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[
"Do motivational sayings actually help people in any way?"
] |
[
false
] | null |
[
"I think what you're getting at is the \"power of positive thinking\" idea that's been gaining popularity for the last few decades. The idea is that believing you can do something will make you more likely to succeed at that task.",
"I've read in several places that this sort of thing may actually have a negative effect. When things don't go well, people blame themselves for not thinking positively enough, instead of acknowledging that the task may have been difficult or that they may have failed for reasons outside their control.",
"I know the book 59 seconds by Richard Wiseman has a section on this and the book Bright Sided by Barbara Ehrenreich is all about this topic, although I have not read the latter. ",
"I'm pretty sure I have heard this topic addressed in podcasts, but I can't think of which ones right now. Anybody else have some sources for this?"
] |
[
"I thought this was interesting, so I did a quick lit search. I wasn't able to find anything about motivational sayings, per se. Not that that's surprising, though; it's a very narrow part of what could generally be called positive thinking.",
"There is some research into positive thinking, namely in an applied sense with medicine and education. There's a little bit of basic psychology out there, but not a whole lot with any empirical data.",
"This article",
" seems fairly interesting and relevant. It's basically addressing the psychology of 'fake it till you make it' or the 'power of positive thinking'. It's based on the 'winner's effect' which can be supported empirically in mice. This is a long way off from the complication of humans, but it certainly seems quite plausible that there would be some effect.",
"Certainly, it is an attractive hypothesis that some self-deceptive confidence or optimism would be adaptive, whereas too much would be detrimental. At a certain point, you'd be deluding yourself and making poorly informed decisions. One could imagine a fitness maximum at a certain level of optimism. However, evolutionary arguments like that are quite difficult to support and very often specious.",
"How motivational quotes and other tropes are involved in all of this is a yet more complicated question. It would seem that the idea here is to cultivate optimism, so begs the question of whether this is possible or effective. As another poster pointed out, this cultural phenomenon implicitly states that changing one's outlook in this way is possible. If this is not the case, then that would be understandably frustrating, and perhaps counterproductive."
] |
[
"What about \"people like me\" who despise such pithy annoying tropes and feel more negative after reading them? Now a comically oriented ",
"-motivational poster would be right up my ally but those seem to affect others negatively. Maybe we should forget about them?"
] |
[
"What’s the most reactive element?"
] |
[
false
] | null |
[
"Dioxygen difluoride is a stronger fluorinating agent than fluorine, for example.",
"Things I won't work with",
". A chemical so reactive that it explodes in contact with nearly everything, including water ice at cryogenic temperatures. You are lucky if it \"just\" starts a big fire."
] |
[
"Fluorine is the most electronegative (electron-taking) element, so it is a good answer. OTOH, Cesium is the most electropositive (electron-losing), so it is also a good answer. It would be difficult to decide to decide which is the most reactive since their reactions are so different. "
] |
[
"Not necessarily. We can make elements even more reactive by putting them in the right compound. Dioxygen difluoride is a stronger fluorinating agent than fluorine, for example."
] |
[
"Are there any sets of planets that orbit around each other while also orbiting their sun?"
] |
[
false
] | null |
[
"Yes. The Earth and moon orbit each other while going around the sun.",
"In general, if we have 2 or more planets orbiting one another, we pick the biggest and define it as a \"planet\", and the smaller one or more we call \"moons\". But in fact the Earth orbits the moon just as much as the moon orbits the earth - this is what creates the tides."
] |
[
"I had assumed that size was a factor in if something was a planet (pluto), so I guess I meant to ask if there are planets close in size that orbit each other as well as a star."
] |
[
"From Wikipedia - Relative size",
"\"Comparative sizes of the Earth and the Moon, as imaged by Deep Impact in September 2008 at a separation of 50 million km[87]\nThe Moon is exceptionally large relative to the Earth: a quarter the diameter of the planet and 1/81 its mass.[43] It is the largest moon in the Solar System relative to the size of its planet, though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass.[88]\nHowever, the Earth and Moon are still considered a planet–satellite system, rather than a double-planet system, as their barycentre, the common centre of mass, is located 1,700 km (about a quarter of the Earth's radius) beneath the surface of the Earth.[89]\"",
"If you want to quibble about where astronomers draw arbitrary lines, you would need an astronomer.",
"The fact is, The earth orbits the moon just as much as the moon orbits the earth.",
"Judging from the wiki entry i would gather the line (to \"define\" something as a double planet) is drawn at the collective system of both objects orbiting a point (having a center of mass) outisde of the larger bodies radius."
] |
[
"If I donated blood while drunk, would the recipient of my blood be drunk when they receive it?"
] |
[
false
] |
Obviously this wouldn't be allowed, just wondering if it would carry over or if the alcohol would break down by itself while the blood is stored.
|
[
"Short answers: No to the thread title, yes to your description.",
"Longer answers: Being \"drunk\" is a bit of a subjective term, but let's stick to the legal definition of higher than 0.08 BAC. So let's say you're HAMMERED at a 0.30 BAC. Standard donation is one pint, which represents approximately 10-15% of your blood. If the recipient got just your one pint, it would be diluted into their other blood. So, if one pint of 0.30% blood is transfused into a sober recipient, their BAC would become approximately 0.03-0.04, not drunk. Although yes, the alcohol would be transfused.",
"To get \"drunk\" through a blood transfusion, the recipient would need to receive 3+ pints of your blood (or similarly high BAC blood, since they'd never let you donate 3 pints)."
] |
[
"As a layman, other than plasma and whole blood, what other options would there be?"
] |
[
"As a layman, other than plasma and whole blood, what other options would there be?"
] |
[
"If the universe cools as it expands, won't it get to a point where it's at Zero Kelvin, therefore violating the Second Law of Thermodynamics?"
] |
[
false
] |
[deleted]
|
[
"It won't reach zero K. The temperature can decrease forever and still not reach zero, though the decrease has to happen more and more slowly as time goes on, of course.",
"Oh, and you mean the third law of thermo, not the second."
] |
[
"It's also worth noting that you can never reach zero Kelvin, only asymptotically approach it."
] |
[
"Why is this?"
] |
[
"Are there any cosmological phenomena that we strongly suspect will occur, but the universe just isn't old enough for them to have happened yet?"
] |
[
false
] | null |
[
"White dwarf",
" stars will eventually stop emitting light and become black dwarfs. There aren't any old enough in the universe for this to have happened yet and it's estimated that it could take about a quadrillion years. "
] |
[
"There's a couple of things that are predicted by different mutually-exclusive cosmological models and we don't know which, if any, are actually correct.",
"Big Crunch",
"Big Rip",
"Vacuum genesis",
"heat death of the universe",
"False vacuum",
"Ekpyrotic event",
"Unfortunately, all of these things are end-of-the-universe scenarios so it would be impossible to actually observe them occurring."
] |
[
"There are indeed such theories, but for now according to all the observations, the universe seems to expand with a faster rate and will only keep expanding forever. For the universe to contract, it need a large portion of matters in it, but now almost all observations show matters only made up ~25% of the universe (in terms of energy)."
] |
[
"Can we only spot exoplanets which are in systems with a similar orbital plane to ours?"
] |
[
false
] |
If Kepler spots planets by the dip in brightness of their star when they pass in front of it, does that not mean we can only spot planets which orbit their star on a similar orbital plane to ours?
|
[
"They don't have to be on the same plane as us, but it is much easier to detect exoplanets in systems that are ",
" to us, i.e. their orbital plane is aligned along our line of sight."
] |
[
"Edge on to our line of sight is not the same as being on a similar orbital plane, though. \nIf you are at either pole and look up and see an edge-on system, its orbital plane will be almost orthogonal to our own."
] |
[
"No. ",
"There are several ways to detect exoplanets ",
"Wiki",
"You can detect the planet crossing the star. The planet blocks some light and we can note the dimming of the star's light. This requires the planet to get between us an the star. That means it doesn't work if we're looking at the star system from one of the poles of the star.",
"However, we can detect planets in other ways too. We can see the 'wobble' of the star as big planets gravitationally pull the star. This is done by measuring the Radial Velocity.",
"We can also use Microlensing where the planet's gravity deflects a background star's light than just the parent star. This requires two stars to be almost exactly lined up, meaning it can't be done on every star system.",
"There are other ways too listed in the article above. Enjoy!"
] |
[
"If gravity is caused by the formation of curves in spacetime, does the electromagnetic force have a similar underlying cause?"
] |
[
false
] | null |
[
"No, electromagnetism isn't caused by any sort of curvature of space-time. In fact, you can input Maxwell's equations into general relativity and make predictions on how the two theories interact. In quantum field theory, you can interpret electromagnetism to be \"caused\" by the interaction of matter with a massless spin-1 particle.",
"Now there is a geometric reformulation of electromagnetism, but it doesn't involve the curvature of space-time. It involves a lot of complex (but very beautiful) mathematics, and models electromagnetism in terms of the geometry of a \"fiber bundle over space-time.\" This is totally overkill for a layman explanation, but I wanted to mention it in case you had seen it."
] |
[
"Gravity depends on the amount of mass in the object.",
"The motion of an object under the influence of gravity does not depend on its mass.",
"This behavior is crucial to the notion that gravity is not a conventional force between objects, but a consequence of motion through curved spacetime. In general relativity, every object travels on a geodesic (the curved geometry equivalent of a straight line). If the motion depended on any property of the object then this idea would fail.",
"You might ask: If objects all follow geodesics, then why don't they all follow the same (spatial) trajectories? The answer is that the curvature is in spacetime, not space only."
] |
[
"In order to attribute a force to the geometry of spacetime, it has to affect all objects the same way. That holds for gravity, where (for example) all objects fall with the same acceleration. It doesn't hold for electromagnetism, where the force depends on the amount of charge in the object."
] |
[
"How are the two images each of my eyes perceive joined into one?"
] |
[
false
] |
From my perspective, I see one image of the world around me, not two side by side. How does this happen?
|
[
"The slight disparities in objects' horizontal position that each of your eyes feeds into your brain are compared and combined within the visual cortex. The process is called ",
"stereopsis,",
" and it's one of the three or four fundamental ways we achieve depth perception and convert the two-dimensional images on our retinas into a three-dimensional mental \"map\" of our immediate surroundings.",
"Interestingly, not everybody has the facility to the same degree. For example, it's been posited that many professional athletes' cortexes can process the information faster and more accurately than average. With a 3D model of their immediate surroundings more quickly available to their conscious mind, and with finer detail, they are more likely to excel in areas like sports, where instantaneous and accurate depth perception is crucial for achieving instantaneous and accurate reactions.",
"In contrast, some visual artists may actually process ",
" optimally than normal - which perhaps gives them an advantage in converting a world normally conceived in 3D, back to the two dimensions of their canvas or screen, with a more pleasing fidelity."
] |
[
"I can back up your last paragraph about artists. I've been drawing/painting since 4 years old. I've had a below average depth perception my whole life and it's easy for me to translate what I see in 3D into a 2D drawing on a piece of paper or on a digital drawing. ",
"Although most people can learn how to do this while having excellent depth perception, I believe it's going to be much harder."
] |
[
"Thank you! That makes good sense."
] |
[
"Why is cold considered the absence of heat, instead of the other way around?"
] |
[
false
] | null |
[
"Heat is a measurable thing (energy). Cold is the absence of that measurable thing. Dark is the absence of light and dry is the absence of water/liquid for the same reason.",
"A room is empty because there are no people in it. A room is not full because of the absence of emptiness."
] |
[
"Think about it this way: Heat is energy. The material has a certain amount of energy which correlates to its temperature. If you take away the energy, you take away the temperature, and if you put more energy into it, you raise the temperature. Things get colder when they lose energy. Because of this, it is only logical that we work with what we ",
" and what we can measure and call it heat."
] |
[
"Heat and temperature are concepts created to explain the average kinetic energy of all the molecules in a system. If all the molecules in the system move more rapidly, they are said to be hotter. ",
"Cold is the absence of heat because the \"thing\" that is absent is kinetic energy; the vibration and movement of molecules. ",
"Heat is not the absence of cold because that would be saying the \"thing\" that is absent is the absence of kinetic energy, something of a double negative. ",
"That being said, you can think about heat and cold in whatever way you wish- they simplified concepts to help us understand atomic movement in a way that is useful. Just don't lose site of what they represent. \"Don't pick up that pan, its atoms are moving extremely quickly relative to the movement of atoms in your hand\" isn't an effective way to help your buddy from burning him or herself."
] |
[
"Who are some influential but relatively unknown/underappreciated scientists, and what were their major contributions to science?"
] |
[
false
] | null |
[
"John Bardeen",
". He invented the transistor which is responsible for pretty much all modern technology. He's also the only person to have won a physics Nobel Prize twice. ",
"Yet for some reason I've never met anyone outside of the University of Illinois who knows who he is."
] |
[
"Dr. John Craven",
", former Chief Scientist of the Navy's Special Projects office.",
"He contributed extensively to the development of deep submergence technology. He also helped create the Natural Energy Laboratory of Hawaii.",
"I highly recommend his book ",
"The Silent War: The Cold War Battle Beneath the Sea"
] |
[
"I never knew who ",
"J. Willard Gibbs",
" was until I took thermodynamics in college. Dude was a giant of science.",
"He devised much of the theoretical foundation for chemical thermodynamics as well as physical chemistry. As a mathematician, he invented vector analysis (independently of Oliver Heaviside)."
] |
[
"Is the capability to control our breathing exclusive mechanism to humans, or can animals do it too?"
] |
[
false
] |
Also what is the purpose of this mechanism? Why not just have fully automagic breathing we cannot control? WHY DID YOU DO THIS EVOLUTION?
|
[
"all sea going mammals can selectively hold their breath.. ",
"it's not a mechanism, it simply exerting control over your body. ",
"How would you speak properly if you had to deal with automatic breathing?"
] |
[
"There's a TED talk about how humans might've had aquatic mammalian ancestors. The lady talking goes a bit into the subject of our breathing control."
] |
[
"I was under the impression that this was hokum, you might be talking about something else though. ",
"http://scienceblogs.com/pharyngula/2009/08/oh_no_not_the_aquatic_ape_hypo.php",
"linked from Pharungula",
"http://www.aquaticape.org/"
] |
[
"Can heavy-metal surgical implants, such as a titanium maxilla reconstructive plate or wire mesh produce any long-term neurological effects due to the deterioration of the implant? [Medicine]"
] |
[
false
] | null |
[
"From wikipedia: \"Titanium is considered the most biocompatible metal due to its resistance to corrosion from bodily fluids, bio-inertness, capacity for osseointegration, and high fatigue limit. Titanium's ability to withstand the harsh bodily environment is a result of the protective oxide film that forms naturally in the presence of oxygen. The oxide film is strongly adhered, insoluble, and chemically impermeable, preventing reactions between the metal and the surrounding environment.\"",
"In other words, your body can't break it down."
] |
[
"Titanium is generally fine for use in implanted devices. There are other metals though, like cobalt - chromium, that elicit unfavorable immune responses. With all implanted devices that undergo some mechanical motion, wear particles are generated due to friction. In the case of metals like titanium, the immune system doesn't respond to the levels of particles generated during normal device function. However, cobalt-chromium wear particles cause chromium ion toxicity which can lead to localized tissue death. This is the main reason for the failure of DePuy Synthes' failed Acetabular hip replacement which they settled for millions of dollars."
] |
[
"Could any other complications arise should more of the implant become gradually exposed and visible over time? Such as screws protruding from the gums etc (hypothetically speaking)?"
] |
[
"How do fish get around beaver dams?"
] |
[
false
] |
Obviously, fish getting blocked by man made dams is a major engineering problems, so why is that not so much of a problem for beaver dams? If it isn't, why can't we just apply the beaver solution to our man made dams?
|
[
"For one thing, they are vastly shorter. For another, they are relatively temporary...often getting washed or overtopped in flood events. And finally, they are generally a few leaks or spillways. The dams are also limited to relatively small creeks and streams.",
"We can't apply the beaver solution because three foot high dams that flood over every rainstorm aren't particularly useful for what humans are trying to do with dams"
] |
[
"Not an expert, just learned a bit from undergrad, so please correct me if I get anything wrong.",
"Many fish that migrate up streams small enough to be dammed by beavers have evolved significant jumping ability. A good example of this is salmon - which are impressive leapers in order to get around obstacles like waterfalls, and can clear beaver dams as well.",
"Obviously, manmade dams are much, much larger - fish aren't anywhere close to being able to clear them. ",
"But having said that, fish ladders actually do what you're suggesting, to some extent. By creating a path around the dam that involves many small jumps instead of one massive one, they can allow fish to move around the dam. It isn't a perfect solution because it does still restrict the movement of fish, but it's better than nothing and is applying the idea that you're suggesting."
] |
[
"There are some exceptions of course! The Wood Buffalo National Park has a dam extending nearly a kilometre after all.",
"Still, I don't imagine even that one is terribly exclusionary to whatever local fish might be in the waters."
] |
[
"Is it possible to force our bodies to produce a second set of adult teeth later in life?"
] |
[
false
] |
It doesn't seem like producing a second set of teeth would be terrifically taxing on our system, especially in an era of extremely cheap nutritive calories and calcium supplements. Could we trick the body into growing a new set of adult teeth without significant side effects?
|
[
"They're working on growing replacement teeth from human stem cells. Here's some of the recent work, from 'Cell Regeneration Journal': ",
"http://www.cellregenerationjournal.com/imedia/1338585422989841_article.pdf?random=614086",
"\nBut it's still pretty primitive. It would be more interesting if were possible to find some trigger that caused your body to grow a whole new set of replacement teeth (without the surgical implantation and all that). And since a few (mutant) people do grow more than the usual two sets of teeth in a lifetime, that seems to be not utterly impossible... but I'm not aware of any actual research in that area."
] |
[
"(Soon to be dentist here) This is not a baby's skull. Teeth develop as you grow with first primary teeth coming in around 6 month old, and the last permanent tooth developing around 16 years old. This is an incorrect picture and explanation. Research is currently being done to try and use stem cells to grow new teeth that are your own, which would be pretty amazing. "
] |
[
"General Dentist here (not really a specialist in development or genetics just regular old dentist). Your teeth form from specialized embryonic cells. Your baby teeth are starting to form by about week 7 of embryonic development. The adult teeth bud off of the adult teeth at about week 20. I assume with enough genetic manipulation a continuation of that process might be possible however there is a major obstacle that I see in preventing that from being successful. The undifferentiated cells are gone not long after week 20 and so set number 3 would need to be forming right away. This would mean that set number 2 needed to be very small - basically like another set of baby teeth - to accommodate another set of teeth (and basically defeat the purpose of the 3rd set that you wanted in the first place). Teeth in a baby (as you can see from the photo that has been posted here) take up a significant amount of space in your head. Good luck getting another set in there. There are too many other important structures that would be compromised. Wikipedia's tooth development page has a lot of good pictures and interesting information if you are curious."
] |
[
"About Vlatko Vedral's book Decoding Reality..."
] |
[
false
] |
I'm a mathematical nitwit, but I'm fascinated by all the concepts and possibilities opened up to me in Vlatko Vedral's book . Any further reading? Or does have sound arguments to follow on along this path?
|
[
"Most of us (myself included), aren't familiar with the contents in this book (since we haven't read it). Would you mind elaborating on what concepts and possibilites in particular fascinated you?"
