title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"How would a toroidal universe affect relativity?"
] | [
false
] | [deleted] | [
"I'm not sure if I understand your question, but it seems to be about whether relativity allows globally periodic spaces or spacetimes. The answer, I believe, is yes. Relativity only makes statements about the ",
" structure of spacetime, not the ",
" structure. For example, general relativity stipulates tha... | [
"I also am not sure that I understand your question, but I want to make a few points:",
"what appeared to be a straight path from our perspective actually had the same curvature as the horizontal cross section at the object's latitude",
"The usual model of a 2-torus in 3-space looks curved, but that's just an a... | [
"Ah, yes, that paradox. Acceleration is the key, because it's what makes our frames of reference different—your velocity from my perspective equals my velocity from your perspective, but we can each measure our accelerations ",
"."
] |
[
"Are we prepared to handle a direct hit from a CME?"
] | [
false
] | Are there procedures in place for when the Earth is hit by a coronal mass ejection? What are they? What would be the short term effects? Long term? This is coming from a guy who just learned what a CME is an hour ago. | [
"A CME occurs when an explosion on the Sun sends a ball of plasma (and magnetic field) off the surface of the Sun in some direction. If the CME is aimed at Earth it could cause problems when it collides with the Earth's magnetic field, sending showers of high-energy particles through the Earth's atmosphere.",
"Th... | [
"Disclaimer: I work with people who do this type of work, but I don't do it myself, so this knowledge is second hand.",
"This topic is something that's undergoing active investigation. Probably the biggest short-term effect would be geomagnetically induced currents in the world's power grids. The large and sudden... | [
"Because that's expensive, and for the most part they don't simply blow up. These events are rare. "
] |
[
"Which newspapers or news organisations do you find report science well?"
] | [
false
] | Im only an undergrad but I have found the Guardian and Independent to be quite good ...although the independent did report on some research done by a lecturer of mine and kind of missed the point lol Are there any newspapers more experienced scientists favour? | [
"For mainstream American news outlets, there's very few good ones to pick from. The New York Times is an all-around very good newspaper, and they have pretty good science reporting. They're the best I've seen, of the mainstream outlets, at not sensationalizing their science articles. ",
"I also enjoy Scientifi... | [
"ars technica has by far the best science coverage\n",
"http://arstechnica.com/science/"
] | [
"...seriously?"
] |
[
"What makes common bacterium grow slowly in cold temperature?"
] | [
false
] | What's the mechanism that starts failing when it gets too cold for a bacteria? And more specifically, why is it failing? A quick google search tells me it's some enzyme required for multiplication, I find this a bit too vague and I couldn't get a much better answer while searching further. | [
"Not all bacterial growth is slowed by cold temperatures--some bacteria, including those that live in large bodies of water or in the arctic, do well in cold or even freezing temperatures.",
"Most microbes have an optimum temperature range. Many disease-causing pathogens (although not all) are really well adapte... | [
"All chemical processes slow down as you decrease temperature, this is known as ",
"Arrhenius' relationship",
" . Decreasing the temperature will decrease the rates of multiplication, repair, metabolism, and all processes. Because these functions all depend on each other, they slow even more than any indi... | [
"Thank you for your response!"
] |
[
"Given a high-resolution picture of either a sunrise or sunset, can you tell which one it is?"
] | [
false
] | Suppose you have an extremely high-resolution (say, on the terapixels scale) picture that was taken at either just after sunrise or just before sunset. Is there a reliable way to determine whether such a picture is of a sunset or a sunrise? For example, are sunrises in some location a characteristically different color... | [
"Previous thread",
". Sunset looks different to sunrise because there are more particles (dust etc) in the air in the evening."
] | [
"If you had a sufficiently high resolution, high contrast camera on a very stable tripod, you would be able to see a slight smear, as the sun would move slightly while the picture was exposed.",
"The smear would give the direction of the sun, and from that you could get whether it was rising or setting. "
] | [
"CCDs typically take longer to desaturate than saturate, resulting in asymmetrical behavior.",
"Film, on the other hand, should give a more symmetrical image where it would be difficult to determine direction of motion. "
] |
[
"Don't know how to title it but it has to do with fire and a glass bottle."
] | [
false
] | [deleted] | [
"You'll require a lot of alcohol, and I don't think you'll be able to displace enough water in him, but I see no reason not to try it."
] | [
"A small amount of rubbing alcohol (isopropyl alcohol) has been poured into the bottle and allowed to vaporize, displacing the air in the bottle. The flame can only burn at the gaseous interface between the vapor and the outside air. ",
"Here's another video of the same effect.",
" "
] | [
"If it were hydrogen the gas would go up.",
"It's some heaver-than-air gas."
] |
[
"How does the body adapt itself to increasing physical activity?"
] | [
false
] | For example - in the gym, on day 1, I could barely walk a kilometer without breaking into profuse sweat and being short of breath. After about 15 days now, I can easily walk that much distance in half the time with barely any sweating. How does this happen? | [
"Exercise causes damage to your muscle, as part of repair your muscles start developing new blood vessels. Frequent running increases vessel density, which allows the muscles to get more oxygen and nutrients > less stress-induced catabolism."
] | [
"Classic ",
"r/askscience",
". Most well mannered subreddit I've ever seen."
] | [
"So why do I sweat lesser now as compared to day 1?"
] |
[
"Confabulation Question: Can one knowingly implant false memories in ones own head?"
] | [
false
] | Can one knowingly implant false memories in ones own head? If so, how? It is not important to believe the memory. It is only the vivid recall of this false memory that is important. | [
"Try hypnosis, but I don't know how you would hypnosis yourself, and weather or not you could remember when you weren't under hypnosis.",
"Carl Sagan's The Demon Haunted World",
" deals with this and alien abduction as well as religious encounters."
] | [
"I am not sure what you mean by knowingly, but with enough reinforcement, yes. This is why psychotherapy is/was so controversial with respect to childhood memories. "
] | [
"Yes. One example I know of: Lieing so much, that you begin to believe the lie yourself."
] |
[
"Why doesn't a compressed spring heat up?"
] | [
false
] | I have a limited understanding of physics, and I was wondering why potential energy doesn't always have a thermal byproduct? Is it because it is only potential energy instead of kinetic energy? Or is it still 'actual' energy, just in a stored form? I understand the materials of the spring will eventually break down (du... | [
"Fun experiment at home:",
"Take a (clean...) rubber band and put it against your lips.",
"Extend the band while keeping the contact with your lips. You should clearly feel a small temperature increase.",
"Maintain the band extended a few seconds.",
"Release (slowly, no need to hurt yourself :) ) the tensi... | [
"A compressed spring does heat up, however, most springs have a fair bit of surface area to dissipate the heat so it is hard to feel it. The ehat is essentially representative of inefficiency associated with the spring's storage, and most springs are pretty efficient. However, if you put were to put a spring in an ... | [
"Why doesn't a compressed spring heat up?",
"As mingy said, it does heat up a very little bit, due to friction, just not enough to be noticable by a human.",
"I was wondering why potential energy doesn't always have a thermal byproduct",
"Because not all potential energy is thermal energy. Thermal energy is ... |
[
"Is there a physical limit to data transfer rate? Is there a fundamental limit to the interval between the transmission of two bits of information?"
] | [
false
] | I have read that information cannot travel at a speed greater than the speed of light. However, is there a fundamental limit on the distance between bits? I guess this should put a limit on the data rate flow. The E-t uncertainty might suggest that transmitting at higher energies wll make higher data rates possible. Is... | [
"It's important to distinguish between latency and throughput. Throughput (or sometimes called bandwidth but I'd like to avoid that word here for reasons which will soon become clear) measures how many bits can be sent through a channel per second. Measured with megabits per second or gigabits per second or somethi... | [
"Have a look at the Shannon-Hartley theorem:\n",
"http://en.wikipedia.org/wiki/Shannon-Hartley_theorem",
"It basically says that the information transfer rate is limited by the bandwidth of the channel and the signal to noise ratio. More energy means a higher signal to noise ratio and higher data rates."
] | [
"This would be considering a packet to be the whole backpack of dvds. For very tiny packets that make up transmissions, latency and throughput would seem to be the same to me. It'd be different if you receive multiple packets at once I guess. What I'm thinking of is something like, let's say a packet is 8kb, and it... |
[
"How does Curiosity stay in contact with Earth when Mars is on the opposite side of the sun?"
] | [
false
] | I know the Mars rover is equipped with radios. But while Mars is on the opposite side of the sun, wouldn't the signal have to travel through the sun to reach Earth directly? How do they manage to overcome this problem? | [
"Mostly, they don't. This event, called a solar ",
"superior conjunction",
" with Mars, is relatively rare, and so we manage to keep mostly-continuous communication with Mars orbiters and probes. Before explaining what happens in a solar conjunction, it's worth taking a deeper look into the MSL/Curiosity teleco... | [
"There is a difficulty in these communications due to launch size/weight limitations: the spacecraft always have small, low-power radio dishes. This means that to receive their weak transmissions from across the solar system, we need giant radio dishes to get the signal. NASA uses the huge ",
"Deep Space Networ... | [
"Not a stupid question at all. They're maximum practical speeds - that is, it's possible, under realistic best conditions, to transmit at those speeds. But actual speed varies according to the link state (signal strength and error rate).",
"In particular, the UHF relay system from the MRO to the MSL uses a specia... |
[
"Why do I feel so awful when I am sick?"
] | [
false
] | null | [
"IL1, for the most part. There are others, though.",
"It's a cytokine made by inflammatory cells fighting off the cold virus and it has global effects. It can make your muscles ache, make you tired, make you nauseous, and give you fever. It has local inflammatory effects, but if you have enough of it circulating ... | [
"I would think that TNF-alpha would have the stronger inflammatory effect. IL-1 certainly is a part of it though. ",
"And yes, it's about keeping you still, not hungry (so you won't go hunt) and away from the rest of the clan/tribe/dorm. The fever is part of the actual defense, though.",
"Do you have a source f... | [
"Hart in the mid-late 80s, and Kluger (Klueger?) around the same time, but a little later. ",
"Here",
" is a review, but just about everybody cites Hart.",
"I listed IL1 because AFAIK it's better documented than the TNFa effects as far as the sickness behavior responses go. IL6, PG's, and a bunch of others ar... |
[
"Why don't you feel hungry when you're sick?"
