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[
"Airfoil physics: Why does the air flowing the top of a wing *have* to catch up with the air flowing underneath it?"
] |
[
false
] |
This seems to be the key point to how an airfoil works, but I mean, it's not like they're inseperable lovers or anything... My apologies if this has been asked before, but i was reading back through xkcd and the title-text in got me thinking...
|
[
"It doesn't. This is a common misconception that has its own name: equal transit time fallacy",
"http://en.wikipedia.org/wiki/Lift_(force)#.22Popular.22_explanation_based_on_equal_transit-time"
] |
[
"Even when I was in grade school this never made any goddamn sense. I was so happy when I found out in college that it was bullshit."
] |
[
"Shorter, eh?",
"But how do wings work then?",
"Fucking Wings, how do they work?",
"http://en.wikipedia.org/wiki/Angle_of_attack"
] |
[
"Can the human body survive without any viruses?"
] |
[
false
] |
It is a known fact that we cannot survive without bacteria that preform a multitude of tasks in our bodies such as digesting food. In light of the new virus cure that MIT has developed, if we removed all viruses from our bodies will we survive? Hence, do we harbor beneficial viruses like we do bacteria? Furthermore would removal of all viruses slow adaptive evolution, harm our immune system development or cause any other unforeseen problems?
|
[
"The human virome (all viruses that can be found in the body) is pretty massive. For example, over 1200 viral genotypes can be found in human feces. These viruses, mostly bacteriophages, surely play an instrumental role in shaping the bacterial communities of our bodies. However, it is unclear how these viruses benefit or hinder human fitness. I would go out on a limb and say that humans would not be as healthy without viruses. "
] |
[
"Layman here(Biochem. undergrad), but given that the majority of eukaryote viruses replicate via the ",
"lytic cycle",
", the final step of which destroys the host cell, I highly doubt that there are any viruses out there which are beneficial to the host, I'm sure an expert can maybe shed more light on this if I'm wrong.",
"It appears to have been ",
"suggested",
", though, that the immunosuppressive properties of certain ",
" play a role in gestational immune tolerance."
] |
[
"You're genome is littered with ancient viral DNA that have integrated into your genome. They make up a lot of intergenic/non-coding sequence. Knowing that viruses shaped our genomes back in the day, I'd say taking them away (thus preventing further impact on our genome) would really change our evolution in the future. ",
"Unrelated note.. there's actually a virus that infects a virus out there! Its call sputnik (a virophage) and it infects a mimivirus (really big virus) that's infecting a host cell. ",
"One thing you may not think of, but viruses can infect more than just humans. Therefore engineering a virus that will preferentially infect something that's harmful to us like a bacterium or a parasite could make these little guys useful. "
] |
[
"Why are the gas giants in our solar system so vividly colored?"
] |
[
false
] |
The gas giants in our solar system appear to be made mostly of the same stuff (90%+ hydrogen/helium). The other trace constituents such as water, methane, hydrogen sulfide, etc., are colorless. Why then are the gas giants so beautifully colored? Why does Jupiter have such a wide variety of colors whereas the other gas giants are essentially one hue? Why are the four gas giants such different colors? What makes Uranus so much smoother in texture than all of the other gas giants?
|
[
"Gas giants are brightly colored because of the other 10%. Water, methane, hydrogen sulfide etc. are individually colorless, but when you mix them all up and bombard them with UV rays for a long time you can get chemical reactions going that make some funky sulfur-organic type compounds. I don't think they make anything in more than trace amounts, but it's enough to color the clouds.",
"Uranus is smoother in texture just because it has less intense weather going on. And that might have been a fluke, the Voyager probes might have flown by it during a relatively quiet period. The Hubble space telescope has caught images of Uranus since then that show signs of more active features."
] |
[
"All good, but just to expand on this: the generally accepted hypothesis for Jupiter is that the planet is almost entirely cloaked in bright white ammonia clouds. The zones keep this bright white color because the tops of the clouds are quite high in those locations; in the deep brown belts, though, the ammonia cloud tops are a bit deeper, exposing a thin overlying brown haze layer of hydrocarbon aerosols that colors the clouds below. As you mention, these are various carbon/hydrogen/oxygen/sulfur compounds that have been chemically altered by ultraviolet light impinging on the top of the atmosphere, producing substances not entirely different from smog.",
"It still remains an unsolved problem exactly what chemical is responsible for making the red color of the Great Red Spot, a puzzle collectively known as the \"Jovian chromophore problem\". There are a few good candidate chemicals that have been suggested, but no conclusive evidence of a single candidate just yet.",
"Uranus is smoother in texture just because it has less intense weather going on. And that might have been a fluke, the Voyager probes might have flown by it during a relatively quiet period. The Hubble space telescope has caught images of Uranus since then that show signs of more active features.",
"Yep, this was one of the main subjects of my PhD dissertation. It's important to point out that when Voyager flew by in 1986 and saw a quiescent atmosphere, the planet was at solstice. The Hubble images that showed Uranus with many more active features occurred around 2006, during the planet's equinox. Since the planet has a ridiculous axial tilt, it's quite possible that what we're seeing here is the result of intense seasons."
] |
[
"Uranus and Neptune have a lot more water in them. It's thought that Jupiter and Saturn are basically hydrogen and helium around a small rocky core, with the H and He turning to liquid, then eventually maybe solid form as you get closer to the core and the pressure increases. Its thought that Uranus and Neptune have a thousands of km thick hydrogen and helium atmosphere, with more thousands of km of water/ammonia slush beneath that before finally getting to the rocky core."
] |
[
"Does other viral respiratory illnesses like common cold or influenza also cause long lasting cardiopulmonary or neurological sequelae like COVID-19 is doing?"
] |
[
false
] | null |
[
"Short answer: Yes ... Maybe. It's complicated",
"The long term side effects of various virus infections have been a part of research for some time now. It is hard to correlate these diseases with certain virus because the symptoms are usually long term and show up later in life. There have been some viruses maaaaaybe linked to varius cardiovascular diseases or diabetes and even alzheimer's research, some papers (that I won't link cuz I'm lazy) found \"viral factories\" in patients brain autopsy. ",
"The virus may affect the respiratory system the most severly and effectively, but apart from your lungs the virus can still spread and affect other parts of your body through the bloodvessels.",
"If the virus is able to spread systematically (inside your bloodstream) and finds a cell it can bind to, it can and will most likely try to infect said cell. This cell could be any organ of your body that the virus can identify. The virus can also mutate inside your body to attack other organs (although at a much smaller scale). ",
"Edit: more info"
] |
[
"Yes. Influenza is well-known to ",
"increase heart attack risk",
". And in the aftermath of the 1918 flu there was an \"",
"encephalitis lethargica",
"\" wave, which may have been related. Also, as ",
"/u/Typhun",
" mentioned GBS is known to be associated with influenza."
] |
[
"Yes. ",
"Guillan-Barre syndrome and viral myocarditis are some of the more well known illnesses associated with viral infections. GBS is even associated with flu vaccines. ",
"Though not a respiratory illness, untreated HIV can result in dementia."
] |
[
"If the Earth's core is molten because of all the heat when Earth was created, is the core slowly losing heat?"
] |
[
false
] |
[deleted]
|
[
"Yes, but not as quickly as you may imagine. According to my textbook, The Solid Earth, An Introduction to Geophysics 2nd Ed. Fowler pg 371 about 20% of the heat lost at the earth's surface originates from the core.",
"Lord Kelvin ",
"famously",
" tried to calculate the age of the earth based off of heat transfer in the earth. He came up with 20-100 million years old. This of course is very incorrect as the actual age of the earth is 4.54 billion years old. One major factor he did not take into consideration was heat generated by decay of radioactive elements within the earth. When an atom undergoes decay, some of the energy that was holding the atom together gets converted to heat. It's the same basic process that nuclear reactors use.",
"Whether the core will completely solidify is a matter of debate because the ",
"phase diagram",
" of iron is very poorly studied (due to experimental constraints) at the temperatures and pressures that exist in the core."
] |
[
"The bulk of the heat inside the planet actually comes from ",
"radioactive decay",
", not from leftover formation heat.",
"The original heat from the formation of the Earth probably only accounts for ",
"5 to 10%",
" of the total heat present at this point.",
"There are other sources of heat within the planet aswell. The wiki gives a ",
"short summary",
", if you're interested.",
"Basically though, even though there is a net heat loss, there is heat being generated all the time by a variety of processes. The total heat loss seems to be in the region of ",
"40-45 TW",
", whereas radioactive decay alone is believe to be generating ",
"860 EJ/yr",
", which is equivalent to about 30TW. This obviously slows the cooling significantly, as ",
"/u/NV_Geo",
" mentioned."
] |
[
"Thank you for expanding. Those links were very enlightening. It's incredible to think that supernovas from billions of years ago produced enough energetic atoms that they are still heating the Earth today. I suppose either way that is true, but somehow it is even cooler that it is radioactive elements inside the Earth causing the 11000 degree temperatures."
] |
[
"Why does color fade when left in sunlight for extended periods of time?"
] |
[
false
] |
We have a rack of DVD cases next to the window, and recently I've noticed the covers have all faded in color. Strangely the red ones seem to have faded far more than any of the others.
|
[
"The short answer is that sunlight causes irreversible changes in the compounds and molecules that gave a material its color in the first place, in a process we call ",
"photodegradation",
". As a result of these changes, the material gradually loses the ability to specifically absorb (and reflect) different parts of the visible spectrum, creating a faded appearance. ",
"To look at things a bit more closely, the color of the dyes used in clothing, colored paper, etc., depends on the detailed arrangement of atoms (and their bonds). For example, ",
"take a look at the structure of this common dye called Orange II",
". Notice how there are two rings with alternating double bonds (we call these aromatic rings), linked by a nitrogen-nitrogen double bond. This extended ring structure is what allows this compound to strongly absorb blue and green light and to reflect the yellow-red part of the spectrum. Now as you might expect this compound will initially have a ",
"vivid orange color",
". However, if you expose this dye it to light, over time this color will go away and you will be left with a product that is mostly clear, ",
"as shown here",
".",
"So what exactly happened that made the color go away? Well, in one word ",
"photochemistry",
" happened, namely light promoted chemical reactions. Now these reactions can be very messy, ",
"for example here are some of the pathways you may see",
", and in fact multiple reactions often play out at once. However, what is important is that these reactions destroy the initial chemical structure of the dye and break it up into smaller bits. As a result, a layer of this material will ",
"slowly lose its ability to strongly absorb visible light",
". ",
"Now this was just one specific example, of course in other cases dyes will have completely different structures and will be destroyed by different mechanisms. However, quite often the net effect of these changes is that they will reduce the ability of molecules and compounds to absorb in the visible part of the spectrum. As a result, as you allow colored materials to be exposed to light (and air), often you will find that over time they will lose their vivid color and will take on a dull off-white appearance. This effect is very similar to old-fashioned chemical bleaching."
] |
[
"Eventually, yes, but it would take more than just a few years.",
"First, sunlight is ",
" brighter than any ordinary light bulb. Humans have trouble appreciating just how much brighter, because your eye has a logarithmic response to light (doubling the physical brightness does not double the perceived brightness) and furthermore your pupils automatically reduce the amount of incoming light in bright conditions, meaning it won't look as much brighter as it really is.",
"In bright sunlight, a given square meter of ground is receiving about 1000 watts of sunlight. That already sounds like a lot compared to a typical 60W light bulb, but then you need to consider that an incandescent light is only something like 2% efficient, so it's only giving off around 1W of light. Sunlight is ",
".",
"Furthermore, the higher-energy the light, the more likely it is to damage molecules. Sunlight has quite a bit of UV light in it, whereas an incandescent bulb produces virtually none. It would take a very, very long time for a typical indoor light to bleach the color from something (unless the dye is particularly non-lightfast, of course)."
] |
[
"Yes, but in this case it is a measure of the amount of energy delivered to a specific area per unit of time that is important. Watts are a good measure for this and lumens are not. The pigments in dvd covers do not care how us humans perceive brightness vs actual intensity of a light source."
] |
[
"Why don't animals have more than 2 eyes. Or eyes in cool places like on the back of their head?"
] |
[
false
] |
If animals had eyes on the back of their head wouldn't it increase their vision?and that would be good for herbivorous animals right.
|
[
"Some animal ",
" have multiple eyes. Spiders, for example, generally have eight (and as many as twelve) though only the two front-facing ones are developed enough to detect complex shapes; the remaining ones are rather primitive and only detect the presence or absence of light. Horseshoe crabs have ten, though again, only two are complex. Scallops have up to 100, but they are all simple light/dark sensors. But their arrangement lets them act like a grid, so they can detect movement as light passes along them. ",
"As to your question about prey animals, like herbivores, their large sideways-facing eyes give them a very broad field of view, up to nearly 180 degrees to either side. So rabbits, for example, can see motion occurring behind them. (IIRC, rabbits actually have a blind spot directly ahead and behind.) But they sacrifice the overlapping visual fields that animals with forward-facing eyes have, so they have poor-to-nonexistent ability to see 3-D, and tend to have poorer depth perception."
] |
[
"It's axiomatic with regard to evolution that traits which are, on the balance, detrimental to reproduction tend to disappear. But evolution also gets stuck at local fitness maxima (one famous example being the recurrent laryngeal nerves) and the mere fact that a trait isn't observed in the wild doesn't mean it would not be beneficial on net. I don't think we can confidently say that the benefits of having additional eyes for a two-eyed animal would definitively be outweighed by the penalties, merely that the pathways which would lead to such a development have, to this point, been pruned off."
] |
[
"to add onto this, as to the question of why the ones that have two don't have more, that's a matter of energy expenditure. it takes more energy and/or more complex neurology to make use of. and evolutionarily speaking, nature doesn't generally add extra body parts unless they're necessary; if anything, ones that provide no evolutionary benefit but are more complex often degrade and disappear over time."
] |
[
"How do we know that radioactive decay is truly random?"
] |
[
false
] |
[deleted]
|
[
"How do we know that this decay is non-deterministic?",
"Certain theorems (whose names escape me) prove that either determinism is false, or the variables required to make the universe deterministic are the same everywhere (",
" but not ",
" a violation of general relativity/causality). That is, they're not local.",
"Anyway- Radioactive decay follows all of the requirements of ",
" random events, so it is simplest to call this process random.",
"This refutes determinism, but still allows ",
"Stochasticism",
" which is like determinism, except there are random things."
] |
[
"Basically, radioactive decay is a quantum process, and by Bell's Theorem ",
"http://en.wikipedia.org/wiki/Bell's_theorem",
" there are limitations on whether such processes can be predicted. In general, quantum processes are either random (i.e., cannot be predicted) or violate locality (non-local variables determine the outcome), or the universe does not obey quantum mechanics (for which there is a phenomenal amount of experimental evidence.) ",
"edit: to clarify, the 'phenomenal evidence' supports QM, so its unlikely the universe does not obey QM, if that was unclear."
] |
[
"Based on how we define randomness, ",
"it is not possible to prove whether or not it truly exists.",
" Some people are happy to treat unpredictability and randomness as equivalent, but they are not. Unpredicability certainly exists and ",
"the Halting problem",
" proves that fully deterministic processes can produce fundamentally unpredictable results. People who claim that true randomness exists in quantum processes are generally relying on assumptions made by the Copenhagen interpretation of QM, as it is the most widely accepted interpretation. "
] |
[
"Recently watched Mermaids: A Body Found on the Animal Planet Channel. My question, on an evolutionary level, how viable is the Aquatic Ape Theory?"
] |
[
false
] |
The 2 hour episode on this seemed a bit far-fetched, however the idea that certain apes may have possibly thrived in or near a beach to then later adapt to watery surroundings doesn't seem so crazy. Any thoughts?
|
[
"It doesn't seem ",
" crazy at first pass, no, but there's very little evidence in support of it, and a fair bit against it.",
"I'm not personally qualified to talk in any detail about it, as I'm not really an anthropologist, but I'd recommend the following resources:",
"http://www.sciencedirect.com/science/article/pii/S0047248497901469",
" (which is unfortunately paywalled, I think)",
"http://johnhawks.net/weblog/topics/pseudoscience/aquatic_ape_theory.html",
" (Hawks, the author of this post, is a relatively well known anthropologist at the University of Wisconsin; the main point is in the final paragraphs)",
"and lastly",
"http://www.aquaticape.org/",
" is probably the best resource out there.",
"The aquatic ape hypothesis is a curious one, because it does a pretty good job of looking like a legit scientific hypothesis. It's just that it was thoroughly rejected by the anthropological community some time ago. ",
"Elaine Morgan",
" just can't seem to admit that she was wrong though, and the idea is attractive sounding enough to convince Animal Planet execs to sink years into producing documentaries that have very little to do with actual modern science, so ",
"here we are",
"."
] |
[
"While the points the theory as it's known are excellent, they are mostly explained by unrelated phenomena. (E.g., hairless is a result of it carrying fewer parasites (important in social situations) and not being necessary to keep us cool with our super-sweat powers)",
"However, there are some points it raises we have no solid alternate theory for. (E.g., nose shape)"
] |
[
"It's a nice hypothesis that is not supported by evidence.",
"The alt-hypothesis (Now a developing theory.) is that humans became hairless after becoming bipedial to enhance the cooling action of sweating.",
"This (In addition to many other musculoskeletal changes ",
" being able to carry water) allows a single human to chase large prey animals to death.",
"http://en.wikipedia.org/wiki/Persistence_hunting",
" ",
"http://en.wikipedia.org/wiki/Endurance_running_hypothesis"
] |
[
"How do animals with extremely sharp teeth/claws/beaks keep them sharp? Wouldn't they become dull over time?"
] |
[
false
] | null |
[
"not necessarily. For the most part wear only happens under forces that are large enough, or against surfaces that are hard enough. ",
"Teeth solve this problem by being really hard, and the sharp ones arent generally used against harder things. I.e. dogs arent using their sharpest teeth to chew on bones, theyre using their duller rear teeth. Those teeth are also bigger and can take larger forces. ",
"Claws solve this problem in many cases by being hard enough to only wear minimally for their general use (cutting flesh or digging) but soft enough to be sharpenable against something in the environment--often tree bark/wood--and then growing at a rate similar to the wear rate. This is why cats claw up furniture/upholstery, to try and sharpen their claws."
] |
[
"Human finger nails grow continuously and we either wear them of cut them. Cat claws also grow continuously but the keratin has a more obvious onion like layered arrangement, the current outer layer is not having new material added to the base instead a new claw is growing in through the middle of the old claw. Then every couple of months the outer claw detaches and is shed, this ensures that any over worn claw is replaced with an entirely fresh sharp claw on a regular interval",
"Btw: this applies to small cats, i'm not sure about big cats, I'd assume they have a different nail growth pattern."
] |
[
"Worth noting that cats shed their claws now and again, giving then a fresh claw ready for further sharpening."
] |
[
"Humans are known to help out an animal if it's stuck, injured or in problems in the wild. Are there any animals that are known to help other animals or humans in distress?"
] |
[
false
] | null |
[
"There are ",
" of cases of animals saving humans and other animals. I am going to stick to purely wild animals (no pets, no livestock, no zoo animals) saving humans, because I find them the most interesting.",
"In 2005, a 12-year-old Ethiopian girl was saved from kidnappers by ",
"three lions",
", who then stayed with her until rescuers arrived. Some have theorised that the lions originally planned to eat the girl, but were then confused when her cries sounded like those of a cub in distress.",
"In 2000, a teenage boy jumped off the Golden Gate bridge in an attempted suicide. A ",
"California seal lion",
" repeatedly swam around him and kept lifting him to the surface to breathe. There are ",
"numerous reported cases",
" of dolphins doing the same thing for drowning people, or else warning divers of the presence of large sharks.",
"In 1974, a 52-year-old woman caught in a shipwreck was saved by a ",
"sea turtle",
". Bizarrely, the animal allowed her to ride on its back for 36 hours until she was rescued.",
"In one of my favourite cases, the human in question didn't actually need to be saved! In 2013, a National Geographic photographer was videoing leopard seals in the Antarctic. A massive female began approaching him very closely - alarming, since leopard seals have been known to kill humans! But this female instead began bringing him penguins. First live ones, then wounded ones and eventually dead ones, going so far as to shove them right into the camera lens. The photographer came to the conclusion that, for whatever reason, the female leopard seal was ",
"trying to feed him",
".",
"There are other cases! Animal altruism and empathy has been well-documented."
] |
[
"In 2003 a group of elephants released a bunch of captive antelope.",
" Conservationists thought the elephants were coming to take some of the food but instead, they circled the compound and one opened the latch to the gate. The antelope left, followed by the elephants, who never touched the food."
] |
[
"Elephants have been reported many times to help humans and animals, although the case is more often than not \"helping by simply avoiding to crush someone under their enormous weight\". The ",
"Wikipedia article",
" gives several examples of elephant helpfulness. In general, elephants have very strong feelings of mourning, compassion and empathy both towards their kin and other creatures, and it seems they're very aware of how fragile most things are compared to themselves.",
"Elephants are the best."
] |
[
"Billions of years ago when the universe was considerably smaller, was matter smaller too? Was there less space separating the electron from nuclei and was the width of a single proton less?"
] |
[
false
] |
If this was the case, then is it understood what this might have meant for atomic physics?
|
[
"No. The size of atoms depends on a few fundamental physical constants. You can look at the formula for the ",
"Bohr radius",
" to see this:",
"a",
" = hbar/(m",
"*c*alpha)",
"On the right hand side you have the Planck constant, the mass of the electron, the speed of light, and the fine structure constant. To the best that we can determine, none of those constants have changed since the beginning of the universe (and there have been serious attempts to look for these changes by observing very distant objects). ",
"So atoms were the same size for as long as the four fundamental interactions (strong, weak, E&M, and gravity) have existed. The expanding universe just provides more space for the matter to move around in. "
] |
[
"none of those constants have changed since the beginning of the universe ",
"This isn't quite true, the coupling constants (including the fine structure constant) experience something called running, which is where the value of the coupling constants changes with energy scale. When the universe was very very young (on the order of seconds), the fine structure constant and therefore the strength of electromagnetic interactions would have been different than they are today.",
"This is a very nitpicky point, though, since the temperature of the universe at that point was far too high for atoms to exist, anyway."
