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[
"Is there a formula to explain the ever expanding space?"
] |
[
false
] | null |
[
"You're looking for the Friedmann Equations."
] |
[
"Would you point me to the correct one, they all confuse me a little :) "
] |
[
"You probably want either or both of the first two under the \"equations\" section: ",
"https://en.wikipedia.org/wiki/Friedmann_equations"
] |
[
"How did our distant ancestors cut umbilical cords, like the time before knives. Maybe a sharp rock?"
] |
[
false
] | null |
[
"Does that environment really need to be simulated?",
"Not that I doubt you, but I'm curious because some humans are quite adept at living in cold climates, compared to the warm environment you're describing."
] |
[
"Does that environment really need to be simulated?",
"Not that I doubt you, but I'm curious because some humans are quite adept at living in cold climates, compared to the warm environment you're describing."
] |
[
"Do they just have to hang around attached to a placenta until then, like they’re the Orphan of Kos?"
] |
[
"When something is thrown at us or unexpectedly falls, how can the brain calculate exactly where to position the hand to catch it, sometimes in milliseconds?"
] |
[
false
] | null |
[
"The brain is basically a very powerful computer and can calculate how something is going to move as well as working out how to move your hand to catch something. Some of this is learned - how things fall but a lot of it is calculation. If you were to do it on paper it would be some very complicated calculus.",
"\nSports scientists have shown that when catching something over a longer distance - a thrown or hit ball for instance - the catcher will move and adjust their speed so that the trajectory of the object remains mostly constant from their point of view and the brain recalculates as it goes as that is simpler calculation than working out where something is going to land then rushing there and waiting for it."
] |
[
"I'm very curious to hear the answer to this. I assume it has to do with reflexes but i think that reflexes vary from person to person. ",
"So as a follow up question, I'd like to know why some people have better reflexes than others."
] |
[
"The brain is basically a very powerful computer",
"That's a model, it's not necessarily true. For most purposes this is a useful way to think about the brain's workings. But one shouldn't be seduced into thinking that brains = computers. ",
"the catcher will move and adjust their speed so that the trajectory of the object remains mostly constant from their point of view and the brain recalculates as it goes as that is simpler calculation than working out where something is going to land then rushing there and waiting for it.",
"This is very interesting, but the gradual descent of a thrown ball is a different thing entirely than what OP asked for, because it is slow and predictable. Quick reactions are entirely different. I remember in cognitive neuro we learned about this. And the body moves on the basis of very little sensory information, activating \"motoric scripts\" that are broad and nonspecific. For example moving your hands rightwards and upwards in order to cover some broad region where the ball is likely to pass.",
"Don't take that explanation as authoritative, though. I hope someone can point to the research on that, because I can't find it right now (it was cited in Gazzaniga's introduction to cog neuro which I sold). I'm mainly pointing out that your comment, though interesting and insightful, is not really relevant to the OPs question."
] |
[
"How can a Boltzmann brain just arise from random entropy?"
] |
[
false
] |
This is without a doubt one of the strangest physics things I've ever found. All I can find is this small and either very technical or very whimsical web pages. Secondary question: Is the Boltzmann brain theory held in any particular regard today?
|
[
"Searched",
"Relevant ",
"discussion",
"Original question by ",
"bryce1234",
"Could some explain the Boltzmann brain hypothesis?",
"Relevant comment courtesy ",
"Hairy_Hareng",
"Ok. I have read the wikipedia page and I have a little bit of knowledge of probabilities and entropy.",
"It seems to me like the BBH (boltzman brain hypothesis) claim is the following: - the universe is in a state of maximum-entropy / increasing entropy, yet we still observe within this universe local organisation hot-spots (earth, a human being, etc)",
"this observation can be explained by saying that these are the results of random fluctuations around the entropy equilibrium: if we look at the results of 10.000 results from a heads or tails flip, we might see some pockets of 1111100000, and, while these might surprise them on their own, if we consider whole sequence, then we see that these are just a random fluctuation. Thus, if we could see the whole universe, we could / should see that these organisation pockets are very few. We are likely biased by the fact that we, as humans beings, evolved in one such organized part of the universe (try evolving a mind inside a helium cloud: it's a bitch)",
"this is where the bullshit start imo: If our current level of organization, having many self-aware entities, is a result of a random fluctuation, it is much less likely than a level of organization which only just creates stand-alone self-aware entities From this sentence, the wikipedia article claims that it is more likely to have stand-alone brains forming out of nothing that would observe the world around them. These are the so-called Boltzman-brains",
"Now, I think this is grade A bullshit, because the claim from the article which I quoted is simply unprovable. Furthermore, entropy maximisation is not uncompatible with some degree of organisation: for example, if you look at a simple model for a H20 atmosphere in a gravity field, you get an organisation in a liquid layer (sea) and a gazeous layer (atmosphere). Lastly, some systems also take a very long time to get to the equilibrium: for example, the moon rotating around the earth is not in equilibrium and will stop in a very very far future (can't remember the time constant).",
"I think the BBH results from a philosophical mis-interpretation of entropy.",
"Relevant follow-up courtesy ",
"Ruiner",
"I like your post, but just let me clarify what Boltzmann exactly had in mind:",
"*We are not in Equilibrium! That's obvious from the fact you and I exist.",
"So now, if you have a room filled with gas, you should expect that it will be evenly distributed. The reason is not due to the dynamics (as long as the dynamics are chaotic in a sense), but due to the fact that the phase space is coarse-grained in a way that the microstates that correspond to non-equilibrium have almost-0 measure. Or in other words, it's really unlikely that all the gas will sit in the corner. And that's the whole point of equilibrium and the second law.",
"Now a small deviation: entropy will not always rise! This was shown by Poincaré. If you wait long enough, you'll have some periods where all the gas will sit in the corner, but the timescale for that is very big compared to what we can observe. But in any case, given a system, if you were to wager on how it would evolve, you would always bet on \"equilibrium\".",
"So the idea now is this: since we are not in equilibrium, we must be a very unlikely configuration. Not impossible, but unlikely. But of course, you can always escape from this by claiming special initial conditions, but Boltzmann didn't like that, he wanted a \"natural\" explanation. So he postulated that all the out-of-equilibrium state of the universe was due to a very large fluctuation that must happen (because of Poincaré).",
"Of course, that is completely silly! Not because it's false, but because all of the physics is based on the fact that likely events will happen, so why would you start by justifying your existence by stating that we are just some unfortunate coincidence? Well... but still, Boltzmann was by far the biggest genius in 19th century physics, and it's a shame that he killed himself over it, and most of the problems of modern physics still can be traced back to Boltzmann..."
] |
[
"The idea is that your random gas molecules will bounce around randomly, and eventually, by sheer chance, line up in a configuration that an external observer might identify as sentient (or some other low entropy configuration). One such configuration, of course, is the universe we see today, with us in it. Of course, this seems staggeringly unlikely, because it is - the assumption is that you have an infinite amount of time to work with, and so even staggeringly unlikely events happen eventually.",
"I'm not really qualified to comment on whether this is considered total hogwash these days, but this is the idea he was trying to convey."
] |
[
"Thanks my robotic friend. What I take away from this is that the theory is not something anyone really takes seriously anymore, but I'm still unsure how a bunch of random gases becomes sentient."
] |
[
"If there is no water on Mars, what creates the formations on the Martian landscape that look so similar to formations on Earth such as the Grand Canyon?"
] |
[
false
] |
Looking at the photos from Curiosity and other Mars rovers, I'm struck by the apparent similarity between the rock formations on Mars and places we have on earth specifically the Grand Canyon in the US. Having visited the Grand Canyon and being in awe that "water could create such a giant hole in the earth" it strikes me as odd that a place devoid of water could have nearly identical structures. If it's simply wind and atmospheric gases, wouldn't the erosion be visually different? EDIT: This should read liquid water.
|
[
"At this point, we're almost certain that Mars once had liquid water on its surface...",
". You simply don't get dendritic erosion features like ",
"these",
" without some kind of liquid doing the erosion - and water is the obvious choice here.",
"(Side note: the really big valleys, in particular Valles Marineris, were likely ",
" caused by water erosion, but by tectonic rifting.)",
"That said, this explanation opens a whole new question, namely where did this liquid water go? ",
"In order for a planet to support liquid water, there must be enough atmospheric pressure to maintain it in a liquid state. At pressures lower than its so-called \"triple-point\", water can only exist as ice or vapor - just like how carbon dioxide in our atmosphere can only exist as solid or gas, but can become a liquid at higher pressures.",
"The current working theory is that atmospheric pressure used to be much higher on Mars, high enough for abundant liquid water to flow. The pressure started dropping when Mars' volcanoes started going extinct. (All atmospheres slowly lose gas to space, but in Earth and Venus' case, this is replenished with gases released from volcanic activity.)",
"When the pressures become low enough, this water was forced into either ice or vapor form. A good deal of it turned into subsurface ice, as has been confirmed to exist by the Mars Phoenix Lander. A good deal of it likely interacted with iron on the surface (most of Mars' surface is actually rust). Finally a good deal of the vapor portion likely escaped into space.",
": Mars almost certainly used to have liquid water, which is how many (though not all) of its ",
"numerous valleys",
" were carved out. This water the turned to either vapor or ice as the pressure dropped too low to support liquid water."
] |
[
"Common theory is it once had liquid water, much like earth. Due to when the core solidified/the tectonic plates merged, it either evaporated or solidified into ice(found at the poles)."
] |
[
"You don't get ravines, gullies, and dried lake beds/river systems with just sandblasting. Sure, wind may cause erosion, but water is the number 1 cause of erosion in landforms, and is a much more influential factor than wind. Since water is such a great solvent, it can flow through channels and pick up sediments, thereby dissolving ions within it and causing downcutting in the channel. Simultaneous uplift combined with downcutting can result in extremely deep gorges, which is what we see on Mars. On Earth, our closest example of this is the Grand Canyon. ",
"So yes, sandblasting could have had an effect, but water is a much more likely candidate. "
] |
[
"Are there any land macro-animals (ignoring insects etc) that have a population in the billions like humans?"
] |
[
false
] | null |
[
"19 billion",
"\"Up to 7 billion\"",
"\"which, everyone agrees, outnumber us — but no one seems eager to count\"",
"\"About the same as rats\"",
"1.4 billion",
"\"About 1 billion\""
] |
[
"I find it interesting that 3 of those categories are specifically bred in large numbers for human consumption. I wonder what the \"natural\" numbers would be, if we hadn't domesticated them?"
] |
[
"Thank you."
] |
[
"What are we seeing when an aircraft breaks the sound barrier?"
] |
[
false
] |
Whenever you see a picture of an aircraft breaking the sound barrier, you see a cone of smoke or vapor around it, what the heck is that?
|
[
"Those pictures are not necessarily the aircraft breaking the sound barrier, just that the conditions in the flow cause the water vapor in the air to condense."
] |
[
"To add on, it usually occurs when some parts of the flow around the aircraft have become supersonic while other remain subsonic. "
] |
[
"its water vapor in the air condensing. ",
"when the shock wave from breaking the sonic barrier decompresses the air gets considerably cooler from the expansion and it causes the water in the air to condense. "
] |
[
"Does the Moon's gravity leave any geological traces that are identifiable in Earth's strata over time?"
] |
[
false
] |
I mean, are there any geologic markers on Earth that have been identified to track the historical path of the Moon around the Earth, to identify when the Earth first captured the Moon?
|
[
"Two points, first a clarification and then an answer to the meat of the question.",
" The Earth did not \"capture\" the Moon. The standard model is that a proto-Earth, around 90% of the mass of the current Earth, was struck by a Mars size impactor, usually called Theia. (e.g., ",
"O'Neill, 1991a",
", ",
"O'Neill, 1991b",
"). As described by O'Neill, the general idea is that impactor hits the proto-Earth, the impactor is vaporized along with most of the mantle of the proto-Earth, and that much of this proto-Earth/Theia mixture recondenses to form the modern Earth with the rest forming the Moon. This is generally what is seen in a variety of models of this impact (e.g., ",
"Canup, 2004",
", ",
"Wada et al., 2006",
", etc). The requirement of a decent amount of mixing and then this mostly homogeneous material accreting both back onto the Earth and forming the moon is a requirement to honor a variety of geochemical/isotopic constraints (e.g., ",
"Jacobson et al., 2014",
", ",
"Young et al., 2016",
", etc). ",
" There is a (sparse, but existent) geologic record tracking changes in the Earth-Moon distance, which has been increasing through time (e.g., ",
"Bills & Ray, 1999",
", ",
"Meyers & Malinverno, 2018",
"). This ",
"figure",
" from Meyers & Malinverno shows a few datapoints where the Earth-Moon distance has been estimated by using tidal rhythites (e.g., ",
"Mazumder & Arima, 2005",
") compared to a model (the red) and extrapolation of current tidal dissipation rates of ~3.8 cm/yr (which we've known for quite a while cannot be a constant rate as it would imply a much younger age for the Moon than fits with other geological evidence).",
" geochemical and isotopic evidence along with tracking the Earth-Moon distance allows us to estimate the timing of when the Moon formed following the Moon-forming impact."
] |
[
"There remains ambiguity about the exact timing, but a variety of different approaches suggest the moon-forming impact happened around 100 +/- 50 million years after the beginning of condensation of the solar system. Some of these were already cited above (e.g., Jacobson et al., 2014, Young et al., 2016), but there lots of other work that have attempted to constrain the timing (e.g., ",
"Bottke et al., 2015",
", ",
"Fischer & Nimmo, 2018",
"). By \"proto-Earth\", we refer to a differentiated body (i.e., the planet had separated into core, mantle, and crust) that had accreted most of its mass, but given the degree to which this body was resurfaced by the impact and/or mixed with the impactor, it was distinctly different from the Earth that formed after the impact. While there is not a \"geologic record\" of this in the sense of preserved material at the surface from prior to this impact, as highlighted in many of these papers, we can work out the timing from various isotopic systems (e.g., the Hf-W system discussed in the Fischer & Nimmo paper)."
] |
[
"In some ways I suppose one could say that the moon is the geological record of the impact."
] |
[
"Question on Length Contraction"
] |
[
false
] |
My current understanding of length contraction is best represented by the ladder & barn scenario. A man has to bring a 5m long ladder into a barn that is 4m long. A stationary bystander watches the man travel at .6c, and the ladder fits into the barn due to length contraction. However, from the reference frame of the man with the ladder, wouldn't it be the barn which seems to contract? Wouldn't the ladder not fit at all? If this is the case, I gather that special relativity explains that this does not defy any law of physics and both men are correct. Can someone just verify if my understanding is correct, or please correct my misconceptions?
|
[
"Only events have to be the same in all frames of reference. \n\"The ladder fits in the barn\" is not an event. \"The front of the ladder leaves the barn\" and \"the tail of the ladder enters the barn\" are two events that are separated spatially.",
"\nThus, it does not violate relativity if they happen at the same time in one frame of reference, and at a different rate in another.",
"An a little more complex example is: ",
"\"A train and a tunnel both have have proper lengths L. The train speeds towards the tunnel, with speed v. A bomb is located at the front of the train. The bomb is designed to explode when the front of the train passes the far end of the tunnel. A deactivation sensor is located at the back of the train. When the back of the train passes the near end of the tunnel, this sensor tells the bomb to disarm itself. Does the bomb explode?\" ",
"The answer is, that the bomb does explode in all frames of reference, since the explosion is an event. The signal can only travel at or below the speed of light from the back of the train to the front. At the time the signal has reached the front of the train, the front has left the tunnel in all frames of reference."
] |
[
"Yes, that's correct. This does not violate any laws of physics, but it does violate out intuition about the simultaneity of events.",
"The statement \"the ladder fits into the barn\" can be rephrased in terms of spacetime events as \"the front of the ladder leaving the barn (event 1) occurs after the back of the ladder enters the barn (event 2).",
"Event 1 happens at a different place than event 2 (at the back versus the front of the barn) and are in fact \"spacelike\" separated, which effectively means that they are not causally connected (one cannot cause the other to happen, they're independent events). Special relativity says that the order of spacelike separated events can depend on which reference frame you're in. So it's okay for one person to see event 1 happen before event 2 which the other sees the opposite. This means that it's possible in one person's frame the ladder fits while the in the other it does not."
] |
[
"Thanks! This makes sense"
] |
[
"If casein gives cheese its structure, what's the protein that gives tofu its structure?"
] |
[
false
] | null |
[
"You're correct, I should have said \"non-enzymatic\". For tofu they use salts alone (AFAIK) to coagulate the soy milk into \"curds\". "
] |
[
"Cheese doesn't get its \"structure\" from casein per se, but rather from chemical transformations and coagulation of protein suspensions (mostly casein) in water that eventually gives you a solid water-insoluble material. The same thing happens in tofu-making but AFAIK the coagulation is purely chemical (no enzymes are involved, to my knowledge) and there isn't a single protein that dominates. "
] |
[
"Cheese doesn't get its \"structure\" from casein per se, but rather from chemical transformations and coagulation of protein suspensions (mostly casein) in water that eventually gives you a solid water-insoluble material. The same thing happens in tofu-making but AFAIK the coagulation is ",
" [emphasis mine] are involved, to my knowledge) and there isn't a single protein that dominates. ",
"You're suggesting that enzymes are not chemical. That's... hopefully not your intent.",
"Perhaps what you meant is that the protein coagulation in tofu is purely ",
"? I don't know if it is or not, myself.",
"According to Wikipedia's extremely vague article on soy, it's principally \"glycinin and beta-conglycinin\". However, this is not given a composition estimate, and it's hard to find.",
"Most sources seem to describe the bulk of protein extracted overall, and don't describe what specific proteins are present."
] |
[
"Is it true that over the course of billions of years, the moon's revolutions around the Earth will cause the Earth's rotation to slow, giving us more hours in the day?"
] |
[
false
] |
I seem to remember that I heard back in elementary school that something to do with the Moon's revolution is causing the Earth to slow down and in a few million (or billion, I heard this a long time ago) years we will have more than 24 hours in a single Earth day?
|
[
"Fair enough. I'm an astronomer, so anything that happens in less than a billion years is fast!"
] |
[
"Yes. Tidal friction is (very) slowly slowing the Earth's rotation to match the moon's orbital period. At the same time, the moon is gaining the Earth's lost rotational momentum, and being flung out to space (at a rate of a few centimeters a year). Neither of these things will happen fully before the sun dies, but the Earth will rotate slower than it does now by then."
] |
[
"The process is slow on human timescales, but it's not ",
" slow. Fun fact, back when dinosaurs were around the length of a day was 21-23 hours! Also the moon was closer and would've looked even more impressive at night.",
"The current rate is that the day gets longer by a couple milliseconds every century."
] |
[
"If 80% of matter is dark matter, how do they send probes to mars without taking dark matter into account?"
] |
[
false
] |
[deleted]
|
[
"Dark matter in our area has a relatively uniform density and a very low density, it doesn't clump up like regular matter does. Like driving a car, yes the air is there, but we don't really care about it, unlike the trees which have a significant impact on where we drive.",
"And looking at some numbers, let's say we had a Sun's worth of dark matter (2 x 10",
" kg) spread over a cube 4 light years on a side. That would give a mass density of 10",
" kg/m",
" The amount of dark matter in a 1 AU sphere (Earth's orbital radius) would be about 10",
" kg. That might seem like a lot, but the sun converts about 10",
" kg of matter into energy every second, meaning the Sun will burn through 10",
" kg in about 6 hours, so it's so small as to be negligible.",
"So even if there is a gravitational influence due to the dark matter, the Sun completely dominates our local neighborhood and our measuring techniques are not sensitive to measure let alone worry about it."
] |
[
"Dark Matter is called 'Dark' because it interacts so weakly with regular old matter/forces. The effect is negligible unless you're describing the motion/shape of very large/gravitationally strong object, like galaxies."
] |
[
"It's right, we only know of its existence because of gravitational effects. That means it doesn't interact nongravitationally (or it interacts only weakly) with regular matter, because if it did, we could have detected it by other means. This means that dark matter particles would normally pass through ordinary matter almost undetected. We already know of a particle that does this (the neutrino).",
"This also means that there is no way for dark matter particles to clump together like normal matter (because those cohesive forces are electromagnetic in origin), so we believe that they are distributed in a diffuse halo around each galaxy. You can think of it like a dilute \"atmosphere\" that surrounds the galaxy: gravity manages to keep the dark matter from escaping, but it's not strong enough to condense it into objects.",
"Their joint contribution would account for that 80%, but, as ",
"/u/DeadeyeDuncan",
" says, in scales smaller than a galaxy the gravitational effect would be negligible."
] |
[
"Why aren't animals with bigger brains smarter?"
] |
[
false
] |
According to this wiki article: Elephants and whales have more neurons than us. So why aren't they smarter?
|
[
"Same reason an amputee doesn't get smarter.",
"Brains are designed by evolution to control a body of a certain size.",
"A genetic quirk that makes someone smaller doesn't change that basic design. "
] |
[
"If you normalise to body mass it becomes much clearer. See the plot here:",
"http://www.rpi.edu/~eglash/eglash.dir/ethnic.dir/race/eq.gif",
"Above the line is smarter than average, and vise-versa. ",
"The idea is, I think, that a larger body simply takes more processing power to run than a smaller one, and you need to factor this out. (Source: a Richard Dawkins book, I'm not a biologist)."
] |
[
"The amount of prefrontal cortex is also an important factor. ",
"I did a quick google search, and the first article that popped up is from my University! It's pretty neat, click ",
"here"
] |
[
"Is there a physical limit to the quality of image sensors?"
