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[
"If CO2's sublimation point is -78.5C, and the coldest temperature recorded in the Antarctic was -89C, would there have been cardice on the ground as well as regular snow/ice? Were there any observations made about this?"
] |
[
false
] | null |
[
"Arguably the lowest recorded temperature is actually ",
"92ºC",
" observed via infrared satellite imagery. Theoretically, a ",
"large amount of dry ice",
" should be observable to the Landsat satellites, but Earth's atmosphere doesn't have enough CO2 for significant accumulation. ",
"The last askscience",
" thread has a better explanation of the chemistry than I could ever give.",
"For historical perspective, the -89ºC minimum was recorded by station personnel at the Soviet Union's Vostok Station in 1983. The temperature measurement has been ",
"verified",
" but there doesn't seem to be any further records on the event. This isn't surprising given the limited resources likely available to the station crew; dry ice doesn't look any different from regular snow and ice, especially in the middle of the night, so the only way to differentiate would be with chemical or spectral analysis. Vostok ",
" primarily an ice coring station, but it's also very small so they likely don't have much in the way of testing equipment, especially back in the early 80s. (Ice cores are shipped back to mainland institutes for analysis.) So given the extreme temperature and limited resources, Vostok wouldn't have made observations of CO2 even if there was a significant accumulation."
] |
[
"The main problem is that CO2 content in air is in the 300-400 ppm range and thus you won't see condensation at that temperature with such a low partial pressure. Dry ice would still try to evaporate (sublimate) if you had some and put it out in the open air, because it wants to make the CO2 content of the air get into equilibrium with any solid or liquid CO2 that is around, and the CO2 content in air is nowhere near that equilibrium concentration. Sort of like how snow \"evaporates\" (sublimates) even when it is colder than 0 degrees C. It is a slow process but the direction is toward making more gas and not condensing the existing gas. You have to raise the relative humidity to condense water from air. or solid and liquid water and air will convert into gas (vapor). Same idea applies to CO2."
] |
[
"The sublimation point is the equilibrium between dry ice and a 100% CO2 atmosphere (at sea level pressure). If our atmosphere would be pure CO2 then dry ice would have formed. The atmosphere is only 0.04% CO2, it has to be ",
" colder (about -140 C) before dry ice will form."
] |
[
"Today my professor taught us that Phosphorus is the primary limiting factor in fresh water ecosystems while Nitrogen does the same in salt water and soil systems. What is it about these systems that limits them to different elements?"
] |
[
false
] |
I am a first year ecology student and we have recently been learning about eutrophication and the effect of nutrient runoff into fresh and saltwater ecosystems resulting in hypoxic "dead zones". We studied a local example in Lake Washington where hypoxia was a result of phosphorus eutrophication from human waste/sewage dumped into the lake in the 50's. When phosphorus in the sewage was identified as the limiting factor causing the algal blooms, treatment plants were installed for the sewage and the water quality improved and surpassed initial measurements. A similar example in the gulf of Mexico is a result of nitrogen fertilizers running off the Mississippi watershed and causing a huge deadzone in the Mississippi river delta. I asked my professor what it was that made them dependent on different elements but he wasn't sure. I don't have a background in chemistry or biology so I was hoping someone could help me out! The only thing I can think of is something to do with salinity or the metabolisms of the primary producers due to pH/salinity differences in salt/fresh water systems. Could anyone with a bit more understanding try to put it in a way that a simple Geologist like myself would understand or point me towards some readings that may further my understanding of the processes at work? A bit on Hypoxia/Dead Zones in the Gulf Of Mexico Lake Washington Study
|
[
"1st thing of interest is the Redfield ratio number: the ratio of carbon:nitrogen:phosphorus is 106 C:16N:1P for marine life (dead or alive). For 1 molecule of phosphorous the life form had/needed 16 molecules of nitrogen and 106 molecules of carbon.",
"Nitrogen is not a limiting factor in freshwater systems because freshwater systems are generally much more shallow than the ocean have an abundance of plant, microbial, and animal life/death that provide a source of nitrogen and nitrogen fixation of organic nitrogen molecules (meat..dead..or urine) into inorganic nitrogen molecules. Phosphorous is more of a limiting factor because phosphorous primarily comes from erosion from rocks and its presence in the lakes, streams, and rivers are transient and eventually end up in the ocean. So the vast ocean has an abundance of phosphorous from erosive processes on a global scale. Nitrogen is the limiting factor because sources of nitrogen may quickly sink and be out of reach of autotrophic species who need both sunlight and the nitrogen source to proliferate. Additionally, the ocean is a much more competitive environment so whatever nitrogen is present and fixed to the right form for primary production is rapidly utilized. ",
"Iron has also been identified as another limiting element in marine primary productivity."
] |
[
"Thank you for this easy to understand explanation. I feel a little embarrassed since I study quite a bit of Geology as well and had a strong inkling that the phosphorus abundance in the oceans was related to a geologic process and nitrogen was more limiting due to it's atmospheric nature.",
"The Redfield ratio is also very interesting to look at.",
"Thanks for helping me understand this a bit more."
] |
[
"No problem. I wrote this before dozing off really late yesterday so I apologize for any typos. The nitrogen cycle is actually a bit more complex than the phosphorus cycle as different types of organisms can produce 4 classes of nitrogen products: ammonia based, nitrate, nitrite, and nitrogen. With phosphorus, it's a simpler inorganic/orthophosphate form to organic cycle with autotroph and heterotrophs. It's been a while but if you want I can dig up some notes on the nitrogen and phosphorus cycles.",
"I can't recall the paper I read once upon a time, but in a particular marine realm where algal blooms with subsequent hypoxia events occur (coast of Washington/Oregen I believe was the site), there was 2x the phosphorus available in the water, with regards to the Redfield ratio, and when eutrophication rich with nitrogenous wastes (typically ammonia/urea based) entered the ocean from anthropogenic and natural freshwater effluence, the blooms would be observed. ",
"Also something to keep in mind is that the Redfield ratio is not absolute and many investigators have proposed variations of the ratios. Nonetheless, the 106C:16N:1P is the original or standard. I remarked about iron and when applied with the Redfield ratio, it's something like 106C:16N:1P:0.001Fe. People have entertained the idea of dumping a lot of iron into the Southern Ocean to mitigate anthropogenic CO2 inputs but the carbon cost of refining and transporting enough iron to have an effect would exceed the benefit and cost a lot of money. Nonetheless, I think it's good to be aware that iron, and quite possibly other nutrients, can be limiting factors for marine primary productivity in addition to nitrogen products. "
] |
[
"Do other languages indicate sarcasm in speech the same way as English?"
] |
[
false
] |
That is, stressing and drawing out the sarcastic portion of the sentence, raising the pitch a bit. I.e., if you were at a concert and thought the band sucked but your friend liked it, "Isn't this band great? "Yeah, they're " I guess in other words, if you listened to a language you didn't understand, could you tell when the speaker was using sarcasm simply from the sound?
|
[
"Here is one journal that can be looked at for information: ",
"Acoustic markers of sarcasm in Cantonese and English.",
"Direct Cantonese-English comparisons revealed one major distinction in the acoustic pattern for communicating sarcasm across the two languages: Cantonese speakers raised mean F0 to mark sarcasm, whereas English speakers lowered mean F0 in this context. These findings emphasize that prosody is instrumental for marking non-literal intentions in speech such as sarcasm in Cantonese as well as in other languages. However, the specific acoustic conventions for communicating sarcasm seem to vary among languages.",
"Another one: ",
"Prosodic cues of sarcastic speech in French: slower, higher, wider",
"Our data show that sarcastic productions are characterized by utterance lengthening, by increased f0 modulations and a global raising of the pitch level and range.",
"One final one: ",
"Prosodic Consequences of Sarcasm Versus Sincerity in Mexican Spanish",
"Sarcasm resulted in decreases in speech rate and F0 mean and increased stressed syllable length in attitudinally relevant words. In expressions of sarcasm, males significantly decreased F0 range and movement in relevant words and stressed vowel intensity in all words. They also displayed\nevidence of an utterance-final circumflex F0 configuration, namely in cases of sincerity. ",
"pros·o·dy",
" ",
" "
] |
[
"Yes. The first study showed that English speakers indicate sarcasm by lowering the voice, while it's the opposite for Cantonese. French speakers draw out the words and raising the voice. Mexicans slow their speech and emphasize certain parts of the words.",
"So actually it's pretty different from language to language, despite having the same source-language."
] |
[
"The prosodic marking of sarcasm (stress/intonation/etc) should vary a lot from language to language, simply because different languages have different prosodic systems, and emphasizing something you don't really mean will be done differently. ",
"But it's interesting to note that \"emphasizing something you don't really mean\" is a practice typical of a lot of languages (I don't say \"all\" simply because I don't know that for sure). Speakers can somehow indicate that they didn't literally mean what they said, one of the focuses of the field of pragmatics* within linguistics. People often exploit ",
"basic assumptions in the communicative process",
"---for instance, that you can assume your conversational partner isn't communicating something false or completely irrelevant---and make a statement assuming correctly that your interlocutor will read sarcasm into statements that would otherwise seem completely incongruous. This is because you know your listener will assume you are ",
"flouting a maxim",
" of conversation to make a point, rather than being nonsensical. ",
"To give an example, let's say your friend drops a plate and breaks it on the floor. You liked that plate, you're angry. You say:",
"Wow, you are SO graceful.",
"What you actually want to convey here, probably, is that you DON'T think your friend is graceful, since they just dropped a plate. But in context---let's say you look pretty grumpy, and your friend is well aware that what they did is objectively non-graceful---your interlocutor will understand that you are flouting the maxim of Quality (roughly, \"tell the truth\") rather than meaning to literally convey a point that contradicts reality.",
"*I do linguistics, but I'm not in the sub-field of pragmatics. If I have inadvertently put something together wrong, correct me!"
] |
[
"Why doesn't your metabolism speed up when eating a lot of calories?"
] |
[
false
] |
I know that when you're fasting, your metabolism consumes less calories to conserve energy, so if you're eating to many calories, why doesn't your body burn calories faster?
|
[
"We do. Just not enough for some peoples' intake...\nPost-prandially (after a meal) we speed up our basal metabolic rate via 5-HT, insulin, secretin and a plethora of other hormones that respond to increases in blood sugar levels, satiety and even the lower GI stretching. (etc.)\nHowever, that is more aimed at priming cells to use this fresh batch of potential energy, rather than burning off already accumulated energy. In fact, too much and frequent-a consumption of food promotes the propensity to store and deposit food as adipose, and slow down the metabolism for \"winter\" as it were."
] |
[
"You are correct, but the heavier man uses more energy mainly because he ",
" more; he doesn't need more because he is big or something like that. This does not directly answer OP's question, which was why do we not burn more calories when we eat too much (presumably he meant when also corrected for our body's needs)?",
"The short answer is because of evolution. During our evolutionary history food was scarce. This means that the species that has a \"nothing is wasted or left unused\"-policy with respects to food intake would have an advantage. We never burnt, nor do modern humans burn, the extra calories just because we didn't need them; we store (most of, anyway) the excess energy in the form of fat in our fatty tissue.",
"Food in big enough quantities that obesity would become a problem, is a relatively recent issue. The dominant selective force has been the threat of starving to death, and not eating oneself to death. There simply has not been a reason to evolve a way to deal with obesity, since so few individuals ever got a chance to become obese. "
] |
[
"It does. Metabolism is just the set of processes going on in an organism, and a shorthand for the energy consumed by those processes.",
"Your metabolism is based roughly on your mass, activity level, and food intake. Raise any of those and your metabolism goes up. A 200 pound man has a much higher metabolism than a 100 pound man because he's maintaining twice the mass at 37 degrees. Everything goes up. He not only has to eat more but he also expends more energy just resting.",
"For you, it's highest during exercise and right after a meal."
] |
[
"How powerful/fast of a CPU could we produce if it were the size of a typical video card? The size of an entire motherboard?"
] |
[
false
] |
[deleted]
|
[
"Yeah, making the circuits bigger would make it much worse. In general smaller circuits are more efficient because the same signal is transmitted over a smaller distance. Instead, you want to increase the effective area of heat dissipation, which is what all cooling devices do in some sense or another."
] |
[
"They would be able to support higher temperatures, but they would be much slower. I don't remember the exact numbers offhand, but to illustrate - roughly - a CPU accessing its level 1 cache is 10 times slower than the processor speed. Level 2 cache is 100x slower, ",
". The same CPU accessing its RAM is about 10,000x slower. Size is very important."
] |
[
"The ",
"Larrabee",
" cpu was a ",
" large processor (it had 32 cores of with 4 hardware threads, giving an effective core count of 128 using 16-wide SIMD units), and was something like a ",
"square inch",
". The ",
"next generation CPUs",
" in that line are expected to be about double the number of processors, but the same size.",
"So, how powerful are these processors? At 1Ghz the Larrabee would retire 512 distinct x86 SIMD ops/clock, or 512 gigaops/second. (The part is superscalar, so theoretical throughput is twice this rate.) In terms of 'GPU' performance numbers this equates to ~1 tera-op (madd) or ~1.5 tera-op (madd + v-pipe). The next gen part with double the cores would be at ~2 tera-ops / 4 tera-ops. (The Bonnel uses equal A/B superscalar pipes.)",
"Assuming you could cool it, putting 8-or-so of the MIC would be about the size of a video card, and would be ~16 tera-ops/second. Of course, you're going to need something like a 1600-2500w continuous power supply. A 'motherboard full' (assuming a reasonable sized desktop) would be in the 1/4--1/2 peta-op range, but would consume, say, >75kw. You'd probably singe your socks if you kept it under the desk."
] |
[
"Does gravity work on the time 'dimension' or just the spatial 'dimensions'?"
] |
[
false
] |
I don't exactly know what I'm asking here. But if there were a of some kind that were slightly 'before' some other , would that bring the 'forward'?
|
[
"With a Newtonian view of gravity, such a question doesn't really make sense. Time is just a label that we use to distinguish different states of particles and how they change. So things at different times don't have effects on things at later times, except indirectly, by causing motion that changes the states at all the times in between.",
"In an Einsteinian view, in fact, time is ",
" to gravity but not in the way you think. Newtonian gravity within the framework of general relativity is interpreted as ",
". (Disclaimer for experts: sort of.) But still things at different times don't have ",
" (like exerting forces) on things at later times, they only cause changes in gravitational fields that propagate through spacetime to affect particles later."
] |
[
"Yep, that's right. In fact changes in gravity propagate at the speed of light."
] |
[
"Not only does gravity warp the time dimension, the fact that it does is really important in explaining why you appear to fall in a gravitational field.",
"Imagine a ",
"Minkowski diagram",
", with x as the position coordinate and time on the y axis. A slope of 1 represents moving at the speed of light. If you are in deep outer space and not moving, your path would be a straight line on the y-axis. In other words, you remain at x=0 as time advances.",
"Now we put you in a gravitational field. That curves the time axis, so instead of a straight line it looks like a parabolic arch curving to the right. However, your path still looks like a straight line pointing up. So at t=0, x is still zero. But because the time axis is curving away from you, in the future you will be to the left of x=0.",
"Now let's put this into a non-inertial frame of an observer standing on a planet. This amounts to \"straightening\" the y-axis (i.e. the time axis) out again. Your straight line path now gets warped, so it looks like a parabola instead. So we now interpret this as you falling (accelerating towards negative x) in a parabolic path. Just like Newton predicts.",
"Curving the spatial dimensions helps to explain why light bends around a star, but this curving of the time dimension helps us understand the more practical case of what happens to massive objects falling under the influence of gravity."
] |
[
"How does quantum indeterminism affect macroscopic events?"
] |
[
false
] |
Can quantum indeterminant events snowball/butterfly effect into changes at larger scales, or does it not affect anything beyond the movement of particles? Do all states of affairs observable to us with the naked eye still obtain out of necessity as in classical determinism?
|
[
"Due to ",
"sensitivity to initial conditions",
" being a general property of many-particle systems, and macroscopic things being made out of ~10",
" atoms, certainly quantum indeterminacy generally produces ",
"butterfly effects",
" that propagate to large distance scales. The answer to your second question depends on your ",
"interpretation of quantum mechanics",
". For example ",
"Bohmian mechanics",
" is a classically deterministic theory, while in the ",
"Copenhagen interpretation",
" the outcomes are assumed to be fundamentally random. The ",
"Everettian",
" interpretations are objectively classically deterministic, but subjective measurements are fundamentally random."
] |
[
"Quantum mechanics is a deterministic theory. Heisenberg's Uncertainty is a general feature of ALL wave phenomena, whether quantum wavefunction or ocean wave. ",
"Your first point depends on the interpretation. The second one is very debatable. Sure you can derive the Kennard uncertainty from the point of wave mechanics, but the quantum mechanically uncertainty is more fundamental in my opinion. You always have an uncertainty for two observables whose commutator does not vanish. The position/momentum case just gives you the classical Kennard limit, but you also get different relations like for angular momenta."
] |
[
"Right, I had the Copenhagen interpretation in mind when asking the second question."
] |
[
"Vodka used to treat dog with anti-freeze poisoning, what is the pathophysiology behind this?"
] |
[
false
] |
I'm curious as to how the worked on a biological level, as this is a treatment I've never heard of for humans. Is it something canine specific? How did the alcohol stop the renal failure?
|
[
"Antifreeze poisoning is due to the ",
"ethylene glycol",
" in it. Ethylene glycol by itself is not intrinsically toxic (and in fact has a rather sweet taste). However, it can be metabolized into glycolate, glyoxylate, and oxalate, which can cause organ damage (particularly to the kidneys) as well as lead to a ",
"metabolic acidosis",
". One way to treat these problems is to decrease the rate of metabolism into the toxic end-products. ",
"Ethanol is a competitive inhibitor of the enzyme",
" (alcohol dehydrogenase), so giving alcohol can decrease the rate of formation of toxic compounds. However, giving alcohol is associated with a number of logistical issues, so other compounds like ",
"fomepizole",
" are preferred (in humans at least). (A target goal of concentration around 22mmol/L or 0.1BAC is usually recommended.) Patients given alcohol dehydrogenase inhibition therapy should also be given cofactor supplements like folic acid, leukovorin, and thiamine. Other aspects of treatment include giving sodium bicarbonate to counter the acidosis, as well as dialysis to remove the toxic compounds from the blood. ",
"(Methanol poisoning is treated similarly due to similar pathways/mechanisms.)"
] |
[
"Humans can and do ingest ethylene glycol, this treatment is not really similiar to chronic liver injury due to alcoholism. It seemed like that's what you were implying, so I wanted to clear that up. "
] |
[
"Works for people too. The ethanol binds to the same sites (enzymes? I don't really know specifically) as the alcohols in the antifreeze. The ethanol bond is much stronger and thus displaces the antifreeze, preventing the antifreeze from doing anything. You keep those sites loaded with ethanol until the antifreeze has been passed. ",
"According to wikipedia, the ethanol binds to the enzymes which would otherwise break the ethylene glycol down into two other compounds which are poisonous. The ethylene glycol is then passed through the digestive tract."
] |
[
"Why do nails stick in car tires instead of being shot out due to tire pressure?"
] |
[
false
] | null |
[
"There is a lot of friction between the tire tread and the sides of the nail. There is only a very small surface area (the end of the nail) for the pressure to act on, so the net push outwards is very small, not enough to overcome the friction against the sides of the nail."
] |
[
"Apparently, 2.4mm is roughly the diameter for \"13 gauge\" nails, commonly used in construction. So 1.2mm would be the radius, and we can calculate the area at pi * r",
" . Also, my tire pressure is roughly 207kPa.",
"The cross-section of the nail and tire pressure on that area will tell us how much pressure is being put on the nail, trying to push it out.",
"A = 2 * pi * 0.0012m = 0.0000090 m",
" .",
"Force (in Newtons) = 207kPa * 0.0000090 m",
" .",
"F = 1.87 Newtons, which is about the amount of force that something 200 grams exerts, just sitting there due to Earth's gravity. That's not a lot of pressure pushing it out.",
"The force pushing the nail out is based on the cross-section of the hole, and so the radius of the nail itself. The friction holding it in is based on its circumference. The area increases with the square of the radius, while the circumference increases just with the radius. So, the larger the nail, the more likely it is to be pushed out by tire pressure, since the pressure pushing it out will increase quicker than the friction holding it in."
