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"[Weekly Discussion Thread] Scientists, do you use the scientific method?"
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[
false
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This is the sixth installment of the weekly discussion thread. Today's topic was a suggestion from an AS reader. Topic (Quoting from suggestion): Hi scientists. This isn't a very targeted question, but I'm told that the contemporary practice of science ("hard" science for the purposes of this question) doesn't utilize the scientific method anymore. That is, the classic model of hypothesis -> experiment -> observation/analysis, etc., in general, isn't followed. Personally, I find this hard to believe. Scientists don't usually do stuff just for the hell of it, and if they did, it wouldn't really be 'science' in classic terms. Is there any evidence to support that claim though? Has "hard" science (formal/physical/applied sciences) moved beyond the scientific method? Please have a nice discussion and follow our rules If you want to become a panelist: Last weeks thread:
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[
"Speaking from the biological and medical sciences, I can say I use the scientific method closer to the way it is defined by Karl Popper than by the way it is defined by grade school science teachers. It is infinitely frustrating to have to instruct every year of graduate students that you advance science by rejecting probable hypothesis, and that it is of comparably little use to support existing hypotheses. The best studies contrast the two or more most likely hypotheses, and are guaranteed to reject at least one.",
"If you set out an experimental design that does not have a good chance of rejecting a prominent hypothesis, it is not a strong experimental design. "
] |
[
"Speaking from the biological and medical sciences, I can say I use the scientific method every day. It's more of an automatic process going on in a scientist's thinking than any kind of formal breakdown into steps. Practically speaking, the scientific method is a cycle that can be entered at any point, as an observation commonly precedes a hypothesis or sometimes a surprise within an experiment can lead to a new hypothesis, etc. ",
"The only near exceptions I can think of is scientists involved in search and discovery or large screens such as high-throughput drug screening or genomics screening. In this case, there is often no clear hypothesis and it is more of a \"see what we get\" approach. This is also the case with SETI or things like that. But it isn't really fair to call it an exception because the results usually lead to interesting science and a considerable amount of science goes into the setup. ",
"Edit for broadening of second paragraph"
] |
[
"Probably this won't surprise anyone, but mathematicians certainly don't use the scientific method in a recognizable form (although there's more observation → hypothesis → experiment than you'd expect in the craft of mathematical research)."
] |
[
"Light has been slowed way down and observed, but where did the energy come from to speed it back up?"
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[
false
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So there have been experiments that have slowed light down enough where we could observe them, but then as the particles pass through the experiment, they speed up again to their normal speed. How? You need some kind of force to speed up or slow something down. What is making the light speed back up again?
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[
"So the answer to the question about energy is pressure energy. Non-straight motion energy is said to be pressure energy.",
"And that's where the force comes too: pressure."
] |
[
"I don't really know which experiment you are talking about, but it has most likely to do with quantum entanglement and nanoscopic mirrors, or the manipulation of phase or group speed. None of them actually slows down single photons, they only interact with the beam as a whole, causing strange speeds to appear, but under an enormous information loss, thus no interaction in the common sense. You can't slow down single photons and therefore you can't speed them up either. I might tell you more if you could link to the experiment, you are reffering to. "
] |
[
"They were talking about it on NPR yesterday. It was one of the sciencey shows (Radio Lab) they have and they interviewed the lady that developed the experiment. Sorry for not having more info on this but going by memory, she slowed down light down to something like 17 m/s using a bunch of lasers, so while the light was passing through her experiment it was at that speed, but then after it sped back up to C. ",
"Here's her wiki page:\n",
"http://en.m.wikipedia.org/wiki/Lene_Hau",
"The whole slowing down of light (and the page even states she ",
" altogether) is crazy enough, but as per my initial inquiry, how did it speed up again?"
] |
[
"If atoms are made up of protons and neutrons and protons and neutrons are made up of quarks, then what could quarks possibly be made up of?"
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[
false
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[
"As of right now, we don't think quarks are made of anything besides quark. There has to be some \"lowest layer\", and we think that quarks are that lowest layer for neutrons and protons and the like. All experiments we have conducted seem to show that quarks are fundamental, but it's also possible they're made of something even more fundamental we don't know of yet."
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[
"And what might strings be made of? is it turtles all the way down?"
] |
[
"This right here. The standard model of particle physics is to (what we currently believe are) fundamental particles as the periodic table is to elements. The only other option at the moment is string theory, but it's yet to achieve experimental validation. "
] |
[
"What is the best (and most realistic) option for a warp drive?"
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[
false
] | null |
[
"There isn't a realistic one."
] |
[
"But what about Alcubierre drive?"
] |
[
"The Alcubierre drive wasn't meant to be taken seriously as a method of propulsion, it's just an interesting theoretical result of applying general relativity. It would need negative energy densities to work, which don't exist."
] |
[
"How fast am I going?"
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[
false
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[deleted]
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[
"Relative to what?"
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[
" because it's a great question (perhaps it gets asked regularly); the answer is pretty mindblowing, to me :D ",
"The question is in fact meaningless, because it assumes the existence of something called ",
". It is in fact not possible to take an object and measure its velocity in such a way that every observer, at every point in the universe, can agree on how fast it is going. The only way we can measure motion is by observing objects in a relative reference frame. ",
"And there is no universally motionless object which we can all use as our reference frame, so in fact, there is no such thing as motion unless it is relative to another object. Scientists once believed that one such possible \"universally-motionless\" thing that everyone could measure themselves against ",
" exist, and they called it the ",
"aether",
". In one of the most remarkable results in scientific history, the ",
"Michelson-Morley experiement",
", the aether was found not to exist, which gave some weight to the idea of absolute motion (and absolute space) not existing. ",
"This realisation, which all started with a question exactly like yours, was one of the big motivations that brought along the Theory of Relativity, now of course one of the most important theories in physics! ",
"If we apply this train of thought to your second question, we can see that there is no actual way to define the term \"all motions\". We can say \"What if the Earth stops moving relative to the Sun\", and \"What if the Sun stops moving relative to the galaxy\", and so on, but we will never actually get far enough in this series of questions to ask what happens when ",
" motions stop, because there is no reference frame in which all objects are moving. Weird huh! ",
"See Osymandius' ",
"reply",
", however, for an estimation of our movements relative to the galaxy, Sun, and Earth."
] |
[
"Asked a number of times in the past",
"."
] |
[
"Will a power outlet that has a lower number of amps than is typical (i.e. 9 amps vs. 15) not be compatible with some electronic devices?"
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[
false
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[
"Typically no. Unless the device requires more current than the outlet is able to provide, which is unlikely with small electronic devices. Most electronic devices are even compatible with a range of voltages, instead of only operating on a single voltage."
] |
[
"So my electric piano has 13 watts of power consumption and has this kind of power supply \"Power supply (DC12V 3.5A), POWER switch\"",
"http://www.korg.com/us/products/synthesizers/krome/page_4.php",
"This is what I've heard about the power outlet at the place I'm going:",
"\"About 9 amps. Enough for fan, computer, small amp pulls.\"",
"Compatible? THANK YOU SO SO MUCH This is a huge deal for me."
] |
[
"Absolutely enough. The 3.5A is the maximum current that your device would need. So 9 amps would be more than enough."
] |
[
"Some deeper questions about the double slit/quantum eraser experiment"
] |
[
false
] |
Hey guys. I recently stumbled upon the and my understanding is that, when they set up recording devices that automatically delete what they recorded after the particles land, the particles form an interference pattern. If it doesn't delete the information, they don't interfere. To me, this is absolutely astounding, that these particles can seemingly "see the future." I have several questions, and I'm looking for further documented experiments (if any). Has anyone conducted experiments like these? What were the results? Thanks for your time!
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[
"Can you give me a link to where you describe them deleting it? I do not believe this is true and you may be misinterpreting something. This has nothing to do with whether or not somebody is observing, it has to do with whether the device is interacting with the electron to determine where it is. The interaction itself causes it to act like a particle and not a wave."
] |
[
"The wikipedia article on ",
"Delayed Choice Quantum Eraser",
" has a bit more information about the erasure aspect:",
"In a quantum eraser experiment, one arranges to detect which one of the slits the photon passes through, but also to construct the experiment in such a way that this information can be \"erased\" after the fact.",
"In practice, this \"erasure\" of path information frequently means removing the constraints that kept photons following two different paths separated from each other.",
"In one experiment, rather than splitting one photon or its probability wave between two slits, the photon is subjected to a beam splitter. If one thinks in terms of a stream of photons being randomly directed by such a beam splitter to go down two paths that are kept from interaction, it is clear that no photon can then interfere with any other or with itself.",
"If the rate of photon production is reduced so that only one photon is entering the apparatus at any one time, however, it becomes impossible to understand the photon as only moving through one path because when their outputs are redirected so that they coincide on a common detector then interference phenomena appear.",
"In the two diagrams to the right, photons are emitted one at a time from the yellow star. They each pass through a 50% beam splitter (green block) that reflects 1/2 of the photons, which travel along two possible paths, depicted by the red or blue lines.",
"In the top diagram, one can see that the trajectories of photons are clearly known — in the sense that if a photon emerges at the top of the apparatus it appears that it had to have come by the path that leads to that point (blue line), and if it emerges at the side of the apparatus it appears that it had to have come by way of the other path (red line).",
"Next, as shown in the bottom diagram, a second beam splitter is introduced at the top right. It can direct either beam towards either path; thus note that whatever emerges from each exit port may have come by way of either path.",
"It is in this sense that the path information has been \"erased\"."
] |
[
"So it doesn't matter whether or not someone actually observes it, it really matters on whether or not it will be possible for the outcome to be recorded indefinitely? Very intriguing. Now what about the death of the observer? Arguably every person viewing it will die, and the information will be \"deleted.\" What happens if it will be viewed by a person and then the information permanently deleted from the machinery? Surely the machinery can't last forever either though.",
"Thank you for answering."
] |
[
"What causes this colour effect on the rocket engine?"
] |
[
false
] |
If you watch the engine during firing, there's a band of colour that slowly moves across the rocket bell. Is this the camera or something to do with heating?
|
[
"Engineer here (who works with video): This effect comes from the camera shutter speed \"beating\" with the lighting (just like beat notes in music, but for video). This is a very common effect. If fluorescent or LED or other non-incandescent lighting is used the light might look continuous to your eye, but is actually pulsing (and in the case of fluorescent is pulsing reddish with bluish). If the camera shutter is synchronized with the lighting, you get fixed color bands, and if sync is a little off, the color bands creep. ",
"This happens so often there are tools in video editors to fix it (see here: ",
"https://www.youtube.com/watch?v=JZ8ci73LOio",
"). I tried to find you a good video on youtube of the effect but the best I got was the editor video in the link above. The guy doesn't show the effect in \"real time\" so you have trouble seeing it, but trust me, I see this all the time. It is quite a nuisance. ",
"Fun fact: since the bands are horizontal, you know that is how they are scanning the detector array. If it were scanned left and right the bands would be vertical."
] |
[
"Photographer here: To my eyes it looks like a ",
"moire pattern",
" caused by fine visual details in the bell going in and out of sync with the pixels in the camera's sensor, possibly due to vibrations in the bell and/or the structure housing the bell to which the camera is mounted. "
] |
[
"I think you will see it ",
" there during the whole video. At the very beginning, before engine start, you'll see darker/lighter horizontal bands (about 1/3 the length of the nozzle) creeping up the nozzle. Maybe your monitor isn't adjusted to see them on the dark nozzle, so in that case look at the area around the lights on the ceiling - you'll see it there. The effect is there throughout the whole video. ",
"Let me point out where you ",
" see it: Look at the area around the engine flame or the daylight areas in the background. There reason is that in those places the primary illumination does not have the flicker that the lights do. When the engine cone heats up it starts to mildly incandesce which lightens it's color. However most of the illumination still comes from the artificial lighting, so you see the bands. Another interesting fact: most solid-state camera sensors tend to respond to near-infrared, and an infrared cut-off filter is installed in the camera to help suppress that response. I'll bet that nozzle brightened up some, but I'll bet it wasn't that bright to the naked eye - the camera accentuated it. If you want to see this effect for yourself, take a solid-state camera (like your cell phone), turn on the camera and look at the picture while you point your TV remote control at it. I'll bet dollars to donuts you'll see the near-IR from the remote in your phone camera, but you won't be able to see them with your naked eye.",
"Enjoy that experiment - it's a good way to tell if your remote batteries are good :-)"
] |
[
"What role does working memory have in work ethic, taking initiative and career success?"
] |
[
false
] |
This is in response to seeing the MIT post about intelligence vs. persistence: As I understand it working memory is the attribute by how we retain and manipulate information. Remembering a phone number, retaining what you just read, telling a story without mixing up the sequence, etc… So in a goal for example; How does the mind organize the task, and retain an accurate relationship between Specifically:say you want to update your resume and apply to a job. It has many sub-tasks such as editing, finding a synonym, etc. How many are there? How much time will EACH take in relation to finishing? So my guess is if one has a poor working memory, you get confused. The path to the end is an UNKNOWN variable and you have trouble “seeing it done.” Initiative? Well you do not start because the steps, time and effort are so UNDEFINED. You can’t hold it all in your mental “staging area;” too many moving parts make it difficult to realize how much delay you must endure to get gratification. Or you are 20 minutes in and you cannot gauge your progress relative to the finish line. Where were you again?? How many times did I reread that sentence?? You lose confidence that your effort yields the output. POOF! Wind out of your sails, back to Reddit, slacker. If you have a high working memory capacity, maybe you CAN focus on that last task with confidence. You see the steps and how long they will take with more clarity. You’re motivated because of vital feedback that your effort means you’re 20% closer, and not somewhere between '10% oh maybe 25%... hell, what's on TV??' So there is my premise. Here are the questions: What research exists on working memory capacity and efficiency in the work place? Any general population studies test the correlation between successful people (income/happiness) and working memory capacity? I have heard of aids like nootropics and brain training, like dual-n-back. What research is out there to show the effects of nootropics or brain training on working memory? Has research shown that they translate into job/task efficiency and motivation? And to sum it all up; does research exist to show how working memory effects attention span? Note: I know we aren’t computers and we all have working memory limits. I’m interested in degree. And there’s no doubt most people, even objective researchers, would not take so kindly to the suggestion that drive and work-ethic rely on some genetic, cognitive ceiling. I understand that. I hope it doesn’t resonate too strongly. Thanks for taking a look at this. And a thanks to the mods for helping to clean it up and get more out of it.
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[
"Let's assume that working memory is an observable indicator of the latent factor, \"intelligence\". Along with things like quantitative ability, verbal ability, and spatial ability, memory is going to be higher for those who are smarter. Many suggest the idea of 7 +/- 2 \"chunks\" of information is the typical range of most human working memory capacity. That is, we can remember somewhere around 5-9 random groups of organized information at any given time. That doesn't answer your question though, but we're getting there. ",
"Intelligence and efficiency in the work place is one of the most largely studied things in organizational psychology. Frank Schmidt and John Hunter spend many years arguing that there is no better predictor of future job performance than intelligence, with corrected meta-analytic validities in the .50 range (very big for social sciences). Importantly, most research now suggests that this relationship is mediated by job knowledge. So, smarter people can remember more, and therefore they can acquire more job knowledge (more chunks), and also can acquire it more quickly than less-smart people, and it is job knowledge that relates to job performance (they also suggest a direct effect as well). Unfortunately, much of their work comes from unpublished military data samples, and this can be biased because the military may only be interested in hearing reports of what's a significant relationship (file drawer problem, so to speak). Some of my recent work puts the estimate more in the .30-.40 range--still quite substantial. ",
"If you're not thinking about intelligence as working memory, at least realize they are very highly correlated, and thus you're going to get the same pattern of relationships I just mentioned for intelligence-performance results.",
"Ganzach (1998) did a study of intelligence and job satisfaction. He didn't really find much of a relationship there. ",
"Judge et al. 2010",
" did a study on general mental ability (a battery of tests) and subjective well-being and found a .19 correlation, and economic well being at .32. They also found positive relationships between intelligence and subjective and objective health. I think Judge had a better method and measure than Ganzach, but feel free to check it out yourself.",
"Haven't really seen much in my journals relating to question 2 or 3, but I worry for question 3 that there is some overlap in the construct you're assessing. Your method would need to cleanly parse out a measure of both working memory (usually digit span), and some measure of attention span. Not exactly sure what the latter would be, it's a bit out of my research area."
] |
[
"I disagree with your point about the relationship between intelligence and motivation. Social cognitive theory (Bandura) would say that motivation largely means self-efficacy, or the belief that one can achieve or be successful at any given undertaking. Self-efficacy mobilizes effort and persistence over time. If you think you can do something, you're more apt to work towards doing it (let's not bother with discussing perceived task importance though). One could also use goal setting, effort, or just plain motivation as variables as well. ",
"Again, ",
"Judge et al., 2007",
" meta-analyzed this literature and found a .20 correlation across 26 studies between intelligence and self-efficacy. I more recently compiled for a meta-analysis these broader variables for motivation and found a slightly larger value, about .23. Now this is not strongly related, but certainly noticeable and meaningful. "
] |
[
"Perhaps I can add to this great response with some specifics on the working memory construct. It is worth noting that working memory ",
" attention and specifically we call it \"higher order attention\" (which is different from being-able-to-maintain-focus type of attention). Working memory is intimately tied to executive functions (e.g. problems solving etc) and cognitive control. Some believe that functions such as cognitive control (and consequently working memory) are the most important part of intelligent cognition as it is a strong indicator of the flexibility an individual has in dealing with novel information. Here are a couple of references I found with a quick search for further reading: ",
"here",
" and ",
"here",
". ",
"With respect to wellbeing and job performance etc, again I am not sure about specific articles on working memory but like the previous answer ",
"IQ is strongly related to a variety of better life outcomes",
" and the strong correlation between working memory and IQ suggests similar relationships. Clinically speaking, individuals with poor working capacity have significant problems in daily life. This can take the form of memory problems (ie. they cannot attend long enough on the information to learn it), difficulties with appointments etc. Individuals with below average working memory would find complex tasks to be difficult (as you discussed in the OP) and therefore are more suited to jobs that have structure in the processes they need to do.",
"One final point that cannot be under emphasised is that there is no reason to suggest that IQ or working memory ability has any direct relationship with motivational achievement. They are subsumed by different neural circuitry (although there is some overlap) and motivation is more likely associated with basic attention rather than working memory."
] |
[
"Does putting helium into an object (say, a box) make it lighter? Would it weigh less on a scale versus the same box without helium?"
] |
[
false
] |
The box would somehow be sealed with the helium inside of it. My logic is that you can put helium into a balloon and it rises, therefore it couldn't even be weighed because gravity can never pull it down. If you could put helium into a box, would the helium "pull" the box upward, making the box weigh less?
|
[
"That completely depends on the size of the box, not the weight.",
"A 5ft cube of air weighs about 10 lb, and the same cube of helium weighs 1.4 lb, so you would see a 8.6 lb decrease, regardless of how much the box weighs. "
] |
[
"A box of one cubic meter would be about ",
"1 kg lighter",
" if it was filled with helium instead of air."
] |
[
"Well, you're replacing the air inside with helium, which weighs less than normal air. So yes, unless the box previously had a vacuum inside of it."
] |
[
"How can I cheaply cool my room?"
] |
[
false
] | null |
[
"You can't get much cheaper than subsidized electricity.",
"If the initial cost is prohibitive, find a used one cheap or free on craigslist, freecycle, etc."
] |
[
"Put a white sheet over any windows in the room you are trying to keep cool. Keeping sunlight out is the easiest way to keep a room cool. Don't just throw any old sheet over, though. Specifically a white one to REFLECT the light. "
] |
[
"Get yourself a cheap window air conditioner for $125.00",
"http://www.amazon.com/Frigidaire-FRA052XT7-000-BTU-Window-Conditioner/dp/B003F4TH6G",
"Depending on the cost of electricity where you live, you should be able to run it for no more than $.10/hour. (500 watts @ $.14 per kilowatt hour = $.07 per hour.)"
] |
[
"Would repetitive consumption of a incredibly hot pepper (Carolina Reaper, etc.) eventually yield lesser physical response?"
] |
[
false
] | null |
[
"Capsaicin, the spicy component of hot peppers, does indeed cause desensitization of the TRPV1 nociceptor with prolonged activation. This seems to underlie some of the effect of topical capsaicin against several types of neuropathic pain.",
"https://www.ncbi.nlm.nih.gov/pubmed/20932251",
"\n",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3462404/"
] |
[
"To add onto this comment (which explains it very well), this phenomenon is known as receptor desensitization and is part of the reason why returning drug addicts get an overdose. If you do a certain drug (or in OPs case you take a hot pepper) over time your receptors will be desensitized through different mechanisms, but when you stop and you don't take these drugs anymore your receptors will (to a certain extent) revert back to basal levels of activation. So when a drug addict goes back to the same dose of drugs before he stopped, he will often OD."
] |
[
"To add onto this comment (which explains it very well), this phenomenon is known as receptor desensitization and is part of the reason why returning drug addicts get an overdose. If you do a certain drug (or in OPs case you take a hot pepper) over time your receptors will be desensitized through different mechanisms, but when you stop and you don't take these drugs anymore your receptors will (to a certain extent) revert back to basal levels of activation. So when a drug addict goes back to the same dose of drugs before he stopped, he will often OD."
] |
[
"If the Moon gets further away from the Earth every year, is the strength of the tides lessened?"
