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[
"Could I get a more clear and in depth explanation of the cosmological constant?"
] |
[
false
] |
So I just watched and really enjoyed it. Although it's a little bit out of date now, it gave me a better grasp on what exactly was discovered by the LHC and a better understanding of the Higgs Boson and the competing theories surrounding it (Supersymmetry vs. Multiverse, etc.) The biggest question I came away with was, what exactly is the cosmological constant? Why is it so important and what allows it to dictate so much of the physical nature of our universe? I think I understand that it defines the energy density of the vacuum of space. My basic understanding is that this means that this value is sort of the sweet spot where matter will sort of reach an equilibrium in interstellar/intergalactic space in terms of the density of particles? Is that on the right track? Just to clarify, I'm not a scientist by any means but have a pretty strong grip on Physics/Astronomy from a layman perspective, or at least I think I do lol. Thanks!
|
[
"Basically gravitation can be concentrated in the Einstein field equations, which are",
" = constant ",
" is a tensor representing curvature, and ",
" is the stress-energy tensor of the contents of the Universe. So, the energy-momentum content of spacetime makes it curve.",
"(the constant is actually 1/the Planck force)",
"However Einstein (and others) found that the most general form of the equation was",
" + Λ",
" = constant ",
"Where Λ is an unknown real number, the cosmological constant, and g is the metric tensor. There are no possible additions we can makd to the equation for reasons I can't say.",
"What is the effect of including the cosmological constant, as opposed to having it = 0? Λ (when positive) induces a repulsion between all objects. It effectively drives an expansion.",
"A Universe devoid of matter, ",
"=0, but with Λ>0, expands exponentially.",
"Now Einstein saw in this the possibility of making a stable stationary eternal Universe (at the time, the known Universe was basically the Milky Way, which looked pretty unchanging and uniform): you can balance the attraction between the stars with the repulsion. Sadly, this solution is unstable, as was first noted I believe by Eddington (like an upright pencil). So Einstein and others discarded Λ, since Λ=0 fitted observations and Ockham and so on.",
"At the same time it was discovered that galaxies ",
", and Hubble's law. After a while it became accepted that Hubble's law was due to an expanding Universe. Note that an expansion does not require a Λ, just like a thrown ball does not need a force pushing to keep it rising. The initial 'kick' was primordial, and the attraction would try to slow the expansion down.",
"In the 30s and 40s it was discovered that the quantum fields that give rise to matter and interactions have a zero-point energy in their vacuum state (the vacuum is the lowest-energy state). This vacuum energy had a stress tensor of the form:",
"_v = k ",
"With k a constant and g the metric tensor as above. If we plug it into the EFEs without Λ:",
" = c (",
" + k ",
")",
"where T is the stress-energy of ",
" of the Universe's contents. We can move the term to the left:",
" - k c ",
" = c ",
"But that's the EFEs ",
" a cosmological constant Λ = kc. Then vacuum energy acts precisely like a cosmological constant.",
"That's a big problem, because the standard model vacuum energy is massive. Way too large, it would have ripped the Universe aparts in a planck time. So people are starting to think about this ugly discrepancy. Maybe there is both a \"geometrical\" Λ on the left and a \"content\" Λ on the right and they cancel eachother someway (this is not impossible but extremely unlikely).",
"This was exasperated by the fact that around 20 years ago it was discovered that a cosmological constant ",
" needed. The Universe's expansion is indeed accelerating. So there is a Λ (very small). Today that Λ is placed on the right, added to the rest of the stress-energy, and called dark energy. The difference between the left or the right hand side is presently mostly philosophical.",
"We are, surprisingly, at a point in the evolution of the Universe where it's switching between matter-dominated (decelerating) expansion and dark energy-dominated (exponential) expansion.",
"So we have a minuscule dark energy and no way to match it with theory. There are many different ideas about how this mismatch is solved, but my preference would go into the class of proposals that the theory of everything will include a procedure to compute the cosmological constant exactly and it turns out this small. An effective theory such as the SM is not guaranteed to give effectively good estimates of Λ."
] |
[
"To try and put this in perspective:",
"There is an experiement which demonstrates something called the casimir effect. This is basically where two very very thin (Low mass) metal plates are placed very close together. The gravitational attraction is designed to be almost 0, and so is the electromagnetic, and van der waals forces etc. Ultimately there is no interaction between the plates. However what we find is that the plates are pushed together slightly. This is caused by the \"Energy Density of the Vacuum\" which spontaneously produces particles at all points in space, existing for miniscule amounts of time and then disappearing, not violating Heisenberg's uncertainty principle (Not Breaking Bad :P). ",
"We observe this effect because inside the plates, only certain size wavelengths of particles can exist (half wavelengths to be exact). However outside the plates there is somewhat \"more vacuum\" than inside the plates, and so the spontaneous creation of particles causes a pressure on the plates pushing them together. ",
"This effect is well documented, and has an associated \"Energy density of the vacuum\". When we discovered that the universe was accelerating in it's expansion, and we reignited the cosmological constant as this force, we hoped this casimir effect might be the answer. However, our observations show that the energy densit of the vacuum in the casimir effect is approx.~ 120 orders of magnitude larger than the apparent cosmological constant required to explain Dark Energy! This is an incredibly large error (Stupidly large). ",
"So, I hope this gives you some real world idea of the most likely candidate for the cosmological constant, despite the error hopefully we can fix that. ",
"Source: Dissertation on Dark Energy and the Cosmological Constant. (I can send you my paper if you want). "
] |
[
"I think you are on the right lines. From my research, the casimir effect is seemingly the best \"fit\" for what we think the cosmological constant is (A kind of outwards pressure spreading the universe apart at an accelerating rate). However that error of 120 orders of magnitude is just too damn high (:P). Either on some kind of galactic, hubble scale the casimir effect has a kind of inverse square law that reduces it by 120 ofm, that would be awesome, or there are definitely other variables. ",
"I will ",
"link",
" you to my post in Kurzgesagt which details my belief about whether the cosmological constant version of General Relativity is really the full picture, or if it is incomplete with regards to massive length scales (like the universe). "
] |
[
"can plants get \"fat\"?"
] |
[
false
] |
as in make more energy than they use and store it on their body? Or is it all well regulated? I know some plants can store energy in roots (potatoes I think?) so is this what they do instead?
|
[
"There are some issues with terminology, but in a sense, yes! They do make energy and store it, and in a somewhat parallel way to humans",
"In humans, we store energy (generally) in two forms - fat (adipose tissue) and carbohydrates (",
"Glycogen",
"). Glycogen is what we call a \"polymer\" of glucose blocks. Pretend that a single glucose molecule (the basic sugar that our body metabolizes for energy) is a lego. If I wanted to store all my legos, I could keep them loosely in a box. However, the body likes to be neat so instead of just tossing them in there, our body will connect the legos into stacks (\"polymerization\") for storage in order to save space as well as keep them separate from the free legos which I want to use for energy immediately. These stacked legos (glucose polymers) are our glycogen. One caveat would be that in real life, we can stack legos in a straight line, but glycogen is ",
"branched",
". Glycogen is stored mostly in the liver and muscles, and when we need energy our body chips away at our lego stacks in a process called ",
"glycogenolysis",
" liberating individual legos which can be metabolized for energy in the muscle, or liberated into the bloodstream for use wherever need be by the liver.",
"Plants have a parallel mechanism, with a few differences. In plants, our stacked legos are called ",
"starch",
". Starch consists of a combination of amylose and amylopectin. ",
"amylose",
" is linear, with no branches, and ",
"amylopectin",
" is branched and is similar to glycogen with the exception of the types of saccharide bonds between legos.",
"I should also note the difference between complex and simple carbohydrates. A simple carbohydrate is that free lego. Sugary foods are high in simple carbs. A complex carbohydrate is the polymerized form - starch. Breads (brown bread more than white), potatoes, rice, etc are all high in complex carbohydrates.",
"The parts of plants which we eat (i.e potatoes, rice) are the site of complex carbohydrate storage. I'm not familiar with the plant biology here, so I'd let someone with more experience detail the specifics about plant anatomy. But to answer your question, the potato we eat IS their fat, although it isn't fat in the sense you might think (analogous to adipose tissue) but rather fat in a conceptual sense (stored energy).",
": Including this reply I typed up further below:",
"Yes! It's actually a common misconception that eating fat makes us fat in a different way than eating carbs makes us fat. The body processes our food into energy through ",
"the same pathway, whether fat, protein, or carbohydrate!",
" They each just enter this cycle at different points.",
"Essentially, cellular respiration is used to derive energy from all three macronutrients. Fats and proteins are all broken down into intermediates of cellular respiration, and then enter the cycle directly to eventually lead to energy.",
"Gaining (or losing weight) is just a function of thermodynamics. If I expend less energy than I put in, that extra energy has to be conserved. Our bodies primarily conserve energy by creating and storing fat in adipose tissue. Likewise, if I expend more energy than I consume, that extra energy has to come from somewhere because energy must be conserved. Then, our body will break down our stores of fat and provide energy to fill the difference. When it comes to losing or gaining weight, it is important to account for what we call Basal Metabolic Rate (BMR), which is how much energy our body expends on keeping us alive. Homeostatic processes (maintaining fluid balance, temperature, brain activity, everything) are biochemical processes which require energy - lots of it.",
"For example, my BMR is about 2000 kcal/day (8368000 Joules, equal to about ",
" (",
"source, interesting to read!",
")). If I eat 3000 calories, 2000 will be used by my body to stay alive. The other 1000 will be stored as fat. If I went swimming and burned 500 calories, only 500 calories will be stored as fat."
] |
[
"Perhaps the only downside would be that animals would be more likely to eat them to use the starch. But plants have known this for millions of years; why do you think they make sweet fruits around their seeds? "
] |
[
"are there any adverse effects for a plant which stores an abundance of starch? (strain on structural or vascular systems, etc?) Or is it like a savings account for them, where having more stored (\"fat\") is only positive?"
] |
[
"Question on diffusion in respiration"
] |
[
false
] |
[deleted]
|
[
"Wait, how do you know P02 in the lungs remains the same? We inhale air, of which approx. 20% is O2, and exhaled air contains approx. 15% O2.",
"Take a deep breath and hold it in. You are using that oxygen right now, but the total pressure remains the same because you closed the system by holding your breath. The difference is made up of waste gases like CO2."
] |
[
"Unless you have a heart attack, the blood in your lungs is in constant motion. You should never get a chance to reach equilibrium with the outside.",
"On the other hand, with the second part of your question, you have anticipated the need for hemoglobin in blood. We cannot simply rely on diffusion to keep us alive.",
"Once oxygen gets into your blood, it binds to hemoglobin, where it ceases to behave like a freely diffusing gas. Each hemoglobin protein contains 4 identical subunits, each of which can bind one molecule of oxygen. They have a complicated relationship with each other in terms of how O2 binding in one affects the binding affinity the others have for O2. It is carefully tuned such that all 4 will bind O2 at high values of PO2, but will quickly unload all 4 when it reaches a region of low PO2."
] |
[
"The pO2 does change; the degree to which it changes varies greatly depending on the person doing the breathing, what the person is doing, and environmental conditions (temperature, humidity, etc). Typical, resting exhaled breath will have around 15-18% oxygen in it. "
] |
[
"Why does some metal turn red when heated?"
] |
[
false
] |
I was roasting s'mores with my family one night when we decided to put on a cage-like cover. After a minute or two, the metal was red, and I questioned this for the first time. I want to know what exactly it is that makes it the red color. Can anyone help? : Thank you all so much! Your answers are exactly what I needed.
|
[
"This is one of the most important questions in physics",
"."
] |
[
"The metal \"wants\" to lose the heat (energy). It can do so by emitting energy as light.",
"Remember Roy G. Biv? Those letters represent the colors of visible light, from the visible light with the least energy (red) to the visible light with the most energy (violet). And I repeat, that's just ",
" light. Before you notice it turns red, it will be emitting infrared light, which you can't see. If you keep heating it, it will start emitting orange, yellow, green, blue, indigo and violet light. When it's emitting all of these colors at once, they merge into white light, and you get \"white hot\" metal. That is, unless it has melted before that point."
] |
[
"OOO just said it will start ",
" those colors, which is true. It just doesn't look like it because it's also emitting all the ones below it as well."
] |
[
"By what mechanism are the minature transistors inside a modern microprocessor turned on and off?"
] |
[
false
] |
I was trying to comprehend how a modern processor works today, and I realized I had one critical piece of information missing. I know that at the smallest logical level, a processor is a very large array of transistors arranged to create discrete components like adders, memory, opcode decoders, etc. I also know that it is the action of turning on and off these transistors which decides the machine's state. My question is specifically, HOW does a computer cause that switching action to occur? Meaning, what physically happens that makes the input line of the transistor high or low?
|
[
"Taken to the limit, almost every transistor in a CPU is going to be gated by an output of another transistor in the CPU ",
" an external signal (from say an oscillator that provides a clock, or an input port) ",
" be effectively ungated by being tired to a rail in some scenarios (always on or even more rarely always off).",
"Considering that almost all external signals as well as supply rails (with the notable exception of ground) are outputs of transistors themselves, The answer basically becomes \"transistors most of the way down\".",
"Tracing it to the periphery of a computer system, there are mechanical switches (like power buttons and keyboards), sensing elements (like temperature and light sensors), piezoelectric crystals (for oscillation), analog signals (like your audio-in or even WiFi and Bluetooth), etc. Those are the eventual non-transistor sources of input signal to the sea of transistors. The simple ones (like a mechanical switch) can typical connect to a gate of a transistor relatively directly or maybe with a few resistors. More complex ones require multiple transistor and non-transistor components to digitize the input ( like analog to digital converters, RF front ends, oscillator circuits, etc.)"
] |
[
"Yep! That's how transistors work. Unfortunately, that's not the question I was asking."
] |
[
"The basic idea is that metalloids, such as silicon, can behave both like metals and non metals (i.e. conducting or non-conducting). With silicon you can make a semiconducting transistor, which can be made both to conduct or insulate depending on if you apply a base current to it or not.",
"A simple transistor has 3 points: 1) Collector, 2) Emitter and 3) Base.",
"http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Transistor_Simple_Circuit_Diagram_with_NPN_Labels.svg/720px-Transistor_Simple_Circuit_Diagram_with_NPN_Labels.svg.png",
"When there is a high current to the Base, the Collector and the Emitter forms a circuit and the transistor is \"On\", and when there is low current to the Base the transistor is \"Off\"."
] |
[
"Why does a rainbow split light into discrete colours rather than a range of the whole visible spectrum?"
] |
[
false
] |
A rainbow consists of definite bands of colour rather than and infinite gradient of changing colours.
|
[
"A rainbow ",
" consist of a continuous spectrum. You may ",
" it to contain discrete colours, but the quantization is the result of your perception, not how a rainbow splits.",
"For example, you can look at ",
"this sample spectrum",
" and pick out a set of colours, but there is much more displayed than you discern."
] |
[
"Plus much more than what your monitor can display correctly :)"
] |
[
"By the way, the spread of colors in a rainbow is not a pure spectrum (although it is indeed continuous and not banded) because of the way a raindrop scatters a certain color in multiple directions, causing mixing. Also, the extended, non-point-like, nature of the sun contributes to color blurring. In contrast, the spread of colors created by point-source white light (like sunlight through a slit) traveling through a prism or a good diffraction grating ",
" essentially a pure spectrum.",
"http://en.wikipedia.org/wiki/File:Prism_compare_rainbow_01.png",
"Also, people often mistake the spectrum to be banded and therefore assume there are only six spectral colors (ROYGBV). In fact, there are an infinite number of spectral colors, we just don't have names for most of them."
] |
[
"How do fish heal underwater? Why don't they bleed to death? Also, are there less infections for underwater cuts?"
] |
[
false
] |
Not just little fish, but sharks and rays as well.
|
[
"Fish heal much like we do: a lesion occurs, immuno-responses occur, skin regenerates.",
"What's protecting them from infection is a few things. 1) slime coats that shed off bacteria and parasites, 2) scales, 3) tough skin. ",
"Slime coat is interesting because the slime coat is constantly secreted and replenished and that's why fish are slimy. The slime captures bacteria, parasites, and other things and sloughs it off the body. Salt baths are how we can treat aquarium fish to treat parasite loads. (For you aquarium guys, you can dip some of your fish in 5ppt salt baths for about 5 minutes and that'll help promote coating).",
"We just talked about slime, so let's discuss scales. Scales are extremely tough. Ever try cutting one in half? You can cut human skin 3 times over before you can get through a scale. Hell, look at this ",
"set of gar scales",
". Very tough armor. It's like plate mail for fish.",
"Skin is very tough in fish too. It's a tough organ to pierce, as it should be, and it lies just beneath the scales. So, not only do pathogens have to get through the slime, they have to get through the scales and into the open cut. So this is mainly why fish are tough enough to avoid getting sick from conventional diseases like you and I can catch.",
"But, one other thing when it comes to cuts in fish, most of the fishes' body cavity are below a massive layer of muscle tissue which can be quite thick in some species. It also lacks significant blood arteries and veins in the musculature itself. Thus, most \"heavy bleeding\" in fish really comes from internal bleeding, not from cuts on the body.",
"Edit: As a side-note, heavy bleeding tends to source from piercing the 1) kidneys, 2) heart"
] |
[
"This is normal and very common in fish. Here's an awesome paper that tells you everything about the subject because 1) it's really cool, and 2) it'll take forever for me to shut about fish.",
"http://salamander.uky.edu/srvoss/425f09/Shao_et_al.pdf"
] |
[
"I'm not him, but I might know the answer.\nFirst off, evolution is probability, not purpose. The one who reproduces more (often) isn't necessarily the strongest, or fastest. It's the combination of being more apt and being lucky.",
"Second, and more to the point: Regeneration is a very energy/matter and time expensive process. Scarring is faster and much \"cheaper\" for the body.",
"Speculation: If you were injured enough that scarring would not suffice in order for you to survive, chances are that you wouldn't be able to live long enough to regenerate the wound. You know, because you are really injured.",
"edit: also, cancer"
] |
[
"Can you detect a ruptured eardrum with altitude pressure?"
] |
[
false
] | null |
[
"As someone that has had their eardrum burst, you will know if you have your eardrum burst. It hurts like hell and the best way I can describe the sound change is that it sounds windy all the time. I was kneed in the ear while underwater, the pressure of the water burst my eardrum."
] |
[
"Most traumatic ruptures of the eardrums heal within a week. Barotrauma as you are describing only results in perforation if the change in pressure is large enough. You might just have experienced great movement across your tympanic membrane resulting in pain, either that or the membrane healed quickly. Did you experience bleeding? Perforation of the tympanic membrane most often results in bleeding from the ear canal."
] |
[
"You are assuming that the rupture is big enough that the pressure difference of exterior vs interior is immediately equalized. It could well be that the tear is small enough that the pressure buildup is still noticeable."
] |
[
"How big would Noah's Ark have to be to house two of every species of animal?"
] |
[
false
] | null |
[
"It was removed because of the issues I mentioned, but the best answer was probably:",
"Warning: I'm having to make a few assumptions here.\nIf [1] these numbers are correct, there are a 933,253 animals that would have had to go on the ark. That's after you subtract the fish, mollusks, crustaceans, and corals. I also subtracted out all of the \"others\" category and dropped \"insects\" to 800,000. Presumably some of the \"others\" can live in water. The rest of that category plus those subtracted from the insects hopefully compensates for all of the insects and other animals that could live in water.\nThere are quite a few estimates re: the size of the average animal. Most estimates say the average sized animal on the ark was the size of a sheep, and that the median size was that of a rat or mouse. However, these estimates don't include insects which, while small, add up to a lot when you're talking about nearly a million of them. I'll make another wild assumption here that insects and arachnids will take up half of the space on the ark.\nWe'll assume that the invertebrate animals average about the size of a sheep. I've personally never measured a sheep, and there are so many types of sheep out there that it's hard for my Google-fu to locate an average size. We'll assume that your average sheep is around 2.5 feet tall, 3 feet long, and 1.5 feet wide. That seems about right, but feel free to plug in your own numbers if you think I'm wrong.\nWe can't just cram all of our 61,410 sheep into a giant sheep cube. They'll have to at least have space to stand next to one another, and this is assuming that they don't have to move at all. Going with that assumption, you can assume that each sheep takes up (3 * 1.5 = ) 4.5 square feet of floor space. Height doesn't really matter, because you can't stack sheep and presumably the ceilings are at least high enough for Noah and his family to walk under them.\nThat means that the vertebrate animals on the ark would take up (4.5 * 61,410 = ) 276,345 square feet of floor space. Double this due to my assumption that the insects will take up an equal amount of space. That means that the ark needs to have 552,690 square feet of floor space.\nNoah's ark was 300 cubits long, 50 cubits wide, and 30 cubits tall. It had three decks. This means that it had (300l * 50w * 3 decks = ) 45000 square cubits of floor space. A cubit is around 18 inches, or 1.5 feet. That means that the ark had (450 * 75 * 3 = ) 101,250 square feet of floor space.\nIn order to get the ark up to 552,690 square feet of floor space, you would need to increase its width and length by a little more than 125%. This means that it would need to be slightly more than 1050 feet long and 175 feet wide.\nNote that I'm also leaving out the need for food, water, and other supplies, and any space for the animals to move around. In reality, it would need to be a lot bigger than this.\nEdit: As usual, I did the hard work and screwed up the subtraction. Changed 31,005 to 30,705 and adjusted the other numbers accordingly.\nEdit 2: Didn't double the number of animals. Adjusted numbers accordingly."