] |
[
"It was all new to me, in the sense that I had heard about quantum information before but only started to understand the implications through the ",
" of this specific book.",
"\nActually the whole of it, almost page after page.",
"\nWell, not literally ",
", because I ",
" it as an audiobook. Two times in a matter of half a year. "
] |
[
"Ah ok. Well if it's quantum information you're interested in, then what I suggest would depend on your background. Are you able to follow the mathematics necessary for physics? Could you understand a graduate level textbook (it's a graduate level topic)? I don't know of many lay books written on QI unfortunately."
] |
[
"Why doesn't type 2 diabetes induce weight loss?"
] |
[
false
] |
Since type 2 diabetes results from severe insulin resistance, the hormone responsible for nutrient partitioning, wouldn't a high insulin resistance mean your body cannot use the glucose it receives (and thus cannot induce anabolic processes such as building muscle or storing fat)? I understand why it is harmful to have hypoglycemia resulting from excess sugar in the blood but I don't understand why the body wouldn't lose weight once it starts developing a resistance to insulin (and I can't seem to find an answer online).
|
[
"Type 2 Diabetes MAKES you fat, it's not being fat that gives you Type 2 diabetes.",
"Obesity does contribute to diabetes. Visceral fat produces resistin (a hormone which induces insulin resistance) and pro-inflammatory cytokines (which impairs insulin production in the pancreas).",
"Interestingly, some research suggests subcutaneous fat has the opposite effect - protects against diabetes. See here:",
"Visceral adipose tissue increases, and subcutaneous adipose tissue decreases the risk of insulin resistance and T2DM in humans.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4038351/",
"On average, raised abdominal obesity increases risk of type 2 diabetes more than twofold.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658023/"
] |
[
"\"cannot induce anabolic processes such as building muscle or storing fat\" this is incorrect. The processes don't operate normally but they still operate. Type 2 Diabetes MAKES you fat, it's not being fat that gives you Type 2 diabetes. Some suspect that the recent massive increase of T2D is in fact a result of low level long term food based mercury poisoning via Fructose and Corn syrup."
] |
[
"Yes once fat it worsens it and there is a difference with fat at the skin vs fat around the organs but T2D itself will make you fat."
] |
[
"Do we know if the acceleration of the universe itself is accelerating?"
] |
[
false
] |
I was listening to astronomy cast about the cosmological constant and they started talking about the acceleration of the expanding universe. I've always wondered, do we know if the acceleration is constant or changing? Theoretically if the acceleration's acceleration is negative, couldn't the "big crunch" and the one where everything kinda stops (I know it doesn't really stop, it's an asymptotic thing), still be viable?
|
[
"There are a couple terms to know.",
"Acceleration of acceleration is ",
"snap",
", or the fourth derivative with respect to time.",
"We know that the acceleration, or second derivative, of the ",
"scale factor",
" is positive, which means that the rate (speed, or first derivative) of expansion of the Universe is increasing.",
"We also know according to measured values of ",
"Hubble's constant",
" that the current speed of expansion is about 68 km/s/Mpc, which means that every second across a distance of a megaparsec, space is growing by 68 kilometers.",
"Unfortunately, it's really difficult to measure the snap of the Universe over the vanishingly small time scales in which humans live. I did some looking around and found ",
"an old but relevant arXiv paper",
" on the subject. It asserts in the abstract that our ability to determine the third and fourth derivatives of the cosmological scale factor is \"likely to remain weak for the foreseeable future.\"",
"See ",
"/u/xxx_yyy",
"'s comment below."
] |
[
"Your reference is 11 years old. In fact experiments in the planning/construction phase will measure the next derivative (or two) of the expansion. This measurement is important to understanding the equation of state of the dark energy. Expect results in the 2020's."
] |
[
"I didn't know that, thanks! Do you know of any specific experiments?"
] |
[
"Why does volume level sometimes appear to be non-linear?"
] |
[
false
] |
[deleted]
|
[
"Quite simply - volume isn't linear! It's measured in dB which is logarithmic."
] |
[
"Mostly because the energy required to accelerate the speaker cone faster (make a higher pressure soundwave) isn't linear but the samples are."
] |
[
"Nature doesn't really care whether we use decibels (logarithmic) or absolute units to measure how loud a noise is. The reason we use decibels is because the values are more intuitive to work with."
] |
[
"Is this absurd situation problematic (relativity/physics)?"
] |
[
false
] |
I understand that, as posited in the FAQ, a 5 light year rod between two planets cannot transmit information faster than light, because the pressure wave required to propagate information through the medium most certainly moves more slowly than light. Additionally, I've read that if a train is going .9C and someone fires a bullet going .9C on that train, the added speed, despite mathematical intuition, will still be less than C from any reference frame due to relativistic effects. Then I got wondering about an absolutely ridiculous situation: Say you have a spaceship, and you have a piece of yarn over 300,000 km long, completely stationary, and you have this string attached to the back of a spaceship which begins moving. I understand that the entire string move at once, because the same issue of the pressure wave being provided from the movement of the spaceship must propagate throughout the entire medium before uniform motion can be established. However, once the yarn does assume uniform motion, is there any inherent problem with a yarn of this length moving at any uniform velocity, considering it's over "300,000 kilometers" of yarn moving per second, even though the object itself is traveling at a much lower speed? Additionally, I wondered the same question for, say, a guitar string. Again, the pressure wave from plucking a 300,000+ km guitar string would take a time to propagate throughout the entire string, but if it did, would the string contract to under 300,000 km from any reference frame? And finally, what if you attached a string from the surface of a tidally locked planet to the surface of its tidally locked moon, and then plucked it. Would the string simply break, or is there even a problem with this situation (aside from the absurd mechanics of actually implementing it)? : Just adding that in the last situation, the fact that the planet and the moon are greater than or equal to the distance between Earth and our moon is important to the framework of the question, as the distance, for my imagined situation, must be greater than or equal to the "distance" of light in 1 second, 300,000km.
|
[
"No inherent problems. I think you were getting confused by \"300,000 kilometers per second.\" This does not refer to the dimensions of the object at all."
] |
[
"considering it's over \"300,000 kilometers\" of yarn moving per second",
"Moving what per second?"
] |
[
"The photon will end up 35 meters short. (That is, it will end up 35 meters short if we observe the length of the moving string to be 300,000 km.)",
"I'm guessing that you are attempting to create a paradox by next asking how it appears that the speed of light is not C from the viewpoint of the string?"
] |
[
"What's the difference between sugars in fruits vs. those in candy/soda/processed foods?"
] |
[
false
] |
Put alternatively, why do individuals, on average, prefer eating candy over fruits, when there seems to be a lot of sugar in fruit to make it equally if not more appealing to us? Further, are there even more fine-grained differences, such as those of cane sugar vs. HFCS vs. "natural" sugars?
|
[
"HFCS is a syrup of glucose and fructose (two monosaccharides) with a variable amount of fructose, 42-55% for the liquid syrup.",
"In fruits, you have both glucose and fructose (some plants have lactose, but it is rare). The ratio of glucose to fructose differs based on the fruit, with berries having much more glucose rather than fructose and there really being no common theme for the fruits with more fructose than glucose. (Edit: The ",
"fructose malabsorption",
" page on Wikipedia has some info about common fruits. Although my personal opinion is that if you ",
" eating fruit, you don't need to micromanage fructose content. Its just dietary pedantics)",
"On a molecular level, there is no difference between the sugars ",
". I cannot speak authoritatively as to why people like candy over fruit, but perhaps that is more olfactory (due to the flavoring agents added) rather than due to the sugars.",
"That being said, fruits bear other vitamins/minerals and vitamin-like compounds which exert health benefits (quercetin, pyrolloquinoline quinone, sulforaphane, anthocyanins, etc.). Whereas 'junk food' really doesn't have much fancy stuff in it."
] |
[
"Also, whole fruit contains a lot of fiber, which is not found in juice or processed sugars. Fiber helps you to feel fuller when eating the fruit (you don't get this response from pure HFCS), lowers variance in blood sugar levels, and can even help with diabetes."
] |
[
"The real problem with HFCS as I see it is not its chemical composition, but the fact that because of corn subsidies, it is extremely cheap. This allows people to put sugar in tons and tons of foods that otherwise would not have it, as well as to cheapen the price of junk food. It basically facilitates the over-consumption of sugar."
] |
[
"Will water ice melt faster if allowed to drain, or remain in the meltwater?"
] |
[
false
] |
Say I want to melt a block of water ice. One option is to arrange for the melt water to drain away, thus reducing the mass that needs to be heater. However, the water that drains away will cary some heat out of my system. Which effect will dominate? Does it depend on the geometry of the ice block, or perhaps the method of heating?
|
[
"If your heat transfer rate is not high (e.g. you just have it sit in a room temperature environment, not over a fire) then both ice and water will be at the melting point while the ice melts. All the heat will melt ice, so it's only a matter of \"collecting\" as much heat as you can. Water provides a good contact to container surfaces, so keeping it in is probably a good idea in most cases."
] |
[
"On one hand I agree with your premise, but you are overlooking the fact that the air will be much warmer than the meltwater. Not sure if the temperature difference would be enough to overcome the difference in thermal conductivity."
] |
[
"Why not try it?",
"I would expect so.",
"Air is a poor heat conductor and so would do a bad job transferring heat into the frozen cube. ",
"Liquid water on the other hand is quite a good conductor of heat. ",
"If heat can efficiently transfer into the water, e.g. from the container the cube is sat in, I would expect this would increase the melting rate.",
"The water would also provide an additional surface for the heat from the air to flow into."
] |
[
"Is it possible to build a clockwork based CPU unit? Or even entire computer? What kind of speed and power would it have?"
] |
[
false
] |
Assume we have unlimited resources. What could be the maximum speed and power of such device? Could it reach lets say at least Pentium 1 (P5) ? How big it would be?
|
[
"One of the best ways to understand how computers work on a nuts-and-bolts level is to ",
"play Minecraft",
".",
"Lots and lots of Minecraft",
". You probably start out just trying to make a cool door for your base, but you can progress to building a machine that counts by linking T flip-flops and then a full adder by linking XOR gates and so on and so on until you haven't seen the sun in a week but have a working arithmetic logic unit in your creative world (the part of a CPU that does math).",
"Logic gates can be made of anything. Redstone is just easier to see than silicon transistors and cheaper to play with than gears and springs. Silicon is appealing because it is ",
" compared to early electromechanical computers and much more compact."
] |
[
"Consider Charles Babbage's ",
"difference engine",
"This mechanical calculator \"consists of 8,000 parts, weighs 5 tons and measures eleven feet long and seven feet high\". And it is able to do exactly one computing task: \"calculate and tabulate polynomial functions\". ",
"Obviously with modern materials we could make something similar, but smaller and lighter in weight. But still if you want to get to P5-scale computing it's going to be cumbersome. P5 contained (says Wikipedia) 3.1 million transistors. Say you need 1 gram of mechanical parts to replace the computing power of each transistor (which is pretty optimistic, I think). Then your mechanical P5 would weigh in at 3100 kg. "
] |
[
"Logic gates can be made of anything",
"You know what's cooler than redstone though? ",
"Crabs."
] |
[
"What caused the New Madrid earthquakes located in the dead center of the North American tectonic plate, far away from any subduction zone or slip-strike faults?"
] |
[
false
] |
[deleted]
|
[
"Let's start with a general explanation. The ",
"New Madrid earthquakes of 1811-1812",
" were what we refer to as ",
"intraplate earthquakes",
", i.e., they occur in the interior of a plate. Intraplate earthquakes occur infrequently compared to their interplate counterparts and typically occur in zones of pre-existing weaknesses within the interior of a plate, most commonly ",
"failed rifts",
" (e.g., ",
"Gangopadhyay & Talwani, 2003",
"). In addition to having very long recurrence intervals (i.e., the average time between events), intraplate earthquakes also appear to have very long ",
"aftershock",
" sequences, lasting 100s to 1000s of years after the main shock (e.g., ",
"Toda & Stein, 2018",
").",
"In terms of what causes intraplate earthquakes, there have been a variety of models, but they all generally rely on the idea of localized zones of weaknesses (like the faults associated with a failed rift) interacting with the regional stress field within a plate to allow one or more of the faults within this zone of weakness to overcome their strength and fail, causing an earthquake (e.g., ",
"Iio & Kobayashi, 2002",
", ",
"Talwani, 2017",
"). While we think about stress and strain being concentrated at the edges of plates (where interplate earthquakes occur and are a manifestation of the build up and release of this strain, caused by stress), the interior of plates are under stress as well because the plates are moving, i.e. the edge forces which drive plate motion impart a stress to the entire plate. A crude analogy would be pulling a rug by one edge. The interior of the rug while you're pulling it is under stress, and generally the rug moves because the internal strength of the rug is greater than the stress (i.e., it doesn't rip). If your rug was a little bit elastic and had a few randomly oriented slices in it though, when you started to pull, some of these slices might open and close a bit as the stretchy rug was pulled along the floor. These little tears activating occasionally would be something like intraplate earthquakes. If you go through some of the linked papers, you'll see that the specific details and the models proposed for intraplate earthquakes are exceedingly more complicated and there is still a fair amount of debate with regards to the specifics and importantly, intraplate earthquakes are commonly considered within the context of a compressive stress within the plate which doesn't really match with our elastic rug analogy, but this gets the (very) basic idea across hopefully.",
"Now, with specific reference to the ",
"New Madrid events",
", these are associated with an ancient rift, specifically the Reelfoot rift (e.g., ",
"Csontos et al., 2008",
"), as is common to zones of intraplate earthquakes. It's been argued that a segment of the Reelfoot rift is anomalously weak due to elevated temperatures (e.g., ",
"Liu & Zoback, 1997",
") and this seems sufficient to generate an intraplate earthquake in simple mechanical models given the background conditions (e.g., ",
"Kenner & Segall, 2000",
"), though this has been questioned (e.g., ",
"McKenna et al., 2007",
"). There is also debate about whether the New Madrid zone is actively accumulating strain (i.e., building to another earthquake sequence sometime in the future), many papers assume that it's generally winding down (see McKenna et al), but there is some evidence that it may be accumulating strain (e.g., ",
"Liu et al., 1992",
") and coupled with other evidence, leads some to suggest it is still active (e.g., ",
"Page & Hough, 2014",
"). While a zone of weakness associated with the ancient rift undoubtedly played a role in generating or allowing a sequence of intraplate events to occur, there have also been arguments about external triggers driving the initiation of the sequence including erosion (e.g., ",
"Calais et al., 2010",
") or melting of the northern hemisphere ice sheet (e.g., ",
"Grollimund & Zoback, 2001",
").",
" as a set of intraplate earthquakes, the New Madrid events have slightly unclear causes but are related to the presence of preexisting zones of weakness within the interior of plates and the interaction of those zones of weakness with the background stress field within the plate. They may be triggered by outside influences that modify the stress on these zones of weakness (e.g., changing surface loads) or simply by slow accumluation of strain eventually overcoming the strength of these weak zones, or some combination and/or different explanations for different intraplate earthquakes."
] |
[
"Induced seismicity",
" can cause intraplate earthquakes (or interplate earthquakes for that matter), but is best considered separately from naturally occurring intraplate earthquakes. Most induced earthquakes associated with oil and gas extraction (e.g., like those seen in ",
"Oklahoma",
") are not caused by fracking, but rather by wastewater injection (e.g., ",
"Jackson et al., 2016",
"). Fracking itself can very rarely cause felt earthquakes (e.g., ",
"Bao & Eaton, 2016",
"), but this is definitely the exception rather than the rule."
] |
[
"Wastewater is produced even without fracking (e.g. formation water) and injection was/is a common way to deal with wastewater before widespread application of fracking to unconventional reservoirs. Fracking does certainly increase the volume of wastewater and thus the volume being injected, but it is demonstrably false to say that (typically) fracking causes induced seismicity. Fracking can be done with low risk of induced seismicity if wastewater is dealt with differently."
] |
[
"Is \"Space Dilation\" a Thing? (Question from a Layman Trying To Understand Time, Space, and Spacetime)"
] |
[
false
] |
I've been thinking about since the moment it was posted, and one thing I've been wondering ever since relates to the following quote: By the way, this is why time dilation happens: something that's moving very fast relative to you is moving through space, but since they can only travel through spacetime at c, they have to be moving more slowly through time to compensate (from your point of view). Now, if a friend and I were to be inside a vessel moving along an arbitrary X axis through space at whatever speed you please, and I begin to move along the perpendicular Y axis while my friend stays in place, am I moving "slower" along the X coordinate than my friend? The same way I'm moving slower through time when I move perpendicular to it? This question may be extremely misguided. I have no idea.
|
[
"The comment you quote doesn't make any sense. Spacetime is nonEuclidean, and the ",
" between the space and time components of 4-vectors is important, not the sum.",
"Your question is interesting. Your answer is correct. Here, the statement, \"no speed can exceed c\" does make sense. So, if a particle that is moving along x with v",
", then feels a force along y, its v",
" will decrease, because v",
" + v",
" must be < c",
". ",
"This can be shown by Lorentz transforming the velocity, but that's a bit much for a Reddit comment."
] |
[
"If I get your question correctly, by \"space dilation\" you may simply be talking about the phenomenon of length contraction, which is certainly an effect of special relativity. For example, let's say we lived in a world where the speed of light was only about 12 mph. if someone were to ride past you on a bike going about 11.9 mph, they would appear to be shortened in the direction of travel; the distance from his back tire to front tire would appear to be merely inches to you (assuming you're standing still). This phenomenon arises from the same calculations as those which result in time dilation (Lorentz transformations)."
] |
[
"So, if a particle that is moving along x with vx, then feels a force along y, its vx will decrease, because vx2 + vy2 must be < c2.",
"Your use of c here confuses me. Are you using it to represent light/\"time\" speed or was it a random variable? Or is the c we use to represent light speed capable of representing the movement of the vessel in my hypothetical as well?"
] |
[
"Is there anything more center in an object than its center of gravity?"
] |
[
false
] |
This might be touching on the philosophical, but when doing physics and simplifying reality for the sake of solving a problem, is there any phenomena that's more of a literal point-particle than the exact center of gravity of an object?
|
[
"It depends on the context, I suppose. If you're talking about gravity, then the center of gravity is probably the most \"center\" you can get. If you're talking about inertia, the center of mass (which appears to be the same as the center of gravity, although we aren't entirely certain). If you're talking about E&M, the center of charge would probably be more relevant."
] |
[
"If you're talking about inertia, the center of mass (which appears to be the same as the center of gravity, although we aren't entirely certain)",
"Not if the object is in an inhomogeneous gravitational field. The center of mass is independent of said field, the canter of gravity is not."
] |
[
"You're right, in an inhomogeneous field (OP - that just means the force of gravity isn't the same everywhere on the object), the center of mass is not the same as center of gravity."
] |
[
"Is there a scientific consensus on gluten? What is it?"
] |
[
false
] | null |
[
"I'm afraid I don't understand what you are getting at. Gluten is a protein. Do you have a question beyond what can be found on wikipedia? "
] |
[
"I'm asking about the gluten intolerance fad, specifically. "
] |
[
"As in, \"Do people have a gluten intolerance and how common is it?\" something like that? I recommend making a new post phrased more closely to that; the current post doesn't seem to quite get at that."
] |
[
"Is Human/Animal transplant possible?"
] |
[
false
] |
Could an animal part successfully be transplanted onto a human subject? Either an organ or, more outlandish, a limb. Could it be possible in the process of a complete blood transfusion of human blood to the animal limb also a preservation process to keep both human and animal tissues healthy and functioning, it could work.
|
[
"We've done this many times. ",
"One story here",
"A lot of tissue today still comes from animals. Heart valves from cows/pigs are still in use for example.",
"Even ",
"PBS",
" did a special not that long about this exact topic as well. (Albeit with some terrible biases and less of a focus on the science)",
"A limb however, is a much much greater challenge, and presents many more risks than the things that we have so far accomplished. ",
"Xenotransplantation",
" has many risks and other concerns associated with it.",
"As a related aside, check out this story: ",
"Dr. Robert White transplants monkey heads",
" or ",
"Dr. Demikhov makes a two headed dog."
