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[
"Why do the elderly respond to cold weather more than younger people?"
] |
[
false
] | null |
[
"Thanks for the explanation!"
] |
[
"Thanks for the explanation!"
] |
[
"15 degrees?!?! ...Do you mean Celsius?"
] |
[
"Why is sunburnt skin noticeably warmer to the touch?"
] |
[
false
] | null |
[
"Exactly. One of the main components of inflammation is heat (the other \"cardinal signs\" are redness, swelling, pain, and loss of function). This is due to increased blood flow to the area. ",
"Sunburns are inflamed because there has been trauma and cell death in the area. "
] |
[
"I can't give you a medical reason but, as a very pale descendant of Ireland, I'm guessing that, since sunburn does damage to the outer layer of skin, the warmth is due to the red blood cells traveling to the area to begin the repair process. You may notice the same thing happens to an infected cut. The area around it will become red and inflamed. I don't believe it's the infection that's warmer but the blood cells there to combat the infection/heal the damage. "
] |
[
"Thanks for verifying that! "
] |
[
"Is iPhone X’s Face ID Infrared Safe?"
] |
[
false
] | null |
[
"Hi SirBeethoven thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"‘Computing’"
] |
[
"Computing"
] |
[
"Why are there fresh and salt water varieties of most aquatic life, but no freshwater cephalopods?"
] |
[
false
] |
There seems to be at least somewhat-analogous pairings in fresh and salt water for most types of aquatic life, but there doesn't seem to be a single cephalopod that lives in fresh water. Why are there no freshwater octopuses or squids?
|
[
"osmosis.",
"Freshwater dwellers have salty blood relative to the water around them. Without a mechanism in place to control it, osmosis would equalise salt concentrations between the animal and the water surrounding it, pumping salt out of the body and flooding it with freshwater. A sodium pump, like that found in freshwater fish species, uses chloride cells on the gill surface to actively absorb sodium and potassium ions from the environment. Any excess water taken in at the same time is excreted as urine.",
"Marine dwellers have the opposite problem, and need to conserve fresh water while expelling salt. Cephalopods pump seawater through their gills and use their kidneys to filter out fresh water from the ocean. Salts and waste water are channelled through the funnel.",
"ie, they never developed a sodium pump that would help them cope with osmotic change in freshwater.",
"www.abc.net.au/science/articles/2013/01/16/3670198.htm"
] |
[
"Great question! Echinoderms (urchins, starfish, sea cucumbers, brittle stars, sea lillies) also can’t be found in freshwater because they use seawater as their blood."
] |
[
"That's a great explanation for the differences in biology, but I feel like it doesn't really answer the question. Is there something about cephalopod biology that's incompatible with that kind of sodium pump? Or did it just not evolve by pure coincidence?",
"Like starfish just use straight seawater as their blood, so they don't have any kind if pump system. At least not at this scale. But fish have both directions of pump, dolphins have both directions of pump, but why can squid only have one?"
] |
[
"Do electrons rotate while they are circling the nucleus?"
] |
[
false
] |
[deleted]
|
[
"Electrons are neither circling the nucleus (strictly speaking) nor rotating on themselves.",
"The fact that they possess both an orbital angular momentum and an intrinsic angular momentum (spin) can therefore be seen as a bit confusing.",
"To better understand the origin of the first, you should know that electrons can be found around the nucleus in a sort of clouds called orbitals. They cannot be localized on an orbit because of Heisenberg indetermination principle. Beside that, the attempt to build a solar system-like atom was pursued for a while but, as an accelerated charge irradiates, such a classical object would be terribly unstable and the electron would collapse on the nucleus.",
"It is the shape of its distribution around the nucleus that gives the electron its angular momentum. You can find a ",
"classification of orbitals",
" according to the value of their angolar momentum and its (quantized) spatial orientation.",
"The origin of the intrinsic angular momentum is more complicated (it's easier to show that it has to be half integer). \nTo understand that electrons are not small rotating particle; it can be checked that if you imagine subatomic particles (protons as well) as spinning charged spheres, they can't get to their actual magnetic dipole moment without spinning way faster than the speed of light. Thus it makes no sense to try to describe them that way.",
"The first experimental results were indeed quite puzzling and the rotating electron idea was proposed by someone and rapidly dismissed by Pauli. Later Dirac was able to derive his equation whose solutions describe half-integer spin massive particles.",
"You can check ",
"Stern-Gerlach experiment",
" for more info.",
"Edit: What I wrote about showing spin has to be half integer might be very wrong. Because now that I think better I don't remember how. Of course we can measure it but that was not what I meant..."
] |
[
"These are analogous to the rotation of the Earth around the sun and the rotation of the Earth around its axis",
"Careful here. There's truly no classical analogy to electron spin and making that analogy leads to incorrect physical intuition. "
] |
[
"These are analogous to the rotation of the Earth around the sun and the rotation of the Earth around its axis",
"Careful here. There's truly no classical analogy to electron spin and making that analogy leads to incorrect physical intuition. "
] |
[
"Why is the expansion of the universe attributed to dark matter and not just momentum from The Big Bang?"
] |
[
false
] |
[deleted]
|
[
"You mean \"dark energy\" rather than \"dark matter\" - but yes, it's because of the acceleration of the expansion. Before the late 1990s, the expansion ",
" considered to be more or less just momentum from the Big Bang, with gravity predicted to slow the expansion. The expansion isn't slowing though, it's speeding up - dark energy is the name given to whatever is causing that acceleration, but that's just about all we know about it, along with the fact that whatever it is makes up the majority of the stuff in the universe at this point."
] |
[
"So, there's an interesting aspect of how gravity works. Imagine if the earth was a hollow shell, and you were inside of it. At first we would assume that the shell's gravity would pull us, but here's the thing: there is shell to the right of you, ",
" shell to the left of you. ANd the two opposing attractive forces cancel each other out. The best part is that, even if you aren't in the center of the shell, but near one side, and you have material on that aside that is closer (and because the force goes as 1/r",
" where r is distance) you would think that it would pull on you harder, but there's also ",
" material on the other side. And the math just happens to work out that no matter where you are within the shell, if you close your eyes, there is no measurable difference between being within a shell or there being no shell at all.",
"In other words, all the material \"outside\" of you pulls on you equally, and that's the same as not pulling on you at all.",
"BTW, this mathematical result is one of the special cases of an even more powerful result called Gauss's Law."
] |
[
"yes, simply by ",
"newton's shell theorem",
"which states that ",
"If the body is a spherically symmetric shell (i.e., a hollow ball), no net gravitational force is exerted by the shell on any object inside, regardless of the object's location within the shell.",
"because we see isotropic expansion in the universe, even if there was tons of matter outside the visible universe, they would have no gravitational influence over us, since we're inside it."
] |
[
"Just how much \"stuff\" is there and how do we know?"
] |
[
false
] |
When scientists talk about knowing how many atoms/particles there are in the universe, does this mean in the "observable universe"? And how have they determined that amount anyway? I have heard that general relativity allows for the expansion of space faster than the speed of light, so is there stuff out there that is impossible for us to observe? Is it possible that our universe contains mass/energy that is beyond the scope of our observation? If this is true, and we were to travel instantaneously to a galaxy billions of light years away, would their observable universe look very different from ours? Would they be able to see galaxies that we can't see? Or do we know that the expansion of space faster than the speed of light has not happened yet precisely because we can still see the CMB?
|
[
"I can't answer all your questions, but I'll do my best to answer the ones I can.",
"When scientists talk about knowing how many atoms/particles there are in the universe, does this mean in the \"observable universe\"?",
"Yep. We don't really know how big the universe is (and to my knowledge it could very well be infinite), so we can't estimate the number of atoms in the whole universe. Just the part of it that we can see.",
"I have heard that general relativity allows for the expansion of space faster than the speed of light, so is there stuff out there that is impossible for us to observe?",
"I believe so. And actually, because the universe is expanding faster than the speed of light, the amount of stuff we can observe is going to decrease over time. It's one of the more depressing conclusions of current science, I think. According to our current knowledge and theory, the universe will eventually reach the point where the sky is completely empty because the nearest stars are still outside the observable universe.",
"If this is true, and we were to travel instantaneously to a galaxy billions of light years away, would their observable universe look very different from ours? Would they be able to see galaxies that we can't see?",
"Well, the observable universe actually has a radius of about 46 billion light years, so if you traveled billions of light years away you'd probably still be within our observable universe. I assume want to know what we would see if we could instantly travel far outside the observable universe.",
"The current belief is that the universe is homogeneous, meaning it looks roughly the same everywhere, and isotropic, meaning it looks roughly the same in every direction. So if this is correct, then their observable universe would look pretty similar to ours. They would still be able to see galaxies that we can't see, though. Actually, that would probably be true even if they did only travel a few billion light years, still well within our observable universe. Because there would be some galaxies from which the light had reached their location but hadn't yet made it to Earth. But their overall observable universe would look pretty similar to ours, even though the exact galaxies and stars in it would be different."
] |
[
"I'm not the OP, but thanks very much for this answer. On a related note, roughly how many atoms are there in the observable universe?"
] |
[
"About 10",
" ",
"according to Wolfram Alpha",
". (In general, Wolfram Alpha's a pretty great tool for looking up things like this)"
] |
[
"Do you get blackbody radiation from a pure gas?"
] |
[
false
] |
What are the characteristics of a material that allow it to emit blackbody-like radiation? In a cloud of molecular gas (i.e., a star forming region), will you only get blackbody radiation from the dust? Or will you also get blackbody radiation from the gas?
|
[
" object",
" at a temperature higher than 0K will emit some blackbody radiation. To put it a bit more precisely, all objects will emit some thermal radiation, the spectrum of which is weighted by ",
"the blackbody spectrum",
". But the actual spectrum you get will depend on the material in question. The reason for that is given by ",
"Kirchhoff's law of thermal radiation",
". This law basically says that an emitter will be as good at emitting thermal radiation at a given frequency as it is at absorbing energy at that frequency. The reason for this effect goes back to the basics of quantum mechanics. In order to produce (or absorb) a photon with a given energy, you need two things:",
"There need to be ",
"two states separated by an energy close to the energy of the photon.",
"The EM field has to be able to mediate the transition from one state to the other. These transitions are said to be ",
".",
"For things like metals with a large number of free electrons, you are decently close to this ideal scenario. So for example, the tungsten filament in an incandescent lamp will produce a broad, black-body like spectrum, ",
"as shown here",
". On the other hand, in a low pressure gas lamp, you will instead see a bunch of sharp lines ",
"as shown here",
". These simply correspond to the allowed electronic transitions for that particular element.",
"*made of ordinary matter"
] |
[
"Again, it depends on exactly what kind of fire we are talking about. But for instance if you are talking about the flame of a candle, or the a typical fire in a wood burning fireplace, the answer is yes. As the organic components start burning, they will spit up a bunch of soot. This soot in turn will ",
"radiate like a typical blackbody as seen here."
] |
[
"A hydrogen/oxygen fire is blue, and can be barely visible.",
"Here's",
" a picture of a Space Shuttle main engine firing. You can see the blue of the Hydrogen flame in the rocket's bell, but can barely make the flame out against the background."
] |
[
"What is \"reality\"? How much do we really \"see\", and how limited are we by our senses to the true nature of the universe"
] |
[
false
] |
[deleted]
|
[
"But how could they change from 17 to 27 if time is just a relative illusion?"
] |
[
"Hate you. So much."
] |
[
" You are standing ",
" to a perilous cliff, off of which many a would-be philosopher-king has tumbled to an ignominious death. Take about four steps back ",
"The short and direct answer to your question is that none of that could possibly matter less, and thinking about it is a complete waste of time.",
"That sensation you're feeling right now, that slight feeling of disorientation like a sort of dizziness? It's not deep philosophical profundity. It's just the mind's natural response to near-toxic levels of vapidness.",
"That's not an insult. Learning to distinguish the vapid from the profound is one of the hardest things young scientists struggle with, and a skill that the typical non-scientist has never had need to master. But rest assured, you're not on untrodden ground. The world is full of people who, at seventeen, had a thought that shook them to the core, then at twenty-seven looked back and realized it had just been silly."
] |
[
"It is often said that humans are no better at detecting lies than chance; are we any good at judging intelligence?"
] |
[
false
] | null |
[
"Hi ana1ytics thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"'Psychology'"
] |
[
"Psychology"
] |
[
"How do engineers prevent the thrust chamber on a large rocket from melting?"
] |
[
false
] |
Rocket exhaust is hot enough to melt steel and many other materials. How is the thrust chamber of a rocket able to sustain this temperature for such long durations?
|
[
"There are a few different designs to cool the “bell”. Some have small tube-like paths throughout for fuel to travel through it, removing some of the heat and pre-heating the fuel. Some use ablative material that slowly flakes off removing some of the heat with it."
] |
[
"Yes,",
"regenerative cooling with fuel",
") is the main answer."
] |
[
"I'm sure they know what they're doing; it just ",
" dangerous: \"Our new car gets rid of the inefficient radiator-and-coolant system—now all those red-hot metal parts are cooled directly with gasoline!\""
] |
[
"Why is our body able to fight certain viruses/diseases and eventually develop anti-bodies but can't for others?"
] |
[
false
] |
When it comes to diseases like measles, in most cases, once our body fights off the disease we are granted lifetime immunity. When it comes to the flu, immunity is mostly temporary because of mutation. But what about viruses such as HSV or HIV/AIDS where we have to rely on medication for the rest of our lives to keep fighting? Why is our body unable to recognize the virus and fight it to develop natural immunity over time?
|
[
"HSV and HIV are able to hide from the immune system in very different yet effective ways. HSV (as well as other herpesviruses) infects and becomes latent in neurons. Our nerves are typically left alone by our immune system because they last our entire lives, you don’t want to target nerves with an immune response (see ",
"GBS",
"). This is also why rabies treatment is best as early as possible, it is another virus that hides in nerves although it slowly works its way to the brain (where it is ~100% fatal).",
"HIV is a retrovirus meaning it turns its RNA genome into DNA (backwards from everything else in biology) and inserts that DNA into your genome. HIV also targets a subset of T cells which are important for your immune system, weakening it and making it more difficult to fight the infection. Modern antiretrovirals can essentially eliminate HIV but they are unable to cure it because of its integration into the host genome. So many HIV patient’s today are positive only in name, if you tested them they’d be negative but the DNA/viral instructions are still present."
] |
[
"People do develop antibodies against HIV—that's the basic sense of \"seropositive\", literally, serum-tests-positive for anti-HIV activity. The blood serum is the liquid, watery part of the blood, after removing cells and other particles. So \"seropositive\" means having antibodies; which is to say the immune system's been exposed to HIV (in this case) and knows about it. It actually doesn't imply anything regarding the state of the infection or disease; drugs can bring the viral infection down to undetectable levels, but a patient will still be seropositive, because that's a statement about the immune system and not about the virus",
"Note that you can be seropositive to any antigen, it's not specific to HIV. Whenever you get vaccinated you become seropositive to something, it's the principle. Though the amount of antibodies can decrease over time, depending on the type of antigen, exposure context, and person",
"The problem with HIV and all chronic infectious diseases is that they're very good at hide-and-seek"
] |
[
"This is fascinating and a really great explanation, thank you for sharing!"
] |
[
"How come the exact same flight computer, RAD750 is being used on both Curiosity (2011) and the Mars 2020 rover, have there been no improvements in almost 10 years?"
] |
[
false
] | null |
[
"It is extremely expensive to qualify stuff for space applications, even more so when it is for a flagship science mission. For electronics normal testing will include:",
"In some cases the tests need to be performed with the same production batch as the one that you are going to fly.",
"As you can see this is a shitload of testing, so when you know that something works you try to stick with it. The whole idea behind Curiosity and Perseverance (Mars 2020 new name) is that they are based on the same platform. They try not to reinvent the wheel (pun intended) if they don't have to. So the chassis, power system and main computer are the same.",
"And this is also not considering software testing which can be more complex and take even more time than hardware for space applications.",
"Edit: forgot the obvious but there is also not a ton of manufacturers who will design a build radiation hardened processors and chips. So it's not as if you had a huge amount of choice.",
"Edit 2: Forgot all the EMC testing. Testing what happen if there is a short circuit, what happen if there is electromagnetic noise nearby or on the same power line. How much EM radiation is it giving out?"
] |
[
"It's more than that, actually. The RAD750 was released in 2001 and was first flown in the Deep Impact probe in 2005. Why are we using 20 year old technology?",
"Beyond the cost of building new technology, as ",
"/u/electric_ionland",
" says, you have to ask what the value of having a faster processor would be. Most space missions, especially those that go beyond Earth Orbit, are limited by bandwidth and communication windows more than computational power. More computational power would be nice, since most rover operations are done autonomously by the system itself, but it would be an evolutionary advance instead of a revolutionary advance. The rover could perhaps gather more data points and evaluate more potential paths when it's driving itself, which might mean slightly safer and smother driving, but it's clear that the existing system is working fine and has been for years. ",
"Also bear in mind that many space-based missions have a much lower computational requirement than the Mars rovers. They are somewhat unique in their requirement for plotting and executing autonomous actions on a planet. Many space-based missions just fly through space and really only return science data and telemetry, so a faster chip is not going to particularly improve those missions. What this means is that the market for fast chips in space is mostly limited to things like Mars rovers, or to put it in numbers, the demand is something on the order of one processor per year. ",
"Second, one of the ways that modern chip designs provide more computational power is miniaturization. However, miniaturization also makes chips more susceptible to failure. In particular radiation-induced failures, because the smaller feature size means that the energy threshold needed to cause something like a bit flip is commensurately smaller. The result is that the traditional mechanism for getting more processor performance would result in worse environmental performance, and that second thing is explicitly what these chips are supposed to be good at. ",
"This is not insurmountable- you could add better shielding to the chip for example, or I'm sure there are other clever solutions as well. But this all goes back to the measure of cost- this makes the development of higher performance chips more expensive than you'd otherwise expect. ",
"Ultimately, the chips aren't going to get better until the increase in performance would justify the increase in cost. The manufacturer isn't going to build the chips until there's a customer willing to buy some. Whenever they do decide to build more powerful chips it's essentially going to have to be a collaboration between the space mission planners and the chip builders, because nobody is going to make the first move on their own."
] |
[
"For space application it is usually either a pendulum hammer and a swing table or actual explosives. You can sometime do it with sin bursts but it is not as good."
] |
[
"If you had a pen, a paper, and ten seconds, what's the biggest number you could write? What's the best tactic?"
] |
[
false
] | null |
[
"You will be interested in the following read : ",
"Link",
"This gives a very long and detailed answer to this exact question."
] |
[
"It depends on how long it takes you to write different numbers. 9 is bigger than 1, but you can write a 1 really fast.",
"Regardless, exponentials get big fast. 9",
" is 387420489 and 9",
" is 2.9512665e+94 which is huge. But far larger is the number 9",
" So writing just 5 characters you could write the nested exponential expression 9",
" (you could skip the parentheses if you were handwriting it and could use superscript). Your base and exponents cannot actually BE 1, obviously, but if you can write two 1s faster than one 9, you could do 11",
" etc. ",
"The factorial function grows very quickly as well. At low values exponentials grow faster, but when you are taking the factorial of a number and comparing it to an exponential using a relatively small base, the factorial will eventually take off.",
"So get a jump start with (9",
" then nest factorials\n(((9",
" etc...\nAnd somebody correct me if I'm wrong, but I think that can be simplified by dropping the parentheses out to:\n(9",
" etc",
"EDIT: To answer the question about what the biggest number is, the short answer is that it is far larger than I can give you a direct expression of. Google's calculator function won't even take 9",
" and remember that 9",
" already has about 100 digits in it.",
"In 10 seconds, using any of the techniques regarding nesting exponentials or factorials I mentioned, I'm going to guess you could ",
" represent a number which would fill both sides of the page if printed in 8 point font. Possibly a number that would fill 100, or 10,000 pages. Because that's the kind of growth at each step that nested factorials will give you."
