-existing conditions that require you to limit your intake. Water can reduce the risk of infection, as well as the post-infection symptoms and length of almost any disease, but there are exceptions. Do your research accordingly. It's not something you want to automatically assume.",
" **TL;DR Starts here**\n",
"After three days of drinking the recommended daily volume of water, you ",
" ",
" notice: ",
" ",
"Especially in the morning. I chose the term \"Better\" energy because it's not that you have more of it, just that your metabolism changes. You'll start to lose weight, because it's a bit of an appetite suppressant. I notice a much more effective sleep cycle. ",
"Headaches have many causes. They're very disruptive to life, and should not be considered \"normal\". Depending on why you experience yours, water may be the perfect solution. WebMD can probably give you a good idea of the types you experience, and if water will help. Mine were solved completely.",
"If you're prone to cramps or sprains... from exercising, nutrient deficiencies, or even your time of the month... water will reduce their frequency and severity.",
" ",
"Your immune system honestly becomes more effective. Very important in the long run. I get sick maybe once a year. And that's even with occasional contact with nephews who have no sense of hygienics.",
"I'm outside a lot. As an Irish American, I don't tan very well. I do, however, maintain healthy looking skin. This is partially due to my diet, but not completely. I can put it this way: ",
" For that reason, I'm sticking this here.",
"Pretty quickly, you find creative flavors and additives to put in your water. You can't help but learn a bit about Nutrition in the process.",
"At the very least, it dilutes each system. Your sweat will have higher water, less salt. Your mouth will have a constant refresh of fluid - dissolving sugars that may be coating your teeth and tongue. ",
"Get a home soda machine. You can control exactly what's in your soda. Health nuts love this because it's hard to find soda that isn't packed full of harmful chemicals.",
"I use sucralose sweetener. (The perfect sweetener) You can get it in the store as SPLENDA, but it contains two other filler ingredients that aren't researched as much as they should be. It's fine as far as today's research goes, but you never know. If you are concerned, go for pure. Pure sucralose can be purchased online fairly cheap. Do your research. It doesn't cause any diseases whatsoever, takes tons of stress off your insulin production system, and takes a lot of calories out of your diet. It has it's side effects (a day or two of gas for a small percent of users during initial use) but it's still healthier than sugar.",
"I use well water. You can use mineral water. It's the same thing. Side note: No matter where you live, well or city water, get it tested. It's not that expensive, and can tell you a lot. If you have old pipes, test the water from the faucet furthest from the manifold. Most water diagnostics labs are well-versed and happy to give you suggestions. I have a basic carbon filter, as per their suggestion. Reverse osmosis is a more common suggestion, especially for city water.",
"Buy frozen fruits for flavoring. They're cheap, effective, have higher nutrient densities, aren't generally sprayed with preservatives, and store nicely.",
"Vitamin and mineral supplements will multiply your health effects. This goes without saying, but yeah. Use them to spruce up your water.",
"Carry a bottle around with you. Drinking small amounts throughout the day is much better than large quantities at scheduled intervals. Helps the most with appetite this way, too. Do some research into the bottle's ease of use, effectiveness, durability... you might as well spend a bit on it. It should get a lot of use. Do research into the materials it's made of, too. There's a lot of not-so-safe materials they use to store foods. You'd be surprised."
] |
[
"Which line of latitude divides the land-surface area of Earth into equal parts?"
] |
[
false
] |
Related questions: Which line of latitude divides the water-surface area of Earth into equal parts? Which line of latitude divides Earth's population into equal numbers? I would answer the question myself, but I have no experience with or access to GIS software. Maybe someone with an ArcGIS license can help me out? Question inspired by . .
|
[
"So, I calculated it using Mathematica and the WorldPlot package.",
"Here are the results:",
"For land",
"For Water",
"NOTE: I used the ",
"Mollweide projection",
" to ensure equal areas on the map.",
"For water, It is substantially at the equator (actually +1 degree), as for land, it appears to be at about 32 degrees latitude.",
"I've uploaded the Mathematica notebook I used to generate the plots at 2shared ",
"here",
".",
"Finally, for you're enjoyment, is the ",
"World cut at 32 degrees",
", colored red and blue",
"EDIT: The graphs are not to be taken too seriously, they don't seem to be too reliable"
] |
[
"I'm having trouble understanding how the water cut off can be at the equator when the land cutoff isn't. Isn't every point on the surface defined as either land or water?"
] |
[
"You're right, see my other comment ",
"here",
", doing the calculation a little more carefully puts the line for halving the water in the southern hemisphere, and at a less extreme value (as we should expect since there is more water than land anyway)."
] |
[
"What possible ecological purpose could fleas and ticks serve? Could they ever be eradicated?"
] |
[
false
] |
[deleted]
|
[
"Asking for the ecological purpose of something is akin to asking-- ",
"What is the evolutionary purpose of...?",
"This is from our Biology FAQ. Such questions a difficult to answer as an animal may be successful to the detriment of others. However, there are some animals which feed on ticks such as ",
"Guineafowl",
" and ",
"certain species of wasps",
". These have even been introduced into areas as a means of population control of ticks."
] |
[
"To this type of biological enquiries you need take this step: stop thinking that every organisms has a role and everything is anthropocentric.",
"Organisms aren't in the ecosystem because they have a role they perform inside of it, they ",
" on the ecosystem, in nature nothing is good or bad, ",
". The sudden abundance of fleas and ticks on your locality may be related to environmental changes, either human-related (",
" habitat modification) or human-unrelated (",
" population dynamics of this animals may be related to the abundance of their hosts).",
"Consider that ecosystems are ",
" systems, a slight chance in the network could carry a big change, which may appear unrelated at the beginning. Maybe ",
" is a good option, it is nature's way of regulating populations of some organisms, it doesn't erradicate completely the population of the target bug (therefore, it still can carry its \"ecological role\" if it has any), it relies in a completely natural method (predation, parasitism, etc.)."
