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Assume you have something that generates heat at N degrees. If this heat source were stuck inside an oven and there was little to no way the heat could escape, would the temperature inside the oven eventually go above N degrees? The second law of thermodynamics says that heat flows from hot to cold. If the system somehow found itself in a state where the temperature of the oven is higher than the temperature of the heat source, then the net flow of energy would be from the oven to the heat source. The oven would cool down and the heat source would heat up.

Why do images flip in a magnifying glass at a certain point? So I was looking through a magnifying glass and I noticed that when I looked at an object that was about three feet from the magnifying glass (how close it was to my eye was irrelevant... I think), the image in it completely flipped. This picture is helpful. The lens actually works the same in both directions. (In this picture an object way off to the left is giving off light.) Normally the glass would magnify things for your eyes because the object will appear larger (the light from the object takes up more of your vision) if your eye is between the lens and the focal point. Once you get to the focal point, all the light will be in one point on your eye (which can be very dangerous if you're looking at a light source, you can burn your retina). Once you get past that, you can see that the light hitting your eye will be flipped upside down.

What do moles do during floods? Though I cannot find what I'd consider to be highly scientific sources (lots of gardeners answering), moles dig their tunnels deep enough and at specific angles to avoid water getting into their nests. The soil saturated with water only goes so deep, and established mole tunnels are deeper than this level. This is why "flooding out" moles doesn't always work; they're counting on water getting in, so they build their nests and tunnels accordingly. Some moles do just die though, due to being on or near the surface, or having relocated recently enough that they don't have established tunnels.

Cell Respiration Alright maybe this should be in biology but it’s a question so I put it here. In school I have to make my own lab for cell respiration. We had done a lab that if you activated yeast and put it with molasses in a test tube with a stopper and "U-tube"? it would release CO2 (I think) and you would see bubbles in the water. So when I created my own lab I decided I would change the molasses with other things and see if the yeast still did cell respiration. So I tried it with yeast and corn syrup, and a yeast-sugar solution. So my question is should the yeast have done cell respiration with those things. I'm asking because this lab is a worth a huge part of my grade and I want to make sure it wasn't human error for not working. If cell respiration shouldn’t have occurred then I’m fine. I have made a quick drawing of what the lab was like to hopefully help you understand what I was describing. Sorry if my grammar is not the greatest. Help would be appreciated thanks! Well, firstly, yeast will die if it is too warm. I think that room temperature is ideal but i definitely wouldnt go over 40C. Secondly, you need to make sure there was no preservative with the corn syrup. Preservative preserves by killing microbes, such as yeast. Check the label on the side of the bottle. You should see bubbles in this set up provided you have enough yeast and dont overload the solution with sugar. Too much sugar and the yeast will die. You could collect the CO2 in a test tube and then identify it as CO2 using by seeing if a small flame is extinguished when placed inside it. Remember that CO2 is heavier than air, however.

What stops water from continually sinking through the ground? (Primary school science question) My year 4 class started looking at soil composition today and one of the students asked why water doesn't keep sinking through the ground. I promised them I'd have an answer by tomorrow (Sydney time), so I'm hoping the kind people at can help me help them! Apologies if this isn't the subreddit to ask this question. Feel free to advice of a more appropriate subreddit if there is one. Thanks! Well, there's a number of things at play here. Pick and choose which bits you want to use in the explanation at their level. Chemical wetting. Soil can have lots of clay minerals in it, and these will hold on to water molecules when they are available. Capillary action. Fine pore spaces within the structure of the soil enable water surface tension and adhesion (how well water sticks to a particular substance) to be a powerful enough force that the moisture remains in the porous structure. This is the same thing that will draw water up a capillary tube https://en.wikipedia.org/wiki/Capillary_action Impermeable bedrock. Soil sits on top of a solid bedrock, and water can flow into the soil much faster than it can flow into the rock. It's like having a sponge sat on a brick. If you keep pouring water on the sponge, yes some water will gradually seep into the brick, but the sponge will start losing water out of its sides before the brick is completely wet. Through motion. Related to point 3, when there is rainfall or groundwater uphill, that water will take the easiest path downhill, and that is usually through the soil. So even through it may not have rained where you are, if it has rained upstream the soils downstream will moisten after time. All of these things are quite easy to demonstrate in the classroom, and you can even do some experiments. If you have access to an oven and a mass balance you can even calculate water amounts in an object; wet the object, weight it, then dry it in the oven over night and weight it again. The lost mass is the mass of water. This is how we do it in the lab, and it can tell you all sorts of things about a rock. FOr example, if you soak a rock for a day or two, weight it, dry it, then weight it again the amount of water you'e lost is equal to the amount of space in the rock. You'll get really big values for sandstones, and relatively small values for igneous rocks and clays and shales.

Wavefunction collapse is faster than the speed of light. Doesn't this just mean that they used math to answer the question? I keep reading about how researchers are measuring the speed of the collapse of the wavefunction by sending entangled particles to two different locations, measuring one, and then checking the other. I have recently had a conversation where it was explained to me that a wave function is not just math. My questions are so: 1. At its most naive, entanglement just means that if I know the identity of one, by the magic of math, I know what the other is. How do we know that the collapse of the second is an actual physical event. My spider sense goes crazy when people tell me that they can only prove a freaky experiment works by using a bunch of random numbers and classical conservation laws, but I know that a lot of people have worked on this that are smarter than me. edit: deep dyslexia sucks. Spiders and bats are not the same thing You're asking questions at the very heart of Quantum Mechanics. People disagree on how to interpret QM. So when you say How do we know that the collapse of the second is an actual physical event. the answer is we don't. Some consider the wave function physical 'real'. Some don't. If the wave function is not real, then clearly its collapse is not real either. Niels Bohr famously threw out realism. That is, it's a mistake to think physics describes som underlying realty, it's simply a tool to predict the outcomes of measurements. To ask what is happening is simply a non sensical question (according to him). the standard collapse of measuring particle 1 Not familiar with the term 'standard collapse', but I think you're suggesting is known as a hidden variable interpretation of QM. That he outcome was already predetermined before your measured. This is certainly possible, but there's a result known as bells theorem that shows that if that is true, then the universe must communicate faster than light(non local).

How do bugs actually stick themselves and walk on walls and ceilings, y'know, like Spider-Man? They’ve usually got little claws on the ends of their legs and they grab onto the texture of the surface. They’re also extremely light, so it doesn’t take much friction to hold them to a surface. You’ll note that the larger the insect is, the rougher the surface needs to be for it to climb. Consider this image to see the claw I’m talking about.

What is it about a digital camera's sensor that results in noise artifacts in low light settings? I understand that stronger lighting means more information to outdo the noise, but why does the noise appear in the first place? Part of it is thermal noise. The electrons in your sensor have some thermal energy associated with them, and can trip the sensors. When you have a high light intensity, the signal generally outweighs the noise. But in low light conditions, the noise is much greater in comparison to the signal.

How is a mosquito proboscis physically capable of puncturing human skin? Human skin should be way too dense and strong for something so small and fragile like a mosquito. How is this possible? It uses two maxillas to cut its way into the skin so the fascicle can enter while the labium remains on the surface of the skin. Think two little rotary saws that cut their way into you while a syphon gets slowly lowered down. Its not even a puncture at the scale the mosquito is working at.

What happens if a gun is fired inside a pressurized cabin? (Like in an airplane) Today my military friend was trying to tell me that if a gun was shot at a high altitude in a pressurized airplane, that passengers would die from the force of the blast from the muzzle. (Not the bullet, unless of course it hits someone). He also went on to say that if the cabin is open to the air (depressurized) that the gun would act normally. I do not think that would be correct. The cabin is not extremely pressurized to allow for major changes (like what you might think of as the exploding safe episode of mythbusters). Airplane cabins are generally kept at pressures similar to high land altitudes. See here from wiki: A typical cabin altitude, such as the Boeing 767's, is maintained at 6,900 feet (2,100 m) when cruising at 39,000 feet (12,000 m) So what they are saying is that the cabin pressure is the same as the pressure at 6,900 ft elevation. So if what your friend was saying is true, you should be able to kill someone with just the force of the blast at a mountain altitude of 6900 ft. We all know you cannot do this.

How do photons interact with eachother? Generally photons don't interact with each other, but in a non-linear medium it is possible. For example, two photons can combine to excite a molecule to an excited state with an energy difference equal to the sum of both photons (two-photon absorption TPA, a third-order process), or two photons can combine to result in a third one, and many other interactions become possible. Answering "how" is not very easy without a lot of math, and quantum mechanics. The wikipedia page on NLO is a good place to start.

If the gas in a solar nebula is blown away as soon as the star becomes hot enough for hydrogen fusion, why are there different-sized stars? It's my understanding that all stars, at least ones that weren't formed in the early universe, were born in solar nebulae. The gas cloud spins around, and at the very center a star begins to form from accumulating dust and ices. Eventually this young star becomes so massive that the pressure its weight creates causes its core to begin fusing hydrogen atoms. Once this happens, most of the free-floating particles in the gas cloud get blown away, and most star and planet growth ceases. Since hydrogen fusion begins at a specific temperature, this would imply that all stars formed in this manner would have roughly the same mass, as they stopped growing once they became main sequence stars. However, this is clearly not the case, as main sequence stars can range in mass from a few percent the mass of the sun to ~100 solar masses. What's causing this size difference? The one thing I could think of was chemical composition, because it would cause a difference in density and therefore pressure, meaning a star would need a different mass to achieve H-fusion. However, it doesn't seem likely to me that this would single-handedly account for the vast range of possible star masses. Either there's something else causing the difference, or I simply don't understand how great an impact chemical composition makes. Once the hydrogen cloud is disturbed, the force of gravity causes different-sized clumps to form. Each of these may become a star. The arbitrarily-sized pocket of the cloud begins to collapse. The hydrogen molecules ( atomic hydrogen) which comprise this cloud are all attracted to the center of mass of this clump before even the proto-star core is formed. So they all gain velocity towards it proportional to the total mass of the cloud. The bigger the cloud, the greater the speed at which they are racing towards the core when the core finally reaches the temperature at which fusion begins. When the core ignites, it exerts this "blowing out" outward force on all the incoming particles, however, this force must overcome the attractive force of the mass of the core the total velocity towards the core that they already attained. That part of the remaining cloud which is moving too fast or already too close will add to the mass of the star, and this amount of trapped gas is what varies.

Is there a correlation between 1 cal = 4.184 J and water’s heat capacity of 4.184 J/g°C? I’m in an online introduction class to chemistry. Today’s lesson covered energy, temperature, heat capacity and such. There was one part of the lesson that said 1 calorie is equal 4.184 joules. Later in the lesson there was a part that said water’s heat capacity is 4.184 J/g°C. I noticed that numbers were the same between the two. No where in the lesson did it address this similarity. So I was wondering if there’s a reason that these numbers are the same or if some there is some kind of correlation out side of having joule as part of the measurement? Or is this just coincidence? It's not a coincidence at all. The "calorie" unit is defined to be the amount of energy required to increase the temperature of 1 gram of water by 1 Kelvin (or °C, which represents the same temperature increment). As such, it is directly linked to the heat capacity of water. The heat capacity of water depends on the pressure and starting temperature, so the amount of energy that 1 cal represents changes slightly with these variables. The conversion value of 4.184 corresponds to water at atmospheric pressure with a temperature somewhere around 18 °C. It was picked as the standard conversion rate between calories and Joules.

Can you compare torque and horsepower? I am kind of confused by were one reddit user suggests you can directly compare torque and horsepower, yet another user says you cant. In the discussion only the users you say you can compare them have the upvotes, although my intuition would say you cant. Who is right here? Is this reddit being stupid or is it me just being dumb? You have to very careful, while they both share similar units, they are expressing different quantities. Horsepower is a unit of power, or energy per time. Torque is a psuedovector with units of energy per radian (degrees in a circle), because it's a psuedovector, it has direction as well as magnitude. You can think of torque as the energy needed to change angular momentum, so if you integrate torque through some angle, you get energy. If we have an angular frequency, then the inner dot product of torque and angular frequency gives you the power, which we can freely express as Horsepower if we want to. In short, they are different, but related quantities. Comparing them is only appropriate if you know the rotation of the system or commonly in engineering, the RPM.

