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[
"What would happen if two people were to attach an IV directly to each other?"
] |
[
false
] | null |
[
"This is essentially what the first human blood transfusions were. The first transfusions were in the 17th century, both human/human (not great), and sheep/human (bad - it didn't help that they used non-sterile sheep vessel for the transfusion). ",
"If you're on death's door and desperately in need of blood volume and RBCs, a random IV link would most likely be beneficial. However, blood groups were only discovered in the early 20th century and you also have to remember that the earliest transfusions transferred whole blood - i.e. white blood cells as well as red. ",
"What would follow would be a systemic and profound immune reaction as both the donor and host blood recognised the other as foreign with wholesale secretion of proinflammatory cytokines. "
] |
[
"Are white blood cells filtered out of whole blood donations today? "
] |
[
"Yes, otherwise the white blood cells may start attacking the person who's had the transfusion."
] |
[
"Is there a correlation between cancer and body mass?"
] |
[
false
] |
What I mean is that, since cancer is mostly a stochastic process, a bigger number of cells (which most of the time implies larger mass), at equal environments, should show proportionally higher cancer rates. Is that true? What if we only take into account lean body mass?
|
[
"Look at PubMed and there are a plethora of studies finding various associations between BMI and cancer",
"Meta analysis of 141 articles - \"Increased BMI is associated with increased risk of common and less common malignancies. For some cancer types, associations differ between sexes and populations of different ethnic origins\"\n",
"http://www.ncbi.nlm.nih.gov/pubmed/18280327",
"Another study from Gastroentology - Based on a meta-analysis, increased BMI increases the risk for colon but not rectal adenoma.\n",
"http://www.ncbi.nlm.nih.gov/pubmed/22245665",
"\"One study, using NCI Surveillance, Epidemiology, and End Results (SEER) data, estimated that in 2007 in the United States, about 34,000 new cases of cancer in men (4 percent) and 50,500 in women (7 percent) were due to obesity. The percentage of cases attributed to obesity varied widely for different cancer types but was as high as 40 percent for some cancers, particularly endometrial cancer and esophageal adenocarcinoma.\"\n",
"http://www.cancer.gov/cancertopics/factsheet/Risk/obesity"
] |
[
"I was more interested in just mass rather than BMI. Obesity has its own problems that everybody knows, including increased risk for some cancers. Rather, I'm interested in the fact that large, not necessarily obese individuals, may show increased cancer risk, just because they have more tickets (cells). "
] |
[
"No. There is no study that demonstrates what you are saying."
] |
[
"How did Newton derive the Law of Universal Gravitation?"
] |
[
false
] |
I just learned the Law of Universal Gravitation in my physics class, and I understand well what it means and how to use it to calculate gravity...but how did Newton derive it? I've done some Googling around but I can't find any solid step-by-step proof of it.
|
[
"Observations demonstrated that the planets in our solar system orbited the Sun in ellipses. Newton discovered through his investigation (IE invention) of Calculus that a body undergoing acceleration proportional to the inverse square of their distance would travel in an ellipse. He then made a mental leap and realized that observable natural laws we see on Earth also are obeyed in the heavens, and thus concluded that the process that causes an apple to fall to the ground is the same force that keeps the Moon in orbit around the Earth and the planets in orbit around the Sun. He then reasoned that every particle in the universe acts on every other particle with this force, meaning that the force between two objects must be related to each of their masses.",
"It was this series of mental leaps that led to his deduction of the law of gravitation. There was very little theoretical derivation involved; it was mainly an assertion which turned out to be demonstrably accurate. The gravitational constant G was not known for nearly a century afterwards when it was finally empirically measured. No known first principle derivation can produce G, so it remains an empirical observation."
] |
[
"Exactly how Newton derived gravitation can be found in his Philosophiæ Naturalis Principia Mathematica. ",
"However, from a more approachable standpoint: you can take Kepler's Laws of Planetary Motion, which are based on observation, and derive the Newton's inverse square law. It is a fairly standard homework problem for intermediate mechanics level physics students. ",
"Essentially, you start with Kepler's 1st law - make sure to include the radial and tangential unit vectors - and take two time derivatives. You will get an acceleration that has a piece in the radial direction (r-hat) and a piece in the tangential direction (theta-hat). Newton makes the assumption that the force between two celestial bodies acts only on the line between them, i.e.: only in the r-hat direction. Therefore, the terms in the theta-hat direction must equal zero. ",
"By setting these to zero you get an expression that expression that is equivalent to conservation of angular moment. dL/dt = 0 & L = r",
" d(theta)/dt. You can leverage this new found constant into the rest of the second derivative to arrive at the inverse square law."
] |
[
"Newton actually modified Kepler's Laws of planetary motion which had previously assumed that the Sun was immovable.",
"Because for every action there is an equal and opposite reaction, Newton realized that in the planet-Sun system the planet does not orbit around a stationary Sun.",
"Instead, Newton proposed that both the planet and the Sun orbited around the common center of mass for the planet-Sun system.",
"Newton simply changed this to include centre of mass as a consideration.",
"Newton defined the force on a planet to be the product of its mass and the acceleration. What he changed was Kepler's assumption that: ",
"A) Every planet is attracted towards the Sun.",
"B) The force on a planet is in direct proportion to the mass of the planet and in inverse proportion to the square of the distance from the Sun.",
"Here the Sun plays an unsymmetrical part which is unjustified. So he assumed Newton's law of universal gravitation:",
"A) All bodies in the solar system attract one another.",
"B) The force between two bodies is in direct proportion to the product of their masses and in inverse proportion to the square of the distance between them.",
"The gravitational constant that he posited was not calculated till much later."
] |
[
"What do people mean when they say that Special Relativity \"causes\" Magnetism?"
] |
[
false
] |
I've heard people claim that special relativity is the source of all magnetism. Can someone clarify what this means for me? Is magnetism therefore not its own separate "thing", but only an emergent phenomenon of electrodynamics applied to relativity (in other words, is magnetism not really a separate phenomenon after all, but merely electrodynamics in relativity)? Also, how does this factor in with magnetic monopoles?
|
[
"Yes, magnetism is a consequence of the principle of relativity. To see how this works in the case of magnetism, imagine a wire which contains positive charges and negative charges equally, so that the entire wire is electrically neutral. Now suppose that all of the negative charges start moving to the right. In this reference frame, because the negative charges are moving, the will be Lorentz contracted. As a result, the negative charge density will be slightly larger than the positive charge density, and so there will be an electric field surrounding the wire. If we place a positive charge somewhere near the wire in this frame, it will be attracted to it.",
"Now suppose we move into a frame where the positive and negative charges are moving in opposite directions at the same velocity. The Lorentz contraction will be the same for both of them, so the wire will be electrically neutral. But if you see the positive charge attracted to the wire in one reference frame, you must see it attracted to the wire in ",
" reference frame. So even though there's no electric field, there must be ",
" field which is providing a force on the positive charge. This field is the magnetic field."
] |
[
"So, there are a few ways to approach this. ",
"First, Classical, the existence of magnetism as defined by Maxwell's equations. In this sense, magnetic fields are not a result of any of their own charges. (No magnetic monopoles have ever been measured) (this is unlike E fields, which are directly related to their source, positive and negative charge). Next: What are B fields? Well, they are in essence described by currents (moving charge), and changing Electric fields (notice the derivatives with respect to time). In all of these cases, the two fields are related through some sort of \"time\" phenomenon. In this sense, it makes sense to trivially say that relativity will play an important roll. E fields and B fields are things that move at the speed of light (the force carrier is a photon for E&M forces) and therefore Relativistc effects will be important in these derivatives. In fact, maxwells equations are actually accurate even under relativity, its sort of a self-consistancy that is wonderful. In fact, studying E&M gave us our first understanding of relativity in a way, and gave the motivation for it. It is also important to note that, under the rules of special relativity, one is able to greatly simplify Maxwell's equation since the two topics are closely related and coexist very well. ",
"See here",
" ",
"Next: Quantum, in this case, we can talk about the fact that \"permanent magnetism\" in all its forms is essentially caused because of Special relativity. This is because when you want to fix Schrodinger's equation such that it is consistant with special relativity, you get Dirac's equation. When these corrections are added in, a unique phenomenon presents itself. Spin! The electron spin is a \"solution\" to Dirac's equation in a way. As well as anti particles. Both of these are results that come out mixing the fundamental postulates of quantum mechanics with the fundamentals of special relativity. And, the result of spin, is what gives materials their magnetic properties. A material where all the spins align in one direction and hold this are said to be ferromagnets. So in this sense, permanent magnetism only works because fundamental particles have spin, this spin which is caused by relativistic effects being added to the simplest model of quantum mechanics. ",
"All in all, E&M is as a whole closely related to relativity, and without combining the two, its impossible to have a complete self-consistant picture. In a way, this can be said for all fields of physics, but specifically in this case, the development of E&M led to the understanding and development of relativity. "
] |
[
"+1",
"Here's a simpler example if it helps.",
"You have 2 electrons \"at rest\" and you \"let them go\". What do they do? They repel each other. They start accelerating away from each other in some manner. Given that we know the rest mass of electrons, we know how much force they apply.",
"Now let's observe this same phenomenon, but let's do it while we're zooming past the electron in an inertial frame that's travelling at 0.99c with respect to the first one. From the new frame, it looks like the electrons are zipping past us and it looks like they are much much more massive due to being in motion. And yet, we know that the two situations must be equivalent with respect to what they predict. Instead of going through the work of actually transforming the force that we derived (accounting for time dilation and length contraction and mass change etc.), we make up a \"fictitious\" force that says that parallel moving electrons attract each other and call it the magnetic force.",
"Hence why you hear physicists say the magnetism is just an artifact of electrical phenomena when it's correctly frame-boosted - i.e magnetism is just the relativistic corrections to electrical interactions."
] |
[
"Do different species of animals ever interbreed?"
] |
[
false
] |
If so, which and why? If not, how do these animals know not to mate with one another? Would two different species of apes be more inclined to mate than, say, a cat and a dog? And again, how do they know?
|
[
"Yes, there are species that ",
"interbreed naturally",
" (PDF). The thing is, discrete species are part of a human construct to quantify biological diversity. In actuality the lines are much more blurred. That's why there's no unified species concept; there are actually ",
"many species concepts",
". They're context-specific, because sometimes the inability to genetically interbreed is important. Sometimes geographic separation is important. Sometimes a high degree of morphological similarity is important (for example in the fossil record). While it's important to quantify life, it shouldn't be done at the expense of recognizing that it's more complex than the taxonomic system we place on it. Many closely-related species can hybridize and produce fertile offspring. ",
"While it's not natural, ",
"domestic cows and bison",
" can hybridize and they're not even in the same genus. Here are a few other examples of completely natural hybridization:",
"There are multiple instances of this happening with crocs, like ",
"this hybrid",
" between a Cuban crocodile (",
") and an American crocodile (",
"). ",
"The American black duck ",
"hybridizes with the mallard",
" often. ",
"The black-capped and Carolina chickadees ",
"hybridize where they overlap",
" (PDF).",
"The barred owl has been invading the range of the spotted owl and ",
"hybridizing",
" (PDF).",
"Grizzly bears and polar bears",
" have been known to hybridize.",
"While these events can sometimes be made more common by humans causing things like habitat loss, they have also occurred without any human intervention at all."
] |
[
"Could you clarify what you mean by \"natural?\""
] |
[
"There are species that absolutely ",
"interbreed naturally",
" (PDF). What you're mentioning is one species concept among many, and there's nothing that prevents some species from interbreeding and producing fertile offspring.",
"There are lots of instances of this happening with crocs, like this hybrid between a Cuban crocodile (",
") and an American crocodile (*C. acutus). ",
"The American black duck ",
"hybridizes with the mallard",
" often. ",
"The black-capped and Carolina chickadees ",
"hybridize where they overlap",
" (PDF).",
"The barred owl has been invading the range of the spotted owl and ",
"hybridizing",
" (PDF)."
] |
[
"Does our brain have a equivalent of binary code or pixels?"
] |
[
false
] | null |
[
"I'm not quite sure I understand your question. Neuronal firing can be thought of as a digital or binary process - they either fire or they do not. However, the relationship between input and output is non-linear. "
] |
[
"When a neuron fires an action potential, it is all or nothing black and white and that's what you'll hear often.",
"However, the inputs that determine whether an action potential fires or not are analog meaning there's a gray area. It combines the strong inhibitory, strong exitatory, weak inhibitory, weak excitatory inputs and the sum of those inputs determine if the an action potential fires down the axon like a diverse bunch of officers arguing to the president whether or not he should fire a nuclear missile.",
"It is also worth noting that the neuron can express the power by changing the frequency of the action potential even though its an all or nothing process. Imagine blinking a camera flash once every so often means weak output and blinking rapidly means strong output. ",
"Storage of the information can come from the weakening and strengthening of the input/output between neurons. It's believed that protein synthesis changes the structure of the neuron and builds more protein based receptors and channels. ",
"Inhibiting synthesis of some proteins will appear to interfere with the expression of their memory or the conversion of short to long term memory in laboratory animals."
] |
[
"Well, first off you have to understand that you've asked a question that covers a WHOLE LOT OF GROUND.",
"But, to try to answer some of it in straightforward terms:",
"No, I would say that our brain does NOT really have the equivalent of 'binary code.'",
"The brain encodes information in a lot of different ways. With computers, a bit is always a 1 or a zero, even when it's being stored or crunched in different parts of the computer. But in the brain, information is constantly re-encoded in different coding schemes. Take your photoreceptors, for instance: The first cell that picks up light and turns it into an electrical signal does so in a non-binary fashion: It simply sends a stronger signal along to the next neuron if the light is stronger. It is not \"all-or-none.\" But the next cell does NOT encode the information that way: The next cell either 'fires' or does not; it isn't capable of firing more or less strongly, it just fires. It can only encode information by whether or not it fires, and when it fires, etc.",
"So only two cells in, you can see (ha ha) that the way the nervous system represents the information has changed once already. It changes again many times before it gets to the point that you're consciously aware of it. Later on, after it's been processed more, your brain isn't really representing images like pixels (i.e. breaking the image down into pieces and separately encoding the brightness/color of each piece), but instead it represents images like vector graphics: One cell says \"over there, there's a line that is slanted at 32 degrees\" and another says \"and up over here, there's the end of the line,\" and so on and so forth to make up an image. There are other cells that detect motion, and other cells that detect patterns, ",
" Later on, it gets even more separated: You have different sub-sections of the visual cortex devoted to analyzing different features. One area specializes in analyzing the input to detect faces. Another area analyzes the same input to decide what color an object is (sort of like adjusting white balance on a camera). Another area specializes in figuring out WHERE objects are. One interesting consequence of this is that you can lose one of these abilities but keep the others: A brain injury in just the right place might leave you perfectly capable of knowing what an object is, what color it is, what it's called, etc., but completely incapable of judging where it is relative to you.",
"And at every level of that system, there are many, many different coding schemes that the brain uses. Some things are encoded by ",
" neuron fires (i.e. one neuron fires if it detects a corner, another neuron fires if it detects a straight line), others are encoded by how rapidly a neuron fires (e.g. more rapid firing might indicate a more intense stimulus)... In the auditory system, some frequencies (different tones) are encoded by the cochlea by what frequency a neuron fires at, while ",
", other frequencies are encoded by which neurons fires and neural firing frequency has nothing to do with the frequency of the sound stimulus.",
"It's complicated."
] |
[
"Why can't i move my eyes smoothly?"
] |
[
false
] |
Why do our eyes jump from spot to spot when we're looking around? I find that i can only move my eyes smoothly when i'm tracking something that is also moving smoothly.
|
[
"Your eyes move in small \"jerks\" called ",
"saccades",
". Interestingly, you are effectively blind during a saccade, as the brain simply ignores any information sent to it during that time. The reason for this is to avoid sending useless blurry image data to your brain.",
"The exception to not seeing things during a saccade is if, during a saccade, you manage to form a stable image on your retina. You can experience this if you're riding in a car or train, and looking out the side window. If the vehicle is moving to your left, then quickly glance from left to right, and you should get a brief \"flash\" of a stable image when the angular velocity of your eye matches the speed at which the landscape is passing you.",
"Anyway, there are two ways that you can move your eye without a saccade. Your mentioned one of them, which is called ",
"smooth pursuit",
". When you're tracking a moving object, you automatically keep the image of that object stable on your retina via smooth eye movements.",
"The other way that your eyes move smoothly is the ",
"vestibulo-ocular reflex",
". If you look forward and turn your head to the side, your eyes will automatically move smoothly in the opposite direction to keep your vision stable."
] |
[
"thanks!"
] |
[
"Also as long as you don't move your head you can never see your own eyes move in a mirror."
] |
[
"Do galaxies revolve around the universe?"
] |
[
false
] |
If the earth revolves around our solar system because of the sun, the sun revolves around our galaxy because of a black hole, do our galaxies revolve around the universe? If they do, because of what? And if there are other universes possibly they revolve around a gravitational force?
|
[
"No, they move gravitationally through galactic clusters (although that can't really be called orbit), and in terms of large scale structure the clusters gradually get farther from each other because of the expansion of the universe."
] |
[
"Your question implies that the universe has a centre around which galaxies would revolve. But the universe has no centre. Think of the expanding universe as the surface of an expanding balloon (a 2-dimensional analogy for our 3-dimensional universe). Just as the surface of the balloon has no centre, the universe doesn't either."
] |
[
"But, they will just pass right through each other for the most part, since matter is so spread out in galaxies.",
"Sort of. ",
"This video",
" is a simulation of the Milky Way/Andromeda collision from the University of Toronto. As you can see, relative to the ",
" the disturbance caused by the collision is rather severe. It just won't have a significant impact on local planetary systems.",
"Bonus: ",
"this site",
" has a simulation of how the night sky will change during the collision event."
] |
[
"What determines whether a projectile pushes the object it comes into contact with aside or penetrates it?"
] |
[
false
] |
For example: If I push my hand towards you - you will move away from my hand. If a bullet is fired towards you - the bullet will go through you. Is there an equation based on the size of the object and the speed? I'm sorry if its a stupid question but I'm really curious.
|
[
"The simple explanation of this is stress limits. All materials have properties called Young's Modulus, which is a value of stress around which a material begins to permanently deform, and Ultimate Tensile Strength, which the maximum stress the material can experience before weakening/failing. Say your hand had a pushing surface area of 0.5 ft",
" and you push with an evenly distributed 50 pounds of force. The stress you induce, ignoring shape and other complicating factors, is 100 pounds per square foot, or force/area. Not a huge amount of stress.",
"In the case of a bullet, the force is a bit harder to determine. This requires using the impulse equation, which, simplified, is:\n AverageForce * Time = (Momentum_2 - Momentum_1)\nThis equation states that the average force on an object is equal the the change in momentum (Mass*velocity) divided by the time that the force is applied. Typically for a bullet impact, the time of application will be small, while the momentum change will be fairly big. This means that the average force can be very high. Now, going back to the stress definition of force/area, a bullet has a small area upon which it can apply this large force, meaning that the bullet causes much higher stresses than your hand. ",
"Depending on the level of stress generated, you can cause no noticeable damage (stress < Young's Modulus), a dent (Young's Modulus < stress < Ultimate Tensile Strength), or material failure/piercing (Ultimate Tensile Strength < stress). There are a myriad of other complicating situations you can take into consideration, but this is the general set of rules that determine material interactions such as this set of examples."
] |
[
"Very detailed explanation - Thank you!"
] |
[
"as two bodies come into contact, they deform",
"As something deforms, it stretches/compacts/shears/torques locally. This creates stress.",
"If/when the local stress exceeds a yield strength limit, there will be permanent deformation- think bending a paperclip",
"If the stress exceeds the ultimate strength limit, then there will be tearing, or breaking",
"it's a little more complicated with tissue, since there's fluid and elastic materials all jammed together"
] |
[
"What I'm assuming is a physics question: What is happening with my capri sun?"
] |
[
false
] | null |
[
"Alright, take two. Wall of text ahead, but I tried to be very thorough:",
"I believe you're increasing the pressure of the air inside of the container, making it more difficult to push the straw - and the air contained within the straw - deeper inside of the Capri Sun.",
"You may recall from high school chemistry/physics something called the Idea Gas Law, which should be relevant in this situation: PV = nRT. We can ignore some chemistry and make a few assumptions (closed system, no mass transfer through container walls, isothermal) and it essentially becomes PV = constant. This means that if you change the pressure or the volume, the other variable must change so that P*V is the same as what it was before. When you push the straw in, you're decreasing the available volume for the air molecules to float around in (decreasing V) so P must increase. This becomes more applicable after you suck most of the air out of the Capri Sun, as this makes the volume of air in the straw larger compared to the volume of air in the container, so V will decrease by a larger relative amount (say, possibly something like 20% compared to getting maybe 2% if the Capri Sun was full). In either case, as the volume decreases, the air pressure with increase, so it will be more difficult to push the straw farther in. The different volume changes will affect the pressure differently, so this is why it's more difficult when the thing is empty.",
"A similar effect should happen if you try to pull the straw out after sucking the air out with the straw farther in. In that case, you'd be trying to increase the volume (V goes up), so P must go down. The decreased pressure acts like suction, opposing your motion. So it goes both ways."
] |
[
"I've been working a lot with fluid mechanics lately, and if I'm understanding the question correctly, you're noting how much more difficult it is to slide the straw by plastic vs. easier to slide by water (or possibly air). In either case, the fluid (water or air) can deform itself to the movement of your straw, whereas the plastic is less willing to do so. The plastic case involves friction, whereas the fluid case involves viscosity (essentially a fluid friction). The viscosity of water is fairly low and the viscosity of air is essentially negligible in most situations.",
"Let me know if this isn't an answer to your question."
] |
[
"I don't think this answers my question but you sound like you know what your talking about. I'll describe my situation with as much detail as possible. My caprisun is empty. My straw is in the top, the hole that the straw is stuck through is tight enough around the straw that when I blow into it the bag expands and when I suck it collapses in on itself. When there is air in the bag, I can slide the straw up and down easily. When I suck the air out of the bag, and cover the straw so no air can go back in, it is much harder to slide the straw up and down; It feels as if there is more friction when I slide the straw through the hole. Why is this?"
