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[
"Why does stimulated emission release two photons rather than 1?"
] |
[
false
] |
In stimulated emission, an electron in an excited state is struck by an incident photon. This causes the electron to emit two photons in the same direction and phase as the incident photon. Why does this occur as opposed to emitting one photon in such a manner, and later spontaneously emitting the second photon?
|
[
"Sort of. ",
"Because energy is quantized, there are discrete energy levels at which the target electron can live.",
"If the electron is in an excited state, and it interacts with the correct frequency electromagnetic radiation (i.e. a photon) the disturbance will cause the excited electron to fall into a lower energy state, the energy difference being equal to the energy of the initial incident photon. That's why only certain frequency photons will cause this phenomenon to electrons at specific energies; the incoming photon must be exactly at a multiple of 1 electron quanta of energy. "
] |
[
"The photon behaves both as a particle and a wave. It's not just a single defined point particle that \"happens\" to interact. It's also an electromagnetic field, that is defined at every point in the Universe. Even though, in some limits,a photon can be treated like it is exactly at one point in the Universe, in reality it's a wave packet.",
"If one were to write out the full quantum relativistic Lagrangian for this interaction, you could see that there is a cross term between the EM tensor of the photon and the wave function of the electron. "
] |
[
"That's not how stimulated emission works, the original photon isn't absorbed. Photons aren't just like little particles zipping along and running into things, they are packets of electromagnetic waves, which means that they are composed of oscillating electric and magnetic fields. When these oscillating fields interact with an electron that can change energy levels at the same energy as the photon it creates an effect that encourages the electron to change states, and to do so in a way such that it's phase aligned with the original photon."
] |
[
"In the chemical reaction of photosynthesis, all the Hydrogen comes from water. Why is it that additional Hydrogen ions are taken in during the process? Why do Hydrogen ions not build up in the thylakoid because of this?"
] |
[
false
] |
When I say chemical reaction I’m referring to 6H20 + 6CO2 -> 6O2 + C6H12O6 Edit: To clarify, I know that the chemical reaction has balanced Hydrogen on both sides. My questions is that since this is balanced, the only source of Hydrogen that should be necessary for photosynthesis should be water. Yet, in photosynthesis Hydrogen ions are obtained both from water and from another source as electrons go from photsosystem 2 to photosystem 1. Why is there a second source if water should be able to provide all the Hydrogen ions necessary?
|
[
"I think the additional hydrogens you are talking about are a part of a proton gradient that is established over the thylakiod membrane as a way to store and utilize the light energy taken in by the chlorophyll. ",
"What is actually happening when chlorophyll absorbs light is that electrons within the chlorophyll molecule are being \"excited\" to a higher energy state as the specific shape of the chlorophyll molecule catches the light. ",
"These excited, high energy electrons are then passed between other molecules(proteins) that interact with the chlorophyll. The energy stored in those electrons can then be used by the proteins to perform various functions for photosynthesis. One of these is the creation of a proton gradient. ",
"Something to understand about water is that it is not really just a bunch of H2O molecules. Water actually exists as a constant equilibrium of whole [H2O] molecules and separated [H+] and [OH-] ions. Individual water molecules are constantly breaking apart and re-forming, but there is a constant ratio of together vs apart that is generally maintained. ",
"During photosynthesis, some of the proteins I mentioned earlier use the energy they take from that high energy electron to pump H+ ions across a membrane. (They can do this because the water in the cell is constantly breaking apart and re-forming.) By doing this, there are now more H+ ions on one side of the membrane and more OH- ions on the other. This results in an electrical potential across the membrane. ",
"Other proteins are then able to use the energy stored in this electrical potential for other, different functions. (Something similar happens with cellular respiration and the electron transport chain, just with energy from food breakdown rather than light.)",
"So long story short, I think those hydrogens you're seeing are part of that gradient; they will get recombined into water when the second set of proteins lets them back through the membrane in order to use the energy stored in the gradient. Since at the end of everything they end up back together as water, they are not included in the net reaction. "
] |
[
"Thanks for the thorough response. This makes sense. On further inspection it seems the H+ ions travel back to the OH- concentration outside the thylakoid due to the e field or diffusion and they must go through the ATP synthase which makes ATP with that energy. ",
"Looking back at it I think my confusion arose from a diagram of the light reactions. The diagram showed all the H+ ions, the ones from surrounding fluid and ones from the 6H20, leaving the thylakoid through the ATP synthase. However, wouldn’t it only be the H+ ions originally from outside that would escape? The 6H20 hydrogen ions would need to be used to produce glucose wouldn’t they?"
] |
[
"Well the chemical reaction you are referring to is correct. if we are able to radioactively label each of the reactants, we would find the same atoms in the product. It's been a while since i've taken biology but I seem to remember that hydrogen ions are responsible for things other than the direct reaction themselves. maybe they provide energy via the hydrogen ion gradient?"
] |
[
"Are arctic mammals cold all of the time?"
] |
[
false
] |
Why or why not? I was watching a program on polar bears and thought, "Wow! They must be freezing!" Then I realized if it were that big of a problem, they probably would have migrated? I hope this isn't the stupidest question you've ever heard...
|
[
"I think you're getting downvoted for your third paragraph, which is a shame because no-one else has commented on the excellent point you make in your second paragraph.",
"Discomfort is an adaptation too, to induce a behavioral remedy to a survival challenge. If there is no behavioral remedy, discomfort is pointless."
] |
[
"yeah but do they feel cold all the time? do they perceive cold as we do?"
] |
[
"Those animals which do not migrate in winter and those in areas where weather can get below freezing... so most of Canada, Russia, and parts of USA for example, have special adaptations to deal with freezing temperature, lack of food and lack of fresh water (snow is difficult to eat, and often access to running fresh water posses a bigger problem for arctic/winter animals then the lack of food). Stored body fat and/or a steady supply of food is why mammals are able to withstand near freezing or below freezing temperatures. Mammals regulate their heat internally, thus by eating food or using stored food (fat) they can generate the heat needed to survive. Humans do this too, our core body temperature stays the same, even if our extremities are cold/exposed. After a certain point/length of exposure/temperature humans (and other mammals) will experience ",
"hypothermia",
".",
"Some examples of adaptations to life in the cold are:",
"Polar bears",
" have a thick layer of fat - a great insulator. Their skin is black, but their fun is clear so and heat from the sun is absorbed.",
"Arctic foxes",
" and hares have thick fur with many layers to insulate heat. They and other cold-adapted animals, including birds have ",
"counter current heat exchange",
", where warm blood delivers heat to cold blood - this makes the blood medium temperature or it distributes the heat more evenly in the body for example.",
"Seals, walruses and cetaceans have thick layers of blubber to keep in heat. ",
"Emperor penguins",
" also have many adaptations.",
"Other birds, like owls have feathers which provide a lot of insulation. Smaller birds, like the ",
"black-capped chickadee",
" stay in regions of Canada throughout the winter (like in Calgary, where temps can get below 30 degrees Celsius), they are just able to do this because each day they must find the right amount of food to generate heat for the whole night. They also can lower their body temperatures at night and go into a sort of ",
"torpor",
". Some do not make it, and the colder it is the more food they need that day to survive.",
"And there is also this book: ",
"Arctic animals and their adaptation to life on the edge"
] |
[
"Could someone explain exactly how enzymes work?"
] |
[
false
] | null |
[
"Enzymes are protein or nucleic acid complexes that through their structure lower the potential energy required to leave one steady state and move to another. Furthermore an enzyme can use potential energy stored in one molecule to force a reaction in another molecule from a low energy state to a higher energy state.",
"However if you are litterally asking how enzymes work? Well they are all different and far from all mechanisms are known."
] |
[
"Enzymes work in a sort of lock-and-key relationship with their substrate or substrates. When a particular substrate bumps into its matching enzyme, some weak bonds form causing changes in the enzyme's shape as well as the substrate's bond energies. By doing this the enzyme becomes an environment in which a particular chemical reaction is energetically favorable. ",
"This is the most rudimentary explanation of a catalyst enzyme, as there are enzymatic reactions that occur in cells which are immensely complex and scarcely understood."
] |
[
"Enzymes lower activation energy for a given reaction by facilitating the transition state between substrate and product.",
"The transition state is the high-energy intermediate between substrate and product. If the substrate achieves this state it can without further energy input transition to the product (or just as likely back to substrate). Because all reactions that are catalyzed by enzymes also occur without the enzyme (although much, much slower) you can think of this structure as unlikely to appear without help.",
"The active site in the enzyme will have a three-dimensional shape that is complementary to the transition state and therefore stabilizes the transition state. This increases the chances of 'spontaneous' transition from substrate to product for a given temperature and thereby lowers the activation energy. The interaction between enzyme and substrate in the transition state will also often give small changes in the structure of the active site that further help the substrate transition to product.",
"In the transition state the molecule will just as likely go 'back' to substrate as it will 'proceed' to product. Because of this, the enzyme will not change the amount of substrate and product at equilibrium, it will only influence the time it takes for a given reaction to reach equilibrium."
] |
[
"Why do films look so strange and unnatural when displayed on monitors with extremely high refresh rates?"
] |
[
false
] |
A few years back, I remember seeing The Empire Strikes Back playing in the window at a high-brow electronics store called Bang and Olufsen. The monitors were flatscreens and apparently had a high refresh rate. The movie looked as though it was filmed in a BBC studio and was very offputting. I assume if one were born with this technology in place, it would not be so strange. But perhaps not...
|
[
"Motion smoothing. The Empire Strikes Back was not filmed at such a high frame rate, but modern TVs can use interpolation techniques to \"reconstruct\" intermediate frames. ",
"Here",
" you can read about the effect and how to disable it on most TVs."
] |
[
"Films have been shot at 24 frames per second ",
"since the 1920s",
". You've formed a psychological link between the low frame rate and \"movie-ness.\" A monitor or TV with a high refresh rate might still only show the film at 24FPS, but some modern sets will construct new frames to give the film a smoother look. People don't like this effect, even though it is much more life-like and realistic.",
"Since most television shows (especially cheap Soap Operas) and home video cameras shoot at a higher frame rate (typically 30 or 60FPS) you associate \"unnatural\" or \"cheap\" video with higher frame rates. When a film is converted to a higher frame rate, it looks less like a film to your eyes, even though you're getting a more accurate representation of what's going on."
] |
[
"Most films run at 24 fps. Camcorders and digital video recorders often have higher frame rates (say 60 fps). These are often used by sitcoms and cheap TV because they are unable to afford film. Unfortunately, this means that people find higher frame rates look unnatural, and associate them with home movies or cheap TV. ",
"Cinematographer Naim Sutherland claims the following:",
"“The goal of motion pictures is not to recreate reality, it’s not even to show reality…By not showing enough visual information, we force the brain into filling in the gaps… it draws you in even more. It’s part of how you let go to the point where you can laugh or cry or feel tense or afraid or elated.”"
] |
[
"Does the injection site affect which cells express the spike protein from the mRNA Covid vaccines?"
] |
[
false
] | null |
[
"Most important cells are in the draining lymph nodes and details of injection site won’t change that"
] |
[
"Is there a paper/study that can expand on this further? This seems to be in the direction of what I was asking..."
] |
[
"previous questions in ",
"r/askscience",
" list some of the relevant literature"
] |
[
"Hey fellow scientists of /r/askscience, I've started a subreddit to help increase access to articles for those doing research. Need an article fast for an article/grant but your institution doesn't have access? Maybe a redditor can help"
] |
[
false
] |
ILLiad can be slow and you might not get the article you need in time but for a while now I've been asking friends at other universities to get me an article their school has access to that mine doesn't and I figured this sort of exchange could benefit others. I've created the subreddit to facilitate this exchange. As long as we keep things relatively anonymous and low key, I don't think we'll have any problems. While we're on the subject... does anyone have access to Current Protocols in Neuroscience? I need article if anyone could help. Thanks! edit: fastparticles hooked me up with the article so I don't need anyone to get it anymore. Thanks!
|
[
"See also ",
"/r/scholar",
"; most of the requests I've seen have been fulfilled quite quickly."
] |
[
"While I think this is a fantastic idea I'm pretty sure it violates the licenses of those websites so I don't think it would fly on reddit. I am not an expert in this though.",
"I sent him the paper. I will help out other people assuming I don't get swamped."
] |
[
"This is a good idea! I would help out when I can, provided I don't get swamped with requests, I already do this for a number of colleagues at smaller institutions with more limited resources.",
"Unfortunately I do not have access to the article you need but I have some knowledge about brain microdialysis if you need some info.",
"Also you can email the corresponding author about the paper and he/she will likely send you a copy (its flattering to them that someone has interest in their work), seeing as the paper you want is from the intramural NIH campus they are almost obligated to send you a copy if you ask for one. "
] |
[
"How does symmetry give rise to forces in Quantum Mechanics?"
] |
[
false
] |
I have read somewhere that forces are caused by symmetry groups of Quantum mechanics. Can anyone explain intuitively why this happens?
|
[
"I'm pretty sure OP is referring to Gauge Groups like SU(3)xSU(2)xU(1), which describe the standard model forces."
] |
[
"The simplest example is that local U(1) gauge symmetry of electrons implies the existence of photons. There's a global gauge symmetry in the Schrodinger equation that says you can multiply the wave function by any phasor (magnitude one complex number) and still get the same answer. If we want to make this a local symmetry, i.e. we can multiply every point in space by a phasor and still get the same answer, we find that the minimal consistent theory now includes photons.",
"I kind of intuitively think of this as if we say that we can modify the phase of an electron arbitrarily at any point without changing observables, we're still changing the momentum of the electron (see the KE term in the Schrodinger equation) and so the momentum must be going into another field -- the A vector gauge field, or photon."
] |
[
"If you frame your description of the physics in a particular way it can look a bit like the symmetries cause the forces, but you can argue how useful that perspective is.",
"For example, you could write down a theory of free non-interacting electrons and positrons (or any spin 1/2 particle/antiparticle) which has a global U(1) symmetry. If you then demand the U(1) to be a local symmetry, you find the only way to do this is to introduce a vector field (the photon) with all of the properties of Mawell's E&M built in. From this point of view it can look like by forcing a global symmetry to be local you've forced non-interacting particles to become interacting, so the symmetry has \"caused\" the force. I think this is where people are coming from when they make those kinds of statements."
] |
[
"It's accepted that quantum entanglement can't be used to transmit information, but is there any reason it can't be used to coordinate action?"
] |
[
false
] |
Alice and Bob both have an entangled photon. Before heading off in separate directions with their respective photons, they agree that positive spin means buy milk, negative spin means buy bread. Hasn't this allowed them to do something they couldn't have done before? That is, separate by an arbitrary distance and then coordinate their actions faster than light? Of course, they could do the same thing when they initially met up, but what if not deciding on which thing to buy until some amount of time has passed is for some reason important? I feel like either I'm missing something, or what I'm suggesting is accepted and considered trivial.
|
[
"What specifically is Bob or Alice doing that even requires entangled particles here?",
"You might as well seal two envelopes with instructions for one for milk and one for bread and give each of them one envelope at random. The entanglement is needless complication."
] |
[
"I mean you could do that too with the envelopes. Also, ",
"do the same thing at the same instant in time regardless of how far apart they are",
"I can arbitrarily rig a reference frame that this is true as well as reference frames where this is false. Simultaneity of independent events (correlated or not) is not a sacred in special relativity. "
] |
[
"I think I see what he's getting at.",
"Create an entangled pair of photons in phi plus bell state and send one photon to Alice and one to Bob, who are widely separated. Alice and Bob both agree to measure in a diagonal basis before hand, so they know that their outcomes will be correlated. If Alice measures |+>, so will Bob. If Alice measures |->, so will Bob. Neither one can control what they measure, so FTL signalling is not possible. ",
"However, if they agree in advance to take an action based on measurement outcome instantly after measurement, they can potentially both do the same thing at the same instant in time regardless of how far apart they are. However, nobody could accurately predict which of the two things Alice and Bob will both do with better than 50% certainty, assuming there's no bias in their system. ",
"This shouldn't be too mind-bending. Really, this is already being done by the lights on their measurement devices. ",
"Edit: I just wanted to add that this ability to use entanglement for coordination is well known, and is the basis for ",
"\"quantum pseudo-telepahy\""
] |
[
"How did scientists contain something 4 million degrees F?"
] |
[
false
] |
[deleted]
|
[
"\"Temperature\" in this sense is somewhat misleading, it's really just derived from the mean kinetic energy of a set of particles with an energy distribution. If you multiply the temperature in [K] by Boltzmann's Constant (8.617e-5 [eV/K]), you'll get the average kinetic energy in electron volts. For a fusion reactor operation at 200 million K, this comes out to roughly 17keV, or about the same energy as the electrons hitting the back of an old TV cathode ray tube. No longer so impressive, eh?",
"Additionally, magnetically confined fusion plasmas are also under vacuum and incredibly sparse. So while the \"temperature\" may be high, there is so little gas that the amount of heat energy contained is very low. Kind of like how you can have a hot cup of boiling water, but the total heat energy it contains is still far less than a swimming pool of water at room temperature.",
"If the magnetic field confining the plasma were to disappear, the hot particles would collide with the walls and transfer their energy, thus cooling down. The effect would probably make the walls get locally hot and ablate a thin layer of material, but the overall energy deposited wouldn't necessarily be catastrophic."
] |
[
"You use a magnetic field to trap the (electrically charged) particles."
] |
[
"The surface of the sun is only 5000K, so that's not really very much compared to temperatures achieved on earth.\nThe fusion core under construction in france (ITER), for example, will reach temperatures of up to",
" 150 million K.",
"They achieve those temperatures using three different types of heat generators. ",
"1)Neutral Beam Injection ",
"2)Ion Cyclotron Heating ",
"3)Electron Cyclotron Heating ",
"for more information, please read this ",
"explanation",
". "
] |
[
"Is there a difference between taking short or long breaths?"
] |
[
false
] |
[deleted]
|
[
"There is a major difference. Total lung capacity is about 6 liters. 150 ml of that space is anatomical dead space (nasal passages, oral cavity, etc) and doesn’t participate in gas exchange. This means rapid shallow breaths are a waste of perfusion to the lung. ",
"Second, rapid shallow breathing removes more CO2 from the body. This increases the pH of blood resulting in respiratory alkalosis. This leads to smooth muscle constriction and decreased cerebral perfusion."
] |
[
"Actually yes! There is multiple steps that happen when you breath in. First you take in air which your body processes the oxygen out of. But the big thing is that is removes the carbon dioxide from your body back into the air. Taking short shallow breaths can lead to a build up of carbon dioxide in the blood. This is done by increasing the flow in of oxygen but not allowing your body to process and remove the carbon dioxide from the body. This will cause dizziness due to this build up. ",
"",
"So it does depends on how short. If you mean normal as short and long as in deep then generally not. When moving you tend to need a faster supply of oxygen and also to remove the carbon dioxide so you tend to breath faster. But on a normal day sometimes a deep breath can be relaxing as its a huge boost in oxygen to the body with a full release in breath. ",
"",
"So, a deep long breath when relaxing can boost your mind and body while it is necessary to do fast breaths when exercising.",
"",
"Great question!"
] |
[
"Taking short shallow breaths can lead to a build up of carbon dioxide in the blood. This is done by increasing the flow in of oxygen but not allowing your body to process and remove the carbon dioxide from the body. This will cause dizziness due to this build up.",
"What would be the mechanism behind that? I've studied some respiratory physiology but I don't remember that happening."
] |
[
"Why is the ozone layer thinnest around Antarctica, why is ozone depletion not evenly spread around the world?"
] |
[
false
] | null |
[
"From wikipedia:",
"http://en.wikipedia.org/wiki/Ozone_depletion",
"Reactions that take place on polar stratospheric clouds (PSCs) play an important role in enhancing ozone depletion. PSCs form more readily in the extreme cold of Antarctic stratosphere. This is why ozone holes first formed, and are deeper, over Antarctica. Early models failed to take PSCs into account and predicted a gradual global depletion, which is why the sudden Antarctic ozone hole was such a surprise to many scientists.",
"There is a temperature difference between the north and south poles that accounts for the difference in the depletion of each. "
] |
[
"Ozone Depletion also takes place particularly within the ",
"polar vortex",
" of the southern hemisphere.",
"The chemistry of the Antarctic polar vortex has created severe ozone depletion. The nitric acid in polar stratospheric clouds reacts with CFCs to form chlorine, which catalyzes the photochemical destruction of ozone. Chlorine concentrations build up during the polar winter, and the consequent ozone destruction is greatest when the sunlight returns in spring. These clouds can only form at temperatures below about -80°C.",
"And, because of the temperature difference mentioned above, this becomes one of the contributing factors to the southern hemisphere's thinner ozone layer."
