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[
"Does the diet of an animal really affect the taste of the meat?"
] |
[
false
] |
This question stems from something often trotted out when people talk about eating roadkill, or seagulls specifically: "They eat nothing but rubbish, they will taste terrible". But does that fact really affect the taste of the meat? I'm assuming the main diet of seagulls (in towns) is "rubbish" like discarded human food. To my un-biology trained mind, surely the processes of digestion would filter out the waste products before they make the meat taste different? P.S: I know killing and eating seagulls is illegal (at least here in the UK). I'm not interested in the legalities, but in the science.
|
[
"I am not seeing a lot of science here to back up these claims except that people's personal experiences are such that organic tastes better then non-organic, or grass fed better then grain fed. But these are biased opinions. The only way to truely test this idea of better tasting meat is a blind-taste test. Where you don't know what you are being fed before you make you judgement. Edit - I am not aware of any such test.",
"Moreover, you could not compare pig meat to say deer meat, or cow meat because these are different animals. The test, to be free of biases would have to be the same species, and you can't know what type of diet the animal ate.",
"In a documentary called ",
"the trouble with experts",
" they explore these subjective notions of what is better and who we trust with these opinions and if they are actually right. Turns out, more often then not, experts are wrong - or they tend to be 50-50.",
"A famous test done on several top wine experts had them do a blind taste test of some very cheap and very expensive wines. 50-50 that they guessed which one was the expensive which one the cheaper bottle. Moreover they tended to make up the \"notes\" and \"body\" of the wine - turns out they were just guessing. Only one or two consistently guessed right.",
"I guess what I am trying to get at here is that the only definitive support for better tasting meat based on how its raised needs to be conducted as a blind-taste test. Peoples subjective opinions cannot be considered fact here."
] |
[
"It can. A diet high in carbs leads to more white fat in meat. This noticeably changes the flavor of the cooked product. "
] |
[
"Capercaillie (big grouse-like bird) eats pine needles, flesh tastes like turpentine! Terpenes have robust, aromatic structures. Maybe it simply diffuses through gut? Digestion would not break down terpenes (toxic) only to re-form them in muscle, and yet the birds are inedible."
] |
[
"After hearing the news about the \"habitable\" planet 12 light years away, I'm curious to know how long it would take us to get there given today's technology."
] |
[
false
] |
I'm referring to this report: If we were to send some kind of probe or satellite or even a lander of some kind, how long would it take us to 1) get something there 2) begin receiving data on that objects findings Obviously it would take 12 years at the speed of light, and we're no where near capable of reaching those speeds (right?).
|
[
"1) To get something there, it would take a very very very long time. There is a theoretical upper limit on how fast you can get a rocket going from the ground. The reason being this: to get a rocket going faster, you need more fuel. More fuel means more mass. And eventually it just stops being worth it to add more fuel to get it going faster. I am a scientist, not a rocket engineer, so I won't pretend to be able to do the back of the envelope calculation for you. ",
"Anyway, ",
" But I also doubt the Voyager 1 was built with the intention of running it at the maximum possible speed out. Anyway, I'll let an actual rocket scientist do the real numbers. I can also think of at least half a dozen other design problems aside from speed.",
"2) To get data back, it would have a 12 year communication lag, plus however long it takes for it to find something worth telling us about. ",
"Edit: Regarding point 1, we'd need to know the mass of the probe we want to send to solve the ",
"rocket equation",
" which will tell us how fast we can get it going. "
] |
[
"It's very hard to say anything definitive about this, but here are some points to consider, partly inspired by all the other discussions going on in Reddit about this.",
"There have been various studies on interstellar ships, see ",
"Project Orion",
" and the later developments section in that page too for more recent similar studies. These are serious studies, not just scifi speculation, so they can give you some kind of an idea. But much of it isn't tested technology, just guesses on what we probably could do, so it's far from guaranteed that we could actually do something like that right now. Maybe after 10 or 20 years of further studies if we decide to actually pursue one of the plans. The estimates with these studies would range from about a century to a few thousand years.",
"With chemical rockets, that is technology routinely flown right now, I would say that we could probably get to something like 50 to 100 km/s escape speed from the Sun. If you take ",
"New Horizons",
" for example, a fairly recently launched probe that also set the record for fastest Earth relative velocity, that could probably have escaped at about 50 km/s if the delta-v use was optimized more for fast escape speed. That comes from just first falling close to Sun and then doing your escape burn there which will get you more orbital energy per delta-v due to ",
"Oberth effect",
". And we could probably squeeze a bit more delta-v out with current technology so 100 km/s seems like something we maybe could do right now. And that gives you a travel time of about 36,000 years.",
"Ion propulsion isn't really the key to fast interstellar travel either. Just by using the ",
"rocket equation",
" and getting (optimistic) values for current technology we can see that we'll be lucky to get to a thousandth of light speed with that. For Tau Ceti at 12 ly that would mean tens of thousands of years for travel time. You could maybe combine this with other things but still, we're talking at least many thousands of years.",
"You should also consider the option of putting all the effort into researching faster propulsion systems than launching as soon as possible. If we're assuming 1000 year travel time for launch right now, and you can improve on that by just 0.1% per one year of research, then after one year the travel time would be 999 years, so launching then you would arrive at the same time as launching right now. If you think you can improve your travel time by more than 0.1% per one year of research, then your best option is to just concentrate on researching right now. We can calculate the optimal time of launch with this. If travel time right now is T, and you can improve on it by, say 1% per year, then time to arrive, counting from now, if you first do x years of research is",
"T*0.99^x+x\n",
"(0.99 being 1-1%.) We can then put in T=1000 years for an estimate of travel time for a launch right now (quite optimistic), the curve of that function will then have a minimum at x=230 years. That means that if you want to arrive as soon as possible, you should first spend 230 years researching and then launch."
] |
[
"You also need to factor in fuel to slow down, effectively halving your potential speed. ",
"To expand on this, there are a few feasible (with great expense) ways we could cross 12 light years in fewer lifetimes.",
"Project Orion being one of them, unfortunately tests were ended in the early 60ties when bans on nuclear warhead tests came into force. (0.033c, 363.6 years)",
"http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29",
"Expanding on this, there are NASA developed plans for fusion based propulsion using a fission reactor as a power source, considered somewhat feasible by NASA with some more development. (0.045c, 266.7 years)",
"http://en.wikipedia.org/wiki/Project_Longshot"
] |
[
"Does the opposite of the placebo effect work?"
] |
[
false
] |
I've heard of the "nocebo effect". But for instance, say you take a drug to cure seasickness, you KNOW it is a drug that cures seasickness at 100% success rate, but is it possible that it does not work because you don't believe it will?
|
[
"Relatively speaking, this would still be the placebo effect. You're believing in an outcome regardless of whether or not its chemically working."
] |
[
"Yes, it is possible, but it's still the placebo effect that is at play. "
] |
[
"So it is possible?"
] |
[
"Do people with Parkinson's Disease experience mood changes as a result of the loss of dopamine?"
] |
[
false
] |
I know that senility is an eventual symptom, but I'm more curious about what happens as a direct consequence of the loss of dopamine. I've always been under the impression that dopamine was partially responsible for feelings of pleasure (thus its relation to addiction). Does that mean that people with Parkinson's Disease have reduced feelings of pleasure?
|
[
"(I've wondered this in the past, but the most recent episode of Curb Your Enthusiasm got me thinking about it again.)"
] |
[
"It's not quite as simple as less dopamine = reduced feelings of pleasure, but yes, Parkison's disease is associated with anhedonia (inability to feel pleasure from normally pleasurable activities). Way back in the day I was actually a research assistant on a study looking at anhedonia as a marker of the disease in family members of patients with known genetic subtypes of Parkinson's, and while it was a really small sample size we did find a modest effect that anhedonia might pre-date the motoric symptoms of Parkinson's. The other thing to note is that the treatments for Parkinson's (L-dopa, dopamine agonists) have been associated with problematic pleasure seeking behaviors (hypersexuality, gambling problems, etc) and is something doctors watch out for when prescribing those meds."
] |
[
"according to ",
"one estimate",
", 56% and 60% of PD patients suffer from depression and apathy, respectively. most estimates of the prevalence of depression in PD fall in the 30-50% range. i'm not sure how much of that is caused by degradation of dopamine pathways vs. other quality of life stuff though.",
"BUT! since you mentioned addiction and pleasure: a subset of PD patients exhibit impulse control disorders, including pathological gambling, binge eating, hypersexuality, impulsive cross-dressing, and excessive shopping. these behaviors are usually ",
"more prevalent",
" in patients receiving dopamine agonist treatments. one possible explanation for this is that the degeneration of dopaminergic neurons in PD begins deep within the brain and then gradually spreads forward; but impulse control is primarily a function of parts of the prefrontal cortex. so to treat the dopamine loss deep within the brain, the typically prescribed levels of PD medications end up effectively overdosing the relatively intact dopaminergic neurons in the prefrontal cortex.",
"sorry. i used to work in a PD lab and i still get pretty excited about this stuff. :)"
] |
[
"My 9yr old asked me why some substances can exist as liquid, solid, or gas - like H2O - and some can't, like wood. Explain for me?"
] |
[
false
] |
What determines what states a substance can exist in? Is it a simple matter of how complex the compound it? Water is H2O, a cotton shirt or wood table is more complex... I'm making stuff up - help me keep my kid asking good questions. Thanks!
|
[
"Is it not the case that wood is a composite material, so having \"liquid wood\" wouldn't make much sense because it's a complicated structure that only makes sense as a solid?"
] |
[
"Wood does melt! If it is heated without oxygen present it undergoes pyrolysis through which gaseous, liquid and solid products are made.",
"http://en.wikipedia.org/wiki/Pyrolysis",
"A paper discussing molten cellulose, ",
"http://pubs.rsc.org/en/content/articlelanding/2011/ee/c1ee01876k"
] |
[
"Well, to put it simply. \"Wood\" is made up of cellulose, which is made up of repeating polymers of glucose (sugar). The glucose is a combination of carbon, hydrogen, and oxygen, which - when heated - will ignite and form ",
" water, carbon (solid), and carbon dioxide. You can then change the forms of carbon accordingly. ",
"So, in fact \"wood\" can exist in separate states if you think about \"wood\" as the product of several other compounds. ",
"However, the reason wood as your 9yo sees it cannot change forms is because the components (cellulose again) that make up wood are bound by...well...bonds(carbon to oxygen to carbon bonds specifically)... in a certain arrangement and spacing that keeps them locked into one form (solid). Any breakage in those bonds would result in a change in state, however, the product would cease to be wood (becoming ash).",
"In non-science terms - what you see as \" solid wood\" is just a human \"made up\" name for a lot of cellulose stuck together. There is no made up name for what wood would be in liquid or gaseous form because that would be too complex and rare so we call them by their real names - carbon, oxygen, and hydrogen.",
"Very smart child. Encourage him or her to continue with science/ask more science questions/expose them more. You have a winner."
] |
[
"Is it possible for eyes to change colors? If so, then how is it possible?"
] |
[
false
] |
Hello ! Everyone always tells me my eyes change colors, but i don't believe them. I always think, how can that be possible? So after hearing it again today i decided to take it to the experts to find out if it's possible. If it is possible, why and when does it happen? Is there a name for this condition? How common is this condition?
|
[
"Yes it can! Eye colour has to do with the pigmentation (type of pigment and density of pigment) in the stroma of the iris. Some glaucoma medications (prostaglandin analogues) can cause darkening. ",
"Some diseases that affect the sympathetic nervous system inputs to the eye (like Fuchs heterochromic cyclitis, or Horner's syndrome) can cause a lightening of the iris, because the sympathetic inputs to the iris seem to stimulate melanin production. In fact in old age, our eyes become a little lighter in colour (more blue) because of a slight reduction in sympathetic tone and possible natural age-related depigmentation.",
"But in your case, it is much more likely that different lighting conditions are the culprit. Brighter lighting probably make your eyes look more blue, and lower lighting probably more green.",
"Edit:\nAs fallwower980 said, pupil size can change the pigment density, which is another reason which luminance can alter the colour."
] |
[
"Related question. A girl at my school had one brown eye and one blue. Over 5 years her blue eye started turning brown, starting with a fleck at the top. By the end of school, her eye was brown to the bottom of the pupil but blue under the pupil, with a straight horizontal line. What could cause that?"
] |
[
"Not quite. More common with congenital but certainly can occur with acquired",
"http://www.ncbi.nlm.nih.gov/m/pubmed/17878817/"
] |
[
"My google fu has failed me, so r/askscience tell me: what is the current rate of the Suns expansion?"
] |
[
false
] |
As it fuses hydrogen into helium, the Sun will expand. What are the current estimations for that rate of expansion?
|
[
"Layman here, I would have thought that because it is in Hydrostatic equilibrium, that it would remain roughly the same size, and not expand at all until it reaches the next stage in its stellar life cycle.",
"Reddit please feel free to correct me if I'm wrong or expand on my answer if I'm correct."
] |
[
"I'm not sure where to look it up online (and I'm not with my textbooks right now), so here's how I would think about it.",
"You are correct that the sun expands while still in the main sequence, just quite slowly. This is the same as saying that it moves up and to the right on the HR diagram.",
"The expansion should be quite slow and should depend on y, the mass fraction of helium. I don't think that increases from the cosmological abundance ~.25 to much higher than .35 or so over the course of the lifetime of the sun (about 10% of the hydrogen in the sun gets burned into helium on the Main Sequence).",
"I'm not sure how R depends on y, but I'm sure it's some power law. Regardless, a change of ~40% shouldn't lead to an increase in radius much bigger than a factor of 2. So I'd guess the answer is on the order of 1 solar radius per 10 billion years."
] |
[
"The sun is reasonably steady, and isn't currently expanding apart from some oscillation. Not enough H has fused to He to start the expansion yet. "
] |
[
"Is the speed of random mutation to a genome affected by environmental stress?"
] |
[
false
] |
Do the mechanisms that control mutation operate less effectively during sickness, starvation, etc?
|
[
"As far as I know the machinery itself (ie DNA polymerases, proofreading enzymes, DNA damage repair pathways, etc) is not affected by environmental stress factors, although oxidative or metabolic stress *within the cell* may influence them in the same way that all proteins will be influenced - if theyre getting oxidized or not getting the cofactors they need theyre gonna misfire to some degree.",
"However when an organism is stressed in some way it has to compensate to return to the normal state, and in many tissues this means killing off the damaged parts and producing new ones (skin recovery from sunburn, intestinal epithelium regeneration after big time diarrhea). More DNA copying means more errors given the standard rate of a few errors per genome copy. So, while the machinery works just as well as under normal conditions, the added work load makes the chance of error higher. This is why tissues with the highest rate of turnover are the among the most likely to produce cancers."
] |
[
"The ",
"genome shock hypothesis",
" was first really put forth by McClintock and is the idea that hybridization or stress could cause disruptions in the suppression of transposable elements. Transposition is not really mutations, but the general idea is the same.",
"The selective mechanism put forth was that if a population is dying off, it might as well attempt to change, even if those changes are more likely to be deleterious."
] |
[
"Is the speed of random mutation to a genome affected by environmental stress?",
"Yes, evolutionary speaking environmental stressful conditions favor selection (in larger populations) over time as opposed to drift. ",
"Do the mechanisms that control mutation operate less effectively during sickness, starvation, etc?",
"In an organism? Definitely, look at cancer for example - a poor lifestyle increases the chance of mutations. ",
"Evolutionary speaking? Who the heck knows. I don't think that you can really say that a given environmental stressor causes a \"less effective\" or more effective regulation because the truth is that we still don't understand all the mechanisms behind the modulation of gene expression throughout evolution. These are called epigenetic changes, and they look to be somewhat random in certain instances. A good intro to Population genetics text would be a great resource for you."
] |
[
"We can see galaxies created shortly after the big bang because their light is only just reaching us now. But something has always bothered me about this."
] |
[
false
] |
The further away a galaxy is, the longer its light takes to reach us, and consequently the further back in time we can see. Okay, I get this. How far back in time can we see? I've been told almost back to the big bang. Wait, hold on! But WE were at the big bang too! So shortly after the big bang, that same galaxy would have been much much closer to us. In this case, wouldn't it's "young" light have already passed by us? Unless we are each heading in the opposite direction, travelling at close to half the speed of light. Then this makes sense to me. I think. No sure if my rambling is making any sense. Can someone explain this to me?
|
[
"This isn't actually a problem. The object is fixed in space, it is space ",
" that is expanding. Therefore, the recession speed of the galaxy is only relative to us, not to space itself, and there is no speed of light limit on the expansion of space, as JimboMonkey said."
] |
[
"Does this mean, that space expands faster than the speed of light?",
"Space is expanding at a more or less constant rate almost everywhere, so a sufficiently large stretch of space does indeed expand faster than light."
] |
[
"I'll just add that you have to take into account the expansion of the universe, which is not limited by the speed of light. There can in fact be galaxies that are \"receding\" from us at faster than light speed."
] |
[
"Can radiation be blocked by means of energy?"
] |
[
false
] |
... rather than as typically by matter? Can one make a "lead curtain" that runs off batteries?
|
[
"Our ",
"Magentosphere",
" is a good example. Although I am not sure it fits your definition of energy.",
"It can stop Alpha particles, which are a type of radiation. But it isn't so good with beta and gamma radiation."
] |
[
"That doesn't annihilate the photon, but only alters its probability to be found at certain points in space. The wavefunction for photons describes the same thing as it does for particles, i.e. the probability density and interference just modifies that. ",
"Theoretically, if you want to quench the probability completely, you would need another photon emitted exactly with the phase difference of pi with the exact same frequency and direction, i.e. the same origin. Not to mention the restrictions imposed by the uncertainty principle, this is definitely not a way to block radiation."
] |
[
"As has been said already, for alpha and beta radiation, this would be possible by electric and/or magnetic fields.",
"For x-rays/gamma rays, i.e. high energy photons, one needs to consider the laws of conservation of energy and momentum. While it is possible to ",
"transfer both with electromagnetic fields",
" to classical particles i.e. particles with ",
"rest mass",
", I'm not aware of any mechanism for this to be possible in photons. Not even with two high energy gamma ray producing matter - antimatter pairs since this also needs some kind of particle as scatterer in order to satisfy the momentum conservation.",
"If there is a possibility I'm not aware of, please correct me."
] |
[
"What makes Swedish iron ore so special?"
] |
[
false
] |
In both WWI and WWII, the German factories turning out weapons were heavily dependent upon steel produced from Swedish iron ore. In WWI, the supply of this ore via merchant ships in the Baltic was protected by Germany's High Seas Fleet (which otherwise did not have much of a purpose). In WWII, the supply of Swedish iron ore was so critical to Germany's war effort that it was the primary reason Hitler invaded Norway (nothing can be shipped from Sweden to Germany via the frozen Baltic in the winter, so ore travels overland by rail to the coast of Norway and thence to Germany by ship; hence the need to invade Norway to secure the ore supply year-round) and why he had plans in place to invade Sweden if necessary. What exactly are the chemical properties of Swedish iron ore that made it so desirable for steel production? Why was Germany unable to produce sufficient steel for its war effort using only the iron ores available in the areas of Continental Europe under German control? What was "wrong" chemically with those ores as far as steel production was concerned? I'm not sure this is exactly a "science" question, more about geology/manufacturing processes etc.
|
[
"Swedish iron ore is very pure (specifically low sulphur content). Before the modern ",
"Linz-Donawitz-steelmaking",
" process, sulphur impurities were very costly to remove.",
"However the main reason Germany desired Swedish steel was not for its quality but its quantity. 40% of Germanys prewar iron ore supplies was imported from Sweden.",
"Wiki-article which might be of interest:",
"https://en.wikipedia.org/wiki/Swedish_iron-ore_mining_during_World_War_II",
"EDIT: Typo."
] |
[
"Party it has to do with the purity of the ore. For some reason the iron content of the ore in Sweden was higher than anywhere else in Europe. Part of its reputation comes from the fact that the king of Sweden brought in experts from around Europe to work the ore & the exchange of knowledge resulted in hire quality steel.",
"My own ancestors came from France, engineers brought by Sweden's king for exactly this purpose."
] |
[
"The demand for iron ore in mainland Europe started in the iron ages, and for thousands of years, all of the ore came from mainland Europe. Hence, there simply wasn't enough left to be used on such a large scale ",
".",
"Northern Sweden ",
" has never been densely populated, hence has never had much reason to dig for ore on large scales.",
"It's just for the last few decades that we get ores from countries like China, do the first few steps there, and then transport it to Europe to make it actually valuable."
] |
[
"Why are we left-handed or right-handed?"
] |
[
false
] | null |
[
"This question",
" was asked earlier today."
] |
[
"That didn't answer my question. That link was about personality types."
] |
[
"Yes, yes it was. I fail at multitasking for the day. ",
" question",
" was asked earlier today. Thank you for pointing out my mistake."
