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[
"When investors say that stocks outperform things like bonds in the long run (as they have over the past 100 years), couldn't that outperformance just be an artifact of that particular 100 year timeline?"
] |
[
false
] |
When looking at for investments, one can clearly see the stellar performance of equities over the long haul. That being said, we know that we can center in on certain 20-25 year time spans throughout that century where the return characteristics look drastically different. If this is the case, then couldn't the entire 100 year period demonstrating the attractive returns for stocks be an aberration over hundreds or thousands of years, especially considering how since pre-history? And how could we hope to know? Is there a statistical/probabilistic way to be understand whether our "long-run" returns are in fact indicative of some sort of deep principle regarding average returns in a market economy?
|
[
"In order to answer this question, we would need to first answer one bigger question that is the topic of many books: Is the stock market random? If the answer is yes, then one can answer your question in the manner that you have asked. We need only find the standard deviation and calculate the chances that over 100 years, the results could have been different. Much like if you flip a fair coin 100 times, there is a chance, however small, that you will get 75 heads and only 25 tails. This is what you are essentially asking, and I will let a statistician answer that part.",
"If however, we conclude that the stock market is not random, but instead there is a reason for the outperformance, then it is not really a chance or probability problem. Take for example two plants, one which grows better in sunlight and one which grows better in shade. You plant both in an open, sunny part of your yard. Over 100 years, the first plant will grow taller every time. Extending the time frame will not change that. Over the short term, the shady plant may beat the sunny one though, because there are cloudy days as well as sunny days. So as long as the sun is mostly shining, then the sunny plant will win. Only a change to the system, such as a larger tree growing over the area and covering them in shade, can change that.",
"So, what is the “sunny” equivalent for stocks? I would argue it is economic growth. So long as we have strong economic growth, I believe stocks will outperform bonds in the long term because of how those asset classes are structured. Bond holders receive a fixed return based on the coupon rate. There is limited upside. Common stock holders on the other hand, have no upper limit on the upside and receive all gains after everyone else that is higher in the capital structure gets paid (the government, senior creditors, subordinated creditors and so on). Add in the tax deferred nature of stocks (only taxed when sold) versus interest on bonds which is taxed when received, and you further tip the long term in favor of stocks (apologies for being US–centric. Tax laws may differ elsewhere). There are many other factors in this complex system, but I will leave it at that.",
"Now let’s take a doomsday scenario, where the world enters a permanent recession. Say a global plague that slowly decimates our population to only 10 million people in 100 years. In that scenario, I would guess that bonds would outperform stocks as there is little to no upside for economic growth.",
"I’ll add one last comment. When most people say “bonds” they often mean US treasuries, as shown in your graphic. However, this ignores a large portion of the credit market, which is Corporates - both investment grade and high yield. I’d be curious to see a 100 year study of high yield bonds (if they existed back that far) vs. the stock market. HY bond returns are often correlated to economic growth, while US treasuries might actually have a negative correlation to economic growth. They certainly did in 2008."
] |
[
"Piketty does an analysis of historic investments and returns in his book, and claims the uber-wealthy do most of their investment in BONDS and RENTABLE REAL ESTATE, both of which return 3-4% per annum. Equities \"should\" be pegged to growth in the economy, which Piketty shows pretty clearly averages around 1%. The differences in growth, since WWII, occurred from the destruction of capital in the two World Wars. Because capital was scant, its creation led to most robust growth than any other long-term period in history. ",
"Bonds don't grow 3-4% a year because they grow at the same rate as the economy. They grow because of time discounting. ",
"Anyway, I don't want to make the point that Piketty is absolutely correct. He makes long draw-out arguments based on massive historical datasets. You would likely find his work interesting. The book is called \"Capital in the 21st Century\", and it is not a short read. "
] |
[
"Stocks are basically ownership of a company.",
"Bonds are basically loans to a company.",
"If loans to a company were more profitable than ownership of a company (in general), most people would not want to own a company anymore. ",
"Ownership of a company ",
" on average more profitable than \"just\" lending money to a company. "
] |
[
"Are solar panels worth buying now?"
] |
[
false
] | null |
[
"Not a science question."
] |
[
"How is it not a technology question? Basically asking if the technology of solar panels is improving so quickly that it worth waiting a year or two to buy them because they will get better "
] |
[
"We don't offer advice here."
] |
[
"Is there any natural evidence of the higher dimensions or have we totally made the concept up?"
] |
[
false
] |
It makes sense (though I can barely comprehend it) and was wondering if there has been any real sitings of fourth dimensional objects or activity. I was thinking maybe in quantum level since I heard the physics there doesn't behave normally?
|
[
"I think in context the question is referring to spatial dimensions."
] |
[
"Is there any natural evidence of higher dimensions or have we totally made the concept up?",
"I think the answer to your question is no on both counts. There is no explicit evidence of extra dimensions, but it is also not a totally arbitrary suggestion, as there are phenomena that are nicely explained by extra dimensions, as I'll explain below. (By contrast, if I said, \"Suppose there's a particle with a mass 1 million times that of a proton\" without any particular reason for doing so, it would be fair to say that was totally made up, even though such a particle might be consistent with everything we know to date.)",
"The most compelling argument for extra dimensions, in my estimation, goes back to the Kaluza-Klein proposal. Here's the idea. We know general relativity arises from a principle in four dimensions (three of space, one of time) that says whatever coordinates you use to describe things, the laws of physics take the same form.",
"Now what if you had this principle in five dimensions (four of space, one of time)? Five dimensions can work empirically, provided one of them is tiny. Will there be any artifacts of this extra dimension for us? It turns out that there are, and one of them is quite good: starting with gravity in five dimensions, we wind up with gravity in four dimensions ",
" also electromagnetism in four dimensions! So one principle gives us these two forces. The downside in this particular example is that there is an additional particle predicted that is not seen in nature, so this simple scenario doesn't work.",
"But, nonetheless, the ",
" might work; with enough extra dimensions, you can in fact get all of the known forces (weak, strong, and electromagnetic) as artifacts of higher dimensional gravity.",
"When you add to this that the only (apparently) successful quantum theory of gravity introduces extra dimensions, and just the right number to be able to give us the known forces, the conclusion I think I'd reach is not that the idea of extra dimensions is totally made up, but that it can be used to explain things in the real world (things we don't have a good explanation for), and so they are an idea worth exploring."
] |
[
"It is possible to ",
"predict the implications of extra dimensions and then look for signs of those implications",
". However, thus far, there have been no positive results and the universe is three dimensional as far as we know."
] |
[
"Why is the shape of the universe assumed to be a 3-manifold?"
] |
[
false
] |
From the Wikipedia page on "shape of the universe": In practice, more formally, the debate seeks a 3-manifold that corresponds to the spatial section (in comoving coordinates) of the 4-dimensional space-time of the universe. Why? Wouldn't a plain 3 dimensional shape represent the spatial section of a 4-dimensional universe which has 1 time dimension? A would correspond to the entire 4-dimensional spacetime of the universe, There are 3 spatial dimensions to the universe, not 4. A 3-sphere models 4 dimensions.
|
[
"Because ",
"time doesn't have a Euclidean coupling to space dimensions",
".",
"Edit: thinking about this more, I may have misunderstood your question, so please feel free to correct me."
] |
[
"We aren't using a 3-sphere to model the spatial part. To our best understanding, the spatial subspace of space-time is an infinite Euclidean plane."
] |
[
"Then what are we using the 3-sphere to model if not the spatial section of the universe as it said in the quote from the Wiki article?",
"Because a 3-sphere is a ",
" dimensional object with positive curvature, which makes it a good model for a universe that has positive spatial curvature.",
"Why is it an infinite Euclidean plane? Is there any empirical basis for modeling it as an infinite Euclidean plane?",
"Analysis of the cosmic microwave background radiation suggests that the universe is largely homogenous (the same everywhere), anisotropic (the same in all directions), and flat (no spatial curvature). The simplest 3-manifold with these properties is infinite Euclidean space."
] |
[
"Would a sample of cesium decay slower if it were traveling near light speed? Would it stop decaying if it were traveling exactly light speed?"
] |
[
false
] |
If so what properties are involved? Did einstein figure this out?
|
[
"If you observe it from an outside frame of reference, yes, it would appear to decay more slowly. If your frame of reference is within the same system as your cesium sample, it would appear to decay at the same rate as ever. ",
"Time dilation applies to everything."
] |
[
"It would be a fresh, non-decayed sample, because less time would have passed in the system that our cesium has been moving in than to other, slower moving observers."
] |
[
"The cesium used in atomic clocks is specifically just the cesium-133 isotope, which is stable and doesn't decay."
] |
[
"Question about methylation."
] |
[
false
] |
When referring to methylation in biology are we talking about dna methylation only. I have noticed links between neuro diseases and methylation and also methylation tests. Are methylation test diagnostically useful? and with regard to the illumina test would it be possible to categorically say or not if a gene was silenced? Also whalt sort of sample would be supplied. I was imagining that each cell would likely have a different methylation pattern or fingerprint.
|
[
"When referring to methylation in biology are we talking about dna methylation only.",
"DNA methylation is the most well known epigenetic modification. In addition, histones can be methylated or have a large number of other modifications like acetylation, phosphorylation, ubiquitilation and others. ",
"Epigenetic modifications are a way of controlling the expression level of genes without modifying the genes at the DNA level. These modifications are reversible and generally change from cell type to cell type.",
"I have noticed links between neuro diseases and methylation and also methylation tests.",
"Epigenetic modifications are different for every cell type. Any cell that has aberrant activity is likely to harbor different epigenetic modifications than their healthy counterparts.",
"Are methylation test diagnostically useful?",
"Methylation tests can be useful for diagnostics. I could be wrong, but I don't believe any test is CLIA approved for diagnostic use today. "
] |
[
"Thanks for your help. How straightforward is it to know if a gene is being effected by examining a methylation array?"
] |
[
"Bioinformatically, quite straight-forward. We can use tools like the ",
"genome browser",
" to display histone modification tracks. However, ",
" genes have their transcription effected in a sense by histone modifications. Nucleosomes, histones and the covalent modifications that appear on the histone tails (approx. 1/3 of the protein) are quite crucial in controlling gene expression (and it appears, particularly tissue-specificity of expression).",
"There's an interesting database of their roles with literature citations here: ",
"http://www.iiserpune.ac.in/~coee/histome/index.php",
"To actually get this data in the first place (talking histone modifications here), we need to do ",
"ChIP-seq",
", which is time-consuming, expensive and a general pain (although there are pretty good antibodies to most epigenetic marks these days now).",
"If you want to try looking at this data yourself, go to the genome browser and try figuring out how to display human, switch on the H3K4me3 track (Histone 3, Lysine 4, trimethylation) and search for a few genes (try Sox2 with an ES cell H3K4me3 track - it would be active, I would guess - and H3K4me3 is a mark of active transcription)."
] |
[
"What happens to bugs (e.g. mosquitoes) when they bite a human and the human has natural insecticides in their system (caffeine, nicotine, cocaine, psilocybin) or even alcohol... do they die or get high?"
] |
[
false
] | null |
[
"According to ",
"this",
" article, concentrated doses of stimulants such as caffeine caused a distortion in mosquito behavior, followed by death.....so both.",
"I wouldn't think the levels of these stimulants could be high enough in the bloodstream for it to have a lethal effect on mosquitoes, though.",
"Also, I couldn't resist linking ",
"this relevant commercial",
"."
] |
[
"In fact, there is a drug that is already used in many parts of Africa to treat river blindness and elephantiasis that has been shown to kill mosquitoes that bite humans with this drug in their bloodstreams. Obviously this has implications for helping reduce malaria. ",
"Source"
] |
[
"I really wish I could answer this, because I'd love to give those little mother fuckers what they have coming to them."
] |
[
"Does every part of us become replaced over time?"
] |
[
false
] | null |
[
"Everything, except stable cells that don't actively divide: nerve, muscle, ligaments, cartilage undergo constant division. The cells with the highest turn over rate are our skin cells, and the lining of our gastrointestinal tract."
] |
[
"As far as I know the cells in your brain don’t regenerate. Neural pathways are one of the few “one and done” cells and cell structures in our body, and that’s why it’s difficult to come back from brain injury, and why drugs and addictive chemicals are terrible for your brain. But it’s been a minute since I’ve taken an anatomy class."
] |
[
"except stable cells that don't actively divide",
"Even they replace a good fraction of their molecules over time - I'm not sure if there are any that don't get replaced at all."
] |
[
"what is the statistical distribution of the numbers from 0 to 9 in the decimal places of pi (or any other irrational number)?"
] |
[
false
] |
E. g. in 3.1415926535 there are 10 decimal places, 2 of which are the number "1", ergo it appears 20 % of the time. (My intuition would be, that it converges to 10 % each.)
|
[
"We don't know, but it's conjectured and considered very likely that the decimal digits are distributed evenly. This is what is meant by a ",
"‘normal’ number",
".",
" Almost all numbers are normal, but it is surprisingly hard to prove that a specific number is normal.",
"This is not true for all irrational numbers, and it must be determined on a case by case basis. Here's an example of a number we know is normal:",
"0.123456789101112131415161718192021222324…",
" Actually the definition is a tad more restrictive. It also requires that all pairs of digits occur equally often (1%), all triplets, etc.",
" Normality depends on base. By ‘normal’ I mean ‘normal in base 10’."
] |
[
"very likely that the decimal digits are distributed evenly.",
"...",
"It also requires that all pairs of digits occur equally often (1%),",
"I realised I've never seen this in practice, so if anyone is interested: ",
"I wrote a short piece of code to calculate the occurances of each digit and each pair of digits in the first 100,000 and 1,000,000 digits of pi, generated strings of 100,000 and 1,000,000 numbers with Mersenne Twister for comparison and plotted the results:",
"Single digits",
" and ",
"digit pairs",
". The solid lines are with pi, dashed are with randomly generated numbers. Cyan and blue are for 100,000 digits, magenta and red for 1,000,000. ",
"It's not very pretty, I did it quickly & on impulse, but it does give a visual indication to why normality is conjectured to be a property of pi – of course, they're just finite sequences and I didn't include any higher n-tuplets of numbers (mainly because plotting them would be annoying), but it might be, I don't know, reassuring? Amusing? Something?",
"EDIT: Had the pictures in wrong order, oops."
] |
[
"We know that almost every number is normal (in the sense that if you pick a random number between 0 and 1, the odds of it being normal is 1",
"I want to give a rationale (not proof) for this, in case anyone is interested. Consider the set of binary numbers between 0 and 1 with n digits. Let N(n,p) be the number of these numbers with a fraction p of their binary digits equal to 1. ",
"Say n=20, and p = 1/20, then you have 20 possible numbers: 0.[19 zeros]1, 0.[18 zeros]10, and so on. ",
"On the other hand, with p=0.5, you have 184756 possibilities. See ",
"http://en.wikipedia.org/wiki/Combination",
" for how to calculate this number. The general expression is N(n,p)=C(np,n(1-p)).",
"In general, as n increases, N(n,p) becomes very sharply peaked around p=0.5. For large n, a reasonable approximation is N(n,p) is e",
" with H= -p ln(p) - (1-p) ln(1-p). If you plot this function, you will see what I mean about it becoming sharply peaked near p=0.5.",
"The same idea works in other bases, but in base 10, for example, you have a fraction p1 of the digits equal to 1, p2 of the digits equal to 2, and so on.",
"tl;dr: As n increases, a bigger and bigger fraction of the possible numbers of length n are normally distributed. In the limit n goes to infinity, almost all numbers are normally distributed. "
] |
[
"Why do clouds clump together rather than an even spread as the molecules are free to move?"
] |
[
false
] |
Is there cloud tension? Is it just London forces?
|
[
"Anywhere that you see puffy discrete cumulus clouds is an indicator that there was rising warm, moist air. As that air was lofted upwards, it expanded to match the local pressure, cooled, and some of the moisture condensed out to form a cloud.",
"You can't have these rising warm convection cells everywhere. For an atmosphere to be stable, every rising mass of air must be matched with an equivalent mass of air sinking. Besides, there's generally only enough heating for this rising air to occur in a few discrete locations. (Note, however, that for unstable escaping atmospheres found on hot, low-gravity planets you actually can see the entire atmosphere rising in a process known as Hydrodynamic Escape...but that would be very bad if it ever happened on Earth.)",
"So, cumulus clouds tend to form as clumps wherever air is rising, and there generally tends to be cloud-free conditions between them wherever the atmosphere is stable or sinking.",
"With that said, some clouds are more stable than others, and can diffuse out over time. Very high wispy cirrus clouds are formed off the top of thunderstorms, and tend to diffuse across the sky as the upper level winds winds carry them away from their originating storms. ",
": Clouds are localized because rising air currents are localized."
] |
[
"Clouds are localized because rising air currents are localized.",
"Which, of course, begs the question - why are rising air currents localized?",
"It's been observed for about 100 years that convection in the atmosphere tends to organize in such a way that downdrafts occupy roughly 9-10x as much spatial area as updrafts. But it's not entirely clear ",
" that should be the case. In fact - understanding why (in the moist atmosphere) convection organizes this way is one of the most important questions at the forefront of meteorology."
] |
[
"I saw a mathematician give a colloquium presentation about this. She built a hierarchy of simple physical models that incorporated different levels of complexity. She found that models below the level incorporating gravity waves had an even spatial distribution between cyclonic and anticyclonic systems, while models above that level were spatially dominated by anticyclones like the real atmosphere. I thought it was a clever way to approach the issue, though it doesn't answer what the connection is between anticyclone dominance and gravity waves."
] |
[
"Is this a geometrical rationale for the \"360 degrees to a circle\" convention? (or a coincidence?)"
] |
[
false
] |
Playing some kids’ geometric puzzle pieces (and then doing some pencil & paper checks), I realized something. It started like this: I can line up a sequence of pentagons and equilateral triangles, end-to-end, and get a cycle (a segmented circle). There are 30 shapes in this cycle (15 pentagon-triangle pairs), and so the perimeter of the cycle is divided then into 30 equal straight segments. You can do something similar with squares and triangles and you get a smaller cycle: 6 square-pentagon pairs, dividing the perimeter into 12 segments. And then you can just build it with triangles - basically you just get a hexagon with six sides. For regular polygons beyond the pentagon, it changes. Hexagons and triangles gets you a straight line (actually, you get a cycle out of these, but it isn't of segments like all the others). Then, you get cycles bending in the opposite direction with 8-, 9-, 12-, 15-, and 24-gons. For those, respectively, the perimeter (now the ‘inner’ boundary of the pattern - see the figure above for an example) is divided into 24, 18, 12, 10, and 8 segments. You can also make cycles with some polygons on their own: triangles, squares, hexagons (three hexagons in sequence make a cycle), and you can do it a couple of ways with octagons (with four or eight). You can also make cycles with some other combinations (e.g. 10( ) pentagon-square pairs). Here’s what I realized: The least common multiple of those numbers (the number of segments to the perimeter of the triangle-polygon circle) is ! (at least, I’m pretty sure of it.. maybe here I have made a mistake). This means that if you lay all those cycles on a common circle, and if you want to subdivide the circle in such a way as to catch the edges of every segment, you need 360 subdivisions. Am I just doing some kind of circular-reasoning numerology here or is this maybe a part of the long-lost rationale for the division of the circle into 360 degrees? The wikipedia article claims it’s not known for certain but seems weighted for a “it’s close to the # of days in the year” explanation, and also nods to the fact that 360 is such a number (can be divided lots and lots of ways - which seems related to what I noticed). Surely I am not the first discoverer of this pattern.. in fact this seems like something that would have been easy for an ancient Mesopotamian to discover.. * * * * For those who don't understand the explanation above (i sympathize): to be clear, this method gets you exactly 360 subdivisions of a circle . , not a tautology, as some people are suggesting.. I thought it was an interesting coincidence because the method relies on constructing circles (or cycles) out of elementary geometrical objects (regular polyhedra). The most common response below is basically what wikipedia says (i.e. common knowledge); 360 is a highly composite number, divisible by the Babylonian 60, and is close to the number of days in the year, so that probably is why the number was originally chosen. But I already recognized these points in my original post.. what I want to know is whether or not this has been noted before or proposed as a possible method for how the B's came up with "360", . Thanks!
|
[
"It's neither the rationale or a coincidence. :) ",
"The rationale is that 360 is \"highly divisible\". When all you have to work with are integers you tend to divide things up into a number that you can make fractions of very easily. 360 gives a good amount of accuracy with divisibility. ",
"An hour is split into 60 divisions for the same reason, a foot into 12 divisions, etc, etc...",
"The fact that you can construct these patterns is a direct consequence of that highly divisible number, not a coincidence."
] |
[
"This is correct. All of these are examples of “Base 60” or Sexagesimal number systems that were passed down to us from the Babylonians. You can easily divide several important whole numbers into equal parts, which is great before calculators (and still great today, every one of 1/2, 1/3, 1/4, 1/5, 1/6, and 1/10 fractions of an hour are used regularly somewhere)",
"https://en.m.wikipedia.org/wiki/Sexagesimal"
] |
[
"And, as I recall, the Sumerians, from whom the Babylonians inherited the system, used base 60 because it originated from the practice of counting the 3 bones in each of 4 fingers using the thumb, resulting in counting to 12 on one hand.",
"If you then use the five fingers of the other hand to count each full set of 12, you end up with the ability to count up to 60 using two hands.",
"I believe the leading theory is that this practice came about because two different schools of hand counting, one using 5 (fingers and thumb), and the other using 12 (finger bones), merged together at some point, and simply multiplying them into a base 60 system kept everything in neat fractions."
] |
[
"Why are black holes always portrayed in 2-d"
] |
[
false
] |
To clarify, I mean why is the spiraling matter always depicted as a disc (like ) instead of a sphere? Shouldn't the entire hemispherical face of the star be sucked off and revolve spherically around the hole? Side question. Why are there two pillars perpendicular to the disc? I think it has something to do with radiation emission but it's been a while since I've learned about black holes
|
[
"The rotation causes the gases to be \"flung\" out into a plane perpendicular to the axis of rotation. It's the same reason why most galaxies are flat. ",
"Basically if you take any fluid and spin it, it will flatten out (in the absense of other forces that can stop it ). In the old days sheets of glass would be made this way. A small blob of molten glass was placed n the middle of a huge disk, and then the disk was spun until the glass had flattened out into a thin sheet."
] |
[
"Accretion disc"
] |
[
"conservation of angular momentum"
] |
[
"Why is the Earth flat?"