] |
[
"Mostly a first guess, based on the idea that you'll have a ring of contact between the two objects, the three parameters that I can see being the coefficient of friction between them, the thickness of the tire contacting the nail, and the circumference of the nail. Kind of a \"spherical cow\" approximation.",
"A smaller penetrating object, say like a sewing needle, intuitively seems like it's less likely to be blown out compared to something large like a spike of steel rebar, and I was trying to find an explanation of \"why\"."
] |
[
"Do automatic weapons have any other power source except for the explosion of the gunpowder in the bullets?"
] |
[
false
] |
You hear of guns that can shoot at so many hundred rounds a minute, but what determines this speed? Guns don't have batteries, right? So does it use some of the energy from the explosion of the gunpowder in the first bullet to move the second bullet in and fire that? So what would determine the number of rounds per minute? How much energy it has to do the change over and how much resistance in moving a round in? Could you speed it up somehow? I have no real experience with guns, so forgive me if this is a dumb question.
|
[
"It's only a dumb question if you don't learn anything from the answer.",
"Let me first explain the action of an M16, and then I can illustrate changes that'll make a difference, in order to address the other questions you raise.",
"We'll start with 1 round ready to fire, and the gun ready to go. When you pull the trigger you release a a hammer which is pushed forward by a spring. The hammer hits the back of the firing pin, which hits the primer in the back of the round. The primer gives out sparks, which causes the powder in the casing to start burning. As it burns, it gives off a known amount of gas, which pushes the bullet out and forwards into the barrel of the gun and eventually out of it.",
"In an M16, and indeed most other modern rifles, there is a small tubes that comes out of the top of the barrel and back into the body of the rifle. Some of the gasses will travel down this tube with a high pressure, and be used to cause things to happen. In an M16 these things include unlocking the bolt and partially propelling it (in its carrier) backwards towards the back of the gun - it's assisted by gasses still in the barrel. As the bolt carrier moves backwards it compresses the recoil spring, and pushes the hammer back down, where it's held by a catch. As it moves backwards, the brass casing from the round that's just been fired becomes exposed to the ouside world via the ejection port, and the ejector (powered by the ejection spring) in the front of the bolt throws that casing out of the side of the gun. Finally, the bolt carrier reaches the back of its travel, and begins to come forwards again, powered by the recoil spring that it compressed on the way back. As it does so, the front lip catches the top of the back of the next round sliding it forwards up the feed ramp into the chamber. The bolt carrier also catches the latch that has caught the hammer all the way back and releases it, allowing the hammer to come up to a position where the trigger controls whether it is released or not, and as the hammer is moving to that position, the bolt locks in to place again.",
"So, with all of that in mind, what we have is called a gas-operated rifle. There's a couple of things that can be done to make it run faster - firstly the pressure from the gasses can be increased, and secondly the recoil spring can be made stronger. If you lot more powder into the rounds to make then give off mroe gasses, you'll get bullets that travel faster and heat up the barrel more (through friction) as they do. Sicne there's more gasses there will be more gasses at higher pressure operating the gas-driven components. The other method is to make the existing amount of gas take longer to leave the barrel, which means it's at a higher pressure in the barrel. One well known method for doing this is to put something on the front of the barrel that slows down the rate at which the gasses leave the barrel, to non-supersonic speeds. This has the effect of making the \"bang\" after the bullet much quieter. It's called a supressor.",
"A harder recoil spring will mean the part of the cycle where the bolt comes forward again is sped up.",
"Obviously, there are reliability concerns with each of these methods, and so some research will need to be done to each to figure out how to work around common defects.",
"BUT WAIT, THERE'S MORE... There are some guns that are not gas operated. Let's take the 1911 pistol as our example here, although a lot of handguns fit this model. The 1911 is a recoil-operated gun. When you pull the trigger, you release the hammer which is powered by a spring in a similar manner to the M16. The spring hits the firing pin and sets off the primer, burning the powder and pushing the bullet out - this much is the same as the M16. What happens in the 1911 next is where it's different. The burning gasses are not just pushing the bullet out of the barrel. They're trying to push the bullet and the back of the barrel in different directions as they expand, similar to the air in a balloon pushing the two sides of the balloon apart. The barrel moves back a short way before stopping. The slide (the top section that encases the barrel) continues backwards, compressing the recoil spring, just like the bolt does in the M16. A similar casing eject and reload happens, and the slide moves forwards again, eventually catching the barrel and moving it back in to place and locking together with it.",
"So, in both cases, all of the energy comes from the burning gasses, and at some point some of it is buffered in a spring, so that the direction can change.",
"There are also, as other people have mentioned, some guns which use electricity for some things - the Gatling gun on the A-10 warthog is spun by electricity, and the Metal Storm range use electricity for setting off the caseless rounds, which means that they can load several rounds into one barrel, and set each one off in turn. They're a whole different kettle of fish.",
"EDIT: Refer to bolt carrier rather than bolt, in appropriate places. Also correct a typo or two."
] |
[
"Most automatic weapons redirect a small amount of the exploding gases to power the mechanism. Some larger automatic weapons may use an electrically or hydraulically driven mechanism. A few experimental-type pistols and rifles have used spring, electrically or pneumatically driven mechanisms, though none have ever been popular.",
"Faster doesn't always equal better. Most modern individual weapons are engineered to slow down the rate of fire. Why? Control. 3 bullets accurately on target are usually better than 20 bullets from a bucking automatic weapon. The Army went from fully-automatic rifles to rifles which fire three shots in a burst every time you pull the trigger.",
"Wanna see something spiffy and silly? Youtube \"Metal Storm\". Electrically-fired projectiles firing hundreds of thousands of rounds per minute."
] |
[
"I have never heard such a distinction before. Please provide some source for this.",
"Non-externally powered firearms usually considered machine guns include the M2, M1919, M1917, M60, M249, M240, and scores of others from non-US armies."
] |
[
"Could you fly a helicopter/drone on Enceladus?"
] |
[
false
] |
With NASA's planned Orbilander going to Enceladus, could it host a small rotorcraft like Perseverance did with Ingenuity? I read it does have an atmosphere of water vapor.
|
[
"No, to the point that it's not what you would informally call an atmosphere.",
"I was going to post something about so-called surface boundary ",
"exospheres",
", but it's not clear from an initial read to what extent Enceladus is hanging onto the outgassed materials for long enough for it to count."
] |
[
"A prime candidate for flying helicopters/drones would be Titan; that moon is unique in being the only one in our Solar system with a considerable atmosphere. It's even ticker then Earth's. The problem is that it's very cold (90K)."
] |
[
"NASA is working on a Titan helicopter: ",
"https://en.wikipedia.org/wiki/Dragonfly_(spacecraft)",
"Unlike Enceladus it has a significant atmosphere."
] |
[
"How close do a particle and its antiparticle have to be to annihilate?"
] |
[
false
] |
Would it also matter through wich interaction they annihilate by? Since the electromagnetic force has a much further range than say the weak force would electron-positron annihilation be able to then occur further away via electromagnetic interactions rather then weak interactions?
|
[
"For any interaction among fundamental particles (whether it counts as annihilation or not), there isn't a sharp cutoff. The probability of the interaction becomes lower as the trajectories of the incoming particles get further apart.",
"Each individual reaction has a cross section, and if you set that cross section equal to πr",
" and solve for r, that will give you a rough estimate of the distance above which the interaction probability becomes small."
] |
[
"The cross section for ",
" scattering under a Coulomb potential is infinite (under some approximations), but elastic scattering is where the two particles basically just bounce off each other, or even just perturb each others' trajectories a bit. That's not annihilation. To get the cross section for annihilation, you have to look to inelastic processes, i.e. those where the particles actually interact, so the Coulomb potential is not involved."
] |
[
"I thought the scattering-cross section of a coulomb potential was infinite, so would the particles be able to annihilate at any distance just with less probability?"
] |
[
"What are the equations governing the Strong and Weak nuclear forces?"
] |
[
false
] |
The basic equations of gravity and electromagnetism are taught in high school. I've taken university physics (including basic problems with Schroedinger equations) and I've never seen an equation for the or the (even the wikipedia pages referenced here don't have them). I've never seen them in a textbook. I've never found something I recognize as an equation for them online. Why is that? How is the force of interaction calculated?
|
[
"Strong force",
"Weak"
] |
[
"There aren't any is the short answer.",
"Force, as classically defined, is about a change in momentum. We've come to learn that all of these momentum exchanges are governed by the exchange of particles called \"gauge bosons.\" Each force has at least one boson associated with it. EM exchanges photons, Weak exchanges W, Z bosons, and Strong exchanges gluons. ",
"Only the electromagnetic force is long range enough to have a classical approximation as a force like the coulomb potential. One can treat the strong force between protons and neutrons as a ",
"Yukawa potential",
", but again this is just an approximation of what's going on more fundamentally. In the case of potentials, a particle with some \"charge\" placed somewhere in the potential has some potential energy = charge * potential. The directed rate of change of the potential energy gives the classical Newtonian force.",
"The weak force isn't necessarily important for its \"force\" of exchanging momentum, but that as it exchanges momentum it changes particles from one type to another (an electron to a neutrino for instance)",
"I'll also link you to the ",
"r/sciencefaqs about the fundamental particles",
" to help your reading."
] |
[
"great answer."
] |
[
"Question in regard to science news."
] |
[
false
] | null |
[
"Hello: This submission is stuck in the spam filter, and probably won't be let out mainly because it is not something we really discuss here. However, you might be interested in looking at the sites ",
"physorg",
", and ",
"ScienceDaily",
". Thanks! "
] |
[
"Thank you very much! :)"
] |
[
"You're most certainly welcome. And, if you find some scientific ideas in those sites that you don't understand, or want to know more about, come back and ask a question, and hopefully one of our panelists can help!"
] |
[
"Is the radiation we receive throughout our lifetime from everyday electronics even close to harmful to us?"
] |
[
false
] |
Im talking about things like computers, microwaves or cellphones. I know its not a huge significant amount, but over long periods of time(years, not hours) can they have effects on humans?
|
[
"Radiation isn't a summing process. Either the radiation has enough energy to cause damage, or it doesn't. Computers, microwaves and cellphones do not emit or receive radiation with enough energy to cause ionization in your body. "
] |
[
"Because they are exposed to ionizing radiation, which is able to damage cells or RNA. A microwave oven for example only emits weak non-ionizing radiation. It cannot cause damage to your body. "
] |
[
"Keep in mind that microwaves and radio waves carry less energy than visible light. So if ",
" waves are energetic enough to damage cells, then we're screwed anyway :)"
] |
[
"A sphere is the solid with the highest volume/surface area ratio. Is there a solid that's the opposite of it? That is, that has the lowest volume/surface area?"
] |
[
false
] | null |
[
"Another easy example where one can verify this property oneself is this: Consider a cube whose sides have lengths a=b=c=1. Now, double a and halve b. Do this again. And again and again. After n steps, you end up with a new solid whose sides have lengths a'=2",
" b'= 2",
" c'=1.",
"\nThe volume here is still 1, but the surface is 2 + 2",
" + 2",
" which tends to infinity. Therefore, you can construct for yourself a solid with arbitrarily small volume/surface ratio."
] |
[
"No, there can't be. There are families of solids (for example, those used in the construction of the ",
"Menger sponge",
") whose surface area increases without bound while the volume tends to zero; given one solid in the family, you can always find another one with a lower volume to surface area ratio. The limit itself is not properly speaking a solid, but a fractal."
] |
[
"Yes many fractals can be constructed in such a way to have positive or 0 measure with positive surface area."
] |
[
"What keeps us from re-capturing CO2 at the source?"
] |
[
false
] |
According to article, a company is re-capturing CO2 from the atmosphere, turning it into carbon pellets, and then into diesel fuel. Why can't we make those carbon pellets straight off of the exhaust pipe? Or can we?
|
[
"Sure you can, but then you need to use a good deal of the energy you get out of burning your fuel in the first place just to do this. ",
"CO2 is formed because it is the stable product of carbon and oxygen combustion. The actual energy you release and use to power your car comes from breaking the more unstable bonds in the fuel and creating the new stable bonds in the CO2. If you want to turn that CO2 into something like coal you need to break all those C-O bonds at least which requires a lot of energy, or if you want something like a liquid fuel you need to break apart the water product as well to free up some hydrogen (and at which point you will have used up all the energy the original fuel provided).",
"The process requires electricity, but if the start-ups use renewable electricity they can produce diesel that is carbon neutral.",
"That quote is from the article you linked. In order to get a process like this that makes any sense we need to take energy from a non-carbon source and use that to reduce the CO2 back to a usable form. We \"lose\" that energy but we can gain a portable and energy dense fuel and so theoretically it can still be a good option."
] |
[
"Actually, the energy you need to break the carbon-oxygen bonds is the same as the amount you can gain from burning the fuel you make afterwards. Since nothing we do is done at 100% effectiveness, the result is a net energy loss, and in turn even more CO2 released.",
"If the point is to save CO2, we are better off using the renewable energy directly in engines or electronics instead of adding an extra step with loss of energy to the equation."
] |
[
"The biggest pet peeve of any engineer that understands thermodynamics is when people want to string energy conversions in series."
] |
[
"How will Voyager 1 keep its antenna pointed at Earth once it crosses the heliopause?"
] |
[
false
] |
Does the spacecraft have thrusters or does it use torquing coils to interact with the heliosphere? How does communication actually find its way back to Earth (if its not LOS that is)?
|
[
"Voyager 1",
" is at about 122 AU from Earth. Earth's entire orbit ",
"subtends an angle",
" of less than 1 degree, about twice the angle subtended by the moon viewed from Earth. It has a ",
"3 axis thruster system",
", and has only used about half of the fuel it started with."
] |
[
"What were you thinking would knock it out of it's current alignment?"
] |
[
"Well I was thinking along the lines of them not using a very tight beamed transmission. At the distance they are at relative to each other, a few degrees of spread in the broadcast would cover the whole region of the target. Given there aren't many patterns in natural radio wave sources the return would stick out but weak. Since they are talking about a bow shock being crossed I'd say voyager is also heading out ahead of the sun. It would be ideal for it to head straight ahead to conserve power while achieving interstellar space also."
] |
[
"Explaining Mechanical Advantage in Rope Pulley Systems"
] |
[
false
] |
I was hoping that someone would be able to show me how to calculate how much mechanical advantage someone gains from a rope pulley system ie. 3 to 1, 5 to 1, how do you figure this out?
|
[
"I think it's useful to count the number of strands pulling ",
" on an object. Since the tension must be the same in the entire rope, each loop adds an extra force of tension to the system. (need pictures to illustrate...)"
] |
[
"In a block and tackle system, you've usually got a standing block and a moving or running block. The mechanical advantage is the number of \"parts\" of the line that run through or are attached to the moving block.",
"Here's a diagram of several ways you can reeve a tackle system: ",
"Picture",
".",
"In this picture, the running block is the one at the bottom, the one with the hook. That's where you'd attach your load.",
"Let's look at the left system (the gun tackle). It's got two \"parts\" of the line running through the moving block (one going in, one coming out). This will give a 2:1 mechanical advantage. The next system over (the luff tackle) has those two parts, plus a part made off to that moving tackle. That's a 3:1. The next one has two parts going in, and two parts coming out. That's 4:1. Got it?",
"Keep in mind that when you add more parts to your system, you have to pull more line to lift the same distance. Also, you eventually get to a point where you can add more sheaves, but it just adds more friction. It stops being worth it at some point, which is determined by the frictional coefficient of your blocks.",
"Hope that helps."
] |
[
"I drew us a picture: ",
"Picture"
] |
[
"Why is electricity cheaper at night?"
] |
[
false
] |
I'm in the UK and my electrical company charges less for electricity at night when I assume night time is when more people are at home and using more electricity for lights, televisions, computers and heaters. Is it more efficient to produce and distribute electricity at night? Sorry if this question is more economical than science .
|
[
"Residential demand is only a piece of the puzzle. Business demand during the day outweighs that at night.",
"Take a look at ",
"this",
". Overall demand is higher during the day. ",
"This image",
" shows demand from a hot California day in 1999 -- commercial demand peaks during the day, and even residential demiand peaks at 6pm."
] |
[
"It's cheap because homes, offices and other power hungry places are mostly switched off. It takes a lot of work to power down power plants and so by offering incentive for people to run washing machines and such overnight, can even out the demand."
] |
[
"not only that but they literally need to put it somewhere. That's why they'll sell it to other markets [like Canada to the states] at a loss."
] |
[
"Rockets need to expell mass to go forward, but if you expell the mass at greater speed then less mass need to be expelled, couldn't Rockets just expell the mass at very high velocity to reduce the amount off mass needed to be carried?"
] |
[
false
] |
The biggest problem with rockets is that they need to carry a large amount of fuel, but what I'm wondering is that a possible future solution to this is to use ion drives that use magnets to expell some amount off mass but to just use a nuclear reactor to increase the amount of energy in the magnets and expell the mass at higher speed to carry less off it. Also could it then be possible to expell only a few particles at extremely high velocity to only have to carry an extremely low amount or am I missing something? Now I know that you can't expell the mass at or beyond the speed of light but even then you can still add and ever increasing amount of energy and therefore momentum giving you greater thrust. Is this possible or is there some physical reason of why it can't happen, I'm speaking from a purely hypothetical standpoint and using technology in the distant future, maybe using super conducting magnets or something. I would love to know some thoughts on this. Thank you P. S. I'm new to reddit so I'd just like to say hi and sorry if I'm doing something wrong, I'm not too clear yet on the rules :)
|
[
"It's true, that the faster your exhaust travels, the less fuel you need. However, it costs energy to accelerate your exhaust, and higher exhaust speeds require more energy. The result of this is that you also have to budget for how much energy you can generate, as well as what the energy efficiency of your exhaust is. It turns out that ",
"propulsive efficiency",
" peaks when the speed of your exhaust is equal to the speed of your rocket, so using an engine with near light-speed exhaust will be extremely energy inefficient, so you would probably be energy limited, instead of reaction mass limited."
] |
[
"This is exactly what rocket scientists have been working on for decades, and is the principle behind ion engines. As a matter of fact, a measure of a rocket's capability is \"specific impulse (Isp)\" which describes the power of an engine by its exhaust velocity. This is factored into the Tsiolkovsky rocket equation, which measures its total \"delta-V\" or ability to accelerate.",
"The problem is not a theoretical one, but an engineering one. We are already doing as well as we can at making the exhaust as fast as possible. Engines with extremely high Isp generally can't reach high thrust-to-weight ratios, because they expel so little propellant. On the other hand, we have launchers, which have extremely huge thrust, but poor Isp in comparison. Different rocket parts are put together in stages to maximize the efficiency of all types needed. :)"
] |
[
"By inefficient, i mean energy inefficient. You spend more energy for less delta V. So the tradeoff you get is that although you need to carry less reaction mass, you now need to carry more energy."
] |
[
"Why doesn't HSV-1 transfer to other parts of your lip? Does genital herpes function the same way?"
] |
[
false
] | null |
[
"Herpes resides in your nervous system, not your lips. The infection you see as a cold sore is an inflammation response to a newly reactivated bit of virus at the tip of a nerve under the skin that colonizes some minor damaged tissue on the lips.",
"The reason it is reactivated is not clear: herpes is usually dormant for awhile after infection then spontaneously pops up due to signals we don't entirely understand. It can cause sore on just about any place with lots of nerves or weak tissue, so it can get in the eyes or on the fingers. ",
"But as for the reason it doesn't spontaneously shift it is likely the same reason you don't immediately get cold sores after your first infection: newly infectious virus particles don't cause immediate symptoms, and you already have antibodies and a latent infection.",
"This is borne out by the fact that immunocompromised people do get long spreading lesions called \"knife cut\" lesions and potentially life-threatening outbreaks."
] |
[
"I would like to clarify a bit on immunocompetence and herpes spreading. Herpes does not spread in immunocompetent individuals because their immune system is able to control the herpes infection. However, a competent immune system is not able to develop sterilizing immunity to HSV because it develops latency. During its latent phase the herpes hides in neurons (typically trigeminal ganlion cells in HSV-1 and sacral ganglion cells in HSV-2) and produces an mRNA, Latency Associated Transcript, that regulates the host cell genome and interferes with apoptosis. The development of latency is why herpes infections are recurrent their mechanism of latency, i.e. by hiding in somatic neurons for the region of infection, is why they recur in the same location. ",
"In immunocompromised individuals, herpes infections can spread because their immune system is not capable of controlling the infection."
