title
list | over_18
list | post_content
stringlengths 0
9.37k
⌀ | C1
list | C2
list | C3
list |
|---|---|---|---|---|---|
[
"Is it possible to reverse the reaction in a glow stick so you could make one that was reusable?"
] |
[
false
] | null |
[
"In principle, sure. There's no reason a reversible chemiluminescent system can't be developed. However, I don't know of any that lend themselves to easy regeneration after the light-producing reaction has occurred."
] |
[
"The reaction also releases energy in then form of light, so if you were able to reverse the reaction you would have to impart energy back into the system. "
] |
[
"the reaction inside a glow stick is initiated by breaking a glass vial inside the glow stick, mixing the chemical inside with the vial with the chemical that it is submerged it. Once the vial is broken, the chemicals can't be separated."
] |
[
"Is there a smallest unit of time?"
] |
[
false
] |
I was thinking about time, and how we are affected by things around us like gravity, and how everything happens in "realtime" Is there a shortest period of time that something (anything) can happen? Edit: I understand Plankt time now. But am still very curious if there is a "smaller" period of time that something can happen in. That a force (like gravity) can affect something. Or if it is all truly in real time.
|
[
"No - not as far as we know.",
"The ",
"Planck time",
" is often mentioned in this context - that is roughly the scale at which our understanding of physics breaks down. We aren't sure what, if anything, happens during time intervals that short. But there is no consensus on whether it is the shortest time interval ",
". "
] |
[
"Actually, there's no reason to believe that it is the shortest time interval possible. So there is a consensus, it's just ",
" the existence of the Planck time being the shortest possible time.",
"However, physicists are aware of the possibility that a quantum theory of gravity could include the existence of a shortest interval of time. (Loop quantum gravity does something like this, but more complicated.) So it's not the type of consensus that says \"this is true, period,\" but one that says \"this is true based on what we know so far.\""
] |
[
"We talk about smaller time-scales all the time, since all of established physics is working with time being continuous and differentiable."
] |
[
"When astrophysicists say that a planet is the same size as Earth, do they mean in terms of mass or in terms of diameter?"
] |
[
false
] | null |
[
"Well, you probably won't catch an astrophysicist using a term as vague as \"size,\" particularly not in a research paper - scientists will be specific when talking about radius, mass etc. But when these things get reported out and covered outside the primary literature, the word \"size\" can indeed mean different things. Ultimately, you have to read the context to see what they're talking about.",
"There's another term that might give you context, though: \"Earth-like.\" If a planet is referred to as Earth-like, or something similar, it generally means it's ",
" comparable to Earth. The makeup (rocky, like Earth, not gaseous like Jupiter), density and diameter will be comparable to that of Earth. They might call it a \"heavy\" Earth, which means it's comparable in density, but with significantly more mass, which means it's going to have a higher diameter."
] |
[
"Yeah, I don't see an astrophysicist saying \"same size.\" ",
"But I think OP is probably thinking more along the lines of popular science articles that have headlines like \"Astrophysicists discover planets with the same size of Earth.\"",
"Without context, what would that mean? To me, just based on the headline, I'd think of visible size, i.e. radius. Because if a planet has the same ",
" as Earth but has a considerably smaller or larger radius, it would be a misleading title to me. (Btw, can a gas giant have the same mass as Earth?) Not only would it be misleading, it wouldn't really be as interesting or useful, in my opinion; if scientists discover a very, very dense object with the same mass, it doesn't really do much. ",
"EDIT: For what it's worth, Wikipedia has a ",
"list of Solar System objects by ",
", and it's arranged by radius",
"."
] |
[
"Whichever gives them the most sensational press coverage :P.",
"eg: ",
"Kepler-22b",
" was discussed as being 'twice the size of Earth' which is true in terms of radius, but probably has a mass and volume more than 10 times that of Earth.",
"eg: ",
"Gliese 581g",
" has also been expressed to be 'three times the size of Earth'. However, due to the method used to find the planet (radial velocity), we only get a minimum mass for the world. So actually the mass of GJ581g (if it even exists) might be substantially more.",
"So take all figures for an exoplanet's size with a pinch of salt and make sure you read further to determine what they actually mean. Or, as has previously been stated, check the paper itself which should be much more clear than sensationalist science journalism."
] |
[
"How is it that pathogens with very high mortality rate don't go extinct simply by the fact that they kill their victims before they can spread it to others?"
] |
[
false
] | null |
[
"If it still exists it means it was able to find new hosts. Some are very contagious and able to contaminate others before the death, others can spread from cadavers, others can survive in the environment (air, water, ground...) and many have animal hosts. ",
"Rabies have animal hosts, for example. Tetanus survive on the ground, cholera spreads via water, Yersinia pestis (the plague) and anthrax have survival forms wich helps them survive without hosts for decades."
] |
[
"Tetanus is an amazing example. Clostridia tetani (tetanus) and it’s relatives Clostridia botulinum (botulism) and Clostridia difficile (C-dif) among others, are a genus of obligate anaerobic, endospore forming bacteria.",
"These bacteria evolved to live in the absence of oxygen and exposure to oxygen is actually toxic to them. Living on earth, this presents a challenge, and as such, these bacteria evolved the ability to form endospores to survive when they are severely stressed as when exposed to the oxygen rich atmosphere. An endospore is essentially a nearly indestructible protein sheath which contains the vital elements of the bacterial cell in which the cell goes into a dormant state until conditions improve.",
"By nearly indestructible, I mean nearly indestructible. These endospores can remain dormant, waiting for conditions to change for thousands to millions of years. They can survive dehydration, boiling, radiation, disinfectants including alcohol, peroxide, and bleach, and even the vacuum of space. Only temperatures in excess of boiling for long periods (hours), or under high pressure (autoclave), or incineration, or prolonged exposure to high frequency radiation (x-rays, gamma rays) will effectively denature the spore."
] |
[
"Here's a paper on how ebola behaves",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7061886/",
"\"One-health approach is likely to provide a good understanding of the drivers of spillover events from forest-dwelling fauna to forest interfacing humans, which will enable Ebola prevention and control at source. To reduce the risk of wildlife-to-human and human-to-human transmission, public health officials need to emphasise that EVD results from direct contact with blood, secretion and excretion of infected humans or animals, or indirectly through contact with contaminated fomites, environment or objects. A better understanding of the ecology of wild animals concerning pathogen transmission is critical to the overall control of EVD in Africa. The one-health paradigm provides opportunities for public education and control because EVD is an animal virus that is transmitted to humans.\"",
"In other words, it has a natural reservoir that it doesn't kill."
] |
[
"What determines a sapphire color?"
] |
[
false
] | null |
[
"Sapphire is made up of a lattice of aluminum atoms and oxygen atoms, but it's really hard to get a pure lattice, and sometimes other metal atoms get mixed in. All these metals interact with light in different ways, and the result is a variety of colors.",
"If there's chromium, then the stone will appear red.",
"If there's vanadium, then the stone will appear purple.",
"If there's titanium, then the stone will be colorless.",
"If there's iron, then the stone will be pale yellow to green. ",
"Surprisingly enough, if both titanium and iron impurities are present together in the right proportions, the stone will be deep blue!"
] |
[
"It would be colorless and transparent."
] |
[
"What would happen if it was pure lattice? "
] |
[
"Why do NSAIDS antagonize THC effects?"
] |
[
false
] |
By personal experience, anecdotical evidence and I know that Non steroidal anti inflammatory drugs like aspirin and iboprufen antagonize THC effects. In other words they sober you up very fast. Can anyone here explain me why they do it? Thanks, guys.
|
[
"I'm going to try and make this is as coherent as possible...but it's tricky. THC does its thing by binding to a cannabinoid receptor (CB1), which is where most of the high comes from. ",
"The reason why you have cannabinoid receptors in the first place is that you have an endogenous cannabinoid system, with anandamide being the main poster child of that. Anandamide is derived from phospholipds (arachadonic acid).",
"NSAIDs block the enzyme cyclooxygenase (COX), which normally makes prostaglandins that have roles in inflammation/fever/etc. Prostaglandins are derived from arachadonic acid, similar to anandamide. Therefore, the systems definitely share a common denominator and probably have lots of complicated interactions. ",
"Your article linkes to this: ",
"study",
". Apparently cannabinoids like THC cause induction of arachidonic acid and create prostaglandins and somehow they aid in the 'high'. ",
"This ",
"article",
" says that chronic THC alters the cyclooxygenase system, decreasing the potency and efficacy of NSAIDs used. I'm assuming this works in reverse, but it's most likely a very, very complicated interaction depending on how often you smoke."
] |
[
"Thank you so very much for this great answer. It was puzzling for me to watch someone uncomfortably high take a couple advils and be as good as new in a few minutes. "
] |
[
"No prob! I'm curious though if this happens more with people who smoke very regularly, or have you noticed this effect even after not smoking for awhile?"
] |
[
"Where does breastmilk come from and where does it come out of on the nipple?"
] |
[
false
] | null |
[
"Breast tissue contains specialized cells calls lactocytes that take in nutrients from the blood, and secrete milk into a spongy network of tubules (very similar in structure to your lungs' network of bronchioles and alveoli, but in reverse) that store and transport milk. These tubules all meet up at the nipple, via approximately 20 milk ducts per nipple.",
"The ducts themselves don't do anything unusual, although they do have protective cells nearby (Montgomery glands) to keep them plugged and lubricated with an antibacterial oil when not in use.",
"Edit: Need to buy a thesaurus."
] |
[
"Thanks, I was really wondering and my buddies had no clues so I came to the pros and they delivered."
] |
[
"Is this system just underdeveloped in males, or does it not exist at all?"
] |
[
"Without an alarm or other external source for waking us up, what prevents our brains from being asleep forever?"
] |
[
false
] | null |
[
"You have a really complicated internal clock called your circadian rythym that helps you know when to sleep and wake up. In short you have neurons that run in a loop, activating and deactivating themselves (a bit like a Redstone clock actually if you play minecraft), and similar proteins too that inhibit their own production so they come in waves. Essentially, using these complicated systems and synchronizing them frequently with light and other stimuli, your body can determine when to sleep, when to wake up, how to regulate temperature, and so on. This system would wake us up after about eight hours of sleep by stopping melatonin, and increasing seratonin, dopamine, acetylcholine, and norepinephrine production. Without the external cues though our body has a tendency to drift from 24 sleep cycles to slightly longer cycles (anywhere from 15 minutes to several hours longer, depending on the study.)"
] |
[
"It's actually called CLOCK (I know, biologists are great at naming things. Stands for Circadian Locomotor Output Cycles Kaput) and it can bind to its own section of the DNA and prevent it from being transcribed. So as more of it is made, the higher the chance it is bound more often and less of it is produced, then as it degrades over time it begins to be produced more and more again, restarting the cycle."
] |
[
"What are these self-inhibiting proteins and how does this work?"
] |
[
"AskScience AMA Series: I'm Kevin Esvelt, head of the Sculpting Evolution group at the MIT Media Lab and an inventor of CRISPR gene drive - AMA!"
] |
[
false
] |
Hi, my name's Kevin Esvelt and I'm a scientist working on molecular, evolutionary, and ecological engineering. I played a very minor role in developing CRISPR genome editing and was evidently the first to realize it could be used to build gene drive systems capable of engineering populations of wild organisms. If you haven't read about gene drive - and even if you have - I highly recommend reading this by Dylan Matthews of Vox. Relatedly, I'm a strong advocate of more open science, beginning with as a small and high-profile field trial of pre-registration in tech development. Finally, we in try to carefully consider our and publicly . We'll be on at 2pm eastern (19 UT) - AMA! EDIT: Last Week Tonight with John Oliver did a about this just last night! EDIT #2: Our guest needs to take a break, but will be back later tonight to answer many more questions.
|
[
"What are your thoughts on the movement to make all scientific publications open to the general public? Would this be useful or does a lack of contextual knowledge make it better to force inclusion of experts/scientists?",
"What should a scientists role become if all publications were made freely available? "
] |
[
"Ok. You're the person to answer!",
"When we modify a gene and insert it into a multicellular host, how does that gene propagate? Since there are a vast number of non-modified cells why don't their descendants (as it were) overwhelm the cells with the new gene through sheer weight of numbers?",
"Or in other words, how does CRISPR cause system-wide changes without modifying the majority of cells?"
] |
[
"First, I’m pasting many of these from a Google Doc, which is is why these may go up quickly. ",
"In general I think it’s better if research is open rather than closed. Especially for publicly supported studies, there is no obvious reason to restrict the results to affiliates of dues-paying organizations rather than the general public. In many cases it’s difficult even for us to gain access to all relevant articles for a given project; I can only imagine how frustrating it must be for people who aren’t similarly affiliated. In my opinion, the only publicly funded research that should not be made public is that which clearly falls under the definition of “information hazard”: true information that if disseminated can cause harm. Blueprints for nuclear weapons and dangerous viruses certainly qualify. ",
"As for open science, I support going further than open access and changing incentives to encourage pre-registration of research plans in select subfields, because the current system of closeted research is tremendously wasteful: we never learn about studies that don’t pan out, so we often go down the same blind alley. It’s also impossible to know if we’re wasting our time pursuing a project that ten other labs are working on. Better to intelligently decide to collaborate or compete and easily find collaborators. But it’s also unwise to radically change a critical complex system all at once; better to start small, try it out, and scale up if appropriate. So I support public pre-registration of all research plans involving gene drive, and we’ll see how it goes from there.",
"I don’t think this changes the role of scientists; we’ll still be the ones who do this for a living, but I’d welcome help from anyone remotely interested in helping."
] |
[
"How much time will it take for the CMBR to cool to radiowave frequencies? Won't this have an effect on free electron spins?"
] |
[
false
] |
If free electron spin is affected by radiowaves, then won't they be affected by what is at some point a cosmic radiowave background radiation?
|
[
"There isn't really that sharp of a line microwaves and radio waves - the EM spectrum is a continuum. ",
"CMB peaks at 160 GHz, RF generally speaking extends from 300 GHz down to a few kHz. In this sense, the CMB is already 'radio waves.'",
"But maybe if you want to call anything above 3 GHz a microwave, then you'll have to cool the universe by another factor of 50ish. ",
"Let's make a really rough estimate for how long this takes, assuming a constant expansion rate. It took 13 billion years for the universe to expand to its current size, so it will take another 13 billion to double in size, thus cutting the CMB temperature and (frequency) in half. As an approximate rule of the of thumb, this means that every time you double the age you cut the frequency in half. ",
"Since 2",
" ~ 50, then we will need to wait about 5.5 times the current age of the universe for the CMB to shift down by a factor of 50. That's an ~70 billion year wait. Don't hold your breath. "
] |
[
"The energy of an electron spin transition depends on the magnetic field it is in. Most chemical reactions involving unpaired electrons won't be affected much even if there is a strong radio background at the right frequency (for an unpaired electron in Earth's field).",
"Many electron transfer reactions that involve the combination of two radicals are spin selective - the reaction might go faster or slower depending on the spins of the electrons involved. However, the energy difference between these states is extremely small in a weak magnetic field, so except at very low temperatures, you already have nearly equal population of the different spin states.",
"Exciting a transition between these states causes population transfer from the lower-lying state to the higher one (absorption of radio waves) but also transfer from the upper state to the lower one (stimulated emission of radio waves). If this is done long enough (like with some continuous background), these effects will balance each other out and you will have equal population of the states (in the terminology of magnetic resonance, the transition has become \"saturated\"). But this saturated population distribution is very close to the thermal equilibrium state that we started with, so it won't have a significant impact even on a spin-selective reaction.",
"The possible exception to this is for some photochemical reactions in which the initial spin state is not the thermal equilibrium state. One such reaction is thought to be involved in magnetic field sensing by birds, and there is some evidence that RF radiation can affect this process. However, these effects are still weak for most reactions."
] |
[
"The CMB is incredibly faint, it's not going to effect biology. Compared to the radiation from the sun, or the black body spectrum of anything on the earth's surface, the CMB is a tiny bit of noise. "
] |
[
"Can we actually see electrons, or do we just see the air being heated up when we see electricity?"
] |
[
false
] | null |
[
"Whenever you see something, what is happening is that the object is emitting a photon that hits your eye. So if by \"seeing\" the electrons you mean seeing the photons emitted by electrons then yes we do see electrons.",
"However, its worth noting that basically everything you see in your daily life is from photons being emitted by electrons. For instance, how a mirror works is a photon will hit a silver atom and transfer it's energy into one of the valence electrons. However this excited state is unstable and the excited electron will release that extra energy by emitting another photon. So the light that we say is \"reflected\" by a mirror is really just photons being emitted by electrons on the mirror."
] |
[
"Sparks are electrical plasma. If we lived in a Neon gas atmosphere, sparks would be red-orange. The usual violet color of an electric spark is produced by nitrogen and oxygen line-emission.",
"Interesting trivia: a vast number of movable electrons, such as the electron-sea of metals, is an extremely good reflector. So we could say that electrons look like a silvery fluid. In wires, it's the silvery/metallic stuff that flows along during an electric current."
] |
[
"do we just see the air being heated up when we see electricity?",
"I think here you're referring to the plasma arcs created by lightning, a spark, or a tesla coil. In that case what you're seeing is the visible glow of air in its superheated plasma state, where the molecules that make up the air are stripped of their electrons by a very strong electromagnetic field, and begin to flow through the field in their ionic state. They release their extra energy in the form of visible light, as the electrons return to the ions."
] |
[
"A Brotherly Debate 1: How do I explain evolution to my stubborn brother."
] |
[
false
] | null |
[
"http://www.talkorigins.org/faqs/evolution-fact.html",
"is a good source for highlighting the difference between facts and theories if he is hung up on that definition. If he doesn't understand the mechanism of gradual change, I've found this to be a helpful visual aid. ",
"http://4.bp.blogspot.com/-i94qZqIJolY/TcNdIM9emkI/AAAAAAAAALY/8dACHdxg6MM/s1600/the+difference+between+micro+and+macro+evolution.jpg"
] |
[
"I like this one a lot."
] |
[
"If only you knew my brother... this one didn't go over well, because he said playing the piano is a skill that is categorised differently from a physical trait."
] |
[
"When you taste something sweet after eating another sweet thing, the second thing doesn’t taste as sweet. Is that due to the taste receptors themselves not firing as often or is it your brain filtering out the signal?"
] |
[
false
] |
Also when you eat something salty and then other flavors are more intense, is that physiological or psychological?
|
[
"By \"psychological\" I'm assuming you mean further upstream in the sensory pathways.",
"On this timeframe, it's mostly sensory adaptation. Which is physiological. The receptor cells essentially get fatigued and don't respond as strongly to a second stimulus.",
"On a longer timeframe, it would be more psychological. For example, if you eat a lot of salty food for a few weeks, you would habituate to salt. So a salty stimulus would not taste as salty as before your salt binge. I'm not sure you could rule out some contribution from sensory adaptation in this case though. There could well be longer term changes at the receptor level too."
] |
[
"Salt actually does suppress the bitter sensation. So it can make fruit taste sweeter"
] |
[
"Is that why some people roll cucumbers in salt, to suppress the bitterness of the skin?"
] |
[
"How likely is it that we will be able to manipulate/create wormholes for space travel?"
] |
[
false
] |
I feel like it's the only solution to the fact that we can't travel faster than light.
|
[
"There are two ways to solve the Einstein field equation. You can either start with a description of the matter, energy, momentum, fields and so forth over a region of spacetime then solve for the resulting geometry, or you can start with an arbitrary geometry and solve for the stress-energy tensor.",
"Wormholes arise when you do the second thing: start with an arbitrary geometry and interrogate the equation to see what configuration of stress-energy could produce it.",
"In this case, the answer to that question is \"none.\" There is no possible configuration of stress-energy that could lead to a wormhole geometry. Wormhole solutions are interesting mathematically, not physically.",
"In other words, no."
] |
[
"It's not an intents-and-purposes, as-far-as-we-know thing. The answer's just plain "
] |
[
"The universe doesn't give a crap what any of us want."
] |
[
"Why does my biology teacher tell us that the formation of bonds between atoms stores energy and the breaking of them releases it, when my chemistry teacher tells us the opposite?"
] |
[
false
] |
The chemistry teacher just says that the biology teacher is wrong, but there has to be a reason why it's taught.
|
[
"The chemistry teacher is 100% right, and the biology professor is half-right. Regardless of the bond (meaning, an attraction between atomic fragments), breaking it will require an energy expenditure and forming it will release energy. ",
"It is true that you can store energy in the form of high-energy (less stable) bonds, but breaking them doesn't release the energy. The energy release comes from the net chemical reaction that produces ",
", more stable bonds to replace the less stable ones in the starting materials. ",
"Despite being one the most fundamental concepts in chemistry, it is generally not appreciated by people who likely only took general and organic chemistry (which includes most biologists). This tends to propagate the misconception that ATP releases energy when the phosphoester is broken."
] |
[
"Your chemistry teacher is talking about spontaneous chemical reactions. Your biology teacher is talking about the use of metabolic energy to drive reactions \"backwards\" which is done to create high energy bonds as a way of storing energy. Nobody is wrong, and they should certainly know that."