] |
[
"Thank you for your reply. I guess many like to train people to think that every living thing has a role, and we should never try to eradicate a species because humans are bad and unnatural, while animals are helpless and important. I just do not view fleas and ticks in this light, and I wish that we could eliminate them from the planet entirely, as controlling them can be tedious and expensive. "
] |
[
"Could enough neutrinos gather within a small enough spot that their gravitational pull would keep them together?"
] |
[
false
] |
I know that they are virtually massless, and therefore they are traveling at near light speed but I am curious to the theorical ability of this happening.
|
[
"In fact, massive neutrinos should cluster gravitationally. We have never observed it becasue it is very difficult to observe their gravitational effects, because they make up such a small fraction of all them dark matter mass. ",
"However, the trick to their clustering is not to put them all in a small spatial volume, the length scales on which neutrinos cluster are HUGE! As you may know, the force of gravity can act over very very long distances. And so a \"blob\" of neutrinos would in some ways act similarly to a blob of hot gas floating freely in space. It would have a mass and therefore a gravitational field, but it also has pressure. The definition of pressure in nearly non-interacting particles is of course more difficult, but let's say for now that it has mostly to do with their velocities (i.e. bigger velocity -> bigger kinetic energy -> bigger \"pressure\"). So, in our hypothetical isolated blob of neutrinos, their gravity would keep them together but this \"pressure\" would push them apart. At some point they would reach an equilibrium and the pressure = gravity and so the giant (we're talking millions of light years) cloud would be kept together as a (relatively weakly) bound object.",
"EDIT: Of course, if you \"cooled them down\" enough, i.e. slowed them down, the clustering scale would get smaller. If you wanted to make a bound object like a planet, you would not only have to slow them down from the velocities they have now, but somehow also slow them down after they fall together under their own gravity, because if you didn't do that, they would just fly through each other and keep oscillating around their centre of mass. If you managed to do that, you would get something like a strange neutrino gas planet."
] |
[
"Yes, I think quite likely. This is how dark matter is postulated to be distributed. It overlaps with regular matter, providing for example giant potential wells in which galaxies could safely form."
] |
[
"If you did have an exotic neutrino gas planet, how would it interact with normal interstellar gases? Could it eventually form a spatially overlapping planet made of both neutrinos and regular atoms?"
] |
[
"How do Saturn's rings spin in relation to the planet's spin?"
] |
[
false
] | null |
[
"Saturn’s rings orbit at the orbital velocity of their altitude, between 24000 m/s at the innermost rings to 1470 m/s at the outer edge. The equatorial rotational speed is about 9600 m/s, which is much slower than surface orbital velocity (as expected, otherwise the planet would fly apart)."
] |
[
"Left unsaid in this otherwise excellent answer: they rotate in the same direction, on the same axis, directly over Saturn's equator."
] |
[
"Most of the moons in the ring do rotate with the ring. Some of the outer moons don't."
] |
[
"Is there a difference in power usage when using the volume connected to headphones as opposed to the volume on your phone (when listening to music)"
] |
[
false
] |
In the interest of prolonging battery life (and hence music listening duration): Say I am listening to music on my phone with headphones in. Not those normal ear bud ones, but a good gaming set. Normally I pump the phones volume up to max and control the volume with the headphones. But today I thought that this might be 'using the most power' from the phone, at no matter what volume I put the headphones. Would I be better off controlling the volume on my phone to give the best chance of the longest battery life or is the power required to output sound through headphones so insignificant anyway?
|
[
"So this can be tricky. It really all depends on the architecture of the amplifier circuit being utilized. A lot of differential amplifiers are biased using a current source and are actively loaded. This means that they pretty much have the same amount of current flowing through them regardless of how much gain is achieved. However op-amps do exist that will draw more current under heavier operation. ",
"In the end it won't matter much. If there is any change in current draw it would be minuscule on the level utilized by headphones. "
] |
[
"That's mostly true, though some portable devices have a transition where turning the volume up goes from one amplifier mode/class to another, which can cause a substantial bump in power consumption at a certain level."
] |
[
"I knew the difference would be pretty pathetic (very small currents involved etc). ",
"Is it safe to consider this like a circuit with 2 variable resistors in series? Where the overall resistance affects the power consumed?"
] |
[
"electron transitions releasing photons. What is going on?"
] |
[
false
] |
Chemistry student here. So, when an electron moves from an excited state down to its ground state it can release a photon with energy equal to the energy lost by the electron, which we then detect as electromagnetic radiation. Is this photon created because the motion of the electron causes an oscillation in the electric field, which creates electromagnetic waves? If so, how can this photon have any sort of defined direction of motion? shouldn't the single photon be emitted in all directions sort of like dropping a stone on a calm pond? What is going on here physicists?
|
[
"Yeah in chemistry only delta-l = 1 transitions are allowed which makes the spectral lines of these transitions very strong but coupling of the electronic and vibrational wavefunctions can give delta-l = 0 transitions. ",
"What does it mean to have a multipolar transition, i'm assuming that's an l=2 to l=0 transition, but how does it affect the radiation coming out? are there two photons to conserve the angular momentum or something?"