] | [
false
] | null | [
"When you're sick with something like the flu, your body mounts an attack that includes increasing certain circulating molecules in your bloodstream. This inflammatory response has effects on your nervous system such as making you sleepy, reclusive, and lethargic. It also leads to a decrease in appetite. This phen... | [
"What is the evolutionary advantage? Shouldn't the body need more energy and nutrients to fight off infections or repair damaged cells when sick?"
] | [
"My background is in physics not biology, so maybe someone else can handle this more adequately. ",
"Some of the behaviors can be thought of as ostracizing in order to slow infection, and the body is potentially using its resources elsewhere and not wanting to devote resources to digestion. Chronically ill patie... |
[
"Can you explain me quantum decoherence in simple language?"
] | [
false
] | null | [
"To understand this, it probably helps to start with quantum coherence. At a simplistic level, coherence can be thought of as the information that the quantum system holds. More precisely, it is a measure of the relationship between different possible states of the system. Quantum computers rely on this information... | [
"Wow, just finished my first year of my PhD in physics and I understand coherence/decoherence mathematically but your red ink in a lake analogy definitely made everything click intuitively."
] | [
"Glad that it helped you! The intuition is often much harder than the mathematics. You can follow mathematical logic and yet have no idea what you are doing.",
"To quote Einstein: \"If you can't explain it simply, then you don't understand it well enough.\" I try to approach my maths and physics with this in mind... |
[
"Does gas actually get cooler when it expands in vacuum?"
] | [
false
] | For example if I puncture a gas tank, it cools down since escaping the gas is working against the pressure of the environment and the energy is taken away from the internal energy of the gas. The work done by gas is taken away from the internal energy of the gas --> T drops. However if I take the tank to interstellar s... | [
"What you're describing is called a free expansion of the gas, which is an irreversible process.",
"You're correct in saying the internal energy stays constant, but U is only a function of T only for ideal gases. So for ideal gases free expansion is isothermal, but real gases do change in temperature. ",
"In fr... | [
"What your basically describing is the ",
"Joule-Thomson effect",
", where gas expands through a small hole to a larger volume. It is irreversible, but not quite the same as free expansion (i.e. if you instantly increased the volume of the container holding the gas). You are right that an ideal gas won't decrea... | [
"Real gases in free expansion lose internal energy (Q)",
"No, they don't, the internal energy stays constant. The temperature lowers. Also the symbol for the internal energy is U.",
"and entropy (ΔS = ∫dQ/T, or am I mistaken here?) increases accordingly.",
"That formula is for the variation of entropy due to ... |
[
"If antibiotics beat your infection, does your body still become more immune to it? Why or why not/to what degree?"
] | [
false
] | [deleted] | [
"It depends.",
"The immunity you get following an infection results from the presence of antibodies that your body produces to identify and fight the bacteria (In the case of a bacterial infection).",
"If you need antibiotics to fight an infection, there's likely three main reasons:",
"1: You would probably h... | [
"Wow, thank you so much! That was a fascinating and thorough answer to something I couldn't find by googling.. you rock! The fact about shingles is a fun tidbit too! :)"
] | [
"Thank you, I added the appropriate flair."
] |
[
"Does a young zero-energy universe which is still sub-plank size violate the uncertainty principle?"
] | [
false
] | Layman here, If our universe was once small enough to be susceptible to quantum mechanical effect, if we say that the overall energy in the universe at any time is zero, doesn't that violate the uncertainty principle? It implies that it is impossible to simultaneously measure the present position while also determining... | [
"The ",
"zero-energy universe",
" hypothesis states that the total amount of energy in the universe is exactly zero. When the energy of the universe is considered from a pseudo-tensor point of view, zero values are obtained in the resulting calculations. The amount of positive energy in the form of matter is ex... | [
"Well, we don't have a quantum theory of gravity yet, and we'd need one to understand anything going on at sub-Planck length scales. You could even say that the difficulty in answering your question comes from the same problem that's preventing us from creating a consistent quantum theory of gravity: GR needs its ... | [
"I don't understand your question :(",
"What is a zero energy universe?"
] |
[
"How does a plant keep track of large amounts of time? Not day/night. For eg. Kurinji plant in Western ghats of South India blooms every 12 years with consistency."
] | [
false
] | It is predictable enough that Govt. has put up ads for tourists to watch this in July 2018. Swathes of hills get blanketed by this blue flowers. | [
"Each plant possibly has it's own internal timer using some mechanism, but each plant's timer is inaccurate and unreliable, so they take a vote by constantly monitoring each other via the ",
"chemicals they release",
". That way, the few plants that want to flower a year early detect that the other plants aren... | [
"Basically, there are three questions:",
"They all have similar answers: a process will create a certain subtance, like a protein, that causes an effect when it passes a threshold, but not before. Putting water into a bucket doesn't make you grandma shout, unless you put in enough to make it overflow.",
"Questi... | [
"Sure. For 1: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414745/",
"And for 2, you're correct. It is mostly speculation. But it's a reasonably widely accepted hypothesis. ",
"https://www.ncbi.nlm.nih.gov/m/pubmed/27477130/",
"Edit: the most useful term to Google is \"mast seeding\" if you want to kee... |
[
"Has anyone found a practical replacement for lithium ion batteries yet?"
] | [
false
] | [deleted] | [
"A company in Arizona, called Fluidic Energy, is doing some pretty exciting research on Metal-Air-Ionic-Liquid (MAIL) batteries. They won an ARPA-E grant, and have already been field-testing some of their battery designs. The MAIL batteries would eventually cost about the same as a lead-acid battery, but would st... | [
"the only one I know that is being heavily looked at is lithium air batteries for car use. Others can say better then I if they will work out, but someone has to start a comment. "
] | [
"Were those the ones that electric car companies were planning on using; where you'd just swap batteries once you use one up?"
] |
[
"Why does blue light penetrate deeper than red light in oceans?"
] | [
false
] | [deleted] | [
"Any given material will respond differently to different wavelengths of EM radiation. This is know as the absorption spectrum of the medium and it's origin arises from the resonant frequencies of the molecules in the medium.",
"For water the absorption spectrum is peaked around the red region of light and is muc... | [
"Right, now I've taken a look at the composition of Earth's atmosphere (Nitrogen is by far the most abundant) but this is without water vapour, and when the do give water they give it not in ppm or ppb but as follows:",
"At any moment, the atmosphere contains an astounding 37.5 million billion gallons of water, i... | [
"Hi there, just saw this follow up now.",
"Firstly what you need to know to answer your question is that the strength of the interaction between the EM wave and medium is dependent on the number of molecules per unit volume in the medium. For many cases, including this one, this relationship can be described by a... |
[
"Can single-cell organisms get cancer?"
] | [
false
] | null | [
"https://www.reddit.com/r/askscience/comments/3657hz",
"No, not \"cancer\" by definition, but they could get a mutation that makes them \"immortal\" and reproduce without limit. Such a colonly would probably kill itself off by using up all its resources too quickly, though."
] | [
"Cell biologist here, You dont wanna do that unless you're super sure you can keep the \"starvation\" extremely localised, otherwise the tissue and its surroundings becomes necrotic and the patient will die from toxic shock as there is too much cell debris to be taken care off by macrophages and such. Thats also wh... | [
"Just when you think cancer is not complicated enough, it pulls another card our of his sleeves."
] |
[
"Hey /r/science, question. What is it called when your body gets used to the feeling of your clothing on you, and the feeling subsides?"
] | [
false
] | I could be wrong, but I thought that there was some sort of medical term for either what makes this happen, or the state itself. I put on clothing, then I don't notice it after a little bit. Is there a word for this? Thanks! | [
"Bingo! You are my new god. Thanks!"
] | [
"Bingo! You are my new god. Thanks!"
] | [
"I've always heard it called \"sensory fatigue.\" Same thing though."
] |
[
"Can LEDs emit other types of EM radiation?"
] | [
false
] | [deleted] | [
"The discovery of IR emitting diodes preceded the invention of LEDs, so yes. ",
"http://theinstitute.ieee.org/tech-history/technology-history/timeline-the-evolution-of-the-led",
"Considering that blue and \"white\" LEDs are relatively new (I was born in the 1980s, so marketable blue LEDs still seem new to me si... | [
"As the main difference between near UV, visible light and near IR light is our eyes' ability to see it, many technologies that work over visible range, tend to work in those ranges as well. In case of LEDs, I've found these extremes:",
"232 nm UV-C LED",
"7 μm IR-C LED",
"So roughly speaking, you can have LE... | [
"The color depends on the band gap size and these are typically at electron volt scales, so with this principle you won't produce much higher energy photons than visible light. Here's an article ",
"https://en.wikipedia.org/wiki/Wide-bandgap_semiconductor",
" talking about wide bandgaps which already correspond... |
[
"Why do diatoms have cell walls made of silicon? (biology)"
] | [
false
] | I was wondering why diatoms have cell walls made of silicon but no other eukaryote that I came across did as well. What kind of advantages does this give a diatom over other algae and why would the usage of this inorganic element be beneficial over the use of other, assumed more readily available, organic compounds suc... | [
"Primarily, defense. Eating diatoms is like eating little bits of glass, not many zooplankton are able to eat that.",
"As for why diatoms arose, it has been hypothesized that the rise of grasses on land contributed to the evolution of diatoms by liberating more silica into the water. I can't remember the referenc... | [
"That's really interesting thanks for the info and sorry I took so long to respond. I was studying for my microbiology class and I thought that it was really interesting that any kind of microorganism would use something like silica for defense and wondered when it actually came about and what environmental influen... | [
"Here's ",
"the paper",
" I was talking about. I think it's a really interesting hypothesis for the origin of diatoms. The paper's been cited quite a few times since, so maybe looking around through the related literature will be an enlightening experience. Happy hunting!"
] |
[
"Why does Euler's number appear in physics?"