] |
[
"simple questions regarding air pressure?"
] |
[
false
] |
📷 not sure if i understand air pressure properly can someone correct my statements below if they are wrong... thanks
|
[
"Air pressure is caused by air molecules bouncing off of surfaces. Water pressure is also bouncing off surfaces but because water has significantly less compressibility it can't be \"pressurized\" the same way air can.",
"Cold air moves slower than warm air which means that it both hits surfaces less frequently and with less force(slower molecule=less force)",
"Most fridges are designed to equalize pressure between the inside and the outside so that the door will be easy to open (as sealing the door and having lower pressure inside would make the door not want to open). Because the fridge air pressure is roughly the same as outside air when the air in the balloon cools it is reduces in pressure which cause it to reduce in volume.",
"If you were to put a balloon inside an airtight jar or similar container and then put that inside a fridge it would be less likely to shrink (the rubber of the balloon will shrink a little bit when chilled)."
] |
[
"I would say 1 and 2 are correct (enough at least, technical specifics don't really matter here to me)",
"If you had a sealed chamber 3 would also act as you describe. But a standard fridge/freezer cannot be sealed (you would never be able to open the door) so as the air inside becomes less energetic outside air pushes in and normalizes with room pressure, eventually reaching an equilibrium between those forces, with more air particles in the freezer than when you closed the door. The balloon still has the same number of particles, meaning at the less energetic temp it will be deflated"
] |
[
"The other thing going on in #3 is that the air pressure in the balloon is also fighting against the elasticity of the balloon itself.",
"As others have described, ",
" the fridge were sealed ",
" the balloon was just a barrier between the two amounts of gas that did not exert any forces of its own, then yes, the pressure inside the balloon and inside the fridge would decrease proportionally and the volumes would not change.",
"But in real life, the fridge is not sealed, so more air molecules get pulled into the fridge to keep equal pressure with the outside (if this didn't happen, you'd have a hard time getting the door open). Also, the balloon has it's own elastic force that is trying to pull itself back to the shape it was before it was blown up, so while the pressure inside the balloon lessens as temperature drops, the elastic force of the balloon trying to contract does not change and overwhelms the lowered internal pressure. ",
"The combination of the internal/external pressure differential and the lowered internal pressure relative to the balloon's elastic force result in the contraction. "
] |
[
"Are all phobias explained by past experience or is this a myth?"
] |
[
false
] |
We've all heard of obscure phobias, but are they all explainable? do they even need an explanation? can people be born with them etc etc
|
[
"It also has to be towards an object that the brain has the potential to develop a phobia to.",
"I do not think that is true, and I'm not really sure it makes sense.",
"Using your gun example, the only thing we can conclude from that statement is that no ",
"fear conditioning",
" occurred. This can be defined as \"a form of learning in which an aversive stimulus (e.g. an electrical shock) is associated with a particular neutral context (e.g., a room) or neutral stimulus (e.g., a tone), resulting in the expression of fear responses to the originally neutral stimulus or context. \" ",
"This is a very strong form of learning and one needs a strong PERSONAL experience to form a phobia: not simply from being saturated with images of gun induced violence on the news and on TV."
] |
[
"I wouldn't know, but I'm pretty sure all of them are due to experience. People are inherently born with a fear of heights though (see the visual cliff experiment), but this isn't a phobia in my opinion...humans are ground dwellers, and should be afraid of being high up, evolutionarily. We need to be taught to not be afraid/"
] |
[
"A phobia is defined as \"an ",
", intense and persistent fear of certain situations, activities, things, animals, or people\".",
"The brain does not come hard wired with such things. Phobias are a form of fear association learning that is necessarily required to occur through learning/experience."
] |
[
"Is it possible to predict matter's chemical properties based solely from the elements that make them and how there of bonded?"
] |
[
false
] |
A example would be water which is H2O and hydrogen peroxide which is H2O2 but have completely different chemical properties. Would i be able to make a guess to the chemical properties of H3O6?
|
[
"yep, the differences between HOH and HOOH are pretty evident. The O-O bond is quite weak, with a low bond dissociation energy (~140 kJ/mol), while HOH is quite strong, with a high bond dissociation energy (~460 kJ/mol). The bond dissociation energy is simply the amount of energy it would take to degrade (break apart the chemical structure) the molecule. ",
"Understanding bond dissociation energies ",
"can be fairly experimental",
". The energy of light is inversely proportional to its wavelength. This means that higher wavelength light contains lower energy. by keeping the power source constant and by shining a laser on a sample until is breaks, you can calculate the bond dissociation energy of the sample. From this, a database can be determined and referred to.",
"Understanding why some bonds react and others do not is not always intuitive. For example, there is an ongoing debate on why a peroxide is unstable, with prevailing theories revolving around crowding of repulsive lone pairs and high electronegativity of the O-O single bond. However, that only partially explains the science and ",
"does not account",
" for the extremely wide dissociation energies of peroxides with different substituents. However, while the black-box is a debate, the end-result is well known and tabulated and can be used to adequately predict reactivity of other molecules.",
"So to your example H3O6, that molecule first of all cannot exist. The most charitable way of describing this molecule is through a chain of 6 oxygens (5 peroxides) with a hydronium ion on one end. This would be too unstable to ever exist in nature."
] |
[
"What he said. Chemical reactivity can be \"intuited\" from identifying the molecular (bonding) geometry and presence of functional groups. Additionally the spectra across the EM field can be predicted if the geometry is known -or- the geometry can be deduced by analyzing the spectrum in a specific spectral region and/or multiple regions. This is the basis of modern chemistry and underpins many analytical techniques used in medicine, molecular biology, astrophysics, and on and on... Essentially, the relationship between structural geometry and physical and chemical properties is one of the important successes of modern science and the technology that has shaped the modern world. The number of applications resulting from various spectroscopic analytical techniques would fill a phone book. It's utility and ubiquity cannot be overstated."
] |
[
"Almost entirely, yes. That is one of the important achievements of Chemistry. However, when dealing with large numbers of atoms instead of individual ones, additional information is sometimes required such as external pressure, temperature and volume of the system and it's surroundings."
] |
[
"How did people wash themselves and clean their clothes and utensils before the invention of Soap?"
] |
[
false
] | null |
[
"Soap was invented in prehistory. For the most part, in the event that someone wanted to feel cleaner, they washed themselves and their stuff in the river. Rainwater going through wood ash produced lye, which when mixed with fat that had cooked over the fire made soap. People were often near rivers, and often cooked near rivers, and eventually noticed that certain places below these fires had this goop that got their clothes cleaner. After some dicking around they figured out how to reliably make that goop, and called it soap. Fight Club had this explanation with human sacrifices, but regular cooking would work just as well. "
] |
[
"Soap is real old, actually. It predates the Babylonians. But some people would also use oil (or oil mixed with sand or ash, so it was exfoliating) to wash. We know for sure ancient Greeks and Romans did this, because they had dedicated tools called strigils, but it's likely the practice is a lot older. The idea is you slather on oil (olive oil, in the case of the Romans), massage it in to break down dirt and grime on your skin, and then scrape it all off to remove the dirty-oil-combo. The oil cleansing thing was particularly associated with athletes who had to bathe more often the average bear, but they weren't the only ones who did it - regular people did it too. But it may have been more popular with people who bathed very frequently because basic soap is really harsh and didn't always lather super-well (worth noting, some of what we thing of as 'soap' really isn't. Soap results from lye or soda ash mixing with fats and undergoing a chemical process called saponification. Body wash, 'beauty bars', shampoo, shower gel, and hand soap are generally not soap. Theyre a mixture of surfactants - like detergents and foaming agents - and skin conditioners and fragrance). Removing swear and dirt with oil probably would have been a lot gentler on their skin. Although I'm dubious about the gentle-ness of scraping it off with a metal tool... Smooth wood sounds nicer to me!",
"Side note to that story, oil cleaning has never totally died off. Oil cleansing for skincare is very popular right now - although it lacks the whole scraping off part. Oil cleansing is great for removing makeup (because it breaks down waterproof products really well) and a lot of people find it less drying and irritating, which improves the quality of their skin over time. Oddly enough, some people with acneprone and oily skin have great results with oil cleansing. ",
"You might have also heard of conditioner washing or 'co-washing'. It's the process if using conditioner to scrub the scalp to break down oil and dirt, rather than shampoo. It's popular with people who have curly hair, as harsh ingredients in shampoo can cause damaged, frizzy hair. Although only certain conditioners can be used - nothing with silicones will work as they can only be removed by those harsh shampoo ingredients. ",
"Also, some ancient peoples actually used ",
"soapberries or soapnuts",
" - when you crush the fruit with water, it produces a lather. It might also have some antimicrobial properties. I'd imagine the soapy properties were discovered the first time someone tried to eat them :)"
] |
[
"you never washed or saw someone wash a pot with river sand (like when camping or something)? Also, water is a pretty good solvent by itself especially warm/hot water. So water and grit would be enough for most things."
] |
[
"Do birth control pills delay the onset of menopause in women?"
] |
[
false
] | null |
[
"Med student here skimming through old notes.",
"Overall, age of menopause is an average of 51 years.",
"It looks like the the clear determinants of menopause are:",
"All of the other supposed determinants are iffy - age of menarche, race, stress levels, diet, environment, etc.",
"Overall, menopause is NOT associated with the age when you first got your period. Doesn't matter if you started bleeding when you were 10. Doesn't necessarily mean you'll stop when you're 40, or 50, or 60.",
"Some studies show variations in menopause age for certain ethnic groups, but I'm going to assume this is also iffy and not necessarily definite. (Age of menarche/first period, however, is definitely earlier in the black population and no one knows why).",
"Didn't see anything about oral contraceptives delaying menopause, so I'm going to assume it's another one of those things that have been studied without conclusive results. However, just as a side note, just because you don't ovulate when you're on birth control doesn't mean you're \"saving\" the eggs. The follicles are dying like clockwork anyway. The only difference is that they never got ovulated so you couldn't get pregnant.",
"I guess the strongest determinant is genetics. It'll just happen when it happens.",
"I'll defer to an OB/Gyn or reproductive endocrinologist if anyone else wants to add to the conversation."
] |
[
"Of interest, a woman has approximately 50,000 eggs at first ovulation, and roughly 10,000 at menopause. The ~40,000 eggs are lost through both ovulation as well as ",
", or simple loss that doesn't produce eggs (e.g. ovarian cysts and others).",
"Related to what harharharbinger said: the early onset of menses is a contributor to hormone-sensitive cancers such as breast cancer. The risk of cancer drops off immensely after menopause - due to the loss of exposure to the hormone cycles.",
"However, certain birth control pills (e.g. estrogen pills), while prevent menses, still maintain - if not increase - the risk of cancers due to maintained exposure to hormones."
] |
[
"Short answer: no.",
"Long answer: As harharharbinger has stated, even when you're taking the pill, your follicles are still dying. You just aren't releasing the egg cell in that follicle. Birth control pills are not designed to hasten or delay menopause (the former is possible, the latter is most likely not). They are merely designed to make you (basically) not ovulate. Certain types of birth control can hide the typical signs and symptoms of menopause. As a woman gets close to the age of menopause (typically around 50), gynecologists will typically ask them to stop taking their birth control pill and take blood tests a week afterwards to determine if the FSH levels are in the menopause level. There has been no evidence (that I could find) that says the pill delays menopause."
] |
[
"What makes an allele dominant?"
] |
[
false
] |
Do all dominant alleles have something in common with each other that recessives lack?
|
[
"There are a couple mechanisms:\n1) Dose dependence.\n2) Neomorphs- they do something the other alleles don't.\n3) Poison subunits- they damage large complexes by binging to the."
] |
[
"This previous post should help.",
"There are difference reasons for alleles to be dominant or recessive, so, no, there is no one thing they have in common. As described in the post to which I linked, we do have an idea of some of the fairly common reasons why some are dominant or recessive, but the reason is not always clear."
] |
[
"If i recall, there are dominant negatives that are neomorphs and poisoned subunits that are not dominant negatives as well. But yeah, you're right."
] |
[
"How does lightning \"know\" which direction is the path of least resistance?"
] |
[
false
] |
: Is lightning looking for a general minimum resistance, or only a local least resistance in the area of the next molecule? That is, does lightning for the least resistance path, or is it "moving" from one molecule to the next, looking only for which of the adjacent molecules has less resistance? Over how wide of an area does lightning search for a path of least resistance (i.e., is there lightning that travels horizontally for long distances before going to the ground?)
|
[
"You have a large boulder. The surface is pretty irregular.",
"You pour a bottle of water onto the top, and you notice that water flows down specific paths - sometimes along existing channels, other times almost at random, like slowly pouring water down a pane of glass.",
"How does water \"know\" where the channels (i.e., low points) are?"
] |
[
"I didn't really get a great glimpse of the leaders in the video MonkeyNin posted but I found one here ",
"http://www.youtube.com/watch?v=8waV48897o4",
" at around 14 secs in."
] |
[
"Damn that's cool looking. The more I learn, the more I find out nature already beat us to the hard stuff.",
"Thank you!"
] |
[
"What's an example where a monosaccharide forms into a disaccharide and how would this further progress to a polysaccharide?"
] |
[
false
] |
Simply, I want to know the overall process on how these saccharides function together. I know that they can bond but how does the water molecule get eliminated to form the disaccharide. How do the monosaccharides form a large chain to create a polysaccharide?
|
[
"It's biosynthesis, usually, so enzymes catalyze reactions powered by phosphate groups being split. Sucrose, for instance, is made by the enzyme sucrose-6-phosphate synthase, which takes activated (phosphates attached) forms of glucose and fructose and sticks them together. Starch, the classic polysaccharide, is made in a pretty similar manner, except that it only uses glucose. Starch synthase just grabs phosphorylated glucose and sticks them on the end of the growing chain. It might seem strange to spend energy to store energy, but the advantage is that these giant molecules of starch won't diffuse out of the cells, but are readily converted back into simple sugars for use later. Spending a little to put it in the bank and have a reliable source of fuel is well worth the energy used in polysaccharide synthesis. "
] |
[
"Would like to add the benefit isn't just of starch not moving out of the cell and losing energy from to he cell, but that starch is osmotically inactive compared to glucose. Storing glucose would draw so much water into cells."
] |
[
"Thanks for your reply! Clears up a lot of the confusion I had regarding the biosynthesis of saccharides. "
] |
[
"Can mass be relative?"
] |
[
false
] |
[deleted]
|
[
"There is a relativistic mass. It's γm. If you use it, then F=γma...",
"That's not true though and only one of the ",
" reasons why relativistic mass is a useless concept. The force ",
" is ",
" parallel to the acceleration ",
"."
] |
[
"Actually, energy and mass are not exchangeable. In a manner of speaking, mass is one type of energy, but not all energy is mass. (It gets complicated, but that's the basic idea.)",
"Mass is invariant, meaning that it doesn't depend on your reference frame."
] |
[
"To suggest that there is a relativistic mass is to suggest that the internal structure of our object changes depending on our reference frame. It doesn't make sense to say that the amount of matter present has changed, hence why we've ",
" mass to be a Lorentz scalar, as ",
"/u/RobusEtCeleritas",
" mentioned. ",
"To quote Taylor and Wheeler (and Wikipedia): ",
"\"The concept of \"relativistic mass\" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass - belonging to the magnitude of a 4-vector - to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself.\"["
] |
[
"How is the process of splitting H2O with electricity reversed?"
] |
[
false
] | null |
[
"You burn it. Hydrogen and oxygen with a heat source make fire which releases a lot of energy and makes water as the only product. Alternatively you can use a hydrogen fuel cell which does essentially the same thing, just extracting the energy through an external electrical circuit rather than through heat."
] |
[
"So a candle at my house doesn't make water... it requires H and O to happen and I would imagine there isn't enough H?"
] |
[
"The only way it would not make water is if there were no hydrogen, and that is extremely unlikely for any material that would behave like a normal candle. Is this a specific claim of the candle, and if so does it say what it is made from?"
] |
[
"What is the limit to how fast air can enter an aircraft engine?"
] |
[
false
] |
I am going to specify what I mean with my question. At cruise conditions, the mass flow through an engine can be approximated using the airspeed and the frontal area of the inlet. However, on take-off, the air has to be sucked from the surrounding environment, so what is the limit, if there is any, to how much air can an engine suck in? What is the hard limit of how much an engine can suck in let's say, relative to its frontal area?
|
[
"Well the absolute limit of mass flow per unit area is when the inlet is ",
"choked",
" i.e. air is entering at the speed of sound, however the inlet itself would never be choked on a subsonic engine like a high bypass turbofan. Instead the compressor, and possibly the fan depending on the design, would be choked at some point, and that would set the limit for mass flow. The exact amount of air you take in will vary with temperature and pressure, and engines are very carefully designed to ensure the choking condition doesn't limit them at key points such as takeoff and top of climb. A supersonic engine is slightly different as its intake will be ",
"designed to control the shocks",
" caused by supersonic flight, but there will still be a limiting point either in the intake or the compressor where flow is choked."
] |
[
"You could make air hit the fan blades at higher speed, yes, though it would require some kind of converging-diverging intake which would be a poor design choice for numerous reasons. But the absolute limit to the mass flow rate of fluid you can suck in is reached at this choking condition. For air with a ratio of specific heats of 1.4, this mass flow is equal to 1.281*minimum area of the intake*stagnation pressure/sqrt(1005*stagnation temperature). For a stationary fan in the Martian atmosphere that you list, if we assume it has the same properties as carbon dioxide at that temperature (cp=780 J/kg, cp/cv=1.36) then the maximum mass flow rate you can achieve per unit minimum area is 1.97 kgs",
"m",
". ",
"At the minimum area point, likely to be in the fan blade passage, the flow speed is sonic. Your reasoning based on molecular velocities is flawed because, even in the thin Martian atmosphere, the ",
"Knudsen number",
" is low enough for the fluid to be considered a continuum where particles regularly interact with each other. Compressible flow physics is weird, and transonic fan design complex, but you can reason this limit like this:",
"The speed of sound is the speed at which pressure waves travel in the fluid. It is therefore also the speed at which information about the state of the fluid in one region can travel to another region. Now consider a converging-diverging duct with constant pressure at the inlet and variable pressure at the exit. As you first start to lower the exit pressure the fluid starts moving, accelerating through the throat of the duct and decelerating in the diverging section to match the exit pressure. As you continue to lower exit pressure the flow accelerates more and more, until at some point flow is sonic at the throat. This means that the fluid is moving in one direction as fast as pressure waves can travel in the other i.e. information can't travel back upstream. So if you lower the exit pressure further, the inlet flow will have no information about his and flow can only remain sonic at the throat. The duct in this example is directly analogous to the engine."
] |
[
"The hard limit is 14.7psi when airspeed is zero. That's the hardest you can suck air into the engine if you had a fan which created a perfect vacuum. If you have some airspeed, then you are essentially ramming air into the engine and then your hard limit is 14.7psi plus the ",
"stagnation pressure",
" at that airspeed. If you are nearing the speed of sound then shit gets all wonky and there are shockwaves involved and comprehensibility effects start popping up and usually your efficiency goes down so you get diminishing returns as airspeed increases above M=1."
] |
[
"iss stil orbits inside the atmosphere?"
] |
[
false
] |
this information could be wrong but the iss orbits at circa 400 Km while the earths atomosphere continues to 480 km, does the iss compensate for the atmospheric drag in some way or is there just so little air up there that it doesnt really matter? sources:
|
[
"The atmosphere is very thin up there, and it would definitely feel like a (lethal) vacuum to a human. However, it is enough to produce a little bit of drag that slows it down. So every now and again, they need to give it a bit of a boost.",
"There's a nice plot ",
"here",
" of the ISS's height over time. You can see that the ISS gradually drifts downwards, and then suddenly has a big boost upwards every month or so. The orbit isn't long-term stable without, and the ISS would eventually crash into the Earth if it was left alone. But the cost of boosting it every now and again is way cheaper than having to fly up twice as high (or more) every time a mission goes up there."
] |
[
"i would assume little debris getting some drag, too. So the orbit clears itself, am i wrong?"
] |
[
"But the cost of boosting it every now and again is way cheaper than having to fly up twice as high (or more) every time a mission goes up there.",
"Higher up would also mean higher radiation doses for the humans (and the electronics) - this is independent of the atmosphere, the shielding due to Earth's magnetic field gets weaker if you fly higher."
] |
[
"How much do all the living organisms living on planet Earth's crust contribute to the force of gravity of Earth?"
] |
[
false
] | null |
[
"It's pretty much a wash- all of the mass of living creatures came from the earth itself and, to a small extent, the atmosphere. There is essentially no difference between the gravitational effect of the mass of living organisms and what the gravity would have been before the atoms were organized into living beings."
] |
[
"To answer the additional question, according to the wiki ",
"the biomass of all plant and animal life on earth",
" is around is around 560 billion tonnes. That number possibly doubles if you include bacteria.",
"The force of gravity and size of said sphere that much mass exerts at its surface depends on the density of the sphere. As for the contribution this has to the earth's total gravity, it would be vanishingly small when you consider the mass of the earth is a little less than 6x10",
" tonnes compared to the generous estimation of biomass of 1x10",
" about 1x10",
" % of the total"
] |
[
"Interesting, hadn't thought of that. Thanks for the quick response, sir."
] |
[
"Why do airplanes tilt when turning? Why can't they turn without tilting?"
] |
[
false
] |
Essentially what i'm asking is why can't a plane turn from facing north to facing east without tilting vertically at all? why cant you just increase thrust on the engines on the left side of the plane so that it is moving faster that the right, thus turning the plane without tilting or banking it.
|
[
"They can. There is a ",
"famous incident",
" where the pilots were forced to fly this way when the controls gave out.",
"The reason they don't normally fly this way is for efficiency and comfort. When a plane turns, the ailerons are tilted on the wings at the same time the rudder is turned. This banks the plane as it turns so the passengers don't feel the g-forces and get airsick. Redirecting the airflow over the plane gives the pilot much finer and quicker control over the aircraft than changing engine power. Also, changing the engine power affects the lift on the wings, so maintaining the proper altitude would be difficult."
] |
[
"This banks the plane as it turns so the passengers don't feel the g-forces and get airsick.",
"To clarify, they still feel the increased g-force, it's just directed downward rather than at an angle to one side."