] |
[
"Chlorine radicals cause ozone depletion. These are all over the world. Now, the question is not only why the ozone hole is over Antarctica, but also why it ",
"only becomes significant in Spring",
". This is because the chlorine radicals get 'tied up' in compounds which do not cause ozone depletion. They form these compounds in the Winter, then when it heats up in Spring, UV light breaks these compounds down and releases chlorine radicals. Now, we have a large amount of chlorine, which means the ozone destruction speeds up and we get a hole."
] |
[
"Is there a reason we do not put our Depleted uranium/fuel rods on the moon, or in space?"
] |
[
false
] |
Was watching aftermath and was talking about some of the bi-product of nuclear energy and it's storage lastings hundreds and thousands of years, so I was wondering why don't we put them in space where it is constantly cold or into the sun?
|
[
"It's extremely expensive to launch things into space, especially given the number of launches it would take to remove all the waste accumulated over the past 60 years. Also, if a rocket exploded during launch, radioactive waste would be strewn over a wide area. Aside from that, it would be an effective long-term solution."
] |
[
"At about $20,000/kg and 3,000 short tons per year, it would cost the US about $60 billion annually just to get our waste into orbit."
] |
[
"Plus depleted uranium is useful in a number of applications, mostly due to its enormous density.",
"It's 1.67 times as dense as lead.\n",
"http://www.wolframalpha.com/input/?i=density+lead+vs.+uranium",
"Plus I think you are associating nuclear waste with depleted uranium, and while it certainly is a by-product, it is not nearly as dangerous as nuclear waste.",
"You see depleted uranium is the left over from the uranium refining, where you remove the less fissile uranium to enhance it's purity. ",
"What is removed is depleted uranium. It is mostly composed of less radioactive isotopes, and is thus less radioactive. Because it's less radioactive, it can be used for civilian applications (counterweights, ect). ",
"Nuclear waste, on the other hand, are what the uranium inside the reactor decayed into. These contain a lot of different highly radioactive materials, and is probably what you meant when you said \"bi-product of nuclear energy\"."
] |
[
"If I were to make a mechanical clock from scratch, how would I know how long a second or a minute actually was?"
] |
[
false
] |
[deleted]
|
[
"You wouldn't. A second is an arbitrary measure; while it has been defined in terms of fundamental physical constants, it's not possible to measure the resonance of cesium with a purely ",
" clock."
] |
[
"I would try to get the number of seconds between two consecutive sunrises to match what the daily paper and/or an astronomy website says the interval should be. Are you contemplating a primitive scenario where you have no access to a paper? Hmmmm... You may need a longer calibration period than one day."
] |
[
"bit of a late reply, and you probably won't see this, but a 1 meter pendulum is roughly 1 second per swing.",
" "
] |
[
"Why is my pee omni-directional somtimes"
] |
[
false
] | null |
[
"Most men only use their penises for two activities, which means that men generally ignore what their penises are doing the rest of the time. Despite your best efforts (or possibly because of them) you will see or think of something sexually stimulating during your daily activities (or accidentally rub up against something and experience manual stimulation), which will cause your reproductive organs to spring into action. Your internal reproductive organs will secrete some seminal fluid (natural lubrication) as a result of this involuntary reaction to sexual stimulation. ",
"If the stimulation is very short and does not continue into sexual activity, the production of seminal fluid will stop and your penis will go back to its usual non-sexual activities (I am not making this up: moving around on its own within your trousers, dodging the movements of your testicles as they regulate the temperature of your sperm, etc.). Since most men do not take multiple showers in a day, that seminal fluid will stick around in your penis. Some of it will have made it to the tip of your urethra, causing the opening to stick shut. ",
"When you next urinate, the edges of the urethral opening at the tip of the penis will spring open first, but the center, with more surface area to stick together, will stay stuck for a second or two. This will cause the urine to squirt out the sides of the urethral opening, initially forming two streams. As the stream continues and knocks away at the dried seminal fluid, eventually the entire urethral opening completely unblocks, and the two urine streams merge into one."
] |
[
"Thank you very much"
] |
[
"You're right, It's not the Testicles that regulate the temperature of the sperms, it's the scrotum. "
] |
[
"What is the purpose of facial hair and why don't women grow it?"
] |
[
false
] |
[deleted]
|
[
"Everybody is a mutant, otherwise we wouldn't be people."
] |
[
"This paper ( ",
"http://www.frontiersin.org/behavioral_neuroscience/10.3389/neuro.08.045.2009/abstract",
" ) posits that human beards and lion manes evolved convergently- to protect the male from intra-species attacks. Women wouldn't grow beards because it is men who were competing against each other for mates."
] |
[
"From the cited paper:",
"Like the lion’s mane, male beards are widely assumed to be somewhat adaptive in the context of providing a visual aid to identification of gender at a distance; in advertising social dominance; or as sexually attractive to women (Barber, 1995 )",
"As an Asian man who cant grow a beard, am I a mutant?"
] |
[
"Women between 65-69 are 5 times more likely to die after a hip fracture. Is it the fracture itself or something else that leads to increased mortality?"
] |
[
false
] |
[deleted]
|
[
"Combination of things. ",
"One is that after a hip fracture, a person is less likely to be very active, and being active correlates to a longer life. So in a sense the fracture caused that decline in life expectancy. ",
"A much smaller number might have complications related to the fracture, or to the treatment, that could be an issue. ",
"Most likely though is statistical bias. Its like saying \"people who have had a heart attack are \"X\" times more likely to have problems with their knees. Well, yeah, heavier people have more heart attacks, and also worse knees. Similarly, women who may have balance issues, or encroaching dementia, tremors, or who are not taking proper care of themselves, are more likely to fall and break their hip, and also more likely to die. "
] |
[
"From what I recall from my bachelor course where we talked about this, it isn’t the fracture itself but other factors. A hip fracture alone, you are likely if it is a particular bad one to do some serious damage to your femoral artery as well, if you sever this artery you’re going to bleed out in something like 10 minutes (? Don’t quote me but it was very quick) ",
"Women in that age bracket typically have low bone mineral density so weaker bones so the fracture itself is usually worse. If they are also sedentary , a lot of them don’t regain ambulation which has obvious effects on your quality of life but also other co morbidities related to extended bed rest. ",
"To some degree as others have touched on, it is a “correlation”, so not causative, the hip fracture typically has a negative effect on other medical conditions they already suffer from. "
] |
[
"The hip fracture population has mortality rate approaching 20-30% at 1 year post fracture. This high mortality rate can be attributed to a few factors.",
"Pre-existing illness: People who fracture their hips from a fall from standing height are usually already frail. The fall and fracture can be a result of poor bone density, impaired balance, dementia, heart or lung problems, vision problems, deconditioning, etc. People who fracture their hips are also generally older.",
"The fracture itself, surgery and its complications: infections, bleeding, choking on food, blood clots/thromboembolism, myocardial infarction, stroke, deconditioning, brain bleed, pressure sores, etc."
] |
[
"If there was another planet with the same orbit time as Earth, would we know?"
] |
[
false
] |
Hey all, If there was another planet with the same amount of time to orbit the Sun as Earth, but was on the far-side of the Sun, would we know? Dan O.
|
[
"Yeah, because Earth's orbit is elliptical and not circular we would still see it at times. Also, the probes we've sent to Mars and Venus and other planets would not have reached their destination if there was another planet on the other side."
] |
[
"The elliptical/circular thing doesn't necessarily mean that we'd see the planet - if it had the same eccentricity that the Earth's orbit does, and has the periapsis line up with the Earth's periapsis, then we wouldn't see it because it would still always be opposite the sun.",
"Also, the ",
"Hill sphere",
" of the Earth really isn't that large - unless probes launched passed nearly exactly opposite the Earth's orbit, it wouldn't necessarily cause the probes to be diverted.",
"The best way to determine whether or not there was a planet opposite Earth would be to see if the Earth is orbiting slightly faster than the known ",
"gravitational parameter",
" of the Sun would suggest. If there was a planet opposite Earth it would be pulling the Earth a little bit extra on top of how the Sun is pulling it, so it would cause the Earth to orbit faster than the gravitational pull from the Sun alone (roughly circular motion + greater inwardly directed force = higher velocity)."
] |
[
"Yes. For one thing, it wouldn't be able to stay exactly in the same orbit over time. Perturbations from other planets would delay it or speed it up, so eventually it would become visible, and really it would eventually wreck havoc with the Earth's orbit. For another, it would perturb the orbits of other planets so that even if we couldn't see it, we could detect its presence through those perturbations."
] |
[
"Why are we able to eradicate some diseases via vaccines but not others?"
] |
[
false
] |
Humanity was able to eradicate smallpox in the wild thanks to a worldwide vaccination campaign. Obviously, we are far less successful with influenza. Is this due to the mutations/strains of the influenza virus making eradication impossible? If so, does the smallpox virus not have similar mutations?
|
[
"Only two diseases have been eradicated: Smallpox and ",
"Rinderpest",
", which is a disease of cattle. ",
"Guinea worm, a parasite disease of humans, is ",
"close to eradication",
", although there were some setbacks this year. Polio is also on the track toward ",
"eradication",
".",
"Polio, rinderpest, and smallpox eradication depended on vaccination. Guinea worm doesn't have a vaccine, and its eradication depends ",
"mainly on education",
".",
"What are the requirements for an infectious disease to be eradicated? Ideally it should ...",
"Smallpox met all those requirements, and it was a horrific enough disease that governments and agencies world-wide were willing to put in the effort to eradicate it. ",
"Influenza fails 1, 3, 5, and 6. There’s no chance of eradicating influenza in the near future, but it has very little to do with mutation rate, which at most affects #5 (and then only partially; mutations are only a small part of the problems with influenza immunity). ",
"Further reading: ",
"The Principles of Disease Elimination and Eradication"
] |
[
"When it comes to influenza specifically, the big number of strains comes from the fact that influenza virus has a fragmented genome. That enables it to exchange some parts of its genome with different ones in case a human or animal is infected with two or more different strains. That's why we have lots of different influenza strains which makes the disease harder to eradicate.",
"With smallpox, it was several factors that made it relatively easy to eradicate. One was that vaccines were at the time in a very positive light and the campaign to eradicate smallpox was met with little resistance. It was also the first vaccine to be developed and it took a very long time to actually eradicate the disease. It was also relatively deadly and easily recognizable, meaning that the populace was scared of it and avoided the sick. There's probably other reasons."
] |
[
"most virusses and bacteria have what we call a reservoir, an animal or the soil which allows them to replicate or survive. For example the clostridium tetani bacteria can survive years in the soil. We will probably never be able to eradicate those diseases completely.",
"Some pathogens however have no such thing, for example the polio virus. Polio only affects humans and thus it can be eradicated. We've already eradicated polio strain 2, strain 1 and 3 are being eradicated as we speak (strain 1 is only endemic in Nigeria, Pakistan and some other countries).",
"Another issue is that some vaccines target toxins that bacteria produce. The bacteria can replicate and make us a bit ill but the major \"pathogenic factor\", their toxins, are stopped. This means that there is no herd immunity for these diseases with vaccines, nor can we eradicate those diseases. An example of this is the difteria vaccine (if i recall correctly). ",
"Another problem are the anti-vaxxers."
] |
[
"Why is coconut oil supposedly healthy?"
] |
[
false
] |
So I've seen the new "fad" (for lack of a better word - if it is based on sound science, I suppose it isn't a fad...) in the health food stores of selling coconut oil as the healthiest oil for cooking. What is the reason it is supposed to be healthy? Coconut oil is a saturated fat, which in epidemiological studies have been shown to worsen the blood lipid profiles. Coconut oil is supposedly better because it is a medium chain fatty acid. How does this lead to it being healthy? Is it because it bypasses the chylomicron pathway and instead of being delivered to the peripheral tissues goes straight to the liver for metabolism? What are the health benefits of coconut oil supposed to be? I heard it was that it oxides less when heating, but that surely can't be all of what's involved here...
|
[
"Perhaps you already know all this, but the main thing with MCTs is that their intake promotes their oxidation. This is in complete contrast to LCTs, which are preferentially directed towards storage when other fuels are available. Consequently MCTs elicit a higher thermic effect than \"normal\" dietary fats, and they also seem to be more satiating. Put together, these facts suggest that MCTs might be effective in promoting fat loss, and experimental studies have indeed found support for this idea.",
"MCTs can also be useful when reducing carbohydrate intake because they provide a rapidly available source of energy, and they are much more ketogenic than LCTs.",
"dustingebhardt's answer was wrong about everything. Coconut oil is not suitable for high-heat cooking; its smoke point is <180 °C."
] |
[
"Actually, if its a saturated fat, by definition it is not an omega-anything. So any omega-3s in there that skew the ratio towards the healthful ratio would be from the non-saturated portion, which is very small. It would make more sense to stick with flaxseed oil for that. ",
"Flaxseed oil does have a low smoke point though. Does that mean that coconut oil is mainly beneficial just for cooking uses?"
] |
[
"It's supposed to have more medium chain triglycerides. MCT help alzhimers. MCT are also an alternative, non-glucose way of energy via ketone bodies, i think the advocates also say that this makes you lose more fat because it puts your body into \"use ketone bodies not sugar\" mode.",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2604900/",
"For the record: Every doctor i have ever asked has told me that coconut oil is one of the least healthy because of the saturated fats. I agree with the docs."
] |
[
"Why is a boat propeller so small compared to the size of the boat it's propelling?"
] |
[
false
] |
I've grown up around boats all my life and have been wondering this for quite some time. My family's 23ft power boat's propeller isn't even a foot in diameter (from edge to edge of the blades if it were spinning and making a full circle). A 93ft boat that runs charters in my town has 2 props that aren't even 3 feet across. How/why does this boat size to propeller size ratio work?
|
[
"While a larger diameter propeller is generally more efficient than a smaller one, the boat propeller size will be typically a function of the boat's draft. The bottom of the propeller should be above the boat bottom, to avoid damaging the propeller against the sea bottom. The top of the propeller should (there are exceptions) be deep enough to avoid sucking air in."
] |
[
"I've wondered the same thing, and I don't know the answer. Maybe a better question is \"why is the vehicle size to propeller size ratio so different between boats and planes?\" In that light, I wonder if there is some material property of the fluid that affects the ratio - viscosity or density or compressibility?"
] |
[
"Suppose you don't care about draft: you want to make a ship that can only sail in deep waters. How large would the optimal propeller be?"
] |
[
"A question about Human cell regeneration."
] |
[
false
] |
Ok, while watching QI, a question was posed about 'How old are you' and in typical QI fashion it was a trick question, where the true answer was based on the fact that every (roughly) 5 years or so, you regenerate every cell in the body. If this is true/remotely true, do brain cells do the same? And if yes, how do the connections between neurons and what-not stay there, and how does the neuron itself not go away...or, how does it not play in to affecting memories/knowledge/motor functions/etc. I'm going on the assumption that the 'wiring' of the brain makes it function a certain way and that if a certain 'wire' was gone, wouldn't the system malfunction? Also, very sorry for my lack of scientific knowledge here, Biology isn't my strong suite.
|
[
", which is the generation of new neurons, only occurs in certain parts of the adult brain. Many of the neurons you are born with are, in fact, the ones you're stuck with until they or you die. However, even \"permanent\", non-replicating cells need to be replenished; over the course of 5 or so years, every neuron will essentially have been rejuvenated with new versions of their old parts (new amino acids replacing the old, and so on). Think of it as gradually replacing parts of a car over the years. After 5 years of replacing the tires, exhaust pipe, and other parts, the car will still be that same car, but rejuvenated. Pretty sure they were referring to this phenomenon in QI."
] |
[
"Cells have very varied rates of replacement...so dismiss anything about trying to generalize that.",
"In terms of brain cells, you should understand that there are two main types: neurons and glia. Glial cells do readily divide, migrate, get replaced, etc. whereas neurons are not generally undergoing such a dynamic process. Neurons are constantly nourished by proteins such as neurotrophic factors (BDNF, GDNF, many others) which keep them going and allow them to branch and make new connections if needed. You are right in thinking that it would be probably catastrophic if we had to constantly replace neurons and repeatedly had to rebuild and reconnect all the networking between them.",
"However, this lack of neuronal replacement can cause problems later in life as the main mechanisms that regulate a healthy cell can go awry and lead to things like Parkinson's and Alzheimer's disease. On the other hand, the constant replication in other cells is what tends to lead to cancers.",
"Just to add, most neuroscientists used to believe that the neurons you were born with were the only ones you got. That only recently has been understood to be false, as there is the process of ",
"neurogenesis",
" in certain brain regions that allows for replacement of neurons and/or additional neurons. Although this is not really all that understood, especially in humans. "
] |
[
"every (roughly) 5 years or so, you regenerate every cell in the body.",
"This isn't true, as far as I know. Different types of cells in the human body have different lifespans.",
"Some cells are very short-lived; for instance, ",
"intestinal epithelial cells last about 5 days before they are shed",
".",
"Other types of cells are longer lived. ",
"This paper",
" dates the lifespan of some muscle cell types to be about 15 years in adults.",
"And while it has been shown that neurogenesis can occur in the adult brain, there are several studies like ",
"this one",
" that show that virtually all neurons in the brain are as old as the individual."
] |
[
"Energy equals mass times the speed of light squared. How can light be squared when the answer would be greater than the speed of light? which can't be exceeded?"
] |
[
false
] | null |
[
"I'm not sure how else to say it... you're saying, essentially, how can E be greater than c? They aren't the same units. So it doesn't make sense to compare them that way. That's like saying how can 10 feet be bigger than 5 kg? Look, you're also multiplying c by m so c*m > c. Again, this comparison doesn't actually make any sense. "
] |
[
"I'm not sure how else to say it... you're saying, essentially, how can E be greater than c? They aren't the same units. So it doesn't make sense to compare them that way. That's like saying how can 10 feet be bigger than 5 kg? Look, you're also multiplying c by m so c*m > c. Again, this comparison doesn't actually make any sense. "
] |
[
"186,000 miles/s * 186,000 miles/s is not equal to 355,000,000 miles/s. It equals 355,000,000 miles",
" / second ",
" That is ",
" the same thing as 355,000,000 miles / s. It does not say anything about any mass being accelerated to or moving at c and applies perfectly well to objects that are at rest. (Also note that E=mc",
" is not the full equation). "
] |
[
"If I gain 10 lbs of fat, lose it, and then gain 10 lbs again, am I \"refilling\" those same fat cells before creating new ones?"
] |
[
false
] | null |
[
"When you gain weight, your adipose tissue cells swell with fat causing them to greatly expand , then divide if they get big enough. When you lose weight, the cells shrink down to their minimum size as their fat reservoirs are depleted, but the cells themselves remain put. So someone who was once obese and is now a healthy weight has a whole lot more fat cells (though mostly empty) than someone who was never obese.",
"Edit: What I was paraphrasing here was an unsourced slide in a powerpoint lecture. ...great. Annnd, the wording in the specific topic of fat cell death/division doesn't appear in the corresponding textbook chapter. I have shamed the name of science. Please defer trust to the several PhDs and PhD candidates who have already commented here on this thread."
] |
[
"http://www.nytimes.com/2008/05/05/health/research/05fat.html?_r=0",
"Every year, whether you are fat or thin, whether you lose weight or gain, 10 percent of your fat cells die. And every year, those cells that die are replaced with new fat cells, researchers in Sweden reported Sunday.",
"The result is that the total number of fat cells in the body remains the same, year after year throughout adulthood. Losing or gaining weight affects only the amount of fat stored in the cells, not the number of cells.",
"The finding was published online Sunday in the journal Nature.",
"Oddly, ",
"adipocyte apoptosis",
" might be a cause of obesity related disorders, like insulin resistance, fatty liver, and general inflammation."
] |
[
"Nice response.",
"Is there any way for your body to breakdown these empty cells?"
] |
[
"While reading the Wiki on \"Project Longshot\", which was a proposed craft to fly to Alpha Centuauri I was stunned to see that the proposal included transmitting data via laser to Earth for the duration of the flight. My question is RE: the accuracy required for such a transmission."