] |
[
"This was asked two weeks ago - unfortunately, the number of off-topic replies meant we had to shut the thread down. It's probably not a good idea to let this out into the open so quickly :/"
] |
[
"Oh sorry about that. Do you remember what the answer was? I did a search and it didn't come up. Thanks"
] |
[
"When birds pull their wings down they get pushed up into the air. How come when they push their wings up, they do not descent the same amount they flew up?"
] |
[
false
] | null |
[
"The movements of the wing are more than just an up and down motion, which is covered briefly in this paper looking at how ",
"wing stroke changes as birds grow to adulthood",
". This is why they also have the ability to fly up and forward, and in some cases ",
"hover and fly backwards",
". ",
"Both the upstroke and downstroke of the wingbeat are actively controlled by muscles around the wing, and they give birds the ",
"ability to manipulate their wings to maneuver in the air",
". Birds also use their tails in flight to assist in maneuverability and generate lift. "
] |
[
"Because they change the shape of their wings as they move, creating the conditions for lift. ",
"They also change the amount of air that can pass through the wings at any one point. ",
"This video",
" is really good at showing how the feathers change through the cycle. ",
"But the video is not correct (i.e. it's simplistic) in treating bird flight as simply pushing upwards against air resistance and then allowing the air to pass through the wings on the upstroke. Bird wing aerodynamics are much more complex than that, involving changes in 3D-topology, ",
"trailing",
" ",
"vortices",
" and resulting lift -- all of which is ultimately explained by ",
"Kelvin's circulation theorem",
" and the ",
"Kutta-Joukowski theorem",
". ",
"In fact, if you watch the video closely, you'll see that the bodies of the birds don't follow a simple ",
" dynamic. It's more complex.",
"The air doesn't just sit there being pushed up and down. As a result of the flapping, all the air around the bird forms a complex set of vortices and differing pressure areas that lift the bird up and move the air down (all relative to a set, bounded volume of air around it).",
"Each bird is different (for example, hummingbirds exploit changing topology; touching their wings on the backstroke) and bats and insects have different ways to deal with the aerodynamics too.",
"The full story is ",
"here",
". This book seems to be at the cutting-edge of current knowledge; my knowledge is from the 80's, so a little rusty!",
"tl;dr You need fascinating unversity-level math to explain it (which I find ultimately frustrating, as I'd like to be able to explain it (even to myself) more easily)."
] |
[
"When you're swimming, and you push your arms down to your side to propell forward, why don't you move backwards the same distance when you bring your arms back up for another stroke?",
"Because when you bring them up, you bring them up close to the body and presenting minimal area for wind/water-resistance in the direction of travel. To move forward/upward, arms/wings are extended to present maximal area in the direction of their pushing."
] |
[
"Why can't we eat wood?"
] |
[
false
] |
I understand that we (humans), can't digest wood because our digestive tract doesn't contain the necessary bacteria ect... Why can't we add the correct prokaryotes that termites etc... use to our bodies to make use of all the woods? Om nom nom. *edit, Could we be made to? What would it take?
|
[
"We lack the digestive enzymes necessary to break down the polysaccharide, cellulose, that makes up the fiber of wood.",
"As for why we haven't taken on a set of prokaryotic symbionts... the answer is evolutionary- i.e. wood doesn't taste good to us, it wouldn't provide nutrients that we couldn't otherwise get, we don't have the digestive tract to handle it (intestine splinters, anyone?), etc. Evidence indicates that humans evolved in a place (N. africa) where there wasn't a lot of water. Not much water = not much fun to eat wood.",
"In short, our bodies just aren't set up to handle the nutritional and mechanical aspects of wood consumption. That would be my guess."
] |
[
"Rabbits eat their poo, but cows upchuck the food.",
"Also, technically, it's not the cow that digests cellulose, but symbiotic bacteria. No eukaryote can digest cellulose."
] |
[
"Rabbits eat their poo, but cows upchuck the food.",
"Also, technically, it's not the cow that digests cellulose, but symbiotic bacteria. No eukaryote can digest cellulose."
] |
[
"Why do streams seem to originate from mountain tops?"
] |
[
false
] |
At least here in Japan, most streams emerge from the ground quite near the tops of mountains. Even relatively small mountain tops (area-wise) will have a continuous stream emerging some 30 meters down from the peak. This, of course, joins with other streams emerging farther down or from other mountain tops and that is the source of almost all of the rivers I have seen here. So, my question is, is all that water emerging near the peaks from rain which actually fell on those peaks? (And is then just percolating down, following gravity, and happening to find a crack for an outlet?). Or, is there some other mechanism in which the water is actually forced up toward the tops of the mountains, gravity, before it finds an outlet? I spent more than an hour searching google for this but wasn't satisfied by the answers I found. TIA.
|
[
"Higher elevations are generally colder than lower elevations. On the windward side of the mountain, wind (caused by air pressure differentials) pushes air up the side of the mountain until it reaches the point at which the air can no longer hold the moisture. Cold air can hold less moisture than warm air. So, when the air cools, it has to release some of the moisture. The more it cools the more moisture has to be released.",
"Stream form from water following the path of least resistance (mainly)."
] |
[
"Hence the underlying question \"How did it get uphill?\""
] |
[
"The simplest way to go about this would be starting with the ",
"hydrologic cycle",
". So essentially water evaporates, is transported by moist air over land and water is delivered as rain. ",
"The next step is why does it rain? Wind moves the moist air over land, where it may rain. For rain to occur, the moisture in the air must condense. There are three ways for this to occur: the first is by attaching to dust particles in the air, known as ",
"condensation nuclei",
"; the second is by accumulating excess moisture to the point where the moisture can condense to itself; and the third is through a decrease in air temperature, an expansion of air volume, or a decrease in air pressure.",
"So why do stream tend to be associated with foothills and mountains? The simple answer is that it has to do with the increase in elevation; but, it's a little more complicated than that. As moisture laden air is pushed upward in elevation, the pressure decreases with the increase elevation, causing a decrease in pressure, in turn causing an increase in volume, which causes the temperature of the air to decrease, releasing moisture. Once the water reaches the soil surface, there are two options: the water can either ",
"infiltrate",
" into the subsurface, or flow overland via ",
"surface runoff",
". As the water travels down the mountain due to gravity, the water accumulates into stream or rivers -- if it does not evaporate, become part of a a groundwater system, become snow, or become an addition to a glacier -- and moves downward due to gravity within what is known as a ",
"drainage basin",
".",
"This ",
"book",
" is a good place to start if you're interested in hydrology. Hope that helped."
] |
[
"Is there a healthy way to prolong sleep?"
] |
[
false
] |
I always wake up too early and I feel that I chronically don't get the sleep that I need. After waking up I feel like I was hit by a truck and I can't fall asleep again. It's been lasting for years now and it really is very serious. It stresses me, I get fatter, my brain is always fatigued. In the mornings I often have morbid and unpleasant dreams. Maybe it's somehow relevant. I know it doesn't sound like much but if this could change my life would improve dramatically. Besides that I'm not stressed, my diet is ok, I rarely drink, don't smoke, play sports, I am in my twenties. I tried a lot of things (like: not eating before sleeping, changing bedsheets everyday, wearing sleep masks, earplugs) and nothing helps. Any advice?
|
[
"I have some sort of a disorder ",
"Why do you keep going back to this? I keep telling you that based on what you're saying you need better sleep hygiene, as it sounds that you have a form of insomnia, and the BEST treatment for insomnia is sleep hygiene. If you truly believe that you have a disorder then this is not the appropriate place for this discussion and you DO need to go back to a doctor. "
] |
[
"This is bordering on medical advice, so if people think it is, I'll delete it. Anyway: Go to bed earlier. Many people mess with their natural sleep drive by staying up later than they should, and get angry when they don't sleep in as late as they'd like. Some of it likely has to do with sleep drive, and another big part of it is that you're likely waking during a REM cycle. You need to wake from non-REM sleep, and your best bet is to try to go to bed 15-30 minutes earlier. If that doesn't work, try setting your alarm clock later by 15 minutes for a week. If that doesn't work, try setting your alarm clock earlier by 15 minutes for a week. If that doesn't work, go to a doctor. "
] |
[
"Any casual advice for a mid-twenties guy who both can't seem to get to sleep or get up in the morning? "
] |
[
"Elon Musk once said that Rockets won't be able to run on electricity because of Newton's Third Law. Is this true?"
] |
[
false
] |
Source: Elon mentions it around 2:20.
|
[
"It's true for any practical purpose. Conservation of momentum (which Newton's third law expresses) requires some mass to be expelled from the craft. A caveat here is that more momentum can be achieved by using a higher exhaust velocity (which is why we bother to burn propellants instead of just pumping them out) for the same mass.",
"There are a few \"electric\" rocket engines, which are called such because they use electricity to increase the rocket's exhaust velocity. The reason this is necessary is because kinetic energy is proportional to the square of velocity, while momentum is just proportional to the velocity, which means more and more energy needs to be supplied to the exhaust as its velocity increases. To make up this gap, electricity is used, but they still need a small amount of mass to use as exhaust.",
"If we generalize to a relativistic model, you could hypothetically use massless particles (like photons) to propel your craft since massless particles nevertheless have momentum in relativistic models. However in this case, you'd need so much energy that it would itself be a noticeable amount of mass via energy-mass equivalence."
] |
[
"Cars have a road to push off of. Rockets use their exhaust gas to \"push of of\" and move them forward."
] |
[
"Friction on the road.",
"Rockets have no friction in outerspace, as in they have no road to grab on. "
] |
[
"When was the last time molten lava was naturally present on the surface in the continental USA?"
] |
[
false
] |
I know the lower 48 states have lots of volcanoes, particularly on the west coast, and there have even been some relatively recent eruptions (most famously Mount St. Helens). But to my knowledge, those recent eruptions have been explosive gas and ash, not lava. The presence of massive ancient lava flows in states like Idaho and New Mexico indicate that volcanoes with lava do exist in these though. Basically, what I'm wanting to know is when the last time there was a Hawaiian-style eruption with flowing lava, and/or molten lava present on the surface, even if not part of a major eruption -- there's not a place like this in the continental USA currently, right?
|
[
"I don't have a definite answer, but the youngest basaltic lava flows I can think of in the contiguous United States are at ",
"Craters of the Moon National Park",
" in Idaho. The youngest flows there are about 2250 years old."
] |
[
"The last time a basaltic volcano erupted in the lower 48 was about 720 years ago, at the black rock desert volcanic field in Utah.",
"There are many, many volcanoes in the western US due to the great basin's extension. "
] |
[
"Are you asking about the contiguous US or continental US? I only ask because you mentioned the lower 48. Technically Alaska is part of the continental US, and it looks like there were several reports earlier this month regarding Mount Veniaminof and lava flows."
] |
[
"Are all ants in a colony genetically same?"
] |
[
false
] |
[deleted]
|
[
"Similar, but not the same. Precisely how similar depends on a whole bunch of details.",
"If an ant colony has only one queen, the workers are all sisters. During her youth, before the queen founded the nest, she mated with one or more males. (The ant mating season is when you see winged ants flying around; those are males and fertile females looking for mates. The males die after mating, while mated females shed their wings and become queens.) The queen stores the sperm from these matings, and will use it to fertilize all the eggs she will ever lay.",
"How closely related the workers of a single queen are to one another depends on how many mates the queen had during her mating period. If she only mated with a single male, the workers are all full sisters; if she mated with several, they'll range from full to half sisters depending on whose sperm was used to fertilize a given egg.",
"Many ant species may also form nests with multiple queens, either because the nest was founded by multiple mated females or because additional mated females joined as queens during later mating seasons. If a nest has multiple queens, the queens are often relatives, so in that case one queen's workers are something like cousins to another queen's workers.",
"However, ant relatedness is also complicated by the weirdness of ant genetics. Male ants are born from unfertilized eggs, so they have no fathers, and therefore only one set of genes instead of two. This also means that if two workers share a father, they inherited the exact same DNA from him (unlike the usual situation, where two full-siblings inherit a random 50% from each parent). This increases the amount of genetic variation shared between two sibling workers: two full-sibling worker ants share 75% of their genetic variation, whereas two human full-siblings (for example) share 50%."
] |
[
"No, she was never a worker. Because she was fed a special diet as a larva, she was born with wings and functional reproductive organs.",
"And yes, when someone tries to use animal sexual behavior as a moral yardstick for human sexual behavior, it seems unlikely that that person is aware of the stunning and bizarre diversity of nature. :)"
] |
[
"So, is a male ant basically a clone of the queen, just male?",
"Not quite a clone. He only contains half of his mother's genetic variation, so she's 50% related to him, just like my mother is 50% related to me... but he also contains no ",
" genetic information that ",
" come from his mother.",
"Like, the way a new ant colony is formed is by sending out a queen's DNA to mix with another queen's DNA through the worker",
"Not sure what you're suggesting here. I think you meant to say male, not worker? The workers are sterile females. A new colony is formed by offspring of two different colony's queens, one of whom is a fertile female (and hence the offspring of her queen and some previous lover of her queen), the other of which is male (and hence borne of half of his queen's genome)."
] |
[
"Why does metal (i.e. a metal spoon) get hot when it’s bent?"
] |
[
false
] | null |
[
"Because you are putting energy into the spoon, and deforming past it's ",
"elastic limit",
".",
"The force you apply multiplied by the distance you bend it is Work. This Work MUST be conserved. This Energy goes into Potential energy of the elastic deformation, and all the rest goes into heat (in the end).",
"If this was a perfect spring, this energy would be tied up in the potential energy of the spoon. Once you stopped holding on to the spoon it would spring back fully. However this is not the case, because the spoon is yielding once you get past a specific point, and only springs back a little.",
"This means the deformation is NOT in the elastic region like a spring, but is permanently plasticity deforming. So, where can the energy go? As the metal crystals begin to slide against each other the work of your hands is transformed into the random kinetic motions of the metal atoms. This increases the temperature of the spoon.",
"So, this is why a paper clip quickly heats up as you bend it, but a doing the same thing to a spring does not!"
] |
[
"All metals do. It's just that some are easier to bend so take less energy to do so. Other metals fracture in a brittle fashion before they can deform much."
] |
[
"Adding to this question, why not all metals show this behavior (at least in the same magnitude)?"
] |
[
"i have chickens. they wander about all day long and interact with one another. how much do they know about what theyre doing?"
] |
[
false
] |
is everything they do an empty-headed chemical instruction? what about when they walk over to another chicken and cluck at them then walk away? was that "thought" about at any level? mind boggling.
|
[
"Keep discussion on topic and focused on answering questions scientifically.",
"Please keep discussion civil. Name calling, insults, racism, sexism, etc. will not be tolerated.",
"Please follow the ",
"r/askscience",
" postig guidelines."
] |
[
"Keep discussion on topic and focused on answering questions scientifically.",
"Please keep discussion civil. Name calling, insults, racism, sexism, etc. will not be tolerated.",
"Please follow the ",
"r/askscience",
" postig guidelines."
] |
[
"Keep discussion on topic and focused on answering questions scientifically.",
"Please keep discussion civil. Name calling, insults, racism, sexism, etc. will not be tolerated.",
"Please follow the ",
"r/askscience",
" postig guidelines."
] |
[
"If I want my oven to get to 100C, will it get there faster if I set it to 200C?"
] |
[
false
] | null |
[
"Depends on what kind of controller the oven has. If it's a simple on/off (i.e. if the temp is below a certain setpoint, turn heater on, and if above, turn heater off), then no. If it has some sort of proportional control (i.e. the amount of heat being generated is proportional to the error between the temperature set-point and the current temperature), then yes because the error term generated is greater. I would imagine most run-of-the-mill cooking ovens just have on/off in which case it won't matter."
] |
[
"i can't see any real benefit from a \"proportional control\", so i would assume they are all the \"on/off\" type "
] |
[
"If it's testable, it's worthy of scientific investigation, all questions lead to enlightenment. "
] |
[
"Which way should I face the opening in my disposable coffee cup while driving to minimize the chance of spilling?"
] |
[
false
] |
When putting my coffee cup in a cupholder, I usually face the opening towards the back of the car (6 o'clock). Sometimes if I know I'm not going to make a left turn, I might face it toward the right (3 o'clock). What's the most efficient way to set my cup down to minimize the probability of it spilling? I started thinking about other possible solutions like 7 or 8 o'clock positions since I never really accelerate at an angle.
|
[
"If you discount \"slosh\", the coffee will peak opposite the direction of acceleration. When you hit the accelerator the coffee pools at 6 o'clock, when you corner at 3:00 or 9:00, when you brake at 12:00. So you really want to choose a point between these that is least likely to be opposite the direction of acceleration. As long as you aren't accelerating tangentially (speeding up) during, or just prior to, cornering, the OP has actually got it pretty spot on by assuming 7:00 or 8:00!",
"EDIT: And thanks for finding those numbers. I did a quick search previously but couldn't turn up anything reliable either!"
] |
[
"If you discount \"slosh\", the coffee will peak opposite the direction of acceleration. When you hit the accelerator the coffee pools at 6 o'clock, when you corner at 3:00 or 9:00, when you brake at 12:00. So you really want to choose a point between these that is least likely to be opposite the direction of acceleration. As long as you aren't accelerating tangentially (speeding up) during, or just prior to, cornering, the OP has actually got it pretty spot on by assuming 7:00 or 8:00!",
"EDIT: And thanks for finding those numbers. I did a quick search previously but couldn't turn up anything reliable either!"
] |
[
"I think upwards would be best."
] |
[
"When life expectancy was 30, did people die of 'natural causes' or did they all die horribly from disease?"
] |
[
false
] |
I'm curious as to how people actually passed away at this age and what was the cause. Was lack of health and hygiene enough for the body to wear away faster, or did they all get diseases and pass away in sickness?
|
[
"A life expectancy of 30 doesn't mean that most people died around age 30.",
"The reason for shockingly low life expectancy statistics for most of our history is that there was a high infant and early childhood mortality rate. You were in fact more likely to die as a infant or young child; otherwise, if you survived until adulthood, you could reasonably expect to survive into your fifties or sixties. See ",
"this",
" list on Wikipedia, which has life expectancies for various time periods calculated from birth and then calculated after age 15 or 21. There is a very big difference."
] |
[
"The numbers of people living into their 80's and 90's is statistically smaller until the 20th century."
] |
[
"The numbers of people living into their 80's and 90's is statistically smaller until the 20th century."
] |
[
"Where are bananas' seeds contained?"
] |
[
false
] |
Most fruits, like watermelons, apples, and grapes, have easy-to-spot seeds, but I've never noticed any seeds contained in bananas. Are the ones we eat genetically modified to contain no seeds or are the seeds located someplace other than inside the peels?
|
[
"They don't have any. They're all cloned (split from a tree and replanted) from a single mutation, which is why bananas are so prone to disease. We lost one species, the ",
"Gros Michal",
", to disease (not entirely lost, but the disease was widespread enough to prevent the economic distribution) already. ",
"They're the prototypical definition of monoculture.",
"The disease we lost them to is ",
"Panama disease",
", and were beginning to lose our current crop, ",
"the Cavendish",
", as well. Although there's some research going on to create Panama resistant versions. "
] |
[
"Here's a link to a recent SciShow video which is basically this above comment in video form, with a bit of extra trivia. And theme music.",
"https://www.youtube.com/watch?v=ex0URF-hWj4"
] |
[
"Bananas are not \"genetically\" modified in the sense that people talk about \"genetically modified organisms\" or GMO.",
"All agricultural crops, including bananas, are technically genetically modified from their ancestral counterparts through selective breeding. However, the definition of GMO is that some form of recombinant DNA technology has been used. In this sense, bananas are not GMO, and it's actually quite hard to genetically engineer them because they are clonally propagated. "
] |
[
"In the last 5-10 years, there’s been tremendous efforts made by many of the first world countries to curb carbon emissions. Have we made a dent?"