] |
[
"The other posts here have covered passenger comfort, and the desire to keep the airflow over the wings coming from directly in front and not from the side. I'd like to add one further thing: airliners and most aircraft (modern fighter jets being a notable exception) are designed for stability in yaw, pitch and roll. In general, pitch stability is provided by the horizontal stabilisers, roll stability is achieved by slightly angling the wings up (so the tips are higher than where the wing connects with the fuselage), and yaw stability is provided by the vertical stabiliser (the vertical tail fin). ",
"The basic idea is that when all the control surfaces are set neutral, the plane should continue flying in a straight line and not deviate (on any axis). To show how this works, let's take the example of yaw. These surfaces are aerofoils, so yawing will create an angle of attack for the airflow over the vertical stabiliser, creating a sideways force ('lift', as far as that stabiliser is concerned), that tends to turn the plane back towards its original heading (a little hard to imagine the vectors involved, but trust me it works!). So while turning by using the vertical tail rudder to make the plane yaw is possible, the plane will 'fight' against this somewhat and try to return to the original heading, due to this design for stability."
] |
[
"How do we have such accurate maps of the Milky Way if we are inside it?"
] |
[
false
] |
It makes sense for galaxies like andromeda that we can see but how are our maps of our own so precise if we are on one of the spiral arms?
|
[
"We really don’t. Most of it is still unmapped and what we have mapped is mainly what’s right around us and what’s so big off in the distance that you can see it clearly from earth with our telescope technology like nebulas and very large stars."
] |
[
"Those pictures are a mixture of data and guesswork. They're created from careful data collection over the past hundred years to identify and map tens of thousands of stars, followed by clever design and construction of automated mapping satellites to identify another ",
" stars in the past ten years, plus a whole lot of educated guesswork to fill in the remaining ",
".",
"Our maps of the galaxy have improved by an incredible amount in the past decade thanks to the ",
"Gaia",
" satellite, but 99.5% of the galaxy still remains unmapped."
] |
[
"If you're inside a building, you can tell what shape it is by seeing where the walls go. Equivalently, we can trace the spiral arms and other structures of the Milky Way by looking at where the stars are.",
"It's not fundamentally that hard, it's just time-consuming because there are such a large number of stars. Gaia made this process faster because it autonomously searched for stars and determined their positions and velocities, whereas in the past more human involvement was required."
] |
[
"Do field lines compress on a quickly moving magnet like air waves on a jet?"
] |
[
false
] |
Can a magnet break the ‘magnet’ barrier like a plane breaking the sound barrier?
|
[
"In a vacuum, no. The propagation speed of electromagnetic fields is the speed of light. As the magnet moves faster, time dilation causes the waves to always move away from it at the speed of light from its frame of reference. It can never \"catch up,\" just like any other physical object with mass. ",
"However, there are mediums where the speed of light is considerably less than in a vacuum. In these instances, the magnet (or charged particle like an electron) can physically move through the medium faster than light can propagate through it. This is conceptually the same as breaking the sound barrier. ",
"Similar to how the sound waves building up causes an audible sonic \"boom\" of a set frequency, a charged particle moving through a dielectric can cause an emission of visible light. An example is Cherenkov Radiation, which is a ghostly blue glow that comes when ",
"radioactive nuclear components are submersed in water",
"."
] |
[
"Absolutely, but the effect of relativistic doppler is only on the wavelength of the light. Not the speed at which it propagates. The magnet in this example would still perceive the electromagnetic waves zooping out away from it at the speed of light. It's just that the light would get more and more blue-shifted as the magnet's speed increases."
] |
[
"It is possible to compress magnetic field lines and increase magnetic flux:",
"https://en.m.wikipedia.org/wiki/Explosively_pumped_flux_compression_generator",
"If a magnet or other source of magnetic field ( electrons/charge carriers moving in a loop) would be moved through some substance then yes magnetic field lines might be compressed. It also depends on the source of the magnetic field and and the material in which the source of the magnetic field is moving."
] |
[
"So I sliced my Ring Finger washing dishes... Why does my Middle Finger feel like it's sliced too?"
] |
[
false
] | null |
[
"The median nerve innervates the thumb, index, middle, and half of the ring finger along with their nail beds. I suspect that your body is experiencing some difficulty distinguishing pain in that last split of the nerve between the fingers. You might have some nerve damage, it is probably worth seeing a doctor if you have not already.",
"http://upload.wikimedia.org/wikipedia/commons/a/a7/Nerves_of_the_left_upper_extremity.gif"
] |
[
"I did not slice my middle finger... :P"
] |
[
"The ring finger and the middle finger are served by the same nerve, as Phage0070 pointed out to you. You've caused enough damage to the surrounding tissue to swamp the ends of the nerve with information."
] |
[
"What exactly is the barycenter of a pair of binary stars?"
] |
[
false
] |
I understand that the barycenter is the fixed point two stars rotate around, but I have no idea what causes it. Like, how is it chosen? Can the barycenter change during the lifetime of the binary stars? Any insight would be welcome.
|
[
"Well, if you ignore the pull of the galaxy, there are no outside forces on the pair of stars. No outside forces means the center of mass will never change velocity. No matter how the stars orbit, the center of mass has to remain at the same velocity.",
"It can't change unless there is some kind of outside forces or MASS LOSS from one (or both) of the stars. "
] |
[
"I'm not sure what you're asking. After formation, they are in orbit in whatever orientation/speed/position they happen to be in."
] |
[
"Any time two things orbit around each other (like the moon around the earth), they orbit around a central point. The moon is much smaller than the earth, so it's not an equal pull. The point that they orbit around is under earth's surface. If the moon were larger, you'd see the center of mass move away from the middle of the earth toward the moon, and when it gets above earth's surface, we'd say that the earth and moon orbit each other. That center of mass is the barycenter. So yes, in a way, the stars in a binary system are having a kind of \"tug of war\". They're each pulling on the other one (and their speed is what keeps them from hitting)."
] |
[
"Why does fission release a lot of energy but the weak nuclear force doesnt?"
] |
[
false
] | null |
[
"What weak processes are you thinking of?"
] |
[
"The weak nuclear force causes decay and when an atom decays it ejects a smaller atom, if im not mistaken right? What makes this different than fission that fuels things"
] |
[
"The weak force causes ",
" kinds of decays (beta decay and electron capture), but not others. Fission is something which can happen as a decay or as a reaction, and they both tend to release similar amounts of energy for nuclides of similar masses."
] |
[
"Is there a formal way of deciding what fraction of a game is chance?"
] |
[
false
] |
The card game of "war", in which players flip cards and compare their values without ever making any decisions is clearly entirely probabilistic, (each player will win half the time, as long as the deck is perfectly shuffled before each game.) The game of chess has no probability involved because the game state is entirely dependent on input from the players. These are examples of games at the extreme ends of the scale, but is there a way of assigning a specific value of how much probability plays a part in a game for those that are in between the extremes?
|
[
"I'm not sure how developed the concept of ",
" is. There is a paper by Jakob Erdmann from the Friedrich-Schiller-Universitat that deals with the concept. ",
"Here is the pdf link.",
"Their goal is to create an algorithm for automatically determining the extent of chance and skill in a game."
] |
[
"I feel the problem intrinsically lies in the somewhat ambiguous terminology.",
"To distill this issue, one can look at the game of connect 4. There are strategies and general concepts, but a perfect game has the first player win every time. Does this mean, assuming who goes first is set randomly, the game is completely chance?"
] |
[
"While it is believed that ",
"chess is solvable",
" it is not yet known how it would be solved. We don't know if white could always force a win, if black could always force a win, or if either player could always force a draw. Without that information, we can't say if the randomness of the starting color makes a perfect game of chess random.",
" Sorry for the Wikipedia link, I'm not up for searching any more deeply right now."
] |
[
"How powerful a magnet would you need to effect the iron in a persons blood?"
] |
[
false
] |
Follow up, could someone be kill this way?
|
[
"Wiki on Human Iron Metabolism:",
"Most well-nourished people in industrialized countries have 4 to 5 grams of iron in their bodies. Of this, about 2.5 g is contained in the hemoglobin needed to carry oxygen through the blood, and most of the rest (approximately 2 grams in adult men, and somewhat less in women of childbearing age) is contained in ferritin complexes that are present in all cells, but most common in bone marrow, liver, and spleen.",
"Wiki on Red Blood Cells:",
"Approximately a quarter of the cells in the human body are red blood cells.",
"enotes:",
"How many cells are in the human body?",
"Depending on the source, that figure varies from 50 to 75 trillion cells.",
"Let's call it 60 trillion cells, so 15 trillion of them are red blood cells which have hemoglobin for oxygen transport, of which all need a little bit of iron to do so. If there are 2.5g of iron dedicated to these 15 trillion cells and we assume that it is divided evenly, then that's ~0.17 picograms of iron in a single red blood cell. So that means we need a magnet that can affect a source of iron that constitutes a mere 0.17 pg.",
"From ",
"popularmechanics",
"\nWhat is about the strongest known magnet is a neutron star with a magnetic strength of 100 billion Teslas.",
"Ian McKellen is ",
"according to this",
" 180cm tall.",
"If we use ",
"this picture",
"We notice that Ian McKellen's hand is about no greater than his height away from any part of the other actor's body.",
"So now, if someone can find the proper equations to use (if there are any that pertain to tiny objects - another forum post on this topic said that they thought iron in the blood was weakly paramagnetic)..",
"We have the mass of any particular source of iron (0.17pg), the farthest distance any of those sources could be from the magnet source (180cm) and an example real-universe magnetic strength of 100 billion Teslas.",
"Can anyone help? It's FOR SCIENCE!!! (...even if we're ignoring the magnetic permeability of a few million iron atoms that are connected to something biologically and the internal forces that go along with that and probably several other relevant laws of physics since the Magnetic superpower doesn't actually exist, lol)"
] |
[
"The magnetic field of a magnetar is strong enough to kill you via the diamagnetism of ",
". I'd say that's more significant than iron."
] |
[
"At a distance halfway to the moon, a magnetar could strip information from all credit cards on Earth.",
"Wait a minute...",
"TylerDurden1976 (talk) 21:00, 21 August 2010 (UTC)",
"I knew it!"
] |
[
"Would an object travelling close to the speed of light experience friction due to the hydrogen in space?"
] |
[
false
] | null |
[
"Absolutely. However the intergalactic medium is so thin that the main obstacle is actually the cosmic microwave background, which dominates collisions with protons. In this recent paper ",
"here",
" the interaction of a relativistic spacecraft with the redshifted CMBR is studied and it is found that a gigantic amount of energy is lost to \"friction\" and emitted with a very characteristic signature. This by the way allowed to place constraints on the possibility of alien spacecraft traveling relativistically anywhere close to us."
] |
[
"Per that article, the CMB effects start to play a role only at speeds ",
" close to speed of light (",
", which is 99.99999999999999999% of the speed of light). "
] |
[
"No friction. But there are two interactions you should consider. One would be with matter. Atoms may absorb or scatter a photon. Next is gravity (or really the distorted space-time). Energy warps space time according to Einstein's field equations in General Relativity. Light will follow the path of minimizing time to its destination, but in this ",
" space, the ",
" are not straight as we see them. Hence effects like gravitational lensing and the precession of the parahelion of mercury."
] |
[
"How do space agencies prevent germs and bacteria on their rovers (Mars Rover) from contaminating the planet they visit?"
] |
[
false
] |
Or do they even try and prevent it? Am I correct in thinking that the scientists have something in place to stop living organisms/bacteria contaminating Mars when objects come in contact with the planet? If so how is it done?
|
[
"They clean and sterilize the object before it's launched. This eliminates any food for bacteria or microbes. ",
"Also, space is incredibly hostile to life. Several months of cosmic rays, unfiltered UV radiation, and freezing cold will kill all but the hardiest of microbes. "
] |
[
"All that, and we ",
" found evidence that some of the rovers had life on them at some point. Life is incredibly stubborn. Lol"
] |
[
"There are pre-flight bakeouts at over 100 C as well as cleaning everything down with alcohol. Lots of work is done to keep human contamination (skin, hair, etc) off, because it leads to being a tasty food for bacteria. ",
"There are also limits for how close the rovers can get to potentially life-bearing areas depending on how clean they are, too. "
] |
[
"We know many species of animals are now extinct. Are there any extinct plants in the world? How did they reach extinction?"
] |
[
false
] | null |
[
"Plants go extinct for the same reasons animals go extinct - they can't survive in their ecological niche anymore. Maybe a new species of plant crowds them out, like in rainforests where plants are in an arms race to grow taller faster. Maybe a new parasite or disease kills them off, like Dutch Elm disease. Maybe climate change kills them off, like an ice age. Or maybe changes to the atmosphere kill them, like the great oxygenation event.",
"Wikipedia has a long, if incomplete, ",
"list of extinct plant species",
". Many species of plants have gone extinct in recently recorded history. If you travelled back in time, the plant life would be as obviously different from modern species as animal life would be. The ",
"first forests",
", which generated much of the coal we find today, were dominated by giant ferns and club mosses that don't exist today."
] |
[
"Man-made reforestations of burned areas is a serious one. For example in Greece, from 1900-today, for reforestation of burned areas like hills and mountains, they use pine trees ( easy to propagate, grow well in the dry conditions of Greece, etc.). The pine needles (leaves), once they fall on the ground and start decomposing, they lower the soil's PH. Many endemic orchids and other species, went extinct in these areas because they could not survive on these new acidic soil conditions."
] |
[
"Here is a list of endangered or extinct plants: ",
"Endangered and Extinct Plants",
"This lists 5,773 plants that we know to be endangered or extinct. There however will be more plants that we have yet to find in fossils or will simply never know about. Chances are there are more extinct plants than there are extinct animals, animals can adapt more (eg. migrate to a warmer climate) to keep alive where as plants must relay on the local conditions being habitable. "
] |
[
"Why is the radiation from Chernobyl and Fukushima so intense, when Uranium has a half life of billions of years? Shouldn't it be minimal?"
] |
[
false
] | null |
[
"Nuclear power plants make energy by splitting uranium nuclei in two: \"nuclear fission\". The two new nuclei made, \"fission products\", are almost always radioactive and under go beta decay. ",
"A wide variety of fission products are made",
" with a wide span of half-lives, down to sub-second and up to many years. Most will undergo multiple beta-decays on their way to becoming stable nuclei.",
"It's these fission products which dominate the radioactivity in used nuclear fuel, rather than the uranium directly.",
"Further, the energy released by these beta decays accounts for about 7% of the total energy produced in the reactor, and the heat produced is what's usually responsible for meltdowns: even after you stop fission in a reactor, it's still initially putting out about 7% power from this ",
"\"decay heat\"",
", and that heat needs to be removed from the reactor or it will continue to heat up and eventually melt. This is what happened at Fukushima and Three Mile Island."
] |
[
"It's not the Uranium that releases most of the radiation. Once the Uranium is washed away or evaporates into the air it's no longer at critical mass and reacting. The half life of U235 is long enough that it doesn't release much radiation, but it is toxic as a heavy metal metal poison.",
"The dangerous radiation/fallout around nuclear meltdown sites comes not from the Uranium itself, but from all the nasty byproducts that come from splitting uranium. Uranium splits erratically when hit with a neutrons and forms all sorts of weird and exotic isotopes that can't be found naturally, as any naturally occurring instances of those isotopes would have decayed away to nothing long ago. Then those isotopes decay and form new unstable isotopes.",
"TL;DR: Uranium itself is fairly stable. It's the byproducts of the fission reaction that create radioactive waste."
] |
[
"Once the Uranium is washed away or evaporates into the air it's no longer at critical mass and reacting.",
"Actually when there is not a careful geometrical arrangement of Uranium and a neutron moderator it will stop reacting. The Uranium generally does not leave the disaster area. If it easily washed away or evaporated that would be quite dangerous as it could be ingested or enter the lungs.",
"but it is toxic as a heavy metal metal poison.",
"It is also toxic as a alpha radiation emitter (if it enters the body). U238 ammunition is a health risk too."
] |
[
"Why do laser pointers look \"grainy\" or look like they are a bunch of dots when you look at the laser point on a surface?"
] |
[
false
] |
[deleted]
|
[
"As Sycosys said, the grainy pattern is called a \"speckle pattern\".",
"Basically, the lenses that are in front of the laser are far from perfect, and there are random fluctuations in the air as the laser light travels through it (turbulence, etc.). This causes distortions on the wave front as the light propagates, leading to destructive (dark spots) and constructive (bright spots) interference. ",
"This is not special to laser light, btw. It is just that the light for these lasers is so bright and coherent that the distinction between the bright and dark spots is very pronounced. If the laser was just a bright source of thermal light, there would be no coherence (no single pronounced wavefront), which is equivalent to saying that there would be many completely different speckle patterns of lower brightness superposed on top of each other, leading to the pronounced pattern to be washed out, so that you'd perceive a much smoother distribution of light.",
"You can see the same type of coherent speckle pattern when you look at an ultrasound.",
"edit: spelling of sycosys' name\nedit: typos"
] |
[
"There's also the fact that because of the coherent emission, microscopic imperfections in the surface it is reflecting off of causes the interference patterns. ",
"If I'm not mistaken, that's actually the dominant source, and the sub-speckles are the other factors. The fact that the speckles appear to shift and change when you hold it generally has to do with the fact that your hands aren't keeping still to a fraction of a wavelength of light, and are constantly shifting position and angle minutely."
] |
[
"The speckle pattern would exist even if the laser lenses were perfect and the beam were traveling through vacuum.",
"The optics of our eyes are just as important in perceiving laser speckle."
] |
[
"Is it possible/practical to build a \"filter-feeding\" ship that is powered by Uranium from seawater?"
] |
[
false
] |
[deleted]
|
[
"That's sounds like a Brussard Ramjet, except a boat instead of a spaceship.",
"Anyway, I don't think so. The amount of uranium you'd get is tiny compared to the massive amounts of power to run a ship. Also consider that given its density uranium is more likely to be found at the bottom of the ocean."
] |
[
"As I understand it, there's two big downsides.",
"First, it's really slow. The process is basically submerging huge sponge-like objects into the sea, waiting for water to filter through them so they can collect the uranium, hauling them back up, and processing them.",
"Second, the net energy return is barely positive. You have to spend so much energy in processing that it's almost not worth doing.",
"Now, the second issue is solvable - you use breeder reactors to increase your energy output from a given amount of uranium by, like, a factor of fifty. But then you've got a much more complex breeder reactor system, which isn't really practical to put on a boat. (And isn't politically practical to put on land.)",
"And when all is said and done, you have a giant slow boat towing hundreds of cubic meters of sponges around behind it, which is perhaps not the most useful thing we could be doing :)",
"Seawater uranium may well solve our limited uranium issues, someday in the future once we finally get around to breeder reactors, but from what I know it's not practical for self-collecting on ships."
] |
[
"So in a sense, it'd be about 500,000 times more practical to build the same sort of contraption that "
] |
[
"Have human beings ever created a new species?"
] |
[
false
] |
We're in AP Biology discussing speciation and the argument desperately needs some hard supporting facts. Microevolution is most definitely observable, but have we ever truly accomplished speciation? Pardon the awkward wording; I'm trying to pay attention. Currently we're discussing pigeonesque chickens.
|
[
"Bananas, broccoli, cauliflower, lettuce, maize, dogs, etc, etc. Humans have artificially selected for any number of desirable characteristics in indigenous species--some to the point where interbreeding is no longer possible."
] |
[
"This ",
"picture",
" was a favourite of one of my genetics professors. The difference between species is phenotypically observable to say the least."
] |
[
"Yes. That's correct."
] |
[
"Can we consistently define a set of all possible ways a function can asymptotically grow with total ordering on it?"
] |
[
false
] |
[deleted]
|
[
"to your first point, there are many functions that grow faster than exponentials...consider, for instance, the ackerman function.",
"Or how about, consider f(n,k) to be n followed by k \"up arrows\" followed by n. This would grow faster than any exponential in either n or k. ",
"Going even higher, the busy beaver function grows faster than any computable function (provable by the fact that the halting problem is undecideable). You could then apply all sorts of other functions to that....like composing the busy beaver function bb(bb(n))...and then you could get even more absurd by having an independent variable stating the number of times you compose the busy beaver problem of itself",
"so bb(bb(bb(n))) = bbc(n,3). ",
"On your secont question: two functions are either in the same complexity class, or they aren't. (BTW you should be using big-theta here...not big O). The question boils down to, given two complexity classes, can you always generate another class which lies in between them? My intuition says that the answer is \"yes\". This is trival for polynomials, as each degree yields a new class. For exponentials, you need a new type of function. Such functions can be defined and do indeed exist. Here is a paper from the 60's that describes one such method:",
"http://journals.cambridge.org/download.php?file=%2FJAZ%2FJAZ2_03%2FS1446788700026902a.pdf&code=f11663b5b7b785b79ea5e022a6df2e32",
"It covers fractional logarithms and exponentials.",
"Whether you can create a half-composition of non-computable function (busy beaver), I don't know."
] |
[
"What you are asking for is a description of the ",
"order type",
" of the order you've constructed. (BTW: this is only a partial order).",
"I'm pretty sure this is wickedly complicated. For a start I suggest you read ",
"this",
" concerning such classes of functions where the domain and range are the natural numbers.",
"I might ask the question over there myself."
] |
[
"great link, thanks"
] |
[
"If I had an aquarium filled with distilled, deionized water, how long would it be before fish could live in there?"
