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[
"How much does a 15 minute 110°F shower raise your core body temperature (if at all)?"
] |
[
false
] | null |
[
"Your body temperature would rise a tiny amount but it wouldn't be much, the body is good at regulating temperature and many vital bodily functions don't work well if the body's temperature is far from its normal temperature. As for the magnitude of the change, there are too many variables involved and I'm too lazy to estimate heat transfer coefficients right now."
] |
[
"The water that is on the skin evaporates cooling the body acting as sweat. This is in a shower. If submerged this cannot happen causing body temperature to raise faster. This is why you should not be in a hot tub for a prolonged period of time."
] |
[
"Isn't the primary mode of temperature regulation perspiration (at least on the cooling end the spectrum)? How does being in an essentially 100% humidity environment effect said cooling?"
] |
[
"Imagine there is an asteroid the mass of a fridge floating in space and isn't gravitationally affected by any other object. Could this asteroid have its own tiny satellite?"
] |
[
false
] | null |
[
"Yes, it could."
] |
[
"Well, OP asked \"the mass of a fridge\", not necessarily the same shape. Anyway you're right that with a low mass it cannot be expected to be spherical. But wouldn't this effect become negligible at a certain distance? After all ",
"243 Ida",
" does not look spherical at all and it has a satellite."
] |
[
"I wonder if the asphericity would destabilize the orbit. e.g. the monopole is cancelled by orbital velocity, but then the not-insignificant quadrupole tanks it."
] |
[
"If photons can't escape from a black hole, how can a charged black hole repel or attract electrons outside?"
] |
[
false
] |
Wasn't it photons that give electromagnetism?
|
[
"I'm sure there's a deep quantum-field-theory explanation of this that makes perfect sense, but I'm not qualified to offer it. Probably something about virtual photons be localized excitations of the electric field itself and not discrete particles emitted by sources of charge, or words to that effect.",
"But there's a purely classical approximation that works perfectly, as far as anybody's been able to tell so far. In the reference frame of any observer who ",
" a black hole's charge is distributed symmetrically on its ",
" and is not in its interior at all. In other words, if you stay outside the black hole, you can consider that all of its charge — and for that matter, all of its mass — lies on a spherically symmetric shell of zero thickness outside but infinitesimally close to the event horizon.",
"The shell theorem says that the electric field of a point source of given charge density has exactly the same properties as the electric field of a static, spherically symmetric shell of the same charge density, and in fact the two fields are indistinguishable from any distance. The same thing is true of mass and gravitation: from a distance, you can't distinguish the gravitational field of a point and the gravitational field of a spherical shell of the same mass."
] |
[
"Simplistic answer",
":",
"It is known that black holes can have charge, and therefore a static electric field. The question is, how does this field escape the horizon? In that, I should remind you that the horizon is the surface through which one cannot send any signals. ",
"Now, signals (i.e. photons) involve time changing fields. Indeed no such signal can come out of the horizon. However, the electrostatic field of a charge does not convey any signal; it can therefore escape from the black hole. In technical parlance it is a space-like object, and those can cut across horizons. Or differently, in the language of excitations of the electromagnetic field (the photons)- there are transverse and longitudinal photons.",
"The transverse ones are those we see, and travel at the speed of light. The longitudinal ones are those which \"are there\" in space, they do not convey any signal and are the static fields of the charges.",
"I found a ",
"few books",
" basically just restating the above, but I don't feel any more enlightened."
] |
[
"Have a look at the ",
"Virtual particles FAQ",
", in particular question 4 (\"Do they go faster than light? Do virtual particles contradict relativity or causality?\"). In which context, my guess would be that there wouldn't be a problem with a virtual photon \"crossing\" an event horizon: it doesn't ",
" propogate across it, and it doesn't carry any information."
] |
[
"If transparent objects can refract electromagnetic waves of the visible spectrum, can they similarly affect other waves on the spectrum, say UV rays or X-rays?"
] |
[
false
] |
And on the other end of the spectrum as well - what sort of materials could affect radio waves and microwaves?
|
[
"You can actually do an experiment to show how infra-red radiation can be refracted. Take a prism and shine a white light through it, to make a rainbow. If the light is strong enough, you'll find that the area just past the red band is warm after some time, even though there's no visible light hitting it."
] |
[
"Conductors also have an affect on EM waves. They do not necessarily refract, but they can block. The metal mesh around your microwave generates image currents that prevent the waves from leaving the cage."
] |
[
"Be aware that 'transparent' actually means 'transparent for a certain range of wavelengths'. Usually, that means the visible part of the EM spectrum between 350 and 800nm.",
"But yes, materials that do not strongly absorb a wavelength will refract it according to the refractive index."
] |
[
"If someone adds an addictive substance to your food without you knowing, how would your mind react, would it get you addicted and how would it know what exactly you are addicted to?"
] |
[
false
] | null |
[
"Hi Gone4Gaming thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Psychology"
] |
[
"‘Psychology’"
] |
[
"Why do I experience short bursts of \"dizziness\" before going to sleep?"
] |
[
false
] | null |
[
"Welcome to AskScience. Please make the titles of your posts descriptive, and ",
"Unfortunately we cannot provide any diagnosis or other information for you. There is almost always a way to make your way into a free clinic presuming you're in the first world."
] |
[
"You're right, sometimes the community gets it right. That said there is NO WAY they can properly diagnose you via reddit, it's impossible and dangerous and if it was allowed, sooner or later it WOULD harm someone, it's only a matter of time.",
"I understand your concern of course, but believing that nothing would be done is a roadblock to your own treatment. We can treat almost anything nowadays, it's not always effective, but in medicine we do at least try unless it's entirely futile. Please don't bury yourself in the mindset that you won't be treated for whatever may be occuring."
] |
[
"Providing medical advice is against the Reddit TOS, not a specific rule to this subreddit. I would not trust medical advice from the internet, and anyone who claims they can diagnose you is full of shit. ",
"There are too many variables to make an appropriate diagnosis from your post, or any post over the internet. You require a physical examination, it's as simple as that.",
"The reason I can't suggest or condone this in any way is that if someone posts valid advice that makes sense, and you take it, and happen to be the 1 in 1,000,000 person who that's the opposite of what to do said advice for, you could die or be seriously injured. Please, don't take chances with your health.",
"Make the time to see a physician, find a way to see a physician. If you cannot afford this, or cannot find one try ",
"/r/assistance",
" perhaps someone there can help you find a physician or lend you the money to pay for a visit."
] |
[
"Why, neurologically, do people urinate when extremely frightened?"
] |
[
false
] |
[deleted]
|
[
"Urination and defecation is an instinctive mammalian response in order to make you less appetizing to predators, and to signal to others that danger is near. Neither are terribly relevant for humans anymore, but the instincts remain."
] |
[
"The short answer is it's not your brain doing it. Your brain finishes with the business after it tells your body that it's scared. After that your adrenal glands (sitting on your kidneys) take over and start pumping out epinephrin which causes you heart rate to increase, your breathing to hasten etc. One of the side effects is a relaxation of the bowels and bladder. ",
"It's a parasympathetic response which means it's out of your control, which is probably why you asked the question in the first place. Your body does it on its own without further input from the brain. Once it's triggered, you're just along for the ride."
] |
[
"Thanks for your comment, but I am looking for a more technical description of the biological happenings in the brain associated with those instincts you mentioned."
] |
[
"With all these beautiful colors you see in pictures of nebulas in /r/space, what colors will your eyes actually see of those objects in space?"
] |
[
false
] |
For example:
|
[
"We image the sky in the entire spectrum of light; may it be microwave, gamma, infrared, UV, radio, visible, etc. Each apparatus is different of course. ",
"So if the picture is taken in the visible spectrum those indeed ",
" the ",
" colours. \nWe humans see a very small piece of the entire light spectra, but to observe and better understand the pictures taken in other regions, they are false coloured.(usually an index or legend accompanies the picture for guidelines for observations, it also usually accompanies the region in which it was as captured). \nWe can't see the other frequencies, the brain has no colour for it, hence there is no 'colour' in the sense of it. "
] |
[
"I like to think about when you blow smoke through a dense beam of light and you see all the complex patterns the smoke makes as it swirls around. These patterns are all around you all the time but since it occurs in the invisible gas that is our atmosphere we rarely get glimpses of this complex pattern. The smoke is simply a medium to make the invisible visible to us. "
] |
[
"Thank you! Exactly what I was looking for!"
] |
[
"Is a 128 Gb memory stick just made up of two 64 Gb chips \"glued\" together or is it an entirely different technology that suddenly occupies half the space?"
] |
[
false
] |
Memory sticks are so big on comparison to the chip inside them, so I guess they could stick 10 chips in it and create the "biggest ever" memory stick rather easily... Edit: I'm happy that my most successful post ever on Reddit has been this unpretentious, near ELI-5 on AskScience, one of my favorite subs!
|
[
"I've worked in the storage industry, though not specifically on this type of device, so I might be missing a few minor details. Hopefully this will help, though.",
"A quick search found ",
"this",
" article which is focused on high-performance programming. SSDs are very similar in relevant ways to USB sticks.",
"In general, there are 3 major components to a flash drive (or even SSD). There's the raw flash chip(s) themselves. There's the flash translation layer which is what makes the flash chips look and act like a drive. And then there's the interface controller which provides USB connectivity (or SATA connectivity, or whatever).",
"When it comes to the engineering of these devices, there are lots of things to be considered including assembling costs, defect rates, market desire and willingness to pay.",
"Using more than 1 flash chip means you have to pay more for additional assembly costs, if only the extra machine time to install it.",
"The flash translation layer is also designed to handle a certain number of flash chips. (I'm assuming it's a separate IC, but SoC design keeps changing things). In general, supporting more chips means more connections which means more silicon and a larger packaging. If you can support a lot of flash chips you are likely able to support higher throughput (which is why SSDs are usually much faster than flash drives even for similar capacities). But if you're trying to go for cost minimization, you might use a shared bus if the flash chips support it and you're willing to take on additional debugging headaches.",
"The interface layer probably isn't that interesting.",
"If I was tasked with designing a USB memory stick of a particular capacity, I'd probably check to see if the cost of two smaller flash chips plus the cost of a translation-layer chip which supported two flash chips, plus costs of manufacturing, etc., were more or less than the cost of a single larger flash chip with the simpler translation layer, etc. And then do that. Because in this space customers seem to care almost exclusively about price and capacity to the exclusion of all else."
] |
[
"Speed. For example not all SD cards can transfer at the same rate, and if you get one that is too crappy, it may not work for some purposes (e.g. video recording). ",
"Number of times you can read/write to the memory can also vary."
] |
[
"> Because in this space customers seem to care almost exclusively about price and capacity to the exclusion of all else ",
"As a consumer in this space, what else is there to look for?"
] |
[
"Why does interlocking my fingers one way feel so natural, but the other way feels completely foreign?"
] |
[
false
] | null |
[
"These answers suck.",
"He's asking why it ",
", not why he's right-handed..."
] |
[
"I just looked around and found this - is it inaccurate? ",
"http://udel.edu/~mcdonald/mythhandclasp.html"
] |
[
"I just looked around and found this - is it inaccurate? ",
"http://udel.edu/~mcdonald/mythhandclasp.html"
] |
[
"Can someone explain the \"Ultraviolet Catastrophe\" that led to the creation of Planck's Constant and the birth of Quantum Physics?"
] |
[
false
] |
I understand that contemporary theories of the time about how black bodies would radiate energy led to certain bodies radiating infinite amounts of energy, but what was it about those old theories that led to such a result? Every reference I have come across just brushes over this and focuses more on our understanding now. Please help me understand why we were so wrong back at the turn of of the 20th century and what we were thinking before we realized that we were wrong. I believe it is helpful to everyone to know exactly how we were wrong, before any individual can then set forth with confidence on a new path of learning what is right. Thank you.
|
[
"That has nothing to do with black holes."
] |
[
"A black body isn't a black hole, but I can see the confusion. A black body is an idealized material, but many materials are close enough that we consider them black bodies. Basically, if you heat up a black body, it radiates that energy away as light. The hotter the body, the brighter the light and the shorter the wavelength. This is why hot/molten metal glows red, then orange, then yellow."
] |
[
"It's fairly simple - the model and equations they used said the intensity of the light from a black body should be be inversely proportional to the wavelength, raised the the fourth power. Thus, as wavelengths got smaller and smaller, the intensity according to the equation would very quickly approach infinity. Obviously this wasn't the case in testing, so the model and equations must have been wrong."
] |
[
"Does gravity affect how hard your heart pumps blood through your body? ie. is laying down less taxing, or say in a zero gravity environment?"
] |
[
false
] | null |
[
"Yes.",
"Within two to three days of weightlessness, astronauts can lose as much as 22 percent of their blood volume as a result of that errant message. This change affects the heart, too. \"If you have less blood,\" explains Dr. Victor Schneider, research medical officer for NASA headquarters, \"then your heart doesn't need to pump as hard. It's going to atrophy.\"",
"Source",
"To summarise, in zero gravity, the blood pressure is fairly uniform as apposed to on earth where blood pools in the legs resulting in a higher pressure there. Because of the increased blood pressure in the brain, the body starts dumping blood to reduce the pressure, as a result the heart does not need to work as hard."
] |
[
"With average blood volumes for males being about 5 Liters, give or take based on weight, where does the liter of blood go in 2-3 days?"
] |
[
"Yes. Your body has to fight gravity to pump blood upward while you're standing. When you experience hypotension (too little blood pressure) gravity wins, not enough oxygenated blood gets to your brain, you faint/fall over. Now your body has less work to do while face down, passed out in a public space. Your veins also have valves to prevent back-flow which assists in getting the blood upward."
] |
[
"Why don't babies and puppies learn how to walk similarly?"
] |
[
false
] |
[deleted]
|
[
"This is a good question and it sheds light on the developmental stratagy of an animal and the evironment they exist in, ans how theyve adapted to it!",
"Dogs come from wolves, who generally need their young to be as mobile as possible as quickly as possible to aid in their survival.",
"Human babies need to come out quicker simply because ",
". The child has a greater period of vulnerability (that is, childhood) to allow for that huge brain and the period of learning and devwlopmwnt it takes to fill it up. Humans are also more capable of carrying a child and so the child's mobility is perhaps less important, though I can see flaws with that reasoning. ",
"EDIT: ALSO, a study found correlation between the brain sizes of animals and how long they take to walk. I'll need to dig for it."
] |
[
"I would have never thought about the size of the head as a factor for this.",
"I don't have a reference, but essentially, humans have comparatively large heads because of our large brains. That's a problem, though, when it comes to childbirth; given the way our hips are constructed, if the baby's head gets too big when it's still in the womb, it won't be able to fit through the birth canal. So humans give birth to our young when their heads are still small enough to fit, and as a consequence, our babies are not as developed when they're born compared to newborns of other species. They do a lot more development outside of the womb after being born.",
"Also I'm interested in what you say about the ability to carry babies with us and it would be nice to read some studies on this.",
"This is simply due to humans being bipedal and having arms and hands capable of holding babies and carrying them with us. Dogs don't have an equivalent mechanism for that. (Some other mammals, especially the primates, have a similar ability to carry young using grasping limbs. Sometimes, it's the mothers holding the babies; other times, it's the babies being able to hold onto the mothers.)"
] |
[
"I would have never thought about the size of the head as a factor for this.",
"I don't have a reference, but essentially, humans have comparatively large heads because of our large brains. That's a problem, though, when it comes to childbirth; given the way our hips are constructed, if the baby's head gets too big when it's still in the womb, it won't be able to fit through the birth canal. So humans give birth to our young when their heads are still small enough to fit, and as a consequence, our babies are not as developed when they're born compared to newborns of other species. They do a lot more development outside of the womb after being born.",
"Also I'm interested in what you say about the ability to carry babies with us and it would be nice to read some studies on this.",
"This is simply due to humans being bipedal and having arms and hands capable of holding babies and carrying them with us. Dogs don't have an equivalent mechanism for that. (Some other mammals, especially the primates, have a similar ability to carry young using grasping limbs. Sometimes, it's the mothers holding the babies; other times, it's the babies being able to hold onto the mothers.)"
] |
[
"GMO's? Science on the subject rather than the BS from both sides."
] |
[
false
] |
I am curious if someone could give me some scientifically accurate studies on the effects (or lack there of) of consuming GMO's. I understand the policy implications but I am having trouble finding reputable scientific studies. Thanks a lot! edit: thanks for all the fantastic answers I am starting to understand this issue a little bit more!!
|
[
"It all depends on the modification",
"I'm going to expand on that a little bit, because it's critically important. Every food crop GMO that I am aware of is transgenic; that is, the genes being inserted are not artificially created, they are instead taken from another plant (or animal) and inserted into the crop cultivar's genome. Examples include genes inserted into tomatoes to produce a protein that makes them resistant to frost damage and genes inserted into potatoes to make them toxic to their primary insect pest (the Colorado potato beetle).",
"The fact that it's transgenic is important because it means that, to some extent, the products of these genes are already vetted. We aren't creating entirely new genes (and subsequent proteins) out of thin air. The anti-freeze protein in the tomato was already safe to eat when it was in a flounder; it doesn't magically become toxic in a tomato (things like acidity can change protein folding dynamics and so it must be tested for safety again in the food system, which it was).",
"The case of the transgenic potato is especially sad. Here's an excerpt from ",
"a review paper",
" regarding the fate of these potatoes:",
"Potatoes were among the first successful transgentic crop plants (An et al. 1986). Genetically modified potatoes expressing Bacillus thuringiensis delta-endotoxin that is toxic to the Colorado potato beetle were sold in the U.S. from 1995-2000. Although well-received at first, they were discontinued after only five years of use because of consumer concerns about genetically modified crops, grower concerns, and competition with a new and highly efficient insecticide imidacloprid (Grafius and Douches 2008). ",
"Why is this sad? Because the potato was fine. It successfully resisted the potato beetle and allowed the growers ",
" onto their fields. However, because of consumer mistrust and a host of fear-mongering by anti-GMO organizations, use of the potato was discontinued and farmers went back to using lots and lots of insecticide. This cognitive dissonance from environmentalists (which I consider myself to be) really frustrates me. ",
"Responsibly created GMO's are not the ticking time bomb that people have been led to believe, and they may actually hold great benefit. However, I believe they should be approached cautiously and used only after methodical testing (this seems self-evident); they shouldn't necessarily be the go-to solution when simply switching cultivars or better agronomic practices could achieve the same thing. They're also a bit of a patent minefield; should genes be patentable? The US Supreme Court will be debating this presently with respect to human genes; it might have implications for genes in other species.",
"Edit: Removed the tomato trademark name because I had named the wrong one, thank you scsp85."
] |
[
"The problem here is that there's no reason to treat \"GMOs\" as a cohesive group. You can use genetic engineering to insert all kinds of genes. The health effects, if any, will depend entirely on what genetic modifications you do. You can add a section of noncoding DNA which reads \"MCwaffle was here\" to corn and it won't do a thing. You can add the genes to produce digitoxin and it will make the corn poisonous. It all depends on the modification."
] |
[
"I worked with GMOs for a period of time in the mid-2000s before exiting the field to pursue different work, largely because I got sick of trying to defend myself to strangers that magically became more qualified than me after seeing a YouTube video or documentary.",
"The quality of critique against GMOs is almost universally terrible. If you see a study get published stating health risks in existing GMOs, it's probably best to count to 20 and then Google for critiques. You'll usually find retractions.",
"So, why does that always seem to happen?",
"Well, for one thing, the most common thing we insert into GMOs to help them survive is the ",
"RoundupReady gene",
", which confers the ability for the plant to break down what's normally a deadly toxin into an inert compound that doesn't harm the plant. The protein that results from the coding sequence for the RR gene looks pretty much like any other plant protein. It plays a part in the ",
"Shikimate Pathway",
" which is specific to plants. It's far enough removed from people evolutionarily that the resulting biochemical products are unlikely to overlap with human biology much.",
"This is a trend you see a lot of. Things we insert into plant genomes tend to be pretty far away from humans on the evolutionary tree.",
"The other thing that gets inserted into plants a lot are ",
"Bt proteins",
", which act on the guts of insects. They're derived from a bacteria that's, again, pretty far evolutionarily from humans. There was a scare in the late 90s when ",
"StarLink",
" corn got into the human food supply. Scientists hadn't fully evaluated the possibility of an allergic reaction. This was the biggest worry, that an allergic reaction would occur. This is different than a toxic reaction, where the Bt would have an effect on some specific pathway in the body. Our concern was just that human bodies hadn't seen this much Bt before, so would they freak out and think it was something they needed to attack? It turned out nobody had an allergic reaction to the Bt, and up until current day there are to my knowledge no documented cases of Bt allergy in humans.",
"For those who are organic fans, ",
"organics also use Bt as a topical pesticide.",
" It's a pretty inert chemical to humans.",
"There have been documented cases of growing resistance to Bt strains in pests, and this is something that GMO researchers are aware of. There are a couple of things that they attempt to do to alleviate this issue. One is to plant a \"refuge\" area of non-modified crop. The idea is that the pests will breed in this refuge area and maintain the wild-type phenotypes. If a resistant mutant pops up in the larger crop area, it will breed with the wild types and statistically, it's extremely likely the trait will not continue in the population. It'll effectively get washed out.",
"The other approach is that scientists hope they can discover at least one other target with similar efficacy to Bt, but a totally different mode of action. If only 1 in 1,000,000 pests can randomly develop a gene that makes it immune to one pesticide, then there's only a 1 in 1,000,000,000,000 chance that it will simultaneously develop an immunity to two by mutation. If it needs both to eat any of the crops, then the barrier to entry will probably be too high. If you have a commercially viable corn plant that can do this, just start minting your own money.",
"SO, on to copyright. Copyright issues are real, and shouldn't be dismissed out of hand. This is a real debate, and it probably is stifled by the imbalance of money in the system. Whether genetic material is inherently a patentable resource is worth talking about and sending your congresscritter correspondence indicating what you think is best.",
"BUT in most of the cases of people being sued by GMO producers, they were clearly breaking the law. Regardless of what anybody tells you, it's pretty unlikely from a biological standpoint that a farmer's crop over 500 acres will be any more than .5% or so GMO just because \"a truck carrying GMOs drove by\" or \"there was a field down the street growing GMOs.\" In general, even though pollen can fly pretty far, the plants that are closest win out. It's basic physics. As you get farther away from the plant, the pollen it produces gets more disperse, and it has less competitive advantage compared to the plant that's RIGHT THERE next to the existing plant. Soy (a major GM crop) self pollinates, so it's even less likely for this to happen here. In most legal cases there are upwards of 10-20% GMO presence in crops or more. As a plant biologist, that's a pretty unlikely thing to see from a neighboring farm.",
"Then there are environmental issues. When it comes to resistance, it's usually not that big of a problem. We're fairly unlikely to be overrun by mutant corn or soybeans because they're basically dependent on humans to keep them alive. We've modified them so much over time that they're extremely unlikely to pass their genes on into wild species of other plants. They can't interbreed. It's like being afraid that a mutation in donkeys will spread to humans. Even if somebody was out there having sex with donkeys and exchanging genetic information, it's pretty unlikely it would pass into people. ",
"Grasses are more of an issue. I'm a little wary of crops like canola and hay, because they're fairly similar to grasses and could conceivably pass their genes on to wild type grasses. There are even RoundupReady GRASS stocks now, and those seem like a pretty bad idea.",
"So that's my take on the whole thing. I think that a lot of people follow a gut reaction and latch onto pseudoscience, because it's readily available and simple to produce (Research without peer-review or publication? Sign me up!). When people cherry pick studies that they \"feel\" should be true, that goes counter to the scientific method, and it makes it very difficult to ask the sort of questions that get funded for further research. And yes, there is money in play. A number of FDA and government policies regarding GMO studies have probably been influenced by corporate lobbies. My exposure internal to these companies is that the science is sturdy and not terribly controversial, but the fact that you would have to trust me without seeing the primary documents is sort of ridiculous. This is a whole other issue wrapped up in protecting trade secrets and international trade targets and macro things that an economist would really do a better job of explaining than me. I would personally be all for more openness and public availability in these processes, but I don't know the best way to go about it.",
"There's plenty to be worried about and criticize about GMOs, but the best way to go about it is to dig into the primary literature, or better yet, get an education in plant science starting with the basic biology of plants. I think it's good that people have opinions on these issues, it's just sad that for the most part the resources that are available are not the best.",
"Additionally, it's very difficult to be a hard-liner in science. Very few issues are clearly black and white, and scientists get used to seeing opinions of this type as a red flag. If somebody is an absolutist, their opinion will eventually be discredited in most cases. The truth in most of these cases ends up lying somewhere between the extremes."