] |
[
"When I add CO2 to water, why does it taste different? Am I tasting the CO2 or is it enhancing some of the flavors that are already present?"
] |
[
false
] | null |
[
"The carbon dioxide dissolves to form carbonic acid and bicarbonate ions, so yes you're tasting the CO2. "
] |
[
"Just to elaborate a little bit- Sourness is a taste affiliated with acidity, meaning the carbonic acid is detected by the same cells responsible for tasting other acids in any foods (e.g. citric acid in oranges or tartaric acid in wine)"
] |
[
"To unnecessarily add on, the addition of CO2, by lowering the pH, also affects the speciaition of tons of other species in solution, so you could be tasting compounds that existed at a very low concentration at your starting pH and become exponentially more concentrated as the pH changed. This included affecting the sorption phase distribution and functional group structure of organic acids and bases, some of which can be tasted at concentrations below standard detection limits. "
] |
[
"A question about Coulomb Force and its equivalence in real life ?"
] |
[
false
] |
So i was solving a question " Two 1 Coulomb charges are placed 1 km apart the force on them will be " Answer was 9000 Newton . Now when we life weight of ground suppose 100 kg it takes Mg newton that is 980 Newtons . My question is why we cannot see that 9000 Newtons force around us and why it doesnt affects us plus i am sure there are hell lot of charges around 1 km distance
|
[
"Because everything is pretty close to neutral in charge.",
"The Coulomb force causes positive and negative charges to attract each other, to form atoms etc. Two neutral atoms don't attract each other very much. Their protons push away from each other, their electrons push away from each other, but their protons attract each others electrons, and their electrons attract each others protons. These forces almost entirely cancel out. It's only at very short distances that you can \"feel\" that the electrons and protons aren't in exactly the same place, and this is basically how atoms stick together to form molecules.",
"Generally, you can only have very weak net charges, because the Coulomb force is so strong that any strong charge will cause electrons to fly away or get drawn in, and the charge will become mostly neutralised. If you have too strong a charge, the electric field (i.e. the Coulomb force) is strong enough to rip electrons right off the atoms in the air, and you get a spark or basically an arc of lightning, as the electrons are pulled towards the positive charge/away from the negative charge.",
"This even happens in space, where everything is an ionised plasma made up of positive ions and negative electrons. You don't have strongly positive or negative regions of space for very long, because the plasma will be forced to flow to cancel it out.",
"Just to bring that all together: positive and negative charges cancel out, generally things end up close to neutral because positive and negative charges attract each other so much, and you end up with weaker net forces than you might expect."
] |
[
"A neat question I've read that puts this whole neutrality thing into perspective is, \"What would happen if you lost 1% of your electrons?\" That seems like a fairly small imbalance away from neutral... but the Coulomb force is so strong that even that 1% imbalance in electric charge would contain so much energy that it would cause an explosion big enough to "
] |
[
"Generally, you can only have very weak net charges, because the Coulomb force is so strong that any strong charge will cause electrons to fly away or get drawn in, and the charge will become mostly neutralised",
"An everyday example of where you see this in action is when you get a static shock when you walk across carpet in socks or something. That spark you feel when you reach for the door is caused by returning you back to neutral from the few micro-Coulomb's of charge you have built up. And this brings up why getting a 1 C charge is next to impossible- even at a few uC (1E-6 C), the electric force is so strong that electrons will start to jump through the air to a conductor in order to get you back to neutral."
] |
[
"If mass matters in the solar system with relation to gravity (Jupiter vs Mercury for example), why doesn't that apply to mass of smaller objects (a feather and a bowling ball). Why do those two fall at the same rate?"
] |
[
false
] | null |
[
"For some people equations work best to explain something, so let's give this a try.",
"Force of Gravity (F) = G*m1 *m2/ r",
"Say m1 is the earth and m2 is the bowling ball or feather. And they are both the same r from the center of the earth.",
"Now the rate they fall is determined by the acceleration with the following equ:",
"a = F/m2",
"Sub this into the first equation.",
"m2* a = G *m1 *m2 / r",
"the m2s cancel out and your acceleration is just dependent on the earth's mass. This works since the acceleration of the earth is so small. If two objects with similar mass was used then you couldn't just look at one since both would be moving towards each other.",
"a = G*m1 / r"
] |
[
"Yes I think OP is asking why the feather and the bowling ball fall at the same rate if their specific gravity is the different.",
"The answer is, they aren't ",
" the same. Over a long enough distance of fall, with no air resistance, you would see an infinitessimally small difference, about the same as the percentage of difference in mass between the bowling ball and the feather... as a fraction of earth's mass. ",
"So this means... lat's say a bowling ball is 7 KG. Earth's mass is about 6 000 000 000 000 000 000 000 000 KG, so the bowling ball is .000000000000000000000001166% of earth's mass. The difference in the rate of fall is this percentage divided by distance between mass centers",
" The the mass of the bowling ball has an effect on its rate of fall, but a very very small one. The feather, on the other hand, at let's say .01 grams... which is hugely different from the bowling ball but in terms of a percentage as earth's mass... not so much. Since the bowling ball is already barely a septillionth of earth mass, the difference can't be larger for any item that weighs less than a bowling ball. ",
"So in a vacuum, the difference in velocity between the two items is measured in a septillionth of a percentage of the total momentary velocity of the item divided by distance between mass centers",
" A very small number indeed. "
] |
[
"Point was if m2 was large enough then m1 would move towards m2 while m2 moves towards it. If your reference point was on m1 then m2's rate of \"fall\" would be higher than what the equation above shows."
] |
[
"Is there a good way to simulate a fiber optic internet connection between two computers?"
] |
[
false
] | null |
[
"Huh? To what end? What are you trying to determine?"
] |
[
"I was wondering how much if a difference I would notice using a fiber optic internet connection, which can supposedly send a gigabit per second, as opposed to copper cables like we have in most of the USA, which usually get something more like 10 megabits per second.",
"I don't know of anywhere near me that has a fiber optic internet connection, so I was wondering if there is a way to connect two computers with something like a USB chord, and then video chat between the two computers or view webpages that are being hosted locally on the other computer.",
"What I'm really trying to get at is the qualitative difference between these two connection speeds. If there is a better way to get a feel for the difference between them I am open to suggestions."
] |
[
"You will not see any qualitative distances at such a short distance. ",
"Twisted pair actually can support over 100 Mbps at under 100 feet (see fig 3, PDF)",
". Fiber optics sets itself apart in how little the data rate drops off over distance. This is not something you can test with two computers.",
"Furthermore, the difference will only manifest itself in the data rate. Many applications (such as video chat) require a certain bits per second to work correctly. But, having a medium which supports higher data rates will not improve the quality over one which just supports this minimum. So you get an all or nothing effect. ",
"Of course in other applications, like downloading videos, you will see a difference. But in terms of streaming live content, there should not be a large difference."
] |
[
"Sorry, another question regarding the speed of light. And no, it's not about FTL."
] |
[
false
] |
The way I understand it, we know that the speed of light is the maximum speed allowable in the universe because light will always go the maximum spacelike velocity allowable in the universe. Or, all of its 4-velocity is in the spacelike dimensions. None in timelike. We know this because when we examine light mathematically we find that it will simply travel at the maximum allowable velocity, no matter what. So we measure the speed of light and say, "OK, that's the max." Light doesn't set the limit, something else does and because of the nautre of light, light is uniquely situated to show us what that limit is. This completely blew my mind when I first got it. Hell, just the ideas involved in getting to that conecpt blew my mind. The following is based on that overly simplistic understanding. So if the above is wrong, please correct me. What is the something? Do we know? If so, what is it? If not, what are the most reasonable ideas?
|
[
"You are right that the speed of light, the \"universal speed limit,\" is not set by light. Moreover, I think you are really on the right track towards understanding this fundamental idea in physics, which is always really nice to see in this board. In General Relativity, gravitational radiation also propagates at the speed of light. Another way to think about it is the speed of massless particles (the graviton is supposed to be massless).",
"So what is that speed and where does it come from? Perhaps the best way to think of it is as a geometric factor that converts between temporal and spatial dimensions. Think of the units on speed: [distance]/[time]. So if you multiply a time by a speed, you get a distance. So if you want to put space and time on equal footing, we need a factor to convert between the two. That's because when we defined the second and the meter, we weren't thinking about spacetime.",
"This is why a lot of theoretical physicists just define things such that c = 1. It's not very helpful for making observations and conducting experiments, but it certainly simplifies the math and makes it clear that distances and times are essentially the same thing."
] |
[
"Nothing \"sets the limit.\" You're — due respect — way overthinking it.",
"How many inches in a foot? Twelve, right? So we can define a constant, call it ",
" and say that ",
" = 12 inches/foot.",
"Now, ",
" is this true? What \"sets\" the value of ",
" The answer is the ",
" sets the value of ",
" The foot is ",
" as being equal to twelve inches.",
"Now, how many meters are there in a second? Sounds like a stupid question, right? Well it's not. Meters and seconds are ",
" It's just that ",
" we use meters (and inches and miles and light-years) to measure ",
" lengths, and seconds (and minutes and months and years) to measure ",
" lengths. But that's ",
" convention. There's nothing ",
" about it. It's purely customary.",
"So back to the question. How many meters are there in a second? There are 299,792,458 meters in a second. We can define a constant — call it ",
" — and say that ",
" = 299,792,458 meters/second.",
"What \"sets\" the value of ",
" Definition. That's the ",
" of a meter. It's ",
" as being 1/299,792,458th of a second.",
"Now, let's go back. How many feet are there in a foot? Another seemingly dumb question, but this time the answer's obvious: There's ",
" foot in a foot. One foot per foot, that's the ratio of feet to feet.",
"How many seconds are there in a second? One. The ratio of seconds to seconds is one second per second.",
"Could it ever be anything ",
" than that? Can the ratio of seconds to seconds — or feet to feet, for that matter — ever be, say, 1.2? No! That's pure nonsense. One second per second is ",
" Because one equals one. One doesn't equal anything ",
" than one, so the ratio of seconds to seconds can never be anything other than one second per second.",
"And a meter is ",
" as being exactly 1/299,792,458th of a second.",
"Therefore ",
" will ",
" be exactly 299,792,458 meters per second. Because all we're doing is taking the ratio one-second-per-second — which is ",
" — and substituting in the ",
" of the meter.",
"So what \"sets\" the definition of ",
" The fact that one equals one. It's really ",
"(Now, ",
" is the meter defined as being 1/299,792,458th of a second? Ask the French. It could be anything. It could be defined as ",
" one second, if we wanted it to be. Which would make our units of timelike separation and our units of spacelike separation numerically equal, meaning the value of ",
" would reduce to what it really is deep down: Just one.)"
] |
[
"distances and times are essentially the same thing",
"woah"
] |
[
"Why isn't combination therapy long term?"
] |
[
false
] |
Combination therapy (using numerous therapies/drugs to treat a disease) is used I believe when treating bacterial infections to prevent development of drug resistance. It's basically used because the chance that a colony of bacteria is resistant to a number of antibiotics simultaneously is very unlikely. And so my question is; why isn't combination therapy the answer to antibiotic resistance? (sorry if it seems like a silly question! Thanks to all responses in advance :) )
|
[
"Combination therapy will increase the number of generations needed to achieve resistance, but it will not increase it to infinity. Pathogenic bacteria will still slowly evolve resistance to the antibiotics, but it gives us more time to come up with novel treatments. "
] |
[
"Sequential administration of antibiotics (try A, when A stops working switch to B, and so forth) is pretty much rigging the game for bacteria (and I should note that pathogen resistance is found in almost every class of pathogenic organism: virus, bacteria, protist, fungus, etc.). Combination therapy helps, but is not perfect. For instance, we're already seeing resistance to ACT (artemisinin combination therapy) in malaria.",
"The key is to recognize that resistance is not an all or nothing proposition. Bacteria can be partially resistant to a treatment. And people can be imperfectly treated, so the pathogen is not entirely eliminated during a treatment (or can pass on the pathogen before treatment is completed). In such cases, the ones that survive ",
" (even if they would be eventually killed by the treatment) are the ones deferentially found in the population. If the pathogen has partial resistance to one of the treatments in combination therapy, it will probably outsurvive the pathogens which are fully susceptible to all the treatments. So partial resistance accumulates, just as before.",
"In fact, some people originally thought that combination therapy would hasten the evolution of resistance, because the pathogens would be exposed to (and thus, evolving resistance to) all the treatments simultaneously. Quantitative modeling was a major factor in determining that the combination therapy approach would actually prevent more problems than it causes."
] |
[
"Also, keep in mind expense and side-effects. Using multiple drugs at one time means paying more and exposing your patients to more drugs than possibly needed. I don't know if I've ever seen someone prescribed combination therapy for the purpose of treating one bacteria with good susceptibility to a given antibiotic (other than in specific populations or specific infections that require combination such as TB or Pseudomonas in CF patients). A lot of the time, when people are given a cocktail of antibiotics, it's because we want to cover a wide range of possible pathogens. As we find out what is causing the infection, we narrow the treatment as much as possible and try to get patients on an antibiotic regimen that is manageable for them (considering method of administration, price, side effects, number of pills needed per day, and length of treatment)."
] |
[
"How does fat \"burn\" when we exercise? Where does it go?"
] |
[
false
] |
[deleted]
|
[
"You forgot acetone, acetoacetic acid, beta hydroxybutyric acid. Ketones, which is why fat metabolism is ketogenic.",
"Glycerol is an interesting resulting byproduct, well not interesting that it is there but what becomes of it. With amino acids pyruvate and lactate, these will form into glucose. It is a homeostasis maintenance cycle to avoid hypoglycemia while providing energy from non glucose source. ",
"This all occurs when lowered glucose levels result in lower insulin production. The pancreas alpha cells activate due to low serum insulin levels. These produce glucagon. This does a number of things. It causes the liver to release glucose converted from glycogen stores. Insulin causes adipose lipoprotein lipase activation (which mediates triglyceride ingress in adipocytes) and it's presence reduce glucagon which activates hormone sensitive lipase (mediates triglyceride egress) thus reducing its activity. Lacking this the reverse occurs creating a ratio of low LPL and higher HSL from glucagon which results in adipose release of fats at a higher rate than uptake. Activation of muscle cell LPL to uptake fat allows the fats now present in volume in the blood from the enzyme ratio change in the adipose and use those instead of glucose for energy.",
"It is anaerobic and I'm pretty sure CO2 is not a byproduct of ketogenic fat metabolism. "
] |
[
"You forgot acetone, acetoacetic acid, beta hydroxybutyric acid. Ketones, which is why fat metabolism is ketogenic.",
"Glycerol is an interesting resulting byproduct, well not interesting that it is there but what becomes of it. With amino acids pyruvate and lactate, these will form into glucose. It is a homeostasis maintenance cycle to avoid hypoglycemia while providing energy from non glucose source. ",
"This all occurs when lowered glucose levels result in lower insulin production. The pancreas alpha cells activate due to low serum insulin levels. These produce glucagon. This does a number of things. It causes the liver to release glucose converted from glycogen stores. Insulin causes adipose lipoprotein lipase activation (which mediates triglyceride ingress in adipocytes) and it's presence reduce glucagon which activates hormone sensitive lipase (mediates triglyceride egress) thus reducing its activity. Lacking this the reverse occurs creating a ratio of low LPL and higher HSL from glucagon which results in adipose release of fats at a higher rate than uptake. Activation of muscle cell LPL to uptake fat allows the fats now present in volume in the blood from the enzyme ratio change in the adipose and use those instead of glucose for energy.",
"It is anaerobic and I'm pretty sure CO2 is not a byproduct of ketogenic fat metabolism. "
] |
[
"Ketogenisis is not the only form of fat metabolism, or even the preferred form. In general fatty acids undergo beta oxidation to form acetyl-coa which then is processed by the krebs cycle, producing CO2. Whether the acetyl-coa is made from glucose as a consequence of glycolysis or from fatty acids the krebs cycle is the preferred path. Ketogensis is mainly a fall back when more energy is needed from fatty acids than the krebs cycle can handle."
] |
[
"If energy were no object, what are some scaleable ways to pull CO2 out of the air and bind it to some solid?"
] |
[
false
] |
[deleted]
|
[
"At this point it is more a question of efficiency than low energy approaches. As per your example, let's say I have 500MW of nuclear electricity. What is a better use of that energy - to pull out 1 unit of CO2 from the air or to displace 3 units by shutting down a coal power plant if comparable production?",
"At some point in the distant future we can focus on using excess energy to pull CO2 from the air but for now our biggest challenge is to displace existing fossil fuel use."
] |
[
"You can actually convert it directly to carbon if energy is no object. I did some reasearch on this when I was bored and I wanted to design some form of CO2 -> C + O2 device and I thought I would share. ",
"So the first step is getting pure CO2 since the concentration in the air is actually quite low. The method I initially planned was bubbling air through a solution of calcium hydroxide in order to make some calcium carbonate. The process behind this is to take CO2 and form carbonic acid in water and then removing that acid by reacting it with a basic solution. The calcium carbonate can actually then be decomposed back into the Calcium Hydroxide with heat and will release CO2 gas which can be collected. Now as it turns out this isn't a great solution and a better method involves using amine and copper electrodes. If you ",
"skip to 1:00 in this video",
" you can see the method. ",
"Now the second part is the bread and butter of the system, it involved taking magnesium dust and igniting it in concentrated CO2 gas. This is a spontaneous reaction which forms magnesium oxide and carbon as a solid! This can be seen ",
"in this video",
". Now technically you could also react it with other metals like lithium but magnesium is a bit nicer to work with and is cheaper since there will inveitably be some loss in the next step. ",
"Lastly we would want to recover our magnesium from the magnesium oxide. We can do this with electrochemistry by forcing an electrical current through the molten salt. I scoured around for papers on doing this but really I have only seen hard expermients on doing this with Sodium Chloride which is done in something called ",
"downs cell",
" . Now if we want some numbers on the efficiency of the electrolysis it will take 96.5kC of charge to reduce one mole of Magnisum. The process could theoretically take place with a difference of around 5V or so but realistically an overvoltage would be used, lets say its about 10V instead. 96.5kC*10V= 268Wh. Thats about 4 or so cents in electricity per mole of magnesium depending on how cheap electricity is. Which would be 8c per mole of carbon dioxide. And a mole of carbon dioxide is 44.01g of it. So we have a cost in just electricity for the reduction at the end of around $1.80 per kilogram of carbon dioxide. And that doesn't even account for all the other components. "
] |
[
"I'm sure there are people here more knowledgeable than I am on this particular issue, but what you're looking for is called ",
"carbon sequestration",
" or ",
"carbon capture and storage",
".",
"The simplest of these are using biological systems, like trees or algae, that naturally use photosynthesis to \"fixate\" carbon as biological matter, i.e. make more trees or algae. The catch is that we have to leave them there or we're just releasing the carbon back into the air, so we would run out of space for trees, and we don't know the downstream effects of runaway algal seeding.",
"Another way is the chemical approach, where you turn carbon dioxide into carbonate minerals. While this happens naturally over geologic time, it can be sped up by just applying heat and pressure to CO2 and certain common mineral oxides, like silicates, aluminates, and calcium oxides. CO2 also naturally forms carbonic acid in the oceans, which could be neutralized into a mineral form by using large quantities of basic salts.",
"Some miscellaneous, more useful ideas include using CO2 as an ingredient in ",
"plastics",
" or ",
"cement",
"."
] |
[
"Does science believe that animals have names for each other like humans do?"
] |
[
false
] |
I'm sorry, I don't know a more intellectual way of wording this.
|
[
"Yes. Dolphins have a signature whistle, which accounts for over half of all the whistles they produce, and is unique to each individual, kind of like signing off every comment with your username. In a recent study ",
"published in Proceedings of the Royal Society",
", King et. all found that ",
" dolphins will use another dolphin's signature whistle to call them, kind of like summoning another Redditor by mentioning their username. Even cooler, they found that vocal copying occurred more frequently between dolphins that were close to each other, and highest among calves and their mothers. In conclusion, the study notes:",
"Besides humans, bottlenose dolphins appear to be the other main example of affiliative copying with such individually specific learned signals, although some parrot species do use vocal learning to develop labels for social companions [50–52] and therefore deserve further investigation in this context. Further studies are also needed to elucidate whether copying such signals is different from sharing learned contact calls or adjusting acoustic parameters in communal displays as found in other birds and primates. "
] |
[
"This is amazing! If they have advanced communication like this how have we not managed to communicate with them in a 2 way conversation yet? "
] |
[
"Really the important word there is \"",
"\". ",
"It seems like they have a complex language with structure and syntax. But we've never been able to understand it if it's there. ",
"The really cool earlier work on the dolphin names though found that the calf's names are a variation of their mother's names.",
"\nWhich would mean that they don't just have names, they effectively have surnames as well."
] |
[
"How do we know that all the physics constants are constant in the whole universe?"