] |
[
"Probably something like \"the 11111th Busy Beaver Number\" is the biggest well defined (although in this case unknown) number you could write down very quickly.",
"According to the rules, I have fifteen seconds. I write:",
"S",
"(G), where G is graham's number, exponentiation is functional iteration, and S(m) is the m-th busy beaver number.",
"Does that count?"
] |
[
"If I sat in a tube of 100% pure ethanol/alcohol, what would happen to me?"
] |
[
false
] |
Assume I didn't have any breathing issues.
|
[
"This is way off topic, but since it's ",
"/r/askscience",
" I figure no one would really mind. ",
"Having a 100% ethanol solution is extremely difficult (technically, a perfect 100% ethanol is essentially impossible) but you can get very close with some tricks. When you have a mixture of water and ethanol, distillation can be used to take advantage of the different boiling points of the two liquids in order to separate the mixture into the original components- water and ethanol. When you heat up a water/ethanol mixture, the ethanol has a higher vapor pressure or lower boiling point; that idea is taken advantage of when separating the two. ",
"Normal distillation of ethanol will form an azeotrope with water at about 95.6% ethanol, the remainder water. That means that no matter how many times you distill the alcohol, you'll never get rid of that remaining portion of water because the ethanol and water now evaporate together in equal proportions that were identical to the liquid state. A 50/50 mixture of ethanol/water might be distilled once to get to 75/25, then 85/15, but when you get to 95.6/4.4 and boil the solution, the vapor is still 95.6/4.4 and it doesn't change the liquid left behind. In order to get a higher purity of ethanol, the water must somehow be driven off of the mixture without taking that same ratio of the ethanol with it. The method I hear of most is \"cracking\" or \"breaking\" the azeotrope with benzene.",
"In this case, benzene acts as an ",
" and it reacts with the ethanol and water in a way where the water can then be driven off. What happens is the benzene now forms a three-way azeotrope of alcohol/water/benzene that is even easier yet to evaporate from the previous ethanol/water. So, a little bit of benzene is added to the ethanol/water solution, it attracts both substances, and then it is evaporated. When this happens all of the water boils off with the benzene (as well as ",
" of the large portion of ethanol) but there is still a large amount of ethanol left behind. But just because all of the water leaves doesn't mean the mixture is now 100% ethanol. What really happens is that there is now some excess benzene left in the solution that stuck with the ethanol molecules, which then needs to be separated. However, the benzene can't be completely separated, as there are always a few ppm (parts per million) of benzene left behind which is toxic to humans. This is why humans can't drink ethanol that has been cracked with benzene.",
"There are other ways to fully distill alcohol that don't leave the poisonous benzene behind, but the only one I know of for sure is the use of a molecular sieve and the reaction of a hydroxide with the water. Both methods probably produce pretty close to 100% ethanol without benzene, however I believe if that ethanol is exposed to air, it will absorb the moisture out of the air and no longer be 100% ethanol.",
" Some people say that \"medical grade\" ethanol is 100% ethanol without the benzene left behind. That is partially true. There isn't any benzene left behind (they probably use the molecular sieve or chemical reaction of the hydroxide with water to get the ethanol, but I'm not sure), but it's actually only ~99.5% ethanol, and <0.5% other chemicals.",
"For example, USP/ACS grade alcohol has traces of methanol left behind, some \"residues\" whatever they may be, and must be only < 0.2% water. Not quite 100% perfect. Still, this is called Absolute Ethanol, which is labeled as 100% ethanol.",
"There are other grades that you can look at ",
"here",
", which is where I got the above information of USP/ACS grade ethanol."
] |
[
"The last death of 2004 on this list",
"You would die. You'd absorb it across your skin, as ethanol can diffuse through a cell membrane, and being that there's a point at which your BAC is too high for continued bodily function."
] |
[
"And it would hurt. A lot. Not that I've tried it. But don't try it. Really. At least not with vodka."
] |
[
"Is it possible that what we perceive as bad smells is the brain's interpretation of possible danger? For example, consuming spoiled milk or inhaling toxic gasses that may cause disease."
] |
[
false
] | null |
[
"Absolutely! Over time humans have learned which smells relate to disease or danger. This is why rotting flesh smells so horrible to us. A mini-scale version of this happens when you get sick after eating (or perhaps drinking too much of) a certain item. Your brain associates that taste/smell with being sick and makes you queasy the next time you see it. ",
"This is also kind of related to why seeing other people puke makes you feel sick. "
] |
[
"I have often wondered if this aversion or attraction response applies to colourful food items as well. Such as finding colourful vegetables attractive. Mind you, there are some very poisonous bright red berries out there..."
] |
[
"I had always asked myself this question. Good thing you asked. Great question!"
] |
[
"What causes the core of a nuclear reactor to glow?"
] |
[
false
] |
Is it the reaction, or is it the actual fuel itself?
|
[
"Cherenkov radiation from electrons moving faster than the phase velocity of light through a medium (for example, water). "
] |
[
"Cherenkov radiation has nothing to do with an acceleration of the particle. It is similar to a sonic boom for light where constant supersonic speed will produce it as well."
] |
[
"Cherenkov radiation has nothing to do with an acceleration of the particle. It is similar to a sonic boom for light where constant supersonic speed will produce it as well."
] |
[
"[Physics] How many times have we found the Higgs-Boson?"
] |
[
false
] |
Okay, as much as my knowledge goes, we have only found the Higgs-Boson at CERN and also that the ratio of number of positive experiments vs negative experiments is really poor. That is, number of failed experiment >> number of successful experiments. Now, I could be wrong. But I would stand by that I am not. So in this case, we are completely going against the scientific method. Higgs-Boson is yet to found in a lab other than CERN and we hardly seem to find it even after having found it already once. How come the scientific community accepts this? You would say that CERN has reputation, I would say that this is a bias and science requires that other labs/teams get the same result. We should atleast get the number of successful experiments higher than the failed ones. You have any thoughts?
|
[
"The Higgs boson was found at the LHC (as opposed to the Tevatron or elsewhere) because the LHC provides a higher center-of-mass energy. The mass of the newly-found Higgs boson is completely consistent with it not having been found at previous experiments. So no, the situation is that the number of \"failed\" experiments is: zero. The two detectors at the LHC have discovered the Higgs boson independently through multiple decay channels (ie a form of independent sub-experiment), in accordance with what we might expect given its apparent mass."
] |
[
"That was a detailed and juicy answer. Thanks buddy! Really appreciate you helping me."
] |
[
"The answers already here are quite full, though there is one interpretation of the phrase \"That is, number of failed experiment >> number of successful experiments.\" which wasn't mentioned.",
"That is that it is a very rare occurrence that the Higgs is produced (and detected) in the LHC compared to the total number of events. So somebody could easily mistakenly call any event that the Higgs is not produced in a \"failed experiment\".",
"However this is not so, if there were a roulette table and you were watching for the existence of the outcome \"0\" if you saw that it occurred 1/37 times (or 1/38 in the US) you wouldn't be concerned about the ratio of \"failed\" experiments to successful ones."
] |
[
"How and why does the last electron in the outermost shell of an atom determine what element it becomes?"
] |
[
false
] |
[deleted]
|
[
"It doesn't - its the number of protons in the nucleus that does"
] |
[
"It's not so much the final electron as the total number of outer-shell electrons. These are the ones that are most available to take part in chemical processes such as bonding or ionisation, and so different numbers of outer-shell electrons will lead to different behaviour. For example, carbon has four outer-shell electrons and can combine with four hydrogen atoms to form methane. Boron has three outer-shell electrons and combines with three hydrogens to form borane (found in nature as the dimer diborane).",
"Or, to take an alkali metal example, sodium has a single outer electron which is fairly easily lost to form Na",
" and compounds like NaCl or common table salt. Magnesium, on the other hand, has two outer electrons that are readily removed, so it combines with two chloride ions in its salt rather than just one.",
"The key concept is that in nearly all normal chemistry, electrons below the outermost energy level are considered inaccessible for the purposes of bonding, ionisation or pretty much anything else. To access them simply requires too much energy in nearly all cases - so only the outer electrons count."
] |
[
"Umm... What? Electrons have nothing to do with what element a given atom is."
] |
[
"How does water become super clear in the wild? What happens to suspended solids, algae, and plankton?"
] |
[
false
] |
There's a photo that showed up on the front page that showed crystal clear water in a stream ( ); some of you may have seen images of the water off the coast of the Maldives, which is so clear row boats in the water look like they're floating in air. How does water get this clear without filtration and sterilization in the wild? Why doesn't algae and other life and biological residues fill it up and make it cloudy? In the case of the Maldives, aren't there plankton in the water? In the case of the stream in Sweden linked above, you can see dead grass in the water; if it flowed there across any sort of land and if the stream or pond has dead plant matter in it, why hasn't it carried suspended biological residues into the water? (And lastly, is it possible to simulate those processes for man-made ponds?)
|
[
"If the water is completely lacking nutrients then nothing will grow in it and it'll stay clear. Tropical ocean water is nutrient poor, and the Swedish mountains (the Scandes) are composed mostly of limestone. Lime is used to reduce acidity in fertilizer polluted lakes, so I'm assuming it causes the water to become nutrient poor somehow, although I don't know the exact process.",
"From an ecological point of view, algae might be suppressed by a herbivore under no predation pressure.",
"Oh and the picture is most probably real. Streams this clear are not at all rare in the Scandes."
] |
[
"If you look closely at the wrist, you can see the waterline, showing that the hand is actually submerged in water."
] |
[
"I have dived in water this clear, the water I dived in was subterranean, and I filmed the source. So in this case the really cold water from a limestone area was freshly flushed through the lake. If this came from snow melt, or subterranean sources, then there is no place to pick up the detritus in the water. It would be interesting to see the water temp. ",
"Temperate waters typically have lots of phytoplankton in it, whereas warmer coral seas are filtered by the coral, increasing the visibility such as seen in the Maldives photo. "
] |
[
"[Engineering] How are the wings on large commercial planes able to support multiple turbine engines and jet fuel without collapsing?"
] |
[
false
] |
[deleted]
|
[
"Short answer is that they're built strong enough to handle it.",
"The answer that will blow your mind a bit is that the wings would need to be STRONGER if the engines were mounted elsewhere. The wings produce the lift, which counteracts gravity, so the weight of the engines along the wing actually counteracts the lift force to reduce the shear and bending moment experienced by the wing.",
"The spar of the wing is what carries most of that load. I believe most larger planes have a front spar and a rear spare which essentially brackets the fuel tanks. You also have things like ribs and stringers and such which provide additional strength for torsion and the skin itself takes the shear loads.",
"Here's an FAA document that talks about aircraft structures: ",
"https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_ch01.pdf"
] |
[
"It's pretty amazing.. I'm a pilot myself, and the light planes that I fly are the equivalent of aluminum cans. We're talking skin thicknesses of .025\" to probably .040\" in the higher stressed areas. That's the thickness of a few sheets of paper..",
"I'm always a little amazed coming from what I fly when I board a commercial airliner and feel the heavy skin at the entrance to the door. Must be 3/16\" or so... ",
"Long story short, engineers determine the loads that individual pieces in the airframe will encounter and choose appropriate material based on that.",
"Your example, an An-225, is quite an example of mega engineering!"
] |
[
"Certification for commercial aircraft requires the structure to handle a static load at least 1.5 time the once-in-a-lifetime limit load. Check out ",
"this",
" Boeing 777 test to failure. Deflections of the wing are in excess of 30ft from resting position at the time of failure for other models! The wings are a very important structure of the aircraft, and designed as such. There are very generous factors of safety and redundant load-paths built into these. The main thing to realize when looking at these is the load vectors during flight. As stated in another comment, lift is acting opposite of the wing, fuel and engine weight loads for most of the flight. On the ground the directions are similar (and even in some aggressive dive scenarios), but during flight the moment (force applied at some distance, think wrench) induced by lift carried by the wing spar and reacted in the fuselage wing box is reduced by engine, fuel and wing weights. "
] |
[
"What would actually happen if the Higgs boson was found? What impact would this have on physics?"
] |
[
false
] |
Also, more importantly, what if it isn't found?
|
[
"What is it?"
] |
[
"The Higgs boson? A really long discussion. The shortest possible answer I can think of is that the photon, W and Z bosons are all a family of particles. Except the photon is massless and the W and Z bosons are ",
" heavy. The Higgs mechanism is the process by which the W and Z bosons get their mass and the photon remains massless. The mechanism is then meant to be the process by which all fundamental particles gain their rest mass. "
] |
[
"Not a physicist, but I think the situation is that physics will go on as usual when it's found.",
"If it ",
" found in the expected energy range, there will be a lot of heavy drinking and late nights, tufts of hair torn from scalps in frustration, as thousands of scientists try to figure out a workable solution without a Higgs boson, or with a Higgs boson at a dramatically different energy level, or ",
" over old data to see if it hasn't been missed somewhere in the glare of a past discovery or something like that."
] |
[
"With our current knowledge, is there a maximum speed a spacecraft could travel?"
] |
[
false
] |
I understand that it is theoretically possible to get arbitrarily close to c, and that c can never be reached or exceeded by anything with mass. However, with our current understanding of energy and propulsion systems (both current and theoretical) is there a realistic maximum speed a spacecraft could reach?
|
[
"The fastest man made object:\n\"NASA'S Juno Mission spacecraft will slingshot around Earth towards Jupiter, accelerating to 25 miles per second along the way and becoming the fastest man-made object in history. A .50-caliber bullet travels at about half a mile a second, by contrast -- nowhere near the blistering speed of Juno.\"\nSource: ",
"http://www.foxnews.com/science/2013/10/09/nasa-juno-spacecraft-to-become-fastest-man-made-object-as-it-slingshots-around/",
"The speed of light in a vacuum is 186,282 miles per second\nSource: ",
"http://www.space.com/15830-light-speed.html",
"So the fastest we have been able to travel is about 0.01% the speed of light. Note that this was achieved using a slingshot maneuver rather than relying solely on propulsion."
] |
[
"You seem to be well informed, let me ask you a question. I read recently that theories has been developed for the possible construction of a drive that could allow for faster travel working on the warp bubble principal. I believe it wasn't thought to be practical because of the energy consumption the device would require.",
"Here is my question. I'm 38. Any chance I'm going to see any spectacular scientific progression in this area, in my lifetime?"
] |
[
"A little bit of both. ",
" under relativity it could exist, but we have no evidence to suggest that it does.",
"Although when you state it like that, it's kind of like saying that unicorns ",
" exist, but we just haven't found ",
" yet either. Current science suggests that such a substance is nothing more than wishful thinking."
] |
[
"Why does diarrhea have the potential to hurt the rectum so terribly?"
] |
[
false
] | null |
[
"So we would stop putting dangerous things up there and live longer."
] |
[
"So we would stop putting dangerous things up there and live longer."
] |
[
"So, is that actually what causes the burning sensation after eating spicy foods that give you diarrhea? Or are you also getting burned by the capsaicin?"
] |
[
"What are some of the *smaller* mysteries in science right now?"
] |
[
false
] |
We'd all like to know what dark matter is or how to cure cancer, but what are some of the coolest small mysteries out there in science right now? Stuff like some metal behaving in thus-far-unexplained ways in a magnetic field or a chemical reaction doing unexpected things in zero gravity or light from some star having unexplained spectral components -- stuff like that. And let's not limit this to physics :)
|
[
"What happens in the final seconds of cytokinesis. Scientists know that the cells separate (obviously) but truly have no idea as to the physical aspects of the divide. It is a biophysics research topic at my university."
] |
[
"We still do not know what group of Gymnosperms (seed plants) evolved into the flowering plants. Fortunately, there are a few promising theories, but the fossil \"smoking gun\" has not yet been found. Most Paleobotanists set the date for this evolutionary split sometime in the Late Triassic period, 245–202 million years ago, but there are other theories which push the date much earlier."
] |
[
"Why Misophona happens. ",
"Misophonia is essentially developing anger, even rage when specific sounds are heard. Usually ordinary sounds like chewing, breathing, tapping fingers, coughing, it can be anything really. But nothing happens when the person is doing these things themselves. ",
"Reactions are completely involuntary, and can get violent. I myself have this afflication. I haven't done anything really violent except crushing a glass cup in my hand, cut some of my hand and a bit of my arm. ",
"I would like to know the cause!"
] |
[
"How do \"Ninja Rocks\" (Al2O3 Ceramic shards from sparkplugs) shatter glass so easily?"
] |
[
false
] |
Aluminum Oxide (Al2O3) Ceramic has a Moh hardness of 9, and tempered glass is what, like, 6? But that isn't the whole story. How does the structure and surface tension of the glass come into play? How would one protect their car windows from this? Would a custom sheet of InvisibleShield work, or is there something by 3M that's substantially cheaper? In case you've never heard of Ninja Rocks: It's the tiny ceramic shards of a sparkplug that are thrown at a car window for quick and easy breaking and entering. It's crazy how tiny an effective piece is.
|
[
"Basically anything that's hard enough and sharp enough to make a deep scratch in the glass will cause it to fail catastrophically. The tempering process concentrates stress in the outside of the pane, which inhibits crack propagation. Unless the crack is large/deep enough, in which case, the glass tears itself apart.",
"The escape hammers that you see in stores that are intended to help you break car windows in an emergency are quite often made of plastic, with a tiny hard point made of hardened steel, or sometimes ceramic/carbide.",
"A thin layer of plastic on the outside would probably be a good defense against this sort of thing. Of course, then you'd have a maintenance issue, because the plastic just isn't going to wear as well as glass does.",
"I don't have any product recommendations, but InvisibleShield is just a tough polyurethane film with sticky stuff on the back. I imagine any of the products that are sold as \"security\" films for window glass would work for this application."
] |
[
"Do you have any kind of source for that claim, because it doesn't seem very likely (hence the downvotes, I assume). Tempered glass doesn't generally make a loud noise when it shatters, anyway."
] |
[
"I will have to look for it. The police officer who took my statement asked if I heard anything. They found a broken spark plug head next to the glass. he said if they did it right it does as I mentioned. He wanted to know because if there was noise it could have been amatuers."
] |
[
"Do Nucleic Acids have anything at all to do with Cellular Respiration?"
] |
[
false
] |
Does DNA or RNA have any business in the process of Cellular Respiration? Thank you in advance.
|
[
"ATP, or adenosine triphosphate, is obviously composed of the nucleoside adenosine, which is in turn composed of the nucleic acid adenine and the sugar ribose. ATP is the main product of cellular respiration, produced via glycolysis and at the end of the electron transport chain from ADP. So yes.",
"DNA and RNA polymers, however, such as those found in the nucleus, do not have any direct effect on respiration that I know of other than in the production of relevant proteins, so if you're talking about those specifically, then no."
] |
[
"Directly, no. Obviously the DNA and RNA encode the proteins involved in the process, but other than that, they play no role. DNA and RNA are primarily in the nucleus of the cell. Cellular respiration takes place in the cytoplasm and the mitochondria. "
] |
[
"I needed that point made clear, thank you!"
] |
[
"What classifies a sickness as the \"flu\" and why do we have flu seasons?"
