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[
"How exactly is it that a protein can catalyze a reaction with shape?"
] |
[
false
] |
I'm pretty sure I understand the basics, where two atoms\molecules can fit almost perfectly into a 'slot' that allows them to interact at a precise angle - I suppose what I'm asking is how is it possible for a protein to have a slot that holds the -exact- shape of an atom or molecule? What does it look like? From my understanding proteins themselves are usually much bigger than active sites, what does the rest of the protein do? Do some proteins catalyze the same reaction better\faster than others? Exactly how precise does the shape need to be? furthermore, I always kindof thought of atoms/molecules as not so much a defined shape, but more like tinker toys that weren't placed together in any particular order, or maybe even tree branches. Do proteins not only allow for the shape to enter, but allow complex shapes to move in a specific way? If so, that's amazing, but I wish I could actually see it happening
|
[
"I suppose what I'm asking is how is it possible for a protein to have a slot that holds the -exact- shape of an atom or molecule? What does it look like?",
"The combination of 20 amino acids can yield a startlingly large set of shapes, but it's not ",
" shape that matters, also the charges, hydrogen bonding etc that allows another molecule to \"fit.\" It really does look like a pocket though - you can see the basic shapes in crystal structures and the 3D models generated from them (",
"here's",
" a random picture I found from google).",
"From my understanding proteins themselves are usually much bigger than active sites, what does the rest of the protein do?",
"This is true. The rest of the protein often provides structure for the active site, but is more often used for various regulatory purposes. Sites that can be modified to activate or de-activate the enzymes, domains necessary for interacting with other proteins in a complex, sometimes just regions required for getting the enzyme to the right location in a cell.",
"Do some proteins catalyze the same reaction better\\faster than others? Exactly how precise does the shape need to be?",
"Yes, there are a lot of different versions of catalytic enzymes that work with different efficiencies. Sometimes completely different enzymes that have co-evolved to do the same or similar things.",
"Do proteins not only allow for the shape to enter, but allow complex shapes to move in a specific way?",
"Yeah, proteins are not locked in a rigid conformation, they're constantly gyrating... and sometimes they get mis-folded or un-folded. Enzymes usually have to change shape in order to catalyze a reaction, or change shape to be turned on and off. Usually the binding of a substrate in the active site is what induces a shape-change that forces the substrate into a new position, favoring the chemical reaction."
] |
[
"This question really deserves a more in-depth answer, but I can't do it right this instant. I can mention the two major things I'm a bit surprised no one has mentioned....",
"The general notion is that enzyme function involves lowering the activation energy between reactant(s) and product(s). It does this by stabilizing the transition state, usually involving various contributions from electrostatics, geometry/conformation, and so on. That is, by reducing the activation energy barrier by tightly interacting with the transition state, more reactants are likely to form product. Being able to tightly bind the reactant is not quite so important. Another critical element is controlling the substrate's exposure to solvent, as well as the enzyme active site. One might envision this being a more pressing issue in the case of hydrophobic substrates.",
"Also, there can be remarkable diversity in the nature of enzyme active sites and/or substrate binding sites. Some are caverns and can accommodate multiple small molecules - others are far more restrictive. "
] |
[
"You have the correct basic idea. It is kind of hard to visualize, so ",
"here's a handy animation",
"! In that gif, a hemoglobin enzyme changes its entire configuration very slightly in order to bind an oxygen (O2) molecule. Proteins are composed of combinations of ~20 different types of amino acids (each with a different side chain). Sections of the protein are folded in such a way that, yes, the shape of the hole is exactly (or very nearly exactly) the shape of the substrate. Charge also plays an important role in how proteins recognize their substrates. The parts of the protein that aren't the active site play structural roles to make sure that certain amino acid side chains are pointed in exactly the right direction to form the aforementioned active site.",
"So, to answer your questions, yes, yes, yes, and yes! It is very amazing, and it does allow complex shapes to move in specific ways, and some proteins do catalyze the same reaction faster/better."
] |
[
"Is there anything in the universe that truly stands still?"
] |
[
false
] |
The moon moves around the earth moves around the sun...what does the sun move around?
|
[
"Yes and no. Any non-accelerating object could be said to be stationary in its inertial frame of reference. However no non-accelerating frame of reference is privileged over any other, so there is no absolute way to define a stationary object."
] |
[
"Isn't the Cosmic Microwave Background Radiation used as the universal reference frame?"
] |
[
"The sun moves around the black hole at the center of our galaxy. Whether or not our galaxy is moving depends on the reference frame it is viewed from. Velocity is relative, which means that there is no way to tell if something is \"moving\" or \"still\" other than to compare it's speed to the speed of other objects."
] |
[
"If we could stop out telomeres from shortening, could we live forever?"
] |
[
false
] |
Could we? Why do they exist? And what role do they play in our bodies?
|
[
"No.",
"First off, humans do not run out of telomeres within a normal lifetime. We aren't meant to. Telomeres are there as an anti-cancer mechanism. If a cell line begins dividing very rapidly, telomeres ",
" run out and useful DNA would start to be lost for each generation.",
"And secondly, even if we had a \"perfect\" version of telomerase that would always completely restore our telomeres after every DNA replication, we would still be subject to DNA damage and harmful random mutations. And certain genes seem to turn on and off as we get older, which is the one of the primary causes of the changes we see with aging, but the mechanism by which this happens is ",
"heavily debated.",
" "
] |
[
"Sadly not. ",
"Telomeres are like the \"aglets\" (the bits of plastic on your shoelaces) that stop your laces unraveling. They are part of your DNA that doesn't actually code for anything, no instructions are writen on this part of your DNA for anything.\n During DNA replication your DNA shortens slightly, at first this shortening eats into your telomeres and then when you have no telomeres left it eats into your DNA. Having shortened DNA leads to possible genetic diseases as your are starting to lose coding DNA!",
"Even if we had Telomeres of steel that never shortened we'd still get ill. This can be shown just by looking around you, many young people get terminal diseases whilst their telomeres are still almost as long as they'll ever be!",
"So, we couldn't live forever, but maybe we could stop a few disease of old age. As we get better at curing diseases like cancer and pulmonary disease we'll have to start looking at problems of genetic disease and telomere shortening!"
] |
[
"Thanks for the info, I was hoping I that I could live forever... I guess not."
] |
[
"Is there an established way to deal with an invasive species? Is it better to intervene, or let nature take its course?"
] |
[
false
] |
I know that invasive species are often brought into a new environment, and they end up wreaking havoc on the ecosystem. I was wondering whether efforts by humans to "correct" the mistake end up actually working, or end up doing more harm than good.
|
[
"This is a more complex problem than this: Not all new species are actually invasive, and usually, it takes time to see whether they are. There are numerous species that are currently on the list of \"could be or become invasive\". Then, if a species turns out to be clearly invasive, something usually is done about it (for example often, if you keep an individual of that species in your own four walls, you can be punished by law if you set it free - though that does not work as well as it should). However, there's only so much humans can do, and it rarely is enough to actually \"correct\" the mistake fully. A lot of times there simply isn't really much you CAN do. Furthermore, a lot of measures that are taken do end up doing more harm than good as you said, especially such a domino as happened in Australia: Importing one species to rot out the species we just previously imported. Also, a lot of countermeasures don't only harm the invasive species, but other species as well.\nIn the end, there's not really a matter of fact here, but generally, people try to intervene if the species is actually invasive and intervention is possible. Not intervening at all is not really much better though, because that will just result in local species becoming endangered or extinct."
] |
[
"Very good explanation. Indeed what humans can do is currently not enough when a specie gets out of control. It is difficult if not impossible to control the relations each animal or plant have with each other.",
"A good way to at least relief the problem is to introduce specific parasites (usually against agricultural plagues) or through genetic modification on some organisms of the population like is currently being done with Aedes aegypt mosquitoes."
] |
[
"Well, a \"good\" way is relative. The problem with bacteria is that since they have short lifespans, are haploid, and can horizontally adopt genetics, they're likely to mutate. And try getting THOSE back in control afterwards. Not to mention, that usually, genetically modified bacteria is often resistent towards antibiotica.\nAs for parasytes that are not antibiotica, well, those are even harder to get in control afterwards, so in the end, you might just be replacing one plague with another. Also, there's never any guarantee that they don't end up damaging other organisms too. Still, it's effective, and should be taken in consideration.",
"I think there's not actually much genetic modification with the mosquitos but I'm just going by what I've heard on uni, I haven't actually looked it up. Thought that I heard that all they do is castrating males, and letting them roam free again. These males will still be concurrence to other males, they will also eat, and take space, but they won't reproduce, so that over time, the population will decline. That is relatively safe, since humans don't end up messing around too much with nature, but it takes longer to work, and doesn't have such a strong effect - also, it's only sufficient to reduce a population, if you want it to vanish in one place, you won't succeed like that."
] |
[
"Why do planets rotate in any particular direction?"
] |
[
false
] |
Somebody asked a question about planets orbiting the sun, but mine's actually about the direction of the planet's spin, which leads to the day-night cycle: why do planets rotate in any particular direction? Earth, for instance, rotates west-to-east. Why is this? My guess would be either something to do with conservation of angular momentum, or simply as a further artefact of the Earth forming from the same accretion disk (?) that all the other planets formed from. Also, in case that's not enough: how does tidal locking occur?
|
[
"conservation of angular momentum, or simply as a further artefact of the Earth forming from the same accretion disk ",
"Bingo. Both are correct. Mass that's moving has a tendency to spin when it clumps into a mass like a planet, and since it maintains this momentum pretty much forever in space."
] |
[
"You've already got a good deal of the answer figured out here...conservation of angular momentum of the initial debris disc from which the planets formed. ",
"The original large molecular cloud that formed our solar system had a very slight rotation to it. As it collapsed down to form the Sun and the debris disc from which the planets formed, its angular momentum had to be preserved - similar to how when a spinning ice skater pulls his arms inwards, his rotation rate increases. ",
"Similarly, as the debris disc started clumping to form planets, they too had to maintain this initial angular momentum as the mass became centrally concentrated. This is expressed today as the rotational direction of each planet. ",
"It's worth noting that rotational ",
" were likely much faster than Earth's current 24-hour day. Earth has slowed down considerably as the Moon recedes away from us, transferring our planet's rotational angular momentum to the Moon's orbital angular momentum. This hasn't really happened for the gas giant planets since they're so much more massive than their moons - both Jupiter and Saturn's day are only about 10 hours long.",
"So when viewed from the North Pole looking down, 6 of the 8 planets rotate counterclockwise (and even the Sun, too), and as explained above, we think we have a pretty good handle on why this is. Right now the hottest area of active research in this field is why a couple of the planets - Uranus and Venus - ",
" rotate the same way. Venus rotates backwards very, very slowly (one rotation takes 243 Earth-days), and Uranus is essentially rotating on its side.",
"It was pretty fashionable 20 years ago to say that their weird rotations were due to a giant impact. After the manned Apollo missions that essentially proved that our Moon formed from a giant impact with Earth, suddenly \"catastrophism\" became all the rage in astronomy, replacing the long-held beliefs that such global processes only occur through gradual change. Suddenly, this became the answer for everything - Why is Uranus rotating on its side? Probably got hit by something. Why is Saturn's moon Iapetus two-toned? Probably got hit by something. Why does Neptune have an anomalous source of heat? Probably got hit by something.",
"The problem is that when you have a hammer, suddenly everything looks like a nail. Uranus is big - if you carry though the calculations, it turns out to be very difficult to transfer enough energy to Uranus to tilt its rotational axis without completely destroying the planet. As a result, the pendulum of scientific explanations is starting to swing back to favor gradualism, at least for certain processes (Venus may very well have been hit by something - the jury is still out on that one).",
"There's been a considerable amount of research to suggest that Uranus' tilt may be solely due to a few billion years of tidal interactions with the other gas giant planets, slowly but surely pulling it on its side. We're still a long way from knowing for sure, though - the initial planning phase of a dedicated Uranus spacecraft is just getting underway now, so perhaps we'll know a lot more if that project ever gets funded and built.",
": Your guess is completely right - angular momentum conservation from the primordial debris disc. Why Uranus and Venus rotate differently is still an unsolved problem in planetary science."
