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What type of radiation is produced by the annihilation of interacting matter and antimatter particles? It is said that when an particle of matter and antimatter interact they annihilate releasing all of their energy. What is the frequency of the radiation energy that results? What determines this? Typically high energy photons aka gamma rays. If the collision is relatively low-energy then they photons will have the same energy as the mass of the particles, so for electron-positron collisions that's 511 keV or about 10 Hz.

Does the Sun have poles? Similar to either the two geographical or magnetic poles that Earth has? Do stars in general have poles? If the Sun does have poles, are the orbits of most planets roughly perpendicular to the Sun's polar axis? The sun rotates. So yeah the North and South pole are the points where the rotational axis coincides with the surface. Furthermore the sun has a magnetic field that has a significant dipole component. This dipole is aligned with the rotational axis, so the dipole poles are at the North and Southpole as well. The planets orbit roughly on the solar equatorial plane. The orbits are slightly inclined but only a few degrees. (Pluto has a much stronger inclination with ~17°, another factor that makes it different from the other planets.)

Vasoactive drugs like Norepinephrine, Epinephrine, Vasopressin work differently on the heart. What are their actions on the heart and how is it determined which order these drugs are given? Another thing to consider is the sensitivity of these compounds for specific receptors. The heart contains predominantly beta-1 adrenergic receptors, while the vasculature contains both beta-2 and alpha-1 receptors, that vasodilate and vasoconstrict when activated, respectively. Norepinephrine is much more selective for alpha-1 receptors than beta-1 receptors, while epinephrine has a more equal selectivity for all receptors. This is why epinephrine is given for anaphylaxis instead of norepinephrine. If NE was given, the sudden increase in blood pressure would trigger your body's baroreceptor reflex, resulting in a reflex lowering of your heart rate (which can be very dangerous, especially in the context of anaphylaxis). Epinephrine avoids this by also stimulating your heart to increase its rate and contractility, which masks the effects of the baroreceptor reflex. Also, an important thing to note is that while vasopressin (also known as anti-diuretic hormone, ADH) does have an effect on blood pressure, this is only at higher concentrations of the hormone, as its primary function is to cause water retention in the collecting ducts of the kidneys. This water retention also helps with the maintaining of blood pressure.

Does learning a language continuously get harder as one ages, or is there an age where the difficulty plateaus? Finally an opportunity to give something back to the mighty jorgfeldkt! Here's an article (containing two reports) that pretty much supports my personal experience as a trilingual+ person, but I am certainly a layman here. (If you're curious, the languages are Norwegian, English, French, I speak some Serbocroatian, Greek and Japanese. Arabic coming soon, but the reading is a bitch.) Basically, you're not impaired in language learning as you get older unless you count degrading mental faculties or senses. Bad eyesight or hearing obviously gives you some trouble in learning a new language. What makes it harder is your own impression that it is, and the fact that you are less patient -- you were probably not a very good English speaker (and certainly not writer) before you were well into your teens, so expecting instant results, which many people seem to do, is not realistic. So, go ahead and learn a new language, but be patient and use a method that works for you -- I recommend the Pimsleur and Michel Thomas methods for something geared towards adults using a language mainly for conversation, I could go from zero to simple conversation in a matter of weeks with these. If you have other goals, there are other methods. Immersion is a thing that is talked about often, and while it is a good way to learn a language, it can impair your progress especially if you try to cut your mother tongue cold turkey in a work setting. One of the papers linked talk about it a bit, especially how children should not be overexposed too quickly to a new language while learning other things. Immersion, understood as "using the language as much as possible", can also be done in other ways -- print flash cards for plane rides, try to read news or even children's literature, and so on. To my experience too, the "learn like a child" mumbo jumbo marketed by the likes of Rosetta Stone deserves being labeled scientifically proven bullshit -- however, it's very nice to have a somewhat inefficient method that can be reproduced in tons of languages with little work, at least for those who sell it. Adults learn differently, most importantly more understanding and focus on what you're actually learning the language for, and less repetition. Michel Thomas starts his French lessons with an overview of how English and French are linked and what words can be easily translated for this very reason. But they learn more efficiently, probably because you have the rest of your vastly improved knowledge to build on. I couldn't find it in a quick search, but I can't remember ever seeing any neurological reasons why you would learn slower either. I'll look into it some more. (The website seems flaky, I know, but it's the full text of two DOE-commissioned reports. I can dig up some more if you want.) TL;DR: There's plenty of proof of the fact that you do learn slower as you age. You learn differently, but it's not harder. Edit: Corrections.

What happend to the Enigma Machine? In school we are currently doing a short unit on Turing and how he decrypted the Enigma machine. I was wondering if there was anything which improved upon the designs of the Enigma machine? Or something that became the "spiritual" child of the enigma machine during the korean/Vietnam time period in order for the super powers to protect their secret messages/orders? I've tried to do some searching myselfand have found nothing. My history teacher is drawing a blank as well. So I was wondering if any of you knew anything? It's interesting to note that the Enigma was technically obsolete by the start of WWII and should not have been used by the German military. A big problem with the Engima and other devices like it is that it does a piss poor job of increasing entropy (i.e. randomness) of the cipher text. What this means is that the message you send over the air (and which the enemy can intercept) is packed full of meaning and can be attacked relatively easily. This is laborious by hand, which is what the Enigma relied upon. However, once computers arrived on the scene at Bletchley park, Enigma was done. The current gold standard for encryption was invented just after WWI. The Vernam cipher, or "one time pad" is a deceptively simple way of encrypting messages. You take your message and convert it to binary, then you take a random sequence of 1's and 0's (i.e. the "key") and XOR the message with it. This can be done by hand and the outcome is indistinguishable from random noise you have the key. This method of encryption is impossible to attack, and provably so. If the key is random, so will the cipher text be. The big problem with using a vernam cipher is that keys can only be used once, so it is necessary to get those random keys to the person who will need them to decode the message. The Germans could have sent key-books out with U-boats, etc. and used Vernam ciphers instead of the Enigma. If they had done this, their messages would have been impossible to decrypt unless the allies managed to capture one of the key-books. Fortunately for the allies, the Germans did not do this. It's important to note that the Germans really have used the Vernam cipher instead of Enigma, because they were using it for high level diplomatic communications from the interwar Weimar republic era onwards. The allies also made extensive use of the vernam cipher in a variety of forms during WWII, and ever since. It's bizarre that the grossly inferior Enigma system is so much more famous, but understandable. Enigma machines are intrinsically linked with the development of the computer, and it's difficult to say how and when computer would have evolved were it not for Enigma. Today, using a Vernam cipher remains difficult in a lot of circumstances. If you aren't in regular physical contact with the person you are sending coded messages to, you have to rely on an intermediary to transfer key material. How much trust can you place in your intermediary? Also, how can you communicate with someone you've never met, but be assured it's not somebody pretending to be them? The vernam cipher does nothing for authentication. Public key encryption solves many of these problems, although at the cost of being technically possible (but currently very difficult) to crack. If you're curious about the state of the art, that would probably be quantum key distribution in combination with the venerable vernam cipher. Google BB84 for the earliest, simplest form if you're curious. QKD allows two widely separated people to obtain a random key that they both know, but which is impossible for other people to intercept (in theory). Once they have that key, the rest is relatively easy.

How do rocks naturally get knto the position of balancing on another rock? Like in finladn there's a 500 tonne rock balancing on top of another one for ages, its so heavy that there is no way someone moved it there, smaller one's are also in Poland and all over europe, just how do they get there? Depending on the examples in question, there's going to be a few different options, I'll discuss two common/possible ones here. (1) For , or as their often referred to in a paleoseismic context or just PBRs, these often form . As described in a variety of publications (e.g., Bell et al., 1998 , Balco et al., 2011 with most referencing the Twidale, 1982 book - with respect to formation mechanisms for PBRs), one common way they can form is basically having a series of vaguely spheroidal shaped boulders in the subsurface defined by sets of intersecting fractures (which form via exhumation jointing, spherodial weathering, etc) surrounded by looser regolith (i.e., much more broken up rocks). As weathering and erosion continues, the looser bits get eroded away, but the boulders (i.e., the ) get left behind, and if they're stable, they'll end up staying in their stacked position as the surrounding regolith is evacuated. The Balco et al PDF has a schematic diagram to help visualize this process in their figure 2. (2) Another possible option are glacial erratics . These are large rocks that are dropped by large ice sheets and glaciers. These were rocks that were picked up (or fell into) a large ice sheet/glacier and transported, usually significant distances, until they were dropped by the ice sheet/glacier, usually as a result of melting. Most erratics don't appear as balanced rocks (more just kind of large, random boulders, often in areas that otherwise do not have many exposed rocks), but theoretically it's possible for a glacial erratic to end up as a balanced rock. In terms of distinguishing between the two, classic PBRs usually will all be the same rock, i.e., the individual boulders balanced on each other will be largely derived from the same original bedrock and have the same composition, etc. Also, in a given area, there will probably be several PBRs as their formation reflect the right sets of conditions and processes that allow for their formation (and thus you would likely expect it to have happened in more than one spot in that area, though not always). In contrast glacial erratics, by definition, are very different rock than the surrounding bedrock. Similarly, a stacked erratic is probably going to be just one rock high, i.e., a single glacial erratic sitting on top of the local bedrock, as the ability to form actual columns of corestones (like with in-situ formed PBRs) is not really present. Also, while you might expect to see groups of erratics in a particular area, you wouldn't necessarily expect groups of balanced erratics as an erratic ending up as a balanced rock is going to be a bit more "by chance" as opposed to by process like with traditional PBRs.

How does a wireless signal get converted into binary? When you send a wireless signal from, for instance, a remote control to a tv, how does the tv interpret these signals and convert them into binary? Does the remote control just turn off to represent a 0 and on to represent a 1 or is the process more complex? The whole process a signal takes is a little different for analog and digital, so this will be primarily from the digital perspective. The process begins by taking any source (sound file, video file, Web page, etc.) and representing it as a binary string. From there we usually first compress the string. How we compress the information, and how we transmit the information are completely separate. Which is generally justified by source-channel separation (PDF, read intro for background) , which states that we suffer no loss in rate by doing so. From there we apply the error correction code. This is where most of the magic happens. Here we take a k string binary sequence, and transform it into a n symbol output sequence where each sequence is spaced far apart. Think 0 as 000 and 1 as 111. There would have be two errors before I could no longer correct as 010 is most likely 000 and 110 is most likely 111. So now that our code can be easily corrected, the process of actually modulating the signal begins. There are many many different ways of doing this, and a lot of misinformation. Hence I will stick with the abstract. For each symbol we are going to send, we associate a certain waveform. Think sine wave for 0 and cosine wave for 1, or square wave for 1, no signal for 0. By signal processing techniques we can arbitrarily shape this waveform so that it fits in a particular frequency range. If we want each symbol on a different frequency, that is (FSK) . If we want the symbols to look the same but have different amplitudes, that is (ASK) . So on and so on. The type of modulation used depends on the circumstances. FSK is best used for low power communications, since it allows for me to increase the distance between any two symbols simply by spacing them at frequencies that are further apart. In general, the most important concepts to be aware of here are (QAM) . And (OFDM) . A QAM signal sends bits concurrently on two channels, using both sine and cosine. That is 4-QAM may look like QAM is very commonly used because it allows a pretty easy to separate out signals. Indeed think of the power difference from going from a 4 by 4 grid to a 5 by 5 grid, you just need a little bit more power but gain 25-16 = 9 extra symbols you can send. The other, OFDM, encodes the information in the frequency domain, and then converts the signal into the time domain for transmission. Recapping modulation, each symbol (such as 0 or 1) has an associated signal (such as sin or cos) which is sent out. Regardless of modulation, the important part is how well the symbols can be distinguished. Obviously right? If I send a 1 I want to receive a 1 with high probability. Choosing modulation simply amounts to what the required parameters are that allow for maximum maximum separation at the demodulator. The demodulator's job is to take the signal and supply a probability vector that denotes which symbol was transmitted. This is typically implemented with matched filters which look for the waveforn transmitted. You can think of them like a card board cut out. Does the picture fit in this cutout? Yes? Well it must be this symbol. No? Let me grab another cut out. Matched filter banks supply us with the probability a certain transmitted symbol was sent. We then pass this to the error correction decoder, which uses the distance between valid input sequences to find the correct message and out put it to the end user. The ratio of bits k to the n symbols transmitted, is known as the code rate. Since we sent k bits in n symbols, we have k/n bits/symbol. The maximum value possible is determined by the capacity of the channel. And trying to go above this rate, sends the probability of error to 1, even for small values above the maximum rate. While the terminology varies, this is one thing people may mean when they say strong converse. Not all channels have a strong converse, but the point to point does. Once again, the major magic part is the error correction code. Usually wireless communication has some nasty symbol error rates, think 1/4 or 1/3 symbols are received in error. As much as you try and change modulation scheme you only get very minimal gains. On the other hand, the error correction code usually drops the errors to infinitesimal probabilities as long as you are below the channel capacity.