] |
[
"Yeah in chemistry only delta-l = 1 transitions are allowed which makes the spectral lines of these transitions very strong but coupling of the electronic and vibrational wavefunctions can give delta-l = 0 transitions. ",
"What does it mean to have a multipolar transition, i'm assuming that's an l=2 to l=0 transition, but how does it affect the radiation coming out? are there two photons to conserve the angular momentum or something?"
] |
[
"Interesting, thanks for the link"
] |
[
"what body organ actually generates the body heat? by what chemical process is it created?"
] |
[
false
] |
as far as i know (please correct me), we pretty much have all the same organs as cold blooded beasts, except i guess some have jacobson's organ. so how is it that cold-blooded creatures don't make heat like we do? what do we have that they don't have? consider birds, even: warm blooded and they're closer to reptiles than we are. what's the x-factor there?
|
[
"Heat is generated across the body with burning of sugar. The difference between cold and warm blooded has to do with temperature ",
". Warm blooded (and this a range, not a binary state) organism generate heat for the purpose of maintaining a temperature. Thermoregulation involves cooling (sweating, flushing, etc.) and heating (burning more, shivering, etc.). The regulation involves both local responses (you will flush in response to local heating) and hormonal response primarily from the hypothalamus. "
] |
[
"Since the parent comment is gone, I'll fill in the gap. Thermogenesis, or the generation of heat, occurs mostly in brown adipose tissue, and by uncoupling the electron transport chain complexes from ATP synthase. The ETC complexes work to establish a proton gradient, which ATP synthase breaks down by allowing protons to flow through it, generating ATP by the process that I described above. However, these two processes can be unlinked through a protein called thermogenin. What it does is to allow protons to flow back into the membrane through means other than ATP synthase. Because the protons aren't only coming in through ATP synthase, energy is being lost as heat, rather than being converted to the phosphate bond between the beta and gamma phosphates. ATP synthesis stops becoming efficient, but it doesn't halt altogether; that would spell death for a cell.",
"Because this occurs only in mitochondria, brown adipose tissue is specially adapted to have more mitochondria than normal adipose tissue, hence its brown color. There is another tissue with high mitochondrial levels as well - muscle. This is the basis for shivering; by activating muscle pairs that work against each other, little net movement is created, but quite a bit of heat is. However, this is not as efficient as adipose tissue thermogenesis, since some energy is lost when the conversion from chemical to kinetic to thermal takes place.",
"Additionally, you can create heat by activating two opposing cycle at the same time, like lipogenesis and lipolysis. Since entropy states that overall entropy must increase, more energy goes into making a molecule than is contained in its bonds, with the extra energy being given off as heat.",
"EDIT: My post seems to imply that shivering is related to chemical thermogenesis. It is not. Starving a cell of ATP would be a terrible way to lead it into heat generation via motion (which requires ATP to do)."
] |
[
"Since the parent comment is gone, I'll fill in the gap. Thermogenesis, or the generation of heat, occurs mostly in brown adipose tissue, and by uncoupling the electron transport chain complexes from ATP synthase. The ETC complexes work to establish a proton gradient, which ATP synthase breaks down by allowing protons to flow through it, generating ATP by the process that I described above. However, these two processes can be unlinked through a protein called thermogenin. What it does is to allow protons to flow back into the membrane through means other than ATP synthase. Because the protons aren't only coming in through ATP synthase, energy is being lost as heat, rather than being converted to the phosphate bond between the beta and gamma phosphates. ATP synthesis stops becoming efficient, but it doesn't halt altogether; that would spell death for a cell.",
"Because this occurs only in mitochondria, brown adipose tissue is specially adapted to have more mitochondria than normal adipose tissue, hence its brown color. There is another tissue with high mitochondrial levels as well - muscle. This is the basis for shivering; by activating muscle pairs that work against each other, little net movement is created, but quite a bit of heat is. However, this is not as efficient as adipose tissue thermogenesis, since some energy is lost when the conversion from chemical to kinetic to thermal takes place.",
"Additionally, you can create heat by activating two opposing cycle at the same time, like lipogenesis and lipolysis. Since entropy states that overall entropy must increase, more energy goes into making a molecule than is contained in its bonds, with the extra energy being given off as heat.",
"EDIT: My post seems to imply that shivering is related to chemical thermogenesis. It is not. Starving a cell of ATP would be a terrible way to lead it into heat generation via motion (which requires ATP to do)."
] |
[
"When will we have enough data to understand whether a 12 week gap between mRNA vaccines (as in the UK) affects long-term protection?"
] |
[
false
] | null |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"Fair enough. I thought there would be a fairly definitive answer to this, but perhaps I was mistaken."
] |
[
"Probably another 6 months before there's a writeup, I would estimate"
] |
[
"Portuguese Man O' Wars are a collection of organisms that function as one entity. How do they come together to begin with?"