] |
[
"Venus actually rotates in the opposite direction from the other planets. Likely from one or many large collisions in its past changing its spin. Other theories include gravitational effects of its dense atmosphere from the sun.. etc.."
] |
[
"When a guy cums does it come from both testicles simultaneously?"
] |
[
false
] |
Or just one per ejaculation and they alternate? Or does one operate for so many years then retires? What happens if a testicle gets cancer and must be removed, how is ejaculation affected?
|
[
"When a guy has a correct vasectomy, the sperm stays with the testicles and whatever remains of vas deferens tubing yet connected to the testicles, dies there and is reabsorbed as waste. The testicles usually sense that there's a build-up of sperm and produces less going forward."
] |
[
"Thanks for the detailed answer. ",
"So when a guy has a vasectomy, where does the semen \"go\"?"
] |
[
"Thanks for the detailed answer. ",
"So when a guy has a vasectomy, where does the semen \"go\"?"
] |
[
"How much light is absorbed in the deepest part of the ocean?"
] |
[
false
] |
I just read about this new material and was wondering because i thought the deepsea was one of the darkest places on earth.
|
[
"It's dark because the water above it is kilometers thick, not because the water is inherently dark. If you were to turn on a (waterproof, pressure proof) flashlight down there, it would illuminate."
] |
[
"Absolutely. In the open ocean light can penetrate further than at the coasts due to a lack of sediment, but the end of the euphotic zone (area with light) is around 200 meters."
] |
[
"In addition, the red end of the spectrum gets absorbed (scattered) first and can't penetrate beyond the first 10 metres or so. If you ever go SCUBA diving, you will notice that the deeper you descend, the only colours that are visible from the sunlight penetrating the water are blues and greens. For this reason, underwater photographers need to use their own light source to bring out the full spectrum of colours."
] |
[
"Is there a difference between electrical impulses sent to the brain by different sensory organs (say, between an impulse sent by the inner ear and one sent by the optic nerve)?"
] |
[
false
] |
Or are they the same type of electrical signal and the brain somehow differentiates between them to create different representations?
|
[
"Doctor here:",
"The signals are exactly the same electrical impulses, sent down the axon of the neurons, mediated by the sodium potassium pump and gated ion channels, but the signals can be sent up to 300 Hz (on average) or 300 electrical impulses per second, the nervous system does not waste energy sending more signals than the receiving part of the body can receive and respond to.",
"So take for example a muscle cell, they can only contract a maximum of 30 times a second on average, up to 50 times per second for some extreme top performing athletes, so the nervous system would never send more than 50 signals per second through a motor neuron because the muscle can’t contract any faster. It would just be a waste of energy and electrical signaling. Where as an organ or a gland can receive a higher number of impulses per second and different frequency of impulses would be different messages.",
"A message of 78 impulses per second would be a different response from a certain gland than a message of 22 impulses per second, or a message of 268 impulses per second. Long story short, glands secrete hormones or fluids. So a higher frequency of electrical stimulation would be a higher secretion response from said gland. And the body modulates the hormone levels based on neurological feedback loops (signals into the brain from sensors all over the body) and increasing or decreasing the electrical or nerve stimulation of the gland responsible for the hormone in question.",
"Hope that helps!!!",
"I guess I didn’t actually answer your question because I focused on efferent nerves in my answer, and you asked about afferent nerves, lol.\nEfferent means leaving the brain and afferent is entering the brain.",
"There is no difference in the electrical impulses sent by the ear vs eye but the frequencies of signals will differ to encode different messages.",
"The real difference is that the ear and all its components are all an external organ that transmits signals into the brain, where as the eyeball, retina, and optic nerve are all part of the brain itself.",
"Also both these senses integrate many different types of sensors into a cohesive perceived output. Simply think cones vs rods. Different receptors see color vs black and white, then the brain integrates all information into your sense of sight.",
"In the ear different frequencies of sound are picked up by different receptor cells and integrated into what you hear, a song with simultaneous bass and treble.",
"The signals are the same electrical pulses per second but the pattern or frequency is different.",
"“Processing Patterns of Optic Nerve Activity in the Brain. A possible answer is suggested by a recent finding that central neurons integrate optic nerve signals with synaptic time constants on the order of 300–500 ms” This means we can only see so many frames per second.",
"“Thus, the neural output of the auditory nerve can follow the temporal structure of the waveform up to frequencies of about 5000 Hz.” This means we have a much higher range of hearing; the distance between the high notes and the low notes."
] |
[
"On a tangent: it has been established that electrical signals pretty much propagate with the same speed all across your nervous system.",
"This means that for instance when you touch your toe with your finger, your brain receives the sensation from your toe several tens of milliseconds after it receives the sensation from your finger, and then both of them are tens of milliseconds behind the signals received from your eyes.",
"Yet when you perform that act, they all seem to happen at the same time."
] |
[
"I edited my post to add everything after hope that helps! :-)"
] |
[
"Are there any homemade \"filters\" people can make so they can watch the solar eclipse on Sunday?"
] |
[
false
] |
First off, I hope this belongs here. I think it's more of an askscience question than an askreddit question. But I'd really like to watch as much of the solar eclipse as I can, but I obviously know enough to not look directly at it. So, are there any homemade lenses or filters we can try so we can look at it? If not, what is the best way to do it?
|
[
"Welding glass (the bits that go in a welders mask) is a good option, and cheap as chips."
] |
[
"You can make a camera obscura.",
"http://www.exploratorium.edu/eclipse/how.html"
] |
[
"Check out ",
"NASA's page on Eye Safety During Solar Eclipses",
"It says \"The safest and most inexpensive of these methods (to view the eclipse) is by projection, in which a pinhole or small opening is used to cast the image of the Sun on a screen placed a half-meter or more beyond the opening. Projected images of the Sun may even be seen on the ground in the small openings created by interlacing fingers, or in the dappled sunlight beneath a leafy tree. Binoculars can also be used to project a magnified image of the Sun on a white card, but you must avoid the temptation of using these instruments for direct viewing.\"",
"It also says ",
". I would ",
" use a homemade filter because anything you make at home will not be specifically designed to look at the sun. It gives a few examples of inexpensive filers that can work but I would not use anything you can make at home. That is because if your read the whole thing all those filters have thin layers of chemicals that attenuates ultraviolet, visible, and infrared energy and anything you make won't do that. ",
"Edit: Expanding a few things"
] |
[
"What is physically happening in the eye that causes it to hurt when looking into bright light?"
] |
[
false
] | null |
[
"You are literally burning your eye.",
"Light or photons interact and transfer energy to receptors in your eyes. More light, brighter and concentrated means more higher energy photons that are more packed together are entering the eye. All that energy has to go somewhere, some is lost as heat energy, heating the eye causing discomfort, and some is transferred directly to the brain.",
"Essentially you have a temperature raising rapidly, as well as massive overload of receptors which are in turn over sending massive signals to your brain, overloading neurons as well. Essentially it's a triple wammy. "
] |
[
"There is an increase in temperature of the tissues leading to physical damage. Also, overstimulation of receptors and neural transmission has a detrimental effect, ya man bagit, dominate"
] |
[
"Id presume it is the strain your iris undergoes as it contracts. Im not sure if the stimulation of your ganglion cells are linked to the sensory pain pathways, though my best guess is that they are not."
] |
[
"Why does 1/3 of the human population sneeze when they look at the sun? Why only 1/3 and not all of us? And why does it happen in the first place?"
] |
[
false
] |
Thank you guys for replying! I really appreciate the responses
|
[
"Nobody knows exactly. But \"photic sneeze reflex,\" which is what you're referring to, does not offer a significant evolutionary advantage or disadvantage to those who have it or don't, so there's no reason its prevalence would change significantly unless it was tied to another more important trait. It's like earlobes -- some are attached and some are free, and there doesn't appear to be a real reason why."
] |
[
"Do you have a citation for this? "
] |
[
"The 33% prevalence could be contested. Neurologist Louis Ptacek, one of the few scientists to study the phenomenon, says no one really knows the prevalence but he puts it at something like 10%.",
"http://www.diffusionradio.com/2010/08/photic_sneezing_and_a_naked_sc.html"
] |
[
"Question about cancer survival statistics relative to time of diagnosis"
] |
[
false
] |
Suppose that I am diagnosed with a brain tumor at a very early stage but that nonetheless it is incurable, and I forego treatment. Despite not being treated, my post-diagnosis lifespan will be lengthened due to the early detection; it will take longer than otherwise for the tumor to grow large and kill me. Is this sort of scenario taken into account in statements like "early detection of cancer X can increase survival time by Y"? In other words, when early detection increases survival time, is it necessarily due to the cancer being more treatable at an earlier stage? Does the "survival time" subtract off the time taken to reach a later stage cancer from the time of diagnosis, in order to remove the bias described above?
|
[
"Unsurprisingly, the answer to your question is complicated and depends on the statistics that have been gathered for a particular condition. Also, your answer is likely to be different depending on whether you are talking to a statistician or a physician. ",
"The quick answer is that early detection will make it appear as if treatments are more effective and that the disease claims fewer lives. So this effect is exaggerated in the no-treatment scenario you describe, but the data would be hard to come by. ",
"The problem you are describing feeds into a long standing debate on early detection, overestimation of disease and the benefits of therapy. ",
"Bottom line is, most cancer statistics are going to lump all diagnosed cases in the denominator and go from there. Most survival is going to be compared to the general population to estimate the effect of the cancer. There may or may not be treatment adjusted and stage adjusted statistics available. Good, well-controled and well-collected and well-reported clinical trial data can be great for this purpose. Practically, though (and most relevant for an individual patient), unless the rate of disease progression is monitored from date of detection, it is difficult to know whether a treatment is improving survival with early treatment vs. treatment after later detection. The rate of tumor growth from patient to patient is just too variable. ",
"The best statistics available do take into consideration your concern. Those are adjusted for length bias (failing to consider progression rate), lead time bias (time between detection and when clinical signs would appear) and a bunch of other technical issues on stage progression in addition to treatment effects."
] |
[
"This is an excellent question, and it makes the interpretation of cancer screening studies difficult. The problem is called lead-time bias. The best way to get information about whether a cancer screen is actually useful (prolongs life) is to do a randomized controlled trial, where you split people in to two groups and screen only 1 group. If you look at how long people survive after diagnosis, then the data will be affected by lead time bias, so that's not the ideal comparison. What you need to do is look at how long people survived from the date they entered the study. If the overall survival is the same, but the survival since cancer diagnosis is longer by a few months, then you know that you just found the cancer a few months earlier, and that was the only benefit. ",
"Basically we want people to live longer overall, not live longer with cancer."
] |
[
"Great answer, thanks!"
] |
[
"Why are there antibacterial medications but not antiviral medications (or are there)?"
] |
[
false
] |
I was sick this weekend and was on the phone with my doctor to get some medicine. He indicated that he would not be prescribing antibiotics because based on the symptoms it sounded like a viral infection, not bacterial and I would simply have to wait for it to subside. Are there antiviral medications for other sicknesses? If not, why?
|
[
"As the others have said there are fundamental differences between bacteria and viruses the main being that bacteria are self-sustaining organisms where as viruses are completely dependent on a host. ",
"Antibiotics target specific parts of the bacterial life-cycle that are unique to the bacteria and not used in any way by us so as to have no side affects. However, since a virus hijacks the cells own mechanisms to its own ends, anti-viral drugs come with side effects. Because of the side affects, antivirals are only ever used when absolutely needed. So if you have a cold or something that isn't threatening you're life, it's better just to wait to get over it than suffer the side effects of taking drugs.",
"There are lots of antiviral drugs, acyclovir, gancyclovir and ribavirin as some broad examples. Then there are many specific drugs, Tamiflu and Relenza for flu and a whole host of drugs that can be used in HAART treatment for HIV. ",
"The main reason for there not being drugs against a certain virus is that we may not know enough about that virus or we just can't find anything to target that gives enough of an effect against the infection without having too many side affects."
] |
[
"A bit ELI5:",
"Bacteria and virus (virii) are different problems. A bacteria is a functional cell, that has a metabolism, can duplicate on its own, eat and so on. A virus is just a piece of genetic material with a shell that let it infect one of your cells and use it to reproduce.",
"Having its own metabolism, it is easier to find a selective \"poison\" that disrupt only bacterial metabolism, because viral metabolism is atually YOUR metabolism. That's why antibiotics are useless against viral infections like common cold: you have just to wait that the little soldiers of your immune system recognize and kill viral particles and infected cells."