] |
[
false
] |
Looking at this histogram it seems that the vast majority of the landmass lies between 0 and 1000 meters, whereas the majority of the oceans lies below -2000 meters. So if we lowered the ocean level by, say, 1000 meters we would have the majority of the land mass above 1000 meters. Is there a process, which "flattens" the earth, i.e. makes it so that the majority of the land mass is fairly close to ocean level?
|
[
"robotrebellion has the exactly correct answer, ",
".",
"The majority of the oceans have a low sea floor because oceanic crust is ~7 kilometers thick (roughly), pretty consistently. So it \"floats\" (note: not literally floating) on the mantle (mantle is almost all solid, not liquid) at the same height in most places. It is higher near mid-ocean ridges because it is hot and less dense (as the primary reason) and it is lower near subduction zones because it is colder and denser. The reason most of it is below 2000 feet just has to do with the amount of water on the planet.",
"Continental crust is thicker, and more varied in thickness. It is also less dense. So on a whole, continents are a much higher elevation than oceanic crust. Which is why there is such a large difference between the two.",
"Within a continent, you can have varying thicknesses of crust. However, most of this difference is accommodated with \"",
"mountain roots",
"\", rather than mountains extending up into the sky. If you add 5 kilometers of mountain onto the surface of the planet, it will sink somewhere in the ballpark of 4 kilometers down before reaching ",
"equilibrium through buoyancy",
". The point is that it is hard to elevate land much above the rest of the continent. It requires ",
" of matter to do so.",
"Now we get to erosion. The taller something this, the more susceptible it is to collapsing under its own weight. Furthermore, the more elevation something is at, the larger the erosional effects on it are. You get more slope for water to erode away (which is a huge player in erosion), you get a larger concentration of rain on the mountain front (which is why you get such massive monsoons against the Himalayas), and at high elevations you encounter ",
"glacial buzz-saws",
" that can absolutely shred mountains apart (on long time scales). Wind buzz-saws may also play a substantial role at high elevations, but I don't think there is a consensus on them yet.",
"There are other factors as well that limit mountain height. As I mentioned with mountain roots, most of the mountain is inside the planet. As it extends downward, it heats up and can be shredded apart from below, (one mechanism being ",
"eclogite delamination",
"). ",
"This paper",
" covers a number of these effects in the Andes. It has some math and modeling, but I think you can probably get some useful information from it even if you ignore all that.",
"If you took out enough water to lower ocean levels by 1000 meters, then elevations would increase by 1000 meters. You would start to erode the edges of the continents faster, since there is now more slope for erosion to act upon. The atmosphere would also drop by 1000 meters, so the snow line would drop 1000 meters, exposing more of the planet to the glacial buzz-saw effect. Ecologite delamination would ",
" increase its rate. So the results would be complicated, but on a whole they would increase erosion.",
"You would slowly start to erode back toward sea level. But 1000 meters of continent is a VAST amount of rock - you would not end up in a rough \"steady state\" like you see in the picture you posted anytime soon. Remember - the majority of mountains/land is inside the planet. As you erode the surface, the land will \"lift\" up to balance out the buoyancy (read up on my link about this if you find it confusing). ",
"As an analogy, drop an ice cube in a glass of water. Most of it will be below the surface, but some will be above the surface. If you hold a heat source to the top of the ice cube, you will \"erode\" away its surface. But you won't just erode away the top of the ice until it is all below the water level, right? Instead, as you erode, the ice cube will lift up. The same % of the ice cube will remain under water no matter how much you melt away.",
"The crust is similar, at least in the basic ways. So if you dropped sea level by 1000 meters, you would have to erode the 1000 meters ",
" an even larger amount of the root of the continents. As you erode the 1000 meters, the continents (or mountains) will lift up, creating more rock to erode. So in order to return to what you see in your image, where most of the continents are between 0 and 1000 meters, you'll have to erode somewhere around 5000 meters of rock ",
". As a side note, this is why eroding mountains can take a long time even with all the erosional forces I explained. In order to erode a 4 km mountain, you might have to actually erode something like 20 km of rock, since the mountain will continually lift up as you erode away the top of it.",
"This is still a simplification, but I hope if gives you a little bit of an idea about the underlying forces acting on your question. In short, it's complicated - there are entire courses on this subject (entire courses on ",
" of this subject). Let me know if you have any questions."
] |
[
"Could ",
"erosion",
" be such a process?"
] |
[
"You get more slope for water to erode away (which is a huge player in erosion), you get a larger concentration of rain on the mountain front (which is why you get such massive monsoons against the Himalayas), and at high elevations you encounter [3] glacial buzz-saws that can absolutely shred mountains apart (on long time scales). Wind b",
"I want to emphasize this part of your response. We can re-word the question from \"why is it so flat\" to \"why does it have shallow slopes\". And that helps us see the answer. Steep slopes, pointy things, erode faster. "
] |
[
"Does gravity work differently underground?"
] |
[
false
] | null |
[
"The ",
"shell theorem",
" is a useful starting point. For a homogeneous spherical body, gravitational acceleration decreases linearly as you approach the center and it would be zero at the center. The Earth is not a homogeneous body, specifically, its ",
"density varies as a function of depth",
" where the big jumps in density reflect major compositional differences between the crust, mantle, and core. Incorporating this variable density with the shell theorem, we can calculate what the ",
"gravitational acceleration would be as a function of depth",
" (the blue line labeled 'PREM' is the relevant curve here, the others are simpler versions). What you can see is that because of contrast in density between the crust, mantle, and core (i.e. the mantle denser is than the crust, and the core is denser than the mantle), gravitational acceleration actually (slightly) increases through the mantle. However, it's important to notice the scale here, and basically the gravitational acceleration is close to that of the surface (i.e. 9.8 m/s",
") for the upper 2000 km of the Earth so this is not an effect you would notice if you were in a mine shaft or something (or even at the bottom of deep wells given the deepest we've ever drilled is ",
"~12 km",
")."
] |
[
"Would the 100km above me create a gravitational field oposite to the \"main one\".?",
"The gravity from the surface layers above you is counteracted by the gravity of the surface layers on the other side of the planet.",
"Suppose you're 100 km down. You can conceptually split the planet into two parts. An outer shell that's spherical, 100 km thick everywhere, that you are inside (just touching the inside surface in one spot), and an inner sphere that you are standing on. Now the net gravitational force of that outer shell on you is ",
" as proven by the shell theorem. So you only need to worry about the parts of the Earth deeper than you are.",
"That's an approximation for a spherical non-rotating planet. In reality there will be slight adjustments because Earth is rotating, oblate, and has varying topography and geology."
] |
[
"But the linear decrease is not a bad approximation if you want a general idea and don't want to wrangle with pages and pages of detailed calculations, all with data uncertainties anyway.",
"I mean, you don’t ",
" to wrangle with all that. Given the helpful context that you’ve just provided then we could just look at a graph of ",
"free fall acceleration with distance from the Earth’s centre."
] |
[
"AskScience AMA Series: Emergency Medicine"
] |
[
false
] |
[deleted]
|
[
"Trauma doesn't make you feel that way I find.",
"If anything, it's actually some of the staff at times that can make you feel that way. Some of the things people do to each other, or themselves.",
"I've never felt that way, but some of my worst memories and times are when staff do things, or say things that are inappropriate, and seeing what one human can do to another, especially their own children.",
"At the end of that all though. There's a hurt person, a hurt child, or a person who hurt themselves, and they still need to be fixed, they still want the hurting to stop, especially if it's mental. No one commits suicide because they don't hurt inside, they do it because they can't think of any other way to make the hurt stop. We're all human, and everyone deserves medical care regardless of the cause of their injuries in my opinion.",
"My job is to make hurting stop. My duty is to make things better when people don't think they can get better. Not much else has ever mattered to me other than to make people feel better. If I can't fix it, if no one can, I do my best to make it easier, to make it hurt less. "
] |
[
"Just a reminder to all: ",
"medical advice"
] |
[
"That's a tough one...",
"Massive burn victims have lost a ton of fluid. The formula for fluid resuscitation in a burn victim means that a 90kg male with burns to 60% BSA will get 21.5L of fluid in the first 24 hours. This can easily double in certain circumstances as well.",
"In terms of sheer blood volume loss:\nI had a young lady with a ruptured ectopic pregnancy. Her Hgb was around 4.0 if I recall(12 is normal). Probably the lowest lab value I've seen for that off the top of my head. Typically when you get below 8, you need a rapid transfusion. I'm sure I've seen lower in some of our multi-traumas, but not one that survived off the top of my head. If I had to make a guess at the blood volume she'd lost, I'd be betting somewhere around 2L of blood. Blood loss is all relative to a persons size as well.",
"There's probably been lower that have lived, but I don't remember their exact values, she was recent is all."
] |
[
"Has there been a higher peak than Mt. Everest on Earth throughout its history?"
] |
[
false
] |
Im not thinking a higher mountain in total like the Mauna Kea, but rather from sea level upwards.
|
[
"This is one of the most asked questions in the Earth Sciences category on this sub, for example, here are a variety of answers to this question (or flavors of this question): ",
"1",
", ",
"2",
", ",
"3",
", ",
"4",
", ",
"5",
", ",
"6",
", ",
"7",
", ",
"8",
", ",
"9",
", ",
"10",
", ",
"11",
", ",
"12",
", ",
"13",
", ",
"14",
", ",
"15",
", and more that I got tired of linking.",
"In short (and without rehashing all of these answers or parsing out the spurious ones), there are a variety of mechanisms / properties that impose limits on the height of mountain ranges on average and the height of individual peaks within those ranges. These limits are not precise (despite what some comments in the various links above suggest) and depend a lot on the details, many of which are hard to estimate for extant mountain ranges let alone past mountain ranges. With that uncertainty in mind, we generally think that the Himalaya represent something near the limit of the absolute height mountain ranges can reach. In terms of quantitatively estimating the height of past mountain ranges, there are techniques that allow us to make rough estimates (e.g. ",
"paleoaltimetry",
", ",
"geothermobarometry",
", etc), but in general these would only tell us about the average elevation of a range (and with pretty large uncertainties again), not the height of individual peaks. Thus, ",
"."
] |
[
"Oh man, so here we go. The major factors that control mountain height are the planets gravitational field, and the strength of the material you are building with. It also has to do with how buoyant the crust is compared to the mantle. Imagine you're building a sand castle. If you want to make it higher, you use wet sand. That represents stronger material. Or you build it on the moon, so it doesnt collapse on itself. Lastly we have buoyancy. From measuring how fast continents float back up after glaciers melt we have a pretty good handle on this one. If you build a mountain too high, that crust gets too heavy, and you reach an equilibrium point where if you keep adding material it sinks at the same rate, and gets no taller. ",
"We do not think there has been any major change in gravity, the bulk composition of the crust or mantle since we have had continental crust. (Change in composition enough to dramaticaly alter its structural properties). ",
"On earth large mountains like this are formed by continental colisions, or orogenys. This is becuase we have plate tectonics. In addition, it means that the plates move too fast over mantle plumes to allow a massive mountain to form over them. This is why we see Hawaii and not Olympus mons. A massive supervolcano, say from a new mantle plume head coming up is so large that it does not form a mountain, but what's called a large igneous province (LIP). Basicaly a massive ass lava flow which covers a significant chunk of a continent and likely causes a mass extinction. See deccan traps and Siberian traps. ",
"TLDR for the last 3 billion years or so which we have had plate tectonics and continental crust, no processes would cause the variables to change."
] |
[
"A related question then: Do we have any reason to believe that these factors that limit the height of mountain ranges (and peaks) have differed throughout the Earths history?",
"As a corollary, is there something that could change (or is changing currently) to change these factors in the future?",
"Finally are the factors that lead to catastrophic geological events and the events themselves something that could change this (i.e. the creation and eruption of a supervolcano)?"
] |
[
"Why can't we treat viral infections using blood transfusions?"
] |
[
false
] | null |
[
"Short answer: ",
"we can",
". ",
"Long answer: we can transfuse blood plasma containing antibodies against a virus into an infected individual and it well help them fight off the infection, however they still need to produce their own antibodies and B cells specific to the virus to overcome the infection completely and be immune to infection later. Antibodies alone don't provoke the kind of large-scale and lasting immune response required to completely eliminate a viral infection. "
] |
[
"Thank you for the information, that's very interesting!"
] |
[
"Viruses rarely infect just the bloodstream. There are indeed viruses that infect red blood cells such as the parvovirus however once the virus finds its infection site like the neurones for herpes virus it's quite pointless to do a blood transfusion because it won't really affect the virus that much. We can put antibodies but then our immune system won't develop a memory and so you may get reinfected again."
] |
[
"If all life on Earth has one common ancestor, then why don't humans (and other life) share some of the best evolved characteristics?"
] |
[
false
] |
[deleted]
|
[
"But with characteristics like photosynthesis out there, why did natural selection/evolution choose to leave that out?",
"It didn't. We evolved to eat plants. Photosynthesis needs a lot of surface area to work and we can't carry enough plant material around with us to keep us alive."
] |
[
"Some traits evolve after a split with a last common ancestor. For instance, humans and plants share a eukaryotic single celled ancestor that was not photosynthetic. Only after both linages split did the plant lineage develop photosynthetic abilities. So that humans, and all of our ancestors were never photosynthetic. Thus for humans or even other animals to be photosynthetic it must arise independently, that greatly reduces the odds of this happening. There is also a cost and benefit to each trait, and a species must balance out these traits. Moreover the only way to get a trait (like being photosynthetic) is if you have a random mutation for such a trait. Natural selection can only act on what is already present in an individual it cannot work on traits that do not exist. That being said corals (which are animals) have taken up photosynthetic algae (plants) in a symbiotic relationship. The algae provide nourishment to the coral and the coral provide the algae a place to live.",
"As to why we don't have 4 eyes or 10 eyes ... well as with most other traits \"if it ain't broke, don't fix it\" tends to apply. Two eyes works just fine and so two eyes sticks. No need to improve on what does not need improving. ",
"You seem to have good basic understanding of evolution that being said evolution has no goals, no direction. No one species is better then another. Finally other species are not trying to be more \"human\" or \"more plant like\" or \"spider like\". "
] |
[
"Also, evolution does not neccessarily imply continued improvement."
] |
[
"Is a person standing at sea level on the Equator traveling about the Earth's axis faster than a person standing at sea level at the 49th Parallel? If so, approximately how much faster are they traveling?"
] |
[
false
] | null |
[
"When we speak of circular motion it is important to remember that there are two type of velocity we can speak of. The first is angular velocity, so how quickly a body moves around that circle. Because both people in your example are fixed on a rotating body, their angular velocity will be identical because they pass through the same number of degrees of the circle in the same amount of time. The second velocity we can talk about is tangential velocity. That is, how fast a body is moving tangentially to its orbit. In your example, while both people have the same angular velocity, the person at the equator is moving through a much larger distance and is thus moving much faster, in that regard.\nEdit: Corrected the word angular velocity."
] |
[
"Yep. Assuming the earth is about spherical you just have to look at the difference in the circumferences of the two circles traced out by their paths. The radius of the earth R is 6400km, and the radius of the circle around the 49th parallel r is 6400km*cos(49 degrees) = 6400km * .66 = 4200km. ",
"So, the circumference of the equator circle is C = 2piR = 40,200 km, and the circumference of the 49th parallel circle is c = 2pir = 26,400 km. \nIt takes about 1 day (86400 seconds) to go around either circle, so the person at the equator is travelling C/86400s = .465km/s = 1040mph, and the person at the 49th parallel is travelling c/86400s = .306km/s = 685mph. ",
"So the person is travelling about 400mph faster."
] |
[
"I've always heard 'radial velocity' used to mean the component of velocity pointed away from the origin. Maybe this is a difference of disciplines but \"angular velocity\" is more commonly used in physics and astronomy."
] |
[
"What is the difference between EMSA and DNase I footprinting?"
] |
[
false
] | null |
[
"Holy shit! A question that's right in my wheel-house! Wall of text incoming! ",
"TLDR: They're useful in different scenarios, so pick your poison. ",
"EMSAs (electrophoretic mobility shift assays) and footprinting do kind of measure the same thing. They both let you observe interactions between protein and DNA (or RNA). ",
"There's a trade-off though: EMSAs are conceptually simple -- you just mix your protein and DNA and run it on a gel, and if your protein binds to DNA, you'll see that as your DNA progressing more slowly through the gel -- but they're not very informative. They don't tell you where precisely on a given DNA molecule your protein binds or how many proteins bind at a time. Furthermore, EMSAs can be a technically challenging, since for a successful experiment, they rely on the protein-DNA complex having a certain threshold stability. If your complex is prone to falling apart or is transient in any way, it won't be able to migrate through the gel intact, and you either won't observe binding at all, or you'll see a smear. ",
"Footprinting, on the other hand, is extremely informative. It can tell you at a resolution of single nucleotides, where exactly your protein's binding site is and what the sequence is (if you run a sequencing ladder with it, often done with Sanger or Maxam-Gilbert sequencing). It can also tell you if there are multiple binding events. Additionally, it can give you some information on what effects the protein is having on DNA secondary structure, which can manifest as increases in cleavage in regions outside of the footprint itself (",
"here's",
" an example of a footprint I did a while back to illustrate what I mean. Reading from left to right, you'll see a protection in region B, which is where the protein binds. In region A, you'll see an enhancement, a band actually getting stronger, which indicates that the protein is modulating secondary structure outside the binding site itself. On the far right side you can also see a Maxam-Gilbert sequencing ladder that I cropped a lot, since this hasn't been published yet.). ",
"In addition, footprints avoid the issue of weak protein-DNA complexes that plague EMSAs. This is because in a footprint, you observe the interaction between the two by how it affects DNase I cleavage patterns, not how well your DNA migrates through a gel. In a footprint all that you're running is cut up fragments of DNA -- your protein and DNase have been removed and aren't affecting anything. ",
"The problem with footprinting is that it's among the more technically challenging biochemical techniques out there, much more so than EMSAs. There are many variables that need to be considered, the most important being how much/how long to digest your DNA -- in many cases there's only one precise set of conditions that actually gets you a visible footprint. This actually requires a bit of physical dexterity, since you need to be able to consistently and reproduceably cleave all of your samples. If, say, you do an experiment that requires 2 minutes of cleavage, and you sneeze and accidentally cleave for 2 minutes and 5 seconds, your experiment is kaput. Footprints are sought after because of how informative they are, but years, decades even, can go by where a protein and a DNA sequence are known to interact without a successful footprint. The picture I showed you above is the first of that particular interaction, which was first described almost 20 years ago. ",
"The long and the short of it is you pick the method that gives you the information that you need. Do you just need to know if protein X interacts with DNA sequence Y? Or maybe you want to get some kinetic data? I would go with an EMSA. Do you need the precise binding site? Go with a footprint. ",
"Source: Molecular Cloning, Structure and Mechanism in Protein Science, and a hard, bitter, PhD. "
] |
[
"Thanks so much! I'm taking a course in cell bio and this really helped to clarify the differences between the two techniques. "
] |
[
"Of course! Let me know if you have any more questions or if something I said was unclear. "
] |
[
"Does every object exert gravity on all other objects within the (visible) universe?"
] |
[
false
] | null |
[
"Yes, anything with mass exerts a gravitational pull, the more mass, the more gravity."
] |
[
"This is a very common question, so I've decided to add it to our AskScienceFAQs:",
"http://www.reddit.com/r/sciencefaqs/comments/135cd1/does_gravity_stretch_forever_is_the_big_bang_like/"
] |
[
"Mass is not necessary."
] |
[
"Are covalent bonds always technically polar when two different non-metal elements covalently bond?"
] |
[
false
] |
I had a clash with my AP Bio teacher. Her test question was "A covalent polar bond is most likely when..." And the choices were: A: when one atom is more electronegative than the other, B: (Incorrect answer) C: (Incorrect answer) D: When there is a bond between two different nonmetal elements. According to Barron's review for AP bio, a polar covalent bond is always the case when two different non metal elements are covalently bonded because they all have different electronegativities. They said "at any case." I asked my teacher about this issue, because based on my understanding, both A and D are correct, but I had to choose one. Barron's never failed me before so I chose D. Aren't both answers technically correct? She told me that Barron's is wrong and that if the difference in electronegativities is small enough, the bond is considered to be nonpolar. Is she right? Or is she making assumptions? I think that Barron's is more detailed and accurate but that's why I'm asking. Did I choose the wrong answer?
|
[
"Technically both are correct, but D is the better of the two choices. Ultimately this questions comes down to how you define your terms, which is one of the problems with Chemistry. ",
"Before going on, I need to mention that I love Chemistry and I believe it to be one of the most important subjects, but Chemistry has its problems just like any other subject.",
"This problem that relates to Chemistry is almost entirely an empirical science. As a result, chemical laws are empirical laws, and thus have many exceptions. Also, terms are empirical in nature and have many \"exceptions\" where they imply something that isn't true. For example, we call any increase in oxidation number oxidation, even though many of these reactions don't involve oxygen.",
"The problem that relates to your problem is the definition of a bond. The best definition of a bond is the forces that push a group of particles into the arrangement with the potential energy of the arrangement at a local minima. In basic chemistry, this translates to atoms either sharing or stealing electrons. We say that when the difference of electronegativity is low, it is nonpolar. When medium its polar. When its great its ionic. Actually, once you get past basic chemistry, you will learn that some pairs of atoms with a difference in electronegativy will be polar while another pair of atoms with a higher difference in electronegativity wont be. The problem is that polar and non polar are very ill defined, ion is slightly better defined in circumstances where the cations and anions are separated, but there are some circumstances where ionic bonds are as ill defined.",
"Is this answer going into too much depth? Yes",
"The important thing to know is that you are in a high school, ap class. As a result, you aren't learning a subject but learning a test. Most of what you learn is incredibly ill defined and is just defined well enough to get the 5."
] |
[
"D is technically correct, but incorrect nonetheless. ",
"Since the answer states two different elements that are non-metals will have a covalent polar bond, it takes into account that these elements are (1) dissimilar, and (2) non-metallic, resulting in a polar covalent bond between them. However, not all polar covalent bonds are considered to be \"polar\". There is a certain range of polarity between bonds, and that range depends on the electronegativity difference. If the electronegativity difference is small (>0.4), the bond is considered to be \"non-polar\".",
"A is correct. "
] |
[
"In all honesty, A is not really correct since it hasn't specified which atoms. As an example Chlorine is more electronegative than Sodium, NaCL, while very polar, is not covalent. If they had spent the time to simply specifying organic molecules this question would be a lot more clear.",
"Question is silly."
] |
[
"Is gravity a constant?"
] |
[
false
] |
Like at what point do we achieve weightlessness in space, is there an exact point? Also how is gravity strong enough to keep the moon in orbit, but weak enough to allow me to walk around?
|
[
"1) Weightlessness is when you fall at the exact rate as your surroundings. You can achieve weightlessness at any height, assuming you had somewhere to fall. If you're standing on a scale in a falling elevator, the scale would read zero.",
"2) The simple answer is just because the moon is more massive than you are. There's more to consider, but it's a bit complex to describe without equations."
] |
[
"I'm going to approach this with Newtonian gravity. There's a much more complete theory developed by Einstein that I imagine others might reference here called General Relativity. But Newton is close enough to the truth to answer these questions.",
"So let's go with weightlessness first. Suppose you're in a space shuttle that's orbiting the earth. Well the fact that you're orbiting means that you still have gravity \"pulling\" on you if you will. The shuttle is falling toward earth, and you're falling with the shuttle at the same rate. So you don't notice any acceleration relative to the shuttle. Much like weightless amusement park rides, or partial weighlessness in an elevator. ",
" the shuttle is also moving ",
" in addition to falling. And it's moving so ",
" forward (and you with it) that as it falls it keeps \"missing\" the ground. So it's in continuous free-fall, and you appear to float as if there were no gravity at all. ",
"As for your second question.. can you jump as high as the moon? I mean the moon's pretty far away. Gravity does do a pretty good job of keeping you \"stuck\" to the earth. The moon is larger, but it feels a greater force, so it feels the same acceleration towards earth that you would feel if you were that far away. The force between two massive bodies is F=GMm/r",
" where M and m are the masses of the two bodies, G is the gravitational constant and r is the distance between the centers of the two. And we know that F=ma, so ma=GMm/r",
" , the m's cancel and we get a=GM/r",
" . The acceleration from gravity is only a function of the \"attracting\" mass and the distance you are away from it."
