title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"How can bosons ever evolve to be in the same state?"
] | [
false
] | Bosons are characterized by being the ability to be in the same quantum state at the same time, e.g. a laser can be made by "piling" a bunch of photons into the same state. However, doesn't unitarity guarantee that if two quantum systems start out in different states, they stay in different states? Or can this only occ... | [
"I mean you engineer the device to produce many particles in the same state. They don't \"randomly\" just evolve into it. You're neglecting the whole device that is making that.",
"A many particle system of Fermions can't have multiple fermions in the same state. States need to be antisymmetric in exchanging part... | [
"There seems to be some misunderstandings going on because to be honest I don't understand any of your follow ups. Have you seen the math of a laser? (Gerry / Knight, quantum optics book, chapter 4 talks about interactions of atoms with classical and quantized electromagnetic field.) You have product states of the... | [
"The time evolution for a laser is not unitary. There is strong coupling to the environment that allows the thing to work. Likewise, a Bose-Einstein condensate created using atomic vapours relies on coupling to the environment, otherwise it cannot cool down."
] |
[
"How do I go about looking for an academic paper? (more in description)"
] | [
false
] | I am looking for a certain article that I remember seeing on reddit a few months ago. It involved an experiment some zoologists did in the 1970s by transporting lizards in the pacific from a "hostile island" to a "tropical paradise". This change in environment prompted a radical change in anatomy and behavior yet not D... | [
"If you don't have a subscription to any kind of journal database (Web of Knowledge, PubMed, etc), you can try Google Scholar.",
"However, without more details to search under it might be very difficult to find the specific paper you're looking for.",
"Usually I'll search under key words such as the author, spe... | [
"First Google hit for \"Lizard Evolution\"",
".",
"This reveals that ",
"Duncan Irschick",
" is probably the dude in question. He's made it easy for us by having a cool website!",
"Publications and pdf files for D. J. Irschick",
".",
"Except that's a lot of words and I'm feeling lazy. Skimming the \"... | [
"This sounds like work done with Anoles in the caribbean. I suggest using google scholar to search for ",
" and experimental evolution. And then going into the references of those papers."
] |
[
"How do infants and toddlers who barely speak get diagnosed with eye problems, when we have no way of knowing if they're able to see things just the way they are ?"
] | [
false
] | Recently saw a video where a baby got correction glasses and was able to see it's parents properly for the first time. How do parent get to know their kids have issues with seeing and even if they do, how are doctors able to correctly prescribe them glasses | [
"Parents may include an eye examination as a routine check on an infant's health.",
"There are diagnostic tools that will measure the focal point of an eye's lens. Myopia, nearsightedness, is caused by the lens focusing in front of the retina. Hyperopia, farsightedness, is caused by the focus behind behind the re... | [
"Beyond eyeball checking diagnostic tools, parents can also pick up on signals from their kid.",
"For example, if you kid looks in a book sees a bus and says \"Bus!\" cause they like buses, but then you walk by one on the street 40 feet away that is within the child's central vision and they do not react, you can... | [
"To get the prescription, they use ",
"retinoscopy",
" with infants, which is a technique for objectively measuring the error the eye.",
"There's a similar fully-automatic technique called an \"autorefractor\" that can measure this as well, and you've probably even had it done if you've got glasses. It's the... |
[
"What's stopping us from having cars that drive themselves?"
] | [
false
] | It seems like the communications technology is there so what gives? Is it costs, logistics, safety issues? When can I finally tell my car to drive to work and go back to sleep? | [
"Communications technology is not the only requirement: the main obstacle to producing cars that drive themselves is pattern recognition. It is easy to include road and navigation data in a driverless system, and a car with this information could navigate from point A to B. Issues arise, however, once unknown facto... | [
"Google actually has some that they're working on which are capable of driving on public roads. I believe at the moment they're required to have someone in the drivers seat to use them legally, but they're working on getting Nevada to allow them to run fully autonomously. Check out ",
"http://www.smartplanet.com/... | [
"Liability. ",
"Yes, there are technological hurdles, especially in terms of pattern recognition and infrastructure, but we could address those. However, even if we developed a safe and practical car, the company that sold it would be liable if anyone got hurt, and in the real world something will always go wro... |
[
"Is it by coincidence that we consider North as \"up\" on maps and globes?"
] | [
false
] | [deleted] | [
"Jerry Brotton wrote an interesting book called ",
" that does cover this specific topic in terms of map orientation.",
"Unfortuantely, I am out of town, and don't have access to my library to provide you the relevant passages. I will check back on this thread next week when I get home to see if there has been... | [
"Did an early cartographer just consider that they were in the upper hemisphere of Earth, and drew it like that, so it became the norm?",
"No. In fact medieval European cartographers generally drew maps with East being up. There have also been Japanese maps with no clear up. All labels where placed so that the ca... | [
"It's actually a general rule in Astronomy, called the ",
"right-hand rule",
". Basically you extend out your right arm, and curl in your fingers to your palm in the direction of rotation of the object. Then, the direction that your thumb is pointing is considered \"North\". This is how all celestial objects ar... |
[
"How does something as large as a city affect the crust/mantle below it? Could a city become so large and heavy that it would collapse or compress the earth underneath?"
] | [
false
] | Always wondered how something as massively heavy and all-covering as an urban area (with sewers and sediment of more ancient city walls below etc) manages to not just sink. | [
"I'll try to make this as clear as possible. ",
"Firstly, your answer is no (at least with respect to the crust/mantle). As far as compress the earth underneath, speaking in purely scientific terms, any weight will compress the earth underneath, whether it is 100,000 lbs or 1 oz. The degree of compression is wh... | [
"Well, I'm a geotechnical engineer, and you're both right. You're just talking about different things. Preconsolidation pressure is most definitely thing. And we don't just imagine it. We measure it. It's very important for estimating ",
" due to an applied load, which is needed if you want your floors to re... | [
"Well, I'm a geotechnical engineer, and you're both right. You're just talking about different things. Preconsolidation pressure is most definitely thing. And we don't just imagine it. We measure it. It's very important for estimating ",
" due to an applied load, which is needed if you want your floors to re... |
[
"What exactly are the mechanisms inside the core of an atom which determine exactly when it will decay?"
] | [
false
] | I mean it seems random to us, but like anything else it must be governed by some mechanism right? Google did not help me with this at all. | [
"You ",
" determine when it will decay; it's fundamentally random (according to certain interpretations of QM)."
] | [
"But if its random then how is it caused?",
"Whenever your system can reach a state of lower energy without violating any relevant conservation laws, it ",
" do so. So an unstable nucleus will decay to a nucleus with a lower mass.",
"There must be something that happens to causes it to go from \"not releasing... | [
"Does that mean the universe is not deterministic?"
] |
[
"Mathematically, what does it mean to \"control for\" a factor? And can I trust a study that claims to do so?"
] | [
false
] | For example, a hypothetical study might say "controlling for alcohol intake, smoking increases the risk of heart disease". For an example of something I'm unsure about trusting, towards the end of TED talk, the presenter says that his results, (about the relationship between income inequality and well-being), still sho... | [
"Before I get around to answering your question, I want to clear something up:",
"Generally, I don't know what to make of social science studies that claim to control for 'big' things, like education or income, which seem to correlate with so many other things.",
"I see the word \"correlate\" used a lot when pe... | [
"in a statistical 'generalized linear modelling' sense, 'controlling' for a factor is a way of partitioning some amount of variation in a set of observations, to account for known variation associated with different factors. For example, if you're looking at how nutrition affects adult height, and you know that mal... | [
"The simplest way to control for a variable is just to make it into an independent variable. For example, continuing with your alcohol/smoking example, a researcher could group the subjects not only by tobacco intake, but also by alcohol intake. In this one could use an ANOVA to analyze the effects of both alcohol ... |
[
"What kind of scientific evidence do we have that global warming is caused by CO2 or any other greenhouse gasses?"
] | [
false
] | null | [
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"You question is either commonly occurring or has been recently posted on ",
"/r/AskScience",
". It may also be answerable using a Google or Wikipedia search.",
"To check for previous similar posts... | [
"Here are a few pasts thread on the topic:\n",
"https://www.reddit.com/r/askscience/comments/avedpr/ive_seen_the_charts_for_temperature_rise_the/",
"https://www.reddit.com/r/askscience/comments/bpq8vg/what_proof_do_we_have_that_co2_is_a_greenhouse/",
"https://www.reddit.com/r/askscience/comments/btdtje/what_m... | [
"Here are a few pasts thread on the topic:\n",
"https://www.reddit.com/r/askscience/comments/avedpr/ive_seen_the_charts_for_temperature_rise_the/",
"https://www.reddit.com/r/askscience/comments/bpq8vg/what_proof_do_we_have_that_co2_is_a_greenhouse/",
"https://www.reddit.com/r/askscience/comments/btdtje/what_m... |
[
"With MRI Magnets being ridiculously strong, Why don't they affect compasses, systems, animals, etc ?"
] | [
false
] | I have heard that MRI magnets are something like 60,000 x stronger than the earth's magnetic field. If this is true, with thousands of them in operation world wide. Why aren't compasses, animals who navigate by the earth's north pole, instruments, and even the earth's magnetic poles affected by them ? | [
"Mainly size. The Earth's magnetic field has is poles at opposite ends of the planet so the field covers the entire world. But with a magnet such as one from an MRI the polls are very close together and so the field is pretty tight, and doesn't really extend far beyond the actual magnet. "
] | [
"This! And that is on purpose. MRIs are designed in a way to create a high magnetic flux density in a small volume (where the patient is placed). Limiting the spatial extent of that field is crucial to achieve those high flux densities.",
"A spatially larger field with similar flux density ",
" influence its en... | [
"A colleague recently re-purposed an old medical MRI magnet for use in a detector system. The stray fields from the magnet are a big concern, with modern magnets taking great care to have both shielding and compensation coils so that outside the magnet no strong residual fields exist. The regulations pertaining to... |
[
"Am i as genetically similar to my daughter as my daughter is to my mother? (and other genetic questions)"
] | [
false
] | I understand human beings have 23 pairs of chromosomes each, and in only the last pair determines the sex, however, I received 23 half pairs of chromosomes from my mother and then have passed on said chromosomes to my daughter. Does this mean that my mother is as genetically similar as I am to my daughter as my daughte... | [
"Well, for one thing, you have your mother's mitochondrial DNA but your daughter doesn't have yours."
] | [
"OP is male."
] | [
"OP is male."
] |
[
"Do animals experience menstrual cramps?"
] | [
false
] | null | [
"Yes. However, not many animals menstruate. Humans and old-world primates are about the only animals that undergo menses with the exception of bats. "
] | [
"Having offspring that don't coincide with seasons means that you have to be able to provide food and protection any time of year."