] |
[
false
] |
This is a question about how gases dissolve in liquids. Assume STP and the water is not being agitated. The volume of the aquarium is obviously important, so let's just say it's 20 L. Let's assume there is absolutely no oxygen (or any other gases) in the water at the onset. What is the concentration of oxygen required for a run-of-the-mill goldfish to "breathe" and how long will it take the tank to reach that concentration? Related, since I think about this in my daily life when I make solutions in the lab: if I have vacuum degassed a solution and it's in a sealed bottle opened for 1 minute every 7 days, will there be appreciable re-gasification (is that a word?) of the solution in a month, six months, a year?
|
[
"Tricky. Some fish, like the goldfish and carp, are very good at handling anoxic conditions. The crucian carp, a very close relative, ",
"can remain active under these conditions",
" , and goldfish are very tolerant too. Furthermore, any goldfish placed in anoxic water will gulp at the surface...it doesn't have a lung to actually breathe the air, but it can pass agitated surface water over its gills, supplying oxygen. Other fish can directly breathe air.",
"Now a commonly brought up issue is that distilled water is very isotonic and harms fish. However, freshwater fish can survive in distilled water fairly well. I don't have a good citation on it, but ",
"this",
" shows that even some brackish water fish can survive for up to two weeks in distilled water. And freshwater fish are adapted for water at salinities much closer to distilled. It's not the best for them, but they can take it, because really the difference from standard freshwater's osmotic level isn't that huge. ",
"So basically, I think you could drop a goldfish or other adaptable fish in right away and it would have a decent chance of surviving. But this has more to do with the adaptability of the fish than the properties of water."
] |
[
"I work in a lab too, and use various degassing techniques for HPLC purposes.",
"There are various ways to degass solvents including vacuum, sonication, helium sparging, boiling, and most HPLC systems now have inline degassing systems.",
"Your vacuum degassed solutions will \"regass\" very quickly. Probably less than 24 hours.",
"The only way to keep your solution from redissolving atmospheric gases is to store the solution under a pressurized helium headspace.",
"If you have any questions about this as it applies to your specific proceedures, send me a message and I can give you some ideas.",
"How long it would take for completely degassed water to dissolve enough oxygen to support a goldfish...I don't really know. Probably 24 hrs, unless the water is agitated, circulated, or sparged with air...then it would happen very quicky...a few minutes maybe."
] |
[
"On what part?"
] |
[
"Is hydrofluoric acid strong enough to destroy dna?"
] |
[
false
] |
I know certain acids like hydrofluoric acid can be used to chemically dissolve organic matter, but is it strong enough to destroy the DNA of that organic matter beyond the ability to use it for identification purposes? This question came to me while watching season one of Breaking Bad, when Walter and Jesse are looking to dissolve a body in acid. It would certainly help with hiding the body, but I'd wondered if those remains were found, would law enforcement be able to use whatever DNA was left for matching purposes.
|
[
"Hydrofluoric acid isn't a strong acid- it's pKa is 3.17. The tissue damage primarily comes from the fluoride. So no, it isn't a strong enough ",
" to destroy DNA... But fluoride does not discriminate. Given enough time and fluoride, it can damage DNA beyond identification. "
] |
[
"The concentration in drinking water is very low (0.5 to 1.0 mg/L according to wikipedia) and so would not have harmful effects. A small amount is beneficial for oral health but there isn't enough fluoride in floridated water to start causing damage elsewhere in your body."
] |
[
"Based on my assumption? Absolutely not. That's the equivalent to saying \"a fall from 2,000 meters onto concrete is almost certainly fatal to humans. So, based on this assumption... it is not unreasonable to think that a fall from 2 mm would also be almost certainly fatal.\"",
"I'm only addressing the falacy of the assumption. The risks/reward analysis of fluoridated drinking water has been done to death (by legitimate scientists who aren't selling things) and is rather clear."
] |
[
"When astronomers discover a planet..how do they know if its in the goldilocks zone of the star,the temeprature on the planets surface,the orbital period of the planet,what class it is,whats the diameter,mass?"
] |
[
false
] | null |
[
"A read through the wikipedia page on ",
"exoplanets",
" would answer all of those questions and provide interesting details. "
] |
[
"Thank you sir."
] |
[
"They can tell visually the properties of the star (mass, size, intensity).",
"Based on the frequency of the dimming coupled with orbital mechanics tells them distance from the star.",
"Based on the magnitude of the dimming they can get the approximate diameter since they know the orbital distance."
] |
[
"How do giraffes (and other leaf-eating animals) get enough protein?"
] |
[
false
] | null |
[
"A lot of people here are talking about the scientific definition of protein, which I think is missing the spirit of the question (despite being technically correct).",
"When push comes to shove living organisms really just need the chemical building blocks for their proteins/lipids/nucleic acids. In addition to carbon, a lot of what we are is essentially made up of nitrogen, potassium, sulfur, sodium, etc. If you have these core building blocks you can theoretically make anything, so if you eat something living you should get plenty of it (as they are made up of it as well). However many carnivores and omnivores have lost the ability to synthesize some of what we need from scratch. These synthesis pathways can be energetically expensive, and if you are getting the product from what you eat (meat) there is no evolutionary pressure to maintain those synthesis pathways.",
"That is what people are talking about with essential amino acids and essential fatty acids. Those are just amino acids and fatty acids that our cells have forgotten how to make (so we need to get them from our food). Animals that can't get those amino acids and fatty acids from their food can usually just synthesize them from scratch as the evolutionary pressure to maintain the pathway never went away.",
"The full story is a little more complicated, the synthesis of macromolecules can turn into a rabbit hole pretty quickly and I am not the person to explain it."
] |
[
"Even leaves have protein in them. Rubisco is the name of the protein that grabs carbon dioxide out of the air and sticks it into sugars during photosynthesis and it is the most abundant protein on earth. There are lots of other proteins in plant tissue. To get enough the herbivores just need to eat a little more leaves and poop out the extra materials they don’t need."
] |
[
"Some plant structures like cell walls contain a great theoretical source of proteins but are impossible for our bodies to digest because of the difficulty of breaking the bonds between structural polymers plants produce, like cellulose. ",
"Herbivores have a variety of strategies for getting enough nutrients from just plants, but giraffes are specifically ",
" which means that they have multiple stomach chambers which can break down plant molecules bit-by-bit. ",
"The first two chambers are filled with microbes which ferment the plant matter which the ruminants swallow, after which they vomit up remaining unbroken particulate matter to be chewed and redigested. This process is called \"chewing cud.\" ",
"Plant fiber, when broken down, yields dangerous volatile fatty acids, so the third stomach chamber absorbs these chemicals to filter what gets passed to the fourth chamber, the true stomach. ",
"The fourth chamber functions much like our stomach does, completing the final steps of digestion of the now thoroughly processed plant material. ",
"In this way, large herbivores can extract a usable amount of protein from plant structures, even though a human would die of malnutrition trying to do the same. ",
"More information about ruminants here,",
" and honestly the ",
"Wikipedia page for ruminants",
" actually does a pretty good job of explaining them."
] |
[
"How long would a human survive, if their bone marrow was completely removed?"
] |
[
false
] |
[deleted]
|
[
"Bone marrow makes your red blood cells and a red blood cell lives about ",
"120 days",
".",
"One would assume they are all equally spread out over that time so some are brand new and some are about to die and everything in between.",
"The question then remains is how much of your red blood cells can you lose and still survive? That I do not know...hopefully someone else can answer that. Remember though the creature will suffer diminishing capacity over time as it loses red blood cells. At the very end it may be alive but would be catatonic.",
"Seems a lousy way to go too since you are, after a fashion, slowly suffocating to death. Sure you can breathe but your body's ability to oxygenate itself would be diminishing. Not sure how it would be experienced but bet it is no fun."
] |
[
"As a followup to Zerowantuthri's comment, ",
"here's some information on anemia",
". Combined with ",
"an article on hemoglobin",
", and we find that the hemoglobin concentration for the average adult male is 13.8 to 18.0 g/dL (grams of hemoglobin per deciliter of blood). Let's go for the best case scenario and say 18 g/dL.",
"The article on anemia says that anemia is life-threatening when hemoglobin concentrations reach <6.5 g/dL. So hemoglobin can drop to approximately 36% of max levels (for a best-case-scenario adult male) before becoming life-threatening. If we assume that hemoglobin concentrations drop off linearly over 120 days, then you'd last for about 77 days before hemoglobin levels dropped below 6.5 g/dL.",
"As for symptoms:",
"Most commonly, people with anemia report non-specific symptoms of a feeling of weakness, or fatigue, general malaise and sometimes poor concentration. They may also report dyspnea (shortness of breath) on exertion. In very severe anemia, the body may compensate for the lack of oxygen-carrying capability of the blood by increasing cardiac output. The patient may have symptoms related to this, such as palpitations, angina (if preexisting heart disease is present), intermittent claudication of the legs, and symptoms of heart failure."
] |
[
"Once the bone marrow is destroyed, the number of blood cells starts dropping, but death won't be from a lack of red cells but rather from the inability to produce new white cells. As time goes on they will be increasingly vulnerable to infection and will die from that. So it wouldn't be immediate, but certainly within a couple of weeks."
] |
[
"Do both magnets and gravity behave differently at hot and cold temperatures?"
] |
[
false
] |
Relating to electronic components with heat and lack of heat, does a magnetic bond strengthen or weaken depending on what the temperature is? Same question regarding gravitational force.
|
[
"Magnets: The bond doesn't generally weaken or strengthen with temperature, but permanent magnets will undergo a phase transition at some point causing the spins that add up to create a coherent magnetic field to randomize. This will cause two \"bonded\" magnets to no longer attract each other.",
"Gravity: Whereas a permanent magnet is a collection of dipoles oriented in the same direction, all matter attracts all other matter gravitationally, so there's no way any analogous phase transition can occur."
] |
[
"While technically true, this effect is entirely negligible until you reach temperatures such that kT is comparable to mc",
", where m is the mass of a particle in the system. For something as simple as hydrogen, this is on the order of ",
"10",
" K",
"."
] |
[
"Gravity: Whereas a permanent magnet is a collection of dipoles oriented in the same direction, all matter attracts all other matter gravitationally, so there's no way any analogous phase transition can occur.",
"There is a correlation between temperature and gravity though. If I increase the temperature of a system, I increase its energy. Since the stress-energy tensor is the source of the gravitational field, the energy of the system affects its gravitational interaction."
] |
[
"When we hold an image too close to our face, we see it as blurry. Is it possible to intentionally print a blurry image so that when held at the same distance, it becomes in focus?"
] |
[
false
] |
[deleted]
|
[
"If we print something that is blurry, then holding it close will only make it blurrier! Our eye has a lens behind the pupil that focuses the image into a smaller image, which can cause out of focus images.",
"You may want to take a look at this: ",
"http://en.wikipedia.org/wiki/Focal_length",
"Anyway, what do you mean by an inverse blur?"
] |
[
"Nah, if you print it blurry then you miss details which could otherwise be seen when focused properly. The brain can do a lot, but it can't add details on its own. "
] |
[
"That's not how it works. Glasses improve focus: how you perceive the image, not the image itself. The image is what it is, you can try to focus as much as you like but you won't create detail that isn't there. Otherwise, we could store an 1080p film on a floppy disk.",
"There are plenty of ways to create optical illusions so that our perception of an image varies on our distance from it, but we can't display two states in one pixel.",
"Alternatively, just find a near-sighted guy."
] |
[
"How exactly does quantum tunneling work?"
] |
[
false
] |
Spurred by (hover over red button), I realized I never fully understood how quantum tunneling works from P-Chem. How exactly does a particle without enough energy pass through a mountain of potential energy?
|
[
"Because the mountain is not infinitely high. Let's think about 1-dimensional solutions to the Schrodinger equation. The solution to the equation is completely determined by the choice of the potential. In quantum mechanics, if a potential is not infinitely high, then the wavefunction is nonzero on the other side of a potential barrier, even if the energy of the incoming waves is less than the potential energy barrier.",
"This is sort of hard to describe in words, but you can play with these ideas yourself in this physics applet:",
"http://phet.colorado.edu/en/simulation/quantum-tunneling",
"Try varying the height of the potential barrier and the energy of the incoming wavepacket. You'll see that the wavefunction never really goes to zero on the other side of the barrier."
] |
[
"Using Tex the world",
"If we have a barrier on the right with a particle/wave coming in from the left",
"~~__",
"_",
"Where the barrier has some height V(x)=V solutions to the Schroedinger equation will look like",
"[;\\psi (x)\\sim e ",
" k x};]",
"to the left, and right, of the barrier, ",
"[;k=\\sqrt{E};]",
"In this case",
"[;k\\in\\mathbb{R};]",
"And [;\\psi(x);] is a wave, like a sine or a cosine. ",
"Inside the barrier however",
"[;k=\\sqrt{E-V};]",
"For tunneling we are concerned with ",
"[;E< V;]",
"and therefore",
"[;k\\in\\mathbb{C};]",
"and [;\\psi;] becomes a decaying exponential in that region.",
"The problem is obviously considerably more involved than this, reflection and transmission is not taken into account. But this is mathematically how it works. "
] |
[
"Mathematically, it's because when you solve Schrodinger's equation for non infinite potentials you get an exponentially decaying wavefunction instead of a classical region of non existence.",
"Physically? I have thought about it a little for particles. When they are incident on a barrier they do not instantly lose their energy, but dissipate it in a finite time. If the barrier is thin enough, it can tunnel. As for systems like the harmonic oscillator, it hurts my brain. "
] |
[
"Is there a limit to the amount of available randomness in the universe?"
] |
[
false
] |
I'm not sure if this should be categorized as physics or mathematics.
|
[
"I don't understand the question. Define \"available randomness\"."
] |
[
"If you are referring to entropy and thermodynamics, then yes, the limit would be heat death of the universe. This will occur when everything is the same temperature, so no more work can be done, basically meaning that the world is at maximum disorder."
] |
[
"It's maximum disorder, though it may not seem like it.",
"\nThe disorderness of something can be defined as its likelihood to occur randomly.",
"\nIf you were going to randomly distribute all energy across the universe, the chance to get an even distribution is absurdly high.",
"\nMeanwhile, the chance to get a distribution even remotely resembling how it is right now is absurdly low. ",
"You can read more on ",
"wikipedia",
"."
] |
[
"Why do you lose consciousness in a rapid depressurization of a plane in seconds, if you can hold your breath for longer?"
] |
[
false
] |
I've often heard that in a rapid depressurization of an aircraft cabin, you will lose consciousness within a couple of seconds due to the lack of oxygen, and that's why you need to put your oxygen mask on first and immediately before helping others. But if I can hold my breath for a minute, would I still pass out within seconds?
|
[
"Because when the air pressure drops, the partial pressure of oxygen in the air drops lower than the partial pressure of oxygen in your blood - and as your lungs aren't strong enough to hold pressure in, the pressure in your lungs drops to be about the same as the outside.",
"So the oxygen diffuses out of your blood and into the air. At the same time, the carbon dioxide does, too - which means that the acidity sensors that tell you that you need to breath don't trigger, so you don't realise that you need to breathe.",
"By breathing air enriched in oxygen, the partial pressure increases, allowing oxygen to diffuse into your blood as it should."
] |
[
"This is the correct answer you're looking for OP. Low atmospheric pressure hypoxia is fundamentally different from garden variety respiratory depression because the partial pressure of oxygen is so incredibly low at those altitudes, oxygen reverses flow from the body into the air because normal flow of oxygen from the alveolar to blood and then tissues requires a narrow range of oxygen partial pressures and if it's disrupted, oxygen can flow the wrong way triggering hypoxia response much faster than if oxygen is simply cut off but partial pressures remain standard as they are at our everyday living sea level."
] |
[
"Keep in mind that pressure and volume are inversely related. So if he holds his breath during depressurization, his lungs would expand due to the pressure decreasing. He may eventually be unable to hold his breath due to the volume of air in his lungs expanding. This is why when you get trained for SCUBA diving, they tell you to always breathe out when ascending (the pressure is going down)."
] |
[
"Could a solar sail spacecraft carry its own laser emitter to provide propulsion or does a laser push its own emitter backwards?"
] |
[
false
] |
There’s a classic physics problem that asks why we don’t put fans on our sailboats to power our boats when there’s no wind? The obvious answer is that the fan will always provide equal or more impulse in the opposite direction than it provides to the sail. Does this same principle apply to solar sails? If you had lasers on the back of a space ship pointed at solar sails in the front, would you move or would you end up stuck in place, i.e. do lasers apply a force back onto their emitters? If they do, much like how you can have a fan boat that just uses the fan for propulsion, no sail involved, could you just power a spaceship by just firing lasers in the opposite direction? I get that this kind of defeats the purpose of solar sails which are supposed to be super light and capable of traveling without needing a power source that could run out of energy. Plus solar sails would either be powered by the sun or massive solar arrays on earth which would provide much more energy and impulse than what the ship could carry with it. I’m more just asking from more of a theoretical standpoint than a practical one.
|
[
"The obvious answer is that the fan will always provide equal or more impulse in the opposite direction than it provides to the sail.",
"This isn't why we don't do that. Not that Mythbusters is scientifically rigorous, but they did make some cool experiments and in this case, they got it right. ",
"You certainly can power a sail boat by blowing a fan into a sail",
". While it's true that the fan is blowing the boat \"backwards,\" the air molecules bouncing off the sail will bounce back with some speed, meaning the change of momentum of the air hitting the sail is higher than the momentum of the air leaving the fan, so the the net change of momentum still is forward (you can think of situations like this as black boxes. Draw a box around the entire contraption, and see where particles are leaving the box, and with what momentum. That will determine the motion of the object, you don't have to concern yourself with what is happening in the box). A more practical example of this phenomenon is ",
"thrust reversal",
", which is how a jet aircraft comes to a stop, even though their motors are still running the same way as when they take off. ",
"So, why don't we power sail boats this way? Because it will always be better to just turn the fan around, and blow. The same for your solar sail question. Yes, you could shine a laser at your solar sail to propel your aircraft, but instead you could just point your laser backwards and propel yourself that way."
] |
[
"This isn't the answer I expected and I love it more because of that. Thanks for the knowledge internet stranger!"
] |
[
"Black doesn't really make light disappear, it just converts it to heat and re-radiates it as infrared.",
"This infrared produces thrust.",
"For a thin black sail, both sides of the sail are hot and both are producing thrust. Not much motion happens.",
"For a thick (insulating) black sail, a dark-colored blanket, or an asteroid the size of a golf ball, the heating is uneven so the thrust is uneven and mostly pushes away from the light. For the important case of a small spinning asteroid (most asteroids spin), ",
"the thrust is offset from the direction of the light",
" because the hot side is continually rotating into shadow while still cooling down and producing thrust."
] |
[
"What happens inside the body to make someone \"Wake up\" from a coma?"
] |
[
false
] | null |
[
"First, there needs to be an understanding that a coma is most likely the result of a traumatic brain injury and therefore, the outcome for coma and vegetative state depends on the cause, location, severity and extent of neurological damage. ",
"Following this, if people are to actually wake up from a coma, there is usually extensive damage to their bodies or brains; they may start waking up from a coma for perhaps only minutes a day to a few hours to fully functioning. ",
"Certain researchers (for a good review go ",
"here",
") have inserted electrodes into the thalamus and delivered electrical impulses that has caused people to wake up from comas, so thalamic activity (in short, the thalamus is essentially a relay station in the brain between the brainstem and cortex + a whole lot more), and cross talk between different areas of the brain are thought to be necessary. Additionally, research in watching the brain go under anesthesia, with a technique called fEITER, (cool article ",
"here",
") seems to suggest something similar: that there is a communication interruption in the brain, resulting in the loss of consciousness. "
] |
[
"Clearly it will depend a great deal on the cause of the coma and there are many causes, which we can think of as either primarily neurological, or not.\nThe non neurological causes are the easiest - these are when a process that causes usually some sort of general metabolic upset effects global brain functioning. This would include coma caused by uncontrolled diabetes, (either very high or low blood sugar levels), drug overdoses, abnormalities of blood chemistry such as high or low sodium levels, or very severe infections other than in the brain. When the underlying problem has been treated, or the drug has been metabolised, then the patient will gradually wake up from the coma.\nFor a primary neurological process to cause a coma it is usually fairly extensive, or has particularly effected a portion of the brain involved in wakefulness (the brainstem area). These may well result in irreversible damage and so some patients may show very little recovery at all from the coma. However some causes, especially traumatic brain injury, result in an area of localised swelling (oedema) around the damaged area. While the damage may be irreversible, the oedema will often improve over a period of days to weeks, and this is often responsible for improvements seen early in the course of recovery."
] |
[
"Tack on question: What leads up to this? During the coma is the body preparing for waking up or is it something sudden?"
] |
[
"How does glow in the dark work?"
] |
[
false
] | null |
[
"The main thing behind is called phosphorescence. Googling can produce lots of info with that term.",
"For info, here is a quick summary:",
"Basically, an electron goes trapped in a meta-stable high energy state. It will eventually decay. How long that takes depends on several things, but the point is that it will take an amount of time that you or I could notice (not nanoseconds).",
"When the electron does lose the energy (relaxes), it does so by releasing a photon. That is the light that you see. Repeat with billions of atoms in a glow in the dark object and there you have it."
] |
[
"Which type? Glow in the dark paint, glow in the dark frisbees, watches with nightlight, fireflies or glow sticks?",
"Chemiluminescence is typically mixing an oxidizer with a phenol in presence of fluorescent dyes (fluorophores). The oxidation/chemical reaction releases energy that is absorbed by the dye which is excited and releases photons of different wavelengths. Luminol chemiluminescence is another type you see on CSI shows. Fireflies use luciferase, ATP and oxygen. Phosphorescent paints/plastics absorb visible light photons and releases them slowly. Some watches had phosphors mixed with a radioactive substance like tritium to glow for years.",
"Cat urine \"glows in the dark\" under a blacklight by absorbing UV energy and releasing photons in visible spectrum."
] |
[
"Good answer, I'd like to add however:",
"Another mechanism is simple fluorescence where the electron simply drops to the stable state really quickly without having any meta-stable state available to it.",
"This is how certain glow in the dark compounds work. However you need to shine some sort of light on it. This is the basis for those dyes that light up under UV light (say at a night club or rave) but are transparent and invisible when only lit up with visible light.",
"There are many minerals that fluoresce. I previously worked on florescent dyes, fun stuff.",
"Edit: I'm dumb, glow sticks fluoresce, however they never absorb outside light in the process. It is the result of a the chemical reaction that produces the dye in an excited state."
] |
[
"Do black holes really appear 'black'?"