] |
[
"How bright is space? If I'm floating through the galaxy with my friend, would he be illuminated?"
] |
[
false
] | null |
[
"Depends on where in the galaxy you are. There will be some photons reflecting off your friend - that's evident because we can see stars in any direction.",
"But generally, yeah, you'd be able to see your friend, at least dimly. If you go out at night in the desert during a new moon, you'll notice that you can read by starlight."
] |
[
"How bright is space? If I'm floating through the galaxy with my friend, would he be irradiated?"
] |
[
"Uh, moonlight or starlight? If I go stargazing when the moon isn't out, I know it's too dark to read."
] |
[
"If obese people are in poor health because of excess fat, why can't this all be removed via liposuction or surgery?"
] |
[
false
] |
I was Googling this earlier and it says it's dangerous to remove lots of fat, but I couldn't find a good reason why.
|
[
"Fat can be dangerous to remove because it's not avascular - there are still blood vessels running through it and removing it will cause bleeding. In some parts of the body, there are large, superficial arteries and veins running in fat that a surgeon would be at risk of damaging. And fat doesn't just lay right under your skin - it can infiltrate deep into some parts of your body, under muscles and near organs. Some superficial nerves can run in fat, too, and you'd risk losing sensation to your skin or even innervation of some muscles.",
"And \"being fat\" is more of a symptom than a cause. Even if you could remove all the fat that shouldn't be there, that wouldn't mean you just reversed all the bad effects of poor diet. Cardiovascular disease from atherosclerosis (build-up of cholesterol and fatty acids on the inside of arteries) and diabetes (insulin receptors becoming less sensitive from constant stimulation) would still be big problems."
] |
[
"The problem when obesity causes severe health issues (such as diabetes or cardiovascular disease) is not just excess adipose tissue (although this may be the root cause), but accumulation of fat in areas it shouldn't be because our normal adipose tissue storage areas have been \"overfilled\"; this ectopic fat accumulates in and around organs, such as within liver cells, which is a major cause of the health issues concurrent with obesity. It is physically impossible to remove this fat surgically. ",
"Gastric banding (limiting stomach capacity to enforce calorific reduction) may be offered in extreme circumstances where lifestyle interventions have failed to reduce weight, although there is a \"sweet-spot\" where a patient has to be large enough to warrant the surgery but not so obese that the risk of surgery exceeds the benefits of the banding."
] |
[
"Could surgery do anything/remedy some of the latter problems you mentioned?"
] |
[
"If the earth is curving away from me in any given direction, why do I experience the horizon as being at eye level?"
] |
[
false
] |
I was standing on the beach, and I noticed that the horizon line felt to me that it was at eye level. But the earth curves away from me because I'm standing on a sphere, right? Can anyone explain the perceptual cockup that is occurring here?
|
[
"TL;DR - It's just a geometry problem. The radius of the earth is much, much longer than you are tall, so the angle at which you have to tilt your head to see the vanishing point of the horizon is very small.",
"I wrote the math up to explain it, but it is long and dense. Take a look at ",
"this diagram",
" to help understand where these equations are coming from.",
"The equation for a circle is:",
"x",
" + y",
" = r",
"Where x is horizontal location and y is vertical location. x=0 and y=0 at the center of the circle. Convert it into a function of x:",
"y = sqrt( r",
" - x",
" )",
"If we know the radius of the circle and the x location, we can find the y location. The equation of the slope (derivative) at any point is:",
"slope_oncircle @ x = -x / sqrt( r",
" - x",
" )",
"The farthest point you can see is the point at which your line of sight is tangent (the line \"kisses\" the slope) to the curve of the earth. The slope of that line is:",
"slope_lineofsight = (y_tangentpoint- y_eye) / x_tangentpoint",
"The two slopes have to be equal, so express that in an equation:",
"-x / sqrt( r",
" - x",
" ) = (y_tangentpoint- y_eye) / x",
"Plugging in for our y_tangentpoint equation above:",
"-x / sqrt( r",
" - x",
" ) = (sqrt( r",
" - x",
" ) - y_eye) / x",
"Multiply both sides by x and by sqrt( r",
" - x",
" ):",
"-x",
" = r",
" - x",
" - y_eye*sqrt( r",
" - x",
" )",
"y_eye*sqrt( r",
" - x",
" ) = r",
"Solve for x:",
"sqrt( r",
" - x",
" ) = r",
" / y_eye",
"r",
" - x",
" = r",
" / y_eye",
"x",
" = r",
" - r",
" / y_eye",
"x = sqrt( r",
" - r",
" / y_eye",
" )",
"Therefore the slope of the line of sight is:",
"-sqrt( r",
" - r",
" / y_eye",
" ) / sqrt( r",
" - r",
" - r",
" / y_eye",
" )",
"sqrt( r",
" - r",
" / y_eye",
" ) / sqrt( r",
" / y_eye",
" )",
"sqrt[ ( r",
" - r",
" / y_eye",
" ) / ( r",
" / y_eye",
" ) ]",
"sqrt( y_eye",
" / r",
" - 1 )",
"And finally, the angle is the arctangent of that value:",
"theta = arctan[ sqrt( y_eye",
" / r",
" - 1 ) ]",
"The radius of the earth is about 6400km, and the height of your eye is about 2m (0.002km) higher than that, so plugging in:",
"angle = arctan[ sqrt( 6400.002",
" / 6400",
" - 1 ) ] = 7.91 * 10",
" radians = 0.045 degrees.",
"This means that your eyes only have to tilt down by 0.045 degrees to see the edge of the horizon. If your height was comparable to the radius of the earth, this angle would be a lot higher. For example, if you are up in a space ship 1000km above the earth, you would have to tilt your head down 30.1 degrees.",
"edit: ",
"Relevant xkcd."
] |
[
"Brilliant! Thank you!"
] |
[
"This isn't a direct answer to your question exactly, but if conditions are clear you can actually see distant ships heading out to sea dip below the curvature of the earth on the horizon. "
] |
[
"What does the percent ionic character of a bond actually mean in terms of electron probability density?"
] |
[
false
] |
[deleted]
|
[
"From a molecular orbital theory standpoint, percent ionic character manifests in the coefficients of the atomic orbital wavefunctions that are used in the linear combinations forming your bonding and antibonding orbitals. For HF, what it means is that the filled bonding orbital is comprised primarily of fluorine's 2p orbital with a little bit of hydrogen's 1s orbital mixed in. The empty antibonding orbital will exhibit the opposite pattern of coefficients."
] |
[
"My question is more on what does on mean in terms of probability densities. The electron isn't on fluorine, it's around fluorine in a molecular orbital. How does that 89% change the probability density in terms of bonding. How does the sp3 orbital containing that electron look? Is it literally just closer to fluorine? How does this work for D-block elements?"
] |
[
"Qualitatively, it means that the electron has a higher probability of being found \"on\" the fluorine rather than in the small area where there is orbital overlap. When I say \"on\" I mean that it will likely be in the fluorine domain of the orbital rather than the \"shared\" or overlapping area of the orbital. "
] |
[
"Is space quantified?"
] |
[
false
] |
I suppose that it is not, but then, when an object moves from position A to position B, does it traverse an infinite number of positions? If it takes time to move from one of these infinitesimal positions to the other, it would take infinite time to arrive to position B, right? How is this dilemma solved?
|
[
"Is space quantified?",
"We don't know if space is quantized or not. Currently, there is no evidence suggesting that it is quantized, so all of our best models assume that space is continuous. This includes both general relativity, and quantum mechanics (yes, you read that right -- quantum mechanics assumes a smooth, continuous spacetime; it is the ",
" and their ",
" which are quantized in QM, but not space itself).",
"There ",
" theories where spacetime itself is quantized. One such theory is called ",
"loop quantum gravity",
". However, neither LQG nor any other theory of quantized spacetime has been as successful at describing the universe as GR and QM are able to describe.",
"when an object moves from position A to position B, does it traverse an infinite number of positions?",
"If space is continuous, then yes. This is currently how our existing models work.",
"If it takes time to move from one of these infinitesimal positions to the other, it would take infinite time to arrive to position B, right? How is this dilemma solved?",
"This is not right. There many be an infinite number of positions, but moving between adjacent positions takes an infinitesimal amount of time. This is why limits and calculus were developed -- to help us sum over an infinite number of infinitesimal quantities, and get a finite answer.",
"The dilemma you're asking about is commonly known as one of ",
"Zeno's paradoxes",
" -- where Zeno claims nothing can ever move because to move some amount of distance requires you to first move half that distance, and then half of the remaining distance, and so on forever. What Zeno didn't understand is that the amount of time each \"jump\" takes gets smaller and smaller, tending toward zero, and that the limit of this series is actually not infinity, but is a finite number (so a finite amount of time, to move the total distance). Each jump gets you closer and closer to some finite value rather than an infinite value. Eventually after that finite amount of time has elapsed, you are at your destination.",
"Hope that helps!"
] |
[
"Imagine you divide the path from A to B into 10 equal divisions, and it takes you exactly 0.1 seconds to traverse each division. You'll go from A to B in 1 seconds. Now, divide it into 1000 divisions, and now it takes 0.001 seconds to traverse each divsions. You'll still go from A to B in 1 second.",
"As you increase the number of divisions, the time to cross each one takes less time - and the end result is the same: It takes 1 second to get from A to B.",
"As the number of divisions approach infinity - the trend continues."
] |
[
"Awesome reply, what a pity that the post didn't succeed :)",
"You fully replied my doubt, although I still need to get my head around that infinitesimal stuff..."
] |
[
"Double-slit experiment and the speed of light"
] |
[
false
] |
The best way I can think of the ask my question is to set up a thought experiment, and have it explained why it is impossible. The following ascii illustration precedes the caption. Imagine a double-slit experiment, where one slit (A) is always open, and there are two more slits (B) and (C) where exactly one of (B) and (C) are open at any one time. There is a point source (X) of photons providing the illumination for the experiment, and there is a point (D) where constructive or destructive interference can be observed. For the sake of clarity assume that (X), (A), and (D) are collinear. Assume (C) and (B) are appropriately far away from (X), (A), and (D), where "appropriate" will become clear soon. Emitting an extremely short burst of photos, they will travel from (X) through (A) and to (D) at the speed of light. They will also travel through (C) or (B), and either cause constructive or destructive at (D) depending on which (C) or (B) is open (the distances were chosen to achieve this). If the photons to go through (A) must also go through (C) or (B), couldn't you send information at FTL from (C) and (B) to (D)? : James-Cizuz mentioned that this question is flawed, so I'll try to present the question in a way that removes the FTL nonsense. Set up the apparatus first by turning on (X) and opening (C). Slide (C) up and down until at (D) destructive interference is observed. Close (C) and open (B) and slide it up and down until at (D) constructive interference is observed. Turn off (X). Now flash (X) so that it is on only very momentarily (that is, only on for a shorter time that it takes light to travel a distance of CD minus AD). Close (B) and open (C) and repeat the flash. What do we see at (D) for both runs of the experiment? Why?
|
[
"Surprisingly, no one has mentioned ",
", but this question all comes down to coherence. Waves interfere when (1) they have the same frequency, and (b) they are locked in (relative) phase. Otherwise they average out to some nominal amplitude, and the patterns wash out.",
"You should know that with modern synchrotron and free-electron laser x-ray sources, and holographic lenses called zoneplates (which work by diffraction from multiple slits), this situation you describe occurs all the time. So the topic has both relevance and testability in the real world.",
"Also, you can forget about quantum properties here: this physics is all covered by simple waves and applies as well to light/sound/water whatever kind of waves you want.",
"When a photon passes through a screen and creates interference at a measurement point, it's the temporal coherence that makes the interference possible. That means that even though the path length is different (and hence the travel time is different for each path) the wave is still behaving ",
" well enough to interfere (constructively or destructively, etc.) It's not really two photons making the path through two slits. It's the ",
" like a ripple on the surface of a pond, expanding outward and passing through obstacles. If you have a bright point source, there's lots of photons, but they'll all do the same thing, and the recorded intensity will be linearly proportional to the number of photons.",
"As OP knows, some light sources (like many kinds of lasers) can have high temporal coherence, so the lateral width of the diffracting screen, and the largest path length differences, stay smaller than the path lengths over which the wave's coherence would break up. That's the textbook case.",
"But OP also knows that there are short-pulse sources, for which the time-duration of the pulse is ",
" than the time lag caused by the path length differences in the diffraction experiment. In those cases, there will be no interference observed at the detector because the (A) part of the wave will arrive at a different time than (B or C) part of the wave. You could set up several different slit distances to ",
" coherence, and that's precisely what many authors have done.",
"Intimately tied to this is that wave theory teaches us that a short pulse must be comprised of a broad range of frequencies (a topic for another discussion, if you like), and a broad range of frequencies is how temporal coherence is destroyed. (The thought-experiment limit here is a delta-function pulse in time, which has a complete, white spectrum in frequency.)",
" So the answer to your edited question is that when there is enough temporal coherence for the given path length differences, you'll see the textbook interference you expect. But for short-pulse light sources, where the temporal coherence is smaller than the time lag induced but the various path length differences, the interference will not occur because the waves arrive at the detector at different times, so you will see some nominal intensity values that you can calculate from single-slit diffraction and linearly added intensities (no interference)."
] |
[
"What influence do slits (B) and (C) have on the diffraction pattern, given that they are further away from (D) than (A) is, and understanding that light going from (X) to (D) through (A) is as fast as possible?"
] |
[
"This one really hit it on the head for me, great explanation."
] |
[
"Help me understand time."
] |
[
false
] |
So I was reading Hawking's Brief History of Time, but can't get my mind around how gravity affects time. For instance, GPS satellite clocks run faster in orbit than clocks on earth because they experience less of the earth's gravity. Why? I imagine a simple clock where say a crystal vibrates at a certain frequency, a microcontroler counts the vibrations and increments the segments of a digital display to the correct numbers. What does gravity have to do with that process? or a spring turns gears which turn the hands on a clock. Where is gravity involved? Maybe the electrons powering the clock move faster with less gravity? Or what about human aging? I know the concept of time being relative, between earth observers and near light speed travelers, but i can't get my mind around how that would look in the real word, biologically for instance. Any help would be much appreciated by my exhausted little mind. Edit:spelling
|
[
"Maybe the electrons powering the clock move faster with less gravity?",
"Firstly, stop trying to think of a mechanical explanation; it has nothing to do with how gears or electrons move. Time ",
" slows down, and the effect can be shown to apply to things that have no moving parts whatsoever, like a single atom of an unstable nuclide which takes a little bit longer to spontaneously decay when it's near a massive body than when it's far away from one.",
"Secondly, by the equivalence principle it's not just gravity that causes this but any accelerating frame of reference. If you got into a dragster and accelerated down the track your clock would run ever so slightly slower than that of someone in the stands for the duration of the acceleration. (This is not saying that the dragster would have to get to a significant portion of the speed of light. This effect is different and only occurs while the dragster is accelerating; once it hits 300 MPH or whatever its top speed is and it coasts the effect is gone.)"
] |
[
"to be specific: gravity doesn't \"bend\" it at all. Mass-energy does, and gravity is just a derived result ",
" that bending."
] |
[
"We've discovered that space and time are not independent. We live in something called a spacetime ...",
"http://en.wikipedia.org/wiki/Spacetime",
"Gravity bends this thing. So that's why gravity affects time.",
"It turns out this is really the best description of reality. Weird, huh?"
] |
[
"Whats left in the soil onece it becomes \"barren\" & can soil be truely \"barren\"?"
] |
[
false
] |
Thank god you guys are here, i was having a long thought out conversation the other day and came upon the concept of barren soil. Please explain this to me in a way i can understand! Lets start out with fertile soil; Now we plant plants until all the nutrients have been depleted, whats left in the soil? To my understanding we have organisms that can derive energy from damn near any materials in existence. I mean theres plastic consuming mushrooms at this point! In my mind, if there is a physical material there. then in my mind there is an element or nutrient there. which can be used by an organism for energy. The only thing i can think of (Becides Drought Conditions) Is IF the plants consumed everything useable, that would only leave concentrated deposits of poisons. I deeply appreicate an explanation, the more detailed and in depth the better! Thanks you guys and gals!! :D >.> >.< <.<
|
[
"Good soil is soil that is capable of supporting life, by definition, and barren or degraded soil cannot support life or not as well as it used to. There are a number of ways this can happen.",
"First, the main thing a plant needs from the soil is just water. It doesn't need all that much other stuff (\"nutrients\"). A plant gets energy from the sun and most of the plant's structure is gotten from the air itself. Remember photosynthesis- this takes carbon dioxide from the air, plus water from the ground, and combines that to make sugar (C6H12O6). That sugar is then used elsewhere in the plant to fuel cellular activity and is broken down to be the building blocks for lignin and cellulose (both are just carbon, hydrogen, and oxygen), which comprise most of the plant's structure. By elemental composition, ",
"over 95% of a plant is just those three elements",
": carbon, hydrogen, and oxygen, which are just carbon dioxide and water.",
"A plant does need \"nutrients\" as well, usually nitrogen, phosphorous, and potassium, plus some others. In nature those nutrients are naturally recycled into the soil through the decomposition of organic matter, but in farming we can replenish this stuff through the application of fertilizer.",
"So- nutrients aren't really the problem. The real issue is that soil needs to be able to hold the right amount of water for the plants that need it. Too little water and the plant can't photosynthesize, and too much water can cause fungal or bacterial problems. There are some secondary factors too- the soil needs to be mechanically strong enough to give plants something to grab onto, but also loose enough to allow plants and supporting animals/insects to move through the soil. In other words, you typically want a kind of loosely packed, rich, dark soil full of little bits of wood, leaves, and other organic stuff that soaks up and holds water, but not too much water. ",
"So, the biggest part of good soil is having the right mix water-bearing content, and the biggest threat to good soil is actually erosion. That loosely packed, granular material can easily be picked up and carried away. Rainwater can wash it away during rainstorms. The wind can blow it away from unprotected topsoil. The lighter, water bearing, organic content is removed, and the heavier, denser, mineral content is what remains. Erosion and other processes can also cause compaction, which reduces the capacity of the soil to hold water, even if it has the right mix of stuff.",
"Farming processes in particular can cause lots of erosion very quickly. Think of the dustbowl in the US Midwest around the turn of the last century. Farmers removed all the natural ground cover that holds soil in place, then churned up the ground through tillage and exposed the light fluffy organic stuff, and then the wind picked all that up and moved it away from the farms where it was needed. Dust storms could carry hundreds of tons of material away in a single go, leaving dry, rocky, mineral-heavy soil behind.",
"The good part is that soil isn't really a non-renewable resource. We can always turn bad soil into good soil by restoring the desirable mechanical properties the soil should have. The problem is that this costs money and effort, and it can be avoided in the first place through the use of sustainable farming practices."
] |
[
"Thank you! this was the awnser i was seeking! :)"
] |
[
"Remember that soil does not exist without life. Fungi, plants, and microorganisms originally broke down rock into “soil”. Today, soil is a complex mixture of old soil, dead plants, dead fungi, dead animals, dead microorganisms, silt and sand, urine and feces, and many other things."
] |
[
"Would there be any catastrophic events if the moon was wiped out?"
] |
[
false
] |
If the moon was all of a sudden gone, would it affect Earth in any major way? EDIT: Thanks for the replies! I know I don't want the moon destroyed now.
|
[
"animals would go batshit without the moon to guide their natural rhythms.\nwe would lose the tides, and more importantly the earth's rotation would be affected, we would start to wobble. right now the moon has a stabilizing influence on our rotation. The moon also acts somewhat like a shield for large meteors picking off alot of them before they hit us so our odds of a deep impact style strike go way up. ",
"if the moon were to break apart into pieces we'd be well and truly fucked when the first big chunk of it hit us."
] |
[
"Source for this? I'm pretty sure the moon does the lion's share of the work."
] |
[
"One recurring nightmare of mine is a Deep Impact asteroid hitting the moon instead of the earth, everyone is happy, but the impact pushes the moon a little too much towards the earth. Long story short, it falls toward us."
] |
[
"How does Circadian Rhythm/clock work for the blind?"
] |
[
false
] |
If circadian rhythm is based mainly on the external stimuli of Sunlight/light, does it function well for the visually challenged? If so, how?
|
[
"The answer depends on the cause of the blindness. The brain's internal circadian clock is very accurate and will run by itself, but it is normally synchronized by outside sources, typically light. This can 'entrainment' can be done by rods and cones, and/or intrinsically photosensitive retinal ganglion cells (ipRGCs).",
"If the visual impairment spares some of these cells, they can still entrain the internal clock even in the absence of typical vision. If the visual impairment spare none of these cells (eg. enucleation), the internal clock will run close to 24-hours but will eventually fall out of sync with clock time.",
"Please see the recent Sleep FAQ for more details:\n",
"http://www.reddit.com/r/askscience/comments/1x9s0e/faq_friday_what_have_you_wondered_about_sleep/cf9g8xg"
] |
[
"Doesn't skin have a feedback for light?"