] |
[
false
] | null |
[
"The answer to your question depends on what you mean by \"quality.\" If by quality you mean angular resolution (i.e. the smallest feature you can image), then yes. The ultimate angular resolution of an image is limited by a process known as diffraction. An imaging system that can image at its minimum angular resolution is known as \"diffraction-limited\". You may find the ",
"Wikipedia page",
" on this helpful. ",
"I'll add that there has been a lot of work recently in the fields of plasmonics and nanoscopy that allow for sub-diffraction limit imaging (Google Scholar shows me over 15,000 results from 2016 alone for the search term \"beyond the diffraction limit\"). So, yes there is a physical limit, but there is also a lot of research going on to help us bypass it.",
"For other definitions of \"quality,\" I would imagine that there are other physical limits in place. "
] |
[
"Most of the diffraction-limited applications can be improved with a physically larger sensor (your cell phone is only so good, but if you build to 10 meters in diameter, it's a telescope and works much better). The issue with the larger ones is noise, that is as you build it larger you force the light to be spread over a larger area, requiring larger sensors (and having the effect of spreading the light from the object over a larger sensor). That makes the sensor dimmer and you need to make it more sensitive, at the extremes you're talking a very small amount of photons on each pixel, and you have to deal with thermal noise on the sensor and other sources like cosmic rays, that is when dealing with low light it gets difficult to separate out from the background noise. There are tricks to reduce this, like chilling the sensor."
] |
[
"Yes. I'm not going to give a sharp bound, but there definitely exists one: for example, you could be collecting and recording every single photon that arrives perfectly. Any sensor will necessarily be no better than this, so there exists some kind of upper limit. "
] |
[
"Do scientists have the knowledge and/or capability to manipulate genes?"
] |
[
false
] |
There is an enzyme in animals and humans called , which breaks down uric acid. However, the gene for urate oxidase in humans is non-functional. Do we have the technology currently to "fix" this gene and somehow activate it?
|
[
"Yes, we do. Work related to the manipulation of genes is being performed fairly frequently in labs. For instance, I finished a semester-long research project doing just that in nematodes, and I'm still working on my undergrad!",
"The main issue with genetic manipulation is that while we have made many significant advances in the last decade, there are still MANY things we don't understand. Our genes are much more than linear codes. They're more like a blueprint. Many little pieces working together in mystifyingly precise sequences and patterns. For this reason, we don't fully understand the effects changing a gene may have on other genes and thus the organism as a whole. ",
"The ultimate goal of genetic manipulation, as you are hinting at, brings about many ethical concerns as well. It seems biologists are still at a bit of an impasse as to what is considered ethical in the field of genetics, since it's still relatively new to us. A professor of mine once commented that the ethical considerations in biology were more crucial than ever because of the expansion of medicine in relation to burgeoning fields like genetics.",
"This leads us to use what are called \"model organisms\": simple creatures, like nematodes, drosophila, etc. that have quick reproductive cycles, simple physical characteristics, and limited/no consciousness. Limited consciousness means fewer ethical considerations. As studies continue to delve into the effects of genetic manipulations on these organisms, we will continue to learn more about genetics on a macro scale, as well as the possible applications in humans. Until then, we focus on simple, small organisms in order to limit the potential risk."
] |
[
"Yes, we are still learning a lot and are still pretty early in it. However, it's a lot more common then you think. I was talking to a Chemical Engineering buddy over at Kodak, and he was telling me how they genetically make bacteria who's byproduct is used to make the ink in your printer. ",
"The problem with humans, is we are a lot more complex, one small change can have massive effects. So right now we don't have the technology to fix it and be certain that we aren't messing up something else."
] |
[
"We do have the technology to fix the gene, but it's dangerous; we don't have the understanding to be sure it won't screw something up in a way we don't understand. In simple organisms (bacteria, or well-studied plants or worms) we do this kind of thing all the time. Of course, a lot of the time we end up with some horribly screwed up organism. No tears are shed over a deformed nematode or non-viable ",
", but taking that risk with a human child is another matter entirely. And the gene interactions in mammals are many times more complex than those in most model organisms. Also, most methods of inserting new/fixed genes are kind of scattershot— they have a large chance of inserting the new gene in the wrong place and breaking something else. (In a bio lab you might transform a hundred seeds to get a few correctly-transformed ones.)",
"On the flip side, though, ",
"gene therapy",
" ",
" used to treat some particularly difficult genetic diseases in humans. Gene therapies don't usually go for the ",
"germ line",
", though, so they're not inheritable— we typically try to 'patch' the genome in just the particular somatic tissues that are having the problem, to limit the potential side effects. People are ",
"thinking about germ line gene therapies",
" though, we're just not there yet."
] |
[
"Do the bubbles on cappuccino insulate it? Will it cool faster if I sip them from the top of my coffee?"
] |
[
false
] |
I've always assumed that the bubbles on top of a cappuccino have an insulating effect, meaning that it stays hot for longer. But recently I've started to theorise that the top surface of the bubbles might have a higher surface area than plain coffee meaning that there is more evaporation and therefore faster cooling.
|
[
"basically you are correct. The air that is trapped in the bubbles has a MUCH lower convection coefficient than your coffee does. It DOES insulate your coffee but by a very small amount. I would do the math and all right now but I don't have any paper and pencil. I would also need to know the thickness of a bubble and the surface area which I woudln'nt know how to find out. ",
"Don't forget that the amount they insulate is nothing compared to the walls of the mug that disipate heat much faster."
] |
[
"My girlfriend and I were discussing this about bubble bath the other day, we decided to get a USB thermometer and do science! Yay! Still waiting for it to be delivered, I'll publish graphs in a few weeks"
] |
[
"to add on to this great explanation, the reason why styrofoam is a great insulator is because it has air trapped in it. Why is this good? Because air is the best insulator there is (apart from a total vacuum) but only when it's not moving. Those bubbles trap the air and minimize the circulation of the air and that is why we don't use plain fiberglass bricks for insulation but we use fiberglass threads that trap air. "
] |
[
"How fast was the meteorite that landed in Russia traveling?"
] |
[
false
] | null |
[
"Russian Academy of Science have estimated it as 33,000 kph on entering the atmosphere. ",
"http://www.bbc.co.uk/news/world-europe-21468116",
"That 'sonic boom' may have been the shockwave triggered when the meteor hit the atmosphere (or a denser layer within the atmosphere), hence the long travel time before anyone heard it."
] |
[
"Are you referring to the meteorite that landed over Chelyabinsk? If so, the Russian Academy of Sciences ",
"estimated that",
" the meteorite weighed about 10 tons and:",
"\" entered the Earth's atmosphere at a speed of at least 54,000 kph (33,000 mph), shattering about 30-50 km (18-32 miles) above ground.\""
] |
[
"about 33,000 km/ph or for those of you that still haven't caught up with the 20th century its 20505.25 m/ph."
] |
[
"How do snow leopards survive huge falls without alot of damage or death?"
] |
[
false
] |
Hey guys, I was looking at a documentary about big cats and was fascinated by the hunting behavior of snow leopards. There's a lot of footage of them hunting and plummeting 100+ meters from mountains and surviving unscathed, while almost any other animal would break in half. What is the science behind them taking blows from falling so well?
|
[
"Leopards, lynx, house cats, and most other felines have several defining features that allow them to fall and land from great distances.",
"The main one of which is that they have a lot of skin and little mass, most of this excess skin is found in between the limbs and torso (That why cats look like they wear baggy pants when you pick them up.) ",
"This is paired with a subconscious reflex. when they fall from a height that they would be damaged from, they spread out all of their limbs into a position that would stretch out all of this skin into a larger surface area to increase drag, allowing them to slow down. and in the leopards case, they have extremely flexible bones and impact resistant pelts, allowing them to take great tumbles."
] |
[
"I knew cats could fall for great distances, but not that the Snow Leopard had extra adaptations that make it even more fall resistant. Thank you for your answer."
] |
[
"You’re welcome! I imagine the impact resistance is of value to a creature that spends 90% of its day on cliffs."
] |
[
"Does temperature affect how quickly a person would bleed out?"
] |
[
false
] |
If two people of the same age and health were to sustain the exact same stab wound to the chest, but one in temperatures below freezing and the other in a hotter climate who would die faster?
|
[
"There is a saying in emergency medicine that goes \"they aren't dead until they are warm and dead\".",
"It is true that if you were stabbed and bled out while you were hypothermic it would take longer for your cells to die (because your metabolism is slower), which would theoretically give you more time to bring someone back. ",
"However, the ability to bring someone back from bleeding out, especially in field combat conditions is… next to nil. You would need surgical capability to clamp off the injured blood vessels as well as access to a blood supply for a transfusion. ",
"And if you are bleeding out, resuscitation is irrelevant until you fix the bleeding out; if there is no blood to move around, CPR is pointless.",
"Sidebar: this is why modern combat uniforms have built-in tourniquets: if you can prevent bleeding out, then you have a chance. If you bleed out, it's too late."
] |
[
"I won't comment on a body below freezing, but patient's who are hypothermic have a much higher morbidity in trauma/hemorrhage. This is due to the \"lethal triad.\" The blood coagulation system is impaired in the setting of acidosis, coagulopathy, and hypothermia. Thus, hypothermic patients do not clot as well. "
] |
[
"Theoretically, the warm one would bleed out slightly quicker because the blood would be thinner/less viscous at a warmer temperature, thus flowing more quickly. Additionally, blood vessels tend to constrict, somewhat ",
"powerfully",
", when exposed to cold conditions. As a caveat to the blood constriction, though, your body will also shunt blood away from the extremities and towards the chest (by constricting the peripheral blood vessels in the aforementioned manner) in extreme cold to preserve the vital organs, so the effect of the constriction of blood vessels in lessening the bleeding rate may be mitigated somewhat by the fact that more of your blood is circulating in your chest where the hypothetical stab wound is.",
"So, in sum, I think the warmer person would bleed out more quickly."
] |
[
"Why are kids these days allergic to everything?"
] |
[
false
] | null |
[
"I've removed your question because it's asking for an explanation of an assumption, without providing evidence for existence of the assumption. If you want to repost, an acceptable re-phrase would be something like, \n\"Has there been an increase in the prevalence of allergies?\" and the text can then ask, \"I'm wondering if allergies are more prevalent than they used to be, or if they are simply being diagnosed more frequently. If they are more prevalent, what are the current hypotheses to explain that?\"",
"All the best."
] |
[
"Thanks doc. That was my first post to AskScience. "
] |
[
"No problem. Welcome to AS, we're glad to have you here (even though you did post in AS 20 days ago :)... I won't tell). Let me know if you have other questions."
] |
[
"How do insects climb onto walls and ceilings?"
] |
[
false
] |
I wonder how insects such as spiders and most bugs are able to stick themselves on to walls & ceilings
|
[
"baloo_the_bear explained it well enough, but I don't think that's the only mechanism that works. Some lizards are able to climb walls because they have millions of tiny little hairs (or hairlike structures) on their feet.",
"They don't use glue or something, it's just a neat physical effect called van-der-Waals force. Basically, by increasing the area of contact, you increase the grip (much like with broad tires, but on a molecular level)."
] |
[
"Could we scale these processes up and allow larger items to do the same? Or is there an upper limit where the force can't carry so much weight?"
] |
[
"We can, and we do.",
"http://www.stanford.edu/group/mota/education/Physics%2087N%20Final%20Projects/Group%20Gamma/gecko.htm",
"http://www.popsci.com/scitech/article/2008-04/gecko-tech"
] |
[
"Would covering the roof of a building with a reflective shade material cool it by a noticeable amount?"
] |
[
false
] |
This is what I mean: Would putting something like that on a roof make any difference? Would mounting it a few inches above the roof make any difference?
|
[
"This would make a big difference on a sunny day. This would change the ",
"albedo",
" of your house, meaning that less sunlight is absorbed by your house, and thus less radiative heat actually warms your house. One proof of this is that houses in hot climates in Europe are painted white allot, this helps to keep them cool."
] |
[
"An interesting phenomenon of this is that in some cities such as Philadelphia, PA, you can view economic areas in aerial photographs via the white roof painting that has been done to help with the summer heat."
] |
[
"would it make a difference if the shade material just laid on the house, or was suspended a couple of inches from it?"
] |
[
"Why can't we precisely compute orbits?"
] |
[
false
] |
I know some of it is due to relativistic effects, but what natural forces/processes lead to the uncertainty?
|
[
"What makes you think we cannot? We can predict solar eclipses 1000 years into the future easily - ",
"here is a table for the 30th century",
".",
"The accuracy of the predictions depends on a lot of things, but mainly on time. Over time even small uncertainties in initial parameters add up to larger uncertainties. Relativistic effects are not an issue as we know them. Poorly known things like outgassing from comets is an issue. Chaotic motion (=small changes in initial parameters lead to large deviations in extrapolations) can be an issue, but it is not relevant over a million years for most large objects. It is important for objects that pass close to planets, as their orbit can change a lot from a single fly-by, and the change is very sensitive to the initial parameters."
] |
[
"Well, of course you can never reach mathematical exactness if your calculation depends on measurement values."
] |
[
"That doesn't play a relevant role for millions of years unless you consider comets or similar objects with planet-crossing orbits."
] |
[
"What is the minimum amount of time needed to take a water molecule from boiling point to freezing point?"
] |
[
false
] |
[deleted]
|
[
"Note that temperature is only well defined when talking about a large number of particles; one single water molecule doesn't have a boiling or freezing point."
] |
[
"You can drop a solution of water from boiling to freezing instantly using the triple point."
] |
[
"That's for convection, but there are other methods as well - laser cooling, for example."
] |
[
"Can simple invertebrates like snails feel pain? How can we know for sure either way?"
] |
[
false
] |
Thought I'd ask this question again, it was asked 5 years ago in this thread "Do insects and other small animals feel pain? How do we know?" . It got some very good replies. Especially from . I'll paste some of it here, but please read the whole thing, it's amazing. Let's start off by saying that this question has been examined with increasing interest since the 1980s but interest has always been around because of the evolutionary and philosophical question of why do we interpret the environment in the ways we do (in the realm of pain)? Because of how close crustaceans are to insects, I will focus on crustaceans. Elwood and Barr, the two papers I put up there, publish heavy in this realm and have some nice reads, but they pretty much focus solely on the behavioral aspect, not the neurological aspect. In fact, Elwood et al. 2009 (referred to in the wikipedia article) examined grooming behavior when chemicals and stimuli were applied to exoskeleton and chemoreceptive areas (namely the antennae are highly receptive to chemicals). They saw that when applying pain-killer chemicals to antennae, it increased grooming of the antennae which was the same response when they put caustic sodium hydroxide on their antennae. That is to say: pain-killing molecules elicited the same exact response as if there was sodium hydroxide on them. They even pinched them for the mechanical response: same thing. Thus this research is more evidence for the flight response and receptors detecting unfavorable conditions than it is for pain. It's specifically this part that I am very interested in and wondering if any new research has been made the past 5 years. So if the behaviour itself isn't a good indicator of if they feel noxious stimuli or not- then how can we know?
|
[
"In some studies with mealworms, when touched with a hot metal rod, they would cower away. This concludes that \"hot, no touchy\" is a basic instinct in this creatures as it is in us. ",
"However, we can't say they feel \"pain\" as we do, since we have specific areas in the brain that process pain. With infinitely different nervous systems, let alone brains, we can't say what goes inside them, only that they react like we do when we feel pain."
] |
[
"Former pain researcher, though I used rats. ",
"This sounds really technical & legalistic, and other people with different training may have a different answers, but this is how I was trained.",
"We used various methods to measure analgesia. In my field, because you’d need language to report it, pain (or emotion) isn’t really a thing that is studied. I imagine it would be even more true for invertebrates. You would study their avoidance of an unpleasant sensation."
] |
[
"Pain is an emergency signal the brain uses to control our behavior in order to increase our survival probability. It can be infered that most lifeforms that need/have this type of response can actually \"feel\" it."
] |
[
"Does electromagnetic spectrum goes to infinity?"
] |
[
false
] |
And can we discover something even higher than gamma-rays?
|
[
"Since I answered the same question yesterday, I'm just going to copy-paste what I said there - note this is talking about how high the energy of photons can go, but the same as saying how high the frequency of the EM wave is. ",
".",
"Answer:",
"We actually don't know. The highest energy photons detected are in cosmic rays, with energies ~100TeV or so and we don't actually know very much about them, like the details of the processes that generate them (see this article: ",
"www.theguardian.com/science/2013/feb/14/cosmic-ray-mystery-solved",
").",
"Whether photons can just keep going to higher energies or not is really anyone's guess right now, and I personally think that it ultimately comes down to whether there is any way to generate photons with arbitrarily high energies - if there isn't a way to do this, then there's not that much point in asking what they'd be like.",
".",
"Whilst finding my post, I thought this side note might be of interest:",
"Gamma rays tend to behave more like particles (photons) than waves because their wavelengths are so short that they only really interact with one atom at a time, allowing them to be modelled as particles in almost all situations. Conversely, radio waves experience strong reflection and diffraction from everyday objects and so have to be treated as waves. However, in very complicated applications this may be too impractical and a kind of combination technique called 'ray tracing' may be employed instead."
] |
[
"Physics kind of break down when a photons Schwarzschild radius exceeds its wavelength (roughly at the size of the Planck length, 10",
" m). ",
"At the other end if a photons wavelength is larger than the diameter of the observable universe, it wouldn't be detectable.",
"But one could argue that in a theoretical sense, a spectrum is an infinite and continuous range of values in a continuum. "
] |
[
"Shouldn't there at least be some theoretical limits based on what we think we know about largest and shortest possible distances, the total energy size and age of the universe etc?"
] |
[
"Why did this orange juice residue crack into rectangles? [from /r/mildlyinteresting]"
] |
[
false
] |
It makes sense that the pieces would be smaller on the outside, where the layer of juice was thinner, but why are the pieces so perfectly rectangular? . It reminded me of the post from a few months ago.
|
[
"There was an article in Scientific American a decade ago or so (can't find it) that delved into why mud cracks form right angles where they meet. It has to do with stress relief -- if there's an existing crack, say, N-S, the stress in the E-W direction has already been relieved. When another crack propagates into this region that has only stress N-S, the crack will bend so that it meets the old crack at a right angle."
] |
[
"My best guess is that because of the high sugar content and other crystalline ingredients in the orange juice, after drying these particles formed into a generally uniform shape according to their molecular structures. ",
"Basically like how regular ol' crystals form, the individual particle's shapes will affect those around it and thusly how the entire structure will look in the end. "
] |
[
"Those don't look like single crystals. The shapes aren't all that uniform, and there is no evidence of ",
"preferential crystallization",
" of pure compounds (try freezing some soda: you'll see pure ice crystals around the edge of the container, with the impurities (sugar, colorants, etc.) being pushed into the fraction that freezes last).",
"They are some sort of ",
"dessication cracks",
" formed as the slurry of pulp and other components of the juice dried out and shrank, but I am not sure why they broke in rectangular lines. ",
"Similar phenomena",
" in geology show different shapes that depend on the mechanical properties of the rock."
] |
[
"Why are deuterium and Tritium isotopes of hydrogen, but not their own element?"
] |
[
false
] | null |
[
"Because they have one proton in the nucleus."
] |
[
"But why does that matter? Hydrogen has no neutrons but Deuterium and Tritium do, shouldn't that be enough to classify as a new element?"
] |
[
"The element is defined by the number of protons only."
] |
[
"When you \"lose your voice\" from a cold or the flu, what is actually the physiological cause?"
] |
[
false
] |
People sometimes grow extremely hoarse, even to the point of "losing their voice" when they are ill with upper respiratory infections. I'm a bit ashamed to say that, even with a degree in speech and hearing, I really don't know how to explain this phenomenon. Is it due to secretions coating the vocal folds? Is it due to some sort of swelling or inflammatory process? Does the virus or bacteria infiltrate the voice mechanism itself in some manner, or cause the body to mistakenly attack itself in this area? Also, is the same idea at play when a person loses their voice from overuse (e.g. excessive shouting and yelling), or is that something different that just sounds similar?
|
[
"Laryngitis is an inflammation of the voice box (larynx).\n",
"http://en.wikipedia.org/wiki/Laryngitis",
"Vocal cords are muscle in the larynx. When you talk, air going past the vocal cords vibrate to make your voice. So when your vocal cords are inflamed or swollen, your voice is changed (hoarseness or raspiness) or lost entirely.",
"A cold can cause the inflammation, as can vocal straining (like too much yelling or coughing) or allergies. "
] |
[
"People can still talk (albeit with altered voice) with nodules on their vocal folds. It seems counter-intuitive that inflammation alone would be able to completely \"lose\" someone's voice. ",
"At any rate, what does the inflammation ",
" to cause a person to lose their voice I wonder? Does it make the vocal folds too stiff to produce noise as air passes through? Make it hard or impossible to approximate the vocal folds? I guess I'm still not seeing the big picture here. "
] |
[
"It's the swelling. Inflammation causes vasodilation in the tissue, so fluid and and cells can permeate it. This causes swelling, and the change in shape of the vocal chords changes the sounds it can produce, or make you lose your voice"
] |
[
"How are antibodies transferred to a newborn through colostrum? Why can't I drink antibodies instead of being vaccinated?"
] |
[
false
] | null |
[
"I'm a PhD in Molecular Medicine and Genetics.",
"Antibodies get transferred to the baby during the last three months of gestation, across the placenta. Like cows (and pigs and lots of other mammals), human babies have porous stomachs that allow the antibodies from breast milk to pass into their bodies.",
"Unfortunately, this is passive immunity: the baby is making no antibodies for itself and is meant to be a \"boost\" as you said, for the time that the baby is susceptible.",
"Over time you lose the channels in your stomach that allow antibodies through. However, some vaccinations are available orally, like the oral polio vaccine, but this is because the virus specifically infects the gastrointestinal tract."
] |
[
"From the ",
"Wikipedia",
" page on colostrum:",
"This oral transfer of immunity can occur because the newborn's stomach is porous. This means that large proteins (such as antibodies) can pass through the stomach wall. The newborn animal must receive colostrum within 6 hours of being born for maximal transfer of antibodies to occur. The stomach wall remains somewhat open up to 24 hours of age, but transfer is more limited."
