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[
"How can a super massive black hole have a average density below that of water?"
] |
[
false
] |
Is says , that: It goes on to explain why that is, but I fail to understand the explanation given. Could some of you wiser guys explain it to me...maybe not like I'm five, but kinda... Thx.
|
[
"Because it is very dense in a tiny area, but its effective size is gigantic. So a really small bit of it is extremely dense and the rest of it consists of nothing at all.",
"EDIT: the rest of that paragraph goes on to say that a small increase in mass causes a large increase in the black hole's effective volume. So the more massive it is the less dense it is as a whole, since a little mass makes it much bigger.",
"It's kind of a silly thing to say, really, and not very relevant to anything. It's not like the average density of a black hole has any particular meaning. It's still a very dense object surrounded by an area from which light cannot escape."
] |
[
"The size of a black hole isn't super well defined, but a classical way to look at it is like a uniformly dense sphere whose radius is the Schwartzschild radius. Supermassive black holes have hundreds of million times the mass of the sun and a radius on the order of light-hours. Doing the math does indeed yield a density below water.",
"Taking general relativity into account though, it doesn't really make sense to treat the thing as a uniform sphere."
] |
[
"The Schwarzschild radius is proportional to the mass m of the black hole. If one black hole is twice as massive as another, it's Schwarzschild radius will be twice as large.",
"However, when we calculate density, we divide the mass by the total ",
". Volume is proportional to r",
" . So, m is proportional to r in the numerator and r",
" in the denominator, for a grand total of 1/r",
" . The density falls off as 1/r",
" .\nIf you need a little example with made up numbers:",
"m=10, r=2, volume=(4/3)πr^3=33.5, so density=10/33.5=0.3\n",
"For a mass twice as big, Schwarzschild R is twice as big:",
"m=20, r=4, volume=(4/3)πr^3=268, so then density=20/268=0.07\n",
"Notice how the density has lower for the larger mass. Thus, if a black hole is massive enough, the density will eventually reach below that of water."
] |
[
"How have the nutritional value of crops such a wheat changed over the last 1000 years and why?"
] |
[
false
] | null |
[
"This is nearly impossible to determine considering the chemical makeup of our foods hasn't been studied with modern peculiarity for very long. The history of enrichment and GMO sourcing would be a good start and you can almost rest assured that fortified foods are fortified for a reason. Unless there is a repository of un modified seeds not unlike the plant ark we'll never know as many of the components of these plants degrade, deaminate and deteriorate with exposure to air, water, light and anything else the cosmos throw at it. All in all we're better off now than ever for energy abundance as our foods, while overconsumption is a problem, offer more energy density and nutritional broad spectrum coverage than ever before.",
"MS in exercise science, health and human performance. I teach upper tier nutrition for performance as well as frosh/soph collegiate intro to nutrition courses.",
"A forensic anthropologist or evolutionary biologist might have better info."
] |
[
"We're still deep in the gluten scare sadly. I remember this but am not able to source it right now, care to do the leg work for me?"
] |
[
"No one really knows. Plants haven't been bred for nutrition until very recently. You have to remember that nutrition as we know it is a very modern concept. Vitamins have only been ",
"discovered in the past one hundred years or so",
". ",
"People did figure out that eating certain things could help with certain health problems, like eating citrus and scurvy. But they weren't breeding citrus plants to have higher amounts of Vitamin C because they didn't have any idea of Vitamin C let alone a way to measure it in a given piece of fruit.",
"At the most basic level, plant breeding is based on what will survive in a given area. Modern day plant breeding focuses on things like disease tolerance/resistance, high yields, and how well something will ship.",
"Currently the hot area is ",
"CRISPR",
" - lots of potential there."
] |
[
"Has anyone tested to see if Protons, Neutrons or Electrons (or whatever else) is responsible for gravity?"
] |
[
false
] | null |
[
"Take a google at \"gravitons\""
] |
[
"So. First, if there is such a thing as gravitons, wouldn't it be valuable to find out if it's part of the neutron or proton?",
"Second, I don't buy the gravity is a \"force\" like the other four forces. The other forces decay over time, gravity does not. It remains the same regardless of the age of the particle and is dependent only on mass. ",
"When I press down on a trampoline, I am exerting a force only on a tiny part of that trampoline and the trampoline then propagates that effect without me exerting any force on it. ",
"By the same token, think of space as a massless fabric that collapses at each atom. Let's say it collapses that fabric into a different dimension. Then the fabric of space time is dragged into that hole and is stretched ever so slightly. That stretching propagates through the fabric of space as it is pulled towards every atom (or proton, or neutron, or electron?) and you get enough of them together and it stretches space quite a bit. ",
"But it's not a 'force'. It's just a teeny weenie little tear in space time. "
] |
[
"A graviton is a theoretical fundamental particle -- just like a photon isn't part of a proton, neither is a graviton. Take another look at the wiki. I also recommend taking a look at the FAQ here and searching ",
"/r/askscience",
" for gravity - there are many of descriptions that you can find that may be informative."
] |
[
"Any hope for commercial nuclear fusion of heavier elements?"
] |
[
false
] |
So most efforts are focused on hydrogen fusion (deuterium+tritium) if I understand correctly. What makes us not even consider Carbon+Carbon fusion for example? Is there any chance we might better control that process ?
|
[
"Carbon nuclei have a +6 positive charge.",
"Pushing two +6s together is much harder than pushing two +1s together. The +1s are even easier if they're a bit chonky, so D-T or D-D (deuterium and tritium). These +1s are still right at the very edge of our technology, though.",
"This difficulty is known as the Coulomb barrier, and it's conceptually identical to pushing two similar magnetic poles together against their repulsion. You're asking \"What if we make the magnets stronger?\""
] |
[
"Muon-catalyzed fusion isn't currently viable because you have to put more energy into creating the muons than you get from the fusion reactions that occur before the muons decay. And even if you're using muons, the coulomb barrier is lower for lower-Z elements."
] |
[
"The reactions rate for fusion of two isotopes is proportional to the reaction's cross section.",
"You can see common fusion reactions cross sections plotted ",
"here",
".",
"Essentially, anything not on this plot is not considered viable as the reaction rates (cross section) is simply too low. And even more-so, I would argue that deuterium+tritium fusion is the only true viable reaction with current technology.",
"",
"In addition, fusion of these large isotopes would likely require extreme temperatures, and Bremsstrahlung radiation increases with both charge and temperature, so you would also increasing your loses due to radiation significantly while decreasing your fusion reaction rate when attempting fusion of heavy elements."
] |
[
"Why do so many prescription meds have a side effect of \"suicidal thoughts\"?"
] |
[
false
] | null |
[
"It's becoming more common knowledge among psychiatric circles that dopamine's role in depression may have less to do with mood regulation, and more to do with motivation, as discussed ",
"here",
". ",
"Studies with rats",
" indicate that varying levels of dopaminergic action affect reward motivated behavior, and another study (which I am unable to find, for some reason) interviewed both psychologically \"typical\" individuals and individuals with depression who interact with friends, concluding that individuals with depression reported enjoying activity with friends just as much as control subjects, but lacked the desire to seek out the interaction on their own. Because so many antidepressants affect dopaminergic action, whether directly, or by secondary inhibition (in the case of SSRIs), increasing available dopamine may generate higher levels of motivation, without a corresponding increase in mood, which is why suicidality is highest within the first 14 to 21 days after beginning antidepressant therapy. Interestingly enough, we've been seeing in the last few years that ",
"ketamine",
" virtually eliminates this two to three week latency period, as it increases mood within hours of administration, with effects that appear to be incredibly long lasting."
] |
[
"It's becoming more common knowledge among psychiatric circles that dopamine's role in depression may have less to do with mood regulation, and more to do with motivation, as discussed ",
"here",
". ",
"Studies with rats",
" indicate that varying levels of dopaminergic action affect reward motivated behavior, and another study (which I am unable to find, for some reason) interviewed both psychologically \"typical\" individuals and individuals with depression who interact with friends, concluding that individuals with depression reported enjoying activity with friends just as much as control subjects, but lacked the desire to seek out the interaction on their own. Because so many antidepressants affect dopaminergic action, whether directly, or by secondary inhibition (in the case of SSRIs), increasing available dopamine may generate higher levels of motivation, without a corresponding increase in mood, which is why suicidality is highest within the first 14 to 21 days after beginning antidepressant therapy. Interestingly enough, we've been seeing in the last few years that ",
"ketamine",
" virtually eliminates this two to three week latency period, as it increases mood within hours of administration, with effects that appear to be incredibly long lasting."
] |
[
"It's becoming more common knowledge among psychiatric circles that dopamine's role in depression may have less to do with mood regulation, and more to do with motivation, as discussed ",
"here",
". ",
"Studies with rats",
" indicate that varying levels of dopaminergic action affect reward motivated behavior, and another study (which I am unable to find, for some reason) interviewed both psychologically \"typical\" individuals and individuals with depression who interact with friends, concluding that individuals with depression reported enjoying activity with friends just as much as control subjects, but lacked the desire to seek out the interaction on their own. Because so many antidepressants affect dopaminergic action, whether directly, or by secondary inhibition (in the case of SSRIs), increasing available dopamine may generate higher levels of motivation, without a corresponding increase in mood, which is why suicidality is highest within the first 14 to 21 days after beginning antidepressant therapy. Interestingly enough, we've been seeing in the last few years that ",
"ketamine",
" virtually eliminates this two to three week latency period, as it increases mood within hours of administration, with effects that appear to be incredibly long lasting."
] |
[
"Once land has become a desert (e.g. Sahara Desert or Gobi Desert) is there a way to revert it back to usable land?"
] |
[
false
] |
So I know due to climate change and other factors our deserts are growing. When I googled this subject I could only find information on stoping the spread of deserts. I could not find any information on if land that was previously desert could be fully reformed and use for something like farming or even if a forest could thrive in that area.
|
[
"My understanding is that the ability to un-desert an area is dependent on why it’s a desert to begin with. ",
"The Great Plains of North America were called “The Dust Bowl” in the 1930’s because it had become a desert. Changes in agriculture practices have reversed the desertification and the area is now the bread basket of the US. ",
"The Sahara desert in the northern part of Africa started kinda the same way as the Dust Bowl, over-grazing, etc, and might be possible to reverse by human intervention, but maybe not and would take an unbelievable about of effort to even try to accomplish. ",
"The deserts of Antarctica are pretty much just stuck that way until the continent drifts to a new location relative to everything else on the surface. Polar ice cap melting is such a problem because the poles don’t actually get all that much precipitation. There are polar ice caps because what little does fall sticks around for thousands of years. Warm it up a bit and there’s still very little precipitation, but now the water doesn’t stick around anymore."
] |
[
"Ecologically/geographically, deserts are ",
" by precipitation. Less than 250mm in a year, it's a desert. More, and it isn't. Plant life tends to follow precipitation very closely. If there's more rain, you get more grasses and shrubs growing. When you hear talk about desertification and reversing it, people are generally talking about the health of plant communities in semiarid regions bordering on deserts. The plant communities are often more vulnerable to grazing and plowing and too much of either can destroy them even if rainfall doesn't change. Climate change causes more literal desertification when rainfall levels drop (likely in the American Southwest), but will also increase rainfall in some places (I have seen models forcasting increases in the middle East). ",
"When deserts go away plants basically just grow on top of them, with a succession of plants colonizing bare ground and sand and rock and producing better soil which other species colonize."
] |
[
"Hypothetically yes.",
"Realistically not with our current technology.",
"Deserts exist in places where water doesn't reach (commonly).",
"There are a lot of ways this can happen, rain shadows, cold (and thus not able to host moisture) air moving from high altitudes towards the poles, areas where the warm moist air from the sea circulates close to shore and leaves more inland areas dry, and a few other causes.",
"Given that we know the causes, it's rather possible (at least hypothetically) to change them.",
"In the case of rain shadows, removing the mountain range. In the case of close circulation, moving certain mt ranges would change the wind patterns significantly.",
"Most other causes have similarly absurd solutions.",
"Basically, we know what causes a desert, and we can fix it (hypothetically at least), but we have nowhere close to the technology required to do so."
] |
[
"Does a magnet stuck to a fridge become less powerful over time? What if I keep taking it off and putting it on the fridge?"
] |
[
false
] |
Do magnets ever degrade? Edit: If they do degrade then what is happening to make them degrade (at an atomic level).
|
[
"In short, yes, they'll slowly degrade over time. Very slowly, and for multiple reasons. There are quite a few factors that would control the loss rate of magnetic strength, but essentially the ",
"magnetic domains",
" will slowly become unaligned at an extremely slow rate. Today's \"hard\" permanent magnets lose strength somewhere on the order of 0.1% over the course of a decade or so. Other \"soft\" magnets, the kind you wouldn't put on the refrigerator, will lose magnetic strength a little quicker, but I don't even have a guess on that time frame. I'd assume it would vary quite a bit with something called the coercivity of the magnet.",
"Now I'm curious as to whether the magnet will lose its strength faster by being stuck to the refrigerator, or if left on a wooden counter top. I would think it would lose strength faster on the counter top, since there is nothing to encourage the magnet to keep its domains aligned, but I've never thought about this until now.",
"But anyway, increasing temperature in the room the magnet is sitting in will shorten the time it takes to degrade. This can be explained simply with energies: the hotter the magnet, the more thermal energy, and therefore the greater the chance that thermal energy will randomly misalign one of the magnetic domains.",
"At the (sub)atomic level, the individual electrons will keep their intrinsic magnetic properties. It is only the whole of the magnet that will lose its magnet strength extremely slowly over time. The magnetism of the entire magnet is generally a reversible process. If we have a magnet that somehow lost strength, we could theoretically restore it by putting it in a strong magnetic field.",
"But this talk was under the assumption that the physical material itself kept intact. That is, I talked about the magnetic domains misaligning, but what about the atomic structure itself? That also would change very slowly over time, which also depends on temperature and other factors in the environment such as acidity. Atoms will move due to atomic dislocation, and lots of stuff happens along the grain boundaries of the lattice, and lots of magnetic domains will be affected at those grain boundaries as well (the magnetic domains don't cross the grain boundaries, they ride along them). If the material degrades mechanically, it will also degrade magnetically to some extent. This will depend on the quality of the magnet material, for lack of better words. Of course, this is also nothing but a thermal event, right? Atomic movement comes from thermal energy in each of the atoms, so really, thermal energy is our enemy.",
" At very, very low temperatures, it is my assumption that the magnet will not appreciably lose magnetism over time. I'm also curious to know whether or not we could take a magnet to 0.1K and see if it loses magnetic strength over time. Basically, I'm wondering if they'd fail for some other quantum reason. My guess would be no, but that would be a very ",
" layman guess.",
"Some people think if they take two magnets and put both of their North poles together (so they repel), that they'll ruin the magnets. They think the energy of the magnets will get spent up faster. That's not really the case, as it will be your fingers, hands and arms that will be supplying that energy in order to keep the magnets where they are. The magnetic fields themselves are quite efficient. "
] |
[
"Wait, what?"
] |
[
"Wait, what?"
] |
[
"Can a gun put a bullet into orbit on the moon?"
] |
[
false
] |
I'm just curious, if I shot a gun on the moon could the bullet go into orbit around the moon? Also, if it could, is it possible for the orbit to be so low that there would be cause for concern that the bullet could travel around the moon and hit the person that shot it? (if they dont move) Science needs to answer this so we will be prepared for the future moon war.
|
[
"Better use a railgun"
] |
[
"\"Yes\" to the first question, and \"kind of\" to the second. A bullet will only maintain a circular orbit around the moon if the velocity of the bullet and your height above the center of the moon obey a certain relationship. In reality, the precision with which you would need to know the velocity and height would be ridiculous if you wanted to hit a target as small a person. Below I show the kind of calculations you would need to do. (I am operating under the assumption that the person with the gun can float at the distance of his/her choice from the moon, i.e. they are not on the surface.)",
"From the kinematics of a circular orbit:",
"accel. = v",
" / r",
"But from Newton's model of gravitational attraction:",
"accel. = M_moon * G / r",
"Combining:",
"v",
" / r = M_moon * G / r",
"The muzzle velocity, mass of the moon, and G are all givens. M_moon = 7.36 * 10",
" kg, G = 6.67300 * 10",
" m",
" kg",
" s",
"r_stableorbit = M_moon * G / v",
"Using the equation above, you can plug in your muzzle velocity to determine how high above the center of the moon you need to be. If your bullet travels at 1000 m/s, then you need to be 4,909 km up. If you are lower, the bullet will eventually hit the ground. If you are higher, the bullet will not follow a circular orbit."
] |
[
"That's a common misconception. True, there's no oxygen, but what's truly necessary is an oxidizer, not necessarily oxygen. Gunpowder comes with its own oxidizer (Potassium Nitrate, or saltpeter), and therefore a gun could be fired in space..."
] |
[
"How does elevation affect the pressure inside a soccer ball?"
] |
[
false
] |
A football referee here, needing help understanding a rule concerning a football's pressure. The text states the ball (is) of a pressure equal to 0.6 - 1.1 atmosphere (600 - 1,100g/cm2) at sea level (8.5lbs/sq in - 15.6 lbs/sq in) Basically looking for someone to break down the aforementioned rule into "Lehman terms." Also how does this rule change, - if at all - for someone living at an elevation of 645m?
|
[
"Do you mean layman's terms?",
"The figure that matters is ",
" air pressure - how much higher is the air pressure inside the football than the air pressure outside, and the gauges used to measure ball pressure should already be measuring that. You should just be able to pump up the ball, and then test it with the pressure gauge. If the gauge is calibrated in PSI, you want 8.5 to 15.6. If it's calibrated in atmospheres you want 0.6-1.1."
] |
[
"Yes, layman's terms, thank you. ",
"Just so I really understand, would a completely deflated ball have a atmosphere or PSI of 0? That is, the pressure inside the ball is equal to the pressure outside the ball? "
] |
[
"We need to distinguish between absolute pressure (which is the difference relative to vacuum) and relative pressure (the difference relative to the outside of the ball).",
"At 0 PSI relative pressure, the pressure inside and outside the ball are the same. That should happen with a 'flat ball', even one that isn't deflated enough to look like a giant pasta shell.",
"e.g. these balls are probably at close to 0 PSI relative.\n",
"https://www.bostonglobe.com/sports/2015/07/26/footballs/GBfXQAzFzbqh8gCwUHADTO/story.html"
] |
[
"Is it actually possible to reconstruct what a person sees by reading their brain waves?"
] |
[
false
] |
This sounds really cool, but I am somewhat skeptical. How do brain waves carry enough information as to allow reconstruction of entire images? Do these scientists work in ultra controlled environments where they basically already know certain wave patterns correspond to certain images? Or do they actually manage to this calibre of information from brain waves? I thought a big problem with interfacing our biological brains with digital technology was the fact that information is not necessarily stored in each person's brain in an objective manner, i.e. there is no universal brain pattern for "cat" or "dog". I'm a little confused, anyone care to shed some light on this awesome but skeptical technology? Thanks!
|
[
"NO!",
"It's hugely misleading. There have done two separate experiments, and are presenting them side-by-side in a very misleading manner.",
"Experiment 1:",
"Show a bunch of people some different videos, 5 different categories and analzye their brain activity. Create a classifier that can predict which video category they are watching.",
"Experiment 2:",
"Create an algorithm that creates pictures of a certain category.",
"Final Part:",
"Take the brain data, have an algorithm select the category, and then create a picture from that category.",
"",
"They then played these two side by side, as if the AI-created footage was reconstructed from the brain activity. It was not. If you fed it chicken mcnuggets, it would still create a similiar picture. For example, look at 3:09 in the video. A face is shown, and the 'reconstruction' is another very specific face, which looks NOTHING like the picture. The algorithm selected the 'face' category, and then created a random face picture."
] |
[
"I agree the paper itself is not misleading. Just the video on its own gives the impression that it's converting the brain activity into images, which is not true and is misleading.",
"Science is great, and comes with many caveats, which is described in the papers. But when videos like these are released, and seen by many without context, a lot of people get misled."
] |
[
"They are describing the principle of operation in the paper:",
"“The 20-dimensional EEG feature vector obtained after dimension reduction stage (see “Feature extraction and classification” section above) is mapped into the latent space of a pre-trained image autoencoder, which is capable of reconstructing natural images of several pre-learnt categories. An image decoding model is independent of any neurophysiological data and can be trained beforehand considering just a set of stimuli images”",
"That’s not misleading tbh, and they don’t hide the fact that there are two networks. The whole concept is interesting and straightforward, I don’t really see the problem (I’m referring to the latest version of the paper on arxiv)",
"And as to the different face, read description under the image, they are referring to copyright of the original image"
] |
[
"Getting struck by lightning numerous times."
] |
[
false
] |
I've heard that when a person (or thing) gets struck by lightning, their chances of getting struck numerous times thereafter increase. Is this true? If so, why?
|
[
"It is possible that rather than increasing someone's chance of being hit by lightning, the first strike identifies people who are more likely to be in situations where one would be struck by lightning. That is, if we didn't know anything about someone, our expectation that they will be struck by lightning would be the total number of lightning strikes divide by the total number of people. ",
"If we know that some person spends every day perched on top of a steeple, we might estimate their chance of being hit as the number of people struck while on a steeple / the total number of people who spend their days perched on steeples, which will likely be higher.",
"Being struck by lightning gives us some information (probabilistically speaking) about the victim; we don't know for sure that they were doing something risky, but they're more likely to be from a group of people that are struck more often."
] |
[
"As far as physics is concerned, there is no reason for their chances to increase of getting struck multiple times. If anything it would decrease because they would take cover during a thunderstorm. One assumes that they would want to avoid getting hit by lightning a second time, as it is quite painful."