] |
[
false
] |
Where do we stand on present day global carbon emissions vs say 10-20 years ago?
|
[
"The ordering of that stacked graph there is unfortunate, because it hides the decreases in US/EU because they're stacked on top of \"rest of world\" which has been going up.",
"In other words, industrialized nations have been making progress, but it's overshadowed by emerging economies. On the other hand, India and China are investing massively in solar as they industrialize, so it could actually be way worse."
] |
[
"The ordering of that stacked graph there is unfortunate, because it hides the decreases in US/EU because they're stacked on top of \"rest of world\" which has been going up.",
"In other words, industrialized nations have been making progress, but it's overshadowed by emerging economies. On the other hand, India and China are investing massively in solar as they industrialize, so it could actually be way worse."
] |
[
"Having said that, is there an opportunity for new emerging economies to leap-frog straight to the greener technologies in their industrialisation?",
"A Green Leap Forward, so to speak?"
] |
[
"Why do house cats have slit pupils but big cats (lions, tigers, cheetahs, etc) have round pupils?"
] |
[
false
] | null |
[
"Here",
" is a fun article about it. The summary is that pupil shape has a lot to do with your position in the food web as a predator or prey, and the mode of hunting a species employs.",
"From the article: If you have a vertical slit, you're very likely to be an ambush predator, says Banks. That's the kind of animal who lies in wait and then leaps out to kill. He says these predators need to accurately judge the distance to their prey, and the vertical slit has optical features that make it ideal for that."
] |
[
"Great article. Also wroth adding this bit.",
"But that rule only holds if the animal is short, so its eyes aren't too high off the ground, Sprague says.\nAnd while a small pet cat has vertical slits, Sprague says, \"the larger predators, like lions and tigers, have round pupils.\"",
"Tigers are mostly ambush predators I believe, but because they are high enough off the ground the vertical slit is perhaps less useful.",
"Interestingly, the [Pallas cat], which is about the size of a domestic cat and is also an ambush hunter, has round pupils. I wonder if that has something to do with the environment they live in."
] |
[
"But for anyone wondering, cats are quite a distant relative to the wild cats, a dog is more closely related to wolf than a cat to a lion",
"Correct. In fact, the species ",
" includes wolves, dingoes and domestic dogs. They aren't just \"closely related\" to wolves -- they are the same species. (The subspecies for domesticated dogs is ",
")"
] |
[
"Question About Non-Newtonian Fluids and States of Matter"
] |
[
false
] |
[deleted]
|
[
"1) First rule of science: never speak in absolutes. So I won't say that any fluid won't behave in a non-Newtonian regardless of the conditions. However, there is a reason that while they seem to behave similarly, water is Newtonian while oobleck is not. It all has to do with how the materials behave under flow. Oobleck is a mixture of water and starch, which is a polymer. When you put a lot of force on these polymer molecules, they actually form temporary crystals in the mixture which causes the whole thing to behave more like a solid. This causes the viscosity of the entire fluid to increase as you apply greater force on it (we call this force \"shear\"). This is precisely the definition of a non-Newtonian fluid: a fluid that does not have a constant viscosity for any given shear. With water, it seems to solidify because of surface tension, which actually doesn't cause a change in its viscosity, but makes the surface act more like a solid when stressed.",
"2) Knowing that a non-Newtonian fluid is something that has a shear-dependent viscosity, that means it's impossible to have a non-Newtonian gas. Viscosity is a measure of a material's resistance to deformation; since gases have no such resistance, they have no viscosity and therefore cannot be classified as Newtonian or non-Newtonian fluids.",
"3) Change in volume is a poor way to differentiate liquids from gases because, as you said, liquids can be compressed. Simply put, gases expand to fill their container while liquids do not.",
"4) As with 3, a better way to define the difference between solids and liquids is that liquids readily conform to the shape of their containers.",
"5) No, the states of matter are pretty defined, with certain rules and properties clearly defining each (e.g. the equation pV=nRT defining a perfect gas). The only time you really start seeing overlap is when you get into things like supercritical fluids, but these aren't really practically encountered. It sounds like you just probably haven't had the best teachers in your chemistry classes.",
"6) Yes! Non-Newtonian fluid get their properties from the materials (usually polymers) mixed in with them. There are actually an incredible number of materials in everyday life that show different types of non-Newtonian behavior. For example, oobleck exhibits what is called \"shear thickening\" behavior because it seems to stiffen up when you put force on it. Ever notice how toothpaste seems to perfectly hold its shape on the bristles, but very easily squirted out of the tube, though? That's because it is a \"shear thinning\" material, or a material that actually becomes easier to flow and deform under stress. ",
"There's a whole field devoted to studying material flow and deformation called rheology. It's really fascinating stuff, and I'd definitely encourage you to keep following your curiosity!"
] |
[
"2) Knowing that a non-Newtonian fluid is something that has a shear-dependent viscosity, that means it's impossible to have a non-Newtonian gas. Viscosity is a measure of a material's resistance to deformation; since gases have no such resistance, they have no viscosity and therefore cannot be classified as Newtonian or non-Newtonian fluids.",
"I disagree with this point. Gasses absolutely have a viscosity. "
] |
[
"That's what I get for typing this off the top of my head. Looks like you're absolutely right about gasses having viscosity. But I still don't think it's possible for a gas to behave like a non-Newtonian fluid since there are so few intermolecular interactions. If you know more about this, please tell. I'm curious myself now."
] |
[
"Millions of stars are in the area of a sky covered by a pin's head. How do radio astronomers know which radio waves are coming from which star when they point their radio telescopes to the sky?"
] |
[
false
] |
Shouldn't what they get be white noise? Radio waves from millions of stars at different points in space and time arriving together?
|
[
"Sadly we currently are not able to detect individual stars that far away. The farther we get outside our galaxy the harder it is to detect individual stars. There are certainly millions and billions of stars out there but we can only see a small fraction of them. We detect galaxies instead and estimate the number of stars. "
] |
[
"If you're a person? No. If you're struggling to observe a radio signal that's a million times weaker than a cell phone? Yes."
] |
[
"Radio astronomer here! This really depends on several things. First of all, one big detail here is a radio telescope's resolution on the sky, as they are definitely not all created equal- one that I use is experimental at a low frequency range, for example, so we lack resolution more than the size of the full moon in the sky. (Which may sound bad, but we are also imaging the entire sky, so...) Obviously though most telescopes have much better resolution than this, so to answer your question...",
"Radio astronomy is a funny beast because unlike optical astronomy your radio telescope gets a whole lot of signals arriving from all different places in the sky at once, and then we have the task of filtering out all this noise to see which specific source that noise is coming from. Picking out this signal from a specific place in the sky involves a lot of \"tricks\" to tease out a signal buried in noise, which is why radio observatories don't let you take a cell phone there for example- your cell phone is ",
" noisier than any radio signal from outer space, so it can completely swamp out those faint signals! A bit trick in my toolbox to give you an idea is for every 11 minute observation we will then spend a few minutes observing a calibrator source, which is one of the brightest radio sources in the sky also up at the same time. (They are about 10 sources with names like Virgo A, Cassiopeia A, Cygnus A- A meaning brightest radio source in that constellation- and we call them the \"A team\" sources bc we have a sense of humor.) A bright sources is of course far easier to observe than a fainter one, and have much more extensive observations so we have modeled their signals far better, and then you can use this to work out what the radio sky was like at the time and subtract any ill effects you don't want in your observation.",
"Further, to get the resolution we're talking about, a really important part of it is collecting radio signals not just from one dish, but many dishes spread out all across the globe, in what is called Very Long Baseline Interferometry (VLBI- sorry I'm on a train, else I'd link something for you!). Basically if you're measuring very precisely your timing (with atomic clocks and the like) you can add up these signals and correlate them together... which gives you a radio telescope that's effectively the size of the Earth! It turns out this resolution is good enough to know where one photon came from in the sky over another just a little further away, based a lot on the timing of how the signals were received.",
"Finally, pointing longer at the sky also helps a lot. Ultimately the limitation for a telescope is its background noise limit, called the confusion limit, but this goes down with sqrt(2) over time. So if you were looking at a background of 5 Janskys (our unit in radio astronomy) at 11 minutes but your source is 3 Jy that you want to observe, you could see it really easily if you observe for a half hour. As such, the longer you observe, the more sources you can distinguish.",
"I hope that answers your question, but let me know if something is unclear!"
] |
[
"Is there a \"smallest\" divergent infinite series?"
] |
[
false
] |
So I've been thinking about this for a few hours now, and I was wondering whether there exists a "smallest" divergent infinite series. At first thought, I was leaning towards it being the harmonic series, but then I realized that the sum of inverse primes is "smaller" than the harmonic series (in the context of the direct comparison test), but also diverges to infinity. Is there a greatest lower bound of sorts for infinite series that diverge to infinity? I'm an undergraduate with a major in mathematics, so don't worry about being too technical. Edit: I mean divergent as in the sum tends to infinity, not that it oscillates like 1-1+1-1+...
|
[
"If you have two sequences f(n) and g(n) (where the nth term of the sequence is the sum of the first n terms in a given series), then one way to define \"divergence speed\" is to look at lim",
" f(n)/g(n). If it's zero, then f is \"slower\" than g, and if it's ∞ or -∞ then f is \"faster\". If it's anything else, then they're approximately the same (for example, if you let f(x) = x",
", g(x) = 2x",
"+1, then you get 1/2).",
"By this definition, there is no slowest series. Given any sequence f(n) that goes off to infinity, it's clear that lim",
" ln(f(n))/f(n) = 0, so you can always find a slower one.",
"Edit: I see a few comments asking about this so I'll paste it up here.",
"I probably should have been more clear what \"f\" and \"g\" are. I wasn't expecting it to get to the top of the comments.",
"Let's say you have a sequence a(n) that you're interested in. For example, a(n) = 1/n. Then we define f(n) to be the nth partial sum (1/1 + 1/2 + 1/3 + ... + 1/n). In this case, f(n) is also a sequence, and lim",
" f(n) is equal to the series (a(1) + a(2) + a(3) + ...).",
"Then ln(f(n)) is the natural log of the entire partial sum, ",
" the sum of the natural logs (that would be the sum of ln(a(n))). We know f(n)->∞ because we only care about divergent sums in the first place, so naturally ln(f(n))->∞."
] |
[
"No. Suppose there was some smallest divergent series, call it sum[f(x)]. The series sum[f(x)/2] will also diverge, but be \"smaller\"."
] |
[
"This response should be higher. I think it's most likely what OP was asking about.",
"I'd add that rather than talk about one series diverging faster/slower than another, we're really talking about one function diverging faster/slower than another (the partial sums). One can then prove:",
"If f(x), g(x) are two positive, monotone increasing functions such that lim (g/f) = infty, then one may always construct a function h(x) such that:",
"\n1. f(x) \\geq h(x) \\geq g(x),",
"\n2. lim (h/f) = lim (g/h) = infty ",
"(This also avoids the \"multiply by a constant\" answers which are perfectly correct, but probably unsatisfying to OP)",
"http://en.wikipedia.org/wiki/Hardy_field",
"edited to correct inequalities which were reversed."
] |
[
"Can you represent PI in a finite number of digits in any number system?"
] |
[
false
] |
From a computer science course I know that you cannot represent the number 1/10 in a binary number system. But you can do it in a decimal number system. Is there a system where you can represent PI in a finite amount of digits?
|
[
"Of course, we could always use base pi to represent numbers, with which pi has the trivial representation \"10\". But surely non-integer bases are not what you are talking about. (They're also a lot of trouble anyway. For instance, if the base is algebraic then some numbers can actually have infinitely many expansions that all terminate.)",
"If the real number ",
" has a finite expansion in some ",
" base ",
" > 1, then ",
" is equal to",
"x = a",
"b",
"+a",
"b",
"+...+a",
"+a",
"/b+a",
"/b",
"+...+a",
"/b",
"with a",
" some integer between 0 and ",
"-1. This expression can just as well be written as",
"x = M/b",
"where M is some integer. Therefore, ",
" must be rational. Since pi is irrational, there is no integer base in which pi has a finite expansion.",
" So I came back to 27 new messages and 1500 upvotes. I did not think this topic interested that many readers. But good to see! Follow-up to some common questions and comments:",
"First, distinguish between a number ",
", which can be defined and exists independently of its representation and \"",
"\", which is a numeral or representation of ",
" in a certain base. To make clear that I mean a specific base representation I will enclose an expression by quotation marks if the base is clear or, if I want to denote the base explicitly, I will write a subscript after the digits. So the expression 23",
" means \"23 in base 10\" (the number 23) and the expression 23",
" means \"23 in base 4\" (the number 11).",
"Non-integer base representation works just how any integer base works. Fix your base ",
" > 1. The \"digits\" of your representation are all non-negative integers ",
" ",
". Then the representation",
"\"d",
"d",
"...d",
"d",
"d",
"d",
"...\"",
"(where each d",
" is a digit) is the number",
" = d",
"b",
"+d",
"b",
"+...+d",
"b",
"+d",
"+d",
"b",
"+d",
"b",
"+...",
"The digits can be found recursively using a ",
".",
"Let's do an example to make this clear. Since our base is b = π, our possible digits are {0, 1, 2, 3}. Now pick your favorite number ",
". For sake of clarity, I am going to let ",
" = 8. Note that π",
" > 8, so the first digit of our representation is in the \"tens\" place. We have",
"[8/π] = [2.546...] = 2",
"(The notation [.] means that we round down to the nearest integer.) So the \"tens\" digit of 8 in base-π is just \"2\". Okay. Now we subtract off what we have so far, and then divide by the next power down.",
"[(8-2π)/1] = [1.716...] = 1",
"So the \"ones\" digit of 8 in base-π is \"1\". Now subtract off what we have so far again, and divide by the next power down.",
"[(8-2π-1) / π",
"] = [2.252...] = 2",
"So the \"tenths\" place of 8 in base-π is \"2\". Subtract off again and divide by the next power down.",
"[(8-2π-1-2π",
") / π",
"] = [0.791...] = 0",
"So the \"hundredths\" place of 8 in base-π is \"0\". Next. Subtract off, divide by the next power down.",
"[(8-2π-1-2π",
"-0π",
") / π",
"] = [2.486...] = 2",
"So the \"thousandths\" place of 8 in base-π is \"2\". At this point I think you get the idea. So far, we have that",
"8",
" = 21.202...",
"If you want to keep going, WolframAlpha is more than happy to do it for you.",
"8",
" = 21.20211200210000003...",
"Some terminology if you are not familiar:",
"A real number is ",
" if it is the root of a polynomial with integer coefficients. Otherwise, the number is transcendental.",
"Suppose ",
" is algebraic. The minimum degree of all polynomials for which ",
" is a root is called the ",
" of ",
". So if ",
" is algebraic of degree 7, then any polynomial for which ",
" is a root must be at least degree 7.",
"Some properties of representations in different types of number bases:",
" All numbers have at most two expansions. If a number has only one expansion, it must be infinite. If a number has two expansions, then one expansion terminates and the other expansion ends in an infinite trail of digits equal to ",
"-1. For example, \"1\" and \"0.999...\" are equivalent base-10 representations of the same number, just as \"1\" and \"0.2222...\" are equivalent base-3 representations of the same number.",
" Just as with integer bases, some numbers have terminating expansions and some don't. However, a number can have infinitely many expansions. If a number has a terminating expansion, then it has only one terminating expansion. (But the number can still have infinitely many infinite expansions.) It is possible (actually, typical) for a number to have uncountably many infinite expansions.",
" Every number has at least one expansion.. and that's all you can really say. If a number has a terminating expansion, it has infinitely many terminating expansions (see below for an example). So this type of number base is particularly pathological since not even terminating expansions are unique.",
"Interestingly, note that there is no base in which ",
" numbers have a unique expansion.",
"Okay, now for an example with an irrational, algebraic base. Let ",
" be the unique real root of the equation",
"b",
" = b",
"+b+1",
"(For reference, the root is approximately ",
" = 1.8393, which means that the valid digits in this base are {0,1}.) Then the number b",
" has (at least) ",
" representations: \"1000\" and \"111\". In fact, we can use the equation above to write ",
" power of ",
" as a sum of other powers of ",
" with coefficients that are valid digits. For example, multiply the equation by b",
" to get",
"b = 1+b",
"+b",
"So then the number ",
" has the representations \"10\" and \"1.11\". Essentially, in this base, whenever there is a string \"1000\" anywhere, we can always replace it by \"0111\". For example, consider the number ",
" = ",
"+1 (approximately 2.8393), which has the representation",
" = 11",
"We can write this instead as",
" = 10.111",
"Then we can shimmy over the last \"1\" to get",
" = 10.110111",
"Shimmy it over again to get",
" = 10.110110111",
"..and, well, you get the picture. We have an infinite sequence of representations, all of which terminate and all of which represent the same number. This is a general phenomenon for any algebraic base of degree at least 2. (Note though, the greedy algorithm explained in the previous section always gives a unique expansion. In the previous example, it gives ",
" = 11",
". So we can always canonically choose a unique expansion even if there are infinitely many by just declaring ",
" expansion to be that which is given by the greedy algorithm.)",
"There seems to be some confusion between the definition of a rational number and theorems characterizing rational numbers in terms of base representations. The ",
" of a rational number is:",
"A real number ",
" is ",
" if it can be expressed as the ratio of two integers. Otherwise, it is ",
".",
"The word \"rational\" literally means \"quality of a ratio\". So the numbers 2/3, 9/10, and 1235325423/122145268 are all rational. The numbers √(2), ",
", and ",
" are irrational. (Proofs that they cannot be expressed as fractions of integers are readily available online.) ",
" Whether a number is rational is not dependent at all on the number base.",
"However, we do have the following theorems:",
"If a number ",
" has an eventually periodic expansion in some integer base ",
" > 1, then ",
" has an eventually periodic expansion in all integer bases ",
" > 1.",
"A number ",
" is rational if and only if its expansion in some integer base ",
" > 1 is eventually periodic.",
"(\"Eventually periodic\" includes \"terminating\" because a terminating expansion can always be followed by an infinite trail of repeating 0's.) The first theorem means that we can strengthen the second by replacing the word \"some\" with \"all\". ",
"Note that these are theorems that relate rationality to their representations in number bases. They are not the definition of a rational number. Also note that the theorem specifically talks about ",
" bases. For non-integer bases, the theorem is not true. For example, π is irrational, but its representation in base-pi is \"10.0000....\" which is eventually periodic."
] |
[
"I just wanted to quickly add a less technical summary of ",
"/u/Midtek",
"'s excellent answer.",
"An irrational number is one that can not be represented as a ratio of two integers. In any basis, you can always multiply and divide a finite expansion by a power of the base to represent it as a ratio of integers.",
"For example, if we wanted to write 5.123 (in decimal) as a ratio of integers we could just multiply the top and bottom by 1000 and represented it as the integer ratio 5123/1000. The same principle hold for all integer basis so all numbers that have a finite expansion must be able to be expressed as a ratio of integers and in turn be rational. Pi is irrational and therefore can not be finite in any integer basis."
] |
[
"There is a little bit more alebra involved to go from repeating rational decimal to fraction, but this proof works on any repeating rational decimal. We'll use 1/3 for this example.",
". ",
"X =0.33333... ",
". ",
"Multipy both sides by ten. ",
". ",
"10X =3.3333... ",
". ",
"Subtract these two equations. ",
". ",
"10x = 3.33333.....\n ",
" x = 0.33333..... ",
"-------------------- ",
" 9x = 3.00000.....",
". ",
"Divide both sides by nine. ",
". ",
"X= 3/9 ",
". ",
"Reduce the fraction ",
". ",
"X = 1/3 ",
". ",
"Boom. There's the algebraic proof that .333333.... is rational. Based on the length of the repeating section you may have to use a different factor of 10. (x100, x1,000, etc.) ",
". ",
"Edit: formatting ",
". ",
"Edit #2: ",
"The more I think about it, there is one more interesting implication of this proof: ",
" x ",
"------------",
"(10 ^ n) - 1 ",
" \n ",
"Where X represents the repeating part of a decimal number less than 1, and n represents the number of digits of X. (In this case X must be a natural number.) A little more simply: ",
"For example, take the repeating decimal 0.142857142857........",
" \n ",
"142857 (the repeating digits) ",
"------- ",
"999999 (six 9s because there are six repeating digits) \n ",
" ",
"Reduce this fraction",
" to find that 0.142857142857..... is equal to 1/7. Pretty neat trick, huh? \n ",
" ",
"Here",
" is the above equation expressed as a function within in wolfram alpha. You can replace the very last number with a number that represents the repeating part of a decimal number less than one and it will return the corresponding fraction."