] |
[
"If you held the tweezers there for the rest of time, the atom would remain smaller for the rest of time, no?",
"That's correct, but the universe being smaller is just like taking the atom from a big box and putting it in a smaller box. It doesn't imply anything like tweezers pushing the electron into the proton.",
"According to the Big Bang Theory, there was a time when all the matter in the universe occupied a dense enough region of space for such conditions to exist whereby the atom is made smaller by an external force.",
"There was a time in the early universe when the temperature was so high that indeed atoms would experience high pressures, but there are two things to keep in mind:",
"1) In such cases in the early universe, atoms didn't exist at all, because the universe was so hot that atoms were fully ionized. And earlier still in the history of the universe it was so hot that nuclei hadn't even formed yet.",
"2) The fact that atoms may experience pressure due to a high temperature or density related to the universe having been smaller is separate from a question that is often asked in which people are confused that the actual expansion or contraction of space would itself cause the atom to be bigger or smaller. The expansion or contraction of space has nothing directly to do with it, for the reason I originally gave. "
] |
[
"What is Quantum Field Theory?"
] |
[
false
] |
I am merely just a curious passerby with no background in physics. My interest was sparked by this podcast , talking about how the universe has no 'physical point' as you go smaller and smaller past the atom. May someone explain the ideas and concepts of Quantum Field Theory? More specifically, what really are the particles that make up the universe, and how are other basic physics interpreted though this theory? Also, what readings do you advise as to gain a better understanding of this subject?
|
[
"This had just popped up on the front page a few days ago, take a look at the explanation by ",
"Sean Carroll",
". He answers the question very basically there, though if you watch the entire lecture he goes into further detail. "
] |
[
"But in an atom, the probability of finding an electron (or the 'electron density') is in fact highest at the nucleus, and drops off smoothly as you get farther away from it",
"Whoa hold on that depends. Some of the radial hydrogen wavefunctions blow up at the origin, others go to zero. "
] |
[
"I stopped listening to that as they started to repeat the common misconception that 'atoms are mostly empty space'. It's just not true in any meaningful sense. The only true bit is that atoms are very large relative their nuclei. But there is no great distance between the nucleus and the electrons. As quantum-mechanical particles, electrons do not occupy definite locations, we can only say the probability of where they might be. But in an atom, the probability of finding an electron (or the 'electron density') is in fact ",
" at the nucleus, and drops off smoothly as you get farther away from it. So where in this more-empty and less-empty space is there truly 'empty space'? They talk as if the electrons occupied specific 'orbits' at definite distances from the nucleus. That was true of the old Bohr model of the atom, but that hasn't been scientifically relevant since 1926. ",
"I'm going to take a guess and assume they go on to say something along the lines of \"according to quantum field theory, everything is made up of fields, which are made up of nothing\". (Lawerence Krauss has sold a lot of books making that claim)",
"I find that very misleading as well. Fields can have different states. If fields are 'nothing', then not all \"nothings\" are the same. A 'nothing' that has properties is not nothing if you ask me. If not a logical contradiction, then it's at least contrary to how fields are treated in actual quantum field theory, where they are definitely 'a thing'. ",
"The standard model of particle physics holds that there are a set of fundamental fields and also fundamental particles. Fields and particles are two sides of the same coin in QFT (and they're both abstract concepts anyway)."
] |
[
"Is there a limit to what resolution the human eye (and brain) can process?"
] |
[
false
] |
Following on from this question is there a limit to what we can see.
|
[
"Take a look at these past posts:",
"http://www.reddit.com/r/askscience/comments/m9bro/what_resolution_does_a_human_eye_see_at/",
"http://www.reddit.com/r/askscience/comments/eu58a/the_resolution_of_our_eyes/",
"http://www.reddit.com/r/askscience/comments/okot2/what_resolution_do_human_eyes_see_in/",
"There are plenty of other posts on ",
"/r/askscience",
" along the same lines. The search feature is a great way to explore ",
"/r/askscience",
", since a lot of great questions and answers get buried because of the high volume."
] |
[
"Could you clarify what you mean by \"resolution\" and \"process\"?",
"Obviously, we don't see at infinite resolution, because we can't see (distinguish) things even at the micrometer scale.",
"However, the brain doesn't exactly subdivide images into discrete, regular units of an image's \"area.\" It doesn't have a specific, fixed resolution in the sense of pixel density."
] |
[
"I heard on an ABC science program, that the raw output from a human eye is not even something you'd accept as a good image on your TV. Can't find the program link unfortunately.",
"But the idea was that the brain compensates for the lack of image clarity from the eye by interpolating images and basically a lot of \"post-processing\". Perhaps someone in the right field can elaborate on this process.",
"Bottom line; the image we \"see\" is much clearer than the image our eyeballs produce by themselves. So one could reasonably assume that we are already hitting the upper limit of image clarity, because the brain is already doing lots of work to clean it up.",
"I am curious, however, how much the brain compensates for lack of focus. It's possible we have imperfect focus, but things \"seem\" in focus anyway - to a point - because of all that post-processing."
] |
[
"What causes the change in our perception of a spinning object, such as a hubcap on a car, to appear counter-clock wise and switch to clock-wise or vice versa?"
] |
[
false
] |
What causes the change in our perception of a spinning object, such as a hubcap on a car, to appear counter-clock wise and switch to clock-wise or vice versa? I had always noticed this while in car rides or in commercials on tv but never put much thought into the optical illusion. Is this phenomenon different for other people?
|
[
"No idea."
] |
[
"This isn't a hubcap thing. It's a framerate thing. If your rotational frequency is slightly more than your framerate, then spinning things will look like they're going backwards. Basically, it's the camera doing this."
] |
[
"Known as \"aliasing\" if you're talking about video. I think the explanation for vision might be somewhat more complicated."
] |
[
"Can you generate energy from atomic vibration?"
] |
[
false
] |
As most of us learned is high school, atoms vibrate based on temperature, faster=hotter. What I want to know is, could you get room temperature material, use the vibrations to generate energy, and dispose of the cooled material?
|
[
"In principle, if you had a cooler material to transfer heat to, you could extract usable energy from that process. However, it is not possible to get usable energy by transferring heat between two objects at the same temperature, or from a cooler object to a warmer one. Doing so would reduce the total entropy of the system, violating the laws of thermodynamics."
] |
[
"Under normal circumstances, you cannot get usable energy from the heat content of an object that is at room temperature. But suppose that you live in the outer solar system, on a moon that is covered with the snow formed from freezing methane, nitrogen, etc. Any object at room temperature would be capable of causing these types of snow to turn into a gas. And that expansion can run a turbine and generate usable energy. Of course, travelling to the outer solar system just so that you can extract usable energy from the heat content of room temperature objects is almost certainly more trouble than it is worth. "
] |
[
"Someone asked essentially the same question ",
"here",
", so I'll repost my answer to that question:",
"So the proof that what you're imagining is not possible is known in thermodynamics pedagogy as ",
"\"the equivalence of the Clausius and Kelvin statements of the second law\"",
".",
"You're imagining a device which uses heat to produce work, but without rejecting any heat to a cold reservoir, and so not requiring a difference in temperature between two reservoirs. This already violates of one the 2nd law of thermodynamics in one of its forms (Kelvin's statement of the law), but we can make the problem even clearer. In ",
"this diagram",
" (from the earlier link) then your proposed device is the imagined engine on the left, and we have connected it to a Carnot engine, which is a reversible heat engine. The Carnot engine is using the energy provided by your imagined engine to move heat from the cold reservoir to the hotter one (as the efficiency of the Carnot engine eta is always less than 1). The total effect of the these two engines is then to transfer heat from the cold reservoir to the hot one, without using any energy, which is clearly not okay (this directly violates the Clausius statement of the 2nd law), as it decreases the entropy of the engines/reservoirs system as a whole. Therefore your imagined engine is impossible.",
"There is no way around this in the future. The laws of thermodynamics sit somewhat separate from the rest of physics in that they are essentially the direct consequence of the statistics of large numbers of particles, and don't depend on what theory you use to describe those particles. The laws of thermodynamics will therefore never be superseded by some more advanced theory with a loophole, because the laws of statistics will never change."
] |
[
"If I have a device powered with 2 AA batteries, and the device is at 50% battery life, but I only have 1 AA battery left; would switching only one battery increase the battery life of the device?"
] |
[
false
] |
i.e. I have an xbox controller that is powered by 2 AA batteries. My controller is almost dead, at 20% battery life. If I switch out only one battery for a new one, does that increase the battery life of my xbox controller? Or does it remain at 20%?
|
[
"It increases it, but not as much as you'd think because the new battery winds up charging the old battery, so energy is lost to heat that would otherwise be useable energy. You could actually damage the batteries doing this unless they are rechargeable batteries."
] |
[
"If they are in parallel then this is dangerous even with rechargeable batteries as you could get large currents and the batteries might overheat.",
"If they are in series you get a very small increase in running time as you can discharge the weaker battery slightly more now."
] |
[
"It is dangerous to do so.",
"The problem is that you do not want to reverse charge batteries. Things will look good when you put the new battery in, but the flat battery will keep discharging. It will fully discharge, and then the fresh battery will start pushing current backwards through the battery, trying to reverse-charge it. This causes lots of problems, which will include making the flat battery leak.",
"Don't do it."
] |
[
"Are most Hypergiant stars already dead?"
] |
[
false
] |
Got a question are most Hypergiant stars already dead? Due to the fact they only live for millions of years. Or are hypergiants still being created? Second question is it safe to say most of the visible/ observed Hypergaints we know such as UY Scuti, and Canis Majoris have died now? Apologies for the stupid question but i was struggerling to find an answer on google for this, as it only pertains to blue giants of the largest type. Most questions similar are around stars in general meaning all sizes which means they can live for billions of years, but mine is only about the hypergiants that are noted to have much shorter lifespans of millions of years. taking into account the distance light has to travel and their relative shorter lives i thought its worth a go asking.
|
[
"I can’t speak to whether hypergiant star formation is greater/lesser/the same as early phases of the universe, but I can at least take a stab at your much simpler second question.",
"Hypergiant stars that are in constellations visible to the naked eye must be both bright ",
" relatively close. Apparent brightness is inversely proportional to the square of distance, so even the brightest possible stars will be ",
" too dim to see unassisted from a million light years away. From Wikipedia, giant stars in Scutum and Canis Major constellations are only thousands of light years away. E.g. UY Scuti is listed as ~9kly (+/- 1k) away. Even though hypergiant stars have much shorter lives than the sun (millions rather than billions of years), the time lag from light speed delay is only thousands of years. Stellar evolution is much harder to predict over such short time scales."
] |
[
"What kind of gibberish is this answer?"
] |
[
"What kind of gibberish is this answer?"
] |
[
"Fossils - How do fossil hunters know which rocks have fossils in them, before they split them?"
] |
[
false
] |
I was watching pawn stars where one guy brought in some rocks that he split himself, that contained very good looking fossils. How on earth did he know that those would have a fossil on the inside of them?
|
[
"According to my paleontologist friends: They don't know. They go to sites where fossils have been documented and just keep splitting until they find something. "
] |
[
"Thank you. That question has been bothering me for a long time. Wow...so they just keep cracking open rocks until they find a fossil huh? I don't doubt that is the way they do it...but it just sounds a lot less efficient than I had thought."
] |
[
"Some fossil beds are quite rich so it isn't as painful as it sounds. Additionally nature does a lot of the work for you: naturally broken surfaces may reveal fossils."
] |
[
"Spatiotemporal perception of the Big Bang"
] |
[
false
] |
Ok so can someone please explain to me (or direct me to info on) information on how the spatiotemporal Big Bang relates to our perception of it? To explain my question further - why is it, if we are detecting photons from close to the origin of the universe (temporaly), should we not perceive a photonic origin? The universe is expanding, meaning that the photons are borne with this expansion(?) effectively making them curve through spacetime (?), but surely there would still be measurable variations in intensity indicating a specific origin. Thoughts? CMB radiation and astrophysics are by no means my shtick so my brain ain't got all the necessary cogs, but I'm keen to know and happy to engage...
|
[
"You seem to be using words in ways that are entirely new to me. In particular, I have no idea how you're defining \"spatiotemporal,\" \"photonic,\" \"borne\" or \"curve.\" Or, for that matter, \"origin.\"",
"Let me see if I can clear some of this up.",
"Once upon a time, the entire infinite universe was filled with a very hot, very dense plasma made up mostly of hydrogen ions — individual protons, in other words — and electrons. All the ",
" that made up this plasma was very energetic, so it was constantly emitting electromagnetic radiation. But because the ",
" was so hot and dense, an individual photon couldn't travel very far before it interacted with a proton or an electron.",
"But over time, things changed (for reasons I won't go into here in an effort to avoid confusing you further). The energy density of the entire universe fell to the point where hydrogen nuclei — again, single protons — and electrons could get together in a fairly stable way to form hydrogen atoms. At about this time, the ",
" of a typical photon became quite large. In other words, one of those many photons that was skittering around the universe could expect to travel quite a long distance before it interacted with anything.",
"Those photons are still around today, filling all of space. They've been redshifted by a factor of about a thousand, so they lie within the microwave part of the electromagnetic spectrum now, but we still see them everywhere we look. That's what we call the cosmic microwave background, or CMB.",
"Sometimes the CMB is referred to as the emission from the \"surface of last scattering,\" but this can be very misleading to laymen. The surface of last scattering isn't a ",
" surface, like a great wall in space. Rather, it's a \"surface\" in spacetime, corresponding to every point in the universe at a given point in time. That given point in time was about thirteen and a half billion years ago, or about 300,000 years after the beginning of the Big Bang. The light emitted at that time continues to fill the universe today, just as light from your lamp fills the room you're in right now. Everywhere we look, we see that light, not because it's shining at us from some kind of sphere surrounding us, but because it "
] |
[
"I really don't understand your question. At some point in the past the universe was very dense and hot so it was a opaque plasma. If you look far enough you can still see that plasma, that is what the CMB is."
] |
[
"Thanks for your reply, and I apologise for the ignorance from which I am trying to comprehend.",
"Does this mean that the CMB map depicts the perceived density of microwave radiation?"
] |
[
"Can we, or will we be able to in the future, see \"outside\" of the observable universe by measuring the effect of gravity objects from outside that limit on the objects at the edge of the observable universe?"
] |
[
false
] | null |
[
"If the light from the object hasn't had time to reach us, then the transit time of the gravity from the far object to the close one plus the time for the light from the close one to us also wouldn't have time."
] |
[
"If we were able to infer planets we couldn't see by observing the effect their gravity was having on objects we could see would the same type of effect hold true for the outer extents of our vision in the universe?",
"If we cannot do this yet, but should in theory be able to at some point, what types of technological developments are necessary for it?"
] |
[
"This is essentially what was done with the recent BICEP2 result. We can see back to about 400,000 years after the big bang in the cosmic microwave background, but before that the universe was opaque to light. However, they were able to see the gravitational imprint from beyond that. Other ways to do that would be direct gravitational wave detection, or primordial neutrino detection.",
"If you're asking about seeing the gravitational pull of objects outside the observable universe, we wouldn't be able to see it because gravity travels at the same speed as light."
] |
[
"What can we expect the world in terms of population, famine, resources to be like in 40-50 years?"
] |
[
false
] | null |
[
"There's a thing called the \"Rule of 70\". Basically, you take the \"human growth average\" (which is 1.1% at the moment) and divide it into the number 70. So, if the human growth average (HGA) stays constant for the next 70 years (which it definitely won't), it would take roughly 70 years for the human population to double.",
"However, you may have noticed that countries around the world are starting to have a negative HGA. A good example is Germany. The reason why their HGA is now negative is due to their country's culture catching up with their technology. Here is how a country's population is affected by medical/technological advancement. ",
"pre-modern: both the child birth rate and death rate are relatively equal, and both quite high. ",
"early industrialization: Greater wealth means better food/health/sanitation. As a result, children don't die as much. However, the culture still calls for a massive birth rate. This creates a population explosion. ",
"Mature industrialization: The child birth rate declines because they aren't as much of an asset, and they're also getting more expensive. ",
"The child birth rate declines even further and matches the death rate. ",
"The world averaged as a whole is currently at stage 3. ",
"It's generally accepted that the world's population limit is ~11 billion with today's current technology. Possibly 12 billion if we realllly scrimp and save. However, it's also speculated by others that the population will hit a plateau at around 9 billion, optimistically. Keep in mind the 11 billion population is only possible if everyone has a vegetarian diet. ",
"If the planet doubles in population and hits 14 million, we will not be able to support it (with current agricultural technology). Basically, the earth's carrying capacity depends upon human technology, rather than the environment so much. Take a look at the Green Revolution in the 40's. ",
"Can we safely predict some nations will be stable? Yes. Germany is an example of going \"further\" than stability, and is declining in population. The U.S. is also declining in its HGA (though is definitely still positive). Basically, just refer to the 1-4 step process. ",
"However, there are problems in Africa. They entirely skipped the early-industrialization period, and are basically between step 2 and 3. There is a problem because the technology came from the outside world, rather than within. Therefore, their culture is not changing, and their child birth rate is still ridiculously high, even though their death rate has plummeted. ",
"If I got anything wrong, someone please correct me. I've got some notes on this that I can't find at the moment, and so this is from memory. (aside from some google searches on the current HGA and things like that).",
"edit: Just a little factoid: There is only .76 acres of arable land ",
", and that number is going to just keep on going down. Especially if we keep degrading the soil we use...but that's another story. "
] |
[
"Well, going by the 1-4 step model, I'm assuming that China will level out. It's industrializing extremely fast, so I'm not surprised by the population boom its been having for a bit now. The culture will probably \"catch up\" with the technology, but I have no idea of a time frame. Plus, I expect the chinese government will want to curb population growth sometime in the future, and will probably put forth propaganda to help that happen.",
"I'm not educated enough on what's going on in India to comment :/"
] |
[
"Well, going by the 1-4 step model, I'm assuming that China will level out. It's industrializing extremely fast, so I'm not surprised by the population boom its been having for a bit now. The culture will probably \"catch up\" with the technology, but I have no idea of a time frame. Plus, I expect the chinese government will want to curb population growth sometime in the future, and will probably put forth propaganda to help that happen.",
"I'm not educated enough on what's going on in India to comment :/"
] |
[
"Why is immunity to a disease determined only by the amount of circulating antibodies in the blood and not by other things as well such as T cells or Memory B cells specific to the disease?"
] |
[
false
] | null |
[
"It isn't. Antibody titres ",
" with specific immunity to a particular pathogen, and they certainly are a crucial component of adaptive immunity (see ",
"agammaglobulinemia",
") but are not the ",
" determinants of immunity (as you alluded to). We ",
" also determine if a patient is immune by isolating CD45RO",
" CD45RA",
" central memory T cells specific to the antigen of interest. This, however, is considerably more time-consuming and expensive than measuring antibody titres (which can be done by performing serial dilutions and ",
"ELISAs",
")."
] |
[
"Thank you. How about if a patient has memory B cels and memory T cells specific to the pathogen but very low or no free serum antibodies towards the pathogen. Would they still be considered immune?"
] |
[
"What we're talking about is the distinction between, and relative contributions of, ",
"cell-mediated immunity",
" (T cells, NK cells, antigen-presenting cells, etc. all working together to orchestrate and tune the immune response) and ",
"humoral immunity",
" (an antibody response). ",
"Most often, these responses act synergistically, but the relative importance of each depends on the nature of the infection. They also feed back into one another: antibodies coat (",
"opsonize",
") a target by binding with their variable (",
"Fab",
") ends while their constant (",
"Fc",
") regions stick out. Macrophages and other cells have Fc receptors on their surface that bind the antibody-target complex, then they internalize it and load the antigenic peptide onto MHC Class II for presentation to T cells. T cells activated by cells presenting antigen in this way can then differentiate into Th (T helper) cells that, in turn, ",
"provide B cell help",
" that stimulates the production of more antibody. Alternatively, in some contexts antibody binding can promote ",
"antibody-dependent cell-mediated toxicity",
" by NK cells, macrophages, eosinophils, etc.",
"Each can occur in isolation as well, though: CD4+ Th1 T cells cause ",
"Type IV hypersensitivity reactions",
" in the absence of a humoral response, for example, while some pathogens stimulate and are resolved by humoral immunity only, with no contribution from or requirement for T cells. "
] |
[
"Why are there no apes, monkeys, etc. native to North America?"
] |
[
false
] | null |
[
"While South American monkeys did make it up into central America and Mexico, the climate and topography of the southern United States (think Arizona, New Mexico, Texas) does not foster a good habitat for those types of animals. Monkeys and apes are adapted to climbing trees, and any monkey that attempted to migrate northward would have probably died of exposure in a desert or flat grassland. ",
"Also, most monkeys survive eating tropical fruits and flowers, and the types of trees native to the US do not have those food sources (Arizona has a lot of evergreens, for instance). ",
"Source: evolutionary biologist "
] |
[
"How the ancestors to new-world monkeys got to South America is unclear, it is theorized that a small number were stranded and rafted across the, then relatively small, Atlantic Ocean. ",
"Edit: I just decided to share the prevailing theories and I get downvoted; I love it."
] |
[
"This happens regularly, animals are swept out to sea and float on logs or such and land on opposite shores. However they are normally quickly eaten - unless they are more fit than the animals in their niche and can find food easily and safely."
] |
[
"Does your beard grow faster if you shave it often?"
] |
[
false
] |
I saw this in a thread in an ask reddit about myths and I would like if somone could give me more information on why this is a myth and what can cause a beard to grow faster.
|
[
"No. There is absolutely not reason to think it does biologically, and there is no evidence that it does. ",
"Perception can fool you good, though. After you've shaved the next day, all growth is a lot more beard than you had before! The next day, it doubles! The third day, it grows by another 50%! Then 33%. 25%. 20%. 17%. 14%. 13%. 11%. 10%. Well, you get the idea.",
"By the time you have a long beard, it only grows by a tiny bit compared to what you already have. Shave again, and the next day you see enormous amounts of growth!",
"People are just easily fooled."