] |
[
false
] | null |
[
"The flu is caused by the influenza virus. It is uniquely distinct from many other pathogenic viruses that might produce similar symptoms. Flu seasons are in part caused by the cyclic ways our society responds to changes in the actual seasons. Wet rainy/snowy weather tends to push people into closer contact in indoor places like large buildings, public transit facilities, etc as they avoid the weather outside. Such places enhance the transmission from person to person. From there, our mobile society takes care of the rest as people carry infections from the workplace into the family out to the schools and so on in a vicious cycle. That is one of several proposed explanations for a phenomenon that doesn't really have a conclusively determined cause. ",
"Here",
" you have a nice run down of other factors that I don't specifically remember from my infectious disease class."
] |
[
"The actual Flu is caused by the virus Influenza. However, people tend to misuse the term a lot because there is a lot of illnesses that cause similar symptoms(bit of a fun fact, a lot of symptoms you often experience during illnesses are often not caused by the pathogen, but by your own immune system reacting to it).",
"As for flu seasons, it's not a rock-solid answer, but generally the theory is that everyone is more crowded inside during cold weather, meaning the virus can transmit easier."
] |
[
"Thank you! Very informative"
] |
[
"Neil deGrasse Tyson in his AMA said quarks only come in pairs and that if you wanted to separate them the amount of energy needed is the exact amount to spontaneously create another pair out of thin air. How does a proton get 3 quarks without leaving a freely floating one somewhere?"
] |
[
false
] |
Link to his quote:
|
[
"The quote:",
"2) That Quarks come only in pairs: If you try to separate two of them, the energy you sink into the system to accomplish this feat is exactly the energy to spontaneously create two more quarks - one to partner with each of those you pulled apart.",
"This is a mistake, or possibly an oversimplification. Collections of quarks must be \"color neutral\" (it's like being electrically neutral). This can be done with quark-antiquark pairs (mesons) or triplets of quarks (baryons), if they have the right combination of colors.",
"More complex combinations might also exist but until recently there was no evidence for them. See ",
"this",
"."
] |
[
"I'll try explaining it with reference to this diagram:\n",
"http://www.quantumdiaries.org/wp-content/uploads/2012/06/tau_decay.jpg",
"I know it looks weird, but it'll get covered. So, to look at an example of what's happening here. So, we start with that particle on the left, which decays, leaving a down quark (which is the top line) and X (don't worry about that, just trust that that can happen). Now, the next thing that happens is that X decays into two up quarks (again, trust me on this). Now the next thing that happens is what matters for that question of yours. You'll notice that right now, we have a down quark at the top, all by itself, and two up quarks down at the bottom. So now, because of that down quark by itself, a new pair is brought into existence. the down antiquark joins the down quark to form the top particle. The brand new down quark joins those two up quarks to form a proton.",
"So basically, to get a proton, that free floating quark isn't free floating, it'll join up with some other quarks somewhere as well.",
"EDIT: Fixed because apparently I understand particle physics and not left vs right"
] |
[
"More complex combinations might also exist but until recently there was no evidence for them. See this[1] "
] |
[
"How are \"super-organisms\" like termite and ant colonies able to evolve new behaviours?"
] |
[
false
] |
[deleted]
|
[
"Actually ant communities can shun individual members. Some ant colonies perform basic healthcare by isolating and banishing ants with contagious fungal infections. They're literally picked up by healthy workers and carried out of the nest.",
"Similarly there's actually remarkably little direct communication between ants. Unlike bees ants do not tell other ants where to find a food source for instance. Ant foraging behavior is a great example of a hive mind. Imagine the following...",
"Using this process none of the ants actually actively communicated with one another. They did however unwittingly apply a very efficient amount of man (ant) power to the logistical problem of getting the food to the nest. A large food source will create a powerful scent trail attracting many foragers, a small food source will be gone before it attracts many ants.",
"It's a great example of how individually unintelligent creatures manage to create intelligent solutions to problems, ie a hive mind. Ants are particularly good at this.",
"Of the top of my head various ant species practice... logistics, war, slavery, agriculture, life stock husbandry, health care, sanitation, architecture, thermal regulation, moisture regulation, airflow regulation, career management, a great variety of surprisingly deep military tactics, search and rescue and much, much more. On top of that there's a great many species of flora and fauna that evolved to benefit from ants in both parasitical and symbiotic relationships. For instance those aphids that excrete honeydew in exchange for the protection of the ants. (you thought they farted sugar water for the fun of it?)",
"One of my favorite little examples is how many ant species actually have sort of a career path for their workers. Often young and inexperienced workers spend their time in the deepest part of the nest performing the easiest of tasks like clearing up rubble or feeding larvae. As they grow older they move onto more responsible tasks like excavating rooms. More complicated but ultimately just starting in a small room and making it bigger. When they grow older still they become tunnel diggers, excavating new tunnels and actively planning out the colony layout. It's not until they near the end of their life cycle when they are most experienced (and nearing their deaths) that they participate in surface duties like taking out the trash and foraging for food.",
"Some ant species even have something of a retirement plan. Ant species that perform heavy duty outdoors labor like weaver ants that spend a lot of time cutting leaves with their mandibles will sometimes grow so old that they are physically no longer up to their task. These workers are given a place inside the nest performing lighter duties not requiring heavy mandible power.",
"Ants are amazing and I could ramble on forever about them."
] |
[
"If you think that's cool, you should check out ",
"ants that do agriculture",
" and ",
"ants that take slaves",
".",
"How are individual members of a hive/colony-type system able to deviate from their normal behaviours without risking being shunned by the other members of their community?",
"All ants in a single colony are basically clones, produced by a queen and her dead mate. A single ant doesn't know much about what it's doing, and thus doesn't really deviate from any normal behaviors, nor can it be \"shunned\" by the community. But the colony as a whole exhibits emergent intelligence. ",
"Even if individual ants could introduce radical new behaviors, as you suggest, this would not be passed down genetically. That said:",
"Once an individual finds a successful new behaviour, how is it passed along to the other members of the colony?",
"When an ant finds a new source of food, it can tell the other ants and recruit others to help forage it. Now, as for things like new behaviors, it would have to evolve in the same way that behavior in a large, multicellular organism evolves. Colony A and B recognize aphids as a source of food. Colony A forages the honeydew without harming the aphids, but Colony B eats both the honeydew and the aphids. Colony A survives longer and produces more daughter colonies, which evolve to apply protection instincts to aphids such as moving them to healthier areas and protecting them from predators. These colonies also live longer and produce more daughter colonies."
] |
[
"One of my biggest \"whoa\" moments on this topic was when I drew a parallel between a human body and an ant colony; the main difference is that the body is a big connected lump and an ant colony is a bunch of non-physically-connected insects. Intelligence can emerge from a network of neurons that have more-or-less defined behaviour, and (to me, at least) something similar is happening in an ant colony."
] |
[
"Can anyone explain how mind over matter appears to reduce pain?"
] |
[
false
] |
Some people say that mind over matter can actually reduce the amount of pain you feel. Does this actually work? If so how?
|
[
"1) Pain is your body screaming for attention. If you divert your attention to something different, you have less space for noticing pain.\n2) Adrenalin surge (such in fight or flight response) can actually reduce your perception of pain. If you find a way to trigger an adrenaline spike, you will feel less pain, since your body is prompted to ignore it (it would slow you down or render you less effective in combat)\n3) Scientist have proven that you can reduce pain by swearing (",
"https://www.ncbi.nlm.nih.gov/pubmed/19590391/",
")"
] |
[
"Hey i think that the nature of pain is diverse. There is a signal that come frome the painfull point and reach different part of the brain. \nOne part is the sensitive one associated with the point on your body and the overactivation of this part induce pain. But there is another interesting part that is activated, the emotional one ( amygdal hypocampe... ). According to the interpretation of your emotionnal system, the feeling of the pain will be totaly different."
] |
[
"Yes this does work! When we stop focusing on the pain, it becomes just another stimulus in the many stimuli of our environment. There is a proven theory that you remember how painful something is only by its last few moments. I know there was some testing done where subjects are exposed to a certain amount of high pain for a minute. The first group was exposed only to that minute of high pain. The second group, however, experienced 30 seconds on top of that minute of duller, less hurtful pain. When asked about their experiences later on, the first group reported the experiment as very painful while the second reported lesser amount of pain than group one even though they had more pain altogether. This is all purely cognitive and not physical. This testing was done by Daniel Kahneman in 1993."
] |
[
"How do we check if something has \"taste\"?"
] |
[
false
] |
The calls it a "colorless, odorless, non-toxic, inert, monatomic gas". How do we know it's tasteless? I hardly imagine anyone putting liquid helium, which boils at 4.2K, on their tongues.
|
[
"Elements in a gaseous state can still find themselves making their way towards your tongue. Take gasoline, for example; you don't have to drink the stuff to know what it tastes like because you can still taste them fumes. The same principle applies for helium - if you ingest a portion of it (I.E., sucking on a balloon), and don't taste anything, it can be stated that it's a tasteless element."
] |
[
"Aside from noting \"this substance appears to be toxic\", I'm not entirely sure. That really opens up a whole can of ethical worms, though."
] |
[
"Ah, that simple.",
"Does this not cause problems related to exposure? What if you were checking something's taste and it turned out toxic? "
] |
[
"At a quantum level, does distance become discrete also, like energy?"
] |
[
false
] |
I know that at a quantum level, energy is transferred only in discrete amounts. I'm wondering if the same becomes true of distance - is there a level where two discrete, non-equivalent points exist such that no intermediate point exists between them?
|
[
"This one gets repeated often.",
"The Planck length unit is not magical. It's just a very small unit of distance. It should not be taken as evidence that space is quantized."
] |
[
"there's no evidence to suggest that it does. Some beyond-standard physics proposals suggest that it may, but we would need evidence to confirm any of those."
] |
[
"In some theories, \"yes\". Here are two examples:",
"1) A theory called loop quantum gravity (LQG), which attempts a canonical quantization of general relativity (GR). Just like momentum and position of a particle become operators in ordinary quantum mechanics, things which are numbers in classical GR become operators. In normal quantum mechanics, becoming an operator means that instead of having just being a number, the operator has an \"expectation value\", and other moments -- specifically a variance, from which you can define an uncertainty.",
"Now, length in LQG is not an observable operator, but area and volume are observable operators, and they are in fact quantized. So in this theory, it seems that there is a smallest spacetime area and volume you can have. That area or volume could be roughly the same in all directions or fat in one and skinny in the other, as long as the area or volume is preserved. This area or volume is in fact proportional to the square or cube of the Planck length. So in a sense, distance becomes discrete (but really area and volume, not distance).",
"2) Non-commutative geometry. I don't really know anything about this. However, it does promote geometry to operators as well. I'm not sure if these operators are quantized. However, I think that there is a minimum variance for things like position. This is in contrast to the regular quantum mechanics situation, where it's just the product of position and momentum variance of a particle that has a minimum value. Here, nothing can be localized to smaller than a particular distance scale. In a sense, space is quantized.",
"Note that there is no experimental evidence for any of this. However, it's reasonable to believe that physics changes at the Planck scale. Almost anything can happen, including geometry not being meaningful anymore."
] |
[
"I'm a geneticist, but I'm curious. Of the other geneticists out there, how do you think genome sequencing will change clinical care and how long will it take?"
] |
[
false
] | null |
[
"Well, a few months ago, I heard a lecture from a researcher at UT Southwestern, ",
"Dr. Michael White",
" talk just about his approach to finding cancer drugs that were specific to a patients given genetic mutation that was causing the disease. There are a lot of papers that you could look through there, but you may want to start ",
"with this one",
". ",
"What's great about this is we will have drugs that can knock out or slow down the disease at it's cause, rather than just slowing it down in a more global way. I think it will change the way we look at some of the current treatments, and they will seem barbaric. Like Avastin, a cancer drug that blocks vascularization, which slows down the growth of tumors. It is such an unspecific treatment, but right now it is great because it's the best we've got. ",
"As far as when is this going to happen? Well, it's already started. Patients are already being sequenced and treated based on what they find. This is raising some interesting questions. For example, if I am looking for a mutation that caused a certain loss of vision in a patient, but then find, while searching, that they have a mutation linked with colon cancer, do you tell them? It seems like the answer would be yes, but it is a much deeper issue than it seems at first. Interestingly enough, this was exactly the topic that",
" Science Friday (on NPR) was about today",
". "
] |
[
"Did you also listen to this discussion on NPR today?"
] |
[
"This may be more suited to ",
"/r/asksciencediscussion"
] |
[
"Why isn't there muscle cancer?"
] |
[
false
] |
We hear all the time about brain cancer, skin cancer, lung cancer, breast cancer, stomach cancer, etc., but why do we never hear of malignant, cancerous tumors from developing in muscle tissue? Is there something unique about the makeup of muscle fibers that prevents abnormal growth? EDIT: I'm specifically referring to skeletal muscle and why rhabdomyosarcoma (RMS) is rarer than other types of cancer. (Thanks )
|
[
"There are- rhabdomyosarcoma, for example. ",
"It's comparatively rare though because there isn't much turnover of cells in the muscle, and they don't get much exposure to carcinogens. Any lining of the body has a high rate of cell division, and that's where errors creep in. ",
"Imagine photocopying the instructions for baking a cake every time you baked one, but instead of using a master copy you used the previous photocopy. And there's a little gremlin who can come in and change a number or a letter at random, and you don't know what the gremlin has been doing. ",
"The first cake is fine. And so is the 2nd, 3rd, 4th etc. Until eventually you can't quite tell if it's 5 or 6 ounces of sugar. Or what that squiggle means that you're supposed to add a teaspoon of. This is what happens with cancer. The photocopying is cell division, and the gremlin is the action of carcinogens on the DNA of the cell. Most of these errors get caught, either by the error checking in the cell division mechanism, by the immune system which kills off cancer cells, or by the cell simply ceasing to function properly and dying. ",
"Muscle cells don't duplicate very often, unlike your skin or the lining of your bowel. Your lungs, skin, bowels etc are all basically linings, and so have loads of cell divisions going on all the time. Rhabdomyosarcoma is commonly a disease of childhood, as this is when muscles are growing and the cells are dividing. When someone trains a lot in the gym, they don't actually get new cells in their muscles, it's that the existing cells develop more muscle fibres within them, so the individual cells get bigger. ",
"Basically, the muscle cells are like a cake recipe that you bake once a year. Skin, bowel, etc etc are cakes that you bake every day. Lungs are cakes with a particularly disruptive gremlin, if you're a smoker. "
] |
[
"Wow thanks! So this is also why bones and ligaments aren't afflicted with cancer as often because they're not primarily composed of living cells?"
] |
[
"Pretty much. There are lots of living cells in bones and ligaments, but many of them don't do much in the way of division once you're an adult. ",
"Leukaemias and lymphomas are kind of bone cancers though- they're due to those changes effecting the source of the blood cells, namely the bone marrow. ",
"What's more common for cancers in bone is when a different type of cancer spreads (metastasises) into the bone. Bone is quite a common place for cancers to spread to, and has pretty poor outcomes (like any metastasis)."
] |
[
"How do we calculate the wavelength of spectral lines for elements other than Hydrogen? Or is this just something we observe and use as a fingerprint?"
] |
[
false
] |
Context: I'm a teacher trying to relate neon signs to spectroscopy and the study of distant stars. I have a decent understanding how we can use the Balmer-Rydberg series to calculate values of the emission lines given off by hydrogen, but can we apply this to other elements? What about neon?
|
[
"The hydrogen atom (and ions with only a single electron) have remarkably simple analytic equations which you can solve for the energies of all of the excited states.",
"No other atom is this simple. As soon as you have more than one electron, you've broken some of the nice symmetries of the system, and you've got an equation which can't be solved analytically for the bound state energies and wavefunctions.",
"In order to calculate the energy spectra of these atoms, we need to resort of approximations and/or numerical methods.",
"We have techniques like ",
"Hartree-Fock",
" and shell models which we can use to make predictions about the structure of many-body systems, like multi-electron atoms, and nuclei.",
"And then of course we have experiments, where we can just measure the excited state energies of atoms."
] |
[
"You use a computer to crank through the math of quantum mechanics. ",
"But just to be clear, the Balmer series is a RESULT of quantum mechanics and falls out of solving the Schroedinger equation for a nucleus of charge 1 and 1 electron system. If you want to know helium then you simply repeat the calculation for a nucleus of charge 2 and 2 electrons. However, at helium already things are much more complex to solve than hydrogen because now you have 2 electrons interacting with each other in addition to their interactions with the nucleus. It's this inter-electron interaction that is a huge mathematical pain in the rear and basically means you can't just solve the Schroedinger equation with a pencil and paper for larger atoms and instead need to use a computer."
] |
[
"Well, you would need to solve the Schrodinger equation for the atom in question which is tough. There are approximations you can make so that the equation reduces to the hydrogen case. You can also explain-away terms on the equation of you understand why they're irrelevant based on the assumptions. For example, we should be able to ignore the complicated nuclear interaction terms if we're operating at low energies. ",
"Theoretically you'd have to get the energy levels as a function of the angular momentum, then calculate which states are allowed transitions (the disallowed states will have a probability of exactly zero), then subtract the differences between the final and initial energy level to get the energy of the photon, then you can calculate the wavelength of the photon and thus its \"color\". "
] |
[
"How plausible is radioactively enhanced evolution?"
] |
[
false
] |
Could we take a separated but large population of the human race and expose them to high levels of non-lethal radiation in order to increase the rate of mutation in their genetic code. Understandably the majority of the mutations would be terrible and more often than not would result in horrendous forms of cancer. But provided that the population reproduced quickly enough how likely would it be that either the surviving population was resistant to that radiation or some favorable mutations occurred. Maybe this would be better thought of involving rats since they reproduce more quickly and the obvious ethical dilemma. Has anything like this been attempted before on any species?
|
[
"We already do that.",
"Link"
] |
[
"I would suggest to use bacteria, since they don't have such a complex DNA for starters, and they have a reproduction rate that is a lot higher (and with humans and rats you would have to mutate the sperm cell or ovum to really get the mutation going on by reproduction). ",
"Also you would be able to keep a much larger population.",
"And with these simple cells, you might just use UV light.",
"So with that out of the way, many of the mutations in the DNA might just be on non-coding parts of the DNA, and therefore have no to little effect.",
"But on the coding party oif the DNA you might get a favorable mutation.",
"Even if it would be easier to genetically engineer the cell."
] |
[
"Started thinking about the odd creatures around chernobyl, which led to me deciding to build a race of super crickets."
] |
[
"How widespread is empathy among different species of animals?"
] |
[
false
] |
Mammals and birds tend to live in groups, and display some level of sociability. I've seen in documentaries lions helping each other when a member of the pride gets injured or something. What about reptiles or fish? I ask, because I encountered on , and I can't really think of this in any other way than a good Samaritan helping his fellow turtle out of a bad position. Is that a misinterpretation, or is this kind of behavior way more common than I had originally thought?
|
[
"It's actually a very realistic representation on animal behaviors. One concept that I had trouble learning about in biology courses was idea of altruism. It's basically the most severe form of selflessness and absolute helpfulness. For example, if I jumped in front of a bullet for someone, disregarding my well-being to help them, that is altruistic. It's seen in many, many species of animals - more so the ones that are highly social like Meerkats.",
"Humans aside, some living things are genuinely good "
] |
[
"Well, to modify this a little, complete altruism--the willingness to sacrifice one's self for any member of the species--is selected against. The commonly used example is the outdated idea that lemmings would commit mass suicide to prevent overpopulation. All it takes is one lemming to decide not to do this, then pass on this \"selfish\" trait to its offspring, and within a few generations it spreads to the entire population.",
"However, what is fairly common is kin selection--the willingness to sacrifice one's self for any individual that is closely related. Because this is still ultimately protecting one's own genes, this can be selected for. In species like meerkats, that spend their whole lives in family groups, the end result is effectively the same as altruism. But you wouldn't expect this behavior in animals without a family structure."