] |
[
false
] |
. Relevant excerpt: The reactor would also be used to power a laser for communications back to Earth, with a maximum power of 250 kilowatts. For most of the journey this would be used at a much lower power for sending data about the interstellar medium, but during the flyby the main engine section would be discarded and the entire power capacity dedicated to communications at about 1 kilobit per second. My question might just boil down to fairly rudimentary trigonometry at its core, but I have some relevant follow ups which I think will make this more than just a simple math problem. : What is the required degree of accuracy when beaming information from 4.3 light years to hit any part of the Earth, let alone a specific receiver? Or am I looking at this the wrong way and such a transmitter would sort of behave like a shotgun and accuracy isn't as paramount as I'm imagining? from 4.3 light years away, how many fractions of a degree difference would still see the data hit the Earth? How much of the sky does the Earth inhabit from 4.3 light years away? Follow up: This was just a proposed craft, but we have plenty of probes out in space which are beaming back data. How do we manage to keep those connections established?
|
[
"The relevant math here is the diffraction limited ",
"\"Airy disk\"",
", which represents an angle of 1.22 times the ratio of the wavelength of light (lambda) to the diameter of the aperture (d). For tiny angles this gives a value for \"feature size\" to be 2.44 * lambda/diameter * distance. If you plug in some likely parameters (such as 400 nm blue light, 10 m diameter mirror, and 4.3 ly baseline) then you end up with an answer around 3 million kilometers (and an angle around 2 hundredths of an arcsecond).",
"Realistically any signal from 4.3 ly away is not going to be pinpointed down to only the size of the Earth, it'll bathe a large region around the Earth with the signal. Even the numbers above would be rather challenging to achieve the necessary pointing accuracy, but spreading the light out to a larger beam size would be easy (though would lower overall throughput). It might make more sense to mass produce a lot of receiver spacecraft and space them around the inner Solar System to allow for a decent degree of pointing error while still maintaining a fairly high data rate and small beam size."
] |
[
"I'll follow up on this a bit. Let's say you wanted a small fleet of detector satellites around the inner solar system. The technology to pack and unfold large structures in space is pretty well established:",
"http://www.boeing.com/defense-space/space/bss/factsheets/702/702fleet.html",
"The Boeing 702HP telecom satellite uses the giant unfolding dish for an L and S-band RF antenna, but the same principle could be applied to a mesh covered with very sensitive photodiodes.",
"Alternately, an inflatable structure could be used, or a rigid unfolding structure covered with sensors, not terribly dissimilar in shape from a large telecom satellite's solar array. The size of the solar arrays on a 6000 kilogram telecom satellite is quite small when folded for launch, but when extended can be quite large. The actuator technology to unfold these is a proven science (though there have been rare cases of satellites having their usefulness curtailed by one half-unfolded solar array). ",
"Satellites could be positioned at L3, L4 and L5:\n",
"https://en.wikipedia.org/wiki/Lagrangian_point",
"Putting large satellites at Lagrange points is a somewhat established procedure:\n",
"https://en.wikipedia.org/wiki/Herschel_Space_Observatory"
] |
[
"I thought that the definition of a laser is that it does not spread out. Is that true only at short distances?"
] |
[
"How do you easily find updated information on an organisms taxonomy?"
] |
[
false
] |
While researching Northern White Rhinos I found they might be an entirely new species and not just a White Rhino subspecies. If this is the case, is there any reliable scientific source that can announce this fact if it were to come true. I know of some sources, however they are slow at updating, when an organism is announced as a new species instead of a subspecies...
|
[
"As far as I know there's no comprehensive database for this sort of thing. Tree of Life web aims to do it but is nowhere ",
" to being complete, even for common animals. ",
"http://tolweb.org/",
" Wikipedia has nearly everything but quality is variable.",
"Also bear in mind that you often have constant fighting about whether or not things are proper separate species. Some paper will name it a new species, a few years later another paper will say \"no\" and things will go back and forth for decades. So in some sense there's no point waiting for an official declaration. You either won't get one or you will get too many."
] |
[
"Possibly the NCBI's Taxonomy DB is more compete than ",
"/u/atomfullerene",
"'s suggested TOL link, check ",
"http://www.ncbi.nlm.nih.gov/taxonomy",
"Edit: I double checked, NCBI's Taxonomy DB only covers 10% of organisms I the genbank. So not a very comprehensive list. ",
"Although in both cases these DBs reflect a \"best efforts\" attempt to represent settled, consensus opinion on organism taxonomy. As such they will lag somewhat behind the cutting edge arguments around what should or should not be a species in any given sub-discipline. "
] |
[
"So in some sense there's no point waiting for an official declaration. You either won't get one or you will get too many.",
"This really, really depends on the extent to which a clade's taxonomy has been formalised. Solanaceous plants have an active and somewhat formal body of taxonomists who do produce \"official\" taxonomic decisions for the sol plants community it to work with. In most other fields it is very ad hoc in exactly the manner you describe. "
] |
[
"How does LSD cause hallucinations?"
] |
[
false
] |
What is the mechanism of action that causes humans to see visual hallucinations after ingesting LSD? Please go as in depth as possible!
|
[
"I can get you started, but I won't be able to answer all of it. LSD is a serotonergic psychedelic, along with drugs like DMT and psilocybin, which means that it binds to serotonin receptors. It acts as a partial agonist for these receptors, particularly 5-HT2a. Its action at the 5-HT2a receptor site is ",
" responsible for its psychedelic effects. ",
"I really can't tell you anything more in-depth than that, unfortunately. ",
"It's worth adding that there is no true answer to your question, because no one knows the exact reason that LSD causes hallucinations. But someone can probably get you pretty close."
] |
[
"Considering how complicated it is to make in a lab, how the hell did they come up with the formula to make it then? How did they know it would do what it was going to do?"
] |
[
"Albert Hoffman's ",
" random experimentation. ",
"Let me explain: Albert Hoffman was a chemist working for Sandoz Laboratories. He was isolating the active components of something called \"ergot\", a fungus that causes hallucinations when consumed in large quantities, along with lots of unpleasant side effects that make it less than desirable as a recreational drug. He was synthesizing a number of chemical derivatives of lysergic acid, or LSA, a chemical found in ergot. ",
"He only realized that one of those derivatives, LSD-25, was psychoactive after he ",
" dosed himself while working with it and felt its effects firsthand. He then dosed himself on purpose with a larger amount on April 19th, 1943, a day now remembered as \"bicycle day\" because he first felt the effects while riding his bike.",
"So basically, it was a fortuitous accident. Albert Hoffman wasn't even trying to synthesize a psychoactive drug. ",
"Incidentally, chemicals derived from the ergot fungus are commonly found in medicine and the nootropic community today, and most of them are not at all psychoactive. LSD-25 and a select few of its analogues (AL-LAD, LSZ, etc) are really the exception to the rule. "
] |
[
"Does any other animal need a \"balanced\" diet, as in can a bird survive by eating only a single insect?"
] |
[
false
] |
Like is there any fish or mammal that wouldn't be able to survive if they just had a single source of food?
|
[
"The idea of a \"balanced\" diet is a decidedly human one. See, as we became better and growing a processing our food we didn't have to worry about food scarcity so much. We began to have true options in our diet. Having a choice led many to neglect certain foods that they find distasteful. Meaning they neglected vitamins and nutrients only found in significant concentrations in those foods.",
"While in the wild there isn't an option. The wild animal has evolved to survive of the food it can find in the local area. It eats when it can because it doesn't know when it will become a meal or find it's next meal. As such its \"balanced\" diet is what it automatically consumes as food. The only time their diet can become \"unbalanced\" is from human food.",
"Which is why pet and livestock food is carefully formulated to ensure that they are getting the same vitamins and nutrients they'd get from their natural diet (plus some extra stuff we found boosts growth and longevity). For instance a cat can't eat dog food as dog food lacks the amino acids cats need. Though a dog could survive off cat food as it has extra nutrition it doesn't use (though you shouldn't because cat food is very calorie dense meaning your dog will likely become overweight quickly)"
] |
[
"I know I’m abit late to this but yes animals do need a balanced diet, in some sense. Look into Nutritional Geometry and the concept of nutritional rails and how they effect an animals fitness landscape; some animals may actively regulate by eating more of one food than another- if they have choice and eat more than one select food. Also the may self regulate by simply eating more or less to get more or less of whatever nutrient they require- this is all however assuming an animal can choose freely. ",
"Here is a study by my professor into how bee larvae prioritise nutrition.",
"Austin, A.J. and Gilbert, J.D., 2018. The geometry of dependence: solitary bee larvae prioritize carbohydrate over protein in parentally provided pollen. bioRxiv, p.397802."
] |
[
"Animals all have different biologies to humans. For example most other mammals produce vitamin C in their livers so they don't need to eat it in their diets. So in this way many animals can be perfectly fine just eating bugs or grass or whatever. They are specifically made to do so.",
"However if we were to figure out what an animal needs to run optimally and fed it a diet based on its specific biology then yes, you would see increased longevity and decreased health problems. ",
"We do it for things like ours dogs and probably live stock animals but most animals that live on simple diets don't really live long enough for us to care, reproduce fast enough for it not to matter and live just fine on simple diets."
] |
[
"About when did humans (or our ancestors) begin boiling water?"
] |
[
false
] |
and before that did everyone just have constant diarrhea?
|
[
"We really don't know when humans started cooking. Well-educated estimates vary wildly."
] |
[
"It's ridiculously huge, like 50,000-2,000,000 years ago.",
"Super early prehistory like this is out of my expertise though, so I'm not really qualified to make judgments about who's right."
] |
[
"this article suggests that it could be as old 500,000 years ago: ",
"http://daha.best.vwh.net/boiled/history.html",
"\n(TL;DR see the 4th paragraph)"
] |
[
"I do not understand time dilation. How can a clock on a spaceship move slower than an exact same clock on earth?"
] |
[
false
] | null |
[
"You always travel through spacetime (a fourdimensional fabric) with the speed of light. ",
". Even now, when you're probbably sitting comfortbly in your chair. But since you are not moving through space, you are moving with the speed of light through ",
". If you now start to move around through space, you have to start moving slower through time, so that the resulting velocity through spacetime is the speed of light again. "
] |
[
"IMO its a bit confusing to say that we are always traveling though spacetime at the speed of light. The technically precise thing to say is \"the magnitude squared of the velocity 4 vector is always c",
" I'm making this pedantic distinction because 4 vectors are not normal vectors. For nomal vectors, the distance formula is:",
"R",
" = X",
" + Y",
" + Z",
"For 4 vectors, the magnitude squared is:",
"-R",
" = X",
" + Y",
" + Z",
" - c",
" T",
"Notice the minus sign! When people say that we are always moving at the speed of light, they are referring to this equation:",
"(1/T",
" ) (x",
" + y",
" +z",
" - c",
" t",
" ) = - c",
"Where T is the time measured by the MOVING CLOCK, t is the time on STATIONARY CLOCK, and x, y, and z are the distance THE STATIONARY OBSERVER saw the space ship travel.",
"Edit: \nAdded a minus sign."
] |
[
"If the traveling clock has stopped accelerating and is now moving at a constant velocity relative to the earth, both observers would see the other clock as going slow."
] |
[
"What is anti-matter?"
] |
[
false
] |
Please answer questions like: Where is it found? Do regular-matter elements share properties with its anti-matter counterpart? (e.g. is anti-chlorine poisonous like regular chlorine?) Is it dangerous like it is portrayed in movies in video-games? Is dark-matter the same thing as anti-matter? If not, please explain what dark matter is too. any other interesting facts are definitely welcomed
|
[
"I like to err on the side of caution and not have to explain that \"it doesn't interact at all\" means \"we don't see any photons and have no reason to expect that we will therefore\". For all intents and purposes, yes, dark matter doesn't interact electromagnetically."
] |
[
"Side note: It is REALLY nice to see in the matter of minutes (there are currently six replies to this question and it was posed only thirty five minutes ago) that four of the top level replies have all been lengthy, accurate and well written. Makes me feel all warm and fuzzy :)"
] |
[
"The difference between regular and antimatter is that various quantum numbers are flipped. An antielectron(positron) has electric charge +1 instead of -1, antiquarks are antired/antigreen/antiblue instead of red/green/blue, and various other things.",
"It's not really \"found\" anywhere. Cosmic rays have some antimatter in them, and we artificially produce some, but we don't know of anywhere where there are just chunks of antimatter hanging out.",
"Antimatter elements would act (nearly) exactly the same for antipeople as regular elements do for us. Antimatter elements wouldn't have meaningful properties at all for us, because...",
"Large quantities of antimatter would be extremely dangerous. When an antiparticle touches its regualr particle counterpart, they annihilate and release two VERY energetic photons. Very energetic meaning that a kilogram of antimatter would cause energy release six orders of magnitude higher than the bomb dropped on Hiroshima. However, since we can't find or produce that much antimatter, it's not something we need to worry about.",
"Dark matter is not the same thing as antimatter. We know two things about dark matter: there's a lot of it, and it doesn't interact more than a very very tiny amount through electromagnetism (it probably doesn't at all). We're still trying to figure out what it ",
", because we can only detect it through its gravity right now."
] |
[
"When released, does a helium balloon accelerate or travel upwards at a constant velocity?"
] |
[
false
] |
Also, what would cause the balloon to act in said manner?
|
[
"The terminal velocity of a helium balloon is about 2 meters per second, according to my calculations and assumptions. It would accelerate until it reaches around this speed. There would probably be some second order effects as the atmosphere gets thinner."
] |
[
"Over a short time scale it accelerates until it hits its terminal velocity and rises at that rate.",
"Over a long time scale it will rise into air that is at a lower pressure and less dense. The lower pressure may cause the balloon to expand and the lower air density reduces the balloon's buoyancy. The combination of these two effects would change the terminal velocity. At some point the balloon would fail because of extreme temperatures or low external pressure. If it didn't fail then it would reach a point where it was neutrally buoyant. (neglecting wind and solar radiation for this discussion)"
] |
[
"See iorgfeflkd's response above."
] |
[
"Why does Moore's Law, the law that states that computing power approximately doubles every 2 years, advance at such a linear pace if the continuing advancement of computers requires innovative approaches?"
] |
[
false
] |
How do we keep finding space on flash drives for instance so that their storage capacity continues to increase at such a predictable pace?
|
[
"I'd say it's a trend. Its fits on a graph over the last 30 or so years and and is projected to continue on the same trajectory "
] |
[
"One thing I'd like to point out is Moore's law originally that the same amount of transistors would double in density every 18 months. Due to innovation we changed the law... So it's not really like a law... Maybe a hypothesis?"
] |
[
"It's worth noting that Moore's law is no longer active (in processors) and will come to a crashing halt at some point over the next 5 - 10 years - at least with it's original parameters (doubling the density of transistors). This is because Silicon transistors \"go quantum\" if the manufacturing process is 7 nanometers, current chips have a manufacturing process of 14 nanometers, and Intel Canon Lake chips that will be released in 2016/2017 will have 10 nanometers. ",
"We could swap the material used, but this will only lead to a temporary solution that may push it back a few more years. Fundamentally, the current basic architecture of processors is at the end-stages of its life. There may be massive innovation that pushes the effect of Moore's law onwards (which I personally believe will happen), but the Moore's law as it was stated is in its death throws. "
] |
[
"Why did Homo sapiens evolve with less hair?"
] |
[
false
] |
Wouldn't it have been beneficial for the species to have kept its hair as we migrated to colder climates?
|
[
"The general theory is that we evolved in warm african climates, and then recently migrated to colder climates. When we began to spread out, we had already started wearing clothes. When we where in africa we evolved less hair because it is easier to stay cool with less hair. Humans sweat. Sweat evaporates faster, drawing out more heat, if it is not obstructed by hair."
] |
[
"There is a common theory that relative lack of hair was a beneficial adaptation, because it allowed for much more efficient cooling. This allows humans to run long distances without fatigue, a trait that is somewhat unique. While there are plenty of animals that can outrun us in a sprint, there are relatively few that beat us in endurance, which leads to a style of hunting called ",
"persistence hunting",
" which is thought to be how we got an early a leg up on other species."
] |
[
"You would get less sunlight, but I would say hair has more to do with temperature regulation. Skin color has more to do with sunlight absorption and vitamin D synthesis. "
] |
[
"What does a \"two-mile-wide tornado\" mean? Is the funnel cloud literally two miles in diameter?"
] |
[
false
] | null |
[
"Meteorology graduate student here. We generally measure the size based on damage assessment surveys. Generally the condensation funnel will cover most of the rotation. That being said, extremely strong winds still exist just outside the funnel. The tornado is \"fed\" by what are known as inflow jets. These are bands of extremely strong winds that flow directly into the tornado vortex. These do damage, though the damage is usually much less than the vortex itself. ",
"Also, a couple of terminology things I'd like to point out since I see a lot of things being used incorrectly in this thread:",
"F-scale vs. EF-scale: A few years ago meteorology began using the EF scale to measure tornado damage. This represents an update from the old scale to take into account newer building codes and advances in the science with regard to wind speed.",
"Mesocyclone or \"Meso\": The mesocyclone is a rotating updraft of a thunderstorm. Thunderstorms are created and maintained by rising air. Supercells take advantage of the wind environment in which they are created to \"tilt\" this updraft. This means that the updraft can be maintained for long periods of time as it doesn't rain back on itself (this would be sinking motion that would fight against the rising motion). The wind environment can also cause these updrafts to rotate, though that process is a little more complicated. ",
"Wall cloud: A wall cloud is a lowering of clouds within the mesocyclone. It represents the area where the updraft into the thunderstorm is the strongest, and thus is usually the area where a tornado will form.",
"Funnel cloud: A funnel cloud is an area of enhanced rotation that is usually seen \"dropping\" from the wall cloud. This is the beginning of a tornado that has yet to fully reach the surface. Once the funnel cloud touches the ground, it becomes a tornado. ",
"Edit: Here is an example of inflow jets into a tornado from someone who was WAY too close to the Tuscaloosa tornado on 4/27/11. You'll see them begin around 3:40 near the ground once he gets the camera stabilized. As a point of note, you should never, ever be this close to a tornado if you can help it. Tornadoes do not always travel in straight paths and can move in almost any direction very suddenly. This man is very lucky.",
"http://youtu.be/5ohIVzIZLuQ?t=3m15s"
] |
[
"There really isn't a definitive answer to that question. The size of funnels vary greatly depending on conditions. You can have violent EF5 tornadoes with a needle like funnel and weak EF1 tornadoes with a mile wide funnel. The only way we can come close to measuring funnel width at the ground is by post storm damage assessments."
] |
[
"Those violent winds ",
" the funnel cloud are still part of the tornado. They do damage assessments, they look for touch down, follow it's path, and look at the swath the tornado cut to get width. ",
"For instance, the tornado that destroyed Greensburg Kansas was estimated at 1.7 miles wide, which is wider than the actual city. Due to the fact that everything around the city was farmland, and the whole city was destroyed they can only estimate the size because of no other damage indicators, because pretty much everything that could be destroyed was. ",
"This image here",
" kind of illustrates the point I am trying to make. Just because you can see the funnel, doesn't mean that you're seeing the ",
" tornado. It can whip up debris and dust and hide it's funnel size, not to mention if they get rain wrapped they become even harder to follow. Funnel size is not an accurate indicator of the actual size of the tornado, it's just what you can see. "
] |
[
"How does a video game or software randomly decide something?"