] |
[
"Why is there no lag between video and sound on my portable Bluetooth speaker but every car I have been in with Bluetooth has noticeable lag between audio and video?"
] |
[
false
] | null |
[
"I mean using your cell phone and trying to watch YouTube or something"
] |
[
"We can't really comment on anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"I'm not really looking for speculation. I know there are different types/frequencies of Bluetooth and I was thinking more along the lines of perhaps they use a type in cars that is more prone to lagging behind the video for whatever reason."
] |
[
"Why do salt crystals form in almost perfect cubes?"
] |
[
false
] |
At the beginning of last summer I left a bottle with a salt and water substance out in the living room. when we came back from vacation the water was gone and in bottle salt crystals had formed. Now what I don't understand is how the crystals formed in almost perfect cubes. Shouldn't there just be a thick flat layer of salt at the bottom?
|
[
"Crystal shape is defined by the packing of the individual atoms/molecules that make up the substance the crystal is made of. Ice is made up of the packing of water molecules, rock salt is technically called ",
"halite",
" and is the results of close packing of sodium and chloride ions.",
"In the packing structure of halite the sodium and chloride ions sit in a three dimensional grid. In this grid each chloride is surrounded by six sodiums and each sodium is surrounded by six chlorides. This is what is known as a ",
"cubic crystal system",
" and is what determines the shape of the crystal when it grows."
] |
[
"I think you really have two separate questions here: why are salt crystals cubic, and why did my scenario result in fewer, macroscopically large crystals vs a flatter layer of many more finer crystals? ",
"I'll answer the latter question and leave the first one to someone else. Crystallization from solution entails a competition between the nucleation of new crystals and growth on existing crystals (along with other processes). The rate of these processes depends on the supersaturation of the solution in different ways. (Approximately speaking) high supersaturation favors nucleation and lower supersaturation favors growth. Slow evaporation results in low supersaturation. Thus, growth dominates and there are fewer and larger crystals instead of the many small crystals you'd expect if there was more nucleation.",
"Slow evaporation is a common technique for scientists that are trying to grow large crystals, e.g. for crystallographic characterization. ",
"Edit: last couple sentences in the first paragraph edited for clarity"
] |
[
"Nucleation (crystals initially forming) require molecules to meet and collide. That is far more likely to happen at higher supersaturations (i.e. when there are a lot more of them).",
"When there is low supersaturation, molecules are likely to meet crystals that have already formed, not other molecules. Hence, growth is favoured over nucleation.",
"That is a grossly simplified explanation, but it should be digestible to most people."
] |
[
"Is there a fundamental particle at every point in space?"
] |
[
false
] | null |
[
"Called virtual for a reason - they're fictitious representations of a more complicated underlying mathematical structure. It's somewhat misleading to believe that there actually ",
" little particles popping into and out of existence."
] |
[
"Now i'm intrigued. I'll take whatever you can tell me about this.\nAlso, thanks for probably clicking on a negative comment and then even correcting me."
] |
[
"In a \"pure physics\" sense, for most reasonable time scales, a point of space can be measured to have no object occupying it. For sufficiently short time scales, there is a corresponding uncertainty in the energy present in the system, and you can't be certain that there's nothing there. ",
"In our actual universe this is largely difficult to achieve in practice as the CMB pervades most of \"outer\" space, and even experiments on earth shielded from the CMB and other sources of particles still have neutrinos and dark matter flowing through them, even if they can't be detected (easily)."
] |
[
"[Computing] Does streaming a YouTube video use the same amount of cell data as downloading the entire thing?"
] |
[
false
] |
Title. For example if I streamed a normal YouTube video, would I use more or less data streaming it compared to downloading it with say: YouTube Red?
|
[
"Streaming ",
" downloading. The term \"streaming\" refers to playing back a media file while it's downloading -- the same data has to to end up on your computer regardless of whether it's being written to a file or immediately played back and then discarded.",
"That said, each YouTube video is available in multiple separate formats, codecs, and resolutions, and audio and video are stored separately. When you play a video, your computer initially receives a file called a DASH manifest that enumerates all of the available audio and video options, and then chooses which streams to play back based on local configuration data, e.g. what codecs your browser supports and how much bandwidth is available. If you use separate interfaces to save vs. stream a video, you may be selecting different files from the server, which may have different sizes. You can use ",
"youtube-dl",
" to see all of the individual streams available for a given video, with sizes listed for each, by invoking it with the ",
"-F",
" parameter."
] |
[
"I can field this one.",
"Youtube uses a form of network aware quality adaptation that will switch your stream to a lower bitrate stream in times of network congestion, to prevent client media players from buffering and interrupting playback.",
"So, the answer is that a stream in 1080p quality ",
" be the same bitrate as a 1080p download of that same source...but there is no real guarantee. You could get the same content, in a different codec/container combination for the download vs the stream, and if that were the case, you can bet that the files would not be identical. ",
"Plus, then you have the overhead of chunked encoding schemes vs the TCP overhead of transferring a file via a non streaming protocol download. We could extrapolate some numbers here, but this would have to be tested via a controlled environment.",
"And THEN on top of all of that: Wireless data providers use third party media transcoding services that can transcode, transrate, and rateshape these streams to avoid network congestion. My last company made a LOT of money doing that, until youtube and netflix went to HTTPS.",
"The TLDR is that its a very complicated answer."
] |
[
"No, answer the dern question. Is it more because of TCP overhead or less because of decreased bitrates during congestion?"
] |
[
"AskScience AMA Series: I am paleontologist Hans Sues, I study late Paleozoic and Mesozoic vertebrates. Ask Me Anything!"
] |
[
false
] |
Hi Reddit, I'm Dr. Hans Sues. I am a vertebrate paleontologist who is particularly interested in late Paleozoic and Mesozoic vertebrates. I first became interested in fossils when I was four years old and, as a high-school student, started collecting animal and plant fossils with a group of amateur collectors. Later I studied earth sciences and zoology and received my Ph.D. in biology. I have worked as a university professor and curator for many years. I am now Senior Scientist in the Department of Paleobiology at the Smithsonian's National Museum of Natural History. My field research has taken me to many countries around the world. I have done a lot of and a about fossils for general audiences. I look forward to talking with you! I will begin answering questions at 12 noon Eastern Time (16:00 UTC). Username: MESOZOICGUY
|
[
"Just got the most hilarious commentary with the lovely headline \"You are stupid - but Satan loves you\"",
"I quote:",
"\"Just seen you going to answer questions on Reddit about Palizoic and Mezosoic eras being what you claim are 65 to 540 million year ago.",
"You're obviously a simpleton but even so you may be able to operate a calculator and work out this equashun: Earthworms build topsoil at the rate of one inch per five years.",
"Therefore if Earth was 540 MYO there would be 540 divided by 5 = 108 million inches of topsoil everywhere.",
"Clearly there isn't and therefore you head has been stuffed with garbage.",
"Darwin actually proved Earth is young and The Flood was a worldwide catastrophe about 4,350 year ago and during the 330 days of downpour, inundations, drain-off and drying all the land creatures were buried in deep sediments that idiots like you label Mesozic, Cretinous etc.",
"Mary Schweitzer has had the grace to admit that she know her silly 65MYO dinosaur tissue is wrong but she is going to believe it anyway - so why are you so deluded as to believe there was masses of dinosaurs 540 MYA?",
"Instead of prattling nonsense why not do the world a favour and go poking about the secret storerooms and drag out some of those Nephilim giant bones?\"",
"This, folks, is why we need to get better science education in our schools!"
] |
[
"The largest dinosaurs were longer than the largest mammal today, the Blue Whale. However, the Blue Whale attains much greater body weight and thus still is the largest backboned animal of all time."
] |
[
"Do I assume correctly that you are talking about commercial fossil hunters? Academic paleontologists in North America are very divided on this. (European and Chinese researchers usually work with commercial and private collectors.) I know many commercial fossil collectors and welcome them as long as they abide by all laws for collecting and show professional standards in other respects (example: accurate, detailed records for sites with fossils)."
] |
[
"If light is massless, how can it have energy and still follow E=MC^2?"
] |
[
false
] | null |
[
"E = mc",
" only applies for massive particles which are not moving. A photon is both massless and ",
" moving.",
"The full equation is:",
"E",
" = (pc)",
" + (mc",
")",
".",
"For a massless particle, m = 0.",
"So this simplifies to E = pc, where p is momentum."
] |
[
"p = mv also does not apply to a photon, it is an approximate equation for the momentum of a slowly-moving, ",
" particle.",
"A photon has both p and E not equal to zero, but it has m = 0.",
"Also, aren't all particles moving unless they're at absolute zero?",
"If you have a massive particle all alone in space, unaffected by any external forces, you can always choose a reference frame such that it's at rest."
] |
[
"p = mv also does not apply to a photon, it is an approximate equation for the momentum of a slowly-moving, ",
" particle.",
"A photon has both p and E not equal to zero, but it has m = 0.",
"Also, aren't all particles moving unless they're at absolute zero?",
"If you have a massive particle all alone in space, unaffected by any external forces, you can always choose a reference frame such that it's at rest."
] |
[
"Does acupuncture work?"
] |
[
false
] | null |
[
"You won't get anyone giving you medical advice here, but acupuncture is still controversial and most scientists will tell you it's no better than placebo. The problems associated with conducting acupuncture studies make the waters murkier too and there are many studies fraught with methodological inconsistencies and errors. "
] |
[
"most scientists will tell you it's no better than placebo",
"That's a funny turn of phrase, given that placebos themselves can be tested against each other and found to have variable levels of effect depending on things like color of pill / bottle, person who dispenses them, etc. And also that even when the subjects KNOW the treatment is a placebo, it looses little effectiveness.",
"If a placebo is more effective than no treatment, is there any reason to not use it? As placebos go, acupuncture has a decent evidence for positive effect in pain management, likely because it considered some time and mental investment is results on the part of the recipient, and maybe throws in a bit of guided visualization."
] |
[
"To piggy back off this comment, chiropractors lobbied for a licensing requirement under the pretense of quality control. It was never intended to be an endorsement of efficacy. The only area that chiropractic treatment has any efficacy is for lower back pain, and the results are no more impressive than standard PT. Any claims beyond that are wholly unsupported by the evidence, and unfortunately there are documented cases of chiropractic treatment resulting in injury and death. However, infrequent those instances may be, the risk doesn't seem to justify potential benefits."
] |
[
"Do the kinds of collisions created in supercolliders ever occur naturally?"
] |
[
false
] | null |
[
"Yes. There are extremely high energy cosmic ray collisions happening in the atmosphere right now."
] |
[
"The most intense particle collision known to have occurred on Earth involved the so-called Oh-My-God particle at over 20 million times the energy in LHC collisions.",
"You're comparing a \"lab frame\" energy to a center-of-mass frame energy. The center-of-mass frame energy of the OMG particle colliding with a nucleus in an air molecule would be much less than 20 million times the energies of LHC collisions."
] |
[
"Furthermore, these collisions are much higher energy than in the LHC, up to a million times higher, or more.",
"The LHC is the highest energy particle accelerator ever built by humans, but in comparison to naturally occurring collisions from cosmic sources, it's actually a pretty low energy beam."
] |
[
"When you eat something that is labeled as having a certain number of calories, what percentage of those calories does your body actually absorb, and how much is left in the excrement that is produced?"
] |
[
false
] |
I realize that the answer is probably based on a few variables, like what kind of food it is, and the metabolism of the person eating it.
|
[
"In his book ",
"\"Catching Fire\"",
", biological anthropologist Richard Wrangham has a very nice section on the measurement of food energy and how it's worked through the human body. ",
"As MarineBoy said, it's the science on the subject is pretty soft, but it does seem clear that the traditional method of using a calorimeter is not very good. It appears that the type of food, and even the preparation of the same food, affects our uptake of calories from it (Wrangham 2009). ",
"According to Wrangham, it follows that cooking food is essentially a way of \"digesting\" outside the body. This allows us to make better use of it once it gets to our stomachs. He suggests that cooking may even be what \"made us human\" because it freed up calories that we would normally have used for digestion and allowed them to instead go to brain development. "
] |
[
"In his book ",
"\"Catching Fire\"",
", biological anthropologist Richard Wrangham has a very nice section on the measurement of food energy and how it's worked through the human body. ",
"As MarineBoy said, it's the science on the subject is pretty soft, but it does seem clear that the traditional method of using a calorimeter is not very good. It appears that the type of food, and even the preparation of the same food, affects our uptake of calories from it (Wrangham 2009). ",
"According to Wrangham, it follows that cooking food is essentially a way of \"digesting\" outside the body. This allows us to make better use of it once it gets to our stomachs. He suggests that cooking may even be what \"made us human\" because it freed up calories that we would normally have used for digestion and allowed them to instead go to brain development. "
] |
[
"Here is a BBC documentary on the subject: ",
"http://www.youtube.com/watch?feature=player_embedded&v=rf_OWun4Y04"
] |
[
"Avagadro's constant. How'd they do that?"
] |
[
false
] |
I was always curious about how this number was calculated. What was the model of experiment(s) that determined it? A quick google search tells me it was related to charge and mass of the electron, but beyond that I wanted to know the particular methodology of the experiments that got it to within 5 or so sig figs. I work in a completely unrelated field, but my first major was chemistry and I was always curious, especially given the precision of the number and the time it was determined (no computers?!?). My educational background in relation to this question; I was a chemistry major at a decent science school in the US who dropped out senior year (p-chem got me).
|
[
"It wasn't determined ",
" early, it took well over half a century from Dalton proposing his theory of atoms until they actually got a handle on the scale of them. The first, very rough approximations were due to the kinetic theory of gases. Maxwell (one of the pioneers of that) in 1873 ",
"made the estimate",
":",
"the size of the molecules of hydrogen is such that about two million of them in a row would occupy a millimetre, and a million million million million of them would weigh between four and five grammes.",
"(10",
" is 1.66 mol, H2 weighs 2g/mol so 3.3 grams - not bad)",
"The first really accurate experiments (although by that, I only mean a single significant digit), just after the turn of the century, were due to Jean Perrin, who wrote a whole book about it (available ",
"here",
") He determined Avogadro's number through in 13 different ways, summarized in a table on ",
"page 206",
". Brownian motion (which Einstein had recently done the mathematical theory for), scattering of light, radioactive decay, etc. ",
"Prior to this, when it was only the kinetic theory of gases and statistical thermodynamics that gave evidence of atoms (outside chemistry), quite a few physicists, such as Mach, remained skeptical to whether atoms existed, or whether they were simply a kind of conceptual model. Perrin's experiments settled that debate for good. (Among ",
" though, the debate had mostly ended after the ",
"Karlsruhe Congress",
" in 1860)",
"Even today it's not the most accurate constant around, it's dependent on how much a kg is, and that in turn is still defined by a lump of platinum in Paris. At some future date though, we're probably going to redefine the kilo to be a particular number of atoms, setting Avogadro's number to a fixed exact number. (much as the speed of light redefined the meter so 'c' will always be the same number - although the length of a meter might change!)"
] |
[
"This was exactly what I wanted to hear. Thank you very much! The links to the literature I particularly appreciate."
] |
[
"In addition to Platypuskeeper's excellent response, the first answer with some real accuracy (in terms of significant figures) did not come until Millikan determined the charge of the electron. The charge of a mole of electrons was known (the number of coulombs per mole) so this allowed the calculation of the number of electrons in a mole of electrons by a simple conversion. "
] |
[
"How does polyethylene (both high and low density) crystallise?"
] |
[
false
] |
From what I've read, crystallisation plays a major role in the properties of polyethylene. However, I have been unable to find information about how these crystalline regions are formed. Even if you provide the name for the method of crystallisation, that would be much appreciated. Of course a full length answer would also be much appreciated. Thanks!
|
[
"Polymer crystals are rather different to other crystal structures.\nWhat you'll typically see is regions where the polymer chains are neatly \"stacked\", doubling back end to end. Between these \"crystal\" areas, you get more typical amorphous areas, where the chains are arranged randomly.",
"Basically, polymers stack together in some areas because it's favorable to do so, but at some point continuing this rigid arrangement would involve a lot of strain/unlikley arragnements, so it ends and there is a \"disordered\" region.",
"You could try looking at section 5 in this book (it has a google preview that might show you enough) ",
"http://www.cambridge.org/us/academic/subjects/engineering/polymer-science-and-engineering/introduction-polymer-physics"
] |
[
"From my research, I have figured out that polymers have crystalline and amorphous areas, which is why they're semicrystalline. So I gather that the only reason why there are crystalline areas is because it is more stable for the polymer to be arranged that way?"
] |
[
"A crystalline region occurs because there is enough of some given interaction in the polymer (van der waal forces, pi-pi stacking, hydrogen bonding etc) to overcome the strain energy of packing so neatly in a given area. However, as Devil noted above, this packing causes strain energy, which must be accounted for somewhere else in the system, and causes amorphous regions where the strain energy overcomes the other interactions and you get an amorphous area. It should be noticed that all most the most carefully crystallized and designed polymers are mostly amorphous. Polymers labeled semicrystalline are often <20% crystalline. Polymers, by their nature are pretty crappy at crystallizing, they are too large, and entropy highly favors amorphousness."
] |
[
"After sunlight exposure in vacuum, does the ISS hull become charged due to the Photoelectric Effect? If so, does this create any technical problems?"
] |
[
false
] | null |
[
"ISS has a ",
"plasma contactor",
" to dissipate any charge built up on its structure:\n",
"http://science1.nasa.gov/science-news/science-at-nasa/2001/ast13nov_1sidebar/"
] |
[
"It is really outstanding how many details have to be dealt with to make those missions possible. The technology employed to solve problems most of us would never think of blows my mind.",
"Thanks for your reply!"
] |
[
"IMO, space agencies are the biggest hubs of human intelligence. These guys are hyper efficient problem solvers. It's my dream to one day write code for a space agency."
] |
[
"Why does flat carbonated water taste so bad?"
] |
[
false
] | null |
[
"There's carbonic acid from the carbonation in the water, which has a bitter flavor."
] |
[
"I take it that this is the reason that fizzy water tastes different in the first place, too?"
] |
[
"Pretty much. There might be some other things that are different. Maybe the carbon dioxide has a flavor."
] |
[
"Will keeping my room at a lower temperature (about 60 degrees F) increase my resting metabolic rate?"
] |
[
false
] | null |
[
"I read something in The 4 Hour Body (Tim Ferris), that suggested something along those lines. But he was looking at the thermic effect of being in a swimming pool. Since water is 25x (IIRC) more thermally conductive than air, you can sit in a pool for a an hour or two and get a similar effect. Or you could take an ice bath for a shorter time and get similar results. I don't think the trick was to get to shivering temperature, but just to get to the point where your body has to burn a few extra calories to maintain the proper core temperature.",
"If you want to learn more on the subject, check out the book. I think he's only got one chapter dedicated to this topic, but the rest of the book has a bunch of other cool stuff."
] |
[
"It has been going around for a couple years that drinking ice-cold water is another method to increase your body's metabolic rate.... slightly.",
"This Wall Street Journal article",
" references a this ",
"actual study",
" on the effects of drinking cold water:",
"Here is an excerpt of the article: ",
"This study demonstrated an increase of up to 25% in REE following the drinking of 10 ml kg−1 of cold water in overweight children, lasting for over 40 min. Consuming the recommended daily amount of water for children ",
". These findings reinforce the concept of water-induced REE elevation shown in adults, suggesting that water drinking could assist overweight children in weight loss or maintenance, and may warrant emphasis in dietary guidelines against the obesity epidemic.",
"I would guess that cold outside your body would have a similar effect to cold inside your body. Not very much effect though."
] |
[
"I think I'll check that out at some point, appreciate it"
] |
[
"Does odor have mass?"
] |
[
false
] |
Or is odor just a property of mass? Could I physically measure odor and in what units? If I leave a place and my clothes smell like something from that place, is it because I am carrying the odor or small particles of the object that had an odor?
|
[
"When you smell something it is because airborne molecules have found their way to your olfactory receptors. You are smelling tiny little bits of whatever is producing the odor, sort of like a fine dust in the air. The mass of these particles will vary depending on chemical structure and how concentrated they are in your nose, but you can think of the mass of an odor that way if you want. "
] |
[
"So when you notice foul smells, take care not to think about the tiny little bits of whatever that just went in your nose."