] |
[
"People are easily fooled.",
"More accurately, people's brain are adapted to think logarithmically and not linearly."
] |
[
"Another example may be that you feel the time went a lot slower when you were younger."
] |
[
"Rogue planets ejected from solar systems:"
] |
[
false
] |
What is the probability that some have serially (obviously over a period of time) encountered other stars and increased velocity due to a "sling shot" effect? Relative to the currently assumed number of rogue planets in the Milky Way, how many might have acquired significant relativistic speeds (say near .2 or .3c)? And lastly, what would happen if a rogue the size of Neptune entered our system and impacted the Sun at .3c?
|
[
"First of all, I wouldn't really call .2 or .3c \"relativistic,\" there aren't really very large relativistic effects. The phrase relativistic speed is highly context-dependent, but a good benchmark would be around .866c.",
"Second, it would be extraordinary, dare I say impossible, for a planet to escape a solar system with speeds at .2 or .3c due to interactions with the other planets or the star. I suppose it's possible an exception could occur if the system was a binary system of two neutron stars or something, but a system composed entirely of main-sequence stars and relatively normal planets will not achieve those kinds of ejection velocities, because the interacting bodies would collide before they got close enough to transfer that much momentum.",
"What's more, there simply isn't enough momentum to get something that fast. By multiplying the orbital speed of Mercury times its mass, we get the orbital momentum of Mercury is 1.564×10",
" kg m/s. We can compute this for all the planets and sum it up to get 3.225×10",
" kg m/s. If this was ALL transferred to Mercury somehow, and all the other planets stopped dead in their orbits, Mercury would only be going about .326c. And that's if ALL other planets transferred ALL their momentum to Mercury, the lightest planet.",
"For a bit of perspective, the fastest object we've ever observed - I should say macroscopic object, subatomic particles move all kinds of speeds - is the star S2, which in it's orbit around the black hole Sagittarius A* moves at up to .02c.",
"Finally, you ask what would happen if Neptune hit the sun travelling at .3c. Well, it would impact the sun with 4.46×10",
" J of energy. For context, this is as much energy as the sun outputs in about 35 million years. Furthermore, I assume that the force would help Neptune's 8.194×10",
" kg of hydrogen fuse almost instantly, resulting in an addition 5.16×10",
" J of energy released - another 400,000 years of solar output.",
"So in short, the effects would be fairly devastating."
] |
[
"Great answer!",
"What about when galaxies collide? With the relative velocities of, say, the Milky Way and Andromeda, how much could a planet or star's momentum change?"
] |
[
"We don't know.",
"Galaxies are pretty empty places, meaning that it is quite likely that our Solar System would not be impacted severely by the eventual merger of the Milky Way and Andromeda."
] |
[
"Why don't we just irradiate all our food products?"
] |
[
false
] |
Instead of pasteurizing things or preserving them chemically, why don't we just irradiate our food and then seal them up, keeping them safe forever? I've heard of this before, but it doesn't seem to be very widespread. Wouldn't that pretty much get rid of any chance of food poisoning or other similar conditions?
|
[
"Looks like you have your answer. We don't irradiate all our food because of all the consumers who can't be bothered to ",
"understand the process.",
"The food is irradiated, people. not you."
] |
[
"Radiation causes mutations in DNA, which can lead to cancer. This seems like a terrible way to keep food fresh when you look at the effects it has on other things.",
"Are you worried about your food getting cancer? You know it isn't alive anymore, right?"
] |
[
"Radiation causes mutations in DNA, which can lead to cancer. This seems like a terrible way to keep food fresh when you look at the effects it has on other things.",
"Are you worried about your food getting cancer? You know it isn't alive anymore, right?"
] |
[
"How does one actually test for horsemeat?"
] |
[
false
] |
Here in Europe they are testing all our meat for horse as it turns out that much of our cheap 'beef' is actually horse. What is actually required to prove horse or beef? Can you tell under a microscope?
|
[
"It's come through DNA testing. "
] |
[
"It was minced. It was determined by DNA testing. ",
"Although now, apparently there are concerns it was donkey meat. "
] |
[
"If it's minced and mixed with ground beef, then only DNA testing would help. However, if you have raw steaks, the horse meat is leaner, darker and has a different texture and taste, so if you are a food inspector you would be able to tell the difference. Similar to how buffalo meat is different from beef."
] |
[
"If a grenade can kill a group of people so easily, why can a single person jumping on it walk away from the ordeal?"
] |
[
false
] |
Was reading up on the recent Medal of Honor recipient...
|
[
" Out of several dozen historically documented.",
"So I would say the odds of survival are 100 to 1 or less.",
"The first is Pfc Jacklyn H. Lucas, druing the battle of Io Jima in WW2. Pfc Lucas had the sense to cover two japanese grenades with his M1 steel helmet and using his rifle to further shield his body. He was still severely wounded in the arm and leg and carried a large amount of sharpnel around for the rest of his life. Lucas received the congressional medal of honor.",
"The second was LCP Matthew Croucher, a Royal Marine, in Helmand province Afghanistan, in 2008. After stumbling on a tripwire grenade booby trap, he had the presence of mind to pin the grenade to the ground with his combat rucksack, then tuck his arms and legs against his body in a fetal position. He was also wearing heavy body armor which was badly damaged and almost certainly saved his life. Croucher was awarded the George Cross."
] |
[
"Generally they do not.",
"A person does not jump onto a grenade intending to save himself. He does it in order to shield everyone else around him-- saving their lives by the almost certain sacrifice of his own. That is why it's considered a rare act of bravery, enough to earn medals.",
"In the rare cases the person has survived, it's because he placed something between himself and the blast. For instance there's one example where a British Marine ",
"Matthew Croucher",
" threw himself down with his backpack on top of a grenade. The explosion shredded the pack and threw Croucher away, but he escaped fatal injury because the pack absorbed some of the blast energy and the shrapnel was stopped by his body armor."
] |
[
"The most dangerous part of a grenade is the shrapnel and not the actual explosion.",
"True",
"A person's body can redirect the force of the blast since energy takes the path of least resistance.",
"Not even close.",
"the pressure wave of an explosion follows the \"Inverse square Law, so the force of an explosive rapidly decreases with distance."
] |
[
"Can radio waves outside the visible light spectrum be thought of as colors we cannot see/ comprehend?"
] |
[
false
] |
I have had friends for years try to blow my mind saying that every radio waves is a different "color" that we cannot see or observe and so there are colors we cannot comprehend. I have never really thought that they were correct in that thought so I am wondering if there is any basis or discussion as to whether or not these waves are colors we cannot see or just waves.
|
[
"Yes! The different frequencies of visible light are what we detect as colors. You can totally make the same argument for larger differences in frequency. ",
"No! The only reason color has meaning to us is that we have specific structures in our eyes that parse a very small part of the spectrum that way. Since almost no creature has similar structures for waves (especially radio) outside the visible spectrum (a few creatures are on the edge of visible, namely IR and UV) there is no color analogy to be made. ",
"So it's a philosophical question. And like all philosophical questions, there isn't a definite answer. "
] |
[
"it is more accurate to say that both radio waves and visible light consist of electromagnetic waves. mirriam-webster defines color as a visual perception of light, a definition which most would agree does not extend past the visible spectrum.",
"radio waves and visible light are of the same nature, but they are not the same based on our definitions of each. they are defined to exist in different frequency ranges."
] |
[
"It'd be more accurate to say that the visible light spectrum can be thought of as electromagnetic waves we can detect with our eyes. Colors are just how we differentiate between those within the range that we can detect."
] |
[
"Can you describe in Layman's terms how science believes other dimensions exist? And the proof behind this belief?"
] |
[
false
] |
I was watching a science show and it was mentioned that physicists believe there can be multiple dimensions, they said something like 10 or 11, happening at the same time as ours. How do they have any proof for that? What are they basing this idea off of? Is it a widely accepted idea or are there only a few that believe in multiple simultaneous dimensions?
|
[
"The requirement for extra dimensions emerges in ",
"string theory",
". 11 is the number of dimensions required in M-theory. All those theories are attempts to describe the universe with a single theory (i.e., encapsulate both general relativity and the standard model in the same mathematical framework), and require the extra dimensions in order to be mathematically consistent. As far as \"proof\"- all the theories thus far which describe both general relativity and the standard model require additional dimensions to work mathematically. So there is mathematical reason to believe there may be more dimensions. However, there is not yet any direct experimental evidence for dimensions beyond the 4 readily apparent spacetime dimensions (though experiments have attempted to probe the existence of very small extra dimensions by checking whether the inverse-square law of gravity holds at very small distances. Thus far, it does.) I would say it's neither widely accepted nor that \"only a few believe it\". String theory is essentially irrelevant to physicists who are not working on string theory (because it has not yet made any falsifiable predictions) so I (and I think many others in physics) are basically agnostic about whether there are a bunch of additional dimensions (since they have no thus-far measurable effect on the world even if they do exist.)",
"edit: As a disclaimer, my experience is in experimental physics, not theoretical physics. I'm sure a string theorist would give you a more positive view of string theory if they responded."
] |
[
"String theory hasn't yet made any predictions (besides supersymmetry, which is a requirement for string theory) that are testable ",
". Just because we don't currently have the means to falsify the theory doesn't mean it isn't falsifiable.",
"NINJA EDIT: Also, string theory is done in ten dimensions (and M-theory in 11) not because it makes the math simpler but because it is actually required for the theory to be consistent."
] |
[
"As far as \"proof\"- all the theories thus far which describe both general relativity and the standard model require additional dimensions to work mathematically.",
"I don't believe this is true. I'm not an expert on Loop Quantum Gravity by any means, but I'm fairly certain it doesn't have any particular requirement for extra dimensions. In fact, I've heard of models in which dimension isn't a fundamental property of the universe at all, but rather an emergent property."
] |
[
"For Maritime Archeologists: Name the top five shipwrecks that no one has heard about."
] |
[
false
] |
Also, bonus points for talking about what was historically cooked aboard these shipwrecks.
|
[
"Top five that ",
" has heard about? Tall order!",
"But here are a few you ",
" not have heard about, in no particular order. These aren't the five most significant or anything, but they're cool, and important for various reasons.",
"Sutton Hoo",
" was not a wreck, but an Anglo-Saxon burial from the 7th century. There're really beautiful artifacts from the site, including a helmet that's become iconic.",
"Blackfriar I is a 2nd century ship found in London. It's neat because it may show frame-first construction of a native style, rather than the mortise-and-tenon construction typical of the Romans who ran the place. Mortise and tenon means that the planks were held together along the edge with pegs and slots, rather than by internal frames. In any case, it's definitely different than what was going on in the Mediterranean.",
"Serce Limani, an 11th century ship which sank in Turkey, is also important. It doesn't have any mortise and tenon joints at all, and is one of the early examples of naval architecture. It was built in some sort of units, and the frames were spaced in multiples of that. The keel and posts were built first, and then a pair of midship frames. The shipbuilder would have added a couple more frames, and then put planking on the bottom. Once the bottom of the hull was described, the shape of the rest of the ship could be determined, and it was finished. The ship was carrying glass, which was likely some sort of glass-recycling effort. It would have been steered with a pair of rudders hung from the quarters.",
" was a small French ship which sank in 1686 in Texas. This was an early attempt by the French to colonize the Mississippi river, but a poor map misled them and they wound up in Texas. Combinations of poor decisions, ineffective leadership, bad luck, and hostile natives led to their colony getting into some trouble. Then their last remaining ship, ",
", sank, and that was the end. Their leader, La Salle, tried to convince people to walk to the French settlement at Quebec with him, but they wound up killing him. A couple guys did walk to Quebec, and survived. In 1995, the ship was discovered, mostly intact on the bay floor. It was raised whole, and while the final publication isn't out just yet, there are a multitude of artifacts aboard, including most of what you'd need to start a colony. That ship was built with doubled internal frames, which is a construction method usually connected with the 18th century. It was also a \"ship kit\" that had all of its frames numbered, so it could be assembled in the new world. Because of space issues, the French wound up building it in France and sailing it across to the new world itself. Lots of artifacts, new shipbuilding techniques, and the first European permanent settlement in Texas make this one a big deal.",
"The fifth is a bit of a challenge. I want to go with ",
" or Kyrenia, but those are pretty well known. Instead, I think I'll break with the spirit of the question a little and go with a ",
" of wreck - the ships buried under cities. One of those, the Ronson ship, was found in Manhattan, what's now several blocks from the water. It was most probably a mid-18th century ship, and only the bow was recovered. Another example of this sort of thing is ",
", a wreck found just next to the Transamerica Pyramid building in San Francisco. It was a whaling ship that brought gold rush folks to California. Like so many others, its crew abandoned it for prospecting when it got there, so it was turned into a floating warehouse. A doorway was cut in the side, and it was built on, and built on, turning into more of a building all the time. Finally, fire and landfill took their toll, and Niantic was buried... only to be rediscovered in the late 70s. I chose this last pair of examples to illustrate that shipwrecks sometimes lie under our feet as well as under the waves - steamboats frequently wound up miles from the rivers they sailed on, due to shifting rivers.",
"This was a long post, but I'm glad someone finally asked something in my wheelhouse!"
] |
[
"It varies based on jurisdiction. What follows is not legal advice.",
"It depends on where the shipwreck is and who owns it. Navies don't give up title to their ships, for instance. That means the ship and everything on it belongs to them, forever.",
"Other than that, it depends ",
" on the jurisdiction.",
"But let's talk non-legally for a minute. When you remove objects from the wreck, you're stealing them from ",
". I firmly believe that cultural heritage belongs to you as much as me, her as much as him. And breaking up the collection, moving it to places it can't be accessed and likely won't be conserved... that's not right. Further, you're limiting the ability of researchers to learn anything from what you've taken from a wreck site. Artifacts can be incredibly helpful in figuring out what went on with a wreck, and it's stealing part of the data set if you take them. ",
"This isn't to say that private individuals or companies can't do great archaeology. It's just that frequently treasure hunters ",
". It's just not their goal.",
"Last, the economics of treasure hunting are not great. The vast majority of ships weren't carrying any precious metals. Even if they were, it costs a fortune to find them and get to them. There have been very few financially successful treasure-hunting ventures.",
"In short, don't treasure hunt. :)"
] |
[
"You're one of my favorite ",
"/r/askscience",
" panelists, and I found myself amazed that no one really asked you questions on your fascinating subject. Also, ",
"this",
". :)"
] |
[
"Are there any plants or animals that are bioluminescent in the infrared spectrum only?"
] |
[
false
] |
Would this be possible?
|
[
"Hot blood animals, like mammals and birds, emit in the IR all the time, so in a sense they're bioluminescent in the IR only unless they are also standard light bioluminescent."
] |
[
"Can you legitimately call black-body radiation \"bioluminescence\"?",
" "
] |
[
"Electromagnetic energy emitted in the IR region is just as ",
" as any other. The difference is that IR energy is broadly absorbed by many molecules, including those in the air surrounding the emitter, in such a way that a good portion is converted to heat energy."
] |
[
"When you squint really hard, why do you hear a rushing wind like sound?"
] |
[
false
] | null |
[
"I believe what you are describing is a contraction of the ",
"tensor tympani muscle",
". This is a muscle that actually functions to dampen sounds, particularly those produced by other functions of your head, such as chewing.",
"I am able to contract this muscle voluntarily and create the wind-rushing, or roaring type sound. This also happens when I yawn. When this occurs I generally cannot hear other external sounds, or they are dampened to the point that they are unintelligible. "
] |
[
"Congrats! You are an ear rumbler. ",
"Short summary:\nYou have the ability to control your tensor tympani muscle, which is used to control your cochlea in response to loud sounds. This creates a rushing, rumbling sound in your ear. Some people can only do it with eyes closed, some for only a limited time. Some people experience a clicking sound before rumbling. It varies from person to person. I can do it by closing my eyes, opening my mouth wide, or just normally, but for a short time. ",
"It is a very rare trait. Other ear rumblers can be found at ",
"r/earrumblersassemble",
" ",
"Welcome to the club!"
] |
[
"Oh wow I did not know that this wasn't something everybody can do.",
"I can literally do this continuously and make different noises. I get these different crackling sounds too and can move the muscle so that I hear only that or only the rushing sound or both.",
"I also contract that muscle to pop my ears or 'valsalva'"
] |
[
"What makes us wake up when we've had enough sleep?"
] |
[
false
] | null |
[
"This is a common question here. I'll copy my answer from ",
"the last thread on this topic 2 weeks ago",
".",
"Besides environmental stimuli, there are ",
"two main processes that regulate sleep",
". It is the combined effect of these two processes that causes us to fall asleep and awaken at particular times.",
" The brain has a master ",
"circadian clock",
" that keeps an approximately 24-hour schedule. The clock resides in a region of the brain called the ",
"suprachiasmatic nucleus",
" (SCN). There are ",
"connections from the SCN to several other sleep-regulatory regions of the brain",
", allowing the SCN to promote sleep and wake and different times of day.",
" During wake, certain ",
"sleep-promoting chemicals accumulate in the brain, including adenosine, nitric oxide, and some cytokines",
". These chemicals are then cleared from the brain during sleep.",
"These two processes are integrated by certain sleep-regulatory neural circuits. ",
"A circuit in the hypothalamus/brainstem called the ",
" is thought to play a central role",
". When the overall signal for wake (",
"from circadian, homeostatic, and other processes",
") exceeds some critical threshold, this circuit switches abruptly into 'wake mode'. This activates a ",
"population of neurons in the brainstem and hypothalamus that express wake-promoting neurotransmitters",
", flooding the cortex and thalamus with these neurotransmitters.",
"There are a number of other subsidiary systems that help to express variations in the circadian and homeostatic processes, making sleep and wake states more robust. These include hormones like ",
"melatonin",
", whose release is timed by the SCN's signals to the pineal gland, although melatonin is not ",
" for sleep and wakefulness. Individuals who express no melatonin (",
"e.g., tetraplegics",
") still naturally sleep at night and wake up in the morning, they just have slightly worse sleep quality on average."
] |
[
"I have a link to an article discussing that which I'd just end up copying verbatim, so I'm just going to post it here.",
"The gist of it is that the body prepares you for waking up by releasing a hormone called ACTH (adrenocorticotropic hormone) about an hour before you prepared to wake up.",
"http://m.psychologytoday.com/articles/199905/the-stirring-sound-stress"
] |
[
"Do neurologists have any idea where that critical point is when the threshold is exceeded? Or is research still being conducted on it? "
] |
[
"why does our minds make clocks sounds like 'tick, tock' when in fact it's just 'tick, tick'"
] |
[
false
] | null |
[
"In a pendulum clock, the pendulum engages an ",
" ",
". Since both sides of the escarpment are not the same, it will make a unique sound for each direction its travelling.",
"http://en.wikipedia.org/wiki/Escapement"
] |
[
"*Escapement",
"TIL Escarpment is also a word, but with an entirely different meaning.",
"He's absolutely correct though. And it's not just in pendulum clocks either, all mechanical clocks (and wristwatches) have these escapements that make the ticking noises, and they're always asymmetrical."
] |
[
"Oops. Edited."
] |
[
"If velocity is relative, can I say I am travelling at c from the view point of a photon?"
] |
[
false
] | null |
[
"Something moving at c does not have a valid rest frame, it would violate the postulates of SR. So you cannot make any statements about the \"viewpoint of a photon\"."
] |
[
"I'm reading about special relativity now and I'm still trying to wrap my mind around the concepts. The rest frame that you mentioned is the inertial frame of reference, correct? So does the photon have a non-inertial frame of reference even though it is no accelerating?"
] |
[
"The rest frame that you mentioned is the inertial frame of reference, correct?",
"The frame I talked about (the rest frame of a photon) ",
". That's why it's impossible to even talk about the \"point of view\" of a photon."
] |
[
"Why do cold drinks/foods trigger the cough reflex?"
] |
[
false
] |
For bonus points, why does it not happen to everyone?
|
[
"Irritation of the sensory branches of the ",
"internal laryngeal nerve",
" at the base of the tongue and epiglottis, and perhaps other branches of the ",
"vagus nerve",
" distributed along the esophagus, triggers the motor branches of the vagus nerve, and may induce the cough reflex."
] |
[
"This happens to me to too, although i don't know why. "
] |
[
"Who is upvoting this? Isn't that what the OP is trying to do?"
] |
[
"How come aeroplane windows are so small?"
] |
[
false
] |
I've looked back at photos of planes going way back, and the windows have been tiny for ever. Surely we can do better. I like to look out during take-off and landing, and I like to look at the clouds. Unless I have the window seat, I can't see jack.
|
[
"First of all, for reasons of aerodynamics, they must be round. Square windows resulted in cracks in the fuselage and thus crashes. Second, the windows must be equipped with extremely durable panes inside and out for resistance to both ground and high-altitude pressures and temperatures, which are at extreme opposites, as well as wildly varying climate variables. Last of all, the window size isn't really a concern for aircraft manufacturers. Passenger photo ops and ganders at skylines just aren't a concern as opposed to carrier safety issues. "
] |
[
"I should also mention that having windows at all is a huge hit to the strength of the aircraft structure. Windows are basically a bunch of little holes in your cylindrical body, which must be designed around to maintain the integrity of the structure. "
] |
[
"There haven't been many advancements in the fuselage structure of aircraft. Most fuselages are still made of aluminum and with similar structures of aircraft 40 years ago. However, now with carbon fiber beginning to make its way into the fuselage structure windows are allowed to increase in size since the minimum thickness of carbon fiber has enough strength to support bigger windows. This is the reason the windows on the 787 are much larger then other similar aircraft. "
] |
[
"Why is Cantonese categorized as a 'dialect' of Mandarin?"
