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[
"My 4 year old wants to know: Why do magnetic fields exist?"
] |
[
false
] | null |
[
"Most people being honest will tell you they don't know. There are very few people I'd accept an answer from, because you're trying to explain why a fundamental force exists. You can ",
" magnetic fields from electric fields, but that fails to explain why it is present. Getting to the real root of the answer requires that you're very good at piecing information together and have read a lot of physics material.",
"It'd be like trying to explain gravity. The closest we've got is \"some sort of bending in space/time\" which is ",
" unintuitive.",
"Best to tell your kid that even grown scientists have trouble with it, and that it is a great question."
] |
[
"That's an incredibly deep question for a 4 year old! Were they just introduced to magnets? Tell them that magnetic fields and electric fields go together like two sides of the same coin.",
"Electric fields come from charges. ",
"Magnetic fields come from when those charges move around."
] |
[
"You know those hairy rubber balls for kids? When you hold it still you get spiky hair pointing out away from the ball, this is our electric field. When you move the ball around or spin it, the hair gets warped around, this is our magnetic field. Think a 4 year old would get that?"
] |
[
"Why isn't the human body comfortable at 98.6 degrees if that's our internal temperature?"
] |
[
false
] |
It's been hot as hell lately and got up to 100 yesterday. I started to wonder why I was sweating and feeling like I'm dying when my body is 98.6 degrees on the inside all the time? Why isn't a 98 degree temp super comfortable? I would think the body would equalize and your body wouldn't have to expend energy to heat itself or cool itself. And is there a temperature in which the body is equalized? I.e. Where you don't have to expend energy to heat or cool. An ideal temperature. Edit: thanks for all the replies and wealth of knowledge. After reading a few I remembered most of high school biology and had a big duh moment. Thanks Reddit! Edit: front page! Cool! Thanks again!
|
[
"Your body is a like a heater that is always on; it cannot be turned off because that heat is produced by and required to maintain a delicate environment for your life processes.",
"Heat only flows from hot to cold. If temperatures are equal, there is no cold for the hot to flow to.",
"If 98F is ambient temperature then the constantly-produced heat in your body has nowhere to flow to. The heat will build up in you and you will overheat.",
"The rate of heat flow is proportional to the difference between the hot and the cold. Even if your internal temp reaches 105F+ and outside is 98F the heat flow would be small.",
"We evolved sweating as a way to cheat this by using evaporation to pull away heat from our skin. When water evaporates, it actually cools down when doing so, because changing a liquid to a gas takes energy (heat).",
"This works so long as the surrounding air isn't already full of water. Once it is full, sweat stops evaporating and you will overheat no matter what. This kills people."
] |
[
"So your body puts about the same heat out as a 50w lightbulb.",
"You're constantly making heat, constantly metabolizing. ",
"If it's around room temperature, you are able to radiate the heat away without using any sweat. The variance in temperature is able to keep you feeling fine as is.",
"But the closer you get to the temperature our bodies run at, the less heat you are able to passively let off. So you sweat to use the power of evaporating water. Assuming it's not humid out this works well for a while, in fact, it works even past our own body temperature so long as you stay hydrated. But if it's kinda muggy out, then you can't lose the heat faster than it builds.",
"And so. You overheat. Just like a car going through a desert. The coolant and engine is hotter than the outside, but as outside nears closer to the car's temp, it can't drop all that heat away fast enough.",
"[Edit: Wow this blew up! I hope my explanation makes sense to you all. I tried to ELI5 it as much as possible so even the people from the back of the class understand it)"
] |
[
"So what is happening then in hot tubs or especially saunas where the temperature is often well over 98.6?"
] |
[
"Why does heat try to escape?"
] |
[
false
] | null |
[
"http://en.wikipedia.org/wiki/Entropy",
"This has been removed because it’s a commonly occurring question on ",
"/r/AskScience",
" or a question that can be answered easily through a single Google or Wikipedia search. To check for previous similar posts, please use the subreddit search on the right, or Google site:reddit.com",
"/r/askscience",
" ",
"For more information regarding this and similar issues, please see the ",
"FAQ."
] |
[
"Thanks for the link to the wikipedia page. Unfortunately, I'm finding this to be a bit too complicated for me to understand still. Could I submit a question to explain it like I'm 5 instead?"
] |
[
"Hi there,",
"I'm not a mod of ",
"/r/explainlikeimfive",
", but from my perspective, I don't see why not. Good luck!"
] |
[
"Is it important to drink a lot of fluids when sick with a flu or common cold?"
] |
[
false
] |
[deleted]
|
[
"The vast majority of the time, your body can get rid of excess water. There are a few pretty specific instances when you can get overhydrated, ill tell you about two really quick.",
"Psychiatric conditions: There are certain psychiatric disorders in which a person feels the need to be constantly drinking water, called polydypsia. These people will drink tons and tons of water throughout the day, which can lead to symptoms i will discuss below.",
"Endurance athletes: Excessive amounts of exercise leads to loss of water AND electrolytes. If, during the course of a marathon, a runner only drinks water and never grabs any of the Gatorade that they have available, you can see symptoms of overhydration in them during or after the race. ",
"They lose too many of their electrolytes and dilute what remains with the water they are taking in, which can lead to cramps, dizziness, vomiting, and confusion. I may also see a slower heart rate and a weak pulse. In extreme cases, this can become so severe that the cells in the brain swell, which can lead to seizures, coma, and even death. ",
"Remember these are extreme cases! Dont sit in fear of drinking your glass of water!"
] |
[
"Even if you are not bedridden with a very high fever and sweating, if you have the flu or a \"cold\" you will have a somewhat elevated body temperature. Because of this, your body will be losing more water than normal, even if you cant notice it (much of your daily perspiration is unnoticed anyway). ",
"The common thought is to drink 8 eight oz glasses of water per day even if you are healthy, but we were taught (I am in medical school) that this can be detrimental because it is far too much. However, when you are sick, depending on how much diarrhea/vomiting you have, this much or even more may be necessary in order to prevent dehydration.",
"I couldn't find any literature to refer to so I apologize, let me know if you have any more questions."
] |
[
"I've often wondered about that eight glasses of water thing. I'd heard it's too much as well, but I've never heard what ill effects that level of overhydration can cause. The human body seems pretty adept at getting rid of excess water--or maybe I just have a tiny bladder."
] |
[
"Can you put out fire with petrol?"
] |
[
false
] |
I was wondering if it would be possible to put out fire with petrol. Would the 'wetness' of the petrol put out the fire if there was enough of it, or would the petrol alight too quickly for that to happen?
|
[
"If you can exclude oxygen from the reaction then yes. This is not the case for things like gunpowder though since they have their own oxidant in the reaction already."
] |
[
"If you had a sufficient volume of gasoline, at a temperature far below its flash point, MAYBE. It's all about heat. If enough of the gas gets to its flash point, in contact with oxygen and the flame, it will light. "
] |
[
"I should have added, you can extinguish a lit match in high flashpoint fuels, like diesel or JP-8, don't try this at home please."
] |
[
"is there a correlation between the Sun's activity and Global Warming?"
] |
[
false
] |
The temperature where I live (Ontario, Canada) rose 16 deg. C higher than average for this time of year. This corresponds directly with the solar flare activity reaching earth. Can this be coincidence and can it explain why global warming is occurring? Edit: Thank you all for your answers.
|
[
"There are several effects that solar activity might have on Earth's climate.",
"First, of course, is direct luminosity changes. If the Sun's energy output varies by even a fraction of a percent then that could still have a significant impact on the Earth. In general the long term average of solar energy output is fairly stable (other than the regular variations of solar cycles) though it does fluctuate a little over longer time periods and the difference between normal sunspot activity and \"maunder minimum\" periods appears to be significant.",
"Second, solar activity specifically in regards to the solar wind will impact the cosmic ray flux at Earth, which will affect cloud formation. The effect of cloud cover on climate is still poorly understood but definitely significant.",
"Overall we can discount short-term effects such as what you have observed as merely random correlations, there's no plausible mechanism for significant temperature changes due to solar flare activity.",
"Over long time periods there is some evidence that the Sun's activity has an effect on climate, but ultimately we just don't know. We don't have good records of Earth's weather and the Sun's activity to make any firm conclusions. What evidence we do have seems to indicate a correlation between \"maunder minimum\" sunspot lulls and climatic cooling, but even that is rather tenuous."
] |
[
"Solar activity varies between minimums and maximums every ten years. This is a constant trend that has not changed for millions of years. This recent solar storm has occurred because the sun is nearing a solar maximum in 2013. Meanwhile the process of global warming is completely unrelated. We have released so much carbon dioxide into the atmosphere in such a short space of time that it is having an effect on our climate. Carbon dioxide acts as a blanket around the Earth stopping outgoing radiation from escaping into space. In 1850, carbon dioxide was 280 parts per million, it is now 340. Even if we stopped producing carbon dioxide right now, it is likely that the global average temperature will rise 4 degrees Fahrenheit. Although this may not sound like much, past events in the Earth's history with a similar rise in Carbon dioxide levels and temperature led to mass extinctions and dramatic climate change. Global warming is without doubt caused by human activity. If we continue to produce carbon dioxide at current rates, we could see the average global temperature rise more than 15 degrees Fahrenheit. This would be absolutely cataclysmic for the human race. As for the recent warm front that changed the temperature so dramatically in ontario, this is an isolated event which is merely part of the earth's climate becoming more and more extreme. "
] |
[
"Good stuff here. I just wanted to add that while solar cycles aren't really responsible for daily or very short-term changes in weather or climate, they can occasionally factor in on slightly longer time scales, such as a year. Solar maxima and minima will occasionally cause some deviations, such as ",
"The Year Without a Summer",
"."
] |
[
"What happens in a light bulb when it burns out? Is it random or is there someway to know it's about to happen?"
] |
[
false
] |
Every light bulb I've ever had has always blown out when I'm trying to flick it on, is it possible for them to burn out in the middle of use? If I never turned off the light assuming a constant surge free power source, would the light stay on forever?
|
[
"The filament of a light bulb is just a thin piece of metal, usually tungsten. When it's heated, little bits of tungsten can evaporate away and make slightly thinner spots. The thin spots tend to get hotter since the same amount of electricity is passing through a thinner wire, which increases the evaporation rate. Eventually the spot gets thin enough that it breaks under the sudden thermal stress when the filament heats up.",
"This is one of the reasons to use halogen bulbs. The halogen gas helps deposit the evaporated tungsten back on the filament, and so the filament can last longer and run hotter."
] |
[
"You're right, I left out the effect of turning the bulb on and off hundreds and thousands of times. This causes fatigue in the filament. I posted a link to wikipedia in a comment above that can help ",
" things. Eh? Eh? Who says there's no room for humor in AskScience?"
] |
[
"The commenter was right, thermal shock does have a large effect on the filament. Your argument against it could be thought through more carefully, though.",
"Consider this: the difference in temperature between winter and summer is, say, 50 degrees C (122 F). The difference between room temperature and the temperature of the glowing filament is around 2000 degrees C. Linear thermal expansion is a function of the change in temperature, so adding 50 degrees to the temperature difference makes it ~2050 degrees C. This would be considered relatively negligible."
] |
[
"Why is Australia filled with so many dangerous animals/plants?"
] |
[
false
] |
I saw a thread in reddit mentioning a tree that can kill you... And it has really gotten me wondering, why are so many deadly animals and plants (venomous/poisonous) found in Australia? I mean, I think I understand evolution, but why would such a large number of them be found in Australia? If I recall correctly, I remember watching a documentary in Discovery about the ten deadliest animals, and like six or seven would be found in Australia... That's insane! So, is there any reason for this or is Australia just unlucky? I read though all the replies, but I can't reply to all to say thanks. But this has been highly educational, so thank you! It appears it was a misconception from my part. I'll be honest, I used to believe I would never have the guts to visit Australia, but now I feel like I could go.
|
[
"Australian ecologist here: my god, there is a lot of rubbish being touted in this thread.",
"Okay, first up: there are not more dangerous animals in Australia then elsewhere. This is a misconception fueled by silliness and exoticism. The famous list of Australia having nearly all of the world's most venomous snakes comes from a terrible LD50 study that only used five or so overseas snakes for comparison. To get a more accurate impression of relative venom toxicity, check out Dr Bryan Greig Fry's ",
"LD50 page",
".",
"For the question of why we have so many venomous snakes here to begin with, one has to look at the dispersal of snakes within Australia. First there was the best snakes of all (fact), the ",
"-- primitive snakes that branched off the snake family before pythons evolved. Australia was pretty empty with just these guys around, so when the ",
" came down from Asia, there was lots of space for them to diversify into. Elapids are very venomous snakes with fixed front fangs: cobras, mamba, etc. All venomous snakes in Australia are descended from these elapids.",
" Since elapids were the main game in town for so long, they diversified to take over all niches, from super-venomous (which get a lot of attention) to nearly lacking venom all together (which no-one pays much attention to!). So Australia has a diverse range of venomous snakes, not just highly venomous ones. Focusing on the big hitters and making ridiculous guesses as to why they're here is missing the bigger picture.",
"The very venomous sea snakes that we have are simply land elapids that diversified into the oceans.",
"Our spiders are not more venomous that those of anywhere else in the world. We haven't had a spider-bite fatality since the '50s, and even then it was children and the elderly that succumbed. ",
"South America and Africa have many more venomous species than Australia, including more venomous lizards and venomous mammals (!).",
"Edit: I worked out some ratios of lethal snakes:non-lethal snakes for a few different countries ",
"here",
". Australia ain't so bad."
] |
[
"FYI \"passively toxic\" is the same as poisonous. Venomous is used when toxins are used offensively. IE; frogs are poisonous, snakes are venomous."
] |
[
"This is absolutely incorrect, because there aren't more dangerous animals in Australia than elsewhere in the world. You're speculating and providing the wrong answer."
] |
[
"The size of the solar system is usually measured by how large it is from end to end, but how \"tall\" is our solar system?"
] |
[
false
] |
I know there's no relative up or down (or top or bottom) in space, but how large is our solar system measured up and down perpendicular to its plane?
|
[
"It really depends on which objects you want to include in your definition (the \"length\" of the solar system depends strongly on your definition too), and even then, what you're using as a reference plane. The ",
"Oort Cloud",
" a (hypothetical but commonly accepted) body of comets orbiting the sun is roughly spherical, and extends probably a light year. So, if you count this region, the solar system's extent is about the same in each direction.",
"The main body of the torus-shaped Kuiper Belt, which extends about 50 AU (far beyond Neptune, which orbits at ~30 AU) but is a few orders of magnitude smaller than the Oort Cloud, extends about 10 degrees from the plane of the planets, so counting this region, the thickness of the solar system is about",
"2 (50 AU) sin(10 degrees) ~= 9 AU.",
"NB the Kuiper Belt does include many objects with higher orbital inclinations (that is, that make a larger angle with the plane of the solar system), but the density of these objects is much lower than that in the main body of the belt.",
"Finally, if you just look consider the major planets (no Pluto), you'll find that that the one that travels the furthest from the \"invariant plane\" is Neptune, which moves as far as ~0.38 AU from the plane. (The invariant plane is, roughly speaking, the best physical approximation to the plane of the solar system, weighting objects by angular momentum; this is almost the same as the Earth's orbital plane.) In other words, you could specify a cylinder whose ends are parallel to the invariant plane that is only ~0.75 AU thick---in particular, less than the distance from the Earth to the Sun---that would contain the planets through the distant future. (In fact, you might be able to find a much thinner cylinder that would contain the planets, but to find its thickness, you'd need to know the orbital inclinations of the planets relative to the others' orbital planes, and I don't have this data handy.)"
] |
[
"Thank you for the incredibly detailed answer. I've got a potentially silly follow-up question, but: If I'm remembering my basic astronomy correctly, the asteroid belt isn't spherical, right? It's roughly a ring the encircles the inner planets?",
"Would the \"height\" of the asteroid belt be comparable to the diameter of that imaginary cylinder you described? ",
"Thank you again for your time."
] |
[
"More or less by definition, yes, though there are many asteroids whose orbits bring them closer to the Sun than Mars or farther than Jupiter (some have quite interesting orbits, like the Trojan asteroids, which co-orbit with Jupiter about 60 degrees ahead of or behind it). Like the Kuiper Belt, the bulk of the asteroids have a modest orbital inclination (<= 20 degrees for the asteroid belt)",
"Using a figure of 3.2 AU for the outer radius of the main asteroid belt and 20 degrees for the maximum inclination, the approximate thickness of the asteroid belt is",
"2 (3.2 AU) sin (20 degrees) = 2.2 AU, which is a few times thicker than the cylinder I mentioned.",
"Virtually all asteroids have inclinations less than 30 degrees, but some have much higher inclinations (for example, the orbit of the recently discovered 2010 OA101 is inclined 84 degrees from the plane of the solar system). Here's a graph of the distribution of inclinations versus orbital radius:",
"http://en.wikipedia.org/wiki/File:Main_belt_i_vs_a.png",
"Also, note that Eris (a minor planet larger than Pluto) has a highly inclined orbit---about 45 degrees. Its orbit is also eccentric, but a lazy calculation shows that you'd need to thicken the previously mentioned cylinder to 26-68 AU to include its orbit."
] |
[
"So Earth's magnetic field protects us from cosmic rays, why not generate one around space craft?"
] |
[
false
] |
As I understand it Earth's magnetic field isn't all that strong though it is large. Would it be too difficult to generate a magnetic field without damaging electronics or communications? Or would it use too much electricity? Or would it create some kind of charge problem?
|
[
"It is possible, there's actually a ",
"paper",
" on just that subject. Generally speaking it's more efficient to create a magnetosphere than merely a magnetic bubble. The reason why it hasn't been done yet is that it hasn't been absolutely necessary. The biggest danger is in interplanetary space, and the probes in interplanetary space are unmanned and use radiation hardened electronics anyway. Also, the radiation shield would interfere with some measurements (particle flux, magnetic fields, etc.) which are important for some missions. I expect we won't see this sort of thing be implemented until interplanetary manned spaceflight is more common."
] |
[
"It's a serious question, if the idea is impractical - let them know why. I assumed ask science was for teaching people stuff, not demeaning their questions."
] |
[
"It's a serious question, if the idea is impractical - let them know why. I assumed ask science was for teaching people stuff, not demeaning their questions."
] |
[
"How do we know how good animals' eyesights are? Aside from observation (watching a hawk hone in on its prey from 200 ft high), how is it determined?"
] |
[
false
] |
From time to time I wonder how poor eyesight affects an animal in the wild. I imagine if I had to live life in the era before eyeglasses, I would be so screwed, even as a human. I can't imagine what kinds of detrimental effects poor eyesight would be on an animal in the wild. I'm very curious as to which animals (besides bats) have naturally poor eyesight?
|
[
"There are two types of photoreceptors, rods and cones. Rods are more sensitive to light (dim light can activate them), cones give us details, colours, acuity, etc.",
"There is a segment in the retina called fovea centralis, within which is the macula. The macula has only cones, so when the light hits the macula, that's the clearest the image can get. Birds have a superior vision to humans because they have two maculae, while we have only one, so this is one criterion of good eyesight (# of maculae, size of maculae, # of rods vs. # of cones, etc.)",
"detrimental effects poor eyesight would be on an animal in the wild",
"Not necessarily. Evolution solves it for them by compensating them with another ability.",
"I'm very curious as to which animals (besides bats) have naturally poor eyesight?",
"Fish, so they rely on pheromones/chemicals. Moles, they rely on Eimer's organ, etc."
] |
[
"I don't think this answers OP's question, but it is cool information nonetheless."
] |
[
"Yes, I guess I'm unclear on how I'm asking it, and I hadn't thought out my question well. I guess through dissection, we can determine what kinds of cells (rods and cones) they have. And then I wonder how we know how each cell functions. I guess that part would be done through lab experimentation with live animals? Then after that, through further dissection of more species, we can extrapolate how well each animal sees. But what I really don't understand is how we know an animal can see for example 1000 colors if we don't have the ability to see those colors ourselves."
] |
[
"Can we make elements of the period table in the lab?"
] |
[
false
] | null |
[
"I mean huge amounts of them, in the scale of thousands of metric tons for example.",
"No, we can't do that.",
"We can create small amounts of certain nuclides at a time using reactors, and ",
" small amounts of pretty much anything you want using accelerators."
] |
[
"very small amounts of pretty much anything you want using accelerators.",
"So, we know actually how to make the elements, accelerators. But the problem is the energy needed?"
] |
[
"The energy, the cost, and the time it would take to create macroscopic amounts of material is just totally unfeasible."
] |
[
"The typical rule of thumb is chemical reactions occur more quickly by increasing temperature. Are there reactions that occur more quickly at 'cold' temperatures?"