] |
[
false
] |
[deleted]
|
[
"The tidal forces used to be a lot stronger back in the early epochs of our planet's history. snooptray is correct, the tides' strength will lesson over time. I wonder what will happen when we lose them entirely..."
] |
[
"That's the idea that some people (like myself) have. What sort of effect will losing the tides have on ocean ecosystems, especially ecosystems that are structured around having nutrients transported by tidal forces? Destruction of those ecosystems could cause a ripple effect."
] |
[
"That's the idea that some people (like myself) have. What sort of effect will losing the tides have on ocean ecosystems, especially ecosystems that are structured around having nutrients transported by tidal forces? Destruction of those ecosystems could cause a ripple effect."
] |
[
"What's the consensus (if there is one) on Benjamin Libet's \"readiness potential\" experiments?"
] |
[
false
] |
I've read many criticisms from philosophers, but haven't found many statements from neuroscientists leaning either way. Is it accepted as fact that decisions are unconsciously made before the agent is aware of it? (There's some info on this here: )
|
[
"yes there have been modern updates on this experiment and it is commonly accepted that your brain makes decisions before you are consciously aware of them (and shockingly, sometimes will make up explanations for those decisions after the fact).",
"http://www.nature.com/news/2011/110831/full/477023a.html#B1"
] |
[
"interesting idea. does knowing seems to imply conscious awareness? one might argue even a thermostat can make a decision (namely whether to turn the heat on)."
] |
[
"correctly, you make your decision before you THINK you are aware of it.",
"if it can be shown that you make your decision before you think you do, why can't it be that you know of your decision before you think you know?"
] |
[
"If pi or other irrational numbers are normal, then can they be used to compress data by referring to where in pi each string of data occurs?"
] |
[
false
] | null |
[
"No. The value you'd need to point to the sequence would, on average, take up as much space as the sequence itself. ",
"Edit: To the other answers here: Storing 100 bits of random data takes on average about 100 bits. I don't care how fast your computer is or how much time you spend. 100 bits it is. Otherwise you'd basically be breaking math. "
] |
[
"That's an interesting idea, but for it to be fruitful you'd need to know infinitely many digits of the normal number. Check out the ",
"Pi-Search",
", where you can search the first 200 million digits of pi. That's a whole lot of digits, but my phone number doesn't appear in them. Neither do the first 8 Fibonacci numbers. Etc.",
"Unless you want to break down all the data you're encoding into small chunks (in which case the encoding barely saves any space), you won't be able to do much with this."
] |
[
"Do you have any idea how long it would take to calculate 200 million digits of pi? probably hours. Also, what is \"constant memory\"? Are you referring to the hard drive or Random Access Memory?"
] |
[
"How analogous to light waves are sound waves?"
] |
[
false
] |
I've just been wondering this ever since I heard that scientists found out they might use sonic black holes to study how cosmic black holes because. But do light and sound behave similarly enough for this to be viable?
|
[
"So can sound"
] |
[
"We call them phonons."
] |
[
"I'm not sure about your sub questions but to take a stab at your primary question: they really aren't that similar. Light waves are transverse waves and sound is usually longitudinal. Sound absolutely requires a medium and light can travel through a vacuum."
] |
[
"Why is the hole in the ozone layer over Antarctica? Why does the ozone not diffuse into an even layer around the Earth?"
] |
[
false
] | null |
[
"Ozone depletion is due to chlorofluorocarbons (CFCs) in the stratosphere above the Antarctica and to some degree the Arctic. Under the right conditions, CFCs can undergo a reaction that releases chlorine ions, which break up ozone molecules. For a couple of reasons, this is most dramatically observed above Antarctica:",
"Meteorologically, the atmosphere above Antarctica is largely isolated from the rest of the world, a phenomenon called the 'polar vortex.' It’s essentially a persistent, giant cyclone over the Antarctic continent. Therefore, the loss of ozone there isn't replaced quickly with influx from the surrounding atmosphere.",
"The reaction that breaks CFCs up to release chlorine ions occurs under very, very cold conditions and when high energy (ultraviolet) photons are present. During the winter in the Antarctica, the stratosphere becomes cold enough for the reaction to occur and in the early spring when the stratosphere starts to receive sunlight again, UV light causes the reaction.",
"Another phenomenon of the Antarctica stratosphere, and sometimes the Arctic stratosphere, is that it becomes cold enough for ice to crystallize out (approximately -80 degrees), creating polar stratospheric clouds (PSCs). Reactions on these ice crystals speed up the chlorine ion production which depletes the ozone faster, so there is a correlation between PCSs and ozone depletion thus PSC monitoring is part of the data collected when assessing ozone depletion.",
"CFCs are everywhere in the atmosphere and ozone depletion due to CFCs occurs worldwide, but in the Antarctic and Arctic, where the stratosphere becomes cold enough for PSCs, ozone depletion is most severe.",
"Source: I spent 8 months in Antarctica collection data on the ozone hole as it forms in early spring."
] |
[
"Here",
" you can see point one demonstrated quite clearly. If you rotate the globe to the north and south poles you can see that at all times there are a ring of weather systems around the south pole, isolating it, while no such thing exists around the north pole."
] |
[
"This ",
"Link",
" might show it better (adjusted the settings)"
] |
[
"I was looking around on Google maps and I found some frozen (?) lakes in Russia with periodic lines on them. I'm wondering what those lines are and how they're created"
] |
[
false
] |
I linked a few examples, though the first one is the most obvious. The first thought that came to me is that, somehow, the waves on the lake managed to freeze, but it doesn't make too much sense when I think about it. The lines themselves follow the same direction in all the bodies of water, which seems strange to me.
|
[
"pretty sure it has to do with either the watermarking from google, or perhaps the passes the satellite was making to take the pics, they appear on many large bodies of water all over on google maps."
] |
[
"If I may ask, why does that mean it is not natural?"
] |
[
"That would be a huge formation. Something occurring regularly and at that size would be a very interesting and well studied/documented phenomena. Therefor, if we haven't heard of it and it isn't easy to find information about, it's probably not real."
] |
[
"Do humans use pheromones like animals in ways, e.g., to mark things, for others to detect, etc.?"
] |
[
false
] | null |
[
"I'm no expert. However, I do remember a lecture on the olfactory system in which my professor spoke of a few studies regarding humans picking up chemosignals. One of them looked at state anxiety of females when exposed to the sweat of males who had high or low state anxiety. The females exposed to the high state anxiety sweat showed increases in their own state anxiety. Another one had to do with mothers and their infants. In a blind test, the mothers could often (can't remember how often - but higher significantly higher than chance) pick out their infant's clothes over the clothes of other infants. To answer your question, it would seem that we do use pheromones. To what extent? I don't know. There are likely other examples of humans using pheromones that I'm unaware of.",
"Edit : Found an article about sweat & state anxiety - ",
"http://www.ncbi.nlm.nih.gov/pubmed/20929974"
] |
[
"Another example is with attraction. People in your reasonably close family smell in a way that stops family members from being attracted to them. Its an evolutionary mechanism to prevent incest."
] |
[
"Humans (also) have a organ called, Jacobson's organ, this is a chemoreceptor which detects (or 'senses') pheromones (which in essence are chemicals) secreted by other humans. Humans use pheromones to attract the opposite (or same?) sex. This pheromone gets secreted in sweat. Companies also use pheromones in deodorant and perfumes(The axe effect).",
"They have done studies in which males and females wore a shirt for a day or two, the opposite sex would then smell the shirts, not knowing who's it was and choose which shirt they preferred. Turns out, you would prefer the person with a complete different immune system. This refers to the smell ",
"/u/TheGreaterest/",
" was talking about.",
"Little fun fact; woman who take birth control pills end up choosing the wrong male, they choose a male with a similar immune system.",
"Another fun fact; woman who are ovulating are feeling 'more attractive' and send out a signal (secrete a pheromone) to let the males know.",
"With this said, yes humans do use pheromones in ways animals do when it comes to attraction. You may want to look up jacobson's organ. "
] |
[
"Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Are you looking for something like ",
"this map",
"?",
"Units are what I think you are asking about and it does look sufficiently different than the ",
"gravitational anomaly map",
"."
] |
[
"The sky is, in fact, blue in all directions, and you can see that fact in ",
"pictures from space",
". ",
"When you're looking up at the sky during the daytime, the background behind the sky is just the blackness of space, so the scattered light in the atmosphere is almost always the brightest thing in your line of sight (unless you're looking at the Sun or Moon).",
"However, when you're looking down at the Earth's dayside surface from space, that surface is brightly lit by the Sun and so it's brighter than the atmosphere. As a result, you basically see the surface of the Earth, slightly blue-tinged by the atmosphere."
] |
[
"Celestia is great, but I much prefer ",
"SpaceEngine",
". It's a program made by a crazy russian to give ",
"accurate",
" locations of objects that we know about, at any point in time, much like Celestia. BUT, SpaceEngine will randomly generate planets, stars, nebula, and entire galaxies, down to centimeter accuracy, if we don't know what is out there for sure. It's really cool to go ",
"planet hunting",
"."
] |
[
"Why does the smell of fast food linger more than the smell of other foods?"
] |
[
false
] |
Is there a scientific reason as to why the smell of fast food seems to linger longer than the smells from other foods, especially in confined spaces such as airplanes or cars? [edit] Holy cow this blew up much more than I expected, thanks for the informative responses!
|
[
"It has to do with partitioning. ",
"The way smell works is that a few molecules or tiny droplets of an object (or a volatile component of some substance) takes to the air and a few molecules of it end up in your nose. There, some of it dissolves into the mucous of your nose, and then various receptors recognize parts of the molecule and try to match it to something you've smelled before. ",
"The problem happens when after dissolving in mucous, the molecules don't want to leave anymore. There's an equilibrium between molecules dissolved in mucous and molecules dissolved in the air, and if that lies to the left, the odor will be more persistent. The best example of this is called ambergris, ",
" ",
" that is used to make tiny amounts of expensive perfume smell rather strong.",
"The confined space effect is a little different I think. If something is generating airborne particulates, carrying out that process in a confined space will keep all of the airborne things in one place making them very concentrated. More things to smell -> stronger smell (sort of). Sometimes that smell can follow you around either because it condensed onto your clothes, skin, hair (e.g. vaporized fats like bacon grease condensing into liquids and solids) or because it's a particulate or volatile that gets stuck in the bubble of dust that follows you around all day (this is why sometimes you can tell where a person has been and what they've been doing just from smell).",
"Edit: Thanks ",
"/u/SalishSailor",
" for the fact check."
] |
[
"Can you please elaborate on this \"bubble of dust\" you speak of?"
] |
[
"No, it's a ball of waxy stuff thought to encase foreign objects in the digestive system. It gets excreted and then does float around for years and harden as you describe, but doesn't start out as a liquid. An analogy would be the tonsil stones that sometimes form in the back of your throat from bacteria, food and minerals.",
"http://news.nationalgeographic.com/news/2012/08/120830-ambergris-charlie-naysmith-whale-vomit-science/",
"http://en.m.wikipedia.org/wiki/Ambergris"
] |
[
"I have read that phytic acid is responsible for our teeth not being able to regenerate themselves. Is this true? Can teeth heal if allowed to?"
] |
[
false
] |
There are supposed studies that have been done that indicate that removing phytic acid from the diet, along with introducing a proper balance of nutrients that teeth need to grow, will allow teeth to regenerate. I have to say, the argument is a bit convincing, but I want the trusted people at askscience to weigh in, if they will. The argument presented is that phytic acid, found in most unsprouted grains and plants, prevents the absorption of key minerals that our body needs to maintain our teeth. Supposed studies are discussed, but I can't find them apart from the web page promoting this sort of thing.
|
[
"If that is the case, then it is very likely just a myth made up to make money."
] |
[
"That's the thing, they're not selling any products. Sites that claim this just advocate reducing phytic acid intake."
] |
[
"Hmm. Still sounds kinda hoaxy."
] |
[
"Why is the definition of mass not \"quantity of matter\"?"
] |
[
false
] |
I understand the idea of mass and how it comes from the fact that we can apply the same force on different kinds of objects, and those objects will respond differently depending on the nature of those objects. And that the units of mass are essentially arbitrary and refer to the International Protoype Kilogram, which is an object made of platinum iridium alloy. My question is, if i have a bunch of feathers that have a mass of 10kg, and a lump of steel that also has a mass of 10kg, they will both behave similarly when a certain force is applied to them, however they are obviously different in size, density etc. So what are the similar characteristics between the lump of steel and feathers which give them the same mass? Do they have the same amount of matter; electrons, protons and neutrons? and if not, what is it that gives them mass?
|
[
"The prototype kilogram isn't meant to be a fundamental definition of mass, but rather something that is easily reproducible (you just need a copy of the brick). You could define a kilogram as a certain number of silicon atoms , but that's harder to reproduce.",
"For most purposes, the mass of an object is just the sum of its constituents, down to the protons, neutrons, and electrons. There are some subtleties that the energy that binds these particles together also contributes to the mass, but this isn't relevant until you're dealing with nuclear physics.",
"\"Quantity of matter\" is an alright definition (although a bit circular, given the definition of matter), but I prefer something along the lines of \"rest frame energy\" or the operational \"the property of a thing that makes it hard to move.\""
] |
[
"You could define a kilogram as a certain number of silicon atoms , but that's harder to reproduce.",
"In fact, that's exactly what they're doing",
"."
] |
[
"I know that GP said it wasn't relevant unless you are dealing with nuclear physics, but I think you will find it is relevant here. The amount of mass something has isn't just a function of how many protons and neutrons it has, but also its energy. Look up something called the \"mass defect\". ",
"Case in point: lead-208 is \"missing\" a full 1.7 proton masses from what you expect it to have. ",
"Also read this very informative piece about exactly what mass is by ",
"fermilab",
". It is written to the layman and is very interesting (and mercifully short). "
] |
[
"Are there any advantages to DNA being a double helix?"
] |
[
false
] | null |
[
"1)The bases are more protected / less exposed to mutagens on the inside of the helix so less mutation.",
"2) If a base on one strand is mutated then the correct base can be deduced from the base on the opposite strand since they are complementary.",
"3)If replication were to take place using just one strand as the template a further replication event would still have to take place in order to get the actual sequence as all the bases on the first replicated strand would be the opposite of the actual sequence. So one may as well start with two strands as a double helix in the first place."
] |
[
"Ah, thankyou!"
] |
[
"in addition, certain mutations and base-pair sequences create shapes in the double helix that can be recognized/repaired by enzymes"
] |
[
"Why does urine form bubbles after peeing in a toilet but water does not?"
] |
[
false
] |
Is it because of the temperature difference (98.6F vs room temp) between the water and urine, or because of the other contents of urine (urea) creating some sort of odd fluid conditions creating bubbles, or something else?
|
[
"bubbles are usually caused by soap like molecules. Water from the tap is relatively urine is no where near as pure. If I were to make an educated guess it would be a combination of sugars, water soluble fats and proteins ala desk flyer's link.",
"edit for a slightly longer explaination... Soap molecules have two parts to them. One a hyrdofilic or water loving part. This part is really sticky just like water and will readily stick to water and other polar molecules furthermore by bringing these polar parts together energy is released by bringing these molecules together and to break these links energy must be put into the system. ",
"The other half of the soap like molecule is very nonpolar and doesn't like to stick to anything. no huge amount of energy is released by bringing it close to another molecule. so now the molecule is in a position that the sticky part wants to be in water and the non sticky part wants to get out of solution so that its space can be replaced by sticky molecules(i.e. water) that ctually like to be near other stick molecules.",
"To accomplish this feat the set of molecules that make up our system enter into a low energy confirmation, bubbles and a monolayer of our soap like molecules on the surface of the polar solution."
] |
[
"http://www.buzzle.com/articles/bubbles-in-urine.html"
] |
[
"Doesn't really answer my question of what causes the bubbles to form, just that being dehydrated or sick can cause excess proteins to build up which form bubbles."
] |
[
"Questions about Quarks"
] |
[
false
] |
What exactly are quarks? Are they made up of smaller molecules or are they, to our current understanding, the smallest unit of matter? What are strange and charm quarks, and why do they have those names?
|
[
"Quarks are what protons and neutrons and some other less important things are made of. There is no evidence or other reason to suggest that they are made of anything smaller. Quarks either have plus or minus 1/3 or 2/3 the charge of an electron. The most important quarks are up and down quarks, which protons and neutrons are made of. The other ones are strange, charm, top, and bottom. Strangeness originally got its name because people weren't really sure what it was, just that it was there. Charm, probably somebody thought it went well with strange. Top and bottom are sometimes called truth and beauty."
] |
[
"To clarify one point, a molecule is a chain/collection of bonded atoms. So no, there are no molecules in a quark. I could go into a little detail on quarks themselves, but I'll leave it to someone with a more comprehensive knowledge!"
] |
[
"What exactly are quarks? ",
"They are the elementary fermions which carry strong-force charge (or color charge). This is as opposed to, say, leptons (like the electron) which are the elementary fermions which do ",
" have color charge.",
"Are they made up of smaller molecules or are they, to our current understanding, the smallest unit of matter? ",
"Both quarks and leptons appear fundamental (at least to the energy scales we've probed them, which is something like 10",
" meters now).",
"What are strange and charm quarks, and why do they have those names?",
"For some reason unbeknownst to us, nature contains 3 copies of all of the quarks and leptons.",
"The electron has two heavier sisters: the mu and the tau, the up quark has the charm and the top, and the down quark has the strange and the bottom. There are also three neutrinos, but they don't have clever names.",
"These heavier counterparts are otherwise identical to the ones we know and love. A charm quarks behaves just like a very heavy up quark, and a strange quark behaves just like a down. (Here behaves means that all of the charges it does or does not have are exactly the same, so that it interacts in the same ways). The only difference is the mass. Again, there's no agreed-upon reason why this is so.",
"Why do they have those names? Well, the strange quark was named such because particles started popping up that were created in strong interaction processes in pairs, but when left alone couldn't decay that way. They decayed only through weak interaction processes. The property was described by a conserved quantity called strangeness (because it was strange and unexpected), that eventually was understood to be because these particles contained a different kind of quark not present in protons and pions, which naturally was called the strange quark.",
"Then the story goes that people were frightened by the name, and the idea of \"strange matter\" so as a half-joke the next quark predicted was called \"charm\" in the hopes people would like it better."
] |
[
"You are constantly very very close to biting your own tongue. Why doesn’t it happen more often?"
] |
[
false
] | null |
[
"Two main factors are at play here. The first is proprioception. The second is pain. ",
"Proprioception is the body's sense of where its parts are located. Meaning even if you close your eyes you know where your arms are. This extends to your tongue, your body tracks it while it's still and when it's moving.",
"Pain is caused every time you bite into your tongue. This reinforces the idea that you don't want to bite your tongue.",
"Putting those together, your brain tracks your tongue and knows that putting it in the biting path is bad so you learn not to do that after some practice. ",
"Edit: Learned I used negative reinforcement incorrectly."
] |
[
"To add to that, i'd suggest there's also some aspect of design. Whereas we have evolved tongue and teeth placement, size, and position to avoid biting the tongue in the resting state, or by accident in normal chewing or swallowing actions. Even if we do misjudge the tongue is sensitive enough and jaw agile enough to make adjustments before any real damage is done."
] |
[
"Interesting side note here. I remember reading an article at some point in the past about how the game Mirrors Edge was messing with people's proprioception"
] |
[
"Why does human excrement, though often varying in odor due to individual diets, retain such an unpleasant smell?"
] |
[
false
] | null |
[
"The odor in feces is caused by hydrogen sulfide produced by bacteria in your gut."
] |
[
"The answer is complicated, but you may find ",
"this article",
" in the NY Times on \"disgust\" enlightening."
] |
[
"It's not so much that hydrogen sulfide smells disgusting by default and vanilla smells nice, but more that we are genetically coded to respond to specifically hydrogen sulfide (and lots of other \"waste\" products) with disgust as it's typically found in stuff that it's evolutionary beneficial to avoid, such as feces and decaying stuff.",
"Had vanilla smelled like feces and feces like vanilla, we would find vanilla disgusting and feces nice."
] |
[
"Do larger people require more sleep than smaller people?"
] |
[
false
] | null |
[
"Short sleep duration is associated with just about every obesity measure you can name (BMI, bodyfat%, leptin/ghrelin levels, etc). ",
"Cause and effect are, at this point, strongly favoring that people who CHOOSE to get less sleep cause physiological consequences that make them gain weight. However, I wouldn't completely rule out other hypotheses at this point. ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2398753/"
] |
[
"What about tall people? Will someone who's 6'5\" require more sleep than someone who's 5'9\", assuming they are both approximately the same BMI?"
] |
[
"No tl;dr. ",
"Obese people eat more calories than they burn, period. They were likely obese in development. However, if YOU could control their dietary intake, you could make them thin. No one walked out of internment camps in WWII fat. ",
"Of course, that's rude and insulting, and we don't live in an environment in which caloric intake is closely controlled. People DESIRE to eat, are presented with OPTIONS to eat, and CHOOSE how much to eat based on their hunger and options. A wide array of factors relates to food choice and hunger, and sleep, and stress, are really, really, big factors. "
] |
[
"Is there such thing as anti-dark matter?"