] |
[
"Super-zap is referring to only the few milliseconds following the first strike. After that, the air would have mixed enough to return to its previous conductivity."
] |
[
"How exactly is memory stored in our brain?"
] |
[
false
] |
I mean like I know it is stored in specific areas of the brain but at the molecular level,how does it "stay"?
|
[
"Memories, as far as we know, are not stored on a molecular level. They are stored as patterns in neuron arrangements. Human memory is actually incredibly different from what you're probably used to - computer memory."
] |
[
"To put it succinctly, the latest and most supported theory is that your brain stories memories in the connections (called synapses) between your neurons. There's a principle developed by neuroscientist Donald Hebb that goes \"what fires together wires together.\" This means that if two neurons that are connected to each other activate at the same time, the connection between them will grow stronger the more they fire together. Conversely, if these two neurons didn't fire together, their connection would weaken. This phenomenon, and the molecular changes that underlie it, is considered the basis for memory in the brain.",
"One example of this \"wire together, fire together\" phenomenon is in our vision. If someone put an eye patch on one of your eyes when you were born and left it there for the first few years, you'd be permanently blind in that eye, even after the patch comes off. This is because the neurons that take visual information from the outside world and send it to the networks in your brain to be interpreted would be dormant: with the eye patch on, they wouldn't be firing at all, so the neurons they're connected to wouldn't be firing along with them. This would cause these connections to weaken, so when you take the patch off, you won't be able to see through that eye. Your brain \"remembers\" that you can't see through that eye.",
"Another example is with your motor function. If, instead of putting an eye patch on when you were born, someone tied one of your thumbs to your hand. Like the eye patch turned off visual stimulation to your brain, causing the connections with deeper sensory networks to weaken, turning off the motor function of your thumb would cause the connections to the deeper motor networks in your brain to weaken, and your thumb would never work properly.",
"These are just two examples of the many, many, ways your brain changes all the time. Your brain \"remembers\" and \"forgets\" things based on your experiences to refine the networks in your brain to (ideally) make it fit your environment better and make you a more functional person."
] |
[
"Thanks to visual representations (we are not aware of), it is stored as individual \"images\", but not what we actually see.",
"\nIt is an overall form of an object, which is very simplified. The weight of a single memory (object/s) is clasified by its value it represents. Values are building rocks of memory, from the first time we started associating as kids, to this day."
] |
[
"Should I still get the COVID vaccine if I’ve already had COVID?"
] |
[
false
] |
If the purpose of a vaccine is to stimulate antibodies as if you were exposed to the disease that you’re being vaccinated for, then why should people who have already had COVID still get the vaccine?
|
[
"The CDC has ",
"Frequently Asked Questions about COVID-19 Vaccination",
". They say:",
"Yes, you should be vaccinated regardless of whether you already had COVID-19. That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19. ",
"There's also a somewhat more technical page at ",
"Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States",
", where they say",
"Data from clinical trials indicate that mRNA COVID-19 vaccines can safely be given to persons with evidence of a prior SARS-CoV-2 infection. Vaccination should be offered to persons regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection. ...Vaccination of persons with known current SARS-CoV-2 infection should be deferred until the person has recovered from the acute illness (if the person had symptoms) ...While there is no recommended minimum interval between infection and vaccination, current evidence suggests that the risk of SARS-CoV-2 reinfection is low in the months after initial infection but may increase with time due to waning immunity. Thus, ",
", persons with recent documented acute SARS-CoV-2 infection may choose to temporarily delay vaccination, if desired, recognizing that the risk of reinfection, and therefore the need for vaccination, might increase with time following initial infection.",
"As that last part suggests, the concern really isn't that infection won't lead to immunity -- scientists are confident that after you're infected, you're immune. The problem is that infection leads to ",
" immunity. A mild or asymptomatic infection still leads to immunity, but it's often much lower than after a more severe case of COVID; and even severe cases might not give a strong, ",
" response in everyone. By comparison, the vaccines ",
" drive immunity to at least the highest level seen after most infections. So if you're infected, you're very likely protected for some time, but you won't know how long you're protected for. The vaccines all show every sign of giving good, consistent protection that will last for years."
] |
[
"Please explain this to me because I don’t understand. Your body doesn’t constantly produce every type of antibody it’s ever made. So why would this vaccine be any different than say a polio vaccine? It’s not like your body has been consistently making polio antibodies since your vaccine, yet we don’t worry about how the length of that immunity.",
"And as for the severity of the covid case, what do they do to the vaccine that drives a higher level of immunity? As far as I know vaccines are either dead versions, a weakened version, or a piece of the virus. So how is this vaccine which isn’t as high of a dose as a severe infection going to “drive” a higher level of immunity?"
] |
[
"Because you're being lied to. Vaccines produce a response in your body that mimics fighting the real virus. When you have a real virus your body has the same response."
] |
[
"Is it possible that dark matter and dark energy are just misconceptions?"
] |
[
false
] |
I only have a layman's understanding of cosmology, but this is something I've been wondering about. I've heard that maybe WE THINK that the universe's expansion is accelerating because our local cluster is flowing like a river(dark flow) to some point in space, therefore skews our perceptions of the speed of expansion. As for dark matter, is it possible that our models of gravity just need to be modified? Maybe we don't understand some of our fundamental laws as well as we think? I've been trying to get a primer with wikipedia, but there seems to be glaring holes in our understanding of the universe. EDIT: Stumbled on this very relevant article today:
|
[
"Dark energy and dark matter are ",
" results. They're called dark because we can't see them directly, we only see hints of them. There is no theory that explains either of these results, so it's clear that we don't understand some of our fundamental laws as well as we think we do. ",
" modification to ",
" physical law you can think of that explains these observational results, and is consistent with with our current knowledge, is valid. We refer to them as energy and matter because observationally that's what they look like, and we have to call them something."
] |
[
"As with most really deep questions, the answer is both yes and no. Yes, there could be another theory that isn't Einsteinian general relativity (i.e. that evolves differently on large scales, or something) that doesn't require the dark matter / dark energy tweaks on the cosmological scale. But that theory would have to reduce to general relativity in all the cases that have been empirically tested, or else it would be falsified by those cases. And, since Einsteinian general relativity works so well within its domain, we might even keep using it, and referring to those perturbations (that are present in the new theory) as \"dark energy\" and \"dark matter\". Which is the \"No\" part of the answer.",
"This idea -- of holding on to a useful description even if the underlying theory changes -- happens all the time in physics and astronomy. We still use Newton's laws and talk about gravity as if it were a spooky action at a distance, even though we really know that gravity works differently (Newton's laws aren't Lorentz-invariant, for one thing). ",
"As an extreme example, Ptolemaic epicycles went out of fashion with kepler, but some planetary folks down the hall from me still use them in their cutting edge planetary dynamics work, because epicycles are a useful way to describe perturbations in a planet's orbit."
] |
[
"Yes, it is possible that our understanding of gravity is wrong. ",
"However, \"maybe there are more neutrino-like particles we haven't discovered, yet\" is a much more reasonable claim than \"I have disproved Relativity\"."
] |
[
"Why does holding something close to my eye put things into focus around its edges?"
] |
[
false
] |
Sorry, this is hard to explain but if I'm looking at something closely so that it's blurry (particularly under 6" or so) and then put my thumb right in front of my eye, the thing I'm looking at comes into focus around the edges of my thumb. One interest effect is that light appears to "bend" towards my thumb. I'm thinking this might be like the effect that you get when a camera appears to zoom in and out when focusing. For example, if I look at a vertical line on my computer monitor very closely so that it goes out of focus, then put my thumb in front of my eye so that it almost blocks the line, it actually appears to bend the line toward my thumb as it comes into focus. I drew this lame diagram to help explain:
|
[
"I don't want to answer in reply to brolix, but I am not 100% sure what is happening since I am unable to reproduce the issue you are discussing. I am guessing it might have something to do with something like the ",
"knife-edge effect",
". Optical properties change around edges of things, especially things that are radiating heat, so it is possible to be any number of things, assuming that it isn't just simply your eye re-focusing."
] |
[
"You are seeing the effect of ",
"stopping down",
" the biological camera that is your eye. ",
"The eye works by focusing light that enters your iris onto your retina. That is to say, light that leaves a particular place on the object you're observing should all land on the same place on your retina, regardless of where it passed through the iris. The required focal properties of your eye's lens depend on the distance between the eye and the object you're viewing. Normally, your subconscious vision system autofocuses the lens without your conscious control -- but you can see it working by shifting attention from object to object.",
"When an object appears out of focus, that is because you eye's focusing optics aren't working correctly for that particular object: light that leaves a particular place on the object lands on slightly different parts of your retina, depending on where it passed through your iris. Placing a sharply defined blocker (like your thumb) between your eye and the object of interest blocks many of the rays that would otherwise pass through your iris. That shrinks the area of your retina that is illuminated by each little part of the object, which makes the focus look sharper.",
"The bending you describe in the linked images is a result of blocking out particular parts of the optical ray bundle that is entering your eye, which shifts the apparent centroid of the bundle: if you block out (say) all the rays on the right side of the bundle, the whole object will appear to shift left a bit. Depending on the direction of the apparent bending, your eye is either overfocusing or underfocusing. If the object bends ",
" the thumb in the geometry you describe, you are focused behind the object (acting farsighted). If the object bends ",
" from the thumb, you are focused ahead of the object (acting nearsighted). ",
"Stopping down the aperture works great for sharpening up an image, at the cost of losing illumination -- less light from the object actually enters the eye, so the image looks fainter/darker. ",
"If you notice this effect all the time (without consciously defocusing your eyes), it probably means you need glasses: normally your eye should be able to find and lock onto focus of whatever object you pay attention to. Optometrists have equipment to measure the basic corrections needed to make a clear image on your retina; and they prescribe lenses that make those corrections."
] |
[
"This is not true. Gravity is not strong enough on such a small scale to have any such effect."
] |
[
"How can I demonstrate the relationship between the work done on a spring and the change in potential energy stored by the spring?"
] |
[
false
] | null |
[
"Hi Theuniversal82 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.",
" ",
" "
] |
[
"Physics"
] |
[
"Physics"
] |
[
"Physics thought experiment question re: gravity"
] |
[
false
] |
I have a thought experiment I first made up when I was a teenager, and occasionally returned to, but I realized recently there are one or two things I don't know how to answer for myself. The thought experiment is this: If you imagine a perfectly spherical solid planet, let's assume earth like density, and you remove an arbitrary small "slice" off of one spot on the sphere, let's say 1/100 of the diameter of the sphere in and discard that slice, so you have a sphere with a "perfectly flat" surface in one area, what would you perceive it's gemoetry to be like while standing at the center of that flat surface? Elsewhere on the sphere I think it's clear you'd perceive the landscape to be "flat" all around you as the gravitatonal attraction at all other points would be equal, but at the center of that slice, where it's "actually flat" you'd be closer to the center of the sphere and gravity would be stronger, and the entire slice would be gravitationally attracted to that spot closest to the center right? But what shape would it "feel" like it had, gravitationally? My initial assumption was you'd feel you were at the bottom of a bowl, but on rethinking it recently, I realized it might appear to be the bottom point of a cone, or perhaps a parabola? I've used this to explain to people that it's not poetic language when we say mass warps space, but an actual, possible to experience reality, but I'm uncertain which situation is correct. Also, a friend of mine who's a photographer brought up a related question, how dense would the planet have to be to have a noticeable effect on the path that light takes, and would that slice being removed substantially effect light's curvature near the slice?
|
[
"Do you mean something like ",
"this?",
"The gravitational potential on the x-axis V(x) = -GM/sqrt(h",
" + x",
" ), where G is the gravitational constant, M the sphere's mass and h the height from the center of mass. If the maximum value of x is 2R/100, h ≈ R. We can then plot the ",
"gravitational potential.",
"edit. you can see that the difference between the center and the edges is only 0.02%, so you wouldn't even notice it "
] |
[
"It's worth noting that this is just an approximation, since you're treating the planet as a point mass and just looking at the distance from that point."
] |
[
"That is assuming the slice is small compared to the sphere, right?"
] |
[
"What is happening to the air in a Lamina Flow Engine that makes it work?"
] |
[
false
] | null |
[
"I took thermo in college (shortly after the earth cooled), so I should be able to wrap my head around it."
] |
[
"I took thermo in college (shortly after the earth cooled), so I should be able to wrap my head around it."
] |
[
"Lamina seems to be a popular mistake for what should be laminar flow. Thanks."
] |
[
"A laser of a few watts can reach the ISS, how many watts are needed to reach the moon?"
] |
[
false
] |
Also, what kind of math would I need to calculate this?
|
[
"There was a really nice ",
"thread",
" about this many years ago that answers it better than I could. The answer it seems for a laser is a few megawatts.",
"Note that for radar (so radio waves), the Arecibo Observatory has a peak power output of about 2 megawatts (depends on the frequency band). Radar studies can be done of many solar system objects, including other planets, and so the answer for that is it probably takes much less power than a megawatt to reach the moon. But, that's more because radio photons are energy \"cheap\". There's a radar image of the Moon (and Venus) viewable ",
"here",
"."
] |
[
"How dependent is it upon the capability of the receiver? I ask because IIRC Project Starshot wants to send a signal back to Earth from Alpha Centauri ~4 LY with a 1 W signal (crazy small payload on the order of a few grams). But it was going to have some crazy array back on Earth (the same one that accelerates it to 0.2c) that was going to be listening."
] |
[
"I assume you're talking about receiving on the radar side of things since I was mostly talking about transmission? I don't quite understand how they are going to want to do that at the moment. My understanding was that Starshot is not going to do the experiment but rather be the technical feasibility study for seeing how we could hypothetically do it. So that'd probably be on the table. However, I don't really see how we're going to be able to see a signal of that power at the moment."
] |
[
"Is electrical reactance strictly an AC power concept?"
] |
[
false
] |
Is it applicable to a DC power circuit with a step, or sine input? I am interested in a RLC series circuit with DC power, being applied a ramp input specifically. It is on a breadboard. The ramp is varied from 2-3 msec. Do I need to do these type of calcuations: ?
|
[
"Thanks for the link! Example 2 is basically what I need to do. I am familiar with basic derivative/integral type stuff (16 years old), but have never used fourier series. It seems like I can just replace the interval [-1,1] with my interval t = [0,2.4msec] or use the data points from my DAQ as n = [0, 130]. What does the 'n' used in figure 2 of that link represent? The number of terms in the fourier series? Would that be equal to the same number of data points in my voltage vector?",
"So basically we have some initial term (a0) and then pairs of cosine(an) and sine(bn) terms? That is similar to the underdamped equation for voltage in series RLC here - ",
"http://en.wikipedia.org/wiki/RLC_series_circuit#Underdamped_Response",
"."
] |
[
"Without worrying about the details of your setup, any periodic function (like your ramp input) can be expressed as a sum of sines and cosines via the fourier series. Just find the fourier coefficients, treat each term as if it was a separate AC input and find the resulting output, and sum the output of each frequency (weighted by the fourier coefficients) to get the circuit output.",
"edit: this assumes all the electrical components are linear- resistors, capacitors, inductors. If you're using nonlinear electronics this approach will not work."
] |
[
"How can I express the input in terms of fourier series specifically? I have 2 vectors, time and voltage. It makes a roughly linear ramp from 0-5V, and takes approx 2 msec to reach the full 5V. ",
"Is there someplace online I can read more about what you have mentioned here above?"
] |
[
"Question on how separation of a bound quark generates new quarks, rather than an isolated quark?"
] |
[
false
] |
It is believed that if one quark was somehow pulled out away from a particle such as a proton, color confinement says the energy of the binding would become so great that it generates a new quark/anti-quark pair -- one to replace the removed one, and one to be bound to the removed quark, thus preventing an isolated quark. My question is this: with all the energy building up as the quark's separation distance increases, how does that energy "know" to produce just the right pair of new particles to allow the removed quark to separate out into a new quark pair? Why doesn't that increasing energy produce other particles along the way, throwing out a lepton pair here, a neutrino there, and so on. Why does it "wait" until the energy is just right, and then produce the exact right colored quark/anti-quark pair to make a new meson or what have you, which can fly off, happily ever after? It seems like in particle accelerator collisions, it's just a randomish spray of particles from the high energy gloop. How does confinement get it exactly right on the first try?
|
[
"Why doesn't that increasing energy produce other particles along the way, throwing out a lepton pair here, a neutrino there, and so on",
"There is not enough energy to create leptons or neutrinos without also balancing out the quarks. If you want to use the system's potential energy to create particles, you have to ",
" the potential energy of the system, otherwise you've gotten energy for free. If have two isolated quarks and you then create a lepton, you ",
", so there is still a large potential energy in the configuration. If you want to spend energy to create particles you have to actually ",
" it, and the only way to spend it is to balance out the colour charges."
] |
[
"The strong force (color/gluons) only interacts with other quarks. So when two quarks are separated, the \"strong/color\" force is increasing--it is that force/energy the creates the quark/anti-quark pair. Because only quarks carry color charge, only quarks will be produced by the increase in color force.",
"Color force/strong force is a bit different in that it gets stronger as you separate the charges, but the reason you can produce leptons and quarks from particle/antiparticle collisions is that eletcromangetic and weak forces affect both classes of particles (leptons, quarks) while strong force only produces effects on quarks.",
"Also as to that \"goop\" you refer to in collisions, a lot of effort goes into sorting through the collisions to find the right one--there is a lot of noise precisely because one gets a lot of junk coming out of collisions. Part of detector design is deciding whether or not to record an event for analysis as accelerators produce a ton of data. Multiple collisions per second (looked it up and according to the LHC, they have 600,000,000 collisions per second). ",
"source"
] |
[
"It's not that the energy ",
" to be spend to bind the isolated quarks, it's just that ",
". You might be thinking that when you pull two quarks apart there's this big pile of energy that you can just use, but that's not how it works. The energy when you pull quarks apart is ",
" energy, so it only makes sense to compare differences. You only get the energy out of the configuration if you move to a configuration with less potential energy. Adding a lepton does not change the potential energy of the quarks, so you don't get to use it to make the lepton. You can only get energy out of the situation by moving to a configuration without isolated quarks."
] |
[
"What happens to the space where groundwater is removed?"
] |
[
false
] |
Does it become an empty void in the earth? If civilization is built on top of the groundwater well, could it collapse as a sinkhole?
|
[
"Air takes its place when ground water is removed. the supporting earth around the well must be more than strong enough to withstand the weight of anything on top of it. "
] |
[
"I think you might be thinking of huge underground caverns where ground water is stored. This does occur sometimes, but most of the ground water you'll come across exists in the porous earth - in between the tightly compacted sand, dirt, and rocks. When it's brought out of the ground, either by wells, geological phenomena, plants, or whatever, air moves in to take up its place. The wikipedia article's not bad:",
"http://en.wikipedia.org/wiki/Water_table"
] |
[
"Sinkhole"
] |
[
"Does energy cause motion?"
] |
[
false
] | null |
[
"To cause a motion, you must supply a force to it. Energy, in it's most basic dimensions, is a force x distance. "
] |
[
"Momentum is the generator of translation. ",
"changes in momentum are due to force, which can be due to some potential or force mediating particle."
] |
[
"The ",
" of energy from one thing to another ",
" cause motion. For example, when two bodies collide, one will transfer kinetic energy to the other, which can cause it to move. But transfer of energy does not ",
" to result in motion. For example, if you run an electric current through a wire, some of the energy is transferred to the wire in the form of heat (which it then conducts or radiates away, typically)."
] |
[
"Do all fundamental quantum field theories have to be gauge theories?"
] |
[
false
] |
To what extent is gauge symmetry a requirement? Related Question: Do any known ways exist that describe the same physics in QED using some other mathematical apparatus which doesn't have the U(1) gauge group in it?
|
[
"This is going to get technical, but to add to the other good answers: there is no way to imbed a massless spin-1 particle into a four-vector field without including gauge redundancy. I use the word redundancy rather than symmetry here (see also ",
"/u/squarlox",
"'s response) because it's really forced on you from the math: massless particles only have two independent degrees of freedom (helicity +/-1), while a four-vector with constant magnitude has three. The only way you can keep this consistent is to only consider two of these degrees of freedom physical, and the second just an unphysical gauge choice. So if you want to describe a theory of massless spin-1 particles with a local action (=a Lorentz scalar built out of casual fields), you're forced into gauge theory. So it's not that all fundamental theories need to be gauge theories, but all theories with massless high-spin particles described by a local action.",
"This actually applies to all massless particles with spin>1/2, including the graviton (spin-2). The gauge invariance for the graviton is related to coordinate-invariance in GR."
] |
[
"No, but gauge theories are more predictive, and therefore more useful scientifically. U(1) gauge symmetry ",
" electromagnetism. But of course we could have QED without knowing anything about gauge theory. QED happens to possess U(1) symmetry; there is no way around that. "
] |
[
"For simplicity let me just work at the classical level.",
"Classically, a symmetry is a mapping that takes one solution of the equations of motion into a new solution. By a solution of the equations of motion, I mean a complete prediction for all the observable quantities at all times.",
"Gauge symmetries are often said to be \"redundancies of description\". What is meant by this is that they are not really symmetries: they don't change observable quantities, so in a sense they map one solution of the equations of motion into itself. They arise sometimes just in the way that a theory is formulated, if it is formulated in terms of quantities which are only related to the physical observables, instead of the observables themselves. Such formulations can sometimes be simpler in some ways than descriptions using only the observables.",
"So, you could hope that any theory you can describe by a gauge theory also admits a description in terms of observables only. Indeed, this is possible for electrodynamics, and it is simple at the classical level: one can just use Maxwell's equations for the electric and magnetic fields (the physical observables) instead of the vector potential (which is gauge-dependent.)",
"At the quantum level QED can also be formulated in terms of the physical fields, but this is widely regarded as not as useful or as simple as the U(1) gauge theory description."