] |
[
false
] | null |
[
"At the scale of a single individual reaction this is ha hard physical fact rather than a mere \"rule of thumb\". A stable compound is a local minimum of energy in terms of the geometric coordinates of the atoms, and the potential-energy surface is continuous. That's a formal way of saying you ",
" have to go up in energy to get from one stable compound to another. There is always a \"transition state\". ",
"Per the ",
"Eyring equation",
" that relates the transition state to the reaction rate, it can only increase with T as long as the energy difference from the reactant state to the transition state (ΔG), is positive - which it must always be. So no. No ",
" reaction rate will go slower increasing temperature.",
"(Note I'm talking about ",
" here, i.e. the number of molecules reacting per second. The \"speed\" of a reaction in the sense of the time it takes to get from reactant to product is not relevant to that, the limiting factor is how many molecules have enough energy to get over the transition state barrier, and that depends on the molecules' temperature. A catalyst increases the rate but not necessarily the speed)",
": if you have multiple reactions going on at the same time, the situation can be more complicated. Say reaction A produces your product while the competing reaction B consumes it, so ",
" rate at which your product is produced is then going to depend on the rate of A minus the rate of B. The reaction rates of both A and B will increase with temperature, but they don't necessarily increase by the same amount. Reaction B may overtake A with increasing temperature and you will then end up producing ",
" of your product per unit of time. ",
"The net or effective rate at which your product is being produced would in that scenario decrease with temperature, even though the rate of all the individual reactions increases."
] |
[
"There are examples of a reaction rate increasing at freezing temperatures. The reactants stay in solution and the concentration of them is increased.",
"Here is one example of this:\n",
"http://pubs.acs.org/doi/abs/10.1021/jp9525806",
"There's another recent example of this occurring for an enzyme-catalyzed reaction but I can't seem to find it.",
"Edit: It was actually an oxime ligation that I was thinking of:\n",
"http://pubs.acs.org/doi/abs/10.1021/acs.bioconjchem.5b00611"
] |
[
"An important case of this: B can be the reverse reaction to A. If A is exothermic (releases energy), its reaction rate will typically increase slower than the reaction rate of the reverse reaction. The ",
"Haber-Bosch process",
" has this issue for example. You want high temperatures to speed up the reaction - but at high temperatures the reverse reaction is even faster and your yield is low. Reactors typically run with just ~20% yield and let the gas cycle through the reactor multiple times."
] |
[
"How do we experience life as a single conciousness if there is no 'central hub' for the brain? Or is there?"
] |
[
false
] | null |
[
"We don't know.",
"\"Consciousness\" isn't even slightly-well defined."
] |
[
"Since every atom in your body is replaced roughly every seven years, I would lean more towards the idea that continuity of experience is an illusion and you weren't actually that person you see in a seven year old photo, that person is gone.",
"But no one knows for sure, consciousness is ill-defined."
] |
[
"That isn't actually true - it appears that many atoms, especially those in the brain, remain for an entire lifetime (or much of one).",
"Besides, if you argue that a change of a specific atom for another identical atom would change a person's consciousness, then you have to invoke some law of physics that nobody knows of yet. Since as we currently understand our universe, there is no meaningful difference between one hydrogen atom and the next besides their location in time and space. You would also have to invoke a way in which consciousness can be tied to individual atoms, at least in part - which may indeed be true but it hasn't been shown yet.",
"I'm not disagreeing with your conclusion, I also have the hunch that the most simple answer is that continuity of consciousness is an illusion - but science doesn't really support any such claim (as you allude to with your last sentence, so I guess you knew that)."
] |
[
"Conceptual explanation for the sum of all natural numbers (1+2+3=-1/12)?"
] |
[
false
] |
Sooooo.... I was looking for advice on my dating profile and everyone freaked out about the "sum of natural numbers "(I had it listed on my things I think about). And now I'm a bit concerned because I show this example to my high schoolers when they ask me to blow their minds and I want to make share I'm not misleading them when I explain this to them conceptually. I understand there are rigorous proofs, hand wavy proofs, controversial proofs, BUT, I want to see if this makes sense conceptually as this is how I've been explaining it to my students. Ok so I generally use the proof from that So if we take the series ,1-1+1-1+... and we were to use it model a light switch and consider on=1 and off=0 and we keep flipping the light switch on and off (for infinity) then the total number of photons, the total intensity, the total luminosity in the room is 1/2 what it would normally be at any moment in time (avoiding any sort of multi-photon or non-linear effect) and this is true as long as the switch is being flipped on and off. As soon as you stop, this no longer represents an infinite process and will equal either 1 or 0. Is this okay? Is this an accurate description/analogy? Secondly, if that conceptual example is satisfactory then can we say the same of the sum of all natural numbers? It is not a trick, or a fallacy but a meaningful answer that is only true within the context of a problem and is only true when the process in question is infinite? Third, is it fair to say that the answer we get is meaningful within the context of a specific problem in a field like Quantum Field Theory, in the same way that an answer like 1/0 would be meaningful in Cosmology? My kids really get into it and they have taken it upon themselves to try to "prove" other infinite series on their own. Its pretty amazing. Their answers are WRONG, but the effort and the spike in their level of interest, specifically in math, is insane. I'd like to keep using it. Anyway, thanks for reading and for any insight you can offer.
|
[
"Here is what's really going on:",
"The sum 1+2+3+... does NOT equal -1/12. Rather, there are regularization techniques that have us replace the infinite sum 1+2+3+... by -1/12.",
"In mathematics, we can define something called the Riemann zeta function. For complex numbers with real part greater than 1, there is an infinite series representation of the zeta function:",
"zeta(s) = 1/1",
"+1/2",
"+1/3",
"+...",
"Now through complex analysis, you can extend the zeta function to other values of ",
", and it turns out that zeta(-1)=-1/12.",
"Now what happens if you get the sum 1+2+3+...? This sum diverges -- unambiguously, it diverges. It does not equal -1/12.",
"However, suppose you encountered this expression and wanted to see if there was a way to make sense of it. The technique of zeta function regularization says this: If you get this sum for something physical, let's think of it as a situation in which you expanded something in a series where you shouldn't have because the series was not well-defined. So, in this case, you imagine this sum has arisen because you at a fundamental level had zeta(-1), but wrote it out using the infinite sum expression that is only valid for numbers with real part > 1. If you did that, you would incorrectly write",
"zeta(-1) = 1/1",
"+1/2",
"+...=1+2+...",
"So we take the divergent infinite sum and replace it by zeta(-1), that is, -1/12. But this does not mean the sum of the natural numbers is -1/12.",
"(Copied from my ",
"answer in another thread",
".)"
] |
[
"What i really don't like about that numberphile video is that they sweep things under the rug in a misleading way.",
"So if we take the series ,1-1+1-1+... and we were to use it model a light switch and consider on=1 and off=0 and we keep flipping the light switch on and off (for infinity) then the total number of photons, the total intensity, the total luminosity in the room is 1/2 ",
"The important thing to note is that you're not calculating the ",
" here, you're calculating the ",
". The sum you describe does ",
" converge, however we can ascribe to it a useful value: it's average. Again, this is ",
" the value of the sum if you were to carry it out by hand to infinity!",
"Remember, for (infinite) sums you can simply do it for n terms - it's easy. Just do it. You can do this using a very rudimentary computer program or even excel. Simply make a list of the first 100 integers and add them...then the first 1,000, then the first 1,000,000 and so on - you'll see the sum's 1) don't converge and 2) they certainly don't converge to -1/12.",
"I came across a great ",
"video",
" by Mathloger on youtube. he does a pretty good job explaining how the result comes about in all its subtleties and emphasizes that the notion that the sum of all natural numbers being equal -1/12 is completely outrageous and a total misunderstanding/misrepresentation of the ideas he discusses in the video."
] |
[
"please don't teach them that, especially not with the numberphile video in this handwavy way, it's extremely misleading. please don't teach things you don't understand well enough.",
"i'm sure there's a lot of challenging things, that you understand well and might motivate them in the same way.\nteach them ordinary sums, they are challenging enough. convergence is astounding enough sum 1/2",
" = 2. things like 0.999... = 1 are often misunderstood but can be explained with convergence, sequences and series.\nusing different summation methods is something much more subtle. finally, to define 1+2+3 ... = -1/12, you don't just use some off the shelf \"organic\" summation method (as may be the case for 1-1+1-1+...). for more details check the better video:",
"https://www.youtube.com/watch?v=jcKRGpMiVTw",
"that will answer most of your questions.",
"not the numberphile one. the numberphile one is extremely bad and wrong (even the follow up video, russian talking about gold nuggets).",
"the basic problem in the numberphile videos is that they deny all subtleties, claim the steps they are doing don't need a sophisticated justification, and that it is indeed ",
" that is -1/12.",
"also you should check this post on ",
"/r/math",
" and the discussion",
"https://www.reddit.com/r/math/comments/4g0llp/ramanujan_making_sense_of_123_112_and_co/",
"besides when teaching about complicated things (note the about), you will always simplify and leave details out. be sure to mention that \"this isn't 100% correct\", \"there's more subtleties involved, here, here and here\". put warning signs up. math isn't naive calculation without questioning the steps.",
"the math isn't in performing the steps but in justifying the steps. that's the most important thing.",
"so even if you don't put in the effort to justify all the steps rigorously, you should mention that they need a some mathematical effort and rigour to properly justify. and don't use this physical proof attempt (light switch). it's problematic. \"proving maths by physics\" is problematic as a whole. you don't prove a mathematical statement with a light switch (i have graduated in math and physics, so i have a heart for both, but no, you don't prove math with physics). the most you can do is ",
" some mathematical notion by using physics."
] |
[
"Can bacteria, viruses, etc. get diseases just like humans or plants?"
] |
[
false
] |
If bacterium, viruses, fungi, etc cause disease, can they themselves get a disease?
|
[
"Bacteria can be infected by ",
"bacteriophages",
", and they can be predated upon by ",
"bacterivores",
".",
"Viruses can be infected by ",
"virophages",
", though these are much rarer than bacteriophages and have only been discovered relatively recently.",
"Fungi can be infected by ",
"mycoviruses",
", and they can be predated upon by ",
"fungivores",
" – including humans! They can also be infected by bacteria and even other fungi.",
"You may also be interested in the concept of ",
"hyperparasitism",
", wherein a parasite acts as a host for a different parasite."
] |
[
"I wonder if there are virovores and we just haven't discovered them yet 🤔"
] |
[
"Vira are probably too erratic to count upon for sustenance, meaning that only vira themselves would be capable of existing in a state that would allow this, but since they aren’t alive/capable of autonomous replication they wouldn’t be viable for reproducing via another virus either.",
"It doesn’t mean it doesn’t exist, but it’s very unlikely.",
"There are plenty of life forms that can break down (and probably utilise) vira, but ultimately that would not be a primary source or sustenance."
] |
[
"At what speed, in MPH, is blood pumped around the body?"
] |
[
false
] | null |
[
"Cardiac output is about 5.25 L/min, or 5,250 cm",
" /min",
"Aortic root diameter is about 2.4 cm on average, with cross sectional area of 4.5 cm",
"Therefore the average speed of blood flow in the aorta is 1167 cm/min.",
"Convert to MPH and you get about 0.5 MPH on average.",
"That said, the heart pumps blood in a non-continuous motion, so the speed fluctuates above and below that average with your heartbeat. The peak ventricular ejection velocity can be measured by echocardiogram and peak values as high as 3 MPH are possible (although 1.5 MPH would be a more typical peak velocity."
] |
[
"I am not a medical doctor. But, curious about the answer to your question, I found some journal articles on the subject.",
"Velocity of Blood Flow in Normal\nHuman Venae Cavae",
"Evaluation of blood flow velocity in the ascending aorta and main pulmonary artery of normal subjects by Doppler echocardiography.",
"Doppler echocardiographic measurement of flow velocity in the ascending aorta during supine and upright exercise.",
"The question is tricky to answer because blood flow is obviously highly pulsatile, so its velocity varies throughout the course of systolic & diastolic cycle of the heartbeat. It also varies depending on where in the circulatory system the measurement is taken: blood flow velocity is much higher through the aorta and the superior vena cava, for instance, than through the capillaries. It also varies depending on the age of the subject measured and whether the subject is exercising or at rest, standing or recumbent.",
"In short, the sort of answer you want is going to be a fairly vague and meaningless one. But judging from these articles and a few others I've been scanning, it seems that the resting rate in the superior vena cava and aorta varies between 35 cm/sec (.78 miles/hr) and 120 cm/sec (2.68 miles/hr) with a mean rate around 48 cm/sec (1.07 miles/hr). "
] |
[
"This is an interesting question. You might feel your heartbeat and your radial (wrist) pulse nearly simultaneously and be tempted into thinking that your blood is traveling that fast around your body. Alas, what you are feeling is just the pressure wave (which is damped gradually by the compliance of blood vessels so that your capillaries feel no pulse at all).",
"To answer this question, consider that since the vasculature is more or less a closed circuit, total volume flow remains constant as you move through the levels of branching. In other words, the same volume per unit time passes through the renal artery as through its branches, as through those branches' branches, so on and so forth. Flow = velocity * cross-sectional area (verify by unit analysis: cm",
" /sec = cm/s * cm",
" The cross-sectional area of any given level of the vasculature increases with branching. I.e. the total cross-sectional area of all the capillaries > that of the arterioles > small arteries > muscular arteries > elastic arteries > aorta. So if flow is constant, then mean linear velocity decreases with branching.",
"If you do the math, you get the 0.5 mph cited below for the aorta, but this drops precipitously to around ~0.03 cm/sec (0.0007 mph) in the capillaries. Compare to a snail's pace, estimated by some as 0.1 cm/sec (0.002 mph).",
"Red blood cells move slower than we might think even in the large arteries. It takes an RBC around 5 seconds to get from your heart to your wrist, for example.",
"Total circulation time from left atrium to left atrium is usually about 1 minute.",
"TL;DR: Your red blood cells crawl through your capillaries slower than a snail's pace.",
"Source: Boron and Boulpaep, Medical Physiology"
] |
[
"Can you drain a AA battery by touching both ends with your fingers?"
] |
[
false
] |
If I were to hold a AA battery with my index finger on one end and my thumb on the other for a long enough time, would the battery get drained?
|
[
"I just measured my thumb-finger resistance as ~1 MΩ. (I tried to approximate the contact area you would get with a battery, but that number will still vary a lot depending on how moist your skin is.)",
"1 MΩ connected to a 1.5 V battery means 1.5 uA of current will flow. According to the Wikipedia page on AA batteries the capacity of an alkaline is roughly 2 A-h. Divide the capacity by the current and the answer is that you will drain the battery 1.3 million hours, or about 150 years, which is much longer than it would take the battery to self-discharge on it's own.",
"EDIT: typo, days -> hours"
] |
[
"I wet my fingers and used two nickels to increase the contact area and the result was around 200 kΩ. A common ",
"CR2032",
" has a voltage of 3 V and capacity ~200 mAh so you would drain it in roughly 1.5 years, which is significantly shorter than the battery's shelf life. There are other lower-capacity batteries that you could drain even more quickly, but probably not in an amount of time that you would be willing to hold a battery between your fingers for."
] |
[
"It's a combination of several factors. First, the voltage is higher, so more current will flow if all else is equal. Second, the tongue is generally wet, which makes it significantly more conductive (lower resistance) than dry skin. Third, the terminals on 9v batteries are right next to each other, while on a button cell or a AA battery they are on opposite sides of the battery. If you touch both ends of a AA battery, you've probably got your thumb on one end and a finger on the other. The current has to flow all the way down into your hand and back up a different digit, which means that the path is much longer than the path taken by most of the current when you touch a 9v battery with your tongue. A longer path means more resistance, and therefore less current flow."
] |
[
"How does evolution work on the most basic of levels?"
] |
[
false
] |
This is going to be difficult for me to put into words, and may sound extremely dim-witted, so please bear with me. When an animal evolves, even slightly, how does that animal's DNA know how to develop itself in order to get better acclimated to its surroundings? In other words; on a molecular level, is the DNA structure somehow communicating with the animal's anatomy in order for it to revise itself for the animal's betterment? How does the DNA take in information from the host body's surroundings and then have an answer as to what it can specifically change within itself to give future generations an easier life? Imagine this hypothetical situation. A group of people begin living in a lightly flooded area. Slowly and after many years of living in this forever moderately-flooded area, the offspring begin developing webbed feet. How does the DNA/genetic composition of those people recognize that webbed feet will give them an easier time when walking about?
|
[
"There is nothing willful about evolution. It is a blind process.",
"Let's think about your genome and your descendants for a second. Your genetic code is composed of about 6 billion bases (each A T C or G in your code is one \"nucleotide base\") spread out over 46 chromosomes (a chromosome is just a linear molecule consisting of a bunch of As, Cs, Ts, and Gs lined up in a row (note that it's actually 2 sets of 23 chromosomes, where you have two copies of chromosome 1, two copies of chromosome 2, etc.). And of course, the order of the sequence on the chromosomes is important! ",
"So, when your sexual organs produce gametes (sperm or egg, depending if you're male or female), it does so by having a \"",
"germ cell",
"\" divide in a special way such that the gamete winds up with only one set of 23 chromosomes (i.e. just one of chromosome 1, one of chromosome 2, etc.), such that each chromosome is a mosaic of the two that you had, with the proportions being largely random (and you can read up on ",
"genetic recombination",
" and ",
"meiosis",
" to get a better sense for how this works). That's all a bit beyond the scope of the question though....",
"Anyways, the DNA on each chromosome is double stranded, and the bases pair one another in a particular way. A pairs with T, C pairs with G. So if a short segment of your DNA reads:",
"ATGCATG",
"then it's complementary strand will read",
"TACGTAC",
"if you're reading it in the same direction.",
"When this cellular division to produce gametes happens, the cell has to duplicate the DNA molecule in order to make sure that both of it's daughter cells wind up with double stranded DNA. It does this by breaking apart the two strands of the molecule and using each one as a template to reconstruct the missing half (it can do this because of the exclusive way in which the bases pair with one another). So there's an enzyme, called a ",
"DNA polymerase",
", that comes along and reads the code of the one strand, and lays down bases across from it to create a new complimentary strand. ",
"However, it's not perfect. Sometimes it makes mistakes, and puts down the wrong base. You've just had a mutation (or rather, there's just been a mutation in a gamete that you could pass on to your kids). So I said these polymerases aren't perfect, but they are pretty damn good. Of the 3 billion base pairs that you pass on to your kids, they'll have mutations at roughly 60 bases, relative to your genome. That's really not a lot, but it's enough for evolution!",
"Ok, so that's one way random mutations can happen, and it's by far the most common. However, you can also have ",
"insertions",
" and ",
"deletions",
" (which are what they sound like), ",
"translocations",
" (where big chunks of DNA get cut out and moved to different places in the genome), ",
"inversions",
" (where chunks of DNA get flipped around in reverse order), and a number of other more intricate things. ",
".",
"Ok, so then this is where ",
"natural selection",
" comes in: ",
"Some of these mutations, ",
" will wind up being beneficial to the organisms that carry them. Individuals who ",
" to wind up with these mutations (again, by chance), will wind up surviving to reproductive age and having kids more often than those who don't, specifically because of the advantage the mutations they carry afford them (i.e. very much not due to chance), and as such those mutations will tend to spread through the population over long enough time scales. ",
"Many mutations will be deleterious (disadvantageous), and as such individuals who happen to carry those mutations will be less likely to survive and reproduce, and thus those mutations will tend to not ever make it up to a high frequency in the population. ",
"Many mutations are completely (or very nearly) neutral in effect, so they'll just drift around randomly within the population, until perhaps one day the environment might change, and they might suddenly become either advantageous or disadvantageous, in which case natural selection will begin to act on them as described above.",
"So in the case of your hypothetical situation, we first would have to accept that having webbed feet actually ensured the people that had them a better chance of surviving long enough to reproduce than people who didn't have webbed feet. If this was true, then the population still has to wait around for a mutation for webbed feet to appear by chance before natural selection can begin to act on it. Also note that this example portrays evolution happening in a very simple \"one gene, one trait\" framework, when in fact nature tends to be more complicated. While these sort of traits do exist, current research is starting to suggest that the majority of natural selection may act on traits that are underwritten by very large numbers of genes in a much more complicated manner. For example, there are something like 200 genetic loci known to be associated with human height, and there are estimates that that number may actually be as high as 600, with each locus having a small effect on its own, and natural selection acting on them all in concert to produce the differences in heights we see between populations today (note: this is still just a hypothesis. We don't actually have strong genetic evidence for selection one height yet, that I'm aware of, but I wanted to give you a sense for a real trait that had this complex sort of genetics going on)",
"Ok. Hope I didn't ramble all over the place too much and that that was understandable. I've glossed over a lot of details, because individual paragraphs alone could be the topic of study for many week long units in an undergraduate course, but I hope I've given a good overview. Let me know if anything was unclear."