] |
[
false
] |
[deleted]
|
[
"Nobody knows for sure what dark matter is. One of the most prominent possible candidates is called a WIMP: a Weakly Interacting Massive Particle. A WIMP may be identical to its own anti-particle (like the photon), or it may have an anti-particle that differs in some new kind of charge that is only \"felt\" by other WIMPs. One often speaks of a \"dark sector\" that may include many dark matter particles; this sector could, for example, look exactly like the particles in the Standard Model (complete with strong interactions among themselves, and anti-particles), but which only interact weakly with the Standard Model particles."
] |
[
"Depends what dark matter turns out to be made of. It's electrically neutral (or else it would interact with light), and anti-particles have the opposite charge of regular particles, and the opposite of zero is zero. However, neutral particles like neutrinos can still have anti-particles with the opposite chirality (which way they spin vs which way they move), although it's an open question whether neutrinos and anti-neutrinos are the same thing or not. ",
"Here",
" is a random paper that discusses such a case for dark matter."
] |
[
"We don't understand enough of \"dark matter\" to even start discussing anti-dark matter. But if it's actually matter composed of particles, then DeBroglie's equation will say that yes there is \"anti-\" Dark matter."
] |
[
"Does Premium Unleaded fuel really clean my engine as advertised?"
] |
[
false
] |
Hey all I was filling up my car today with standard 91 Octane (Australia) when I started reading the spiel on the pump about premium (98 octane). I am aware of how octane numbers work, and that premium shouldn't offer any mileage benefit to my car as it is designed to run on standard. However, is there any validity in the claim that premium will "clean my engine". What sort of additives would enable this anyway, or is it just advertising BS?
|
[
"There are really two separate issues being conflated here. First is \"engine-cleaning\" fuel additives, second is the fuel's octane rating. The two are independent.",
"Engines with higher compression ratios (high-performance vehicles, basically) have increased risk of having the fuel-air mixture detonate in the piston instead of deflagrate; this is known as engine \"knock\" and is mitigated by using fuel with a higher octane rating. In this sense, higher octane ratings ARE necessary in performance vehicles, as knock will damage the engine.",
"But as for the \"engine-cleaning\" fuel additives... Well, technically, they work. They do in fact lubricate the cylinders, reduce corrosion, and prevent build-up in the fuel system. But the fact of the matter is, an engine in good maintenance that hasn't been left unused for extended periods of time doesn't really NEED it all that much. Every once in a while, a good fuel system cleaning is good maintenance, but claiming that you benefit from having this included in every tank of gas... well, it's nowhere near the miracle they make it out to be.",
"Edit: I see the modifications to the OP, and I'm afraid I don't know what the commonly-used \"cleaning\" additives are."
] |
[
"The cleaning additives are detergents. Collectively called \"deposit control additives\" or DCA's.",
"What they do is prevent buildup of deposits (carbon compounds) in two critical areas: The fuel injectors, and the intake valves. Injectors have very fine nozzles that atomize gasoline into very fine droplets. If it should become clogged, the droplets will be larger, and combustion will be less efficient. DCA's remove deposits and prevent them from forming altogether. Intake valves need a tight, clean seal to ensure that compression is where it should be. If they become gunked up, gas mileage will go down.",
"Now, to the ultimate question: no, premium gas probably won't clean your engine any better than the cheap stuff. They all have detergents in them as mandated by the government."
] |
[
"What about performance vehicles that \"require\" certain octane levels? Is it really important "
] |
[
"How long does it take from the moment my brain decides to send an action command (moving my arm) to the moment i actually do the action?"
] |
[
false
] | null |
[
"The electrochemical signal that causes your arm to move happens before we are able to recognize we have made the decision to move our arm. ",
"This has caused some interesting debates on the reality of free-will in neuroscience."
] |
[
"The most basic way your brain could 'tell' your muscles to move is through activation of corticospinal neurons in ",
"primary motor cortex",
", which project to ",
"motor neurons",
" in the spinal cord, which in turn activate and cause contraction of opposing groups of muscles. According to ",
"this paper",
" (figure 3 specifically), that whole circuit can operate quite quickly, on the order of ",
" (or less). ",
"More complicated movements or movement sequences, which also involve activation of supplementary motor regions or cerebellum, thalamocortical feedback, feedback from sensory systems, etc, should take considerably longer when all is said and done. So, 10ms should be treated as being close to a lower limit estimate for your question. "
] |
[
"The simple answer is at least 10ms since the velocity of the signal along the nerves are around ",
"100m/s",
". The scientific name is ",
"mental chronometry",
" or reaction time and is of 150 to 200ms, but it include the perception time..."
] |
[
"How an SSRI affect your brain?"
] |
[
false
] |
[deleted]
|
[
"Hopefully I'm not taking your question too literally, but SSRI = Selective Serotonin Reuptake Inhibitor. Serotonin is a neurotransmitter (one of many) that your brain cells use to communicate (basically, they spit little puffs of it on each other). After the serotonin \"does its job,\" it's taken back up into the neurons and repackaged so it can be reused (hence: \"reuptake\"). An SSRI interferes with reuptake so the serotonin can hang out longer and have more of an effect.",
"No, an SSRI doesn't only affect the right side; serotonin is used everywhere in the brain. An SSRI might affect some places more than other (that's the \"selective\" part) but there's no right/left differentiation that I'm aware of. ",
"I won't comment on mental exercises, as this might be taken as \"medical advice\" and being new around here, I don't want the reddit nerds to come rough me up. :-P",
"Disclaimer: I'm a researcher, not a clinician, so perhaps an MD or someone else taking SSRI's might chime in here. "
] |
[
"Well, there are a number of drugs that are SSRI, so it's more a question of which one you were prescribed rather than what formula the manufacturer used. Some might have less adverse side effects than others for you. But that's something you should discuss with your physician."
] |
[
"Fundamental neurochemistry is, relative to other scientific fields regarding the brain and nervous system, quite well researched, however, large-and-broad-scale interactions between chemicals in the brain, groups of neurons, and the ways in which specific chemicals (in this case, SSRIs) act on brain subsystems, to use a broad term, or perhaps more useful, the ways in which they affect the functioning of the brain as a whole, is not all that well understood.",
"In pharmacology you can (sort of) make a distinction between \"clean drugs\" and \"dirty drugs\". You rarely call a substance the former, but sometimes you use the latter term, \"dirty drug\", to emphasize that the substance's working is not very specific and has a broad range of actions, ",
" of which have the effect desired by the researchers.",
"The truth, however, is, that there are many levels of \"functional units\" in the brain: one neuron is a functional unit, a single synapse is one, a neuron with all its axons and dendrites is another scale, a cluster of neurons which constitute a subnetwork is another one; also, one type of neuroreceptor, not localized but distributed over the entire brain, is again a ",
" kind of functional unit.",
"It is not possible to cause a ",
" specific effect on the brain and in effect on the mind/psyche by introducing a single substance into the brain; also, even though they are called Serotonin ",
" Reuptake Inhibitors, they are not at all that specific. Most SSRIs are also NRIs (Noradrenaline Reuptake Inhibitors; this is true for Venlafaxine, for Fluoxetine in high doses, and true to some extent for most SSRIs). Some are even additionally DRIs (Dopamine Reuptake Inhibitors), and that is just referencing the most well researched neurotransmitters and receptor subtypes.",
"The gist here is, when it comes to neuropharmacology, most substances used today are \"dirty drugs\", so, basically, to answer your original question, no, not all SSRIs will have the same effect on you, since aside from their main advertised mode of working, they influence the brain in many ways which are not advertised, and in equal if not even more amount in ways we haven't researched yet.",
"It is an extreme oversimplification to think of the brain as a \"soup\", where adding a single ingredient, and thus changing the overall \"taste\", has a specific effect on a partial subsystem ",
".",
": No, not all SSRIs will act the same on you. They are not completely Serotonin-specific, and vary in their profile, and thus will have a different effect on you; even their Serotonin reuptake functionality differs in effect between substances."
] |
[
"Why do they say that the spin of a pair of entangled particles is not determined until observed?"
] |
[
false
] |
[deleted]
|
[
"This is a very common question here. Please read up on ",
"Bell's Theorem",
" and perhaps do a search here in ask science for \"entangled particles\" and then feel free to ask if you have any follow up questions. "
] |
[
"I've tried reading bell's theorem before. I find wikipedia can be difficult for things like this, because it can seem as though it is written in a way as to be understood by people that already know what the article is talking about. ",
"I would really like to understand bell's theorem, and how he arrived at it. How he figured out that this must happen.",
"I don't mind simplified explanations, or analogies with real world things. I don't need a specific description of the equipment he used to observe events that arrived at this conclusion. ",
"I would just like to see the logic behind it. ",
"Bell's theorem is something i would really like understand. ",
"So far, all i know is that it states that particles will be entangled. ",
"In another thread i was told that bell's theorem was an explanation as to why it would be impossible to get non quantum particles to behave in a quantum manner, which i don't understand either."
] |
[
"Really? I have yet to find a proper simple explanation for it, though it does seem to be all over the place. Even searched YouTube, found some videos about it, but not really any proper ones. Personally, makes me feel like the moment I grasp the concept, I should make one myself."
] |
[
"Are there \"waves\" on the top of the atmosphere like waves ossn the ocean?"
] |
[
false
] | null |
[
"Yes, there absolutely are. Any time you have a gravity field and a fluid with different density layers, you can make waves. It gets a little tricky, though, because the atmosphere doesn't really have a top: it just gets thinner and thinner as you go up. And yet, the atmosphere sloshes up and down and back and forth, just like the ocean does.",
"There are two main kinds of waves in the atmosphere. First, you can have large-scale sloshing motions of the whole planet's atmosphere all together: these are called \"atmospheric tides\", and can be caused by the pull of the Moon or Sun, or by solar heating of the atmosphere. Second, you can set up waves along interfaces between different density layers ",
" the atmosphere. These \"internal gravity waves\" are usually smaller, and generate the stripy cloud patterns you're probably familiar with:",
"https://blog.radarscope.app/hubfs/blog-files/gravity%20wave%20clouds.jpg",
"\n",
"https://youtu.be/YGg0SxRYAvA"
] |
[
"First, you can have large-scale sloshing motions of the whole planet's atmosphere all together: these are called \"atmospheric tides\", and can be caused by the pull of the Moon or Sun, or by solar heating of the atmosphere.",
"Just to add, we're fairly sure these atmospheric tides and their interaction are what's responsible for slowing down the rotation of Venus to an almost-standstill (",
"Ingersoll & Dobrovolskis, 1978",
"), acting like a enormous drum brake on the planet."
] |
[
"But it wouldn't look like a \"wave\"",
"If clouds are present, you very much can see these waves. For example, ",
"this video",
" clearly shows gravity waves in the atmosphere (which are essentially buoyancy waves, and not to be confused with ",
" waves)."
] |
[
"Why does the inverse square law of light (and gravity) happen?"
] |
[
false
] |
Instinctively I understand THAT light sources get dimmer over distance. But, since light goes on forever unless it runs into something, why in space do light sources appear dimmer over distance and why does it happen according to the inverse square law (as opposed to a linear or other rate)? Also, is this related to the drop off in gravity over distance? I am especially curious since I can understand the "finite-ness" of a quantum packet or object but I thought gravity was a continuous depression of space-time.
|
[
"Inverse square laws happen a lot with things that spread out over a given area. If you have a light source at the center of a sphere of radius R, then the light is being spread out over an area of 4 pi R",
"; so the intensity goes like 1 / R",
".",
"This happens pretty much anytime that you have a source being spread out uniformly - so light, gravity, electric force, sound, and so on."
] |
[
"To elaborate a bit, it's a result of having three dimensions. If you visualize a field strength as being represented by lines emanating radially from an object, you can see why:",
"In a one-dimensional universe, the density of lines stays the same no matter how far away from the origin you get, because there's only one dimension for them to travel in.",
"In a 2D universe, lines spread out as 1/r",
"In a 3D universe, they spread out at 1/r"
] |
[
"... and ",
"My understanding is that string theorists are hoping to find a modification to the inverse square law at short distances as evidence for the \"hidden dimensions\"."
] |
[
"Do all materials release heat when they are elastically deformed like rubber?"
] |
[
false
] |
When rubber bands are cyclically loaded they release a noticeable amount of heat. Do other materials like steel also release heat when elastically deformed (albeit a much smaller amount)? What about when steel is plastically deformed?
|
[
"This is not entirely true. When elastically deforming an object, the energy that deforms it becomes the potential energy that will deform it back when you remove the deforming force. In case of steel (say a steel spring) this is stored as strain energy of bonds that hold the crystals of steel together. Elastically deformed steel springs don't heat up much (which you can easily verify yourself). ",
"In case of elastomer bands specifically, stretching one ",
" of the band, which heats it up; the force that a stretched rubber band applies is not a strain force in nature (the polymer molecules themselves don't appreciably stretch), but an ",
" force, which is also why, when the band contracts after dissipating the heat produced by stretching it, it becomes colder. Here's a more in-depth ",
"explanation",
"."
] |
[
"All solids are technically viscoelastic (meaning they both flow plastically and deform elastically under strain); all of them therefore exhibit some level of heat dissipation under elastic loading. Plasticity is generally facilitated by the movements of dislocations through a structure, which will naturally lead to energy dissipation through internal \"friction\". In metals, the amount of energy dissipated in elastic deformation is generally very small, especially compared to energy dissipated during plastic deformation. Some metals, e.g. high-tin bronzes, have especially low elastic dissipation/internal damping and for that reason make good bells and other musical instruments."
] |
[
"I think the confusion you got is because of the assumptions in my post and on the page you reference. I've said: \"when the band contracts after dissipating the heat produced by stretching it, it becomes colder [than the ambient temperature]\". I've phrased it this way to make it clear that a rubber band can be used as a heat pump, where heat is absorbed in one place and rejected in the other.",
"The page you reference assumes an adiabatic process, i.e. the heat is not exchanged with the environment at any time. In that case, you still have the rubber band absorb heat, but because it isn't ideal, some energy input is always lost to friction between polymer chains. As a result, as you cycle the rubber band between stretched and non-stretched, it will continuously heat up, but less than if all of the energy input you provided went to heat directly, as with e.g. plastic deformation of a metal."
] |
[
"Will an immunosuppressant drug allow you to receive an incompatible blood type transfusion?"
] |
[
false
] | null |
[
"In theory - yes. In practice - this is never going to happen.",
"If a patient needs an urgent blood transfusion, there will not be time to wait for the immunosuppressants to kick in, and anyway the patient will be in too critical a state to also compromise his or her immune system.",
"If the patient does not require the blood urgently then it would be a lot simpler and cheaper to just wait till you have matching blood."
] |
[
"Immunosuppresents are given to most if not all organ transplant recipients as matching is a lot harder than with just using blood types. Each cell has a marker saying \"this is you\" so your immune system doesn't attack it, when another body part is integrated, these markers aren't the same, and most will never find a perfect match (pretty much only identical twins)",
"So we make up for this by suppressing the immune system for any transplant even If the blood group's correct.",
"In reference to if the blood type is not matched; the immunosuppresents would need to be a high potency and then that can lead to the person dying of simple diseases. The other issue is they can still reject if your body's stubborn enough so we try to avoid that."
] |
[
"So I'm guessing they also try to ABO/Rh match patients for HSC transplantation? I know these patients can convert to a new ABO phenotype, do you know if they retain memory for antigens? Do they naturally make antibodies corresponding to their new phenotype? Is it possible that HSCT can cause a primary response to non-ABO antigens and cause GVHD?",
"Are these just silly questions?"
] |
[
"How do photons exist within an electro-magnetic field?"
] |
[
false
] |
I have been learning a lot about electro-magnetism recently, and I have tried asking this question to a few people already but none of them seem to know the answer. Do the electric and magnetic fields lines around a magnet mean that that area is filled with photons running along the field lines? Are there photons in EM fields constantly, or only when a ferrous/charged object enters them? Is there an easy way to calculate the wavelength and frequency of these photons?
|
[
"It's absurd to say the EM field is not quantized, since e.g. the loop corrections to the electron magnetic moment, which are an intrinsically quantum phenomenon, have been measured to an extremely high degree of accuracy. ",
" fields are quantized, that's a basic tenet of quantum field theory, of which, say, the standard model is one very well-tested example. \nThat doesn't mean that the field has to come in discrete chunks which seems to be the strawman you are targeting; it does imply that two physically permissible field configurations must have actions which differ by an integer number of hbars, and in some cases these can be thought of as photons."
] |
[
"Yes, disturbing the EM field will cause waves to propagate, so in that case there will be photons, but in the steady case there is a field and no photons."
] |
[
"No, photons are quanta of the EM field, the same way gluons are quanta of the gluon field and electrons are quanta of the electron field.",
"They ",
" an energy but that doesn't mean they are quanta ",
" energy."
] |
[
"How fast do radioactive things boil water?"
] |
[
false
] |
I read somewhere that nuclear power was just using nuclear things to boil water and using the steam to spin a turbine. Is it really that much more effective than burning something else to do the same thing? Also is that the best way to be using nuclear power? I imagined it would have been way more complicated than boiling water.
|
[
"I read somewhere that nuclear power was just using nuclear things to boil water and using the steam to spin a turbine.",
"Yes, although \"nuclear things\" doesn't just mean a pile of radioactive material. Inside the core of a fission reactor, there is a self-sustaining chain of neutron-induced fission reactions occurring. That is what generates the energy to spin the turbine.",
"Is it really that much more effective than burning something else to do the same thing?",
"A single exothermic nuclear reaction typically releases millions of times more energy than a single exothermic chemical reaction.",
"Also is that the best way to be using nuclear power? I imagined it would have been way more complicated than boiling water.",
"There may be other ways, but using a heated gas to spin a turbine is simple and effective."
] |
[
"SPERT",
" - that time the U.S. government and Phillips blew up a purpose-built nuclear reactor in Idaho, featuring terrible 1950s slow motion footage and parts of a nuclear reactor impacting the ceiling of the building. The third version of SPERT (the government didn't stop at one) boiled all the water around the core in about 20 milliseconds, and blew apart around the 500 millisecond mark.",
"If your measure of success is boiling water fast enough to blow the roof off the building using the force of the expanding cloud of steam then nuclear is good at that. ",
" Power reactors are designed in such a way that it's not easy to cause runaway increases in reactivity and a prompt critical. Great amounts of money ",
"and a few lives",
" were spent discovering how to ensure that steam explosions and throwing control rods like searing javelins aren't even options."
] |
[
"Turns out, we are very, very good at turning boiling water into energy with turbines in what’s called the Brayton cycle, sometimes exceeding 50% efficiency. It is possible to do direct thermoelectric conversion, like in RTGs, but that’s inefficient. We also have magnetohydrodynamic generators, which can only do around 20% right now. Just because reactors use steam, though, doesn’t mean they aren’t immensely complicated. The turbines are the results of thousands of hours of computer optimization and the core itself is significantly more complicated than just a lump of uranium, as it must maintain a controlled neutron chain reaction. ",
"Edit: by the way, when you ask “is it more effective than just burning stuff”, the answer is yes. For one, a kilo of reactor grade uranium has the equivalent energy of a few traincars or so of coal. In fact, it is possible to convert nearly .1% of an enriched fissile’s mass into energy, which sounds tiny until you realize how huge c squared is."
] |
[
"Are nuclear weapons test safe?"
] |
[
false
] |
Why is it that places like Chernobyl and the other plant in Japan are dangerous to visit for prolonged periods of time where as places like Hiroshima, Nagasaki and multiple nuclear test sites are safe to visit? Isn't it technically the same thing, but one is a weapon and the other one is just being used for it energy? Also, what about the nuclear fallout from atomic weapons tests? Doesn't the wind transport the nuclear particles? I just don't understand why nuclear weapon tests are safe and the real thing is dangerous...
|
[
"Why is it that places like Chernobyl and the other plant in Japan are dangerous to visit for prolonged periods of time where as places like Hiroshima, Nagasaki and multiple nuclear test sites are safe to visit?",
"Atmospheric testing ",
" release fallout into the atmosphere. However since the 1960's or so, most, if not all nuclear tests have been conducted underground. Underground testing doesn't release fallout into the atmosphere.",
"If you ever get a chance to visit a test site, you can walk right up to the craters without getting much of a dose (you shouldn't go down into them though).",
"That being said, the fallout from a nuclear weapon is different than something like a reactor meltdown without containment, like what happened in Chernobyl.",
"Isn't it technically the same thing, but one is a weapon and the other one is just being used for it energy?",
"There's ",
" material inside a reactor core than in a warhead. So if the core melts down and there's no containment, there's the potential for much worse spreading of fission products, assuming a worst-case scenario. The fallout from the Chernobyl meltdown was greatly exacerbated by the fact that there wasn't containment.",
"Also, what about the nuclear fallout from atomic weapons tests? Doesn't the wind transport the nuclear particles?",
"Yes, wind definitely transports the fallout around once it's free in the atmosphere."
] |
[
"To give an idea of the energies involved: The Hiroshima explosion released an energy of about 60 TJ, that's the power output of a single nuclear reactor block in a few hours. Nuclear reactors run for months without refueling, they need way more material. In addition they don't have to be made as light as possible, unlike nuclear weapons they are not supposed to fly."