] |
[
"Just to tack on a (hopefully useful) bit.",
"Antiviral drugs do exist, and their goal is to help your body recognize viruses better while they're floating around, or to prevent them from binding to your cells and getting inside. One problem is that these antiviral methods work by targeting exterior proteins. These proteins mutate reallyreallyfast, and it is hard to make any drug that has a lasting effect."
] |
[
"Does travelling faster than the speed of light create observational time travel?"
] |
[
false
] | null |
[
"Physics says you can't reach the speed of light, let alone go faster. You are asking what the laws of physics say would happen if you break the laws of physics. There is no meaningful answer to such a question."
] |
[
"This is not a stupid question by any means, simply an unanswerable one with our current understanding.",
"The topic itself is fascinating, but all discussion on it is pure speculation and this subreddit does not allow such things."
] |
[
"This is not a stupid question by any means, simply an unanswerable one with our current understanding.",
"The topic itself is fascinating, but all discussion on it is pure speculation and this subreddit does not allow such things."
] |
[
"Large Scale Renewable Energy Projects?"
] |
[
false
] |
I'm doing a project about large scale energy projects such as the Arizona Solar Tower, Iceland's use of geothermal energy, France's tidal power plant, etc. The project focuses on how there's no one "end all" solution to renewable energy. My question is, what other kinds of large scale renewable energy projects are being implemented around the world?
|
[
"A significant amount of Brazil's transportation fuel is sugarcane ethanol."
] |
[
"Germany",
" has a wind farm in the ocean "
] |
[
"There's a slightly different type of solar thermal power project in Spain.\n",
"http://en.wikipedia.org/wiki/Andasol_Solar_Power_Station",
"Are you interested in the viability of these projects? "
] |
[
"Why did the Fukushima nuclear plant switch to using fresh water after the accident?"
] |
[
false
] |
I was reading about Operation Tomodachi and it mentioned that the US Navy provided 500,000 gallons of fresh water to cool the plant. That struck me as odd considering they could just use sea water. After doing some digging was all I could find. Apparently they using sea water but wanted to switch over to using fresh water. Any idea why?
|
[
"Salt is corrosive. As water boils in the core, the salt concentrates, and you get deposits that impinge heat transfer. With enough salt you can eventually have molten salt which is harder to manage. If you had any intact fuel, the salt and sediment from raw water will plug the fuel inlet debris strainers, preventing adequate cooling (this can be bypassed by raising water level above the steam separator skirt, but was not in the emergency operating procedures at the time). ",
"Fresh water is the best option."
] |
[
"Spent fuel rods need about 10 years of cooling. Not sure about these since they weren’t “spent”, but not forever.",
"They will need to be sequestered/contained for many lifetimes however."
] |
[
"Because generally they are still hot enough to heat water to hot, but not boil it to create pressurized steam that could power a turbine."
] |
[
"If we have two quantum entangled particles A and B, and we measure B's spin state does that collapse the superstate of particle A's spin?"
] |
[
false
] |
Suppose you had an infinite set of Quantumly Entangled particles, each set could be described as [A,B] and you decide an order, IE: 1[A.B], 2[A,B], 3[A,B]... etc etc. Now, we load all A particles into machine which can measure whether or not the particle’s spin is in a superstate or not (similar to the double slit experiment where if the particle is measured before it passes through the slit, it’s state’s collapsed and it doesn't generate an interference pattern). All B particles are then loaded into a machine which measures them one at a time, forcing particle B into one state and particle A into the opposite state. If we collapse the state of particle 1B's spin first, would that affect the measurement of whether particle 1A’s Spin state has collapsed into a single state? After all, we haven't measured particle 1A at any point, we have only measured particle 1B. If so, could we not then use this system for faster than light communication by virtue of simply measuring whether or not particle 1A's spin is in a superstate?
|
[
"I understand your confusion. You need a slightly longer version of what entanglement is. A particle can have several properties, such as position and spin. When we say two particles are entangled, we really mean that one property of a particle is entangled with the property of another particle. So the spin of two particles can be entangled, but that will have absolutely no influence on the ",
" of the particles. The double slit experiment would be completely unaffected.",
"You can play around with things and try to get more creative, but the end result will always be the same, you cannot communicate via entanglement, "
] |
[
"could we not then use this system for faster than light communication by virtue of simply measuring whether or not particle 1A's spin is in a superstate?",
"You can't measure whether a particle is in a superposition state or not. So, no. "
] |
[
"We both have two magic boxes that spit out 1 or 0, once a day, with 50% probability. Both our boxes appear to be random, but are actually linked: if we met up and compared notes we would find that both of our boxes always spit out opposite numbers. Despite this, there would be no aspect of observing an individual box that would tell us the other box is even ",
", forget knowing which value it spit out. Correlations can't be found just by watching one side."
] |
[
"Why is the air in the ozone layer so cold?"
] |
[
false
] |
[deleted]
|
[
"The ozone layer is found in the stratosphere, in fact it defines the stratosphere. Temperature increases with height in the stratosphere, because oxygen absorbs many kinds of UV light.",
"That's unusual, for the most part, the atmosphere is transparent to the light incoming from the sun. The ground absorbs this light and is warmed by it. The ground in turn radiates, much lower frequency light, infrared. The atmosphere is not transparent to infrared, it absorbs it and is warmed by it. In this way, the atmosphere is heated from below; and near surface temperatures are higher than those aloft in the troposphere.",
"Now, you ask, why is the surface warmer than the stratosphere if both regions are absorbing light from the sun? Because the energy of the light absorbed by the surface is much greater than the energy of the light absorbed in the ozone layer. Both because a much wider range of frequencies of light are absorbed by the surface, and because there is more incident light from the sun at those frequencies."
] |
[
"I dont think you fully answered my question, as i was thinking more in the proximity(+-10km) of the ozone layer, the temperature is way higher than the ozone layer itself."
] |
[
"First of all, the ozone layer is in the stratosphere. And as described above one can say that the stratosphere is defined by the ozone layer based on the temperature profile.",
"It is possible that you are confusing the ozone layer with the tropopause? This is the height that separates troposphere and stratosphere. It is colder than the air below since temperature decreases in the troposphere, adiabatic cooling is the reason for this. It is colder than the air above it because UV is absorbed in the stratosphere, as described above."
] |
[
"Does the flow of traffic have any noticeable effect on wind patterns?"
] |
[
false
] |
I have read that jellyfish' pulsating movement has an impact on ocean current. There are tons of animals moving about the planets surface but none with as much energy as automobiles traveling at quick speeds in such predictable routes. So can we plot this impact or are predominating cells to large to be affected by this?
|
[
"This is actually a really good research question. After a quick search I didn't come up with much on the topic. I would expect that if there is any effect it would be only on highways with both fairly heavy traffic and high flow speed. Other local conditions might dominate though, hard to say whether the traffic effect would be detectable or not."
] |
[
"Some napkin math tells me the effect would get lost in the mix; I'm pretty sure:",
"(number of jellyfish * mass of water pushed per jellyfish per day) / (mass of the ocean)",
"is greater than",
"(number of cars * mass of air pushed per car per day) / (mass of the atmosphere)",
"I'm assuming that since jellyfish are much more numerous than cars and push water as their only form of locomotion, AND since cars are kept from falling by the normal force and not their own pushing, AND since cars are off much more often than on, the car-wind effect wouldn't be as significant as the jellyfish-current effect."
] |
[
"Cars contribute to ",
"Urban Heat Islands",
", which in turn affect the local wind patterns. So I think the answer would be affirmative, but the effect is (probably) relatively small compared to the other causes of urban heat islands."
] |
[
"How can we see light from the beginning/early universe?"
] |
[
false
] |
If we can observe the light, that would either mean that we 'beat' the light to our current location, or that the light somehow goes around the universe in circles. What am I missing here? Also, what is the earliest light we can see relative to the start of the universe?
|
[
"because the universe is expanding faster than light",
"That's not really a true statement. Some parts are expanding away from us faster than light, and other parts aren't. The expansion rate can't be described in terms of a speed, though.",
"The theoretical limit for how much universe we can see is about 13.7 billion light years in every direction",
"Due to the expansion of the Universe, that distance is larger than 13.7 billion light years - it's actually something like 46-47 billion light years. The reason is the the distance light travelled a long time ago has expanded to be much larger. So take a photon's journey to Earth, take a million year leg of that journey 10 billion years ago, and the million light years it travelled then are now a bigger distance. Add all those up and you'll see the size of the observable Universe ",
" to be larger than 13.7 billion light years."
] |
[
"The early universe was a time, not a place. It happened everywhere. So the light we see today from the early universe - particularly the ",
"cosmic microwave background",
" - originated many billions of light years away. Because the Universe is far, far larger than we can see, we'll continue receiving light from the early universe from more and more distant places for a long, long time to come."
] |
[
"Absolutely. One of the most important things we've learned about the Universe is the ",
", that (on large scales) the Universe is uniform. There are no preferred or special places. So what would it mean to say the Big Bang happened here or there? It's more consistent with what we know to say that it happened ",
". Space itself is expanding, rather than the stuff within a fixed space."
] |
[
"How do moles, and other animals that dig tunnels, keep their tunnels ventilated?"
] |
[
false
] |
I know that's a problem with human miners, but does that have more to do with coal dust and whatnot, or is carbon dioxide buildup just as bad?
|
[
"Some of them don't, they adapt to it. Naked mole rats are somewhat adapted to a higher CO2 level than surface air. "
] |
[
"I can't answer the main question, but for human miners the problem is a compounded gas and particulate buildup. Gases of concern include CO2 and methane/ethane/natural gas of any kind, while particulates include any kind of aerosolized particles like coal or silica dust."
] |
[
"Moles in particular, but digging animals in general, are often located up very close to the surface, especially when compared to human miners. It's a lot easier for air to diffuse through a few inches of soil than through a few hundred feet of rock. There's also a lot less distance between opening and animal, usually"
] |
[
"What happens if a male takes birth control pills?"
] |
[
false
] |
If a male takes them daily like a female does, what chemical changes would he expect? How long would it take for the effects to be noticed?
|
[
"It depends on the amount taken. Some medications used in male-to-female hormone replacement therapy have the same active ingredients as birth control pills, but in different concentrations, so you would expect symptoms in the broad category of development of female secondary sex characteristics. One of the first symptoms to appear would be enlargement of breasts (gynecomastia); other symptoms would include decreased body hair, shrinking of testes, and erectile dysfunction. "
] |
[
"And don't forget changes in mood and behavior due to hormonal imbalance"
] |
[
"Would those symptoms persist even after stopping consumption of the pills? "
] |
[
"How do so many different languages have similar inflection patterns?"
] |
[
false
] |
For example, questions end in upward inflections and statements downward in so many varied languages. Why are such patterns so pervasive?
|
[
"You are talking about ",
", rather than inflection. Could you give examples of the \"so many different languages\" that you are thinking of? It will allow us to better get a sense of whether we are dealing with related or unrelated languages."
] |
[
"But even among Romance and Germanic languages, patterns are different. For example, French and Spanish usually use a falling final intonation for questions, unless a question word (e.g. ",
", ",
") is absent from the sentence. The fact that you are able to 'often guess correctly' means that you are not able infer intonation patterns automatically in Korean, which to my mind suggests that you are minimizing your failures and focusing on your successes, and trying to find out cross-linguistic information based on that (and the fact that all but one of the languages you cite are related and spoken in the same geographic region). Moreover, if you are able to detect certain patterns, that allows you to rule out those patterns in future guesses. In other words, once your girlfriend has verified what a simple declarative sounds like, you can differentiate that from other types of sentences for the future, which means you are better able to detect later intonation patterns by process of subconscious deduction."
] |
[
"My girlfriend is Korean and I can often correctly guess correctly (as verified by her) whether her speech with other Koreans is a question, a statement of fact, patronizing sarcasm etc. That's a language that seems different enough from the Romance and Germanic languages I am used to hearing, and yet has similar intonation for similar situations."
] |
[
"Why do scientists believe blood will boil if a human is exposed to the vacuum of space? Is this based on evidence?"