] |
[
"The DNA does not respond to its surroundings. Evolution is not goal driven. It occurs blindly through a series of random steps.\nSo what happens is as DNA is replicated occasionally there is a mistake in the copying (transcription). This occurs very rarely, usually once every multiple millions of base pairs, but as we have roughly 15 billion base pairs there is actually often many mistake per individual. Usually the mistakes do nothing. They occur in non coded regions, or don't really affect the proteins which they code for. However sometimes the do cause an effect.\nUsually this effect is negative and the individual is out competed by everyone else. However sometimes the mutation is beneficial. In this case the individual is more likely to reproduce and have its offspring reproduce. After a while every individual will contain this new mutation.\nWhat we have to realize is evolution does not occur on an individual level. Evolution occurs on the global population level. Only when the distribution of genes in a population changes can we say that evolution is occurring. I hope this makes sense."
] |
[
"It seems you have confused transcription with replication, or perhaps just accidentally typed the wrong word -- it happens! But for accuracy's sake, a correction: When mutations occur during DNA replication, those mutations are heritable, and can be acted upon by natural selection as you described. If there are errors in transcription (when DNA is \"transcribed\" to mRNA in the process of gene expression), those are not heritable. The effect of that error could range from nothing to ultimately the expression of a harmful protein, depending on the type of error and gene in question."
] |
[
"Coming from a 3rd year electrical engineering students perspective, I know how static electricity works but what I don't know is why it works essentially. What I'm asking is; why do some materials hold a better charge than others and while one material likes to gain a negative charge, Visa versa?"
] |
[
false
] |
By Visa versa I mean another likes to give away electrons. I figure it has to do with surface area in some instances like with fur or styrofoam but with glass and other non conductors that can have the same surface area I don't know where these extra electrons or holes are stored.
|
[
"Our basic understanding of static electricity still seems to be pretty murky.",
"There is some evidence that static charging is not mediated by electrons and holes per se, but rather by ionic separation (a molecule splits apart into positive and negative ions, each of which resides on a different surface). Different materials reside at different parts of the triboelectric series based on their ability to stabilize different types of ions.",
"There have been demonstrations of making systematic changes to a material that change its position in the triboelectric series in a predictable way. See ",
"https://pubs.acs.org/doi/abs/10.1021/am501557m",
"Surface area has to do with the amount of charge a material can \"hold\", but not with the sign of charging. (This is why toner particles used in photocopiers are so small -- high surface area to mass ratios)",
" that it is well-established that humidity helps to dissipate static charge (presumably by slow neutralization of charges due to ion or electron mobility on water-rich surfaces or through moist air). Materials that are very hydrophilic (tending to absorb or bind water on their surfaces) tend not to be able to build up or maintain a static charge."
] |
[
"Differences in shoe materials and surfaces, frequency of contact with conducting surfaces, perhaps skin conductivity, etc."
] |
[
"Posting what I think is an appropriate follow-up question:",
"Last week we had a party. We had a bunch of balloons, all the same size, all made of the same latex. They all had foil confetti stuffed into them and were then inflated. Half were inflated the normal way, by breathing into them. The other half were inflated with helium from a canister. ",
"I tried to show my son how you could rub a balloon on your jumper repeatedly until it amassed enough overall charge on the surface that it would stick to the wall. After rubbing different balloons we noticed that in the balloons containing air, the confetti distributed itself evenly across the inner surface of the balloon once it became charged. In the helium-containing balloons, on the other hand, the majority of the confetti just sat in the bottom of the balloon, seemingly not attracted or repelled by any charge at all.",
"What is the explanation for this? Does the gas inside the balloon somehow affect the ability of the latex to pick up or retain an overall charge?"
] |
[
"As Earth's helium supplies dwindle in the future, is it feasible that it could be supplied as the byproduct of fusion reactors?"
] |
[
false
] |
Estimates place our supply of helium from 10-30 years worth, and falling fast.
|
[
"http://www.cbsnews.com/2100-205_162-6797764.html",
"http://digitaljournal.com/article/321439",
"http://www.guardian.co.uk/science/2012/mar/18/helium-party-balloons-squandered",
"http://www.sciencedaily.com/releases/2008/01/080102093943.htm"
] |
[
"Estimates place our supply of helium from 10-30 years worth, and falling fast.",
"Citation for this, please? I've read about this, but I think it would be useful to have some context."
] |
[
"yeah it could be supplied from fusion to a degree at least (depending on how much fusion is going on around the world). I wonder what the He",
" production would be though."
] |
[
"Radiation suits in Chernobyl accident?"
] |
[
false
] | null |
[
"What do you mean by \"radiation suit\"? You mean like a shielding suit? Because those still aren't used.",
"Anti-contamination clothing is common, and you can see it being used in the TV show. But that's not for shielding radiation, it's meant to act as a barrier between your body and the contamination in your environment. The suits are then cleaned or disposed of once you exit the contamination zone. It just limits the spread of contamination.",
"It's not practical to walk around with tens of pounds of lead strapped to your body, so people don't generally wear shielding on their bodies."
] |
[
"A “shielding suit” is not something that actually exists, I was just using to mean some suit lined with lots of lead to stop gamma rays. Like the lead aprons you wear when you get an x-ray, but full-body, and probably thicker. That’s what I assumed you were envisioning.",
"It just seems as if most people are walking around with little or no protection.",
"Yes, that’s pretty accurate. That’s a combination of Soviet negligence, and the fact that it’s not really practical to wear radiation shielding, just anti-contamination clothes to stop the spread of contamination."
] |
[
"I obviously don't know much about radiation, haha. Yes, I guess I meant the \"moon suits\" with the reflective material and air supply. Are those shielding suits? ",
"It just seems as if most people are walking around with little or no protection. On the show, and in the actual images from the accident. The miners were walking around naked ffs! The medical staff just had on their basic medical ppe, etc. I understand it's difficult to work in bulky equipment, but it still seems better than the alternative. ",
"Is that a clearer inquiry?"
] |
[
"Would there be higher gravity if Earth didn't spin?"
] |
[
false
] |
Does the Earth's spin cause an outwards centrifugal force. Theoretically if there was a planet with earth's mass that didn't spin or span slower would it have a higher gravity? I assume that if there is a difference its negligible though.
|
[
"Yes, the apparent gravity and your apparent weight would be a little bit greater at the equator if the earth weren't spinning (I specify the equator because the effect is not felt at the poles).",
"As for how much, you can calculate the magnitude of the centrifugal force pretty straightforwardly. Earth surface gravity is about 9.8 m/s",
", and if we want to compare to this we need a centrifugal acceleration with the same units. You get this from one length (the earth's radius) and one time (the earth's rotational period). All together, you get",
"(6400 km)* (2*pi/1 day)^2 ~ 0.03 m/s^(2)\n",
"Put another way, that's a 0.3% change in apparent surface gravity if the earth were not rotating."
] |
[
"0.3%. That's actually a lot more than I expected. Thanks a lot for answering my question btw!"
] |
[
"so, a person weighing 100kg would be 300g heavier, about a can of coke. but for something thats hundreds of tons like rockets, it would absolutely be significant!"
] |
[
"When we use wind farms and watermills to produce energy, where would the energy have been used before we \"took\" it? Are there any negative effects of this?"
] |
[
false
] |
[deleted]
|
[
"wind mills would slow the wind, but insignificantly",
"watermills/dam turbines do the same thing for rivers, slow the flow",
"I doubt a watermill would have any significant effect, a Dam though would significantly reduce the energy of the river downstream...\nDams have much more drastic upstream effects tho, basically turning a river valley into a lake, but this isnt a direct result of taking energy out of the river through the turbines "
] |
[
"This doesnt make sense to me. On an interval over the dam a significant portion of the rivers energy would be taken out by the turbines. Reducing energy downstream not related to water being held back initially.",
"No?"
] |
[
"Part of the energy taken out is the potential energy of the difference in height from where the water enters and exists the Dam.",
"So, that will reduce the speed of the water, but if the Dam wasn't there a lot of that energy would have gone out of the water (as it does not speed up continually) in the surrounding material.",
"If we assume that the water going in the Dam and the water coming out of it have the same rate, then the difference in lost energy by the water is just the difference between extracted energy by the dam and the energy lost by interacting with the river bed where the dam replaced it.",
"I don't think there would be much difference.",
"Before the dam is full, the rate of water in and out is different, which will significantly affect the river downstream.",
"That's my thinking."
] |
[
"How Much of Sexual Dimorphism Can be Attributed to Genetics?"
] |
[
false
] |
I found some data about sexual dimorphism, from wikipedia and other things, but it doesn't tell me how much of it is directly linked to genetics... How do different upbringings, lifestyles, etc. affect sexual dimorphism?
|
[
"Sexual dimorphism is defined as the phenotypic difference between males and females of a species. Generally, sexual dimorphism can be classified into sexual characteristics (primary or secondary), morphology (body size/shape/features), ornamentation (think brightly coloured birds) and behaviour. So of all of the above the first three: sexual characteristics, morphology and ornamentation are all controlled solely by genetics assuming no unusual circumstances e.g. prolonged exposure to androgens during development can affect female sexual characteristics. Behaviour is the set of traits that can be most moulded by lifestyle. But behaviour is a fairly small part of sexual dimorphism since most behaviours associated with differences e.g. mating/courtship rituals are innate behaviours and are not learned.",
"That being said, in relation to humans gender identity and sexual dimorphism are separate. Gender is the idea of what males and females should be and do which can be heavily influenced by our complex society. "
] |
[
"I was especially curious about sexual dimorphism in terms of physical appearance, as it came up before and I didn't know and couldn't find out."
] |
[
"I was especially curious about sexual dimorphism in terms of physical appearance, as it came up before and I didn't know and couldn't find out."
] |
[
"What happens with the CBR when you move?"
] |
[
false
] |
Ok, so I understand there's no such thing as absolute motion, you always need a frame of reference to determine your velocity. But the cosmic background radiation is pretty much the same in any direction you care to look, right? So assume a frame of reference in which you are currently stationary. Now start moving in any given direction. Will the CBR coming from ahead of you be blue shifted and the CBR behind you red shifted? If no, why not? And if yes, wouldn't measuring the red/blue shift of the CBR give you an absolute measure of velocity?
|
[
"Well, it implies there ",
" a frame of reference you could preferentially call \"at rest with respect to the universe\", but not that ",
". The typical picture you might see of the CMB (eg. ",
"https://www.esa.int/ESA_Multimedia/Images/2013/03/Planck_CMB",
") has already had the anisotropy due to our motion through the universe removed (because there's interesting physics astronomers like to study hiding in the small scale variations which are otherwise dwarfed by the dipole anisotropy due to our motion). For example, you can see it looks much different without this dipole removed in figure 2 of this paper: ",
"https://arxiv.org/abs/1506.01907#:~:text=5%20Jun%202015%5D-,The%20Cosmic%20Microwave%20Background%3A%20The%20history%20of%20its%20experimental,and%20its%20significance%20for%20cosmology&text=This%20review%20describes%20the%20discovery,the%2050%20years%20that%20followed",
". In fact, measuring this dipole anisotropy is one of the primary ways of understanding the velocity of our local Galaxy group.",
"So we can define a special rest frame, but that doesn't make ",
" special. Phew! Copernican principal lives on!",
"ETA: \"ok, maybe WE aren't special, but what if we discover a Galaxy that IS perfectly at rest, what would that mean?\" It would mean that particular galaxy is moving perfectly in line with the universe's expansion, with no additional perturbation, nothing more. The majority of galaxies (including ours) are moving roughly in line with the universe's expansion, with minor velocity offsets due gravitational interactions and random initial conditions."
] |
[
"Yep, it does get blue shifted in one direction and red in the other (and if you move at the speed of relativistic particles it can get weird when it gets so blue shifted that the photons are super high energy, see for example the GZK limit ",
"https://en.m.wikipedia.org/wiki/Greisen%E2%80%93Zatsepin%E2%80%93Kuzmin_limit",
")",
"And based on this reference frame you could indeed say there is a preferred reference \"rest\" frame of the universe. Despite this philosophical discomfort, the laws of physics still apparently work the same in other inertial reference frames, so that's why physicists nonetheless say that all inertial reference frames are just as valid."
] |
[
"You can say that about anything. Me and my friend can determine our individual velocities relative to the rest frame of the earth, but that still doesn't mean the Earth's rest frame is special. You and I and the Earth and the CMBR are all things in space and we all have a rest frame, but none of those frames are some special absolute frame, they are just the frames for those particular things.",
"I understand the temptation to call the CMB frame an absolute frame because it's a pretty special thing: it's homogenous and isotropic, very old, present throughout the entire visible universe, but again regardless of the specialness of the thing there is nothing special about that frame. The workings of the fundamental forces are not dependent on motion relative to the CMB. As we currently understand the universe, physics is governed by the symmetries of gauge groups and a spacetime manifold which both, by construction, do not ever identify one reference frame as more fundamental than any other.",
"For practical purposes, yeah it could be useful. We could establish some intergalactic civilization and for purposes of law and commerce and navigation and whatnot the intergalactic department of measurement standards can declare that all motions shall be reported in terms of relative motion to the CMB, which I imagine might be a wise choice because that can be measured from anywhere we might travel. But in terms of the laws of physics there is nothing at all special about the frame of the CMB other than it is the frame where the CMB happens to be."
] |
[
"If I get the covid vaccine while I am breastfeeding, how long is my baby protected by my antibodies?"
] |
[
false
] |
[deleted]
|
[
"Well at least here in Germany and for the Astra Zeneca Vaccine, we have a question that reads „Are you or could you at all be pregnant or are you breastfeeding?“ if yes then that is a reason for you to actually be not vaccinated"
] |
[
"That's not how immunizations really work, more of an, already immunized for full measure, would expect little to none based on this article."
] |
[
"And i seriously doubt enough time has gone by to research this accurately"
] |
[
"How close in hardness do two materials need to be in order to scratch each other?"
] |
[
false
] | null |
[
"Thank you for asking, and for providing and explanation! That makes a lot of sense.",
"Maybe you could liase a follow up question though? It makes sense that a larger area will present some imperfections of varying hardness, but once that layer is removed, or assuming the surface area in contact to be perfectly uniform for both materials, would they chip/scratch at equal rates? Like, instead of a diamond needle on a large diamond, what about two diamond discs rubbing together?",
"Like, I understand why something really hard (metal) can scratch something really soft (chalk), but I'm curious about what happens if the materials are much more similar. "
] |
[
"Thanks a lot for the explanations!"
] |
[
"My attempts at reasoning through this one are that, under pressure, on the microscopic level, materials compress, becoming more dense. Does this equate to an increased hardness? I have this nagging suspicion that how close the two materials have to be is related to the force squeezing them together. I didn't study much stress/shear or materials though, so I'm kinda stuck there. Also not entirely sure how I would research this."
] |
[
"What would happen if we 'bled' a volcano? Would it release pressure, or would it make things worse?"
] |
[
false
] |
[deleted]
|
[
"it would completely depend on the type of volcano that you're trying to 'bleed'. If you're looking at a volcano that has a magma chamber filled with andesites and rhyolites (a very quartz rich magma) (see any of the volcanoes around the Ring of Fire\") then drilling a hole to it would be pointless as these magmas have an extremely high viscosity. Not to mention that we don't have the drilling technology to even drill into material that hot. These chambers are usually under a tremendous amount of pressure, and drilling a hole in it (not that we can even drill a hole large enough to have much of an effect) would result in decompression at that point, thus consuming the drill and it's workers. ",
"Now, if you have a basaltic chamber, such as those you find in shield volcanoes (see Hawai'i), then the product is not under so much pressure and the volcanic product has a much lower viscosity. However, these are not the types of volcanoes that cause massive destruction through exploding for just that reason. Any small crack, fault, or unused magma-tube is exploited by the very low-viscosity magma, and pressure never has time to build up. ",
"TL;DR: no, the viscosity of the magma that produces explosive volcanoes will not respond to any kind of drilling technology we have these days. ",
"*edit: See ",
"here",
" and derivative pages for an explanation of the different types of lava, their compositions, and how the chemical components alter the type of volcano and the nature of their viscosities. "
] |
[
"The ",
"Ring of Fire",
" is composed of andesitic volcanoes. These volcanoes have a very high percentage of quartz, thus making them gloopy and viscous. This means that it can create seals and build up massive amounts of pressure within a magma chamber. However, this also means that if you tried to drill a hole, the hole would have to be large enough to cause a decompression where you want it (I have no idea how large a hole would have to be, but it would need to be exponentially greater diameter than the 4\" or 9\" drills we have these days), otherwise, the magma would go up the tube a little ways, get stuck, and seal it. "
] |
[
"The ",
"Ring of Fire",
" is composed of andesitic volcanoes. These volcanoes have a very high percentage of quartz, thus making them gloopy and viscous. This means that it can create seals and build up massive amounts of pressure within a magma chamber. However, this also means that if you tried to drill a hole, the hole would have to be large enough to cause a decompression where you want it (I have no idea how large a hole would have to be, but it would need to be exponentially greater diameter than the 4\" or 9\" drills we have these days), otherwise, the magma would go up the tube a little ways, get stuck, and seal it. "
] |
[
"what is the difference between an electron and a black hole electron?"
] |
[
false
] |
given that they are both treated as point particles, i'm imagining that the 'energy density' around the 'center point' of an electron is insufficient? something like that but phrased in a way that makes sense? how could one theoretically confine an electron's energy to a sufficient density? how would the interactions of such a particle differ from a normal electron?
|
[
"That's the whole point of the idea: that if a black hole could exist that had the same mass and charge as an electron, it might be indistinguishable from an electron.",
"The trouble is, such a black hole would be impossible given our current understanding of gravitation. Well. Not exactly impossible, but rather such a black hole could never be stable. It would evaporate instantaneously through Hawking radiation. Of course, Hawking radiation is still just a theory, ",
"a recent paper",
" suggests that it might have been observed under laboratory conditions. So as of this moment, it looks like the score stands at black hole electrons nil, regular electrons several million."
] |
[
"I might be mistaken, but I don't believe that a black hole of that size would evaporate by Hawking radiation. Hawking radiation works by the fact that vacuum fluctuations occur at the event horizon, with one particle being sucked into the black hole, and another being ejected out. However, because the size of this black hole is SO small, and the wavefunction of any particle created by vacuum fluctuations is actually larger than the blackhole itself, means that the particle would not actually fall into the black hole, or this would be incredibly unlikely (and thus the lifetime of the black hole would be very large)."
] |
[
"To tell you the truth, I'm not sure.",
"To tell you more truth, I don't really understand what a naked singularity is.",
"I'm not fully versed on GR, which is a weakness of mine."
] |
[
"How do we *remember* smells?"
] |
[
false
] |
For example, i can tell the difference between a peruvian and an indian mango by smell? How does the brain create a point of reference for this comparison? Also, What is the mechanism of this comparison? This question can also be extended to tastes.
|
[
"The olfactory nerve is unique to the other sensory nerves in the fact it has direct connection with the limbic system and the hippocampus, structures involved with emotion and memory. Your other senses primarily synapse in the thalamus before extending to other areas of your brain and their connectiona with the limbic system and hippocampus aren't as extensive.",
"It is postulated that this close interaction with the olfactory nerve and the limbic system and hippocampus attributes to the strong connection between smell, emotion, and memory.",
"As for how you are able to discern different smells, that is something I am not entirely familiar with the details of. In short, you have receptors for various discrete chemicals that your brain perceives as having a distinct \"smell\". When you detect a particular \"smell\" this is the result of both a combination of discrete receptors being activated and also the rate at which they are being activated. "
] |
[
"to answer the question, you really have to extend it to: \"How do we remember?\" Smells in your head are just another type of information in the brain, so you remember them in a similar way to the way you remember what your car looks like, the color of flowers, the feel of cotton. it's all just sensory input"
] |
[
"True! Although there is also some evidence to say that smells associated with emotional things are 'remembered' in the older, deeper brain regions, which is why the smell of home is so powerful."
] |
[
"Does your body's production of Vitamin D change depending on your dietary intake of Vitamin D?"
] |
[
false
] |
[deleted]
|
[
"That particular question either has not been addressed, or it is not documented in this summary. ",
"http://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get-the-vitamin-d-my-body-needs/",
"Here:\n",
"https://en.wikipedia.org/wiki/Vitamin_D",
"\"The evidence indicates that the synthesis of vitamin D from sun exposure works in a feedback loop that prevents toxicity.\"",
"This would seem to indicate that your body will stop producing to avoid toxicity, so if you have \"enough,\" it will like stop production in sunlight."
] |
[
"inflammation/infection will also effect your dietary absorption of vit d and well as the conversion to the active hormone. "
] |
[
"Nope, it all depends on your nutritional requirements. Vitamin D synthesis requires ATP, which means that it actually costs your body some energy to make. It doesn't want to do this if there is a lot of vitamin D around, so the enzymes in the pathway are inhibited by high vitamin D concentration.",
"If you take a lot of vitamin D, it will probably be broken down and made into something more useful. Or, you might pee it out."
] |
[
"How many planets have we found like earth? And how many of them are in a good distance for us?"