] | [
false
] | I understand that Euler's number is an infinite sum of 1/n!, but what I don't understand is why things like the decay and growth of nuclear radiation can be perfectly modeled by this number. I guess you can have this discussion with pi, but to me it is more obvious why pi comes up in physics, whenever the circumference... | [
"It all boils down to",
"d/dx ( e",
" ) = e",
"e is the only base for which the above is true. e",
" being invariant under differentiation means this function will be paramount to the solution of linear differential equations, which are the heart of physics. In fact, you can see that e in physics almost nev... | [
"There might be a more mundane answer to your question, depending on what you're asking. Is exponential growth in the sense of y = a",
" is reasonable to you, and you're asking why you often see the base a = e in physics? That's actually a choice. It's because whenever you have an exponential you can rewrite it s... | [
"exp(x) is the function which is its own derivative. Any time you have a quantity which changes at a rate which is directly proportional to that quantity, e is going to come up. A non-physics example is population growth.",
"You also see e when you're dealing with complex numbers because it's the polar representa... |
[
"When a beam of light passes through a sheet of glass, is it the same photons coming out the other side?"
] | [
false
] | So, basically, when light hits a transparent object, the energy from it excites the atom(s) it hits, and is transferred through in a chain reaction of excitations. When the energy reaches the other side, a photon is given off, right? Can it be said that this is the same photon, or would it count as a completely new pho... | [
"From what I've read, asking about the identity of such particles is a moot question, they are ",
"indistinguishable",
". We can never tell if any particle photon is the same photon we observed before. This has lead to some pretty funny conjectures like the idea that there is only ",
"one electron in the enti... | [
"To put this to bed, let's have some actual physicists answer the question. ",
"Why is it clear",
" and ",
"what's going on with the refractive index",
".",
"TL;DR, the glass is clear because the band gap is too high for (at least visible) ",
" to be absorbed, and light speed is reduced because the ",
... | [
"A few fates of the photon.",
"-Photon has enough energy to promote an electron to an excited state. For molecules of particular structure, the subsequent delayed electron relaxation and photon emission are observed as fluorescence. ",
"-Photon energy is absorbed via atomic dipole and a new photon is re-emitted... |
[
"Since Hubble is moving at a fast rate in orbit. How does it take pictures with such a long shutter time?"
] | [
false
] | Since Hubble is in orbit and moving pretty fast. How does it stay stationary enough to take a picture with a 30 minute open shutter? | [
"The objects it looks at are generally so far away that the angle towards them does not change as Hubble moves.",
"You can take a photo of a distant mountain out of a train window, and it won't be nearly as blurry as the trees rushing past right next to you. This is the same principle, except on a much larger sca... | [
"The question's already been answered, but let me just put it in perspective.",
"Let's say Hubble is taking a picture of Neptune. It's really faint so it's going to be a 20 minute exposure, or one side of Hubble's orbit to the other.",
"Neptune right now is 4.374 billion kilometers from Earth. The diameter of H... | [
"That's still pretty darn far away."
] |
[
"When two objects in space are moving towards each other, do they both have kinetic energy? If so, where does that energy come from?"
] | [
false
] | null | [
"Anything that's moving has kinetic energy."
] | [
"So the energy comes from gravity?"
] | [
"Not necessarily."
] |
[
"Do animals have any idea of their own mortality?"
] | [
false
] | Obviously, most animals don't have any concept of death, but what about animals that mourn their dead, like Elephants? Elephants have graveyards, so they must understand some sort of division between the living and the dead. Are they at all aware of the fact that they, themselves, will die one day? Has much research be... | [
"That's a very layered question!! While it may seem an obvious element, one of the things preventing us from having a definitive answer is that we can't ask the animals! There is simply no way to test it. And I'd be surprised if anyone has actually done any pointed research on this topic because there's so much wor... | [
"A little piece of anecdotical data that seems to indicate that chimps could grasp (some of) the concept of death: ",
"http://ngm.nationalgeographic.com/visions-of-earth/visions-earth-2009?image=2#/1109-chimps-714.jpg"
] | [
"That is truly haunting."
] |
[
"Does the frequency of a radio station affect the resulting sound quality?"
] | [
false
] | I have a radio transmitter that plays my iPod over my car radio and I recently changed the frequency from 107.3 to 90.1 and perceived a change in the sound quality for better. It sounded richer and I was wondering if it was my imagination or if the frequency that a radio station broadcasts would have any impact on the ... | [
"If there was any difference in the quality of sound, it was likely due to lack of interference from other stations."
] | [
"It's possible that the reason for this is because of the antenna in your iPod transmitter. This antenna may be better suited for transmitting at the higher frequencies in the FM radio band because of the geometry of the antenna, among other things. "
] | [
"FM broadcasts modulate the frequency of the carrier frequency, so they need a band to allow the frequency difference from the modulation process. This is the size of the broadcast band (0.2 MHz), and it is fixed. They also add some safe distance between stations to avoid crossover. Because the band width is fixed,... |
[
"Are we always seeing into the past?"
] | [
false
] | Take the test were in you learn of the speed of sound and the speed of light. A man with a hammer hits down on an anvil and you observe this from 50m away. You see the hammer hit before you hear the sound, but if light has to travel that distance aren't you seeing it in the past as well? At this distance, the time you ... | [
"Yup, you are seeing the past because light takes travel time. When we started observing the moons of jupiter, they calculated when the moons would go in front of the planet, and found that when Jupiter was furthest away, the moons would cross the planet late. What they pieced together from that was that light was ... | [
"Network latency is noticeable at much lower time intervals than your reflex latency. For one, the network latency is added on top of your reflex latency rather than operating in parallel. The more important effect though is that you know when you clicked the button, you aren't reacting to it, so it's far easier to... | [
"I wonder how much in the past? Someone help me out.",
"A good rule of thumb is that light travels about a foot per nanosecond. So you are seeing an object 10 ft away from you as it was about 10 nanoseconds ago."
] |
[
"In units of energy per second, what is the least amount of light it takes for humans to be able to see something?"
] | [
false
] | Humans can see outlines of things in dim, even dark conditions. But how dark? Do we know approximately how much light energy striking our eyes it actually takes to make something visible to an average person? | [
"As an aside: pupil dilation has very little to do with how you adapt to darkness. It takes less than a second for the pupil to close or open completely (you can try this yourself: look at a mirror in a dark room, then turn on the light while watching your eyes; your pupils will shrink rapidly) but it can take many... | [
"10 photons per second of yellowish-green light can be detected",
" Roughly 10",
" W/m",
" if I'm doing that conversion correctly. ",
"That, of course, assumes a completely dark room to observe it. "
] | [
"I once spelunked with a high school group. When we reached the deepest part of the cave, our guides had us extinguish all our lights and wait for our eyes to get to a stable state (still not able to see anything, there was zero visible light, so therefore pupils maximally dilated), and then passed out wintergreen... |
[
"How does our body control how much blood flows into specific areas?"
] | [
false
] | If I hold my hand up for a minute or two, it becomes pale. If I do a handstand for a minute, my head becomes red. If I stand on my feet however, everything seems fine and I don't get troubles with not having enough blood in the upper parts of my body. How do we control that? | [
"Things like this are pretty complex. Blood flow is regulated both locally and systemically through different mechanisms. Locally, metabolic byproducts and other vasoactive compounds cause arterioles to constrict or dilate. As a general rule, byproducts and waste will cause blood vessels to dilate and cause more bl... | [
"The simple answer is that it maintains a more or less constant blood pressure. Since Pressure = Flow x Resistance, each individual organ can control its own blood flow by altering its resistance (at the level of the arterioles)"
] | [
"You always have to think about which specific body part needs blood in a survival perspective.",
"I do physical evaluation tests, I bring people at their cardiovascular maximum. In order to give these tests, we learn how the body adapts during the effort. For example, the blood flow to the digestive system dimis... |
[
"What scientific discovery do you think would help progress humanity as a whole the most? And why?"
] | [
false
] | null | [
"Grand unified theory, I would assume."
] | [
"Aliens."
] | [
"Nuclear fusion. An immediate and outcompeting \"screw you\" to polluting fossil fuel companies whose only claim to legitimacy is that we currently have no other option. I have to commute to work, and I'd love to not screw over the child I want by doing what I have to do to feed him."
] |
[
"Is gravity the strongest at the surface of the earth?"
] | [
false
] | My morning shower got me thinkin. If you are on the surface of the earth, you have a huge amount of mass underneath you pulling you down. Now let's say you dig a hole a few miles deep. You have less mass below you and now some mass above you effectively pulling you back up. All of this is speculation and was wondering ... | [
"That would be true if the Earth was a sphere of uniform density, but since the core is much denser than the mantle and crust, gravity peaks at the barrier between the mantle and the outer core. ",
"Graphs for comparison.",
"You can think of this as the amount of less dense \"stuff\" that the mantle/crust adds ... | [
"As an addendum, this is not a unique or even uncommon characteristic for a planet. The most dense materials will tend towards the center of the planet thanks to gravity. The highest gravity on most planets (especially those with a fluid core) is going to be higher beneath the surface. "
] | [
"The basic model you would see in most intro classes (see xenneract's graph, the constant density line) would peak at the surface of the planet. ",
"Why? Inside a spherical shell of constant density, the net force of gravity on a body is zero. If we treat a solid sphere as a bunch of concentric shells, the only m... |
[
"Can someone give me the \"run through\" on diarrhea?"
] | [
false
] | While sitting on the john for the fourth time yesterday evening, the thought entered my head: What causes diarrhea? I know some general information (Large intestine usually should absorb water, but for some reason fails to), but was hoping someone would give me dirty details. Thanks. | [
"Some bacteria ( like C.diff) produce enterotoxins, which cause havoc with the cellular machinery of the epithelial layer in the gut. The end result being much more water being pumped out into the lumen of the intestine, causing looser stools. ",
"The cramps and explosive events are also caused by spasms in your ... | [
"It can also happen with certain infections when your body tries to force as much water back through your intestinal lining and speed up your peristaltic contractions (which hurts like shit, I might add) to flush it out as fast as possible.",
"That's why something like norovirus gives you high-pressure, crampy, l... | [
"If you want some general information why don't you just read the ",
"wiki article",
" on it?"
] |
[
"Do astronauts have internet in space? If they do, how fast is it?"
] | [
false
] | Wow front page. I thought this was a stupid question, but I guess that Redditors want to know that if they become a astronaut they can still reddit. | [
"They do, the ISS has it's own network with ",
"68 specially modified ThinkPad A31s and 32 ThinkPad T61ps",
" connected to the station's ",
"wireless down link",
" to the Earth via ",
"Ku band satellite relay",
". The speed is roughly equivalent to that of consumer DSL (10Mbps down, 3Mbps up) but with c... | [
"Mostly thermal modifications, without gravity you don't get heat convection and so they need additional cooling to radiate heat away from the inside bits. They also had to be adapted to use the ISS's power grid, they don't use standard 110 or 220v AC up there, their main power is 28v DC. "
] | [
"What kind of modifications have to be made to your standard ThinkPad to make it space-worthy?"