] |
[
"There was an article some years ago that suggested that, but all the evidence since shows that light on the skin cannot entrain the central clock."
] |
[
"What's the deal with cosmological constant? Does it still hold a value in the formula for General Relativity?"
] |
[
false
] |
For reasons that don't need to be introduced, I've been watching some videos about the cosmological constant. In every video I watch, the host will say something along the lines of "Einstein introduced this constant so that his equations would work under the assumption that the Universe was static. However, with Hubble's discoveries that the Universe is expanding in the 1920s, it turned out that Einstein's original equations were indeed correct, and the cosmological constant could be removed from them". However, in every written source (Wikipedia, for example, but just the general written form of the equation), the equation for General Relativity is still given using the cosmological constant. So which is it? Is the cosmological constant 0 and it's just included in the equations out of respect for Einstein, or is the cosmological constant real, and the YouTube hosts were over-simplifying a complicated history of the constant?
|
[
"So Einstein's constant is no longer correct? A new constant is used that has a different value?"
] |
[
"So Einstein's constant is no longer correct? A new constant is used that has a different value?"
] |
[
"Makes sense. Thank you!"
] |
[
"What color is a neutron star?"
] |
[
false
] |
I understand that color is produced by interactions with electrons, but since a neutron star doesn't have a lot of them, what color will it be?
|
[
"Neutron stars are made of ",
"-degenerate matter",
" and are the result of a supernova and gravitational collapse of a large star. Using ",
"Wien's law",
" it is possible to calculate that most of the EM radiation emitted by a neutron star is in the x-ray range, and this is how we typically look for them (by looking for x-ray sources). ",
"This can then be plotted as a blackbody curve, a graph as shown by the example in the Wien's law link, which shows that the emitted radiation would gradually \"drop off\" from the x-ray peak as it increased in wavelength towards the visible spectrum, so it can be expected that the neutron star would emit ",
" visible light in the blue-violet (near-UV) end of visible light.",
"However this comes with some further problems. Neutron stars are incredibly compact objects, so any emitted visible light would be subject to some ",
"gravitational red-shift",
". Assuming that most of the visible light is emitted from the surface as \"blue light\", ~475nm, then it would appear more \"red\", ~665nm, for a typical neutron star (~2 solar masses, ~10km radius). As ",
"/u/RRautamaa",
" pointed out, I forgot that some of the UV will be redshifted to near UV and visible, which may cause the neutron star to appear more blue/white.",
"However because neutron stars are incredibly small, they aren't very luminous and are thus difficult to image in the visible range (think we've only managed to see a handful of close neutron stars in visible spectrum, e.g. with Hubble) so you wouldn't really \"see\" it as that colour, unless you were potentially quite close and then you have other issues such as high levels of radiation and gravitational gradient to worry about!",
"There's quite a few caveats and uncertainties in there, such as ignoring the magnetic field and rotation of the neutron star (this leads to pulsars). Hope it's sort of helped though."
] |
[
"You're forgetting that even though there is a redshift, there is also UV rays emitted that shift to visible blue. Together, the curve is near flat, which appears bluish white to the eye.",
"Neutron stars have been also imaged directly. It's made up that they would be visible only close by."
] |
[
"Most welcome. I've not done astro in a few years now so I may have glossed over some things, so I'd welcome any corrections by actual astrophysicists.",
"As for reflection no, a neutron star would likely not reflect any light. Stars are considered \"good\" blackbodies meaning that they absorb all incident EM radiation, so rather than \"reflecting\" light as we imagine it, it would likely absorb the incoming photons and re-emit them."
] |
[
"When light enters a black hole and then fails to exit it, would the black hole not cause the light to slow down below the speed of light which, should be impossible for light in a vacuum?"
] |
[
false
] | null |
[
"The geometry of space time inside the event horizon of a black hole is very different to \"normal\" space. Once you cross the event horizon, time and space do a kind of swap, meaning that no matter what direction you travel or how fast, you always move closer to the centre of the black hole. So once a photon crosses the event horizon, it doesn't slow down, it literally has no path through space to get back out.",
"EDIT: There's a nice piece ",
"here",
" which explains it better."
] |
[
"The light gets \"destroyed\", it stops existing when it hits the singularity (or whatever might be there)."
] |
[
"This is one of the few extreme circumstances where you have to use general relativity to even get a reasonable approximation of what it happening. Here you can't think of gravity in the Newtonian sense where it is simply a force pulling objects closer (especially since gravity is effecting light which has no mass and therefore in Newtonian physics it shouldn't be effected by gravity at all). Instead, you must think about gravity being a property of space-time itself and that the high concentration of energy within that space (the black hole) is bending space time itself into a funnel like shape causing the light to circle the black hole still at the speed of light in all non-inertial frames. At no point is the light slowing down; instead, it's path is being bent around the black hole (atleast that is what you see as the observer)."
] |
[
"Writing a short story featuring a neutron star. Need science advice."
] |
[
false
] |
I am writing a short story featuring a neutron star. Speculate; What would happen if a rogue neutron star entered our solar system? It's destined to slam into Earth and destroy it but along the way surely it would have other effects. If there are any scientists that would like to weigh in I would love your input and proudly acknowledge you should the short story sell. Thanks!
|
[
"Ignoring the phenomenal improbability for a second, it would almost certainly be travelling at breakneck speed, so the effects would be brief. Without more details it would be exceptionally difficult to give you an accurate answer, as speed, mass, trajectory, current planetary positions etc all make a large difference.",
"One thing you could try is buying something like Universe Sandbox from steam. It's not absolutely flawless, but it's based on real physical laws and isn't bad, plus it comes with a built in model of the solar system. So all you'd need to do is learn how to stick a mass reminiscent of a neutron star in, lob it at the pre-existing solar system model, and you've got a reasonable idea of the gravitational effects."
] |
[
"Incidentally, I own said program and just tried it a couple of times. Both times it ended up pretty much scattering the planets and chucking the sun off in a random direction as well. The planets either follow the path of the sun or the path of the 'intruding' star, depending on where they are at the time and how fast it's moving. Either way, the solar system didn't make it."
] |
[
"As the other posters have pointed out, the effects depend heavily on the path that the neutron star takes through the solar system. Any path could potentially be devestating, but there are two which lead to particularly spectacular results.",
"1) The obvious one: the neutron star comes close to the earth. First and foremost, if the NS gets about as close as the Sun we're all going to die. Once the NS's gravitational pull on the Earth is comparable to that of the Sun, we probably won't be able to maintan our nice temperate orbit and will eventually experience significant changes to the climate as the Earth moves closer to or further away from the Sun. The size of this effect is dependant on how close the NS gets to the Earth and on how fast it is moving (the longer it's close to us, the more pronounced the change will be). I don't have any experience with the program/game/sim that ManditoryMaturinal suggested, but it seems like a good way to play around with the various ways it could play out.",
"Of course, the above statements are true for any similarly sized star (roughly the mass of the sun). At these distances, gravity doesn't care what a star is made up of. That's no fun. If we want the NS to really show off, we need it to get even closer to Earth.",
"First, let's talk about radiation. As an object gets hotter, the radation it emits undergoes two tansformations: First: there's more of it. Second: a larger percentage of its photons will be in the high-energy range (if you want a more quantifiable way of thinking about this, look up \"Blackbody radiaition\"). The high-energy photons (X-rays and gamma rays) are more important than the increase in radiation because while neutron stars are very hot, they're also very small (their radius is on the order of a few kilometers), which ends up making an average NS millions of times less luminous than the sun. Despite the low luminosity, the high energy phtotons and charged particles will cause plenty of mischief. Satelites will be rendered useless, humans not protected by the Earth's ozone will be fried, the Aurora Boealis will look spectacular, etc.",
"If the NS gets even closer than that, the Earth will experience the wonderful process know as \"spagehtification.\" Since the gravitational pull of the NS gets stronger as the Earth gets closer, there will eventually come a point when the difference between the force on the close half of the Earth and the far half is large enough that is splits in half. As the Earth falls closer, the same process will happen to both the halves, then the quarters, then the eights. The earth will start to look like a long stand of spaghetti being extracted from a sphereical bowl (complete with tomoto-sauce-colored colored lava spewing out in all directions once the crust cracks). Go to the very bottom of this post for order of magnitude estimates for when all this would happen.",
"Obviously, no-one survives past this point, but if they did, they would witness General Relativity-related wierdness (for example, space-time is curved so extremely near the surface of a NS that you can actually see more than half of its surface). I won't dally here too long lest I make a mistake and anger a physicist whose GR-fu is mightier than my own.",
"2) The less obvious case: the neutron star comes close to/hits the sun. At first, this might sound like a less exciting outcome. After all, we want the earth to be destroyed, right? Well, having the NS come in close contact with the Sun will probably kill the Earth in a more spectacular way than a close pass.",
"First, let's look at the case where the NS does a close pass of the Sun, but doesn't quite hit it. The graviational pull of the NS will rip plasma away from the surface of the Sun and form something called an accretion disk. The particles within an accretion disk are packed extremely tightly and are thus subjected to extreme pressures and temperatures. This pressure gets partially relieved by ejecting huge clouds of ions into the surrounding area. As I mentioned before, the temperature means that the disk will release large amounts of X-rays. In addition to this, the particles that hit the surface of the NS are so heavily accelerated by its gravitational pull that they will be going at appreciable fractions of the speed of light and will release absurd amounts of energy. As a whole, the disk should be thousands of times brighter than the Sun, with all that energy concentrated in the deadlier types of photons and cosmic rays. This kills the humans.",
"Now, let's say that the NS actually hits the Sun. Collisions on stellar scales are very very complicated and no-one understands them completely, but whatever happens will kill us. There will be a huge amount of energy released. Much of this will come from the same places that the energy in the accretion disk came from, but on a ",
" larger scale. If the NS is moving at ~0.01 c (as kouhoutek suggested), the effects will be even more pronounced, as you will be having the relativistic in-falling particles smashing into similarly fast particles going in the opposite direction. There is also the tantalizing possibility that the added mass of the Sun will cause the neutron star to transition to an even denser state (releasing even more energy in the process, of course), but to the best of my knowledge, such a process is not well understood.",
"WARNING: Slight maths beyond this point. I can go into more detail for anyone who is interested. I encourage you to check my math, as I am notorious for plugging in numbers incorrectly.",
"[1](Using the Earth's Roche limit around a 1 solar mass NS as a guide, spaghettification should happen when the neutron star is about as close as our moon. Surprisingly, the NS's radiation probably hasn't killed us by this point. Using the Stefan-Boltzmann Law, I estimate that the power emitted by the NS over the surface should be P = A * sigma * T",
" = (50,000 K)",
" * (6e-8 W/m",
" /k",
" ) * (50 km",
" /1e6) * 6 * 1e-6 ~ 1e14 W. This is about 1/1000 of the rate at which we absorb energy from the Sun. Note that this does not take into account the more exotic effects of high energy cosmic rays penetrating our atmosphere. Presumably someone could stay on the far side of Earth and be just fine.)",
"[2](When the NS is within the orbit of the moon, the gravitaional field due to the NS is about G * 1 Solar Mass/ 1 light second ~ 10",
" J/kg. The Earth is racing towards the NS at about 500 km/s, which is on the order of a hundred times faster than that Apollo rockets. The end is nigh.)",
"[3](Doing order of magnitude estimates based off of wikipedia's information on the solar wind (which I, admittedly, know little about), when the NS is within the orbit of the moon, the charged-particle flux (and thus Aurora Borealis) should be somewhere between a hundred and ten thousand times as strong (Let's be conservative and go with 100). Every time the NS gets twice as close to the Earth, the Aurora will get four times as strong. Using this as a rough guide, I'd guess that astronauts start dying when the the NS is within ~10 Moon orbits and the satelites go when it is within ~5 Moon orbits. These are very rough estimates and I hope someone can improve upon them.)"
] |
[
"How does the ISS handle debris on its solar panels? How often does the ISS get hit with debris?"
] |
[
false
] | null |
[
"Hey, this question is right up my alley!",
"Bit of background: I've done testing and analysis for the ISS program on this exact topic, including hypervelocity impact testing into ISS solar cells at NASA's White Sands Test Facility back in 2014.",
"Second question first: the ISS gets hit more or less constantly. This is largely a function of just how big it is. A back of the envelope analysis we did several years ago suggests that the solar arrays are struck by something big enough to cause degradation approximately once every ten minutes. Downlinked imagery supports this - on one returned solar array image, we were able to count nearly 200 strikes on an area covering less than four square meters.",
"As far as how it is handled: there's not much we can do other than to monitor performance and plan accordingly. With a few notable exceptions, individual MMOD strikes to the solar arrays have very little effect, but the accumulation of strikes presents as a gradual loss in power production capability over time. To combat this, you try to predict the rate of degradation and size your arrays so that they will produce the needed power at end of life.",
"In the case of ISS, the degradation rates from all sources used in the early 1990s when they were designed ended up underpredicting the overall rate of power loss. They are currently exploring sending up new arrays to augment power production at some point in the future."
] |
[
"A brick sized object would be, depending on where on ISS it hit, anywhere between devastating and nearly instantly catastrophic.",
"Fortunately, most objects that big, of which there are relatively few, are able to be tracked, so we can see them coming and get out of the way.",
"Most of the stuff that hits ISS is very small, less than a millimeter in size. Objects that small pose nearly no threat to the well-shielded habitable portion of ISS, but they are a threat to various pieces of hardware outside."
] |
[
"A brick sized object would be, depending on where on ISS it hit, anywhere between devastating and nearly instantly catastrophic.",
"Fortunately, most objects that big, of which there are relatively few, are able to be tracked, so we can see them coming and get out of the way.",
"Most of the stuff that hits ISS is very small, less than a millimeter in size. Objects that small pose nearly no threat to the well-shielded habitable portion of ISS, but they are a threat to various pieces of hardware outside."
] |
[
"Would arrows to indicate direction and/or movement (specifically on the pioneer spacecraft) really be unintelligible to non-humans?"
] |
[
false
] |
[deleted]
|
[
"I doubt they could understand it, for many reasons.",
"Now, we can't actually do experiments on extra-terrestrials to answer questions like those, but we could do it on children which do not have any preformed cultural conceptions. I can only offer anecdotal experience, since I have a kid myself and I can tell you that the things we take for granted as indicating a direction are completely meaningless to a young child.",
"Another good example of how difficult it is to translate something foreign without a reference point is how important the Rosetta stone was.",
"Also, there is more to interpreting an arrow than just the direction. ",
"First off, there is the issue of significance. An alien race viewing the plaque would have to understand that the markings on the plaque (or the plaque itself) was significant and that they are not noise. There is no general algorithm to distinguish noise from information.",
"Second, they need to be able to understand where markings begin and end. They may not have the same semantics of boundaries between symbols that we do.",
"Third, they need to understand that the arrow is a direction indicator and does not represent an object itself or something else.",
"Edit: Removed unfinished sentence",
"Fourth, they need to understand that the arrow denotes a direction along the length of the arrow. An equally valid interpretation is that the arrow denotes a boundary between the two halves of the plaque separated by its major line.",
"Fifth, they would have to distinguish which direction the arrow denotes, which is completely open to interpretation. Maybe they see the convergence point of the arrow as an origin (i.e. a \"fountain from which multiple lines spring\") and the major emerging line as the destination."
] |
[
"Any discussion of the psychology of non-terrestrial intelligences is going to be speculative as hell. A sapient alien species might well be able to interpret an arrow as indicating movement; alternatively, they might not be able to understand symbols at all. We just don't know. With that in mind, I think arguing that hypothetical aliens ",
" find it meaningless is a perfectly valid point. ",
"Edit: A ",
"vaguely related thread",
" from ",
"r/math",
" just popped up on my front page, talking about what alien mathematics might be like. You might be interested in taking a read through that. "
] |
[
"Sounds contrived to me. Your examples with children and the rosetta stone are irrelevant. Children lack experience and to some extent intelligence and symbols are different from newer writing systems.",
"I think you underestimate intelligence and deductional skills."
] |
[
"How do wild creatures get through unusually cold weather?"
] |
[
false
] |
The Northeast US is having an unusually long, deep cold snap. Humans and domestic pets are holing up inside, farmers are keeping cows in the barn -- but what about the wild birds? The deer and the chipmunks? Which species are unphased by this, going about their usual business? Which ones are taking special measures? Which are being stressed or threatened? Where do they all until it warms up again??
|
[
"I can weigh in on birds. :)",
"Birds’ feathers provide excellent insulation against the cold, and many species grow extra feathers in the late fall to give them more protection during the winter months. There is also an oil that coats birds’ feathers which provides insulation as well as waterproofing. This is exuded from their ",
"uropygial gland",
" located near their tail. Birds also have a layer of soft, insulating feathers called ",
"\"down\"",
" (you can see it's soft, and fluffy) which traps their body heat, minimizing heat loss.",
"Birds’ legs and feet are covered with ",
"tight, overlapping scales",
" that reduce heat loss. They can also constricting blood flow, which reduces heat loss, by controlling the temperature of their legs and feet separately from their bodies. Aside from this you may have noticed that water fowl, such as ducks and geese, can tolerate cold water. This is a great adaptation called ",
"\"counter current heat exchange.\"",
" How this works is the warm arterial blood flowing away from the heart warms up the cooler venous blood heading towards the heart. This exchange keeps their feet from freezing while standing exposed or floating in water. ",
"Here is a diagram to help you visualize this process.",
"Birds are ",
"endotherms",
" or warm-blooded (we don't really say warm-blooded anymore, but I know folks are familiar with the term). This means they create their own heat from their metabolic processes. Birds also have a much higher resting metabolic rates than humans do. The average bird’s body temperature is 105 degrees Fahrenheit (40 degrees Celsius). ",
"This page has a lot of great information on bird metabolism.",
"Birds, along with other animals, can build up a fat reserve during the Fall to prepare for harsh winter months. They gorge on food for the entirety of the Fall, which gives them a protective fatty layer. ",
"More great info and photos here",
". In humans, we turn ",
"brown adipose tissue",
" into heat, but this specific tissue type ",
"is not found in birds",
".",
" - birds fluff out their feathers in cold weather. This action creates air pockets that add additional insulation. This is where that layer of fluffy down comes into play!",
" - certain species of birds will flock together in winter to keep warm for the evening. We see this in the ",
"America crow",
" (",
") around sundown in the cooler months. Near me at 4pm beginning in the Fall you can watch them gather together in large groups. During the Winter months I also notice Dark-eyed Juncos, Black-capped Chickadees and Northern Cardinals flocking with conspecifics but also with other species.",
" - allowing the Sun to do the hard work, birds can keep warm (like other animals) by ensuring they are spending time in the sun.",
" - shivering keeps birds warm just as it does with humans and other animals.",
" - During torpor a bird reduces their metabolism when their body temperature is low. Their bodies then require fewer calories to maintain a comfortable body temperature. Interestingly, due to their high metabolism, Hummingbirds enter torpor every evening so as not to use all of their energy reserves overnight.",
" - you'll often see birds tucking a beak or one leg up into their feathers to minimize heat loss. You'll probably notice ducks and gulls doing this all the time! They do it in the summer as well as it's a comfortable resting position for them."
] |
[
"Bees form a ball inside their hives where they all huddle together and swarm around one another to keep warm. The bees in the middle get to be warn and sleep while the bees on the outside do the work, and then they rotate in and out in shifts."
] |
[
"So basically, the feet get less warm this way (but less heat loss also, as heat loss is based on the temperature difference between 2 objects). The heart also gets less chilly blood returned to it, so less thermal shock."
] |
[
"One thing astrophysicists/theorists never talk about when discussing interstellar travel is how hard it would be stop a ship traveling at close to the speed of light. Is it somehow easier to slow a ship down than speed it up? Have any potential methods for doing this been discussed?"
] |
[
false
] |
[deleted]
|
[
"If you have a ship capable of reaching relativistic speeds, slowing down is the least of your worries. In fact, slowing down is dead easy. Just use attitude jets to turn the ship around, and fire the engines pointing the other way. ",
"The only caveat there is that you have to start firing the engines in reverse early enough. If you fire the engines continuously, you'll have to switch from accelerating to braking at the halfway point of your journey to avoid overshooting your mark."
] |
[
"That is truly one of the big outstanding problems to the field. Because at those speeds, realize that what you have isn't so much a pebble hitting your windshield but a collision in a particle accelerator. The atoms of the thing you're \"hitting\" smash into the atoms of your ship and produce a ",
" of very hard radiation that preferentially shoots down the axis of your ship (due to the relative momentum of your ship and the particle). Furthermore, even the cosmic ",
" background will be blueshifted in the direction of travel, and at sufficiently high speeds will be blue shifted into the gamma ray spectrum. Meaning you're continuously flying into a \"cloud\" of gamma rays, so you'll need a lot of radiation shielding just from the ambient ",
" in the universe. And don't use radar, because as much as the CMB will blast your ship with gamma radiation, your radar will blueshift for the people in front of your ship (like the planet you're heading toward) into the gamma spectrum as well. So yeah, there are a ",
" of physical problems with traveling at relativistic speeds."
] |
[
"That is truly one of the big outstanding problems to the field. Because at those speeds, realize that what you have isn't so much a pebble hitting your windshield but a collision in a particle accelerator. The atoms of the thing you're \"hitting\" smash into the atoms of your ship and produce a ",
" of very hard radiation that preferentially shoots down the axis of your ship (due to the relative momentum of your ship and the particle). Furthermore, even the cosmic ",
" background will be blueshifted in the direction of travel, and at sufficiently high speeds will be blue shifted into the gamma ray spectrum. Meaning you're continuously flying into a \"cloud\" of gamma rays, so you'll need a lot of radiation shielding just from the ambient ",
" in the universe. And don't use radar, because as much as the CMB will blast your ship with gamma radiation, your radar will blueshift for the people in front of your ship (like the planet you're heading toward) into the gamma spectrum as well. So yeah, there are a ",
" of physical problems with traveling at relativistic speeds."
] |
[
"Ac vs DC"
] |
[
false
] |
How come since all of our appliances us DC power and the electric companies send us AC current don't we just put a convertor on our house? That would save us space with all of our appliances not needing those huge power bricks.
|
[
"Lots of the power usage in you home requires AC, such as your refrigerator, air conditioner, etc."