] |
[
"The mechanism is poorly understood but we do know what herpes genes are activated first. Since PNS neurons lack DNA polymerase, the LAT activates transcription of the herpes own thymidine kinase genes in order to replicate. Also, the protein ICP0 has been shown to be required for initiation of transcription of many of the HSV genes. Triggers that have been associated with reversal of latency include, UV light, stress, and hormonal changes.",
"As a side note, in addition to immunocompromised individuals from AIDS and chemotherapy, the disseminated form also occurs in infections of neonates"
] |
[
"How close are we to \"test tube babies\"?"
] |
[
false
] | null |
[
"I'm not sure exactly what you mean, but we've had \"test tube babies\" (in vitro fertilization) since the 70s... "
] |
[
"Oh I see. In that case, not at all close"
] |
[
"Yes. But how close are we to continuing that process and keeping it outside the body for the duration of pregnancy"
] |
[
"After the heart stops, how long do synapses keep firing? And other questions."
] |
[
false
] |
[deleted]
|
[
"Archives d'Anthropologie Criminelle, 1905:",
"\"Here, then, is what I was able to note immediately after the decapitation: the eyelids and lips of the guillotined man worked in irregularly rhythmic contractions for about five or six seconds . . . I waited for several seconds. The spasmodic movements ceased. The face relaxed, the lids half closed on the eyeballs, leaving only the white of the conjunctiva visible, exactly as in the dying whom we have occasion to see every day in the exercise of our profession, or as in those just dead. It was then that I called in a strong, sharp voice: 'Languille!' I saw the eyelids slowly lift up, without any spasmodic contractions . . . Next Languille's eyes very definitely fixed themselves on mine and the pupils focused themselves . . . After several seconds, the eyelids closed again, slowly and evenly, and the head took on the same appearance as it had had before I called out.",
"\"It was at that point that I called out again and, once more, without any spasm, slowly, the eyelids lifted and undeniably living eyes fixed themselves on mine with perhaps even more penetration than the first time. Then there was a further closing of the eyelids, but now less complete. I attempted the effect of a third call; there was no further movement and the eyes took on the glazed look which they have in the dead.",
"\"I have just recounted to you with rigorous exactness what I was able to observe. The whole thing had lasted twenty-five to thirty seconds.\""
] |
[
"The electrically active cells will fire at their basal rates until they can't maintain their electrolyte gradients (Na+, Ca++, Cl- out, K+ in). For most neurons, this will be \"not at all\", but doubtless some have an underlying rhythmic pace a la pacemaker cells in the heart. ",
"A fair proxy for the farthest out you could imagine a cell firing would be rigor mortis, which occurs after about 3 hours because calcium is no longer sequestered outside of the muscle. I expect that the neurons would go a bit quicker simply because their architecture and physiology is more delicate.",
"That said, one neuron does not a nervous system make."
] |
[
"There was a russian experiment where a guy hooked up a severed dog's head to a pump. The head responded to several different stimuli: light, sound, tactile. ",
"Footage from the experiment"
] |
[
"Why exactly does E=MC^2 ?"
] |
[
false
] | null |
[
"Ah. That's actually pretty interesting. He came up with his theory for how electromagnetism works when the source is moving (what we now call special relativity) and looked at what happens when the object emits radiation. He realized that his theory implied that as radiation with energy E is emitted, the mass must drop by an amount E/c",
" in order to preserve symmetry between different reference frames. He finishes off with an underwhelming conclusion:",
"It is not impossible that with bodies whose energy-content is variable to a high degree (e.g. with radium salts) the theory may be successfully put to the test. If the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies.",
"http://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf"
] |
[
"I was thinking more along the lines of a derivation/explanation of how Einstein came about forming this equation."
] |
[
"You should really really read this book: ",
"Why Does E=MC",
" (And Why Should We Care?)",
"http://www.amazon.com/Why-Does-mc2-Should-Care/dp/B004LQ0ICE/ref=sr_1_1?ie=UTF8&qid=1302835764&sr=8-1"
] |
[
"Does the effectiveness of Positive/negative reinforcement change if the receiver is aware that they are being used? Why/why not?"
] |
[
false
] | null |
[
"Motivation is a really interesting subject, and one with a ton of nuance between a number of different factors that all interact with one another. Largely, reinforcement models are used for things like behavior modification, for aspects that tend to be very deeply seated within the psyche (like hoarding), or physically addictive (like cocaine).",
"For the behaviorists that would typically use positive/negative reinforcement the subject is an animal (human or otherwise) that does things (On a side note, negative reinforcement is the least effective, at least with children in educational settings). The things that the animal does can be predicted, controlled, and changed. Whether a subject was aware of the reinforcement or not doesn’t really matter if, as a strict behaviorist, only the observable actions were measurable. So, if I can put words into BF Skinner’s mouth: no, awareness doesn’t change anything. This apparently plays out in practice, if you were to look at casinos, which rely heavily on reward schedules, you would find that gamblers keep on gambling even when acknowledging that “the house always wins.”",
"BUT! If you are interested in the awareness of the system by the subject, then you can look into a number of different motivational theories that would suggest that YES! there is an change in motivation and behavior if the system is understood. Mostly, though, the theories are a bit incongruous with the idea of reinforcement (very different philosophical underpinnings between reward/punishment, and socio-cultural context). That said, goal achievement theories place a lot of weight on the autonomy of the individual within that social context. In that case, you could make the argument that knowing that someone else is setting the goal and rewards would be in conflict with the individual making a choice about their achievement. ",
"This gets all sorts of messy with attribution theory, expectancy-value theory, and any number of other models. Within those, a strong reinforcement (like grades, or money) will still persist when the student feels like they are being used, if the balance between tolerating being used, and receiving the reward is in the favor of the reinforcement."
] |
[
"Hey, thanks! I learned probably as much from this post as I did from all of my \"Intro to Psychology\" Class last semester..."
] |
[
"Board certified behavior analyst here. The answer to this question is no, not if you have a true reinforcer (or aversive stimulus, for negative reinforcement). Often times we think we are using positive reinforcement when we say \"good job\" or the like, but that isn't necessarily reinforcing for everyone. ",
"Praise might even become conditionally aversive (i.e., the opposite of reinforcing, but only in a certain context), if the person being praised becomes aware that you are trying to change their behavior. ",
"Edit: Some more information: Some reinforcers (and aversive stimuli), especially those necessary for life, are effective at birth (e.g., water, food, warmth, physical touch). Others, however, must be learned. Praise is among the reinforcers that must be learned (this happens through pairings with the reinforcers you are born to like, or previously conditioned (paired) reinforcers). ",
"Learned reinforcers are probably more likely to be affected by the receiver becoming aware of their use, compared to unlearned reinforcers. This goes back to unlearned reinforcers generally being necessary for life. Someone is also more likely to 'reject' reinforcement if the behavior that is being conditioned is one that the receiver doesn't want to change. In those cases, you probably shouldn't be attempting to condition that behavior. "
] |
[
"What would be the \"evolutionary\" reason for us wanting to be completely covered by blankets (can't be exposed, can't have arm dangling over)?"
] |
[
false
] | null |
[
"I think the question is flawed. There has not been any evidence that indicates what you're claiming is true for all people. "
] |
[
"What I mean is that there is no evidence to indicate that an evolutionary reason exists."
] |
[
"Just because it's not true for all people doesn't mean the question flawed. Not everyone is light skinned and not everyone practices rape, but you can still ask about evolutionary reasons for those things."
] |
[
"How do we determine how many stars are in The Milky Way?"
] |
[
false
] |
I've tried to look this up, but every site that I go to either goes into detail explaning how we estimate the number of stars in galaxies, but never much for the Milky Way. So how do we do it?
|
[
"Stellar counts are always a guesstimate from an assumed distribution of stellar masses and overall stellar mass of the galaxy. To work out the mass distribution, we can literally just count up stars, using differences in their spectra to work out what their masses are. To get the total mass in stars, we can look at other galaxies like the Milky Way, both in real observations (where we can estimate the total stellar mass from the total luminosity) and in computer simulations, or we can extrapolate from the stars we measured masses for.",
"Fundamentally there's no great difference between doing this for the Milky Way and doing it for other galaxies - you just need to carefully account for the fact that we only see the portion of the galaxy in the direction we look."
] |
[
"It's because we can get an outside view of the other galaxies, but we can't get a full view of our Galaxy, since it's well... Really big, and we are inside it. Imagine if you were on a cruise ship and so another, you can't see your ship but you can see the other one in it's full size."
] |
[
"thank you for that, but that isn't the question I asked. The question was (essentially) how did we come up with the estimate for how many stars are in the Milky Way."
] |
[
"If alpha centauri went supernova, how long until the effects reached Earth?"
] |
[
false
] |
I mean all of the stars in the alpha centauri system.
|
[
"Alpha Centauri A and B are each about the size of the Sun. The third, proxima centauri is much smaller. All are too small for a supernova. At the end of their lives A,B, and the Sun will grow into red giants eventually blowing off most of their mass leaving a white dwarf.",
"(It won't happen) but if a supernova were to happen that close, we'd all die from various problems caused by the emission equivalent of a whole galaxy just 4 light years away. It would take ... 4 years..."
] |
[
"How far away is the nearest large enough star?"
] |
[
"150 light years, but it'll be a few million years before it will have a chance of going supernova."
] |
[
"Particle accelerators - is bigger always better?"
] |
[
false
] |
Let say we are able to build a particle accelerator the size of earth's orbit around the sun and are able to harvest 1% of the sun's output as energy source. What types of experiment would we be able to perform that we cannot now? Would the size of Mars' orbit and 2% of the sun's energy be much better, a little better, or about the same?
|
[
"So it's kind of a combination of things. First it matters what particle species you wish to collide. Light particles like electrons and positrons generally are accelerated linearly, to reduce syncrotron radiation. Protons and the like get the advantage of circular accelarators (you can keep passing the particles through the same accelerating gradient rather than building a huge series of gradients). But to build a circular accelerator you need to ",
" the particles. That's generally done using a magnetic field. But we can only make our fields so strong (with current technology) so that limits the amount of force we can exert. So keeping force constant, higher momentum protons will need larger turning radius, and ",
" why particle accelerators keep growing in size."
] |
[
"so the size doesn't really matter here exactly (I'll presume that the engineering challenge of providing the acceleration within some length is solved by the same magical engineers that let us harvest 1% of the sun's energy). But let's say after all the energy losses 1% of the sun's energy (let's say in 1 second), can be dumped into your particle bunches, with let's say, 10",
" particles in the bunches. That's something like ",
"10",
" eV per particle",
". We don't even have SI prefixes to describe that high of a value. Anyway, we can use Heisenberg uncertainty principle to flip this momentum around into a length-scale, approximately h/p. since we have the kinetic energy E, the momentum is p=E/c, so our length scale is hc/E ",
"which is something like 10",
" m",
", about 10",
" times than the planck length, but about 10",
" times larger than the smallest discrete space time ",
"ruled out by the Integral experiment",
"."
] |
[
"ah, so let me put it this way, there's one remaining test of high energy particle physics. At a certain energy scale, we expect that the strong force will behave an awful lot like the electroweak force ",
"about 10",
" eV",
", so we'd be able to probe that scale along the way (we have about 10",
" more energy than necessary to meet that scale).",
"What I was trying to more say is that you can think of particle accelerators as making increasingly smaller \"probes\". We have trouble resolving atoms with visible light, because the light is bigger than the atoms themselves. So we use higher energy light, or more commonly electrons with even smaller wavelengths. Or we can accelerate particles to very high momentum and probe the internal structure of quarks. So my length scale argument is that this collider could measure physics that happens on the length scales of 10",
" m or so."
] |
[
"How large would an asteroid need to be to have enough gravitational pull so that a human could walk along it without needing to \"hold on\"?"
] |
[
false
] |
For clarification by "hold on" I mean being able to walk in a standard space suit and not need and special foot clamps or the like.
|
[
"hop around like a kangaroo",
"A lot of people would approach this question in terms of escape velocity but that's not a good way to look at it because even if you cannot reach such velocity, it'll still be quite uncomfortable to be able to launch yourself up several hundred meters by a mere jump, even if this jump leads you back down eventually.",
"To make things short, consider the following thought experiment - you are partially or fully submerged in a pool of water. You try to walk but it's really hard. You have to try hard to stay near the floor if you are fully submerged. This is a lot like what it'll be like on a less dense planet.",
"Here's how it works in the pool. The buoyancy provided by the water partially cancels out the force of gravity and you can simulate what it's like to be on a planet with low gravity or even microgravity.( For example, NASA uses a ",
"neutral buoyancy tank",
") to simulate space walks. Now, as most of us have tried to walk when partially submerged, it's actually hard to walk properly. One problem is the water drag, it makes it difficult to move. But the more severe problem is that you can't just walk forward that easily. You push off and you are off the surface and then you come down a bit forward. That's not a walk anymore. This is the same kind of thing you will see on a big space rock. Even the moon's gravity is not strong enough to make walking comfortable. In fact, look at how astronauts on the moon walked - they didn't. ",
"They hopped instead",
", because it's a lot easier.",
"So my answer is that to \"walk along\" one needs a fairly massive body, somewhere between the size of the moon and the size of the Earth (mass vs radius). Of course, you can hop around and call it walking. After all, it does work. By why can't we walk properly.",
"The answer is actually quite spectacular. ",
". Let's briefly analyze a step forward.",
"this",
"Once you get walking it's a matter of keeping it smooth and efficient. And humans are quite efficient at walking. We're basically made for walking and running.",
"So, the major force involved in walking is the force of gravity. If this force is not strong enough, your body will not be pulled forward fast enough. Since we are not familiar with this kind of thing, we won't feel comfortable walking like this. Certainly, the astronauts on the moon didn't feel like doing it. Actually, you CAN still walk on a less massive body, but it'll have to be much much slower. If the acceleration due to gravity is 1/k that of Earth's gravity, walking will be roughly sqrt(k) times slower (I'm lazy to do the exact calculations)."
] |
[
"I won't use the bean, because that's both irregularly shaped, difficult to pack, and meaningless to anyone who isn't familiar with the silver bean in Chicago. Hopefully these other calculations will give you a sense of the scale.",
"A sphere with a radius of 5.6km has a circumference of around 21.9 miles, meaning that if you put a stake in the ground and drove away from it in a straight line at highway speeds (assuming you're following the 55mph speed limit), you'd run over your stake from the other way in under a half hour. ",
"The largest gun ever used in war was Germany's Paris Gun, which was capable of shelling Paris from 71 miles away. Hence the name. If you set up the Paris Gun on this asteroid and aimed it at the horizon, the shell would miss the ground entirely and go sailing off into space roughly tangent to where you fired it.",
"The largest atomic bomb ever detonated was the Tsar Bomba, a Russian-made 58-megaton behemoth, was strong enough to knock the plane that dropped it 1 kilometer from its altitude. That was even after the plane had gotten 28 miles away. Our granite spherical asteroid could be easily hidden in the Tsar Bomba's mushroom cloud, which was 25 miles wide. Our asteroid is, however, slightly larger than the fireball the Tsar Bomba produced (5 miles across—the fireball, that is).",
"This last one is just for you, MagicWishMonkey. Chicago is around 12 miles across, on its widest east-west line, starting from its easterly city limit to the shores of Lake Michigan. You could line up two Chicagos on our planet and you'd be left with some overlap.",
"Hope this helps."
] |
[
"In order to walk on a body, the escape velocity would have to be greater than the speed of the movements a human makes whilst walking. My best guess is ~5m/s.",
"The best way to get a relationship between mass and escape velocity is via conservation of energy.",
"GMm/r",
" = 1/2mv",
"You can eliminate the radius from the equation if you know the density of the asteroid; probably about \\rho=2g/cm",
"I get M=sqrt( ( v",
" / (2G) )",
" *1 / \\rho ) = 2 * 10",
" kg.",
"About 30 million times smaller than the moon. "
] |
[
"Is it possible to learn physics concepts on your own?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
" because of its open-ended or speculative nature. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"How were the photographs of Betelgeuse taken?"
] |
[
false
] |
In astronomy 101 I learned that stars are point sources of light. Even the most powerful optical telescope cannot resolve a star into a disk. If this is still true, how were the recent photographs of Betelgeuse taken? Are these photographs at all or are they digital representations of spectrographic data? (with apologies to the moderators for second pass at this)
|
[
"If this is still true",
"It's not. That phrase has been taught in Astronomy 101 for decades but technology has moved on. We now have telescopes powerful enough, and optical processing techniques sophisticated enough, to generate a true disc image of a star. We can get true optical images, not just digital simulations. ",
"Betelgeuse was the first star that we were able to resolve into a disc. It was chosen for that because it is relatively large and made for the easiest target. But there have since been many others. ",
"In fact our telescopes are now so good, we can even get a direct look at the planets around some stars. We've done that many times. You can see data about all directly imaged exoplanets on the ",
"NASA exoplanet archive",
"."
] |
[
"Betelgeuse is actually the third largest star by angular diameter in the sky after the Sun and R Doradus. With 50 milliarcseconds (mas), it appears almost as large as Pluto (60 to 110 mas, depending on its distance).",
"With current, modern telescope, that is large enough to simply point the telescope at it and resolve it as a disc.",
"With other stars, it's a more difficult task and requires more sophisticated methods: by linking several telescopes, it's possible use interferometry* to reconstruct a picture of much smaller and/or distant stars like ",
"Altair",
".jpg) (which has only an angular diameter of 3.2 mas).",
"(* Essentially the same method used by the Event Horizon Telescope team to get the picture of the black hole in M87, but in visual wavelengths.)"
] |
[
"In terms of raw resolution, seeing a planet as isolated dot can be easier than resolving features on a star. The orbits are usually larger than the stars (trivially true within a specific star system, but also if we look at different systems). The contrast needs to be much better, however.",
"Resolving features on an exoplanet (without using phase curves) - that's still far away."
] |
[
"Why don't we pass down our vaccinations to our offspring?"
] |
[
false
] | null |
[
"In the adult body there is only a select population of cells whose DNA will be used to create the offspring. These cells are called germ cells and arise from the precursors in the germline cells. In other words, only sperm and egg cells will be used to make the offspring, and so if the offspring is to inherit any traits the traits would have to be encoded in the DNA of these cells.",
"You are right to think that when your body becomes immune something happens to your DNA; it changes. However, the DNA in the vast majority of your cells stays the same and it is only the DNA inside your immune cells (B and T cells to be specific) that changes. Once they recognize a pathogen (a disease-causing agent) and they get the green light to mount a response, they will (among other things) start to divide and mutate to perfect and further increase the effect of their bacteria/virus-killing",
" ",
" "
] |
[
"There is a certain amount of inherent immune system that we ARE born with. These are immune cells such as macrophages that will attack bacteria on sight, or kill virus-infected cells. This kind of general immunity IS passed down, but that's not what vaccines do. ",
"Acquired immunity (the kind you get from vaccines) relies on B and T cells. These cells \"learn\" to recognize threats after the first exposure, and each subsequent exposure will elicit a stronger response. Because you acquire these immunities in response the the threats you receive during your life, those genes aren't in the DNA of your reproductive system where they can be passed down to your children.",
"This makes evolutionary sense as well. It takes a lot of energy to generate this immune response and keep your antibody levels high enough to confer protection. Offspring will encounter different diseases than their parents, so there's no selective push for them to waste energy protecting against something that isn't a threat anymore.",
"A small note: mothers who breastfeed their babies confer passive immunity to the child through breast milk. If a mom was vaccinated for chicken pox, say, the baby will have her antibodies and be protected. In a way, this is rhe parent passing on their vaccinations, just not in a way that will last. Once the child stops breastfeeding, those antibodies will go away and the kid can get chicken pox. Babies are born without an immune system, and don't really develop one until six months of age, which is why a lot of childhood vaccines are given at that age. There are some given earlier though, and I didn't pay enough attention in immunology to remember why."
] |
[
"This isn't true. IgG Antibodies do cross the placenta, but their lifespans are finite (the last maternal antibodies tend to fade around six months of age). The real reason immunity isn't permanently transferred is because the actual WBCs which produce the antibodies indeed don't get passed, so once the antibodies are metabolized, baby's immune system is on its own"
] |
[
"Why do sneezes typically come in two's?"
] |
[
false
] |
A student asked me this the other day... I was about to dismiss the question as coincidental, but I thought about it. Sneezes do come in two's or multiples of two's a lot of times. Coincidence? Or is there a biological purpose? EDIT: Since no one agrees with my original premise... How about why sneezes are always more than one?
|
[
"Confirmation bias."
] |
[
"I always have a minimum of 3."
] |
[
"I usually have one, sometimes two, never three or more. I know people who have three or more.",
"And yes, I'm talking about sneezes and not other things."
] |
[
"If you drop an electric appliance into water and then remove the appliance, does thew water stay charged?"