] |
[
"Can stress or intense fear actually cause your hair to turn grey?"
] | [
false
] | I feel this is a common pop culture concept (Futurama, Twin Peaks, etc) but I don't know if it is science based at all. Admittedly the examples I provided are both from non-serious shows, but I believe I've seen this concept in more reality-based media before. To clarify for those who asked, I meant "Can stress cause y... | [
"scientific american article on this ",
"http://www.scientificamerican.com/article.cfm?id=fact-or-fiction-stress-causes-gray-hair",
"Excerpt: ",
"Does stress accelerate this demise of the melanocyte population? \"It is not so simple,\" Fisher says, noting that the process of graying is a multivariable equatio... | [
"Trick question!\nWhen your hair goes grey, it's really actually white and just appears grey contextually. There's no such thing as ",
"grey hair",
"."
] | [
"I can think of tonnes of anecdotal examples, but wonder if this isn't mostly coincidence due to the fact that people tend to reach the apex of their careers (and hence get in to high pressured, stressful situations) in their late middle age, which just happens to be the age when the grey starts for most. "
] |
[
"Why can't certain animals catch certain viruses?"
] | [
false
] | So the idea for this question came when I saw somewhere in the world they were using dogs to deliver beer to people quarantined in their homes. Some research on google showed me dogs, chickens and certain other aninals can't catch the coronavirus. Why is that? | [
"Viruses are essentially hyper complex organic compounds, they require a specific chemistry and conditions to do what they do. ",
"It's like asking why not every key can open every lock, only viruses are keys that destroy the lock once it opens creating more keys...",
"The simple explanation is that the viruses... | [
"Viruses have to become very very specialized in order to efficiently exploit the extremely complex cell machinery of a species. In addition viruses have to become very very efficient in avoiding a large number of barriers and countermeasures.\nIt is like a band of movie bankrobbers. They plan everything to the det... | [
"Ohh. Now I get it, thanks so much man. Btw I had always had trouble thinking why viruses were non living things since every layman is told germs cause you to get sick and you can kill germs, so I was puzzled if you can kill something, isn't it alive. Now it kinda makes sense. So basically can I think of virus the ... |
[
"How can a microSD card be so compact?"
] | [
false
] | [deleted] | [
"A standard microSD is 165mm",
" Subtracting a bit of area under pins and such, you're left with closer to 130mm",
" If you convert that straight to nm",
" you have 1.3*10",
" nm",
" A 32nm transistor takes up 1024nm",
" approximately, so just dividing that in, you can fit ~125 billion transistors on a ... | [
"This is an excellent response. I'll just point out that on a CPU the power consumption is only partially due to transistor switching. Just as important is that those switching transistors have to drive a signal through interconnect, and the resistance and capacitance of the interconnect is responsible for much o... | [
"This is an excellent response. I'll just point out that on a CPU the power consumption is only partially due to transistor switching. Just as important is that those switching transistors have to drive a signal through interconnect, and the resistance and capacitance of the interconnect is responsible for much o... |
[
"My baby daughter puts anything and everything in her mouth...how is this behaviour so common when it seems like such a massive evolutionary disadvantage?"
] | [
false
] | Given that the vast majority of things are inedible, and potentially lethal through choking or toxicity how come babies are always trying to put things in to their mouths? | [
"Evidence is showing that exposing a baby to the environment (putting things in their mouths) allows the baby's immune system to develop appropriate to the environment. Putting the baby in a germ free environment ",
"seems to cause allergies in later life",
"This is going to hurt most parents, but studies are ... | [
"Yup, I've read that it could be seen as a \"sampling\" behaviour alongside the Hygiene Hypothesis",
"https://en.wikipedia.org/wiki/Hygiene_hypothesis"
] | [
"Well most things are edible in that they can be consumed and won't poison you. Many, many things are not digestible but it's somewhat benign to swallow something that isn't digestible that you later pass.",
"Choking hazard aside, there's typically not a great number of things that are toxic in your environment. ... |
[
"Magnets stick together one way and repel the other. If you had something that could clamp some big magnets together while they were trying to repel. Overtime is there any reaction?"
] | [
false
] | null | [
"Yes. The magnets would start to demagnetise each other. That is one of the ways we use to demagnetise permanent magnets, by placing them in an opposite magnetic field."
] | [
"Wouldn't it be easier practically to heat up the magnet?"
] | [
"Yes. Unless you want your magnets to have a certain strength, then using an external magnetic field would make it easier to control."
] |
[
"I've heard of antiparticles (positrons, antineutrino, etc) and antimatter but i'm still not sure if we have confirmed it's existence. Do they exist? If so, what is the process we went through to discover them?"
] | [
false
] | [deleted] | [
"Yes, antiparticles have been confirmed to exist. They are observed in a wide variety of particle physics measurements, usually as a by-product or intermediate step in a physical process being studied. One extremely common antiparticle is the ",
"positron",
", if you want more detailed information reading the... | [
"As a continuation of that, there's even a good use for the properties of positrons. OP may want to check out ",
"PET scans",
"."
] | [
"You're welcome, though I am very surprised that a professor teaching quantum mechanics would not be aware of the regular observations of antimatter in experiment. Was there some more technical question being discussed that wasn't covered here?"
] |
[
"If you received a blood transfusion from someone with blood cancer, would you get blood cancer?"
] | [
false
] | null | [
"It's very, very unlikely. While there are a ",
"few famous case reports of cancer being transmitted",
" from person to person by something like an accidental needle sticks, cancer risk for blood transfusion is probably not an issue.",
"For example, this large study of almost 350,000 transfusions showed only ... | [
"It is unlikely for a few reasons:",
"1) your immune system is much more likely to prevail against the few immune cells in a transfusion of whole blood. This is why Tasmanian devils can give STD cancers (they lack alloimmunity)",
"2) many blood transfusion products have been pre-treated to prevent complications... | [
"Donated blood is separated into its constituent parts by centrifugation. The red blood cells that pellet to the bottom and the plasma that rises to the top are used for patients, but the lymphocytes, which migrate to an oily looking layer in between called the \"buffy coat\" are discarded or used for research. A... |
[
"When something painful happens in a dream, what is happening when you wake up? Example inside"
] | [
false
] | So I just had an absolutely CRAZY dream. is a link to it because I don't want to explain it again in that great of detail. In said dream, I lose my middle finger and the tip of my index finger on my left hand. They while I was dreaming, and after waking up, they continued to hurt for a little bit. Now, approximately... | [
"Just last week I was dreaming my leg was in pain and when I tried to stand up, my feet couldn't touch the ground because I was levitating. I woke up immediately and realized I had a cramp in that leg and walked it out.",
"My point being that our mind recognizes pain that occurs while we are asleep and blends it ... | [
"From my experience, pain in dreams is the direct result of a pain stimulus in actuality (like rolling on to painful surface while sleeping). I've had dreams where I've been stabbed and shot, but they didn't hurt because no actual stimulus was attached to them."
] | [
"Pain is partly a construct of the brain and partly actual pain. So, the pain you felt in your dream could be either of the two cases - ",
"you were actually hurting your fingers and the dream incorporated it.",
"your brain physically manifested the pain from your dream.",
"For ex. ",
"http://www.ncbi.nlm.n... |
[
"How big are nebulae, what causes them, and what do they form later on?"
] | [
false
] | I'm just really curious to know about nebulae, and as the topic says, I'm trying to grasp a few basic concepts about them. Any additional information you can provide about them would be helpful! Also, do all stars become nebulae, and are all nebulae formed of stars? | [
"Not a full answer to your question, but it should be pointed out that there are sources of nebula other than stars.",
"\nIn the early universe there was only nebula, and remnants of that form the largest known nebula, the size of galaxy clusters: ",
"http://en.wikipedia.org/wiki/Lyman-alpha_blob_1",
"."
] | [
"Nebulae do come in all different sizes, and even their creations vary. There are those created by stelar explosions (i.e. the Crab Nebula). These are created when medium to large stars (eventually even our star) end their lives. When the stars explode, their debris is scattered around. You may have heard of the as... | [
"formed through the gravitational attraction of the interstellar medium, the matter in between stars",
"Is this matter which is present in what we call empty space? Like empty space between Earth and any other planet?\nAlso, what causes them to attract if the matter is just spread out? ",
"Also, great answer."
... |
[
"Why don't we just keep probes in orbit around objects, instead of doing fly-bys?"
] | [
false
] | We have Cassini-Huygens orbiting Saturn right now, couldn't we have done this with other probes? New Horizons is going to Pluto, why not just keep it there to do science for a while? | [
"Two reasons, really: ",
"One is that in order to get to Pluto in a tolerable amount of time (~10 years) NH has to move very fast, using a gravitational slingshot. This means that if we wanted to slow it down to orbit Pluto, we'd have to expend a huge amount of propellent (which we don't have) in order to get rid... | [
"Money. ",
"It takes way more delta-v (fuel) to deliver a probe into orbit than it does to do a flyby. Especially when you are sending crap all the way out to ",
" Pluto. To establish orbit around a body, you need to begin decelerating once you are out there. This takes fuel. To get the fuel out there, you... | [
"The USSR launched about 40 reactors in orbit and the US launched one"
] |
[
"Why can i pick up AM stations from long distances at night?"
] | [
false
] | I'm in Alabama, last night in my car I picked up a talk radio station from Cleveland Ohio and listened for a little while. What factors cause those radio waves to travel so far? | [
"\"During the day, MF (medium frequency) signals travel by groundwave, diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter. However, after sunset, changes in the ionosphere cause MF signals to travel by skywave, enabling radio stations to b... | [
"AM stands for Amplitude Modulation. FM stands for Frequency Modulation. AM radio waves tavel through the ground and the air. FM radio waves only travel through the air. That's why a mountain (or a long tunnel) will block an FM signal but not an AM one. FM is \"line of sight\" transmission."
] | [
"Read the day/night info about ",
"the ionosphere",
"."
] |
[
"How did multicellular organisms originate?"