] |
[
"The biology teacher is probably most concerned about how molecules like ",
"ATP",
" are used to store and transport energy around the body. ATP is said to contain ",
"\"high-energy phosphate bonds\"",
", however as the wikipedia article explains, this name can be misleading:",
"The term 'high energy' with respect to these bonds can be misleading because the negative free energy change is not due directly to the breaking of the bonds themselves. The breaking of these bonds, as with the breaking of most bonds, is an endergonic step (i.e., it absorbs energy, not releases it). The negative free energy change comes instead from the fact that the bonds formed after hydrolysis-or the phosphorylation of a residue by ATP-are lower in energy than the bonds present before hydrolysis (this includes all of the bonds involved in the reaction, not just the phosphate bonds themselves). This effect is due to a number of factors including increased resonance stabilization and solvation of the products relative to the reactants.",
"So the chem teacher is right, but in some contexts it can be useful to think of the bonds as storing energy."
] |
[
"Is it possible and practical to create a new form of internet network, that would not require isp providers and so, would be protected from any filtering and censorship, by connecting individual computers directly between each other?"
] |
[
false
] |
This is a very old idea, liberating Internet from censorship and filtering. Around 10 years ago, when I was very fond of programming and computers some guy told me once, that Internet is something that can connect and unite all people. He said that Internet (the way it was back then) is an idea of free communication for everybody, and if Internet is ever to be censored, a new kind of network will evolve. Independent from isp providers, government entities and filters. A network that will interconnect every single computer directly. I think this idea is very actual today. The questions remain: 1) Is it possible to create such a system? 2) Is it practical to create such a system? 3) Is now a good time for such a system?
|
[
"Also ",
"/r/DarknetPlan",
" has a lot more info and is much larger."
] |
[
"After the SOPA incident last year, many people realized that laws like that would eventually pass - and they were right.",
"Therefore, they set out to build a network precisely as you described, by using overlapping wifi networks to send signals from computer to computer. ",
"You can read more at the subreddit for this kind of network, ",
"/r/Meshnet",
" "
] |
[
"Networking Engineer here, yes it's possible, in fact that's what the Internet is: a network of connected devices (sadly, it's not a series of tubes :( )",
"Now, is it practical?",
"Well first you must understand that for example if your machine has a public IP address, if I know it I can reach that machine from ",
" on the network (assuming no security). There are ways to resolve public IPs to say NAT devices (which takes a public IP and \"loans\" it to multiple machines) to make one address represent many machines.",
"Filtering and censorship are merely ways to hide machines that may have questionable content from say a user searching for something. This happens when you referenced a filtered search database, but if you reference one not filtering anything, then those sites will show up. ",
"Finally is it what we need to do? You can set up your own server to provide services to other people already. It's just not feasible because:",
"It costs a lot of money",
"No lunch is ever truly free.",
"People are greedy and tragedy of the commons happens. ",
"Besides, ISPs and IXPs provide over ",
" speeds around the world. You just can't simply replace that speed and potential bandwidth. ",
"Edit: I did this on my phone quickly, if you have any questions, feel free to ask, I'm off to go fuck with some routers."
] |
[
"Why can't spicyness be rinsed off easily?"
] |
[
false
] |
[deleted]
|
[
"It's not soluble in water, but it is soluble in fat. That's why milk works better."
] |
[
"You need a non-polar solvent. ",
"Solvent Classification.",
"A girl I knew as an undergraduate accidentally got some spicy material on her recreational equipment (she went to the loo halfway through me teaching her to make Texas style Chilli).",
"We washed it off with a big 5 litre economy jug of cheapo cooking oil. I'd never imagined that a scenario that involved her naked and me oiling her up could be so profoundly unsexy."
] |
[
"This is exactly why we use this word:",
"http://en.wikipedia.org/wiki/Piquance",
"Piquant vs. \"hot\" and/or \"spicy\"",
"Use of the word \"piquance\" eliminates potential lingual ambiguity arising from overlap in meaning with the words \"hot\" and \"spicy\" which usually requires a determination or assumption of meaning based on context.",
"Instead of \"hot\" simply referring to temperature, and \"spicy\" being used to refer to the presence of spices (many of which are not actually piquant), the former two words are often used as synonyms for the latter, a word less commonly employed in reference to the characteristic which in regards to taste it solely defines, which is pain associated with the sense of taste.",
"For instance, a pumpkin pie can be both hot (out of the oven) and spicy (due to the common inclusion of ingredients in its recipe such as cinnamon, nutmeg, allspice, mace and cloves) but is not actually piquant. Conversely, pure capsaicin is piquant, yet is not naturally accompanied by a hot temperature or spices.",
"Unfortunately, people just don't use it much."
] |
[
"What was the atmosphere like when dinosaurs existed? Could humans have breathed the air?"
] |
[
false
] | null |
[
"There are no direct measures of atmospheric oxygen from that period. There are a few ideas out there about potential ways to determine atmospheric O2 concentration that far back in time. They are: Stomatal density of fossil leaves; stable carbon isotope ratios of soil carbonates (pedogenic carbonate); stable carbon isotope ratios of fossilized amber; and numerical mass balance modeling. There's a pretty decent review of all these ",
"here",
" (Tappert et al., 2013). ",
"The proxy record of oxygen history (with big, big error bars and caveats in mind) is that atmospheric O2 was ~10% (% of the atmosphere, today it is 21%) until 70 million years ago, when it jumped to 15%. Around 50 million years ago it fell rapidly to 10% again, before slowly increasing over the past 50 million years to the present value of ~21%. ",
"The mass balance model indicates that atmospheric O2 began slowly increasing from 10% to modern values about 140 million years ago. So, at the beginning of the Cretaceous, oxygen was 10%, and at the end of the Cretaceous, oxygen would have been close to 15%-17%. I'm not sure what human tolerance for oxygen is (not very scientific google searching revealed 19.5% as the minimum amount for breathing, but I don't know if that's right!).",
"Hope this helps!"
] |
[
"You should link them, I'd love to see them. The 15%-35% number comes from sedimentary charcoal records - this is the oxygen concentration window within which combustion reactions can occur and form charcoal. The idea is that wherever there is charcoal in the sedimentary record, atmospheric O2 must have been between 15 and 35%. The authors of the paper I first cited offer a few criticisms of this idea - mainly that wind could decrease the amount of O2 necessary, and that the charring process of charcoal formation requires low O2, even though combustion requires 15%-35%.",
"Accuracy is in the eye of the beholder on this matter, I think. People who trust in charcoal records, and their subsequent conversion to %O2, calculate 26-30% oxygen during the Cretaceous. People who trust in carbon isotopes in plant matter calculate 10-15%. Some sort of independent verification would be excellent, but right now we don't really have any..."
] |
[
"Is the linked source accurate ? because other sources talk about 15%-35% oxygen during Cretaceous. "
] |
[
"Will humans one day be able to create a robot with ai that is conscious and self aware?"
] |
[
false
] | null |
[
"I've been reading up on articles such as the simulation argument, and wonder if we will get to the point where we will fully understand the workings of the human brain. I've seen plenty of statistics that say in years to come we will have the ability to create computers with greater computing power than the human brain but this says nothing for being self aware or having conscious thought "
] |
[
"I've been reading up on articles such as the simulation argument, and wonder if we will get to the point where we will fully understand the workings of the human brain. I've seen plenty of statistics that say in years to come we will have the ability to create computers with greater computing power than the human brain but this says nothing for being self aware or having conscious thought "
] |
[
"I believe that the answer is yes, assuming civilization does not collapse before then. Humans are just very complicated machines made of organic materials, so I see no reason why we won't be able to build something completely analogous with different materials. "
] |
[
"How are cepheid variable stars different from other stars?"
] |
[
false
] |
[deleted]
|
[
"A Cepheid variable star is a star that changes it's luminosity over certain period of time. This by itself does not make Cepheids different, since stars change their apparent magnitude over the course of their life.",
"However, Cepheid variable stars do this periodically and their period is tied with their absolute magnitude. Thanks to this, we can calculate the distance to the star using distance modulus. Objects that can be used to calculate distance, such as mentioned Cepheid variable stars, are called 'standard candles'. For example, you can calculate the distance to a distant gallaxy using Cepheid variable stars in said gallaxy with good uncertainty."
] |
[
"I'm just going to tack onto this response. While it's true that cepheid variables are among our most accurate distance measures, forming an important rung in the most precise cosmic distance ladder used to infer the Hubble constant from type Ia supernovae, they are still individual stars. This means we're limited by the absolute magnitude of the stars, and angular resolution of our telescopes when observing them. As a result, we can only use cepheids to measure quite nearby distances, not distances to very distant galaxies."
] |
[
"Thank you, indeed, this is true.",
"However, I would just add that supernovae type 1a are currently being revisited, IIRC, and we might end up with conclusion that supernovae 1a are not actually as accurate as we believed they are. So, I would like to hijack this post and ask you if you know about this. I have heard that someone wrote a reseach paper with conclusion that supernovae type 1a might be inaccurate, and if they really are, we could correct this mistake and end up not needing dark matter to explain some phenomena. Do you know something about this? If so, I would be very thankful if you could point me to some reliable articles about this, I would like to expand my knowledge about this, instead of saying \"I heard/someone said\"."
] |
[
"Why does our stomach start to growl when we get hungry?"
] |
[
false
] | null |
[
"Bilology"
] |
[
"Bilology"
] |
[
"The stomach is trying to process food, so it starts to move, but because there is nothing there to process, it'll create those noises. The term is referred to as, \"boborgymi\", IIRC, I'm not sure if I spelled it right, but I believe that's the general explanation in a nutshell. "
] |
[
"Can elastic deformation become plastic with time?"
] |
[
false
] |
For example, if a straight metal bar was deflected so that it was elastically deformed, is there any process that could lead to the bar not returning fully to its original state if it had been left deflected like that for a large period of time? I'm interested in both reasonably common external factors, and internal factors (imagining that the bar was kept in a perfectly controlled environment at standard pressure, temperature, etc).
|
[
"Materials can suffer \"creep\", which is slow plastic deformation over time. Rate of creep is mostly governed by temperature (and stress, of course). Most metals don't show appreciable creep at room temperature, and need to be heated to a significant fraction of their melting temperature before it becomes a problem. Thermoplastic plastics will creep at low temperatures, thermoset and heavily crosslinked rubbers will generally not."
] |
[
"There are many mechanisms that could cause plastic deformations in a material over its elastic deformation range. One is fatigue. Repeated elastic deformations do cause changes at the molecular level that can eventually cause plastic deformations or even gross failures (like cracks).",
"https://en.wikipedia.org/wiki/Deformation_(engineering)#Metal_fatigue"
] |
[
"Yes, and you probably see it all the time in things like shelves around the house. With stronger materials this is less likely to occur but on a microscopic level weak spots in any material may fail fairly regularly. Elastic limits represent an assumed structure with anticipated makeup and microfissures. Constant loadings and fatigue exacerbate imperfections in the structure of the materials and cause the failures you are asking about."
] |
[
"Why is cancer dangerous? Whats the problem with having uncontrolled division of cells? How does that pose a problem?"
] |
[
false
] | null |
[
"It depends on the organ and location of cancer. Keep in mind \"cancer\" is not a single disease but many different kinds, with different mortality rates. The danger can be from mechanical compression, metabolic changes, or combination of both. ",
"Brain cancer, for example, expands in a confined space, and will cause increased intracranial pressure. Compression on other parts of the brain can cause neurological, neuromuscular changes.",
"Leukemia is a cancer of white blood cells where immature and non-functioning white blood cells proliferate and crowd out the bone marrow. The person becomes susceptible to infections due to lack of functioning immune cells. Because red blood cell and platelet productions are also affected, there will be anemia, bruising/bleeding as well.",
"Liver cancer causes a whole slew of metabolic issues because of the many important functions of normal liver in our body. Normal liver metabolizes chemicals (we often say it \"detoxifies\"), produces proteins that help blood clot, produces bile that helps digestion of fat, and stores glycogen for regulating blood sugar level. As cancer progresses, all these functions are lost.",
"If cancer is advanced and metastasis occurs where cancer cells break off from original location and seed in distant organs, now you have multiple non-functioning organs."
] |
[
"In addition to this, cancers can produce their own chemicals. Rogue hormone producing cells can signal the body to do things it wouldn’t otherwise do, as other cells in the body can’t differentiate between legitimately produced hormones and rogue cells. Cancer cells can also produce various toxins which can have a wide range of impacts on the body."
] |
[
"Always worth remembering that tumours are physical objects; as they grow they can invade tissues or occlude vessels, like the trachea, bronchi, bile duct, blood vessels, anything really. ",
"If you've got a mass growing somewhere it shouldn't, it can push on bodily structures and impair the function. If it does it enough, things can get bad.",
"Also, remember that malignant tumours metastasise - this means bit break off a travel elsewhere in the body, creating secondary cancers. If there's enough of this occurring, the problems mentioned are amplified and outlook plummets."
] |
[
"Why do we believe that a planet needs to have water for aliens to survive?"
] |
[
false
] |
I know this might sound a bit crazy but. Why is it that we are always looking for water or oxygen? Surely there must be a way for an organism to live without these two blocks and they may be able to substitute for them. I don't understand the saying "without water there is no life on other planets" Getting PMs that are saying only ignorant people say this well reddit your hero says it as well : What renders a planet, indeed, suitable for life? Well, clearly, you want a planet that has some water on it, because water is the cocktail mixer that allows the chemistry of our bodies to even work. : If we want a planet with liquid water, then it can't be too close to its star; that would make it too hot, and the water would boil away. And it shouldn't be too far away, either; too cold, and you'll likely get an ice ball.What everybody really wants to find is a little rocky planet, whose distance from its star is juuust right, a "Goldilocks" planet with oceans of liquid water. But hunting down a planet just like ours has been a daunting task. In fact, not long ago, we hadn't found any planets beyond our solar system, none at all. They're so far away and so dim, they get lost in the glare of their own suns, the stars they orbit. Source :
|
[
"We don't believe that a planet needs to have water for aliens to survive. We do know that all lifeforms we have ever encountered need water to survive. We therefore (with only one piece of data) look for what we know.",
"Say, as an analogy, you found an unlabeled cardboard box on the street and somebody told you that there was at least one apple in it. Would you guess that the box contained mostly apples or at least mostly fruit or foodstuff, or would you guess that the box contained lightbulbs or pencils or ",
" and someone just happened to drop an apple in? This is why we look for apples and things like apples (i.e. water) instead of looking for something we don't even know what it looks like."
] |
[
"Water has multiple advantages that are beneficial to the formation of life. ",
"One is its very high specific heat capacity, it needs a lot of energy to change it's aggregate state. This helps because it allows water to remain fluid while solved molecules are provided with the energy needed to react. Its boiling point is much higher than that of methane and other alcanes and it has a generelly large range of fluidity.",
"Another is it's polarity and the fact that it builds hydrate hulls. That and another very important phenomenon, osmosis, allow the most basic principles of life to work.",
"Water is not always needed for photosynthesis, though, as bacteria such as ",
"http://en.wikipedia.org/wiki/Purple_bacteria",
" show. They can live without either water or oxygen supply.",
"(I'm no native english speaker so please excuse the simplicity of the comment and I might have gotten some terminology wrong)"
] |
[
"Water may not be absolutely necessary, but it's good choice. You need complex chemistry to have life and if you need solution where the reactions should take place, water is very good neutral candidate. Other possible solvents that are sometimes considered are: ammonia, methane, methanol, hydrogen fluoride, hydrogen sulfide, hydrogen chloride. ",
"The temperature range where solvent is liquid is also important. For example, if you have life where methane is solvent, that usually means very slow reactions. Possible evolution might happen in very slow pace and not progress very far. On the other hand, you might need to mix water with something like hydrogen peroxide to have liquid solvent at all in very cold planets like Mars. ",
"It is theoretically possible to have organic chemistry where oxygen is replaced with chlorine, but it's unlikely because chlorine is not so abundant and it would easily be end up being part of salts. ",
"I think wast amounts of free oxygen in planet is not possible without life, so it might be reason why we look oxygen. Its sign that interesting chemical reactions are going on. ",
"I'm not chemist, and this is essentially chemistry question. So I might e wrong on everything. "
] |
[
"Do plug-in electric vehicles have a smaller carbon footprint than hybrid vehicles?"
] |
[
false
] | null |
[
"Except that burning fossil fuels at one large, efficient plant generates less carbon than burning fossil fuels in many small, inefficient plants. "
] |
[
"You open up a whole can of worms with that. Imagine the variables, where the oil was extracted (tarsands, middle east, offshore) vs the coal (cost of human life(s), mountaintops, surface mining). The impact of refining and transporting oil while coal is more domestic. You could go on and on but I just can't answer those questions...",
"I was just trying to answer the question which creates the smallest carbon foot print; burning petrol or getting electricity from the socket (which probably comes from coal). "
] |
[
"That depends on where you're getting your home power from. If you're local power comes from fossil fuels then I can't say for sure whether a hybrid or an electric would have a smaller footprint. If the power in your home comes from a renewable source then of course the plug-in will have less of a footprint. ",
"I hope to one day install enough solar panels in my home (I live in Florida) to be able to run my household solely off solar power and then not only would I not have to pay a power bill, but if I also invested in an electric car I would never have to pay for gas either. "
] |
[
"If temperature is the average speed of particles, why is there \"wind chill\" and not \"wind warmth\"?"
] |
[
false
] |
Forgive my ignorance, but I would think that if it were windy, that would mean that you would be feeling particles hitting you at a much faster average speed than if there were no wind. So why does it actually feel colder, instead of warmer? And does this effect only apply to air that's already cold? If hot enough air blows at you, will it feel warmer than it would if it were stationary, for instance?
|
[
"From a ",
"previous post",
":",
"When it's windy, it feels colder because normally in still air your body will heat up air that is semi-trapped around your skin; the more the air heats up, the less heat you are losing and the warmer you feel.",
"When it's windy, the air doesn't linger around your skin, and is constantly replaced by cool air. Therefore, you are always losing heat and do not manage to warm the air up.",
"Also, there might be an effect of greater evaporative cooling; most quickly moving air would prevent a local saturation of water vapor and allow you to lose more heat through increased evaporative cooling."
] |
[
"At room temperature, the average speed of molecules of air is ",
"993 miless per hour",
", so wind speed has very little effect on the temperature of the air.",
"Wind chill is caused by the evaporation of water from the skin, which is increased when a breeze blows on it and decreased when the air is humid."
] |
[
"Check ",
"this",
" out."
] |
[
"Scientists of reddit! Settle a bet for me. What affects the temperature of the seasons if it's not the tilt of the earth on its axis?"
] |
[
false
] |
Cross post from askreddit, wasn't sure where I should put this. At stake in this bet: the very usefulness of Reddit. My friend thinks we are all sexless geeks. Prove him wrong by showing him how geeky you are! Whoever answers this question first (he's asking books, pshh) wins. Here's what I think I understand: The tilt of the earth on its axis of rotation makes the seasons, because of the angle at which sunlight hits the planet's surface. So the less sunlight the earth gets (shorter daylight duration + the more acute the angle at which it hits the earth's surface), the colder it is, right? But here's my question: The shortest day of the year, the winter solstice, comes in early December. It begins the winter season. If the thing I said above about sunlight were true, the winter solstice would come smack dab in the middle of winter--the coldest day, the least sunlight. So what is it that makes winter last until March, getting progressively colder until then, if the earth is getting progressively more sunlight during that time. Residual cold in the oceans? Please someone explain to me!
|
[
"Check out what's called ",
" for the answer to your question. In a nutshell, it's the oceans and the rate at which heat radiates away versus stays."
] |
[
"the earth's eccentricity is very minute.",
"from wikipedia\n",
"http://en.wikipedia.org/wiki/Season",
"\n\"Compared to axial tilt, other factors contribute little to seasonal temperature changes. The seasons are not the result of the variation in Earth’s distance to the sun because of its elliptical orbit.[2] Orbital eccentricity can influence temperatures, but on Earth, this effect is small and is more than counteracted by other factors; research shows that the Earth as a whole is actually slightly warmer when farther from the sun. This is because the northern hemisphere has more land than the southern, and land warms more readily than sea.[3] Mars however experiences wide temperature variations and violent dust storms every year at perihelion.[4]\""
] |
[
"All orbits are elliptical.",
"If you look really closely there are deviations from that, but elliptical is the general form."
] |
[
"Do space launches account for the flight path of existing satellites?"
] |
[
false
] |
As more satellites are launched into space I would imagine that there is an increased risk for collisions. Is there a map of current satellites as well as space junk?
|
[
"To an extent yes. As for a map of space debris, this is publicly available at ",
"https://celestrak.com/",
". Celestrak publishes the ",
"Two Line Element sets",
" for everything that is observable to the ground (with only a few items missing such as a handful of spy satellites I believe). These TLEs give you the data needed to figure out where an object is at any point in time. They're only accurate for a short time though, and so the catalog is updated regularly (really anytime an object is observed). This can be every few hours for especially big things like the ISS, but may be days and sometimes weeks for new smaller objects."
