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Does the moon cause tides in the mantle of the Earth similar to the tides it causes in the ocean? Actually, it is estimated that the earth internal heat was 3% the effect of the friction caused by the moon pulling the mantle over the years. This has caused the moon to lose it's orbital height slightly and you can make some estimates of the early times of the moon based on model and calculation of the earth internal geology although this is not very accurate.

Muscle memory and brain injuries Does muscle memory remain after any brain injury/trauma where there is memory loss? For example, a weight lifter ends up with a brain injury and is not able to train for a few months, and also ends up with some memory loss that might or might not be about his weight lifting. Does the muscle memory still remain or will the lifter have to start from scratch? Muscle memory is actually stored in both the basal ganglia and the cerebellum, the cerebellum is a part of the brain dedicated to motor control. The basal ganglia is a much deeper structure in the brain and is responsible for a lot more then movement; including cognition and emotion. Losing the ability you train for is called detraining and is a crucial part of athletic performance. When an athlete follows a programme, in the off season they will dedicate time to train for new abilities and the in season training is supposed to preserve these abilities. Different abilities such as endurance or strength are lost at different speeds. So to answer your question; yes the weightlifter would have to start from scratch as they would have lost the strength, speed and also would be less accustomed to the stress that exercise places on the body.

If the earth rotated on a horizontal axis like Uranus would it make much difference to life on earth? Edit: For anyone who doesn't know about the rotational axis of Uranus and what this question is about, see this . The seasons would be very extreme. Basically the polar circles would be at the equator, and all seasonal effects now only happening at polar regions would affect the whole globe to some degree. All of Europe and United States for example would experience several months of polar night in a year, meaning that the Sun does not rise at all. Obviously this would affect temperatures greatly. The opposite then happens in the summer, the Sun would stay above the horizon throughout the day. Both of these effects would also be much stronger than they are now. Now in the polar regions the Sun might stay above the horizon through the day but it is still very low all that time so the temperature doesn't get very high. With the axis of Earth tilted 90 degrees, the Sun would stay almost directly overhead for months at a time at the polar regions, there would be hardly any change between a day and a night. Basically you have a time period lasting months which is equivalent to the midday of current equatorial regions. I won't speculate what exactly this would have done to the evolution of everything but the change in seasonal variation is so extreme that certainly it would have had some kind of an effect.

Could or do steam power plants close to coastlines double as desalination plants? They can't use salt water in the boilers or turbines. Regular tap water is not even good enough. Steam power plants use incredibly pure water (the contaminants are measured in the low ppm). This water is heated in excess of 600 Degrees and many of the contaminants found in un-purified water would react with and corrode the boiler and turbines. So yes the water that is boiled would probably be quite drinkable. however because it needs to be pure to be used in the turbines, it would be far too expensive to use it as drinking water. The plants that do desalination use the steam, after it has exited the turbine, to heat and boil seawater to desalinate it. The ultra pure turbine water is recycled and fed back into the boiler. EDIT: Wikipedia link about Thermal power stations and their water and boilers

Statistically speaking, is there any Isaac Newton in my bowl of porridge? Was pondering this thought with a colleague. Is there any chance any of his molecules are in my breakfast? There will be about 10 million atoms of Isaac Newton in every ounce of your soup. The same is true for any other person who ever lived. You are what you eat. I mean that in a very literal sense too; your body uses the food you eat to build tissue and it uses the water you drink to subsist. By this logic, Newton wasn't just one 150 lb chunk of meat walking around, but he was constantly replenishing and replacing atoms in his body. Basically, the longer you live, the more 'stuff' that has been a part of you over the course of your life. The atoms in baby Newton are probably long since gone in the frail oldman Newton, so again, the longer you live, the greater your lifetime total of atoms that were once apart of you. Assume Isaac Newton consumed about 1 kg of matter every day of his life. This would be some mixture of different elements, but it's mostly water, so let's just work with that. This wouldn't be a bad assumption either, as water makes up more than 50% of the food-mass in your average diet. Since water has an atomic mass of 18 (two A=1 hydrogen, one A=16 oxygen), we'll say that about 55 moles of water passed through Newton every day of his life. This works out to a little more than 10 water molecules per day. Newton was 84 when he died, so let's say that about 10 molecules of water passed through him over the course of his life. How does this compare to the total number of water molecules on earth? Wikipedia tells me the water content of the earth is about 1,338,000,000 km - which gives me a total of about 10 water molecules on earth. If we assume that the matter that Isaac Newton consumed in his life has been well distributed back into the environment through the water cycle, then we can calculate the number of Newton's atoms that are in a given mass will be given by: (No. Newton Molecules in your soup) = (No. Atoms in your Soup) x (No. Newton Molecules) / (No. Total Water Molecules on Earth) Since that last fraction is about 10 , that roughly tells us that any collection of more than 10 water molecules has pretty good odds of containing some atoms from Newton, and it turns out that these are good odds. It means that for every of water that you have, about 10 million atoms in it must have passed through Isaac Newton. Of course, there's nothing unique here about Isaac Newton- this math is true for pretty much every person that has ever lived. There's only so much water in the world, and we've been re-drinking it for as long as we've been around, so statistically, in the average glass of water, you've got a taste of the overwhelming majority of humans who have ever lived. You've got Einstein, Alexander the Great, and even a little bit of Hitler, all mixed together with the atoms of billions more. Also dinosaurs, but let's not get into that.

If a predator had an endless supply of prey, would they get fat? So theoretically speaking, if a predator has access to an unlimited supply of prey, which take minimal effort to catch and eat, would that predator typically just continue eating as much of that prey as possible and subsequently get fatter, or would there be a reason for the predator to regulate its hunting/ eating as to not get fat? It depends on the predator. Some animals will stop eating when they are full. Most large animals will consume enough food today that they can go tomorrow without food. There is a limit to how many days food they are willing to store. Some predators are also prey and they have to maintain the ability to run. In the case of humans, I think that there is too much research on what tastes good and food companies have figured out how to sell us more than we should eat.

When integrating a linear reciprocal function that can be factorised, should you factorise the function before integrating? This might be a stupid question, however I have noticed that when integrating a linear reciprocal function which can be factorised, you get different results depending on whether you factorise it or not. For example, if you integrate 1/(3x + 9) without factorising, you get 1/3ln(3x + 9) + C However, if you factorise 1/(3x + 9) first and integrate 1/(3(x + 3)), you get 1/3ln(x + 3) + C My question is, should you factorise a linear reciprocal fuction before integrating it? I thought that maybe the constant of integration would account for the difference, however I can't see how that would work for definite integrals. Sorry if I'm being an idiot. I thought that maybe the constant of integration would account for the difference, This is correct. ln(3x + 9) = ln(3(x+3)) = ln(3) + ln(x+3), so the difference is the constant ln(3). however I can't see how that would work for definite integrals Constants of integration never affect definite integrals. If F(x) = G(x) + C, then F(b) - F(a) = (G(b) + C) - (G(a) + C) = G(b) - G(a).

Why is it bad if air bubbles get into your bloodstream? The heart muscle contracts and pushes blood forward. The air will travel through your circulatory system until it gets to your heart. Because air can be compressed much more than liquids can, the heart squeezes the air but it just pushes the air molecules closer together instead of pushing the air forward, meaning blood is no longer flowing. Your blood is not being oxygenated and your organs starve.

I can keep my eyes active while closed, to a slideshow of 5 crazy morphing images/second. What's going on? I can do this too! It's usually scary monster faces that merge and morph randomly every second or two. I thought I was the only one!

Does an interferometer add or multiply together signals? Is it either? I'm studying honours physics right now and have to get an understanding of interferometers, specifically in the context of astronomy and interferometer telescope arrays. However, I'm having some trouble as we only covered the basics of interferometers in undergrad. We went over stuff like the Michelson-Morley experiment and obviously did wave interference, but not as much in terms of modern application. It seems to me that devices where multiple light beams are sent to interfere directly, and then detected, are called interferometers. This makes sense to me as you are using the interference of the two signals to measure something or to filter noise. But, in the notes I have for my project, the basic example of an interferometer array made of two telescope dishes looking at some source has the signal correlation be a multiplication instead. I understand that this would also show you where the signals correlate, and would cancel out some random noise that is specific to one of the telescopes. But this doesn't really seem like it is interference. Or am I just doing wrong something really basic to do with interference? Thanks. There are a couple things that you could be referring to: 1) There are a number of trig identities that turn adding two trig functions into multiplying two trig functions. One that you may have seen in class is the beat frequency: Add two waves with similar frequencies, and it becomes one wave with the mean frequency, multiplied by sin(Deltaf*t) 2) Cross correlation function multiplies one signal by a time shifted version of another, then integrating, with the largest value indicating the actual time difference.

AskScience AMA Series: I'm David Pogue, tech and science writer, and host of NOVA PBS' new series Beyond the Elements. AMA! A former weekly tech columnist from 2000 to 2013, I'm a five-time Emmy winner for my stories on , a bestselling author, a five-time TED speaker, and host of 20 science specials on PBS. My most recent special is a mini-series called " ," a sequel to my 2012 documentary " ," which has become a staple in science classrooms worldwide. The new show's three one-hour episodes take me on a worldwide quest for the key molecules and chemical reactions that make up human civilization, including concrete and fertilizer, plastic and rubber, fire and venom, explosives and hot peppers. I've written or cowritten more than 120 books, including dozens in the Missing Manual tech series, which I created in 1999; six books in the line (including , , , and ); two novels (one for middle-schoolers); my three bestselling books of tips and shortcuts (on , , and ); my how-to guides and ; and my 620-page magnum opus, . After graduating summa cum laude from Yale in 1985 with a distinction in music, I spent 10 years conducting and arranging Broadway musicals in New York. I won a Loeb Award for journalism, two Webby awards, and an honorary doctorate in music. I live in Connecticut and San Francisco with my wife Nicki and our blended brood of five spectacular children. For a complete list of my columns and videos, and to sign up to get them by email, visit . On Twitter, I'm ; on the web, I'm at . I welcome civil email exchanges at , and of course, AMA! I'll be on at noon (ET; 16 UT), AMA! Username: David Pogue! I used to love your tech reviews. Feels like a long time ago, when the internet was a different place. I see you continue to be insanely prolific. I'll check out some of these links. Question? What's your favourite element?