] |
[
"It's worth clarifying some of the replies so far. Transmission of DC is more efficient than transmission of AC. Alternating current, by definition, has to change directions in the power lines. This change doesn't happen instantly, and is governed by the ",
" of the lines. Changing a voltage across a given inductance creates a fakey resistance called ",
", which makes for lossier transmission. DC has none of this, except the initial reactance when establishing the magnetic flux in the power line. Both AC and DC are subject to additional ",
" inherent in the aluminum or steel cables used for long-distance power transmission, and are equally affected.",
"What AC was way better at, was conversion. Given an alternating current, it's trivial to couple two coils of wire with an iron core and shuttle the power around between voltage and amperage. Mains frequency is a compromise between higher frequency for transformers and lower frequency for transmission line reactance. The faster you get the frequency, the smaller the transformers can be. The slower you get the frequency, the fewer AC losses you have from reactance.",
"Nowdays, we have devices that engineers of the 1800s would have wet themselves for. A buck converter with high frequency synchronous rectification (800khz?) can hit DC to DC conversion efficiency exceeding 95%. A mains-frequency transformer doesn't come close, and will be larger, heavier, and more expensive. It's such a dramatic difference that some power grids ARE using DC for long distance power transmission, because modern technology has made it completely viable.",
"If the grid were to be rebuilt completely (say, after a meteor or volcano levels a continent), it likely would be rebuilt with DC. There's almost nothing that AC does better with modern semiconductors."
] |
[
"Some appliances actually don't use DC power, it is also much cheaper and more efficient to send AC power. Transformers, which are used to efficiently facilitate the transportation of electricity by being able to step up or step down the voltage, require AC. Transformers are common in power lines but some appliances use transformers as well. Having a big converter in your house to turn all the power into DC would make your house overall less energy efficient and would require some appliances to turn it back in to AC just to function. There is a good chance your house electronics would function properly but it would be less efficient and may interfere in unforseen ways.",
"Edited out misinformation.",
"Hope this helps."
] |
[
"Why isn't nanocoating more common (yet)?"
] |
[
false
] |
The last few years I have seen many videos/articles showing off the effects nanocoating have. As in clothes that can't get dirty, cars, all kinds of objects. But why is it that this isn't or at least seems to be not that common. Also I've heard they already put it on cars, but often it doesn't seem as effective as some of the videos/articles show. So are there a lot of different kinds of nano-coating with varying degrees of effectivesness (and cost)? How come we don't see this on alot more products?
|
[
"At least with the ultrahyphobic materials, the biggest problem is adhesion. The problem with nothing sticking to your coating is that your coating doesn't stick to surfaces! ",
"There are chemical ways of doing these adhesion, but it's hugely different to do something in a lab and on an industrial scale. Developing new processes is expensive and time consuming. ",
"Let's look at production of ultrahydrophobic glass. As it stands right now, the process and production of float glass is pretty standardized. The plants are built. Now if we want to make a bond with the surface we will have to silanize it. Then you have to do the reaction with the nano particles. I will assume the glass coming off the plant is silanizable, however it might not be. So now we have to treat the surface - which will involve washing the glass with the aptly named piranha solution. Then needs to be washed, dryed, silanized, quenched, nano particles manufactured, cleaned, concentrated, batch tested, and then coupled to your surface. The overhead for optimizing these processes on an industrial scale are quite large."
] |
[
"I will assume the glass coming off the plant is silanizable, ",
"I don't know of any glass that cannot be silane modified, would love to hear of one if you know of it.",
"A bigger problem than all the issues you described is lifetime. A nano-coating is not mechanically robust. It will deteriorate and scratch and fail, quickly. "
] |
[
"Dirty glass can't be effectively silane modified. Hence a definite requirement for cleaning if being moved sites, and a probable requirement even if coming straight off the line. Further more yes this is what we are talking about. The difference lies in coating versus surface modification. Surface modification is stable relatively. Coatings are not. "
] |
[
"How does an electric arc choose it’s path in air (ex: a lightning bolt or Tesla coil)?"
] |
[
false
] |
They all seem so very random, but is there an actual scientific or mathematical equation for the path/arc they create? Or is it just randomly jumping from one molecule to the next?
|
[
"First, watch the video linked by ",
"/u/sxbennett",
" - it's an amazing video showing what happens in a lightning strike. I've shown that same video to many others in the past to illustrate what's going on.",
"But in more detail: The air in our atmosphere is non-conducting in general, so charges can build up in two separate locations without them immediately cancelling out due to current flow.",
"However, if you apply a sufficiently high voltage to air (or any other gas), the story changes. In every gas, there are some random electrons floating around that aren't bound to an atom and under the influence of an electric field, these electrons will accelerate. As they fly away, they'll bump into molecules in the gas, lose part of their kinetic energy and then start over again. If the electric field is strong enough, then these electrons can gain enough energy between these random bumps to strike a molecule hard enough to knock an additional electron free from the molecule, leaving behind a positive ion (this process is called \"impact ionization\"). At that point you've got 2 free electrons accelerating in the field. These will free more electrons and so forth.",
"This phenomenon is called an \"electron avalanche\" and it happens whenever the electric field is above a certain threshold value, called the breakdown voltage. The field between a thundercloud and the ground doesn't exceed this breakdown voltage, which is a good thing, because otherwise we might get large scale ionization of the air.",
"So how do things get started then? Previously, I made no statements regarding the profile of the electric field and implied that it was mostly homogeneous. However, various objects can locally distort the electric field. In a cloud, ice particles can have sharp tips that function as a needle. Directly around such a sharp tip, the electric field is greatly enhanced, possibly to values above the breakdown voltage.",
"So you have a field that is generally below breakdown, but with certain areas where there is something that locally enhances the field above the breakdown voltage. In such an area, a stray electron can set off an electron avalanche, creating a large amount of ionization. Since electrons are much lighter than ions, the electric field, electrons will move much faster than ions under the influence of the electric field. In fact, in the timescales involved, one can assume the ions are essentially stationary.",
"What happens now is a somewhat complicated process where the blob of free electrons moves with the electric field, leaving the ions behind. This means that the area is no longer electrically neutral since the negatively charged electrons become separated from the positively charged ions.",
"This process results in the formation of a structure that resembles a finger: an elongated channel with a plasma that is mostly electrically neutral with a curved tip that contains a net charge. This charged tip replaces the sharp edge of an ice particle (or any other sharp object) in creating the local enhancement of the electric field and will generate more electron avalanches ahead of it and this process causes the tip to move forward and the channel to extend.",
"This process is visualized somewhat in ",
"this image",
" which depicts the electric field of this system in a computer simulation at various time steps.",
"In the space away from the tip, the field is about 20 kV/cm, which is below the breakdown voltage in air (~32 kV/cm). At the tip of the channel, the field is very much enhanced to well above the breakdown voltage, causing a large amount of ionization. Meanwhile, inside the channel, there's a plasma with a large amount of both positive and negative charge from previous ionization events, making the channel highly conductive, but also reducing the electric field. These propagating \"fingers\" are called \"streamers\".",
"Now, away from the small scale processes and back to lightning. What happens in a lightning strike is that a cloud of these streamers springs forth and propagates through the air. Following this is a larger structure called a \"leader\" which is essentially an upscaled version of a streamer. The tip of the leader has many streamers extending from it to create a path of ionization. The leader is the thing you see in the aforementioned video.",
"Leaders often propagate in steps, where it propagates for a while, then stops and moments later restarts, potentially in a different direction or with additional branches. The exact mechanism of the stop-start process is not well understood, but it's assumed that the leader stops when the tip becomes to smeared out, reducing its ability to enhance the electric field ahead of it. Once more charge flows in from the original source (e.g. the cloud) through the already established channel, it may restart again.",
"Once the leader connects to the other side (either directly or through another leader that emerged from the other side), a conducting channel is formed between positive and negative sides. At that point, charges can flow freely and this results in a large current rushing through the channel. This current rapidly heats the gas in the channel and causes it to emit a lot of light. The light we see as the lightning bolt, while the rapid heating causes a thermal shockwave that we hear as thunder.",
"The path of the lightning bolt is determined by the path taken by the leader. The actual path is very hard to predict, because while a lightning strike is a phenomenon with a lengthscale of an order of magnitude of a kilometer, it is affected by fluctuations at very small scales. In general, the path will prefer following the direction of the electric field and in the case of a lightning strike that's simply vertical. However, various atmospheric properties (such as local temperature variations) can make certain branches of the leader propagate more easily than others. And once a leader is propagating in a certain direction, it tends to stay its course. That is, until it comes to a stop. Once the next step of the leader starts, the direction may change.",
"So there's no real way to predict the path of such a discharge, because the path is determined both by local fluctuations of gas conditions as well as by a certain amount of \"randomness\". The same holds for discharges from Tesla coils, because the mechanism of action of these discharges is fairly similar."
] |
[
"If you watch a ",
"slow-motion video",
" of a lightning strike, you'll see that before it hits the ground it sends out small \"feelers\" that go out somewhat randomly, but mostly downwards. Once one touches the ground, the path it took gets very bright (this is the most visible part of a lightning strike) as it carries a massive current between the clouds and the ground. Lightning happens when there's a big enough potential difference between the clouds and the ground so the air breaks down. The plasma created by the initial electrical breakdown follows the local path of least resistance, which is why it moves randomly, but then once there's a line that touches the ground and lets the potential difference equilibrate all the current travels through that path."
] |
[
"Not a studied scientist, but as I understand it:",
"Electricity usually takes the path of least resistence. ",
"Imagine water-molecules randomly moving around, bumping into each other and creating random volumes of slightly more or less density. ",
"Lightning is caused by a difference in electric potential between the clouds and the ground. One side wants more, the other wants to give it, but there is an insulator in between. Air. Both sides constantly \"reach out\" trying to get or give off this extra energy. As soon as a direct path, where all molecules are close enough together for them to take energy and pass it on instantly, that energy instantly rushes through that \"wire\", just like it will when you plug a wire in the outlet. ",
"In general, the air is an insulator, unless there is a path of molecules, close enough together, for the electricity to bridge from one to the next, without any gap in between. As soon as that's the case, the energy transfered through that route increases dramatically, creating heat and the lightning/thunder combination we know. ",
"",
"Tesla Coils are slightly different, because it's not such a clear pole to pole interaction. "
] |
[
"Would it be possible to throw a baseball around the moon into orbit?"
] |
[
false
] |
Hi I'm new to so I apologize if this is poor formatting or has already been asked. Aroldis Chapman currently holds the record for fastest pitch at 105.1 mph, (Hypothetically) If he was standing on the moon would this be enough to launch the baseball into orbit around the moon because of the moons decreased gravity? If not would it possible to put a baseball into orbit around the moon at all or would an unforeseen factor like the gravity of earth make it impossible?
|
[
"What you need is the lunar orbital speed, which is 1.7 km/s. That's still over 36 times faster than the fastest pitch."
] |
[
"If this is a contest, ",
"S/2009 S 1",
" has a mean diameter of 400 meters. Assuming it's spherical and made of ice, escape velocity should be about 0.1 m/s."
] |
[
"If this is a contest, ",
"S/2009 S 1",
" has a mean diameter of 400 meters. Assuming it's spherical and made of ice, escape velocity should be about 0.1 m/s."
] |
[
"Is it possible to contain and harness the energy from a sun that is small enough?"
] |
[
false
] | null |
[
"I'm not sure what this question is asking. Could you clarify? All of our energy ultimately comes from the sun, and we have harnessed and contained it."
] |
[
"I'm curious if it is possible to use a much smaller sun in place of nuclear plants, or hydro plants etcetera. Or to use it for other purposes. "
] |
[
"This is far too speculative for our panelists to answer. The smallest stars are still larger than most planets. There's nothing that would be the size of a power plant."
] |
[
"Does the gradual movement of the Magnetic North Pole alter climate in any way?"
] |
[
false
] | null |
[
"No. The magnetic poles are entirely different from geographic poles. The motion of the elements in the core would not be sufficient to alter Earth's spin, it's angular momentum will always be conserved."
] |
[
"there has been more geological activity",
"[",
"]",
"Especially under Yellowstone",
"From the actual ",
"Yellowstone FAQ",
" site:",
"\"Another caldera-forming eruption is theoretically possible, but it is very unlikely in the next thousand or even 10,000 years.\""
] |
[
"Thanks!!"
] |
[
"Scientists 'split' the electron? I don't believe it, what can r/askscience tell me about this story?"
] |
[
false
] |
I don't believe it, this would be all over the news if it were true.
|
[
"Science reporting is really really ",
" bad; even if it's from a more reputable news source, you should treat it with about the same credibility as your friend's fishing stories. The article is just completely wrong, and completely misrepresents what was actually done."
] |
[
"I can't claim to understand the specifics of the paper, but I understand the journalist's problem.",
"Basically, all fundamental particles, like the electron, are described as excitations in a fundamental field. A reasonable analogy is ripples on the surface of a pond or pulses traveling along a stretched string. The theory that describes them is called quantum field theory.",
"The cool thing about quantum field theory is that it can be ",
" applied to all sorts of physical situations. For example, in a solid, one has all of the atoms arranged in a lattice. This lattice can be excited by pushing on a few of the atoms, the resulting compression will propagate down the lattice like a wave. ",
"You can treat this vibration of the lattice like a particle in quantum field theory, and it works very well. It is typically called a phonon. Such 'particles' are often called quasiparticles.",
"These researchers were doing something with electrons which caused some excitations that could be described in terms of quasiparticles, and the journalist mistook these quasiparticles as new sorts of fundamental particles. "
] |
[
"In the solid state, there are a variety of pseudoparticles--that is, propagating effects (like an ",
"exciton",
" or a ",
"phonon",
") that behave like particles and can be theoretically modeled as them. When you deal with solid state systems that are very small, you begin to see strange confinement effects. That is, the pseudoparticles in the system start to act weirdly. This paper basically says that, if you confine two electrons very closely together, you might see the magnetic and electronic centers of the electrons move separately."
] |
[
"Does the amount of time it takes an ice cube to melt directly proportional to it's temperature?"
] |
[
false
] |
Would an ice cube that had been stored at 0 degrees F melt more slowly than one that had been stored at 10 F? If so, what's the mathematical nature of this relationship? Edit: Apologize for the grammar in my title.
|
[
"A good way to perceive this is that the melting point of a material (at whatever pressure) is the temperature at which its liquid and solid phases can coexist in thermal equilibrium (i.e. no net energy transfer)"
] |
[
"So what happens if you add an amount less than 344.774 J but greater than ~2.1 J (say, 210 J) to 0C ice? "
] |
[
"So what happens if you add an amount less than 344.774 J but greater than ~2.1 J (say, 210 J) to 0C ice? "
] |
[
"Why don't animals like rams get concussions when they run head first into things? Can we build helmets based on their ability to protect athletes?"
] |
[
false
] | null |
[
"Livescience",
" did a piece on why woodpeckers don't get concussions from constant head-banging. To sum the evidence from that article, the bird's neck has strong muscles that absorb shock, the peripheral components like beak and eyes are cushioned by tertiary structures which prevent impact damage, and most importantly the brain is surrounded by a spongy bone-like tissue which has a relatively high capacity to absorb shock, and which is in direct contact with brain tissue.",
"Studies provide strong evidence that what ",
"u/MestR",
" has said is incorrect. The head and neck circumference ratio (HNCR) has been studied with regard to its impact on the likelihood of concussion in contact athletes, ",
"here",
" for example:",
"For HNCR, there was no consistent association observed with the exception of female hockey players.",
"That is to say, in most cases ",
" the size of your head, or the ratio of the size of your head to your neck, or by extrapolation the size of your brain, is not a significant influencing factor on the likelihood of concussion, unless considered alongside other causal factors such as BMI.",
"The reason why animals like rams and woodpeckers do not damage their heads in the process of performing their daily survival and reproduction related tasks is because they have developed highly specialized tertiary structures to protect their heads and associated organs."
] |
[
"and also dont the tongues of woodpeckers wrap around the skull?"
] |
[
"I don't know why you have -4 points, I've seen multiple sources that state that the tongue moves to the back of the head",
"http://www.birds.cornell.edu/wp_about/biology.html",
"http://www.talkorigins.org/faqs/woodpecker/woodpecker.html",
"Edit: Huzzah he's positive, reddit understands!"
] |
[
"What's the difference between infrared heat and warm air heat?"
] |
[
false
] |
[deleted]
|
[
"There is no such thing as \"infrared heat.\" Heat is a type of energy that corresponds to how fast things are \"jiggling around.\"",
"In order to make it so the components of a system \"jiggle around\" at about the same rate as its surroundings, the system will absorb/give off heat. ",
"There are three methods of heat transfer: conduction (when the jiggling passes through two touching objects), convection (when some kind of fluid carries fast-jiggling particles into regions of slower jiggling), and radiation.",
"What you're describing is radiation. The extra heat is released from the system in the form of light. The frequency (color) of the light is determined by how much energy is being released. For most living beings, the heat our bodies radiate is at energy levels corresponding to infrared light.",
"Infrared light is light that has a frequency too low for us to see. It's basically a redder version of red, but our eyes can't perceive that color."
] |
[
"Warm air can radiate in the infrared range, but it depends how warm the air is. Most heat transfer in gases is through convection.",
"And yes, the sun is extremely hot. It radiates across the entire EM spectrum, peaking somewhere in the visible light region (which is probably why we evolved to see the region of the spectrum that we do).",
"And no, most of the time when you feel warmth, it's NOT from radiation. Conduction and convection are far more common. But when you're sitting in the sun, feeling warm. It's partly because of radiation from the sun. Mostly UV. Not much infrared from the sun makes it through the atmosphere."
] |
[
"Warm air can radiate in the infrared range, but it depends how warm the air is. Most heat transfer in gases is through convection.",
"And yes, the sun is extremely hot. It radiates across the entire EM spectrum, peaking somewhere in the visible light region (which is probably why we evolved to see the region of the spectrum that we do).",
"And no, most of the time when you feel warmth, it's NOT from radiation. Conduction and convection are far more common. But when you're sitting in the sun, feeling warm. It's partly because of radiation from the sun. Mostly UV. Not much infrared from the sun makes it through the atmosphere."
] |
[
"Does time travel slower at the center of galaxies?"
] |
[
false
] |
[deleted]
|
[
"If time travels slower when nearer to high gravitational masses, does time travel slower for things nearer to the center of galaxies where there is a high density of stars and perhaps a supermassive black hole? ",
"Yep. Spot on.",
"And, more of what I'm really trying to get at here, does this affect our perception of space in general? Maybe I'm fundamentally misunderstanding the concept of time dilation, but does time traveling slower near high gravitational masses affect how we see them? ",
"As gravity is the curvature of space time, light gets curved near massive objects (see ",
"http://en.wikipedia.org/wiki/Gravitational_lens",
" for some examples). In addition, light gets red-shifted when it originates from a point of higher gravitational acceleration. (See ",
"http://en.wikipedia.org/wiki/Gravitational_redshift",
"). There is no fundamental differences in appearance though.",
"And how the universe ages...? ",
"Age, as well as time, is subjective. For instance, the age of the universe is in the reference frame of a point at rest relative to the cosmic microwave background and (I presume) from a reference frame of a non-existent or very weak gravitational field. From a point which has been in a gravitationally accelerated reference frame, the universe is younger.",
"Do stars at the fringes of galaxies then age faster than stars at the center?",
"They would age faster due to gravitational time dilation yes, but there is another form of time dilation which makes time slow down for objects in higher relative velocity. As stars in the fringes of galaxies moves at a higher orbital velocity than the stars close to the centre, the relative velocity time dilation counteracts the gravitational time dilation.",
"An analogous case is time correction for GPS-satellites relative to the surface. Their local time is sped up to to lower gravitational acceleration but slowed down due to higher orbital velocity. Here is a wikipedia article about that subject:",
"http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Special_and_general_relativity"
] |
[
"Does the velocity time dilation completely cancel out with the gravity time dilation, or does one \"overcompensate\" the other, like with the satellites around Earth?"
] |
[
"My guess would be yes, I've thought about these kind of things myself. There's never such a thing as \"Zero-G\" though; and I'm not sure how much of a difference you'd have being in some orbit around the SMBH in the center of the galaxy and standing on Earth - as there is very very little difference until you're actually close to an event horizon.",
"So; \"in space\" near the center is slower than \"in space\" in the disk; but \"in space\" near the center is faster than \"on Earth\".",
"At least, that's what I ",
" and I could be completely wrong."
] |
[
"How do we determine the next word we want to use when we speak?"
] |
[
false
] |
I was talking to a friend about the process we use in our minds to determine the next word we want to use when we speak. He thinks it works more by raw, brute elimination. I think it works more like a Markov chain where we store words commonly used after another word/phrase. I.e. to say "How are you": His method: How -> ... are -> .. you? My method: How -> are -> you? Are either of us right? Or is there something totally different?
|
[
"There is quite a lot of research on language production, and it's not my particular area, so I can only give a very general answer.",
"First off, we can rule out a naive Markov chain model which would be based on a linear sequence of words. If there is one clear finding, it is that we both produce and perceive language in terms of syntactic constituents (i.e. words and phrases that belong within larger phrases). So rather than generating each word independently, you generate phrases which have a particular structure and then you fill in the dots. ",
"For instance, consider the word \"give\". Give is a verb that takes a particular set of arguments, there has to be a giver, something being given, and then someone receiving that thing. Not all verbs take the same set of arguments. Take \"donate\" as an example. While you can say \"I gave the underfunded library a computer\" it sounds weird (at least to me) to say *\"I donated the underfunded library a computer\", rephrasing as \"I donated a computer to the underfunded library\" sounds much better. So if you want to communicate that you gave/donated this computer, you can't really plan out the full sentence unless you've picked which of those verbs to use. So you're going to be generating the subject and verb, and then once you've picked out \"donate\" you know you can't produce \"the library\" next, so you generate the phrase corresponding to the object being donated, and then you generate the prepositional phrase. This happens all based on the behind-the-scenes syntax and does not happen in a linear fashion (like an n-gram model or something).",
"Now, in producing particular words I think the idea of working through the whole vocabulary is definitely out, particularly if it were being done in some kind of random order. There are/were models of perception that argued when you listen to a word you're basically considering all possible words that would match what you've heard so far and you start narrowing down as the word is uttered (my understanding is that this model is outdated or at the very least a great simplification). For production, the general idea is that you start with a concept you want to express. From the set of possible ways of expressing that concept you're activating morphemes and phonemes and the most strongly activated are what you actually pronounce. That's a vague outline of the process and there's 50+ years of experimental (and now neuroimaging) work fleshing out the details of that process. You're certainly correct that frequency of forms plays a role in activation, but there are also lots of other factors at all levels (semantic/syntactic/morphological/phonemic) which can influence activation and create things like speech errors."