] | [
false
] | [deleted] | [
"It makes sense, doesn't it? Basic symbiosis -- two cells together have a better chance of filling both of their metabolic needs than both on their own.",
"There are a few factors that limit cell size. Most notably, the ability of a cell to intake nutrients through its surface area increases as the square of its ... | [
"Something to consider - bacteria are known to communicate with one another, ranging from ",
"quorum sensing",
" to forming ",
"biofilms",
". Also, for example, cellular differentiation is observed with cyanobacterial ",
"heterocysts",
". The delineation isn't quite as sharp as one might initially sus... | [
"Another example of where drawing the line between unicelluar and multicellular is blurred: the group Myxogastria. ",
"http://en.wikipedia.org/wiki/Myxogastria",
"tl;dr lives freely as single cells, then congregate to form large reproductive structure which produces spores."
] |
[
"Why aren't fish as large as whales?"
] | [
false
] | [deleted] | [
"I suspect that it has to do with a couple of factors, including:",
"A cursory internet search suggests that there isn't quite enough research to ascertain which of these factors is most important, but it's likely that they all play a role.",
"Consider the reverse question; why is the ",
"smallest marine mamm... | [
"Some of them are as large as whales, but whales come in different sizes well ( many of which are actually fairly small ). None of them as big as a blue whale, the biggest of whales. But the Whale Shark and also the Basking Shark can be in found in the 25-42 feet range typically. That's on par medium whales. Though... | [
"So guess my question is more why is the biggest organism in the ocean a mammal when fish are more diverse and populous? "
] |
[
"Does NASA or any other space organisation have satellites orbiting other planets? if not, why not?"
] | [
false
] | null | [
"Don't forget Venus, Ceres, the moon, and the comet 67P. Also, the MESSENGER probe around Mercury just recently concluded operations and is no longer in orbit."
] | [
"There are scientific probes orbiting Mars, Saturn, and Mercury."
] | [
"Absolutely - ",
"here's",
" a list on Wikipedia of all spacecraft that ever orbited planets other than Earth. Perhaps the most notable one today is Cassini, a probe that's been orbiting Saturn since 2004. It is responsible for many of the beautiful photographs of Saturn and its moons."
] |
[
"What is the effect of impurities on boiling point?"
] | [
false
] | My understanding is that the boiling point of a mixture is lower than the boiling point of its constituent compounds (although I could be wrong). Why is this? Do the boiling points of the compounds have to be different for this to work? | [
" This is exactly what I was looking for! Thank you!"
] | [
"Actually it's ",
"boiling-point ",
"."
] | [
"Epistaxis is correct about boiling-point elevation, but another effect which has to do with liquids only. The boiling point for mixtures can either increase or decrease depending on the intermolecular forces between the components.",
"Here's some phase",
" diagrams of mixtures where the boiling point of the mi... |
[
"Are there any materials with variable weight or mass? Can anything be done to achieve this?"
] | [
false
] | I saw a funny picture on the internet here: , and it got me thinking. Is there any naturally occurring substance that has variable weight? (I now realize mass is probably hard to change.) Are there ways to change the weight of a material such that, if it was placed on this picture, the change in weight would truly gene... | [
"The simple answer is no. The accurate answer is, a little. All matter is subject to ",
"conservation of mass",
". However, ina non-closed system, you could insert energy, which increases mass by m=E/c",
" The reverse reaction happens in nuclear fission: mass is reduced and energy is dissipated."
] | [
"Anodes and cathodes (eg: in batteries) can change mass, but that mass has to be added or subtracted from the surroundings. I believe it also requires net electrical energy input in order to get a cycle happening as per your diagram.",
"Perpetual motion machines are impossible. Those (proposed) that involve chang... | [
"Are there ways to change the weight of a material ",
"I'm not sure if this counts:",
"Wikipedia: ",
"Woodward effect",
"As I understand it (my understanding may be wrong) the Mach Effect or Woodward effect theorises that when electrical energy is temporarily stored in a capacitor or inductor of a tuned cir... |
[
"Friend who has a concussion just told me that she can't sleep for longer than 2 hour intervals, or she might die. Is this true? Can someone explain?"
] | [
false
] | null | [
"We can't really comment on anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] | [
"That's fair. In general, is this a common problem associated with concussions though? Or does it have a name?"
] | [
"I recommend posting such questions to ",
"/r/askdocs",
" instead"
] |
[
"Is it possible that there are beneficial contagions, like in that episode of Red Dwarf?"
] | [
false
] | It stands to reason that happier, healthier people are more likely to, , exchange fluids with other people. A well adapted, hard to detect organism would at least have a good evolutionary reason to take care of their course. Of course everyone knows there's beneficial bacteria in our bodies, but is it possible these sy... | [
"Absolutely a possibility. They appear to have an effect on ",
"fly mating preference",
".",
"So far it's been hard to study (because of the diversity of the bacteria, the fact that many bacteria don't grow in lab conditions, etc), but bacteria have been known to produce vitamins and hormones that our bodies ... | [
"People with Sickle Cell Anemia are immune to malaria. I know this isn't a contagion, but it's an example of an advantageous disadvantage."
] | [
"Brundlefly",
" upvotes!"
] |
[
"What would happen if a water-tight but not air-tight container filled with air was submerged in water?"
] | [
false
] | The first question is whether the container is rigid. If it's not then the container would contract until the pressure is equal inside and outside of the container, and I think this would be enough for most or all of the gases to dissolve in the water, depending on the pressure and depth. I'm not sure what would happen... | [
"If it is a rigid container nothing would happen as water can't get it. Air can get out but the only way that would happen is if the pressure inside the container is greater which won't happen if the container is submerged. ",
"If the container isn't rigid then as the pressure increases it would force the contai... | [
"Although I don't understand how you would have a material that is water-tight but not air-tight while not being rigid as well.",
"It would be like a rubber balloon made out of a porous material with gaps big enough for N2/O2/CO2 molecules but not for H2O. "
] | [
"I'm sorry, but your understanding on this issue is incorrect. what matters is the partial pressures. also, Gore-Tex is a material that is water tight but not air tight while not being rigid. There are a variety of other materials that can do this as well, many of them are used in the making of coats."
] |
[
"If it is now possible to reconstruct visual information in the brain using fMRI, can we record dreams?"
] | [
false
] | Recently, there was a link posted on that showed the reconstruction of images from a person's brain using fMRI. I was wondering if this technology means we could also reconstruct the visual activity during REM sleep. From this YouTube video: The left clip is a segment of the movie that the subject viewed while in the m... | [
"Hey - I actually work in the lab that did this work, and though I was not an author on this paper I know the study extremely well, so I think I can clear some things up.",
"1) Reconstruction of the images are from the visual system. Not whole brain, though I believe, the whole brain data was used (I'll have to d... | [
"Hey - I actually work in the lab that did this work, and though I was not an author on this paper I know the study extremely well, so I think I can clear some things up.",
"1) Reconstruction of the images are from the visual system. Not whole brain, though I believe, the whole brain data was used (I'll have to d... | [
"I'll answer this by addressing what I think is a misconception. This study did not do \"pattern matching\" in the way that I think you imply. Let me start by saying what I think you're saying, and then I'll say what actually happened. So what I think you're saying is this: to reconstruct a video from a brain image... |
[
"Why do I always see the same repeating pattern when I close my eyes?"
] | [
false
] | [deleted] | [
"It is most likely a form of closed eye halucination (can be seen even with eyes open). I don't know the mechanism, but I get them as well.",
"http://en.wikipedia.org/wiki/Closed-eye_hallucination"
] | [
"Those might be ",
"phosphenes."
] | [
"Floaters",
" perhaps?"
] |
[
"Are nootropic drugs a scam?"
] | [
false
] | I've been hearing a lot of about these; the companies pushing them seem to be very good at marketing, hiring celebrities to give testimonials and the whole kaboodle. But is there any scientific evidence proving they can make a real difference, or is it all smoke and mirrors? I'm also wary of anything that's not a contr... | [
"Nootropics aren't a real drug class. They are a sort of made up term for things that ",
" help cognitive function. ",
"The things on onnit.com are supplements/nutraceuticals that are branded in a way that are more brain health-focused. I'm not saying they have no science to back them up, but the science they... | [
"If you're looking for things that make you visibly smarter, then you probably won't find them. There are substances that are harmless enough and, like HoboZoo said, ",
" help, but it won't be something out of a science fiction movie. Research and healthy skepticism is probably most useful at this point, as there... | [
"Yeah that site is mostly bullshit and regardless a huge waste of money. If you do the research yourself though (or check out ",
"/r/nootropics",
") there are substances which have no known negative affect and have been shown to promote brain function. Again caffeine itself is the basic example."
] |
[
"Can someone explain the relationship between frequency, wavelength, voltage and energy across a band gap?"
] | [
false
] | I'm working on a lesson (student teaching[not physics]) and physics is absolutely not my forte. My goal is to have students take voltage across a resistor connected to a photodiode that has an LED shining light into it. Obviously there will be a different voltage depending on the wavelength of the light, but I'm not su... | [
"I don't think you're going to get the results you want. While there is a relationship between light frequency and energy, the photodiode will not respond linearly to this. ",
"http://en.wikipedia.org/wiki/Photodiode#/media/File:Response_silicon_photodiode.svg",
"The 2nd problem you'll have is that a bunch of ... | [
"There's a reason that it took people a long time to work these things out.",
"Generally speaking, the voltage that the LED puts out is related to the color, and the current is related to the intensity of the light, but LEDs aren't exactly simple devices. (If you're confused about how LEDs work, how are you plan... | [
"The energy per photon depends on the frequency according to ",
"E = h nu ",
"where E is the energy per photon, h is Planck's constant, nu is the emission frequency.",
"The wavelength is related to frequency by",
"nu = c / lambda",
"where c is the speed of light and lambda is the wavelength. So you could ... |
[
"Could someone please attempt to explain entropy to me in a fluid dynamics context?"
] | [
false
] | I have recently started a job as an aerothermal engineer and have had trouble understanding exactly what entropy is in a physical sense. I've encountered it in a few cases, for example, viewing entropy plots to locate pressure shocks over aerofoils, but I can't grasp exactly what it is. | [
"Entropy (both in computer science and physics) is a measure of the number of possible states of a system.",
"Creating entropy somewhere means you have taken a certain path in reality, out of a great number of others. The greater the entropy increase, the greater the number of possible states your system can have... | [
"A thought experiment:",
"You have two thermally isolated volumes of regular air separated by a a magical membrane.",
"Initially, the two volumes are at thermodynamic equilibrium; that is, they have the same concentration of each type of gas on both sides of the membrane, at the same pressure and temperature. ... | [
"High entropy means that a lot of microstates can give rise to the same macrostate, while low entropy means that the number of microstates giving rise to the same macrostate is small. To take the (probably faulty) example of sand, a beach is high in entropy, because the exact location and orientation of the sand gr... |
[
"Does your brain go to a physical place when you think?"