] | [
"It's not, and that's why it makes sense. Having babies that need food and protection at any time of year is hard. Having babies that are basically helpless for several years is also hard. That's why very few organisms have those qualities."
] |
[
"Does the ammount of muscle cells in the body increase through exercise?"
] | [
false
] | [deleted] | [
"The answer is a bit complicated, and depends on the type of exercise. Your typical mature muscle cells don't undergo mitosis to increase the number of cells following exercise. There are satellite cells that reside next to muscle cells that asymmetrically decive to replenish the muscle cells. Muscle cells are also... | [
"Thank you"
] | [
"Going along with that, muscle cells gain more nuclei during exercise, and have a literal muscle memory, as if you stop working out for a while, the nuclei remain and help get back to the former muscle mass prior to stopping."
] |
[
"Is thermal motion truly random?"
] | [
false
] | Excuse my ignorance in advance. I keep seeing these visualizations of thermal motion and it's just energetic atoms or molecules bouncing off of each other and walls. What makes this truly random? It seems like given the initial conditions the motion is predictable. | [
"It seems like given the initial conditions the motion is predictable.",
"What do you mean by random? In a classical situation with little balls bouncing off walls like you describe then the process is indeed - in principle - predictable. By \"random\" in this sense we mean that the objects positions and veloci... | [
"If we ignore, for now, the complexity of even trying to model the motion of Avagadro's Number of particles, we can try and determine whether the initial conditions are even predictable.",
"One example of initial conditions might be a small number of particles at low temperature i.e. a Bose Einstein condensate.",... | [
"This actually becomes an issue in creating very low pressures. Eventually the gas stops acting statistical and you have your ping pong balls. You need to use different types of pumps like turbo pumps which basically smack the molecules in a certain direction towards the roughing pump. Also you put cryotraps which ... |
[
"Since when water freezes, it expands, how is it that ocean level would rise when iceberges melt. Shouldnt they lower due to the decrease in ice?"
] | [
false
] | It just logicaly doesn't make sense. Is there something I am missing? | [
"Floating ice will not affect sea level. However, the ice on land (Greenland, Antarctica) will flow into the sea when it melts, thereby causing the sea level to rise.",
"If all the ice on Greenland were to melt, the sea level would rise over 7 meters."
] | [
"Adding onto this. Drop an ice cube into a glass of water. The water amount will remain close to the same when the ice cube melts. :)"
] | [
"and most of the ice is actually on land",
"https://water.usgs.gov/edu/watercycleice.html",
"Remember that rising seas would not damage the planet - they've gone up and down dramatically before - but they would have an enormous impact on human societies due to the way we've built our infrastructure. Most major ... |
[
"A simple F=MA problem that frustrates my brain."
] | [
false
] | I have had a basic physics question that I can't really settle within myself. If a car is moving at a constant speed then the forces acting on it must be equal to zero... Yet what happens when you take something like friction into effect? Would you or would you not need another force to overcome the friction and there... | [
"If your car is coasting along (ie engine not actively powering wheels) and you include friction, then your car will be slowing down gradually. Friction between the wheels and the ground (rolling friction) would manifest as a force in the direction opposite of the car's movement, resulting in a small acceleration ... | [
"Assuming the car is undergoing no acceleration, the net force acting on the car is zero. Thus the forward force being generated by the combustion within the engine (assuming a combustion engine of course...) is just equaling all of the frictional forces acting against the car (the friction of the movable parts of... | [
"Oh my God THANK YOU. I think the last sentence especially helped me understand this."
] |
[
"Does dimethyl mercury evaporate at room temperature?"
] | [
false
] | I saw a video on this… about the chemist that died back in 1997. Pretty scary stuff. I was wondering does this evaporate completely? Like someone can’t put some on a commonly touched item to contaminate people…. Or can they? | [
"It has double the vapor pressure of water at room temperature, so it'll dry up relatively quickly. This, and the risk of gassing yourself with the vapors (plus the risks intrinsic in creating the substance in the first place), makes it an impractical contact poison."
] | [
"Okay so I will start with a direct answer with little context, \"It depends on how you define evaporate\". Does any amount of dimethyl mercury enter the vapor phase? Yes, is it very much/is it a rapid process like the evaporation of acetone? No, not exactly, but it has double the vapor pressure of water, thus evap... | [
"I saw vapor pressure, but I wasn’t for sure exactly how that translates to me"
] |
[
"Field of a permanent magnet"
] | [
false
] | Assuming constant magnetization of the material, how does the field of a permanent magnet (lets say a bar magnet) depend on its shape and size? For example, if I wanted to induce the most possible current in a loop by moving a magnet, and the cost of the magnet is dependent on weight or volume, how could I compare magn... | [
"Well, the magnetic field of a permanent magnet is just the aggregate field of the magnetic moments of its component atoms (or molecules), so to get the total field, you would simply take the sum of each magnetic dipole moment.",
"Realistically, you can't do that, but assuming constant polarization and knowledge ... | [
"If OP knows the shape and material, and assumes the material is uniform, s/he can approximate field strength around the magnet numerically. ",
"I have done similar numerical solves, but I am hesitant to sink in lots of time helping OP, unless this is something s/he wants to do, i.e. not a random whim. "
] | [
"If you want to maximize energy, minimize losses. Any flux from the magnet that is not passing through your wires is putting energy into magnetizing the air. You must minimize the air gaps.",
"It also depends on how fast you plan to move the magnet. At high speeds you need to consider eddy currents that will flow... |
[
"How does the frequency of treatment affect recovery time and rate?"
] | [
false
] | [deleted] | [
"Talking about leukemia treatments and radiation is sort of a pandoras box because then you start talking about the supplemental chemotherapy as well as the subtype of leukemia. Let's just talk about antibiotics.",
"MRSA stands for Methacillin resistant staphalococcus aureus. Basically it's a bacteria that has be... | [
"Sorry. There is not enough information to answer this question. What kind of medicine are you talking about here, and recovery from what kind of illness?",
"Antibiotics have peaks and trough that have to be kept in therapeutic range so scheduling is key, for instance.",
"There are no general rules of thumb wit... | [
"I guess this sort of answers my question actually. I edited the initial question to be a little more specific. The purpose was that it could have been any ailment; I wanted to know how important is the scheduling of treatment to the overall recovery process. And does the scheduling become more important when treat... |
[
"Ref: Voyager leaving Heliosphere and traveling through interstellar space."
] | [
false
] | Wouldn't electromagnetic signals and from interstellar space travel travel further with lower signal to noise ratio, i.e., be easier to interpret over great distance, given that the background radiation is a well know quantity. Or can we produce comparable signals with enough power from within solar system? | [
"You're onto something, but you've stated it a little awkwardly. First, for a receiver at earth, the noise power in the receiver is independent of the distance to the transmitter. It's more influenced by the direction (in the case of a tracking antenna) and atmospheric effects on earth. (Rain both attenuates the... | [
"Sorry friend, I think you might benefit from working some figures out for a couple cases to see my point. Imagine a satellite moving from 2m to 3m, and the ratio of their path loss (1/3",
" / (1/2",
" = .444.. Now one from 4m to 5m, (1/25)/(1/16) = .64. While it's true that the power level has decreased in... | [
"There's gas and dust in interstellar space that absorbs radiation. "
] |
[
"Why do people take iodine pills for radiation exposure?"
] | [
false
] | I just learned about the synthesis of triiodothyronine and thyroxine and it got me wondering what benefits does iodine have against radiation exposure? Like when people in Chernobyl were given them | [
"During a nuclear explosion, one byproduct is radioactive iodine (I-131). This can bioaccumulate in the thyroid and damage it or lead to thyroid cancer. One way to prevent that is to swamp the body with non-radioactive iodine (mostly I-127) so that you don’t absorb the radioactive version."
] | [
"It's a bit like giving ethanol for methanol poisoning then?"
] | [
"Your thyroid gland takes up iodine naturally, and radioactive iodine-131 is a common waste product from nuclear plants. Taking iodine pills in a nuclear emergency basically saturates your thyroid with safe iodine so that it doesn’t absorb iodine-131."
] |
[
"Why do black men tend to develop keloids instead of regular scar tissue, and why don't we see keloids present in other races?"
] | [
false
] | Does it actually occur in other races, simply at a lower rate? Why don't black men develop normal scar tissue? Is this also an issue with black woman? If not, why is it limited to only black men? | [
"Good question, and the answer is not completely understood (typical). ",
"Firstly, we do know that individuals predisposed to keloid (and hypertrophic scar) formation have increased expression of TGF (transforming growth factor) beta (they also have increased VEGF and CTGF) following skin trauma, which is the pr... | [
"Keloids form more frequently in Polynesian and Chinese persons than in Indian and Malaysian persons. As many as 16% of people in a random sampling of black Africans reported having keloids. White persons are least commonly affected."
] | [
"But why?"
] |
[
"Catalyst - Do you need a catalyst to convert CxHx - H2O + CO2, Carbonmonoxide - CO2 and NOx - N2 + CO2 or would those reactions also happen without the catalyst?"
] | [
false
] | [deleted] | [
"Let me clarify your reactions as best as I can understand them:",
"CxHx <--> H20 + CO2",
"2CO + O2 <--> 2CO2",
"the last one was tricky to understand. Do you mean:",
"N2 + O2 <--> NOx ?",
"For your answer, these are all combustion reactions. You should do some general reading on combustion. Wikipedia's a... | [
"Upvotes to semitones; there will be some overlap with our answers.",
"CxHx -> H2O +CO2",
"This is a combustion reaction, so oxygen is needed on the reactant side. A little bit of energy is required to start the reaction, so no catalyst is required.",
"CO -> CO2",
"CO oxidation can occur with oxygen as the ... | [
"You don't \"need\" a catalyst for any reaction. They can all happen by themselves but a catalyst makes it go faster."
] |
[
"Physics How do time and space connect to become what is described as spacetime?"
] | [
false
] | Repost because my last attempt got caught up in the spam filter. If time can be seen as a spatial dimension, then the units should be able to be comparable, right? For example, 1 meter in the y dimension of space is equal in magnitude to 1 meter in the x dimension of space. So then, 1 meter in the y dimension would be ... | [
"To add to the distinction with what little I know, four-vectors' (vectors in 4 dimensional spacetime) magnitudes are calculated with something kinda similar to the Pythagorean theorem:",
"R (dot) R = (ct)",
" - ( x",
" + y",
" + z",
" )",
"The fact that the term with time and the term with the spatial ... | [
"Sorry for the late reply. I can't thank you enough for this. This is a very difficult question to word, and finding an answer has been very hard. This is exactly what I was looking for."