] |
[
"In the past few years we've found increasingly compelling evidence of what humans describe as 'altruism' in a number of species. Perhaps the study that received the most press was one using rats, in which it was found that a rat will go out of its way (physically exert itself, or even give up the opportunity to eat a bunch of chocolate chips) in order to free a fellow rat from a cage. (",
"http://www.scientificamerican.com/article/will-you-rat-me-out/",
")",
"The thing to keep in mind with this sort of study is that 'true' altruism is rare, even in humans. Social animals benefit from having other members of their species nearby and safe/healthy, due to safety in numbers and the added efficiency of hunting or foraging with group-mates. For example, ravens will 'selflessly' call other ravens to them when they find a dead animal to eat, but this is often because the animal has been found on the territory of a more dominant raven, and calling in other intruders can help fend off the aggressive resident. (",
"http://www.theguardian.com/science/2015/jan/26/rationing-ravens-merciful-monkeys-can-animals-be-altruistic",
") Generally the term 'reciprocity' is preferred over 'altruism' in these cases.",
"You asked specifically about fish and reptiles: I don't know of many well-documented cases in fish, though there's the famous example of cleaner wrasse fish nibbling harmful parasites off of larger fish (of course, the wrasse get a meal out of that!) Blue-throated side-blotched lizards are known to team up in pairs of males to cooperatively defend a territory and help each other attract mates, and one will sometimes even give up its chance to reproduce so that the other one can. (",
"http://seedmagazine.com/content/article/lizards_provide_evidence_for_a_theory_of_altruism/",
") The caveat? These partnerships were always formed between lizards who were related to one another, resulting in indirect fitness when the other lizard reproduced. But this kind of mutualism between related individuals is particularly common throughout many species."
] |
[
"When healing from a cut or gash (may or may not require stitches), what happens to the damaged blood vessels? Do they reconnect perfectly, are new ones formed, or do damaged veins and capillaries just have a dead end now?"
] |
[
false
] | null |
[
"Small blood vessels (capillaries) will be stimulated t grow back into hypoxic tissue by growth factor proteins that the hypoxic cells send out. This is called angiogenesis, and it happens all the time. For a skin cut, that's about it. ",
"Large blood vessels are more complicated. This is called vasculogenesis, and it takes a long time, and often doesn't happen at all, leaving you with an ischemic (hypoxic) limb that hurts. "
] |
[
"Both. When you get cut most blood vessels will reattach albeit not always in the exact same location. However there won't be any dead ends for long, because the body will reabsorb the material in the blood vessel to make a new one. Think of a pipe that gets broken, you can use pieces of the broken pipe to build a new one right next to where the old one was."
] |
[
"Like House? "
] |
[
"How much power does the 49ers new stadium lose from it's massive solar panels being red?"
] |
[
false
] |
as opposed to being black?
|
[
"I can't find the specs, but consider the following:",
"If the panels are red, then that means that the higher energy photons are being absorbed while red is being reflected.",
"The photoelectric effect is energy dependent. It the photoelectric cells are not activated by red light, no matter how much red light falls on it, it won't generate a milliamp. In that scenario, reflecting the red light has no effect on the power output."
] |
[
"Are you suggesting that 25% efficiency for a PV system is bad? Because typical values for most available systems are ",
"well below that",
". 25% is damn good for a PV system."
] |
[
"Are you suggesting that 25% efficiency for a PV system is bad? Because typical values for most available systems are ",
"well below that",
". 25% is damn good for a PV system."
] |
[
"Why exactly do humans, and presumably other animals, perceive different wavelengths of light as different distinct colours?"
] |
[
false
] |
Why have we evolved to perceive them at all? Why is the perception of distinct colours needed?
|
[
"One prominent theory for color perception is to recognize good food sources, for instance, young (greener) shoots and leaves, flowers. Better color discrimination improves the ability to recognize them.",
"http://gandalf.psych.umn.edu/groups/gellab/Wurm93.pdf"
] |
[
"Polychromatic sight provides a wide array of evolutionary benefits over monochromatic sight. Differentiating food sources from morphologically similar inert or poisonous materials ",
" you touch, smell, or taste them is highly advantageous. Distinguishing a predator's color in a morphologically uniform visual field (a tiger is orange and black, the forest is green brown and grey) is a distinct advantage as well."
] |
[
"Color emitted is a by-product of chemical composition, thus it is not illogical to infer that by the time polychromatic sight evolved there were distinct differences in chemical composition that might result in a distinct color for distinct organisms. ",
"Remember for plants that it is most likely that pigments, and distinct proportions of pigments re-emitting at different wavelengths, evolved not to hide or scare off predators but to better acquire energy from sunlight. ",
"At the same time it is logical to assume that evolutionarily ancient animals developed accessory pigments for reasons other than to hide from or scare off others. For example, the fact that skin pigments protect internal organs from the damaging rays of our sun. There might have been hundreds of mutations that would confer this benefit in separate species. Not all of them would evolve to use melanin, as is observable across the modern tree of life.",
"edit: some typos and for clarity"
] |
[
"Can fire burn while submerged in liquid oxygen?"
] |
[
false
] |
For the sake of the question, a candle.
|
[
"Yes, and you'd better stand back."
] |
[
"Okay - but could a fire burn if encased in solid oxygen?"
] |
[
"Almost 12 hours and no one posted the ",
"Man From LOX",
"?",
"The heat from a candle is enough to vaporize some of the liquid oxygen, and use it to accelerate the combustion, which produces more heat, and the chain reaction continues until the fuel is exhausted. You do not want to fool around with LOX. ",
"Also, trivia time, since LOX has a higher liquefication temperature than lN2, an open container of liquid nitrogen will actually liquefy the oxygen out of the air, and since LOX is denser than liquid nitrogen, it will collect on the bottom of the vessel. Eventually, you'll have a pale blue pool at the bottom of your liquid nitrogen, and when the N2 boils off, be careful!"
] |
[
"Lightning \"Duration\" from Back to the Future"
] |
[
false
] | null |
[
"Each strike lasts a few dozen microseconds, and a \"bolt\" usually has a few strikes separated by 30-40 milliseconds. ",
"You'd basically have zero leeway, and the technique in the movie would never work. What he should have done is arrange a long rail system, so Marty would have several hundred feet of connection, or have the hook grab a ring connected to an insulated wire, so again he'd be able to travel several hundred feet while still connected. The system in the movie would never work. ",
"But considering the Delorean is always traveling at more than 88 mph, due to the motion of the Earth, scientific plausibility is not really a focus of the movie."
] |
[
"Oh yeah, I never thought about that. Maybe the wheels have to be turning at a certain rate in order to engage the time... module... things? Course then you could just hook it up to the transmission and do it at a lower speed. Or maybe just have a \"do time travel\" button.",
"Hmmm, anyway, thanks for the info - it's exactly what I wanted to know!"
] |
[
"I think it had to go 88 relative to the earth. "
] |
[
"Has teen acne been around since prehistoric times? Did cave-dwellers have zits? Or is it related to modern eating, exercise, pollution, etc.?"
] |
[
false
] | null |
[
"Based on responses here it made me wonder, are there cultures in the world that have more or less acne than others?? Like if you compared the average teen in USA vs the average teen in India, would one have more or less than the other??"
] |
[
"According to ",
"this article",
" modern hunter-gatherers have much lower incidence of acne than industrial peoples, although the causes are not known. I can't vouch for the article, but it's thoroughly referenced",
"Edit to actually address the question: it's a reasonable inference from this that prehistoric people would also have less acne than modern industrialised people"
] |
[
"There's have been studies showing certain ethnicities/races seem to be more acne prone due to their physiology causing some to produce more sebum than others. Of course environmental factors also play a role so it's not all down to genetics but there seems to be something to race and acne"
] |
[
"Why does the body stop growing?"
] |
[
false
] |
[deleted]
|
[
"I know ",
"this",
" is not a scientific source but it makes a few valid points.",
"First off, a human ancestor (or maybe it was a competing species) did grow much larger at one point about 1.5 million years ago. It was too inefficient because the surface area of the skin was not large enough to cool them off fast enough.",
"Sorry for being so vague but it's been a while since I saw ",
"Walking With Cavemen",
". It does mention this."
] |
[
"Growing takes a lot of energy. Once you've reached optimal size, it makes little sense to waste energy by getting bigger."
] |
[
"I asked this question today a couple of hours ago! Upvote for some answers."
] |
[
"Does a magnetic field affect water molecules?"
] |
[
false
] |
As water molecules have a small magnetic moment
|
[
"MRI doesn't align water molecules though - that is, it doesn't really force the molecule to adopt a particular orientation with regards to the magnetic field. What lines up is the nuclear magnetic moments of the hydrogen atoms in water."
] |
[
"Correct. This produces a repulsive force. Although it is very weak, given a strong enough magnetic field, you can ",
"levitate water or things mostly made of water",
". "
] |
[
"Correct. This produces a repulsive force. Although it is very weak, given a strong enough magnetic field, you can ",
"levitate water or things mostly made of water",
". "
] |
[
"Why is the earth's crust thinner under the oceans?"
] |
[
false
] |
When teaching my students about plate tectonics, I got asked why exactly the crust was thinnest under the oceans and thickest under mountain ranges. The mountain ranges one is fairly easy to explain, but a long Google search later I still can't come up with a good explanation. Can anyone help me out here? I promised them a definite answer tomorrow :)
|
[
"Oceanic crust, forming at mid ocean ridges and subducting at the trenches is like a conveyor belt",
". It maintains a relatively constant thickness, 7km +/-, due to the melting/cooling/insulation as described by Sycosys.",
"What he/she did not address is why there is a much ",
"thicker continental crust",
". This is due to differentiation, which is really just the separation of lighter rocks, that \"float\" rather than being subducted. It is like the skin on a boiling soup, it just keeps piling up.",
"This is why the ",
"oldest rocks on the planet",
" (4+ billion years old) are part of continents, whereas the oldest oceanic crust, ",
"ophiolites",
" notwithstanding, are on the order of ",
"170 million years old",
": warning PDF."
] |
[
"What about the obvious explanation that areas where the crust is thin will have lower elevations than areas where the crust is thick, and water will fill the areas with low elevations?",
"It doesn't explain why the crust underneath the oceans is thin: but it explains why the oceans are above the areas where the crust is thin.",
"I just wanted to point out that you guys might be over complicating things. ",
"Basically, you and Sycosis are assuming the kid has thought of things that they might not have thought of. Sometimes things seem so obvious that they don't need to be pointed out, but when dealing with children we need to take special care to mention them."
] |
[
"The oceanic crust is formed at the mid-oceanic ridges as mantle heat forces rock to the surface. As the mantle pushes up, this crustal rock cools at a fairly uniform rate/thickness of about 7km. ",
"The reason it works out this way is that the underlying temperature of the mantle is directly related to how thick it gets before solidifying, this occurs over time.. Fast hot mantle rises quickly while cool mantle rises slowly",
"the Vast majority of the mantle underneath the mid ocean ridges is of a fairly uniform temperature and is pushed upwards about 7km before solidifying. Cool mantle has crustal thicknesses nearer to 5km, and very hot mantle, such as the hotspot creating Iceland has a crustal thickness near to 20km. "
] |
[
"Question about gravity"
] |
[
false
] |
The more massive the object the more gravity the object has, makes sense and I get that (hope that is right). Had one of those TV science shows on in the background and they were talking about pulsars, neutron stars, etc. The mass of a star compressed to something 10 miles across or compressed to the size of a house. This is where I had that RCA dog in front of the phonograph moment. The show said that when the star is compressed to such a small size the gravity becomes extreme. So is gravity in fact an effect of an amount mass per a unit of space? The mass of a star, spread out over the volume of a star, has a certain deformation effect on that volume of space. The same mass of the same star, concentrated in the volume of a neutron star, has far greater deformation of the volume of space since that volume is so much smaller. Not just how massive but also how much space that mass occupies? So amount of "stuff" plus how much space that "stuff" takes up in space determines the how strong gravity is?
|
[
"I think some brain cells just clicked. Thank you. ",
"If I stand on the 'surface' of a very dense object, I effectively very close 'to all of it' so I experience more gravity. If I stood on the surface of an object with the same mass but dispersed over a very large area, I'm standing next to 'far less of it' so less gravity.",
"It really felt good reading your response and feeling it all fall in place, thank you!"
] |
[
"Given an arbitrary distance from 2 objects of the same mass, you will feel the same gravitational force. A denser object simply allows you to get closer to its gravitational center with all of its mass being \"below the surface\".",
"If you shrunk the earth to the size of a marble, the orbits of all of the satellites would be unaffected."
] |
[
"Remember the movie \"Despicable Me\", when Gru shrank the moon? If someone did this, and truly compressed the moon down to the size of a pool ball, yet it had the same mass, there would be no significant change in its orbit, or the earth, and the moon would still cause about the same tides on earth. It's gravitational effect on the earth would be the same, even though it was far far denser.",
"This discounts a few things, like the energy RetraRoyale mentioned required to do the compression (that was SOME battery in Gru's shrink ray!).",
"And, as others have made clear, if you were to hold that pool ball sized moon in your hand like Gru and Vector did, the gravitational effects would be quite horrific. You may even get rending effects since the gravitational pull near your palm would be far greater than that near your shoulder.",
"On a final note, and I think this is obvious but might bear saying: It's not being \"near the surface\" of a massive object that causes the higher gravitational effects, it's being /near/ the object. The \"surface\" of the object has no special properties. I don't know why I mention this, but some of the explanations by others had an odd sort of emphasis on the \"surface\" of the massive object."
] |
[
"Wondering what Jupiter would look like without all the gas in its atmosphere"
] |
[
false
] |
Sorry if I may have screwed up any terms in my question regarding Jupiter, but my little brother asked me this same question and I want to keep up the "big bro knows everything persona".
|
[
"You cannot think of Jupiter as some kind of Iron based - or telluric (terrestrial) kind of body with a massive atmosphere surrounding it. \nIf the core is believed to be a massive iron soup, much hotter than the core of the Earth, it is so BECAUSE of the inward pressure caused by the massive amount of gas of the atmosphere above it. Already, above the iron core, the hydrogen atmosphere is not in a gaseous phase but in a metallic state (its atoms are rearranged and form regular lattices like carbon forming diamonds under massive pressure and slow cooking). Think of Jupiter as a failed star, a very massive object yet not massive enough to get its internal pressure big enough to start thermonuclear processes in order to become a genuine star."
] |
[
"We're not sure, but it's thought to have a rocky core but we do not know exactly what the makeup is. We do not currently posses technology capable of surviving the pressures of diving into Jupiter's atmosphere.",
"Here's a good overview from Wikipedia: ",
"Jupiter: Internal structure",
". Encourage your little bro to keep asking questions!"
] |
[
"Generally, ",
"Brown Dwarfs",
", which are the Jupiter-like bodies who ",
" made it to stardom, start at around 13 Jupiter masses, and run all the way up to around 90 Jupiter masses. Brown Dwarfs typically fuse deuterium and (the bigger ones do lithium ",
" fusion), but they can't do hydrogen->helium, so they sputter out once the easy fuel is exhausted.",
"Edit: Lithium ",
" fusion."
] |
[
"Is there a fixed amount of matter in the universe?"
] |
[
false
] |
I've been wondering, since there is no way to destroy/create matter, does that mean that there is a fixed amount at least in the observable universe? Thats all really, I pretty straight forward question I couldn't find an answer to on google.
|
[
"Is there a fixed amount of matter in the universe?",
"No -- matter can be created and destroyed in a number of processes, such as ",
"pair production",
", ",
"fusion",
", etc. So too can (rest) mass be created and destroyed.",
"The related conservation law is the law of conservation of energy. Since mass is a potent form of energy, mass is ",
" but not exactly conserved: it is possible to convert mass into other forms of energy. Matter, however, (in terms of number and type of particles) is not conserved except for certain \"classes\" -- ",
"baryons",
" such as protons and neutrons, and ",
"leptons",
" such as electrons -- and those may only be approximately conserved. We have lingering questions about their conservation because of the apparent imbalance between matter and antimatter.",
"there is no way to destroy/create matter",
"There definitely is. We do this at particle collider experiments all the time -- creating new matter, of both known and unknown types, and recording its interactions to study it and refine our models of reality. That is how we first discovered the Higgs boson, as well as many other particles.",
"There is only no way to create or destroy energy.",
"Anyway, if we rephrase your question as, \"is there a fixed amount of energy in the universe?\" the answer is somewhat technical and depends on the kind of universe we live in (which we are not sure of, empirically). If we live in a finite universe (that is to say, a universe with a finite volume), the answer is \"no,\" because our universe is expanding and energy is not conserved in an expanding, finite universe. If we live in an infinite universe (where the volume is infinite), technically the answer is \"yes,\" the amount of energy in the universe as a whole is fixed to be infinite, but any slice of finite volume will not have energy conserved within it, and so will have changing energy over time.",
"Hope that helps!"
] |
[
"Create/destroy is not the right word. Matter and energy can be converted into other forms. Fundamental law of physics is we cannot destroy matter. Law of conservation of mass."
] |
[
"Create/destroy is not the right word. Matter and energy can be converted into other forms. Fundamental law of physics is we cannot destroy matter. Law of conservation of mass."
] |
[
"How did such a diverse Universe form from a Big Bang singularity?"
] |
[
false
] |
I only have a basic understanding of the fundamentals of this, but what I'm wondering is since at the point of or just before the big bang all matter was a part of the singularity and I'll assume uniformly compressed, why did it not form a perfectly ordered universe? Since there would be no outside interference (I'm assuming again) this disorder would have to come from within. So what caused this disorder? Was it the matter itself, was the "bang" decentralized, or something wildly different?
|
[
"The diversity that we observe in the Universe today was likely seeded after an epoch of rapid expansion (called inflation) in the early moments of the Universe. Although the Universe was extremely homogeneous and isotropic at that time, quantum fluctuations caused small overdensities which, by gravitational collapse, grew quickly (well, fast compared to the Hubble time.) They eventually collapsed into the first stars and then (by a mechanism that isn't very well understood), galaxies formed."
] |
[
"Don't forget that there have been generations of stars before the current stars which have seeded the current galaxies with the different diverse elements."
] |
[
"What LV426 said.",
"The ",
"cosmic microwave background radiation",
" is ,in a way, an image of these fluctuations."
] |
[
"How accurate is Path Integral Formulation?"
] |
[
false
] |
So Path integral formulation is how people calculate the most probable route for a particle to take. But, how accurate is it? I mean, how good is it at reliably calculating the route a particle will take? Are these the type of calculations they would do at CERN to make particles cross paths?
|
[
"well the universe just doesn't have the certainty that appears to be a part of classical physics. (",
"Then again it doesn't exist in classical physics either",
")"
] |
[
"What is your background? The math of the path integral formulation is considered to be advanced so this is generally only discussed in post-graduate level textbooks. If you want the main concept but not all of the details, a section in Merzbacher's QM ",
"textbook",
" explains it in a neat way, and the rest of the book has a lot of the background on the relationship between classical and quantum mechanics (in particular the Hamilton-Jacobi method) "
] |
[
"it won't tell you ",
" path a particle will take. all it outputs is the likely probability of certain outcomes over others. And yeah, it works really well."
] |
[
"What happens underground as more and more oil is extracted?"