] |
[
false
] |
I feel like this is such a dumb question, but I honestly don't know the answer. Say there is a bath tub full of water and I drop my hairdryer into the water while it is turned on. If I unplug the hairdryer and pull it out of the tub, will the water still be charged?
|
[
"No. To put it in non-scientific terms, the water makes it easier for the electricity to jump from the appliance to your body and then to ground, but does not itself retain electricity. ",
"That's academic, however, as modern bathrooms are required by electrical code to have a ground-fault circuit-interrupting outlet, which means that if you drop your hair dryer into the water, the outlet can detect that the electricity is no longer grounding where it should be, and quickly cuts power to the outlet. In a properly-functioning GFCI, this happens too quickly for you to get hurt by the electricity. The \"properly-functioning\" bit is why there's a test button on the GFCI - you hit that to create a ground fault to make sure that the outlet cuts power when one happens. You know it's working right if the reset button pops out."
] |
[
"Gfci's can react as fast as 1/30 of a second, and will trip with an imbalance as low as 4 miliamps"
] |
[
"Keep in mind that water doesn't conduct electricity, the impurities in it do."
] |
[
"Why was expansion of space greater than 10 times lightspeed 12.85 billion years ago, but has since slowed down and is now accelerating?"
] |
[
false
] |
Given that we can see galaxies as they were approximately 900 million years after the Big Bang And further given that those above mentioned galaxies were at least 20 billion light years apart from far edge to far edge at 900 million years after the Big Bang. Then we can deduce that at that time these galaxies were flying away from each other at an average speed of, or at least, the expansion of space was proceeding at an average speed of, over 10 times the speed of light. We can calculate that by assuming that, in the most conservative case, we are at the center of the Big Bang, and the most distant galaxies were at least 10 billion light years distant from our location at that time. If these galaxies show a red shift of z=8 or less , and that equates to a speed of significantly less than a relative speed of 10 times the speed of light. And further, if space is currently expanding at an accelerating rate Then the above considerations mean that the expansion of space was faster than it is now, and so at some time slowed down. Yet now the expansion of space is accelerating, so the expansion of space has speeded up after it previously slowed down. So my question is this: What possible mechanisms can possibly explain why the expansion of space was greater than 10 times the speed of light 12.85 billion years ago*, but has since slowed down and is now accelerating? *(Date of the "Big Bang" = approx. 13.75 billion years ago, minus 900 million years = about 12.85 billion years ago).
|
[
"When the universe was dominated by dark matter in the past, the expansion rate was slowing down. This is because normal matter acts normally... its gravity attracts things, and thus slows down the expansion.",
"Recently, the expansion rate has been speeding up. This is because dark energy now dominates the universe, and it has the property that, roughly speaking, it pushes things apart.",
"So your question, it seems to me, boils down to the question of why the amount of dark matter and dark energy in the universe have the relative values they do. And no one knows the answer to this."
] |
[
"An ignorant and naive non-scientist such as myself might conclude that the addition of \"dark energy\" and \"dark matter\" and the \"expansion of space\" are simply ad hoc additions to prop up the flawed big bang theory and other shortfalls of current scientific theory.",
"You might conclude that, but you'd be wrong. This is how science works. From the outside these things may seem cobbled together, but they are actually very carefully formulated. Moreso, dark energy and dark matter are not additions to any model yet, because we don't know what they are. They are more like place holders. ",
"Such an ignorant and naive non-scientist as myself might also assume that the fact that distant galaxies are traveling away from us faster than the speed of light would disprove the Special Theory of Relativity's conclusion that nothing can travel faster than the speed of light (notwithstanding the so-called \"expansion of space\" and the fact that GR does not explicitly forbid faster than light travel).",
"You might assume that, but you'd be wrong. The expansion of spacetime and the limits within that spacetime are two different things. General Relativity allows spacetimes to do what they like, as long as they're solutions to Einstein's equations. This is consistent with Special Relativity and the bounds placed on the speed of travel.",
"Such an ignorant and naive non-scientist as myself might also conclude that Schrodinger's cat and the vacuum catastrophe prove that quantum theory is fundamentally wrong, and is not explanatory, but simply at best a very accurate predictive mathematical tool that applies in some limited cases.",
"You might conclude that, but you'd be wrong. Quantum mechanics works well and has been experimentally tested. Your issue seems to be one that many people have with science: you can't accept the limitations of what it can answer. For some reason you think that some theories hold truth beyond their predictions. This isn't true. Everything is just a model. All of science is just an accurate predictive tool. It cannot answer questions any deeper than that. ",
"Does anyone else feel like we should just stop patching up old theories and try to start fresh with the current observations of the way things are now, and reconstruct from scratch a theory of everything? ",
"In physics we are constantly trying to start fresh. There are hundreds of theories that are invented and die without you ever hearing about them. These theories have to stand not only against current observations, but the observations of the past. The issue is that our understanding of these observations in the past is so rich that any new theory must match, or be able to incorporate, the predictions of the old theories. "
] |
[
"This is a really intriguing question! And for someone (like me) who has no possibility of answering it, I look forward to the equations and lingo surrounding a possible theory / answer!"
] |
[
"Got questions about archaeology, shipwrecks, or the archaeology of shipwrecks? Ask them here!"
] |
[
false
] |
Ask away! This isn't really an AMA, as I'm not keen to talk about myself too much, but I'm happy to answer questions about the field!
|
[
"It would be irresponsible for me to put that on the internet.",
"Let me clarify: professional ethics that let me stay in the scientific community (publishing, presenting etc) don't let me help artifacts enter the private trade. Telling people \"here are three rich wrecks\" on the internet falls too close that unethical boundary.",
"Also, I'm not legally allowed to disclose the positions of certain wrecks. Archaeological sites are even an exemption to Freedom of Information Act requests!"
] |
[
"Have you read Throckmorton's \"The World's Worst Investment: The Economics of Treasure Hunting with Real Life Comparisons\"? It lays out the case pretty nicely for the unprofitability of most treasure hunting projects.",
"I have no problem with private archaeologists. I do have a problem with treasure hunters. You can tell the difference easily: Are they selling artifacts? If so, they are acting unethically. If you do good archaeology, you publish it, and you keep the collection together and available for future study, I have no problem with you."
] |
[
"Sidenote: One weird but interesting application has been to use lead from",
" shipwrecks to line neutrino detectors",
". "
] |
[
"In thermochemistry is ΔH=q, or is ΔH=-q?"
] |
[
false
] | null |
[
"I understand that q can be negative (exothermic) or positive (endothermic). From what you are saying, the signs of ΔH and q are always the same. When enthalpy is increasing (positive ΔH), then heat of the system is also increasing (positive a). Then vice versa for enthalpy decreasing and heat leaving?"
] |
[
"I understand that q can be negative (exothermic) or positive (endothermic). From what you are saying, the signs of ΔH and q are always the same. When enthalpy is increasing (positive ΔH), then heat of the system is also increasing (positive a). Then vice versa for enthalpy decreasing and heat leaving?"
] |
[
"Thank you."
] |
[
"Does a star oscillate between ignition and non-ignition at the beginning?"
] |
[
false
] |
So the gas cloud collapses and finally reaches the pressure and temperature to ignite as a star. But then I am thinking, the fusion explosion of the ignition pushed gases outwards, reducing the pressure. Does it happen that the pressure get reduces so much, that ignition stops again? Then we have to wait until the gravity pulls everything back in again, igniting a second time. Then third, forth... and so on. Like a pendulum. Until the star reached it's equilibrium between gravity-pressure and ignition-pressure. Or does it ignite once and burns until the end, because the equilibrium is reached the first time? And as a bonus: Does it happen that a star ignites, but then pushes too much gas away as solar wind, so that it kills itself of 'shortly' after and now no longer has the gravity to ignite a second time?
|
[
"So the gas cloud collapses and finally reaches the pressure and temperature to ignite as a star. But then I am thinking, the fusion explosion of the ignition pushed gases outwards, reducing the pressure. Does it happen that the pressure get reduces so much, that ignition stops again?",
"First off, fusion ignition is probably a more gradual process than that. The uncertainty principle means that even when a nucleus doesn't have enough energy to cross the coulomb barrier and fuse with another nucleus, there is still a small chance of quantum tunnelling occuring and fusion happening. As the core of the protostar gets more and more dense, the material heats up, and fusion becomes more and more likely. So it is probably a more gradual process.",
"That said, there is still a great deal we don't know about the exact process of a protostar turning into a hydrogen-burning (",
": this is an astronomy colloquialism, it means fusion, not any kind of chemical burning) star. This is because the object is still shrouded deep in its natal dust cloud when this occurs. Hopefully when the James Webb Space Telescope is up and running we'll be able to answer this in more detail.",
"And as a bonus: Does it happen that a star ignites, but then pushes too much gas away as solar wind, so that it kills itself of 'shortly' after and now no longer has the gravity to ignite a second time?",
"This probably does not occur. The outer layers of the star, which are the parts that can be pushed away as solar wind, are usually not contributing significantly to the star, so their loss does not greatly alter the central core."
] |
[
"Not just ",
" more gradual, but definitely more gradual. Different species (e.g. lithium, deuterium) start fusing at different temperatures, and their energy generation rates have different temperature dependencies.",
"YSOs (young stellar objects) are often variable. The prototype, T Tauri, expels blobs of gas in bipolar outflows. Supposedly they have high magnetic fields, are fast rotators, and are in this dusty environment of the protostellar nebula.",
"Check out HKT (Hansen, Kawaler, and Trimble's book ",
") for more details.",
"Caveat: I study GR, not stars."
] |
[
"Your teacher is correct-- the hydrogen \"burning\" which fuels stars is a nuclear fusion reaction, like what happens in a hydrogen bomb, not a chemical reaction like when we burn methane or some other chemical by oxidizing it.",
"Astronomers frequently refer to the nuclear fusion which powers stars as \"hydrogen burning\". In more massive, evolved stars, \"helium burning\" takes place, where helium nuclei are fused together to form more massive elements. Astronomers assume that other astronomers automatically know what is meant by these terms, but we should definitely be more careful with such terms in general.",
"Side note: there is a certain nuclear fusion process known as the ",
"CNO (for Carbon-Nitrogen-Oxygen) cycle",
", in which hydrogen atoms (i.e., protons) fuse successively with carbon, nitrogen, and oxygen. In stars somewhat more massive than the Sun, this is the main power source, rather than the ",
"proton-proton chain",
". So there is a certain kind of hydrogen burning which actually ",
" utilize oxygen, but only for nuclear fusion and decay, not for any chemical reaction."
] |
[
"Avogadro's number is the accepted number of molecules in one mole of a substance. How was this number derived and what experimental evidence proves it to be the correct number?"
] |
[
false
] |
I understand that it was Loschmidt who truly determined this quantity, and I have read that his calculations involve the average velocity of molecules in a gas and their respective diameter, but this just raises further questions in my mind. How does one measure the average velocity of individual molecules? How does one measure the diameter of a molecule?
|
[
"Here is an easy experiment that gives you a rough approximation. It may give you an idea about how you can measure it:",
"Have a cylinder of a certain material lets say monocrystalline silicon. You know the mass, you can measure the volume. This means you can calculate the density of your cylinder.",
"You know the crystal structure of silicon from x-ray-experiments. So you know the bonding length of the silicon atoms within the crystal structure. That means you can calculate the density of one crystal cell, and, if it is a perfect monocrystal, it should be the same like the density of the cylinder.",
"Now, because you know all of this, you can calculate how many atoms there are in your cylinder using the volume. You also have the mass of the cylinder, and the mass of one single silicon atom. You can now calculate how many atoms you have in your cylinder, and how many atoms per mol.",
"Now, when I did this (very archaic) experiment in my first semester I got 6.07 +- 0.036 E 23 1/mol.",
"Now everything better than this basically involves a lot of math."
] |
[
"No, ",
"Loschmidt's number",
" is a different one. I'd credit ",
"Perrin",
" with the most accurate determinations of his day, recounted in his book ",
"Atoms",
" (",
"). (Or just ",
"skip to the results",
" on page 206) They were sufficiently accurate and done in so many different ways, for it to have finally settled the debate on whether or not atoms existed."
] |
[
"http://en.wikipedia.org/wiki/Avogadro_constant#Measurement"
] |
[
"Why is there this weird pattern of frost on my airplane window?"
] |
[
false
] | null |
[
"What hole?"
] |
[
"The pressure-regulating cylindrical tunnel that's more visible in the second picture. It seems to connect the gaps of two panes of window."
] |
[
"http://www.quora.com/Why-does-a-frost-ring-form-in-a-circle-around-the-inner-hole-in-airplane-windows"
] |
[
"Whats sulfuric acid for? Other than dissolving dead bodies?"
] |
[
false
] | null |
[
"Generally you don't use sulfuric acid as a solvent, though it can be useful in certain circumstances where nothing else can dissolve your organic compound as it can protonate and solvate nearly anything.",
"In the lab it is mostly used in diluted form as a versatile strong acid for a wide range of tasks, as well as a reactive compound to stick sulfate groups onto things. Outside of the lab it is used as a chemical precursor, cleaning agent, catalyst, battery electrolyte, etc. There are hundreds or thousands of different ways that people use sulfuric acid on a daily basis, many of which you probably do yourself without realizing."
] |
[
"So can you buy straight sulfuric acid at a store or just like in diluted forms? "
] |
[
"I think concentrated sulfuric acid is restricted but you should be able to buy less concentrated grades. "
] |
[
"If forced to spin, whether for a game or as a contest, what is the most effective way to avoid sever dizziness?"
] |
[
false
] | null |
[
"According to my daughter who used to dance, you just get used to it. Spotting just gives you a way to maintain orientation while your inner ears are going crazy.",
"Also, my sifu once gave us a one day bagua seminar, where part of the the practice was spinning. You don't get over being dizzy, you just learn how to maintain your bearings while dizzy."
] |
[
"Do what ballerinas do. Keep your head in one position and turn it fast and stop, fast and stop, fast and stop. This is precisely why they do this - to not get dizzy."
] |
[
"It is an orientation thing. Keep a reference point.",
"from ",
"wikipedia:",
"The goal of spotting is to attain a constant orientation of the dancer's head and eyes, to the extent possible, in order to enhance the dancer's control and prevent dizziness."
] |
[
"What part of the \"stink bug\" actually smells?"
] |
[
false
] | null |
[
"The adult pentatomoid odours are due to light yellow oily materials produced by paired tubular glands and accessory glands. Their secretions are accumulated in a single reservoir (occasionally in paired reservoirs) situated ventrally in the metathorax. This reservoir opens to the exterior at each side between the middle and hind coxae. In the larvae, stink glands are present in some of the dorsal segments of the abdomen. On moulting to the adult the dorsal abdominal glands are repiaced by those in the ventral region of the metathorax, apparently without significant change in function. In adult Oncopeltus fusciatw (Dallas) the secretion from the tubular glands is not unpleasant, whereas the stink is either the product of the accessory giands or it may result from a reaction between these two secretions. Even in the larvae which carry their unpaired dorsal scent glands on the fourth and fifth abdominal segments, the secretions of each differ. The anterior gland is responsible for the typical unpleasant odour, whereas the posterior gland secretes an inoffensive material ( JOHANSSON, 1957).",
"from 'Characteristics odour components of the scent of stink bugs' by D.F. Waterhouse et al, 1961, Journal of Insect Physiology.",
"Basically the stink bugs have glands in which the smelly liquid is being made and stored. They can release it when they experience an attack. The exact chemical components named in the paper are hex-2-enal, oct-2-enal, and dec-2-enal."
] |
[
"Could you perchance tell me which of those chemicals is also present in cilantro (as I find it to smell/taste just like stink bugs)."
] |
[
"Stink bug chemicals and cilantro taste are indeed similar chemicals (aldehydes)!!!",
"http://chenected.aiche.org/chemicals/stink-bug-breakdown/",
"Spectrometry to determine at least two of the compounds present in the stink bug \nodor: the aldehydes trans-2-decenal and trans-2-octenal",
"Cilantro taste is really interesting because people know some genes involved in how people interpret that taste: ",
"http://www.nature.com/news/soapy-taste-of-coriander-linked-to-genetic-variants-1.11398",
"One of those genes, OR6A2, encodes a receptor that is highly sensitive to aldehyde chemicals, which contribute to the flavour",
"Wonder if those genes affect how people react to stink bug smell too."
] |
[
"Watched Hawking's 'Curiosity' last night, question: if there was no time before the Big Bang, why at a specific instant did the universe spontaneously come into existence?"
] |
[
false
] |
I thought the program was great for the layman and although I wish they had gone into how some parts of the universe are into more detail, it would have taken too long and not been relevant to the question. Related (same, reworded) question: If the conditions of the pre-bang singularity (is that what you'd call it?) were unchanging because there was no time, then there was no internal change to cause the Big Bang. And there's no external change because there is no anything. This is sort of similar to paradox (which isn't really a paradox, it has a fundamentally flawed assumption, right? That there are universal, discrete instants in time.) Perhaps there is no answer. Hence the term "spontaneously". I suppose to someone not versed in quantum physics and the beginning of the universe, "spontaneously" means "magic", with some underlying cause. We have to dispel that connotation/assumption. Thanks in advance.
|
[
"Imagine that you want to make a long trip and decide to always go north.\nIt's easy: you know how to use a compass, you just have to follow this direction. But then you reach the North Pole. Some people have warned you that the concept of \"north\" is a bit singular there. Your compass isn't indicating anything useful anymore. You can ask the friendly polar bear there in which direction is north: he will answer that your question is meaningless, that all directions are south, north ceases to exist at this point.",
"Here it's the same thing, except north is \"past\", south is \"future\", the Earth is spacetime and there are no polar bears."
] |
[
"I think what he is asking is what was before time?",
"What is north of the North Pole?",
"If change requires time then how could the universe change to suddenly have time?",
"I don't have an answer because I don't have any words to describe it. \"Suddenly\" is time-related so isn't relevant in this context. My best answer would be that the Universe doesn't \"change\" to have time.",
"If you are on the north pole the concept of north is replaced with the concept of south... it doesnt just stop existing. It gets changed to something else. What about time? If I stand on the north pole and look around all I see is south. If I stand at t=0 and look around what would I see?",
"North ceases to exist at the North Pole. Everything is south.",
"Past ceases to exist at the Big Bang. Everything is future.",
"If matter cant be created or destroyed then there must have been something before time.",
"Matter can be created or destroyed actually. But let's replace it with \"energy\" for that matter. Energy is conserved, so where does it come from? Well, conservation means it doesn't vary with time (if we don't want to go into technical details). So let's get back in time and see if it applies. The answer is yes until we reach the singularity. And at the singularity? We can't answer because we don't have any previous instant to compare it to. It's not that it's not conserved, it's really that conservation doesn't mean anything anymore. It's like carrying a thermometer to measure the temperature as you go north: is it colder north from the North Pole? So where does this energy come from? That's another meaningless question: it means \"where was it before\" but there wasn't any \"before\".",
"I'm sorry, all our concepts assume some underlying time. So most of our questions are totally irrelevant in such a context."
] |
[
"I think what he is asking is what was before time?",
"What is north of the North Pole?",
"If change requires time then how could the universe change to suddenly have time?",
"I don't have an answer because I don't have any words to describe it. \"Suddenly\" is time-related so isn't relevant in this context. My best answer would be that the Universe doesn't \"change\" to have time.",
"If you are on the north pole the concept of north is replaced with the concept of south... it doesnt just stop existing. It gets changed to something else. What about time? If I stand on the north pole and look around all I see is south. If I stand at t=0 and look around what would I see?",
"North ceases to exist at the North Pole. Everything is south.",
"Past ceases to exist at the Big Bang. Everything is future.",
"If matter cant be created or destroyed then there must have been something before time.",
"Matter can be created or destroyed actually. But let's replace it with \"energy\" for that matter. Energy is conserved, so where does it come from? Well, conservation means it doesn't vary with time (if we don't want to go into technical details). So let's get back in time and see if it applies. The answer is yes until we reach the singularity. And at the singularity? We can't answer because we don't have any previous instant to compare it to. It's not that it's not conserved, it's really that conservation doesn't mean anything anymore. It's like carrying a thermometer to measure the temperature as you go north: is it colder north from the North Pole? So where does this energy come from? That's another meaningless question: it means \"where was it before\" but there wasn't any \"before\".",
"I'm sorry, all our concepts assume some underlying time. So most of our questions are totally irrelevant in such a context."
] |
[
"How exactly does chronic high blood sugar cause damage to the body?"