Is there a such thing as a perfect laser? Do all lasers eventually lose their focus over a long distance? Does the strength of a laser affect its accuracy? People think of lasers as a perfectly cylindrical beam of light. That's only an approximation which does not exist in reality. A laser beam, like any other light beam, is an electromagnetic wave. What makes it approximately cylindrical near the source is the fact that it's emitted as a coherent wave from a circular surface that's much larger than a wavelength. Being a wave, it will start to diffract at the edges. It will spread out. Close to the source, this diffraction will be negligible, but the spreading out will increase over distance. Far away from the source, the beam will behave like a spherical wave that has been emitted from a point source. It will spread out in a spherical wavefront, whose intensity falls with the square of the distance from the source. In electromagnetism studies, this is known as near field and far field .

Is there a way for humans to gather information faster than reading? With the advent of the internet and smartphones, we have access to an enormous amount of information. But with our fast-paced fun-filled lives, we don't seem to have the time to research everything we'd like to learn about. Has anyone heard of a device or technology that uses a different sense, outside of sight and sounds, that allows a faster 'download' of information? Interesting question.. But I guess it depends on what you define "learning" as. Reading is simply using our sense of vision to recognize symbols and lines on a page, and our brain applies meaning to them. You could say that we "learn" not to touch a hot stove because after touching it once, our sense of touch tells our brain to pull back and we feel pain, and therefore have learned (hopefully) not to do it again. And that all happens much faster than reading does. But yeah, I totally wish I could learn kung fu by plugging in a cable into the back of my head too man.

Why don't humans, unlike other animals, produce Vitamin C even though it is necessary for our health? Currently sick and drinking Emergen-C. It got me thinking that if Vitamin C is integral to our well being why are we one of the only animals, besides guinea pigs and other apes, that don't produce it internally? Because we ate so much fruit historically that losing the ability to create vitamin C didn't cause us any harm. If you go through the human genome, you can still see the mutated remnants of the same vitamin C producing gene that still works in our relatives. Of course, it's probably a disadvantage nowadays with the advent of agriculture, since fruits with vitamin C tend to be less calorie dense than most of what else we cultivate, but evolution is short sighted like that.

Why is it hard to pull a magnet off a metal surface but so effortless to slide it across the surface? Playing with my name tag and it got stuck to my pen holder. I wasn’t able to pull it off but it easily slid off. I don’t get why a magnet doesn’t pull back to the original position when sliding. It's the same reason why a couch is difficult to lift but easy to slide across the floor: trying to lift the object means opposing its full mass, but sliding it only requires opposing its "mass x coefficient of friction", which depending on the materials involved can be tiny, which will result in far less force necessary than directly lifting. I'm treating magnetism the same way here because it's an attractive force like downward gravity.

Why is the aurora borealis phenomenon typically only visible at higher latitudes? With recent solar activity I had read an article that showed this phenomenon visible farther south than normally seen and it got me wondering. That is where Earth's magnetic field is the . The auroras are caused by solar winds being deflected strongly and ionizing parts of the upper atmosphere.

Why is the salinity of the worlds oceans not constant? simple answer is saline water is denser than fresh water, and the cycle of evaporation to precipitation generates fresh water, which eventually ends up back into the ocean and due to density, it floats on top. another cycle happens near the poles where cold saline water freezes and also differentiates freshwater from hyper saline.

Most sites say cats become malnutritioned if fed only meat and never any "cat food". Is this a marketing scam, or how would wild cats have been able to survive in nature? Been reading about how one would provide a full nutritious plate to a cat without using super processed "cat food"s, and this always strikes me as weird (seeing as cats are obligate carnivores). Wild cats survive by eating animals. Not just what we call "meat" (muscle tissue), but organs, bones, entrails, and the contents of the digestive systems of those animals (mostly plant matter.) That gets them a lot more varied nutrition than just muscle tissue (which they do need to be healthy.)

Are quantum dot solar cells all hype? There seems to be a lot of hype regarding nanocrystals/ quantum dots for solar cells. Could someone explain something to me? A lot of the cool effects like tunable bandgap and strong absorption come from the quantum confinement. Quantum confinement implies that the electrons and holes are confined to a very small space. This seems completely opposite of what you'd want to do for a solar cell, which is to move the generated electrons and hole out to contacts. If you enable movement of electrons and holes, you destroy the quantum confinement. If there's all of this hype out there for making super efficient and cheap solar cells using quantum dots, I'm obviously missing something. What am I missing? TLDR: Quantum dots confine holes and electrons to a very small space. Solar cells move electrons and holes. How do quantum dot solar cells make sense? Cross posted from : In the ground state, they are confined. In the electronic excited state (if they work), the electrons and holes should be mobile. This relies on there being a suitable donor or acceptor nearby to keep the process going.

Can being crushed by magnetic field? Saw this youtube and I'd really like to know the physics behind it. This effect can be replicated at home (less impressively but more safely) with a fridge magnet and a sheet of aluminum. Just set the aluminum at an angle and let the magnet slide down it. You will notice that the magnet slides more slowly than if you replaced the aluminum with wood. Here's what is happening. The changing magnetic flux through the aluminum induces eddy currents in the metal, which in turn induce a magnetic field that interacts with that of the permanent magnet. Same principle in the video, only here the changes in flux density (resulting from the large current spike through the coil associated with the discharge of the capacitor) are big enough for the forces to distort the aluminum.

Are there any studies on the long term health effects of very light smoking (1 or 2 cigarettes per day)? I've been a light smoker for about 10 years. I keep it around 1 or 2 per day and usually stop completely during the winter since I don't smoke indoors and it gets too cold outside where I live! I was looking at studies on light smokers but it's usually defined as way more than 1-2 per day. Sometimes it's less than 20, or less than 10. That's not my definition of light smoking. Cancer is believed to be a stochastic effect. This means that the probability of getting a disease is proportional to your exposure to cigarette smoke. So a light smoker would have a lower chance of getting cancer but not a zero chance, ie there is no safe amount of tobacco smoke that won't give you cancer. It's like driving a car, someone who drives for hours every day is more likely to be in a car crash than somebody who drives for 10 minutes once a week. However, a car crash isn't certain or impossible for either group. Other long term health effects of smoking such as high blood pressure, emphysema, chronic bronchitis etc are deterministic. For these, there is a minimum amount of smoke needed to cause damage and the damage increases with exposure to tobacco smoke. You can smoke lightly and be fairly confident you won't get these problems.

Why (in technical terms) the video cards are the best for Parallel Computing? What the GPU's and memorys from Video cards have, that make them good for that? Modern GPUs are best described as vector processors with specialized instructions for graphics rendering. A vector processor is very much like a CPU (actually, it a type of CPU in some architectures), but it is designed to perform the same instructions (or sets of instructions) on multiple pieces of data. Think of it like this: Imagine a simple problem where you wish to multiplay a number (let's say 5) by a set of numbers (say, 50000 numbers) and produce a list of the results. What would be faster? Get one guy who's good at math to do them in sequence, or 500 4th graders who maybe aren't so hot at math, but are absolutely capable of doing task in a reasonable amount of time, dividing the work among them. Obviously, the latter. Even though our math wizard will perform these multiplications ten to a hundred times faster than the average fourth grader, he won't be able to keep up with the fact that there are 500 of them doing it. However, there are situations in which this technique does not grant you performance benefits. In fact, the technique may even slow you down. Imagine you have a list of 100 numbers, and you want to perform a complex operation on them, with the caveat that the next number in the sequence relies on the results of the last number in the sequence: There are clever ways that this can be parallelized, but for the sake of argument, lets say we can only use a naive implementation. The math wizard will get through this problem way faster than your pool of 4th graders (and may even know a trick or two to optimize the process). In this case, your faster, more complex, single core would do a better job.

Why do men tend to only go bald on the top of their head and not on the back or sides? Citation? This is all insanity. Male baldness is thought to be predominantly caused by hormones called androgens. The hair follicles on the top of the head have more androgen receptors. The hormonal cause of male pattern baldness is demonstrated through the fact that people with hormonal deficiencies or disease, especially those which prevent or inhibit a person from going through puberty, do not ever suffer any hair thinning or baldness in the typical pattern as is seen in those who do. Cite

Does the use of LSD cause anxiety, OCD, or other neurotic tendencies latter in life? What about other "entertainment" drugs kids use - are there any studies that tie them to psychological problems later in life? After seeing the question about Marijuana being linked to schizophrenia, I wanted to ask if there is any scientific research linking LSD to neurotic tendencies when people get older. What about other recreational drugs like speed, etc? Anecdotally, most of my childhood friends who were acid-freaks have now have major OCD or anxiety issues. Most have to take Ambian or something like that to calm them down enough to function. There is very little formal research into the long term effects of LSD. The work that was done while it was legal suggests that it has significant potential as a tool in psycho-therapy. That it can be a significant aid in overcoming addictions. And that it is pretty useless at creating drug fuelled super-soldiers. Anecdotal evidence suggests that it may unbalance some people (as with cannabis - degree of prior conditions may be relevant). "Flash-backs" might be a form of PTSD. Anecdotal evidence can be heavily biased. e.g. it might be that mentally unbalanced people are more likely to seek out drug experiences through existing dis-satisfaction with life. There are a vast number of 'entertainment' drugs (to the point where it may be easier to list drugs that aren't used for entertainment). Some are also prescription drugs and have (reasonably) well understood short and long term effects. Knowledge on illegal drugs varies. As such, you will need to narrow your parameters somewhat. wiki on recreational drugs.