] |
[
false
] |
My understanding is that to extract oil from normal underground oil fields, explorers need to pump water instead, to replace it. What happens down there as we extract all those millions of barrels of oil around the world? Will the underground earth strata not get destabilized somehow?
|
[
"Oil extraction from conventional reservoirs (reservoirs that don't need fracking for production) can lead to land subsidence. In particular in coastal areas, this can lead to flooding. It can also lead to the damage of buildings and roads. It is thus common practice to inject water to fill the pore space that was occupied by the oil. This process also maintains the pressure in the reservoir which helps with production. In so-called unconventional reservoirs, i.e. those that require fracking, water injection is not feasible because the reservoirs are too tight for injection. These reservoirs are of low porosity (around 5%), the amount of oil produced is relatively small (perhaps 5-10% of the oil in the reservoir), and the reservoirs are generally quite deep. For all these reasons, unlike with conventional reservoirs, land subsidence is not of concern with unconventional reservoirs. It is barely measurable with the most precise techniques and presents no negative issue. These formations also produce water with oil and gas. This water does get re-injected into some porous layers. This wastewater injection is considered responsible for earthquakes in Oklahoma and other mid-continent states in the US."
] |
[
"With regards to \"sucking\": there's not a vacuum pump at the top, so perhaps \"squeezing\" would be a better description. A vacuum wouldn't help much, anyway, because surface pressure (14.7 psi) is already quite low compared to typical reservoir pressures, which can measure in the hundreds or thousands of pounds per square inch.",
"Basically the oil and gas gets squeezed up the straw by the pressure of the reservoir, and sometimes we inject more fluids - water or gas - to further raise the pressure in the reservoir. Over time, the reservoir pressure drops and the well stops producing. Typically there's still quite a lot of oil left in the reservoir, we just can't get it out (economically) because the pressure's too low."
] |
[
"With regards to \"sucking\": there's not a vacuum pump at the top, so perhaps \"squeezing\" would be a better description. A vacuum wouldn't help much, anyway, because surface pressure (14.7 psi) is already quite low compared to typical reservoir pressures, which can measure in the hundreds or thousands of pounds per square inch.",
"Basically the oil and gas gets squeezed up the straw by the pressure of the reservoir, and sometimes we inject more fluids - water or gas - to further raise the pressure in the reservoir. Over time, the reservoir pressure drops and the well stops producing. Typically there's still quite a lot of oil left in the reservoir, we just can't get it out (economically) because the pressure's too low."
] |
[
"Do solar systems have an electric charge?"
] |
[
false
] |
I've been reading about lots of stuff lately which has included atoms, the strong and weak forces, and electrons not really being per se. I've also been reading articles like and thinking about space, and scale. I can't help but notice that what is happening in the vacuum of space sounds a lot like the micro-swaps of information between protons and neutrons that creates the force that binds them together and leads to the detectable charges we understand as electrons. It just seems like vacuum is demonstrating the quanta information exchange we see at an atomic scale, with suns and planets functioning as de facto protons and neutrons, which makes me naturally wonder if this creates a charge (or multiple charges / "electrons") for a solar system, or maybe even further at a galactic scale. Is it turtles all the way up and down, so to speak? Or do we only see the electron effect of built up charges from quanta-style interactions at the atomic scale? Or, do I not understand any of this even close to how things actually work, and I should probably just go back to playing video games and smoking pot?
|
[
"I think the reasons for the solar system having a net charge are a little more mundane than that, actually. In general, solar systems coalesce out of a big cloud of gas and dust that is scraping against itself and generating pockets of static charge, similar to how clouds build up a static charge before equalizing with the ground through lighting. However, sometimes some of that charged mass can escape before it trades charge with its surroundings and becomes neutral. For example, a cluster of asteroids carrying a static charge might get flung into interstellar space, leaving behind the solar system with a net electric charge.",
"As far as fluctuations in the quantum vacuum giving rise to a net charge, there's no evidence for that which I'm aware of. If vacuum fluctuations were to give rise to charged particles, they do so pairwise, which means you won't see particles with a positive charge being generated spontaneously without their corresponding negative particle. This has to do with ",
"conservation of charge",
", which in turn ties into conservation of energy. Every place in the universe has some electric field (however weak), so if you spontaneously generate a positively charged particle all by itself, there is a corresponding amount of work that needs to be done to put it into the surrounding electric field. This would mean that energy (the work done to insert the new charged particle into the universe) would be created, which isn't allowed. I don't think I have done the best job in the world explaining, but the short answer is that net charges can't be created by vacuum fluctuations. If particle pairs are being generated in the solar system, they're going to be very close together and won't be escaping each other, so the whole system remains neutral."
] |
[
"I feel like there are a couple of different questions blending together here. As to whether the solar system acts like an atomic system with the sun/planets/sundry stellar bodies acting as fundamental particles, the answer is essentially 'no' (or at least, it lacks many of the features of an atom). ",
"In the article you linked, it sounds like the central idea was that scientists detected the polarization of light from a neutron star, which is hard to do because it is so far away, and the effect is relatively weak. This is because it takes enormous field strengths for the magnetic field of the neutron star to polarize light. In ordinary matter such as a ",
"calcite crystal",
" which changes the polarization of light, it is easy for the light to interact with the crystal as it passes through. In the case of a neutron star, the incredibly powerful magnetic field warps the (quantum) vacuum so much that it begins to polarize light similarly to how a calcite crystal does (cf. ",
"magnetars",
"). This is important because it takes a mindbogglingly powerful field to do this, so we don't see it very often. Usually the effect is weak, and it is hard for photons to be polarized by the vacuum, so the polarized light is faint. In the link about magnetars, one of the example stars would have a magnetic field that would be fatal to humans at 1,000 km simply because it is so strong it pulls our molecules apart and prevents the chemistry of life. That's the sort of field you need to see a strong polarizing effect.",
"To answer your question as I understand it, it isn't so much a case of stars interacting with each other through fundamental particle interactions as protons and neutrons do. Rather, the stars affect the fundamental particles around them (in this case, photons), which travel to us carrying information about that interaction.",
"On another note, it is possible (probable, even) that our solar system has a net electric charge relative to other far away solar systems. Nature likes things to be electrically neutral, but since we can't trade electrons with far-away stellar objects, the solar system as a whole retains a net charge (either positive or negative, I couldn't say). This is similar to when you scuff your feet on the carpet to build up a static charge. You keep the charge until you contact another object with a different charge, at which point you feel a zap as electrons transfer from you to the object."
] |
[
"On another note, it is possible (probable, even) that our solar system has a net electric charge relative to other far away solar systems.",
"It may be that this is really the answer I was looking for, and the answer given is effectively \"Yes\", but I want to unpack all of that a little bit more and make sure I'm 'grokking' all of this.",
"Assuming our solar system has a net electric charge relative to other far away solar systems, what would you say is creating that charge relative to other systems (the sun alone?)",
"And, if not the sun alone, is it possible or likely that quantum vacuum fluctuation is contributing to that charge (again, relative to other solar systems)?",
"Perhaps of note, I am not asking these questions with the perspective of the classic Newtonian atom model but am more considering all of this using ",
"the quantum model",
"."
] |
[
"Why does carbon absorb so much visible light?"
] |
[
false
] |
As it is known, the colors that we observe with our eyes depend on what type of light wavelengths are absorbed by the mass of an object, being white no absorption at all, and black almost complete absorption. Carbon is very black and I wanted to know why does it absorb so much radiation or types of wavelengths in the visible light. Thank you in advance.
|
[
"Visible light is absorbed by a material when it can excite an electron from one energy level to another. If the energy of a photon is equal to this energy gap, it will be absorbed (in the simplest case - there are some additional selection rules that complicate this). So in simple terms, carbon absorbs a lot of different wavelengths of light since it has a lot of different states that the electrons can be excited to.",
"Why is this the case? Now we have to consider the electronic structure of carbon in more detail. In solid materials, the individual atomic orbitals interact and combine to form ",
"\"bands\"",
" composed of many closely-spaced electronic states. Electrons occupy one band (termed the valence band) and can be excited to an unoccupied band at higher energy (termed the conduction band, since electrons in a partially-filled band are usually mobile). The separation between the valence and conduction bands determines the type of material: a wide gap means that a lot of energy is required to excite electrons, and the material will be an insulator. If the gap is smaller, it's easier to excite the electrons, and the material is termed a semiconductor (the difference between a semiconductor and an insulator is sort of subjective). If the gap is zero, such that you get one big continuum of partially-filled states, you have a metal. Similarly, the band gap determines what wavelengths of light the material will absorb. For a semiconductor, the large number of states in each band means that the material will absorb a wide range of photons ",
" the band gap energy, but nothing below the band gap (since there are no states to excite to within the band gap).",
"So what about carbon? Not all carbon absorbs a lot of visible light: graphite and amorphous carbon certainly do, but diamond does not have any transitions that absorb visible light. So the arrangement of the carbon atoms is important, and we can conclude that dark forms of carbon have a small band gap (absorbing all visible light, and even some infrared light), while diamond has a large band gap (absorbing only ultraviolet light). It's a bit hard to explain why this is the case without considering the physics in detail, but there's a general principle that can help a bit. In graphite and graphene, carbon atoms are arranged in sheets with 3 of carbon's 4 valence electrons involved in forming sigma bonds between carbon. The remaining valence electron can delocalize across the lattice of carbon atoms. Other dark-colored forms of carbon like amorphous carbon (coal, charcoal, glassy carbon etc.) and fullerenes have similar domains of these sp",
" bonded carbon atoms. In contrast, in diamond, all 4 of the valence electrons are involved in sigma bonding and are not delocalized. In general, as an electron can delocalize over a larger space, ",
"the difference in energy between electronic states decreases",
". So forms of carbon with a delocalized electron have small band gaps and absorb a lot of visible light."
] |
[
"Well, thank you very much for such a thorough explanation. I definitely forgot about diamond and it helps explain the reasons behind this phenomenon.",
"As a follow up questions. Do you know what are the wavelengths of energy absorption by graphite and amorphous carbons? I know the absorption of light for this structures of carbon is not limited to visible light, but it also goes into Infrared light.",
"This all makes sense considering the smaller band gaps due to delocalization of the electrons, unlike in diamond, and the lower energy provided by Infrared light. However, is it clear if the absorption of electromagnetic radiation by these structures go up to a particular wavelenght? For example, does the absorption stop at the the far-infrared, or does it even go up to microwave?",
"Thanks again for your response! :)"
] |
[
"In addition to what ",
"/u/pyrophorus",
" explained, we should not forget just how much the morphology of the surface or particles of a material can change the appearance. ",
"Consider a piece of polished platinum compared to ",
"platinum black",
". Likewise, consider the color of soapy water in a vial versus colorful interference of a thin soap bubble."
] |
[
"Is Pluto still growing? I know it passes through the kuiper belt so it's still making alot of collision right? Does that mean it's still adding mass? Planetary sci."
] |
[
false
] |
I was watching story bots with my kids, the one where they talk about how planets form that's what brought up the question.
|
[
"No. Most planetary mass was added by slowly accreting smaller particles into the proto-planetoid from the proto-planetary disk. This process has long since finished as any material left un-accreted when the Sun 'turned on' would have been blown away by the stellar wind. ",
"Collisions will have different effects depending on the energy of the collision. Small bombardments (think asteroids on earth) don't have enough energy to unbind anything, but they're also small enough that the amount of mass they're adding is negligible. High velocity impacts like were common in the early solar system can add or remove mass. For instance the Moon is believed to have formed from material ejected from the proto-earth after a collision with a mars-sized planetoid. Earth still net gained mass in that (+Mars - Moon - Space Dust). ",
"As ",
"/u/Baron_Bosc",
" also pointed out, the rate of collisions is also very very small today. Even in regions like the Asteroid Belt, Kuiper Belt, and Ort Cloud, it is exceedingly rare for objects to intersect."
] |
[
"There’s a big difference between what we imagine proto-planetary disks to be like and the present day Kuiper Belt. While I’m sure collisions between bodies still occur, the objects in the Kuiper Belt have, by now, settled into stable orbits around the sun, and there is enormous amounts of space between them. Formative and disruptive activity (such as interactions with Neptune, which gave Pluto and many other Kuiper Belt Objects their oblong orbits) happened long ago. ",
"There are a lot of experts on here, but I’m not one of them! I think I’ve got the gist of it. Maybe someone can correct me and/or add some more detail."
] |
[
"All planets are gaining mass from space debris raining down on them, but the rate is negligible. Earth gains about 50,000 tons a year from dust and meteorites falling into it, but it also loses about 100,000 tons of atmosphere a year so there's a net loss of mass."
] |
[
"Have we ever ran out of a natural resource?"
] |
[
false
] | null |
[
"Three that come to mind are all animals that were hunted to either extinction or nearly, all because of European expansion into North America: Stellar's sea cow, the passenger pigeon and the bison.",
"In all three cases, the animal at first seemed like an inexhaustible source of easy meat. European hunting equipment like guns made short work of these massive populations, and in two cases caused the extinction of the species. Bison have in a way recovered and are sustainably farmed now, but their decrease in number caused the collapse of several plains people's way of life. ",
"Actually, giving this a little more thought, humans have eliminated countless species from hunting over our ",
"tens of thousands of years of prehistory",
". Our species has being the driving factor in large mammal extinction for the better part of 80 000 years, including ",
"giant ground sloths",
", ",
"mammoths",
" & ",
"mastodons",
", ",
"glyptodons",
", ",
"Moa",
", ",
"Elephant birds",
", ",
"Irish Elk",
", ",
"500 pound wombats",
", the ",
"Huli beasts",
", ",
"Diprotodons",
".",
"I could go on"
] |
[
"Old growth (I.E. Large sizes) of hard woods. My parents had a dining table made of a single piece of maple split in half so the wood grain mirrored on each side. You just can't find that today except antiques or recycled."
] |
[
"I remember reading a few years ago that we would soon deplete the entirety of the world's helium supply. The most recent article I can find about it is ",
"here",
".",
"EDIT: Apparently, ",
"there is some disagreement",
" in the scientific community about whether a mass helium shortage could become a problem."
] |
[
"What could be the first signs of intelligent alien life?"
] |
[
false
] |
In the science subreddit i've been reading about the 5 earth sized planets that live in their respective star's habitable zone. Is there any possible way that we could confirm intelligent life on one of those planets (or any other planet) by making some observation here on earth. Science fiction has told me aliens will make their presence known by either showing up in spaceships, or by sending us some radio message, but both of these situations seem pretty unlikely. What if (for example) an alien race flooded their atmosphere with some synthetic element. When we turned our mass spectrometers towards those planets would we observe a situation that could not possibly exist naturally? Would it actually be strong evidence that intelligent life was responsible? Or will scientists pretty much have to assume that any weird observations have natural explanations? What other reasonable observations could we make from afar that would be strong evidence for alien life?
|
[
"http://en.wikipedia.org/wiki/Wow_signal"
] |
[
"Oh shut the fuck up please.",
"Why do you think our evolution is so special? Wherever extraterrastrial intelligent creatures have evolved, I'm sure they went through the same thing: agressively domaniting their own biosphere etc."
] |
[
"I had never heard about this, fascinating. Thanks for the link!"
] |
[
"Where does the mass go when not conserved in chemical reactions?"
] |
[
false
] |
I have read that mass changes in chemical reactions, for example through making and breaking bonds, but it is too small to detect. In balanced equations for non-nuclear reactions, there are the same number of protons, neutrons and electrons on both sides. If the equation is balanced, where is the mass change? Do the electrons/neutrons/protons slightly change their mass, or is the mass change hidden somewhere else?
|
[
"For example, a take a reaction like ",
"2H",
" + O",
" -> 2H",
"O.",
"The mass of one water molecule is smaller than the sum of half the mass of H",
" and half the mass of O",
".",
"Or even more simply, combining two oxygen atoms to make O",
", the mass of one O",
" molecule is a tiny bit smaller than the mass of two separate O atoms.",
"The chemical bonds that form between atoms contribute negatively to the total energy in the center-of-mass frame, so they reduce the mass of the system as a whole. It’s not individual protons/neutrons/electrons that are losing mass, it’s the entire bound system.",
"Since chemical bonds have energies on the order of eV, the mass equivalent is on the order of (1 eV)/c",
", which is tiny compared to the many GeV/c",
" masses of molecules.",
"For nuclear reactions, it’s more pronounced, because the “bond” energies are on the order of MeV, a million times larger."
] |
[
"In the nuclear case, the changes in mass are easily detectable. ",
"Masses can be measured very precisely, for example with a Penning trap. And you can calculate the difference between the mass of the bound nucleus and the sum of all the individual protons and neutrons. We call this the \"mass defect\", and there are ",
"tables of them available for reference",
".",
"We know how it works theoretically because it's just a straightforward application of the proper definition of mass from Einstein's special relativity.",
"The chemical case is no different physically than the nuclear case, the numbers are just smaller."
] |
[
"Or is mass a property of a system and not actually a property of the separate protons/neutrons/electrons that make up the system?",
"Yes, exactly."
] |
[
"How are space elevators supposed to maintain their speed when transporting mass from earth to the orbit?"
] |
[
false
] |
Because of newtons first law, the object that is being moved towards the counterweight would require horizontally (or rotational) effecting force in order to maintain it's route. I came into this conclusion because the counterweight orbits the anchored body and it should turn around the body faster than the body itself and applying vertical force to the climber doesn't cause it to gain horizontal (in this case rotational) speed. The speed required must be gained by slowing the counterweight which could lead to an imbalance and possibly break the whole system If what I said was true, how are physicists planning to overcome the slowing caused by carried objects?
|
[
"They steal the energy from the spin of the earth in the same way that when you spin a sling in takes energy from your hand. The entire line is under tension as the counter weight is past geostationary orbit. It's being flung around."
] |
[
"No...",
"A stable space elevator has its effective* center of mass slightly above geostationary orbit and has a constant tension in the cable even at sea level. Raising a payload won't change that. Raising the payload accelerates the payload in forward direction and slows the elevator, making it lag behind slightly. The tension provides momentum forward, while the center of mass being above geostationary orbit makes sure the elevator doesn't fall down and also maintains the tension.",
"*weighted by gravitational acceleration minus centrifugal force"
] |
[
"The counterweight must be ",
" heavier than the travelling carriages and their cargo, one reason folks talk about capturing an asteroid and parking it in the appropriate position.",
"Since we'll presumably have things going in both directions, returning carriages/cargo will require a force in the other direction, minimizing/cancelling cumulative effects on the counterweight.",
"It'll presumably also have some corrective thrusters just to make sure as well."
] |
[
"Do animals have to learn how to swim like humans or are they just born with that ability?"
] |
[
false
] |
Swimming in humans is something that must be taught and it is not something that we are just instinctively able to do. Do animals like jaguars or tigers that swim and use the water for hunting but are not dependent on water have to teach their young how to swim? If these types of animals are not exposed to water or not taught by their parent, do they instinctively know what to do or would they drown?
|
[
"Babies cannot swim instinctively. When placed in water their survival reflexes force them to move their arms and legs but babies will drown. They cannot hold their breath and cannot keep their heads above water. Thrashing is not swimming. Do not put babies of any age near water without strict supervision."
] |
[
"Babies cannot swim instinctively. When placed in water their survival reflexes force them to move their arms and legs but babies will drown. They cannot hold their breath and cannot keep their heads above water. Thrashing is not swimming. Do not put babies of any age near water without strict supervision."
] |
[
"So is it likely that we lost this ability to swim as we became less dependent on water bodies as a resource and the natural ability to do this as a baby is just a redundant evolutionary thing?",
"I just wonder if we are unique in this situation or if an adult tiger for example would drown if it weren’t exposed to water as a baby, especially if it was raised by humans as an orphan."