] |
[
false
] | null |
[
"These guys are really cool! They are part of the class Hydrozoa which is part of the phylum Cnidaria which includes jellyfish and corals etc. All of these types of animals have some sort of life cycle that cycles between two forms. The medusae which are what your traditional jellyfish is and a polyp which is a sessile non mobile form. Then there are inbetween forms. Note that some such as coral only have polyp forms. ",
"Now to the Man o war! The Man o War starts out in a larva stage called a planula. A planula is a small oval shaped organism that will eventually develop into a polyp form. This polyp will eventually reproduce asexually meaning all of the offspring will be genetic clones of that one polyp. But what's interesting in colonial Hydrozoa like the Man o War is that these offspring will only have certain genes turned on making them specialized. Each offspring of that original planula is now specialized to a certain task to help the colony. ",
"These specialized individuals are called zooids. There are really a few main types of zooids. You have the gastrozooids which are specialized for feeding. Gonozooids which are specialized for reproduction and all future offspring will come solely from these individuals. Finally some colonial Hydrozoa such as the Man o War also have dactylozooids which are special individuals which have cnidae cells with nematocysts. These guys are cells that can sting which is what is characteristic of the Cnidaria phylum. ",
"So to summarize: the basic larva form, the planula, does its normal thing and grows into many polyp like forms which differentiate and specialize to certain tasks. We call these specialized individuals zooids. So they don't really \"come together\" like you might think but rather arise from one organism. You might ask but how do they get that bell-like structure? How is that one organism? And that bell is just one super specialized zooid. ",
"The Portuguese Man o War is part of what we call Siphonophora which also includes other colonial organisms like Praya which is the longest predator in the world. It is even longer than a blue whale! Fell free to ask more questions and I'll do my best to answer them! "
] |
[
"What differentiates \"one organism\" from \"many organisms living in a colony\"? Surely there are many simple many-celled organisms that are like the Man o War."
] |
[
"Sure! I'm not actually too familiar with Praya but I do know it is also a colonial type of organism similar to the Portuguese Man o' War. So it too has specialized zooids and what makes it so long is that its \"tentacles\" are extraordinarily long. It is a predator like all Cnidaria because it eats other non-plant organisms and actively hunts. I say actively because Cnidaria can't necessarily see their prey but it does hunt. And I say \"tentacles\" because they are not made up of a bunch of cells in one organism but rather many zooids. A blue whale for example is a predator as well because it eats plankton (which includes phytoplankton as well as zooplankton) but what is really cool is that Praya is even longer than a blue whale (but certainly not more massive!)."
] |
[
"How many fields are there in QFT?"
] |
[
false
] |
Let me explain. Particles don't exist. What we experience as a particle, is actually the excitation of a field that extends throughout space. So here is my question. Say you have two electrons sitting next to each other. Is there one field that is excited in two places to produce two electrons, or is there a field for each electron? Do all electrons emerge from the same field or does each electron emerge from their own individual fields?
|
[
"There is one electron field. All electrons and positrons emerge from this one field."
] |
[
"Yes, one field for each type of particle. A field is something that can take different values at different points in spacetime. (Classically, these are just functions, while in quantum field theory, of course, the math changes a bit, but the idea is basically the same.) Of course, a field can vanish at some locations or times, but that doesn't mean the field can't act there."
] |
[
"I have a (reasonably important) nitpick: ",
"What we experience as a particle, is actually the excitation of a field that extends throughout space.",
"does not mean",
"Particles don't exist",
"What it does mean is that particles are not simply small hard spheres as people initially imagined. Even the much more complex (both conceptually and mathematically) QFT model is still \"only\" an approximation, of course. For instance, we don't know yet how to include gravity properly into the particle wave function."
] |
[
"How much radiation is still on Marie Curies notebooks?"
] |
[
false
] |
I just read that Marie Curies notebooks will still be radioactive for another thousand years at least because of the masses of radium and polonium that she and her husband handled. The books are kept in a box lined with lead in Paris - but what I could not find was the level of radiation in a unit like Sievert or Becquerel. Does anybody on here know this by chance?
|
[
"A distinction to make: Bq is a unit of activity, it is a measure of disintegrations per second of a radionuclide. Sievert is a unit of dose equivalent, it is a measure of ionizing radiation absorbed by the body. You measure the activity of a particular radionuclide (like radium or polonium) in Bq, but the biological effect of this radiation is measured in Sv (from all radionuclides cumulatively). ",
"To answer your question, different activities were measured for different kinds of radiation at different parts of the notebook (front and back covers, inside pages) with different methods (direct measurement, wipe test, gamma spectroscopy). ",
"The front/back covers were measured to have approximately 200 Bq/cm2 for Ra, and lower activity was measured for the inner pages. Wipe tests can pick up loose contamination, better to measure radionuclides that can be inhaled when inspecting the notebooks too closely (without protection); activities were measured in the range of ~0.030 Bq/cm2 for alpha radiation and up to 0.740 Bq/cm2 for beta radiation. Gamma spectroscopy measured 120 kBq for Ra-226 and 1 kBq Th-232. The report also estimates dose equivalents but keep in mind these estimates can have fairly large uncertainties. ",
"Source"
] |
[
"Much obliged!",
"Also thank you for clearing up the difference between these two units. I just looked up how to convert Bq to Sv and apparently this can not be done easily. Yet my intend of the question was to find out how dangerous these notebooks really are. So Sv would be the better unit I guess, therefore just to get an estimate: is 200 Bq/cm2 a lot of radiation in terms of damage to the body?"