] |
[
false
] | null |
[
"The information we have about exoplanets is limited. We know roughly their size, distance from their sun, and relative density, the periodicity of their orbit, and we occasionally get spectral data from planets that happen to pass in front of their sun. However, as we have never compared our estimates to actual findings (ie going to the exoplanet) none of this is confirmed. However we can use these same tools in our solar system and compare them to probe data, so it's definitely not baseless. That being said, there have been thousands of exoplanets discovered, mostly tight orbit gas giant's termed \"hot jupiters\" because of their effect on their sun and how quickly they orbit, we can see the sun moving ever so slightly. These take the least amount of time to discover. If you could imagine trying to discover another planet in a similar situation to earth. It would take multiple orbital periods to confirm the discovery, this is several years in our timeframe and that's just for one planet. We have found several planets we think could be in the \"goldilocks zone\" that have relatively the same density and size as earth. However we will have to wait until the james Webb space telescope is fully operational in the 2020s before we start getting truly accurate spectral data from exoplanets. The number of planets we get that data from will be limited by several factors, being knowledge of their periodicity, planar alignment with the jwst, and timing of alignments. So in short. We've found a few that might be like earth, none of them are even remotely close (reachable by modern methods in our lifetime) and we don't know for sure if they are truly like earth. ",
"The true fun comes with the advances in observational techniques, and transportation methods that change all those answers"
] |
[
"Stuff like this really depresses me, knowing i'll probably never set a foot on another planet, let alone into another solar system.\nKnowing of all these planets out there and potential alien life and us being unable to reach out properly or even communicate, at least in my lifetime, just gives me a huge existential crisis.\nThis may be due to the influence of Star Trek etc. but humanitys efforts should, if not focused, at least be increased towards conquering space and being able to reach out.\nOtherwise, we'll just go extinct one day.\nSadly, none of us will probably live to see this, at least as long as we keep exploiting each other for personal benefit."
] |
[
"They are finding new things out all the time. The division of NASA that evaluates potential non newtonian drives still had several candidates that haven't been tested or have been inconclusive. Though they did pretty much rule out the em drive. A non newtonian drive is the way to the stars. Basically direct translation of electricity to thrust. We don't know of anything capable of this in the vacuum of space YET, but people are looking and there are several possibilities. Among other even more exotic methods such as the warping of space time to create thrust (yes that's a real thing they are working on) we might not live to see humanity populate the stars but we'll still probably be around for the beginning of that era. Sounds like fun to me. "
] |
[
"What is the limiting factor of putting power through a wire?"
] |
[
false
] |
What is the limiting factor of transmitting power safely through a wire? Is it the voltage, current, or power? If you're putting a certain amount of power through a wire, does it matter if its high-voltage/low-amps or low-voltage/high-amps? Edit: Does it matter if it is AC or DC?
|
[
"Voltage * Current = Power or E*I=P. If you lower the voltage, you increase the current (though a transformer lets say)... and vice versa. Power though, will always remain the same.",
"Current is the key factor for wire though. How much current that can go through a wire is determined by the resistivity of the metal, and the diameter of the wire itself (if round).",
"The larger the wire, the more \"area\" current can flow though. If too much current is sent through a wire that is unable to handle it, the wire will heat up and melt.",
"Power grids are setup to transmit high voltage and low current. This allows the transmission lines to be made smaller, thus saving weight and most importantly, cost.",
"As for AC and DC, The root-mean-square (RMS) value of an AC voltage is the equivalent of a DC voltage that can deliver the same amount of energy to a load.",
"In short, it's the same as long as you are going off the RMS voltage of an AC source and not the peak value. DC though, can only be transmitted a few miles, not hundreds of miles like AC."
] |
[
"If you drop voltage, then yes, current must also lower in a resistive circuit (if the resistance wasn't what changed)... but, we're talking power.",
"We're talking a perfect transformer now (no I",
" R losses). Since there is no load (like a resistance), there is no \"work\" done.",
"Take a 10:1 transformer. Input 100 volts at 1 amp, and out of it you will get 10 volts at 10 amps. The power, as per E*I = P, remains unchanged on the primary \"and\" the secondary.",
"Now, run that 10 volts, 10 amps through a load, then yes, Kirchhoff's rules and Ohm's law then apply to show the load \"using\" the power."
] |
[
"Ah, I must have missed the transformer part. Was trying to imagine a load that could dictate power without simply turning off."
] |
[
"How much bacteria or virus material is in us at the height of an illness? (cell number and/or mass)"
] |
[
false
] |
When we are ill, what is the volume, mass, or number of cells of bacteria or viruses that is present in our bodies? Can someone make the amount of bacteria in our bodies tangible please? Thank you scientists!
|
[
"You need to watch this:\n",
"http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html",
"Basiclally you're 1 trillion cells. At any one time your have 10 trillion bacterial cells in or on you.",
"Most organisms are not what you think they are: being a homgenious collection of cells. "
] |
[
"Let's take the example of VIH infection.\nThe number of copies of the virus in circulation varies depending on the time since the infection, but at the peak concentration (a few weeks after infection), there can be a few millions of virus per ml. \n120nm diameter, times, say 5 millions, is in volume, 0.0000005 % of the blood. And blood is a small fraction of the human body (roughly a percent or less). So, at peak, the HIV corresponds only to a few parts per trillions.\nTherefore, the volume of HIV particles, even for a very dangerous amount, is very small compared to the volume of the body. \nFor other infections of course the numbers can vary. But this gives you an idea."
] |
[
"Thanks! A teacher of mine showed me this in school, but I'm referring to the specific pathogen that is causing someone to be sick."
] |
[
"Why are stomach transplants so uncommon?"
] |
[
false
] |
[deleted]
|
[
"You can, indeed, live without a stomach. IANAE on any of this, though, so I'll leave your other questions to others."
] |
[
"You eat very small portions more often. They don't necessarily have to be mashed/ground, but they do have to be well-chewed. The pancreas/liver release protein-degrading enzymes/products, and they're typically sufficient, again as long as you eat small quantities at a time. And yes, the stomach does have some antimicrobial properties, but so do the intestines, and probably they are more robust in that function than the stomach."
] |
[
"It's always a risk-benefit analysis. The stomach is not necessary for life, and on its own is generally not worth the detriment of life-long immunosuppressive therapy. But if someone were to need a liver transplant, which would save their life, and also happened to need a new stomach, that can be done (this is a rare scenario)."
] |
[
"Why does twisting a cork make it easier to pull out of a bottle?"
] |
[
false
] |
[deleted]
|
[
"Leverage. You can apply far more torque by twisting than you can do force by just pulling upwards. The length of your arm/wrist/whatever you use can amplify the force you are applying with respect to just pulling."
] |
[
"Leverage. You can apply far more torque by twisting than you can do force by just pulling upwards. The length of your arm/wrist/whatever you use can amplify the force you are applying with respect to just pulling."
] |
[
"Kinetic friction is less than static friction. Twisting the cork is the easiest way to get it to move, and thus to lower the frictional forces. It is then easier to pull upwards out of the bottle."
] |
[
"Why can light waves travel through space but sound waves can't?"
] |
[
false
] | null |
[
"Sound is a vibration of a material, and so it cannot exist where there is not a material to vibrate.",
"Light waves are electromagnetic waves; they are thing unto themselves, not the vibration of something else, and thus can exist in the vacuum of space."
] |
[
"No, please no.",
"Fields are ",
" a quantum thing. Fields may be quantized, and you get a quantum field theory, but there are many classical fields: for example the electromagnetic field (aka light), or the gravitational field. Trying to find out how to quantize the gravitational field is a big thing right now: quantising the electromagnetic field was 'fairly straightforward', but no one really knows exactly how it should be done for gravity.",
"The gravitational field essentially works like this: you start out with an empty spacetime which is flat, as in: it's geometry is basically euclidean (there is some small text here: it's geometry is actually Minkowskian, which is as 'close' to euclidean as space-time can get). What does it mean to have euclidean geometry? That the shortest path between two points is a straight line. ",
"If now your hypothetical universe has some blob of mass , then the shortest path between two points (in space-time) will start being ",
" lines instead of straight lines. That's essentially what gravitational fields do (or are), curvature in space-time.",
"Time-dilation is certainly ",
" the central concept in general relativity, but a byproduct of it."
] |
[
"I think it's necessary to point out that the standard model is ",
" otherwise known as QFT. It is an ",
" of a QFT."
] |
[
"Is the number of colors infinite? If not, how many colors are there? Also, is there a definition of red, orange, etc. and who define this, or is it arbitrary?"
] |
[
false
] | null |
[
"can you divide the spectrum of light infinitely? sure. Can the Human eye distinguish between infinite gradations? no, not really.",
"You may find the results of ",
"xkcd's color survey",
" interesting."
] |
[
"well we do have some nominal definitions, but they're not hard and fast rules. 635 nm is red, 530 nm is green, and 445 nm is blue. (mostly because we can make rather common lasers in these colors)"
] |
[
"Color definitions are arbitrary. In fact, ",
"many languages use the same word for \"blue\" and \"green\"",
", and ",
"Homer's useage of strange colors like \"wine-dark\" seas and \"bronze\" sky",
" have led to some interesting insight into the division of the color spectrum of Ancient Greek."
] |
[
"What is unique about aloe vera that makes it so good for sunburns?"
] |
[
false
] | null |
[
"The abstract from this paper about wound healing: ",
"http://www.ncbi.nlm.nih.gov/pubmed?term=9562243",
"Wound healing is a fundamental response to tissue injury that results in restoration of tissue integrity. This end is achieved mainly by the synthesis of the connective tissue matrix. Collagen is the major protein of the extracellular matrix, and is the component which ultimately contributes to wound strength. In this work, we report the influence of Aloe vera on the collagen content and its characteristics in a healing wound. It was observed that Aloe vera increased the collagen content of the granulation tissue as well as its degree of crosslinking as seen by increased aldehyde content and decreased acid solubility. The type I/type III collagen ratio of treated groups were lower than that of the untreated controls, indicating enhanced levels of type III collagen. Wounds were treated either by topical application or oral administration of Aloe vera to rats and both treatments were found to result in similar effects.",
"Review article looking at burn healing: ",
"http://www.ncbi.nlm.nih.gov/pubmed/17499928",
"Aloe vera has been traditionally used for burn healing but clinical evidence remains unclear. We conducted a systematic review to determine the efficacy of topical aloe vera for the treatment of burn wounds. We electronically searched relevant studies in MEDLINE, CINAHL, Cochrane Library, HealthSTAR, DARE, South-East Asia Database, Chinese Databases, and several Thai local Databases (1918-June 2004). Only controlled clinical trials for burn healing were included. There were no restrictions on any language of publication. Two reviewers independently extracted data on study characteristics, patient characteristics, intervention, and outcome measure. Four studies with a total of 371 patients were included in this review. Based on a meta-analysis using duration of wound healing as an outcome measure, the summary weighted mean difference in healing time of the aloe vera group was 8.79 days shorter than those in the control group (P=0.006). Due to the differences of products and outcome measures, there is paucity to draw a specific conclusion regarding the effect of aloe vera for burn wound healing. However, cumulative evidence tends to support that aloe vera might be an effective interventions used in burn wound healing for first to second degree burns. Further, well-designed trials with sufficient details of the contents of aloe vera products should be carried out to determine the effectiveness of aloe vera.",
"My summation after looking at some papers:\nThere are a ton of organic chemicals in aloe vera gel (the inside of the leaves) and these help with revascularization of the skin after damage, rebuilding collagen, increasing the rate of epithelialization by the effect of acemanan (mannose-6 phosphate) to stimulate fibroblasts, with additional anti-inflammatory, anti-microbial, and moisturizing effects.",
"The article from 2009 states that the investigators were surprised at the little amount of research performed on aloe vera and burn healing (which probably indicates poor funding for it in general), and that there isn't any quality control with commercial products so you may not be getting the essential chemicals which help with burns.",
"Edit: I like how thunderdome, dunnp, and I all referenced to the same meta paper. "
] |
[
"I had this same question awhile ago, due to years of it being recommended by parents, friends, pedestrians....etc. However, I could find very few conclusive studies documenting it's effectiveness. It's wikipedia article addresses most parts of the controversy and cites ",
"this",
" paper that concludes aloe vera does reduce healing time for first and second degree burns."
] |
[
"I never even realized it was supposed to help with healing. I used to filet aloe leaves and use the jar of aloe goo on sunburns just because its cold and feels really really good on burnt skin. Never even considered that it would actually help heal anything. "
] |
[
"Can a better space telescope be built today?"
] |
[
false
] |
Hubble initially cost 400 million. Let's say I have one billion now. Can I build a better space telescope than Hubble or is it still the best we can build and put in space?
|
[
"https://secure.wikimedia.org/wikipedia/en/wiki/Very_Large_Array",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Very_Small_Array",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Very_Large_Telescope",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Very_Long_Baseline_Array",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/One-Mile_Telescope",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Square_Kilometre_Array",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Large_Millimeter_Telescope",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Giant_Metrewave_Radio_Telescope",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Submillimeter_Array",
"\n",
"https://secure.wikimedia.org/wikipedia/en/wiki/Long_Wavelength_Array_(LWA)"
] |
[
"We've done ",
"an IR telescope",
" and are ",
"working on another",
"."
] |
[
"as pointed out theres the James Webb telescope, to replace the Hubble telescope. theres also an enormous ground based telescope that is being worked on, can't remember the name of that project though :( "
] |
[
"If there were a mass the size of an electron that doubled in size every 24 hours, how long would it take to consume the visible universe?"
] |
[
false
] | null |
[
"Hi Zachvehlert thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Hi Zachvehlert thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Hi Zachvehlert thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Can someone please explain to me the concept of light cones?"
] |
[
false
] |
I've been getting interested in science again lately so I downloaded the kindle version of "A Brief History of Time." I've gotten as far as this part and now I'm having trouble picturing how light cones work in my head. Are we actually talking about a cone that the light from a specific light source would make as it travels outward through space and time from it's origin? Or is it more of a diagram that what would be affected by what happens at a particular event in space time? Or am I way off?
|
[
"The light cone is a somewhat abstract way of visualize how things are connected in time and space. The light cone simply shows how far away things can be from an event and still be causally connected as time goes by.",
"When an event occurs somewhere (event A), information about this event can be transmitted no faster than the speed of light, that means another event (event B) can only be caused by event A if event B is inside event A's light cone. If event A happened at location 0,0,0 and time 0, and event B happened at time T, then the location of event B must be inside the sphere with radius c*T.",
"The light cone is just called a cone because we consider all spatial dimensions to be identical and so only show two of them."
] |
[
"The \"cone\" isn't the actual thing; it's the shape of the graph when you describe the actual thing.",
"The origin is a point, the \"now\" if you like. For every unit of time that passes, light travels a certain distance. If you talk about a year, everything more than a light year away is outside the light cone. Nothing that occurs at \"now\" could affect that thing a year from now, and nothing that thing did within the last year had any effect on \"now.\"",
"The thing you're describing goes in all directions, not a cone. But if you draw it on paper in a graph of time x distance, rather than time x direction, you can draw it as a cone (well, two cones, past and future), to easily visualize whether or not a different \"now\" affects your own \"now\" in either direction, by whether it's inside or outside the cone."
] |
[
"Here's the typical way they show it",
". Imagine that, instead of being 3 dimensional, all of space is two dimensional, and that you're standing still. The big, flat plane in the middle of the image is space at the actual present time - how everything is at a given moment. If you go up or down, the line directly through the center of the graph (labelled \"time\") represents your location at different points in time; points horizontally off of that line represent other locations at that same point in time. ",
"Now, it takes time for light to reach you, so when you see something farther away from you, you're actually seeing it at some point in the past. This means that what you ",
" see is, for example, everything close to you X units of time ago, then everything a bit farther 2X units of time ago, then everything even farther 3X units ago, etc. If you were to plot what you saw on the above image, you would then see a circle - representing everything close to you - at a point X units below you on the time axis, then another, wide circle, representing everything a bit further, 2X units below you, etc. ",
"If you imagine, instead of just a few circles, you've got a circle for every single distance from you, and each one at a corresponding time, you end up with a series of increasingly wide circles going back in time, creating the \"past\" light cone you see in the image. The \"cone\" is just a way of visualizing all of the past moments that you can see at the present time - obviously the real universe is 3 dimensional, so the reality is a bit more complicated. ",
"Similarly, the \"future light cone\" in the image represents all of the locations that will see light coming off of your present location, and the times at which those locations will see that light - the further in the future you go, the further away the points will be that are be seeing your light for the first time, so you get another cone, just upside down."
] |
[
"Could astronauts in orbit for long periods be prophylactically treated with medications for osteoporosis and perhaps muscle stimulating medicines to prevent atrophy?"
] |
[
false
] | null |
[
"Edit: I noticed after typing this that your question is about prophylaxis. So presumably you mean before they launch. My bad. ",
"I don’t know what current practice was, but when I was in university one of the professors I worked for was working with NASA on a stimulation device to prevent osteoporosis. They had found that small amounts of vibration help stave off bone loss more than high impact so he developed a belt/harness you could wear covered in small vibrating motors to help reduce bone loss. As far as muscle loss, the astronauts already undergo an exercise regime to help reduce muscle (and bone) loss."
] |
[
"Ok, my NASA friends have got your back! ",
"Here",
" is the official NASA roadmap for research about mitigating bone loss related fracture risks, and ",
"here",
" is the specific section that discusses prevention mitigation. ",
"Regarding medication they say that since there is a very low chance of a bone breaking on current missions, pharmaceuticals are currently considered a plan B for use on future exploration/longer term missions and their use will be reconsidered/researched as those become more likely."
] |
[
"That’s interesting- you thought prophylactic as in before launch.\nI thought prophylactic as in before disease sets in, but while they are in space. As in, treat them like post-menopausal women with Vitamin D and Miacalcin or alendronate."
] |
[
"I read recently that Jupiter itself is shrinking by 2cm per year. Does this mean it will eventually dissapear? How will this work?"
] |
[
false
] | null |
[
"Jupiter is just compressing because its getting colder. It cannot compress infinetly so it will never disappear. Infact, rigth now its only shriking at half the speed than what it did when it formed, and it will continue to slow down."
] |
[
"The Sun won't expand enough to consume Jupiter. Only enough to consume Mercury, Venus, and maybe the Earth."
] |
[
"And even if it did it would happen in 7 billion years, long after the sun has become a supergiant and likely destroyed Jupiter in the process."
] |
[
"I understand trigonometry and it's identities but I am having trouble understanding it intuitively. I've read and seen all the unit circle definitions and I grasp that perfectly. It's just that, I'm looking for an explanation that doesn't rely on geometry?"
] |
[
false
] |
[deleted]
|
[
"but these probably won't make things clearer for you.",
"I whole-heartedly agree with this. The whole point of sine, cosine, tangent etc are to understand circles and triangles. Why does sin(x+y)=sin(x)cos(y)+cos(x)sin(y)? Because of ",
"these triangles",
". If you separate the trig functions from circles and triangle, you've separated them from everything that gives them value."
] |
[
"but these probably won't make things clearer for you.",
"I whole-heartedly agree with this. The whole point of sine, cosine, tangent etc are to understand circles and triangles. Why does sin(x+y)=sin(x)cos(y)+cos(x)sin(y)? Because of ",
"these triangles",
". If you separate the trig functions from circles and triangle, you've separated them from everything that gives them value."
] |
[
"First, it may be useful to consider that trigonometry could exist with no other meaning than to triangles, or the unit circle. If all you wanted to do was study those, trigonometry gets you a long ways.",
"Anyways, consider a polar coordinate system. A point is defined by how far it is from the origin, which will be R, and what direction it lies from the origin, T, which is measured from the x axis. Clearly, any point defined by its polar coordinates corresponds exactly to a point defined in rectangular coordinates. It turns out that this relationship is x=Rcos(T) and y=Rsin(T). You can see that this works for the unit circle if R=1.",
"From this perspective, we see that trig functions are a way of describing where stuff is by pointing in a direction and going there, when before they were described by how far you go to the right and up. There are other examples, such as the motion of something which repeats itself. As you see more examples, it will probably start to make more intuitive sense."
] |
[
"How scientifically founded is this: \"Bohm believes the reason subatomic particles are able to remain in contact with one another regardless of the distance separating them is not because they are sending some sort of mysterious signal back and forth, but because their separateness is an illusion.\""
] |
[
false
] |
In reference to Is there any other serious scientists that truly believe we are living in a hologram/illusion? If so why has the general science not embraced this idea yet?
|
[
"What? That's nonsense. Interpretations of quantum physics are both important ",
" highly scientific. Just because we might not yet have been able to find, e.g., a way to test out different interpretations of quantum mechanics doesn't make them unscientific: they still have to be able to explain what we observe in our labs.",
"Bohmian mechanics is a very well—if somewhat contrived—thought out interpretation which has taught us much and more about the nature of reality."