] |
[
false
] |
I know we presume black holes to be black because their gravity is too immense for even light to escape. What about the light that passes just along the event horizon? Doesn't it bend around the black hole as an orbiting satellite would do? My question is that if light was heading towards the black hole from all directions and much of it bending around it, wouldn't the black hole appear bright like a star?
|
[
"black holes that are actively consuming matter are actually quite bright, The accretion disc heats up to incredible temperatures as matter accelerates into the gravity well. ",
"Black holes that are dormant are just pure darkness. Any light that ends up in an orbiting pattern is forever lost to us, and the only thing we see is light from behind the black hole, via gravitational lensing. "
] |
[
"Yes, you are correct that given the right configuration of a background light source and a black hole between it and the observer, the black hole could act as a ",
"gravitational lens",
", just as any massive body would. The light still isn't being emitted from the black hole, just being bent around it in such a way that it appears to be coming from the black hole.",
"The required distances and black hole mass for this phenomenon to be seen means that we cannot see it in any known black hole with our instruments (",
"http://link.springer.com/article/10.1007%2FBF00640494",
" (paywall)). ",
"We still see gravitational lensing in black hole candidates, but the light is not shining straight from them towards Earth."
] |
[
"Even if the accretion disc is bright, isn't the hole itself and everything inside the event horizon black?"
] |
[
"Why is gyroscopic precision 90 degrees out of phase?"
] |
[
false
] |
I used to know this, but have forgotten..
|
[
"thats a cool explanation, but why is it 90 degrees out of phase, and not 47, or 123?"
] |
[
"If I hit the ball very hard and it was rotating slowly, wouldn't it reach its peck deflection before 90 degrees, and likewise if I hit it very softly and it was rotating very fast, could it not complete multiple revolutions before it reached peak deflection?"
] |
[
"Imagine a ball on a string anchored to some sort of floating point that violates physics. There is no gravity, and the ball is horizontal and moving counterclockwise. When the ball is on the east, you hit it down. Now instead of going north, it's going north and down a little. But it still moves in a circle, so instead of east, north, west, south, etc. it's east, north+down, west, south+up, etc. Instead of moving counterclockwise around up, it's moving counterclockwise around up+north."
] |
[
"Do bigger cat species also land on their feet?"
] |
[
false
] |
When a cat, falls, it always lands on its feet. Do bigger cat species also do this? Presumably cat-sized wildcats do, but what about bigger cats like bobcats, lynxes and cougars? I think it would be hilarious if lions and tigers could do this, but I doubt it.
|
[
"The Soviet shot put team doesn't have much to do in between the Olympics."
] |
[
"Larger animals are less maneuverable than smaller, just because of more mass, so all other things being equal, larger cats are at some penalty here.",
"Not sure just how important this is in practice. ",
"My hunch is that anything up to the size of a cougar/leopard/jaguar should be pretty good at this. (And notice that that size range is also the break for \"handle arboreality well\". Lions and tigers might just be too big to be able to do this as well as their smaller cousins.) "
] |
[
"I pity the poor grad student doing this experiment."
] |
[
"Why does choked flow happen and why it is related to the speed of sound ?"
] |
[
false
] |
I'm diving into the venturi effect (example: rocket nozzles and chocked flow happening in the admission valve of a ICE) and it seems that when the gas approaches the speed of sound, the flow starts to choke. Why does this happen ?
|
[
"To preface this answer: information about a medium travels at the speed of sound in the medium. So if you change the conditions of a flow at one point, the effect on the medium travels at the speed of sound upstream in the medium.",
"If you imagine a venturi nozzle and a flow condition where the speed of sound is achieved at the throat, and your downstream flow is travelling at greater than the speed of sound, any disturbances downstream of the throat won't propagate upstream. Picture yourself splashing around in a river where the flow travels faster than the wave speed; no one upstream of the river will be able to see your splashing around. Now there are two ways to achieve a choked flow scenario from here: ",
"If you try ",
" forcing the flowrate to increase upstream of the nozzle (perhaps by increasing power on a compressor), you end up forcing air to get to Mach 1 before the throat. If you picture it does that instantaneously before the throat, because of how supersonic flow behaves it will actually decelerate to subsonic flow just downstream of the Mach transition. And speed up again and slow down again, etc. etc.. This just creates a bunch of shocks in your convergent nozzle where heat is generated but the flow doesn't speed up. And once it gets to the throat, it hits mach 1 anyways and accelerates in the divergent section.",
"If you decrease pressure downstream, on the other hand, you get a situation of underexpansion at the outlet of your pipe system. Unlike subsonic flow where the information about the new reduced downstream pressure propagates through the system quickly and stabilizes the flow pressures and velocities, the underexpansion remains at the outlet in the form of an expansion fan. Remember: information can't travel in a medium faster than the speed of sound, and if the flow travels faster than the speed of sound, the information downstream never propagates to the rest of the system.",
"EDIT: Changed \"increase pressure upstream\" to \"increase flowrate upstream\". Your behavior from the reservoir leading up to the throat will not depend on absolute pressure of the reservoir."
] |
[
"Oh wow, that's very helpful.",
"I always felt it was very unintuitive. I knew that it had something to do with the speed of sound and propagation; but I've never seen it so laid out. I knew about flow upstream being affected by the downstream, but I never quite connected the dots that it would break down at the speed of sound."
] |
[
"If you already have the necessary background, only the last two paragraphs need to be read.",
"Choked flow is the condition where a decrease in pressure downstream of nozzle does not cause an increase in mass flow through the nozzle. ",
"In a rocket nozzle, the pressure gradient between the combustion chamber (before the nozzle inlet) and the nozzle exit accelerates the gas. The high pressure from the combustion chamber essentially shoves the gas to the lower pressure at the nozzle exit.",
"The converging-diverging nozzle is designed in such a way because at subsonic speeds, a fluid will increase in velocity when it is pushed into an area that is shrinking. At supersonic speeds, the opposite is true - an increase in area that the flow can pass through causes an increase in velocity. This relationship is derived through momentum conservation, mass conservation (continuity), and the isentropic equations for a perfect gas.",
"At the first part of the nozzle, which is converging, subsonic flow speeds up. When the flow reaches the throat, where the nozzle switches from converging to diverging, the flow will be at Mach 1 (if a high enough pressure difference between nozzle inlet and exit is achieved). Once the flow is Mach 1 at the throat, it will accelerate to supersonic speeds through the diverging section.",
"Now, to answer your question. At some point, before pressure at the nozzle exit goes to zero, the flow at the throat of the nozzle will become Mach 1 and thus the flow in the diverging section will be supersonic. The fastest way information can travel in a fluid is at the speed of sound. The ‘information’ that the nozzle exit had a lower pressure than the nozzle inlet is communicated by molecules bouncing off each other starting from nozzle exit to inlet. But when flow is supersonic, no Information is communicated upstream, molecules won’t interact in such a way that information can be carried up supersonic flow.",
"Thus, the gas at the converging section of the nozzle has no way to tell that exit pressure has decreased if the flow is already supersonic. The information being sent to it in the form of molecule interaction making its way upstream does not occur. So we should expect no changes in the flow conditions, and this includes no changes in mass flow. When flow in the diverging section goes supersonic, choked flow occurs."
] |
[
"How does sound volume add up?"
] |
[
false
] |
So, imagine I have one jet engine running, which produces 130 dB. What would happen, if i place 10 jet engines right next to each other? What would happen to the volume? Would it be 10 times louder, thus resulting in a 140dB volume? And on a more physics level, do soundwaves add up, cancel eachother out, or what?
|
[
"Here's the basic rule, if the sound sources are not intimately connected to eachother, the sound ",
" adds. This would cover your situation with the jet engines. If the sound sources are intimately connected, then things get more complicated.",
"I'll first talk about the unconnected sound sources, like your jet engines. Sound Pressure Level is measured in decibels, and is one of our standard ways of describing how much sound is begin experienced. SPL=10log10(p",
" / pref",
" ) dB where p is the acoustic pressure and pref is the acoustic reference pressure (normally 20 µPa). Sound ",
", on the otherhand is a proportional to pressure squared. So, if I have two sources, each putting out pressures p1 and p2, then the total pressure p is given by p",
" = p1",
" + p2",
" . You might recognize this as the relationship of the pythagorean theorem (which is no coincidence!).",
"Putting that back into the SPL equation, we see that the total SPL is given by 10log10(p1",
" / pref",
" + p2",
" / pref",
" ). If p1 = p2 then we get the simple relationship 10log10(2)+10log10(p1",
" / pref",
" ). As it turns out 10log10(2) is approximately 3, so ",
". Likewise, 10log10(10)=10, ",
" just like you said.",
"That brings us to another interesting point, loudness. The human hearing system is somewhat strange and nonlinear in that double the acoustic pressure does not make sounds seem twice as loud. Instead, there are a series of curves that have been empirically found that correspond well to our perception. Interestingly, though, you can get pretty far with the rule-of-thumb that an increase of 10 dB sounds twice as loud. Thus, your theoretical situation would equate to the jet engine sounding ",
". Unfortunately, damage to our hearing system is rather directly tied to sound power, so while the jet engine would only sound twice as loud, it would be 10 times more dangerous to your hearing!",
"The only real point left is constructive vs destructive interference. As I mentioned before, if your sources aren't intimately connected, then the sound powers will add. The reason for this is that the sounds are not \"coherent\" with eachother, and thus fall somewhere in the middle on the range of constructive and destructive interference. As an analogy, which actually has some solid theoretical grounding, consider a triangle with two equal sides, where you vary the angle between those sides and measure the length of the opposite side. At a right angle, you get the familiar a",
" + b",
" = c",
" relationship. If the angle is 180º, then then \"side\" is just the sum of the two sides you started with (which now form a line). If the angle is 0º, then the \"side\" is essentially 0. The first situation corresponds to \"incoherent addition\" where the sources are unrelated, the second corresponds to \"perfectly constructive\" interference, and the third corresponds to \"perfectly destructive\" interference. Because all three do come up at different times, they all have physical relevance. So the answer to your last question \"do soundwaves add up, cancel eachother out, or what?\" is simply \"yes\" on all counts."
] |
[
"Thanks for the detailled explanation! The last part was a bit confusing though. Thanks!"
] |
[
"I was worried that it might be. Here's a second try.",
"Suppose I had a series of numbers that went:",
"+1, 0, -1, 0, +1, 0, -1",
"Now, suppose that I had two of those sets that I was adding together, but I can't be certain if either series starts with a +1, 0, or -1.",
"If they both start with +1, then the sum is going to be",
"+2, 0, -2, 0, +2, 0, -2",
"That's constructive interference.",
"If one starts with +1, and the other starts with -1, then I just get.",
"0, 0, 0 ,0 ,0, 0, 0",
"Which is destructive interference.",
"If one was at 0 and the other was at +1, we might get",
"+1, +1, -1, -1, +1, +1, -1 ",
"Which we'll say is somewhere in between.",
"What's interesting is if we summed the squares for the original signal, we'd get 4. If we summed it for the constructive we'd get 16 (4 times the original!). If we summed it for the destructive we'd get 0. And if we summed it for the in-between we'd get 8 (2 times the original)."
] |
[
"Is it theoretically possible to melt pure carbon?"
] |
[
false
] | null |
[
"Here is a phase diagram for carbon",
"You can see it requires gigapascals of pressure (thousands of atmospheres) in addition to very high temperatures. The way to achieve this would be to massively compress carbon with some sort of explosion or rapid compression wave, similar to how the National Ignition Facility compresses hydrogen in an attempt to fuse it."
] |
[
"Yes, but since it has the highest melting point of any element how would we be able to hold it while melting it?"
] |
[
"It would probably be only temporary, or you could just have thick walls in which the inner part gets ablated. Probably any realization of this would use a very small sample, which could be held in the middle of a larger vacuum chamber. The main tool for holding things at really high pressure is the diamond anvil, which of course is made of carbon."
] |
[
"Chances of survival in a tsunami?"
] |
[
false
] |
I've been wondering what exactly makes a tsunami as deadly as it is. I guess from the outside, it's pretty easy to underestimate the sheer force of the water and the suspended debris but I can't help but think that some of it must be survivable provided I'm a good enough swimmer. What would be my best bet if I can't avoid the wave? On a related note, what part does electricity or swallowing to much toxic seawater have in this?
|
[
"I got dumped out of a raft on a rafting trip. I have no idea how fast the current was but it was August so, relatively speaking, current wasn't too fast and the water was the warmest it was going to get. We had been given directions on what to do if we ended up in the water: assume a sitting/reclining position with feet pointed downstream and rest with feet against a rock if you happened to find yourself at a calm point in the river. I was wearing t-shirt, shorts, Tevas and a float vest.",
"Falling in the water was the biggest shock. The lower temp just inches below the surface caused me to gasp and I didn't breathe normally for the rest of my short ordeal. I remembered to point my feet downstream but the rush of the current seemed very strong. Between trying to control my breathing and being carried along by the current, I couldn't see anyone else in the river or try to look for the aforementioned calm spot toward which I could maneuver for rescue.",
"Despite wearing the vest, the water pushed my head under several times. I remember looking up at the sun through a few inches of water and wondering how I'd get my head up to take a breath. Suddenly, the water would push me up long enough to breathe, then it would push me under again. This how people drown: silently. There's no time or energy left to scream for help.",
"I finally managed to push my feet up against a rock toward which I drifted in the middle of the stream. I tried to stay put, hoping that another raft would be along to pick me up. But the water pushing up against me from behind was really strong. I didn't have the strength to keep pushing back with my legs in order to maintain position. So I let go. Luckily, the rapid gave out shortly after that and I floated in calm water until a raft came by.",
"Tl;dr: There's very little chance you could survive what's sure to be a freezing cold ocean wave flowing at maximum force even if you could keep your fully-clothed wits about you. Which you can't."
] |
[
"I'm not sure that swimming skills would help much. Someone looking at tsunami videos ",
"estimated",
" the velocity of the recent tsunami in Japan over land near the Sendai airport at 5-6 m/s. World-caliber swimmers go about 2 m/s during a race -- but that's in nearly-perfect conditions. In a tsunami, you'd be wearing clothes and swimming in extremely rough water.",
"So you wouldn't have much choice about where you'd be going, you'd be in rough (and possibly very cold) water with tons of debris and unpredictable currents, you'd be weighed down with wet clothing, and you might be submerged at unexpected times. If you hit something stationary, it'd be like you swam into it twice as fast as an Olympic swimmer goes. Imagine hitting a pool wall like that, and then getting pinned there (the water's still coming!) while debris comes your way at that same speed and the water level possibly continues to rise -- that probably wouldn't end well.",
"If you absolutely couldn't avoid the wave, I'd say you'd probably want to find something large and buoyant and hope for the best. You really wouldn't want to swim for it."
] |
[
"That's like saying that someone who's skilled with a shovel would have a reasonable chance of surviving a meteorite impact."
] |
[
"Why do some mushrooms grow in rings?"
] |
[
false
] |
I know they are referred to as circles (or fairy circles), but the mushrooms only appear on the edges of the circle which is why I use the term "ring". To be more specific, why do the mushrooms appear on the edge of the circle and not in the center? My guess is that the ring is the product of outward expansion and depletion of resources in the center. But it's just a guess and in no way scientific.
|
[
"I don't know if we know for sure exactly why fungi that produce fairy rings only produce fruiting bodies on the outer most edges of the mycelium. I think that the #1 \"just-so\" story right now is what you've already mentioned, that is, as the mycelium grows outward there is a depletion of resources in the center, and so the fungus will want to produce fruiting bodies as far away from the center as possible. It is also important to note that by producing fruiting bodies on the edges of the mycelium, the fungus increases the area that new spores can travel to. If it were to only produce fruiting bodies in the center of the mycelium, there is no guarantee that the new spores will travel to an area that hasn't already been colonized by the same mycelium.",
"Edit: Okay, I think that I may have misunderstood the question slightly. I assumed that you knew about mycelium and your question was asking why fungi that produce fairy rings ONLY send up mushrooms on the outskirts of that mycelium, rather than the center. That is a little more unknown, but the reason that we see a fairy ring in the first place is because most of the fungi actually exists as a network of hyphal tubes that grows as an outwardly expanding circle--this network is known as a mycelium. Mushrooms, or fruiting bodies, are actually only a small part of a much larger organism whose purpose is to produce spores that will be dispersed and grow into another mycelium."
] |
[
"Not exactly. What we typically think that a fungus is, i.e. a mushroom, is actually only the fruiting body of a much larger organism. Much of the fungus actually exists as an underground network of hyphal tubes, known as a mycelium. These networks typically grow as an outwardly expanding circle, and so what we see as a fairy ring are fruiting bodies that are being sent up on the outskirts of that network.",
"http://en.wikipedia.org/wiki/Mycelium"
] |
[
"Maybe better asked in ",
"/r/mycology",
"."
] |
[
"How does circumcision affect HIV infection rates?"
] |
[
false
] |
I keep hearing everyone talk about how effective circumcision is in preventing HIV infection, but how could that possibly be true? All you're doing is removing skin! I should say that I'm very much against child circumcision, but in the interest of being intellectually honest, I would love to know what askscience has to say about it.
|
[
"Removing the penis entirely has 100% reduction in transmission."
] |
[
"The proposed mechanism is of keratinization of the glans penis. The skin of the glans penis is nonkeratinized stratified squamous before circumcision. Afterwards, it keratinizes. This is thought to reduce the adhesion and penetration of HIV to the man. Hence the reduction in female -> male transmission."
] |
[
"Seconded. "
] |
[
"Why hasn’t a cooling equivalent of the microwave been invented for mass production?"
] |
[
false
] |
I shouldn’t have to wait a whole hour when my beer isn’t cold enough goddamit
|
[
"It is easy to add heat: Just blast it with radiation. Microwaves are practical but any type of radiation would work. What is the opposite? Make the object emit a lot of radiation. Well, you can't. Objects naturally emit thermal radiation, you can avoid external radiation hitting the object and then wait for the object to cool on its own due to the emitted radiation. That takes a while and the direct cooling effect is limited to the surface.",
"You can also bring the object in direct contact with something very cold and use thermal conduction. That is rarely practical and it cools from the surface only, too."
] |
[
"... they have, in effect. ",
"Blast chillers are real, but super-cooling a carbonated beverage in a can or bottle is probably not the best idea. ",
"https://www.hotelrestaurantsupply.com/BEV-CF031AG.html?gclid=Cj0KCQiA2ITuBRDkARIsAMK9Q7MAPubsdHjCEi6rgrTiClLbpAcpnmlRk778jUDQg1a8S7jcAhHBIqUaAsVREALw_wcB"
] |
[
"That thing doesn't seem very effective. It notes that it chills from 194F to 37F in 90 minutes. That's about 1.6F per minute assuming a linear cooling curve. That means it would take 25 minutes to cool beer from 77 to 37. An ice water bath would work faster than that. See comment below."
] |
[
"Why do some earthquakes cause major tsunamis but others only minor tsunamis? What factors are at play?"
] |
[
false
] |
There was just another major earthquake in Japan ( ) that affected the region that had previously been affected by the Fukushima-related earthquake. There were reports of a 20cm high tsunami reaching the shore. This new earthquake is reported to have a magnitude of 7.3, which is more powerful than the Fukushima-quake which had a magnitude of 7.1, but it has produced a tsunami that wouldn't be noticed by a seasoned surfer. What factors are at play in causing some earthquakes to create devastating tsunamis?
|
[
"Great question. Although there is a serious misconception here to deal with first. Earthquakes of the same magnitude can indeed have completely different tsunami generating potential. However, the big Honshu Earthquake in March 2011 was a Magnitude 9, not a 7.1, so was 1000 times more powerful.",
"But back to the question as asked: Basically it's to do with displacement of water. For example, todays earthquake occurred at ",
"about 36 km depth",
". Todays slip was also at a shallow angle (as shown by the beachball diagrams - if you're not sure how to read them, ",
"see here",
").",
"Now, fault movements at depth do not often show much displacement once you get to the surface, whereas shallow earthquakes can rupture the surface quite significantly. That has the potential to move the water above it, and so generate a tsunami. Steeper faults mean a given displacement is going to move a greater volume of water, so those factors combined result in the differences seen today.",
"This animation is quite nice for demonstrating how a fault movement generates the tsunami in the first place. ",
"https://www.youtube.com/watch?v=qQ9Mw_rtDng"
] |
[
"Yes, to some extent. The reason the Boxing Day 2004 Tsunami in East Easia was so terrible in its effect was that it occurred in relatively shallow water. In a deep body of water there is more accomodation space, so the displacement can be mitigated somewhat."
] |
[
"That makes perfect sense. ",
"Does that mean it has to do with the amount of displacement relative to the amount of water above it?",
"e.g. 1m of displacement at 10m depth would be worse than 1.5m's displacement at 20m's depth?"
] |
[
"Why does the Up quark have so much more mass compared to the other quarks?"
] |
[
false
] | null |
[
"You mean \"top quark\", right?"
] |
[
"The short answer is \"we don't know.\"",
"One of the goals of the experiments at the Large Hadron Collider (LHC), is to search for the Higgs Boson. This is a so-far hypothetical particle that could be used to explain the nature of mass. The theory (called the Higgs Mechanism) is that a Higgs Field permeates all space, and couples (\"interacts with\") to all the particles that we observe to have mass. Some particles couple more strongly to the Higgs, and some couple more weakly. In the Higgs Mechanism, the mass of a particle is directly proportional to that particle's coupling to the Higgs Field.",
"So, I haven't answered your question, but if the Higgs mechanism is shown to be real, then we can at least rephrase it: \"why does the top quark couple so much more strongly to the Higgs field than the other quarks?\". We still don't have an answer, but we're searching."
] |
[
"My bad -- yes. Thank you."
] |
[
"If human cloning were legal, would a scientist be able to clone a human from HeLa cells or would the numerous generations of cells grown in the laboratory, intentionally or unintentionally, have had too many mutations to be of any use for human cloning?"