] |
[
"Yeah, now the only thing that remains is if this immunity is just temporary or not..."
] |
[
"How is it possible to filter out all the waste, drugs, and bodily fluids that end up being flushed down the toilet, and come out with such clean potable water?"
] |
[
false
] |
There's so many things that people throw down the drain and toilet like food, human waste, drugs; I guess the simple answer is filters, but how strong of filters or counter chemicals do we need to have in order to squeeze out clean water?
|
[
"It’s not the filters you are thinking of but biofilters. Wastewater is aerobically and anaerobically digested by microorganisms at wastewater treatment plants. There bacteria and fungi etc. break down drugs and chemicals that are carbon based. Heavy metal type wastes fall out and are removed as sewage sludge."
] |
[
"Wastewater treatment is a multi-step process. The first step is a simple mechanical cleaning - screens filter out any larger debris that would mess up the later stages, and settling basins are used to let sand and other dense suspended solids sink to the bottom, and let oil and other less dense stuff float to the top, where they can be removed.",
"After that comes a biological stage, which may be of varying complexity, depending on the size of the treatment plant and how stringent the requirements on the effluent quality are. One of the simplest (at least in operation, but not in theoretical modelling) is a ",
"trickling filter",
", where the wastewater is trickled through a bed of originally gravel, but in more modern days often synthetic media, where a biofilm of bacteria growing on the filter medium degrades the various organic substances present in the wastewater.",
"More advanced are the various kinds of ",
"activated sludge",
" processes - this is what the usually , which can in themselves vary in complexity, from a simple single aerated basin, to complex multi-stage systems with different aerobic, anoxic and anaerobic basins. But the primary function is the same as with the simpler trickling filter: Bacteria in the wastewater turn the organic substances in it into primarily water, carbon dioxide and more bacterial biomass, while organic and ammonia nitrogen contained in the wastewater is oxidised to nitrate. Under anoxic conditions, nitrate is then reduced to nitrogen gas, and the most sophisticated systems also manage to sequester phosphorus and other mineral nutrients contained in the wastewater into the bacterial biomass, which then is removed as excess sludge, which can be processed further into fertiliser.",
"A serious problem though are trace substances like drugs, or also certain waste products from industries, especially if they are xenobiotic chemicals that the bacteria cannot break down very efficiently, especially as those are often toxic to the bacteria as well. There are further treatment steps after the secondary, biological treatment stage that can deal with them, such as treating the wastewater with ozone, which oxidises organic compounds, or filtering with activated carbon, but they of course add to the cost and complexity of wastewater treatment."
] |
[
"And then happily dumped into nearby rivers and streams for the local fauna to merrily drink or live in. Yay three-eyed fish and two-headed toads! ",
"/S"
] |
[
"We've cloned sheep. We've cloned a lot of mice. Some folks want to clone mammoths. How hard is it to clone a tree?"
] |
[
false
] |
I was reading recently about a species of mahogany that yielded the finest furniture ever made--so fine, in fact, that it went extinct from over-use. With all the recent talk about resurrecting the mammoth, it struck me that bringing back a species of tree, a much simpler organism which has many close extant relatives and a large amount of genetic material available (largely in the form of chairs) seems like it'd be relatively easy. Are there any impediments to cloning plants the way we'd clone animals? EDIT: I realize that it's very easy to clone plants by their own mechanisms, and that that's how many food crops are grown. Obviously, this wouldn't work with long-dead wood.
|
[
"Plants are easy to clone. You just take a cutting of it, shove it in the ground, and boom, clone. Cloning from straight DNA in plants is vastly harder.",
"Plants are NOT simple organisms, no matter how boring they look. They are just as complex as humans in just about every metric you pick - genome size, number of genes, specialization of cells, etc. In fact, plants can have extremely complex and confusing genetic makeups - redwoods, for instance, have 6 sets of chromosomes, compared to our two.",
"Further, molecular biology with plants is incredibly difficult. Aside from having complicated genomes, they have big thick cell walls that make a lot of standard techniques difficult. Cloning in animal cells is done by ripping the nucleus out of an egg, and adding the nucleus from a target cell. The very tiny surgery required to do this is a lot harder when you have to deal with a rigid layer of cellulose.",
"The only reason we've made more progress in genetically engineering plants is because nobody cares if you kill them. Kill one measly human and everyone's all human rights this and mad scientist that."
] |
[
"Some ferns have THOUSANDS of chromosomes in each cell."
] |
[
"We have been cloning plants for centuries, even before we knew what cloning was.",
"But cloning from ",
" tissue can be a problem."
] |
[
"Why is methionine always the \"start\" codon for proteins?"
] |
[
false
] |
Taking a couple biology classes and both have mentioned that methionine (AUG) is the first codon for proteins, but I haven't found anywhere in the text books or online as to why this specific sequence of nucleotides is always what starts a protein. My microbiology instructor didn't know either. I figured Reddit would probably know.
|
[
"Interestingly, AUG is actually not the only start codon, though it is by far the most popular. ",
"Alternative start codons",
" include GUG and UUG. The most interesting thing is that these alternative codons are still translated as Met, regardless of what they typically code for, by using a special start codon tRNA.",
"So, we come back to the same question: why Met? As far as I can tell, nobody really knows."
] |
[
"The tRNA that carries methionine to the ribosome contains a CAU anticodon that recognizes the AUG start codon. This tRNA also associates with several translational initiation factors that bind to the 5' mRNA cap in eukaryotes and promotes the formation of a pre-initiation complex with the small ribosomal subunit. This complex containing the Met-tRNA then scans the mRNA and upon recognition of the AUG start codon protein synthesis begins. "
] |
[
"It could be just chance. Perhaps it was just coincidence that in the early origins of life, methionine was chosen to be the start codon. ",
"And since it works and without any significant selection pressure to change this, it was conserved and passed through the phylogenetic tree. ",
"This is kind of similar to the fact that our bodies only metabolize D-glucose and not L-glucose and how nature prefers L-amino acids to D-amino acids. They're enantiomers with basically identical chemical properties, but nature holds prejudice over one of the two forms. A lot of scientists have hypothesized that the selection of one of the enantiomers was purely by chance and conserved throughout evolution.",
"I'm sorry I can't really find a concrete source on this since it's a bit of a mystery in the scientific community, but interesting nonetheless!"
] |
[
"When in tense or scary situations, why does the heart beat faster? Does increased blood flow make you more alert or capable?"
] |
[
false
] |
The hormone adrenaline causes the increase in heart rate, but why?
|
[
"The nervous system has a few branches; one of the branches of the central nervous system is the sympathetic division. It is autonomic, meaning it is involuntary, and involved in the \"fight or flight\" reactions we have. In scary situations, this branch of the nervous system is active and causes several physiological changes including higher heart rate, constriction of peripheral arteries, dilation of pupils, decreased saliva production, reduced digestion, etc. All of these changes are meant to help us in situations where we may need to run or fight. ",
"Our heart rate increases because this allows more blood flow to muscles and vital organs. This allows these body locations to get more oxygen as well as more glucose for fuel as glycogen is simultaneously broken down in the liver during this process."
] |
[
"Does increased blood flow make you more alert or capable?",
"It makes a big difference for muscle function. Increased blood flow brings more oxygen to the muscles, which lets them work harder for a longer time before becoming fatigued. ",
"If you're about to get into a fight or run away from a predator, improved muscle function could save your life."
] |
[
"I see, thanks!"
] |
[
"How do scientists know how much dark matter a galaxy has or doesn't have?"
] |
[
false
] | null |
[
"You take a galaxy and measure the rotation speeds of the stars. When you plot them on a graph of orbital speed Vs their radial distance, you'll see that it doesn't add up. There should be more mass present to account for all that speed. Then you figure out how much mass should be there for the stars to be going that fast and voila. (Simplified version)"
] |
[
"It’s worth mentioning we can also just take ",
"a picture of dark matter",
" with a telescope to measure it. Gravity causes visible red shifts, so all we had to do was find a galactic collision in the sky and the dark matter would slide past the regular matter due to how weak it interacts before condensing back with regular matter. This collision situation allows us to isolate dark matter’s red shift absent regular matter."
] |
[
"Hey DudeFocus!",
"So the initial observations which pointed to dark matter were made by an astronomer called Fritz Zwicky in the 1930s. He was looking at a cluster of galaxies known as the Coma Cluster took measurements on how much matter there was based on the light he observed, and how much matter must be there for the cluster to be gravitationally bound. This is known as a matter to luminosity ratio and he calculated that the M/L factor for this cluster is much to great: he was missing a significant amount of mass. This would later be shown to be what we call dark matter today (or what he called Dunkel Materi” in his original paper!) ",
"In regards to galaxies, we can look at specially spiral galaxies and measure how fast objects are moving at different distances from the center. Based on the luminous or baryonic matter of the galaxy we can predict that the speed of Rotation of these objects would fall off pretty quickly with distance, BUT we measure this ‘rotation curve’ to be flat as distance increases. The speed of objects in spiral galaxies stays about the same as you go away from the central bulge. This points to there being a large concentration of matter outside the galaxy which would gravitationally influence the baryonic matter within the structure that we can see. This unseen matter is what we call dark matter.",
"If you have any questions feel free to ask! I’d love to help.",
"Source: astrophysics major"
] |
[
"Why aren't the *sub*species of brassica rapa just considered different *species*?"
] |
[
false
] |
I guess the question is, what's the difference between subspecies and species, at least in the plant world? there even a clear distinction?
|
[
"One really important thing to understand is that ",
" difference (IE, difference in shape) has surprisingly little direct relationship with ",
" difference. You can change a very few genes and produce a plant that looks totally different. Or you can change a lot of genes and produce a plant that looks almost exactly the same. ",
"So the visual differences between, say, cabbage and broccoli aren't actually representative of a deep genetic difference."
] |
[
"For the record broccoli, kale, cabbage, kohlrabi, cauliflower, Brussels sprouts, and collards are all the same species: ",
".",
" (in OPs title) include white turnips, box choy, tatsoi, mizuna, Chinese/Napa cabbage, and broccoli raab."
] |
[
"The concept of species existed before we knew of genetics. Back then, it was mostly based on morphology (do they look different) and whether you could observe interbreeding.",
"Now, with the ability to sequence genomes, species concepts can also be investigated using for example the phylogenetic species concept (how closely related are they).",
"There is no true definition of species. As a human example, we often say neanderthals were a different species, even though they interbred with modern humans.",
"To go back to plants, they are in general very flexible with their breeding/self recognition, such as grafting being an option between very different plants.",
"In general, to be seen as a species, you have to be genetically distinct, and have barriers to interbreeding."
] |
[
"Is there something genetically or physiologically that makes someone a \"morning person\" vs not?"
] |
[
false
] | null |
[
"A similar question was asked a while ago ( ",
"What makes one a \"morning person\"? Is it possible to condition yourself to be this way?",
" ). Here's a copy-paste of what I replied then: ",
"Your natural body rhythms are largely determined by your T (tau), or circadian period. Basically this means, if we locked you in a room where you controlled the light, your meal-times, your entire schedule, after settling in you would see that everybody has their own natural day-length. It seems that T is strongly genetic, both in animals and humans, though it may change with age.",
"Turns out, most humans have a T of a little over 24 hours (24.2 I think is the most commonly cited number). So your average person, if allowed to free-run as I described, would settle into a schedule in which they started a new day every 24.2 hours. However, pretty much nobody free-runs. Your circadian rhythms are entrained mostly by light (though definitely by other sources to an extent, but light is the main one), so each day when your first exposed to light, your clock \"resets,\" so to speak. Since most people have a T of OVER 24 hours, this means they start their day a little before they meant to. It also means they end their day a little later than they should. This is what's known as \"eveningness,\" or being a \"night owl.\" Some people of course have a T of less than 24 hours, so they will start their day a little earlier than they should: Their body says yesterday is over maybe 20 minutes before the next day actually starts, and they tend to wake up early. This is termed \"morning-ness\" or being a \"morning lark.\" Going along with the genetic kick, there are inherited diseases at both of these extremes: ",
"Familial Advanced Sleep Phase Syndrome",
" (T much shorter than 24 hours) and ",
"Delayed Sleep Phase Disorder",
" (T much longer than 24 hours). ",
"(General source for this, in a pinch.)"
] |
[
"Yes, it's genetic in ",
"Chronomedicine",
" it's generally accepted that people are born with tendencies to sleep and wake at certain times. ",
"Further (scientific) reading for the layman: ",
"http://www.amazon.com/Body-Clock-Guide-Better-Health/dp/0805056629/ref=sr_1_2?s=books&ie=UTF8&qid=1351787725&sr=1-2&keywords=chronobiology"
] |
[
"I'm not going to give you a source on this one (because I'm at work--in a lab that studies circadian rhythms!), but I remember it being mentioned in a lecture I attended by a guy who does this stuff in humans; in fact I'm pretty sure this exact question was asked. His theory is that it's because a certain personality type tends to be in charge, and it's possible that this is correlated with a T<24. Possibly people who are more productive in the morning are seen as better workers and promoted to leadership positions more often.",
"Though keep in mind, even if you are not a morning person you can increase morning productivity by going to sleep earlier (like 8 instead of 11) and waking up earlier (3 instead of 6), with a bright light on at 3 AM. You still won't be as productive as you might be in the late evening, but more so than if you were still groggy at 8AM due to light interrupting your natural tau."
] |
[
"What happens to an airplane if it gets struck by a lightning bolt?"
] |
[
false
] |
[deleted]
|
[
"not much typically, unless it's a carbon composite. The aluminum body on most airplanes routes the lighting around the fuselage and allows the bolt to continue on its merry way."
] |
[
"Its true. Bill nye said it in his lighting show"
] |
[
"Most airliners get hit at least once a year"
] |
[
"Is plant growth ever limited by CO2 availability?"
] |
[
false
] |
First, I'm not a global warming denier! I know that this reasoning was advanced by oil companies to put a positive spin on CO2 emissions. It's amazing what a small part -- 0.039% -- of the atmosphere is CO2, especially after reading on Reddit that most of the dry mass of plants is pulled out of the atmosphere, not the ground. So do plants benefit from having CO2 more readily available? I did check Wikipedia and found this: "Plants can grow up to 50 percent faster in concentrations of 1,000 ppm CO2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients.[44] Some people (for example David Bellamy) believe that as the concentration of CO2 rises in the atmosphere that it will lead to faster plant growth and therefore increase food production.[45] Recent research supports this position: elevated CO2 levels cause increased growth reflected in the harvestable yield of crops, with wheat, rice and soybean all showing increases in yield of 12–14% under elevated CO2 in FACE experiments.[46][47]" from So does this mean that plants will help mitigate increasing CO2 concentrations by pulling increasing amounts of CO2 out of the atmosphere? Do climate models already take this into account?
|
[
"The problem with that is that while plants might grow faster, they don't necessarily live any longer. So if you're talking about crops, or grasses on the great plains, they are still going to be harvested and rot every year, so that CO2 goes right back into the atmosphere. The ocean ecosystem is probably not CO2 limited, or at least it's much more limited by other nutrients like iron. Things like rainforests that are \"mature\" already have their growth balanced by death. If you add to the growth rate, you might not store more CO2 in those forests in the long run, because you might just turn over the forest faster.",
"The upshot of all this is \"it's complicated\" and nobody knows for certain. If plants could just use CO2 that much faster, then you would wonder why CO2 levels were rising at all. It's quite likely that plants already ",
" mitigating global CO2 rise, so the rate we're seeing already takes into account the effect of increased photosynthesis. It's just that no one knows what the shape of the curve should look like, since we don't have accurate measures of CO2 release, uptake, or any of the other variables."
] |
[
"Quick correction - the atmosphere is ",
" CO2, not 0.39%. "
] |
[
"Yes. It is actually thought that plants evolved during a period in which more CO2 was readily available. Some plants have even developed methods for coping with lower levels of CO2. Specifically, ",
"C4 Fixation",
" is thought to have developed more recently (in evolutionary terms)to combat waste caused by photorespiration (fixing oxygen as opposed to CO2). ",
"especially after reading on Reddit that most of the dry mass of plants is pulled out of the atmosphere, not the ground.",
"Don't forget that nitrogen is NOT obtained from the ground. All nitrogen that plants take in is fixed from the air by bacteria or lightning.",
"Edit: Removed previous edit."
] |
[
"what is the highest temperature achieved by man?"
] |
[
false
] |
i was watching Vsause's video where the commentator said that the LHC reached a temperature of 1 exakelvin (1 x 10 C). on the wiki page of temperature, it says that only a temp of 10 trillion K was produced by the LHC (also the source page cannot be found to verify that). the Huffington Post says the highest temperature achieved by man was only 4 trillion C. which one is to be believed?
|
[
"This confusion likely came from a ",
"short scale/long scale",
" mixup - 10",
" is a trillion on one, but a million trillion in the more common short scale used in the US.",
"So, yes, the LHC can routinely get up into the 10",
" K range, and since the LHC is in Switzerland, they'll call this a trillion kelvins - even though in the US, we'd call that a quintillion.",
"As for the question of what the actual highest temperature achieved has been - the 1×10",
" quoted by Vsause, or the 10×10",
" you say Wikipedia gives, or the 4×10",
" you say HuffPo gave, I can't speak to that. But at least, they're all within an order of magnitude now that you understand the short scale/long scale distinction.",
"I will say this - temperatures at the LHC are derived from measurements performed by an experiment called ALICE. Alice doesn't actually measure temperature like a thermometer, but the energies of heavy ions (and at this point, I'm outside my expertise, so feel free to jump in and correct me, anybody). Scientists can then use those values to estimate the temperature of the quark-gluon plasma that was created, and that conversion can take time.",
"Therefore, it's absolutely reasonable that when vsauce made the video, the highest confirmed temperature was 1×10",
", even though higher temperatures had been achieved. Perhaps shortly after, those new temperatures were confirmed and HuffPo reported that, and of course, Wikipedians are eager to update every page as soon as new news comes out. This rapid rise in temperature is made all the more plausible since the LHC didn't start at it's highest operational energy, and they've been ramping up ever since it went live."
] |
[
"This is absolutely correct. ",
"The paper cited quotes what I consider the most precise measurement of the temperature, which is 1.8x10",
" K.",
"However, this is the temperature at what is called \"freeze-out\", when the quark-gluon plasma produced in a lead-lead collision has expanded and cooled enough to transition to hadrons (protons, neutrons, kaons, pions, etc...). The temperature in the early stages of the collision is harder to approximate, and it is also an open question as to how long exactly the medium takes to thermalize. The initial temperature is higher, but by less than an order of magnitude. ",
"10",
" is a factor of a million too high, and you cannot convert the center-of-mass energy of a collision to the temperature of the produced medium simply by dividing by the Boltzmann constant. A bullet has an energy of about 500 Joules, or 3x10",
" eV. If you divide that by the Boltzmann constant you get about 3x10",
" K, which is extremely silly."
] |
[
"10",
" is much more reasonable than 10",
" based on everything I've read. ",
"This paper",
" quotes a temperature of 156 MeV, which when divided by the Boltzmann constant yields 1.8x10",
" K. ",
"An order of magnitude calculation, 7 TeV divided by the Boltzman constant is ~10",
" K, so maybe that's where the 10",
" figure comes from? Either way it's off by a factor of a million."
] |
[
"When was the last time the moon was hit by a large enough meteroid that it would have been visible from earth?"
] |
[
false
] | null |
[
"There are periodic flashes on the moon (a few have even been recorded) that are thought to be from meteor strikes. Unfortunately, because the moon lacks and atmosphere, we do not get as big of a fireworks show as we do when meteors hit the Earth. This means we don't see most of the ones that impact even though they are about as frquent as those that impact the Earth."
] |
[
"Right the photos of flashes on the moon are so notable because they are so rare even though the moon is observed and recorded ~continuosly by humanity.",
"If we could actually see all the impacts the moon gets that are too small to make noticable flashes it would be quite the show, day in and out. Unfortunately the vast majority are too small to make big flashes.",
"One note: NASA impacted the moon with a spent rocket stage that was followed closely by a satellite meant to observe the collision. Despite knowing when and where the collision would be and the fact that the sensitive instruments we're relatively close to it, the resulting flash just barely got above the noise floor of the instruments and was not visible to people through the cameras despite NASA predicting it would be."
] |
[
"Here",
" is one from March 17th, 2013. The flash was imaged from earth, and LRO was able to image the resulting crater, showing both before and after the impact."
] |
[
"Does someone who is \"in shape\" run a mile using less ATP than someone who is not \"in shape\"? Why?"
] |
[
false
] | null |
[
"It depends on a lot of factors. To simplify things we'll assume identical weight and body composition between the two people, because different masses will require different amounts of work to move the same distance. So now we have two different people of identical weight and body composition running a mile, one is fit and one is not, so which one uses more ATP? It depends, \"fitness\" is a multifactorial phenomenon, there are dozens of individual components to fitness that act independently and also interact with each other. If we isolate some of the more important performance factors for running, we can determine situations in which they might use the same amount of ATP, and situations in which they won't. Two of the most important factors that determine running performance are critical pace (pace at lactate threshold) and VO2max. If these are the only differences between the individuals they will use the same amount of ATP to run a given distance, the more fit individual will just be using a smaller percentage of their maximum ATP production capacity. \nThe other two most important factors in running performance are ",
" (how well an individual converts fuel substrates into ATP, measured as an amount of ATP produce per unit of oxygen consume, or P/O ratio) and ",
" (how well an individual converts ATP driven muscular contractions into forward movement). Efficiency doesn't vary greatly between individuals who are reasonably fit, so we'll assume efficiency is the same. Economy on the other hand, varies tremendously, so much so that it may turn out to be more important than maximal aerobic capacity as we research it more. So if the individuals are identical in every way except for their economy, they will use different amounts of ATP to cover a given distance. You can picture this difference by imagining smooth, quiet, graceful runners (Mo Farrah) to someone who stomps along, banging loudly with every footstrike, waving their arms around, rolling their head side to side, and having too much up and down movement - that person would obviously require more ATP to cover the same distance.",
"TL;DR - It depends, people with the same body composition and economy will use the same amount, with different economies they will use different amounts. It depends how you define fitness. ",
"Edit: PS - an interesting side note is that up to a certain point, the speed at which this mile is run doesn't matter! As long as an individual is running at a pace at which running is more comfortable than walking, they will use the same amount of ATP, regardless of how fast they complete the mile."