] |
[
"If electrons act as both particles and waves, what properties in the wave form is oscillating?"
] |
[
false
] |
Is it the energy, velocity, position, mass, existence?
|
[
"The waveforms correspond to probability amplitudes. Electrons behave in such a way that, in most situations, their observable properties like position, momentum, and energy are spread out over many possible values. The exception is that immediately after we make a measurement we know exactly what value the electron has for the property we measured. ",
"The mass of the particle is different: in the standard model, the mass of elementary particles like electrons are constant - they do not vary probabilistically. It's possible that one day our understanding of this will change - either because of more precise measurements, or potential new theories that go beyond the standard model - but for now the electron mass does not seem to oscillate. ",
"As for the property of \"existence\", this can also be probabilistically spread out in quantum theory. In situations where particles can be created and annihilated (such as in high energy particle accelerators), it can make sense to talk about measuring the number of particles in a particular region. There might be some probability of measuring 0 particles, 1 particle, 2 particles, and so on, and in those situations there will be a \"wave form\" to describe that spread out probability. "
] |
[
"I would say that the waveforms are \"field strength\". The reason why this appears to be related to probability is that an interaction is a probabilistic event, which has higher probability for larger field strengths.",
"The electron is an \"electron field\", which is to say that it is a field that displays certain quantum numbers - electric charge -1, weak isospin -1/2, spin 1/2, etc. These quantum numbers describe how the field behaves under certain symmetry transformations (U(1)_EM, SU(2)_W, etc). And symmetry transformations are the origin of interactions, as all quantum mechanical interactions are simply symmetry transformations."
] |
[
"I understand your point, but I'm not so quick to concede ontological primacy to the second quantized (field theoretic) description of quantum phenomena. The electron field is an operator-valued distribution. The terms appearing in the Dirac Lagrangian are creation and annihilation operators, and I would debate that these do not correspond to electrons themselves, but rather that the electrons correspond to the coherent fock states which are acted upon by the electron fields. This description necessarily presupposes the existence of many particles, and to my knowledge it is incapable of describing a system with an exact number of particles. ",
"More philosophically, if we relax the dogma of reductionism and recognize that both the first and second quantized forms of quantum theory are ",
", then Occam's razor clearly identifies ordinary quantum mechanics as the preferred description of a single electron. This, along with wanting to give a \"textbook\" level of explanation, are my reasons for choosing the first quantized description in answering this question."
] |
[
"How badly have CFC's destroyed the ozone layer? Is it getting better or worse? What will the effects be?"
] |
[
false
] | null |
[
"Since the Montreal Protocol, CFCs are no longer in production though it may still be used in limited amounts in old appliances in developing countries. However, it will take time for CFC to disappear from the atmosphere, and it is not certain when the ozone will start recovering.",
"This website",
" has a few diagrams that may illustrate the situation, in particular observations on the amount of ozone with time. If you have library access, ",
"Science",
" has a recent news article on reports of measured recovery.",
"Ozone absorbs UV-B radiation, so a depletion means a higher penetration of that wavelength and thus higher chances of skin cancer. Unfortunately, the recovery of ozone is projected to increase the warming on the surface (see ",
"this",
" and ",
"this",
" -- warning: research articles)."
] |
[
"This",
" is the key graph I think, and it agrees with what I've seen when environmental physicists give colloquiums. It ",
" the ozone layer is recovering, but it's going pretty slowly."
] |
[
"the international reaction to the cfc/ozone problem has been showcased as a success story which gives hope that humanity is able to tackle global environmental problems. ",
"http://www.universetoday.com/27561/ozone-success-story-nasa-video-of-enviro-action-that-worked/"
] |
[
"Is there a meteorite at the bottom of every lunar crater?"
] |
[
false
] | null |
[
"There may be shards of the original impactor found in and around some craters, but a monolithic çhunk of rock is unlikely.",
"The average lunar impact occurs at approximately 15.5 km/s (vs about 18 km at the top of the atmosphere on Earth). With no atmosphere to decelerate, heat, or shock the object, the object's kinetic energy remains undiminished until impact.",
"Impact with the lunar surface produces a shock wave which spreads out from the site of the impact and back through the impactor. The shock wave fractures the rock and excavates a large cavity (much larger than the impactor). The impact sprays material — ejecta — out in all directions. The impactor is shattered into small pieces and may also melt or vaporize.",
"On Earth deceleration, heating and shock begin in the atmosphere which may partially or completely disrupt the impactor before... er, impact. Any surviving fragment, having been slowed, may survive its final impact at the surface."
] |
[
"To compare energy scales a little: At 15.5 km/s, the specific kinetic energy is ~120 MJ/kg, while vaporising initially cold iron should take somewhere around 10 MJ/kg."
] |
[
"Not necessarily. ",
"Meteors are classified into three categories: stony, metal, and stony-metal. Metal being the most sturdy and likely to survive an impact.",
"Besides composition the other large factor is speed, no matter what it’s made out of if it’s going fast enough it WILL blast itself into dust.",
"So based on the composition of any meteor there is a maximum speed if you want any significant remnants left over. "
] |
[
"Why can't they make pregnancy tests like a blood glucose meter?"
] |
[
false
] |
Why don't they make pregnancy test that are similar to a blood glucose meter? Doesn't the same hormone exist in the blood. Is it just because ppl don't want to prick themselves? I just thought this would be easier then the pee on a stick.
|
[
"The hormone indeed is in the blood but a lot of people have a fear of needles, which would make it more difficult for them to obtain a sample, plus there is the process itself which involves a sterilizing swab, some pain, and another swab to stop the bleeding, none of which are required to pee on a stick, so yes there is quite a bit of \"ppl don't want to prick themselves\". Also, there is the equipment side of it of it: a glucometer is used often to monitor blood sugar (up to 4 times a day on someone using a basal-bolus insulin regimen) over long periods of time (several years), and at the same time give a value for the sugar concentraion in the blood, while a pregnancy test will typically be required much less frequently to confirm or rule out pregnancy, and not need to be more sensitive beyond a urine hormone level differentiating between \"pregnant\", \"uncertain\" or \"not pregnant\". ",
"Typical values used by commercial test",
". It therefore makes economic sense to have the test disposable, and not invest any money into making the test reusable or making the device quantify the level of the pregnancy hormone in blood (or urine for that matter)."
] |
[
"Thanks, I was just thinking back to when my wife and I were trying to get pregnant. The difficulty she had with the pee on stick method (the first few times she used it) and the cost of buying it multiple times. "
] |
[
"If she doesn't mind sharing, what was the nature of her difficulty? Was it in getting the pee onto the stick, or reading the test?"
] |
[
"Why is a group of clouds often on an equal altitude instead of varying in altitude?"
] |
[
false
] | null |
[
"This is not a hard fast rule of course, but it is true that in most weather regimes, clouds all seem to \"hang\" around the same height. The key to understanding this is realizing that clouds are not \"objects\" like lakes or mountains or lego bricks; they are just \"blobs\" of air that have cooled to the point where water vapor can condense into cloud droplets. There's nothing really holding them together, it's just a bunch of air that happens to be hanging around in the same place. If you got a strong enough fan running, you could definitely \"blow\" a cloud apart (though we're talking one huge fan here) under the right circumstances.",
"For your typical cumulus cloud (",
"like these",
"), the process of cloud formation starts when a pocket of air near the ground is warmed by the sun. Eventually, this \"bubble\" of air warms up to the point where it is less dense than the air around it, and begins to rise as an updraft. As this air rises, it cools due to expansion (known as ",
"adiabatic cooling",
"). If the conditions are right, eventually it cools to the point where the water vapor in the air begins to condense into cloud droplets, and a new cloud is born. ",
"This cooling due to expansion happens at a constant rate (known as the ",
"adiabatic lapse rate",
"), so air which starts at the same temperature and humidity is going to start condensing at the same height. Since the temperature and humidity near the ground don't change a lot with horizontal distance (under most circumstances, temperatures only vary by a few degrees over hundreds of miles or kilometers), the clouds which form from this process all end up starting at roughly the same height.",
"You can actually see a pretty cool consequence of this on the leading edge of many thunderstorms: where cooler, moist air from the storm meets warmer, drier air from in front of the storm, you get what's know as a ",
"shelf cloud",
". The cloud heights in the cooler, wetter air mass are much lower than the cloud heights in the warmer, drier air mass ahead of the storm, ",
"leading to the appearance of a \"shelf\" of cloud dropping down from the storm",
".",
"This is a pretty simplified picture, but in general it describes the process by which clouds form in most weather regimes. Let me know if you have any questions!"
] |
[
"I would say it's unlikely. The heights of the bases of clouds depend primarily on the difference between the dew point and temperature of the initial lifted bubble of air. While there will be increases in average temperature in most places, the moisture will likely also increase, and I would expect these effects would largely cancel out. That said, this is an area that seems to have little or any study, so it's certainly possible I've missed something.",
"The heights of the tops of clouds are actually limited by the ozone layer, which causes heating in the upper atmosphere that forms a \"lid\" keeping storms from growing above a certain point. This point is called the ",
"tropopause",
", and while it does get higher with increasing surface temperatures, it's not going to increase a noticeable amount even in the most pessimistic global warming scenarios."
] |
[
"Typically, the air temperature is a gradient, falling off with altitude. The base of the clouds begins at an altitude which is a function of the dew point. That's the temperature at which water droplets condense out of the air. That's why the bases are ",
" flat and just about level with each other, minus some chaotic swirliness. "
] |
[
"Why does ethanol have a health hazard of 2, while isopropyl has only 1?"
] |
[
false
] |
I am referring to the NFPA 704 health hazard rating which is a 2 for ethyl alcohol, but for isopropyl alcohol it is a 1 Isopropyl is significantly more toxic than Ethanol upon ingestion, so why is it considered a lower health hazard? Does it have to do with some other exposure, besides ingestion?
|
[
"The NFPA diamond is generally a quick guide for firefighters to assess the hazards of a substance or area at a glance. It's not the be-all, end-all of toxicological standards. You're right, that the LD50 values of isopropanol make it more toxic than ethanol, even though they're really pretty close. 20-30% different really isn't much when you consider that cyanide, a 4 in health hazard, has an LD50 value is 1000 times lower.",
"If I had to take a stab at why, the rationale might have something to do with the metabolites of isopropanol and ethanol. Isopropanol is metabolized to acetone by liver alcohol dehydrogenase, which, itself, has a health rating of 1. Ethanol, on the other hand, is metabolized to acetaldehyde, which has a rating of 2. ",
"It probably has more to do with what treatment is needed if someone is acutely exposed to ethanol or isopropanol, which I'm not familiar with. ",
"Something does seem to be off with these values, because methanol is metabolized to formaldehyde, which is wildly toxic, and methanol has a health rating of 1, even though its LD50 is almost identical to that of isopropanol."
] |
[
"I'll try to answer, but my English on this matter is not that good, so I'll try my best to make it comprehensible. I'm speaking as a pharmacist.",
"What uberhobo said is correct, but there's a little more. ",
"A fact we need to remember: the ketone generated by the alcohol methabolism/biotranformation will always be more toxic than the alcohol that has generated it.",
"Ethanol (ethyl alcohol) is transformed into acetaldehyde by alcohol dehydrogenase. The isopropyl alcohol (or 2-propanol) will be metabolized into acetone. They're two different substances, although they belong in the same chemical \"family\" (ketones).",
"There's this comparison between acetaldehyde and acetone that might me interesting to you: ",
"http://www.transtutors.com/chemistry-homework-help/aldehydes/acetaldehyde-and-acetone.aspx",
"So, back to the main subject: acetaldehyde is known to be more toxic than acetone. AFAIK, there're no known effects for the chronic exposure to acetone such as cancer. As these safety scores are measured by things that are already known and not by suppositions, what I'm saying is that acetone is less toxic than acetaldehyde by the lack of evidence of its hazardousness in certain kinds of acute and chronic exposures.",
"The acetaldehyde, in other hand, is known to be carcinogenic in chronic exposure, for example, while there's no concrete evidence for the same effect and exposure period by acetone. ",
"The acute toxic effects of the acetaldehyde include flushing of the skin, accelerated heart rate, mental confusion, shortness of breath, nausea, vomiting and others. They are directly related and referred as the cause of \"hungover\". They can happen when you drink too much alcohol. The acetaldehyde dehydrogenase is responsible for transforming acetaldehyde into acetic acid, but it has a limit. Too much ethanol makes too much acetaldehyde and its biotransformation enzyme meets a bottleneck, letting the ketone accumulate itself. This is highly used as \"shock treatment\" in alcohol abuse patients by using disulfiram, which is a drug that \"shuts off\" aldehyde dehydrogenase.",
"I think I've already covered why ethanol is more toxic than isopropyl alcohol and even went further than I needed. I hope this helps. "
] |
[
"I can't really make that call. LADH has a high affinity for ethanol over methanol (and most likely isopropanol, too), so it can knock out acetaldehyde at a somewhat faster rate than acetone, which might have some effect. However, I have no idea what other fates the alcohols and their metabolites have in the body."
] |
[
"Why does infrared radiation make things hotter than visible light?"
] |
[
false
] |
Basically the title. Also why does this occur despite the fact that visible light caries more energy per photon?
|
[
"You're absolutely right in that visible photons can heat things up too - the two questions here are (a) how much energy is there in photons of which wavelength (visible or infrared), and (b) how well does the surface getting hit absorb photons of different wavelengths.",
"So let's start with part (a), which for many sources (like sunlight, or an incandescent lightbulb) is governed by Planck's blackbody law. As you can see in the first figure ",
"here",
", a 5000K blackbody peaks in the visible range of the spectrum. The amount of energy coming from a blackbody in a particular wavelength range is given by the area under the curve... and there's a lot of area under the curves out in the infrared region. More area means more power, which means way more infrared photons given the lower energy per photon.",
"Of course you could build a source, like a laser, or LED light, where all or most of the radiation comes out in the visible, which would be different and not have any (or much) IR power at all.",
"Getting on to (b), how much power is absorbed at a given wavelength depends on the material doing the absorbing. That factor is called the \"emissivity\" (how well the material emits photons at that wavelength), or the \"absorptivity\" (how well it absorbs them), and those two numbers are equal despite the different names. Here's a ",
"relevant plot",
" for a couple materials - black paint (about the same emissivity in the visible and infrared), vs white paint (much more absorbing in the infrared than visible).",
"If you look into this more, be aware of the difference between the \"near infrared\" (one to few microns wavelength, where hot blackbodies like the sun or an incandescent bulb) put out a lot of power, and the \"thermal infrared\" (say 10 microns and thereabouts wavelength) where room-temperature-ish objects emit their blackbody power. It can be a bit confusing when people make tables of solar absorptivity and \"emissivity\" in the infrared, when they don't specify the wavelength region of either."
] |
[
"thank you so much"
] |
[
"If both are absorbed equally well by the surface, they will heat the surface about the same. But our eyes are very good at picking up visible light-- enough visible light to \"feel warm\" would be very, very bright. On the other hand, we have no good way to tell how \"bright\" infrared radiation is, so we don't even notice it until there's so much of it it feels warm."
] |
[
"When did we know that birds are descended from dinosaurs?"
] |
[
false
] |
I remember back in school, some 25 years ago, that I was taught that birds and dinosaurs were related but that there was no real evidence. Did paleontologists (or whoever knows these things) not know back then, or was my teacher's information just outdated?
|
[
"Almost as soon as the first ",
" was formally described by Richard Owen, other scientists noticed the many similarities between this \"first bird\" and certain dinosaurs. Within 5 years—so, 1868—you had Thomas Huxley loudly banging the \"birds and dinosaurs are related\" drum, as well as Cope and a few others. When the 1870 \"Berlin ",
"\" revealed its dinosaur-like teeth, the comparisons to ",
" were hard to miss. Owen himself never liked the idea, but a lot of contemporary biologists did. It was a fairly popular, but not ",
", hypothesis within biology.",
"But in the 1920s, a Dane by the name of Gerhard Heilmann argued—quite persuasively at the time—that birds could ",
" have evolved from dinosaurs. Dinosaurs, you see, had at some point in their evolutionary history lost their collarbones (clavicles). Birds ",
" clavicles (fused together into a single \"wishbone\") and it was a popular idea in the '20s that once a trait was lost it could not be re-evolved. So birds must have branched off the reptile line before dinosaurs did. Heilmann put birds as descendants of the \"thecodonts\", a (now-obsolete) group containing the crocodile-like ancestors of dinosaurs, pterosaurs, and modern alligators and crocodiles. Heilmann's position was attractive enough that the \"birds are dinosaurs\" idea was effectively put to rest, and for the next several decades the textbook answer was \"birds are some kind of thecodonts, but not ",
"-thecodonts.\"",
"It was ",
", discovered in 1964 and described formally in 1969, that started pulling scientists back into the \"birds are dinosaurs\" way of thinking. Ostrom spent several more years after ",
" comparing ",
" and ",
", arguing that their skeletal similiarities couldn't be the result of simple \"convergent evolution\". (Alan Grant in ",
" mentions this specific argument of Ostrom's: \"And look at the half-moon shaped bones in the wrist. No wonder these guys learned how to fly.\")",
"This was still just one hypothesis, however; there were still a lot of \"birds are thecodonts\" advocates, and there was a competing hypothesis that, based on skull features, birds were ",
". All three arguments were swirling around paleontological circles.",
"In 1986, Gauthier published his cladistic comparison of birds and dinosaurs, and showed that—by sheer number of shared anatomical traits—birds pretty much ",
" to be some kind of theropod dinosaur. Birds weren't \"thecodonts\", they weren't crocodylomorphs, they were ",
" dinosaurs. If your teacher was telling you 25 years ago that there was \"no real evidence\" that birds were dinosaurs, they were giving you out-of-date information.",
"Of course, there was also no Internet 25 years ago, so although your teacher was at least a decade behind, not having access to the most current information was a little more understandable than it would be today.",
"The final clincher for any holdouts (absent a handful of ",
" \"contrarians\" like Alan Feduccia) was the explosion of feathered bird fossils and feathered dinosaur fossils that started coming out of China in the '90s. Some dinosaurs were even originally described ",
" birds, so covered with feathers were they, and only after publication recognized as bird-like dinosaurs instead of dinosaur-like birds. This would have been right around 20 years ago, just after your school experience. By the end of the '90s pretty much every paleontologist was back on board Cope and Huxley's 130-year-old \"birds are dinosaurs\" train, and hopefully your teacher was, too."
] |
[
"Continental drift theory was accepted ",
" fast, and surprisingly recently. A number of lines of evidence came together in the mid-1960s...the Alaskan Good Friday earthquake (which my parents both experienced firsthand) providing direct evidence of continental subduction, the ship ",
" taking deep-sea core samples proving seafloor spreading, new seismology data coming in from all over the world...",
"The paper ",
"Seismology and the New Global Tectonics",
", published 1968, brought together a number of different fields of study and lines of evidence and said \"hey guys, plate tectonics is real\" and...as I understand it, that was pretty much it. Very few people had a good understanding of why earthquakes happen and volcanoes erupt, and then suddenly everybody understood exactly why earthquakes happen and volcanoes erupt."
] |
[
"The idea was proposed back in the 1860s. It was the 1970s however before it started to become accepted in the scientific community and the evidence from fossils was available to really prove it. It would be the mid 80s before the deal was sealed by cladistics: Gauthier, Jacques. (1986). \"Saurischian monophyly and the origin of birds\". For all those dates add in 1-10 years for it to filter down to teachers and text books depending on how much an individual teacher paid attention to the latest developments in paleontology. "
] |
[
"Does the electronegativity of an element in an acid (fluorine in HF) share any relation to how strong the acid is?"
] |
[
false
] |
I know that acids basically just have a bunch of naked protons which “steal” the electrons from other substances, but does the electronegativity have anything to do with how strong this reaction is? If not, what does?
|
[
"Electronegativity is the measure of how strongly an element will pull the electron density off of another atom in a covalent bond. This is not a 1:1 measure of the acidity. ",
"The acidity of a substance doesn't depend on the species with a proton. Chemicals do not give up protons because they want to get rid of protons. The reason something is acidic is because when it does lose a proton - it becomes the conjugate base - the more stable this species is the more acidic the acid form will be. ",
"So you have these negatively charged conjugate bases that need to be stabilized. To do this, the more the negative charge can get spread out the more stable it will be. To do this, three things help: ",
"Size: The bigger the molecule is, the more acidic it will be. HI is more acidic than HF.",
"Resonance: Resonance structures help pass around extra electron density so no one atom has to hold onto it. All of the polyatomic ions that make strong acids have lots of resonance structures. Also phenol is much more acidic than cyclohexane.",
"Electron withdrawing groups: Here is where electronegativity can help. Adding a nitro group to a phenol makes it more acidic. A carbonyl on a carbon makes a hydroxide also on that carbon more acidic (carboxyllic acid vs alcohol). ",
"Turns out fluorine is really small. So even if it is electronegative, it isn't big enough to handle a negative charge on its own, so it makes a weak acid. Chlorine on down are bigger and are much more acidic. "
] |
[
"It can etch glass and is very corrosive but it is considered a weak acid. It does not completely disassociate, there is still some HF molecules in aqueous solution, while something like HCl will basically be all H+ and Cl- with no HCl left."
] |
[
"Isn't HF an extremely powerful acid?"