What exactly does a scintillation counter measure? I've done a bit of gamma ray spectroscopy, and I'm trying to interpret my results, but I don't know enough about scintillation counters. So lets say a gamma ray comes in, generates and electron-positron pair, and then undergoes a few compton scattering events. The positron annihilates with an electron. So, what gets measured by the photomultiplier? There are several different things all with different energies. There might be 3 or 4 gamma rays with different energies (traveling in different directions), a few electrons with different energies (also traveling in different directions), and maybe theres some interactions between the compton electrons and the scintillator that gives off some lower energy photons. Can the detector "see" high energy gamma rays that don't undergo any scattering? Can it see the compton electrons? What about gamma rays and electrons that get scattered at some large angle (say, backwards and out of the detector)? Are these partially detected in some way, or are these completely invisible? At first, I thought the scintillation counter was literally counting the number of photons with particular energies, but if that were true I cannot explain my results. When thinking about radiation detection, I like to start at the end and work backwards. At the end, you have a device that measures an electrical impulse. This impulse represents one detection event - also since you are taking an energy spectrum, the size of the impulse represents how much energy was detected. The impulse is generated by the photomultiplier tube. This takes visible photons and converts it into an electrical signal. The visible photons are generated by scintillation events. This happens when a free electron roaming around inside your scintillator falls into a lower energy state. Free electrons are generated from ionization events. Usually, you have one very energetic electron that comes crashing through your scintillator, ionizing hundreds or thousands of atoms along its path. These very energetic electrons were generated through interactions between your gamma rays and the atoms of the scintillator - compton scatter, photoelectric effect, and pair production. So the only thing your detector is able to see is ionization energy left behind by the gamma ray. Let's say one of your gamma rays undergoes compton scattering, and subsequently escapes. Your detector would see a signal equal to the energy of the compton electron, but not the gamma ray. In pair production, you often see "escape peaks." This is when one or both of the 511 keV annihilation photons escapes. You would have a full-energy peak (representing the full gamma ray energy), and two smaller peaks at 511 keV and 1022 keV behind it. So to sum it all up - take the energy of the photon entering the detector, and the energies of all photons that leave. The difference of these two values is the signal that the detector records.

How do we keep track of human genetic change? How much change would need to occur before scientists could say a new species of humans has evolved? I recently saw an exhibit about the brief period when neanderthals and homo sapiens co-existed, both of which could be classified as humans. I've been fascinated with the prospect of different species of humans coexisting ever since. How much would some homo sapiens have to change before we would classify them as a different species? Do we currently measure this change in any way? Does increased mobility prevent any one group from deviating so substantially that it would become a different species? This is a good question, and it's one for which you would find a lot of contention among biologists. The problem is that we do not have a single definition for species. As humans, we like to put things into discrete categories, but real organisms don't necessarily obey our rules. Now, for mammals like ourselves, we are generally ok with defining a species as a group of individuals that can produce viable, fertile offspring. However, given current genetic evidence we would consider our own species and neanderthals as a single species under that definition. Moreover, there isn't really a strict genetic cutoff for what defines a species. In the plant and fungal kingdoms, we see many organisms lumped together as the same species when, on average, they might have less genetic identity than a human and a chimpanzee. This means that we couldn't really put a number on the amount of change that would be required to produce a new species of humans - rather, it would likely depend on key changes occurring in specific genes required for successful reproduction to take place. With respect to your second question, increased mobility (and mating) will ensure that groups are less differentiated from one another genetically. Speciation requires that groups stop exchanging genes and thereby undergo evolution (mutation, genetic drift, selection, recombination) separately. So, yes, increased mobility (if accompanied by the production of fertile offspring) will prevent speciation.

What is the physical significance of a commutator in Quantum Mechanics? It is my understanding that you can use commutators to determine the uncertainty relationships between some observables but I am still having a hard time understanding what the physical meaning of the expression [A,B] is. Also, in addition to the one application above, what else can they be used for? Hm. It's a mathematical construct which literally tells you whether two operators commute. IMO, it doesn't have a "physical" meaning beyond that on its own, just like there is no particular physical meaning behind the "+" or "-" operator beyond the literal meaning of "add" and "subtract".

Why is human beard hair so much coarser than either body hair or head hair? Is it simply a matter of evolution? As beard hair shields a hunter's face against the elements while hunting, it would obviously be an advantage to have facial hair that is stiff and loose to mitigate wind chill or precipitation. What proteins are in beard hair which aren't found in other types of hair? I would love to have any information you can provide on this topic. Hair coarseness is a function of the thickness of each individual shaft of hair. Beard hairs are coarser than scalp hairs because they are individually thicker than your head hairs. One of the main things that influences hair thickness is the size of the dermal papilla, the space the root of the hair shaft sits in at the base of the follicle. Dermal papilla size is characterised both in terms of the space afforded within the dermal (skin) matrix and the number of cells at the dermal papilla. Table 2 in the following paper shows that the dermal papilla in male beard hair follicles is around 4 times the size of dermal papilla in male scalp follicles. So we might expect that beard hairs are thicker than scalp hairs http://ac.els-cdn.com/S0022202X15406700/1-s2.0-S0022202X15406700-main.pdf?_tid=d76ae1b6-3561-11e7-a265-00000aab0f01&acdnat=1494408180_3ef85226c926ada6bdd37aae4e068499 This paper (figures 4 through 7) show that follicle size is roughly correlated with hair shaft thickness at different body sites, although they don't specifically measure the dermal papilla size (which would be rather invasive). http://ac.els-cdn.com/S0022202X15306291/1-s2.0-S0022202X15306291-main.pdf?_tid=6e7ddb36-3561-11e7-a5ee-00000aacb362&acdnat=1494408004_b8c74d07766baecfbeff46a1f8d98c18 That's the proximal, specific reason beard hair is coarser than scalp hair. Also worth noting that follicle density is lower on the face than the scalp and that likely increases the perception of coarseness as the fingers can better resolve each individual hair when the face is stroked. http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8019.2008.00214.x/full Is it simply a matter of evolution? It certainly appears to be an evolved trait. Beard growth shows strong sexual dimorphism; males have obvious beard growth and women very little. This kind of marked sexual dimorphism is usually taken as evidence that the trait is primarily influenced by sexual selection rather than some other environmental selection. Another piece of evidence that this is a sexually selected trait is that beard hairs come in around the onset of sexual maturity, which strongly suggests they are a signal of sexual maturation. https://en.wikipedia.org/wiki/Sexual_selection It seems unlikely that exposure (wind chill, precipitation etc...) is the cause. We have no evidence that males spent less time sheltered than women in the Paleolithic period during which Homo sapiens evolved. For many hunter-gatherers men do typically hunt but women spend significant time out gathering (fun fact: grandmothers gather significantly more calories per day than the men acquire through hunting). Also humans evolved near the equator and I'm not aware of any evidence that extant hunter-gatherers living on or near the equator show any gender based differences in sheltering. Worth noting that women do hunt in some hunter-gatherer groups but I don't think they've started growing beards. Although perhaps they've just not had enough evolutionary time... ;) What proteins are in beard hair which aren't found in other types of hair? Beard and scalp hairs are both constructed from type 1 and type 2 keratin. There's no specific proteinaceous difference between beard and other hairs. Edit: In case people revisit this answer. Some people are asking what is the evolutionary reason beard hairs are thicker than scalp hairs. I'm not aware of any work on this nor on how we could assess this. The above answer is kept largely to what Science does know about beard hair thickness and the evolutionary drive for beard presence. Coming up with an evolutionary Just-So story about the Why of it would be much too speculative. Not all traits are under strict evolutionary selection so beard hair thickness may just be an artefact of the process which matures pubic and beard follicles

How were heavy vehicles steered before the popularization of power steering? Manual steering requires a lot of force even with a moderately heavy vehicle such as a mini-van, but power steering wasn't really around commercially until the 1950s. How did heavy vehicles such as cargo trucks get around this problem? Many older vehicles used what is called "worm and sector" steering which used a worm gear to turn a meshing section of the Pittman arm, which in turn moved the wheels. Today, this has been replaced with recirculating ball steering which operates on a similar principle, only the worm gear moves metal balls which mesh with the Pittman arm, instead of the worm meshing directly. To counteract the increased force, large trucks usually have larger diameter steering wheels as well as a smaller effective gear ratio, so you will sometimes see that semi drivers will have to turn the wheel more times to make a turn as compared to a car.

Can black holes be used as giant space mirrors? Black holes have strong enough gravity to prevent light from escaping. Could they also have light orbit them, such as how planets orbit stars? If so, would it be possible for black holes to have a slingshot effect on light, essentially sending it back in the direction it came? I read an article that explained that being next to the black hole the light would bend so much that you would be able to see the back of your head in front of you. I thought that was interesting anyone want to do some scientific poetry on that ?

Do babies need to breathe after birth if the umbilical cord is not cut? Babies clearly breathe after birth since they cry, but if the umbilical chord were left alone, would they to? Does the mother stop supplying the baby with nutrients/oxygen after birth? There is so much to this, so I’ll try to be brief, but also cover the gist of what occurs. If placenta is still pumping attached to baby, baby will continue receiving oxygenated blood for awhile, but that varies on a case-by-case basis. Some of baby’s blood volume gets squeezed back into the placenta during birth, so those moments after birth give baby time to get some of their blood volume back from the placenta. That extra blood that goes back into the placenta is also making the placenta heavy, which helps to encourage the process of detaching from the wall of the uterus. If it’s still attached to mom and baby and still pumping, baby will continue receiving oxygenated blood from mom via the placenta even if baby is born. The placenta can take varying amounts of time to detach—usually within 10-15 minutes. It can take much longer (even hours), although in most hospital settings they won’t let it go on for more than 15-30 minutes without intervention. This time where baby and placenta are both attached gives baby time to transition and clear the lungs of fluid. The first 3-5 breaths that baby takes are actually pushing that fluid into the alveoli where it will be absorbed. During those first breaths (or first few helping breaths provided by a bag/mask in the case of baby needing some help with transitioning), baby is using the oxygenated placental blood. Only after that occurs is baby even relying on room air. Once baby starts breathing room air, the whole circulatory system changes. The blood that was bypassing the lungs entirely up until that point now enters the lungs where it gets oxygenated and gets circulated through the body. I’m a midwife who primarily does homebirths, but I have also spent several years doing birth center births. At home and in the birth center environment, we usually practice delayed cord clamping/cutting, which means that baby stays attached to the placenta for as long as the parents want. I’ve seen a placenta keep pumping for 2 hours on more than one occasion even after it was no longer attached to mom. It is unlikely that there is any useful amount of oxygen available to baby in the placental blood after the first few minutes, but it doesn’t hurt to keep them attached. Most of the time the placenta is done pumping by the time it comes out. When doing a resuscitation, most midwives will leave baby attached to the placenta. In the hospital the cord is typically cut within 30 seconds. If a delayed cord clamping is requested, it usually happens in under 3 minutes. They will always cut the cord before resuscitation in the hospital setting.

Why did Nordic people evolve to have thin bodyhair and blonde hair while people in hotter regions have thick bodyhair which would be better suited to colder climates? In terms of heat insulation, why didn't people in colder climates evolve to have thick and dark bodyhair which would help you keep warmer. And on the contrary, shouldn't people in hotter regions have blonde hair which would reflect sun and perhaps no bodyhair to keep cool? Or does the sun have an effect that makes hair darker? The differences in hair has a negligible effect on your ability to survive northern climates: humans won't survive the winters anyway without clothing, so your hair matters little. What matter is sunlight. Near the equator the intense sunlight is a problem, causing sunburns and skin cancer, so darker skin and hair that absorbs the sunlight before it can cause damage is beneficial. Near the poles the lack of sunlight during winter months is a much bigger problem, as vitamin D is synthesized in the skin when it is exposed to sunlight. When sunlight is the bigger problem, having lighter skin is beneficial.

Does it take the same amount of energy to slow down a space craft as it did to get to that speed? That depends. It can take less, more or the equal amount of energy due to gravity assists. But let's imagine there is no matter around you. To move forward you need propulsion, and to stop you need the exact same amount of propulsion in the exactly opposite direction. However, in real life there are several things that makes this not this easy. There is no such thing as stopping in space, because you're always pulled towards mass, be it the Earth, the Sun or any other object. In fact, the spaceship is also pulling the Earth towards it, even though it's a microscopic pull that can't be measured. Due to the amount of entities in space, scientists often use gravity assists to adjust the velocity of spacecrafts, and gravity assists do actually take a small amount of the planet's orbital energy and you can decelerate relative to the Sun (assuming the planet is orbiting the sun.) *Completely forgot about the fact that you have fuel with you. Thanks -KR-

What is in between galaxies? after seeing this picture ( ) I became curious about what is in between galaxies. I know it's a bit of a silly question but is it just empty space or is there more to it? Any info is greatly appreciated. The 'intergalactic medium' (IGM) is mostly a rarified plasma. The heating mechanism depends on the particular environment -- the gas between galaxies in clusters tends to be very, very hot indeed (millions of kelvin), and emits in the X-ray. This is generally heated via gravitational shockwaves, as the gas falls into the massive gravitational potential of the cluster. Other galaxies, with very active central black holes, can also dump energy into the IGM (which heats it up). (EDIT... some people are taking issue with 'gravitation shock waves'. I was trying to say 'shock heating' in a non-fancy way).