] |
[
"And the moon is traveling at over ",
"1 km/s",
". You're traveling at 0km/s, and for comparison, a car at 60mph is traveling at 0.0268 km/s. If you were traveling at 1km/s at that distance from the Earth, you'd miss the ground too.",
"Simplified: imagine a system of just the Earth and the Moon. Think of the Earth as a point, the Moon's orbit as a perfect circle around the Earth, and the Moon as a point at 3 o'clock traveling counterclockwise. The ",
" of the Moon is 1km/s straight up (not curved!). The Earth's gravity is what causes the circular path. If the Earth were to magically disappear completely, the moon would fly off in a straight line at 1km/s.",
"This is the same reason why space shuttles don't go straight up. They need a big enough horizontal component of their velocity to achieve orbit. If they went straight up, they'd come straight back down.",
"It's just a question of going fast enough in the right direction such that gravity keeps you in orbit but can't pull you to the ground."
] |
[
"If hydrogen and carbon are in abundance, why can't scientists 'manufacture' hydrocarbons?"
] |
[
false
] |
An increased supply would stabilise crude prices, which is good for producer and consumer — and with volume would become cheaper than traditional extraction. Is it at all possible?
|
[
"They can. It takes energy. We get most of our energy from burning the very things you want to make. Burning oil to make less oil is necessarily wasteful and more expensive than just using it directly. However, if we used another source like solar energy, this would be a way of getting \"fossil\" fuels without mining them. Then you have to ask if there is a point to that, if we already have enough solar production to make it feasible. I would say yes, because hydrocarbon fuels are a good way to store energy (for now; it would be better to use a cleaner alternative)."
] |
[
"Let's review for a minute here. A natural hydrocarbon is the result of sunlight which once shined on a prehistoric plant. The plant used the sunlight to split H2O and CO2, producing H and C which it turned into sugars. The sugars contained only 1-2% of the original energy in the sunlight. Eventually this plant happened to be buried, and over millions of years of heat and pressure its sugars decayed into simpler molecules: hydrocarbons. ",
"Now, scientists can replicate this. But note the 2% efficiency! The energy to split the H2O and CO2 has to come from somewhere, and it has to be more than the energy in the final fuel. Scientists might be able to be more efficient than plants, even perhaps 10 times more efficient with enough research, but this would still only be 20%. They will be buying a lot of energy to make a small amount of hydrocarbon fuel. ",
"Let's look at the economics of this ideal, 20%-efficient process. 1 gallon of gasoline has an energy content of 33 kilowatt-hours (kWh). A kWh is the unit we buy electricity in; it costs around 7 cents. With 20% efficiency, we need 100%/20%, ie 5, times more electrical energy: 33 kWh * 5 = 165 kWh. 165 * 7 cents = $11.55/gallon of gasoline. At the pump, you would be paying that plus tax, shipping, and profit. That's not going to be cheaper than traditional extraction for a long time. "
] |
[
"Plus there's all sorts of other uses for hydrocarbons than fuel. Plastics are pretty nice to have."
] |
[
"Why can't we remember smells as well as sights?"
] |
[
false
] | null |
[
"At a technical level, we dont understand the brain at that level of detail yet.",
"However, a lot of this is a more evolutionary question than one about the underlying mechanisms. Think of asking 'why can dogs swivel their ears but humans cannot'. Mechanically, thats because we dont have the muscles, but really, its because in our evolutionary history it wasnt important for us, so those abilities were not developed.",
"So it's likely the case that it is not that our brains couldnt be organized to be able to recall smells from scratch better, just that such ability was not selected for, and as such, the necesary brain organization for that did not evolve for us. On other hand, once you do smell something, you can certainly recall a whole lot of associated memories, including smells, so it is not that smells arent hooked into our memory system well, just that the 'simulation' part of evoking smells doesnt seem to be as strongly selected for as the 'simulation' part for visual memories.",
"Interestingly enough, we as humans can't tell how exactly other animals experience memory and perception. So it is possible that there are other animals that can vividly bring up at will, smells of things they have experienced in the past, much better than humans can."
] |
[
"You don't remember sights that well either, your brain just convinces you that you do. You can go back to something that looks unrecognizably different from when you saw it last, your brain matches the general pattern and overwrites the non-matching characteristics in your (deteriorated) memory of how it looked, and then tells you: oh yeah buddy -- exactly as you remembered it.",
"Disclaimer: Some individuals actually do have a remarkable ability to remember visual details. They are able to remember images as well as everyone else ",
" they are able to remember images."
] |
[
"IIRC my neuroanatomy, the olfactory system (which processes the sense of smell) has pretty close connections to the hippocampus which codes for long term memory processing.",
"Smell is actually very powerful at eliciting memories and emotions."
] |
[
"Is it possible to make \"chords\" of visible light?"
] |
[
false
] |
In music, a major chord is formed by simultaneously playing a note, a second note at 5/4 the frequency of he first, and a third note at 3/2 the frequency of the first. Are there any special properties, or appealing aesthetics, of combinations of light waves that differ by simple fractions in this way?
|
[
"No, it isn't.",
"The ear and eye are very different beasts, the ear can pick up both pitch and intensity of sound. The ability to hear the sound at any pitch allows us to appreciate the harmonics.",
"The eye can only detect intensity. The reason we can see different colours is because we have 3 different colours of cone cell in our retina, and the combination of the intensities of the 3 lets our brains figure out what the colour we're seeing is. It's kind of like the brain is getting a digital reading of the colours we see, instead of an analogue reading, so we couldn't get the same subtleties our ear gets."
] |
[
"While the following tidbit might not be exactly what you're talking about, consider the color magenta. Magenta is known as an extra spectral color in that there is no single frequency of light that would produce such a color to one's retina. Rather to make magenta, multiple colors must be combined."
] |
[
"The human eye can't perceive the exact nature of the spectrum, since it relies on just 3 cone cells. It can only see the \"average\" color. Two colors that additively create yellow (red and green, as in LCD subpixels) look like yellow, even though no actual yellow light is present. Also, unlike the human ear, our eyes can't even even cover one octave of EM frequencies (",
"430–790 THz",
" so there's definitely not as much range to work with. But consider color combinations, which have clear mathematical definitions. Complimentary colors (and other combinations) could certainly be seen as chords, though I don't know if they correspond to simple fractions as musical chords do."
] |
[
"Photon beam through an absolute zero crystal prism. What happens?"
] |
[
false
] |
Would the absolute zero temperature cause any weird effects? Such as slowing down the beam, messing with the visible spectrum, etc.
|
[
"The prism is a crystal lattice of atoms. ",
"Since it is at absolute zero, ignoring quantum mechanical subtleties meaning that this is impossible (absolute zero would mean exactly known momentum AND position, violating the Heisenberg uncertainty principle), the atoms are standing very, very still. Temperature essentially means the kinetic energy of the atoms - at room temperature, they are jiggling around a whole bunch.",
"I don't know a lot about optics really, but I would expect that since the crystal lattice is more or less stationary, with no pesky ",
"phonons",
" shaking around the atoms and therefore the electric potential (which is what the photons interact with). you will have a more \"clean\" system than if it was at room temperature. So if you normally saw some absorption peak around a certain wavelength, or some scattering subject to a ",
"Gaussian distribution",
" for example, I would think that the peak would be narrower. But I don't think anything \"strange\" would happen just because it was very cold."
] |
[
"Well, remember, absolute zero isn't a thing you can reach, it's a limit. Like light speed. You can get as close to light speed as you like, but never reach it. Same with absolute zero.",
"I'm sure that somebody with experience in optics might be able to come along and tell you about light NEAR absolute zero (if there's even anything to tell, I don't know), but until then you can read about laser cooling on Wikipedia, a technique that uses light to being objects down to near zerp. It has even been used to bring a 1 gram coin-sized mirror down to 0.8 kelvins! ",
"I'd link, but I'm on mobile."
] |
[
"Often, the temperature T goes into an expression that looks like exp(-ΔE/kT) with k being the Boltzmann constant. If you happen to be interested in some kind of physical process that has ΔE comparable to kT you will be sensitive to even these incredibly tiny changes in temperature."
] |
[
"Does a container with a perfect vacuum in it float?"
] |
[
false
] | null |
[
"It would if the container weighed less than the volume of air it has displaced. Lets assume we have a 1 meter cube of pure vacuum, this would displace just over 1kg of air, and hence, if the container itself weighed slightly less 1kg, it would float.",
"However, at sea level, air pressure is about 100000 pascals, or 100000 Newtons/m",
" . So each wall of our cube would be experiencing 100000 Newtons of force on it, trying to crush it inways, equivalent to 10 tonnes, 2 times the bite force of a T. Rex or the thrust of an F22 Raptor.",
"So if you can make something that weighs 1kg, and can withstand 10-60 tonnes of weight, you've got yourself a floating vacuum.",
"FYI, for these calculations it makes essentially no difference if we're talking absolute vacuum, or a practical, 99% vacuum."
] |
[
"The first lighter-than-air crafts ever designed were ",
"vacuum airships",
". Nearly a century before the first hot air balloon flew."
] |
[
"However none were actually successfully made. The application was just theorized."
] |
[
"If the international space station was not orbiting earth and just stood still as if it were held up on a pole or something - so it wouldn’t crash to earth, what amount of gravity would the occupants feel?"
] |
[
false
] |
I’m wondering about how much the gravity decreases at the height of the ISS.
|
[
"About ",
"88% as they do at sea level",
". The ISS orbits the Earth ~400km above the surface, which sounds high, but the law of universal gravitation uses the distances between centers of mass- so for something orbiting the Earth, it's from the center of the Earth, which is ~6000km. So, for something being ~6400km vs ~6000km, there's just not a big difference."
] |
[
"That's an interesting question, as the OP asks about being stationary relative to the surface, not non-rotating relative to the COM, which would include some angular effects.",
"The centripetal acceleration (a) is:",
"a = r ω",
" ,",
"where r is the radius and ω is the angular speed in radians/unit time. Given:",
"r = 6.771x10",
" m (assuming the stick holding up the ISS is at or near the equator)",
"ω = 2π/(24x60x60) rad/s",
"we find",
"a = ~3.6 cm/s",
"from angular motion, versus",
"a_grav = ~860 cm/s",
"from gravity. The effect of the ISS-on-a-stick rotating with the earth is therefore less than half a percent of the effect of gravity.",
"This should come as little surprise, as the effects of rotation on a person standing at the equator is ~0.3% at most, and the ISS in the OP is only a few hundred km above that compared to the radius of the earth being several thousand km (and also making one revolution every 24 hours).",
"Similarly, geosynchronous orbit, where the angular and gravitational effects are equal for one orbit every 24 hours is almost 36,000 km from the surface of the earth, where the gravitational effects are much lessened, and the angular effects much increased."
] |
[
"What about \"centrifugal\"? forces?"
] |
[
"How do stereograms work?"
] |
[
false
] |
How do the optical illusions stereograms work? I understand it has something to do with the layering of 2-dimensional images, but could someone explain it further? Here are some examples.
|
[
"When you see something (e.g. a tree, a car, a tornado), you're actually seeing two images at the same time, one from your left eye and one from your right eye. Your brain interprets these images and comes up with a perception of the world with depth. ",
"A stereogram exploits this idea by showing your right eye one image while showing your left eye an image nearly identical, but different enough that your brain is tricked into thinking it has a different depth. Usually, you'd be focusing on one specific point on the image, but crossing your eyes gives each eye a specific image to look at."
] |
[
"Ok, I understand that but you don't have to cross your eyes to see it do you? My friend said that he was seeing it and his eyes were not visibly crossed."
] |
[
"Certain stereograms -not sure if any of the ones you've posted apply- can be seen both by converging the eyes (i.e. crossing your eyes) and by diverging your eyes (i.e. pretending to focus on an object far in the distance). Should one be this way, diverged eyes should appear normal. Nevertheless, most stereoscopic images that do require the converging of the eyes don't need you to cross your eyes excessively. It's possible that it's far too little to notice."
] |
[
"How would you escape an autoclave?"
] |
[
false
] |
I recently started working at a lab where there are a few autoclaves, approximately 4 feet tall, 3 feet wide, and 6 feet deep. Definitely large enough to fit a person. What would you do if you were trapped inside? There doesn't seem to be any emergency escape button/cord on the inside to prevent this situation. How long would you have until you passed out/died from the pressure/heat? Has anybody else thought about this? Edit: Thanks for all the advice and stories! Very helpful
|
[
"This doesn't help you at all, but I work at a hospital and inside the morgue there is a big yellow sticker by the door that says ",
"YOU ARE NOT LOCKED IN!\nTURN KNOB REPEATEDLY TO ESCAPE"
] |
[
"Ever considered cooking with it? I imagine it'd work like a slow cooker....\nTake a bone to the lab... throw it in the autoclave... add some broth, a potato. Baby, you got a stew goin'!"
] |
[
"In college, we made lemon pepper chicken in an autoclave once. It was delicious and fell right off the bone. Maybe almost too tender."
] |
[
"Regarding the Demon Core?"
] |
[
false
] | null |
[
"Is it that neutrons are blocked by it because they're so big? But electrons (the ionizing radiation) is small enough to pass through?"
] |
[
"It doesn't reflect ",
" of them. Many of them still escape."
] |
[
"So when the core is going critical it's producing so many neutrons at an exponentially increasing rate and THOSE are the radiation?"
] |
[
"Would a rigid container whose contents were a vacuum such that the weight of the container was less than the weight of the volume of the air it displaced, would it float?"
] |
[
false
] |
[deleted]
|
[
"Yes and the idea has been around since 1670. The problem is finding a material strong enough and light enough.",
"See ",
"http://en.wikipedia.org/wiki/Vacuum_airship",
" for more info."
] |
[
"Of course it would float, why wouldnt it? This is assuming you could build a material strong enough to support a vacuum that was light enough not to overpower the buoyancy from having a vacuum in the first place."
] |
[
"Yes. In fact, a vacuum is technically the most buoyant thing you could fill a container with, though as others have mentioned, a container strong enough to withstand the outside air pressure without being crushed while still being lighter than the displaced air would be hard to find."
] |
[
"Does the parents fitness at the time of conception affect the metabolism of the child?"
] |
[
false
] |
[deleted]
|
[
"There is growing evidence that supports Lamarckian methods of inheritence. For a really thorough analysis check out the ENCODE project and literature involved in epigenetic inheritance. ",
"This is the best example I could think of"
] |
[
"Yes, it can have a large effect (and it's actually the area of my research!) For example, children born to mothers after developing overt diabetes are around 10x more likely to develop diabetes in later life, compared to children born prior to maternal diabetes. (",
"link",
")",
"Similarly, children born after mothers underwent extreme weightloss have reduced later-life BMI compared to children born before maternal weightloss.",
"Animal studies have demonstrated widespread physiological changes in offspring born to mothers on a high-calorie diet or obese during pregnancy, including reduced ability to oxidise fats in the liver, reduced activity and increased feeding, and increased susceptibility to heart disease. (",
"link",
")",
"There is also some evidence for paternal affects, mediated via epigenetic changes in sperm, affecting offspring. For example, in mice, high-fat fed fathers produce offspring predisposed to reduced pancreatic function, and thus risk of diabetes in later life (",
"link",
")",
"All in all, many experts believe that these epigenetic changes during early development are contributing to a vicious cycle of obesity, with offspring born to obese parents being physiologically \"primed\" towards obesity and thus being at greater risk of having offspring similarly affected.",
"Review"
] |
[
"This isn't the whole story but ",
"Gestational Diabetes",
" can be caused by a high sugar diet. There are many other drugs that have effects but I think they are less related to your 'fitness' parameter; such as alcohol and the wrong isomer of thalidomide."
] |
[
"How are the floaters I see in my eye in focus?"
] |
[
false
] |
People have asked about floaters on here before, but what I'm wondering about is how I can see them so clearly. If I hold a book a few inches from my face the text is too close to focus on, but floaters are in my eye, yet appear to be fairly in focus. How can that be?
|
[
"The closer they are to your retina, the sharper their shadow, and the more in-focus they will appear to be."
] |
[
"Hmm interesting. Am I seeing them upside down? So an L shape floater to me might look like a 7 to someone looking in if they could see it?\nThanks!"
] |
[
"No and yes. You see them \"correctly\" but an observer outside the eye would see the floater upside down because they see the image which is reversed. Surely you know that the brain again reverses the images, so it is a bit confusing to discuss what is upside down and what is correct."
] |
[
"On the link between \"information content\" and DNA"
] |
[
false
] |
I've been trying to do some research recently on DNA. I am involved in a long-term, email debate but it is very civil. We both agreed we'd use this as a method to increase our own knowledge of the subject. He seems to be arguing from Dembski's Specific complexity, stating that since DNA contains information (sent between DNA and received by the proteome) that there must be an intelligence behind it (paraphrased). I am in disagreement with this but am having trouble wrapping my head around the concept of information in DNA. AskSci hasn't been my first go-to. I have found a number of videos detailing how the genetic code arose and how evolution can increase the information within an existing genome. That said, I cannot find (or wrap my head around what I have found) a relatively easy to understand explanation on how DNA came to contain "information". I disagree with this definition of information, but still have no satisfying answer. I've searched high and low but thought AckSci would be a beneficial place to turn to. Anything way you guys can help would be greatly appreciated! EDIT: Clarification
|
[
"Dembski, as in William Dembski? The \"Creation Scientist\"? The one who is using the field(s) of computer science, search algorithms and neural networks to \"disprove\" evolution via \"No Free Lunch\"?",
"/r/AskScience",
" is not supposed to be a go-to place for people having arguments, nor as your magical solution to arguments with Creationists. ",
". You won't be able to change this persons mind. They'll come up with a new idea, or new reason. This is how conspiracy theories work, too.",
"Give up and save yourself the sanity."
] |
[
"He seems to be arguing from Dembski's Specific complexity, stating that since DNA contains information (sent between DNA and received by the proteome) that there must be an intelligence behind it (paraphrased).",
"This is a combination of begging the question and a non sequitur. Call him on it. It's a logical fallacy, and although using it does not prove him wrong, it does invalidate this specific strategy. ",
"If he doesn't back down, you may want to just walk away slowly. That would be my advice. But if you don't, this assumption is what you need to attack; that if there is information in it it must have an intelligence behind it.",
"You need to get him to attack it himself through questioning. This is NOT attacking it yourself. Do not argue with his responses beyond pressing for an actual and clear answer.",
"1) What do you mean by \"intelligence\"? What do you mean by \"information\"? ",
"2) How does he know that statement to be true? ",
"3) What predictions would it make if it were true?",
"4) What would be different if it were not true? ",
"Another tactic would be counterexamples, but these are unlikely to work for the reasons I'll list below.",
"These would include:",
"1) Tidelines. The ocean is not intelligent, nor is the beach, but the location of the seaweed line at the beach tells you how high the last high tide was.",
"2) Tree rings. Trees are not intelligent, but they record information in their rings.",
"3) Weather conditions. The current wind, humidity, temperature, etc are bits of information that can be used to predict future weather. But the air is not intelligent.",
"The problem is, that he is (very likely) starting from the assumption that there is an intelligence behind everything, so any example you give he will use as further proof of that intelligence.",
"There isn't much you can say to this, he's left the realm of science. You can't prove him wrong because the existence of God is nonfalsifiable. Completely nonscientific."
] |
[
"Everything contains information, pretty much by definition. How else could you identify anything? Information is any characteristic of an object, such as it's weight, color, size, chemical composition, behavior, etc. ad infinitum. DNA contains plenty of information, but other than the rather important nature of that information, at least as far as we are concerned, it is no more special than any other identifiable matter."
] |
[
"What would happen if you tried to light a match in pressurized oxygen?"
] |
[
false
] |
If you have a chamber of pure O2 ie: a hyperbaric oxygen chamber is it possible to light a match in that environment or would the atmospheric pressure be to much?
|
[
"Because of the abundance of O2 in the environment around the match, the entire match would burn extremely rapidly, in fact it may burn so rapidly as to essentially be an explosion."
] |
[
"Many lab demos show that if you take a burning item and submerge it in liquid oxygen, it will burn VERY aggressively.",
"In fact, here's a demo of ",
"a hot diamond dropped into liquid O2 will burn away",
"The liquid oxygen is at room temp so it's boiling and very very very cold.",
"I believe the experiment involves the Leidenfrost Effect where the evaporated oxygen gas helps keep the generated heat in.",
"I'm not sure you could strike a submerged match at this temp and get ignition.",
"However, that was at standard pressure, so the boiling oxygen was very very very cold. AFAIK oxygen can be a liquid at room temp if the pressure's high enough, but the pressure needed is so high it's not as practical as keeping it cold.",
"If the temp wasn't so low, the reaction would be easier to start."
] |
[
"Would the increased pressure have any effect as to how quickly the match would burn? "
] |
[
"[Engineering] Would building a house in a glass box keep the house warmer in the winter and cooler in the summer?"
] |
[
false
] |
If you had a giant glass box, and then built a single-story 2 bedroom house inside of the glass box would the house stay warmer in winter? In summer, would the house stay cooler? Would the air act as an insulator? Thanks!
|
[
"I think there are two different things that you need to think about. First, having the house-in-a-box (and some air between the two) would help the house keep a more stable temperature versus the outside world. This isn't to say that the house will be intrinsically warmer or cooler, but rather that its temperature will change more slowly in response to the outside temperature with the box present. ",
"Secondly, though, you've created a giant greenhouse. When the sun hits the glass box, regardless of season, it is going to get quite toasty inside."
] |
[
"Could you make the box tall, and in the summer open the top so the chimney effect keeps the house cool, and then close the box in the summer to keep it warm?"
] |
[
"If one assumes that the house has a heater then it would be warmer in the summer and colder in the winter. Warmer in summer because more of the suns light would get in and heat air that could then not escape. Colder in winter because glass is not nearly as good a thermal insulator as the stuff typically used in house construction. Thus any heat you generate would be lost much more efficiently (which isn't a good thing in this case). WITHOUT a heater it would likely not make much a difference in winter, you'd just be as cold as whatever the temperature is outside, glass or otherwise.",
"In other words, in winter the sun isn't doing a good enough job to warm your house, which is why you need a heater. A bit more sun isn't going to compensate for that. But glass is not an ideal material for keeping that heat you generate in your furnace."
] |
[
"Are there planets with mountains so high they extend past the atmosphere so you could literally climb your way into zero gravity looking over the curvature of the entire planet?"