] |
[
false
] |
I've been wondering this for a long time and has never really found an answer to this. When a game has a certain percentage chance of getting a critical hit for instance, how does it decide wether or not give you one? I don't quite understand how a computer can just randomly decide something without having a real conscience. It's not like in real life where you can flip a coin or something, it has to have a certain pattern instead, right?
|
[
"Well that depends - are you asking what algorithm they use to determine a critical hit? Or how the random component of that works?",
"Because the former is basically \"whatever teh programmer wants\". But how an RNG (Random Number Generator) works is much more interesting.",
"As you've apparently surmised, computers are deterministic. They don't do things randomly - everything has defined inputs and defined outputs. So how do they generate a random number, right? That's why ",
".",
"They use what's called a \"pseudorandom number generator\" (PRNG) which is a program that ",
" random. It's not. It's just a mathematical formula that's so crazy it ",
" random... but it is still deterministic.",
"It can't pull the number from nowhere, so it needs an ",
". I put in a 1, I get 81. I put in a 2, I get 875. I put in a 3, I get 294.",
"What's important is that, being deterministic, when I put in a 1 again, ",
".",
"Now, to make it simple, they sometimes hide this input number so it loops on itself - so I only provide the ",
" number, and then each subsequent run of the PRNG, it will just use the last number it generated.",
"So I put in a 1, and I get 81, and then I don't have to put in something again - it will use 81 next time to get, say 788 for me. And then I'll ask it for another number, and it will use 788 as its input to generate... say... 294.",
"What's important is that this is ",
" deterministic. If I start up a new RNG, and I seed it with the number 1 again? It will still return 81, 788, 294, etc. in that order.",
"This is called \"seeding\" a random number generator. If you play minecraft, that word sounds familiar - many procedurally-generated videogames will let you provide a \"seed\" - now you know what that means! The \"seed\" is the first number for the RNG, so if you use the same seed to run the procedurally-generated world twice, you get the same world twice, because it wen through the same pseudorandom numbers in the same order.",
"Now, what if I don't provide a seed? Well then the computer needs to find a seed by itself. The clock works. The current date and time is always unique. You can get pretty good random numbers by seeding from the clock (note, a computer's \"clock\" includes the date). Seed from a number that is the total number of milliseconds that's passed since January 1st, 1970.",
"The challenge is when you need to be really sure that nobody else can figure out your random number. It needs to be a secret. This is important for encryption. Everybody knows what time it is, and if they know your pseudorandom number generation algorithm, they can make the same numbers.",
"That's when sources of \"entropy\" are important. Source of chaos that the computer can read to find something ",
" random it can use to seed the RNG. Fluctuations of the electrical power supply is a good source for this, for example. Reading this data is slow, so it's still just used as a seed - after that initial fetch from the truly random source, the computer still just calculates the next random number from the previous ones.",
"edit: on Entropy, the most ",
" source of randomness is quantum physics. Quantum physics are fundamentally random. And the easiest-to-detect form of quantum physics? ",
".",
"So here's a video of some guys using deadly radioactive Strontium-90 to generate random numbers",
"Seriously, if you like computers and you like videos, if you have a question about computers look up Computerphile on Youtube. They do ",
" work.",
"edit2: wow, this blew up like nothing I've ever written. Okay, I feel I should clarify something: these are toy examples. A real, proper PRNG is dealing with much larger numbers than 788 (a 32-bit integer has 4 billion values, and a 64-bit integer has 18 quintillion values) and then they're hammered into the range the programmer wants ",
" the PRNG is done calculating them. Second, the \"input\" can be more than just the one previous value. For example, the Mersenne Twister is one of the most common PRNGs, and it stores ",
" of old random numbers and uses them all to help generate the next one."
] |
[
"One company, I forget which, uses a wall of fecking lava lamps to seed their random number gen.",
"A wall. Of Lava lamps."
] |
[
"CloudFlare. They use it for ",
" random number generation as opposed to pseudo random number generation like the parent explained. For things like games a PRNG is usually sufficient but for things like generating secure keys real world entropy like the LavaRand system are the way to go.",
"https://blog.cloudflare.com/lavarand-in-production-the-nitty-gritty-technical-details/amp/"
] |
[
"Consider the feeling you get when you're zooming down a roller coaster. Would this feeling be the same if you were really, really tiny?"
] |
[
false
] |
I don't know much about the physics behind roller coasters, but I believe it's a relationship between g-forces, the weightlessness feeling of free-fall, and gravity's forces all interacting with your body. If you were to somehow create, say, a roller coaster for ants, you'd be traveling much shorter distances up and down (although, at that size, they'd seem just like a normal roller coaster.) How would it feel if you shrunk yourself down and took a ride? : I guess a more realistic question would be how would it feel for insects or small creatures traveling on a shrunken-to-scale roller coaster?
|
[
"I'm going to Palin this and talk about something else: really tiny things generally have a much bumpier ride because of Brownian motion. You don't notice the effect of atoms bumping into you randomly, but when you're smaller than a millimeter you start to. So for microorganisms moving through water, it's akin to a person walking on a really shaky boat."
] |
[
"I would assume they would feel about the same. The acceleration is what causes the funny feeling, and that acceleration doesn't change when you scale the ride, even if you scale the speed. "
] |
[
"This is what I was thinking but then, one has to consider things like air resistance. I'd imagine there'd be a much more profound effect upon the roller coaster itself at that level. ",
"But if you ignore that, then yes you'd get the same feeling I should think, as long as you have your semi-circular canals were still intact.",
"Fun fact: alcohol changes the density of fluids in your semi-circular canals so that the normal fluid that's supposed to be there, and the alcohol itself have created a concentration gradient. This leads to constant movement of the fluids in your ear and thus why the room 'spins' when you're exceedingly drunk. ",
"Also, when you have someone in the next room crashing on your sofa going \"the room is spinning! Make it stop damn it!\", tell them to put their foot on the ground, because the body 'trusts' information from its proprioceptive tracts more than from the vestibular tract. There's limits to that though with things like vestibular disease. "
] |
[
"Why don't seeds sprout while inside the fruit?"
] |
[
false
] |
[deleted]
|
[
"Healthy fruit contains Plant growth regulators (PGRs) which prevents seeds from germinating, when the fruit dies or the seeds are removed, the seeds are no longer exposed to these chemicals and can germinate freely."
] |
[
"Some do, and this is known as ",
"vivipary.",
" It is occasionally seen in tomatoes- people bring home the tomato, and they find they have small seedlings growing inside when they cut it open.",
"For the most part, vivipary is undesirable; seedlings need to be established under the right conditions. Seeds may have chemical or physical barriers to germination, such that certain changes must occur prior to the seed germinating. These seeds must be ",
"scarified or stratified",
" (or sometimes both) in order to effect germination."
] |
[
"Seed dormancy is an interesting phenomena, and is based on the presence/absence of certain plant-specific hormones. ",
"Here",
" is the wiki of it, but in short, there are two hormones involved, Gibberellin (GA) and Abscissic Acid (ABA). ",
"Increased levels of GA will trigger the germination of seeds, whereas increased ABA levels will maintain the dormancy of a seed. Expression of these two hormone classes is relative to a number of external factors, such as temperature, humidity, and other hormone levels.",
"What likely happened in your case is the apple was stored under conditions that increased GA levels. The seeds inside started germinating. If the apple had gone uneaten, the seedlings would have expanded, consuming the flesh of the apple, and grown into a seedling."
] |
[
"Does salt water help heal wounds?"
] |
[
false
] |
[deleted]
|
[
" post absurd speculations regarding individual's health; unless you have good citations/references or you are a qualified health professional."
] |
[
" post absurd speculations regarding individual's health; unless you have good citations/references or you are a qualified health professional."
] |
[
"osmotic shock",
"In your case, open wounds are always an invitation to infection. Seawater contains far more variety of microbes to just deal with its salt content. "
] |
[
"Is the steam emitted from a nuclear power plant radioactive?"
] |
[
false
] | null |
[
"Nope. It's just regular steam as the water does not come into contact with anything that is radioactive.\nNuclear is one of the cleanest forms of energy we produce with very little waste and a lot more reliable than other clean energy sources and produces much more energy for its footprint size."
] |
[
"This is so frustrating to me because it's not impossible to process high-level waste into fuel that can be reused and low-level waste that can be disposed of safely, but there are no facilities that do it in the US. If we really invested in it we could have a system that doesn't leave behind any high-level waste but there just doesn't seem to be the will for it politically. Instead we're just letting all of our waste pile up, not in reprocessing or long-term storage, and hoping the problem will go away if we don't think about it.",
"I don't mean this as a slight against nuclear engineers, I understand all of the work and research that is going into these technologies, but at the highest levels there's just no action being taken."
] |
[
"I don't think that's correct, coal and nuclear have very similar efficiencies of around 35%. Natural gas is much higher, but once again nuclear has the edge in energy density and GHG emissions."
] |
[
"How quickly can food \"run through you\"?"
] |
[
false
] |
I hear people say, "oh man that food is running right through me" as they scamper off to the bathroom 20 mins after they ate. Is there any truth to this? I guess the question is how quickly can the body consume, digest, and expell a meal?
|
[
"Food generally takes about eight hours to pass through you. More rarely, it can take only two or three hours. But if someone is running to the bathroom within just a few minutes, then that is because the food they just ate caused the intestinal tract to start convulsing to move food through it, which caused an increase need to move what was already sitting in it."
] |
[
"Does water (and other liquids) pass through significantly faster?"
] |
[
"More likely the new food is causing intestinal irritation (or they're just full/gassy) and the peristalsis & pressure are pushing out previous meals. But I've seen upper GI exams where barium was in the colon after only 30 minutes (2-4 hours is more normal)."
] |
[
"Has the orbit of the earth around the sun changed in any significant way since the earth was first formed?"
] |
[
false
] |
The moon is slowly receding from the earth, so its orbit around the earth has changed as it used to orbit closer in. Has there been any similar change in earth's orbit around the sun?
|
[
"There is orbital decay due to gravitational radiation, but that is really really slow. According to my calculations, the Earth is getting closer to the sun at about 350 femtometers per year, which is approximately zero. In five billion years, that's about a millimeter. I imagine brownian motion from the interplanetary medium or the radiation pressure of the sun (both tiny effects) have a stronger effect than that."
] |
[
"Why would the earth get closer if the sun is constantly losing mass?"
] |
[
"Gravitational radiation. But that has essentially zero effect."
] |
[
"Can I have an explanation on what the strong and weak forces are?"
] |
[
false
] | null |
[
"The strong force is very similar to the electromagnetic force, but instead of the \"charge\" being a real number, it's a 3-component vector. Additionally, the strong force is very strong, and interacts with itself. So that makes calculations involving the strong force difficult. The strong force is responsible for the binding of atomic nuclei.",
"The weak force is different than the strong and electromagnetic forces, in that it's got a much shorter range. The weak force is weaker than both the strong and electromagnetic forces (at typical energy scales). The main relevance of the weak force to your everyday life is that it causes certain kinds of nuclear decays."
] |
[
"The coupling constant is small, and the mediator particles have huge masses, so the force has effectively zero range."
] |
[
"What level of explanation are you looking for?"
] |
[
"Einstein's Theory of Relativity, explain? Are there different tiers of time progression?"
] |
[
false
] |
[deleted]
|
[
"Your question is kind of vague, but here's my best guess at answering it:",
"Time's rate of passage will change, relative to a stationary observer, if you travel at a different speed to them. The rate at which your experience of time, compared to the observer, varies is determined by your relative speed. \n",
"This graph",
" shows how time will \"dilate\", i.e. slow down from the observer's point of view, as you get closer and loser to the speed of light."
] |
[
"I think, to take the last sentence... don't think of the \"present\" as being universally true. It's only ",
" present. Someone at a different altitude, or travelling really fast with respect to you will disagree on which events constitute \"the present moment.\" And therefore, you may disagree about what constitutes the \"past\" and \"future\" as well.",
"And when you want to talk about how long elapsed between the tick-and-tock of another's clock, many people may disagree. The clock itself (in its frame) will tick at 1 second (say). But others may think it ticks more slowly, like once a minute or hour or year. And they're all equally correct."
] |
[
"Do you have a specific question?"
] |
[
"What controls/limits the amount of current a battery can supply?"
] |
[
false
] |
Example: a 1600mAh battery may have a maximum output current of 100mA. Obviously the capacity is 1600mAh, but what's limiting the current? Why? What limits how much current a charger can "accept" and store? Why?
|
[
"Very good explanation. The only thing I might add is the question appears to be what is actually limiting the current, which is going to either be 1) In the case of very simple/cheap/low power devices ensuring that your design will never have a current drain greater than the battery can handle or 2) Adding active circuits, a fuse, or something similar that prevents too much current from being delivered.",
"Some of the latter may be designed to protect the electronics as much or more than the battery or to prevent fires in the case of a short circuit. If you designed a device to have a maximim current draw of 10 amps, and it's drawing 30, something has gone very wrong, and that much current in the wrong place could easily start a fire."
] |
[
"Very good explanation. The only thing I might add is the question appears to be what is actually limiting the current, which is going to either be 1) In the case of very simple/cheap/low power devices ensuring that your design will never have a current drain greater than the battery can handle or 2) Adding active circuits, a fuse, or something similar that prevents too much current from being delivered.",
"Some of the latter may be designed to protect the electronics as much or more than the battery or to prevent fires in the case of a short circuit. If you designed a device to have a maximim current draw of 10 amps, and it's drawing 30, something has gone very wrong, and that much current in the wrong place could easily start a fire."
] |
[
"batteries aren't just electricity in a box, they are tiny chemical power plants. the chemical reaction has a set voltage it can produce, and the ",
" at which that chemical reaction occurs is controlled by the current. ",
"the chemical reaction that happens to give you electricity also produces heat. the most common failure for a battery when it is asked for too much current is that it overheats and destroys itself. lead-acid batteries can melt their casings, boil their sulfuric acid electrolyte, etc. the excessive current may also cause unwanted reactions. to go back to the car battery, they sometimes produce hydrogen gas, which is combustible. ",
"what limits the amount of stored power is the amount of chemical reactants inside the case. all of the contents start separate, are consumed, and turn into something else. charging a battery really means turning the stuff inside back into what it started as. once all of the original components are back to their starting position, you can't create more by dumping in more electricity. "
] |
[
"Could \"polarized\" matter ever exist in a similar manner to polarized light?"
] |
[
false
] |
With polarized light, you can do things like project two images onto the same screen, and separate them back out with special glasses (as with 3D movies). Is there any analogue to matter? I.e. can matter exist as "transverse" waves that don't interfere with one another?
|
[
"This is wrong. MRIs work because hydrogen nuclei have a magnetic moment, so in the presence of an external magnetic field they will align parallel to it. Radio waves are then used to knock them into a different alignment, and the change in magnetisation as they return to their previous alignment is measured. The time taken for the nuclei to recover depends on the local environment, so you can distinguish between different types of tissues.",
"It doesn't really have anything to do with electrical gradients or dipole moments."
] |
[
"This is wrong. MRIs work because hydrogen nuclei have a magnetic moment, so in the presence of an external magnetic field they will align parallel to it. Radio waves are then used to knock them into a different alignment, and the change in magnetisation as they return to their previous alignment is measured. The time taken for the nuclei to recover depends on the local environment, so you can distinguish between different types of tissues.",
"It doesn't really have anything to do with electrical gradients or dipole moments."
] |
[
"Yes! Matter can exhibit a similar behavior. This is called ",
"spin polarization",
" and depends on how the spin of the object relates to some direction. A common application is electron polarization. If this direction is the direction of motion, then it's referred to as helicity."
] |
[
"How do 'anti-fogging' products work when applied to your (car) windows ?"
] |
[
false
] |
I would like to know how to decrease condensation forming on the surface of a window, inside a car. There are online videos which show that shaving cream does this well compared to application-specific products, why is that so? A quote from the safety-sheet of a popular anti-fog product shows the following ingredients: " 3. COMPOSITION/INFORMATION ON INGREDIENTS substance(s) Chemical Name CAS No Weight-% Trade Secret WATER 7732-18-5 60 - 100 * ISOPROPYL ALCOHOL 67-63-0 7 - 13 * DIPROPYLENE GLYCOL MONOMETHYL ETHER 34590-94-8 3 - 7 * *The exact percentage (concentration) of composition has been withheld as a trade secret. " Can I make similar a solution at home and will it work - water, isopropyl alcohol (7-13%), monomethyl ether (3-7%) ? My knowledge of Chemistry is very limited so please explain in a "explain like [n]" manner :) Thanks
|
[
"Yes, but what prevents condensation from forming into drops on the window? How does starch affect this ? I have seen people test applying starch from a potato on video, but it doesn't work as well, compared to different mixtures of methyl alcohol, glycerol and others."
] |
[
"If the condensation beads up you can see it, but if it is absorbed and spreads out you can’t. \nThe juice of a fresh cut potato has starch in it so that is a cheap alternative I used in my youth. ",
"The layer of starch will last until it washes or is washed away. Forever on the inside of my car windows. "
] |
[
"The water soaks in to the starch. Or wets the layer of glycerol. Not sure if a zero residue such as alcohol can work after drying. "
] |
[
"Would it be possible for life to emerge within the goldilocks zone of a star WITHOUT a planet?"
] |
[
false
] |
Is it possible for the ingredients necessary to sustain carbon-based life to exist in a sort of atmospheric cloud within a solar system? What might a society of sentient beings evolving from this hypothetical form of life be like?
|
[
"One problem comes to mind is that without a large celestial body to create the gravity (and thereby atmospheric pressure) required for a liquid medium, ice would sublime into vapor in the vacuum and heat of the nonplanetary \"goldilocks\" zone. (This is why we observe in vapor trails from icebound comets that fly within the Earth's orbital radius.)",
"The chemical reactions that sustain life as we know it would be very limited. Though we have evidence that the building blocks of life (amino acids, carbohydrates, etc.) can be formed in an interstellar, non-planetary medium, there's no evidence so far that life can exist without a liquid (generally accepted to be water, though there exists the potential for other media to satisfy the same needs) medium in which the chemical processes necessary for life can be carried out. Life is inherently a dynamic process that requires the interactions of relatively large molecules; in the solid state without a fluid medium in which those molecules are mobile, there is probably not enough molecular motion for those collisions to be frequent enough to produce the rich chemical equilibria that life involves.",
"Granted, our definition of life's limitations continues to expand, but that's my analysis."
] |
[
"You might enjoy \"The Smoke Ring,\" a sci fi book on this concept."
] |
[
"Start with ",
". That's the first book, and ",
" is the sequel."
] |
[
"If artificial trees are powered by a coal power plant, can they still produce a net reduction of CO2, while the coal plant still produces a net gain in power?"
] |
[
false
] | null |
[
"Never heard of an artificial tree until now. What do you do with the CO2?"
] |
[
"from wikipedia: \"The CO2 would be captured in a filter and then removed from the filter and stored.\""
] |
[
"I know but where and how?"
] |
[
"What is money, exactly? If I discover a ton of gold buried in my backyard, does the value of all other gold drop a proportionate amount? How does one create \"new\" wealth, exactly? Are economic gains necessarily offset by economic losses somewhere else?"