] |
[
"I am more interested in limbs. Limbs without a human equivalent such as tails, paws, fins, or ears. "
] |
[
"Ethic's boards would not allow such a procedure to occur at the majority of the centres equipped to do such a thing.",
"The problems that present after this are those of control. I'm presuming you want the limb to be controllable. Nerve regeneration, and connection and innervation is something we're barely able to manage in small tissue allowgrafts. Xenografts would multiply this problem, and I know of no information relating to the effects of joining animal and human sensory and motory control nerves.",
"The problems of rejection grow exponentially as you increase the amount of tissue grafted as well."
] |
[
"flair:'Neuroscience' If you were to \"mentally practice\" tennis, would the parts of your brain normally associated with actually playing tennis (especially movement) be activated as a result?"
] |
[
false
] |
If those parts are activated, why are your limbs not actually moving? EDIT: I accidentally broke my flair first time 'round, sorry.
|
[
"Similar regions corresponding to that activity would but not the motor neurons. Mental practice is very beneficial however it has to be accompanied with actual practice and going through those motions. Mental practice on its own will not be sufficient. "
] |
[
"There are case reports and use of functional MRI allows us physicians to see what parts of the brains are indeed active ",
"Here is a good article to read.",
"https://www.nature.com/news/neuroscience-the-mind-reader-1.10816",
" "
] |
[
"Any source for that information? I've been curious about this for a while"
] |
[
"How do I safely switch my sleep schedule?"
] |
[
false
] |
I just started a new job and finished my two week training. I start night shift on Monday at 6pm to 6am. What is the safest way to flip my days and my nights?
|
[
"Food"
] |
[
"I've abruptly switched sleep cycles many times before and there is absolutely nothing wrong wi"
] |
[
"the second option works for me twice a week. i work 4 nights. wednesday is my shambling day- i stay up all day so i can sleep through the night, then be functional thursday and friday. friday night i stay up all night to prepare for saturday night's shift, and am just as much of a zombie, but since i don't interact with anyone it's nowhere near as interesting. it is kind of weird how it makes for a 6-\"day\" (as in waking) week..."
] |
[
"Why is not completing a full course of antibiotics dangerous?"
] |
[
false
] |
I understand it increases the bacteria resistance, but why? If resistant strains are caused by the antibiotics killing off all bacteria apart from ones that have had a random mutation that makes them resistance then why does not completing the full course have any difference? If the partial course kills off all the non-resistant bacteria then it will be the same as taking the full course, but if it doesn't completely wipe out the non-resistant bacteria then it would be the same as not taking any antibiotic at all... The antibiotic can only be a driving force for selection not mutation
|
[
"I think the disconnect here is that the antibiotic-resistant bacteria are ",
", not immune. It takes more antibiotics over a longer time period to make sure that they're dead.",
"Failing to do so results in the resistant bacteria potentially reinfecting you, and increasing the probability that they'll be able to mutate into something even ",
" resistant (since they're stating from a resistant strain)."
] |
[
"Let's say you're sick with some bacteria. There's probably billions of them floating around in you. So you go to the doc and he says \"hmm, looks like you need some antibiotics.\" So you go an take them. Anyhow, let's say 1% of them can resist this antibiotic. So in the first 24-48 hours, you wipe out billions of them, but the remaining 100 million or so (remember, 1%) are cooking along going \"eh, not so bad\". The antibiotic is putting a metabolic burden on them, though, so they are not as fit as their (now dead) peers.",
"Then they start repopulating. Phase two, bitch! Never saw that coming. Except for your immune system, who was tackling the job from Day one, like an aid worker at ground zero, fighting an uphill battle, until the reinforcements arrived (the antibiotics), and your immune system says \"Sweet zombie Jesus, thank you Spacedementia87 and your foresight in helping us fight the good fight.\"",
"Now here's the catch: bacteria replicate ",
" rapidly. Like, they divide every 30 minute on average. Under optimal conditions, they could repopulate in less than a day (different bacteria are vastly different, I use this only to tell a generic story, your mileage may vary). But these aren't optimal conditions. As long as you keep dosing the little guys with antibiotics, you maintain the pressure (we call it selective pressure) to keep that resistance gene around and keep making whatever enzyme it is and (usually) power it--that all takes energy, which the bacteria could otherwise use to fight the immune system or reproduce. ",
" this can be a slow process, though. It will take 10-14 days for your body to produce antibodies specific to this infection.",
"So, you decide to stop taking the meds. Pressure lifted, but your immune system isn't ready yet. BAM! You just brought a knife to a (tiny) gun fight! The bacteria reproduce, quickly, ",
"all** have the resistance gene*! You go back to the Dr., and you get more antibiotics, and sure, they might keep the bacteria in check, but now your immune system is fighting billions of bacteria again, and, well, yeah, sucks to be a lymphocyte that day!",
"Moral: finish your meds. A side note--bacteria can share genes, between species even. And since there are so many more bacteria with that resistance gene in your body, they could share it with other bacteria. Which is roughly how these multiple-drug resistant bacteria came to be--we bred them through our laziness (and indiscriminate use of antibiotics, but that's another story)."
] |
[
"There was a discussion on this a while ago, with ",
"one excellent comment in particular",
" that got bestof'd."
] |
[
"Relationship between the Thickness & Magnetic field penetration of a type-II superconductor?"
] |
[
false
] |
As I'm learning more about the " " relevant to type-II superconductor's, I'm curious if there is a proportionality between a material's thickness, and the magnetic field penetration? The greater thickness = Greater expulsion?
|
[
"Meissner effect is present in all superconductors, not just type-IIs (it's actually the defining characteristic of a superconductor). And the energy of the expelled magnetic field is the energy that the superconductor \"saves\" by condensing, so it tries to expel it uniformly from all of it's volume. That effect is not perfect, in a sense, as the surface supercurrents have limited capability to do so, which leads to a thin layer on the surface, where the magnetic field is not completely zero and the thickness of the layer is called the magnetic (or London) penetration depth. In type-I superconductors, the Meissner effect gets stronger with thickness when the superconductor is thinner than its penetration depth, but once you cross that threshold, the inner volume doesn't see any magnetic fields and the thickness doesn't matter.",
"In type-IIs, it's a bit of a different story, because those will actually let magnetic field into the volume through flux tubes called ",
"Abrikosov vortices",
". Those are small tubes of weakly superconducting volume, that carry a quantum of magnetic flux and are screened from the rest of the material by rotating supercurrents (thus the name)."
] |
[
"Are London's equations still applied to this phenomenon?",
"No. London equations assume constant and uniform order parameter in the whole superconducting volume. You need to locally suppress it to allow a vortex to form, so you either use the Ginzburg-Landau equations or BCS theory.",
"Meaning, the depth of Fluxon's penetrating the SC(type-II) still relies to the thickness of the material? Where thick SC's could have volumes where the fluxon's are none.",
"Once a flux tube enters the superconductor, it has to also exit. It cannot just stop inside the superconductor (or inside any material, this is mostly because magnetic field have zero divergence). This has nothing to do with superconductor thickness",
"The flux goes through and it has supercurrent circulating around it, which confines it to an area of roughly coherence length squared and decays at the distance of the penetration depth, like ",
"this",
". Again, nothing to do with the superconductor thickness."
] |
[
"Thank you for that. ",
"I'm reading more(beyond the link provided) about the Fluxons. Are London's equations still applied to this phenomenon? Meaning, the depth of Fluxon's penetrating the SC(type-II) still relies to the thickness of the material? Where thick SC's could have volumes where the fluxon's are none.",
": Reviewing the link you provided again, it seems true and I missed that. Also, referenced in the equations:"
] |
[
"Need help debunking alternative medicine [Biology, Atomic Physics]"
] |
[
false
] |
So, my mother has gotten into alternative medicines which I consider to be total malarkey, such as this . What these devices claim to do is " exposes the electrical current to a natural subtle energy field composed of a range of frequencies that are vital to your health". I've taken the shield in question apart, and it appears to be a simple lightbulb with motion sensor. Can anyone see a problem to point at to prove the fraudulency of this "house shield" Of course, if there turn out to be truth behind this, I'll eat my shoe.
|
[
"How about the part that says:",
"Any results from the use of any products offered are due to the body's natural ability to care for itself as intended by our Creator.",
"If that's not a tacit admission that their products do nothing at all, I don't know what would be."
] |
[
"So, for science I went to read this website. But you don't have to: ",
"Safe~Connect Plus+ House Shields soften and reformat the electrical emissions with 200+ encoded balancing frequencies for home or office! This thoroughly exposes the electrical current to a natural subtle energy field composed of a range of frequencies that are vital to your health, keeping you safe and grounded. One House Shield protects up to 2000 sq ft. For a two-story house, we recommend using one upstairs at one end and another downstairs at the opposite end of the house. These Shields are approx. (110 mm/4 inches) tall from the base to the tip and come in stylish designs. Even though these plug-in units are created with an LED bulb, the bulb will eventually go out, but the energetic harmonious field will not stop being emitted – thus they last forever. Just plug these attractive Shields into any outlet as you would a night light, and it will make your entire home and office safe from the weakening effects of electrical wiring, appliances, computers, vacuum cleaners, etc.!",
"I really don't know what to say about this. I is such nonsense that there is no gripping point to start arguing against it... Can someone else try?"
] |
[
"Yeah, I have heard about it before, but it's absolute nonsense. \nHere's one that (kind of) debunks that electricity would cause cancer. ",
"http://www.cancer.gov/cancertopics/factsheet/Risk/magnetic-fields",
" ",
"It is hard to search for this, anyway, because if you search for electricity and health you end up with all kinds of websites claiming that there ARE health issues. One big warning sign is when they give a list of all kinds of different diseases, without explaining why electricity would attribute to them.",
"Then again, even when there would be diseases caused (partly) by the amount of electricity around you, there is NO WAY that this shield could prevent that. As I see it, this shield is made of a LED and glass, and the LED will use electricity to create light and, the website claims, when the LED is broken, the shield will still work (but, I'm pretty sure, will strangely enough not use electricity anymore, because the LED is broken)."
] |
[
"Could dogs and cats live longer, if we bred them that way?"
] |
[
false
] |
So I was thinking today: over the past 100 years or so, the life-expectancy of humans has increased dramatically. This is, I would assume, due to advancements in medicine and technology. This led me to wonder...are we able to breed dogs and cats to live longer, given our medical technology, and for some reason (cost, ethics, etc.) we haven't? Or did they live shorter lives in the past and medical advancements have already increased their lifespans?
|
[
"can longevity be a selectively bred trait? yes absolutely. but it isnt medical technology that gave us the modern dog, it was old fashioned selective breeding programs. eg; breed the 2 longest living dogs available together, and repeat for many generations. modern medicine and quality nutrition are still the strongest factors for living a long healthy life though."
] |
[
"semen samples, then wait."
] |
[
"You don't know how long they are gonna live while they are still fertile.",
"Breed cats. Collect sperm cells and eggs while they are still young and fertile. Wait until cats all die. Note which cats lived longer. In vitro fertilize eggs of the longest living female with the sperm of the longest living male. Breed cats. Rinse, repeat.",
"If you want to have a healthy mix of genes, which looks like a good idea, do it with several populations of cats in parallel and mix them at each reproduction round (cross longest-living female of population A with longest-living male of population B, and viceversa).",
"Yes, it would take a very long time, but it is definitely possible."
] |
[
"[physics] How are rigid bodies affected by spacetime curvature?"
] |
[
false
] |
explains a Lovecraft story by saying that the characters are inside a bubble of spacetime curvature, so everything around them looks distorted by gravitational lensing. But the explanation makes it sound like things only distorted, but otherwise retain the shape they would have in Euclidean space. Is this scientifically accurate? : If I were to find a mile-long rigid rod and drop it into a bubble with negative spacetime curvature, would it stay straight?
|
[
"There is not such thing as a truly rigid body. A mile-long rod is made up of atoms held together by chemical bonds. (This is related to another common question about ",
"why a perfectly rigid rod can't be used to communicate faster than light",
".)",
"The curvature of spacetime is just gravity. Ever seen a beam bend under its own weight? That is the curvature of spacetime affecting a rigid body. Edit: As mentioned by others, a better example is ",
"tidal forces",
" which distorts bodies purely through gravity alone (the same way the moon affects our tides)."
] |
[
"I don't quite like the example though. The beam is not bending due to a variation in gravity. The gravity is affecting the entire length of the beam almost uniformly. It is the strain it experiences from the gravitational loading while being supported at one/both ends that makes it bend. ",
"I read your post and it made it sound like the gravity alone was making it bend."
] |
[
"Ever seen a beam bend under its own weight? That is the curvature of spacetime affecting a rigid body.",
"Not quite. The curve a beam makes bending under its weight depends on the rigidity and density of the material, not on spacetime curvature alone.",
"A better example would be something falling in free fall. Throw a rock and watch the parabolic curve it makes, that's the curvature of spacetime."
] |
[
"How exactly do Black Holes die? If nothing can escape a Black Hole, how can they evaporate?"
] |
[
false
] | null |
[
"The mechanism proposed by Hawking in his original paper follows.",
"Particles pop into and out of existence all the time. They \"borrow\" energy from the vacuum, pop into existence as a particle-antiparticle pair, and then swiftly collide and annihilate. This is a known fact.",
"Now comes Hawking's original speculation. Near a black hole, something funny happens. There's a distance from the black hole called the event horizon - anything closer than that distance necessarily falls in, while anything further out can escape if it goes fast enough. When these particle-antiparticle pairs pop into existence near the event horizon, sometimes one will go in and the other will go off into space. It appears to the outside world that the black hole has emitted a particle. The energy to create those particles is not \"repaid\" by annihilation, hence their masses must add up to zero because total energy must be preserved. But since the particle emitted must have positive mass, we must observe the infalling particle to have negative mass, thus reducing the mass of the black hole.",
"An alternative conceptualization imagines pair production just INTERIOR to the event horizon. Particles sometimes do something funny called \"tunneling,\" where they disappear and reappear a short distance away. It's possible that particle pairs are being produced inside the event horizon, and then one particle is tunneling out.",
"At the end of the day, it's not exactly known by what mechanism Hawking radiation occurs. We know that it MUST occur in order for the laws of physics to be consistent, as far as we understand them. Black holes are perfect black bodies, and that entails black body radiation. ",
"It should be noted that every black hole we have ever observed emits less Hawking radiation than it absorbs from background sources like the cosmic microwave background. A black hole would have to weigh as little as a moon for it to be losing mass."
] |
[
"This phenomenon was first observed in a counted cloud chamber experiment by P. Blackett, which won him the 1948 Nobel prize in physics. This experiment is now down every year in college physics labs around the world. You can perform it yourself at home; ",
"here are directions for making your own cloud chamber.",
"Further evidence for pair production was demonstrated by Lawrence Livermore when they shone the petawatt Titan laser at a gold target. The energy excited the pairs, allowing them to separate before annihilation and be counted.",
"Perhaps the coolest evidence of pair production is supernova SN2006gy, which was likely caused by increased pair production rates destablizing the star causing it to explode."
] |
[
"Anti-particles have positive mass as well, in general.",
"The short answer is, the infalling particle would have positive mass in its local frame but to an outside observer, it would appear to have negative mass, simply by nature of being the infalling particle. "
] |
[
"How small would an object have to be to orbit my body?"
] |
[
false
] |
I understand that we all have mass and there for we all have some sort of gravitational pull. I was just wondering if there could be a small enough object captured in my own gravity that would orbit me. I'm not sure of the physics for this to happen, but would I need to be still or rotate on a platform. Or would the object be so small that it wouldn't be affected by my gravity. Like atom size or things like quarks and smaller particles. Thanks for any imput.
|
[
"Objects in orbit will have the same radius and time period of orbit regardless of their mass (i.e. a satellite and a person could orbit the Earth at the same radius and velocity). As a rough guideline, in outer space an object could orbit a human (of mass 80kg) at a radius of 1m in almost exactly one day. The time period is proportional to radius",
" and (mass of body about which the object is orbiting)"
] |
[
"There is no upper limit. Keep in mind that when you are orbiting an object, both you and the object are actually orbiting around a common center of mass. The orbital period around that center of mass is different for you and the object."
] |
[
"We can say there are no other interacting gravitational bodies. The mass of the object to orbit you can be an orange, a bowling ball, a grain of sand, or something smaller. As long as the velocity of the orbiting object isn't great enough to escape orbit with a given distance, it will remain in orbit, although moving very, very slow. It's all ratios with those constants.",
"If you're 50 kg, and lets say an orange weighs .1 kg, and it's .1 meters away. The gravitational force is 3.335e-8 N. The math regarding orbital periods and escape velocity, get's much too complicated for me. I would estimate that the orange's velocity would need to be so low, it would take days or months for one orbit."
] |
[
"How does a diagnosis of a mental disorder work?"
] |
[
false
] |
[deleted]
|
[
"Mental health professionals, such as psychiatrists and psychologists, are certified, trained clinicians that can diagnose a mental disorder. These mental health professionals use the DSM-V (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition), which is the latest edition. This manual is published by the American Psychiatric Association (APA)."
] |
[
"Can I add diagnosis can also be made using the ICD-10 (WHO, 1992)"
] |
[
"Yes a therapist decides. There are specific criteria for most disorders, but very broadly speaking, it tends to be able to be summarized as a disorder if:",
"It has been going on for a good long while (many months typically, 6 is common across definitions of different ones), AND ",
"It's \"ruining your life\" in some substantial way. Typical sufficient ways being things like causing you to not hold down jobs, causing you to lose important relationships, causing you to fail at major goals, or just hate yourself all the time, and definitely anything including self harm or harm of others, AND",
"The method by which it is harming your life fits a characteristic pattern as per the specific disorder in question. (If the above two things are true, there's probably some disorder, but you would still need to / want to categorize the right one correctly). Such as if the harm is coming from complete lack of motivation, lethargy, hopelessness, that's more likely to be depression. If it's a mixture of that and manic, over-hyped phases in certain ratios, it's more likely to be bipolar disorder, etc.",
"But again there's a lot more detail than that therapists train on. Individual ones may have longer time periods required, only include some sorts of negative results, or whatever. I'm just trying to loosely summarize the \"typical\" trajectory of a diagnosis of many types of common disorders."
] |
[
"How much mass does the sun lose per second as light - photons - alone?"
] |
[
false
] | null |
[
"Let's find out!",
"If we go to ",
"the sun's Wikipedia page",
" and look at the infobar on the right, it says, in \"Physical Characteristics,\" it says solar luminosity is 3.846×10",
" W, or 3.846×10",
" J/sec. So every second, it sends out 3.846×10",
" J. ",
"Now we just plug in the most famous formula ever:",
"e=mc",
"3.846×10",
" J = m×(299792458 m / s)",
"3.846×10",
" J = m×8.98755179 × 10",
" m",
" s",
"4279252114.33 kg = m",
"So, the sun loses about 4.3 billion kilograms a second."
] |
[
"The sun emits ",
"6.3E6 W/m",
" of electromagnetic radiation from its surface",
". The ",
"surface area of the sun is 6.088E12 km",
", or 6.088E18 m",
" Multiplying these gives roughly 3.6E25 W, or Joules of energy per second. Using the old E=mc",
" this comes out to roughly 4E9 kg of mass (four billion kilograms). ",
"Oooh! Dang, I was off by a little bit (",
"http://en.wikipedia.org/wiki/Orders_of_magnitude_(mass)#106_to_1011_kg",
"). I guess the lesson is...wikipedia is much faster than calculating."