] |
[
"Yes, mission planners and FAA know the orbits of all active satellites and keep track of dead ones and debris. When putting up new satellites, orbital altitude is set so that two objects don't cross paths (never guaranteed, but they get the probability really low).",
"If a close approach is detected, one or both spacecraft may perform an avoidance maneuver. ",
"Or they might make the wrong bet and collide",
" which has thankfully only happened once between two satellites (debris strikes still happen).",
"As for the launching part- if you're sending a rocket up to a higher orbit, I'm sure they do check to make sure the launch trajectory won't cross paths with any spacecraft, but passing through lower altitudes quickly, plus the fact that space is huge, means that getting hit on your way up like you see in WALL•E is effectively impossible.",
"tl;dr smart people do watch out for speedy space metal"
] |
[
"Then you end up with a ",
"huge cloud of orbital debris",
" that will cause problems ",
"for decades to come."
] |
[
"Are the effects of different carcinogens/mutagens cumulative?"
] |
[
false
] |
I joke with people that I'm not overly cautious about lab safety (e.g. I don't freak out if I spill a drop of benzene on myself, though I do wash it off immediately) because I smoke cigarettes, so it's not going to be the benzene that kills me. Is that actually true, or are the effects cumulative/additive, assuming it's the same tissue (e.g. inhaling residual benzene fumes & cigarette smoke)? Does it depend on the type of DNA damage (like oxidative vs UV, and/or deletions/insertions vs DSBs)? Or does that not matter, because all of them can result in changes that can result in cancer?
|
[
"Cancer is extremely complex. It is characterized by a number of different changes within the cell such as self-sufficiency of growth factors, evades apoptotic signals, immortality, able to metastasize, etc. Each of these characteristics are controlled by large pathways, and dozens of proteins. Therefore, there are a number of changes that have to occur for a cell to become cancerous.",
"A single mutation is very unlikely to do this. For the most part, mutations tend to fall into either being silent or missense (change in amino acid of the protein product). These generally do not have a huge impact on the protein product (missense can, but it really depends on how different the new amino acid is from the original, and where the mutation occurred within the protein). Therefore, cells generally don't even notice these changes. Although, nonsense or frameshift mutations (which can occur from 1 nucleotide changes) can cause huge problems for a protein such as producing truncated/inactive forms, or overly long proteins due to the loss of stop codons from frameshifts. Even then, this is only one gene product that has been grossly changed. This isn't enough to push cells into a cancerous state, but definitely makes them a little more sensitive to it."
] |
[
"Cancer cannot occur from a single nucleotide mutation but requires at least 3 modified nucleotides, although some estimates are higher. The type of mutation is very important but in general the effects are cumulative. The only exceptions are when either the damage is repaired or the effect induces apoptosis or necrosis, killing the cell. It's important to recognize that the danger of carcinogens lies with their ability to exceed the bodies natural ability to repair genetic damage. Iirc, your dna is mutated over 10",
" times a second (thats for nonsmoking, nonchemists)"
] |
[
"What's the underlying principle that means cancer can't occur from a single nucleotide mutation? "
] |
[
"This article seems highly sensationalized. It's about using quantum computing to break complex encryptions. Is this actually any threat?"
] |
[
false
] | null |
[
"No. It is true that quantum computers can do prime factorization in polynomial time (\"quick\"), ",
"something we have known since 1994",
". However, we are nowhere near building a quantum computer powerful enough to do this.",
"There are other cryptographic systems which are not easily broken by a quantum computer and research is being done into new systems which are resistant to quantum computers. Cryptography would evolve, like it has been doing for centuries. For more information see the wikipedia article on ",
"Post-quantum cryptography",
".",
"The only thing that would treaten crypthography as a whole would be a ",
"proof that P= NP",
". "
] |
[
"Even then there are techniques based on physical properties of circuits that could be used to encrypt data.",
"And bear in mind that P doesn't mean it's fast. If there an algorithm requires N",
" to break and N to use, it is practically secure even if it's in P."
] |
[
"In general, if you cite NaturalNews on any matter whatsoever, you are almost certainly wrong."
] |
[
"What would happen if every mosquito on earth dropped dead right now?"
] |
[
false
] |
This includes every mosquito egg, larva, etc from every mosquito species.
|
[
"Depends on the region you are considering. In the arctic, which has very low species richness, you would have removed one of the key links in the very short food chain. Migratory song birds which feed of the adults would go hungry and probably fail to breed. Char and lake trout who feed off the larvae and nymphs would loose their main food source. These effects would then work up and down the food chain.",
"INB4 \"blackflies will take up that niche\": Blackfly larvae could not substitute for mosquito as they live in biofilms on rocks in springs with strong current. Mosquito larvae colonize small stagnant pools and lakes and ponds with low currents. very different conditions."
] |
[
"Mosquito disappearance might have negative impacts of short term (several years) macroinvertebrate species richness but would more than likely be overcome by increases in other benthic Dipteran populations that inhabit similar environments. Behavior change would occur with predators who primarily fed on mosquitoes and focus more on midge larvae or other similar larvae. There is some evidence showing that in areas with high midge populations there are lower amounts of mosquito species that would inhabit similar environments. A new field of study is also the effects of microorganism diversity on the species composition - which is suggesting that mosquito larvae affect the diversity of microorganisms and that negatively or positively effect other insect populations. ",
"Another aspect is that we would have incredibly low amounts of mosquitoborne disease. The amount of cases of Dengue infection each year is around 500 million worldwide. Malaria is around 190 million incidence, and then we can think about all the other diseases like: yellow fever, West Nile, La Crosse virus, Eastern Equine, Venezuelan Equine, Rift valley, Japanese encephalitis, and the list goes on. Mosquitoes have one of the greatest impacts on public health and are direct drivers of selection."
] |
[
"Can you provide some sources on migratory song bird feeding behavior in the arctic? The last I've read about their feeding behavior is that it is mostly comprised of Tipulidae and/or larger insects. Also, please show any evidence for fish feeding on mosquito hatches. Many mosquitoes in arctic regions hatch out in floodpools from snow melt. Permanent water species that are near lakes are not going to be in areas with heavy fish activity. Mosquitoes do not routintely oviposit in areas with large amounts of predators, they can sense their presence with special organs on the ends of their front tarsomeres. The primary predators on mosquitoes are other insects not vertebrates. Dragonflies, scorpionflies, diving beetles, and almost any other predacious immature insect is a predator of mosquitoes. Adult dragonflies are predators of adult mosquitoes, this was specifically documented by Edman & Haeger in 1972. Mosquitoes are not a large source of energy to large animals (relative to the mosquito) and the energy expenditure is typically more than the energy gained."
] |
[
"If there's no up or down in space, do other planets rotate horizontally compared to earth?"
] |
[
false
] |
[deleted]
|
[
"There's no \"east pole\" because of the way \"north\" is defined. North is the direction around which you rotate counterclockwise. Always. The angle between a planet's north pole and the solar system's north pole is called the ",
", or axial tilt",
". It's surprisingly easy, over the long term, to tilt a planet's axis via precession and external torques: even a small perturbation, repeated in-phase every orbit, can add to a very large change in angular momentum over time. Famously, Uranus has near 90° obliquity (like what you're thinking), and Venus actually goes the other way -- its north pole is actually pointing toward Ecliptic south, i.e. it rotates retrograde.",
"In fact, the surprise with the Earth is that its obliquity is so ",
" (i.e. it is so well aligned with the solar system). It turns out that having a large, close moon (as we do) helps with that a lot. Most of the angular momentum in the Earth-Moon system is stored in the Moon's orbit, and the Moon's orbit is closely coupled to the Earth's spin axis. This has prevented Earth's obliquity from changing as much as it otherwise might."
] |
[
"Uranus' rotational axis is pretty much at 90 degrees to everything else (more than, in fact)."
] |
[
"All of the solar system (sun, planets, moons, astroids, etc) came from the same starting material (a protosolar nebula) , and that material shared angular momentum.",
"Because of that, you find that pretty much everything in the solar system is more or less on the same plane, rotating together. There are of course variations. ",
"You ask if they \"could\" rotate perpendicularly, and of course they could, there is nothing stoping it."
] |
[
"Why is Hawking Radiation limited to black holes?"
] |
[
false
] |
[deleted]
|
[
"Because it's crucial that there be an ",
" - a surface inside which light can't escape. No horizon, no Hawking radiation. The usual picture (it's not perfect, but it's a nice analogy) is that Hawking radiation happens when a pair of virtual particles pops up near the horizon. These virtual particles are constantly coming into existence, everywhere, all the time, but normally they annihilate back into nothing before we ever notice the difference (their existence does have some observable consequences, like the ",
"Casimir effect",
").",
"Near the event horizon, though, one of the virtual particles can fall into the black hole, leaving the other one to escape out and become a real particle. It's these escaped virtual particles which we see as Hawking radiation.",
"Now, you can have horizons without having a black hole. Our Universe has a horizon (the furthest distance we can communicate), and that has associated \"Hawking radiation\" (although it's miniscule). This is also thought to have been true in the very early Universe, when the \"Hawking radiation\" produced was ",
"imprinted",
") as fluctuations in the matter density of the Universe. Incredibly, the predictions of this theory agree very well with the observed structure in the Universe, suggesting that this \"Hawking radiation\" was the seed for all of the galaxies and clusters that we see today.",
"Moreover, any accelerating observer will have a local horizon, effectively due to some things not being able to catch up with them, and so any accelerating observer ",
" sees a bath of radiation, even when an observer at rest (or in constant motion) doesn't see anything! ",
"This effect",
" is very closely related to the Hawking radiation as seen by observers close to the black hole's horizon."
] |
[
"It's more that the event horizon doesn't allow the virtual particles to get back out, and annihilate with their partners. This produces a single well-defined boundary - the event horizon - from which Hawking radiation is emitted.",
"In the case of a very strong gravitational field that's not a black hole, there are at least two key differences:",
"We're talking about photons, which travel at the speed of light - a very strong gravitational field doesn't affect them as much as it affects matter. Anything short of an event horizon won't produce the same effect. Keep in mind that the particle description is just a high-level model, that's not perfect; a better description would be in terms of fluctuations of a field. Particles in the everyday sense of a localized point-like entity don't really come into it, and as a result the behavior isn't quite what you might expect if it were a pair of point-like particles.",
"Even if some small number of virtual particles do become separated as a result of a very strong gravitational field, there's no single boundary where this would happen, so you wouldn't get the effect of radiation from a single boundary, as with an event horizon."
] |
[
"It's more that the event horizon doesn't allow the virtual particles to get back out, and annihilate with their partners. This produces a single well-defined boundary - the event horizon - from which Hawking radiation is emitted.",
"In the case of a very strong gravitational field that's not a black hole, there are at least two key differences:",
"We're talking about photons, which travel at the speed of light - a very strong gravitational field doesn't affect them as much as it affects matter. Anything short of an event horizon won't produce the same effect. Keep in mind that the particle description is just a high-level model, that's not perfect; a better description would be in terms of fluctuations of a field. Particles in the everyday sense of a localized point-like entity don't really come into it, and as a result the behavior isn't quite what you might expect if it were a pair of point-like particles.",
"Even if some small number of virtual particles do become separated as a result of a very strong gravitational field, there's no single boundary where this would happen, so you wouldn't get the effect of radiation from a single boundary, as with an event horizon."
] |
[
"How come our muscles get tired even when no work is being done?"
] |
[
false
] |
If for example there was a large heavy rock rolling down a hill, and someone were to hold it in equilibrium, afaik no work would be done in the act of just holding the rock in position. But something like that would still obviously cause the person's muscles to become fatigued. What's going on?
|
[
"If we were a solid object we wouldn't be doing work, but the human body is made to be able to move. We could have been made like robots who could \"lock into position\" and so not do work when holding stationary, but the evolutionary solutions is muscles that contract, so that even if we are not moving on a large scale, on a microscopic scale work is being done, as chemical energy is converted to microscopic movement against a force, which is then ultimately converted into heat. Some of the chemical energy is converted to muscle tension (mechanical potential energy) but ultimately as that tension is released during muscle relaxation work is done on a microscopic scale as atoms move small distances against forces. "
] |
[
"Even a robot locking in position may need to exert some power to keep part of the robot in position.",
"A human standing still will still need to maintain some muscle tension as most joints have muscles on both sides. Eg the lower arm is lifted with the biceps and moved back with the triceps. It's near impossible to let it hang without any tension in both muscles.",
"And muscles also help in maintaining body temperature. So even if you are not doing anything, if it's cold your arm muscles will contract to restrict blood flow in the arm to limit cooling of blood.",
"So unless you are in a coma you will \"use\" your muscles."
] |
[
"Yep. I've worked with all kinds of motors and power transmission. If it's direct-drive or low reduction, you'll need a motor brake or some external braking system, otherwise it will generally freely move. An outside force which meets with a braked system will be stopped unless there's enough energy there to overcome the braking, in which case the brake will resist the change in motion by friction (converting the energy of movement into heat). With stepper motors and such, there is a constant energy supplied when in position to maintain that position and an outside force needs only overcome the electromagnetic force making the stepper stay next to the coil energized to make it move. Usually the types that ",
" require something still locking it into place are drives with a very high reduction, and even those sometimes only get away with it by utilizing the properties of things like worm gear drives to achieve that. Even seen a pretty clever system on a drive using linear actuators, where the vertical axis has a pneumatic cylinder calibrated to take most of the weight of the moving assembly, so that the assembly is nearly \"weightless\" to the actuator.",
"As for OP imagine it like this. Imagine only, because doing this in real life can damage your transmission in your car. But let's say you stop on an uphill grade. If you let off the brake in an automatic transmission car, it may start rolling backward slowly. This can be considered to be like muscles at true rest. Now push the pedal just a little bit and the car comes to a standstill, but does not start moving forward. This is the holding a boulder exactly in place, but it is taking more fuel (energy) than just letting it roll. Now push the gas more and here is your physical exertion to push the boulder back up the hill."
] |
[
"Theoretically, could a person's head or brain be kept alive and conscious separated from the body?"
] |
[
false
] | null |
[
"It's never been done with humans, but monkeys, dogs, and rats have had their heads severed from their bodies and kept alive. (",
"source",
")."
] |
[
" the whole brain could be kept alive without even the head, which is why philosophical arguments like \"brain in a vat\" do not violate any scientific principles (note that it's still not science, since it's not falsifiable). The point is that we can already replace real stimuli with electrical impulses to the same effect, so functionality will remain in tact.",
"Support systems for the brain in this case would be a major non-trivial engineering/medical feat, so this is not currently possible; but theoretically... sure. You may find some interest in the head transplant experiments that occurred decades ago. Monkey heads were swapped.. the monkey lived for minutes, if I recall. But there's a ",
"video",
" available on the experiment (have fun with that)."
] |
[
"Artificial lungs are in animal testing stages, and artificial hearts already exist!"
] |
[
"What was the Vacuum Catastrophe and what is vacuum energy density?"
] |
[
false
] |
[deleted]
|
[
"This is a bit of a handwavy argument in Cosmology and Particle Physics, which says that from quantum field theory, we expect the energy density (basically what it sounds like: how much energy you have per cubic meter of space, or some other preferred unit) of the vacuum to either just be zero, which intuitively makes sense OR 10",
" kilograms per cubic meter (having converted energy to mass). This is from trying to somewhat arbitrarily sum over all of the energy states of the vacuum, but saying the vacuum can't have wavelengths smaller than the Planck length. ",
"On the other hand, from measuring things like Supernovae distances, from which we are able to calculate the acceleration of the expansion of the universe, we calculate that the driving force of this accelerated expansion must be something like a vacuum energy, with a mass density of 10",
" kilograms per cubic meter. Notice that this is 10",
" times smaller than what we expected. This is a crazy big number and if you accept this argument, it's pretty catastrophic.",
"P.S.: The reason why we think that the accelerated expansion is caused by something like a vacuum energy is because if you do the calculations of General Relativity, it turns out that the substance causing the acceleration must have a constant density as the universe expands. Now this can happen if more and more of this stuff is constantly generated (which I believe would violate a lot of laws) or it is intrinsic to space itself. Like vacuum.",
"P.P.S.: I didn't calculate the numbers above, I found them on ",
"this page",
", which happens to also explain this answer much better!",
"P.P.P.S.: I find this stuff very very complicated, I've tried summarising the gist, so my explanation is definitely not exhaustive and infinitely precise."
] |
[
"It's funny, I just got to the office now and a colleague of mine pointed out ",
"a paper",
" that came out today by a guy who has a seemingly really nice and common-sensical solution. The solution he suggests is that basically only very large wavelength modes have an effect on gravity, so we're doing this calculation a bit wrong and the predicted energy density comes out much smaller.",
"Going to read the full paper now, to see if the calculations make sense. If somebody cares I can come back and tell you what I think!"
] |
[
"This paper is a fully scientific paper, aimed at experts, so don't feel bad if you find it difficult! To be honest, some of the stuff is going over my head too. Luckily my colleague knows this stuff really well."
] |
[
"Is there a limit to calorie intake in a period of time?"
] |
[
false
] |
Does the body have a limit of calories in can store from food consumed in a certain amount of time? What I mean is, if I eat within 1 hour say 50,000 worth of calories (say I'm eating high calorie nuts like cashews and pecans). After some time the food is digested and removed from my body. During this period, did my body intake 50,000 worth of calories? Is there a limit? is it dependent or something else?
|
[
"If you were to consume 50,000 calories, the densest form you could eat it would be pure fat, which would be roughly 12 pounds of pure fat (9 calories per gram of fat). Your body would likely slow down your speed of motility of the fat from your stomach to your intestine so that there would be enough time for it to all be absorbed. If your body could slow down the rate enough, you would absorb all 50,000 calories of fat and likely store it (minus the calories it took to digest the fat). If your body cant slow down the rate of emptying enough, you would overwhelm the enzymes, and bile salts that emulsify and break down the fat, and some would just pass through into your colon. This second option is much more likely as you can have a greasy stool with a much lower amount of eaten fat. Also eating 12 pounds of fat in one sitting would be near impossible. "
] |
[
"This.",
"You'll just have to sit on the toilet for a ",
" long period of time if you do eat that. Unless your stomach is the most powerful stomach in the world, then you'd be storing all of it."
] |
[
"All animals have a maximum rate that they can sustainably absorb energy from food. For human endurance athletes, ",
"http://jeb.biologists.org/content/204/18/3183.full.pdf",
" says that the physical activity level (PAL) maxes out at about 4-5. PAL is defined as \"average daily metabolic rate as a multiple of basal\nmetabolic rate.\" To see what is the basal metabolic rate, see ",
"http://en.wikipedia.org/wiki/Basal_metabolic_rate",
" . ",
"This is not the limit of how much energy a human can use for physical activity. It is the limit at which the body can absorb energy from food. It is possible to exercise enough that your body can't replace all the calories that you burn, no matter how much you eat."
] |
[
"How do we know there was a single common fish ancestor that got out of the water, and not several?"
] |
[
false
] |
How do we know it was just one, and not several of them in different situations? That would explain the different evolutional trees occurring.
|
[
"The premise isn't necessarily that we're descended from one single \"Fish\", but rather that we all evolved from one single \"Something\" at some point.",
"We can look at shared features and shared DNA that carries from one ancestor to the next and we can measure the differences within and between groups.",
"So we can see these points in time where a major split occurs: One family grew \"lungs\" and one or more did not. So we can see the ancestors of the ones that didn't and the one that did and compare similarities up until that split point.",
"If your question is more \"How do we know that two similar species didn't evolve separately, then interbreed\", the answer is: We don't. ",
"In fact, recently we think cross-species mating and interspecies hybrids were a lot more common than early Darwin theory would suggest - Homo sapiens, for example, have a not insignificant quantity of Neanderthal DNA in their lineage."
] |
[
"Well lots of fish come out of the water, you've got mudskippers and walking catfish for example. And there probably were multiple fish coming out onto land going way back to the first land vertebrates. ",
"But we know that, eg, birds, mammals, amphibians, and reptiles didn't all come from separate colonizations of the land. For everything but amphibians, it's quite clear all form a single group called \"amniotes\" which have a unique egg structure with layers of membranes which allows the egg to avoid drying out on land. ",
"Amphibians are the odd group out, but even they are quite clearly a part of a larger group including amniotes, an share a number of features in the limbs and skull. ",
"On top of that, genetic evidence unites all these animals as more closely related to each other than to any living fish. ",
"So I guess the answer is that there ",
" really any different trees, instead all the land vertebrates show strong evidence of being on the same tree, and that's ",
" people think there's a single ancestor. If there were separate trees that needed explaining, people would think there were multiple ones."
] |
[
"we don't know that it was only one. There's a number of fossils of things that are intermediate between a totally aquatic fish and a 4-legged amphibian. A lot of the time, we only have a few specimens here and there, and we connect the dots beteeen them to make a single trail. But, some are from the same time as each other - so it couldn't have been one single species evolving in a line. So, it's probably more accurate to say that a group of related fish species evolved steadily onto land. What we DON'T see evidence of two totally unrelated lineages evolving onto land in two different ways.",
"Think about human evolution - you could say that only one species, Australopithecus afarensis, evolved into one species, Homo sapiens, but there were lots of hominid species that branched out and tried different things."
] |
[
"Does it take more energy to heat a house/apt by turning the thermostat off when you leave, or just turning it down slightly."