] | [
"Sorry for the late reply. I can't thank you enough for this. This is a very difficult question to word, and finding an answer has been very hard. This is exactly what I was looking for."
] |
[
"Assuming that a person could float in space without being killed, how much further does he have to be to see the entirety of Jupiter at once?"
] | [
false
] | null | [
"further than what?"
] | [
"From the atmosphere of Jupiter"
] | [
"Oh. Please post calculation requests to ",
"/r/theydidthemath",
"."
] |
[
"Can a Rh negative male be injected with Rh positive blood to harvest Rhogam?"
] | [
false
] | Since Rhogam is a blood product made from Rh- mother exposure to Rh+ fetal blood, could a male be injected with Rh+ blood to get the take advantage of the immune response and harvest his IgM before the body starts creating the IgG? I couldnt find if this is done or not, and was brought up in class. Edit: Is it done? ... | [
"No.. That's what you want. You only have a four month window to get the byproduct of sensitization. Once your body starts creating the IgG it's game over for making rhogam (IgG can be passed through the placenta, and antibodies against fetal blood is never good)... And a main reason that there has been shortages... | [
"No.. That's what you want. You only have a four month window to get the byproduct of sensitization. Once your body starts creating the IgG it's game over for making rhogam (IgG can be passed through the placenta, and antibodies against fetal blood is never good)... And a main reason that there has been shortages... | [
"We know we have a 72 hour window from the trauma causing the crossover of the blood till we can give the Rhogam before the IgM cascade to IgG will be inevitable in mothers. We know 72 hours because of the way the testing was done (in pregnant women in prision..If a trauma happened on friday, nobody was qualified ... |
[
"How much do we know about abiogenesis?"
] | [
false
] | As far as I know the science behind how life began at the current time is almost 100% hypothetical. That's for pretty obvious reasons: it's pretty hard to do experiments to try and replicate the process without simulating an entire solar system, and there's no fossil evidence or anything like that left for us to study.... | [
"Your question summarizes one of the most important issues related to this field of study (and related to the larger field of evolutionary biology, in general): we have a sample population of one. All life on Earth (that we have observed) is descended from a common ancestor, and thus the product of a single succes... | [
"Definitely, finding another set of life from a separate abiogenesis event would be amazing from a scientific point of view, especially if we were able to study its biology. I'm sure biologists dream about that sort of thing.",
"Also I just came across a paper that did a bayesian probability anaylsis which conclu... | [
"Remember that if we're working under the assumption that life is unique to the earth in the whole universe (not impossible), then we're utterly wasting our time looking for the answer to how it began. ",
"The real answer would have to be so mind-numblingly far-fetched that it could never be replicated in a lab."... |
[
"How long could you actually swim in a swimming pool full of liquor before your body succumbs to alcohol poisoning as the liquor absorbs into your body?"
] | [
false
] | null | [
"From ",
"Quora",
":",
"You would find it much harder than usual to swim and may drown in an unusually horrible way, for two reasons:",
"1) Distilled liquors have quite a bit lower density (and thus less buoyancy) than a swimming pool because alcohol is lighter than water. You cannot float in 80 proof alcoh... | [
"If it were changed to standing neck-deep in a pool of ethanol with some method of breathing clean air how long would it take?"
] | [
"Assuming the body's orifices are tightly sealed and that the concentration of alcohol outside the body is significantly higher than that inside (which is valid for a pool with significantly higher volume than the body and will remain valid well past when the alcohol reaches fatal concentrations), the rate of trans... |
[
"Is it possible to calculate the g-forces one would experience at the event horizon and/or the singularity of a black hole?"
] | [
false
] | null | [
"But once matter is there... it can never get back out of that area bounded by the event horizon. "
] | [
"But once matter is there... it can never get back out of that area bounded by the event horizon. "
] | [
"I've asked this several times, but never got a reasonable answer.",
"Why is speed used to define the point of no return?",
"Escape velocity is a concept thus: the speed at which you have to go to escape a gravity well ",
".",
"On earth, for instance, we can escape Earth's surface by never actually reaching... |
[
"What would have been on the land when “life” first crawled out of the water?"
] | [
false
] | null | [
"If you mean 'animals', the first animals to colonize the land were arthropods during the Silurian. ",
"Near lakes, rivers, and the coast, there would have been very primitive plants (think moss and bryophytes) and early land fungi. The rest of the land would have been largely barren."
] | [
"Neil Shubin has a very interesting book called “Your Inner Fish” that discusses how life transitioned from water to land. I won’t try to repeat his points here as I would be doing so by memory, and it’s not my area of expertise. But this book as well as his others are great for this question."
] | [
"Animals may have sporadically ended up on land prior to plants evolving, but the first actual land animals postdate primitive plants. Land plants emerged in the very late Ordovician, with early land animals emerging during the Silurian."
] |
[
"Apparently all US Presidents, save one, are related. Given the time scale, is this really that remarkable?"
] | [
false
] | Question is based on this video, A fb friend prone to conspiracy theories posted it and I'm curious to get some insight on whether or not this is at all something by which to be impressed, especially given that the common ancestor was a British King from the 12th Century. | [
"No. It's not even the slightest bit remarkable.",
"You have two parents, 4 grandparents, 8 great grandparents, 16 great",
" grandparents, 32 great",
" grandparents, etc. In general, you have 2",
" great",
" grandparents.",
"If we take 25 years to be your average generation time, and start the clock in ... | [
"How remarkable is it that Van Buren is not part of that family tree (as far back as the girl traced at least)?"
] | [
"JJBerg is 100% correct. Absolutely unremarkable. ",
"This",
" is an excellent overview (written at the layman level) that you may want to send your friend.",
"Key point:",
"Until you understand the fundamentals of genealogical math, you will likely remain impressed with these famous cousin connections, but... |
[
"If light travels at \"c\", then does that mean stars will continue to \"appear\" if you have a telescope pointed in one direction?"
] | [
false
] | null | [
"Yes, but it will be a real-time process. Imagine that we have 3 stars with no velocity difference between them. Star A is at x=0, B at x=5 Ly, and C at x=10 Ly. No relative ",
" velocity, so we can imagine that each star is using the same clock. At t=0, A and B explode. For the next 5 years, an observer where A ... | [
"I don't see how that relates to stars appearing. Ten days is a very long exposure time, and probably needed for distant light sources. But ten days is an extremely short time interval to actually see any difference in the depth of the observable universe.",
"I would be more inclined to believe it was to see \"de... | [
"At the time of the big bang, the universe was the size of a point",
"This isn't correct, as far as we know."
] |
[
"Does microwaving alter food nutrients?"
] | [
false
] | I have been microwaving eggs and it has been suggested to me that the microwave rays burn the protein/fats/nutrients. Is this accurate? | [
"I did a couple of pubmed searches, and I couldn't find any readily accessible information. One study showed that microwave prep slightly reduced the beneficial effects of legume starch, but they were comparing microwave prep to raw beans, not to beans cooked via another method.",
"This",
" seems to have some g... | [
"All cooking changes the nutritional content of food.",
"This blew my mind when I first found this out. Especially with regard to how cooking affects how many calories are made available to the body: ",
"http://blogs.discovermagazine.com/crux/2011/12/08/why-calorie-counts-are-wrong-cooked-food-provides-a-lot-m... | [
"All cooking changes the nutritional content of food.",
"This blew my mind when I first found this out. Especially with regard to how cooking affects how many calories are made available to the body: ",
"http://blogs.discovermagazine.com/crux/2011/12/08/why-calorie-counts-are-wrong-cooked-food-provides-a-lot-m... |
[
"Could we change the course evolution takes?"
] | [
false
] | I was thinking about the movie and I got to thinking, is it possible to change the course human evolution takes in order to give us special abilities, such as breathing underwater? From my understanding of evolution, and please correct me if I'm wrong, things evolve to adapt to their surroundings for survivability. Co... | [
"We cannot ",
" our bodies to adapt to our environment in the evolutionary sense. For people who aren't well educated in evolution and natural selection, the term \"adaption\" is a tad confusing.",
"The previous theory of evolution is known as the Lamarck's theory of evolution (",
"http://en.wikipedia.org/wik... | [
"First off let's remember that evolution is not something that happens overnight or even over a lifetime. Evolution is a result of natural selection. Natural selection is the concept that traits will be passed on by survivors. It goes well with survival of the fittest which means that an organism that is more well ... | [
"Possible? Yes\nPlausible? No",
"Human race will most likely perish before anything like that happens. Don't mean to sound like a buzz kill :)"
] |
[
"Can the immune system target specific elements inside the cell?"
] | [
false
] | [deleted] | [
"It kind of depends what you mean by \"target\". The immune system can certainly ",
" elements inside the cell, and determine that they are foreign and need to be destroyed. The immune system can't really specifically remove those foreign elements, though (though there have been arguments that under some conditi... | [
"Interferons and interleukins are two good examples of it.",
"Interferons can be produced by infected cells or immune cells in response to infections or tumors. One of their functions is to slow down replication of RNA to slow down the replication of the pathogen or the cancer cells. And interferons also targets ... | [
"The immune system can't really specifically remove those foreign elements, though (though there have been arguments that under some conditions it can). In general if a cell contains harmful foreign elements, the immune system rapidly identifies it and destroys the whole cell.",
"That definitely depends. Systems ... |
[
"How did they carry out genetic identification before the human genome project?"
] | [
false
] | Ok, so I keep seeing references of DNA fingerprinting around the 1900s to 2000s. I see the reference to engineering E. Coli to create insulin. Or identification of genetic diseases using the various blotting styles. The question I have here is... How did they know what gene and sequence to look at? I know they can cert... | [
"So DNA sequencing techniques were available before the Human Genome Project. The main drawback was that they were slow and laborious, and could only sequence very small amounts of DNA (think hundreds to a thousand or so base pairs, which is on the order of the size of a gene). So, it was feasible to get the sequen... | [
"Most genetic studies involve a technique called \"polymerase chain reaction\" developed in 1985.",
"In this technique, a strand of DNA get copied repeatedly, in the millions, to make it detectable and readable.",
"Interesting Background here",
" ",
"The technique is done by adding enzymes and raising and l... | [
"We still knew about genes before the human genome project, we just didn't know all the genes. Before the human genome project we could amplify small parts of the genome with ",
"PCR",
" and sequence them.",
"The genes themselves were first discovered centuries ago. Many genes were first discovered by breedi... |
[
"If I throw a baseball at 90 mph, does that mean my hand must be travelling at 90mph before it releases the ball?"