] |
[
false
] |
edit: thanks for the helpful answers, everyone
|
[
"To massively oversimplify:",
"There are two sides to the equation: Money, which includes dollar bills, credit cards, gold, and anything with no intrinsic (or mostly no intrinsic when it comes to gold) value that we arbitrarily assign value as a way to more easily barter and trade. The other side of the equation is stuff we buy money with, including pretty much everything else (televisions, faucets, matresses, etc. etc.).",
"If you fix the quantity of money (i.e. no new gold or dollar bills), and increase the amount of stuff you can buy with money (i.e., more people build televisions etc.), then all of a sudden money becomes more valuable. There's a lot more it can buy and less money to buy it.",
"The opposite is also true. Fix the quantity of goods, but arbitrarily increase the supply of money, and the value of money goes way down. This is how inflation happens. When you print massive amounts of money, its value plummets and that's how you get hyperinflation (google and you can get some pretty impressive examples. you can buy trillions of Zimbabwe dollars for almost nothing.) This is the same thing that would happen if you found that ton of gold in your backyard. There would be more gold you could use to buy stuff, but the same amount of stuff to buy, causing inflation. (It's of course much more complicated than that, especially since gold does have some intrinsic value by being pretty so it can be used in jewelry and a good electronics component. For purposes of this question I'm just treating it like money.)",
"So to answer your last question, you create new wealth by creating new stuff (and it doesn't necessarily have to be stuff, exactly, it can be luxuries like massages, etc.). Who gets that wealth is determined by a whole host of other things and is way too complicated for an answer here. It's basically what our entire economy ",
".",
"The money supply is mostly separate from that. Printing more or less money is (mostly, in an over-simplified world) irrelevant to the wealth equation. It just means that your wealth consists of more or fewer arbitrary dollars. (Explaining why it's not truly separate is again an answer that is far outside this simple answer, involving the fact that people are not purely rational, the practical difficulties caused by over-inflation or the opposite, deflation, and other real world effects that make the simple model very very messy. It's why we have a Federal Reserve with very smart people trying to manage our money supply.)",
"Source: Former economics major though that was a long time ago.",
"Edit: See also this answer from a metafilter thread:",
"http://ask.metafilter.com/69290/Ripping-up-money-to-make-money-worth-more#1035559"
] |
[
"its not the knowledge that causes the value to go down (inflation) its the addition of the money in circulation. Even if no one ",
" more money was added, if enough is added it will start having effects. ",
"example: say every sunday you have a potluck dinner with some friends. Everyone brings some food they made and you always bring two cakes for dessert. But two cakes aren't enough for everyone, someone always loses out on a piece of cake. This makes it more valuable because its a rare commodity, not everyone gets cake. Say one week you makes the cakes a bit bigger, it won't make much of a difference, maybe a mouthful more for each person, and in the context of a whole dinner that isn't much. But say one day you came with 3 cakes instead of two. the \"value\" of the cakes has now gone down, not only will everyone get a slice but there will be extra. With each additional cake you bring the value of the cakes go down. But your friends bring the same amount of food they normally do and you have no new friends coming. There will always be extra cake. And if we translate that to the real world, the cake is money (duh) and the other food are the goods and other stuff that is created/traded. If there is a glut of money, its value goes down because there is just so much to trade, you don't need it all, but you have it. "
] |
[
"/u/arrogantsob",
" addressed the money supply issue pretty well in his top-level comment, so I thought I'd address the last question:",
"Are economics gains necessarily offset by economic losses somewhere else?",
"No. The idea that economics is necessarily zero-sum is depressingly pervasive. The fact that it's so widely held is in my opinion incredibly damaging due to its implied presence in many (most?) economic discussions (at the policy level or otherwise).",
"Economics is fundamentally about trade, or transactions. A trade is assumed to be consensual, and we'll just consider trades where asymmetric information doesn't play too massive a role (i.e. enough to cancel out the trade benefits)*. Given that the trade is consensual, both parties must think that they're at least slightly better off making the trade than not. Essentially by definition, you have an economic gain on both sides, with no offsetting economic loss necessary.",
"For a clear and straightforward example, imagine that you and I are marooned on a desert island. I tend to hang out on my side of the island, and you hang out on yours; we're separated by a broad stream which we'll consider as impassable. On my side of the island, there's tons of tree cover, so I have more wood than I could ever make use of, and on your side, there's tons of durable rocks, great for using as tools. We can't get to each other's resources, so I'm stuck with tons of wood and you're stuck with tons of rock, and we both make do trying to hunt and fish as best as we can.\nOne day, a tree falls over and dams the stream (there's plenty of other fresh water), removing the blockage to trade between our two sides of the island. Suddenly, we can combine my wood with stone spearheads and make awesome spears and hunt much more easily; we have better flint with which to ignite my firewood, etc etc. We are both much \"wealthier\" due to the removal of an impediment to trade, and there was no economic loss in our two-person economy to offset it.",
"As silly as the example may have sounded, the removal of unnecessary trade barriers (the stream) and the creation of increased productivity through technology (the fire/spear) are both ways that wealth can be added to the economy at large. In an economy as complicated as the modern global economy, there do tend to be some losers in ANY situation, but their loss is not large enough to offset the gains. This toy example of a two-person economy can be expanded to modern economy examples without too much difficulty, but I thought that keeping the economy as simple as possible would be the most illustrative. ",
"*This is to exclude cases like the purchase of snake oil, because the buyer ",
" they're getting real value in the form of a cure for their ailment, and this distorts their actions."
] |
[
"Can someone please disprove the idea that vinegar is a cure to acid reflux?"
] |
[
false
] |
So I was reading around about vinegar. I saw somewhere that it's good for acid reflux. It's one of those email forewords that I highly dislike. I was discussing this with someone recently and they won't believe me. That didn't make sense at all to me. Acid reflux is due to too much acid. Adding a lower PH acid(its ascetic acid not HCL) just dilutes the acid, but water would work much better. >_>?
|
[
"You should always hold the source of such claims accountable for explaining themselves. There is no logic from a chemistry perspective in the claim. There may well be biological processes at work, as I have seen several people claim that it is effective. However, these claims, without scientific research, amount to as much as saying that you should not eat before swimming or feed gremlins after midnight.",
"Amusingly, ",
"one website",
" recommends vinegar as a cure for acid reflux. They list a ",
"reference",
" at the end of their article that clearly gives the following advice: ",
"\"Prevent heartburn by limiting acidic foods, such as grapefruit, oranges, tomatoes, or vinegar\"",
"\"Want to avoid GERD symptom triggers? You may want to cut back on chocolate, mint, citrus, tomatoes, pepper, vinegar, catsup, and mustard. \"",
"So again. Hold the people who come up with these ridiculous claims accountable for proving them. "
] |
[
"Vinegar is acetic acid (CH3COOH), stomach acid is mostly hydrochloric acid (HCl). Adding one acid to another does not reduce the acidity of a substance; this is essentially the same as 'fighting fire with fire'.",
"Traditional antacid tablets (e.g., Tums/Rolaids) are made of calcium carbonate (a base) which acts to neutralize the pH of stomach and esophageal contents."
] |
[
"It's like putting me, a 25-year-old nerd, in a middle school soccer team. My mediocre physical prowess is amplified only because I have a larger frame than my fellow competitors.",
"Now imagine putting me in a professional soccer team. What little skill and physicality I can bring is nothing compared to the worst of their players.",
"Whether I contribute to the team is dependent on my skill and athleticism compared to the team's. Just like whether an acid will contribute to the pH of a system is dependent on its strength, and the environment it is in."
] |
[
"Questions about natural selection/mutation. What is the evolutionary advantage of dominant/recessive genes?"
] |
[
false
] |
Random imaginary example. 5000 years ago, tribal times. My child has a mutated gene, X, which causes him to have much bigger lung capacity. In terms of natural selection, assume he's at a big advantage. However this mutated gene is recessive. When my mutant child has children (and he will have many, for his bigger lung capacity means he can catch lots of food and provide for many women), of his children will have his bigger lung capacity. Because none of these children have his big lung capacity, the amount of children have will tend to be be the same level as everyone else without the mutation, so therefore the spread of the evolutionary "superior" gene for the big lungs is just the same as the evolutionary inferior "normal" lungs. All of his children may even die, because although they have the gene for the superior lungs, they don't actually manifest themselves, which would mean the end of the line for the big lungs gene, even though it's evolutionary superior. So what is the point in recessive/dominant genes? Doesn't that just mean evolutionary superior things that are recessive get suppressed/limited spread? How would the evolutionary superior genes spread? Would be great to get a step-by-step numerical example.
|
[
"Firstly it needs to be said the whether a gene is dominant or recessive is a matter of biochemistry, not evolution. A dominant gene might be for example an enzyme that produces a pigment, where as its recessive counterpart does not. This would mean that if you have just one copy of the gene, you are going to express this pigment, and if it is under regulation, you are going to produce the same amount if you have one copy or two. So you would say the gene is dominant.",
"So you can see that a gene being dominant or recessive is a matter of the chance mutation, and thus doesn't need to have evolutionary advantage.",
"Secondly while as you point out a recessive gene will have ",
" selective pressure applied to it, unless the gene dies off before it is expressed in a homozygous individual, it will still be selected for if it is positive. ",
"Recessive genes won't be suppressed simply because they are recessive",
", they will just become more common in the population more slowly."
] |
[
"The gene has no reason to be selected out - having it is never negative, so it will just potter around in the population until two copies come together and then it will be selected for, so will increase as a portion of the population (all be it slowly).",
"It is probably worth mentioning that there is rarely such a thing as a truly dominant or recessive gene. Normally things lie some where in the middle, where having one copy is going to do at least something."
] |
[
"the mutant's children may have slightly better lungs than the other humans, but not as pronounced as the original mutant?",
"Precisely. As an example in the opposite direction, a female with both X chromosomes missing the functional gene form for clotting agents will have hemophilia. A female missing only one of these genes will simply bleed slightly more profusely when injured.",
"(a male has only one X chromosome, so it's pretty much all or nothing for him.)"
] |
[
"What does mantle material look like?"
] |
[
false
] |
If we were able to dive down and photograph mantle material what shapes/colours would we see? what are some every day objects that we could compare it to as far as its viscosity?
|
[
"And here's a typical mantle xenolith, surrounded by the (dark) crystallised magma which brought it up.",
"http://newswatch.nationalgeographic.com/files/2012/11/3_xeno_close-933x700.jpg"
] |
[
"There is no shortage of mantle rocks exposed at the surface in Ophiolitic complexes.",
"The rocks are mainly ultramafic (meaning low silica and high Fe and Mg content), with the main types beeing peridotite, dunite, and hartzburgite. Because of their high Fe and Mg content and mineralogy (olivine, clino- and ortho- pyroxene, oxydes), the rocks are dark green. At the surface they quickly weather to medium brown (hence the term \"",
"\" in \"Dunite\")",
"From these rocks, we see a lot of evidence of subhorizontal crystal stretching, which gives them a somewhat ribboned look, although some layering is also seen, at times, due to magmatic segregation (less dense mineral float to the top of a layer, dense ones sink to the bottom). Examples: ",
"http://origin-ars.els-cdn.com/content/image/1-s2.0-S0009254111002853-gr2.jpg",
"At the surface, they are commonly crossed by veinlets of asbestos. These are not really present ",
" in the mantle, but form through mechanical breakage and chemical reaction with hot seawater while the rocks are brought up to the surface."
] |
[
"Dat olivine!!!",
"Lovely!"
] |
[
"If Kepler is orbiting the Sun (ie. moving really fast), how can it remain focused on a single patch of sky with such precision?"
] |
[
false
] | null |
[
"It's focusing on things ",
" far away, on the scale of many light years. So even though it's moving fast, the most that the stars will shift in its field of view is the parallax of the star - the very closest star has a parallax of less than .8 arcsec.",
"TL;DR: The fluctuations are ",
" small, especially on the time-period of a few days."
] |
[
"No, it can maintain its orientation (to an approximate, but nearly precise degree) no matter where it's pointing.",
"Keep in mind that the satellite won't be rotating constantly as it circles the sun (i.e. it won't always be pointing directly away from the Sun no matter where it is in its orbit - replace \"directly away\" with any other direction)."
] |
[
"So...that means it must be pointing either upwards or downwards, otherwise it would have to rotate somehow to keep the same spot in view. ie. it can't be looking anywhere on it's orbital plane"
] |
[
"How do satellites like Voyager 2 know where to aim their lense?"
] |
[
false
] |
Does NASA program it to just flail about and hope it captures something?
|
[
"So I work on the Navigations team for OSIRIS-REx. There's a few things that need to be done in order to properly point a camera (or an antenna) at something.",
"The first (and most important) is you need to know what is known as your \"attitude\". Attitude is simply the mathematical concept of \"how you are oriented\". This is done in a variety of ways but one of the simplest and most accurate ways of doing this is by using a \"star tracker\". Basically, you mount a camera on your spacecraft, have it take a picture of some stars, and then identify what stars you're looking at. We know where those stars are located \"in the sky\", so therefore the spacecraft can figure out which way the camera must have been looking to have seen those stars, and thus figure out how the whole spacecraft must have been oriented. (There are a variety of other sensors that help with this process. Photodiodes for identifying the location of the sun. Rate gyros for measuring angular rate., Etc.).",
"The second thing, is that you need you to know where you are. This is the process known as orbit determination. For spacecraft near Earth, this process is extremely easy as they can use the GPS network to identify their location. However for deep space probes, the process becomes a bit more complicated. Typically we'll use the Deep Space Network (DSN) to estimate a spacecraft's orbit. The DSN is a large collection of huge ground based antennas across the planet, which are capable of talking to deep space probes. It can get us range measurements (by timing how long it takes a signal to get to the satellite and back again). It can also get the \"range rate\", or the velocity along the line of sight vector (by measuring the Doppler shift in the spacecrafts signal). It can also get what is known as Delta-DOR, which is a bit more complicated and uses quasars, but allows us to identify the azimuth and elevation angles to the spacecraft. With those 3 measurements, we can accurately estimate the orbit of a spacecraft, and thus accurately predict where it is and where it will be.",
"Now if you know where something is that you want to look at, say .. a planet, then this problem is very easy! You know where you are, and how you're pointed, and you know where you want to point. So it's trivial to then calculate how you should be pointed to look a certain object. This is typically done using reaction wheels.",
". So in short, by looking at the stars, you can identify where you're pointed. By using the Deep Space Network to study the spacecrafts signals, you can identify where you are. Then it's just a matter of deciding where you want to point, and slewing yourself such that you're pointed there!",
"Let me know if any of this doesn't make sense, or if you have any follow-up questions! I hope I was able to communicate this clearly "
] |
[
"There is very very little for Voyager 2 to take pictures of. The cameras are long since disabled to conserve energy and keep the probe running for as long as possible. ",
"But, in general, probes need to stay oriented to communicate (they have a really narrow antenna and low output effect of the radio). The orientation is also used to aim the instruments (including cameras) for data collection. In the voyager probes, the orientation is the job of the Attitude and Articulation Control Subsystem. It tracks the sun and a few stars to measure the orientation of the probe, and then have a number of thrusters and gyroscopes to control the probe and keep it pointing in the correct direction. "
] |
[
"In theory, it is essentially the same. In practice it can be quite difficult. I've never had to deal directly with anything like that, as most of the \"observation\" type things I've had to work with are with distant and relatively slow moving targets. ",
"However the idea is the same. The Entry, Descent and Landing (EDL) operations of probes are extremely well coordinated. The exact trajectory is planned, and refined continually as you get closer to the event. This kind of \"trajectory design\" is a back and forth process, where the guidance and controls teams will decide how it should enter, while the Navigations teams tell them exactly where they are. (This changes due to solar radiation pressure, anisotropic thermal emission, drag, n-body effects, momentum desaturation maneuvering, etc.). But by the time it comes for EDL itself, the trajectory is very well known. So then it just becomes a matter of knowing that trajectory. (NOTE: when I say knowing that trajectory, that means knowing both the time and location of all the planned events). It is then the control systems job to make sure the spacecraft stays as close to that planned trajectory as possible.",
"So MRO was instructed to take an image in a specific location at a specific time, because it knew the planned EDL trajectory for the MSL, and MSL did it's best to stay on that trajectory.",
"Don't get me wrong, it's definitely harder than many other observations, and it also requires a fair amount of luck (for example, MRO being in the right place at the right time to have seen it), but it's definitely achievable!",
"Edit: I'd just like to emphasize in case this didn't come across. The MRO imaging the MSL and it's parachute was absolutely wild. It took an enormous amount of planning and coordination. I worry my explanation made it sound like I was dismissing it, so I just want to emphasize I think it is one of the most amazing photographs ever taken!"
] |
[
"How is it that hydrogen and oxygen (gases) make water, a liquid?"
] |
[
false
] |
[deleted]
|
[
"Unlike O2 and H2, the water molecule forms a ",
"dipole",
" that attracts other water molecules, so it is liquid instead of gas at normal temperature and pressure."
] |
[
"What we're talking about here is the forces between the molecules. If the forces are very strong, all the molecules stick together into a solid. If they are weak, they can stay disconnected and float around as a gas. If it's in between, you get a liquid.",
"The bonds between hydrogen molecules aren't strong. This is the same for between oxygen molecules. However, water is different: because it's made of two different types of atom (Hydrogen and water), it's not totally \"balanced\". Oxygen atoms are better are \"pulling\" electrons than hydrogen atoms, so you end up with one side of the water molecule being a little negative, and the other side a little positive. Because positive is attracted to negative, this means one end of one molecule is attracted to the other end of another molecule. This makes the forces between molecules stronger than in pure hydrogen or pure oxygen. Because the bonds are stronger, it forms a liquid instead of a gas."
] |
[
"This reaction needs a high activation energy and is exothermic, so the temperature is usually high enough to make water vapor, a gas. But to answer your question, water has a lower boiling point (exists as a liquid at the same temperature that hydrogen and oxygen exist as gases) because water molecules have higher intermolecular forces due to hydrogen bonding. "
] |
[
"Why does time seem to speed up as we get older?"
] |
[
false
] | null |
[
"I read an article arguing that the perception of time is based on new, unique experiences. At a very young age, almost every experience is new, and will thus stand out in your memory. As you age and have experienced more, the likelihood of an event being completely new dramatically decreases.",
"As less event stand out vividly in your memory (or affect your subconscious in a profound way, for that matter), time seems to speed up, because it feels like less is actually happening. In a sense, our body is measuring time in terms of a finite amount of \"stuff happening to us\" and as fewer remarkable things happen, time seems to speed up.",
"I can't remember the source, sorry."
] |
[
"Well then I'll keep it here until something sourced is presented, because thus far, that's the only answer that's been given, and whether it's helpful or not, layman speculation is still an answer in a subreddit designed to answer questions.",
"Once a panelist posts, or someone cites a relevant paper, I'll gladly delete it, as I usually do."
] |
[
"I think the rule is correct, and I understand it.",
"Speculation should be allowed to be posted, but should be downvoted. They are not mutually exclusive. ",
"You can take three words of my post out of context and project anything you want, at least read the rest of the sentence."
] |
[
"If it wasn’t for pants or belts, would belly fat be distributed down your pelvis too?"
] |
[
false
] |
I’ve noticed that belly fat stops right around my belt line and I see it in many other people too. The traditional “beer belly”. Is that caused by where you wear your pants? Like if I wore my pants lower, would fat start to deposit there more. Hopefully I’m wording this so it makes sense.
|
[
"Try reversing the cause and effect in your head and see if it makes more sense. Is our body shaped because the clothes we wear, or did we end up designing clothes that best fit our body shape?",
"Hope this answers your question."
] |
[
"Your body is pre-disposed to accumulate fat in certain areas. Your arms and legs are frequently moved, and if they were chubby that would make them more difficult to move. That might slow you down enough that a predictor could catch you. Your chest can't be restricted by padding because you need to breath, and if you'r running from a predator you'll need your entire lung capacity. But your belly? The only thing that the extra padding could possibly restrict is your digestion, and if you're fat then you can afford to slow down your digestion. So that's where the fat tends to accumulate, at least at first. Your butt and your boobs are 2 other places, your butt for the same reason, it doesn't restrict your movement, and your boobs because they're designed to store fat for breastfeeding a baby (yes, even in men, it's a vestigial trait in men)."
] |
[
"I suspect it may have to do with accumulation of visceral fat. When we get fatter, it's not just the fat layer under the skin, but also we're gaining fat surrounding internal organs, which is called visceral fat. Upper abdomen contains a lot of organs -- liver, stomach, intestines, pancreas, spleen, and so on. So, if you add extra layer around them, you can imagine the volume that protrudes can be quite a bit. Under the belt line, there aren't as many, just bladder, some intestines and uterus for women.",
"Here's a nice radiographic image you can check out:",
"http://w-radiology.com/abdominal_ct.php",
"Click on \"Sagittal view\" to see sideways."
] |
[
"Why does our brain have receptors for rare drugs that we wouldn't normally ever encounter, such as LSD?"
] |
[
false
] | null |
[
"The receptors aren't specifically for LSD. They're serving their own regular function related to normal brain behavior. Then, every once in a while a scientist will discover/invent a new chemical that happens to fit one or more of the existing receptor sites."
] |
[
"Drugs like classical psychedelics (LSD, mescaline, psilocybin) mimic the effects of serotonin, a neurotransmitter. They have a similar enough \"shape\" to fit the same receptors site as serotonin. The presence of these substances in plants served as an evolutionary advantage for said plant. It works as sort of mild poison. An animal that eats a psychedelic containing plant would probably refrain from doing so in the future.\nIt is also important to note that not all drugs mimic neurotransmitters at the receptor. In fact, many of them do not bind the receptors at all but instead boost the synaptic content of neurotransmitters. A good example of this would be amphetamines and many, many antidepressants. These trick our neurons into releasing much more of the neurotransmitter than normal or prevent the breakdown or reuptake of the neurotransmitter from the synapse.\nOther drugs, such as alcohol and benzodiazepines, bind entirely novel sites on neurotransmitter receptors. These are the real mysteries of the drug world because there are no known natural molecules that bind at that site. And so for these your question remains. Maybe we will discover endogenous molecules that bind at these sites in the future, but right now it still remains a mystery."
] |
[
"That's a rather loose use of \"purified\", given that ergot-infested rye doesn't contain LSD."
] |
[
"Is the current snowpocalypse caused by global warming?"
] |
[
false
] |
I got in an argument with some co-workers who scoffed at me when I said the current snowpocalypse (as well as the previous ones) is all part of global warming (or technically Climate Change, but I never could make that point after first saying it was global warming). From my understanding, weather (cold fronts, warm fronts, hurricanes, etc) is nature's pressure release valve. Global warming is heating up the world and creating more energy (causing more pressure to build up) and so we have more severe weather not just in the summer when it's hot, but all year round. In summer we have heavier hurricanes, more thunderstorms. In winter, heavier snow, more blizzards. Is this right?
|
[
"As far as I know, it's impossible to say whether any one storm is caused by global warming, but it is said that the frequency of such storms can be expected to go up as the earth warms."