] |
[
"This hologram idea is developed starting at ",
"Bohmian mechanics",
", which constitute a ",
" hidden variable model (and thus cannot be refuted by, e.g. Bell's inequality) which so far has proven to be entirely consistent with observations. It's just somewhat contrived and might fail a close shave with Occam's razor. On the other hand, that razor is more of a guideline than a good method to determine whether a particular theory is correct.",
"\"General\" science does embrace these ideas: there are plenty of people studying the foundations of quantum mechanics and its interpretation. It's just not something that we really need to conduct our daily lab work which we get funded for."
] |
[
"Does he have any math describing this connection?"
] |
[
"Dolphins use echolocation to visualize objects around them, and are able to make a wide variety of sounds. Can they reproduce the echo or sound image of an object in order to communicate it to other dolphins?"
] |
[
false
] |
For example, to say the word "fish", could they reproduce the sound image (or a simplified version) of a fish?
|
[
"No. They use language to talk with other dolphins. They don't throw their voice like to make the sound wave look like that of a ricochet because that wouldn't work. The dolphin that is looking with echolocation specifically needs to make the noise so they know precisely how long it has been since their sound was sent and in what condition it comes back to know where things are. ",
"It's like me dropping a coin down a well, if you don't see me do it then you have no idea how long it took to hit the bottom and therefore how deep it is"
] |
[
"It's not really possible to do that. Think of sonar like a strobe flashlight in the dark. Every time it strobes, the photons bounce off the surrounding objects and return to the eye, right? For a dolphin, the 'strobe light' is the 'clicks' they make, and the 'eyes' are the sac on their forehead.",
"But having a strobe flashlight in your hand doesn't give you the ability to recreate the image your eyes saw, for someone else. It's just a single point-source of light. Yeah, it can change the color and brightness of each flash, but that's not really the issue. You would need to recreate every single point that was visible to your eye, INSTANTLY. Your flashlight cannot physically be in multiple places at once, so it cannot show multiple points of light simultaneously.",
"You ",
" physically move around your light source, but that would just be multiple separate points. If your screen showed you a \"picture\", by just blinking one pixel at a time, would you know what the picture was? It would just be a dot moving around on your screen. ",
"And for a dolphin, their 'flashlight' is literally their head - they'd have to move their head in a very detailed shape to \"paint\" using sound pulses... and it would still be pretty useless.",
"EDIT: ",
"In order to recreate an sonar 'image' or 'video' for a dolphin, you would need an entire 'screen' of dolphins (or speakers) perfectly stacked, facing the 'audience' - each one representing one 'pixel' - and synchronously firing off clicks in the correct frequency at different volumes, to 'paint' using sound. An 'audience' dolphin would not be able to gauge the 'distance' (since they measure time-lag between their own click and the echo), but they would probably be able to 'see' the image you are trying to show them."
] |
[
"I have a hard time understanding the difference between \"acoustic communication\" and language.",
"Human communication (excluding all technology) is acoustic communication, right? Or am I missing some crucial detail?",
"Edit:\nAlso excluding sign language."
] |
[
"How come light traveling across the universe/galaxy is not affected by the sources from which it was emitted?"
] |
[
false
] |
To provide some further insight, a photon is emitted from a star, and this star has gravity. The light from the photon is moving fast enough to escape the gravity. But if this photon comes close to a black hole, it can be warped and bent around it, or captured into it by crossing the event horizon. So we know that gravity can effect light; then would not gravity from the things behind the photon (that is, things from the point where the photon was emitted) have some kind of pull on the photon, slowing it down? I guess another way to state this is, if the event horizon of a black hole can alter the course/speed of a photon, why can't galaxies and stars 'pull' on photons and cause their speed to slow down over huge distances?
|
[
"Light is affected by the gravity of everything, not just black holes. Like you say, light can be deflected by gravitational fields. We notice this from starlight being bent around the sun during total solar eclipses for instance.",
"And gravitational fields also affect the energy of photons, but not by slowing them down. Light must always travel at the speed of light, so gravity changes light's energy another way: altering the light's frequency. This is called ",
"gravitational redshift",
".",
"So, as in your example, when light is emitted from a star and escapes the star's gravity, all that light loses a little bit of energy to escape, and thus becomes slightly redder."
] |
[
"E = mc",
" is not the full equation, and as you noticed, breaks when dealing with light which has 0 mass, implying all light has 0 energy. The actual equation is ",
"this one",
".",
"And yes, there's actually 3 different kinds (sources) of redshift. Cosmological is from the expanding universe and is usually the dominant factor when we're looking at things really far away like other galaxies. Then there's red/blueshift from motion (Doppler shifts), which is what we measure as redshifts for stars moving toward/away from us in our own galaxy. And finally there's gravitational redshift, which is caused by gravitational pulls, and we really only notice that for very strong gravities (black holes, neutron stars). "
] |
[
"E=mc",
" has nothing to do with this. The energy of a photon is E=hf. The universe simply demands that things without rest mass move at the speed of light. The photon must lose energy as it travels up the gravity well, but it can’t slow down, so instead the frequency is reduced (wavelength is increased).",
"You can also have redshifting from the expansion of space (cosmological), and you can have redshifting from the motion of the emitter (Doppler). There are many ways to stretch out a photon."
] |
[
"What do we mean when we say one charge is negative and the other is positive, and what is the difference between the two?"
] |
[
false
] |
Do we know what charges actually are? Any further expounding on electricity would be welcome as well!
|
[
"Charge is just a property, like mass, that some particles have. It's a conserved quantity. That is, for a closed system, the total amount of charge it contains doesn't change. Thus charge can only be created or destroyed in pairs of opposites. There's not much more to be said about ",
" than that.",
"Now there is a little more that can be said about why charge exists, but it's pretty abstract. There's a theorem by a woman named Emmy Noether that says that if a system has a continuous symmetry then there is a corresponding quantity that is conserved. Here's an example: if a system has translational symmetry, then (linear) momentum is conserved. Translational symmetry means you can \"move the system over\" in some direction and all of the physics will still work the same. If a system has time translation symmetry (that is, if you can view it at two different times and it's behaving the same) then the system conserves energy.",
"Now there's a more abstract type of symmetry, called a ",
" symmetry, that electromagnetic fields obey, so there must be a corresponding conserved quantity. It turns out that this conserved quantity is electric charge."
] |
[
"Charge describes the coupling of a particle to the photon (electromagnetic) field. It is a fundamental property of a particle, and is irreducible in the sense that there is nothing underlying the electromagnetic interaction: it just ",
". What we call \"electricity\" is merely the motion of charges, and what we call \"magnetism\" is the result of charges moving quickly enough that the equations of special relativity become important (which they do fairly regularly).",
"If you want to know more about charge -- like why there's only positive and negative charge, and not a third type, or why opposites attract and like charges repel -- the answers come from quantum field theory. Chapter 1 of Zee's ",
" has a surprisingly accessible explanation... well, surprisingly accessible for a textbook on the current most detailed theory of Nature."
] |
[
"First, charge being positive or negative charges is an arbitrary convention created by Ben Franklin back in the day. We know that like charges repel, unlike charges attract and that the strength of these forces is proportional to the product of the amount of charges. By assigning one type as positive numbers; one as negative numbers it makes it simple to say: F = - k (q1)(q2)/r",
" But there isn't anything intrinsically \"negative\"/\"positive\" about one type and the convention could easily be switched. (Some argue since electrons primarily are seen transmitting electric charge, that it would make sense to have electrons have positive charge; but we are left with the conventions we were given).",
"In particle physics, charge is just a number assigned to different particles. E.g., electrons have a charge of -1, up quarks +2/3, down quarks (-1/3). (A proton is a composite particle composed of uud making net charge of +1, where all are in units of the fundamental charge ~ 1.6x10",
" C.). Charge is related to how well light (the propagator of electromagnetism) couples to particles. (In units of hbar=1=c, the strength of the coupling is q",
"Feynman wrote a very good book ",
"QED",
" describing the quantum mechanical view of how light interacts with charge to the lay audience.",
"Others talked about how charge is the generator of the U(1) gauge symmetry of electromagnetism. While that's true, and very useful in particle physics (when talking about group theoretic properties or generalizing to other forces), it isn't particularly insightful. Or explains how charge arises as we don't really know why the symmetry arises."
] |
[
"How does energy have weight?"
] |
[
false
] |
Say in the compressed spring example, the spring gains more (potential) energy. And from E=mc2 the spring has more mass and therefore has more weight, assuming earth gravitational field. How can I imagine this Energy as having more weight?
|
[
"Well, first realize that the majority of the mass in the uncompressed string is also due to energy, namely the binding energy in the strong force that keeps the baryons and atoms together. The higgs mechanism gives mass as well, but not nearly as much as the binding energy.",
"Realize that energy is what bends spacetime and creates gravity, whether that energy is free or contained within binding energy of \"matter\". "
] |
[
"I Apologise beforehand if I don't word my questions clearly enough, it's something I'm working on. ",
"Say E=mc",
" we can see that Energy = Mass. So if I boiled a bowl of water I am adding energy to it. Based on this equation the water would have more mass! Well where did the mass come from?? Well the energy I put into it. Now let's weigh the heated water and we find that it weighs more than unheated water.",
"I don't understand how energy can have mass and weight. Does heating it do something to its electromagnetic field causing more weight? "
] |
[
"I Apologise beforehand if I don't word my questions clearly enough, it's something I'm working on. ",
"Say E=mc",
" we can see that Energy = Mass. So if I boiled a bowl of water I am adding energy to it. Based on this equation the water would have more mass! Well where did the mass come from?? Well the energy I put into it. Now let's weigh the heated water and we find that it weighs more than unheated water.",
"I don't understand how energy can have mass and weight. Does heating it do something to its electromagnetic field causing more weight? "
] |
[
"It is theorized that chloroplasts and mitochondria were once their own organisms. If we took them out of their host cells, could they maintain life as their own free-living organism today?"
] |
[
false
] |
[deleted]
|
[
"To add to what others have said here, plastids (mitochondria and chloroplasts) once had complete genomes, but over time most of the genes that started out in the plastids have been moved into the nuclear genome. For a sense of scale, mitochondria have about 1,000 proteins (gene products) working inside of them, but human mitochondria only encode 13 genes in their genomes."
] |
[
"Yes to both. The mitochondria (and the chloroplast) have their own, unique DNA. And the genes that those genomes contain can vary between species (as different evolutionary linage have moved different genes from the plastid to the nucleus. This is part of the evidence that supports the endosymbiont theory).",
"As for our cells using them, the genes contained in plastids make proteins that form the enzymatic cores of the protein complexes that produce energy (either through respiration in mitochondria or photosynthesis in chloroplasts). But the proteins encoded in the plastid have to work closely with proteins encoded in the nucleus for us to live. So neither set of DNA is useless. To emphasize the importance of mitochondrial DNA, I'll tell you that there are a number of rather horrible human disease caused by mutations in the mitochondrial DNA. ",
"The United Mitochondrial Disease Foundation's website",
" has an easy-to-understand discussion on mitochondrial diseases."
] |
[
"No, that wouldn't work. As you say, it is theorized that mitochondria and chloroblasts were individual organisms and that they formed a symbiosis with other cells. The fact that they still contain fragments of their own DNA supports this theory.",
"Through evolution, these organisms have come to specialize in a certain task to their host cell (e.g. production of ATP) and have given up other functions essential to survival."
] |
[
"How does gravity bend space in 3 dimensions? The usual depictions shows only 2. (Related, what \"shape\" is the universe?)"
] |
[
false
] |
Let's see if this makes any sense: Another redditor made this about the universe being "planar", and it reminded of how most depictions of gravity look something like , which I assume is quite simplified. But if everything is 3D, how should this look as opposed to these 2D depictions? How planar really is the universe? I tend think of the universe as a giant dark room with stars/planets/galaxies etc. floating all over in three-dimensional space. Is that totally incorrect? But then thinking of it as something planar with things "sitting" on top doesn't seem right at all.
|
[
"We have to very careful here—we have two separate concepts: Spatial curvature and spacetime curvature. Spacetime curvature tells you about the gravitational sources present, but ",
"spatial curvature, called k,",
" tells you about the density of the universe. When you seek pictures showing sphere, saddles and planes, remember these are 2D toy examples. The real slices are 3D space slices at some fixed time. If we lived in a flat 2D+1time universe, then you could imagine each slice being a plane and when we stack all the planes for t1, t2, t3 etc... we get the full spacetime.",
"There are three types of shapes simple shapes we usually discuss (there are more possible shapes, but we will not discuss them here): ",
"k = 0, flat universe. It is \"critically dense\" and thus will expand forever, but the Euclidean angles of triangles will be preserved.",
"k = -1, negative curvature. It is \"under dense\" and things will runaway expand.",
"k = 1, positive curvature. It is \"over dense,\" so gravity will eventually win and things will crunch back together in the future.",
"This is analogous to the situation of throwing a ball away from the Earth which is bound to the Earth with energy E.",
"I throw it will exactly energy E. It leaves the Earth, but it's speed forever approaches zero, but it will never come back.",
"I throw it with greater than E energy. It leaves the Earth, but will always retain a finite kinetic energy.",
"I throw it with less than E energy. The ball will leave Earth, slow, stop and fall back to Earth.",
"On the small scale, the universe has an approximately flat spacetime with little bumps everywhere from stars, planets, asteroids, etc... etc... The argument ",
"/u/VeryLittle",
" is making is that on cosmological scales—where galaxies are essentially grains of sand—it is believed that spacetime is flat and infinite via experiment. However, the other two shapes are not technically excluded, but the universe seems to be very close to the critical density with k=0.",
"While we have some ideas on why this is, via inflation, this honestly is a great mystery for why this is the case.",
" Relativity doesn't have a preferred time, but because of some incredible symmetry in our universe, there seems to be a preferred time for all objects following the Hubble expansion."
] |
[
"Say you're trying to make a map of the earth. The problem is that paper is flat and the surface of the earth is curved. There's two basic ways to do it. One way, is to have a warped map. Or rather, multiple warped maps, since one map will always be missing at least one point. For example, most maps you see don't contain the north and south poles. You have to keep track of how it's warped in different areas to work out the angle between two vectors, whether or not a curve is straight etc. This is what mathematicians do. It's what the math of General Relativity does.",
"The other way to do it is to embed it in higher dimensions. Basically, just use a globe. Use a spherical map to correspond to a spherical territory. This works fine with the surface of the earth. Mostly because that actually is a two-dimensional surface embedded into higher dimensions. But not everything is. This method is easier for people to wrap their minds around though, so people tend to use it to try to explain curved geometry to lay people.",
"Spacetime is not some kind of fabric sitting in a higher dimensional space. It's all there is. It's just that angles and distances don't work like they do in Euclidean geometry. You can think of a sheet with dimples in it as some kind of metaphor, but you have to remember that it's just a metaphor."
] |
[
"The comment about the universe being planar was basically saying that if you walk in one direction you don't end up coming back around to where you started. ",
"The 2D depictions of gravity bending space are just doing the best they can... The best way to \"depict it in 3D\" would be ",
"something like this",
". But honestly the \"2D version\" is more meaningful.",
"You have to realize that the ",
" the 2D plane is being warped is not referring another dimension. Better to think of the z-axis here as a measure of gravitational potential."
] |
[
"Do photon transistors exist?"
] |
[
false
] |
And if they do, what would they look like physically, what media would they use, like current ICs use silicon? Are light-based or photonic computers a possibility? Would they be significantly more efficient than our current electronic ones?
|
[
"They do indeed:",
"https://en.wikipedia.org/wiki/Optical_transistor",
"Photonics aren't at all my thing, but I understand that a generic issue with photonics is that the wavelength of light is quite large relative to an electron's de Broglie wavelength and thus any computing devices based on photonics must be necessarily upscaled in size, which means even if photons are faster, you may still lose in terms of Moore's law vs. an electron based device like a MOSFET. I believe this is why there's such an emphasis on transducers, i.e. switching an optical signal into something else like a polariton (see Polaritonics).",
"And if they do, what would they look like physically,",
"You can see in the wikipedia link that this isn't easily answered as there's no one way to implement a non-linear \"switching\" behaviour using light. And of the many strategies the fundamental principle can be dramatically different. But at the end of the day you need a feedback mechanism, where concentration of light positively or negatively affects the ease of transmission of light through a material or system."
] |
[
"All-optical switching is achieved by employing materials with nonlinear optical properties. Certain materials have a refractive index that changes with the intensity of incident light: you can make an optical transistor by using a light source to modulate the refractive index, and another source so modulate the signal. Physically they can be made by inserting along the beam path a section of active material, with the signal beam being \"bent\" into different directions according to the varying refractive index."
] |
[
"Certain materials have a refractive index that changes with the intensity of incident light",
"I always thought that the kerr effect happens in all materials in high enough intensities (although some have it stronger than others). "
] |
[
"What method do they use to date wooden artifacts?"
] |
[
false
] |
I was wondering, can they use carbon dating, or is that just for animals that have consumed carbon-14. And is tree ring dating pretty much useless due to the fact that the wood would have been shaped (pardon the pun).
|
[
"Yup, we use tree rings! It isn't immediately obvious how, given that tree rings appear to be useful only if we have an entire cross-section from a tree's birth to its death, but that's a shallow assumption. Trees from the same forest tend to develop similar ring patterns, since their living conditions are identical. Researchers can compare and match these ring patterns from trees that were grown at the same time in the same region, and build a chronology for the entire region. Using this chronology, we can then identify when and where a particular sample of wood was from, simply by matching it to our library of tree patterns.",
"Currently, the following chronologies exist:",
"",
"If tree rings are not visible, we can use radiocarbon dating, or carbon-14 dating. This method is applicable to all forms of life, since we are carbon-based lifeforms. There are some adjustments that have to be made based on atmospheric content of carbon-14, the type of lifeform, and varying levels of carbon-14 in the biosphere, but they all essentially depend on the ratio of carbon-14 to carbon-12.",
"While there are advances in the detection methods and calculations since radiocarbon dating was conceived in the late 1940s, there are a few problems to this method of dating wood (or any carbon-based sample).",
"One problem with radiocarbon dating is its sensitivity to contamination from modern carbon-14. This is a major issue, since there is significantly more carbon-14 in the atmosphere due to the last 70 years of nuclear weapon testing.",
"Another problem with radiocarbon dating is that carbon-14 has a radioactive half-life of 5,730 years. This means that any sample older than ~50,000 years barely has any carbon-14 left to be dated."
] |
[
"Cheers mate"
] |
[
"All living organisms take in carbon-14. Including plants.",
"So carbon dating wood is absolutely a possibility. However, there are problems with dating wood that have to be accounted for.",
"Trees-- as most everyone knows-- grow by adding new growth annually, and this takes the form of \"rings\" if the tree is cross-sectioned. Every year, a tree produces a new ring, which consists of two parts: \"early wood,\" and \"late wood.\" I'm not going to touch on the dendrochronology aspects of things since ",
"/u/dragmehomenow",
" has covered that quite well.",
"Dendro can be great, and so can radiocarbon dating, but we have to be very cautious-- especially today, where radiocarbon dating has become increasingly precise, and (we hope) equally increasingly accurate.",
"Radiocarbon dates are typically expressed as a mean value with a standard deviation. That's why you usually see a carbon-14 date expressed as one number +/- a smaller number. E.g., 5730 +/- 30 rcybp (radiocarbon years before present). After some additional calculations-- basically converting radiocarbon years into calendar years-- we get to an actual estimate of years before present.",
"Here's the problem.",
"Materials make their way into archaeological sites in a lot of different ways. Wood, for example, could have been used as construction material, part of a composite tool, or as fuel.",
"In these different ways of being introduced into the archaeological record (through use and eventual discard / deposition) wood of the exact same age, and felled at the same time, could enter the record at very different times.",
"Used in construction in a dry environment, a large piece of wood might last for decades, if not actual centuries. Timbers in the Pueblo ruins in the American Southwest are dry and in good enough shape to be dated via dendrochronology. Some of them are at least 1000 years old. But imagine if some of them were burned 500 years ago. A radiocarbon date on the burned timbers wouldn't date the actual event during which they entered the record (the fire). It would date when they were felled, 1000 years ago.",
"That's a problem.",
"A tool handle might be used for many years after it was fashioned.",
"Firewood-- especially dense heartwood from a tree like a live oak-- might lie on the forest floor for years before being collected and used as firewood.",
"Problematically, we often don't know where in a tree a piece of wood came from, either.",
"A very large tree, say 800 years old, might be felled, split, and used for construction, or as fuel. So then you have the issue that a piece of wood from the interior is nearly 800 years old. The outer wood is much younger.",
"Inner pieces would give a date of 800 years, while pieces from the outer portions of the tree would come out a lot younger.",
"If a tree was felled to be used as fuel, the youngest outer wood would actually be the timing of the event during which the wood entered the archaeological record. But the inner wood might be burned as well.",
"Picking through the remains of a fire 500 years later, you might get pieces of wood with very different radiocarbon signatures. Some with young dates close to when the fire actually was built, and some with dates literally hundreds of years earlier.",
"From the same tree. In the same fire pit.",
"These are all examples of what's generally referred to as the ",
". We recognize the potential issues, and we can even (sometimes) control for them.",
"But it's a big enough issue-- especially if all you have is a fragment of charcoal without species ID or any indication of where in the tree it came from-- that most archaeologists today avoid wood for radiocarbon dating if at all possible.",
"The preference is for shorter-lived species of plants or animals.",
"Annuals like dense nutshell (hickory is common in the SE US, because of how much it was used and how well it preserves) are great. Animal bone ",
" be good if it's not a species living near a waterway eating a lot of aquatic species. Deer antler is great, because deer don't live long, and they shed their antlers annually."