] |
[
"/u/codyish",
" wrote ",
"at a pace at which running is more comfortable than walking",
"Note the \"at a pace at which\". What is meant, I think, is this: Consider a normal walking pace. Walking is then more comfortable than running at that pace. ",
"Now consider a faster pace, at which it is difficult to walk that fast. It is then more comfortable to run, given that you have to maintain the same pace. ",
"Walking at walking pace will however always be more comfortable than running at a running pace. "
] |
[
"What do you mean by \"running is more comfortable than walking\"? "
] |
[
"Why is it hottest after summer solstice, but not before?"
] |
[
false
] |
Where I live (Pacific NW) it is always cool and raining until the end of June, but then gets into the high 90's+ from July till September. Shouldn't it be hotter equally before and after the solstice?
|
[
"http://en.wikipedia.org/wiki/Seasonal_lag"
] |
[
"The Solstice is the peak in the ",
" of energy arriving in the Northern Hemisphere. The land temperature is determined by the amount of ",
" energy. That's the difference.",
"So long as the rate of energy arriving is higher than the rate of energy leaving (being radiated back into space), the temperature of the land will continue to increase. On land, this carries on for a few weeks after the Solstice.",
"The oceans continue to absorb energy for a couple of months after the Solstice before they become warm enough to radiate more out than they take in, so their temperature will usually peak in late September. The temperature of the oceans in turn affects the temperature on land, especially closer to the coast."
] |
[
"Makes sense, thank you both for excellent answers."
] |
[
"Why does the plastic bag 'trick' work with magnetic strips on Credit cards?"
] |
[
false
] |
[deleted]
|
[
"The card reader has a small induction coil that detects a succession of magnetic and non-magnetic zones in the card’s magnetic stripe. When the card is pulled through the reader, each magnetised zone makes a small electrical pulse as it passes the coil. The zones are arranged to encode the data needed to complete a transaction.",
"The magnetic stripe of your Card is made of fine particles of a magnetisable oxide embedded in a plastic binder. It can get damaged in many ways. When the card reader is reading the card a scratch or other defect in the magnetic stripe can cause a spike in the signal that a too-sensitive reader will interpret as a tick, meaning that the encoded data will fail the parity check and will cause a bad read.",
"Wrapping the card in plastic bag increases the distance between the card reader head and the magnetic stripe, thus reducing the strength of the signal and smooths out fluctuations and hence the card swipe works.",
"SOURCE: ",
"http://www.tipsandtricks-hq.com/bank-card-or-credit-card-plastic-bag-swiping-trick-100"
] |
[
"I once contacted a card manufacturer about this. The tech told me the reason that it works is that card readers have an automatic gain control, that is they adjust the amount of signal the cards reader amplifies from the weak voltage the reader head produces when you swipe the card. When you use the the bag or tape the initial signal is weak due to the increased distance from the head so the gain is set to maximum levels and this enables the card reader to read a magnetic strip the has damage more effectively. Newer card readers have dynamic gain control that continuously varies the gain based on the head output, they are the ones that read the cards more reliably. Sorry I don't have a source for this."
] |
[
"I believe it will."
] |
[
"Do fat people have strong hearts?"
] |
[
false
] |
Do fat/obese people have stronger hearts than those thinner than them? I know strong is a vague term, but I'm not sure how to explain it. For example, if a person weighed 300 pounds, and lost 100 pounds, would they subsequently have increased blood volume capacity and faster heart rate?
|
[
"I have been told by others on here that fat/obese people would actually be very healthy (perhaps healthier than average people) with strong muscular frames from years of carrying excess weight if they decided to lose the weight. ",
"It's like wearing 30-50lbs training weights all day, every day all over your body.",
"I've also noticed, anecdotally, that women who are overweight and lose it usually look better than women who have been thin their entire life. "
] |
[
"Yes and no. For some one who is extremely obese (500 lbs and up) the heart thickens to allow for stronger contractions. if this person were to lose weight (say down to 350 lbs) the heart would remain thick but would pulse less. So yes they have \"stronger\" hearts than an average sized person, but no the heart is not \"stronger\" in a way that it is better than an average sized person. "
] |
[
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767922/"
] |
[
"Do magnetic and/or electric field have any influence on time and space?"
] |
[
false
] |
According to Einstein, gravity has influence on space and time. Does magnetic field have influence on time and space? Does electric field have influence on time and space?
|
[
"As other people have pointed out, the answer is yes, but there’s something in the way you phrased the question I want to focus on. You said that gravity curves spacetime, and wondered if other forces do as well.",
"It’s much more accurate to think of matter and energy as curving spacetime, and this effect is ",
" gravity. Gravity ",
" spacetime curvature. So in that sense it’s on a different footing than the other forces.",
"All of the forces are carried by fields - for example, the electric and magnetic forces are carried by the electromagnetic field - and fields have energy, so they do curve spacetime, which is to say, they gravitate. ",
"EDIT: I should add this effect is absolutely tiny unless the strength of the electric or magnetic field is absolutely enormous. ",
"EDIT EDIT: Probably the most famous (theoretical) example of this effect is a charged black hole. The spacetime curvature around such a black hole is different than for an uncharged one. That is to say, charged and uncharged black holes gravitate differently. This is ",
" the electromagnetic force that charged black holes have. "
] |
[
"Yes, all energy contributes to the stress-energy tensor and the curvature of space-time so that includes energy in the electric and magnetic fields"
] |
[
"I'll provide two different explanations in case you find one more helpful than the other. The first one is mine, and the second one is quoted below from a Scientific American article. While mine speaks a little bit more loosely with certain definitions, it has been a useful way for me to think about some things.",
"One of the important things in physics to remember is that energy is equivalent across forms. By this I mean, electrical energy can be converted into mechanical energy and so forth. Joules was one of the big pioneers in this field and that's why \"Joules\" are used as a universal unit for energy. Another important thing to remember is that Einstein's special relativity paper showed that all forms of energy contribute to the mass of a body. This is often stated as the \"mass-energy equivalence,\" and people often point to the equation E = mc",
" to discuss this issue (although I would point out that the equation is actually E = γmc",
" , where γ is based on the velocity of the body; but that is a slightly different issue). ",
"As was realized by Newton, mass causes gravity, and it makes sense that this would somehow be true in general relativity as well. However, in special relativity, we already know that mass and energy are related, so logically it should be energy, not mass, that causes gravity. As we know, however, energy is just one component of a four-component four-dimensional momentum, so perhaps we should be including momentum as well. (Sidenote: this last sentence is a bit of a jump, but it relates to the \"γ\" value in Einstein's equation above, and its derivation might take us off the rails. However, if you're curious, this wikipedia article gives a good in-depth summary of the issue: ",
"https://en.wikipedia.org/wiki/Four-momentum",
").",
"In fact, it turns out that not only do the momentum and energy come into the equations, but also the way they are flowing or being transferred plays a role as well. The whole source is not just the energy, or even the energy and the momentum, but something nastier that should properly be called the \"stress-strain-energy-momentum tensor.\" But, because even physicists can’t get their mouths around this phrase, it is more commonly called the stress-energy tensor or \"energy-momentum tensor\" or even just the \"stress tensor\" (or sometimes, just Tμν). In Einstein's field equations for general relativity, the stress–energy tensor is the source of the gravitational field, just as mass density is the source of such a field in Newtonian gravity. While the stress-energy tensor contains many components (sixteen in all), just one of these components, the time-time component, is the actual energy density (which is proportional to the mass density).",
"This is where your question is answered. The time-time component of the stress-energy tensor accounts for the electromagnetic field having an influence on the space-time continuum, thereby causing gravitational fields under general relativity.",
"If you'd like a slightly more detailed coverage of this issue for an undergrad level understanding, this ",
"lecture paper by Eric Carlson",
" is a very good overview in my opinion. I would also recommend his slides titled \"General Relativity\" for one of his undergrad courses (",
"found at the bottom here",
"). To really get the full experience, put the slides in presentation mode and click your way through.",
"This ",
"article in the Scientific American by Charles Torres",
" provides a better detailed answer in layman's terms than I could probably provide. I've quoted the article below:",
"Electric charges and magnets do indeed \"distort space,\" but this happens on a couple of levels.",
"First, a word of background. According to the current best theory of gravitation, which is contained in Albert Einstein's famous general theory of relativity, a gravitational field represents a curvature of space-time, rather than a distortion of it. Anything that carries energy, momentum and stresses is a source of a gravitational field, that is, a curvature of space-time.",
"Electric charges and magnets are manifestations of certain types of matter, most particularly electrons. Since matter carries energy (via Einstein's famous relation that energy is mass times the speed of light squared), such objects will have a gravitational field and so they will distort space-time. So one way in which a charge or a magnet will distort space-time is by virtue of its matter. That answer may not sound too impressive, but there is more. . . .",
"You see, electromagnetic fields themselves carry energy (and momentum and stresses). The energy density carried by an electromagnetic field can be computed by adding the square of the electric field intensity to the square of the magnetic field intensity. As another example, a beam of light (produced from, say, a laser) consists of an electromagnetic field, and it will exert a force on charged particles. Thus the electromagnetic field carries momentum. Because an electromagnetic field contains energy, momentum, and so on, it will produce a gravitational field of its own. This gravitational field is in addition to that produced by the matter of the charge or magnet.",
"A simple example of the gravitational (or space-time curvature) effect of electric charges arises in the \"Reissner-Nordstrom\" solution to Einstein's gravitational field equations. This solution describes the gravitational field in the exterior of a spherical body with non-zero net electric charge. (The solution describing the special case in which the net electric charge is zero is the famous \"Schwarzschild solution\" to the gravitational field equations.) From the Reissner-Nordstrom solution, it is clear that the motion of test particles in the gravitational field of the spherically symmetric body depends on whether or not the body carries a charge. Just as the Schwarzschild solution can be extended to describe the famous phenomenon of a \"black hole,\" the Reissner-Nordstrom solution can be extended to describe a \"charged black hole.\" For an electrically charged black hole, the gravitational field of the hole includes a contribution due to the presence of an electric field.",
"I do not know (and I doubt) whether this aspect of gravitational theory (that electromagnetic fields produce gravitational fields) has been directly tested by experiment. The difficulty is that the gravitational field produced by a typical electromagnetic field you can produce in a laboratory is predicted to be very, very weak. A better place to look for gravitational effects due to electromagnetic fields would be in astrophysical objects carrying a significant net electric charge. Unfortunately, to my knowledge, such objects are expected to be hard to come by. So while the answer to the question is definitely \"yes\" according to theory, the experimental status of this effect appears to be somewhat open.",
"If you want to read more about some of these ideas, you might try Space, Time, and Gravity, by Robert Wald (University of Chicago Press, 1992). This book is aimed at non-specialists. For a more detailed mathematical treatment, you can consult any text on the general theory of relativity."
] |
[
"Is the \"record meteor\" related to the \"record asteroid\"?"
] |
[
false
] | null |
[
"It is more likely a coincidence than crashing Slitheen vessel, and it is probably even odds with being related to the asteroid. The problem is that if too large a chunk of the asteroid broke off, we would notice a difference in size. If too small a chunk broke off (that we couldn't see), it would disintegrate fully in the atmosphere. "
] |
[
"This is a very poor answer. The OP didn't at all state that the event required meteorites to be relevant and there are many meteorites much too small to detect that impact the ground every day. Where do you get 50% probability from?",
"edit: Also jokes aren't allowed on askScience."
] |
[
"In part. You can also estimate it by the impact crater left."
] |
[
"For Astronomy/Physics buffs: questions about black holes, time travel, and the information paradox. Huge post."
] |
[
false
] |
[deleted]
|
[
"I have no credentials, so feel free to correct any errors I have made. Also, my responses are limited to my own knowledge, but the topics you've brought up are interesting to me. ",
"What does it mean to go to \"another time\"? It seems like that phrase presupposes that some overarching mechanism keeps track of time on various planes of space. I know that isn't true, but I'm forced to question the entire precept of 'time.' What is time if it is a concept external to us? Does traveling through time only make sense to an observer that operates with a different frame-of-reference? If you were the only person in the world would traveling through time be impossible because the only frame of reference is one's self?",
"Time is another dimension. If you walk down the street, you're moving in one dimension. If you walk up some stairs, you're moving in another dimension. Time is just another dimension that we move through, we just don't perceive it quite the same as we do the 3 spacial dimensions.",
"If you were a NASA engineer and crafted a robot with a camera and an internal clock that could hypothetically go through a wormhole undamaged-- what would the effect on the internal clock be relative to an external clock that is stationed in NASA? Would engineers notice a difference in the robot's internal clock? Would the clock slow down while the robot is in the wormhole? Would it be de-synced with NASA's clock after coming out of the wormhole?",
"Near a black hole, time slows down for the observer, so I would imagine the clocks would slow down relative to us on Earth. However, as far as what else is happening inside the wormhole, I have no clue.",
"The graphic used by the show demonstrated that the center of a black hole connects to another point in space/time (like this). What does that other point refer to? Is it another universe? Is it the same universe in a different time? What sustains those multiple dimensions of space that cross multiple segments of time? Are there an infinite number of potential universes, given that one wormhole could lead to a universe with more wormholes with a different set of universal destinations, ad infinitum?",
"Not really sure on the specifics of your question but I do know that the Lorentz Factor deals with the effects of time dilation/contraction at relativistic speeds, so you might want to check that out. I know it goes something like this, though: As your velocity through space increases more and more, your vector through the dimension of time must shrink.",
"The show said that \"space/time\" rips under the pressure of enormous gravity. Is there some mathematical formula that determines the quantity of gravity necessary to rip space/time and, if so, how do physicists determine that?",
"Not sure on the actual math, but I do know essentially what happens. In a star that has the mass to potentially become a black hole, as the fuel is expended, more and more iron is formed and compressed into the core because there isn't enough fuel to maintain the temperature. I believe it's the temperate that keeps it from collapsing onto itself. ",
"Think about it in Earth terms. Earth has mass and has a certain gravitational pull due to that mass. That's how we maintain satellites in orbit and what not. When a massive star burns off all of it's fuel, the rest of the elements condense into iron. It's so incredibly massive that it collapses onto itself. It's like an extreme version of an asteroid being pulled into a planet by the planet's gravitational pull. ",
"The show said that, hypothetically, if you could get in a space shuttle and fly the speed of light for a while and then come back to Earth, you will have aged less than people on Earth. How does this work? How does your biology/ whatever dictates aging know that you're going the speed of light and slow down relative to an Earthling? Is it just that the molecular reactions that govern aging slow down relative to an observer, and therefore you've actually aged less?",
"This occurs because the speed of light is constant in all frames of reference. When you approach relativistic speed (near lightspeed) you essentially move out of an observers frame of reference, I think. Someone else is going to be able to explain this better, as I still have trouble wrappintg my brain around it. What's interesting, though, is that traveling near lightspeed actually cuts travel time for those moving at such a speed. For those observing, it still takes as much time as you would expect it to take to reach a destination. ",
"Also, keep in mind that we perceive movement relative to matter. Light isn't necessarily moving RELATIVE to matter. If someone more educated than myself can help you grasp this, then you'll really begin to grasp relativity. "
] |
[
"breakbread covered a lot of it but I'll just address #4.",
"In string theory, strings are fundamental so not really made of anything. Same as electrons: they're not made of anything, just fundamental. Strings are part of a wider concept called branes, which I don't really understand.",
"There's no experimental verification of string theory yet, although it's hoped that the LHC could provide evidence of something called supersymmetry, which is a step in the right direction."
] |
[
"Thank you very much for your thorough reply! "
] |
[
"How do large clusters of fires like California is having affect the weather?"
] |
[
false
] | null |
[
"Locally, as in directly over and around the fire, it is capable of creating its own weather. It does this by creating immense amounts of heat, pulling air upwards. This leave a low pressure area that wants to be filled. New air fills this lower pressure area creating wind. This process feeds back upon itself, and when combined with steep canyons or other topographic features can create incredibly fast moving fires that move against the prevailing winds. ",
"they don't commonly have an affect at a larger scale, fires are mostly influenced by weather, not vice versa. We get fires here when there are dry, powerful, Santa Ana winds that make a normally easily containable fire (car accident, cig butt, falling power lines,etc) move rapidly and spread uncontrollably. In rare cases the fires ash can contribute to cloud formation, helping firefighters put a stop to the fire if wind pushes these newly formed clouds over the fire. in the most extreme cases the fire's ability to create its own wind and storm clouds can create a fire tornado. ",
"Source: me, a firefighter and college forestry courses",
"Edit: thanks to ",
"/u/sirkazuo",
" for bringing up the ability of fires to create their own storm clouds. Scroll down to his response to this comment for good links. Added to post for correctness."
] |
[
"they don't have an affect at a larger scale",
"Not in California, but wildfires ",
" capable of altering the weather to an even greater degree. When a fire is large enough and the conditions are right, they can create a ",
"pyrocumulonimbus cloud formation",
" in the sky over the flames which in a lot of cases rains on the fire and helps put it out, but it in even more rare circumstances it can in turn spawn an actual ",
"Fire Tornado",
", which is exactly as terrifying as it sounds."
] |
[
"I've found me to always be the best source of information."
] |
[
"Why do commercial jets have rounded noses?"
] |
[
false
] |
Fighter jets have a more pointed nose but for some reason commercial jets do not. Why?
|
[
"Commercial jets fly at subsonic speeds and at those speeds a spherical leading edge (i.e., rounded nose) has the least drag of any shape. At supersonic speeds the shock wave created by the aircraft becomes a bigger factor in drag than the aerodynamic drag. The shock wave will begin at the forward most point of the aircraft traveling faster than sound (i.e., at the nose) and forms a cone aft. The angle of the cone decreases as the speed of the aircraft increases. If an aircraft component gets outside of the cone formed by the nose, it will create it's own shock wave and drastically increase the drag on the aircraft. By having a sharp pointed nose, a fighter jet is designed to keep the entire aircraft behind the shock wave."
] |
[
"The Concorde is another relevant example for this difference, being a supersonic commercial aircraft (with the associated pointed nose)."
] |
[
"The Concorde has a ",
"Droop-Nose",
" that would be lowered for visibility when on the ground and during take-off/landing, once in actual flight it would be raised to the normal position."
] |
[
"Does the stomach have pain receptors?"
] |
[
false
] | null |
[
"TL;DR: Yes.",
"The presence of afferent nerves (related to sensations being sent towards more central parts of the nervous sytstem like the brain or spinal cord) in the gastrointestinal system (which includes the stomach) has been known for a very long time (e.g., ",
"Bailey & Bremer 1938",
"). This includes the conduction of 'pain-related' signals, though it would be better to call them ",
"nociceptive",
", given that we typically reserve the term 'pain' for the conscious feeling of pain.",
"What is a relatively more recent area of interest is the role of those signals in conscious pain perception. This is presumably what you are most interested in, and the answer is that a subset of pain receptors in the stomach send signals related to conscious perception of pain. From ",
"Saper (2002)",
": \"In general, visceral afferents that enter via spinal nerves convey information concerned with temperature as well as nociceptive visceral inputs related to mechanical, chemical, or thermal stimulation (",
",** Ammons 199**2), and the spinal afferents seem to be the principal source for these modalities reaching conscious perception.\" Saper's review article does a good job explaining in a thorough and more technical way the research on conscious pain perception based on afferent signals in the internal organs."
] |
[
"That makes sense, thank you very much."
] |
[
"That makes sense, thank you very much."
] |
[
"Why are the cracks on glass opaque?"
] |
[
false
] |
[deleted]
|
[
"Light moving between different mediums (air, water, glass) gets a little bit bent; this is why drinking straws look bent when put into a glass. When the glass pane is smooth, the bend is minimal, since it only transitions twice (in and out). When it breaks, the glass becomes super rough, and air and glass get jumbled up. Now light is making that transition hundreds of times, so it gets all bent out of shape. All of the colors sort of blend together, giving a ‘white’ appearance. This is also why snow is white."
] |
[
"What do you mean by monochrome? If you put a bunch of snow on a red floor, it’ll still look white because very little of the light is making it all the way to the floor and then all the way back. If you shine a red light on it, you will get a red effect.",
"Basically, snow is so good at scattering light that the surroundings matter much less than what kind of light you shine on it."
] |
[
"Snow is ice, so yes, each individual snow flake is transparent. But each one bends light in its own accord, so the light that reaches your eye is a mixture of all colors but without defined shape: white, imageless white.",
"The same happens with glass dust, for example. If you fill a jar with molten glass and let it solidify, you'll get a transparent glass block (this is the equivalent to a block of ice). But if you fill it with glass dust you won't be able to see through it, it's going to be white and opaque (equivalent to snow).",
"Edit: This, as the previous user said, has to do with each phase having different refraction coefficients (aka how much it bends light); a pencil inside a glass of water looks deformed because of this bending. The problem is that, if you have thousands of different bendings altogether (like in a pile of snow) the light arrives so mixed that it doesn't conserve the image, only the light itself. That's why it's white (all wavelengths together).",
"This can be seen everywhere: gaseous water is transparent, but vapor are tiny droplets suspended in air, and that's why clouds are ",
" above an altitute, sometimes very abruptly: above that altitude gaseous water condensates and scatters light. Most plastics are transparent, but most have inorganic particles or crystals inside that form another phase and scatter light and make them opaque. A clean glass edge is transparent, but usually those edges are rough and each roughness scatters light in a different angle, making it opaque (here another fenomenon also takes place, but let's leave diffraction for another day xD)"
] |
[
"Why are antiviral medications so much less prevalent than antibacterial?"