] |
[
"They have no rest mass, but because E=mc",
" as the sun radiates energy it loses the corresponding amount of mass."
] |
[
"Why does your body temperature drop when you sleep, while it also gets colder at night?"
] |
[
false
] |
I understand that it saves energy to drop your body temperature, but if we were outside, we would freeze to death. Since we sleep at night, and the temperature drops at night, it makes more sense that we would warm up. It doesn't make sense to me how dropping in temperature would be an evolutionary advantage. But I'm sure I'm missing something, and I'm hoping you guys could help me out. Thanks!
|
[
"Well since your heartrate slows down, you don't work (means your muscle don't work too much), and your brain shuts down, you don't generate as much heat as a side product.\nSo your body would just use energy to heat up your body by for exsample shivering.\nNow since the Energy transfered - from your body to the air surrounding you - rises with the temperature difference (Q=k",
"dT, in which dt is (T(body)-T(air)),you loose more energy the warmer your body is, since A is just how big you are, and k is mostly for example how windy it is.",
"So your body cools down because you would lose a lot more energy when you just would keep your 36 °C all the time. And since you need all the energie you can get to hunt the next mammoth in the morning, you should better cuddle up with your family in a cozy cave to not freeze to death."
] |
[
"It's actually the other way around-- it is not that your body temperature drops when you fall sleep, it is that a drop in body temperature makes you sleepy. Even if you stay awake all night, the body temperature drop will occur. And even if your activity level is constant in day and night, the body temperature drop will still occur. This is all part of your circadian rhythm. ",
"Source: ",
"http://www.sciencedaily.com/releases/2010/10/101014144314.htm",
"As for why, the authors of the above study posit it might be due to an evolutionary artifact that we evolved from species that were more reactive to external temperatures than humans are. (Someone correct me on the terminology if I'm wrong-- I know very little about the science behind evolution)."
] |
[
"Correct me if I'm wrong:",
"Most of your muscles are ",
" inactive when you fall asleep. Your parasympathetic nervous system also takes the lead while your sympathetic nervous system calms down. The results of this is vasoconstriction in systemic blood vessels/vasodilation in enteric blood vessels. That said, since your muscles get less blood and are less active, their cell metabolism drops, which reduces the amount of heat produced by your body. ",
"Your enteric blood vessels dilate, so your digestion kicks in, which brings your GI cell metabolism up, producing more heat than usual, compensating for the lack of muscle activity.",
"The evolutionnary advantage here would be that your body redirects blood flow to tissues that are being used at the moment: without redirection, you'd waste resources on your muscles while you are asleep. If those processes wouldn't happen, you'd probably lack the resources to get back up in the morning."
] |
[
"Which species are flourishing that we don't hear about?"
] |
[
false
] |
We hear a lot about species going extinct in the news - are there any species that have seen a large growth of population in recent history?
|
[
"The wolves in Yellowstone National Park have responded very well to the 1995 Wolf reintroduction program. Though this is perhaps a little misleading as the wolves that were reintroduced were not endangered and was not the same species that had been hunted to extinction within the park's borders. ",
"As an aside the reintroduction of the wolves was key to reducing the high elk population, and also saw the beaver, and bison populations increase as a result of the redistributed resources. ",
"Yellowstone is a wonderful place, and I highly recommend visiting. ",
"Here's an article from 2011 reflecting on the 15th anniversary of the start of the program",
". "
] |
[
"Many of the species that are well adapted to live alongside humans in cities are increasing in both population and range as urban areas take over the landscape.",
"In North America, there are coyotes, raccoons, opossums, rats, pigeons, house sparrows, geese, starlings and other species (most of which we consider pests) that are thriving by adapting to the new environments we provide.",
"Invasive species that are accidentally moved into new areas by human transport also thrive when taken away from the natural enemy complexes that exist to control them in their native environments. Emerald ash borer, quagga & zebra mussels, Asian carp, snakeheads, gypsy moth, and wild boars are just some examples.",
"In the oceans, crab-eater seals (that feed on krill) exploded in population when humans nearly wiped out their chief competitors - the baleen whales."
] |
[
"I have read that both deer and crow populations in North America are much higher than they were before Europeans came.",
"Despite loss of habitat, being killed by cars, and regularly hunted, the deer benefit greatly from an increased food supply from farms.",
"Crows have also long benefited from increased food at farms. But more recently they've adapted well to urban/suburban areas. There's lots of food that can be scavenged from trash and yards, and they are less likely to be shot."
] |
[
"Would it be possible to boost into space and hang there 'solar-stationary' for a year and wait for the earth to rotate back to your position?"
] |
[
false
] |
I'm guessing it'd take huge amounts of energy get there, but once free of our planet's gravity well, could your spacecraft just 'hang in space' while the solar system revolved? Am I missing something elementary? EDIT: For clarity, I meant to boost to a point where you could 'hang' without expending lots of energy to stay in place while the rest of the solar system moved.
|
[
"Actually I don't think you could.... without an impossibly large supply of fuel to constantly thrust you away from the Sun. Since you are no longer obiting the sun, you would fall into it, without a constant thrust in the oposite direction."
] |
[
"Earth's orbital speed is about 30 km/sec, so you would have to spend a lot of energy getting to that speed. On the other hand, getting to a geosynchronous orbit around the Earth only requires getting to around 3 km/s, so it would be much cheaper just to stay in stationary orbit around the Earth."
] |
[
"So if you boosted away from earth to 30km/s in the direction opposite to its solar orbit, you'd be in a stationary position relative to the sun? Regardless of cost/feasibility... you'd then need some energy to stop from falling toward the sun? "
] |
[
"Does our heart muscle ever cramp up like the rest of our muscles? Is that what a heart attack is?"
] |
[
false
] | null |
[
"A couple things are different between heart muscle and skeletal muscle. ",
"First: Oxygen. The heart is the first organ to get freshly oxygenated blood. This means it doesn't go aerobic as often or as severely as skeletal muscles (normally or during exercise).",
"Second: The heart is primarily a fat burning organ. This means it uses beta-oxidation of fatty acids to make fuel for its mitochondria which does not go through glycolysis and does not make lactic acid. ",
"Third: Even though the heart will choose fat if it has a choice, it is not picky. It will burn just about any fuel it has available. glucose keytone bodies, pyruvate, and lactate ",
"source",
". So even if lactate does build up, the heart can use some of it as fuel. ",
"So it is very rare that a healthy heart, unless pushed to the extreme of physical activity, is going to hit a point where lactic acid actually accumulates as it does in skeletal muscles",
"An unhealthy heart, one with a blockage in the coronary artery will have oxygen starvation and have to rely on anaerobic respiration which will produce lactic acid as a byproduct. ",
"source"
] |
[
"A heart attack is a myocardial infraction, which basically means the heart muscles aren't getting enough oxygen to respire(contract) and stop working. If I remember correctly a cramp occurs when there is a high build up of lactic acid in respiring tissue, which is a by product of anaerobic respiration. But the fundamental ideas are similar as both tissues cannot respire, a heart attack is a lack of oxygen where as a cramp is a build up of c02 and lactic acid. ",
"Tldr heart attack is lack of oxygen, cramp is build up of co2 and lactic acid"
] |
[
"But... ",
" the heart cramp from lactic acid buildup?"
] |
[
"What's the oldest telescope still in service and making meaningful discoveries and contributions?"
] |
[
false
] | null |
[
"good question considering telescopes don't really wear out, so a well made telescope could be used and useful for a long time.",
"But I don't know the answer, the only one that comes to mind is the Panama telescope, but I do not think it is still in use, but was for a long time.",
"Panama tele",
"edit: That is \"Yerkes Observatory\" I believe, in that pic"
] |
[
"I believe you're talking about the ",
"Yerkes 40-inch refractor",
", built in 1897. I've never heard it called the \"Panama telescope\", and I know folks who use it for research. ",
"Its location is now pretty light-polluted and there was a brief consideration a few years ago from the University of Chicago to tear it down for condo developers. Last I heard, though, it's still being used for asteroid surveys."
] |
[
"There is a 1.2m telescope at the Observatoire de Haute Provence that is still used for science and was ",
"originally installed in Paris in 1872",
"! The camera is from the 1980s though, which makes it a real pain to use..."
] |
[
"If certain micronutrients affect the absorption of each other, how do multivitamins work?"
] |
[
false
] |
I would guess the vitamins are combined in certain ratios? Or manuracturers don't care?
|
[
"multivitamins don't necessarily work",
"with a lot of these products, manufacturers don't care. if you are going to purchase vitamins, definitely do your research first because there is a whole lot of snake oil and not terribly a lot of scientific support."
] |
[
"Additionally, many supplements don't even contain what's on the label. There is zero federal testing and more or less no accountability in the US.",
"Citation",
"Additional ",
"Citation",
" about low efficacy",
"Another ",
"Citation"
] |
[
"It's complicated...",
" In addition to certain nutrients effecting others, there are certain suppliments whose contents just do not translate into the same effect that eating the same substance would have if eaten from a naturally occuring food. There are tons of substances in food that we do not understand, but almost certainly play some role in allowing us to properly digest and absorb the other nutrients in the food. "
] |
[
"What would dumping molten gold on a person's head actually do?"
] |
[
false
] | null |
[
"Death would almost certainly be by suffocation, assuming the gold covers the mouth and makes its way into the windpipe. You'd probably have 10-20 seconds of 'useful' agonising consciousness before passing out due to lack of oxygen (as the person would be breathless before due to fear, not breathe in in perparation, and be using a lot of oxygen struggling in fight or flight). Brain death, maybe a couple of minutes, I'm not sure what the timescale is for suffocation."
] |
[
"Additionally, death may occur due to burn sensations, tachycardia and high BP, as well as through the weight of the immense pressure of the gold quickly cooling around the cranium due to vast temperature differences between the gold and your body."
] |
[
"Okay, this question intrigued me, so I did some sleuthing. Unlike the other poster, I don't think suffocation is the primary way to die because of this, I think rather it'd be the immense temperatures being inflicted on the brain. Think of how dangerous it is for someone to have a fever of 105 F (sorry for non-SI units). Obviously, this is acute so the threshold is likely higher, but I do think it is illustrate of the danger of high temperatures. ",
"Now, obviously, your skull is a very good thermal insulator, and it would likely protect you from a lot of the thermal shock. It'd actually be a pretty cool heat flow problem, actually, but unfortunately I don't have the time to sit down and figure that one out. But my best guess is that you would get perhaps a couple tens of C increase in T at the brain skull barrier in areas where the skull is thinner. ",
"This would cause severe problems. It would essentially stop all brain function in the affected region. The blood brain barrier would ",
"cease",
" to really function, causing brain death in short order. I'm very far removed from biology, so I don't know if that strictly would be enough to kill you, or whether it'd be the shock, but anyways, that's my 2 cents. ",
"Interestingly death by molten gold has been done before, at least in ",
"legend",
", though that mechanism was ingestion."
] |
[
"If heat is how fast particles are moving around in a volume, then why doesn't wind feel hotter than stationary air?"
] |
[
false
] | null |
[
"Heat is how fast particles are ",
" moving around.\nIf there is some wind, heat is not given by the general motion of the air, but by the random motions of the particles that adds to it. So wind doesn't change the temperature.",
"And wind feels colder because it removes more heat from your body."
] |
[
"http://www.reddit.com/r/askscience/comments/faf9j/if_temperature_is_the_average_speed_of_particles/",
"http://www.reddit.com/r/AskReddit/comments/egnyk/if_temperature_is_kinetic_energy_how_does_cold/",
"http://www.reddit.com/r/AskReddit/comments/cjpn6/if_the_temperature_of_a_gas_is_the_speed_the/",
"and a followup:",
"http://www.reddit.com/r/askscience/comments/fbbjf/following_on_snailhunters_earlier_question_at/"
] |
[
"Because velocity of particle that's \"responsible\" for temperature is ~10 times bigger than velocity of wind. At 70F average air molecule is moving at speed close to 1000 miles per hour. Helium for example is moving close to 3000 mph. Heavier particles move slower, but still way way faster than any wind.",
"http://www.newton.dep.anl.gov/askasci/chem03/chem03448.htm"
] |
[
"Does the scientific method and our study of the universe assume that the laws of physics are unchanging ?"
] |
[
false
] |
The scientific method, as I understand it, pretty much hinges on the repeatability of observations from the same experiment. This then allows you to change one variable at a time and learn. Our study of the universe sometimes brings up light from stars that are millions of light years away. We infer distance, time, content, size/shape from this "old" light. Is there a reason to be sure that the laws of physics are unchanging? If they are not, both the above activities would be jeopardized from a learning point of view, right? In other words, of all the n parameters (some known, some unknown) in the mathematical equations describing or modeling the behavior of the universe, what if time itself is a parameter? Or the space coordinates ?
|
[
"The important thing is to make testable statements rather than just declarations. \"If this constant varied in space or time, how would we measure that?\" is a more powerful question than \"what if things are changing?\"",
"With the former, you can do stuff like ",
"this",
"."
] |
[
"First line in the introduction: \"Some constants of nature are thought to be more constant than others\". TIL. thanks :)",
"But while that's interesting, my question is not limited to changing constants. Maybe it's more of a ",
"/r/philosophyofscience",
" question. if the \"laws\" were unpredictable and changing with space/time, science might be hard to the point of impossible. Good for us that we haven't seen any evidence of that so far."
] |
[
"A mechanism for physical laws to change form completely is not really considered likely. I mean what kind of example would you give? Gravity suddenly becoming repulsive? Electrons disappearing?",
"You got to remember that the predictions made by physical sciences don't just have to match observations of current phenomena but also can be tested against the evolution of the universe. Allowing constraints to be placed on how much they have changed.",
"Iorgfeflkd brings up the idea of our physical constants changing with time, this is far more seriously considered possible. Even though we have no understanding of how such a thing might happen we at least believe it to be within reason for it to happen and have conducted many tests in order to assess if they are indeed changing and, if so, by how much. "
] |
[
"How were the first precision instruments made?"
] |
[
false
] |
As humanity developed more advanced tools over time, the tools built to make more tools had to be more and more precise. For example, in order to build a mill or a lathe, you need a very flat surface, so you have a good reference for the position of the cutting head. But these tools are just made on larger mills and lathes. At some point if you go back far enough, somebody must have thought, "I want to build a mill" and needed a way of machining a hunk of metal perfectly flat. How did they do it? And how did reference flat surface get created? It's turtles all the way down, right? Anyhow, I'm wondering what techniques are used to create references -- flat surfaces, spherical surfaces, level surfaces, straight lines, square corners, etc. -- without having those things to begin with.
|
[
"This is a broad question and no doubt people from many fields will have things to add, but I can tell you a few aspects of it. First of all, it's generally an iterative process, in which you use available tools and measuring techniques to create more precise tools. If you want to make a precisely shaped instrument, the first step is to get some sort of blueprint/drawing/design/outline. At least since the Greeks, the use of a compass and straightedge to create straight lines and precise geometry has been well understood. ",
"This site lists a number of the many, many geometrical shapes and angles that can be drawn with simply a compass, straight edge, and pencil",
". The Greeks, of course, did not have algebra, so they relied quite strongly on geometry in their mathematics. Never underestimate the capabilities of a geometer with a steady hand. With a level, a basic saw, and some sandpaper you can make a piece of wood quite smooth. If you want a straight vertical line, hanging a string from a weight is quite effective. If you're just doing a basic mill, you can probably see any significant deviations from flatness by eye. Many of the geometrical/trigonometric techniques from surveying land are quite well suited to measuring deviations from flatness.",
"A blueprint is less helpful for making something spherical, but as it turns out, if you have two surfaces that are very approximately spherical (something achievable more or less by hand and eye) and you grind them against each other while rotating them around, they will become more and more spherical. This is basically how lens grinding (for spherical lenses) was done for a very long time: a lump of glass would be cut down to a roundish shape, and then a spherical object covered in pitch would be used to grind against it, and it would progressively approach a more and more spherical shape. Many early astronomers, including Galileo and Herschel, ground their own lenses or made their own mirrors.",
"During the modern period, some of the main drivers of precision technology have been clocks and firearms, followed later by steam engines, followed by automobiles and aircraft. This has been an iterative process of improvement for the most part, although some innovations like lasers have drastically improved our ability to measure small distances. Modern telescope manufacturing processes use lasers or other light to precisely measure the shape of the mirror (mirrors have completely supplanted lenses in modern astronomy)."
] |
[
"I highly recommend you read the book ",
" by Bryant and Sangwin. Another excellent book is ",
" by Moore. ",
"There are many techniques that can be used that involve a mixture of mathematics and ingenuity to get precise surfaces. One example: You can make straight edges or flat surfaces using a technique that involves 3 edges or surfaces. Let's say we want a straight edge. How do you tell if an edge is straight? Well, if you have two straight edges and you put them next to each other, they will \"fit\" with each other. There will be no gaps or anything like that. The problem is that your straight edges could actually be curved edges, where one edge is concave and the other is convex. You need a 3rd edge to compare to the other two. If all three \"fit\" together, then you know you have a straight edge on all three. "
] |
[
"Depends what you're doing, things like weight, well that's totally defined by us, so the method is get a ",
"hunk of something and say that is 1kg, it's the IPK",
". More precise/accurate scales are made by simply attempting to get it to measure this weight more accurately (or more precisely, they copy the IPK by making a hunk of metal, and making it match the IPK's mass using a balance). Other measurements are done this way, define the unit, and make the tool measure it right.",
"Things like a flat surface, well that's easy to define mathematically, and as such you can test your equipment using math (for example, use triangles to measure it in different ways, if it's flat you should get the same answer for all points). As we get better equipment we can make more accurate measurements, and improve our tools (and really, all the tools are made accurate by just doing X, measuring the result, and adjusting the tool to match the measurement, tight tolerances help make it consistent, and that's really where much of the work it. When you get to the new modern tools, well they actually do that while working, that is if you say move 1 foot, they actually move one foot, then measures itself, and repeats the process until the measurements agree (closed loop feedback) .",
"TL;DR: measure measure measure."
] |
[
"Is decline in fertility caused by multiculturalism?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines",
"/r/AskScience",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Hi,",
"Couple of things that would improve it a lot are the following:",
"Cheers."
] |
[
"How should I restate my question or do you have a different sub that would be better suited?",
"\nThanks :)"
] |
[
"and [Physics] The Solar Storm of 1859 disrupted communications equipment across the globe for 5 days, what impact would a similar event have today on our technology?"