] |
[
"I've heard that distilled water leeches minerals from the body. Is this true or supported with any evidence?"
] |
[
false
] |
It seems to be somewhat of a stretch being made with regards to the claim. I thought that with osmosis, even if the claim were true, that this "pure" water would be somewhat absorbed even more into the body.
|
[
"As far as I know, there isn't any published scientific research supporting the idea that drinking distilled water (as opposed to hard water) significantly affects the levels of minerals or the levels of mineral absorption/secretion in a person.",
"It has been ",
"speculated that because some non-distilled drinking water contains essential minerals, it may be beneficial to one's health",
", but I don't think it is known whether the minerals in water significantly contribute to anything.",
"Many seem to doubt the importance of mineral content in water since it is so low compared to the mineral content found in food."
] |
[
"I'm sort of skeptical of this idea, specifically this part as it relates to the OP's question:",
"The higher the inorganic content is in a per million count, the less effectively water transmits organic minerals to tissue sites.",
"Do you know where this idea comes from? I've seen it elsewhere on the internet but could never find a scientific source for it."
] |
[
"It seems to be just the opposite",
". This definitely isn't a scholarly resource, but they suggest that it increases mineral absorption rates. Distilled water has reduced inorganic mineral content (these are bad, linked to \"a wide array of degenerative diseases\"). Their absence encourages the absorption of organic minerals, which are important for daily function."
] |
[
"For the physicists of AskScience! A mathematical question on Energy-Displacement Graphs (for the experts/brave)"
] |
[
false
] |
[deleted]
|
[
"This may not be ",
" definitive answer, but here's how I see it. You're integrate kinetic energy minus potential energy from one point to another (those points are fairly arbitrary; you've set it to be where the two are equal, but that can be redefined by resetting the zero point of the potential energy. So let's just take these two be two arbitrary points). That's a quantity called the ",
"Lagrangian",
", and its integral over time is called the ",
"action",
"). The action is one of the most useful quantities in all of physics, because it turns out that Nature likes particles to take paths which minimize (or maximize) the action. The path classical mechanics tells a particle to take from point A to point B will invariably have a lower action than any other possible path between A and B. The action principle is extremely important and lies beneath practically all of modern physics."
] |
[
"I found this really helpful, thank you so much"
] |
[
"Well, it's close to the concept of ",
"action",
", and in specific, the ",
"Lagrangian",
" or ",
"Hamiltonian",
" formalisms of physics. I mean not your area thing, but I think if that kind of question interests you, learning \"advanced\" classical mechanics (Lagrangian and Hamiltonian; ie mechanics past Newton's laws) You'll be quite interested.",
"To me, all of physics, and by extension everything in the entire universe can be summarized by the \"Least Action Principle\"; from this all things descend. "
] |
[
"Why can't we control our involuntary muscles?"
] |
[
false
] |
Something that I've always wondered about. Why can't we control our heart beat, our digestion, or any number of involuntary processes?
|
[
"Same reason you can't turn on the garbage disposal with the bathroom light switch; the hookup's not there. ",
"You can train yourself to affect your heart rate, though; scare yourself, calm yourself, etc, but that's more indirect."
] |
[
"From an evolutionary perspective its because they are safer if they are automatic. Even humans didn't properly understand the most basic physiology until a few hundred years ago. ",
"The diaphragm is an interesting example of a voluntary muscle with an involuntary override."
] |
[
"Control of your heartbeat is incredibly useful in stressful situations (and when you really want to upset your nurses in the hospital). "
] |
[
"Can we soon look forward to a period during which the ocean provides more and more food and raw materials for the exploding world population of humans?"
] |
[
false
] |
[deleted]
|
[
"We are really messing up the oceans. No amount of new technology will allow us to extract more from 99% of the already over exploited populations (we have sort of hit our peak, but even if it did advance what would be left to fish?). Of those that are doing well its usually because they are too far out (meaning that the energy required to catch them - time to go out, time to pay fisherman, gas which all add up to $) is less then what you get when you sell them at market. To make up for this loss many governments subsidize the fishing industry, meaning they pay fisherman to go out an fish even if it costs more then its worth. Sometimes stocks are doing well because they are being protected, but the oceans are an interconnected ecosystem. Its not like land, where there are more or less separate areas. What happens in one end of the Atlantic effects the southern end, one side of the pacific the other. So that if stalks in general are declining the very fabric of the food web is weakening, if we reduce species to levels that are practically extinct for all intents and purposes this will negatively effect our \"good\" stocks. ",
"Moreover, policies put into place to day to protect fish stocks are ineffective, and we are deluding ourselves if we think otherwise.",
"Marine protected areas: are usually areas where they are of little value. ",
"Sometimes they are put in areas where fish breed and this protects fish breeding habitat, and allow for the trageted fish stocks to recover and even 'spill over' into unprotected areas",
". But more often then not there is a very large list of other things that you can extract by various means from that place. The protection offered by an MPA is only effective if the list of things you can extract isn't too long (preferably none) and only if this is enforced by law. Here is a list of ",
"global mpas",
", they represent under 5% of the total world ocean surface. Moreover only a fraction of these are 100% no take zones, usually some sort of fishing or trapping can take place. This does not help the majority of fish species that are migratory. As soon as they leave these protected areas they are allowed to be caught. ",
"Max sustainable Yeild (MSY): fancy language for saying how much fish you should catch based on how big a stock is, how many fish are in each age-sex class (infant, juvenile, adult, old adult) and still make it sustainable. The biggest problem here is that there are hundreds of ways to calculate MSY and few of them actually agree with each other and most do not take into account that other predators in the sea (sharks, other fish) need to eat too. Moreover, calculating (estimating) how many fish are in each age-sex class correctly can be a nightmare - if you don't get the actually population numbers right how do you know how many you can fish?. Different countries set different limits, there is little agreeance. We also tend to think extracting 50-80% of a prey species (like fish) is sustainable, when in nature predators never exceed 20% of their prey stock, and usually they sit around 5-10%. So we are acting like 'super predators' and this is not sustainable. MSY and other calculations have proved questionable in the past, it is not a reliable way to fish sustainably.",
"We tend to catch large yummy fish, but older fish produce more eggs/more young. If we catch all the old fish, then what tends to happen are there are not enough baby fish being born. The funny thing is with some fish species ",
"See atlantic Cod",
" they need a certain population density to breed. Meaning, they need some amount of breeding adults to produce enough eggs and sperm so that the densities are high enough that they actually get fertilized. If we mess up stocks enough, they never recover, because they are below the threshold of recovery...case in point Atlantic Cod. ",
"Nobody is policing the oceans. So if I wanted to go out and fish the crap out of an endangered species I would have (relatively) no problem doing so. A good case: ",
"ban on whaling",
". Bad case: illegal whaling still continues.",
"How do we fix this problem?",
"Stop the bombing of coral reefs for the exotic aquaria pet trade",
"dead zones",
"WWF overfishing",
"Greenpeace overfishing",
"Canada Gov on overfishing",
"Wiki on overfishing",
", ",
"overexploitation",
", ",
"Max sustainable yeild",
"...",
"Overfishing",
"End of the line",
"Sharkwater",
": Warning can be graphic.",
"Unnatural history of the sea"
] |
[
"No. the human population has exceeded the Earths carrying capacity. Energy budgets of aquaculture are likey much less efficient than natural systems. The increased use of shrimp farms and the like will very likely hasten the destruction of marine food chains. Increased release of nitrate and phosphate into the marine environment is resulting in increased incidence of and larger areas of anoxic dead zones. ",
"Read up on Garret Hardin: \"If humans don't control their population, nature will do it for them\".",
"I don't care if I'm down-voted on this."
] |
[
"If you can provide studies that support what you say no one will have to downvote you."
] |
[
"What wavelength range is cherenkov radiation?"
] |
[
false
] |
[deleted]
|
[
"It depends of the velocity of the particle and the properties of the medium in which the Cherenkov radiation is being emitted. The ",
"frank-tamm formula",
" can be used to calculate the energy radiated at a particular frequency."
] |
[
"So use the relevant properties of your medium (which I'm assuming is water) and the average velocity of your particles. Put everything into Mathematica (or whatever program you typically use) and have it graph the spectrum."
] |
[
"Specifically, I'm measuring cherenkov radiation from a research reactor in a pool of water. "
] |
[
"What are the conditions needed for Fossils to form? Can we replicate those conditions?"
] |
[
false
] | null |
[
"Fossils can be made in several different ways, but in most cases something needs to cover the remains and prevent them from being broken down by the passage of time. Things like tar and mud have been really good for this and it’s similar with small insects and amber. If you coated something recently in epoxy and prevented oxygen and decomposers to have access it would be similar to that. We have plastination now though and that’s better than fossilizing so we’ve already got tried and true methods of preservation for science."
] |
[
"Say we bury a plastinated creature, it would take a white before it gets destroyed right?"
] |
[
"For a fossil to form you need to have an organism not only die but be isolated in an inaerobic enviornment quickly after death (Which is why tar pits, landslides, and such things are good at doing that) and then hope that itll stay like that for a while. And while that is easy to replicate, there are easier methods to achieve the same effect."
] |
[
"Why is there a desert on the Arabian peninsula?"
] |
[
false
] |
The Arabian peninsula is surrounded on water on 3 sides and has mountain ranges that could catch precipitation coming from the red sea, Persian gulf and Arabian sea. I know that its an extension of the Sahara but shouldn't there be areas on the peninsula that do have good amounts of precipitation?
|
[
"The bodies of water it's surrounded by are not large enough to have meaningful effects from trade winds, or cyclic winds that carry water from other climate zones and dump it there.",
"Coastal mountain ranges typically capture precipitation that trade winds pick up as evaporate that's accumulated as they travel thousands of kilometers across an open ocean, and oftentimes through different latitudinal/climatic zones (where warming and cooling can increase or decrease their water-carrying capacity). ",
"The seas surrounding SA aren't that large. Most of the winds that arrive on the peninsula have, instead, been traveling over mostly arid land by the time they arrive. Thus, no precipitation to capture, and the little that does evaporate off of one of the seas (as wind doesn't converge on at inland SA from 3 different directions) isn't enough to create strong rainstorms. ",
"There are likely other factors at play, but you can read more about the basic functionality of these cycles here:\n",
"https://www2.whoi.edu/site/globalwatercycle/"
] |
[
"The mountains do receive greater rainfall than the rest of the peninsula.",
"The area gets very little rain, outside of the rainy reason; underground aquifers capture most of it, and it's very hot besides. The areas at elevation, near mountains and near the coast do\nproduce some verdant land, but these mountains aren't the Himalayas, plenty of clouds pass\nright on over.",
"The tl;dr is, water is rare and disappears quickly in most places."
] |
[
"Chances are the Persian Gulf and the Arabian Sea are deserts themselves, meaning very low rainfall. I remember reading quite a while ago that the desert conditions that affect Los Angeles extend pretty far out into the Pacific ocean."
] |
[
"What could have caused a tick to detach after only and hour or two?"
] |
[
false
] | null |
[
"We can't comment on personal anecdotes / isolated events without resorting to speculation which we always try to avoid."
] |
[
"Any suggestion as to where I might go to find relevant information? Everything I’ve been able to find suggests this is not a usual occurrence and I’ve become extremely curious"
] |
[
"Unfortunately no, but maybe the folks at ",
"/r/findareddit",
" can help find the right place to ask."
] |
[
"Science, please tell me this is complete bullshit."
] |
[
false
] |
crosspost from by BeerSensor (who does not agree with the article)
|
[
"Total, unadulterated BS.",
"Edit: I was going to add in here a more measured discussion, but on re-review, literally every sentence in the third and fourth paragraph is utter bullshit. Not one fact is correct. It's difficult to even explain how completely and thoroughly ludicrous it is. In some ways, it's really quite impressive how incredibly full of crap this man is.",
"Edit 2: Ok, I keep getting drawn back to this like a fly to... Anyway. I had to find out if this guy actually believed what he was saying. Found ",
"this.",
" If you want a second serving of pretentious drivel, dig in!"
] |
[
"Just for fun, I'm going to go through and point out each piece of BS that I come across. I'll start with paragraph three, since the first two just set up the question.",
"Wine cells: Wine is not an organism although I suppose there are probably living things in wines. The living things do not constitute the substance we think of as wine; that honor goes to ethanol and assorted other chemicals which are definitely not alive.",
"All living things have a magnetic polarity: Electromagnetism is very important in certain aspects of biology, but I have never heard of an organism or a cell having a definite polarity, except firing neurons I suppose. All cells have a potential across the membrane, but not from one end of the cell to another. Both of those are very weak electric potentials, with no identifiable magnetic activity.",
"The positive pole is more highly charged like the North Pole: Physics 101, no such thing as a magnetic monopole. And anyway, while it is true that electricity and magnetism are two sides of the same coin it makes no sense to say that one magnetic pole is more highly electrically charged than the other.",
"Northern lights but no Southern lights: Simply wrong as B_Fee said.",
"Wine cells stay upright, spinning on their axis due to magnetism: No, that's electrons, and \"spin\" is not a description of what it's physically doing because electrons are not balls. It's like he saw half an episode of Nova or something. And there are no wine cells.",
"Commonly demonstrated in laboratories: No?",
"Pores on the molecule's surface: Molecular surfaces are rich with detail, it's true. But they don't have pores. And if they did, pore formation wouldn't depend on earth's magnetic field.",
"Something about against the cat's fur: Molecules don't have a preferred way of being stroked because they don't have brains.",
"Dislodges anything on the surface: So at this point we've somehow got shit sitting on the surface of molecules and it gets knocked loose if you swirl the wrong way. Molecules are small. Things don't nestle on their surfaces like crumbs in cat fur.",
"Barrel flavors in outer layers: Wine is a liquid. Everything's mixed up. There are no layers.",
"I'll stop there, but I'll leave with a ",
": This article came directly out of Ralph de Amicis's ass. You can still see the poop cells."
] |
[
"I thought I had chronic diarrhea. Turns out that I had been working in the magnet factory too long. Just had to realign my poop cells."
] |
[
"How are primes calculated for RSA?"
] |
[
false
] |
Why is it hard to calculate the factors of n, for a 1024-bit key but easier to calculate factors for 1024-bit p and q for a 2048-bit n? Is it because calculating primes is easier than calculating numbers with exactly 4 factors (including 1 and the number itself)?
|
[
"This answer is good. But I want to expand on two aspects.",
"It's just \"get random number\", \"check if large enough\" and \"check if prime\" untill you have 2 suitable primes.",
"One thing worth emphasizing is that you really need to go back to get a random number each time you loop. Some people think you can save resources by checking if p is prime, and if not looking at p+2, then p+4 and so on. The problem is that this makes your distribution highly non-random. So for example, if you were doing this with 3 digit primes, 127 is very likely to get hit, but 101 won't be unless it is high on the spot. See ",
"discussion here",
".",
"Also, regarding needing to check all primes in a range, that is the naive algorithm for factoring, the ",
"number field sieve",
" does not work that way."
] |
[
"In one direction you need two primes, which can",
"It's just \"get random number\", \"check if large enough\" and \"check if prime\" untill you have 2 suitable primes.",
"In the other direction you need to more or less check ",
" primes between 10",
" and 10",
" - 1, so π(10",
" - 1) - π(10",
" ), or about 3.8×10",
" That includes"
] |
[
"It's just \"get random number\", \"check if large enough\" and \"check if prime\" untill you have 2 suitable primes.",
"I would also point out that the naive \"check if prime\" step where you try all factors up to the square root would be pretty slow in practice. ",
"Instead, typically a probabilistic primality test is used instead, such as the ",
"Miller-Rabin test",
". This is much quicker, but it's possible the selected number ends up being composite, albeit with a ",
" low probability."
] |
[
"Is the sense of understanding of a 3 year old fully developed?"
] |
[
false
] | null |
[
"What does \"sense of understanding\" mean?"
] |
[
"If they really comprehend what I'm saiyng. Like sometime she say \"I want story before bed!\" mildly crying and I tell her \"if you continue you won't have a story\" and she say \"I WANT STORY!!\" then Throw a fit or cry, which make her unable to have story."
] |
[
"If you mean something like causal reasoning (how one thing causes another) or deductive reasoning (if p then q, p, therefore q), both of these continue to develop with large changes occurring around the age of 4"
] |
[
"How were maps made accurate before satellites were invented?"
] |
[
false
] | null |
[
"Trigonometry. ",
"Measure the distance and angle from one place to another then measure the angle to another point from those two and you know exactly where each point is relative to one another. Continue across an area and you have a map. "
] |
[
"Well, yes. Even today it's mostly a lot of trigonometry - or more specifically, triangulation. The GPS works on the principle of measuring your distance from three known points. These ",
"tachymeters",
" you see used in geodesy are basically extremely precise yardsticks used in tandem with a compass to determine exact relative position of points on landscapes."
] |
[
"Early cartographers did it the same way that we do in modern times. By using simple geometry. Instead of interferometry and satellites to measure distances/heights and angles, they were forced to use yardsticks and shadows, which made the maps look a little ",
"off",
" on large scales, but the general idea is stayed the same."
] |
[
"Why are there six types of quarks instead of two?"
] |
[
false
] |
[deleted]
|
[
"Yeah, that. In particle physics, a decay is a process in which a particle changes its identity, or actually ",
" into some other particle(s). It's not a case of a particle breaking apart into constituents. ",
"Outside of particle physics, some kinds of decays do involve something breaking apart into its constituents. For example, in the context of radioactivity, alpha decay is a nucleus breaking apart. But beta decay involves a transformation of one particle into other things."
] |
[
"Yeah, that. In particle physics, a decay is a process in which a particle changes its identity, or actually ",
" into some other particle(s). It's not a case of a particle breaking apart into constituents. ",
"Outside of particle physics, some kinds of decays do involve something breaking apart into its constituents. For example, in the context of radioactivity, alpha decay is a nucleus breaking apart. But beta decay involves a transformation of one particle into other things."
] |
[
"It's because there are a lot of phenomena that were first discovered experimentally, and looked (almost) exactly like one thing at the time, but then later on, when the theoretical explanation was worked out, it became clear that they were something else entirely. E.g. elementary particle decays looked just like radioactive decays for a while. Spin originally looked just like little rotating balls. Color charge acts like color in the sense that the combination of the three is neutral (like white). Of course, by the time it becomes clear that the physical phenomenon is something different from what the word normally used to mean, the name is already \"stuck\" in common use among scientists."
] |
[
"If you fly from the South Pole to Quito, Ecuador, where does the ~460 m/s rotational speed come from?"
] |
[
false
] |
You go from 0 speed relative to the center of Earth to having a horizontal speed of around 460 m/s near the equator. Where does this come from when flying?
|
[
"The aircraft will steer a tiny bit to the right on average. As seen by the aircraft, the Coriolis force makes it deviate to the left. Countering that (to fly straight on a map) makes it keep up with the rotation of Earth."
] |
[
"The air induces a drift just like an ocean current induces a drift on a boat. At each location along the path, you'll be flying through air which is in motion relative to a fixed coordinate system. The further north you go, the higher the average speed of the air, i.e. the air near Quito will on average be moving east at about the same speed as Quito. And that air is pushing you to also move east. To not end up with an Eastward velocity, you'd have to steer the plane westward to cancel out the push of the air on the airplane."
] |
[
"A rocket starting from the pole that doesn't care about the rotation will end up crossing the equator with no velocity along the equator in an inertial reference frame, i.e. it will move west as seen from the ground."
] |
[
"When you drop a rock into a pool of water, is there a way to predict the pitch of the sound that is made?"
] |
[
false
] | null |
[
"Some work to simulate similar effects... ",
"https://youtu.be/On4ODNwJ424"
] |
[
"Everything has something to do with quantum mechanics doesn't it ? And i do know that the simple act of observation changes the way \"something\" behaves ;)"
] |
[
"Ok, thanks."
] |
[
"Rubbing alcohol or hydrogen peroxide?"