] | [
false
] | null | [
"At least the tips of your fingers have to. You see, once the ball has left your hand, there is no way it is accelerating anymore. That means, the ball has the highest velocity just as it leaves your hand. Your hand therefore has a speed of 90 mph at the moment you throw.",
"Edit: Holy, that thing has blown up si... | [
"This is in contrast to a football or soccer ball which is compressed during a kick and comes off the foot faster than the foot is moving."
] | [
"Baseballs do that too, but they do it when being struck by a bat. See: ",
"http://www.maxbats.com/images/bats/find-your-max/ball-compression.jpg"
] |
[
"Southern Blot Help. My blots keep coming out looking like attached figure\"E\", in which it looks like all the genomic DNA is being hybridized. Any Advice?!?"
] | [
false
] | Please look at . Not sure why, but it happens all the time. I can barely make out the bands and I need to determine if there is another band about 1000bp shifted. Any advice would be really appreciated. | [
"Could you be using to much dye? (I cant remember what it's called) It looks like there's an even streak across the entire lane, which is probably dye not DNA fragments. ",
"Sorry if it's no help, I just started running those this month, and still haven't mastered it myself"
] | [
"If the DNA is not dyed, how are you getting a good look at it? In my lab, we view the gel under a UV light to see they dyed DNA"
] | [
"Try ",
"r/askscitech",
" as well."
] |
[
"Why does it feel so good to get a \"back rub\"- but not as good to get a \"front-rub\"-? -and please hold back any sexual jokes."
] | [
false
] | Are the nerves/muscles more superficial? Is it because of extensors vs flexors? I've always wondered about this- | [
"Your back muscles are under the strain of holding you upright all day. ",
"Your front is mainly softer tissue. ",
"Your back protect your internal organs and is rigid. ",
"Your lower front would allow the massager to press on those organs. "
] | [
"Front rubs feel ",
", especially on the upper pectorals and anterior deltoids. Maybe you're not giving/receiving in the right places?"
] | [
"And how does a person go about doing this? I'm not really sure if I am using my core muscles or not; I don't know how to tell."
] |
[
"The farther one looks into space, the farther one looks back in time."
] | [
false
] | Hi everyone. It is sometimes confusing to me when people maintain that the farther one looks into space, the farther one also looks back in time. I am a layperson in physics, but from what I know about special relativity, it seems that one cannot posit an inertial frame of reference for all of the universe. So how can ... | [
"Cosmologist use what they call comoving coordinates, where a stationary observer sees the universe as isotropic. All the galaxies are more or less stationary in this coordinate system. As you can guess, this 'grid' follows the expansion of the universe and the proper time experienced by comoving observers is rough... | [
"Based on your question, it seems you're implying that an event can only be said to have happened once YOU receive information that it has happened. ",
"And before it's said, the friend surprise visiting and seeing a star from 1000 light years away blow up are not different when looked at from an information pro... | [
"If someone throws a baseball at you, what good would it be to say that he threw the baseball when you caught it?"
] |
[
"Can any flavor (e.g. \"blueberry\" or \"cheese and onion\") be expressed as a combination of relative amounts of the five basic tastes (sweet, bitter, sour, salty, umami), just like colors can be expressed as RGB?"
] | [
false
] | , then: , then: why not? What do people mean when they say there are "five basic tastes"? What other factors are necessary in order to recreate a taste? | [
"No:",
"The five basic tastes are what the taste buds on your tongue can detect. Flavor, however, is much more than that. It works in conjunction with the nose. That is why you do not smell a lot when you have blocked nose.",
"It might be possible to decompose the taste (only tongue), but even the taste is not ... | [
"Flavors are determined by a staggering array of chemical compounds, but there is some work being done towards a theory of complementary flavors. ",
"Here's a research letter regarding it."
] | [
"I was reading the wiki entry for Taste after a similar question some time ago and there is apparently a sixth taste: ",
"metallic",
"."
] |
[
"Is there any way to prove that anything really exists?"
] | [
false
] | null | [
"This is really a philosophy question and should be posted to a philosophy sub."
] | [
"I'm looking at the question from a physics point of view, like is there a certain type of atom analysis or something to prove existence of other things, are there electrical impulses from the brain that prove consciousness?"
] | [
"You are presupposing that atoms exist. This is really a philosophy question."
] |
[
"Is there a limit to how bright a light source can be? In other words, is there a limit to the density of photons in a given place at a given time, or is this hypothetically limitless given a sufficient source?"
] | [
false
] | Assuming you had a limitless source of photons, could a limitless amount of them be concentrated into a beam of light, or is there a limit to their density? | [
"They have energy density, so they gravitate.",
"They don't have rest mass."
] | [
"In theory, if you were to concentrate enough light in a volume, the light would collapse to form a black hole. However, there's not a practical method for doing such a thing."
] | [
"It would be more accurate to say that rest mass is one potential form of energy, and all energy contributes to gravitational effects, regardless of what form it might be."
] |
[
"How do GPS receivers get their position from GPS satellites?"
] | [
false
] | So I know that GPS receivers look for satellites and calculates its position based on that, probably through triangulation. But how does the receiver communicate with the satellite? Does the receiver send out radio signals that get picked up by satellites, or do the GPS satellites continuously broadcast radio signals t... | [
"GPS satellites have very precise atomic clocks (which are monitored and kept accurate by very, VERY accurate atomic clocks on the ground). They are also told their orbit parameters by the monitoring ground stations. This very precise time and pretty darn precise location is broadcast by the satellites continuously... | [
"Wouldn't the satellites also have to transmit their own location for the receiver to be able to triangulate? ",
"Also, why would the transmission area be the shape of Europe? GPS works in the oceans, too, so it would make more sense for the transmission area to be anything with a line-of-sight to the satellite (... | [
"Wouldn't the satellites also have to transmit their own location for the receiver to be able to triangulate? ",
"Also, why would the transmission area be the shape of Europe? GPS works in the oceans, too, so it would make more sense for the transmission area to be anything with a line-of-sight to the satellite (... |
[
"Why does exercise help us lose weight?"
] | [
false
] | Obviously, exercise allows you to burn more calories more quickly, but wouldn't that just cause you to become hungrier faster, meaning you'll eat more? So that in the end, regardless of how much exercise you're doing (or not doing), all that matters for weight loss is that you eat less than your body says it wants you... | [
"Yes, the key is to spend more than what you take in.",
"all that matters for weight loss is that you eat less than your body says it wants you to eat",
"Not really, because if you are not active enough the body will find other ways to cover the deficit, such as reducing muscle mass to reduce upkeep energy requ... | [
"To clarify: muscle loss is still weight loss, so OP is correct. But yes, exercise and sufficient protein intake will help make sure that more of the lost mass is actually fat and not muscle."
] | [
"In order to burn a pound of fat, you need to expend 3800 more calories than you take in. If you exercise more, and eat more, you'll essentially stay the same weight. (This isn't exactly true, but it is the gist.)"
] |
[
"How can stars cool down as they gain energy?"
] | [
false
] | With the semi- recent talk of a gas reaching negative Kelvin values I decided to check out how this was possible. Apparently the confusion arises from our interpretation of temperature. After reading a helpful explanation ( ) I think I understand the mathematics of it but not so much the theory. Why is it that as energ... | [
"They don't \"cool down\" as they gain energy, they actually become hotter (as in more willing to transfer heat). Temperature (in a thermodynamic sense) is not a measurement of how hot something is. From the laws of thermodynamics we can define temperature (T) as a measurement of how much entropy increases (dS) per... | [
"Great Explanation. Follow up question- How is it that the discovery of the Quantum Gas that goes into 'negative Kelvin' can actually result in a combustion engine with a >100% efficiency? "
] | [
"http://www.sciencedaily.com/releases/2013/01/130104143516.htm",
"It says, \"Matter at negative absolute temperature has a whole range of astounding consequences: with its help, one could create heat engines such as combustion engines with an efficiency of more than 100%. This does not mean, however, that the law... |
[
"Are the orbits of the planets in our solar system flat, or largely on a similar plane? Why? If so, are planets in other solar systems the same?"
] | [
false
] | null | [
"The solar system formed from a disc of gas, which is why all the planets formed in the same plane. This disc formed from the collapse of a cloud of gas. As interstellar gas is pretty turbulent, any chunk of gas will have a bit of spin to it, which basically gets amplified as it cools and collapses under gravity, u... | [
"While many discs will be flat and aligned with their host star they are not as simple as was once though. ",
" ",
"Misalignment between the hosts spin vector and the discs orbital vector are pretty common (",
"Franchini et al. 2018",
"). Some ways this can happen is by truncation of the molecular cloud by ... | [
"To put some numbers to the \"flatness\" of the Solar System:",
"The invariable plane of a planetary system is the plane passing through its barycenter perpendicular to its angular momentum vector. (In the Solar System, about 98% of this effect is contributed by the orbital angular momenta of Jupiter, Saturn, U... |
[
"If two different viruses invade one cell, which virus wins?"
] | [
false
] | null | [
"It depends! Very complicated question with many examples.",
"I actually do a pre molecular/immuno technique to see if a cell is infected by one virus by trying to infect it with another that has a much more pronounced effect. ",
"If the second virus can't infect then you know that the cell was infected with th... | [
"It’s very unlikely to happen at all",
"There are viruses like Hepatitis D which can only reproduce if a cell is infected with another virus, in this example that is Hepatitis B. Considering there are viruses that require coinfections to reproduce I wouldn't claim it is very unlikely to happen."
] | [
"That's rather interesting. I had never thought you could do that. May I ask if this is research or a testing lab?",
"As a follow up if I may, could we use a stronger virus that is benign or easily eradicated as a counter agent to another virus that is more pathogenic? Perhaps as a form of prophylaxis?"
] |
[
"Is there a scientifically viable explanation of quantum mechanics that suggests the universe is deterministic?"
] | [
false
] | null | [
"Determinism usually means that you can ",
"fully predict the future given the initial conditions of the system.",
" If you have those initial conditions you will never be surprised.",
"In De Broglie-Bohm, all of those initial conditions exist but you still cannot look at them. Determinism with no spoilers is... | [
"Determinism usually means that you can ",
"fully predict the future given the initial conditions of the system.",
" If you have those initial conditions you will never be surprised.",
"In De Broglie-Bohm, all of those initial conditions exist but you still cannot look at them. Determinism with no spoilers is... | [
"Both ",
"de Broglie-Bohm",
" and ",
"Everettian (ie Many Worlds)",
" interpretations of quantum mechanics are deterministic. "
] |
[
"How easy is it for a person to lose and gain brain cells?"