] |
[
false
] |
[deleted]
|
[
"We don't know ",
". But every observation we can make in our observable universe has pointed to them being the same within our observable universe. So we have to take a piece from the philosophy of science and invoke the principle of parsimony. If we were to ",
" that they vary with location in space, then that is an unfounded assumption. And a scientific description of the universe asks us to make the fewest unfounded assumptions about it. ",
"So they could. But the universe could also be unicorns and rainbows outside of our observable universe. The scientific description however, is that the universe is just more and more of the same. The same stars and galaxies all governed by the same physics."
] |
[
"This is actually a very compelling question even though it can sound silly before you start to think about it.",
"It seems like others have pretty satisfactorily answered your question so I won't clutter this up but I did want to provide a link to a wiki article relating to this about the cosmological principle.",
"http://en.wikipedia.org/wiki/Cosmological_principle",
"Basically it describes our method of thinking about the universe, and how we have to assume we are in a spot that is NOT special and is the same as everywhere else. We have to assume this because if we didn't we would have no way of figuring anything out about the rest of the universe (we can only test what we can see from our frame of reference, we have to speculate on other reference frames and hope they are consistent)"
] |
[
"yes, there have been hypothesized versions of that. metastable vacuum states (ie, it collapsed once, but only so far, and could collapse again) are an example. There are hypothesized cases where the collapse happened subtly differently in different regions of the universe... interesting ideas, but not scientific understanding."
] |
[
"What causes smoke from combustion?"
] |
[
false
] |
Admittedly, as a high school sophomore (year 10), my knowledge is rather limited, but why does smoke form from a fire when the generic formula for combustion is Hydrocarbon + oxygen -> CO2 +water ?
|
[
"So is ash a result of incomplete combustion?"
] |
[
"Smoke can be made up of many compounds. The amount and type depends on how much oxygen is available to the fire, the temperature of the fire and what is being burned. Except in carefully controlled circumstances, anything you burn will have impurities and won't burn evenly.",
"Smoke from a well oxygenated wood fire is mostly composed of ash."
] |
[
"Yes, exactly. From ",
"wikipedia on combustion:",
"Complete combustion is almost impossible to achieve. In reality, as actual combustion reactions come to equilibrium, a wide variety of major and minor species will be present such as carbon monoxide and pure carbon (soot or ash). Additionally, any combustion in atmospheric air, which is 78 percent nitrogen, will also create several forms of nitrogen oxides."
] |
[
"Are we among the earliest generations of intelligent life in our galaxy?"
] |
[
false
] |
Please feel free to rip apart this back-of-a-napkin estimate: Given these numbers, the odds are not too bad for life in our galaxy, but not necessarily for intelligent life at this point in time.
|
[
"While no one has an answer to your question, you may find it interesting to review ",
"the Drake equation",
". Since we have no method for surveying other solar systems for life (yet), all we can do is consider the factors that go into it. The Drake equation summarizes those and leaves the unknowns as variables. By manipulating it you can get various answers for the number of currently active intelligent civilizations in the milky way galaxy. ",
"If you want to play around with the equation, there are ",
"Drake equation calculators",
" that will save you time. Have fun!"
] |
[
"You're not the first person to consider this possibility."
] |
[
"also, keep in mind, intelligence isn't the \"goal\" of evolution. It's worked well for our species, but plenty of others have come and gone and done very well for themselves without it. It could be that the selection pressure to generate intelligent life is very low generally, or that intelligent life exists very briefly (on cosmic scales) for a variety of reasons."
] |
[
"What does nuclear waste actually look like?"
] |
[
false
] |
Google images says it looks like a yellow barrel. I wanna know what's inside!
|
[
"It depends on the type of waste.",
"If you are referring to \"Nuclear Waste\" as \"Spent Fuel\", the stuff we take out of reactors, then it looks exactly like the fuel we put ",
"INTO the reactors",
", ",
"except it glows when it is under water.",
". Inside the rod, originally you start with ",
"uranium fuel pellets",
". After being \"Spent\", the pellets tend to break crack and break a little. In our current process, we do not remove the pellets from the fuel rods, we just keep them in the rods for disposal.",
"If you are talking about other types of waste, the more mid or low level stuff, then it depends. A fair amount of \"radioactive waste\" is stuff that happens to have radioactive particles stick to it from being used in a contaminated environment. Examples of this would be ",
"protective clothing",
" or tools. The appearance doesn't change, it just happens to potentially have radioactive material on it due to being in a contaminated area.",
"Then there is liquid/solid waste product. By waste product, I'm referring to either water which has radioactive material that is in solution, which for all intensive purposes looks just like water, or solid products. Solid products are what we generally refer to as \"sludge\". Typically a nuclear plant will take radioactive water and evaporate the water out for re-use in the plant. The parts that dont evaporate build up and create a kind of sludge when settled. This is a bit more goopy looking and generally is never seen outside of tanks because it is concentrated radioactive material.",
"Other radioactive waste products include ",
"small resin pellets",
". Resins are small pellets of anions and cations used to separate ionized radioactive waste products and clean up/purify reactor water."
] |
[
"Piles and piles of these:",
"http://upload.wikimedia.org/wikipedia/commons/2/28/Fuel_Pellet.jpg"
] |
[
"Pretty boring. Can look like metal, powder, liquid, chemicals. Nuclear waste just means that a Geiger counter scan shows counts per minute that is high enough to classify it as waste.",
"Here's some fuel rod and liquid rad waste which has been undisturbed for several decades.",
"https://en.wikipedia.org/wiki/Hanford_Site#Cleanup_era"
] |
[
"What is actually happening when you get dizzy from say spinning in a chair? Is there a quick way to nullify these effects?"
] |
[
false
] |
[deleted]
|
[
"Would spinning backwards stop the effect?"
] |
[
"Would spinning backwards stop the effect?"
] |
[
"Shake your head (like you are saying no) vigorously, to lessen sensation of dizziness. "
] |
[
"Is it possible for planets to safely orbit a black hole as if it were a star? Why dont't the stars at the centers of galaxies get pulled into the black hole?"
] |
[
false
] | null |
[
"Is it possible for planets to safely orbit a black hole as if it were a star?",
"Yes. Gravitational pull is determined by mass and distance. Black holes act like any other massive body with respect to gravitation (so long as you stay outside the Schwartzchild radius).",
"The idea that black holes \"suck things in\" is a gross misunderstanding of the situation. It's just that anything that happens to intersect the black hole gets \"trapped\"."
] |
[
"I think what you mean is that no one is teaching the layman about black holes except for Hollywood, and Hollywood black holes are giant space vacuums."
] |
[
"Building on AnteChronos' answer, perhaps an example would help.",
"Say you are standing on the surface of the earth and you weigh 100 pounds. The gravity of the earth pulls on you with a force of 100 pounds.",
"Now imagine the earth were squeezed down to the size of your thumb. All that mass concentrated in a tiny volume would create a black hole about three quarters of an inch wide enshrouding it",
"Imagine, however, that instead of sinking down together with the receding surface of the earth during this crushing process, you remain hovering in your place, while the land withers away beneath your feet. In the end you will find yourself about four thousand miles above the surface of that black hole.",
"Here's the important part: you would still weigh 100 pounds, and the black-hole earth would still pull on you with a force of 100 pounds."
] |
[
"What is the physical structure of a brain?"
] |
[
false
] | null |
[
"It is not liquid. You can go to a butcher and buy a brain. It is solid."
] |
[
"I did clearly know it wasn't a liquid (I don't like my physics teacher) but they were arguing that because it's squishy/mushy it fills the shape of its container."
] |
[
"Squeeze a sponge and hold it in your hand. It molds to your hand. It is not liquid."
] |
[
"How do caterpillars become butterflies?"
] |
[
false
] |
I've always been taught the basics, caterpillars eat a lot, weave a cocoon, stay there for some time and come out with a new body and wings. But what exactly happens in the cocoon? What is the body breaking down into - amino acids/individual cells/ different tissues - and then rebuilding / reconnecting? And what guides the rebuilding? If they've broken down into primordial goop, is there's still a brain directing the reformation?
|
[
"They don’t completely liquify in the cocoon, that’s an urban myth. When a caterpillar goes into the cocoon, parts of its old body start to break down, but certain essential groups of cells don’t. They’re the starting point for most of the major features, like eyes or wings. ",
"Some caterpillars actually have underdeveloped butterfly parts inside their bodies, which start developing when they’re born, but only fully develop in the cocoon."
] |
[
"Ohhhh okay so it's a little like Caterpillar puberty then? The parts were there but didn't kick in until a certain age/ time. The parts that break down- are your parts composed of stem cells or something like that? So they have the capability to reform into wings/a new body?"
] |
[
"I study insect development so maybe I can help you out. Think of the pupa as just another stage on the way from egg to larva to adult. Metamorphosis is completed in the pupa but is a much more gradual process than you might think! Things are already happening well before the pupa forms. Also FYI most of my knowledge is in fruit flies but the big picture is the same in butterflies.",
"All insects that go through metamorphosis have what are called ",
"imaginal discs",
" inside the larva. These are little sacks of cells that contain the cells that will become the external adult structures (wings, legs, genitals, eyes, antennae, etc. They're even arranged inside the larva vaguely like the body plan of the adult–six little leg discs underneath, wing discs to the side, eye/antenna discs on top, etc. See this ",
"awesome image here",
". Most if not all imaginal disc cells in the larva already 'know' what type of cell they will eventually become in the adult.",
"So when pupation happens, pretty much every other cell dies besides the ones in central nervous system and the imaginal discs, as well as a couple other internal organs and structures. And what's left undergoes massive growth and reorganization to form the adult. ",
"Here's a beautiful visualization",
" of what happens with just the wing in fruit flies.",
"The 'how' part of your question is an entire field called developmental biology! Animal development is a complex and fascinating process which is why I chose to study it. Hopefully you can see from the beautiful stripes and lines in that video that cells use different signals to set boundaries and give info to cells about what to be.",
"Some more info:",
"good short overview",
"This now-classic paper"
] |
[
"If you fill a torus completely with water and begin rotating the torus, does the water inside begin rotating as fast as its container, or is there always some amout of friction between the interior of the torus and the water it contains?"
] |
[
false
] |
I'm wondering whether a salt water filled graphene torus could be rotated to generate electricity. As a follow up: If you nest a static torus inside the rotating torus, anchoring it with magnets, would that allow for energy to be generated?
|
[
"The water would eventually spin as fast as the toroid because the walls of the toroid would \"pull\" on the water with friction. The water would never be able to go faster than the toroid if the toroid is accelerating or keeping it's rate of spin. This could be used for energy storage as a flywheel but would be extraordinarily inefficient."
] |
[
"No, why would the water start rotating as fast as the container? It will speed up to the speed of the torus due to friction.",
"The follow up - is it a smaller torus. Like, one inside the hole of the torus, or one within. Actually, I don't think it matters. Why on earth would this generate energy? I mean, it is possible that the rotation in the first torus could be harnessed. However, this is just a silly inefficient flywheel."
] |
[
"True, I was reading this article at work",
", and it seems you are right, but of course, I'm trying to come up with something that utilizes the properties that graphene has recently been shown to display. So, instead of water, what if I used a Paramagnetic Ionic Liquid and nested another torus inside the larger torus, filling the space between them with this PIL. The inner torus would be suspended with magnets, so the magnetic field might then disrupt the flow of the liquid, keeping the liquid from reaching the speed of the external torus and maintaining friction at those points. ",
"Howabout this? How would this act in the vacuum of space? I am imagining the internal torus as a sort of battery, where the energy generated by the friction on its surface is stored within it, and the internal surface of the external torus as the agitator along with the external surface of the nested torus. Of course, something needs to keep the external torus rotating, so I'm aware this isn't some sort of perpetual motion device, and I don't mean for it to look like I'm suggesting that."
] |
[
"With evidence growing of autoantibodies in patients with persistent Long-COVID-19 symptoms, what is the outlook for this large population of survivors?"
] |
[
false
] | null |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"I'm asking about existing knowledge around autoantibodies and how they affect chronic disease - it's a large topic and not speculative"
] |
[
"There’s no information about the scenario in COVID, so any answer must be speculative. If you can broaden the question to cover well documented scenarios that can be answered from published literature the question could be approved."
] |
[
"How is fructose imported into the cell?"
] |
[
false
] |
I recently learned that diabetics can eat fructose fruits. After I thought about it this was unsurprising considering there is no reason to think fructose is imported via the prototypical insulin pathway that imports glucose. But this made me wonder how fructose actually is imported into the cell. I looked around and found out that GLUT5 is the main transport protein in the process, but I could not find much about it in the literature. Any help would be appreciated, Thank you!
|
[
"GLUT5 transports fructose into the body through facilitated diffusion. For instance, in the small intestine, the epithelial cells contain GLUT5 on their apical sides (Facing into the lumen of the intestines). This transporter moves fructose via facilitated diffusion. So, the concentration is higher in the lumen of the intestine, which favors the transport of fructose into the cell. To maintain the concentration gradient that allows for this, the basal side of the epithelial cell (Facing the capillaries) also transports fructose via facilitated diffusion. I don't quite remember this transporter, but I do know it is less specific than GLUT5, because it transports both fructose and glucose by facilitated diffusion."
] |
[
"There is no active transport of fructose whatsoever? Wouldn't this lead to fructose in the urine, and wouldn't it be terribly inefficient?"
] |
[
"I'm not sure of the specifics of the nephron and the kidney, I just remember GLUT5 participates in facilitated diffusion of fructose in the gut epithelia",
"I can assume that the nephron also participates in FD to reabsorb fructose in the proximal convoluted tubule.",
"I'm not saying this is universal, I'm just saying GLUT5 participates in FD of fructose in the gut. Other GLUT's might exist that do active transport of fructose. "
] |
[
"Are black holes disc shaped or actually spherical?"
] |
[
false
] |
Because black holes are usually represented as a disc on a single plane, I wondered what I would see if I were able to orbit one on its equatorial axis. Are black holes actually spherical but represented artistically as a disc? Thanks! EDIT: I'm grateful to all who answered. An additional thought: Because a black hole is spherical, objects can enter from any direction, are the rays emmitted dispersed in all directions like the Sun? I ask because again, artistically it is always represented as a jet from the center. EDIT: Are their exaples of a black hole with bodies orbiting it with different planes? I realize that most Galaxies, Solar systems, etc. tend to lie on a single plane.
|
[
"A non-rotating black hole will be perfectly spherical, if it rotates, it will bulge out in the middle like the planets do. "
] |
[
"This is correct and should be the top answer. Furthermore, all non-primordial black holes should have angular momentum and therefore an event horizon which is an oblate spheroid (bulging at the equator). Since primordial black holes have never been observed, ",
"."
] |
[
"However, even quickly rotating black holes are still only a few centimeters bulgier at the equator than pole to pole."
] |
[
"If a simple robot is designed to move towards the sun at a given rate, what path will it trace during the day?"
] |
[
false
] |
[deleted]
|
[
"Springtime on the equator: Robot goes in one direction, stops, robot goes in the other direction ends up where he started. --> Line",
"Springtime Europe: Robot starts out going east and slowly shifts his direction until he ends up going South and finally goes west. Draws a pretty good half circle.",
"Summer in Europe: Robot starts out going northeast, switches slowly south and to northeast. Looks like a pretty closed C after someone sat on it :-) (the robot spend less time going south, than it spends time going west resp. east)",
"http://en.wikipedia.org/wiki/File:Sun-path-polar-chart.svg"
] |
[
"Here",
" is a screen shot of a quick LabView program I made. It uses an existing subvi that calculates the sun's location (altitude and azimuth). ",
"Here",
" is a reference website I used to make sure the sun path data was correct. The path graph starts at point (0,0) and uses the azimuth angle to calculate the next position, always moving a distance of 1. ",
"In the Sun Path graph, East is at 90",
" West is 270",
" North is 0",
" and South is 180",
" . In the Robot Path graph, East is Right, South is Down, West is Left, and North is Up. Want to see another path for a different location?"
] |
[
"Polar regions in the summer: Robot will travel in 24-hour circles, all summer long. "
] |
[
"If placed in a controlled environment, do trees that normally undergo seasonal leaf Abcission stop losing their leaves?"
] |
[
false
] |
[deleted]
|
[
"I'm not any kind of expert, but no one else has answered this; so I looked it up, and I'll try my best.",
"From what I'm reading, deciduous abscission results from a decrease in production of auxin in the leaves. This triggers a physical change in a dual layer of cells connecting the leaf to the tree, called (appropriately enough) the abscission layer. The cells of this layer change shape, eventually separating the leaf from the tree. The process also seals the stem.",
"The decrease in auxin is caused by environmental changes associated with the change of seasons. With that in mind, I would presume that deciduous trees kept in a controlled summer-like environment that never changes would not undergo abscission.",
"This would normally be bad for them, as abscission is an adaptation to winter weather, but in a controlled constant environment, they would not be threatened by that. (Also, a cold environment would just trigger it anyway.) However, it's thought that abscission serves some other purposes, too, such as reducing insect damage (by just discarding and regrowing damaged foliage). Abscission also helps control cavitation, but that's also a seasonal problem, and in a controlled environment would presumably be less of a problem. In sum, it sounds to me as if abscission would not be necessary in a controlled environment, and so would be less likely to occur."
] |
[
"There is also a decrease in photosynthetic efficiency in foliage as it ages, which would cause problems in the long term if the light environment were held constant. This is the reason that evergreen trees, which hold their foliage for multiple growing seasons, also shed old foliage. For instance, eastern white pine foliage only lasts for about three years, on average, so the tree will shed about a third of its needles annually.",
"Trees are well adapted to balancing the cost and benefit of keeping tissues alive. This is why the lower branches of trees die off as the tree grows. At some point, the shade from higher branches will cause the photosynthetic rate of the foliage of a lower branch to decline to a point where the branch as a whole is not producing enough photosythate to support itself. Since there is no net benefit to the tree, that branch will die off.",
"While the foliage of a deciduous tree may not have necessarily declined that severely over the course of the growing season, the loss in productivity would certainly cause die off over the course of time."
] |
[
"There was a photo posted here a couple years ago that had a row of trees that were in various stages of turning color, because they stood in front of a building that blocked the evening sun at different times to the trees. Basically created an artificial difference in the amount of sun each tree got as you went down the row. The trees closest to the building were in full fall colors and those furthest were fully green. "
] |
[
"When have coral reef been wiped out and come back?"
] |
[
false
] |
[deleted]
|
[
"Importantly (and correctly) the previous poster indicated that 'reefs', not specifying a particular organism that built the reefs, have come and gone. Large reef complexes, as structures, have existed at a variety of times during Earth history, but the organisms that built them at these different times have not always been the same. A good example are the ",
"rudists",
", a now extinct type of bivalve that built reefs during the late Jurassic and Cretaceous periods and died out during the K-T extinction (i.e. the same extinction that took out the dinosaurs). In the Cambrian, ",
"Archaeocyatha",
" were reef builders. At other times, organisms that are in the same class as modern corals (i.e. ",
"Scleractinia",
") have also been reef builders throughout the Phanerozoic, e.g. ",
"Rugosa",
" or ",
"Tabulata",
". In most cases, the organisms that were dominant reef builders at some time were wiped out in an extinction, there would be some time without a dominant reef builder, and then a new class of organism would evolve to fill the ecological niche left vacant by the extinction of the last reef building organism. This is pretty analogous to what we generally see in the fossil record, i.e. organism(s) A evolve to fill a niche (i.e. live in a specific place, eat in a specific way, etc), organism(s) A get wiped out in an extinction, organism(s) B evolve to fill the niche that is now vacated, repeat."
] |
[
"Is the current alarm over the ecosystems (like the decline of the Great Barrier reef) warranted considering reef ecosystems seem to be cyclic?",
"Considering it would take millions of years to come back? Depends if you value biodiversity"
] |
[
"Is the current alarm over the ecosystems (like the decline of the Great Barrier reef) warranted considering reef ecosystems seem to be cyclic?",
"Considering it would take millions of years to come back? Depends if you value biodiversity"
] |
[
"[Physics] I have some questions abour light. How can polarizatiom, bifrigence, and transmission be explained considering the quantum nature of light?"