Are solar panels in hotter places more efficient than solar panels in other, cooler temperatures? By hotter places, I mean surface level temperature and the temperature you see on the weather Does it even make a difference ? If so by how much? The technically correct answer is that lower temperatures are more efficient, the thermal coefficient is about -0.4%/⁰K, see PV panel datasheet example (pdf) , however, that colder temperature usually means the sun is lower in the sky, losing energy due to air mass . Find locations of interest on https://pvwatts.nrel.gov/ and compare the "AC Energy (kWh)" on the last page.

Reddit, my bedroom is directly above my kitchen. Every time someone switches on the microwave, my internet freezes for whatever the duration of the time set. Why is it doing this, and how can I stop this happening? Interference. You can stop it by using a hard-wired connection instead of wireless. Failing that, reposition your wireless access point or your microwave.

Ask Anything Wednesday - Engineering, Mathematics, Computer Science Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away! In the future do we think they might be able to delete memories? I’m thinking brain mapping technology. EMDR, neuroplasticity but using computers to actually reprogram us, rewire us. PTSD and survivors. Too sci-fi or an actual possibility?

Will the push to cloud services eventually lead to bandwidth saturation? I remember hearing a few years back that there was barely enough bandwidth to keep up with the mobile devices in existence, this was ~5 years ago. Of course, I believe it was offered as a defense against criticism of Comcast pricing, so take it for what its worth. But, reductum ad absurdum- will moore's law eventually be unable to keep up if we move ALL services, software, and data storage to the cloud? I think it will, thats why I'm sticking with my desktop, linux, and local music and move storage. I don't think the cloud is the future and everyone will eventually be back to the desktop. Mobile devices are subject to frequency limitations; there are only so many channels to transmit on and once they are in use you are at capacity. This can be combatted with shorter range coverage, which we already see in the use of WiFi. Many locations within the range of one cell tower can reuse the same WiFi channels because they are too far away to interfere with each other. Wired cloud devices are safe because more machines with more wires have no intrinsic choke point of interference with each other.

What is it about copper that gives it anti-microbial properties? Why does bacteria die when it comes in contact with it? Copper produces hydrogen peroxide and oxygen radicals via the Fenton reaction. Lipid peroxidation in the bacterial outer membrane ensues, eventually leading to a loss of membrane integrity and cell lysis. A recent paper reported 10 cells being killed in less than 3 hrs.

A question on herbivores, protein and evolution. Two questions, actually: 1) How do herbivores 'get' the necessary protein (and other dietary necessities for animals) without eating other animals? Have they evolved some method of coping with not eating meat in ways that humans and other omnivores have not? 2) What are the evolutionary advantages of having to hunt and kill your food? Why would any animals have evolved to be carnivores? Thanks! 1) Plants have protein. Plenty of humans eat only plants and don't suffer from protein deficiencies. 2) Other animals are the most dense source of food energy around, so if you can catch and eat another animal without spending too much energy in the process, it's a pretty good way to spend your time. Herbivores spend a lot of time eating to stay fed. Carnivores spend a lot of time sitting around, comparatively.

What FOV do humans have (like in video games)? Can it very from person to person? The field of view is close to 180 degrees. But the resolution are the extreme edges is very low, only able to detect motion. Most of our field of view has low resolution, a human eye only has around one megapixel. Nearly all of that is concentrated in a tiny area in the centre of our field of view, about the width of your finger when your arm is outstretched.

Is there any functional difference between a capacitor and a rechargeable battery? The hell are you talking about? That's not just crude, that is completely and utterly wrong, and is absolutely not a good way to visualize anything! Capacitors absolutely don't create some "pulsation", although they are frequently used to pulsation coming from rectifiers.

Since the event at CERN that proved the existence of Higgs bosons/Higgs field, can we now see this event happen regularly now we know ‘where’ to look? It doesn't quite work that way. There never was a single event at CERN that proved the existence of the Higgs. What happened was, they announced a few years ago, and detailed in subsequent paper, a statistical analysis of the decay products detected after countless collision and deduced the existence of a subatomic particle with all the attributes of the Higgs. From the way the physics is done today, there isn't really a place we can look and say "There it is! That's the Higgs!" The evidence is always indirect. At these large particle accelerators, beams of protons are directed into each other, resulting in collisions that produce a shower of short-lived subatomic particles that are observed and recorded. The volume of data from these experiments are huge. After tedious and painstaking analysis, a statistical spread of what was detected is examined and may or may not show something that matches the predicted properties of a particular particle.

Which 'light' does photosynthesis use exactly? Ultraviolet? Been searching but most sources say it uses 'sunlight' or 'light energy'. I want to know exactly which kind of light it is. Can you technically shine a UV lamp onto a plant and promote photosynthesis? Chlorophyll a absorbs most strongly red light, while chlorophyll b absorbs blue light most strongly. The light that's left over is green light which is why plants look green. Check this out for more detail: http://hyperphysics.phy-astr.gsu.edu/hbase/biology/ligabs.html

How can extra dimensions be 'small' in string theory? And how do these additional dimensions enable string theory? Think of a cylinder, the direction "around" is always at right angles to "along". Now imagine that the cylinder is very (or infinitely) long but has a small diameter

Does biking uphill require more energy than running uphill? Naive analysis: If we assume that the two modes of transportation have no energy losses, then we just compare the change in energy between the initial and final states. Assuming you are stationary at the start and end, the relevant energy is the gravitational potential energy E = mgh. Walking, you only have lifted your weight (say 85 kg). Cycling, you have brought your bicycle as well (say 15 kg). So cycling would appear to require more energy. Better analysis: However this answer is probably wrong because cycling and walking are not equally efficient. Cycling requires about half the energy per unit distance as walking on flat land. Suppose the hill road is 1km long and rises by 100m. Cycling a 15kg bike, you would expend about 110 kJ (using wikipedia's numbers) against air resistance and friction, and ~ 100 kJ against gravity (approximating g as 10). An 85kg person walking would expend about 220 kJ against friction and ~ 85 kJ against gravity. In this example (100m rise over 1km distance), cycling is probably more energy efficient -- a savings of 95 kJ. A steeper rise or heavier bike makes the difference smaller. Note you probably will feel more tired cycling, because cycling probably goes up the hill more than twice as fast as walking, and therefore requires a higher power input. In this example a cyclist (16 km/h) has an average power input of ~ 1kW, while a walker (4 km/h) has an average power input of ~ 340 W.

How do planets lose their atmosphere? Can earth lose its atmosphere? How long would it take? To start you off see Wikipedia: Atmospheric Escape . Given that Earth is pretty massive and that the atmosphere is shielded by Earth's magnetosphere, the Earth doesn't undergo appreciable atmospheric escape and thus won't lose its atmosphere in the lifetime of the solar system.

How did all the gases in the Earth develop if it formed out of gas clouds of hydrogen? I know that the Sun developed from nebula of hydrogen and helium and the planets formed out of gases that surrounded the Sun by accretion. I also know that before oxygen started liberating from the ocean there was an atmosphere of ammonia, water vapor, carbon dioxide etc. How did all these gases form? The earth itself didn’t form from hydrogen. First generation stars form out of the light elements first, burn bright and hot and relatively fast, making heavier elements in its core. When one goes nova, it spews out heavier elements like carbon and iron, from which second generation stars (like our sun) are formed. They burn smaller and denser and cooler. During the formation, the spinning matter forms an accretion disk, which eventually gives rise to planets. So the earth, everything in it, and everything on it, including you and I, were formed in the crucible of a giant star’s core billions of years ago. As Carl Segan said: you’re made out of Star Stuff.

Why do mitochondria have their own separate 'mitochondrial DNA'? Do other cells or organelles have their own separate DNA? Is it some relic of the very distant past? It is in fact a relic of the past. Early in the history of life, we believe the eukaryotic ancestor enveloped an aerobic bacterium, but rather than digesting it, it lived within the cell. Eventually, the eukaryote and the bacterium would exchange genetic material, and the two would become interdependent on one another. This is what we call endosymbiotic theory. And there is predicted to be 2 primary events (mitochondria from aerobic bacteria, and chloroplasts from cyanobacteria), and 3 secondary events (green algae and their chloroplasts being taken up by other eukaryotes). You can recognize these events through a few characteristics: extranuclear, circular genomes, independent reproductive cycles, and multiple membranes.

Noah's Ark Thread REMOVED So is this an appropriate place to ask that this subreddit be removed from the default home page? EDIT: Hey guys lets move the meta-discussion here where it's more productive. Thanks

Why can a rocket fly straight up without wings and doesn't tip over? Large commercial rockets are actively steered. Either the engines are 'gimbaled' (the angle is adjusted) constantly, or small sideways-pointed rockets are fired as needed, to push the rocket where the computer is programmed to send it. Smaller rockets without adjustable engines or controls normally cause the rocket to spin as it flies, so any off-angle forces are canceled out. Doing this without fins is tricky, which is why smaller rockets generally do have fins.

How much, if at all, does a human skull grow during adulthood? Thank you for the rude response. Also, please see the sidebar: "Please keep discussion: Civil On topic Scientific (i.e. based on repeatable analysis published in a peer reviewed journal)"

How does your immune system directly help with the digestion of food? Aren't enzymes specific to one purpose? I always thought that enzymes were made for one specific function and that certain enzymes were made to break down a certain kind of carbohydrate or fat or whatever you're digesting. Then I read and got all confused. A nutritionist recently told my father that by eating a bag of sun chips, given that it is not a natural food (natural carbs, fats etc), it is not broken down by the digestive system but by the immune system. The implication is that by involving the immune system and the digestive system it takes away some energy of the body when running. (He is a marathon runner). She also told him that milk is broken down by the immune system. Hence, milk is not a good food. Is this true at all? The idea of your digestive system appropriating enzymes from your immune system is completely false. Enzymes used by the immune system are produced and used in the cells that make them, they don't go to a central depository that gets shared out.

If alien observers detect the earth through the Transit Photometry method, would it be possible for them to realize earth is inhabited due to our artificial lights? The limitations and capabilities of astronomic measurements are highly speculative? The signal-noise-ratio of transit detection is speculation? Light occlusion methods such as those already used to detect exoplanets( http://www.eso.org/public/news/eso1024/ ) are speculative future tech of which no one know the limitations of? Are the only questions that are allowed here those whose answer can be found on simple.wikipedia?