] |
[
false
] |
It seems like we have a lot of defenses against bacterial infections, and have had them for quite some time. I'm curious why it appears that anti-viral equivalents are so much less pervasive? And the ones we have, seem so much more dangerous than the antibacterial counterparts.
|
[
"There are fewer unique targets, since viruses mostly use our own cellular machinery. We end up having to target the few enzymes and proteins they have, such as viral proteases or reverse transcriptases. We can also sometimes produce neutralizing antibodies that target viral surface proteins, which opens up some new options, but even there we also have to be careful that the viral epitopes aren’t too similar to human proteins. ",
"In contrast, bacteria have whole suites of enzymes and proteins that are often unique or significantly different than their human analogs, so we can build compounds targeting them that are less likely to interrupt human cells."
] |
[
"Yes, this is a great answer. To add one more thing, because viruses need to hijack host cells to divide, most of their active life - the time when their limited set of enzymes are working and are susceptible to drugs - is spent inside host cells. So any treatment also needs to get inside our own cells, and not do too much damage to our own cellular machinery once it's in there."
] |
[
"So the basic idea with therapeutics used to treat parasites of all sorts is that you want a target that is as unique as possible, because that reduces the odds that it will gum up your own machinery. ",
"When a virus enters a cell, it generally breaks open to reveal its own genetic information, which either directly (for double strand DNA based viruses) or indirectly (for single strand DNA and RNA viruses) read by the cellular machinery to produce new viral proteins and genomes. The enzymes that covert the genetic information (such as reverse transcriptases) or break apart viral proteins (proteases are needed when multiple peptide products are translated as one big piece) are some of the only ones directly from the virus that will be different enough for small molecule drugs to target them. Targeting the cellular machinery involved viral replication would block vital cellular functions, so that would put you in territory akin to chemotherapy where you’re hoping to kill the problem before you kill the host."
] |
[
"How does medication (pills, etc.) expire after a certain period? What makes it \"go bad\" or become ineffective?"
] |
[
false
] | null |
[
"Typically this is due to chemical degradation of the active ingredient (into inactive or possibly harmful forms), or some kind of physico-chemical change to another ingredient (e.g. degradation of the excipients required for controlled release of the active ingredient over time, crystallization or settling of liquid formulations due to degradation or evaporation of carriers, etc.)"
] |
[
"It's important to note that these are incredibly slow processes and most medication is perfectly effective past their expiration dates. These are dates that the manufactures can ",
" effectiveness, but ",
"studies have shown the vast majority of common medications have multiple decades of shelf life",
". The US army also studied over the counter medications like aspirin and Tylenol in an effort to prevent waste and came to the same conclusion. "
] |
[
"Yes, I agree that the shelf life dates are incredibly conservative when it comes to the chemical degradation of the drugs themselves. I think the dosage form issue may actually be the bigger one, in many cases; for example, the drug itself may be chemically \"perfect\" but the pill no longer dissolves in the stomach at the same rate. Things like that. ",
"For simple medications it probably doesn't matter. "
] |
[
"Is there a part of the US that is unlikely to get a natural disaster?"
] |
[
false
] | null |
[
"ten states with the least number of declared emergencies",
"Mesa, Arizona is the safest overall city. supposedly."
] |
[
"Yeah, I can see that. Anywhere dry is going to have less natural disasters and most natural disasters are weather related. And less moisture= less dangerous weather."
] |
[
"Tornados."
] |
[
"If our cells constantly replace themselves, how do our bodies or even individual organs get worn out?"
] |
[
false
] |
Cell replication, as far as my freshman, non-biology-major coursework puts it, is a cell making copies of itself based on instructions passed down through generations. How does the cell, the organ, and the body age if they are constantly being replaced with new copies on the cellular level? As a side question, what organ(s) would last the longest if they were able to run independently? Which organs or parts of the body wear out the fastest?
|
[
"Terminally differentiated cells often are unable to proliferate further. Unless there is a stem cell population replenishing them, once they die, they're gone. Additionally, for organs like the brain, if a cell is lost, the neighbors may not be able to compensate for the lost cell's activity.",
"Cells themselves age for a variety of reasons. Oxidative damage tends to accumulate throughout a cell's life. If the cell is proliferative, their telomeres will shorten until they express telomerase to extend them, or they cut into coding regions and the cell is instructed to die.",
"As for which organ would go the longest, I'd vote for testes, because of a germline population that produce sperm, they would be best equipped to combat cellular senescence. Or blood cells. Hematopoetic stem cells are also quite prolific.",
"And the most fragile, I'd say either the nervous system, the pancreas, or the kidneys."
] |
[
"I'd vote heart, its the only organ that doesn't change, the cells onky multiply and divide once, an old man has twice the amount of (and the same cells) he was born with in his heart, they don't die off, hince why it doesn't get cancer"
] |
[
"Terminally differentiated cells can become cancerous, and primary heart cancers certainly exist. Mostly sarcomas and mesotheliomas. They just are relatively rare."
] |
[
"Does the extra co2 in the atmosphere from factories and cars benefit plant life?"
] |
[
false
] | null |
[
"The simple answer is no. In lab settings, increasing CO2 concentration has been shown to increase plant growth - but under these conditions plants are not limited by other factors such as water or nitrogen. But it does not work the same way in the natural world - water and nitrogen tend to be the limiting factors to plant growth - not CO2. So you could pump as much c02 into the atmosphere as you want, the plants wont grow unless they are given additional quantities of water and fertilizers. ",
"The extra CO2 in the atmosphere has consequences on other aspects of plant growth including but not limited to: rising temperatures and changing rainfall patterns. These two factors, play a larger role in over all plant health then the concentration of C02. So basically a plant will die of heat or water stress before the benefits of CO2 kick in.",
"These articles does a great job of explaining this in a finer detail:",
"http://www.skepticalscience.com/co2-is-good-for-plants-another-red-herring-in-the-climate-change-debate.html",
"http://www.sciencedaily.com/releases/2002/12/021206075233.htm",
"http://www.newscientist.com/article/dn11655-climate-myths-higher-co2-levels-will-boost-plant-growth-and-food-production.html",
"From this last article: \"Studies of past climate changes suggest the land and oceans start releasing more CO2 than they absorb as the planet warms. The latest IPCC report concludes that the terrestrial biosphere will become a source rather than a sink of carbon before the end of the century.\" Basically at the end of the day the environment can only absorb so much CO2, then the cycles break down and CO2 accumulates at higher rates in the atmosphere.",
"I don't have time to go into the CO2 cycle and how climate change might effect it, perhaps somebody else could provide that additional information."
] |
[
"back yourself up"
] |
[
"Here's an experiment in which scientists raised CO2 concentrations in a natural setting. They laid PVC pipes in areas of forest and pumped CO2 into the open air. They found that poison ivy growth rates increased by 149%, so the effect might depend on the specific plant. (",
"NPR",
")"
] |
[
"Does wood harden if it's underwater?"
] |
[
false
] |
I've watched a few documentaries and read a few articles about the founding of Venice and one thing that they all mention, is that the Venetians used wooden beams as supports due to the lack of a solid foundation. They would drive these beams into the water and the soft soil until they hit bedrock and, according to these (secondary) sources, the wood overtime hardens instead of rotting as (I assume) the wood remains underwater and isn't exposed to the air. Is this true? And if so, what is happening to the wood to make it 'harden'?
|
[
"Wood rots much slower under water because most fungi can't attack it under water, instead microfungi and and bacteria break it down. Much slower than on land i should add. The broken down area is filled with water. The poles of Venice are mostly European larch who are very resistant to micorfungi and bacteria. But there are also poles that are made out of alder, elm and poplar, these arn't as resistant and and there are poles in very bad condition due to the breakdown."
] |
[
"Was it known that European larch was more resistant to microfungi and bacteria when it was first being used? Or was the Larch used to replace another type of wood once larch was discovered to be more rot resistant?"
] |
[
"I don't have a good source for this but the use of the different woods might indicate that the builders simply took what was availble."
] |
[
"Animal behaviors against each other?"
] |
[
false
] |
If Animals can't communicate ...most animals anyways, how do they learn social behavior, It's always confused me why an alligator will attack anything that moves , but if it comes across another gator it won't attack it, I'm sure the answer is simple, but I just can't grasp it? Thank you everyone to who commented : ]. this has really helped me, upvotes all around!
|
[
"Animals DO communicate, just not through human language. They respond to the sights, sounds and smells of other animals. Even humans and animals communicate. Some animal behavior is instinctual and programmed hormonally or genetically. Other behaviors are learned or some combination of inherited and learned. Dogs for example have inherited behaviors which enable them to be social animals and live in packs. However, they also have learned behaviors... a dog, for example, can change through ",
"operant conditioning",
"... either learning new behaviors or losing old behaviors. "
] |
[
"Animals absolutely can communicate with each other. Vocalizations, facial expression, body language, and even chemical signals are kinds of communication. Have you ever seen dogs interact with each other? Watch their bodies as they interact. The way they hold their tail, make eye contact, hold their posture, hold their ears, curl their lips all are signals to each other saying things like \"I want to play,\" or \"I don't want to play\" or \"I'm afraid of you,\" or \"I'm uncomfortable,\" or \"You're encroaching on my space,\" etc. Most communication is instinctual (just like a baby doesn't have to be taught how to smile or laugh or grimace) but some is taught by the mother and littermates. ",
"In social animals, certain \"manners\" and communication methods are taught or refined early on. They learn by watching each other or by trial-and-error communication with others. I'll give some examples using the species I know best, dogs. One \"rule\" they learn is to respect a more dominant-acting animal or risk an altercation. If they fail to recognize another dog's (like their mom or bossy siblings) \"Hey, I'm the boss, here!\" body language, and do something like try to take their food, they get bitten, which is how they learn. Another communication skill learned by dogs is to perform a \"play bow\" before attempting to initiate any rough play, so the other dog knows his buddy is not being aggressive. They'll realize that without the play signal, the other dog might bite too hard, thinking a real fight is happening.",
"Your second question is not related to communication, really, as an animal can naturally tell prey from predators or conspecifics (fellow members of its species). An alligator knows another alligator is not a good prey and thus will not attack it."
] |
[
"To add on the other posts, animals can also recognize individuals. Social animals especially have the ability to distinguish others based possibly a combination of factors including: familiarity, smell, pheromones (MHC complexes), sounds/vocalizations. Thus, they can tell who might be an ally, or an unknown - potentially harmful individual. "
] |
[
"Is it possible that my subconscious is secretly working against me in any way?"
] |
[
false
] |
Or does it do its bidding with some sort of understanding of what my consciousness wants it to be working on? lol. I know my subconscious is a busy little bugger, I just hope it has no malicious intentions. So far it has only helped me, such as memorizing stuff in my sleep, or giving me dreams that teach me how to react to absurd situations.
|
[
"Or going any deeper."
] |
[
"Or going any deeper."
] |
[
"Subconscious is a level of description for cognitive processing, it is not a \"thing\" that can have intensions of its own. Unless you have suspicions of having a particular mental disorder such as Dissociative identity disorder, I would not be worried."
] |
[
"While playing music off my phone in the car, will the rate at which my battery drains differ if I have the volume on max for the phone and low on the car or vice versa?"
] |
[
false
] |
For example: I plug my phone into the car AUX(non charging) and put the volume on the phone at 100% and the car at level 10 OR I put the Volume on my phone at 50% and the car at level 20(numbers are arbitrary). Is there a difference in the rate at which the battery will drain?
|
[
"Yes, there is a protocol, it's called Ohm's Law. A speaker is a low resistance and an amplifier front-end is a very high resistance."
] |
[
"It will make a very tiny, negligible difference. Increasing the volume on the phone will increase the average output voltage, but since this signal is only going into the high-resistance front-end of your car sound system it will draw very little current and therefore power.",
"FWIW, if I have a stack of volume controls (like videoplayer > OS volume > speakers), I tend to leave all the controls at 100% apart from the last one."
] |
[
"Higher voltage, but the input of the receiver is super high impedance, so higher voltage won't actually increase the power drain by a whole lot, and it starts out pretty negligible to begin with. "
] |
[
"Why do we measure ppm by volume for gases all the time and not by weight like water and soil?"
] |
[
false
] | null |
[
"Likely because the molar volume of gases is pretty much the same for everything. So if you take 1 mol ethanol and water, ecaporate it and have the vapor and gas ethanol at the same pressure and temperature they will have the same volume.",
"For liquids and solids its different for each compound and element, using weight here makes more sense. As gas has an easy determined amount of particles we can use ppm for better quantification of components."
] |
[
"For my work, I sometimes use photo ionization detectors to measure VOC concentrations in the air. The instruments give readings in ppmv. I have always assumed that the use of volume was because it was a relatively easy calculation based on the flow rate of the internal pump in the instrument.",
"The same would work for samples collected in a summa canister, which has a known volume. ",
"If I am wrong, someone please correct me"
] |
[
"Depends on the application. In gas phase analysis, PPM is more useful because you often care about volume and percentage of contaminant more than mass of contaminant. For example, gas chromatography or mass spectrometry.",
"For example, if you're analyzing a pure N2 or argon gas atmosphere for a semiconductor manufacture application, pretty much any contaminant above a certain ppm threshold will cause the batch to be flawed.",
"Flow rate is also regulated in many analyzers of this type, which means you have a fixed volume of gas going into an analyzer. You can do some matrix algebra to get masses from the ppm/percentage data if needed."
] |
[
"Would it be theoretically possible to cast a sculpture out of rock?"
] |
[
false
] | null |
[
"example A",
"example B",
"example C"
] |
[
"Several artists actually ",
" produce artwork through the process of casting natural lava.",
"Their websites should provide the answers you seek as to methods and whatnot."
] |
[
"Do you have any examples of this?"
] |
[
"Are there circumstances where scientist and pharmaceutical companies don't have to go through the FDA to release a drug?"
] |
[
false
] |
(Not sure if the FDA is the organization that handles this type of thing but bare with me here) I'm talking in extreme circumstances. Like the human race is dying alarmingly fast, and if someone doesn't come up with a cure/vaccine soon we're headed for extinction. (i'm being very dramatic here but i'm getting to the point) In an instance where people are dying rapidly and science does come up with some drug that helps, i know that trials and testing take many years. But in the event the human race doesn't have that much time, can pharmaceutical companies release the drug without following the "necessary procedures"?
|
[
"The FDA is able to ",
"fast track drugs",
", including reducing testing requirements, under some circumstances.",
"Fast track is a process designed to facilitate the development, and expedite the review of drugs to treat serious conditions and fill an unmet medical need. The purpose is to get important new drugs to the patient earlier. Fast Track addresses a broad range of serious conditions.",
"Pharmaceutical companies can't just release a drug in the USA without FDA approval. At the same time, the FDA is only for the USA, and while other regulatory agencies are often just as stringent, some might be more lax or willing to pass something through due to exigent circumstances."
] |
[
"I'm not sure if exceptions are made in those circumstances. But there are normally human trials as part of the approval process, and doctors/patients are likely to agree to participation in cases like the ones you describe. "
] |
[
"Just fyi, \"right to try\" is ethically dubious and not really in the best interest of patients as much as pharma companies. It sounds compassionate, but patients are basically paying money to be human guinea pigs. Below is a well written article about the issue:",
"http://thehill.com/blogs/congress-blog/healthcare/311259-right-to-try-misses-the-real-issue-there-is-another-solution",
"long-ass edit: ",
"as ",
"/u/Jenkinsd08",
" mentioned, \"right to try\" is different from the \"compassionate use/extended use\" provision. The article above discusses the difference but I still felt compelled to elaborate as it seems relevant. The FDA approves 99% of appeals for compassionate use/expanded access. And all of those requests are for people who are not already participating in clinical studies. Clinical studies are better because a) they move drug development forward but also b) the standard of patient treatment is higher. So basically if a patient is not in a trial and the FDA rejects an appeal for compassionate use, \"right to try\" lets patients directly request the drug from the company.",
"Often people think that those with terminal illness have \"nothing to lose\" therefore we should let them try anything, but in fact taking an untested drug can cause a tremendous amount of pain and suffering, as well as shorten the time that terminally ill patients do have, and rack up huge hospital/drug bills that the patient may be responsible for.",
"the specific drug needs to be shown to have value in treating the terminal condition that would otherwise kill you",
"As far as I understand the issue, this may be true of compassionate use/expanded access (I assume that is part of the FDA's criteria for the 99% approval) but it is NOT true of \"right to try\". Under right to try, patients can request to use any drug that has gone through phase I trials. It does not need to have gone through phase II trials.",
"From wiki:",
"Phase I trials are often referred to as “first-in-man studies” as they are the first stage of testing in human subjects. They are designed to determine the maximum amount of the drug that can be given to a person before adverse effects become intolerable or dangerous. Normally, a small group of ",
" will be recruited...",
"Once a dose or range of doses is determined, the next goal is to evaluate whether the drug has any biological activity or effect. Phase II trials are performed on larger groups (100-300) and are designed to assess how well the drug works, as well as to continue Phase I safety assessments in a larger group of volunteers and patients. Genetic testing is common, particularly when there is evidence of variation in metabolic rate. ",
"*",
"So just to break down the issues with \"right to try\" (again, not talking about compassionate use as approved by the FDA) and why I used the phrase \"guinea pig\" (even though it was hyperbole):",
"Drug has only been shown to be \"safe\" in a group of under 100 healthy people.",
"Terminally ill people are far more likely to experience adverse effects. Not to mention that everybody metabolizes drugs differently and the drugs may interfere with other medications the patient is on.",
"A full ",
"two thirds",
" of drugs fail phase II clinical trials.",
"If the FDA denies compassionate use, it is probably for a damn good reason, considering that they are scientists who have looked at the clinical data and they DO APPROVE 99% of the drugs.",
"The drugs and related care will NOT be covered by insurance. In a perfect world, the drug company would foot the cost, but they are under no obligation to.",
"The patient may develop toxic side effects. For example, the drug causes kidney failure or lung problems for the patient that they otherwise would not have had. The patient gets put on dialysis or a breathing pump. The quality of life of the terminally ill patient and their family is affected, the hospital charges them an extra $100,000+ for which they are fully responsible.",
"If a clinical trial ignores deleterious effects of a drug and neglects to cease treatment, they can get in serious deep shit later. No such guidelines exist for right to try (not sure about compassionate use).",
"Ultimately the only people who will risk the cost and toxicity of a new drug are going to be very, very desperate. The drug company still gets to study how the patient reacted to the drug so it is in their interest to treat as many people as possible this way. For example, they learn that \"this drug causes severe lung damage and seizures in some patients\". But the ultimate cost and suffering that the drug caused will fall on the patient. The drug company will suffer no consequences and they learned something new about their drug.",
"If there are issues with toxicity, it is WAY easier for them to cover this information up because it's not part of a clinical trial.",
"Hopefully this was informative for some people. I saw a lot of misinformation about \"right to try\" when it was in the public eye. I'm not really a \"big pharma conspiracy\" person, but they have lobbied HEAVILY on this one and it definitely serves them without adequately protecting patients and their families.",
"Also, these regulations are just for the U.S. European medical approval guidelines (CE) tend to be more lax AFAIK. As for a situation like OP was describing, it's important to realize these laws and regulations are flexible, so we could certainly alter them to reflect current needs in the case of an epidemic or something."
] |
[
"Is space trash really a problem (today)?"
] |
[
false
] |
According to United Nations Office for Outer Space Affairs there are almost 5000 satellites orbiting around the earth. It is a lot, but they also have a huge area they can moving through. I imagine travelling in circle around a perfectly smooth earth surface with my super fast vehicle. On the earth there are other 5000 vehicles like me. The chance to crash with someone seems really low. Even identify and see someone else passing by, to be honest. In addition, all the satellites are orbiting on different heights, so the chance od two objects to collide seems to me really low. I know, I simplified a lot the problem (e.g. there are also small debris). And since the launch are getting cheaper and cheaper the number of satellites up there is going to drastically increase. But TODAY, is it really a problem? Have anyone seriously calculated the chance of crash? Thanks for all replies and sorry for my English.
|
[
"Have anyone seriously calculated the chance of crash? ",
"Yes. It is calculated at design time for every satellite.",
"Unfortunately the question is a bit more complicated. You can't say it has X% probability of crashing because such a statement is missing an important point: the size of the object you receive an impact from. If you consider just any paint flake or dust grain no matter how small, then the probability is trivially 100% because every satellite gets hit after a few weeks in orbit. ",
"So you actually have to ask about the probability of crashing with an object of diameter d or larger. This parameter d will decide what kind of shields you can put on the external surfaces of your spacecraft to resist smaller objects, and then you can live with the probabilities of being impacted by a larger one.",
"There are good models for that. ESA uses Master 2009. NASA has a similar one. Most of this knowledge comes from crater counts on spacecraft that have been long enough in orbit and were brought back to Earth, including NASA's LDEF, ESA's Eureca, and the ISS MPLM modules.",
"Numbers are in the order of magnitude of like, impacting by an object of 1cm or larger with a probability of 0.1% per m",
" of spacecraft external surface and per year. Even though this number looks small, it actually grows quickly when you integrate over a large surface and a long mission duration. Consider, for instance, that the ISS was designed for a probability of penetration of the pressurized shell of 24% every 10 years, and a probability of catastrophic event from penetration of 5% every 10 years. (In space context, ",
" means death or severe injury of a human). Those numbers are disturbingly big.",
"Source: ",
"https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060026214.pdf",
" ",
"That report also explains how MMOD shields work in case you're curious. But in short, have a first layer so that the incident object is broken into smaller pieces and even vaporized, so that the fragments hit the second and successive layers over a much larger surface and it becomes easier to resist."