] | [
false
] | [deleted] | [
"Well my neuropathology teacher told us that there is still some sort of neurogenesis on adult brain on the sub ventricular area and the hippocampus area (Like you gain a few hundrerds neurones every day) but you have a few thousands that die every day too.",
"As for glial cells, they keep the capacity to divide... | [
"To further, further add, the number of neurons isn't really as important as you might think. Moreover losing them, through a process called pruning, is part of the normal development of the brain. In fact, a lack of pruning has been associated with mental disabilities including autism, and disorders such as schizo... | [
"To further, further add, the number of neurons isn't really as important as you might think. Moreover losing them, through a process called pruning, is part of the normal development of the brain. In fact, a lack of pruning has been associated with mental disabilities including autism, and disorders such as schizo... |
[
"Hypothetically, if Time Travel were to exist, how would we measure the rate of travel?"
] | [
false
] | [deleted] | [
"(time of object/system/reference frame/whatever you're attempting to time travel relative to)/(time as experienced by you/those within or passing through the time machine)"
] | [
"It really depends on the type of time travel.",
"To make an analogy with something we know, forwards time travel, the rate can be measured with the Lorentz factor, which can be thought of as a ratio between time passed for you and time passed on Earth (or wherever).",
"If you're travelling faster than light th... | [
"Seconds per second."
] |
[
"Why is that, when things are heated up, they turn orange, red, or yellow?"
] | [
false
] | Like iron. Heating it up to melt it causes it turn yellow or orange. Why not blue or green? | [
"The name of the effect you're asking about is ",
"\"black body radiation\"",
". All objects (including you) emit light, with the frequency of that light depending on how hot the object is.",
"The ",
"color",
" of light is determined by its frequency, or mixture of frequencies. The order matches the ",
... | [
"Good answer. Note that a better name for the physical effect is \"thermal radiation\". Blackbody radiation is a really an idealized model of thermal radiation, which typically does not hold exactly true to the thermal radiation spectrum coming from real-life objects."
] | [
"All objects above absolute zero emit thermal radiation as the vibrations of atoms in the material are spontaneously converted into electromagnetic radiation. This radiation covers a broad range of frequencies, and the spectrum of frequencies emitted depends on the temperature of the material. At room temperature... |
[
"A question about the expansion of the universe."
] | [
false
] | Let's say that I could find 2 galaxies equally as distant from each other as they are from our galaxy to form an equilateral triangle in space. Provided that we could get an accurate measurement of the distance between them and came back and observed them at a later date would it still form an equilateral triangle? Wou... | [
"First, keep in mind that galaxies have their own motion and direction regardless of expansion. So in your example, the three galaxies are moving on their own - with their own local groups, etc.",
"Expansion does not actually move galaxies - but rather, simply creates more space between them.",
"Since the force... | [
"scientists don't tend to do things like that.",
"http://en.wikipedia.org/wiki/Metric_expansion_of_space#Observational_evidence"
] | [
"Fair enough, I forgot about the motion of galaxies in relation to being pulled by gravitational forces. So let's say we could observe the motion of the galaxy and add/subtract their regular motions from the measurement. I understand that the expansion comes from empty space but I am still curious if we have been a... |
[
"Why is it typical to feel an uplift in mood after a psychedelic trip dispite causing downregulation of 5ht receptors?"
] | [
false
] | Assuming the user was not traumatized for some reason, which is quite rare, it's often reported ingesting a psychedelic drug leaves you with a lasting sense of well being, happyness, and connection to others. See the john's hopkins research for instance. It's also been shown in rats that 5ht receptors rapidly down regu... | [
"Serotnin's reputation as a happiness hormone is undeserved. It's role is more of as a stressor and if a person benefits from SSRI's it's quite debatable that it has anything to do with increasing serotonin levels. Danny Roddy summarized the ",
"research on serotonin and psychedelics in a recent post",
"."
] | [
"That article kinda read like someone trying to cherry pick data and mold it around their own idea of what's happening. I don't believe SSRI's work particularly effectively for treating depression, to say so is oversimplified, but while that is why they were designed they anticipated there would be side effects due... | [
"MDMA effects levels of serotonin, norepeniphrine, dopamine and oxytocin. Norepeniphrine is a catcholamine, so that energizes people (makes them want to dance their ass off). Oxytocin is undoubtably the hormone that makes people feel all love-y and huggy and like everyone is their best friend. In the theory of sero... |
[
"Where did dust come from?"
] | [
false
] | [deleted] | [
"It’s made up of everything and anything pretty much, although the thing that’s commonly said is that a high percentage of dust is dead skin cells. Technically it came from space but in the end we all did and everything does. "
] | [
"As long as we have air flow to pick up and carry fine particles of skin and sand and notes and their “emissions” etc. we will always have dust. If you think of how much dust could exist in the air in a sealed room and you see how dusty an old closed up house gets, there is a ",
".",
"All cleaning up does is mo... | [
"As long as we have air flow to pick up and carry fine particles of skin and sand and notes and their “emissions” etc. we will always have dust. If you think of how much dust could exist in the air in a sealed room and you see how dusty an old closed up house gets, there is a ",
".",
"All cleaning up does is mo... |
[
"How does jump height scale with animal size?"
] | [
false
] | So I have a book on mathematical dynamics that does a few fun calculations with biology. One of the claims that is reasoned is that the height an animal can jump does not scale with the height of the animal. Does this claim actually bear out in reality? Can a flee jump a comparable height to a larger animal, for exampl... | [
"Yes, but work is force*distance. My legs are much longer than a flea's, so they exert force over a longer distance, thus doing more work."
] | [
"I see what the misunderstanding is. You are answering whether jump height is proportional to L. That is, is jump height ~L",
" My question is whether jump height is constant with respect to L. That is, jump height ~L",
" Which asks whether size doesn't matter for jumping."
] | [
"Their legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 7 inches (18 cm) and horizontally up to 13 inches (33 cm).[3] This is around 1200 to 2200 times their own body length, making the flea one of the best jumpers of all known animals (relative to body size), second only to t... |
[
"How precisely did Einstein get led to postulate that the speed of light is invariable for all frames of reference?"
] | [
false
] | I understand that the speed of light in a vacuum is constant in all frames of reference. Further, I understand that due to this one fact, Einstein was able to derive (with his theory of special relativity) many amazing things, such as length contraction of moving objects, time dilation, energy-mass equivalence, and so ... | [
"He looked at Maxwell's equations, the ones that determine the speed of the EM field, and he looked, and he looked...",
"And then he went \"huh, that's funny, the speed of the EM field is this constant divided by that constant, ",
". So the speed never changes. Well, that's bizarre. So, if we assume for an inst... | [
"Obligatory Irregular Webcomic"
] | [
"This won't be quite what you're looking for, but it at least fills in a small piece of the puzzle.",
"Before Einstein was born, light was known to have wave like properties. A natural follow up question was \"What is the medium that light waves travel through\". Scientists at the time assumed that medium existed... |
[
"What happens on an atomic scale when water is boiled?"
] | [
false
] | So my college entry biology professor (with a doctorate) just told my summer school class that when water boils, the hydrogen and oxygen atoms split and bind to each other, forming H2 and O2. I have always been taught that water vapor is just water molecules that are heated to a gaseous form. Also, if what he said is ... | [
"Your biology professor is incorrect. There is no chemical change in the water. The H2O does not split into H2 and O2.",
"You have been taught correctly, that water vapor is gaseous water.",
"For your hypothetical, if you ",
" have H2 and O2 gas, they wouldn't necessarily explode unless you have an ignition s... | [
"Oversimplified, but when water boils, enough heat has been added to water molecules that they gain kinetic energy, causing the interactions between water molecules to become more transient and letting some water molecules escape into the gas phase (water vapor). ",
"In contrast and also oversimplified, in order ... | [
"Thank you, I thought she was wrong, but I couldn't point to an exact reason as to why. "
] |
[
"Could electrolysis of water efficiently provide fuel for a hydrogen fuel cell?"
] | [
false
] | Well, I not quite sure how a hydrogen fuel cell works. However, I do know that the energy produced comes from the exothermic reaction of hydrogen and oxygen coming together to form water (I think it gives off about 55 kJ of energy per one mole O and 2 moles of H). But, wouldn't it take 55 kJ to decompose water into H a... | [
"No, you're right. But that doesn't mean hydrogen fuel cells are worthless. Hydrogen Fuel cells are not energy creation devices, they are energy transportation devices. They are a way to carry energy, in a very dense way. ",
"Why is this useful, you may ask? Let's look at a car, for instance. A standard V6 car is... | [
"Yes, that's the first law of thermodynamics. The reaction of H2 and O2 to water takes the same amount of energy in both directions. But due to heat losses/the second law of thermodynamics, neither the fuel cell or electrolysis cells would ever be 100% efficient. ",
"So there's little point in using electrolysis ... | [
"70% efficiency is incredibly high, actually. And burning hydrocarbons isn't \"green\" but it isn't necessarily less green than using electrolysis, as that electricity has to come from somewhere. And somewhere most likely means a fossil fuel burning plant. "
] |
[
"When you inhale dust/ dirt/ pollution, does it stay in your lungs? And if so, does your lung clean itself?"
] | [
false
] | null | [
"There are special immune cells in the lungs called alveolar macrophages. These cells engulf inhaled particles, and degrade them using enzymes and acids (inside lysosomes).",
"However, certain types of dust particles cannot be degraded. This includes coal, aluminum, asbestos and silica. These particles accumulate... | [
"What happens to those things that are trapped? What happens if it’s not trapped?"
] | [
"What happens to those things that are trapped? What happens if it’s not trapped?"
] |
[
"During the Ice Age did deserts exist?"
] | [
false
] | [deleted] | [
"Those areas are simply too cold for the water to be in a useable state for life, but, it's the lack of precip that really matters."
] | [
"The dictionary does not provide a scientific definition, only a colloquial one. Scientifically, a desert has little precipitation, or available moisture. Parts of Antarctica absolutely are deserts."
] | [
"Maybe I'm mistaken I always thought deserts were defined by the lack of precipitation, but maybe not."
] |
[
"Is climate change responsible for the current droughts and starvation in Africa?"
] | [
false
] | I've read that climate change affects Africa proportionately, and that many large bodies of water have already dried up. Is climate change responsible for the current droughts and humanitarian crisis in the Horn of Africa? | [
"Disclaimer: Not a climate scientist",
"Although an increase in the frequency of events like this is what you expect from climate change, I think you cannot say whether or not any single event is due to climate change."
] | [
"In the long term, I'd say local politics and economics are the primary cause. If they had a stable government that fairly enforced property laws, a decent education system, and a primarily capitalist form of economics, the problem would at the least be far less then it currently is. That is to say they'd be making... | [
"That's a good question. From what I understand, it is really hard to separate the effects of climate change and drought from the other relevant factors like geopolitics, agricultural policy, military conflicts, and global food markets, but hopefully someone more qualified than I can give a good answer."