How much heat does the moon redirect to earth? For an average distance between the moon and the earth. Is the amount of energy transfer phase dependent? Is it proportional to the level of light received? Doing the math it's about 107 GW. That sounds like a lot, but that's for the whole Earth. For comparison, the Earth gets about 174 PW from the sun directly, which is about 1.6 million times more. Also it does depend on the phase. What I just gave is average. During a full moon you'd get double that, and during a new moon you'd get none. Edit: Come to think of it, the albedo doesn't matter. That just changes whether it's reflected radiation or blackbody radiation we're getting. It still emits just as much as we absorb. Although our greenhouse gases will reflect more of the infrared light. Ignoring the albedo, it's 891 GW , and it's a 196,000th of what we get to the sun. Also, someone else brought up solar eclipses, which would block more light than the moon would reflect back. It reflects back based on how much of the sky it fills, but it blocks light with a probability from how much of the zodiac it fills, since that's the part of the sky that the sun and moon travel through.

Yoga: Are the benefits of yoga scientifically proven? If yes, how did the inventors of yoga make up the asanas and know their benefits? Penn and Teller did an episode of Bullshit on yoga. They claim that all of what is modernly known today as 'yoga' in America was invented very recently (I think the 60's) and just artificially tied to ancient stuff to give it credence. Is stretching, strength training using your own body weight, and regular exercise good for you? You bet! Body and mind are known to improve from these conditions. Edit - claims require evidence. I don't have to prove yoga isn't magic. Yoga advocates (including instructors of yoga classes I personally attended) do not merely argue yoga is a good exercise/meditation practice. They claim the asanas and other positions are somehow an enhanced way of doing things. That the breathing and 'finding your center' within these stretches opens up your mind beyond normal self- or guided-meditation and exercise. If you want to argue that yoga is more than just an analogous exercise routine, that requires evidence.

A couple of questions about memory. Why do I often recall completely insignificant memories? For instance, I have this memory of when I was a kid, going grocery shopping with my mom, and I happened to run into this other kid with whom I went to school and was only moderately friendly. It was a completely uneventful occurrence, yet it pops into my head a lot. That brings me to my second question: How does the brain decide what information should be stored as a short-term memory versus a long-term memory? Using my previous example, why is that any more important than remembering what I ate for dinner last Tuesday (which I can't)? Memory works by associations. It's really difficult to make any 100% definitive statements here, but this is most likely what happened: Odds are you were surprised to see your neighbor. Surprise at seeing your neighbor (especially if you haven't seen other people you know at the grocery store often before) triggered dopamine release. Yeah, yeah, dopamine is the pleasure neurotransmitter and all that, but it does other things, too. Especially relating to novel or unanticipated events. (One of the reasons why people like trying new things is, not coincidentally, dopamine.) Dopamine is great at helping form memories (if you're looking to learn more about this, type dopamine + ltp into your favorite science search engine). Thus, you formed a memory of a seemingly uninteresting event. Your second question is much more interesting. This is a very, very hotly debated topic in the literature. The generally agreed upon idea is that the more connections a memory has (that is, the more things you associate it with), the more easily recalled it is, and the older a memory is, the more stable it is. A couple candidate proteins play some role in induction of memory formation (CREB, CaMKII) and stabilization (PKMzeta), but at this point, we really have no idea of the specifics of how they work. Pretty much every other Nature Reviews Neuroscience has a review article on this, but I can't find a good open access one to link to at the moment. The view I'm most fond of is that long term and short term memories are the same (long term differing by more PKMz expression and being somewhat more interconnected with other memories leading to easier recall). However, I am not an expert on this subject, and therefore am not to be trusted under any circumstances. One final slightly unrelated bit - no matter how old your memory, every time it is recalled, it needs to be re-encoded (a process requiring protein synthesis) or it will be lost. Stuff like a simple bump on the head (hard enough to knock you out) can destroy not only your short term memories, but any long-term memories you recently recalled (in the last ~2 hours).

Would spraying blood-spatter at a crime scene with ammonia (like in Boondock Saints) really ruin any DNA evidence? I've also heard the same mentioned about bleach; would that work as well? Given modern molecular techniques, I don't think the aforementioned Boondock Saints scene would be as accurate as it may have been back then. There are now DNA extraction kits that are specifically designed for old, contaminated, or mishandles samples. These "forensic kits" have several wash stages that remove chemicals such as ethanol and ammonia, resulting in fairly decent readings. I've used them in the past to extract DNA from ~125 year old moths who had been subjected to some harsh chemical treatments. We were able to get useful DNA out of it.

If sea turtles return to their birth beach, how do the species ever spread to new areas? Every article I can find on sea turtles shows that female sea turtles return to the beach where they were born to lay eggs, most likely through sensing location via the Earth's magnetic field. Yet sea turtles are found the world over, so how do some female turtles find new beaches? This review gives a good overview of the genetic structure of populations of all 7 sea turtle species. Some key relevant points: 1) The natal hypothesis of female nest site choice is supported in populations which overlap in overall territory but not in nesting location or genetic markers (see figure 1). However, natal homing is not infallible, as the authors put it: Among the thousands of female sea turtles tagged on the beach, a tiny percentage are observed nesting far outside the range of their previous nesting site (e.g. LeBuff 1974), and mtDNA surveys also indicate occasional nest-site shifts (Reece et al. 2005). These ‘gravid waifs’ are probably essential to the prosperity of sea turtles, as absolute natal homing, over the 100-million-year history of this group, would be a strategy for extinction. 2) Juvenile sea turtles form large feeding groups, but don't necessarily stay located offshore of the beach where they were hatched (see figure 2). It's possible that females which don't return to their own hatch site migrate with their feeding group. 3) Migration plays a major role in all 7 species, and each species has an ideal habitat, but there is lots of overlap and hybridization, as well as significant gene flow within species (see figure 3). During migration, water flow and temperature can impact destination, quoting again: Ridleys and loggerhead ( ) also show more recent colonization between ocean basins, probably mediated by warm-water gyres that occasionally traverse the frigid upwelling zone in southern Africa.

Do the calories in fruit increase as they ripen? No, not exactly. Fruits tend to taste sweeter as they ripen because ripening is a form of decomposition. The polysaccharides in fruit that represent the energy stored begin to break down into smaller molecules that are easier for our body to break down into glucose meaning less time is needed to digest the fruit. No calories are added or lost and digestion is a mostly passive process so no extra energy is needed or saved.

How do you prove that time is a dimension? One of my friends doesn't believe that time is the 4th dimension and I haven't been able to prove him wrong and need some help. Tell him there's a great party you'd like him to join you at, at your friend Bob's. When he asks you when the party is, respond by pointing out that if time isn't a dimension then that question is meaningless.

Are fighter aircraft noticeably "weighed-down" by their armaments? Say a fighter pilot gets into a combat situation, and they end up dropping all their missiles/bombs/etc, how does that affect the performance of the aircraft? Can the jet fly faster or maneuver better without their loaded weaponry? Can a pilot actually "feel" a difference while flying? I guess I'm just interested in payload dynamics as it applies to fighter jets. It's a huge difference. The weight changes the stress on the airframe, and if external the ordnance produces lots of extra drag. For example, a f/a 18 is rated for +7.5g and -3g maneuvers when light, but at full weight only +4.8g and -1.8g. Here are some study cards for an f/a 18: https://quizlet.com/13297122/fa-18-limts-and-prohibited-maneuvers-flash-cards/

How does altitude (atmospheric pressure) influences our hearing? Does the difference in atmospheric pressure make a noticeable difference to how we perceive sounds? Assuming the back of your eardrum is the same pressure as the atmospheric pressure (ie, your ears don't need to be popped), then no, the pressure difference doesn't really have an effect on your hearing. This is, of course, assuming that you are at a reasonable pressure where the air is still breathable (not in the vacuum of space). If there is a pressure difference, however, it will effect your hearing, because your eardrum will be pushed away from its equilibrium position where it's most sensitive.

What is uncertainty principle and what is it's significance? You want to see an electron. What do you do to see that? You shoot some photons aka light on it to 'see' it and this causes the electron to get more unstable and hence it becomes impossible to track down its original "position". Hence, the uncertainty. This is what is given in our science textbooks. It seems like it is dumbed down to it's basics. Can someone please give a more elaborate yet easy to understand explanation of the uncertainty principle and explain it's significance in physics? The uncertainty principle is a mathematical consequence of the way that position and momentum are related in quantum mechanics. Here is a slightly more accurate (but still handwavy) picture: A particle with a definite momentum has a definite (de Broglie) wavelength. Something with a definite wavelength essentially has to look like a sine wave (via the Fourier transform, if you're curious.) But a sine wave looks basically the same at all spatial positions, so there's no information about the particle is. On the other hand, if you know exactly where the particle is, you have no real way of assigning it a wavelength (since there aren't two points to measure between) and therefore you don't know its momentum. The mathematical formula that expresses this is: (uncertainty in position) * (uncertainty in momentum) >= hbar / 2 where hbar is the reduced Planck constant, which is (kind of) a measure of "how quantum" the real world is.

What does the band of muscle at the back of the head do? I've been looking at the muscle anatomy of the head and I'm confused. There's a band of muscle at the back of the head in between the ears and I don't know what it does. The area surrounding it seems to be mainly composed of tendons so I'm not sure why this muscle is there. Does anyone know? I assume you're referring to the occipital belly. Some believe that the occipital belly, at the back of the skull, and the occipitofrontalis muscle, at the front of the skull, are essentially the same muscle, but others classify them as two separate muscles. As far as I know, the occipital belly muscle helps move the scalp back and that's about it, so it could be part of the muscular system that helps us create facial expressions (since pulling down on the back of the scalp would also move the front of the scalp)

How do scientists determine the gravitational pull of exoplanets? Whether or not we know the gravitational pull of an exoplanet depends on how we detect it. For most exoplanets, the best we can get is an estimate of size by observing how much of a star's light is blocked when the planet passes in front of it. But without knowing the planet's density, we can't know its mass, which is what we need to figure out its gravity. The primary method we have for determining the mass of an exoplanet is the radial velocity method. When we observe stars, there are dark absorption lines (from various atoms) in their spectra. We know where these lines are supposed to be. If a star is moving toward or away from us, then light coming from the star will be squeezed or stretched respectively by the Doppler effect, which shifts the positions of the spectral lines. If we notice that a star's lines move back and forth very regularly, we can infer that it is being nudged by another object in orbit of it. If we can't see another object and the star is only being nudged a little bit, then it's probably an exoplanet. The duration of this cycle is the exoplanet's year. The maximum shift in a line corresponds to the star's speed. These two pieces of information tell us what effect gravity is having on the system, from which we can estimate the mass of the whole system (star+planet). If we already know the mass of the star (estimated based on its spectral type, say), then the difference is the mass of the planet.