] |
[
"But especially for avoiding creation of more and more debris.",
"That's exactly what debris mitigation guidelines are focused on. A defunct satellite in orbit doesn't pose a lot of collision risk by itself, but if it releases fragments every time it is impacted then it is slowly but constantly contaminating the orbit. Deorbiting it at the end of its operational lifetime is definitely desired. If that's not possible, then avoid fragmentation by removing all energy from the satellite (discharging batteries, emptying fuel tanks, etc)."
] |
[
"Thank you so much for the great reply! The report is super interesting.",
"catastrophic event from penetration of 5% every 10 years. (In space context, ",
" means death or severe injury of a human). Those numbers are disturbingly big.",
"They are. I work on railway safety and residual risks of catastrophic events is not even comparable. Ok it is a completely different context, but still...",
"My question started thinking about the several proposal for removing not working satellites from orbit. Your answer makes me think these projects are useful not so much for removing the satellites themselves in order to avoid crash with other object. But especially for avoiding creation of more and more debris."
] |
[
"Can you decide if a chemical compound is basic or acidic just by looking at it's structural formula?"
] |
[
false
] | null |
[
"Formula itself, no. Knowing the structure (i.e., where the bonds are), then yes. This is especially true for organic compounds.",
"We know how a functional group behaves with regards to accepting or donating a proton, so their presence in the compound will give clues to what it will do. However, as with all areas of chemistry, the presence of some groups will influence how others behave - for example, a chlorinated site in the vicinity of a carboxylic acid may make it more acidic.",
"At the end of the day, how well one can predict the properties of a compound is a mixture of fundamental knowledge and experience."
] |
[
"There's plenty of software that predicts pKa (H+ dissociation constant) from molecular structure based on the principles (electron density distribution) that ",
"/u/rupert1920",
" mentioned. Here's an abstract which mentions some by name and shows a comparison of their predictions:",
"Comparison of Nine Programs Predicting pKa Values of Pharmaceutical Substances"
] |
[
"Use this website:",
"http://www.chemicalize.org",
"It's not very advanced, but its quite easy to use. Just type in something like \"4-methylpiperidine\" or \"morphine\" or draw a structure, and it will give you the pKa's and tell you what the charge will be at any given pH."
] |
[
"If a runny nose, sore throat and sneezing are the body's way of dealing with the common cold, does suppressing the symptoms with medication prolong the infection?"
] |
[
false
] | null |
[
"Not really. These symptoms are largely a result of the immune system dealing with the common cold, not the sole mechanism by which the body deals with the infection.",
"A sore throat occurs as a result of tissue damage. This is caused by both the virus and the immune response against the virus. You get a runny nose as a result of increased mucus production. The increased mucus production is caused by immune cells responding to the infection as well as by the infected cells themselves. Sneezing/coughing is caused by stimulation of neurons, again due to he virus and the immune response against it.",
"However, because the cold is caused by a virus, the primary means of elimination will be through immune cells specialized in killing virally infected cells. Mostly CD8 T cells and NK cells. These cells target infected cells and cause those cells to commit cell suicide. Other cells gobble up the remnants of the virus and cells and eliminate them. So preventing a runny nose, sore throat, and sneezing will do little to the cellular response mounted by these immune cells. Cellular immunity is pretty robust. (This is a very general answer. There exists innate and adaptive immune arms that handle infections differently that I didn't go into.)",
"But just to add a touch about these symptoms and how they can be important. A sore throat indicates to you that you are infected and you can respond accordingly (thinking, \"hey I'm sick!\") Sneezing and coughing help expel pathogens by moving around mucus that has collected them. A lot of this mucus is disposed of by the digestive tract after you swallow it. And finally, mucus is important for protecting your mucosal tissues like the throat. Immune cells and cells of the tissue can cause elevated mucus production. It is a sugary, sticky fluid that captures pathogens and prevents them from adhering to cells. Often it is filled with other goodies that kill pathogens. Your body uses mucus to kill microbes/flush them away and therefore ramps up production during an infection. However, once a virus enters the cells in the tissue it will be up to the cellular immunity to eliminate it rather than mucus. "
] |
[
"Am I mistaken that rhino-viruses evolved to present the symptoms of excess mucus production, coughing, and sneezing as a way of propagating in new hosts? Or is it a coincidence that we respond to this particular clade of viruses in this way?"
] |
[
"It is likely that some pathogens have taken advantage of sneezing and coughing. I personally don't know of any specific pathogens that do this via a distinct mechanism that directly causes coughing/sneezing.",
"I looked into rhinoviruses doing this and found this review: ",
"http://bmjopenrespres.bmj.com/content/3/1/e000118",
"Sounds like it's not a direct mechanism. Rather, it is a side effect of the immune response to the virus. That is, the virus doesn't bear some protein that induces neuron activation triggering coughing. Instead it is hypothesized to be due to immune signaling molecules, tissue damage, and/or increased mucus production having an effect on the neurons.",
"Here's another review, which falls more in line with immunological mediators causing the coughing instead of a direct viral mechanism: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4532602/",
"So I'm not sure I would agree the rhinoviruses evolved to actually cause these symptoms. Instead I would say they evolved to take advantage of the immune response and subsequent symptoms in order to more readily spread. I hope that makes sense."
] |
[
"How do we know we share a common ancestor with the great apes (chimpanzees, gorillas, orangutans)?"
] |
[
false
] |
I know we share a majority of our DNA with them. Is that the only evidence we have? (I'll point out I do believe in evolution, and I do believe in this common ancestor theory with the great apes, I'm looking for a more technical "how do we know this")
|
[
"When you say \"share a majority of DNA\" it may be helpful to expand on that and explain why it is that the DNA we share is such a positive identifier of our mutual ancestry.",
"Lets focus for a moment on ",
"chromosome 2",
". All Hominidae have 24 chromosomes, except for humans. We have only 23 chromosomes; if humans were really related to the other Hominidae why would we have a different number of chromosomes?",
"Well, here is the testable and falsifiable part of the evidence based approach we use to determine ancestry. One might hypothesize that if we have 23, but our proposed ancestors all have 24, that there could potentially be a loss of a chromosome. This would not be altogether compelling, because it might come off as just writing off the differences to square the circle. What would be really immensely compelling would be if ",
". If this were the case then there would be consistency between total genetic elements, but more importantly there would be a ",
" Think about it, if we weren't directly related then we would have had to develop a single chromosome from our lineage which matched ",
". The probability of that is astoundingly low even over an immense time interval.",
"And what do we see in chromsome 2: A ",
"vestigial centromere",
", ",
"inverted telomeric repeat sequences",
", sequence homology, everything we would expect from a relatively recent fusion of two chromosomes.",
"Our chromosome 2 is the perfect reference point to assuage the most common sorts of denial of this sort of ancestral relationship - that we were just filling in gaps, and that we couldn't really let ourselves be wrong because we would just pick up the pieces and put them into place. The claim that our chromosome 2 developed from fusion of Hominidae chromosomes 2A and 2B is a falsifiable claim, and in fact if research had not so strongly asserted the validity of the claim it is likely that we would see different avenues of research into human ancestry.",
"Sure, we could bring up other unifying traits of the Hominidae to support the claim. Broad incisors, underdeveloped canines, legs that are longer than arms, males larger than females on average, lacking a tail, opposable thumbs, a distinctly big toe, lack of ",
"ischial callosities",
", upright or semi-upright skeletal structure, ",
"dental formula",
", omnivory, complex social behavior, loss of tree dwelling behavior outside of the basal Orangutan group. None of these is particularly interesting alone, but together they are very compelling.",
"Still, until molecular techniques of the last couple decades the search was very much an active process - people were actively disputing hypotheses of direct descendence and the conversation was very meaningful and productive. After modern genetic analysis was performed and verified the extent of the current dispute rests with online-only publications like ",
"this",
" and ",
"this",
". Methodologies so porous and conclusions so pre-established that no reputable peer review process could miss the glaring oversights - this is the extent of the dispute at present."
] |
[
"DNA is not the only evidence we have, although in my opinion it is the best (it really makes an airtight case against any other possible configuration). Huxley and Darwin, for example, showed by comparative morphology that humans and great apes had a common ancestor well before DNA was ever discovered."
] |
[
"One of the two best lines of evidence we have has already been mentioned, the fusion of chromosomes 2A and 2B. The other, my personal favorite (and what I've spent the last few years of my life studying), are endogenous retroviruses and other mobile genetic elements, specifically the way insertions of these elements in related species form a characteristic pattern that is best explained by common ancestry.",
"What are mobile elements? They are chunks of DNA that have the capacity to jump from place to place in a genome, either through a 'cut and paste' mechanism, where the chunk pops out of wherever it's inserted and then reinserts itself somewhere else, or 'copy and paste,' where the chunk makes a copy of itself which then inserts somewhere else. I'm ignoring the cut and paste guys from now on because they're less relevant to this discussion.",
"The copy and paste tribe, often known as 'retroelements,' are remarkably useful markers of ancestry and evolution. Why? Two reasons. One, their choice of insertion site is almost completely random. Second, once an element inserts itself, it can't get out, it's in there permanently. In combination, this means that any time you see two species with the same type of element inserted in exactly the same spot, you can be confident that their common ancestor had that same insertion; conversely, if a third species ",
" have that insertion, you can be confident that the first two are more closely related to each other, ",
" share a more recent common ancestor than they do with the third species.",
"So then, what we can do is look at all the various retroelements present in our genome, and the genomes of other related species, and we will see a pattern develop of presence and absence of various insertions. Some will be present in nearly every species we look at; those must have inserted in the common ancestor of those species, and thus must be very old. Others will be only present in a subset of the species, and thus are younger. As we look at elements present in progressively smaller subsets of our relatives, we can slowly build our family tree, narrowing down from order to family to subfamily, until we find a set of insertions present only in us, and one other genus. That genus is ",
" the chimps and bonobos, our closest living relatives.",
"There is a third reason these insertions are especially useful, compared to other types of genetic variation: for the most part, once they insert, they are unimportant to the proper functioning of the host cell, one of the quintessential types of 'junk' DNA. As always, there are exceptions to this rule (and many those exceptions are incredibly interesting, some involve the most remarkable case of convergent evolution I've ever heard of, others have played important roles in the evolution of immunity -but I digress), but, in general, they appear to have slowly degenerated over the eons, as you would expect of a non-functional piece of DNA. ",
"Why is this useful? Because it means that this pattern of insertions that we see, that so nicely reproduces our family tree, is not simply an artifact of how similar or different two species are functionally. Two organisms of similar design might be expected to have similar functional elements, regardless of whether they are related to each other. But to share the same mistakes, that strongly implies common ancestry. This is similar to the way mapmakers will include small errors in their maps, to catch plagiarists; if all the important stuff is the same, the plagiarist could claim random happenstance. If their work has the same typos? Clearly a copy. Mobile genetic elements are, in a way, evolution's watermark."
] |
[
"is there a speed limit at which current GPS technology becomes useless to ascertain the objects current location with accuracy?"
] |
[
false
] | null |
[
"Only kind of relevant, but I remember reading on Reddit that if a GPS is going over 1,000 MPH it, by law, must shut off because it is likely guiding a missile. So to narrow down your speed window (assuming the above is true), a GPS is able to track at over 1,000 MPH."
] |
[
"It's actually 1000 knots, and there's a limit of 11 miles in altitude as well, but that as far as I know is an export limitation from the United States (receivers that operate past those limits are classified as munitions). ",
"There's nothing inherent in the satellite signal that could prevent a receiver from operating past those limits, it's purely a legal limit."
] |
[
"Before the answer, consider how GPS works: ",
"A satellite in orbit will transmit a signal according to an atomic clock. On the ground in the receiver, another signal is generated. Both signals are generated at the same time, and when the signal from the satellite reaches the receiver the difference is then calculated to be the distance between the two objects (because the signals propagate at the speed of light).",
"Getting several signals simultaneously will get you more dimensions of accurateness. So, unless I miss my mark, you should be able to attain an accurate result from a GPS unit, until you start hitting a fraction of c. ",
"Now, that said, your accuracy level may vary. With a standard GPS unit (just off of the satellites) you should be able to get an accuracy rate of roughly within 20 meters. I don't know how speed affects DGPS or RTK GPS, but considering that both operate off of transmitted signals, I believe that they would also be accurate (down to 10cm)."
] |
[
"how come people who snore are not woken up by the noise?"
] |
[
false
] | null |
[
"The short answer is that it actually ",
" wake you up. A close relative of mine suffered from this for many years before having it surgically corrected.",
"From ",
"the American Association of Oral and Maxillofacial Surgeons",
":",
"\"Snoring of this magnitude can cause several problems, including marital discord, sleep disturbances and waking episodes sometimes caused by one's own snoring.\""
] |
[
"This is from 1998 but it was the first relevant source that I found via my phone (also explains poor formatting, my apologies):",
"www.jhu.edu/news_info/news/home98/apr98/serena.html",
" ",
"Basically, when we are sleeping, the frontal lobe screens what we are hearing and decides if a sound is worth waking up for. In a person who snores, the sounds that they are making may be determined to be nonthreatening, so they stay asleep. As for the how/why and way things are selected, someone in the relevant fields may be able to help."
] |
[
"Yes, K-complexes are involved, however more recent research has actually shown that sleep spindles may be more important, as they have been found to be directly related to an individual's ability to maintain sleep in the presence of auditory stimuli. "
] |
[
"Why does water turn yellow when electric current passes through it for some time?"
] |
[
false
] |
When I was young, I used to play around with electricity quite a bit. One "experiment" I did was to take 12v DC and pass it through a glass of water via two copper conductors. I noticed that, after several hours, the water becomes yellow and cloudy. I'm assuming this is some sort of chemical reaction, but what was happening?
|
[
"Thanks! This sub is so awesome."
] |
[
"Thanks! This sub is so awesome."
] |
[
"Incidentally, this is the best way to clean cast iron that has a liner of carbonized gunk on it."
] |
[
"Why does a liquid run down the side of a glass when pouring it?"
] |
[
false
] |
When I pour a liquid from a mug into another container, it runs down the side of the mug. Why does this happen?
|
[
"Due to both the high surface energy of the ceramic surface and the lower interfacial energy of the ceramic-water interface. ",
"The lowest energy state is when the water is covering the ceramic and so the water will adhere to the mug as it is poured out."
] |
[
"Hot chocolate (made from milk) is not even a single liquid, as ",
"milk",
" itself is already \"fatty droplets\" in water, which is called an ",
"emulsion",
"."
] |
[
"The liquid will take the path of least resistance where resistance is the breaking of surface tension. So if you had a superfluid (one with 0 friction) it would fly out the end of the cup instead of wrapping around. If you have a very viscous fluid, say glue, it will hold onto the edge so tight that it will end up pooling into a drop directly below the lip of the cup."
] |
[
"Why Do Moths Fly Towards Light Sources?"
] |
[
false
] | null |
[
"They use the moon as a guide for traveling I believe. So they think the light source is the moon. Of course I could be wrong."
] |
[
"No this is pretty much it. Richard Dawkins writes about this briefly in The God Delusion. If I had the book on hand I'd get the quote."
] |
[
"That's it. I knew I read it somewhere."
] |
[
"What would happen if we split a proton or electron?"
] |
[
false
] |
Would it give off energy like when you split an atom?
|
[
"Electrons are elementary particles as far as we know, so they can't be \"split\".",
"Protons are not elementary, so they can be \"split\", however it requires very high energies. It's done at places like the CERN, with the LHC."
] |
[
"Aren't isolated quarks not a thing? The energy required to split a proton would result in multiple hardrons, right?"
] |
[
"There's no reason to believe that any miniature black holes are actually being produced in any collider that currently exists."
] |
[
"In perfect conditions, what is the furthest a bullet could possibly fly? For the sake of the question, we'll say standard 5.56x45mm NATO."
] |
[
false
] | null |
[
"Depends on your definition of perfect conditions. In a total vacuum, for example in space, and absent of external forces like gravity, it could travel forever. ",
"But I'm assuming that's not what you mean, and if it's not, I'm unable to answer further."
] |
[
"The equations involving air get a little bit tricky, but without considering air and considering a bullet fired horizontally from the height of a person (1.70m) we can do some math: ",
"Time for the bullet to hit the floor = (height*2/gravity acceleration)",
"Horizontal distance traveled: time*speed of the bullet ",
"If we consider gravity acceleration as 9.82 m/(s",
" and the speed of the bullet as roughly 900m/s we have approximately 530 meters that the bullet can fly. ",
"I don't post this as a top comment because it's useless for your question, since air will have two effects: it will make the bullet take longer to fall and it will also decrease its horizontal speed. Surely a mathematician or physicist can give a better answer",
"We could also do the math for a shot in an angle, which could travel further but this comment will probably get removed and I think you had high school physics (though many people haven't yet so that's why I am posting)."
] |
[
"I'm saying no wind, no humidity, just gravity and air. Sorry if I'm not being specific"
] |
[
"When you lose weight, where does it go? How does the mass leave the body?"
] |
[
false
] |
I've been trying to get fit lately, and have lost three pounds. It got me thinking - where does "the weight" go when you lose it? In other words, how does the mass leave your body? I understand that when you lose fat, the fat cells shrink, but the actual mass must escape the body somehow. I can only think of four ways mass could possibly escape the body - through the excretory system (urine or sweat), the digestive system (defacation), or the lungs (in the breath). So, when you lose fat (or muscle, in the case of muscle atrophy), where does it go? Before you laugh, let me say that I'm pretty sure you don't fat. But I'm curious. Do we know? How does it happen? Thanks.
|
[
"With the help of oxygen, cells eat carbon containing molecules like glucose and fatty acids, and respire CO2 and H2O. The CO2 is in solution in your blood and travels to the lungs, where you exhale it in exchange for more O2. A 140 lb person exhales about 1 kg (2.2lb) of CO2 each day from basal metabolism, more if they are active. The H2O either gets used in other places or goes out through your urine. The net loss is about 270 grams of carbon, and around 110 grams of H2O, per day."
] |
[
"Yes, you can lose a tiny amount of weight just by breathing harder without otherwise exerting yourself, but if you hyperventilate you'll pass out, so that's not really a good weight loss plan. When you exercise, you breathe harder to get rid of all that CO2 that's being dumped into your bloodstream by your muscles working, and to pull in more O2 to continue the process.",
"Gauging how much you're breathing is a good way to gauge the efficacy of a workout, and in fact when people are doing a study on the energy used in exercise, they capture the air you're exhaling and measure the amount of CO2 in it. Your heart rate is an indirect measurement of this, because your heart beats faster to move more blood from your muscles to your lungs, and back out again. But the only way to know exactly is to measure your breath.",
"Your body breaks down blood glucose, glycogen, fatty acids, and protein all the time, but at different rates. As glucose and glycogen stores are depleted, more and more fatty acids are used for energy, and that's how you lose body fat, it gets burned up and exhaled."
] |
[
"Yes, you can lose a tiny amount of weight just by breathing harder without otherwise exerting yourself, but if you hyperventilate you'll pass out, so that's not really a good weight loss plan. When you exercise, you breathe harder to get rid of all that CO2 that's being dumped into your bloodstream by your muscles working, and to pull in more O2 to continue the process.",
"Gauging how much you're breathing is a good way to gauge the efficacy of a workout, and in fact when people are doing a study on the energy used in exercise, they capture the air you're exhaling and measure the amount of CO2 in it. Your heart rate is an indirect measurement of this, because your heart beats faster to move more blood from your muscles to your lungs, and back out again. But the only way to know exactly is to measure your breath.",
"Your body breaks down blood glucose, glycogen, fatty acids, and protein all the time, but at different rates. As glucose and glycogen stores are depleted, more and more fatty acids are used for energy, and that's how you lose body fat, it gets burned up and exhaled."
] |
[
"Do adjuvants have any medical use outside of vaccines?"
] |
[
false
] |
I know about aluminium hydroxide and how it's used to increase the immune response when putting in vaccines. The virus protein interacts with the immune system , leading to an acquired immunity. Aluminium hydroxide increases this effect. But here's the thing. In the case that there's already a virus or pathogen there, and there's already an immune response in the body (albeit a weak one), can aluminium adjuvants alone serve to boost immune response and increase chances of recovery? Or is it's effectiveness dependent on an already weakened antigen?
|
[
"They are also used in cancer therapy. Often, but I believe not necessarily, in combination with other immunotherapy, such as cancer vaccines. \nUseful links:\n",
"https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/immune-system-modulators",
"\n",
"https://www.frontiersin.org/articles/10.3389/fchem.2020.00601/full"
] |
[
"I’d like to know too. I remember reading about a clinical trial where they had just the adjuvant as a control, and they had a response rate similar to the actual drug. So I’d guess “yes, needs more research” and probably applies to some diseases more than others."
] |
[
"I can give you a bit of a more frank, less technical and comprehensive answer that may help. If this helps add to the other answers, great. If not, ignore me. ",
"Adjuvants work locally as well as systemically, but not both in equal measure. They are especially active at the site of the injection. A vital part of the desired vaccine-induced immune response relies on the adjuvant and vaccine antigens being in relatively high concentrations in the same place in the body.",
"If you just injected a person with an adjuvant only and they already had the virus on-board, you may see a very mild increase in overall immune response in the form of a slight elevation in body temp and very, very mild systemic inflammation, but it wouldn't be nearly enough to affect the course of the infection. You would also have a local inflammatory response at the site of the injection but without the vaccine along with it, you just get a sore arm with no benefit.",
"The adjuvant triggers local inflammation which calls white blood cells to come running, or rolling and oozing as the case may be. These white blood cells (macrophages/dendritic cells/Antigen presenting cells) are stimulated by the adjuvant to grab the vaccine antigen particles that are highly concentrated in that area and (long story short) present those viral particles to the immune system so they can pump out new lymphocytes (another kind of white blood cell) to target and kill specifically the strain of virus that was in the vaccine. ",
"I don't know if that clarifies or obfuscates things!",
"Edit: typos, clarification"
] |
[
"If one conjoined twin dies, can the other survive?"