] |
[
false
] |
Are our communications satellites shielded sufficiently to survive this? could they function through it? How would terrestrial technology be affected? Asking how greater society would be affected is probably going to fuel conjecture, so I think it would be best to only mention impacts on greater society if an impact is directly linked to an impact on our technology.
|
[
"It could cause global disruption, it might do nothing.",
"Pretty much all the effects in technology from a solar flare are from the coronal mass ejection, CME, that are normally associated with big flares.",
"Are our communications satellites shielded sufficiently to survive this? ",
"No but that isn't a worry, the large amount of energetic particles could certainly knock out some satellites. The increased drag from the CME will cause other satellites to have to expend fuel to stay in orbit, shortening their lifespans. Big flares are generally associated with a loss of contact with many satellites but some are reconnected with over the next few days.",
"Really though, there is no difference between a big CME and several small CMEs in terms of what happens to our satellites so it isn't a huge problem. ",
"It could be dangerous for astronauts in orbit. We normally have plenty of warning (2-3 days) for smaller flares but for the biggest, like the Carrington event, we have maybe only 18-24 hours. That is still plenty of time to evacuate astronauts if it is deemed unsafe and shielding on manned spaceflights tend to be stronger than unmanned.",
"How would terrestrial technology be affected?",
"On the tame side of the spectrum radio would be disrupted. The change in the ionosphere at the time of the flare from increased ionization will disrupt communications, the arrival of the CME and it's affect on the magnetic field of the Earth will also disrupt communications.",
"On the frightening side of the spectrum are geomagnetically induced currents (GIC). ",
"What causes these currents are the magnetic field that has been dragged along with the CME from the Sun squeezes and reconnects with the magnetic field of the Earth. How much the Earth's field is squeezed depends on the strength of the CME and the alignment of the fields (anti-aligned is ok, aligned is bad). This changing magnetic field produces an electric potential across the surface of the Earth. ",
"In the case of Carrington, this potential drove such high currents in the telegram wires that some caught fire and some electrocuted operators. The total voltage is proportional to the length of the conductor and we don't have wires as long as telegram wires really so we may not expect quite so widespread fires but we do expect damage to transformers.",
"Just a few tens of Volts DC from these GIC will cause a transformer to overheat. If this continues over several hours then this overheating can become so bad that the pressure in the oil coolant causes the transformer to burst, taking out electricity supply.",
"In the case of ",
"an event in march 1989",
" these GICS were big enough to take out 15 transformers in south africa and, even worse, cause a cascade of failures of transformers in Canada that resulted in large black outs.",
"If a flare the size of the Carrington event hit we would expect this to be repeated on a large scale.",
"The solar physicist in me has to constantly remind people that this risk is real and we should be working on early warning and protective systems (so they will pay as to research it) but at the same time I accept that these events are rare and the consequences? Not that scary.",
"The long term recovery could be problematic. An expert on GIC by someone who simulates them in order to find weakspots in the UK electrical grid where transformers are most at risk once told me: there are limited companies who make transformers; transformers are widely varied so are not very interchangable; there is no stockpile of spares that can be switched on and they can take years to make.",
"This could mean that a widespread global failure of transformers could take a lengthy time to fix but at the end of the day, it is just electricity. The grid can be repaired and solar flares+associated CMEs do not damage small scale devices.",
"The electric field that produces the GIC are of the order of millivolts per metre so your computer, with no wire over a metre, is 100% safe."
] |
[
"could it take down the GPS system temporarily? GPS is essential for some things."
] |
[
"It'd be quite unlikely for GPS to go down. Signal strength may deteriorate (may lose connection to satellites sporadically, especially on smaller recievers) and GPS accuracy suffers, on the order of metres, during geomagnetic storms."
] |
[
"Is the human body immune to the effects of a magnetic field no matter how strong?"
] |
[
false
] |
I know that an alternating field can have various effects, but what of a stable one? Say you had some magical permanent magnet that can put out 10, 100, or even a million tesla's, is there any point where that magnet would have a noticeable effect on me?
|
[
"Yes - at high enough magnetic fields, diamagnetic effects come into play. ",
"Around 16 T is enough to levitate a frog",
"."
] |
[
"The field in an MRI aligns the spins of atoms in your body. This is definitely a noticeable effect although not from your subjective point of view. "
] |
[
"So what would happen as I approached this hyper-powerful magnetic field? How would I notice its effects?"
] |
[
"Is it possible to test the (conductive) continuity of a single wire when you only have access to, but can't connect, the two ends?"
] |
[
false
] |
The situation I'm thinking of is an electrical wire that runs through a wall between two rooms. You can attach whatever devices to the ends you want, but there can't be another connection between the rooms and you can't use the ground/earth.
|
[
"There is a way to test the (conductive) wire length using resonances, basically setting up the wire as an antenna and measuring its frequency response and pulse echo duration. The equipment you would need for this is quite sophisticated and expensive though (at least for easy measurement. You could probably do it using a frequency generator, and oscilloscope and some time)."
] |
[
"You didn't quite think this through, did you?"
] |
[
"If this is simply a thought experiment, many options come to mind.",
"If it is a practical problem in need of a solution: Assuming you can access both rooms, connect one end of the wire to 120vac house current. Use ",
"one of these",
" to test at the other end."
] |
[
"Why don't we poop when we sleep?"
] |
[
false
] | null |
[
"The outer Sphincter (in the anus) in a voluntary muscle, only the inner sphincter is involuntary.",
"Here",
" is the wiki entry. Don't worry the pictures are drawn, no photo's"
] |
[
"This is the correct answer since noise seems to be getting upvoted now a days."
] |
[
"While this is true, it's somewhat of a non-issue in this thread, as the correct answer was posted 32 minutes after the initial question. ",
"But yeah, this is actually one of the few places in reddit I don't really want to see jokes. The mods often mass delete irrelevant comment chains when they start to outpace the actual answers, though, and I appreciate that. "
] |
[
"How do scientists find the melting point of the substances that melt at the highest temperatures?"
] |
[
false
] |
For instance, if you wanted to find the melting point of Bismuth you could just put it in a vessel made of something like platinum, that has a higher melting point. But how would one find the melting point of a substance when there are no other substances of a higher melting point to use as a container?
|
[
"Right, you could for example take a big block of that material, and melt it with, for example, a laser just at one point and determine the temperature via radiation.",
"Like a huge solid block of ice, you can still have a pool of melted water on its top without the water melting down the whole block."
] |
[
"Right, you could for example take a big block of that material, and melt it with, for example, a laser just at one point and determine the temperature via radiation.",
"Like a huge solid block of ice, you can still have a pool of melted water on its top without the water melting down the whole block."
] |
[
"Indeed. Here is a ",
"figure",
" taken from a paper describing the measurement of the melting point of tungsten. A laser is used to heat a tungsten rod and cameras record when the material liquefies. The temperature may be determined from the emission spectrum.",
"Source: Hiernaut, J-P., et al. \"Determination of the melting point and of the spectral and total emissivities of tungsten, tantalum, and molybdenum in the solid and liquid states with a six-wavelength pyrometer.\" High Temperatures. High Pressures 18.6 (1986): 627-633."
] |
[
"How is the queen ant or bee determined? Can there be more than one? What if she dies?"
] |
[
false
] |
[deleted]
|
[
"I suggest posting to Biology."
] |
[
"I'm not too sure about the ants, but I imagine it's similar to the bees. The queen bee is raised to be queen from the larval stage. It's a regular worker larva, but it gets fed much more, and then develops into a queen bee. Bee larvae are raised in cells in the honeycomb structure. The queen cells can be distuingished from the worker cells by their larger size.",
"Once a new queen hatches, she will either have to fight and kill the old queen, or leave the hive, taking a part of the colony with her to form a swarm, thus making a new colony. The old queen will actively seek out and eliminate younger rivals. If a hive is really big, it can contain multiple queens (this part I know is true for ants as well. There are extremely large ants colonies in the South American jungles).",
"If a queen dies without there being a new queen, the workers will make a new one by feeding a larva. If, for some reason, the colony should be out of larvae, they're pretty screwed. It's possible to transplant a new queen into a hive, but I'm not sure how common this is in nature."
] |
[
"Its not possible in nature. If the hive gets to a point where there are no larva and loses the queen its done. The situation would occur when a newly raised queen goes out on a mating flight and doesn't return. Some of the workers may start laying, but they can only lay drones (males) since they are unfertilized. Eventually the worker population dies off through attrition, and there is nothing left but half raised drones which also eventually die."
] |
[
"On the subject of human mutations."
] |
[
false
] |
The more I've read into the world of genetic engineering, and after seeing posts today about the fluorescent cnidarian protein and human cell fusing, I honestly wonder if we could alter our DNA to work with different types of proteins from other species. To further that, since they would be the dominant cell in our body, if injected/replaced, would they not continue to replicate and eventually our existing cells? Imagine having our skin modified to be semi-translucent, then re-enforced with chromatophores to be able to change skin color and effectively blend in. I'm not as sober as I'd like to be writing this, but basically I'm asking you guys why this possible. Thanks guys!
|
[
"In the specific case you're imagining (fluorescent skin), the answer is no, at least with current technology.",
"Humans actually only have very tiny amounts of constantly replicating cells. There are only three places in the entire body that have these cells (stem cells) - the bone marrow (you need to constantly make red and white blood cells), the basement membrane of our skin, and the GI tract (you need to constantly replace the linings of your gut and your skin).",
"If you somehow managed the monumental task of making your artificially crafted cells invisible to the immune system, then they can proceed, very generally in two ways:",
"a) They have no signal to stop dividing, and will become a tumor that will potentially kill you",
"b) They behave just like your other cells, and stop dividing because there's no reason for them to keep dividing",
"The body's attitude towards cell count maintenance is generally \"if it isn't broken, don't fix it\". If there's no reason for a cell to divide any more than its neighbours, then it won't. There are many, many biochemical signals that ensure this - if they didn't work, we'd be getting cancer all the time (and some people ",
" have mutations in these processes that makes them more likely to get types of cancer).",
"The only case in which I can see this working is if you ",
" from a certain area with your artificial stem cells. For example, sickle cell disease (in which a mutation in your DNA screws up your ability to make proper red blood cells) can be treated by first radiating most of your bone marrow stem cells (known as hematopoietic stem cells, or HSCs) to death, and then replacing them with the transplant cells.",
"Ripping out the entire lining of your skin from your entire body, replacing a specific layer, and then putting the skin back is probably a little too intense a procedure to do with current technology."
] |
[
"There are only three places in the entire body that have these cells (stem cells) - the bone marrow (you need to constantly make red and white blood cells), the basement membrane of our skin, and the GI tract (you need to constantly replace the linings of your gut and your skin).",
"The limbus (eye) also has corneal stem cells."
] |
[
"Thank you so much! Exactly what I needed to know.",
"On the other hand, though, I still wonder if, with the aid of future technology and gene mapping/programming, we could get to where ",
"a) They have no signal to stop dividing, and will become a tumor that will potentially kill you",
"no longer poses a threat."
] |
[
"How do test-negative case-control studies ensure that they don't just lead to negative tests despite actually being infected and symptomatic?"
] |
[
false
] |
In particular, how does one make sure that the vaccine does not simply make detection of the virus more difficult without actually providing increased protection, i.e. you're symptomatic but test negative? Edit: This new study came out that shows those who test negative but have symptoms are quite often COVID-positive:
|
[
"With COVID, the vaccines (that the US and many other countries distribute) are mRNA vaccines, which only contain enough genetic material to have our cells make a specific protein (the spike protein). The PCR tests defect for other, more specific genetic materials in COVID, and therefore don't test positive for vaccines. Rapid tests test for N proteins, which, again, aren't produced with vaccination."
] |
[
"I recommend you against believing too strongly in unpeer-reviewed and uncredited publication."
] |
[
"I think you got the question backwards? It's not about whether the vaccine makes you test positive despite not being infected, it's about the vaccine making you test negative despite actually being infected (and symptomatic, even).",
"I just don't see how the vaccine would somehow get rid of viral genetic material (what the PCR test detects) without getting rid of the infection itself and its associated symptoms. That doesn't really make sense. Less RNA = less virus = less disease."
] |
[
"What is the connection between energy and information in a system?"
] |
[
false
] |
I mean in very general terms what is the relationship between these two properties of a system/process. It seems we can describe process more completely with both together rather than either form alone.
|
[
"Energy and entropy are independent thermodynamic variables. For a general system it is almost always possible to prepare a state with sensible given values of E and S."
] |
[
"1/T is partial S partial E at constant V, not total dS/dE, which basically answers most the rest of your question. Of course if you fix volume or specific volume then you're only left with one more independent thermodynamic variable. But in general you don't, there are two, and you can get any value for E and S. Trivial example: the ideal gas with the Sackur-Tetrode entropy. S clearly is the sum of an energy dependent term and a volume dependent term. So you can choose any value for E and then choose the entropy you want by changing V (though there is a lower bound on S given E)."
] |
[
"1/T is partial S partial E at constant V, not total dS/dE, which basically answers most the rest of your question. Of course if you fix volume or specific volume then you're only left with one more independent thermodynamic variable. But in general you don't, there are two, and you can get any value for E and S. Trivial example: the ideal gas with the Sackur-Tetrode entropy. S clearly is the sum of an energy dependent term and a volume dependent term. So you can choose any value for E and then choose the entropy you want by changing V (though there is a lower bound on S given E)."
] |
[
"Are Alpha Particles Affected by Electrons?"
] |
[
false
] |
I learnt radiactivity in school today and learnt about the Geiger–Marsden experiment.When my teacher mentioned that alpha particles passing by the nucleus would be diverted because alpha particles have a positive charge and the nucleus is positively charged I asked if electrons would have any effect on alpha particles she simply said it was unlikely that the particles would ever come close to the electrons and then went on with the lesson. My question is is this true,if so why? And even if the number of instances was very small theoretically if it did happen would the alpha particles be affected or not and if not why so?
|
[
"When my teacher mentioned that alpha particles passing by the nucleus would be diverted because alpha particles have a positive charge and the nucleus is positively charged I asked if electrons would have any effect on alpha particles she simply said it was unlikely that the particles would ever come close to the electrons and then went on with the lesson.",
"Your teacher has it backwards. Alphas in matter ",
" interact with the electrons. Every once in a while, they interact with a nucleus.",
"And even if the number of instances was very small theoretically if it did happen would the alpha particles be affected or not and if not why so?",
"The alpha particle is much heavier and moving much faster (in a quantum-mechanical sense) than the atomic electrons. If you shoot alphas into a block of matter, it will collide with ",
" atomic electrons and lose energy to ionization and excitation of the nearby atoms."
] |
[
"We have to remember that alpha particles have a kinetic energy on the order of 5 MeV, so they need to be slowed down considerably before they can meaningfully participate in chemistry. The slowing of alphas in matter is due to energy losses to ionization and excitation of nearby atoms."
] |
[
"Alpha particles interact with both electrons and atomic nuclei. The key to understanding the Geiger-Marsden experiment is conservation of momentum, and the fact that alpha particles are ",
" than electrons, but much lighter than most atomic nuclei.",
"Imagine a car driving down the highway that collides with a bird. The bird is going to have a bad day, but the collision won't affect the path of the car much. On the other hand, if the car collides with an 18-wheeler, it's going to deflect the path of the car a ",
".",
"Atomic collisions are a lot more elastic than car crashes, and nuclear collisions happen through electric forces at a distance rather than physical contact, but otherwise it's the same deal. (I picked a car, a bird, and an 18-wheeler because they have similar relative masses to alphas, electrons, and nuclei.)"
] |
[
"What warms up a car's water temp faster? Higher rpm, or lower rpm"
] |
[
false
] |
Higher rpm will have more combustion cycles per second, but at a lower force exerted per cycle (e.g. the engine can push the car easier). Lower rpms will have less cycles per second, but will be lugging (which generates more heat, from my understanding). If there is a significant difference, which is it? I'm speaking from a cold-start standpoint. My question comes wanting to get the heat going as fast as possible on a cold day. EDIT: I guess I wasn't clear. I am not talking about revving the engine in the driveway. I am talking about the engine being under load (e.g. which gear choice would heat the car up faster for the same speed?)
|
[
"Higher RPMs have larger frictional losses (pistons are moving faster), and result in more air being pushed through the engine. Larger frictional losses mean the engine warms up quicker. More air being pushed through the engine means that the velocity of combusted fuel-air is higher when it leaves the engine (agian remember that the pistons are moving faster). Higher velocity means a higher heat transfer coefficient (also more turbulence which results in higher convection coefficients), which would also warm the engine quicker. You could argue that the cold air entering the engine is moving faster as well, and you'd be correct, except the engine temperature (probably close to 200-300F) is closer to this cooled air temperature than the combusted temperature, so a higher RPM would still result in added convective heating (heat transfer for convection scales very close to the temperature difference).",
"Result: even under load higher RPMs will heat the car quicker."
] |
[
"It is more about work done than RPMs. If you sit in your driveway and rev the cold engine, the engine only has to move the mass of the cylinders and crankshaft, which it can do easily. In general, the system inefficiencies due to heat loss are a linear function of work done - if it requires 100 joules/rev to move the cylinders and crank only, and 10% of that is lost to heat, you end up with a heating potential of just 10 joules/rev. However, if it requires 1000 joules/rev to move the entire car 5mph, then you get 100joules/rev of heating potential by doing that. Basically, increasing the revs without increasing the work increases the heating potential linearly, while increasing the work ",
" RPM increases the heating potential exponentially until it reaches equilibrium.",
"What this means is that revving the engine in the driveway has only a marginal impact on heating the car over letting it idle in the driveway. You really need to make the engine \"do work\" in order to make it warm up faster. I am sure you notice this - the minute it takes you to get from your driveway to the entrance of your neighborhood probably warms your car more than letting it idle in the driveway for 10 minutes. ",
"edit - clarity."
] |
[
"If you are not accelerating, and travelling on flat ground, my guess is that it wouldn't make much difference because the inertia of the car is doing more work than the engine once you are at speed. If you are accelerating or going up hill, a lower gear lets you accelerate (do work) faster, meaning you do the same work over less time, increasing your instantaneous energy consumption, as well as the corresponding heat losses. If you accelerate at the same pace in each gear the increase in work required to accelerate the engine components in the lower gear might slightly increase your heating potential, as would the increase in exhaust back-pressure at higher RPMs. ",
"To answer your question, accelerating hard, up hill, in low gear would be the optimum way to heat up your car quickly. "
] |
[
"If alcohol kills bacteria, why don't adults do shots of vodka or tequila to cure sore throats or other bacterial sicknesses?"
] |
[
false
] | null |
[
"In short: because it's short lived, topical at best. The infection in your throat goes deeper than just surface tissue.",
"However! This is why things like that ",
" prescribed in Ye Olde Days -- because it did give temporary relief. However, it was short lived and also had the side affects of alcohol to go with it. These days, other medication is just a smarter and safer route."
] |
[
"Also, the concentration of alcohol required to kill most bugs is higher than your can achieve in your body tissues by drinking liquor. The use of alcohol for cold symptoms predates knowledge of bacteria and is more of a symptom reliever than a \"short-acting killer of germs.\""
] |
[
"This is not correct. Hand sanitizers like Purell aren't very effective even at a 60% alcohol concentration. That is why they are required to be 70% or 140 proof. Drinking any significant amount of 140 proof alcohol is a very unpleasant. For infections like a sore throat, the bacterial affection is very superficial. Deeper tissue bacterial infections would be like an abscess, which is much more serious. Drinking alcohol to kill the infection would only work in theory, since it would quickly get diluted and you'd have to drink an unreasonable amount. ",
"The goal of prescribing an antibiotic is to prescribe a narrow an antibiotic as possible that kills only the type of bacteria you are concerned about while sparing as much of the normal flora as you can. Ethanol kills pretty indiscriminately, in addition it is very hard to tolerate effective concentrations. "
] |
[
"If the formerly frozen parts of the earth are \"greening\", will the effects global warming be reduced?"
] |
[
false
] |
My understanding is that global warming is caused by certain gases, like CO2, being trapped in Earth's atmosphere. If there are more plants due to a rise in temperature and those plants remove gases like CO2 from the air, shouldn't the effects of global warming be lessened?
|
[
"The greening of arctic territory does not happen in isolation - it occurs in tandem with effects such as expanding desertification. However, desertification happens nearer the equator. Near the equator a degree of latitude represents a much larger surface area than a degree of latitude near the poles. ",
"It's not a simply 1:1 relationship, and while the greening in arctic areas will have ",
" mitigation effect agains the associated desertification, it will be miniscule compared to the methane release from thawing tundra."