] |
[
"Bq is a measure of the activity of a radionuclide, whereas Sv is a measure of biological effect of radiation. The unit of Bq is just s",
" Sv is J/kg, or energy absorbed per mass. The conversion from the radioactivity of a source (in Bq) to the biological effect in the body (in Sv) is not very clear for a few reasons: ",
"Sv is an equivalent dose. This differs from Gray (Gy, which has the same units as Sv) in that it quantifies things like biological effect (some organs are more susceptible to radiation) and quality factor of radiation (different kinds of radiation are more harmful than others). ",
"There are large uncertainties when calculating the equivalent dose. These uncertainties can come from measurement (intrinsic detector efficiency, background noise, geometric efficiency), uncertainty in the interactions of radiation in the body, and uncertainty of stochastic effects. ",
"The actual exposure to radiation is not the same as the activity of a radionuclide. Your exposure can be lessened by shielding (ie: the cover of the notebook and the air between you and the book provide some protection), standing further away from the notebook (inverse square of distance law), and shortening the time spent lingering near the notebook. ",
"As an illustrative example, suppose you were given 2 slightly radioactive cookies; one with alpha decay, and one with gamma decay. You would be perfectly fine to hold the alpha cookie in your hand as alpha particles would be stopped by the dead layer of skin of your hand. You could even eat the gamma cookie (still not advisable, but if you ",
" to, you could), and be okay because gamma rays would tend to pass through your body without depositing very much of their energy. On the other hand, eating the alpha cookie is a very bad idea because the range of alpha radiation is very short (remember holding it in our hand is alright) so all the energy is dumped into your body and harms tissues/cells. Alpha particles dumping their energy into the dead layer of skin is fine, not much harm is done. Alpha particles dumping their energy into the soft tissues of the body internally is quite bad. Not to mention most alpha emitters eventually decay to lead, which is highly poisonous. Holding the gamma emitter in your hand wouldn't do very much because most gamma rays will just pass through your hand/body without interacting much. ",
"And finally to answer your question: 200 Bq/cm2 of an alpha emitter would depend on the surface area of the notebook. The report also lists 120 kBq from 226-Ra for the notebook as a whole. In general, there is not much danger, provided you don't swallow the notebook. The real hazard comes from loose particles (like from the pages of the book) that may be inhaled if a person inspects the notebooks without protective equipment."
] |
[
"Is it theoretically possible for a particle accelerator such as the Large Hadron Collider to create a black hole since such high forces are involved?"
] |
[
false
] |
-If so, is this helpful in any way? eg: Insight into other dimensions. -If so, could it be controlled/eliminated? -Or would it consume Earth eventually if one was created?
|
[
"And even without black hole evaporation, a black hole that tiny would never get close enough to anything to absorb it and gain any mass. And cosmic rays constantly bombard the earth with more energy than the LHC can produce, so if destroying the world was that easy, we'd already be dead."
] |
[
"And even without black hole evaporation, a black hole that tiny would never get close enough to anything to absorb it and gain any mass. And cosmic rays constantly bombard the earth with more energy than the LHC can produce, so if destroying the world was that easy, we'd already be dead."
] |
[
"And cosmic rays constantly bombard the earth with more energy than the LHC can produce, so if destroying the world was that easy, we'd already be dead.",
"This is the most common argument used to placate people who worry we might destroy the universe, or at least our corner of it, with the LHC or other colliders. Not only do cosmic rays bombard us with more total energy, but the ",
"highest energy cosmic rays",
" are much more energetic than what we produce in the LHC."
] |
[
"In modern understanding, how [in]valid are IQ scores?"
] |
[
false
] | null |
[
"IQ scores are extremely good indicators of what they are meant to measure: generalized reasoning ability, such as the ability to learn from past experience. ",
"This study",
" and ",
"this one",
" found that childhood IQ was an excellent predictor of various indicators of success later in life; often better than socioeconomic status. ",
"That said, IQ is not a guarantee of success, or of being a nice person, or of being a hard worker, or of anything except reasoning ability. Duh. All it indicates is that other things being equal, those with higher IQs do better than those who do not, and it's very hard to believe that it would correlate so well with so many things if the effect were due to confounding.",
"However, IQ is also cultural. As a country develops, average IQ scores rise by about 3 points per decade (\"the Flynn effect.\") This is not the result of teaching specific skills: IQ tests don't measure factual knowledge, and the parts of the test that are the most abstract (Raven's progressive matrices, if you're googling) are the ones that show the Flynn effect most strongly and that correlate best with success. Being industrialized and modern and educated does make you smart. "
] |
[
"IQ scores compact results based on a vast array of topics related to conceptual understanding and use the average performance in comparison to a general population. While intelligence does have a tendency to correlate with scores due to one's awareness and ability to interpret patterns rising with intelligence, often times one's ability is reserved to factions of understanding not accurately determined by a test.",
"A team from the Belgian Franz-Robert research university found a vast variation between scores of groups when questions were rearranged, changed slightly, and incentive was given to score well. In addition, teaching groups weeks before how to recognize patterns frequently found in tests which simple analysis could determine allowed them to perform up to 20 points better than a control.",
"Ultimately, IQ tests test your ability to take an IQ test, and the correlation between that and intelligence is far from direct."
] |
[
"I haven't read up on the Flynn effect, but it would seem to me that the correlation found between higher IQ and industrialization/modernity/education may really just be a correlation between IQ and wealth. If you can afford to eat well, nourish your child, talk to them a lot and give them stimulation when they're young, you're already leagues above the people living in many cultures. I'd predict that if things like wealth and nutrition were controlled for, a less significant difference would be found. If you already know of such a study though, I'd maybe rescind my comment. "
] |
[
"How do you study microbes that don't respond to lab cultures?"