] |
[
false
] |
If it is better to turn the thermostat down slightly, then how much? In both cases, how come? Does the size or layout have an effect?
|
[
"The purpose of the furnace is to replace heat lost through the walls and roof of the house. The rate of heat loss is proportional to the conductivity of the wall material, the area of wall, and the temperature difference. ",
"The first two of those you can do nothing about, but the smaller the temperature difference between inside and outside, the less heat will be lost. ",
"Thus it is always more energy efficient to turn the thermostat all the way down. Although it might not be as comfortable when you get home. "
] |
[
"Agreed, and as a cautionary note, if you live in a cold climate and turn the heat down too low, you risk water freezing in the pipes and bursting them."
] |
[
"You could imagine that there could be some set of temperatures (rather than 55, 60, and 68) where it's more efficient to keep the heat higher.",
"There is no circumstance in which it is more efficient to keep the heat higher. The higher the temperature, the more heat is lost. The purpose of the furnace is to replace lost heat. It's that simple. Keeping the thermostat at 65 instead of 50, for instance, requires the furnace to cycle more frequently during the day, which ALWAYS requires more energy than allowing the temp down to 50, and then pumping it back up to 70 when you get home--- because the house was losing heat at a more rapid rate at 65 than it was at 50."
] |
[
"Antibiotic Resistance - how does that work on the individual level?"
] |
[
false
] |
To simplify my question, I always tried not to take antibiotics (or general medicinal drugs for that matter) unless I have to, under the notion that if i ever do need to take antibiotics, it will have a stronger effect on me, possibly helping me overcome health problems that would otherwise take longer to cure. So my question is, does avoiding antibiotics (or similar drugs) until absolutely necessary the smart thing to do? or should I just take them anyway whenever there is a slight need, since it actually doesn't matter?
|
[
"You should take antibiotics only when prescribed by a doctor, but when prescribed, take the entire course as directed. ",
"You seem to have a common misconception - you don't become resistant to antibiotics, the bacteria that are infecting do. If you don't take them as directed, the chances of ",
" becoming resistant are higher, and that means it will become harder to treat. Likewise, using antibiotics when they're not indicated can drive resistance in other bacteria that get increased exposure. Again, follow your doctor's directions.",
"You might want to read this recent piece about the misconception about antibiotic resistance:",
"http://www.theatlantic.com/science/archive/2015/11/people-are-really-confused-about-antibiotic-resistant-infections/416118/"
] |
[
"On an individual level it is always better to take the antibiotics (if we only look at resistence). Its only bad for the population. However, since everyone is part of the population it will have also an effect on the individuals of this population. \nAntibiotic resistance (mostly) do not effect pathogenicity, therefore it doesn't matter on an individual level. \nWhy you need to take antibiotics 10 days? Antibiotic resistance is mostly not 100%. So the growth rate is still reduced. So if you take antibiotics and a few bacteria cells get resistant they need longer to grow to a critical mass. So why 10 days? Because after a week your immunsytem kicks in and kills the remaining bacteria no matter if they are resistant or not. \nThe chance that you develope a multi resitant commensal bacteria by yourself due to antibiotica use is very low, while the chance to aquire such a bacteria from someone else in a hospital is very high."
] |
[
"Thank you, that is pretty much what I was wondering but could not phrase correctly myself. that clears that up for me!"
] |
[
"If all substances try to move towards the most stable state, why do we have substances that are not stable in the first place?"
] |
[
false
] | null |
[
"Some substances can be trapped in what is known as a \"kinetically bound state\". It's an energy state that isn't the lowest, but the substance stays there anyway. There is always an energetic cost to convert from one state to another, and sometimes it is just too high for it to happen.",
"Diamonds are an example. Given enough time, they will spontaneously become lumps of coal, which has carbon atoms arranged in a lower energy configuration. But to do this, you will need to completely change the bonding of the carbon atoms involved -- and in this situation it is extremely hard to do.",
"Is this helpful?"
] |
[
"Imagine a slope on the side of a mountain that is perfectly smooth. You put a ball on it. What happens? It'll roll down the hill.",
"The top of the mountain represents the high energy state, the bottom represents the low energy. Remember that high energy = least stable, and low energy = most stable. As we can see here, if we put the ball at a high energy state, it'll naturally want to fall to get to a lower energy state.",
"Now imagine that the mountain slopes down, but about halfway down the mountain, it slopes back up again, creating a sort of well or dip on the mountain side, and then it slopes back down. So now when we roll the ball down the mountain, it'll get stuck in that dip. So while the ball, if allowed, would prefer to be in that lowest energy state (the base of the mountain), it's stuck at a middle energy state (in the middle of the mountain).",
"Now, you can add a bit energy to the ball by pushing it, which can knock it out of the dip, so that it comes back down to the bottom of the mountain.",
"This is how chemistry and physics work. While there's almost always a lower energy state that a molecule or particle can be in, it's usually \"stuck\" in these energy states because there are these dips in their energy diagrams. You can usually knock these systems down by putting a bit of energy into them.",
"One example is wood. As you know, if you light a match to a piece of wood, the wood will light aflame until it becomes ash. In this case, the unburnt wood is the high energy state, and the ash is the lower energy state. The reason the wood doesn't just naturally turn into ash is because its stuck in an energy dip. You can knock it out of that energy dip by using the match, the little fire from the match is equivalent to the little push you can give the ball on the mountain to knock it out of the dip.",
"So when you use the match on the wood, you knock it out of its energy dip, and it \"rolls down the energy mountain\", which we see as it lighting on fire, until it settles at the \"bottom of the energy mountain\", when its done being on fire and has turned to ash.",
"Does that make sense?"
] |
[
"It has to do with conservation of energy. If you place a ball atop a frictionless U-shaped hill, it will roll towards the \"most stable\" state at the bottom, but then once at the bottom, kinetic energy will carry it back up to the top on the other side. \"Stability\" is just a lower energy state, and the energy must go somewhere. "
] |
[
"This may sound stupid but do animals of the same species that have lived in different countries have the same \"language\"?"
] |
[
false
] | null |
[
"Not a stupid question, there's a lot of research going on in to that exact question. Here for example we see that the mating calls of cricket frogs are different depending on where they live, due to adaptation to environments with different acoustic qualities ",
"geographic variation in Animal communication systems",
" ",
"I'm aware of a lot of other cases of populations with different ' regional accents' whales of the same species who sing in different frequencies, finches with different melodies to their songs, chimps with differing lengths of calls, even domestic cattle with different ways of saying 'moooo.' ",
"What would be really interesting to know is whether any animals capable of semantic representation, such as chimps or prairie dogs which can have a specific call to indicate a specific predator or prey species or individual member of the group have in-group calls not recognised by outsiders of the same species. "
] |
[
"To distinguish a 'word' as apart from a 'call'.",
"For example, perhaps a species of monkey has a general call which means 'danger' but a species of chimp living in the same jungle can say 'danger jaguar!' 'danger snake!' etc. That is the calls carry more information than just general mood. Strictly I should have written 'lexical semantic representation' "
] |
[
"You're sarcasm a) isn't suited for this sub and b) shows a lack of understanding of my question. You're either being willfully obtuse or don't understand that I was very clearly asking about regions. Human beings didn't look at a map and say \"let's speak a new language\" different methods of communication developed in different countries. At the same time, however, there are instances of communication (things like smiles and laughs) that are universal. My understanding of animal behavior was that communication was primarily done through body language but I wasn't sure. My question was asking about whether or not that body language was universal and whether or not animals used vocal communication to \"speak\" to one another or whether it was just to communicate some arbitrary message (A roar being a warning rather than a specific roar meaning that another animal should step back). "
] |
[
"Asteroid planned to 'hit' earth next year. How likely is this?"
] |
[
false
] |
Taken from this article; How likely is that the impact will happen? Has this asteroid been in orbit of our solar system? Follow up: If this is a hoax, say that an asteroid this size will hit earth, what will the damage radius be?
|
[
"The article is a hoax. Ignore it.",
"DA14 is a -3.29 cumulative on the ",
"Palermo Scale",
". Anything under -2 is not considered something to be given serious impact consideration. In other words, not even worth mentioning.",
"Answering your other question... Even if you assume the worst about the makeup (a stealthed iron core), it wouldn't be as bad as Tunguska, most likely. Some rough numbers:",
"Your Inputs:\n Distance from Impact: 100.00 km ( = 62.10 miles ) \n Projectile diameter: 44.00 meters ( = 144.00 feet ) \n Projectile Density: 8000 kg/m3 \n Impact Velocity: 7.82 km per second ( = 4.86 miles per second ) \n Impact Angle: 48 degrees \n Target Density: 2500 kg/m3 \n Target Type: Sedimentary Rock ",
"Energy:\n Energy before atmospheric entry: 1.09 x 1016 Joules = 2.61 MegaTons TNT\n The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.5 x 103years",
"Major Global Changes:\n The Earth is not strongly disturbed by the impact and loses negligible mass.\n The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).\n The impact does not shift the Earth's orbit noticeably.",
"Atmospheric Entry:\n The projectile begins to breakup at an altitude of 1170 meters = 3850 ft\n The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 7.46 km/s = 4.64 miles/s\n The impact energy is 9.94 x 1015 Joules = 2.37 MegaTons.\n The broken projectile fragments strike the ground in an ellipse of dimension 0.0675 km by 0.0502 km",
"Crater Dimensions:\n What does this mean?",
"Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.\n\nTransient Crater Diameter: 908 meters ( = 2980 feet )\nTransient Crater Depth: 321 meters ( = 1050 feet )\n\nFinal Crater Diameter: 1.14 km ( = 0.705 miles )\nFinal Crater Depth: 242 meters ( = 793 feet ) \nThe crater formed is a simple crater \n\nThe floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 112 meters ( = 368 feet ).\nAt this impact velocity ( < 12 km/s), little shock melting of the target occurs.\n",
"Thermal Radiation:\n What does this mean?",
"At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.\n"
] |
[
"Fantastic input and elaboration on this subject, thank you very much for this thorough explanation!"
] |
[
"Not a 'hoax' per se. The asteroid in question is on the Official NASA Near Earth Object Program site.",
"Definitely sensationalist and alarmist wording in the article, yet, their assertion that there is little that can be done in the next 11 months while inappropriate in the context of impending doom, is not inaccurate.",
"Also to put the above posters fancy math in clearer terms, there is a \"99.978%\" chance that it will ",
" earth. So, sleep tight."
] |
[
"What is the largest an animal could possibly be?"
] |
[
false
] |
I was reading about the largest organisms in the world on wikipedia and got to thinking. I know that on Earth, an organism's size peaks out because at a point they can't have enough muscle to keep themselves standing. Just making something bigger and bigger doesn't work, so no King Kong is going to happen here on Earth. But on a planet with lower gravity, or a different atmospheric makeup, could larger and larger animals be possible? Is there a point where, regardless of the environment the creature is in, it's not possible to be any bigger? That the creature would collapse under it's own gravity, or biological processes just would not function anymore?
|
[
"There is a whole (contentious) field of study that kind of asks this question called ",
"allometry",
". ",
"Basically, it says that many things scale at very different rates. For example, if you increase the size of a sphere, the surface area increased at a rate of ",
" while volume increases at a rate of ",
" ",
"These scaling laws, if they're real (the contentious part), strongly affect a whole bunch of animal properties. For the purpose of your question, it limits size for a number of reasons (of which I'll just give a couple):",
"since your mass increases at a much faster rate than your size, your skeletal structure (whatever that may be) reaches a limit where the skeletal integrity won't be able to support the mass. This is the \"gravity\" issue people are referring to.",
"the rate of diffusion doesn't change as mass gets bigger, which means that oxygen diffusion through your body (which happens in all animals - even mammals at the facet of capillaries) will start to be ineffective as you get bigger. This ",
" be why larger animals have slower metabolisms - because they don't have enough oxygen to have fast metabolisms (physiologists, please correct me if I'm wrong - I'm going off memory of a couple of Brown papers I read four or five years ago).",
"this one I'm going out on a limb, so please take it with a grain of salt: the speed of nervous reactions is not instantaneous, so even if you solved the other scaling issues, my guess is that a giant body would be very uncoordinated (literally). I suppose this could be solved with a decentralized nervous system, but I'm not sure.",
"Fun question!"
] |
[
"I always thought it was heavily related to the amount of oxygen in the air."
] |
[
"I wish I could give you a good response, but whatever I say is going to be mostly speculation (I've only read a couple of papers on this subject).",
"But, for some reason, I ",
" that since diffusion is still required, even just at the capillary scale, there are still problems. ",
"Sorry for that unsatisfying answer - if you research it and figure it out, let me know!"
] |
[
"How much sleep is really necessary for one to get through the day?"
] |
[
false
] |
I tend to get only about six hours of sleep a night. With a coffee in the morning and possibly an energy drink in the afternoon I'm able to handle a full day of high school plus the commute to my school without getting too tired. How much sleep to we really need to function with a decent amount of energy?
|
[
"Adolescents, children and young adults require more sleep than middle aged people do. A typical high school student requires 8.25 to 9.25 hours of sleep a night. Lack of sleep has negative effects on health and intellectual functioning.",
"http://en.wikipedia.org/wiki/Sleep#Optimal_amount_in_humans",
" "
] |
[
"I would define it as without getting worn out of tired. If I were to get really drowsy during the day and maybe fall asleep in class, I would consider that not decent."
] |
[
"We don't understand sleep very well. We can only assess skills and then ask how much sleep they believe they got and draw a correlation (both with general IQ and changes in amount of sleep). Your question asked both about \"functioning\" and \"getting through the day\". How do you define functioning or getting through the day...or \"decent\"?"
] |
[
"How are satellite images captured and edited?"
] |
[
false
] |
[deleted]
|
[
"There are tons of Earth observation satellites, many with regular cameras for natural color images. There are some ",
"free images",
" and then some ",
"better images if you pay for them",
"."
] |
[
"Landsat images are different than what you’re looking at, as they have specialized uses. They’re multi-spectral, meaning that they’re taken in specific colours (and often outside human vision range), with the specific intent of seeing large scale features on earth. Different plants are different greens, and absorb/reflect different colours of light. SO using this kind of imagery, you can tell (say) a pine forest from one primarily of Douglas Fir, from Maple... Or in the case of looking at the prairies, evaluate how much Canola, Flax, Wheat, Soy, etc.. is being grown based on the imagery.",
"Landsat isn’t there to let you see your house, but to look at the big picture, and that it does quite well."
] |
[
"Landsat images are different than what you’re looking at, as they have specialized uses. They’re multi-spectral, meaning that they’re taken in specific colours (and often outside human vision range), with the specific intent of seeing large scale features on earth. Different plants are different greens, and absorb/reflect different colours of light. SO using this kind of imagery, you can tell (say) a pine forest from one primarily of Douglas Fir, from Maple... Or in the case of looking at the prairies, evaluate how much Canola, Flax, Wheat, Soy, etc.. is being grown based on the imagery.",
"Landsat isn’t there to let you see your house, but to look at the big picture, and that it does quite well."
] |
[
"How small could you compress the universe if the fundamental forces didn't exist?"
] |
[
false
] |
The only thing holding atomic nuclei apart is electrostatic forces, right? (Ignoring kinetic energy for electrons and things). Is there a similar deal for quarks/leptons? If the 4 basic forces stopped working, could an atomic nuclei be condensed? Could a hadron? How about a quark, or a lepton? Could the whole universe be condensed to a point, or do things at that level actually touch each other in some way?
|
[
"If the 4 basic forces stopped working, could an atomic nuclei be condensed? Could a hadron? How about a quark, or a lepton? ",
"No, not without a lot of energy at least. ",
"All quarks and leptons are fermions, and fermions cannot occupy the same state - it is called Pauli exclusion. If you want to start putting fermions in a well defined finite space - call it a box - then you can pack two into the lowest energy state, and two more into the next highest energy state, and so forth...",
"The more fermions that you want to pack in the box, the more energy you need. The smaller that the box is, the bigger the difference between energy states and the more energy needed to pack a given number of fermions into the box.",
"This is the case even for completely non-interacting fermions, with the fundamental forces completely turned off.",
"In fact, on the order of half of the resistance of a common metal to being compressed comes from Pauli exclusion, not from electrostatic repulsion.",
"EDIT: You absolutely need gravity to provide the energy needed to compress fermions to arbitrarily small volumes."
] |
[
"In fact, on the order of half of the resistance of a common metal to being compressed comes from Pauli exclusion, not from electrostatic repulsion.",
"Damn, that's very interesting. ",
"I'm a bit confused. Say you have a point location, and you put a fermion in it with the lowest possible energy. If you took a second fermion in the next energy state, would it occupy the exact same point/physical space? I mean totally hypothetically, if you had infinite energy and could exert infinite force, could you potentially make infinite fermions occupy the same amount of physical space as a single one? Do we know if that would produce a gravitational field of the same strength as a mass that contained an equal number of fermions?"
] |
[
"Electrons are also subject to the pauli exclusion principle."
] |
[
"Is the space-elevator just a \"pipe-dream\"? Why, or why not?"
] |
[
false
] | null |
[
"The material strength requirements are a bit unrealistic, they have to start imagining things like carbon nanotubes that are a hundred miles long, with no defects. ",
"Seems pretty pipe-dreamy to me."
] |
[
"They have strange properties, although immensely strong in the axial direction, they are quite weak in the radial direction. Although a 1 mm nanotube cable could hold more than a ton of weight, you could probably cut it with a dull pair of scissors. Any sort of shear forces would be a big problem (like say wind?) ",
"Just to make matters worse, any impurities of boron or nitrogen in the nanotubes seem to result in failure. You can make them out of only carbon, but then there are those annoying cosmic rays, that tend to hit nitrogen and turn it into carbon-14, if they hit carbon, they would stand a good chance of making boron-12, which would suddenly be a defect, leading to failure of the material."
] |
[
"They have strange properties, although immensely strong in the axial direction, they are quite weak in the radial direction. Although a 1 mm nanotube cable could hold more than a ton of weight, you could probably cut it with a dull pair of scissors. Any sort of shear forces would be a big problem (like say wind?) ",
"Just to make matters worse, any impurities of boron or nitrogen in the nanotubes seem to result in failure. You can make them out of only carbon, but then there are those annoying cosmic rays, that tend to hit nitrogen and turn it into carbon-14, if they hit carbon, they would stand a good chance of making boron-12, which would suddenly be a defect, leading to failure of the material."
] |
[
"What is the ghosting i feel after a day on roller coasters?"
] |
[
false
] |
today, i visited a theme park, and spent a good chunk of my time upside down, spinning, and falling. Every time i do this, that night, tonight included, i feel the exact same G-forces applied to me. pressure to my head, then pressure to my rear and feet. it washes. this "ghosting" starts as soon as i settle down for the night, and lasts for hours. oddly enough, it doesnt start until a few hours after leaving the park and being home. is it an inner ear thing? i would think my ear would have settled down after an hour or so of riding. is this common, and what the heck is going on?
|
[
"Inner ear makes sense, you have small stones that sway when your head moves.",
"The other is that all the swirling has created some current in your cerebrospinal fluid. maybe more or less of it gets reabsorbed when you jostle around and you're high or low."
] |
[
"you have small stones that sway when your head moves.",
"Wait what? I'm guessing I missed that chapter."
] |
[
"http://en.wikipedia.org/wiki/Otolith"
] |
[
"Does Alzheimers/Dementia affect muscle memory?"
] |
[
false
] |
Sorry if this is a stupid question, but do memory loss diseases affect motor skills/muscle memory? Or is something like that lost when other memories are lost. Thanks
|
[
"Hmm the answer here is dual. Technically yes, but not for the reason you'd expect. ",
"What people (and probably you as well) think of when they think of Alzheimer's is a memory disease. This is because Alzheimer is a neurodegenerative disease, and the hippocampus is among the first areas that get compromised.",
"\nNow the hippocampus is the area responsible for storing new memories and creating them and. So Alzheimer causes memory formation loss and subsequently memory retrieval by the degeneration of more and more brain space. ",
"However, this part of the brain is not responsible for learning motor skills or ''muscle memory''. In fact studies show that people with Alzheimer's not only can still ride a bike or whatever, but they can in fact also still ",
" new motor skills. Interestingly, they can do so without explicitly remembering learning the skill itself*. ",
"This is because motor skills (formation) and motor execution/planning are not skills that are dependent on the hippocampus, but rather cortical or striatal regions. ",
"HOWEVER Alzheimer's ",
" just a disease of the hippocampus. It's a neurodegenerative disease of the entire brain, it's just most apparent in the hippocampus. Because the entire brain is affected, you can indeed see mild motor problems in early-stage Alzheimer. Motor learning will eventually become compromised as well as motor execution* *. Eventually any skill will be near impossible to conduct or learn. ",
"So yes, muscle memory will eventually be affected. However, this process has nothing to do with the typical view of Alzheimer's being a memory disorder. ",
"*",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2039835/",
"\n* *",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3121966/"
] |
[
"I asked mum (who is a nurse in an aged care facility) and she said that muscle memory does get affected. ",
"So, I went I look up a couple of sources, and found this for you!",
"https://www.reddit.com/r/askscience/comments/2dd7rj/do_alzheimers_patients_lose_muscle_memory_as_well/?st=ISEBARX3&sh=6db2289b"
] |
[
"Muscle-memory isn't \"muscle-stored memory\". When you train your muscles, you're really teaching your brain how to properly activate and coordinate the motor neurons that activate muscle.",
"Yes, your muscles seem to \"know\" what to do, but that's because your brain has learned the pattern and will just repeat the sequence of signals it knows.",
"See: The very first google result for muscle memory.",
"Note that this is separate from a golgi-tendon stretch reflex, which is initiated by the muscle and you have no control over.",
"Golgi-tendon reflex"
] |
[
"What exactly causes burns?"