] | [
false
] | null | [
"I'm not sure what you mean. Can you rephrase the question? Are you asking if you imagine being in some other place?"
] | [
"Like when you think of anything, does your brain sometimes take you to a physical setting that you’ve visited before to think about whatever you were going to think about?"
] | [
"I'm still not quite sure what you mean. Like if you are thinking about something that happened on your front steps do you go there to think about the event?",
"There's nothing explicit like that, but it is the case that being in the same environment where you learned something makes it easier to remember (",
"... |
[
"Was there gravity before, and during, the Big Bang?"
] | [
false
] | I've been going down the rabbit-hole of the FAQ and the answers on the Big Bang seem to all mention that the Big Bang happened everywhere and with infinite matter. I'm having a hard time understanding if all matter was just a hot plasma before the Big Bang, why it didn't collapse due to gravity? Why didn't the universe... | [
"There probably wasn't gravity as we know it during the first moments after the big bang. At high energies, fundamental forces cannot be described as separate interactions -- for example, shortly after the big bang, the electroweak interaction split into the electromagnetic and weak interactions. During the ",
"P... | [
"Also, the inflationary period happened immediately after the separation of gravity from the other forces. This distributed the mass of the universe so that it became smooth and homogeneous. This also means that the mass of the universe was spread out enough so that gravity became significantly weaker than the othe... | [
"My current understanding is that it ",
" infinite but we don't have any proof or proving it is impossible. We can't detect any curvature to the universe but if it's big enough maybe we just aren't using sensitive enough means."
] |
[
"What dictates how big our atmosphere is?"
] | [
false
] | I tried searching and found some interesting topics, but nothing about this actual question. So what dictates how big our atmosphere is? Is it random? Is there some set proportion for all planets? Thanks! | [
"there are some questions about this. ",
"Venus lacks a significant magnetic field",
", is closer to the sun, but has significant atmosphere."
] | [
"Planetary mass (gravity) and magnetic field. The magnetic field deflects incoming solar wind, which will strip away the atmosphere, as happens with ",
"Mars",
"."
] | [
"One thing to keep in mind, the gasses that get 'sucked' in by gravity aren't always able to stick around. Earth is too small to support the atmosphere it came with (Hydrogen and Helium) so they bled off into space.",
"Thankfully, volcanoes decided to spew out massive amounts of CO2, which worked out pretty well ... |
[
"How quickly do humans lose weight when fasting?"
] | [
false
] | I realize there is a lot of variability in humans and what "fasting" means. Make whatever assumptions you want to facilitate an interesting answer. Thanks. | [
"You ",
" lose a good deal of water weight and some lean mass as well.",
"15lbs of fat can easily be 25-35lbs scale weight."
] | [
"A rule of thumb is that to gain or lose 1 pound of fat is the equivalent of ingesting or burning about 3600 calories of food. A second rule of thumb is that an average, sedentary human being needs about 2000 cal/day to maintain body weight.",
"If you're fasting,that means you're consuming no calories for the dur... | [
"Again, this is assuming that you live an otherwise sedentary lifestyle"
] |
[
"What's the difference between the \"heat death\" and \"Big Rip\" models of the ultimate fate of the universe?"
] | [
false
] | (Prefacing this with: I'm not a professional science person, I just love me a bitta space. I'm working on a prose-poem-y thing about anonymous sex and end-of-universe scenarios and I like to think I know a reasonable amount about both, but I only really have first hand experience of one of them and want to be as accura... | [
"The heat death of the universe is when the universe reaches maximum entropy, and no motion is ever possible again.",
"The big rip is the idea that as space keeps expanding, everything will keep expanding until the point that sub-atomic particles are torn apart. ",
"The difference is in that in the big rip matt... | [
"Seems like you're committing a bit of a fallacy. You're saying since change stops, time stops. But that doesn't follow. Change needs time to happen, but time doesn't need change to happen. Time just allows FOR change to happen, but it doesn't require it. "
] | [
"A big rip could happen so distant in the future that the universe could be considered dead at this point.",
"Unlike the big rip, a heat death is a very slow process."
] |
[
"R. Feynman said once we don't understand why 1/2 spin particles obey Fermi-Dirac statistics enough to reduce it to a freshman level. Has it changed since? Can we do it several decades later?"
] | [
false
] | Some things are, if not understandable, at least 'graspable' to both freshman and a layman - like Pauli's exclusion principle. But can 'we' (a collective, education-oriented science world) explain it like I'm 18 and clueless about higher mathematics? | [
"Well, I think you have to take as your starting point the idea that fermions have an antisymmetric wavefunction. This tends to be thrown out as just \"a brute fact\" that this is the way the universe works. The pauli exclusion principle and fermi-dirac statistics both follow from this fact. It's easier to show the... | [
"TL;DR- ",
". :)"
] | [
"well, when you want to put it like ",
"."
] |
[
"When you shave down a magnet on one of its poles, does it naturally adjust while conserving net magnetic attraction or what?"
] | [
false
] | [deleted] | [
"It helps to understand what actually makes a magnet magnetic.",
"Every atom has something called a magnetic moment. Basically, every atom behaves like a tiny (very weak) magnet with a north and south pole. In most materials the atoms are all oriented randomly, but if the arrangement isn't completely random, th... | [
"While I have no doubt this answer is correct, I feel like I know less about magnets for having read it."
] | [
"Thanks, but knowledge just ruins the magic. ",
"..Like the day I found out where eggs came from."
] |
[
"Can architecture influence (human) decisions/behavior?"
] | [
false
] | For example: Can we design bridge which will make people change their mind if they decide to commit suicide? | [
"Yes, and I can think back to a NYTimes article where they mention how the architecture of two bridges affected suicide rates. It wasn't visual/psychological like you'd expect, it was a difference in the height of the fences. You can climb over both and expect to die but one was slightly higher and the difference i... | [
"Vision scientist in training here! My intuition is that, as others have said, the only easy way to do this is to change certain aspects of the bridge that, through how they appear visually to people, alter peoples' ",
" for their environment--that is, what can the bridge/environment be used for? A really tall fe... | [
"Thank you very much! Very interesting reading."
] |
[
"Why do bees/wasps/flies and other flying insects get trapped by windows?"
] | [
false
] | I know it might seem silly, but I was just wondering if there was a scientific reason that flying insects seem to easily find their way into an open window, but spend the next couple of hours slamming head first into the part of the window that is closed. Is it easier for them to fly in than it is to fly out? | [
"Entomologist here. Couple things to note...",
"While certain groups of insects are capable of latent learning (e.g. using landmarks for orientation and the like), they are completely incapable of insight or transfer learning. That is to say, in many situations, insects are unable to apply previous experience. ",... | [
"And now we know why ",
" went into entomology!"
] | [
"That is really interesting! I clearly misunderstood bee navigation, I thought that they could 'remember' where specific locations are for collecting nectar?"
] |
[
"If we see \"worst case scenario\" climate change, which species will die and which will thrive?"
] | [
false
] | Also someone should define what is the worst case scenario. | [
"We cannot say for sure what will happen. But the categories of species thought to be most at risk include:",
"alpine species, which may get \"pushed up off the mountains\"",
"polar species (\"pushed off the planet\", basically)",
"especially, arctic species dependent on pack ice (polar bears, ringed seals an... | [
"Generalists always do well in times of rapid change. Rats, seagulls, roaches, pigs, humans, dandelions. Being able to live in many different habitats and eat many different foods pays off in the long run.",
"Overspecialization can be an evolutionary dead end. E.g.: cheetahs are the fastest land animal, but sprin... | [
"Generalists always do well in times of rapid change. Rats, seagulls, roaches, pigs, humans, dandelions. Being able to live in many different habitats and eat many different foods pays off in the long run.",
"Overspecialization can be an evolutionary dead end. E.g.: cheetahs are the fastest land animal, but sprin... |
[
"Why do soft drink bubbles attach themselves to the outside of the cup?"
] | [
false
] | As above, I've also noticed they stick to a straw as well. | [
"The bubbles nucleate around small imperfections in surfaces. Its how the bubbles start. But mostly look up nucleation of gasses on glass.",
"Edit: even seemingly smooth surfaces are rough when viewed under microscope. You can check out the internets plethora of information on both subjects. Science rabbit holes ... | [
"Awesome thank you"
] | [
"Do you know why the same phenomenon doesnt happen with beer?"
] |
[
"Do you have to cook potatoes?"
] | [
false
] | When I was a kid my grandma would feed me the raw potato bits she did not use. I know you have to cook the bacteria and stuff out of other foods like meat, but you do not have to cook carrots, so is it okay to eat raw potato? | [
"http://www.utsandiego.com/news/2009/aug/05/1f5focusm195324-pros-and-cons-munching-raw-potatoe/",
"The potato plant produces a number of defensive (toxic) substances in the upper plant (leaves, stems and above-ground fruit), but they are not in the below-ground tubers, which are the “potatoes” we're familiar with... | [
"As noted by many people here, raw potato tuber is not toxic to humans. Follow the linked advice from ",
"/u/mutatron",
". ",
"However, speaking as a home cook (that has learned the hard way on underdone potatoes): potatoes contain a pretty solid carb load of ~12.44 g per 100g of potato (according to the USD... | [
"Actually potatoes do not need to have turned green or sprouted to have measurable and sometimes high levels of solanine present. Although it is rare for potatoes to accumulate enough solanine to be actually toxic.",
"Humans are also able to tolerate a lot more solanine than you would normally expect in a mammal ... |
[
"Some Cameras in space appear to degrade quickly over time, why is this?"