How can light be both a wave length and particles? If you think weird, how about electrons? They're both waves and particles too. On one level -- "it just is". On another... It boils down to something in the philosophy of science, called . It turns out that the concepts of "particle" or "wave", convenient as they are for learning, don't really correspond with actual categories of thing that are found in the real world. The common example of a mismatched category is the imaginary colors "bleen" and "grue" - say, bleen things might appear blue on odd-numbered days and green on even-numbered days, or vice versa. You can describe the world of color perfectly adequately in terms of those colors, but it would be more awkward than using the familiar ones you're used to. That's because most things aren't really bleen or grue by that definition, so you might say "The sky is bleen on odd numbered days, but grue on even numbered days, how can it change colors like that so routinely?". The concepts of particle and wave are sort of like the colors bleen and grue -- they don't match, exactly, with how the Universe itself behaves, so objects in the Universe (like light) have some of the characteristics of each.

PHYSICS: Are there events between atomic or subatomic particles where the collision is not perfectly inelastic? Are there events between atomic or subatomic particles where the collision is not perfectly inelastic? This may be a silly question but my searches haven't given me a satisfying answer. Thanks! Also I'm new to posting on AskScience and couldn't figure out how to apply a field to the question. Sorry. Edit: nvm Honestly, I'm not sure I've ever heard "perfectly inelastic" be used to describe a collision that was not macroscopic. A perfectly inelastic collision means that the maximum amount of kinetic energy is removed from the system by the collision. In the case of colliding rubber balls, this means the balls stick together when they collide. Some energy is used up deforming the rubber, some energy is lost to heat, etc. If you collide two hydrogen atoms though, you can get an inelastic collision because some of the kinetic energy the hydrogen atoms had can be used to excite electrons. In some sense, two hydrogen atoms can collide and stick together as a hydrogen molecule, but the process of forming the molecule releases energy, so this doesn't fit the definition of a perfectly inelastic collision either. So I believe every collision between atomic/subatomic particles can be classified as elastic or inelastic (but not perfectly inelastic). You get elastic collisions between particles with no internal energy levels (electrons, photons, etc.), and you can get inelastic collisions between particles that have energy levels that can be excited by the collision (atoms, nuclei, protons, etc.). Elastic collisions are also possible with the latter set of particles. Because inelastic collisions probe the energy levels of the particles, they can be used to probe the internal structure of these particles. For example, inelastic collisions were used to figure out that protons were actually composed of quarks. Sorry for the long-winded answer. Let me know if you still have any questions.

Does synesthesia hamper the sense it manifests in? Say you have a synesthesia where you see the letter A as red. You are shown a paper with a yellow A and a blue A. Can you tell that the letters are of different ink colors? Is it as easy and quick as compared to one with no synesthesia? Do you expererience both colors, only semantic or only visual or do you experience a blend or mix of them? I can always see what color letters are printed in. Like as I'm typing this, my words are clearly white. Usually the colors I see from synesthesia manifest as a translucent highlight around the word or the color would feel like it's encasing my brain. (Wonderful description, I know.) If letters or words are printed in a color that doesn't match up with my brain colors, it'll make me feel nauseous because the colors are oh so very wrong in my brain. I also won't be able to "see" my brain colors that well. The association is still there, but it would feel like my brain colors and the color actually on paper are fighting.

How can I calculate the weight of a cubic meter of fat? I understand that there are different fats, I have no further knowledge of the type of fat... how can I roughly calculate the weight per kg / Tonne / cubicmeter? Thanks for any help, I don't know where to start on this one... Weight per kg is exactly one kilogram. Weight per metric ton is exactly 1000 kg. The cubic meter is the only challenge. Here's what I found: http://www.aqua-calc.com/page/density-table/substance/animal-blank-fat-coma-and-blank-bacon-blank-grease According to this, the answer is 870 kg for bacon grease type fat.

Is there a reason why we can't invent a device to objective measure pain level? I imagine if there was a device that could actually tell you how much pain someone is in, that would have a world changing effect on everything we know. Is there a reason why this is not feasible? What are the limitations to creating such a device? Pain can't even be defined, let alone measured. Seriously, try to define pain! In the end it doesn't really matter because pain is a subjective experience. It doesn't matter what caused the pain, only how much you are in and that's pretty well measured by asking the patient 'on a scale of 1-10, 1 being no pain and 10 being the worst pain imaginable'.

Are telescope images of objects such as galaxies that are hundreds or thousands of light years across, are they distorted? My thought process is that if you look at a galaxy from an angle that would put one end of the galaxy dozens if not hundreds of light years closer to us than the furthest end, would that mean that we are looking at a distorted image? They are, but only by an imperceptibly small amount. Stars in the outer edge of a Galaxy will be moving at about 200 km/s. Their light takes about 100,000 years to cross the galaxy. So in that time stars on the far side will have moved about 70 light years, so ~1/1000th of the entire galaxy's size.

Why does a television's signal strength increase while I'm touching the antenna? It's happened on numerous occasions and I was curious as to why it happens. I also wanted to know how to emulate this without having to touch it to keep the signal strong. By touching the antenna, you are effectively increasing the size of the antenna. And while bigger isn't always better, this does allow TV signals to be picked up more clearly in some cases. (It could just as easily make it worse, but how often are you touching the antenna when the signal is good?) You could try extending the antenna with an unwound metal coat hanger, which may help. Or get cable.

Why is there a very high-pitched sound coming from my CRT television? What is making it? Not sure if this falls under Physics or Engineering. The frequency that the CRT puts out is a direct function of the refresh rate of the screen and the number of scan lines on the screen. If you take 29.97 (the refresh rate of an NTSC signal) * 525 (the vertical resolution of an NTSC signal) = 15734, which is the frequency of the tone produced by the TV. Source. http://en.wikipedia.org/wiki/Cathode_ray_tube#High-frequency_audible_noise

How come similar latitudes north and south don't experience the same climate? Base on it seems like southern hemisphere locations which are equidistant from the equator are not as cold as their northern counterparts. What causes this? There are influences on climate besides latitude. At the gross scale and for this observation, the primary reason is the relative proportion of a given latitude that is land vs ocean, where the southern hemisphere has more ocean on average. Continental climates generally have larger temperature ranges than the climate over large bodies of open water, i.e., the ocean.

When and how did we learn the position of the planets in the solar system? For example in what year did we found that Jupiter is the 5th planet from the Sun? How did we learn that Saturn was similar in size but even further and in the 6th position? Although I'd like to encourage more history of science questions here, I'm not sure how many answers you might get. If you don't get an answer, you can also try /r/askhistorians , /r/historyofscience , or /r/philosophyofscience

Does putting Vitamin E lotion on your skin actually do anything? I did a pubmed search for articles with "topical vitamin E" in the title. There is a paper that showed that it reduced UVB (but not UVA) skin damage in swine skin, when combined with a commercial sunscreen, compared to the sunscreen alone. Other than that, studies looking at potential benefits for surgical scars, doxorubicin-induced oral mucositis, and something called "yellow nail syndrome" have all been negative.

I have a keen interest in martial arts but want to know how is this possible? What's the trick? Can anyone here explain what is happening here? [Sorry its a video link] (Oh hey, something on AskScience I'm actually qualified to talk about!) I trained martial arts in China for two years in my early twenties. I lived as the only foreigner in a school amongst a bunch of super hardcore dudes, some of whom were part of the school's performance troupe. I've seen a 15 year old boy, no more than 120lbs, do the spear-in-the-neck trick. I also saw a slight, 16 year old girl get the sticks broken on her limbs and torso. I saw numerous exhibitions of "unusual feats of strength and skill" which were almost always attributed to qi/chi. In every single case there was always something that seemed off -- I'd played around with card tricks before so was very attuned to acts of misdirection and such. I went there having watched videos like the one linked, thinking that there was a possibility some of this stuff was real. I came back home being quite certain it was all bullshit. The people doing these things are in insanely good shape. They usually train 30-50 hours a week, and most of the guys who get to the exhibition level start when they're 4-7 years old. They are hard as fucking rocks, but I assure you they have no magical powers-- if anyone here had trained 40 hours a week for 15 years from a young age, you'd most likely be able to do some of the same things. Others have gone over why the physics of what's shown in this video don't necessarily kill someone-- as long as they're in good enough shape. I got a chance to see behind the curtain while I was there-- while these sort of guys are training. They practice those little "qi" embellishment movements in the mirror, and have coaches pick apart their grunting technique. I don't want to devalue the incredible physical abilities of them-- it was truly awe inspiring to see what that much dedication can do for/to the human body, but when it comes to these demonstrations, it's just as much about showmanship as physical abilities. Rather than thinking of these people as 'spiritual warriors', just think of them as circus performers, and it begins to make a bit more sense. As for the actual qi thing, everything I was taught, and everything I saw, I can fairly confidently say that "concentrating your qi" is merely an analogy for concentrating your attention to your lower abdomen area (and visualizing any movements that involve your core) while expanding your diaphragm extremely hard. PS - While I'm at it, let's go over this whole 'Shaolin' thing. Shaolin was an abandoned temple until movies made it popular in the 1980's, then it became a huge industry. Most of the original style was lost when the temples were destroyed and outlawed during the Great Leap Forward . Now, there are something like 180 schools in the town surrounding the old temple, with ~100,000 students; the largest school has over 30,000 students alone. The higher-ups in the Shaolin temple are not monks, they're businessmen with shaved heads and robes. They have fancy pads and pricey cars, know nothing of the martial arts, and don't ascribe to any of the religious tenets-- I got to eat dinner with one of them once-- he had two prostitutes with him, ate meat, and drank heavily. The next day I saw him with two different prostitutes. It's all marketing. Huge business.

How much larger would Earth's diameter have to be before life would be affected by being that distance closer to the sun? The habitable zone for our solar system, for an Earth-like planet, is approximately 0.99AU to 1.688AU according to the study done by Kopparapu et al. 2013 . If we take the lower limit and expand such that we're 0.01AU closer to the Sun, that would make Earth's radius increase from 6371 km to 1,502,349 km. Note the radius of Jupiter is 69,911 km, and the radius of the Sun is 695,500 km, so this scenario is ridiculously unphysical. edit - words

COMPUTERS: When you take an image off of one machine, and apply it to another (using ~Acronis) How similar are the machines/OS's/HDD's on a low level? We use it at my company and we are interested! Disk imaging software typically does a byte by byte copy of the original disk, so the HDD should be near identical after copying a disk image. Granted there will be small differences -- e.g., one HDD may have different number of platters, etc and map stuff to different locations. Also if you use an old hard disk there may be certain sector/blocks that are no longer used (e.g., checksums were failing in that block so the hard disk controller stopped using them) and writes elsewhere instead. Similarly, there may be underlying differences in the technology (e.g., SSD drive at a low level is quite different than HDD).