] |
[
"I've noticed that when in an enclosed space, you will often hear the same word be used in quick succession by two speakers in two different conversations within earshot of each other. ",
"Example:\n2 people, a and b talking in one corner, \n2 people, c and d taking in another ",
"A to B: I find that we have to be really thorough* when checking through this spreadsheet ",
"C to D: what did the boss say to you? \nD to C: She was very thorough*. She asked about the...",
"*at around the same point ",
"First I noticed this I thought it was just my brain being primed to notice the last words I used being used by others in the office. ",
"Since then I've continued to notice it in others too, and the frequency and usage (often using awkward grammar or archaic homophones to make the word work in their sentence) lends itself to suggest that it's actually the brain using the subconsciously collected recently understood words as a quick result when looking for the words to convey the meaning they seek. ",
"Not a nicely scientific finding, but interesting preliminary observations."
] |
[
"[Cognitive Psych PhD who focuses on language about half the time]",
"This question is much too broad to answer effectively in a reddit post, apologies, it's a bit like \"How does your liver know what molecule to make next?\" or \"Which piece of wood will a hurricane pick up next?\" or something. It's VERY complex, and will involve simultaneously, all of the following and much more, for example:",
"Your language's grammar and its hundreds of rules that must be followed usually. (order of the whole sentence)",
"How formal the situation is (different word choices, \"bro\" versus \"sir\" etc.)",
"How rushed you are (choose contractions or slang or key words over detailed explanations)",
"Do you have any sort of impediment like being drunk or are you chewing something? Or are you a child without enough vocal manipulation skill yet? This can make you choose \"mama\" instead of \"mother\" even if you know full well what mother means. Orcan make you choose \"uh huh\" if you're chewing, instead of \"I agree\"",
"Do you have inside jokes with the person?",
"Do you have ANY other of a hundred different types of common ground with the person? Shared life experiences, memories, code words... Are you looking at the same object currently, even? If so, that will mean you probably won't bother to choose words that describe the object, since you know that's redundant for them.",
"Your assessment of your conversation partner's mood. You may choose less aggressive words if you're walking on eggshells with a pissed off person.",
"Does an idiom exist that covers this situation? if so it may spill out all as one idiomatic unit, temporarily ignoring most of the above rules, including grammar, normal meanings, formality, etc. in many cases.",
"Are you trying to be quiet so as not to wake somebody up or get caught doing something? You may choose fewer words, or ones that don't have as many loud pops in their syllables.",
"Would leaving out a word, given the intricate context of the situation, body language, and everything else, be such that it would accidentally mislead the person or come across as a lie? If so you might takes pains to not leave it out.",
"Conversely, do you WANT to lie or mislead? You will of course choose totally different words...",
"This really is \"every single aspect of human communication and society\" that is playing into this.",
"Anyway, in case it's not clear from above, neither of the suggested solutions is the case: brute force, nor Markov chains. Although patterns of common pairs of words do ",
" assist your choices, it's more to do with just assisting you being able to speak fluidly than meaning, I'd say, most of the time.",
"Exceptions would be some cases like the above mentioned idioms, where a whole sequence is pretty much set in stone. Or some rare words like \"tat\" which is pretty much 100% of the time going to be preceded by \"tit for\". But these are very very much the exceptions, not the rules."
] |
[
"If the sun suddenly disappeared, would it take 8 minutes for us to feel the gravitational effects?"
] |
[
false
] | null |
[
"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."
] |
[
"Please use the search function. This exact question has been asked here countless times."
] |
[
"Thank you! :)"
] |
[
"gDNA preparation: Why is fragmentation required?"
] |
[
false
] |
During preparation of gDNA for NGS library construction, why is it important for the gDNA to be fragmented?
|
[
"Fragmentation is performed before most NGS sequencing not just gDNA sequencing, it's also done for things like ChIP-seq* and RNA-seq.",
"Most sequencing machines (like Illumina's ",
"sequencing by synthesis technology",
") can only sequence small reads, up to about 250bp at the most. 100 is very common and even just a few years ago you'd more often see reads of ~40bp. Often you don't even sequence your entire fragment; fragments are usually around 250bp while most reads are 50-100bp. Optionally you can sequence both ends of the read (and depending on what kind of sequencing you're doing and the availability of an already sequence genome you can infer the middle part). ",
"This video explains how sequencing by synthesis works",
". I believe the reason there is a limit on sequencing length is because with each nucleotide added there is a chance for error so the longer the read the more errors. At some point the sequence becomes largely unreliable. This is why ",
"sequence quality decreases towards the end of the reads",
".",
"*",
"ChIP-seq",
" is a bit different in that you don't just sonicate because because of a technological limit of the sequencing machines, ChIP-seq would be be useless without fragmentation because you couldn't pinpoint where your protein was binding. The shorter the reads the higher your resolution.",
"Newer technology still underdevelopment like ",
"Oxford Nanopore sequencing",
" can sequence much longer reads. Nanopore sequencing doesn't synthesize anything it more or less directly reads the DNA as it passes through the pore."
] |
[
"This will depend on what type of library/sequencing application you are using the DNA for. In some cases, it has to be broken and re-ligated to itself in small loops for the technology to work, in other cases, tags have to be added to the ends.",
"In any case, breaking the DNA into smaller fragments will make your samples more uniform, as it's almost impossible to extract fully intact large DNA molecules, and you'll get inconsistent results from samples that have broken to different degrees. Fragmenting them in some ways makes different samples more consistent. Fragmenting long DNA also reduces viscosity, something that is a problem with a lot of technologies that use microfluidics."
] |
[
"Thank you! Very helpful explanation :)"
] |
[
"Is it possible to come up with a scientifically perfect diet for optimum human function?"
] |
[
false
] | null |
[
"No. There is too much genetic variation in the metabolism of certain compounds to develop a single perfect diet. It is possible to develop personalized diets once we have a firm grasp on the above mentioned metabolic variations. But where's the fun in that? I'd rather have a steak than a bowl of goop :)"
] |
[
"I think he was looking for something a little more specific"
] |
[
"To add to scarabear's answer, variations in environment, gut-flora, circadian rhythm, nutrient absorption etc. all affect what each individual needs and when they need it. There is evidence which supports the idea that humans have functioned well off of diets ranging from high fat/low carb to low fat/high carb so it is hypothesized the body has the ability to adapt to enviro/diet given sufficient time. However, advancements in transportation have pushed humans in a direction that evolutionary principles simply can't keep up with. Thus if one person is genetically predisposed to absorb more iron (think high elevation populations), they will eventually have different dietary intake needs than another person who does not have the same genes. ",
"tl;dr it's possible to figure out ideal serum levels of nutrients but dietary intake targets are constantly changing due to physical adaptation."
] |
[
"What are the gases in bloated Lithium-Ion batteries?"
] |
[
false
] | null |
[
"This happens when lithium in the battery reacts with moisture in the air. Lithium reacts with water to form hydrogen gas and lithium hydroxide. Since lithium is so reactive with water, lithium ion batteries must be air-tight so that water can't get in, but sometimes it gets in anyways. The reaction of lithium with water releases a lot of heat as well, enough to cause the hydrogen released to immediately react with oxygen in the air; this is a combustion reaction in which hydrogen gas serves as the fuel, which will consume the hydrogen gas and oxygen to form more water, which will in turn react with the lithium and restart the cycle.",
"2Li + 3H2O -----> 2LiOH +2H2",
"2H2 + O2 --------> 2H2O",
"https://people.wou.edu/~courtna/GS361/Energy_From_Fossil_Fuels.htm",
"https://www.thesciencehive.co.uk/group-1-alkali-metals-gcse",
"https://periodictableguide.com/why-are-alkali-metals-so-reactive/",
"Edit: The water produced from the combustion reaction alone is not enough to sustain the reaction with lithium, however, so additional water is needed to keep it going."
] |
[
"Just to note, the products of water ingress are much more toxic than just hydrogen. Water catalyses a cascade of reactions that produce nasty compounds. The lithium exists as LiPF6 usually in batteries and decomposes by the following equations:",
"LiPF6 --> LiF + PF5",
"PF5 + H2O --> POF3 + 2HF",
"You do not want to breathe any of these substances.",
"Source: ",
"https://www.nature.com/articles/s41598-017-09784-z"
] |
[
"Assuming no other faults, bloating of the battery is due to degradation of the electrolyte at the anode and cathode.",
"Gases at the anode include H2, CO, olefins and alkanes.",
"Gases from the cathode is predominantly CO2. ",
"The reactions for these contain a lot of assumptions like what the solvent actually is, the electrodes etc. but an example is a carbonate CO(OR1)(OR2) (the electrolyte) reacting with the cathode and producing an ether (R1)O(R2) and CO2.",
"Source: ",
"https://www.frontiersin.org/articles/10.3389/fenrg.2014.00059/full"
] |
[
"Why Don't Organs Feel Fatigue Like Muscles?"
] |
[
false
] |
Perhaps I worded this question in a bit of an odd manner. As an avid powerlifter and bodybuilder, I know muscle soreness (more specifically DOMS - delayed onset muscle soreness) like it's the back of my hand... or arm... or leg. You get the picture. But while I was in the shower today, hurting like nobody's business from my first workout back after my attempt at the stay-at-home-marathon, I wondered why my brain and heart (and all the other useless meat bags we lug around all day) never seem to get worn down like my muscles do. From that, I suppose my question can be broken down and rephrased as such: •Why don't our organs get "sore" after heavy use? •Is that what headaches/heartburn are? •Can your organs atrophy if underused? •Are our organs just super crazy strong from all of the beating and thinking and breathing and whatnot that they've been doing for like, ever? Hopefully the Reddit Hive-Mind can provide me and any other curious ones with some enlightenment. Cheers!
|
[
"3 things: ",
"A lot of organs aren't muscles.",
"It's comparitively hard to put strain on organ muscles, compared to movement muscles.",
"We lack the required nerves to feel muscle soreness in most internal organs."
] |
[
"Well that was quick and painless. Thanks for the answer!"
] |
[
"To answer your bullet points (since the guy above hit the nail on the head) you can make some organs hurt.",
"Sensory organs like your eyes and ears can get sore from over stimulation (e.g. Going to a concert, staring at lights) so this kind of counts as overuse? You're subjecting them to more stimulation than they're used to.",
"Your brain can get sore from overuse, but a lot of times it's more due to being dehydrated.",
"Most organs that aren't muscles are connected to a blood supply and won't atrophy unless they have their nutrition cut off. Blind people can still possess eyes, and they don't dissappear over time even though they don't use them. ",
"HOWEVER! If you look at the bigger picture over millions of years, organs can shrink and eventually dissappear if consistently not used or underused. They also grow if they are used or relied upon lots. Star nosed moles and other subterranean species have completely lost their eyes because they don't really need them! So in a way, yes, our organs will dissappear without use. But it'll take a few million years to do that."
] |
[
"Do super viruses like the one seen in The Stand exist? And if so why do we create them?"
] |
[
false
] |
For those not familiar with the book a super flu is released in a government lab that kills most of the worlds population. The virus was designed to overcome defenses and adapt to counter them. So I was curious if science does have these sorts of viruses and what the point of them would be?
|
[
"The creation of a \"super virus\" happened late last year and controversy surrounded it for months. It was a type of bird flu that was extremely dangerous. Scientists created it to study what evolutionary steps a virus would have to take to get to an \"Armageddon virus\" state. ",
"Modern labs (BSL-4 labs) that handle this type of pathogen are extremely safe, so the risk of a synthetic virus escaping is fairly low (usually... Google \"Fort Detrick\"). What bothered most people about this synthetic bird flu strain was that the scientists wanted to publish how the made it and some were afraid that these instructions would get into the wrong hands. ",
"Personally, I was not scared. I'd venture to say there are probably more people in the world with the knowledge and resources to build a nuclear weapon than there are people who could feasibly engineer a super virus. "
] |
[
"\"Scientists created it to study what evolutionary steps a virus would have to take to get to an \"Armageddon virus\" state.\"",
"Perhaps too subtle, but that's what I was saying, here. ^"
] |
[
"\"Scientists created it to study what evolutionary steps a virus would have to take to get to an \"Armageddon virus\" state.\"",
"Perhaps too subtle, but that's what I was saying, here. ^"
] |
[
"What is the real benefit of shivering when it's cold?"
] |
[
false
] |
I learned long ago in school that when our muscles shiver, it generates heat. What I'm now wondering is, how would we be affected by the cold if we were incapable of shivering? Would there be a significant difference in our body temperature?
|
[
"We would still maintain homeostasis, but we would be forced to do it through different mechanisms. Shivering is a simple way of generating heat by muscle use.",
"Human infants and hibernating animals use ",
"non-shivering thermogenesis",
" to generate heat."
] |
[
"I'm digging through some old notes and textbooks to try to find the data for humans, but in the meantime animal studies should be sufficient for your answer.",
"In normal environments (as ren5311 linked to) non-shivering thermogenesis is adequate to maintain homeostasis (constant core temperature). However, shivering is a fantastic way of generating some valuable (potentially life saving) emergency heat. In ",
"cute baby lambs",
" shivering increased metabolism (and therefore heat production) by 15%. In an emergency situation shivering can become extremely vital to survival.",
"If I find better data I'll post it, I recall the amount of heat you can produce with shivering is quite tremendous. You'd be much better off with your shivering mechanism intact."
] |
[
"Way off. Goosebumps don't make you heavier. I think the world your looking for is \"volume\", and still no.",
"Goosebumps are a vestigial reflex from when we had hair covering our entire bodies. What produces goosebumps in humans forces all the hair to stand up in other animals, trapping air between the strands creating an insulating effect.",
"Additionally, you might notice you get goosebumps when your scared or nervous, this same reflex was evolved as a defense mechanism, to make the animal look larger. Imagine a dog protecting your house from a bear."
] |
[
"Phases and concentration gradients"
] |
[
false
] |
I know that a phase is a body with a specific composition distinct from its surroundings. But what about a tank of saltwater that is saturated at the bottom, with concentration falling linearly until it reaches zero at the top? Does that count as one phase? Not a phase at all?
|
[
"It's a solution. So long as the salt doesn't precipitate out, the intermolecular picture is a constant picture from saturated bottom to unsalted top. If there were precipitated moistened salt environment under the water, that layer would function as a separate phase, as the salt dominated behavior of the solution (I start with a beaker with 500g NaCl, add 3 mL of H20) is clearly different than the water dominated behavior (I start with 500 mL of H20, add 3 g NaCl). At least onc, somewhere in the middle of the concentration fight, the behavior of the solution should abruptly change. Those shifts are the phase boundaries. ",
"Think of it like this: for steel phases, we essentially go from an iron crystal, slowly increase the number of defects in the form of contaminants, mostly carbon, until a point is reached where adding more carbon changes the behavior of the lattice, by making the primary structure iron carbide, not iron. With enough excess carbon, the lattice will shift again, to a carbon lattice with defects from the iron. What's even more fun is when those states start to be in equilibrium with other phases: a combination state where some domains have melted, but other crystal grains are still stable as solids."
] |
[
"Great answer. What about with sugar instead of salt? A saturated sugar water solution at room temp contains a good deal more sugar than water, so is the solution sugar-dominated at that point?"
] |
[
"Well, with alloys, where two metals are mixed into a solution, you can have a phase in which the crystalline structure of either contributor can dominate any given crystal grain, with the other component(s) mixed in as defects. So, my guess is that this sort of phase dominates around the saturation point of water. There should come some point where the behavior as more sugar is added or less water used should suddenly change. I'm thinking of the point where sugar no longer dissolves at all. At that point, there has been a phase shift. As for the relative ratio of water to sugar at saturation, I can't tell you. I've not studied it much."
] |
[
"Why can't we make a balloon that never loses air or helium?"
] |
[
false
] |
Inspired by . Won't it be sad when it droops away into a meaningless pile of rubber? WON'T YOU SAVE THE DINOSAURS, ASKSCIENCE?!
|
[
"There's a process called permeation where the gas molecules or atoms actually move through the interatomic spaces of the enclosing material. This puts a limit on ultra-high vacuum systems, but is also relevant for balloons. "
] |
[
"Also helium gas diffuses through solids at a fast rate due to the molecule's small size and is used to detects leaks in industrial settings"
] |
[
"They use metric as well. You should be proud, Americans get to learn two ways of doing the same thing!"
] |
[
"Why does the colour of a laser change, when the laser is shining through olive oil?"
] |
[
false
] |
[deleted]
|
[
"What you are observing is fluorescence from the chlorophyll present in the oil."
] |
[
"That's awesome!"
] |
[
"Hah, i'm doing a social service project as part of my ochem lab where we teach secondary school kids about fluorescence. We're using red, green, violet lasers, a black light and run up the mill highlighters. You can try it for yourself, it's inexpensive (plus the violet laser is awesome) and it's awesome. One of our highlighters, i think it's the orange one, fluoresces almost identically to your olive oil under the green laser.",
"If you're lucky and you chill the olive oil/highlighter ink, you may see a change in the fluorescence's colour, which is called thermochromism. Nurdrage has an awesome ",
"video",
" on this."
] |
[
"Why is baking soda used so frequently as a cleaning agent?"
] |
[
false
] |
I know baking soda is sodium bicarbonate, and when mixed with water forms a basic solution. What I don't understand is why this solution would be good for, say, cleaning grease/oil off a stove. Can baking soda and water itself act as an emulsifier? Also, I don't know if this is related or not, but how does baking soda "deodorize"? Can dry baking soda, in its powder form, really react with any acidic odors? Is there enough moisture in the ambient atmosphere to ionize baking soda to form the hydroxide ion?
|
[
"Baking soda is also used as a cleaning agent because it is abrasive when made into a paste (when fully dissolved it is basic/alkaline so it dissolves grease).",
"As for use as a deodorizer, most foul odors are acidic or basic molecules, both of which baking soda can neutralize (and make less smelly). It can handle both acids and bases because it acts as a buffer."
] |
[
"Why or how?"
] |
[
"In a word, saponification."
] |
[
"Theoretical questions about the transfer of data between two points."
] |
[
false
] | null |
[
"Would it be possible to send and store data with light without that wire?",
"Kind of like a wireless fios? ",
"Sure, for example via laser. ",
"If that was possible could we put some kind of orb in space that could send light pulses like the sun throughout the solar system and act as a sort of a galactic internet?",
"I wouldn't phrase it quite like this, but yeah, we might do something like that someday. ",
". ",
"(Protip: Our galaxy is over a billion times bigger than our solar system - be careful not to get them mixed up.) "
] |
[
"It's most definitely possible, although you'd want a laser or possibly some other form of radiation, the idea of light based data transfer is used quite commonly, one example is an opto isolator, another would be a laser modem. These methods aren't too efficient for a galactic internet, so to combat that you'd want to try some other mode of data transportation, possibly through quantum entanglement which is supposedly 10,000 times faster than light (if achievable)."
] |
[
"You can't transmit information through quantum entanglement."
] |
[
"What is the purpose of these tendons connecting each finger to one another, like in this gif? [GIF Included]"
] |
[
false
] | null |
[
"These are the tendons of the extensor digitorum, the muscle that helps you extend your fingers back towards the top (dorusm) of your hand.",
"The connections between them are cleverly named as the \"intertendinous connections of the extensor digitorum.\"",
"They are part of the reason you cannot move one finger without the other fingers moving."
] |
[
"Ohh that's pretty interesting. Is there a specific purpose to those little connections between fingers? Thanks for the answer! I saw a similar gif a while ago and I've been curious about it. It always baffles me how complex the human body is."
] |
[
"Thanks for the replies, man!"
] |
[
"What would happen if one face of the Earth faced the sun year round, for ever?"
] |
[
false
] |
What if a planet like Earth (ok let us say plain old Earth), at its current distance from the sun, orbited the sun in a way that only one face of it ever only faced the sun (like the Moon orbits the Earth). Assuming the poles were at a right angle from the point of the earth that faced the sun at all times. What would happen to the atmosphere? Would anything happen to the dark side of the Earth?
|
[
"Here's a better answer: ",
"http://www.lifeslittlemysteries.com/2491-world-stopped-turning.html"
] |
[
"that would be bloody hot on day side, I could crunch the math if you want to, but there would be a lot of factor to think about"
] |
[
"you can ignore the more complicated stuff. i am just looking for a rough estimate. i have been considering this for a long time and am greatly interested. but if it would be too complicated or tiresome then never mind. "
] |
[
"How does a Kale, a Cabbage and a Brussels Sprout still belong to the same plant \"family\" while displaying such varied structures and growth patterns?"
] |
[
false
] |
How did they become so different? Did they all start from a common ancestor or did they evolve parallel to one another?
|
[
"Wooh! An answer I finally actually know. So all three of them are descended from the same common ancestor. Which is actually still very common today. They all come from the wild mustard plant. I’m not sure how long ago, but at some point after humans began agricultural practices we realized that if you place two plants with traits that you want near each other the offspring will display those traits even more. Rinse and repeat. So with Brussels sprouts, the wild mustard plant has tiny bulbs that run along the stem of the plant. Over many generations we selectively bred for having larger bulbs, until we arrived at the modern version of the Brussels sprout. The same is true for kale, where we just bred the plants that had larger leaf structures closer to the base of the plant. And cabbage was bred by selecting plants that had a closer structured bud. It’s the same thing as us breeding horses to be larger, or cows that produce more milk. Also, just because you breeding these plants for specific traits, that does not push the original genus out of existence. Does that make sense? I can provided some sources, this was just me writing up what I remember from biology."
] |
[
"They're not just in the same family (Brassicaceae, which also includes things like mustard and radishes), they're actually the same exact species, ",
".",
"One thing to keep in mind is that the vegetables you buy in the store are all different parts of the plant. Kale is the mature leaves, cabbage is an apical bud, and Brussels sprouts are axillary buds. If you look at the whole plants that these different vegetables come from, you'll see more similarities. For example, here's ",
"kale",
" and ",
"cabbage",
" and ",
"Brussels sprouts",
". As a bonus, here's ",
"broccoli",
", which is a cluster of flower buds from the same species and here's the ",
"wild plant",
" they're all derived from.",
"Obviously, there's still differences when looking at the whole plants. These differences are because of selective breeding by farmers taking advantage of pre-existing variation found even in the wild ancestors. This is similar to how we developed ",
"the variety of different dog breeds",
" we see today, for example.",
"So they started from a common ancestor ",
" they evolved (by artificial selection) in parallel. Those aren't really two different options. Any organisms that diverged from a common ancestor have evolved \"in parallel\" since that divergence to arrive at their current forms."