Why aren’t waterfalls just eroded to slopes? I can understand that water needs some place to go and sometimes the easiest path is over a ledge. However, I would think that the power of erosion would convert these waterfalls into smoother inclines. Are waterfalls usually just the result of recently redirected water where the forces of erosion haven’t worn it down yet? Are tectonic plates moving faster than the forces of erosion can act? Are the rock found at many waterfalls more resistant to erosion? Thanks! The most powerful weathering happens in two places in a waterfall system. The critical edge, the place with the least support. And the vertical edge, where falling water has a lot of force and there is not much vertical support. These two places happen to be where the defining features of the waterfall are (edge before the drop and the cliff face). Since these places experience much stronger weathering than anywhere else, the general shape of the waterfall remains. It just recedes up the stream over time (see the erosion of Niagara Falls). For example: picture a waterfall with big rocks at the edge before the water tumbled down. In the event that these rocked get swept down what do you expect to happen? Generally the water creates a new critical edge some distance back and now the water begins falling directly onto rock/sediment that is clinging to the side of the cliff.

If electric cars become the norm, is it likely it would be economically feasible to own a gas powered car? Let's say would it be feasible for a middle class guy? It takes a while to change production of large scale oil fields. What would happen is that as people started switching to electric cars, the demand for fuel would fall relative to supply, causing a glut of inventory and leading to lower prices. The lower cost of fuel would serve to stem the tide of people switching to electric. A similar thing happened with alternative fuels in the mid 80's when the threat of development pushed gas companies to produce more gas, keeping inflation adjusted prices BELOW where they were in 1979 for TWO DECADES. Eventually, either 1) oil companies would reign in and eventually phase out production (but don't weep for them, they are all heavily invested across the board in energy production), or 2) we would reach some sort of medium between the cost of energy and the cost of gas, with a decent number of each on the road. This is, of course, ignoring any government intervention to push vehicles from one energy source to another.

Why could this PVC I am analyzing have endothermic peaks near the melt point when PVC is an amorphous solid? This is run on a DSC. I think I solved the problem. I looked at the pan my tech have me and there is a brown line around the ridge of it indicating some off gassing has occurred. I'm guessing that was the problem.

Will running a humidifier in a warm, dry, closed room cool the room? Specifically, does increasing the humidity of a closed system affect the temperature? What about an open system (window opened in the aforementioned room, for example)? I suppose the humidifier produces some kind of heat while running, but I'm not sure if that's important for this question. With a usual swamp cooler setup you will have positive pressure inside the residence with a cracked-open window or door in the region where you want cool air to flow through the building. If the humid air can't escape then you will saturate the air which may marginally reduce the temperature at first but then you're stuck in a still-pretty-hot and, even worse, humid room. I've done this with a portable evaporative cooler I own and it is not pleasant and does not produce a measurable difference in temperature on my thermometer. It just makes it feel like you're in a swamp.

Why do we develop tolerance to certain drugs? Why don't we develop a tolerance to others, antidepressants for example? Tolerance is caused when a drug blocks a specific receptor on a cell, we'll use morphine and the mu receptor which is located throughout your body as an example, a cell that has all of its mu receptors blocked for an extended period it will try to compensate by increasing the rate at which it produces more mu receptors, once more receptors are being made it will take more drug to ensure all the receptors are being blocked. Antidepressants generally act by blocking specific proteins on nerve cells that act as a pump, technically called reuptake transporters, for neurotransmitters (seratonin, dopamine, norepinephrine) this results in more neurotransmitter being left outside the nerve to bind to receptors on other nerve cells. What the nerve cell detects from this is lower levels of neurotransmitter being brought back into the cell. Rather than producing more pumps the nerve compensates by producing more new neurotransmitter, with a net result that more neurotransmitter is released, which is what is ultimately responsible for most of the antidepressant effect of the drugs; this process can take a few weeks which is why when you look at studies antidepressants typically take a few weeks to reach full effect. I'll admit objectively it may seem that people build up a tolerance to antidepressants but this is mostly because they aren't terribly effective to begin with and depression is very recurrent so many patients will relapse even if still taking the antidepressant Hope that helps

If our skin cells die and regenerate so much, as well as most of the other cells in our body, why are tattoos still visible after so many decades? Our skin has several layers, the top being composed of the epidermis (keratinized dead layers of cells) and the dermis (where your nerves, blood vessels, and epithelial progenitors are). These layers are held together and the cells are positioned by the extra cellular matrix, which is comprised of carbohydrate fibers and proteins. All tissues in your body have this as it helps organize and hold your cells in place. The ink from a tattoo is deposited below the dermis and into the extra cellular matrix. Some of it gets into cells, and when they die the ink fades. This is why tattoos will fade with time. What remains, however, is the ink that has dyed the matrix. This is also why tattoos are so hard to remove: you can't just kill the cells because the dye is not contained in any cells. It's part of the matrix surrounding your cells, so lasers are used to break down the dyes directly

When touching something without looking at it, why is it difficult to distinguish cold from wet? I first noticed this the other night while in bed, I reached my hands across my sheets and thought I felt something wet. It turned out to just really cold. It got me thinking and I tried out a few objects blindfolded, such as a cold ceramic dish, a cold glass, and porcelain. Is there anything to this or is it purely anecdotal? Maybe a better question is, do we have the ability to detect 'wet' directly or is it only through a combination of temperature and texture that we determine that something is 'wet'?

Is it possible that the end of the sunspot cycle could significantly slow down global warming? Sunspots, the enormous magnetic storms that erupt on the sun's surface as the cycle builds, might disappear entirely for the first time in approximately 400 years. If the reported trends continue—a big if, other researchers note—a hibernating sun would have only a slight cooling effect on climate I'm not entirely so sure about that "slight cooling effect on climate"... We know SO little about the Sun's cycles and solar variability ( over timescales lasting more than several decades, since we barely monitored the Sun before a few decades ago). And assuming that this IF happens, then the last time this happened was the time of the Maunder Minimum, when you had snowfall and freezing temperatures (in both Europe and North America) during SUMMER. I would hardly call that "a slight cooling effect" (see ) - although if it happens again, I don't think it will be as severe as what happened during the Maunder minimum. In fact, my fear is that it would entirely discredit the climate modelling community just because they neglected solar variability. Already, I'm afraid that the climate modelling community (along with the broader scientific community, which has vehemently defended the modelling community) might be discredited (by the popular opinion) in 5-10 years, because there are other cycles that can cause an apparent lapse in global warming for around a decade (it's just that the warming in the 1990s was superimposed upon a warming part of the possible cycle, and we now might be heading towards the cooler phase of that cycle, which explains why the last 10 years haven't really seen much of a strong warming trend): But it might give us a lucky break of several decades. That being said, I'm definitely not counting or betting on that happening, and do not think the argument should be a factor towards laxer policies towards CO2 mitigation. Even if it did happen, I highly doubt it would result in anything similar to the repeat of the Maunder Minimum. I'm just anticipating that this be possible, and that if it is possible, then we must at least prepare for its slight possibility (and that maybe we can't completely be 95% confident that global warming is going to be as catastrophic as the IPCC thinks it is). By the way, I actually work with climate modellers, and am in no way sympathetic to skeptics of anthropogenic global warming (although I do have a fair amount of respect for both Dyson and Lomborg, though I don't like it how Dyson also tries to use some of the more scientifically irresponsible arguments). I am open to alternative sides of the data and interpretations, since I'm still just learning (and haven't gone through the entire IPCC pdf yet). With all that being said, does anyone think that the emerging field of could help us better quantify variations in the solar output (especially in the past?) See for a recent science paper (conducted on stars SIMILAR to the sun) Considering how low sunspot activity was the last few years (It was a very deep minimum) and yet we still had extremely hot years (indeed the 2000's were a good deal hotter than the 1990's I'd say I wouldn't count on it.

Are comets constantly shrinking? That is to say, are they losing mass through their dust trail? That is to say, are comets like Halley's comet going to disappear one day? Comets are constantly losing mass. There is a finite number of passes a comet can do before it "turns off". However, common belief is that the comet won't just disappear but rather change. Comets lose ice more than they lose dust. It is assumed that eventually a comet could develop a surface that is a good enough insulator to allow it to stop the mass loss. However this would fundamentally change the comet into something else that does not behave or look like a comet.

If Thorium is so abundant and cheap, why is it so hard to get a sample of? video from "Periodic Table of Videos" stresses how hard to get Thorium is, but every proponent of Thorium ever has noted that a major benefit of thorium is that it is so abundant and cheap to mine... So which is it, and if it's both, then how is this inconsistency settled? Are people just throwing away Thorium because it has no use currently? I would still expect there to be SOMEONE selling nice thorium spheres or cubes for classrooms... Edit: I'll clarify that I'm not asking about Thorium reactors or LFTRs or MSRs.... Just why is it so hard for a to get a , and when he does why is that sample so tiny? As far as I understand Thorium emits only alpha particles which are easily stopped by the lightest of shielding and might even be safe to handle with only gloves... I'd assume would be selling chunks of it! Thorium is abundant and cheap to mine compared to other similar elements, but it is still extremely rare compared to common metals like iron and aluminum. The main problem is that if there's no industrial use, there's no proper market and no economy of scale. A mine isn't going to be profitable if the only demand for their product is from people who think it's neat.

A question about redshift Okay, redshift. The distance between me and a galaxy far, far away increases because the universe is expanding, and this shows up as a redshift. In analogy: if I have a magic box from which an ant shows up every second, i get one ant per second if I put it on my desk. If I glue the box to a balloon, and I blow the balloon up, I get less ants per second. Even though the ant still move at their maximum speed-of-ants, they arrive slower. So, the ant-delay (redshift) is a measure of the speed with which the balloon is inflated (the universe expands). Yes? Now, we know that the speed with which the universe expands is increasing. So, younger objects in the universe exist in a faster-expanding universe, and should have a higher redshift. But instead, the really high-redshift stuff is truly ancient. What am I missing? I feel you are complicating things: If a light source moves away from you the wave length of light you observe from it gets longer - this is red shift - and if it moves faster it gets more red shifted. The universe is expanding everywhere and all the time thus the more distant objects are more red shifted Attempt at clever analogy: Take a balloon and make an x on it, then make a y close to the x, and a z on the other side. Pretend you are x, y a near by galaxy and z a far away galaxy. Inflate the balloon and y will move away from you, but z will move faster away from you. Works?

Is it possible that there are stable super-heavy elements (beyond atomic number 100)? Is there a law against it or is possible just taking a large amount of energy? Probably not. There is a proposed island of stability . However, this is a relative descriptor, as being able to work with something that might last for minutes to days would allow much greater depth & breadth of study than something which decays in fractions of a second. It might also be of interest that some physical models propose the notion of proton decay , so as to temper the notion of "no decay at all" that you seem to be working with here.

Why aren't airplane fuselage and/or wing surfaces dimpled? If dimpling significantly reduces drag on a golf ball, why can't a similar principle be applied to airplanes? If I remember correctly, Mythbusters tested dimpling on cars and concluded that it did improve fuel efficiency. Before adding some other factors I'd like to add to what u/cantilene said; turbulence reduces flow separation and thus adverse pressure gradient. BUT, it increases skin friction significantly, the other form of drag along with adverse pressure gradient. With a golf ball you have no choice but to accept the possibility of adverse pressure because it is so "blunt", but an aircraft wing is generally not (except extreme conditions). So if you add dimples you add a whole lot of skin friction and drag vs. laminar or even transitional flow. To add to this, think about the weight and manufacturing involved with dimpling something. The surface area of a dimpled object is MUCH greater than that of a flat object. That is more material and thus more weight. Aircraft usually have to be very careful with their weight. In addition, the manufacturing process to create sheets like that would add significantly to the already high cost of large aircraft. And finally a slight rant, mythbusters is not a scientific source. They do not follow the scientific method and several of their "conclusions" have been misleading and perhaps even down right wrong.

How is our body able to create the material our nails are made from? Hair and nails are composed of keratin . Keratin is an extremely stable protein that is made as a very long, coiled fiber (sort of like a stretched-out slinky). The subunits of proteins, including keratin, are added piece by piece - imagine linking shower curtain rings together, one-by-one. These subunits are called amino acids. The properties of the amino acids and the overall 3D structure of the coiled keratin cause multiple strands of keratin to aggregate together! The base of your nail makes new keratin all the time, and it sticks to the rest of the keratin being made until you get a (finger/toe)nail!