] |
[
"Your nose is basically a particle detector. For something to have an odor, airborne particles have to reach the olfactory receptors in your nose.",
"Apparently there is a way of measuring odor strength quantitatively.",
"http://en.wikipedia.org/wiki/Odor#Measuring_odor_concentration",
"The aricle is also quite informative about odors in general. "
] |
[
"If I was to freeze water that contained a dangerous bacteria, such as a strain that caused dysentery, would it sterilize the water similar to boiling?"
] |
[
false
] |
In a controlled environment: the water is pure aside from the bacterial strain, placed into an ice cube tray, and frozen. Would it have any effect? If not: could the bacteria remain cryogenic?
|
[
"Bacteria can form cysts or endospores to endure unfavourable environments until conditions improve. While the freezing would undoubtedly kill many of the bacteria, it is not guaranteed to. Even autoclave sterilizers that use 121 degree celsius heat to kill bacteria are not 100% efficient in doing so, and while not exactly the same as in the situation you described, bacteria is routinely frozen in glycerin solutions and rethawed in the lab."
] |
[
"Related point: Sometimes it is a toxin (typically a protein) that the bacteria produces, not the bacteria itself, which causes negative symptoms. That's the case with staphylococcus aureus, which can cause food poisoning. If it's the toxin that is the problem, freezing won't have an impact as proteins are stable at cold temperatures. "
] |
[
"So labs can put the bacteria into a completely frozen state and thaw them without damage? Thank you for the answer, too."
] |
[
"Why does the Earth's crust have different densities? Like how is oceanic crust always more dense than continental crust? Is this a way to determine if a dead planet had an ocean or not?"
] |
[
false
] | null |
[
"Why does the Earth's crust have different densities? Like how is oceanic crust always more dense than continental crust?",
"Composition. ",
"Oceanic crust",
" is primarily ",
"mafic",
" igneous rock (i.e. basalt or gabbro) with an average density of 3.0 g/cm",
" ",
"Continental crust",
" is more variable in composition, but on average is more equivalent to a ",
"felsic",
" rock and has an average density of 2.7 g/cm",
" The extremely simplistic view of the origin of this difference in composition is the process of ",
"partial melting",
" and plate tectonics. If you partially melt the mantle (as you do at mid-ocean ridges) you end up with basalt. If you start to partially melt basalt (as you do at oceanic-oceanic subduction zones) you end up with an intermediate composition (between mafic and felsic), i.e. an ",
"island arc",
". If you smoosh island arcs together to build a larger mass of less dense intermediate material and then start to partially melt that (like you do at oceanic-continental subduction zones) you end up with a felsic rock. Repeat for a few hundred million years and you end up with distinct portions of plates that are oceanic and continental material.",
"Is this a way to determine if a dead planet had an ocean or not?",
"Maybe? The process described above (i.e. the formation of continental crust) appears to be a direct consequence of long-lived, Earth-like plate tectonics. In turn, the existence of Earth-like plate tectonics ",
"appears to require large quantities of available water",
". Whether this formally requires the existence of a global ocean at some point, I'm not as sure and maybe somebody more grounded in either the initiation of plate tectonics or planetary geology could weigh in on that point."
] |
[
"Generally, melting point increases as a function of pressure, so as a rock gets deeper, it gets harder to melt the minerals that make up the rock. The melting at subduction zones is primarily from the addition of water, which lowers the melting point of minerals. The water is primarily released during dehydration reactions, which are in part controlled by the pressure, so the increase in pressure does play a role in melting, but it's not as direct as implied in your comment."
] |
[
"Does compression due to water factor into this at all, or is it mostly related to those geological processes you mentioned?"
] |
[
"When an airlock is breached in outer space, what happens to the air that gets sucked into the vacuum?"
] |
[
false
] |
Let's say that a spaceship has a compromised airlock. The air is sucked out through the breach, and everyone onboard dies. What happens to the air that gets sucked out of the spaceship and into the vacuum? Does it disperse like dust? Does it stay in one place? Does it drift in one direction forever?
|
[
"Good point. If you hadn't included that, people never would have known that I was referring to currently understood science. :)"
] |
[
"Suction is a macroscopic effect. Particles in an area are constantly moving in all directions, and this motion averages out under static conditions. When containment in space is lost, there is an unbalancing of particle motion at the barrier between the pressurized area and the unpressurized space. More particles are moving outward into space, and no particles are moving into the ship from space.",
"On that level, it is easy to see what happens to the air particles - they continue on the trajectory they had when they left the ship. Remember Newton's law: a particle in motion stays in motion until acted on by a force. Once the particle leaves the ship, it continues on its trajectory until affected by another force."
] |
[
"Suction isn't a force. There are only four forces - EM, weak, strong, gravity.",
"Once the particles are in space, \"temperature\" is no longer a good descriptor of them because they aren't a coherent gas. They are individual particles flying in specific directions. Thus, the Joule-Thomson effect doesn't apply."
] |
[
"Questions from 2nd Graders about Animals - Students posting from 3:30 - 4:30 EST"
] |
[
false
] |
Dear AskScience, First of all, thank you for once again interacting with my students and ! You're all my favorite people on the internet, and you always go above and beyond. I am currently working with a group of 2nd graders once a week during an afterschool program. We are working on a project to create a book about animals, in which each student will contribute a page. Each student has chosen an animal, examined a picture of it, and generated questions about that animal. They have made some predictions about their questions, and are now seeking answers. We have discussed several ways students can research the answers to their questions. One resource that isn’t often talked about is asking an expert. This is where you come in, AskScience! Our 2nd graders are very eager to learn and are excited about getting to ask scientists about the animals they have chosen. Some questions are more in-depth than others; as an expert, perhaps you might be able to supply them with some additional information, fun facts, or prompts that might lead them into asking deeper questions. On my end, I will be walking around monitoring responses, helping students to understand and respond to the answers, and generate new questions. When this is over, the students will be writing a few sentences about their animal, will find or draw some pictures, and will compose a page that will go into the final, published book. Please remember that these students are about 7 and 8 years old, so choosing appropriate language is important! I have absolute faith in the AskScience community. (I would ask if anyone has a potentially offensive/inappropriate username, they post on a throwaway. ) The students will post on a shared account: "2ndGrader". I will be posting on my own account. Hopefully everything will go smoothly! Again, thank you so much for being a wonderful community, and thank you to the individuals who are taking the time to respond to the children. If you have any questions, please feel free to PM me!
|
[
"We ask our users to help the moderating team keep this discussion friendly and age appropriate by judicious use of reporting and voting.",
"Remember to target your science-based answers to a 2nd grade level. Follow up questions or additional interesting information is encouraged, but top level is reserved for the kids:",
"Kennedy: Siberian Tiger",
"Darrian: Cobra",
"Porter: Lynx",
"Kaiya: Bat",
"Damari: Bald Eagle",
"Cynthia: Rock Hopper Penguin",
"Maddie: Thorny Devil",
"Ashly: Baboon",
"Emily: Hydromedusan Jellyfish",
"Kennedy: Ostrich",
"Kennedy: Atlas Moth",
"Maddie: Poison Arrow Frog",
"Maddie: Monitor Lizard",
"Lexie: Okapi",
"Lexie: Morpho Butterfly",
"Olivier: Electric Eel",
"Maddie: Jackson Chameleon",
"Lily: Ruffed Lemur",
"Sophie: Bald Uakari",
"Olivier: Anaconda",
"Cynthia: Zebra",
"Cynthia: Peacock",
"Ashly: Knob-tailed Gecko",
"Ashly: Pygmy Marmoset",
"Some of those near the bottom could use some attention. Remember, regular AS rules apply - layman answers are encouraged, just please make sure answers are correct and sourced if possible!"
] |
[
"Hello Darrian!",
"1) Snakes hiss because they want to warn other animals to stay away from them! They don't want to get hurt, stepped on, or beaten up.",
"2) Some snakes will wag their tails because they are will use it as a warning call (rattlesnakes) or they may use the tail wag to distract their enemies so they can escape. ",
"3) Snakes taste with their tongue, but instead of how we taste things like you and I can do, snakes taste the air. When you see a snake flick his tongue, he is tasting the air. The reason why it is forked is that there are two little holes in the roof of its mouth that they stick their tongue into in order to figure out what it is they are tasting."
] |
[
"I can help with the whisker question. Whiskers are just like regular hair, except they are thicker and connected to more nerves, which help animals feel through the whiskers. It's like how you can feel when someone moves their fingers through your hair, except much much more sensitive.",
"When cats, dogs, otters, Siberian tigers, or other animals with whiskers are in a small place or a dark place, their whiskers help them get an idea of their surroundings, kind of like you might feel your way down a dark hallway with your hands.",
"In fact, hundreds of thousands of years ago, ",
" used to have whiskers. Some people still have beards and mustaches, but these would have been whiskers more like a cat or a dog."
] |
[
"How and why does scratching relieve an itch?"
] |
[
false
] |
I'm talking about general itches which result from skin irritation, like a tickle or a mosquito bite. What I don't understand is how a sharp utensil like a fingernail can stop the itch, or at least offer brief relief until the itch returns. How is it that scratching has this effect?
|
[
"Not to hate, but: ",
"I'm not sure scientists consider it mundane. Scratching has a lot of negative consequences (it can be absolutely terrible for your skin), its a symptom of a lot of diseases, and it's a side effect of a lot of drugs. As a noxious stimulus, severe itching isn't a lot better than severe pain. There would probably be good money in a cure for itching, too. I think the more plausible explanation is that itch and the scratch reflex are complex neurological phenomena, so despite solid efforts, their neurological bases haven't been teased out completely yet. "
] |
[
"Those are all very good points and a much more plausible explanation.",
"Today I learned to be less flippant with my comments on AskScience. "
] |
[
"Coming from a medical student:",
"This was discussed in our neuroanatomy class, my teacher made it seem that scientists don't really know. I just tried looking on the internet further, found an article with this line: \"Currently, there is no proven hypothesis on the functional basis of scratching the kind of transient itch we experience every day.\" The article was written in May 2011, so I guess new information could have come out, but if so, I haven't seen it. ",
"Source: Class notes, ",
"http://www.yalescientific.org/2011/05/the-mechanisms-and-perception-of-itch/"
] |
[
"What causes a specific note to be produced when feedback is looped through an amplifier back to the pickup?"
] |
[
false
] |
Hey guys, I was playing my guitar today and I noticed when you crank the amplifier gain and have your volume at a reasonable setting, you generate a feedback loop. This isn't new but what I noticed was the note it produced, it was inline with the harmonic points of the string, and not the note of the open string itself. My previous physics knowledge taught me that a harmonic is a temporary node on the string, similar to a fret except that it isn't a physical node. When a harmonic is struck, the entire string has energy producing the wavelength but it is completely stationary at the node point. These nodes are perfect divisors of the entire length of the string, causing the frequency to multiply linearly (1st harmonic is the open string, 2nd harmonic is the string divided in half, 3rd is the quartered string and so on). What causes the string to produce a note that coincides with the harmonic points on the string, but without any nodes? As a footnote, if you have a guitar play the E harmonic on the A string (7th fret), it's an E5 apposed to the A3 you play with the open string. That E5 is the note my amplifier feeds back to my pickup, except there's no human interaction creating the note. And it isn't a harmonic played by the string.
|
[
"Yes that explains the feedback loop, but what determines the frequency the loop is producing? If I were to pluck the string that builds energy I get as I mentioned, an A3, or the 5th string I'd get just that, an A3. When frequency is resonating in the instrument it produces a completely different note. ",
"Edit: I'm more confused as to why this particular string is building a feedback loop, while other strings completely nullify the effect, and why that string doesn't produce the note it would at open position."
] |
[
"image",
"If a string is vibrating at its fundamental frequency (say, 100 Hz), the entirety of the string is up, then down. This vibrational mode is easily excited by a sound source at that frequency, located 'above' the string in that image.",
"If the speaker instead produces a 200 Hz tone, this could potentially excite the second harmonic of our string. However, if the entirety of the string is approximately equidistant to the speaker, then the speaker pushes equally on the left and right halves of the string (see image).",
"The mode shape of the second harmonic is the left and right halves of the string moving in opposite directions. One half is moving up, while the other moves down, then they reverse directions. Pushing on both halves in the same direction therefore does not excite this mode.",
"If the speaker produces a 300 Hz tone, it would excite the third harmonic of our string. Because this vibrational mode is 'lopsided' (2/3 of the string is moving upwards, while 1/3 is moving downwards, then the directions reverse), it is still easily excited by a relatively distant sound source.",
"A 400 Hz tone corresponds to the fourth harmonic, but because this again involves exactly half the string moving upwards while the other half moves downwards, it shouldn't be excited much by a relatively distant sound source."
] |
[
"The susceptibility of the string to excitation by a nearby speaker seems greatest at odd-numbered harmonics, since those involve unequal quantities of string moving towards and away from the speaker. Even-numbered harmonics have the same amount of string moving away/towards, which would seem to lower the response, though orientation of the string relative to the speaker could change this.",
"Lower frequencies have greater energy associated with them, but are also usually somewhat attenuated by the amplifier circuit to prevent a 'muddy' sound.",
"My guess is that these two effects combine so that the product of amplifier gain and string susceptibility is greatest at a middle-ish frequency, such as 500 Hz. A particular string harmonic near that peak will be the one which develops into feedback. So perhaps your D string (146.8 Hz) has the greatest response with its third harmonic (440.5 Hz), and that's the feedback frequency."
] |
[
"How does a sheet of laminated paper or thin metal make a wobble-wobble sound when you...wobble it?"
] |
[
false
] |
I'm talking about this kind of thing:
|
[
"This is caused by a process called buckling (in this case: elastic buckling). When you put lengthwise force, e.g. bending stress, on a thin piece of material it will start to yield (strain) a little bit as you increase the force. At some point, the material will not be able to withstand the force anymore and yield to the side, quickly relieving the stress on the material. The stored up elastic energy is then released all at once as an impulse, which on a sheet of material creates that wobble-wobble sound."
] |
[
"When the board is flexed, there is some warping that resists deformation, until it suddenly plops through. According to \"Musical Instrument Design: Practical Information for Instrument Making\", this causes vibrations in the sheet that make the wobbling sound.\n",
"https://books.google.se/books?id=CuHi9edzELEC&pg=PA53&lpg=PA53&dq=wobble+board+acoustics&source=bl&ots=MimB6XV8II&sig=AcV34nvGDnFasMBcHdOTTuGtfg4&hl=sv&sa=X&ved=0CFgQ6AEwCGoVChMIv9yCzq_ZxwIVRowsCh19SQE9#v=onepage&q=wobble%20board%20acoustics&f=false"
] |
[
"Wouldn't it be the same principle as a regular string? Only because it's a planar object and the frequency of the wave propagated by stress in the material differs depending on which portion of the sheet you're bending it would produce several soundwaves at once?"
] |
[
"Is it possible for a planet to rotate about two axis' at the same time?"
] |
[
false
] |
With the Earth, the North and South poles are essential frozen because they aren't as exposed to the sun as much as the equator. Is it possible for a planet to rotate about a second axis, essentially constantly changing which poles are frozen or a tropical paradise?
|
[
"In 3D space, rotations on any number of axes can be reduced to rotation about one axis - so any planet that rotates about two axes is merely rotating about one axis that's the sum of the two rotations."
] |
[
"That's actually really simple to understand.",
"\nI drew you a little picture, just picture how the ball would spin if he would spin on both shown axes.",
"http://m.imgur.com/odaLB4o"
] |
[
"That occurs because of the ",
"tennis racket theorem",
", which applies to objects with three different moments of inertia - like the T handle in the video you linked to. For a cube or sphere, this would not occur.",
"It's really cool because it was only discovered in 1985 - it's a phenomenon that wasn't readily noticed here on Earth but readily apparent in space. But now that we know it exists we can see ",
"some occurrences",
", like in the eponymous tennis racket."
] |
[
"Why does matter travel through time in only one direction?"
] |
[
false
] |
Or is that a misconception based on our perception of reality? EDIT: Expanding slightly... Matter seems to travel in the other three large dimensions relatively freely. Why should time be any different?
|
[
"We don't know."
] |
[
"You are making it seem as though time is a complete illusion. We might not perceive objective reality but that doesn't mean our perception isn't veridical to some degree. It's the only mode of perception that means anything to us, so it means ",
" to us. "
] |
[
"You are making it seem as though time is a complete illusion. We might not perceive objective reality but that doesn't mean our perception isn't veridical to some degree. It's the only mode of perception that means anything to us, so it means ",
" to us. "
] |
[
"Why don't non-spiraling galaxies collapse on themselves?"
] |
[
false
] |
Since there's no rotating motion, there isn't anything to counteract the average gravity, right?
|
[
"When you see the word 'spiral' in order to describe a galaxy, it simply denotes how the galaxy is visually structured in order to make it easier to classify all the different types out there. The lack of the term doesn't imply the galaxy isn't rotating, because they all are.",
"Hope that helps."
] |
[
"Elliptical galaxies have stars with more randomly oriented velocities. Their stars still have a \"standard deviation\" of velocities (also called a velocity dispersion) that is comparable to the rotational velocities of stars in elliptical. So basically you have a lot of stars in lots of different orbits rather than a single plane of orbits."
] |
[
"Elliptical galaxies don't have very much bulk rotation."
] |
[
"Will you lose your cigarette addiction if you're in a coma for a long time?"
] |
[
false
] | null |
[
"It sounds like what OPs really wanted to know was \"is there anything about a coma that would leave addictions in their place or slow down the withdrawal process\". Do we know anything about that?"
] |
[
"It sounds like what OPs really wanted to know was \"is there anything about a coma that would leave addictions in their place or slow down the withdrawal process\". Do we know anything about that?"
] |
[
"Not solid science but damn near relevant experience."
] |
[
"Would it be possible to design a spring with variable stiffness depending on an applied electrical current?"
] |
[
false
] |
Say I want to design a constant force translational spring with a decent amount of play. For a constant force Fc, I guess the spring would have to obey Hooke's law F = kx, where k would equal to Fc/x. Are there any materials where one could vary the stiffness using a current, or otherwise achieve a similar result? Current designs for constant force springs seem to have very little play. I could use an actuator but want to keep it as light as possible.
|
[
"Not quite what you're looking for, but there are magnetorheological dampers, which are hydraulic pistons filled with a ferrous fluid. An electrical current is applied to an electromagnet- usually just a spiral of copper wire inside the piston, and this causes the ferrous particles in the fluid to align, thereby increasing fluid viscosity. The piston becomes more difficult to move. If the electric current is relaxed then the fluid looses viscosity and the damper becomes more able to move. The amount of electric current can be fine-tuned in order to fine-tune how much force is resisted by the damper.",
"So you could have a spring next to an MR damper, and by modulating the damper you could modify both the apparent stiffness of the spring as well as the apparent restoring force. The problem with this setup is that the maximum restoring force is limited above by the natural stiffness of the spring (when fluid viscosity is zero), so you can have the spring's natural restoring force or you can reduce this. However, the apparent stiffness can be much larger, since the natural spring with a high viscosity state would lead to an overall resistance to compression that is greater than either the spring or MR damper individually.",
"In other words, you're going to have to do active control and you've got options for force response and this is going to make the entire system a look lot more complex that just a spring with a variable stiffness. Because you need active control you probably want to figure out whether the spring is being compressed or is relaxing, so you'd probably need a linear distance encoder or an LVDT in the system as well."
] |
[
"There are actually magnetorheological elastomers, where the iron particles are embedded in a rubber or urethane which accomplish stiffness modification with magnetic field similar to MR dampers: ",
"https://en.m.wikipedia.org/wiki/Magnetorheological_elastomer"
] |
[
"So when the current is turned on, my piston would have much larger stiffness, and when turned off the fluid inside would relax making it less stiff?",
"Sounds familiar"
] |
[
"Quantum superposition"
] |
[
false
] |
First time asker, and will most likely have to rephrase or explain this more deeply, since i don't understand the subject as well as i would like to, but here goes. In quantum superposition is a particle which can be observed as two particles actually representing the opportunities that particle has at that moment, and does the particle "think" that it is not being observed so it shows it's potential locations. Or are locations even meaningful in quantum physics? Like i said the question isn't very clear, but i hope someone could shed some light upon at least one of the things i was asking.
|
[
"After you test the particle, the experimenter-particle system is in a superposition of \"experimenter sees particle in A\" and \"experimenter sees particle in B\". You only experience one branch of the superposition though; some people think this implies that an \"alternate universe\" is created where you experience the other."