] |
[
"Atmospheric nuclear weapons tests aren't safe. But that's separate from your question, which is about nuclear fallout.",
"Both nuclear weapons tests and nuclear power accidents release most of their radioactive contamination in the form of fission products, the split pieces of uranium or plutonium atoms. In a reactor, the total fission product load can be pretty high after it has been running for awhile (as was Chernobyl's case), mixed in with a lot of other reactor components (graphite, uranium fuel, etc.). In a bomb, the total fission products are related to the size of the reaction; in the Hiroshima and Nagasaki bombs, about 1 kilogram of material reacted. This is also mixed in with some uranium (and plutonium for Nagasaki), and vaporized bits of the bomb, but it's the fission products that make the fallout deadly. ",
"Chernobyl was a ground-level, low-yield explosion that blew the top off of the reactor and sent burning graphite and fission products into the air. These products were both high in volume and not ",
" hot, so they went up, traveled a bit, and came right back down again. This is why the areas around Chernobyl are still contaminated today, though you ",
" visit them without any harm. You just shouldn't ",
" there, because it will increase your cancer and miscarriage rates. (And if one one or two people live there, nobody will probably notice the increase, since it is probabilistic and small; if 100,000 people lived there, you'd start seeing a big increase in medical cases.)",
"Hiroshima and Nagasaki were airburst nuclear explosions. Their fireballs did not touch the ground and did not mix with much dirt or debris. As a result their fission products stayed relatively \"light\" and hot, and so dispersed over a wide distance before they fell out of the cloud. What this means in practice is that they had time for the most-radioactive (shortest half-life) products to decay, and no particular place got a large dusting of them (it was diffused, in other words). So there was no significant contamination on the ground, which is why their background levels are about the same as they are today.",
"What if they ",
" been set off on the ground? Well, there would have been a contamination problem. You can see this today: if you visit the Trinity site today, where a prototype of Nagasaki bomb was detonated only 100 feet off the ground, it is still a bit radioactive (several times more radioactive than \"baseline\"). And even that is the result of site having been cleared with a bulldozer in 1952, and waiting ~75 years. ",
"But why can I even visit Trinity today, if it was once covered in radioactive glass? Because the decay rate of fission products ",
"is pretty steep",
". Even very radioactive fallout becomes pretty weakly radioactive over time. That \"weak\" contamination, if the original was high enough, can still be enough to be a long-term health hazard if you live in it for decades and decades. But it means that you can ",
" such areas after the fact without incurring more radioactivity than you otherwise pick up in your life. I spent about 5 hours at the Trinity site this summer and picked up about the same radiation dose as I did on the flight out to New Mexico from the East Coast — which is to say, a tiny amount.",
"To get to one other aspect of your question: yes, the wind moves fallout from nuclear tests around. If the fireball detonates low, and mixes with dirt/debris/sand/coral/etc., then it tends to deposit most of its fallout as \"local\" fallout, which is to say, directly downwind of the detonation. These are the \"fallout plumes\" you frequently find maps of, like ",
"this one from the Castle Bravo test in 1954",
". If the fireball detonates very high in the air, and does not mix with anything, then you don't get significant \"local\" fallout, but you do contribute to \"global\" fallout, which is to say, it stays in the upper atmosphere for awhile (sometimes years, for very large bombs), and sort of dusts the planet more or less equally (or at least the hemisphere it is in). That means that you contribute to the overall background radioactivity a bit. A few tests doesn't increase it that much, but a lot of tests can — this is why in 1963 the US and USSR agreed to stop testing in the atmosphere, and only test underground, which (ideally) doesn't release off-site radioactivity (except in accidents, which did sometimes occur)."
] |
[
"Why do bananas and other fruit rot so much faster when they are in an enclosed space with one another?"
] |
[
false
] | null |
[
"Ethylene is a fruit hormone that is naturally produced by fruits. When green bananas are kept in a brown paper bag, they will ripen faster!",
"Rotting would be related to the concentration of ethylene in the surrounding gas. Also bacteria that causes rotting can easily proliferate to other fruits when they are kept closer together."
] |
[
"To expand on the ethylene thing, ethylene causes fruit ripening, more ethylene makes fruit ripen faster, but it also has a positive feedback loop: the more ethylene there is, the faster more is produced. The ethylene is also released as a gas, so it propagates to adjacent fruit and kick starts ethylene production there. This is why you can ripen fruit very quickly by leaving it in a plastic bag (no gas escapes) with an overripe banana (high ethylene production)."
] |
[
"To expand further, ethylene is a byproduct of incomplete combustion, so if you have a greenhouse, using internal combustion engines inside of it can increase the concentration of ethylene, negatively affecting your plants.",
"More relevant to post-harvest physiology, if someone had a flower or a climacteric fruit in their lap as they were sitting in a car in a traffic jam, that flower or fruit would undergo accelerated wilting or rotting due to the ethylene from the car engines around them.",
"source: I'm a PSU Agroecology student studying for Horticulture midterm on this very subject, among other things. PLANTS!"
] |
[
"Do black holes get bigger from absorbing all the light that falls into it?"
] |
[
false
] | null |
[
"Yes."
] |
[
"so do they just keep getting bigger and bigger? is that why there are supermassive blackholes in the center of many galaxies?"
] |
[
"Hi magictron thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
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", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Is there a method of detecting current in human tissue in 3d space"
] |
[
false
] |
So, as i pour over ECG's I always wonder, surely there is a better way. I studied most of my physics in the Irish equivalent of high school so its not exactly my strongest subject, but is there a way , theoretically at least, to detect moving changes in membrane voltage of about -70 to + 40 miliVolts running in muscle thats about 1-2 inches beneath more muscle. No electrodes , just perhaps, stand the patient in an EM field, which i know can react to new currents within it, and then analyse the change in field, and compute the vectors of current within it. Anyone think its possible? Anyone can point me to some resources/want to design same with me. (note: I really hate putting stickers on chests. This is how far i will go to avoid it )
|
[
"This is how magnetoencephalography works, but the magnetic field involved are really, really small. Like, one trillionth as strong as the Earth's magnetic field."
] |
[
"And magnetoencephalography."
] |
[
"Another big problem is that the scull sort of blurs all of the signals. "
] |
[
"Would new leaps in protein folding computation produce many non-functional proteins?"
] |
[
false
] |
In school I learned about how a protein is folded into the native via , but outside of school I learned about how computers are currently incapable of solving protein structure. Then today I watched the that was posted earlier and I learned that the issue with NP problems, such as protein folding, is that you cannot directly solve an NP problem, you instead have to search for correct solutions. So a sudoku solution is easy to check for correctness, but for protein folding, would the correct "solution" be the lowest energy state ? If so, it seems to me that it is possible for proteins to be folded in a lower energy state than the native, functional protein, thus producing non-functioning proteins as the only correct solution.
|
[
"I don't think the P=NP problem really applies to protein folding because the solution to a protein folding problem cannot be checked any more quickly than it can be calculated. ",
"I mean there are obvious cases that can clearly be flagged as wrong, such as impossible bond angles, but they are trivial so we can ignore them, also a good model won't ever converge on these impossible conformers anyway.",
"So how would you computationally check that your reasonable looking protein conformation is the global minimum? You start your calculation all over again with different initial parameters and see if the convergence conformation is the same and make sure you haven't gotten trapped in a local minimum that your calculation method has failed to account for. This is tricky in practice because ",
".",
"i.e. checking your calculation takes exactly as long as actually making the calculation.",
"In practice the models we use effectively check themselves as they calculate because they are iterative models; they check solution n against solution n-1 until the difference is insignificant. There is much more to it than that to stop the model getting stuck in local minima, but that's a deep, dark rabbit hole that you ",
" don't want to get into."
] |
[
"From my understanding, the researchers that did it dissolved the proteins and then used some kind of mechanical flow to produce the conditions that allowed the protein to re-fold into the native state. ",
"This is similar to something we do in biochem labs when our proteins made from bacteria aren't immediately soluble. Dissolve in urea or guanidinium hydrochloride, then dilute to the point where the chemicals have small enough effect on the protein that the protein can reach the native state on its own again. It's notoriously difficult because most proteins would rather go back to the aggregated state. Finding the right conditions to coax a protein into the native state takes a lot of hard work, and may be impossible for a given protein."
] |
[
"In practice the models we use effectively check themselves as they calculate because they are iterative models; they check solution n against solution n-1 until the difference is insignificant",
"and",
"different initial parameters",
"answers my question perfectly. Thanks!"
] |
[
"With the exception of therian mammals, did any other clade of synapsids give birth to live young?"
] |
[
false
] |
Is there any evidence to suggest that other clades of synapsids were viviparous too? Did viviparity arise only once in synapsids?
|
[
"My guess is that nobody knows because the non-therian synapsids are known only from fossil evidence, often skulls/teeth, and it'd be quite tricky to figure out whether or not a species has viviparity just from the skull and teeth.",
"However viviparity is relatively easy to evolve. Many elasmobranchs have evolved it, caecilians (legless amphibians) too, and it's evolved dozens of different times in the lizards and snakes. The only group of vertebrates that seems to \"have trouble\" evolving viviparity is the birds - some 10,000 species and not a single one of them viviparous - most likely because of flight constraints (pregnant females are heavy).",
"So given the patterns seen in all the other vertebrates I wouldn't be at all surprised if viviparity evolved several times in early synapsids."
] |
[
"The only group of vertebrates that seems to \"have trouble\" evolving viviparity is the birds - some 10,000 species and not a single one of them viviparous - most likely because of flight constraints (pregnant females are heavy). ",
"How about ratites? They arey flightless for quite some time now."
] |
[
"My guess is that nobody knows because the non-therian synapsids are known only from fossil evidence, often skulls/teeth, and it'd be quite tricky to figure out whether or not a species has viviparity just from the skull and teeth.",
"However viviparity is relatively easy to evolve. Many elasmobranchs have evolved it, caecilians (legless amphibians) too, and it's evolved dozens of different times in the lizards and snakes. The only group of vertebrates that seems to \"have trouble\" evolving viviparity is the birds - some 10,000 species and not a single one of them viviparous - most likely because of flight constraints (pregnant females are heavy).",
"So given the patterns seen in all the other vertebrates I wouldn't be at all surprised if viviparity evolved several times in early synapsids."
] |
[
"Since humans are drilling so much oil out of the ground, are there large empty caverns underground where the oil used to be?"
] |
[
false
] |
Humanity has drilled a lot of oil since the late 1800’s. What happens to all the empty space where the oil used to be? Is it just empty air pockets now or does it fill in with dirt?
|
[
"Not exactly. The oil is held in rock in the formation, think of squeezing a wet rag with the rag being the formation. The oil goes and formation stays. ",
"Fracturing is the process of opening that rocks natural permeations so the oil, water, and gas can flow out more efficiently. ",
"Of course there may be some exceptions and others who may speak with more authority than I do. "
] |
[
"Not exactly, in the olden days oil would seep out of the ground on its own (even still in places like the tar pits in California), things like salt caverns can hold oil.",
"But I would guess the pictures of the oil shooting out of the ground that your talking about would be after a hole was drilled with the oil coming out under the pressure of the formation. The well that I'm currently on is 10k foot below ground level and is flowing naturally at 6,500 psi, so it can flow out with some good force behind it. ",
"Like I said, someone else can speak more accurately and with more authority than I can, I'm only a low level field hand. "
] |
[
"Oil is most commonly produced from porous sedimentary rocks. It doesn't come from caverns, but tiny microscopic holes or gaps in the rock. It comes gushing out when we drill through the non-porous rocks above because the fluid is under enormous pressure.",
"The pores are never really emptied, they just stop producing oil as the pressure equalizes. The rocks still contain a mixture of oil, water, and gas, but we can't get it out easily because it's no longer pressurized."
] |
[
"Why is cancer sometimes untreatable?"
] |
[
false
] |
[deleted]
|
[
"It can become inoperable by invading deep inside sensitive tissues such as the brain, or by spreading far enough through vital organs so that removing the tumors would kill the patient (such as the lungs or liver). Stage IV means that it has spread to other parts of the body. The majority of chemotherapy drugs don't specifically target cancer (they are malfunctioning human cells so it's very difficult to effect them without effecting other healthy cells). Because of this they instead target mechanisms of cellular reproduction, this hits cancer cells hardest because they are reproducing rapidly but also effects healthy cells causing the side effects such as hair loss and digestive problems. Increasing the dose would end up killing the patient, likely in an agonizing way similar to radiation poisoning. If the cancer has spread farther than there is hope of treatment eliminating it than it often becomes a choice, let the disease take it's course or try to fight it and possibly extend the life by a short time at the cost of chemo side effects in addition to the disease (and great expense if you're in the USA)."
] |
[
"We don't know how that has worked, so we cannot say that it is going to work for cancer. There is a hypothesis that the treatment works only in cases with a weak virus or far away from the brain, thus putting the patient in coma slows down the spread of Rabies, giving the immune system more time to fight the disease. In the case of stage IV cancer the disease has already spread too far, and thus putting a patient into coma is simply going to shorten their conscious life. Search for \"Milwaukee Protocol\" for more details."
] |
[
"First of all, every medication has something called \"therapeutic range\", which is the range of doses in which it's strong enough to be useful and not so strong that it will serious harm you (or kill you).",
"At some point, every medication is seriously harmful, so if you \"just increase the power\", you will kill the patient. Possibly kill them in a more unpleasant way that the cancer itself would.",
"Second, cancer does many types of damage to the body.",
"For example, as a tumor grows, it pushes on nearby organs, which could permanently damage them; for example, a brain tumor can push on your brain in a way that cuts off circulation to the brain, and so you get brain damage. Treating the cancer at that point (whether surgically or medically) would not nothing to reverse the brain damage. ",
"Third, cancers develop resistance to chemotherapy. By definition, most cancers consist of cells undergoing rapid division and mutation; as a result, they evolve to be resistant to chemo drugs in much the same way that bacteria evolve to be resistant to antibiotics — so you might start with a cancer that drug X works against, then you take drug X and it kills off cancer cells that it works on, and leaves behind all the ones that are resistant. Congratulations, now you still have cancer, but it's resistant to that drug. ",
"So, you can't just add more chemo because: you'll probably kill the patient, the cancer probably developed resistance, and there is probably fatal collateral damage from the cancer."
] |
[
"If an object keeps gaining speed on its way into space will it continue to accelerate within the vaccum of space? If so, for how long? If indefinitely, what happens when it reaches the speed of light? Finally, have we ever recorded or somehow glimpsed a solitary object travelling at the S. O. L.?"
] |
[
false
] | null |
[
"Massive particles cannot travel at the speed of light. Indefinite acceleration is possible, but the speed will just asymptote to ",
" from below."
] |
[
" is the speed of light. "
] |
[
"By c do mean the limiting curve? "
] |
[
"are there any statistics on the prevalence of Naegleria fowleri throughout each country and each countries respective case counts?"
] |
[
false
] |
[deleted]
|
[
"Probably can’t find stats because the amoeba grows best in warmer waters, hence why it is most prevalent in the southern half of the US. You can probably take an educated guess and say the cases are similar to Minnesota, which has two total ",
"reported cases",
"."
] |
[
"We talked about the Minnesota cases on the Halloween episode of the Strange by Nature podcast last year. They tested a number of lakes in the county where a known lake had the amoeba and most of the lakes contained the amoeba. It is probably quite common but rarely causes a problem. You can listen here. It is the first segment of the show. ",
"https://podcasts.apple.com/us/podcast/strange-by-nature-podcast/id1552464409?i=1000539869101"
] |
[
"This might be more of an epidemiology question and therefore medicine, but I'll give it a shot.",
"I could not find any reported case of primary amoebic meningoencephalitis (PAM) in Canada. Currently it is being ",
"tracked by the CDC",
" within the United States but it appears no other countries are performing active data collection on cases (but I have no real good way of effectively surveying other countries health organizations' data aside from scanning citations and looking at case studies). I found ",
"three",
" ",
"papers",
" ",
"of interest",
" which might expand on this knowledge.",
"Currently there are very few cases worldwide, with 431 reported since 1961, and probably fewer are actually ",
" infections because of the difficulty in ruling out other causes of meningitis. Given the possibility of a false positive of PAM with the rarity of infection, my take is that it is not a relevant public health concern for most of the world (and especially in colder climates), so tracking and research is sporadic. As for its prevalence, it seems fairly common around the world, albeit in similar environments (warm, stagnant, fresh water). It might be difficult to know the true spread of ",
" as disease surveillance (AFAIK) is woefully underfunded."
] |
[
"Does sunscreen really expire?"
] |
[
false
] |
All my sunscreen from last year is expired, and that shit is expensive. Does it really expire, or become less effective, with age?
|
[
"Shelf-life can be a tricky thing to say anything definitive about without knowing how it was set. It could be because the active component oxidizes to a level at which it no longer give the coverage claimed (a performance limit.) ",
"Alternatively, it could be the limited by the active period of a biocide that inhibits bacterial growth, which would be more of a health and safety limit.",
"In other cases, it could be marketing deciding that they can increase sales by making products go out of date sooner."
] |
[
"If the active component is TiO2 (titanium dioxide or titanium oxide) then no, it won't go bad. That's rusted titanium, and it photocatalyzes so it protects you from sun."
] |
[
"It depends on the ingredients.",
"In a ",
"natural",
" ",
"Zinc oxide",
" based sunscreen, the zinc will never lose effectiveness. However, the vegetable oils will eventually go off and separation may occur.",
"The list of more modern ingredients is large and would be difficult to classify: ",
"http://en.wikipedia.org/wiki/Sunscreen#Active_ingredients",
"I did find a lot of references to an FDA 3 year minimum effectiveness period, however none provided citations to back that up."
] |
[
"Why do all domestic cats grow to roughly the same size when domestic dogs can vary in size greatly?"
] |
[
false
] |
[deleted]
|
[
"Cat breeds do come in a large variety of sizes, from tiny Munchkins to very large Maine Coons."
] |
[
"Dogs were specifically bred to perform certain tasks for people, and as a result physical traits vary greatly between the different breeds. Cats, on the other hand, were not selectively bred for such purposes and so the different breeds look relatively similar."
] |
[
"Pretty much. Cats have not been bred for specialized purposes for nearly as long as dogs. Working cats, for example, mainly caught vermin - and they're already the right shape for that. Working dogs could be set to a wider variety of tasks, which called for a variety of body shapes. BIG dogs for guarding, small dogs for living indoors, short-legged dogs for going after burrowing animals, long-legged dogs for racing ...",
"Actually, a lot of the more noticeable differences in cat shapes today are really recent. If you went back sixty years, you'd find that the Persian breed had normal faces, that Siamese were not so pointy and frail, that Munchkins just didn't exist, and so on. The trend towards breeding cats into more extremely varied shapes really only took off in the 1950s. "
] |
[
"Wasn't sure which subreddit to post this in. My right side has been getting weaker but my left has been strengthening."
] |
[
false
] | null |
[
"I am sorry, but medical advice violates Reddit's Terms of Service so we do not allow it. However if you are wondering what is up you can try contacting a medical professional."
] |
[
"I'm not asking for medical advice, I just want to know why this is happening. It's not really bothering me, I haven't even considered going to the doctor about it. "
] |
[
"I can understand that. But when asking a medical question about yourself, it is unfortunately considered medical advice."
] |
[
"Pauli's Exclusion Principle - Does It State All Electrons Everywhere Must Occupy Different Energies?"
] |
[
false
] |
Here in the UK we have a prominent physicist named Brian Cox (who's occupying a similar place as Neil deGrasse Tyson does in the 'States, in terms of public science discussion), who just had a show on TV wherein he explained Pauli thus: That no two electrons can have the same energy, and that as he heated a diamond (by rubbing it between his hands) and the energy levels in some of its electrons increased, all the other electrons in the universe would shift to make sure . Now I thought I was passingly familiar with quantum phenomena but this was a new one to me. I was also under the impression that the up/down pair of electrons in the lowest energy level in any given carbon atom (for example) would have the same energy as the electron pair in any other carbon atom's lowest level. Not so?
|
[
"No. It says that two identical fermions (like electrons) can't occupy the same energy state. For example, two spin-up electrons can't both be in the 1s orbital (the closest to the nucleus). However, in two adjacent atoms, the electrons in the 1s orbital will both have the same energy, but still not be degenerate because it's a different atom."
] |
[
"I think you are correct. The Pauli exclusion principle isn't even really about energies, it's about quantum states. Two electrons may not occupy the same quantum state, but this isn't the same thing as not having the same energy.",
"I don't know what Cox actually said, but perhaps he was making some big simplifications to cram things into popular science. You could certainly make vague statements about energy and the universe using the Pauli exclusion principle, which might sound something like what you recall. For instance, we could certainly say that no two electrons ",
" can have the same quantum state, but this sounds more impressive than it really is because most of them are in different places which automatically makes their states different."
] |
[
"What the Pauli exclusion principle really says is this: the wavefunction describing all of the electrons in the universe must be completely anti-symmetric under exchange of any two electrons in the universe. Luckily, most electrons are pretty non-relativistic and therefore pretty well localized in space. The as iorgfeflkd suggested (but was not sufficiently explicit), you can ",
" treat systems one at a time because the electrons are well localized.",
"However, it's still true that (according to QFT) the entire wavefunction everywhere in the universe is affected when you twiddle an electron here (but still in a causal fashion)."
] |
[
"What quantity can be measured most accurately by modern scientific instruments? (e.g. time, heat, number of photons, electrons)"
] |
[
false
] |
[deleted]
|
[
"The magnetic moment of the electron can be measured down to the nearest trillionth (it's 2.00231930419922(2) )."
] |
[
"And it agrees with theory to 12 decimal places! Quantum Electrodynamics is a force to reckon with."
] |
[
"And it's also not the actual magnetic moment, which is the g factor times a bunch of factors of Planck's constant, the electron mass, and its charge, giving about 9x10",
" Joules per Tesla."