] |
[
false
] |
I've heard of these cancer cells taken from a lady named Hela Lacks (I don't remember how to spell her name). According to what I've heard scientists not only were able to keep the cells alive outside of their human host, they were able to reproduce them in the lab. In fact, according to the places I've read, they have become a sort of medical weed contaminating all sorts of places and equipment. I'm wondering what would happen if a person tried cloning Ms. Hela from the latest generations of cells.
|
[
"(It's Henrietta Lacks - check out the book about her life and the story of these cells: ",
"http://rebeccaskloot.com/the-immortal-life/",
")",
"HeLa cells are so far removed from anything that resembles human cells there's no chance you could do much with them beyond culturing them in a dish. They've accumulated uncounted genetic alterations over time. Some researchers have proposed that we should think of them as a different species, because they've altered their genome so much as to be dramatically different than non-mutant human cells. ",
"http://gizmodo.com/5990907/the-human-cells-we-use-for-research-are-kind-of-a-genetic-disaster",
"But even other cells used for tissue culture in the lab are probably not viable for this kind of experiment. Any cell that readily grows under cell culture conditions outside of their normal tissue tends to have mutations that allow this growth to happen. So any kind of cell line would be unsuitable for any kind of cloning work.",
"All this is nothing to say of the ethical problems involved. Human cloning is generally considered to be unethical, cloning using cells with known defects would be even more so."
] |
[
"That already exists"
] |
[
"The point was it would never work. All you'd get are tumours. "
] |
[
"Where does all the heat go?"
] |
[
false
] |
Ok, here's a simple problem that's been bothering me and which i haven't been able to find an answer for: Things in the world generate heat. Our bodies, most living things, our computers, factories, cars, etc. So where does all this go? Immediately the answer is "dissipated into the air": but then where? The logical assumption would be "vented into space"... but I don't understand how. Does heat just radiate without a problem into a vacuum? Does the earth act like a pot of water: only holding so much heat/water and then discarding the rest? Really simple problem but I cannot fathom the answer. Also please try to keep this on top (ie no global warming debate). Thanks!
|
[
"Everything gives off light at a frequency distribution and power proportional to their temperature. This is called ",
" So a room-temperature cricket ball in the intergalactic void would radiate light, mostly in the infrared. Each time the cricket ball emits a photon, its temperature will drop slightly, changing the frequency distribution and power of its emitted radiation. Eventually it will come into thermal equilibrium with the vacuum around it, at around three degrees absolute.",
"So too does the Earth radiate. On the side facing the sun, of course, the Earth absorbs much more light than it emits, but on the night side, the Earth radiates heat away into space."
] |
[
"Because when one object emits blackbody radiation, it's not raising the temperature of another object by exactly the same number of degrees. It's raising the temperature of a hundred billion trillion objects by an immeasurably tiny fraction of a degree."
] |
[
"That'll do it. Thanks."
] |
[
"[Mathematics] Is there a faster way to multiply (large) numbers?"
] |
[
false
] |
[deleted]
|
[
"F(n) = O(n",
")",
"That should be O(n",
") or about O(n",
")- otherwise you would be better than O(n).",
"https://en.wikipedia.org/wiki/Karatsuba_algorithm"
] |
[
"F(n) = O(n",
")",
"That should be O(n",
") or about O(n",
")- otherwise you would be better than O(n).",
"https://en.wikipedia.org/wiki/Karatsuba_algorithm"
] |
[
"What is faster to do in your head is highly subjective. Computers usually use pretty much the algorithm you describe because when done in binary you only need to do multiplication with 2",
" which can be done easily by shifting bits. ",
"The algorithm actually becomes trivially easy to do even by hand in binary. 34x12 is 100010 x 1100 so ",
" 100010\nx 1100\n 10001000\n+100010000\n=110011000\n",
"which is 408. You just write the original number once for each 1 in the other number shifted left by the position of the 1 and then sum it all."
] |
[
"For \"breakthrough\" Covid cases in fully vaccinated people that are deemed to be \"mild\" (presumably in terms of symptoms), is there still danger of other hidden internal damage (i.e. heart, lungs, etc)?"
] |
[
false
] | null |
[
"It isn't completely understood yet, but most likely no. ",
"The damage is caused by a positive feedback loop leading to either immune cells killing infected cells or the cells killing themselves.",
"Antibody responses actually inhibit this process, greatly reducing the overall inflammatory response. The antibody response is quicker and stronger in vaccinated individuals, so the cytokine storm response should be minimal."
] |
[
"Most of the damage caused by the SARS-COV-2 virus is due to an inflammatory reaction by your immune system. When you develop this condition it is called covid-19. This is called a cytokine storm, and it is an overreaction by the immune system that causes massive inflammation; usually as a result of the immune system attacking the affected tissue en mass. If you only have a mild case, It usually means that your immune system has detected and caught the virus early enough to prevent a massive infection and thus your unlikely to have the damaging cytokine storm."
] |
[
"The cytokine storm and it's inflammatory results are not the only symptoms that cause long term damage. There are neurological issues, not fully understood, but unrelated to the above, that cause long term brain fog, dizziness, and olfactory nervous problems. There are also other symptoms that can cause harm outside of the storm.",
"Recently, there have been studies that show even if you have a mild case of Covid-19 that long term after-effects can be highly (over 50%) likely in young populations (long hauler Covid.) Before spreading this outdated info anymore, please see at least these two links:",
"https://arstechnica.com/science/2021/06/even-mild-covid-in-young-people-often-leads-to-long-term-symptoms-study-finds/",
"https://www.nature.com/articles/s41591-021-01433-3?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=3_nsn6445_deeplink_PID100017430&utm_content=deeplink",
"And also continue to read up on \"long haulers\", \"Breakthrough\" cases (people that have been fully vaccinated) etc."
] |
[
"Why do some males grow so little facial hair?"
] |
[
false
] | null |
[
"That doesn't explain places like India or the Middle East."
] |
[
"Very good point. I looked up Afghanistan's climate, and it said temperatures can get as low as 15 degrees F in the winter. India has a much warmer climate in the winter at around 65 degrees F."
] |
[
"Genetics governs how much facial hair is grown, and evolution is what would have influenced perceived differences in the quantity of facial hair in different \"ethnicities\""
] |
[
"What is the scale of the largest structures that are expected to hold together despite the metric expansion of space?"
] |
[
false
] | null |
[
"Clusters and superclusters of galaxies are something like 1 million light-years and are not expanding.\nBut there is also what we call the \"cosmic web\" which is a network of filaments joining these clusters. The typical size would be 10 or 100 millions light-years. Matter is accreting to the clusters via these filaments, so in several billions years it will disappear.",
"http://en.wikipedia.org/wiki/Cosmic_Web#Large-scale_structure"
] |
[
"Metric expansion only increases the distance between things that aren't ",
" in any way.",
"You don't start seeing the effects of metric expansion until you get out to scales where the gravitation of ",
" is negligible. For comparison, our galaxy masses about ",
" the mass of our ",
" So to start seeing the effects of metric expansion, you need to look at distances so great that the gravitation of ",
" is so small you can just ignore it."
] |
[
"How do we know they're not expanding? "
] |
[
"What causes gravity?"
] |
[
false
] |
Just a quick question. Are there any recent theories or information regarding the origin of the force of gravity? I understand that the more mass an object has, the greater its gravitational influence, but I'm asking where does the force of gravity reside inside of that mass? My current hypotheses are either that it's a by-product, or some form of electromagnetism, or that it's a product of a force inside individual atoms. Are either of these viable?
|
[
"Well it actually isn't really a force. It only looks like a force due to some really interesting properties of our universe. That's the current consensus. ",
"Let's start with a basic principle. We know that all observers must agree that light travels at c, the speed of light (in a vacuum). The resolution is to realize that because they ",
" agree on c, that they will disagree on measurements of distance and time when they're moving with respect to each other. Now when they're moving without acceleration, that is a ",
" case of relative motion, and thus the disagreements on measurements of space and time are described by... Special Relativity. And since each observer ",
" whether they are moving or the other, neither measurement of space and time is more ",
" true than the other.",
"When an observer accelerates though, acceleration ",
" be detected. (feeling pinned to your seat when flooring the gas, eg) And some new math needs to come in to play to describe the disagreements in space and time measurements for these accelerated frames. Particularly as the fact that you're accelerating means that you'll disagree with measurements that you made just a moment ago. ",
"Now let's switch gears for a moment and go back to that \"knowing you're accelerating\" bit. Imagine you're in a box. The box hasn't any windows. But you're standing on the floor of it. Could you tell if the box was sitting on the surface of the earth, or if it was being accelerated \"upwards\" by a rocket in some deep space (where it's not being gravitationally affected by any nearby masses). Suppose instead of standing you were floating around in the box. Are you floating around because you're in deep space away from mass and gravity, or because the box is in free fall toward some massive body? ",
"The answer is no. In both cases, there is ",
" difference between the effects of acceleration and gravitational effects. And this is where a theory about making sure that the speed of light is universal becomes a theory about gravity. You see the math we did above for the accelerating frame? (and by \"did\" I mean \"I mentioned and ignored entirely what it is\") Well you can construct an expression of mass and energy called the Stress-Energy tensor that is related to the ",
" of spacetime around it. All of those disagreements about length and time measurements between observers in relative motion become summarized in this curvature.",
"So now we go and do some \"physics.\" Newton's framework is a little too simplistic to work in for what we need to do, so we usually work in a slightly more advanced system called \"Lagrangian\" mechanics, or its very close relative \"Hamiltonian\" mechanics. In these mechanics frameworks, we have derivatives. Derivatives are rates of change with respect to something, like the rate of change of location with respect to time is velocity. Well now you have to include additional terms where you describe not only how an object's position varies in space and time, but how space and time vary with respect to... space and time. (Because of this curvature/disagreement over measurements issue). And when you include those new terms, gravity ",
" out of the equations. Even though you didn't put in a term for a force, or a gravitational potential energy. Gravity is an emergent property of this ",
".",
"And furthermore, this new gravity gets more things right than the old Newtonian gravity did. For instance, Newtonian Gravity couldn't correctly calculate Mercury's orbit, it was off by a ",
"very tiny amount",
". When General Relativity came along, it was able to answer the question within the experimental limits. ",
"If someone had ever thought to look at the positions of stars ",
" blocked by the sun during an eclipse, they would have noted that the position appears to shift just slightly. But light is massless, Newton's gravity can't affect it. And even if we fudge Newton's gravity by taking a massless limit, it's off by a factor of 2 from what General Relativity predicted. This was confirmed in the famous Eddington Expedition."
] |
[
"\"Recent?\" No, not recent. The theory explaining gravity is called general relativity, and it's going to be a hundred years old in five years. In short, gravity is an optical illusion that results from the relationship between stress-energy and geometry.",
"I hope you take this in the most polite, constructive and encouraging way possible: Gravity's a solved problem, in all but the tiniest of details. While I think it's great that you're thinking about it on your own, you should probably be aware that it's kind of old news at this point."
] |
[
"Care to elaborate if you wouldn't mind, how does it cause two stationary bodies to move toward one another?",
"It doesn't. The presence of stress-energy changes the geometry of spacetime such that the future of a nearby small object points toward the source of gravitation.",
"Where does the acceleration of gravity originate from?",
"There isn't any. The acceleration is created by whatever is ",
" you from falling.",
"An electric field is produced from an electrically charged object. This charge comes from the loss, or gain, of electrons.",
"Yes, that's exactly unlike gravitation in every respect.",
"Where does the origin of the force of gravity come from?",
"There isn't any. It's an optical illusion. It's the appearance of a force where no such force exists. Change your frame of reference from the stationary observer to the freely falling object and the apparent force vanishes entirely.",
"What causes mass to acquire the force of gravity?",
"Objects move inertially through the geometry of the universe. The presence of stress-energy — mass makes one of many contributions to stress-energy — defines that geometry."
] |
[
"How does bleach change the colour of clothing?"
] |
[
false
] | null |
[
"The other two answers are correct, but I wanted to answer a question that you ",
" asked. Your question was how does bleach remove color? A similar question, with a really cool answer is how does bleach make my white clothes look brighter?",
"Bleach contains molecules called optical brighteners. These molecules absorb light in the ultraviolet range of the EM spectrum (which you can't see) and re-emit that light in the visible spectrum (which you can see). This is called fluorescence. Anyways, it's pretty cool because if you see someone wearing a nice, new white shirt you might think \"Man, their shirt is so bright it looks like it's ",
" light.\" Well guess what, it ",
" making light. It's converting the sun's UV light to visible light which is what makes a white shirt look so bright. ",
"This same absorption of UV light and emission of visible light is also why white shirts (and teeth) glow under a black light. Laundry detergents and toothpastes have optical brighteners in them to \"whiten\" your clothes and teeth."
] |
[
"Dyes produce the phenomenon of colour because they contain chromophores - molecules or parts of molecules that absorb electromagnetic radiation in the visible region. This then leaves only certain colours of light to be reflected from the material. Bleaches are strong oxidising agents and they are capable of breaking down these chromophores into smaller units that lack the same ability to absorb light - so the normal effect of bleach is to whiten things since all colours get reflected."
] |
[
"Bleaches tend to be either oxidizers (like to take away electrons) or reducers (like to give away electrons).",
"by reacting with the pigment molecules and either (a)removing an electron, thus breaking chemical bonds to break apart the pigment molecule, or (b)adding electrons, thus altering the chemical bonds (e.g turning a double bond into a single bond, etc) and changing the way the pigment interacts with light"
] |
[
"Do protein shakes actually help you build muscle?"
] |
[
false
] |
I'm assuming that you are eating an average American diet in addition to the protein shakes. A lot of my friends swear by their protein shakes, but I was under the impression that the average American already consumes way more protein than they need. Furthermore, I have never been told by any athletic coach to supplement my diet with extra protein in the form of these shakes--the closest I've heard from them was to drink chocolate milk after a workout. Do these protein shakes actually make a difference, or is it just a marketing ploy? edit: grammar.
|
[
"There seems to be a lot of disparity in the 1.0-1.5 grams of protein as to whether that is per pound or kilogram of bodyweight. In Arnie's bodybuilding encyclopedia I believe it says per kilogram, although I have seen both used extensively on the internet and other books. It only takes a quick Google to check that.",
"\nFor me in kgs (79) that would be between 79-118.5 grams.",
"\nFor me in lbs (174) that would be between 174-261 grams.",
"\nThere isn't even a cross over. Could you clarify at all on where it should really lie? Although I said about the quick Google with all the sources, I struggle to know which are actually reliable. "
] |
[
"There seems to be a lot of disparity in the 1.0-1.5 grams of protein as to whether that is per pound or kilogram of bodyweight. In Arnie's bodybuilding encyclopedia I believe it says per kilogram, although I have seen both used extensively on the internet and other books. It only takes a quick Google to check that.",
"\nFor me in kgs (79) that would be between 79-118.5 grams.",
"\nFor me in lbs (174) that would be between 174-261 grams.",
"\nThere isn't even a cross over. Could you clarify at all on where it should really lie? Although I said about the quick Google with all the sources, I struggle to know which are actually reliable. "
] |
[
"as an extra question that bothered me for a while: what if I just eat meat for dinner everyday? can that be enough/better than those protein shakes?"
] |
[
"We've reached > 500 panelists!"
] |
[
false
] |
*Welcome, new panelists! * I had a 22-day backlog in processing panelist applications, but that's behind us now. If there's a typo, wrong color, or just plain wrong tag text, please let me know! Also, if you think you've been skipped, now's the time to tell! It was quite a list, so I'm sure there are mistakes here and there. ** Regardless, go forth and answer questions! ** Also, a reminder: Above all, keep in mind the guidelines in the right side-bar.
|
[
"As a lurker in this subreddit I genuinely thank all the awesome contributions people have done, I've learned a lot, it's like a turn based discovery channel."
] |
[
"Who wants old cookies?"
] |
[
"I've learned a lot, it's like a turn based discovery channel.",
"Does that mean we'll have ice trucker, logger, and crab fisherman contributors? "
] |
[
"Since energy cannot be created nor destroyed, where did it come from?"
] |
[
false
] | null |
[
"There are two schools of thought on this. Neither one is unambiguously correct; both are basically valid.",
"One school of thought says that the universe has some total energy, and that that total remains constant. If you were God, and thus you were omniscient, you could add up all the energy in the universe at any instant of time, and find that it's the same as the energy at any other instant of time. That means the total energy of the universe ",
" is exactly the same as the total energy of the universe that the very instant of the start of the Big Bang.",
"In other words, the universe just ",
" some constant total energy. It's an intrinsic property of the universe that doesn't depend on anything at all. It just is.",
"The other school of thought says that if you describe some types of energy with positive numbers and other types with negative numbers, you find that the total energy of the universe at all times is ",
" This is different from saying the total energy of the universe is ",
" because it implies that energy in fact ",
" be created, as long as the amount that comes into existence is exactly balanced out by an equal amount of the other kind of energy. As long as the total sums to zero, it doesn't matter if you have one unit of each kind, or a hundred billion trillion units, because they cancel each other out exactly.",
"Of course, this may sound like mathematical trickery of the sort from which accounting scandals spring forth. But it actually makes a lot of sense. You see, in classical mechanics the total energy of a closed system is equal to the sum of all the kinetic energies ",
" the sum of all the potential energies. It's this total that stays constant over time. When a mass oscillates at the end of a spring, potential energy gets converted to kinetic and back to potential again. In the real world, with real masses and real springs, some of that energy becomes heat along the way and radiates outward, but if you ignore that and just consider an ",
" spring-and-weight system, you find that the total energy is the sum of the kinetic energy in positive numbers and the potential energy in ",
" numbers.",
"If this principle holds true for the universe, then it's not necessarily the case that energy can't be created or destroyed. Only a more subtle rule applies: energy can only be created ",
"From where I sit, there's a lot of acceptance of this basic idea in principle, because it just makes so much ",
" But it's not known for a fact that this is in fact true in our universe. It's known that as long as time-translation symmetry holds — and it does appear to do so, all the way back to the first instant of the universe — the total energy of any closed system must be conserved. But whether the universe started out with some quantity of energy which never increases or decreases, or whether it started out with ",
" energy but the total energy and potential energy can fluctuate wildly as long as they remain equal to each other, is not known. On the scales we interact with, it turns out both of those reduce to exactly the same thing, so it's not clear just how to distinguish between them practically."
] |
[
"The universe was opaque to light until about 380,000 years after the Big Bang.",
"This line really piqued my curiosity.",
"I found a bit of reading material on this idea",
" in case anybody else finds it interesting. I'd be fascinated to hear/read a bit more about it too if anyone wants to provide.",
"It makes sense from the few sentences I've read (too much energy in the universe still at that time), but the whole concept is entirely new to me. "
] |
[
"Of course, the third school of thought on this, which I advocate, is that energy can't be defined for the universe as a whole, since the FRW metric doesn't have a timelike Killing vector, and so it is meaningless to talk about the global energy of the universe."
] |
[
"What actually makes us be warm blooded? What is the actual mechanism?"
] |
[
false
] |
Like, I know warm blooded animals maintain their temp internally and cold blooded animals don't, but does that happen is my question. Also, could a human get an operation that would convert them to being cold blooded, like a lizard? If so, would you need a lot less food? I know this seems like a stupid joke question, but I am actually serious and curious.
|
[
"An area of you brain called The hypothalamus regulates temperature. Certain conditions can muck up with this - e.g. when you are fighting a bacterial infection your body makes itself warmer, or when you take certain drugs, e.g. alcohol can make you hypothermic - but without the hypothalamus you would die (it has other functions involved with the endocrine system, e.g. regulating growth, metabolism via thyroid hormones etc) so I don’t think there is any way you could become ‘cold blooded’.",
"Temperature itself uses a multitude of systems including sweating, dilating blood vessels close to the skin and reducing metabolic rate to cool the body, and shivering, diverting blood to the internal organs and increasing the metabolic rate to heat the body."
] |
[
"In addition to the items discussed on other comments, there are also some tissues specifically meant for generating heat. Brown adipose burns through a relatively large amount of energy keeping babies necks the right temperature. (probably mostly for the spinal cord?) Adults have brown adipose too, but it’s less clear the purpose, at least according to Wikipedia."
] |
[
"A human, or an endotherm for that matter, would not be able to undergo an operation to become an ectotherm (cold-blooded). The term \"cold-blooded\" actually misconveys the idea of ectothermy. It's not that a lizards blood is cold, but rather they have to use outside sources to gain body heat (sunbathing for example). Endothermy (warm-bloodedness) actually mediated the evolution of mammals.",
"Endotherms generate body heat through metabolism and don't require outside sources of heat. They've developed different mechanisms of managing that heat to either stay warm, or to cool down. Mechanisms of managing heat include countercurrent heat exchange, vasodilation or vasoconstriction, sweating, and more as well as behavioral methods. The hypothalamus can be considered as the thermostat, however, the source of heat comes from metabolic processes."
] |
[
"What causes logs to turn white while burning, and why do moving black patches appear?"
] |
[
false
] |
I was camping this weekend, and I noticed that the burning logs that were already white had black patches moving up and down the log. What causes this phenomenon?
|
[
"The ash that is produced is composed of several products. Some of of it is incompletely combusted carbon which tends to be black. Other components are due to other elements in the wood such as magnesium which forms white magnesium oxide when burned. The colour fluctuations you see while it is burning is due to blackbody radiation. When a surface doesn't emit light of its own (luminescence) it is considered black. When heated, the body starts to emit radiation at low frequency first (infrared, which we feel as heat). As it gets hotter, the frequency of the radiation increases to red, orange, and then white. The hotter the object the higher the frequency of radiation emitted. The temperature in the fire fluctuates due to convection currents causing areas of the wood to change temperature resulting in the colour of the blackbody radiation to change as well. When it's very hot it appears white, if it cools off it appears black again."
] |
[
"This is speculation, but the dark patches may be emitting light as well, just not as much so they appear dark. Sunspots, for example, are very bright but appear dark since they are less bright than the surrounding solar material."
] |
[
"The white product of wood combustion is ash.",
"I'm not certain about the moving black patches though. Another reaction? Heat disturbing the layer of ash? I have wondered about that myself."
] |
[
"[Physics] I have a couple of questions about gravitational waves?"