I Can't Figure Out Climate Change Ok, first of all, no, I am not some right wing lunatic that thinks global warming/climate change is a plot by the filthy liberals to take my guns or something. I just have a few questions that I'd be too embarrassed to ask to real life friends. 1.) I 100% agree that both the world is getting warmer and that the carbon dioxide level in the air is going up. Humans obviously have caused this increase in carbon dioxide. My question is: How do we know this increase in carbon dioxide is the cause of the rise in temperature? Is the answer just "greenhouse effect" and that's it? Do we know that holds on a huge scale, like, well, the earth? 2.) From the statistics I have taken in both high school and college, it has been repeatedly slammed into my head that extrapolating data/models into the future is an very inexact science, at best. How do we know the current trends in temperature will continue? Carbon dioxide will continue to increase, for obvious reasons, but if it is causing the warming, how do we know it won't hit diminishing returns? 3.) I keep hearing that the line of no return for doomsday temperature increase is six degrees Celsius. Could someone explain why that would be so damaging to the health of the planet/humanity? Any answers would be appreciated. Sorry if they're dumb questions, I know this is an old-ish topic. RealClimate.org and SkepticalScience.com have well researched answers to most climate questions so I would mostly just point to places at those sites. The planet is not warming up uniformly. For me, the most compelling evidence is the many detailed signatures of global warming predicted by models have now been observed: empirically observed fingerprints of anthropogenic global warming . If the warming was caused by something other than greenhouse gases (such as changes in solar activity, volcanoes, El Nino), it would be characterized by a different set of fingerprints. The detailed changes that have been observed in the structure of the atmosphere and ocean are consistent with greenhouse gas induced warming and inconsistent with all other postulated mechanisms. Future predictions are not based on extrapolating current trends. Rather, future predictions of temperature are based on running climate models with concentrations of greenhouse gases expected in the future. So the your question really reduces to How reliable are climate models? . See also the page at the IPCC. In summary, confidence in models comes from their physical basis, and their skill in representing observed climate and past climate changes. I'm not sure why some people talk about 6° as opposed to 5° or 7°. There are several concerns. One is that we reach some tipping point which shifts the climate into a different regime. Once we pass a tipping point, even if we stopped burning all fossil fuels, the climate would not return to its present state for thousands of years. Another concern is agriculture. It would be very challenging to match today's agricultural output on a a planet 6° warmer. Finally there is the ice. It is probably already the case that Greenland is going to melt over the next few hundred years which will create 6 meters (20 feet) of sea level rise. If the temperature increase is enough to also melt Antarctica that will add another 60 meters (200 feet) to the oceans. I'm not sure what temperature increase will result in melting the Antarctic ice cap but I hope we never exceed it. edit: formatting and wordsmithing.

How can we be sure of the precision and accuracy of modern measurement tools? Suppose I have defined a 'redditmeter' [rm] in some acceptable way (that is - I can always know that this 'thing' that I measure is indeed rm units in size). After a few months, a new way was invented to measure 0.5rm, so on so forth - we get to the smallest scales. I logically conclude that this process is a very crude way of what happened in the way we humans measure things like length, weight etc. But how can we be sure that the scales we measure today are actually accurate? if we can measure 0.5rm with 99% accuracy, then measuring 0.25rm might have even less accuracy, going all the way to 1*10 rm. How can we know that our measurement tools are actually acceptably precise? Or to put it in another words - How do we check our most modern and precise measurement tools? Thank you for your current attempts of answering, but my question wasn't how can we be sure that a kilogram is a kilogram. To clarify furthermore - How can we be sure that the most modern measurement device actually measures with a good enough precision and not with it's measurement fault being 50% of accuracy (50% of times or 50% of given value). Currently, most units of measurements are derived from fundamental physical properties. For example, the meter is defined as the distance that light travels in a vacuum in 1/299792458 seconds. There is no ambiguity or inaccuracy in this definition, because it's defined relative to an unchanging constant of the universe. If you look up various other units, you'll see that they are defined in this same sort of way. This was done to avoid any confusion as to the accuracy or measurement issues with picking a set of units.

How does a CPU decide which instructions use which RAM addresses? (In terms of digital logic) I've spent a small amount learning about digital logic to further my understanding of computers but 1 thing I can't really understand is how the computer decides that RAM address X will be allocated for program Y and then after processing other instructions can come back to address X and can still associate it with program Y. It doesn't. When the CPU powers on it's hardcoded to run some code from somewhere. x86 for instance, will start executing whatever happens to be at address FFFF:0000, which is where the BIOS code is located. The BIOS initializes some hardware and tries to find a disk to boot from, loads the boot sector from there and executes it. Then the OS starts up. Processes are all up to the OS. While the CPU certainly has functionality to help with multitasking, and the architecture places some constraints on things (eg, on x86 VGA video memory is at segment A000, so you can't go loading programs there), it's really up to the OS to decide how to handle multitasking (if at all), and how to allocate memory to different programs and how to keep track of all that.

Does scratching a (non-contagious) rash, such as poison oak, help or hinder healing? I recently came in contact with poison oak and it itches to high heaven and scratching it is almost the greatest feeling ever before it starts itching again. I understand that itching helps bring more blood to the area. Aside from itching so much that you break the skin and cause more damage, does scratching speed up the recovery? The rash caused by poison oak is due to a T cell mediated reaction to the toxin urushiol. If you were recently exposed, scratching would make it worse because you are more likely to spread the toxin to other parts of your body. Once the toxin is removed and you're left with the rash, scratching wouldn't do anything to speed up recovery because the problem isn't lack of immune response, but in fact an undesired effect of your immune system. Scratching could also make things worse by introducing bacteria into the wound possibly leading to a secondary infection.

Do bugs have muscle tissue? How do insects or arachnids move their legs? Yes, they do have muscle tissues. However, their muscles are slightly different from mammals. Insect muscles do not need to be constantly oxygenated to function. They mostly just need sugar that comes from the hemolymph (insect blood), and can get away with less oxygen. In the laboratory, we can perfuse insect muscles in hemolymph-like saline for hours, and they can still move when stimulated. Insect and arachnids move their muscles similar to how we move ours. Both arises from the firing of motorneurons that leads to muscle depolarization and contraction. There is a fine difference though, in that insect neuromuscular junctions are mostly glutamatergic while mammalian ones are mostly cholinergic (i.e. they use different neurotransmitter for signals).

Is it possible for 2 total strangers be more genetically similar than 2 siblings? I recently came across a photo collection of strangers who look almost identical, which left me with 2 questions: When 2 people look alike does that mean they are genetically similar, or is it just an anomaly that they ended up looking the same? Is it possible for 2 total strangers (regardless of looks) to be more genetically similar than 2 siblings or relatives? If so, how often does this occur in nature? If not, why not? Thanks! :) EDIT: I was in no way implying any specific definition of "sibling" versus "stranger", nor referring to separated twins (still genetic siblings and social strangers), nor implying that adopted siblings aren't truly siblings. Sorry for any unintentional offense. Possible? Certainly. Probable? Highly unlikely. They have to be in the same family lineage, though the odds would still be astronomical even then. Basically, imagine a parent has two kids. With a crazy toss of the dice, one parent (say, dad) passes one half of his genes to one child, and the alleles to the other child. Bear in mind that all humans share 99.9% of their DNA so the only part of the passed DNA that would have to match is that remaining 0.1%. This helps the odds, though they're still pretty slim. They both separately have kids, and those kids, through another crazy toss of the dice, also get ONLY the genes directly passed by the original father (their grandfather). Do this for a few generations and you could have a male and female that are so far separated that they don't even realize that they're related. They meet, make beh-behs. Now, same crazy toss of the dice and their offspring now gets both halves of the alleles that were initially passed by the original ancestor. In this one in a bagazillion situation, you would have a genetic "clone" of the original. So depending on how "closely" you'd want them to be similar for the purposes of your question, people vaguely in the same lineage be able to match up better than their direct family members. (This is why DNA testing always says it's "99% accurate". They have to leave themselves an "out" for the near impossible "what-if" scenarios.) Edit: changed the word "trillion" coz too many nerds were getting hung up on it.

How do most antidepressant drugs cause weight gain? Do they make us eat more? Does it change the metabolism? Can they be used in anorexia? The mechanism of weight gain by antidepressants is still under study, but can be explained by the antagonism effect on the histamine-1 (H1) and serotonin 5-HT2C receptors, and the disruption of leptin signaling. The evidence is strongest with histamine-1 antagonism. Histamine-1 Receptor: Blockage of this receptor is shown to increase carbohydrate craving and intake. Tricyclics, antipsychotics, monoamine oxidase inhibitors (old-school antidepressants), and mirtazapine (Ki=0.14-1.6, very high affinity) have a large degree of H-1 antagonism. Serotonin 5-HT2C Receptor: Antagonism of this receptor leads to increased appetite, though may result in acute, transient weight loss. Fluoxetine is observed to have this effect. Leptin Hormone: Valproate and lithium are observed to block the effects of leptin, a hormone that helps suppress appetite. References: Abosi O, Lopes S, Schmitz S, Fiedorowicz JG. Cardiometabolic effects of psychotropic medications. Horm Mol Biol Clin Investig. 2018 Ricken R, Bopp S, Schlattmann P, et al. Leptin serum concentrations are associated with weight gain during lithium augmentation. Psychoneuroendocrinology. 2016;71:31-5.

If Planck length is the smallest length possible, then isn't the smallest volume possible 1 cubic Planck length? Does this mean that the universe is made of tiny cubes? Contrary to what you often read or hear, the Planck length is not the smallest length possible. The Planck length is part of a system of units called Planck units or natural units. In this system, a number of commonly used constants of nature are set to 1, for ease of calculations (the constants drop out of equations when they're rescaled to Planck units, making equations easier to read and manipulate). In the system of Planck units, the base unit for length is the Planck length, just like the meter is the base unit for length in the SI (Système International, the default set of units we all know and love (except Americans)). The Planck length is, in some theories in physics, close in value (within a factor 10) to notions such as the shortest measurable length, but there is no indication that space is discretized in Planck-length-sized blocks.

Your input on a cosmological thought experiment... Sitting here wondering about how fast something travels as it enters the event horizon of a black hole. Let's say I am falling towards a black hole and I have a flashlight. I shine this flash light in the complete opposite direction in which I am falling. In other words, I shine the flashlight away from the blackhole. By definition light cannot escape the gravity of a black hole. So what would happen to the light being emitted from my flashlight? If light cant escape and the event horizon is thus the line where the escape velocity balances with the speed of light (Schwarzschild radius), and therefore beyond that point the speed at which something falls towards the singularity should be faster than the speed of light. A particle traveling faster than the speed of light would have infinite mass. If so, this would no doubt be like a puncture in space time. Well redditors, what do you guys think? I have not though this out very thoroughly as it is something I just recently pondered. Please fell free to correct me, challenge me, or maybe even expand on my thoughts. Thanks Inside a black hole, moving towards the centre is mathematically equivalent of moving forward in time, and moving away is equivalent to moving back in time.