] |
[
false
] |
Just a cool thing to imagine
|
[
"Atmosphere and gravity are two different things!",
"In terms of atmosphere, there isn't a hard cut-off where the gas just disappears - it slowly gets less and less dense as you go up. The International Space Station actually feels drag from the atmosphere and has to boost itself a little bit every now and again, or else it will slowly drift down and eventually crash into Earth.",
"But you can have a mountain so big that the atmosphere at the top is much much less dense than the atmosphere at the bottom. On Mars, the huge Olympus Mons is big enough that the atmosphere at the top is 1/20th of the pressure of the atmosphere on the surface. By comparison, the atmosphere on Mt Everest is about 1/3rd of the pressure of the sea level atmosphere on Earth. So if you climbed to the top of Olympus Mons, you are kinda getting close to being in a vacuum - although the atmosphere of Mars is pretty thin to start with.",
"Gravity is quite different though. The atmosphere is typically a thin layer on the surface, but gravity extends forever, just getting weaker with distance. Satellites stay up not because they are \"outside\" of Earth's gravity, but because they're going fast enough to counter the Earth's gravity. You wouldn't expect mountains to form so large that their peaks are moving so fast that they're escaping a planet's gravity, because planets ",
" by gravity, and the top of the mountain wouldn't really be attached very well. This mountain would have to extend to geosynchronous orbit, which is about a tenth of the way to the Moon. You'd only expect this to happen with artificial constructs like a space elevator."
] |
[
"And, inconveniently, the mass of such a large mountain would likely create some degree of gravity on it’s own."
] |
[
"This mountain would have to extend to geosynchronous orbit, which is about a third of the way to the Moon.",
"1/10"
] |
[
"In the line of evolution, has there been a point where prehistoric humans shared the same intelligence level as dinosaurs? Would that mean dinosaurs had a chance of human-like levels of intelligence if they didn't get screwed with extinction?"
] |
[
false
] |
[deleted]
|
[
"You seem to be under the assumption that evolution has either a goal or forgone conclusion that intelligence would rise over time, in a way comparable to humans. Sharks have been around as a suborder ",
"since the time of the dinosaurs",
" without approaching human-like intellect. Evolution is just the natural result of a population with heritable traits under environmental pressures.",
"Beyond that, it's hard to measure intelligence level of living creatures we can perform tests on (ex: ",
"mirror test",
"); much more so for a fossil record with essentially no soft tissue."
] |
[
"You're assuming that evolution always drives organisms towards greater intelligence. Very high intelligence is one possible trait that, apparently, increased our ancestors' survival enough for it persist in the population. As one of the other commenters said, there are many lineages that have been evolving for millions or billions of years without ever developing intelligence, because ",
". Bacteria have been evolving and changing since near the beginning of life, and there are plenty of very successful lineages of bacteria that are pretty clearly not intelligent.",
"If you're asking if dinosaurs could have ever developed intelligence, then I believe it's conceivable, if they'd happened to be in a place where intelligence would provide a distinct advantage. But they didn't, as far as we know"
] |
[
"I am not an evolutionary biologist, but I am going to go ahead and say that anything that we would recognize as \"human\" or even \"human-like\" would be smarter than a dinosaur. ",
"Furthermore, there are a lot of cool theories as to why we are as smart as we are, and most of them include some characteristic (such as hand dexterity, which allows for tool making etc.) that was not shared by dinosaurs. ",
"It's a cool thought though. "
] |
[
"Can someone explain the AU, Astronomical Unit?"
] |
[
false
] |
[deleted]
|
[
"We use the AU mostly to refer to distances within the solar system - for example, the distance from the Sun to Saturn, or to the Kuiper Belt. We also use it to describe similar distances in other star systems, say, the distance between two binary stars, or between a star and its planets. There's nothing special about it, it's just a convenient and easy-to-define length scale to use to describe these things.",
"If you want to describe much shorter scales, like the distance from your bedroom to the kitchen (the most important distance!), obviously you don't use AU. You use feet or yards. To describe the distances between cities, you use miles, or kilometers if you're from somewhere funny.",
"A light year is about 63,000 AU and the nearest star is a few light years away, so AU also clearly don't work to describe distances to stars or bigger things. Astronomers actually rarely use light years; more commonly they use parsecs, with 1 parsec being about 3.26 light years, and which is not (contrary to what Han Solo says) a unit of time. A parsec has a less intuitive definition than a light year - it's the distance to a star which has a ",
"parallax",
" of 1 arc second - but since we use parallax to measure distances to nearby stars, this is much more useful to astronomers than light years (which are quite arbitrary and physically meaningless).",
"If we want to talk about yet bigger distances, say the distances between galaxies, we stick with parsecs, but add prefixes. The distance to the center of the Milky Way is a few thousand parsecs, so we use kiloparsecs. The distances between galaxies are frequently megaparsecs, or even gigaparsecs. The scale of the observed Universe is some number of gigaparsecs, so luckily we don't have to use any units crazier than that."
] |
[
"It's arbitrary in that sense, but not arbitrary in that it's an extremely convenient thing for astronomers to use. So perhaps \"convenient\" would have been a better word than \"arbitrary.\" In either case, light years are neither, and that was my point :)"
] |
[
"search the reddit for \"second\" There was an interesting thread a few days ago about defining the second. It all boils down to the babylonian affinity for sexagesimal. (and the large number of factors in 60) I think that particularly for degrees, there may be some coincidence with the number of days in a year as well."
] |
[
"If I tap my fingers to the beat of a song in my head, is there a delay between my thought of the song and the movement of my finger that I don't perceive?"
] |
[
false
] |
When I 'play' the song "Mary had a Little Lamb" in my head, I can tap my finger along with it, and it seems like my finger and my thought are in sync. But doesn't it actually take some time (hundredths of a second, I think) for muscles in my finger to respond to a command in the brain? So is the song in my head actually slightly ahead of my finger movements? Or does my brain make my finger move before the particular note enters my mind? Or is there no delay?
|
[
"Your brain is making your finger move so that your perception of your finger landing and the perception of the rhythm in your mind line up. In order to do this, the brain has to start the motion of the finger before the corresponding note hits. Your brain is thinking ahead without you even realizing it, and adjusts timing and velocity on the fly as you tap louder or softer or start getting other fingers or your whole hand or arm involved. It's really a remarkable capability!"
] |
[
"In musical terms this is called \"anticipation\" or \"anticipating the beat\". You have a memory or sense of language about how it's supposed to sound and, just like speaking in unison, it probably wasn't synced up the first time you tapped along to a song. Physical expression of rhythm is a learned trait. "
] |
[
"Like how a bassist will begin to strum, or a drummer will bring their drumsticks down, a fraction of a second before a song starts? "
] |
[
"Is it possible for a particle to be completely still? If so, what are the implications?"
] |
[
false
] |
Shower thoughts. I became curious.
|
[
"\"Completely still\" depends on the observer's motion. Your question is equivalent to \"Is it possible for a particle to have a perfectly known velocity? (not necessarily zero)\" ",
"This is possible in classical physics (only in an idealized situation, of course). ",
"In quantum mechanics, however, it means that the wave function has a perfectly known wavelength, which is only possible if the position is completely unknown (",
", the probability is spread out to infinity). That situation cannot be produced by any localized process. This is an example of Heisenberg's uncertainty principle."
] |
[
"Quantum mechanics is probabilistic. If we want to know where something is or where it's going, all QM gives us is the most likely position/momentum, which we call an \"expectation value.\" Formally, the expectation value is what we would expect the most common result to be if we measured an ensemble of identical systems.",
"QM also gives us something called a \"standard deviation,\" which is, in a rough sense, how much we can expect an actual measurement to differ from the calculated expectation value. If the standard deviation is very low, you can expect a measurement to give you something very close to the expectation value. And, conversely, if the standard deviation is high, you can't really expect a measurement to give you something close to the expectation value.",
"In more lay terms, standard deviation tells us the level of ",
" in the expectation value.",
"Anyway, you can demonstrate mathematically that the product of the standard deviations in momentum and position, for any given function, have to be greater than or equal to a specific value (h/4pi). That's the Heisenberg Uncertainty Principle.",
"In more lay terms, the more definite a particle's position is, the less definite its momentum is, and vice versa. So, if you try to confine a particle to a small area (for example, shooting it through a slit), you suddenly have no idea which direction it's traveling. Or, if you try to keep its motion very precise (such as stopping it), you suddenly have no idea where it is.",
"edit: If you're still not getting it, there are lots of layman-friendly explanations of the uncertainty principle ",
"here",
". ELI5 has much less scientific rigor and precision compared to ",
"/r/askscience",
", but it's often more accessible."
] |
[
"OK.",
"In classical (Newtonian) physics, a particle can be completely still. However, \"completely still\" is not an absolute concept, because it depends on the motion of the observer.",
"In quantum mechanics, it is impossible, due to the uncertainty principle."
] |
[
"If at L1 and L2 between Earth and the Sun, an object would have the same orbital period as Earth, what is the orbital period between L1 and L2?"
] |
[
false
] |
Between L1 and Sun, the object has a shorter orbital period than Earth. At L1 it has the same orbital period as Earth. Beyond L2 an object has a longer orbital period than Earth. At L2 it has the same orbital period as Earth Then say if there was an object between Earth and L1, does that mean the object has a longer orbital period than Earth? If there was an object between L2 and Earth, does it have a shorter orbital period than Earth? How come the moon, in relative to the Sun, has the same orbital period as Earth, since it's between L1 and L2? Thanks!
|
[
"Take a quick look at Kepler's laws of planetary orbits, and you'll stumble upon his third law, which says for orbiting bodies (let's say planets) the farther away you are from the thing you are orbiting (let's say the sun) the longer your period is. The exact mathematical relation says that the period squared is proportional to the semi-major axis of your elliptical orbit cubed. And the proportionality constant depends on the mass of the thing you are orbiting around.",
"The points L1 and L2 are actually unstable lagrange points. If we put something on one of these points they will go around the sun in the same amount of time as Earth, but if we were to push one away from the point a little bit it would continue to move away from the lagrange point and no longer have the same orbital period as Earth.",
"So if we think things closer to the sun than Earth will go around the sun in a smaller period of time than Earth, and things farther from the sun will go around in a longer period of time, why do these two points exist?",
"Well, Kepler's law neglects the effects of the other planets orbiting around the sun, and it is the gravitational attraction to Earth that causes things to stay at these two lagrange points.",
"For L1, which is between the sun and the Earth, we would expect a satellite placed there to go around the sun at a faster angular velocity than the Earth, but the extra pull of gravity from Earth causes the satellite to slow down and it matches Earth's angular velocity.",
"L2 has the opposite effect. It is on the opposite side of the Earth as L1, so we would expect it to have a smaller angular velocity than Earth, but Earth's gravitational acceleration speeds it up until their orbital periods match.",
"Now that we are all on the same page about lagrange points, let's answer your questions.",
"If we naively assume Kepler's third law, an object between L1 and Earth (closer to the sun than Earth) would have a shorter period than the Earth, and an object between L2 and Earth (farther from the sun) would have a longer period. However, because of the gravitational interaction with Earth the objects would eventually be pulled towards Earth and impact the planet, or miss and be accelerated past it to a new orbit.",
"The moon orbits the Earth, not the sun (hopefully this isn't new information). This means that the moon moves around the Earth, and the Earth moves around the sun. So of course the moon will have the same orbital period as the Earth does around the sun.",
"And for the moon you can use Kepler's third law, and some classical mechanics to find L1 and L2 points for the Earth moon system, which would move around the Earth at the same angular velocity that the moon moves around the Earth."
] |
[
"Nope. Those ones are stable for the Earth-Sun system (and almost all systems as well)! In order for them to be stable the mass of the bigger body has to be about 25 times as massive as the smaller body, which is true for almost every system.",
"If something starts out at either L4 and L5, and is displaced a little bit it will orbit around the point rather than moving away from the point as if it were at L1 or L2."
] |
[
"How bout L4 and L5? Are they also unstable? "
] |
[
"How does the smoke of large wildfires affect insect populations?"
] |
[
false
] | null |
[
"Since you specified honey I'll respond regarding honey bees. It unlikely to have any effect on honey prices as honey is produced world wide and on that scale of things wildfires are very localized. You could see some rise in locally produced honey if there is a specific crop for that area that was destroyed by the fire and takes time to replenish. I expect Tupelo prices to increase next year because of the damage from Hurricane Michael along prime Tupelo production regions, but that production is all done in a few weeks in spring.",
"The current season across the northern hemisphere is also one of low honey production, particularly in CA which is probably where you are referencing forest fires. Most honey gets produced in spring/summer or early fall when the majority of flowers bloom not late fall/winter. In most places honey production times are not going to be the ones with dry forest fire prone conditions. Nectar sources for the bees dry up as the forests do with lack of rain.",
"Bees can be rather tolerant of smoke, as beekeepers we use smoke on purpose to calm the hives so we can work them. Its use covers up the pheromones they use to communicate. Once we introduce it to the hive they will immediately start fanning to ventilate the smoke out of the hive. They will continue to do so until its gone. ",
"It is possible to smoke a hive out, to force them to abscond and leave for a new nest site but it takes a lot of smoke. In general as a wildfire approaches a hive will hunker down and do its best to ventilate the hive fanning to bring in fresh air and push the smoke out. Bees are very loathe to leave behind all their stores, larva and likely the queen. A colony absconding at a moments notice is a dead colony. The queens are usually too heavy to fly properly and would not be able to escape with the majority of workers. Without a queen or eggs/larva the colony would fail as there are no reproductive members left even if they avoided the smoke/fire.",
"Even more smoke will have the same effect on insects it has on people if they can't get out of it: suffocation and death. "
] |
[
"A ",
"paper",
" published less than 2 months ago actually covered this. Haze smoke had a negative effect on the development of butterflies, from their health to length of development time (slower is bad). However, the cause is not likely to be of suffocation or particle obstruction in their breathing tubes (tracheae), but more so from direct toxic effects. Actually, I'll post this to ",
"r/science",
" since it's recent, interesting, and quite relevant."
] |
[
"Wow, what a comprehensive answer - thank you!"
] |
[
"How does Boron's ability to absorb neutrons work and does absorbing neutrons affect the atom?"
] |
[
false
] |
Boron is often used in nuclear reactors because of its ability to absorb neutrons. How can Boron do this without becoming super heavy or otherwise changing itself?
|
[
"The boron ",
" change. It undergoes neutron capture reactions. Neutron capture looks like:",
"X + n -> ",
"X + γ.",
"That means that the nucleus is transmuted to a heavier isotope of the same element, and a gamma ray is released."
] |
[
"I'm so disappointed. "
] |
[
"\"Beaver\" isotope?"
] |
[
"How were the water masses on earth and how did they function before trees or plants appeared?"
] |
[
false
] |
So, I before plants ever existed I suppose there were already water masses like oceans, seas and, I suppose, the cycle of rain water already existed. Therefore there must have existed already rivers, right? Should we imagine that time where plants didn't exist then like naked ground and rock with rivers running down to the sea? The question might be a bit obvious for some but I have a hard time imagine such a landscape. Would it have been like say... the Colorado Canyon but without any kind of plant or tree around? excuse any typo, I'm not a native English speaker and you might find errors in the text:) thanks in advance!
|
[
"One aspect of your question that is discussed quite a bit is what rivers were like prior to the evolution of land plants. Specifically, there is a lot of evidence that ",
"meandering",
" rivers require significant cohesion of their banks to form, where this cohesion is usually provided by vegetation and that in the absence of vegetation, the expected form of rivers would be primarily ",
"braided",
" (e.g., ",
"Murray & Paola, 2003",
", ",
"Crosato & Saleh, 2010",
", ",
"van Oorschot et al., 2015",
"). This in turn is often cited as a reason for why meandering rivers do not seem to be well represented in the stratigraphic record before the development of land plants (e.g., ",
"McMahon & Davies, 2018",
"). Now, the trick is that there are examples of meandering rivers forming in areas without vegetation to stabilize their banks, for example in the submarine environment on Earth (e.g., ",
"Peakall et al., 2000",
", ",
"Das et al., 2004",
") and in the past on extraterrestrial bodies like Mars where we don't think plants ever existed (e.g., ",
"Weihaupt, 1974",
", ",
"Matsubara et al., 2015",
", ",
"Lapotre et al., 2019",
"), so clearly other mechanisms are able to stabilize river banks to the point where meanders can exist. However, the general consensus from both modeling and observational records is that while there would have been isolated meandering rivers on Earth prior to land plants, there would have been substantially fewer of them and most rivers would be braided channels of some sort."
] |
[
"Thanks for such a detailed answer! I think somehow I had imagined them like braided rivers, but that was just a lucky guess. Then the cycle of evaporation and rain would have been essentially the same, right? Was the earth as warm as it is today? And would that somehow affect the formation of rivers?"
] |
[
"This is too broad to be answered. Abundant vascular land plants developed in the ",
"Silurian",
" (though the colonization of land by simple photosynthetic organisms began in the ",
"Ordovician",
"), so the period before land plants represents > 4 billion years of Earth history. You would need to narrow the temporal scope of your question to get an answer."
] |
[
"Would you still be \"weightless\" in a geostationary satellite?"
] |
[
false
] |
This mentions that astronauts in the ISS are subject to 90% of the gravity you and I are feeling here on the surface. The illusion of weightlessness is due to the fact that they're in "freefall" around the Earth at orbital velocity, and if we built a tower that high we could walk around unhindered. So what if the satellite was geostationary? Would the zero-G "freefall" occur or would it behave like you were standing in an orbital-height skyscraper?
|
[
"Geostationary satellites are still in freefall, so you'd still feel weightless.",
"A geostationary satellite orbits the Earth with an orbital period of one day (as compared to, say, the ISS, with an orbital period of around an hour and a a half), which is why it can stay over the same spot on the Earth. But is still orbiting."
] |
[
"For one thing, geostationary orbit is a lot higher than where the ISS is, so Earth's gravity is only about 2% as strong there as it is on Earth. You would still feel weightless on such a satellite, just like on the ISS, and for the same reason.",
"So what if the satellite was geostationary? Would the zero-G \"freefall\" occur or would it behave like you were standing in an orbital-height skyscraper?",
"The two situations are actually the same. If you built an infinitely tall skyscraper, you would feel normal weight at ground level. Your apparent weight would decrease as you climb. At ISS-level, you would feel about 90% of your normal weight. It would keep decreasing until geostationary orbit, where you would be in freefall (apparent weightlessness). If you pulled yourself further up, you would be able to stand on the ceilings, as the direction of your apparent weight shifts outward."
] |
[
"Absolutely correct. Geostationary satellites are still in free fall, their speed is simply matching the direction and speed of the earth's rotation."
] |
[
"Why do the various SSRIs work differently?"
] |
[
false
] |
If they all work by blocking serotonin reuptake, why do they seem to have differing efficacy among patients? Are there other active elements that differ from one SSRI to another? Are the differences really enough to warrant a doctor prescribing paroxetine for a patient when sertraline doesn't produce the desired result?
|
[
"The SSRI is a general mechanism. Each drug has slightly different receptor affinities, which can translate to substantial enough differences in drug activity as to warrant a bunch of different drugs in the same class. Switching to a new drug can make all the difference. ",
"This isn't limited to SSRI's. There are dozens of different antihistamines, just as a random example, and someone who doesn't respond to Zyrtec may have complete symptom remission if they take Claritin. "
] |
[
"Just to branch off of this, these drugs may have different pharmacokinetic properties as well. Differing half-lives, ability to cross the BBB, metabolism, liver enzyme interaction, etc. all influence the drug's ability to function well in a specific patient or condition."
] |
[
"Selective Seretonin reuptake inhibitors aren't really quite selective, and have activity at norepinephrine and dopamine transporters, they bind with different affinities to their transporters, and they will be distributed through the body slightly differently. That will explain why they are differences.",
"Connecting this to psychiatric care is a little tricky, because the not so secret secret about them is that just increasing levels of seretonin doesn't really explain all of their effects. One particularly thorny issue is the couple week lag in real efficacy. So its somewhat of a mystery really why they work at all, so their differences really have to be tested and assessed in a clinical environment and judged on those merits."
] |
[
"What causes light refraction at the leading edge of an airplane wing at cruising altitude/velocity?"
] |
[
false
] |
I noticed it once and now I see it every time I fly (unprecedented exit row streak). It's a very thin "layer" if you will where the light is refracted. It's barely noticeable, looks like it can't be more than 1 cm, but most definitely there. Also, the light appears to to bend at an angle towards the fuselage, not towards the tip of the wing. I get that light refracts as it transitions between two mediums, and I get that moving air behaves like a fluid, but there is most certainly moving air ahead of this very thin "layer" where light is refracted. Why just at the leading edge?
|
[
"The refractive index of the air varies with its density. This can be observed when you look through a column of rising hot air over a flame. The hot air is a lower density than the room temperature air, and the difference in their refractive indices causes distortions in the light passing through.",
"I suspect that the air on the leading edge of a wing will be compressed more than the air surrounding it, and will thus demonstrate a variance in refractive index."
] |
[
"I'm not disagreeing with either of you. It's just that, although temperature was used as an example of refraction, it wasn't stated as a reason this phenomenon is observed on a wing. Hence \"in addition...\""
] |
[
"Agreed. The air at the leading edge is the highest pressure. The air just above that moving over the wing is at a much lower pressure. The two density differences so close together causes a visual difference."
] |
[
"What Would I Have To Do To Power My House Completely Off Renewable Energy?"
] |
[
false
] | null |
[
"Depends a bit on how \"off the grid\" you want to go.",
"The average American household uses around about 14 000 kWh of electricity a year ",
"(source)",
". This means about 38 kWh per day. This is quite a lot. A well set-up 1.5kW solar panel system in Sydney, Aus would produce about 6kWh of energy per day on average ",
"(source)",
".",
"Assuming similar returns wherever you live, you'd need about 6 of these sets to offset your energy use. Let's call it 7 sets, because the figure above assumed a high efficiency set up. A quick google found a price of ~1 800 US per 1.5kW system (not including installaton), you might be able to beat that though. That would come out to 12 600 dollars.",
"However, we've cheated in this. Your peak production from your 10.5kW system (I've no idea how possible this is, I suspect it wouldn't be simple wiring) would probably be around the middle of the day. That is, when no one is home and your energy consumption is quite low. Say you watch TV on your flatscreen for a few hours each evening, none of that power is being provided by you. ",
"This solution is \"off the grid\" in the sense that you produce as much energy as you consume, but most of it isn't actually used by you. Instead you're (hopefully) selling it back to your utility for a decent price. You could buy a 10kW wind turbine for about 50-65k installed apparently. This might be slightly more consistent during the times you use power, but you'll probably still end up buying a lot of power / selling your excess. Obviously both wind and solar are dependent on external factors.",
"Another renewable option would be to buy some property with a fast flowing creek. If you then built a house next to it, and installed some sort of turbine or hydroelectric dam system (something like ",
"this",
") you would get a much more consistent base-load power source. Supplement this with solar or wind and you might be able to go completely off grid. It wont be cheap though.",
"Alternatively, you could invest in a whole heap of batteries (which you'll need to replace every few years), or possibly some sort of flywheel (which you'll need to hope doesn't shatter and send chunks of metal flying very quickly).",
"If your goal is more environmental rather than cost-saving / personal reasons, then you may want to consider moving to Washington state. I believe a lot of their power comes from hydroelectric systems?",
"Summary:\nFor about 13 000 grand you could ",
" produce enough solar power to roughly neutralise your production/consumption. You wont be \"off the grid though\". About 50-65k would get you a nice wind turbine. A lot more (and some land with the right characteristics) might let you build a hydroelectric scheme and get a nice baseload production. A lot of money would let you buy batteries or some other storage system (or you could just only watch TV when the sun is out).",
"Or you could move to Seattle and buy a much smaller solar system to go carbon-free (ish)."