] |
[
false
] |
Idk if this is the right sub for this and I'd previously posted on the megathread a week or so ago but here goes: I was reading an article on the NY Times app, and at the end of it it says "only three days before the black hole chirp...antenna readings were plagued by radio interference." and earlier was mentioned how a group known as Bicep "claimed to have detected gravitational waves...They later acknowledged that their observations had probably been contaminated by interstellar stardust." So could it be possible that LIGO's readings were polluted by radio interference? Also, did VIRGO or any of the other interferometers detect the same as LIGO did? Thank you in advance.
|
[
"In reverse order:",
"Unfortunately, there were no other gravitational wave interferometers running that could have detected the signal that day. This would have not only provided more data, but also allowed better spatial localization of the source.",
"Could this be radio interference? Very, very unlikely. The black hole merger signal is very distinctive, and would not be simulated by things radio interference. In addition, radio interference would not take the same form at Livingston and Hanford with a 7 ms separation.",
"One of the initial possibilities, which was ruled out, was whether the signal might have been an accidentally unlogged data injection -- a simulated signal which can be sent through so they can see how the whole process is working -- as other than that, it's hard to imagine how a signal of the given form would be generated. But radio interference just wouldn't create something that looked like two black holes merging."
] |
[
"Thank you for your answer. Much appreciated."
] |
[
"The fact is, gravitational waves could help us learn about dark matter! G-waves are a new way to see the Universe, since before their detection we could only use electromagnetic radiation (light) to observe cosmological phenomena, and light is pretty useless when dealing with dark objects such as black holes and dark matter "
] |
[
"Cleaning and Seasoning Cast Iron: What's Going On?"
] |
[
false
] |
Two-part question, that arises from reading through a good deal of advice on the web that's sometimes contradictory, usually anecdotal, and often lacking hard information to justify why a given method is superior: First, what's an ideal way of cleaning cast iron cookware (regular iron, no chrome coating or enamel) that has burnt, crusted food and perhaps some rust on it? Methods I've heard include: • Soaking in a lye-water solution • Using electrolysis • Running the iron through an oven's self-cleaning cycle • Soaking in a vinegar-water solution What would any of the benefits or drawbacks of these be/why is one method more effective than another? From what I've read so far, some only work for the crusted food/grease (lye and the self-cleaning oven) whereas others are just for the rust (vinegar). So far I've only heard caution on the self-cleaning for the heat (concerns that the self-cleaning cycle would be too hot and cause the iron to change composition somehow and irremediably rust over), and the vinegar for the possibility of an excessively long soak dissolving too much of the iron. Second, what's really the ideal way of attaining a good seasoning on a pan? I know that taking a clean pan coated with oil and heating it will cause the oil to transform into a nice smooth surface, and with age this gets better, but especially after cleaning a pan down to the iron, I'd want to know what is most effective for speed and quality. For example, one quick seasoning method I've read involves coating the pan with a really thin layer of oil, throwing it into an oven upside-down, heating to 500 °F, letting it cook for an hour, then turning the oven off and leaving it for a few hours until it cools down - variations include getting the pan hot before adding oil, using temperatures lower than 500 °F, choosing oils with high smoke points, etc. What's ideal in your view (or what's unnecessary) and, most importantly, why?
|
[
"I just picked up a cast-iron skillet from a second hand store and had some of the same questions. I came across a site that uses some science based techniques and goes into a little further detail as to why seasoning is important and how it works. The site can be found ",
"here.",
" The lady seems pretty knowledgeable on the subject and I am thinking about using a variation on her technique. "
] |
[
"Thanks for the link - yes, I'd seen that post, but then read elsewhere that the oven method of seasoning can damage a pan - so I wanted to get some other folks to weigh in. (I think the oven is safe, but I know nothing about polymerization of oil onto iron etc.)",
"Yeah, I just got an old (1890s I think) skillet myself that puts my non-stick stuff to shame. Astoundingly better than the rough-texture new stuff one finds in the market."
] |
[
"Soaking in a lye-water solution",
"That'd work. Seems kind of over-kill though. Why not just use a metal brush (at worst)?",
"Using electrolysis",
"I don't see how that'd work, really. And it wouldn't be the most practical method even if it did. Electrolysis is used for removing patina from silver, but that's a whole different thing. ",
"Running the iron through an oven's self-cleaning cycle",
"That'd amount to burning the junk off. It'd probably work too, but again, seems like a waste of energy just for a pan. (actually I think it's a waste of energy in general.. it's a stupid way of cleaning ovens. Do modern ovens even have that functionality anymore?)",
"Soaking in a vinegar-water solution",
"Would be less efficient than lye, and corrosive to the pan. Although lye is more dangerous to handle. (use rubber gloves and goggles)",
"I'd just clean it with a brush and detergent after letting it soak for a half-hour or so in hot water and detergent. A wire brush if necessary, which removes the rust as well; as it shouldn't be more than just some surface rust anyway. After that, just rub some oil on there and wipe off any excess oil. The point is just to keep the thing protected from air/water, so it doesn't rust. If you heat the oil, it'll flow easier and you'll have an easier time coating it with a thin layer, but the elaborate procedures you're describing sound like massive overkill really. ",
"Bear in mind that rust, at the quantities you'd get it from a skillet, is harmless. If anything, it may be beneficial; people (in particular women) are often closer to having an iron ",
" than toxic levels of it."
] |
[
"Election diffraction confusion."
] |
[
false
] |
I was curious to know whether or not the two angles produced when electrons are accelerated towards a crystal (of unknown material) are due to two separate planes (with 'n=1' substituted to the Bragg equation nλ=2dsin(θ)) so there are two separate plane separations 'd'. Or alternatively, it would be due to n=1 and n=2 producing different diffraction angles. I cant seem to find any mention of the integer values of wavelength in any documents online and I assumed that because the incident electrons have the same energy that the De Broglie wavelength had to be the same. In which case, the first idea would be correct.
|
[
"What do you mean by \"the two angles?\" Electrons will be diffracted by a crystalline material at a number of angles, each corresponding to a certain crystallographic plane with a reflection allowed by the structure factor. So each diffracted beam is due to a different d-spacing. the different n values in the Bragg equation correspond to higher order reflections, but these can generally be ignored. Does this answer your question?"
] |
[
"Yes, sorry about being vague in my question. I was discussing a problem with one of my peers after a lecture on the topic. The two angles are the angles produced when electrons were fired at a crystal film to produce a cone shape of diffracted electrons that hit a screen to produce two rings (from the two cones). "
] |
[
"Okay, so in this case you had a polycrystalline sample. This gives diffraction rings rather than spots because the electron beam hits enough randomly oriented crystallites to cover all azimuthal angles. ",
"For the material and 2theta range you measured, the sample gave two diffraction rings. These originated from the two diffraction angles satisfying both the Bragg condition and the structure factor selection rules specific to that material. ",
"The reasoning is kind of complicated but, in crystallography, you can ignore the higher order (n > 1) reflections. Also, to answer one of your other questions, an electron beam will typically be mono-energetic. Prior to hitting the sample, they will all have roughly the same wavelength."
] |
[
"Can you fill a black hole?"
] |
[
false
] |
No matter can escape the gravity if a black hole, but what happens to the matter in the hole and could you "fill it up"?
|
[
"That becomes a very complicated topic very quickly. The simple answer is: probably.",
"The reason we \"need\" dark matter is because of supermassive black holes. These are black holes at the center of almost all, if not all, galaxies. They have masses ranging between 10",
" - 10",
" (maybe 10",
" solar masses. The issue with these large masses is that no current accretion (mass falling onto/into an object) models can explain how these black holes became this large in the timespan of the universe, if they began as 10-100 solar mass black holes (the expected black hole mass left after a very massive star goes supernova). ",
"Now dark matter could come into this in two ways. If dark matter is included in the accretion models, that could possibly explain how the black holes became so large (since dark matter is about 25% of the universe while baryonic matter is only about 5%). But the moment you bring dark matter into the accretion model, you must also consider other effects. There are feedback processes in accretion that occur. The faster an object accretes matter, the more radiation is produced by that matter (simply because higher density and/or higher velocity produces more collisions and radiation from charged matter). That radiation would slow down the accretion of baryonic matter. To add on top of that some of the more promising dark matter candidates are their own antiparticle. So when they collide with each other, they release even more radiation (and a lot of it). This is not generally observable because the density of dark matter in most of the universe is not high enough (the cross section of these candidates is very small). But near black holes that density would be much higher and dark matter collisions could become very common. That would lower the rate of dark matter accretion, just because the dark matter is annihilated, and the radiation produced would further slow the accretion of baryonic matter. So you can imagine how complicated accretion models could become.",
"The other way dark matter could be included is through dark stars. These are a proposed star that initially forms from a large amount of dark matter gravitationally clumping together. This clump would slowly self-annihilate. Meanwhile, baryonic matter would fall onto the dark star. It's possible that eventually all, or at least most, of the dark matter self-annihilates and all that is left is baryonic matter and we get a normal star. But this star could be much, much more massive than the stars we've observed so far. Thousands to hundreds of thousands of solar masses. This occurs because the dark matter core allows more gas to accrete before fusion begins. Once fusion begins the radiation would push away any more gas from falling onto the star. These very massive stars could form very massive black holes, hundreds to tens of thousands of solar masses (maybe larger). That may be a massive enough beginning to eventually become a supermassive black hole from standard accretion processes.",
"But there is also a theory that dark matter is not required. It's possible that very massive black holes could have formed from the spacetime fluctuations of the very early universe or even from the Big Bang itself.",
"The explanation for supermassive black holes is still a very open subject. Dark matter could be an explanation, but it's not necessarily ",
" explanation."
] |
[
"The event horizon of a black hole scales with the mass of the black hole. r_h=2GM/c",
" for a Schwarzschild black hole, where M is the mass. What we really mean by the mass of the black hole is the energy content of the black hole (since E=mc",
" So any energy that crosses the event horizon is added to that total energy content, be it photons, baryonic matter, or even dark matter. So no, you cannot \"fill up\" a black hole. It will just continue to grow."
] |
[
"Do we 'need' dark matter to make our expectations of black holes' sizes match observations?"
] |
[
"How can ants lift up so much weight if they are so tiny? What are their muscles like?"
] |
[
false
] | null |
[
"It's nothing special, just a side effect of them being tiny. An ant-scale piece of your muscle could probably lift about the same amount. A human scale bit of ant muscle could lift about the same amount as you could."
] |
[
"It's not necessarily that their muscles are different in any fundamental way (although I'm sure there are difference between your muscles and ant muscles, these differences do not account for the apparent difference in strength). It's simply a result of ",
"allometric scaling",
". The strength of a muscle is proportional to its cross sectional area. In other words, it scales as a square of the radius of the muscle. Volume and weight, however, scale as a cubic powers of linear measurements like muscle radius and body length.",
"So it's really just the result of a basic fact about geometry, in that as x increases (where here x is some linear, i.e. one dimensional, measure of size), x",
" increases faster than x",
" and thus body volume and weight increases faster than strength does. It's just a fundamental fact of nature, and atomfullerene is spot on, in that if you could shrink a human down to ant size, they would appear to have super human strength, while an ant of human size's muscles would be too weak to support their exoskeleton."
] |
[
"Could you please elaborate?"
] |
[
"Can rocks really move through soil? Is the ground not as stagnant as it seems? repost from /r/askreddit"
] |
[
false
] |
first round: I was talking with a farmer and he told me a story about a giant boulder appearing in a field his family has worked for decades. We live in a very sandy area in West Michigan. Does this really happen? Is it limited to sandy soil or does it happen in clay and other soils too? Thanks! Also, in my research I've found terms like "uplift" and "frost heave". Is that it? I'm researching this for work and how these moving rocks affect buried pipes.
|
[
"This certainly happens in places where the ground freezes. Many New England farmers complained about fields that every season there would be a new crop of rocks at the surface, which they would carry to the edge of the field and add to the stone fences.",
"Depending on where you live, there is an ",
"expected frost depth",
". Michigan typically freezes to a depth of 5 feet (7 feet for Yoopers). Any foundation that you build must go to below that depth.",
"The foundation also has to go straight down on the sides. ",
"If it's tapered the foundation can be lifted",
" Your rock might have this effect.",
"Any buried pipes should also be below the frost line. If they were not that deep you have bigger problems.",
"In the long run, soil above the frost depth can move in hexagon circulation cells, resembling boiling water, but ",
"moving much much more slowly"
] |
[
"Happens all the time. The process is called \"frost heaving\", and it is realy easy to grasp: When water freezes and expands, it pushes againt everything above it. Large rigid objects such as rocks have enough surface area for that force to find a purchase and are pushed upward. When the ice melts, the mud and sediment collapes in the space under the rock. The wikipedia entry should tell you way more than you really want to know (",
"http://en.wikipedia.org/wiki/Frost_heaving",
")...",
"I once came across an interesting occurence of frost heaving on a soil-less outcrop in Labrador. A cubic fracture-bound block of rock about 1.5 meters across had been jacked up out of the outcropping that way about 1 meter. Every little lamination on the block had a counterpart in the surrounding rock; twas pretty neat. "
] |
[
"Seems plausible. If you have a container with several sizes of objects when shaken the largest objects will be more likely to be near the top and smaller objects on the bottom. This is called ",
"granular convection",
". The wikipedia article even mentions stones working their way up as an example."
] |
[
"Why do we have fingerprints?"
] |
[
false
] |
Follow up: What kind of evolutionary process led them to exist.
|
[
"Tactile friction. They help us grip things."
] |
[
"Are they a function of evolution? Mutation?"
] |
[
"Everything was once a 'mutation', but the useful ones tend to stick around. Things that are useless now were once useful and we haven't 'evolved out of them' yet, i.e. the appendix doesn't have a major use anymore. Fingerprinted mammals must have performed better in their environment than their non-fingerprinted counterparts and thus it became a dominant thing."
] |
[
"CERN is trying to reach an arbitrary level of certainty to accept the higgs boson. What is that arbitrary level?"
] |
[
false
] |
This relates to an earlier post I made.
|
[
"That arbitrary level is called 5 sigma. This places the chance that the data is a statistical anomaly at 1 in 1.7 million. The Higgs is currently measured to a significance of about 3 sigma, which means there about a 1 in 300 chance that the bump they see is a statistical fluke. ",
"I in 300 seems pretty like pretty good odds, but physicists have been burned before. Also, we've performed well over 300 particle experiments, so we expect 3 sigma bumps to come up all the time. Five sigma bumps, however, are usually a sign that we've discovered something. But, just because and event is incredibly unlikely, doesn't mean it won't happen. There's a small chance that we could measure a 5 sigma bump and have it be nothing."
] |
[
"Another interesting aspect of the Higgs search (at least, I'm not sure about other particle physics experiments) is the look-elsewhere effect. Since the scientists are looking at a wide range of masses, it's to be expected that unlikely events will happen.",
"By analogy, take a look at ",
"this xkcd",
".",
"So the scientists at CERN take into account this effect and use it to determine how likely their signals are based not just on the one mass they're looking at, but instead all of the masses they're looking at."
] |
[
"In medicine or psychology or whatever maybe, but in particle physics you need to be 99.9999% certain."
] |
[
"Why does thunder rumble so long?"
] |
[
false
] |
Lightning flashes in much less than a second. Sound travels at about 340 m/s or so. Suppose a lightning stroke is 1000 meters long, and you're standing so that it points directly away from you. Then I'd expect the thunder to last about 1000/340 ~= 3 seconds. That's a pretty short rumble, considering the generous assumptions I made. Does thunder echo between clouds or something? Is heterogeneity in the air to blame?
|
[
"I'm no expert, but I'm pretty sure that most of the rumble you hear is a combination of the lightning bolt being really long, as you said, and the sound echoing off the ground and trees and houses and everything else around you. Thunder is crazy loud, so it is able to echo pretty easily even over long distances, causing the rumble to last for a long time."
] |
[
"Good you calculated that, i thought it might be nonlinearity of the medium; different frequencies of sounds going at different speeds, but i don't remember hearing that much of a different pitch over time, and doubt that sound in air is that nonlinear..(Unless at extreme amplitudes, but the lightning will only produce those very locally) Also a difference in speed of even 60m/s over 3km is merely 2s, the longer ones i have heard are at ~10s.. (Or are those strikes really 15km away? 60m/s difference seems huge though)",
"So i am ",
" that sound is bend as the sound is bend back downward as the speed of sound becomes lower at lower air pressures high up. (I mean, it bends due to different wave speeds, just as in refraction) Edit: eh maybe i am being stupid, what sort of lengths would it have to travel to be bend like that... Not really an expert reply :)"
] |
[
"It's rumble time is likely also a function of the length of the bolt. If you assume the bolt is perpendicular to the ground and 2000 feet long, and strikes 4 times during 0.3 seconds (from wikipedia article on lightning), considering it a right triangle with you at the far point, you can see that it's going to take longer for the sound of the top of the bolt to reach you than the sound from the bottom of the bolt. Echo is likely to be as strong or stronger than this though. "
] |
[
"As Earth’s land masses shift due to tectonic movements how does it impact global weather patterns? Is it measurable?"
] |
[
false
] | null |
[
"On geologic timescales (i.e., millions of years), the motion of plates and consequences thereof definitely impact climate. Some important processes (but not an exhaustive list) are 1) opening and closing oceanic gateways and resulting changes in ocean currents, 2) latitudinal distribution of landmasses, e.g., whether there are large landmasses at the poles or not, 3) development of mountainous topography and a variety of orographic effects associated with these, 4) weathering feedbacks that modulate CO2 concentration in the atmosphere, etc.",
"However, generally on (geologically) short timescales, i.e., less than a few thousand years, there are limited impacts of plate motion on weather or climate. This is largely because plate motion (and resultant things like mountain building, rifting, etc) proceed slowly. At some point, for any of these gradual processes, a particular threshold will be crossed that will induce a change (e.g., a particular mountain range reaches a height to start serving as an effective barrier to precipitation, or a rift valley connects to the ocean, floods, and becomes a new oceanic corridor, etc), and this might occur \"quickly\" but until that threshold is crossed, the very slow, gradual changes do not have a measurable effect on short term weather processes."
] |
[
"It can possibly be measurable in the time scale human have existed. ",
"That being said, you can clearly deduce that tectonics have a climate impact over long time periods. For example the creation of the Himalayas by the Indian subcontinent moving north has no doubt transformed the climate over time. Both the sheer altitude and the rain shadow that prevents monsoon rain from reaching Tibet are examples."
] |
[
"Wow. Thank you!"
] |
[
"Did some animals develop \"smell camouflage\" ?"
] |
[
false
] |
It seems like a lot of animals developped strong camouflage skills to avoid being spotted by the eye. But since a lot of predators use mostly their sense of smell to track down their prey, how come those preys did not evolve to no smell anything? For example, deers have a very strong smell, making it rather easy for wolves to them. Why didn't the deers with the weakest smell got selected by evolution ?
|
[
"There are definitely some examples that I think can be comfortably placed into this category. I'm not aware of many examples of this sort of thing with large mammals, but there are quite a few insects that use olfactory camouflage to hide themselves from predators or prey (this might just be bias on my part though, since I study insects). There are several species of caterpillars that live inside ant colonies and either disguise themselves as larvae (so that the ants feed them), or sometimes just straight up eat the ants themselves, and being able to produce the right pheromones to prevent ants from attacking them is pretty essential (see ",
"Akino et al. 1999",
" for example). ",
"Here's a cool video",
" showing how this works, and furthermore showing a parasitoid wasp that ",
" uses pheromones to influence the ants so that it can get to the caterpillars. I did find one non-insect example in the form or pirate perch, which appear to use some mechanism that is still not fully understood to hide their chemical signatures from potential prey species (",
"Resetarits and Binckley 2013",
").",
"To speculate a bit, I suspect the reason that camouflage of this sort might be less common in, say, deer as you suggest is that their predators probably aren't totally dependent on scent. As a general principle, it's clear that visual information is both more precise (since scents can spread over an area), and also more instantaneously available (since scent does not travel at the speed of light). So while scent can be useful in longer-range tracking of prey, I would guess that at a certain point predators such as wolves switch to visual tracking (i.e., once they actually find a deer and start pursuing it). Ants in contrast are much less visually oriented than most mammals, so in the example above where a caterpillar is trying to hide right in the middle of an ant colony for extended periods of time it makes sense that visual camouflage is less relevant. Of course, there are many other possible considerations as to why a species may not have evolved olfactory camouflage too: scent may be important to them for intra-specific communication, or it might just be impractical for them to refrain from producing chemicals that are important to their survival in other ways (e.g., for metabolic purposes).",
"If you are interested in further reading on this topic, I came across an entire book that seems relevant: Michael R. Conover's 2007 \"Predator-Prey Relationships: the Role of Olfaction\", the first chapter of which is available to ",
"read online here",
" (full disclosure, I did not read the book so I don't actually know how good it is)."
] |
[
"In the case of the deer, deer musk probably developed to become \"muskier\" to attract a mate. Being able to attract a mate also means being able to pass on your genes to offspring. The deer has to hope this musk doesn't attract wolves as well...",
"That is still an excellent question though, since smell can be used to repel one species and attract another, or attract a mate.",
"A very smart idea is for a fly to smell like something \"inedible\" to a bird (eg, surrounding trees) in addition to blending in visually with its environment - camouflage) I wouldn\"t be surprised to discover many insects that eat tree sap in order to 'smell like' a tree which isn't edible to the bird. This may add to its survival advantage, and ensure those genes pass on. By the same token, similar forces are selecting for improvements in bird smell acuity as well- the birds that can discern tree sap from the insects that eat it, are the ones that will survive. This \"hidden ecological war\" is occurring all around us if you look closely. And is what makes ecology fascinating :)"
] |
[
"Or, the musky buck does attract more wolves, but hasn't been eaten yet, so his muskiness is an honest signal of fitness that the female would be wise to select for."
] |
[
"When you recieve a blood donation, what happens to the DNA of the blood you recieved?"
] |
[
false
] | null |
[
"Normally, red blood cells have no nucleus at all. So no DNA there.",
"If you receive white blood cells, they generally don't reproduce, so the DNA gets digested and recycled with the rest of the cell when it dies.",
"If you receive a bone marrow transplant, it will have stem cells that can keep making more blood cells. The recipient now has blood cells with the donor's DNA."
] |
[
"Correct and it should be noted that people who receive a bone marrow transfusion can have a problem with the donor immune system attacking them. It is called graft vs host disease and it can happen in blood transfusion as well although to a much lesser extent. That is why transfused blood is ideally leukoreduced ( as in have the WBC washed off it"
] |
[
"Theoretically, yeah.",
"Practically, sometimes, we're working on it.",
"Realistically, it's often vastly simpler to make a new person than to alter an adult."