] |
[
false
] |
I understand that burns can be caused by a variety of different sources (radiation, chemical, electrical, friction, etc.), and it seems that most of these are in some way related to temperature extremes. So why do all these different sources cause similar injuries? Is there a similar underlying cause? If so, what is that cause?
|
[
"In addition to heat, chemicals (specifically acids/bases) and radiation (including UV light) can cause protein denaturation leading to a burn. After the initial injury (heat/chemicals/etc) the body reacts by producing an inflammatory response which leads to blisters, swelling, and many other changes we associated with burns. "
] |
[
"You can check this out for yourself by cracking open a raw egg and throwing ethanol on the egg. It'll slowly turn into a normal cooked egg. It'll go even quicker if you throw an acid on it. (However, don't eat said egg.)"
] |
[
"Temperature changes such as extreme heat denatures proteins, which means they unfold and reform their shape at certain pH's and temps. Naturally, this kills the cells and skin layers that these proteins are made of. That's what causes protein-rich food like eggs to cook as well."
] |
[
"If I have to wake up in 30 minutes, is it worth going to sleep now? At what point (if any) would it be better to just power through the night?"
] |
[
false
] | null |
[
"Studies suggest that 20 minute naps are ideal for a quick energy boost. If you go beyond that you have a high chance of waking up in a deeper sleep state and end up with something called 'sleep inertia', which is something that makes you feel groggy. Waking up in sleep stage 1 is ideal.",
"Reference: ",
"https://en.wikipedia.org/wiki/Sleep#Stages"
] |
[
"The broad answer to this is REM cycles, but with as little time as 30 minutes, you're probably better off with a \"nap\" than a \"sleep\"...some people can train themselves to enter a state just short of sleep that can be significantly restorative with just 10-15 minutes. As for powering through the night, it's gonna catch up with you eventually regardless, but if you need to be alert in the first couple hours of your day, it might actually be better to just power through the night, because of the aforementioned REM cycle issue. However, if you can power nap, that never hurts."
] |
[
"That's interesting, thanks! How would someone enter and keep themselves in a state just short of sleep? If I went to lie down at 5:30am I would definitely just fall asleep instantly. How would one enter this mental state and nap instead of just sleeping?"
] |
[
"What shape is the universe?"
] |
[
false
] | null |
[
"The ",
" universe is a sphere of radius 46.5 billion lightyears centered at Earth.",
"What do I mean by the observable universe? Well, the universe is currently 13.8 billion years old. The furthest objects we can possibly see are ones whose light was emitted 13.8 billion years ago. But due to the expansion of the universe in that time, those objects are now even further away! After all, they've had 13.8 billion years to move away from us. If we could measure the distance to them now, we'd find that distance to be 46.5 billion lightyears.",
"Beyond that 46.5 billion lightyear sphere, we don't know what the universe looks like. It might go on infinitely forever in every direction (infinite, unbounded). It might start repeating itself after a while and have identical copies of the same \"unit cell\" tessellated over and over again (finite, unbounded). It might just have a boundary and end somewhere (finite, bounded). We don't know, and have no way of knowing.",
"Bonus fun fact: If the universe did repeat the same bit over and over, and the \"unit cell\" was smaller than our observable universe, we'd possibly be able to detect it by seeing the same object in multiple locations on the sky. Astronomers have carried out searches for such a repetition in the cosmic microwave background, and there appears to be no indication that we're in a repeating universe."
] |
[
"We haven't found any evidence of this yet, but it's one of the stranger possibilities. :)",
"Actually, it's one of the most normal possibilities there is! There are three most-basic geometric shapes the Universe could be: flat, open, or closed. Flat is what you'd expect, \"normal\" 3D space (plus time). Open is kind of like a 3D version of a hyperboloid. And closed means that the Universe's spatial geometry is like the 3D version of a sphere, where all paths come back around the other side. Any ",
" possibility is in fact quite a bit more exotic."
] |
[
"We have also looked for light echoes from a closed universe, where light moving in a straight line through three dimensional space eventually comes back to its source from the opposite direction. Stare far enough, and long enough into space in any direction and you see the back of your own head. :)",
"We haven't found any evidence of this yet, but it's one of the stranger possibilities. :)"
] |
[
"Has there been a disease that was beneficial to humans?"
] |
[
false
] | null |
[
"It depends on how you want to interpret that question. Let's take a classic example: ",
"sickle cell anemia",
". Individuals who carry both alleles for sickle cell have the disease, which is serious. However, individuals that have only one allele for SCA are protected from ",
"malaria",
". ",
"So is the disease beneficial to humans? No, not if you have both alleles. But you might make the case that it is beneficial if you are an unaffected carrier."
] |
[
"From a certain point of view, there's an interpretation of how the Black Plague helped the 50% of Europe who survived it (from ",
"http://www.livescience.com/2497-black-death-changed-world.html",
")",
"Social effects of the plague were felt immediately after the worst outbreaks petered out. Those who survived benefited from an extreme labor shortage, so serfs once tied to the land now had a choice of whom to work for. Lords had to make conditions better and more attractive or risk leaving their land untended, leading to wage increases across the board.",
"The taste of better living conditions for the poor would not be forgotten. A few decades later, when lords tried to revert back to the old ways, there were peasant revolts throughout Europe and the lower classes maintained their new freedoms and better pay.",
"The Catholic Church and Jewish populations in Europe did not fare so well.",
"Distrust in God and the church, already in poor standing due to recent Papal scandals, grew as people realized that religion could do nothing to stop the spread of the disease and their family's suffering. So many priests died, too, that church services in many areas simply ceased. "
] |
[
"Early 20th century physician Julius Wagner-Jauregg used malaria to 'cure' syphilis. It was known as ",
"malariotheraphy",
". He won a ",
"Nobel Prize",
" for it."
] |
[
"Why does soda/soft drink go flat only when opened?"
] |
[
false
] |
[deleted]
|
[
"The partial pressure of the carbon dioxide in the liquid in greater than that of the atmosphere. The pressure will equalise and therefore the carbon dioxide will leave the liquid, making it go flat.",
"This is why the bottles are pressurised when you buy them. The increased pressure balanced the partial pressure of the canon dioxide in the liquid and the atmosphere in the bottle, keeping the carbon dioxide in the liquid."
] |
[
"You could use tonic concentrate / quinine syrup / other bitters and mix it with soda water at time of use— I actually enjoy operating a soda siphon, the soda in them doesn't go flat quickly (since it stays pressurized), they're cheap to operate, and the siphons look nice in that early-mid-20th-liquor-sideboard way. ",
"'s parent's generation.",
"Or you could just make sure to drink enough that you go through a bottle's worth of gin & tonics before the tonic goes flat…"
] |
[
"You could use tonic concentrate / quinine syrup / other bitters and mix it with soda water at time of use— I actually enjoy operating a soda siphon, the soda in them doesn't go flat quickly (since it stays pressurized), they're cheap to operate, and the siphons look nice in that early-mid-20th-liquor-sideboard way. ",
"'s parent's generation.",
"Or you could just make sure to drink enough that you go through a bottle's worth of gin & tonics before the tonic goes flat…"
] |
[
"Is it feasible to make a nuclear powered steam train?"
] |
[
false
] |
By using the heat of radioactive decay to boil the water. Or would it be more effective to use that energy to power a turbine that then powers an electric engine? How would one look? Obviously no tender needed for coal, but would it be heavier because of the shielding? What if it runs out of water? I'm picturing this massive black beast at the station, that leaks steam and hums gently due to the reactor. :P EDIT: Just to clarify. I just want to know if I can get a steam engine running by using radioactive decay as a heat source instead of burning coal.
|
[
"It's not impossible, but it's probably unfeasible. ",
"There's patents and designs for all sorts of these things- nuclear powered ",
"space ships",
", ",
"submarines",
", ",
"planes",
", ",
"trains",
", (plantains?) etc etc. ",
"That last link about nuclear trains is something I found in the news- I'm not sure how reliable that source is or how likely it is to come through, but, as is tradition, if it sounds like mad science it's from Russia.",
"The nuclear powered planes never got built though, for precisely the reason of weight and radiation shielding, and I expect a similar issue to arise if those Russians try to build that train. ",
"The difficulty is that nuclear power is expensive, especially building and deploying the reactor, even if you had a suitably scaled design that could fit in a locomotive (I'm not a nuclear engineer, so I'm not entirely sure how feasible this is).",
"Nevertheless, I doubt you'll ever see widespread deployment of 'personal nuclear reactors' on the scale of trains and cars because they are dangerous when mishandled. Nuclear fuel and power generation is concentrated in a few very well guarded places - power plants, national labs, and military installations. An eager terrorist party would have a much easier time getting their hands on a nuclear car or nuclear train (if they existed) and making a mess with that material. Of course, it's a common misconception spurred by Hollywood that nuclear reactors can be detonated like bombs- nothing is further from the truth. But, if radioactive material were included in an explosion driven by conventional explosives it would make quite the mess. That's not to say that the radioactive material would enhance the explosion, but rather that it would spread two things: dangerous radioactive material, and panic. "
] |
[
"There were a number of issues. The plane could certainly fly with the added weight and shielding, but this limited payload capacity, maneuverability and performance (and thus survivability). Additionally, even if you could carry enough energy content to fly indefinitely, flight crews could only loiter for so long and the airframe can only handle so long without regular scheduled maintenance. These were bigger concerns to the USAF than loss of core integrity on impact. Had we not developed ICBMs, it's not clear the Aircraft Reactor Experiment program would have been discontinued, even despite all those pretty serious problems. "
] |
[
"You can make a fairly small nuclear reactor. I believe I have seen estimates as low as 500 watt as the smallest feasible fission reactor. Certainly this might be more expensive than a gas turbine or diesel engine, but practically speaking the design of reactors allows them to be much smaller than most people think, it just usually isn't worthwhile from an economic standpoint. Unless you don't have access to fuel. Because you're in space.",
"The only people who are interested in very small reactors are NASA mission planners, here are a couple papers on small reactors:",
"http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100033102.pdf",
"http://www.lpi.usra.edu/meetings/marsconcepts2012/pdf/4384.pdf",
"There have also been plans to design small \"nuclear battery\" reactors to power remote Alaskan towns and military bases to avoid the logistical problems of transporting fuels to hard to reach areas. So reactors can be fairly small, I don't really think it's worth it to use them to power locomotives though, as the associated regulatory and safety burden would probably be prohibitive. "
] |
[
"How long would an astronaut have to be on the ISS to experience one second of time dilation from those of us on earth, due to relativity?"
] |
[
false
] |
I was just listening to where he mentions how many times the ISS went around the earth while he was onboard, and this thought popped into my mind as I contemplated traveling at that incredible velocity for an extended period of time.
|
[
"About 90 years."
] |
[
"Calculate the Lorentz factor, substitute 8 kilometers per second for the velocity, subtract 1, divide a second by the result."
] |
[
"This graph",
" on the Wikipedia page for time dilation is helpful. The x-axis is orbital altitude (in Earth radii) and intersects the y-axis at 1 (Earth's surface). The y-axis is how many microseconds they lose per day.",
"I don't like how the altitudes (ISS/GPS/GeoStat) are horizontal lines. They should just be points along the curved red line, imho. ",
"Anyways, the ISS is pretty low and appears to loose about 24 microseconds/day (0.000024 s/day). So they loose a grand total of 1 second in 1/0.000024 = 114 years.",
"I think iorgfeflkd was ignoring the effects of general relativity. The ISS is low enough that they're not ",
" significant. But you can see it makes a difference. About 6 microseconds per day it seems. (you get 90 years with a loss of 30 microseconds/day)",
"You can see that GR takes over around 1.5 Earth radii. Everything higher up than that passes through time ",
" than on the surface of the Earth, because of their distance from Earth's mass. (edit: and because of the reduced orbital velocity)"
] |
[
"Is there a way to estimate thermal properties of theoretical alloys?"
] |
[
false
] |
I am currently working on a project that involves many metals melting and reforming into a solid. It made me wonder if there would be a way to estimate the new thermal properties such as conductivity of the new material. I originally tried a simple weighted average of the conductivities, but when comparing that known alloys it is an extremely poor estimation. I have found a lot of papers that propose methods for finding conductivities of alloys made up of two metals, but I am working with potentially much more. I was wondering if there was a way to estimate the conductivity of the new alloy or at least put bounds on it. Sorry if this is a simple question i have almost no experience with material science.
|
[
"Yes, you can use numerical techniques like Density Functional Theory or Molecular Dynamics"
] |
[
"In principle yes, but even if you're an expert in the field you may occasionally estimate them wrong.",
"What you would first have to do is find out what the atomic structure is. Is it crystalline or amorphous? What's the crystal structure? From this you can get a good estimate of the conductivity and the phonon spectra, which are the major contributions to thermal conductivity. ",
"So the major difficulty is really to find out how your compound looks like on the atomic scale in terms of crystal structure, valence, bonds and magnetism. If you don't have this, you cannot estimate the thermal properties."
] |
[
"As other commenters have made clear, this is a very difficult problem. You can use numerical methods like molecular dynamics but it's very computationally expensive and is hard to extrapolate bulk quantities from. You also have to make sure that you're accurately modeling your alloy on the atomic level. How well do your metals mix? Will they coexist in the same crystalline lattice or will they separate into different phases?",
"Modeling a new material is not something that can be done as a generalization. You need to understand exactly what is going into your material and then tackle it in a rigorous way. If you alter the composition or substitute a different element, you have an entirely different problem."
] |
[
"Can I train myself like a dog?"
] |
[
false
] |
When you train a dog, every time he's successful, you can give him food, and he associates it with the success, so he gets better. Can I do the same with myself? Like, for instance, when I manage to play that guitar riff, I eat a M&M's. Will I get better that way?
|
[
"It's also not the same scale of task - learning (or wanting to learn) a guitar riff is not the same as telling a dog to sit. If he were to get someone else to reward him with something small like a treat for doing very small tasks, it would be similar. Rewarding yourself is related to motivation; rewarding in classical conditioning requires someone else to do the rewarding, generally speaking.",
"Also, motivation is incredibly related to learning and how receptive one is to new information. There are scores and scores of journal articles and books on the topic. Not all educators rely upon motivational theories as their underlying learning theory when teaching, but many do."
] |
[
"It's also not the same scale of task - learning (or wanting to learn) a guitar riff is not the same as telling a dog to sit. If he were to get someone else to reward him with something small like a treat for doing very small tasks, it would be similar. Rewarding yourself is related to motivation; rewarding in classical conditioning requires someone else to do the rewarding, generally speaking.",
"Also, motivation is incredibly related to learning and how receptive one is to new information. There are scores and scores of journal articles and books on the topic. Not all educators rely upon motivational theories as their underlying learning theory when teaching, but many do."
] |
[
"There's more going on internally with humans than with dogs (generally speaking) but lots of child rearing techniques use similar techniques of small 'token' rewards for specific behaviors, which over time breeds more of the desired behavior. You can certainly use rewards as a way to motivate yourself, but it's not simple classical conditioning in the way in which it is implemented with dogs.",
"Also, an interesting thought is the way we respond to our smartphones - with their variable schedule, variable reward conditioning. It's part of what hooks us to them, and the beeps and buzzes of receiving messages. We don't physically become attached, but we do become mentally motivated to keep the phone around at all times (for many people.)"
] |
[
"Research has been done on the effect of gut microbiome on behaviour. Has any research been done on the effects of sharing elements of one's microbiome with a partner, through things like kissing and oral sex, might have on behaviour within the relationship? [medicine] [human body]"
] |
[
false
] |
See title
|
[
"We know that the microbiome does spread from person to person. In fact, a simple kiss can transfer thousands of bacteria. I can think of two effects this would exhibit on your health and behavior.\nFirst, as two peoples' gut biomes align, they would start craving similar foods. As far as we know, the strongest behavioral effect a biome has on its host is the ability to manipulate what it eats. Ie. If we eat a lot of vegetables, the fiber loving bacteria in our gut will grow more dominant, and will cause us to crave after the type of foods the bacteria likes. In fact, those foods will start tasting better to us, since it has been shown that the bacteria can indirectly alter our brain chemistry. This is very real.\nSecond, people who live together and share similar microbiome profiles will show similar levels/types of oral decay and periodontal disease. This is relatively new research, but the thousands of bacteria that inhabit your mouth and form the plaque on your tooth surfaces play a large role in your oral risk factors to decay and perio, as well as dictating the microbiome profile in you gut. Theoretically, a skilled dentist could predict the state of your mouth by simply taking a sample of your oral bacteria. It's a little more complicated than this, and I'm not the expert to ask about this, but your microbiome has a much larger effect on your health and behavior than we give it credit for."
] |
[
"Lol, I have a bunch on this for a post I was saving. To answer your question, not specifically for behavior that I’m aware of, but a previous commenter got it right that our dogs GI microbiome mimics their owners. ",
"The punchline of my eventual post is that cunnilingus may be a source of probiotics."
] |
[
"I know that there are studies that show that people who live in close quarters do have more similar microbiomes, not only from kissing etc, but also from sneezing, fecal particles being spread, etc. \nI also remember hearing something about a study comparing microbiomes of pets and their humans, but I can’t remember what findings they found. \nThe aspect of behaviour with that though is a fascinating question. "
] |
[
"Is sad music sad because we grew up associating it to sad movies? Or is it because the melody is objectively sad?"
] |
[
false
] | null |
[
"It's the dissonance. The pitches of minor chords are not in very symmetrical frequencies. This dissymmetry is somewhat unappealing to the ear, and is therefore associated negatively."
] |
[
"I'm thinking because maybe they use minor keys? Or they have a lot of different minor chords?"
] |
[
"This leads to the next question: How is it that minor keys seem sad to many?"
] |
[
"Can characteristics of same plant species vary from one place of growing to another?"
] |
[
false
] |
I'm just reading about some plant healing effects, how it's less effective if it was grown in Europe instead of Egypt, and I find this absurd.
|
[
"Yes, plenty of plant attributes change depending on light availability, soil composition, local competition, weather, nutrient availability, water availability, etc. While every plant species is different, most are highly adaptable and can change in significant ways depending on environmental context. As a general example, a plant that grows under a lot of shade cover from other trees may grow to be very tall to get more sunlight, but may have smaller leaves to compensate for the stem energy allocation. On the flip side, if this plant grows in an area with no shade above it, it may grow to have a short stem with larger, broader leaves to maximize immediate photosynthesis. These attributes could then carry over to something like the 'healing effects' given in your example; because the plant allocated more energy to a certain structure during growth, that structure could have a different effect on our bodies if we ate it.",
"tl;dr - Most plants can allocate energy towards different structures and functions to maximize their fitness given the environmental context. This changes the characteristics of full grown plants."
] |
[
"I got my bachelor's in ecology, but I know very little about herbal remedies. So I can't really give an informed testimony on the 'synthetic vs herbal' argument. But at face value, that statement seems like it could hold some water"
] |
[
"So is it also the argument in favour of synthetic medicine that uses same active ingredients for its effect as herbal remedies over said herbal remedies? Since that implies that herbal medicine could have doses that vary wildly, which can be dangerous in some cases. "
] |
[
"Would a laser that produces light outside of the visible spectrum damage your eyes in the same way a typical colored laser would?"
] |
[
false
] | null |
[
"Yes, it can actually be more damaging because with a visible laser your blinking reflex will protect your eye after the first fraction of a second."
] |
[
"It depends on the wavelength.",
"Near IR has very similar effects to visible light, but, like ",
"/u/iorgfeflkd",
" says, can be more dangerous because it won't cause a blink reflex.",
"Other wavelengths cause other effects, due to being absorbed by different parts of the eye. I stole this table from ",
"Wikipedia",
":",
"**wavelength** **effect**\n180–315 nm (UV-B, UV-C) photokeratitis (inflammation of the cornea, equivalent to sunburn)\n315–400 nm (UV-A) photochemical cataract (clouding of the eye lens)\n400–780 nm (visible) photochemical damage to the retina, retinal burn\n780–1400 nm (near-IR) cataract, retinal burn\n1.4–3.0μm (IR) aqueous flare (protein in the aqueous humour), cataract, corneal burn\n3.0 μm–1 mm corneal burn\n"
] |
[
"Yes. In fact, any laser >5mW (ie pretty much anything other than your standard cheap red pen-style laser pointer) can potentially be pumping out enough scattered UV to damage your retinas",
"I think you're confusing UV (ultraviolet < 400 nm) with IR (infrared > 700 nm). UV cannot damage retina, as it is absorbed by eye lens. Also, only ",
"DPSS",
" pointers produce a lot of IR (almost all green, some red and blue ones) due to the way they work. That IR won't be scattered at the output, but still be a laser beam, dangerous for the eye. Most red laser pointers use just laser diodes, so they produce almost no IR even at high power."