] |
[
"What differentiates two similar elementary particles?"
] |
[
false
] |
If elementary particles are the fundamental building blocks of everything, this means that they themselves are not made up of anything but themselves. So what is it that distinguishes, say, two distinct up quarks?
|
[
"Two particles of the same type cannot be distinguished, they are ",
"fundamentally identical",
"."
] |
[
"What distinguishes them is that one is over here and the other is over there. But it does not make sense to ask what would change if they swapped positions, as though they had identities. There may be a high probability of detecting an electron at position 1 and at position 2, but you can't say that electron 1 is at position 1 and electron 2 is at position 2.",
"It is a bit more complicated because we aren't actually deally with position 1 and 2, but a host of statistics. But electrons differ only in having different statisics, and they have no identity beyond those statistics."
] |
[
"u/RobertEtCeleritas",
" 's explanation is perfectly accurate, but allow me to build a bit.",
"Forewarning, gonna approach this from a Quantum Field Theory perspective, and I am not a professional, I just have hobbies.",
"So, on top of what was already mentioned, which is that particles of the same type are indistinguishable (which is bore out by much experiment by the way), arguable they are also literally the same object, or sort of part of it in some sense.",
"So imagine a pool of water with like waves or in general perturbations on it. A tidal wave on that pool of water could look an awful lot like object on the pool, but on the other hand there is a sense in which it is still just part of the pool of water as well, just in a particular state.",
"So, the waves are the particles, but they are just excitations of the water, so what is the pool? The pool is a field. That view of waves, in a rough sense, is analogous to the Field Theory view of particles, with some important caveats. First of all, the water fills all of space and needs no container, so ditch the \"pool\". Then, there are multiple fields and all of them are at every point in space, so imagine you could have different liquids all overlapping at every point in space. Also, water resolves into atoms eventually, but fields don't, they are the fundamental object, so forget being able to break it down into anything more fundamental. Also, imaging these overlapping liquids can interact in a bunch of different ways, and then you're imagining the universe like a Quantum Field Theorist.",
"And this includes all particles. There are electron fields, and neutrino fields, and literally any particle has a field in QFT.",
"Important notes: 1) these are much more abstract and mathematical than like a body of water, so a field more accurately something that takes on a value at every point in space, the water was only a rough analogy, 2) just like water resolves into atoms when we look closely enough, fields could become something more fundamental well we understand high energy regimes well enough, but as of now they aren't shown to and QFT is the best tested theory in all of science, 3) there could be better analogies than waves on water that get the structure or behavior of particles more right, but it was only meant to show how something can seem distinct when it part of a larger whole in reality, so don't take the picture of a wave to seriously.",
"Also, please correct me if you know better anyone"
] |
[
"Since planets rotate around suns and suns around galaxies, could we be feeling the effects of relativistic time dialation in relation to other planets?"
] |
[
false
] |
The news release about Voyager I got me wondering about this. We know that time dialates as an object approaches the speed of light, and iirc mass increases. Is it conceivable that we on earth are already feeling these effects, and that we could come across a planet of similar size and composition as Earth, but time and mass are completely different due to its planetary and solar orbit speeds? Edit: maybe I mean solar and galactic orbit speeds. Edit 2: and what does this mean for our observations of distant parts of the universe if our galaxy is careening along at a high speed?
|
[
"And the time taken to make one revolution is the same for both. ",
"That's where you're going wrong: the galaxy isn't a solid body. It doesn't need to have the same period per revolution at every radius. The inner parts take less time to do a revolution than the outer parts. This isn't possible for a pancake or a record (it'd be torn apart), but it's fine for a non-solid object like a galactic disc."
] |
[
"One key concept in time dilation/special relativity is that there is no preferred inertial frame of reference. Also, mass equivalence is a misleading concept that has been largely abandoned by physicists. ",
"Other than that, I'm not really sure what you mean about observing an Earth-like planet. In general terms, objects in our local cluster are gravitationally bound to us, and aren't moving at relativistic speeds in relation to us. Orbital speeds of planets around stars are also not fast enough to be relativistic, in nearly all realistic circumstances.",
"So yes, we could possibly observe another planet, but it's unrealistic that it would have such a high velocity relative to us, and even if that were the case, we would just know that there's a slight difference in perceived time on Earth vs. on that planet. There's nothing \"completely different\" about that."
] |
[
"Our solar system is orbiting the centre of the Milky Way at around 250 km/s. An object near the centre of the galaxy would be revolving at a much slower speed than us. Let's say they are orbiting at 100 km/s, the difference is still 150 km/s (2000 times slower than light).",
"Although these aren't exactly close to relativistic speeds, I would say that there would still be some time dilation.",
"Since neither our Solar system nor the other object is in an accelerated frame of reference, I am not sure what effect that would have on my answer above."
] |
[
"Quantum Physics Question: Is the state 1/sqrt(2) | 0> - 1/sqrt(2) | 1> equal to -1/sqrt(2) | 0 > + 1/sqrt(2) | 1>"
] |
[
false
] |
Sorry if this isn't the right place to ask. If we have the two canonical states on 1 qbit. |-> = 1/sqrt(2) | 0 > - 1/sqrt(2) | 1 > |+> = 1/sqrt(2) | 0 > + 1/sqrt(2) | 1 > If you invert the |-> state you will get -1/sqrt(2) | 0 > + 1/sqrt(2) | 1 > This is not the same as |-> right? It would be its own thing -|-> , or is there a simplification. Sorry for the uninteresting question, but I don't have anyone else to talk through this stuff with. In other words -|-> is not equal to |+> or |-> right? If I was to take the eigenvectors of a Hamiltonian matrix, I could not say that a base state is |-> if I got -1/sqrt(2) | 0> + 1/sqrt(2) | 1> as an eigenvector.
|
[
"In other words -|-> is not equal to |+> or |-> right?",
"It's not equal as a vector, but it ",
" equal as a state. This is because the difference between -|-> and |-> is just an overall phase of pi (e",
" = -1), and states that differ by an overall phase are indistinguishable. Note that this does ",
" mean that the states",
"(|+> - |->) / sqrt(2)",
"and ",
"(|+> + |->) / sqrt(2)",
"are the same; now the phase isn't an overall phase and it becomes meaningful.",
"If I was to take the eigenvectors of a Hamiltonian matrix, I could not say that a base state is |-> if I got -1/sqrt(2) | 0> + 1/sqrt(2) | 1> as an eigenvector.",
"You could. Any scalar multiple of an eigenvector is also an eigenvector. In this case, you know that -|-> is an eigenvector, so you know that every scalar multiple (including |->) is also an eigenvector."
] |
[
"Actually, it would be an eigenvector with eigenvalue L. Let's just call the state -|-> ",
" to make readability easier. Then ",
"(-|->) = ",
" for any scalar ",
".",
"We know that H",
" = L",
". Then let's look at H(",
"). For this we have",
"H(",
") = ",
"H",
" = ",
"L",
" = L(",
"),",
"so if ",
" is an eigenvector of H with eigenvalue L, then every scalar multiple of ",
" is also an eigenvector of H with eigenvalue L. Now, in quantum mechanics we always use normalized eigenvectors, so we require |",
"| = 1, but we can choose any complex number ",
" so long as |",
"| = 1 and still have",
"|",
"| = |",
"||",
"| = |",
"| = 1.",
"Thus, when we pick ",
" to be our basis element corresponding to the eigenvalue L, we could just as easily have chosen -",
", or i",
", or e",
", or any other multiple of ",
" provided the scalar has norm 1."
] |
[
"It was for a homework question, but it wasn't this exact problem. This is just a subproblem that I needed to complete the whole thing. Not trying to cheat; I'm trying to learn. "
] |
[
"Why are acoustically guided weapons an option in the ocean but not in the air?"
] |
[
false
] |
[deleted]
|
[
"Ships are extremely slow (say 15 m/s / 30 knots) compared to the speed of sound in water (1500 m/s). What that means is that acoustic detection is practically instantaneous -- when the sound waves hit you, the target hasn't moved far.",
"Warplanes travel a significant fraction of the speed of sound (or well above it) so acoustic tracking isn't ever going to be very good. In fact for an approaching supersonic aircraft, you literally cannot hear it at all, so it's physically impossible to track it acoustically. There's also a lot of attenuation of acoustic waves in air -- you certainly can't hear an airliner cruising overhead at 30,000 feet.",
"I'll add that there is significant effort put into reducing the acoustic noise generated by aircraft for stealth reasons. It's especially a big deal with helicopters which are loud as hell, typically fly very close to the ground, and are desirable for clandestine use."
] |
[
"To add, EM waves don't travel very far in water and so you can't really use them to track targets."
] |
[
"Also the speed of sound in water is significantly higher ( over 4x ) than in air, and can propogate over longer distances."
] |
[
"How satellites measure underground water level ?"
] |
[
false
] |
How do satellites estimate the underground water level ? What changes in local environment signify higher underground water level ?
|
[
"Using ",
"gravimetry",
".",
"The maps are based on data from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites, which detect small changes in the Earth's gravity field caused by the redistribution of water on and beneath the land surface. The paired satellites travel about 137 miles (220 km) apart and record small changes in the distance separating them as they encounter variations in the Earth's gravitational field.",
"The changes in the strength of gravity are minute and not even close to being noticeable to a person on the ground. Gravimeters, however, are sensitive enough to detect those small changes."
] |
[
"That's fascinating! How do we create the sensors to be so precise? "
] |
[
"I'm not too familiar with the exact instrumentation on the satellites but a basic gravimeter consists of a mass hanging from a spring. By measuring how much the mass causes the spring to expand/contract you can calculate the change in the force of gravity acting upon the system. That's the principle at any rate."
] |
[
"What is the black spot that was on a CERN diagram? is it just a blotch or dust particle that got picked up?"
] |
[
false
] |
[deleted]
|
[
"That is where the beam passed through a ceramic screen on its way to the beam dump. The beam dumps are long, water-cooled rods of carbon encased in steel, designed to absorb the energy of the beams when they get ejected out of the LHC. Each beam can contain around 150 MJ of kinetic energy, which is about 10% that of a typical lightning bolt. The beams get ejected in a spiral pattern in order to spread out the energy and prevent stuff from melting.",
"https://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/components/beam-dump.htm",
"The image you link to is the BTVDD (Beam TV Dump Detector) which is just one part of the beam dump monitoring system. It consists of a radiation-hard camera pointed at a special ceramic screen that will emit light in response to ionising radiation. The black dots are where the beam passed through, and you can make out part of the typical spiral that a full beam would make.",
"Check out the following link for some more technical details and diagrams, particularly the plot showing the typical spiral and the diagram of the apparatus at the bottom of the third page.",
"https://accelconf.web.cern.ch/accelconf/d07/papers/tupb28.pdf"
] |
[
"Do you have any more context for that photo?"
] |
[
"It's a photograph that displays on this page after the beams have been dumped and before new beams are injected",
"https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHCBDS"
] |
[
"Is imposter syndrome prevalent in scientific communities?"
] |
[
false
] | null |
[
"If you go on and meet personally your profs, do PhD, etc, you will see how the whole thing is set up, that most of everybody is just normal people with stupid days and they usually look super smart on a tiny slice of knowledge that they have spent the last 15-20 years on (so no wonder they can blow a BSc student out of the water, it's the adult equivalent of you flexing your calculus skills on a kindergarten).",
"Yes, there are a couple legit geniuses here and there, but most are just people and some really mediocre as well. You are fine."
] |
[
"While I can't tell you whether it occurs more often in scientific than in other communities, I can at least assure you that quite a number of people I've talked to in the scientific field feel that way. \nIf I were to find a reason for that, I assume that by acquiring all that detailed knowledge about certain processes, some of them rather simple and others highly sophisticated, you start to realise that we actually know very little to nothing at all. At some point, one always reaches the barrier of \"we don't know yet\" or \"we have a theory, but it is not yet proven\" and more often than not, this barrier comes rather quickly. Combined with the fact that we're taught things that have been researched over years, decades or even centuries within a few weeks, almost making it impossible to reach a profound understanding of things beyond the surface level, easily leads to a feeling of knowing nothing and therefore not deserving any of the credit given. ",
"TL,DR: Some do better, some do worse, but a lot of scientists face these doubts"
] |
[
"Every skilled profession has to deal with imposter syndrome."
] |
[
"Where to find ground-based Ultraviolet spectrum data?"
] |
[
false
] |
I am looking for text files or xml or some kind of database which has ground based measurements of ultraviolet light. Something which has irradiance vs. wavelength. I have seen a lot of plots of the spectral irradiance at the surface even at ultraviolet wavelengths but have not been able to find datasets that these are made from.
|
[
"If you can get hold of '",
"', I'm sure it would be in there. "
] |
[
"I think you are (or were, this thread is 3 months old!) looking for the ",
"AM1.5g",
" (air mass 1.5, global irradiance) spectrum.\nedit: (",
"more data",
")"
] |
[
"Thanks! That was exactly what I was looking for with good resolution; it will still be very useful in the future.",
"I ended up using the irradiance in space and multiplying by the transmission obtained from different sources and interpolating down to one nm resolution for the UV range.",
"All our readings ended up being within about a factor of two of what was predicted before calibration.",
"This would have definitely saved some time and instilled some extra confidence into our design calculations."
] |
[
"Why does abstaining from porn/masturbation/orgasm temporarily decrease as opposed to increase libido?"
] |
[
false
] |
[deleted]
|
[
"I think the reason we might assume libido to increase is because we intuitively accept the idea that our behavior is controlled by basic drives (hunger, sex, etc) and that we work to return these levels to some kind of homeostasis. This is essentially what the psychoanalysts argued with their \"steam engine\" theory of anger (also known as 'catharsis theory'), in that you have to \"let off steam\" sometimes so that you don't take it out on other people and so you can get it under control.",
"Turns out, these ideas of behavior aren't very accurate. Drive theory turned out to be a very poor explanation for behavior, and it reached the point where to explain behavior, we had to keep creating new \"drives\" like \"money drives\" and \"exercise drives\" etc. It became unscientific, unparsimonious, and was dropped from science (a good discussion can be found in Mazur's \"",
"Learning and Behavior",
"\"). This isn't to say that there aren't foundational or basic biological elements which influence, direct, or control certain behaviors, but just that thinking of them in terms of \"drives\" or us trying to \"satisfying urges\" doesn't explain behavior very well.",
"Whilst it may make sense to us on an everyday level to believe that \"venting\" can relieve an urge to do something, ",
"the actual fact is that the opposite occurs",
". What happens is that standard behavioral laws still apply to our behavior; that is, if the consequence of an action is pleasurable, then we are more likely to repeat it (operant conditioning). So instead of relieving our urges, we actually start to strengthen these associations and make them more likely to occur again in the future. This means that if we're angry and we go beat up a punching bag for 30 minutes, our anger will increase and we will be more likely to snap at people.",
"The same principle applies to all behaviors, and so it should apply in the case of abstaining from sexual gratification. When you abstain, you are not only reversing the effects of habituation on sensitivity, but you're also putting yourself through a kind of \"",
"extinction procedure",
"\" where you are decreasing a behavior (in this case the \"urge\" or \"libido\") by removing the positive reinforcement that comes along with it. ",
"And then there's the fact that you're breaking a number of behavioral chains and sequences by abstaining - so previously turning on your computer late at night might have led to a certain activity, now all it signifies is that you're browsing reddit or ebay or something. These cues that trigger behaviors are discriminative stimuli, and just like people who try to quit smoking but find it more difficult to resist when they're drinking (because they used to do the two together), you can get the same thing with activities like masturbation. Changing your behaviors can break these behavioral chains, which in part account for the associated feelings of arousal and our libido. ",
" Basic behavioral mechanisms can account (at least in part) for the phenomenon you described - operant conditioning, habituation, extinction, etc. "
] |
[
"Well I have no evidence or research to back this up, but I would have assumed that it would be temporary - at least for most people. This is due to the simple fact that 1) there are many, many cues which can trigger a behavior that can be difficult to get rid of for ingrained patterns (which is why it's hard to shake bad habits), and 2) genital stimulation generally feels pretty good, so even when you're not actively engaging in masturbation, there's still touching from cleaning them in the shower, accidental effects of fabrics rubbing against them, for guys there are erections from arousing visual stimuli, etc, and all this will usually make people want to keep doing it rather than abstain completely. ",
"Whether it returns to the \"original levels\" or not is dependent on the consequences of the behavior. Different patterns of reinforcement whilst re-creating similar behavioral sequences may result in it being less frequent, or perhaps even more frequent. "
] |
[
"Well I have no evidence or research to back this up, but I would have assumed that it would be temporary - at least for most people. This is due to the simple fact that 1) there are many, many cues which can trigger a behavior that can be difficult to get rid of for ingrained patterns (which is why it's hard to shake bad habits), and 2) genital stimulation generally feels pretty good, so even when you're not actively engaging in masturbation, there's still touching from cleaning them in the shower, accidental effects of fabrics rubbing against them, for guys there are erections from arousing visual stimuli, etc, and all this will usually make people want to keep doing it rather than abstain completely. ",
"Whether it returns to the \"original levels\" or not is dependent on the consequences of the behavior. Different patterns of reinforcement whilst re-creating similar behavioral sequences may result in it being less frequent, or perhaps even more frequent. "
] |
[
"Does it matter environmentally if we lose rare species? Why do we try to conserve rare species?"
] |
[
false
] | null |
[
"Webs do best with many buttons for nature to tweak. When you reduce the web to just a few species, the web falls apart, especially when faced with great change it must respond to. Do this enough and our entire planet goes sterile in many regions. A famous example is loss of wolves from Yellowstone and then elk overpopulation and then destruction of Aspen trees. If left unfixed, we could lose something as magnificent as Yellowstone's magnificent Aspen forests, which nature and evolution fine tuned to that area over a very long period of time.",
"\"We concluded from this that the failure of aspen to regenerate was caused by an increase in the number of elk following the disappearance of wolves in the 1920s rather than by a rapid behavioral shift to more browsing on aspen once wolves were gone from the park,\"",
"http://www.sciencedaily.com/releases/2010/09/100901111636.htm",
"Now yes, would life come back in and fill the void? Yes, something would grow there, but it would not be the unique ecosystem that developed there originally. The Earth is healthier and better able to respond to change the more diversity it has, the more solutions it has to try, in order to keep life going. Think about how boring the world would have been if mammals hadn't been there and sprung to the forefront after whatever disaster killed the dinosaurs.",
"Also as someone that does drug discovery from natural sources, I must say it is very beneficial to maintain extremely rich species diversity. You never know when the next great drug will come from some tiny rare species that would be missed forever had the ecosystem been lost.",
"Regaining diveristy once it is lost can take an ENORMOUS amount of time-",
"\"Earlier analyses indicated that life on Earth recovered quickly after the Permian extinctions, but this was mostly in the form of disaster taxa, such as the hardy Lystrosaurus. The most recent research indicates that the specialized animals that formed complex ecosystems, with high biodiversity, complex food webs and a variety of niches, took much longer to recover. It is thought that this long recovery was due to the successive waves of extinction, which inhibited recovery, and prolonged environmental stress to organisms, which continued into the Early Triassic. Recent research indicates that recovery did not begin until the start of the mid-Triassic, 4 million to 6 million years after the extinction; [62] and some writers estimate that the recovery was not complete until 30M years after the P–Tr extinction, i.e. in the late Triassic. [4]\" ",
"http://en.m.wikipedia.org/wiki/Permian-Triassic_event",
" ",
"Four to six million years is not a time scale humans can even fathom or deal with, considering we are only maybe 50,000 years old ourselves.",
"When you hear about a loss of species be very worried. To lose species in our short time frame is absurd compared to the natural very slow loss of species that occurs naturally and associated gaining of new species that replace them. Our unnatural destruction of species is way too fast for evolution to respond with new species to replace the lost diversity. We are in fact in the midst of the sixth great extinction event in Earth's history, and we are causing 100-1000 times greater loss of species diversity compared to the fossil record before the arrival of humans.",
"http://m.guardian.co.uk/environment/2010/mar/07/extinction-species-evolve?cat=environment&type=article",
" "
] |
[
"From a scientific standpoint, nothing presents a better basis for technological and medical advancement than reverse-engineering existing biological structures.",
"There are many instances where a limited number of animal species have been observed to manifest unique abilities. If those rare species are lost, then the ability to borrow from their adaptations to further our own technology and medicine at an accelerated rate is most likely lost.",
"An example is ",
"circular polarized light detection",
" in a couple of species of Mantis Shrimp."