] |
[
"And also important is that this greening is coupled with increased albedo. ",
"To explain for the OP, ice reflects far more solar radiation back into space than plants (or bare rock) does. So when ice melts, the planet as a whole absorbs more radiation, which means it has an easier time heating up. ",
"I don't know whether a decreased albedo is going to have a larger impact than increased greenery (even ignoring desertification), but from what I've heard from climatologists I suspect the answer is \"yes, by a lot\". If someone knows the numbers for sure, I would love to hear them."
] |
[
"The new vegetation will sequester carbon but not as fast as we're releasing new carbon."
] |
[
"How do you differentiate between a Random process and Deterministic but Chaotic process?"
] |
[
false
] |
The following claim is made in the (with citation): But does "error" in a chaotic process always increase exponentially (or in a defined manner), can it not be randomly(apparent) distributed too? Further, the article goes on to explain that deterministic data may appear random based on the number of dimensions (measures) used to describe each state of the process, but start to appear deterministic with more (sufficient) number of dimensions. Would this mean that we can't conclude, that any random process is truly "random" as there are infinitely more dimensions one could keep adding to check if it is deterministic (but stops due to lack of resources)? EDIT: Plenty of Ninja Edits for clarity
|
[
"The only truly random physical process we know of is measurement in quantum mechanics. Lots of people including some Einstein guy thought that this business of missing dimensions was precisely the issue. Btw, 'dimensions' here doesn't mean some exotic extra spatial or time dimensions stuff, it just means missing data. ",
"Like you not knowing the temperature at the time of measurement or the humidity in the air or something.",
"Anyway, Bell devised a ",
"set of equations",
" that takes into account any kind of hidden variable (which is a fancy way of talking about those non-accounted for dimensions), and came to the conclusion that if there were any sort of hidden dimensions that would make QM deterministic, an experiment he came up with would have outcome A. If there weren't it would have outcome B.",
"People ",
"did the experiment",
" and outcome B shows up all the time, albeit with some ",
"caveats",
".",
"So we think, QM is truly random."
] |
[
"that takes into account any kind of hidden variable",
"This isn't strictly true. Bell's theorem only rules out ",
" hidden variables, and only under the assumption of free choice of measurement setting (amongst other assumptions). It does not rule out non-local hidden variables or a superdeterministic theory."
] |
[
"Thanks, I do understand what dimensions would mean, as you said missing data, as I called it measures (or dofs) since it doesn't have to be missing as much as unaccounted for. But certainly, it would include \"exotic extra spatial and time dimensions\" as well?",
"Thanks for the info on QM, will look it up."
] |
[
"Wouldn't it be easier to survive for bacteria, viruses, parasites etc. if they didn't cause symptoms or even kill humans?"
] |
[
false
] |
[deleted]
|
[
"Yes, definitely, and many symptomless viruses or virus-remnants are a permanent part of our DNA, which have been integrated into our genome at some point in the past and since then enjoy a free ride during human reproduction. If I recall correctly, these virus remnants account for (possibly way) more than the actual \"coding\" parts of our genome. As for bacteria, our gut is full of non-pathogenic versions which feast on the food we eat. Some are beneficial for us (e.g. they help to digest food or keep worse bacteria out) but some are just neutral.",
"On the other hand, many pathogens create symptoms on purpose as part of their lifestyle, to encourage transmission to new hosts. Sneezing, coughing, any expulsion from the body might be induced by the pathogens themselves as much as it is a reaction of our bodies to get rid of them. This explains why sometimes, we cough/sneeze/throw up way more than seems useful."
] |
[
"These are great questions let's start with them one by one.",
"wouldn't it be much more intelligent for the pathogen to get some sort of camouflage, in order to survive in our bodies for a longer time?",
"Exactly! Pathogens are always trying to evade the host response, some are good at it and some aren't. Take a virus like HIV - there's always a pool of latently-infected cells biding their time and causing the virus to re-emerge just when you thought you cleared it. However the pathogen's true goal is to reproduce and it is not going to simply hide and wait at the cost of reproduction and spread. Natural selection will choose the pathogens that balance these needs of \"camouflage\" and \"spread\" in a favorable ratio.",
"I mean, if they didn't cause any symptoms, they wouldn't be treated, right?",
"This isn't necessarily true (symptoms and treatment don't always go hand in hand), but there are cases of pathogens which have extremely high prevalence in the population at large, but which are (for most people) largely innocuous and therefore never treated. For instance 90.8% of people over 80 are positive for ",
"HCMV",
".",
"Why is it that there are lethal viruses?",
"This gets to the heart of the issue of virulence. Take a look at the evolution section ",
"here",
". The major point is that there are a lot of tradeoffs. Rapidly moving through the host is a good thing in terms of viral spread, but killing the host quickly is bad. There are a lot of factors here and some balance point must be found.",
"why are there some \"germs\" that our body cannot kill?",
"This is pretty complicated, but the quick answer is that, for giardia, the pathogen is using a tactic called ",
"antigenic variation",
" to hide from your immune system. Essentially it scrambles the \"code\" on it's surface that your immune system would recognize and then target. By changing that code it's able to avoid the immune system. "
] |
[
"My lay understanding is that a lot of pathogens which are very negatively symptomatic or fatal in otherwise healthy animals or humans are those which have crossed a species barrier and are therefore not in their native hosts. Aids comes from monkeys but doesn't kill monkeys, chicken pox doesn't usually bother chickens, swine flu doesn't usually bother swine, cow pox doesn't usually bother cows... In fact that only high fatality epidemic disease I can think of affecting humans where pathogens jumping the species barrier wasn't an issue is small pox. My (again lay) understanding in that case is that because humans are such social animals a host can be a community rather than an individual, doesn't matter if person X dies if you can then go and infect neighbours A, B and C. "
] |
[
"A couple of questions about Planck's constant."
] |
[
false
] | null |
[
"I know it's a near infinitesimally small number",
"This doesn't make sense... It's a quantity with units, not a ",
". Sure in the SI unit system it has a value of ~10",
" but I could equally well conceive of a unit system where it has a value of 1 or a unit system where it has a value of 10",
" "
] |
[
"Maybe that's the way I need to approach it. I'm very interested in this field but I find myself getting tripped up trying to visualize numbers exactly. Astrophysics and cosmology has always fascinated me but I recognize I am an infant in terms of understanding. Thank you for your response"
] |
[
"You're asking for an entire history lesson. I'll give the short version, if you want more you'll have to be more specific. ",
"He was trying to explain why black bodies emit radiation/light the way they do (heat up iron and have a look). He suggested that only light with certain energies could be emitted. These energies would have to be an integer multple of this constant. ",
"How did he find the value? You look at how things radiate and find the value so your equations correspond to your experiments. ",
"I'm sure there's a perfectly fine wikipedia article about it. What exactly don't you understand?"
] |
[
"If I am immune to x disease and give blood, will the person receiving my blood have the same immunity due to my antibodies being inside him?"
] |
[
false
] | null |
[
"If the person received your plasma, they would then indeed possess your antibodies--for a short amount of time, and at a small percent of your total plasma proteins (depending on how many units of plasma they received from you, and if you're currently making that particular antibody) However, the recipient will not possess the B cells (plasma cells) capable of making said antibody, so they will not be able to mount a secondary immune response upon exposure to the disease using antibodies that were originally yours."
] |
[
"No, but they will die off and not be replaced.\n Your bone marrow and thymus create your immune cls."
] |
[
"Would a bone marrow transplant have the effects closer to what OP was thinking about?"
] |
[
"What are skin tags?"
] |
[
false
] |
[deleted]
|
[
"I actually just went to the doctor regarding one which I thought was a mole. If I remember correctly they are basically excess skin that has been pulled or tugged and stays that way. They are common in areas where you have a lot of movement like armpits elbows etc. If they are small the doctor can just cut them off. Otherwise if it is bigger they remove them with a scalpel and possible give you a stitch. I had a small one on the side of my neck, the doctor sprayed cooling spray on the area and used some scissors. It healed just fine."
] |
[
"That's interesting. So it's a repetitive motion that causes the skin to grow into that shape?"
] |
[
"Yeah usually from clothes rubbing against the skin."
] |
[
"If our body raises the temperature to combat infection, but we take medication to reduce that temperature, will it increase the risk of the infection?"
] |
[
false
] |
Also why does the body overheat itself to the point where it can damage itself, even the brain?
|
[
"The short answer is yes, antipyretics will increase the duration of an infection. Temperature is closely regulated by the hypothalamus during fever, and in most cases will not result in long-term damage to the body as the heating is carefully controlled. ",
"Fever responses increase effectiveness of immune cells",
" in addition to the protein denaturation/destabilization from the increased temperature. ",
"Here’s a journal article from WHCP on Fever",
". "
] |
[
"Fever that reaches dangerous temperatures are generally characteristic of infections that are systemic and uncontrolled, for example when bacteria enters the bloodstream (bacteraemia) or a severe influenza virus infection. These can lead to an overabundance of immune signalling molecules, the so-called \"cytokine storm\" - a kind of runaway chain reaction of the immune system. This is what we call immunopathology, the immune system harming the body. Any immune reaction is a balancing act between strong enough to control the pathogen and so strong it harms the host itself. ",
"Here's a review on the concept of cytokine storm in infectious disease: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294426/"
] |
[
"Thanks"
] |
[
"How long could the human race survive without the sun?"
] |
[
false
] | null |
[
"Not long. Barring the catastrophic collapse of society killing many of us, we would (relatively) quickly freeze to death.",
"If the sun disappeared, in about a week, average global temperatures would be ",
"below 0 degrees F (-18C)",
". This represents about a 50F (28C) drop from current temperatures. The drop would be greater in areas that were warmer to start with, so it's likely that most of the inhabited areas of the planet would be unbearably cold within a week, and below -40 F within a month. In a year, almost everywhere would be below -100 F (-73C), which is clearly unsurvivable without drastic measures, and supplies to counteract the cold would be exhausted well before this. The hardiest and best-prepared of us (think: access to a nuclear reactor or geothermal generator, as well as huge food stockpiles) might hold out several decades, but life would be unsustainable."
] |
[
"Granted, none of this is ",
". The sun can't just up and decide not to exist anymore."
] |
[
"Nonscientist here, but I imagine not very long. Plants and phytoplankton use the sun in photosynthesis. So they would die off if they could not adapt fast enough. Then when you follow the plants and phytoplankton up the food web other animals that rely on them as food sources or food sources of food sources etcetera would die out. Leading eventually to humans who would also die out unless they could find a way to grow nutrients/foodstuffs artificially.",
"In fact now that I am thinking of it. Maybe it would not be that hard. All food would have to be grown using alternatively powered grow lights, but I guess it is possible. In that case indefinitely, but a large portion of the population would starve because of food restriction.",
"Edit: Indefinitely, until geothermal and other forms of energy go kaput."
] |
[
"Why does electrical conductivity increase in a partial vacuum but then drop way off as the vacuum approaches perfect?"
] |
[
false
] | null |
[
"For a neutral gas to electrically conduct, we require some small degree of ionization of that gas. Essentially, we need to discuss weakly ionized plasma, or in this case a ",
" weakly ionized plasma. As plasma physics is horrendously complex, anything I say here probably cannot be generalized to all plasmas. Plasmas also suffer from the fact that their behavior changes considerably depending on external EM fields. We also need to be wary if the positive ions which are much more massive and usually slower moving contribute to the overall current in a significant way. Anyway, in our system, the movement of charge is dominated by collisions between negatively charged electrons and neutral particles. The equation of charge acceleration is just,",
"where u is our average electron velocity. m is just the mass of the electron. If the velocity of the electron fluid varies with position, then there is a nonlinear part in our equation which shows up on the left hand side. The rest is the Lorentz Force. A simple model of F_collisions can be given by",
"The key parameter we're interested in is this \"v\" which represents the frequency of charge collision with neutral particles. The interpretation of this equation in our air situation is then: A weakly ionized gas will conduct current due to external fields (like a 9V battery placed across a tube of gas), but the low number of charge carriers, and the high frequency of neutral-electron collisions means the conductivity will be very low.",
"Let's write this explicitly by ignoring the nonlinear parts and setting the magnetic field to zero.",
"When the current is steady state, du/dt = 0. We define J as the current given by J = -enu where n is number density of charge carriers in the gas.",
"0 = eE+vmu",
"J = (ne",
"/vm)E",
"The conductivity is then (in our very idealized case)",
"Now we can answer your question. By reducing the pressure of the gas, both the frequency of electron-neutral collisions v and the number density of charge carriers n decreases. But the collision frequency drops faster, so the overall conductivity increases. But only up to a point. Once the pressure gets low enough there just isn't enough charge carriers around and the conductivity drops as well."
] |
[
"The concepts are related, but it is important to note we're not discussing breakdown which is what Pashen's law is about. We're discussing the electrical conductivity of a neutral gas which is still very much an insulator and this has a very low conductivity. Once breakdown occurs the gas has a large conductivity due to ionization uninhibited avalanche. And the arc itself is different what what is called \"glow\" discharge.",
"The relationship to Pachen's law is about how the carrier-neutral collisions inhibit the generation of enough carriers to support discharge. The pressure and length controls the collision rate. The essential part is that carriers become uninhibited as the pressure decreases, but then you aren't making enough carriers as the pressure gets too low.",
"We can say the steady state conductivity of a gas tracks with it's breakdown voltage."
] |
[
"Are we talking about the conductivity of a gas or a plasma? It's a bit unclear."
] |
[
"How do electromagnetic radiation travel?"
] |
[
false
] |
[deleted]
|
[
"An electromagnetic wave (EM) that propagates due to alternating electric and magnetic fields at perpendicular angles as shown ",
"here",
" . A change in the electric field induces a change in the perpendicular magnetic field, which in turn induces another change in the electric field. These alternating changes allow the EM wave to propagate. The wavelength of wave is determined by the length of the oscillations of the EM wave, which is directly related to the initial energy. "
] |
[
"And why do electromagnetic fields propagate in this manner at all? Well, Maxwell's equations describe electromagnetism very well, and looking at Ampere's law and Faraday's law you can see that one can derive a wave equation out of that, called the Helmholtz equation.",
"Essentially though, Faraday's law says a changing magnetic field causes a change (in time) in the electric field, and Ampere's law says a change in the electric field causes a change in the magnetic field. (Maybe it's the other way around). So if you have an oscillating charge (oscillating means going back and forth, quite simply) it will create an oscillating electric field which makes an oscillating magnetic field, and that is an electromagnetic wave that propagates. "
] |
[
"Also, ",
"this page",
" has ",
"some animations",
" which OP may find enlightening."
] |
[
"What happens when you pop acne?"
] |
[
false
] |
I would like to know specifics.
|
[
"When you pop a pimple you are squeezing hard enough to force out all the pus, germs and oils from the infection site, which is so violent that it momentarily rips your skin open (very minorly but can cause scarring) you are also letting all the oil, germs and dead skins cells out from the clogged pore and onto your hands and face, leading to further infection and possibly more popping "
] |
[
"An elegant, if disgusting, explanation.",
"Pus is usually an active battlefield between bacteria and your immune system. Bacteria get under the surface somehow (almost always via a sweat gland). Neutrophils, large immune cells that engulf anything that doesn't identify itself as friendly, are drawn by the smell of trouble and will crawl out of nearby capillaries (diapedisis). This is often a long, drawn out battle and a lot of pus is the remains of dead neutrophils who died for the cause."
] |
[
"But doesn't the body have to then clean up all of this pus after, and if so, how does the clean up occur, how long does it take? Details would be very greatly appreciated. Your answer is eye opening, but it doesn't tell anyone how long they will have to wait for it to clear up itself. "
] |
[
"What is the reason for the dim lines when you spin a \"ball\" of glowsticks? [video]"
] |
[
false
] |
I'm familiar with the visual illusions of a tire looking like it's spinning backwards, and I'm pretty sure this isn't that. I've noticed this before but I ran into it again tonight and I was really curious. The following video kind of shows what I'm talking about if you ignore the framerate artifacts: There are these thin black lines that are about as wide as the glow sticks that make up the ball. I know for a fact that light is being emitted from those spots, so why isn't the ball an uninterrupted blur of light? Not sure if it matters, but there are 12 glowsticks that make up the ball. The effect seems to be related to the perspective of the viewer. In the linked video (and in person), they never "move" from where they are at, regardless of how fast the ball spins.
|
[
"I'm familiar with that.",
"I'm curious why the thin horizontal black lines appear at regular intervals independant of the rate of rotation. It is hard to pick out in this video, but there's the \"normal blur\" and then a set of about 10 or so thin black lines that remain dim in every frame."
] |
[
"Good question, I assume it would have something to do with the rotation of the glow sticks syncing up with the frame rate and exposure of the camera, as well as syncing up with the scanning motion of the camera. "
] |
[
"That's exactly why I was asking this question. That phenomenon happens in person, too, which makes me doubtful that it's just a result of the cameras scan rate.",
"It also happens independent of the rate of rotation (which can be seen in this video). If it was merely a framerate issue, then those dark lines should appear to move when things spin faster or slower (like car tires or a fan blade do)."
] |
[
"Radar \"blind spots\" due to differing diffraction indexes"
] |
[
false
] |
In Physics today, my teacher was telling me about how when they fly jets to avoid SAMs, they will do it in a radar 'blind spot' of the sky which is calculated from the different diffraction indexes of the sky (from weather conditions) and processed by a computer to give a model in where a radar cannot see you. The same applied with submarines and the use of sonar. I was wondering exactly, how EXACTLY does this work, what other applications it has, am i naming it correctly, and how you can exactly predict what the refraction index will be at a certain point (especially with weather conditions and varying concentrations of different things in air). I just mainly wanted to know more about it as I find the concept very interesting.
|
[
"So I am radar mechanic can give some information. To answer your main question; that is something I have never heard of, and in my radar I don't really see how weather conditions can create a blind spot. However I can inform you on some interesting blind zones of radar theory.",
"Most radar for air traffic have a processing technique call Moving Target Indicator, designed to discern the difference between very tall not moving things, and moving things. It does this by comparing consecutive PRTs and cancelling anything that didn't move. However an issue this causes is that if an aircraft travels at a certain speed and creates a Doppler shift that is the same as the PRF of the radar the aircraft becomes invisible. This is blind speed.",
"Blind speed may be determined by this simple formula:",
"Blind speed (in knots) = wavelength of transmitted pulse (in cm) X PRF (in PPS)/102.8",
"This is countered by having systems with staggered PRFs.",
"An aircraft can also produce a Doppler shift that produces little or no output from a phasedetector and become invisible to the radar. This condition is called blind phase. This happens when the aircrafts radial velocity = 0 relative to the radar."
] |
[
"as much as I love askscience i'm just happy someone finally asked about radar. "
] |
[
"Woah that's pretty cool!",
"Thank you heaps for that, I do love hearing about this stuff."
] |
[
"If you shine a torch on a flame, does it create a shadow? Why/why not?"
] |
[
false
] |
I tried it myself but couldn't see anything, but it was hardly a highly scientific experiment.
|
[
"Here in my room, I have windows. It's pretty dark outside, but not pitch black. It's bright in the room. When I look at the windows, I see a reflection of the brightly lit room I'm sitting in. I can't see what's outside. That doesn't mean the glass isn't transparent - it is 95% transparent. I know there's a dim image coming through that glass from outside and hitting my retina. But I also know there's a much, much brighter image that's coming from inside the room and hitting the ",
" on my retina. The two images are blended. Because one image is so much brighter, my eyes aren't \"smart enough\" to separate the two images.",
"I think that's what's happening with the flame: your retina is receiving the image of what's behind the flame, but your retina is also receiving the image of the flame itself, the two images are projected on the same place on the retina. Because the flame is much, much brighter, it's your eyes can't separate out the two images. But that doesn't mean the flame's not transparent."