] |
[
"If they have a common ancestor, and they were created by selective breeding, does that mean they could still be bred together today? As someone stated in a different comment, they're exactly the same species. ",
"So could I plant some kale near some brussel sprouts and cabbage, and somehow eventually get a child plant? "
] |
[
"What is the purpose of Restriction Sites in DNA?"
] |
[
false
] |
All I can get from my textbook and Wikipedia is that the Restriction Enzymes are thought to have originally evolved as a defensive mechanism against viral invasions, but why are there Restriction Sites at all? Is it used in DNA replication? In repairing damaged sections?
|
[
"Restriction sites are just specific DNA sequences that are targeted by the enzymes. The sequences occur naturally in the DNA. You have to think of it the other way around: the enzymes evolved to target certain DNA sequences that are unique to a genome or genome location. For example, the sequence AGGATA may occur with more frequency in a viral genome and, so an organism that is infected by this virus would have a defensive advantage by developing enzymes to target and break the DNA containing this sequence."
] |
[
"I'd like to add that the bacterium protects its own genome from the restriction enzymes. Restriction sites in its own genome are often methylated (usually on C's, I think that's the one that is generally methylated but I'm not sure) which means that the enzyme will recognize and cleave restriction sites of viral origin (ie, kill the virus) but not sites of bacterial origin (so it won't just cut up its own genome willy-nilly). I don't know enough about restriction enzymes so I'm not sure what other modifications are made to the DNA to protect it, but I'm pretty sure this is one of the main ones."
] |
[
"Keep in mijd viruses do not have their own DNA replication machinery so they have to use that of a host. Therefore, the virus introduces its DNA into the cell and makes it code for virus proteins. Restriction enzymes are a form of defense against this."
] |
[
"Epilepsy: Effects of a seizure on consciousness/awareness"
] |
[
false
] | null |
[
"This article",
" does a decent job of summing up definitions of various seizure disorders.",
"Basically, the ",
" of a subclass of seizures (complex) includes an alteration of consciousness. Generalized complex seizures are defined by a loss of consciousness. Focal-onset partial seizures do not involve an alteration in consciousness and originate in a localized region of the brain, however, these seizures tend to \"generalize\" soon after and affect consciousness. But again, I think you'll find that there are a wide-range of seizure symptoms, some of which involve alterations/loss of consciousness and some that do not, and these semiologies are what differentiate the seizure disorder classes. ",
"I can't speak much on focal locations of seizure activity that are more prone to impairing consciousness, maybe someone else can expand on that."
] |
[
"Thanks. Do you know more about the transition from the lower to the higher states? Do patients get halucinations?"
] |
[
"I'm not sure what you mean by \"lower to higher states\", can you expand on that?",
"Yes, patients definitely can have hallucinations (auditory, visual, olfactory). In the context of a seizure, these are often termed \"auras\", and usually occur right before the onset of the seizure episode. Usually, these hallucinations are a signal to the person that they are about to have a full-blown seizure in a matter of seconds. The type and quality of the aura is directly related to the location of the seizure onset.",
"I work in a pediatric neuropsychology clinic and attend epilepsy clinic-rounds; some very interesting cases come through in which the child experiences auras. The type of aura usually gives us a hint of the location in the brain. For instance, one child had strange smells and a strange taste in his mouth (described as gasoline and burned hair)... another child reported intense feelings of fear before his seizure. Both of these things indicate a temporal lobe/amygdala origin.",
"I'd recommend you read Oliver Sacks' \"Hallucinations\". It is a very lay-friendly text that has entire chapters devoted to hallucinations experienced during seizure auras and migraine auras!"
] |
[
"Am I reading this article incorrectly, or does a reaction involving only 6 molecules give off the same amount energy as a 7-layer burrito?"
] |
[
false
] | null |
[
"Energy values for reactions are almost always quoted per mole. So one mole of H",
"S combines with four of FOOF to give that amount of energy. It's not suggesting that one molecular reaction event gives that much off."
] |
[
"H",
"S+4FOOF→SF",
"+2HF+4O",
" (+433kcal).\nHere, 314g of reactants result in 433kcal. This is a lower energy density than a 7-layer burrito, which has 283 grams and yields 510 kcal. The difference is in the activation energy and speed of the reaction.",
"edit: subscripts"
] |
[
"That is for every 602000000000000000000000 molecules."
] |
[
"i was reading an article that mentions GABA and how different isoforms mediate “fast” and “slow” hyperpolarization. what is meant by “fast” and “slow” in the context of hyperpolarization?"
] |
[
false
] | null |
[
"Could you link the paper? It is hard to know what you are referring to based on this question alone. I'm guessing you are talking about fast or slow afterhyperpolarizations, which are usually mediated by different types of calcium dependent potassium channels with faster or slower kinetics. I suppose you could also be talking about the activation of GABA-A versus GABA-B receptors. GABA-A receptors are ion channels that mediate fast chloride entry into the cell when GABA binds versus GABA-B receptors that are g-protein coupled receptors and act much more slowly."
] |
[
"https://pubmed.ncbi.nlm.nih.gov/16402094/",
"I also wanted to clarify; My P.I. referred to benzodiazepines as an agonist of GABA, but this paper mentions that they potentiate GABA by increasing channel frequency; this is confusing to me and i have to present an overview of it at our lab meeting on friday. Thanks."
] |
[
"I agree with the paper, I don't think I would technically call it an agonist. ",
"Read sections 6, 7, and 8 of this more recent review",
" for a better explanation."
] |
[
"Is mercuric chloride as dangerous as mercury?"
] |
[
false
] | null |
[
"Mercuric chloride - like mercury salts in general - is more toxic than metallic mercury. Metallic mercury tends to go through the body and come out the other end with limited effect, but soluble salts get absorbed and cause serious poisoning."
] |
[
"On a continuum Mercury salts are less dangerous than organic forms of mercury. Methyl Mercury is poisonous to a greater extent than Mercury salts. ",
"One measure of how dangerous a chemical is called LD 50. This is the amount of a substance required to kill 50% of some thing. Generally rats, mice, or guinea pigs are used to create this number which is adjusted by the weight of the animal.",
"Mercury (the metal) has a relatively high LD50. A higher LD 50 means that more of the stuff is required for lethal toxicity. A case of a dental worker injecting the stuff into their veins and surviving shows the relative toxicity. ",
"https://www.nejm.org/doi/full/10.1056/NEJM200006153422405",
"The Mercury compounds are more dangerous:",
"Mercury Chloride has an LD50 of 32 mg/kg. Methyl Mercury has an LD50 of ~29 mg/kg. \nDimethyl Mercury has an LD50 of 0.05 mg/kg. ",
"Dimethyl mercury is an incredibly scary compound where a drop on a gloved hand can be fatal. ",
"https://www.osha.gov/publications/hib19980309"
] |
[
"Mercuric chloride is toxic, so you should be careful when handling it. It's a solid at room temperature and I would recommend masking up whenever you work with any powdery or crystalline solid that can get in the air and into your lungs while working with it, regardless of its overall toxicity (also, the Wikipedia article on it says it has a tendency to sublime, so that's another point for a proper respiratory PPE). If you're doing this for school, I would hope your instructor makes the hazards and precautions clear and you shouldn't be afraid to ask questions or raise concerns to them."
] |
[
"What does it mean to \"be Bayesian\" in terms of a way of thinking?"
] |
[
false
] |
I'm familiar with and how it's used in problems, but I've heard people talking about having a Bayesian way of thinking in general, or statisticians subscribing to a Bayesian way of thinking. What exactly does this mean? Is there more to Bayesian reasoning than just solving probabilities?
|
[
"Frequentists, the usual sort of statistics, define probability as the long-run average of a lot of repetitions of an event. ",
"Bayesians define probability as the degree of belief; a subset of them argue that these beliefs are largely personal, and only asymptotically approach the same value with repeated observations.",
"There are two sorts of Bayesian applications. First is a whole class of Bayesian statistics, which explicitly incorporate your prior beliefs in something and tell you how to change your beliefs. As an example why this is useful, suppose you want to know if a coin is fair. You strongly believe that the probability of a heads is .5, so if you flip the coin 100 times and get 47 heads, you are likely to believe it is still very close to 0.5, rather than the frequenist estimate of 0.47.",
"There's a second kind of Bayesian thinking, however, which is probably what you're hearing about here. This is Bayes as a philosophy of science or model of reasoning. Bayes' theorem gives you a good model for how to change your beliefs given new evidence. Being Bayesian in this sense means looking for evidence which would radically change your viewpoint according to Bayes theorem, and valuing multiple lines of evidence appropriately."
] |
[
"To expand on this, frequentists are not limited to long run averages. ",
"To make inferences on an unknown population parameter, a sample is collected from the population and one of a number of estimation techniques are used. The most common one being maximum likelihood estimator, which is the value of the parameter space that maximizes the likelihood- this is not saying the most likely value of the parameter which is important in the Bayesian perspective.",
"It turns out with distributions such as Poisson, Binomial, Normal distribution that the location parameter maximum likelihood estimate is the mean. If I recall correctly, it's not the same for beta distribution and certainly the long run average is not for all of them. The typical strategy is to use the central limit theorem when applicable to say the mean is normally distributed and then the delta theorem to find a function of the mean that would lead to a minimum variance unbiased estimator.",
"The key thing about frequentists is that all estimation is based on the data itself. On the Bayesian perspective, you put a prior density on the unknown parameter space. Maybe your belief of the probability for a coin toss follows a beta density with specific coin parameters. Maybe you have no information about the unknown parameter and want to use an uninformative prior such as the uniform distribution.",
"Using Bayes theorem, it can be shown that the probability function of the parameter given the data is a combination of the likelihood of the data given the parameter (which is the part only frequentists use) and the prior density. The resulting probability function is often intractable unless using specific prior densities (Monte Carlo or other estimates can be used when not using these specific prior densities) but the key thing is that you get a resulting probability function for the unknown parameter(s) given the data.",
"From a Bayesian point of view, using the assumed prior, we can actually find the most likely value of the parameter and this is often chosen. You can actually find the probability of the parameter bring within an interval called credibility interval which frequentists often think they are doing when finding a confidence interval.",
"In terms of null hypothesis testing, we never say we have enough evidence for the null... just whether or not we have evidence for the alternative. In Bayesian approaches, can actually estimate the probability of the null hypothesis.",
"Just some rambling while I'm out at a bar on my mobile phone."
] |
[
"Thank you! The second kind hits the nail on the head because I've also heard it discussed in regards to building a model for automation or robotics, so that makes sense."
] |
[
"Why do the electric field lines at the end of two parallel plates curve?"
] |
[
false
] |
I believe it is called the end-effect? However I would like to know why this happens. Here is a picture of what I mean: Edit: Thank you all very much!
|
[
"If you're inbetween the plates at the centre, and the plates are much wider than their distance, they are well approximated by infinite parallel plates and so the field lines are straight.",
"If you instead zoom out and look at the whole thing from a distance, they look like an electric dipole, whose field lines look like ",
"this",
"These are both approximations to finite parallel plates that hold in two opposite limits. Inbetween, the field lines will interpolate. So at the middle they look mostly straight, as you move out they start bulgin out and very far away they get the shape of dipole field lines."
] |
[
"To add to this, and get an intuitive idea of why these tow limits have these shapes, you can consider a point charge. ",
"https://upload.wikimedia.org/wikipedia/commons/d/d9/Electric_field_of_a_point_charge.svg",
"Its pretty democratic and spreads out in all directions. Now imagine if you stack three of them together lets label them (abc). So charge b shoots out some field lines to the left, to the right, and straight ahead. So do a and c. \nThe field lines to the right from a kind of cancel out the field lines to the left from b. In the same way the field lines to the left from c cancel out the field lines to the right from b. ",
"After doing all these cancellations, we have some field point directly up, at the centre, but the bits of field from a and c that point AWAY from b have not been cancelled. So they kind of ``bend out\" ",
"Now consider: ",
"a b c ",
"d e f",
"You get the same pattern but flipped, and you can kind of connect the dots to get the picture you are asking about. "
] |
[
"Just finished up engineering physics at college.. the field lines are an average vector of the sum of the forces acting on a particle. When the proton reaches the top it wants to get as far away from it's positive charged plate (like charges repel) as possible. this initially sends the particle on the path of least resistance, or straight up (or down depending on where you're looking) from the charged plate. However shortly after the intensity of the pull from the negative plate (opposites attract) grows on average as it gets further from the positive plate and gets pulled closer to the negative plate. It still has enough initial velocity to break this intensity, but the plate bends the proton in the x-direction slightly, which subtracts from the initially strong y-direction forces. Eventually you see the arrow seemingly perpendicular with the plates again because the momentum picks up and the intensity of the pull from the negative plate pulls on the proton at that point the same amount the positive plate pushes it. ",
"Finally the proton travels further slightly and now the pull of the negative plate is stronger than the positive plate and this curves it back to the negative plate.",
"Reminder that field lines are not direct paths but averages of the cross product of the vectors of velocity and the magnetic field. "
] |
[
"If someone has a cervical or thoracic spinal cord injury with total loss of motor function below the lesion but some intact sensation, will they still have motor reflex arcs below the level of injury?"
] |
[
false
] |
[deleted]
|
[
"From what I recall from school, reflex arcs only occur in the spinal cord. There is no/minimal brain involvement, that's why it's a reflex and not a voluntary motion. If you have a cord transection at any level, you will have no reflexes below that point because there is no activation of the spinal cord. I'm sure someone will correct me if I'm wrong."
] |
[
"When you say total loss of motor function, I assume you mean total loss of ",
" motor function. Otherwise there would be no reflexes since they involve motor function.\nVoluntary motor function requires an intact signal path from the brain to the skeletal muscle. Somatic motor reflexes are not voluntary, and do not require that same intact signal path since the brain is not involved in those (not all at least; I don't recall if the brain is involved in some reflexes).\nSo if I've interpreted your question correctly, the answer is yes.\nOne caveat is that skeletal muscle will atrophy in the absence of nervous stimulation, so it could be that eventually they will have atrophied to the point that somatic reflexes no longer function."
] |
[
"IIRC, reflex arcs by definition do not project to the brain: there is sensory input from an organ, the afferent fibers carry it to the spinal cord, and from there the signal is immediately relayed back to the effector organ.",
"For example, the bulbocavernosus reflex (anal sphincter contraction after stimulation of the glans of the penis) will be intact if the spinal cord is transected above level S2. Because the afferent and efferent fibers are carried by the pudendal nerve, arising from S2 to S4, and there's no mediation from the brain."
] |
[
"I was staring out onto a lake, and the reflection of the moon on it, and there was just a big black line going horizontally through the reflection, like a shadow... what causes this?"
] |
[
false
] | null |
[
"Were there any trees behind you?"
] |
[
"Could it have been a log or something in the water? Did it move with the moon over the course of hours as the moon moved in the sky?"
] |
[
"I know dude, i was just kidding!"
] |
[
"There is a lot of talks recently about herd immunity. However, I read that smallpox just killed 400'000 people/year before the vaccine, even with strategies like inoculation. Why natural herd immunity didn' work? Why would the novel coronavirus be any different?"
] |
[
false
] | null |
[
"I think the gap in your understanding is that herd immunity doesn't stop the disease existing, it just represents the mathematical steady-state of the disease in the human population. Keeping that steady state requires continual new infections.",
"Estimates of smallpox r0 are 3.5-6, so we are looking at something like 80% of the population needing prior exposure to prevent epidemics.",
"When herd immunity keeps the disease moderately suppressed, you have a growing wave of children with limited immunity who are fresh fuel for the disease; they will facilitate an outbreak eventually.",
"I imagine 400k/yr fatalities represented the long-term-average, steady-state burn of smallpox in the population to keep it just sub-epidemic.",
"PS. smallpox had a fatality rate of 30% (and surviving it wasn't exactly fun), so unlike chickenpox people are not going to try and catch this deliberately..."
] |
[
"30% was the rate for the entire population. For the older population it was closer to 70%. In some populations it was over 90%. People compare the coronavirus pandemic to things like the black death and smallpox have no appreciation for how lethal acute illness was in the not so distant past."
] |
[
"Except that there is a widespread and highly effective vaccine for rabies."
] |
[
"Why do physical bodies attract with a force proportional to their mass?"
] |
[
false
] |
I always thought that nobody knows for sure why physical bodies attract with a force proportional to their mass. However, they know a vast amount about these observable proportions. Am I wrong?
|
[
"Because we live in a universe with gravity."
] |
[
"Each subatomic particle curves spacetime a set amount, so an object that consists of more of them would curve spacetime more."
] |
[
"right, as well as any additional corrections like binding energies being stored or subtracted from the mass. Fun thought: up and down quarks are 3-5 MeV. Protons are ~950 MeV, but only have 3 quarks. The rest is the binding energy of the proton. Same with the neutron. The electron is only about 0.5 MeV, so the bulk of the mass of everything is just the binding energy of the nucleons."
] |
[
"Reading or listening, which is more difficult?"
] |
[
false
] | null |
[
"I don't have too much to add to gwyner's and GretalRabbit's responses. The question is incredibly hard to answer in a straightforward way. There are a thousand factors that can affect the perceived difficulty of a task, and defining and measuring \"difficulty\" objectively is quite, well, difficult. ",
"Here are some things to consider: ",
"Spoken language is quite different from written language, so you'd have to specify whether you're asking whether the ",
" utterances are easier to read or to listen to, or whether ",
" spoken and written utterances differ in their level of difficulty. ",
"There is no good way to measure \"how much of the brain\" is being used. I'm no expert on this by any means, but my impression is that the fMRI doesn't give you much useful information about what kind of process is actually going on in the brain, or whether it's \"hard\" or \"easy\" processing. ",
"As GretalRabbit mentions, people have very strong preferences/inclinations when it comes to whether they deal better with sounds or with imagery (there's a huge body of literature on learning styles). ",
"As gwyner points out, reading gives you the chance to pause and consider what the text means up to a certain point, whereas while listening you have to understand utterances while new information is continuing to pour in.",
"Again, taking up a point gwyner made, there are people who can read, but can't listen: I can read Danish but I would have a hell of a time understanding a normal-paced conversation. There are others who can listen but can't read: basic illiteracy, or people who grow up speaking one language with their family, but learning to read and write a different language at school. So you can clearly acquire these skills independently from each other, meaning that an L2 learner who focuses more on one skill than the other will definitely find the skill he/she has focused on easier than the other skill. ",
"Now for some unbridled speculation: spoken language is more nuanced than written language. There is a lot of information encoded in supersegmental features like stress pattern, rhythym, tone, pauses, etc. None of this is available in written language (though punctuation tries to make up for this somewhat). Now, I don't actually know whether this should make listening harder or easier than reading. If you're reading, you might have to try to read between the lines and figure out things that would have been obvious in speech, like sarcasm. Maybe trying to figure that stuff out is more \"difficult\" than simply decoding that information from the supersegmental phonetics? ",
"It just occured to me that it is surely also relevant whether we're talking about your native language or a language you're trying to learn. A lot of processes that are quite automatic for your L1 are super difficult for L2, depending on your level. ",
"I know I didn't really answer your question. I'm sure a hardcore applied linguist would have more to say on the issue, but I'm not sure we have one of those around here. "
] |
[
"I'm not sure of any scientific details/reasons, but from experience different people find listening easier, while others find reading easier. This is particularly relevent to learning styles- I learn better from reading and writing, whilst my sister loves to listen and talk about things to learn."
] |
[
"I'm not a linguist but I am a polyglot (IANALBIAMAP?) Most of the time you will find listening to be more difficult to learn, unless you've grown up listening to a language all your life and just need to become literate. ",
"As reading will go as slow as you want it to and you can use a dictionary to augment your own vocabulary, it tends to be easier to pick up. Listening requires an enormous amount of practice, hearing things that you don't understand and maintaining concentration anyways. (TV is incidentally a good trick to keep focused)"
] |
[
"Why do boomerangs come back when you throw them ?"
] |
[
false
] |
[deleted]
|
[
"when it is spinning the blades on one side are spinning into the wind (not really wind, but the oncoming airstream) and thus creating more lift, compared to the blades on the other side which are going with the wind. More lift on one side of the boomerang causes the entire object to tilt and turn, thus the boomerang flies in a big circle coming back to the thrower. It does not travel in a straight line and suddenly perform a 180* and come back, as observed in Zelda."
] |
[
"do you read ",
"this",
" first?"
] |
[
"I did, but there seems to be no explanation both detailed and not too hard to understand."
] |
[
"How do mixed drinks retain an even distribution, even after being undisturbed for prolonged periods of time?"
] |
[
false
] | null |
[
"It becomes a solution , of miscible substances. Water, alcohol, sugar, are all soluble.\n",
"http://en.wikipedia.org/wiki/Solution"
] |
[
"Read the article about solutions. That explains it."
] |
[
"Read the article about solutions. That explains it."
] |
[
"How would a 'sonic boom' affect a human in free-fall?"
] |
[
false
] |
A man is going to attempt to break the speed of sound by free-falling from very great height. If he breaks the speed of sound will there be a "sonic boom", and how will it affect him?
|
[
"I actually had this discussion with someone earlier today. Their explanation (which may turn out to be wrong, none of us are experts) was that this fellow only stands a chance at breaking the sound barrier due to the altitude he is jumping from and the fact that the air is considerably thinner that far up. As he moves closer to the Earth, the air would become less and less thin and exert more of an opposing force against his fall, thus slowing him down."
] |
[
"A sonic boom is simply the sound an observer hears from the supersonic N-wave that is generated from an object traveling at supersonic speed. Felix Baumgartner will break the speed of sound and thus he will generate supersonic shock-waves, but since he is breaking the speed of sound so high up and in such thin air, those waves might not be heard by observers on the ground.",
"As for the effects on his body, it's hard to tell. At sea level, NASA did a study that showed that traveling at supersonic speeds will literally tear a human body to shreds. On the other hand, read about the story of SR-71 pilot Bill Weaver who survived the break-up of his airplane at 78000 feet and Mach 3.18! ",
"http://learningfromdogs.com/2010/04/18/sr-71-blackbird-breakup/",
" The low-pressure air at high altitudes means far less stress is exerted on the body. I'm pretty sure Baumgartner is going to be fine."
] |
[
"I think his question was about slowing down from 700 mph not the effect of going said speed. He will be slowed down with multiple/ separate chutes. He will pop a smaller chute early to slow him down enough to pop a larger/main parachute that will allow him to land"
] |
[
"Neutron-Neutron strong nuclear force?"