] |
[
"I'm not sure we have the intelligence or know enough to ever make that distinction, and the loss of any species, a unique thing that may have taken an enormous amount of time to develop seems like something we should try to prevent if we can. "
] |
[
"How do marine mammals survive without fresh water to drink?"
] |
[
false
] | null |
[
"Marine mammals get their fresh water from the food they eat (ex: fish). ",
"Many dolphins in captivity are \"watered\", which is basically tubing water into their stomachs (painless and trainable), to make sure they get water that may have been lost in frozen fish during processing. Other methods of ensuring hydration are ice cubes and gelatin.",
"Gelatin has widespread uses for marine mammals who require lots of hydration.",
"But marine mammals do have kidneys that are much better than most animals' at filtering out excess salt.",
"Source: worked with dolphins."
] |
[
"cats also have extremely efficient kidneys that are capable of getting hydration from saltwater",
"everyone should have a cat."
] |
[
"Cats CAN drink salt water.",
"http://en.wikipedia.org/wiki/Cat#Physiology",
"I hate the idea of a democracy of half educated idiots deciding what is or is not a scientific answer via voting.",
"Talk about the blind leading the retarded.",
"*and in case the future is different, thehatman9's correct answer was being downvoted when I wrote this."
] |
[
"How much light is there out in deep space?"
] |
[
false
] |
Science fiction generally shows ships and their hulls reasonably visible no matter where they are in space. How realistic would this be? Say we have a space ship some 2 light years from earth, halfway to alpha centauri, so no where near a major source of light. Is the total 360 degree coverage of stars going to create enough star light to make a hull of a star ship quite visible or are the unlit parts likely to be quite black? And likewise, would a rogue planet or other large object essentially be invisible until you run into it?
|
[
"create enough star light to make a hull of a star ship quite visible",
"On Earth we have the sun as a good point of reference for what \"bright\" is. In space your reference would need to be a star in your field of view. No matter how dark the hull, if you have no stars in your FOV, you can simply increase your gain to make any photo arbitrarily bright.",
"The human eye may be limited though, so depends with what are you measuring the brightness."
] |
[
"You can't increase the gain without problems. Thermal noise will probably stay the same and make the picture grainy."
] |
[
"You could not just increase the gain to make the photo very bright as this would cause a lot of issues due to noise."
] |
[
"How much of the energy that goes into a PC is transformed into heat? How does it compare to a space heater?"
] |
[
false
] |
I've just asked myself this since my old PC tower does warm up my room when it's on and after all, both a space heater and a computer produce heat by sending electricity through wiring, right? The computer's is just more intricate ... I was also wondering if this would make a computer doing calculations (CERN, folding proteins, cryptocurrency, ...) an efficient replacement for a space heater on either an individual or humanity-wide level.
|
[
"Pretty much all of it. Some of the energy is converted into sound waves (spinning fans), but when these strike objects and walls, the energy is absorbed and turned into heat as well. Only the sound and light emissions that directly leave the room/house (through windows or doors) don't contribute to heating up the room. But that's a tiny fraction of the total energy.",
"So, yes, you can use a computer as a replacement for a space heater. If you use a regular resistive space heater, then a computer would be no less efficient in terms of energy consumption. If you make it do something productive with its CPU/GPU cycles, you could argue that it's more cost efficient than a resistive space heater.",
"However, if your heating comes from any other source, such as gas heating or a heat pump system, then the computer will lose out in efficiency. In many houses, such a form of more efficient heating is applied, so large scale application of computers as a heat source will likely not be efficient."
] |
[
"You need quite efficient CPUs/GPUs to recover a large fraction of your electricity cost that way."
] |
[
"Essentially all of the energy becomes heat. The space heater will likely be more reliable, and less sensitive to dust. It would also likely have a thermostat, set to shut off the machine at human levels of discomfort rather than computer levels of discomfort. Space heater might be less sensitive to dust and electrical transients. "
] |
[
"Family members are posting on Facebook that there has been no warming in the US since 2005 based on a recent NOAA report, is this accurate? If so, is there some other nuance that this data is not accounting for?"
] |
[
false
] |
I appreciated your response, thank you.
|
[
" As ",
"/u/joekercom",
" points out, ",
"the 2005 date is not arbitrary",
". In 2005 NOAA began collecting climate data from a new network of weather stations due to criticisms about the validity of the existing weather station network. The data since 2005, from both the new and the old networks, does not show a significant warming trend. The misconception here is that this new network is more accurate than the existing network and that a lack of warming in the new network's data refutes the existing observations of warming in the USA. This is not the case.",
"The whole purpose of the new network (called the US Climate Reference Network) was not to replace the existing network of weather stations, but to measure the validity of the existing network's data and determine whether there are baises in the data due to things such as urban development. We did not know whether the existing weather station network was accurate, but we do know that the USCRN is a \"pristine\" weather station network that should be free from bias. Here's the important point: ",
"When researchers compared the results from the USCRN with the existing climate station network, they have found that the data from both networks largely agree with each other.",
" What this means is that as far as we can tell, the existing climate data network that NOAA has been using for decades has not been strongly biased by external factors other than genuine climate change. ",
"Thus, while the 2005 date is not arbitrary, it is neither the beginning of a new era of climate data that rejects all previous observations. It's the opposite, the climate data collected since 2005 only supports the idea that the long-term warming trend we have seen here in the US and elsewhere is a genuine climatological phenomenon, and not due to unseen bias in the data collection methods. ",
" Just a nice source from ",
"/u/kilotesla",
" showing how the new network (USCRN) compares to existing climate data networks used by NOAA:",
"New network USCRN vs old networks",
"They're right, but there are four things to keep in mind here: ",
"The year 2005 is an arbitrary date. ",
"Over time there is a clear warming trend in the USA.",
" Go back to 1990 and there is a demonstrable warming trend, go back to 1980 and there is a very clear warming trend. ",
"US temperatures since 2005 have not been significantly rising, but they're already hot. All temperatures since 2005 have been above the historic average. If there was no warming trend, we would expect some years to be above the average and some years below. ",
"Changes in local weather patterns can dominate the warming trend in the short term, and the USA is a very temperate country. For example, El Nino vs. La Nina temperature conditions in the Pacific ocean can greatly influence the USA's temperature in any given year, with two of the hottest years in the last 15 being hot El Nino years. ",
"The years 2015-2018 are the four hottest years on record globally. The global warming trend is clear, and the local variations in weather that have stalled warming in the USA will not continue forever."
] |
[
"we would expect some years to be above the average and some years below",
"Worth pointing out that basically the same as the arbitrary date thing. The core issue is cherry picking the data."
] |
[
"I thought the issue was getting your scientific data from Facebook?"
] |
[
"What would a magnetic field look like in/around a toroidal world?"
] |
[
false
] |
I've been looking at this , and the author was very curious about what the what they'd look like, but He couldn't be bothered to figure it out. If any of you have any other ideas/facts/statements about this, I'd love to know!
|
[
"I'm not sure such a question can reasonably be answered. Look at the other spherical planets we know of. Even Venus, relatively the same size as Earth, has practically no magnetic field. Magnetic fields seem to be pretty specific interactions of materials that allow for a spinning metal core that generates such a field. I doubt a toroidal planet would have such a structure. "
] |
[
"Yeah so the thing is, the Earth generates its field because a liquid metal core surrounds a solid metal core. And as the Earth turns, that liquid metal sloshes around and undergoes \"convection\" (kind of like how if you heat a pot of water you can see water rise up, go across the top, then sink back down). As that liquid metal moves around from the convection and other forces, it generates a magnetic field. ",
"But in a Toroid, you don't have the same kind of core. But the way the rotation and the core would be configured would be the answer to your question. But I'm not even sure I \"buy\" this idea that a toroidal planet could exist, let alone how its materials would differentiate from metals to rock. Would they be embedded toroids, a ring of solid metal with a ring of liquid metal around that? Would the metal concentrate on the interior wall? Heck does this proposed toroidal solution even allow for materials of varying densities to exist, or is it only a \"solution\" when the thing is perfectly homogenous...",
"So many unanswered questions that you need to get covered before you could get to the question of its magnetic field."
] |
[
"Well I mean hypothetically, If the earth was naturally a torus, and was stable in it's shape at least for a while, Then would the magnetic field cycle radiation down into the center or something? (I love the study of magnetism, but being only 15, I don't know enough about the physics of it.)"
] |
[
"Will endangered animals, if saved from extinction through Human Intervention, face the threat of inbreeding and recessive genes?"
] |
[
false
] | null |
[
"They already do. Tiger populations in Asia, for instance, are extremely fractured because their territories are separated by human development. As a consequence, problems resulting from inbreeding are very common.",
"There's a lot of species that are still doing fine in terms of numbers but are threatened because their population is spread apart and isolated to the detriment of the gene pool."
] |
[
"They're stop gap measures at best really. Animals often don't like to use those.",
"There's wildlife bridges all over my country like that, they're virtually unused. One of them is famous for costing millions and being equipped with camera's and sensors to track the way wildlife use the bridge. In five years time it detected a single hedgehog crossing a bridge big enough for entire herds of deer and boar to cross.",
"They called it the 15 million euro hedgehog."
] |
[
"There are also efforts to deal with habitat separation; one such effort near Los Angeles will allow mountain lions and other wildlife to mingle across the 101 freeway safely, thus opening the gene pool to a greater source of diversity. ",
"https://inhabitat.com/87m-wildlife-bridge-in-california-will-be-a-haven-for-mountain-lions/"
] |
[
"does the amount of tension a wire is under affect its ability to conduct electricity?"
] |
[
false
] |
If so is it only to a minute extent?
|
[
"Yes, mechanical strain affects the resistance of a conductor three ways.",
"\nThe resistance of a wire is (rho)L/A, where rho is the conductivity of the metal, L is length and A is cross-sectional area. If you stretch the wire, L goes up, A goes down, and rho goes up because the molecular bonds are being strained. The effect of rho changing is small in metals, but much larger in semiconductors.",
"\nAll three of these effects, taken together, are why we can measure stress and strain on objects with strain gages -- a subject well worth googling."
] |
[
"same material with the same length and area, but not under tension",
"Well, in order to test that you'd have to have two pieces of wire, one longer and thinner than the other; then stretch the shorter one until their dimensions match. But yes, the stretched one would have a slightly greater resistance because of the effect on molecular bonds."
] |
[
"Putting something under tension changes it’s length and area. You are comparing the same length of material with the same area (pre tension) but at the length and area you have created post tension. ",
"If you compared something under-tension that had the same length and area under tension as the control not under tension you would be comparing two different materials."
] |
[
"Why is the black hole photo so big?"
] |
[
false
] |
[deleted]
|
[
"The photo is taken using a technique called interferometry. The idea here is that you combine radio waves received on opposite sides of the globe to make an interference pattern - some parts of the waves add together, others cancel out. This tells you that the radio waves travelled a slightly different distance to each of your radio telescopes, and you can reverse that to figure out where the radio waves came from, down to extremely high precision. This gives you extremely high resolution.",
"However, you can't just save the image at each site and combine the images. You actually need to record all of the details of all the radio wave you received, and combine all of the radio wave data together to see the interference pattern. This takes a huge amount of data.",
"The higher the frequency, the more time resolution you need to have in the data. This is part of why we can only do this with radio waves (and sub-mm etc), which have long wavelengths and low frequencies. With visible light, the frequency is so fast that we can't record data that fast, and certainly can't store it. Instead, we have to physically combine the beams of light in a machine, which means we are limited to telescopes on a single site, and can't spread them out across the world. But even at radio frequencies, the amount of data is so big that it's more efficient to ship it by boat than over the internet."
] |
[
"Basically yeah - one of the reasons things got delayed for a while was because there was bad weather in the arctic, I believe"
] |
[
"So we're shipping pallets of hard drives around? That's awesome"
] |
[
"In an asymmetric encryption algorithm, can a private key be used to encrypt information with a known outcome to prove that a message came from a trusted source, or would this reveal how to decrypt all messages encrypted with the public key?"
] |
[
false
] | null |
[
"Yes, and it is done all the time. This is what we call 'signing' a message with a private key - take a plaintext message, take the checksum of that message, and encrypt that checksum - a known outcome - with the private key. Any user can then look up the public key, decrypt the cyphertext, take the checksum of the message, and compare them.",
"This is also the basis of cryptocurrency."
] |
[
"And to address the second part of the question: knowing the original message does not compromise the security of a ",
" cryptographic system, but it can definitely help an attacker crack a bad one."
] |
[
"This works with ",
" encryption schemes, for example with RSA. The keys are exchangeable in the sense that there is no difference which one of the keys you declare as the private one and which as the public one. Both can be used to decrypt a message that was encrypted with the other.",
"However, other encryption schemes do not necessarily have that property and cannot be converted into signing algorithms that easily. For example ElGamal (which is often used in combination with elliptic curves) doesn't have this property. The signing algorithm (EC)DSA which is often used in conjuction with ElGamal works differently than the encryption/decryption algorithm."
] |
[
"Are there any \"surefire\" ways to detect a black hole?"
] |
[
false
] |
From what little I know about them, it seems that we usually detect them by observing something else interacting with them. Objects being sucked in and releasing x-rays or seeing an object orbit "something invisible". I've heard about work on gravity wave detectors and even they would depend on a black hole interacting with another large mass. Are there any devices we could potentially put on a spaceship that would guarantee it never accidentally travels into a black hole?
|
[
"Just as an aside, the chances of \"accidentally\" colliding with something in space are very very remote. Space is very big, and collectively, everything in it takes up very little space. Even hitting planet sized objects with our probes takes significant calculations."
] |
[
"Your question seems to come from a fundamental misunderstanding about black holes and/or gravity. Black holes are not giant magical death orbs that swallow up everything around them (well, they kind of are...) and nothing can escape. It is no harder to escape a black hole than it would be a star of equal mass.",
"So why is your question about black holes instead of stellar mass objects in general?",
"Are you talking about fast travel where you would run into one or are you talking about slower travel where you might pass by one and get trapped in its gravity well and fall in?",
"If you are talking about relativistic travel where the ship is (possibly) traveling too fast to detect the gravity through an accelerometer or other method in time to avoid the source then the problem exists for stars as well as black holes. A ship traveling so fast that it doesn't have time to dodge a black hole would have just as much of a problem dodging stars.",
"You might see stuff about \"star maps\" in science fiction, and while it often involves getting around from place to place, it could also involve avoiding stars. As Han Solo says: \"Traveling through hyperspace ain't like dusting crops, boy! Without precise calculations we could fly right through a star, or bounce too close to a supernova and that'd end your trip real quick, wouldn't it.\"",
"If you are talking about slower speeds (less than relativistic) then it's not as much of a problem. We don't want to fall into stars anymore than we do black holes. A \"slow\" moving ship would have an accelerometer (probably many) that could detect gravity nearby gravity sources. So the ship would know something was there. The difference is that if it's a star then the crew/computer will probably see something that is obviously a star well before they are in danger of hitting it. But with a black hole they are still going to see something. The should be able to see an accretion disk or gas jet or gravitational lensing if the black hole is somehow by itself."
] |
[
"It is not functionally equivalent, no. Not when you're close to the event horizon. "
] |
[
"Can commercial airlines fly upside down (loops, rolls, etc)?"
] |
[
false
] |
While flying into Denver today I remembered a strip from Calvin and Hobbes: Calvin--imagining himself a pilot--competes against a rival pilot to land his aircraft first. In one of the final scenes, Calvin "switches on the 'Fasten Seatbelt' light and does a barrel-roll" (or something to the effect). Could this happen IRL on, say, Southwest Airlines flight #4279 with service from Tampa to Denver? Could a pilot roll a plane if necessary? Can a commercial airline perform 'roller coaster-esque' maneuvers such as rolls, loops, etc? (Sorry for a long post! Sorry if repost! Searched and couldn't find anything.)
|
[
"I can't speak for specifically all commercial planes, but here is a video of as well as interview of test pilot Tex Johnson executing a roll in a Boeing 707,",
"\n",
"https://youtu.be/Ra_khhzuFlE"
] |
[
"There's also the most exciting FedEx delivery flight ever, in a DC-10:",
"Tucker pulled the plane into a sudden 15 degree climb, throwing Sanders, Peterson and Calloway out of the cockpit and into the galley. To try to throw Calloway off balance, Tucker then turned the plane into a left roll, almost on its side. This rolled the combatants along the smoke curtain onto the left side of the galley. Eventually, Tucker had rolled the plane onto its back at 140 degrees, while attempting to maintain a visual reference of the environment around him through the windows. Peterson, Sanders and Calloway were then pinned to the ceiling of the plane. Calloway managed reach his hammer hand free and hit Sanders in the head again. Just then, Tucker put the plane into a steep dive. This pushed the combatants back to the seat curtain, but the wings and elevators started to flutter. At this point Tucker could hear the wind rushing against the cockpit windows. At 530 mph, the elevators on the plane became unresponsive due to the disrupted airflow. Tucker realized this was because the throttles were at full power. Releasing his only usable hand to pull back the throttles to idle, he managed to pull the plane out of the dive while it slowed down.",
"Calloway managed to hit Sanders again while the struggle continued. Sanders was losing strength and Peterson was heavily bleeding from a ruptured artery. Sanders managed to grab the hammer out of Calloway's hand and attacked him with it. When the plane was completely level, Tucker reported to Memphis Center, informed them about the attack and requested a vector back to Memphis. He requested an ambulance and \"armed intervention\", meaning he wanted SWAT to storm the plane. When Tucker began to hear the fight increase in the galley, he put the aircraft into a right turn then back to the left.",
"https://en.wikipedia.org/wiki/Federal_Express_Flight_705"
] |
[
"Background for anyone else since I was very confused:",
"Calloway was a disgruntled pilot who intended to kill Sanders, Peterson, and Tucker (The flight Crew) with the hammer and then crash the plane, making it look like an accident so his family could rake in that sweet 2.5 million dollar life insurance policy."
] |
[
"Are lightning bolts fractal?"
] |
[
false
] |
[deleted]
|
[
"and a ",
"gif",
" of lightning in slow motion"
] |
[
"Picture of a guys ",
"lightning strike scar."
] |
[
"Yes",
", lightning is known form patterns consistent with DLA, which are known to be fractals."
] |
[
"What happens if a galaxy is discovered which is estimated to be older than the age of the universe?"
] |
[
false
] | null |
[
"It means there is an interesting scientific problem to work on!"