] |
[
false
] |
Why is Cantonese categorized as a 'dialect' of Mandarin instead of a separate language? When one thinks of dialect, it tends to be the same langauge with slight variation due to local culture or isolation. British English is a dialect of New York English which is a dialect of Texas English which is a dialect of Australia English. Mandarin and Cantonese, on the other hand, have very low mutual intelligibility, almost about the same as English versus Spanish. There's an idiom in cantonese for this. It's "the chicken and the duck trying to communicate with each other". They might look similar, but don't let that fool you; one can only quack while the other bwarks. There's no way they can understand each other. It's easier to see swedish as a dialect of norwegian than mandarin a dialect of cantonese. Here's an example of a popular song, with the same lyrics, sung in both and .
|
[
"I don't think that is quite correct. Cantonese is actually considered a dialect of Yue Chinese while Standard Chinese (what many people refer to as 'Mandarin') is a dialect of Mandarin Chinese. The term Chinese refers to a whole family of related languages that are mutually unintelligible but share some key characteristics like grammar and writing system. ",
"Sauce: ",
"http://en.wikipedia.org/wiki/Chinese_language",
" "
] |
[
"I've never heard Cantonese referred to as a dialect of Mandarin. I have very commonly heard both of them referred to as dialects of Chinese. The line between what constitutes a dialect vs. a language is not scientific, it's political....as some one here already said, a language is a dialect with an army and a navy."
] |
[
"Classification is important, absolutely. However, there is no benchmark by which we can say that A and B are separate languages, as opposed to being two dialects of the same language. All we can do is mark degrees of similarities or differences. ",
"As a person who has resided there, all the \"dialects\" of Chinese are indeed referred to as \"Chinese\". Yes, this is an oversimplification, there are at least 6 different major groups and at least dozens of subgroups, but in general they are called \"Chinese dialects\". And interesting comparison would be India, where much closer variants are often referred to as entirely separate languages.",
"Again, the final answer of what makes the difference between a dialect and a language (or at times even an accent) is the political party in charge of the area in which it is used."
] |
[
"How does an ulcer in your mouth heal?"
] |
[
false
] |
I thought of this due to an ulcer in my mouth. It seems to me that it is under constant assault to extremely harmful bacteria. How does it heal under those conditions? Why doesn't my mouth just rot out?
|
[
"If you're talking about a canker sore, this is incorrect. The underlying cause of ",
"canker sores",
"/oral ulcers are not known, but is not usually caused by herpes simplex. If you're talking about cold sores, then you have the herpes simplex virus, or very rarely in the case of what's commonly referred to as a canker sore.",
"In terms of the healing process, I can only speculate based on what I know about wound healing, but ",
"most of the bacteria in our mouth are beneficial",
" and again, while the cause is generally unknown, it's hypothesized to be an immune response, meaning it's not generally an infection that causes the pain but rather the immune response to mucosal damage or whatever the hell causes canker sores ( I get them all the time and I hate it). These would presumably heal under the normal wound healing pathways once the immune response has subsided, which would involve reepithelialization of the membrane primarily."
] |
[
"If you're talking about a canker sore, this is incorrect. The underlying cause of ",
"canker sores",
"/oral ulcers are not known, but is not usually caused by herpes simplex. If you're talking about cold sores, then you have the herpes simplex virus, or very rarely in the case of what's commonly referred to as a canker sore.",
"In terms of the healing process, I can only speculate based on what I know about wound healing, but ",
"most of the bacteria in our mouth are beneficial",
" and again, while the cause is generally unknown, it's hypothesized to be an immune response, meaning it's not generally an infection that causes the pain but rather the immune response to mucosal damage or whatever the hell causes canker sores ( I get them all the time and I hate it). These would presumably heal under the normal wound healing pathways once the immune response has subsided, which would involve reepithelialization of the membrane primarily."
] |
[
"When your new cell growth rate is larger than the bacterial cell growth rate, your healing starts.",
"A lot of this is generalized, and more vague than it actually works, but immunology is pretty awesome to learn about."
] |
[
"Why does adding or removing just one element from a compound change the properties of the compound so much, making it sometimes even deadly?"
] |
[
false
] |
[deleted]
|
[
"There is a general answer to your question and a different answer to your specific question.",
"The general answer is that adding or removing one atom from a molecule changes the molecule's thermodynamic stability and less stable compounds are more reactive and thus tend to be better at messing things up by reacting with important chemical in the body. An example of this would be Cl- the chlorine ion, and OCl-, the hypochlorite ion. The chlorine ion is very thermodynamically stable and generally not toxic in reasonable quantities (its in table salt). OCl- is the active ingredient in bleach and is very reactive, which means it tends to react with just about anything in the body and cause lots of damage.",
"CO versus CO2 is a bit different. CO is toxic because its very good at binding to the iron ions in hemoglobin, much better at binding than oxygen. It prevents the body from transporting oxygen and causes oxygen starvation. Why it is so good at binding to ions is explained by ",
"ligand field theory",
" and the details of the energy levels in O2 and CO. Long story short, CO has a strong overlap between its unfilled pi* orbitals and most metal's d orbitals while O2 doesn't because of its different electronic structure, so CO will displace O2. CO2 doesn't have the same effect because it has different electronic states than CO.",
"There is also the answer for biological molecules, which is completely different and not my field."
] |
[
"Thanks for the reply, i understood the first half of your answer, about the stability and thermodynamics of compounds, but the second half mostly blew over me."
] |
[
"The short of the second half of his answer (CO2 vs CO) is that hemoglobin transports oxygen and CO2 through the bloodstream. CO, on the other hand, does not allow this exchange, and instead binds tightly to the iron in hemoglobin, preventing that molecule from carrying oxygen. Enough CO exposure = no oxygen in your blood, no matter how much you breath in."
] |
[
"What is stopping us from developing an alternative to the old fashioned rocket fuel launch?"
] |
[
false
] |
I'd be willing to bet that most you of immediately thought of the proverbial Space Elevator after reading the title, but that's not mainly what I'm referring to. I already know the answer to THAT question: There is no material that we can mass produce efficiently and relatively cheaply enough that has enough tensile strength to reach the desired altitude. Carbon nanotubes are a possibility I think, but we haven't come close to perfecting that technology yet. No. What I'm thinking about is more along the lines of a rail gun launch platform. Imagine a mile long rail, enclosed by a tunnel (possibly a vacuum), that slowly but surely bends toward the sky. At one end, a space ship with crew and cargo is loaded, and using magnetic propulsion, is accelerated to cosmic speeds capable of entering orbit. I'm not sure of the math behind it, but even if the G-forces required would crush a human, it could still be used to launch satellites and materials into orbit. This would at least turn the current rockets into a human-only method, greatly cutting fuel requirements for launch. Am I missing something that would make this impossible or impractical? Why haven't we already invested in this?
|
[
"Ok, let's assume you want to bring a satellite into geostationary orbit, which is pretty typical, I'd say. According to ",
"Wolfram alpha",
", that's 42000km from the core of the earth and it needs to have a speed of 3km/s.",
"That gives us the amount of energy the satellite needs, and thus the velocity it needs if you want to shoot it up there with no further propulsion, using E_kin = m/2 v",
" and E_pot = GmM/r. According to my calculations, that comes out to be around ",
" 10km/s (thats roughly mach ",
" 8, no big deal). And I didn't even include friction by the atmosphere, which is going to be enormous (think incoming space shuttle, and those probably never reach that kind of velocity by a long shot).",
"To accelerate that on a mile long rail, that would mean that, at a constant acceleration rate, the satellite would experience 3200g, where the acceleration depends linearly on the length, so 10 miles would give you 320 g. Now I am no engineer, but I'd think that even satellites are too fragile to withstand these kind of forces, not to mention the effort it takes to evacuate a 10 mile long tube. Given that this is even feasable, cause accelerating a payload weighing a couple of tons to ",
" 10km/s with magnetic fields sounds like a real challenge to me.",
"Maybe some railgun expert can tell us more.",
"Edit: In fact, friction might be the biggest problem. After the payload leaves the tunnel at over 15km/s it is going to hit a wall of air and most likely explode. But as I said, I am a theoretical physicist, not an engineer.",
"Edit2: Oops, made a small mistake, 15km/s is more than the escape velocity. Should be around 10km/s. Fixed it above"
] |
[
"I've always thought the ",
"Launch loop",
" looked interesting. Seems more feasible than a space elevator, at least. "
] |
[
"I think the major draw back to a rail gun type approach is that you would have to launch the vehicle at approximately sea level and deal with the huge aerodynamic drag.",
"A much more feasible method is to use a reusable conventional aircraft to transport the rocket to high orbit and launch it from there. This is what SpaceShipOne did.",
"An alternative is to use balloons to lift the rocket into (potentially) the stratosphere."
] |
[
"Can someone explain the phantom radio station I am picking up in my bathroom?"
] |
[
false
] |
I keep speakers in my bathroom to listen to music when showering. I never turn them off (lazy) and I leave the audio jack hanging over the TP holder so it doesn't lie on the floor. One day I'm in there and I hear classical music, very quietly. I turn the speakers up full blast and I can faintly hear some kind of radio station playing this music. I am fairly familiar with radio waves, but I always thought that the signals required a receiver to be decoded while traveling over the air. TL;DR: faint classical music coming from bathroom speakers, no radio (receiver) involved.
|
[
"What you're picking up is likely an AM radio signal; Amplitude Modulation is very “simple” in that it doesn't require a lot of technical effort to demodulate. In consequence, it often gets picked up by inadequately shielded audio circuitry of all kinds (or in your case, probably the dangling audio cable, which acts like a wire antenna) and, if there's enough amplification, becomes audible."
] |
[
"Diodes (also see rusty bolt effect) and tuned circuits help pick them up, but if it's strong enough you will hear it in your toaster. I live close enough to massive AM towers that it's a chore to NOT hear it on all my stuff (even my air conditioner motor). ",
"Surely you've heard the cell phone blips/chirps on speakers/recording equipment. They even sell cell phone 'charms' with a light in them that's powered by the cellphone chirp signal your phone makes, so you can tell you're getting a phone call. "
] |
[
"The only things you need for a simple AM radio receiver are an antenna, a tuned circuit, and a rectifier. This is how a ",
"crystal radio works",
". So, probably your amplified speakers inadvertently have all three components.",
"Find a list of broadcasters near your house here, ",
"http://fmscan.org/main.php",
" You are probably receiving from a nearby broadcaster."
] |
[
"When Humans die, do our bones eventually decompose?"
] |
[
false
] |
[deleted]
|
[
"In humid warm places bones can break down in a few years easy due to bacteria and fungi. In a cool dry place they can easily last hundreds of years. Preserved by mummification they can go thousands. Fossilization, we’re talking indefinite preservation (although its technically not bone at that point since it all gets remineralized). So the short answer it is all depends on the environmental conditions"
] |
[
"Not that i know of. We have bog bodies that are like 10,000 years old. Its the anoxic environment that keeps the bodies preserved. But eventually on a geologic time scale the bog will be gone/dry up so other factors could come into play."
] |
[
"In the case of \"bog people\", does the acidic environment eventually dissolve the bones?"
] |
[
"What would the cancelled Superconducting supercollider have achieved?"
] |
[
false
] |
In news articles at the time they kept on saying it would lead to more powerful rockets which got my space obsessed childhood self excited, but they never said how, was that nonsense?
|
[
"I wouldn’t say that it’s nonsense, since many new technologies come out of fundamental science research areas such as particle physics. ",
"To answer your main question, if the SSC was indeed built, the energies of the colliding particles would have far succeeded the LHC energies. The main purpose would have been to test the standard model of elementary particles, and make new discoveries in particle physics research. All of the science that has come from the LHC (perhaps the biggest being the Higgs discovery) may have first happened at the SSC, or at the least would have been in competition. "
] |
[
"It would have achieved energies (40TeV) three times higher than that of the LHC. Basically, that is a range in which new physics might lie. It would have discovered the Higgs Boson obviously. On top of all that, it would have made America dominate in high energy physics. ",
"However, I don't see how it could have lead to more powerful rockets unless there is some technology used for the accelerator which might also be useful for building rockets (which I don't know anything about but I doubt anyway).",
"You might be confusing something, since in 1993 the funding for the Advanced Solid Rocket Motor was cut along with the funding for the Superconducting Supercollider. I think the funding was cut for both in one vote:",
"https://www.bloomberg.com/news/articles/1993-11-28/the-super-collider-buck-gets-passed"
] |
[
"It's impossible to say. The immediate benefit to the \"every-man\" would likely be through engineering spin-offs related to unexpected innovation that fell out of trying to tackle the extreme engineering challenges that come from such a project.",
"I am not a particle physicist and the field of physics I'm from is the one where the guy (Phil Anderson) is from who arguably killed the SSC project by saying to congress they PARTICLE PHYSICS that would come out would not produce any meaningful benefit to physicists outside particle physics or to things like semiconductor technology. However, with that being said, I tend to be of an opinion that goes something like this:",
"First, look at the technological progress and economic activity that only exists because of particle accelerator physics in general: CRT televisons, X-ray scanners (CT, airport security, manufacturing reliability x-rays, etc.), Computing technology (silicon chips are made using, what's called impurity implantation by a particle accelerator), cancer radiation therapy, materia hardening, seran/cling wrap production (no joke), medical instrument sterilization, food preservation, chemical analysis, medical diagnostic testing and so much more.",
"Then, think of all the tax revenue that is generated every year from all of that technology (not to mention lives saved and lives enriched though better technology). If you include not just the accelerator industry but all the industries (like modern electronics and computers) that can only exist because of accelerator technology, that's likely hundred of billions in tax revenue every year in the US alone.",
"In my mind, that's the \"gift\" to society of ivory-tower physicists wanting to learn more about particles. And, in some sense, as long as the budget for such endeavours stay under that number, society is \"ahead\". And yet, something like the SSC would've cost less than a billion a year over its lifetime. So, likely less than a fraction of one measly percent of the yearly dividend that this crazy, ivory-tower endeavour pays off for us every fiscal year.",
"So I say if they're in agreement that it's of benefit to them then we should fund it, without asking what the clear immediate benefits would be, because no one can know that."
] |
[
"I sat in disbelief as my physics professor told the class that cell phones emit EM waved that will fry your brain because they are the same thing as microwaves and UV waves. Was he BS'ing or am I just terribly misinformed?"
] |
[
false
] |
Radio waves (and microwaves for that matter) are non ionizing right? And any microwaves being emitted by a cell phone are insignificant, right? EDIT: There are way more comments than I have time to reply to, so here’s some general info. This professor is actually incredibly smart, and one of the best teachers I’ve had. So he’s not an idiot. I am sure this is what he said. There is a reason I had a look of disbelief, and its not because I was shocked to hear what he said was true. I was appalled that he would make this up. I just wanted to ask some experts to be sure. The general consensus seems to be, surprise surprise, he was wrong. I will ask him about it tomorrow. He likes to joke around a lot, so it may have been a poor attempt at humor. Everyone in the class believed him except for me.
|
[
"You're correct; (Edit: The poster, ",
" the professor's assertion, since some people apparently don't read more than the title) Cell phones emit in the microwave region, which is non-ionizing.",
"UV is also non-ionizing, but have far more energy. Enough to excite electrons in many organic compounds, which causes chemical reactions. (Most notably, DNA damage through neighboring thymine bases reacting with each other)",
"There are some plausible but unlikely ways microwaves ",
" cause damage, but little reason to think that it'd be significant at those low intensities. (And no solid empirical evidence that cell phone radiation is harmful at all) Fundamentally though, microwaves can't really do any damage that heat in general doesn't do."
] |
[
"Relevant xkcd",
"Randall Munroe also once pointed out that the potassium in a banana will cause you to absorb more ionizing radiation than any amount of cell phone use."
] |
[
"The coal that comes from the ground is slightly radioactive. This is then burned and released into the atmosphere as waste. Material in nuclear plants is contained. "
] |
[
"How does the SpaceX rocket not tip over when launching so slowly?"
] |
[
false
] |
The rocket looks to barely deviate from vertical and maintains alot of control at what looks to be a low velocity. It looks like it would be top heavy and start to tip as it launches.
|
[
"Thrust vectoring. The rocket nozzle's orientation and thrust is continuously varied based on feedback from on-board sensors. When the rocket tries to tip, the engine adjusts to rotate it back the other way. ",
"This landing vehicle prototype",
" has a camera on the engine which shows the thrust vectoring adjustments very clearly. "
] |
[
"To add to o0DrWurm0o's comment, which is quite correct, ",
"this",
" is what happens when those sensors fail. In this case gyroscopes failed due to a software error and the self-destruct mechanism was activated to prevent the Ariane 5 rocket from falling on populated areas."
] |
[
"I remember hearing that the transport pads for spaceships had a laser on the bottom that would cause the pad to move along with the ground so that the shuttle did not tip over. Does the s function the same way?"
] |
[
"How does electricity flow through a substance?"
] |
[
false
] |
[deleted]
|
[
"Metals are able to conduct electricity because the electrons aren't really bound to the individual atoms. Rather, the electrons float loosely and are able to move about freely.",
"Batteries have a negative end (with an existing surplus of electrons; it doesn't \"create\" them) and a positive end (with a lack of electrons). When the two ends are connected by conductive material - such as a wire, the electrons are attracted to the positive end. Electrons at the end of the wire move into the positive end of the battery. They are replaced by electrons further down the wire, and so forth, until you get to the other end of the wire, whose electrons are replaced by those from the negative part of the battery. So the electrons themselves \"flow\" like water."
] |
[
"You can think of it this way. The electrons flow in one direction for a short period of time. If for instance, they flow through something like a light bulb, this will generate heat/light (regardless of direction). Then then switch directions for the same duration of time, which again, generates more electricity. The flow is alternating back and forth very quickly. The net movement is zero (or thereabouts) but the velocity is non-zero.",
"tl;dr: The electrons wiggle to make work. The work powers things."
] |
[
"something to keep in mind is that the electrons are doing more \"pushing\" than flowing, if you switch on a light the electrons that move through the switch will take hours to get to the filament in the bulb - but the wave of electromagnetic potential propagates at a significant fraction of the speed of light",
"because the electrons are moving within the realm of quantum electrodynamics, it isn't possible to describe what is happening in a classical sense, but it is very roughly analogous to a water heating valve",
"the pipe is full of water and the valve allows the current to circulate everywhere in the pipe immediately, but the water molecules at the valve take time to get farther down the system"
] |
[
"If you are on a train, that’s traveling very fast, and you jump. Would you land in the same spot you jumped off from, or would you smash into the back of the train car?"
] |
[
false
] | null |
[
"If it is at a constant speed, the same spot"
] |
[
"Whys that?",
"Edit: never mind I thought it through. I understand it. I was thinking about if that person was constant or stationary, but since he is touching the train, the train is pushing him along, if he jumped he would continue his path of forward movement along with the train, because he wasn’t stationary he was moving with the train.",
"I thought about it like if you were in a skate board, moving fast, and you jumped, you would continue to fly forwards in the air, because you were already moving forwards along with the skateboard, it wasn’t just the skate board moving forwards. Idk. Idk why it took me a second to grasp but I get it."
] |
[
"Relativity",
". If you flew to the back you could find an absolute rest frame."
] |
[
"How does testosterone make people become sexually attracted to others?"
] |
[
false
] |
I remember the day I started liking the opposite sex, but I don't understand how testosterone goes from my gonads to my brain to doing something in my brain that makes me start noticing figures and long legs. What does testosterone do once it reaches my brain that makes me like the opposite sex?
|
[
"I cannot break this down exactly the way you want but...testosterone does not control physical attraction. It may have a small part in overall attraction, such that you are man therefore you like women. Bam. ",
"There is a ton of research directed towards physical attraction. The coolest influencer of physical attraction, in my opinion, is our immune systems. Scientists have seen that people (on average) are more physically attracted to those with opposing immune systems, from themselves. For example, you may have a specific resistance to the common cold built into your genetics/immune system. A woman lacking that resistance may be more likely to find you physically attractive because (biologically) she senses your immune system complements hers. If you and said woman had children, your children would have a combination of both immune systems. ",
"Hope this helps. Google scholar and pub med are good primary sources to skim. ",
"Edit: testosterone is a steroid hormone produced mainly utilized by the male body to mature. It's real job in your body is mostly to give you your male features. (Testes (development/drop), prostate development, facial hair, increased muscle and bone mass, etc. )"
] |
[
"Testosterone facilitates sex drive, it's undetermined what role it plays in orientation though."
] |
[
"What about people who say they are attracted to their same sex?"
] |
[
"If a person were on a spacecraft with a stretched-out orbit would he or she feel the acceleration and deceleration as the craft approaches perigee/apogee?"
] |
[
false
] |
[deleted]
|
[
"No. When you \"feel acceleration\" in a car or roller coaster, what you feel is the contact force, your seat is pushing on you to keep you moving at the same velocity as the vehicle.",
"But while in a spacecraft in orbit -- any orbit -- your acceleration is always equal to that of the vehicle, so there's no contact force and nothing pushing on your skin that you can feel."
] |
[
"unlike other everyday forces, gravity acts equally on all the atoms in your body, so you can't feel it in isolation. Most everyday forces have to act on you through whichever part of your body they are contacting. The force must be transferred to other parts of your body, which you can feel.",
"This is exactly right. And for extra confusion, we use \"weight\" to describe gravitational force, and we say you're \"weightless\" in orbit, but in orbit gravity is the one force you definitely do have."
] |
[
"No. At all times the acceleration felt by the astronaut and the spacecraft are equal, so the relative speed of the astronaut to the spacecraft is always zero. In simpler terms, the astronaut experiences microgravity in the reference frame of the spacecraft even if accelerating at a very high rate in a reference frame centered on the planet."
] |
[
"Why do I sweat when I eat spicy food?"
] |
[
false
] |
Not just spicy and temperature hot things. Things like hot sauce, hot cheetos, etc.
|
[
"Capsaicin",
" the chemical that makes hot sauce hot interacts with receptors that sense heat."
] |
[
"Since Tactless_Atheist has already give the gist of the answer, I shall refer you to the link that can answer in full - ",
"http://www.scientificamerican.com/article.cfm?id=why-is-it-that-eating-spi"
] |
[
"Some foods are thermogenic. They increase metabolism and make the body generate more heat. Green tea is another.",
"What I'd like to know is whether capsaicin is as thermogenic as it feels. It feels so much more powerful than green tea or stimulants. Is it?"