] |
[
"What are the consequences of Baby Dynamic Yoga?(Re-Post from /r/videos)"
] |
[
false
] |
Saw this this morning and thought there has to be some other long term effects that go beyond We've all heard about Shaken Baby Syndrome. What about the strain on their limbs and joints? OP:
|
[
"i would be surprised to find out that this didn't harm the babies..."
] |
[
"i know the removal policy for ask science....but does it apply when something is clearly not science, not medicine, and obviously child abuse",
"on the plus side there's no way baby dynamic yoga can cause brain damage, because there is no chance those children inherited any intellect from their parents"
] |
[
"It's strange, yes, but not obviously child abuse. It may do damage; we don't know but clearly the babies are not being harmed outright or on purpose. I do know that they used to say weight training was harmful to children but now we know that it's not. Best to let science come out...Also it would be interesting to know the actual point of this \"yoga\"?"
] |
[
"Inspired by Interstellar: What happens to the rotation of a large planet orbiting a black hole?"
] |
[
false
] |
Imagine a roughly spherical planet orbiting a black hole. This planet also rotates around its own axis. What happens if the planet is big enough that the passage of time is significantly different on the near side than the far side? I understand the passage of time on the near side would be relatively slower than on the far side. What happens to the velocity of the planet's sides in the rotation? Are they different? Does the physical shape of the planet warp over time to "correct" for the relativity difference?
|
[
"The reason for the time dilation that happens isn't directly due to the black hole itself, it is more to do with how fast the planet needs to orbit the black hole to maintain a stable orbit. If the planet is moving too slow it would just get sucked into the black hole. So for a stable orbit near a black hole that would result in the time dilation as shown in interstellar the planet would need to be moving at a significant portion of the speed of light. (Maybe someone who understands how to calculate time dilation can calculate how fast it was going for 1 hour local to equal 7 years on earth)",
"As for the time dilation difference across the planet it would be quite insignificant i.e 1 hour on close side of planet = 6.9999999999999999999 years 1 hour on far side of planet = 7.00000000000001 years",
"Regarding the rotation of the planet, the gravity shear is pretty high on a black hole, and high gravity sheer can more easily result in an orbital body becoming tidally locked like the earths moon. "
] |
[
"Doing a quick, back-of-the-envelope estimation with WolframAlpha, I got 0.999999999867c for the planet's effective velocity without gravitational effects using only special relativity, though I feel that general relativity is required in this situation. "
] |
[
"Time dilation also happens due to large bodies of mass, does it not?"
] |
[
"Does the expansion of the universe affect the value of the Planck length? How do we know? How can we even know?"
] |
[
false
] |
While staring at the ceiling above my bed and thinking about the universe (quite literally), I was wondering about the implications of its expansion as best as a layman could. I was particularly concerned with the question whether the expansion of the universe is the consequence of a general expansion of space-time, or if the universe expands within a given space-time. To my layman understanding, this would have a drastical impact on how we can actually measure the universe's expansion, leading to my question if the Planck length remains static during the expansion or if it's somehow directly tied to it, and if we are even capable to measure it under these circumstances and in the light that is probably quite difficult to experimentally prove the value of the Planck length anyway. tl;dr: Is there a predictable effect of the universe's expansion on the value of the Planck length and can we verify this prediction by measurements? Are we even capable to measure it?
|
[
"No, the Planck length is just a length constructed from physical constants, which are constant. It is smaller than what can be measured. However, from what you're asking it sounds like you have the idea that the universe is fundamentally made of Planck-sized pixels, which isn't the case."
] |
[
"Can I ask how you came to that understanding? I'm curious as to how this gets spread."
] |
[
"No - the Planck length is defined by the square root of two constants divided by a third constant. L_p = (hbar*G/c",
" )",
" None of those constants are thought to be affected by expansion so therefore the planck length is not either. To put it another way - given the way the planck length is defined - if it changed with the metric expansion we would not see a metric expansion. ",
"The planck length is far too small for us to measure now or in the foreseeable future, so even if it was changing that is not something we are going to be measuring any time soon! (to give you an idea - the radius of a full stop in comparison to the radius of the universe, is roughly the same ratio as the radius of the planck length in comparison to the full stop. "
] |
[
"Why do we feel euphoric after we evacuate our bowels?"
] |
[
false
] | null |
[
"Haha just found this after browsing comment history. Let me take a stab at this. You can thank pressure on your prostate which forms into the g spot in females. "
] |
[
"Hmmm . . . do I feel grateful or stalked?",
"Edit: Regardless, thanks for giving an answer."
] |
[
"It's ok to feel both. "
] |
[
"Would it be possible for an antenna to emit light in the visible spectrum?"
] |
[
false
] | null |
[
"Hi Jack_Mackerel thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Physics"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"Also consider looking at ",
"our FAQ",
".",
"For more information regarding this and similar issues, please see our ",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Future Helium Alternatives?"
] |
[
false
] |
After seeing this reddit post in energy i became curious in possible futures of this technology. But many of us science types are aware that helium is not a renewable resource and is actually on its way to becoming a (kind of) a rare gas. So the question i submit to you askscience is: are there any gasses that we could use in our foreseeable future that is lighter than "air" completely stable yet abundant enough that we could use in an everyday technology?
|
[
"One of the main uses of Helium is to cool things down to 4K. Hydrogen has a boiling point of 20K and is thus useless as a Helium replacement."
] |
[
"Well, if we ever manage to use fusion as a power source, then we would get helium as a byproduct of hydrogen fusion. Using just fusion power, and assuming I did the maths right, we'd need to fuse ~350 tonnes of hydrogen per year (this seems really low, I might have missed something here) to meet our current (2011) energy requirements, this would produce just below 90 tonnes of helium per year."
] |
[
"Laser cooling is for tiny amounts of gases. Say you want to operate the LHC. Then you need super conductors to reach the necessary magnetic field strengths, which means you need to cool down tons of material to 2K. Not doable without Helium.",
"Helium balloons are for children's birthday parties and completely irrelevant in comparison to cutting edge research or operating medical equipment with super conductors such as MRIs, etc. "
] |
[
"If we defined the meter as a static portion of the width of the universe (so as one expanded in size, the other did proportionally), about how much would our meter be expanding in, say, an hour?"
] |
[
false
] |
By “width of the universe”, I’m not talking about the universe, but rather I’m referencing the rate at which space itself seems to be expanding. (Although I would be interested in using the observable universes growth as our constant as well). Perhaps my question doesn’t have enough constraints to be answerable, or perhaps it’s already a well-observed constant? My apologies if it’s easily calculable. I just wouldn’t even know where to go looking for info on this, or how to rigorously describe my question, for that matter.
|
[
"You've described exactly what we refer to as the \"Hubble constant\", H_0. Typically instead of your \"one meter reference separation\", we are talking about the distance to a (distant) galaxy. And instead of saying \"how much further per hour\" we ask \"how fast does it appear to move away from us\". That's just like putting your eyeball at one end of your \"meter\" and asking how fast the other end appears to be moving away.",
"The current value of the Hubble constant is about 70km/s/MPc. That is, if a galaxy is 1 Megaparsec away, it appears to be moving about 70km/sec away from us. What's really happening is that space is expanding so that 70 km is added to the distance between us every second.",
"I have to say, the Hubble constant in those units is useful for astronomers (because galaxies are MPc to GPc away, and you can measure their apparent velocities in km/s), but it's a horrible unit otherwise.",
"To answer your \"1 meter\" question, we just need to convert\"(km/s)/MPc\" to \"(meters/s)/meter\". 1 Megaparsec is 3 x 10",
" meters, so we find",
"H_0 = 70 (km/s)/MPc= 70 x 10",
" m/s / (3 x 10",
" m) = 2.3 x 10",
" (m/s)/m",
"You asked how much it expands in an hour, which is 3600 seconds, so we have",
"delta_L = L * time * H_0 = 1meter * 3600 s * 2.3 x 10",
" = 8 x 10",
" m",
"For reference, a proton has a diameter of about 10",
" meters.",
"Space is vast, the universe is old, and those little bits add up.",
"",
"**** Note: objects, such as meter-sticks, bound by atomic forces, do not expand as the universe does so. Neither do gravitationally bound objects such as the Sun, the Earth, the Solar System, or the Milky Way. Only in the vast empty reaches of space can we think about this \"one meter reference separation\" posited by OP.",
"Edit: Wow, many thanks to those of you who gave so much positive feedback, and so much bling! I'm happy so many of you found this interesting and helpful. This is a great community, and thanks to the mods for making work."
] |
[
"This is a beautiful response. Thank you! I wish I could give more than one upvote..."
] |
[
"I appreciate the positive feedback even more than the upvote! :) Glad it was helpful."
] |
[
"What is the coldest recorded temp in the Arctic or Atlantic oceans?"
] |
[
false
] |
The salinity of the water would vary, and effect the temp, but how low can it get in a super dense volume of salt water?
|
[
"There definitely is an absolute answer to this. You need to use calculus regarding the relationship between temperature, maximum (or a more robust calculus to consider optimized if it is not linear enough) salinity, and change of state temperature point.",
"Unfortunately the change of state temperature is still poorly understand so questions like this are based on physical data gathered from experiments. From such we have what are called phase diagrams. ",
"I won't link you to any as I'm not sure what salt you mean in your general question, and for your specific question about the coldest temp I'll merely remark that I've been taught 4C as the most dense oceanic water can get before freezing which it does at -1.9 or so...but if you mean measured temperatures of ice as opposed to water I have no idea."
] |
[
"I'll merely remark that I've been taught 4C as the most dense oceanic water can get before freezing which it does at -1.9 or so...",
"This is not true. For pure water, the maximum density occurs at 4C but it is not the case for salt water. Water with typical ocean salinity (3.5%) does not have the inflection point at 4C and continues to get denser the more it is cooled until it reaches the freezing point.",
"The freezing point of seawater (about -1.9) puts a bound on the coldest and densest waters in the ocean. Here is a ",
"section of temperature north-to-south through the Atlantic ocean",
" based on observations from the World Ocean Circulation Experiment. The coldest bottom waters are formed around Antarctica but as the cold water sinks to the bottom it entrains warmer water, thus the coldest temperatures observed in the open ocean are about -0.4",
" C. "
] |
[
"Just a related tangent:",
"as others mentioned, the freezing point of typical seawater is about -1.9. It varies with exact salinity, of course. You definitely see temperatures this low in the very surface waters of the high latitude oceans, particularly in the winter seasons. You have cold arctic/antarctic air chilling the water, and as water temperature approaches -1.9, you get this soupy crystalline mixture referred to as frazil ice. Eventually, you get sea ice formation.",
"For more info on arctic/antarctic ice, see ",
"http://www.whoi.edu/arcticedge/arctic_west03/facts/facts_ice.html"
] |
[
"Are omozigote twins like clones?"
] |
[
false
] |
Except of DNA mutations, are omozigote twins comparable to clones looking at their DNA? If no, why? Thanks and I'm sorry for my bad english.
|
[
"Yes, homozygote twins descend from the same sperm and egg which means they will get the exact same DNA replicated to each embryo when the fertilized cell splits into two parts. Except for mutations later during the fetus stage, their genome is exactly alike"
] |
[
"The fathers and the uncles genome is exactly identical. Whether it would've been twin 1 or twin 2 being the father, the kid would with high probability look the same being either twin 1's or twin 2's biological offspring. With mother 1, twin 1 and twin 2 could get the same looking kid (depending on which chromosomes were inherited). \nSo yes, the kid could be genetically the son of both of them, but being the biological offspring to only one of them."
] |
[
"So, if one of the twins has got a child, the kid is \"genetically son\" of both of them, is that right?"
] |
[
"If the four dimensions of space and time are intertwined, why can we not rotate an object into \"time\" the same way we can rotate an object in 3D space?"
] |
[
false
] |
Forgive me for being naive, but this seems like an intuitive question.
|
[
"You can “rotate into time”, just change your speed. Mathematically, changing between different reference frames looks like hyperbolic rotations that mix spatial and time coordinates. Using some identities from complex analysis, you can think of hyperbolic rotations as regular rotations, by imaginary angles."
] |
[
"Not really, unless you consider a flip to be a rotation. Certainly no continuous rotations exist."
] |
[
"Question",
"Is it possible to rotate something of a single dimension? "
] |
[
"Is there a correlation between the complexity of an organism and the genetic diversity of its species?"
] |
[
false
] |
What sorts of species have very low genetic diversity? High? How do humans compare relative to the rest of life on Earth?
|
[
"There is no particular reason that genetic diversity and \"complexity\" (which is fairly difficult to define quantitatively) would be correlated. Genetic diversity is dependent on many factors, including:",
"These and other factors that affect genetic diversity can be highly variable from species to species, and so it's not really possible to predict genetic diversity by any features as broad as \"complexity\". That said, there are some more specific predictions that can be made, such as that sexually reproducing species should have higher genetic diversity than asexual species, species with more inbreeding have reduced genetic diversity, etc.",
"Of the factors listed, population size is sometimes used as a sort of proxy for genetic diversity. Specifically, we talk about \"effective population size\", which is the size of a theoretical ideal population that shares similar characteristics to the real population. Effective population size is always smaller than true population size, since there are many things that make real populations non-ideal (e.g. some individuals die before reproducing, some individuals have more offspring than others, and population sizes naturally change over time). ",
"Surprisingly, humans have an effective population size of only around 10,000 (",
"Source",
")! (I've also seen some estimates that are a bit larger, but still less than 100,000). This may seem crazy compared to the current true population which is approaching 8 billion, but the reason our effective population size is so much smaller is explainable by a few facts. Firstly, our population has been growing exponentially for hundreds if not thousands of years (",
"see graph",
"), which by the way is pretty much unprecedented in the natural world for this duration of time, and this means that there just hasn't been enough time for the number of mutations you'd expect to see in a population of 8 billion to accumulate. Secondly, there's also a pretty good amount of evidence that even before human populations started to grow rapidly, we also underwent at least one and possibly multiple significant bottleneck events where our ancestors' true population dropped into the small tens of thousands (",
"Source",
").",
"That got kind of longer than I had planned, but I hope it addressed some of your questions! "
] |
[
"Genetic bottlenecks can drastically decrease the genetic diversity of a species regardless of the organism’s complexity. I think genetic diversity is really determined by the environment that species is in, which is why you see an increase in biodiversity as you get nearer to the equator. "
] |
[
"Great answer, thank you!"
] |
[
"How do radios work? (and other devices controlled by radio waves) How is the sound information encoded onto the wave, and how does the home radio turn the light information put back in the speakers?"
] |
[
false
] |
I understand that radios (like what is in your car) need electrical power (from batteries/wall outlet/car) and get radio waves that are from transmitters. Radio waves are a kind of light wave. However, in my daily experience with light, information is not encoded onto the light wave other than color (and maybe amplitude.( This is another thing that is unclear to me. What is the amplitude of a light wave? Is it even meaningful to say "the amplitude of a light wave"?) How is the sound information encoded onto the wave, and how does the home radio turn the light information put back in the speakers? Thanks so much!
|
[
"There are different methods of encoding, for instance ",
"Amplitude Modulation (AM)",
" encodes the signal in the amplitude, ",
"Frequency Modulation (FM)",
" in the frequency, ",
"Phase Modulation (PM)",
" in the phase, and so on. I am going to dive into a bit more detail, but I want you to know that I am restricting my discussion here to analog communications.",
"Anyway, a signal should be thought of as a time-dependent function ",
"(example)",
", which for discussion purposes we will denote by ",
". It is important to note that this signal, will generally have a finite range of frequencies that it occupies, something termed ",
"bandlimited.",
" Modulation allows for the radio stations to effectively determine the center location of the bandlimited signal. In practice you see this when tuning into different radio stations, you are essentially setting the center frequency for demodulation purposes.",
"Anyway, the final transmitted signal, call it ",
", will depend on the modulation, as mentioned before. But, for the purposes of discussion, assume we have a carrier signal ",
", where ",
" represents the center frequency. For AM the transmitted signal is ",
", for FM the transmitted signal is (simplified for presentation) ",
", for PM the signal is (once again simplified) ",
". Observe, in AM the amplitude of the carrier signal is message dependent, in FM the frequency of the carrier signal is message dependent, and in PM the phase of the carrier signal is message dependent.",
"This signal is then sent to the anetnna, which generates an ",
"electromagnetic wave",
" defined by the transmitted signal."
] |
[
"Thank you! In, say, a phase-modulated wave, how does the information of phase shifts(which is only one variable, f(t) get turned into the sound information (which has many variables—frequency, amplitude, for multiple waves)"
] |
[
"Directly, ",
" is what your speakers will reproduce. ",
"What you are calling variables, are better thought of as the terminology used to describe signals. That is they can be used to help describe aspects of the signal ",
" or the transmitted signal ",
", but ",
" is the signal your speakers reproduce and ",
" is the electromagnetic signal that the antenna sends.",
"In that sense, the radio sends the signal ",
", using the modulation described, and the receiver extracts ",
" and sends this signal to speakers. The speakers then reproduce ",
" with audio waves, which you then hear."
] |
[
"Can I overcharge an electronic?"
] |
[
false
] |
Is it possible if I leave my phone or something with a rechargeable battery on the charger too long for it to be damaged somehow?
|
[
"This is the case with cheap electronics using batteries other than lithium. All lithium battery chargers are \"smart\" with circuitry to prevent overcharging, as that could result in a fire. ",
"Some cheap electronics that still use the older style NiCd and Nimh battery technology use trickle charging - electricity at a low current and constant voltage. These chargers do overcharge the battery, but the low charging rate means the batteries don't get too damaged from being overcharged. In recent times you can find these systems in use with cheap power tools."
] |
[
"Aye, cellphones and other things with recharging circuits generally have stuff in them to stop the charging process once the battery is sufficiently full."
] |
[
"As long as you are using a charger designed for the device you are charging you should be fine in most cases. ",
"One exception would be a battery charger for car batteries. Some will turn off automatically when done charging or after a set period of time. Some will not and will destroy the battery if left on for a prolonged period of time. "
] |
[
"Last night I dreamed that a nuke went off in the distance and I went and talked to my father before the blast got to our house, what would be the formula for calculating the amount of time you have between seeing a nuke go off and the explosion actually reaching you?"
] |
[
false
] | null |
[
"If you are in the vaporization region, the formula is t=0 seconds. Seeing light is being burned by the light.",
"If you are going to be hit by the acoustic shockwave, then it will be slightly higher. The shock wave would be an acoustic event. I don't have the best knowledge of acoustics, so I would put my first estimate as the wave traveling at mach speed (depending on altitude and conditions, this can vary -at least- in the range of 660 to 760 mph). For \"reasonable\" applications, you see the light \"effectively\" instantly.",
"If you want to get technical, if the blast occurs near ground, you have to consider seismic activity separately, but my point is you don't realistically have this conversation (unless several nukes are dropped)."
] |
[
"Not exactly, the shockwave loses velocity extremely quickly. If you want an exact formula:",
"http://www.saecanet.com/astronomy/515-calculation-of-blast-waveradius-and-expanding-velocity.html",
"If you don't want to do that math, then just know that the speed of that wave is dependent on the air, time, and the blast itself. It doesn't maintain lethal pressures for more than a few seconds. The speed of the wave can exceed the speed of sound (depends on the explosion). However, if you aren't dead within a couple seconds, your time of death becomes unknown. It would be due to fire, debris, or radiation. None of those can be calculated directly.",
"http://en.wikipedia.org/wiki/Blast_wave",
"http://en.wikipedia.org/wiki/Effects_of_nuclear_explosions#Blast_damage",
"http://www.fas.org/nuke/intro/nuke/blast.htm",
"Edit: Found an old article that is far more descriptive. ",
"As the shock wave expands and cools to around 3000 degrees, it stops glowing and gradually also becomes transparent. This is called \"breakaway\" and occurs at about 15 milliseconds for a 20 kt bomb, when the shock front has expanded to 220 meters and is travelling at 4 km/second.",
"http://www.cartage.org.lb/en/themes/sciences/chemistry/nuclearchemistry/nuclearweapons/firstchainreaction/effectsnucl/weaponeffects.htm"
] |
[
"Thanks for the answer!\nI don't know what the range of the acoustic shockwave is, but assuming a mile is inside that range - If I'm a mile away by your calculation I would have about 5 seconds, right?",
"(1 mile) / (710 mph) = 5.07042254 seconds"
] |
[
"How much data is transferred across the internet in one second?"
] |
[
false
] |
Hello, I'm curious as to how much data (in bytes) is transferred across the internet in one second. For the purposes of the question, transfer across the internet is assumed to be anything that gets transferred through your ISP from a computer or other such device. So, a local network file transfer doesn't count, nor does the universities local mail server. Thank you very much.
|
[
"This is old data, but 494 exabytes of data was transferred across the globe on June 15, 2009 according to the Digital Britain Report. ",
"That's 6.6 × 10",
" bytes, or 5 995 terabytes per second (Using binary prefixes rather than SI). Likely it's many times larger today."
] |
[
"Note the word \"also\". ;)"
] |
[
"What is the law that states computer growth is exponential?",
"Applying that, imagine what the data transfer is today. :D"
] |
[
"What was the daily temperature during the “little ice age”?"