] |
[
"The old 'travelling at the speed of light and turning the headlights on' chestnut"
] |
[
false
] |
So someone posted an explanation to this problem here: . My question regarding it is here:
|
[
"You can't travel at the speed of light, period. If you're travelling very close and you turn on the lights, the light appears to be going at the same speed for you, and someone at rest. This is one of the principles of relativity, that the speed of light is the same in all inertial frames. If you're travelling at 50% the speed of light relative to something, and you fire a missile forward at 50% the speed of light relative to yourself, it's not going the speed of light, it's going at 80% the speed of light.",
"The actual formula for adding velocities v1 and v2 is v=(v1+v2)/(1-v1 x v2/c",
" ). v=v1+v2 only works for things moving very slow. You can show this with a Taylor expansion."
] |
[
"Another way of addressing it (which I personally prefer, but it's really a matter of taste) is that going from one inertial reference frame to a differently moving inertial reference frame is equivalent to a hyperbolic rotation.",
"In a circular rotation, the angles of rotation add; rotating something by thirty degrees and then by forty degrees is exactly the same as rotating it by seventy degrees.",
"But the geometry of special relativity is hyperbolic rather than circular, so what adds when you combine transformations is the ",
" angle ",
" which is equal to the hyperbolic arctangent of the ratio of the relative velocity between reference frames to the speed of light. For small ",
" ",
" is very close to ",
" over ",
" which is why at low velocities you can just do simple vector addition and get answers that are close enough.",
"Whether you prefer the algebraic formulation or the trigonometric one is, in my experience, a matter of whether you're more comfortable with equations or geometry. There should be little doubt which side of that line I'm on."
] |
[
"It would be better if you could state the question directly so people don't have to do a bunch of homework to find out what the question is."
] |
[
"What does AskScience think of stem cell treatments for organ transplant recipients?"
] |
[
false
] |
I'm interested to know what AskScience thinks of this study. My questions:
|
[
"Is there really hope for stem cell treatments to aid in transplant patients?",
"Most definitely there is. This is an active area of study and one that does show promise. There's a lot of unknown, and years of study ahead before this becomes common-place, but it's definitely something that is being examined. That said not ",
" bone marrow recipients are able to entirely avoid rejection drugs and the reasons for this are extremely complicated, but relate at least partially to different tissue markers. What's being done here is basically tantamount to providing a bone-marrow transplant as well as a kidney transplant. This will not be possible in all cases, and increases the risks of graft vs. host disease as well. There are many hurdles.",
"Is this something that those in the medical field have dreamed of doing but never realized until now?",
"I'd say no, we just haven't have the technology in place to perform some of these things until recently, and then of course it has to be proven in animal models before it's scaled up to human trials, at least typically. ",
"Is the study reputable?",
"It's not really a study so much as a case-analysis of an experimental procedure. It worked in this specific circumstance well, that doesn't unfortunately prove very much. I also can't find the original notes to it anywhere, so it's tough to deeply examine.",
"Is there any hope of one day using stem cells to actually repair damaged organs?",
"We are studying the possibilities of self-grafts and cloning organs, but these technologies face considerable hurdles as well."
] |
[
"Thank you for this reply. The story's been in the news quite a bit lately (locally here in Chicago) and it's hard to tell what to make of it. When I first heard of the trial I thought it had been proven out in multiple cases but I can only find information on the one patient cited in the article. ",
"Just for curiosity's sake I have these follow-up questions, to which you're obviously under no obligation to respond, but if you have the time... "
] |
[
"What are the challenges to self-grafts and cloning organs?",
"We don't have a reliable way to grow most tissue on a large enough scale to be able to provide what is necessary to replace tissue style transplants. Though a couple weeks ago there was a post about a trachea that was done this way, it was again a first.",
"Cloning organs presents even greater challenges, as on top of getting down a matrix for it to grow properly, how do we care for the organ while it's in vitro? We don't have ways to provide blood flow, nutrients, and remove waste, nor are we able to regulate hormones necessary to function and growth nearly as well as the body. Also, time frame. Most transplant patients don't have the time to wait for an organ to be grown large enough to function for them. We haven't reliably found a way to speed up organ growth.",
"Are transplant anti-rejection drugs as dangerous as they sound?",
"They're definitely not the easiest drugs to manage from a physician's standpoint as they require constant tweaks and testing to ensure adequate levels to minimize side-effects and still protect from rejection. The biggest risk they carry obviously is that your immune system is much, much weaker as a result, this means that every small illness you or I handle normally is potentially life-threatening post transplant. It necessitates vast lifestyle changes that not all people adapt to well, or maintain well, post op."
] |
[
"Why do people feel stiff when it rains?"
] |
[
false
] |
My muscles always feel tight when it rains and I've heard several other people complain that their bones ache. What causes this?
|
[
"When it begins to rain and as it rains, air pressure rises. This rise in barometric pressure causes more strain to be put on the muscles and joints in order to support the body as it will weigh slightly more. People who have arthritis, sprained muscles, or another ailment of the sort will be able to feel these changes when a storm is approaching due to the rise in pressure placed on their bodies. My grandma can tell with near certanty when it is going to rain and how bad it will be from the increased pain she feels in her bones"
] |
[
"Changes in Barometric pressure."
] |
[
"I would love to see the papers on this."
] |
[
"If I had a super precise weighing scale, would my weight change as I breathed in and out?"
] |
[
false
] |
[deleted]
|
[
"Yes, water leaves our lungs as we breathe out, also we breathe in O2 and breathe out CO2. You would lose weight for both reasons.",
"It wouldn't however be an up and down cycle, for reasons others have posted. It would be a slight drop with each exhale."
] |
[
"To add to this, an average human being exhales ",
"250mL of CO2 per minute",
". Converting this to grams (and taking into account the oxygen you breathe in) you lose about 0.134g per minute. ",
"0.25 L * 0.001m",
" /L * ",
"1977g/m",
" * ",
"12g",
" / ",
"44g",
" "
] |
[
"It doesn't so much 'ignore' it, as 'not include' it. He was talking about the CO2 only.",
"You can come up with a good approximation of the water losses (of respiration, you also constantly lose water by perspiration) by:",
"finding the tidal volume of your lungs (varies for each person, [units m",
" /breath]), ",
"multiplying by the average number of times you breathe in a minute [units (m",
" /breath)*(breath/minute)=m",
" /minute]",
"taking that flow rate, the vapor pressure of water at 98.6F (body temperature), and following ",
"Raoult's Law",
" you get really close to the measurable value",
"My apologies for not having the time to do the math myself, hope this helps."
] |
[
"If you could somehow evenly apply an increase in the rate of neuronal action potentials across the entire brain, what effect would that have?"
] |
[
false
] |
What effect would that have if you had a mild increase? moderate increase? severe increase? Would it be dangerous? Healthy? Would you 'use up' your brain faster (haha probably the least scientific way to describe this)? Would it 'fill up' your brain?
|
[
"There is actually already a well studied way to apply an increase in the rate of neuronal action potentials across the entire brain. ",
"Electroconvulsive Therapy",
".",
"But really at almost any level of intensity this would just be like giving someone a seizure. "
] |
[
"What about TDCS or TRNS?"
] |
[
"I heard the military was experimenting with tDCS for training drone pilots.\nHeres a related article.\n",
"http://www.newscientist.com/article/mg21328501.600-zap-your-brain-into-the-zone-fast-track-to-pure-focus.html"
] |
[
"How early do you think a child should learn about SR, GR, and QM? How about calculus, topology, complex analysis? What do you think is the most important thing to teach to a middle-schooler?"
] |
[
false
] | null |
[
"They should learn about them when they're interested in them. The most important part in my development as a physicist was that my parents made sure to encourage my curiosity. ",
"When I was kid I liked to take apart electronics, and they let me. I wanted to learn to program, they let me. When I wanted to to learn to draw and paint, they let me. ",
"In my senior year I didn't win any science awards, I won the award for top art student. But after high school I chose science and now I'm in the last year of my PhD in theoretical physics. "
] |
[
"Which geographic area, I mean. Your assessment strikes me as unlikely pessimistic."
] |
[
"In my opinion, the scientific and math ",
" are much less important than a scientific mindset - critical thinking, critical analysis, problem solving, logic, and curiosity. ",
"If these cornerstones are developed, then all else will follow. ",
"Laying that foundation is a process that starts in infancy (yes, I've read enough cognitive and developmental psychology to feel confident in that statement). As the child grows older, it'll want to explore all these subjects at its own pace, and the parent's job then is to expose the child to the subjects so it knows they're there to study, and to help with whatever adult supervision is necessary.",
"This is what I will strive to do as a parent, if/when I have a child."
] |
[
"What is the Physical Consistency of the Surface of the Sun?"
] |
[
false
] |
Yes, it's a big ball of plasma, but what is its surface like? If you had sufficient protection from the heat, radiation, and the like, would you be able to "stand" on it, like you could a solid? Or would it be more like a liquid that you could swim in? Or would you just fall through?
|
[
"If you have a magical space suit that can resist the pressure, you'd eventually reach a point at which you're neutrally buoyant and float, but otherwise you'd be compressed too and just keep sinking. The density at the Sun's core is 150 times the density of water but it's still a plasma with no solidity to it since the particles are all moving too fast to bond to each other and hold each other in place as a solid."
] |
[
"You'd fall through; the ",
"visible surface of the Sun",
" is a gas (technically a plasma, but it would feel just like gas) with a density of 1/1000th of Earth's atmosphere at sea level, and there's no solid surface, it's just gas that gets denser and hotter the deeper you go, all the way to the core."
] |
[
"The part of the Sun that people usually call the “surface” is the photosphere, which is the point where light coming from the core can finally move freely in a strait line. Really the Sun has no surface, it’s plasma all the way through.",
"If you were to become invincible and start falling onto the Sun, at first it would be like entering the atmosphere of a planet. It would start very thin and get thicker as you go down, but unlike a planet it will not stop. It will just keep getting denser and hotter as you go down, eventually it will get denser than water and you’ll start being buoyant. Even if you weigh yourself down and make it to the core it would still be a plasma that’s hot and dense enough to sustain nuclear fusion. Close to the core there will no longer be gravity although the pressure and temperature will be immense under the immense weight of the entire Sun under the super powerful Solar gravity.",
"Basically, it’s atmosphere all the way through. Even though higher pressures will raise the condensation and freezing points of all materials, the raise in temperature you get from diving into the Sun more than makes up for that."
] |
[
"Why is Athlete's Heart considered a benign condition whereas Hypertrophic Cardiomyopathy is potentially dangerous?"
] |
[
false
] |
More specifically, does anyone know what the underlying difference(s) are that would make the former 'benign', while the latter is considered the leading cause of sudden cardiac death, especially in athletes?
|
[
"These are pretty good answers, but there's a central idea buried in there that I just wanted to state outright:",
"Athletic conditioning gives you a heart that is slightly bigger, but much more efficient at pumping. Hypertrophic cardiomyopathy gives you a very big, floppy heart that is extremely inefficient at pumping blood. "
] |
[
"Athlete's heart is from conditioning, causing a strong and efficient heart. Cardiac output is high. ",
"Hypertrophic cardiomyopathy is genetic. The key is that \"the normal alignment of muscle cells is disrupted, a phenomenon known as myocardial disarray. HCM also causes disruptions of the electrical functions of the heart.\" These things would decrease cardiac output, which can cause kidney or brain damage. The heart beats faster to compensate for low cardiac output. This makes the heart require more oxygen. The heart can become starved for oxygen and start to become necrotic, further decreasing its effectiveness. Electrical disturbances can cause sudden cardiac death as the heart may simply stop beating. "
] |
[
"The response was already in the links you provided :",
"This is because athlete's heart is a normal, physiological adaptation of the body to the stresses of physical conditioning and aerobic exercise.",
"Hypertrophic cardiomyopathy (HCM) is a primary disease of the myocardium (the muscle of the heart) in which a portion of the myocardium is hypertrophied (thickened) without any obvious cause.",
"So one is an adaptation of the heart muscle the other a defect in the heart muscle."
] |
[
"How can we really know the size of extra-solar planets?"
] |
[
false
] |
So we've found 3 'Earth sized' planets recently. If we find these planets by the wobble of the star, or by the dimming of the star as they pass in front, how can we tell the difference between a larger than earth sized planet, and an earth sized planet with a moon? like for example could these be pairs of smaller binary planets? How do they account for this? Massive Edit: Thanks for the responses! It seems like the general attitude is that it wouldn't make a big difference to the measurements anyway. The reason I asked this is because I've heard that having a moon could be, or is, either essential or greatly beneficial, to it's capacity for harbouring life. When people announce 'earth sized' planets, where they could actually be ever-so slightly smaller but with a moon, the implications to the probability of life outside our own solar system are huge. I am making a game about travelling to other systems to find planets, it's all based on a procedural system generator. So the probability of moons and life is super important for that, and just interesting to me, I wouldn't be making it otherwise. My tutor was like 'that's going to be super tedious and boring if it's based on science'. But the more we find out about them, the more it seems extra solar planets in general, and even ones that could harbour life, aren't as rare as people assumed.
|
[
"how can we tell the difference between a larger than earth sized planet, and an earth sized planet with a moon?",
"Bear in mind that the amount of light blocked by a transiting planet in front of its parent star is a function of the radius ",
", so it's not greatly affected by the additional presence of a moon.",
"So for example: the Moon's radius is just about 1/4 of the Earth's radius. That means if we saw the Earth + Moon in transit, we'd see an extra (1/4)",
" = 1/16, or an extra 6% dip in the brightness of the transit when compared to a transit of the Earth alone.",
"If you run through the math, that would mean we'd estimate the Earth being just 3% larger than it actually is. That's still pretty close to the inherent error in the measurement, so it's really not going to greatly affect our final science result; you're talking about the difference between a planet with a size of 1.00 Earth-radius and 1.03 Earth-radius - it's still basically an Earth-sized planet.",
": Moons are small compared to their parent planet, and have an even smaller effect on the brightness dip of a transit, so it really wouldn't matter very much.",
" to include your Massive Edit:",
"The reason I asked this is because I've heard that having a moon could be, or is, either essential or greatly beneficial, to it's capacity for harbouring life. ",
"This is true.",
"Some folks throw around the idea that having a moon might help with slightly suppressing the number of meteorite impacts, but that's really not the primary reason why a moon is beneficial for life...it's far more based on stabilization of the climate.",
"Seasons are caused by the tilt of the rotational axis. Earth's axis is tilted 23 degrees, which gives us some seasons, but they're relatively mild compared to some other planets. Since our large Moon gives us a relatively constant tidal force over time, the absolute direction of our axis changes, but the actual amount of tilt stays pretty stable at 23 degrees...at most it varies between 22 degrees and 24 degrees over million-year timescales.",
"Now, compare that with Mars. Since Mars has no large moon, the primary tidal forces are from the Sun and Jupiter, which are quite chaotic compared to our own Moon's steady tidal tugging. As a result, simulations have found that Mars' axial tilt has varied between a 0-degree axial tilt all the way to a 60 degree axial tilt. That means over million-year timescales, its climate has varied between no seasons to crazy intense seasons. That kind of erratic climate is really not conducive to life, and some have suggested it helped with the dessication of the planet's ancient oceans.",
": Having a moon stabilizes your seasons, which is good for life.",
": See the comment from ",
"/u/K04PB2B",
" below. It would seem more recent calculations have suggested that a large moon may not be necessary for a planet to maintain habitability...which is good news for astrobiology. Obligatory hat tip to the orbital dynamicist dudes and dudettes out there."
] |
[
"Earth has an exceptionally large moon for its size, too (if our own solar system is any indication)."
] |
[
"A simplified version of the technical definition of a binary is that the system barycenter is outside the primary.",
"The Earth-Moon barycenter is close but not quite outside the Earth. It's ",
"73% of a radius",
" away from the center. Close, if you squint. So the Earth kind of 'wobbles' over the course of a month.",
"Pluto-Charon is a true binary. Pluto ",
"definitely orbits around a point in space",
"."
] |
[
"Would an exploding/imploding star create a shockwave?"
] |
[
false
] |
I am aware that space is mostly empty and shockwaves would require matter to build up, but as a star expands during it's death would the matter being expelled create a shockwave, and could this shockwave push planetary bodies away from the star, creating a rogue planet? Or would they just be inevitably swallowed by the star?
|
[
"Well as I understand it space is not a void, and there will be massive amounts of matter released during the explosion at rapid speeds. could this be enough to cause a shockwave?"
] |
[
"There is an entire area of astronomy geared toward studying what are called \"bow shocks,\" where the shock wave from a stellar event moves through the gas in the surrounding region of space. Bow shocks sometimes refer to the flow of surrounding gas around a star, and the resulting high and low pressure (and density) pattern as explained ",
"here",
" and ",
"here",
". ",
"Here is a photo of a bow shock around LL Orionis",
"Another photo",
"and an ANIMATION!"
] |
[
"While it wasn't a full blown supernova, these images of ",
"V838 Monocerotis",
" can provide a pretty decent idea of what one may look like. "
] |
[
"When measuring the mass of an electron (9.11*10^-31kg) is this the mass when the electron is at rest or when moving with relativistic velocity?"
] |
[
false
] | null |
[
"The modern definition of mass is a quantity which doesn't change with the speed of the particle. So the mass of the electron is the rest mass, which is the same no matter how fast it's moving.",
"We can't determine particle masses from first principles."
] |
[
"I'm somewhat confused. From General Relativity we know that mass does change when approaching relativistic velocities. As an electron will always (I think) be moving with relativistic velocity, if it's mass at that speed is 10",
" kg, then at non-relativistic velocities the electron should have less mass, right? What is the mass of a stationary electron vs that of a natural state electron?"
] |
[
"From General Relativity we know that mass does change when approaching relativistic velocities.",
"This is only true using a different definition of mass; one which isn't really used anymore.",
"Electrons are not always moving at relativistic speeds, they can be moving quite slowly under everyday circumstances."
] |
[
"What happens if you throw an object during uniform circular motion?"
] |
[
false
] |
If you were holding an object (say a ball) and were travelling in a uniform circle (say on a roundabout) what would happen if you threw the ball? I know that if you just let go of the ball, its force would be its centripetal force in the horizontal direction perpendicular to the circle (F=mrw ) and gravitational force in the vertical (F=mg due to such a small distance). If you physically propelled it instead of letting go, would this just add a horizontal force parallel to the circle, so that you just resolve the two with pythagoras? Or would you have to use some other calculation to resolve the net horizontal force? I think I'm right in thinking the vertical force would remain constant though.
|
[
"The moment you let go of it, there is no centripetal force on the ball anymore. That was from you holding it the circular path. So from a top-down view (and neglecting drag), there are no longer any forces on the ball. It continues moving in a straight line at a tangent to where you released it.",
"If you throw it instead, you're imparting an extra velocity to it in whatever direction, with respect to yourself. But there are still no forces on the ball from a top-down view once you let go.Add this velocity vector to the velocity vector of your travel around the circle.",
"The vertical travel is just due to gravity and can be solved in isolation. Consider initial velocity, acceleration, time taken, solve for velocity at any point in time."
] |
[
"Would I be right to think the two horizontal velocity vectors are perpendicular to one another? Assuming the ball was thrown straight forward in the direction I was facing. So the resultant velocity would be a",
" + b",
" =c",
" where a is the tangential velocity and b is the extra velocity from throwing. "
] |
[
"That depends in which direction you are throwing the ball, I'm not sure you've specified this anywhere. You say straight forward in the direction you are facing, but which direction are you facing?"
] |
[
"Would it be possible/of any benefit to paint the inside of a swimming pool in a super hydrophobic coating?"
] |
[
false
] |
I realise it's possible, but perhaps wildly impractical? Would the water behave differently to the point where you wouldn't want it for your backyard pool? If not, could there perhaps be benefits in such a treatment towards limiting the growth of algae or something similar? Thanks in advance, Science!
|
[
"Superhydrophobic coatings are indeed useful for preventing biofilm formation in situations where you can't use chlorine, such as food processing, bioreactor fermentation, and high purity chemical synthesis."
] |
[
"Would coating the hull of a boat with hydrophobic material have any kind of impact on the boat?"
] |
[
"It could certainly be done, the cost would be large but not unreasonably so. The observed effects would be minor curiosities, consisting mostly of bubbles sticking very tenaciously to the walls (the walls would wet eventually as they were touched, or just due to the large pressures in deeper parts of the pool). About the algae, I would just be speculating, but chlorine already takes pretty good care of that."
] |
[
"Would we ever be able to interact with alternate dimensions/universes according to the theory of Multiverse?"