] |
[
"Why do people say that right after the big bang, the Universe was very small? Wasn't the universe just as infinite then as it is now? Isn't it more accurate to say it was very dense?"
] |
[
false
] |
How can the universe be described as small? If the Universe was infinite at the big bang, but everything was very close together, doesn't this just mean that it was very dense? I don't study physics but I have some understanding of a cosmology but this description has always bugged me and no one ever addresses it.
|
[
"Measurements of the curvature suggest that it was indeed infinite but denser than it is now, although the error bars on those measurements include a universe that's non-infinite but ",
" larger than our observable portion can ever be.",
"Effective science communication is hard work, I guess a few things got muddled on the way"
] |
[
"There are two length scales I think you may interested in. ",
"One is the size of the \"observable universe\". If we think about two points at opposite sides of that, then in the past they were obviously closer together. This is what some people are probably referring to when they say \"the universe was smaller\". ",
"Another length scale is the size of \"all of space that exists, whether or not we can see it now, or will ever be able to see it\". I think that's what most of us mean by \"the universe\". We don't know that length scale; we know it's a fair amount bigger than the size of the observable universe, and it could be infinite. The simplest, most-pleasing-to-a-theorists-eye models say it's infinite. That doesn't mean it actually is. ",
"And of course, if it is infinite, it was always infinite, and will always be infinite, in all directions.",
"So you're right, a better way to talk about the early universe is to refer to how things were closer together, so the density was higher. Kudos to you for being a positive force for using the right language! Keep it up."
] |
[
"That would only happen if the universe has positive curvature, ie it was some sort of hypersphere.",
"If it's infinite, you won't wrap back to your starting point."
] |
[
"Would it confuse your brain if you switched sides on your eyes?"
] |
[
false
] |
I was curious how wired the brain is to seeing what it sees. Brain games talks about all the assumptions the brain makes. I started wondering what would happen if you switched them with special binoculars. So the right eye saw what the left normally sees and vice versa.
|
[
"If the input stayed consistent, then the ",
"brain would probably adapt and correct",
"."
] |
[
"I doubt it would correct - sensitivity to binocular disparity is laid down pretty early, and people with poor or no stereo sensitivity (stereo-blind) rarely recover it even with a lifetime of binocular experience (strange counterexamples like Sue Barry and Bruce Bridgeman notwithstanding). Reversing the encoding of binocular disparity would require unlearning and then relearning the assignment of disparity to depth, which sounds even more difficult than going from stereo-blind to stereo-sensitive.",
"And it's not as simple as just changing your 'labeled lines' - you have phenomena like Da Vinci stereopsis, where monocularly-visible surfaces are seen as ",
" a surface depending on whether 1) it's to the left or right and 2) the monocular portion is seen in the left or right eye. This is a process even more complex than disparity encoding, and it's hard to imagine it could be inverted...",
"*** edit",
"an important difference between binocular depth perception and the orientation of the visual scene (which is what seemingly \"corrects\" in the prism adaptation experiments) is that scene orientation is already very plastic - you tilt your head, or look up or down, or lie down on your back, or even hang upside down, and the world continues to look upright and normal (mostly). visual orientation is only loosely tied to the orientation of the eyes in space. on top of that, it's motor-sensory phenomenon, mostly processed in parietal cortex, whose entire visual function is to be plastic and learn/adapt to new circumstances.",
"but binocular depth perception is much more rigid - neurons in early visual cortex (V1, V2) have tuning for specific ranges of binocular disparity, and these are tied into the formation of surfaces, perception of things like occlusion and transparency, all at a pre-attentive level of processing. and the early visual cortex is built for transmitting local statistics of visual stimulation, which are relatively stationary - the low-level statistics of natural scenes are all very similar - an edge here is the same as an edge there, and disparity means the same here as it does there - so there's much less need for massive plasticity in those areas (which is why it's difficult to evoke and rarely obvious)."
] |
[
"Initially it would look like if you looked at the pictures in ",
"/r/CrossView",
" in parallel view, or the pictures in ",
"/r/ParallelView",
" in cross view. Eventually your brain would probably adapt and see the world with correct depth."
] |
[
"How to determine the function of a human protein based on the function of a homolog from another species?"
] |
[
false
] |
What type of experiments can be done (short of actually experimenting on a human embryo) to determine the function of a human protein thats homologous to a well-characterized and understood protein from a model organism?
|
[
"You can express and purify the protein in some other system (bacteria or insect cell culture) and perform experiments ",
". If there are assays for the protein's presumed function that can be performed outside of a cell they can tell you a lot about the protein: what it binds to, how strongly it binds to its partners, you can do ",
" assays for (de)phosphorylation, (de)ubiquitination or other protein/DNA/RNA modifications.",
"Since you know the homolog, you could see if the human protein can replace the model organism's version of the protein. First you knock the native protein out/down and then express the human version.",
"You'd never work in a human embryo. You'd use cells in culture. These are human (or monkey, or dog, or hamster or whatever other species you work with) cells that can be grown in a plate or flask. Primary cultured cells come from an animal, but most people work with immortalized cell lines. These are often from cancers and they will keep dividing forever. You can order from thousands of different cell lines ",
"here",
".",
"In your cultured cells you can: knock the protein down, over-express the protein, knock down the native protein and express parts of your protein, knock down the native protein and express mutated forms of your protein, express a fluorescently tagged version and look where it goes, look at the localization in mutants or after application of drugs. You can do whatever experiments you feel like in your cultured cell line."
] |
[
"to add to this you can also do a variety of experiments if you've cloned the protein of interest. expressing the protein in a heterologous expression system can allow for a variety of characterization experiments to determine protein function. additionally, if the crystal structure of the homolog has been resolved, you might also be able to use it to model the human equivalent."
] |
[
"Thank you! This was quite helpful!"
] |
[
"What about running water makes it less dangerous than stagnant water?"
] |
[
false
] |
I understand that you get are less likely to get diseases from drinking running water than stagnant water, but what about running water makes it so much safer than stagnant water if it is the exact same water?
|
[
"In stagnant water you get an incubator effect. If you take sterilized water, free of bacteria and running sterilized water and you compare them they will be exactly the same after a few days. ",
"The problem with stagnant water is a) because nothing moves, bacteria have a easy time feeding and b) it becomes a feeding ground for mosquitos. ",
"I think this is about the gist of it, maybe someone else can explain it better."
] |
[
"Thanks!, this is off topic of the original question but do you know if the mosquitoes get the diseases they carry from both the water and the human or just breed in the water and then carry diseases between humans through bites. Or are mosquito eggs somehow harmful?"
] |
[
"Mosquitos bite a person with the disease and carry it to the next person.",
"They are the vector (carrier) of some diseases like malaria and dengue."
] |
[
"Why are atoms always arranged the way they are, with protons and neutrons at the center and electrons orbiting?"
] |
[
false
] |
Was just thinking that I've never seen a diagram with an orbital neutron inside the electron cloud, or an electron-neutron cloud being orbited by protons. They seem intuitively like they should at least be possible, if not common. I'm aware that antimatter is inverted, but my understanding is that it's made from inverted particles as well, and those are also always in the same arrangement.
|
[
"The length scales of bound states are set by the properties of the particles involved and the interactions between them.",
"In an atom, there’s two kinds of bindings to consider: nucleons to other nucleons, and electrons to nucleons.",
"The interactions between nucleons lead to bound states with length scales of femtometers. And then bound states between electrons and protons have a length scale of Angstroms (or the Bohr radius divided by Z for an atom with Z protons).",
"So there’s a clear separation of around 4-5 orders of magnitude between the characteristic size of the nucleus and the characteristic size of the electron cloud.",
"And this ",
"agrees with experiment",
"."
] |
[
"I wouldn't use the words \"bounce and float\". The electrons are still \"clumping\" around the nucleus, just at a distance ~10",
" times larger than the size of the nucleus itself.",
"And yes, neutrons generally don't significantly interact with electrons, only nuclei."
] |
[
"I'm going to try and say this back to make sure I understand it:",
"The force(s) binding nucleons (protons and neutrons) together is stronger but has a short reach, so once they get anywhere near each other they form a clump.",
"The force(s) binding electrons to the nucleons is weaker but can act over a much longer distance, so they tend to bounce and float around the clumps formed by the nucleons. If there was a neutron out in that cloud, it would just fly off until it gets close to another nucleus and gets stuck there?",
"Is that broadly correct?"
] |
[
"Is there any scientific basis for so called \"Hitting Weather\" in baseball? When it's warm out most commentators say home runs are likelier to hit."
] |
[
false
] |
Usually they mention it on hot clear days. Today it was clear skies in the high 80 degrees fahrenheit (27 C) and just so happened that more home runs were scored than normal. That got me wondering about what is behind this phenomena and if it had any facts to back it up. Does it have something to do with air pressure, maybe less resistance? Or does the heat effect the forcess that impact the ball? It's not about wind adding to velocity, "hitting weather" doesn't necessarily have to be a windy day and most of the time isn't associated with wind conditions. Compare this to cold weather which is said to have the opposite effect.
|
[
"Sure, when it's hot out, the air density is lower, so the drag on a baseball is lower and you can hit further. Occasionally airlines deal with the same issue -- they have to cut weight because the temperature at the runway is overly high, and this makes the air less dense which makes the airplane produce less lift.",
"It's the same reason why the Colorado Rockies stadium was known for producing a lot of home runs -- high altitude also producing less dense air.",
"to put some number on it, at sea level if you're 20F hotter than normal, that's about a 4% decrease in air density. That leads directly to a 4% lower drag on a baseball."
] |
[
"http://www.engineeringtoolbox.com/moist-air-properties-d_1256.html",
"\n"
] |
[
"Blake street bombers! "
] |
[
"What experiments are currently being conducted to discover what dark matter/dark energy is?"
] |
[
false
] | null |
[
"There are 3 main experiment types ongoing in the search for a particle candidate of dark matter.",
"First is what is known as \"direct detection\", whereby you infer the existence of dark matter in our galaxy by it's interactions with a large body of material (your detector). Typically these are noble liquid and the dark matter interacts with the nucleus of these liquid. The LZ experiment is an example of a direct detection experiment,",
"Second is known as \"indirect detection\", where you try and observe the photons produced from the self-annihilation of dark matter in our universe (similar to electron+positron annihilations). FermiLAT is an example of such an experiment.",
"Lastly is \"collider experiments\", where you collide particles in a particle accelerator with enough energy to produce dark matter. The detectors aren't able to detect the produced dark matter, instead they infer the existence of dark matter from the imbalance in momentum (should be balanced due to the conservation of energy). The Large Hadron Collider (LHC) has a few results for such searches.",
"I am not so familiar with experiments on dark energy."
] |
[
"You can't be sure. But you do it in the hope that it will. It would not be the first time that a new particle was discovered as missing energy/momentum. And if you don't see anything, you can at least set new upper limits on the strengths of possible interactions between hypothetical dark matter particles and hadronic matter, which helps constrain theories, which may eventually lead to some better ideas."
] |
[
"To piggy back off this question, if dark matter has hardly interaction with baryonic matter, how can we be sure that slamming baryonic particles together will infer presence of dark matter? Maybe I'm largely misunderstanding this process, but I'm looking to get educated. "
] |
[
"Could you slow down radioactive decay by speeding a radioactive isotope to relativistic speeds (99.9999999% the speed of light)? Just a thought experiment. Kinda Like the twin paradox but with 2 decaying isotopes."
] |
[
false
] |
[deleted]
|
[
"Yes."
] |
[
"In principle yes, but in practice this is not what we do.",
"In order to study highly unstable nuclei, we need to produce them on-site at the time of the experiment. We produce them using certain types of nuclear reactions which work best in certain energy ranges. The energies that we use in nuclear physics experiments are not terribly high. In a typical \"fast-beam\" experiment, the particles in the beam are moving at about 50% of the speed of light. At this speed, the time dilation factor is only about 1.15. So the effects of time dilation only increase the lifetime of the particles by about 15%, which is not really enough to make a difference.",
"If we wanted time dilation to be more significant, we'd need to do experiments at higher energies. But at higher energies, the reactions which produce the highly unstable nuclei are not as effective."
] |
[
"In principle yes, but in practice this is not what we do.",
"In order to study highly unstable nuclei, we need to produce them on-site at the time of the experiment. We produce them using certain types of nuclear reactions which work best in certain energy ranges. The energies that we use in nuclear physics experiments are not terribly high. In a typical \"fast-beam\" experiment, the particles in the beam are moving at about 50% of the speed of light. At this speed, the time dilation factor is only about 1.15. So the effects of time dilation only increase the lifetime of the particles by about 15%, which is not really enough to make a difference.",
"If we wanted time dilation to be more significant, we'd need to do experiments at higher energies. But at higher energies, the reactions which produce the highly unstable nuclei are not as effective."
] |
[
"Does an eye \"absorb\" a proton?"
] |
[
false
] |
So I am looking at the sky, at all the ancient stars. And the photons from those stars may have travelled for thousands of light years to get to me. When the photon strikes my retina, and alters (I think) the molecules, is the photon converted to energy and is now more or less a part of "me"?. Every time I look at the night sky, am I taking on a little more of the heavens, no matter how slight?
|
[
"Yes, this is an accurate description of the absorption of photons by the retina. ",
"They've traveled a very long distance for a very long time (in your frame of reference) to reach you. Once they hit one of the rods or cones of your eye, they convert to a chemical form of energy which is transmitted to the brain. ",
"Note: Your title has a small typo. Photons and protons are distinct. "
] |
[
"Then this should blow your mind.",
"Since time slows relative to the speed of light, does this mean that photons are essentially not moving through time at all?",
"Neil Tyson deGrasse replies:",
"yes. Precisely. Which means ----- are you seated?\nPhotons have no ticking time at all, which means, as far as they are concerned, they are absorbed the instant they are emitted, even if the distance traveled is across the universe itself."
] |
[
"This is certainly possible, but many of these absorbed and re-emitted photons will be scattered from their original trajectory. The reality is that some fraction of the photons will have a \"direct connection\", while some will have \"pit-stops\" along the way. The ratio will depend upon atmospheric conditions, the color of the star, and the direction you're looking. "
] |
[
"The CDC claims smoking a hookah for an hour is equivalent to smoking 200 cigarettes. I would like some clarification."
] |
[
false
] |
[deleted]
|
[
"So, the CDC website cites ",
"this",
" WHO regulation recommendation (that provides a good reference on how water pipes actually work and where the smoke comes from) which cites ",
"this",
" 2004 paper which seems to be focusing more on calibration of a smoking machine used in toxicology studies rather than trying to make the claim you mention in your question. The author (Shihadeh A) is concerned that previous assessments of the toxins in a given smoking session were undershooting the actual values. ",
"A single smoking\nmachine test was conducted using the current smoking\nmodel given in Table 3, in accordance with the methods\nspecified in the cited study, and the total particulate matter\n(TPM) collected was found to be 1.10 g. This is considerably higher than the 0.40 g previously measured using the\noriginal 100 puff smoking protocol, indicating that the\ncurrent model will likely yield considerably greater tar and\nnicotine from a single smoking session than previously\nreported. ",
"Since this was old, I looked into more recent articles by this author and found ",
"one",
" directly comparing cigarette smoking and water pipes in terms of nicotine exposure, carbon monoxide exposure, and heart rate. ",
"Relative to a cigarette, waterpipe tobacco smoking was associated with similar peak nicotine exposure, 3.75-fold greater COHb, and ",
". Waterpipe and cigarette influenced many of the same subjective effect measures. These findings are consistent with the conclusion that waterpipe tobacco smoking presents substantial risk of dependence, disease, and death, and they can be incorporated into prevention interventions that might help deter more adolescents and young adults from experimenting with an almost certainly lethal method of tobacco use. ",
"In this paper, the author mentions concerns about polycyclic hydrocarbons. ",
"This",
" article mentions them again: ",
"In any case, discussions of whether the water or the tobacco temperature reduces smoke toxicant content from some maximal level may be made moot by the fact that, in a single use episode with water in the waterpipe and a relatively low tobacco temperature, a waterpipe produces an average of 90,000 ml of smoke that, relative to a single cigarette, contains about 6 times the CO (Table 2), 46 times the tar (see Table 2), and more than 50 times the quantity of some carcinogenic polycyclic aromatic hydrocarbons,53 as well as heavy metals such as lead and arsenic.18 ",
"So, the original claim seems to lack support from the author it cites, but he and associated authors assert that smoking a water pipe for a typical duration leads to far greater exposures to some chemicals. "
] |
[
"The actual research and CDC releases do not obviously imply, as you say \"that smoking a hookah = smoking 200 cigarettes, ",
"\"",
"It says:",
"A typical 1-hour-long hookah smoking session involves inhaling ",
" inhaled from a single cigarette",
"It then goes on to say that this is not healthy. A statement you agree with. It makes no numerical comparison in terms of health risk, it only makes the ",
" statement that hookah smoking is not a healthy activity.",
"Even the first few Google hits don't say \"in terms of impact on health\", they just let you assume that by leaving off the volume bit. It's hyperbolic and misleading, but hey....",
"welcome to the wonderful world of science reporting",
". ",
"Inhaling any form of particulate matter is bad. In addition, there are substances in tobacco that will make it through the bubbling of a hookah that can still adversely affect your health. Particulates will also make it through and any particulate matter in your lungs is bad. There are volatiles in tobacco that will also cause problems. ",
"Bottom line: Smoking a hookah is probably healthier than smoking, but in the same sense that drinking a large soda with lunch every day is healthier than drinking a quart of heavy cream with lunch every day. ",
"I wouldn't make a habit out of either."
] |
[
"Tar and ash, which are carcinogens, are formed whenever biomass is burned."
] |
[
"Is wood alive? At what point does the tree go from being alive to dead?"
] |
[
false
] | null |
[
"It depends on the wood, and what you’re definition of “alive” is. Your salad is technically “alive”.",
"A typical cross section of wood consists of an outer bark layer, which is composed of dead corky cells. Beneath that is a super thin layer of live bark cells. The phloem is an active layer of tissue and is found under the bark. It is used to transport sugars developed in the leaves via photosynthesis to the roots for use and storage. ",
"Next comes the cambium layer. Oh the cambium...This is the actively growing layer of tissue that adds to secondary growth (outward; girth)on a trunk or branch and acts as a barrier between the phloem and xylem . Below the cambium is the xylem, or sapwood which supplies nutrients and water from the roots up to the branches and up through the leaves. This is the “supply line” for the tree, and is still alive. It is usually several rings thick, depending on the tree.",
"From here on inward, you’re still seeing xylem, but under the sapwood is what’s referred to as the heartwood. Nothing goes on here, there is no transfer of water or nutrients. It is not living, but is still a part of a living organism. This would be like our hair or fingernails, it’s composed of cells that are no longer in use but still an integral part of the tree as it adds tremendous strength to a a branch (imagine how a hollow rotten branch breaks before a healthy one). That’s getting into CODIT, which is a whole other thing...",
"A tree as an individual organism would be considered “dead” if it is no longer fulfilling its duties as a living organism ie transpiration, respiration, photosynthesis etc. You could cut a tree off at the root flare it would still be alive if the roots are still growing and can push out new growth. This happens a lot. There are oaks that are hundreds of years old but look like a bush because they get burned off every few years in prairie fires. When all the roots die, the tree will soon be gone or is already dead. There can be pieces of the tree that survive and grow more roots, but we’re getting existential there and is not common at all...",
"Thanks for letting me brain vomit on your sub, I need to nerd out sometimes.."
] |
[
"You could cut a tree off at the root flare it would still be alive if the roots are still growing and can push out new growth. This happens a lot....",
"For all the devistation wrought by the blight fungus upon the American chestnut, this feature is the saving grace that has allowed the species to functionally survive in its native range. When the disease, manifesting as a canker growth, manages to completely spread around the entire circumference of a trunk, the tree has been effectively \"killed\" by the fungal infection, with no more normal growth possible through the diseased portions of the once living tissue. However, as long as the root is viable, the tree will continue sending up new shoots that may grow for a few years before the blight fungus infects and kills them too. Until a blight resistant strain is developed and introduced, the once great American chestnut is hanging on by a thread in its native Appalachian range. Just a little longer... These hills and valleys may yet once again host mighty giants."
] |
[
"So just to clarify on \"living\" vs \"dead\", the sapwood has active cells in it (DNA transcription, protein synthesis, metabolism) and the heartwood does not?"
] |
[
"What organism do we share the least DNA with?"
] |
[
false
] | null |
[
"For all existing life on earth it would be the earliest deepest branching member of the bacteria, Aquifex a hyperthermophile. For animals it would be the deepest branching member of the Eukarya presently thought to be the diplomonad parasite Giardia."
] |
[
"I think he is saying that the living thing we are farthest from is the bacteria, and the animal we are farthest from is Giardia."
] |
[
"I was looking at molecular evolutionary distance from humans. Within Class Mammalia farthest from humans would be the monotremes (echidna and platypus)."
] |
[
"How do phones know what the date and time is when they're turned on after being off?"
] |
[
false
] | null |
[
"Older phones have a small timing chip with a small, dedicated voltage source (battery, capacitor, w/e) that does not turn off with the phone. Newer phones ask the cell tower, and barring a response, either show noon or the time stored on such a chip."
] |
[
"Does this mean that if a newer phone is disconnected from a cell service, it won't receive the information?"
] |
[
"I'm not sure whether the time is broadcast openly or requires an actual 2-way connection, so I don't know."
] |
[
"How large of an impact did the 2010 eruption of Eyjafjallajökull have on the CO2 levels in our atmosphere?"