] |
[
"That's not an accurate statement of the many-worlds interpretation. The universe ",
" have already decided which state the particle is going to be in; through Bell's theorem, you can prove that such a universe would not behave like ours does."
] |
[
"That's not an accurate statement of the many-worlds interpretation. The universe ",
" have already decided which state the particle is going to be in; through Bell's theorem, you can prove that such a universe would not behave like ours does."
] |
[
"What defines a sound's \"texture\"? Like how some guitars sound softer, some rougher, etc."
] |
[
false
] |
I understand that sound waves have frequencies and amplitudes, but I don't understand why two sounds that have the same frequencies and amplitudes can make different noises. Another example is peoples' voices. Why does my voice sound different than my friend's voice and also different than my dad's voice, etc. There are so many people in the world that if freq. and amp. are the only defining aspects of a sound, people would have to have very similar voices. I hope I'm making this question understandable. Thanks so much for any help. The real internet is too hard for me.
|
[
"As I don't know too much about physics, I can't go too much in to the nitty gritty of it, but what you are referring to is called \"Timbre\" (pronounced TAM-ber). This is the quality of a sound separated from it's pitch and loudness. I can play the same pitch on a piano as on a guitar at the same volume but they will sound different due to their timbre. This is an effect of the composition/quality of the strings, the wood the instruments are made of, amplification medthods, and even the room you are in. It has to do with what combination of harmonics each instrument is producing as well as the \"attack\" and \"decay\" of the sounds.",
"http://en.wikipedia.org/wiki/Timbre",
"EDIT: smelling"
] |
[
"See this image here",
". Different instruments can have the same volume (amplitide) and same pitch (frequency), but completely different sound.",
"It's because they have ",
"different waveforms",
". Thinmk about them as having different shaped waves.",
"(Ironically, all waves can be reduced to a sum of different sine waves. ",
"See this article on fourier series for more details",
")"
] |
[
"This is the correct answer. To OP, A simple example of a Timbre is a sine-wave vs. a square wave (both can have the same frequency and amplitude). Now you can imagine any type of shape that repeats at any frequency, and have a certain volume (amplitude). That's why people voices are different. and that why 'Octates' exists (i.e. the 'shape', can be the same shape 'compressed' twice/n-times and vibrating at the same rate/frequency). I hope this helps."
] |
[
"How does soap work to get rid of odors and bacteria?"
] |
[
false
] |
[deleted]
|
[
"Let's say you're washing your hands in two hypothetical scenarios: 1) You just ate an orange and don't want your fingers to smell like a fruit 2) You haven't bathed or washed your hands in days and now they're starting to smell.",
"In the first case, you could argue that some of the smell is coming from fat soluble compounds, and the introduction of soap/scrubbing helps dissolve them in water and wash them away.\nIn the second case, chances are the smell is coming from compounds produced by bacteria. Just like in the first case, soap can help them dissolve in water. Additionally, soap helps removal of bacteria from your hands as their outer membranes are considerably \"fatty,\" and soap/scrubbing helps remove them from your hands and wash out into the water."
] |
[
"Soap is a surfactant, so the most basic explanation as you said is that soap molecules have two ends, a hydrophilic (water loving) end which attaches to water molecules, and a hydrophilic (water hating) end that attaches to oils and dirt. When you wash your hands, one end of the soap molecules attaches to the dirt and oils on your hands, and the other end attaches to the water. So the entirety of the molecule with the dirt attached gets pulled away by the water. \nSoap also lowers the surface tension of water.\nThe odours are due to bacteria. They also get washed away in the same process. The less bacteria, oils and dirt on our skin the cleaner we are. "
] |
[
"Here's an illustration: ",
"https://www.sarthaks.com/21470/explain-the-cleaning-action-of-shop",
"Basically the hydrocarbon tail of soap molecles will stick to the surface of dirt or bacteria membrane pulling it away from the skin. In presence of water, the molecules form micelle trapping the dirt in the core with the heads(polar) coming in contact with water. So washing away with waters removed these micelles with trapped dirt. "
] |
[
"Is using anti-bacterial hand sanitizer as healthy as actually washing your hands?"
] |
[
false
] |
[deleted]
|
[
"It depends strongly on your situation.",
"In everyday life there is no reason to use hand sanitizer because washing your hands is better for your health. First of all, what you want to remove is potentially harmful bacteria and viruses. Washing your hands properly does this. You don't even need to get rid of ALL the pathogens because infections are dose dependent (e.g. you need a certain number of a particular pathogen for it to cause an infection) - this number varies a lot between pathogens. (The number is quite high for certain food borne bacteria while it's is extremely low for say norovirus...)",
"Second, when using sanitizers or antibacterial soaps you may compromise on your normal flora, that is, the beneficial bacteria colonizing your skin without causing infections. What these bacteria do is still under investigation but in general it is believed that they inhibit colonization of other, potentially pathogenic, bacteria.",
"Third, given that your skin is intact you are not going to get infected. The skin is quite thick for a microbe and they are not, in general, known to be able to \"drill\" themselves through it. The risk comes about if you touch your eyes, nose, mouth... or food with those dirty hands allowing a easier entry route for the pathogen (again take in count the type of pathogen and the number of them required for an infection).",
"In some situations, however, there may be a point to use that hand sanitizer. That would be if e.g. taking care of a sick person - especially if this happens in a hospital. You may not have time to wash your hands as often as you should and more so.. you're skin would dry out if you did! Thus, hand sanitizer is an excellent option. Also, say you're getting some fast food and don't have possibility to wash your hands - sanitizer might be a good idea."
] |
[
"Overtime, the bacteria may become resistant to sanitizers. Especially the non-alcohol ones. Also, you don't flush the debris away. You rub the dirt into your hand. "
] |
[
"At least for anti-bacterial soap, there seems to be ",
"no documented health benefits",
" over normal hand soap..."
] |
[
"Is it possible for microorganisms to leave our planet without aid of rockets or other advanced mechanics?"
] |
[
false
] |
I realize that weather balloons can go fairly high, but not enough to escape the gravity well. I also have heard theories that some bacteria on earth may have come from asteroids/other planets. Is this only possible as a result of massive impacts/asteroids/planetary impacts? Removing rockets from the equation, would it be possible for small enough organisms, spores maybe, to escape the atmosphere?
|
[
"Ejecta from large bolide impacts can escape the Earth's gravitational influence. Also, we know that extremely hardy life exists on our own planet- they're known as ",
"extremophiles",
" and they can survive under extreme physical and chemical conditions. The combination of these two things have lead people to suggest that life can make natural interplanetary journeys. I haven't seen much compelling evidence for this having happened, but the theory is an interesting one.",
"Another phenomenon which may eject material out into space are volcanic eruptions (if they are sufficiently large/the planet has a small enough mass- i.e. Io). I don't know whether they'd make a possible vector for organisms."
] |
[
"Panspermia: ",
"http://www.spaceref.com/news/viewpr.html?pid=7089",
"Mushrooms spores are < 5 microns in size in some species, and could survive in space according to some researchers. Not fact, but worth further investigation. Fungi are very important to breaking down raw materials to make them ready for plant and animal life."
] |
[
"It is ",
" easy for impact ejecta to escape Earth's gravity; there are no cases where a volcano has erupted material at greater than escape velocity. Meteorites have been ejected from the Moon and Mars by low angle impacts on these largely airless, low-gravity, worlds. It would require a very large impact to eject material from Earth. "
] |
[
"If someone has a fully sealed iris (like the One that recently reached front page), why can't doctors simply cut a pupil into the iris?"
] |
[
false
] | null |
[
"A pupil is not the lack of iris. If you were born with no lips they would not appear by cutting the area directly above and below the mouth hole. It would bleed and begin the normal healing process. This would work out far worse in the situation involving an eye."
] |
[
"The iris wouldn't function the way it's meant to (constriction and relaxation) so the person would likely have extreme sensitivity to light. This is one among many problems that could result: blocking of the drainage system of the eye --> increasing eye pressure resulting in damage to the optic nerve (glaucoma). At her age it would also be useless as that eye has been deprived of any sensory input since birth; therefore, the photoreceptors and the brain area responsible for interpreting those sensory inputs are underdeveloped and would not result in good vision (amblyopia). Also, usually any defect in the anterior segment of the eye is associated with other developmental abnormalities in other areas of the eye which might further contribute to a poor prognosis. "
] |
[
"Could I have a link to that post?"
] |
[
"Why do we cry?"
] |
[
false
] |
I'm talking about tears due to emotion, not normal physiological lubrication or irritant removal. Evolutionarily, it seem like a terrible idea to have a stress response that includes obscuring your vision and making your nose run. What advantages could crying confer to a species that makes it so widespread in humans?
|
[
"Beware assuming your cultural norms apply to humanity as a whole."
] |
[
"It's an open question. ",
"Wikipedia lists several working theories.",
" Note that the last one specifically addresses your 'obscured vision' dilemma, in that by signaling submission by outwardly displaying a handicap which indicates that your defenses are lowered, others in a group might be more willing to give assistance"
] |
[
"Humans are an extremely social species. You have to consider many traits with regard to how well they enhance fitness in a group. I presume crying would alert other people to know something is wrong."
] |
[
"What colour was the cosmic background radiation?"
] |
[
false
] |
More importantly, is it more likely that it was a long wavelength colour, or a low one? (My understanding is that over time, the wavelength of the light from the cosmic background radiation got longer and longer, until it reached infra red, sorry if I'm misunderstood.)
|
[
"At recombination (when the universe became clear), the temperature was around 4000 kelvin, so it was glowing red."
] |
[
"No leave it up."
] |
[
"Thank you! Now that I have my answer, do I just delete this, or do I leave it up for anyone else curious?"
] |
[
"Can cats survive their own terminal velocity?"
] |
[
false
] |
I heard this was true, but I'm not sure. If this is true could a cat survive a fall from an airplane or, if it were properly insulated from cold and low pressure, space?
|
[
"Yes"
] |
[
"great graph"
] |
[
"Disregarding the cat's survival; terminal velocity is terminal velocity, whether you fall from the minimum point to reach it or the outer edge of space just means you have a longer fall till you reach the ground at the same velocity."
] |
[
"Does tanning decrease vitamin D intake?"
] |
[
false
] |
Whenever someone is regularly outside, do they absorb less vitamin D because of the melanin their body produces? Do "whiter" parts of a person's body take in more vitamin D than "tanner" parts?
|
[
"Melanin does block vitamin D production in the skin. It's a problem for dark skinned people in northern climates. For light skinned people, getting a tan decreases production, but you get something like 10,000 or 20,000 units per hour when sunbathing, so it doesn't take much exposure to get what you need. "
] |
[
"How much is one unit? What kind of number is \"daily recommended dosage\"? (i realize vitamin time spans are probably larger than days, maybe asking about monthly recommended dosage makes more sense?)"
] |
[
"Vitamin D isn't absorbed through the skin. For vitamin D3, specifically, UV light converts 7-dehydrocholesterol into vitamin D3. VD3 is then hydroxylated in the liver, then kidneys, through activating pathways to make the active form (1, 25, dihydroxy vitamin D3). "
] |
[
"Why does it take so much longer to tune to a digital channel than an analog one?"
] |
[
false
] | null |
[
"It doesn't take longer to tune in, however it does tak longer to display an image. Digital image streams are generally 'differential' streams, that is, since each frame is so similar to the one before it, it's easier to compress and transmit only the differences between each frame. Once in a while, a 'key frame' is transmitted, which is essentially a whole frame, not just the differences. Until your receiver gets a key frame, or until it gets enough of the stream to build a whole picture (i.e. all pixels have changed since tuning in) it just displays a blank."
] |
[
"The main reason is that digital channels contain compressed information, and proper decompression is only possible from certain points. ",
"Video contains key frames which encode the whole picture, and other frames which only encode changes between frames. There, proper decompression must start at a key frame. If display started at another frame, the image would be very messed up until the first key frame.",
"You may notice this effect when the signal is weak and there is occasional corruption. Instead of disappearing at the next frame, the corruption lingers for a bit and is transformed by rules describing changes between frames. Then, it suddenly disappears."
] |
[
"The problem is that digital channels require you to \"tune\" to a station. To \"preload\" adjacent stations, there would have to be two separate tuners. Also, there are bandwidth restrictions to consider, many digital channels take up the entire available bandwidth to display, whereas web pages, once loaded, generally do not consume bandwidth."
] |
[
"What do you call the protein on the surface of CD4+ cells that allows other cells to know ita infected?"
] |
[
false
] |
When HIV goes away from the cell it manifested,it takes with it the host cell membrane(cytoplasm),which helps the bioinformatics(protein molecules of HIV) to hide and not be detected by the system. Is there not any protein/enzyme on the surface of the cytoplasm that shows that it was once infected? And that the HIV virus is just using it as a front line to hide itself? What do you call the protein on the surface of CD4+ cells that allows other cells to know its infected?Is it MHC 2?
|
[
"cell membrane(cytoplasm),which helps the bioinformatics(protein molecules of HIV)",
"I'm very confused. The cytoplasm is the inside of the cell, the cell membrane is the membrane. Bioinformatics is a field of research.",
"I'll let an immunologist respond to the rest."
] |
[
"Your question is a bit confused so not quite sure what you are asking, but I think the answer to your final question there is T cell receptors. Antigen-presenting cells take up foreign cells/viruses and present peptides from those pathogens on the MHC 2 receptors on their cell membrane. The CD4 receptor and the T-cell receptor (they act as co-receptors) bind to the MHC 2 receptor of the antigen-presenting cell. If the peptide presented on the MHC 2 receptor is a foreign one then an immune response may be triggered. ",
"Your overall question seems to be how do HIV viruses not trigger this process? The answer is they do and not all infections with HIV will result in a permanent infection. But the fast evolution of the virus and the ability for it to vary the peptides which may trigger an immune response is one of the ways it avoids the immune response of the host and can establish a permanent infection. There are other ways that HIV can modulate the host immune response to its advantage as described ",
"here"
] |
[
"As other answers mentioned, you have a lot of words getting used incorrectly in your post. However, in a more general sense, the answer is MHC I. MHC I is responsible for the presentation of antigens within the cell by nearly all the cells in the body -- MHC II is primarily used by professional antigen presenting cells and is loaded by antigens produced in the endolysosomal pathway."
] |
[
"How does NASA \"download\" images from Hubble?"
] |
[
false
] |
I mean, what's the mechanism for some technician at NASA to connect to Hubble, and download the images? How are they stored on Hubble? As computer image files (jpg, tiff etc) or some other way? How big are the files? How fast is the transmission rate between Hubble and Earth? I've always been fascinated by this sort of stuff
|
[
"After some reading looks like they are microwaved from the hubble to the TDRSS communication sattilites, then that is microwaved to the White Sands Antennae Array",
"Here is some info from ",
"Nasa.gov"
] |
[
"While I don't know much about the hubble, someone in my lab was working on a ",
"GIS",
", and he briefly explained how modern Earth facing satellites work. In other words, this is second hand.",
"The key problem is that they capture data orders of magnitude faster than they can ever hope to transmit it. Many satellites now have pretty powerful processors on-board that try to prune the data and only pick out what it thinks will be the important information. I don't know anything about these algorithms, but they can be easily reconfigured and upgraded. The ground control can even request very specific info if desired (i.e. send me these coordinates at full zoom and full resolution). They can also request that some feature like a weather system is photographed in multiple spectra and that one spectrum (i.e. infrared) determines the resolution of another (optical, radar, depth, etc.).",
"Consequently, I guarantee that they compress the bejesus out of every chunk of bits that get transmitted.",
" I just remembered a great ",
"example",
". The Galileo spacecraft had a communications malfunction, so they upgraded the software mid-flight to improve the compression."
] |
[
"This is quite correct. Hubble was designed to use the TDRS relays to get data to the ground, so it knows (i.e. on-board equipment was designed for this specific purpose) how to interact with the TDRS constellation. ",
"The other half of the equation is how the data is interpreted when it reaches the ground station, or wherever its final destination is. Again, when the Hubble was designed, they had a formal specification that told them how to store data on board the spacecraft. The ground had a similar specification that told them how to interpret the 1s and 0s coming on the downlink. "
] |
[
"What's actually going on, in physics terms, in Bose- Einstein Condensate?"
] |
[
false
] |
I asked my HS teacher this question today and he seemed dumbfounded, so here I am guys. See title. I know all about absolute zero, motion ceasing, bosons in the lowest quantum state, and all, but I was curious as to what really happens.
|
[
"I know all about absolute zero, motion ceasing,",
"First, let's be quite clear here, BEC does ",
" involve motion ceasing and does ",
" involve absolute zero. Both of these are impossible.",
"The real phenomenon at the heart of BEC is...well, exactly what you then said. The bosons all enter the lowest quantum state. That's basically the be all and end all of what BEC means, though of course there are many complexities and subtleties to a deep description. Do you have a particular question, something about the explanation you don't get? If you 'know all about' bosons in the lowest quantum state, you know all about what's actually going on in BEC phenomena."
] |
[
"Just curious if there were any more complexities by chance. And for the record, I realized that right as I typed it that someone would point that out. Thanks though!"
] |
[
"There are many complexities. The exact math and physics behind it is nontrivial. ",
"Here's a video",
" that may be of some help. "
] |
[
"'Dropping' things from orbit."
] |
[
false
] |
So, I've been having vivid dreams and thinking in vectors again (uh oh!). I hear people talk about the concept of 'dropping' things from orbit, usually to use as weapons. The more I think about it, the lowest-energy way to 'drop' something from LEO onto the surface would be to propel it from your current trajectory, no? It seems that aiming 'down' at the target would actually take more energy, since as your altitude drops, the projectile would 'get ahead' of the target. Can someone draw some pictures? Would a small mass-driver-type weapon need some base amount of propulsion and guidance to effectively be used from LEO? Would it make more sense to drop from a geosynchronous orbit (much higher altitude, but at least the surface below is 'steady')? Overall, what are the implications for hypothetical orbital weapons platforms? What would happen if I was in LEO and tossed a baseball (or shot a gun) backwards? What about 'Earthwards'? Would either projectile hit the earth (assuming no atmosphere)? If so, which projectile would get to the ground first?
|
[
"You're right. If you want to blow up something directly below you, the lowest energy way to do that would be to fire the projectile almost exactly against your orbital velocity (you'll want to account for how much the earth rotates during the time it takes for your bomb to fall.)",
"If you throw an object down with insufficient relative velocity, you might not manage to hit the Earth at all. In general, all bound orbits are elliptical, so you might just end up going from a circular orbit around the Earth's center of mass to an elliptical one. Of course, some of those elliptical orbits intersect with the surface of the earth...those are collision courses.",
"If you want to hit a target below your orbit with the minimum amount of energy imparted to the projectile (neglecting the atmosphere), then the optimal solution is the fire the projectile backwards from the other side of the earth with exactly enough energy that it's apogee (furthest from earth) is where you fire it from and its perigee is at the surface of the earth (on your target). Such a trajectory would actually hit the target \"horizontally.\""
] |
[
"From geosynchronous orbit, the problem of missing the Earth is worse than LEO, not better. If you gain an inward velocity, you don't maintain the same angular frequency. It's not as if you spiral into the planet.",
"What you are saying about propellant makes sense. ",
"Regarding de-orbiting a 1 kg object, I don't really know. De-orbiting takes advantage of the atmosphere, which is hard to calculate without the help of models and a computer."
] |
[
"(neglecting the atmosphere)",
"Incidentally, wouldn't this path send you through more of the atmosphere than any other possible route?"
] |
[
"What is it that prevents \"Irish cream\" from going bad? Why doesn't it need to be refrigerated?"
] |
[
false
] |
[deleted]
|
[
"It's the alcohol. Most microbes cannot tolerate an alcoholic enviroment. As a rule of thumb, it takes upward of 60% alcohol to reliably kill the things off, but even the lower 15-20% content in Irish creme will inhibit the growth of most of them.",
"There are two main reasons it doesn't curdle. First, fat inhibits the curdling reaction, so the manufacturers use cream with a high fat content. Second, they mix the products in a carefully controlled manner, so the cream does not become acidic fast enough or in high enough concentration to curdle immediately."
] |
[
"Baileys was one example, there are plenty of Irish creams out there. And I'm asking more about the chemical process: what is it that stops a product that usually degrades fairly quickly even while refrigerated from going bad at room temperature for years?"