What prevents the "polishing" of any white surface to make it a mirror? To my (limited) understanding, the only difference between a mirror and a piece of paper is the way light is reflected off the surface, with a mirror being perfectly predictable and paper creating a bunch of "noise." They both reflect all wavelengths of visible light, but one is opaque. Is that because of the surface texture of the paper, and if so, why can't all white objects become perfectly reflective with enough polishing? If it's down to a molecular scale, is there a chemical treatment that can have that effect? I think if you take the idea out of it having to be white, it will make more sense. Copper, bronze, brass, etc. can all be polished to a mirror finish and reflect an image well, it will just be that color. You can even see yourself reflected in a screen when it goes black! So it is the surface/construction/density of the material. With the given example of paper, the material is quite fibrous, and not dense. No matter how smooth you got the surface, by any reasonable means, it wouldn't ever be even enough to clearly reflect. Now compare to a metal, or obsidian. The material is dense enough and truly solid enough that an even smooth layer capable of reflecting light can be achieved via polishing. TL-DR little bumps on the surface of paper scatter light, and paper (there is glossy paper but I think that is more the coating reflecting light, not truly the paper itself) can't really be polished due to it's construction. An even, more dense material that can form a smooth, reflective layer, could be. You may also want to just look into mineral luster. Wow, that looks awful typed out in the modern Era, but it's a science term.

Are space-based solar panels different than Earth-based solar panels (and if so, in what ways)? Yes! They are more expensive! So, for a ground based solar panel what you care about it $ per watt. So to setup a solar panel for my house I would want the cheapest solution that gets me to 5kW. So I might pay between 2-8$ per watt installed. These panels will be as cheap as possible, with cells under 1$ per watt. This means generally means a polycrystalline solar panel. It is a single layer assembled from many crystals of silicon. Because of the Shockley–Queisser limit their theoretical maximum efficeny is 32%. In reality their effiency is between 12-20% . Why is this? Because the solar diode needs to be setup to absob Photons, and kick out an electron at a specific voltage. Any Photon that doesn't have enough energy to get to this voltage is lost to heat. Any Photon that has than this voltage loses all extra energy to heat. You only get 1 voltage per layer. Now for a space based solar panel? Suddenly cost is not relevant. Even if we lauch the absolute cheapest solar panel, the price is 10,000$/kg. This so dwarfs the cost of basic solar panels that any weight and efficacy savings is critically important. So, how do we get around the SQ Limit? By stacking Layers! Now we can have our high energy photons in 1 layer, then medium energy in 1 layer, and low energy in another layer. This allows us to maximize the efficiency of the solar cell, while exploding the cost! However we can now get efficiency around double that of a basic solar cell, with >30% efficiency possible. So a nearly 2x power per gram, what about cost? Try over 900$ per watt! for a 3 junction solar panel. Compare this to new single junction solar cells that are less than 1$ per watt.

If our solar system is moving through space at hundreds of Km/s, does that mean Astronauts 'at rest' are as well? I know it's all about references frames and I assume the answer to be yes but I've never heard this really mentioned before and I wanted insight from someone who really knows. Also what does this mean for space travel? From what I can find, our solar system is orbiting in the milky way (or something along those lines) so does this movement of or solar system need to be accounted for for just about anything in space the same way you travel faster going against the earth's rotation in a plane? I know it's all about references frames but from the rest of your text, I get the feeling as if you think that there is some true zero velocity. If that is so: You're mistaken. Spacetime itself doesn't care about speed, and there is no true zero speed. The only kinda-quasi-objective zero speed one could make up is that in which there is no red/blue shift in regards to the CosmicMicrowaveBackground. But that has nothing to do with how spacetime functions. It is indifferent. In an otherwise empty universe, a lone spaceship would literally have no speed, no matter how much it accelerates. Yes, it would technically become faster. But it could do that for eternity (and indeed keep going faster) without experiencing change in relationship to spacetime. It just. Doesn't. Matter. So, what do we have to account for? Depends on what we want to achieve. But for all our local intents and purposes, it doesn't matter that we're orbiting the center of the galaxy, because the time spans (estimated 225 to 250 million years) are too great and our activities are too locally confined.

When it's said that areas of the brain "light up" via electrical signals, are there actual photons in the brain that get emitted? I assume you're referring to fMRI (functional magnetic resonance imaging) or PET (positron emission tomography), the results of which are often talked about in terms of the brain 'lighting up'. Both don't measure electrical activity but other markers of brain activity. In the case of PET, a radioactive tracer molecule is injected, that way, you can infer where brain activity has taken place by looking at where the signal coming from its radioactive decay is the most active. The tracer molecule will typically be chemically very similar to either glucose (used to provide energy) or some other molecule used in the brain. For example, you might find that the radioactive signal is greater in brain region a than b on a given task, so you'd conclude that it's involved in task performance, but b might not be. fMRI makes use of the fact that the magnetic properties of oxygenated and deoxygenated blood are different - this means you can distinguish between the two using magnetic resonance imaging, although the signal is quite faint. The maker of activity measured is called the blood oxygenation level dependent (BOLD) response - this is based on the assumption that brain activity will use up oxygen, so areas that were particularly active will change over time in terms of the oxygenation levels of the blood. The statistics are pretty complex, but when you see colourful images of both PET and fMRI results, the bright spots where the brain 'lights up' really are just statical maps of your signal, with the signal being the markers of brain activity described above. So in this sense, nothing in your brain literally lights up, but the measured signal shines some light on where and how brain activity might occur under specific conditions

Would it be possible to build invincible / very resistant car brakes that would need little or no maintenance? I was thinking about it the other day as I was going to the garage to fix my brakes, again ! As long as we're still using disk/drum brakes, probably not. The stopping power comes from friction between your brake pads and the disk/drum on your wheel. In order to generate that friction, there have to be surface interactions between the two. The pads have been designed specifically to wear slightly more than the brake itself, so that maintenance costs are lower. (Imagine if you had to replace the wheel every 50,000 miles). That said, there are other paradigms for braking. The Prius and other electric vehicles use regenerative braking - the motion of the wheel turns a generator which harnesses that energy as electricity, charging the battery and slowing the car. But this system isn't good for quick stops - it relies on the braking being slow and smooth. Essentially, the braking system takes the kinetic energy of your car moving and moves that energy somewhere else. Traditional brakes turn it into heat via friction. Regenerative braking turns it into electricity via magnetic fields. To this day, we haven't really come up with a better way to quickly and on-demand remove energy from the system - the current way it's done is better than other ways we do it.

What determines the ideal cruising altitude for an airplane? I assume various factors such as the shape, size, weight, thrust, the density of air at various heights, etc. play a role. How do these (and any others I missed) factor into calculating the ideal cruising altitude? "Ideal" can mean different things. Primarily, the first major factor will be the overall weight of the aircraft, and that will vary from flight to flight depending on fuel and passenger loads (the added weight of them). That will initially limit the height the aircraft can climb to (which will normally be below it's maximum service ceiling, the maximum altitude it is certified for), and it won't be economical for it to climb any higher (if it is still below it's service ceiling) until some fuel has been "burned off" during cruise flight. Then it could do a "step climb" to a higher cruising altitude (if the flight was going to be long enough) to possibly be more economical. This usually happens on larger aircraft (like a B777 or B747, etc) on long overseas flights taking numerous hours. But... Another factor would also be the wind directions and speeds at the altitudes the aircraft fly (referred to as "winds aloft"). At commercial flight altitudes it is not uncommon to find headwinds and tailwinds exceeding 100+ knots, so it may be more economical to fly at a certain altitude instead of the aircraft's best "no wind" performance altitude for a given situation. "Dispatchers" for the airlines figure all of it out before the pilot gets to the aircraft. The pilot is given a "flight plan profile" based on the projected aircraft weight and winds aloft for the flight (there are other factors, but these will be the main two that will determine the cruising altitude). Source: I've been a licensed pilot for over 40 years. EDIT: If you want to look at a more detailed example containing the math of some of it (but still good narrative explanations too), click here. https://aviation.stackexchange.com/questions/3272/how-do-pilots-decide-what-their-cruising-altitude-will-be

can someone please explain how light from a flame is electromagnetic in nature? My physics textbook says light shows wave and particle nature but I'm having a tough time relating this to real life. It defines EMW are caused by charges oscillating periodically to give perpendicular electric and magnetic waves. In the case of a lit candle, how do I relate this? In classical electrodynamics, the mathematics produces a wave equation which has solutions that self propagate at some speed called "c". These waves can impart energy and momentum onto electric charges and be produced themselves by charges. These waves are the things we call light and they travel at the speed of light, known as "c" in vacuum. Light is produced classically when a charge accelerates. Consider an electron, it will have electric field lines which look like this, https://upload.wikimedia.org/wikipedia/commons/thumb/9/95/VFPt_plus_thumb.svg/480px-VFPt_plus_thumb.svg.png If flick the electron with my finger, those field lines will respond to the changing position of the electron, but this will not happen instantaneously. The field at some distance X away won't know the electron moved until at least some time T = X/c. The flick will cause a "shockwave" that radiates away from the center at the speed of light. This shockwave is light. The produced light looks like this, http://www.tapir.caltech.edu/~teviet/Waves/empulse.html If I very precisely wiggle the electron at a constant rate, like rocking a baby in a cradle, I will continuously produce radiation at a single frequency or color. Doing this I can produce any color I want. Taking this concept further, I can absorb or emit radio waves (which are also forms of light) using an antenna. The Wikipedia page on dipole antenna has some really cool animations showing this process, https://en.wikipedia.org/wiki/Dipole_antenna Now we can introduce quantum theory which requires light to come in packets called photons, which you've probably heard about. Photons have an energy which is proportional to their frequency, the shorter the wavelength (more blue) the more energy each photon has. It is still correct to call light "oscillating magnetic and electric fields," but we can't use purely either the wave or particle picture. Photons are quantum objects and thus has aspects of both, but are truly neither. This quantum behavior is important as it turns out all objects emit light in a very specific way called blackbody radiation, but the wavelength spectrum given off at room temperature cannot be seen with the human eye. You can picture all the trillions of atoms in your body as wiggling some amount depending on their temperature. Wiggling atoms produce radiation as outlined above. Now: Let's get to candle flames. When a candle burns it primarily produces light through two mechanisms, Incandescent soot particles are little hot chunks of carbon. They are hot enough that the radiation they produce is noticeably in the visible spectrum of light. Atomic and molecular transitions of broken up molecules. Because of quantum mechanics, these only occur at specific wavelengths, like this butane spectrum, https://upload.wikimedia.org/wikipedia/en/2/26/Spectrum_of_blue_flame_-_intensity_corrected.png A regular fire is usually a mixture of these two.

On this cloning a wooly mammoth thing...I'm not a scientist, but based on the technique wouldn't the resulting mammoth have elephant RNA? And does it matter? Sorry if this is a dumb question. I am concerned that donaldjohnston has been unclear, so let me clarify: the egg into which the mammoth DNA is placed would contain RNA from the egg donor, meaning that they would be elephant maternal RNA and elephant proteins, including transcription factors. If the elephant RNA, proteins, and proteins translated from maternal RNA are similar enough to the mammoth equivalents to activate the normal developmental pathways of the very early embryo (and this is a "if", the mammoth embryo will start to produce its own RNA and proteins, and take over its own development (as all embryos do at some point). The maternal molecules will soon be degraded completely, and will disappear. They are not, in any way "passed on". After a short time, none of the molecules within the mammoth embryo will be any different from those in a mammoth growing within another mammoth. There would be no lasting inheritance of elephant RNA.