] |
[
false
] |
I understand that this is not the place for medical advice but is there is a difference between the two or are they equally efficacious in terms of their aseptic properties? Or is one used over the other in certain circumstances?
|
[
"Hydrogen peroxide is an inferior antiseptic(an anti-microbial used on skin or mucus membranes) because tissue catalases can break it down into O2 and H2O. It can be used as a disinfectant (cleaning surfaces), however.",
"Alcohols are better because they are not broken down by enzymes as readily as hydrogen peroxide (your liver metabolizes alcohols but this is irrelevant when applying small amounts of alcohols to your skin or mucus membranes). Ethanol is effective, but isopropanol is both less volatile and more potent so is preferred. However, alcohols do not kill bacterial spores. In fact, fatal infections have followed attempts to sterilize medical instruments with alcohols because of the danger of spores.",
"To sterilize most medical instruments hospitals will use something known as an autoclave. It is essentially a giant pressure cooker, and uses steam at a pressure of around 15 lb/in",
" and a temperature of around 120 Celsius for roughly 15 minutes to kill all microbes and their spores.",
"To sterilize your skin for surgery surgeons will use iodine-based solutions like povidine-iodine(trade name: betadine), which are effective against even spores. Furthermore, these solutions leave a lasting iodine residue meaning the effect continues post-application.",
"This isn't medical advice, simply a statement of fact regarding antimicrobials."
] |
[
"Good info - one correction: it's 15 PSI, or lb/in",
" , not lb/ft",
" . For reference, 15 lb/ft",
" is a paltry 0.1 PSI."
] |
[
"I used the wrods antiseptic and disinfectant separately because they are specific medical terminology which refer to different things. Antiseptics are antimicrobials that are applied to human skin or mucus membranes. Disinfectants are antimicrobials that are applied to non-human surfaces, such as medical instruments or countertops. For this reason, antiseptics are generally weaker than disinfectants, since the most powerful antimicrobials can be used on surfaces whereas only a limited subset of those which don't harm patients can be used on patients.",
"If you re-read my first paragraph in light of that information you will see I mentioned H2O2 is an inferior antiseptic but is used as a disinfectant."
] |
[
"Why does both heating and cooling my house dry out the air?"
] |
[
false
] | null |
[
"With very few exceptions, air has a certain level of water vapor in it, which is what we refer to as humidity. Air can only hold so much water vapor in it until it is completely saturated, and this is what we mean when we say the (relative) humidity is 40%: currently, the air has 40% of the maximum amount of vapor it can hold. The amount of vapor air can hold is dependent on temperature and warmer air can hold more vapor while colder air can hold less.",
"A related quantity is called the dew point, which is the temperature where the relative humidity (RH) would become 100% (the air cannot hold any more water). So if the temperature is 70F and 50% relative humidity, the dew point is 60F, which means if we cooled the air to 60F without adding or removing any water vapor from it, the RH would be 100%, which makes sense since cold air can't hold as much vapor as warm air.",
"So when you take your 70F/50% air and run it through your air conditioner, it is cooled to well below the dew point. Since you can't have greater than 100% RH, that means that some of the water vapor has to come out of the air. When it gets pumped into the room, it gradually warms back up to 70F, but since it lost some water vapor in the air conditioner, your relative humidity will now be lower.",
"Similarly, when you heat air, you're raising the amount of water vapor it can hold without actually adding any vapor to it, so your RH will go down.",
"As an aside, natural gas heaters produce water vapor as a product of combustion, but I don't know if that vapor makes it into the heated air or is condensed/exhausted elsewhere.",
"EDIT: Corrected a dew point typo"
] |
[
"In a properly sealed gas heater, the combustion gases pass through the heat exchanger and out of the flue, never interacting with the inside air."
] |
[
"This is why I like cooking with gas. The combustion products from a gas cookstove stay in the house and help with the RH."
] |
[
"Would space elevators have opposite \"gravity\" at the top due to centrifugal force?"
] |
[
false
] |
I know its not actual gravity, but it was hard to phrase the question without using the word like that. I can provide a diagram if needed.
|
[
"No and yes. In a sense, you have this \"opposite gravity\" while on earth's surface due to the fact that the earth is a rotating reference frame.",
"Space elevators are geosynchronous--they don't move around while on the surface of the earth--meaning that the weightlessness we typically attribute to objects in orbit (which are actually in free fall) doesn't apply. As you move further from earth's surface, the (apparent) force of gravity does decrease, and part of this is accounted for by the increased required centripetal force due to increased distance from the surface. But you would still feel a gravitational effect.",
"The point at which you would begin to feel the effects due to centripetal acceleration is, assuming the space elevator's mass to be negligible, the point of geosynchronous orbit, about 22 thousand miles above earth's surface. At this point, the speed of earth's rotation is just enough to keep you in free fall, balancing the gravitational force. Any further and earth's gravity won't be sufficient to keep you in, and you'll start to feel centrifugal forces. "
] |
[
"depends on what you mean by the top. You'd have gravity pulling downwards, and a centrifugal force pulling upwards (ignoring other effects).",
"m w^2 r - G Me m/r^2 = Fnet = 0",
"therefore r = 0 or r = G Me /w^3 (the latter being geosynchronous orbit)",
"r larger than this, have a dominant centrifugal term, smaller than this r has a dominant gravitational term. I suppose one could make a space elevator long enough that it would have no net (in rotating frame) forces pulling to earth (there would be incredible tensile forces of course)."
] |
[
"No, the top of the elevator would only be moving a little faster than the earths rotation, around 1000mph, to overcome gravity it would have to move around 17000 mph. Since the elevator is connected to the ground, this isn't possible.\nYou're thinking of the elevator like a rotating space station, think of it more like what it really is: a realllly tall building. You don't feel less gravity at the top of a skyscraper (nothing significant anyway), and the same would be true of a space elevator."
] |
[
"What does empty space on a HDD consist of?"
] |
[
false
] |
[deleted]
|
[
"It doesn't matter, and in cases where it's space that formerly held contents it will depend on the former contents. More important is the file table that tracks where things are stored on the drive. Places where things aren't stored simply aren't assigned to a particular file."
] |
[
"There are certain hard coded regions of a hard drive which contain metadata about how the drive is used. This is just a standard, or convention, which enables drives to be used effectively. The first information is the partition table, and this tells the operating system which different chunks of the physical hard drive are formatted as logical drives. Additionally the partition table specifies a code defining the format of the drive (such as ntfs, ext3, fat32, and so on).",
"An operating system accessing the data within the partition would read data structures off of specific physical sectors of the drive relative to the start of the partition, depending on the format type. And these data structures would tell how the available storage capacity is used. For example, in a FAT formatted drive the physical sectors on the disk are grouped into \"clusters\", so they can be kept track of with less data, and then the file allocation table (or FAT) will be a simple linear array containing as many elements as there are clusters on the disk, and each of those elements will either contain the number (address) of the following cluster in the file or a marker noting that this is the last cluster in the file. This is paired with a root directory which is essentially a file in the same place on the disk all the time which contains a list files in the form of names paired with some flags and attributes (such as read only or hidden) as well as the starting cluster of the file and the total length of data in the file.",
"Now you might see how you can use these two data structure to store and retrieve data in files. For a given file you will know the starting cluster, so you can look that up in the FAT and then find out the list of clusters that the file lives on. Then you can use simple math to translate the cluster numbers to physical hard drive sectors and read off the data. And since you know how many total bytes are in the file you know when you can just throw away the remaining data in the last sector.",
"Additionally, you can cram the directory format into files themselves, so you can create files that have a special flag marked to indicate they are sub-directories, and in this way you can have a hierarchical directory structure quite easily.",
"Anyway, as you can see the \"empty space\" in a hard drive is just space that hasn't been assigned to a file yet and been written to. It could be zeros but it's more likely to just be random data."
] |
[
"This is how programs like ",
"Recuva",
" work. They read the raw data still on the drive, ignoring the FAT."
] |
[
"Using Liquid Breathing, or Total Liquid Ventilation (TLV), for SCUBA diving"
] |
[
false
] |
Hi! I'm an avid scuba diver and a student interested in resuscitation science. I learned about liquid breathing or "liquid ice", as the researcher I talked to called it. His team is developing TLV that can induce therapeutic hypothermia during emergencies. The wiki mentions the possibility of using it in diving. There are several gas mixtures scuba divers use. The most common, of course, is air. A lot of advanced divers use nitrox to reduce decompression illness. Trimix is the most technical (and expensive!) one. Liquid breathing seems to trump them all. So my questions are 1) what do you think of the use of liquid breathing in non-medical situations, 2) what would be some pros and cons, and 3) when would it be most appropriate to use? Thanks in advance!
|
[
"I think you're talking about Perfluorocarbons (PFCs), which can dissolve large quantities of oxygen into solution. It has also been looked at as a potential synthetic blood for blood transfusions.",
"A couple of things that have been noted here but should be explained.",
"First, one of the largest problems with PFCs is that they wash out the surfactant in your alveoli. The surfactant keeps the surface tension in your alveoli low so that it doesnt collapse on itself. When you pump the lung full of PFCs, the surfactant gets washed out, so when you remove the PFCs, your lung collapses.",
"Second, gas exchange is almost impossible with liquid breathing. Breathing has two functions, both of which are of extreme importance for living. First, breathing absorbs oxygen which is needed to survive (duh.) Secondly, breathing expels waste carbon dioxide that builds up in your body. ",
"Imagine again that your lung is a giant balloon. If you inflate and deflate and deflate the balloon constantly, you're adding fresh air and dumping out old air, which is how your body functions to absorb oxygen and dump carbon dioxide. Now imagine you fill that balloon with water. Adding new water and dumping out old water now becomes much harder. now, oxygen will slowly get removed from the liquid, and carbon dioxide will begin to build up in the liquid until you die.",
"Want to try to create some kind of pumping system to pump in fresh liquid into the lungs while removing the waste liquid? Good luck trying to design such a pump system. Most likely if your pump is too strong, the lung with either explode or collapse (a large positive pumping pressure will cause parts of the lung to explode, and a large negative pumping pressure to remove waste liquid will cause the lung to collapse)",
"Anyways, I think thats about it. Anyone who knows more than me can feel free to add on to my statement, or correct me if I'm wrong."
] |
[
"My cousin is a deep sea under water welder and he says that although such liquids exist (like the ones from the movie The Abyss) the process of removing them from your lungs and reintroducing air is currently not feasible; if this problem could be solved it may be useful in deep sea diving situations, but I don't know about many other situations "
] |
[
"Flushing the liquid from your lungs. "
] |
[
"Light cannot escape the gravitational pull of a black hole. So where does the light go?"
] |
[
false
] |
I mean, why is the black hole not lit up when the light gets "absorbed"
|
[
"Fun fact: If you were orbiting a black hole, and say you were invincible,the gravitational pull of said hole would be so strong that light would orbit, enabling you the ability to look forward and see the back of your head."
] |
[
"When dealing with fictional things that ignore the laws of physics, you may find it hard to explain them through laws of physics."
] |
[
"This is a short and highly informative video on what might happen when you travel into a black hole- I recommend you take a look.",
"http://www.youtube.com/watch?v=eI9CvipHl_c"
] |
[
"Why don't we use microwaves for heating the water in our household water heaters?"
] |
[
false
] |
[deleted]
|
[
"It's rather unnecessary and more costly. ",
"Microwaves are not a better or faster way to heat water compared to conduction. The reason they cook food faster than an oven is because the radiation causes dielectric heating in the food, rather than heating a metal element which then through some air gap heats the food. Compare a microwave oven to an electric kettle, where the heating element is in contact with the water, or an induction stove top, where the stove heats the pot directly in contact with the water, and you are looking at near comparable heating times for these conduction heating devices. The faster one is the one that has a higher power rating, the method is rather irrelevant. Where as if you stuck the water in an oven and turned it on, it would take significantly longer (and waste a bunch of energy on heating air). Not that speed even matters that much, tank heaters are more common than tankless so it doesn't matter how fast it is it's just going to sit there and insulation is the real consideration. There really isn't any advantage to microwaving a tank full of water compared to sticking a heating element inside, which is basically 100% efficient. So if you are going electric, there is no point. In fact, the magnetron and resonant cavity tank design are only going to cost more and be more complicated. As well, the magnetron is going to make heat and that heat probably isn't going into the water and some of the microwaves are going to escape losing some efficiency but also making electrical interference. ",
"On the other hand you have natural gas, which is the most common source for water heaters when available. The answer here is just a matter of economics, natural gas is a lot cheaper than electricity, though that is location dependent. In most places you get at least two times the energy per dollar with natural gas, so any small efficiency differences really don't matter. So if you have natural gas, you are going to go with it. If you have electricity, you are going to use the simpler and cheaper heating element method. "
] |
[
"It would probably be a little less efficient, and would use a lot more complex equipment than a simple resistive electric heater.",
"An ordinary electric heater is actually very nearly 100% efficient: if you have a coil of wire immersed in water, pretty much all of the electrical energy expended in the coil is transferred to the water as heat. If we use this electrical energy to generate microwave radiation instead, most of the microwave radiation will be absorbed by the water as well (some might be reflected and end up heating other parts of the apparatus), but in order to do this, we need more expensive equipment than a simple coil.",
"There are multiple technologies used to generate microwave radiation, and the best option for a given application depends on factors like the power needed and the microwave frequency. Home microwave ovens use a ",
"magnetron",
" to generate microwaves. Magnetrons have metal chambers that have a resonant frequency in the microwave regime, just like a tuning fork or the chamber in a guitar for audio frequencies. Bunches of electrons are fired at these metal chambers, which excites microwave-frequency oscillations in the cavities (like striking the tuning fork or plucking the guitar). The klystron is a similar device that has a more stable output and can be used to amplify microwaves from other sources. Both magnetrons and klystrons can be used at very high power and find use in radar systems and particle accelerators. For applications that require less power, like some communications and scientific equipment, ",
"special diodes",
" can be used that generate microwave frequency electrical signals.",
"As an aside, it turns out you can actually do better than 100% efficiency for electrical heating by using the electrical energy to move heat around instead of just converting it to heat. In this \"heat pump,\" heat is pumped from a colder area to a hotter one. Refrigerators and air conditioners are also forms of heat pumps, the only difference is that in these cases we care about the cold side more than the hot side. Moving heat from a cold object to a warmer one doesn't happen on its own and some energy input is required. This ends up as waste heat that can further increase the temperature of the hot side of the pump. Heat pumps are used for heating, but the equipment required is a lot more expensive than a simple gas or electric heater (even though they are more efficient)."
] |
[
"Just to expand on heat pumps, it's \"efficiency\"* is called Coefficient of Performance (COP), which is how much heat you can move for each unit of energy you put in, and it's necessarily better than 1 in theory. ",
"https://en.wikipedia.org/wiki/Heat_pump#Coefficient_of_performance_.28COP.29_and_lift",
"You can see in practice heat pumps easily achieve COPs of 4, that is, it will use just 1/4 as much electricity to your heat water as a resistor or microwave would.",
"*Note: I put efficiency in quotes because the true efficiency of heat pumps should be in comparisson to ideal heat cycles, not heat per watt."
] |
[
"Does it make sense to wash dishes with the bubbles because \"that's where the soap is?\""
] |
[
false
] |
I'm man enough to admit there's no 6-year old behind this question, just me. I just won't admit it in the title. <ahem>
|
[
"This is outside of my panel expertise, but I spent a summer working for a major consumer products company in their soap areas.",
"The primary reason that consumer soap lathers (makes bubbles) is because consumers are conditioned to believe that if the soap doesn't lather, then it isn't cleaning anything. There are many commercial soaps that do not lather, like dishwasher soap, which is why you're always told to never put your sink dish soap in the dishwasher.",
"The bubbles do serve the helpful purpose of letting you know where you haven't properly rinsed yet, and what parts of the dish you have cleaned.",
"And yes, for dish washing soap you're intended to use by hand, bubbles are indicative of a higher local concentration of soap which by their very nature will tend to be at the surface of the water."
] |
[
"I knew water it a fairly good cleaner compared to other liquids, and that adding soap made it 'wetter,' but I was never sure if the suds were a super-soapy zone, or just a secondary indicator of a sink full of sufficiently-soapy water. Thanks."
] |
[
"This is a great answer. So you're saying, then, that there's no benefit to liquid hand soap that foams out of the bottle? it's as shameless as Selsun Blue (\"it tingles so I know it's working\") ?",
"Which, incidentally, is a product that deserves a good deal more mockery than my google search has turned up. In their ad, they bluntly acknowledge that it is functionally identical to Head and Shoulders ... Except for the tingling."
] |
[
"Why don't we purify saltwater using the solar still concept on a large scale?"
] |
[
false
] |
The drought in Cali is what got me thinking. I picture something like this: a stream of saltwater in a trough surrounded by a transparent pipe. Sun evaporates the sea water, water condenses on roof of pipe then flows to the bottom, creating a stream of clean drinking water. What am I missing? Is it cheaper to do it another way, would this not work?
|
[
"To get any reasonable flow of water you need a massive area and you need to cool the condensation surface. When you say it condenses on the roof of the pipe, where does that heat go and how fast is that heat transferred? In many of the places where you'd want to try this type of desalination the ambient temperature is so high that you won't get much condensation on an air cooled pipe. You need a large temperature difference so that you get a large difference in saturation pressure of water (i.e. relative humidity). When considering those factors many other options for desalination scale better in terms of productivity and cost."
] |
[
"ramk13 has explained it well, but I would like to offer an alternative prospective.",
"What you are describing--evaporating seawater via solar power to obtain unsalted water--is essentially how cloud forms and how rain works. In another word, the nature is already doing the purification for you. By controlling the condensation with objects such as transparent pipes, you may be able to make the entire process a bit more efficient, but not by too much. "
] |
[
"One part that you are missing is what you do with the remaining salt-slush (brine). This salt-slush isn't safe for consumption, and must be disposed of, or excess energy needs to be utilized to further dehydrate it to make it a consumable. Do you dump the salt-slush back from the source where you obtained it? creating hyper-salination spots in the source, killing any creatures who encounter it? or spend the extra cost/energy/oil to make it in to table sea-salt?",
"Edit: some reading on the subject: ",
"http://www.ffc.org.au/FFC_files/desal/Whatisdesalination-factsheet-1.pdf"
] |
[
"What makes the molecules in an object stick together?"
] |
[
false
] |
This is probably pretty basic science, but why do molecules in a solid stick together rather than fall apart from each other like sand?
|
[
"It depends on the solid. In ",
" materials, you essentially don't have individual molecules anymore, rather the molecules clump together in a giant network with the same kinds of bonds as you have within the molecule. Effectively, a crystal is a single giant molecule in a repeated pattern. (E.g. a salt molecule, is NaCl - sodium chloride. A salt crystal is simply -Na-Cl-Na-Cl-Na- in a three-dimensional square/checkerboard kind of pattern, each Chlorine bound to six neighboring sodiums, and vice-versa, like ",
"this",
")",
"Non-crystalline solids, wood or plastic for instance, are a bit different. They're composed of many different molecules, and aren't necessarily totally solid either (the molecules can move a bit - hence they're also a lot more elastic than most crystals). In those materials the individual molecules are distinct, and they're instead held together by ",
" forces. ",
"As Jericho here says, these are basically due to the electrical attraction between molecules, caused by the fact that the charges in a molecule aren't perfectly evenly distributed (they have what's called an electrical ",
"). For instance, water is H2O, and shaped at an angle, where the oxygen atom has a slight relatively-negative charge, and the two hydrogen atoms have a slight relatively-positive charge. So water molecules 'stick' to each other when they orient themselves so that the hydrogens in one point to the oxygen in the other (because opposite charges attract). (This intermolecular bond is known as a ",
", because it's a particularly strong and important one)",
"There's another, weaker kind of intermolecular force which is known as the London force. Unlike the dipole forces I described above, the London force occurs between ",
" molecules. One way to describe it, is that the electrons around the atoms in the molecules are always in motion, and so the charge fluctuates a bit. This fluctuation leads to there occasionally being a bit more negative charge on one side of the atom/molecule than on the other. This attracts the electrons in a nearby molecule, and causes it to become a bit unbalanced as well. (an 'induced dipole moment') The end result being that the two molecules attract because of this. This is what holds together non-polar substances (ones that don't have a 'positive' and 'negative' end), like fats."
] |
[
"Atoms have a positivity charged nucleus surrounded by negative electrons. The total charge of an atom is zero, but the electrons aren't always evenly spread on the surface of the atom (or molecule), leading to areas with different charge. If the kinetic energy is low enough, these charges cause them to stick together. Increase the heat, and the material does fall apart (melts)."
] |
[
"That's a perfectly okay, albeit simplified, description of Keesom forces, which is one of the most significant intermolecular forces. "
] |
[
"Can someone please explain why dead weight appears to feel heavier than standard weight?"
] |
[
false
] |
[deleted]
|
[
"It's a matter of the clumsiness of handling a floppy body instead of a rigid weight.",
"If you were to try to move a 150 pound cooler, you would have an easier time with that than moving a 150 pound body simply because the cooler is both compact and rigid in comparison. "
] |
[
"To elaborate on this: Your arm muscles obviously have to exert the same amount of force to hold the person up. But that's not all that carrying someone involves; you ",
" have to use stabilizing muscles to keep them centered. If they're conscious they will instinctively do some of this work, and if they're not it all falls on your muscles."