] |
[
false
] | null |
[
"Not a whole lot. The wikipedia page which describes the various ",
"effects of the eruption",
" estimates ~0.15 million tons of CO2 were put into the atmosphere. That seems like a lot, but it is nicely put into perspective by the immediately following line that the disruption in air travel caused by the volcano caused an estimated 1.3-2.8 million tons of CO2 not to be put into the atmosphere by jets. It can be important to take these numbers with a grain of salt, as other discussions suggest that the 0.15 figure might be the amount per day during the eruption, e.g this ",
"page",
", but the total amount expelled by the volcano remains small in comparison to human contributions.",
"For a more general discussion of volcanic vs anthropogenic contributions of CO2 to the atmosphere, the USGS has a nice discussion of it ",
"here",
"."
] |
[
"According to the climate science referenced here: ",
"http://youtube.com/watch?v=gh9kDCuPuU8",
" by scientist Richard Milne, the yearly impact of humans on the climate is 100 times that of all the volcanoes that go off in a year. Based on that, I supposed the answer would be almost nothing globally. I am at work but I will try to find you the timestamp later. I would recommend the whole video though. Its not really about climate change although climate change is the story telling mechanism."
] |
[
"The magazine for the AGU had a ",
"great article about this",
" (human vs. volcanic CO2 input)"
] |
[
"What would happen if you lit a match on Saturn's moon Titan?"
] |
[
false
] |
[deleted]
|
[
"Your basic red safety match contains red phosphorus, potassium chlorate, a bit of carbon and various binding agents and fillers. You rub it against a surface and the friction increases the temperature until it ignites and the phosphorus reacts with the potassium chlorate.",
"Your first obstacle to this task will be that it is freezing cold on both Saturn and Titan and friction matches will be trying to reach their ignition temperature from a much lower starting point. Give it all you've got or bring another source of heat.",
"If you do manage to strike a match the potassium chlorate and the phosphorus will react. Titan has a really dense atmosphere and really low gravity, so the flame will be a rather odd shape and probably close to circular like it is ",
"in space",
". Saturn has very high gravity and the density depends on how far down you went.",
"You will not have long to marvel at this behavior because there's plenty of fuel but the only oxidizer available is the potassium chlorate that was in the matchhead from the start. Once it is gone the match will go out even faster than matches normally do.",
"You may be trying to blow up the atmosphere. If it were possible then a passing meteor would have done it long ago, and it won't hold a flame because there's no oxygen or other potent oxidizer in either place."
] |
[
"There aren't any usable amounts of oxidizer (like oxygen) in Titan's atmosphere so any fire would be unable to \"breathe\". Also, the match wouldn't even completely light itself as the wood requires oxidizer too. The tip ",
" burn like \"normal\", but I'm not sure if the phosphorus mixture requires an oxidizer or not."
] |
[
"Let's say there was an oxidizer in Titan's atmosphere. What would happen?"
] |
[
"Do rainbows refract more than the visible spectrum of light?"
] |
[
false
] |
Being that we are only humans and can only see the visible spectrum of light on the EM spectrum, do rainbows show more than just light we can see? Towards the red side, is infrared light emitted? Towards the violet side, is ultra-violet light emitted?
|
[
"Yes they do, in Neil Degrasse Tyson's ",
" he mentions that the very discovery of ultra-violet light made by ",
"Hershcel",
" is due to observations made on rainbows essentially. Here is a ",
"diagram",
" that is a pretty good illustrator. "
] |
[
"And on a related note, Herschel discovered infrared light by sending sunlight through a prism to create a \"rainbow\"* and then placing a thermometer in the space just before red and detecting a temperature increase, indicating the presence of light.",
"*A spectrum created by a prism is technically not a rainbow because it is not created by rain drops and has slightly different physics, but it has the same basic pattern: a spreading of light into different spectral components by the dispersion properties of a material."
] |
[
"Super short answer: Yes. As previously stated they do. ",
"Longer answer: ",
"Here's",
" the mathematical relationship needed to understand what's happening as the light enters and leaves the rain drop. Now go over to ",
"this page",
" to get the values of n (the refractive index) for each wavelength you're interested in and plug it into the ",
"Fresnel equations",
" to see how much light is internally reflected off the \"back\" of the drop for you to see. Once you've solved both of those, you will be able to see the exact (theoretical) amount of light you get, and at what angle, at each wavelength you want to know about!"
] |
[
"Since we are constantly generating new skin cells, what causes a scar to form and stay?"
] |
[
false
] | null |
[
"There are several types of scars. As a wound heals, a few different proteins are present, including elastin, fibrin, and collagen. Collagen and elastic are found in your skin, and provide a scaffolding to which your cells can attach. Trauma disrupts this scaffolding, and part of the healing process involves rebuilding it. Most scars result from too much collagen being in the wound after the healing process is over. ",
"EDIT: The ",
"wikipedia",
" article has some good information. ",
"EDIT2: cleaned up my response since so many people are seeing it"
] |
[
"The collagen and elastin create a mesh that the cells exist within. The cells may be replaced but to my knowledge the collagen/elastin mesh remains."
] |
[
"But what makes the scar keep its shape and color after multiple generations of cells? How do new cells in a fibrosis know how to arrange the collagen fibres if that information isn't in the DNA? Sorry if this is a stupid question, it's been a long time since my last biology class."
] |
[
"Are there any materials/elements that are liquids at cooler temperatures and solids at warmer temperatures?"
] |
[
false
] |
[deleted]
|
[
"Yes, helium-3 and helium-4 both exhibit this behavior near a certain combination of temperature and pressure. But at still warmer temperatures, the substances melt again. For helium-3:",
"Below 0.3 K, the liquid has a lower entropy than the solid, and both the enthalpy and entropy of fusion are negative. It is an interesting exercise to start with liquid ",
"He at ",
" = 0.1 K and ",
" = 3 MPa and heat it isobarically. At about 0.6 K, the liquid solidifies with the absorption of heat. Heating the solid to 0.65 K causes it to melt, again with the absorption of heat!",
"Source of quote: ",
"http://books.google.com/books?id=BnMh9Xj3TUcC&pg=PA93",
" ",
"See ",
"http://ltl.tkk.fi/research/theory/helium.html",
" for a phase diagram with the dip of the freezing line",
"For more discussion, see ",
"https://en.wikipedia.org/wiki/Freezing#Exothermicity",
" "
] |
[
"It's also used in porn for fake semen, and as a lubricant. And in labs to support the growth of cells. And to treat constipation. It's cool stuff really."
] |
[
"Methylcellulose, a gelling agent used in foods, is somewhat like this.",
"Imagine a reverse gelatin, where gelatin gels are liquids when hot and set when cooled, methylcellulose gels set as they heat up and melt as they cool.",
"Of course they're not a true solid they're a suspension of liquids in a carbohydrate lattice."
] |
[
"Why does my house plant seemingly never die of old age or get sick like my dogs and I?"
] |
[
false
] |
[deleted]
|
[
"Aside from plant pathogens (which I'm not familiar with), common causes of plant death in nature include root rot, animals and bugs eating them, extreme heat and cold, lack of sunlight, lopsided growth that causes it to uproot itself. Your plant is kept away from most plant-specific dangers and/or agers, and since I assume its not a tree it won't uproot itself, so it is free from dangers out door and/or wild plants face.",
"The most likely cause other than the outdoor dangers which it has avoided, would the excessive woody growth and decreasing ability to generate apical growths could endanger its livelihood. When plants get very old sometimes (just like human but it depends on the species) their growth slows and they stop generating the new buds and offshoots that they did when they were young. They become dependent on what ever leaves and tissues they have left. When those leaves become damaged from drying out, tearing, or burning from the sun, since the plant no longer can create new growth, it looses the ability to photosynthesize and just dies from lack of food (plants need both light and water to make food). It really depends on the species, but assuming you keep it perfectly this is the only danger for a house plant pretty much I'd say. ",
"Plant and animal experiences and chemical interaction with the world are different, so that may explain the difference in life span.\nAnimal specific dangers include stress, physical trauma, exposure to pathogens and eating bad food. Most animals are under some form of stress regularly (even if they're at desk jobs away from pathogens and physical trauma) and sleep deprivation as well. The chemicals from stress cause cell aging and death, and later in life put a limit on our body's ability to renew cells. Plants don't have brains and toxic stress chemicals that damage their cells because they obviously don't have brains or nervous systems (as I understand). I don't know why their stress response isn't as toxic to them as animals is for them, but I'm guessing it's the result of a more complex system. The more complex a system is the more easily things can go wrong. In this case, stress chemicals meant to keep us safe as we navigate the world happen to also be toxic for us at higher levels. "
] |
[
"Great! I liked your question actually. I hadn't thought about it before. To figure out from a specimen if it's old, you'd likely need to know both what an older plant of its species tends to look like, and also what environmental stresses that plant experienced. A tree might be very old but just look like a young member of its species because but it had grown very much because it grew in a place where there was too little sun light, and water for proper or regular development. Alternatively a plant that underwent a lot of stress like animals nibbling it, and mineral deficient soils, could end up looking ragged and have no new growths and be mistaken for an old plant. ",
"I'd say in nature the longer lived plants are the ones that can survive harsh conditions better, so those would be mostly trees although Welwitschia which is not a tree can live for over 1000 years. With trees the more rings and larger trunk, the older it is. With things like Welwitschia it puts out a certain amount of new growth every so many years, so you could count the leaves or places where the leaves fell off. Root growth might be a good indicator in some species, but it could vary depending on conditions. Sometimes there are species that put out growth every year, so you can mark that like tree rings or leaf growth (as in Welwitschia), but not all species have a marker of growth. Other than that, it really will depend on the characteristic growth patterns of the species, and the environmental exposure. So, for certain species there may be good indicator like trees say, but otherwise it could be very difficult to tell."
] |
[
"Great! I liked your question actually. I hadn't thought about it before. To figure out from a specimen if it's old, you'd likely need to know both what an older plant of its species tends to look like, and also what environmental stresses that plant experienced. A tree might be very old but just look like a young member of its species because but it had grown very much because it grew in a place where there was too little sun light, and water for proper or regular development. Alternatively a plant that underwent a lot of stress like animals nibbling it, and mineral deficient soils, could end up looking ragged and have no new growths and be mistaken for an old plant. ",
"I'd say in nature the longer lived plants are the ones that can survive harsh conditions better, so those would be mostly trees although Welwitschia which is not a tree can live for over 1000 years. With trees the more rings and larger trunk, the older it is. With things like Welwitschia it puts out a certain amount of new growth every so many years, so you could count the leaves or places where the leaves fell off. Root growth might be a good indicator in some species, but it could vary depending on conditions. Sometimes there are species that put out growth every year, so you can mark that like tree rings or leaf growth (as in Welwitschia), but not all species have a marker of growth. Other than that, it really will depend on the characteristic growth patterns of the species, and the environmental exposure. So, for certain species there may be good indicator like trees say, but otherwise it could be very difficult to tell."
] |
[
"If a person is born without all senses would they have any experience?"
] |
[
false
] |
If the mind is related to the body because it is how it acquires any information about the world, is it possible for someone who is born without any sense lack the ability to gain experiences/memories. As if he/she is just a husk of a person, or incredibly comatose. But in this case, he hasn't seen the world therefore having no memories of it, which could be similar to living in a world of total blankness and having no consciousness that he/she is alive.
|
[
"If they absolutely had no senses; no vision, no hearing, no proprioception, no autonomic sensations, no sense of emotion; then I would imagine yes they could never have an experience or memory. But the question is rather un-answerable. Perhaps the sensory starved systems of the brain just start firing from the lack of input and create some experience we cannot fathom. Or, the neurons are pruned so severely due to a lack of input and the person simply dies. Or if there is truly no sense data at all, CO2 levels in the blood could not be sensed, and the person would die rather quickly. "
] |
[
"It might be interesting to answer the question from the assumption that the question is referring only to the \"five senses\" of touch, taste, sound, smell, and sight. This way we can assume that the person can in fact regulate things like CO2 levels, blood glucose, internal temperature, etc. so that they do not necessarily die from the inability to maintain homeostasis (I doubt that an embryo with the inability to \"sense\" anything would ever develop successfully to produce a human).",
"There are certainly people who have learned to adapt with both deafness and blindness at the same time. There are also people who cannot \"feel\" objects - they would not feel a burn from a hot stove for example. Both groups of individuals may have been born this way due to genetic factors or other disorders that manifested during embryonic development. This is different from an individual who may have lost or altered their sense of taste or smell (or sight or sound) due to an illness/brain damage. In the former, the neural circuits have never developed whereas in the later, the circuits developed and then were altered or damaged. ",
"If an embryo did not develop the necessary nerve circuits for the five senses, it would be very difficult (perhaps impossible) to stimulate further brain development in the baby once it was born. I would imagine that the child would suffer the severe developmental delays that babies who do not receive adequate hands-on care from other humans develop. The baby might die from lack of brain stimulation - certainly there could be no neural development through the common methods of stimulation (breast-feeding, voice recognition, etc.). I am not sure if there could be anything done for the baby at this point in terms of traditional or non-traditional therapies and this is simply because all of our experiences are based on having some sense of the world around us. Simply because of how biology works, it is likely that the baby would die from lack of brain stimulation. If somehow the baby survived and did live in a stable comatose state, but it had no readable brain waves/no brain activity, then it would not be meaningfully alive.",
"If there was a way to stimulate the baby's brain somehow through a very non-conventional but safe means, it might be possible to see neural growth. Of course, it would be hard to ascribe characteristics to the internal experience of someone who develops a brain that cannot receive any conventional sensory input. Perhaps we would see neuron development directed to other sense types that humans do not normally express. Humans have a surprisingly large toolkit for adapting to environmental states and stress. If the baby survived the initial sensory deprivation and brain growth did occur (probably very unlikely), it would be fascinating to see where neuron development was directed."
] |
[
"it is likely that the baby would die from lack of brain stimulation",
"Never heard of this before, could you link some source on that?"
] |
[
"How do museums preserve the soft tissue remains of mummies (like the Mawangdui lady) and mammoths?"
] |
[
false
] |
Their remains aren't even put in the extreme cold. And does decay still happen at a rate higher than their natural rate?
|
[
"You cannot let wet organic material dry out. If you do, it's ruined. Like, forever-ruined. The cells collapse, and it turns to dust. If you don't want to keep it hydrated, you have to replace the water with something else. Historically, that's been polyethylene glycol, though in recent years people have been experimenting with silicone oil."
] |
[
"Lady Dai from Mawangdui is kept in an oxygen-free case. Ötzi the glacier man is kept in a cold wet box, very similar in conditions to the glacier."
] |
[
"hmmm, I'm pretty sure Otzi still experienced slow rates of decay in the wild. Might it be preferable to keep him in something that isn't wet?"
] |
[
"Can someone answer a question about the expansion of the universe for me?"
] |
[
false
] |
I've heard quite a few times that the universe is expanding, and that the expansion is accelerating. Anytime I've heard this, it's explained that the galaxies close to us are moving away in all directions, and the further out you go, the faster the galaxies are moving away from us. Some even to the point where they may exceed the speed of light. What I don't understand is how that shows the expansion is accelerating. Since the galaxies that are the farther away would be the youngest and closest galaxies to the big bang, wouldn't that make sense that they're traveling faster back then? The expansion after the big bang was, as far as I know, already suppose to be faster then the speed of light. So if galaxies at the edge of the universe are traveling close to or faster then that speed, I think it would make sense. Can someone explain this idea of accelerated expansion in a way that I can understand, and show me where I'm mistaken?
|
[
"Anytime I've heard this, it's explained that the galaxies close to us are moving away in all directions, and the further out you go, the faster the galaxies are moving away from us.",
"We need to revise this before we go further.",
"What you've described there is the ",
" effect of metric expansion. As we look at the sky, and most particularly measure the spectra of distant luminous objects, we see what ",
" motion. It ",
" that things are moving away from us, and that more distant things are moving away from us faster than less distant things.",
"But this is ",
" It's just ",
"A little historical context: There are two things to think about here. One is the Big Bang model of cosmology generally, and the other is Hubble's observations of astronomical redshifts.",
"One might assume that the observations came first, and then a theory was developed to explain them. But delightfully, this turns out not to be the case. The theory actually came first, and Hubble's later observations were the first hard evidence in support of the theory.",
"So it turns out that no one ever believed that the Big Bang was a cataclysmic primordial explosion that sent galaxies rocketing through space like bits of shrapnel. The maths of metric expansion — which follow naturally from Einstein's work on gravity — were actually quite well developed before the first redshift observations were made. So the redshift observations just dropped right in to the new model.",
"So what ",
" that model? Well, Marko gave you some of the basics. The essence of it is that the distances between fixed points in the universe are increasing over time. Take any two points, measure the distance between them, then wait a reasonable amount of time — say a dozen billion years. Measure the distance again and you'll find that the distance has increased. The two points ",
" But the distance between them is not fixed.",
"How can this be? The geometry of our universe is not static, basically. It can change. That's just something you need to accept as empirical fact.",
"Okay, so we have these fixed points in space, and the distance between them changes. When viewed from a single point at a single instant, it ",
" that objects sitting out in space at those fixed points are receding from us, and that their speed of recession is proportional to how far away they are. But we know that isn't the case. It's just an optical illusion.",
"We also know that ",
" the rate of expansion were ",
" — in technical terms, the second time derivative of the scale factor were zero — we would see relatively close objects (a few hundred million light-years away) with some apparent velocity, and we'd see more distant objects with some ",
" apparent velocity. Because the ",
" velocity of recession when the metric expands at a constant rate is a function of distance. If the metric is expanding at a constant rate of, say, one meter per megaparsec per second, then a thing one megaparsec away will appear to recede from us at one meter per second, while a thing ten megaparsecs away will appear to recede at ten meters per second, and a thing a hundred megaparsecs away will appear to recede at a hundred meters per second. ",
" part is just simple arithmetic!",
"Which brings us naturally to the question of whether the metric is expanding at a constant rate or not. It's not like we have historical records of metric expansion going back a billion years that we can plot on a chart. Instead we have to draw inferences. Luckily we have a cheat, provided to us by God or Mother Nature or however you prefer to metaphorically personify the laws of physics: type Ia supernovae.",
"It turns out, conveniently, that type Ia supernovae are just ",
" consistent astronomical events. They all have the same cause, they all evolve in the same way over time. They're as consistent as a McDonald's hamburger. So we can look out into the sky with telescopes and find type Ia supernovae happening in other galaxies — this turns out to be fairly easy, since a type Ia supernova can outshine its entire parent galaxy. Because these events are so monotonously consistent, we can make quite precise measurements of their spectra and their luminosity curves over time. Both of these measurements tell us about what the geometry of the universe was doing at the times those supernovae occurred. In that way, we really kind of ",
" have historical records going back a billion years, and we can plot those records on a chart and suss out a trend.",
"When we do that, we find that our observations are ",
" consistent with a constant rate of metric expansion. Instead, our observations are consistent with a rate that's gone up and down over time. We built some mathematical models that make the rate of expansion a function of various things — radiation density, matter density, vacuum density and so on — and found that one of those models matched the observations to a high degree of precision. That model is now the standard model of cosmology, because it describes a universe that looks very, very much like the one we see when we look at the sky.",
"So to sum up, don't think of distant galaxies as moving through space, because they aren't. Think instead of changes in geometry over time, because that's what's happening. When we talk about accelerated expansion, we're talking about the way the ",
" of change in geometry changes with time, which really is just a means to an end to suss out the relationship between the geometry of the universe and the contents of the universe."
] |
[
"That ",
", by itself, show that the expansion is accelerating. To understand why, I'm going to first have to explain what the expansion is.",
"So in geometry, there's a function called the metric, which describes how distances work in some given geometry. The easiest nontrivial example of this is the 2 dimensional Euclidean metric: ds",
" = dx",
" + dy",
" (If you don't know what the d means, feel free to ask, but it's not really important here). You can also have more interesting metrics; for instance, the Minkowski metric ds",
" = -dt",
" + dx",
" + dy",
" + dz",
"So how does expansion work in here? Well, metrics don't have to just involve +- d(whatever)",
" You could have ds",
" = 1, or ds",
" = dx",
" + 5dy",
" or any number of strange things. What we're interested in is a modification of the Minkowski metric: ds",
" = -dt",
" + a(t)*(dx",
" + dy",
" + dz",
" That a(t) in front of all the spatial terms is a time-dependent scale factor, and it means that the spatial distance between two points depends on time. This phenomenon is called metric expansion.",
"However, a(t) itself isn't a very natural way to view metric expansion. I can describe its purpose in the metric pretty well, but it's not as clear at all what it means in terms of observations. Instead, metric expansion is most frequently described in terms of the Hubble constant, the time derivative of a(t) divided by a(t). This can roughly be described as the rate of metric expansion; precisely, it's the amount of additional distance that grows between two points a unit distance apart, per unit time. Notice that as a consequence of this, galaxies which are further away will move faster.",
"When we say expansion is accelerating, we mean that the second time derivative of a(t) is positive. This absolutely does not follow from the fact you mentioned; we just explained that with the first derivative. The evidence that a''(t) is positive is complicated and I don't understand it, but my cosmology friends assure me that it's very strong. ",
"Interestingly, though, that fact doesn't mean that the Hubble parameter is increasing. If you work through the math, you'll see that it's possible for H'(t) to be negative and a''(t) to be positive, so long as the latter is large enough. So it turns out I don't know how to intuitively explain what accelerated expansion looks like, welp"
] |
[
"Electrical (or plasma) cosmology provides and much clearer and startlingly strong model than current gravitational cosmology would like to admit.",
"We ",
" need to leave the crank pseudoscience out of it, please. You're not talking about a legitimate alternate model accepted by a minority of cosmologists. You're talking about hoo-hoo-ha-ha nonsense."
] |
[
"Is our sense of time affected by the rate of chemical reactions?"
] |
[
false
] |
So if our biological chemical reactions occurred as quickly as nitroglycerin breaks down into gases, would our perception of time be different?
|
[
"grad students can consent. mice cannot."