] |
[
false
] |
What I don't understand about polarization is how quanta of light can become elliptically polarized. My understanding is that each photon has a pair of perpendicular, transverse electro and magnetic waves [why is there the electromagnetic component? How does it interact with matter?] how does this photon become elliptically polarized? I'm reading (the wiki article on polarization)[ ] and, in the polarization state section, I'm confused about when they discuss how shifting a component of the electromagnetic wave introduces a circular polarization. Is this talking about adding photons together? I've also heard about polarizing light and then splitting it into perpendicular polarizations- how is this possible? If all the light is in one orientation and wavelength, wouldn't this split photons in two? I've done experiments where light can be polarized to a certain amount by passing through a certain length of material, and changing the length changes the orientation of polarization. How can a homogenous material 'spin' the orientation by a certain angle depending on the time light spends in it? I've also heard lay explanations of how light is coherently transmitted (as in glass) but I still don't understand. I know that light interacts with the electrons in a certain way as to slow it down- how can all of the light interact with electrons and yet all maintain coherence? Are they being absorbed and instantaneously retransmitted, or is there a different interaction? How does the electronic structure of a material exactly change how light interacts with it? Finally, I have a bonus question about snell's law, or the principle of least time. I see this explained as how light will find the shortest path between two points in materials of different refractive indices, always illustrated by thus graphic . I don't get what this graphic trys to display- light can take any path and be refracted at any angle from the starting point- this looks as if light only takes one path from the starting point, through the material. Can somebody clarify this for me?
|
[
"Perhaps a lot will be clearer if you get the ",
" nature of the measurement of light's polarization. Classically, light is a transverse electromagnetic wave. When one measures a photon's polarization it assumes a definite value, i.e. some orientation. To say that light is ",
" means that all electric field directions of every photon in a beam will have equal probability to be measured. If the light is ",
" then it can be measured in one of only two states. \"Circular polarization\" means each possible state is described by a plane waves of equal amplitude but differing in phase by 90°. If the light is \"elliptically polarized\" then it's unmeasured state is described by two simultaneous plane waves of differing amplitude related in phase by 90°. It can also be called elliptically polarized if the amplitudes of the two states are equal but the relative phase is other than 90°. So an unpolarized beam of photons say, or a single photon with a polarization at some angle relative to your measuring polarizer say, is not split into two when sent through a polarizer, rather each photon takes one path or another according to probability.",
"Concerning your next group of questions about how light propagates through dielectric solids like glass... There is only free propagation, absorption, and scattering. Scattering can be either elastic or inelastic. Scattering theory is a rich subject because materials are so diverse in composition. The most common form of scattering in isotropic media like the atmosphere and dielectric solids composed of small molecules is an elastic form of scattering called Rayleigh scattering. Rayleigh scattering occurs when a photon penetrates into a medium composed of particles whose sizes are much smaller than the wavelength of the incident photon. In this scattering process, the energy (and therefore the wavelength) of the incident photon is conserved and only its direction is changed. Rayleigh scattering has a simple classical origin: the electrons in the atoms, molecules or small particles radiate like dipole antennas when they are forced to oscillate by an applied electromagnetic field. This is not an absorption and re-emission. If the scattering sources are stationary, then this secondary radiation is phase locked to the driving electromagnetic field. So perhaps this is what you mean by \"coherent transmission\". But even for a truly coherent source of photons, from a laser say, the coherence length is shorted by the presence of the dielectric.",
"Lastly, your bonus question... You ",
" to read Richard Feynman's, ",
"QED: The Strange Theory of Light and Matter",
". Light propagates as a wave, even single photons. It therefore takes all possible paths, not just the path of least time! It's just that only those paths which arrive at the detector in phase will result in a non-zero amplitude. And for a single ray of light passing from one isotropic medium to another of different index of refraction, there is only one path that satisfies that condition, the path of least time. Anyway, you will love the book and will come away understanding light much better."
] |
[
"I can't explain the polarization of single photons, but I can try to help with the electromagnetic explanations.",
"As you said, light changes velocity when it enters a material such as glass. If all the light (from a coherent source) spends the same amount of time in the lower velocity medium, all the waves will be delayed equal amounts, so they maintain coherence (ie no relative phase shift). This can be accomplished by having a perfectly flat piece of glass. Diagram here: ",
"http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v8/0150/003f.gif",
"Now birefringent materials slow down light, but they do so differently depending on the polarization. Birefringent materials have a \"fast axis\" and a \"slow axis\", which are exactly what they sound like. If light is polarized parallel to the fast axis it moves faster through the material than light polarized parallel to the slow axis. Take a coherent light source polarized at 45 degrees relative to the fast axis of a birefringent crystal. Since were talking about waves, a 45 degree wave can be explained as the sum of two equal components, one parallel to the fast axis (vertical) and one perpendicular (horizontal). When this wave encounters the material the two components are now traveling at different velocities. This causes a phase shift between the horizontal and vertical components, and the degree of phase shift will depend on how long they spend in the material (ie how thick the material is). If the phase shift is exactly one quarter period, this results in circularly polarized light. Different types of optics are designed to have different phase shifts ",
"https://en.wikipedia.org/wiki/Waveplate",
"You can play around with polarization mathematically with 3d plots. Plot (x, sin(x), sin(x)) to get a 45 degree wave. If you apply different phase shifts to either the y or z components, you can see what the resulting wave would look like. For example, you can get circularly polarized light with (x, sin(x), sin(x+pi/2)). You can also get different angles by changing the relative amplitudes of the horizontal and vertical components, ie (x, sin(x), 2sin(x)).",
"Not sure if any of this answers your actual question, but I hope it helped."
] |
[
"how does this photon become elliptically polarized?",
" ",
"Is this talking about adding photons together? I've also heard about polarizing light and then splitting it into perpendicular polarizations- how is this possible? If all the light is in one orientation and wavelength, wouldn't this split photons in two?",
"It doesn't. Photons are \"circular polarized\", that is they have left or right hand spin. Massive amounts of photons add up to behave like classical EM waves, the photons are just small chunks of the net field with the same properties. All the photons don't share the same polarization as the field. ",
"Also, the photon count is not defined, there is an inherent uncertainty to it. You can't keep track of say 1,000,000 going in and then 1,000,001 coming out and conclude that one was split, and that has nothing to do with our measurement technology. ",
" ",
"As for polarization and the various types, consider it like this. Forget about the magnetic field for a second. The electric field can either oscillate up and down, or left and right. The amount it can oscillate in either can be of different magnitude and phase. If we have no vertical and just horizontal, we have horizontally linear polarized light. If we have equal magnitudes vertically and horizontally and in phase, we get it oscillating linearly at 45 degrees. If we have equal magnitudes vertically and horizontally but they are 90 degrees out of phase (quarter cycle), we get circular polarized light. The net electric field has a fixed magnitude and just rotates, which should come as obvious if you have dealt with the unit circle and it's relation to cosine and sine (90 shifted sinusoids) of equal magnitudes forming it. If we swap the phases, we get circular polarized light spinning the other way. If we have some other combination other than these perfect examples, we get an ellipse. Circle and line just being special cases of ellipses really. ",
"I'm confused about when they discuss how shifting a component of the electromagnetic wave introduces a circular polarization",
"Consider what i just said. If we have linear light, but then we but it through a material with some sort of asymmetry structure between vertical and horizontal that just shifts the horizontal component, the result is going end up as a circle, or at least an ellipse. The length can be a factor as it determines how much one component is delayed. ",
"I've also heard lay explanations of how light is coherently transmitted (as in glass) but I still don't understand. I know that light interacts with the electrons in a certain way as to slow it down- how can all of the light interact with electrons and yet all maintain coherence? Are they being absorbed and instantaneously retransmitted, or is there a different interaction? How does the electronic structure of a material exactly change how light interacts with it?",
"The original wave remains in tact. The material, depending on it's electronic structure, reacts to the field and emits a secondary wave. Interference results in a net wave of shorter wavelength and the same frequency with a lower phase velocity. The electronic structure dictates how much interaction the electrons have. ",
"Coherency is maintained because the material is uniform, there is the same relative permeability as just a simple positive scalar all through out. If you had impurities or defects, you get scattering. If you have a more complex relative permeability with a complex value, imaginary value, tensor, etc. you get more complex effects that just perfect refracted transmittance. ",
"the principle of least time",
"You confusion is that you are missing the fact that the start and end points are defined. Yes, the light can go anywhere, but this principle is about the path from A to B and only the path from A to B. If you define points A and B with a medium interface in-between, and then draw any path you want, the shortest one will be the one obeying Snell's law. The direct path isn't the fastest, as it spends to long in the slow medium. The going straight to the interface through the slow medium isn't that fastest as it makes the path too long. Doing a zig zag on the way there isn't the fastest as it makes the path longer. Snell's law is the fastest way between A and B, out of all the impossible paths that some fictitious light could have taken. It has nothing to do with the light choosing anything or restricting it to only ending in one spot. "
] |
[
"What's a viable energy source you know about that most people aren't aware of?"
] |
[
false
] |
It seems we've all heard something about solar, wind, nuclear, biofuels, algae, petroleum, geothermal, and hydrogen. Do you know any other energy-dense materials/processes (e.g. , lightning, non-negligible forms of human power) that might have promise - if not now, then perhaps in the next few decades?
|
[
"Thorium nuclear power, and molten salt reactors in general. The current generation of nuclear power is dead, but most people know nothing about the next generation."
] |
[
"You know what I know about that most people aren't aware of? The fact that we cannot harness \"zero-point energy\" for anything, or at least, anything useful. And that all the people claiming to do so either want lots of attention or lots of your money.",
"So... beware of those guys. Seriously. "
] |
[
"no, by its definition it's not useful. Think about it, how can you extract energy from something that is defined to be in its lowest energy state. I know people like to think the way you do, but there ",
" impossible things in the universe, and we've learned a lot about them over time."
] |
[
"Light is usually presented as traveling, ie the speed of light or how it is propelled out of a flashlight. What is the force that moves light?"
] |
[
false
] |
Basically I want to know what causes light to travel in the first place. Is it just inherently in motion, or is there an external force that causes it to move?
|
[
"Yes, momentum is a fundamental property of photons (like all particles). The momentum of a photon is h/λ where h is Planck's constant and λ is the wavelength of the photon. ",
"A force is actually something that ",
" momentum, so no force is needed for something to keep going with the same momentum."
] |
[
"Also, keep in mind that unlike a gun, in which a bullet has mass, and thus inertia, and began at rest, the photons coming out of your flashlight have no mass, and therefore always travel at the speed of light. The \"push\" comes from the electricity that excites the filament causing the electrons to jump energy states and release photons."
] |
[
"Thanks to both of you. After posting I got to thinking that it was something fundamental regarding photons but this clears up the fog for me "
] |
[
"Do viruses become resistant to natural human antibodies similar to antibiotics? If so, wouldn't bacteria eventually become superbugs no matter if we use antibiotics or not?"
] |
[
false
] |
Also if we someday manage to build micro/nano robots that can destroy bacteria using laser or something similar, could bacteria evolve and become resistant to that as well?
|
[
"Quick point first, you seem to be conflating bacteria and viruses. Those are ",
" different things. You have more in common with a tree than a bacteria does with a virus. Antibodies and antibiotics are also very very different, and don't really have anything in common beyond a similar name.",
"But to answer the question in your title: things cannot really become resistant to the antibodies in our body, for a few reasons. First, our antibodies are more or less randomly generated, and unique to each person (I can go into more detail here if you want). So if some virus was \"resistant\" to the antibodies of one person, that wouldn't necessarily help it against anyone else. Second, unlike with antibiotics, the antibodies don't actually kill anything, they \"just\" make it easier for other parts of our immune system to find and combat whatever is infecting us.",
"So how our immune system works doesn't have that much to do with so-called \"super-bugs\". Their emergence is near entirely due to how we have been using (and over-using) antibiotics.",
"Minor edit: on your question about bacteria killing nanorobots. It very much depends on how those robots work. If they release chemicals or something, there might be resistance to that. Or maybe not, depending on the chemical. Other methods might be better, for instance pretty much nothing can survive being boiled. But I'm probably out of my depths, with these future killer machines :)"
] |
[
"\" First, our antibodies are more or less randomly generated, and unique to each person (I can go into more detail here if you want).\"",
"Please do.",
"\"So if some virus was \"resistant\" to the antibodies of one person, that wouldn't necessarily help it against anyone else.\"",
"If this was the case then how would you explain say, an IV immunoglobulin resistant pathogen?"
] |
[
"Yikes, got called on it. Better find me some textbooks :)",
"It seems I spoke too rashly before. Your question on IV immunoglobulin resistant pathogens is rather puzzling, I dont have a good answer. ",
"Antibodies are proteins that are more or less \"Y-shaped\". The stem is one of a few different types, and determines which \"type\" of antibody it is, but this stem doesnt really vary much. The interesting part is in the \"head\" of the Y, which is the part meant to attach to the bacteria, or virus, or whatever else that's present in your body that shouldn't be there.",
"When creating the antibody, the antibody producing cell has a repertoire of a bunch of different small DNA fragments that each code for some specific string of amino acids. These DNA fragments are shuffled, and stiched together. This gives a rather large amount of possibilities for distinct antibodies. So the heads of the antibodies are not completely random, and they are put together by a distinct set of different short chains, but there are a LOT of different possible combinations. While these antibodies may not be completely unique as I previously claimed, theres a lot more different ways antibodies can look than there are humans, and for any given bacteria/virus/whatever, there are a lot of different ways to make antibodies that will stick to them.",
"So when these antibodies are made, they're released into the body. If one of them, pretty much just by chance, happens to stick something, another cell comes to check what it stuck to. If it was some part of your body, thats supposed to be there, that particular antibody gets scraped (and if this process fucks up, you've got an auto-immune disease on your hands). If it sticks to something that ",
" be there, the antibody starts getting mass produced, the \"blueprint\" for it gets archived, and your body goes nuts on whatever is invading.",
"I think that more or less covers it. Hope I made some sense :)"
] |
[
"Do cats or dogs ever kill large birds of prey?"
] |
[
false
] |
I know the opposite happens, but I can't find any incidents of pets killing large birds iof prey. Is this known to happen? Are there any predators that are likely to go after predatory birds?
|
[
"All large birds of prey are vulnerable to predators when they are on the ground, but there aren't any animals that actively hunt them. As eggs and nestlings, they are very vulnerable if a parent is not on the nest."
] |
[
"The fact that birds of prey can fly away and make very fast escapes means that anomalies like the ones you're thinking about are very rare because of the way that the two don't really cross paths as often as the others do, for example if a bird of prey ever lands on the ground it isn't for very long, And dogs and cats won't actively hunt them due to their sheer size."
] |
[
"Yes I'm aware of that, but I'm interested in these types of anomalies, and recorded instances of such. For example, jaguars have been seen killing and eating crocodiles, wildebeest killing lions, falcons mobbed and killed by gulls etc. Certain breeds of dogs were originally bred to be able to protect cattle against predators for example."
] |
[
"Are there any significant instinctual behaviors in humans, aside maybe from language? Like; moles dig, birds build nests, bears den & hibernate, etc."
] |
[
false
] |
So many animals have instinctual behaviors that are universal to their species, but don't seem learned or passed down. Like bird species that build particular shape nests, beavers make dams, or animals that burrow or migrate, etc. And the animals obviously have no idea why they do those things. Is there an equivalent in humans? The only thing that come to mind really is language; our brains seem built for it and crave communication. But it's not like we are driven to build nests without knowing why. Maybe some parenting instincts, or fear of the unknown perhaps? Not sure if I have sufficiently stated the intent of my question, but thanks for considering it.
|
[
"Sucking on a nipple."
] |
[
"fucking"
] |
[
"Humans instinctively build themselves into social hierarchies. When you look at it, most of human interaction is based on either figuring out where you stand or in increasing your stature. ",
"We also instinctively categorize things. This is more a function of our cognitive processing, but it happens. ",
"We instinctively recoil from dead things, but crave things with a high energy content (sugars). ",
"We do lots of things instinctively."
] |
[
"If the earth isn't a complete sphere, are their certain points on earth where gravity is actually pulling at a slight angle and not directly down?"
] |
[
false
] | null |
[
"Don't we usually define \"straight down\" to be the direction in which gravity points? "
] |
[
"One of the motivators of the ",
"Cavendish experiment",
" was the survey of the Mason-Dixon line. The surveyors found a small systematic error that they couldn't quite eliminate. As it turned out, their plumb-bobs weren't quite pointing perpendicular to the reference ellipsoid because of the existence of the Allegheny Mountains. This meant their instruments weren't level and were giving them bad angles between their reference points. Knowing the density of the Earth would have allowed them to correct for that error. Hence, the Cavendish experiment to weigh the Earth.",
"Another fascinating Survey was the Great Survey of India. It's amazing what contributions surveyors gave to science. It's hard to imagine today how important those efforts were and how precisely they were able to measure the world."
] |
[
"By \"straight down\", I believe he means perpendicular to the surface of the Earth."
] |
[
"Why is North America and Europe largely void of native marsupials like sweet Platypuae or awesome koalas/kangaroo?"
] |
[
false
] |
I know there are a few marsupials native to NA and Europe, and I've heard of some kangaroos in some French forest, but why are all the sweet animals in Australia?
|
[
"Basically it has to do with continental drift and the isolation of Australia (and South America). South America eventually became connected to North America which resulted in placental mammals migrating and taking over niches there. Australia is still isolated and therefore the marsupials have been relatively left alone. ",
"UC Berkeley has a good webpage on the subject: ",
"http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html"
] |
[
"I sort of asked the opposite question a while ago here: ",
"http://www.reddit.com/r/askscience/comments/jvtiz/why_were_rabbits_so_invasive_in_australia/"
] |
[
"Came here to show the same link from Berkeley! Its pretty crazy how it managed to isolate one type of animal.\nAlso if you want to learn about a really cool marsupial is Australia check out the honey possum.",
"http://en.wikipedia.org/wiki/Honey_possum"
] |
[
"Is the DNA in one cell the same as the DNA in all of my other cells?"
] |
[
false
] |
[deleted]
|
[
"Central dogma is that yes. Every cell in your body (with the exception of your sex cells, as they are haploid containing a random 50% of your DNA) carries the same DNA. This is your \"germ line\". At the high school or even undergraduate level, this is probably the extent of what will be covered.",
"By and large, the above is true, however the always more complicated \"real life biology\" has exceptions to that rule.",
"Every time your cells duplicate and divide, there is a risk of an error. These are somatic mutations. ",
"The somatic mutation rate in the early development ranges between 3.13 x 10",
" and 1.20 x 10",
" per nucleotide per cell division which leads to the estimate that each individual carries, on the average, approximately 359 post-zygotic mutations",
". These are random, and largely go undetected. Somatic mutations continue to occur throughout your lifetime in every cell type that undergoes division. It is typically ",
"somatic mutations that lead to cancer",
".",
"There are also the \"special cases\" in your immune cells (T cells), where the ",
"immunoglobulin genes rearrange into unique and diverse configurations during cell maturation",
". And mature red blood cells contain no DNA at all, as the nucleus is degraded and removed in order to make more space for hemoglobin (i.e. oxygen to be carried to your tissues)."
] |
[
"It has long been thought that the DNA is the same, albeit with epigenetic variations that allow for differential expression of parts of the DNA. But recent evidence is beginning to show that different cells can have different DNA.",
"This",
" study looked at a specific gene, BAK1, in relation to a specific health condition. What they found is that some cases of the allele responsible were seen in aortic tissue for healthy and affected individuals, while the same allele was not found in blood samples.",
"Another",
" study found that skin cells can have different DNA, after analyzing cells grown for a few years. Although the skin cells are very, very, similar, as many as 30% were found to have Copy Number Variations (CNVs), which are pieces of deleted or duplicated DNA that are attributed to errors in mitosis."
] |
[
"Generally it's the same DNA in each of your cells, directly copied with each cell division since you were a single cell. There's a few exceptions, where a cell may not have exactly the same DNA as the rest:"
] |
[
"Can you cool yourself quicker by breathing cold air vs drinking cold water?"
] |
[
false
] |
[deleted]
|
[
"I am reposting this as a top level comment as it seems to address your question more directly than as a simple retort to others.",
"First take the tidal lung volume as 0.5L. According to wolfram alpha the mass of a half liter of air is 0.64 grams and obviously the mass of a half liter of water is 500 grams. So take the difference between their heat capacities as 4 (as others stated) and let's set per breath the equivalent amount of water at the same temp required is about 0.003.",
"Now then if we take 12 breaths per minute it only takes 4h to reach equilibrium. It is relatively easy from here to see how slight difference would effect the overall result.",
"Assumptions are that the water consumed and air inhaled are both the same temperature. It is also assumed that full heat equilibrium is achieved each breath."
] |
[
"for me, if I see 4 vs seeing 1 in a back of the envelope calculation...I'd call them both 1. Pi is approximately 1 in back of the envelope calcs if you're looking at orders of magnitude. I'm not going to be discussing order of mag calculations anymore in this thread, it's digressed off topic and really doesn't matter"
] |
[
"I don't understand what you mean by cool yourself.",
"Are we talking about your internal temperature(as in a fever) or are we talking about the fact that you feel markedly warm from exercise or the like?",
"I'm not even sure I can properly answer this for you, but I can prevent some of the false information that's coming out from being taken as fact."
] |
[
"Has VY Canis Majoris become a BlackHole \"in earth time\"? Would this be the closest BlackHole to earth?"