] |
[
"\"Dead Weight\" is simply the unrelieved weight of a thing. A conscious person would make some effort to support themselves, ideally, by placing their arms around your neck or something to that effect. But a conscious person who simply went limp would still be considered \"Dead Weight\". ",
"There is no literal difference in weight or mass between a dead person and a living one. Unless you're into that 21 Grams movie, but come on."
] |
[
"Why do nucleons lose mass when they bind into atoms?"
] |
[
false
] | null |
[
"Because of the nuclear force, they go into a more energetically stable configuration, a lower potential energy, and release that potential energy in the form of electromagnetic and kinetic energy, similarly to an exothermic chemical reaction. It is difficult to get more specific than that, since the nuclear force is not as well understood as gravity or electromagnetism. I can tell you that neutrons tend to stabilize nuclei with a lot of protons. The protons of course repel each other, and so as you get to nuclei with higher and higher charges, you need more and more neutrons per proton to stabilize them."
] |
[
"When they bind into stable atoms, they release energy in the form of heat and electromagnetic radiation. E = mc",
" of course. E = mc",
" for chemical reactions too, just like with nuclear reactions, it's just that nuclear reactions involve a lot more energy so you can actually measure the mass change easily."
] |
[
"I know that mass and energy are interchangeable in this case, I could as well phrase the title \"why do nucleons have to lose mass/energy to form a stable atom\". "
] |
[
"Is the metric expansion of space occurring in some form at all scales, or only for astronomical distances?"
] |
[
false
] | null |
[
"The expansion does happen at all scales. The rate of the expansion is measured at approximately 74 kilometers per second per ",
". A megaparsec is a little over 3 million light years, or about 20 thousand trillion kilometers! So shrinking that down to a human reasonable scale that's an expansion rate of about 4x10",
" m/s per kilometer, or 4 attometers per second per kilometer. So a kilometer of space around you will increase in size about the size of an atomic nucleus every second.",
" 8)"
] |
[
"This is not correct. Metric expansion of space does not happen at all where gravity is significant. It's not like expansion is happening everywhere but gravity keeps matter together, expansion of space can only happen where gravity is insignificant. ",
"/u/shavera",
" has written a couple of ",
" good comments about it. I'm on mobile, so I can't access my saved comments right now, but I'll link a couple of his comments later. "
] |
[
"Not only is gravity strong enough on this local scale, but on the scale of galaxy clusters its still strong enough to keep the galaxies in a given cluster bound together."
] |
[
"In semiconductor chip manufacturing, how do they move the wafer or the stencil with nanometer accuracy for the many layers?"
] |
[
false
] |
[deleted]
|
[
"I know that some of them use piezoelectric actuators. For example:",
"http://www.pi-usa.us/products/Nanopositioning_Scanning_Stages/Nanopositioning_Stage_Basics_Piezo-Driven_Nano-Positioning.php"
] |
[
"Right, I have the same experience when I did labwork. The first rough movements are done with motor actuators. The small adjustments with piezoelectric actuators. I think piezoelectric actuators are the only ones reliable enough at those tiny distances."
] |
[
"The same way they align components onto circuit boards, actually. There's a 1,000,000x size difference but despite that the marks can even look relatively similar. Here's some for ",
"MEMs",
", which are still 100x larger than next generation transistors but pretty much the same principles.",
"The wafers are transported between machines in contained units so you don't have to worry about manipulating and securing the wafer. Then you can just zoom in on the fiducial and get it as close to centered as you can. It'll already be pretty accurate just because we are ",
" good and making perfectly sized and shaped holes. ",
"In addition to piezo actuators (which come in many forms) some semiconductors use specialty ",
"linear motors",
", which can have sub-nanometer precision over a much larger range of motion. "
] |
[
"What happens when T-Cells or B-Cells are in the blood for too long?"
] |
[
false
] |
We only really use them when we're infected with something, right? So, I imagine that they get deployed and leave after the job gets done....but what happens if the just chill in the blood?
|
[
"Most of them usually don't, they chill in the lymph nodes. In case of infections, the relevant ones multiply and get deployed to the blood stream to reach the infected tissue faster. Catching activated T- or B-cells in the blood is seen as a clinical sign for chronic infection or an autoimmune disease and should be checked further."
] |
[
"This is absolutely not true. Healthy immunocompetent adults have 1-4 ",
" T or B cells per mL of bood."
] |
[
"This is absolutely not true. Healthy immunocompetent adults have 1-4 ",
" T or B cells per mL of bood."
] |
[
"How does soap work?"
] |
[
false
] |
I'm guessing that there is a part of soap that is soluble in water, and another part that is soluble in oil. That's what I assume; does anyone know what really goes on?
|
[
"Yup. Detergents are amphipathic: they have hydrophilic (interacts with water) and hydrophobic (does not interact with water, but does with oils/greases) regions which allows them to interact with both water and water-insoluble compounds. This lets them break up bits of grease into water-soluble structures."
] |
[
"As an expert, I endorse this answer and encourage the OP to use Google."
] |
[
"More specifically, they have a ",
" oily/hydrophobic region (hence volume), and typically ",
"such that they forms ",
"micelles",
" in aqueous solutions (see article for pretty pics). These micelles are what encapsulates the grease.",
"Israelchivili"
] |
[
"Any more recent developments in the theory that the universe isn't expanding more and more rapidly, but that time, itself, is slowing down?"
] |
[
false
] |
[deleted]
|
[
"How could we perceive time slowing down? I assume that slowing time will necessarily slow the chemical reactions in our bodies, and thus slow our thoughts. Thus, we would never perceive time slowing down, since our thoughts are still in sync with everything else.",
"For that matter, how could we measure time slowing down without an outside reference frame that was not slowing down?"
] |
[
"We would get the same result because the slowing would affect our measurement, the particles being measured and our perception equally. "
] |
[
"Consider two locations A and B, with time \"faster\" at B than A. Assume we have two identical clocks. At either location A or B, the clocks tick at the same rate, so there's nothing amiss. But if we separate the clocks to A and B for some time, and then bring them back together, we would see that the clock at B is now running ahead of the one at A. This much is true even with relativistic time dilation: instead of \"locations\", imagine two bodies A and B moving at different speeds, A faster than B.",
"From what I can infer from the blurb in the post, the paper hypothesizes that time is slowing down across the universe. How is this observable at all? Well, what we observe today about a place X 1 billion light years away from us is really what was occurring at that location 1 billion years away. If time was \"faster\" 1B years ago, then we would observe clocks running faster at X than here. This is true for any \"clock\", whether a chemical reaction or the movement of supernovae. So supernovae at X would be moving faster than we might expect them to. Put another way, the farther away the supernovae are, the faster we would observe them to be moving, even if they were moving at the same speed at any given time.",
"I'm not a physicist, so I might be wrong, but does that make sense? ",
"Edit: Got the direction of time dilation wrong earlier."
] |
[
"How much do stars expand when going supernova?"
] |
[
false
] |
[deleted]
|
[
"NaN%",
"In the case of core-collapse supernovae, the outer layers are ejected at up to a few percent c. The nebula is in no way gravitationally bound, and will just expand and disperse over time. One could perhaps compare it to the difficulties in describing the size of a smoke plume.",
"For Type Ia supernovae, the above applies to the entire star."
] |
[
"The sun can't go supernova, so this would require some rather silly assumptions to cause one. If it's anything like a normal supernovae, see my previous answer."
] |
[
"That explains why I couldn't get an awnser. What about if specifically our sun went supernova? Thanks for the response btw!"
] |
[
"Are reptiles as prone to over-consumption of resources when compared to mammals?"
] |
[
false
] |
I read this and wondered if reptiles, such as the Komodo dragon, could be at risk for a massive die-off for similar reasons, such as having no natural predators. If that comic were about reptiles and not mammals, would it still be the same outcome? Could reptiles manage their food source in different ways, such as not having to eat nearly as much as a similar sized mammal, or would they become fat and lazy to the point they eventually overshoot their limit?
|
[
"link appears broken"
] |
[
"I think the big difference here is that these were primary consumers. Lizards such as ",
" are opportunistic scavengers and carnivores. Once you have predator-prey relationships, a dynamic cycle is established that keeps both populations in check.",
"Why dont giant (herbivorous) tortoises, like on the Galapagos, undergo this type of boom-bust cycle, you say? They have predators as babies. "
] |
[
"My apologies. I've fixed the link."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"You would test for antibodies to the virus to see if the vaccine worked.\nMost of the vaccines won't grant you immunity outright. Most people may end up more or less immune, but many people will only end up resistant to the virus and can still contract COVID. Life won't be going back to normal for at least another year or two."
] |
[
"Hi, I was wondering have Koch's Postulates been satisfied (in full) for every disease we have identified? What is accepted medically as 'satisfied'? ",
"Further, do we even need to satisfy all of Koch's Postulates to prove a causitive link between a pathogen and a disease being caused and if not, why not? Do asymptomatic carriers not 'disprove' this? ",
"Finally, are there any inherent logical flaws in Koch's Postulates (including the updated version)? For example some that don't explain the causitive link between pathogens and disease?",
"Thank you in advance if you answer this!"
] |
[
"Hi.",
"How was determined the daily amount of vitamins for a person? ",
"Some sources say that we need to take vitamins, some do not. But even if the deficit is prooven by the tests (which is the question in itself: how do we know how much should be there?), there is a dosage of the said vitamin. Where does it come from? ",
"Thank you!"
] |
[
"Can humans adapt and survive with Martian gravity?"
] |
[
false
] |
Let's imagine a future Martian colony... People who aren't interested in a return trip to Earth. They would lose bone density on Mars, but would that be okay if they stayed on Mars? If they traveled to Earth for the first time, would they be able to build their body up to function on Earth? I'm writing a scifi screenplay for a class and I want to remain as true to science as possible.
|
[
"They would lose muscle mass as well since everything weighs less. If they tried to retain earth-like muscle mass/bone density by working out and such yes (the astronauts on the ISS do this). They could also gradually get their bodies used to the lower gravity using the same method. If they decided to instantly go from Earth muscle mass/bone density to the much weaker Martian needs, then I'm not entirely sure what would happen as there is no precedent, but I would assume it would be something like a gravitational version of the bends."
] |
[
"From 9877 A.D., we note the following in our Encyclopedia Solsystica:",
"exoskeleton: \n People from low gravity worlds have great difficulty moving about on worlds of higher gravity. Such a low gravity worlder can feel that his or her body weighs two to ten times what it should on a higher gravity world.\n The exoskeleton is a device which clamps on to the human body and supports it relieving much of the pressure that the higher gravity force puts upon the relatively frail human body. A well designed and well fitted exoskeleton can totally eliminate the possibility that the wearer’s bones will be broken by gravity stress.\n In cases where the difference between the wearer’s home world is no more than twice the G-force of the world visited, the exoskeleton is powered by the wearer’s muscles using levers and gears to assist the wearer. Martians commonly wear only muscle powered exoskeletons when doing business on Terra as they are proud to be able to move with only their muscles as power. \n When the ratio of low-to-high gravity exceeds 2-to-1, the exoskeleton suits are design with motors that do the moving and lifting without relying upon the wearer’s muscles at all. In the case of gravity ratios of over 8-to-1, even breathing must be assisted, and so the whole torso is encased in a powered shell.\n The exoskeletons are made of aluminum where minor gravity differences are the case. Titanium is the material of choice for the greater gravity differences, although very expensive exoskeletons are often made with lightweight carbon polyfibers. Usually the exoskeletons are worn over the ordinary clothing as no one would be fooled into believing that a low-gravity worlder was a native to a higher gravity world being visited regardless of how smooth the motor assistance is. However, in the case of diplomats and wealthy business men who must stay extended period on a higher gravity world, close fitting exoskeletons are sometimes worn under ordinary clothing."
] |
[
"Yes, but they would loose a lot of muscle mass. Also, going back to earth after an extended period of time could be dangerous unless they exercised frequently."
] |
[
"The Pauli-Exclusion Principle doesn't apply to Bosons because muliple Bosons can occupy the same quantum state. Does this mean that the Pauli-Exclusion principle doesn't appl particles with spin numbers that are integers?"
] |
[
false
] | null |
[
"but what about particles with spin numbers that are integers?",
"Those are bosons."
] |
[
"A boson, yes."
] |
[
"So any particle with a whole spin number is considered a bison?"
] |
[
"If I add nicotine to the water of my hydroponic tomatoes, will the tomatoes have nicotine?"
] |
[
false
] |
[deleted]
|
[
"This is a great question.",
"The quick answer is no. The plant takes in nutrients (chemicals it has a use for) and breaks them down to smaller units that it then uses to build plant structures. At first guess I would say it would have no effect and certainly not be in the plant.",
"In the case of nicotine, ",
"this",
" says that my short answer is wrong, as the nicotine will effect growth. It will not be a product in your tomatoes, but will effect growth."
] |
[
"So hypothetically, one could breed for nicotine content and eventually arrive at tomacco organically?"
] |
[
"Tomatoes have small but significant amounts of nicotine present naturally.",
"http://www.nejm.org/doi/full/10.1056/NEJM199308053290619"
] |
[
"When throwing stuff, does our brain actually try to calculate how hard it has to throw for the item to land at the desired point? Or does it just estimate based on experience?"
] |
[
false
] |
I am just wondering wether the brain is secretly awesome at physics or just good at weight / strength estimation.
|
[
"Well there are no citations nor any reference to any work done on how the brain does this kind of processing. So that \"answer\" just knds of reiterates your questions with the word evolution thrown in. "
] |
[
"Our brains are wonderfully equipped to handle classical physics calculations on the fly. ",
"How? Or are you just assuming the brain implements some kind of proxy newtonian mechanics?"
] |
[
"Our brains are wonderfully equipped to handle classical physics calculations on the fly. ",
"How? Or are you just assuming the brain implements some kind of proxy newtonian mechanics?"
] |
[
"How serious is the proposition that life could have been brought to Earth by a meteor?"
] |
[
false
] |
[deleted]
|
[
"the idea is known as panspermia. And I think while we're learning more and more that organic compounds necessary for life exist in space (and thus are either easily synthesized, or could have been synthesized in space and landed on earth), I think the consensus is that \"life\" did not arrive from space."
] |
[
"Well I personally don't think that its fully implausible. I'd give it a 10% probability and life having started in earth itself a 90% possibility.",
"The fact is that panspermia is not completely impossible or out of the blue when compared to what organisms seem to be able to do in the Earth itself, but given that we have ",
" about life elsewhere and good indications for life having started here itself, this theory need not be considered. Only if in the future we find serious issues for the possibility of life having originated here, may we consider panspermia as the predmoinant theory.",
"EDIT: I see no reason why comets and rocks could not travel from one solar system to another; sure they might take a few billion years to do that but heck we have a 13 billion year history."
] |
[
"We have thirteen billion years, though life on Earth is four billion years old so we only have nine billion years to play with. Certainly there was no life in the very early universe... I'm not sure how many billion years it was before we had a significant fraction of enough heavy elements to form rocky planets, but it was quite a few. So we've shaved quite a few billion years off both ends, and we're getting to the situation where there's not a helluva lot of time left for the whole process to happen.",
"Also let's not forget two other constraints. Firstly, if there ",
" life on an exoplanet, then it'd have to get kicked off the planet by a ",
" collision that sent rocks flying off with sufficient speed that they actually left the star system and sailed off to ours. And these rocks ",
" if they're going to continue to harbour life -- I would consider this rather unlikely in such a high-energy collision. Secondly, the life has to survive the voyage somehow (or else just happen to pop back to life when it reaches Earth). "
] |
[
"Is time real?"
] |
[
false
] |
Physics often refers to time as a tangible thing. I've always thought it was a human created idea so I wonder, is time a real thing? If so, how do we know it it is and what is it? A dimension or a fluid field of some kind? If time is real then does that mean the past still exists in some form?
|
[
"In physics time is understood to be a dimension. By ",
" we mean a degree of freedom. The three (or more?) spatial dimensions tell us ",
" things are relative to each other, and time tells us ",
" things happen relative to each other. Time is as \"real\" or \"unreal\" as the spatial dimensions."
] |
[
"Time is real in precisely the same way that length is real."
] |
[
"Yep. Time is as real as space. In fact, they're two sides of the same coin - that coin being ",
"spacetime.",
"If so, how do we know it it is and what is it? A dimension or a fluid field of some kind?",
"As Amarkov ",
" said, it is a dimension in the same way that length, width and height are dimensions, i.e. a degree of freedom through which stuff can move.",
"If time is real then does that mean the past still exists in some form?",
"Yep. Take a look up into the sky on a clear night. You'll see light that left stars long before you or I were born."
] |
[
"Is a mature dog more intelligent than a human baby?"
] |
[
false
] |
I always see these videos of babies playing with the family dog and it always seems to me in those videos that the dog is the more....grown up (?) being in that shot. Is there any merit to this kind of thinking?
|
[
"Yes, the intelligence of different animals is often compared to humans at some developmental age. ",
"http://www.popsci.com/blog-network/kinderlab/why-your-dog-smarter-my-baby",
"Intelligence is not a one-dimensional measure, however, so the real answer is that it depends on how you define your measure. "
] |
[
"Glad you added that last sentence! I do agree with what you said but to play devils advocate I wanted to mention a scenario where I think the baby would have more measurable intelligence. If you define intelligence as the ability to learn and absorb completely foreign and new information then the baby is much smarter. In that instance the human baby might just be the most intelligent being on the planet, in my opinion that is at least."
] |
[
"Maybe the baby could be said to be the best learner, but I wouldn't say smartest or most intelligent. By that reasoning humans get less intelligent as we age ...."
] |
[
"In terms of physics, how does one propel themselves on a swingset without touching the ground?"
] |
[
false
] | null |
[
"In the simplest terms, you contract your muscles to shift the center of mass away from being directly underneath the pivot point. This causes torque that is mediated by the tension on the rope. You can see how this happens if you find a swing that looks like a boat and place a heave ball on one end. As it rolls in the boat, it will make the whole swing move."
] |
[
"To add to this, swinging seems intuitively weird to someone thinking about the physics because it seems to break conservation of momentum: an isolated person is able to get himself moving from a stopped position. In reality, the person is not isolated. When the person contracts his muscles to change his center of mass, he is pulling on the rope which pulls on the bar on top which is in contact with the ground. As complicated as it seems, getting going on a swing is not that much different than simply standing on the ground and jumping up (in terms of the energy that is transferred from muscles to body motion by pushing off of something)."
] |
[
"Small motion seems kind of obvious, but I believe you're asking how does one start from a stationary swing and get their center of mass to have large swings? This requires first a small perturbation of the rope, then you need to pull up and move your body higher out of the potential during a certain part of the swing (up swing) and release on another part of the swing (down swing, though I maybe wrong on where to do it, it's been years since I've been on swing). You effectively transfer your momentum through the rope and into the swing set/Earth. The action of lifting, swinging, releasing, swinging, repeating more or less acts like a pump or motor where you pull yourself higher in the potential and release when it benefits you. "
] |
[
"Why do you float to the surface despite when deep in the sea there is a great pressure on you?"
] |
[
false
] | null |
[
"You are receiving an equal pressure from all sides, and it largely cancels out. The net force you receive is equal to the force required to hold a you-sized portion of water in equilibrium against gravity. Basically, if you replaced yourself with a you-sized portion of water, then that water should really be stationary - it's not going to shoot up to the surface or plummet to the seafloor unless there are other forces involved. So it must be receiving the right amount of pressure to support it against gravity. When you replace that water with a person, it doesn't change the amount of pressure you receive.",
"So what it comes down to is whether you weigh more than a you-sized volume of water. If you weigh more than water, then you don't receive enough net force to support you against gravity, and you sink. If you weigh less than water, then you receive too much net force to solely support you against gravity, and you float upwards.",
"It turns out the human body is quite close to the density of water, so we end up being able to swim up and down and float decently without sinking rapidly or shooting up to the surface all the time."
] |
[
"You are receiving an equal pressure from all sides",
"You don't have equal pressure on all sides. Hydrostatic pressure is denisty * g * h. Pressure is higher the deeper you go, and this slight imbalance results in buoyancy force."
] |
[
"When you dive, your equipment has extra weight which will make you want to sink overall. This is offset by having an air bladder, which is inflated during the dive at a level to cause neutral buoyancy. As you dive deeper, the bladder compresses, reducing the buoyancy force. So you have to add some of your diving air back to the bladder to maintain neutral buoyancy."
] |
[
"A Quantum Physics Primer?"
] |
[
false
] | null |
[
"Awesome - Thank you for this. I'll ask there! "
] |
[
"Awesome - Thank you for this. I'll ask there! "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/asksciencediscussion",
"/r/physics",
"/r/suggestmeabook",
"If you disagree with this decision, please send a message to the moderators."
] |
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