Undiscovered Mathematics So as the legend goes, Newton discovered differential and integral calculus to describe planetary motion. Is it possible that there is more math to discover that is necessary to describe the universe? eg. Algebra, Trig, Calculus, ??? For example, might there be quantum mathematics? The answer is of course , if history is any indication at all. Physics has always been a (the?) major source of new mathematics, and it is as true today as ever. Roughly what tends to happen is that physics is written down using some mathematics that already exists (more or less), but a deeper study of the physical theory leads to a deeper study of the mathematics. This in turn may lead to a nicer formulation of the physical theory, which then leads to more mathematical development and more physics, and so on and so forth, and the subjects feed off of each other in this way. Calculus and Newtonian mechanics is one example. It is of course the case that Newton just came out of nowhere, developed all of the principles of classical mechanics and calculus himself, and that the theory was somehow "finished" right then and there. Newtonian mechanics led to its reformulations Lagrangian mechanics and Hamiltonian mechanics --the mathematics here is well beyond what Newton came up with, and it is difficult to overstate the importance of these ideas to current math and current physics both. More recent examples include relativity and the subsequent development of differential geometry, quantum mechanics and the development of, among other things, functional analysis (by Von Neumann , for example), string theory and the development of, for example, Gromov-Witten theory and its influence on the study of moduli of curves , Chern-Simons theory and its influence on knot theory , etc (much of this from Edward Witten , a Fields medal winner), and about a billion other things. So my point is, the interplay between physics and math has always been strong, and still is, and the distinction between the fields is often blurred. There is more physics to be discovered, which there is more math to be discovered, and vice versa. The answer to all of your questions is yes.

Do we possess the computational power to simulate the origin of a single celled organism from non-living material? Essentially no. Not in the sense that you are probably asking the question. We almost certainly don't have enough computing power to simulate enough molecules and a large enough environment to go from non-living material all the way to cells. But even if we did have the computing power there are many, many steps in that process where we literally have no information. So building a simulation would be something of a lot of guess work.

Where can I get some Renografin 60? Help me, Reddit Ask Science, you're my only hope. I'm not sure about asking for prescription medications, even one that is just a radiopaque substance with no clinical effect, on reddit. Doesn't Bracco make it any more? If not, then I would suggest contacting distributors like Cardinal, McKesson, or Owens & Minor. If you're not using this for human use, but just for experimental purposes, they may have expired supply they may be able to contribute for your use. If you're using it for human use, I know it has 2 year shelf life, and you're probably out of luck.

How would the Earth be different if it had three moons of equal size, equally spaced on the same orbital plane? That's not a stable configuration, it would decay and eventually at least one of the moons would either be kicked out of the system or fall to Earth, and another would either suffer the same fate or have to move to a higher or lower orbit. Having two massive moons on the same orbit doesn't work.

Is sexual anxiety a new human trait or has it been around for centuries? Short answer: Yes (probably). Science answer: A study on macaques revealed that males had difficulty achieving orgasm (less than 2% of time) if the female didn't make noise during sex. When they did shout, ejaculate rates rose to 86%. Source: (It had to be the Germans) http://rspb.royalsocietypublishing.org/content/275/1634/571 This directly shows a relationship between males ability to perform sexually based on reaction from the female, albeit in monkeys. However! More science tells us monkeys are relatives to apes, which I would relate to humans with confidence. I'm unaware of sexy studies in closer related species, or of any psycho-historical study with the foundation (see what I did there?) that related the males performance to social factors. Sounds most interesting. My condolences, things will get better.

What would happen if you uniformly increased the pressure inside a perfect sphere of perfectly consistent material? If the material of the sphere was perfectly consistent, such as that there are no areas weaker than others, would the sphere ever break? In what manner would it break? I realise that an argument could be made for air pressure resulting in a rupture at a point where more force is exerted for a moment, so assume that the pressure provides uniform force in all directions. Well, the sphere will break once the pressure is high enough to push apart the bonds. As long as the material is not perfectly stretchy or something to that effect. Same as with a chain where all the links have the exact same strength, each link is still breakable.

Can a person get the same strain of Norovirus within a week or two of getting rid of it? I work in an aged care facility, and we are at the tail end of a disatrous Gastro outbreak. Now we have some residents getting it for the second time supposedly, and I'm a little skeptical regarding the legitimacy of these seconds bouts. I've looked online for an answer to this, and only found conflicting opinions with no sources (yahoo answers etc...) Furthermore, if you can get it twice, can someone please explain what the mechanism is? Does the virus mutate? Can it lay dormant? Thanks! edit: Thanks so much for the thorough answers, everyone! Both I and the RN here found this all fascinating. The nurse in particular (@64yrs old) found 'the reddit' to be amazing... just to touch on some questions: Yes, at the onset of the outbreak a Doctor (whoever it was) tested for and confirmed Norovirus. And there seemed to be some concern regarding why any resident here would be getting gastro twice... unfortunately all I can say about that is there has been an influx of very young and poorly trained new staff making many observable errors... making this outbreak drag on and on... I'm trying hard train them etc, but I'm night staff and barely see any of them! And I certainly know how bad the Norovirus is... I was the first Staff member to get it this time! Anyway, thanks again Science community! Yes you can. But it's highly unlikely and shouldn't happen but is completely possible. You should be immune to the strain you just cleared for a short period (if you weren't then how would you ever get over it!) but this doesn't last long a few months in very fit and healthy people, the elderly probably have less effective immunity that doesn't last as long. So how can you be infected again? This can happen for a number of reasons. 1) It's a different strain (completely different, a different bug, or slightly mutated). 2) Your immunity has passed. The immunity doesn't last very long but the elderly aren't able to mount a great immune response (especially right after a d&v outbreak!) So I suspect that they could well be getting the same bug twice or even a lightly mutated version noroviris is a fairly fast mutator. There's no point doubting it you'll never get rid of the outbreak if you don't put in place rigorous controls at the first sign of trouble.

Can you find the Mona Lisa in a Mandelbrot fractal? Apparently when one goes deep enough into any arbitrarily coloured Mandelbrot fractal one can find amazing structures. Is it possible to find the Mona Lisa painting in there when given enough time and resources? for reference: No. Just because something is infinite doesn't mean it will have every possible permutation of values. For example, imagine a pattern like 10100100010000100000... It could go on forever and never repeat. No where in that sequence of numbers will 123 ever appear. In spite of the infinite complexity of the pattern, it isn't guaranteed to have every combination of numbers.

What other things like seeing our nose and breathing we ignore by default? We do this all the time with things that aren't changing in our environment. For example, when you first put your clothes on in the morning you feel them on your skin, but, very rapidly you stop noticing them. Now that you've read this, you might become aware of your clothing again! The same applies to ambient noise like traffic from the street or the ticking of a clock in your room.

Why are the noble metals so unreactive? From what I have gathered so far it seems that the inner electrons have more energy than the outer electrons. But I don't know how this all ties into it. If you are explaining it could you explain it in the most layman terms as possible so I can grasp the concept. Because we live on a planet covered in water. The best way to understand this, look at the electrochemical series , and scroll down to 0, which corresponds to Hydrogen. Now, observe the metals below that point - Your "noble" metals. Basically, the "noble" metals stay in their metallic elemental form because anything that react with them will preferentially react with water to give back the noble metal. But anything that react with them would typically react with water , so that first condition doesn't even typically need to happen.

A question on nuclear decay and the number of nuclei. The number of nuclei of a number of atoms after a time t can be defined with the equation: N = N(0) e The half-life (T) is therefore when N = N(0)/2, and so: N(0)/2 = N(0) e ; ... ; T = ln/λ If we were to represent N(0)/2 vs time on a graph, we would get this graph: As can be witnessed, there's a horizontal asymptote of x = 0. Since the y axis represents the number of nuclei left, this means that there will always be (an ever-decreasing) radioactivity. That is all fairly simple and such, however, if that is right, that means that no matter how long you leave a sample out to decay, you will literally never run out of your sample, and furthermore, it implies that you can even never get to N = 1 because if you can't run out of your sample, you would also suddenly lose the radioactivity. AND IF the sample could ran out so that N = 0, it would mean that there won't be any radioactivity anymore in any case. This has confused me, because obviously this is physically impossible, but the math states this is so. So what is the actual scenario in real life cases? The maths is statistical, it's describing a totally perfect situation where arbitrary amounts of radioactivity are allowed, including fractions. In real life, this is of course not the case. The mathematical model is a very good match when you have many radioactive nuclei because on average everything works in the ideal way. But when you have few nuclei left, they can no longer quite fit this curve. Since the decay of any particular nuclei is totally random, the last few atoms could stick around for a long time, or all decay at once, or anything in between. On average, they'll show the ideal behaviour from the curve. Also bear in mind that this is all statistical. That mathematical curve perfectly describes what really happens, even in the ideal case with loads of nuclei. It's only ever a good prediction. The idea of averages is very important, because that's what the maths is telling you the behaviour of.

What is the psychological mechanism that causes things like songs or food to "get old"? If I listen to a song I like a lot, after a while I get bored of it, and eventually I'll start to downright dislike it. The same thing happens to everyone with certain foods, movies, even places and people. I just wonder why something I really enjoy can turn to something I actively avoid simply through being exposed to it too much. What drives this change? While you wait for the scientists to show up, here is the Wikipedia entry on The Coolidge Effect : In biology and psychology, the Coolidge effect is a phenomenon—seen in nearly every mammalian species in which it has been tested—whereby males (and to a lesser extent females) exhibit renewed sexual interest if introduced to new receptive sexual partners, even after refusing sex from prior but still available sexual partners.

Why is there only one species of human? There are a variety of reasons, but here are two: 1: Due to our technology and general intellect, humans around the world have been able to live in far more similar conditions than another, equally distributed species. 2: We are a relatively young species . Since the migration from Africa and the general distribution throughout the world, we didn't have enough time to develop to many unique genetic traits in various isolated populations. Now that the world is so much smaller due to technology, that will never happen. It should be noted that various groups did undergo independent evolution leading to changes in skin colour, sand slight changes to things like bone and muscle structure, certain desease immunities and other minor differences, some of which we were directly responsible for, such as lactose tolerance which is more prevalent among populations who historically milked cows.

What caused the super-continent Pangea to split up in the first place? Is that same force still driving the plates in their movement? Just a wee piece of general mislabeling that really grinds my gears as a student of geology, There is absolutely, categorically, completely, no layer of liquid (or boiling) magma in the mantle. There is a liquid outer core, which is composed of iron and nickel, which is not magma. The mantle may behave as an incredibly viscous liquid over geologic time, but it is not magma. Magma/melt will only form under certain geologic conditions of temperature and pressure, and is very localised. (a good thing too or volcanoes would erupt everywhere)

How would I determine how long it takes my apartment's stale air to be replaced by fresh air with all the windows open? Every weekend and some weekdays as well I have an argument with my wife about opening the windows and letting out all the warmth and letting in as much frigid fast flowing wind as possible. She's convinced it's necessary and it is nice to have fresh air but I at least would like not to prolong the torture if possible. What would I need to do to determine how long it takes for the complete volume of air in the apartment to be replaced by the air from outside? I'm guessing it really couldn't take that long because as we're on the third floor up and as soon as the windows are opened, very strong winds come in and blow every object in the house on to the floor and shake the bathroom mirror on it's fixtures. How do I approach this question? In scientific settings you'd seal up the house and add a tracer to the air. A tracer is inert (no reaction/adsorption), doesn't separate (no condensation/settling), and is originally present at a constant quantity (usually zero). Once you mixed the tracer in, and you were sure it was distributed evenly through out the house, you could start the flow and sample the concentration of the exit air periodically. You could then keep track of how long it would take to remove all the original air, since its removed in proportion to the tracer. If you wanted to do this experiment in a fish tank, you could use red food coloring to give you a water analogy. A common gaseous tracer is SF6 (sulfur hexafluoride). I'm guessing like most people you don't have easy access to the analytical tools necessary to measure gas concentrations, so you can't perform a tracer test. Whether or not you run a tracer test, there are several other things you may be able to measure that might help you (some already mentioned in other comments): air changes per hour (ACH)

Curvature of Earth and its effect on travel. On a trip from India to US recently, I saw the path that my flight took, because they display it on your monitors. In image, the yellow line is the path that it actually took, but from what I understand, red should be the shortest path. So, I told this to a friend and he was like, "Well, it's the curvature of the earth that makes this the shortest path.". I was all like, "Oh OK.", but when I got around to thinking about it, I couldn't actually understand why. Could somebody explain why? OR did my friend not know what he was talking about? The shortest path between points on the surface are great circles . Due to the way the globe is projected on the map, they appear as curves. This is, of course, barring any other aviation considerations such as jet streams.

Do humans (or other animal species) give off ultra-violet colors similar to flowers that we can't see? Is that why bees circle us? Or is it merely our scent? Or is it just a warning for us to get the fuck out? Apparently, they look like they've been smeared with pitch. Here's a link to two pictures one is taken using a regular RGB camera, and shows a person with sunscreen applied to half his face - this is not visible, and he just looks like a regular joe. the other is taken with a UV-sensitive camera, and shows how this sunscreen UV light in one half of his face. (For fairness sake, I should note that mechanical sunscreens, based on ZiO or TiO reflect and scatter UV light, and chemical sunscreens absorb UV light..)

How does radiation cause mutations? Simply put, radiation breaks the strands in your DNA. The DNA can repair itself, and it usually does this quite well. A fraction of the time though, the repair process isn't done properly. This means the DNA is now slightly modified, which can affect the next generation of cells.