] |
[
"Some of the answers below are good, but I have actually worked as a renewable energy contractor and I can tell you the first thing you are going to want to do has nothing at all to do with your renewable energy system.",
"You are going to want the most efficient home you can buy/build. For every dollar you spend on efficiency you will save 3-5 dollars on your renewable energy system.",
"This means, no vampire loads (things that draw energy even when they are \"off\"), the most efficient heaters/coolers/whatever. Heavy insulation, utilizing passive solar (making sure your windows are on the right side of the house, correct planting of trees, etc), LED lights, and the whole raft of other efficiency matters. Your end goal is to use AS LITTLE energy as possible. ",
"Once you have slimmed down to the absolute minimum of energy needs (for a good example google Passive Houses in Germany, they are so well insulated that the heat of the people living in them is almost enough to keep them warm all winter), you are ready to install the renewable energy system.",
"First thing you need to do is figure out what sort of resources you are dealing with.",
"Got a lot of sun? Maybe solar electric and solar thermal panels will work for you.",
"Got a lot of wind, and a big field with no trees/other obstructions maybe a wind turbine would work for you.",
"Near a hill with a stream on it, maybe small scale hydro would work for you.",
"Live near deep bedrock maybe you can use geothermal. ",
"Perhaps a combination of all these technologies.",
"Then you need to figure out if you want to be all the way off grid, or still \"grid tied\" as a backup.",
"If you want to be completely off grid you will need a battery system to store up extra energy for use later. Its not always sunny and the wind wont always be blowing. You will size the battery system based on your energy needs (again this is why you want to use as little energy as possible)",
"You can also store up hot water this way by having a bigger tank, the bigger the tank the bigger your \"thermal battery\" is. Solar hot water is one of the cheapest and easiest ways to heat a home/provide hot water needs.",
"If you want to be grid tied, then you will not need a battery system (unless you want to plan for grid failure), instead you will need a grid tied inverter. This device will convert your renewable energy (dc) into grid energy (ac) (please forgive me, I am simplifying this quite a bit).",
"The inverter will draw power from the grid when you are not making enough, and put it back for others to use when you are making too much. If you live in an area with net billing your electric meter will spin backwards when you put energy onto the grid, and spin forward when you take it off, if you make more then you take in a month they send you a check! (depends on your local laws).",
"Hope that helps, let me know if you have any questions.",
"tl:dr\n1. efficiency\n2. location appropriate resources\n3. battery system or not\n4. Grid tied or not"
] |
[
"I should also add, the price of these systems really depends on a lot of things, including the kind and amount of government subsidies in your area. You can dramatically reduce costs using the methods I mention above."
] |
[
"Is the useful energy released from ATP losing its phosphate group... mechanical energy? Is everything that my body does a result of tiny bomb-powered propulsion engines?"
] |
[
false
] |
I was trying to figure out what kind of energy is released when ATP is broken up, and I came across . Most of the comments are a little over my head, but the top comment mentioned that proteins have binding sites for ATP, and that the release of the phosphate group causes the proteins to change shape. The description in the comments almost makes it sound like the release of the phosphate group propels the rest of the protein in a predefined way like a carefully calculated little explosion. A tiny rocket propulsion. Am I wrong to imagine that this is a little like changing an asteroid's shape and trajectory by strategically detonating bombs on specific points on the asteroid's surface? Does this mean that when my muscles move, it is the result of proteins contracting under the force of billions of tiny explosive forces? I hope so. Oh please let it be true. I want to be a machine moved by billions of tiny rocket-propelled proteins.
|
[
"I hate to break it to you but it isn't mechanical energy or like small explosions. It's what is often referred to as chemical energy or chemical potential energy. In essence, there are a lot of different bonds between atoms, for example, a Carbon-Carbon bond such as in graphite or diamond, has a different energy level to a Carbon-Hydrogen bond, such as in Ethane (a gas that can be used as fuel). ",
"In ATP you have bonds between phosphate groups (specifically between a Phosphate-Oxygen-Phosphate, so two bonds technically). This is known as a pyrophosphate bond and is very high energy. When I talk about energy here you can imagine a higher energy state as being a ball that is high above the ground, and a low energy state is a ball low down. If you were to drop both balls onto separate see-saws, you would be able to throw something on the other side of the see-saw further with the higher ball, because it would be travelling faster. ",
"This is analogous to how ATP is used in enzymes, although you don't have to 'drop' the molecules to release the energy, instead they react, breaking their bonds to form new bonds. ",
"I hope this is clear but please don't hesitate to ask for clarification."
] |
[
"http://www.researchgate.net/publication/10774066_ATP-induced_conformational_changes_of_the_nucleotide-binding_domain_of_NaK-ATPase/file/e0b4951a75c5fbef88.pdf",
" ",
"Molecules like sodium... right. Honestly it seems like either you have a secondary school level education in this or English isn't your first language. I genuinely don't mean to be rude this time, but trying to speak from a position of knowledge without a firm grasp of what you are talking about is misleading."
] |
[
"It's a paper not an article, and I'd say conformational change is pretty mechanical. Why do you keep putting that in quotes? I was making the point that sodium is not a molecule."
] |
[
"What would happen if a very large amount of \"Pharaoh's Serpent\" was ignited?"
] |
[
false
] |
[deleted]
|
[
"Firstly it can't create mass, it changes form and increases its volume. I would assume that if you did ignite that large of an amount the same reaction as before would take place just on a larger scale. The actual rate of the reaction likely would not change due to an increased reactant quantity, and your limiting reagent would likely be the oxygen fueling the reaction."
] |
[
"Didn't southpark do an episode on lighting the worlds largest \"snake\" firework? ",
"Seems like that would be the result."
] |
[
"http://en.wikipedia.org/wiki/Summer_Sucks",
"Does that answer your question? ;)"
] |
[
"If a child were to not EVER come in contact with another human/lifeform, how might it act?"
] |
[
false
] |
[deleted]
|
[
"They're what we call ",
"a feral child",
" (not the most sensitive name ever). The most famous case is ",
"Genie",
". ",
"tl;dr human contact is very important for proper development. What's more, we have critical periods of development (think about how hard it is for adults to learn new languages) where we learn certain things far easier. Over time the child will show more normal development if exposed to other adults but the effects ",
" felt forever."
] |
[
"I still remember my first year psychology professor saying, slightly annoyed, \"You know we could skip most of this stuff if they would just kidnap a baby and lock it in a dark room for 15 years\""
] |
[
"Fitting username?",
"Yeh, that's the frustration with psychology. There's so much we could study if it weren't for pesky ethics. Most of the seminal studies would have 0 chance of being approved now. \"Oh, you want to terrify a baby over and over to see if it gets scared of a toy? Sure, that seems alright!\""
] |
[
"Do the various dog breeds derive from a common dog ancestor, who derived from wolves -- or, does each dog breed correspond to a domestication of a corresponding wolf breed?"
] |
[
false
] |
In general, the diversity of dog breeds is a mystery to me.
|
[
"All dogs derive from a single domesticated wolf ancestor--or possibly (they're not sure) wolves started living with human ancestors and diverged from the rest of the wolves and so the wolves that lived with human ancestors were their own separate breeding group for tens of thousands of years before domestication. But the point is, dogs are descended from one or just a few domesticated populations, and most breeds are less than 500 years old. Though over time there has been interbreeding with wolves. And it might be that there were a few domestication events, like in Europe, Asia and Africa."
] |
[
"Thank you!"
] |
[
"This domestication can actually be seen in foxes. It hasn't taken many generations to produce dog like traits like floppy ears and docile behavior in ",
"foxes",
". "
] |
[
"Since DNA degrades as we age, would a clone made with an older person's DNA sample have a shorter life expectancy than a clone made with a young person's DNA sample?"
] |
[
false
] |
Possibly a related question: Why is it that humans are able to produce offspring with "fresh" DNA, yet we are unable to maintain the integrity of our own DNA over time? Edit: Thank you, everybody for your very informative answers. TLDR: clones are essentially as normal as if they were naturally born. There is a very fine balance between healthy cell repair and cancer, and we haven't quite figured out how to control it reliably yet.
|
[
"Maybe but one of the first things that happens in cancer cells is that a lot of those mechanisms get turned back on"
] |
[
"So if these repair mechanisms can be triggered in humans, is this how aging could be slowed?"
] |
[
"So if these repair mechanisms can be triggered in humans, is this how aging could be slowed?"
] |
[
"What factors could you change to direct evolution?"
] |
[
false
] |
Ignoring hands-on selective breeding for a second, if you wanted to make a species evolve to be suitable for a given habitat, what factors would speed up the process? I'd imagine you change their habitat gradually from their current one towards the desired one, but what else would speed up the process? Anything else?
|
[
"Larger is better, since it means their is more variation and a higher probability of mutations. ",
"Radiation is mostly causing damage to germ cells, and I do not know if or how it could effect a population in a whole. different radiation treatments can have different effects. A danger is created so many defunct organisms that they don't stand a good chance of reproducing anyway. ",
"Environment is huge. Organisms are already highly adapted to their current niches. Change occurs when they have to adapt to new ones. Look at Lenski's experiment on ",
" if you want to learn more."
] |
[
"You can't really change the process of evolution unless you do something like genetic engineering. What you are really talking about is setting the parameters under which natural selection will take place (though I guess in this case not so natural). ",
"If you have a large enough population with a large degree of genetic diversity, then the fastest way would to put them immediately into this new habitat, the ones surviving being the best adapted. If not enough would survive to form a viable population then you would have to do it in increments, but each increment would have to be a big enough jump that large portions of the population wouldn't survive, eliminating the poorly adapted from the breeding pool. You would then have to wait for the population to recover and develop genetic diversity before going to the next habitat, incrementally closer to the desired one. ",
"This will be a pretty slow process, the biggest limiting step being the development of sufficient genetic diversity that there is a reasonable chance that sufficient members of the population will be able to survive in the next habitat. Something that sped up mutation rate might help as long as it wasn't so extreme that it slowed population recovery too much. Radiation probably wouldn't be a particularly good choice unless you were talking about microorganisms, some sort of DNA intercalating agent that could be absorbed throughout the body (and particularly in the germline cells), might work better. "
] |
[
"Well you could put it into the water supply, which would probably be the easiest delivery mechanism. I'm not sure if you are thinking that they are in a farm like environment or free range. If you had some sort of relatively contained water source, it would be best, so as to avoid dilution of the chemical and to prevent its spread into the environment at large. "
] |
[
"Why are suicidal thoughts such a common side effect of so many medications?"
] |
[
false
] | null |
[
"I’ll add that some antidepressants (like Prozac) have black box warnings for increased risk of suicide because these medications can improve a person’s motivation before they start to improve their mood. Typically we say it takes up to 6 weeks to see a full benefit from antidepressants. Now, say you’ve got a patient who is extremely depressed, and they’re so low that they don’t even have the motivation to attempt to kill themselves. Then they start Prozac, and after 3 weeks they start to notice an increase in energy and motivation, but not mood, because that may take longer. Now they go out and buy a gun or rope or whatever and attempt suicide (and may or may not succeed) whereas before they were still depressed but didn’t act on it because they were frozen in inaction. This is how it was explained to me by my psychiatry attending. "
] |
[
"This is why we stress that patients should be reviewed by their prescriber 3-4 weeks after starting treatment. 'It may make you feel worse before you feel better' is a warning I've said a thousand times as a pharmacist."
] |
[
"Your mood is regulated by chemicals in your body and brain, if you take drugs or medications that can interfere either directly or indirectly with any of these pathways it can cause you to feel low or stressed or strung out. This can result in you having thoughts of suicide. It's important to know that while we can look at a medicinal molecule and say we know it will work in a certain way in a certain pathway we can't know if that is all it will do. The body is a very complex place and there is plenty we don't know and can't account for. For example let's say you take a medication with a molecule in it that fits a receptor that stimulates red blood cell production. Let's say this molecule has a high affinity for calcium ions for example, in the presence of a high amount of calcium that molecule bonds to it and becomes a slightly different molecule with a slightly different shape. This new molecule now coincidentally fits a different receptor, we didn't expect this because it is a receptor we haven't mapped yet and don't fully understand. Now you have a different result. That would be a direct form of interfearance, now say the new molecule is useless but it has taken the calcium ions away from being used elsewhere this indirect interfearing with another pathway. Knowing this it's easy to see why such extensive medical trials are necessary before a drug is mass-produced. Now that being said even if a drug passes a trial it may show adverse effects in some users but not enough to end production of the drug, these end up on warning labels just in case. Since suicidal thoughts is very subjective I also would argue it is put on many labels as a just to cover the companies ass measure. ",
"Anyway the tldr, the hormones that regulate mood are very important to human function and are part of very complex pathways, these pathways can be easily intefered with by drugs and interactions can be unexpected and unplanned. There is a lot we don't know and so many trials are nescecarry, as mood is also subjective it is an important legal measure for companies to cover their bases even if they don't think any such interactions may take place. "
] |
[
"Why can the lone star tick bite make you allergic to red meat, if that very same allergene your body starts reacting to has always been present in the meat itself?"
] |
[
false
] |
So I've heard that getting bitten by the lone star tick will make you allergic to red meat, specifically to saccharide "alpha-gal", present in most mammals, except humans. I wonder why we don't develop this allergy by eating the meat itself. Wouldn't that sugar circulate the body and be detected as foreign anyway? I'm sure I'm missing an important mechanism here, I just can't figure out why the body is fine with it as long as it's exclusively eaten, but after a bite you can't eat it anymore. I'm really curious about this acquired allergy.
|
[
"It doesn't happen when we eat alpha-gal because alpha-gal is not dangerous. The immune system confuses alpha-gal with the dangerous tick proteins after exposure to the tick proteins. ",
"Immune cells generally learn to attack proteins. A protein is shaped kinda like a puzzle piece. It has a shape on the outside where it can attach to things.. Immune cells attach to these puzzle pieces so they can't attach to anything else and do damage. That's how they \"deactivate\" foreign proteins, viruses, etc. When the immune system attacks a protein it creates memory immune cells that keep the shape that fits into that protein puzzle piece so that if the protein returns it can be identified by the immune system, and trigger an attack on that protein.",
"When ticks bite you some of the proteins & stuff from their recent meals (generally mammals) get into the bite. When the immune system shows up, in addition to the tick's proteins which are causing damage, another thing they find ",
" is a mammal saccaride called alpha-gal. They make memory cells to protect against alpha-gal ",
" - it's just present when & where the tick proteins are causing damage. The immune system is confused.",
"EDIT: alpha-gal is the only true food allergy triggered by a non-protein. It's not totally known why but the theory is it just ",
" a lot like a protein to some people's immune systems."
] |
[
"This is a great explanation, but worth noting that \"Alpha-gal\" typically refers to asparagine linked glycans (oligosaccharides on glycoproteins) that are terminated with alpha linked galactose. The allergy is still caused by a protein, it's just the sugar component acting as the antigen. Glycans are fairly common antigens."
] |
[
"To answer part of your question: You don't develop allergies from eating the meat itself because we digest the meat before we absorb it. In other words, our digestive systems take whole proteins and break them down into amino acids before we can absorb them. Whole proteins in the blood stream trigger immunologic responses; but amino acids don't."
] |
[
"How does the Arecibo Observatory account for all the water and debris that might accumulate on it?"
] |
[
false
] |
As you can see this radio telescope is located on the ground where (I think) water and debris may easily enter. Do the observatory personnel somehow clean all the water and dirt up even after a heavy rainfall?
|
[
"They have a hole in the center through which excess water and debris are drained.",
"More importantly, the radio waves which they observe are largely unaffected by any debris or water on the dish that may still be there after the rain has stopped."
] |
[
"Drained to where? My impression was that a karst sinkhole connects with a natural groundwater system of some kind, is that the case here? Or is this drain man made?"
] |
[
"I don't know what their drainage system is like.",
"But I am quite sure they have something suitable for the amount of rainfall that would fall on a surface of that area.",
"I got curious and looked around:\nThe amount of precipitation they get on average ",
"annually",
" at Arecibo is 54.5 inches. The average days with precipitation according to the same source is 126.",
"This means they get on average 10.99 millimeters of rain per day it rains. Or 0.01 meters. The area of the dish is ",
"73,000 square meters",
".",
"This gives us a total of 805 cubic meters of rain water per day on average. With 264 gallons per cubic meter, that gives us 212,520 gallons of water a day.",
"Mind you, this based off of the annual average. They probably get some serious raining some days.",
"So, they have a draining system that can handle quite a lot of water, or otherwise the facility would be called lake Arecibo."
] |
[
"Ask science: Are there atoms floating through space (like small particles we can't see but are everywhere) or is it mostly empty? Would the suns gravity effect something so small?"
] |
[
false
] |
This is bottling my mind right now.. you know, like when your mind is in a bottle. edit: oops typo, should be "affect".. that sort of thing usually drives me crazy when others do it..that's what I get for posting something late at night whilst stoned!
|
[
"Yes, there are atoms floating around in space. Gravity affects them, but not very much, and it turns out that radiation pressure (or getting hit by light) affects them much more."
] |
[
"Are there atoms floating through space",
"Yes. No doubt about it.",
"Would the suns gravity effect something so small?",
"Yes -- gravity affects all matter. It happens that, for small masses in the solar system, solar radiation pressure might easily be a more powerful force, and drive small particles away from the sun.",
"But the principle holds that all mass is affected by gravity, according to this equation:",
"[; f = G \\frac{m_1 m_2}{r^2} ;]",
"Where:",
"f = force, Newtons",
"G = universal gravitational constant",
"m1 = mass of attracted object",
"m2 = mass of attracting object",
"r = distance separating the two objects",
"Obviously m1 and m2 are interchangeable."
] |
[
"I think the problem is that the AskScience reddit doesn't have that feature enabled."
] |
[
"How many tumours/would-be-cancers does the average person suppress/kill in their lifetime?"
] |
[
false
] |
Not every non-benign oncogenic cell survives to become a cancer, so does anyone know how many oncogenic cells/tumours the average body detects and destroys successfully, in an average lifetime?
|
[
"I don't think we can reliably estimate how many \"pre-cancers\" a healthy immune system can detect and destroy, but one of the major complications after a solid organ transplant is the risk for developing cancer due to the severe immune suppression needed to prevent transplant rejection. According to this article by Webster et al. (2007): \"Cancer is a major source of morbidity and mortality following solid organ transplantation. Overall risk of cancer is increased between two- and threefold compared with the general population of the same age and sex. Recipients of solid organ transplants typically experience cancer rates similar to nontransplanted people 20–30 years older, and risk is inversely related to age, with younger recipients experiencing a far greater relative increase in risk compared with older recipients (risk increased by 15–30 times for children, but twofold for those transplanted >65 years)\". So you can theorize that the immune system catches some in younger people (depending on the overall health of the person-some people have things that predispose them to developing cancer), with the immune system being unable to keep up as we age. Webster AC, Craig JC, Simpson JM, Jones MP, Chapman JR 2007. Identifying high risk groups and quantifying absolute risk of cancer after kidney transplantation: A cohort study of 15,183 recipients. Am J Transplant 7: 2140–2151"
] |
[
"Wow. This is maybe the best answer I have ever seen on here. With citations, source and everything!"
] |
[
"I’ve had a transplant, and I was told forever. Though the longer you have it, the less you need. I’m 5 years out and still at full day 1 dose levels. I have an overactive immune system, so we’re struggling to fight off the rejection."
] |
[
"What is an 'observation' in quantum physics?"
] |
[
false
] |
Having read about quantum superposition, an observation is said to collapse the superposed state, but what is an observation? is it merely photons bumping into the particle we're trying to observe? or is it interpretation by a "conscious" observer? if it is the former then almost every place is filled with some kind of radiation (if not anything at least thermal radiation) which would make it almost impossible for anything to be in a superposed state anywhere.
|
[
"Imagine that you have a whole universe (or system) with a single particle in it. There's just one particle described by a very simple wave-function.",
"But how do would you know that there's a single particle? You observed it by sending some other particle at it. ",
" And since there is ",
" a single particle, then the wave-function is also different.",
"So basically, you made a simplification that was physically invalid; you shouldn't have assumed that there was only a single particle. Wave-function 'collapse' is basically a mathematical means of correcting this oversight. The wave-function changes from one that is invalid (really it's just a poor approximation of reality) to one that is more acceptable.",
"In Newtonian physics, you can talk about the behavior of a particle with the assumption of 'observer independence' because the act of observing -- of collecting information about the particle -- has a negligible effect on the physics. In quantum physics, this is simply not true. A single photon is enough to change the outcome of the experiment.",
"So the 'observer' is really just other particles that you're not talking about. Like the wave-function of your detector or apparatus. (Or even the wave-function of the rest of the universe.) When we talk about the wave-function of a particle, we are making a simplification that the wave-function is separable from the rest of reality. This is not always a valid assumption. Sometimes other things ",
" matter."
] |
[
"Yes, Schrodinger came up with the thought experiment to show how ridiculous the Copenhagen intepretation is. "
] |
[
"Isn't this the critique that Schrödinger's cat is supposed to represent?"
] |
[
"Ideas can't hurt...can they?"
] |
[
false
] |
In discussions I often hear the claim that ideas cannot harm people; however, I suspect that they can. From my understanding, there is research showing that stress is detrimental to physical health. I am wondering what evidence there is demonstrating that ideas, perhaps those of ideologies, actually have physical effects on people. Are there ideas that can like malicious software attacking human hardware? Is there much evidence backing up nocebos such as the bone of death? Can thoughts kill? If ideas can harm us, what are scientifically backed ways of inoculation and defense?
|
[
"The idea of harmful ideas, or images is common in science fiction. One of my favorites is \"",
"BLIT",
"\" by David Langford, about an image that is fatal just to look at. But as far as I've been able to tell, sci-fi is all they are. There's no evidence of any specific meme or thought-form that causes physical damage.",
"Hospital nurses (like me) have many stories of patients who, on being told they had a terminal illness, apparently \"gave up\" and died before the illness seemed severe enough to be fatal. However we also have stories of people who had great attitudes, were bound and determined to beat the illness, and died early anyway. So, anecdotes are not much help.",
"Research seems to indicate that willpower or despair does not significantly affect mortality. There is some correlation between depression and poor outcomes, but it may be that the depressed patients are those who are sicker to begin with. That is, more serious illness may cause depression, rather than the other way around.",
"As for the \"aboriginal bone of death,\" there are conflicting accounts (probably because it makes such a good story), but the reliable ones seem to agree that the target does not instantly drop dead. Rather, upon realizing he has been cursed, he stops eating and caring for himself. If death follows soon, it apparently comes from dehydration, malnutrition, and lack of self care. "
] |
[
"I'd be willing to bet that the human nervous system is far too robust to be hacked by some BLIT style attack, or similar things I've read in stories (like a tune so catchy that anyone who heard it would just waste away humming it). We've got built-in \"get used to the stimulus\" and \"get bored of the stimulus\" filters, and are usually quite capable of ignoring ideas we would rather not think about.",
"The most reasonable idea, I think, would be something causing lots of chronic stress, which can indeed be hazardous to your health."