] |
[
false
] |
Aerospace/Electrical engineer here. I came across an article on BBC last night about Felix Baumgartner's attempt later this year to attempt a skydive at the highest altitude ever, 36.5km (120,000ft). The article states that his blood "will vaporize" if his suit loses pressure. I assume the reporter equates blood boiling to vaporizing. Is this based on sound science or just what scientists think will happen? This is obviously difficult data to obtain. The reason I ask is that there were a lot of skeptics in the science community in the 1960s that claimed humans wouldn't be able to survive microgravity but that was proven wrong.
|
[
"Blood will boil but it will take a very long time. We have empirical data from accidents in vacuum environments. ",
"Soyuz 11",
" returned to Earth but in the process was depressurized resulting in the death of the cosmonauts on board. The bodies did not show substantial physical damage such as blood boiling off. However, over time, in a vacuum that sort of thing will occur, but one will be dead for quite some time before serious loss of liquid occurs. "
] |
[
"Phil Plait PhD, aka the Bad Astronomer, recently posted a video about this. In summation, no the blood will not boil because we are a relatively closed system, so blood in our veins isn't immediately exposed to the vacuum of space.",
"http://blogs.discovermagazine.com/badastronomy/2012/01/31/qba-what-happens-if-you-are-exposed-to-the-vacuum-of-space/"
] |
[
"The problem is with dissolved gasses in the bloodstream. It is similar to what is faced by scuba divers surfacing too quickly - a rapid downward change in pressure causes dissolved gasses in the blood to form bubbles, which can kill. If you have access to a vacuum chamber, put a glass of water into it and turn it on. As the pressure drops the water wil start to boil."
] |
[
"Help for a budding young scientist?"
] |
[
false
] | null |
[
"If you want organic chemistry, then Organic Chemistry by Clayden, Greeves, Warren and Wothers is really good, if a little expensive :/\nSource: I have a copy..."
] |
[
"r/science",
" might have been better, but I will try answering nevertheless.",
"Disclaimer: I'm not American, so some of this may not apply there.",
"First, be absolutely sure that it is really what you want. Careers in science are pretty difficult to get, the competition is fierce, hours are long and the pay sucks for most of your career. Google \"don't become a scientist\" and read what you find with all your heart. Additionally, you may want to read [PHD Comics](",
"www.phdcomics.com",
") and listen to ",
"this illustrating song",
".",
"Do ",
" listen to undergraduates. They don't know anything about real science, but are usually very enthusiastic. If you are interested in the reality, listen to what Ph.D. students and postdocs say, perhaps also young professors. Senior professors became scientists when there were a lot of jobs in academia, so their experiences do not reflect the current reality.",
"Second, I'm going to quote some redditor's professor: \"specialize first, generalize later\", or something like that. There are very few scientists in the world who have done significant contributions in several fields. You don't need to (and shouldn't) decide the exact sub-field or thesis title right now, but you should be ready to dive into one, and only one, subject. It is useful to learn ",
" other subjects, but on the level that does not require much technical knowledge. The reason for that is that real science is frigging hard, and by spreading your interest in the early phase you find that you don't know any subject well enough to be able to publish anything.",
"Third, which is somewhat counter-intuitive to the previous point, learn math. You don't need to become a mathematician, but you should be comfortable with all levels of math that can be encountered in your field. I think it would be a safe assumption to learn as much as hard undegraduate math as you can in college. I don't know how much math is needed in purely lab-work, though, but if you are planning to ever use the word \"theory\" in your writings, you will find math very helpful.",
"Third point five, learn to program. Again, you don't need to become a C++ master, but being able to write data processing and numerical modelling scripts is ridiculously helpful in almost any area of life.",
"Fourth, do not go easy on yourself. Don't trust grades. If the course is easy, you can get perfect score without ",
" understanding the subject. In real science, being able to mechanically calculate something or being able to remember trivia is worth nothing. You need to be able to understand things very deeply and be able to make logical connections between things. Most of all, you need to be able to think with your own brain, since there is nothing else you can rely on if you become a scientist.",
"I don't have an opinion about learning subject matter beforehand. I don't know how that works. Most of the science stuff you will learn in the university is not wikipedia-level fun-to-read stuff but very technical and very detailed. If you really want to do this (and I'm not saying it's a bad idea), you should get some books that your future college uses in its intro courses."
] |
[
"Thank you for the well-articulated reply:",
"One: It's moreso a hobby-plus-one than a career, but I will look into it regardless. I'm actually enrolled for Renewable Energy!",
"Two: An excellent point that I definitely need to take into consideration. I suppose i'm trying to be too much of a 'Renaissance Man'. Chemistry has always resonated with me the best, so I'd say that that is definitely what I'm aiming for.",
"Three, Three-point-Five: Math is pretty solid for me, I was in AP Calc my senior year and was proficient in it. Any recommendations on languages to learn? I started teaching myself Python a few months back, but it never progressed very far.",
"Four: That was exactly what I disliked about my vocational education (Electronics). 90% theory (shoddy theory, at best), and 10% practical work. "
] |
[
"How does blackbody radiation work?"
] |
[
false
] |
I'm clearly stuck with some misconceptions about how blackbody radiation works, but am having trouble figuring out where my thinking is wrong. (This is not a question about uv catastrophe.) I'll try to trace my line of thinking below and would appreciate anybody pointing out my misunderstandings. When a blackbody absorbs electromagnetic radiation how that energy gets absorbed depends entirely on the radiation's frequency. Some frequencies cause molecular vibrations, rotations, bending...other specific frequencies cause election excitation. When the object reaches thermal equilibrium (determined by the absorption of frequencies causing various vibrations), it begins to emit energy to maintain an equilibrium. It emits energy both through heat and light. The light is due to only the relaxation of elections to lower energy states. This means the emitted light is only "returning" the radiation in various frequencies that went into electron excitation - not the radiation that caused vibrations. If (and that's a big if) the above is an appropriate way of describing it, it seems as though backbodies should not emit continuous spectra, but line spectra instead. I want to justify this by saying there are so many interactions in a solid that weird stuff happens with the orbitals and energy levels so there's nearly an infinite number of possible states for excited electrons. This would imply zooming enough, the continuous spectrum would actually look like a line spectrum (I know, blackbodies are an idealized situation anyway). An overarching concept: Is ALL light attributed the excitation/relaxation of electrons? Hopefully that articulated something about what I'm trying to understand... Thanks y'all.
|
[
"When a blackbody absorbs electromagnetic radiation how that energy gets absorbed depends entirely on the radiation's frequency. Some frequencies cause molecular vibrations, rotations, bending...other specific frequencies cause election excitation.",
"Yes, although the microscopic details of what kinds of excitations are happening is not relevant to the derivation of the black body spectrum. All that matters is that each mode of the electromagnetic field is absorbed and emitted in quanta (photons).",
"When the object reaches thermal equilibrium (determined by the absorption of frequencies causing various vibrations), it begins to emit energy to maintain an equilibrium. It emits energy both through heat and light. The light is due to only the relaxation of elections to lower energy states. This means the emitted light is only \"returning\" the radiation in various frequencies that went into electron excitation - not the radiation that caused vibrations.",
"Thermal equilibrium is independent of any microscopic property of the black body. That's one of the really nice results of thermodynamics: thermal equilibrium just means that the object has the same temperature as its surroundings. Nothing else matters. ",
"Furthermore, the black body doesn't just start emitting radiation at equilibrium, it's ",
" emitting and absorbing radiation. Once equilibrium is reached, the amount of energy being lost by emission is equal to the amount being absorbed.",
"Heat and light are the same thing for these purposes, as derivations of black body laws neglect the fact that the body may be able to have heat conducted or convected to and from it. So the only heat transfer mechanism relevant here is radiation.",
"And the black body can emit any frequency that it absorbs, so the point about the outgoing frequencies being different than the incoming is not really true.",
"If (and that's a big if) the above is an appropriate way of describing it, it seems as though backbodies should not emit continuous spectra, but line spectra instead. I want to justify this by saying there are so many interactions in a solid that weird stuff happens with the orbitals and energy levels so there's nearly an infinite number of possible states for excited electrons. This would imply zooming enough, the continuous spectrum would actually look like a line spectrum (I know, blackbodies are an idealized situation anyway).",
"Transitions between discrete states gives a set of discrete lines in the absorption and emission spectrum, but as you mentioned, solids don't really have discrete levels anymore, but rather continuous bands of allowable energies. And electrons can transition to and from continuum states, which don't have discrete energies. For example, take an electron capturing onto a proton and forming a hydrogen atom. If we set the zero for potential energy such that an electron at infinite distance from the proton with zero kinetic energy has zero total mechanical energy, and we say that the electron captures into a bound state of energy -E', and send in an electron from infinity with kinetic energy E, the electron will make a transition from a continuum state with energy E to a bound state with energy -E'. This transition will occur through the emission of a photon with energy E + E' (assuming the transition is direct into the bound state without any kind of cascade). E' is a discrete energy determined by the structure of the Coulomb potential, but E is a continuous energy. It's the kinetic energy of the free particle that we sent in from infinity; it can take on any non-negative value. So therefore the photon energy E + E' is also a continuous value. And we can go a step further and discuss free-free transitions, where the electron emits a bremsstrahlung photon and remains in an unbound state afterwards, where both the initial and final energies of the electron are continuous.",
"So this illustrates that there are processes in which the energy absorbed or emitted are not discrete. It's these kinds of processes which make the spectrum of thermal radiation continuous rather than discrete.",
"An overarching concept: Is ALL light attributed the excitation/relaxation of electrons?",
"There are other ways to generate photons, for example nuclear transitions which emit gamma rays. In our everyday lives, it's often the behavior of electrons which is responsible for the light that we encounter. But as described above, that doesn't mean that light spectra always have to be discrete."
] |
[
"Thank you! This helps immensely - I really appreciate your answer."
] |
[
"Last thing -- when you have a lot of atoms close together, you don't have neat electron energy levels anymore, they separate out into a band."
] |
[
"Why doesn't air settle into its component gases?"
] |
[
false
] |
As air is composed of several different gases each with a different density, why doesn't air settle into layers of different gas? I understand winds mix them, but I would've thought over a long time they would settle out somewhat
|
[
"Yes wind and other meteorological effects mix the gases as you and other commenters have stated. But I don't think that truly answers the question, and an answer can be arrived at without even considering meteorological effects.",
"",
"When thinking about this are you picturing a layer of oil sitting on top of a denser layer of water? Well gases behave quite differently to liquids.",
"The molecules in liquids interact regularly and comparatively strongly with one another and so two very dissimilar liquids can separate (i.e. have an interface on the order of nanometres or less). More specifically you can think of this as: the energetic gain from letting the liquid molecules interact with themselves is enough to overcome the entropic gain of mixing the liquids (see Gibbs free energy etc.). Then gravity can place the separated phases one on top of the other.",
"Gas molecules though, for all intents and purposes, don't interact with one another. And so there's essentially only the entropic gain from mixing which is driving the mixing of different gases. This means that we don't observe phase separation like we do for liquids.",
"",
"",
"Ignoring meteorological effects and temperature changes, all gases exponentially decay in pressure (density/ concentration) with altitude. This is expressed with the ",
"barometric law",
". And, as stated above, we can essentially treat each gas independently. This allows us to define a ",
"scale height",
" for different molecules depending on their mass, which defines the altitude at which the gas's pressure has dropped by a factor of e.",
"The scale heights for N2, O2 and CO2, on Earth are 7.4 km, 6.5 km and 4.7 km respectively. So over 100s of meters we wouldn't expect to notice much difference in gas concentration due to altitude. In fact, using these scale heights, over 100 meters we'd expect to see a 0.3% enrichment of N2 (the lightest gas) which is certainly not phase separation."
] |
[
"Have you ever seen a boiling pot with rice, or small noodles or so, in it? The rice doesn't settle on the bottom because steam bubbles keep rising up and keep the rice and the water in motion.",
"It's similar in the atmosphere. The sun warms the ground. The ground heats up the air near the ground. Also moisture evaporates. The hot air, being less dense, rises up. That stirs the air and keeps it mixed. Like the boiling rice.",
"There's a maximum height to which the hot air from the ground will rise. As the hot air rises, it cools down and eventually is no longer hotter than the surrounding air. The heat energy is converted into potential energy. That is energy that something has by virtue of being high up. If it falls down that potential energy is converted into speed.",
"This maximum height is called the tropopause. It's not a fixed height. It depends on a number of things but you can google that if you are interested.",
"Below the tropopause is the troposphere. That's where we live. That's where all the weather happens. Above it is the stratosphere; so called, because it is stratified or layered. It does not get stirred and has pretty much settled."