] |
[
false
] | null |
[
"It's really difficult! For those few brave souls who do venture into this line of work (not me), there are a few options.",
"If you're thinking that this sounds like sort of a contrived, artificial system, and that you might lose valuable information by taking the protein out of the context of the rest of the bacterium: congratulations! You are not a biochemist. (Joking. Mostly.) Let's move on to another option:",
"But what if you are not fortunate enough to have a closely-related microbe that you can culture easily? Well, there's always the just-try-harder approach to culturing microbes:",
"Some bugs are not easily culturable, but that doesn't mean that you flat-out can't do it. For example, some gut bacteria are what we call ",
"strict anaerobes",
", which means that they are killed by atmospheric levels of oxygen. These are a pain to work with, but it actually is possible; scientists have developed an ",
"array of technologies",
" that allow us to grow these bugs.",
"Other organisms can't be cultured in artificial media, but you can grow them if you provide them with a biological host. For example, the ",
"bacterium that causes chlamydia",
" will only grow inside of cells. This is annoying and makes it difficult to work with, but you can actually grow it in the laboratory as long as you're willing to maintain cultures of ",
"-infected cells.",
"To take this one step further, the bacterium responsible for leprosy, ",
", can only be grown successfully in ",
"nine-banded armadillos",
" (or, somewhat less successfully, in the footpads of mice), and even so it takes many months before you can get enough bacteria to do an experiment with.",
"And finally, maybe the most important answer of all:"
] |
[
"Great question. What you are describing is the Great Plate Count Anomaly problem. It isn't necessarily that they are impossible to culture but rather you have to find that special combination of conditions which enable them to grow. This can go from almost impossible to difficult. As an example we had numerous strains of Clostridium obtained from ATCC. One of them for whatever reason was discovered to need L-rhamnose (a special sugar that can be found in your intestines) to grow and the product sheet specified this. I grew them all in the media without rhamnose first to see if it was really needed. Sure enough that strain didn't grow. I added rhamnose to the anaerobic broth and cultured it again and it grew like crazy. If you were isolating bacteria and you didn't have rhamnose in your isolation media you would never find that strain. The same thing repeats over and over and you never know what signal or temp or atmosphere or co-culture organism, etc. you need to encourage your \"unculturable\" organism to grow.",
"http://microbiologybytes.wordpress.com/2013/09/17/great-plate-count-anomaly/"
] |
[
"Good answer. Just wanted to add that species representing unknown domains of bacteria are present everywhere, even in your mouth. For instance, ",
"TM7",
".",
"No one knows how to culture them.",
"I always thought that this would be a great project for an amateur interested. Because, I don't know of any professional scientists who would spend time trying to culture something like T7. ",
"If you could culture it, it would have significant impact on science."
] |
[
"What are the scientific facts against governmental mind control?"
] |
[
false
] | null |
[
"Hi there. That Putin mind control ray thing is not evidence. The link it sends to is a page which no longer exists which is published by a tabloid newspaper. That is not a primary source. While certain electromagnetic (and even ultrasonic) emitters can certainly cause pain, there is not a scrap of evidence to demonstrate mind control. In fact, the state of neuroscience at the moment we know certain areas of the brain are responsible for certain things, but we have no way to reliably make any kind of control. It's a bit like having a globe which shows the layout of the continents, and then giving it to someone and asking them to navigate their way around London with it.",
"When exceptional claims are made the burden of proof is on the eprson making the claims, not the rest of society to debunk it. There is no evidence for mind control ",
".",
"Conspiracy theories are rife on the internet, and there are plenty of people who will - with good intention - try and go out to get believers of these theories to change their miinds. Unfortunately, you cannot reason someone out of a belief they did not reason themselves into in the first place - in other words, if someone has decided to believe something on the basis of no hard evidence, hard evidence will not get them to change their mind - often it will just drive them deeper into the conspiracy mindset. I would strongly urge you to go and take a peak at both ",
"/r/conspiracy",
" and ",
"/r/conspiratard",
" to see both sides of the story. ",
"As far as releasing this into ",
"/r/askscience",
" goes, I'm afraid we specifically disallow 'debunk this' type posts for exactly the reasons I just stated. Ther eis also the fact that part of this appears to be treading on the 'medical advice' line. You can try your luck in our sister sub ",
"/r/asksciencediscussion",
" if you like, or perhaps even the ",
"/r/conspiratard",
" sub I mentioned earlier.",
"Edit - you might find this an interesting read too ",
"http://www.scientificamerican.com/article.cfm?id=the-conspiracy-theory-director",
"There's also some great reading here ",
"http://en.wikipedia.org/wiki/Conspiracy_theory"
] |
[
"Thank you for your in depth reply. I did not read the side bar, because I didnt think this would be common. Should I delete it? I just don't want to lose your response in my archives. Also, this was very kind of you"
] |
[
"NO need to delete it, I've removed it from our queue so no-one but you and I can see it now.",
"My pleasure to help, and good luck with whatever you decide to do. Mental health problems and conspiracies are unfortunately common bedfellows (see the psychology section on that wiki article for examples). I can only really recommend that you try and get your friend to seek professional help. There's not a lot you can do about conspiracy thinking, although in ",
"/r/conspiratard",
" there are plenty of examples of former conspiracy theorists who saw the light."
] |
[
"What's the deal with Sodium Laureth/Lauryl Sulfate and should I be worried about it?"