] |
[
"I'd agree. Humans are too good at perceiving, inventing, and communicating ideas and information. If any members of our species were susceptible to mental-death-by-meme, they were probably weeded out of the gene pool shortly after we invented language.",
"Chronic stress can cause cause long-term health issues, but it's not really by the process OP is asking about. Mental stress is a subjective thing. There's no kind of specific idea that will \"infect\" a person and cause a stress response."
] |
[
"How were ancient rope suspension bridges built across large gaps in terrain?"
] |
[
false
] |
Specifically how were they built above large drops? Would they need an extra long rope so they could climb down and then up to secure it from the other side?
|
[
"There were a few ways to do it, but one common way was to get one or two long pieces of thin string or rope across, then use that to pull a larger rope across. ",
"One method was to tie two pieces of light rope to an arrow and shoot the arrow over the river. One of the ropes would be tied taught at each end. Then, from the side opposite the archer a ring was put around the taught rope. Then the end of the other light rope was tied around the ring, and a thicker rope was also tied around the ring. Then the archer would pull on the light rope, and it would drag the thick rope back to the archer’s side of the river. From there, the archer could tie an even thicker rope and have it sent back over. ",
"When they built the first bridge over Niagara Falls, a similar method was used. But instead of archers, a boy flew a kite over the falls."
] |
[
"Check out the ",
"Wikipedia article",
" about it. The section titled “Charles Ellet, Jr.'s temporary bridge” talks about it."
] |
[
"Would you happen to have a source for that Niagra Falls bridge? Seems like a very interesting way to do it, I'd like to read more about it!"
] |
[
"Do languages affect our ability to feel different types of emotions? Would a bilingual person feel a wider range of emotions due to knowing more emotional vocabulary?"
] |
[
false
] |
[deleted]
|
[
"Linguistic relativity is the idea that language affects thinking. The strong version of this hypothesis is that languahe determines thought. Without a word for a concept, one cannot think of that concept. However, this idea is near universally discredited. There is a weaker hypothesis, that language influences thought. There is some evidence that shows that language can influence thought in small, insignificant ways.",
"Your question is asking about the strong version of linguistic relativity, si the answer is no. Learning more words for emotions does not unlock more emotions. Different languages may describe emotions in different ways, but for the most part, we all feel the same emotions."
] |
[
"Excellent point there. I don’t know about ",
" more emotions, but a polyglot would be able to ",
" subtleties of emotion by borrowing words from other languages. If I could pick a second language, it would be German. They have (very long) words for amazingly specific things. ",
"Here is just one list of words German words like that. ",
" "
] |
[
"Excellent point there. I don’t know about ",
" more emotions, but a polyglot would be able to ",
" subtleties of emotion by borrowing words from other languages. If I could pick a second language, it would be German. They have (very long) words for amazingly specific things. ",
"Here is just one list of words German words like that. ",
" "
] |
[
"Why are some acetylcholinesterase inhibitors classified as poisons and others as safe pharmaceuticals or even nootropics?"
] |
[
false
] |
Solanine is a poison in potatoes and sarin is a nerve agent/chemical weapon while galantamine is a pretty safe pharmaceutical and huperzine A is an OTC nootropic, despite the fact that all of them are acetylcholinesterase inhibitors. Why is that?
|
[
"Side effect profile.",
"Solanine is a saponin, so it destabilizes cell membranes. Cell toxins don't make good medicine.",
"Sarin is an irreversible inhibitor, which means that it binds to the cholinesterase enzyme covalently. Replacing these enzymes can take up to a week, so the increase in acetylcholine inevitably becomes life threatening."
] |
[
"AChE inhibitors are used for treating Alzheimer's but so far, they don't seem to be that beneficial. Alzheimer's is believed to be caused by the death of cholinergic neurons, and AChE inhibitors would result in less ACh broken down and thus more ACh present. However, Alzheimer's is more complex than that and has other factors involved in this complicated neural circuitry. Our current technology is also limited in being able to target specific groups of neurons. AChE inhibitors target other neurons that we don't want them to so they have side-effects such as nausea and decreased appetite. We also don't fully understand Alzheimer's, let alone the brain."
] |
[
"I'm going to ignore the Altzhiemer's treatment bit; I'm speaking generally here. ",
"If the effects were identical, and the only difference were the potency, then yes. However, it's rarely that simple. It's pretty typical of chemicals that affect neurotransmission to have more than one effect."
] |
[
"When you wash your skin with lukewarm or hot water after you’ve been in freezing temperatures, why does it feel like the skin is burning? Is your body actually in danger or are the nerves misinterpreting what is happening? Are there other examples of this situation?"
] |
[
false
] | null |
[
"This happens because when your body gets cold it constricts blood flow to the extremities first so that it can maintain heat in the core areas of the body such as the brain and and abdominal. This causes nerves to shut down in the extremities which is why you don't feel as much pain when you are cold and any pain you feel seems duller. Then when you introduce sudden heat to the area it is a huge boost in energy to these nerves that were pretty much shut down and this energy causes them to surge and reconnect with the central cortex and you experience this as pain. Also, when they are hit by the sudden heat your nerves have to preform a kind of calibration to readjust themselves to what is actually painful."
] |
[
"Most nerve cells in humans don't send signals all the time. A thermal receptor in your skin does not constantly report how warm it is, but reacts to change - because this is the interesting information for your brain to take action. In our skin, we have two types of thermoreceptors - one that reacts to 'cold' and one that reacts to 'warm'. Warm-receptors fire when things get warmer, and fire less when it gets colder. The 'cold' receptor is basically an inverted 'warm' receptor, thus their firing rate increases during cooling and decreases during warming. ",
"Some cold receptors also fire if they sense really hot temperatures, resulting in a sensation of 'ice-cold' when touching something hot (paradoxical cold). ",
"So if you wash your cold hands in lukewarm water, its basically a firework of warmth-thermoreceptors all screaming 'its getting hotter!!!' causing a tingling or burning sensation. This is due to the rapid change of temperature. This of course is usually an alarm signal, yet you are not actually in danger (in this situation). ",
"Another example is the opposite. You jump into a 22°celsius pool on a hot summer day and feel like you are freezing but feel more and more comfortable within minutes. "
] |
[
"Running a freshly frostbitten area under even room temperature water can actually cause much worse damage to the flesh. On the other side of things placing severe burns under cold water will cause it to blister faster and more agresively. I believe under normally safe temperatures it just feels like it is burning, but at extreme temperatures where the skin is already damaged it can be more dangerous for it be exposed to the opposite temperature of water. "
] |
[
"What’s the point of flightless birds? Why didn’t they evolve additional limbs if their wings are effectively useless?"
] |
[
false
] | null |
[
"Hi thomas_ja 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",
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", 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.",
" ",
" "
] |
[
"Earth sciences "
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"This question is based on fundamentally flawed premises. Please conduct some background research and revise your question if you wish to resubmit.",
"It suffers from issues listed in the AskScience ",
"guidelines",
". The question may be written in a way we believe does not contribute to scientific discussion at ",
"/r/AskScience",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Is it possible to have a black hole so small that its effects on its surroundings are negligible?"
] |
[
false
] | null |
[
"One theory is that yes, you can have a black hole with a mass of only a few thousand kilograms and an event horizon smaller than an atom. The problem is that thanks to Hawking radiation, the lifetime of a black hole like that is short unless you feed it matter."
] |
[
"A black hole has no more mass or gravitational influence than the matter that it is made of, and so if you were able to make a black hole by smashing together two hydrogen atoms, it would have the same effect on its surroundings as the gravity of a helium atom - negligible. "
] |
[
"Say, it was possible to keep such a black hole sustained. Would it be something that we could see and possibly get close to ?"
] |
[
"Why Isn't There Nothing? (Non-Philosophical Approach)"
] |
[
false
] | null |
[
"I would add that consciousness only exists where it can; in parts of the universe where nothing exists, there is no one pondering why nothing exists. Thus, if nothing existed, there would be nobody to realize that this was the case."
] |
[
"Sorry, I know you're aware, but this is much more philosophy of science than science. So you may want to consider ",
"r/philosophyofscience",
" instead actually."
] |
[
"Thank you. I'll look into this venue as a location to pose this inquiry. "
] |
[
"How does running effect gene expression? What does that mean?"
] |
[
false
] |
I have heard that when people run on a consistent basis, that it have a positive effect on gene expression. What does this mean? If someone who did not run before began to run consistently, what changes would one witness in that person in terms of gene expression?
|
[
"Im on mobile, so this will be quick with a source. But, stresses on the body causes differential gene expression to create proteins designed to help the areas that are stressed. Since we are not as physically charged as our prehistoric ancestors we don't have the same amount of gene expression in certain areas. It's theorized that physical activity helps \"normalize\" our levels of gene expression based on our prehistoric ancestors in which our genome was built.",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290514/"
] |
[
"Just about any activity you do a lot has some effect on gene expression. ",
"Ever notice how you get tired and/or are physically bad at some things, but the more you do them, the better you get? That's gene expression. Even tolerance to alcohol or drugs is gene expression, ultimately. Some things get up regulated, other things get down regulated on the cellular level.",
"When it comes to running, I have heard for example that AMPK-activated protein kinase gets up-regulated, which is involved in cell metabolism, specifically fatty acid oxidation. It's a good thing to have this upregulated if you are doing endurance exercise -- as the more efficient a fat burner you are, the less you rely on a limited supply of glucose and the more access you have to fats during exercise. Athletes (and ketogenic dieters!) typically are much better fat burners than your average untrained sedentary human, and this is a gene expression-related thing."
] |
[
"Gene expression simply refers to the types and amounts of transcripts(RNAs) produced by genes in a genome. ",
"There are many ways and multiple levels at which gene expression can be controlled. Many of these level have a kind time frame associated with them. For example, DNA binding proteins can turn expression on and off quite quickly, whereas, chromatin remodeling (DNA is wound around chromatin) could have long term effects on the expression of a gene. Or even more long term such as DNA methlyation that chemically alters the DNA in a region (I have heard of studies showing that these patterns can be passed to offspring)",
"You need to consider the types of transcripts that are produced. There are four main types of genes in eukaryotes: protein coding, pseudogenes, long non-coding RNAs (lncRNA), and short non-coding RNAs. There are numerous subtypes of each of these here is a good link explaining them if you are interested ",
"http://vega.sanger.ac.uk/info/about/gene_and_transcript_types.html",
"Believe it or not the majority of human genes are not protein coding but lncRNAs. Although, this is a bit misleading as protein coding genes are generally expressed at much higher concentrations. Furthermore, protein coding genes are much more ubiquitously expressed than lncRNAs. In fact many lncRNAs seem to be tissue specific citation: ",
"http://www.ncbi.nlm.nih.gov/pubmed/22955988",
" . Explaining lncRNAs function in a general way is a bit difficult but many are known to be involved in regulation of gene expression. ",
"So what effect would running have on gene expression? First this would be highly dependent on the tissue and time you measured (circadian rhythms also seem to have a wide reaching effect on gene expression ",
"http://www.pnas.org/content/111/45/16219.short",
"). (From here is just speculation) However, generally speaking, in the short term you would see lots of proteins for repair or growth being made such as myosin (muscles) and or hemoglobin (for carrying oxygen in blood). You might also see some lncRNAs getting produced that control the strength of the response your body has to the exercise. Then over the long term your genes might get modified to have less of a response to exercise in order to conserve energy. Your blood carrying higher hemoglobin concentrations would carry more oxygen requiring your average heart rate to become slower. Which could cause all kinds of regulator changes in your heart. Lower pulse causes changes in your arteries... You can see how complicate this gets and saying something has a positive effect on gene expression is kind of impossible. Although running would certainly have a positive effect on most people's health. "
] |
[
"Forced and sympathetic vibrations"
] |
[
false
] |
What's the difference between forced vibrations and sympathetic vibrations? For example, a guitar string forces the body of a guitar to vibrate at the same frequency as the string. Forced vibration or sympathetic vibration?
|
[
"I don't see how this explains the difference between forced and sympathetic vibrations though."
] |
[
"The key to understanding sympathetic vibrations lies in understanding the concept of damping: ",
"http://en.wikipedia.org/wiki/Damping",
"Depending on the damping of our system, there will exist certain resonant frequencies at which driven oscillations will increase in amplitude and undriven frequencies will \"sustain\" for a long time. At non-resonant frequencies, driven oscillations will be attenuated, and undriven oscillations will die out relatively quickly.",
"We can approximate a sinusoidal driving source by one vibrating string, though we know that a plucked string will eventually decay as it gives its energy up to other parts of the system and the outside world.",
"If we allow some amount of time for our driving source to excite the instrument and suddenly turn it off... resonant components of the instrument such as a sympathetic string (with a resonant frequency equal to some harmonic of the driving source) will continue to vibrate, and oscillations in components which do not have resonances near the driven frequency will decay quickly.",
"In reality, we \"turn down\" the amplitude of the \"driving oscillation\" over some time as the \"driving string\" vibration decays after plucking (because, again, it has transferred its energy to the outside world, or other parts of the system).",
"In reality, We have transferred energy from the \"pluck\" to the environment over the course of some time, and the vibrating string is only an intermediate pseudo-driver that sits between the \"pluck\" and the rest of the system."
] |
[
"To clarify: \"sympathetic vibrations\" are oscillations which are exited indirectly by our driver (probably through elements which are not themselves highly resonant, and which will not to continue to resonate long after the source is turned off), and can continue to resonate after the source is turned off."
] |
[
"Why are suicide rates rising despite all kinds of new anti-depressants and therapies?"
] |
[
false
] | null |
[
"It'd be a good time to point out that that is the way all medicine is practiced. Are you at a risk of a heart attack or stroke? Let's proscribe you some anticoagulants, like heparin or warfarin. If we have a hard time maintaining the numbers we want with warfarin, go back to heparin... ",
"People's bodies are complex, and react to drugs differently. It'd be silly to think that mental illness treatment is any different than \"regular\" illness. The only real difference is that instead of measuring your insulin response or your clotting, you're measuring \"how the patient feels.\""
] |
[
"I don't believe that suicide rates ",
" rising. ",
"According to these OECD data",
", suicide rates have remained fairly steady. You would expect an increase in the ",
" of suicide as the population increases. It is still interesting to speculate about why suicide did not decrease as our antidepressants got better, but I do not have enough background to post my speculations here. "
] |
[
"Same goes with somatic medicine. Knowledge of aetiology is not necessary in order to treat an illness."
] |
[
"What is the ‘curvature of spacetime?’"
] |
[
false
] |
In General Relativity, gravity is the curvature of space time, and it makes sense to me how objects can move as a result of the curvature of space, but I’m having a hard time (hah) seeing how time gets into the picture. Specifically, what does it mean to say that time ‘curves’? Curviness is a spatial property, by definition. Is it a metaphor for something deeper? Or am I totally missing the point of general relativity?
|
[
"Curviness is a spatial property, by definition.",
"No, it doesn't have to. Mathematicians have more general definitions of curvature. You could call it \"deformation of spacetime\" if you like.",
"Take a flexible cube, where places of equal height mean things happen at the same time and left/right/forward/backward is regular space (so one dimension is time and two are space). Now squeeze the cube in some irregular way. Suddenly things that were at the same time before are not, what was an equal time difference before can now be very different, and so on.",
"It is difficult to imagine a third spatial dimension in addition, and the analogy is not perfect, but that's how spacetime can be distorted."
] |
[
"Curviness is a spatial property, by definition",
"This thought comes from our oldest and most fundamental understanding of geometry, which was formulated in large part by Euclid. You might have ever heard the term \"Euclidean Geometry\" or \"Euclidean Space\". At the time of its creation, it was an attempt to describe what space is as we (humans) understand it. Because of its intuitive nature, we are often taught about mathematics using exclusively euclidean geometry. That is, we are taught that space is \"flat\". That you can draw a nice neat grid of evenly spaced boxes, and that the parallel postulate holds. You've probably heard the parallel postulate many times, and it is certainly intuitive to you and to everyone. The idea that you can have parallel lines, so long as they can be joined by a straight line at right angles to both.",
"But one of the goals of mathematics is to generalize our understanding to be more useful. Just as we developed generalizations on the \"size\" of space (generalizing to 4, 5 and even infinite dimensional space), and the \"behavior\" of space (such as the creation of complex numbers), we began to develop generalizations of the \"shape\" of space. And so, after thousands of years of accepting that space is \"flat\" and euclidean, in the 19th century we mathematicians started to contemplate what happens if we relax the parallel postulate. This led to the development of non-euclidean geometries. Spaces that were no longer \"flat\" (that is, the idea of space being a nice evenly spaced grid was gotten rid of). Riemann and others continued to expand upon the ideas, creating the fields of differential and riemannian geometry. The study of not just curved objects in a flat space, but now the study of a space that is itself curved (and perhaps, continuing to deform!). ",
"Here are some pictures comparing them.",
" Remember, the idea is that *space itself* is curved in these diagrams. NOT that these are curved objects. This means that, doing mathematics and drawing \"straight lines\", is different. The generalized term for \"straight lines\" by the way, is ",
"geodesic",
")",
"It was the development of riemannian geometry that almost directly led to einstein's development of general relativity. As it enabled gravity (a previously poorly understood force) to be completely reframed not as a force, but rather as an emergent behavior, coming directly from the curvature of spacetime.Without getting into the mathematics of it all (which, I'll admit. I do not fully understand... at least at this point in my career!), the fundamental idea is this:",
"Einstein started with Newton's first law: that objects in motion tend to stay in motion unless acted upon by an outside force. But he now generalized this motion to not only be through \"space\" but also through time. He unified the two concepts into a single structure he called \"spacetime\". The idea was critical to the development of special relativity. the idea being that all objects are always traveling at c ( the speed of light) through spacetime. Thinking this way leads naturally to the understanding that the faster you move through space, the slower you move through time, and vice versa (as the magnitude of your motion through spacetime must remain constant). With this understanding, you can actually derive the ",
"lorentz transforms using only pythagorean's theorem",
"! But he noted this only worked in \"flat\" space, with uniform motion (That is, no acceleration of any kind). It was a \"special case\" (hence the name, special relativity!)",
"But the next step, was the generalization of the idea of spacetime (thus creating the theory of \"general relativity\"). The primary idea we're concerned with, is what happens if the space you are traveling in is no longer flat. Newton's first law must still hold. You must travel in a straight line unless acted upon by an outside force. But what does a straight line (geodesic) look like, if space is curved? And what does it mean for time to be involved?",
"Imagine for a moment that two objects sit at perfect rest with respect to one another, in a flat spacetime. Then the arrows of their velocity are wholly in the direction of time. That is, time passes, and they just sit there next to eachother, never drifting apart of getting closer. Now imagine that one of the objects deforms spacetime around it. Even though both objects start stationary with respect to one another, there arrows are now no longer wholly in the direction of time. There is a space component to them now. So even though they are still moving at the same speed as the first scenario, they are no no longer moving exclusively in the time direction, but are now actually moving through space towards one another! And this curvature continues to redirect more and more of their spacetime velocity from the time direction to the space direction, so they are (from an observers perspective) accelerating.",
"To be clear, I've oversimplified a bit here. Partially due to not being an expert in this particular topic (so if anyone has input or corrections, please feel free!), but also to avoid diving too deep into the weeds. For a visualization, ",
"I think this video actually does a great job!",
" The whole video is decent, but the most relevant part to your question starts at around the 16 minute mark."
] |
[
"They don't get applied to time, but to ",
". Time for any given observer is defined by choosing a certain direction within that 4-dimensional non-Euclidean space, with distances along the time axis measured in metres via",
"x",
" = c·t"
] |
[
"When did humans start to cook their food?"
] |
[
false
] |
And why? Obviously we can survive without cooking meats, but now most people (in the US) have only had raw meat a handful of times, if ever. What sparked this change?
|
[
"https://www.google.com/search?hl=en&site=&q=when+did+humans+start+to+cook+their+food&oq=when+did+humans+start+to+cook&aq=1v&aqi=g-v2g-j2&aql=&gs_sm=e&gs_upl=543l6069l0l7398l29l25l0l1l1l0l363l4070l2.17.3.2l24l0"
] |
[
"We can survive without cooking ",
" meats, many however cause illness and seeing how it was long in the past, almost certain death. Most people stayed in one area so they only really had access to a few types of meat, so they couldn't get meat that they could eat raw. Also, they had very little sanitation, so raw meat likely had extra bacteria also assuring it would harm them. I assume most tribes begin cooking their meats when people begin dying when they didn't. Not sure of an exact time, but I imagine it's very soon after mankind began eating meat at all."
] |
[
"There is some evidence that suggest that we have been cooking food prior to even being human, with Homo Erectus (learned this in arch but here is the wikipedia on them ",
"http://en.wikipedia.org/wiki/Homo_erectus",
" )",
"look at 'use of fire' and 'sociality' in sociality it suggests that they were believed to have a basic hunter-gather (which more than suggests they cooked meat) also at this time you see a major shift in eating patterns from mostly vegetables to mostly meat "
] |
[
"How often do new craters appear on the moon?"
] |
[
false
] | null |
[
"I don't know if the results of the Lunar Impact Monitoring study have been published yet, but they've spent much of the past two decades observing the near side of the Moon when it's over halfway in shadow to try to guess the rate of impacts. Because the lower end of impact velocities is still outrageously high, each impact above a certain small size makes a detectable flash.",
"https://www.nasa.gov/centers/marshall/news/lunar/overview.html",
"A large impact would be pretty noticeable and they're exceedingly rare these days. We can tell how recent a crater is by the brightness of its \"rays,\" the wispy arms of ejecta that radiate out from a large impact. Two of the most recent large ones are Tycho and Giordano Bruno. Tycho is thought to be 100 million years old. It was once thought that Giordano Bruno might have actually been witnessed in 1178 by Canterbury monks, but now it seems more likely it happened around 4 million years ago. Things move slow up there, these days, so it's hard to tell.",
"https://en.wikipedia.org/wiki/Tycho_(lunar_crater)",
")",
"https://en.wikipedia.org/wiki/Giordano\\_Bruno\\_(crater)"
] |
[
"Quite frequently, like every day.",
" ",
" ",
"Source",
"So, in less than 4 years, and by looking at 1/15 of the lunar surface, they detected 222 craters larger than 10 m across. Extrapolating a bit, that's 222 x 15 / 4 = 832 new craters/year, ",
" across the whole lunar surface."
] |
[
"I'd like to add that many planetary scientists would consider the moon a planetary body, and one of the criteria is having cleared its orbit / path of debris."
] |
[
"Are the “good” neurotransmitters produced when we exercise caused by the physical act itself, or the feeling of accomplishment from achievement?"