] |
[
"This. exactly. Anyone who says climate change caused one event or another is lying. Climate change is about long-term trends in weather patterns globally. So if we have more of these events in the next 10 years than we've had in the past ",
" is climate change. "
] |
[
"You're on the right track. If the planet is generally warmer, the oceans will be generally warmer. If the water is warmer, more of it will evaporate. If there is more water vapor in the air, then there is more available to condense and fall as snow or rain when the conditions are right.",
"One snow storm in isolation doesn't make a trend though. An unusually cold winter in one area doesn't disprove global warming either. It's the total effect over a long period of time, and we are very poor judges of slow long term changes."
] |
[
"How is queen bee becoming a queen bee ? Is it natural or is it acquired ?"
] |
[
false
] | null |
[
"Any female bee can become a queen bee based on diet, so it is an acquired trait.",
"Extra information (aka me info-dumping on bees because I love them):",
"The way bee sexes work is that the queen can lay fertilized (two sets of chromosomes, one from her and one from a mate) and unfertilized (one set of chromosomes, only from the queen) eggs. The unfertilized eggs become male bees and the fertilized eggs become female bees.",
"The vast majority of fertilized eggs hatch into worker bees. They are female, but sterile and cannot usually produce eggs. However, if the worker bees decide that the hive is too crowded, or that their queen is sick, they will build a special place for her to lay an egg called the \"queen cup.\" It's much larger than a normal honeycomb cell. She'll lay a perfectly normal fertilized (female) egg in there and then forget about it. Then, once the egg hatches the worker bees feed it tons of food and royal jelly. The proteins in the royal jelly activate parts of the baby bee's DNA that are normally suppressed, and she grows into a queen bee. She's big, female, and fertile.",
"If the hive is too crowded, then the old queen bee will leave with a large portion of bees and start a new hive somewhere else before the young queen hatches. If the old queen is sick, then the worker bees will kill her before the young queen hatches. Queens never cohabitate.",
"Once the new queen emerges successfully, she'll go on a \"nuptial flight\" where she meets drones and collects a lifetime supply of sperm. This takes a few days, and sometimes she gets eaten by a bird. This is the worst possible thing that can happen to her hive. Since they're fresh out of eggs (from killing the old queen a few days ago) they can't turn any new larvae into queens (a queen bee made in a normal cell, as opposed to a queen cup, is called an 'emergency queen'). In this scenario, some worker bees will start laying eggs. However, since they've never mated, their eggs are unfertilized and hatch into drones. These drones fly off and (hopefully) propagate the hive's DNA by mating with a queen. The rest of the hive dies :(",
"So, yeah! Royal jelly and lots of food is what makes a queen bee, not genetics. Royal jelly is a very complex mixture of protein and other molecules, so it's hard to know exactly what part of it switches off the \"worker genes\" and turns on the \"queen genes\"."
] |
[
"From Wikipedia :",
"\"All bee larvae are fed some royal jelly for the first few days after hatching but only queen larvae are fed on it exclusively. As a result of the difference in diet, the queen will develop into a sexually mature female, unlike the worker bees. Queens are raised in specially constructed queen cells.\"",
"Apparently there are already Queen larvae chosen from a previous queen from a hive."
] |
[
"Actually fascinating, thank you for your bee knowledge!!",
"I am especially amazed by the emergency queen scenario, and the last ditch attempt to send drones out to fertilize another hives queen... It is incredible how strong and crafty the instinct to survive is in nature..."
] |
[
"Siema to ja xd"
] |
[
false
] | null |
[
"Xdddddd"
] |
[
"Xdddddd"
] |
[
"Xdddddddd"
] |
[
"Why are birth defects of the ear (like preauricular pits) sometimes indicators of kidney defects?"
] |
[
false
] |
[deleted]
|
[
"http://www.oregon.gov/dhs/odhhs/pages/tadoc/hloss13.aspx",
"http://www.annualreviews.org/doi/abs/10.1146/annurev.med.60.052307.120752?journalCode=med",
"I don't have access to the second one unfortunately, but unless you wanted a really technical step-by-step breakdown, I think that the categories outlined in the abstract should suffice."
] |
[
"Here",
" is the second article in its entirety. It's a good overview of the main ear/kidney syndromes."
] |
[
"My sister was born with a messed up ear. Deformed and deaf in one side. Her twin died of potter's syndrome and was born without kidneys. I don't know much about it but I would also be interested in knowing the reason for this."
] |
[
"Is it actually possible for fetuses to grab things/stick their hands out during surgery like they so often do in TV shows?"
] |
[
false
] | null |
[
"http://www.snopes.com/photos/medical/thehand.asp",
"tl;dr: if mom is under anesthesia, baby is as well. Baby would be just as unconscious as mom."
] |
[
"Don't they quite frequently give just an epidural? If so would that knock the baby out? From what I know of how epidural work it wouldn't."
] |
[
"np, this bothered me when i got that email chain letter back in the day. Seemed inhumane to be operating on a fetus that was conscious enough to grasp your hand."
] |
[
"Do virtual particles create a residual energy at the quantum level?"
] |
[
false
] |
To my knowledge residual particles are able to pop in and out of existence taking the form of a subatomic particle before passing on. With newtonian physics I know that energy can not be created or destroyed. But at the quantum level is it possible that these virtual particles come into existence, posses energy and give off energy to their surroundings? Is there any residual energy left behind in this situation?
|
[
"An inexact way to think about this is that the Heisenberg uncertainty principle allows you to \"borrow\" energy from nowhere but requires you pay it back in full in a very short time. So you can have particle pairs appearing but they must then completely disappear very rapidly. So they cannot pass energy to their surroundings in any Newtonian sense.",
"This does not mean they have no effect, in fact the Casimir effect - conducting plates in a vacuum feel a teeeny force pushing them together - can be thought of as resulting from virtual photon modes (although the explanation is not unique as virtual particles are more mathematical machinery than hard physical objects). In short the indirect effects of virtual particles pervade quantum field theory - especially renormalisation - but they do not directly leak energy to universe in any newtonian sense."
] |
[
"Thank you for the response. My inquiry arose when I pondered if their could be an \"energy leak\" at the quantum level. This energy leak would then force expansion beyond the planck length. Once the planck length was reached macroscopic objects could then come to being.\nThis came to me when I was thinking about entanglement and superposition. An object is only recorded once a macroscopic object collapses the wave function of probability to bring its qualities/quantities to light. The \"observer\" causes the reality, the quantum enigma. I am still in my very early years of a physics degree so I do not fully know if these concepts are correct, they are only from my readings and subjective comprehension. \nIn theory, if there were a thermal expansion or sorts, this leak of energy, in the quantum level everything would have to expand. This expansion then brings the universe beyond the planck length where a macroscopic object could \"observe\" the microscopic universe, collapse its wave function, and bring it to reality. Thus, the big bang.",
"I am looking for any flaws in this logic."
] |
[
"Unfortunately there are many flaws in this logic. Firstly in a big-bang scenario the entire fledgling universe is quantum, there are no observers or macro-systems to \"bring it to reality\". In fact its reasonable to assume an explanation of the big bang should only involve quantum objects (there is no macroscopic world as yet). This is because the macroscopic world emerges from quantum effects, it is not some independent phenomenon, its rules result from underlying quantum processes. This transition from quantum to classical regimes is not well understood, but its quite clear that observing quantum systems does not necessarily make them classical or \"more real\", they can well have properties prior to observation (our predictions of these are merely not completely deterministic). The energy leak you propose would require the uncertainty principle to be constantly violated and would also mean that there could be no conservation of energy in any way, as infinite amounts of energy could be constantly leaking from the quantum scale. Additionally this scenario would make gravitational collapse (i.e. forming galaxies and planets and stars) impossible as leaking energy would simply blow gravitational structures apart constantly (so instead of an accelerating expansion of spacetime between galaxies we would see an expansion between individual atoms)."
] |
[
"Will things stop sinking at a certain depth?"
] |
[
false
] |
Just as balloons will reach an even stand point when floating, will a rock eventually reach a point of so much pressure it cannot float any lower, if dropped into the ocean? I want to go fishing in the marinara trench
|
[
"The density of water some changes very little, around a couple of percents at most by the time you get to the Mariana Trench ) however, the density of a rock is usually several times that of water.",
"What determines buoyancy is the relative density of an object compared to the one of the fluid around it. Another way of looking at this is: if the weight of the water displaced by the object is less than the weight of the object then the object will sink.",
"A minor point of terminology. A rock is not floating down, it is sinking."
] |
[
"The rock also experiences the buoyant force."
] |
[
"The pressure on a rock is on every direction around it. Which means that there's not resultant force acting of the rock. The only force action on the rock is gravity. But that logic the rock should fall until reach the bottom or it breaks from the pressure."
] |
[
"Is it true that \"non-mineral water\", for example filtered rain water, does not dehydrate the body as well as the aforementioned?"
] |
[
false
] |
Some people said that because rain water doesn't have electrolytes, it's not as hydrating. I think that's rubbish but am curious to know.
|
[
"Do you have a reference for this? (I'm aware that it's parroted all over the web; I mean a real reference, with numbers and citations.) It seems ridiculous on the face of it, because it implies that the food you eat has no electrolytes. You say, for example, that drinking distilled water would cause you to lose sodium, yet every processed food piece that Westerners eat is soaked in salt. The contribution of drinking water to normal electrolyte balance must be tiny, such that the first bite you take in the morning far outweighs all the water you drink in a day."
] |
[
"Rain water is water. And only water is hydrating. Hence the \"hydro\" root of the word \"hydration\". Electrolytes (sodium and potassium salts) are not hydrating. ",
"The point of electrolytes is to help retain water and to replace the loss of minerals through sweating. But they are pretty much pointless for most people under most circumstances. You might benefit from them if you're doing back to back triathlons on a hot day."
] |
[
"Drinking demineralized water actual has serious side effects as it does not contain minerals/salts your body needs. It's consumption will cause your body to lose stored mineral (calcium, sodium, potassium etc). Over time this will have adverse health affects due to low electrolytes which are required for proper cell functions. "
] |
[
"Does science \"prove\" things??"
] |
[
false
] |
I often hear people say things like "Science does not prove things" I usually hear Popper mentioned along with this claim. Please use examples. For example, is it proven by science that, lets say, leaves break down and become part of the soil??
|
[
"The purpose of science is to build a logically consistent framework useful in modeling the universe. Describing something logically consistent within its framework doesn't necessarily mean it is a physical phenomena or even happens. It simply means it is not contradicted by our body of knowledge.",
"You could say it only proves things to itself, so long as you accept the logical ",
"axioms",
" which have been described from observation."
] |
[
"For people not engaged in the practice of science, this is mostly a linguistic confusion. When people ask \"does science prove this\" they tend to mean \"does science show that this is true\". In that sense, yes, science can prove a lot of statements true, for most intends and purposes.",
"Here is how you say the same thing in the science lingo: Using the scientific method, we can find evidence to support claims.",
"You don't use the word \"proof\" because it means \"a demonstration that the one sentence is logically consistent with some other sentences\". While being able to demonstrate logical consistency is a fundamental skill in science, \"proving\" something in the scientific context doesn't mean \"showing something true\" the same way it does in daily language.",
"Philosophers of science say \"science does not prove things from first principles\" because we do not know the \"first principles\" of how the universe works. Science is the endeavor to figure out those rules. It's a matter of trial and error, and empirical observation. Scientists do not just sit in their chairs and show if some claims are logically consistent with some rules of the universe that somehow only they can know. In that sense, no, science does not prove things.",
"tl;dr If somebody says \"science does not prove things\" and thinks it's a cool statement, that statement is probably wrong in the way the person understands it."
] |
[
"It's easy to go wrong either way on this one. If you assume every scientific hypothesis is God's truth, you're making an error. On the other hand, if you assume that it's impossible for anyone to know anything, then you're also making an error.",
"The scientific method is a tool for learning things about the world. It's not the key to omniscience, but neither is it a waste of time."
] |
[
"If the Hubble Telescope cannot take pictures of pluto, how is Hubble currently hunting for smaller objects further away than pluto for the New Horizons spacecraft to visit?"
] |
[
false
] |
Link to what I'm referring to:
|
[
"As ",
"/r/adamsolomon",
" said, Hubble can take pictures of Pluto. The problem is that Pluto is so small and so far away that it's hard for Hubble to take a good, high-resolution image of Pluto. ",
"What this article is talking about is that Hubble will be looking for new objects for New Horizons to visit. Hubble isn't going to be able to take nice, high-resolution images of these objects, either. We will look for something that looks interesting, then send New Horizons to investigate further!"
] |
[
"Hubble can certainly ",
"snap photos of Pluto",
"."
] |
[
"Hubble wont be able to see anything in detail, but will be able to see if there's ",
" there. Basically it will stare at the patch of space New Horizons is flying towards and see if anything moves. More details ",
"here"
] |
[
"If we have been using HeLa cells for so many years, how can company still have low passage number HeLa cells in stock?"
] |
[
false
] |
Wouldn't all the HeLa cells been already passaging many times in order to generate huge amount of stock for sale?
|
[
"Most types of cells used in a cell culture systems (e.g. HeLa cells) can easily be grown to really large numbers without having to passage them too often. Passaging just means that you take the cells from one surface (or one suspension) onto a new one, ususally with a smaller number of cells.",
"These cells are then fractioned into small numbers (usueally still more than 100k cells) that can be frozen in liquid nitrogen at 77 K (or −196 °C).\nIn this frozen state the cells can survive for several decades and be thawed up and reproduced when needed. \nThere are special institutes keeping copies of these nearly original cells which a company can order and use for their research. Or they can simply freeze and store the cells by themselves.",
"Source: I am a lab technician working with cell cultures"
] |
[
"A \"passage\" in cell culture isn't defined in terms of time in culture/cell divisions. In theory, you could produce any number of cells within a single passage, you just woudl have to choose a large enough growing surface."
] |
[
"Depends on the cell type. Fibroblasts especially need cell-cell contact or they just won't grow, so you can't split them out too thinly."
] |
[
"Why doesn't my brain know when it's dreaming?"
] |
[
false
] | null |
[
"I would actually argue that your brain does not know.",
"We know that your brain is active during sleep, especially during certain phases. These electrical firings are no different than real firings you would receive during actual daytime activity. For example, your motor cortex will be active and firing if you are moving in a dream (actually it is causal in the other direction, so you would be moving in a dream if your motor cortex is firing).",
"It's the reason that dreams often make no sense. Your brain is attempting to interpret the signal inputs, and the signal inputs are not based on anything. For example, you are \"seeing\" in your dream but your receptors in your eyes are not being activated by light, so the resulting \"seeing\" is caused simply by activity in your visual cortex. Your perceptual systems are essentially shut off during sleep, all experienced perception during dreaming is quite artificial.",
"However, we really don't know a whole lot about dreaming. Lucid dreaming, for example, is a very interesting topic (there's debate about whether it's real and, if so, what it's actually manipulating).",
"Source: I teach an undergraduate sensation & perception course. Dreaming is roughly related to the topic."
] |
[
"Sounds like you need to visit ",
"r/luciddreaming",
" "
] |
[
"in your dreams, your brain processes everything that needs to be worked on technically, your brain knows, it's just that you yourself do not realize it. But you can train yourself to realize if or if not you're dreaming, that is by \"controlling if everything is normal\".\nif checking your wristwatch or your hands becomes a normal, frequent habit during you being awake, you will end up doing this in your sleep too. this is important, because in dreams, the time is all messed up and clocks never work, also your hands are the scariest things ever been attached to your body, so you have a method to control if you are awake or not if in doubt.\nhere you might want to be careful about staying asleep when you found out about dreaming, because then you will be able to control the dream (if you don't already do it)"
] |
[
"How is a orb weaver spider able to make a large web that pans over 10 feet across? They obvious can't fly, so how do they do it?"
] |
[
false
] | null |
[
"I have seen them do this. They first climb to the highest point of attachment and using a continuous web tread \"bungee jump\" to the lower point. They can repeat this for other web connections and then start filling in the space between the vertical strands. If there is a gentle wind blowing, they can attach to one point and let the wind blow them horizontally to another point. Another way of spanning the distance is to throw a web on the air and wait for it to stick to another point.",
"Basically, once they establish the main lines, it is mostly a matter of filling in. I have seen them \"bungee jump\" more than 10 feet. As much as 20 feet (~6m)."
] |
[
"Some spider can hop pretty far with their web in tow, a la \"spiderman\". Honestly there are hundreds of ways spiders spin webs, entirely evolution-driven."
] |
[
"Oh yeah, they like to find drafty areas in the hope a wandering fly will pass through"
] |
[
"Is there anywhere that models predict will get nicer to live because of climate change?"
] |
[
false
] |
Every time I read about the impacts of climate change, it's stories of ecological collapse, droughts, hurricanes, and so on. Is there anywhere that models predict the climate will get more moderate, the land more arable, and with more abundant fresh water? To put another way, what's the best place to move to minimize the negative impact on my family?
|
[
"First off, \"nicer to live\" requires individual value judgements because not everyone is the same in what they like. By conventional metrics, most places are going to be losers in climate change but if the mean temperature was a bit warmer there will be some places which will generally be considered more pleasant places to live. Canada and Russian will be warmer but they will still have long dark winters. New York will get more like Miami and some people love Miami. It's known we are altering the climate but exact predictions of regional details are not as certain. It's not yet time to be homesteading new places based on predictions of climate 100 years in the future.",
"Rainfall and precipitation are also important factors in quality-of-life. While rain is inconvenient for picnics it essential for agriculture. Climate change is going to alter rainfall patterns but it's not as predictable which places will get hotter and drier and which get hotter and wetter. Storminess is also expected to increase for most places in the mid-latitudes. Timing of rainfall is also important - does it all come in winter or is it spread out through the year? It is unfortunately those places which are already struggling (Africa, Southeast Asia) which are forecast to have some of the worst negative effects on agriculture."
] |
[
"My understanding is the regional impacts of climate change have not been determined. It isn't completely clear when, or even if, the thermohaline circulation will stop. If it stops in your lifetime, you are likely to experience an ice age in short order. If it doesn't stop, Ohio is more likely to feel like Georgia in 2050 than be frozen. \nI think the really scary things are the political and economic impacts. What happens if the Sierra Nevadas can no longer supply summer irrigation water to the California agricultural valley? What happens if Hansen is right when he speculates about 10 feet of sea level rise by 2065? Do the Feds cover the relocation costs of north of 30 million Americans? Where does that money come from? What happens when Bangladesh has to move 50 million + people whose homes are now under sea water? Does India just absorb them, likewise with the refugees fleeing Africa to Europe right now? Does Europe just absorb millions of uneducated desperately poor Africans? These are the questions (and all the ones I haven't thought of) that worry me. \nUgh. I can't write anymore. This is depressing. Learn to garden. Learn to make your own energy. Try to live someplace with access to protein (like wild animals.) We are in trouble. "
] |
[
"Focussing simply on climate (and ignoring any political instability, climate refugees, economic impacts etc), the UK and Ireland are predicted to have increased risk of severe flooding in winters, but warmer and drier summers. So depending on how close you live to a river, it might or might not be nicer."
] |
[
"Why do photons always go 299 792 458 m / s in a vacuum? A marble can go various speeds."
] |
[
false
] | null |
[
"See the instructions in the autogenerated comment"
] |
[
"Hi extreme_douchebag 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.",
" ",
" "
] |
[
"Physics"
] |
[
"Bright, slow moving light in night sky, eventually dims and disappears."
] |
[
false
] |
My friend and I were out front of my apartment at around 9:30pm, in Ohio. In the sky, directly above our heads, we notice a rather bright object moving slowly across the sky in a straight line, from west to east. After a couple minutes, the light seemed to slow down considerably, almost to a stop. Shortly after it began to dim and eventually disappeared in a dark orange glow. There is a rational explanation for this light. I've read that satellites very closely exhibit this behavior, but are generally no brighter than a regular star. This was many times brighter and larger than even the brightest star. As a rough guess I would say it was 5 to 10 times larger and brighter than Jupiter when seen with the naked eye. It probably was a satellite, but it doesn't seem like it would be that large or bright or directly overhead. If this is normal for a satellite, please let me know. I also do not think it was a meteorite because of its slow speed and lack of a tale. What do you think it was?
|
[
"I'm willing to bet it was the ISS. ",
"Here",
"'s the best times for sightings for Columbus, Ohio.",
"From that site: At 9:19 PM on Aug. 31, the ISS was visible for approximately two minutes flying roughly from the northwest to the east-southeast. This sounds just like what you described.",
"Also, upvote for fellow Ohioan!"