] |
[
false
] |
Full disclosure: I'm writing an article for a mag and I need to touch on this a bit. My understanding so far is that people dislike it because it (they? not sure of the difference between the two) is a surfactant which means its function is to break surfaces down (ie your hair to allow the moisturiser etc to penetrate) and there are worries that it could break down the surface of your skin and get into your brain and cause cancer? Do I have the basics of that right? And, as with other ingredient worries, like BPA, is this mostly shrugged off by the scientific community? It certainly seems like every other shampoo still has it in. Are there ingredients other than SLS we should 'be worried' about?
|
[
"I'll give you two answers:",
"1) You're writing an article for a magazine? Shouldn't you be interviewing a scientist like, in person? You don't know who the hell we are...I could be making this shit up!",
"2) Full disclosure: I spent a summer interning for a major soap company.",
"I'm a materials person, so I know a good deal about surfaces and surfactants and such. As a physical scientist, I'm not personally aware of any studies regarding the safety or carcinogenicity of SLS (maybe a biology panelist will be willing to chime in on this).",
"However, I am qualified to say this: No, SLS will not break down the surface of your skin and get into your brain and cause cancer. Thats not how cancer works, its not how surfactants work. ",
"Using the term \"shrugged off\" implies that scientists just kind of threw this molecule out into the field and didn't bother. As it turns out, soap is regulated by the FDA especially since people started putting triclosan (antibacterial agent) into it. SLS has been tested by the FDA and shown to be non-carcinogenic. As far as I know, BPA was never required to go through any such tested because it was not intended to be ingested or applied to the human body.",
"If you're interested in learning how surfactants work I'm happy to help, but I really think you should be interviewing a scientist in person."
] |
[
"In that case, I'd stay away from cosmetic chemists. Good people, I'm sure, but probably not the best to answer these types of questions about SLS for you. You're going to want to find a biophysicist or a biochemist who works with cell walls or cell membranes. There are even people who do surface chemistry with cells who are probably eminently qualified to authoritatively answer this question. If you were to tell me where you are (say, what major cities are nearby) I would be willing to browse a couple university websites to find someone for you."
] |
[
"Chemist working with membranes here. SDS is a surfactant, and certainly busts cell membranes when in contact with them; this is generally not a concern for skin application, since skin is keratinous \"dead\" layer whose function is precisely to keep your cells protected from unwanted chemicals."
] |
[
"How are some drugs capable of entering the blood stream through the mouth?"
] |
[
false
] |
Drugs like immodium have variations that allow them to enter the blood stream through the mouth, and therefore faster. Why do some drugs, like painkillers, not have this?
|
[
"Short answer, they do. A significant number of drugs have ODT versions.",
"Pain killers, for example, have IV, Sub-dermal, topical, Intramuscular, intranasal, inhalation, etc.",
"If you're curious, look into first pass metabolism (liver breaks down the drug before the rest of the body gets it). Will explain it further."
] |
[
"The best way to administer most drugs if you want bioavailability is IV. That, by definition, is 100% bioavailable. Drugs that go through the oral route must be absorbed in your intestines, progress through the portal venous system, where most undergo first-pass metabolism by your liver before entering your systemic circulation. Therefore, some of the drug will already have been converted into something else. This in many cases is bad because the drug that you give is the active form. But in some cases, you might want that first-pass metabolism because it's the drug metabolite that actually has the best activity."
] |
[
"So regarding immodium specifically I think you might be mistaken. There is very little immodium that successfully goes from the GI tract to the bloodstream, except in the case that the user has lesions/breaks in their GI tract that could allow more to enter the blood or if the user drinks an excess of immodium. Immodium works by binding to opiate receptors within the GI tract to slow down GI muscle contractions and therefore increase fecal retention time. So it’s never intended to enter the blood because it performs its function entirely within the gut.",
"More generally, to answer your question about why some oral drugs CAN enter the blood effectively, it’s important to have some basic knowledge about transport across the cell membrane (which would be required to go from GI tract to blood). Uncharged, small, water-insoluble molecules can easily pass the cell membrane on their own. Most drugs do not fall into this category because most drugs are fairly bulky and sometimes very water-soluble. That being said some bulky, water-insoluble drugs can pass the cell membrane this way to a small extent, especially if their concentration in the GI tract is very high relative to concentration in the blood/cell. I believe this is the case for Imodium, a bulky, water-insoluble drug. If a drug can not pass the cell membrane on its own like this, the only (pharmaceutically practical) alternative is to cross the cell membrane by inducing endocytosis (I.e. bind to a cell receptor that causes the cell to “eat” the drug and then pass it out the other side and into the blood). Basically, this means that your drug has to be artificially designed to “fit” the receptor of choice (no easy feat, but possible) or it has to be a naturally occurring compound that fits the receptor either by chance or for various evolutionary reasons (nicotine and CBD for example). It may also be possible for a drug to be “eaten” by an immune cell that could carry it from the gut to the blood/lymphatics, but I don’t know enough about gut immunity to speak to this very confidently. If this method is indeed real, it may require that the drug be attached to a much larger protein or particle because immune cells generally only like to “eat” particles of a certain size range. A drug molecule wouldn’t be nearly big enough on its own.",
"Sorry for the long winded, perhaps overly complicated answer. "
] |
[
"What keeps everything in place in your body when you're in space? How comes the food doesn't float in your oesophagi when you try to eat?"
] |
[
false
] | null |
[
"same reason you can eat while upside down. Gravity helps but the muscles do the work."
] |
[
"I assume you meant 'red.' On earth gravity pools the blood wherever the body is closes to it, meaning your feet when standing and your head when upside down. In microgravity(space) blood will will spread evenly evenly around body, but not to the degree being upside down on earth would cause.",
"http://en.wikipedia.org/wiki/Human_adaptation_to_spaceflight#Fluids"
] |
[
"wow you can eat upside down? I never tried. What about our head becoming red when we're upside down, why doesn't it do the same thing in space?"
] |
[
"Black holes \"slow down\" time. Is there an astronomical phenomenon that \"speeds up\" time for a handful of people? Could we use it to \"get ahead\" in the galactic race for domination/survival?"