] |
[
false
] |
I know high blood sugar can cause organ damage, eye damage and can lead to people needing amputations, but why is this exactly? Whats going on in the body? Edits: Thank you all so much for your responses, I'm reading through all of them.
|
[
"Glucose is a surprisingly reactive molecule. When it's carried in the blood, it reacts with both hemoglobin (creating Hb1Ac, which is monitored in diabetics) and the vessel walls. This can make vessel walls rigid and leaky.",
"The effects are first seen in the microvasculature, which due to their size are more vulnerable to these changes. This leads to problems in the retina of the eye (diabetic retinopathy), the kidneys (diabetic nephropathy) and the peripheral nerves (diabetic neuropathy).\nThe larger vessels tend to be affected later, but in regards to type 2 diabetes, obesity plays a massive role here too (though high blood pressure can also affect the smaller vessels).",
"I'm only a medical student, so if any of this is inaccurate, feel free to correct me. Hope this helps!"
] |
[
"The damage is always occurring, it's just that at lower levels of blood sugar it occurs at a rate that the body can deal with and repair.",
"If you want to know more, look up AGE (advanced glycosolation endproducts) and RAGE (receptors for advanced glycosolation endproducts) - a mechanism that mediates some of the damage, and some of the fixing, of these problems.",
"Specific cutoffs such as 125mg/dL or 11.1mM are used because they are markers that indicate impaired glucose tolerance (the specific basis for these values having something to do with population percentages above and below those values and natural history of those patients in previous studies) as opposed to it 'suddenly' causing a problem at that level.",
"Although, at 30mM of glucose in the blood, glucose overwhelms the kidneys ability to reuptake that glucose so you develop glucosuria (glucose in your pee) which is, coincidentally, how the Romans detected and named diabetes (by tasting it)"
] |
[
"But we always have glucose in our blood. why is 125 mg/dL the cross-over point for when it starts doing damage versus not?"
] |
[
"Do we know how close we are to the center of the universe?"
] |
[
false
] | null |
[
"We are at the center of the observable universe. Beyond that it is thought to be unbounded with no center."
] |
[
"That makes sense. I didn't know if we had any idea about the size of the universe outside what is observable"
] |
[
"This should answer your question:",
"http://youtu.be/5NU2t5zlxQQ"
] |
[
"If water boils at 100 degrees Celsius and turns to steam (water vapour), how is it that we can see water vapour in our breath when it is cold?"
] |
[
false
] | null |
[
"Steam is actually invisible, if you boil a kettle and look at the spout you will notice that the air is invisible for about an inch or so, than you see the vapour. What you see is when the air starts to cool down and the water vapour becomes visible (condenses). The higher the temperature, the more water vapour the air can hold. On a cold day, your body is much warmer than the outside air, so the air in your body holds more water. When you breath out, the air starts to cool and the water vapour begins to condense."
] |
[
"We see ",
" water vapour after it is exhaled. This happens because the air we exhale expands and cools as it leaves our body. Cool air holds less vapour than warm air so some of the vapour in our breath turns to small droplets of water."
] |
[
"Dry steam is invisible, it is hot enough to be water ",
", wet steam is what we're familiar with, it contains water gas and saturated water droplets. ",
"http://www.corrosionpedia.com/definition/420/dry-steam"
] |
[
"Could quantum entanglement be used to transmit information almost instantaneously over large distances?"
] |
[
false
] | null |
[
"No",
".",
"[...] no-one knows the state of the particle until it has been observed, but you still cannot affect the state of the particle [...]"
] |
[
"No. You ",
" use quantum entanglement to transmit information, but doing so requires some other information which would have to be transmitted at the speed of light."
] |
[
"You can't influence the outcome of a measurement on that entangled system in such a way that someone on the other end could tell if you'd influenced it or not. So you'd have to tell them something classically anyway."
] |
[
"How can GPS co-ordinates have poor precision?"
] |
[
false
] |
As I (hand-wavily and probably incorrectly) understand it, GPS co-ordinates are calculated from the round-trip distance to 3-or-more known-position satellites. The intersection of the ensuing spheres gives the location. But GPS-enabled apps always provide a "confidence radius", which they're "pretty certain" that the user is in, rather than an exact location. How is that the case? The only imprecisions I could think of are the signal speed of the satellite signal, or the processing time of the satellite itself, and I would guess that both of those would have a tiny variance (in the latter case, the satellite could return the processing time along with its response to take that out of the equation).
|
[
"http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System",
"The sensitivity of the GPS signal is quite high. The following is to give you some perspective:",
"Light travels around 30 cm in a nanosecond.",
"The height GPS of satellites is listed as 20,200 km. Light travels that distance in 67,379,947 nanoseconds (the shortest distance between the ground and a satellite, in practice this will be longer due to the satellite not being directly overhead).",
"A 10 meter inaccuracy can be caused by a discrepancy of around 33 nanoseconds. That's around an error of about 1 in 2 million.",
"So, things like atmospheric variations can affect the travel time. ",
"Not to mention that GPS has to account for time dilation due to ",
". And it's likely so sensitive that some error is introduced due to natural variation of Earth's surface gravity.",
"So, how can GPS co-ordinates have poor precision? "
] |
[
"Keep in mind that the gps you are using is not the best technology available. The government/military restricts the use of the best available to stop people from making mischief/missiles. See SPS vs PPS for more information."
] |
[
"Understood - thank you!"
] |
[
"What is the default state of the muscles that are responsible for closing your eyes?"
] |
[
false
] |
If you were to turn 'off' the muscles that open/close your eyelids, would your eyes stay open or closed? I know that the majority of the time when people die, their eyes stay open, but it is possible to close the eyes and have them remain closed. When we go to sleep, we almost feel like our eyes are wanting to naturally close, but when we're awake, it's very easy to keep them open, so would that mean that we're using our eyelid muscles constantly when we are awake? Edit: grammar
|
[
"If your eyelid muscles were off, your eyelids would generally be droopy/mostly closed.",
"We have muscles to open AND to close the eyes. If they're paralyzed, then the eyelid will do whatever friction+elasticity dictates. ",
"If someone does have a paralysis of their eyelid muscles, a patch is often applied to the eye to force the eyelid completely closed, so that the eye doesn't get dry and damaged by the inability to blink.",
"Yes, we are using our 'opening' eyelid muscles constantly when we are awake. We are using our 'closing' eyelid muscles a little bit when we are asleep."
] |
[
"\"There are multiple muscles that control reflexes of blinking. The main muscles, in the upper eyelid, that control the opening and closing are the orbicularis oculi and levator palpebrae superioris muscle. The orbicularis oculi closes the eye, while the contraction of the levator palpebrae muscle opens the eye. The Müller’s muscle, or the superior tarsal muscle, in the upper eyelid and the inferior palpebral muscle in the lower 3 eyelid are responsible for widening the eyes. These muscles are not only imperative in blinking, but they are also important in many other functions such as squinting and winking. The inferior palpebral muscle is coordinated with the inferior rectus to pull down the lower lid when one looks down. Also, when the eyes move, there is often a blink; the blink is thought to help the eye shift its target point.\" - Wikipedia"
] |
[
"Ah so there are muscles dedicated to independently opening and closing, meaning that having relaxed eyelid muscles would result in the eyelid remaining how it is?"
] |
[
"How does non-ionizing radiation such as gamma rays actually cause damage to our bodies?"
] |
[
false
] | null |
[
"Gamma rays are ionizing. Non-ionizing radiation starts in the UV range.",
"At any rate, even non-ionizing radiation can break some of the weaker chemical bonds or hydrogen bonds (UV to visible light) or cause heating (infrared and microwaves can directly heat body fluids). "
] |
[
"Ultraviolet with wavelengths less than 125nm, extreme and vacuum ultraviolet, has energies of more than 10 eV and would be ionizing. "
] |
[
"Where is the transition from ionizing to non-ionization radiation? I thought that UV (or at least some UV) could ionize."
] |
[
"What'd happen if water was frozen inside a sealed, rigid, unbreakable container? Would it not turn into solid ice? Would it require lower temp to freeze it?"
] |
[
false
] |
I know if typical material would break under stress from the expansion. But what if the material is so strong...could anything possible contain the frozen water?
|
[
"If it was rigid enough, it would form a different form of ice that forms under greater pressure. ",
"Ice VI",
".",
"And no, Ice-Nine isn't like in the book."
] |
[
"I'd say it like \"The ice has enough of an energy deficit to bring an entire glass of room-temperature water below its freezing point.\""
] |
[
"\"The types are differentiated by their crystalline structure, ordering and density.\"",
"-Wikipedia"
] |
[
"Are phonons a type of electromagnetic wave?"
] |
[
false
] |
[deleted]
|
[
"Phonons are not electromagnetic waves, they’re mechanical oscillations (or at least the quantum version of them)."
] |
[
"Although this is, I suppose true, it's quite a bit of semantic gymnastics. When light \"travels\" through a medium it does so as a dressed wave of electrical polarization. The quantum version of this, when appropriate, is the POLARITON. Polaritons are excitations of polarization just as plasmons are excitations of charge density, magnons are excitations of magnetic moment and PHONONS are excitations of sound/atomic displacement. There's really no way to recover a statement that phonons are light.",
"That being said, I'm pretty sure the OP just misheard/misunderstood the term \"optical phonon\", which is a type of phonon, so named because it's typically excited BY light (not because it is light)"
] |
[
"Phonons are in now way EM waves. If one did want to assign a quantized excitation to the polarization waves that are truly meant when people haphazardly talk about \"light in a medium\", it would be something like a polariton.",
"That being said, you sure you didn't mishear \"optical phonons\" and misunderstood what was meant by that? Optical phonons are gapped phonons, meaning you need a minimum amount of energy to excite them. This is in contrast to acoustic phonons which are gapless. Optical phonons are so named not because they ARE light, but rather that they're the phonon that is typically excited BY light. ",
"I'd err on the side that a professor of chemistry know what a phonon is an you misunderstood the term optical phonon."
] |
[
"Is it possible for a dormant virus to lyse an entire human body?"
] |
[
false
] |
So ever since high school bio I've always wondered something stupid. If a virus were somehow able to infect a zygotic cell, inserting viral DNA and entering a dormant life-cycle, would it be possible for the DNA to remain dormant into an adult's life where all the cells in that person's body contained the DNA at which point whatever cue would turn on expression of the viral DNA causing a mass lysing event? Essentially, Melting Man. Couple of legitimate reasons why this couldn't occur that I tossed around: -Virus Specification- given that viruses are highly specified and incredibly small, it may not be possible for a single virus to have the capacity to both infect zygotic cells and upon lysing in any number of somatic cells, infect or interact with all those cell types as well -Differential Expression of genes- the virus would need mechanisms to allow any or all somatic cells to express its genes given that the cells will have long since specialized in function and gene expression. So guys, humor me. Any ideas; is Melting Man a possibility?
|
[
"Usually one virus only infects a single locus, at random. Loci are \"locked away\" as chromatin topography changes during specification and then differentiation. However, there are many genes that must be on for almost all cells. Lamin A/C, Histones, ion channels, basic metabolic transport proteins, enzymes, etc. ",
"Site specific viral transduction has been shown",
". Triggers for entrance into the lytic phase are usually cellular stress. ",
"In one Bacteria-Phage symbiosis, a Transcription Factor in the Bacteria activates the phage's entrance into lytic activity",
".",
"So let's play a thought game (ethics aside):",
"We engineer a virus to specifically introduce its genetic information near one of the aforementioned \"background\" genes (that are almost always in a region of euchromatin) with a high transduction efficacy. Within it's code is a promoter that is de-repressed by tetracycline induction. Once the promoter is active, the viral lytic genes are expressed. Induction is not always successful but with billions of cells in the body derived from the infected zygote, we should get enough to elicit a response",
"We have a collection of IVF Zygotes, prepped and ready for introduction of our \"Melting Man\" virus. They are freshly fertilized and introduced to the virus directly after. We impregnate several women (to get a statistically significant N size).",
"We let the children grow up into adults, hopefully they don't take tetracycline before they are reach 18. At age 18 we give them tetracycline and essentially euthanize them in the process. If successful, viral lytic activity will most likely proceed like a severe Ebola Virus infection. A medical examiner might call it an acute viral hemorrhagic fever. Cells would rupture, prompt an immune response, inflammation ensues, fever. A mix of anaphylactic shock, global hemorrhaging and ultimately \"melting.\" I doubt it would be melting though as there are many fibrous and keratinous tissues that will maintain their structure. ",
"So now you know that it's ",
" Is it worth it? Is it pragmatically feasible?",
"It's certainly not ethical, even with animal subjects. Can you think of a benefit to the research?"
] |
[
"This process is essentially a way to systematically and conditionally cause an organism to decompose. Doing so in a multi-cellular organism would appear to have few uses, but in the biofuels industry it may have promise.",
"Consider an algae which you can program to 'pop' in such a way that it releases its contents in an approach favorable to fuel production. You grow a batch of algae, add some tetracycline and watch the batch lyse in an orderly manner that favors your biofuel somehow.",
"This approach is also potentially valuable in quickly decomposing multicellular organisms. Lets say you breed a cow for its...liver, or something, but the rest of the animal is for some reason inedible and unusable. You expose the carcass to the viral trigger, wait a few days, and you end up with goo."
] |
[
"Not a very good idea, It is difficult to predict the effects of a virus like this leeching out into the environment.",
"I opine that there are easier, cheaper, and safer ways to approach any example you mentioned above.",
"Even still, I find it awesome and amusing that we are talking about something like this."
] |
[
"A question regarding hangovers"
] |
[
false
] |
Possibly the wrong subreddit but in the interests of my poor head I want to approach this scientifically. So, hangovers are mainly caused by dehydration right? Does this mean if I was for example to drink lots of Vodka and orange, the orange juice would act as hydration? I'll possibly get destroyed by all the scientific minds here but it seems plausible. Please help me and my poor head. Edit: Ok so thanks scientific chaps. It appears my dastardly plan of drinking OJ with vodka is futile. I appears that I either need to A: Reduce the ratio of vodka to OJ which isn't conducive to my tastes. B: Hydrate said liquor is consumed or C: discover a decent source of vitamin B12 I think I'll go for a mix of option B and C. Thanks guys,
|
[
"Coconut juice is supposedly naturally isotonic. ",
"Replying here as well so both OP and Dimpl get an orange-red."
] |
[
"Alcohol is diuretic, meaning that it causes the body to lose more water than it takes in. Therefore, if you consume many non-alcoholic fluids while alcohol is present in your system you will simply pass them. Instead, it's critical to wait until the alcohol has started to work its way out of your bloodstream (typically 1 or more hrs after your last drink, depending on how much you've been drinking of course) before you rehydrate. I typically wait 1 hr, drink a tall glass of water, and hit the hay - seems to work like a charm. Also, I believe drinking causes a Vitamin B12 deficiency which can compound your hangover woes. Luckily brewer's yeast is rich with B12, so if you're drinking homebrew beer you've got an edge on your fellow drinking buddies!"
] |
[
"I have a hangover cure I wrote many years ago that I reverse engineered. Here it is for your listening pleasure.",
"This discovery came from trying to see what supplements would help the osteoarthritis in my spine. Incidentally, I observed that many of the supplements that I was taking noticeably decreased the morning-after pain that most of us recreational drinkers become accustomed to.",
"Here is my regimen, take it or leave it:",
"1) Multivitamins are gods if you take them at night before you go drinking. If you take them in the daytime, they are all used up when it comes time for you to polish your liver.",
"2) I take multivitamins high in B before going out. My preference is GNC's Men's Ultra Gel capsules. (Note that I have no financial arrangement with GNC, nor do I own its stock.) These capsules are easy on the stomach and can be taken without food. This alone removes most of the pain of the day after.",
"3) MSM (methyl sulfonyl methane) is a compound I take to help regenerate my cartilage and, surprisingly, it seems to help with the \"oogy\" feeling you get in your gut the next day. However, if you are a martini fiend, there is nothing I know of to help you with the next day's \"vodka belly.\"",
"4) Coenzyme Q: I take two 50 mg capsules before bed, and the next day, I can wake up with energy and start the day like it is Wednesday, not post-binge day.",
"If you do not care to follow the entire regimen before you go out drinking, then you can take these little miracle workers before you pass out. But if you must take only one, take the multivitamin high in B complex. You will thank me the day after.",
"Enjoy your lack of hangover.",
"-- Alex Zavatone",
"Take before you go out or go to bed",
"Before you go to bad or before you go out: ",
"Co Enzyme Q - energy the next day",
"Alpha Lipoic Acid",
"MSM",
"L-Acetyl Carnitine ",
"1 GNC Ultra Mega Gel Capsule. (Note: name needs more adjectives) ",
"glug a glass of water.",
"Next day, wake up with no pain, all set and ready to go."
] |
[
"Can you tell from a persons blood work, what kind of diet this person eats and/or if someone engages in physical activity?"
] |
[
false
] |
Maybe a stupid question, I don't know, but can you tell in general (illnesses and extremes like malnutrition aside) for example if someone is eating more or less meat or no meat at all, or a lot of vegetables and/or fruit or not? How does physical activity show up in a blood work? Can you tell how much physical activity someone engages in and -maybe as a bonus question- what kind of sport someone does (for example swimming vs running or both of them vs weight lifting)?
|
[
"I see both responses so far have mentioned blood glucose tests and their limited timeframe, which is true, but ",
"hemoglobin A1c tests can tell you a patient's average blood sugar levels over the past few months.",
" It's used to identify how diabetic patients have been managing their diet. "
] |
[
"Not likely, mostly because blood tests really only give a very limited snapshot of what's going on at a point in time. You might be able to make some very limited inferences as to what the person does from the blood test alone, but I'll get to the point in a moment. ",
"For instance, if I eat a candy bar right before a blood test it's going to show high glucose - clearly not indicative of my overall diet, unless it consists of only candy bars, but that's an extreme example. This is why we request patients fast (",
") before a blood test.",
"To give another example, if I go lift weights right before a blood test then odds are my blood test will show elevated levels of testosterone and inflammatory mediators from muscle damage, assuming that I draw my blood in the 30 minutes or so after I work out. After some hours (I don't know how long), levels will have normalized due to recovery. The caveat to this is if a person exercises consistently. In that case a person's entire baseline will move upward (for something like testosterone). Would you be able to tell what kind of exercise a person performs? No. The only conclusion you could make is that the person exercises consistently, and even that would be a tenuous association. For something like testosterone, there are myriad ways to boost it that don't necessarily involve exercise. ",
"The point? Blood work is usually not done without a patient interview/physical examination beforehand, in which case the patient will likely tell us about their exercise/dietary habits. The exception to this rule I can think of are cases in which we're screening for something specific like elevated glucose, drug metabolites, etc. ",
"Hope this helps!",
"EDITS: Fleshed out a point, accidentally a word",
"- ice "
] |
[
"Given the wide availability of supplements, it's very difficult to tell the difference from an omnivore and a well-supplemented vegetarian/vegan.",
"Taking that aside, only animals are sources of vitamin B12. Thus, presence of vitamin B12 in the blood suggests sufficient animal (meat, eggs, etc.) intake. If there are abnormalities, that can be detected in the blood as well - such as anemia etc. that may stem from the diet. ",
"A lot more information can also be gained if you drew blood right after a meal. High amounts of fructose suggests recent meals of fruit. Different amounts of different types of fats are very indicative of what we just ate. However, the body is pretty good at converting all the things we eat into a few common \"currency\" nutrients that circulate in our blood: glucose for sugar, arginine and glutamine for amino acids. Given enough time after a meal, these are pretty much the only things we'll find in large quantities in the blood.",
"Physical activity is an interesting question. We can detect ",
" health from blood-work, but this doesn't eliminate cases of genetic contributions to high cholesterol and the such. ",
"There can be clinical suggestions as well, for example if you have early Type II diabetes, we would detect an increased blood insulin; Type II diabetes is highly correlated with overweight/obesity. Circulating levels of hormones such as leptin and/or estrogen roughly correlate with fat mass, and can be measured as well.",
"If you ",
" finished exercising, your blood can tell if it's been highly anaerobic (oxygen-lacking) by levels of lactic acid or bicarbonate in your blood. Heavy muscle-building exercises also cause some muscle cells to break open, releasing muscle specific proteins such as troponin (which is also released after a heart attack from the dead cardiac muscles) and creatine phosphokinase (CPK). These proteins last in the blood a bit longer (hours) and can infer weight lifting."
] |
[
"How does one particle \"know\" the charge of another through photon exchange?"