Will the Covid vaccine go to people that have caught Covid already? Since the vaccine just gives your body a little piece (mRNA) of the virus would catching the actual virus do the same thing for your body? Making people that have caught Covid and survived immune to the virus since their body has already dealt with the virus and knows what to look for. I remember around June - July that nobody was sure if you became immune once you caught Covid. but with this vaccine and how it works, it would make sense that you would be immune after catching covid. So with that, has anyone heard of "Covid survivors" getting the vaccine? Or am I wrong in thinking you'd be immune after catching Covid? We don’t know how long natural immunity to COVID (that is, immunity after natural infection with wild virus) lasts, and probably the answer is something like “between three months and thirty years, depending”. Several studies have found long-lasting immunity following clinical cases of COVID, but there are also a handful of cases of repeat infections. The bottom line is that natural immunity probably So though there’s no official guideline yet, it’s been suggested that (for now) COVID survivors not get the vaccine for 90 days after they recover, given that vaccine is in short supply. After 90 days, they would be put in the same priority baskets as everyone else. Over the next few months we will probably get a better idea of what proportion of recovered patients are immune for various lengths of time, and decide if 90 days is the right period or not. And as vaccines become more available, there will be less concern over sparing it and recovered people will be put in the standard lineups. The A.C.I.P., which makes recommendations to the Centers for Disease Control and Prevention about vaccine distribution, said at a meeting on Wednesday that people who had not been infected should get priority over those who contracted the virus in the past 90 days. “At some point we’ll need to figure out whether 90 days is the right number,” Dr. Maldonado said. But for now, “people who have evidence of infection recently should probably not be vaccinated at first in line because there’s so little vaccine available.” — ‘Natural Immunity’ From Covid Is Not Safer Than a Vaccine

Do all stars have the same photospheric composition? I googled this question and only received vaguely related articles and blog posts. I would assume the photospheric composition of a star changes whit the different stages of a stars life cycle (O to M classes) but I would like to know for sure rather than accept false information. For a main sequence star, the outer layer generally remains constant until it reaches the red giant phase. Red Dwarfs would steadily grow in helium as convection currents mix their core with the outer layers. If the star is between .4 and 4 solar masses, the star will undergo a set of thermal pulses where it ejects large portions of its atmosphere, this will certainty change its composition. After this point it will retain a core of carbon, oxygen, and neon and will become a white dwarf.

Evolutionary advantages of viruses? I'm currently watching BBC Horizon - Are We Still Evolving and they are discussing viruses. A virus is effective at producing copies of itself and thus pass on it's gene via evolution. The thing that troubles me is fatal viruses. If fatal virus kill their host, there is technically a point when viruses will run out of hosts before it learns to jump to a new species. Would that not make it a disadvantage to be a fatal disease? Of course there is a complex interplay between viruses evolving possible host species as well as hosts evolving defense mechanisms, but it seems that if a one species, fatal virus existed, it would spread rapidly killing the host species and killing the virus itself due to lack of hosts. Is the interplay so complex that the death and defense of each species balance each other out? Won't one organism eventually lose given enough time or does evolution work too fast to have this happen? On one hand is a virus that infects and goes to a high serum titer (uncountable zillions of copied viruses in the blood, semen, gut, mucous, and tissues) causes enormous systemic symptoms and sheds everywhere through diarrhea, vomit, coughing, etc. This virus will spread fast and very likely impair or kill the hosts it infects. On the other is a virus that infects slowly and subtly over years with only a sparse presence in tissues and fluids that could lead to its transmission. This virus will spread very slow and likely have far less acute impact on the host's health. Obviously there are "in-between" strategies, but grossly, there is always a balance between these strategies. For every bug's pathophysiology, the infection process optimizes based on selection and descent with modification (like always). Ebola hemorrhagic fever is easily the most terrifying viral infection to me, because it infects quickly, kills quickly, and is virtually impervious to medical therapy (in "The Hot Zone" the author is told the only known cure is to consume an entire bottle of whiskey the night after an exposure). But an Ebola virus epidemic runs its course quickly and then disappears as quickly as it starts. So where does it come from? It comes from bats, probably. And in bats it does not cause hemorrhagic fever. It's quite possible that the Ebolavirus natural history has been one of epidemic spread through primates (or other mammals) then establishing endemic reservoir populations in bats and so on, back and forth throughout its history. HIV infection classically has two phases. First, an acute phase with high viral titer and peak infectivity over the course of days to weeks. This ends once the host's body mounts an effective immune response. Then there's a chronic phase, when the virus kills the hosts immune system and the viral titer slowly creeps up as the immune system impairment continues. As it turns out, HIV has an opportunity to spread during both phases. The first because the titer is so high, the second because its duration is so long.

Where and how did the Spanish flu start, and what caused it to spread so rapidly? I know that ww1 was a major contributor for the spread of it but what else, and I keep finding different theories on what animals caused it, some say horses and some say pigs. So reddit please help me out here. This was posted on Reddit a few months ago and, if iirc, the answer is.... It seems to have begun in a rural area of Kansas. It would've stayed there, for the most part, if not for World War 1. Infected young people went to boot camps and shared the flu. Then most of those people were transferred to other bases, and spread it there. Eventually, the soldiers went to war overseas and the flu was given to our allies AND to our enemies. Whenever anyone went home, the flu tagged along.

Why are planets and moons spherical? I haven't seen any planets that are oddly shapes so far. Similar thing to asteroids, why are they not as perfectly spherical as planets? A sphere is the most compact form of matter So any large lump of matter will tend to form a sphere as gravity pulls everything to the center of mass, packing it as tightly together as possible Slightly smaller masses like most asteroids or smaller moons (Martian moons Phobos and Deimos for example) can still maintain their more random shapes. But if we had the technology to gather up the asteroids and bring them together, the resulting lump would become more and more spherical as we proceeded, no.matter how unevenly we added material.

Why do some of my wife's favorite foods nauseate her now that she's pregnant? I know that this is not uncommon. In my wife's case, she loves barbecue. Pulled pork, brisket, slow smoked, the whole bit. But, now she's pregnant and even thinking about slow cooked pig is enough to get her feeling sick. What's the physiological reason for this? What evolutionary purpose would this serve? From an evolutionary perspective, "morning sickness" is thought to serve a protective function for both the mother and the fetus during early pregnancy. Before we had such luxuries as pasteurization and proper food storage, foods such as meat were more likely to contain parasites and pathogens, and toxins in strong-tasting vegetables, than blander foods. These would be most harmful during early pregnancy, when the basic steps in organogenesis occur (i.e. first ten weeks or so). This is the period of maximum sensitivity to teratogenicity since not only are cells differentiating rapidly, but damage to developing tissues and organs becomes irreparable - exposure to teratogenic agents during this period has the greatest likelihood of causing a structural anomaly. Further, the mothers body during pregnancy is in an immunosuppressed physiologic state, such as to prevent rejection of a fetus that is "half-foreign" tissue by the maternal immune system - creating an immune-privileged environment for ingested pathogens/parasites to infect and spread. Though, if its any comfort to your wife, it usually lets up for many women past the first trimester. And the chances of her getting a parasite from your brisket are slim. Unless you're doing it wrong. In which case, hey survival of the fittest.

Why are self antigens not considered foreign? Antigens are usually thought of as something foreign causing an immune response, then why doesn't our body attack our self antigens. If we have self-antigens that are tolerated, then they aren't really antigens, since they don't cause harm? I'm confused Thank you Something is not an antigen by itself. To a bacterium, its antigens are just proteins that do something. To our immune system, an antigen is something that an antibody binds to, either free floating or on a T-Cells membrane (that‘s how they detect antigens). Self-antigens are just normal (surface) proteins that the immune system responds to in autoimmune diseases, thereby causing all kinds of symptoms. The term doesn’t make a lot of sense without autoimmunity.

Why do babies have a distinct baby smell? Why is it that babies all smell pretty much exactly the same when all adults smell a different kind of foul (without any deodorant/perfume/cologne)? Is it because we load them up with baby powder? I'm sure not all parents do that(but maybe it's hidden in their items, like diapers?), so I can't figure out why they all smell very similar. Basically, I'm asking if there is a biological explanation behind their smell? http://www2.citypaper.com/columns/story.asp?id=2139 It seems men may like it even more than women. As a man, I can say babies do smell great. I can see this helping to change behavior from hunting and mating to taking care of a child. A trait like that could be selected for by evolution in the very care-intensive human child.

Do people with tetrachromacy perceive electronic displays differently? So I've been interested in for a while now, and while fiddling with my monitor settings, a thought occurred to me: The pixels of LED monitors are made up of red, green, and blue LEDs. If someone with tetrachromacy can see a fourth primary color, would trichromatic monitors seem to display the wrong colors to them? For instance, if they took a photograph with a digital camera and then viewed it on the screen, would the colors be "off" from what they see in reality? Yes in theory - a tetrachromat by definition would need four fixed primaries to match an arbitrary target color (like something they see in the world). But as far as the literature is concerned, there's evidence for a single tetrachromat (and it's not perfectly convincing, though that is a cool paper).

Do foods have different caloric values for different animals? Not a full answer to your question, but an example: Humans cannot digest cellulose, the main components of the cell wall in plants. Some animals like Cows however can (with the help of all their stomachs and their microbiome). Thus the nutritional value of plants like grass is vastly different between cows and humans. As for the energy derived from simple sugars like glucose, this will be very similar among all animals, since the machinery and proteins responsible for these processes are virtually identical in closely related species like other vertebrates. Edit: Typo and clarification

There is a video of a man folding a piece of paper with a hydraulic press 7 times. The 7th time seems to essentially break the piece of paper, what happened here? Here is the video I'm referring to. After a quick literature search, the answer appears to be rather boring and straightforward: most likely what happened was the following: 1) Paper is largely made up of a forest of irregular cellulose fibers, as shown here at high magnification . When pressure was first applied, the fibers became compacted together, but their internal structure did not significantly change. 2) A further increase in pressure caused rapid local heating. 3) The heating led to pyrolysis , i.e. a messy series of reactions that we throw together under the umbrella term "decomposition." In the end what was probably left was a mess consisting of fibers in domains with different packing, some plastic-like patches, and bits of what is essentially char. The best source I could find was this paper where they could study how you can try to transform cellulose into a plastic. As the introduction explains: But when heating pulp or paper, the common experience is that they rather reveal incineration than plastification These researchers observed a similar result when they just subjected cellulose to uniaxial pressure (i.e. pressing it on one axis, like in the video). It was only through a careful combination of laser irradiation, pressure, and torque that they managed to transform the fibers into compact glassy disks. link

Please explain what "quantum tunneling" is, and why does it happen. I only know one thing, that companies that make processors like Intel, AMD, Nvidia and others have trouble making processors smaller than a few nanometers (smallest now is about 22nm as far as I know, I personally posses a 32nm one) because at that scale a phenomenon called "quantum tunneling" causes electrons from transistors to jump wildly across the circuit (correct me if I'm wrong). Why does this happen? Take an egg carton and cut off the top. Then put a marble inside one of the dimples. No surprise, the marble will stay there forever because it doesn't have enough energy to jump over the top and into another dimple. Now, shrink everything down to the size of electrons and nuclei. The marble represents the electron and the egg carton represents the potential landscape that the nuclei of atoms set up for the electron to move in. At this tiny scale, a funny effect happens in which the marble can hop into another dimple, ! This is quantum tunneling. Thin film transistors consist of a thin layer of oxide that separates a metal and a semiconductor. The oxide acts as an insulator. As transistors shrink, this oxide layer has to as well. When it gets too thin, the effect of electrons tunneling across the insulator becomes a huge problem. The insulator isn't acting like one anymore.