] |
[
false
] | null |
[
"Has VY Canis Majoris become a BlackHole \"in earth time\"?",
"Doubtful. It's only 4000 lys away, which is still a short amount of time for stellar evolution even for massive stars. ",
"Would this be the closest BlackHole to earth?",
"No. A0620-00 is closer to Earth"
] |
[
"a. Theres no evidence of it. So the best bet is 'no'. Theres little point in trying to guess the state of things that are effectively completely out of ability to determine. From our personal frame of reference it hasnt happened yet. Its still to occur in the future.",
"Not sure about the distance..."
] |
[
"We can't tell and the answer is probably no.",
"However, one more point that is related: When two events occur close enough in time that light hasn't had time to get from one to the other, relativity doesn't allow you to order them.",
"So for instance, New Horizons is about 5 light hours from Earth now, and I'm typing at 4.30pm my time. A message sent from Earth at 2am would have been received at (about) 7am and an immediate reply got to Earth at (about) noon.",
"To an observer on Earth, a message sent at 10am my time should have arrived at New Horizons at 3pm, 90 minutes ago. We might say that the clock ticking 3pm and the message reaching New Horizons were simultaneous events.",
"BUT - to an observer in a different reference frame, these two events may not be simultaneous at all. They may consider my clock ticking noon to be simultaneous to the message being received.",
"Relativity states both are equally correct and simultaneity is meaningless.",
"As such ",
" we detect light of that star becoming a black hole (4000 years ago) we cannot say it is one now, as there are frames of reference in which it is not."
] |
[
"If you get electronics wet, after the water evaporates, why doesn't the electronics return to normal?"
] |
[
false
] |
Does water blow up electronic circuits or something? I don't seem to understand how by simply for water and electronic devices to make contact it will affect the little metal pieces that intertwine.
|
[
"It's not the water itself, distilled water isn't a good conductor. But tap water or rain water consists of enough salts to conduct electricty up to the level damaging it.",
"That said, getting electronics damaged happens mostly due to shortcuts in powered electronics. If there is no power source peresent, most electronics will work again if cleaned properly before powering up again."
] |
[
"Often, there are minerals in the fluid that do not evaporate. These can often cause electrical components to short or damage them in another way. Fluids are especially good at delivering their solvents into hard to reach places, and those places on, say, a circuit board, are not always happy when there are foreign minerals invading their components."
] |
[
"Does this mean that some problems can be remedied by rinsing with DI/distilled water?"
] |
[
"Solving world hunger with enzymes? Why not?"
] |
[
false
] |
We have pills which give us enzymes, such as lactase, which allow us to digest certain sugars, such as lactose in dairy. Why then is it that we cannot make a pill for cellulase, enabling people to digest the cellulose in plants and possible solving world hunger? Does it have anything to do with the fact that it is never found naturally in the human body?
|
[
"Because world hunger is not a food problem. ",
"It's a problem of delivery. Most of starving people and people who don't get enough nutrients, live in unreachable areas. Those areas can be unreachable due to natural caused (common in SE Asia, due to rainy season, etc.) or due to man-made problems (wars, other conflicts).",
"The reason scientists want to introduce Golden Rice in south east Asia countries (rice with Provitamin A) is because these areas are unreachable for most of the year, there is no where to keep food (it would be spoiled), etc. and not because we want to poison poor children with GM rice."
] |
[
"Animals that digest cellulose aren't relying on just one enzyme.",
"They have very complex bacterial cultures, often distributed over a much longer intestinal tract, to pull off this feat.",
"Even so, many of them do a mediocre job: cows, for example, produce mass amounts of methane (which means untapped energy, not just greenhouse gases)",
"If you think about it, livestock is a very old way of turning cellulose into human-suitable nutrition. It allows us to use a lot more of the plant matter we grow (well, in today's industrial farming, things are different) for nutrients."
] |
[
"The point he is trying to make:",
"Because world hunger is not a food problem.\nIt's a problem of delivery.",
"What you just said:",
"world hunger would be solved. We would not need any mass transportation of food.",
"So you both agree the problem is delivery. Where is he wrong?"
] |
[
"What causes the noise from speakers when you touch a speaker cable?"
] |
[
false
] |
Just using the end of an aux cable here
|
[
"Mainly how sweaty your skin is, and how tightly you grip (to a point). "
] |
[
"Do you mean that you have an Aux cable plugged into the amp, and when you touch the free end you get noise? ",
"Your body has various properties that are electrical (but have nothing to do with the electrical nerve impulses). You are a conductor of electricity, but a very poor one. Your body has capacitance (the ability to store electrical potential or charge). It has a very small inductance. But probably the most important one for this issue is that your body acts like an antenna. ",
"You are constantly picking up radio waves (and other electromagnetic waves) from the environment. Probably the largest of these is the \"60 cycle hum\" from power lines (in the USA; 50 cycle some places). If you were to grab an oscilloscope (a device for measuring electronic waveforms) you'd probably see that you have a fairly large 60 Hertz signal going through your body all the time, which you pick up from power lines in your house. An amplifier can pick this up and amplify it, along with its \"overtones\" (multiples of 60), making a hum. "
] |
[
"Oh ok, I get it, thanks :) What sort of factors affect our conductance? Because having another person touch the cord provided a deeper sound. "
] |
[
"Why do rubber bands deteriorate the way they do?"
] |
[
false
] |
I'm sure you've encountered decades-old rubber bands that have become crusty and friable. I came across one that was almost completely "caked" onto an old set of engineering plans. So, what's behind this transformation?
|
[
"Strain crystallization",
" would be be primary guess. Rubber remains, well, rubbery because the polymer chains are unable to align. By applying stress, the polymer chains are able to crystallize over time making the rubber brittle.",
"Rubber bands are made from natural rubber which is primarily poly-isoprene. This polymer contains double bonds which are able to be oxidized. Over time, this breaks down the polymer chains themselves.",
"So there you have it: the rubber itself is slowly chemically degraded, and a stretched rubber band will slowly embrittle due to crystallization."
] |
[
"My guess (not an organic chemist) is oxidative damage. Rubber is just a polymer of organic compounds in such a structure to make it stretchy, but many organic molecules will degrade from oxidation as bonds are broken and structure falls apart."
] |
[
"It doesn't necessary have to have a 'springy structure' at the molecular scale to have the elasticity. If it consists of little strings at the molecular scale, thermal motions push at the sides, making the strings wanted to be curled up to a degree. These pushes at the side effectively try to pull inward when the little wires are forced to be straighter.",
"(edit: no expert on topic, just one mechanism)The strength of the force can be estimated by estimating the size of the phase space(how many speeds and positions it could in principle take) as dependent on energy and position Ω(E,x), if one can write that as Ω(E,x) = Φ(E)θ(x), then a potential V corresponds to θ(x)=exp(2V/τ). See ",
"here",
" for an outline for the derivation. Put simply, you can relate the 'jiggle room' of the strings depending on the coerced length and temperature to get the effective potential.",
"Strain crystallization, as etothepixi mentions fits as a way this process wouldn't work anymore, it suggests things aren't mobile anymore."
] |
[
"Mood effects from binaural sound?"
] |
[
false
] |
I've been hearing for a number of years about this "phenomenon". Sites and products such as I-Doser insist that these effects are real, and have no problem charging you insane amounts for the "doses" (up to 200 bucks for a SUPER SECRET ONE! ) My question to you, is ANY of this close to legitimate or scientifically proven or is it just teenagers listening to static that's really a big fat placebo?
|
[
"I will try the mp3 (if I still have it) on my current girlfriend tonight and report back. FOR SCIENCE.",
"EDIT: Mission failure. Girlfriend hereafter known as #2 lasted about 3 minutes before giggling uncontrollably while ripping off the headphones and asking me what in the world was I making her listen to.",
"After a brief explanation #2 was willing to try again at a later date."
] |
[
"It's been discussed before, ",
" though I don't believe there is a good scientific consensus. We know that some frequencies impact EEG recordings, but we don't yet understand whether or not it has any implication on mood (other than anecdotes of course). "
] |
[
"This would be a lot easier to judge if any of their research were published. Since it's all for-profit, I doubt we'll see any of the research any time soon (if ever). "
] |
[
"Is Gibbs energy of activation same as Activation Energy?"
] |
[
false
] |
I am solving a problem involving calculation of the activation energy of the and I've read that to calculate that, I need to add the of the reaction and the activation energy. In the problem, the Gibbs energy of activation was given instead of the activation energy.
|
[
"Activation energy usually refers to the change in internal energy required to overcome a barrier where as the free energy of activation is the activation energy plus the entropy term.",
"Seems like a poorly worded problem."
] |
[
"In this case it's the same thing.",
"",
"We normally refer to the Gibbs Free Energy of a system (maximum work a system can do at constant pressure and temperature) to differentiate it from the Helmholtz Free Energy (maximum work the system can do at a constant volume and temperature). Most chemistry work is done using Gibbs thermodynamic systems because that's the type of system we can work in: it can exchange heat but not mass and the system volume changes to keep the pressure constant. A beaker of liquid is a basic example of this. Once you've defined the thermodynamic system, referring to the Gibbs Activation is kind of redundant.",
"The Gibbs and Helmoltz Activation Enthalpies are actually the same for a lot of homogeneous reactions in the liquid state, since its the sum of the enthalpy change and change in pressure multiplied by the change in volume. Significant differences arise for heterogeneous reactions and homogeneous gas phase reactions."
] |
[
"i thought of it because when transforming the arrhenius equation, an activation energy explicit form will give you Ea = -RTln(K/A) which looks like the change of gibbs energy interpretation."
] |
[
"What stops the gravity-wave-measuring laser beam from being influenced by the gravity wave?"
] |
[
false
] |
Therefore, if a gravitational wave passed through a detector such as LIGO, presumably it would affect the structure and the light equally. The LIGO structures might contract, but the laser beam would also be bent, resulting in no effective change to the behaviour of the laser beam. To put it another way, if spacetime is represented by a sheet of grid paper, with the gravitational wave detection laser travelling 10 grid spaces and back again, then it doesn't matter whether you curve, bend or scrunch the paper up into a ball - the "laser" still has 10 grid spaces to travel so it wouldn't detect the changing of the paper's structure. Is this reasoning correct? I don't understand how you would be able to use a laser to detect gravitational waves if the waves would influence the laser beam in such a way as to cancel out any change it may otherwise have measured. Note that I am assuming gravitational waves distort spacetime, leaving the distance between atoms unchanged, rather than placing actual pressure on objects and making the atoms temporarily move closer together. If gravitational waves caused atoms to move closer together then presumably you could detect them the same way you detect any other pressure wave (e.g. increase in heat due to friction, piezoelectric effect, etc.) But of course if gravitational waves don't cause atoms to move closer together then the distance between atoms will be the same, so of course the distance the laser light must travel would also remain the same, leading to no detection of the wave. What am I missing?
|
[
"the \"laser\" still has 10 grid spaces to travel so it wouldn't detect the changing of the paper's structure.\nNote that I am assuming gravitational waves distort spacetime, leaving the distance between atoms unchanged, rather than placing actual pressure on objects and making the atoms temporarily move closer together.",
"I think I understand your image, which is one of the piece of paper just warping but the grid points being spaced the same. In reality, you do get a net stretching or compressing of spacetime, visualized in ",
"this image",
", where you can see the grid points, represented by the circles, changing size drastically. So, the path length will actually change, and the time between laser pulses will vary. ",
"If gravitational waves caused atoms to move closer together then presumably you could detect them the same way you detect any other pressure wave",
"Pressure waves require a medium, e.g. sound waves are air molecules bouncing back and forth. The gravitational waves are part of spacetime, so the only way you can perform experiments is by sticking \"test masses\" in it and seeing how they move. ",
"The biggest problem is that the waves are very, very weak. In the LIGO band, you expect something like a ΔL/L ~ 1e-21 shift, or lower, at a gravitational wave frequency of 1-10000 Hz range. That means that the 4 km length of LIGO shifts by 4e-18 m, which is much, much smaller than the width of a proton. Pulsar timing experiments have a ΔL/L ~ 1e-15 over the 1e-9 to 1e-6 Hz frequency range or so, which amounts to path length changes of tens of meters over thousands of lightyears."
] |
[
"So in other words what you're saying is, the paper is temporarily having more grid spaces inserted (crammed, if you will) into it so that two points that were 10 grid spaces apart are now 11 grid spaces apart (then shortly afterwards only 9 grid spaces apart, and so on), and you can measure the distance (since 11 > 10), right?",
"Doesn't this imply that gravitational waves will literally stretch and squeeze matter, causing a tiny amount of heat to be produced? If so, given the distance these waves travel, that would require an enormous amount of energy heating that much matter even if only by a small amount.",
"Presumably then a gravitational wave that has travelled through a star would be weaker than one that has only travelled through empty space, as the one that went through a star as used up some of its energy stretching and squeezing all the matter in the star?"
] |
[
"I did my MS research for LIGO and I think the easiest way to address what you're talking about is to discuss how a gravitational wave interacts with the test masses (mirrors) of the LIGO interferometers.",
"Remember, an interferometer doesn't tell you how far light has traveled, it tells you about the ",
" between two paths. This is a key distinction, a Michelson interferometer like those used in LIGO (or really any interferometer for that matter) tells you about the ",
" in length between the two arms.",
"Keeping that in mind, a gravitational wave (GW) is a quadrupole wave, which means that it expands space-time in one direction, while ",
" in the orthogonal direction. Since the LIGO detector arms are at 90 degrees relative to one another, this means that in the presence of a passing GW, one arm will grow and the other will shrink. This means that it doesn't matter how the gravitational wave distorts the path light takes along ",
" arm, since each arm will be perturbed in a different direction (one contracted, the other expanded).",
"Hope this clears things up a bit.",
"If gravitational waves caused atoms to move closer together",
"I believe ",
"Weber Bars",
" do exactly this."
] |
[
"How does a wax candle burn"
] |
[
false
] |
I know that the flame causes the wax to melt, and capillary action causes the now liquid wax to move up the wick, protecting it from the flame, and the wax is then vaporized and used as fuel, but what actually happens to the gaseous wax? Why does it produce the light and heat associated with a flame?
|
[
"This is an odd question. I hope my chemical background is enough to give you the answer you want.",
"Candle wax is usually just a mixture of hydrocarbons in the C20-C40 carbon range. They're really simple molecules. They're waxy because of the length of the molecules. If they were shorter, they'd be liquid (C8 is octane, the main component of gasoline). Longer and they'd be more solid. You get the idea.",
"Anyway, hopefully the similarity to gasoline makes it more obvious why the waxes burn. It's pretty much that same reaction in both cases.",
"Oxygen from the air meets the wax at high temperature, and the reaction produces CO2 and H2O, which escape as gasses. CO2 and H2O have lower energy levels than the wax molecules, so the reaction gives off heat and light (since energy must be conserved). There is no \"gaseous wax\" since it's converted to CO2 and H2O.",
"I hope this explains it. Feel free to ask for clarification. Most chemistry textbooks will have good explanations of combustion, if you need a source."
] |
[
"Technically, the wax combusts in gas phase, it is liquefied, drawn into the wick, vaporized, and combusts as a vapor. The smoke will contain CO2, CO, H2O, and various unburned hydrocarbons. "
] |
[
"Yup. Most of the light actually comes from incandescent soot, too. Because waxes are largeish molecules, they tend to burn incompletely - the hydrogen gets stripped off easily, and then the carbon backbones tends to agglomerate to form soot - these particles are then heated by the flame and emit light due to blackbody radiation. The soot continues to oxidize and mostly burns off toward the top of the flame zone unless the flame is externally cooled (which is why the flame gets sooty when it gets blown around)."
] |
[
"Why can't I use lenses to make something hotter than the source itself?"
] |
[
false
] |
I was reading What If? from xkcd when I stumbled on It says it is impossible to burn something using moonlight because the source (Moon) is not hot enough to start a fire. Why?
|
[
"When the single point is hotter than the source, it starts radiating light back at the source. A lens is a passive device, remember - it takes no energy to operate, so the light must flow equally in both directions. If you heat something with a magnifying glass under the sun until it's as hot as the sun, it starts glowing with the same temperature and now sends an equal amount of heat ",
". Similarly, if you used a magnifying glass to heat something with the light of the moon, as soon as the thing you were heating is hotter than the moon, it reflects the same amount of energy back at the moon."
] |
[
"Some users, like ",
"u/Jake0024",
", make the correct argument from thermodynamics that heat travels from hot to cold. What is unsatisfying about this argument is that it goes against our intuition about how lenses work. After all, can't we just focus an image of the moon down to an arbitrarily small size? And the smaller we make it, the more concentrated the light gets and the hotter it can heat something up. ",
"The problem with this intuitive argument is that the simple lens equation we were taught in high school or college is a lie. Or rather, it is an approximation for small angles. For a lens that takes an object at position o and focuses it to an image at position i, the magnification is supposed to be M=i/o. So just get a shorter focal length and i will get arbitrarily small, right?",
"But this approximation for the magnification comes from the conservation of ",
"etendue",
". Here is a simplified version of how it works: If the lens has a radius r, then we can define an angle theta_o=arcsin(r/o) and an angle theta_i=arcsin(r/i) on each side of the lens. The conservation of etendue tells us the magnification will be:",
"M=theta_o/theta_i",
"In the small angle approximation arcsin(x)=x, so this reduces to the formula we learned in school. But when you try to really focus the image down to a small spot, you won't be able to use the small angle approximation on the image side - the image sits very close to the lens now. And theta_i can't get any bigger than π/2. So we get:",
"M=2*theta_o/π",
"Since the moon is far from the lens, we can justify a small angle approximation there and write:",
"M=2*r/(π*o)",
"So the magnification is actually proportional to the diameter of the lens (2*r) in this limit of a highly focused beam. Aha, so we can still focus the moon down to an arbitrarily small spot! Unfortunately, the total light collected by the lens is proportional to its diameter squared. So a tightly focused image of the moon has the same intensity per square meter, whether it is created by a giant lens or a tiny one. It turns out this limit is equal to the intensity per square meter at the surface of the moon. Therefore, the moon can't heat things up any hotter than they would get sitting on the surface of the moon.",
" If you move past the small angle approximation you learned in school, you find there is a limit to how small you make your image of the moon. This prevents you from using moonlight/sunlight/etc for reaching arbitrarily high temperatures with passive optics.",
" A single mode laser behaves as if the light is coming from a point source, so you can focus laser light down to very small spots and heat things up to arbitrarily high temperatures. This doesn't violate thermodynamics either, because lasers effectively have a ",
"negative temperature",
" that can transfer heat to any positive temperature system."
] |
[
"This thread has a large number of responses simply restating passages from the link in the original post, low-effort assertions of fact, speculating on causes, or giving anecdotes, which have been removed. Please keep top-level comments to detailed, expert explanations of ",
" this phenomenon does or does not occur."
] |
[
"Can mosquitos spread COVID-19?"
] |
[
false
] | null |
[
"Very unlikely. This is a respiratory virus, and the levels of viremia are much too low for any arthropod vector (mosquitoes, biting flies, gnats, etc) to ingest enough to carry an infection mechanically or biologically. More to the point, none of the coronaviruses that I'm familiar with have insects as biologic vectors (meaning the viruses are not capable of replicating in insect cells).",
"Closest you'd come is if someone coughed heavily on a mosquito and then you snorted that mosquito up your nose."
] |
[
"Extremelly, extremelly unlikely. For the same reason mosquitoes do not spread HIV. The vast majority of mosquito borne diseases are not transmitted by the mosquito injecting infected blood from one person to another, the viruses actually have to infect the mosquitoes. That's why dengue, zika, chikungunya tests in mosquitoes most of the times target the salivary glands of the mosquitoes (yes), because that's where those viruses replicate in the mosquitoes. Mosquitoes then inoculate anti-coagulant substances when feeding, and those anti-coagulant substances are present on mosquitoes saliva, only then are the viruses inoculated in a new host. Thus, as HIV, if coronavirus does not infect the mosquito and does not migrate to it's salivary gland, the they very, very likely do not spread COVID."
] |
[
"This is a majority of the answer. Typically mosquito borne diseases are spread through blood(obviously). So you’re not going to catch anything with respiratory or digestive from them. ",
"On top of that, for a mosquito to vector a disease it has to be able to survive in the mosquitos own digestive tract. Not just “a” mosquito either, most of the time a virus is only capable of surviving in certain mosquito species. ",
"Lastly, most mosquito borne diseases aren’t viral. Usually a “larger” form of parasite.",
"It’s been a while since I’ve learned this, so feel free to fact check."
] |
[
"What are goat's pupils horizontal? What purpose do they serve?"
] |
[
false
] | null |
[
"Their predators are almost never attacking from above or beneath them. Natural selection has made detection of movement on the the same plane high priority. The same goes for deer and many prey animals. The shape of the pupil gives them a sort of panoramic view of their surroundings so they can see what is important."
] |
[
"Follow up question. Why are octopus pupils horizontal?"