] |
[
false
] |
Particle A exchanges a photon with particle B. Maybe if they are oppositely charged, the exchange causes them to move a little closer together. What is it about the photon itself that "tells" one particle to move either toward or away from the other?
|
[
"Forces don't really work by particles shooting force carriers at each other. So it's definitely not as if two charged particles interact because they're shooting lasers at each other! Virtual particles that we say mediate forces are like ripples in the underlying ",
". It's the field which tells charged particles where to move and how, depending on their charge. The field contains all that information. The virtual photons are what we use to describe the various physical processes that make up this interaction, but they're really more of a mathematical tool than physical particles (hence the name virtual!).",
"There's a ",
"great blog post",
" by Matt Strassler clearing this up."
] |
[
"Don't think of the photon as a particle, think of it as a fluctuation of the electromagnetic field. The fluctuations propagate through the field and \"tell\" each particle what to do."
] |
[
"Thanks, that was a great a read!"
] |
[
"In math, is the order of operations arbitrary? Meaning is there a real reason x and / comes before + and -, or is that just the order we decided and as long as the operations are consistent and that's what really matters?"
] |
[
false
] | null |
[
"That article contains a rare sighting of anyone remembering or even knowing about Forth."
] |
[
"That article contains a rare sighting of anyone remembering or even knowing about Forth."
] |
[
"It's possible to change the order of operations and rewriting all notation accordingly so all equations continue to have the same meaning, as we have a parentheses system (and fractional notation) that manually overrides the order of operations.",
"Notation and the order of operations within it isn't so much arbitrary as artificial, but it has a reasonable goal of trying to convey consistent structures with as little unnecessary notation as possible.",
"It just happens that (very broadly) multiplication being done first is desired more often than addition, and then subtraction in turn, so you may as well assume that it is the default unless otherwise notated."
] |
[
"Can Neutrons decay into an anti-proton and a positron?"
] |
[
false
] |
I've never heard anything about it and can't find anything on the subject. I know that regularly free floating neutrons decay into protons and electrons, but could they decay into a positron and anti-proton? Changing into an anti-proton and a positron would still conserve both charge and mass. The only law it would seem to disobey is the law of conservation of Baryon number, but I know that that law has been proven to be only approximately conserved. I'm not concerned so much about how likely it is as much as the possibility.
|
[
"No. It would violate conservation of ",
"baryon number.",
" Protons and neutrons have a positive baryon number, while anti-protons and anti-neutrons have a negative baryon number. ",
"Beta decay, which allows a neutron to turn into a proton by spitting out an electron and an anti-neutrino does conserve baryon number and therefore it is possible (and is the dominant mode of neutron decay). "
] |
[
"But couldn't an anti-neutron do this? That should be no problem."
] |
[
"Correct"
] |
[
"Could a laser be made from sound as it is from light?"
] |
[
false
] |
Civilizations from other times and places used sound to move heavy objects, bore tunnels and power engines, according to the Seth Materials. If this were true, could we do this in our civilization? I'm guessing that to start we'd have to control and amplify the sound energy. So, my question: Could a laser be made from sound?
|
[
"Yes, there are ",
"SASERs",
".",
"Here",
" is an article from ",
" about the first such device."
] |
[
"I was just walking in to explain why I thought it would not be possible. That's unbelievable!"
] |
[
"I'm not sure I believe that this was a SASER. Audible frequencies have a very long wavelength. If I understand SASERs correctly, then the coherency of the produced beam is still related to the size of the aperture, in wavelengths.",
"It is far more likely that the shopping mall demo was an application of phased array technology."
] |
[
"Electrons aren't really particles, however, they have a velocity. To me, this seems incongruous. What am I misunderstanding?"
] |
[
false
] |
[deleted]
|
[
"Electrons are particles and 'physical entities' as far as anything is. In fact, they're elementary particles, so more particle-ish than most particles. What I mean by 'elementary particle' here is that they have no known constituent parts, no observed internal structure. Electrons interact with things as if they were an infinitesimal point in space.",
"But they're very lightweight, so they behave very quantum-mechanically. That means they don't ",
" a well-defined position in space; they're 'spread out' and we can only say the ",
" of where they're likely to be is. Heisenberg's Uncertainty Principle prohibits things from having an exact position and/or momentum - not just electrons, but ",
". All particles, even macroscopic objects. It's just that the uncertainty is so small relative the mass and size of large objects, that it's undetectable, but at the atomic/molecular scale the spreading out of electrons is large enough to be quite important. But in QM they still interact as if they were point charges, just point charges that have a number of possible locations. If you want to calculate the electrical force from it, you'd calculate the force from a point charge at location ",
" and multiply that with the probability of the electron being at location ",
", and sum that up over all the possible locations. ",
"An ",
", on the other hand, is ",
" an electron. It's a description of the energy ",
" that electrons can have when they're bound in an atom or molecule, and together with that, the probabilities of where the electron in that orbital is likely to be when it's in that state. Electrons are fundamentally indistinguishable (unless they have opposite 'spin'), so while you can talk about orbitals being 'occupied' or not, you fundamentally can't say ",
" electron is occupying it, which is why the orbitals are what's interesting.",
"As with their position, and for the same reason, they don't have an exact momentum either; it's 'spread out'. The ",
" momentum of an electron in an atom is actually zero (which makes sense, as if they had a net momentum in some direction, they should go flying off). But the average ",
" of the momentum (p",
") is ",
" zero. Their average kinetic energy (which is Ek = p",
"/2m, just as in classical mechanics) is thus ",
" zero. ",
"But in Special Relativity, the kinetic energy in terms of momentum is Ek = sqrt(p",
"c",
"+m",
"c",
") - mc",
" , for which p",
"/2m is just a first-order approximation. So that's the relationship you have to use instead, and the difference between classical and quantum mechanics is that the momentum p is a simple variable classically, while in quantum mechanics, you have to deal with a statistical probability-distribution over the possible values of p. "
] |
[
"They 'look' quite different. Free, moving electrons have a net momentum for starters, and their probability distribution (which is thus moving through space) can have an almost-arbitrary shape. Except that the shape of the probability distribution (regardless of situation) is related to the kinetic energy (again per the uncertainty principle), the more precisely located a particle is to a specific region of space, the more the momentum is spread out, and vice-versa."
] |
[
"They 'look' quite different. Free, moving electrons have a net momentum for starters, and their probability distribution (which is thus moving through space) can have an almost-arbitrary shape. Except that the shape of the probability distribution (regardless of situation) is related to the kinetic energy (again per the uncertainty principle), the more precisely located a particle is to a specific region of space, the more the momentum is spread out, and vice-versa."
] |
[
"Do identical twins develop at exactly the same rate?"
] |
[
false
] |
Assuming a near identical diet and environment will identical twins develop at exactly the same rate? Ie teething, growth spurts and general development
|
[
"In theory? But the genes x environment interaction is so complex and it’s nearly impossible to hold all environmental factors constant for individuals so I don’t think this could actually happen in real life. Maybe in a laboratory setting but that’s beyond unethical "
] |
[
"Nope. Even before birth that ship has sailed. There is a competition for resources during gestation that usually puts one twin developmentally ahead for life. Not hugely...not even significantly to most...but the differentiation already begun. "
] |
[
"Twin studies have shown that even monozygotic twins with maximum genotype overlap still have genetic variations between them which then manifests in phenotype.",
"In other words, no, even identical twins will not develop at \"exactly the same rate\", they will have variation, even if it is only slight."
] |
[
"What is the driving force behind the expansion of our universe?"
] |
[
false
] | null |
[
"In a sense, it's pressure.",
"Imagine a box of air, sealed up tight. Subject that box to heat of some kind, say by lighting a fire under it. What happens inside the box? Well, the pressure goes up, of course.",
"But now imagine it's a ",
" box, one that can grow and shrink freely. If you heat up ",
" box, something different happens. The pressure inside doesn't go up. Instead, the box gets bigger. The air inside the box wants to expand as it heats up, so the walls of this magic box simply slide apart, driven by the pressure of the warming air inside.",
"That's essentially how metric expansion works, except there's no box.",
"The equation that describes the geometry of the universe is called the ",
" It includes a coefficient called the ",
" The scale factor represents, in a sense, how big that magic box is at different times. Over the past ten billion years, the box has grown larger, pushed apart by the pressure of the stuff inside it. It continues to do so today. That's what we mean when we say the ",
" is ",
"So what's the origin of this thing-that-acts-like-pressure? Well, it's ",
" obviously, since the universe contains everything that exists. But more specifically, there are three components. There's what we call ",
" what we call ",
" and what we call ",
"Cold energy is mostly matter, like you and me and our sun. It's stuff that has very little momentum compared to its mass. It exerts an effective pressure on the geometry of the universe, pushing outward on the walls of our imaginary magic box.",
"Hot energy is stuff that has a lot of momentum compared to its mass. Light is hot energy, as are neutrinos. Hot energy also exerts effective pressure on the metric, albeit in a subtly different way.",
"Dark energy is something else. It's a type of energy that ",
" as the metric expands. This is hard to imagine, because it's so different from anything in everyday life. It's as if you had that magic box full of air we talked about before, but you waved your wand and made it grow. What would you expect to happen? Obviously the ",
" of the air inside would ",
" since we're holding the amount of stuff constant and increasing the volume of the box, right? Well, dark energy doesn't work like that. As the metric expands, the density of dark energy remains ",
" Which makes it unique.",
"These three things together all exert a sort of pressure on the metric, forcing it to expand. Each one of them dominates at different times. Early in the history of the universe, hot energy drove metric expansion, because the effective pressure created by hot energy was much larger than the pressure of cold energy or dark energy. But the density of hot energy falls faster than the other two, so over time it became less dominant, until cold energy contributed more pressure than hot energy did. But that era either has recently ended or is ending now — the data are inconclusive as yet. But either we already have, or will in the next few billion years, enter an epoch in which dark energy is the driving force behind metric expansion, because the pressure it creates will be larger than the pressure created by either of the other two."
] |
[
"Well, RRC is probably just human, and he/she gets irritated or frustrated at things like anyone else."
] |
[
"Don't think RRC needs me to be a white knight here but in my opinion if someone is really, completely wrong about something you shouldn't be afraid to tell them so, and you shouldn't have to sugarcoat it, especially not on the internet. People that are actually knowledgeable on the topic shouldn't have to feign humility to avoid stepping on some oversensitive toes..."
] |
[
"Can we tell whether an object is in front or behind us based solely on hearing?"
] |
[
false
] |
[deleted]
|
[
"Yes we can because sound reflections on ears, shoulders etc. depend on the direction of the sound source. Stuff like that never ceases to amaze me.",
"From Wiki:",
"\"Sound localization in the median plane (front, above, back, below)",
"The human outer ear, i.e. the structures of the pinna and the external ear canal, form direction-selective filters. Depending on the sound input direction in the median plane, different filter resonances become active. These resonances implant direction-specific patterns into the frequency responses of the ears, which can be evaluated by the auditory system (directional bands) for vertical sound localization. Together with other direction-selective reflections at the head, shoulders and torso, they form the outer ear transfer functions.",
"These patterns in the ear's frequency responses are highly individual, depending on the shape and size of the outer ear. If sound is presented through headphones, and has been recorded via another head with different-shaped outer ear surfaces, the directional patterns differ from the listener's own, and problems will appear when trying to evaluate directions in the median plane with these foreign ears. As a consequence, front–back permutations or inside-the-head-localization can appear when listening to dummy head recordings,or otherwise referred to as binaural recordings.\"",
"http://en.wikipedia.org/wiki/Sound_localization",
"edit for typo"
] |
[
"That wiki page may need editing. First of all, let's assume you want a really specific test. So, you fix the position of a sound in the horizontal plane, and makes its fore-aft mirror position the other test. In other words, we will test localization of sound in front of, and behind, but with the same interaural timing cues. ",
"What you will find is that the remaining cues for localization are predominantly based on spectral filtering by the pinna (outer ear) and to a lesser extent the head. The cartilage in your pinna sets up a sound reflection/refraction that is frequency selective, and it will selectively dampen a narrow band of sound that depends on the direction in the vertical plane (which also contains the front/back information as one of its dimensions). This \"notch\" is coded for in the dorsal cochlear nucleus - if the cat work from Eric Young's lab translates into humans and it probably does. It does require broad spectrum of sound though - so it will not work for narrow band sounds. For higher frequencies you still may get some selective head filtering (shadowing) that is different for front and back, but for a narrowband, low, frequency sound front/back discrimination will be nearly impossible. ",
"Tl;dr The ear filters sound selectively based on position in the vertical plane, and your auditory system is sensitive to these cues. It only works for broadband sounds. "
] |
[
"It's worth pointing out that our lateral perception works more consistently than our median perception."
] |
[
"Can electrons be polarised like photons?"
] |
[
false
] | null |
[
"In short, yes.",
"At a fundamental level, the polarization of light waves is an artifact of the spin of the photons, so a beam of photons in the same spin state will be a beam with a specific polarization. Thus, if we take a collection of electrons and get them all in the same spin state will be polarized."
] |
[
"Not only does it have applications, they are well-known and really important too",
"."
] |
[
"Many thanks, does this electron polarisation have any current real world applications? "
] |
[
"Hubble Telescope has been producing the best space images for decades, and is still going. Is it about to become obsolete or should we make another/better version to spread the workload?"
] |
[
false
] | null |
[
"It is great, and we want it to keep running as long as possible, but we are building new instruments to improve things.",
"On the ground, adaptive optics technology mean that we can get ",
" the same resolution as Hubble within the atmosphere. The next generation of 30-metre size telescopes are underway, and will be a successor to Hubble in the sense that they will take sensitive high-resolution imagery in visible wavelengths. There are two projects - the Extremely Large Telescope in Chile, and the Thirty Metre Telescope which is supposed to be on Mauna Kea in Hawaii, but may or may not end up there.",
"There's also the James Webb Space Telescope, which will be an infrared space telescope with about the same resolution as Hubble. It's harder to get high resolution in infrared. This will be another successor, as a high resolution imaging space telescope, although not actually in visible wavelengths.",
"As for space telescopes in general, ",
"there are lots",
", with new missions going up all the time.",
"Edit: Also, ",
"here",
" is a nice comparison of the sizes of present and upcoming telescopes, for a more visual answer."
] |
[
"Well said! Some definitions for anyone wondering:",
"Adaptive optics is a really cool process. The observatory shoots out a laser into the sky and is able to see a reflection coming from the atmosphere. The laser went straight out, but coming back it's a bit wobbly from all the atmospheric interference (clouds and water droplets). This information of how the laser light changed is sent to a computer, which then ",
" accordingly. Now the wobbly part is countered by the mirror and the image is undistorted."
] |
[
"There are two projects - the Extremely Large Telescope in Chile, and the Thirty Metre Telescope which is supposed to be on Mauna Kea in Hawaii, but may or may not end up there.",
"There is also the ",
"Giant Magellan Telescope",
". Smaller than ELT and TMT but still much larger than any existing telescope."
] |
[
"So i tried applying super glue with a Qtip, moments later got a cloud of awful smelling smoke and the glue was almost instantly dried. Wtf?"
] |
[
false
] | null |
[
"Cyanoacrylate (crazy glue) ",
"reacts",
" strongly with cotton."
] |
[
"What were you applying the glue to?"
] |
[
"plastic, but I never got that far. It started smoking momentarily after glue hit qtip"
] |
[
"How do bee-eater birds bee-proof themselves?"
] |
[
false
] | null |
[
"Many animals create an antivenom for certain venoms they come into contact with often. I don't know if this is the case with bee eater birds.",
"Venom is not dangerous if ingested. I could swallow an entire vile of rattlesnake venom and be fine. So when a bird eats the bee, it doesn't have to do anything special to the venom. The stomach will deactivate it.",
"I also think that these birds will try to catch the bees in mid air. Not really allowing time for the bees to sting. I'm sure their beaks are designed to squash and kill the bug before they sting. Obviously if they sting the beak it won't do any damage to the bird."
] |
[
"What about for the physical damage of the stinger making a puncture? Is it negligible or would they have an extra tough stomach?"
] |
[
"I'm honestly just guessing. But I would say they try not to eat the stinger, but if they do, it would probably be negligible damage. Most bees have a venom sac, they have to choose to squirt the venom through the stinger. So if it's already dead, it won't be squirting venom. That's what causes the problems The venom, not the stinger."
] |
[
"What is the most \"painless\" way to prepare a lobster?"
] |
[
false
] |
In my country (Belgium) there is currently a huge discussion going on about how to prepare a lobster as a meal. This was sparked by a chef who, on national television, cut a living lobster in half (lengthwise), ripped out it's legs and arms and put it on the barbeque. His argument was that the taste of the lobster is the best if it is done this way. Regarding alternative methods, there are people saying that putting the lobster in a kettle of boiling water for approximately a minute is a better way. Both these methods seem pretty painful to me, however I'm not certain if crustaceans experience pain the same way humans do. I know for a fact that decapitation of humans will result in a painless and immediate death, so could this be considered an acceptable way of "killing" lobsters, based on scientific grounds? If not, what would be a better way?
|
[
"I work next door to a lobster lab and they brought a guest speaker in last year whose specialty is crustacean pain. Though it is impossible to know for sure what the subjective experience of an animal is (or for that matter, from a philosophical point of view, ",
"), there has been a rough consensus that if an animal \"acts like\" a human experiencing pain, and has appropriate neural circuitry, we should assume it is experiencing pain. ",
"For example, from a review I'll link to below: \"A common approach is to use argument by analogy (Dawkins 1980; Sherwin 2001): if an animal responds to a potentially noxious stimulus in a manner similar to that observed to the same stimulus in humans then it is reasonable to argue that the animal has had an analogous experience (Sherwin 2001). However, Sherwin (2001) notes differences in the acceptance of this argument depending on the species rather than the behavior: observers of a dog or primate writhing in response to an electric shock accept that the animal is experiencing pain, whereas much the same response in an invertebrate is often dismissed as irrelevant to the question of pain. \" ",
"Due to those inconsistencies, it's been proposed that possible pain should be evaluated as to whether the animal meets these criteria:",
"suitable receptors (does it have nociceptors - pain receptors.)",
"a suitable central nervous system (is it capable of integrating sensory information from multiple different sources, in some sort of central nervous system)",
"physiological changes in response to presumed-painful stimuli (e.g. stress hormones elevate, heart rate increases, etc)",
"avoidance learning (animal learns not to do something associated with painful stimuli)",
"protective motor reactions (animal withdraws limbs, tucks tail, tries to get under cover, etc)",
"tradeoffs between stimulus avoidance and other activities (e.g. animal chooses not to do something it would normally do if it's learned a \"noxious\" [presumed painful] stimulus would be encountered) ",
"responsiveness to opioids, analgesics, and anesthetics (if you dull the nociceptors, do all the above behaviors disappear and does the animal go back to normal behavior)",
"and, the most controversial one, cognitive ability and sentience. It's very unclear whether this should be on the list at all. (Is it necessary to be \"sentient\" or even \"intelligent\" in order to be capable of perceiving pain? If so... ",
" intelligent?)",
"Lobsters meet every criterion on that list except possibly the last one (though even there, they turn to be more intelligent than most people realize. Not super smart, but not just \"preprogrammed invertebrate robots\" either). So - there's no way to prove lobsters can experience pain, but there's reasonable evidence that they ",
". That brings us to how to kill them. When vets and researchers deal with vertebrate animals, we operate on the principle that if an animal ",
" experience pain, we should go right ahead and assume that it ",
", to be on the safe side. Any vertebrate that showed the same reactions that lobsters do to noxious stimuli would be assumed to be experiencing pain and there would already have been research into humane methods of euthanasia. Crustacean research is running behind the curve on this. The American Veterinary Medical Association, for example, has only a single page about aquatic invertebrates in its huge manual on euthanasia methods. However, in that single page, they do recommend a \"two-step process\" for aquatic invertebrates where you first knock the animal out and then kill it. Boiling is acceptable for step 2, the killing, but they state clearly that boiling by itself, without a step 1 first, \"is generally not considered to meet acceptable standards for euthanasia\". Later they say \"pithing, freezing and boiling... are not acceptable, however, as a single-step procedure, nor as the first step of a 2-step procedure....Methods of killing that do not cause rapid death or that cause trauma prior to loss of consciousness are not considered humane methods of death, or euthanasia.\"",
"In the talk by the crustacean-pain researcher last year we were basically advised to \"stun them or deactivate the nervous system somehow\" before boiling them, and we were also shown a picture of a commercial machine called a \"CrustaStun\" that basically stuns them with an electric shock. Other methods commonly used in home kitchens are chilling in a fridge for a few hours, which apparently does slow down the animals' ability to process sensory stimuli, or cutting through their nervous system lengthwise by basically splitting them in half. However I haven't seen any of those methods formally evaluated but you can see the split method illustrated ",
"here",
" on Trevor Corson's site; and I recommend his book on lobster natural history, it's great.",
"So, it sounds like the tv chef the OP describes maybe did the right thing (cutting them lengthwise). ",
"Here",
" is a 2011 pdf review on the general topic of pain in invertebrates; ",
"here",
" another 2011 pdf review on anesthesia and euthanasia methods for invertebrates, ",
"here",
" is the AVMA's 2013 guidelines for acceptable euthanasia methods for vertebrates and invertebrates.",
"Sorry for length, hope that was helpful",
"tl;dr - chill them or split them down the middle; and hope future research confirms that that works."