Does Hydrogen Peroxide kill bacteria? Hi, So I got into a debate elsewhere about whether H2O2 can actually kill Bacteria. There was also suggestion of it "promoting healing" etc. of which I am more dubious. Peroxide breaks down into Water and Oxygen free radicals, and my understanding is that this breakdown is catalysed by biological matter, and the free radicals screw up chemical structures in the cell walls. Anyone got any citations they can offer, alongside a TL:DR? Obviously I am referring to the low percentage stuff you can get in brown bottles from a pharmacist. Neutrophils and macrophages actually make their own H2O2 (really starts as superoxide ion, O2 --superoxide dismutase--> H2O2) to kill bacteria as part of their oxygen-dependent killing mechanism. So yes this is a pretty good approach to killing bacteria. Another enzyme, catalase, is present in our bodies that breaks down the dangerous H2O2 into H2O + O2. Some bacteria also have this enzyme and therefore may be resistant to killing with H2O2. Source: Murray, Patrick R., Ken S. Rosenthal, and Michael A. Pfaller. Medical Microbiology. Philadelphia: Elsevier/Saunders, 2013. Print.

Are there any methods of recording uncertainties without observing them? Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state. My question is, are there any methods, theoretical or real, to record such things for future observation? For example, is it possible to freeze a quantum state in time so that it may be observed later on, and the data recorded? And as a further question, in quantum mechanics, what exactly counts as observation? Is it only human observation, or can it also be animal observation? What about mechanical? And does changing the observer create a difference in the observed state? There's a lot of questions in this post and some things you seem confused on, so I'll try to address each thing one by one. Let's start with the confusion. Quantum Mechanics has many particles and functions which are in a state of uncertainty until they are observed, where they collapse into a single state. You're confusing with . An "observable" (a property that you can measure, like position, momentum, spin, etc.) has "eigenstates", which are quantum states corresponding to a definite allowable value of the observable. You can put a quantum system in a superposition of multiple eigenstates. A superposition is just a linear combination of multiple states. (For example, a chord of CEG on the piano is just a superposition of the sounds of C, E, and G.) When you measure the superposed system, it will collapse to one of the eigenstates with a probability proportional to "how much" of the eigenstate was in the superposition. is a related, but separate concept. The uncertainty between two observables describes how much information you can simultaneously gather about both properties. Mathematically, two observables do not share a common set of eigenstates, they will have an uncertainty relation between them. Conceptually, let's take the classic example of momentum and position. Suppose I have a slinky and I make waves in it that travel down the slinky. If I measure the wavelength of the waves that I make, I actually get a distribution of values centered around some dominant frequency. The only way that I can get an value for a wavelength is if I make a standing wave , which has an exact wavelength. But this gives me no information about the position of the wave, because it is spread out over the entire slinky! This is a very close analogy to how things behave quantum mechanically - uncertainty is not specific to quantum mechanics, it describes general scenarios where knowledge of one property precludes knowledge of another one. Okay, on to your remaining questions. My question is, are there any methods, theoretical or real, to record such things for future observation? For example, is it possible to freeze a quantum state in time so that it may be observed later on, and the data recorded? There are quantum states that have observables which do not evolve over time, but the "phase" of a quantum state evolves at a rate proportional to the energy of the system, so to "freeze" a state would involve cooling it to absolute zero, which isn't possible. And as a further question, in quantum mechanics, what exactly counts as observation? Is it only human observation, or can it also be animal observation? What about mechanical? And does changing the observer create a difference in the observed state? This is actually an open question in physics and there isn't a single answer that is universally agreed upon. However, as much as pop-sci media would like to have you believe otherwise, an observation doesn't have anything to do with consciousness, so a human observation or an animal observation or a mechanical observation are all the same. Changing the observer with another macroscopic object makes no difference. The actual process of wavefunction collapse is also poorly understood. There are a lot of theories with varying degrees of credibility interpreting this, including the many-worlds interpretation , GRW theory , and the (most popular) Copenhagen interpretation .

How can gene modification work in a fully mature adult? I understand how we can change the DNA info in a single cell and all but how does this spread to the rest of the body? It makes sense with a zygote because the single cell will split and become all the cells in the body but how does this work with a living breathing adult organism? How would injecting a shot containing genetic info into my arm cause the cells in my feet to get the same cancer blocking (just an example) genes that go to my scalp and lungs etc? A key thing to remember is that many tissues such as the intestinal lining, various immune cells, and red blood cells regularly replicate. If you can genetically change the stem cells that then divide and differentiate, you can change those downstream cells. The methods used to induce the genetic modification can, theoretically, target all cells in the body that express a given receptor or other mechanism to provide specificity. Just like a flu virus infects a large number of cells, the genetic modification technique can do the same.

Is it possible for an anion to exist in solution without a cation and vice versa ? Yes, this is actually the basis for bioelectricity used in our nervous systemand muscles. Our cells actively seperate ions to create electric and chemical gradients that can be used to power other reactions (typically transport accros the membrane). The inside and outside of the cell are separate solutions seperated by a membrane. If there is a difference between total charges (cations-anions) inside and out then a voltage difference is created. In extreme cases like electric eels these voltages can be added in series to potentially deadly levels.

Do ants (and other small bugs) take fall damage? Technically yes, since they are falling downwards, but their terminal velocity is not nearly high enough for any real damage to occur. Plus, most bugs have strong exoskeletons or squishy bodies that can absorb impacts very well relative to their size.

Do we have a man-made satellite with a big elliptical orbit around the earth? And if we do what would be the purpose of this orbit? Yes! A good example of a very useful large elliptical orbit is a Molniya orbit . It serves the same kind of purpose that a geostationary orbit does, however it's designed so that most of its orbit is spent being directly over a much higher latitude. This is very useful for countries like Russia which are far enough north that a geostationary satellite would see it as "slanted" due to the curvature of the Earth. A Molniya orbit allows the satellite to spend most of its time looking directly down at high latitudes, while also staying generally over the same spots on Earth all day. EDIT: Another example would be a Tundra Orbit which has a period of one day, instead of half a day.

What do you catabolize first during starvation: muscle, fat, or both in equal measure? I'm actually a Nutrition Science graduate, so I understand the process, but we never actually covered what the latest science says about which gets catabolized first. I was wondering this while watching , where the contestants frequently starve for 21 days. It's my hunch that the body breaks down both in equal measure, but I'm not sure. EDIT: Apologies for the wording of the question (of course you use the serum glucose and stored glycogen ). What I was really getting at is at what rate muscle/fat loss happens in extended starvation. Happy to see that the answers seem to be addressing that. Thanks for reading between the lines. Finally something in r/askscience where my degree can be of use (PhD in muscle biology) Whenever you stop eating, your substrate preference will be about 2/3 fat and 1/3 carbohydrates. Those carbohydrates will come from stored glycogen in your liver and muscles. When those glycogen stores run out, the liver will try to defend the blood glucose through gluconeogenesis, synthesizing glucose from amino acids from protein broken down elsewhere in the body and glycerol from triglycerides. This metabolic phase is characterized often by decreases in blood sugar and associated tiredness and hunger. It is also the phase in which muscle catabolism progresses at the fastest pace. However, 12-24 hours after running out of glycogen, the body will gradually go into ketosis, in which the liver synthesizes ketone bodies from fatty acids. These ketone bodies can substitute and/or replace glucose in the metabolism, reducing the need for breakdown of protein for amino acids for gluconeogenesis. After a couple of days the substrate preference will have changed to 90% fat and 10% carbohydrates, thereby reducing muscle catabolism strongly. This state can be maintained for as long as there is enough fat. The longest documented therapeutic fast was 385 days during 100+ kg weight loss in an obese patient. Mind you that a kg of bodyfat contains enough energy to go for 3-6 days depending on body size and activity level. Ketosis and relying predominantly on fats will continue until only the essential bodyfat stores are left at approximately 5-7% in men and 10-14% in women. At this level the substrate preference for fats disappear and muscle catabolism increase sharply again. At this point death will usually occur within very few weeks.

If there's no ultimate frame of reference, how do we know the Universe's age? Could some other civilization in a different galaxy measure CMBR and derive an age other than 13.7 billion years? The age of the universe is given as measured in the CMB frame, which is the unique frame in which the CMB appears isotropic. In all other frames, the age of the universe is strictly smaller.

Question about possible containment methods for Japan's Fukushima nuclear plant. Probably stupid, but.... Is it possible to contain the Fukushima nuclear plant with a sort of temporary sheet-like cover using the coordinated efforts of helicopters and/or cranes? I realize the plant is right on the shore which would make it quite difficult as there are many obstacles, but wouldn't it work if there were some sort of a "clamp/brace wall", if you will, built just off shore in order to hold whatever would be used as a cover? Any other possibilities? What, exactly, is even being done/discussed in regards to figuring out how to contain it? They actually are doing this. They are building outer structures with new overhead cranes and a system for fuel cask transfer to the ground level. They are additionally adding more structural supports and putting in HEPA level or greater air filtering to prevent radioactive particulate from escaping. Here is one article: http://www.world-nuclear-news.org/RS_Fukushima_fuel_removal_buildings_1904121.html

How close could a manned spaceship get to the sun? The astronauts must be able to survive and return to Earth, in a ship designed specially for this mission - not just a normal one that for some reason comes into course with the sun. Also, what about an unmanned no returning probe? Could one be built that could even get to the surface before burning up or being crushed by gravity? First, things do not simply fall to the Sun. Or they do but they constantly miss the Sun. When you leave Earth, you're going about 30 km/s, 90 degrees off of the Sun. If you intend to get to the Sun, you need to cancel most of this speed somehow. So far the probe that has left Earth with the greatest speed is the New Horizons , with a speed of 16.26 km/s, relative to Earth. Had we launched that in the opposite direction of Earth's orbit, it would have gotten an orbital speed of about 14 km/s around the Sun and would have made a new record in closest approach to the Sun at about 0.1 AU away, but that's still 20 solar radii away. But actually, New Horizons did have enough propellant to make it into the Sun had we wanted it to go there. Because there's a more energy efficient way to go there than cancelling all the orbital speed of Earth right away. The way to do it is to first fly as far away as you can, theoretically infinitely far for the optimal case but something a bit less will do for us. So you get to the solar system escape velocity and fly away. New Horizons had even a greater velocity than this. When you're somewhere way past Pluto, your velocity will slowly approach zero, but never quite get there, if you had escape velocity when you started. Then you use your engines just a little bit to cancel your remaining velocity. Now you're stationary relative to the Sun and will indeed just fall in it. So, it turns out that the most energy efficient way to get into the Sun (without using gravity assist tricks) is to first escape the solar system and then fall into the Sun. In other words it is easier to send something completely away from the solar system than to send it into the Sun. Then with a little bit of finesse, you could loop around the Sun instead of hitting it with a velocity of about 600 km/s. And now we need to worry about shielding against the heat of the Sun. And also about getting the astronauts back home, although that turns out to easier than you might think. When you're at the closest point to the Sun you can make huge changes to your orbit with only a small amount of fuel. So the orbit there could be changed to meet up with Earth again half an orbit later. Do note that this method of getting to the Sun is very time consuming. We're talking several decades here.

If I am allegic to house cats, am I also allergic to big cats (lions, tigers, pumas, etc)? Do all cats carry the protien that makes me unable to be around cats, or is it specific to the domestic house cat? It would sound cooler to say "I'm allegic to panthers and cheetahs" instead of "keep that little cute kitten over there away from me!" According to this test of IgE and IgG4 reaction to Fel D 1 from many of the big cats - it looks like your answer is yes...you can say "Get that Beast away from me! I am allergic to its relative Lions, Pumas & Siberian Tigers!"

How does the concentration of sugar affect the fermentation in beer? Will more alcohol be produced with more sugar? Or less? This is for an EEI I am doing at school, thanks in advance :). Up until a point, the more sugar there is the more alcohol will be produced. Basically alcohol is a byproduct of the bacteria's respiration, so the more sugar they have to metabolise, the more alcohol they will produce.

Graphene surface area. I was reading an article on graphene supercapacitors when I came across this line The resulting graphene electrode is highly porous. A single gram of this stuff has a surface area bigger than a basketball court. It is from this article in the MIT review of technology. The electrode to which they refer is in a "coin shaped cell" so presumable its about the size of a quarter, give or take a bit. How is it possible to have such a large surface area if the coin size electrode is made up of graphene, which I understand to be a hexagonal lattice. What surface are they referring to? The surface of the sheets of graphene themselves? or the surface area of the constituent atoms? Are there as many sheets of graphene in the cell as there are quarters covering a basketball court? Thanks. When discussing porous materials surface areas, we normally speak of gas-accessible areas. This is the "real" surface area, that stuff can actually get to and interact with. More formally, we measure the amount of gas adsorbing to surface of the sample, then back-calculate the area using the size of the gas molecule and the mass/volume of the material. This is normally measured as an isotherm, and modeled with Langmuir or BET theory. Edit: It's probably relevant to mention that if your surface is electrochemically active, your can use this to determine surface area instead. It's more practical for very small samples (<25mg), but is somewhat poorly defined.