] |
[
"Something went wrong with your scale height values. Nitrogen should be very close to oxygen, while CO2 will be at ~2/3 of their value."
] |
[
"Why does salt \"bring out flavor\" in food, even sweet foods like cookies?"
] |
[
false
] | null |
[
"Check ",
"this",
" out if you got the time. From the coolest cooking show ever, they get all into the history and science every episode."
] |
[
"You have different taste buds (sweet, sour, bitter, salty, umami) that have receptors for their respective tastants. The more of these taste buds that are stimulated in the passage of food, the greater the intensity of perceived favor. So by adding salt to a dessert, the cook, whether knowingly or not, is increasing the intensity of his or her food by activating more taste buds. The same is done with onions where a cook will sautée some of the onions and caramelize others to activate as many receptors as possible. ",
"Edit: should have read: each taste bud is composed of receptors for the 5 tastants. "
] |
[
"Here's all the segments of that episode. He gets into the flavor properties in the second segment.",
"S7E0P1",
"S7E0P2",
"S7E0P3",
"S7E0P4"
] |
[
"Does the absolute value of d(telomere length)/dt decrease with time as someone gets older?"
] |
[
false
] | null |
[
"The data is probably too noisy to measure that.",
"Here's",
" a graph of telomere length vs age for 299 healthy subjects. Original is ",
"here",
".",
"It looks to me that d(telomere length)/dt is constant with time, but this is measured in a population and not in a single individual."
] |
[
"Theoretically, unless the cells become cancerous, telomere length decreases at a fairly constant rate. Hoewer, there are telomerases that reverse this process, the older we become the less active these telomerases become. ",
"So, I would say yes."
] |
[
"Oh, well, I would expect that less telomerase would increase the absolute value of d(telomere length)/dt - since it would speed up the process of decay",
"The thing is - though - don't cells divide more slowly as their telomeres shorten? Telomere length is shortened when cells divide, but when cells take longer to divide (as a result of aging), then maybe this effect eventually outpaces the effect of reduced telomerase?"
] |
[
"How did Lance Armstrong pass hundreds of doping tests over a period of almost a decade?"
] |
[
false
] | null |
[
"Lot of informations about this can be found in the USADA report, but lets look first at the idea that he \"passed hundred of doping tests\".",
"Firstly he directly tested positive to cortisone in the TDF in 1999, but he got away with it with a backdated prescription. See USADA report page 32 ",
"http://cyclinginvestigation.usada.org/",
"Secondly, some of his urine samples from the 1999 Tour were later (2005) tested positives for EPO (the retesting was conducted as part of a research project into EPO testing methods). See ",
"http://en.wikipedia.org/wiki/Lance_Armstrong#1999_Tour_de_France_urine_tests",
"Thirdly, in his affidavit to USADA Floyd Landis says that Armstrong tested positive in the 2001 Tour de Suisse but that Armstrong and his team manager managed to bribe the president of the UCI to get it away. See point 17 of ",
"http://d3epuodzu3wuis.cloudfront.net/FL+Landis%2c+Floyd+Affidavit.pdf",
"Finally about the way to avoid detection: Armstrong was helped by some doctor specialized in doping, they knew how the test worked and how to circumvent them. Those test were far from perfect. Among other things:",
"-They scheduled their whole doping program to be able to avoid detection (knowing the detection time of each product).",
"-EPO was not detectable in 1999.",
"-They started to inject EPO intravenously to lower the detection time.",
"-They measured their bloods level and used saline to lower them and avoid being positive (there is one instance it happened while Lance was allegedly taking a shower and the doctor in charge of drug testing was waiting outside).",
"-They knew in advance about some of the test.",
"-They used at lot of blood doping (extracting their own blood and re-injecting it months later during tour de france) which is not yet easily detectable.",
"Read the report and the affidavits, everything is in it.\n",
"http://cyclinginvestigation.usada.org/",
"Here is the table of content:",
"E. How Lance Armstrong and the USPS Team Avoided Positive Drug Tests p129",
"Avoiding testers during window of detection p131",
"Using undetectable substances and methods p135",
"Understanding limitations to the testing methods p137",
"Use of saline infusions and micro-doping of EPO p139",
"the report ",
"http://d3epuodzu3wuis.cloudfront.net/ReasonedDecision.pdf"
] |
[
"Here is a very detailed Question and Answer with a Blood Passport panelist. If you read the entire thing you will understand how one can get away with it.",
"http://nyvelocity.com/content/interviews/2012/behind-scenes-contador-cas-hearing-michael-ashenden",
"Highly simplified you take a performance enhancing drug. You then take other drugs to mask that performance enhancing drug. Then you take another drug to hide the effects of the drug that you took to hide the first drug. You have your own test equipment so you can test yourself and your team members and make sure your \"levels\" are in balance. "
] |
[
"They do, and they did. Lance's old samples tested positive. ",
"http://usatoday30.usatoday.com/sports/cycling/2005-08-24-armstrong-samples-details_x.htm"
] |
[
"Family dispute over simple probability problem: please help solve! (X-post from r/learnmath)"
] |
[
false
] |
We were talking about this over dinner and I was told by my older brother that I am thinking "far too simplisticly" and that "math is much more complicated than I imagine." This is the problem: A garden tool is a certain years old. The only info you have is that it is at least 10 years old. I claimed that, with that info, there is more chance that the garden tool is older than 12 years than there is chance that it is younger than 12 years. My reasoning was that we know the object's age, as it has to be at least 10 years old, could be 10 or any number starting from that, ad infinitum. Therefore it would be much more likely to be any age above 12 than happen to be either 10 or 11. My brother, on the other hand, claimed that was too simplistic thinking, because "probability is not attached to reality" and that someone knowing maths would see that the chance that the garden tool, which is at least 10 years old, is either younger or older than 12 years is actually 50%-50%.
|
[
"Your brother's reasoning is, of course, wrong, as he would also be led to conclude that there is a 50% chance that it is at least 13 years old, a 50% chance that it is at least 14 years old, and a 50% chance that it is at least 100000 years old.",
"The actual probability of it being at least 12 years old depends on far more information than is given in the problem. If you assume that garden tools have been made and distributed at the same rate since the beginning of the universe, then of course the probability that it is older than 12 years is very high, but that's probably not a realistic assumption."
] |
[
"Your brother is using the ",
"Principle of Indifference",
". In this case it's used wrongly and comes up with a contradiction. In particular:",
"Applying the principle of indifference incorrectly can easily lead to nonsensical results, especially in the case of multivariate, continuous variables [e.g. the age of a tool]. A typical case of misuse is the following example."
] |
[
"Squidfood and nicksauce have good answers here, but I'd like to point out a difficulty in talking about probability here.",
"What do we mean by \"probability\" in a situation like this? The tool has an exact age, so in a sense the probability of it being that age is 100%, and of all other ages 0%. However, because you have limited information, you don't know which age that is.",
"So I think the question you're probably asking is \"If I was repeatedly presented with garden tools of unknown age greater than 10 years, what portion of those tools are older than 12 years, and what portion younger?\"",
"In order to come up with an answer a question like that, you MUST have some kind of prior knowledge about the population of tools from which the one you are shown is chosen. Is it randomly taken from all garden tools made in the history of the universe? Is it randomly taken from all garden tools within your neighborhood? The population from which it is taken will give you your answer."
] |
[
"Could someone tell if Venus rotated the 'wrong' way around without going into space?"
] |
[
false
] |
Could someone tell a planet's rotational direction without actually sending something to look at it?
|
[
"Yes",
". We knew about Venus' retrograde rotation in the 1950s, and we had good estimates of its rotation speed in the 60s."
] |
[
"I believe astronomers can use the ",
"doppler effect",
" to gauge the rotational velocity of a body. Light reflected from the side of the planet \"approaching\" us will be blue shifted, and red shifted on the side receding."
] |
[
"Radar, rather than visible light was used to determine this, but yes. Doppler shift and the echo time delay.",
"http://adsabs.harvard.edu/full/1967AJ.....72..351D"
] |
[
"Is it possible for a deck of cards to be shuffled accidentally into perfect order?"
] |
[
false
] |
Can one even calculate the probability of this event?
|
[
"The number of possible shuffles of a standard deck of cards (52 cards) is 52 * 51 * 50 * ... * 1, or otherwise written as 52!. This number is approximately 8 * 10",
" (an 8 followed by 67 0's).",
"To get an idea of how unimaginably large that number is, lets assume that we can create a billion different deck-orderings every second. That's 3.6 trillion per hour or 86.4 trillion per day. At this rate, it would take about 10",
" days to exhaust all possible orderings. Or about 3 * 10",
" years. For reference, our universe is about 1.5 * 10",
" years old.",
"The chance of shuffling a deck of cards into one specific order is so incredibly small, that it is effectively impossible. You stand a better chance at trying to win the jackpot in the lottery multiple times in a row.",
"edit: To anyone with the urge to reply \"So you’re telling me there’s a chance?\": This joke has already been made (repeatedly). Find some new material :)"
] |
[
"Here's how it was explained to me once, to get an appreciation for it:",
"Imagine you shuffle a deck of cards once per second, every second. You shuffle 86400 times per day.",
"You start on the equator, facing due east. Every 24 hours (86400 shuffles), you take one step (one metre) forward. You keep shuffling, second after second, each day moving one more metre. After about 110 thousand years, you will have walked in a complete circle around the Earth (I know: you can't walk on water. Just ignore that part).",
"When you have completed one walk around the Earth, take one cup (250mL) of water out of the Pacific Ocean. Then, start all over again, shuffling, once per second, every second, taking a step every 24 hours. When you get around the Earth a second time (another 110000 years), take another cup of water out of the Pacific Ocean.",
"Eventually (after approximately 313 quadrillion years, or so, about 22 billion times longer than the age of the universe), the Pacific Ocean will be dry. At that point, fill up the Pacific Ocean with water all over again, and place down one sheet of paper. Then, begin the process all over again, second by second, every 24 hours walking another metre, every lap around the Earth another cup of water, every time the Pacific Ocean runs dry, refilling it and then laying down another sheet of paper.",
"Eventually, your stack of sheets of papers will be tall enough to reach the Moon. I think it goes without saying that, at this point, the numbers become very difficult to comprehend, but it would take a very very very very very long time to do this enough to get a stack of paper high enough to reach the Moon. Once you get a stack of papers high enough to reach the moon, throw it all away and begin the whole process again, shuffle by shuffle, metre by metre, cup of water by cup of water, sheet of paper by sheet of paper.",
"Once you have successfully reached the Moon one billion times, congratulations! You are now 0.00000000000001% of the way to shuffling 8 * 10",
" times!"
] |
[
"That's the best way I've seen it be put. That's mind boggling how big that number is"
] |
[
"Do the nodes and the anti-nodes in a stationary wave have equal energy or is energy non uniformly distributed?"
] |
[
false
] | null |
[
"The nodes of a standing wave are the points that never move. They have zero energy density. The anti-nodes are the points that move the most. They have the most energy. It really depends on what kind of wave you are talking about (wave on a string, electromagnetic wave, sound wave, etc.). Typically, the energy density of a wave is proportional to the square of the amplitude of the wave. So if you have a perfect sine shaped standing wave with the form A sin(k x) sin(ω t), the average energy density will be proportional to sin",
" (k x)."
] |
[
"Is there really no energy associated with the derivative of the field?"
] |
[
"Thank you very much for answering."
] |
[
"Neutron Stars or Black Hole?"
] |
[
false
] |
I know the basics of supernovas, black holes and neutron stars. The thing i don't understand though is why a supernova leads to a black hole or neutron star? Is there a reason a supernova creates a black hole or a neutron star, or is it just a coincidence, or do we simply don't know?
|
[
"As far as I can tell, three solar masses is the mass of the largest neutron stars and the smallest black holes. The stars that gave birth to these compact objects, however, would have been much more massive, as most of the mass would have been blown off during the supernova."