] |
[
false
] |
According to the Theory of Multiverse, there exists an infinite amounts of alternate scenarios in an infinite amount of different universes. Some people like to think of this as "Well, at least I got in some other universe", but I think it's scary because if we interact with these other universes, how do we know we're remaining in one universe and some super-civilization isn't doing multi-universal experiments on humans with wormholes, etc. beaming us to universes extremely similar to ours (but of course unnoticed to the subject). Basically the question is not whether we can, but if it is to interact with these other universes/dimensions?
|
[
"According to the Theory of Multiverse, there exists an infinite amounts of alternate scenarios in an infinite amount of different universes.",
"There is no \"Theory of Multiverse\". There are several things that are occasionally ",
" that, but nothing to which the term can properly apply. For details on the most common meaning of the phrase, see my comment in response to the question \"",
"Is multiverse an accepted theory or is it just an extreme hypothesis?",
"\"",
"Your question appears to be about the implications of Everett's many-worlds interpretation of quantum mechanics (the second one I discuss in the above link). ",
"See palanoid's link to a proposed in-principle test. Note that these sorts of interactions don't necessarily provide for ",
", let alone the transference of matter \"between worlds\" (a phrase that I'm almost certain doesn't actually make sense).",
"You can read more about the Everett interpretation ",
"here",
"."
] |
[
"I don't think it's by definition. ",
"http://arxiv.org/abs/quant-ph/9510007"
] |
[
"Actually, thinking about it a bit, I suppose it has to be that way. There's no way the branches could ",
" decohere."
] |
[
"Is there an evolutionary trait that causes there to be a low percentage of natural leaders compared to those that follow?"
] |
[
false
] |
I'm just curious as I can't imagine a world where everyone was a leader or a follower. It always seems like there is a natural flow to society with those who lead and those who fall in behind. Is there any reasoning for why this is? Evolutionary reasons or situational reasons?
|
[
"Because an extraordinary trait is defined by the fact that it is not average.",
"I do not agree with you, that some people are born leaders or something like that, but the above statement is true nonetheless. "
] |
[
"It is impossible to prove or disprove conjectures like this.",
"However, statistically, by definition the majority of people cannot be leaders."
] |
[
"I think it's more that the worse leaders fail to become leaders, and thus accept follower status (or enter a parallel society)"
] |
[
"Do organelles in animal cells, as well as their number and function, differ from species to species?"
] |
[
false
] | null |
[
"Hi lc412 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"I'm on mobile, how do I add a flair on Alien Blue?"
] |
[
"Read the message you just responded to"
] |
[
"Can you have concussive force in space?"
] |
[
false
] |
For example, if an explosion takes place say 20 meters from me on Earth that would cause massive internal trauma due to concussive force, will the effect be the same in the vaccuum of space? Not counting heat/shrapnel of course.
|
[
"Not likely. What you're talking about is damage from the shockwave that propagates through the atmosphere after the explosion. Without an atmosphere, there's nothing to propagate the shock. You may be hit directly with the expanding gas from the explosion, but this will be very weak in most situations - the damage from an explosion is caused by the energy it adds to the air, not by the amount of gas it deposits."
] |
[
"So where does that energy go instead?"
] |
[
"The mechanisms can be somewhat different, but explosions can be very damaging in space.",
"Rather than a blast, what you get is more an intense pulse of electromagnetic radiation - heat and light. When it hits an target, the radiation pulse vaporises the surface of the target. This then can produce a destructive shockwave within the target. For a person in a spacesuit, there's your cause of internal trauma.",
"An explosion in space will also produce shrapnel if the bomb is designed for it. And at very close range the hot gases from the explosion could be damaging."
] |
[
"If the ratio of the modulus of elasticity to density of aluminum and steel are so similar, what goes in to the decision to use one over the other?"
] |
[
false
] |
First, I will need to back up the title. I'm going to use numbers based on 4130 and 7075, because they are both relatively common high-strength alloys. Modulus of elasticity = 205 GPa, Density=7830kg/m ratio: 2.68*10 m / s (I don't know what this unit is. Keeping it to show calculations are consistent with each other) Modulus of elasticity = 71 GPa, Density = 2823kg/m ratio: 2.52*10 m / s Wouldn't this mean that a structural member made out of 4130 would actually be lighter than one from 7075 for the same stiffness? Obviously I'm missing something here, because the folks building airplanes didn't just pick aluminum because they felt like it. One thing that occurred to me when thinking about bike tubes is that the aluminum tube will be thicker than the steel, possibly making it more difficult to dent. Is that it? Edit: if this is bogus just let me know. I'm really trying to figure this out.
|
[
"For airplanes Aluminium is easier to work with, because sheets of the right strength are thick enough. Steel sheets of sufficient thickness to have sufficient strength would be so thin that they are difficult to work with (plus there would probably be quit a lot of bending involved).",
"For tubes, the stiffness does not increase linearly with wall thickness and radius so that by making a larger and thicker tube out of aluminium which weighs the same as an equivalent steel tube, you get a much more stable structure. Or a structure just as stable, but lighter. That is why its used in bikes.",
"http://wiki.answers.com/Q/Why_is_aluminum_used_to_build_aircraft_instead_of_steel",
"http://en.wikipedia.org/wiki/Aluminium_alloy"
] |
[
"There are a couple of factors at work here. Other properties, such as tensile strength and various thermal properties are a major consideration when selecting materials for structures in airplanes & similar things. ",
"As you point out, though, for similar stiffness or strength, an aluminum member will be thicker than a steel one. This means that an aluminum structure will have a much larger cross section, rendering it much more resistant to flexure and buckling. Again, this is a major consideration in aircraft structural design (wings, anyone?). This effect is described here: ",
"http://en.wikipedia.org/wiki/Second_moment_of_area",
"Edit: Added Reference"
] |
[
"So. Coming from a background in Materials Science, this is a great question. ",
"Many factors go into selecting a material, and they change based on the application. They can include: ",
"Mechanically:\nDensity, Modulus (tensile, bulk, etc), specific modulus (modulus per density), shear strength, tensile/compressive strength, ductility/elasticity, thermal expansion properties, etc ",
"Non-Mechanical:\nCorrosion resistance (rust or galvanic action, etc), cost, weight, machinability (ie, how easy to produce, shape, cast, join or weld, etc) and cost of machining (ie, titanium costs shitfucktons to machine/cast, compared to casting alu, or machining steel) ",
"Overall, a lot of it also comes down to design. Basically, assuming you used a given material, what would your design specs need to be, and what are the costs for manufacturing it, plus any servicing that would be expected over some lifespan of the product. ie, with planes, a common calculation is something like 20 years of \"expected servicing costs\" and \"usage costs\" (like fuel, etc) ",
"At the end of the day, it also isn't a pure numerical decision. Marketing/business teams have a big say because of what they decide will \"sell\" better. ie, carbon fiber is sexy and cool, so even if it costs more, people may pay more for it! ",
"EDIT: Fixed formatting. Also, credit to KToff for also mentioning machining/workability, and to OnlySaneMan for talking about differences in design requirements per material"
] |
[
"Question on Relativity"
] |
[
false
] |
I've got a bit stuck on this relativity question: How fast would you have to travel to get from the Earth to the Sun in one minute, assumiong the Earth is 8 light minutes from the Sun. I've been thinking about this for the last couple of days and just can't seem to get my head around it.
|
[
"How fast would you have to travel to get from the Earth to the Sun in one minute, assumiong the Earth is 8 light minutes from the Sun.",
"You would need to travel at 0.9923 times the speed of light. Of course, you will only reach the sun in 1 minute according to your watch. The people on Earth will see you moving in slow motion and your journey will take just over 8 minutes according to them."
] |
[
"Thanks, would you be able to show me how you worked this out?"
] |
[
"It seems to me you just have to solve the equation",
"(d/v)(1/gamma)=60 s",
"Where gamma is the Lorentz factor.",
"I get 99.2% the speed of light."
] |
[
"Do educational facilities ever BUY cadavers for educational purposes, or do they rely 100% on people to donate their bodies to science?"
] |
[
false
] |
If they do, in what kinds of circumstances does that happen, and what on earth does the facility pay the family?
|
[
"At universities near me the cadavers are essentially borrowed/rented, and are always donated, never bought. Universities can have them for four years before all remains are returned and cremated. Only in very special circumstances can body parts be kept as a permanent specimen."
] |
[
"So, things like rare growths in the brain or the like. Changes in physiology due to different diseases. Specimens that haven't been seen before.\nOther universities might have more freedom, but ours are quite respectful by ensuring the body is complete when cremated."
] |
[
"So I have a pretty neat little fact regarding my universities bone collection. Our medical school is fairly old (going back to the 50s) and at the time that they were looking to expand their bone collection for anatomy education, the go-to route was to buy them from india. However, I dont know what the legal reasoning for this was THEN or even how it technically is NOW. Either way, i found it really neat to know that all of our hundreds of skulls, limbs, ribs, and entire skeletal specimen are actually from Indian people. ",
"The anatomy professor at the time I found this out jokingly mentioned that if we ever heard him speaking to the bones while in the lab, he was just asking for blessings from his ancestors surrounding him, lol."
] |
[
"List of 26 things that did \"not make sense\" 4-8 years ago according to NewScientist. Current status?"
] |
[
false
] | null |
[
"I'm not sure about any of the others off the top of my head, but I know that the 'Bloop' has been considered solved. The answer: ",
"ice quakes",
"."
] |
[
"The bit about hybrid origin of species.....it's well known that new species can form from hybrids between fairly closely related groups (think two species in the same genera, and you'll get the right idea). There's a much more controversial idea that in some cases the weird shifts between larval and adult forms of creatures are due to hybridizations between distantly related groups (think different classes or even phyla). This is a super cool idea, but the evidence doesn't really support it at this point."
] |
[
"Actually Morgellon's disease was investigated by the CDC and the ",
"results were published last year",
". The disease is a poorly characterized constellation of symptoms including formications (feelings of insects crawling under the skin), skin symptoms including fibers growing from the skin, and some systemic symptoms (fatigue, etc). All in all it was really very odd, and there was a large lay lobby that proposed it was caused because of an undescribed infection (not impossible by any means). ",
"It was investigated in the Kaiser Permanente cohort, where it was found that patients had no identifiable parasites or mycobacterium, or any other biotic etiologic cause. The fibers arising from the skin were similar to cotton fibers from clothes, with evidence of dyes present. Notable was the high rate of substance abuse in patients, which can be for a large number of reasons. ",
"The sort of current synthesis is that this is due to a delusional parasitosis, in which patients have psychosomatic symptoms. Notice that this is not to say that they do not have a disease, nor is it to say that they are not suffering. By all standards these people are really suffering, but not much can be done for them at present."
] |
[
"Why does wasabi have a really strong and spicy taste that lasts for a small amount of time compared to chillies which last for a long amount of time?"
] |
[
false
] |
I recently felt this when I put too much wasabi on my sushi, it was spicy for about 30 seconds but then the sensation went away.
|
[
"Wasabi, as with mustard and horseradish, has enzymes that break down compounds called glucosinolates that are present in these plants. The reaction produces isothiocynates, which are the 'hot' compounds you notice when eating those. The glucosinolates and the enzymes producing them are water-soluble, so drinking water will flush them away.",
"Hot peppers on the other hand, derive their 'heat' from the presence of the compound ",
"capsaiscin",
", which is not very water-soluble (13 mg per liter of water), and so drinking water doesn't do much to remove it. ",
"Both these compounds bind to the heat receptors in your mouth (and if you're note careful, other parts too), specifically one called ",
"TRPV1",
". It's entirely possible capsaicin binds more strongly to TRPV1 and causes a more long-lasting effect that way as well, but I don't know offhand if that's true or not (or whether it's even been studied)."
] |
[
"Chilies belong to the genus Capsicum, and get their hotness from a molecule called capsaicin and it's derivatives.",
"Wasabi on the other hand gets its hotness from thiocyanates.",
"The thiocyanates found in wasabi are rather small molecules and therefore quite volatile, which is why you quite often feel the burning in your nose as well.",
"Depending on where you got the wasabi, it might also be that it isn't really wasabi at all. Quite often horseradish is used as a substitute, and that also contains thiocyanates"
] |
[
"It is the case that capsaicins have a higher binding affinity to the TRPV1 receptor than the isothiocynates. Oil and water solubility are really neither here nor there."
] |
[
"Were we taught to smile when we're happy or is do we smile for natural reasons? As in, what makes us smile?"
] |
[
false
] | null |
[
"While it's a combination of genetic and societal influences, smiling is largely thought of as a natural, innate response. We can observe smiling in blind infants (Freedman, 1964). If blind infants, who are unable to witness anyone smiling at all, smile when exposed to happy environments, we might be able to infer something about the \"innateness\" of this trait.",
"Also, many physiological factors also suggest that it's a reflexive response. One fun study showed that the way your mouth sits can influence how you feel (Strack, Martin, & Stepper, 1988). For example, if you hold a pencil in your mouth, between your lips, it simulates a frown, and you will report more feelings of sadness, regardless of your previous internal states. However, if you hold the pencil between your teeth, simulating a smile, you will report more feelings of happiness. Kind of silly, but hey, it works! Your body responds to your facial cues in a way that would suggest smiling is a reflexive, physiological mechanism.",
"Finally, studies have shown that smiling is universal. This is to say that regardless of geographical location, regardless of culture, smiles all mean the same thing. It's one of the few things that everybody has in common: you smile when you're happy. Other emotions/responses seem to be universal, such as that of fright, sadness, and anger. Paul Ekman's work has centered around a lot these \"cultural constants\", and if you're interested in the subject, I highly recommend seeking out some of his articles.",
"\n",
"Freedman, D. G. (1964). Smiling in blind infants and the issue of innate vs. acquired. ",
", 5(3‐4), 171-184.",
"Strack, F., Martin, L. L., & Stepper, S. (1988). Inhibiting and facilitating conditions of the human smile: a nonobtrusive test of the facial feedback hypothesis. ",
", 54(5), 768.",
"Ekman, P., & Friesen, W. V. (1971). Constants across cultures in the face and emotion. ",
", 17(2), 124.",
"Edit: APA format for citations. :)\nAlso, smiling via emoticons are learned responses, not innate, like real smiles!"
] |
[
"From everything that I know, smiling is an innate external response to internal feelings of joy. I believe this is determined by babies smiling very early in life, and the fact that blind people smile naturally, even without a frame of reference.",
"http://www.livescience.com/5254-smiles-innate-learned.html"
] |
[
"Smiling is also universal across all cultures, which is unlikely in a learned behavior."
] |
[
"Is there a human speed limit?"
] |
[
false
] |
I always hear about people breaking records for non-powered travel (like running, swimming, etc.). Is there a limit to how fast a human can run? If so, what is it?
|
[
"The limiting factor is the amount of force that muscles can apply over a given time. Going only off of this factor, the theoretical absolute maximum speed is around 19.3 ms",
" or 43 miles per hour. This is obviously for short distances; for longer distances, cardiovascular and respiratory factors become the limits. ",
"Source",
"This study also explores things like prosthetic leg extensions and finds that they may increase maximum speed. It's an interesting read if you have a few minutes "
] |
[
"Already been an issue. A guy with no feet but leg extentions was not allowed to race in a normal race because it was actually an advantage and not a disadvantage. "
] |
[
"It's generally pretty easy to tell what is and isn't human because you don't run into boundary cases often. But the fastest possible human is a boundary case by definition. They are such that any change makes them either slower or nonhuman. If I started with a human, and then slowly changed them until I got a spacecraft capable of moving at 90% of the speed of light, at some point they'd stop being a human. And unless I can say when that point is, I can't say how fast of a human I managed to make."
] |
[
"According to metric expansion, is there \"new\" space being created between galaxies?"
] |
[
false
] |
If space is expanding between galaxies, what are the properties of that space? When the distances increase, is space being "stretched" or is there "new" space being created in between them? As I understand it, the galaxies themselves aren't moving in the traditional sense of the word. Perhaps my question isn't quite clear, but I guess what I'm asking is, if there were a certain number of planck lengths between 2 galaxies, would that number be increasing as space expands, or do the lengths themselves get longer? If "new" space is being created, what is the process for that/where does it come from?
|
[
"Space isn't really a \"thing\" that is being stretched. All that is happening is the distance between points is getting bigger.",
"Space is also not divided into a number of planck-length \"pixels\". The planck length is important, and you do get some interesting physics happening below that length scale, but it is not actually an indivisible unit of space, except in some not very widely accepted theories."
] |
[
"But if it isn't a \"thing\", then what is the mechanism for the expansion? Space itself is what's expanding correct? As I've understood this concept, the galaxies aren't \"moving\" through space, but the space between them is expanding in all directions.",
"\"Space itself\" isn't really anything. When we say things like \"spacetime bending\", we're just saying that distances and angles don't add up the way you might expect them to. And \"the expansion of space\" just means things get more distant from each other, and the rate at which their distance increases depends on their current distance.",
"Also, if the planck length doesn't represent some type of \"resolution\" of the universe, is there any other metric that does?",
"Not that I know of."
] |
[
"Sorry for the long post, but your questions are deep and have complex answers.",
"Based on your explanation, the\"points\" in space or Planck lengths are not the same as \"space itself\". Would that be correct?",
"Okay, I gotta dispel one misconception you seem to have, before I can explain: Planck lengths are not the same as points in space, nor are they \"indivisible units\" of space, nor \"minimum lengths\" between points of space. They are just a length. They are not special in any way. Space is continuous (there is always an uncountably infinite number of points between any two points, no matter how close they are to eachother, even if separated by only one Planck length).",
"\"Space itself\" is the same as the collection of points that make up the space. Mathematically, a ",
"space",
" is just a set of points, with some additional structure that relates the points. The additional structures can vary depending on your intended model, but typically one of the additional structures is called a ",
"metric",
" -- or distance function -- that assigns distances between the points, making the space a ",
"metric space",
". Distances, as assigned by the metric, can be compared, but only to other distances. So if you want to compare distances, you need a reference distance to compare against, like a ruler. These days we define the SI reference distance, the metre, as exactly 1/299,792,458 of the distance travelled by light in a vacuum in one second, which is constant. The Planck length then is some fraction of a meter, and by extension, some fraction of the distance travelled by light in one second.",
"Although the distance between any two given points may increase, the speed of light is constant. So the \"Planck length\" never changes -- it is always the same distance. But the distance between two points in the space ",
" change, and in an expanding universe, it ",
".",
"So if you have two points, A and B, separated by some distance d = 1 light-year ... and then you emit a photon at A, headed towards B. That photon will travel the distance of 1 light-year per year. But, during that year, the distance between A and B will increase slightly. So when the photon arrives at B, a little bit more than 1 year will have passed, and the photon will have travelled a little more than 1 light-year of distance. The distance between A and B increased, but the reference distance of \"1 light-year\" has remained the same.",
"Does that help?",
"There are theoretically an infinite number of points in space, but space itself is finite?",
"There are an infinite number of points in space (as we currently model it), yes. But, we do not know whether space is finite or infinite. Current measurements are consistent with both possibilties, though if space is finite it must be very large.",
"Regardless, the ",
" between any two specific points is always finite.",
"If space is finite, what that means is that there is an ",
" to the maximum distance possible between any two given points. Consider, for example, the surface of a sphere. If you choose two points on opposite sides of the sphere, that is the maximum distance that is possible between ",
" two points on the sphere (unless the sphere grows larger, in which case the upper bound also grows larger but remains finite). There are still an infinite number of points in the sphere, but we say the surface of the sphere is \"finite\" because you can't have a distance greater than some finite limit.",
"If space is infinite, that means there is no upper bound of distance between two arbitrary points. So you can choose any finite distance you want (even one that is unimaginably large), and there will always be two points in the space separated by that much distance, and two other points separated by more than that distance.",
"Does this mean that distances themselves are just conceptual, or do they actually exist in some way?",
"Distances actually exist. You can reach out and touch the monitor in front of your face, but you can't reach out and touch Alpha-Centauri. Not that you'd want to. :)",
"But, the way we model distances is, of course, conceptual, and mathematical. We can't know for certain whether our model is right, we can only know for certain if a given model is wrong -- by testing it and seeing if it gives wrong predictions.",
"It's a bit like the \"black swan\" problem. If you set out to prove that black swans do not exist by observing the colour of swans, it only takes one observation of a black swan to disprove your hypothesis, but no matter how many white swans you observe, no number of white swans will ever prove that there isn't at least one black swan out there. It will only increase the probability that your hypothesis is correct -- but will never prove it 100%.",
"Hope that helps."
] |
[
"Is it true that a shooter absorbs an equal amount of force into his body as is being projected in the bullet?"
] |
[
false
] | null |
[
"There is a lot of confusion in the answers here about pressure, force, energy, and momentum. Working backwards through that list:",
"Momentum is conserved, so both the shooter and the object hit by the bullet absorb the same amount of momentum. That means if you were floating in space and fired a bullet into someone with the same mass as you, you would both be pushed apart from each other and the change in velocity would be the same for both. ",
"Energy is also conserved, but as a scalar. The chemical energy in the gunpowder is converted into heat and kinetic energy, but that doesn't have to be shared with you and the bullet. In fact, because the bullet weighs less than you do (and less than the gun does), it receives much most of the kinetic energy after the bullet is fired. This also explains why the bullet can do a lot more damage when it hits something than recoil does to you.",
"Force integrated over time is momentum. Since momentum is conserved, that means the integral of force is the same for you and the bullet (with opposite directions). But a high force experienced for a short time can have the same integral as a low force experienced for a long time. The gun acts like a spring so the force you experience is lower than the force the bullet experiences. This is the same reason that cars have crumple zones - an accident is much less dangerous if you spread out the force over a longer time.",
"Pressure is force over area. This is one more reason a gun doesn't hurt you like a bullet does - the force is spread out over a larger area than on the bullet. This is also why a catcher's mitt protects the catcher's hand.",
"So, momentum is conserved, but a shooter absorbs the momentum through a force spread out in time and area. That is why the shooter isn't hurt by firing the gun."