] |
[
false
] |
During the little ice age, the climate was from 0.5 to 2.0 C colder than today. What does that mean in daily high and low temps for summer and winter? This has been surprisingly hard to find.
|
[
"It might be hard to find because it's too vague a question, as the answer will depend a lot on the location of interest. For one example, there are a few long temperature records from central England, so for this location at least, you question is answerable, e.g. ",
"Parker et al 1992",
". Page 20 of that article has average temperatures by month from 1659 to 1990. This range covers much of the coldest parts of the ",
"little ice age",
", but not the entire event (depending on whose estimate of when it started you're going with). From this, and again, for central England only, you can see that there's a lot of variability from year to year (and presumably finer scale variability from day to day), but broadly defined (and doing some rough averaging by eye) the winter months (e.g. December and January) were ~1 degree C colder during the little ice age, whereas the summer months (e.g. June and July) were pretty much the same as the post little ice age period.",
"To answer this question for other locations, you would need either to find similar locations where there are long temperature records or look for papers where people have run climate models to simulate the little ice age to get a sense of what average temperatures would have been like (given what we know about global averages and how the climate system works) in an area without existent temp records."
] |
[
"Earth Sciences"
] |
[
"Earth Sciences"
] |
[
"How much of a problem is space debris for the ISS and shuttles?"
] |
[
false
] |
[deleted]
|
[
"There are no more space shuttles, but for the ISS and other spacecraft, the answer is space debris is a potential hazard, but fairly easily managed. NASA and the DoD track tens of thousands of pieces of debris to ensure there are no collisions. The orbits of the ISS or any other spacecraft can be adjusted to avoid potential collisions if necessary. The ISS is routinely hit with tiny pieces of debris (a few millimeters) but it has shielding so it can handle these routine impacts. Debris in low-Earth orbit doesn't stay there very long, so it's not a huge issue. Debris poses a greater risk to satellites in higher orbits, but no human activity takes place there."
] |
[
"Hi, I'm on the ISS MMOD team.",
"For the ISS orbit, the debris flux is fairly low compared to higher altitude orbits. However the ISS is still costantly bombarded with meteoroids and orbital debris, however most of it is small enough that it does not result it significant damage but it will still cause surface degradation for things like radiators, antennas, and solar arrays, reducing their effectiveness.",
"For the more susceptible or critical ISS systems we make sure they are well protected and are constantly updating our assessments to reevaluate exposed hardware for changes to their risk level.",
"If a particular piece of hardware is determined to have a higher than desired risk level, we can sometimes develop supplemental shielding options to help protect it. In 2016, when the program was planning to relocate PMA-3 to Node 2 zenith (a radial port) from Node 3 Port (axial port) that caused a section of the berthing interface (critical pressure wall, only 1 layer of structure between space and the habitable volume) to become exposed to the environment, we developed a shield to cover the exposed areas and keep the risk down to acceptable levels.",
"However, despite the low amount of debris, and debris avoidance maneuvers that can dodge tracked piece of debris there is still a size range of debris that is large enough to cause a critical failure but too small to track. One of these projectiles hit the photovoltaic radiator on P4 in 2014: ",
"https://www.nasaspaceflight.com/2014/07/iss-managers-evaluating-mmod-radiator/",
"That impact luckily barely missed the fluid lines in the radiator, but we estimate that it was large enough to have caused a failure if it had hit a few millimeters higher.",
"So your question of how much a problem it is: I'd say not a huge problem right now for the ISS (since it is by the far the best protected spacecraft in history) but it doesn't take much to change that. "
] |
[
"what is the protection against a few millimeter debris strike against an astronaut during a spacewalk? Relatively low risk, or the suit can take the hit, or something else?"
] |
[
"How would one go about visualising an imaginary number?"
] |
[
false
] |
And do transformations of real numbers apply to imaginary numbers in the same way?
|
[
"You can picture a two dimensional axis: the x axis represents the real numbers and the y axis represents imaginary numbers. Any point that's not on either axis is a complex number."
] |
[
"A two dimensional vector."
] |
[
"If you want to go further, look up Quaternions. However, they have to specifically constructed. All operations on real or complex numbers will give you a real or complex number."
] |
[
"What is the difference between animals that are considered white meat and red meat?"
] |
[
false
] |
I am wondering if there is some biological difference between mammals such as pigs and cows that causes their meat to be classified in this way.
|
[
"\"Why is pork a \"red\" meat?\nOxygen is delivered to muscles by the red cells in the blood. One of the proteins in meat, myoglobin, holds the oxygen in the muscle. The amount of myoglobin in animal muscles determines the color of meat. Pork is classified a \"red\" meat because it contains more myoglobin than chicken or fish. When fresh pork is cooked, it becomes lighter in color, but it is still a red meat. Pork is classed as \"livestock\" along with veal, lamb and beef. All livestock are considered \"red meat.\" \"",
"Source - USDA.gov"
] |
[
"\"Pigs are lazy animal; they are not as active as cows\" Source?",
"Cows are grazers, while pigs are foragers. Also, anyone who has observed domestic cows and pigs can tell you the pigs move more."
] |
[
"\"Pigs are lazy animal; they are not as active as cows\" Source?",
"Cows are grazers, while pigs are foragers. Also, anyone who has observed domestic cows and pigs can tell you the pigs move more."
] |
[
"Black holes; are they really a \"hole\", or are they a solid, spherical mass?"
] |
[
false
] | null |
[
"They are a solid, spherical mass. Okay so you throw an apple up and it comes back down due to gravity right? But on the moon, there's less gravity because the moon is smaller. You throw an apple up and it goes much higher and comes down much slower.",
"So if instead you landed on a planet twice the mass of earth and threw an apple up, it would come down much harder, because there is more gravity. Keep adding mass and slowly you can't even lift the apple off the ground because the mass is so great. Eventually you hit a point called the Schwartzchild Radius where the size and mass of the planet creates a gravitational field so strong that even light cannot escape from it. Not just apples, and whatever rock could be in there, even light gets sucked back in because the planet is ",
" dense and the gravity is so strong.",
"To that extent all black holes are just huge amounts of matter that create gravitational wells so strong that light cannot escape. Because of this, we cannot \"see\" a blackhole, as no light reflects off it, and it just appears as a dark circle in the sky. Hence a \"black hole\" it looks like a hole in the stars because it's just a dark spherical shape blocking out light."
] |
[
"Actually, in any scenario the apple would get back to your hand going the exact same speed as you threw it up with, or even less if you consider air resistance. The gravity will only change the time scale over which this happens e.g. large gravity->apple goes up and down quickly compared to the same initial velocity with less gravity.",
"The Schwarzschild radius is actually the defining characteristic for black hole formation in terms of mass, and is a function of only mass. For a given mass, if you compress it to a sphere with radius equal to or smaller than the Schwarzschild radius, it will form a black hole. Because, for given densities, the mass of the object will be a function of the density times its volume (which is proportional to the radius cubed, spherically speaking) you can say for fixed materials the radius grows as a function of the cube root of mass, while the Schwarzschild radius is linear in mass. This means that every substance has some point where you can't make a sphere any bigger, it will have surpassed the Schwarzschild radius even if the density is very low.",
"Mathematically speaking, a singularity is formed; \"black hole\" describes the region around the singularity, a sphere with a radius of its Schwarzschild radius. Because not even light can 'escape' a black hole, we can't actually say for certain what the structure looks like inside. Regardless, they are an object, not the absence of anything as 'hole' would imply (unless you think of the lack of reflected/transmitted light as an absence, although they do emit a blackbody spectrum like anything else)"
] |
[
"I assure you I understand both your points, but the OP was asking if black holes were literal holes, I tried to use a more simplistic explanation that didn't delve into the mathematic elements of it"
] |
[
"What happens at the atomic level when you cut something into two? Why aren't you able to put them back together?"
] |
[
false
] | null |
[
"Let's say you cut a piece of stainless steel in half with a magic knife that maintains the structure of all the atoms but just separates them. That would be an ideal cut; just breaking the chemical bonds that hold the material together. Now, what if you tried to put it back together a few minutes later? Somewhat surprisingly, the pieces wouldn't stick together. The reason is that the surfaces of many materials are different from the bulk material on the inside. In the case of stainless steel, the surface gets oxidized by the atmosphere to make a layer of iron oxide a few atoms thick. This prevents the surfaces from making a perfect match again. ",
"So why does this happen? There are two reasons, really. The first is that oxygen will react with pretty much anything it can get its hands on. It makes especially strong bonds with iron. The second is that when you break a bond, you're actually adding energy to the atoms, and this energy can be used to facilitate a chemical reaction with something else that they come in contact with. ",
"Now you decide to get clever and do this same experiment in space, or a good vacuum chamber. If you still use your magic knife so that there is no grain (crystal lattice, really) mismatch when you put your pieces back together, they should stick.",
"This phenomenon of separate two pieces of metal stick together does happen in our atmosphere, especially with stainless steel. It's usually not a good idea to use stainless steel screws to hold together something made of stainless steel. If you screw it in really tight, you can scratch off the protective layer of iron oxide on the surfaces, exposing the pure metal underneath, which can then, over time, form new metal-metal bonds. This process is called ",
"galling",
"."
] |
[
"This is really, really cool."
] |
[
"Ok, that makes sense. Let me try and repeat, so I understand:",
"The reason we cannot put two halves of a freshly cut block of material (you used stainless steel, but I'm assuming the principle remains true for ",
" most substances) is that once separated, the atoms on either end react with oxygen, oxidizing the surface. If we cut a block in half in a vacuum (how necessary is this magic knife?), no oxidization would take place, so the edges would fuse (right word?) on contact.",
"Assuming that last sentence is true, if we folded a material in on itself, would it stick?"
] |
[
"When Baumgartner broke speed of sound in free fall, did he experience complete silence?"
] |
[
false
] | null |
[
"As far as I'm aware, he would continue to hear air hitting his suit. ",
"Let's say that you rode on the Concorde from New York to Paris. At some point over the atlantic, you would break the sound barrier and start travelling faster than the speed of sound. ",
"However, the cabin would not suddenly go quiet - the noise from the engines and the air would not somehow be \"behind\" you, you are not somehow outrunning the noise. ",
"Well... in a sense you ",
" outrunning the noise that is in the air outside of the plane. For example, if there was an explosion beside of the plane while you were travelling faster than Mach 1, you would most likely not hear it - the sound of the explosion would never catch up to you, you would be \"outrunning\" the sound. ",
"However, sound is vibration moving through a substance. The more dense the substance, the quicker a vibration (sound) tends to move through it. So although the speed of sound (in dry air at sea level) is 768mph, it is much faster in water (3316mph), and even faster through a solid like metal or glass. So although you are \"outrunning\" noise that occurs in the air outside of the plane, noise that is generated by the plane itself (engines, air hitting the fuselage) vibrates through the structure of the plane itself, and you can hear all that noise within the cabin without issue. ",
"So yeah - I believe that Baumgartner would have continued to hear the noise of wind hitting his suit even at supersonic speeds, as the suit itself would be generating the noise, and that noise would be transmitted through the suit to the relatively static air inside it that surrounded his ears. "
] |
[
"he would hear sounds from in front of him, even from outside his suit."
] |
[
"he would hear sounds from in front of him, even from outside his suit."
] |
[
"What makes certain genes more dominate than others?"
] |
[
false
] |
Just a general question. For example. If a Caucasian person has a child with a Japanese person.. The Japanese genes will be more dominate in the child. Of course it happens with many more ethnicities than those two but just used them as a general example. Can anyone explain this to me?
|
[
"I'm not a molecular biologist, but there's a problem inherent in your explanation. What happens in homozygous recessives? How do you avoid silencing yourself to the point of having no phenotype at all. Do you have to inherent methylator with the dominant trait? Could it also be possible that gene products may inhibit production of recessive protein epigenetically (not methylation)? Just saying need some solid evidence before we right it off as all methylation, but if I'm wrong please correct me!"
] |
[
"I'm almost completely certain your \"example\" is completely fabricated, based on confirmation bias.",
"Dominance (like all parts of genetics) is extremely complex, so simplification may be in order. Dominance is, in short, caused by the fact that when alleles are expressed, multiple proteins or enzymes may attempt to use the same resources to do different jobs. Their catalysis results in the phenotype of the organism."
] |
[
"I don't think 'Japanese genes' are necessarily 'dominant' over 'Caucasian genes'. Rather, the dominance of different alleles of a gene is largely determined by the nature of the protein that it encodes. For example, defects in structural proteins generally manifest as dominant traits because being heterozygous results in defective protein synthesis, which disrupts the native healthy protein. On the other hand, defects in enzymes tend to be recessive because there is a certain amount of compensation, such that heterozygotes may be asymptomatic (aka gene dosage effect). These rules do not always hold (eg haploinsufficiency with familial hypercholesteremia), but are useful generalizations. "
] |
[
"Why are chimeric plants (and some animals such as lobsters), often split straight down the middle?"
] |
[
false
] |
Examples:
|
[
"Chimerism results from events like spontaneous mutation, transposon action, or mitotic recombination in only some cells of an organism. If it happens very early on--say, at the two-cell stage--then the result is two cells, one with the genotype of the parent and one with the mutation. If it's a visible mutation, and an organism with bilateral symmetry, depending on the development of the organism in question, when the organism grows up the phenotype may be split right down the middle, because the mutant cell will give rise to more mutant cells and the original genotype cell will give rise to more original cells."
] |
[
"Would any differences arise in organisms which undergo spiral cleavage?",
"EDIT: Finally got to a computer, looking at the photos seem to indicate that the same thing happens as with everything else."
] |
[
"I really don't know, actually. It's an interesting question, but development's nearly as far from my area of expertise as you can get."
] |
[
"Does a second dose of vaccine restart immunity or does it carry the 80% protection from the first dose through the whole process?"
] |
[
false
] |
Will you still be 80% protected from the first dose immediately, or a day or two, after receiving the second, or are you back to no immunity until the second dose is fully active?
|
[
"The immunity generated from the first dose doesn’t magically go away. The second dose is there to build on the work of the first dose and remind your immune system what does the enemy look like. In more technical terms, the first dose generates IgM antibodies that serve as an immediate response to the foreign protein your body has encountered, but to build a lasting immune memory, IgG antibodies need to be made. The first dose does a good job at generating those IgM and a bit of IgG. The second dose will boost that IgG production."
] |
[
"The second dose usually has more side effects because you already have an immune system ready to attack what is being injected into your body. It’s a good thing. In fact, I’ve read that one of the reasons that people have reactions during the first dose is because they had COVID and didn’t know about it (asymptomatic)."
] |
[
"Ok, I just wasn't sure that with the second dose if maybe your immune system was too busy figuring out the new dose to fend off outside infection, since the second dose typically has more side effects",
"Thank you for your response"
] |
[
"Difference in color of Zink/Tin?"
] |
[
false
] |
(I'm not aware of if I'm in the correct subreddit) Let's get this straight; How do i determinate, by just looking at it, if a chunk of metal is made of zink or tin? Or if i have one bit of tin and one bit of zink next to each other?
|
[
"Just eyeballing it? I doubt you could do it reliably. You could measure their densities most easily. Beyond that, you'd need the power of qualitative analysis to figure it out."
] |
[
"That's very often a thin layer of oxide that you're looking at instead of the metal itself. It might be enough to distinguish the two metals, but I don't think it would work on a pair of freshly polished metal surfaces."
] |
[
"eyeballing it from wiki pictures (obviously not accurate) seem to have zinc with a blue-er tinge than tin. ",
"Is there any resource that plots some kind of reflectivity spectrum for various metals/materials? Compare the relative reflectivity of blue to red for zinc and for tin, maybe find tin a \"flatter\" distribution?",
"Edit: Spectral Relfectance Curves is the phrase I was looking for."
] |
[
"How do cities of various sizes change weather patterns?"
] |
[
false
] |
This may just be a meteorological coincidence, but I noticed the storm line as it was approaching the Dallas metroplex seemed to be in a nice crescent curve as it passed through Texas, until about 30 minutes ago when it started to pass by Fort Worth. Piqued my curiosity, do cities have an impact on weather patterns like this? Or is it just a coincidence?
|
[
"There was a paper published just a few months ago on this: ",
"Energy consumption and the unexplained winter warming over northern Asia and North America",
". They found waste heat from cities can alter and widen the jet stream, effecting weather up to a 1000 miles downstream."
] |
[
"Large cities can definitely affect weather patterns. For one, skyscrapers and other large buildings cause turbulence in the lower layer of air movement (wind), which will increase the buffeting effects of wind. ",
"Second, the air above a city can be significantly warming than if the urban area was not present. The dark roofs and pavement have a very low ",
"albedo",
", meaning they reflect little radiation (and subsequently increase in temperature). Metal roofs will also increase in temperature due to solar radiation (temperature increase due to solar radiation must be accounted for when designing structures in Canada [NBCC Commentary E, Table E-2]). ",
"This",
" picture shows the surface temperatures for Atlanta, Georgia. ",
"How this relates to weather systems is that one type of lifting mechanism, convection, is caused by the heating of the ground relative to the air. ",
"Convective storms",
" are common in the summer-time after a day of lots of sun exposure. The warmer air at ground level will attempt to rise above the cooler air. When the warm air rises, it will begin to cool. If it is a humid day (high relative humidity), the water vapour will begin to condensate and precipitation will occur. ",
"Ha, sorry, got off on a tangent about storms. I'll stop myself before I go too far. In short, cities can increase the air temperature around them which will aid in the formation of convective storms. ",
"Parts of ",
"this paper here",
" may be of interest to you. "
] |
[
"A sudden increase in surface roughness is going to force convergence at the surface, which will definitely have an effect when the atmosphere is unstable enough to sustain convective storms. The same thing happens along coastlines, when the wind passes from a smooth sea/lake surface onto the land."
] |
[
"will a nuclear bomb produced 20 or 30 years ago still detonate as it is planned?"
] |
[
false
] |
i always wondered what would happen if you deploy a nuclear bomb produced long time ago. obviously nobody has ever tried this so it all very theoretical. to get full force all components have to be very precisely calibrated but nuclear materials decay with time. is there a chance that it will go off but just create a lot of pollution without proper detonation? are the active materials supposed to be renewed once in a while? if so is anybody is doing this in reality?
|
[
"In the US, ",
"stockpile stewardship",
" is one of the big missions of the DOE, and it about exactly this. Making sure that the aging stockpile is still ready to be used at any time, even though since the 1990's we no longer perform \"integrated testing\" of nuclear weapons."
] |
[
"you absolutely need to some kind of live testing to be sure...",
"Well the DOE disagrees. We can do very sophisticated calculations, and various kinds of tests of the subsystems without producing a real nuclear yield. This is what the US is currently doing to maintain its stockpile. And I don't think any nation doubts the efficacy of the American nuclear deterrent.",
"russia has definitely space to do this somewhere in siberia.",
"Having \"space\" isn't really the issue. North Korea has space for underground tests too, and they've used it. The US still has the fully operational Nevada National Security Site, which could resume underground testing if necessary.",
"However the technology exists to detect when people are testing. Even the very low-yield tests that Russia was conducting recently were detected by the DIA. Testing to produce a nuclear yield is prohibited by the CTBT, which the US isn't officially party to, but still observes."
] |
[
"I think the Russians are absolutely doing it too. There is even evidence that they have done some underground testing recently, which the US doesn't do anymore."
] |
[
"Does it matter from which plant pollen comes from when creating a seed?"
] |
[
false
] |
Will pollen from a rose pollinate a lily just the same as any other plant?
|
[
"Pollen is what's called a 'gametophyte' and is one of the reproductive cells from a plant and as such holds 1/2 of the genetic material needed to form a viable seed. it forms on the stamen of the flower, the (usually) longer interior stalk nestled in the center of the petals. reproduction in plants is genetically not really different to anything else. using your example of a rose (Rosacea) and a lilly (Lileae) the genetic material of the two will not combine. however if you got a red rose and a white rose they are both in the same genetic 'family' and as such are able to be cross bred. this is true for the majority of plants, if the genetic material is similar enough to each other in terms of family/species then you can successfully crossbreed plants of different appearance. I would recommend you read about Gregor Mendel and his amazing experiments with plant hybridisation. which further explores the intricacies of genetics (which appear to me to be a lot more 'simple' with plants).",
"Hope i answered your question!"
] |
[
"Some are so different that they don't fit before pollination and other are genetically instable after pollination. There is no simple answer. "
] |
[
"The pollen must work its way down through the pistil into the ovary for proper fertilization. Fertilization doesn't happen immediately upon contact between pollen and pistil. (I don't know what causes the pistil to accept the pollen, it could be surface receptors and such, maybe someone can clarify my schooling isn't at this level yet) ",
"ITo further elaborate on your question. In the case of perfect plants (flower contains both male and female parts) either the plant will stagger its pollen release with its egg development, or it will have certain mechanisms in place where the pistil will either reject the pollen upon contact and not allow for the progression into the ovary. or the plant itself can either block fertilization or completely abort the fertilized embryo.",
"-From a Plant Biotechnology student",
"EDIT: what do you know i found this a couple links after this one. ",
"https://www.reddit.com/r/askscience/comments/3z2rpb/pollen_grains_grow_pollinic_tubes_of_considerable/cyjh2z2"
] |
[
"What type of fundamental force would fire and chemical reactions fall under?"
] |
[
false
] | null |
[
"Basically all of chemistry is electromagnetic."
] |
[
"Thanks man! So 2 follow up questions"
] |
[
"It depends on how you heat them up, but basically anything you can do to them while still remaining within the realm of chemistry (as opposed to accelerating them to very high energies and colliding them) will ultimately be the result of electromagnetic forces."
] |
[
"What Is This \"Imaginary\" Mass That Is Created by the Higgs Mechanism? Layman Explanation, If Possible?"
] |
[
false
] | null |
[
"Can you give some more context for where you saw imaginary mass?"
] |
[
"Actually don't remember where I found that part. I just don't see how that mass is created."
] |
[
"Well there aren’t any physical particles with imaginary masses. The Higgs field gives mass to particles which interact with it, because it has a nonzero vacuum expectation value. That means that the field is not zero even in an empty space. And anything which interacts with that field has some energy associated with that interaction, and that contributes to the masses of those particles."