Would I be able to feel the difference between moving my hand through air and moving my hand through a vacuum? You would feel quite a difference. If we assume that your hand wouldn't undergo any nasty side effects from being in a vacuum, more on that later, you wouldn't feel any wind resistance. In the atmosphere when you move your hand it is pushing the molecules in the air out of the way as it moves. This causes your hand to feel a force acting against the direction you are moving. In a vacuum there are no molecules to push out of the way so no force is felt. The problem with being in a vacuum for humans is that we have a pulse and blood pressure that is acting out against our skin. This is countered by the atmospheric pressure. So if there is no atmosphere, like in a vacuum, our blood pushes on our skin and it can cause us pain and physical damage. Additionally, in a vacuum the water in our blood would begin to evaporate. This would seem to us as if our blood is boiling. This evaporation would put pressure on our tissues and cause physical damage.

Why is Chickenpox more dangerous to adults than it is to children? Chicken pox and shingles are caused by the same virus, herpes zoster. When a person first gets the disease (usually as children) it manifests as chickenpox. Once recovered, the virus still stays in body's nerve cells in a dormant state and can reemerge as shingles. So anyone who gets shingles had chickenpox at some point in the past.

How does a metal detector work? The Wikipedia entry describes it quite well: "The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a magnetometer), the change in the magnetic field due to the metallic object can be detected."

What is the maximum size a tornado can be? edit- on Earth By "maximum size" I'll assume you mean the "Largest tornado path width". The recorded occurred on May 31, 2013 in El Reno, Oklahoma; with a peak length of 16.2miles and width of 2.6 miles with 296mph winds; however this tornado was predicted as a F5 it was downgraded to a F3 [Sources 1 , 2 ]. When calculating the strength of tornados, on Enhanced Fujita Scale (EF-Scale) the highest possible is a F5s (261-318mph) level tornado; with F6s (319-379mph) being highly unlikely.

Are Organelles randomly shuffled in animal cell? Are they placed in a specified pattern? Or just randomly shuffled around? Are they uniform? Of course there is structure! Eukaryotic cells are filled with cytoskeleton elements such as actin filaments or microtubules. Motor proteins such as dyneins and myosin can latch on to these filaments and carry cargo. For example, this is how many marine organisms change color: by moving pigment-filled vesicles towards the inside/periphery of the cell. As for organelles, the Golgi apparatus is positioned using microtubules as a guide and sends vesicles outwards or inwards on them. They act as a 'map' for the cell. Edit: here's a link to a video that helps explain color change. https://youtu.be/foqEeOWVdd0

what is the history behind using deciliters as a denomination for blood tests? how and why did this occur? it would seem to liters or milliliters would be more ”standard” than a tenth of a base unit. was μg/dl and the like simply more convenient? I don't think the units have anything to do with the amount of blood drawn for examination. Think about it: a deciliter are a tenth of a liter, or 100 milliliter. That's still a ridiculously huge amount of blood for a test. The normally used blood collection tubes only hold a couple of milliliters up to 10 ml in the largest ones, if I recall correctly. Even so, you aren't limited in the choice of the unit used by the amount of substance analysed. You could simply convert any unit into another. The difference between mg/dl and mg/l is a factor of ten. Long story short, there doesn't seem to be any reason for the choice of the unit, except maybe tradition and/or convenience of having more manageable numbers.

What decides whether something burns up (like paper) or melts (like steel) when exposed to high temperatures? Burning is a chemical reaction; the molecules in the paper react with the molecules in the air, and the role of heat is to provide the activation energy for that reaction. Melting is a physical reaction; the molecules in steel are vibrating fast enough that the bonds between them cannot hold them in a rigid structure any longer so they begin to flow, and the role of heat is to provide kinetic energy to each of the molecules to increase their vibration. To answer your question directly, what "decides" between burning or melting is whether the object can perform an exothermic reaction with the surrounding atmosphere that has an activation energy below its melting point.

When did animals start defecating? When did multi celled organisms begin to "Package" fecal matter and send it out in one lump? I'm sure there will be better answers later, since I'm not a biologist, but I'll pitch in with a bit of info to get things started. It doesn't really address your question, but it's somewhat related, anyway. Excretion has always been around, since biological processes can create compounds that would be toxic if left unchecked. The easiest way to solve this problem is clearly to throw it somewhere else instead of having to develop a complicated metabolic pathway to neutralize the toxin, or having to isolate the toxins somehow while still carrying them around. Defecation, however, is excretion in the biological sense, which goes against most people's intuition. Rather, urination is excretion, and it serves mostly to filter out ammonia from living cells, either by eliminating it directly or after having converted the ammonia into other compounds such as uric acid or urea. Defecation is merely getting rid of matter that couldn't be digested. Why couldn't it? Well, most likely the organism in question was not selected during its evolution to make use of part of the matter ingested. There are lots of different types of compounds that make living things, and developing biochemical strategies to process all of them is an inefficient use of limited energy, in most cases.

Why is Tritium radioactive? So like charges repel. Protons naturally repel each other because they both have a positive charge. Am I correct in saying that neutrons are sort of like the buffer of atoms? Why then is Tritium radioactive with 1 proton and 2 neutrons? Do neutrons also repel each other even though they have no charge? It's not due to electromagnetic repulsion; the decay is due to the weak interaction. Decays occur if they can. Because the mass of the helium-3 nucleus is less than that of tritium, and the mass difference is greater than the mass of an electron, tritium can turn into an electron and a helium-3 nucleus without violating conservation of energy. Because it can happen, it does.

What about the world would be different if the earth’s axis was tilted 90° instead? Here's a recent discussion: https://www.reddit.com/r/askscience/comments/7ahcfl/uranus_axis_is_rotated_onto_its_side_meaning_it/

How do you visualize a photon of radio frequency? I can visualize photons that fall in visible spectrum. Like right now photons from my screen being emitted by the backlight and hitting the molecules of my retina. Because their wavelength is of the order of nanometers, QM stops me from knowing where each single photon is at any given moment, but what about a photon of wavelength 1 meter? Does it travel like being anywhere in an area of 1 meter? I'm sorry if I'm unable to convey what I'm trying to know because if I already knew I wouldn't be asking in the first place :) In case my question doesn't make any sense, please tell me what I need to know before asking this kind of question again. They describe oscillations in an electric field, over all space. ok, so a photon with wavelength 1m is nothing but oscillation of electric (and magnetic?) fields with a wavelength of 1 meter. And since no atom has electron with such low energy, they pass right through most matter, and you need large antennas that resonate at that frequency to "capture" those photons. Is this all makes sense?

What is the inner monologue for a deaf person like? Considering that they can't imagine "hearing" any more than you can imagine "sensing magnetic fields", yes. Though from various AskReddit threads, it seems to be more a combination of visualization of kinesthetics. Kind of like if you were to imagine yourself performing the "YMCA" dance or something, where you kind of imagine body position combined with the visual.

If the ozone layer was obliterated by a gamma radiation burst, how long would it take to return to normal levels? Would any plant or animal species be capable of adapting to something like that? Answering your followup question first - underwater species and cave species would survive without adaptation. I'm not able to comprehensively answer the main question, except to state that the ozone hole (caused by human use of chlorofluorocarbons, and to a lesser extent other things) is repairing over a timeframe of decades. I can't generalize that to answer it for a complete destruction of the ozone layer worldwide.

What is the next, most basic scientific breakthrough we would need for a complete global impact? A technique to rapidly (re)generate soil and humus that doesn't require a shitton of water. This would allow to reclaim deserts as arable land. Increasing food production and water retention Currently, you can take waste organic material such as cellulose (grass, paper, ...) and use fungi (such as mushrooms) to turn into humus quickly, but it takes huge amounts of water which is generally unavailable in a desert environment.

Will Voyager 1 eventually slow down/stop due to drag caused by gas and dust in interstellar space? I was reading about Voyager 1 today, and found out that it is quite close to leaving the heliosphere, after which it will come into contact with interstellar gasses. Is this likely to slow it down? Or even stop it? interstellar gas is almost non existent (a few atoms per meter) so there is very little matter to actually interact with. Think of the mass of these few atoms vs the entire mass of voyager - many orders of magnitude different. If you mean slow it down relative to its current direction of travel something would have to act on it fairly significantly for this to happen (eg run into a planet/stars gravity) it wouldn't stop, its velocity would be changed in either direction or magnitude by this.

What is it exactly that energy boosting substances like caffeine and ginseng do to our body in order to provide an alert/energized state? Well, for caffeine, it doesn't actually give you energy. Caffeine is an adenosine receptor antagonist. It prevents adenosine from binding to sites in the CNS. Over time as you are awake, adenosine builds up and begins binding to these receptors which induces drowsiness, but with caffeine in your system, this is blocked and you feel less tired and more alert.

What were cows like and how were they able to survive before being domesticated by humans? Slow, docile, seemingly defenseless. I know all these traits were preferred and actively chosen thru thousands of generations of selective breeding by humans, but what were the progenitors like? Many large herbivorous animals are able to survive through sheer size (the larger you are, the less likely you are to become prey) and numbers . Also, aurochs (ancestor to the modern cow), modern cows, and many other ungulates have horns. Docility and tameness can happen within a few generations , and with it may come physical changes.

Are Thymine, Adenine, Guanine, and Cytosine present/used in DNA of all living organisms on earth? Are there any organisms anywhere that dont use ATCG DNA or a variation of it? As far as I’m aware, all DNA for living things is made from ATCG on Earth. There are viruses and such that use single and double stranded RNA which contains uracil instead of thymine, but those are generally not considered to be living things.

Does light have mass? No it does not. It doesn't need to do the things you're describing. It still has momentum. Light consists of electric and magnetic fields. Electric fields move things, magnetic fields move things, and neither of those has mass.

Is all "sense" DNA on the same strand of a double helix (i.e. is one particular strand always the one that gets copied)? Transcription is the process of copying a section of "sense" DNA into a strand of "anti-sense" RNA. When transcription bubbles are created, what prevents the anti-sense DNA from being transcribed? Furthermore, is all "sense" DNA on the same strand of a double helix (i.e. is one particular strand always the one that gets copied)? No. The coding sequence for a gene can reside on either strand of the DNA and hence, there is no fixed strand of DNA that RNA is always transcribed from. As for what's preventing antisense RNA from being transcribed, that would be the gene regulatory elements that are found upstream of a gene. For gene transcription to be initiated, transcription factors have to be recruited to these regions and they are only found on the strand that carries the gene sequence to be transcribed. Edit: Reworded to avoid confusion.

Absolute zero and gas laws According to Gay-Lussac, Boyle, and Charles' laws wouldn't absolute zero bring us to a point where we can make something with no pressure and a negligible amount of mass? If that is the case couldn't we eventually (if we do reach absolute zero) compress liquids for long space travel? Or is there some quantum physics stuff that I am missing that makes this impossible? An ideal gas has zero volume at zero temperature. However, gasses aren't ideal under all conditions. Ignoring the fact that gasses turn liquid or solid at low temperatures, eventually they behave more like van der Waals gasses and you have to take into account their interactions and finite volume.

Can we engineer "evolution" in small organisms (e.g. bacteria) in short periods of time? For example, if we have heat up bacteria in a petri dish to 45 degrees celsius, are we genetically selecting for bacteria that can survive in that temperature? Or if we expose it to chemicals (like soap), are we creating super-bacteria? How long would it take to see meaningful changes in the genetic structure of this bacteria, as compared to larger organisms such as plants and animals. Just adding on to point out that this is abundantly, extremely commonplace in microbiology research, and has been for various purposes for decades. A common teaching lab demonstration of this in undergrad and even high school courses is to generate antibiotic resistant bacteria by creating gradient media and inoculating the side with the lower concentration of antibiotic with a bacteria. Here is a description of exactly this type of experiment .