] |
[
"[Physics] How do the integral and differential forms of Faraday's law and Ampere's law not conflict at points away from \"source?\""
] | [
false
] | For Faraday's law, imagine a loop enclosing a changing magnetic field (orthogonal to the plane of the loop), but larger than the area where the field exists. The integral form predicts that an E field is induced at the loop since dBflux/dt is nonzero, but the differential form predicts that no E field is induced there ... | [
"For Faraday's law, imagine a loop enclosing a changing magnetic field (orthogonal to the plane of the loop), but larger than the area where the field exists. The integral form predicts that an E field is induced at the loop since dBflux/dt is nonzero",
"If the loop encloses the entire magnetic field, then dBflux... | [
"Yeah the curl there is everywhere (0, 0, -2); his link doesn’t actually show the B-field of a thin wire.",
"The B-field outside a thin wire does wrap around it, but it decays proportional to 1/r away from the current, ",
"like this.",
" whereas the linked one actually GROWS farther away from the center. ",
... | [
"This is what I was missing - the curl from the visual rotation is counteracted by the decaying strength of the field. This solves both problems. Thanks so much!"
] |
[
"What exactly are the repercussions from this year's drought on the international food supply?"
] | [
false
] | What can we expect in the next few years? | [
"There has not been a \"lack of food\" in a long time, the warehouses has always been bulging. The distribution and economy is the real thing in this equation, and for us in the rich world, we will maybe see a small rize in price due to lesser supply. It will be far more severe in the poorer parts of the world, bec... | [
"There has not been a \"lack of food\" in a long time, the warehouses has always been bulging. The distribution and economy is the real thing in this equation, and for us in the rich world, we will maybe see a small rize in price due to lesser supply. It will be far more severe in the poorer parts of the world, bec... | [
"One of the aggravating factors is EISA (Energy independence and security act) which mandates a certain quota of ethanol be blended into auto fuels. with a huge reduction in corn production, and an unwillingness on the government's part to suspend the quota requirements, there's going to be problems. Mexico will li... |
[
"Can a black hole be filled?"
] | [
false
] | If a black whole is a 'hole' than it should fill up if enough stuff is put inside of it. I guess the answer to this could also be in what context 'hole' is being used. If by 'hole' it means "An aperture passing through something" and filtering it back into space, then if it's being put back into space, and space is eve... | [
"A black hole cannot get filled up. As more matter is added to the black hole, the black hole gets larger.",
"What surrounds the black hole is a surface called the ",
". Once something crosses the event horizon, it can no longer go back out. The term \"black hole,\" then, should not be taken literally, but r... | [
"Exactly. The definition of the event horizon is that its the point where light cant escape the black hole. Since nothing can move faster than light, its impossible to reach escape velocity."
] | [
"at the speed of light ",
"No, if light cant escape, then something going the same speed as light cant escape as well.",
"(or faster) ",
"Depends on how fast, but still impossible."
] |
[
"Best Science periodical?"
] | [
false
] | null | [
"Cat 2 are supposedly written for a general scientific audience, but are pretty damned specialised. You could add New Scientist to the first category? "
] | [
"Why not approach this empirically (since we don't really know your level of expertise, anyway). Go to a library and take a look at the journals you're interested in, and see if you can understand the articles.",
"My guess is that you'll find something like ",
" or ",
" more suitable for your purposes than "... | [
" may be good for you. As a plus, it is now free with a membership to the American Chemical Society. "
] |
[
"Why was there (if any) a selective pressure for increased genetic variation & diversity in humans?"
] | [
false
] | I am having a slightly difficult time thinking about why there was a pressure for the genome to produce more variation and increase diversity between individuals (i.e. in humans) via mutations, chromosome crossing over, the tendency to be attracted to mates that are more distantly related, and using sexual (vs asexual)... | [
"The more diversity in a population, the better that population can survive against some major event. Therefore, genetic variation is very advantageous.",
"Unfortunately, there is not as much natural selection active in humans today as there was in earlier human species. All the technological advances have made m... | [
"I could see how genetic variation does increase the chance that the population doesn't get wiped out by a major event -- but how did the selection occur in the first place? Doesn't that invoke \"group selection\" as a potential mechanism? I'm not sure I'm convinced by your explanation. "
] | [
"Natural Selection was never about the survival of an individual. Natural Selection occurs at the individual level, but affects the group as a whole.",
"How did it begin? After the first non lethal mutation. If you have two individuals with non-identical genomes, one will most likely be better adapted to survive ... |
[
"Alternative to Google Scholar?"
] | [
false
] | Recently I've noticed cropping up in Google Scholar more and more, as well as some self-published 'journals'. Is there something similar to Google Scholar (e.g. broad spectrum) but something limited to reliable journals? | [
"What you show is disturbing. The fact that it implies some sort of peer review is truly devious.",
"Depends on what field you are in.",
"arxiv for example is a pre-publication repository for physics. Maybe bio has something like it. ",
"If you have access to a university library ISI web of science is the bes... | [
"Google Scholar never promises that there's been peer review, I've turned up lots of publications that are 'grey' literature (internal government publications for example). It's a tool, that's all it is. It's like showing a hammer sometimes bends nails and then asking for a new tool.",
"Google Scholar gives me ... | [
"PubMed is awesome for anything in the sciences and social sciences, and serves as a good quality filter. ",
"I have been known to then use it in conjunction with GoogleScholar to see if the full article is available for free somehow on the internet (if the abstract is not sufficient for my purposes). ",
"Addit... |
[
"Is it possible to stop Mercury (Hg) from moving through soil when placed in a landfill?"
] | [
false
] | I noticed my local rubbish tip was dumping some mercury, and I just wondered - due to it's liquid nature, and most toxic substance's tendency to leech throughout the soil - how do they manage to keep the substance at bay? Do they make it form a compound or something? | [
"You noticed this how and where? It's illegal in a lot of places to dump mercury "
] | [
"You can test whether the mercury will leach from the waste after its processed (i.e. reacted with a precipitant as you said). Whether it leaches or not depends on the chemical form of the mercury and how stable it is. A stable example would be if you embedded the mercury in glass (",
"vitrification",
") then t... | [
"yet they still allow people have mercury dental fillings in some countries"
] |
[
"Could anyone explain how entanglement can not simply be explained by the two entangled particles \"seeing\" each other and fixing their states at creation?"
] | [
false
] | null | [
"I wish it were that simple. Bell's theorem says it isn't."
] | [
"Mainly QM doesn't allow the entangled particles to have a local hidden state (e.g., something dependent on local variables) prior to being measured. The reason is bell's inequality/bell's theorem, which has been experimentally tested (essentially verifying no local hidden variables). Difficult to explain concise... | [
"Am I getting this right(?):",
"No",
"Essentially verifying no local hidden variables means that the observation/measurement was predicted perfectly by a set of mathematical laws, and those laws, which performed perfectly, also violated locality. Nobody ran an experiment directly proving that local hidden vari... |
[
"AskScience AMA Series: We are experts on NASA's efforts to grow crops in space including a harvest just in time for Thanksgiving! Ask us Anything!"
] | [
false
] | Since 2015, using NASA hardware, scientists and researchers have worked with astronauts on the International Space Station to conduct a series of experiments to grow, harvest and eat a variety of crops in space with seeds sent from Earth. The most recent experiment has the ISS crew growing Mizuna mustard using two diff... | [
"Which plants have surprised everyone the most with their performance and which ones have the most potential for going to Mars?"
] | [
"Hello! As I am part of the team responsible for researching new crops on the ground to be applied in space flight, the plant that I found to interestingly not do as well in flight than it did the ground was a cabbage called Tokyo Bekana. Also, while screening some peppers a variety that grew very large and tal... | [
"Do plants grow differently in low-gravity conditions, and if so, how does that impact your research, the choice of crops to bring on a trip, and the requirements for their growth space?"
] |
[
"How do the Chinese send signals back to earth from the dark side of the moon if it is tidally locked?"
] | [
false
] | null | [
"Before landing Chang'e 4, they launched a relay satellite named Queqiao that stays at a point past the moon where it can see both Earth, and the far side of the moon.",
"https://en.wikipedia.org/wiki/Chang%27e_4#Queqiao_relay_satellite"
] | [
"The relay is in a halo orbit around the Earth-Moon L2 Lagrange Point: ",
"https://en.wikipedia.org/wiki/Halo_orbit"
] | [
"Worth mentioning Larange points aren't stable orbits, and require station keeping fuel burns in order to stay there, which means anything you put there is gonna have a finite time. Granted, ALL satellites being put into any orbital regime for a specific task will require station keeping in order to be able to perf... |
[
"Light travels faster in vacuum than through air, so is there a material that could slow light down in a way that we could see it traveling?"
] | [
false
] | So light travels at 299,792 kilometers per second through vacuum and at ~200,000 kilometers per second through air. That's almost 100,000 kmps slower, what's the slowest that light can travel through a material and what material? | [
"In principle: Yes. Light has been slowed to below 10 m/s.",
"https://en.wikipedia.org/wiki/Electromagnetically_induced_transparency",
"I don't have time right now, might write more about it later.",
"Edit: The key here is the introduction in the section \"Slow light and stopped light\". Make the absorption d... | [
"Light travels slower through materials, but not as slower as you said: light speed in air is almost identical to the one in vacuum, in fact in vacuum is 299 792 458m/s, while in air is about 299 720 000. This isn’t such an huge difference, and also other materials can’t slow light down so much that we could see it... | [
"I found this list: ",
"https://en.m.wikipedia.org/wiki/List_of_refractive_indices",
" \nThe highest is the value of the index, the slowest the light goes through the material, according to the formula v=c/n, where v is the speed through the material, c is the light speed in vacuum, and n is the refractive inde... |
[
"How much energy is required for D-D fusion???"
] | [
false
] | [deleted] | [
"There's no single number, but a good measure is the Coulomb barrier. ",
"Here",
" is a calculator, which gives a barrier energy of 476 keV.",
"Most environments in which DD fusion is occurring are not at 5.5 Gigakelvin temperatures (476 keV divided by Boltzmann's constant), so tunneling is playing a large ro... | [
"Thank you!!!"
] | [
"You can calculate that from the cross section."
] |
[
"Are all animals/insects/birds etc equally skilled in tasks necessary to their survival? Do \"stupid\" animals/\"smart\" animals exist (especially in the wild)?"