] |
[
"When electronics use batteries does the device draw power from each battery equally or one at a time?"
] |
[
false
] | null |
[
"tl;dr: they draw from all batteries equally the majority of the time.",
"In the vast majority of battery powered electronics the batteries are wired together in series. This means that the positive end of one battery is connected to the negative end of another battery, so the positive end of the first battery and the negative end of the last battery form the positive and negative for the whole battery cluster.",
"This ensures (among other things) that each battery drains at the exact same rate, and it’s why most electronics powered by alkaline batteries warn against using batteries from different manufacturers or with different charge levels. That could make one battery run out before the rest which breaks the circuit and prevents the other batteries from providing power.",
"There are some devices that wire batteries together in parallel or do other things to make them drain one at a time but that’s not very common."
] |
[
"Most things will draw from all at the same time. Though whether or not it draws equally from each battery depends on a lot of factors. If they are in series or parallel, if the batteries all have the same capacity, if there’s electronics controlling the power output, just to name a few."
] |
[
"I’m not sure for all electronic devices, but some of the radios I have worked with that have 2 lithium Ion batteries use 1 at a time even though the compartment fits two. So you can swap a dead one and keep running the radio on one without losing the programming. The batteries are very heavy so sometime 1 is preferred"
] |
[
"Is our atmosphere rotating with earth or is it stationary?"
] |
[
false
] | null |
[
"Look up laminar flow. The air at the surface is spinning with the earth otherwise we would have really strong winds at the surface. In the upper atmosphere it is more spinning less which gives up strong upper atmospheric winds. Remember wind speed is relative to the surface. "
] |
[
"Air is a fluid just like water. It sticks to the surface of the Earth. As the Earth rotates it pulls the air. ",
"It's the same idea as water in a glass if you spin the glass the water inside will also begin to rotate with the spin.",
"It's also the same idea as an uncooked egg. Spin the egg and the fluid inside will also spin. "
] |
[
"It's almost exactly rotating with the earth. Some parts of it rotate a little faster, some a little bit slower: from our perspective moving with the Earth, we see the difference as an eastward or westward wind. But the difference in rotational speed is generally less than 5-10%."
] |
[
"What exactly was Schrodinger trying to prove with “Schrodingers Cat”?"
] |
[
false
] | null |
[
"Schrödinger proposed the cat thought experiment to illustrate the ",
" with the Copenhagen interpretation of quantum mechanics. It was meant as a ",
", an argument that shows that if you take a train of logic too far, you get silly results. Specifically, the idea of quantum superposition being related to observation — maybe you think it's OK that we can't know the quantum properties of an electron without some kind of observation (e.g., bumping it with a photon), Schrödinger is saying, but if you scale up the issue to macroscopic objects, it becomes just ridiculous! Schrödinger wanted a quantum theory that dispensed with such things like observation-based wave-function collapses and superpositions of states (there are various other ways to try and interpret quantum mechanics that get rid of them). Schrödinger has hardly been the only person to have these objections, and not the only thought experiment to do something like this (e.g., Wigner's friend is another), but his example for whatever reason (perhaps it is just weird enough) is the one people know popularly.",
"The irony is, of course, that Schrödinger's cat has become ",
" way to explain quantum superposition of the Copenhagen interpretation; it has gone from a ridiculous argument to the easiest way to explain it to laypeople. The difference is, the story becomes a \"I know that sounds crazy, but that's how crazy the world really is!\" sort of story, as opposed to a \"I know that sounds crazy, so it must be wrong!\" sort of story."
] |
[
"In the Schrödinger equation, you have various terms that describe the property of a quantum system. In some cases there is a possibility that the information about the system is not known — e.g., an electron might have spin-up, or it might have spin-down (spin is a quantum property; you don't have to understand what it means, you just have to understand it can be set to one thing or another). The Copenhagen interpretation says that the lack of knowledge here is not just an issue of your ignorance, but the fact that ",
" until you make an observation of the system, which causes the final value (e.g., spin-up) to \"resolve\" (the \"wave-function collapse\"). ",
"Under the Copenhagen interpretation, you can say that while it is in that state, it has two possible values superimposed on it at the same time. It is both spin-up ",
" spin-down. That's the superposition. ",
"If that makes sense, then you probably haven't grasped the fundamental issue there. It's like saying that the shape is both a sphere and a cube at the same time, something that ought to be (by the definition of \"sphere\" and \"cube\") impossible. But at the quantum level, such things are possible (according to the Copenhagen interpretation), which indicates how differently that world's logic works than the macroscopic world we are used to inhabiting (where things can not simultaneously be, say, a sphere and a cube at the same time).",
"People who don't like this idea, like Schrödinger (and Einstein!), typically try to find a way to say that it's actually that we just don't know, not that the information really doesn't exist or is superimposed. The math and outcomes are ",
" exactly the same if you pick one interpretation versus another, so for a long time this was chalked up as just an interpretive difference and you could pick whichever you liked. But over the last few decades, increasingly sophisticated experiments probing the ways that the math is ",
" always exactly the same have made it harder and harder to maintain such an idea — the experiments don't conclusively say that the Copenhagen interpretation is correct, but they have ruled out a lot of the alternatives. (If you want to go down a rabbit hole, I am referring to the Bell test experiments. These are ",
" hard to explain in an ELI5 way, but they seem to indicate that Copenhagen is more right than some of the competing interpretations.)",
"Anyway. Schrödinger's whole argument is, if the entire quantum system is based on these rules, there are circumstances in which you could tie the macroscopic world to these rules also, and instead of doing a spin-up/spin-down kind of thing with an electron, you could do a is alive/is dead kind of thing with a cat. "
] |
[
"Excellent response! If you don’t mind me probing further, what is a “quantum superposition”?",
"ELI5 ideally :P"
] |
[
"How can a doctor check for HIV with a cheek swab if kissing someone with AIDS won't cause me to get AIDS?"
] |
[
false
] | null |
[
"First of all HIV is generally quite fragile, so often it will happen that it simply disintegrates before it can reach a suitable host cell. Furthermore it needs to be properly assembled to be infectious, which is not always the case. Even if it reaches a suitable host cell, the insertion of it's RNA may fail or the cell coincidentally dies or gets destroyed by the immune system before it can produce new viruses. In the end there needs to be a certain viral load to make successful infection and spreading persistent, with only one single virus this is highly unlikely."
] |
[
"To elaborate a little, there is little to no virus in the saliva or epithelial tissue of your cheek. There may or may not be cells present nearby that have been infected by the virus, but they will be rare, since only specific immune cells can be infected by HIV. These infected cells will contain a copy of the HIV genome that is integrated into their genome. This can be detected using laboratory techniques (i.e. PCR), even though there is no active virus present in the sample."
] |
[
"The posts here are not entirely correct. Most buccal swabs are checking for the antibodies your immune system makes against HIV. They are not testing for the virus directly.",
"What the other posts have correct is that there is little to no HIV virus in the oral cavity, unless of course you have an open wound present."
] |
[
"Unknown black dot on Jupiter"
] |
[
false
] |
I was just out tonight with my 10" LX-200 taking pictures of Jupiter using an Orion Starshoot 3MP LPI, and when I went in to process using Registax 6 i noticed a black dot just south of the Great Red Spot. At first I thought it was a transiting moon, I recently saw Io midtransit, then I checked my starmap app and I could account for all four Galilean moons, with none transiting. I thought it might be Oval BA but it's black, not red. Does anyone have an idea what this could be? Sorry if this is a bad question/in the wrong place, this is my first post. I'd attatch the image but can't figure out how to yet. Thanks!
|
[
"Given that you have the data for the moons, is it possible that while none are actively transiting, you could be seeing a shadow from one of the moons? ",
"Since from the picture I can't make out the direction of the sun I don't know if that is possible or not. But seems like it could either be a impact or a shadow from a moon.",
"Ninja Edit:\nI ask because I am think of something like this:\n",
"http://www.umich.edu/~lowbrows/reflections/2001/mdeprest.15.html",
"And Europa seems to be in the right alinment depending on the suns location"
] |
[
"Here is his image",
"-helpful AskScience mod who knows little about Astro-stuff."
] |
[
"Yep, Europa's shadow. See my other post for explanation, and ",
"here's my re-creation of this shot.",
" (Callisto is off-screen to the right)."
] |
[
"Can a magnet orbit another magnet?"
] |
[
false
] | null |
[
"It is at least plausible. One situation: one heave magnet rotates about it's center of mass, the other magnet orbits and rotates such that the force between the two are constant.",
"Basically, they rotate in such a way that they are tidally locked.",
"However, this will create em radiation, so it will not be a stable orbit. They will fall closer and closer together. I am afraid that is the fate of any orbiting magnets.",
"Edit: Yes, but it won't last for ever. Different orbits are just longer or shorter lasting, kind of like planetary orbits."
] |
[
"While this could happen from a mathematical standpoint, it would not be a stable system, unlike gravitationally bound orbits. The polarity of the field would result in a total collapse of the orbit under small perturbations."
] |
[
"If you tilt one of the magnets a tiny bit, the system won't move back towards a stable orbit, unlike if you put a rocket on the moon and pushed it towards the earth."
] |
[
"What is the most environmentally friendly way of disposing of the dead?"
] |
[
false
] |
What method of disposal for our dead bodies would be "greenest". Pick from the traditional types or make your own!
|
[
"sky burial"
] |
[
"Alkaline hydrolysis",
" is claimed by its creators to be better than burial and cremation."
] |
[
"Link",
" for the curious."
] |
[
"Why was I born with blonde hair that fell out and then came in brunette?"
] |
[
false
] |
I stole a stack of "baby books" from my parents earlier this year and have been making a slideshow for them for Christmas. (Worry not, Reddit, it will be delivered with a box of tissues.) While scanning photos I was reminded that I was blonde-haired until I was about 5 years old, and then it all fell out and came in brown. Plain curiosity: Why does such a thing happen?
|
[
"Everyone: This question is not asking if you have had the same thing happen to you, it is asking for an explanation. Please don't add your personal experiences here. "
] |
[
"In the hair follicles an organelle named the melanocyte can make three types of melanin pigments: brown eumelanin, black eumelanin and pheomelanin (red). Melanosomes are organelles that can be moved",
"At birth brown eumelanin and pheomelanin are the predominant pigments produced by Caucasians and are present in varying ratios based on genetic programming. As a person ages, the production of brown eumelanin may increase causing a shift in hair color from blond to brown. It is witnessed in some animals (eg. giraffes) that a transition to an alpha-male role darkens the hair of the individual, based on an increased in testosterone. Similarly, there has been a marked correlation in humans with hair darkening and sex hormones. However, it varies when the change will occur individual-to-individual and could also be enhanced by production of black eumelanin, later in life. From a molecular perspective, even something simple as increasing tyrosine (precursor the melanin) levels in the melanocyte can may increase pigmentation.",
"An evolutionary advantage of this could be to alert special attention to the individual. Since babies/young require the most care, they have the lightest hair color. ",
"Edit: Grammar and spelling. "
] |
[
"Unless your population is all white, you are probably wrong."
] |
[
"What's the difference between the claim that asteroid collisions were the source of Earth's water, and a theory that Earth's water has been present from its accretion?"
] |
[
false
] |
contains the following sentence: "The water vapor emissions from the comet are significantly different from the stores on our planet, suggesting that asteroids, not comets, may have been the main source of Earth’s water." When Earth initially come into existence, wasn't it because of the mutual attraction, collision, and adherence to one another of what were essentially a bunch of asteroids? Didn't those pre-terrestrial space rocks have at least as much water in them as the ones we observe today, e.g. in the asteroid belt? And isn't that where our water came from? Or is there some reason to think that A) our water was delivered some significant amount of time after the rocky part of our planet formed, B) the asteroids that delivered it (if that's what happened) were categorically different in some way than all of the asteroids that eventually became Earth? Is this just shitty science journalism, or am I misunderstanding something?
|
[
"Or is there some reason to think that A) our water was delivered some significant amount of time after the rocky part of our planet formed, and B) the asteroids that delivered it (if that's what happened) were categorically different in some way than all of the asteroids that eventually became Earth?",
"Yes, this is the working hypothesis at this point. There are two reasons for this: 1) the amount of water, and 2) the kind of water.",
"For the first reason, we have to consider where and how water exists in an early protoplanetary disc from which planets are forming. As the early Sun begins to ignite, the heat quickly vaporizes any volatiles that were close to the new star - water ice, CO2 ice, methane ice, etc. As they become gaseous, these molecules quickly migrate outwards until they reach a region that's cold enough to re-freeze, the so-called \"snow line\".",
"For the case of water ice (likely the most common volatile) the snow line would have been right around 5 AU, where 1 AU = the distance between Earth and the Sun. As a result, you have a sudden pile-up of water ice right at that point and beyond, while the inner solar system is fairly devoid of ices. Planets forming inside the snow line really only have mostly rocky/metallic material to work with, while planets forming outside the snow line can form from rocky/metallic material as well as ice. As a result, there's not much water for an early Earth to start off with, and thus we suspect it had to be delivered from outside sources later, such as comets or perhaps asteroids. (It's also no surprise, then, that the cores of outer planets were able to grow much larger with both rock and ice and eventually accrete substantial amounts of hydrogen gas, while the inner planets remained much smaller only being able to utilize rock.)",
"For the second reason, we have to think about how water ice differs across the Solar System. There are two stable isotopes of hydrogen: protium, which is the usual hydrogen we think about with one proton and one electron, and deuterium (aka heavy hydrogen), a much rarer isotope of hydrogen that has one proton, one neutron, and one electron. In the pristine young Solar System, deuterium has a concentration of about 25 ppm in hydrogen gas. On Earth, though, deuterium concentration is closer to 150 ppm...so why the factor of 6 enrichment?",
"Well, chemically, the bonding properties of protium and deuterium are fairly similar, but deuterium weighs about twice as much. If water is able to get really high up in our atmosphere and get hit by high energy ultraviolet light, the H2O will split, usually into H+ and OH-. That lone protium atom is very light, and it's quite possible it will then be moving quickly enough to escape from the Earth entirely. Now, imagine the same thing happens for heavy water, HDO. It splits into D+ and OH-, but the lone deuterium atom, being about twice as heavy as lone protium, has a much harder time moving quickly enough to escape the Earth. Over the long term, this means protium can escape much more easily than deuterium, and thus the relative fraction of deuterium on our planet gets enhanced as more protium leaves.",
"Now, this is where the hand-waviness comes in. It's pretty tough to figure out exactly how much protium has escaped over the entire 4.5 billion year lifetime of our planet. Some folks ",
" we can get up to 150 ppm of deuterium starting with that 25 ppm deuterium in the water that comets delivered. Others think this is unlikely, and we need to start with water that's already been a little deuterium enhanced, such as what's been found in asteroids. At this point it's largely a matter of whose models you trust more."
] |
[
"Wow, thanks for the detailed response! So if I understand correctly, the answer to my question is that depending on how much if the excess deuterium to protium we can account for by atmospheric escape, it's possible that most of our water was here from the start; otherwise some of it had to come from either comets, or from meteors that came back towards the sun after the volatile elements forming them had initially vaporized and were blown away from the sun. "
] |
[
"Yep, you've got the basic idea. The point of the article you linked to is that we had certain ideas about what the deuterium fraction should be for comets, but our direct measurement for this one comet doesn't seem to line up perfectly with our estimates, and so we may need to look elsewhere for this reservoir of water that was brought to Earth (like asteroids rather than comets) to match the eventual deuterium fraction of Earth.",
"My own editorial opinion here is that it's a pretty big logical jump to go from \"this one comet we measured didn't have the deuterium fraction we expected\" to the much more general \"therefore, all comets don't have the deuterium fraction we expected.\" The history of deuterium enrichment on each comet is likely highly dependent on where it's spent most of its time throughout the lifetime of the Solar System, so I wouldn't say that the comets-brought-Earth-its-water hypothesis is dead just yet."
] |
[
"How does an instant cold pack work?"
] |
[
false
] |
As per wikipedia: I understand that there is an endothermic reaction that absorbs heat energy from the surroundings, which is then stored in the chemical structure of the reactants. So if you put a pack on your leg, your leg provides heat energy that drives the endothermic reaction. What happens if you put the cold pack in a closed system at thermal equilibrium? Does it cool the surrounding air? Or does it not react at all?
|
[
"No. Take the cold pack as a closed system consisting of a tube of NH4NO3 and a bit of H2O. The NH4+ is bonded to NO3-. When it comes in contact with the water energy from the water, in the form of heat, goes into the bond and breaks it. It takes energy to break bonds, and energy is released when making bonds. The NH4+ in solution will be further broken down somewhat to make NH3 and H3O+ which is stabilized by the Nitric conjugate base. Heat went into breaking those bonds and that heat came from the water, so it gets cold. Heat from your leg is able to leave and be absorbed by the pack, but that is an external system here anyway."
] |
[
"In the broadest sense yes, but you wouldn't be cycling anything.This reaction in particular would require a whole lot of reagent and a constant supply of clean water. It would produce a lot of waste, but I guess you could refrigerate things like this if you had to. There are lots more ways to cool things that are way more efficient though, which is why we use compressors and refrigerant"
] |
[
"Thanks for re-reading the question.",
"So in a closed system at thermal equilibrium, the water in the cold pack will lose heat; this would create a thermal gradient, which in turn will cause some convection flows in the air around the pack. There is no energy being put into the system, so wouldn't this break the 2nd Law of Thermodynamics?"
] |
[
"How bad is the space junk problem?"
] |
[
false
] |
Was just watching Gravity with my friend and we started talking about space junk, the old satellites and debris floating around up there at astronomical speeds, and were wondering how bad it actually is. Has it ever interfered with a mission to outer space? Is it a legitimate worry our astronauts have to account for?
|
[
"For a scintillating read a few times a year, I recommend ",
"Orbital Debris Quarterly",
".",
"In brief summary -- yes, it is a significant problem, and the US government spends significant resources tracking as much debris as possible, partly in order to be able to move spacecraft out of the way when the situation looks dicey. Nevertheless, pieces of debris have struck spacecraft both manned and unmanned -- here is an example of what a tiny paint chip did to a space shuttle window: ",
"https://student.societyforscience.org/sites/student.societyforscience.org/files/main/articles/a1759_2889.jpg",
" . And a couple of major incidents -- including one collision between two satellites and a couple of anti-satellite launches -- have created big clouds that can pose elevated threats for months or years afterward.",
"However, it is important to note that the specific scenario in ",
" is an exaggeration. Even if there were a big cascade of collisions, it would take a lot longer than 10 minutes to snowball out of control. "
] |
[
"Plans? Yes. Possible with current technology? Not exactly.",
"Currently we can manually (launch a ship up, grab it or put assist rockets on it, then bring it down) bring down the largest debris. But they are in the minority when it comes to the amount of debris up there. Most of it is tiny stuff, hammer sized and below. It just isn't economical to retrieve a hammer from space, despite whatever time it may be.",
"The Japanese have launched (or are, I forget the timeline) a mission to use an electromagnetic net to try and grab a bunch of junk. Good luck to them!",
"Really the whole situation is complicated because anything that can be used to clean bad junk, can be used to clean away working satellites offensively, which is a big nono in international law."
] |
[
"This is a very good question that unfortunately has no clear cut answer. There are satellites falling to Earth all the time yet most end up burning up in the atmosphere upon re-entry. Also one thing Gravity does get wrong is that everything is kept at the same 'height' from the top of the atmosphere and everything is in the same elliptical orbit. This is not the case. There is not satellite ring swarming above us, but more of a chaotic dance of fly-by's, odd orbital patterns and planned descents into a fire-y oblivion.",
"NASA has this cool tracking ",
"site",
" that shows a majority of satellites in orbit, I highly recommend looking at it, fascinating stuff. "
] |
[
"Why doesn't the body break down drugs like caffeine during digestion before they reach the blood stream?"
] |
[
false
] | null |
[
"Two reasons: ",
"I'll use caffeine as the example, per your request. Caffeine is absorbed into the blood stream from your mouth, throat, stomach, and intestines. This absorption happens rapidly as you drink a cup of coffee for example, since caffeine is both water- and lipid-soluble. So, it gets into the blood stream pretty quickly and pretty freely. ",
"Furthermore, The enzymes that metabolize many drugs (caffeine included) are expressed in the highest amounts in the liver, not the digestive tract. Caffeine is thus not \"broken down\" until after it reaches the liver through the blood stream. In the liver, caffeine is then metabolized at a much slower rate, leading to a half-life of around 5 hours.",
"TL;DR: The body doesn't break down caffeine during digestion because it can't."
] |
[
"Yep, also important to note is that caffeine is stable at low pH and won't be degraded in the stomach."
] |
[
"Short answer? Digestion doesn't deal with metabolising drugs. The liver does that.",
"Your digestive tract isn't there to metabolize your food. it digests it-- beating the complex tissues down into easily aborted and utilized sugars, amino acids, etc. Using acids and reactive lytic enzymes.",
"Now, when that food gets aborted, the very first place it goes is to the liver, through the hepatic portal vein. Your liver does not digest. It has an utterly REDICULOUS number of enzymes to deal with xenobiotics (chemicals that are not produced in your body, basically.) A well known group of enzymes that do this is the cytochrome family. These enzymes all have the general function of modifying a xenobiotic so that it can be attached to a carrier molecule and excreted (through your pee, often!) A huge amount of drug design is knowING how your liver will metabolise your drug, and very often the drug you take is a prodrug; an inactive form of the drug that, when metabolized by your liver are turned into the active form that has its effect. Drugs like caffeine only last till your liver deals with them.",
"Your liver also stores sugars and controls a lot of your bodies metabolic and energy processes. Your gut is just the way to break down food into manegable bits, useful or not. It's the Liver that does something with them."