How does an Archimedes Screw work? An was used historically for raising water for various purposes. It consists of a helical "screw" inside of a pipe, and as the screw is turned, the water level within the pipe rises. Some descriptions detail a series of wells along the screw that scoop up water and transport the water to the top of the pipe. However, I do not understand how the water actually rises. If the wells are stationary along the screw, how would the well rise as the screw is turned? The animation in the article isn't the best. Think about a stationary screw inside of a closely fitting column, and the whole thing nearly parallel to the ground but at a slight angle. Now consider the area around just one bit of the screw's thread. If you think about it it should be obvious that you can hold water in the bottom part of such an arrangement, only the water above the shaft of the screw could possibly flow out down the screw, everything else is contained within that particular area. Now what happens when the screw turns? Within our sub-section the screw turning is identical to the screw being pushed upward. A rotation of the screw by a small amount leads to the same arrangement as before except with the parts of the screw threads higher. That's where this animation really helps explain what's going on. To the water within one section of the screw the motion of the screw seems to be exactly identical to being pushed up the column. And there's nowhere for the water to go except up as the screw turns. It can't fall out of the "bowl" formed by the wall of the column and the screw threads, so instead it is carried upwards. The wells move because the sides of the screw's thread continuously increase in height along the screw's length. And rotating the screw effectively replaces each part of the screw's thread with another part that is just a tiny bit higher than the one before. It's like climbing a spiral staircase, except the staircase is moving instead of the climber, and it's at an angle which prevent falling down the staircase. Another way to think about it is to imagine the water temporarily frozen in place relative to the screw. The screw turns a little bit, the water stays in the exact same well it was in before, then the water is unfrozen. But now the surface of the water is no longer level, which isn't going to last. The water then flows to make itself level again, and in so doing it falls into a new well that is exactly identical to the old one only just a little bit higher along the column.

Is there a metal that heats up slowly, yet disperses heat quickly? Metals such as aluminum are excellent conductors of heat, but they distribute changes in temperature, whether that be an increase or decrease, quite quickly. Is there such a metal that would heat up slowly (say several hundred degrees above ambient temperature), yet disperse that heat much faster than it was gained? Is such a material even possible? My understanding is that heat capacity depends on temperature, so if the metal heated up slowly at a certain temperature (that is, required a lot of energy to increase the temperature) it would also lose heat at that same rate at the specific temperature. There may be something that would, let's say, heat up slowly and then quicken as the temperature gets higher (decreasing heat capacity with temperature), but this results in something that disperses heat quickly and then as the temperature lowers disperses heat slowly. I don't think it's possible to have what you stated unless the heat capacity depends on more than just temperature.

Is the belief that a comet triggered the Cretaceous–Paleogene extinction still the most widely held belief? If so, can someone explain to me how a comet could have triggered such a mass extinction? In general, the idea that the object that made the Chicxulub crater is at least partially responsible for the K-Pg mass extinction is not really controversial. However, there has been some suggestion that the late Cretaceous was already a somewhat difficult time for many large vertebrates, and so this impact may have been the giant asteroid that broke the camel's back, so to speak. Arens and West 2008 suggest what they call a "press-pulse" model of extinction, wherein several of the worst extinction events throughout Earth's history are associated with the co-occurrence of both impact events changing climates on Earth (mostly due to periods of volcanic activity). There is at least some appeal to this idea, since we know of a few other large asteroid impacts that took place in the past but which don't seem to be responsible for extinction events of anywhere close to the same magnitude as the K-Pg (e.g., the Manicougan crater in Québec, which at best is loosely associated with a minor extinction in the middle of the Triassic; source ). One finding that appears to support this idea somewhat is that many groups of dinosaurs were already experiencing negative net diversification rates (i.e., species were going extinct faster than new species evolved) by the late Cretaceous ( source ). But of course, dinosaurs are just one group of animals that suffered the effects of the K-Pg extinction, and the cause of this decline is not clear, so it doesn't necessarily imply any kind of strong extrinsic pressure. It might be the case that the asteroid impact was pretty much the sole culprit after all. On the other extreme, there is also still a minority of researchers who maintain that the K-Pg extinction was mostly or even entirely caused by volcanic effects, most notably Gerta Keller (see her 2008 paper for example).

May sound stupid but here goes , when we are in the womb and are slowly growing where do those atoms come from that make us or do we make those atoms in the womb ? They come from the food your mother eats while you're developing, as well as your mother herself. No new atoms are created, just rearranged cleverly from food and air and water.

Why is it that you can put so much weight on one side of a barbell without it tipping over? I was at the gym today and I was able to put 90 pounds on one side of the barbell without it tipping over. Why doesn't any imbalance of weight cause it to tip over? If the barbell is supported at each end, then it won't tip over until it's center of gravity is outside the interval between the points where it's supported. If those points are quite close to the end compared to the length of the bar, then the weight you add needs to be much larger than the weight of the bar alone to bring the center of gravity that far over. Another way to think of it is to consider the torque around the end where it would eventually tip. That point of contact is the pivot point, and the torque each weight applies is weight times distance from this pivot. For the weights you're adding, that's a large weight times a short distance. For the bar, that's a small weight times a large distance (half the distance between the supporting points). So the weights your adding need to be proportionally that much heavier than the bar to make up for how much closer their centers of gravity are to the pivot point.

How are sunglasses made to block UV light? I've seen conflicting information on exactly how sunglasses are made to block UV light. Some people say that the plastics used in the lenses naturally blocks UV light so that even the cheapest sunglasses will do an excellent job, while others say you need special 'treatments' to make them UV blocking. So do the plastics used in the lenses for sunglasses naturally block UV light? If not, what 'treatments' are applied to them to make them block UV light? Do these 'treatments' degrade over time? Do they rub off? The clear plastic (CR-39) used in typical eyeglasses is a pretty good UV blocker on its own. Polycarbonate, another common material, is even more opaque to UV. Add a gray tint, and it becomes an effective UV filter . There are coatings that can be applied to any plastic to reduce UV transmittance to zero, and they don't rub off, but I wouldn't pay any extra for it. I will gladly sell it to you though, if someone has convinced you it's necessary. *Edit: extra word word

Have we been able to bond any noble gas element with any metal, and if so, what is the longest we've been able to maintain this bond? Just wondering if there are any computational, theoretical, or experimental areas as far as this subject goes. I'm a applied math student who will be attending school for graduate level physics next semester, and I'm very interested in this subject. Very specific on the noble gas + metal, for example argon and gold or something of that nature. Maybe some sort of high vacuum and high energy process to create these bonds, if only temporarily. Thanks in advance for any answers! I've found you not only a compound with a noble gas metal bond (was expecting this), but I actually found your utterly insane suggestion of a direct nobel gas and gold bond. The Tetraxenonogold(II) cation present in AuXe (Sb F ) Florine makes for weird chemistry.

How many virus cells are needed to make a human ill? First viruses != cells, by definition. They are protein based capsids containing nucleic acids. Sometimes with a lipid envelope. But nothing more. Second, it depends on the virus. There's actually a metric in microbiology called ID50, "Infectious Dose 50". It's similar to LD50. However, instead of lethality. it's the average number of pathogens needed to induce disease in 50% of a healthy population.

What is the significance of RBMK nuclear cores not exploding? The significance in the TV show is that they were denying something that had obviously happened. Reactor 4 was an RMBK and it did explode, but the higher-ups denied it and said that it’s not possible.

Could self aware robots one day make it to other solar systems or galaxies and outlive humanity? And could self aware robots one day be considered living non-carbon based beings? Such hypothetical / speculative / open-ended questions are better suited for our new-ish sister sub /r/asksciencediscussion . Please consider reposting there instead.

How can something like graphene aerogel be lighter than air if it's composed of matter and air? If it's already made of air and then extra matter is added into it to give it a solid body, how could it be even lighter than the preexisting air? The term "lighter-than-air" when used in the context of solids means that the mass of the material that it consists occupies a volume such that the quotient (i.e. the density) is smaller than that of air. It does not account for air that would fill the cavities within. If the aerogel is truly lighter-than-air - like if it consists of hollow cavities without air - then it'll be buoyant in air.

Is there a viable way to shape sound waves? I only mean in the sense of sound not going past a certain point. The basis for this question started for me when I read . I remember reading the part where Ender was first introduced to the Giant's Game by another character. I can't remember the exact quote, but it was something along the lines of: Ender saw (xyz character) playing a different game on his computer. It was interesting because he had never seen it before. He could see the player talking to a giant, but he could not hear what the giant was saying because the sound was shaped towards (xyz character). My question in short, is this. Is there a viable way to shape sound waves so that only a small contained area can "hear" the sound? Yes. Sound is a wave, so with a correctly shaped reflector the sound can be focused on a narrow area. This type of setup often used in museum exhibits to limit the audible narration to a small area. Narrowly focused sound can also make a non-lethal weapon. See parabolic loudspeaker and LRAD .

Why do different substances have different specific heats? The amount of thermal energy in a substance is how much kinetic energy the molecules have, and the temperature is related to the average speed of the molecules (right?). So why is the relationship between the two so inconsistent? I imagine it's some mix of inter-molecular forces and different molecular masses, but I'd appreciate a more thorough explanation. Energy can be stored in translational, rotational, and vibrational modes inside a molecule. It can get even more complicated in solids.

Are very active individuals who retire from their active lifestyles as they age at greater risk of obesity than their consistently inactive peers because they maintain the dietary habits needed to perform maintain their active lifestyle? Unfortunately, there are so many variables at play here that it'd be impossible to deduce. There's a plethora of genetic and environmental variables. Being that we're speaking of those of retirement age there are even epigenetic variables, and the science of epigenetics is so young its still in the womb, so to speak. Find a way to neutralize all those variables, and you basically have one question left: "What has this previously active person decided to fill their time with?". For myself, I'm highly active, but have periods of laziness as well. In those inactive weeks there's a lot of extra time on my hands. I'll find myself eating purely out of boredom, no hunger involved whatsoever. At a certain point my natural motivation compels me toward activity again. So, for myself, I eat LESS when I live an active lifestyle, but thats one person out of 7.1 billion...

Is there an easily achievable pressure, either + or - standard atmospheric pressure, that would significantly reduce the growth of most foodborne pathogens? My thoughts are for humble food storage containers. Of course, refrigeration increases the time before spoilage, and a perfect vacuum would have an effect. But is there any sweet spot above a perfect vacuum where all or most growth of pathogens gets slowed to a crawl? Or perhaps a higher pressure that's not in danger of exploding? I don't see how a perfect vacuum changes much. From my impression vacuum sealing prevents infectious agents from entering mostly from the "sealing" aspect. The vacuum part prevents ice crystals from forming on the surface and "freezer burning". But if you took some meat and had it exposed to some bacteria or something, then vacuum sealed it, it could still quite easily spoil (presuming the bacteria are anaerobic).

Are we past the tipping point for the insect population decline? Not likely. Insects as a group are exceptionally diverse and most reproduce quickly with large numbers of offspring. It will vary strongly from group to group, with heat-loving generalists doing well and specialists (e.g. obligate parasites with rare hosts) hurting the most. Additionally, some are very susceptible to pollution, while others can survive nearly anywhere (e.g. mosquitoes in shallow, ephemeral pools).