] |
[
"It does not create a shadow in the typical sense that light is blocked by the fire, however the increased temperature of the air that composes the flame will have a different index of refraction that the surrounding air and will refract the light. An example of this is the distortion you see on a really hot day right above asphalt or pavement, or when you look through the air that comes out of a plane's exhaust."
] |
[
"Read this comment on another ask science post for what fire is.",
" The flame is not opaque, it is just brighter than the light from the objects behind it, which is why you can't see past it."
] |
[
"Why is the content in the universe localized."
] |
[
false
] |
What I mean by that is why are there galaxies, solar system and in between them nothing. Why isn't the material in the universe equally spread throughout.
|
[
"Because gravity, given a system with slight variations in density, will tend to exaggerate those variations and cause matter to 'clump' together."
] |
[
"Gravity causes local clumps to form. But on a large enough scale, matter ",
" evenly spread out through the universe."
] |
[
"It more or less is. There's a lot of interstellar hydrogen, and dark matter."
] |
[
"If you could artificially pump oxygenated blood through the corpse of a cow, would that help preserve the cow's flesh?"
] |
[
false
] |
[deleted]
|
[
"It depends on when the cow died. If the cells haven't all died due to lack of nutrients, then some of them can be preserved.",
"I remember seeing a rather disturbing film produced by Soviet scientists during the cold war exploring such concepts. Watch at your own risk. ",
"It's informative, but graphic and rather disconcerting."
] |
[
"Severing the brain stem would eventually stop everything in the body, including the heart. The heart, however, contains its own small nervous system that operates more or less separate from the brain. ",
"The brain acts as an integration center for all inputs into the system; that is, the brain receives and processes everything we see, touch, feel, etc. The brain relays to the brain stem, then to the spinal chord, which relays in turn to just about everything. ",
"The heart is controlled by a region of the brain called the ",
"medulla oblongata",
", which rests just above the brain stem proper. This area of the brain controls the ",
" of heart contraction, not the actual contraction. ",
"The actual heartbeat is regulated by two nodes of neurons, called the sinoatrial (SA) and the atrioventricular (AV) nodes. These two neuron clusters are responsible for the actual contraction of the heart. Some neurons in the heart sense when the heart stretches from the entry of blood. This causes the node to fire, which causes a contraction of that area of the heart. The SA controls the contraction of the atrium, while the AV controls the contraction of the ventricles. ",
"Here's a nifty diagram to help visualize the heart",
"By cutting the brain stem, any nerve transmission from the medulla oblongata will stop, but the SA and AV nodes will still function, provided they receive proper nutrients from the arteries which supply blood to the heart. ",
"Since the brain stem has been severed, but the heart is still pumping, all tissues would receive blood (which I presume is being oxygenated artificially), and would technically be alive. Any nervous system activity which requires integration in the brain, however, would be stopped. Maybe some reflexes would function, such as the patellar, or knee-jerk reflex. ",
"Hope this answers your question!"
] |
[
"We keep isolated hearts alive outside the body by pumping oxygenated fluids with nutrients through it. The hearts can usually last up to 6 hours or so. With more sophisticated antibiotics and filtration, I've heard of scientists who can do this for a few days.",
"After that, without a functioning immune system or filtration system like the spleen, bacteria gets the better half of the organ."
] |
[
"What is the difference between B lymphocytes and plasma B cells?"
] |
[
false
] |
[deleted]
|
[
"A plasma cell is a mature B cell that has been activated by antigen. When a naive B cell comes in contact with antigen, it differentiates into mature plasma cells which secrete antibodies and memory B cells which facilitate immune memory.",
"Here",
" is a diagram of the immunologic differentiation tree."
] |
[
"B cells do not circulate, they reside in lymph nodes. Antigen presenting cells (APCs) bring the antigen to them. Everything else is correct though."
] |
[
"Ah thank you for correcting me, overall I'm glad I only stuck my foot in my mouth the one time."
] |
[
"If you can use an antenna to produce electromagnetic waves and visible light is electromagnetic radiation, why you can't tune an antenna to produce waves in that length and make light this way?"
] |
[
false
] | null |
[
"Theoretically, you can. Practically, there are some limitations. I'm assuming by Light, you mean ",
"",
"A user has excellently explained the limitation in one of the answers in ",
"this link",
". I suggest you follow it to know more.",
"Another article ",
"here",
" explains the scenario in much detail.",
"",
"In short, the reason is quite similar to that presented by ",
"effvoniks",
", i.e. because the frequency of visible light is way higher than that of radio or microwaves, their corresponding wavelength is way lower. You need an antenna of the scale of your final wavelength, which in this case is of the order of nanometers. So, currently, it is quite difficult to directly produce visible light via an antenna.",
"",
"Though, if you want, you can always provide high enough energy to an antenna for it to heat up and glow. If you do, be safe and get a video of it!",
"",
"Edit: If you read the answer on ",
"this link",
", it turns out that the ",
" of the material of your antenna matter as well. If the electrons in your metal cannot oscillate as frequently as you want them to be, you cannot produce that high-frequency signal."
] |
[
"Hahaha, just burn the thing is a valid scientific method to make an antenna produce visible wavelengths."
] |
[
"This is a really cool question to think about! It gets right at the problem of how far can you take purely classical physics.",
"If you are open-minded about what counts as an \"antenna,\" you can look at a couple of different ideas.",
"Visible light is 380-740 nanometers, and a carbon atom has a diameter of about 70 picometers. So, if you made an antenna out of carbon, it could only be about 5000 individual atoms long. That is smaller than most individual proteins. Then, you would have to have a circuit to drive it between 430–770 THz.",
"This is perhaps marginally possible. Modern semiconductors have a minimum feature geometry of 10-14 nanometers, which is only about 200 atoms. If you were going to build an antenna that runs in the hundreds of terahertz, it would be difficult to prevent the driving circuit itself from just... being an antenna. So, you would have to build the entire thing out of only 25 geometric features. And, by \"features,\" imagine you were building the components of the circuit with Minecraft blocks, and you can only use that many of them. I'm using carbon as a measuring stick -- semiconductors are usually made out of atoms with bigger diameters, so probably more like 18-20 features. It would take some extremely clever design to make it work on paper, but in practice, something that small would be dominated by quantum effects, and wouldn't behave like a simple oscillator.",
"An antenna is just a thing that allows charged particles (usually electrons) to move around, but constrains them to move in some kind of coordinated way. Usually, it's a wire, which constrains them to move along the long axis of the wire.",
"That isn't the only way to accomplish this. You could also trap electrons in a magnetic field. This has the nice property of creating a natural resonance that relates the charge and mass of the trapped particles to the magnetic field. So, pick your magnetic field and particle type, and the device will resonate at a characteristic frequency called the cyclotron frequency. The equation is ",
" = ",
"/",
".",
"We know the frequency we want (430 Thz), the mass of an electron (9x10",
" kg), the charge of an electron (1.6x10",
" C), and the speed of light (3x10",
" m/s). If you solve for B, you get 810,000,000,000 Tesla. The strongest magnetic field humans have been able to generate is about ",
"91 Tesla",
". Entertainingly, solid copper conductors tend to just kinda explode at 25 Tesla.",
"You could trap the electron in an oscillating electric field, but if you had an electric field oscillating at 430 Thz, you would already have your antenna.",
"This tells us something pretty interesting about how the universe works. It is very difficult to generate electromagnetic radiation in the visible spectrum without some kind of quantum process. You need something that can confine a charged particle like an electron to an extremely small volume of space for it to oscillate that quickly. It's pretty difficult to accomplish this with purely classical physics.",
"If you are able to see something, there is almost certainly a quantum process involved -- even if you discount the fact that the way your eyes work depends on a quantum process."
] |
[
"How much can boiling a pot of water raise the humidity in a building?"
] |
[
false
] |
My question is because at my cabin that is heated by a wood stove it gets very dry and we always put a pale of water on the stove to counter act the fire. With out the water every time you walk around and you touch something you get a static shock. With the water on the stove it stops. I'm just wondering how much change a small bucket of water can make in a whole cabin.
|
[
"It takes a small volume of water to substantially increase the humidity of a reasonably sized room (ignoring losses of water to condensation etc.).",
"Example: to increase the humidity of a 20 m",
" room by 50% at 20",
"C, you'd only need to boil approximately 170 ml of water.",
"Of course the volume of water needed increases when the temperature of the room increases. For example, at 30",
"C you'd need 300 ml of water."
] |
[
"If you think about it the evaporation is even more effective if you factor in that the heat loss from the stove is just heating your house, so you are not wasting any energy."
] |
[
"A 20 m³ room is very small, though. A 50 m² appartment with a ceiling height of 2.4 m is 120 m³. Then you would need to evaporate 1L of water to increase the humidity by the same amount. ",
"Evaporating 1L of water, starting at 20 deg C, would cost you 2591 kJ, i.e. 0.72 kWh, if the tranmission of heat to the water is perfectly efficient.",
"However, if you increase the humidity by other more efficient means such as by using a humidifier that creates aerosols that evaporate, the eventual evaporation of those aerosols absorbs heat from your house, which means the heating system has to work harder to maintain the temperature. As such, evaporating a liter of water on the stove is not as inefficient as it seems."
] |
[
"How was it determined that the speed of light is constant regardless of the reference frame of the observer?"
] |
[
false
] |
I've found sources which state a few facts and its discovery, and I'm aware this very piece of knowledge is the underlying principle that time slows with increasing velocity, but how was this concept discovered in the first place? It seems like more of an accidental result than a hypothesis that was tested, but I truly can't seem to find the origin of this discovery.
|
[
"Maxwell's equations predict that the speed of light in a vacuum depends on properties of the vacuum that seem to be independent of the reference frame of the observer. This is a theoretical prediction from the 1860s. ",
"https://en.wikipedia.org/wiki/Maxwell's_equations#Vacuum_equations.2C_electromagnetic_waves_and_speed_of_light",
"In the 1880s and 1890s Michelson and Morely ran a famous experiment that showed that the speed of light was close to constant in a wide variety of reference frames.",
"https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment"
] |
[
"It was more like several experiments couldn't find evidence that light's speed did depend on the relative motion between source and observer (as would be expected from Galilean relativity), and Einstein tied it together in a framework that didn't require that to be the case, in a way that was consistent with what was known about electrodynamics at the time. You can read about some of those experiments ",
"here",
"."
] |
[
"While I can't comment on what the experimental evidence was, it definitely wasn't an accidental result, and as I understand it Einstein's logic when founding special relativity is as follows. First, he made one important assumption: the laws of physics are the same in any inertial reference frame - there's no reason to assume they wouldn't be. Maxwell's equations, governing the physics of electromagnetism, is dependent on the speed of light; were the speed of light different, in any reference frame, the laws of physics as described by Maxwell's equations would behave differently. The only way to resolve this is to assume the speed of light is the same in every reference frame.",
"From this postulate, experimental evidence was founded, and all the resulting effects of special relativity followed. "
] |
[
"Is there an optimal way to accelerate my automatic transmission car?"
] |
[
false
] |
In any automatic transmission, you can clearly hear the gears shifting, and feel a slight but perceptible little rumble or shift as it happens. When I drive my 2005 Honda Civic, when I feel a gear shift about to happen, I like to ease up on the accelerator slightly so that the shift is a little smoother. If you lay on the gas before a gear shift, the transition is louder and more noticeable. I guess my question is, does this matter whatsoever? In this instance, optimal can mean greatest fuel economy, or best for the long-term health of the car, or anything else that makes sense that I have considered. EDIT: If I'm understanding this correctly, the answer basically seems to be that it doesn't really matter, and that if it does matter, it doesn't matters much, and in ways that aren't readily determined by the average driver, and so aren't really worth worrying about.
|
[
"When you press down hard on the throttle, your automatic transmission assumes you need more acceleration and adjusts by shifting gears at a higher RPM. You will extend the life of the transmission by accelerating smoothly (not flooring it) and increase gas mileage by a negligible amount."
] |
[
"I like the way you think. Similarly, SUVs with an exposed trailer hitch: watch out!"
] |
[
"It's impossible to know, except possibly with some data logging hardware and software, what exactly what effect you are having on the transmission by easing up on the throttle before a shift. Cars have differing methods of determining shift points, firmness (derived from line pressure), and torque limits and they are sometimes very complex lookup tables with multiple inputs. These inputs may include throttle position, MAP or MAF readings, vehicle speed, engine RPM, and operating status (closed/open loop). There may also be predefined tables like shift timing (how long to wait for a shift to occur before increasing line pressure to speed it up). Knowing exactly what you condition you are presenting to the ECM to make these decisions requires reading the data and analyzing it at the moment of the shift command, but also the trends leading up to it. ",
"So besides all of that, you may want to know that a harsh shift does not necessarily mean its more damaging to the transmission. In fact, firm, quick shifts in automatic transmissions lead to less band slippage and therefore reduced heat-producing friction. Heat destroys automatics. Of course, a VERY harsh shift may lead to shock induced failures on other components so it's all relative, but extremely smooth shifting automatics (luxury cars, for example) often have premature clutch band failures. ",
"And fuel economy is likely a wash in your scenario, but generally the slower you accelerate the less fuel you use. "
] |
[
"Is it possible for an atom to have more than 8 valence electrons? If cannot, what is the reason for this?"
] |
[
false
] | null |
[
"Yes, it happens all the time with transition metals and you even see hypervalency with some main group elements that have d-orbitals. d-orbitals hold an additional 10 electrons. ",
"The 8 valence electron rule is a useful teaching tool for high school students to get a hang of chemistry but isn't strictly true for all atoms."
] |
[
"The valence electrons are just any electrons available for bonding. The electrons available for bonding are \"far\" from the nucleus and therefor close to other nuclei and loosely bound to the first nuclei. As you increase in the orbitals (1s,2s,2p,3s,3p,4s,3d,4p.....) the energy difference between the orbitals decreases. ie: 1s is significantly less energetic compared to 2s as 4s is compared to 3d (",
"http://www.bing.com/images/search?q=electron+energy+level+diagram&id=16CD3C68A664AC5A623A308B13D26FD4D8099E12&FORM=IQFRBA#view=detail&id=16CD3C68A664AC5A623A308B13D26FD4D8099E12&selectedIndex=3",
"). Whenever you \"pass\" the lower orbitals, other orbitals have an energy which is similar enough to participate in bonding."
] |
[
"As examples, chlorine ",
"can have 14 valence electrons",
", and rhenium ",
"can have 16",
". "
] |
[
"Which color reflects the most infrared heat radiation?"
] |
[
false
] | null |
[
"Infrared is not visible."
] |
[
"Thank you for your unhelpful answer :)",
"My question was what color reflects the most IR radiation not if it was visible or not... The visibility doesn't matter to me only the heat.",
"Which color absorbs the least infrared radiation heat??"
] |
[
"The color of an object just tells you what ",
" wavelengths it doesn’t absorb, it doesn’t tell you anything about what infrared it does or doesn’t absorb. Since infrared wavelengths are not visible, you don’t learn anything about infrared absorption by looking at the absorption of visible wavelengths."
] |
[
"Do people at the North Pole see different stars than people at the South Pole, would this also be true for people at the equator (seeing different stars than either the North or South Pole)? Also do we map stars/galaxies that are above the South Pole?"
] |
[
false
] | null |
[
"Yes they do. For most regions there are summer and winter constellations that are different, due to the tilt of the earth causing the horizon to block your ability to see certain constellations. There are also different constellations seen by people in the southern hemisphere and people in the northern hemisphere.",
"There are big observatories in both hemispheres, so yes, we do map the stars/galaxies visible from both the north and the south poles."
] |
[
"Actually, the difference is summer and winter constellations is not due to the tilt of the Earth. It is caused by the sun moving across the sky (along the ecliptic) as the year progresses.",
"In the summer, the sun is near the winter constellations, so you can't see them. In the the winter, the situation is reversed. If the sun were extinguished, you could see all the constellations visible from your latitude on every day of the year."
] |
[
"As ",
"/u/ShadowKeeper1",
" noted, different stars are seen from the North and South Poles.",
"Assuming perfectly flat horizons and no atmospheric effects, a person standing on the North Pole during the northern polar night and a person standing on the South Pole during the southern polar night would between each other see all of the stars visible from Earth and yet none of the same stars.",
"This is a long way to say that there are no uniquely equatorial stars-- everything is theoretically visible from one of the poles."
] |
[
"Why do we have to pee? Why can't we just reuse the water and avoid having to orally replenish our body water supply?"
] |
[
false
] |
[deleted]
|
[
"When your urine is concentrated, minerals can be forced out of solution into crystal form, leading to formation of calculi, also known as kidney stones. As you probably know these are very painful and can be extremely damaging to the kidneys and urinary tract.",
"Also, \"toxins\" aren't really what your kidneys are getting rid of. The kidneys regulate hydrogen ion, electrolyte, and mineral concentrations in the blood by reabsorbing or excreting them selectively. By dumping or reabsorbing H+ ions, it also helps regulate pH balance."
] |
[
"To add to this, the filtration process is quite complex. The kidney is broken down into nephrons as the functional unit. The starting point in the nephron of the filtering process is the glomerulus, which is a tuft of capillaries. After the glomerus there are a series of tubules where absorption and secretion occurs until what will be excreted as urine remains in the tubule and is then passed to the bladder via ureter. Past the glomerulus, active resorption against a gradient is minimally utilized in the renal system, with much of the tubules depending on passive process. Because of this, the concentration of particles present and the oncotic pressure greatly effect what is excreted. ",
"As example is osmotic diuresis. A number of things can cause it but diabetes mellitus is a good example. You get high levels of glucose being filtered out by the kidneys, but only some of it is being resorbed. Due to osmosis, the high concentration pulls more water into the tubules and you see polyuria (excessive urination). ",
"To overcome oncotic pressure and osmosis to excrete super concentrated products would require more energy and a differently designed system than the mammalian renal system (or what we understand of it)."
] |
[
"Indeed! In fact, in order for this to work, we would need to have renal systems more like saltwater fish, which excrete extremely concentrated urine to compensate for the fact that they are constantly losing fluid to the surrounding medium due to osmotic pressure, but can only replace it with very concentrated salt water."
] |
[
"What is the upper limit of the Casimir Effect wavelength?"
] |
[
false
] | null |
[
"And with greater distance the greater the total force it exerts",
"Why? It's exactly the opposite"
] |
[
"You misunderstand; I agree higher frequencies generally have higher energies (at least in the electromagnetic sense, and probably in the Casimir sense); I think we can agree the sum of all frequencies that contribute to the Casimir effect is greater than the energy at one single specific frequency.",
"Example: If I have 1w/cm2 of blue light hitting a surface, adding 0.1w/cm2 of infrared light the total is 1.1w/cm2. \nThe question: Is their a known upper boundary on Casimir wavelength? Most of the equations I've seen that relate to it appear to have some undefined upper bound (nothing over the sigma, or I can't interpret it). Thus my question.",
"I suspect the answer is the upper limit is infinite. However, we simply can't measure the effect because it is so tiny, or that to test it would require an infinitely large test chamber. The test plates would need to be the dimension of the wavelengths involved."
] |
[
"Ah - I do see your point. Of course, more HF is allowed between the plates as they move apart ... leaving the lower frequencies to act alone, suggesting they act with less force than the higher frequencies.",
"Question still remains... is there an upper limit on wavelength?"