] | [
false
] | In videos such as: You can clearly see artifacts on the camera appearing over time, from dots to a large line of missing pixels. What causes this? Is it just stray radiation? Why does this not effect some other cameras? | [
"This could definitely be damage from cosmic radiation. It looks similar to the damage that happens to cameras in radiation therapy vaults. I believe the damage is usually from radiation in the form of nuclei hitting atoms in the semiconductor hard enough to knock them out of place and screwing up the crystal lat... | [
"Yes sir. Cameras in space are often damaged by higher energy particles that normally get filtered on its way through the atmosphere. ",
"What you notice on nice dslr photos from space is they have a tooooon of hot pixels, sensor spots that always receive power. I think NASA releases the raw images and the monkey... | [
"One more fun fact, the computers on the ISS are prone to blue screening due to their lack of em and particle shielding. Some scientists also believe that charged particles are to blamed for many random terrestrial blue screens. That's just conjecture but makes me feel better when my tower flips out :D"
] |
[
"When I walk while wearing a sweatshirt, how come the drawstrings swing side to side instead of bouncing in the direction I walk?"
] | [
false
] | null | [
"One factor is that drawstrings can sway side to side with very little loss in energy: any side to side motion you may have while walking is allowed to build up in a resonance. But for front to back, the drawstring loses nearly all its energy every time it hits you: cloth doesn't bounce very well. So even if you wo... | [
"When you walk your speed forward is pretty much constant, you have no acceleration. But when stepping you do a fair amount of side to side motion, especially as high as your shoulders. Because this keeps changing, they swing. "
] | [
"As you walk forward they move with you. Initially they’ll appear to move backward, they are in fact wanting to stay where they are. After you drag them with you they’ll appear to just be moving at the same speed as you. They are swaying backwards and forwards as you walk, just to a small degree.",
"Side to side ... |
[
"Hi, I enjoy Word Finds and I was curious if they exercise or help \"sharpen\" anything in your brain?"
] | [
false
] | [deleted] | [
"I read something ages ago that psychologists tested it and found that word puzzles aren't beneficial, but playing chess can decrease your chances of alzheimers "
] | [
"Cool, thank you. I guess I know what I'm switching too."
] | [
"They'll increase your vocabulary at the very least. Any activity that requires extensive thought \"sharpens\" your brain. If you really want to increase your brain power, play strategy games and puzzles. There's sites devoted to things like this and actually let you evaluate yourself, and track your progress over ... |
[
"If you decrease the volume of a star while keeping it's mass the same, is the star going to have a higher gravitational pull?"
] | [
false
] | [deleted] | [
"It's because when you shrink the radius of an object, you can get closer to the ",
" mass. Let's say you were 1 m from the center of the Earth. That means that all the Earth mass outside of 1 m doesn't affect you (it all balances out), and therefore, only the tiny bit of mass within 1 meter of the Earth's exac... | [
"It's because when you shrink the radius of an object, you can get closer to the ",
" mass. Let's say you were 1 m from the center of the Earth. That means that all the Earth mass outside of 1 m doesn't affect you (it all balances out), and therefore, only the tiny bit of mass within 1 meter of the Earth's exac... | [
"Its gravitational \"pull\" depends only on the mass, with the exception that if the radius is decreased then it will be possible to get closer to the center of mass without part of the mass of the star being above you and cancelling out the field."
] |
[
"Why didn't whales evolve gills?"
] | [
false
] | When the first mammals returned to the sea, why did they evolve blowholes instead of (re)evolving gills? | [
"while a whale with gills may have more fitness than a lung-breathing whale, this does not mean that the trait has to evolve. when the mutations which are the basis for evolutionary change occur, they occur randomly. the genome does not \"know\" to mutate in a certain way to make the animal more adapted to the envi... | [
"Mammals burn and consume energy much faster than other animals.",
"Although I haven't done any calculations, I suspect the surface area of the gills required to support the mammal would be far too large. The oxygen content of water is much lower than the oxygen content of air."
] | [
"The short answer is really just that they didn't need to. They already had the entire lung architecture built, and all that had to change was for the nostril's to migrate up to the top of the head, which is probably a pretty small change, in terms of the underlying genetics.",
"Gills, however, would have had to ... |
[
"How does the body know there is no antibody for an antigen?"
] | [
false
] | So I’ve been reading an immunology textbook and I have gathered that APCs bring antigens into the lymphatic system to present them to lymphocytes, and if there is no existing antibody then the process of generating random lymphocytes from stem cells is triggered. But how does the body know? I assume it can take time be... | [
"It’s my understanding that the antibody discovery process is always ongoing, so the presence of an antigen on APCs will always stimulate cognate naive T/B cells. Once all the circulating naive cells that have a matching receptor have been stimulated, there are no longer matching naive cells",
"Likewise naive cel... | [
"The production of random (naive) lymphocytes is continuously ongoing, there’s no trigger required. You always have a reserve of naive lymphocytes in your body, mostly concentrated in the lymph nodes. APCs present antigens to these naive lymphocytes, and any lymphocyte with relatively good affinity (produces antibo... | [
"Oh wow, OK so it’s an ongoing process. I asked a related question below, but to rephrase here: it sounds like the intense reaction we have to a new virus (or a COVID vaccine for example) is an already existing process happening on a larger scale, not a whole new process being triggered, is that remotely correct?"
... |
[
"If a waterfall is always flowing quickly how does one freeze?"
] | [
false
] | null | [
"The same way that even though water is constantly dripping from the ceiling of a cave, stalactites can still build up - little by little. A small amount of water will freeze at the very top of the waterfall, and this will provide a point at which more ice can build up on top. Over time, the ice will reach the bott... | [
"I find this a bit hard to imagine. By chance, would you have a time lapse of this?"
] | [
"But with the extreme force of the waterfall, one would think that any newly-formed ice would simply go with the stream."
] |
[
"Why aren't neutrinos \"supposed\" to travel away from us?"
] | [
false
] | I read somewhere that neutrinos were observed leaving Earth instead of towards it, which could mean a parallel universe. I mean, if neutrinos come to us from all directions and barely interacts with anything, shouldn't we see equal amounts of neutrinos looking as if it is coming towards and away from us? | [
"I'm assuming you're asking about the article that's been floating around Facebook the last couple of weeks which says scientists discovered proof of a parallel universe from particles traveling \"backwards in time\".",
"These articles are basically pseudoscience. The experiment is real but what the articles are ... | [
"Wow thank you for this very in depth reply, it certainly clears things up."
] | [
"Enjoying reading the answer. It got me thinking, and I had some doubts - ",
"",
"It's entirely possible that I'm missing something obvious, but isn't it possible that the waves underwent another bounce off some large vertical thing like a cliff (which caused their polarization to flip back)?",
"",
"Do th... |
[
"Can we observe two galaxies that cannot observe each other due to distance in space/time?"
] | [
false
] | null | [
"Yes. Two galaxies diametrically opposed at the edge of our observable universe with us at the center would see our galaxy at the edge of their respective observable universes."
] | [
"You want an example? It's going to be two unnamed galaxies in catalogs that are identified by where they are in RA and dec. How does that help?"
] | [
"Oh, I know. I was just trying to demonstrate the possibility with the most extreme example. "
] |
[
"Is it true that people who live in dirty environments have better immune systems?"
] | [
false
] | So I was over at some guys' place today and it was (in my opinion?) very dirty. A lot of pets, a foul smell throughout his house and it was very messy and unhygienic. But then I wondered, do people living in that kind of environment have more developed immune systems than people who live in cleaner environments? | [
"To some extent.",
"First, we need to clarify what a strong immune system is. Very simply put, the immune system is a set of cells and proteins that react to foreign bodies and pathogens (e.g. bacteria, viruses). ",
"For instance, there are five types of ",
" (white blood cells) with different functions (",
... | [
"He's say yes clean environments = bored immune system leads to getting drunk and attacking self"
] | [
"That link to the photos of the ",
" is probably the coolest thing I have seen in months. ",
"Hard to fathom that individual cells have basically evolved the ability to create a destructive \"force field\" to keep us healthy. "
] |
[
"Why are 1, 3, 7, and 9 the only numbers whose multiples can end in any digit?"
] | [
false
] | Obviously 1 can multiply into anything. Multiples of 7 can end in any digit 0 through 9 07 14 21 28 35 42 49 56 63 70 Same for 3 03 06 09 12 15 18 21 24 27 30 And 9 09 18 27 36 45 54 63 72 81 90 But 2, 4, 5, 6, and 8 won't do it. | [
"Quick and easy: ",
"Because 1,3,7,9 are the only numbers less than 10 that share no prime factors with 10. On the other hand 2,4,6,8 share a factor of 2 and 5 shares a factor of 5. The reason that we can check if a number is divisible by 2 (aka even) or divisible by 5 really quickly, by just looking at the last ... | [
"Even + even = even, so no way to get an odd number, ruling out 2,4,6,8. And 5 doesn't either because it's halfway between 10, so it only gives 5 or 0.",
"Aditionally, odd + odd = even, then even + odd = odd. By multiplying odd numbers, you can get both even and old sums."
] | [
"Note that these aren't the \"only numbers\" with that property -- they are just the only numbers smaller than 10 with that property. We also have, say, the multiples of 13"
] |
[
"How do we know what is below the crust of the Earth?"
] | [
false
] | [deleted] | [
"Siesmology uses the waves created by earthquakes to measure the rate of propegation of those waves through the structure of the Earth. The deflection of waves and the time it takes them to get to any given siesmograph around the Earth is then used to calculate the structure of the earths interior. ",
"http://geo... | [
"You may know this, but just for clarification...",
"We are taught in school that there is liquid rock underneath the crust",
"There is indeed ",
" liquid rock beneath the crust, but the mantle is almost entirely solid rock - there is just a very tiny percentage of molten rock.",
"The outer core of the plan... | [
"Fascinating, thank you."
] |
[
"How do racing motorbikes go so low when turning without falling?"
] | [
false
] | Seriously what's that about? It looks like they should just fall. | [
"When turning, you are accelerating sideways toward the inside of the turn. This acceleration is applied at the ground, so if you are on a motorcycle and you don't lean, you will fall over toward the outside of the turn due to the torque. Because they are traveling at very high speeds, the turning acceleration is m... | [
"Thanks you very much. That's exactly what I was looking for. "
] | [
"For a really simple analogy, think about how you get pushed to the right of your car when you make a left turn. It's exactly the same force."
] |
[
"What resolution of digital audio would surpass the ability of our ears to discern between digital and analogue?"