] |
[
"I did some sleuthing and found ",
"this",
". It says:",
"The narrower the pupil in relation to the horizon, the greater the accuracy of depth perception is in the peripheral vision of the animal. The perception of depth must be considered with these animals who spend their time evading predators in a rugged terrain.",
"This makes more sense to me. Prey animals get their big field of view by having their eyes on the sides of their head."
] |
[
"Why does soap lather better in hot water? What kind of chemical reaction is going on?"
] |
[
false
] |
[deleted]
|
[
"Solubility is dependent on temperature, so at a higher temperature more soap can dissolve. A quick ",
"google",
" can give you a lot of information.",
"No chemical reactions take place when dissolving soap in water, it is a physical process."
] |
[
"Also for more info check this page: en.Wikipedia.org/wiki/hard_water"
] |
[
"When we create huge amounts of CO2 It goes to the atmosphere and dissolves with rain and creates a week acid called H2CO3. When the acidic rain come to the earth, It reacts with Calcium carbonate (Limestone) and when they reacts they create Ca(HCO3)2 that is the reason for making water hard. In the hard water the soap doesn't work well and doesn't make bubbles. When you heat the hard water, Ca(HCO3) will divide to CaCO3 (When you heat water in kettle this is the white thing that covers the holes of kettle.) + CO2 + H20 and the water lose it hardness and soap works great with it again.\nP.s. Sorry for my bad english if you didn't understand parts of it, reply Me and I will explain it to you.\nP.s I am a high schooler and I explained what I had learned in high school. If I'm wrong please reply to my comment :-)"
] |
[
"I'm familiar with acoustic and inertial positioning in subsea environments. How does positioning work in space ?"
] |
[
false
] |
[deleted]
|
[
"Generally, optically or by radio."
] |
[
"Why would there be no inertia outside of a gravitational field???? ",
"Oh wait, we can't really escape from gravitational fields…"
] |
[
"If I understand correctly, inertial navigation systems rely on a large gravitational field."
] |
[
"Is there anything specific that pushes a person over the line from \"eccentric\" to \"mentally ill?\""
] |
[
false
] |
-- About 15 people have replied "Amount of money" so if that's your only (non-scientific) response, please don't bother.
|
[
"its very vague and subjective, but the best rule of thumb that you can apply to deciding if anything is a disease is ;",
"\" Does it impact negatively on somebodies life?\"",
"Its not foolproof but its a pretty good guide. If it doesn't effect their \"wellbeing\" then leave them alone, they're not sick."
] |
[
"As a psychiatrist, this is absolutely the most accurate answer to this question."
] |
[
"The short answer is: almost nothing whatsoever. Currently, psychiatric disorders are diagnosed using the ",
"Diagnostic and Statistical Manual of Mental Disorders, 4th edition",
" (DSM-IV), which is supposed to provide empirical, standardized methods for diagnosing various mental illnesses. However, the DSM still leaves a lot of room for interpretation by individual diagnosticians, and the DSM itself has also attracted more than its fair share of criticisms, many of which are outlined in the wiki article. The underlying issue is many border cases (e.g. high-functioning autism, ADD/ADHD, high-functioning depression, multiple personality disorder, etc.) can not be distinguished from \"normality\" consistently. Hence, whether or not a border case will be diagnosed as an illness or dismissed depends largely on the individual diagnostician. An even further underlying problem is that psychology itself is by nature extremely subjective, and many attempts at standardizing disorders end up simply pushing arbitrary definitions onto \"disorders\" to have them fall into arbitrary, operationally defined categories (which often lends itself to ",
"criticism",
"). That is not to say that psychology has not advanced in sophistication since its inception, but it is, as ever, susceptible to fad ideas, misapplication of cause and effect, and attempting to oversimplify an extremely complex interactive system into a standardized list of components. Add in the subjectivity of diagnosis, and all of a sudden the line bordering the \"eccentric\" and the \"mentally ill\" becomes extraordinarily fuzzy. TL;DR: it depends on the doctor, especially with border cases."
] |
[
"What is inside the core of each of the Gas Giants?"
] |
[
false
] | null |
[
"We're not sure.",
"Heavy elements should sink to the bottom, and given how we think planets form there was likely a large (~45 Earth mass) rocky planet that began collecting a lot of gas and became Jupiter. Compression should also have made it rather hot and kept it insulated; conventional wisdom says it is about 24,000 Celsius down there.",
"So, a big incomprehensibly hot ball of rock and metal squeezed down into exotic forms under miles and miles of metallic hydrogen. The laws of chemistry are substantially different (and poorly understood) under such fantastic conditions and there's no plausible way to send a probe down there to look at it."
] |
[
"That was the metallic hydrogen I mentioned. If you look at the periodic table hydrogen is at the top of the group 1 metals (lithium, sodium etc) but we never see the metallic phase on Earth.",
"This might be liquid or solid - we're not sure because the pressures are unreachable even in the lab.",
"Denser elements will have fallen in many times even after formation (Shoemaker-Levy 9, the RTG from the Galileo space probe, other assorted refuse) so it really shouldn't be just hydrogen all the way down."
] |
[
"The following is the relevant bits of this.",
"Following probe parachute deployment, six science instruments on the probe collected data throughout 97 miles (156 km) of the descent. During that time, the probe endured severe winds, periods of intense cold and heat and strong turbulence. The extreme temperatures and pressures of the Jovian environment eventually caused the probe communications subsystem to terminate data transmission operations.",
"Earth-based telescopic observations suggest that the probe entry site may well have been one of the least cloudy areas on Jupiter. At this location, the probe did not detect the three distinct layers of clouds (a topmost layer of ammonia crystals, a middle layer of ammonium hydrosulfide, and a final, thick layer of water and ice crystals) that researchers had anticipated.",
"Some indication of a high-level ammonia ice cloud was detected by the net flux radiometer. Evidence for a thin cloud which might be the postulated ammonium hydrosulfide cloud was provided by the nephelometer experiment. There was no data to suggest the presence of water clouds of any significance. The vertical temperature gradient obtained by the atmospheric structure instrument was characteristic of a dry atmosphere, free of condensation. Only the one, distinctive cloud structure was identified, and that was of modest proportion. ",
"It's important to note that the probe wasn't designed primarily with an exploration of Jupiter's atmosphere in mind. We used the planet as a celestial trash can to avoid contaminating Europa and possibly getting our Earth bacteria in there."
] |
[
"If you jumped onto an electric fence and grabbed on without touching the ground, would you get shocked? And would you be able to keep climbing or would you be continually shocked?"
] |
[
false
] |
Just curious, not trying into break into anything.
|
[
"The few electric fences I have encountered were pulsed DC powered. A high voltage charge is accumulated in the power supply and discharged at intervals into the wires. You would likely feel an attenuated shock every time the fence is powered because your body acts like a capacitor and it takes a little current to charge you up to the same voltage as the wires. Depending on the voltage of the fence and your own chemistry you would probably be very aware of each pulse but not necessarily in pain."
] |
[
"I've seen these DC fences for horses, and they usually alternate hot and ground wires.",
"Touching the ground wires was safe. Getting my little brother to touch the hot wires was fun."
] |
[
"No, In an electric fence you have three resistances to take into account, the wire, the animal and the ground. You always want the animal to have the highest resistance, since this will lead to the highest voltage drop across the animal. The voltage drop is what you feel as \"",
"\", which is usually what you want from an electric fence. "
] |
[
"Do people with a higher occurrence of AT pairs in their genes have a higher risk for mutation than those with GC pairs?"
] |
[
false
] |
[deleted]
|
[
"This is an interesting question, and it's one that's the subject of research right now.",
"The short answer is that all kinds of mutations can happen, and the frequency of a mutation type depends on a number of factors. Interestingly, different types of cancer seem to have different \"mutational signatures\" -- lung adenocarcinomas and lung squamous cell carcinomas, for example, very frequently have high rates of C-to-A substitutions. This is probably a type of damage that's caused by the carcinogens in cigarette smoke. ",
"Source, free in Pubmed Central",
"The most common mutation in the genome is a methylated-C-to-T, because if a methylated C undergoes a reaction called deamination, it looks like a T, and the genome's repair mechanisms treat it as such.",
"But to answer your exact question, no, AT base pairs don't seem to be more prone to mutation because they are joined by fewer hydrogen bonds. It is easier to melt them apart, though."
] |
[
"I absolutely think that each nucleotide has a different probability of being modified (which will then lead to replication errors and then mutation). Hydrogen bonds have little to do with the modification aspect. It's more about chemical structure.",
"\nRegarding mutation, sooo much of our genome is referred to as \"junk\" because we simply don't know enough to understand why it's there. Thus, knowing a gene sequence doesn't provide us with that much information (at least less than what was expected when we started human sequencing). One effort to better understand genes and the genome is to perform massive genome wide association studies (GWAS). Researchers will gather as many sequences as they can to identify single nucleotide polymorphisms that associate with some phenotype. They need a lot of sequences to have the statistical power to make those associations, and even then, they may only discover a handful of nucleotides for a gene that is few kilobases. So, of the 2% of the genome that is coding DNA, and the even smaller fraction of the gene that is being mutated, I would speculate that something larger than single nucleotide polymorphisms is at play. \nSorry to stray from your question. As a final comment, there are a whole slew of non-watson-crick base pairs, which cells can usually identify and repair--but, not always with the highest fidelity, so for genomic modification questions people look at single nucleotides. From a quick literature search, I didn't find any publications remarking global nucleotide modification probability, but I would bet my soul they're different (though from a organismal perspective that difference is negligable). "
] |
[
"Would you be able to confirm or deny that each cancer has a different type of \"mutational signature\" because of the genes that are turned on in that area of the body?"
] |
[
"If you know the frequency or volume of sound produced by moving air, can you determine how fast the air is moving?"
] |
[
false
] | null |
[
"Under normal conditions, a given frequency and intensity will vibrate the air such that the chain of collisions between air molecules will be 340 m/s. This is the speed of sound.",
"Analogously, light may arrive in different colors (frequencies), but the speed is the same."
] |
[
"To add to this, the speed of sound also varies with temperature and humidity. At 0 degrees celsius the speed of sound in air is 331m/s. The higher the temperature the faster the speed. ",
" sound = 331m/s + 0.6T"
] |
[
"Interesting question. There is not any physical law that will give a dorect answer to that, but I'm sure there must be several scholarly articles on modelling that relation, although they are most likely geometry or material-specific.\nThe pitch that comes out of, for example, a flute is heavily influenced by the interaction between air and the flute's walls, which is a really complicated thing to study. (for instance in my university you can take 'Introduction to fluid-container interactions' as a specializing course, but according to what I've been told by people who have taken it you focus more on setting a case-specific framework to design structures and experiments rather than calculating for a random set of materials, fluid, geometry etc.) "
] |
[
"What is the name of the effect where rays of light become visible when reflected off particles?"
] |
[
false
] | null |
[
"Mie was German."
] |
[
"Scattering"
] |
[
"Well, yes, that, but there's a technical term for it, it's named after a person."
] |
[
"Why does the pupil dilate when in heavier thought?"
] |
[
false
] | null |
[
"Dilatation can happen when seeing certain images, either interesting images (Hess & Polt 1960), big list of number,...",
"It can also happen when you try to analyse a complicated sentence, or focusing attention (Beatty 1982, Beatty & lucero-Wagoner 2000). It's called \"task-evoked pupillary response\".",
"Kahneman (1973) and Just & Carpenter (1993) suggest that the pupillary response is an indication of cognitive process intensity. ",
"The pupillary dilatation is also linked to emotional stimuli (whether positive Partala & surakka 2003 or negative Mudd, Conway&Schindler 1990). ",
"The pupil is a sphincter controlled by the autonomous system, and its main function is to control the quantity of light. But it is also modulated by either emotional stimuli or cognitive effort.",
"The precise biophysical mechanisms remain unclear. ",
"However, it has been showed (Rajkowski 1993) that the activity of the locus coeruleus and the pupil diameter were correlated. ",
"But, as you can read in Gilzenrat (2010) :",
"It is important to note that, despite the close relationship between pupil diameter and LC activity, the mechanisms underlying this relationship are not yet understood. There are presently no known anatomic pathways that might mediate this relationship directly, which suggests that these effects may reflect parallel downstream influences of a common source.",
"(possible & coherent candidat : paragigantocellularis nucleus of the ventral medulla ; or see ",
"/u/GrandmaWeary",
" below : Edinger-Westphal nucleus).",
"These studies (see also the study of P3 from Murphy 2011) suggest that pupil diameter in human could be a useful index for LC activity.",
"It is only one part of a complex answer we have yet to determine. ",
"(Note : it's not my specialty field, so please feel free to correct my answer). ",
"(And a small note : these studies show that FC firing rate and pupillary responses are correlated in these specific experiments. It doesn't necessarily mean that every time you pupil dilate, the FC is firing accordingly.)"
] |
[
"I found ",
"this",
" review claiming that the LC has direct, inhibitory projections to the Edinger-Westphal nucleus (EWN), which is well-understood to constrict the pupil. So, higher activity in LC reduces activity in EWN, which then dilates the pupil and would explain the close correlation. From the article:",
"The EWN, the parasympathetic preganglionic nucleus responsible for pupil constriction, receives an ascending input from the LC, which is likely to exert an inhibitory influence via α2-adrenoceptors..."
] |
[
"I thought of the question after reading Kahneman's ",
", where he mentions the pupils response to certain emotionally or mentally charged stimuli.",
"Essentially, though, it doesn't have anything to do with any benefits that added light would confer when presented with said stimuli? It's just a response of the nervous system that isn't really understood?"
] |
[
"What is happening when something becomes \"second nature\" or habit to us, such as tying our shoes? Does it move to a different part of our brain?"
] |
[
false
] |
I'm referring to when people seem to do things automatically after many years of learning them. EXAMPLE: When we first learn to drive, we concentrate all our brainpower on doing everything correctly. A few years later we barely have to think about pressing the gas, brake, steering, etc. Does this information move to the "back" of our brain? Does it get filtered out differently as we get used to these things?
|
[
"I think you're describing the formation of corticocortical connections. When you're first learning something consciously, you rely heavily on a part of your brain called the hippocampus to coordinate activity between the neurons required for the task. If you call upon the brain to do this frequently enough, those neurons will begin to form direct connections and gradually require the hippocampus less and less.",
"Tasks like reading, when learned young, become so ingrained that you can't consciously ",
" when you see words, unless you pull some stupid trick like blurring your eyes. The Stroop Effect tests this, and it'd be fun to look up and try, if you're not familiar with it. ",
"Here's",
" an interactive test to show this to yourself.",
"One of the interesting things that comes of this happens when you have a disease or injury affecting the hippocampus, like Alzheimer's. That portion of the brain will begin to deteriorate, so it's no longer available for retrieval of old memories, or the making of new memories, and the patients will seem to \"regress\" throughout the process, as the only memories accessible to them are the ones in which corticocortical connections have been formed."
] |
[
"I believe this is exactly what I was looking for. Thank you!!"
] |
[
"This learning process is performed in the ",
"cerebellum",
", which underlies the predictive motor movements, postures, and reflexes that we perform every day (and yes, it's actually in the back of your brain). I don't have time right now to explain it, but the learning process in the cerebellum and the circuits/cells involved is very well studied. This is what underlies your ability to type without looking at the keyboard, ride a bike, walk up stairs, etc."
] |
[
"Genetic determinism vs. Free will"
] |
[
false
] |
[deleted]
|
[
"Twin studies offer one type of evidence for the inheritability of certain personality traits. ",
"If you are interested in this subject I would suggest reading a book called The Agile Gene. It is about how nature (genetic predispositions/traits) is turned on by nurture (environment). It really delves into the nature vs. nurture debate; concluding- after reviewing the latest research and studies-that the truth lies somewhere in the middle. It presents evidence for how both nature and nurture have an active and intertwining affect of the development and behavior of individuals. Genes not only act as carriers of genetic information and blueprints to human body structure but also absorb formative experiences and react to social cues. ",
"Here is an excerpt:",
"\"In 1960 a graduate student at Harvard received a letter from George A. Miller, head of the department of psychology, dismissing her from the Ph.D. program because she was not up to the mark. Remember that name. Much later, stuck at home with chronic health problems, Judith Rich Harris took up writing psychology textbooks, books in which she faithfully relayed the dominant paradigm of psychology- that personality and much else was acquired from the environment. Then, 35 years after leaving Harvard, as an employed grandmother, having happily escaped academic indoctrination, she sat down and wrote an article, which she submitted to the prestigious Psychological Review. It was published to sensational acclaim. She was deluged with inquiries as to who she was. In 1997, on the strength of the article alone, she was given one of the top awards in psychology: the George A. Miller award. The opening words of her article were:",
"Do parents have any important long-term effects on the development of their child’s personality? This article examines the evidence and concludes that the answer is no. ",
"From about 1950 onward psychologists had studied what they called the socialization of children. Although there were initially disappointed to find few clear-cut correlations between parenting style and a child’s personality, they clung to the behaviorist assumption that parents were training their children’s characters by reward and punishment, and the Freudian assumption that many people’s psychological problems had been created by their parents. This assumption became so automatic that to this day no biography is complete without a passing reference to the parental causes for the subject’s quirks. (“It is probably that this wrenching separation from his mother was one of the prime sources of his mental instability,” says a recent author, referring to Isaac Newton.) ",
"To be fair, socialization theory was more than an assumption. It did produce evidence, reams of it, all showing that children end up like their parents. Abusive parents produce abusive children, neurotic parents produce neurotic children, phlegmatic parents produce phlegmatic children, and bookish parents produce bookish children, and so on. ",
"All this proves precisely nothing, said Harris. Of course, children resemble their parents: they share many of the same genes. Once the studies of twins raised apart started coming out, proving dramatically high heritability for personality, you could no longer ignore the possibility that parents had put their children’s character in place at the moment of conception, not during the long years of childhood. The similarity between parents and children could be nature, not nurture. Indeed given that the twin studies could find almost no effect of the shared environments on personality, the genetic hypothesis should actually be the null hypothesis: the burden of proof was on nurture. If a socialization study did not control for genes, it proved nothing at all. Yet socialization researchers went on year after year publishing these correlations without even paying lip service to the alternative genetic theory. ",
"It was true that socialization theorists used another argument as well: that different parenting styles coincide with different children’s personalities. A calm home contains happy children; children who are hugged a lot are nice; children who are beaten a lot are hostile; and so on. But this could be confusing cause and effect. You could just as plausibly argue that happy children make a calm home; children who are nice get hugged a lot; children who are hostile get beaten a lot. Old joke: Johnny comes from a broken home; I’m not surprised- Johnny could break any home. Sociologists are fond of saying that a good relationship with parents “has a protective effect” in keeping children off drugs. They are much less fond of saying that kids who do drugs do not get on with their parents. ",
"The correlation of good parenting with certain personalities is worthless as proof that parents shape personality, because correlation cannot distinguish cause from effect.\"",
"TLDR: Twin studies have shown that personality is highly heritable and any socialization theory should control for genes, otherwise it doesn't prove anything at all. "
] |
[
"There's lots of literature surrounding criminal behaviour in people with Jacob's Syndrome (XYY) Many studies performed in in prisons. I would be interested if anyone found hard evidence to suggest that this was linked to criminal behaviour."
] |
[
"I certainly agree with this statement, but what I think the author was really getting at was not the degree of genetic difference between one person and another, rather, that our environment influences how our genes are expressed. Genes, although implacably determinist in nature (always coding for the same enzyme or protein), are far from fixed in their actions. They are constantly regulated by the external environment; promoters switch on and off genes in response to external instructions and regulate the strength and timing of gene expression; DNA methylation binds and inactivates various gene stretches allowing the only certain genes to be expressed and leading to cell differentiation.",
"He says: ",
"<\"Every minute, every second, the pattern of genes being expressed in your brain changes, often in direct or indirect response to events outside of the body. Genes are the mechanisms of experience.”"
] |
[
"If we found the link or solution of the distribution of prime numbers, what could we do with that information?"
] |
[
false
] |
Would it lead to other mathematical breakthroughs or technological increases?
|
[
"It would almost assuredly lead to more advanced and more powerful mathematics. The ",
"Riemann Hypothesis",
" is a question about understanding the distribution of primes. If it is proven, some other theorems that depend on it will also be proved, but this isn't the main impact. Everything tells us that our current math is not powerful enough to answer the Riemann Hypothesis and that a proof of the Riemann Hypothesis will need much more powerful math that we can use to study other problems and to also ask even more difficult and interesting questions.",
"This has already happened. In the 1800s, a problem called the ",
"Prime Number Theorem",
" was open for a long time. It also asked about the distribution of primes. People worked on it for years, but their math was not powerful enough to solve it. Then Bernhard Riemann presented a much more powerful formulation of the Prime Number Theorem using the new math of Complex Analysis (calculus on complex numbers). This was way more powerful that what people were using before and it was not long before they were able to prove it in this new formulation. This formulation changed all of Number Theory by helping us look at things in a more abstract context. But Riemann's formulation suggested an even stronger version of the Prime Number Theorem, which is the Riemann Hypothesis and is still unproven. We think that the proof will do the same thing by causing a paradigm shift in Number Theory. ",
"Another example is the Weil Conjectures, which is a formulation of the Riemann Hypothesis, but for geometric objects rather than primes. This was a big problem for many years, with roots of it going back to before the Prime Number Theorem. This was proved in the 70s by Pierre Deligne using radical new tools created by ",
"Alexander Grothendieck",
", one of (if not ",
") greatest mathematician of the 20th Century. These tools are still trying to be understood and have caused a paradigm shift in Number Theory ",
" Geometry that is still trying to be fleshed out. Grothendieck tantalizingly suggested that prime numbers and geometry are intimately linked, but we still don't really know how. If Grothendieck is right, this will be huge! It will surely lead to a proof of the Riemann Hypothesis and create amazingly powerful math that will allow us to ask even grander questions!"