] | [
false
] | Asking this question after watching a video of a spider spinning its intricate web so it got me wondering as to whether in this example a spider would make mistakes while spinning its web or always get it right the first time, or would a bird always make a perfect nest (eg. the nest of the weaver bird). Video of spider... | [
"Brains are expensive. They take energy that could otherwise be used for moving, growing defenses, or just makin' more babies. All animals existing live in a sweet spot that allows them to do as well as they can with what they have and the requirements of their environment. Being smarter is not always a benefit,... | [
"Another interesting point is that the amount of variability in a trait is strongly influenced by the pressure of selection on that trait. If intelligence is strongly linked to fitness, we would expect to find very little variability in the genes governing intelligence. If intelligence played only a small role in t... | [
"There will necessarily be animals that are better at surviving in their environment than others. The animals that are better at surviving in their environment will reproduce more often, and those less equipped will reproduce less often (or die all together). This is the basis behind Darwinian natural selection."
] |
[
"In relation to a /r/adviceanimals post, how do we know the sun made its 18 revolution around the galaxy?"
] | [
false
] | null | [
"Well, we know the sun is 4.5 billion years old. By carefully studying the motions of nearby stars, we know that the disk of stars in our galaxy, which the sun is a part of, ",
"orbits at roughly 220km/s",
". And we've also measured to distance to the center of the galaxy to be about 25,000 light years.",
"Pl... | [
"One would assume 4.5 billion. A year is how long Earth goes around the Sun, so if the Sun is 4.5 billion years old, etc..."
] | [
"Get the age of the Earth and you have your rough number. As with the Sun's rotation around the galaxy, we might not have been moving at the same speed, in the same position all that time."
] |
[
"What is happening when paper gets wet?"
] | [
false
] | I was curious as to why paper gets mushy and totally changes texture when it gets wet. I have read that paper is made mostly from cellulose, and was thinking that when it gets wet, the water causes hydrolysis between the monomers, which in turn causes the mushy texture because the bonds are broken. I don't know if this... | [
"Paper is mainly held together via hydrogen bonds",
", wetting (introducing water) disrupts the bonding ",
" cellulose fibres. The cellulose chain itself are held together by covalent bond, and would not be affected easily by wetting. That's why cellulose hydrolysis requires ",
"specialised and energy intensi... | [
"My chemistry is quite shoddy, so I won't be able to go into great detail in terms of the physical chemistry (bond strength and energy) involved. However, I can say that ",
"water",
" is quite good at forming hydrogen bonds itself. It seems that, when water is introduced to the fibres, ",
"the molecules can ... | [
"To know what's happening it might be good to look at how paper is made. In the simplest methods, pulp fiber from wood (or cotton or other fibrous material) is chipped and ground and made into a slurry of cellulose and lignen, it then goes through a mechanical alignment process which forces the slurry through a bla... |
[
"If an object is in orbit, meaning it is in free-fall, what stops it from accelerating indefinitely?"
] | [
false
] | null | [
"It's constantly accelerating, but the direction it accelerates in keeps changing, so the average acceleration is zero and it always has around the same momentum. If it's in a circular orbit, it's always accelerating perpendicular to the direction of motion, so it doesn't speed up or slow down. It just changes dire... | [
"Gravity is what changes the direction of the satellite. The object is pulled toward Earth's center of mass which may speed it up or slow it down depending on whether the object is working with gravity or against it. A good example of this is a highly elliptical orbit. At the point where the object is the furthest ... | [
"It just clicked, thank you! The gifs really helped."
] |
[
"On an infinite square grid of perfect one Ohm resistors, what is the equivalent resistance between two points that are a knight's move from each other?"
] | [
false
] | I've been reading XKCD for years at this point, and I like looking into things that appear in the comics. What is the resistance here, how would you work it out, and why is it so incredibly hard? | [
"I was given this as a homework problem in a graduate E&M course. Interestingly, for two points next to each other in the lattice, there is a simple argument to show that the equivalent resistance is R/2. But as soon as you try any other two nodes - the knight move or even just a diagonal - you need much heavier ma... | [
"In case nobody can answer it in a shorter way, this is an old puzzle: ",
"http://www.mathpages.com/home/kmath668/kmath668.htm"
] | [
"This question is indeed about the inverse of the Laplacian on a square lattice. However, this inverse is not well-defined! (The Laplacian of a constant potential vanishes.) When doing the integrals, you have to discard a few infinities, as the infinite grid of resistors is not quite physically reasonable.",
"Rem... |
[
"When did humans start falling in love?"
] | [
false
] | According to , monogamy came with STIs. If that's the case, when did love come along? Did it exist before we became monogamous? Or was it a result monogamy? | [
"It's an interesting question, but I believe the vagueness of it is why it didn't get answered. First you have to define what love is, then you have to define what monogamy is. I'll put my own answer at the bottom if you don't want to read everything in between.",
"Is love a deep rooted emotion of the soul, a s... | [
"Thanks for your thoughtful answer! "
] | [
"You can't really ask techical questions about something like \"love\" without VERY clearly operationalizing what you mean by the term. Otherwise, as a simple example, one might point out that most children love their parents, and that this would not make much sense to have been all that related to monogamy or not,... |
[
"Redshifting- What is it in a nutshell?"
] | [
false
] | Also, how do wavelengths come into play with red shifting? How does redshifting prove the Big Bang theory? | [
"As for evidence of the Big Bang? Nothing's conclusive yet, but many of the galaxies we can see display a Redshift, which imply they are currently moving away from us, which is a good indication of Universal Expansion",
"The evidence is quite strong and at least the basics of the big bang model are considered as ... | [
"Redshifting is when an object appears with a slightly longer wavelength, towards the red/infra-red end of the electromagnetic spectrum, hence redshifting. This occurs when an object is moving away, meaning we observe a longer wavelength. The wavelength observed is essentially the wavelength emitted, plus how fast ... | [
"Redshifting is the same principle as the Doppler Effect, but applied to light!",
"You've probably experienced the Doppler Effect before. The most commonly used example is that of a truck horn which increases in pitch as it approaches you, then fades away as it passes you, making that EEEEEERRRRRRROOooooooowwwwnn... |
[
"Does every planet massive enough to support an atmosphere (e.g., as dense as Mars's) actually have one?"
] | [
false
] | null | [
"Temperature also plays a big role.",
"This is a super important point. ",
"For a specific case in comparative planetology, check out the difference between Mercury and Titan. Mercury is about 2.5x as massive as Titan, and has an escape velocity that's about 65% greater. However, Mercury also has daytime temper... | [
"Temperature also plays a big role.",
"This is a super important point. ",
"For a specific case in comparative planetology, check out the difference between Mercury and Titan. Mercury is about 2.5x as massive as Titan, and has an escape velocity that's about 65% greater. However, Mercury also has daytime temper... | [
"Mass and temperature are both very important. Earth and the Moon are both at the same distance from the Sun, but only Earth has an atmosphere because it's so much more massive than the Moon."
] |
[
"How are we finding such intact remains of Neanderthals, yet Denisovans/other homonins remain out of grasp, so to speak?"
] | [
false
] | null | [
"Neanderthals lived in some of the most heavily dug-over regions on the planet--Europe and the Near East. No doubt the prevalence of archaeologists has something to do with the prevalence of known fossils."
] | [
"My knowledge of archaeology/anthropology is limited at best, but I would speculate that the easy answer (or at least one of them, considering the multitude of potential reasons) would be the availability of Neanderthal bones and dwellings to archaeologists.\n Being our nearest ancestor and having only recently bec... | [
"Person with anthropology degree here (admittedly sociolinguistics was more my jam). Plainly put, the longer the period of time, the more time there is for something to destroy the remains. There are two types of fossils mainly - trace fossils (footprints and the like) and body fossils. Body fossils are your conce... |
[
"How long can individual cells go without food?"
] | [
false
] | I ask because I was wondering if it were possible for a cancer patient to starve themselves to the point where the rapidly dividing cancer cells die but their body can be saved. | [
"not very long. one method of cancer therapy, however, is starving the cells of glucose, since most cancer cells almost exclusively use glycolysis to make energy; while normal cells have several other pathways they can use. if you cut off the glucose, the cancer cells die, but your normal cells live."
] | [
"So is fasting prescribed for patients often? "
] | [
"no, they are given glycolysis inhibiting drugs. you can look here for more info:",
"http://en.wikipedia.org/wiki/Warburg_effect#Oncology"
] |
[
"How does THC intoxication work?"
] | [
false
] | [deleted] | [
"From what I understand, while you feel high the THC is actually bound to cannabinoid receptors in your brain. However after separating from the receptors your body begins to metabolize the THC. That process creates metabolites of THC, or little traces of what it used to be. It's those metabolites that create a pos... | [
"It is a lipid, it's not a fat. \"Lipid\" just means that it likes nonpolar solvent environments, such as oils (e.g. butter) and nonpolar organic solvents (e.g. butane). \"Fat\" means a triester of glycerol and three fatty acids, which THC definitely is not.",
"Different molecules get taken different places at ve... | [
"To add on to this, the reason THC activating cannabinoid receptors produces a \"high\" is the distribution of the receptors in the brain. They are located in the ",
"hippocampus, hypothalamus, amygdala, and basal ganglia",
". The ",
"hippocampus",
" is the key region of the brain where short-term memory is... |
[
"How does a FM Radio antenna deal with the echoed signals?"
] | [
false
] | Hello, When voice is transmitted over a radio, the transmitter transmits it in all directions, and a few of them reach the receiver antenna (in either straight line or through reflections) with different delays. But why doesn't we hear the echo like we do with Sound? | [
"This is called “multipath interference” and it’s definitely a problem for radio communication. But the effect between two copies of a wave a few nanoseconds to microseconds apart is a weakening or garbling of the signal, not something you can hear."
] | [
"Back in the days of VHF television transmissions, ghost images due to receiving reflected signals was sometimes experienced. Those ghosts were only a fraction of a single scan line on the screen behind the main image. That works out to be something around one microsecond delay, far less than the time for one cycle... | [
"Yes, and if the delay was sufficient to hear it, the extra added path length would attenuate the signal so much that it would be too weak for the radio to actually pickup."
] |
[
"If you place a pot of water in the freezer, will it freeze from the edge inwards or the center outwards?"
] | [
false
] | [deleted] | [
"From top/edge inwards to the center.",
"Explanation:\nWater has the highest density at about 4°C [1]. The temperatur of the water in the pot is roughly even, with just slight variations (since the cooling is slow and the water has enough time to evenout). However, these variations make a difference.\nWater at 4°... | [
"Well you proved me wrong. I thought edges and bottom first, to inward. I learned something. Thanks."
] | [
"Water will freeze at the 0°C temperature. So basically the ice limit will follow the area of 0°C. So if you use a simple bottle or a bowl it will freeze from the exterior inward as it is there that the exchange of energy will take place. That is why for instance a frozen river has its top frozen, beacaus it is the... |
[
"Does one experience \"lag time\" when viewing a black hole?"