] |
[
"Alton Brown recommends that you put them in your refrigerator for a little while. Supposedly, that will knock them out. Then, you split the head in half, bisecting the brain and killing them as ",
"/u/icomrade",
" describes."
] |
[
"OTOH we ",
" be fairly certain that destroying the brain first will eliminate any possible consciousness that may or may not exist to experience pain/suffering. I believe once we take that into account it's clear that ",
"/u/icomrade",
" is correct."
] |
[
"if electrons flip poles when rotated, why don't magnets?"
] |
[
false
] | null |
[
"Are you referring to the phase that you get when applying a rotation by 360 degrees to the state vector of an electron? That doesn’t mean that its spin has flipped, it just means that the state vector acquired an overall phase of e",
" when you apply a 360 degree rotation."
] |
[
"i think so, is it only the complex phase that changes? I would have assumed the real probability of finding a particle in either state would change as well under a 360° rotation"
] |
[
"D(θ = 2π)|Ψ> = -|Ψ>, where D is the unitary rotation operator (Wigner D matrix), and |Ψ> is an arbitrary state vector for a spin-1/2 particle."
] |
[
"How would seasons work on a tidally locked pair like Pluto and Charon if they had atmospheres and proximity to a star akin to Earth's?"
] |
[
false
] |
If you had a dwarf planet and moon of similar size, mutually tidally locked, roughly 1 AU from a star similar to the Sun, both with atmospheres similar to the Earth's (regardless of how plausible that is), how would the seasons work? Also, would they necessarily have an erratic orbit like Pluto and Charon?
|
[
"Tidal locks tend to be focused on equators, don't they? How does a two-way tidal lock affect the axial tilt of the two bodies?"
] |
[
"One thing you must know to answer this is why Earth has seasons. The seasons on Earth are a result of the tilt of Earth's axis and actually has nothing to do with how the moon orbits Earth. ",
"The earth has a 23.4 degree tilt from the normal (perpendicular line to plane of orbit around sun). If we start in the northern hemisphere summer, say July, the NH receives more light, receiving the most light (i.e. longest day) on the summer solstice. The SH would receive the least amount of light during this day. Fast forward to winter solstice, the SH is tilted towards the sun and receives more light, thus summer in the SH and winter in the NH.",
"Tidal locking of two bodies means that the moon Charon only ever faces one side of Pluto. Move to the other side, you would never see Charon. ",
"So to figure out how the seasons would work, you would have to look at Pluto's tilt from the celestial plane. The IAU defines Pluto's axial tilt as about 60 degrees. This would result in wildly swinging seasons even if it orbited IN the celestial plane. Since it orbits at 17 degrees tilted to the celestial plane and has a highly elliptical orbit, it would likely have extreme weather.",
"Helpful Wikipedia links:",
"Seasons",
"Tidal Locking",
"(Credentials: BS Physics, Current Graduate student for MS in Physics with concentration in Nanoscience for Advanced Materials."
] |
[
"It doesn't, that's just the angle between the pole and it's orbital plane. Its not affected by Charon's tidal lock."
] |
[
"A question on how things fall when on a moving vehicle."
] |
[
false
] |
Say I am on a train and I drop a sack of pennies. This bag falls straight down in a straight line. It doesn't fall several feet away from me. Why is this? It is because me, the train and the sack of pennies are all moving at the same speed? Thanks!
|
[
"Objects in motion tend to remain in motion unless acted upon by an outside force.",
"The pennies are moving at 100 km/h with the train. You drop them. They continue to move in the same direction at 100 km/h."
] |
[
"Relative motion is sometimes pretty hard to get a good intuition for. At the beginning, you, the train, and the bag of pennies are moving at the same horizontal speed. When you let go of the bag, you let gravity pull it down; the key is that gravity only pulls down, not in any other direction. There is no horizontal force acting on the bag (ignoring air resistance), so it does not change its horizontal speed, and continues at the same speed until it hits the ground."
] |
[
"You're right. It's called inertia.",
"It's the same reason why, if you were standing on the train holding a particular heavy bag of pennies, you'd feel them pulling forward as the train slows down. That's the pennies decelerating. "
] |
[
"When I hit my hand against a wall, what exactly is stopping my hand from going through the wall?"
] |
[
false
] |
I know it sounds like a stupid question. When you're looking at it on an atomic level, what makes atoms (or nuclei) unable to intersect with one another? Why are some subatomic particles able to intersect, but not atomic particles?
|
[
"It's the force of the electrons in your hand repelling the electrons in the wall. The closer your hand gets, the larger that force gets; due to the inverse square dependence of electrostatic forces, you don't notice it until you're pressed right up against it."
] |
[
"Well it explains why an electron of one carbon can't spontaneously enter the orbital of a nearby carbon atom if it is already occupied, so there is repulsion as a result of that as well."
] |
[
"It's not just electrostatic repulsion.",
"There is what is known as \"pauli repulsion\" between atoms. This happens because two electrons cannot be identical (have the same energy and spin).",
"When two surfaces come together, if they are uncharged then quantum fluctuations will cause them to stick together by inducing dipole moments.",
"That is, imagine a system like this:",
"0 0",
"The two atoms have no charge.\nat some moment, a fluctuation causes the system to look like this:",
"0 +-",
"The atom on the left has no charge, but the atom on the right has fluctuated so that it has a dipole. If it were by itself, it would just fluctuate back. However, the force of the right atom makes the left atom fluctuate too:",
"+- +-",
"And there is an attractive electrostatic force between them.",
"As the atoms get too close, however, the electrons begin occupying the same orbitals (having the same energy/spin). This is forbidden. It is not a force keeping them apart - it just can't happen. This prevents the atoms from getting to close. In order to squeeze the atoms together, it is necessary to change the electron distributions of each atom to keep the electrons from overlapping, which requires lots of energy and force.",
"If the nuclei get too close together there is another electrostatic force between the two positive nuclei as all the electrons are forced to the outside, but generally speaking in most atomic interactions this is not as important.",
"The ",
"Lennard-Jones",
" potential is a simple approximation of the interaction between two atoms. One term comes from attractive forces from induced dipoles, the other term comes from pauli repulsion."
] |
[
"Electron diffraction - how did they know that graphite had the atom spacing of the wavelength of an electron if they didn't know the wavelength of an electron before doing the experiment?"
] |
[
false
] |
In the electron diffraction experiment, electrons were passed through a graphite crystal (the atom spacing was similar to the wavelength of the electrons) to prove that electrons produced a diffraction pattern and so also existed as waves. So how did they know that graphite had the atom spacing of the wavelength of an electron if they didn't know the wavelength of an electron before doing the experiment. Trial and error?
|
[
"Thomson observed",
" the ring patterns and saw that their radius depend on the electrons energy. He even related that to the already known ",
"de Broglie hypothesis",
" (λ = h/p), but is not sure what the diffracting systems are (atoms or molecules)."
] |
[
"Thanks for the answer,\nSo the rings related to the electron energy because of the equation E=hc/λ. Where the spacing between rings is λ?",
"And so the λ of an electron could be calculated before its existence as a wave had been proved? "
] |
[
"X-ray diffraction predated electron diffraction by a few decades. They could ",
"compare the electron diffraction to x-ray diffraction",
" at known wavelengths.",
"As other commenters observed, de Broglie had also worked out the theory of particle wavelengths before the experiments were performed."
] |
[
"Learning a foreign language with radio and TV."
] |
[
false
] |
When learning a foreign language, why does have a radio station/TV program in the target language playing as background noise help your listening skills? I'm at a language institute and people do it all the time with successful results, I just want to know why.
|
[
"Listening to your language of study passively helps your brain learn to attribute the sounds of that language as being important. ",
"When your brain is listening it is actively filtering out sounds as unimportant or important. (When speaking about languages and other sounds too.) It is also learning the new combinations of sounds that can occur together in relation to each other and in relation to position inside a word, morpheme, etc.",
"For example say this word: \"Song\". Now say \"ngot\" notice the difference in the pronunciation of \"ng\". In Thai you can start a word with the song \"ng\" sound, but you can't do that in English. So you said \"n\"+\"g\" when saying \"ngot\" rather than the song \"ng\". When passively listening your brain is slowly rewiring the importance of the sounds and their location. Combine this with the active learning that is occurring and you are working to retrain your brain on 2 levels.",
"Everything above is simplified, but should give you a basic understanding. Any other linguists feel free to add to this. My specialty is in Linguistic Anthropology not second language acquisition.",
"Also if you want to trick your brain to do the above trick try saying \"songot\" and slowly drop out the \"so-\"."
] |
[
"Thanks for the response, it sounds legitimate to me. I ask because I'm learning a language to become a Linguist and I always wondered how this works. I had my theories but I didn't know how accurate any of them were."
] |
[
"If you don't know about it already, there's ",
"/r/languagelearning",
" as well as ",
"/r/learnanewlanguage",
" which might help you find other resources. "
] |
[
"When the Apollo astronauts prepared to leave the surface of the moon, they discarded their EVA life support backpacks by tossing them out of the LM. How did they do this without exposing themselves to the Moon's vacuum?"
] |
[
false
] |
With the LM's hatch open, its interior held no atmosphere, so the astronauts had to enter with their EVA backpacks attached and operative. Were they able to disconnect them, toss them out, close the hatch, and repressurize using only the residual oxygen in their suits, or did the LM have the necessary hardware to provide their suits with oxygen until the backpacks were discarded and the LM repressurized?
|
[
"They only tossed the backpacks out, not the whole suit. the PLSS backpack was exactly that, a backpack that connected to the space suit via hoses and electrical connections. When inside the LM, the astronauts simply connected their suits to the LM’s life support system, negating the need for the backpack."
] |
[
"I never thought they tossed the entire suit out; the missing part for me was how the suits connected into the LM's life support system, and whether that connection could be made under vacuum, or if they needed to repressurize the LM, disconnect the backpack, connect the LM life support system, depressurize the LM, toss the backpack, repressurize the LM and then blast off.",
"Hmm, I just had a thought: the EVA checklists might be online somewhere; I'll have to see if I can find one to study..."
] |
[
"The Apollo spacesuit had dual connectors for the life support gases (two inlets and two outlets), along with single connectors for cooling water and for electricity. On early models these are prominent on the chest (they were moved around a bit on suits used on later Apollo missions and Skylab).",
"This means the astronaut can simultaneously connect to both the LM and the backpack, in order to change over without interrupting the gas supply, and to allow the suit and life support systems to be checked before EVAing.",
"https://space.stackexchange.com/questions/42114/why-did-the-hose-connectors-on-apollo-spacesuits-come-in-pairs",
"The Command Module Pilot had a variant suit without the redundant gas connectors, since they would not EVA."
] |
[
"Why does 16 Psyche have such a low density?"
] |
[
false
] |
I read that asteroid 16 Psyche was composed mostly of pure iron and nickel. However, it only has a density of around 3.3 grams per cubic centimeter. How is this possible? If it's really pure iron/nickel shouldn't its density be WAY higher, like at least double?
|
[
"It is very porous. It was probably never completely molten, and its gravitational attraction is not strong enough to get rid of those empty spaces inside either.",
"\"macroporosity of 30-40%\"",
" - meaning 30-40% is empty space."
] |
[
"More like a bag of marbles.",
"30-40% empty space (edited above, took the wrong number) and 50% metal content are consistent with the density estimate."
] |
[
"So is it like a bag of marbles? Or is it like a sponge?"
] |
[
"What is the difference between me flexing my muscles hard vs lifting weights. I feel like if I flex my arm is just as stressed as if it were lifting a weight."
] |
[
false
] | null |
[
"Isometric (tensed , not moving) versus concentric (moving against resistance) contractions are different in that in an isometric contraction, no 'work' (in the physics sense) is done. Mass isn't moved or displaced.",
"From an exercise point of view, it's nearly the same amount of energy required, however studies suggest that any muscle strengthening effect will be limited mostly to the area of the range of motion where the contraction was held. ",
"So if you flex and hold an isometric contraction of the biceps with your elbow at 90 degrees, your biceps and triceps, the antagonist muscle) will get stronger at that 90 degree point, but not much stronger at 170-120 degree elbow angle.",
"Generally it's easier to simply use resistance training through a full range of motion, thus training all angles at once, than training isometrically multiple times at multiple angles."
] |
[
"http://en.wikipedia.org/wiki/Isometric_exercise#Comparison_with_dynamic_exercises",
"Plenty of additional support for the effect out there."
] |
[
"threegigs is correct about only strengthening in that range of motion. While it is the same muscle fibers acting on the forearm and arm to pivot your elbow you have to realize that muscle force isn't constrained to a single plane. There are X and Y components to the force itself on top of the \"line of pull\". Also the length of muscle itself also effects the amount of force it can generate. And to strengthen a muscle you have to work the right amount of force. What your saying about other muscles being used is correct only for multiple joint muscles.",
"For example, make a fist and extend your wrist (wrist extension is the wrist movement for a high five) then squeeze an opposite finger as hard as you can. Then do the same thing but flex the wrist (opposite, like reaching for something on a high shelf) The multiple joint finger flexors (grip strength) are at the optimal position in extension "
] |
[
"Does heating water requires the same amount of energy during the entire process?"
] |
[
false
] |
I was making coffee and was wondering, is the amount of energy needed to raise the temperature of water from 20 to 30 degrees, is the same amount of energy required to raise it from 90 to 100? Yes? No? And why?
|
[
"Almost but not quite. Here is a chart ",
"https://syeilendrapramuditya.files.wordpress.com/2011/08/water_specific_heat_capacity_vs_temperature.gif?w=500&h=300",
"Note the numbers on the left. There is only about 0.5% difference between highest and lowest point."
] |
[
"Almost got it, it's not because the water has more energy, but because it actually changes. Water changes its material properties a bit when it heats up so that it has a higher (sorry if this is the wrong term) heat capacity, or resistance to change in temperature. If water was perfect and nothing changed in it besides the temperature it would take the same amount of energy to go from 10* to 30 as 60*-80. But it changes a bit when it heats up so it takes just a tiny bit more energy going from 60-80."
] |
[
"In everyday practice, no. The water will lose more heat to its surroundings if it has a higher temperature. Thus you'll need to add more heat than it's losing. At lower temperatures it will lose less heat, so you won't need to add as much. Assuming the surroundings are around room temperature.",
"In a situation where the water is not affected by (the temperature of) its surroundings, the answers of the other redditors are correct."
] |
[
"Why do we forget our dreams?"
] |
[
false
] |
Even the interesting ones, I can never hang on to for more than a few hours... I can wake up thinking "That was awesome!" or "That was absolutely terrifying. Turn the lights on.", or "That was the wierdest windmill made of kangaroos I've ever seen," etc. but no matter what, a short time later I can only remember the haziest outlines of what that dream was. Is there a reason for this?
|
[
"Here are a few other posts that may be useful:\nHas some useful answers:\n",
"http://www.reddit.com/r/askscience/comments/h5oyt/why_does_your_memory_of_a_dream_fade_so_quickly/",
"Not overly useful:\n",
"http://www.reddit.com/r/askscience/comments/g1e2z/why_is_it_so_hard_to_remember_dreams/",
"Empty at the moment, but its pretty new so you might want to watch it for answers:\n",
"http://www.reddit.com/r/askscience/comments/hp6dh/why_do_people_remember_some_dreams_but_not_others/"
] |
[
"Yeah, no problem. I did the same as you, but only looked deeper because I knew I saw one before."
] |
[
"Yep, try that search function! ",
"As pineapplol mentioned ",
"this",
" thread from a while back will be helpful to you."
] |
[
"An escalator moves at the same speed whether it's empty or has a lot of people on it. How does the motor \"know\" to change its power output?"
] |
[
false
] |
[deleted]
|
[
"Here's an excellent article about constant-speed motors. I really recommend you read it to get a good overview of how they work.",
"To answer your specific question, escalators and chairlifts and other constant-speed motors are designed to provide enough torque for a maximum load. For something like an escalator this might be a single person on every step, maybe with luggage; in all likelihood, based on the escalator's location, a building code will require a particular size.",
"So: the motors are designed such that they can provide enough torque to move a fixed (large) load at a constant speed. But because of the way the AC motor used to power the application works, you don't need a special feedback mechanism to move at a constant speed - it's inherent in the motor. ",
"How does an AC motor work? ",
"Although there are several different\ntypes of AC motors in use today, by\nfar the most common is the asynchronous\nsquirrel-cage type motor,\nwith an external stator core inside of\nwhich the rotor rotates. The motor\nshaft is attached to the rotor, and the\nrotation of the shaft produces the\nuseful work....The stator is typically made up of\nmultiple coils of copper wire that are\ninserted in slots of a laminated steel\ncore. The number of coils (or poles)\nper phase determines the speed at\nwhich the rotor turns....When alternating current flows\nthrough the stator windings, the magnetic\nfield created by the windings “rotates” around the stator body. The speed at which\nthe magnetic field rotates is called the “synchronous\nspeed” of the motor and is a multiple of the supply frequency\n(in Hertz) divided by the number of poles....In turn, this magnetic field induces current to flow in\nthe rotor windings, creating a magnetic field that is opposite\nin polarity to the stator magnetic field. As the\nstator magnetic field rotates, the rotor body rotates in\nthe same direction, with the rotor magnetic field attempting\nto “catch up” to the stator field. If there were no load\nat all on the rotor and negligible losses, the rotor would\nrotate at negligible slip and very close to synchronous\nspeed with the stator magnetic field. As the load on the\nrotor increases, the rotor speed falls behind the stator\nfield. The magnetic field of the rotor cutting into that of the\nstator as it tries to catch up develops the torque required\nto keep the rotor (and its attached load) turning. This represents the magnetic flux cutting the\nrotor conductors as it slips, producing torque. The\ngreater the load on the rotor shaft, the larger the slip\nand, therefore, the greater the torque produced.\nIn an unloaded motor, there is very little slip and very\nlittle torque produced. The motor is performing only a\nvery small amount of useful work.",
"Basically, the rotating magnetic field in the stator naturally makes the rotor want to move at the same speed -- and as the load increases, and the difference between the two speeds gets larger, the applied torque inherently gets larger. ",
"Interestingly, the motor is wasting a lot of energy (relative to useful work) at a no- or low-load condition and very efficient at a high-load condition. "
] |
[
"As most applications use squirrel cage motors, the speed is probably not identical in no load and loaded conditions. But the difference is negligible. Typically a squirrel cage motor on 50Hz can go from 1500 to 1475 rpm on full load. "
] |
[
"Simply put, they don't. They operate like a servo. A VFD drive spins a 3 phase motor with a tach on the back. The VFD reads the tach signal and adjust the frequency to the drive to adjust it's output speed, resulting in a constant speed regardless of load. ",
"That being said, I'm sure older units may have a constant speed governor and/or transmission to maintain that constant speed, but with microcontrollers being everywhere, modern ones are digital."
] |
[
"So I have a relativistic rock and a flashlight..."
] |
[
false
] |
Let's pretend I have a perfect vacuum, an idealized rock moving at relativistic speeds, and an idealized beam of light. The rock is moving from point A (At relativistic speeds, say .5c), towards the source of the light, which is at rest relative to point A. The light is exerting a pressure on the rock, which deaccelerates it. At some point, the rock reaches rest relative to A, and begins accelerating the other direction. The question is, what speed will the rock be moving when it passes A again? The reason I'm not sure is because of the red/blue shift. As the rock moves toward the light, the light is blue shifted. As such, it has more energy, and exerts a higher pressure that it would at rest. However, when the rock is moving away, the light is red shifted, with less energy, and so exerts a lower pressure. Wouldn't this mean that the rock is actually moving slower when it passes A the second time?
|
[
"I just solved it numerically in Mathematica for a 1kg rock moving at c/2 at t=0 decelerated by a 1000W 500nm light source with zero beam divergence (maybe in one dimensional space?).\nThis ",
"Plot",
" shows position in blue and velocity in red. (There is no scale for the velocity, I couldn't figure out how to plot 2 y-axes in Mathematica.)",
"Point A is at x=0. At t=0 the velocity is c/2~1.5E8 m/s and when the rock passes A again at t=8.56E13 s it has a velocity of ~1.2E8 m/s.",
"Mathematica Notebook",
"no guarantees for accuracy (i'm just learning this stuff myself)"
] |
[
"There is nothing wrong with your analysis.",
"In fact, you can use this doppler shift with lasers to ",
"cool atoms",
" down (though it also relies on the absorption of the photons changing with the doppler shift).",
"Also, I don't think relativity affects this question."