] |
[
"While there have been cases, the more fundamental concept is that proving something has a lot more power and value than simply knowing it is true.",
"The math developed to prove this would be useful for many other problems, even if it doesn't tell us anything we don't already know about primes. ",
"Its about the logic, not the numbers. "
] |
[
"Many have, yes - ",
"see link",
". 10 trillion non-trivial zeros have been checked, and each and every one satisfies Riemann's hypothesis. Most mathematicians expect the Riemann hypothesis to be true. Sadly, many also do not expect to see it proven while they live."
] |
[
"AskScience AMA Series: I'm Brian Greene, theoretical physicist, mathematician, and string theorist, and co-founder of the World Science Festival. AMA!"
] |
[
false
] |
I'm Brian Greene, professor of physics and mathematics at Columbia University and the Director of the university's Center of Theoretical Physics. I am also the co-founder of the , an organization that creates novel, multimedia experience to bring science to general audiences. My scientific research focuses on the search for Einstein's dream of a unified theory, which for decades has inspired me to work on string theory. For much of that time I have helped develop the possibility that the universe may have more than three dimensions of space. I'm also an author, having written four books for adults, , , , and just recently, . and were both adapted into NOVA PBS mini-series, which I hosted, and a short story I wrote, , was adapted into a live performance with an original score by Philip Glass. Last May, my work for the stage , which explores Einstein's discovery of the General Theory, was broadcast nationally on PBS. These days, in addition to physics research, I'm working on a television adaptation of Until the End of Time as well as various science programs that the World Science Festival is producing. I'm originally from New York and went to Stuyvesant High School, then studied physics at Harvard, graduating in 1984. After earning my doctorate at Magdalen College at the University of Oxford in 1987, I moved to Harvard as a postdoc, and then to Cornell as a junior faculty member. I have been professor mathematics and physics at Columbia University since 1996. I'll be here at 11 a.m. ET (15 UT), AMA! Username: novapbs
|
[
"Professor Greene,",
"I read your book ",
" when I was younger and very much enjoyed it. Unfortunately, I haven't reading as much on the topic of string theory since I left university.",
"So are there any new developments or big changes on the field of string theory in the last 15 or so years?"
] |
[
"Well, I am all for healthy debate. And, look, I too am a string theory skeptic. It may sound strange to hear that coming from me. But the fact is, my view of what's right and wrong is ultimately governed by experiment/observation. So, everyone SHOULD be skeptical of ANY theory until such data is available."
] |
[
"A great many advances in past 20 years---understanding the disorder or entropy in black holes, finding exact formulations of the theory, gaining hints regarding the basic structure of spacetime. What we lack is experimental/observational evidence."
] |
[
"What is the truth about GMO'S?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"This topic has been widely discussed. Have a read through these other discussions and if you've got a more specific question after, we'd love to add it!",
"http://www.reddit.com/r/askscience/comments/1ce3v4/",
"http://www.reddit.com/r/askscience/comments/1rwvts/",
"http://www.reddit.com/r/askscience/comments/100wg0/why_is_there_so_much_controversy_surrounding_gmos/",
"http://www.reddit.com/r/askscience/comments/1c0fi4/is_gmo_corn_less_nutritional_than_nongmo_corn/"
] |
[
"Thank you for the links. I didn't want to beat a dead horse I just wanted to learn."
] |
[
"Sure, it's no problem. We just try to avoid too many repeat questions because it can frustrate our panelists and users. If you think of another question after reading through the other posts, we'd love to hear it."
] |
[
"If you streamed a video of a white screen and a video of a vibrant tropical landscape, both in 1080p, would they render at equal speeds or would the white screen render faster?"
] |
[
false
] |
[deleted]
|
[
"It usually depends entirely on the compression algorithm used on the video. If a key-frame & delta algorithm is used, then the white video would download much faster.",
"Key-frame & delta compression works as such (ignoring individual frame compression):",
"Video has an initial key-frame, which is stored as the entire data of that frame. In this frame, the white screen and the landscape would take up the same amount of data.",
"Each frame after this key-frame is stored only as what has changed from the last frame. In the vibrant landscape, assuming a moving camera, or moving objects in the landscape, you would have some minor changes, such as a tree slightly moving due to blowing wind. However, in the white screen video, you would have no change at all, so no change is stored, and there is much less data stored to just say \"nothing has changed\".",
"The video periodically generates key-frames at advantageous points in the video, such as scene changes, or after a set amount of time, in order to both preserve the video data (if the video data was corrupted halfway through, then you'd be changing from the corrupted data, and end up with a broken video), and to reduce the data required to store the video. Having an entire scene change described in a delta frame would take nearly as much data as a key-frame anyway, so a key-frame is used instead.",
"So in this case, the white screen video would download much faster than the vibrant landscape. As far as I know, YouTube uses this compression algorithm, as do lots of current video formats."
] |
[
"In addition, if individual frames are compressed too then the white keyframe could also have a very small size (since the only information needed to specify the whole frame is '1920x1080 pixels of white', rather than needing to describe 2 million individual pixels). "
] |
[
"On PCs the decoding is often done by an ASIC on the graphics card. There will be no difference in the decode time on the ASIC.",
"For software decoding:"
] |
[
"Is there a solution to the twin paradox not related to acceleration?"
] |
[
false
] |
Most of the answers I have read from previous posts point to acceleration being the reason for the twins aging at different rates; however, it appears that acceleration is a common explanation because it is simple to understand but is a misconception. I am unable to wrap my mind around how the two frames are different if acceleration is not the driver for the difference.
|
[
"The trick is that there are actually three frames. A frame of reference moves at a constant speed in a fixed direction. Imagine it like a bunch of trains on parallel tracks, some moving forwards, some moving backwards, all at different fixed speeds. The passengers can't slow down or speed up the trains, but they ",
" jump between them.",
"The idea is that the two twins are initially doing exactly the same thing. There's no difference between Earth moving away from a spaceship and the spaceship moving away from Earth. So both see the other as time dilated. ",
" if one twin turns around - jumping onto another train, switching to another frame - then that breaks the symmetry. All frames of reference agree that this twin did something different to the other. Then it's consistent for that twin to age less than the other.",
"I don't really think it's wrong to think of \"acceleration\" as the cause though. \"Acceleration\" is basically the same thing as changing your reference frame. Maybe it's not the best way to explain it, but it gets the gist. Edit: Just thinking about this now, it's worth emphasising that it's the ",
" in acceleration that breaks the symmetry. If both accelerate in exactly the same way, both will experience exactly the same thing."
] |
[
"A closed universe breaks the symmetry in a different way, it has a natural preferred reference frame. This frame is the one in which the universe is smaller than any other frame (yes, smaller! Any moving observer will be Lorentz contracted, as will as their rulers, hence they would measure the universe to be bigger), and time runs faster than any other frame. ",
"If the stationary twin is in this special frame, the travelling twin will appear less aged after circumnavigating the universe."
] |
[
"Okay, so you're saying you have two twins initially separated by some distance, and they both accelerate towards towards each other at the same rate, until they meet?",
"Here it is still symmetric, and both will see the other as time dilated. This doesn't cause a contradiction, because their times weren't synchronised to start with. Synchronisation is one part of special relativity that people forget about, but it's essential for getting the right answer.",
"We can simplify this by changing from constant acceleration to instantaneous acceleration - i.e. each is moving towards the other at the same fixed speed. Then we are dealing with Special Relativity and not General Relativity. Here, the equations are just:",
"t' = gamma * (t - vx/c",
")",
"t' is the time in one frame, t is the time in the other frame, gamma is the time dilation factor, v is their relative velocity, x is the displacement between the two objects, and c is the speed of light. This ",
" factor is critical. Without it, the equation is just:",
"t'=gamma * t",
"i.e. time just runs at a different rate. But adding this extra factor means that time also ",
".",
"Here, the two twins are moving towards each other, which means that v and x have opposite sign. This means vx is negative, and -vx is positive. This means t' > t - i.e. the other twin appears to be ",
".",
"What happens is both twins see the other as older, but ageing more slowly than themself. When they meet, these two effects cancel out, and both are the same age."
] |
[
"Does the confirmation of the Higgs Boson have any implications for String Theory? Does it strengthen it, weaken it, or have no effect?"
] |
[
false
] |
[deleted]
|
[
"Little effect, there are some theories with large extra dimensions that would require no Higgs (they have their own mechanism producing the same end effect without adding a boson), so those theories are probably feeling it a bit, but otherwise it sheds little light on the landscape. "
] |
[
"Good point, yes the Minimal SUSY extension to the Standard Model (MSSM) has been under pressure for a while due to it usually predicting a lower Higgs mass, but this has been true since earlier accelerators put a lower bound on the Higgs mass that was higher than the desired mass for MSSM. However, this is more a concern for dark matter research (as that community makes extensive use of the MSSM), whereas string theory usually likes to have more supersymmetry (N=4 Yang-mills if you hang out with the AdS/CFT crowd)."
] |
[
"I believe most string theories were already under the assumption that there was a higgs boson. The particular mass it was found at puts in more constraints on possible string theories. It does not have a strong effect on string theories in general."
] |
[
"Are ultrasounds dangerous?"
] |
[
false
] |
I've had three on three different parts of my body over the past month, and now I'm worried that I've had too many and will do some kind of long-term damage. Is this likely? Edit: Thank you very much everyone. I'm learning a lot and am finding the conversation more interesting than I imagined I would!
|
[
"While they are generally safe, using only high frequency sound-waves as an imaging method with no obvious risk (like ionising radiation with x-rays/CT for example), sound waves are still a form of energy and have the potential to cause tissue damage through heating. The risk however is very small and a very long exposure would be required for any likely damage to occur (with maximum clinical times set to avoid this) so for imaging a fully developed adult it should be considered safe.",
"The larger area of concern (and which to my knowledge is still on going in the finer details) is whether ultrasound and more notably 3d ultrasound have any effect on developing foetuses which are much more sensitive to their environment and forces/energy put on them than a developed adult. Though I will leave it to someone with more expertise in that exact area to give any conclusions or definite claims."
] |
[
"You should be fine. I mainly wanted to make the point that there is a potential risk (though it would require a very high exposure) as many people assume that just being sound-waves means there is no possible risk."
] |
[
"To be pedantic, I think doing to a concert might be harmful to your hearing in some small but possibly significant way."
] |
[
"In the lastest xkcd what-if?, it was question of how to prevent the slowing of the earth's rotation, by acting directly on the earth. What if we bombarded the moon instead, bringing it closer to the earth, and tidally locking it on a 24 hour period?"
] |
[
false
] | null |
[
"How intense the bombardment would need to be?",
"This is a drastic change in the orbital energy of the moon, so the scale of things is hitting the moon with a similar mass as itself at a similar speed to itself in the opposite direction.",
"How bad the effect of the tidal force would be?",
"The tidal force is proportional to 1/r",
"3",
", so moving it from 384,000 km to 36,000 km (geostationary orbit) would increase the tidal force by a factor of 1,200. Maybe a geophysicist can tell us how catastrophic that would be. Though curiously the lunar tide would be static.",
"Would that be enough to bring the barycentre of the system outside of the earth and create a binary system?",
"Actually the moon would need to be ",
" away to move the barycenter outside the earth. It's getting close as it is, ~1700 km below the surface."
] |
[
"I had a couple thoughts when reading the above. First, would putting the Moon in a geosynchronous orbit of the Earth put it within the Roche limit and cause the Moon to break up? Turns out that no, it wouldn't. It's new orbit would still be about a factor of 2 times the Roche limit. ",
"http://en.wikipedia.org/wiki/Roche_limit",
"Second, how far out does the Moon have to move (naturally via tidal friction) before the Earth becomes tidally locked to it (where only side of the Earth ever sees the Moon)? Fortunately, to preserve my current state of laziness, someone has worked it out. \"The Moon will be ~50% farther away from the Earth. The Lunar Sidereal Month will be about 47 days long\" which would also be the length of the Earth's day. ",
"http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit4/tides.html"
] |
[
"The moon is 0.0123 earths massive, so the barycentre is at 1.23% of the way between the centre of the earth and the centre of the moon? Is that as simple as that?",
"It's almost as simple as that. ",
"Here's the equation",
". It will be 0.0123/(1+0.0123) of the way from the earth center to the moon center (the 1 is the earth's mass in units of earth masses, since you gave me the moon's mass in earth masses)."
] |
[
"When I'm carsick dad always says to open the window and breathe fresh air. Does this actually help? How?"
] |
[
false
] |
as far as i'm aware carsickness is due to the conflict between the inner ear and eyes, so i'm not quite sure how the air would make a difference. i've googled this to no avail. edit: many thanks for your help, guys!
|
[
"I find that cold air on my face reduces nausea... this can be in a car (by opening a window) or in a plane (by turning the air jet above the seat onto my face)."
] |
[
"I'll bet that you looked out the window when you were breathing the fresh air... thus averting the conflict between the motion cues sensed by your inner ear, and what you saw.",
"Also, it probably got your mind off the carsickness."
] |
[
"I guess feeling the wind helps your body to believe the fact that you're moving and reduces the conflict between the inner ear and the eyes."
] |
[
"What is the main reason we cannot keep Great White Sharks in captivity?"
] |
[
false
] |
I've read briefly on the topic on Wikipedia but was curious as to whether there was some scientific backing as to why it is so difficult to keep this particular shark in captivity. My assumption is that their eating habits don't allow it but I'm hopeful there's a more solid reason.
|
[
"This is not my area expertise, but I'm a bit of a shark enthusiast and I just happen to love a vet so I can try to answer this for you. I don't think there is a well defined reason, though.",
"First, some aquariums have managed to keep Great Whites in captivity for extended periods of time. From my reading, I believe it has to be a gradual effort to minimize the stress on the shark. When it is done in this manner, with some periods of acclimation to captivity occurring in an open ocean swimming pen, the sharks seem to do better. ",
"Often, the animals behavior seems to indicate stress while in captivity. They may not eat and thus have to be released. Alternatively, they may swim oddly and obtain abrasions from awkwardly navigating the encasement, which can lead to infections. It seems to come down to the stress of captivity.",
"Great starting point to read more",
"Or you can go with the idea that a Great White would rather die than not kill. :)~ "
] |
[
"One possible reason for the stress is that in the wild, Great Whites are known to travel huge distances. Great Whites tagged near South Africa have been recovered near Australia less than a year later. It is thought that they may migrate there for feeding or mating."
] |
[
"I think they would eat way too much. Also they need a lot of space. Better let them swim free. "
] |
[
"Why does the dengue vaccine work best on people who've been infected with at least one strain of dengue fever before?"
] |
[
false
] | null |
[
"Dengue is an interesting infection in that the second time you get it, you generally have ",
" symptoms (sometimes life threatening) than the first time are infected. Because getting a vaccine mimics getting an infection, giving the vaccine to someone who has never had Dengue actually ",
" their risk for severe disease if they're exposed. Thus the vaccine is only given to people who have already had it once where it reduces disease severity for future exposures.",
"\n ",
"https://www.cdc.gov/dengue/symptoms/index.html",
" ",
"An interesting question here is: ",
"\nAs far as I am aware we still don't know. One hypothesis is that antibody-dependent enhancement increases the infectivity and misdirects your immune system. This is when your body produces antibodies that bind to the virus and actually ",
" its ability to get into your cells. Presumably this happens after your first infection, and in your second infection (or vaccine) your immune system develops new antibodies or a more T-cell mediated response to infection to better fight it. This article has a lot of good information about ADE in Box 1 and Figure 1 (also talks about ADE & COVID-19 for those interested).",
"\n ",
"https://www.nature.com/articles/s41586-020-2538-8"
] |
[
"Thank you for your detailed answer! I had dengue about a month ago and after I recovered, the doctor told me that now I've had the infection once (it was my first dengue infection), the vaccine is now safe for me to take and I've wondered why the dengue vaccine can't just protect you from all the strains before you have at least one prior infection."
] |
[
"Hi, did you end up getting the vaccine? I live in Puerto Rico and currently have Dengue. I’m freaked out about getting dengue again because I’ve read it can be significantly more life threatening if you get it a second tome. Any thoughts? Thanks!"
] |
[
"If neutrino oscillations imply that neutrinos have mass, then why doesn't the frequency or phase of photons imply that they have mass?"
] |
[
false
] |
As far as I'm aware, neutrino oscillations imply that neutrinos have mass because if neutrinos have a time dependent state then time is passing in their frame, meaning that they're not going at the speed of light, meaning they have mass. Why can't this be extended to the phase of a photon which changes over time?
|
[
"Neutrino oscillations imply that neutrinos have mass because in order to detectably change into a different flavour, at least one of each possible pair of flavours must have nonzero mass (otherwise they would have equal mass). Photons don't change into fundamentally different particles as they whizz along so they don't have that complication."
] |
[
"What arble said. To put it in slightly different words, it is because neutrino flavor oscillations are ",
" that we know at least 2 neutrinos must be massive (and all 3 neutrinos cannot have the same mass; it is still possible for the lightest neutrino to be strictly massless). If neutrino oscillation did not occur, then neutrinos would all need to have the same mass (which could be either massless, or massive).",
"Photons don't oscillate into other particle flavors. Neutrinos are leptons and have lepton flavor number (which is allowed to change via oscillation due to the different masses) but photons are bosons and do not have any associated \"flavor\" quantum number which can change."
] |
[
"Thanks, what you and hikaruzero have said has cleared that up for me."
] |
[
"Can prions affect non-nervous tissue?"
] |
[
false
] |
If prions are simply misfolded proteins, can these misfolded proteins appear in non-nervous tissue? Is it possible that there are prions that mainly affect non-nervous tissue such as muscle tissue?
|
[
"Yes, the main determining factor is whether the prion protein is expressed by a certain cell type. So the prion that causes mad cow disease is found in muscle cells--hence why it is dangerous to eat beef that is potentially infected with the protein. The neurodegenerative process is what is lethal, though."
] |
[
"There is evidence that there are infectious prions in the skeletal muscle as well."
] |
[
"I was under the impression that CJDv was generally from the meat becoming tainted with brain matter during slaughter."
] |
[
"What is the difference between an alloy and a composite?"
] |
[
false
] | null |
[
"I've been rereading a book from one of my materials-science classes, and it has a good explanation.",
"An ",
", by definition, is a metallic solid or liquid formed from an intimate combination of two or more elements. By \"intimate combination,\" we mean either a liquid or solid solution.",
"Then, in contrast,",
"A composite can be different things, depending on the level of definition we use. In the most basic sense, all materials except elements are composites. For example, a binary mixture of two elements, like an alloy, can be considered a composite structure on an atomic scale. In terms of microstructure, which is a larger scale than the atomic level definition, composites are composed of crystals, phases and compounds. With this definition, steel, which is a suspension of carbon in iron, is a composite, but brass, a single-phase alloy, is not a composite. If we move up one more level on the size scale, we find that there are macrostructural composites: materials composed of fibers, matrices, and particulates—they are ",
". This highest level of structural classification is the one we will use, so our definition of a composite is this: ",
"The book is ",
" by Brian S. Mitchell.",
"It may also help to read its definition of phase:",
"A phase is defined as a homogeneous portion of a system that has uniform physical and chemical characteristics. It need not be continuous. For example, a carbonated beverage consists of two phases: the liquid phase, which is continuous, and the gas phase, which is dispersed in the liquid phase as discrete bubbles."
] |
[
"An alloy is a combination of two or more metals that have been melted and evenly blended together. A composite is a material made up of two or more separate materials (not just metal) that have been woven, glued, or adhered together in some other way."
] |
[
"I think it's also valuable to define the difference between an in-situ and ex-situ composite. In-situ are formed similar to steel; you use phase separations, thermodynamics, or some sort of reaction to wind up with two (or more) distinct phases. Ex-situ would be where your second phase is added in its final form and the other is formed around/with it. Think of rebar in concrete, multi-layered structures like carbon fiber/Kevlar panels, etc."
] |
[
"Why do our noses get runny when we cry?"
] |
[
false
] |
[deleted]
|
[
"Your tear ducts drain into your sinuses, which as you can imagine, get runny.",
"Spicy food can cause your eyes to water, but also spices are irritants to your nose, and causes it to produce mucus to try to get rid of the irritants(Also why you sneeze)."