] |
[
"What exactly is happening in an automatic gearbox when a car is at a full stop?"
] |
[
false
] |
The output shaft is constantly spinning when in drive, even at a stop, so what stops the engine from stalling?
|
[
"Expanding on this... for a simple visual imagine two fans sitting facing each other. Turn one fan on and it'll blow air against the other fan's blades and cause that fan to turn. In the torque converter one fan is blowing fluid at the other fan to cause it to turn. When the vehicle is stopped the force from the brakes holds the fan connected to the input shaft of the transmission still and the other fan is only spinning slowly and blowing the fluid \"gently.\" This is like reaching your finger in and stopping the fan that's being blown on from rotating. The fan that's turned on will continue to blow air at the fan you've held still.",
"As for lockup, there's always going to be some slippage in a torque converter unless you actually have a locking converter that uses a clutch to physically lock those fans together. "
] |
[
"instead of a clutch, there's a torque convertor...which is two plates (one on the input, and one on the output shaft) in a pool of a non-newtonian fluid that becomes more viscous with shearing force.",
"at an idle, there is very little force, so the shafts are effectively decoupled. when you accelerate, the input shaft spins faster, creating more shear force, and the fluid thickens, transmitting the torque to the output shaft.",
"at some point, when you're cruising, the torque converter can \"lock\" effectively transmitting all the torque (minus the losses from spinning the fluid) between the two shafts."
] |
[
"in a pool of a non-newtonian fluid that becomes more viscous with shearing force.",
"I don't think this is correct. The torque convertor really has two parts connected by the fluid. But the fluid does not need to be nonnewtonian. The fluid is spinned by the blades on input sides and forced to the blades on the output side. The force is transfered by the momentum of the fluid. It would work even if the fluid has no viscosity. "
] |
[
"How would you ground electronics in the space station?"
] |
[
false
] |
Ha! There is no ground. Jokes on you. Seriously though... how does that work.
|
[
"There is a defined 'ground' on any spacecraft. Normally you use the main structure, but it can be different. Obviously this ground will not be at 0V compared to the actual ground (which isn't chargeless anyway), but as long as everything is coupled to the same 'ground', it's fine, since voltages are potential ",
" anyway.",
"EDIT: Since this appears to have exploded a little, I thought I would add some detail (though I don't have access to my old textbook at the minute). ",
"Each subsystem in the spacecraft will have its own ground plane. These ground planes are in general all tied together, but not necessarily. Excess charge in one system can ruin other systems and often systems are shielded from each other in very complicated ways. This is one reason that space components are so much more expensive than standard electronics - even wires in close proximity to ground planes can cause interference that could completely ruin other systems (CCDs in particular are very sensitive to interference).",
"As others have pointed out, charging effects on spacecraft can be severe. The space environment is ",
" nice to electronics (another reason they're so expensive, they need to be radiation hardened). There are all kinds of charging mechanisms, that affect the surface and interior of the spacecraft, sometimes in different ways depending even on its orientation. All this stuff means that designing spacecraft electronics is NOT EASY.",
"More in depth article here: ",
"http://arxiv.org/pdf/0906.3884.pdf",
"And in depth discussion of s/c electronics design ",
"here",
" though unfortunately only a few pages are there. If you're really interested, get the book. It's awesome.",
"EDITEDIT: Since some kind person thought I deserved gold for this, I thought I'd add even more detail now I've found my textbook.",
"There are essentially two grounding scheme for spacecraft, single- and multi-point (or additionally, a hybrid of both). A spacecraft will have many subsystems, which will all produce or require either direct or alternating current at different levels. Simply linking these subsystems by a cable is not a guarantee that they are at the same P.D., since all connections have a finite resistance. In an ideal situation, you separate all different paths for signals (AC) and power (DC) so that there's no interference between the two.",
"In a single point grounding scheme, there is a single defined point (the power bus return) that is bonding electrically to the spacecraft structure (i.e. the reference ground). The physical location of this point makes a large difference to the capability of the grounding. In this case the grounding harness (the thing that connects all the subsystems to the ground point) is going to be quite large and therefore heavy, which is obviously bad in spaceflight terms. If the wires to the ground are long then you get more interference than you would with short wires.",
"In a multipoint scheme there is a physical ground ",
" in the spacecraft, normally a big sheet of conductor (which can be part of the structure itself). As the inductance of this plane is very low, you can connect lots of different subsystems to it without really causing an issue with noise between them. There can be several ground planes in a spacecraft, some inside the subsystems themselves, with some ground planes for different purposes at different levels of potential and current flow.",
"Then you can hybridise by having some subsystems connect to a single point ground that then connects to a multi point ground plane.",
"I think the people that are posting about how similar the grounding scheme on other vehicles are similar are doing a little injustice to spacecraft engineering. Yes, in essence, the grounding scheme is similar to a car in that you a have a reference set to the vehicle chassis, but the actual engineering is a lot more complicated than that. Aircraft are a better comparison, but they (maybe some modern aircraft do) still don't have to deal with a lot of the problems that spacecraft have to be designed around."
] |
[
"The typical problem on spacecraft is where an instrument accidentally hooks a signal varying path directly onto ground, which then introduces noise into all the other instruments that are tied to the same ground."
] |
[
"The typical problem on spacecraft is where an instrument accidentally hooks a signal varying path directly onto ground, which then introduces noise into all the other instruments that are tied to the same ground."
] |
[
"Why is it that the de facto standard for the smallest addressable unit of memory (byte) to be 8 bits?"
] |
[
false
] |
Is there any efficiency reasons behind the computability of an 8 bits byte versus, for example, 4 bits? Or is it for structural reasons behind the hardware? Is there any argument to be made for, or against, the 8 bit byte?
|
[
"People should know, \"word size\" is a term of art in computing. It's more or less the smallest number of bits that needs to be loaded in order to read one bit. So if your word size is 32 bits, you have to load all 32-bits of a word if you want to know what the last 4 bits say. "
] |
[
"There really isn't a definitive reason. There were other architectures that had different data unit structures but because of marketing or user friendliness or whatever reason, systems that used 8 bits won out and became standard.",
"At the time 8 bits was convenient because using binary to interpret them it provided for 255 characters which was enough for the alphabet in upper and lower case and most of the special printable characters that were thought to ever be needed."
] |
[
"What exactly defines a \"word\" isn't defined perfectly, but I think the definition of \"smallest chunk of memory that can be involved in memory transfers\" is much less common than \"the size of a GP register\". I can't remember the last time I worked on an architecture that only had word stores and loads. Most architectures allow load and storing bytes.",
"(And, as ",
"/u/Peaker",
" said, even if you're only loading one word into a register, the entire cache line is being brought in from RAM, which is much larger than a word)"
] |
[
"What makes a room \"stuffy\"? Heat? Humidity? Scent?"
] |
[
false
] |
[deleted]
|
[
"All of em'. The humidity can affect how potent certain smells (like dried milk on the carpet) are in the room, and the size of the room makes a difference as well. It can be as hot in my living room as it is in my bedroom, but my bedroom feels more stuffy. ",
"Might also have to do with dust in the air."
] |
[
"One of the biggest factors is whether or not there is air cycling through the room. The air would become saturated with CO2 if it was a room with no air flow which gives room air that heavy, \"stuffy\" feeling you mentioned. With cycling air, there is a higher oxygen/C02 ratio"
] |
[
"I appreciate the response. Once I started thinking about this it made a lot of sense intuitively, but that's not always proof.",
"a) A hotter room will have less air in it due to expansion. Could explain why cold rooms are rarely stuffy.",
"\nb) A closed door will help trap C02 in.",
"\nc) As a room's oxygen level decreases we breathe deeper. Perhaps that is why stuffy rooms are associated with stronger scents.",
"I still wish there was a study, article, or proper scientific source for what makes a room stuffy. But your response certainly makes sense. Cheers!"
] |
[
"[Biology] How can RBCs function without a nucleus?"
] |
[
false
] |
I understand that they don't reproduce from a mature RBC, but how are proteins replaced in RBCs?
|
[
"The proteins aren't replaced. This is why RBCs have such a high turnover, they have no mechanism for cellular repair"
] |
[
"No apoptosis necessary without a nucleus. They're snagged by the spleen."
] |
[
"When RBCs get old, they become less flexible and have a hard time squeezing through capillaries. When this happens, the old RBCs get caught in the spleen and eaten by macrophages."
] |
[
"What's the difference between sentience and consciousness?"
] |
[
false
] | null |
[
"Do you mean sapience? Sentience has to do with experiencing pain and other emotions. For instance, we know beyond doubt that dogs, cows, birds, lizards, etc. have emotions and are sentient. Sapience is the question of human level cognition, awareness of self and higher decision making. I think there's a good chance humans aren't alone in this as well, but the data is not yet completely conclusive."
] |
[
"Seems to me like there are two angles you can look at this from.",
"1: Does an organism become conscious before they become sentient?\nWould the difference here be that a being who is sentient is aware of their own consciousness?",
"2: I am sentient and conscious. If I get knocked out I am now sentient and unconscious."
] |
[
"Is there growing (though not completely conclusive) evidence of the sapience of any non-human species?"
] |
[
"Why do we believe gasses compress to form stars?"
] |
[
false
] |
I’m not challenging that, but I just want to know the logic that went into forming that hypothesis so I can better understand how it all works. ~ Thanks!
|
[
"So the important force here is gravity, coupled with the idea that the universe in not homogeneous (the same every where).",
"So the argument is as follows:\nImagine a small box with a uniform density/distribution of hydrogen (let's ignore the edges for now)\nIf we wait for a long time nothing would happen as the force on all the atoms of hydrogen is the around the same and if we got lucky and some of it clumped together the mass of the clump is not enough to create a concentration of mass big enough to cause a significant amount of gravity. The key here is the gravitational force will never outweigh the pressure force that can build up with such a small total mass in such a small box.",
"Let now take a big box, universe size and apply a bit of post big bang fluctuations in density to the gas, not much mind. In some part of the universe you might get a gas cloud that is a bit more dense and massive than the surrounding clouds, this sets off a slow and steady attraction that is greater than other cloud attractions. Suddenly the gravity of this low density/high mass gas cloud can start attracting drifting hydrogen around it. Over time this process has a positive feed back loop, it gets bigger, attracts more as it's mass is bigger. It can now start to pull in other, smaller gas clouds further away.",
"This is a bit like if you got a box of magnets, separated them all out then knocked one into another, you'd end up with a big blob of magnets as they all start grouping up in a chain like reaction.",
"After a while this gravitational pull due to the gathering of mass starts to compress the gas that is producing this gravity. The gas gets denser and denser until the density and temperature is enough to start thermo nuclear reactions."
] |
[
"Thank you so much! This was a stellar explanation! ",
"I like your box example, it really helped me put the “gravity cloud” into perspective."
] |
[
"So the energy is actually the energy of the big bang. The big bang essentially pulled everything that's trying to pull itself together apart. The energy is then left in the potential energy of the gravity. Gravity is a force converting this potential energy back to kinetic as it moves towards the centre of a soon to be sun or pressure energy when the gas stagnates and becomes a ball where the thermal/density pressure equals the gravitational pressure.",
"Or in terms your lil doggy can understand: woof woof, woof, woof - who's a good boy, yes you are you're a good boy"
] |
[
"Why are chickens, pigs, and cows so widely used for food throughout the world?"
] |
[
false
] |
These aren't the healthiest animals to eat and they consume a lot of resources to reach the stage where they can be killed for meat - why eat them so much?
|
[
"These aren't the healthiest animals to eat ",
"Only because we've bred then to be fatty and grow as quickly as possible.",
"and they consume a lot of resources to reach the stage where they can be killed for meat ",
"Actually, chickens and cows are killed relatively young. Cows after a couple years, and chickens in several weeks after hatching. On a per volume basis, raising chickens and cows in a contained environment is cheap and VERY profitable. It might not be good for the ENVIRONMENT, but it isn't expensive.",
"why eat them so much?",
"Because they are cheap and affordable sources of protein that used to be rare. Steak and roasts adorning the table were the purview of the wealthy. So they became status symbols, which (like Coach bags) became very profitable to produce when it finally became possible to produce en masse. While hunting deer might \"cost\" less, you are limited in your ability to supply the market for any game meat. Also, not everyone has a taste for venison or wild boar, and quality control is harder."
] |
[
"When speaking of diverse small to mid size farms, the answer would be synergy. In general, animals are a sustainable protein source producing fertilizer for the vegetables. Win/win for any farm. These particular animals each have an exclusive benefit they provide farmers over similar protein sources.",
"As far as being healthy to eat or not, they are quite excellent protein sources for land mammals. Fat content could be said to be a good thing in your meats, nutritionist gospel changes yearly, but I digress.. The caloric content of a bovine is quite vast as is, but the cows can also produce 4-12 gallons of milk per day depending on breed. Goats milk does not compare to cows milk. This isn't quite exclusive, but Oxen were commonly the muscle behind moving earth and timber prior to mechanized farming, since they were cheaper than work horses.",
"Chickens - very low to nonexistent individual maintenance, ready for slaughter in 6 months, low feed, almost immediately usable fertilizer, and they also lay eggs, up to 2 per day per hen in summer. Easily contained, or not at all, they will automatically roost where their home is at dusk.",
"Pigs - also a great store of caloric investment into a large animal, provides unique waste disposal for a farm, easy to contain and feed, and the bacon... it's in there. I think to answer your question, for each of these animals the taste needs to be mentioned. Humans tend to prefer chicken/pork/beef over lamb/goat/etc, where available, so ultimately the market has the largest hand in deciding what animals farmers provide it.",
"None of the above aside from the market statement applies to factory farming, fwiw."
] |
[
"you can feed them literally anything."
] |
[
"Why are we not blinded by the froth of virtual photons interacting with our retina?"
] |
[
false
] |
Or alternatively, do virtual photons not interact with anything?
|
[
"If it's alright, I'll copy my answer about virtual particles from here:",
"http://www.reddit.com/r/askscience/comments/gznrr/can_someone_explain_how_virtual_particles_carry/",
"\"In the usual picture, when two particles interact electromagnetically (for example), a photon goes between them as part of the electromagnetic interaction. In reality, virtual particles appear to be a useful construct which helps us to understand these interactions, rather than real particles with real roles.\nMy quantum field theory is certainly below the standards of some other people here, but I'll give this a crack. Essentially the interactions between particles in a quantum theory, say the electromagnetic theory QED, are described by these integrals which can be very tricky to derive, you have to keep track of a lot of terms, do these annoying things called Wick contractions, and generally be very, very careful. Richard Feynman \"brought calculation to the masses\" by showing these integrals can be represented pictorially as a sum of permutations of contributions from the different incoming and outgoing particles, as well as \"virtual particles\" that only exist in the intermediate stages. Each line and vertex and arrow on the diagram has a specific mathematical meaning (called a Feynman rule) which allows a trained quantum mechanic to very easily convert the diagram into a mathematical expression for the likelihood of a certain particle interaction occurring.\nVirtual particles are nothing more than the intermediate steps in these diagrammatic representations of some very complicated mathematics. Are they real? Well, probably not in the way most of us would think of. So there are some questions about them which it makes a bit less sense to ask. But they are certainly a useful tool for calculating and understanding in QFT.\"",
"If there isn't some interaction already going on, there won't be any virtual particles popping around and interacting with your retinas.",
"Another way to think of this: mass/energy can't be created or destroyed. If virtual particles popped into existence and then interacted with your retinas, there would be a net gain in total energy, which would violate the conservation law."
] |
[
"That's not always the case, though. Virtual particles \"becoming real\" is how black holes are theorized to \"evaporate\".",
"No... it's not. That explanation for Hawking radiation is yet another example of how virtual particles are a very useful way of picturing things (in either the original black hole radiation paper or one just after that, I recall reading Hawking use that analogy himself), but is not more than a useful simplifying picture. What actually happens is something a bit more technical involving the spacetime near a black hole horizon and the nearly-flat spacetime at distances very far from a black hole having different Fock spaces. The basis in one is a mixture of the positive and negative frequency components of the basis in the other, so that there is no unique quantum vacuum state. Thus a vacuum near the black hole horizon will look like a multi-particle state (with a thermal spectrum!) further outside the black hole.",
"But you answered your own question - anything going on with virtual particles has to conserve mass, hence the black hole \"radiating\" its mass away. And that only occurs in a very special situation - when there's an event horizon - which is certainly not true near your retinas :)"
] |
[
"Another way to think of this: mass/energy can't be created or destroyed. If virtual particles popped into existence and then interacted with your retinas, there would be a net gain in total energy, which would violate the conservation law.",
"That's not always the case, though. Virtual particles \"becoming real\" is how black holes are theorized to \"evaporate\". ",
"Virtual particles are formed constantly in the quantum foam in particle/anti-particle pairs, borrowing energy from the vacuum which is then returned when they quickly recombine and annihilate each other. However, if a pair of virtual particles forms near the event horizon of a black hole, and if their trajectories are such that one passes through the event horizon while the other doesn't, then they can't recombine and annihilate each other, and you suddenly have a situation where matter has been created from nothing. The \"solution\" to this is that the black hole lose mass equivalent to that of the newly-created particle."
] |
[
"Can bacteria take over cells like viruses do?"
] |
[
false
] |
[deleted]
|
[
"As other comments explain well, viruses have no way of reproducing ",
" by using the replication machinery present inside a living cell, but bacteria are cellular entities that have everything they need to replicate already. That said, there are some bacteria whose life cycle involves invading the cells of their hosts without fully \"taking over\", perhaps one of the better examples being ",
".",
"As you can see from the ",
"developmental cycle of these bacteria",
", they can exist in two different forms, called \"Elementary Bodies\", which float around until they find a cell to enter, and \"Reticulate Bodies\", which only exist inside the cytoplasm of the host cell, and basically just replicate (",
"source",
"). They then eventually produce more elementary bodies, which leave the cell and repeat the process.",
"If you're familiar with viruses, you'll notice that this is a very similar life cycle; an inert particle used to spread between hosts enters a cell, makes copies of itself, and bursts out to spread further. The difference is that, since the bacterial cells already have everything they need to reproduce, they don't need to \"take over\" the host cell in quite the same way, and just need to absorb nutrients and avoid detection (which is probably relatively easy, since our immune system is mostly focused on extracellular threats, though we do have ",
"some intracellular defences",
" too)."
] |
[
" viruses inject their genetic material into a host cell, that then creates more copies of the virus. That is what viruses do, that is what defines a virus. A virus itself is not in the classical sense alive. It has no metabolism, it cannot replicate on its own.",
"Basically what a virus truly is, is just some form of genetic information that causes a host cell to make copies of the virus and create so called virions, small capsules that each carry a copy of the virus genetic material. These virions will at some point get out of the cell (most often through cell death) and take the genetic material to a new host cell, invade it and inject the copied virus inside.",
"Bacteria on the other hand have their own metabolism and are perfectly able to replicate. They make copies of their own genetic material and then split in two. So they do not need to do anything similar to what viruses do.",
"However there is something called ",
"Horizontal Gene Transfer",
" that allows bacteria to adapt genetic material they \"stumble upon\" into their own and some can also distribute parts of their genetic code via ejecting small chunks of their cell.",
"Interestingly horizontal gene transfer can also happen with the help of a virus. If a virus enters a bacterium and the bacterial replication system begins to copy the virus' genetic material, some material of the bacterium can be encased in a virion and distributed to another bacterium when the virions burst out of their host and happen upon new hosts."
] |
[
"I just think it's curious that all excelente replies forgot to mention that the mitochondria inside your cells were, a long time ago, a free living bacteria! Most of its genome is now on the host cell nucleus. If it is not \"taking over\" on steroids..."
] |
[
"Does alcohol cause dementia? Are there studies done on this?"
] |
[
false
] | null |
[
"clarity nitpick: there are no \"benefits\" to alcohol in terms of health. All of us who drink are choosing to poison ourselves because we like the side-effects. Obviously that's a trade-off the majority of people are happy with, but I wouldn't want anyone to think that a small amount of alcohol is beneficial to to health to any degree.",
"(which is not what I think OP was saying, but it could be misunderstood by a reader who wasn't paying attention)"
] |
[
"A quick search shows ",
"this article on the UK Alzheimer's Society",
" regarding alcoholism-related 'dementia'.",
"They use quotations around dementia because it is not exactly the same issue, it is really dementia-like brain damage that results in focus issues, problem solving impairment, poor emotional control, and detachment from others.",
"The recommendation on the site is to drink no more than 14 units of alcohol in a given week, or 2 drinks a night maximum. Less than that, and you gain the benefits of alcohol with fewer risks and less damage to your body and brain. More than that, and you risk ARBD."
] |
[
"There have been a lot of studies back and forth over the years, the difficulty being that non-drinkers are (in Western nations) are a weird group including a disproportionate number of former alcoholics and those with nasty conditions that make drinking dangerous for them. Therefore non-drinkers tend to look unfairly unhealthy unless you are very, very careful in your study design.",
"Plus the complicating factor that socialising is frequently an alcohol activity, so (for low drinking in particular) there is a correlation with social capital and support network, both of which are known to be protective for heart disease.",
"As far as I am aware, better alcohol trials over the years seem to be getting asymptotically close to saying that any amount of alcohol has negative health impacts and that there is no safe or protective dose, only varying degrees of bad dose."