] |
[
"Baileys shelf life",
"Baileys is the only cream liqueur that guarantees its taste for 2 years from the day it was made, opened or unopened, stored in the fridge or not when stored away from direct sunlight at a temperature range of 0-25 degrees centigrade.",
"One of the keys to achieving this 2 year shelf-life is in our unique process of blending of fresh Irish cream with the spirits and the whiskey without the use of preservatives. The alcohol acts as a natural preservative for the product.",
"Under normal conditions of storage Baileys has a shelf-life of 24 months.",
"http://www.the-baileys-lounge.baileys.com/en-us/Product-and-Company-Information.aspx"
] |
[
"what is the chemical makeup of a tomato?"
] |
[
false
] |
[deleted]
|
[
"There are literally thousands of chemicals in a tomato, just like any other living organism. The main ones you'll find are water, cellulose, various sugars, and probably citric and malic acids. "
] |
[
"I don't know about all the active chemicals, but tomatoes have a temperature sensitive chemical called \"z-3-dexanol\". When tomatoes are refrigerated that chemical changes and so, makes the tomato taste different. (ref: Alton Brown, Good Eats)."
] |
[
"It's actually (Z)-3-hexenal, and I've never heard any credible reason why cold temperatures would damage it. The only ",
"reference",
" I could find with respect to the cold thing talks about the effect of temperature on an enzymatic system that produces the aroma compounds upon exposure of the tomato flesh to oxygen, but not the aroma compounds themselves. It seems that low temperatures temporarily inactivates the enzymes that make these compounds."
] |
[
"My math teacher in 5th grade told us this formula to find out if a number is prime. I still use it today, but never found it mentioned/proved in mainstream books. Anyone know if it works for all prime numbers?"
] |
[
false
] |
[deleted]
|
[
"This doesn't work, but it's interesting to examine why it appears to work for a few cases more closely. ",
"x",
" - 1 = (x + 1)(x - 1)",
"If x is prime, and x does not equal 2, then (x + 1) and (x - 1) are both even numbers. Let (x - 1) = 2k, then the test is that if k(k+1)/6 is a whole number, then x=2k+1 is prime. Obviously, either k or k+1 is an even number, but k cannot be odd, as then 2k+1 would be an even number and therefore not prime. Then k is an even number, and k+1 is odd. ",
"Let k=2j. Then the test becomes: if j(2j+1)/3 is a whole number, then 4j +1 is prime. ",
"Obviously, exactly one of (x-1)=4j, x=4j+1, (x+1)=4j+2 is divisible by 3, and (x-1) and (x+1) are both even. So what the test actually shows is that if (x",
" - 1)/24 is a whole number, then x is not divisible by 2 or 3. I doubt that it is coincidental that this tests the first two primes, so I assume that somewhere along the line someone misunderstood a method of methodically checking divisibility by 2,3,5,7,11,... to see if a number was prime. "
] |
[
"x=25"
] |
[
"I don't, it's hard to follow. Here's a better one, made ",
" I had caffeine.",
"24 has no prime factors other than 2 or 3. If (x+1)(x-1)/24 is a whole number, then (x+1)(x-1) must be evenly divisible by 2 and 3. ",
"Assume that (x+1)(x-1) is evenly divisible by 24.",
"It is clear that (x-1), x, (x+1) are consecutive integers.",
"Since one of (x-1) or (x+1) must be divisible by 2, both must be divisible by 2 [(x-1)+2=(x+1)]. Since (x-1) is divisible by 2, then x is not divisible by 2. ",
"Since (x-1), x, (x+1) are consecutive integers, one and only one of them must be divisible by 3. If (x-1) or (x+1) is divisible by 3, then x is not divisible by 3. ",
"Hence, if (x+1)(x-1)/24 is a whole number, then x is not divisible by either 2 or 3. ",
"If (x+1)(x-1) is evenly divisible by 24, then (x+1)(x-1)/24 >= 1. Then x",
" - 1 >=24 and x>=5. "
] |
[
"Do bugs sleep? If not, what are they doing when they're not around?"
] |
[
false
] |
You get day bugs, night bugs, some that come out during the morning and some in the evening. But what do they do in their (for lack of a better word) downtime? Bees during the night, moths during the day, that sort of thing.
|
[
"Yes, bugs do sleep. They have a central nervous system which presence seems to indicate the need for sleep. Studies have shown that insects that are forced to stay active during the normal down-time will rest when they are normally active.",
" This would indicate that their down-time is for a sleep-like rest, and not due to other factors.",
"Source: 1. ",
"http://www.popsci.com/blog-network/our-modern-plagues/do-insects-sleep",
" "
] |
[
"Thanks, I just learned a new term -- stealth dining!"
] |
[
"Are there any animals that don't require sleep though ?"
] |
[
"Why do we develop dominance in a certain arm/leg, and are we the only species to do so?"
] |
[
false
] | null |
[
"Which is why when people ask me what my dominant hand is, I simply state, \"Polar bear.\""
] |
[
"There isn't any proven theories about right or left dominance, but its speculated that its simply a stronger signal to one side of the body. its an interesting study as to if nature or nurture is the root of which hand or side a person will prefer. Nurture would be supported because of how many people are 'right-handed', but nature would be supported by the fact that people are left handed. Dominance can also be switched, which shows that it likely just a stronger signal form the brain. in the case of a broken dominant limb, many people end up switching dominance, become left-handed per say, if they broke their right wrist. What we do know is that we are not the only species with left or right dominance. Many other species show favouritism to one side, among these are dogs and Monkeys (which is no surprise). Being left-handed myself I've alway found this question interesting."
] |
[
"There's a tendency to favor one side among at least some other animals. Parrots appear to prefer to use one foot to pick up food, for example:",
"http://en.wikipedia.org/wiki/Laterality#Laterality_in_other_animals"
] |
[
"What's the big deal with magnets? Magnetism, more specifically"
] |
[
false
] | null |
[
"Richard Feynman on why he can't explain ",
" magnets work.",
"He says he can't explain ",
" magnets work. Not how. "
] |
[
"Richard Feynman on why he can't explain how magnets work."
] |
[
"Still worth watching. One upvote each."
] |
[
"What would happen to the string in this scenario?"
] |
[
false
] |
Two objects, A and B, of equal mass are at rest in space and connected by a 10 meter cotton thread. Object A begins accelerating at 500 m/s². Assuming that this is not an ideal string, what happens to the string? My expectation is I haven't provided enough information for a satisfactorily scientific answer, but I'm wondering what specifically I'm missing in my understanding of this situation. If possible, please suppose real world values, i.e., "it's a cotton string, so it has a fairly small breaking point of only XX Newtons. When the tension exceeds XX, the string will break," in a response.
|
[
"Wow, a downvote and no replies? Did I do something wrong? I tried googling this last night for over an hour, and it's ",
" hard to find information about a string physics between two objects without gravity being a factor. I found many results for pendulum problems and ",
" results about guitar strings, but nothing which presented an answer to a question like this."
] |
[
"500 m/s2 would snap the cotton thread."
] |
[
"Thank you! I had thought so, but I wasn't sure how to formulate it exactly. My thought process goes that if it takes 50 Newtons of force to break the cotton thread, it would only take a mass of .1 kg for Object A with the given acceleration for the cotton thread to break. So it would seem that if the mass of object A is non-negligible, the string will break. I do still wonder if the mass of Object B has any bearing on this situation, although I don't know enough about harmonic motion to know if it \"subtracts\" force as it gets pulled by the motion of Object A.",
": And while writing this, st00pid_n00b provided a more complete answer below, involving the mass of Object B, which I'm currently parsing."
] |
[
"Do we have the technology to 'subtract' sound? Like take vocals out of a song for example."
] |
[
false
] |
Suppose a band was playing. Suppose that microphone A was setup to record the total sound that the band was producing. At the same time, microphone B was setup to record only the vocals (maybe via split mic lines and a very elaborate sound proof booth setup). Is it possible to take these 2 recordings and get only the sound produced by the instruments?
|
[
"I recently answered a very similar question ",
"here",
"."
] |
[
"Can I ask a somewhat technical question?",
"You say you use independent component analysis for separating the components of the sound. In this field, what are the advantages of ICA over non-negative matrix factorisation?",
"Most of the astrophysical problems of this ilk are better solved by NMF, as far as I know. "
] |
[
"I'm not very familiar with NMF methods. Do you just use singular value decomposition or a similar linear algebra process to solve for a mixing matrix in that method?"
] |
[
"How come when you fall asleep or your eyes are closed for a while in direct sunlight and then you open them again you see blue for a while?"
] |
[
false
] |
I have always wondered this, and today i thought, why not ask reddit? So why do you see blue for a while after your eyes are closed in direct sunlight for a while? Thanks askscience!
|
[
"i always figured it was because of your eyes filtering out red to compensate for the red sunlight coming through the blood in your eyelids, when the red is taken away(when you open your eyes) everything seems blue by comparison. ",
"You can simulate it if you look at ",
"this",
" for about 30 sec, and then look at a white wall or something. You should see a blue rectangle."
] |
[
"Rhodopsin has a purple pigmentation and is responsible for our ability to see in the dark (whatever little extent that is). So, eyes are close = increased levels of rhodopsin. When you open your eyes, rhodopsin photobleaches if exposed to bright light. Most people experience a white flash. You may see blue partially because of the pigment of rhodopsin, or maybe because of the influence of the blue sky."
] |
[
"To provide a little more background of what you added....",
"The example you are portraying here is color burn, or ",
"'after-image.'",
" The prevailing theory is it has to do with neural adaption, or compensation. ",
"I still stand my ground based on the physiology of rhodopsin. ",
"EDIT: I originally thought green would be the after image, but after trying this myself, I found it to be blue, thus reasoning this edit. I found that the ",
"after image of red, is cyan",
". ",
"If you could provide a source as evidence showing this is the reason, I would completely understand and back it!",
"Until then, while I like your reasoning and example, I will stand behind the physiology of rhodopsin and the effects of coming from dark to light!"
] |
[
"What makes outside air smell fresh?"
] |
[
false
] |
What is it that makes the air from outside feel so refreshing when I let it mix with the “neutral” feeling air of my bedroom? Is there something in the air outside that somehow dissipates when it's enclosed somewhere for a while? Is something psychological going on? What's up with that good-feeling air?
|
[
"Another aspect of \"freshness\" concerns the smells and gasses that are given off by interior furnishings, pets and sweaty people. The longer a room is sealed off, the greater the concentrations of these gasses. Opening a window flushes out these unpleasant smells."
] |
[
"To add, about outside air having a 'good-feeling' property: the brain has a disproportionate demand for oxygen. (Brain weighs about 2% of the body, but consumes 20% of oxygen) So it can be said that the brain is also sensitive to changes in oxygen content in the air we breathe in. More oxygen makes one feel fresh and more carbon dioxide dull and drowsy."
] |
[
"To add, about outside air having a 'good-feeling' property: the brain has a disproportionate demand for oxygen. (Brain weighs about 2% of the body, but consumes 20% of oxygen) So it can be said that the brain is also sensitive to changes in oxygen content in the air we breathe in. More oxygen makes one feel fresh and more carbon dioxide dull and drowsy."
] |
[
"Where do autistic people derive their of morality from? If the ability to feel 'empathy' is not core to our morality, how does the brain derive morals and sense of social justice?"
] |
[
false
] |
Edit: Adding more info to clarify the intent behind this question. I am reading the book 'Tell Tale Brain' by V S Ramachandran. He has a chapter dedicated to Autism, and he stresses that they sometimes have a stronger sense of morality that the neurotypical people. I stressed empathy, 'cos my layman's understanding says our mirror neurons gives us the ability to empathize, which is probably sub-par or insufficient in autistic individuals.
|
[
"What an excellent and thought provoking question. For starters autism spectrum covers a wide range of poorly understood disorders so there isn't a one-size-fits-all answer. ",
"But here is one answer; \"But people with autism may perceive morality differently than normally functioning people because they focus more on the outcomes of situations, rather than the intentions of the people in those situations , said study researcher Liane Young, a researcher at Massachusetts Institute of Technology.\"",
"http://www.myhealthnewsdaily.com/893-autism-morality-outcomes-intentions.html",
"And for a longer read this might be interesting as well;",
"\"She concludes that empathy is not a necessary condition for morality\"",
"http://jeannicod.ccsd.cnrs.fr/docs/00/35/24/45/PDF/Autism_Morality_Empathy.pdf",
"So empathy may be required for ",
" but not necessarily required for morality."
] |
[
"I suffer from aspergers, a mild kind of autism. I feel empathy, i have high moral standards and social knowledge. I just cant show it very well. The fact that i cant show my feelings, often lead to depression and anxiety.",
"Your question is kind of a false assumption. Maybe you should try and rephrase it."
] |
[
"While Autistic individuals may not understand emotions in others to certain degrees I'm sure they understand pain in others.",
"Wouldn't that perhaps underpin a restricted form of empathy? They might not understand that they've upset you or how you were feeling but they would understand if you were injured?",
"(This is probably directed at the Asperger end rather than the profoundly autistic end.) "
] |
[
"How do we know chemical reactions doesn't react with air?"
] |
[
false
] |
for example A+B-> C How do we know there isn't air involved in A+B? Don't you need to have a vacuüm to be 100% sure there is no air involved?
|
[
"We can pretty easily see that oxygen isn't in the products if we can see what atoms make up both the reactants and products, and so for that we can rule out air involvement. If we are a little unsure we can do isotopic studies to actively watch the movement of atoms to confirm.",
"However, your question gets to the point that all chemical reactions happen in some kind of medium, and in chemistry we call that the solvent. It can be air, water, acetone, oil, inside a metal, etc, but by definition there is some area within which the reaction is taking place. It turns out this can play a huge role in how chemical reactions progress.",
"In the simplest case the solvent can interfere with the reaction and become a reactant. If you try to do reduce something in a liquid there can be significant effects of oxygen dissolved in that liquid reoxidizing your stuff. However, as discussed above we can generally track these side reactions and predict them well.",
"The other effect is that solvents will change the way that your reactants come together. For example, when A and B come together you must go through some A---B transition state before you get your final C. If whatever medium your reaction is in is good at stabilizing that A---B transition state then you might be able to make the reaction more efficient, faster, or require less activation energy. A lot of organic chemists spend a long time trying out their reactions in different solvents just to find the one that allows their reaction to work."
] |
[
"To add: many reactions which are known to react with air (usually the oxygen content) are carried out under the atmosphere of an inert gas, usually nitrogen gas. This is done by flushing the apparatus with nitrogen gas and keeping the experiment closed to prevent re-entry of oxygen into the apparatus.",
"EDIT: In regards to the sparge/flush/purge/etc. discussion, I thought flush was the most intuitive sounding term for it in the case of an explanation."
] |
[
"FWIW, I believe sparge refers to a liquid. Nitrogen \"purge\" seems more appropriate here"
] |
[
"What is the 'bump' at rotation of a commercial airplane?"
] |
[
false
] |
At rotation (when an airliner's nose first rises up, during takeoff), there is usually a noticeable 'thump' or 'bump', in terms of both sound and physical sensation. Given that the plane is becoming airborne at that point (i.e., applying increasingly less weight on the wheels and ground), what causes this 'bump'?
|
[
"The thumping sound happens when the wheels hit minimum suspension. ",
"When the plane is on the ground, the wheels are closer to the fuselage because the plane is really heavy, and because of the suspension. ",
"When the plane generates enough lift to get off the ground, the wheels get farther from the fuselage because the suspension system has less weight on it, and the mechanical movement of the suspension system makes noises. "
] |
[
"While I know that landing gear retraction occurs very soon after takeoff (and much sooner than most people realize), this is literally at rotation - as the nose begins rising but the rear wheels are still on (or just lifting from) the ground. "
] |
[
"The suspension hits the end of its travel ",
" when the wheels break contact with the pavement. There's a lot of pressure in those shock struts, so it can make quite a bump. Bear in mind that you don't have any way of knowing when the wheels break contact, because you obviously can't see them.",
"The CRJ-200's are more entertaining when the gear comes ",
". A hydraulic actuator hits the end of its travel with about 3000 psi, and there's a BANG that snaps heads around..."
] |
[
"Why do many physicists seem to assume the existence of an elegant, simple, Theory of Everything? Is there evidence for the possible existence of such a particular theory in the first place?"
] |
[
false
] | null |
[
"One reason is because it is possible to model most of the \"fundamental\" forces using the same theoretical framework: quantum field theory. Moreover, the fact that the electromagnetic interaction and the weak interaction have been successfully unified into a single quantum field theory -- that of the electroweak interaction. Since the strong force can ",
" be described in this framework, and symmetries can be found which ",
" a description of both the electroweak interaction and the strong interaction (though these symmetries do as of yet have other undesirable qualities about them, like having extra particles), it is expected that these two interactions might also be unified into a single quantum field theory one day, producing a GUT -- or Grand Unified Theory, which is one step away from a TOE, or Theory of Everything, which would also describe gravity.",
"Gravity remains as an exception to the rule for the most part ... but even so, it is possible to describe gravity through a quantum field theory, in at least a ",
" capacity. The theory breaks down at high energies and short distance scales because field theories of gravity have the property of being \"non-renormalizable\", but there is still hope for being able to unify its description in some way, because it can at least be described accurately with a field theory in the low-energy/large-distance limit. The question remains of how to deal with the non-renormalizability of gravity, to produce a field theory of gravity that is consistent in all conditions and reduces to general relativity in the classical limit.",
"Hope that helps!"
] |
[
"I think it is partly because so many disparate phenomenon have been unified into single simple theories in the past. For example, phenomena that originally appeared to be unrelated to one another such as electricity, magnetism, and light were all eventually unified into a small set of equations (Maxwell's equations). And then there is Newton providing a few simple rules and equations that explain how the moon orbits the earth for the same reason an apple falls to the ground and so on and so on.",
"However, the \"belief\" that this unification process will continue until the point where everything can be described by a simple set of equations...well, this is the dream to be sure, but not everyone believes in it. In particular I remember reading recent articles by physicists (I want to stay Stephen Hawking, but I can't remember for sure) that have questioned whether or not things will unify in the ways we \"want\" them to. Still it is worth trying for. A lot of \"hunches\" physicists have about their theories have eventually turned into rather remarkable discoveries (the postulated Higgs boson that was recently discovered is an example of this)."
] |
[
"One reason I've heard given as motivation for a search for a Theory of Everything is that Quantum Mechanics and General Relativity are the most accurate theories we've made, and they're mutually exclusive. That is to say, they can't both be correct. That they both can predict so many things so well makes us believe they're approximations of some higher theory."
] |
[
"What would be the significance of discovering a magnetic monopole?"
] |
[
false
] |
I've been wondering this for a while. Edit: I mean this as in both practical significance and also mathematical, i.e. completing any current models.
|
[
"It's actually pretty easy to rewrite Maxwell's equations to allow for magnetic monopoles - you just assume that there is a magnetic charge particle, and the magnetic side of the equations becomes exactly symmetric to the electric side.",
"\nActually, it would make some things much more symmetric, and many attempts at creating Grand Unified Theories of physics would imply the existence of monopoles if they were correct. In short, it would be rather nice if they did exist, and not really a problem at all."
] |
[
"Good answer. Let me just add that if magnetic monopoles exist, it gives us a ",
"nice, elegant explanation",
" for why charge is quantized."
] |
[
"Maxwell's equations are less fundamental than quantum electrodyanamics."
] |
[
"Why is heat emitted as infrared?"
] |
[
false
] |
I understand all objects above 0 Kelvin emit thermal energy in the form of infrared but why is it that specific part of the spectrum and not radio waves or visible light for example?
|
[
"I understand all objects above 0 Kelvin emit thermal energy in the form of infrared",
"Then you misunderstand.",
"All objects above 0 K emit thermal radiation, which takes the form of electromagnetic radiation. The frequency profile and total intensity of the thermal radiation depends on the temperature of the object. The hotter something is, the higher the frequency and intensity of its thermal radiation.",
"Very cold objects will mostly emit microwave radiation. Very hot objects may emit visible light or even UV light. But what's in between are all the objects that have a temperature that's in the range of temperature that we're used to in every day life. These objects emit the bulk (or all) of their thermal radiation in the part of the spectrum that we call infrared.",
"That's why we associate infrared radiation with heat. But there's nothing fundamentally different about infrared radiations. It's just a specific part of the electromagnetic spectrum that happens to line up reasonably well with the spectrum of thermal radiation of objects we're likely to encounter outside extreme conditions."