] |
[
"How does the curved shape of a chopper's blade cause an increase in the speed of air passing above the blade than below it?"
] |
[
false
] |
About airfoils, it's said that a wing's top is curved and its bottom is flat. . This relates to Bernoulli's Principle. I have never been able to understand this fact about airfoils, or to be more precise, I could never...errr... visualize it? How does an increase in surface area (i.e. curved rotor blades) cause an increase in speed of air passing over it? I understand that this speed increase causes a pressure decrease due to Bernoulli's principle, but why exactly does the speed increase?
|
[
"Airflow and the way a wing works is actually a complicated and misunderstood topic.",
"https://phys.org/news/2012-01-wings.html",
" ",
"If you needed a curved airfoil, then a flat wing could not create lift. Many model aircraft that fly fine with flat wings would like to prove you wrong. Less efficient, but still works."
] |
[
"Agreed. In addition, if curvature of an airfoil were the only factor in creating lift, aircraft couldn't fly inverted (that is, upside down). My answer addresses the OC's question, but @joefarmer13 makes an important point.",
"The primary value of the curvature in an airfoil is two-fold: 1) a curved airfoil will deliver lift more efficiently (that is with less drag) than a flat one, and 2) a curved airfoil will provide lift at more extreme flight conditions where a flat one will stall and provide reduced lift."
] |
[
"This is indeed the standard argument that you hear repeated a lot, but it's worth emphasizing that it's completely wrong! In an actual wing there is sheer, and the sheets don't unite at the same position (the air above the wing is faster than the one below). E.g. ",
"here",
" is a video from a wind tunnel which shows this effect."
] |
[
"Would the backscatter scanners at air ports detect objects concealed under rolls of fat?"
] |
[
false
] | null |
[
"No, they don't see anything behind or under skin."
] |
[
"It cannot pick up anything, of any kind, inside your body. The X-rays bounce off of your skin, which is what draws the image. Anything beneath or behind anything denser than skin won't show.",
"Yes, you could hide things in your rectum and they would not show up.",
"A standard metal detector would be much better at detecting metal inside your body, however."
] |
[
"It cannot pick up anything, of any kind, inside your body. The X-rays bounce off of your skin, which is what draws the image. Anything beneath or behind anything denser than skin won't show.",
"Yes, you could hide things in your rectum and they would not show up.",
"A standard metal detector would be much better at detecting metal inside your body, however."
] |
[
"Is there a difference in efficiency of solar power in space compared to on Earth?"
] |
[
false
] |
I was browsing through the astronaut AMA when I thought about the solar panels that they have on space stations. So I wondered if, considering the lack of a huge magnetic field and atmosphere/ozone, more solar power can be gained from the sun when in space rather than on Earth.
|
[
"Efficiency doesn't necessarily increase for more incident light (less atmospheric absorption) since its in the denominator (i.e. power producer per power of light incident). Power output definitely does however. You can get an idea of how much a difference the atmosphere makes ",
"here",
". Solar panels tend to be less efficient under more light so it isn't necessarily a twice the light in twice the power out scheme, but it can be fairly close. The Earth's magnetic field is not relevant.",
"On a side note, solar panels in space are usually ",
"multijunction",
" solar cells because they can be much more efficient. They are much more expensive to manufacture, so they aren't used so much down here, but in space most of the cost is getting it up there, so the more power it makes per weight/size the better. So in that way, solar panels in space are much more efficient.",
"Edit: There are also issues of dirt buildup on the panels which are fixed in space, but issues involving collisions with space debris are introduced. Tactics for keeping the panels aimed at the sun would also be totally different in space compared with Earth."
] |
[
"Very nice response. Almost everything is right on and explained well, however the efficiency goes up in general as light intensity increases. This can be found by looking up concentrator PV or light intensity variation efficiency.",
"While a first approximation would say that just by increasing the amount of light the current scales. However as light intensity increases carriers farther away from the junction can be extracted due to the higher induced internal electric field."
] |
[
"You are indeed correct for traditional architectures. I was thinking of the type of PV I used to work with where the opposite is true, and I should have done some more poking around. Regardless, the increase seems to be fairly ",
"small",
" for the amount of light intensity change we are talking about. "
] |
[
"Why do humans and other animals have multiple eye color possibilities?"
] |
[
false
] |
Is there a reason for this evolutionary or is it just a mutation that never had negative effects so it stayed?
|
[
"It's a mutation with no real drawbacks in terms of survival, so it has thrived amongst the \"normies\" within each respective species."
] |
[
"I am only in first year optometry school:",
"Our eye color depends on the amount of melanin produced by melanocytes in our iris. The more the melanocytes are stimulated to produce melanin the darker our eye color. Thus, people with lighter eye colors have less melanin producing melanocytes than people with darker eye colors."
] |
[
"The iris has two layers, the stroma and the epithelium. In a blue-eyed individual, the stroma (the top layer) is weakly pigmented, and the epithelium has very strong pigmentation. Longer wavelengths of light travel through the stroma and are absorbed in the dark epithelium. Shorter wavelengths of light undergo Raleigh scattering in the stroma (which is very turbid, i.e. \"hazy\"), and reflects back out of the eye as a blue color. It's the same process that causes the sky to appear blue.",
"So, it ",
" genetically determined, because it's still a specification of pigment levels. It just depends on which areas of the eye contain different pigments. Also, yes, it ",
" based on the molecular structure of the iris; those two statements aren't mutually exclusive (that is, they can both be true at the same time)."
] |
[
"What was the big deal with the Y2K bug?"
] |
[
false
] |
I remember back in the end of 1999, people were going crazy about the Y2K bug. They said that once the clocks hit midnight on new years eve, all the computer systems worldwide would crash because the year category would go from 99 to 00. My question is why would this cause such a scare? So some date categories on some computer files would be inaccurate. Why was this that big of a deal?
|
[
"Imagine banks flipping their dates from 1999 to 1900, or going from 1999 to 19100. You'd have interest rate calculations and such operating on wildly inaccurate dates.",
"Any time-critical application could be compromised. Nobody cared about personal files."
] |
[
"Well depending on the system, different things could happen.",
"Some would be lucky that the date would just be wrong.",
"\nWhich has its own problems considering how many businesses use computers for record keeping.",
"Others wouldn't be so lucky.",
"\nThe main problem would be a GPF because the system is trying to store data in a location that doesn't exist.",
"Memory being allocated in a certain way means that you can't go from two-digits [YZ] to three [XYZ]. It's like having an orange in both hands, and trying to pick up a third - you can't hold the third orange without a third hand."
] |
[
"As tempting as it is to say that it was all hype, the truth is that it was a foreseeable problem, and there were many working hours spent working on the solution. There were no worldwide problems because companies did prepare for it. "
] |
[
"What determines the color of the Aurora Borealis?"
] |
[
false
] |
I normally see green, but I hear that different colours can occur.
|
[
"I found the answer here: ",
"http://odin.gi.alaska.edu/FAQ/#color",
"It seems the colour's based on height of the aurora (different atmosphere composition), and also the energy of the excitation. It's not as simple as I thought it would be."
] |
[
"Green is generated by molecular oxygen, while brownish-red by atomic oxygen and blue+red by molecular nitrogen, apparently."
] |
[
"A bunch of the Common gases such as Oxygen, Nitrogen (plus many others) are commonly found as diatomic molescules. Oxygen that we breath in is O2 (i.e. two oxygens bound together)",
"http://en.wikipedia.org/wiki/Diatomic_molecule"
] |
[
"How do remote control cheating dice work?"
] |
[
false
] | null |
[
"In this particular video, the bottom plate is important. It will most likely contain an electromagnet that is powered by the device standing to the side. The dice have a piece of metal embedded on one side. The remote controls the electromagnet, so when the remote is used the side of the dice with the metal is attracted to or repelled from the bottom plate (depending on which button on the remote is pushed)."
] |
[
"That would be logical, but the die is clear, and in some close up shots I've seen of the clear variants, there doesn't appear to be any meal or magnets inside. Additionally, most advertise that you can smash them to bits and not find the mechanism"
] |
[
"I suppose that the material used to make the markings on the faces of the die could be metallic. The 6-face will have more of it than the other faces, so it'll interact with the magnet the most."
] |
[
"Does mankind now possess the ability to roughly predict what evolutionary traits humans will take on in the future?"
] |
[
false
] | null |
[
"It's not possible to predict this, since we don't know what environmental factors humans will face in the future.",
"We can say things like, ",
" - but we don't know for sure whether it's going to get colder, warmer, or what.",
"(Repeat for many, many other factors.) "
] |
[
"Evolution takes such a long time, technology advances are taking place at the equivalent of a blink of an eye. There is no chance that natural evolution will take place for our reliance on technology unless there is a very very long term stagnation.",
"Secondly the natural selection part of evolution doesn't really exist in modern society, and seeing smaller things on screens probably won't help anyone survive longer."
] |
[
"Evolution takes such a long time, technology advances are taking place at the equivalent of a blink of an eye. There is no chance that natural evolution will take place for our reliance on technology unless there is a very very long term stagnation.",
"Secondly the natural selection part of evolution doesn't really exist in modern society, and seeing smaller things on screens probably won't help anyone survive longer."
] |
[
"Why does a black hole gets less denser when you add mass to it? Shouldn't gravity make it even more dense?"
] |
[
false
] | null |
[
"We don't really know what happens when mass goes beyond the Swarzschild radius. Mathematically, at the center of a black hole is a singularity, which is a point with infinite density, but that seems to be unphysical. Since we don't know how matter is distributed in a black hole, we can't really make a definitive statement on its density.",
"Which is why the \"density of a black hole\" is typically defined as the ratio between the mass of the black hole and the volume enclosed by the Schwarzschild radius. This is a reasonable definition in the sense that a homogenous distribution of mass in this entire volume exerts the same gravitational force on objects outside the Schwarzschild radius as a distribution where the mass is more localized in the center or even the limit case where all mass is gathered in a single point.",
"Since the Schwarzschild radius is proportional to the mass and the volume is proportional to the cube of the Schwarzschild radius, that makes the volume proportional to the cube of the mass. And since density is mass over volume, that means that the density is proportional to the inverse of the square of the mass."
] |
[
"The density of a black hole isn't the most meaningful parameter, but here we'll define it as the ratio of the mass of the black hole to the volume enclose within the Schwarzschild radius. The radius here is proportional to the mass, but the volume is proportional to the cube of the radius. If the black hole gets twice as massive, the radius gets twice as big, the volume gets eight times as big, but the density becomes one-quarter as dense.",
"Black holes aren't the only objects with non-intuitive density relations. Planets are like that, with more massive gassy planets being less dense than small rocky planets (Earth is 8 times as dense as Saturn, for example). Even stranger are white dwarves, where the radius gets smaller as the mass gets larger."
] |
[
"If we know that within the schwarzschild radius, is contained everything absorbed by the black hole that hasn't been paid back to hawking radiation, couldn't we start to make assumptions based on speculation and see what might fit the data?",
"There is no data, we have no idea what the mass inside a black hole actually does, though the mathematics can give us some idea.",
"I've always imagined that a black hole is kind of like a tumor: a source of matter/energy",
"Black holes aren't a source of energy, they're simply what happens when a very large star collapses and passes through all of the degeneracy pressures, which causes all particles of a black hole to collapse into a single point/particle area. This happens because the gravity is stronger than the forces which hold particles apart and keep them separate from one another. This is definitely theory, as it isn't possible to observe the interior of a black hole.",
"that coalesces into a point and continues to grow until it reaches a limit, and begins to create a 4th dimensional sink \"hole\" in space around it. The matter inside pushes on space to create a field around it where space is bent so far that the Universal Speed Limit is not enough to escape.",
"This is basically a misunderstanding, black holes do create \"sinks\" in space time, the same way that all mass/energy does, they're just the heaviest and most dense objects known. That doesn't include and an escape velocity greater than the speed of light, which makes them inescapable, but the amount the warp space is enough that an escape path is impossible, once inside a black hole, all paths lead to the center.",
"At it's core, would be an ever increasing gravitational attraction ever increasing in pull, pulling things and absorbing them, gaining more pull, etc etc positive feedback loop. ",
"It's actually possible to orbit a black hole, a lot of things do, though they gain mass due to things which fall within the event horizon, it isn't really a feedback loop though.",
"What would be a good starting point, would be to attempt to start exerting gravitational forces on a cluster of atoms of varying atomic weight, and see how much force it takes for something to happen.",
"That will either tell you nothing, as all the atoms on earth already feel gravitation effects from earth and the sun mostly. In order to see big effects you'd need something like a neutron star at least to start of overcome degeneracy pressure. Gravity can't be generated, so simulating the effects of lots of gravity calls for lots of mass. It isn't remotely feasible.",
"This of course, requires an understanding of quantum gravity, and with it, we'd already reason away most of the mystery here. This is also so radical of a theory of mine that I'm sure most of it is wrong. Still, \"how wrong\" is a question I would like asked.",
"It really doesn't require quantum gravity to try, crashing every planet into the sun and waiting for the sun to die would probably do the job ok, it's just absolutely unfeasible and unthinkable.",
"As for how wrong it is? There isn't really a true part of it, except where it happens to intersect with the world."
] |
[
"Are there any animals besides humans that cook/prepare food in anyway? (x-post from r/AskReddit)"
] |
[
false
] | null |
[
"There are no other animals that are known to cook food to the same extent or quality as us. Only one captive bonobo, ",
"Kanzi",
" taught himself how to start a fire and cook food. Other then that there are no living examples, besides us who are able to accomplish such a task. However, fire and cooked food precedes the arrival of humans and I will get into this later. ",
"There are many other examples of how animals prepare their food on this thread. But none do it in the way or on the scale that we do it. That being said, ",
"some ants farm aphids.",
". ",
"First we can do a comparative analysis and look at what living chimps and bonobos eat. We find modern day chimps hunt for raw meat and it makes up a small part of their diet. The rest is raw fruit and plants. Thus we assume that our last common ancestor with chimpanzees, what would become us, and what would become them, have always eaten raw meat, but again this made up a small part of their diet. They also use rudimentary tools to accomplish this, some chimp groups use sharpened sticks like spears to hunt bushbabies. So the use of tools also likely dates back well into our ancestral ape lineage.",
"Our last common ancestor (LCA) with chimps lived about 6 million years ago and it would split into two lineages. One that would lead to chimps the other to humans. In between many species lived and died. Remember that this LCA was not a human and was not a chimp but its own species.",
" ",
"The ",
"Australopithecines",
" are some of our earliest ancestors of which we have fossil evidence. They appeared some 4 million years ago after the split with our LCA with chimps. There is evidence for them eating meat with tools but not truly hunting, cooking it or even having the ability to control fire. So the australopithecines ate raw meat, fruits and plants. It is also worth nothing that they probably engaged in \"scavenging\" rather then \"hunting\". This is because of the types of tools we find them with. These individuals would have to have had different internal gut morphology to deal with the raw meat and the parasites and bacteria that come along with that.",
"The ",
" lineage appeared about 2.4 mya with ",
" which evolved from an Australopithecine ancetsor. The first humans speciated about 200,000 years ago. Evidence for fire and cooked food dates between 300,000 - 1.8 million years ago. ",
": Excavations dating from approximately 790,000 years ago in Israel suggest that H. erectus not only controlled fire but could light fires. A site called Terra Amata, seems to have been occupied by H. erectus; it contains the evidence of controlled fire, dated at around 300,000 years BC. Despite these examples, some scholars continue to assert that the controlled use of fire was not typical of ",
", but only of later species of ",
", such as ",
".\"",
": Some scientists argue that even the earliest members of the ",
" lineage used controlled fire to cook food, starting with ",
" at around 1.8 mya. They justify this with changes in morphology resulting from this cooked diet like shorter guts and changes in dentition which reflect the new diet.",
"As fire and cooking developed to be more complex/widespread this lead to an even greater varied foraging and extracting diet. It's unclear if every ",
" species used fire (there were lots of them) or how often it was used, or what all the types of food that were cooked. We just don't have enough fossil evidence, yet. We do know that the diet was mostly cooked plants (tubers, fruits...) and that a smaller portion of the diet was made up of cooked meat. We do know that as tools became more refined, and hunting became more efficient meat increased in proportion. Fire, having been used to modify our food also in turn effected our internal gut morphology. ",
"Thus, anatomically modern humans have always had the ability to control fire, and cook food. We are uniquely adapted to a cooked food diet and what we ate changed slowly over time - from our common ancestor with chimps to ",
". What is known is that the control of fire and cooked food precedes our arrival. Our lineage (the ",
" genus) has always been omnivorous, we are adapted to a cooked food diet made up of mostly plants and some meat.",
"It is also important to not that true hunting did not likley arise until we were well into the ",
" genus. The first members of our lineage - the australopithecines and ",
" + ",
" were more scavangers than hunters. While they certainly could have hunted, it was more likely opportunistic - coming a cross an injured animal etc. Hunting only really came into its own with the development of complex tools like spears, throwing spears and much later bows and arrows. From what we know Neaderthals had spears that they could not throw - they had to get really close to the animal and stab it. This increased chances of being injured or killed while on the hunt. Humans invented the throwing spear so that they did not have to get so close to their prey. Decreasing the risk. Before this there is less clear evidence for spear although it is possible H. erectus had them. H. habilis had ",
"oldewan tools",
", H. erectus had ",
"acheulean tools",
" and humans had many tool industries.",
"The next two articles discuss the origins of cooking food, its a highly debated topic. ",
"Human Adaptation to the Control of Fire by RICHARD WRANGHAM AND RACHEL CARMODY.Evolutionary Anthropology 19:187–199 (2010) ",
"The raw and the stolen: cooking and the ecology of human origins. Wrangam et al. 1999. Current anthropology. 40(5):567-594 ",
" - Hunting/Scavenging for meat with tools probable (6 MYA), Hunting/Scavenging for meat with tools (evidence - 4 mya), Control of fire and cooking evidence: morphological (~ 1.8 mya), physical (400,000-700,000 years ago), arrival of humans (200,000 years ago)."
] |
[
"Might not be what you had in mind but a good example would be Spiders and Snakes using venom to aid in the digestive process. "
] |
[
"Certain tribes of japanese snow monkeys wash their food in the sea to add a salty taste scientist presume.",
"It started as a habit of a single female but spread over the whole tribe quite quickly. This is seen as a rare occurance of \"cultural\" behaviour in other species than humans."
] |
[
"Why are ungulates classified by toe parity?"
] |
[
false
] |
I just discovered on Wikipedia that, contrary to my intuition, deer, moose, giraffes, camels, and sheep are all only very distantly related to horses. The former are all Artiodactyla while horses are Perissodactyla. This is rather strange to me because they look very similar and certainly more similar than a moose and an orca do (apparently orcas are also Artiodactyla). How is it possible that orcas and moose are more related than horses and moose? Edit: For clarification, I understand how phylogeny works based on shared ancestry, not morphology. What I am more interested in is any more in-depth background on how the decision was made to classify ungulates based on toe parity, and perhaps anything on how exactly orcas fit into this.
|
[
"It is because we determine things as more closely related if they share a more recent common ancestor. So orcas and moose shared a common ancestor more recently than orca and horse or moose and horse. \nDNA supports Perissodactyla and Artiodactyla (or Cetartiodactyla) as two separate groups. \nWithin mammals, convergent evolution (traits that look similar but do not share a single origin), is pretty common. This makes determining relationships from morphology alone much more challenging! \nIf you are interested in cetacean evolution and how they came about from the artiodacyls you could look into transitional fossils for this group. It's actually really cool (to me anyway) to see the mix of traits as the cetaceans adapted back into life in the water!"
] |
[
"The ungulates (hoofed mammals) often share a superficial resemblance to one another because they are all loosely related. Before the genetic era taxonomists attempted to classify them based on morphology alone. There was a fair amount of guesswork involved in deciding which morphological features were taxanomically relevant. ",
"At some point it was realised that the ungulates fell into two broad groups. Those who's axis of their limb (ie the distribution of weight down the leg) passed through the middle digit, and those who's passed between two digits. The former condition was described as mesaxonic and the latter paraxonic. This formed the basis of the division of the ungulates into the\"odd toed\" Perissodactyla and the \"even toed\" Artiodactyla.",
"There were other morphological features that seemed to follow that same division, lending support to it being a taxonomically relevant grouping. These were things like the presence of horns, the number of dorsolumbar vertebrae, and the anatomy of the skull and femur.",
"It seems that the morphologists got it right in this case. The division of the odd and even toed ungulates has held up after being examined genetically. ",
"The Cetaceans (including orcas) were moved into Artiodactyla based on genetic work, which showed them to be most closely related to Hippos. This relationship was not realised based on morphology."
] |
[
"I can expand on this and answer specifically the question in the title. Organisms are classified based on how closely related they are to one another, not based on a single morphological trait, but a morphological trait can be a convenient way to distinguish between two groups. Even when phylogenies are built from morphological data (not common in the age of molecular biology) they use dozens of traits, which can be as simple as number of toes, but more often are measurements of different body parts or ratios of those measurements. It might be just as correct to say that Perissodactyla and Artiodactyla are distinguishable by the ratio of femur length to pelvis width (just for example, not a real measurement they used), but number of toes is much more convenient."
] |
[
"Why was increase in biodiversity so slow during much of earth's history?"