[Astronomy] How close can we get a man made probe to the sun before it becomes inoperable with today's technology? I understand that Helios I and II are the man made objects that have the distinction of being the closest, but I'm curious as to how close we can get with an unmanned probe using today's technology before it would begin to take enough damage that it'd be rendered inoperable. Here's a good article that addresses your exact question. For a spacecraft, the ability to fly safely near the sun depends entirely on its material, its design, and its fly-by trajectory. Helios 2's perihelion (closest approach to the sun) was ~42 million km. The perihelion of that proposed probe is just under 6 million km, and the probe is scheduled to launch in 2018. Solar Probe Plus pushes the limits of materials science and engineering, and will actually orbit within the corona of the sun, enduring temperatures of 2,600 °F (1,400 °C).

Alternative method for space launch? I have little idea on the practicalities of this idea so I thought I'd throw it out there and see if anyone with more knowledge on the relevant subjects might be able to offer some insight. A big part of the cost and risk associated with space launches is the rocketry. As we know if the payload increases the amount of required fuel increases which increases the payload and so on.. Would it be possible to drill a circular hole in to the earths crust several kilometres deep, much like a geothermal well then at the bottom build a massive pressure chamber for the purposes of firing a payload directly up in to space? I would imagine the interior of the circular well would be lined with a kind of super conductive rail to reduce friction and any human passengers would be held inside some sort of inertia dampening gel bubble (now I'm stretching it!). Thoughts? Also wouldn't gravity be stronger the closer you get to the center of the Earth? No it becomes less due to mass overhead. Check out Newton's shell theorem .

Do we really need to bend over when exiting an helicopter? I mean when walking away, not while exiting the hall. I have a helicopter private pilot license so I can probably give you some additional insight. The rule that you mention is just one out of several rules when passengers approach or leave a helicopter with the rotor blades turning. The point here is that no one wants to have their head chopped off by a helicopter, and while the rotors blades should be parallel to the ground and higher than you, it is not always the case for whatever factors (land inclination, wind gusts, human error, etc). There is also things that could be blown out of your head, pieces of clothes, papers, your actual hair if you have long hair, and you need to be careful with those things as well. You should also never run to get an object if it was blown away. The way you approach a helicopter should always be by the front as well, you should never be close to the rear rotor since it will most likely be at your height as well, unlike the main rotor. Most aviation accidents happen because of negligence or human error, and these rules are in place for security and to try to avoid that accidents so they should always be followed.

1. How does Norovirus make your body vomit? 2. How does the virus leave your body? Does it die inside of your body and get expelled through waste? Your digestive tract has its own specialized, semi-independent nervous system, called the "enteric nervous system". (It has more neurons than your spinal cord, and almost as many neurons as are in a cat's brain and body combined!) Its job is to coordinate all the muscle movements that go into making food move from one end to the other...helping push food along with smooth muscle contractions, and also responding to threats like poison (via diarrhea and vomiting). You have specialized cells in your intestines—enterochromatic cells—whose job it is to communicate what's happening in the intestines chemically to the enteric nervous system (and, via the vagus nerve, communicate to the brain itself). Norovirus seems to be masterful at manipulating those enterochromatic cells (probably through chemicals it gets infected cells to release, as the rotovirus does ). First, the norovirus gets the enteric nervous system to slow down sending food from stomach to intestines . This loads the stomach up with extra food (for extra vomit), because the norovirus is spread to new hosts by vomit and feces. It also gives the norovirus time to reproduce, loading up the stomach and intestines with billions of norovirus to spread. Then the norovirus-infected cells ( "tuft" cells, apparently ...I had thought we still didn't have a good idea) release a chemical that tells the enterochromatic cells to tell the nervous systems (brain and enteric) that it's time to vomit. The enteric nervous system is pretty good at coordinating the vomit reflex from there, stimulating all the right muscles with the right timing so everything in your stomach (and all the new, waiting norovirus with it) comes blasting out. Norovirus-infected cells also trick the rest of the intestinal cells to dump their fluids, Infected cells, as they explode and release new copies of norovirus, also release a toxin that communicates to neighboring healthy cells "hey, instead of absorbing tons of water, why not expel all that water instead?" The wave of extra water can't be reabsorbed by the intestine because all the cells are trying to eject their water instead, and so billions more norovirus ride the ensuing poo-tsunami (poonami?) out the back end in search of new victims. This is why you can continue to have diarrhea long after you feel you've run out of food that you ate...the virus has basically turned on a hose inside your body that continues to flush water out long after the intestines are otherwise empty. Obviously the new, healthy, infection-ready copies of the virus leave with your massive quantities of vomit and diarrhea. I assume you mean "where do the dead, defeated noroviruses go after they've lost?" Much the same as your body's response to any other virus invaders...your macrophages are killing them indiscriminately whenever they encounter a norovirus. Your B-cells, once they figure out how to make a norovirus antibody (and only if enough noroviruses have taken root that the macrophages can't keep up) start churning norovirus-antibodies out in large quantities. These antibodies bind to the part of each norovirus that let it hijack cells...once "antibodied", the virus is effectively neutralized and can no longer infect any cells in your body. The antibody also acts as a handshake for any of your T-cells that come across it, as a signal that the T-cell should destroy whatever the antibody is connected to. Your immune T-cells are also on the hunt, destroying some viruses directly, and also destroying any virus-infected cells before they can release more virus. Cells usually signal the T-cells themselves if they are infected, although norovirus is good at finding rare sorts of intestinal cells that don't bother letting the immune system know they're infected, which can help norovirus infections last a lot longer. So with antibodies gumming up new viruses and T-cells rounding up infected cells and old viruses, pretty soon your immune system is gumming/destroying noroviruses faster than they can make new ones. Eventually every norovirus is either gummed up with an antibody and destroyed by a T-cell, or just destroyed by a T-cell, or destroyed by a macrophage. The remaining debris is either washed out the gut, or eaten by clean-up macrophages on patrol.

Why is the severity of the urge to urinate not always correlated with the subsequent volume of urine? I have noticed throughout my life that at times the urge to urinate can be quite severe, yet when I finally am able to relieve myself the volume urine expelled can be relatively small. However, other times the urge may be less severe yet the subsequent urine production be voluminous. What are the factors that influence the severity of the urge to urinate? Is it more than simply the volume of urine in the bladder? The neurobiology/physiology of micturition is very complex. The Wikipedia article overly simplifies. Certainly mechanical factors of volume and pressure play a large role, and mechanoreceptors do mediate reflexive voiding. However, there are other neurologic subtrates and signaling pathways involved. Firstly, some basic neurobiology of how we pee: The pontine micturition center , AKA Barrington's Nucleus, is the supraspinal region of the brain that is responsible for initiation of urination. This diagram from Nature Neuroscience helps illustrate some of the signalling pathways involved. During bladder filling, the PMC is largely inhibited. One mechanoreceptors reach a certain critical level of stretch, afferent pathways to the PMC activate, leading to activation of the PMC, and increase in parasympathetic tone to the bladder and external urinary sphincter, which in turn leads to voiding. This is reflexive voiding. As we age, we learn to modulate and control reflexive voiding, so that we are able to hold our urine, despite being full. Typical first sensation of bladder fullness is between 150-200 mL, first desire to void between 200-250 mL, strong urge between 250-300 mL, and extreme urge at higher volumes. So, what other factors influence desire to pee? Well, looking first at that illustration from nature, you will notice inputs to the PMC from several other brain regions, notably the periaqueductal gray, but there are also thalamic, hypothalamic, and frontal projections as well. This means emotional cues, fear/arousal, and homeostatic cues can all influence urination and alter the volumes at which we urinate. Beyond neurobiology, there are other receptors within both the bladder mucosa and the detrussor muscle which will influence voiding. There are chemoreceptors within the bladder mucosa which will respond to bladder irritants, most notably within the bladder trigone. This is why people will have urgency when they have a UTI, despite low bladder volumes. Other dietary factors, notably artificial sweeteners, alcohol (beyond its effects on AVP and diuresis), and caffeine, all have direct irritant effect on bladder mucosa. Additionally, the parasympathetic outflow to the bladder is acetylcholine, and the predominant receptors in bladder are M2 and M3. Our medications for overactive bladder, such as oxybutynin or solefenacin, predominantly are anti-muscarinics. Sympathetic outflow to the bladder is norepinephrine. We have less therapies targetted at this arm of the system due to undesirable side effects, but this is why sympathomimetics such as Sudafed will influence urination. Innervation to the bowel also runs via the pudendal and pelvic nerves. This is why bowel conditions like constipation or IBS may also cause or inhibit frequency of voiding. So how does prostate enlargement lead to urgency/frequency/nocturia? These symptoms develop from longstanding bladder outlet obstruction. In response to increased resistance, the bladder hypertrophies, as any muscle will. In turn, you get upregulation of muscarinic receptors, and notably an increase in density of M2 relative to M3. This hypertrophic bladder is both deconditioned, and overly sensitive to parasympathetic stimulation. As such, it will take longer for these symptoms to resolve either with medical or surgical therapy.

Have all of the nuclear detonations on Earth potentially shifted Earth's orbit around the Sun? The answer ranges from to First of all, realize that for a nuclear explosion to have effect on the Earth's position or velocity, it would need to somehow kick up chunks of matter away from the Earth. Otherwise, Newton's laws of motion tell us that if we consider the Earth and its atmosphere as one system, then any internal change of this system cannot change its overall momentum. To put it simply, when you throw a ball away from you, you are pushing on the Earth a tiny, tiny bit, but this change is compensated for by the ball's momentum. As a result, from an external perspective the overall momentum of the Earth doesn't change Nuclear explosions are far larger and messier, but the key idea remains the same. So in other words, to push the Earth, we would need to cause the explosion to propel matter away from us, just like a rocket pushes gases away so it can move forward. In principle we could think of a way to use a nuclear bomb to this effect, where we would explode it right outside the atmosphere so it can push the Earth. But now we have a second problem: the Earth has a huuuuge amount of kinetic energy. The Earth has a mass of 6*10 kg and is flying around the sun at a speed of 30km/s. Now we can work out the total (translational) kinetic energy: E = 1/2 m*v = 1/2 * 6*10 kg * (30,000m/s) = So we get a whopping 3*10 J of kinetic energy. To put that in perspective, the most powerful nuclear bomb ever tested, the Tsar Bomba, had a yield of 2*10 J. In other words, I think it's fair to say that we are pretty safe as it is...

"There is no Dothraki word for 'thank you.'" We're all familiar with the "Culture reflects language" trope in popular culture, but are there linguistic differences to that extent in certain cultures in real life? The trope you're describing isn't the one present in the example. Culture does not reflect language, in real life or in most fiction. The Dothraki are not aggressive and selfish because they lack a concise way to express thanks, they lack a concise way to express thanks because they are aggressive and selfish. This happens all the time in real life. Generally not with appreciation, because there's good reason to think that gratitude is a universal part of human nature, but, yes, when a culture doesn't have a thing, the language doesn't have that thing either. Because how could it? You can't name something that doesn't exist. So, when you have some particular practice that exists in one culture and not another, you get a word in one language and not the other. One example off the top of my head, there is a word that is present in a particular polynesian language, and no other language in the world. It means "a curse upon a name or place, such that speaking it or entering it is bad luck". No other cultures do this, at least not to such a degree, and so no other cultures have a word for it. The word is "tabu". In 1777, Captain Cook visited the island, thought the practice was cool, and brought it home to England, where it caught on and survived as a word for things that are forbidden to speak. This is also an example of how goddamn hard it is to find examples in modern languages that aren't absurdly specific, because of the unlikelihood that people would lack words for basic concepts common to all humankind, and because globalization had a flattening effect: all the cool stuff from every language was borrowed into every other language.

I know Newton believed in absolute time and relative time, I understand why he believed in relative time, but why did he believe in absolute time? What evidence did he have for absolute time? Why did he argue for its existence? Also could you also provide any readings on this if possible Here’s an attempt to begin an answer: from Newton’s : “Absolute, true, and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year.” Relative time, says Newton, is derived by observing motion: so we can measure a day by the earth’s rotation relative to the sun. Absolute time is the underlying physical phenomenon that makes motion possible at all, which is not directly measurable without reference to motion. So by “relative”, it seems Newton means something different to Einstein. Newton assumed that time flows at the same rate for all observers, since he had no reason to assume otherwise given his understanding of the world.

When I look into the sky how large is my field of view? I thought of this question while looking at an airplane. The plane appears to be barely moving obviously the plane is traveling very fast. My estimation is that my field of view on a clear day must be 1000 km First, we should clear up an issue that seems to be causing some confusion. Field of view is most appropriately expressed as an angle, not a distance. This is because we can see very very large objects if they are very very far away (like stars, which are in fact hundreds of times larger than the earth, but appear small because they're so far away). Having said that, Humans have an almost 180 degree field of view in the horizontal direction, and about a 130 degree field of view in the vertical direction ( source ).