] |
[
"It may mean the age of the Universe needs to be re-evaluated, or it may mean that there's something fishy about that galaxy which we need to unravel. At this point - and this used to be not the case, up until the past decade or so - there are enough independent directions pointing to the current number for the age of the Universe that a much more conservative approach would be to assume there's something fishy about that galaxy, and indeed that seems to be the case with BX442, which seems to have its unusually developed spiral shape not because it's older than the Universe, but because of a nearby dwarf galaxy that helped shepherd its formation."
] |
[
"There is an error in the measurement, or something very interesting is going on. "
] |
[
"What benefits would the addition of a third eye bring?"
] |
[
false
] |
Thought about this when a bunch of sweat got in one of my eyes while I was pouring a drink. A second eye allows for much better depth perception. Would a third eye just make depth perception even better, have other benefits, or none at all?
|
[
"Eyes (and cameras) are basically devices for taking in a bunch of light, and sorting it out by angle. If you see something in one eye, you know that it's somewhere along a ray starting at your eye and going out in a particular direction, but you don't know where along the ray it is.",
"Adding a second eye gives you another ray, starting in a different place, and pointing in a different direction. The intersection of these rays is a ",
" point in space; there's no more ambiguity.",
"The best way to improve depth perception (I'll be a bit more specific and define \"improve depth perception\" as \"reduce the uncertainty in range\") is to move the eyes further apart.",
"A third camera can improve estimated positions of points in 3D space just by providing an additional measurement, but I don't think this is much of a problem for animals. The main benefit of a third eye would be, as pointed out in ",
", having another spare."
] |
[
"Another possible benefit would be greater range of vision, if they eye was placed around back of the head. "
] |
[
"Are we brushing aside the liabilities as well? More chances for infections*, needs to be protected under the brow and in a socket, caloric cost, potential epileptic trigger, the added brain circuitry to process more visual stimuli and make sense of it (and the cost of that as well), etc. Who knows, but all these speculation based questions often ignore the cost and just focus on potential benefits which seems unfair. ",
"*Up until fairly recently, a bad infection was a death sentence. The less holes a human has then the better."
] |
[
"If Anti-matter annihilates matter, how did anything maintain during the big bang?"
] |
[
false
] |
Wouldn't everything of cancelled each other out?
|
[
"That is an excellent question, and one that scientists don't yet have an answer for. It's called the ",
"Baryon Asymmetry",
" problem, and the only way to explain it is to change the rules that we've designed for the way physics governs the universe (the standard model).",
"My favourite explanation is that there's a whole region of the universe where everything is made of antimatter. I like to think it's split right down the middle. Let's hope the anti-humans on anti-Earth don't want to visit!"
] |
[
"Let's hope the anti-humans on anti-Earth don't want to visit!",
"Feynman warned us about this. Make sure you ",
"offer to shake hands first",
"."
] |
[
"There are problems with all of the proposed explanations, I simply picked the one that seemed the most intuitive."
] |
[
"How does a tunnel boring machine work?"
] |
[
false
] |
They’re huge and flat so I can’t imagine them drilling.
|
[
"The short answer is: that flat surface in the front carries smaller cutting disks, and the whole plate is slowly spinning. ",
"There is a video here (",
"https://thekidshouldseethis.com/post/how-does-a-tunnel-boring-machine-work#:~:text=With%20its%20rotating%20cutting%20wheel,press%20the%20machine%20forward%20continuously.",
") ",
"It explains the whole process, including how the rubble is removed and the tunnel is secured."
] |
[
"Cool thanks"
] |
[
"The link says it's for kids. Is it ok for an adult to see it, too?"
] |
[
"Why are we the only species that \"requires\" toothpaste?"
] |
[
false
] |
what does ask askscience think about modern dentistry? How much is necessary? Are we screwing up evolution?
|
[
"We're also the only species that's doubled its own lifespan."
] |
[
"We don't require toothpaste. Pry open a monkeys mouth and smell it and then you'll find out why we like it though. (Very much how we don't \"need\" shampoo)"
] |
[
"Find a 15 year old dog or cat, and look in its mouth.",
"Chances are, their teeth are a wreck, to the point the animal would have died long ago in the wild.",
"Lots of animals have shortened life spans due in part to bad teeth, and could benefit from better dental care."
] |
[
"When did blood type AB first evolve?"
] |
[
false
] |
Some people say that AB is the most recent and didn’t occur until the 16th Century when group A populations from Europe and group B populations from Asia began to mix. However, it is known that gibbons and humans both have variants for both A and B blood types, and those variants come from a common ancestor that lived 20 million years ago. Then doesn't it mean blood type AB existed at least before 16th century, while AB is just a mixture of A and B? Which one is correct? What is the scholars' mainstream opinion about it now?
|
[
"Do you have citations for each of these positions? Better yet, do you have an understanding of the ABO system?",
"Here's a decent review of blood types:",
"https://relevantgenetics.com/the-genetics-of-blood-types/",
"Then you start a basic search engine query and find human AB typing predates the blog rumor of 16th century stuff:",
"https://www.rhesusnegative.net/staynegative/blood-types-ancient-hebrews/",
"So the real question would be when did the 'B' allele evolve, and how long did it take for that linage to go mate with the 'A' allele population?"
] |
[
"I am wondering if blood type compatibility is always enough when it comes to donations?",
"No.",
"ABO is the most important compatibility factor, and second is Rh factor (rhesus factor, either positive or negative). Beyond that, there are many other antigen groups that may affect the transfusion. ",
"More on the topic"
] |
[
"This is a great read. I am wondering if blood type compatibility is always enough when it comes to donations? I hear about cases such as organ implants were are different measures taken to ensure compatibility. Is that correct?"
] |
[
"Is there a reason we want more alcohol once we are buzzed?"
] |
[
false
] | null |
[
"Without going into the neurochemical side of things (because others have somewhat covered it here, and it's exceptionally dirty when it comes to alcohol - multiple neurotransmitter systems are involved and even the metabolites of alcohol probably have their own effects)... there are significant expectancy effects associated with alcohol. That is, you expect to feel certain things, and therefore you do. The best example of this is when you start drinking you feel far more intoxicated at say 0.075 BAC than at the same level after you have stopped drinking. ",
"To directly answer your question, it'd be a combination of the euphoria produced by dopamine and endorphins reinforcing the behaviour of drinking, and the idea that more is going to be good. Then there's the positive social effects, relaxation of inhibition, conditioned cue responses, and lots more things telling you that it's a positive experience. This is all happening under your consciousness, so unless you kick in that prefrontal cortex and decide that anothery is a bad idea, off you go. ",
"The other thing is that alcohol is generally consumed over time more slowly than many other drugs. Also unlike other drugs, most of us can describe what overdosing feels like, which I'm guessing is the basis for your question. "
] |
[
"Yeah, definitely. If nearly 1% of your blood is alcohol by weight you're not doing so hot."
] |
[
"Yeah, definitely. If nearly 1% of your blood is alcohol by weight you're not doing so hot."
] |
[
"How does the water supply stay sterile after leaving the treatment plant?"
] |
[
false
] |
Over time wouldn’t the pipes supplying my water build up bacteria inside the pipes? how does the water supply, after it’s left the treatment center, stay sterile and clean for consumption? i live in a city where there’s no apparent issue with drinking water from the tap but if i don’t filter my drinking water, am i inadvertently consuming tons of bacteria by drinking it straight from the tap? Understanding when i wash my hands/take a shower i’m shedding dirt and debris, my drain can get pretty gnarly after a few weeks of not cleaning it, so it makes me sick thinking when the last time the pipe coming to my faucet was cleaned, if ever.
|
[
"Not tons, but plenty. That is perfectly normal and safe except for very sick people. ",
"Basically the water has low numbers of bacteria in it when it enters the system at the plant (it is not sterile though) and a lot of clever engineering has gone into the network to make sure the quality stays good until the end. Keeping dirt, people and sewage out of the pipes, right choice of materials, maintaining proper flow, avoiding disturbances of biofilms, dosing of chloride or ozone, lots of careful monitoring, The people at your local water supply are probably happy to tell you more about their network - especially if it is performing well."
] |
[
"There are some, that's why we use UV too. ",
"Chlorine is also not the same as antibiotics. It's a pretty aggressive oxidizer, there's not that much bacteria can actually do to stop it from destroying their molecules. Enough dosage will always kill. It's kind of like asking why humans have evolved disease resistance, but we're still not bullet proof. "
] |
[
"There are some, that's why we use UV too. ",
"Chlorine is also not the same as antibiotics. It's a pretty aggressive oxidizer, there's not that much bacteria can actually do to stop it from destroying their molecules. Enough dosage will always kill. It's kind of like asking why humans have evolved disease resistance, but we're still not bullet proof. "
] |
[
"What's the best way to avoid a tie in this lottery game?"
] |
[
false
] |
We want to host a lottery game as part of an event. They way it was done before was to ask everyone there to choose 12 numbers between 1 and 50, and then to start randomly selecting numbers between 1 and 50. Anyone who hears one of their numbers said has to sit down, and the winner is the one person left. We did this with about 50 people and it worked fine, but we're now going to do with a larger group (over 100), and are worried it is more likely to be a tie. Would increasing the range or the number of choices improve the probability that there's just one winner?
|
[
"Interesting problem! Given n=50 players who each select k=12 numbers from 1 to m=50, then playing the game as you describe, we can compute the exact probability p(n,m,k) that there is a unique winner (i.e., no tie) as",
"p[n_, m_, k_] := Sum[\n n C[m - j, k - 1] (C[m, k] - C[m - j + 1, k])^(n - 1),\n {j, 1, m - k + 1}\n ]/C[m, k]^n\n",
"which evaluates to about 0.836493. ",
"This plot",
" shows the probability as we vary the number of players up to n=200. As you can see, the probability does not decrease much at all; even with n=1000 players, the probability is still about 0.79585 that you will have a unique winner."
] |
[
"Here is an intuitive way to understand this: When the first number is called, on average 12/50 will sit down. When the second number is called, on average 12/49 will sit down (as everyone had their 12 numbers among the 49 not called yet). This leads to a roughly exponential decay initially. With 100 people we reach an expectation value of 2 after 12 numbers, where less than 1/3 sit down each time. The probability that the last two (or last n>2) sit down at the same time is quite low (~1/10 for two people). With 1000 people we reach this point after 18 numbers, the probability to sit down is still ~1/3 and the probability that the last two sit down at the same time is ~1/8.",
"This is working with expectation values so it just gives a rough approximation, but it is reasonably close to the analytic values."
] |
[
"The probability of having a ",
" winner decreases.",
"And although what the top post has is the right way to go about it, i'd expand a little on the intuition behind it: let N be the amount of numbers called out until you have to sit down. N is almost always very small; even N=1 has 24% chance to happen. However, when it is not; it has a long tail - given you're in, say, 1% of luckiest outcomes, you could still be N=10, N=25 or even N=39 (in the absolute luckiest case).",
"But now since we put a lot of people and look for the \"luckiest\" one, this long tail is very good to have: this essentially tells us that our winner has a lot of options to land on, and it's unlikely that two people will both have the same N - because as amount of people (n) increases, the winner's N tends to increase (a bit handwaving here, since N is a random variable on a distribution), but thus probability of achieving that particular N drops, so for any particular person it becomes increasingly difficult to tie a winner."
] |
[
"what could cause a peak at 642nm in an H2 spectrum?"
] |
[
false
] |
I have a hydrogen gas spectrum tube in a spectrum tube power supply. I have one end of a small bundle of fiber optic strands pointed at the spectrum tube, and the other jammed into the cuvette holder area of a PASCO spectrometer, which is communicating with an iPad via Bluetooth. The 656 nm line is supposed to be there, but I have no idea why I have a peak at 642 nm. What could produce that?
|
[
"potentially stupid question, but have you checked the line is not there with the light source turned off? I've noticed a few \"lines\" before in a mini-spectrometer that were just hot pixels. \nOther than that, there a number of lines close to that from regular room lights.."
] |
[
"The value in the source you cite is based on a diagram where n=2 is 3.44 eV below ionization (instead of 3.4) and n=3 is 1.5 eV below ionization (instead of 1.511), meaning that their red photon has 0.051 eV more energy than it should, which is an extra 2.7%. That accounts for why that source states a value of 642nm -- they have some rounding errors. ",
"Even if they were correct, there would only be one red peak, not two -- it'd just be offset. ",
"Unless if I'm missing something there? "
] |
[
"Is caused by the hydrogen as well.... \nEnergy transition from lvl3 to lvl 2.",
"See:\n",
"https://www.siyavula.com/read/science/grade-12/optical-phenomena-and-properties-of-matter/12-optical-phenomena-and-properties-of-matter-03"
] |
[
"What goes down in the body after a hit to the testicles?"
] |
[
false
] | null |
[
"Hi GoAwayAsYouAre thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Human Body"
] |
[
"'Human Body'"
] |
[
"Most \"genetically distant\" human population?"
] |
[
false
] |
Is there one or several human populations that stick out by being significantly different, genetically, from most other human populations? Not just y-haplogroups or whatever but throughout the genome? Is there, for example, a significant difference between the DNA of genetically isolated populations like the Khoisan, the Andamanese and the the Tasmanian Aboriginals, and other less isolated populations? Edit: does anybody know of any data on the genetic distance of the Andamanese, specifically, to other populations?
|
[
"There are genetic differences among all populations, throughout the genome. These correspond nicely to archaeological evidence about human migrations: every time a subset of a population migrates to a new place, it carries only a subset of the population's genetic diversity. This is called a genetic bottleneck. So Africans have extremely high genetic diversity, as they're geographically the closest to the origin of mankind, while East Asians and Native Americans have the lowest diversity as their ancestors migrated the farthest.",
"If you like graphics, ",
"here",
" is a tree showing the relationships between various human populations, and ",
"here",
" is a map of ancient human migrations.",
"EDIT: clarified"
] |
[
"Here's another link you might like, one of the coolest things I've ever found on reddit:",
"An interactive map of 160,000 years of human migration in 3 minutes ",
"EDIT",
"\nBachwasbaroque just provided a ",
"very recent article",
" which basically seems to invalidate the claim that the folks who left Africa stuck to the coast of Arabia. Anyone know more about this?"
] |
[
"I submitted an article about this two years ago: ",
"\"The three primary genetic divisions of humanity are the Hadzabe, the Ju|'hoansi, and everyone else.\"",
"These two African peoples, despite both speaking a click language, are more genetically dissimilar from each other than any other two populations on Earth."
] |
[
"How do surgeons attach a donated piece of liver to a patient's circulatory system when it's \"cut out\" from a living donor?"
] |
[
false
] | null |
[
"Basically, they keep the vessels of the donated piece intact and just sew them to the recipient's vessels. You can see a representation of these vessels at the link. \n",
"https://hospital.uillinois.edu/Images/IGX/LIVERdonorTransplant.jpg"
] |
[
"I believe their liver will regenerate with new vasculature. They won't have as many large diameter vessels as they did before, but the new small vasculature will find a way to regenerate and make connections with the branches of the portal vein, hepatic artery, and hepatic vein that they have left over. "
] |
[
"Interesting! Thanks! :) But won't the donor need those when the liver regenerates?"
] |
[
"Are there any species that, if went extinct, won't upset the ecological balance?"
] |
[
false
] |
It is considered vital for all species of plants and animals to survive, so as to maintain ecological balance. However, are there any species of animals/insects that can go extinct without having a negative impact on the ecosystem. I think mosquitoes would be one, and also house-flies. They seem to serve no purpose at all.
|
[
"It's funny you mention mosquitoes, because Nature published an article on exactly this topic. They concluded that if mosquitoes went extinct then there would only be minor disruption while certain insectivores adjust their diets. Some birds, spiders, and fish would have some trouble initially, but they would probably cope. ",
"One thing they worry about is the mosquitofish, which eats a large number of mosquito larvae and is used as pest control in many places in the world, such as rice paddies. The loss of mosquitoes could negatively affect their populations, and thus effect their natural predators. ",
"Source"
] |
[
"I'm very leery of the SA analysis. Not for tropical environments, mind you, but for arctic ones.",
"In the arctic, the food chain is very short with limited redundancy. Arctic mosquitoes form clouds there, and are a force of nature to contend with. They are almost more part of the weather than of the fauna.",
"Cut ",
" out and you'll be cutting up the food chain of freshwater fish and migratory songbirds in their nesting areas, and affecting them profoundly. ",
"In tropical areas, I've got no idea."
] |
[
"Sure there are. Consider the ",
"Tiburon mariposa lily",
", which I've seen in person. They only bloom for a few weeks a year, there are only a couple thousand of them, and their global range consists of a single hill. ",
"It would be sad if it went extinct, but I suspect any ecological impact would be too small to be measurable.",
"You could find examples of similar flowers and bugs with tiny ranges all over the world."
] |
[
"Tim Ferris just posted this method of draining one's sinuses - is there any biological basis for it?"
] |
[
false
] |
From : Is there any biological basis for this? I'm normally a complete skeptic, but Tim has prided himself on being a bit of a body hacker.
|
[
"What does he think sinuses are?"
] |
[
"Yes, it jostles the vomer bone and can get congested mucous moving again. I've been doing it for the last few years and when I'm really stuffed up it does help a little. ",
"Another trick is to think about a food that makes your mouth water. If you can trick your body into thinking it's hungry enough that the mouth begins to water, the sinuses will run a little bit as well. Also works for kick starting the GI tract..."
] |
[
"I make no assertions either way on the issue, but here is a perfect opportunity to objectively judge one of his assertions rather than ambiguously question his character."
] |
[
"(Quantum Physics) Can we measure matter and energy of atomic and subatomic particles in 0 gravity? If so what has it proven?"
] |
[
false
] |
[deleted]
|
[
"What do you mean by \"zero gravity\". The effect of gravity in any quantum mechanical experiment will be negligible. However, in principle if one managed taking a coherent stream of particles, separating them into two tracks at different heights and then recombining them one would expect an interference effect due to the slightly different gravitational fields. "
] |
[
"Ah, the experiment designed to test the Santa effect. Never before have we been able to mathematically describes Santa's electron spin resonance in trips both up the chimney and down the chimney. "
] |
[
"There was an experiment a few years ago that launched a Bose-Einstein condensate from a catapult up a chimney and back down, so that the gas could expand isotropically without the influence of gravity. You can read the results here: ",
"http://arxiv.org/pdf/1301.5883.pdf"
] |
[
"If an object is fired down at the Earth from a reasonable height at a speed greater than terminal velocity, will it slow down as it descends?"
] |
[
false
] | null |
[
"Yes.",
"Consider the Space Shuttle.",
"It would enter the atmosphere at great speed and as it passed through the atmosphere it would slow down.",
"Given enough time the speed of a falling object will settle on its terminal velocity (which is dependent on a number of factors). ",
"Also be aware terminal velocity changes with the density of the atmosphere. Terminal velocity is faster in the upper atmosphere where the air is less dense and the speed is slower as you get closer to the earth as the air gets more dense."
] |
[
"No it doesn't. If something is exceeding its terminal velocity, and it doesn't break apart, it will slow down. ",
"Terminal velocity factors in weight and surface area. "
] |
[
"One way to think about this is that terminal velocity is reached when the air resistance and gravitational forces balance. The air resistance is greater the faster the object is moving.",
"If the object is moving downwards slower than terminal velocity, it means the gravitational force is greater in size than air resistance, and so the object will speed up to the point where those forces balance, i.e., to the terminal velocity.",
"If the object is moving downwards at greater than terminal velocity, it means the air resistance force -- which points upwards -- is greater in size than the gravitational force, so there is a net force upwards, which slows the object down until the point where the two forces balance, i.e., to the terminal velocity."
] |
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