] |
[
"Not exactly. Some of it does go into the shooters body, but some is also expended in muzzle climb. In the case of automatic and semi-automatic firearms, some is redirected to operate the reloading mechanism. There are also stock modifications that absorb recoil as well.",
"I'm going to guess that you're getting at \"If the projectile fires from the barrel with enough energy to travel so far and punch a hole in a target, why doesn't the gun harm the shooter?\"",
"The reason is mass. A Colt M1911 pistol is about 1105 grams. The standard round for this pistol is between 12 and 15 grams. I'll use 13 grams from here because it makes the math easier. The gun is 85 times as much mass as the shell, so that same amount of force is spread out significantly."
] |
[
"Worth pointing out that your first claim is only true if the bullet stays within the body of the person shot. A more powerful shot might penetrate all the way through and transfer only some fraction of its energy and momentum to the victim, before exiting on the other side. This can of course still be quite lethal, and the danger of a gunshot wound depends much more on which organ is hit than how much momentum it receives, for obvious reasons. "
] |
[
"What is the largest object that Humans can create/fashion that will have the exact same molecular makeup?"
] |
[
false
] | null |
[
"It's an entropy thing. An exactly perfect crystal has only one arrangement. It would be like flipping Avogadro's number worth of coins and getting all heads. Even if the coins are really unfair (analogous to a very low energy crystal state) some of them will come up tails."
] |
[
"All crystals (graphene included) above 0 K have some defects in the atomic arrangement and because any of reasonable size (including those in the image you linked) are made of so many atoms, it is very unlikely that any two similar ones would have exactly the same number. So for anything large enough to be considered a crystal, the answer is no, two exactly identical crystals effectively cannot be produced. Why do you ask?"
] |
[
"What do you mean molecular layout? Do you mean ",
"single crystal",
"?"
] |
[
"What is stopping light from being projected onto the moon from earth?"
] |
[
false
] |
Specifically, is the ability to do this beyond us right now? Do we not have bright enough or focused enough lights? Is it possible to just colour the moon with light, even if there is no discernible image there? I'd think if it was possible to do it well, we'd be seeing a battle for corporate logos on the moon, so I guess it isn't.
|
[
"Dammit I was about to post the same xkcd. ",
"Of course, we do shine lights on the moon, its just we don't get much light back. ",
"The only remaining continually operated part of the Apollo programme is a long running experiment that fires laser light at a reflector dish put their by astronauts and times the time it takes for the light to get back. Even with a laser, the light spreads out and is disrupted by the atmosphere and only one photons gets back for ",
" quadrillions sent out.",
"(Incidentally the existence of the mirrors in the moon is one of the best explanations against conspiracy theorists who claim we never sent rockets to the moon)."
] |
[
"Dammit I was about to post the same xkcd. ",
"Of course, we do shine lights on the moon, its just we don't get much light back. ",
"The only remaining continually operated part of the Apollo programme is a long running experiment that fires laser light at a reflector dish put their by astronauts and times the time it takes for the light to get back. Even with a laser, the light spreads out and is disrupted by the atmosphere and only one photons gets back for ",
" quadrillions sent out.",
"(Incidentally the existence of the mirrors in the moon is one of the best explanations against conspiracy theorists who claim we never sent rockets to the moon)."
] |
[
"Link to the Apache Point Observatory Lunar Laser-ranging Operations (APOLLO) website",
"They shoot laser pulses at the retroreflectors and get maybe 1 in a quadrillion photons back (and that's with the collecting area of a 3.5 meter primary mirror, as opposed to a human pupil of less than a centimeter). It would be very very difficult to shine enough light to make it visible to the human eye from Earth."
] |
[
"Do plants have immune systems?"
] |
[
false
] |
[deleted]
|
[
"Yes. Typically called \"defenses\" more than an immune system though but they react to pathogens and external threats;",
"http://en.wikipedia.org/wiki/Innate_immune_system#Host_defense_in_plants"
] |
[
"Plants have a two-tiered immune system in which the first tier recognizes pathogen associated molecular patterns (PAMPs) in a way analogous to the mammalian innate immune response, and the second tier recognizes pathogen-specific effectors once they have entered the plant cell. The first line of defense will elicit changes in gene regulation, callose deposition and a reactive oxygen species burst while the second will often result in a systemic response and localized cell death (known as the hypersensitive response or HR). "
] |
[
"An immune system as we humans are used to requires white blood cells, so this is correct."
] |
[
"Since MERS has a high fatality rate (36%) and only about 2500 confirmed cases over a span of eight years, why hasn't it been contained (and basically eliminated) like SARS-CoV-1 was?"
] |
[
false
] | null |
[
"Unlike SARS (and SARS-CoV-2), MERS transmits very poorly in humans, usually only a few steps along a transmission chain, and it has not become established in human populations. All MERS transmission chains start with infection of a human by a camel. So the only way to eliminate MERS would be to eliminate it from camels. ",
"In camels, the virus doesn’t seem to cause any symptoms (or the symptoms are very mild and look like many other harmless conditions). So you can’t isolate and/or treat affected animals, or avoid them while they’re shedding. ",
"That leaves widespread vaccination of the camels as the main hope of eliminating the virus, and that is in fact what groups have been working toward. There are a number of candidate vaccines for camels that look quite promising (",
"Efficacy of an Adjuvanted Middle East Respiratory Syndrome Coronavirus Spike Protein Vaccine in Dromedary Camels and Alpacas",
"; ",
"Blocking transmission of Middle East respiratory syndrome coronavirus (MERS-CoV) in llamas by vaccination with a recombinant spike protein",
"), but since this was until lately a fairly low-profile disease, it hasn’t been heavily funded and has moved at a fairly traditional pace for vaccine development."
] |
[
"Nothing identical to (or nearly identical to) to SARS-CoV-1 has been found in bats, but there’s a family of quite similar ones that includes SARS-CoV-2 relatives too. For example ",
"Close relative of SARS virus found in Chinese bats",
"Divergence of nCoV-2019 to closest non-human relative",
"If that makes you wonder why there wasn’t more investigation of bat coronaviruses between SARS and SARS-CoV-2, well, virologists have been sounding the alarm, and begging for funding to do that, for decades. For example, from 2015:",
"Bats have been recognized as the natural reservoirs of a large variety of viruses. Special attention has been paid to bat coronaviruses as the two emerging coronaviruses which have caused unexpected human disease outbreaks in the 21st century ... Various species of horseshoe bats in China have been found to harbor genetically diverse SARS-like coronaviruses. Some strains are highly similar to SARS-CoV even in the spike protein and are able to use the same receptor as SARS-CoV for cell entry. ... Understanding the bat origin of human coronaviruses is helpful for the prediction and prevention of another pandemic emergence in the future.",
"—",
"Bat origin of human coronaviruses",
"But why would anyone listen to a virologist anyway."
] |
[
"But why would anyone listen to a virologist anyway.",
"Well they might have This Week in Virology on their podcast feed..."
] |
[
"Protein synthesis in chemistry?"
] |
[
false
] |
If a certain protein is composed of a sequence of amino acids, can you simply combine said amino acids to create that protein? Is mixing amino acids a plausible way of creating a protein?
|
[
"You can, up to a point! though it’s a bit more complex than just mixing amino acids together. The standard method of synthesising short peptide sequences - ",
"SPPS",
" - works by fixing an amino acid to a resin surface, then successively adding the amino acids you want until the desired sequence is made. This only works efficiently for shortish sequences, fewer than 100 amino acids. For anything bigger or more sophisticated you need to use the same biological components that cells use, ",
"but this can also be done in a test tube."
] |
[
"I worked in a lab that does this! It is kind of possible. ",
"Heres the general process:",
"First of all, you use amino acids that have been modified to have protected side chains and differently protected amino groups. The C terminal amino acid is bound to a resin as a solid so you can do wash steps between every amino acid. The protected side chains and N termini are to preveng random coupling reactions.",
"From here its a few repeated steps.",
"Add a chemical thats gets rid of the protecting group of the N termini of your chain to allow for coupling.",
"Wash",
"Add your second amino acid/necessary coupling compounds and let them react. ",
"Wash",
"Repeat.",
"Once youve got the full peptide chain you add compounds to remove the protecting groups in the side chains. From there you add an acid that cleaves the peptide from the resin and you can collect your full peptide.",
"Now theres some MAJOR issues with this compared to biologically made proteins. For one thing is that this needs to be perfect. Every time a step makes a mistake and doesnt properly couple you have the wrong peptide even if the rest are added correctly. Wrong peptides end up accruing exponentially, so even a 90% yield per amino acid ends up being a terrible terrible yield. The Symphony X was the instrument we used that gives crazy high yield per step but either the reasonably largest peptides we can make are still shorter than most proteins. We can still use peptides as signaling molecules, substrates, pharmaceuticals, and what my old lab was using them for, biosensors.",
"The other issue is that even if we did make big peptides that could be proteins, biologically relevant proteins regularly get other proteins (chaperone proteins) to helpnfold them to their active form.",
"Its amazing how fast biology is. It takes hours for us to chemically make small peptides of ok yields while biology can whip out many times larger proteins in high yields highly accurately, and fold them in minutes. To top it off theyre making countless proteins in parallel! Either way its still cool how were able to make proteins too"
] |
[
"That's wrong. ",
"Solid phase peptide synthesis",
" is doable, albeit inefficient."
] |
[
"What gasses are inside a cavitation bubble? How does gasses from a liquid end up being gathered into a bubble format?"
] |
[
false
] |
What gasses are inside a cavitation bubble? How does gasses from a liquid end up being gathered into a bubble format? I'm curious if it is possible to purposefully create cavitation bubbles and then harvest them into tanks so that you could extract air out of water.
|
[
"Cavitation bubbles are made of the same substance as the surrounding fluid. That is, if you're generating them in the ocean, they'll be made out of water vapor.",
"You know how water boils at a lower temperature at higher altitudes, so there are often different directions for stuff at sea level vs 10,000 ft? Well, cavitation occurs because the pressure drops so low that the fluid boils without any outside heat input - the boiling point becomes 2°C or whatever."
] |
[
"So no air gasses inside the cavitation bubble?"
] |
[
"\"Air gasses\" (dissolved oxygen, nitrogen, etc.) are at the same concentration inside the bubble as outside the bubble."
] |
[
"If you sum these number patterns (picture in the description) with their palindrome number, the result will always be 1110. Why is that?"
] |
[
false
] |
I was bored in math class, so I started typing some random numbers in my calculator. Then I realized that these numbers in this summed with the palindrome of that same number always results in 1110. Is there any reason for it to happen, or is it just coincidence? These are the possible results: 258+852=1110 456+654=1110 159+951=1110 357+753=1110
|
[
"Two numbers across from each other on a calculator or phone grid will always sum to 10 because of the way they're laid out (and 5 is \"across\" from itself). By choosing only numbers that go through the center of the grid, you're making sure you only choose numbers that are across from each other. When you take the palindrome of these numbers, you're adding each number to the number across from it, which will give you 10 every time. To really see how this is happening, look below:",
"258 + 852",
"(2*100 + 5*10 + 8) + (8*100 + 5*10 + 2)",
"(2+8)*100 + (5+5)*10 + (8+2)",
"10*100 + 10*10 + 10",
"1110"
] |
[
"The across-5-ness is important because the numbers on either side are the same distance from five but in opposite directions",
"4 = 5-1, 6 = 5+1, etc.",
"so the distances cancel and its 5's all the way down. That'll be true for any odd-sized grid, and any line you pick. For example, consider a 5 by 5 grid:",
"1 2 3 4 5\n6 7 8 9 10\n11 12 13 14 15\n16 17 18 19 20\n21 22 23 24 25\n",
"If you pick 11 and 15, for instance, both are 2 away from 13, so sum to 13+13. Even if you pick, say, 2 and 24. The choice of an odd-sized grid just forces the number of numbers itself to be odd, so you can really just unwrap the grid, and pick any pair of numbers an equal distance from the center number. The grid just forces you to pick a whole series of numbers: 258 and 852. But that's not essential.",
"The other thing the ",
" grid is contributing is, because its 1-9, its giving you digits, so you can think of 2-5-8 as 258, which adds to the mysteriousness, but isn't too important."
] |
[
"Your number is A x 100 + 5 x 10 + (10-A) x 1.",
"Its palindrome is (10-A) x 100 + 5 x 10 + A x 1.",
"When you add these, you get (10-A + A) x 100 + (5 + 5) x 10 + (10-A + A) x 1, which is 10 x 100 + 10 x 10 + 10 x 1, or 1110, as you observed."
] |
[
"What happens if I use my 30-day disposable contacts beyond one month?"
] |
[
false
] | null |
[
"This is a medical question or sorts...",
"But the FDA rates contacts at their \"safe to wear\" period. Beyond that, there is a increased risk of damaging your eyes due to any number of factors. ",
"The truth is that there's an organization that extensively tests these things for a reason: wear them for their proscribed time and not longer. "
] |
[
"I asked my optometrist about this. She said the contacts deform over time and you'll lose your acuity slowly for the lense. "
] |
[
"You have an increased risk of eye infection if you wear them for longer. Additionally, as they age, the lenses can crack or rip slightly, which isn't always obvious to the naked eye, but causes quite a bit of discomfort. Or, as they dry out (particularly if you sleep in them), they can actually cut your eye."
] |
[
"Why can cracking a joint release muscle tension?"
] |
[
false
] |
Regularly, I'll have muscle tension and/or pain in my back, shoulder, wrist, etc that seem to be resolved after cracking an affected joint. Just stretching the affected area isn't enough in these cases. Knowing that, fundamentally, cracking a joint is just creating a cavity between the bones (and hence stretching the muscles and ligaments), it's not clear to me why this should be.
|
[
"To be straight, there is no answer backed with scientific evidence to answer this question of yours but there are many theories.",
"I am a D.O. (osteopathic) medical student. One technique we do is called HVLA and involves \"popping\" or as we say gapping a restricted joint. The current running theory is that restricted tissues that limit mobility get congested and build up cytokines and stuff within the tissue. One major product built up is nitric oxide (NO) which is released by endothilial cells in response to inflammation in very small parts to only act locally in that area. ",
"By forcing your joint to move past its restrictive barrier into its anatomical barrier (the normal range of motion allowed before tearing a ligament, muscle or tendon) you force the nitric oxide bubble within all the inflammation to burst (popping noise) and achieve an overall relaxation response resulting in full range of motion being restored."
] |
[
"Most of the studies I've read mention very little about enorphins. It's plausible though."
] |
[
"Im no doctor, but doesnt cracking a joint make your brain think there was severe trauma at that point and thus release endorphins? Wouldn't that be the part that makes it feel like it \"releases muscle tension\"?"
] |
[
"Is the usable mathematics a limiting factor for study of Physics?"
] |
[
false
] |
This is a very long post with a lot of questions: I recall a quote by Einstein saying that he could not proceed further after a point in GR with the general mathematical tools until he was able to use tensors in it. Is it that the more simpler concepts were too inadequate, or was it that it was almost unworkable with those simpler mathematical techniques? Looking at QM, Heisenberg initially worked with Matrices and Schrodinger waves, with the latter method simpler and more intuitive, but both later proved to be equivalent in their approach. Fermat claimed a very elegant proof of his last theorem, but didn't it take mathematics which were developed only recently(20th century) to prove it? And the proof is not elegant(100+ pages). Did the mathematics limit our idea or was it that only Fermat could prove it elegantly? My question being, would future theories rely more on using the most sophisticated mathematical ideas to create a complete model or is that the model be explained with more simpler tools , pointing towards an "equivalence"? And since mathematics is voluminous, would learning very complex models to be applied in physics be justified? Any additional info would be helpful too.
|
[
"From the level of quantum mechanics that I have studied, almost every single form of Schrodinger's equation can be solved using perturbation theory. ",
"That's because in courses they only present you with problems that have known solutions, and are amenable to approximation methods like perturbation theory. By the end of the 2nd or 3rd year of QM and QFT you've seen basically everything that we know how to treat analytically.",
"Basically, if there's a problem that can't be solved exactly by using analytical tools, then there is a method to solve it to many, many digits using intensive computational power.",
"This is not true either. I work on approximation methods related to quantum spin systems, and this is a highly non-trivial problem. In fact, we have hardness results due to the rigorously proven computational complexity of quantum systems. This is the entire reason that quantum computing is interesting. If we could classically approximate, for example, the quantum amplitudes related to Shor's Factoring Algorithm, then there would be much less incentive to build a quantum factoring machine at all. The fact that we believe (on good evidence) that integer factoring is a hard computational problem is an example of what I mean by complexity theoretic evidence against quantum simulability. ",
"To take an example from another domain, quantum chromodynamics (QCD, the Quantum Field Theory which describes the strong force between quarks and gluons) is a strongly-coupled gauge theory which is very difficult to computationally simulate using a discretized lattice spacetime. \"Strongly coupled\" means that perturbation theory is not valid in the range of energies that describe e.g. nuclear physics, and \"gauge theory\" implies that there is an enormous redundancy in numerical descriptions caused by high degree of symmetry involved at every point in spacetime. Even a simple sounding calculation, like computing the mass of the proton from knowledge of it's constituent quarks, has only been possible in the last decade or so, and depends on a series of clever analytic transformations, neglecting all sorts of effects which by all rights should be important, and running on a supercomputer (none of this should take away from what an impressive accomplishment and test of the theory it is to calculate the proton mass). ",
"There are really no shortage of these kinds of examples, and they have important applications too. Some of our best descriptions of condensed matters systems, like high-temperature superconductors, are also described by highly non-linear quantum field theories. One of the most important near-term reasons for building quantum computers is the goal of doing scientific simulations that would be effectively impossible on classical computers of any conceivable size and speed."
] |
[
"I'll leave most of your questions to people more knowledgeable in physics, but I'd like to address the part about Fermat's last theorem. It is generally believed that Fermat didn't have a correct proof; the only known proof requires methods far beyond what was known in Fermat's time, and in fact involves the study of objects that weren't discovered until centuries later.",
"Furthermore, there are several points at which, given the state of mathematical knowledge at the time, it'd be very easy to make a false assumption that would cause the proof to fail. It's not hard to see how Fermat could have mistakenly believed he had a proof.",
"However, just because the modern proof is long and highly technical doesn't mean it's not elegant! The key component of Wiles' proof is proving a significant case of the ",
"modularity theorem",
" (later proved in full), which is a beautiful theorem that ties together elliptic curves and modular forms, two objects of study that arose in very different ways and were originally thought to be unrelated. The proof is so long because this is a seriously difficult result, not because of any lack of ingenuity. (That's not to say a shorter, more elegant proof might not be discovered in the future — but if it is, I bet it'll use techniques that aren't known yet.)"
] |
[
"Possibly.",
"While I haven't studied General Relativity in depth and can't speak to that particular example, in general I can confirm that physics periodically relies on advancements in mathematics to advance itself.",
"The thing is that advancements in physics are largely unpredictable. We don't know what we'll need next, so we don't know whether the next big theory will require no more than matrices (which are pretty basic as far as mathematical tools go), or if it will require something no one has thought of yet.",
"I recall from taking Quantum Mechanics that there were a couple big steps that the founders took in developing it where they had to turn to mathematicians for help. I believe this had to do with group theory or understanding some bizarre functions (of which there are quite a few!).",
"There are many areas of physics where it's clear that there is more work to be done, but most of that work will look like one of the following:",
"The thing about bringing in fresh, revolutionary mathematics is that it requires fresh, revolutionary physics to make it relevant. Einstein needed new math because his theory was redefining the shape of space-time, for which there was no precedent in physics. The founders of quantum theory needed new math (or at least advanced math they weren't yet familiar with) because their theories were based on a probabilistic world, which again was a complete game changer with no previous physics that could help guide the way. Aside from these two theories, physics pretty consistently uses the same pool of relevant mathematics over and over. For physics to again hit the wall of mathematical knowledge like it did with relativity and quantum physics, it would need to introduce an idea that has never been seen before. And we simply don't know how many more times this can happen until we've exhausted the physics to be found. Quantum theory has been called the \"most successful physics theory ever\" (to quote my quantum professor), so it could either be the peak of new physics beyond which nothing will ever be quite as revolutionary, or it could be the first stepping stone to a shitstorm of science that's about to blow our minds.",
"So could new mathematics be needed to create new physics theories? Possibly. I hope so."
] |
[
"Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Taiwan and Costa Rica have an audit branch of government in addition to the three classic branches. What does it do and why do they have it?"
] |
[
"Are there any political systems in the world where the judiciary has oversight over or is otherwise involved in the budgeting process? If so, are those systems successful?"
] |
[
"Ashkenazi Jews have traditionally held finance jobs in parts of Europe and America for the last 800 years or so. They have acquired a money-conscious stereotype as a result. I remember reading somewhere that other cultures have their own versions of the stereotypical money-conscious demographic. Does anyone know what these other examples are, and why this structure has co-evolved multiple times?"
] |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.