What do I hear when the world around me is silent? When there are no children screaming, no cars driving, no air conditioners blowing, when everything is as silent and motionless as is reasonable, what am I hearing? Can I hear things going on inside my head, and, if so, what? First off, you will never be in an environment that isn't permeated by some form of sound. However, when it becomes nearly silent your brain has the ability to cope by tricking you into thinking you are hearing sounds. With every image that you see, your brain registers a sound as well. When you see an event, say an explosion,even in complete silence, your brain will trick you into believing you heard the complimentary noise registered by that image. In this way, yes, you can hear things from inside your own head! More information: http://www.guardian.co.uk/science/blog/2010/may/14/brain-hears-silent-movies

How do cows (and other herbivores) produce protein? Omnivores(like us) and carnivores obviously can easily build muscle by eating meat, beans, nuts, etc... to get their dietary protein and essential amino acids. How do herbivores (that don't eat beans and nuts, such as cows that typically only eat grass) produce the necessary amino acids to build all of their muscle? How are these animals able to synthesize all of the amino acids without relying on other sources, and why are we unable to synthesize the essential amino acids as they can? there are two basic types of amino acids, essential and non-essential. non-essential amino acids can be synthesized essentially from scratch by using various cellular byproducts from various pathways. essential amino acids are amino acids that an organism is not capable of synthesizing by themselves. cows have bacteria in their gut which do most of their amino acid synthesis or cellulose breakdown for them. these bacteria are able to synthesize amino acids from various sources of nitrogen (urea, ammonia, etc), and when each generation dies, the cow digests them and extracts the amino acids from them. having said that, i know that normal cattle on a farm are usually deficient in 2 amino acids: Lysine and Methionine. in a farm, a special type of feed is given to them which contains "protected" versions of those two amino acids. the amino acids are protected because if they were not, the bacteria in the gut would just break them down and make other amino acids from them. regarding cows in the wild, i am unsure as to what exactly they eat, but i imagine it would not be "just grass".

Why can't diabetes type 2 be interpreted as a mechanism of action, instead of a malfunction? Good morning, and please forgive my poor understanding of metabolism. Why can't diabetes type 2 be interpreted as a defense condition, instead of a malfunction? Some chemical threshold has been reached and the immune system decides glucose is a threat and not a primary food, maybe the immune system is just wise. So it wants to prevent sugars from entering the cells. But if new environmental conditions ensue, and the person is starving, the insulin resistance drops, allowing again sugars to feed the cells. This doesn't look like a malfunction, maybe a questionable decision of the immune system, a defense condition. So the solution can't be administering more insulin since the body has enabled measures exactly to prevent insulin from delivering sugar. The solution would be just to stop eating sugars. What am I missing? Thanks in advance. There are multiple theories about type II diabetes. One says that fat is gumming up the works and preventing insulin from having the proper effect on glucose absorption. Another says that is about energy storage; the problem is that glycogen stores are full and that there is no good and quick energy sink for the excess glucose. Intend more towards the latter; if your glycogen stores are full, the only place to put the excess energy is fat. Some people seem to do that well and while they may gain weight, they don't get type II diabetes. Others do it poorly, and may get type II diabetes even while looking thin. I agree that the best solution is to reduce carb intake.

Are there environmental triggers that can "turn on genes" or is evolution purely survival of the fittest and random beneficial mutations? Gene expression and evolution are different but related things. There are plenty of triggers, environmental and otherwise, that can turn on genes. Some of these changes can even affect future generations. For example, children of people who have experienced famine and low caloric intakes during childhood generally pass on a trait to their offspring that increases fat production. This does not require mutations. The study of this is called epigenetics. Evolution is a combination of a lot of factors, including mutations, random selection, epigenetics, and survival of the fittest. Note, not all evolution is a result of "beneficial" mutations. Success is often situational.

Does cork absorb any liquid? I know corks don't absorb water but I purchased a bottle of Crystal Head vodka with the intention of using it as a decanter for my scotch later. My question is if I put my scotch in there will the cork have residual flavor or even residual vodka that could potentially change the taste of my scotch? ( by the way this is a deal breaker because I'm a pretty serious scotch drinker and I don't want my high end stuff to change!) Corks can have surface cracks and open joints especially when left to expand or dry out and can allow leakage through the small gaps in its structure which leaves behind residue from drinks such as wine, which is why cork is generally put in a bottle under pressure. You possibly will get some residual flavour although one would expect the scotch to over power any vodka taste. get a fresh cork.

Why do some people snap better/louder with their non-dominant hand? Me and a few of my friends all noticed that we snap louder with our non-dominant hand. Why does that happen? Is it normal? The snapping sound is caused by your middle finger hitting your ring finger. If you haven't practiced this with your hand your middle finger will hit your palm and make a much quiter noise. However I don't know why you would only be able to do this with one hand and not the other.

Strange behavior in squirrels [X-post from r/biology] My office and I recently noticed some odd behavior from the squirrels outside our window. They started picking the leaves off the trees and dropping to the ground. We noticed it on a Thursday afternoon, and this morning on Monday, they are still at it. Leaves are getting all over the landscaping and the . Can someone please explain what they are doing? Depending on where you are and what species are endemic, I assume this is nesting behavior. Squirrels generally give birth one-two times a year - usually once in spring and maybe once again in late fall. They might be gathering leaves for a nest. Edit: Actually, no, I think it really is leaf nest building. Keep on the lookout for the nests in a few weeks.

Why binary logic in computers? I am currently perusing a degree in computer engineering and I have yet to hear a solid explanation of why binary logic is used inside computers. After making several integrated circuits, I can see why it would be considered easier to work with binary, and how it is more cost efficient since the reduction that can be done with Boolean algebra, but what exactly is preventing us from having more than 2 stable forms of logic? I am not looking for the answer, "because it can either be on or off, 0v or 5v" since it is not true as far as my knowledge. In communication, a signal element can be assigned by voltage, such as 0v is 00, 2v is 01, 4v is 10 and 5v is 11. So in communication, we can have more than 2 states by using something as simple as a potentiometer. You can indeed work in bases that are not binary - ethernet seems to have 5 voltage levels and various buses easily work on logic that is ternary/tristate (pulled-up, pulled-down and floating) or quaternary if you want to make an obscure joke (pulled-up, pulled-down, floating, on fire). The fundamental issue is so: Consider any system for encoding numbers that is based on summing over a something that looks like a geometric series but with various coefficients: a0 b + a1 b + a2 b ... Now, b = 1 is a bit of a special case. It is a unary representation system. It has some severe shortcomings in that the size of the representation of a number grows linearly with the actual size of a number. Writing out 1 million in unary is a thousand times longer than writing out 1000. As you can imagine, it quickly become unfeasible to perform any practical computation using this number system although it is still used extensively in the field of logic and theoretical computer science. For example, see the http://en.wikipedia.org/wiki/Church_encoding of numbers of a rather deep understanding of what "counting" or "numbers" means within the context of computing and why using unary representations is really the only way to go in that context. Now for all the other numbers where b > 1. b = 2 is binary. b = 10 is decimal etc. etc. If you work the math a bit, you can show that for all b > 1, your encoding grows logarithmically with respect to the size of the actual number you are encoding. Now, you can see that the size of the encoding of 1000000 is only as much longer with respect to the size of the encoding of 1000 as the size of 1000 is with respect to the size of 1. For increasing a number by a factor of b, you increase it's encoded length by one unit. You can also see that for any 2 bases b1 and b2, their respective encoded lengths are only off by a factor of b1/b2 i.e. all bases b > 1 are equivalent in terms of representation except for a constant. You may have realized by now that all I was doing was giving you a round about explanation for why log_b x = (log_a x) * (log_b a). It may have given you a more intuitive understanding for this identity. As since computer science tends to deal with the more theoretic and basic aspects of computing in general, we tend to use the simplest structures that get the job done. If base 2 is equivalent to base 10, then why waste time defining complex operations that have to deal with 10 different symbols. We can define it for 2 and then generalize it for 10. It's the same reason why you're taught binary trees first and not ternary trees (they exist) or n-ary trees (they're called tries). Any operation you learn on binary trees (push-down, percolate-up, zig, zag, rebalance etc.) can be generalized to some sensible operation of an n-ary tree. It just makes it superfluous to start with a more complicated structure when a simple one works just as well. Computer science is all about teaching you how to use a certain set of tools and getting you comfortable with combining and repeatedly applying those tools to various problems your encounter. In the interest of making those tools easy to use, we always tend to use the simplest possible representation of a given tool that still conveys all the core ideas without hurting understanding. Edit: Oh and a PS: If you take more upper level theoretical CS courses (as opposed to CE - they are different; I hold degrees in both of them), you may have the opportunity to take a course on the foundations of logic. This very question will be handled quite thoroughly in such a course. You may encounter various different logics and encodings with various different rules that you may consider as "mere intellectual wankery" but that produce surprisingly different results within their various frameworks. You'll encounter http://en.wikipedia.org/wiki/Intuitionistic_logic , http://en.wikipedia.org/wiki/Classical_logic , http://en.wikipedia.org/wiki/Substructural_logic (such as linear logic), various encodings of computation itself in terms of lambda calculus, simply typed lambda calculus, http://en.wikipedia.org/wiki/System_F , Turing machines, regular expressions, http://en.wikipedia.org/wiki/Pushdown_automaton etc. You'll also encounter the wonderful theorems from Church and Godel that put various rather inconvenient inequalities over the capabilities of these various systems. It was at the end of such a course that I truly appreciated how amazingly complex the simple act of being able to add two numbers was and why we use the various common encoding schemes that we do.

Are parasites microflora, microfauna, flora, or fauna? Does it vary for each species? I think I covered it? I will elaborate if necessary. "Parasite" is a role that one organism plays in relation to another. Organisms of all the kingdoms can play a parasitic role toward an organism of any kingdom as well. For example, a plant may be a parasite to other plants ; an animal may be parasitic toward a plant (sap-sucking insects for example) or toward animals (blood-sucking insects). It can pretty much go in any direction; but, normally the parasite is much smaller than the host -- otherwise, it's just predation. In parasitism, the host organism continues to live. : TIL: isn't parasitic toward the , but toward the fungi that are mutualistic to the plant.

When it is quoted that we share '96% of our DNA' with chimpanzees or '99%' of our DNA with other humans, what exactly do they mean? I have a pretty good background in genetics, so feel free to be relatively complex. My question, more specifically, is are they talking about gene loci, individual nucleic acids or alleles. For example: If we have the same Gene, but my Allele is ATAT T and your allele is ATAT T do we share 5/6 (83%) same genetic material, 0% (because our alleles are different), or 100% because we have the same gene. Thanks! The percentage refers to the amount of nucleotide sequence divergence since a shared common ancestor. For the human and chimp genomes, the divergence is in Single Nucleotide Polymorphisms (one base substituted for another base, as in your example) is 1.23 % Source When two ore more genomes are aligned, the algorithms are making assumptions about homology between the two sequences: http://en.wikipedia.org/wiki/Homology_(biology)#Sequence_homology Typically, when nucleotide homology cannot be unambigously determined, it is removed from the analysis. Confusion can arise from mutations that are not substitutions, but are insertions or deletions of genetic material. This brings the total amount of divergence between humans and chimps to about 4% (30 million nucleotide differences and 90 million bases worth of insertions/deletions) Source . Similarity can also be measured a different way-- in genome organization. We have 23 pairs of chromosomes and chimps have 24 pairs. By matching up long stretches of chromosome, we can see how the genomes have been shuffled around in the last 3-4 million years.

How come when I take a shower/bathe in plus-100 degree water it is enjoyable, but not plus-100 weather? Top comment is actually atrocious and does not explain anything at all. Showers heat you up more than they cool you down, and the reason they feel good is because your personal body temperature is low enough that you enjoy the sensation. I assure you that if you spend enough time in a hot shower, you will stop enjoying it, or the shower simply isn't hot enough. The same is true of a hot day, if you are cold, because you've been say, locked in a freezer, and you go outside into 105 degree heat, you'll be loving it until your body doesn't want to heat up anymore. Now it becomes complicated because your body's sense of hot and cold is subjective, and is based on personal experience of hot and cold extremes and average experienced temperatures, so what seems hot or cold will shift as you change climates, of if you go through a spell of locking yourself in freezers or spend lots of time in a sauna. Ultimately though, your body is looking out for itself, and if you absorb heat in a way where there is a net gain, it will feel good if your body is a bit low on heat, and will feel bad when your body becomes heat saturated. This can happen outside, in a shower or in a sauna. When you are outside in 100 degree heat, you are often already heat saturated, and your body is looking for ways to drop heat, but sweating is not very effective at that temperature, so your body transmits displeasure in an attempt to encourage you to find a different condition which is less hot.