What exactly is happening when someone uses skin lotion/moisturizer? I guess I’m asking how skin cells interact with the chemicals in the lotion and where those chemicals go once they’re “absorbed”. While the answer depends on several factors (including what's getting applied to the skin, where on the body it's being applied, what vehicle (or topical agent type - think cream, lotion, ointment, foam, etc) is being used, and what the composition/active ingredient(s) are in that vehicle), let's start with the basics and move from there. If we're talking about things applied for the purpose of moisturizing, the goal is less about direct hydration and more about preventing excess water loss. Preventing water loss from the skin is super important: in fact, it's a primary function of the stratum corneum, the topmost layer of skin that is made of protein-rich cells that have lost their nuclei (colloquially referred to as "dead skin cells"). You can think of these cells as the 'bricks' of our skin: holding them together like 'mortar' is a lipid-rich layer full of things like ceramides, sphingolipids, and more. On the daily, we run into tons of stuff that can disrupt either the bricks or the mortar of this layer: dry weather, friction, caustic topicals or agents, skin diseases, you name it. When the barrier's weakened, there's more points through which water can exit this skin. This escape, called 'transepidermal water loss (TEWL)', is ultimately what results in dry skin. By applying moisturizing agents, you're essentially putting an external 'mortar' on the stratum corneum: this decreases TEWL, and helps to 'rehydrate' skin by making sure excess water isn't lost to the environment. As for 'chemical absorption', it all depends on the properties of those chemicals. The rate-limiting step for absorption from the skin is the stratum corneum: if something has a hard time passing through a lipid-rich environment, it's not going to pass through here so easily. Meanwhile, if you're trying to treat a condition that starts deeper down in the skin, having agents that can readily diffuse through the skin's top layers to exert their effect would be ideal. Hope this helps!

why does bar soap lather differently when it's nearly gone? Here is the answer from a soap maker. When soap is made commercially it hardens and crystalizes from the center out. The seed crystal that forms originally for the crystalline structure of the soap to form around it has a different structure and makeup, IE the core of the soap is different than the fatty exterior.

Why do I cough whenever I clean my ears? So, every time I clean my ears with Q-tips, I cough, sometimes rather violently. Sorry if this is a stupid question, but can someone please explain this? More specifically. It's called the Ear-Cough or Arnold Reflex. One of my small contributions to Wikipedia was adding this very subject (self-serving pat on my own back, I know).

"Greenhouse gas levels highest in 3 Million years". Okay… So why were greenhouse gases so high 3 million years ago? Re: Carbon dioxide concentrations in the Earth's atmosphere are on the cusp of reaching 400 parts per million for the first time in 3 million years. The daily CO2 level, measured at the Mauna Loa Observatory in Hawaii, was 399.72 parts per million last Thursday, and a few hourly readings had risen to more than 400 parts per million. ''I wish it weren't true but it looks like the world is going to blow through the 400 ppm level without losing a beat,'' said Ralph Keeling, a geologist with the Scripps Institution of Oceanography in the US, which operates the Hawaiian observatory. ''At this pace we'll hit 450 ppm within a few decades.'' At the risk of spamming this across reddit today (I posted it here in response to another post), the IPCC's Paleoclimate chapter does an excellent job of explaining changes in climate during the past, and their implications for modern climate change: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch6.html From that chapter: Changes in CO2 on these long time scales are thought to be driven by changes in tectonic processes (e.g., volcanic activity source and silicate weathering drawdown; e.g., Ruddiman, 1997).

What gives a steel cable so much more tensile strength than a steel rod? I thought for sure someone would give you the answer. But I saw lots of just dead wrong answers, like a cable doesn't have higher strength than a rod, that it's more flexible, or that it's denser. But tensile strength, which is the same thing as ultimate tensile strength for a wire, is fracture load divided by true area. The question asked why the wire has a higher strength than a rod. The poster didn't mention alloys, so let's assume the rod and the wire are of the same material. (This is not necessarily true, as a wire may very well have higher carbon content and that could be an additional answer. Steel is a material class, there are many kinds of steel commercially available.) The answer is that wire is cold drawn to a much higher extent than a larger diameter rod. Steel is like most metals, in that there is a marked increase in strength when you deform it. Drawing increases the wire's strength, and also reduces its ductility (measured by strain to failure). Materials scientists will explain this by noting that the microstructure of a cold drawn material has smaller and more elongated grains, and therefore dislocations in the metal crystals have a harder time moving, interfere with each other, and get pinned at grain boundaries very quickly.

With the winter in North America being so long and cold this year, have any invasive species expanding northward been set back? E.g. Southern Pine Beetles? I remember reading which stated that there were issues with pine beetles migrating north. I'm wondering if this cold winter has mitigated the problem, and whether there are any other cases of invasive species whose impacts may have been temporarily mitigated by the cold. A couple of studies have concluded the cold weather has put a serious knock down, but not eradication, the emerald ash borer and asian murmurated stinkbugs http://www.washingtonpost.com/national/health-science/winters-freeze-stopped-ash-borers-and-stink-bugs-cold-but-theyre-primed-for-a-comeback/2014/03/02/93a7fe8a-9fbb-11e3-9ba6-800d1192d08b_story.html

Why has early detection of diseases via dogs not found widespread use in medicine? I have heard how dogs can detect diseases such as cancer or now covid with a surprisingly high accuracy. However I have not seen widespread use of dogs in such a manner. Consistency issues. In some cases, researchers don't know exactly what chemical compounds the dogs are detecting. That remains a hurdle for training better sniffer dogs but also for designing better detection devices. Competition with AI detection devices. Robots are pretty good at this stuff too, plus they work 24/7 and can usually do high-throughput. Difficult to move dogs around - easy to move tiny vials of samples. Standard clinical or pre-clinical testing is very robust and efficient. Compare to that it's more difficult to collect/store/analyze samples of breath, sweat, smelly socks or whatever the dogs are smelling. Trained service dogs cost anywhere from $20k-$50k each. Sometimes higher still. For them to work, a patient needs to visit a clinic that owns a dog or present a dog with a sample. There will be a limit to number of patients per day, per dog. That means cost per test gets very high. Reject dogs and test-on-demand. Ethical questions are breeding dogs do tasks like this. Usually a lot of dogs fail training, and then what? OR how long per day can the dog do tests before it gets fatigued. False positives and false negatives. Skepticism remains high in medical community. Historically, everything is moving to robots and controlled lab testing. Moving back to animals seems like an odd quirk that will quickly be replaced by an AI sensor.

If I'm standing in a completely red room that has a white light source, will a green ball appear black to my eyes? So from my understanding, the reason a red object appears red to us is that it absorbs all visible light frequencies except for red, which it reflects. This goes for all pigments/light combinations. For the sake of this question, lets say that the green ball has no direct line to the white light source, so that all the light hitting the green ball has to bounce off of something red first, thus becoming "red filtered." I suspect that the green ball will still appear green. What am I missing here? Human vision takes a lot illumination into account when deducing color. That is if a lamp is yellow it doesn't that much make you change your opinion on the color of the objects it illuminates. There is a neat optical illusion picture where a object projects a shadow on a chess board. If you compare pixel by pixel the black square in light and the white square in shadow are the exact same color. However for human experience that is different enough that for most it would not cross their mind that they are the same color. This is a psychological effect rather than a physical one. If you entered such a room there would not be any difference for the ball to actually be black than actually be green. It would also be the same thing to just have the walls glow red without any white light source. However if you for example first see it with direct white to green contact which is later broken your brain is smart enough that it realises that the situation is still consistent with the ball remaining green and because color changers are the exception rather than the rule its a decent guess that its still green (or its a better guess than that it suddenly turned black).

How does time near the speed of light work for two different frames of reference? Ok, so I know the classic example of an astronaut leaving earth traveling at near the speed of light and then returning to find that time has passed much quicker on earth than in his speedy spaceship. However, in my astronomy textbook it says that if there are two bodies moving relative to each other and each body had its own clock, both clocks would appear to be ticking slower than the other, depending on which frame of reference you take. So, my question is this: Wouldn't the people on earth be traveling at near the speed of light relative to the astronaut and thus be experiencing time at a slower rate from their perspective than the astronaut? Ah this is the classic twin paradox . Special relativity states that reference frames that are uniform are equivalent. i.e. they are either traveling at a constant speed or stationary. The thought experiment is: if you are on a bus that's traveling at a constant speed, it is indistinguishable from if you are stationary. You can construe yourself as being stationary and the whole world is moving backwards at the constant speed. But the moment the bus accelerates or decelerates, you will be jolted forwards or backwards (this leads to general relativity, beginning with the equivalence of accelerating frames and gravity). So in this case, the astronaut has to accelerate out, decelerate make a round-about change in direction. The people on Earth stay stationary relevant to the astronaut and experience no such accelerations/decelerations/change of direction. The two reference frames are no longer equivalent. This proves to be an simplification - more details are provided in the link above.