] |
[
"In physics, \"idealized\" doesn't mean \"doesn't obey the laws of physics\". In fact it typically means almost the opposite: assume that the equations being used apply precisely, ignoring effects that are secondary to the problem, like friction, or in this case, the effect of the interstellar medium on the velocity of the object.",
"With enough distance between the light source and point a, i feel like his analysis is spot on. ",
"He's correct that the velocity reduction caused by the light when traveling towards the light would be greater than the velocity increase when traveling away from the light. It's just that the example in question couldn't happen even in an idealized situation, without changing the basic laws of electromagnetism."
] |
[
"is it possible to graft a fruit tree onto a non fruit tree?"
] |
[
false
] |
Is it possible to grow a maple apple tree?
|
[
"Persimmon trees and ebony are both in the diospyros genus and can be grafted.",
"What the OP is talking about though is just not done, we don't graft lumber and fruit trees together because it's pointless. For example, persimmon trees have the same wood as ebony, if you grow a persimmon for 50+ years and harvest it, you get beautiful black lumber. There's no need to graft.",
"We also don't use grafting to make \"multi-fruit\" trees, beyond gimmick. While there's always the \"5 fruits in 1\" citrus tree being sold, these types of trees are far from ideal because they won't grow at the same rate.",
"The real use of grafting is to have roots and shoots with different traits. We can graft an apple tree with multiple disease resistances in its root system, to the best possible fruiting apple tree, and take advantage of two disparate sets of traits that might not be possible to breed into a single tree."
] |
[
"Persimmon trees and ebony are both in the diospyros genus and can be grafted.",
"What the OP is talking about though is just not done, we don't graft lumber and fruit trees together because it's pointless. For example, persimmon trees have the same wood as ebony, if you grow a persimmon for 50+ years and harvest it, you get beautiful black lumber. There's no need to graft.",
"We also don't use grafting to make \"multi-fruit\" trees, beyond gimmick. While there's always the \"5 fruits in 1\" citrus tree being sold, these types of trees are far from ideal because they won't grow at the same rate.",
"The real use of grafting is to have roots and shoots with different traits. We can graft an apple tree with multiple disease resistances in its root system, to the best possible fruiting apple tree, and take advantage of two disparate sets of traits that might not be possible to breed into a single tree."
] |
[
"If you grow it out to full size, yes, it's certainly possible to train the tree to keep things balanced, but those kind of trees are more novelties than something you'd grow for commercial fruit production. If you've got a backyard fruit tree, you can go full Elden Rings with your grafting, I've seen a few greenhouse citrus that have a dozen random plants attached - when they get big they're whatever is the main plant (lemon, grapefruit, etc) with a few random limbs of other citrus hanging off.",
"-",
"If you ever see a small citrus plant die, but then magically come back the next year as huge, thorny tree - you've met my favorite graft material: flying dragon rootstock. Stuff is a beast but if the top growth doesn't keep up with its nutritional needs, it'll just form another top half. It also survives hard freezes (unlike most citrus)."
] |
[
"Are dinosaurs more closely related to modern-day birds or reptiles?"
] |
[
false
] |
[deleted]
|
[
"Birds (aves) evolved from theropod dinosaurs. Dinosaurs evolved from basal archosaurs, which were closely related to reptiles. So, it's kind of like this: \"reptiles\" would be your aunt, \"dinosaurs\" would be your dad, and \"birds\" would be you. That's really simplified, but explains the relationship."
] |
[
"Think of it like this: Birds are to dinosaurs as bats are to other mammals. "
] |
[
"Birds are dinosaurs. The following statement is true for dinosaurs and birds:",
"All dinosaurs share more recent common ancestors than any dinosaur and any reptile. ",
"I realize yahoo answers is not science",
"It's bad science. It is awful. There is not smooth transition between animal classes, nor is there a progression from fish to reptiles."
] |
[
"If life originated on Earth more than once, and the descendants of each still exist and are easily found, would we know it?"
] |
[
false
] |
If life originated on Earth more than once, and the descendants of each still exist and are easily found, would we know it?
|
[
"Probably.",
"It is somewhat likely that life ",
" in fact originated multiple times on Earth, but the prevailing theories are that only one lineage has survived to this day...which then diversified into life as we know it. We suspect this because despite the huge differences seen between the 3 domains of life (Bacteria, Archae, Eukaryota), all three share some very key and fundamental aspects. Probably the most important of which is DNA being the \"blueprint\" for any organism's development and life history. Since we have not found any forms of life that use another molecule, or even a slightly different version of DNA, it is a pretty safe assumption that \"our branch\" of life originated, evolved to use DNA first, and later diversified into the 3 domains. ",
"Besides the use of DNA, RNA and proteins are also used in fairly similar ways across all of life. If we were to find a form of life that had a completely novel way to store genetic information, and catabolize cellular processes (other than proteins), that might be a good candidate for alien life or an independent origin of life separate from our own. ",
"For now, these possible differences we might see between separate origins of life are somewhat subjective because we simply don't know what other crazy and diverse ways life can exist. But, if we ever were to come across some organism with completely novel metabolic workings, we would probably have a good understanding of just how different it is from our mechanisms, and we could probably determine if it in fact originated separately. "
] |
[
"Viruses are an interesting case since they are so incredibly simple forms of \"life\". However, they still use similar means to store genetic information (as either DNA, or RNA) as the other forms of life, so while it is difficult to speculate about their origins and how they came about, it is unlikely that they originated separately from the rest of life."
] |
[
"How would viruses fit into this?"
] |
[
"How do we communicate with and control satellites that are millions of miles away? (Like the Rosetta Lander)"
] |
[
false
] |
I have always wondered how we send and receive data to and from satellites that are really far away. What kind of technology is used to do this?
|
[
"/u/katinla",
" mentioned parabolic antennas with a large area for collecting and concentrating signals. Here is how large these antennas can get (notice the cars for scale!):",
"http://mars.jpl.nasa.gov/msl/images/goldstone.jpg",
".",
"This is part of NASA's Deep Space Network, which can still communicate with the furthest human-made thing from earth, the Voyager I probe."
] |
[
"Very interesting. Thank you for sharing!"
] |
[
"It is true that big distances like millions of miles have a strong influence on our communication capabilities due to free-space loss. To be precise this has an influence on the received power, which decreases with the square of the distance.",
"Basically we have two ways of mitigating the issue. First is using high-gain antennas, usually parabolic, so that most of the radiated power is emitted more or less in the same direction. In the same way we use parabolic antennas for receiving, so that we have a large area to collect power from and concentrate it in a small antenna.",
"The other way is decreasing the bit rate, so if a single bit (whether represented by an amplitude difference or a frequency difference) takes more time to transmit then more energy is collected during this time, making it easier to overcome background noise. The term \"energy per bit\" is often found in the literature.",
"This is without mentioning the obvious fact that transmission power must be as high as reasonably achievable."
] |
[
"Electrons have mass and therefor curve spacetime. Why can't we measure that curvature to find position or speed without collapsing the wave function?"
] |
[
false
] |
[deleted]
|
[
"Measurement in quantum mechanics doesn't really have anything to do with our ability to measure things. It's referring more to what information is physically possible to obtain and what happens when that information is obtained.",
"In other words it doesn't refer to any specific means of obtaining the position or momentum of a particle, any method is the same. By definition, if the position or momentum is \"known\" in some way, the wavefunction is collapsed: it doesn't matter how we got the information.",
"If you were to measure an electron by measuring its gravitational field - which seems a ",
" impractical but it's your dime - it's no different from measuring it by, say, probing around for an electric field."
] |
[
"No, you couldn't. You can't perform any measurement without an interaction occuring.",
"To register a measurement, something in your measuring apparatus must be changed by the presence of the object you're measuring, which means there's an exchange of energy between the object and measuring device.",
"For example, the easiest way I know of to measure the curvature of spacetime is to use a scale, and since gravity works both ways you're affecting the planet whose gravity you're measuring when you put your test mass on the scale."
] |
[
"An interaction can occur without the wavefunction collapsing. For example, in an atom, the electron and proton are interacting, but the wavefunction doesn't collapse. This can work because you don't need the position of an electron to know how its electromagnetic field behaves: the wavefunction itself has a spatial location which determines the field.",
"The position of the electron is not the position of the wavefunction: the wave function carries the position information but you have to ask for it specifically. Asking for the electron's position is what will collapse the wavefunction.",
"In other words you could measure stuff ",
" the electron - such as its gravitational field - to get general sense of where the electron is likely to be found without collapsing the wavefunction, but that is different from measuring the electron's position.",
"The whole idea of wavefunction collapse gets really confusing and we end up needing to make these weird qualifications like \"wavefunctions collapse in interactions except sometimes they don't\" because wavefunction collapse is not currently well understood. It's not even clear right now whether or not it's even a thing that physically happens, or if it's just a model which produces the same result as physical reality."
] |
[
"Hey, this is more of a mental health question. I'm coming here because I couldn't find anything on Google."
] |
[
false
] | null |
[
"It could be many different things. I would suggest talking to a psychologist about it as any advice given here would be medical advice and therefore inappropriate. "
] |
[
"This post has been removed. Please observe the rules on the sidebar - Free of medical advice (see reddit's user agreement). If you have any medical questions (including your mental health), please consult a qualified professional."
] |
[
"If your doctor can't personally help with your problem, he or she should refer you to specialist in the field. I would suggest consulting with a psychologist for your problems. It may be costly, but it surely beats consulting the Internet for diagnosis.",
"Hope this helps, good luck."
] |
[
"Why does friction create heat?"
] |
[
false
] |
Friction is the result of microscopic ridges on an object's surface and acting against frictional force generates heat. But if you were a giant, trees would be microscopic, meaning that microscopic is subjective and,thus, the size of the ridges isn't what is creating the heat. So what's going on when I rub my hands together.
|
[
"But if you were a giant, trees would be microscopic, meaning that microscopic is subjective and,thus, the size of the ridges isn't what is creating the heat.",
"This isn't quite true. Ultimately, the interaction between the giant's hands and the trees are due to the interactions between the atoms in each. Regardless of the size of the objects that are interacting, it always boils down to those inter-atomic forces as they come into contact. ",
"The important part is that the surfaces of objects - even ones that seem quite smooth to us - are more like canyons than flat planes, and when the rub against each other it causes these ridges to deform. Deformations store potential energy, and once the ridges 'free' themselves, they bounce back and that potential energy is converted into thermal energy as the particles vibrate and wobble.",
"The quantum mechanics underlying friction are actually incredible complex and not perfectly well-understood. A recent development ",
"seems to have shed some light on how different proposed mechanisms are at play",
". But whether it's your hand over a piece of paper or a giant's hand over a forest, the ultimate source of this heat is the same! The giant will also be smashing the trees and sending pieces flying on a scale that would never happen with your hand, so they are not perfectly analogous."
] |
[
"Beyond the \"bounce back\" point, heat can be thought of as incoherent higher energy states in the system.",
"From that point of view the giant does increase the \"heat\" of the forest by breaking trees apart. The broken bonds raise the internal energy of the system and because it is done in a somewhat random manner, the results are incoherent."
] |
[
"Friction and temperature are not related and that is not what a mercury thermometer does.",
"A mercury thermometer gives you the temperature based on the change in density of the mercury as a function of temperature. Friction has nothing to do with the density of the mercury; it is an intrinsic property of the mercury and is only a function of temperature and pressure. ",
"P.S. By your definition you can change the temperature of the mercury by changing the thermometer from glass to plastic, which will have a different coefficient of friction with the mercury.",
"P.P.S it occurs to me you are probably trying to compare macroscopic friction to Maxwellian collision theory, in which case, you are ",
" correct, but using the term friction in this sense is super duper incorrect and confusing."
] |
[
"Why do we get itchy?"
] |
[
false
] | null |
[
"it evolved as an evolutionary adaptation. People who feel compelled to rub their body where something lightly touched it happened to be more likely to live because they brushed off bugs that could carry disease,poison,ect"
] |
[
"I am interested on this sensation on a cellular level. Can anyone describe the relationship with irritants and dendrites or other involved cells?"
] |
[
"I was recently wondering about why itching causes a compulsive desire to scratch (after a recent bout of poison oak). It seems there is generally no benefit to scratching as it causes further skin damage and does not relieve the itching at all. There has to be a reason we have a desire to scratch at things that itch though, why else would we do it?"
] |
[
"How is earth oriented in relation to the Milky Way?"
] |
[
false
] |
When we look up into the night sky and gaze upon the Milky Way, are we looking towards the center of the galaxy? Does our orientation stay consistent over time?
|
[
"The direction of the galactic center is at a specific point in the celestial sphere, near the constellation Sagittarius. ",
"In this circle",
"."
] |
[
"does that mean the earth spins at a 90 degree angle to the center plane of the galaxy?"
] |
[
"So is the orbital plane of the earth aligned with the plane of the galaxy, or offset by a significant angle? Intuitively, I would expect solar system discs to form on average in the same plane as the galactic disk, but maybe it's more or less random...",
"edit: never mind, quick google answered my own question: it's tipped by about 63 degrees.",
"here's a link"
] |
[
"Is there a way to reverse a chip from being stale?"
] |
[
false
] |
It would be magical
|
[
"Silica gel. It's a moisture absorber. You know, those little packets labelled DO NOT EAT that come in the box with expensive electronics. A fairly large one can be sealed in a bag full of stale Doritos and they will \"magically\" return to crispness in about 24 hours. OK, not magically, it's science. Staleness is caused by moisture. "
] |
[
"This type of sarcastic answer does not help make ",
"/r/askscience",
" a better subreddit."
] |
[
"Staleness is often caused by absorbing moisture. A short (10 min) bake in a very low (200F) oven will undo it. Source: personal experimentation."
] |
[
"Why don't scabs form on cuts to your palms and palm side of your fingers?"
] |
[
false
] |
[deleted]
|
[
"They absolutely do.\nAbout 5 weeks ago I had a thin dog leash gash about a cm into my middle finger and a little into my ring finger (palm side), it scabbed up pretty bad.\n",
"Possibly NSFW",
"\nThat was taken ~5 minutes after it happened, it was more of a rope burn than a slice, so it didnt bleed very much at all, but did certainly scab up for a couple of weeks."
] |
[
"Why is this being down voted when it is the most correct answer? henfeathers asked why scabs form everywhere on your body except your hands when \"they're not needed to stop the bleeding or to keep the wound clean?\"",
"I'm not sure what he is talking about in terms of scabs forming elsewhere when they are not used to clean or protect the skin."
] |
[
"I think he was talking about small wounds such as a paper cut, these tend not to form a scab over the wound on the palms and can remain open for days before healing."
] |
[
"What’s your favourite element and why?"
] |
[
false
] | null |
[
"Chemistry"
] |
[
"Chemistry"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines",
"/r/AskScience",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Wouldn't a starvation diet pull lipids, fats and calcium from all sources in the body and therefore also from the unwanted arterial blockages this lessening them - If not why not?"
] |
[
false
] | null |
[
"By starvation i mean pure fast with water only.",
"I would think that when the body was pulling from fat reserves that it might pull from some constituents of the blockages.",
"Then as body fat reserves were depleted it might pull from more constitients of the arterial blockages.",
"Additionally since the body would be scouring for calcium it might pull hard calcium from blockages.",
"While i think a keto diet might cause the body to scavenge some fats from blockages it seems the fats would not be scavenged since you were still eating fats.",
"Of course its dangerous. I am not suggesting anyone do it.",
"However we know eastern peoples often do true water only fasts for many days. Over a month if they have the fat reserves.",
"And a reviewed paper pointed out that the real dangers are of QT extensions in the heart in very obese people who do not supplement with postassium and magnesium and do true water only fast for more than a month associated with heart arrythmia and sudden death.",
"http://ajcn.nutrition.org/content/56/1/230S.full.pdf",
"Addition recent reviewed studies have shown many other very beneficial immune system rejuvenation as well as brain cell growth stimulation from true fasting."
] |
[
"The problem is that the lipoprotein lipase needed for hydrolyzing the triglycerides in lipoproteins to free up fatty acids are located on the luminal surface of the endothelium. Atherosclerotic plaques are located in the tunica intima between the endothelium lining and the vascular smooth muscle cells of the tunica media.",
"Therefore, the lipoprotein lipase cannot reach the atherosclerotic plaques because they are each located on opposite side of the endothelium. "
] |
[
"But wouldnt there be a break in the endothelium somewhere above the plaque? Didnt some lesion need to start the plaque?"
] |
[
"How many fully grown lions would we need to send into the sun at once to extinguish it?"
] |
[
false
] | null |
[
"This question has little didactic value."
] |
[
"Where should I ask this to get a serious answer then? I'm mostly trying to get an actual answer from someone much smarter than my friends and I, who started debating the troll question \"Who would win in a fight, 100 trillion lions or the sun?\"",
"We did a whole bunch of mass calculations but don't know enough about thermodynamics or physics regarding celestial bodies"
] |
[
"Try ",
"/r/estimation",
" or ",
"/r/theydidthemath"
] |
[
"Do objects have inertia through time?"
] |
[
false
] | null |
[
"Objects always travel through the time dimension. How do you think the second hand on your wristwatch moves?"
] |
[
"Yes but what about two 3 dimensional objects colliding in the 4th dimension while stationary in the 3rd?"
] |
[
"For two objects to collide, they must come into immediate proximity in all 4 dimensions. Objects that would collide in the 3 spacial dimensions, but are separated by time do not collide. Objects that would collide in time and two spacial dimensions but are separated by the third spacial dimension do not collide."
] |
[
"What is the highest velocity an object in space can travel at before relativistic effects take place (or become a problem?)"
] |
[
false
] |
Say I had a fast spaceship and I wanted to zoom around the solar system. How fast relative to the speed of light could I go before the I (or an observer) would experience noticeable shortening, increase in mass, or time dilation? I understand that this may be akin to asking exactly when our distant ancestors became human, in that you can't really pin down one iteration that changes everything, but it's something that I've been thinking about for a while. What is the fastest I could go so that, upon my return, the people on Earth and I have a time discrepancy of only a few minutes or so? So what would you guys say? .01c? .001c? Less? More? Thanks! If my question is stupid or improperly thought-out, tell me and I'll try to rephrase it.
|
[
"The main relation you'll need is the Lorentz factor. This, essentially, describes how big the relativistic effects will be for a given speed. It is:",
"where ",
" is your velocity, and ",
" is the speed of light. This is equal to the ratio of the dilated time (what you observe a clock on a spaceship to do if the spaceship is moving relative to you) to the time in your rest frame (a clock you're holding). It is always greater than 1, since ",
" cannot be greater than ",
".",
"Let's say your voyage lasted 500,000 minutes (roughly a year), and you'd like to observe a total time dilation of 5 minutes. This means that for every 500,000 minutes an observer on Earth measures, they need to measure your clock as having elapsed 500,005 minutes. So we require:",
"This gives ",
"/",
" of 0.0045 (unless I've messed it up), meaning you'd have to travel at 0.0045c (about 3 million mph) for a year to experience 5 minutes of time dilation. "
] |
[
"It depends what you mean by noticeable. In order to experience a 1% change in elapsed time or distance, you'd have to be going 14% the speed of light."
] |
[
"I guess I meant where the effects would be a problem, particularly time dilation, where I would leave and come back and everyone I cared about would be dead. In my hypothetical ship, energy wouldn't a problem until infinite energy is required.",
"So, if my ship was 100 meters long and if I were to travel at .14c, to an observer my ship would be 99 meters long? And if I experienced the trip as taking 100 hours, a stopwatch on Earth would clock me in at 101 hours, right (or am I off because an hour consists of 60 minutes which each consist of 60 seconds?)",
"Thank you for your response, I've never really studied relativity until a few weeks ago and I'm finding it fascinating."
] |
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