] | [
false
] | I am a bit of an audiophile, but I've never looked into this subject. Basically, if there are cameras out there that are able to take pictures with a greater resolution than our eyes can perceive, then it seems logical that there would be a digital audio stream that would be greater than our ears can perceive too. Is i... | [
"'Resolution' in the audio sense would be the sampling frequency. As it turns out, in order to perfectly recreate a sound, you need to record at a sampling rate of at least ",
"twice",
" the highest frequency. Since the typical human hearing goes up to about 20 kHz, anything over 40 kHz should be about enough... | [
"mp3 uses a few tricks to pack most of the useful audio information into a significantly smaller size. for most people constant bitrate mp3 @ 320 kbps with a good encoder should be perceptually identical to the original CD. this is also said to be true for the variable bitrate V0 mp3 which runs at about 260 kbps (... | [
"This is true as far as time sampling goes, but we should also consider the fact that analog audio has effectively continuous amplitude, while digital audio is ",
"quantized",
". Very low amplitude digital audio signals can be pretty distorted by this quantization, so digital audio is often ",
"dithered",
"... |
[
"The Yankees and Red Sox are both blaming the air in London Stadium for their breaking balls staying up instead of falling. How does different air change the drop?"
] | [
false
] | Both teams told Buster Olney yesterday that the lack of air circulation in London Stadium is causing breaking balls not to drop. Wouldn't less resistance give it a BETTER chance at dropping? | [
"This sounds dubious at best. Air density, temperature and humidity are all similar in Boston, NY, and London. The respective stadiums are only double digit meters above sea level. Temperatures may be slightly cooler in London vs across the pond. This could affect play by increasing air density slightly, but I doub... | [
"Air circulation is key to making a ball 'break'. I'd advise you to google 'The Magnus Effect' to learn more, but basically a 'breaking pitch' like a curve ball rotates forward(towards the batter if you will) and it's the air flow coming from under the ball and pusing against the seams that make a pitch 'break' so ... | [
"Has there ever even been a definitive answer as to whether breaking balls actually \"break\", or curve much at all?"
] |
[
"I witnessed this a while ago. How does this happen and why is it such a rare occurrence?"
] | [
false
] | Well, my news feed just exploded with "OMG THE SKY IS SO RED". I am just curious as to how it happens and especially, why is it a rare occurrence? Here is the picture I got from my news feed: | [
"I can't answer for why it appears \"more red\" than other sunsets, but I can explain why it appears red. In short, blue light scatters more than red light. The light from the sun has much more atmosphere to travel through when it's on the horizon, and all the blue light scatters before it reaches our eyes, so all ... | [
"There more particles in the air the more light is scattered. The redness could be due to this being a city which has medium or high amounts of air pollution"
] | [
"Manila, 4 - 6:30 pm"
] |
[
"Is there a fundamental limit to bit rate? Or, is there a limit to serial data transfer?"
] | [
false
] | [deleted] | [
"There is something known as the ",
"Shannon Channel capacity",
" which is the maximum rate at which data can be transmitted through a channel.",
"The formula is: ",
"Capacity = Bandwidth * log(1 + SNR)\n",
"Bandwidth refers to the bandwidth of the channel, for example, ",
"ADSL downloads",
" use 138... | [
"There are hard physical limits (involving trying to encode pulses smaller than the planck length, which happens as you try to get a bit rate of 2x10",
" bits/second (1 bit per planck time)), and since flipping or encoding a bit takes kTln(2) J (3.7x10",
" J/bit) you could only get a certain bit rate with a giv... | [
"USB 3.0 is nowhere near the speed of 100Gbps Ethernet over G.652 / G.655 / G.657 type singlemode fiber, which uses four simultaneous, parallel yet separate 25 Gbps wavelengths. ",
"Even if you ignore 50GHz grid DWDM and use one fiber pair per 100GbE circuit, the capacity of simultaneous 100GbE circuits that can... |
[
"What makes Diet soft drinks 'bad' for you?"
] | [
false
] | null | [
"are not natural, they're man made. Drinking them in high quantities is potentially harmful to you.",
"Non sequitur. There are plenty man made drinks that are safe and much much more natural drinks that are extremely poisonous."
] | [
"In one perspective, Splenda or sucralose as its generic name is pretty much glucose with two of the hydroxyl groups replaced with chlorines. Basically in your body the substance is inert and will pass right through the same form it came in, but under ideal/unideal conditions these alkyl halides become reactive to ... | [
"I know some diet sodas contained an artificial sweetener called Saccharin, which was thought to be able to cause cancer. I do not know if this is still the case."
] |
[
"Could making yourself excessively dizzy have negative consequences?"
] | [
false
] | [deleted] | [
"Um... vomiting maybe?"
] | [
"Immediate consequences = falling over and breaking your wrist, arm"
] | [
"Seizures."
] |
[
"Is Richard Dawkins respected among the scientific community as an evolutionary biologist?"
] | [
false
] | null | [
"I'm a microbiologist that does a fair amount of evolutionary biology, and well, the argument can be made that he's more of a personality or public policy advocate than an actual \"scientist.\" Most of what he publishes isn't original work, but rather reviews or collections of others' work. I kind of lump him into ... | [
"Origin of Species"
] | [
"He hasn't published in a while, but that's mainly because for a long time, his job was to literally inform the public about science. He was a public education chair at Oxford, I think. So all those books were actually just him doing his job. As to whether or not he's respected, I'd certainly say so, but I'm not a ... |
[
"Which spinoff technology from NASA has contributed the most to everyday life?"
] | [
false
] | [deleted] | [
"here are a couple of \"top 10\" lists which might give an idea of some of the options",
"One",
"Two",
"Some of the highlights in my opinion - insulin pump, water filtration, anti-corrosion coating. I think the biggest one that has affected our everyday life is \"communication satellites\" but it would be unf... | [
"Aerodynamic tractor trailer cabs"
] | [
"No question in my mind its the memory foam mattress. Changed my life. "
] |
[
"Do pet pythons recognize their owners and show any animal traits that dogs/cats do?"
] | [
false
] | null | [
"Generally, pythons only coil around things aggressively if that thing is small enough to eat. There aren't many (any?) pythons large enough to eat a typical adult human. That being said, very large pythons, boas and other constrictors can pose a danger to their handlers, but it's pretty rare for people to actual... | [
"Well, you'd certainly get a lot more anecdotes, but those guys are nothing if not brutally honest when it comes to snake-related information. Some of them actually own constrictors large enough to be dangerous and can offer quite a bit of information from that front. There was actually really good information co... | [
"Snakes really aren't particularly intellegent. They may become acclimated to an owner, but unlike a dog, they don't have any sort of real \"loyalty.\" Snakes are not pack animals and they do not make friends. If a snake thinks you are either food or a threat, it may attack you no matter how long you've known it.",... |
[
"Hi r/askscience, two questions about nutrition"
] | [
false
] | [deleted] | [
"Water contains no calories because there is not much you can break down water into while getting energy out of it. Everything breaks down into water and CO2, so for practical considerations and biological, we can consider them as having 0 calories. ",
"Who said the water doesn't \"stay\" in your body. By weight ... | [
"After you eat food, you combine it with oxygen you inhale to extract energy from the chemical bonds. This energy (typically measured in calories) is what you use to move, grow, etc. Now, even though we cannot metabolize water for energy, the vast majority of reactions in the body are carried out in an aqueous (w... | [
"A calorie is just a measure of energy. One food calorie (1 kCal, 1000 calories), is about 4.2 kJ. It's about the amount of energy you need to raise a kilogram of water by 1 degree C.",
"So it doesn't make a lot of sense to ask what they weigh. But, you can talk about the energy density of different foods - ho... |
[
"Why can't ocean water be purified?"
] | [
false
] | null | [
"Because the countries that are at high risk for fresh water 'running out' are often third world countries that can hardly afford the expensive desalination processes. Plus that much, much water is needed for agriculture and transporting water from the sea to inland farms is very expensive. For supplying coastal ci... | [
"Desalination",
" of ocean water for industrial purposes, as well as consumer drinking is widespread and available in areas of the world with limited fresh water availability. Desalination, though, is more energy intensive, and so costs more, than just using fresh water where available."
] | [
"like he said, it is energy intensive and for that reason expensive.",
"In my home of California urban users consume only 10% of our water. We need a ton of water, and especially here in Los Angeles where to pull it from is a looming issue."
] |
[
"What does the \"moment\" in moment of inertia mean?"
] | [
false
] | Title | [
"It might help to think about the problem this way: if you knew the all the moments of the mass distribution over 3D space...first, second, third...up to infinity--then you would know the entire mass distribution. ",
"The laws of motion are generally only applicable for point masses. (This is why physicists somet... | [
"It might help to think about the problem this way: if you knew the all the moments of the mass distribution over 3D space...first, second, third...up to infinity--then you would know the entire mass distribution. ",
"The laws of motion are generally only applicable for point masses. (This is why physicists somet... | [
"It might help to think about the problem this way: if you knew the all the moments of the mass distribution over 3D space...first, second, third...up to infinity--then you would know the entire mass distribution. ",
"The laws of motion are generally only applicable for point masses. (This is why physicists somet... |
[
"If space itself is expanding, is anything happening to time?"
] | [
false
] | [deleted] | [
"Time being \"personal\" simply means there is no universal time, as everyone from Newton to Einstein believed. It's exactly what special relativity proved to us. ",
"If you are standing next to me and we then synchonise clock, and you then move away from me at some significant speed and come back, you will have... | [
"Space isn't relative in the same way time is. For example, the ratio between the average distance between galaxies and the average size of a galaxy is changing, and no similar comparison can be made for time."
] | [
"Space isn't relative in the same way time is. For example, the ratio between the average distance between galaxies and the average size of a galaxy is changing, and no similar comparison can be made for time."
] |
[
"How consanguinity is handled for sperm donors?"
] | [
false
] | If a man donate his sperm, how can he be sure that his kids won't end up marrying each other? | [
"Because there would be an increased chance of genetic abnormalities when they in turn have kids."
] | [
"The coefficient of relationship for half-brother/half-sister is 12.5%. The better sperm donation organizations will do genetic tests on their donors, so add in the low chance of two offspring from the same donor becoming partners and the risk isn't really high enough to try to violate privacy concerns.",
"Keep i... | [
"The coefficient of relationship for first cousins is 6.25% and a lot of people consider it in-breeding.",
"The risk at 12.5% is actually quite high for the progeny to get the same alleles."
] |
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