] |
[
"According to ",
"wiki",
", the limit is much higher than that: about 25 solar masses, depending on metallicity. Below 8 solar masses, a star would not go supernova, jst shed its outer layers leaving a white dwarf remnant."
] |
[
"They both form when stars collapse due to its own gravity. But what determines that when a star collapses, would it become a black hole or a neutron star? The answer is mass. A star which has a mass of about three times of our sun will compact into a neutron star. And a star with mass greater than three solar masses will compact into a black hole. Hope this helps and sorry for bad English, not my native language."
] |
[
"Is it possible for a person to have both gigantism and dwarfism?"
] |
[
false
] | null |
[
"Yes. One dude. Ever."
] |
[
"Picture in giant state",
"."
] |
[
"Needs pics :("
] |
[
"Question about gravity and entropy"
] |
[
false
] |
Can gravitational forces stop entropy from increasing? i.e. billions of years from now, after the sun becomes a white dwarf and then a black dwarf and is no longer emitting radiation, how would its entropy still increase? Wouldn't gravity hold all of the molecules together?
|
[
"The relationship between gravity and entropy is somewhat complicated. I don't understand it well, but Brian Greene lays it out very well in \"The Fabric of the Cosmos\""
] |
[
"Entropy is a measure of energy unavailable to do work. So as long as the sun is hotter than its surroundings, heat will leave the sun, increasing its entropy."
] |
[
"The emitted radiation also factors into entropy. After it's emitted, it'll tend to be scattered, thus increasing entropy overall."
] |
[
"What is the most accurate graphical (visual) representation of a black hole you have come across?"
] |
[
false
] |
I've seen many 2-d interpretations that are misleading as well as those that show a simple black marble poking out of a soup of gas. I envision instead that a distant observer would see a highly luminous accretion "disk" which is not necessarily disk shaped, but is actually enveloping the black hole sphere along with an event horizon membrane which holds all matter that has ever penetrated the horizon in various stages of flattening into the horizon's surface (at the Schwarzschild radius) with a more or less uniform pattern of bright hot gas (time distortion causes all matter entering the hole to take forever to actually enter the hole from an outside observer's viewpoint). In other words, a piano going in may appear stretched and after a very long time only a tiny portion may be seen as actually thermalized while the rest is seen apparently frozen in time at the very edge. However it may very well be impossible to visually penetrate the accretion volume to see what lies beyond it from any viewing angle of a black hole? Anyhow what are your most scientifically accurate graphics of what a lucky astronomer who lives close to a black hole might see from his telescope ?
|
[
"This. It's more than special effects, it's the most current and accurate visualization of what nearing a black hole might be like that we've ever created. Of course the ",
" probably isn't a giant bookshelf though... "
] |
[
"The black hole in the movie Interstellar was unique in that they hired a bunch of general relativity experts, including Kip Thorne, to compute what it would look like."
] |
[
"It's a shame that they decided not to show gravitational redshift and blueshift"
] |
[
"What does the body do with all that extra keratin protein when someone goes bald?"
] |
[
false
] | null |
[
"Well when someone goes bald, usually the hair follicles end up shrinking and don't make any hair. Without any hair being made, the keratin protein is not synthesized in the first place, instead, the amino acids that would've made up the keratin protein are used for making other proteins around the body."
] |
[
"So does that mean someone whose bald will have faster growing nails/hair in other places?"
] |
[
"No. Your body needs what it needs. If you are actively trying to build muscle, then you will require a lot of protein to build both muscle and hair. If you become bald, you just don't need as much protein as before, a tiny amount less for hair, but you still need the same amount for muscles.",
"That is if you become naturally bald. If you shave your head, your follicles are still there, and will still try to grow hair, so it accomplishes nothing to help you build muscle."
] |
[
"Why does my shower curtain blow inwards while water is running?"
] |
[
false
] |
All I want to do is have a shower without the curtain constantly sticking to various body parts.
|
[
"See the aptly named ",
"shower curtain effect",
". There are a number of contributing factors and it likely is a combination of those at work."
] |
[
"This isn't completely true, while the \"chimney effect\" does play a role, you can observe the curtain getting sucked inward with cold water as well.",
"The most famous explanation is the so called Bernoulli-Principle. The Bernoulli-Principle states that a change in velocity corresponds with a change in pressure. ",
"The water that is escaping from the showerhead accelerates the nearby air downwards. This is the change in velocity that I mentioned earlier, we suddenly have a downwards flow of air in our shower. According to Bernoulli, this means that the air pressure in the Shower is smaller than outside. Of course the shower cabin isn't isolated, so the pressure differentials are miniscule, but they're there, and they're big enough to suck the shower curtain inwards."
] |
[
"This explanation makes a lot of sense, but I am almost sure that I have observed the same effect with cold water.",
"I would add to the explanation the effect of (maybe) speeding the air close to the water stream, what would reduce its pressure by an effect similar to the Venturi effect, creating a pressure gradient.",
"But that's pure guess."
] |
[
"What would happen if you detonated a nuclear bomb in the Mariana Trench?"
] |
[
false
] | null |
[
"The pressure of nearly seven miles of ocean on top of it?"
] |
[
"Much wittier than what I was going to say, but in the same regards.",
"Basically a Nuclear bomb would go off and some life would be disrupted. Perhaps depending on how close it was to the sea floor, a crater would also form."
] |
[
"Much wittier than what I was going to say, but in the same regards.",
"Basically a Nuclear bomb would go off and some life would be disrupted. Perhaps depending on how close it was to the sea floor, a crater would also form."
] |
[
"When putting plastic over windows to prevent heat loss in the winter, is there an optimal distance between the plastic and the window?"
] |
[
false
] |
When searching online, it seems that people say <.25" is optimal. However, with the way my (old) windows are constructed, that isn't possible. Am I doing more harm than good by putting up plastic with a distance of 2-4"?
|
[
"As close as possible without touching is optimal, in order to disrupt the internal convection currents (the closer the surfaces are, the slower the air must move). But honestly, my gut feeling of the boundary layer thickness is that .25\" is no different from 2-4\" - that is, both spacings are much larger than 2x BL thickness so there isn't really much interference with the natural convection inside the cell.",
"Entirely apart from that, though, I would be very surprised if you did harm by putting up plastic at ",
" distance. Segmenting that space from the rest of the room is going to help significantly in preventing the cooler air near the window from mixing with the bulk."
] |
[
"Awesome, thank you so much for your answer! My instinct was also that any plastic at all will help, since the older windows are very drafty. I would love to have an infrared camera or something and test the different distances, but that might be for someone with more time and money."
] |
[
"You certainly won't be doing any harm. You could try two different depths and tape a thermometer on the inside glass. Make measurements before sunrise. "
] |
[
"Why are female and male handwriting styles different?"
] |
[
false
] |
It's anecdotal, but from what I've seen, it appears that female handwriting is rounder and smoother than the more blocky and linear male handwriting. Is there any substantial truth to this apparent trend, and, if so, why?
|
[
"Your answer needs sources for the claim of increased fine dexterity in women versus men.",
"The reference to evolution is a nice story. However, like a lot of claims in evolutionary psychology, it is ultimately untestable and not science. You could also construct an argument that men needed to shape their tools to be able to hunt, and this required fine motor skills."
] |
[
"Your answer needs sources for the claim of increased fine dexterity in women versus men.",
"The reference to evolution is a nice story. However, like a lot of claims in evolutionary psychology, it is ultimately untestable and not science. You could also construct an argument that men needed to shape their tools to be able to hunt, and this required fine motor skills."
] |
[
"There are likely to be cultural and social factors. You'll have a hard time writing any Arabic without a lot of circular strokes. You can get away with writing Katakana without many at all.",
"The best way to look at this would be some kind of cross-cultural analysis. If women's handwriting is more likely to contain large, pronounced strokes, then this should be visible in Latin, Cyrillic, Hangul, Katakana, Arabic, whatever.",
"while male handwriting I've seen is more like, \"if I can read it, I'm good\".",
"Have a look at any book prior to the printing press. Monks, who were male, used to write books, and they certainly did not adhere to a good enough attitude."
] |
[
"How fast does antibiotic resistance spread? Will strategies such as reducing the days of antibiotic therapy reduce resistance spread?"
] |
[
false
] |
Some trials propose that antibiotic exposure can be reduced up to 3 days without jeopardizing the life of the patient. Their justification is to reduce antibiotic resistance. However, my question is, how fast does antibiotic resistance develop and spread? Do those 3 days of less antibiotics will actually make a difference?
|
[
"I'm not sure where you got this information so I can't speak for the trials that you read. However, from my study of biology it could actually do the opposite. It's fairly simple from an evolutionary stand point in that antibiotics will kill off weaker and less resistant bacteria first and then after the full course will have killed off all of the bacteria. Now if you were to stop the course early you will be left with the strongest bacteria left that are most resistant and thereby leading to more resistance.",
"This isn't to say that you aren't right but just adding in the fact that those 3 days could be the difference between killing all the bacteria and all but the strongest"
] |
[
"It's a misunderstanding that simply taking an antibiotic \"for the full course\" and not stopping early will always work to reduce antibiotic resistance. \"The full course\", by the way is always a number we kind of make up or guess. Many medical experts advocate stopping antibiotics early for certain infections.",
"Based on that idea, we might wonder why gonorrhea, one of the most rapidly adapting bacteria on the planet, is treated with a ",
"single dose",
" of antibiotic; just a single tablet on a single day. The answer is, unsatisfyingly, there are so many other factors at play. As an example, Azithromycin resistance will pretty much ",
" because it stays in the body forever at sub-therapeutic levels (long elimination half-life). That won't change whether you take Azithromycin for 5 days or 14 days. As another example, ",
"here's",
" an epidemiological study showing that beta-lactam treatment duration for longer than 5 days being associated with higher resistance rates than only 5 days. Leaving an antibiotic in the body for a long period of time increases exposure to it, which allows resistant bacteria to multiply in a non-competitive environment. As you can see, it gets complicated very fast.",
"The most we can really say right now about not taking a full course is that if a pathogenic bacteria is not completely eradicated, it increases the risk of recurrent infection. We need to do a lot more research and continue to refine our therapies as well as our diagnostic measures to understand the shortest effective duration to minimize their use."
] |
[
"We're still trying to figure this out. It's a very complex problem because it has to do more with the bacteria than the antibiotic. And bacterial species are ",
" different. As per basic microbiology, we would expect that bacterial species that replicate more frequently and faster would develop resistance more readily, because the next generation can pass on any resistance genes. But yet we're still trying to figure out ",
"how M. Tuberculosis",
", a bacteria that likes to lay dormant and not replicate at all, is developing so much resistance so quickly. To add to that complexity, different bacteria are found with different prevalence all around the world - so you have to take that into account.",
"Unfortunately, there's no good answer to this question. However, you are correct in that we do want to minimize exposure to antibiotics to reduce resistance. We do know that over a large population and over a long period of time, every single ",
" of antibiotic exposure increases the individual's chance of harboring resistant bacteria. But we don't really know what effect this has on the long term of causing severe and dangerous antibiotic-resistant infections."
] |
[
"10 years ago, athletes making full recoveries from major ligament tears was virtually unheard of. Today, it's par for the course (at least for the pros). What changed?"
] |
[
false
] | null |
[
"Advances in microsurgery techniques, in MRI imaging which can lead to more accurate diagnoses and treatment plans, and in physical therapy approaches."
] |
[
"While I agree with the rehab and surgical procedures part, I have seen a few times where MRI shows no tear of the acl, but the dr wanted to scope just to make sure, and would find grade three ruptures of the ligament. MRI is useful, but it still should just be one of many tools used by an ortho."
] |
[
"The health costs are generally related to the price inelasticity of medical care, and don't actually reflect the true costs of providing an MRI scan. For reference, MRI machines, while they involve a large up front cost, can be in service for nearly a decade - and on average pay themselves off within a single year of use. "
] |
[
"Reddit, why does the bigger cyclist always (in my experience) descend a hill faster than the smaller rider? THIS MAKES NO SENSE!!"