] |
[
false
] |
If there is no electrostatic repulsion between neutrons, why do we not find large groups of neutrons in a stable configuration?
|
[
"Ultimately because protons are less massive than neutrons, so if a many-neutron system can reduce its mass through beta decay, it will. Apparently a ",
"two neutron state",
" has been observed, that decays in 10",
" seconds.",
"However, in neutron stars the massive gravitational potential overwhelms the internal stability, and these can be stable."
] |
[
"To clarify:",
"If the dineutron lifetime is 10",
" sec, it is not due to the decay of a neutron which has a 15 minute lifetime. Lifetimes this short are due to the strong interactions, indicating that the dineutron is a metastable state (slightly unbound)."
] |
[
"Amazing. Thanks for the informative (and fast) reply."
] |
[
"Is global warming accelerated by roads, agriculture and buildings?"
] |
[
false
] |
Roads are black and reflect heat, trees are gone replaced with a field, buildings with black tops, etc... What used to be large expanses of trees are now large farming fields, roads and buildings. Can't this be the source of global warming? Or to what extent is it contributing to it? Thanks for your answers...
|
[
"Yes and no. Recent studies on Land use affecting climate change have proposed that most (if not all) of the observed climatological variation can be explained by land use changes over time (instead of CO2). It's not a widely accepted view in the scientific community though. In any case, Land use changes are more likely to affect the local climate than the climate half way around the world, so it's likely that most areas are seeing a combination of climatological changes induced by land use change ",
" GHG emissions."
] |
[
"Actually, the color of roads in particular is one thing we can change to help with global warming",
".",
"So it is not a source for global warming, but it isn't helping."
] |
[
"No, because developed area on the Earth is extremely small compared to the amount of un-developed land. And then after that you have to consider the amount of the earth's surface that is water."
] |
[
"Making parabolic mirror setup for solar heating: what is the science behind mirrors and reflection?"
] |
[
false
] |
I want a series of mirrors to reflect light onto a single point (or multiple points). I will eventually have them computer controlled. . What mirrors should be used for reflecting light onto a single point? Convex? Concave? What is focal length and how will it be important? How can I determine the maximum temperature a mirror can produce given a certain (focal length?), size/diameter, and angle to the sun? This will be a project made for fun as I'm new to building things and new to electronics. Only experience I have is a little woodworking but I'm also pretty good at computer programming.
|
[
"You need a concave ",
"parabola",
". Satellite dishes are already roughly this shape. A hanging chain or rope will approximate the right curve, but it's actually ",
"catenary curve",
".",
"The temperature depends on too many things to be reliably calculable. What's easiest to calculate is the multiplier value, i.e. \"The focus of the dish receives the equivalent light of 1000 suns.\" if the area of the focus is 1/1000 the area of the dish."
] |
[
"For an ideal mirror, the focal length identifies the position where all the light converges into a point. So for an ideal mirror it should be 0 diameter.",
"For a non-ideal case, I think it depends entirely on how well and how accurately you can manufacture the object. I don't know of any way to calculate the real-world measurement without actually measuring it directly after building the mirror"
] |
[
"If you get a satellite dish, you can use lots of small flat mirrors.",
"See ",
"http://www.cockeyed.com/incredible/solardish/dish01.shtml",
"and",
"http://www.dailymail.co.uk/sciencetech/article-1351935/Eric-Jacqmain-invented-Death-ray-dish-intensity-5-000-suns.html"
] |
[
"How do random number generators work?"
] |
[
false
] |
[deleted]
|
[
"Most computers use a function of the current time, a seed and then a modulus to generate the desired result. A computer cannot by itself generate truly random values.",
"Cryptography software often prompts the user to move the mouse or push the keyboard randomly to generate more randomness into the function. For common use computers do generate a pretty uniform spread of results; so unless you're creating hard-to-crack cryptography or some other really demanding thing (particle physics?) excel's random function should be enough.",
"Wikipedia has a fairly well-written article on the subject here ",
"http://en.wikipedia.org/wiki/Random_number_generation"
] |
[
"I am in a cryptography class so I hope i can answer this one!!",
"Truly random number generators exist in two forms: hardware number generators and software number generators. Intel's hardware random number generator observes temperature values on different transistors. Software random number generators might use times between key strokes, disk access times, mouse movement etc... ",
"Now, it takes awhile to generate enough entropy to create a truly random seed. So, most systems opt for pseudorandom number generators. Pseudorandom number generators work by using a truly random seed to create a very long pseudo random sequence (on order gigabytes). This random seed can be created by either a hardware or software generators. ",
"A good measure of a pseudorandom generator is how hard it is to distinguish a pseudorandom generator from a truly random generator. A secure pseudorandom generator takes time greater than 2",
" to distinguish it's outputs from truly random outputs. That means no computer in the foreseeable future will ever be able to distinguish a pseudorandom generator from a random generator. SALSA20 is a great example of a pseudorandom generator.",
"How do pseudorandom generators work? Tons of bit operations and such. A good pseudorandom generator is made by a team of people and validated by experts after years and years of examination. It's a tough thing to master.",
"Now, for some applications, what qualifies as \"sufficiently random\" can be relaxed. Math.random() in Java is random enough for most programming needs. However for cryptological needs, to be considered sufficiently random, no polynomial time algorithm can distinguish the algorithm from a truly random algorithm in time less than 2",
" This is a very stringent requirement.",
"Many times people mistakenly use algorithms that are sufficiently random for simulations/random code for cryptography. Mega.com used (may still use i haven't checked) Math.random() to generate RSA keys. Although Math.random() appears random to you, it is highly predictable to the NSA. booooo "
] |
[
"Usually computers use something called pseudo random number generators. The word pseudo is often omitted too but it signifies the fact that the numbers aren't in the strictest sense random. However, for many practical purposes they'll do just fine. There are numerous different methods of doing this. Some produce more random numbers than others and may be more suitable for things like statistical analysis or cryptography. But for basic use the algorithm can be very simple. And then there are of course those that you could call truly random that either read some random physical quantity (like very accurate temperature reading of something inside the processor), or the accurate timing of keystrokes and mouse movement, or network traffic or whatever and then do something with that information.",
"But let's focus on pseudo random number algorithms, one such algorithm is the ",
"linear congruential generator",
", which sounds much fancier than it is. It is really very simple, but it's still sometimes the standard random number generator. And despite its simplicity, and known weaknesses, it's perfectly good for a lot of uses, like providing randomness in computer games.",
"So the method requires us to always remember what the previous generated number was, it'll be used to generate the next one. But of course there is no previous number for the first number we generate, instead we just pick some number and pretend it was the previous one. This number is called the seed, and a common way to pick it is to use the time since January 1st 1970 or some other constantly changing number you have handy. Just changing this number by one will cause a completely different sequence of random numbers to be generated.",
"So let's call the previous number (or the seed when generating the first one) P. Then our next random number, let's call it R, is",
"R = a * P + c (mod m).",
"So we have a couple more letters here, a, c and m. These are all constants and do not change ever for one particular generator. But you can build different generators by choosing different values for them. There are some requirements they should satisfy for the method to work well (see the Wikipedia page if you're interested). One particular compiler uses values a=22695477, c=1 and m=2",
" . So our method looks like this now,",
"R = 22695477*P+1 ( mod 2",
" ).",
"So we multiply P, the previous number, by some large number and then add one. And the last part with mod means dividing by 2",
" and taking the remainder. Taking the remainder after dividing by 2",
" for a computer is a bit like us dividing by 1,000,000 and taking the remainder. Simply take the first six numbers (from right) and ignore the rest, so you don't actually need to do any division at all. Computer will do the same thing in binary for the first 32 bits. And that's it, that's the random number generator, one multiplication, add one, and cut off the carry bits after first 32 bits.",
"We can try the generator with smaller numbers to get a feel for how it works. For example, a=9, c=5, m=16 and using the seed 1 gives the sequence 1, 14, 3, 0, 5, 2, 7, 4, 9, 6, 11, 8, 13, 10, 15, 12, 1, ... And it repeats from start. Because next number only depends on the last number generated, it should be easy to see that the sequence will repeat when we encounter the seed number 1 again. Because I chose the a, c and m in a specific way, we got every number between 0 and 15. All in all, at a first glance it looks fairly random.",
"But looking closer we can see some clear weaknesses in the numbers generated. Every number between 0 and 15 is there exactly once. Of course that's not very random at all. Also you can see that it's alternating between even and odd numbers. And if we divide by 4 and take the remainder then you get 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0. If you do the same by dividing by 8 you get 1, 6, 3, 0, 5, 2, 7, 4, 1, 6, 3, 0, 5, 2, 7, 4, 1. There the sequence is longer and repeats only twice.",
"It's said that the high order bits have more randomness than the low order bits. What that means is that if you write the numbers in binary, the bits at the right are very predictable while the bits at the left are less so. So with this particular algorithm, you should avoid using the low order bits. So if you need the computer to make coin tosses, and only need a random number that's either 0 or 1, then you absolutely must not use the lowest bit, which is same as take modulo 2 or checking if the number is even or odd, which unfortunately is exactly what a beginner programmer might first think of if they don't know better. That will result in every other coin toss ending up heads and every other tails, which is pretty much as far from random as you can get. Instead you need to see if the generated number is less than the middle point or greater than that. That uses the high order bits for randomness and results in a pretty random sequence. So even though the algorithm has clear weaknesses, if you know how to use it, it's perfectly fine for a lot of different things.",
"But there are also much better pseudo random number generators where the sequences or regularities are much harder to spot. I just chose to demonstrate with this because it's pretty easy to understand and the weaknesses are quite obvious if you know what to look for. And despite all this, it's still very commonly used so it's not a toy example."
] |
[
"[Biology/Dendrology/Plant Taxonomy] Do trees need the seasons to thrive?"
] |
[
false
] |
Do trees need the seasons to ? For example, could they be kept in-doors, climate controlled, with optimal conditions year-round, and be expected to have unimpeded growth (no tree rings)? Or do they need the lower sunlight, colder temperatures, dryer soil, etc to "hibernate" or "harden" themselves? Will they still hibernate regardless of the weather? If said tree were kept at optimal conditions and it doesn't go into hibernation regardless, and it were fruit-producing, would it produce fruit year-round as well, or just annually?
|
[
"Fruit trees require \"chill time\" --- a certain number of hours where the tree above freezing but below about 10°C --- or they won't set fruit. The amount of time required varies with the species and cultivar. It's a big part of why you can only grow certain fruits in certain climates. If they don't get sufficiently cold in winter, they don't flower in the spring and no flowers means no fruit the next fall.",
"The mechanics of ",
" they need chill time I'll have to leave to someone else - I only know it from the practical side, choosing what types of fruit trees are suitable for planting in my yard."
] |
[
"Depends on the species.",
"Tropical plants have adapted/evolved to not really need it, same with many gymnosperms and their anti-freeze sap. The basis is that there is lower light in the winter. Also the higher risk of freezing causing air bubbles which is VERY bad for the tubelike cells in a tree. Block enough of them with an air bubble and the tree dies.",
"Back to the original question though, trees (specifically angiosperms) need a dormancy which they are accustomed to. Trees \"count\" days of light and go dormant after that. If you take say a sugar maple from Canada and plant it in the Amazon with a box around it to prevent all other factors (e.g. disease, soil type, humidity etc) the tree will \"freak out\" and may go dormant but not know when to break dormancy and die, or freak out that it missed dormancy and \"think\" it's dying. I'm not super familiar with the mechanics, but I have lost a lot of trees by keeping them indoors for the winter (before I studied botany in college). The threshold really depends on the species and clade (gymnosperm/angiospem). But keeping a tree that has acclimated/evolved to have a dormancy period inside will almost always result in tree death. Also the closer you can get to the \"normal\" dormancy period, usually, the better the tree will perform.",
"Also along the lines of being indoors, climate controlled buildings often have very low humidity (and higher air pollution levels due to VOCs) compared to natural environments. It's why harsh environment plants (like cacti, succulents etc) do so well and are often sold as houseplants."
] |
[
"Sorry for the late reply, but thank you for sharing this.",
"So the hibernation of trees is directly tied to their evolution... Meaning that, similar to the way that some fruiting trees are selected for their more desirable fruit, we could cultivate some non-native trees to grow in colder/hotter environments with less/more sun?"
] |
[
"Is there really a risk of data theft via RFID?"
] |
[
false
] |
A family member recently told me they have bought foil-lined wallets for their passports and credit cards to prevent against data theft via RFID scanning. I initially wrote this off as crazy paranoia. However, there's actually a fair amount of information on the subject, but I don't know if that's the whole picture or craziness feeding craziness. I'm interested in knowing whether is this is actually a real potential threat, however minor, or essentially a scam for people to peddle useless 'protectors' on the uninformed public. So, I have three questions: Is data theft via RFID theoretically possible? If so, is it something that could actually be employed by criminals, or is it so technically impractical that it's a non-issue? Is there any evidence it has ever been used by criminals?
|
[
"Another option on the personal level is to simply destroy the RFID chip (hit it with a hammer, or stick your passport in the microwave for a few seconds). Your passport will still function as a passport even without the chip."
] |
[
"Bear in mind that in the US, ",
"\"whoever falsely makes, forges, counterfeits, ",
" any passport or instrument purporting to be a passport\" can be sentenced to up to 10 years in prison.",
" Although they'd have a hard time proving the damage was intentional."
] |
[
"Chip readers don't use the security numbers on the back."
] |
[
"How is Li-Fi faster than Wi-Fi if radio waves and light travel at the same speed?"
] |
[
false
] | null |
[
"The light waves don't travel faster than radio waves. Light is much higher in frequency. Therefore higher bandwidth modulation can be used therefore higher data rates. Also you don't have to worry about too much interference frog neighbour's systems (inside your house or apartment) since the light waves would be confined to your house. "
] |
[
"You are confusing data rate and delay. The signals will arrive at the same time, but the amount of data they carry can be different.",
"In general Li-Fi has a much wider bandwidth it can use due to how directional it is. Bandwidth directly determines the maximum signalling rate before ",
"ISI",
" occurs. Think of 0 and 1, the quicker we must switch between the two, the higher the frequency. The higher the frequency the larger the bandwidth we would need.",
"So Li-Fi with a generally higher bandwidth (and less noise), can switch 0 and 1s faster than Wi-Fi. Therefore the signals arrive at the same time, but Li-Fi has more 0s and 1s, then Wi-Fi, resulting in a faster network."
] |
[
"The capacity to carry data is greater with higher frequencies, all else being equal. Light has a higher frequency than radio waves, so light has a greater capacity for data in a given time frame.",
"\nThink of a light switch you can only turn on and back off once every second. How long would it take you to send '",
"Hello World!",
"' in Morse code? It would take about a minute or longer! Now consider sending the same message where you could turn the switch on and back off a thousand times a second- how long would it take to send the message? Much less than a second! Most WiFi is at 2.4GHz (2.4 ",
" on-off cycles in a second), but even the lowest frequency light is 430THz (430 ",
" on-off cycles in a second), which is well over a thousand times more cycles in a second. This difference in frequency is what allows more information to be sent in a certain amount of time by light."
] |
[
"How does a cell \"know\" what type of cell it's supposed to be, if DNA contains all the genetic information for the entire organism? Can cells (other than stem cells) be tricked into becoming a different type somehow?"
] |
[
false
] |
For instance, could I somehow induce a liver cell to become a kidney cell?
|
[
"During differentiation, asymmetric cell division causes certain gene products (RNA and peptides) to be localized at one pole of a dividing cell, so that only one cell \"inherits\" them. These in turn influence the gene expression profile of the cell they're in. So, for example, if one cell inherits a gene product complement for stem cell maintenance, that cell will stay a stem cell. If the other cell inherits products that drive lineage commitment, that cell will differentiate. ",
"There are also classes of genes responsible for controlling gene expression (whether a gene is available to the machinery that synthesizes RNA) at the genomic level. These genes code for RNA and proteins that wrap DNA into a tight structure called heterochromatin, which prevents any genes in that region from being expressed. In any given cell, this process is more or less permanent in regions containing genes that the cell should not express. The proteins responsible for maintaining heterochromatin are recruited to the appropriate sites by other proteins specific to the cell in question. Additionally, regions of DNA can be \"marked\" for this packaging through modification of the phosphodiester backbone by enzymes called methylases, which are also recruited by tissue specific proteins and RNA. ",
"So for a cell to be \"tricked\" into becoming a different cell, it has to be reprogrammed. These processes have to be reversed and reassigned. And yes, it is possible."
] |
[
"This was actually the subject of some recent Nobel-prize winning work. See here: ",
"http://en.wikipedia.org/wiki/Induced_pluripotent_stem_cell",
"Basically, this guy named Yamanaka discovered that if you express these four genes (the so-called \"Yamanaka factors\"), Oct4 (Pou5f1), Sox2, cMyc, and Klf4, in a cell, you can, with some coaxing, convince them to turn into pluripotent stem cells, a cell type that can be turned into any other cell type."
] |
[
"There's a couple things you want to look at. Of course you want to look at the wiki page on cell differentiation. But you should also check out Boolean networks, which are supposed to be a model of gene regulatory networks. The attractors in the network activation space can be thought of as specific cell types.",
"https://en.wikipedia.org/wiki/Cellular_differentiation",
"https://en.wikipedia.org/wiki/Boolean_network#Classical_model"
] |
[
"Can our organs feel 'pain'?"
] |
[
false
] |
Do we have pain receptors on our organs or rather just our skin?
|
[
"For the lungs: the only pain receptors are on the outside. This means that if you get stabbed - you feel pain 1st as the skin is cut, again when the pleura that lines the ribs on the inside is cut, and again when the lung itself is punctured. However, if we snake a tube through the mouth or nose and down the throat - you will cough and gag when it touches the vocal cord or trachea (numbing with lidocaine reduces this) - but it won't hurt if we do biopsies of the lungs themselves. Most organs work similarly - meaning pain receptors on the outside edge and that's it. "
] |
[
"Not all our major organs are sensitive to pain, however some are, but we do have pain receptors in other places than just the skin.It can be very difficult to find painkillers for Visceral pain.",
"Unrelated but the skin is an organ."
] |
[
"Sorry - don't know enough to answer on the types of pain receptors. But from a what you feel standpoint - when we biopsy the lungs or drain fluid from around the lung - we have to make sure and get numbing medication (lidocaine) on or in each layer as we slowly advance the needle. I only do the \"drain the fluid procedure\" myself. So i numb the skin. Then advance the needle, injecting smaller amounts of numbing medication as I go through fat and a small amount of muscle. Most people don't react to that - minimal pain - but then we hit the pleura (inner rib lining) and apparently it's really painful and sharp. Unfortunately the numbing medication hurts before it numbs too. And even worse is if we have to slice through it (the lining) and put a larger drainage tube in - very painful"
] |
[
"If its true that prehistoric animals and insects were able to grow to such larger sizes because of larger oxygen levels in our atmosphere..."
] |
[
false
] |
then if we hatched some eggs in a oxygen controlled chamber would be be able to grow giant spiders, rats, dogs, etc...? Or what other conditions would have to be in place to do such a thing? And would that also increase the size of humans?
|
[
"This exact experiment was carried out last year!",
"They were able to grow dragonflies 15% larger than normal (although that is nowhere near the 70 cm wingspan giant dragonflies of the past had). The current thinking is that insects are particularly sensitive to atmospheric oxygen levels because of their differing physiology (no closed circulatory system, like mammals have). So: giant spiders, yes. Rats, dogs, probably not."
] |
[
"AFAIK this enlargement due to an oxygen-rich atmsophere has only been proposed for insects."
] |
[
"Unfortunately, I don't have a good answer except to suggest that ",
"large size had something to do with thermoregulation",
": larger bodies retain heat better. I should also point out that the populations were not dominated by large creatures; there were many small (and even tiny) dinosaurs."
] |
[
"Does the act of your nose becoming blocked by congestion have a biological benefit, or is it simply a side-effect of the congestion itself?"
] |
[
false
] |
To expand and clarify, is there some reason why causing one or both nostrils to become completely obstructed, thus preventing them from intaking air, have any benefit to the fighting of infection? Or is the stuffiness merely an uncomfortable side-effect to being congested and infected.
|
[
"When you have a cold your nose doesn't get blocked by mucus and snot, it's caused by the blood vessels in your nose becoming inflamed as a response to to viral infection. Your body expands your blood vessels to enable transport of stuff needed to fight the infection to happen more efficiently. "
] |
[
"A little bit of both. ",
"Mucus is typically a thin, clearish fluid moved by cilia in the nose towards the back of your throat. During cold weather, the cilia doesn't work as well leading to congestion or runny noses. Mucus also contains antimicrobial properties, so producing more when you sick will help trap more bacteria and other pathogens. That's also why your snot changes color when you're sick--it's from the trapped bacteria. "
] |
[
"You're thinking about it the wrong way round, usually the snot in your nose doesn't cause it to get blocked because your sinuses are nice and wide, it's only when you have the inflammation that the snot can complete the blockage. "
] |
[
"Why do vacant orbitals become higher in energy if you add electrons to them?"
] |
[
false
] |
I know that when applying the Aufbau principle, you fill up the 4s orbital before the 3d, but when forming ions, electrons are removed from the 4s orbital first, meaning somewhere along the line, the 4s orbital has increased in energy, to a point where it is higher than the 3d orbital. Why does this happen?
|
[
"The reason this occurs is due to shielding, and the factors that influence how different orbitals shield each other. ",
", meaning that the 3s and 3p shells have been filled and you have one electron that you can either place into either the 4s or 3d, the 4s will always be lower in energy. The reason is that the 4s orbital has 4 radial loops, the innermost of which are capable of cutting through the shielding effects of the first 3 shells. ",
"The 3d orbital, despite having a closer ",
" distance to the nucleus than the 4s orbital, has only one radial loop, and cannot effectively cut through the shielding of the inner shells. ",
"Now, here's where it gets weird. If you start adding electrons to the system (effectively, increasing the atomic number), you will begin populating the 3d and 4s orbitals. Remember when I said that the 3d orbitals have a shorter average distance to the nucleus? That means that the 3d electrons shield the 4s electrons, causing them to feel less nuclear charge, thus driving up their energy. The 4s electrons do not effectively shield the 3d electrons because those inner loops are very small (not much 4s electron density is close to the nucleus).",
"The overall effect is that when removing electrons from atoms that possess 4s and 3d electrons, the 4s electrons will be removed first (usually....)."
] |
[
"Loving the \"usually...\", damn electrons. But thank you! This is what I was looking for!"