Is this BBC video (concerning CO2 and the Greenhouse effect) slightly misguided? Firstly, I accept the theory of AGW and understand the basic mechanisms behind the Greenhouse effect. Here's the video that prompted my question: (Summary for those unable to view, the demonstrator has two lamps, two thermometers and two jars. One jar contains "Earth's Air" the other contains "Air + more CO2". She shines the light on each of them and the jar with CO2 is hotter after a certain period of time.) Now, obviously the greenhouse effect is playing a role. , CO2 has a lower specific heat capacity than air. As there is no mention of how much CO2 is in Jar 2 (and I'd be willing to bet it is a few orders of magnitude higher than 350 ppm) is there any way to attribute the warmer temperature solely to the Greenhouse effect and not just to CO2's lower specific heat capacity? Additionally, would a better experiment be heating the two jars to the same temperature and seeing which one cooled quicker? (Would the CO2 (despite its lower heat capacity) still cool slower...) (My hypothesis is that the slightly lower heat capacity does have an effect but not enough to change the outcome by it's lonesome. But I guess my point in writing all this is that I would like someone to reassure me?) Thank you for reading. :) I have my doubts about this demonstration, but instead of talking about those I'll try to address your questions about it. First, what's being tested is the absorptivity of CO2. If you want to think in terms of specific heat, you have to compare Cv, not Cp. CO2 has a higher specific heat per mol than air. That's why CO2 causes a greenhouse effect in the atmosphere. I'm pretty sure this is your main point of confusion. As for your thought experiment, the CO2 container will cool faster. Objects emissivities are equal to their absorptivities, by Kirchhoff's Law. Since CO2 is more absorptive it is also more emissive.

How will my donated platelets be used? Just a few questions about my platelet donation. Most of the materials I could find referred only to whole blood donation. I had a scheduled donation of platelets at my local Red Cross donor center today. I am a 24 year-old male, 173cm, 70kg, type A+. I was told that I needed a platelet measurement of over 100 to donate at all, and the test on my blood had shown 355. I was hooked up to an apheresis machine for a hour and a half, and they took "three units" of platelets out, which more or less filled a large IV bag (maybe 500mL) and was approximately 1 trillion platelets total. I was told I would "save three lives" with my donation. What are the likely units on that platelet count? My count apparently isn't pathologically high, so how high would it have to be before it's be troublesome? What proportion of my platelets did I just donate, and how much more freely would I bleed if injured now? What sort of patients will receive my platelets (other than hemophiliacs, I guess)? Are they usually given via IV, like I conceive of whole blood transfusions? Is it likely to actually go to three different patients, or possibly to just one who really needs them? You actually wouldn't use platelets for hemophiliacs, since their defect is in Factor VIII of the clotting cascade. Platelet transfusions are important for people with thrombocytopenia (literally, platelet deficiency), which can be the result of pathologies like immune thrombopenic purpura, thrombotic thrombopenic purpura, or disseminated intravascular coagulation. All of these processes use up the patient's platelets, leaving them deficient. Thrombocytopenia can also occur with defects in production (such as from myelodysplastic disorders where the bone marrow fails to produce platelets). For hemophiliacs, you would actually give them desmopressin to increase endogenous Factor VIII levels or concentrated Factor VIII precipitates to directly add to their coagulation factor levels. The range on normal platelet levels is rather large - ~140k-390k/uL. You also don't really get any problems until your levels drop below ~50k/uL. Each 'dose' of platelets generally increases the patient's count by 30k/uL. Platelets can be given as single-donor infusions by IV, or be mixed with a couple of random donors. I hope this answered your questions, and good for you for donating!

How much meaningful data (words) can the average person memorize and be able to perfectly recall at will indefinitely? Say I wanted to memorize a random book, or 5 books, or 20 books, but then I wanted to be able to perfectly recall, or orally recite, the information I have memorized at will. Is there an upper bounds to the amount of information the average person can memorize in this manner and keep it all straight within the context of each source? From my own experience with memorizing various long passages of text, I have to periodically "refresh" myself to maintain the integrity of what I have memorized. This is usually accomplished through simple recitation to myself from memory. I am just curious how much I can realistically memorize. It's limited by number of words to be memorized and number of words need to be recited in a day. Let say you can memorize X words each day. But you also need to recite it at different time interval. Assume you need to recite a word in 1 day after, then 2 days after, then 4, 8, 16 up to 1024 days after (everyone may have different patterns). With this pattern, you will need to recite a word 11 times in order to recall it indefinitely. Turning it around, in average, every day you will need to recite (1+1/2+1/4+1/8+...1/1024)* X words or 2X words. Overall, you have X words to memorize and 2X words to recite in a day. It's up to the person how large the X is and reserve more time to recite if needed.

What is the root cause of certain language speakers not being able to use certain sounds of other languages? The example that made me think of this: Asian language speakers often have problems with the 'R' sound from English. I understand that this can be overcome, but my question relates to the root cause of this inability to vocalize the sound in language without practice. Does this stem from those speakers not having trained their muscles or brain to create this sound (in essence, just needing practice to make them), or is it that they need to teach themselves how to about this sound being part of language. To simplify, can a Chinese language speaker make the 'R' sound while imitating a low dog growl but not in language because of how they think about language, or is the 'R' sound itself mechanically difficult to do? Not sure if this helps... But basically language acquisition works in young children by acquiring different phenomes. A child who grows up speaking Korean will learn different phenomes than a child who grows up speaking English. So I guess in a way it can have to do with practise -- you're just not exposed to the phenomes or sounds throughout your life (specifically childhood which is when language acquisition occurs the most rapidly -- children can pick up new languages much easier than adults). It's kind of like when someone is trying to get you to say something in a different/foreign language. You you're saying it right, and they insist you are still saying it wrong. This is because you can't discriminate between the different phenomes in the foreign language, since you never learned them. Going back to your example -- Chinese people may lot have been exposed to the R sound which is what makes it difficult for them to pronounce that particular sound; they lack the skill since they never learned it. It is definitely possible to learn that sound, it will just take time and practise, especially in adults. Similarly, English speakers can have difficulty pronouncing certain words or sounds in other languages simply because they were not exposed to those phenomes as a child, when the brain is very plastic (which is why children can acquire language and vocabulary at such a fast pace -- the brain is still wiring itself at this time and has higher plasticity than a developed adult, or even adolescent, brain)

Why does it seem like cancer always attacks specific places, i.e. prostate, breast, colon, etc? Can you ever just have a random tumor like on your arm or something? Cancer is the uncontrolled and unlimited division of cells which is why we cant stop aging because we would just be cancer balls Actually, all of us have been cancer-free for 4 billion years of glorious cell division! And through our germ cells, most of us will continue forward for thousands or millions more to come. :) (I understand your point, I just like this optimistic perspective.)

How large could a rocky planet get? I know gas giants have a maximum size before they turn into a star, but do rocky planets have a maximum size before they destroy themselves or otherwise no longer act as a planet? It all really depends on your definition of a rocky planet. Or a rock for that matter. Athleticon93 is right for normally formed planets. Any planet getting really big as just a rocky planet is going to accrete lots of gas too and become a gas giant. But if we want to a really big rocky planet, physics won't stop us for a while Start with a chunk of rock floating around in space. Let's say we borrowed mars for a bit. Don't worry, the solar system won't ask for it back. Now toss a rock down onto it. You have a bigger rocky planet. Keep doing that for a bit. The planet gets bigger and bigger. Surface gravity increases, and for now, the density of material at the core stays the same (ish). Things start to fork at this point though, depending on the thought experiment. First off, just dropping the rocks is going to be a problem. Dumping planetfulls of rocks onto an ever larger planet makes heat. A of heat, which will liquefy, and eventually boil our rocks. This will also drive out any volatiles in the rock; gasses, bound water, sulfur, etc. Pretty much anything that isn't iron or nickel or another high boiling element or very stable compound. For example, limestone, a common rock, will happily decompose to CO2 and CaO. Now our ball of rocks is surrounded by an ever thickening atmosphere of gasses. Whoops, we made a gas giant. So lets start again, but instead we'll teleport our rocks down to the surface. Compaction will produce some heat, but not enough to boil our rocks. The planet could get quite big (somewhere around 3-4 times the radius of the earth), but eventually the compressive forces of gravity will be enough to start severely compressing even solid material. The density of the core will go way up. You'll notice you're adding hundreds of cubic kilometres of stuff and your planet is only growing by tens of cubic kilometers. This is going to make a lot of heat. If our rocks have a fair bit of lighter elements in them (pretty much anything higher on the periodic table than iron), eventually somewhere around 60 times the mass of Jupiter the heat and pressure will be too much and our "rocky planet" will ignite into a very weird star Let's start again, again. We can't use rocks anymore, but we can use iron. Iron is at least a solid, and we can imagine running around on it pretty similarly to a regular planet. Get a big ball of iron and start the teleportation machine again with chunks of iron instead of rocks. Again, you'll see the planet grow, but after a certain point, roughly 2.5 times the radius of the earth, and several hundred times the mass, adding more mass will actually cause the radius to shrink. The iron planet will also be getting very very hot (tens of thousands of kelvin). What's happening is that the additional matter is causing increased gravity, and your planet is no longer being supported by the everyday pressure of electrostatics, like what keeps your feet from compressing a concrete floor. Instead the core is now dominated by electron degeneracy pressure. It's acting like a very hot, ultra dense gas. As you add more iron, you create more gravity. More gravity makes more pressure, more degenerate matter, and a smaller radius. Your "planet" is now a white dwarf. If you let it cool off for a few trillion years you'd be left with a ball of iron that, if you could walk around in about a hundred thousand g's of gravity, you could walk on and would be (sorta, kinda) like a planet. And that's as big as you can make a planet.

What happens to oxygen (gasses in general) that get lost into the vacuum of space? Could (theoretically) we pump oxygen in space to create breathable pockets? Gravity. You need something to "anchor" that gas locally, and only gravity can do that. To have enough gravity, you need a big enough lump of something. That's basically a planet. TLDR: You need a planet to keep the gas from wandering off into space. EDIT: Otherwise the gas cloud just keeps expanding.

Why are the physical electromagnetic fields only the real part of E and B? says that the physical fields are only the real part of E and B, but this is not obvious to me. Since e = cos(x) + i sin(x) We get an imaginary part of the fields in the picture, but somehow these aren't actually a part of the fields, or how should i interpret i? Maxwell's equations are linear. So if and are solutions, so are their real and imaginary parts separately. Writing and in complex exponential form just makes the math easier since exponential are easier to deal with than sine and cosine individually.

Is hydraulic fracturing and shale gas really harmful to the environment? How would it compare to other energy sources including all steps from extraction to consumption? I would link the EPA article but I'm on my phone. Extensive studies have tested the process and find it safe when the proper protocols are followed.

Say there was a pot of water that was heated to 150 degrees fahrenheit, and another pot's water temperature measured 50 degrees fahrenheit, if both were placed in an environment that held a steady 100 degree fahrenheit temperature, which would reach the 100 degrees faster? The pots are the same size, and the water amount is the same. The numbers are essentially arbitrary, and the unit of temperature isn't relevant. The question I'm trying to get across is - if two items were placed in an environment, and one item were just as much hotter than the other was cold, which one reach the base temperature of the environment first? Feel free to correct me on, inquire about, or even dismantle my inquiry; all I ask for is closure. Thank you, This is true if the only heat transfer is sensible heat (proportional to the temperature difference). However, if the pots were open to the air there is also the factor of latent heat of evaporation. The heat loss due to evaporation would be in addition to the heat loss due to temperature difference (delta-T) so the hot water would reach 100° more quickly.

Is there a better measure than expected value for bets that you can only make once? My girlfriend was badgering me to buy a bingo card in a $1000 bingo game once. The cards were $10. I told her we could do it if it looked like less than 100 people showed, because I figured the expected value of the card would be more than the cost under that condition. I realized that we only got to make this bet once, and I think that expected value is the average value the cards approach as you play the game an infinite number of times (right? it's been a while since I took stat). Assuming 98 other people showed up, despite expecting a profit, there was still a 98/99 chance that I'd simply be out $10. Is there another measure that's more appropriate for that situation? It would account for (1) you can only play the game once and (2) the potential profit? So, the distinction here is that expected value is the only statistic that matters if you're allowed to play the game an infinite number of times (i.e., you have an infinite bankroll or can go arbitrarily deep into debt). A related concept (for dealing with a finite bankroll, and either limited or unlimited plays) is a random walk . Assuming 98 other people showed up, despite expecting a profit, there was still a 98/99 chance that I'd simply be out $10. This is almost the definition of a risk-return tradeoff , and is a central problem in investing. Essentially, there are often investment opportunities (potentially including bingo tickets) that have a high expected return, but also a high chance of failure (i.e., losing everything). What level of risk you're willing to tolerate in an investment for a given return depends on a number of factors. If you're interested in understanding these trade-offs, you should read some books on investing. In this particular situation though, there's a major factor you haven't accounted for- that many people at bingo play multiple cards simultaneously. Even if only 50 people showed up, there could easily be several hundred bingo cards in play, making the risk-vs-return question a moot point.