How do we assign time values (in seconds, years, etc.) to events that occurred long before the earth began rotating and orbiting the sun? And are those estimates given in our present fame of reference or the local reference frame? When I hear that something happened X seconds or years after the Big Bang, I always wonder how that number was arrived at, when seconds and years are based on events that didn't begin to happen until just a few billion years ago. It seems like these figures could be derived from something like the hyperfine transition of hydrogen, but even hydrogen atoms didn't exist until 380,000 years (there it is again) after the Big Bang. First I'm going to be pedantic and say that the second is determined in terms of transitions of a Cesium atom, not Hydrogen. To actually answer your question though, even though Cesium certainly didn't exist in the earliest moments of the universe we still know how long those events took because we have made calculations based on things that we can observe in terms of what exist at the time (much of this data comes from the cosmic microwave background), and how those things acted based on the universal physical laws we know to be true. So while the events of the first second after the big bang did not literally happen in "the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", we can say that if there WERE a Cesium-133 atom there, the events would have occurred in that period. Also, the the times are in the local frame because, once again, everything we know is based partially on observed data but mostly on calculations that are done in the frame of the event.

How are program installer files so much smaller than the program they install? In order for it to install something, all of the data has to be there, right? So, how does it work? In some cases, the installer may hold a compressed version of the data. The installed files are decompressed, so they take up more disk space. However, the compression factor usually only gets to about 2 or 3 for typical software. If you're seeing a much larger discrepancy than that, then probably what's happening is that the installer actually downloads the rest of the necessary data during the installation process. You could check for this by disconnecting from the Internet and then running the installer, and seeing if it still works.

Making it's rounds on Facebook: Sodium Fluoride added to our drinking water is poisoning us. Any truth to the claims? I'm not a scientist, but I immediately get skeptical when someone cites a "holistic medicine" website to prove their claim. The following has been posted on quite a few of my friends' walls and I am just wondering if the claims have any real substance. Offspring of pregnant animals receiving relatively low doses of fluoride showed permanent effects to the brain which were seen as hyperactivity (ADD-like symptoms). Young animals and adult animals given fluoride experienced the opposite effect -- hypoactivity or sluggishness. The toxic effects of fluoride on the central nervous system was subsequently confirmed by previously-classified government research. Two new epidemiological studies which tend to confirm fluoride's neurotoxic effects on the brain have shown that children exposed to higher levels of fluoride had lower IQs. A study published in Brain Research shows that rats drinking only 1 part per million fluoride (NaF) in water had histologic lesions in their brain similar to Alzheimer's disease and dementia. All pics are for sharing... so if you wish to use them to help spread the truth, please do! ♥ Reached the 5,000 limit so here's my other page... Feel free to share your posts! UPDATE: This is my first time using , and I am extremely pleased with the quality of these responses. Keep up the good work! Some personal informatio: I work with large amounts (kg quantities) of NaF for the past year in the form of FLiNaK (NaF-LiF-KF) fluoride salt. I've inhaled it a ton. I've definitely had more than 1 ppm in me. Some scientific information: The MSDS says the oral lethal dosage for 50% of humans is: 71 mg/kg. That's much more than whats in water. http://www.alfa.com/content/msds/USA/11561.pdf No information on when it becomes harmful. Around the lab we don't worry about it too much.

Why are neanderthals considered a seperate species to humans if we were able to breed with them and produce fertile offspring, to the point that a large percentage of modern human DNA is derived from neanderthal DNA? Species is a pretty mushy term and there is many species where things are just species because we want them to be or find it useful. Like a polar bear and a black bear can breed but no one is super interested in making them the same species because it's more useful to just pretend because they are different enough.

If cold-brewing coffee takes nearly 12 hours, would continuous mechanical stir/agitation significantly accelerate extraction? For example, putting water with coffee grounds into something like a slurpee machine then letting it run for a while? Or, for an even more vigorous stir, a mixer? If this does indeed accelerate extraction, can we take some wild guesses on how much faster the process could potentially be? Does the possibility exist that with sufficiently energetic stirring, one could obtain similar results to the 12-hour "static" process in a matter of minutes? Generally, stirring the solvent speeds up whatever is going on in it. If you place a sugar cube in water, it dissolves rapidly at first but then as the water around it becomes saturated the dissolution slows down as molecules diffuse away from the sugar cube. Diffusion happens rapidly over short distances but slowly as the molecules go farther. Stirring helps the diffusion and makes the liquid homogeneous throughout the whole container. This being said, it's obvious that the substances in the coffee grounds would dissolve faster in the water. This is a simplified version of this scenario - if we had pure chemicals we dissolve in a solvent. However, since we're talking about extraction, we also have to take in account how fast these molecules go from the coffee grounds to the water phase. This is not my area of expertise, so I can't say for sure. If the extraction happens slowly, the time it takes the molecules to diffuse might not have much effect on the total time of extraction. Then there would be no significant acceleration of the whole process. If you want to know more about this kind of extraction there's a method called maceration used to extract crude chemical mixtures from solid phase (fx plants) into a solvent (fx water or ethanol). When doing maceration you place the solid in a solvent and let it stand for a period of time but shake/stir it occationally. (Sorry if anything is unclear, English is not my native language)

Why doesn't the sun have a metal core? Or does it? I realize the metals may not be liquid or solid, but seems to suggest that the metal composition of the inner and outer layers of the sun are roughly the same, suggesting it doesnt' have a metal core. But the same article suggests the sun isn't churning out elements from its center because it is radiative, rather than conductive. Shouldn't it have quite a bit of the heavier elements that were floating around the solar system while the planets were forming? A bunch of it did end up in the sun, 2% of the sun's mass is heavy elements, not 2% of the total heavy elements in the solar system are in the sun. Huge difference Here is a pie chart comparing the masses of the different objects in the solar system, notice anything? post originally said what it says now, managed to confuse my self changed it to something wrong, and then changed it back. The point is the mass of the sun dwarfs the masses of the other objects in our solar system. For reference the sun is roughly 300000 times as massive as the earth is!! The mass of the heavy elements in the sun is orders of magnitude greater than the earths total mass even.

How do Hard drives of the same physical size have different memory capacity? Say you have a 2.5" laptop HDD. How do HDDs of the same physical size, (such as 2.5" or 3.5") have such varying memory capacities? I know there are different numbers of platters but you can't really fit more than 4 in a standard case i would assume. Is the servo for the read arm just more sensitive? If this is true, can a lower capacity HDD be "recycled" into a higher capacity one by slapping on a higher resolution read arm servo and special drivers? There are several different factors. One of course is the number of platters. But the magnetic medium on the discs, the field strength of the write heads, the sensitivity of the read heads, the placement accuracy of the heads, platter vibration, etc. all determine the raw bit density that can be put onto a platter. One great example of this is that several years ago, the industry transitioned from making the magnetic domains be oriented vertically instead of horizontally, greatly increasing the bit density that could be put on a platter. Nowadays they are doing things like using thermally assisted writes to give the write head more "zing". Then you have some other effects, such as the actual encoding scheme used, the error detection/correction schemes incorporated, etc. that influence the total byte capacity possible for a drive. That is to say, you don't get the total raw bit capacity divided by 8 as the number of potentially usable bytes....some bits are lost as "overhead". After all that, you have manufacturing defects. The drive's controller can mark out some sectors as "bad" and not use them, thereby allowing discs that are not 100% perfect to still be sold. Then there's Marketing, but I won't attempt to explain that.

Why does biodiesel produce less emissions than petrodiesel? I imagine it must have to do with the chemical structures of the different molecules, but I can't find anything that confirms this. Oh, well there are likely to be fewer sulfur compounds in the total process. The sulfur doesn't really get to your tank of gas but it is a part of the oil that comes up that needs to be cleaned out. Although nowdays most of the sulfur is extracted and used rather than just burned into the atmosphere anyways. Essentially every hydrocarbon that you put into an engine will be a hydrocarbon+O2 -> CO2 + H2O reaction.

Effects of solar gravity... Does the gravity of the sun counteract the gravity of Earth to any degree? If so, is there sun based gravity conflicting with the Earth's affecting us at daytime when we are facing towards, i.e. being able to jump a few millimeters higher and the opposite at night? Would this effect be more pronounced for example on a moon of Jupiter where the large body is much closer? Solar gravity is negligible compared to Earth's gravity for a person on Earth. The acceleration due to gravity at Earth's surface is 9.81 m/s . The acceleration due to the sun's gravity for a person on Earth's surface is (Gravitational constant)*(mass of the sun)/(distance from Earth to the sun)^2 which is approximately 5.9 * 10 m/s . So the effect of the sun's gravity on us is about 1000 times less than the effect of Earth's gravity on us.

Why does drinking methanol (CH3OH) cause blindness while drinking ethanol (CH3CH2OH) doesn't? Even though the difference between the two is only one carbon. The compound causing the blindness is actually not methanol, but formic acid, created from methanol in a metabolic process called toxication. Formic acid is a nerve toxin that acts through damaging mitochondria, and the optic nerve seems to be particularly vulnerable to its toxicity. Though, with doses only a little above the dose that can lead to blindness (that is, about 15 ml), toxicity extends to the whole organism with potentially lethal outcome. Fun fact: the antidote to methanol poisoning actually is ethanol. Poisoned individuals are being kept at about 1 per mille, for about a week, by means of infusion.

What is the physical state of victims of cardiac arrest after being woken up? I used to be on the code blue team when I worked in acute care hospitals and no, the person who has been revived after a cardiac arrest doesn't just get up afterwards. They generally look quite shocked afterwards and are taken to ICU because their condition will be guarded until they're stabilized. I forget the exact statistic but we were taught only 11% of people who suffer a witnessed cardiac arrest (another person seeing the patient go into cardiac arrest and starting a code blue) actually go back to the level of functioning (mentally/physically) that they were prior to the cardiac event.

If I could physically manipulate atoms, how much force would it take to smash or combine two? The question is hard to word properly, and I can't help but think I'm misunderstanding how atoms work, but imagine if I was somehow able to hold a hydrogen atom in one hand, and a couple oxygen in the other. With impossible accuracy, would I be able to clap them together and make water or even function as a particle accelerator/smasher? I remember reading a while back that the force of the LHC is something like a mosquito running into you, so it got me thinking about if it would take a similarly weak physical force to smash atoms together if only we could actually manipulate them at that level. A related question that might be the basis for my misunderstanding is if combining hydrogen and oxygen (or any other combination) could even be done physically or of it's some other quirky feature of atoms that wouldn't work if simply smashed together. So would smashing two whole atoms together just make a tiny explosion, and would I be able to produce the force necessary with my hands? I wasn't really thinking about specifically what the LHC was doing, just that the energy was related to something as small as a mosquito hitting me. That got me thinking about if two atoms could be smashed together with a fairly weak physical force, if only I had a hammer capable of smashing two of them together. So ok, switching to what the LHC is actually doing; if I could hold a proton in each hand and clap them together, would I be the most powerful accelerator in existence, or is the force I'm able to produce still far too weak? I guess my overall question is about how strong the repelling force of atoms is, and if that force could be overcome with a toddler using a sufficiently accurate chisel. I know the collective of the force keeps me from being able to walk through a wall, but that's obviously a few billion trillion trillion of them.