] |
[
false
] |
I apologize if this is an ignorant question/if I used the wrong label, but everyone is telling me to exercise to beat my depression (no worries I’m very happy and on meds). They always cite “endorphins!!” - I feel happier immediately after I finish exercising, but I also notice that more than anything I’m just proud of myself for the accomplishment. Does that have any bearing on the “happy chemicals” production, or is it all from the physical exertion?
|
[
"This question really has two parts, and I think you're mixing things up a little.",
"One side effect of running, or any other vigorous aerobic exercise, is that your body will release endorphins. Endorphins are a class of endogenous opiods. When opiods bind to opioid receptors in the in the ventral tegmental area of the brain, they cause in increase in dopamine activity, a neurotransmitter that, among other things, plays a role in reward. This increase in dopamine can produce \"high\" or a \"euphoria\". Other drugs that increase dopamine activity are cocaine, amphetamines, and nicotine. So ",
", endorphins can make you feel good.",
", they will ",
" treat depression. As I'm sure you know, depression is more than just feeling sad, and so just making someone feel \"happy\" often won't do anything to help it. Many theories of depression have to do with reduced serotonin in the hippocampus, and almost every single antidepressant increases serotonin, but has no effect on dopamine. The only antidepressant that I can think of that directly targets dopamine is bupropion, more commonly known as Wellbutrin or Zyban.",
"It is true however that exercise tends to help with depression, but I don't know why. It's easy to make up reasons, but I have yet to see clear evidence for anything. "
] |
[
"That makes a lot of sense actually, and yes, I always wondered why people were connecting depression to it because I know my medication is an SSRI, as are many others. Thank you so much for the thoughtful response and taking the time to sort it out, I really appreciate it!! "
] |
[
"I thought that one of (not saying it is THE) the mechanisms involved is increased BDNF production after excercising. \nA quick google search gives quite a few hits but I doubt one conclusive answer will be given.\nA friend of mine finished her thesis on how depression comes to be and focussed in particular on the neurogenesis theory, she told me something interesting which I didn't know: Depending on the type of depression (manic, major etc. ) different treatments had varying amounts of effectiveness."
] |
[
"Anthropology/History question: Is there a documented shift from polytheism to monotheism throughout the 'evolution' of a civilization? If so, what would cause this shift?"
] |
[
false
] |
I'm wondering how and if the Romans abandoned their plethora of gods. Or the Japanese, their multitude of spirits like Amaterasu (and other Shinto deities). Or the Vikings, their Norse gods. How does this shift happen, and what contributes to the persistence of widescale polytheism, for example Hinduism? Is it inevitable except for special circumstances?
|
[
"Not qualified to speak about the others, but the Romans started to abandon their plethora of gods roughly when Constantine converted to Christianity and, in the years following, he and his successors outlawed pagan religions and made Christianity the official religion.",
"See here."
] |
[
"They all converted to Christianity. Sample size = 1"
] |
[
"This isn't related directly to your question, but to something you said. This is my first post on ",
"/r/AskScience",
" so sorry if I'm breaking any rules.",
"Hinduism isn't a polytheistic religion. It is actually monotheistic. While it does have a large pantheon of deities, all of those deities are just different manifestations of the true God that remains behind the scenes. ",
"I THINK that this \"God\" is basically a timeless, formless energy that manifests itself through all things. I believe that the correct term is \"Brahman\" though I may be confused since I'm not terribly knowledgeable in Hinduism. It can get even more confusing because the priestly class, iirc, were (and potentially still are, though I'm not totally sure) referred to as Brahman as well. There is also a creator deity named Brahma in the Hindu religion.",
"It is quite interesting, but I fear that I am not nearly as up to date on the topic as I'd like to be. I hope I was able to help some despite not directly answering your question."
] |
[
"Why are Newton's formulas considered laws, and Einsteins formulas considered theories?"
] |
[
false
] |
Einstein created the "theory of relativity". Newton however, made "laws". How are the two different?
|
[
"Perhaps contrary to the usage of \"theory\" and \"law\" in general language, \"theory\" is really the stronger term in science, a theory is more complete.",
"As I understand it, a law is an observation, an expectation. We see something happen so we write it down and we expect if we do the same thing over and over then we will get the same result. ",
"A theory is more complex, often with many constituent parts, it aims not just to say what will happen but how and why. It doesn't just predict an observation but provides some accountability of why that result is expected and on what to expect from observations that have never been made. It links previously distinct observations under one governing explanation.",
"Your specific example is perfect, Newton's 3 laws summarise things that were observed to be a truth of nature. We could tell that if you push two different mass objects with the same force then they accelerate at different rates. The whole body of these three laws can be expressed in 3 sentences.",
"On the other hand the theories of relativity are very complex and provide predictive capacity far beyond any of newton's law. Things like time dilation, gravitational lensing were not observed and not expected by anyone until they were recognised as consequences of a broad theory.",
"Hope that helps a little."
] |
[
"Thank you! Very clear and descriptive answer."
] |
[
"A law is a description that, under normal circumstances, can always be reproduced. Like the OP mentioned it does not try to explain, \"why\" and merely concerns itself with, \"what.\"",
"A theory not only goes a step further and explores, \"why\" but there is one more caveat: A theory has never been disproven. As soon as it has been disproven then a new theory will likely take its place. ",
"Laws on the other hand are different. Under very highly specialized conditions (e.g. the big bang) laws begin to break down, or can be \"broken\" -- but this doesn't invalidate the law and a new law doesn't take its place. "
] |
[
"Does an insect, like a fly or a mosquito, have itches?"
] |
[
false
] | null |
[
"Yes, if their exoskeleton gets irritated. (Itch: An uncomfortable, irritating sensation that creates an urge to scratch that can involve any part of the body.) For example, put a drop of formic acid on a cockroach's abdomen, and it will rub the area with its legs to clean it as it's irritated."
] |
[
"How extensive is the nerve system in the exoskeleton itself? I was under the impression that it was just made of (nonliving) chitin."
] |
[
"Well it's comes down to how insects breath. So in a way what gets irritated is the tubes throughout their body called trachea."
] |
[
"If no two particles can occupy the same space and the center of a black hole has infinite density, do particles at the center of a black hole get infinitesimally close, infinitesimally small, or both?"
] |
[
false
] | null |
[
"Actually, it's not true that no two particles can occupy the same space. The statement is that no two ",
" can occupy the same quantum ",
". This is called the Pauli exclusion principle and is the effect that creates electron and neutron degeneracy in white dwarfs and neutron stars respectively. Specifically, this effect results in a finite outward pressure when you try to compress the fermions into a suitably small region.",
"In the first instance, the Pauli exclusion principle prevents objects of insufficient mass from being compressed beyond a certain level due to the action of the Pauli exclusion principle on the electrons in the atomic orbitals of the atoms out of which that object is composed.",
"However, if the object has sufficient mass (about 1.44 solar masses; the ",
"Chandrasekhar limit",
"), the potential energy of the material is such that inverse beta decay is favored and the electrons are captured by the protons in the matter to form excess neutrons. The drop in electron number results in a thousand-fold reduction in volume until you reach a point where the Pauli exclusion principle becomes relevant for the ",
".",
"Now, if the mass is again sufficiently high (in this case the ",
"TOV limit",
"), then the neutron degeneracy pressure is also insufficient to prevent further collapse. We're not sure exactly what happens to the matter after this point, but we don't know of any other degeneracies that could prevent continuous collapse (there's some slightly-better-than-speculation about quark degeneracy, but we just don't know enough about the physics of these sorts of events to really say). In any case, you've now compressed the object inside the event horizon, so it really doesn't ",
" what it's made of."
] |
[
"If you could answer that and related questions, you would have offers from every research body and university in the world within the week."
] |
[
"Since no information can escape a black hole",
" we can't really be certain. I don't think its constructive to think of objects existing within a black hole. Are you familiar with objects being stretched as they approach a black hole? Basically, the gravity well grabs one end of the object more strongly than another, and accelerates one end faster. This causes the object to stretch out. What effect this has on protons and smaller particles is still a mystery.",
"*You can measure the mass, charge, and spin of a black hole based on how particles outside the even horizon behave. Hawkings radiation also transfers some information about the black hole as a whole (get it?). Hawkings radiation has be proven to exist, but not directly observed so we don't know exactly what information it will contain. It is believed (and debated) that once matter enters a black hole, there's no way to tell what it originally was."
] |
[
"Which side of the \"health vs weight\" debate has the greatest amount of supporting evidence?"
] |
[
false
] |
As I understand it the two opposed views are as follows: Health and weight are not causally linked, and many people who are very overweight are very healthy. Health and weight are causally linked; excess weight is a health risk, and causes health risks in its own right. If I am oversimplifying please correct me as I'm basically paraphrasing what I've heard from various people.
|
[
"It's reserve. You have a certain capacity for stress on your body before physiology becomes pathology, and it's both cumulative and synergistic.",
"Say you have a bridge. It gets a lot of traffic. It is also subjected to high winds frequently. It hasn't been inspected in a while. There was an earthquake a few years back, and the damage was never properly repaired. It's in the narrow neck of a bay, so it gets subjected to a lot of tidal rush. There are also a lot of storms in the area, so it gets splashed with salt spray a lot. It doesn't get repainted as often as it should.",
"One day, it collapses. What caused the collapse?",
"There are a lot of bridges that get lots of traffic, so it can't be that. Lots of bridges that get high winds, so it can't be that. Lots of bridges that miss inspections, get damaged, miss a repainting or two, etc....so it can't be those, either. Right? ",
"Of course it was no one of those things, it was the combination. Some are related...the quake damage, the inspections, the paint...all related. Storms and wind and tide again, related. Knock out any one or two of the big ones and the bridge would probably still be OK. But even then...quake damage is bad. Missing inspections is bad. Storm damage is bad. You need to keep an eye on high traffic. All of these things need to be addressed, even if they are not direct, independent killers right now....because they can be. Because they eat at the bridge's reserve.",
"Your body is the same way. being overweight puts a lot of stress on your body, just like that bridge. Your genes may be good, you may not have gotten that one infection, you may not live in a highly polluted area, you may be overweight, but not have high triglycerides, cholesterol, blood pressure, whatever. ",
"But that doesn't mean that being overweight is ",
", it just means that the person hasn't reached their reserve yet. You're still better off losing the weight than not, generally. I'm not talking about being a svelte Adonis here, just not highly overweight."
] |
[
"\"Reserve\" is a general term used in a lot of organ systems, usually applied to single organs or organ systems. Here, I'm applying it more broadly. An example would help, I think. Pulmonary reserve is probably the easiest to understand.",
"Assuming you are an adult male, sitting in front of your computer (playing the odds here), you are moving ~8-10L/min of air through your lungs. Of course, you have the ability to move a ",
" more than that. ",
"Say something happens and you need more air. You'll start to breathe more deeply and rapidly....resting tidal volume is ~0.5L; that is, you move about 0.5L of air per breath. Take a deep breath and you can ramp that up 5, 6, or 7 times (it varies). ",
"Say whatever it is that made you need more air puts a greater demand on you that is keeps up, gets worse. You breathe more deeply, faster...resting breathing rate is ~15-20 breaths/min. You can go as high as 50 or more, though (again, it varies). So sitting still, you move 8-10L/min, but if you need to, you can move hundreds of liters per minute, thousands even. ",
"This difference between resting and maximal is your reserve. ",
"But what is generating that need for more air? Are you going for a run? Having an asthma attack? Nervous about something? Do you have emphysema (lung disease)? Did you just bolt up the steps? Do you have fluid in your lungs because of your heart condition? Did something you read suddenly make you uncomfortably aware of your breathing?",
"Any of those tap into that reserve, and if you have emphysema, you can't run so much before you max out your reserve*, because the disease state has shifted your resting up; you aren't always running up the stairs, but you do always have emphysema. That tax on your reserve is always there.",
"You have the same thing in your heart, blood vessels, immune system, renal system, musculature, etc. This is normally only discussed in terms of a single system, but you often tap several of them at once (go for a run and you tap renal reserves, thermal reserves, cardiac reserves, pulmonary reserves, muscular reserves, and more). Being overweight taps into a lot of these system reserves as a constant state by moving that resting state up, so it's a big risk factor. ",
"By moving your resting needs up with a host of \"always there\" kind of things (like being overweight), you close the window on your reserve, just like the bridge that was weakened by years of neglect.",
"*there is the added issue that some diseases can affect the parameters of your reserve; like you can't breathe as fast anymore, or as deeply anymore, or as efficiently anymore because of the disease...but I left this as a footnote because it's not critical to your understanding of the concept."
] |
[
"But that doesn't mean that being overweight is healthy, it just means that the person hasn't reached their reserve yet. ",
"Be very careful with your terms here! ",
"I think what the OP might be getting at is that this ",
" necessarily true for the classic BMI definition of \"overweight\". Within the \"overweight\" range (say a 6' tall, 200lb man, overweight by BMI standards) a person can have quite good muscle mass, so that losing the \"weight\" equates to losing muscle and increases stress, or can have more fat, which would be good to lose. ",
"Again, it's likely that more people at that height/weight are on the fat rather than muscle side, so from a public health perspective it's the right message. But in terms of the science of individuals, one can improve health by losing the fat, ",
" by \"converting\" it to muscle, heart condition, aerobic fitness while staying at the same weight.",
"If by \"overweight\" you're speaking generally and including the \"obese\" category, you're more on target. "
] |
[
"Is it fair to compare ingesting an amount of food emitting 100 Bq/kg of K-40 to the same amount of food emitting 100 Bq/kg of Cs-137, I-131 or Sr-90 in terms of the biological effects of their decay?"
] |
[
false
] |
What I'm trying to ask: is each Bq the same as each Sv being the same (a weighted dose), regardless of their source? Is a Bq of K-40 as "dangerous" as a Bq of any other radioactive isotope. If not, how are the "dangers" of each source of radiation calculated and how do scientists know which isotopes are present in a sample and in which distribution. Sorry if this is gibberish, I probably have a lot of misconceptions on the subject.
|
[
"No. Different elements will have an affinity for different parts of the body. They also have different half-lives and decay energy. But perhaps most importantly, they all have different ",
" half-lives, which is the amount of time they stay in the body.",
"This is taken into account in radiation protection models via the use of \"committed dose.\" This is the dose, in Sv, that will be received over a period of time after ingesting X amount of some nuclide. So each isotope has its own annual limit of intake. ",
"This site",
" has more info. I can edit my post with the limits of the isotopes you mentioned, if you are interested. I just need to find the textbook that has them.",
"edit: (All numbers in Bq, from Turner, ",
") ",
"Sr-90 has an annual limit of 4x10",
" inhalation, 6x10",
" ingestion. ",
"I-131 has an annual limit of 1x10",
" inhalation, 8x10",
" ingestion. ",
"Cs-137 has an annual limit of 2x10",
" inhalation, 1x10",
" ingestion. ",
"Also, to elaborate a bit more on committed dose. An amount of radionuclide is often measured in Bqs - this is the rate at which atoms in the sample are decaying. If we are exposed to an external source, then the decay rate is proportional to the dose rate. But for ingestion, we aren't just taking in atoms that are decaying. We are also taking in atoms that have yet to decay, but will. So the important quantity is how much dose will be absorbed over the entire residence time of that isotope in the body.",
"edit #2: But once we convert the ingested amount to effective dose (or committed dose), then the \"danger\" per Sv will be equivalent. 100 mSv of internal exposure from K-40 is equivalent to 100 mSv of internal exposure from Cs-137."
] |
[
"But once we convert the ingested amount to effective dose (or committed dose), then the \"danger\" per Sv will be equivalent. 100 mSv of internal exposure from K-40 is equivalent to 100 mSv of internal exposure from Cs-137.",
"Is there an easy way to do this conversion? I want to be able to say: \"ingesting an x amount of isotope y will result in an exposure of x Sv.\""
] |
[
"The annual limits are set at 20 mSv, so you can back-calculate from there. ",
"ex: 10",
" Bq Cs-137 per 20 mSv, so 0.02 microSv per Bq Cs-137."
] |
[
"Frost on car windows"
] |
[
false
] |
I've always wondered why this is. Why does the frost ice over my windscreen and side windows but not those that are nearest a wall? Can anyone help with this?
|
[
"One of my professors actually had to explain this phenomenon in his doctoral dissertation. Here's how he explained it: ",
"Basically, it has to do with what are called \"view factors\" and black body radiation. All object radiate some of their heat as electromagnetic radiation and this radiation depends on temperature and view factor, which can be though of as line of sight. You've probably noticed that it only happens on clear nights/mornings and never happens if your car is under cover. That's because the car effectively \"sees\" the coldness of space (as long as it has clear line of sight) and becomes much colder than it normally would due to a greater driving force. This coupled with its limited contact surface with any other matter (except for well-insulated tires and air, which don't conduct very well) results in it losing more thermal energy than it can gain until it reaches an equilibrium much colder than, say, the grass or the pavement. Because it gets so cold, it \"pulls\" the energy from the water droplets that form and freezes them. This is also why you sometimes find frost on your car even though the overnight low didn't drop below freezing.",
"The side of your car facing the wall probably doesn't have a view of the sky and therefore no frost forms.",
"There are probably other factors at play and an expert could probably explain it better, but that's my understanding of it."
] |
[
"An explanation that doesn't require \"seeing:\"",
"The car emits radiative heat in all directions, as do all objects. The wall emits radiative heat as well, which counteracts the heat radiation from the car towards the wall. The wall and the car trade heat all night, while the car additionally radiates heat into space. Because objects in space are few and far between, as well as far away from us, little to no heat radiates back from space, and the car cools down on the side pointing to space (up, and to any sides without a large object nearby).",
"A carport would radiate heat just like a wall, preventing frosting due to heat loss."
] |
[
"I own a carport and so far (-20° Celcius) no frost on the windshield."
] |
[
"What is the origin of the word \"moment\" in physics? [x-post from r/AskReddit/]"
] |
[
false
] |
The word "moment" in mechanics roughly means how a quantity acts about a given point. For example: "moment of force" (usually just "moment")---how a force acts about a pivot point, "moment of inertia"---how a body's mass is distributed about its center of mass, "moment of momentum" (usually just "angular momentum")---the linear momentum measured relative to a specified point. After much searching, the closest I've come to finding an origin is from the OED: "moment of a balance" n. [after post-classical Latin momentum staterae small weight or counterweight (Vulgate, corresponding to Hellenistic Greek ῥοπή small weight or counterweight (Septuagint); the Hebrew text has šaḥaq dust), misinterpreted in glosses (8th cent. or earlier) as denoting the tongue of a balance] the tongue of a balance. Obs. Any ideas?
|
[
"I came across this explanation in my search, but I don't quite find it satisfying---partly because we already use momentum to mean something completely different. Also, the use of moment always suggests how something acts (or moves) relative to a given point; I'm curious how \"to move\" became \"to move about a given point\"."
] |
[
"A moment is really caused by abstractly moving a force to a new location and replacing it with a force and a moment. That is, a force of 1 N that is 1 m away is equivalent to a force applying 1 N and a moment (a moved force) of 1 Nm here."
] |
[
"Just to clarify: I don't think that knowing the etymology of the word moment (for this context) will help me understand the physical concept any better (this isn't actually a problem). I'm just really curious how this word came to be used this way (either by logic or historical accident or some other rationale)."
] |
[
"How close are we to Digital Immortality? What research is being done on this front?"
] |
[
false
] |
I was reading some articles; first on our radio bubble, then on our attempts to contact life, then on artificial intelligence, then on mind upload... (the old Wikipedia link trail) and I couldn't help but fantasize about a future in my lifetime where anyone with enough money can have their mind digitized and preserved. Is this at all feasible in the near future? How would such a process exist? That is, would we be able to interact with our digital mind? Would it be able to control our body given the proper control systems? Given advances in tissue regeneration and lab-grown organs, could we possibly live forever with a digital mind? I know a lot of this seems like science fiction, but is it really?
|
[
"I think right now it's completely science fiction. Despite popular comparisons, our brains do not work like computers, and our brains are not digital. Right now we understand relatively little about how our brain creates the mind, and thinking about how you would encode a mind into digital logic seems pretty far off. I personally believe, but this is not a scientific claim, that we won't ever be able to fully digitize simply because you really cannot draw a line between your body and your mind."
] |
[
"We've learned a lot in the last 20 years of research, but there is SO MUCH MORE to figure out that to me the idea that we can completely understand the brain within our lifetimes seems a little difficult. The idea of completely mapping the brain is a little farfetched right now- it's just too complex to really even consider it right now. While we will eventually get there, it's going to take a long time. The complexity is just pretty absurd- you want to map the connections between 100 billion neurons, each that can have up to tens of thousands of connections with other neurons. Except each of these connections by themselves are extremely complex- they have extremely dynamic properties affected by multiple factors, and so you will have to take into account things like the what kind of neurotransmitters at each synapse, the number of vescles, the quantal content in each vesicle, the release probabilities, and the fact that all of these can change extremely quickly. People spend their entire lives just trying to research the properties of a few of these connections and the circuits they are in. But just mapping the connections are not enough; the brain is not a virtual system of bits in a computer, you also have to take into account things like electrical synapses between neurons, ephaptic coupling and local electric field potentials that modulate neuronal activity and how they encode information. Now once you have all these connections, realize that each neuron performs computations on these connections it received- these computations are affected by the dendritic morphology, the 3-dimentional structure which changes the electronic properties with which connections are integrated. Except it's not purely structural- the distribution of ion channels, particularly active conductances can change how these inputs are summed in both a spatial and temporal manner. And all this I've mentioned so far is on the scale of single or several neurons- what happens when you have to compute all these for billions of neurons connected together? And if you simplify any of it, you most certainly are not going to get a faithful reflection of the mind or memories.",
"Maybe I'm just pessimistic, but it seems the more I learn about the brain, the more I realize how mind-blowingly complex the brain is."
] |
[
"That's kind of what we mean by mapping- tracking all the connections neurons are making to each other and such. If you can simulate the entire brain completely, then there would be no issue (although you still have to map all the neurons if you are going to encode it in silico). But right now the pure amount of complexity is so far beyond our ability to comprehend or measure, let alone simulate that it becomes difficult. Computations with biological things are still problematic; people are still having trouble even physically modelling a single protein fold, now try scaling that up trillions and trillions of times."
] |
[
"Does seawater become denser as you get deeper? Is this change in density independent of the temperature change?"