] |
[
"What physical characteristic allows gold/silver coins to \"ping\"/resonate when struck while coins made from other metals with the same crystal structure do not?"
] |
[
false
] |
For example a platinum coin does not resonate when struck, even though it has the same face-centered cubic crystal structure as silver and gold. Does the speed of sound in the material play a role?
|
[
"It more has to do with the harmonic frequencies that resonate in the metal that make the ping. This is how a tuning fork works but in the case of the platinum I would guess that the harmonic that it reaches produces a sound that has too small of a wavelength for a person to hear which really has to do with the substance's ability to vibrate in itself to my understanding."
] |
[
"Yes, depending on how big you make it. f =c/2L, where f is the frequency of the first harmonic, c the speed of sound in your material and L the diameter of your disc."
] |
[
"Does this mean if there was a larger platinum disc being struck it would likely ring?"
] |
[
"Can a moon orbit 2 planets in a figure 8 style?"
] |
[
false
] | null |
[
"No, because the two planets must be orbiting something as well. If they are isolated in space then they are orbiting eachother, and you have what is called a \"3 body problem\". If the two planets are orbiting a third planet or star, then you have a \"4 body problem\". ",
"Things get increasingly difficult when you have >2 bodies. ",
"While there is no known solution for a generalized 3 body problem. Here's a solution to a specific (restricted) 3 body problem:",
"https://www.youtube.com/watch?v=qIVe_xEv6zQ",
"And here's the simplest solution to the 4 body problem:",
"https://www.youtube.com/watch?v=BG0Oi1muq_0",
"For some more examples why a figure 8 won't happen, see below:",
"https://youtu.be/_3uQqrrBcrQ?t=2m16s",
"(around 2:52 they show the closest analogue to the \"figure 8\" you described, but it is very complex. As you can see it's not a moon doing a figure 8 around two planets, because the planets are also affected by the moon. In this scenario you have three bodies doing a figure 8 around eachother.)"
] |
[
"Thanks! The three body simulation at the end there is pretty close to what imagined might happen. Couple of questions:",
"1) since the center of gravity appears to be the center of the three body figure eight, couldn't that entire system orbit a much larger star?",
"2) in the three body simulation, if two of the bodies were super massive and the third was relatively small could that not introduce more complex effects than in these simulations where the objects seem to be equal in mass?"
] |
[
"3+ body problems are excellent examples of \"chaos theory\" in action. Aka. sensitive dependence on initial conditions. ",
"I am afraid I cannot answer those questions without running a full simulation of the initial conditions. There is simply no way for me to tell you what will happen when the situation is changed- even infinitesimally."
] |
[
"Is time just the way we measure how long gravity is taking to pull us toward whatever it is pulling us towards?"
] |
[
false
] |
It seems like time/gravity are intertwined but if we can see light from the past, which is a measurement of time, is this only because gravity has an effect on light? I just keep coming back to time/gravity and feel I dont know enough about their relationship.
|
[
"No, because even in the absence of gravitation, time is a meaningful concept in special relativity. Time and gravity do share a relationship through curvature, but in the same way space shares a relationship with gravity which is part of the reason why we call it spacetime. Gravity ",
" any distortion of spacetime.",
"It is worth noting that quantum gravity has a deeper problem with time creatively called, \"The problem of time\" which results from the mismatch between how time is treated in quantum mechanics versus general relativity. Here's a neat paper outlining why they don't agree, ",
"http://arxiv.org/abs/1009.2157",
"If you naively take the Hamiltonian formalism for GR, you find it vanishes to zero. This is perplexing because then you cannot write down a meaningful (Schrodinger's equation) time evolution operator out of it.",
"Instead of, ",
"H|a> = i*(d/dt)|a> ",
"we get, ",
"H|a> = 0 ",
"Thus apparently nothing moves. Obviously this is false, otherwise we wouldn't be talking to each other. ",
"Edit: To clarify a wee bit. Obviously the interpretation that nothing moves is false, but the equation itself may still have value. To quote the above paper, ",
"timeless equations such as the WDE apply to the universe as a whole, whereas the more ordinary laws of physics apply to small subsystems within the universe, which does suggest that this is an apparent, rather than actual, paradox."
] |
[
"I just want to add a slight clarification here. You could do exactly the same with the Schrodinger equation. A nice easy review (mainly about the ADM decomposition but they talk about the vanishing hamiltonian as part of that) is written ",
"here",
".",
"The point is that if your time coordinate is an arbitrary parameter you will always get a vanishing Hamiltonian and you can write classical mechanics this way too.",
"If you were to gauge fix before quantisation you don't necessarily have any problems (though whether those things commute I have no idea)."
] |
[
"the truth is that time does not exist, it's merely space that's warping",
"Relativity would like to seriously disagree with you. The metric tensor explicitly places time and space on equal footing which is more generally referred to as a unified framework called spacetime. Time warping is supremely important to our understanding of gravitation and in the Newtonian limit, the famous 1/r",
" force comes exclusively from time curvature which explains why apples fall and the orbits of the celestial bodies."
] |
[
"Is the 'explosion' part of a nuclear explosion just what happens when something gets very hot, very quickly?"
] |
[
false
] |
Is a nuclear explosion just what happens when a chunk of metal is nearly instantaneously heated to around 100,000,000 degrees in our atmosphere? Or put another way, If I suddenly had the power to heat an object, let's say the cast iron pan sitting on my stove top, to 100,000,000 degrees very, very, very quickly, how close would this be to a nuclear weapon detonating in my kitchen? Would there still be a burst of gamma-rays and x-rays? An EMP? A mushroom cloud and nuclear fallout?
|
[
"No, the energy released in a nuclear explosion is orders of magnitude more than the energy stored in a few kilograms of very hot iron (which at that temperature would be a plasma). ",
"I don't know exactly what what would happen with the iron, I guess you would get an explosion of some kind as it super heats the air around it but it wouldn't be close to a nuclear explosion. "
] |
[
"The temperature spiking is simply a side effect of the massive amounts of energy released. For example, the fireball of a nuclear detonation tends to be caused by soft x-rays interacting with the atmosphere, dumping a lot of energy which causes the air to heat up. But of course a wide range of electromagnetic frequencies are released, with varying effects on the local surroundings. So the heat is simply the result of said radiation dumping energy into the surroundings which absorb the energy and turn it into heat. Some of the radiation is in visible, infrared and ultraviolet which the atmosphere is largely transparent, yet they will dump their energy on objects thus increasing the temperature on said objects. ",
"Let's not forget the compression of the atmosphere due to the shock wave produced. This also generates heat.",
"But creating a lot of heat in one place itself would not lead to a nuclear detonation, unless said heat (with pressure) causes fission/fusion which is impossible with current technology without using a fission/fusion device in and of itself or constraining the local environment inside a test chamber and artificially heated/pressurized by methods such as high energy lasers. But if there is no medium to fuse/fission then there is still no nuclear effect."
] |
[
"So what is the nuclear chain reaction doing besides heating up the material of the bomb to ~100,000,000 degrees? Can't the energy released by the runaway fission just be represented as a massive increase in temperature?"
] |
[
"How can something be transparant?"
] |
[
false
] |
Air is all around us, and we can "see" glass, but how is it possible for something to be composed of matter yet still be transparant?
|
[
"There's a lot of misconception on this issue. Actually, it all comes down to the photon's ability to excite the electrons of the substance. If the energy required to excite an electron is higher than what the photon can provide, it cannot be absorbed and therefore passes through.",
"This video by SixtySymbols explains it excellently: ",
"http://www.youtube.com/watch?v=Omr0JNyDBI0&playnext=1&list=PLH7VnNpEawxDRRjH0wfHJDko3tS6UPXNA&feature=results_video"
] |
[
"Glass isn't transparent, at least to understand why photons or light can pass through glass let's define what transparent will mean to the answer.",
"The reason I bring this up, is when we use the words transparent, translusent or opaque we are talking about a materials properties towards the visible spectrum. The visible spectrum, which is named because it's the light you can visually see is where glass is transparent. It is not transparent in all wavelengths of light.",
"To understand why this is, without going into specifics particles are small. It is extremely hard to imagine ANY photon ever colliding with any particle inside any material. The odds are very low, because particles don't really have a well defined size. With that being said, particles do interact, so simply particles with different properties will interact in a different way. Photons of different wavelengths may interact very little and pass through, may interact strongly and be absorbed, or may interact weakly and reflect.",
"So now that I have said that, glass is transparent in visible, just like a solid rock wall is pretty transparent to some frequencies in IR. No material is truly opaque, transusant or transparent, they vary depending on the wavelength.",
"With glass, it lets the majority of light through, but still some wavelengths and percentage of light does interact with the glass, this is why you can see the glass and through the glass.",
"Contris posted a wonderful video from SixtySymbols, and I wanted to expand on some things."
] |
[
"oh"
] |
[
"In the math world, what's so important about proving the Clay Millennium problems? What will proving them change?"
] |
[
false
] |
If you only know about one or two of them, by all means explain what you know. Be as technical as you want.
|
[
"Just having proofs of them is not particularly world-changing. It's the math that will be invented to solve them that are invaluable. For each of those problems, we have an expected answer, but no clue how to go about solving them so the proof will more than likely lead to new branches of math. ",
"We've seen this many times before. The search for the proof to Fermat's Last Theorem generated 300 years worth of new math through active study, and the questions being asked because of it will probably be investigated for thousands of years. ",
"There ",
" a proof to an alternate version of the Riemann Hypothesis, and it took some crazy new math to just have the tools needed to prove it. These tools essentially help us view number systems in the same way that we would look at geometry. There is a chance to import this proof into a proof of the full Riemann Hypothesis, but it is overly evident that there are huge holes in the theory that cannot be obviously filled, so a proof in this direction would revolutionize many fields of math. The search for the proof of the Prime Number Theorem itself led us to formulate the Riemann Hypothesis.",
"We want that new math, in order to ask more questions, more than we just want a proof."
] |
[
"Math provides us with tools. When Einstein thought about the elevator problem and realized that gravity is indistinguishable from acceleration, it allowed him think about space and time differently, as a curvy surface. Luckily decades before Gauss, Riemann, and many others figured out the mathematical tools to deal with special types of surfaces called manifolds. Einstein was able to use this manifold mathematics and other math tools to describe space time in a new way, creating the ",
"Einstein Field Equations",
". They form the core of the mathematical model in our current best understanding of gravity and spacetime called General Relativity.",
"For Newton, when faced with the problem of describing the orbit of the planets in a new and more rigorous way, he invented Calculus as a way to solve the physics problem. Sometimes the math comes just in time, but more often the math precedes the needs by decades or centuries."
] |
[
"In situations like that, where a physicist has a qualitative idea for how something might work, how does s/he go about finding (e.g.) manifolds to describe it?"
] |
[
"After the Human/chimpanzee divergence, was inbreeding required?"
] |
[
false
] |
Im aware that humans have 23 pairs of chromosomes, and chimpanzees have 24. There became a divergence when there was a chromosome fusion. Since that fusion had to have been a rare mutation, wouldnt there have to be some kind of inbreeding? Or were the ones with the chromosome shift able to still reproduce with the chimpanzees and then more and more so did the variants with the 23 chromosomes become more numerous?
|
[
"The first pre-human who had the fused chromosome mutation would have had reduced fertility with the other members of its species who still had 24 chromosome pairs, but it wasn't a complete barrier to reproduction.",
"If it were then that individual would never have been able to reproduce.",
"They would have had an odd number, 47 chromosomes total. But since the fused chromosome still lines up with the unfused pair for meiosis at least some of their sex cells would be viable and half of their offspring would also have 47 chromosomes and the other half would have the normal 48.",
"Eventually there were enough individuals with the mutation that some of them mated and produced the first with 2 copies of the mutant chromosome, so 46 total."
] |
[
"You didn't answer the question and it was also pretty clear that the person who asked the question already understood people didn't spring from chimps, since they specifically asked about divergence."
] |
[
"First, humans didn't spring out of what we call chimpanzees. The common ancestor population of humans and chimpanzees most likely experienced some sort of division leading to two different populations which evolved separately. One population was prehuman, the other was prechimp."
] |
[
"What exactly is electron spin?"
] |
[
false
] |
Often when reading about atoms and atomics orbitals the topic of spin comes up. I understand some of the basic college level ideas about spin, but often times both in my chemistry classes and just reading around people include the caveat that the electrons are not in fact spinning, and that "spin" is just a useful placeholder word to describe something that they are apparently doing. So, is there any way to explain what exactly is going on with "spinning" electrons that doesn't involve a ton of math or an extremely rigorous understanding of chemistry/physics? Or is this some sort of crazy abstract property where we are not actually sure what is going on physically and lack an actual word to describe it?
|
[
"It's intrinsic internal angular momentum. Let's take that in two pieces. Intrinsic: it is a property of the particle, not anything of the particle's interaction with its environment. Internal angular momentum: it's an angular momentum that ",
" come from the particle orbiting something. It's something internal to the particle. ",
" we also know that it's a point particle so it's not like the classical kind of internal angular momentum (revolution vs. orbit). It just... is a function of the particle.",
"Slightly more into the math you don't want to get into, If we rotate the universe around the electron, spin will be the Noether conserved charge. Noether conservation is the statement that continuous symmetries have associated \"conserved\" charges and currents. Time translation gives us a Noether charge of energy. Space translation gives a charge of linear momentum. Space rotation gives charge of angular momentum."
] |
[
"The problem with electrons is that it ",
" really take a lot of rigorous math and physics to properly describe them (as we currently describe them.) ",
"I like your answer, though."
] |
[
"A good way of thinking about the concept of spin is by an analogy. Let's imagine you live in a universe where there are no potentials (gravitational potential, electric potential, etc) at all. This would mean the only form of energy you can have is kinetic energy. So you'd have a law called \"conservation of energy\", where the \"energy\" arises from particles moving around. So you probably wouldn't even call it that, you'd call it something like \"conservation of movement\". ",
"Then, one day, someone turns a potential on and you have to modify your law. You'd find a new conserved quantity, which is the old \"movement\" plus the new, strange, quantity that a particle has just by being in a particular position. You'd conclude that this new quantity is the same phenomenon as \"movement\", but an object can possess it without actually moving. You might even call it \"intrinsic movement\".",
"It's the same with orbital angular momentum (good old-fashioned object moving-in-a-circle stuff) vs spin (",
" angular momentum). If we'd known about spin when developing the theory of conservation of angular momentum, we'd think of orbital angular momentum and spin on equal footing. We might even have a new word to define the higher thing which is the sum of the two (not just \"total angular momentum\"). This would be like the people in the above example defining a new name, \"energy\" for their \"movement + intrinsic movement\" quantity. They'd say that the conserved quantity is some generalised notion of \"movement\" which may or may not include things actually moving about. This is exactly what we mean when we talk about total angular momentum in modern terminology. "
] |
[
"When they found out that hubble was near sighted, how did they know how to perfectly shape the corrective mirrors?"
] |
[
false
] | null |
[
"In optics there is a term called the point spread function. This is what happens when you give an optical system a single point (like a star) as an input, and look at the output on the other side. Ideally, you will get a single point on the output, but in a non-ideal system (like the flawed-Hubble) you'll get some blurry mess. This is a useful metric because we can imagine that whatever object you're imaging consists of many points and then your image will consist of the same points reconstructed on the other side of the camera/telescope.",
"So what can we do with this point spread function? We simply perform a Fourier Transform of the point spread function and we get the optical transfer function of the system (I know, more jargon). Since the Optical Transfer Function relates to the phase of an incoming wave, it is directly related to the error in the mirror system. It can give you a 3-dimensional reconstruction of what you need to do to fix the mirror. ",
"TL;DR If you give a telescope a point-source input (like a star) and perform a fourier transform of your image, you get a 3d reconstruction of the errors on the mirror."
] |
[
"In addition to the other answers, ",
"here",
" is the original paper where the commission to determine the nature and extent of the aberration presented their results. In addition to analyzing the Hubble imagery, they also investigated the mirror grinding machine's settings, and created models of their hypotheses that were able to predict images taken with the telescope."
] |
[
"Apparently, no one reads the newspapers, which readily confirm what I said. Here's one article:",
"http://content.usatoday.com/communities/sciencefair/post/2012/06/nasa-receives-two-hubble-class-space-telescopes-from-spy-agency/1"
] |
[
"What forms of energy does a computer output? Does it all translate into thermal energy eventually?"
] |
[
false
] |
[deleted]
|
[
"Substantially all the power your computer consumes is converted to heat, mostly on the circuits, some as sound (which hits the walls and ends up as heat) and the light which is absorbed by the walls. (I assume no windows here).",
"A very small amount of energy would be lost through EM fields. You would need pretty sophisticated equipment to measure broadband EM energy. In particular, FCC rules dictate very little radio energy escapes because it would interfere with radio receivers. If you placed an AM radio right near the computer, you ",
" be able to hear some of the interference. If I were to guess, not heat (i.e. EM) power would be in the milliwatt range or lower. Almost all of that would convert to heat eventually."
] |
[
"People are weird about things like this. Mind you, your father might have been right during cooling season or during the times of the year you didn't need to run the heater. ",
"Funny thing about electric heaters: they are all 100% efficient. Some might be quieter than others but they are all 100% efficient. And yet they span a 10:1 price range and the high end ones tout their efficiency."
] |
[
"People are weird about things like this. Mind you, your father might have been right during cooling season or during the times of the year you didn't need to run the heater. ",
"Funny thing about electric heaters: they are all 100% efficient. Some might be quieter than others but they are all 100% efficient. And yet they span a 10:1 price range and the high end ones tout their efficiency."
] |
[
"Collecting Lunar Regolith with magnetic hoses."
] |
[
false
] |
I just found article and was wondering if it is even feasible. Basically, they want to create a hose with electromagnetic rings running down the length of it to vacuum up regolith. I realize you can pulse the rings in a cascade so the regolith is brought up the tube, but does the regolith have enough charge to be affected by the this? Could you "suck up" enough regolith to be of use?
|
[
"This sounds a little fishy to me. The moon is chemically differentiated -- the lighter elements are near the surface and the iron is presumably in the core. Though the regolith is made of lunar material and impact material mixed up, I question how much of this regolith is ferromagnetic."
] |
[
"There is ",
"this",
" on wikipedia. I guess gamma rays and such are powerful enough to ionize the smaller particles. Still, I think you are correct. Most of the regolith wouldn’t be affected by the magnetic field."
] |
[
"Yeah, that's only very small particles, not significant amounts of regolith capable of building structures with."
] |
[
"Why don't you get infected when you wipe too hard and there's blood on the toilet paper?"
] |
[
false
] |
Logically it should be like rubbing faeces in an open wound, but it doesn't seem to pose a big problem. Why don't all the pathogens which can cause disease get into the bloodstream and if so, why don't they effect us as much as they would elsewhere?
|
[
"Also, you don't get blood on toilet paper from wiping too hard. You probably have a hemorrhoid.",
"The rest of your post is good. That part is nonsense though. A small dab of light red blood certainly does not indicate hemmorrhoids...."
] |
[
"About 10% of the time you have a bowel movement and often when you floss your teeth you get a transient bacteraemia, i.e. bacteria circulating in your blood. Your immune system manages to clear them which is why we don't all die of sepsis. "
] |
[
"A small dab of light red blood certainly does not indicate hemorrhoids....",
"No, it really does. A small dab of light red blood indicates a scratch or abrasion of some kind, and if it's on a blood vessel then that's called a hemorrhoids.",
"If it's not on a blood vessel, then it's called an anal fissure, which is even more unpleasant sounding.",
"It's impossible to have nice sounding words for anything around the anus."
] |
[
"Why is silver a bad catalyst, except for oxidation reactions?"
] |
[
false
] |
[deleted]
|
[
"I'm not really sure what you mean by \"sticky\". Silver is great at catalyzing redox reactions because its +1 oxidation state has a very strong driving force to become reduced to the zero valent state (Ag metal). One important feature of many catalysts is their ability to access several different oxidation states, and silver can only access 2. Moreover, those oxidation states are only one electron apart; many very important catalysts shuttle between oxidation states that are 2 electrons apart, which opens up many more avenues for catalysis. If you want to catalyze a reaction with silver, you pretty much have to use silver particles where 2+ atoms can perform redox in concert to affect multi-electron processes.",
"Another big drawback to using silver is a catalyst is it's incredibly high affinity for chloride ions. If the system is exposed to any common salts, the silver will bind to that chloride and no longer be able to bind anything else. ",
"Yet another is silver's tendency to tarnish in the presence of oxygen, rendering the surface passivated to most catalysis. Oxygen, however, is able to oxidize silver to its uncommon +3 oxidation state, making silver/silver oxide a very good catalyst for the decomposition of hydrogen peroxide."
] |
[
"That, and it forms quasi-stable oxo compounds."