How deep in the ground can we find microbial life? The soil microbiota has a very important role in many processes such as nitrogen organication, the production of methane and so on. Is there true limit in depth we can find microbes or are extremophiles able to basically colonize the whole crust? Multicellular life has been found up to 3.6 kilometers deep and microbial life at temperatures of 102C . It's reasonable to suggest that life might be found even deeper. There are probably a few limits to consider: We're not sure if life can survive in environments above the boiling point of water (the 102C temperature of the deep ocean microbes was below the boiling point due to the extreme confining pressure) The brittle/ductile transition in the crust places a hard limit on how far down water and nutrients can percolate in the brittle layers because the rocks here fracture. Below the transition, rocks begin to behave in a plastic manner, meaning any cracks that do form are quickly sealed by rock fusing them shut again. The depth to which nutrients can percolate and remain at levels to sustain life. This is probably dependent on groundwater flow, and how deep water can flow into the crust isn't well understood.

Is the military myth true that you don't hear the artillery/mortar shell that kills you? this was inspired by another question that was asked that if an atomic bomb went off near by you wouldn't see, feel or hear it. So I was just curious if there was any scientific evidence that could prove whether or not you would hear the mortar/artillery shell that kills you. It's no myth. Most artillery shells travel faster than the speed of sound. You, or the area near you, get hit before the sound reaches your ears. Personal experience. While at field artillery school at Fort Sill Oklahoma there was a battery practice firing nearby. The shells passed directly over our position before impacting several thousand yards away. We learned to look up immediately upon hearing the gun fire. We could actually see the shell pass silently overhead. A number of seconds later we could hear the sort of crackling sound the shell made while passing through the air, just like in the movies I add. The point of all of that is if we were the target we would have been hit before we even knew that a gun had been fired.

How does Aspirin inhibit platelets but other NSAIDs don't? Both ASA and NSAIDs such as naproxen or ibuprofen inhibit COX and prostaglandins and all that business but ASA inhibits thromboxane release of platelets and decreases their aggregation. Is it COX 1 vs 2 or is it more complex than that? What makes ASA so special? TL;DR Whats the molecular mechanism behind ASA inhibiting platelets and but other NSAID don' The other NSAIDs do inhibit platelets. It depends upon the ratio of COX1 to COX2 activity of the NSAID. Aspirin, naproxen, ibuprofen are all anti-platelet due to COX 1 inhibition, but aspirin is an irreversible inhibitor of COX1 and so the duration of effect is longer (the lifetime of the platelet). For ibuprofen the anti-platelet effect is reversible - it lasts as long as the dug is in your system (a few hours)

Are the same type of cells found in humans relatively the same size across all humans, or do they vary in size? Similarly, are the same type of cells the same size across species, and other animals, e.g. is a liver cell in a dog the same size as a liver cell in a cat? Not sure about "regular" cells but spermatozoa very in size a lot comparing different species. I did research on fish reproduction and sizes would vary between fish species, though they would be somewhat similar. They differ a lot from other species I also did a bit of research on or saw on the field such as dogs, pigs, bulls and dolphins (and those would be different between each other too, no only on size but in morphology).

Electromagnetism is generally presented as wave phenomena. What is the particle (photon)-based interpretation of wireless communication, or of two charged particles repelling each other? I've just completed a mid-level university course in electromagnetism under electrical engineering, covering uniform plane waves, transmission lines, antennae, waveguides, optical fibres, etc. The entire subject matter was presented by interpreting a disturbance in the electromagnetic field as a wave, e.g. for a basic plane wave, the electric field strength and direction could be given by: E(x,y,z,ω,t) = A e e e . Similarly, we are shown that a charged particle creates a disturbance in the E field, and hence will exert a force on other charged particles. My question is, how should I think about these phenomena as an interaction between matter via photons? I understand that matter particles can be considered in a quantum sense to be entirely described by a wave that represents the probability of that particle's superposition collapsing to that point. Does a similar understanding apply to photons? If so, how does this wave (which seems to be a lot like a field to me) relate to the electric and magnetic fields as I understand them now? And if particles are constantly shooting photons at each other to convey the effects attributed to the electric and magnetic fields, where does the energy for these photons come from? Maybe related, or maybe I am reading the wrong discussions -- I have seen some talk online of electrons having a "cloud" of virtual photons. How can this possibly work if photons travel in a straight line and always at c? Cheers In principle, interaction of matter via photons the interaction of charged objects through changes in EM fields. Let's say you have some static distribution of charge in some volume of space. This distribution generates constant electric fields with constant energy that we might as well call 0. Now, if you change the charge distribution (either by reconfiguring it, or simply by pouring more charge in/taking some of it away), the electric field changes. The consequence of finite velocity for propagation of information and the fact that the change in charge distribution costs energy, is that now you have a EM wave traveling through space (a specific case would be the plane wave), carrying the energy. Once it reaches some other point in space, it will interact with the charge distribution there, changing it and exchanging some of its energy. The gritty details of consequences of quantum mechanics on this process are something, that I'm not sure I would be able to explain (quantum field theories aren't very intuitive), but the gist of it is that the charge distribution can't assume any form, but only discrete states (like, for example electrons in atom can't just fly around to their liking, but are always found in superposition of infinite, but not continuous, set of allowed states). To give you a semi-classical, completely wrong example (that at least hints in the right direction): Imagine you have a semi-classical electron just sitting in there in constant electric field - which is completely against uncertainty principle, but that's beyond the point right now. If you send an disturbance thorough the field (an EM wave), the electron would change it's state (if the disturbance would be periodic, like your plane wave, the electron would start to shake with it), absorbing some of the fields energy. Quantum mechanically, the electron can't be shaking at arbitrary frequency, so to get it from the ground state (it just sitting there) to some excited state (shaking), you have to give it a very specific amount of energy through the EM wave - and that amount of energy hidden in the disturbance of the EM field is what we call the photon. If we wanted to give up the semi-classical pretence, we would need to use quantum-mechanical description of the electron. That doesn't mesh well with classical fields, so you need to find a way to describe the EM field in a similar way. This is done by a formal process called second quantization, during which the photons emerge (mathematically speaking). In this formalism, interaction between particles (electrons) can be mediated by arbitrary number of interaction particles (photons), provided the process obeys conservation laws, that's why they are called virtual. An example would scattering of two electrons. [EDIT: Let's rather not talk about localisation of the collision], they "collide" by exchanging a virtual photon, which transfers the momentum between them (like in this Feynman diagram where two particles with momenta p1/p2 collide through a mediating particle with momentum/quasi-momentum k). As for the cloud of virtual photons, that's mostly a formal thing. The idea is that vacuum and single-particle states have to behave as such (meaning there can be no interaction in the mathematical description of their dynamics). This necessitates introduction of terms to the Hamiltonian that look as if the electron had a cloud of photons around itself.

What happens when you go without sleep? Is it true that you can 'go crazy' if you go too long without sleep? How long would that take if it is possible? What is the mechanism by which this takes place? And how long would it take someone to die without sleep? The longest any one person has stayed awake without the use of any stimulants was 11 consecutive days. Supposedly, people have broken that record, but none of them have been scientifically verified. The individual suffered from moderate sleep deprivation symptoms, but did not die, nor reported any long-term issues as a result. It depends on the individual on how long it would take to 'go crazy'. Some of the symptoms of sleep deprivation include hallucinations, but some people may not experience these, so it's hard to give a blanket statement that would apply to every single person.

How do you calculate the motion resulting from a sound wave? In other words, lets say you have a sound wave at a known pitch, amplitude, etc, going through an object of known mass, etc. Is it possible to calculate the size of the resulting vibrations? If so, how? Thanks. What you're essentially asking is how does a sound wave in air behave when it becomes a soundwave in a material. Well in many ways, it's a similar process to how light interacts with materials. In this, you can even reach a quantum description of sound in materials in the form of phonons. How these waves will behave depends on the dispersion relation of the material. Some frequencies will travel at different speeds within the material and some will get absorbed and attenuated quicker than others. There's also the case of resonance, where the sound wave is completely absorbed by the material and converted into mechanic motion. The mathematical approach can be quite in depth and it really depends on what sound regime you're dealing with and what kind of model you want to you.

Why do some parts of the body seem to be more prone to cancer? I'm especially thinking of breast cancer and cervical cancer in women, what makes those parts so vulnerable? Cervical cancer is actually less common--the reason it's often emphasized is that many instances are preventable. In general, the most common cancers are in areas that are subject to rapid cell turnover, are acted on by hormones that impact growth, and are exposed to environmental compounds that cause either cell death or direct mutations to DNA, because these give a tissue more chances to accumulate mutations. The most common cancers in women are breast, lung, and colorectal (aside from nonmelanoma skin cancers). Breast cancer is usually but not always in the epithelial cells lining the milk ducts--a layer that turns over quickly--and since breasts are a secondary sexual characteristic and important in childbearing, breast tissue is acted on by reproductive hormones--for example, in some women they actually change in size many times during their lives, even without childbearing. There may be additional reasons, as this is not my exact field of study, but in and of themselves those would predispose a tissue to be a more common site of cancer.

What can I put on ice such that a second layer frozen on top will separate easily? I'm planning an ice sculpture but can't build it where I want to present it, and since it's going to be very heavy, I'd like to be able to separate it into layers. If I freeze the first layer, then smear something hydrophobic (butter?) on the ice before filling up the rest of the mold, will they be easily separable? What are other common household hydrophobes? (I hope this question is sciency enough...) How about a physically intact barrier like wax paper or saran wrap? If those aren't tough enough you could do polyethylene sheeting (trash bag material, if thin. you can get thicker at hardware stores) or even something like a tarp.

What is morning breath and what causes it? Bad breath (and even body odor) in general is caused by bacteria. On the tongue, the back is relatively dry and not really affected by brushing, rinsing, etc. This creates a very pleasant environment for bacteria to thrive, and they produce malodorous compounds, which accounts for the vast majority of bad breath. This is more noticeable in the morning because there has been very little activity in your mouth for 8 or so hours, allowing the bacteria to do their thing undisturbed. In order to get rid of the odor, you have to get rid of the bacteria. You can use a tongue scraper or even your toothbrush, you just have to get back there.