] |
[
"Iridium flares",
" and the ",
"ISS",
" can get quite bright. Iridium flares in particular can be much brighter than Jupiter or Venus, almost as bright as a half moon."
] |
[
"If you have a smartphone (at least Android and most probably IOS also) You can get an app that will tell you when and where to look for Iridium flares and the ISS."
] |
[
"Why are Lagrangian points only limited to the orbital plane?"
] |
[
false
] |
Shouldn't there be additional points above and below the plane of orbit where the two gravitational fields provide the correct force vector?
|
[
"No, there are no such points. So the whole Lagrangian points are only relevant in a rotating reference frame so that's what we're going to use. There are three forces present. Gravitational force towards each of the two bodies and the centrifugal force (centrifugal force is very real in our reference frame, don't go on about pointing how it's not a real force). The sum of these three need to be zero for the object to be stationary. Centrifugal force is always parallel to the plane of rotation, not directly away from the central body. And obviously the two gravitational forces are directly towards the two bodies. If you are out of the orbital plane, then you have two forces with a component towards the orbital plane and the centrifugal force is parallel to it so it has no such component. Thus the sum of the forces can't be zero, there's nothing to cancel that component of the gravitational force towards the orbital plane."
] |
[
"At any given point in the orbit, yes- but they won't stay in that configuration. For orbits outside of the orbital plane, as they move through their orbit they will change their location with respect to the other two bodies, thus no longer will the forces add correctly. "
] |
[
"wouldnt there always be a component of the vector pointing back towards the orbital plane and none pointing away from the orbital plane, thus no place where all the forces cancel? "
] |
[
"If radians are dimensionless units can I drop them as needed in calculations?"
] |
[
false
] | null |
[
"The formula you are using is \"arc of a circle\", which is ",
"s = r * theta ",
"but it is only valid if theta is in radians, which is the case here (if it was in degrees, the formula would have been s = pi",
"theta / 180) The formula comes from the definition of radian itself, the ratio of the length of the arc to the length of the circle's radius at a given angle, (2",
"pi",
"pi) so it is just a ratio thus it is dimensionless.",
"Edit: I just realized I only confused you more, for clarification, 2.6 rad/sec means \"the arc traveled by the object in one second divided by the radius of the circle is 2.6\" or \"s (traveled in one second) / r = 2.6\"."
] |
[
"Yeah, that's totally fine. I think the reason it seems \"wrong\" is that the rad unit here simply represents 1. Usually dimensionless units exist to make conversions between quantities simpler, for example the mole allows us to work using convenient quantities of mass instead of molecular masses, and the percent (kind of a dimensionless unit) allows us to work in proportions that we easily understand. But the mole represents Avogadro's number, and the percent represents 0.01, so when we remove those units from the calculation we have to multiply by their associated factors. ",
"Radians exist as a unit to allow us to conveniently convert between circumference and radius - they represent the number 2pi (or 1 over 2pi). However because in this calculation we are already using radius as our length measure, the radian unit simply represents the number 1, and thus we make no change to the calculation when removing it, ie. we divide by 1. ",
"In other words: the phrase \"travels in a circle with radius 21 cm w/ an angular velocity of 2.6 rad/sec\" is equivalent to \"travels in a circle at 21*2.6 cm/sec.\""
] |
[
"Short answer: in your problem, there are 21 cm per rad, or 21 cm/rad. Thus the \"rad\" cancel out.",
"Look at ",
"this picture",
". The red line has length r cm. When the line is folded, you can see that it gives 1 rad, so there are r cm/rad.",
"I am uncomfortable with the whole \"radians are dimensionless units\" thing?",
"As seen above, the fact that rad is a dimensionless unit is not required for this problem. When does it matters? Well, when you sum stuff, they must be of the same unit. It makes no sense to sum 3 cm with 5 kg. Similarly, it makes no sense to sum 3 cm with 5 cm",
" (same base unit, but raised to a different power). This is where rad are different: I am not sure of your current level in mathematics, but the function sin(x) can be written as the Taylor series ",
"sin(x) = x - x",
" /3! + x",
" /5! - x",
" /7! + ...",
". Now, when doing so, you are effectively summing rad with rad",
" , rad",
" , rad",
" etc. This is OK, because rad is dimensionless."
] |
[
"Phase of a single molecule."
] |
[
false
] |
If you have a single molecule of a substance, say water, can it have a phase such as solid, liquid or gas? does the physical state depend on other molecules around it?
|
[
"No, not really. When we think of phases of matter, it only makes sense when we refer to a very, very large collection of particles. Phases of matter strongly depend on the attractive and repulsive interactions between one particle and the others."
] |
[
"Well, a single molecule in vacuum would/does have essentially the same properties as a molecule in the gas phase. Since by definition, the gas phase is the essentially the phase where the molecules are separated to such a degree that the intermolecular forces are insignificant. ",
"So when we calculate the properties of a single molecule in vacuum, we refer to it as a 'gas phase' calculation. But the phase itself is a bulk property, not a property of a single molecule or even a small group of them."
] |
[
"Cool, my friend and I were discussing this and we thought it would either not be a phase at all, or maybe be considered a gas, thanks for clearing it up."
] |
[
"Would heavy metal elements be found in a gas giant?"
] |
[
false
] |
I was playing ME2, and on a gas giant planet was a large deposit of platinum. I'm curious to know how realistic this is (because this game is so rooted in hard science, right?), and what other sorts of elements might conceivably be found in a large gas giant planet.
|
[
"It's not possible to recreate conditions deep inside Jupiter here on Earth. The core should be around 43,000 F and under more pressure than any Earthly diamond anvil can reach.",
"This means questions like \"Is platinum soluble in oceans of white-hot liquid metallic hydrogen?\" aren't fully answerable. You're probably not getting any dropped jewelry back though. ",
"It's probably fair to say that Mass Effect is rooted in hard science... compared to other videogames. It does produce some headscratchers. If I wanted platinum and I was near Jupiter I'd try some of its collection of captured asteroids first, and if I had a probe rated for millions of atmospheres of pressure and 43,000 F I'd build my armor out of probes."
] |
[
"While you're correct that the pressures are beyond what static compression can reach, dynamic compression is approaching Jovian core conditions. ",
"Here",
", for instance, diamond at pressures up to 5 TPa is observed; this is around half that predicted at the centre of Jupiter, but well within the core. ",
"Polystyrene",
" at up to 2.7 TPa has been observed.",
"It's also true that liquid metallic hydrogen is routinely produced, although not at such high pressures; I doubt that solubility measurements would be possible, though, given the short timescale of the experiments."
] |
[
"Technically you could get them. But I don't think they'd be in any significant concentration. The inner Rocky planets of our system got most of their solid mass when the system was forming. An outer gas giant won't get as much.",
"They'd most likely come from capturing comets and asteroids and such. I don't think you'll get a ton of elements after iron in the periodic table."
] |
[
"Is it possible to focus or concentrate anything besides light?"
] |
[
false
] |
[deleted]
|
[
"Don't tempt me."
] |
[
"Well, yes, but AM radio has a standardized frequency range, right?"
] |
[
"Sure. Fresnel lenses for microwaves have been built as DIY projects, and also sold commercially, for quite some time.",
"http://www.tomshardware.com/forum/26365-4-alternatives-dish",
"You could also do mirrors for X-rays. This has been done since quite some time ago for X-ray satellites. But it's more like a tube where the X-rays are just glancing the inner wall at a very shallow angle. It's not a perpendicular reflection.",
"http://en.wikipedia.org/wiki/X-ray_telescope"
] |
[
"Say that atoms found in the island of stability were found to be really stable. What could we potentially use them for?"
] |
[
false
] |
There is something called the island of stability which dictates that it may exist heavy elements that are stable. If we create such elements and their half-time is on the order of years. What could we use this new material for?
|
[
"Some things that we need heavy materials for could be improved if we had ",
" materials. For instance, shielding against gamma radiation. You want something with a high Z so that it's got a lot of electrons which can leech energy from a gamma ray via the photoelectric effect and Compton scattering.",
"Superheavy elements will have higher Z than anything else currently on the periodic table.",
"They could also have some very cool chemical properties, because at such high Z, the atomic electrons have to fill higher and higher orbitals. This means that have larger and larger single-particle energy levels, and relativistic effects start to become important. This can actually change the behavior of macroscopic amounts of that material. The band structure can be completely changed by relativistic effects. You could have materials which you'd naively expect to be metals based on their location on the periodic table, which actually behave like semiconductors. Of course this is all theoretical, since we're talking about elements which might not have been produced at all, let alone in macroscopic quantities.",
"But anyway, there are lots of reasons why we need to pursue this avenue of research and understand the extreme limits of nuclear and atomic physics."
] |
[
"You might find relatively stable nuclides at any of the magic numbers. 126 is a ",
"magic number",
" for neutrons, so it's reasonable to think it might be for protons as well. That's the next one in the sequence, but there are even higher ones as well.",
"And I have some ideas as to why, but why must the electrons be at higher energy shells at heavier atoms?",
"Pauli exclusion limits the number of electrons which can exist in each shell. As you add more and more, you start to fill higher and higher shells."
] |
[
"Elements heavier than Iron exist naturally as products of neutron bombardment. Either in stars, slowly through the s-process (atom absorbs a neutron or two, then after a while decays into a higher atomic number element, then absorbs more neutrons, etc.) or in supernova rapidly through the r-process (atoms absorb lots of neutrons, producing neutron rich isotopes which decay in nanoseconds to higher atomic number elements, which absorb yet more neutrons, and so on, proceeding up the \"neutron drip line\" all the way to trans-Uranics). These various isotopes then either stick around or decay into lighter elements over time, and then we're left with a wide variety of elements. Elements heavier than Uranium don't tend to exist naturally on Earth because all of the instances that were created billions of years ago through supernova activity have since decayed away entirely.",
"But both of those processes have limits. In the case of the s-process that limit is Lead-209/Bismuth-209. Bi-209 absorbs a neutron to become Bi-210, which decays to Po-210 and then to Pb-206. Pb-206 can absorb 3 neutrons to become Pb-209, which then decays to Bi-209. This is a dead-end cycle for the s-process, which renders it incapable of creating heavier elements than these. The r-process also has a limit in the \"gulf of instability\" after the trans-uranics. Elements with atomic numbers above about 115 have extremely short half-lives (milliseconds then microseconds then even shorter) and tend to decay by alpha emission. Even in the extremely strong neutron flux of supernovae that drives the r-process these super-heavy elements simply don't survive long enough to catch additional neutrons and continue accreting nucleons up the period table.",
"But there could be an island of stability around atomic number 120 or so. Even if those elements are long-term stable, with half-lives of billions of years, there would be no way of producing them naturally (realistically no-one thinks that any of the elements in the island of stability will have half-lives nearly that long though). Imagine trying to build a bridge to a distant island and every time you go out and build a pier to extend the bridge it simply gets washed away instantly. That doesn't stop the island existing, but it would stop you from being able to get there by building a bridge."
] |
[
"At what point in miniaturization does engineering transcend the border between it and chemistry?"
] |
[
false
] |
[deleted]
|
[
"This!",
"Having said that, the transition region between microsystem engineering and chemistry happens around the 10 to 100nm feature size, with nano-particles and such. The difference between the fields would more likely be about how the structures are created, with chemists working with their traditional reactions and engineers using top-down approaches typically derived from the semiconductor industry. Really though at this size you understand the behavior of an object quantum mechanically, so it's all physics in the end. :P",
"This size scale is actually much smaller than a cell, and biology should probably get a mention too. "
] |
[
"This!",
"Having said that, the transition region between microsystem engineering and chemistry happens around the 10 to 100nm feature size, with nano-particles and such. The difference between the fields would more likely be about how the structures are created, with chemists working with their traditional reactions and engineers using top-down approaches typically derived from the semiconductor industry. Really though at this size you understand the behavior of an object quantum mechanically, so it's all physics in the end. :P",
"This size scale is actually much smaller than a cell, and biology should probably get a mention too. "
] |
[
"chemistry governs the world around us and is an important part of engineering no matter the scale"
] |
[
"Do any species besides humans cry?"
] |
[
false
] |
I've seen thread, but there are only a few sources there. Is there a good explanation for why we are the only species that cries?
|
[
"Elephants cry."
] |
[
"I don't see how there is a such a huge difference. Of course since our brains have evolved over thousands of years to respond acutely to different forms of crying we would perceive greater complexity in human cries versus animals. However, given that there is research that proves numerous infant (and occasionally adult) mammals cry for emotional/social reasons; I don't see how their crying really differs from ours. ",
"Source: ",
"http://udn.nichd.nih.gov/pdf/mammalian_cry_circuit.pdf"
] |
[
"I am fairly sure most mammals cry to some degree; though the social cues are most likely different. "
] |
[
"If a person is frozen, is there any way to unfreeze them?"
] |
[
false
] |
Or would there be no chance of them surviving?
|
[
"When a person freezes, the liquids in their bodies crystallize. This breaks the cell membranes, leading to death. ",
"There's research looking into ways to prevent this (there is a frog that does it) in humans, but so far it's all research. "
] |
[
"Thanks for the answer, i was just watching a bit to much Futurama, and what happened to Fry seemed a bit fictional, but i wanted to see if it was possible."
] |
[
"Yes, this. There are fairly ways of preserving very small tissue samples so that they can be revived (eg, sperm & eggs at fertility clinics), but the whole \"ice crystals rupturing your cells\" is a huge problem once you try to scale up to an organ."
] |
[
"Can photon sieves reduce noise/background in epifluorescent microscope imaging?"
] |
[
false
] |
I read that scientists are using photon sieves to block unwanted 'light' and increase the resolution of telescopes in space. Can photon sieves, or something similar, be used in fluorescent microscopy to reduce light diffraction recorded by the camera sensor and increase resolution? Similar idea to space, but a different spectra of light. It kind of reminds me of confocal microscopy, but the spatial filter is placed later in the light path, if I understand it correctly. The penalty is a drastic cut in total light that reaches the sensor, but maybe it could be compensated by longer exposure times and averaging frames. I could see useful applications in biology. Thoughts?
|
[
"Ok, I was the topical editor of a well-known journal of optics where the topic included stuff like this, so naturally I have an opinion on such things, but of course it is just an opinion.",
"So the photon sieve pattern you are using is a type of pupil-plane coding. What is pupil-plane coding? It's placing a pattern, whether its a phase or amplitude pattern, in the pupil of an imaging system so that the focused beam takes on a particular shape. Examples of this include the axicon, cubic phase plate, annular aperture, radial polarizer, azimuthal polarizer, etc. The photon sieve appears to be another such pattern. Sometimes these are used to extend the depth-of-field of the image system, sometimes these are used to reduce the size of the focal spot to improve the resolution in a particular dimension. There is a small cottage industry behind each type of pupil-plane coding element which claims superiority for one purpose or another.",
"If the numerical aperture of the system is NA and the wavelength is L, the resolution of the microscope is on the order of L/(NA) and the depth-of-field L/(NA)^2. These pupil plane coding systems can change that a little, allowing some trade off of depth-of-field for resolution, for example, but fundamentally are only going to get some small improvement over the diffraction limit depending on how you measure resolution. For nonlinear",
"\n(e.g. two-photon) microscopy, the improvement might be somewhat greater due to the thresholding effects of the nonlinear fluorescence. Other methods such as PALM or STORM get their improvements by only activating one or a handful of fluorophores at the same time. But the pupil-plane coding approach is very limited in the improvements that can occur and so I wouldn't mess around with it until I had exhausted other approaches that could provide bigger gains depending on what I was trying to image using microscopy."
] |
[
"Thanks for your feedback! I'm currently doing in vivo imaging with miniaturized wide-field fluorescent microscopes... Hoping to improve the resolving power, but very limited what elements I add because of the size/weight of the system. We are experimenting with a few things, but this was my out of the box idea to improve the system... But it doesn't sound like it's worth investing time into exploring."
] |
[
"Seems like there's a little research into its applications in the visible light spectrum: ",
"Huang et al. Ultrahigh-capacity non-periodic photon sieves operating in visible light. (2015). Nature Communications."
] |
[
"This is a debate betwixt Bill Nye and Joe Bastardi from Accuweather on Climate Change. I understand Nye's argument. Can someone help me understand where Bastardi is coming from, and if what he says is accurate?"
] |
[
false
] |
[deleted]
|
[
"Would you care to provide a link to the debate?"
] |
[
"I am sorry, I screwed that one up.",
"LINK",
" to new thread :/"
] |
[
"That's fine, try again with link and we'll take a look."
] |
[
"What would it require to move the ISS to the moon? Could it be done? And how?"
] |
[
false
] |
Is this even possible? I know it’s in low orbit, but I figure it’s got to be easier now that everything is up there. I mean, it's a , people live there. Why not take it to the moon for a week or two? They’ve got big solar panels, right? Could it make it there under it’s own power?? Would it require rocket power to break orbit? Could the ISS then return from the moon and rejoin Earth’s orbit? Clearly I don’t know anything about astrophysics. So, would this be possible, and if so, why hasn’t this be done? And if it’s impossible (or not feasible), why?
|
[
"Its possible, but not logistically feasible. The space station is fragile, any thrust applied would have to be very small and/or very uniform. This men's multiple rockets. ",
"You can't just use solar panels like an electric car, you need rockets. You need to expel mass in order to move in space (simplified), this means strapping some big honkin' rockets to the thing, which would rip it to pieces.",
"It would also be ridiculously expensive (if you could figure out a way to keep the thing from breaking apart). There's no need to do it, it wouldn't benefit anything. "
] |
[
"A solar sail would be an uneconomical way to move the space station. The logistic problems, coupled with the cost, make it unfeasible. ",
"If you want to go to the moon, you design a system specifically for that. Space travel isn't like car travel where just about anything with wheels and an engine will get you from point a to point b. "
] |
[
"The ISS has a ",
"mass of about 4.5x10",
" kg and an orbital velocity of about 7.7 km/s",
". To get it to the Moon, the orbital velocity would have to be roughly doubled, thus we would need to give it about 40 TJ of energy. To put this in more familiar terms, that's about 11 ",
"watt hours or the equivalent energy in about 10 kilotons of TNT. That's a huge amount of energy.",
"Edit: did my initial calculation of energy wrong."
] |
[
"If artificial sweeteners can replace simple sugars such as glucose in fizzy drinks, could they replace more complex sugars like starch in foods like bread and pasta for zero-carb alternatives?"
] |
[
false
] |
[deleted]
|
[
"Artificial sweeteners only work as a substitute for the flavor of sugar, not its other properties. You couldn't make caramel or hard candy out of it.",
"There are sugar-free candies, but they use other things to replicate the texture, like isomalt, which has the physical properties of sugar, without the sweetness.",
"That's why when you buy things like \"Splenda for baking\", it's a mix of splenda and sugar, because in baked goods, the sugar is there for more than just flavor and eliminating the sugar entirely would lead to problems with texture."
] |
[
"Sweeteners like ",
"stevia",
" have very little in common with sugars chemically. It just happens to fit into the receptors on our tastebuds for sugar.",
"Cooking is basically chemistry. If it doesn't match then it will behave very differently in the oven. There's all kinds of polymerization and oxidation needed to produce bread and crust, and engineering challenges like making bread rise without the help of yeast.",
"Sugar molecules have mirror-image forms. We have a metabolism that fits only right-handed sugars, but our taste buds can go either way and also fit the left-handed versions of sugars. There was some research on indigestible left-handed sugars that would have very similar chemical properties to standard sugars - but l-sucrose was too expensive to manufacture in large quantities. I don't think they ever made enough of the substance to try to bake cookies with nonstandard chirality."
] |
[
"Thanks for explaining!",
"Do you know if the 'natural' low-cal sweeteners like Stevia have any potential for this? Could you use whatever molecule that is and make chains like with starch?"
] |
[
"How much is embryonic development affected by gravity?"