] |
[
"It is much more complicated than that, and is a very active area of research.",
"A professor at my school, David Eagleman, studies this stuff. He's a complete badass, check him out: ",
"http://en.wikipedia.org/wiki/David_Eagleman",
"edit: ",
"one of his famous experiments involves using magnetic energy to slow the propagation of some signals in the brain, and if done properly it can make you think cause and effect are reversed in some special circumstances. he also dropped grad students from a tall structure with a quickly-blinking watch to see if the fear of death would help them see what the watch was displaying. they couldn't.",
"many biological reactions happen just as fast or faster than nitroglycerin degradation. something like time perception that involves consciousness must by definition be related to higher-order neural networks in the brain."
] |
[
"he also dropped grad students from a tall structure with a quickly-blinking watch to see if the fear of death would help them see what the watch was displaying.",
"It amuses me to no end that there are rules upon rules about how you can treat lab animals, but pretty much zero regulations about what you can do to grad students. Even more so because there doesn't seem to be much a grad student ",
" do in exchange for course credit."
] |
[
"If 8 years in advance, we detected that an object 1/3 the size of the moon were on a collision course with earth could humanity pull it's resources and save some small percentage of the species? How?"
] |
[
false
] |
[deleted]
|
[
"Could people return to earth after the collision?",
"Post impact earth would be better than mars I think..."
] |
[
"Probably not. Such a large impact would melt a significant percentage of the Earth's crust, vaporise a lot of rocks, fuck up the planet's rotation and day length, possibly alter the orbit depending upon the impact velocity, and make the planet return to a state very similar to one it was in around 4.5 billion years ago."
] |
[
"Simulation of what it would look like:\n",
"http://www.youtube.com/watch?v=LlF8APEkh-E"
] |
[
"Do we know why gravity moves at the speed of light? Do the other elemental forces move at this speed too?"
] |
[
false
] |
question reminded me of something I've always wondered, the speed of gravity. Why is it that specifically, gravity moves at the speed of light? And seeing as the speed of light changes depending on the medium, does the speed of gravity change as well? Does that mean gravity is carried by particles?
|
[
"Yes, that's a group-velocity effect. Light that moves through an electric field can be modeled as a wave phenomenon, and wave phenomena have both phase and group velocities. The phase velocity refers to how the individual wave phase moves, while the group velocity refers to how the wave's envelope moves.",
"Individual photons move at the speed of light. Always. They cannot do otherwise, and it's impossible to construct a scenario in which a photon can be observed by anyone to move at anything other than the speed of light.",
"But rays of light are not individual photons. They're composed of many photons, and have properties distinct from the properties of individual photons."
] |
[
"There's maths involved, but basically it falls fully formed out of the equations of general relativity. The study of the way gravitation propagates through space is a ",
" deep one, involving things like gravitoelectric and gravitomagnetic effects, complicated aberration cancellations and so on. (One should not be misled into thinking \"gravitoelectric\" and \"gravitomagnetic\" have anything to do with electricity or magnetism; the names are just analogies to the way electric and magnetic effects are related to each other.) The short version is that gravitation is intrinsically linked to the geometry of spacetime, and that same relationship also defines what the speed of light must be. They're both fruits of the same tree, in a manner of speaking.",
"The speed of light never changes, ever, period, regardless of where the light is or how you're moving relative to it. You're thinking of group-velocity effects, which are not related to the speed of light.",
"And no, gravity does not appear to be carried by particles, in the same way that electromagnetism is carried by photons or the strong interaction is carried by gluons. It was once assumed that such would be the case, but it turns out it's not possible to make sense of such an assumption. Gravity does not appear to be quantized."
] |
[
"It's other way around. Things that aren't hampered by mass move at that speed. Light is massless, so it moves at that speed. It's just that light is the easiest thing to observe. ",
"Here",
"'s a paper where relativity is derived without reference to light."
] |
[
"If our sun went \"out\", approximately how long until the last human dies?"
] |
[
false
] |
Assuming our sun just "quit" (immediately and non-explosively stops producing heat and light), how long until every human on earth is dead? Consider all variables like the blanket of our atmosphere and resourceful people digging underground "vaults" or similar and exploiting geothermal/nuclear power/heat as long as possible.
|
[
"The earth's surface would become unlivable within a matter of weeks due to the extreme cold. The temperature on the surface of the outer are around –355 degrees Fahrenheit. The earth's surface temperature would rapidly dive to that inhabitable temperature.",
"Geothermal heat from the earth will continue independent from the sun's existence so it would be possible to maintain a livable subterranean habitat . Geothermal electricity generation would also still be possible and because of that, food could be grown underground using artificial lights. Since geothermal energy will be around for a long long time, I think it would be theoretically possible for humans to live indefinitely if proper preparations were made. ",
"I say indefinitely, because if geothermal did eventually die out, humans could transition into uranium/thorium nuclear reactors and eventually into fusion (if discovered)."
] |
[
"http://www.physorg.com/news62952904.html",
"\"the vast majority of the heat in Earth's interior—up to 90 percent—is fueled by the decaying of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232 contained within the mantle. These isotopes radiate heat as they shed excess energy and move toward stability.\""
] |
[
"I'm a bit confused by your association with magma and friction. My understanding is that the only real source of heat from friction is tidal forces. Most \"new\" heat in the mantle is from radioactive decay. Magma is produced through decompression or fluid flux, which don't seem to apply here."
] |
[
"In what fields of science can the hobbyist contribute something?"
] |
[
false
] |
I have taken an interest in aquaponics because there is a lot of experimentation going on - best ways to grow things, control temperature/chemistry, alternative fish feed production, etc. I am aware of protein folding research and would like to know more about how to get started in that. What else is there that I can usefully explore at home, up to say $100K of capital outlay for equipment etc? I have no formal background in science. Mostly software and electronics, but I'm willing to learn something new.
|
[
"Astronomy, The 2009 and 2010 impact events on Jupiter were discovered by an amateur astronomer using a 14 inch telescope."
] |
[
"No one's mentioned it yet, so I guess I should:",
"One possible way to contribute, without any costs, is taking part in ",
"Galaxy Zoo",
". Galaxy Zoo is a project that gets interested non-astronomers to look at images of astronomical objects and try to classify them using a set of simple guidelines and questions. It's pretty quick and easy to learn how to do it, and there's the possibility of discovering a brand new type of object (example: ",
"Hanny's Voorwerp",
", discovered through Galaxy Zoo)."
] |
[
"If money is the only limiting factor, I really doubt that there is any field that you ",
" help by writing software. Protein folding is the obvious example that you can attempt from home, but pretty much every project I've seen would benefit from someone coming in and automating data gathering and analysis, if not design:",
"-Automated ('inverse') design of nanophotonic structures. Currently you basically play guess-and-check to make a good structure, with the 'check' step being a very computationally-intensive simulation. Having a better way of going from 'i want the structure to do x' to 'here is a structure that does x' would be a huge time-saver and is an active research direction.",
"-Extension of current simulation code to GPGPU systems, especially with multiple GPUs. There are plenty of software suites that will perform simulations, but relatively few are both robust enough to handle exotic stuff (like, say, optics in metals) and scalable over multiple cpus/gpus/computers. Those that are are generally so expensive that they're not used in academia anyways.",
"-Data analysis! Generating tons of data is easy, but time and time again I find people counting and measuring cells or nanostructures by hand. And repeating this, frame by frame, over hundreds of frames, each with hundreds of measurements. If you can automate this sort of thing, the people you help will love you forever. If you can make it easy and make it work for lots of different structure types, ",
" will love you and cite you and children will chant your name in the streets while money rains from the sky."
] |
[
"Does light have any inherent \"luminous\" quality to it, or do our brains just interpret it as light?"
] |
[
false
] |
Does light (photons?) have any inherent luminous quality, as in they glow or something similar, or do our brains + eyes just take in light particles, and interpret it as "ok, there are a lot of photons, so I'm going to interpret this as a 'bright' light" or something like that? Not sure if all light is just photon particles, or there's more to it...
|
[
"It is our brains interpret it as light.",
"Our eyes are detectors of electromagnetic waves, and the range it can detect covers what we call the visible light. ",
"All light is just photon particles. The more photons hits the detector (our eyes), the more the detector is excited, so our brain interpret it as being bright."
] |
[
"The photons don't glow - they are the glow of something else. What enables us to see is the photons hitting the photoreceptors in our eyes, and if enough photons hit a single photoreceptor it fires a signal to the brain, which in turn translate it to the color of \"a pixel\" of an image.",
"Our eyes are only able to see photons inside a certain frequency range, otherwise know as ",
"visible light",
". Some animal species have the ability to see light that humans can't see, since thy have different photoreceptors than us. Infrared and ultraviolet light is light (photons) with a longer and shorter wavelength than visible light, respectively. Radio waves and other types of electromagnetic waves are also just ",
"photons with a different frequency",
"."
] |
[
"So our brains just take in photons and says \"ok, this area is bright, this area isn't... let's create a picture for this human\"? Haha probably not very accurate, but is this basically what's going on? Super cool."
] |
[
"My Chemistry homework has this problem on it. I can't solve it, and no one I ask knows how. Help?"
] |
[
false
] | null |
[
"http://www.reddit.com/r/homework"
] |
[
"This question doesn't belong here. Ask your professor. "
] |
[
"The only chemical reaction here was the decomposition of calcium carbonate, CaCO3 -> CaO + CO2. The calcium oxide present in the original mixture didn't do anything. Thus we start by looking at how much mass of the solid mixture was lost in the liberation of the carbon dioxide gas.",
"mass of CO2 liberated from decomposition = 0.689 - 0.474 = 0.215 g",
"quantity of CO2 0.215g @ 44 g/mol = 0.00489 mol",
"Since the decomposition reaction produced 1 mole of CO2 for each mole of CaCO3 originally present, ",
"mass of 0.00489 mol of CaCO3 @ 100 g/mol = 0.489 g",
"mass fraction of CaCO3 in original mixture = 0.489/0.689 = 0.7097 = 71%",
"I'm guessing that the point of the exercise is primarily to practice doing the math and determining the molecular weights. Paper, pencil, & periodic table should be all you need. Keep at it!"
] |
[
"Since something so massive killed all of the dinosaurs all at once, did it kill all of the foliage/nature/plants? Are all the plants we have today completely new?"
] |
[
false
] |
Probably a dumb question. But I've had a few.
|
[
"Wikipedia",
" claims that about 57% of terrestrial plant species became extinct during the Cretaceous-Paleogene extinction event. Note that that number is the percentage of species, not the percentage of individual organisms or the percentage of biomass."
] |
[
"Geologically, it was a blink of an eye."
] |
[
"It didn't kill ALL the dinosaurs. The birds survived. "
] |
[
"Why when you mix Ice with Alcohol and Salt the \"temperature\" goes lower?"
] |
[
false
] |
I just want to know the chemical processes or reactions going on, or what property the Alcohol molecule has that allows this "lower temperature" or better heat acceptance. Thanks!
|
[
"Alcohol and salt water have a lower freezing point. So they can stay liquid at lower temperatures than pure water. So when you add them to ice, it returns to liquid and is able to get much colder before it begins to freeze again."
] |
[
"Actually, if I understand correctly what you are trying to say, it isn't quite right.",
"if you have a mixture of ice cubes and water at 0 C and you add ethanol at 0 C, the temperature will drop below 0 C, so you CAN change the temperature as well as the phase, even when all components added were at the same temp.",
"Reason: Some of the ice will melt to create a new solid-liquid equilibrium within the system, but the melting of the ice will drop the temperature. Overall, the energy of the system will be conserved, but because of the phase change the temperature will drop. ",
"Edit: many of these counter-intuitive (or difficult to wrap your brain around) concepts are covered in Understanding Engineering Thermo, by Octave Levenspiel. It is an intro-level thermo book so it can be understood by most people who have had general chemistry and calculus-level mathematics. I believe the very question proposed by the OP is covered. "
] |
[
"I think the question being asked here is when you mix these items, the system feels like it feels like it gets colder. This is because when the salt is added, and is solvated by the water / alcohol mixture, there is more energy taken in to the system than is given out. When something (anything) is solvated, there are bonds that need to be broken (in the case of salts, the ionic bonds are broken; NaCl is broken into Na+ and Cl-). This requires energy...and endothermic process. At the same time, new bonds are being made (the bonding of hydroxyl moieties in water and ethanol)...making bonds releases energy, but in this case the making of the bonds (an exothermic process) is less energetic than breaking those ionic bonds. Overall, the system has a net gain of energy (pulling energy in) which is takes from the environment around it, including your hands holding the glass you've got these ingredients in; hence, it feels colder.\n[edit to add] the bonding strength between ethanol and ions is going to be pretty poor for a number of factors. when water solvates, big sort of localised chains of water molecules bind together to form a cage around the ion, possible because of the strong h-bonding properties of water. Ethanol, having that small carbon chain on the end of its hydroxyl (OH) group, cant easily form these extended bonds. Bare in mind also that with the water / ethanol mix, intermolecular bonds between water and ethanol are being broken as well when you add the salt, requiring more engery to be taken in (endothermic)."
] |
[
"Why do our eyes tear up when we yawn?"
] |
[
false
] |
Is there a reason for this?
|
[
"Diagram.",
"Normally, tears go from the lacrimal gland, across the eye, into the lacrimal sac, and finally drain away through the lacrimal duct. Note that the lacrimal sac acts as a reservoir for the tears to drain from.",
"When we yawn, our face muscles apply pressure to the lacrimal sac, which causes an excessive amount of tears to be pushed back onto the eye. Additionally, the lacrimal duct is also closed off by the pressure so the tears can't drain."
] |
[
"Part of the reason is that when you yawn, you squeeze your eyes tightly shut. The way that tears flow is that they come out of your lacrimal gland, which is on the upper outer side of the top of your eye; they then flow - in a film - across your eye obliquely downwards and inwards.",
"The tiny black dot on your lower eyelid is called a punctum, and that's where your tear duct starts and where the tears drain away.",
"But if you squeeze your eyelids tightly shut, you close off the punctum, stopping the tears flowing across your eye and into the tear duct, so they build up in the eye. This makes you cry a little bit, which is why tears appear when you yawn. "
] |
[
"Does that mean one could make themselves cry at will by flexing face muscles sufficiently hard? Moreover, is that why Peter Parker looks like he's trying to have a baby when crying for Harry in the 3rd Spider-Man? "
] |
[
"Are photons the only thing that can move at the speed of light?"
] |
[
false
] |
And if so how fast can/do other particles like protons, neutrons, electrons, or neutrinos move?
|
[
"Massless particles move at the speed of light. Aside from photons, we know that there is also gravitons (the particles mediating gravity) and gluons (mediating the strong force) which both are massless and thus move at the speed of light. Massive particles can move arbitrarily close to the speed of light, but they can never reach it. "
] |
[
"massive particles",
"The neutrons, protons, and electrons OP asked about all have mass and thus can never reach the speed of light and neither can anything made of them, unfortunately for humans.",
"Neutrinos are a curious case because they were ",
"predicted to not have mass",
" but experimentally they do seem to have mass and no one is really sure why. Speed measurements show them moving either at or extremely close to the speed of light, and are not sensitive enough to tell the difference.",
"EDIT: words"
] |
[
"Gravitons actually exist? How'd they isolate one ?"
] |
[
"Does a shallow continental shelf reduce the power of a tsunami?"
] |
[
false
] |
I kind of know how tsunamis work, but I'm curious if a wide and shallow continental shelf would have a noticeable impact on the size/strength of a tsunami. From what I understand, a tsunami can travel so far because there's much less resistance in the deep sea, and that when it hits the shelf it starts to rise and slow down, so would a tsunami lose a noticeable amount of energy if it had to travel in shallow waters for a while before hitting a coast?
|
[
"The short answer is that there are trade offs with respect to the steepness of the continental slope (i.e. the transition from the deep ocean to the shelf) and the depth of the continental shelf and it depends on whether you're thinking about wave height or run-up height. ",
"To dig deeper, this paper from ",
"Siva & Behera, 2016",
" used a suite of numerical models to test the effect of continental slope and the depth of the continental shelf on both the tsunami wave height, but also the run-up (i.e. the max elevation on land that the tsunami reaches). They present all their results as normalized, either considering the height of the tsunami wave as it reaches the shelf normalized by the initial height before it reaches the shelf (H",
" / H",
") or in terms of run-up, specifically the amount of run-up normalized by the initial height of the wave (R",
" / H",
"). ",
"What they find, is that in terms of wave height, is that whether variations is shelf depth increase or decrease wave height depends on the slope (see Figure 10). For really steep continental slopes, a a shallower continental shelf reduces wave height (as you assumed), but as the slope gets less steep, this actually flips and shallower continental shelves lead to higher wave heights. Arguably though, run-up is really what we would be the most concerned with as this is really controls how far inland a tsunami can travel. For these (Figure 11), at all slopes, deeper shelves produce higher run-ups for the same initial wave height. This would probably be closest to the spirit of your question, as the run-up height would be the most relevant for thinking about the destructive potential of a tsunami (though this needs to be considered within the context of the shoreline topography, i.e. for a given run-up height, there will be more run-up distance covered if the shoreline has a very shallow-angle).",
"Finally, it's worth noting these are hypersimplified 2D models, so there will be A LOT of other factors that become important considering real slope-shelf transitions and 3D heterogeneity, but this is a good starting point."
] |
[
"As you said before, there are trade-offs. If the incoming tsunami encounters a steep slope, leading up to the shoreline, there will be a greater build up of wave height, with which coastal residents will have to contend. But impacting the slope will also slow the forward speed of the wave, potentially affecting how far inland the water will push (which is also determined by the degree of upslope from the beach)."
] |
[
"This is a great answer, thank you so much. I think I found studies like this when I was reading about it, but I wasn't sure if what I was after was wave height or not, since that seemed different from run-up (which seems like a better word for what I was getting at).",
"Just to make sure I'm not misinterpreting, looking at that paper at figure 5, all else equal, would we expect to see more run-up on the east coast rather than the west coast?"
] |
[
"a question about quantum entanglement"
] |
[
false
] |
[deleted]
|
[
"An important feature of quantum entanglement is that it is inherently a quantum phenomenon and cannot be described using classical observation- so any analogy used which is classical in nature will come up short. You are right, there is something \"very magic\" going on, which I use in the sense that it does not conform to what we consider normal conditions. In fact, being confused or considering it \"magical\" puts you in good company as ",
"even Einstein",
" considered the implications of quantum entanglement to be absurd. Yes, there is an instantaneous collapse of the wave function which bothered Einstein greatly. ",
"However, where the analogy is useful though, is showing why instantaneous wavefunction collapse does not violate relativity- because the collapse does not actually impart any new information into the system. Why? Because the same results can be obtained through classical means. Should you chose to measure now, or measure later- there is no way to use measurements found to communicate anything that you could not communicate using classical methods. Thus, preserving relativity. "
] |
[
"You're right in a sense, but this is related to classical mechanics. When we describe a wavefunction of a particle, the 'wave' describes the probability of finding that particle in space... WHEN THE PARTICLE IS OBSERVED. This last bit is extremely important, because when the particle is NOT observed it's location has no real meaning, it is in superposition, meaning multiple locations at once. When there is a pair of electrons with opposite spin states, when not-observed, each electron has BOTH spin states because it is in superposition. When one is observed, this means the other one obviously has the opposite spin state, but this information isn't known until the point of observation. ",
"Hope that helps! Any more questions?"
] |
[
"It is true, that quantum entanglement does not allow the transfer of information. Saying that it does not violate relativity is therefore technically correct. The collapse of the wavefunction does however violate general relativity in the sense that it is a nonlocal physical phenomenon, which does simply not fit within the framework of general relativity."
] |
[
"Question about life on nearby moons:"
] |
[
false
] |
So I recently turned my telescope to Jupiter, and was pleased to see the Galilean moons. Fantastic! Although Io happened to be occluded by the big planet and I only got to see the remaining three, I'm still pleased as punch that they're out there. In any case, I started wondering about the possibility of life on those distant moons. I could go and gather the details myself, but I'd rather ask the group of astronomers and biologists here for not only the facts, but also their opinions. Nerds, one and all, riddle me these: The possibilities are endless - let's talk about them!
|
[
"Enceladus was recently shown to have liquid salt water, so it's now a candidate. Of course, Mars is always in the running.",
"Not to the best of my knowledge.",
"Pretty confident but not 100% sure. If there's water underneath then the surface would be water ice.",
"I don't think so.",
"Same.",
"There was the recent discovery of an acetylene-hydrogen cycle going on on Titan.",
"I read that there was speculation that life on Titan may have started by panspermia from Earth. It's really too early to say.",
"Io's pretty much a volcano.",
"Enceladus, for one.",
" Enceladus."
] |
[
"That's a bold statement, considering we can't exactly measure the probability of life spawning anywhere else at this time. However, one can only hope there is life elsewhere in our galaxy, let alone our solar system."
] |
[
"I would say that considering how many moons there are in our solar system, something like ~135, I am pretty sure there has to be life, at least single cellular, on at least 1 of them."
] |
[
"How does natural selection make organisms lose useless functions?"
] |
[
false
] |
[deleted]
|
[
"It doesn't always, we still have an appendix but we don't use it!",
"https://en.wikipedia.org/wiki/Vermiform_appendix#Use",
"This is not known, it's assumed, and it is probably not true."
] |
[
"There are a number of important evolutionary forces that shape an organism:",
"1) Positive selection - this is probably what you think of when you say \"natural selection\". Organisms that have a genetic variant that confers a reproductive advantage compared to other organisms multiply and the variant increases in frequency in the population",
"2) Purifying selection - this is the converse of positive selection. Organisms that have a genetic variant that confers a reproductive ",
" die more quickly and the variant is removed from the population.",
"3) Genetic drift - variants that have neither a beneficial or detrimental effect (they are \"neutral\") move up and down in frequency randomly in the population until they are \"fixed\" - reaching either 0% or 100% frequency.",
"So, mutation occurs all the time, introducing new variants of a given gene. Some of these will destroy the function of the gene.",
"If this results in a reproductive disadvantage, these variants will be removed from the population by purifying selection. In fact, purifying selection has to act constantly to maintain our genomes and keep them from being destroyed by the introduction of new mutations - harmful mutations ",
" be removed from the population by selection.",
"However, if the loss of function of that gene has no particular effect on survival, then those variants will evolve neutrally, mostly governed by genetic drift, and by chance some of them will be fixed. So, over time we should expect that drift will eventually destroy everything that is not important for survival in some way."