What would be the effects of a baby being conceived and being born on a larger or smaller planet? im curious how this would effect the biology of a human's growth. This article reviews research on the effects of gravity on cell signaling in the immune system. The research suggests cell signaling is , susceptible to gravity or absence thereof. Development relies heavily on cell signaling, I know for certain neural migration is majorly dependent on cell signaling to tell neurons where to go. If cell signaling is gravisensitive, development is gravisensitive. I doubt a fetus could assemble similarly as on earth. Couple of leaps of logic, hopefully they aren't too bad.

Did the old english language contribute to modern french or did old french contribute to modern english? There was probably some exchange both ways, but more the latter. England was conquered by Normans in 1066, and the class divide between French-speaking nobles and Anglo-Saxon peasantry shaped much of English's early development. For example, many terms for animals are germanic, coming from farmers, while many terms for their meat are french, coming from the nobility.

Is it possible to quicken a planet's rotation? Yes. As an example of what will happen, look at Phobos' eventual fate ( http://en.wikipedia.org/wiki/Phobos_(moon) ). It will draw closer to Mars' surface and eventually hit it. Phobos might break up into a ring first, but that doesn't matter for our purposes. Either way, as Phobos' orbital altitude decreases, its orbital speed increases (the angular momentum of the Phobos-Mars system is conserved). When Phobos strikes Mars, the pieces will stop with respect to the Martian surface, and Mars rotation will have sped up to conserve the total angular momentum. This process is basically the opposite of what happens to Earth and our Moon. As the Moon slowly moves farther away, the Earth's rotation slows.

Is Earth's centre of gravity at its geometric centre? Not entirely sure if this question makes sense. Thanks! Ok..i'm going to try to break this down as I go. Center of gravity from the point of what you looking for is actually the scientific term center of mass where all the accumulative mass from all outside forces = 0. If you wanted to measure this I would try to simplify a few things that I already know, the earth is not a perfect sphere (which I'm guessing is the backbone of this question), there are many discrepancies in the density of many objects included in the earth model here. How do you designate which accounts for more and where and more for less considering the non-perfect spherical shape? This is a pretty tough question (would you agree?). And that is not even considering the earth's different inner layers! The thing that really throws us off is that we have idea of what is in the earth's core, but what if you want to talk about precision center of mass, it will be damn near impossible to find it. Morale of the story, as you go deeper and deeper into science things can get so complicated it is overwhelming, and approximations do need to be made just to get a justificatory answer.

Why do we still drink milk? Are we the only species out there who still consumes milk way after we are done nursing? I don't want this question to come off silly, but there are many other better sources of vitamins, protein, and calcium. Also how much casein should we be consuming as adults, and why is drinking liquid out of an udder appealing to us? there are many other better sources of vitamins, protein, and calcium. Uh, really? Name some. Also how much casein should we be consuming as adults Recent studies have correlated certain polymorphisms of casein in the cow population with lower rates of cardiovascular disease and diabetes, so as far as casein consumption goes, it's not really a problem. Studies in the past haven't conclusively shown that casein has any connection with negative effects on health.

Is a black hole a physical thing such as a planet? What exactly is it? This answer isn't quite accurate. Not trying to play the internet cop, but forum rules clearly say that you shouldn't speculate. a black hole is a collection of mass so heavy it collapses everything around it, including light. Mass is a property, so how can there be a a collection of it? Either you are talking about a collection of particles, which wouldn't be correct if we are talking about black holes in the common understanding, General Relativity that is, or you are simply using the wrong words to describe mass. The earth creates gravity, pulling you towards it, the bigger the object the bigger the gravity, this is why the moon has less gravity then earth. This is just plain wrong, easily proven by the mere existance of white dwarfs and neutron stars. In fact, the more massive an object of degenerate matter is, the smaller it becomes. Also, mercury is smaller than the ice moons Ganymede and Titan, yet it is twice as massive. Surface gravitation is not just about mass, but also about density. That's why 2 objects with the same mass but different sizes have different gravitational pull. By the way, stellar black holes have lesser mass than their progenitor star. Imagine an object with so much mass that most matter collapses Not most, but all matter. And it isn't simply collapsing, it is literally disintegrated. There is no more matter after the infall into the singularity. with a gravity so powerfull that you'd be crushed into a tiny dot if you ever get to close, THAT is a black hole. No. Despite the fact that white dwarfs and neutron stars would crush me just as easily, this isn't a proper explanation of what a black hole is. The simple answer is, we don't really know what a black hole is, because we can't look inside. Therefore we don't get any evidence for or against any hypothesis what could be inside. We can only observe the effects outside of a black hole. Everything within the event horizon is completely hidden to us. Using our best theory on the topic, which is General Relativity, we conclude that there is a singularity in any black hole. The singularity is a quantum object and therefore literally has no size, or regarding the fact that nothing can be smaller than a planck length, it is just as small (note that distances smaller than a planck length have no physical relevance). So asking what it's made of is meaningless, because the singularity is all there is. Around the singularity may be infalling energy/matter however. In a black hole, time and space are changed. Within the event horizon, which isn't a real barrier or surface but simply the distance from the singularity where the escape velocity exceeds the speed of light, all spacial directions point inwards to the singularity, that's why nothing can escape. At the singularity then, space and time as we know them cease to exist. See this video for more information. Keep in mind, that we still lack a proper quantum theory of gravity in the early 21st century. We don't know if singularities really exist or if there are quantum effects that stops the collapsing of matter at one point and stabilize the whole object somehow. We have to discover a theory of quantum gravitation first before we can finally tell what's really going on inside. Until then, General Relativity is our best friend to explain black holes.

How is the total weight of the earth calculated? We know that the acceleration due to gravity is equal to a constant (G) times the mass of the object (M) divided by the square of the distance to the object. We can measure the acceleration due to gravity either on the Earth's surface (9.8 m/s ) or by looking at the moon (one rotation in ~29 days). This allows us to measure GM. Henry Cavendish in 1798 did an experiment using two giant lead spheres of known to create a small gravitational field and measure the constant G, which could then be used to calculate the weight of the Earth.

A (probably ridiculous) question about bees posed by my six year old I was reading The Magic School Bus book about bees tonight to 6 yr old, and got to a bit that showed when 'girl' bee-larvae get fed Royal Jelly, they become Queens, otherwise they simply become workers. 6 yr old the asked if boy bees are fed Royal Jelly, do they become Kings? I explained that it there was no such thing as a King bee, and it probably never happened that a 'boy' bee was fed Royal Jelly, but he insisted I 'ask the internet people', so here I am. Has anyone ever tested feeding a 'boy' larval bee Royal Jelly? If so what was the result? In honeybees, the males are haploid and have only 16 chromosomes. Their genome is entirely derived from the queen. Drones produce sperm cells that contain their entire genome, so the sperm are all genetically identical (except for mutations). The genetic makeup of the female bees is half from the mother and half from the father (male bee). Most female bees are worker bees, the ones that are to become queens are specially selected by the workers to become a Queen. While the Magic School Bus has simplified things for ease, in actuality all larvae in the colony are fed royal jelly, regardless of sex or caste. However, those chosen to become Queens are fed copious amounts of royal jelly which triggers the development of queen morphology, including the fully developed ovaries needed to lay eggs (mostly by changing the DNA methylation patterns in the future queens). So, to get back to the question, if a male larvae was fed the royal jelly "by accident" -- not much would happen as it wouldn't make the male diploid. Now it may cause some methylation changes, which could interfere with behavioral responses of the male, but in general it wouldn't make him a king.

why do different pigments have different absorption spectra? why does the photopigment in blue cones, for instance, absorb light wavelengths that are mostly 430nm, while photopigment in red cones absorbs lights that's mostly 570nm? the difference in absorption spectra of chlorophyll molecules is due to variations in hydrocarbon tail length and side chain type. is there a method to the madness, though? like some kind of simple pattern that i can wrap my mind around, like more side chains = long wavelength absorption? or does the spacing of molecular components directly correspond to the wavelength? what's going on here? (i'm not looking for an explanation of the whole phototransduction cascade) Absorption relations fundamentally come from the interactions between electromagnetic waves and molecules; you can compute, using elementary quantum mechanics and advanced classical electrodynamics, the ways light should interact with a particular molecule, but there is no easy "trick" or correlation, mainly because of long chains and dynamic chemical structures. For example, these chains can behave as scattering antennas sometimes, and more complex molecules featuring many elements are also problematic; gold, for example, has its yellow color due to relativistic effects , so if you don't account for relativistic quantum mechanics in the computation of the bonds in a molecule containing gold, you might get wrong results. In the case of hydrogen, the computation is straightforward and requires no hassle; then, in more complex cases, like in an Ammonia molecule, utilizing intermediate quantum mechanics and some calculators, you can compute the energy spectrum and thus the light emission. In the example of a chlorophyll molecule, things get tricky: we can't calculate things exactly, but utilizing approximate mathematical methods and DFT you can calculate the energy spectrum of the molecules to a high degree of accuracy.

Is rain totally pure, clean water? I have heard that it is 100% pure H20 due to the evaporation process, but somebody else told me that rain molecules form around dirt/dust particle during condensation. Plus acid rain makes it more confusing rain water is not pure H20. Pure H20 is not typically found in nature, only in analytic chemical laboratories and some factories. Carbon Dioxide from the atmosphere is absorbed by water molecules and and turns into carbonic acid, which is found in all rainwater. It is slightly acidic, but typically not harmful to most creatures/plants on Earth. Other chemicals can make a stronger acid in rainwater and thus be harmful. rain water is indeed fresh water, like that you'd find in most lakes and rivers. fresh water is defined having a salt concentration of less that 0.05%, where as salt water (such as the ocean) has a salt concentration between %3-5. And by salt, I mean the chemical definition, not sodium chloride.

Does pouring boiling hot water on a toothbrush sterilize it? At standard pressure, boiling water won't kill everything. And you'd have to keep your tooth brush in the boiling water for about 20 minutes or so to mostly sterilize it. The instant you bring it out of the boiling water though, technically it wouldn't even be mostly sterile any more, as what floats in the air would start to colonize it, plus whatever you're using to hold it with would also serve as a source of recolonization.

If the extinction event of the dinosaurs never happened, how long would they have likely survived? Dinosaurs are still living today, so to speak. It was quite a shock at first (this scientific discovery happened within the past couple decades I believe), but birds are descendants of dinosaurs . Check out the wikipedia page if you'd like to read more. Edit: And I realize this doesn't answer the spirit of the question, which is likely "How long would the now extinct lines of dinosaurs lasted", to which I personally can't give a good answer without a lot of conjecture. Hopefully someone else can for that part :)

What is actually an electromagnetic field? We know what a gravitational field is: the curvature of space-time. However whenever I look for information of electromagnetic fields, the conclusion I get is that a charged particle can make other particles to move without touching them. I know that the answer for this is "the particles do touch each other because their magnetic fields touch" however, this always seemed to me an explanation as magical as the "invisible force working at distance" that Newton described to explain how gravity works. Einstein in the other hand, explained that there is not a force working at distance, but that gravitational fields are nothing but the curvature of space-time. Is there an explanation like this for electromagnetic fields? I mean, do we know what is actually happening to the space between the particles interacting through their electromagnetic fields? The explanation is really not that different from gravity. The electromagnetic field is a "thing" that exists everywhere, charge objects can "deform" it, and charged objects are in term accelerated when in the presence of a deformed field. We are perhaps more familiar with "spacetime" as a thing that exists rather than "the electromagnetic field" which is nevertheless also a thing that exists everywhere.