] |
[
false
] |
Were it possible to conceive a child and carry the pregnancy full term in a zero gravity environment (e.g. aboard the ISS), how would the embryo develop? How much of our terrestrial embryonic development is influenced by gravity? I am NOT aboard the ISS and I have NOT gotten anyone pregnant aboard the ISS! This is purely a curiosity question.
|
[
"It seems that it might not be possible to concieve child aboard ISS and i it was there is high probability of miscariage and severe deformities.\nTry to look ",
"here",
". It is not about humans and it is seven years old, but you will get the idea. "
] |
[
"This is EXACTLY what I was looking for. Thank you."
] |
[
"I think this is one of the larger unsolved questions for human spaceflight. No one knows, and there are somewhat obvious ethical challenges in experimenting."
] |
[
"Is there a significant difference in the structure or behavior of the corpus collosum, between animals with opposing eyes, such as squirrels and deer, versus animals with them at the front, such as cats, dogs, or wolves?"
] |
[
false
] | null |
[
"Why would there be? "
] |
[
"Have you ever noticed in squirrels, the way in which they evade a threat?",
"They turn and run diagonally away in one direction, appear to get frightened all over again, and cross the other way, to run away diagonally, and this repeats. It isn't necessarily ineffective, but it appears as though they don't get much communication about the threat from hemisphere to hemisphere.",
"Edit: they run one way, /then/ turn about 90 degrees, such that it's a different eye that can see the threat. Apologies for the original description being off by a little.",
"So, in general, there is no reason behind something having developed, and in that sense there is no answer to Why? But there appears to me to be evidence that there could be a difference. And I wondered if anyone had ever done research on it, or had separately done research with various animals in this way, and maybe knew something about it. "
] |
[
"Well information from the two eyes goes to both hemispheres via the optic tract not the corpus callosum so I'm not sure what you're getting at..."
] |
[
"Can our brains recognize cause and effect in the context of food poisoning? Allergies?"
] |
[
false
] |
When I say brains I don't mean the conscious, higher-thinking portion of our brain, but the more instinctual part that does stuff like vomiting or fear. This is a kind of specific question, but anecdotally, I see a lot of stories about people getting food poisoning, and if they know where they got it from (say, potato salad), they end up hating it, even if they loved it before. They often say that it's gross and have a very visceral reaction to it, and from what I can tell, not a voluntary one. In a similar but slightly different vein, I'm a spheksophobe (wasps), but didn't start being more than wary of them until I had an allergic reaction to them in primary school (not anaphylaxis or anything, it was called a "severe localized reaction" by a doctor but it made me sick for a week). I get pretty nervous and grossed out looking at photos of them, and heaven forbid I am within ten feet of one, but no amount of convincing myself can make me not scared or sick-feeling. Is this the subconscious brain recognizing that something made us sick after the fact and making us avoid it with a physical and emotional reaction? Or is it our conscious brain remembering what happened and the association is what makes the physical and emotional reaction? Is it related to the thing where people who had cancer as kids wouldn't be able to stand ice cream because they were given it a lot during chemo, and they had to stop giving childhood cancer patients ice cream because of it? If any of you have a resource like a PubMed article or something similar, I'd love to read it.
|
[
"These are called conditioned taste aversions, and frequently form to food that did not cause the illness, but was eaten right before it occurred. ",
"https://www.webmd.com/oral-health/what-is-conditioned-taste-aversion",
"I have a chronic illness that causes gastric issues, and I have issues with aversions to any strong flavors I have right before being ill, even though the food isn't what's making me sick."
] |
[
"I think there's pretty good evidence that our brains are strongly wired to associate flavors with nausea and exhibit aversion to those flavors in the future. There's a series of classic experiments done by John Garcia that showed this with rats...rats would avoid a flavor paired with nausea after a single experience, while a similar pairing of sound or light cues would be learned only slowly and less effectively. Interestingly, electric shocks were easily associated with light and sound, but only slowly with taste. ",
"You can read about it here",
"https://www.americanscientist.org/article/taste-sickness-and-learning",
"As for conscious vs subconscious, I think it'd be better to frame this in terms of emotional vs logical. You eat something, then feel sick, then that food tastes bad to you or makes you feel disgusted. That's a result of association operating on an emotional level...a natural ability of the brain to throw up warning signals after eating something and becoming sick. You don't have to sit down and use your human capacity for higher level general symbolic thought to figure it out step-by-step."
] |
[
"The source you posted says you can get symptoms 30 min after eating in the earliest case. Depends on the pathogen. So immediate food poisoning is possible.",
"Also, if the food has been spoiled for a relatively long time, the bacteria produces lots of toxins, which can make you sick almost immediately when eaten. (Food poisoning vs food infection)"
] |
[
"How hard would it be to detect a Jupiter-sized planet with an orbit perpendicular to the ecliptic (i.e., a polar orbit around the Sun)?"
] |
[
false
] |
And has such a thing ever been theorized?
|
[
"In our solar system? It would be pretty bright and strongly affect the orbits of other objects. Given that Jupiter was known about before anyone knew what the ecliptic is, I don't think you could say we'd missed it just by not looking in the right place."
] |
[
"Have you seen how bright Jupiter is in the night sky? It would be pretty much impossible to miss, no matter what the orbit was.",
"Unless you are talking about an incredibly removed planet beyond the orbit of Pluto, however in that case the probability of its formation is really low."
] |
[
"Not very difficult. Besides visual detection--Jupiter would be an easy target for a small telescope or large binoculars even if it were ten times more distant--its effects on known Kuiper Belt object orbits would be unmistakable. Indeed, it is this very kind of orbital evidence that is leading the current hunt for Planet 9."
] |
[
"What's the highest possible IQ?"
] |
[
false
] |
Now I know IQ measurements are extremely subjective, and no one test can really accurately measure intelligence (if such a thing can truly be quantified), but I was just wondering why some people make ridiculous claims about IQ. From what I have been able to tell, IQ tests for adults these days generally tend to use a normalized distribution. The mean is 100, and the st. dev. is 15 So by putting the numbers into a formula, an IQ of 195 would put you in the 0.00000000011 percentile, which would give you an IQ higher than 9 billion people, or more than there are on earth. But yet some people like to claim to have IQs over 200. is this even possible, or do I understand it all wrong? It would seem like if the "smartest person on earth" had an IQ of 195, then even an omniscient superbeing would only have an IQ of 196. Is this even close to the correct understanding?
|
[
"Theoretically you are correct. But even if IQ scores are theoretically perfectly normally distributed over the entire human population, no test can capture this. People are born and die every second, and there is no way to test every single human.",
"So, an IQ test's scores has to be modeled on a small population and then that model is extrapolated to the whole population. Tests will often fall apart outside its statistical range; for example, a test for normal ranges (e.g. IQs of 60-150) may be too easy for people with high IQs, so a person with an IQ of 170 may get the same score (100%) as an omniscient being with a theoretical score of 195. "
] |
[
"Marylin vos Savant",
" is reputed to have scored and IQ of 228, despite this the worlds most intelligent (according to IQ score) individual is officially recorded as ",
"Kim ung Yonga",
" with a score of 210.",
"For frame of reference, I once took an IQ test that appeared in a popup, and after 10 questions it concluded that my IQ was 230. Then it tried to sell me shampoo. Go figure. "
] |
[
"Tests will often fall apart outside its statistical range",
"This is a common problem with IQ tests. You can't easily make a test that's sensitive enough to cover the normal range, and discriminating enough to tell the difference between 150 and 170 on the high end. SO, you'll see different tests for different expected score ranges, as well as different tests for different ages of subjects.",
"Of course, there's also the issue that nobody really knows what IQ is, other than \"the attribute measured by an IQ test\", which is a nicely circular definition. ",
"If you keep IQ tests to a fairly granular interpretation, they can definitely be useful. For example, in identifying children that would benefit from specialized instruction. Trying to determine anything based on a 10% difference in scores between two people on one test is probably not a valid use."
] |
[
"If the Milky Way Galaxy was the size of a grain of sand [~1mm] how far away would the Andromeda Galaxy be?"
] |
[
false
] |
I'm trying to explain to a friend just how absurdly vast our universe is and using light years just isn't registering with him. I need something that he can relate to a little easier. For example, would it be comparable to the distance from the earth to the sun, earth to moon, USA to Fiji, etc..? Thanks Reddit, you guys are the best! BTW, I did search Reddit and Google prior to asking this so I apologize if it is, in fact, a repost. EDIT: Or any scale comparisons that could help me illustrate just how big the universe is!!
|
[
"Galaxies are actually pretty close to each other compared to their size. That's why they're always colliding and interacting - unlike stars which are quite far apart compared to their size, and almost never get anywhere near each other unless they formed together.",
"So let's say for simplicity that on your scale, 1mm = 100,000 light years. The Milky Way disc would be a little bit bigger than this in diameter. Surrounding the Milky Way are several small satellite galaxies. The Large and Small Magellanic clouds are two of the biggest and closest satellite galaxies. They would be little specks about 1-2mm away from the Milky Way's dust grain. There's a lot of other satellite galaxies, so you'd see a large grand of sand for the Milky Way, with a sprinkling of little specks around it.",
"Barely an inch away (about 2.5 cm), you'd find another grain of sand with a sprinkling of little specks around it. This is the Andromeda galaxy and its satellites. They really are quite close on this scale. In fact, the entire local group of galaxies (which is the Milky Way, Andromeda, all of their satellites, and a few other small galaxies that aren't satellites) would easily fit in the palm of your hand.",
"By comparison, if the Sun was 1 mm in size, then the Alpha Centauri system would be about 30 km (~20 miles) away. "
] |
[
"Great answer!",
"Also, for reference, the size of the observable universe at this scale would be about the size of ",
"these crop circles",
", or about .5 km."
] |
[
"Well... suppose the Earth is 1mm in size. Then the sun is 12m away, so basically the other side of your apartment. Alpha Centauri is more than half way across North America or Australia. And the Andromeda Galaxy is about the distance to Jupiter."
] |
[
"The average temperature outside airplanes at 30,000ft is -40° F to -70° F (-40° C to -57° C). The average causing speed is 575mph. If speed=energy and energy equals=heat, is the skin of the airplane hot because of the speed or cold because of the temperature around?"
] |
[
false
] | null |
[
"You have to be careful when saying things like \"speed = energy\" and \"energy = heat\"; those aren't really true in general.",
"But anyway, if you assume a steady, adiabatic flow of ideal gas around the wings of the plane, we can say that c",
"T + v",
"/2 is constant along any streamline.",
"c",
" is just the specific heat capacity of the air at constant pressure; you can just think of it as some constant that depends on the type of gas.",
"This says that the temperature along any streamline is maximized at points where the flow velocity is as small as possible. Particularly, somewhere on the leading edge of the wing, there will be a point where the flow is stationary. This is called the stagnation point. And the temperature at that point is maximal.",
"Taking realistic values for the heat capacity of air, the speed of a cruising airplane, and an ambient temperature of -40 degrees C, the stagnation temperature is just",
"T",
" = T + v",
"/(2c",
").",
"Or rearranged, T",
" - T is about 33 degrees C. The temperature at the stagnation point is 33 degrees C higher than the temperature of the ambient air.",
"So does being slammed into the wing cause the air in its vicinity to warm up pretty substantially? Yes. Can it still be very cold compared to everyday temperatures? Yes (in this case, it's -40 + 33 = -7 degrees C, still below freezing)."
] |
[
"adiabetic adj. Of, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy. -- ",
"wordnik/adiabatic",
"That's a new word for me. My reading stuttered, having read \"a diabetic\"."
] |
[
"You still wrote it as \"adiabetic\".... it's \"adiab",
"tic\"."
] |
[
"Do subliminal messages really work?"
] |
[
false
] |
I just downloaded a program called "Subliminal Messages." It claims that by flashin text too fast for me to read it can help me do things like quit smoking, have more confidence, etc. Is this true?
|
[
"Almost certainly not. Subliminal messages are just messages that fall below the human threshold for perception.",
"People often connect them with their sub-concious, which is wrong. They have no more effect on your subconscious that any regular message you come across. If it did work, it would almost certainly be in commercials, like every other way of subtly manipulating people is. "
] |
[
"That study was shown to be a complete hoax. The researcher made up the data"
] |
[
"That study was shown to be a complete hoax. The researcher made up the data"
] |
[
"If we can build Nuclear-powered submarines, why don't we have Nuclear-powered space ships?"
] |
[
false
] |
I've always heard that fuel is such a huge cost to space flight and especially leaving the Earths atmosphere, but why can't we use nuclear power for this? Is Nuclear power just not viable for space travel?
|
[
"We do. ",
"However, they are not used for propulsion. In space, propulsion is achieved via changes in momentum. You propel something out of the rocket rearward to make you go forward. Nuclear is not particularly useful for that. ",
"On earth, with gravity, you can apply a torque to the ground for propulsion, making nuclear a lot more useful. Or, even, in a plane, you can rotate a propeller in an atmosphere. Not too hard to conceive of how nuclear could be useful there. In the thin atmosphere of space, you cannot propel those ways - you need to use momentum. "
] |
[
"As others have said, you need a reaction mass to expel backwards in order to get momentum in space. Nuclear power can provide the energy to throw it back, and it'd be useful to throw it faster (increase the specific impulse) so that you need less propellant.",
"Possible ways are:",
"Nuclear-thermal propulsion: instead of burning the fuel, let it heat up by flowing through a nuclear reactor. This can achieve high thrust and an exhaust speed in the order of 8000 m/s. Cons: radioactive materials and fission products can leak into the exhaust (environmental concerns!).",
"Nuclear-electric propulsion: Generate electricity with a nuclear reactor and use it to drive ",
"ion thrusters",
" or other forms of electric propulsion (plasma thrusters, microwave thrusters, etc). This can achieve much higher exhaust speeds, like 50,000 m/s, needing less propellant. Cons: low thrust. Cannot be used to take off from the ground.",
"Nuclear-pulse propulsion: detonate nuclear bombs to push the spacecraft. No need to describe the environmental concerns I guess...",
"As for the \"why\", the main reason is regulations. Nuclear-pulse propulsion is banned by the outer space treaty which forbids nuclear weapons in space. The other two are not accepted by ",
"UNOOSA",
", both for the environmental concerns and because you won't be able to move your spacecraft to a graveyard orbit in case of failure.",
"Of course they may change their minds in the future. Nuclear-electric is the most promising to me because of its relative safety.",
"Note that several satellites are using nuclear power for non-propulsive purposes, though."
] |
[
"https://en.wikipedia.org/wiki/Nuclear_thermal_rocket",
"there where proof of concept engines that worked great without radioactive exhaust, the main obstacle is political, not technological..."
] |
[
"Is it possible to see, with the naked eye, matter-antimatter electron-positron annihilation?"
] |
[
false
] |
According to , it is. According to my Astronomy Professor, is it not, and this video is either not telling the whole story of the experiment, or is completely fabricated "for TV" as the annihilation causes energy to be released in gamma ray form of 511 keV, whereas visible light is only 1 to 3 eV. So, reddit, how is the annihilation as shown in the Through the Wormhole episode possible? PS - I hope there is an explanation; if this turns out to be completely false it's going to crush my soul - I love that damn show!
|
[
"No it isn't.",
"From that video, it looks like a cloud chamber or a bubble chamber, where an energetic particle causes liquid in the chamber to turn into a gas, forming tiny bubbles that you can see. However, these are usually used to detect charged particles, whereas other methods are used to detect photons, so what you're seeing is probably positrons and electrons making bubbles.",
"An annihilation event in a cloud chamber might look something like ",
"this",
" where the two loopy things are the positron and electrons rotating in different directions in a magnetic field."
] |
[
"Morgan Freeman would never lie to you. ",
"First of all, the two-gamma case is the lowest possible number of photons. You can have many photons. Additionally, these photons then interact with other matter, which release multiple lower-energy photons. "
] |
[
"The fact that the video states that positrons are the smallest particles imaginable discredits the video right off the bat. Actually viewing matter-antimatter annihilation is impossible just too small, maybe just maybe they are using something to react with the gammas given off, that would be my guess. I find it hard to believe that they could get PP to occur so frequently within that chamber though, it requires some decently high energy gammas."
] |
[
"What makes a day hotter (or cooler) than another?"
] |
[
false
] |
Specifically, day-to-day increments. Let's get the obvious out of the way: How dynamic is the greenhouse effect? Does it trap enough heat during the night to make a noticeable difference the next day? (For example, after a hot, clear day it will trap some of that energy keeping the night warm and giving the sun a 'head start' to heating the area the next day)
|
[
"In Utah, we have a weather pattern called an \"Inversion\" where cold weather makes all the pollution drop lower to the ground in a thick blanket. It blocks out the sun (like a nuclear winter scenario) and causes the ground to get exceptionally cold in the winter sometimes.",
"Would be great to see a meteorologist get in here and explain all the other stuff.",
"http://en.wikipedia.org/wiki/Inversion_(meteorology)"
] |
[
"So you're right, from day-to-day the Sun's energy input for a given parcel of land will be consistent. However, a parcel of land in the tropics will have a much greater thermal input than a parcel of land near the poles.",
"This difference sets up a strong thermal gradient. Winds in the atmosphere (and currents in the ocean) will flow in an attempt to reconcile this large temperature difference, trying to even out this thermal imbalance. This alone can generate turbulence that will alter the temperature from day to day.",
"When this thermal imbalance is combined with the Earth's rotation, it sets up what's known as a Rossby wave in our atmosphere's jet stream. Roughly 6 wavelengths will circumscribe the planet at mid-latitudes - ",
"this graphic shows an example of this",
". As each peak or trough of the wave passes over your location, you'll experience hot fronts or cold fronts, storms at their interface, etc. Note that these waves are fairly irregular, as well, occasionally pinching off a strong peak to become its own independent storm system, ",
"as shown in this graphic",
".",
"The water vapor in the air can vary somewhat to alter the greenhouse effect and thus day-versus-night temperatures, but the effect is much more noticeable when comparing two different places. If you've ever spent time in wet swampy regions with a lot of water vapor in the air, you know that the night isn't much cooler than the day. On the other hand, places where water vapor is scare such as deserts can have scorchingly hot days, but can cool considerably at night.",
": The difference in temperature between the tropics and the poles starts the wind blowing and can cause day-to-day variation. If you add the Earth's rotation into the mix, this sets up an oscillation that generates heat waves and cold snaps."
] |
[
"Here in San Francisco, we have to deal with what happens in inland California. If it's hot in, say, Sacramento, the pressure decreases and sucks in all of the air from the west. That pulls fog and clouds over San Francisco. However, when it's not so hot in Sacramento, we usually have a nice day because we're not covered in fog. "
] |
[
"Why is there such a debate about the inclusive taxonomy of \"Life\" in regards to viruses?"
] |
[
false
] |
So, I understand why there are always people/scientists debating about wheather to consider viruses "alive" or not. I'm a biology student and I have a focus on evolutionary aspects- I get it. What I don't get is why this deabte has been lasting for so long. When it comes to viruses, of course its never going to be as simple as "biotic or abiotic." It's my opnion that, like in the past, the catagories need to be reconsidered. I think it would be cool if instead of thinking about it as alive or not, just reorganize the phylogeny. There's never been a problem with expanding the tree of life before, right? Maybe we could just call all biotic materials and systems "Anima" or something like that, then give viruses their own superkingdom, and "life" could have its own Giant phyla too. I just think when you're presented with something that redefines boundaries you have to rethink the boundaries (like is always done with taxons). This is way too long for an Askscience post, sorry. Why not just redefine Superkingdom taxons to include viruses? Rethink the way we consider biotic systems?
|
[
"This is the sort of problem taxonomists encounter all the time: once you decide how to quantify something as belonging to a particular set of animal/plant/life something else shows up (is discovered) that defies classification under the old system. Some of the common definitions of 'life' include being able to reproduce, being able to respond to the environment, ",
". If you use strict definitions someone will inevitably ",
"rail against",
" the fact that your definition is too strict. If your definition is too loose you could end up including things which meet your definition, but feel fundamentally 'wrong' (",
" If regular viruses can be classified as life, why not computer viruses?).",
"Does there need to be a dichotomy? Can something be kind of alive or almost alive or ",
"mostly dead",
"?"
] |
[
"Just an IMO, but debates over \"life\" from politics -- creationism, right-to-life, environmentalists -- may be part of it."
] |
[
"Well, that was another thing that I was thinking about. If Protobiotic lipid spheres were still existing today (as they are believed to existed and became the first primitive cells), then where would we classify those? ",
"Just like how viruses have genetic material but cannot reproduce, proto-cells were most likely able to make more of themselves by accumulating more material from the environment and dividing apart, but without mitotic mechanisms or nucleic acid. "
] |
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