] |
[
false
] | null |
[
"Unless they can be separated, no, both twins will die."
] |
[
"If twin A has an aneurysm, how long does twin B have?"
] |
[
"That is something that completely dependent on the type of twins they are, how much blood supply they share, if one is sicker than the other, etc. No real way to guess. Much less than 12 hours."
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Why are migraines so hard to understand? So many people are afflicted, yet so much is unknown."
] |
[
"What is the difference between ADHD and High Functioning Autism?"
] |
[
"It comes and goes because the virus infeccts your nerves and then becomes dormant or 'latent' in the sensory root ganglions - the bundles of different nerves that meet together. In the case of genital herpes these are in your lower back, and in oral herpes (cold sores) they are under your cheek bone.",
"Viruses in general are difficult to cure as they can integrate their own nucleic acid into the host cell. Sometimes as a result the host cell will then make proteins that are chopped into small parts (peptides) which are displayed on the surface of the cell, and act as a signal to the immune system to come and destroy the cell as it is infected. However, sometimes these peptides don't get displayed, or sometimes the immune system doesn't react to the signal, and so the virus-infected cell remains.",
"There are some drugs that stop the virus's nucleic acid from being copied and hence stops the virus multiplying. These include acyclovir which is available as an ointment to put on oral herpes (cold sores). However, in the sensory root ganglions where the virus is dormant and not trying to make copies of itself, these drugs are less effective."
] |
[
"Is it possible to predict the behavior of a substance while only knowing its molecular composition?"
] |
[
false
] |
[deleted]
|
[
"You can do it, at least in principle. (Depending on what you're calculating, what you know, what accuracy you want, how much computer time you have, etc)",
"But there's no simple 'rule' for how these things work. It's a whole subject - chemistry. What you can say and predict from simplified rules and generalizations (i.e. without doing explicit calculations) depends on the particulars of what you're asking about. "
] |
[
"Is that true even in principle? I was under the impression that we cannot yet predict \"simple\" properties like melting point with good accuracy."
] |
[
"It's definitely true in principle. The alternative would be that there's some fundamentally-unknown force of nature acting at the chemical scale, and we don't believe that. ",
"The problem isn't that the fundamental physics of what's going on isn't known, but applying that physics to a model that's as accurate as possible without being computationally untenable. In some situations/compounds melting points can be predicted fairly well. In others, it's very difficult. As systems get larger you get emergent bulk properties. ",
"For comparison, the equations governing the basics of fluid flow (Navier-Stokes equation) have been known for 150 years or so, but we still use wind tunnels and have problems with turbulence. Knowledge of the underlying principles doesn't automatically translate into knowing all their consequences. Even the simplest of systems can exhibit a wide range of complicated behavior. "
] |
[
"If the modern human homo sapien species has existed for hundreds of thousands of years why did civilization only start a little over 10,000 years ago?"
] |
[
false
] | null |
[
"Generally, farming is considered an integral part of civilization, for a couple reasons. Farming creates large food surpluses that can be stored (grains), which support large settlements of people, and farming requires organization of people to tackle communal projects like irrigation.",
"These things aren't necessarily exclusive to farming, but farming does promote them. Sedentism preceded farming in some parts of the world. For example, 15,000 - 17,000 years ago during the Magdalenian, there were semi-permanent villages in especially resource-rich areas. They probably stored food. And 12,000 years ago people built Gobekli Tepe, which consists of monumental stone architecture. That certainly required organization, for humans to quarry and transport blocks of stone weighing 20 tons to the building sites.",
"However, these are isolated instances, and probably they came and went as the climate changed. It was not until agriculture that humans started doing this stuff on a routine and sustained basis. So you can make the case that \"civilization\" had to wait for agriculture.",
"You could then ask why agriculture arrived so late, why wasn't it common 100,000 years ago. There are a couple of reasons why. First is the need. Early agriculture is very hard work and very unproductive. When you're starting off, you haven't yet invented the technologies required, you're working with wild plants that haven't been domesticated and have low yields. In most cases, you're better off not bothering with agriculture and spending your time hunting and foraging instead.",
"So you need a bit of extra incentive or pressure to start agriculture. This may have come in the form on increased population densities, which forced people to invent new ways to produce food. Humans were very scarce for most of human history, very low numbers scattered thinly across a huge landscape. It's only around 40,000 years ago that populations begin a steady and sustained rise, and eventually reach the point where producing food via agriculture becomes time effective.",
"Another reason may be the unsuitability of the climate. For most of the 200,000 years that humans have existed, the Earth has been going through cycles of freezing and warming. This changes climate patterns on a large scale. So it may be that a group of humans starts agriculture somewhere, but before it has really taken hold, the climate changes and people are forced to abandon it and move on. There is some evidence of early agriculture 20,000 - 25,000 years ago, that died out after a while. There may be many other such instances as yet unknown, where rudimentary agriculture began but didn't last.",
"It's only since the start of the Holocene (10-14k years ago) that climate has stabilized into the present warm period. So it may be that in the last 200,000 years, it's only the previous 10,000 years that have really been suitable for long term farming. In which case, you can say that agriculture started pretty much as soon as it could.",
"If you consider the question a bit more deeply, civilization isn't really even 10,000 years old. While there are certainly farming communities that go back that far (10,000 years in Syria/Iraq/Turkey, 9,000 years in the Indian subcontinent ((Mehrgarh), about the same in China, 7,000 years in Egypt) - these aren't really \"civilization\". The four ancient civilizations - Mesopotamia, Egypt, India and China - are more like 6,000 years old, or younger.",
"So the fact is that even agriculture alone isn't enough. You need agriculture that is advanced enough, that has overcome early problems, that has invented basic agricultural technologies, that has domesticated a sufficient number of plants. Then you need increasing populations supported by this agriculture, you need incentive to improve it, for example via irrigation projects. This requires organizing people for public works, which may be the beginning of political organization.",
"So there are a lot of things that have to come together to produce civilization. Among the important ones, I would put sufficient population density, agricultural technology, a need to organize people to do tasks that are beyond a single person. All of these came together around 6,000 years ago."
] |
[
"not that you say so but your question seems to have as a premise that civilization is an inevitability, or that humans will tend to civilise, it may be true but it may not be, civilisation or the tendency to civilise might be rare in the universe even amongst life forms with the capacity to do so. whether it is or isn't it's probably natural process like evolution that doesn't know where it's going. "
] |
[
"One theory I've read looks specifically at the period around when agriculture showed up in the near east and notes a significant drying at the time. The idea is that population growth followed by climate getting worse pushes lots of people into confined areas like the Nile valley. Agriculture takes a lot more effort but it is much more ",
" efficient, and that growing population being concentrated by shifts in climate could have helped push population concentrations above a critical threshold for agriculture to make sense."
] |
[
"Why Tuberculosis is still a major death cause if we have the vaccine?"
] |
[
false
] |
I’m not an anti Vaxxer, without any doubt, but i don’t understand, why are there so many deaths every year 1,4M in 2019) because of a disease that has a vaccine since almost 100 Years? Thanks!
|
[
"The BCG vaccine is not particularly effective, and doesn’t prevent transmission. There is in fact a long-running global effort underway to develop new, more effective vaccines. Some useful background ",
"here",
"."
] |
[
"This appeal",
" from the WHO is also worth reading. I know people who have survived TB and multidrug resistant (MDR) TB — it’s a very nasty disease and the treatments are sometimes even worse. A new vaccine is desperately needed."
] |
[
"A lot of it is due to limited access to medicine, both treatment and prevention. ",
"87% of all TB cases",
" occur in just 30 countries, all of them unevenly developing nations where big chunks of the populace do not have access to modern medicine due to lack of physically accessible providers, poverty, or both. Most of the rest also occur in ",
"countries where a big chunk of the populace lacks access",
" to modern medicine. TB persists at least in part because it takes a long time to treat (6 months!) and it's difficult for poor people and people in places with inadequate health care infrastructure to comply with the whole treatment protocol."
] |
[
"Is it true that an eyemask pushing against your eyes can interfere with REM sleep?"
] |
[
false
] |
I've seen these claims thrown around a little, especially in the context of marketing and reviews of contoured eye masks (eye masks that don't push against your eyes); That feature is important because when you go through REM sleep cycles, your eyes often move quite a bit. This mask, with room to open and move your eyes helps you sleep better through the REM stages. I don't see any evidence or citations for these claims, but the claims seem plausible.
|
[
"in my own experience some masks actually reduce my REM.",
"Do you sleep with an EEG each night? If not, there is no way to confirm this statement. This is not a subjective question, it's an objective one. REM is a measurable, quantifiable, brain state. An individual cannot comment on their own REM state, it is ONLY measurable by EEG. You can promise whatever you want, but without the research to back it up, it means nothing. ",
"So this:",
"He wants to know \"does something touching your eyes decrease REM\". For some people yes, for some people no.",
"is complete and utter bullshit, unless you can provide citations."
] |
[
"in my own experience some masks actually reduce my REM.",
"Do you sleep with an EEG each night? If not, there is no way to confirm this statement. This is not a subjective question, it's an objective one. REM is a measurable, quantifiable, brain state. An individual cannot comment on their own REM state, it is ONLY measurable by EEG. You can promise whatever you want, but without the research to back it up, it means nothing. ",
"So this:",
"He wants to know \"does something touching your eyes decrease REM\". For some people yes, for some people no.",
"is complete and utter bullshit, unless you can provide citations."
] |
[
"I don't know that it's ever been studied directly. However, ",
"this study",
" actually shows that eye masks increase REM, obviously by limited light through the eyelids, which can interfere with melatonin production. The only problem is that this study doesn't specify what type of mask was used, but states subjects could choose from three different types. "
] |
[
"Alright, /r/askscience, how possible are these predictions? *link inside"
] |
[
false
] |
, I find myself highly skeptical to such accounts as "humans will be superhuman". How would we detain our prisoners if they could run rampant? Not just this, but other concepts on this page really make me ponder how possible such a technological explosion is. Scientists of Reddit, what are your thoughts?
|
[
"Easter Island is a good example of a Malthusian catastrophe."
] |
[
"Easter Island is a good example of a Malthusian catastrophe."
] |
[
"God I hate that website.",
"fastparticles and dangercollie have hit it on the head with how impossible it is to predict the future, and with that lies most of my anger towards that site, and \"futurists\" (read: spewers of unsubstantiated claims) in general.",
"But allow me to raise another point: that site claims \"the timeline is based on detailed research that includes analysis of current trends...\", but nowhere on that site will you find the slightest glimpse of any sort of authority on these matters, even if that authority is BS. The contact goes to a general, anonymous email address. They invite submissions from complete randos on the interwebs. ",
"Where's the research? Where's the analysis? Even if it would be all BS anyway. This site claims backing from some line of authority, while its predictions are no better than those coming from the worst science fiction writer (probably Crichton). "
] |
[
"If soil remains dry long enough, do the micro-organisms in it die?"
] |
[
false
] | null |
[
"That's actually an incredibly interesting question. I don't see why not, it would be pretty amazing, if worrying!",
"\nFor the latter question, I don't see that simply drying out the soil would reduce the nutrients, in much the same way that boiling water leaves the salt, although I could easily be wrong."
] |
[
"In some cases, the microbes may die, but many have adapted to conditions, often by mechanisms such as ",
"spore-formation",
".",
"\nIn spore formation, the organism enters a state of reduced metabolism (amongst other biological changes), which allows it to survive difficult conditions.",
"\nA prominent example is many ",
" species, such as ",
" ",
", which can be found in most (if not all) continents. There have even been ",
"reports",
" of viable spores which are over 25 million years old, to demonstrate how hardy they can be."
] |
[
"Just wanted to add to your great explanation with this: Under my knowledge, the only condition that endospores form in is a condition of starvation. So simply being arid isn't enough-- they have to have a lack of nutrients. "
] |
[
"I'm an average male. If I drink an alcoholic drink over the course of 10 minutes, at what time will I be the most inebriated?"
] |
[
false
] |
So say t=0m I start drinking, t=10m I finish, at what t(m) will the most alcohol be in my system? For more specificity, let's say I'm 160lb, 5'10'' tall, and it's 16oz of a 5%(alc./vol.) beer.
|
[
"The not-so-helpful answer: anywhere in a big range of times. Both absorption and elimination rates vary a ton person-to-person, which makes most alcohol-consumption-related rules of thumb unreliable.",
"A frequently cited, but somewhat old, study is ",
"this one",
" (1985), which I can't seem to get a copy of at the moment, but here's how some book on Google Books targeted at drunk-driving defense summarizes its results:",
"University of Oklahoma blood-alcohol expert Dr. Kurt Dubowski has conducted extensive experiments and has found that peak blood-alcohol concentration varied among his subjects from 14 minutes after ingestion of alcohol to 138 minutes after ingestion."
] |
[
"You forgot to convert to metric %ABV..."
] |
[
"And metric minutes."
] |
[
"How do ships sail against the wind?"
] |
[
false
] |
[deleted]
|
[
"I think I can answer this one. I have tried tacking on a square rigged boat, and I have a fairly good understanding of sailing theory. I will answer in two parts. First I will talk about why a square sail is not very good for sailing a close-haul, secondly I will talk about why tacking is difficult on a square rigger.",
"1.: From the website above I assume we agree that what we need for sailing a close-haul is a good aerofoil. It is true that any shape can be used as an aerofoil, but some shapes are better than others. In the following I will list some reasons for why a triangular sail is a better aerofoil than a square sail.",
"Generally efficient wings are long and narrow. Think of the wings of gliding planes which manage to fly on the power of thermal winds alone.\nThis has something to do with the so-called wing tip vortices that are created at the ends of the wing. The vortices carry away a lot of enegy and create drag. Remember that when we are talking about a sail, the ends are the top and bottom edges, the leading edge is at the front and the trailing edge is at the back. Long narrow wings have smaller ends relative to their area and therefore also fewer losses.",
"This picture",
" illustrates the wing-tip vortices on a sail.",
"Square rigged sails are usually not very tall and fairly wide, as you can see in ",
"this picture",
" of a typical square-rigger. This means that they have long wing-ends relative to the area. This makes them very inefficient aerofoils.",
"Triangular sails are much more narrow. In fact their shape closely resembles the wing shape of modern passenger airplanes. This alone should be enough to convince you that they are the better aerofoils.",
"Apart from the overall shape of the sail, another factor is the sail profile. If you google wing shapes, you will see that an ideal wing shape is asymmetrical in the front-back direction. For sails, this profile is sown into the sail. In fact this is one of the reason that modern sails are replaced after some 10 yeas of usage - they loose their profile. When square sails are used to sail a close-haul, either side may be used as the leading edge, depending on which side the wind is coming from. This obviously prevents you from giving them the asymmetrical shape that would be needed for a good wing.",
"The final point which may also have some impact is that the leading edge of a wing should be fairly stiff to be able to cut into the wind - so to speak. On triangular sails this is achieved by having the leading edge attached to the mast, for the main sail, or to a steel wire, for the fore sail. On a square sail this is more difficult and involves tying down the lower front corner (also called the tack) and create tension to the upper front corner. This doen't make as good an edge.",
"The final result is that square sails have a lower lift to drag ratio than than triangular sails. This allows you to sail at a much closer angle to the wind with triangular sails.",
"2.: Tacking is the process of repeatedly turning the bow if the ship through the wind in order to gain a net distance against the wind. On a modern boat tacking is simple because while the bow is pointing into the wind, the sails give almost no resistance. Once the bow has passed through the wind the sails are filled again from the other side and one can sail on. Also, the angle between one close-haul and the other is not so large - typically 90 degrees, making this a swift maneuver,",
"On a square rigged ship tacking pointing the bow into the wind is a bad idea because the square sails will be blown backwards, stopping the ship. There is much more work to be done to tack a square sail. The lower front corner of the sail, i.e. the tack, has to be released and the new tack has to be tied down. In addition, the angle between two tacks is larger. All this makes it much more likely that the ship will loose its speed and won't get though the wind. On a square rigger onw would genrally prefer top gybe, i.e. moving the stern through the wind. However, this involves sailing down-wind for at least a short while which will loose some of the up-wind distance that one is trying to gain.",
"This should be enough for now. I hope I have answered your question."
] |
[
"Ships do overall go against the wind, but not straight forward. This is possible because of triangular sails (square ones make it much more complicated.) They go against the wind with a slight angle. Keel under the boat prevents it from going sideways, so boat can only move either forwards or backwards. As long as wind force is even little bit towards the front - boat will move forwards. "
] |
[
"By ",
"Tacking"
] |
[
"Climate change books/papers/survey papers?"
] |
[
false
] |
Hi everyone, A issue I feel strongly about politically is climate change. Everything I've read points toward the evidence being statistically overwhelming. However being a good scientific sceptic I'd rather not rely on third party sources and would be keen to read the important papers myself. Does anyone have any references to get me started? Any papers claiming evidence against climate change would be good too, along with their rebuttals.
|
[
"I get to link to my favorite video (yay): ",
"http://www.agu.org/meetings/fm09/lectures/lecture_videos/A23A.shtml",
"This talk was given by Richard Alley at AGU a few years ago. He mentions the names of researchers to google and the years of their paper."
] |
[
"OP, here's the ",
"2007 synthesis report",
" and ",
"all the rest",
"."
] |
[
"Start with the IPCC reports."
] |
[
"Do supergiant stars generate more energy in their death than they do in their life?"
] |
[
false
] |
I'm really interested in stars for no particular reason. Earlier today, I had heard a physicist say making a stable wormhole would require amounts of energy equivalent to creating a black hole out of a star—a supernova. Idk if they're right, and the validity of the statement isn't the focus, really. I'm more curious about whether or not the energy output of a supernova exceeds that of the energy output of a star during the rest of its life. Is there even a way to measure that?
|
[
"A star of 8 solar masses might have an output of 4e29 Watts and a lifetime of 80 million years, that translates to an estimated total output of 1.0e45 Joules from fusion energy. I did a quick estimate of the fusion energy released in the last phase of life of such a star as roughly 1.44 solar masses of Silicon et al fuses into Nickel-56 and that came out to about 2e44 Joules, which doesn't significantly change the estimated lifetime output. A Type II supernova releases around 10",
" Joules of energy (99% of it in the form of neutrinos), which is about an order of magnitude more than the energy released by fusion during its life.",
"And that's going to hold up for stars of other masses as well. The triggering condition for a Type II supernova is the formation of a dense Nickel/Iron core of electron degenerate matter at 1.44 solar masses. Pretty much all routes that would arrive at that destination would do so via fusing the same total amount of mass, which would generate the same total amount of energy.",
"There are other ways for massive stars to die (forming black holes, pair-instability supernovae, etc.) but I'll leave that complexity aside for the moment."
] |
[
"In a very, very broad sense, the scales here are similar. A typical supernova is about on par with the lifetime energy output of the Sun. Stars have a variety of lifetimes and luminosities, so there's quite a range of possibilities.",
"But I think you can safely say that they're on par."
] |
[
"Yup. Fusion reaction rates are very non-linear with respect to temperature and pressure. Inside the core of a massive star not only is the pressure and temperature in the exact center higher but the entire volume that is at fusion supporting conditions is also larger, leading to overall much higher rates of fusion.",
"This translates to higher temperatures for the star's surface as well as a larger volume (and thus surface area). Radiated power (luminosity) is ",
" non-linear with respect to temperature, scaling with respect to the product of area and the ",
" power of temperature.",
"Let's look at a real-world example or two. Start off with the Sun, we're going to scale everything else relative to the Sun so the only thing of interest here will be the surface temperature of 5770 Kelvin. Now compare that to Sirius A, a star of 2.1 solar masses. It has a radius of 1.7x the Sun and a temperature of 9940 K. Let's estimate its luminosity based on those figures: 1.7",
" is 2.9 while (9940/5770)",
" is 8.8, and the product of both is 25.5. So with a combined nearly 3x surface area and 72% increase in surface temperature the result is a whopping 25.5x estimated increase in total luminosity. As it turns out the actual figure is 25.4x solar luminosity, so our estimate was right on the money.",
"Let's pick another example, Betelgeuse, a red supergiant star that is about 12x the mass of the Sun with 900x the Sun's radius and a surface temperature of 3590 K. You'll note that the surface temperature is lower than the Sun, because Betelgeuse is actually puffed up in order to reach the conditions that make it possible to radiate away enough fusion energy to keep in equilibrium. Anyway, again you get 900",
" times (3590/5770)",
" which gives you around 120,000 times the luminosity of the Sun, which is within the current measurement error (there is still some ambiguity about how far away Betelgeuse is which affects the estimate of its brightness).",
"Anyway, 25x the luminosity of the Sun translates directly to 25x the rate of fusion reactions and thus a 25x faster track toward depleting that fusion fuel. For a star that is only twice as massive as the Sun. And in the case of Betelgeuse, it's 120k times as fast for a star that is only 12x as massive. Once you get up to stars that are dozens or hundreds of times the mass of the Sun then you get lifetimes that are single digit millions of years or less.",
"On the plus side, this means that stars which are destined to undergo a core collapse supernova live lives that are so short that the chances of planets that could harbor life existing around them would be extraordinarily tiny."
] |
[
"Do rainbows have ultraviolet and infrared bands?"