] |
[
"How do prions infect humans?"
] |
[
false
] |
So I understand that prions are misfolded proteins that can aggregate and block various vital cellular functions like protein transport and intercellular communications. How is it though, that misfolded proteins from another organism can infect me? Why doesn't my body simply break down these proteins into amino acids like it does with other proteins I ingest?
|
[
"Microbiologist checking in!",
"So first of all: I'm glad to see you have the correct basic idea about what prions are and how they work. They can be infectious, but since they're not a conventional pathogen (like a bacteria, virus, or parasite) they're a bit of an oddball.",
"I'll talk about human->human transmission of prion-disease, since I know a fair bit more about that than about potential cases of animal->human transmission (although the mechanism is pretty much the same).",
"Prions are misfolded in such a way that not only are they extremely stable and hard to destroy - they're resistant to proteases, heat, changes in pH, and have been seen to persist unprotected in contaminated soil for ",
" after contaminated animals were burned and buried there - but they're also ",
". Essentially if they encounter the same protein as themselves, but in the normal folded conformation, they \"convert it\", turning it into a misfolded prion as well.",
"So that's the really basic answer to your question: the way the protein folds makes it exceptionally resistant to degradation by normal means (low pH and proteases in your stomach/small intestine) and also allows it to \"replicate\" within your body.",
"A few quick sources: there's a good review of prion diseases in animals and humans ",
"here",
"and another interesting case study of accumulation of prion proteins in human tonsil and appendix tissues ",
"here",
".",
"I hope that helps!",
"edit: the second link also mentions how the body is unable to mount an effective immune response, which is another reason why the prions, once they're in your system, can replicate essentially unchecked.",
"edit",
" fixed the first link"
] |
[
"Thanks for the great links, added to my reading list. I actually do recall hearing that they were protease resistant, but if we can't digest them or use them, why does our body not just flush them out like cellulose and other waste? Or perhaps a better question, how do they get into our system in the first place (assuming they are foreign prions and not due to an in-host mutation)? I had kind of assumed they were brought in through the digestive system, is that assumption even reasonable? ",
"Edit: Wording/clarification"
] |
[
"We know very little about prions, but the currently accepted theory is that the proteins mis-fold into an incredibly stable form of tightly packed beta sheets. This stable isomer is highly resistant to biological and chemical degradation, so it remains in the cell acting as a template that induces further incorrect folding of other proteins. "
] |
[
"Can the Schrödinger equation be derived from first principles?"
] |
[
false
] |
[deleted]
|
[
"tl,dr: If you're going to complain about Schrodinger's equation (or any other equation) not being derivable from more fundamental principles, then you can just make the same complaint when I tell you what the more fundamental principles are.",
"If the answer is no. Then \"well it agrees with experiment\" is no better than any arbitrary curve fit.",
"That is absurd in the logical sense. If I throw a ball in the air and trace it's trajectory, I may be able to fit a curve to the data. I only learn that one particular ball travels in a parabola.",
"But then I try with another ball. I fit that curve and find that it too is a parabola. Interesting.",
"Now I try with a ball of a totally different mass. I find again that it goes in a parabola and indeed with the same coefficients!",
"Now I do the same experiment on the moon. I find that all three balls go in parabolae, but with a different coefficient than on Earth.",
"With more experiments of this kind, I might come up with a physical ",
":",
" = ",
" ",
"I did not derive this from first principles. I discovered it by fitting many curves and finding a pattern in their shapes and dependence on physical parameters. However, this law is far more useful than any particular curve fit, as I have reasonable expectation from my observation of patterns within the behavior of ",
" that this law describes them all, and indeed ",
".",
"You seem to think that laws discovered and validated through experimental study are somehow less good than something you derive from more fundamental principles. This is absolutely false. Consider the state of physics knowledge at any time as a sort of tree, with the most fundamental laws at the root. There are two kinds of study. First, you can study the behaviors which emerge from known laws. For example, you can study turbulent fluid flow. We expect this is well described by basic kinematic principles, but the problem is so complex that it's better to not work from first principles and try to figure out higher level principles. Second, you can go to the root laws and try to figure out what lies beyond. This is like particle physics, e.g. the recent discovery of the Higgs boson.",
"Anyway, the point is that at any time there will always be something at the root. Not knowning what lies beyond doesn't invalidate it or make it less useful. There may always be another layer, and in that case our sort of position on the great tree of physics always looks kind of the same, with some equations at the current root and others further along which can be derived from what are at that point the \"first principles\".",
"Right now, Schrodinger's equation is roughly one level away from the root. You can write down the principle of least action and derive Schrodinger's equation from that if you want. Least action is pretty much the root as far as I can tell, which puts Schrodinger as a second level in the tree right now. Maybe in ten years Schrodinger's equation will be a third level away from the root. We don't know.",
"What does that tell me about nature?",
"The same thing as any other equation. Our theory is just a way of keeping track of how we expect the world to behave when we poke it. Some parts of the theory are more abstract and general than others, but in the end it's all just metaphor so we can model Nature in our brains.",
"If that wasn't helpful please just point out what parts don't make sense or what parts you don't like, etc."
] |
[
"I don't know what you consider first principles, but I don't see why the equation can't be a starting point. I don't pretend to know more than you as I'm in the same part of my education, but my understanding is that Schrodinger's equation is assumed to be true and used as a starting point for deriving other results. This isn't any different from what Newton did with his famous laws. The fact that you could do an experiment and it fits to the equation you assumed/hoped to be true is not damning of that equation. It's the way observational science works. "
] |
[
"Physics for Scientists and Engineers (by Knight IIRC) has a good quasi-derivation of it by starting from the assumptions that matter (like a particle) can be expressed as a wave. Schroedinger got the idea to make a wave equation for matter when De Broglie postulated that all matter has wave properties, and not just photons. The Schroedinger equation is a wave equation."
] |
[
"Plasma formation in stars."
] |
[
false
] | null |
[
"Im currently doing A-Level Physics, and my next exam has an astrophysics unit. Im aware of the thermonuclear process within a star and about the Coulomb Barrier that must be overcome to achieve fusion. But nowhere can I find any explanation of how the nuclei become a plasma in the first place, it is pointless asking my teacher, because any question results in 'You dont need to know that'.",
"It's unfortunate that that's the attitude your teacher is taking (although it may be that s/he doesn't know and is trying to hide that). I'm not sure whether you're asking about the process of creating plasma in general or how stars get hot in the first place, so I'll try to answer both.",
"In general, if you take material and get it hot enough, the electrons will dissociate from nuclei, because they have too much kinetic energy to stay bound in the potential energy well of the nucleus. Stars form out of large gas clouds that collapse under their own gravity. You may be familiar with the ideal gas law-- pressure times volume is proportional to temperature. When this gas cloud collapses, the volume gets smaller, and that drive up the pressure and temperature. When you get up above ~10,000 Kelvin, the vast majority of hydrogen atoms become ionized. Get up to a few tens of thousands Kelvin, and the helium becomes ionized too.",
"Of course, to start fusion you need a temperature of about 10 ",
" Kelvin, so the core of the protostar has to collapse quite a bit for that to happen."
] |
[
"When the electron dissociate from the atom, is there any type of order in the 'plasma' or do they have too much kinetic energy to be bound by other forces (obv except the strong force)",
"Electrons don't interact via the strong force, so the particles in a plasma (electrons and nuclei basically) are just bouncing around."
] |
[
"When the electron dissociate from the atom, is there any type of order in the 'plasma' or do they have too much kinetic energy to be bound by other forces (obv except the strong force)",
"Electrons don't interact via the strong force, so the particles in a plasma (electrons and nuclei basically) are just bouncing around."
] |
[
"Does DNA in sperm/eggs vary and by how much?"
] |
[
false
] | null |
[
"In sperm and eggs, it varies due to chromosomal crossover and selection during meiosis. ",
"Meiosis is a special cell division where a 2n (2 copies of each chromosome per cell), becomes a 4n cell.",
"In this 4n cell, the chromosomes that are nearly identical to each other can exchange information through crossovers. For example if one chromosome has genes A and B and the other has the nearly identical version of these genes (called alleles) a and b, then a crossover between them would result in 1 chromosome having A and b and the other having a and B. After this process, the chromosomes randomly segregate into two 2n cells. After, in the 2nd stage of meiosis, the chromosomes segregate again and form two 1n cells. This means the sperm can have the chromosome that has the Ab product or the aB product. Those are the main sources of variation in sperm and egg, but other sources of variation exist. For example, errors in copying the DNA from the cells that produce the sperm and egg often make single base-pair changes (like A becoming G, or T becoming C, etc.) in the DNA also provide sources of variation, as do copying errors because of polymerase (the enzyme that copies DNA) slipping on DNA-- this occurs at very repetitive DNA and is the cause of diseases like Huntington's disease. ",
"In summary, variation comes from:",
" - every cell in the body, except for germ cells (sperm/egg), has 2 copies of each chromosome, and the process of meiosis means each sperm will have either one or the other. ",
" - each of these chromosomes will not resemble the cell that gave rise to them because crossovers that occur during prophase will separate genes on the same chromosome by exchanging with the other homologous chromosome",
" - random errors due to the enzyme that copies DNA will introduce further variation in the sperm cell",
" - i didn't mention this earlier, but it's the field I study so I should mention it in passing. this has to due with changes that don't involve DNA sequence (like methylation of the bases, modifications to the proteins that pack DNA) that can be passed onto the next generation and lead to variation in gene expression. however, it's currently believed that these changes mainly take place in the egg or embryo, as sperm cells seem to mainly reset the \"epigenome\" as it's passed on",
"Hope this helps!"
] |
[
"Expanding from this:",
"When each parent produces a gamete (egg or sperm) their two chromatids for each of the 22 or 23 chromosomes have a chance of 'recombining' which is an event whereby they essentially swap DNA about a common point.\nDetail here: ",
"http://en.wikipedia.org/wiki/Genetic_recombination",
"Like all cells, there is also a chance that the DNA specific to those cells mutate during the cell's existence. This can come about from a variety of sources (radiation, chance errors in replication, chemical effects). Most of these sorts of errors are corrected by DNA repair machinery (more detail: ",
"http://en.wikipedia.org/wiki/DNA_repair",
") but occasionally something sneaks through.",
"The rate of occurrence of a mutation like these is dependent on the organism itself as well as the efficacy of their DNA repair machinery. Often the repair machinery is actually better at protecting certain regions of the DNA, usually because it is more important to the organisms survival and breeding.",
"The average mutation rate per nucleotide per generation is thought to be around 1x10",
" based on wide scale genomic sequencing studies."
] |
[
"Expanding from this:",
"When each parent produces a gamete (egg or sperm) their two chromatids for each of the 22 or 23 chromosomes have a chance of 'recombining' which is an event whereby they essentially swap DNA about a common point.\nDetail here: ",
"http://en.wikipedia.org/wiki/Genetic_recombination",
"Like all cells, there is also a chance that the DNA specific to those cells mutate during the cell's existence. This can come about from a variety of sources (radiation, chance errors in replication, chemical effects). Most of these sorts of errors are corrected by DNA repair machinery (more detail: ",
"http://en.wikipedia.org/wiki/DNA_repair",
") but occasionally something sneaks through.",
"The rate of occurrence of a mutation like these is dependent on the organism itself as well as the efficacy of their DNA repair machinery. Often the repair machinery is actually better at protecting certain regions of the DNA, usually because it is more important to the organisms survival and breeding.",
"The average mutation rate per nucleotide per generation is thought to be around 1x10",
" based on wide scale genomic sequencing studies."
] |
[
"Why does the Earth have a magnetic field when nearly all the core is above the Curie temperature of iron?"
] |
[
false
] |
I understand that Earth's magnetic field is caused by the iron core, but why is that the case when the core is far above the Curie temperature of iron?
|
[
"The magnetic field of earth is not created the same way as the magnetic field in a permanent magnet, where the aligned orbits or spins (not sure which one) has a lower energy, and holds up to the curie temperature, but more by movement (so you could probably compare it more with an electromagnet. See this page on Wikipedia about it: ",
"https://en.wikipedia.org/wiki/Dynamo_theory"
] |
[
"That article is a bit convoluted, but the upshot of it is essentially that the liquid in the earth's outer core moves in such a way that it can induce a magnetic field from the field which is already there, and this turns out re-generate the original field, which in turns allows the field to be maintained, and so on... ",
"Essentially, the earth's interior works both as a generator and electromagnet at the same time, causing its rotation to be coupled to the magnetic field. The energy to power this electromagnet comes from the interaction between geothermal heat flow and the earth's rotation. ",
"Similar processes are responsible for the magnetic field of the sun, and all kinds of interesting phenomena like sunspots and solar flares. This is an area of active research, and the details are only partially understood. "
] |
[
"The curie temperature is where something loses it's permanent magnetism. ",
"An electromagnet does not rely on permanent magnetism. ",
"That's the simple answer anyway. ",
"http://en.wikipedia.org/wiki/Curie_temperature",
"Regions of magnetism over time within a material can align, this gives an object a permanent magnetic field. After the curie temperature is reached or approached these regions begin to randomize. It's not that magnetism is lost, a coherent magnetic field for the bulk material is lost.",
"A side note is the magnetic field is not caused by the inner solid core of the Earth. It is actually caused by the outer core, which is also largely made of iron.",
"Huge convection currents within the outer core moving iron material past each other acts as a large electromagnet. ",
"The inner core does play a role, without a inner solid core the convection currents would be random and wouldn't create a large coherent magnetic field, there would be bulges in the field and it wouldn't really extend past Earths surface. This is what it's like on Mars, no solid inner core the convection currents are all chaotic and random. The solid inner core acts as a barrier of separation allowing convection currents to be mostly uniform allowing a strong, uniform magnetic field to form.",
"http://en.wikipedia.org/wiki/Dynamo_theory#/media/File:Outer_core_convection_rolls.jpg",
"For the internal workings of the Earth a basic diagram.",
"While Mars magnetic field looks like this.",
"http://i.ytimg.com/vi/hRaXW9Z9V18/maxresdefault.jpg",
"Anyway long story short even after the curie temperature materials moving past each other can still induce a magnetic field."
] |
[
"What causes snowflakes to grow symmetrically?"
] |
[
false
] | null |
[
"The structure in which snowflakes form is dependent mainly on the environmental conditions like temperature and humidity. Since snowflakes are so small, the regions which they form in don't vary much in conditions, causing very similar crystal growth. "
] |
[
"The molecules arrange themselves with the aim of creating the highest structural integrity. ",
"Do they calculate what structure has the highest structural integrity with their tiny molecule-brains?"
] |
[
"The molecules arrange themselves with the aim of creating the highest structural integrity. ",
"Do they calculate what structure has the highest structural integrity with their tiny molecule-brains?"
] |
[
"How do we know what an animal’s field of vision looks like? I.e. how can we tell that rodents see in yellow hues and that certain insects can see UV light?"
] |
[
false
] | null |
[
"Because we can stick electric probes into their eyes and brains and see what happens when we shine different types of light at them. Not even joking. In the olden days we would chop out bits of retina to get the photoreceptors and then measure which wavelengths of light they absorbed or otherwise reacted to. Also not even joking: ",
"https://www.nature.com/articles/339137a0.epdf"
] |
[
"Pretty much the above.\nRhodopsins are specilized proteins that absorp certain wavelength to trigger a G-protein-coupled-receptor signaling cascade leading to depolarisation of the retina cell; thus converting a photon into an action potential to be transmitted to the brain."
] |
[
"Yup! I've done those preps. Totally not fun trying to dissect out the retina under nothing but very dim red light. "
] |
[
"Can you get interference between an electron wave and a photon wave?"
] |
[
false
] | null |
[
"Yes, imagine if you had a microwave oven with nothing in it, you turn it on and induce a changing EM wave(light waves) in the microwave, if there is a single electron in it, it will go in the direction opposite of the direction of the field because it is negatively charged. I hope this helps."
] |
[
"Thanks, what I meant is more interferences in terms of destructive amd constructive interference ..is this possible ?"
] |
[
"Im not too sure on that one. The relationship is: wavelength = h / momentum. h is plank's constant (6.626e-34 Joule * seconds) So if the electron stops moving completely and momentum goes to zero, the wavelength goes to infinity which means frequency goes to zero which means no wave like behavior. But the moment you turn on the microwave, the electron should start moving and behave more like a wave, but I think the probablility wave of the electron should still be a perfect sin wave given no other electrons are there to interfere with it."
] |
[
"In another universe would the laws of physics have to apply?"
] |
[
false
] |
Title says it all...if there were multi-universes would the law of physics exist? Asked a buddy today that question and he said no because of something to do with an equation with particles...is this true? Thank ya.
|
[
"Well we don't know because we've only seen one."
] |
[
"Well there's no way for us to know."
] |
[
"Every universe that exists would have to have its own physical laws, as they're laws that define everything that universe is and does. Whether or not those laws are the same as ours or totally unique is what you would be better off asking."
] |
[
"Is the Earth moving away from the sun like the moon is moving away from the Earth?"
] |
[
false
] | null |
[
"Moon is moving away from the Earth ",
"Sources",
"http://www.space.com/3373-earth-moon-destined-disintegrate.html",
"http://www.bbc.co.uk/news/science-environment-12311119"
] |
[
"Orbital migration due to tides is negligible for the Earth. For realistic parameters, tidal migration is only really significant for planets within ~0.06 AU (Jackson et al 2008). Note that for planets that close they migrate inwards because they're orbiting faster than their star is rotating (whereas the Earth is orbiting slower than the Sun is rotating (1 yr vs ~1 month), and similarly the Moon is orbiting slower than Earth is rotating (~1 month vs 1 day))."
] |
[
"Thank you."
] |
[
"How fast would an indestructable 50c euro coin have to go to destroy earth on impact?"
] |
[
false
] |
If it is at all possible. Wikipedia for coin
|
[
"Very approximately, for the coin to have a kinetic energy that is comparable to Earth's gravitational binding energy, it would need to be going about 0.999999999999999999999999999999999999 times the speed of light. That is a lot more 9's than the \"Oh My God\" particle cosmic rays are reaching."
] |
[
"xkcd did a What-If a pitcher threw a baseball at 0.9c...",
"https://what-if.xkcd.com/1/"
] |
[
"Things can't go faster than light."
] |
[
"How do incoming phone signals cause speakers to make noise?"
] |
[
false
] |
It happens before a text is received on my phone when it is near to a set of speakers, and I've always wondered how the phone causes it. I realise that trying to describe this sound in text may look stupid but it is a sort of thing. Thanks for any help anyone can give.
|
[
"There is not enough power to produce sound on the main coil of the speaker. The signal enters the system at the high gain input of the audio device, and affects microphones as well as speakers. "
] |
[
"All the other answers are missing the key element here: most radio broadcasts won't be picked up by audio gear because they are too high frequency. If you put a speaker right next to your wifi router you won't hear any similar noise, even though the amount of power being transmitted and the radio frequencies being used are very similar to cell phones.",
"The important part is that a specific very popular kind of phone network (GSM) uses TDMA for voice communications, and in this scheme the signals are chopped up into short 4.6 millisecond frames. This has the side effect of creating a 217 Hz radio sideband which quite easily couples to wires and speakers and is well within the audible audio spectrum. More than that, because the phone itself sends signals in pulses at 217 Hz the internal power components of the handset such as the battery, wiring, etc. will be pulsed off and on with a characteristic 217 Hz cycle, creating additional noise. Not all phones have this problem though, pure CDMA phones do not for example."
] |
[
"drove me mad when I used to lay my phone next to my receiver... every hour on the money.. took me days to put my finger on it;) "
] |
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