Two humans are pushed off a building, one with enough helium filled balloons attached to him to make him weigh 1 kilogram, what is the difference between the force of impact on both people? Assuming that the difference between air resistance of the people falling is negligible. Would they both die? Also assuming that this is decently sized building that would kill the other human. Let's disregard air resistance and disregard the change of the buoyant force with height. So we basically have Dude A being pulled down by the Earth; and Dude B being pulled down by the Earth by a rope with a constant force. They're each 100kg, g=10m/s2. The force of the rope is 990N upward. This means that he would feel 10N acting up on his feet by the ground when he stands. If you draw a free body diagram for Dude B, the forces of his weight (100kg * 10m/s2 = 1000N down) and the rope (990N up) counteract each other, leaving his 100kg mass experiencing a 10N force downward. Using F = m * a, his acceleration toward the earth is 0.1m/s2 (as opposed to unlucky Dude A, whose acceleration is a hundred times that). Over 100 meters, Dude A will be going almost 45m/s, whereas Dude B will be going a tenth of that (since he experiences 1/100 the force and acceleration). To put that in perspective, that's how fast you hit the ground after falling a fifth of a meter (jeez that sounds wrong but I've done the math a couple times...)

What makes Chernobyl so much more lasting in radioactive impact than Hiroshima and Nagasaki? (*Hiroshima, Nagasaki or any other detonation location). Is it mostly about volume of material? Or are reactors that much more powerful than bombs in terms of thermal output? Mass of material, delivery mechanism, it's basically apples and oranges. A nuclear detonation annihilates fissile material to produce a massive emission of energy in a short period of time. A nuclear reactor produces electricity from fissile material generating steam when connected to a thermal exchange system of some kind (involving water), relying on the extremely slow decay of the material rather than forcing it to reach supercriticality and annihilate. Little Boy, the bomb dropped on Hiroshima, contained 140 lbs of Uranium. Only the most minute traces of which survived the detonation. Fat Man, the bomb dropped on Nagasaki, contained only 14 lbs of Plutonium. Same as above, it was by and large annihilated. The reactor that exploded in Chernobyl contained 140 of nuclear fuel, and a good portion of this was scattered in the explosion, carried on the winds, introduced into the water, etc, and there's still a large quantity of material left at ground zero. More information can be found here.

Why do you see a sort of “motion blur” in real life? Sounds kinda stupid but I couldn’t find an answer on google as “motion blur” will always turn up something about photography. Basically, what I’m curious about is the phenomenon when there’s a dim source of light in a dark setting (like using a phone in a dark room), any fast movement always translates to a weird trail of light behind the source. Is the light being momentarily burnt into your retina or is something else happening? That is in fact correct! The more technical term is persistence of vision, and it is caused by the photosensitive receptors in your eyes not reacting quickly enough. It's also how most dimmable lights work, instead of lowering voltage and reducing efficiency, one can flicker the lights thousands of times a second to produce a dimmer light that we perceive as continuous. It's called PWM.

How does the momentum of a parent particle affect its decay products? My understanding of this field is very limited, but I'm looking for an answer for the following thought experiment: A hypothetical unstable particle is accelerated into empty space where it will not interact with anything. Within its own timeframe, it is bound to decay into less energetic and more stable particles within a fraction of a second. But since it is accelerated to near c, we'll assume that it will take it one second in the observer's timeframe to decay. After one second in the observer's timeframe, the parent particle decays into two daughter particles. Do those two new particles keep traveling in the same "direction" as the parent particle did, or will the event of decaying cause them to change their trajectory? In the rest frame of the particle, the daughter products will have some moment that adds up to zero. If that rest frame is moving very fast relative to some other frame, in that other frame the daughter products will have momenta such that the center of mass is still moving really fast in the same direction.

Why can electomagnetic waves travel in void, while acoustic waves can't? Acoustic waves are oscillations in some sort of material medium like air or water. Without the material medium to oscillate, there can be no sound. Electromagnetic waves are oscillating electric and magnetic fields, so EM waves can travel through any region of space that contains these fields. The nice thing about electromagnetism is that an oscillating electric field creates an oscillating magnetic field and vise versa. Thus, any oscillation in an EM field can propagate through virtually any region of space.

When calculating thermal expansion, do you multiply the thermal expansion of oxides by their mass percentage or molar mass percentage in a glaze? I’m a ceramicist and I’m making a calculator for glaze analysis. I want my calculator to output the co-efficient of thermal expansion of the fired glaze as calculated by the expansion of the various oxides that make up the glaze, but I don’t know (and haven’t been able to find out) if I should be calculating from the mass or molar mass percentage of the oxides. Let me know if I didn’t explain anything well enough! Ok, I'm out of my tree here, so far that the squirrels are sending out search parties. But as a general note, the coefficient of expansion is 1/V dV/dT. So for a first order approximation, you want the relative volumes, not the masses. So, I'd go by the absolute mass for every oxide in the mixture divided by its density, normalize to the total mass of the mixture and use that as a weighing factor for the respective coefficient of expansion.

A weird question: could a giant pitcher plant dissolve humans? Presume that there is one of those carnivorous pitcher plants, but it was scaled up. Ignoring issues of base fragility and other scaling problems, suppose a human being were trapped in there. Would the fluids inside be able to dissolve them, or would it not be able to decompose our skin like it does insects? Assuming that the person was incapable of moving, and the plant was scaled up enough that it could a) contain a person b) drown said person (which is how it kills its prey) c) secrete enough enzymes to dissolve the person, yes it could eat a human. It has been known to eat small rats, mice, lizards and even birds at its present size. I don't see any reason our skin would be impervious to decay when those animals are not. So, all you need to do is find a way to get a 5-10m pitcher plant and you can dispose of bodies.

What's the most accepted hypothesis (or theory) for the cause (not pathology) of autoimmune diseases? As many people have mentioned, there is no one 'most accepted' hypothesis (or factor, let's say) that is thought to be the primary ccause of autoimmune diseases. However, people haven't given a lot of details on some of the current popular hypotheses, including ones that relate to things you've brought up in comments, like sex. So starting there: As per this paper by Quintero et al -- Almost 5% of the world population develops an AD. Of this 5% approximately 78% are women [1] and it is considered the fourth leading cause of disability for them [2] . Women are at 2.7 times greater risk of acquiring an AD than men [3] . Also Generally, women have a stronger humoral and cellular immune response compared to men. They show a higher CD4:CD8 ratio because of a higher absolute CD4 cell count and a higher level of circulating antibodies [9] . Compared to men, they have more rapid rejection of allograft and reduced incidence and regression of tumors [10] . Which brings them to summarize a number of potential explanatory factors: prolactin stimulants X chromosome thymus X monosomy T cells XXY immune repertoire Microchimerism pathogenesis Y chromosome Aside from sex-based differences, there are also genetic and environmental factors that cause autoimmunity. From Cusick et al : Although host genetic background contributes to the induction of an immune response to self, epidemiological and molecular evidence implicates infectious agents (viral and bacterial) as the principal environmental insults responsible for the induction of autoimmune diseases (reviewed in [ 4 , 5 , 6 ]). Prolonged proinflammatory responses to infections have been associated with the initiation and exacerbation of autoimmune diseases (reviewed in [ 4 , 7 , 8 ]). Inflammation is facilitated by proinflammatory cytokines such as type I interferon (IFN), interleukin (IL)-1β, IL-12, IFN-γ, IL-17, and tumor necrosis factor (TNF)-α (reviewed in [ 7 , 9 , 10 ]). However, these proinflammatory cytokines are critical for clearance of pathogens, suggesting that environmental factors are able to divert the immune response towards immunopathogenesis. Although a number of immune cells are responsible for secreting proinflammatory cytokines, the primary cell types implicated in a vast majority of autoimmune disorders are autoreactive B and T cells, or antibody recognition of self [ 11 ]. While B cells and T cells are specifically called out in that quote, others have pointed toward dendritic cells as a central hub between regular inflammatory responses, tolerance, and autoimmunity.

Why are our brains so high up in our bodies? Since blood is heavily influenced by gravity, and the brain requires a lot of oxygen to function properly, why do we have our brains in the highest part of our body, as it takes a lot of energy for great amounts of blood to be pumped all the way up there? This is due to the evolutionary trend in early chordates (more specifically the craniates ) for cephalization. Sensory organs and nerve bundles gravitated towards one end of the body to eventually form the head with the brain, eyes and nose in the same general region. This general blueprint was passed down through all craniate descendants. This is most easily illustrated when looking at different embryos.

Why do astronomers think themselves immune to the uncertainty principle? Astronomers aren't "immune", really, any more than baseball pitchers are. First let's get straight what the uncertainty principle actually is. There are many uncertainty principles, but the one you are referencing is the classic ∆x∆p ≥ ℏ/2, where ∆x is uncertainty in the position, ∆p is the uncertainty in the momentum, and ℏ is Planck's constant divided by 2π. This says, very simply, that the product of the uncertainty in the position and the uncertainty in the momentum must always meet or exceed this minimal value. This is true for all particles/waves, not just light. It's true for electrons and protons, gluons, neutrinos, whatever. The thing is, ℏ/2 is very, very, small on everyday scales, much less intergalactic ones. It's about 5x10 m kg / s. Just treating a baseball as a single particle to get a feel for the size of the effect, go ahead and calculate the minimal positional uncertainty for a fastball with a speed known to 15 decimal places. It's much, much less than the size of an atom. Our uncertainty in the distances of other galaxies is generally ≥10%. It doesn't matter what precision in the velocity you are after, the uncertainty principle places a limit far, far below the practical limits. Other quantum effects in the detector become important before the uncertainty principle does. It simply isn't important when discussing distance vs velocity of distant galaxies.

What part of honey is antimicrobial? I've often heard that honey is antimicrobial, and it does seem to have an incredible shelf life for something that's mostly sugar and water. What is in honey that keeps it from going bad? Oddly enough, it's the sugar. Honey is so concentrated that it exerts tremendous osmotic pressure, essentially meaning that it sucks the water right out of micro-organisms. In addition, it's fairly acidic, and contains some hydrogen peroxide. You do have to keep honey sealed, or it will absorb moisture and eventually spoil.

If I take half a dose of a drug, does it last half as long, or is it half as effective, or is it a mix of both? For example, if I drink half of a Five Hour Energy, do I have lots of energy for 2.5 hours, or some energy for 5 hours? Or is it somewhere in between? Also, is it different for different drugs, like tylenol or adderall? It would come down to the dose-response curve of the drug. It may be that the drug works but for a shorter time or it may not work at all. You need to overcome a minimal effective concentration or minimal inhibitory concentration and enter a therapeutic range for many drugs. This would be especially noticeable in antibiotics where not surpassing a certain serum concentration could mean that the bacteria are not significantly affected. Think about that sigmoidal plot in the dose-response curve, now imagine a dotted line at some point in the response that corresponds to the minimal amount you must have to feel the effect. If the drug concentration never makes it above that line, then there will not be the effect you are looking for. You then need to think about metabolism and secretion to determine how long the drug will be above that line. Many drugs follow either zero or first order kinetics . Then there are other factors that complicate things like repeated administrations to build up to a desired serum concentration and sequestration in other parts of the body.