] |
[
false
] |
So it's first-principle physics that all things on Earth will accelerate at the same rate (9.81 m/s2) regardless of mass right? I'm a cyclist reddit, and every time I go down a hill with a bigger person they ALWAYS accelerate more quickly!! Assuming the bicycles are the same, and the hill is roughly the same, what gives? I'm thinking that the bigger person has better traction from the higher normal force, resulting in increased efficiency, but then they'd have more rolling resistance and my whole theory falls apart! Help!
|
[
"The force of damping from the atmosphere is proportional to velocity. The acceleration it causes depends on the force divided by the mass. The bigger the mass, the less the deleration caused by air resistance."
] |
[
"Without air resistance the ",
"free body diagram",
" for a guy getting pulled down a hill is just m*g*sin(theta) = ma where theta is the angle of the hill. Here, of course, you can see that the m's cancel, so then you can say \"a = g*sin(theta)\" ",
"But once you add in air resistance, there is a second force on the left side, the force of air resistance. The force of air resistance is a function of speed, surface area and shape. Unless the guy is a lot heavier, the heavier guy doesn't necessarily have a lot more surface area than a lighter guy. So now, we add in the force of air resistance, F(air) and we redo the free body diagram: m*\\g",
"g*sin(theta) - F(air)]/m, or simplifying a = g*sin(theta) - F(air)/m. So, notice the larger the mass, the smaller term you are subtracting away, so the acceleration will be higher. ",
"This is really the same principle as dropping a sheet of paper and a sheet of metal which is the same surface area. The metal will fall a lot faster. "
] |
[
"Put perhaps more simply: Wind resistance is proportional to surface area, momentum is proportional to volume. Bigger people have a higher volume-to-surface-area ratio."
] |
[
"Why are there two bones in our forearms and shins? Does this feature serve some important function?"
] |
[
false
] | null |
[
"As someone who just has his radius head replaced by a prosthesis after a fall and is now working to try to regain his mobility I can answer :",
"the two bones structures alow for rotation in multiples axes.\nthe cubitus alow your arm to flex in and away from your upper arm.",
"the radius alow for your lower arm (and therefore your hand and wrist) to \"roll\" from left to right.",
"Regards"
] |
[
"This is why early tetrapods with them were able to out compete those without, but let's not confuse that with why ",
" have them. Evolution isn't capable of wholesale replacing major structures. We have radii and ulna in our arms, and fibula and tibia, because all land vertebrates do."
] |
[
"I'm assuming cubitus is your languages word for the ulna? Regardless, this is a correct answer. Another good reason would be to split pressure while pushing into two bones, meaning less risk of fracture. It also provides more support for the carpals. "
] |
[
"Is the speed of gravity slower in a medium?"
] |
[
false
] | null |
[
"In the weak field limit, gravitational waves behave in a very similar fashion to electromagnetic waves. In fact the mathematics is nearly identical and if we consider a medium of point mass oscillators (say a thin gas because the math is easier) we can calculate what the \"refractive index\" of gravitational waves in a medium and the accompanying dispersion relation. Thus, while the the effect is small, gravitational waves can slow down in the same way light slows down in glass or water."
] |
[
"So if you read the ",
"correct description",
" of why light slows down in a medium it seems pretty likely that something similar would happen with gravitational waves, i.e. gravitational waves passing through a medium would couple to vibrational modes and get an effective mass, slowing them down.",
"Note that this is essentially a classical phenomenon and doesn't rely on the existence of gravitons, although it is a statement about gravitational waves which we haven't observed yet either. Also note that although this would mean that there would be a slight delay in feeling (at least small) changes in a static gravitational field, unlike electromagnetism there's no way to shield a static gravitational field, because there are no gravitational dipoles."
] |
[
"You misunderstand, OP was talking about gravity fields/waves, which move at the speed of light."
] |
[
"What effect does time dilation have on electromagnetic waves?"
] |
[
false
] |
In the movie Interstellar, video recordings are transmitted from Earth to the crew of the Endurance. This made me wonder if the use of radio transmissions (or other forms of electromagnetic wave communication) could be used to overcome the effects of time dilation experienced by two individuals in drastically different gravitational fields.
|
[
"To keep within your example from Interstellar (spoiler warning!), some of the crew are sent to the surface of a planet orbiting close to a super-massive black hole, and experience time dilation relative to the mothership (Endurance) by a factor of ~60,000. Any signal the crew on the planet try to send back to the Endurance will be 'stretched' as it climbs out of the gravity well.",
"The wavelength of the radio waves will be stretched, and therefore the frequency lowered until it's oscillating 60,000 times slower. The wave itself is always traveling at the speed of light, in all frames, but the frequency of the wave as it is received will depend on the frame of the observer, so it will not serve as a way to 'overcome' time dilation.",
"Receiving information in the form of radio waves from the surface is an observation, just as pointing a powerful telescope at the surface and viewing the people moving 60,000 times slower would be.",
"As a side note, in the film the crew member on board the Endurance seems to have no communication with the crew on the surface and just has to wait years for them to return. It's entirely possible that with such a huge factor of time dilation, any radio transmissions sent from the surface would be far outside the detectable and readable frequency range of the Endurance's communication equipment by the time the signal reaches her 'height' in the gravity well."
] |
[
"Wait a second, wouldn't frequency shift be detected on earth, and it be obvious that the \"ping\" signal is messed up, leading to obvious conclusion? How would it possible not to notice this?"
] |
[
"Yep. You're right, they should have known about the time dilation from the frequency. "
] |
[
"Would A Binary System Of A Star (Preferable a yellow dwarf) And An Equally Sized Black Hole Be Stable?"
] |
[
false
] |
(This is for a sci-fi project of mine). What stars would be best for this binary system? Would it be habitable? Would it be possible to place the planet in between the two celestial bodies? Thanks in advance!
|
[
"Almost any system of two objects will be gravitationally stable. A black hole's gravity is just the same as any other object of the same mass. At long distances, all gravity looks like GM/r",
". It's just that a black hole is so small that you can get close enough that gravity gets strong enough that it stops being Newtonian and starts doing weird General Relativity things - but that is only noticeable if you're very close.",
"The two objects don't need to be close in mass at all to be stable. They just need to have the right amount of relative speed/angular momentum that they aren't going so fast that they just escape each other, and aren't going so slow that they just fall together and merge. There's a big range of possible speeds in-between though, and the two objects can have nice circular orbits, or very elliptical orbits.",
"Though if they are really close together, then one object ",
" start to rip material off the other. This does happen in black hole + star binaries, but also in star-star binaries. It particularly happens when one star goes into a red giant phase, and becomes so puffy and stretched out that the outer layers aren't stuck on very well, and the black hole or other star can start to peel that off to form an accretion disc.",
"Overall, there's no major difference between a black hole and a star here.",
"If you're adding a planet, then that's a bit trickier. Basically, only binary orbits are stable. But you can ",
" binary orbits to get a stable system with lots of objects. There's two options here. Either the planet is so far away from the binary that the binary \"feels like\" a single star, or the planet is much closer to one star than the other object, so that the planet is orbiting that star, and that star and the planet are together orbiting the other object.",
"You can't put a planet in the middle - it's unstable. If somebody sneezes, the planet will be slightly closer to one star/black hole than the other. The closer object will pull the planet more because gravity increases when you're closer. So any slight push will cause the object to spiral away from the centre."
] |
[
"Just to add a bit to what Astrokiwi said",
"Would it be habitable? Would it be possible to place the planet in between the two celestial bodies? Thanks in advance!",
"The system that will feel closest to this would be that the inhabitable planet orbits the black hole, and then the black hole and the star orbits each other in that binary system. However, the event horizon of a black hole with the mass of our sun would be very small (less than 10 miles in diameter), so it wouldn't really play a huge role in the night sky (if that's what you're hoping).",
"You're also not going to get any time dilation from one side of the planet compared to the other, because that's simply not how things work (again, I'm just assuming that might be what you're looking for).",
"Honestly, a planet orbiting such a small black hole in a binary system is not going to be that much different from a planet just orbiting a star. there will just be more \"wobble\" to the night sky, as the planet orbits the black hole.",
"Of course, if the planet orbits the black hole closely you're going to see some crazy tidal waves, and possibly many earth quakes and volcanic eruptions, and if the planet is otherwise in the goldilocks zone, it will be very very hot due to the energy created by tidal friction."
] |
[
"A binary system is never exactly stable, you always emit gravitational waves and the bodies eventually collide. However, this effect is usually extremely weak, and only becomes noticeable for very massive bodies orbiting very close to eachother. Just put the star a healthy distance away from the black hole and it'll be stable for long enough. If you're worried you can use the ",
"formula",
" to check the time it takes for collision."
] |
[
"If I point randomly into the sky, how likely is it that I'm pointing at a star?"
] |
[
false
] |
Edit: phrased differently, If I extend a line from the tip of my finger to the edge of the observable universe, what's the probability that that line intersects with the body of a star? This was inspired by reading about or the "dark night sky paradox".
|
[
"If you take your finger hold it at arms length away from your body, you can block out the sun or the moon pretty easily. So I'm going to say that's your \"pointing\" That's around .5 degrees of the possible 360 degrees around earth. If you only could point along one axis, an imaginary straight line around Earth. Then the amount of stars you would point at would be around the number of galaxies in the observable universe 500 billionish. x the number of stars in each galaxy. 100 billion / 720. Lets just say you'd be pointing at 5x10",
" stars. Now you're asking in ANY DIRECTION. Which is really difficult because now you have to think about the surface area of Earth. Arc seconds/minuts don't really work anymore. If you imagine that that your finger pointing at the sky takes up only a sad 1 billionth of the 3 dimensional sky. Then you're only pointing at 5x10",
" stars in that TINY portion of the sky. I thought this was an interesting thought experiment :) Thanks for asking! Some of my math is not super accurate, and guestimates a lot. But it does make you realize how absolutely huge the universe is, and how much stuff is out there we can't really see."
] |
[
"Yes - a ray of zero width from your finger to the edge of the observable universe will almost certainly never intersect any star, thought it may possibly (but probably not) intersect a galaxy.",
"If half of these rays intersected a star, then the average brightness of the night sky would be the same as half the brightness of an average star. But the night sky is very dark, which tells us that the covering fraction of stars between here and the edge of the observable universe is very low."
] |
[
"Depends on what accuracy you're talking about, but in actual reality, it's quite likely that you're pointing at multiple galaxies, never mind just a star. ",
"The Hubble Ultra Deep Field imaged some 10,000 galaxies, while looking at the darkest part of the sky. Those 10,000 galaxies were in an area that was just 3.4 arc-minutes across. To put that in perspective, that's roughly the size of a 1mm square, 1 meter away from you. It's also 1/10th the diameter of the moon."
] |
[
"Two questions: False Vacuums, Vacuum Metastability events, and the Alcubierre Drive"
] |
[
false
] |
So, I'm writing a science fiction novel, and I'd prefer some rigour in the science bits. I've studied physics, but not near as much as I'd need to in order to speak with any authority (engineer here, hi!). (I understand my questions are insanely generalised and possibly horribly put, but I'll hone down to what I really need once I realise what questions I hould be asking.) So, here are my questions: Supposing that we are in a false vacuum, does that mean that a certain area of our universe is existing in said false vacuum, or does this have to apply to the whole universe? In other words, could only a certain "volume" of our universe possibly be existing in a "protected bubble" of false vacuum? Could a VME qualify as a big bang-like event? --I imagine a VME as follows: a perfectly black-body bubble is generated and expands outward at light-speed. I'm guessing that inside this bubble (if there were anything), there is some new sort of reality with a different set of physics. that's enough for now, and while I did mention the Alcubierre Drive in the title, I'll get to that later, since it's not that central to the novel (or so I think), and is too ridden with improbability as far as we know. Any questions I might have could be cleared up depending on the answers to the first two. So, in case I'm still left with questions, I'll be sure to add them later. Sorry if I come off daft, but I can't help it :(
|
[
"Well, we'll get over the first paragraph of the answer, then :)",
"As far as the second paragraph goes, everything's fine, but I think we have a little disonnance at the last part. \nBy protected, what I meant is that if our part of the universe would be \"walled off\" if we were exist within a \"bubble\" of false vaccum. ",
"Do I have it backwards? I'm thinking the false vacuum as a bubble within a lower energy volume. And when a VME occurs, a new bubble appears within the first and resolves itself at the edges. ",
"You know what? I'm going to take a nap, and then get back to this. I probably made zero sense :P"
] |
[
"No, no, the false definitely has the higher energy. That, I know. I'm just not being very articulate at the moment. I appreciate the time you're taking to try and help me clear this up, though :)",
"And I'm not exactly getting at that :(",
"I guess what I was saying was that I assumed the false vacuum is like a \"bubble\" in a sea of the true vacuum, and when the VME happens, another bubble of true vacuum expands inside the false vacuum, rushing to the edge and effectively erasing the false from reality. ",
"What I was just wondering is what the boundaries would be like. In the original question, what I wanted to know is that if a sector of space exissted in a flase vacuum, would it be like a walled-off bubble floating in a \"sea\" of regular vacuum? "
] |
[
"There would be a significant difference between a VME and a big bang. Specifically, in the big bang all energy originated at a single point. A VME would have matter \"falling in\" to it from the edges. However, you are correct in that there could (theoretically) be some new sort of reality with different physics. ",
"If we were in a false vacuum and part of the universe were in a true vacuum, the edge of the true vacuum would be approaching us at the speed of light and thus we would never know until it was upon us. As to whether it could be protected, I don't know the answer to that. "
] |
[
"Would a 50g object traveling at 280,000m/s really possess the same kinetic energy as a megaton of TNT?"