] |
[
false
] |
Diagrams such as this one: shows how global biodiversity has been increasing very fast during the past 150 million years, despite the K–T extinction event. Biodiversity also exploded until the Ordovician–Silurian extinction. Why does increase in biodiversity between mass extinction events appears so slow between the Silurian and Jurassic period? Is it many smaller extinction events, a badly preserved fossil record, fewer continents..?
|
[
"Punctuated equilibrium, aka 'everything is calm until an asteroid hits'",
"Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little evolutionary change for most of their geological history. This state is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.[1]",
"https://en.wikipedia.org/wiki/Punctuated_equilibrium"
] |
[
"Good question!",
"The first thing to note about that diagram is that 4 of the 5 largest mass extinctions occurred between the Silurian and the Jurassic, with the largest ever extinction event (end-Permian mass extinction) near the point where the derivative changes from negative back to positive (~250Ma). It's important to remember that the red curve is an approximation curve generated by smoothing out the jaggedness of the data, so the depression around ~250Ma has a lot to do with the severity of the end-Permian extinction.",
"The next thing to note is that the weirdest part of the curve isn't the \"stagnant\" Paleozoic, but rather the ultra-high upward trend in the Mesozoic through the Cenozoic. Why that rapid increase? If we think about population growth as an analogy to biodiversity growth, one natural model we could use is the logistic curve. The logistic curve is characterized by having a carrying capacity, and in the case of population growth, the carrying capacity reflects limitation in resource availability (i.e. population cannot sustain constant growth due to finite resources). In the case of biodiversity growth, by analogy one could imagine a carrying capacity set by limitation on niche availability. Following this reasoning, it actually makes a lot of sense that there is a plateau following the Ordovician as the number of niches gets filled up after the Cambrian explosion and the Great Ordovician Biodiversification Event. So, given all that, how is it that following the Great Dying of the end Permian we get this rapid growth? The answer may lie, surprisingly, in the modeling of human population growth. It turns out, that human population growth does not follow the logistic curve all that well. Instead, it follows more closely the hyperbolic curve. What this means is that human population carrying capacity actually increases through time due to technological advancement. Instead of hitting a max limit, human population size increases, which increases the rate of technological advancement, which then increases carrying capacity, which then in turn increases population size, creating a positive feedback. Looking back at the biodiversity curve, a similar thing could be at play, where diversity growth leads to increase in community complexity, which leads to opening new niches, which then leads back to further diversity growth...",
"Thirdly, there may have been some sort of selection at play. If we look at just the ",
"background extinction rate through time",
", we see that it is steadily decreasing. It's possible that life is getting better at surviving as lineages that are more prone to extinction get eliminated. ",
"Sources: ",
"http://www.sciencedirect.com/science/article/pii/S1871174X07000030",
"\n",
"http://www.sociostudies.org/almanac/articles/hyperbolic_growth_of_the_human_population_of_the_earth-_analysis_of_existing_models/"
] |
[
"That is necessarily an incomplete explanation. The K-T extinction event was neither the only nor the largest mass extinction event during the phanerozoic, and biodiversity already seems to be trending rapidly upwards by the mid-Cretaceous, so the meteorite is surely no the only cause. "
] |
[
"If the universe is infinite, how are we getting recurring comets? \"This comet last passed us 10,000 years ago\" hold up, why wouldnt it just, keep going? I understand its path would get swayed by planitary objects, but to go exactly full 360 over and over, and repeatedly pass us? Confused"
] |
[
false
] | null |
[
"Almost all of the non-star things we can see from Earth are gravitationally bound to our Sun. The other planets, the asteroids and comets, moons, etc are all part of our solar system, which means they are bound to the Sun. Most of the planets have nearly circular orbits, so they have very repeatable, normal patterns, while some of the comets and asteroids have highly elliptical orbits (spend a little bit of time close to the Sun moving fast, but spend most of their time far away from the Sun, moving slow). It's these comets with highly elliptical orbits that have these odd patterns you're mentioning. Probably the most famous comet, ",
"Halley's Comet",
" has a very high eccentricity (of 0.96. 1 is the max eccentricity, Earth's is 0.016), meaning it can be up to 35 AU (1 AU is the average distance from the Sun to the Earth), and down to 0.5 AU. ",
"What does it mean to be gravitionally bound? One way of thinking about it is that the total energy of the system (system being object orbiting and the object it's orbiting) is negative. How is it negative? Traditionally we consider gravitational potential energy to be negative- and it gets more negative the closer you get to it. Kinetic energy is positive, increasing with speed. So, if the sum of the kinetic energy + potential energy is negative, then the object is \"gravitionally bound\" to the object it's orbiting. ",
"This is how you calculate escape velocity, and another way of saying it is that the comets are traveling at less than the escape velocity of the Sun",
"."
] |
[
"This is an amazing answer, thank you 👑"
] |
[
"To expand further, the individual stars that we can see are generally gravitationally bound to the Milky Way Galaxy. Our sun and other stars are orbiting the galaxy itself (it gets confusing. Stars individually orbit the galaxy, but they, collectively, ",
" the galaxy.)",
"Entire galaxies aren't necessarily orbiting anything, but they will react to the gravity of other galaxies, sometimes even colliding and combining (like the Milky Way and Andromeda will do in billions of years)."
] |
[
"Are modern day lenses for glasses (the kind you wear) still made of actual glass, or are they plastic now? If they’re made of plastic, how can they correct vision as effectively as actual glass lenses?"
] |
[
false
] | null |
[
"Are modern day lenses for glasses (the kind you wear) still made of actual glass, or are they plastic now?",
"There's a mixture of glass and plastic lenses around. Many have various coatings too, for tinting or scratch resistance.",
"If they’re made of plastic, how can they correct vision as effectively as actual glass lenses?",
"Any material which is transparent to visible light and has a different index of refraction to air can be used to form functional lenses.",
"You could put water in a sandwich bag and use the result as a lens, which in fact is quite similar to how the corneas in our eyes work, and is a technique mentioned in several survival handbooks.",
"Here's an article about polycarbonate vs Trivex plastics in the context of sight-correcting lenses"
] |
[
"To add to the other answer. For a good spectacle lens you want a material with:",
"Various plastics meet these requirements quite well, as does glass.",
"Besides material choice it's just a case of making the lens to a high quality. A good pair of glasses will have lenses made to a precise shape and well polished. The same plastic, if it was used in a toy magnifying glass made to a much lower quality, will make an inferior lens."
] |
[
"There's another \"high-index\" plastic that is used for very high prescriptions, though I don't remember offhand what it's called.",
"Thiourethanes, according to Wikipedia. (I didn't know either, and I wear them!) I hadn't heard that softness was an issue with them. I'd always been told that it was simply because my high prescription meant for very thick, unwieldy edges if the lenses were too wide. I can't wear half-frames for the same reason.",
"High index lenses have less chromatic aberration, and thus afford the wearer a wider field of vision. They are actually thicker than polycarbonate lenses of the same prescription, but the trade-off is acceptable."
] |
[
"What happens physiologically to a crash victim in an airplane crash on impact?"
] |
[
false
] |
My girlfriend passed away a while ago in one and last night I had a rather violent dream about it. I'm sure (or hope) that victims don't die that way, but now I'm wondering how they DO meet their demise. In my girlfriends case specifically, the pilot overshot the runway, crashing into a valley because there was no runway left. It wasn't exactly plummeting out of the sky, but investigations say the pilot probably attempted to abort the landing so I'm assuming the plane was at takeoff velocity. Assuming there was no instant fire, what happens physiologically on impact at that speed? (and out of curiosity, will it be the same for an aircraft that "falls out of the sky"?) (EDIT: It's highly unlikely that anyone can answer what exactly happened in this specific case, so I can't really expect to get an explanation in that respect. Just looking to know what happens in general =))
|
[
"I think you found the right man for this question. I have a airport right by my hospital and I am trained to deal with aviation emergencies. I just need to know what type of aircraft we are talking about. Also what type(s) of aircraft are you interested in hearing about (private prop plane, private jet, charter jet, commercial jet, ",
"? As soon as you get back to me I will be able to help you out. Also if you can give me any additional information I can give you a better answer or at least give you the most probable scenarios. ",
"I would also like to say that I am very sorry for your loss, and I hope this information can help you deal with your loss easier. If there is any details you would like me to leave out to make this easier for you, please let me know. "
] |
[
"The sheer amount of things that can happen in high speed impacts is almost limitless. Cause of death can range from heart trauma, to brain trauma, to loss of blood, to almost anything. If you interested in any specificts please let me know.",
"In the case of commercial aviation accidents there is however a short list of common injuries based on the type of crash. In the events that you have described to me (provided I am interpreting it correctly) most of the injuries sustained are a question of physics. The forces acting on the body can range from minimal to extreme depending on large factors such as the speed of the aircraft, to relativly small factors such as the seat you are in ( this can greatly effect the torques you body feels, and any dampening effects from the split seconds of the impact prior to it effecting you). Realistically there are ",
" too many variables the make accurate predictions. Almost is the operative word here because with some pretty advanced modeling you can make some pretty accurate predictions. I feel I am getting on a tangent here however.",
"I will focus in on the more general inguries so give you the best general insight possible. There are actually multiple impacts to consider. Primarily there is the impact of you as you go forward and (more often then not in plane crashes) downward. This can lead to significant musculal skeletal injuries ranging from fractured femurs, to a fractured pelvis, to a fractured rib cage, to a fractured back, to a fractured skull. Those are really the most dangerous fractures. Femur fractures and pelvic fractures can lead to significant enough blood loss as to cause death. Chest fractures can lead to damaged organs or a heart and also significant internal bleeding. Fractures of the spine or skull can lead to central nervous system (brain and spinal cord) damage that can have numerous effects but it becomes most sever when either you brain stops sending the signals to breathe or you spinal cord is severe also causing you to stop breathing due to what is known as paralysis of the diaphragm (the muscle that causes you to breathe essentially). The next impact to consider is the one that results from anything inside your body coming to a sudden stop when you stop. This can causes significant damage to anything inside the chest cavity or the abdominal cavity. This can lead to interal bleeding, or when these forces are involved, even complete destruction of organs or any pathways between them. ",
"Lastly due to newtons 2nd(?) law. There is a recoil effect to any of these forces causing additional interal or external forces due to recoil and a repeated impact and transition of momentum into force. ",
"Many of these injuries can cause death on their own unfortunately, but a lot of it comes down to very little variations and what can almost seem as luck. These forces will normally be the cause of the majority of fatalities in an aviation accident. However, even if you are able to survive these forces, you may always succumb to death from burning because, even if not immediate, you almost always see fire accompany an aviation crash on land. This is due to the natures of the engines and jet fuel. This is especiallY true if you are damaged in a way that prohibits movement such as a broken leg. ",
"These are just the main causes of death, these are numerous more but these are the common injuries and causes of death you see. ",
"I really hope I helped to give you some insight into everything. ",
"If you have any other questions feel free to pm me or to reply to this. ",
"Edit: I wrote this on an iPad so I appologise if there are any obvious/stupid spelling or grammar mistakes."
] |
[
"Smoke inhalation is not only variable from person to person but also from situation to situation depending on the type of smoke, the volume of smoke, and amount of ventilation. Essentially, if the cabin were to remain mostly intact, it would probably take around 5 minutes from the first sign of fire and first few wisps of smoke.",
"The myth busters actually tackled the brace position and found that it did lead to less trauma, and specifically less spinal injuries. Unfortunately in the case of your girlfriend it seems that the pilot was doing everything in his power to get the plane back up and did not mention anything to those in back. Also if he was landing in poor visibility he my not even have known how dire the situation was and he may have felt that there was a greater probability that he would get the plane back up.",
"Do you happen to know the company and flight number or at least a location and date? I can try to do some more investigation."
] |
[
"Why are our thoughts linguistic/auditory, and not (for example) visual?"
] |
[
false
] |
[deleted]
|
[
"You're talking about some pretty outmoded cognitive psychology. We don't actually have language making up our thoughts (e.g., ",
".) When you start to think about it a bit, you'll find that for our thoughts to be done in language it'd be such a complex garble of information it would not be interpretable. You're referring to the phenomenological experience of cognition. Now, that does exist--to some extent. ",
"To bookend that, we do also have phenomenological experiences of thinking visually. You can try this yourself, think of a tiger. Now, count the stripes."
] |
[
"Do we really reason predominantly linguistically? How would you know? If what you mean by reasoning is explicit, cconscious manipulation of propositions then that's almost begging the question, isn't it. But if you mean draw inferences from data, obviously that's all our brain does, right down to the most basic non-linguistic parts. Even reasoning about other peoples mental states is seemingly nonlinguistic (just think ofhow instinctually you know what not to say when) and yet surely a great deal of that is some form of reasoning (if I say X, he'll punch me in the face; I don't want to get punched in the face, so I shouldn't say X, etc etc). It might be that to ",
" reasoning, we must express it linguistically (tho that's by no means demonstrated) but it's certainly not true that we ",
" in a linguistic mode."
] |
[
"you only think in language, never in pictures, pure sounds (that are not language), smells ...? I do ... I also totally agree with Ilikebluepens, I don't think it is possible to express all thoughts in language in our heads while thinking, it is just that when you try to express them, you will most likely choose language."
] |
[
"Why do spiders have eight legs?"
] |
[
false
] |
Insects have six legs so that they form a tripod when they take a step - they are too small to have a falling part of their gait as tetrapods do. But why do spiders, fairly closely related to insects and often facing similar locomotory challenges, have eight legs? Is this to do with max speed or efficiency when walking and running?
|
[
"Spiders and insects are not particularly closely related. ",
"This estimate from timetree.org",
" says that spiders and ants last shared a common ancestor 581 million years ago. At this time, our ancestors looked like this: ",
"http://upload.wikimedia.org/wikipedia/commons/5/54/Pikaia_BW.jpg",
"One major innovation in the Arthropods is the evolution of ",
" ",
"tagmatization",
", thanks ",
"/u/triloknight",
" This allowed different body parts to have different suites of genes expressed depending on if the segment was fore, midsection, or aft. The number of segments bearing limbs is different in spiders and ants, hence the different number of legs. More on segmentation can be found here: ",
"http://evolution.berkeley.edu/evolibrary/article/arthropods_05",
"Questions of \"why\" in evolutionary biology should always be approached with caution. We will never have any idea why a certain trait may or may not have been adaptive so many years in the past, in a different environment. You may also want to look into the works of Stephen Jay Gould, particularly Wonderful Life, which I believe is available for free somewhere out there. ",
"Much of Gould's work was focused on \"historicism,\" which suggests that much of what we see in the fossil record is \"stuff happened.\" Why did only the five-digited tetrapods survive when we have",
" evidence of tetrapods with other numbers of digits",
"? Probably because, by chance, only the five-digit tetrapods left descendants that survived until today.",
" I made this comment before the two top-level threads (which had many unsupported wildly speculative theories) were deleted. I think this topic would benefit from someone knowledgeable in the field of biomechanics, to specifically answer the challenges in walking with 6 or 8 legs in modern arthropods."
] |
[
"I'm glad you pointed out the distance between arachnids and insects - because in any of the still controversial arthropod phylogenies, the distance between Hexapoda and Chelicerata is quite dramatic.",
"I would like contest the claim:",
"One major innovation in the Arthropods is the evolution of segmentation.",
"Segmentation is not necessarily an innovation specific to Arthropods as it was vitally important in the evolution of various protostomes, namely Annelids, as well as deuterostomes, such as Chordates. I think perhaps a better wording might be that arthropods excelled in innovations regarding ",
", or specialization of metameric units. I apologize if this seems pedantic."
] |
[
"Fundamentally, the scientific consensus around evolution says that this is random and happened to work.",
"When you start asking \"why\" a biological entity is \"designed\" a certain way, you start running up against philosophical questions well beyond biology.",
"Consider, why ",
" we have eyes in the back of our heads? Why don't we have ",
" hearts? Why don't we have a third arm and hand?"
] |
[
"Why don't you get high the first time you smoke marijuana?"
] |
[
false
] | null |
[
"i was ripped my first time"
] |
[
"I didn't get the same results."
] |
[
"I didn't get the same results."
] |
[
"Is is true, as this paper cites, that \"All dwellers at high altitudes are persons of impaired physical and mental powers\"?"
] |
[
false
] |
I was reading this article called , and it cited a 1925 paper by Barcroft with the statement mentioned in the title. That people who live for their entire lives in high-altitude environment suffer some level of damage from the low amount of oxygen despite short-term and evolutionary adaption, and are noticeably less intelligent or physically vigorous as a result. Is there any merit to this?
|
[
"I don't have any scientific evidence but think of this: that was published in 1925 before we really knew too much about genetics. During a time were eugenetics were practiced and believed. ",
"I would not believe it unless it was proved by multiple papers with the last 15 years. ",
"Here is a website researching adaptations for those in low oxygen environments ",
"https://case.edu/affil/tibet/moreTibetInfo/hypoxia.htm"
] |
[
"Thank you for your research :) The link appears broken though."
] |
[
"That's weird. It was definitely there when I linked it. ",
"Well here's another paper, the interesting part about adaptations is near the end ",
"http://anthro.palomar.edu/adapt/adapt_3.htm",
"http://evolution.berkeley.edu/evolibrary/news/101001_altitude",
"I did a casual search for intelligence and low oxygen environments. Wasn't able to find anything. "
] |
[
"Is centripetal force-induced artificial gravity really as simple as we think it is?"
] |
[
false
] |
Considering a rotating circular spaceship, centripetal force would theoretically work... if you is standing still; but if you are moving in any direction in respect to the rotation of the spaceship, wouldn't it change the downwards force applied on you? For instance, if you were walking in the opposite direction of the rotation of the spaceship at the same speed as it is rotating, would you not just start to float? Or in contrast, if you were walking in the same direction as the rotation, would the downward force applied on you increase? --Sorry, not really well versed in the mathematical-physics realm yet, just wondering...
|
[
"In theory, yes, it's that simple. And the disadvantages you point out for walking in the same direction as rotation or opposite to it are correct.",
"In practice: you need to keep the angular velocity below 2 rpm to avoid motion sickness. In order to achieve usable gravity while rotating so slowly you'll need a very big radius and a very big tangential velocity (i.e. many km/h even if it's few rpm). You won't be able to walk or run fast enough to notice the difference in gravity, but a large radius means a very high cost.",
"The idea of making two relatively small habitable volumes connected by a long cable is often brought up in AskScience, but IMO it'd be really difficult (if at all possible) for a spacecraft to dock with your rotating space station if you don't have a non-rotating or slowly-rotating part in the center."
] |
[
"Also, another reason the ring has to be so big is that if it's small, the gravity you feel at your head will be different than the gravity you feel at your feet. Your body doesn't like that... so I've been told."
] |
[
"Yes, but I'm expecting the docking ship to be a very small mass when compared to the space station. For instance Mir was 130 tons, the ISS is 450 tons, a Soyuz spacecraft is only 8 tons."
] |
[
"Can I wash my hands with soap and tapwater in areas with contaminated water, or will the final rinse just recontaminate my hands?"
] |
[
false
] | null |
[
"Did I do it right?"
] |
[
"Did I do it right?"
] |
[
"Did I do it right?"
] |
[
"Besides a large spinning cylinder, what other options are scientists pursuing as a viable option of creating artificial gravity in space?"
] |
[
false
] | null |
[
"In a ",
"beam powered interstellar railway",
", a craft could be accelerated at 1g toward and then away from the destination, so that craft inhabitants would experience normal Earth gravitational acceleration. It would be nice to accelerate faster than 1g to get to the destination sooner, but humans would have a very hard time living in 3g for example."
] |
[
"140 million tons",
"Which is the equivalent of 2.72X10",
" MT... or 5.456X10",
" Tsar Bombas. That's a lot of energy. It might honestly be easier to just take the Earth with you."
] |
[
"140 million tons",
"Which is the equivalent of 2.72X10",
" MT... or 5.456X10",
" Tsar Bombas. That's a lot of energy. It might honestly be easier to just take the Earth with you."
] |
[
"Why does milk spoil if left out but the FDA says you can leave butter out as long as you need?"
] |
[
false
] | null |
[
"Butter has a much higher fat content, around 80%. Compared to milk, which has a much higher water content. The high fat content and low water content of butter makes it less susceptible to bacterial growth. ",
"That’s also why if you’re going to leave butter out for an extended period of time, it needs to be salted butter. The salt also helps keep it from going rancid."
] |
[
"Water. Very few microorganisms can grow in foods with low water content, and butter is down there. At 16-18% water by mass, it has less water than honey and about as much as typical dried fruits. Milk, by comparison, is around 87% water, and a much more hospitable environment for spoilage organisms.",
"A bigger threat to butter is rancidity, as the fats oxidize. This is generally a quality consideration, though, not a safety one."
] |
[
"Thank you for your time and detailed response I appreciate the clarity"
] |
[
"Why do mosquitoes transmit some viruses, like West Nile Virus, but not HIV?"
] |
[
false
] |
I'm in the DFW area and we had a safety training class at work today and one of the topics was west Nile virus. I asked the "safety Rick" why west Nile virus can be transmitted by mosquitoes but HIV isn't. He muttered something about it's changed by our blood.
|
[
"HIV doesn't infect the salivary glands of the mosquito",
", which is required for transmission to another person."
] |
[
"This was asked before, I cant seem to find it, but the amount of blood that is drawn, if it was from someone who is infected with HIV, there wont be enough of the virus in the sample + the possible trade of blood when the mosquito bites another person, to infect the new person.",
"I wish I could remember more but cant :/"
] |
[
"Several reasons:",
"Virus strains evolve to fit their hosts/mode of transmission, and the HIV viruses simply did not evolve to survive inside an arthropod vector.",
"HIV \"dies\"/is destroyed (depending on whether you consider viruses to be lifeforms or not) through contact with Oxygen in the air.",
"Source: Tropical Virology 4th Edition (ISBN 0199570884)"
] |
[
"How much slower do people at the equator age compared to someone at the south pole?"