] |
[
false
] |
The question is serious, although it might sound like it's from a c-movie of sorts. You might need to cut me some slack here. From what I understand (and the movies tell me), time "slows down" considerably close to a black hole. It doesn't slow down noticably for the one being close to the black hole, only for the spectator far away. That's relativity, right? A couple of hours too close "make time fly" for the rest of the universe. Is there an opposite phenomenon, where times starts flying by for a few whereas the rest of the universe "slows down"? Maybe what I'm asking is this: is there such a phenomenen and a way to use it to sort of "cheat" on the speed of advancement and development in relation to the rest of the universe? A chance to "get ahead"?
|
[
"Let's take a few steps back. First of all there is no absolute notion of time to talk about. Second of all you have this mixed up a little, a slow clock gives you what you want.",
"Let's just talk about special relativity, to talk this stuff in general relativity is not much more complicated at this level but requires changing notions of what you mean by accelerating from the intuitive notions you probably hold.",
"The amount of time a \"clock\" (meaning anything which keeps track of time, including the aging of an organism) measures between two events is a MAXIMUM if it is not accelerating. So if you have two people starting at the same place and one sits still while the other accelerates off and comes back the second person will have aged less when they meet up. In principle the second person can have aged an arbitrarily small amount for any amount of aging the first person experienced. So to see what the state of technology on the Earth is in some amount of time you \"just\" need to accelerate hard enough away from the Earth and then return."
] |
[
"So to see what the state of technology on the Earth is in some amount of time you \"just\" need to accelerate hard enough away from the Earth and then return.",
"It should be added that there is no way to get back to the time where you started, so you can't turn that new knowledge into an advantage."
] |
[
"But you could use it to pass time while you were waiting on something to be developed. Say a disease. You zip off really fast and hope they have a cure by the time you get back, but if you stayed you wouldn't survive long enough to see that cure."
] |
[
"Why are Electron Microscopes called Electron Microscopes?"
] |
[
false
] | null |
[
"Electron microscopes use electrons for imaging instead of light."
] |
[
"Do you know how they do that? That sounds fascinating. I wonder if the photons and electrons display similar properties with imaging, or if they have to use an entirely different method?"
] |
[
"There are different kinds of electron microscopes. I think the ",
"Wiki",
" is a good introduction to them."
] |
[
"If Dark Matter is particles that don't interact electromagnetically, is it possible for dark matter to form 'stars'? Is a rogue, undetectable body of dark matter a possible doomsday scenario?"
] |
[
false
] |
I'm not sure If dark matter as hypothesized could even pool into high density masses, since without EM wouldn't the dark particles just scatter through each other and never settle realistically? It's a spooky thought though, an invisible solar mass passing through the earth and completely destroying with gravitational interaction.
|
[
" There actually could have been stars in the early universe, more massive than any that could exist today, powered by dark matter annhilation. ",
" Dark matter doesn't really all clump in one spot on top of itself for the same reason that stars don't - they just don't tend to bump into each other. When you squeeze normal matter the particles will bump each other, and give off heat. This is a mechanism for getting gravitational potential energy out of a gas cloud in order to make it collapse, which allows it to undergo star formation to make compact bodies. Dark matter is what we call 'noncollisional.' The particles essentially pass right through each other, and though they interact gravitationally, they don't have much of a braking mechanism, so they don't tend to collapse into compact objects in the same way atomic matter will. If a dark matter particle does interact with another dark matter particle, it will likely annihilate (in the same way that matter and antimatter annihilates) and produce very high energy photons. ",
"In fact, it's been hypothesized that there were stars in the early universe powered by dark matter annihilation... ",
"Regular stars have a maximum mass. As you add mass, the pressure on the core gets greater, so they get hotter and fuse more, releasing more energy. Eventually, if you keep adding mass, the outward pressure from the core will exceed the inward pressure from gravity and it will have to blow off the outer layers to get down to the mass limit, called the Eddington Limit.",
"Dark matter fixes this. Dark matter is different from regular matter in that it doesn't fuse and it doesn't really interact much, so it can contribute to gravitational mass of a star and make a star much bigger than the Eddington limit. In the early universe when things were denser, dark matter may have been more abundant and formed the seed for stars many times wider than our ",
" called \"Dark Stars.\" The name \"Dark Star\" is a terrible misnomer, because these stars would be bright as fuck, powered by dark matter annihilation n a gas of regular baryonic matter. They would still find a balance between an outward pressure from core heating and an inward pressure from gravity, but it would make for a much bigger star. Inside, dark matter particles and anti-dark matter particles would annihilate producing very high energy radiation, in excess of what's typically released in fusion reactions. ",
"Observing a distant source like this in the universe would be incredibly helpful in figuring out what the dark matter is actually made of - the luminosity of the star should be set by the mass of the dark matter particle, which would help us constrain current particle models of dark matter. ",
"But to really answer your question, I doubt you'll have a tight ball of ",
" dark matter without some other stuff mixing in gravitationally. In fact, we see balls of dark matter all over the place, the problem is that they are the size of galaxies, and they aren't pure (because they have galaxies in them!). "
] |
[
"I think you emphasize the concept of dark matter heated stars too greatly. We don't yet have solid evidence that annihilation does occur, which is the biggest assumption powering this idea and I don't believe there is any current observational evidence to support it either. It's certainly a cool idea, but I feel you should bold the word \"",
".\" ",
"For those interested in reading more, here's the two introductory papers on it, ",
"http://arxiv.org/abs/0705.0521",
" ",
"http://arxiv.org/abs/0806.0617"
] |
[
"Yeah, and maybe it's worth specifying that neutralinos are the top dark matter candidate considered for dark stars. "
] |
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