] |
[
false
] | null |
[
"In fact this is how infrared light was first discovered. ",
"Herschel directed sunlight through a glass prism to create a spectrum - the \"rainbow\" created when light is divided into its colors - and measured the temperature of each color. He used three thermometers with blackened bulbs (to better absorb the heat) and placed one bulb in each color while the other two were placed beyond the spectrum as control samples. As he measured the temperatures of the violet, blue, green, yellow, orange and red light, he noticed that all of the colors had temperatures higher than the controls and that the temperature of the colors increased from the violet to the red part of the spectrum. After noticing this pattern, Herschel decided to measure the temperature just beyond the red portion of the spectrum in a region apparently devoid of sunlight. To his surprise, he found that this region had the highest temperature of all. ",
"And you can even recreate the experiment ",
"http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_experiment2.html",
" Very fun with kids.",
"Some typical results"
] |
[
"This is one of the coolest experiments I've ever heard of."
] |
[
"indeed, good answer - and only a couple of weeks ago I stumbled on ",
"this pretty cool photo",
" which clearly shows where the UV and IR bands sit. ",
"Because of the way the image is filtered, you don't see \" colored bands\" like we can distinguish in the visible region, but if you used, for example, a series of band pass filters, you would be able to see that effect still."
] |
[
"Electromagnet in space: how do the force/attraction work over time?"
] |
[
false
] |
This is based on a thought experiment proposed in a podcast: What happens next? Presumably the two will move towards each other at some point, the force shouldn't act before the information can arrive (i.e. 1 hour). How does it work? I understand this doesn't have to be huge or in space but it makes the concepts easier.
|
[
"Going by Mazwell's equations, electromagnetic fields are disturbances in points in space that influences other nearby points which further influence other further points, and so on.",
"The moment the electromagnet is turned on, the the disturbance is created near the face of the electromagnet, which creates a field that permeates through all of space at light speed. Now this field doesn't diminish when you turn off the electormagnet, fields created at time t0 exists and travel as a \"wave propagation\" at light speed through space regardless of what happens at the source at time t>t0.",
"So in the thought experiment, I'd believe that the ferromagnet would \"feel\" an electromagnetic force one hour later, with magnitude proportional to the strength of the source, and should accelerate for 10 hours unless it either collides with the electromagnet or the 10 hours pass and it ceases to accelerate and travel at constant speed."
] |
[
"Where are you getting 10 hours? Was there an edit or maybe you read the post wrong? I also think you are missing the idea of the thought experiment, what happens to the electromagnet, does it just seem to accelerate after it is turned off?"
] |
[
"I read the post wrong I think. "
] |
[
"Are there any advancements in aircraft that don't use jet or rocket fuel?"
] |
[
false
] |
Say tomorrow we use up our last drop of rocket fuel and jet fuel and whatever fuel propeller planes use; would all aircraft seize to exist? (besides blimps and hot air balloons and stuff like that)
|
[
"We would just make more. Jet fuel isn't that different from gasoline. The only real difference is the length of the hydrocarbons. We could get more jet fuel by just refining it from crude oil, or cracking very long chain hydrocarbons into the kind in jet fuel. If we really got desperate, we could it theory produce it from certain fat compounds. It really isn't possible to remove jet fuel from the world without also removing oil in general."
] |
[
"You already have (unmanned) solar powered electric planes.",
"You can also make nuclear airplanes. I don't know if you can go supersonic without jet fuel (today) but you certainly can fly - propellers attached to electric motors."
] |
[
"http://www.npr.org/2011/09/26/140702387/air-force-and-navy-turn-to-bio-fuels",
" ",
"This is just the beginning, I believe that Honda is working on a hydrogen powered jet as well."
] |
[
"Why do antidepressants vary so much in effects, efficacy and side-effects from person to person?"
] |
[
false
] |
First off, this is absolutely NOT an attack on antidepressants or anyone who uses them - they're clearly extremely helpful for a huge amount of people, and I'm currently weighing up the pros and cons of starting them myself. What puts me off, though (and kind of confuses me) is the huge variation in stories you hear from people who have taken them. There's obviously a vast amount of horror stories online, but there are also a lot of stories of people who have had remarkable recoveries on them (I'm currently in the middle of reading Listening to Prozac by Dr Peter Kramer, and it's an absolutely excellent book which I thoroughly recommend - though it takes a largely pro-medication stance, it's even-handed, empathetic, asks a lot of very valid questions, and contains tons of excellent scientific information in a very digestible writing style. I can honestly say it's been quite reassuring to read a more positive perspective than the scaremongering and horror stories you usually hear in the media.) So why is there so much wild variation in people's experiences of these drugs? Some people seem to make almost miraculous recoveries on them, some people feel a lot better on them but suffer horrible side effects, some people don't seem to get any effect from them at all, and some people end up feeling worse (even after the 3-week adjustment period). Even within side-effects of , there seem to be vast variations in what people seem to experience - some people report feeling sleepy and lethargic, others are so keyed up they can barely sleep. Some report that their libido is all but destroyed, some report that they actually improved their sex lives. Some report a huge decrease in anxiety, others claim they made them more anxious or that the drug gave them panic attacks. Some claim they made them able to feel happy for the first time in ages, others claim that the drug made them feel like an emotionally blunted zombie. Some report their thinking feels sharper and clearer than ever, others report "mind fog" or being unable to concentrate. How can one drug have such vastly different (and in many cases, opposing) effects on patients with the same illness? Doesn't that render the whole serotonin theory of depression rather suspicious? (I'm mostly talking about SSRIs here, I'm aware there are other antidepressants that target different neurotransmitters). Also, is there any other class of drug where the effects are so unpredictable from person to person? From my layman's perspective, most other drugs pretty much do what they claim - if someone takes a medication for low blood pressure, their blood pressure will increase. If someone takes antibiotics, they'll fight the infection. Some may need more of the drug, some may need less, and a few may have allergic reactions or side-effects to the medication, but for the most part it does the job pretty predictably - whereas with antidepressants, it seems to be more like throwing a penny down a well and waiting to see what happens, hence many patients having to spend months trying different drugs (or even combinations of drugs) before eventually finding one that works. Are there any studies on which particular drugs work best for certain patients? I know the brain is immensely complicated, but the wild variations in reported effects seem odd to me, and I'd be interested in hearing any scientific explanations for this. Thanks!
|
[
"I think some of it has to do with the dosages given. For example, when I was put on 20mg of Prozac from nothing, it put me through absolute hell and hospitalized me twice. After that, I was put on a pediatric dose of Lexapro and allowed to gradually increase my dose by 5mg increments every other month or so. A year later, I'm ready to switch back to Prozac. I was hesitant to try it again, but weaning on to it is so helpful so far. I haven't had the side effects that I did before, and I'm getting my energy back a little at a time. ",
"I think because of the nature of SSRIs, it's really important to start off on something you can gradually increase, so you're not putting your body through too much at once. I feel like, from personal experience, that's where a lot of the horror stories come from: improper dosage, rather than the drug itself. Because everyone's genetic makeup is different, that probably impacts which areas of their systems are affected. Maybe some are more sensitive to libido changes, while others are more likely to have appetite changes. It might also have something to do with a person's individual base line for all those things. So like, if my appetite is already poor, I'm less likely to notice loss of appetite and more likely to notice any increase, if that makes sense? "
] |
[
"See ",
"this thread",
" asking the same question from a few years ago.",
" ",
"Basically, SSRI is a class of many different drugs (Prozac is fluoxetine and Lexapro is escitalopram, for example) each with a different structure. This structure can affect how the drug affects you. ",
"Also, is there any other class of drug where the effects are so unpredictable from person to person? From my layman's perspective, most other drugs pretty much do what they claim ",
"This is not limited to SSRIs or anti-depressants.\nFrom ",
"/u/indianola",
" in the linked thread:",
"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."
] |
[
"Part of it is that these patients may not all have the \"same illness,\" as depression has many causes and manifestations.Some may be pure serotonin deficiency, some may be environmental, some may be caused by a completely different neurotransmitter, and some may be misdiognosed. And because serotonin also regulates other functions, like sleeping a food digestion, the effects of modifying serotonin re uptake can be many. And of course, the problem with making a drug for depression that doesn't get people high is that it cannot MAKE you happy like recreational drugs do. Your body still needs to manufacture and your neurons still need to release serotonin."
] |
[
"Why can we store carbohydrates and fat as unnecessary adipose tissues, but not store protein, which actually helps us to grow and repair?"
] |
[
false
] |
Surely meat has been in our diet long enough for us to evolve to store protein in our bodies. We can't use most of the adipose tissue our body stores (especially true in larger people) but we cannot store protein? Just revising for an exam, and the question popped into m head.
|
[
"Fat stores energy more efficiently than protein (i.e. you can get more ATP from oxidizing fat per gram than you can from metabolizing protein). This is partly because fats can be stored extremely efficiently because they are hydrophobic, so a huge associated store of water is not required. The amount of water that is needed to store a caloric equivalent of protein is much higher because proteins cannot be dehydrated in the way that fats can.",
"Protein is also the major 'functional' molecule in biology, carrying out various cellular functions. It seems to me that it makes less sense to use proteins for fuel (under non-extreme conditions) because you don't want your basal cellular functions to be compromised by shifting levels of protein. Of course, if we had evolved a 'protein storage' organ akin to adipose tissue then this might be possible. Though you still have the issue if inefficient storage which would be my answer as to why fat is used."
] |
[
"additionally, a skeletal muscle can lose about 50% protein content on average before significantly weakening in strength. They do function as a sort of functional protein storage in that regard; the protein contents of skeletal muscle are capable of compensating lack of protein or glucose nutrition (via gluconeogenesis) to a fairly good degree. It's just that skeletal muscle is not a dedicated protein reservoir like adipose tissue for fat because the protein contents of a muscle are regulated by muscle usage/training AND protein availability, not protein availability alone."
] |
[
"Energy aside, what about just storing them for their use as building blocks for any future repairs and growth and such. Wouldn't that be pretty darn useful."
] |
[
"Is it possible that we are in a tiny corner of the universe?"
] |
[
false
] |
[deleted]
|
[
"Space expands faster than light.",
"Actually, the expansion rate depends on the length scale. The farther apart two bodies are, the faster they're moving apart. Stuff ",
"more than about 16 billion light years from us",
" right now would be away from us at faster than the speed of light, assuming it's there. Of course, we can't see that stuff, so we're just assuming that the universe continues beyond that distance, since it looks pretty uniform in the range we can see. So...",
"So then isn't it possible that the observable universe is just a tiny fraction of the actual size of the universe?",
"Yes, this is actually the most simple assumption, since the only edge we see is the ",
"cosmological event horizon",
".",
"In other words, isn't it possible the big bang happened >100 billion years ago?",
"No, the age of the universe, is determined by looking at the expansion rate (both now and in the past) and asking, \"If we rewind until everything is in the same place, how long ago is that?\" The answer is about 13.8 billion years. This is true no matter how big the universe actually is (even if it's infinite).",
"The next natural question is, if the universe is infinite, how can everything have been in one place a finite amount of time in the past? Think of it this way. Pick two points in the universe, A and B. Measure the distance between them. Figure out how fast they're moving apart (and how that rate changed over time). Now ask, \"is there some point of time in the past when that distance was zero?\" It turns out the answer is yes. Also, and here's the key idea, ",
" then for ",
" two points in space, the point in time when the distance between them was zero is always the same: 13.8 billion years ago.",
"I found two FAQs about the big bang that might be helpful. I only had time to skim them, but they look pretty good.",
"http://www.astro.ucla.edu/~wright/cosmology_faq.html",
"http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.pdf"
] |
[
"All points are the centre. Every point in space is moving away from every other point in space, the further away it is the faster it is moving away from a relative perspective.",
" Think of it like this... Point A is where the bit of the universe that contains Ap0llo exists at the start of the big bang.",
"Point B is another location where E.T. lives 13.7 Billion years after the big bang.",
"As the Universe starts as a singularity the A and B occupy the same position and both are the centre and all points fly away from all other points. This means that from A's perspective.. Ap0llo looks out and says \"I'm the centre of the universe\"",
"From B's perspective E.T looks out and comes to the same conclusion"
] |
[
"All points are the centre. Every point in space is moving away from every other point in space, the further away it is the faster it is moving away from a relative perspective.",
" Think of it like this... Point A is where the bit of the universe that contains Ap0llo exists at the start of the big bang.",
"Point B is another location where E.T. lives 13.7 Billion years after the big bang.",
"As the Universe starts as a singularity the A and B occupy the same position and both are the centre and all points fly away from all other points. This means that from A's perspective.. Ap0llo looks out and says \"I'm the centre of the universe\"",
"From B's perspective E.T looks out and comes to the same conclusion"
] |
[
"Why does shaking a carbonated beverage cause it to violently erupt after opening it?"
] |
[
false
] | null |
[
"This is more of a physics question.",
"The beverage is a solution of carbon dioxide, various flavorings, and some kind of sweetener. The beverage is pressurized, which is important because the solubility of gases increases with increasing pressure. This means that the beverage has more gas dissolved in it in the closed state than it could hold if it were at atmospheric pressure in the open state. However, gas coming out of solution is not instant and takes time (which is why carbonated beverages take many minutes to become flat). The main way to speed up the dissolution of the dissolved gasses is to introduce nucleation sites or bubble formation. Both of these are somewhat related. Starting a bubble is hard. For a bubble to form, it has to break the surface tension/adhesive forces of the liquid. Growing a bubble is a lot easier than starting one since the surface tension component is proportioal to the bubbles surface area where as the bubble grows with volume (and volume is proportioal to the amount of gas within the bubble). This means that as more gas goes into the bubble, it's easier for the next one to go in.",
"When the beverage is shaken, tiny bubbles form (that are for the most part formed irrespective of dissolved gasses). Since you've introduced a bunch of bubbles, when the beverage is opened, all the dissolved gas has an easy \"exit point\" and can go into all the existing bubbles. So all those tiny bubbles in the closed beverage rapidly expand when the beverage is opened, leading to the violent eruption."
] |
[
"Before the carbonated beverage is opened, there is a layer of high pressure CO2 sitting on top of a layer of water containing dissolved CO2 (and sugar, flavours etc). When you shake it up, instead of the two layers being neatly stacked on top of one another, bubbles of CO2 will be dispersed through the liquid. You can see this kind of effect with a regular clear water bottle if you shake it up, though the bubbles do not persist for as long and are air not (just) CO2.",
"When the container is opened, the high pressure CO2 which was previously contained is now free to expand, to equilibrate to atmospheric pressure. In the case where it was not shaken up, the gas layer on top escapes through the opening without any fuss, and you just hear a hiss. If it was shaken up, the top layer escapes, but then the bubbles of gas dispersed through the liquid are also free to expand. As they do so, some liquid will be carried through as long as the bubbles do not immediately collapse. The harder it was shaken, the smaller the dispersed bubbles will be, which leads to a greater amount of foam carried through the opening (surface area/volume ratio)."
] |
[
"The explanation there is much shorter. You're allowing the gases to dissolve back into the liquid. The extra pressure from squeezing it increases the solubility of the gases, as well as allowing time for the process to occur."
] |
[
"How do we know how old viruses are?"
] |
[
false
] |
I've seen it multiple times that viruses have existed on earth for billions of years, but also that they don't appear in fossils. How do we know viruses are 3-4 billion years old? I've tried googling it but the answer seems hard to find
|
[
"first of all they're the most simple (and yet the most effective) life form, and therefore it's only logical they can represent one of the first steps in the evolution grand scheme (some scientists believe they evolved from a different branch of cells that sort of regressed tho): specifically the RNA ones are the oldest, since oxygen lacked in the old-earth atmosphere and that favoured RNA over DNA.\nStill, they cannot be older than cells themselves, since they need to use them to \"reproduce\".\nVery often some viral genetical mark can be traced way back in old DNA as well, and that can give you some sort if indication of the pathways the virus took to get the genetical configuration it has today, but apart from that it's really hard to put a pin in time.",
"Sorry for my english, it's not my first language"
] |
[
"One method:",
"(1) We can measure genetic drift rate of DNA.",
"(2) We can find partial or whole retro viruses encoded in DNA of animals such as humans because they insert themselves during replication.",
"(3) We can compare the viruses of today to the encoding of the virus in the DNA, and we know the age of the DNA due to the drift rate in (1). We can also therefore determine the age of the virus at time of insertion.",
"",
"Another method:",
"(1) Measure the mutation rate of similar viruses.",
"(2) Find old instances of the viruses from known prior historic periods.",
"(3) Compare the RNA patterns to find the mutations.",
"(4) Calculate the approximate age based on the mutations.",
"",
"Many other methods exist, and generally they line up. Reading:",
"\"Yet, over recent decades it has become apparent that viruses occasionally leave a historical record in their host's genomes in the form of endogenous viral elements (EVEs)\"",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962544/",
"LTR sequence divergence rates:",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048862/"
] |
[
"English is my first language and you’ve explained it better than I could"
] |
[
"What is the actual research behind the benefits and possible negative effects of organic farming, and consuming those products over non-organic stuff?"
] |
[
false
] |
I've been hearing very convincing arguments from both sides about this recently. What exactly does the science have to say? Are people who eat a healthy diet with tons of fruits and veggies healthier if it's organic, or does it not really matter? Does it have a lower environmental impact? Are there any flaws in how the research is done? Do we even know anything at all about the differences? Thank you for your time!
|
[
"Studies have shown that nutrients in organic vs conventional farming are equal, or in favor of conventional farming, taste tests(which are subjective) also show a favor of conventional farming. Blind taste tests consist of not knowing which fruit/vegtable is organic; being told the organic is conventional and conventional is organic to try to weed out bias as well. ",
"Issues with organic farming having lower yield and nutrients is simply genetically modified plants do not count as organic. This includes artificially selected plants; not some people in lab coats messing with genes(which is also not a bad thing if done right and tested) but people breeding traits into plants, such as higher yield, more nutrients, survive in harsher enviroments etc.",
"http://www.ncbi.nlm.nih.gov/pubmed/16403682",
"http://www.ncbi.nlm.nih.gov/pubmed/11833635",
"http://www.sciencedirect.com/science/article/pii/S0301622602003184",
"http://www.food.gov.uk/multimedia/pdfs/organicreviewappendices.pdf",
"Organic farming only has estimates to support 3 to 4 billion people on the planet through organic means, conventional means at this time can roughly support 12-20 billion people. Now this is if all countries adopted only organic, or ONLY conventional using best crops for yield and nutrientional value.",
"A misconception is organic fruit and vegitables do not use pestisides or other chemicals; they in fact do, they are just organic pestisides; aka meaning not man made, naturally found. In some cases these pestisides are worse then conventional pestisides. In the past mistakes were made and certain pestisides were banned, man made pestisides and organic pestisides; because they were harmful to humans. All pestisides used today do not taint the fruit or vegitable they are used on; which is also another misconception.",
"Pesticides used in organic farming include:",
"http://en.wikipedia.org/wiki/Bacillus_thuringiensis",
"http://en.wikipedia.org/wiki/Pyrethrum",
"http://en.wikipedia.org/wiki/Rotenone",
"Also Copper and Sulfer are used.",
"Organic farms do use less pesticides in general and a lot of organic farms pride themselves in no pesticide use.",
"Long story short; through research it tends towards organic farming using less pesticides; but pesticides show no casual link(At least current approved for use pesticides) in causing medical issues, or leaching into the enviroment so even though organic farming uses less pesticides it's not an issue either way. Organic farming actually builds up the top soil and enriches the ground with more nutrients then conventional farming practices; which is good but due to lower yields in most crops, and nutrient values being the same or lower in organic farming we would only be able to feed a fraction of what conventional farming could.",
"So is organic farming bad? Is conventional farming bad? Neither are perfect; neither are great; both have their benefits, and it really depends on the crop."
] |
[
"This is great. Thank you for all the information. Seems that unless you have the disposable income to shell out more for your veggies, it's not really worth it. "
] |
[
"I can't comment on \"big organic\" or \"big conventional\" as I don't buy it.",
"For me I find that goods produced by a home garden and the ",
" organic farms taste better as you can use different varieties, and being small can afford to keep the smaller, less efficient but better tasting ones around. There's also a big difference in animal welfare standards."
] |
[
"How does a rifled barrel improve accuracy and projectile stability? Moreover, how does spinning something (a top, for example) keep it stable?"
] |
[
false
] |
I understand that firearm accuracy increased massively when rifling was introduced. How does spinning a projectile stabilize it and keep it on course? What are the centrifugal/centripedal forces at work here? Is there an optimal speed to spin a projectile at for it to fly straight?
|
[
"More specifically, spinning the bullet gives it high rotational momentum, making it difficult to rotate perpendicular to its current rotational axis, which means more difficult to pitch or yaw (that is, tumble)."
] |
[
"More specifically, spinning the bullet gives it high rotational momentum, making it difficult to rotate perpendicular to its current rotational axis, which means more difficult to pitch or yaw (that is, tumble)."
] |
[
"Thank you very much. That was an excellent answer and this is an excellent subreddit."
] |
[
"Would a person experience the G forces of acceleration and turning at high speeds in space?"
] |
[
false
] | null |
[
"Yes, because these forces are unrelated to gravity, they are due to a change in your motion. F=ma and all that. We only call them \"G forces\" (eg. multiples of the standard earth gravity) to give humans a frame of reference for the total force. If I say the acceleration was 2G, you understand that it makes you feel twice as heavy as normal. If I say you accelerated at 19.62 meters/second, you probably would not have a frame of reference to understand how that feels."
] |
[
"Exactly. Anything with mass has inertia, which resists changes to motion. If your body is moving in a straight line at a constant speed, and then something causes you to slow down or change direction, your inertia wants to keep you doing that same speed in a straight line. The force you feel is the force required to change your motion (in this case, a force acts on the spaceship to change its direction, either its own engines or an external force, and in turn the spaceship exerts a force on you to make your motion change with it)."
] |
[
"What I don't understand is what would be pulling on us if it isn't gravity. Is it just the force of our acceleration we are feeling? Also, thanks for answering!"
] |
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