] |
[
false
] |
Time is affected by velocity. A point on the edge of a spinning sphere is traveling faster than a point at its poles. It stands to reason that these two points should experience time at different rates. My question is, how much of a difference is there? (however minuscule)
|
[
"If you spent all of your life on the equator (40000 km in circumference, goes around once in 24 hours) the time dilatation you will experience is 1.00000000000238 relative to someone standing on the pole (and thus not spinning very fast). \nWhat does this extra 0.000000000238% means? Well, let's say you live to be 100 years old, this means you would have an extra 0.0075 second compared with Santa Claus (assuming he lives on the North pole). Notice that, since time dilatation applies to everything, your brain is also working slower, as are chemical reactions and everything, so you would not be able to notice you are slower. ",
"0.0075 second difference over 100 years, big deal."
] |
[
"How would gravity fit in this?",
"\nPlease bare with my as I might be mixing things up. Does the centrifugal force at the equator cause gravity to have less of an effect on a person than as someone at either poles, and thus effect the time experienced? So is gravity lower (by minuscule amounts) at the equator?"
] |
[
"Another reason is that the Earth is not a perfect sphere. The poles are 'flatter' than the equator so the distance between the poles and the core is less which leads to slightly higher gravity at the poles."
] |
[
"Geologists/Earth Scientists: Will all the current land on earth eventually be \"refreshed\" via subduction?"
] |
[
false
] |
[deleted]
|
[
"A simple steady state mass balance approach that gets to an estimate of the time it takes to recycle the continental crust:",
"The answer is that the crust is recycled, but not really in the way you're thinking of. Continental crust (CC) isn't really subducted much. Because oceanic crust is denser, when an oceanic plate collides with a continental plate, the oceanic plate will be the one subducted, while the continental plate stays on top. So the material that gets recycled and re-introduced by arc volcanism is largely ocean crust (similar to the mantle), and the sediments sitting on top of it.",
"You can also see this in the ",
"age distributions of continental crust",
". The average continental crust was formed ~2 billion years ago, and most of the crust was formed as a part of 3-4 major crust building events. So over billions and billions of years the continental crust persists on the earth. ",
"A good approximation you can make to determine the rate of CC returning to the mantle (equivalent to the subduction you ask about) is that of steady state. So, if we know the rate of CC formation today, and we know the amount of CC on earth isn't changing much, we can say that the amount of CC being lost to the mantle is roughly equivalent to the new CC being formed. That is, d(CC)/dt = CC_formed - CC_lost. We set d(CC)/dt equal to zero, So to a first approximation, CC_formed ~= CC_lost. So if we can determine either CC_formed or CC_lost (both rates), we can perform a residence time calculation. Residence time defined as the average amount of time something spends in a given reservoir or system. We want to know the average amount of time some mass of the continental crust spends on the surface before it is subducted - this will give us a rough estimate of the time it takes to recycle and regenerate the entire CC. ",
"Residence time (Tr) = (total mass or volume of crust)/input or loss rate. It turns out the easiest place to calculate a loss is in subducting sediments. But it's not the CC itself being subducted - it's the sediment sitting on top of the ocean crust that has been weathered from the continents into the oceans. ",
"Estimates of loss of CC to the mantle from sediments being subducted center around 0.7 km",
"/year ",
"(Plank and Langmuir 1998)",
". Let's round that to 1 to make the math easy. Now let's estimate the volume of Earth's continental crust. ",
"Continents cover ~30% of the earth, so the area of CC is Area_earth x 0.3 is about 5x10",
" km",
" x 0.3 = 1.5x10",
" km",
". ",
"Now multiply by the average depth of the continental crust (about 40 km) to get the total volume of continental crust on Earth. \n1.5x10",
" km",
" x 40 km = 6x10",
" km",
". ",
"Now we have our reservoir (volume of CC on Earth) and our flux (from subduction of sediments). Let's calculate the residence time and see how long it will take to recycle the whole CC (again, assuming steady state). ",
"Well, since our estimate is 1 km",
"/year, we just have 6x10",
" km",
" / 1 km",
"/year = 6x10",
" years, or 6 billion years. This is more than the current age of the Earth! "
] |
[
"Which, considering the life cycle of the sun, is longer than the earth has left to exist."
] |
[
"Fantastic, thank you!"
] |
[
"I've been reading on quorum sensing inhibitors, and I'm having a hard time finding an answer to my question. Do they eventually lead to bacteria death? Otherwise, what ultimately happens to the bacteria after their communication is disrupted?"
] |
[
false
] | null |
[
"In some species of pathogenic bacteria quorum sensing is the method that induces virulence. If there are enough bacteria they produce the toxins or whatever that cause the disease. If these pathways are blocked the bacteria would essentially think its alone, and therefore not become virulent. This is a great medical pathway because it does not kill the bacteria, which would make it much more susceptible to gaining resistance. After communication is disrupted the bacteria would continue living, but would not become virulent, even if there were other bacteria present in sufficient concentrations. "
] |
[
"To add, quorum sensing is often used in biofilm production and biofilms can protect bacteria from the immune system "
] |
[
"Sorry if this is incorrect, but your question makes it seem like you believe a quorum sensing inhibitor is literally one \"thing\" that's been discovered that disrupts bacterial communication.",
"This is incorrect.",
"Quorum sensing inhibitors are ANY chemical (Hell, it doesn't even have to be a chemical, but that's what it will be for the most part) that reduces the ability of bacteria to communicate with each other.",
"And remember, its mostly theoretical right now, I don't think there's a single study documenting, say, the successful curing of an infection using a quorum sensing inhibitor (which I imagine will be its principal application).",
"\"They\" do various things. It will vary based on the bacteria, the inhibitor and the environment.",
"For your first question:",
"It's certainly possible that we will someday find a quorum sensing inhibitor that causes some species of bacteria to terminate. ",
"It's also possible we will find one that disrupts their growth in other ways.",
"As to your second question:",
"Again, it varies. And it hasn't been fully explored. You could google some specific examples, but again that doesn't describe what always happens, or the full potential of what these inhibitors could do.",
"tl;dr",
"Probably sometimes."
] |
[
"Some ants cultivate fungus for food and use pieces to start new gardens. Do their cultivated fungus have evolutionary differences to their wild counterparts?"
] |
[
false
] |
I was thinking how different cultivated foods are versus wild ones in the human world.
|
[
"Ants' domesticated fungi are definitely distinct from their wild kin.",
"Here we document reciprocal shifts in the genomes and transcriptomes of seven fungus-farming ant species and their fungal cultivars. We show that ant subsistence farming probably originated in the early Tertiary (55–60 MYA), followed by further transitions to the farming of fully domesticated cultivars ... Modifications of fungal cultivars include loss of a key ligninase domain, changes in chitin synthesis and a reduction in carbohydrate-degrading enzymes as the ants gradually transitioned to functional herbivory. ",
"--",
"Reciprocal genomic evolution in the ant–fungus agricultural symbiosis",
"The crop fungi of attine fungus‐growing ants are suspected to have enhanced genetic variation reminiscent of polyploidy, but this has never been quantified with cytological data and genetic markers. ... This showed that domesticated symbionts of higher attine ants are polykaryotic with 7–17 nuclei per cell, whereas nonspecialized crops of lower attines are dikaryotic similar to most free‐living basidiomycete fungi. ... Genetic variation in the polykaryotic symbionts of the basal higher attine genera Trachymyrmex and Sericomyrmex was only slightly enhanced, but the evolutionarily derived crop fungi of Atta and Acromyrmex leaf‐cutting ants had much higher genetic variation. ... This stepwise transition appears analogous to ploidy variation in plants and fungi domesticated by humans and in fungi domesticated by termites and plants ...",
"--",
"Evolutionarily advanced ant farmers rear polyploid fungal crops"
] |
[
"Thank you very much for taking the time to answer this question."
] |
[
"Technically it's not speculation to point out that quarantine procedures for animals like ants are not as strict when it comes to things that are not pathogenic to them. So, it makes sense that there would be a lot of gene-flow between wild and \"domesticated\" strains, especially in the immediate surroundings. ",
"This is often seen (could be seen as anecdote), with the fungus that follows ants even when they themselves are not harvesters of fungus. Spores are so small that even a meticulously groomed ant can transport them between grooming sessions, or in spite of them. ",
"Let's see if this is acceptable."
] |
[
"When my T.V is on mute, there is still a high pitched noise. What is that noise?"
] |
[
false
] |
i always assumed it was the speakers even though they were on mute, but the speakers blew on a tv in my house and i can still hear it
|
[
"Here's the ",
"device",
" that causes it. ",
"The physical explanation (called ",
"Magnetostriction",
") is that the transformer (which is just coils of wire) is carrying high-frequency alternating current (AC). As the electric field changes due to the AC, the magnetic field around the coil also changes. This magnetic field actually stretches and compresses the metal slightly as the current alternates. If you're alternating at around 15KHz, you'll produce a sound at about 15KHz which is definitely high-pitched.",
"I'm interested in what causes capacitor whine in my graphics card when I push it to it's maximum load. I'm assuming it must be a similar effect. Anybody know?"
] |
[
"Also, anybody much over 35 or so was far less likely to hear the noise.",
"When I was in high school, the new big thing was the mosquito ring/notification tone that was high-pitched enough that most older folks (like teachers) couldn't hear it. ",
"I'm not sure what causes the change over time in some sets versus others. "
] |
[
"I used to repair televisions (way back when they had tubes in them, and not just the CRT!)",
"Some that came in would have this whine VERY loudly, others made no sound at all. But the most interesting thing was that 50% or more of the people I ever asked could not hear it at all. There were some sets that would drive me CRAZY even for the few minutes we had them on the bench, but the owners never complained about the sound. ",
"Also, anybody much over 35 or so was far less likely to hear the noise. "
] |
[
"How much lower would sea level be if all the animals were taken out of it?"
] |
[
false
] |
Not entirely sure how scienc-y of a question this is, but I can't think of a better place to put it...
|
[
"Given that the ocean is very, very big and that even the biggest of animals are very, very small in comparison, I will go out on a limb and say there would be absolutely no measurable difference.",
"Now for numbers, Wiki lists the total biomass of the whole planet at about 560 billion tonns (plants and animals included). ",
"http://en.wikipedia.org/wiki/Biomass_(ecology)",
" Thats 5.6 × 10",
" kilograms, most of which is on land. Perhaps 10% is in the oceans.",
"Most(?) figures list the total mass of the ocean at 1.37 × 10",
" kg",
"Assuming that all the life in the world were compared to all the water in the ocean, you would have one kilogram of living stuff for every 2.4 million kilograms of water. Given that only about 10% of that life is in the ocean, and an unknown ratio of animal:bacteria:plant life, you can not make a for sure estimate but you can reasonably conclude that it could happen and no one would notice a drop in the tides. ",
"edit: the biomass figures dont include bacteria. "
] |
[
"You're thinking of the commonly thrown around statistic for the SURFACE of the planet. There's much more mass beneath the oceans. "
] |
[
"Thank you for being the first and only person to answer. Really - only 10% in the oceans? I'm completely off then, I was imagining a lot more, considering the planet is about 80% water..."
] |
[
"I boiled an egg with a pinch of baking soda in an aluminum pan and it turned black. What reaction happened in there?"
] |
[
false
] |
The surface where the water touched the pan and I can't seem to scrub it away.
|
[
"I'm no chemist (just and engineer), but here's my best guess since there's only one other answer:",
"The baking soda stripped away the protective oxide from the Aluminum, which then reacted with something else in the water. This is where it gets tricky. What order did you add the egg and the baking soda? When did the pan turn black? Do you have particularly \"hard\" water (lots of minerals in it)?",
"It's possible that another aluminum compound formed which took on some other metals from the water as impurities, which in turn gave the dark color.",
"I would say use a lot of baking soda in order to remove all compounds. Or if that doesn't work, try using some sort of acid.",
"Again, I should say that I'm mostly guessing, other than the baking soda stripping oxide thing, so if someone else comes up with a more plausible answer, I'll gladly delete mine per the subreddit guidelines."
] |
[
"eHow suggests it is because of low pH, \"oxidation,\" or high temps in the dishwasher.",
" It also recommends a technique by which it may be removed.",
"I'm a chemist- wish I knew precisely what was going on (I'd like to say it was the sulfur in the egg, but aluminum sulfate isn't black), so I look forward to a more specific answer."
] |
[
"actually the opposite... the black IS an oxidation layer.",
"Go buy a brand new aluminum pot (restaurant supply houses have them, I bought a 10 gallon stockpot for brewing beer) and boil plain water in it. where the water touched will turn dark grey. add baking soda (or oxyclean, what I use for cleanup, but not on my alum pot for this reason) and you will super oxidize the pot.",
"Frankly, the amount in that pot is just fine.... you do not want an aluminum cooking pot to shine, or it will affect your food."
] |
[
"[Rocketry] Is the specific impulse of the space shuttle (LOX/LH2) rocket based on the molecular mass of H2 or H2O?"
] |
[
false
] |
Armchair rocketry fan here so sorry if it is a very basic question. My understanding is that the Specific Impulse (Isp) is inversely proportional to the root of the molecular mass of the reaction mass and proportional to the root of the temperature. Therefore in low thrust/high-efficiency scenarios (e.g. orbital transfers), you want as high an ISP as possible and therefore as light and hot a propellant as possible. Sorry if this is unclear. I guess what I am asking, is if a standard LOX/H2 rocket uses H2O as its reaction mass (flame temperature ~3500K, molar mass 18), than it seems that you can greatly increase efficiency without needing NERVA etc but with conventional methods which heat H2 to a fraction of the temperature (1160K, molar mass 2).
|
[
"It's based on measurement of the engines, of course. But H2O gives the best specific impulse in an ideal rocket engine. The reason is that self-contained rockets have to carry two kinds of supply: ",
", which is matter that contains energy to be used for propulsion; and ",
", which is matter that can be loaded with negative-going momentum and discarded (thereby giving the rest of the rocket forward-going momentum, yay!). The reason you need both is that you need ",
" to load ",
" on the propellant.",
"Dealing with temperature is a secondary concern -- it's easier and better (from the armchair perspective) to deal with the basics of mass, momentum, and energy. Temperature only enters since SSMEs are heat engines, converting chemical energy -> heat energy -> mechanical energy.",
"The kinetic energy of the propellant scales like ",
" ; the momentum of the propellant scales like ",
". The idea is that you want the most momentum per unit propellant you can get - that way you don't have to discard so much of the rocket. So you give it a high exhaust speed as you throw it away (which raises ",
", so your momentum performance improves). But the energy price you pay is proportional to ",
" , so the more propellant-efficient you are the less energy-efficient you are.",
"Chemical energy storage is so marginal for orbital propulsion (it barely carries enough energy) that the only way to make chemical rockets work is by combining the fuel and the propellant. You react the fuel to make free energy (i.e. burn fuel to make heat!), and then you use the reaction products (which are now hot but useless) as propellant.",
"So the most mass-efficient way to make a chemical rocket work is to use reactants with the highest reaction energy you can, and throw the whole shebang out the back of the rocket nozzle after it is fully reacted. That gives you the most available energy per unit expended mass, and also the most available momentum per unit expended mass.",
"If you \"run rich\" to lighten the exhaust products (by putting extra hydrogen in the exhaust stream) then you are spreading your available energy over more propellant - so you are more energy-efficient. But you turn out to be less mass efficient then, since you could replace some of that hydrogen with oxygen and eject the same total amount of mass with slightly more kinetic energy. In terms of temperature, running hydrogen-rich cools the exhaust stream more than it benefits you with the lightness of the individual particles. ",
"The molecular mass really only matters in the case where you are limited in the amount of energy you can put on each particle, but you aren't incurring a large mass hit for carrying that energy with you. Then you want light particles so you can get them going as fast as possible. The energy per particle imposes a negligible mass hit if you are using, say, nuclear power or solar panels to get that energy -- the former because nuclear fuels have about 10",
" - 10",
" times as much energy per gram as chemical fuels, and the latter because you don't have to carry sunlight around with you, you can just collect it and use it as you go.",
"The direction of the trade (heavy exhaust particles, light exhaust particles, etc.) depends on the physics of your rocket engine. Certain types of ion propulsion, for example, are energy-per-particle limited; others are exhaust-speed limited; still others are limited by esoterica like how much the fuel erodes the engine itself on the way out. The optimal propellant choice thus depends on detailed engineering trades.",
"Edit: that BOTE analysis is correct for an ideal engine, but neglects nozzle efficiency. Molecular mass has ",
" effects: the simple one I described and debunked above, and a more complicated one that changes the efficiency of the nozzle in converting heat energy in the combustion chamber to bulk kinetic energy at the exit aperture. In general, you need a larger nozzle/bell for the same efficiency, with heavier exhaust molecules. The nozzle efficiency issue is actually a big one since nozzle/bell mass is a major element of engine design, and a major mass element for the dry vehicle. So, even for conventional chemical thermal rockets like SSMEs, the answer is really just that the optimum depends on the detailed engineering trades for the particular rocket. "
] |
[
"If I remember my college propulsion class correctly, it's the average molecular weight of the exhaust gases. I remember hearing somewhere that sometimes in LOX/LH2 engines deliberately run rich, which puts more H2 in the exhaust, and lowers the average molecular weight of the exhaust, improving the specific impulse.",
"Edit: Just to clarify, I'm saying for a stiochiometrically correct fuel/oxidizer ratio, you should use ",
" g/mol for ",
"."
] |
[
"One of the big advantages of NTRs is precisely that you can use low-molecular-weight gases as exhaust. However, without having nuclear fission as a heat source where are you going to get the energy to heat up the exhaust in a \"conventional\" thermal rocket? The likely answer is a chemical reaction. But that means you need to take the chemical reactants along with you, and if you don't exhaust them after use you're just wasting energy. And there you go, you're back to square one.",
"If you're going to use a low-power electrical system for a thermal rocket then you can't exactly use that to take off from Earth, so you're stuck with a space-only propulsion system, likely solar powered. And if you're going to do that then you might as well go all the way and use a full electric propulsion system such as an ion engine, hall thruster, or pulsed plasma thruster. And again the \"conventional thermal rocket\" finds that it doesn't really fit into a useful niche.",
"Also, most chemical rockets use slightly non-stoichiometric mixture ratios in order to bias the exhaust products toward lighter molecules, increasing Isp. For example, a purely stoichiometric oxidizer to fuel ratio of O2 to H2 in order to produce H2O exactly should be 8:1, but the Space Shuttle Main Engines run at 6:1, which leads to more HO in the exhaust."
] |
[
"What time zone is used in the North and South Poles?"
] |
[
false
] | null |
[
"At the absolute tip of each pole, Greenwich mean time. But the time zones extend all the way to the poles. For example, Antarctic Research bases operate in several different time zones (usually corresponding to their sponsor nations) even when they're fairly close to each other.",
"But truly, you can operate on whatever time zone you want. There's no other people nearby to complain. There's no buses or planes or trains to have a schedule to worry about. With 24 hours of sunlight or 24 hours of night it's pretty meaningless to tell noon from midnight. That's why most travelers just maintain whatever time zone they left from, it makes communication with their home base or nation easier."
] |
[
"Because when time zones were invented, GMT was considered the \"start\", and all other time zones radiated out from there."
] |
[
"Why does it have to be GMT at the absolute tip? All the time zones converge there so shouldn't it be any time zone, and is there an international convention that has been agreed on the time zone at the absolute tip?"
] |
[
"How much does the earth's mass change over time?"
] |
[
false
] |
I've heard the earth is gaining mass because particles/dust from space is always adding to it but is the earth losing mass also? How and to what degree?
|
[
"We lose about 3kg of hydrogen and 50g of helium each second (about 10",
" per year) due to ",
"Jeans escape",
". ",
"http://www.scientificamerican.com/article.cfm?id=how-planets-lose-their-atmospheres",
"We also gain 10",
" to 10",
" kg per year due to meteorites and such.",
"http://www.tulane.edu/~sanelson/geol204/impacts.htm",
"It balances out (to some degree).",
"EDIT: Added a source."
] |
[
"Net is zero, with a negligible fraction escaping as heat. The reasoning is that the solid mass is turned into various gases and soot, which either remain in the atmosphere or fall back to the ground."
] |
[
"Net is zero, with a negligible fraction escaping as heat. The reasoning is that the solid mass is turned into various gases and soot, which either remain in the atmosphere or fall back to the ground."
] |
[
"How did the first sexually reproducing organism come into existence?"
] |
[
false
] |
[deleted]
|
[
"We don't know, but we do have some theories"
] |
[
"At one point, was there an organism that could reproduce both sexually and asexually?",
"There are many such organisms.",
"Bacteria, for example, can undergo binary fission, but they also exchange DNA with each other directly (conjugation) or through a bacteriophage intermediate (transduction). They can also absorb DNA from the environment (transformation).",
"Many viruses also reproduce asexually but will exchange DNA with other viruses if two virions happen to infect the same cell."
] |
[
"The last gender split was during reptiles. Mammals use the XY system with males as hetero-gametes, birds use ZW with females as the hetero-gametes, reptiles use temperature (except for snakes), and insects use the haploid-diploid system (males have only half the chromosomes that females do)."
] |
[
"If food contained no water would it heat up in a microwave?"
] |
[
false
] | null |
[
"Yes, but more slowly. Water is not the only molecule that absorbs microwave radiation. Other molecules have some degree of polarity and get jiggled and heated by microwaves."
] |
[
"The molecule would have to be polar though right?"
] |
[
"Even if it's non-polar there will be some heating from ionic conduction (ie ions will respond to the E-field, producing alternative current in your food). "
] |
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