] |
[
false
] |
[deleted]
|
[
"Another submariner here. In the real world the density of ocean water at different depths can vary greatly but mostly due to reasons other than depth. Water temperature and salinity are what would cause most of the density differences. "
] |
[
"If I had a 1000 meter tall column of water (or any fluid), all at the same temperature, physical conditions, with only pressure changing, would the fluid become denser as I got to the bottom of the column?",
"Yes it would. Water has a low compressibility, but it is compressible, so density would increase with pressure, which increases with depth.",
"There are a few things that influence the density of seawater, including salinity, temperature and depth. If you take these factors singly, then salinity has the greatest effect on seawater density, meaning the reason why seawater is so much denser than tap water sitting on your desk is because of all the salts dissolved in the seawater.",
"In practical terms, if you're looking for causes of density differentials that actually cause ocean currents or the movement of water up and the down the column, then temperature is the number one cause.",
"The reason is that although salinity has the greater effect in absolute terms, in relative terms salinity isn't very variable in seawater, going from about 32 ppt to 37 ppt. This small variation doesn't produce a huge difference in density.",
"Compare that to temperature, which can vary by 30 degrees over the water column. This has a much larger effect on density than the small salinity variation. This is why you can often find a layer of high salinity warm water on top of low salinity colder water. Normally, you would expect high salinity to be denser and therefore at the bottom, but the big difference in temperature (warmed by the sun at the top, cold below) inverts this relationship.",
"If you are interested, it's easy to calculate pressure based density changes in your example. Pressure increases by about 1 atmosphere per 10 meters. At the bottom of your column, the pressure is 100 atmospheres. The compressibility of water is about 46.4 ppm per atm, so at the bottom of the column, 1 cubic meter of water would compress to 0.9954 cubic meters. As a result, if your column were freshwater with a density of 1g/cc at the top, then at the bottom the density would be 1.004 g/cc. That's a pretty tiny change.",
"Compare that to salinity. The average ocean water salinity is about 35000 ppm. So if you keep temperature and pressure constant, just the increase in salinity increases the density by a factor of 1.028, which is a 7 times stronger effect than pressure.",
"Now you could get some pretty big numbers if you went deeper. At the bottom of the Challenger Deep, the deepest known spot in the ocean, the pressure is about 1100 atmospheres. Here the density of water would increase by a factor of 1.054, which is twice the variation caused by salinity.",
"But you have to remember, density variation with pressure is not a dynamic for water movement, because it's a constant relationship - the deeper you go the more pressure there will be. If pressure was the only source of density variation, there would be no density based water movement at all."
] |
[
"Because their internal pressure is the same as the pressure of the water outside.",
"In physical terms, pressure doesn't do much, it's pressure differentials that hurt. If you were to tie a chunk of steak to a heavy weight and drop it off the side of your boat over the deepest spot in the ocean, nothing much would happen to it from pressure. If you could follow it down all the way to the bottom in a submarine, it would look pretty much like it did up top on the boat.",
"This is because meat is made solids and water, and is barely compressible. As it sinks down, the water pushes harder against it, but it has no \"give\" so it pushes right back. The steak and the water remain at equilibrium.",
"The problem for humans is that we aren't all meat and bones, we have lungs too. Lungs are big sacs filled with atmospheric pressure air. Unlike meat, air is a gas and therefore highly compressible. So when the water starts pushing harder against the chest, the air in the lungs will get compressed, and the lungs will get smaller. At large depths, they would compress to pea-sized or smaller, but are prevented from doing so by the rib cage, which has a limit to how much it will allow the chest to contract. So the pressure would snap the ribs and crush the rib cage. Note that this is not a problem for arm bones or leg bones or any other bones, because they're not enclosing an air filled cavity.",
"Mammals such as sperm whales that dive very deep have ribs hinged in a different way, allowing them to collapse as far as needed to squeeze the lungs appropriately for whatever depth they reach. Fish have no lungs, but some have swim bladders which are also air filled sacs. For this reason, fish also prefer a certain depth and don't go too far up or down the water column, staying within the region they're adapted to. If you brought a deep water fish up to the surface, you would find evidence of pressure injury, as its swim bladder expanded. If sudden and severe enough, the fish could explode.",
"Some fish have no swim bladder. Mollusks like squid don't either, and they travel quite far up and down the water column routinely.",
"These are the physical problems of pressure. There are also chemical problems. For example, gases dissolve more easily in blood and tissues at high pressure. All animals use oxygen and excrete carbon dioxide, which are gases. So if humans swam down too deep (breathing pressurized air from a scuba tank so their lungs don't collapse), they would run into problems. Nitrogen would dissolve in the blood and also in fatty tissue such as nerve sheaths, and cause the bends when the diver comes up. You can replace nitrogen with other gases such as helium to prevent that. But too much oxygen would dissolve in blood too, making it oxygen rich and causing oxygen narcosis. You can fix that by using a lower ratio of oxygen in the scuba tank.than in the atmosphere. There are other such problems which get progressively more severe the deeper you go, so there comes a limit.",
"Whales that dive deep have millions of years of evolutionary adaptations to counter these problems. But they still have their limits, couple thousand meters or so. Fish are adapted for certain depths, and if they stay within the range they are adapted for, they are fine. But they can't generally leave that region and go up or down too far without suffering ill effects.",
"In the very deepest ocean trenches, pressure starts to physically alter bodies at the molecular level - changing the conformation of proteins, how they fold. Critters that live at these depths (about 7km or deeper) have special adaptations for that. Some have variants of proteins that can produce a functional 3D structure at depths where the regular version of the protein wouldn't. There are probably many other such adaptations we know nothing about.",
"So in short, pressure doesn't kill, pressure differentials do. Any animals with air sacs can't tolerate a large pressure differential between the air in the sac and the water outside. Specially not if that air sac is protected by rigid bones that will snap if they don't give to the pressure. Such organisms stay within a range where the pressure differential they can tolerate is not exceeded.",
"Depth also brings unique problems in things such as gas exchange or protein conformation or enzyme activity, but an organism can adapt to it. To the life living at the bottom of the sea, we are the weird ones, adapted to live at the surface. In evolutionary terms it amounts to the same thing, each evolving to suit it's environment and is safe enough if it stays within it."
] |
[
"Is it possible for a person to change angular momentum while in a vacuum?"
] |
[
false
] |
I have been wondering if this was possible after seeing the movie . If I were in low earth orbit, would I be able to flail my arms/legs around and be able to start spinning?
|
[
"Here's the answer you're looking for straight from the ISS. They even demo it for you. ",
"http://youtu.be/VJcno_XL4RU"
] |
[
"Not unless you exert a torque on something else, e.g. by throwing something or expelling gas with thrusters. Though tidal gravity forces (the difference between the strength of gravity on one side of your body and the gravity on the other side) will exert torque, the effect is extremely small for something as small as a person. (the tidal torque effect is how the moon ended up with one side always facing the earth). Another possibility would be to carry a wheel with you with a motor and you could transfer your spin to it while still holding onto it. ",
"You can change direction without changing your angular momentum though, if you do ",
"something like cats do when they fall",
". "
] |
[
"I can't intuitively think of a way to emulate the effect of the cat righting reflex, but I imagine something like it can be done.",
"Hold your arms out at right angles to your body but your legs together and in line with your torso. Twist and hold the lower half of your body with respect to the upper half. Then bring your arms back in, and spread your legs out, then un-twist.",
"Like the cat righting reflex, because of conservation of both angular and translational momentum, this move overall does not change one's direction of motion or rotation, only one's orientation."
] |
[
"What would happen if you a popped a balloon full of air in space?"
] |
[
false
] |
Assuming that it's possible for a balloon full of air to exist in space.
|
[
"Nothing too special would happen. Balloons can exist in space if the material is tough enough (hey, space shuttles are basically balloons; big containers full of air!). ",
"A standard, everyday party balloon would probably just expand and pop on its own without you needing to prick it with a needle. But other than that, nothing special. ",
"You also would not hear the balloon pop."
] |
[
"if the balloon was strong enough, it could last in space.",
"popping it would let the air escape, and it would then dissipate very quickly"
] |
[
"This would fall under the topic of rarefied gas dynamics... which I am not an expert in. I have a friend who took a gas dynamics qualifying exam who said that the MIT fluid dynamics film on rarefied gas dynamics was really good. The source is ",
"here",
".",
"My understanding on what happens is you get a shockwave coming from the balloon as the gas expands, but the shockwave is significantly thicker than it would be in the atmosphere because it is expanding into a vaccum."
] |
[
"Why do we know that Pi and E are transcendental numbers, but we aren't sure if Pi^pi or e^e are transcendental or algebraic?"
] |
[
false
] |
[deleted]
|
[
"The ",
"Lindemann-Weierstrass theorem",
" has as a corollary that, for any nonzero algebraic number z (which can be complex), e",
" is transcendental. In the reverse direction, this also shows that for any algebraic number z other than 0 and 1, log(z) is also transcendental (otherwise log(z) must be algebraic and e",
"=z must be transcendental, a contradiction).",
"If we plug in z=1, then we get that e",
" = e",
" = e is transcendental.",
"If we plug in z=−1, then we get that log(−1) = iπ is transcendental. Since the transcendental numbers are closed under multiplication by algebraic numbers, we can multiply iπ by −i to get that (−i)iπ = π is transcendental.",
"Note that this theorem ",
" give the converse statement \"for any transcendental number z, e",
" and log(z) are algebraic\" (which is false), nor does it give the statement \"for any transcendental number z, e",
" and log(z) are also transcendental\" (which is also false), so we cannot just plug in z=e and expect Lindemann-Weierstrass to tell us whether e",
" is transcendental or not, and π",
" isn't even of the right form to be used with this theorem! Different techniques would be required to show that either e",
" or π",
" are transcendental, and we lack such techniques at the moment.",
"What we do know is that e",
" and π",
" are transcendental for any nonzero rational p/q, but this follows pretty much directly from e and π themselves being transcendental. Oh, and e",
" is transcendental too, since that's just (−1)",
", where we can apply the ",
"Gelfond-Schneider theorem",
"."
] |
[
"/u/nijiiro",
"'s answer gives specific reasons why we know that π and e are transcendental. ",
"More generally, proving that a number is transcendental is really hard. You have to show that it can't be the root of ",
" polynomial with rational coefficients. Since there are a lot of polynomials, this sort of proof is hard, and we really don't have that many tools for it, although the other answer has one.",
"Somewhat paradoxically, it's fairly easy to show that in a certain technical sense, most real numbers are transcendental. It's also very easy to cook up examples of numbers that are obviously transcendental, like ",
"Liouville's constant",
". However, if you have some real number whose definition doesn't obviously have anything to do with not being the root of a polynomial (which describes lots of real numbers we care about, like π, e, the ",
"Euler-Mascheroni constant",
", and so on), then it's pretty hard to prove it's transcendental."
] |
[
"/u/nijiiro",
" gives a nice answer. I just wanted to take the opportunity to plug a similar fact which is easy to prove and a bit surprising. It is unknown whether e+pi or e*pi are rational or irrational. However, we do know that if one of them is rational, the other must be irrational. How? Consider the polynomial given by P(x)=(x-pi)(x-e). Clearly this has roots at pi and e. We can rewrite P(x)=x",
" - (e + pi)x + e*pi, so we have that P(x) has coefficients 1, -(e+pi), e*pi. Since P(x) has transcendental numbers as roots, its coefficients must not be all rational (this follows directly from the definition of a transcendental number). So at least one of 1, e+pi, and e*pi is irrational. "
] |
[
"AskScience AMA Series: I'm Nestor Espinoza, and I study exoplanets with the James Webb Space Telescope. AMA!"
] |
[
false
] |
I'm an Assistant Astronomer at the Space Telescope Science Institute (STScI) and an Associate Research Scientist at Johns Hopkins University. Here, I lead teams that focus on optimizing the scientific output from the JWST mission, with a particular focus on exoplanet atmospheric characterization, as well as teams focused on developing cutting-edge science for this exciting field of research using both ground and space-based facilities. I participated on the team that produced the first images and data for JWST (the Early Release Observations ---- EROs) --- and led the analysis that produced the first exoplanet spectrum (of many to come!) that was shown to the public of the exoplanet WASP-96b. I'm also part of several teams working right now on producing the very first scientific results on exoplanet atmospheres with JWST, which range on exciting new science from highly irradiated, gas giant exoplanets all the way to the very first observations with JWST of the small set of terrestial planets orbiting the TRAPPIST-1 star. I was recently featured as one of the experts in NOVA's documentary film, Ultimate Space Telescope, about the engineering behind the JWST. You can watch it here: Ask me anything about: Before joining STScI, I was a Bernoulli Postdoctoral Fellow at the Max-Planck Institute for Astronomy in Heidelberg, Germany. In 2018, I was selected as the recipient of one of the prestigious IAU-Gruber fellowships by the International Astronomical Union (IAU) for my work on the field. I did both my undergrad (2012) and PhD (2017) at the Pontificia Universidad Católica de Chile, in Santiago, Chile, where I was born and raised. I'll be on at 3pm ET (19 UT), AMA! Username:
|
[
"Great question ",
"u/Segesaurous",
" --- I'm just jumping from my chair right now just thinking about it :-). ",
"I think any carbon or oxygen molecule in a terrestrial exoplanet will make me jump out of my chair in excitement!"
] |
[
"Thanks for this question! All my exoplanet dreams are layered, here's a breakdown --- top is the ones I believe will happen soon-ish (next few to tens of years), last ones might vary depending on how we do in the firsts: "
] |
[
"How does searching for exoplanets with the James Webb telescope differ from the Hubble telescope?"
] |
[
"How much bleach could the average man drink before he died?"
] |
[
false
] |
[deleted]
|
[
"By \"bleach\" I assume you mean common household bleach, and not pure sodium hypochlorite. Household bleach is diluted down to about 5%. ",
"First off bleach isn't really a poison, it oxidizes cells, like burning, but without fire. ",
"Just breathing in the vapor from pure bleach would likely kill you before you finished one or two chugs from a bottle. ",
"Household bleach would likely cause such painful damage to your mouth and esophagus that I doubt you could drink more than a few gulps before collapsing in pain. Anything more than that would likely cause enough damage to kill you, and if you hand't died you would wish you had. "
] |
[
"I would say yes, one or two gulps."
] |
[
"So, you're saying maybe one or two gulps?"
] |
[
"Is the universe flat and infinite? How was it \"the size of a tennis ball\" if it is infinite?"
] |
[
false
] |
How are the first epochs of the universe comparable to finite diameters? For example, "x seconds after the big bang, the universe was the size of a tennis ball" It seems like a poor metaphor for lay people, and it just confuses me. How does the universe go from infinitesimal to infinite in spatial expanse?
|
[
"For example, \"x seconds after the big bang, the universe was the size of a tennis ball\"",
"They mean the ",
" Universe, which right now has a radius of 46 billion light years. If the total Universe is infinite, it always has been infinite at any x seconds after the big bang, where x is any positive number."
] |
[
"A point of clarification: i think that these kinds of statements are usually referring to the scale factor, a_0, which is the size of the observable ",
". ",
"So the 'size of a tennis ball' remark should be taken to mean that what is ",
" our observable universe occupied a region of space the size of a tennis ball."
] |
[
"I'm not enough of an expert in GR or topology to say whether or not a mobius-like flat geometry is possible, but I've never heard of it.",
"You can construct a flat Möbius strip in the same way that you construct a flat cylinder or a torus; take a strip-like subset of ",
" and identify the edges. For the Möbius strip, you just identify them backward, like ",
"this",
"Also, I think be_moore's point was an ",
" argument—we can't ever experimentally distinguish between an infinite Euclidean space and a sufficiently large finite other space."
] |
[
"Are steroid alternatives any good?"
] |
[
false
] | null |
[
"We do not give medical advice on this sub. Please speak to your doctor."
] |
[
"Not a problem, they have a pretty wide definition of what constitutes medical advice on this sub, and I myself have been censured for what I thought was an innocent remark. "
] |
[
"Sorry, I wasn't necessarily looking for medical advice, more an insight as to whether or not steroid alternatives work."
] |
[
"What is the cause of excess protein in urine if a person has a protein deficient diet?"
] |
[
false
] |
In a pathology text I read a question that asked about a patient that had a distended belly, edema in the legs, low blood protein, but excess protein in the urine. The text stated it was caused by a lack of protein in the diet. How is it that a person who is not consuming enough protein ends up excreting excess amounts in their urine?
|
[
"Proteinuria is not a normal symptom of kwashiorkor (dietary protein deficiency), although minor glomerular changes are observed. It would make a lot more sense if the proteinuria were causing the hypoproteinemia, not the other way around.",
"http://books.google.com/books?id=bw7esE2kfwUC&pg=PA509&lpg=PA509&dq=kwashiorkor+proteinuria&source=bl&ots=eIw3gcdXlU&sig=bYwCWIq8K985ci91UiweGXXxS2Y&hl=en&sa=X&ei=BVs7VODMIM6QNp3FguAP&ved=0CCcQ6AEwAQ#v=onepage&q=kwashiorkor%20proteinuria&f=false"
] |
[
"The deficiency in protein might cause the body to produce more protein to be digested from its own sources, as the digestive enzymes produced endogenously start to digest the bodies own proteins leading to increased excretion of the proteins in urine. Fasting issues along with protein deficiency could lead to this situation, as its common to have both together. as the enzyme sites on any protein released, as the other food if they are eating other foods would activate the enzymes and as they lack other substrate, there would be an increased level of proteolysis which may present in the urine, though whether this would bypass the kidneys suggests that there is something else going on to cause the proteinuria, as police-ical said. \nfound a good link regarding proteinurea:\n",
"http://books.google.co.uk/books?id=HP2YAwAAQBAJ&pg=PA163&lpg=PA163&dq=kwashiorkor+proteinuria&source=bl&ots=Z0-xYaZ8gY&sig=_0JiXNP-QyXLysv9tGZJkXLRQu8&hl=en&sa=X&ei=xA08VPjSFYvd7Qau-IHgBw&ved=0CEoQ6AEwCQ#v=onepage&q=kwashiorkor%20proteinuria&f=false",
"also ",
"http://www.ncbi.nlm.nih.gov/pubmed/16815497",
" and ",
"http://en.wikipedia.org/wiki/Nephrotic_syndrome"
] |
[
"That was my logical conclusion as well, but I was unsure if I were missing something.",
"Thanks!"
] |
[
"What class of numbers are renormalization group constants?"
] |
[
false
] |
In mathematics and physics, there are constants that can only be determined through methods like renormalization group (roughly speaking, zooming in, squinting, analyzing, zooming in again, etc) or Monte Carlo. An example is the average size of a self-avoiding random walk as a function of length, the physical manifestation of which is the size of a blob formed by a polymer. A simple estimate puts this at 0.6 (so the a self avoiding walk is bigger than the regular random walk of L but renormalization group and Monte Carlo put it at around 0.588. Experiments on polymers put it close to this, but I'm more interested in the mathematical self-avoiding walk and things like that. I was wondering what type of numbers these constants are. If they haven't been written down as roots of a polynomial I guess that makes them transcendental, but has there transcendentality been proved? If they cannot be precisely calculated (only converged upon), does that make them uncomputable? Is there a class of number than can be known numerically but not written in closed form?
|
[
"They're definitely not uncomputable; the fact that we can approximate them arbitrarily close means that they ",
" computable! Similarly, if they are transcendental, i'd guess that their transcendentality hasn't been proven, simply because it's incredibly hard to prove numbers are transcendental. For example, we don't even know that pi + e, pi - e, and pi * e are transcendental."
] |
[
"A number x is algebraic if there is some polynomial p with integer coefficients such that p(x) = 0. Transcendental numbers are not algebraic (and therefore necessarily irrational, otherwise they'd be roots of p(x) = b*x-a)."
] |
[
"Is there a class of number than can be known numerically but not written in closed form?",
"Of course! We have a finite number of symbols (be they numbers or operators) and an uncountable number of real numbers - you can see where this is going. So there are actually infinitely many numbers that don't have a closed form.",
"EDIT: Just as a reference, the finite cardinality of our symbol set implies countability of the numbers we could possibly name."
] |
[
"Does an increase in blood glucose necessarily mean there is going to be an increase in Insulin?"
] |
[
false
] |
I know about how Insulin regulates glucose, but does a small increase in blood glucose mean that the body is going to release more insulin or can the glucose levels lower through a different mechanism?
|
[
"In human biology no process is absolute, and the pancreas continually secretes varying levels of insulin. Blood-glucose is not the only stimulus for insulin release either.",
"However, in a hypothetical system where glucose is the only circulating ligand and insulin secretion is either 'on' or 'off' (no background secretion), the increase in blood-glucose would have to be sufficient to initiate the depolarisation of beta-cell membrane (inc glucose > inc ATP production > dec K+ membrane permeability > depolarisation), in order to open voltage gated transmembrane calcium channels, causing Ca2+ influx and activate the PKC signalling cascade that increases insulin synthesis and release. ",
"In vivo the number of cells which are depolarised will scale with the increase in blood-glucose, however the physiological significance of the increase (i.e. the insulins affect on blood-glucose levels) would depend on baseline levels of insulin and other mechanisms which stimulate or inhibit release.",
"The kidneys can filter glucose from the blood and excrete it in urine to reduce blood-glucose levels, and if glucose levels are high enough it will even cause urine to smell sweeter (a symptom which is often seen in people with diabetes).",
"Hope this helps."
] |
[
"Every time you eat there's an increase in glucose levels, which makes the pancreas produce insulin. No matter how small your meal or snack is. \nAnd yes, to lower glucose levels the only mechanism the body has is the insulin release. \nHowever, when your glucose levels are too low, your pancreas produces glucagon, that works increasing the levels of glucose in the bloodstream (it has the exact opposite effect of insulin)."
] |
[
"When you consume carbohydrates, your blood glucose levels will rise, assuming the carbohydrates are absorbed. The glucose in your blood causes the insulin in your beta cells to be release. It enters the cell through an insulin-independent transporter GLUT2. Once inside the cell, the production of energy from the glucose causes a polarisation changes releasing insulin. This insulin lowers your blood glucose by 'helping' it get into other cells in your body for energy use (through other GLUT transporters).",
"It's possible to cause an increase in insulin ",
" consuming sugar, some GLP-1 is released when food is in the intestines causing glucose-independent insulin release. It is also possible with some anti-diabetic medications to release insulin without glucose, causing hypoglycaemia as a side effect.",
"At the same time, it is possible to consume sugar, increase your blood glucose, and release no (or little) insulin. Pancreatic exhaustion can occur in type two diabetes mellitus, meaning less insulin is released than should be expected, and there can be a complete lack of insulin release in type one diabetes if there is absolutely no pancreatic insulin function left. It imagine it would theoretically be possible to raise your blood sugar by an insignificant amount leading to no insulin release if the pancreas wasn't triggered to."
] |
[
"Why do I experience morning nausea during periods of depression?"
] |
[
false
] | null |
[
"We can't really comment on isolated incidents / personal anecdotes."
] |
[
"Thanks, and I appreciate the difficulty of answering a vague question. ",
"It seems pretty common, from what I can see. However no where I can find explain why, just that it does occur. "
] |
[
"You could try a more general phrasing like: why is morning nausea a symptom of depression? "
] |
[
"Why can't capacitors work like batteries?"
] |
[
false
] |
It seems they have this special property that only allows them to discharge quickly. Several years ago, scientsist were interested in this application, but the interest has seemed to died off. Why?
|
[
"Capacitors don't have the ",
"energy density",
" of batteries. So they are heavier and bulkier than batteries that can do an equivalent amount of work. Chemical bonds are marvelously good at storing energy at high density that is easily recovered and transportable (gasoline, batteries, mars bars, etc)."
] |
[
"Interest has not died off;",
"http://www.physorg.com/news/2011-11-carbon-foam-key-ingredient-battery.html"
] |
[
"Another issue is that a capacitor's voltage is dependent on the charge of the capacitor while a battery maintains a constant voltage over most of its lifetime. Many electronics require constant voltages. "
] |
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