] |
[
"As was already said, you have what is called a Nasolacrimal duct that goes directly to the back of the nose, any time there is an excess of tears produced by the lacrimal ducts, the nasolacrimal ducts take the rest and cause the runny nose."
] |
[
"Very interesting, thank you!"
] |
[
"Why aren't turbine engines used to power cars instead of standard internal combustion engines?"
] |
[
false
] |
As i understand it, turbines are much much more efficient Discarding the variable of cost aside, why aren't they?
|
[
"Not only more efficient, but quieter, and they could use multiple types of fuel.",
"The main excuses were throttle lag (pressing the accelerator, and it takes a few seconds for the turbine to wind up and increase power), and differences in function, like stalling if you floored the pedal too soon.",
"But it was tried once, by Chrysler - they just never put the cars into production: ",
"http://en.wikipedia.org/wiki/Chrysler_Turbine_Car",
" "
] |
[
"Throttle lag is not a major concern. I worked quite a bit on the turbine engine used in the M1 Abrams. There is very little throttle lag in that setup. In fact, an Abrams will accelerate faster than a Hummer.",
"I would point out the main issue is maintenance. A turbine engine is simple in concept, but difficult to service. Also, a malfunctioning turbine engine is far more dangerous compared to a piston engine. ",
"Another issue would be jet blast. I am unfamiliar with the Chrysler concept, but every turbine I have been around (tanks, helos, and planes) produce large amounts of heat exhaust. For instance, if you stand behind the jet wash, you WILL be burned. I don't think this would be great for pedestrians or tailgaters."
] |
[
"They scale up well, but not so well down. This is assuming simple designs. Efficiency can be adjusted by varying the angle of attack of the blades but that adds a lot of complexity for an automotive application."
] |
[
"Is it possible that the human race will keep getting taller in the future?"
] |
[
false
] |
[deleted]
|
[
"There is a limit to how tall humans can get: \nMass increases with the cube of the size, but bone strength increases with the cross section of the bone and thus with the square of the size.",
"At some point we would be so heavy we could not move without snapping our legs."
] |
[
"No, it isn't. The cardiovascular and skeletal systems of the average human would have to do some impressive evolution to support people that tall, and short of some pretty severe mass die-offs (somehow hitting only people under the 1-5% height percentile), 200 years is far too small a timeframe for this to happen."
] |
[
"If we continue to have enough food that it doesn't limit reproduction in tall people then we may. If there is no natural selection either way, sexual selection for tall people will gradually increase our height. Of course, culture can always change and short people may be favored if we are in a famine or low on food."
] |
[
"Could Curiosity (or some other Mars lander) 'populate' Mars with life?"
] |
[
false
] |
I am not sure if bacteria (or other micro-organisms) could survive the flight through space and subsequent re-entry, but if so, considering they have found signs of water, could we essentially begin life on Mars by our actions? (This is of course assuming that life does not already exist and just has not been found). If I have the wrong flair for this question, let me know and I'll change it. I found at least 3 possible categories this could go under.
|
[
"There is almost certainly life on Mars. Life that we sent there.",
"We know for a fact that some organisms are capable of surviving the rigors of space (hard vacuum, radiation) because they've been found on spacecraft that have returned from the Moon.",
"The issue is that they can only survive that way in a ",
"spore state",
", which is a strange 'fugue' like state that is somewhere between alive and dead. ",
"So any of the microorganisms that have survived the journey to Mars will be in a spore state. Even the spores won't last long on Mars due to the harsh environment, but some, maybe only a few, could hide in nooks and crannies of the rovers and still, technically, be alive. ",
"However, they are unlikely to ever become ",
", i.e. reanimate and begin reproduction. This can only happen to a spore under favourable conditions, and requires the presence of water. So it's unlikely to ever happen on its own."
] |
[
"Yep, and this is a serious issue with concepts of missions to Europa and other icy moons. On Mars, there is definitely surviving microbes from Earth, but they likely can't reproduce; they're in a state between living and dead. However, on a Europa mission, if any Earth-microorganism makes contact with the water, say on a drill or submarine... Bad news."
] |
[
"I just find it interesting that we find microbial life in the most inhospitable places on Planet Earth. It makes me wonder if Curiosity just had a shovel if there isn't an ecosystem teeming beneath Mars.",
"My reason for asking this question was the hypothetical situation where we discover water just under Mars and some Earth-sourced bacteria comes in contact. "
] |
[
"Is there any application of the intergral of displacement in regards to time, ie the meter-second?"
] |
[
false
] |
[deleted]
|
[
"The integral of displacement with respect to time has got a name, called ",
" although it does have limited use in physics. It's mainly used for computing costs and such given rates dependent upon time and displacement. But, I can't do it justice in this comment so here's a much better website than my rambly explanation:",
"http://wearcam.org/absement/examples.htm"
] |
[
"One practical use is in PID control systems. I won't try to explain it in detail, but the integral you're asking about, along with the velocity and instantaneous displacement, is used basically to move a system (such as a robot's joint) to a desired state. Here's the wikipedia article: ",
"http://en.wikipedia.org/wiki/PID_controller",
"The integral of displacement over time helps the system get to it's desired location by taking into account not just the distance to the desired location but also how long it's taking to get there."
] |
[
"Great link, thanks for that. I find the author's example to be a bit of a stretch, though. Wouldn't something like \"man-hours\" or... I don't know, power usage, make for a better example?",
"I think that I get it, but the example isn't really making the concept easier to understand."
] |
[
"Is carbon smaller when it is reduced or oxidized?"
] |
[
false
] |
Thank you in advance for your reply!
|
[
"The bond length in methane is ",
"109 pm",
" and the bond length is CO2 is ",
"116 pm",
". Does that answer your question?"
] |
[
"One of those links is to Wikipedia. The other is to two drunk puppies. That creates other questions..."
] |
[
"Oops. Thank you. Apparently I am bad at copying and pasting..."
] |
[
"What would a laser \"gun\" sound like? What about other \"future\" weapons like plasma guns, photon cannons, energy blasts etc.?"
] |
[
false
] | null |
[
"A simple 'photon cannon' exists in your home right now (I'm guessing), and is usually called a torch. What noise does it make when you switch it on?"
] |
[
"Laser guns would likely not make a sound. Maybe a electrical hum of sorts depending on how the device was powered. Photon cannons are just science fiction. As for plasma.... I'm not quite sure."
] |
[
"the click of the trigger, followed by whatever you want it to sound like.",
"best example? electric cars. like gas powered cars and gas powered rifles make a big boom, electric cars and electric weapons essentially... make no noise."
] |
[
"Physics time difference between two points in the galaxy."
] |
[
false
] |
Given: Instant travel and communication between planets. Astronaut travels to planet X on edge of Milky Way Galaxy and tries to make contact with Earth. Is it even possible or will time be moving at different rates? I don't know which reference to use planet x and Earth have the same angular velocity, but their tangential velocity is different. Wish I could be poetic but you'll have to settle for prose, having a hard enough time getting this question out coherently, hopefully this isn't gibberish.
|
[
"Typical stellar orbital speeds range from 210-240kps. There would be almost no effect caused by time dilation. "
] |
[
"There will be an additional effect from the fact that earth will be deeper in the potential of the Galaxy by a bit, and therefore time on earth will seem to run slightly slower from the perspective of planet X. But again, the effect is very, very small. Time on, say, GPS satellites runs a little faster than it does down here on the surface of earth, but we communicate with them all the time, no sweat. "
] |
[
"I don't think you understand time dilatation well. It all has to do with relativity. ",
"this",
" will explain it."
] |
[
"If water was suddenly exposed to the vacuum of space, how rapidly would it freeze?"
] |
[
false
] |
For our hypothetical scenario let's say a liter of water at room temp for the ISS was taken outside (not sprayed, but released in a way that wouldn't cause dispersion) and exposed to vacuum, how long would it take to freeze? Movies like the dramatic "instant freeze" effect because space is supposed to be cold. But if vacuum is actually an excellent insulator wouldn't it slow heat loss? Bonus question my dad had during our discussion: Would water disperse more readily in a vacuum and microgravity environment than it would in a microgravity environment with atmosphere? I said it wouldn't be significantly different because water's surface tension is a result of it's cohesive properties which should operate regardless of atmosphere. EDIT: Thanks for all the great responses people! Learned quite a bit more on the matter than expected!
|
[
"Water would definitely not \"instant freeze\" in space. In fact it would instantly boil!",
"The complete lack of pressure immediately lowers the boiling point of the water, turning it into vapor. This takes care of your dad's surface tension question as well: it's actually impossible for water to exist as a liquid at zero pressure.",
"Like you say, vacuum is an excellent insulator, so cooling down takes time. Eventually though it will cool down through radiative cooling, and assuming it has not dispersed completely the water molecules will clump together to form ice crystals.",
"Here is a longer explanation:\n",
"http://scienceblogs.com/startswithabang/2009/06/29/water-in-space-what-happens/"
] |
[
"The first part is a tough question. You'll have to defer to someone else's expertise as I do not have a definitive answer to that question. \nIt is not within my scope.",
"However to your Dad's bonus question, the microgravity with vacuum vs microgravity in atmosphere there is a definitive answer.\nThe microgravity would not really make any significant difference compared to the contribution of the vacuum.\nLowering the pressure of the water (i.e removing the atmosphere and putting it in a vacuum) will lower the boiling point such that it will outgas or evaporate off.\nIf you look at the phase diagram of water ( ",
"http://www.phy.duke.edu/~hsg/363/table-images/water-phase-diagram.html",
" ) you will notice that as you drop the pressure closer to 0Pa, once you are above 200K (-73 centigrade) or so, your water will turn to vapor.",
"So the vapor will readily disperse in the vacuum situation.",
"In fact looking at the phase diagram, we see that the solid water sublimates at 200K, and all other points above that (i.e higher pressures) are solid at lower temperatures.\nIn fact all other temperature/pressure ranges (within reason) show that the ice in vacuum sublimates before either vapor or liquid can form with atmospheres of any pressure.",
"So the vacuum should always disperse first, if dispersion is possible (i.e not ice)"
] |
[
"Well, sublimation is the process of a solid transforming directly into gas, so you're not asking quite the correct question. But if a small quantity of water was suddenly exposed to space, I suppose that the answer to your question would depend on how much radiant heat (the sun) it was exposed to. In total shadow, I suspect a gallon of water would leave a significant number of frozen chunks behind. In sunlight, it would probably boil off completely."
] |
[
"Anybody know anything about PBC?"
] |
[
false
] | null |
[
"If you want advice on how to help an ill person, that's medical advice too - please ask a doctor, not strangers on the internet. Have you tried calling her doctor?"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"medical advice",
"/r/AskScience",
"Please see our ",
"guidelines."
] |
[
"Where can I post this?"
] |
[
"What does it mean to break the Sound Barrier?"
] |
[
false
] | null |
[
"It means that the object is travelling faster than sound propagates through that medium.",
"It doesn't mean you hear ",
", but if something emitted sounds behind you, they'd never reach you.",
"You can still travel ",
" the compression waves (sounds) coming toward you. "
] |
[
"That kinda makes sense...",
"When you travel into the compression waves... is that how theres this white poof coming out when he fell? Almost like that superman flying scene?"
] |
[
"I assume you're referring to the redbull jump as of late? ",
"Honestly, I haven't seen it. "
] |
[
"How has the homeless population of the world not been decimated by the Corona Virus?"
] |
[
false
] | null |
[
"This is a scientific based question how does that make any sense when there is an absolute definite scientific answer? There is a reason the homeless are doing better and most likely it's because of their immune systems having to cope with them eating out of dumpsters for years on end and living in filth. This question ABSOLUTELY belongs here.",
"I understand the security and reasons you guys remove posts but this is a legit question that I truly believe belongs here."
] |
[
"This is a scientific based question how does that make any sense when there is an absolute definite scientific answer? There is a reason the homeless are doing better and most likely it's because of their immune systems having to cope with them eating out of dumpsters for years on end and living in filth. This question ABSOLUTELY belongs here.",
"I understand the security and reasons you guys remove posts but this is a legit question that I truly believe belongs here."
] |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion"
] |
[
"Why are some axes rotationally stable but not others"
] |
[
false
] |
A few of us in the lab have been thinking about this recently. Take something heavy and rectangular, like a box, and flip it in the air. Depending on the axis of rotation the box will either remain spinning in the same orientation, or move chaotically as it tries to realign itself. It seems that the axes that are stable are those with the largest and smallest moments of inertia. If we think about conserving angular momentum, it makes sense that as the box slows down due to energy losses (say from air resistance, although looking on wikipedia this also appears to be true for satellites in space) then rotation will move to the orientation with the largest moment of inertia as L = I *omega, but I don't understand why the axis with smallest moment is also stable.
|
[
"Asking why is always a funny question, because it is the hardest to answer since you can always ask \"why?\" again. I can describe the mathematics behind this phenomenon and if you believe the math, then you can put faith in the reason it happens.",
"First, the moment of inertia of a rigid object around an origin is a tensor, essentially a 3x3 matrix composed of the the \"principle moments\" along the diagonal of the matrix and the \"product of inertia\" or \"mixed moments\" for the off-diagonal terms. You can choose the alignment of your coordinate system in such a way that the moment of inertia tensor is diagonal, meaning it only has the 3 principle moments of inertia along three axes. ",
"Assuming that the object's principle moments are of 3 different sizes: I1 > I2 > I3, then as you pointed out, rotation along the 2nd axis is unstable. A rigid body rotating freely without external torques or force is described by ",
"Euler's equations",
". Two conserved quantities can be derived from these equations: the total kinetic energy, T, and the total angular momentum, ",
".",
"T = (I1 w1",
" + I2 w2",
" + I3 w3",
" )/2",
" = ",
" ",
"We can use push these conserved quantities together into another conserved quantity: 2 T I2 - |",
"|",
" T, I2, and ",
" are all constants as described above. So if we spin the object around its 2nd axis (pointed along I2), then |",
"| ~ w2 > 0, and w1 = w3 ~ 0. I set them approximately equal to zero so that we allow for perturbation. Then the above conserved quantity becomes:",
"2 T I2 - |",
"|",
" = I1 (I2 - I1) w1",
" + I3 (I2 - I3) w3",
" ~ 0 = constant",
"When you look at this equation you will notice that the ",
" since I1 > I2, and the ",
" since I2 > I3. This allows us to increase the rotation of w1 as long as we also increase the rotation of w3. Essentially rotation of w2 is unstable because the motion can slip into w1 and w3 at the same time.",
"If you redo this argument with either 2 T I1 - |",
"|",
" or 2 T I3 - |",
"|",
" you get the first and second terms in the expansion are both positive or both negative, respectively. Since you can't keep the equation constant while changing the other rotations, you are locked into your original rotations around w1 and w3 respectively."
] |
[
"No. It is not due to just symmetry. This will happen with ANY rigid object as long as the 3 principle moments of inertia have sizably different values. "
] |
[
"Ok, that's interesting thanks. I do believe the maths!",
"I had figured it was something along those lines. I always like an intuitive reason though. I always find physics so much easier to grasp if you can understand it without resorting to mathematics, good though your explanation is. I guess we can boil it down to: perturbations of the system in the w1 and w3 case are not allowed as they do not conserve angular momentum and kinetic energy, while for the w2 case they are conserved if there are perturbations to the system. (I guess like the old balls at the bottom of a valley and top of a hill)."
] |
[
"How do rainbow shots work?"
] |
[
false
] | null |
[
"When the drink was mixed in the pitcher it wasn't one color, it was layered using liquids of varying densities such that the rainbow was vertical. As he pours slowly from the pitcher you get the top layer first, then the next and so on with some of them mixing slightly as you hit the barrier.",
"I believe that youtube clip has a link to a how-to video if you need a visual."
] |
[
"Yeah, I saw that, but why would liquids with different densities mix, then?",
"\nI mean, it's not like water and oil, is it?"
] |
[
"They will mix if you give them a little help, but the density and composition difference is enough so that they won't mix immediately. It requires very careful pouring so that they don't mix right away in the original container."
] |
[
"How 'fast' is the Alcubierre drive?"
] |
[
false
] | null |
[
"There is no limit, in principle, to the speed achievable with an Alcubierre drive. However:",
"It requires negative energy matter, which has not been observed, and the possibility of which is controversial.",
"In a flat spacetime, it also requires the existence of tachyons, which also have not been seen, and the existence of which would create sever causality problems (related to time travel).",
"The Drive itself would enable time travel, due the tachyonic motion it enables."
] |
[
"Ah, so negative energy generator and blahfuturescience time travel turns out not to be possible. Got it"
] |
[
"It just depends how much \"accepted\" physics you are willing to violate."
] |
[
"How exactly does antimatter differ from traditional matter?"
] |
[
false
] | null |
[
"Taken directly from the wiki on ",
"antimater",
": antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles. For example, a positron (the antiparticle of the electron or e",
" ) and an antiproton (p) can form an antihydrogen atom in the same way that an electron and a proton form a \"normal matter\" hydrogen atom.",
"You might be asking instead, how do ",
"antiparticles",
" differ from regular particles? The answer to this is: particles comes in pairs. A particle and its anti-particle. The anti-particle will have the same mass (for gravity) but will be opposite in charge. Interestingly, some particles are their own anti-particle (photons). ",
"There is a lot more to it, and its an active area of research in some regards (there is some asymmetry involved, because it seems as if most of the universe is made up of particles for some reason, not anti particles) and reading up on the wiki articles / following them can be helpful for finding out where we stand in understanding particle physics and the ",
"standard model",
" as a whole. "
] |
[
"There are many different particles. Some, like electrons, protons, and neutrons, form into atoms and molecules. We call these types of things (and the smaller particles they're made up of) 'matter.'",
"Now, particles interact. They merge together, break apart into other parts, etc. One specific interaction is where two particles annihilate each other. When one particle can annihilate another like this, we call it an antiparticle. For example, the electron's annihilated by the positron.",
"For each particle, there's another one that annihilates it. And we find it will have opposite charge, too. The electron has a (-) charge, the positron has a (+) charge. One interesting thing is that the photon has a (0) charge. Since the opposite of 0 is 0, photons are both particles and antiparticles. Photons can annihilate each other. An antiparticle can annihilate its corresponding matter particle.",
"Antimatter refers to such antiparticles, or combinations of them."
] |
[
"What do you mean when you say they will annihilate each other? Truly annihilate or just figuratively? If so, wouldn't that violate the law of conservation of mass?"
] |
[
"Do rockets going to outer space cause any kind of depletion in the Ozone layer?"
] |
[
false
] |
Does it put a temporary hole that leaks any significant amount of ozone?
|
[
"No. A few things you need to realize:",
"The atmosphere is held to the Earth by gravity. It is not held there by some giant wall that can be punctured and leak. To get a significant amount of gas in the atmosphere to float off into space, you would have to turn off gravity.",
"The atmosphere is made of gas, which is fluid. When a solid object travels through a gas, it does not punch a permanent hole in the gas. The gas just flows around the object and reconnects with itself on the other side. There can be short-term low pressure areas just behind the moving object, but no long-term holes.",
"When people say there is a \"hole in the ozone\", they don't mean that there is a literal hole in a wall where stuff leaks out. They mean that there is a region in the ozone layer where ozone density is lower than it should be. It's like saying \"there's a hole in my bank account\". You don't mean there's a literal chasm at the bank under the safe. You mean that there is money missing. It's the same with the \"hole\" in the ozone. Furthermore, the \"hole\" in the ozone is not permanent, but comes and goes in natural cycles. Also, the hole in the ozone has mostly recovered since its worst state in the 1980's.*",
"*UPDATE: More precisely, the rate of change of the ozone hole area has stabilized since the 1980's, so that things are not steadily getting worse."
] |
[
"The hole in the ozone has mostly recovered since its worst state in the 1980's.",
"That's not true. This year the ozone hole measured 24.1 million km",
" whereas the largest hole for any year in the 1980's was 22.4 million km",
". The ozone hole really started to form in the 1980's and it is no where near close to recovering but it is seeing some possible improvements",
". It will take several more decades before it actually recovers",
".",
"http://ozonewatch.gsfc.nasa.gov/meteorology/annual_data.html",
"http://www.esa.int/spaceinimages/Images/2013/02/Total_ozone"
] |
[
"You're absolutely right that some of the gasses would be propelled by the rocket out of their natural position. However it's very unlikely that any of these reach escape velocity. Earth's gravity continues to influence things outside of the atmosphere, too (Quick quip: The reason people on board space stations feel \"weightless\" is because they're actually continuously falling towards Earth. They are also moving very very fast tangentially to Earth as well so their fall can last for dozens of years. So gravity is almost as strong even up there as it is for us down on land. Many people think that as soon as you get to space you're weightless.). Gravity would quickly bring most of the gasses back to Earth."
] |
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