] | [
false
] | I just watched . I can't stop thinking about what two people would experience when A watches B enter a black hole - both with lights that flash every second. For Example: When B draws near the black hole, as time slows and the light blink longer and slower, wouldn't the light emitted grow dimmer, longer lasting, and sl... | [
"For Example: When B draws near the black hole, as time slows and the light blink longer and slower, wouldn't the light emitted grow dimmer, longer lasting, and slower to occur to A?",
"This is spot on! The quick answer is that as we watch an object approach the event horizon of a black hole, we will see it 1) mo... | [
"You are exactly right, there has to be a last pulse/photon, since in its own frame of reference object B will at some point cross the event horizon. However, as you wait to receive those last few photons, the time you would have to wait between pulses would grow longer and longer. In fact, this waiting time will a... | [
"I cant see how it would in practice asymptotically approach the EH without crossing it from A's point of view. I think the pulses would indeed stretch out as you describe, but must eventually Doppler shift and then disappear (stop). From the point at which B leaves A to the point at which B actually crosses the ev... |
[
"How do they keep radiation from contaminating the water which evaporates out of the top Nuclear Power Plants?"
] | [
false
] | Okay, so in Water Moderated Reactors, I understand that they use rods to contain the radioactive materials (usually Uranium-235), and because of the nuclear reactions these rods get really hot and they use the water to cool them down which is where all the water vapor comes from. (Please correct me if I'm wrong about a... | [
"There are separate cooling loops. The water coming off of the huge evaporating towers has not seen any radioactivity, it has been encased in pipes and separate tanks the whole time and used to cool off the inner loop which as far as I know consists of water that may have radioactive impurities."
] | [
"So in nuclear reactors fission heats water in a closed system. Once the water is heated is goes through a pipe system that is cooled with a second set of fresh water that doesn't have any contact with radiation or the contaminated water. So the heat is transferred to clean water that is then used to power the turb... | [
"The vast majority of nuclear power plants use pressurised water reactor (PWR) and boiling water reactor (BWR) designs. In both cases the water running through the reactor pressure vessel is in a closed loop. In a PWR this heats a second closed loop which provides energy to the turbine, whilst in a BWR the the tu... |
[
"In logographic written languages such as Chinese, where characters broadly represent things/concepts/words, do they invent new characters when new things are invented or new words are coined?"
] | [
false
] | The same goes for Japanese kanji characters – do they invent new ones? | [
"In Chinese, if it's a loan word from another language they find a combination of characters that approximate the pronunciation of that loan word. A lot of characters have the same pronunciations, after all. If they can, they select characters with positive and relevant meanings, but otherwise they just try to no... | [
"I think others will answer your question more directly, but just to clarify: Chinese is not logographic.",
"Estimates are that around 3% of characters have logographic origins, and you can't characterise a whole system by 3% of it. One of the terms which is certainly less romantic, but more accurate is that Chin... | [
"I know about the Japanese kana – I was just wondering if the Japanese are making up more/new kanji. I understand that the existence of kana lessen the need for that, but still: Do they ever do it?",
"No, they don't really do that. In Japan there are about 2000 Kanji that people are supposed to learn in school, a... |
[
"How much % banana are we?"
] | [
false
] | [deleted] | [
"Clarification, 60% of ",
". Which is a very small percentage of the entire genome sequence."
] | [
"about ",
"60%",
", apparently."
] | [
"about 25%",
"This is easily calculated after one considers the fact that there are only 4 nucleotide bases from which to choose, therefore two completely random strings of DNA will always be at least 25% identical to each other on average."
] |
[
"Is mountain air really the healthiest/least polluted air?"
] | [
false
] | Is there less polution in the mountains (for example the Alps in France) than in some desolate village at sea-level? | [
"It's not so much the altitude as it is proximity to large cities and prevailing wind patterns. There aren't a lot of large cities with manufacturing and chemical processing plants near the French Alps, for example, and the higher you go, the smaller the population is - therefore, the air is much cleaner. ",
"I... | [
"A lot of the pollution does not settle in the ocean.",
"http://discovermagazine.com/2011/apr/18-made-in-china-our-toxic-imported-air-pollution#.UpLdcz_9WSo",
"http://aliciapatterson.org/stories/china%E2%80%99s-rise-creates-clouds-us-pollution"
] | [
"There are many type of 'pollution', different components in air. The O2, CO or CO2 level are tolerable in certain interval, it just gives you a headache. But there can be different chemicals, becteria, viruses, dust, heavy metals, or even hazardous waste or radiation carried by the dust.\nThe air cleaning 'things'... |
[
"How much neutron star material would it take to equal the mass of earth?"
] | [
false
] | From "A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg, about 900 times the mass of the Great Pyramid of Giza." This made me wonder how much neutron star material would it take to equal the mass of earth? Also, if you were able to break off a piece with mas... | [
"Taking the density at 4.5×10",
" kg/m",
" (there's a range of possibilities, but that's about average), a neutron star with Earth's mass would have a volume of 13,276,000 m",
" , equivalent to a sphere of radius 146 metres.",
"If isolated from the neutron star's gravitational pressure, a small section of n... | [
"You're right.",
"1.086 x 10",
" teaspoons = 5.355 x 10",
" mL = 5.355 x 10",
" cm",
" = 5.355 x 10",
" m",
" = 5,355,000 m",
"As far as how many oil supertankers that is - depends on the size of the oil tanker. ",
"I will mention that if you had a perfect rectangular prism the height and base of... | [
"\"How much\" could either refer to an amount of volume or mass (or moles I suppose), but the context of his question clearly indicates that he means volume."
] |
[
"Why is There a Speed of Sound? Shouldn't the Speed of Sound Vary With the Intensity of the Source?"
] | [
false
] | null | [
"Nope, it only varies with the density of the medium in which it travels.",
"Think of it this way: you drop a pebble and a big rock into a lake. The waves created travel at the same speed, the pebble's waves are just smaller and fade to nothing sooner than the big rock's waves."
] | [
"This is a common misconception of intensity, speed as applied to particles and speed as applied to waves.",
"We are used to the notions of speed of particles - we throw rocks, pitch baseballs, play darts etc. For these, it seems intuitive that the \"harder\" we propel the object, the \"faster\" the object will ... | [
"The speed of sound in a medium will also depend on the ",
"bulk modulus",
" of the material (describes responsiveness to pressure) in addition to the density."
] |
[
"I know a catalyst works by lowering the activation energy but how does it do that?"
] | [
false
] | null | [
"One way that this can work is for the catalyst to orient the reactants in a way that is favourable for the reaction to occur. The reactant-catalyst interactions are low energy, so easily formed, and they position the reactants in such a way that they can react with each other easily. "
] | [
"It depends on the exact catalyst, but generally it works like this. If the reaction A+B->AB has an activation energy of X and a third substance C undergoes the reactions A+C->AC with activation energy Y and AC+B->AB+C with activation energy Z, and Y+Z<X, then the reaction will proceed through the favorable catalys... | [
"To put it simply: usually the catalyst offers a different reaction path that has an lower activation energy. So, it's not the same reaction with a lower activation energy, but rather a different reaction leading to the same product from the same reagents + the catalyst, and the catalyst is regenerated at the end. ... |
[
"Can non-ionizing radiation heat air and water?"
] | [
false
] | null | [
"I can't really answer that without speculating."
] | [
"Yes. This is how the sun (primarily) heats the Earth."
] | [
"Do you think there's a signicant heating impact from human made emr ? (A la climate change)"
] |
[
"Why do some airplanes have raised wingtips?"
] | [
false
] | null | [
"Winglets",
" reduce the aircrafts drag by reducing ",
"wingtip vortices",
". This increases overall efficiency, which can save substantial amounts of fuel. They can also improve stability and handling by increasing the ",
"aspect ratio of the wing",
") without increasing the actual wingspan."
] | [
"very accurate. They do save a lot of fuel particularly on long flights. That is why they are most commonly seen on larger jets."
] | [
"Also the payback time through fuel savings is something like 6 months for an older plane retrofitted with winglets."
] |
[
"How does the air inside the tire of a moving car behave? For example does it \"spin\" at a similar rpm to the tire? Also what effect does centripetal force have on the air if any at all?"
] | [
false
] | null | [
"Tire engineer here,",
"The air does move, and it will be lagged behind the carcass (which is lagged behind the wheel a bit, kind of). The air will lag, but not very much, and the effects are minimal.",
"Currently even the most advanced tire models (F1 or aircraft) do not even model the effect you are talking ... | [
"I can't say I've ever modeled tires with water in them, but there are two interesting things that would happen off the top of my head.",
"One is that the flow of water would add a huge damping effect, meaning that if your tire got stuck suddenly, the flowing water would give it a huge boost of torque, as the wat... | [
"As an aside, a lot of tractor tires are liquid filled to add weight. Solution of calcium chloride, I think, to keep from freezing. My old tractor was filled about 90% with liquid, and each tire with rim weighed about 500 pounds. Guess they are going too slow to notice any sloshing effect, though."
] |
[
"A question about visible lasers."
] | [
false
] | I recently bought a 5mw visible green laser. If I'm in a well lit area, I can't see the beam. However, today I noticed that if I aim the laser at a mirror in my room, so that the returning beam goes right past my head, I can see it. But I can only see the beam after in hits the mirror. Does anyone have an explanation f... | [
"Photons can scatter in air - the effect is called ",
"coherent scattering",
" and affects a lot of processes having to do with light and air.",
"Scattering at small angles (a tiny deflection of the photon) is more likely than scattering at large angles (a big deflection). So when you shine the laser away fr... | [
"Yep. Also, watch out. It's not too far from almost by your eye, to in your eye, blinding you. If you want to continue enjoying the fun and science of lasers, you should really invest in appropriate eye-wear."
] | [
"I will be sure to pick some up as soon as possible."
] |
[
"Why do the colours on my computer monitor appear in negative when i tilt my screen?"
] | [
false
] | null | [
"The LCD (TN type panel) consist of many layers of filters. by tilting your screen, it makes some of the filter not work as design.",
"Here is short youtube video explaining how LCD works.",
"http://www.youtube.com/watch?v=jiejNAUwcQ8"
] | [
"To add to this, there exist IPS-type panels (such as what's used on the iPad and other high-end devices) which are in general more costly than TN panels but provide uniform color for viewers 178 degrees around the front of the panel. ",
"For example, I am typing this on a Dell UltraSharp U2412m IPS monitor. Moni... | [
"Light coming at a flat angle from the screen has passed through a thicker layer of liquid crystal than intended, and is thus more rotated. Colors that were supposed to be blocked may thus pass, and colors that were supposed to pass are thus blocked.",
"Some more details.",
" ",
"Photons",
" (light particle... |
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