] |
[
"Well less energy = less energy for mating rituals, therefore you get picked as a mate less. Less energy for thermoregulation so you might not survive colder winters etc. etc.",
"Above all there is no real concrete road map for evolution, things effectively happen by accident and its hard to nail down exact reasons for gains/losses of function. It could be that eyes were lost for no reason other than random variation when the population was small, and there was no selection disadvantage against losing them."
] |
[
"Why is it that a transformer only starts using electrical energy when a load is placed on the second coil that is not connected to the outlet?"
] |
[
false
] |
The primary coil is connected to the outlet and doesn't consume very much energy but as soon as a load is placed on the secondary coil electrical energy is used. I am trying to understand the relationship between energy and magnetic fields. The more in depth you could be in the explanation the better.
|
[
"Take a transformer with an unconnected secondary. If it helps think of it as if a very small capacitor was connected across the secondary; there's no path for DC current but a very small amount of energy can be stored in the electric field. This isn't really a good approximation but it may help you visualize the analysis.",
"Turn on the power. The primary coil will have a current through it and energize. The iron core conducts the magnetic field into the secondary, creating a current in the secondary. There's no path for the current and once you reach steady-state the charge separation will maintain a voltage across the secondary. No path for power means no power is used.",
"Now attach a resistive load. The current in the secondary coil now has a path to flow. This in turn creates a magnetic field in the secondary coil that is conducted back to the primary in opposition of the original field. This 'acts against' the primary field and when looked at from the source towards the primary input the whole system appears to be different load than just the primary alone. When people talk about reflecting the load across the transformer they mean figure out what the black-box equivalent is which in the end dictates what the supply sees.",
"The same logic can work for an inductive load but becomes trickier to visualize. Attaching an inductive load means that instead of the opposing fields being in-phase you get some arbitrary phase shift in the field induced in the secondary which means things get weird and highly frequency-dependent. The math isn't intractable if you're comfortable with handling complex numbers but it's no picnic.",
"In the end it's all about the currents through the coils. Current in primary creates a field in the secondary and in turn allowing a current in the secondary creates a field in the primary. No current in the secondary means no field affecting the primary and you're left with a rather expensive inductor that has some wonky impedance because it's coupled to another via iron core."
] |
[
"The magnetic core causes the input and output windings to be tightly coupled (that is what it's there for). The two windings act as one. ",
"So when you put a load on the output it is reflected to the input.",
"Without a load, the input is high impedance. When a load is connected the input impedance drops dramatically."
] |
[
"Thank you!"
] |
[
"Nutrient Absorption and Diarrhea"
] |
[
false
] |
Hey AskScience, If I eat a major load of carbs (2000-2500 cal range) and follow it up with something that gives me diarrhea (let's say coffee), will the carbs bypass the nutrient absorption areas such as the stomach and small intestine? The ultimate aim here would be the prevention of a glycemic response, so that the insulin spike wouldn't trigger fat storage. Would the mouth's absorption of carbohydrates be enough to trigger that insulin spike?
|
[
"The short answer here is no. Carbohydrate digestion and absorption is quite rapid. Assuming you had normal gut flora there would still be a a large increase in serum glucose and a corresponding increase in insulin. Even if enough polysaccharides were left in the gut to cause osmotic diarrhea. ",
"Would the mouth's absorption of carbohydrates be enough to trigger that insulin spike?",
"The absorption of nutrients in the mouth is negligible, even compared to what would be absorbed during rapid passage through the duodenum and jejunum.",
"Edit: The long answer depends on a whole host of other factors. I'm happy to go into a ton more detail since I'm currently studying for a test on GI physiology and it would help me study. What is your intention with the question? What aspect of digestion are you trying to get at with this scenario?"
] |
[
"Thanks for your response! Can you cite a source on the speed of glucose uptake in the mouth vs the duodenum/jejunum?",
"P.S. I have no intention of using this practically. My real interest was in the speed of glucose uptake under the conditions of diarrhea."
] |
[
"In ",
"this study",
" they showed that glucose absorption was negligible in the mouth. The main site of carbohydrate absorption is the duodenum and jejunum. This is the fastest site in the body by far because of a number of factors.",
"The surface area of this region is tremendous. The mucosa is folded 4 times in the following structures: plicae circulares, villi, crypts of Lieberkuhn, and microvilli.",
"Polysaccharides (most carbohydrates except for glucose, fructose, and galactose) cannot be directly absorbed, and must be converted to monosaccharides first. Salivary amylase starts the digestion of polysaccharides to mono-, di-, and trisaccharides but isn't extremely efficient. In the duodenum, pancreatic amylase digests the carbohydrates to mono-, di-, and trisaccharides ",
". The di- and trisaccharides are converted to monosaccharides by brush border enzymes. Some polysaccharides are resistant to human enzymes and are transported, largely unchanged, to the colon, where they are digested by commensal bacteria. ",
"The small intestine has a high concentration of membrane transporters to facilitate absorption of monosaccharides (SGLTI for glucose and galactose, and GLUT5 for fructose).",
"Thus, glucose uptake is rapid and sufficient, even with rapid intestinal transport. Problems with glucose uptake could cause osmotic diarrhea, but not the other way around. Problems with glucose uptake would be caused by a specific defect in polysaccharide processing (misformed amylase, lack of bicarbonate secretion in the duodenum, a defect in CCK or secretin, celiac disease, etc.). The problems with diarrhea are typically associated with water and electrolyte loss, not lack of nutrients."
] |
[
"Do atoms get denser as you go up in atomic number, or do the atoms simply get larger and thus retain the same overall density in spite of their increasing atomic weight?"
] |
[
false
] | null |
[
"Density is generally thought of as a bulk property, and isn't really dependent on each atom's properties, but rather the way they pack together. Check out the wikipedia article on ",
"crystal structure",
".",
"At the atomic level, it is difficult to talk about density because that requires knowing something about volume. It is true that the mass of the nucleus increases as the atomic number goes up, since the number of nucleons is increasing. The density of bulk material tends to increase for higher atomic numbers, but not always. For instance (in g/cm",
" ):",
"Al (Z=13) - 2.7",
"\nFe (Z=26) - 7.9",
"\nCu (Z=29) - 8.9",
"\nSn (Z=50) - 7.4",
"\nIr (Z=77) - 22.5",
"\nAu (Z=79) - 19.3",
"\nPb (Z=82) - 11.3 "
] |
[
"Atoms do, in general, get denser.",
"The mass comes almost entirely from the nucleus, but the size is due to the electron cloud around the nucleus.",
"The size of the electron cloud is related, in a somewhat complicated way, to the atomic number. More protons -> more electrons -> electrons in higher orbits -> bigger electron cloud. The size of the electron cloud scales more slowly than atomic number, so this (generally) leads to denser atoms with increasing atomic number.",
"Another important consideration is the number of neutrons in a stable nucleus. As you add P protons to a nucleus, you generally add more than P neutrons. That's why atomic masses are consistently higher than double the atomic number. So, this is contributing as well."
] |
[
"However, the atomic weight is not the only factor in the density. For example, an atom of gold is lighter than an atom of lead, but gold metal is much heavier than lead metal. This is because the atoms are more closely packed, because of the electronic structure."
] |
[
"If there's acid rain, is there such thing as acid snow?"
] |
[
false
] | null |
[
"Yes, there is, and it can be more of a problem than acid rain.",
"For one, when snow is falling it spends more time travelling through the atmosphere before hitting the ground than rain. As a result of this, it has more time to collect pollutants, and can become more acidic than typical acid rain for the same region. There's additional factors that complicate this however, such as the solubility of the pollutant, the temperature and the water content of the snow, etc. (e.g. warmer snow which is more \"wet\" is going to dissolve more than cooler, drier snow.)",
"Once the snow hits the ground, the dissolved pollutants are going to stay in solution, or trapped within the crystalline structure of the snow until it melts. Because of this, snow can pile up and then thaw, releasing all the pollutants and acidic water in a relatively short amount of time. This can have fairly substantial effects on the environment.",
"You can read a bit more about this here:",
"http://www.elmhurst.edu/~chm/vchembook/191acidsnow.html",
"http://dwb4.unl.edu/Chem/CHEM869V/CHEM869VLinks/www.qesn.meq.gouv.qc.ca/cc/acidrain/info6.htm",
"It's been many years since I've studied environmental chemistry, so I've only answered in a fairly basic way in order to not misinform. Someone with more experience in this field should be able to give you a more complete answer.",
"EDIT: Formatting"
] |
[
"Thanks a lot. Considering I have next to no knowledge is this field, your response is more than enough!"
] |
[
"Plus, there are these awesome things called polar straospheric clouds. During the polar winter, it gets so cold that clouds consisting of tiny ice cristals form much higher than they normally would. On these clouds Chlorine reservoir species react with water and HCL, realsing the chlorine in molecules that are broken up by photolysis as soon as polar spring comes. That chlorine then proceeds to break all the Ozone it can get its filthy handy on, resulting in a yearly Ozone low around antarctica in spring. In addition, the reaction takes the HCL out and leaves NO2 on the ice which means there is less NO2 to bind chlorine, resulting in even more Ozone destruction. Stupid snow",
"Edit: took out my claim that HCL is what makes the rain acid."
] |
[
"does carbohydrates (glycogen) turn into fat when not used in a certain amount of time?"
] |
[
false
] |
[deleted]
|
[
"They way I always thought was everything is broken down into simple sugars, and it's the excess sugars that your body stores. Eating to much of anything will make you fat. Carbohydrates produce alot of sugar when broke down and that's why you get fatter faster on a high carb diet. Like I said my understanding I may be wrong and probably am."
] |
[
"Nope, there is no way to convert glycogen into adipose tissue. ",
"Think of glygocen as more of a short term, fast burst energy. It's mainly stored in the liver and muscle tissue to that it can be converted into useful energy and used fast when a person needs it. Mainly used during anaerobic exercise (sprints, weightlifting).",
"Adipose tissue (fat) is more of a long term, slow release energy. It takes longer to convert into useful energy, but there is more energy stored in fat. This is what you use during aerobic exercise (long distance running, swimming). Glycogen is also used to regulate blood sugar levels. ",
"Someone can correct me if I'm wrong, once you have ample stores of glycogen, your body stores more fat. But there is no way to directly convert one to the other. "
] |
[
"There is definitely a way for cells to convert between sugars and fat, it's just a matter of rearranging carbons around. ",
"This diagram is simplified but informative.",
"The second half of the question, though, is under what conditions does your body convert from one to another. If you are starving for sugar or fat, then your body will definitely convert. But if there is an ample storage of both types, then I'm not sure how the conversion is regulated."
] |
[
"What is the rate of acceleration of photons?"
] |
[
false
] |
So the velocity of photons in water is ~2.25x10 m/s and in vacuum it is ~ 3x10 m/s. How fast does light accelerate between the boundary of water and vacuum? Also what causes this acceleration? Not sure if this is the right way to ask this question - perhaps the more correct question is what causes light to slow down in non-vacuum medium?
|
[
"The lower speed in other materials is because photons are absorbed and re-emitted by the atoms in the material.",
"This is not true, and is a commonly held (incorrect) belief. Atomic absorption features are narrow (like an ",
"absorption or emission spectrum",
") and occur over (nearly) discrete wavelengths. The index of refraction is (nearly) constant over large regions of the spectrum. These two spectral shapes are very very different from each other. ",
"Furthermore, the same atoms in different materials can have two very different indices of refraction. For example - diamonds are made of mostly carbon and their refractive index is ~2.4, and the refractive index of carbon black is ~1.1. Both of these materials are made of carbon, but they have very different indices of refraction. ",
"The index of refraction is a bulk material property and to explain it using photons is much more complex than simply absorption and re-emission. In this regard, the wave model provides an easier means of understanding the index of refraction."
] |
[
"The lower speed in other materials is because photons are absorbed and re-emitted by the atoms in the material.",
"This is not true, and is a commonly held (incorrect) belief. Atomic absorption features are narrow (like an ",
"absorption or emission spectrum",
") and occur over (nearly) discrete wavelengths. The index of refraction is (nearly) constant over large regions of the spectrum. These two spectral shapes are very very different from each other. ",
"Furthermore, the same atoms in different materials can have two very different indices of refraction. For example - diamonds are made of mostly carbon and their refractive index is ~2.4, and the refractive index of carbon black is ~1.1. Both of these materials are made of carbon, but they have very different indices of refraction. ",
"The index of refraction is a bulk material property and to explain it using photons is much more complex than simply absorption and re-emission. In this regard, the wave model provides an easier means of understanding the index of refraction."
] |
[
"Okay, but what would the photon model look like?"
] |
[
"Why is the core body temperature of humans seemingly so consistent, when we vary so much in other characteristics?"
] |
[
false
] |
To expand on the title, I'm asking why ideal core body temperature is the seemingly the same for everyone, regardless of age, sex, size, etc etc.
|
[
"It seems to me that some core body temperature regularity is required to maintain the functionality of our cells and organs. I’m sure there are a lot of factors that influence one’s given body temperature. ",
"From ",
"Wikipedia",
": “[Body temperature] depends on sex, age, time of day, exertion level, health status (such as illness and menstruation), what part of the body the measurement is taken at, state of consciousness (waking, sleeping, sedated), and emotions. Body temperature is kept in normal range by thermoregulation, in which adjustment of temperature is triggered by the central nervous system.”",
"This also isn’t a fixed average: it seems like the average human body temperature is decreasing. ",
"Here’s an interesting article on the subject",
". ",
"Another on thermoregulation in humans",
".",
"EDIT (due to OP’s edit): I’m not sure how this didn’t answer your question, even with the clarification. Our temperature is ~roughly~ the same because we all require a specific temperature range in order for our cells and organs to function; this is done via thermoregulation. I included the bits about variance among individuals and populations because some parts of temperature are attributed to minimizable factors, like inflammation, infection, and energy output. Regardless, our bodies are constantly engaged in many thermodynamic exchanges internally and externally, so the idea that our temperature is right on a dot isn’t true either."
] |
[
"The answer is homeostasis, but specifically why an infant and a 60 year old have about the same temp is because of human enzymes. Human enzymes (the chemicals that make our cells, help our organs function, etc) have a certain optimal temperature range in which they function properly. Outside of that range, we’d have a lot of problems. So, like others have mentioned, homeostatic feedback loops make sure our bodies (whether are infancy or as adults) stay within the temperature range where our enzymes can work properly.",
"Edit to add that enzymes are proteins, and proper protein folding is coded within our DNA. Hence the similarity between individual humans, to answer your question."
] |
[
"Why does bacteria grows better on your table top than in your fridge? It's all about environment~ and temperature has a huge deal to do with your metabolism which the process of energy exchange that goes on keeping you (and I) alive.",
"1) Ask yourself what is temperature...\n2) Ask yourself how we measure temperature...\n3) ask yourself how cells work, and why they would need to remain a constant tempuratue.",
"Anyways I'mma answer these in reverse... ",
"While you are complex your cells aren't, you cells don't respond to stimili you recieve, you respond to the stimili they encounter. Your cells do not sleep, they take the food you eat and turn it to energy for themselves and use it in various tasks we refer to as metabolism.",
"Sure it might be weird that our bodies know what temperature they want to be without our input. But we can very well go against that and in turn suffer as a cause. (How many people died being in the cold too long, or lost in the deserts?). ",
"Anyways our body temps aren't relatively constant just as humans, but as a spicies. \nMammals do not vary wildly in the amount of internal energy they need to stay alive. Even me and an elephant have a wildly different life style and average age of mortality, our body temperature works best in the 37degrees C range. That's because that's the optimal condition for gas exchange, reproduction, and respiration to occur. If we are below that point it slows/stops ... If we are warm than that we speeds up/expands.",
"We take our temperature by sticking objects inside of us, and make that object the same temperature as us. When you read a thermometer you are not really reading 'your' temperature as much as you are reading the temperature of the material inside of the thermometor. I'm kinda of weirded out that people saying their average temperature is 95degrees... I mean maybe it's possible but that sounds off.\n(That and the farenheit system really is trash to me, because a couple of degrees in farenheit is fractional of total amount of energy gain or loss in the Kelvin system.)\nBut I digress... Anyone who looks at their thermometer twice ever then tells all scientist they are wrong aren't credible from my perspective. I'm cautious to claim any new observations as solid with all the psuedo-science we already have. Given how easy it is to get an inaccurate temperature result/reading into uncertainties from your average American not being able to use a thermometer properly. I don't trust too much into the core temperature dropping hypothesis, but it can be possible (especially with how the core tempurature of the planet is rising)~ ",
"Anyways temperature is an average of the total movement of energy in our body right. Ask yourself this... Even tho a baby is smaller than an adult, does it eat as much? Obviously not, just like you need less energy to warm up a smaller cup of water to the same tempurature as a big cup... A baby doesn't need as much energy to be the same tempurature as an adult human being. But like an adult, if their temperature isn't maintained it will suffer.\nInterestingly enough a baby, an adult, and even an elephant usually consumes enough to maintain their body temperature. However the idea that nature maintains peak efficiency tho is silly... Mammals typically over consume, by choice/circumstance. Cells don't really have a mechanism to over consume, cells tend to be more efficient with energy (though not always, I mean what is cancer, keloids, etc.) They just use whatever is available until they can't anymore. Cells don't have other cells to store energy in, they store them inside you. And when you don't feed them they burn it till it has nothing left. Then when there is nothing they die.",
"So simply put your body remain a relatively constant temperature, because that's the tempurature it can function on keeping itself alive without overproduction(fat storage)/underproduction(cannibalism). Your body just like every organism on this planet adapted to live in an environment. When that environment changes too much it will suffer. Like taking a fish out of water, or putting a polar bear in the desert. Also that same tempurature is the same exact tempurature many other single organisms need to survive too~"
] |
[
"What is the difference between the observable universe and the universe."
] |
[
false
] |
I have also heard that we can't see past the Cosmic Background Radiation does that have something to do with my question
|
[
"The observable universe is, as the name suggests, the part of the universe that we can actually see. The universe itself may be infinite, but we can onlysee a finite part of it. The CMBR is the oldest electromagnetic radiation, because it originates from the time that photons became free to move around, so any light that is older can't be seen, as the photons weren't free to move."
] |
[
"The Universe is extremely big (it might even be infinitely big, though that's not really important for our purposes), but it only has a finite age. And light - the fastest thing in the Universe - travels at a finite speed. So light has only been able to travel a finite distance since the Big Bang.",
"That's the observable Universe - the patch of Universe, a sphere centered around us, which has had time to communicate with us. Anything beyond that is still part of the Universe, it still exists, but it's beyond what we've had time to see.",
"As for the cosmic microwave background, that's the light that was emitted when the Universe first became transparent. Before then, it was opaque - light would just bounce around from atom to atom, never getting anywhere. So we can't physically see past it."
] |
[
"There are parts of the Universe so distant that light hasn't had time to reach us. Equivalently, in order for light from these places to have reached us by now, it would have to have started travelling ",
" the beginning of the universe. ",
"We can't quite see light from the very beginning of the Universe because it was all absorbed already. The early universe was so dense that it was opaque. The earliest light be can actually see is the CMB radiation, which was finally allowed to freely stream across empty space once the universe cooled down enough for atoms to exist. So the oldest light we can see is from about 300,000 years after the Big Bang. "
] |
[
"What are the main impediments regarding a manned expedition to Mars?"
] |
[
false
] |
Why haven't we been there yet, seeing how long ago the moon landing was? Having read that it would take a mere 8 months, I can't help but wonder: is a trip to Mars that different from one to the Moon?
|
[
"The lack of geopolitical will to do so is the number one impediment, and the only serious one. From a technological standpoint we are much closer to being able to go to Mars in 10 years that we were to getting to the Moon at the time of Kennedy's speech. If President Obama makes a Mars expedition a priority and gives NASA the funding to achieve it, then humans will be on Mars in 10 years, no questions asked. Having a focused goal drives the technological developments needed to make it happen. But even so, we could get to Mars without any radical new technology. There is an excellent book by Robert Zubrin called The Case For Mars, which lays out how it can be done using existing technology (though Zubrin is a bit of a fanatic).",
"Detractors will say that we can't go because of health effects, radiation, etc. But the people saying this are often medical researchers who want funding for pet projects to do the research they say is necessary before we can go to Mars. They also say we should just go back to the Moon first, to develop the technology to get to Mars. This is complete and utter nonsense, and any time spent on the Moon is a detour from getting to Mars. It's so much easier to come up with fictitious reasons why we can't go, then to actually do the work to make it happen. Yes, there is risk involved, but space is a frontier, and you can't push boundaries without taking risk. Ask any current astronaut whether they would take that risk and absorb a bit of extra radiation, and I bet 100% would volunteer to go tomorrow. ",
"TL;DR: Politicians are short sighted and don't care about space. "
] |
[
"Ah. My question answered and my fears confirmed. "
] |
[
"There's a good chapter in Sagan's ",
" that's about this. He basically says it's admittedly hard to justify such an expensive effort when it offers very few short-term political benefits. He predicted that Mars will be reached not by a lone nation but by a coalition of nations in order to regulate costs and speed up tech advancement."
] |
[
"How much acetone exposure is harmful to you?"
] |
[
false
] |
[deleted]
|
[
"Always check the ",
"MSDS",
"."
] |
[
"Acetone has a low vapour pressure and evaporates readily in a warm room. You really should avoid breathing it in for prolonged periods as it's readily absorbed across your alveolar membranes directly into your bloodstream. You're basically getting drunk and a little poisoned on it, from the sounds of things. It's the same reason they advise not breathing in alcohol fumes while you're doing science with alcohol - it can cause your BAC to rise dangerously high very fast, because it's getting an express trip to your bloodstream via your lungs, instead of the usual route through the lining of your small intestine.",
"It's the chief component of nail polish remover so it's not too dangerous to get on your skin."
] |
[
"Hey thanks! I go to art school and it is a common prey of the EPA. I see these all of the time. "
] |
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