] |
[
"I think you confused a couple of things here.",
"In the title you asked, what happens when an electron is added, however in your details you asked about positive ions (where one or more electrons have been removed).",
"So let me attempt to clarify some of this: The energy of an atom can be increased if they absorb photons or a free electrons collides inelastically for example. ",
"If the energy is sufficient, an electron will be elevated to a higher state (or a higher orbital) and - if there is even more energy - the electron might escape the atom. The energy necessary to make an electron escape is called ionization energy."
] |
[
"Are we still immune to eradicated diseases like smallpox or would another pandemic start if the disease re-emerges?"
] |
[
false
] |
[deleted]
|
[
"While some of us have been around long enough to have been vaccinated against smallpox as children, ",
"routine vaccination was discontinued in 1971",
". Some groups of military personnel are still currently vaccinated against smallpox, but by no means all. Unfortunately even for those who have been vaccinated however, ",
"\"Smallpox vaccination provides high level immunity for 3 to 5 years and decreasing immunity thereafter.\"",
"So, even if we assume a population that has been 100% vaccinated, some may remain immune to the disease, but the waning immunity of others means that as time continues, more and more people will be susceptible to the disease. This applies to many diseases, not just smallpox. Immunity to any given disease does not always have a life-long duration. Add to this the fact that the vaccine does not always \"take\". From the ",
"Vaccinia (Smallpox) Vaccine Recommendations of the Immunization Practices Advisory Committee (ACIP)",
":",
"After percutaneous administration of a standard dose of vaccinia vaccine, >95% of primary vaccinees (i.e., persons receiving their first dose of vaccine) will develop neutralizing or hemagglutination inhibition antibody at a titer of greater than or equal to 1:10 (9). Neutralizing antibody titers of greater than or equal to 1:10 are found among 75% of persons for 10 years after receiving second doses and up to 30 years after receiving three doses of vaccine (10,11). The level of antibody that protects against smallpox (variola)infection is not known, but epidemiologic studies suggest that protection against smallpox persists a minimum of 5 years after revaccination (12). Also, the level of antibody required for protection against vaccinia infection is not known. However, when the response to revaccination is used as an indication of immunity, <10% of persons with neutralizing titers of greater than or equal to 1:10 exhibit a primary-type response at revaccination, compared with>30% of persons with titers <1:10 (13). ",
"So obviously not all who are vaccinated become immune to the disease, either due to genetic or acquired immunodeficiencies, or waning of immunity over time. To answer your question then, it is quite likely that if a disease such as smallpox reemerged, it could have epidemic or possibly pandemic potential. Luckily there isn't much risk of smallpox coming back any time soon. ",
"Officially, the only two remaining stocks are kept at the CDC in Atlanta, Georgia, USA, and at the State Research Center of Virology and Biotechnology (VECTOR) in Novosibirsk, Russia",
". Obviously, this doesn't discount the possibility that there may be some \"unofficial\" stocks of the virus floating around somewhere in the world. If you don't think that's possible, ",
"just ask the FDA",
"!",
"On a side note, this also raises the question of whether we should maintain a significant stock of the vaccine after a disease is eradicated. In the case of smallpox, this has been necessitated by the prospect of the virus being modified for use in biological warfare.The ease with which we can genetically manipulate variola virus (and poxviruses in general), along with its extremely contagious nature (it has an ",
"R-naught value of 5-7, compared with influenza's 2-3",
") make it an ideal candidate for a bioweapon.",
"Ken Alibek",
", the former Deputy Director of the Soviet ",
"Biopreparat",
" emigrated to the US, and has provided the US government with many of the details of what was being developed by the Soviets. Reportedly, the addition of the gene encoding human ",
"myelin",
" to smallpox was meant to induce multiple sclerosis in those who survived the initial smallpox infection. In 2001 in the US, a group of researchers discovered that the addition of the mouse gene for ",
"IL-4",
" to ectromelia virus (also a poxvirus, and the cause of mouse pox) ",
"skewed the immune response away from an antiviral Th1 response so much that the virus killed even mice that had been vaccinated against it",
". Theoretically, the same could be done with variola virus.",
"Obviously not all viruses are ideal for use as a biological agent, but even in the case of the eradication of a disease, laboratory stocks are likely to be retained for future research, or for future use as a vaccine platform or therapeutic agent. So while it may be expensive to maintain a stock of vaccine against eradicated diseases, it is also necessary in the case of accidental escape to be prepared."
] |
[
"Smallpox is one of the oldest viruses known to man. ",
"Records of smallpox go back at least 3,500 years, but it's believe to have emerged around 10,000 years ago",
". By the time of its eradication, it was a human-specific pathogen with no other animal reservoirs, which is in fact what made its eradication possible in the first place. Essentially it is incredibly well-adapted to infect humans, and yet its mortality rate still hovered around 30%, which is exceptionally high for a human-adapted virus. Generally mortality rates like that are more common among zoonotic diseases (transmitted from animals) that are by definition not well adapted to humans.",
"Honestly it's hard to say how long it would take for us to evolve such that smallpox is no longer infectious to us. I'd point you to another ",
"comment",
" in a separate thread which addresses how a virus \"knows\" to infect a specific type of cell or organism (known as host-range tropism). Essentially there are numerous parts of the virus life cycle where productive infection can be restricted by a host cell. Unfortunately we don't know exactly what kind of mutations would be required to prevent variola virus from infecting us, but it would likely take a very, very long time."
] |
[
"Follow up question: Approximately how long (from a lower range of say 10% chance to an upper range of say 90% chance (e.g. 10% chance it would take 200 years, 90% chance it would take 1800 years)) would it take humans, given current environmental conditions, to evolve to the point that the current smallpox stocks could not infect us? Or is that not physically possible?"
] |
[
"Are there any toothpastes that are not abrasive? Are mouthwashes abrasive?"
] |
[
false
] |
I base this question on the 2 previous threads that really were left inconclusive.
|
[
"abrasive implies there is some sort of grit mixed in to aid in the mechanical removal of plaque. so mouthwash is definitely not abrasive. there are a lot of toothpastes that are gel, and those do not contain grit, instead they rely entirely on the brush for mechanical removal of plaque, though they are not technically paste. "
] |
[
"Would you by any chance know the name of a gel brand?"
] |
[
"Close up works quite well. ",
"Although, i prefer a my toothpaste a little abrasive or corrosive. I mix hydrogen peroxide and baking powder on my toothbrush once every three weeks to get the stain out while using pronamel on a daily basis."
] |
[
"Would it be possible to power a power plant by using a giant magnifying glass to boil the water?"
] |
[
false
] |
Sure it would be extremely unreliable, but wouldn't it work? How big of a magnifying glass would you need? I feel like it would totally would be worth it to get essentially free energy. Edit: Thanks to Chivalric for the appropriate article.
|
[
"Those exist, in a form. ",
"Here",
" and ",
"here",
" are examples. They aren't exactly magnifying glasses, but they use a series of mirrors to concentrate sunlight and heat oil."
] |
[
"It's called 'solar-thermal' because it depends on heat, and they use mirrors (\"non-focusing optics\") because they can concentrate the power to a single point, rather than an image of the disc, or a spectrum depending on frequency. Also, they weigh less. Moving parts and mechanics are involved, so they are generally less reliable than photo-voltaics (PV). "
] |
[
"I assume you aren't referring to photovoltaics? I don't know of any solar panels that work as you've described. "
] |
[
"Can you charge a capacitor to a higher voltage than it's power supply?"
] |
[
false
] |
I only know the basics on circuits, just curious.
|
[
"Yes, but only with alternating current (AC).",
"You can make a resonant circuit by wiring a capacitor and inductor together in series. The circuit will resonate at an angular frequency given by",
"omega_0 = 1 / sqrt(LC)",
"Suppose we drive this circuit with a voltage drive given by",
"V sin(omega t)",
"It turns out that the amplitude of the voltage you would find across the capacitor would be",
"V_cap = V / [ 1 - (omega/omega_0)",
" ]",
"For values of omega close to omega_0, the denominator can be very small, which makes V_cap bigger than V.",
"EDIT: In order to find this result for yourself, you would have to learn about alternating current circuits. There's an idea called \"impedance\" which really helps understand circuits quite a bit. Once you learn about impedance this sort of thing will be really easy."
] |
[
"Sure. To me switch=AC, but words are only words."
] |
[
"Yes, but only with alternating current (AC).",
"Well, it depends on what you mean by AC. One can definitely turn a lower DC voltage into a higher DC voltage by means of a ",
"boost converter.",
"The thing about those is that one needs a switch that turns on and off at a relatively high speed, so inside the circuit, it's not totally DC but I wouldn't call it AC, either. If one puts enough filtering elements at the output, then the output becomes fairly DC. "
] |
[
"Does a Mayfly, which only lives a day, evolve fast than a human?"
] |
[
false
] |
This might be really stupid but to me it makes sense, kind of. Evolution is about survival of the fittest right, so the more generations you have the faster changes take place and the weak are weeded out.
|
[
"Yes. Generation time has a significant effect on how fast a species evolves. Here's an article about the effect on molecular evolution in bacteria (which can evolve even faster than mayflies):",
"http://onlinelibrary.wiley.com/doi/10.1111/evo.12597/abstract"
] |
[
"Also please remember that generation time in mayflies is much longer than one day. They are ",
" for a day, but live as nymphs under water for at least a year before that. They spend the grand majority of their lives under water."
] |
[
"It's a common misconception that a mayfly (Ephemeroptera) only lives one day. They have four phases: Egg, nymph, subimago and imago. Most of their life is spent as a nymph under water. They live for up to a year before they emerge to the surface and \"hatch\" into an adult subimago. After hanging out for a bit, they molt one last time and become an imago. From there they mate and die - that last part is what lasts a day. For all intents and purposes, they probably evolve at about the same rate as other insects.",
"Comparing the fossil record of both Ephemeroptera and Homo Sapiens, I could make an argument that factors other than the generational cycle time is driving evolution of the species; some species simply \"break out\" - perhaps due to an interaction with the environment. It's believed that evolution is not necessarily linear, but is full of fits, starts and breakthroughs. As far as species go, mayflies are rather primitive and are quite similar to their ancestors from 300 Million years ago. "
] |
[
"If we're in the Milky Way, how do we take pictures of it?"
] |
[
false
] |
If a galaxy contains billions and billions of stars, and we're inside it, then isn't every star we see at night "the milky way"? What are we actually seeing when we see of a picture of the Milky Way? Some beautiful cluster of stars elsewhere in our galaxy?
|
[
"All the ",
"head on pictures",
" of the milkyway are not of our galaxy. They are either simulations/Pc generated pictures or pictures of other galaxies. ",
"We can however see the milkyway from its side like this: ",
"pic"
] |
[
"Wow, thanks for that second pic. I guess it makes sense. It just seems weird, like taking a picture from the back seat and saying \"look, my car!\" lol"
] |
[
"When we take a \"picture\" of the milky way, it is really just a computer generated reconstruction of the milky way. We take pictures in all directions from the earth and use these images to construct a 3d model of what the milky way actually looks like."
] |
[
"Are there any truly stationary points in the universe?"
] |
[
false
] |
As I sit here I'm not really stationary, I'm on a planet in a solar system in a galaxy. On top of that, space itself is expanding. Does anything stand still?
|
[
"Relativity tells us that your question doesn't really have meaning. What I mean is that in Physics you don't ever ask what something's velocity is, you ask what the velocity is ",
". This is what is known as a frame of reference. ",
"So to answer your question, there are definitely things in the universe that are stationary with respect to other things (they just need to be moving with the same velocity vector) but there isn't anything that is stationary with respect to everything in the universe. "
] |
[
"This revelation, that there is no special, stationary reference frame is what lead Einstein to develop special relativity (bit of a simplification). The assumption that there existed a single, stationary reference frame was fairly ubiquitous in physics for a long time. Many believed it was the reference frame in which the luminiferous aether rested. The wikipedia objects on these subjects are fascinating and well worth reading. "
] |
[
"If you think about it, everything in the universe is stationary with respect to itself"
] |
[
"What's the difference between connecting to a network with a Static IP and adding a static ARP cache entry?"
] |
[
false
] |
Do they do the same thing? How do the consequences / behavior from the computer to router differ?
|
[
"Certainly not the same thing. You have to look at what actually happens when computers communicate.",
"Let's say you have several computers in a shared medium. The network cards only know about Ethernet, they don't deal with IP. On Ethernet there's only the local segment and devices are addressed by MAC address. So if you want to send a packet to whatever host has IP address 192.168.1.5, you have to find out its MAC address. That's where ARP comes in. You send an ARP request asking who's got IP address 192.168.1.5 and get a MAC address in response. You cache that in your ARP cache.",
"Then it should become clear that static IP addresses and static ARP cache entries have nothing to do with each other. The ARP cache is local to the host, and is there exclusively for your own use and convenience. Changing your own cache doesn't do anything to the rest of the network."
] |
[
"ARP is used to communicate locally--- i.e. on the same network. ARP is actually a protocol used to learn hardware addresses called 'MAC' addresses. MAC is a hardware address, while IP is a logical address (MAC is burned into your network interface card, while IP is just assigned by you or whatever your preferred DHCP client gives you). ",
"So if we connect 3 computers to a switch and none of the computers have IP addresses, they can still technically communicate with each other through WINS and MAC. Hell, the computer really doesn't know what to even DO with an IP address--- if these three computers had IP addresses and you told computer A to communicate with computer B via IP address, it would use said 'ARP' protocol to find out what computer B's MAC is.",
"IP addressing is needed when communicating with computers on different networks. Your computer actually needs to have the MAC address of a router in its ARP cache, and it just sends a frame up to that router, which turns it into a packet and sends it to the next hop IP address.",
"So, in essence, you can put in a static ARP entry of a computer AND a static IP address of the same computer and it would all be cool, as long as the information is correct."
] |
[
"Ah that makes sense, thank you!"
] |
[
"What's the slowest a commercial airplane can fly and still maintain altitude?"
] |
[
false
] |
[deleted]
|
[
"Like Brent said, it's dependent on a large number of factors, most particularly what kind of plane you're talking about and the operating conditions. But from Googling around, I found that a lightly loaded 737 in level flight and flaps fully extended has a stall speed of approximately 100-110 kts (115-125 mph). As you add more weight, retract flaps, or increase the pitch of the plane, that number will go up."
] |
[
"That would depend on a host of things, the first of which being the question ",
" commercial plane.",
"Each and every airplane has a certain curve of Lift Coefficient versus Angle of Attack. The lift coefficient multiplied by the air density multiplied by the airspeed squared multiplied by the wing area yields the lift the airplane will generate. Knowing the maximum coefficient of lift for the airplane, it's wing area, it's weight (and thus the lift it must generate) and the local air density will tell you the minimum airspeed."
] |
[
"Depends on the airplane, as breintje pointed out. Some small 2-4 seater planes can fly at about 30 mph or less, but I don't think that's what you're talking about. Big jet liners need to go much faster.",
"Also depends on the altitude: The higher the airplane is off the ground, the faster it needs to go to maintain altitude, since the air is thinner at high altitudes and the wings don't generate as much lift.",
"Also depends on who/what is in the airplane. An empty 747, carrying just two pilots, weighs far less than a 747 all full of people and luggage. A 747 full of various cargo can weigh even more. Heavier plane means more speed to keep it in the air.",
"Most airplanes are also able to adjust their wing's profile slightly: When you're taking off or landing, they extend flaps that make the wing generate more lift at lower speeds, so they can safely fly at a slower speed. When they're cruising along, they retract the flaps to get less drag/more speed/better fuel economy.",
"Airplanes have a list of \"V Speeds\", which are the various minimum and maximum speeds for various conditions. ",
"Here's a wikipedia list of all of them.",
"I suppose what you're asking about would be Vs0, which is the stall speed of the aircraft in with the wing in landing configuration.",
"From what I can find, it looks like a 747 has a Vs0 of around 140 knots, or 160 mph. That would be about the slowest a 747 could fly, at approximately sea level, in landing configuration, without losing altitude or control."
] |
[
"If light has energy, it has momentum. But if it has momentum doesnt that mean it also has mass?"
] |
[
false
] |
If light has Energy (E) then according to Einstein it also has Momentum (E²=(mc²)²+(pc)²) but if it has Momentum (p) it also has mass (P=mv). I dont understand. How can something have momentum but no mass? Is p=mv just outdated and a simple formula taught for its ease and can only apply to classical objects?
|
[
"As you surmised, p = mv only applies to classical motion of objects well below the speed of light."
] |
[
"You gave the essential expression in your post.",
"This result leads to p=E/c for an object moving at speed c (which means a massless object) and p=mv/sqrt{1-v",
"/c",
"} for an object with speed less than c (which means an object with non-zero mass)."
] |
[
"It already is: ",
"http://www.reddit.com/r/sciencefaqs/comments/g3qlc/is_light_massless_why_is_it_affected_by_gravity/"
] |
[
"A question about the Hodgkin-Huxley model"
] |
[
false
] |
These science rockstars are definitely amongst my all-time heroes. I was going over their equations, and H&H used the variables m,n, and h to describes the dynamics of voltage gated channels. I was wondering, Why are m and n raised to powers, while h is not? I understand that m and n deal with channel activation and h is the Na channel inactivation. Here's their equation: Ik = gNa m (u - ENa) + gK n (u - EK) + gL (u - EL) I've thought about this for too long, any insight is appreciated =)
|
[
"Cool, thanks. ",
"Yeah I should look at their papers. Physics is still kinda scary to me, but I've been getting more comfortable. Thanks for everything =)"
] |
[
"These exponents were determined by fitting to the experimental data.",
"The interpretation is that there are 3 'm' gates in the protein, which all need to be open in order for the channel to be considered open, but only one 'h' gate which inactivates the channel when it closes.",
"If at some voltage, in steady state (because the gating is time dependent), an m gate has a 50% chance of being open, then the chance of all 3 on the same channel being open is (.5)"
] |
[
"They published 5 papers in the journal of physiology in 1952 which would go over their process of discovery.",
"Membrane potentials were certainly well known about at that time, the first estimation of the diastolic membrane potential was by Bernstien in 1902.",
"The best source I have on this:",
"http://www.amazon.com/Mathematical-Physiology-Cellular-Interdisciplinary-Mathematics/dp/0387758461"
] |
[
"While walking through a Pennsylvania forest, I saw a rock the size of a car. How long has it been sitting there, and where was it before that?"
] |
[
false
] |
[deleted]
|
[
"That's definitely not enough information to give anything close to a definitive answer, but we can speculate a bit. Assuming you did not see said car-sized rock directly adjacent to elevated topography with exposures of similar bedrock (if you did, then it probably is sourced from said exposures and moved through some sort of mass movement), then a good guess would be that it is a ",
"glacial erratic",
". The possibility of it being a glacial erratic would be bolstered if 1) the type of rock was significantly different than the local rocks and 2) you observed it in an area known to be previously covered by the ",
"Laurentide Ice Sheet",
". The northern portions of North America were covered by a large ice sheet several times during the peak of glacial periods over the last ~2 million years. The extents of these ice sheets varied, but portions of Pennsylvania were covered by these ice sheets from time to time, e.g. ",
"this paper",
" has maps of the extent of the ice sheet during the last glacial maximum (check out figure 2 on page 5). If it is fact a glacial erratic related to the Laurentide Ice Sheet, then it probably last significantly moved during the ",
"last glacial maximum",
", but again, without details, it's pretty hard to say too much more."
] |
[
"I don't know if I'm being helpful or pedantic -- maybe both -- but here's a rough translation from Geologist:",
"If it's near a hill, it probably slid down the hill. Otherwise, it probably got pushed there by a glacier around 25,000 years ago. Hard to say how far, though."
] |
[
"This area (PA) is known for its glacial debris.",
"To answer the OP where it came from, maybe Canada!"
] |
[
"Do Xrays, UV, IR, Microwave, and Radio waves all travel at the same speed as Visible Light?"
] |
[
false
] |
I understand that they are not separate entities per se, but rather different wavelengths of the electromagnetic spectrum, but do the difference in wavelenths affect the speed of travel?
|
[
"In vacuum they all travel at the same speed.",
"In a medium the speed can and does depend on wavelength."
] |
[
"When talking waves, Speed = Wavelength x Frequency. ",
"All of these waves are electromagnetic radiation, so in a vacuum they will all travel the same speed: the speed of light, c. So this equation looks like :",
"c = λ * f",
"where c = speed of light, λ = wavelength, and f = frequency.",
"As either the wavelength or frequency changes, the other will do so also to keep the speed at c. So radio waves have a big wavelength but short frequency, x-rays and such will have high frequencies and small wavelengths.",
"Now that's a vacuum, electromagnetic radiation is affected by the medium it is traveling through. You can usually find out how it affects it by looking at a medium's ",
"\"index of refraction,\"",
" which is basically a measurement of how EM radiation slows down upon entering a medium (which is what causes refraction).",
"The new speed at which EM will travel through a medium (which will be some percentage of the speed of light, always less) can actually be dependent on the wavelength. So for instance, air might slow down EM radiation in the \"visible light\" spectrum more or less than it does EM radiation from some other part of the spectrum, like radio. It can be very specific, some media will even completely block parts of the spectrum. This means some example medium (like glass, for example) doesn't have a set refractive index that you can use for all parts of the EM spectrum, you will have to use different indices depending on what is going through it. So that's why when you look at a list of these indices, such at ",
"this one",
" you will see that it also lists the wavelength of light. Those are the correct indices ",
" you are using that wavelength.",
"This is why rainbows and prisms work, actually, as even inside the small visible light part of the spectrum the different wavelengths are affected differently. Because of that, when white light (made of all the colors) enters a new medium such as glass it will spread out into it's constituent colors (aka wavelengths) as some were slowed more than others."
] |
[
"It's also important to mention here that even should light have such variations, c is a bit of a universal constant that we just happened to discover as the speed of ",
" first. More accurately we could call it a unit conversion factor between lengths measured on a ruler and lengths measured on a clock (time). Like how an inch is 2.54 cm regardless of circumstances"
] |
[
"Is it possible to completely saturate a contained area with light?"
] |
[
false
] |
Here's a theoretical question that was posed to me the other night. Let's say you have a room with smooth, connected sides such that no light can escape. Then let's say that you continue to fill the room with light. Is there a point when the room becomes saturated with light such that no more light could be added to the room?
|
[
"no. light being bosonic in nature, do not obey pauli's exclusion principle, so any number of photons can occupy the same space."
] |
[
"Light does exert pressure, which is the principle used for solar sails. There is not much pressure, though, and LASERs blow things up by heat, sometimes with mechanical effects from the heated bit of the object vaporizing."
] |
[
"You are describing a photon gas. It has pressure and will eventually blow up your room. If it is a very strong room, it will probably turn into a black hole at some point.",
"But I guess the answer you are looking for is \"no\"."
] |
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