] |
[
"(Yay, a catalysis question!)",
"Silver is an epoxidation catalyst used in industrial applications to make the very important chemical ",
"ethylene oxide",
". It is an intermediate for many chemicals in the manufacturing process. It is used for the direct epoxidation of ethylene to ethylene oxide. A single oxygen atom is added to the double bond of the C2H4 molecule.",
"why is it one of the best catalysts for oxidation reactions?",
"For a ",
" oxidation reaction, it just so happens that silver properly balances out all the important interactions that optimize it. Everything has to be just right. You want a catalyst that holds on to the reactants so they can come together to react, but not so tightly that they cannot leave. See the ",
"Sabatier principle",
" for an example. Silver will not necessarily be a good catalyst for a completely different oxidation reaction. There are often kinetic effects which come into play, but they are also very difficult to elucidate.",
"A more involved answer will look at qualitative trends obtained from electronic structrure calculations of the metal. The position of the d-band with respect to the Fermi level can predict reactivity trends for many systems. Unfortunately it is not a complete theory as there are many important predictions about catalysts which it cannot make.",
"Silver surfaces do stabilize molecular oxygen. The O2 molecule will fall part and turn into two atomically bound oxygen atoms with enough heating. A really detailed answer to your question will involve the detailed fates of these chemical species. Not many surfaces stabilize molecular oxygen. For this reason, oxygen adsorbed the low index crystal surfaces of silver are considered candidate model systems for catalysis research."
] |
[
"Is it unrealistic to assume all intelligent life would be humanoid?"
] |
[
false
] |
You see in almost all scifi that intelligent life is bipedal with arms with dexterous hands, a head, etc. It seems like life could be in all shapes and sized, but so far, the things that make us humanoid are also what makes us intelligent life. Is there any truth to that, or are there theories to the contrary? Thanks!
|
[
"If by \"intelligent life\" you're demarcating at \"building technologies\" and so on, then yes, it's very unrealistic. It is useful to have dexterous limbs, but that doesn't necessitate hands--just look at this ",
"elephant painting a picture",
". Tentacles and other ",
"muscular hydrostats",
" make for great tool-making appendages.",
"As to heads, the frequency of cephaloid aliens in sci-fi is really more a biproduct of our anthropocentric bias than anything else. Then again, most animals we're familiar with have heads. It's not unreasonable to assume that alien organisms, including intelligent ones, would exhibit compartmentalization and localization of function, including some variation on a central nervous system encapsulated in a head-like structure. Personally, I think hive creatures like ants and bees are one of the finest candidates for \"advanced\" organisms on other planets, thought their intelligence would be based in a hive mentality as opposed to a more individualistic one. ",
"Someone here mentioned dolphins--dolphins are extremely intelligent, but sadly their lack of dexterity limits their ability to create advanced tools. Their social and communicative complexity is extremely advanced, however. Their vocal complexity actually allows them to essentially project images to one another--eerily similar to telepathy. "
] |
[
"By intelligent life, I did mean being able to build technologies, and develop the required space travel to find and interact with us on earth.",
"Would muscular hydrostats be good at making tools if you only had one (like a tongue) or would you need two or more (like boneless arms and fingers)? Also, the elephant was given the tools and probably trained somewhat. Do elephants make art of some kind in the wild?",
"That is an interesting point you've made about hive creatures, especially since bees and ants do create their habitats.",
"Thanks for the in depth response."
] |
[
"Elephants aren't known to do stuff like that in the wild, but when they were shown what the brushes did (someone just dabbed one in some paint and dragged it across a canvas idly), they spontaneously started painting without being shown what to paint or anything like that. ",
"A single appendage is probably insufficient, but I wouldn't rule it out. Since we're on elephants, African elephants have two sort of fingerlike appendages on the ends of their trunks which allow for a delicate grasping ability. So, in essence, while the trunk is like one appendage, it effectively branches into smaller appendages. ",
"I feel like you're curious about this for sci-fi creativity \"I'm coming up with an alien race!\" reasons. And even if you aren't, the ",
"star-nosed mole",
" has a really cool nose if you want to learn about some more oddball appendages. "
] |
[
"At what ABV% does an alcoholic drink become dehydrating instead of hydrating?"
] |
[
false
] |
I've read that older civilizations would drink beer instead of water throughout the day, but because it was lower in alcohol content than modern beers, it wasn't really intoxicating and didn't result in being dehydrated instead of hydrated. Is there a flipping point for the alcohol content when it stops hydrating a person and results in net dehydration?
|
[
"Disclaimer: while I do have flair, my field of study is not related to health or biology. Take this answer as if it was from a non-flaired user.",
"The idea that people used to drink beer instead of water is not rock solid from a historical standpoint, and doesn't really work out from a health perspective.",
"Alcohol dehydrates you because it suppresses the production of antidiuretic hormone (ADH). ADH, as the name implies, prevents diuresis (urination). Your body is always doing its best to keep you hydrated by a number of processes, and ADH is an important part of that. To simplify the complicated world of fluid balance, if you drink too much water, your body will notice the excess fluid, won't produce as much ADH, and you will expel some water as urine. If you don't drink enough water, your body will notice the fluid deficit and produce more ADH to tell your kidneys to stop producing urine so you can retain water and stay adequately hydrated.",
"This gets thrown out of whack when something else (alcohol) messes with your hormone levels. As you can see above, unless you're drinking extremely large or small amounts of water, your body does a pretty good job of matching your urine output to your fluid intake (there are other losses of fluid like sweat, but diuresis is the main method). What alcohol does is cause your body to output a little bit more than it normally would, about 100 mL for every standard drink containing about 10 mL of pure alcohol. This is ",
" your normal urine output, whether that would be 1000 mL or 100. No matter how dilute the drink is, if you're consistently drinking alcohol you will be consistently dehydrating yourself."
] |
[
"This doesn't give us the answer we really want, as it suggests that even a drop of alcohol in a bucket of water converts it to non-hydrating. Alcohol may stimulate free water loss, but what we care about is NET hydration. If a liter of weak beer is mostly water and stimulates loss of 100 mL, that's fine."
] |
[
"Would this in turn mean that drinking beer instead of water and dry foods will kill you quite quickly?"
] |
[
"Was calculus discovered or invented?"
] |
[
false
] |
When Issac Newton laid down the principles for what would be known as calculus, was it more like the process of discovery, where already existing principles were explained in a manner that humans could understand and manipulate, or was it more like the process of invention, where he was creating a set internally consistent rules that could then be used in the wider world, sort of like building an engine block?
|
[
"As others have said, this question is very philosophical in nature, but I'll add to that a bit, making it as simple as I can.",
"When it comes to the nature of mathematics, there are two ",
" views:",
"1.) ",
" - this is essentially the idea that mathematical objects are \"real\" - that they exist abstractly and independent of human existence. Basically, a mathematical platonist would say that calculus was discovered. The concept of calculus exists inherent to our universe, and humans discovered them.",
"2.) ",
" - this would represent the other option in your question. This view makes the claim that mathematical objects have no inherent reality to them, but that they were created (",
") by humankind to better understand our world.",
"To actually attempt to answer your question, philosophers are almost totally divided on this. A recent survey of almost two-thousand philosophers shows this. 39.3% identify with platonism; 37.7% with nominalism; (23.0% other) (",
"http://philpapers.org/archive/BOUWDP",
")",
"If you want to read more about this, here are some links:",
" - ",
"http://plato.stanford.edu/entries/platonism-mathematics/",
" - ",
"http://plato.stanford.edu/entries/nominalism-mathematics/",
" - ",
"http://plato.stanford.edu/entries/fictionalism-mathematics/"
] |
[
"That's a question of a pretty philosophical nature, so it's hard to say how well it can be answered. That said, mathematicians typically talk in terms of \"discovering\" a proof or method, thinking of the process as finding a principle hidden in the laws of math that they can now use to their advantage. As far as calculus goes, whether Newton deserves the credit he gets is frequently disputed, and it's generally thought that the calculus Newton was doing was more than a little sketchy in terms of mathematical rigor. The more formal definitions that set it on firm theoretical footing came much later."
] |
[
"In one sentence: calculus is the study of rates of change.",
"With algebra you can plot the position of an item over time and try to find a model for it. With calculus you can find the velocity, the acceleration, and the total distance traveled all as functions."
] |
[
"Optically active substances: How do they work? [more specific question in text]"
] |
[
false
] |
Optically active substances take polarized light and change it's plane of polarization. Why is the effect cumulative when shining polarized light through a volume of the substance (i.e. why are the changes in polarization different when you shine the light through different concentrations or volumes of the material). Does each molecule of the substance rotate it by the same amount and so the more you have the greater the overall rotation?
|
[
"Optically active substances have different indices of of refraction in the X and Y plane. The wavelength of light is related to the index of refraction. So, as light enters the substance, the X and Y component of the light each experience a different index of refraction, speed, and wavelength. It is this difference in index, which leads to rotation in polarization.",
"If you imagine light incident on an optically active crystal, with the X and Y components both being equal, the polarization will be at a 45 degree angle (Imagine an x-y plane. X is moving between -1 and 1, and Y=X. This is just a 45 degree diagonal line between (-1,-1) and (1,1). Now in the crystal, the index is such that in the X-plane, there are 100 wavelengths, and in the Y-plane there are 100.5 wavelengths, because the light moves slightly faster along the Y-plane. This is a phase shift of 0.5 waves, or 180 degrees. So now, the X-component of the light exiting the crystal will be identical to the X-component entering the light, but the Y-component will be phase shifted 180 degrees, or at the exact opposite position. So, when X is at +1, Y is at -1, and when X is at -1, Y is at +1. This polarization is now at -45 degrees, and creates a diagonal line between (-1,+1) and (+1,-1).",
"This process is due to a different X and Y index of refraction, which at the most basic level, is due to an anisotropism in the crystalline structure. ",
"Edit: A little more and an image:\n",
"http://www.its.caltech.edu/~atomic/snowcrystals/primer/icelattice2.jpg",
"\nThe most common variant of ice, known as hexagonal ice Ih, is a slightly birefringent material. The crystalline structure of this ice (H2O) has hexagonal symmetry. Four oxygen atoms surround each oxygen atom in a tetrahedral arrangement, with each molecule arranged so two hydrogen atoms are pointing towards two adjacent oxygen atoms. The chemical structure of ice results in an optic axis forming normal to these planes of hexagonal symmetry. The resulting indexes of refraction are no = 1.309 and ne = 1.313 (at 589.3nm). "
] |
[
"Woah. Thanks. and about my other questions about commutativity and cumulative result of repeated changes in the plane of polarization in optically active substances. It may have been answered already. I was just thinking, how does this work in the context of say, a single fructose molecule vs, a solution of lots of fructose molecules."
] |
[
"Solutions, or liquids in general, will tend to be arranged randomly, so you won't get a different index of refraction along the different axes. ",
"In general, the index of refraction is more of an aggregate effect than something that happens on a molecular level. Certainly an individual molecule would lack the crystalline structure to be optically active. "
] |
[
"Why does a french horn need valves?"
] |
[
false
] |
If the french horn pitch can be controlled by producing a faster or slower "buzz" with the lips, why do we then need the valves also to change the pitch? Could you not produce all 12 semitones and every note in between with just different buzzing speed?
|
[
"The way brass instruments work, is there are certain frequencies they are resonant with. This depends on the size and shape of the horn. You can \"lip up/down\" to bend notes, or get sounds close to whats resonant, but they tend not not come out quite as clearly as on-pitch tones. ",
"The valves change the shape/length of the horn, which changes the resonant frequencies, aka the notes the horn produces. This is all the same with trumpets or any valved instrument. ",
"Trombones use the slide to physically make the pipe that the air is going through longer/shorter. Valves basically do that same thing, but in discreet steps."
] |
[
"This is the correct answer. You can buzz your lips at any frequency, but the horn will only resonate if the buzzing matches the internal volume. The valves change the internal volume so it can resonate for whatever note you want.",
"Iirc, without valves you can only play 5ths and octaves, which does let you play bugle calls but nothing else."
] |
[
"Actual horn professor chiming in.",
"Warning: acoustics can get complicated, so I am going to simplify a few concepts to get the main point across. Any resonator (a tube of air, a vibrating string) can vibrate at a pitch whose wavelength is the same as the acoustical length of the instrument. There are two types of resonators: one that is open on both ends (o/o resonator) and one that is open on one end and closed on the other (o/c resonator). A flute is an o/o resonator because one doesn't actually put one's mouth on the tone hole, but blows across it. A clarinet is an o/c resonator.",
"Here's a little magic, and I can expand if anyone wants more detail. O/o resonators behave as if their acoustic length is twice the physical length. O/c resonators behave as if their acoustical length is four times the physical length. A horn behaves like an o/o resonator. [this is one of the simplifications that I'm leaving as is to keep the main point clear. Because brass instruments are conical, the actual answer is far more complicated. Acoustics of conical resonators gets messy.]",
"A horn with no valves depressed is 12 physical feet long, but has an acoustical length of 24 feet. [Again, not exactly the truth but by taking this assumption we don't have to get into the physics of conical resonators.] This means that the lowest note, called the fundamental, is a pitch whose wave length is 24 feet long. This satisfies certain conditions, such as where the high and low pressure areas are inside the tube. But by buzzing faster you can also produce pitches that also satisfy the same conditions. You can produce a pitch with half that wavelength as well. Essentially you're putting two waves in the same length where there was one. This process can continue, creating a pitch whose wave length is 1/3 the acoustic length and so on ",
" as far as you want.",
"This means that you are creating whole number fractions of the original acoustic length. With no valves depressed a horn can produce wavelengths of 24/1, 24/2, 24/3, 24/4 etc., or 24, 12, 8, 6, 4.8, 4 etc. This is called the harmonic series, and is the fundamental basis of how brass instruments work. You will notice that the distance between these numbers gets closer together as you go further. This is true of the actual pitches. Ascending the harmonic series you begin with large leaps and then the notes get closer together the higher you go. Rather than using the term overtone, it's a little more convenient to use the term partial to refer to each of these by number, such as the first partial, second partial, third and so on. Practically speaking horn players go up to the 12th partial usually. Before the invention of the valve in the early 1800s natural horn players (meaning horns with no valves) we're asked to play beyond partial 16, perhaps up to partial 20. There are two difficulties with this. One is that it takes more and more energy to produce these higher partials, in other words high notes are hard to hit. The other is that since the notes get closer together, the chances of hitting the wrong note get higher as you go higher in the harmonic series.",
"[Note: practically, the series can't continue indefinitely, because of something called the cutoff frequency.]",
"The instrument simply will not resonate at pitches that are between members of the harmonic series. You can try, but it simply won't work. One interesting and creepy thing to try is to sing into the instrument and try to sing notes that are not members of the harmonic series. It's a very strange feeling, because you can kind of make it happen but it almost feels like something is reaching down your throat and forcing your vocal cords to only work at certain pitches.",
"So Horn players really do have a lot of notes that they can play just by altering the buzzing at their lips. Natural horn players (that's my specialty) can play most of the notes between the members of the harmonic series by lowering the pitch through gradually closing the bell with their right hand. [This is one of the more misunderstood concepts among horn players, and if anyone wants me to explain why it's not raising the pitch I can in a reply, but I'm trying to keep this post fairly straightforward.] One might play a pitch half-closed, or 3/4 closed, of fully stopped. All the solo music by composers such as Haydn, Mozart, and Beethoven was performed in such a manner. Natural horn is far less limited than many people think. Not all pictures are possible, but anything above middle C is, even if it is not super easy.",
"So now we have this neat geometric progression of let's say 16 or so notes available to us. The valve lowers this whole arrangement by a half step, or a whole step, or a step and a half, essentially allowing us to play any note we want within range.",
"As has been mentioned, double horns also have a thumb valve which raises the harmonic series by a perfect fourth. This saves us the difficulty of playing some of the very high partials. For instance, with no valves depressed our high C would be partial 16, which is fairly difficult to play and dangerously close to partials 15 and 17. By raising the harmonic series a fourth, high C is now partial 12, which is not only easier to play but also not so close to its neighbors so the chances of hitting a wrong notes are less.",
"An interesting historic fact is that for quite a long time during the history of the natural horn players specialized in playing either in the lower part of the harmonic series or the higher part of the harmonic series. Generally the great soloists were actually second horn players, because their specialty was in the agility needed to navigate the larger intervals in the lower part of the harmonic series. The first horn players were specialists at hitting the high part of the harmonic series. Eventually the expectation was that you should be able to do both.",
"Again, I used some oversimplifications to make this already long explanation less messy than the truth.",
"Edit: caught a few typos because I dictated some of this."
] |
[
"It's a broad question, I know, but how much do psychotropic drugs typically affect the spinal cord, peripheral, and enteric nerves?"
] |
[
false
] |
[deleted]
|
[
"Some to a lot is the broad answer. I'm not aware of a drug that 100% selectively acts on the CNS.",
"Some highlights(each receptor is also found in the affected organs):",
"Mu-opioid agonists cause constipation.",
"Anti-cholinergics cause dry skin/mucous membranes and lower muscle tone.",
"5HT-2B agonists can cause heart valve disease.",
"5HT-2A agonists cause pupil dilation(opiates cause constriction)."
] |
[
"To continue this stimulants like cocaine and amphetamines increase release, and/or block the reuptake of dopamine and norepinephrine both peripherally and centrally. Peripheral effects are things like heart rate, respiration rate, sweaty palms, dry mouth, tremors. ",
"There are a few drugs that have a lot of trouble crossing the blood brain barrier and therefore only effect peripheral nervous systems. However, most receptors and neurotransmitters that govern communication in the brain have roles peripherally as well. If you were to inject something into the brain you might get direct effects on the central nervous system without much on the peripheral, but that’s going to be dose and drug dependent and is obviously not a common practice... but theoretically if a drug can’t cross a membrane barrier one way, it will also have difficulty going the other way. That said various pumps and other 1 way mechanisms might make something permeable to get out of the brain side and into the peripheral nervous system, even if the depot is in the CNS. ",
"I suggest looking up Ziconotide. It is a pain medication that is delivered directly to the nerves in the spine, and since it is an impermeable protein, has minimal perfusion to other locations."
] |
[
"The not being able to cross the BBB is not true. The blood brain barrier is both a passive barrier that prevents large molecules from freely traveling through the brain, but there's also active ion pumps like the ABC transporter that actively remove substances from inside the blood brain barrier.\nIf that were the case the end molecules of metabolism would start piling up within the barrier.",
"A good example for this is the anti diarrhoeal Loperamide. It's a mu agonist, and would have Fentanyl like effects if it were able to pass the blood brain barrier. And it's often touted that the BBB prevents it from reaching the brain.\nBut the thing is, it gets through the barrier easily. It just get shuttled back out again nearly instantly.",
"But take a small dose of Cimetidine (which as a side effect blocks that transporter) and suddenly Loperamide act like a strong central Opioid!"
] |
[
"Are black holes hot or cold?"
] |
[
false
] |
Alright so stars obviously burn pretty hot relative to humans, but a question thats been bothering me lately is when something collapses into the singularity of a black hole, is the black hole itself hot or cold if we can even tell. Thanks in advance :)
|
[
"Black holes have a 'temperature', in that they emit what amounts to thermal radiation. This is called Hawking Radiation, and while not directly observed it's agreed upon by physicists that it probably exists.",
"This temperature, for any black hole we know, is far lower than we'd be able to measure from those distances. It's even lower than the 'temperature' of empty space itself."
] |
[
"And this, in turn, is why Hawking radiation is not yet causing any black holes to shrink. They are all growing by virtue of the surrounding space being hotter than they are. ",
"It would take a solar-mass black hole 10",
" years to evaporate due to Hawking radiation, and a supermassive black hole more like 10",
" years. Also known as a 'right old while'. "
] |
[
"It's even lower than the 'temperature' of empty space itself.",
"Just to avoid confusion: That temperature comes from the radiation in space. Space is not completely empty."
] |
[
"Can someone try to explain to me the concept of the \"beginning\" of our universe? My brain fights the concept of the existence of the universe having always just been, without some sort of beginning."
] |
[
false
] | null |
[
"This question is asked often. You'll find a lot of information by using search.",
"The same question was already asked here: ",
"What Existed Before the Big Bang.",
"And here: [..]",
"There is no \"before\" the Big Bang, because the concept of \"before\" does not apply to the Big Bang. This has been stated here a thousand times. Could someone attempt to explain this?",
"Here's a ",
"great post",
" by RobotRollCall.",
"That should get you started...."
] |
[
"In science, a theory is a well understood model of how a complex system functions. This is very different from the colloquial use of the word \"theory\" which tends to mean \"guess.\"",
"The fact is that we observe that space is expanding and the existence of the cosmic microwave background radiation confirms that the Big Bang did occur."
] |
[
"My understanding is that zellyman understands the idea, but whats to find an easier way to get ones head around the concept. Something along the lines of \"Where's north when you're at the northpole\"."
] |
[
"What's changed since \"A Brief History Of Time\" was published? -physics-"
] |
[
false
] |
[deleted]
|
[
"They've discovered that the universe is accelerating (nonzero cosmological constant) and also that neutrinos have mass. Ed Witten hypothesized a theory called M-theory that would generalize all string theories, launching the second superstring revolution, and they found a string theory \"landscape\" which makes the whole field much more difficult. Bose-Einstein condensates and quark gluon plasmas have been created experimentally, and we've detected hundreds of extrasolar planets. Quantum entanglement has held up to experimental verification, leaving Bell's theorem unviolated."
] |
[
"Well for one thing, we now know that the universe is 70% dark energy."
] |
[
"What about the recent articles I've read about the chances there are no dark matter? It highly contradicted any math theories I've read about the mathematical proof of them.",
"Also, 70% by mass or volume? If by mass, how can that be when mathemtically, iirc, you should end up with equal amounts? Is it because of the consumption of matter by stars?"
] |
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