] |
[
"How does losing your sense of taste affect digestion?"
] |
[
false
] |
I was taught that as soon as your tongue detects certain tastes (e.g. sugar) your body prepares to process that food (e.g. produce insulin), but if your sense of taste is impaired, does digestion proceed optimally? Is it slowed down?
|
[
"You may delay the initial stages by a bit, but it wouldn’t make much difference overall, as long as the rest of the digestive system is intact. You can consume food without tasting anything (e.g. being fed via a tube down your nose or directly into your stomach) and still digest and absorb that food pretty much normally."
] |
[
"There’s 3 main phases of digestion.",
"Cephalic",
"Gastric",
"Intestinal",
"The cephalic phase is what would be impacted by losing your sense of smell. Basically your brain integrates all the different signals coming in before you’ve actually ingested the food (sight, smell, sound, taste) and begins the process of gastric secretion & ramping up gastric motility. ",
"Just losing your smell wouldn’t have thaaat much of an overall impact though and could probably be compensated for by the other stimuli fairly easily"
] |
[
"You're talking about sense of smell, do you mean taste?"
] |
[
"Why do wind turbines have to be placed so far apart from each other?"
] |
[
false
] |
[deleted]
|
[
"The exact distance apart depends on many factors. At my old university, there was a professor who was exactly studying this. For example, if money were no issue, then you want the wind turbines to be as close as possible! Each one would not produce very much but at that density, together they will still be better. Of course, cost ",
" a concern so there is an optimum spacing. (",
"Source",
"). Here is a quote from the source:",
"For realistic cost ratios, we found that the optimal average turbine spacing may be considerably higher (˜ 15D) than conventionally used in current wind farm implementations (˜ 7D).",
"There is also a limit to how much energy the wind-turbine can ever extract from the wind. That is because if the wind turbine extracted ",
" of the incoming energy, the air behind it would be stopped and that would break conservation of energy and momentum. It's called ",
"Betz Law",
" and is around 71%",
"Finally, you can imagine that the wind coming out of one turbine is now slower and, for lack of a better word, choppier. There is less energy in that down-stream wind. Also, turbines are like little wings. They have their own ",
"wingtip vortices",
", etc that can cause issues with down wind turbines.",
"edited to add additional comment"
] |
[
"It makes sense to have them spaced widely behind a turbine due to turbulence and diminishing returns, but i also read they should be about 4 rotor diameters apart from a parallel perspective. Wouldn't they be ok closer without affecting the other turbine's airflow?"
] |
[
"Mostly it is because the wind is slowed down when powering the rotors.",
"So the air needs some way to gain kinetic energy again, since you want the most out of your investment of the turbine.",
"Sorry, I didn't fine a source atm, but I had a lecture about it at university last year."
] |
[
"How is quantum mechanics responsible for modern-day technology?"
] |
[
false
] |
We hear this a lot but I just wanted to know how exactly quantum mechanics discoveries are responsible for the modern day technology revolution. Perhaps as a start-off point, how did it lead to the invention of a computer? Why would a computer be impossible without quantum mechanics. I have a good understanding of undergraduate level introductory physics. Am a Biology major myself.
|
[
"Exhibit A : ",
"The transistor",
". The Intel Nehalem processor has 2.6 billion of these little fellas, yes you read that right, 2.6 billion of them. Transistors are in every piece of electronics that you own, millions of them.",
"And we wouldn't know how they worked, or be able to design them without understanding how electrical conduction works in solids, and we wouldn't know that without knowing quantum mechanics.",
"And to think the study of microscopic systems was something esoteric at the turn of the previous century.",
"Exhibit B : solar cells, lasers, MRI, nuclear energy, nanotechnology, quantum chemistry, quantum biology (yes this is a thing. studying biochemical reactions, mechanics of proteins, electrons performing tap dances on a chlorophyll molecule) and more things than I care to go into. Anything you use that's not powered by muscle or steam possibly has some quantum mechanics involved somewhere in it."
] |
[
"While I agree with you, I think sarvagnap's original question could be paraphrased as: what modern technologies require an understanding of quantum theory before they can be developed?",
"We can (and did) invent light bulbs prior to discovering quantum theory. Explaining why they work had to wait but they kept us illuminated in our ignorance regardless.",
"All the technologies in BugeyeContinuum's post require a knowledge of quantum theory to show us where and how to discover them. It might be possible to develop them without that knowledge but I think the chances would be very small."
] |
[
"You can't even explain how a lightbulb works without quantum mechanics. Seriously, think about it. How does a lightbulb work? It heats up a piece of metal and the metal glows? The the hell does the metal even glow?",
"How about why things are different colors? Nope, can't explain that without quantum mechanics.",
"It's sort of amazing once you realize that you can't explain how light interacts with matter without quantum mechanics. To think that over the entire course of human history, until quantum mechanics was invented, people had to accept that things glowed red when they were heated up because... they just did."
] |
[
"How would listening to music in surround sound be in Orfield Lab's anechoic chamber?"
] |
[
false
] |
For reference, the . I'm curious as to how an 'echo-less' room would affect listening, and whether it would be an improvement or a detriment to the experience.
|
[
"The specialty of that particular room is that it's the (or at least one of) the most effective soundproofed chambers so it's incredibly quiet and it's said to be quite unsettling. The stories about it freaking people out and people being unable to stay in there are all exaggerations though.",
"Good work on that amazing in depth reaponse by the way! That was a really good read and I think I learnt a few new things from it. Thank you"
] |
[
"To my untrained and wholly subjective ear, it doesn't actually make a huge amount of difference.",
"Obviously in an anechoic chamber you remove the reverb, but note that acoustic energy decreases precipitously with distance anyway (The Inverse Square law), and your hearing system also suppresses small amounts of reverb (The Precedence Effect). So in most 'normal' conditions, reverb isn't a hugely noticeable effect anyway (again, to my untrained ear).",
"That said, anechoic conditions do clearly have a measurable effect on hearing. For example, I've observed that your ability to localise where a sound is coming from is much better in an anechoic room than that in an ordinary room (i.e., due to all the weird reverberations, acoustic ‘nulls’, etc.). However, higher order functions like music perception are affected by a huge number of factors other than reverb, so small amounts of reverb don't appear to make a huge amount of difference (again, in my opinion). This is largely to be expected, as one of the key priorities of our sensory systems is to maintain perceptual constancy (i.e., so an approaching tiger's footsteps sound similar, whether it is prowling across grass or stone). In this way, you can enjoy the same song over different speakers, or in different rooms. Of course, the sound will have a slightly different ‘colour’, and some people may prefer one ‘colour’ over another, just as you might prefer looking at a painting under one type of lighting or another. Most people, however, don’t really have a strong preference, until the conditions become fairly extreme. Even there, though, people's preferences vary (a highly echoic, concrete space can create rather interesting 'wall of sound' effects, but then it isn't great for speech intelligibility if you're staging an opera..)",
"You could, of course, test this yourself, by going into a big empty space (where reverb will also be negligible), and seeing how your favourite music sounds. Or invest in a huge load of egg-cartons and make your own approximation of an anechoic chamber =)",
"This answer is, to some extent, a placeholder, and I'm sure there are a range of views on this issue, particularly as this question largely turns on what each individual considers a ‘substantive perceptual difference’ (Criterion Setting), and what their preferences are. (NB: on which point, I'd note this isn't really a question of physics, but of how our sensory systems respond/interpret physical/acoustic differences).",
"EDIT: Follow-up: I'm not clear what, if anything is special about the \"Orfield Lab\". Anechoic chambers really aren't that special/hard to make, and I'm not sure why it is that, according to OP's link: \"Orfield himself has trouble staying in the room beyond the 30-minute mark\". I'll grant you that it's a bit weird when you walk in (not least because the floors tend to be composed of a springy, wire mesh, so it's like walking on a trampoline), but typically the overwhelming impression is one of being in a very grey, very quiet room...",
"EDIT: Also, see this related question from a little while back, regarding whether 'absolute silence' is possible: ",
"https://www.reddit.com/r/askscience/comments/4lzo6g/is_absolute_silence_possible_in_nondeaf_humans/"
] |
[
"It looks like standard acoustic dampening material that you can buy online. I suppose they might have a 5-star super-silent aircon system, but I remain extremely skeptical that there is a genuine, measurable difference between this and any other anechoic chamber. And even if there is, it is splitting hairs really, since the difference between this and another well-built anechoic chamber will be largely, if not entirely, below any human perceptual threshold. But perhaps I'm just being a sour-puss ;)",
"Now if you want to see/hear something really cool, then check out an anechoic chamber such as ",
"Bernhard Seeber's",
". In his chamber, Bernhard has combined anechoic dampening with absolutely ",
" of speakers, positioned all around the room. Using clever acoustic modelling, these speakers can then be used to simulate different sorts of echoic environments (i.e., the real sound is trapped by the cladding, and then the nearby speakers substitute a new sound, mimicking what would have happened if the wall was ",
" distance away, and made of ",
" material). One minute, it sounds as though you're floating in space, then it's like being in a huge aircraft hanger, then you feel as though you're sitting in a tiny cupboard -- all by changing how/when/what sounds are 'reflected' back to you. Now ",
" really can start to mess with your mind! Seriously, it's pretty incredible."
] |
[
"What would happen if an anti matter photon interacted with regular matter?"
] |
[
false
] |
Or if a beam of the antimatter, say from a flashlight interacted with regular matter.
|
[
"Photons are considered to be their own anti-particle. That is, anti-photons and photons are the same thing."
] |
[
"Two photons can annihilate into e.g. electron-positron pair. So the electron-positron-annihilation is time-reversible."
] |
[
"Two photons can annihilate into e.g. electron-positron pair. So the electron-positron-annihilation is time-reversible."
] |
[
"What is the speed of gravity?"
] |
[
false
] | null |
[
"Light and gravitational waves both move at the speed of massless particles."
] |
[
"Gravitational waves move at the speed of light. You can read about this ",
"here",
" or, for the technical article, ",
"here",
"."
] |
[
"Photons and gravitational waves both propagate at the same speed (in a vacuum), that speed being the speed of light"
] |
[
"Why do different animal lifespans vary so much?"
] |
[
false
] |
[deleted]
|
[
"There are hundreds of contributing factors to the lifespan of any particular species, but generally the biggest include:"
] |
[
"I would argue that stem cell retention is most important (many factors contribute to this). For example rats have a lifespan of 2-3 years while squirrels that are extremely similar to rats in size and metabolic rate can live around 15-20 years. I can not find the link now but it has been shown that tissue specific adult stem cells (I do not remember which tissues) in rats undergo a far fewer number of divisions before they are 'lost' then in squirrels. This could be a result of telomere length, genetic instability, loss of niches and many more. "
] |
[
"But you don`t have to look far for exceptions to this. Lab mice have much longer telomeres than humans, even at the end of their lives, and their lives are shorter than ours by a longshot. They actually usually die of cancer, which is likely caused in part by their long telomeres. ",
"Senescence may play a role in aging, but there isn't good evidence its due to general loss of replicative potential (or telomere loss) in cells in most animals. "
] |
[
"Do tiny-brained creatures feel emotions like humans do?"
] |
[
false
] |
For example, if I picked up and relocated an insect, would it feel danger while I relocated it? Or fear once placed in an unfamiliar place? Or loneliness without its colony?
|
[
"There is no proven answer to this question. We infer animals' state of mind from actions reminiscent of our own, but have no way of verifying that reality. Elephants appear to mourn deaths. Crows and octopuses solve problems to obtain rewards. Fungi find the most efficient path through mazes without anything that resembles a brain. An ant's experience of life is certainly very different than ours, but we don't know what it does or doesn't feel.\nIs worth bearing in mind that the assumption that other life doesn't share emotions is beneficial for us. It's much easier to kill things if you think they don't care."
] |
[
"Exhibiting danger avoidance isn’t enough to prove emotions, and it is usually just instinctual. Trees will change their direction of growth and even “call for help” from other trees when in unsuitable conditions. If you touch a hot pan and quickly pull away you are not exhibiting a fear response, especially since the behavior occurs before the signal reaches the brain. Concluding fear would require evidence of avoidance in the future or some kind of social comforting that ants don’t engage in (as far as we know)."
] |
[
"Well, they can clearly feel fear and danger. That is evident from just watching the little critters scurry. See an ant on the counter? Bang your first on the counter near it and it will run away. That is them interpreting the slam as potential danger and exhibiting fear in the attempt to get away. Likely, these feelings do not carry the weight that human emotions do. Since we have larger and more complex brains we can understand and experience more complex things. Which I would say they probably do not feel lonely as that would be a more complex emotion."
] |
[
"Why is the sun made of hydrogen, while the planets are mostly made of other stuff. How come matter was not evenly distributed when the solar system formed?"
] |
[
false
] | null |
[
"To start... while more types of planet are possible, you have three main classes of planet in the Solar System:",
" These are the rocky ones, i.e. Mercury, Venus, Earth, and Mars. Mercury is an odd case, since its iron content is actually high enough (and its silicate rock content low enough) that some sources classify it as a borderline terrestrial/iron planet instead - although it's not as extreme an example of an iron planet as ",
"COROT 7b",
" probably is.",
". These are your typical \"Jovian\" gas planets, i.e. Jupiter and Saturn. They're made almost entirely of hydrogen and helium, along with some trace elements (which mostly take the form of oxygen-, nitrogen-, carbon-, and sulphur-based compounds), and possibly also with solid cores made of iron and silicates like the terrestrials (Saturn is known to have a solid core, whereas Jupiter's is still difficult to work out). The clouds of these planets are mostly composed of ammonia and ammonium hydrosulphide, although you'd ",
"expect this to change",
" if they were closer to the Sun. Since they have rather starlike compositions, you can think of gas giants as being on a spectrum with brown dwarfs (~13 to ~75-80 Jupiter masses) and stars (above ~75-80 Jupiter masses), where distinctions in their behaviour and physics are merely a matter of how much mass they possess.",
". This is one that \"lay people\" tend not to be aware of, since the gas giant/ice giant distinction is a fairly recent one. These planets (Uranus and Neptune, in the Solar System) are your lower-mass gas planets - although even lighter ones with ice giant-like compositions (a likely example being KOI-134c, which orbits the red dwarf ",
"Kepler-138",
") are called \"gas dwarfs\" instead, confusingly enough. Ice giants are distinguished from the higher-mass gas giants by their higher concentrations of \"ices\" (they don't necessarily exist in this phase, mind you - it's a generic term), i.e. methane, ammonia, and water, which are only found as trace compounds in the larger gas giants. This imbalance is because their gravity is too low to retain more than a small-to-moderate outer envelope of hydrogen and helium - while their outer layers are mostly hydrogen, the planets are thought to only contain about 20% free hydrogen overall. The ice giant-gas giant boundary (i.e. where surface gravity is high enough to retain a large hydrogen envelope) is expected to occur between 50 and 70 times the mass of the Earth, so Saturn (95.15 Earth masses, compared to Jupiter's 317.8) didn't actually scrape over the line by all that much.",
"Now, as to why this occurs... ",
"/u/AsAChemicalEngineer",
" did a great job at explaining the relative lack of hydrogen and helium on Earth relative to the gas planets. Still, another reason why the latter planets have more Sun-like compositions than the terrestrials is because they formed out beyond the \"frost line\". This region is the minimum distance from the sun where temperatures are low enough to allow those \"ices\" I mentioned previously to condense as literal ice grains.",
"Early in the Sun's life, i.e. before and just after it began fusing hydrogen, it was surrounded by a debris disk known as a protoplanetary disc (made from material that had been accumulated from the nebula that first surrounded the Sun, but didn't actually fall into the star), where material was in the process of clumping together to form protoplanets. The disc's composition within the frost line was mostly solid material and loose gas, making it a better place for rocky objects to accumulate overall (as solid material will have a much better chance of clumping - gas mostly just drifts around if it doesn't have a lot of mass to attract it). The rock and iron content in the disc was relatively scarce compared to gas, hence why the terrestrial planets didn't get very large, and also why they would have lost a lot of their initial gas to outgassing, solar winds, etc.",
"However, beyond the frost line, the larger rocky planetary embryos were able to accumulate loads of solid ices, which allowed them to grow larger and larger. Uranus and Neptune stopped growing at fairly low masses (their current masses are about 15.5 and 17 Earth-masses, respectively), and ended up as ice giants as a result, losing a lot of the hydrogen that they had accumulated. However, Jupiter and Saturn had managed to accumulate much more material, and so they became capable of retaining practically all of their hydrogen.",
"As for the Mercury distinction (i.e. much more iron content) that I mentioned before... there are a number of theories, but it's likely that the Sun basically dragged heavier material in the Solar nebula closer to it early on, resulting in a higher amount of iron within the vicinity of Mercury's orbital zone. Another theory that I read about in a recent jounal article (",
"news report here",
") is that much of the silicate content in the innermost portion of the protoplanetary disc was \"magnetically eroded\", and therefore depleted of useable lower-density compounds, due to its proximity to the Sun. In either case, there does seem to be a rather linear drop-off in iron content as you go from the innermost to the outermost terrestrial planets, and this is likely the case for other stars too.",
"Sorry for the long reply, but hope it helps!"
] |
[
"Our planet (as well at the other rocky planets) do not have sufficient gravity to capture hydrogen and helium. Jupiter and the other gas giants did and thus have a lot of both. What was left over was blown away from the Sun's radiation.",
"Oddly enough there ",
" a lot of hydrogen on Earth, but it's mostly trapped chemically, organic and otherwise. Helium is more rare and mostly formed from radioactive decay deep underground trapping it."
] |
[
"Great answer! Just to expand a bit, though...",
"The ice giant-gas giant boundary (i.e. where surface gravity is high enough to retain a large hydrogen envelope) is expected to occur between 50 and 70 times the mass of the Earth",
"...this is also going to depend a lot on the temperature of the planet's upper atmosphere, which in turn depends on their proximity to their parent star. ",
"Uranus and Neptune hang out at a chilly 60 K (-210 C, -350 F), so molecules in the atmosphere are moving pretty sluggishly there. Pulling those planets closer to the Sun would heat them up, possibly enough to give the fastest of the light molecules (i.e. hydrogen) enough velocity to escape the planet and leave only heavier gases/ices behind."
] |
[
"What makes cast iron a good cookware?"
] |
[
false
] |
[deleted]
|
[
"Properly seasoned, cast is non-stick. Its greatest attribute is even distribution of heat. Cast (especially the bigger, heavier pans) need to be pre-heated. They can also be used as baking pans, and some have handles on two sides."
] |
[
"I'm personally a fan of cast iron, but I don't see any possible way you can claim it provides the 'best surface' to cook on. PTFE (Teflon) and the related newer materials used to coat 'non-stick' pans are simply better at that. To the extent that it was quite a technical challenge to get it to stick to the the pan. Which brings you to one of the drawbacks of non-stick pans, especially the older models, which is that the coating was prone to being scraped off or flaking off.",
"The 'seasoning' on cast iron pans is from polymerized oil. It's 'non-stick' but not at all as much as teflon (less hydrophobic, more friction etc). However, with a properly treated cast-iron pan, the seasoning builds up over time so it's 'self-repairing' to an extent from wear and scratches. ",
"So non-stick surfaces are better, but wear out over time. Cast iron tends to be thicker so they store more heat, which is good. But their surface is simply not as good as a non-stick pan. However the surface and pan is more durable in the long run. (As long as it's not exposed to thermal shock; cast-iron is brittle) Most of my cast-iron cookware is older than I am and I expect it to be around long after I'm gone as well."
] |
[
"I should have made it more clear, but I meant taste-wise. I’ve heard that food tastes better when cooked in cast iron rather than non-stick."
] |
[
"How does Hubble's Law affect the size of the visible universe?"
] |
[
false
] |
I'm only a layman in terms of astrophysics, so I'm sure that my understanding of some of the concepts involved are lacking, but I never was quite satisfied with the explanation that I was given in my astronomy class as to the limits of the size of the visible universe. It makes sense to me that being as the Universe is just under 14 billion years old, light emitted 14 billion years ago from points that are (now) 93 billion light years away, is only just reaching us, and anything farther away than that is not visible because the light hasn't had long enough to travel during the entire course of the history of the Universe. So far, so good, but I also know that as the Universe expands, light from distant objects is red-shifted; "stretched", as it were, as it travels through an expanding medium and its wavelength increases. So. Given the rate of expansion of the Universe, at what distance would an object have to be such that any light it may have emitted will be so far red-shifted by the time it reaches us that it is indistinguishable from the background level of radiation in the Universe? Given an object sufficiently distant, such that the increase in the distance between us and it due to the expansion of the Universe is one light-second per second, will light from this object ever reach us? Given the current rate of expansion, how far away is that exactly? Will this ever be the limiting factor on the size of the observable Universe? When?
|
[
"There is a part of space called the observable universe. It is ~93 Billion lightyears across. This is all the light that has managed to reach us. This light is 13.8 billion years old but due to the expansion of space these objects would now be 93 Billion lightyears away from us. Anything further away we can't see because the light hasn't reached us yet and there is the limit when the universe became transparent, so to speak.",
"\nBut space is probably infinite there is a distance at which space exands faster than light can travel. So those parts of the universe are unfortunately too far away for us to ever see them. That is the sad reality. "
] |
[
"Hmm. Well, I see now that I was mistaken about the specific size of the observable Universe as it stands, though not the underlying physical causes of the boundary. I will edit the topic to reflect this. I was simply failing to take into account the past expansion of the Universe's effect on the travel time of light, which makes sense. (Light traveled proportionally faster between distant objects than the current extent of space would allow, being that the speed of light is constant, but there's now more distance to cover.)",
"However, my actual questions remain unaffected. Is there some distance at which (probably billions of years from now) light from distant objects will be so red-shifted and minute as to be indistinguishable from variations in the Cosmic Microwave Background? Is there some distance at which the expansion of the Universe will preclude light emitted from an object from ever reaching us at all?"
] |
[
"Hubbles law IS the expansion of space. There is no difference between the two. \nWell the cosmic microwave background is just normal EM-radiation redshifted. So light from any other source during that period (I am not aware of any other source) will have the same redshift. \nAnd yes there are objects that are further away that we will never be able to see. "
] |
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