] |
[
"These objects emit the bulk (or all) of their thermal radiation in the part of the spectrum that we call infrared",
"Incorrect (\"all\"). The intensity of blackbody radiation at any given frequency monotonically ",
" with temperature. A very cold object radiates only in the microwave band. A hot object may radiate in the infrared, ",
" At any given frequency, the spectral intensity as a function of temperature scales as ",
"1/ ( e",
" - 1)",
"It's just an approximation that at high temperature there's negligible radiation at low frequencies, because there's much more radiation at high frequencies."
] |
[
"There are some very hot neutrons stars and white dwarfs that radiate significantly in xray spectrum."
] |
[
"Besides size conatraints, why couldn't we attach a steam engine to a conventional engine and use the excess heat to give the engine more power/gas mileage?"
] |
[
false
] | null |
[
"We use heat from an internal combustion engine to drive a turbine which forces air back into the intake plenum. This is a turbocharger and it effectively makes great use of otherwise wasted energy.",
"As the engine goes through its 4 cycles (combustion exhaust compression and intake) it releases the exhaust fumes through the head and out the exhaust manifold and traditionally out the back, a turbo intercepts this just after the manifold with a twin turbine housing ( one is the exhaust side and other is intake) the exhaust fumes spin the turbine which spins a shaft which is basiccaly connected to a air pressure pump. The intake side of the turbo draws in freah air and is pressurized and forced back into the intake side of the engine. Thats the general gist of it.",
"Turbos and similar superchargers and a far greater efficiency improver than a steam engine. As a fun educated guess id say in the order of 20 fold.",
"Edit - apologies for mistakes, I quickly posted off my phone just to give OP an answer."
] |
[
"There is an engine that already does this. Look up Bruce Crower’s Six-Stroke engine. It adds an additional two strokes to a standard 4 stroke engine. It injects water into the hot cylinder and creates steam which adds a second power stroke. "
] |
[
"I designed a small part of a power plant that operates in such a way. In general, this is called \"combined cycle.\" ",
"https://en.m.wikipedia.org/wiki/Combined_cycle",
" ",
"This is the plant I worked on. ",
"http://www.duke-energy.com/about-us/edwardsport-overview.asp",
" ",
"As you might imagine, a steam turbine is too heavy to reasonably add to a car and expect efficiency improvement. "
] |
[
"What am I doing to my eyes when I intentionally blur them?"
] |
[
false
] |
Not sure if it's something only I can do or not. But when I sort of "tense" my eyes, my vision blurs. Whats the point of this?
|
[
"Most people can only focus on whatever's in the middle of their field of vision, but apparently some, like you, can change focus at will. When you blur your vision, you're exerting conscious control over your eyes' focusing muscles to make your lens focus on a point that's not occupied by something that would be in focus if it were there.",
"This question came up on reddit a couple of years ago. Some people denied it was even possible, but I don't see why it wouldn't be. For example, if I stare at my computer screen and zone out, first I see two images because the muscles that control stereo vision relax, then it starts to blur as my focus muscles return to their relaxed state. It's hard for me to just \"tense\" and do it though, without something to not focus on."
] |
[
"That seems really surprising to me that other people claim to not be able to do that. I can easily focus my eyes anywhere from ~6'' to infinity at will no matter what I'm looking at. It's an amusing way to entertain yourself by manipulating the star-shaped distortions of street lights at night. (I.e., trying to make them as large as possible without feeling pain.)",
"Is there any good data on this stuff? Like, is there a correlation between this ability and sight problems? Or any data verifying that some people can't do it?",
"I wonder if anybody has ever hurt themselves by straining their eye muscles too much..."
] |
[
"You've got a lens in your eye that is essentially a clear sac of liquid protein. Muscles in your eye can shape that sac into a lens that is adjustable to whatever your brain wants to look at. It's like a dynamic magnifying glass in your eyeball, and some people can control it more than others. ",
"Probably other factors as well that could affect blurriness (shape of the eyeball, iris, etc), but I know that's one of the biggies that you may be controlling at will."
] |
[
"Theseus' body, is there any part of a human that is cellularly or even atomically stagnant?"
] |
[
false
] |
As an extension of the riddle of Theseus' ship I was wondering if all of the human body eventually grows a replacement. I know skin and other cells die and are replaced but what about other parts. I know some things won't heal sometimes like tendons, ligaments and cartilage; do they get replaced? I also thought neurons didn't re-grow. however even if we don't get new individual neurons are the cells themselves static? Or do they get internally replaced at a lower level such that although we can recognize it's existence as contiguous (much like ourselves as we get replaced) that it too suffers from a micro-Theseus dilemma? if nothing is the same how many years does it take to be essentially completely replaced?
|
[
"Sensitive cells in the ear (",
"hair cells",
") are created once, and for life. They are notoriously non-replaceable, and if they die because the ear is exposed to a loud noise, then, well, that's it. No hearing for this set of frequencies, ever.",
"The reason for that is, probably, that the ",
"cochlea",
" is so complex that it can only be built once. You can not repair it, you can only grow it. If I were to give a metaphor, it's about how Egyptian temples were built: they would bring some stones, cover them with sand, put some stones on top, cover it with sand again - and repeat it until the whole temple is built, and covered in sand. And then they would start clearing the sand, while simultaneously carving and painting the stone. A temple that is built like that can not be easily fixed or repaired, as the process of building it can be repeated only once. It's easier to build a new temple than to repair an old one.",
"But back to the body. Even more interestingly, there are parts of the body that need to be ",
" by the time we are born, or otherwise they won't work. One great example are the 3 little bones in the middle ear (the ",
"ossicles",
"). To grow, bones should be alive, and they should have some blood flowing around them. But in the adult body these bones are surrounded by air, not by fluid of any kind, and to work properly, as mechanical amplifiers, they should be light and dry. So they die - in order for us to live. Die before we are born.",
"Another similar example is the lens in the eye. The lens is made of cells (like almost anything in our body), but it also needs to be transparent, and live cells are not transparent. So the cells that make up the lens die before we are born. Unlike for the ossicles, they don't die and dry out, but instead they get rid of all cellular elements, one by one, and in the last final move get rid of the nucleus itself. So now in our lenses we only have cell bodies, filled with a certain transparent stuff, and that's it. It's shells of the cells, empty shells, all for the sake of giving the body some vision.",
"Isn't it nice? I really like the imagery here. A small thing needs to die so that the larger entity could live. It's pretty rich in metaphor. (edit grammar)"
] |
[
"Some cells are replaced far more slowly than others. Sperm and blood are constantly being made and destroyed but osteocytes in your bones take far longer to be replaced (>25 years). Almost every cell in your body will be replaced every decade. ",
"Cartilage, ligaments and tendons can heal and be replaced at a cellular level however if too much damage occurs then the body cannot repair it in the same way as we can't grow back toes etc."
] |
[
"That's really fascinating. so yes dead cells would indeed not change in a human. I just wasn't sure we had any that never got replaced (hair/nails regrow constantly) ",
"so i guess every 7 years you may be a new person, except for your teeth lenses and ossicles."
] |
[
"Must all body proteins be synthesized from amino acids or can ingested protein be used directly?"
] |
[
false
] |
[deleted]
|
[
"I am unaware of any proteins being able to cross the brush boarder or any of the junctions present in our digestive tract. They simply are too large to effectively cross the membrane. As I'm sure you know the process of protein secretion from cells is highly regulated and requires a large pool of snares, binding proteins, and coat proteins to properly export polypeptides. Given the rather unfavorable environment of the intestine and stomach to most proteins folding, any recognition that would be required for vesicular localization would be nullified. "
] |
[
"You are absolutely correct! Creutzfeldt-Jakob Disease (CJD, aka the human form of Mad Cow Disease) and Kuru occur due to gut absorption of proteins. How this is possible, given the protease-laden environment of the stomach and small intestine, has been the topic of a lot of research. There are two prevailing theories. The first is that many immune cells in your intestine are constantly sampling the gut contents for pathogenic materials. This requires taking in proteins whole, or at least large fragments, and then passing them on to the equivalent of lymph nodes in the intestines or even to the enteric nervous system. There was also a fascinating paper that found that prions may be hitchhiking a ride into intestinal cells on Ferritin, which is an iron-binding protein required for iron absorption.",
"So to answer the original question, yes, whole proteins can enter the body, but they are not being \"put to use\" so much as examined for potential harm and, in extremely rare scenarios, causing prion disease.",
"References: \n",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2538961/",
"http://www.sciencedaily.com/releases/2004/12/041220002446.htm"
] |
[
"These mimic enzymes that are functional in the intestinal lumen to break down lactose into it's constituent monosaccharides, glucose and galactose . These are often either are encapsulated to prevent degradation by digestive enzymes or are able to properly function at the low pH of the stomach. The enzymes are not actively absorbed by the body (as addressed in OP's question) and likely are broken down by proteases after their work is complete. "
] |
[
"How do micro-organisms see/sense other things?"
] |
[
false
] |
[deleted]
|
[
"Chemotaxis",
": specialized proteins are distributed on the membrane of the micro-organism, that act as sensors: they can assess the concentration of different molecules, thus allowing the organism to perceive gradients in its environment. It will consequently adapt its behavior: move towards the source of chemoattractant chemicals, run away from chemorepellants. The motion itself is due to the rotation of ",
"flagella",
", which is regulated by chemotaxis receptors (",
"http://www.pnas.org/content/99/1/123.full",
")."
] |
[
"Vaguely related - ",
"quorum sensing",
". Basically, certain microbial behaviors, including motility, are regulated by the population size of a bacterial species in a particular environment. "
] |
[
"Thats amazing! I never knew such a thing existed. Do you think that chemotaxis might be related to how a neuron cell's dendrites and axons find eachother? "
] |
[
"Which would kill you faster, a starvation diet or a diet of ~2000 calories a day of candy?"
] |
[
false
] |
My parents used to me that candy would kill be faster than starvation as a means to dissuade me from eating them. Is the claim true? I'd have to assume different candy would have different effects, but for arguments sake lets say it's just the 'pure sugar' types.
|
[
"Starvation. You'd have health problems from the candy but you'd be dead in a month or two eating nothing at all."
] |
[
"Most likely a lot longer: beer is like floating bread, plus water. Water and bread is better than just water. You could survive for several months on just bud light."
] |
[
"Much less time, because I would rather die agonizingly of dehydration than drink Bud Light."
] |
[
"Does a body of water exhibit a curvature in its surface due to gravity drawing every point on its surface to the earth's center of mass?"
] |
[
false
] |
Stated another way, do opposite ends of a surface of water, being both drawn to the center of the earth with equal force, angle outward? I already know this will be tough to explain, but I'll try. Imagine the surface of a body of water, whether in a glass or a bucket or an ocean, to have edges at points A and B. Gravity draws both A and B toward the same point in the center of the earth. Therefore the force of gravity vector to A must form a very very small angle with the force of gravity vector to B. Does this angle difference manifest in the surface of the water? Scale must matter, and it is probably too small to be realistically observable, but does this phenomenon occur?
|
[
"Yes otherwise, very simply, the oceans would not wrap around the planet."
] |
[
"Yes, oceans have horizons."
] |
[
"Large bodies of water do curve with the shape of the earth. It's not noticeable on the scale of normal day to day experience (in the same way the curvature of the earth is not noticeable). If you are careful about your measurements you can detect this. Someone won some money off a Flat-Earther back in the 1800's doing this. ",
"Bedford Level experiment"
] |
[
"If someone jumped off of a building, and were tackled at full speed right before they hit the ground, would either party survive?"
] |
[
false
] |
I was arguing with my friends recently about this; I will attampt to explain. Someone jumps off of a building and is travelling at a speed that if they hit the ground they would die no matter what. If someone came from the side and tackled the falling person at the last second (maybe 2-5 feet above the ground), would either of them survive?
|
[
"It would be hard to tackle them in any meaningful way without exerting an upward force. A person falling 100m will only take about 0.03 seconds to travel that last meter. If no upward force occurs, that tackle will be little more than a nudge, which will be of no benefit to them, and little harm to our would be linebacker.",
"If upward force occurs, the person's deceleration will be spread out over a greater distance (1 m vs. a few mm) which would improve survivability. That will come at the expense of the linebacker, who would be absorbing the blow.",
"The most likely outcome? Even if the linebacker did everything he could to reduce the fall, the person will likely die if falling from a signficant height. The linebacker faces a lesser, but still pretty serious risk."
] |
[
"There's two components of velocity, and therefore momentum, here; vertical (mostly contributed by the falling person) and horizontal (mostly contributed by the tackling person).",
"Considering the horizontal momentum first, the tackling person will give some degree of their horizontal momentum to the falling person. Assuming a perfect and pretty much instantaneous tackle, it will be shared between the two people.",
"Now, considering vertical momentum. The falling person's vertical velocity is going to be such that the length of contact the tackle can achieve before the falling person hits the ground is pretty small. The amount of vertical momentum that can be transferred to the tackling person is limited by the contact time and the friction between them.",
"How large the friction force between them actually is is pretty hard to estimate, but it's probably safe to assume that it's not going to be sufficient to transfer much momentum from the falling person to the tackling person. (Of course, if it was enough to transfer significant momentum, it would produce a force approaching half the force applied by hitting the ground unaided in the first place!)",
"Therefore, the net result is that the falling person hits the ground with slightly decreased, but likely still fatal, vertical momentum, and also a little extra horizontal momentum which probably won't make much difference. The tackling person will hit the ground a bit harder than had he missed, and also be scarred for life."
] |
[
"PoopMachin3 didn't ask what units you're talking about, but what quantity. If you're talking about velocity it doesn't make a difference whether you're talking about meters per second or miles per hour, but it does make a difference if you're talking about velocity, force, kinetic energy, etc. The laws are upheld regardless of the units, but your original statement doesn't even say what laws you're referring to."
] |
[
"In a rotating black hole, what is rotating?"
] |
[
false
] |
Just something that crossed my mind recently, since the horizon isn't made up of anything. What is the rotating. Or is it just a way to allow for the conservation of angular momentum without having to go inside the BH with our current understanding?
|
[
"The black hole has angular momentum, it may not make sense to speak of anything rotating (at least in a model where you have a 0d point or 1d ring singularity), just like you don't think of electrons as rotating because they have spin."
] |
[
"When a macroscopic object rotates it has angular momentum. Elementary particles can have intrinsic angular momentum (spin) without a sense of \"classical rotation around its axis\" associated with it."
] |
[
"Just to add to this, I believe the rotation is real and noticeable though relativistic frame dragging of the surrounding space-time."
] |
[
"Why do return trips feel shorter?"
] |
[
false
] | null |
[
"Well, this seems quite subjective. I for one find the return trip 'seems' much longer."
] |
[
"I've noticed a similar phenomenon, in that when I'm watching a television program television, playing a game, reading a book, etc. for the first time, it seems to take a lot longer than subsequent times. I will often think \"Wow, it sure felt like it lasted a lot longer\" when I watch a television program again. Is this related to the OP's question? If I had to guess, it would have something to do with the brain paying more \"attention\", if you will, to novel experiences."
] |
[
"+1 to that.",
"I guess it really depends on your state of mind during the trip."
] |
[
"Is there anything at the center of a gas giant? Does it have a metal core of some sort to keep the gas contained in a gravitational field?"
] |
[
false
] |
[deleted]
|
[
"Yes, hydrogen is supposed to be in a metallic state close to the core. That wikipedia article explains it pretty well.",
"Gas would contain itself in gravity the same way Earth's rocks do. All matter has gravity, it's just that it's a very weak force so for it to be perceptible you need a huge mass, like a planet. So if a ball of gas has the mass of a planet, then it pulls with its gravity the same way a rocky planet would."
] |
[
"Yes, hydrogen is supposed to be in a metallic state close to the core. That wikipedia article explains it pretty well.",
"Gas would contain itself in gravity the same way Earth's rocks do. All matter has gravity, it's just that it's a very weak force so for it to be perceptible you need a huge mass, like a planet. So if a ball of gas has the mass of a planet, then it pulls with its gravity the same way a rocky planet would."
] |
[
"With current measurements, it's impossible to know for certain. Theories about the formation of Jupiter suppose that a rocky core about 10 to 40 Earth masses provided the initial gravity to hold all the gas together. But hydrogen is a powerful solvent, and the properties of materials at such high temperatures and pressures are not well known. If it ever existed, that core may have been completely dissolved. Or it may still be there, we don't know.",
"Source: ",
"http://en.wikipedia.org/wiki/Jupiter#Internal_structure",
"Edit: forgot to mention that there are also theories that say the gas holds itself with its own gravity so a core is not needed to form a gas giant."
] |
[
"Animals wake up and execute actions immediately, why do humans take significant time to do the same?"
] |
[
false
] | null |
[
"I find your question interesting, but I disagree with your hypothesis. Having been around various animals throughout my life both in domestic settings and in the wild, my observations have been that animals have a very similar reaction to the state between sleep and consciousness. Animals upon waking are known to yawn and stretch when they're about to sleep or have just awoken."
] |
[
"I think you are mistaking animals sleeping and simply resting.",
"It's like if you were just lying down on the couch waiting for the pizza guy vs. actually sleeping."
] |
[
"Human's are animals. Your premise is false."
] |
[
"Would it be possible to refuel a dying star with a smaller, younger one?"
] |
[
false
] |
My train of thought was taking me to the prospect of Sol becoming a red giant, and I was thinking, provided a body could be moved and collided with a dying star, without disrupting the orbits of its planets, could one extend that star's longevity?
|
[
"Absolutely. This actually happens (though in a slightly different fashion) relatively often to stars in binary pairs where one star is more massive than its partner. A star's lifetime on the Main Sequence (its hydrogen-burning phase, like the sun right now) is correlated with it's mass - higher mass means shorter lifetime. So, in the binary pair, the larger star will \"die\" first, generally going into a giant phase. In the giant phase, the radius of the star greatly increases without a change in mass, meaning the outer layers become increasingly tenuous. If the stars are locked in an orbit close enough to each other, it's possible for the outer layers of the now-giant star to extend into the ",
"Roche Lobe",
" of the second star, which will then funnel hydrogen (read: fuel) onto the smaller star. This doesn't have much effect on the dying star, but will significantly extend the Main Sequence lifetime of its companion. This is what causes ",
"Blue Stragglers",
".",
"Additionally, it's also possible to create Blue Stragglers through stellar mergers, though this process requires very high stellar density regions, and therefore is far less common."
] |
[
"This actually happens in globular clusters, see ",
"here",
". ",
"Here",
"'s a link to a scientific study where they actually observed two stars merging! Isn't that crazy?",
"You'd extend the life of the almost out of fuel star, but you'd significantly reduce the amount of time the younger star would last. Since you're introducing it to a more massive body, it'd use the fuel much quicker than if you'd just left it alone.",
"It'd also be a massive, massive undertaking. ",
"It would also (almost certainly) be pointless and counterproductive, because you're introducing more mass to the center of the solar system, you're making the gravity larger/more. I'm not sure what the correct phrase, but the sun will be more attractive, so unless you give the planets (and asteroids) a bit of a boost, they're all going to change in their orbits, likely coming inwards a bit, if not eventually colliding with the star. "
] |
[
"Sounds neat! Would a red dwarf, for example, perhaps be able to keep a stable orbit for a while inside the expansion of a neighboring star?"
] |
[
"Could someone please provide a layman's explanation to the Susskind Solution to the Black Hole Information paradox and correct my layman's statement of the problem?"
] |
[
false
] |
Here's my statement of the problem:
|
[
"The idea you are talking about is the ",
"Holographic Principle",
". Essentially what it is saying is that the information about the incoming particle is encoded on the event horizon of the black hole. The event horizon is the boundary surrounding the black hole where your escape velocity exceeds the speed light (the black part). The way it encodes information on the event horizon is the gravitational field of the incoming particle curves space and time and thus deforms the event horizon of the black hole. This deformation influences the corresponding discharged particles and information is preserved. You can think of it like dropping a bowling ball on a trampoline. The black mesh on the trampoline is the event horizon and the bowling ball is the incoming particle. The bowling ball falls towards the mesh and when it hits it it deforms the mesh, the deformation determines the trajectory or properties of the particle that is shot back and information is preserved on the mesh about the incoming particle, or how specifically it curves holds the information."
] |
[
"Effectively you can represent the information from the 3-D world, in a 2-D object (the event horizon, a 2-D surface). Much like a hologram."
] |
[
"Yeah, so in the analogy, the 3D components (velocity) of the bowling ball are imprinted on the 2D sheet of the trampoline (as elastic potentials in this example)."
] |
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