] |
[
false
] |
Did a quick calculation, and a 50 gram weight traveling at 280,000km/s would have roughly 1.96 x 10 joules of kinetic energy. A megaton of TNT has 4.184 X 10 joules. Is my calculation correct? Would a 50g object traveling at relativistic speeds create an explosion comparable to a nuclear warhead if it were to collide with say, the surface of the moon? EDIT: Typo. Meant km/s.
|
[
"In which case it's calculated by mc",
" x (sqrt(1/(1-v",
" /c",
" ))-1)",
"You can approximate this as 1/2 mv",
" + 3/8 mv",
" /c"
] |
[
"KE is calculated through 0.5 x mv",
" I make it 1,960,000,000 Joules for a 50 g (0.05 kg) mass at 280,000 m/s.",
"But ultimately yes, a small mass travelling very quickly can impart a lot of energy."
] |
[
"Sorry, meant km/s. Almost light speed."
] |
[
"At what size does gravity become nil/negligable?"
] |
[
false
] |
As the title says, I'm baisically want to know at what size gravity either stops being either detectable or becomes negligable enough to not be noticed? Edit: Thanks for all the answers guys and girls. I think I understand that everything has a gravitational pull but to varying degrees depending on distance and mass? So really the answer to my initial question is none.
|
[
"Honestly, I think that's misstating it ",
" This is more about pedagogy than it is about physics, but indulge me for a moment.",
"I have here a coin. At present, it is heads-side-up. One might ask, ",
" is it heads-side-up? And were one to ask that, the answer might as well be, \"because the tails side is down.\"",
"Which might lead one into a train of thought that contemplates the relationship between heads-upness and tails-upness. One might even write an equation, saying something like ",
" (for heads-upness) = –",
" (for tails-upness). Except one would probably write –",
" + ",
" instead, because that's what we do. And also there'd be an 8",
" in there.",
"And once one did that, one could pat oneself on the back, pleased as pie that the relationship between heads-upness and tails-upness has finally been fully quantified.",
"At which point a student will ask, \"Yes, but ",
" that equation to be true?\"",
"And you will have no answer … unless you take a step back and remember that ",
"It's a misstatement to say that energy ",
" The correct statement is to say that the curvature of spacetime is ",
" the configuration of mass, fields, momentum and so forth. It's not that there's one independent thing, and then another independent thing, and they interact. It's that they are ",
" Energy is geometry; geometry is energy. They are the same fundamental thing.",
"Like I said, that's more a point of ",
" than it is anything applicable to physics. But it comes up a lot, so I thought I'd speak my mind."
] |
[
"The best laboratory measurements of gravity are made by torsion pendulums. There's a group at the",
" University of Washington who does this",
".",
"I'm not 100% sure, because I don't have time to do the calculations, but I think that if you stood next to their torsion pendulum, they could detect your presence via gravity."
] |
[
"If you're okay with saying a fundamental property of energy is that it ",
" ",
" a curvature of spacetime, then we know what causes gravity. If you're not okay with saying that, then, well.. we don't know.",
"edit: see below."
] |
[
"Are there any cognitive (or other) benefits I'm missing out on by listening to audiobooks rather than reading the book?"
] |
[
false
] |
[deleted]
|
[
"By not reading the words, you don't learn their spelling. "
] |
[
"By not reading the words, you don't learn their spelling. "
] |
[
"Well the most obvious thing would be spelling. "
] |
[
"If the Tibetan Plateau is so dry, how come it has so many lakes and is the source of so many rivers?"
] |
[
false
] |
The Tibetan plateau is generally accepted as being an incredibly cold and barren place, and its dryness is usually blamed for this. But not only does it have an abundance of lakes, it is also the source of the Yangtze and Mekong, among others. How is this possible? On a related note, if it does have water, why is it so barren? I was under the impression that plants needed two things to grow - sunlight and water. Yet the plateau's lakeshores are barren and treeless; many do not even had grass in the vicinity. Why is this?
|
[
"It has an abundance of lakes because of snow melt. It doesn't have many plants because of the altitude and the cold. "
] |
[
"places that are cold are also dry. the lakes have water, but further away from the lakes, it is dry."
] |
[
"Thanks for the response guys! I'm still a little confused though.",
"I thought that many of the lakes were saltwater. Wouldn't glacial runoff be fresh water? Also, does that mean that all the rivers coming off the plateau are caused by glacial melt?",
"Why, though, are there is there no vegetation AROUND the lakes, even in the summer when it is warmer? ",
"My questions are partly derived from looking at this website, which illustrates some of my observations:",
"http://kekexili.typepad.com/life_on_the_tibetan_plate/2008/02/lakes-of-tibet.html",
"Thanks!"
] |
[
"Are visible atoms possible?"
] |
[
false
] |
Is it theoretically possible, given the existence of the commonly discussed "island of stability" in atoms with super-large nuclei, to synthesize an atom with a nucleus so large it would be visible to the naked eye?
|
[
"For an object to be visible by light it has to be larger than the light's diffraction limit, which is at most half it's wave length. For visible light that would be about 200 nm. The largest nuclei are about 15 fm. That's 13 million times smaller than what can be observed by light. \nTL;DR - No, nuclei are way too small, even theoretically big one."
] |
[
"I believe you're trying to refer to techniques like Scanning Tunnelling Microscopy (STM), which images the quantum wavefunction of an atom, and Atomic Force Microscopy (AFM) which images its charge density. In no way are these \"simulations\", they're direct experimental probes. ",
"This issue here is that \"look\" is not a \"physics\" word, it's a human physiology word. ",
"Consider our nose. Our nose is a sensor system we meatbags have that pings a signal to our brain if certain molecules fit, like a key into a lock, into receptor sites in our nose. If something that is not one of those molecules enter, there's no ping. So what do atoms \"smell like\"? It's a meaningless question. Smell is not a property of matter, it's a description of the feedback our built-in sensor suite would receive if we probed it. If a gold atom enters your nose your brain gets no signal, because there's no receptor. That doesn't mean that gold atoms are \"odorless\". I know saying \"odorless\" is a common way of phrasing it but it's missing which is fundamental. It's a failure of our sensors, not a property of the object.",
"All in all we have sensors for say pressure (touch), limited range optical spectroscopy (eyes), acoustic spectroscopy (ears) and a couple others and that's it. That doesn't mean, say, an experimental device that detects, say, current, is getting \"not really real data\" compared to our \"really real\" pressure sensors, for example.",
"Similarly, nothing \"looks\" like anything if it's smaller than about 400 nm. Humans only have receptors for light with that minimum wavelength (blue light), if it's shorter than that we get no signal and if blue light passes something much smaller than its wavelength it is essentially unaffected by it. So our optical sensor suite is insufficient to get any meaningful feedback.",
"But we're humans, and we're smart and we've learned how to build more advanced sensor suites than the ones we \"came\" with. And that's really it. ",
"Just because our built-in sensors are too coarse to get a meaningful signal, doesn't mean the data from a better sensor is \"fake\" or a \"simulation\" or in any way less reflective of reality. ",
"Furthermore, there's a fundamental human-centric bias here that optical data is \"superior\" to say charge distribution data. In reality any probe, including optical, is going to tell us only one thing about an object, it's response to that one probe. But an object has many properties beyond its optical spectral response to a certain range of wavelengths.",
"STM and AFM directly image atoms by either detecting a quantum tunneliing current or by observing the deflection of a cantelever due to charge repulsion. Their results are no less \"real\" than the data our eyes pull on light from 400-700 nm. ",
"For a final non sequitor: AFM can actually place individual atoms, which lead to this famous image in the lates 80s:",
"https://en.wikipedia.org/wiki/IBM_(atoms)"
] |
[
"I believe you're trying to refer to techniques like Scanning Tunnelling Microscopy (STM), which images the quantum wavefunction of an atom, and Atomic Force Microscopy (AFM) which images its charge density. In no way are these \"simulations\", they're direct experimental probes. ",
"This issue here is that \"look\" is not a \"physics\" word, it's a human physiology word. ",
"Consider our nose. Our nose is a sensor system we meatbags have that pings a signal to our brain if certain molecules fit, like a key into a lock, into receptor sites in our nose. If something that is not one of those molecules enter, there's no ping. So what do atoms \"smell like\"? It's a meaningless question. Smell is not a property of matter, it's a description of the feedback our built-in sensor suite would receive if we probed it. If a gold atom enters your nose your brain gets no signal, because there's no receptor. That doesn't mean that gold atoms are \"odorless\". I know saying \"odorless\" is a common way of phrasing it but it's missing which is fundamental. It's a failure of our sensors, not a property of the object.",
"All in all we have sensors for say pressure (touch), limited range optical spectroscopy (eyes), acoustic spectroscopy (ears) and a couple others and that's it. That doesn't mean, say, an experimental device that detects, say, current, is getting \"not really real data\" compared to our \"really real\" pressure sensors, for example.",
"Similarly, nothing \"looks\" like anything if it's smaller than about 400 nm. Humans only have receptors for light with that minimum wavelength (blue light), if it's shorter than that we get no signal and if blue light passes something much smaller than its wavelength it is essentially unaffected by it. So our optical sensor suite is insufficient to get any meaningful feedback.",
"But we're humans, and we're smart and we've learned how to build more advanced sensor suites than the ones we \"came\" with. And that's really it. ",
"Just because our built-in sensors are too coarse to get a meaningful signal, doesn't mean the data from a better sensor is \"fake\" or a \"simulation\" or in any way less reflective of reality. ",
"Furthermore, there's a fundamental human-centric bias here that optical data is \"superior\" to say charge distribution data. In reality any probe, including optical, is going to tell us only one thing about an object, it's response to that one probe. But an object has many properties beyond its optical spectral response to a certain range of wavelengths.",
"STM and AFM directly image atoms by either detecting a quantum tunneliing current or by observing the deflection of a cantelever due to charge repulsion. Their results are no less \"real\" than the data our eyes pull on light from 400-700 nm. ",
"For a final non sequitor: AFM can actually place individual atoms, which lead to this famous image in the lates 80s:",
"https://en.wikipedia.org/wiki/IBM_(atoms)"
] |
[
"How does DNA recombination ensure the resulting chromatid is compatible?"
] |
[
false
] | null |
[
"Depends on what you mean by \"compatible\". Structurally, there should not be much difference in the DNA between alleles D and d, so the DNA just goes on in the recombined state. If the genes are involved in gamete function and a certain combination produces a non-functional gamete, then you get a non-functional gamete. The cell may or may not undergo programmed cell death depending on what the resulting genes do.",
"If the gene function/expression is not present in gametes then the gamete goes on just like any other. If it produces a zygote, and the zygote is non-viable then again, there are mechanisms in play depending on where in development the effect of the gene is manifested. ",
"But in general, in biology as a whole, the way errors are dealt with is that they produce something that does not work, so it does not survive/reproduce."
] |
[
"Sometimes incompatable loci are evolved and used by plants to prevent self-fertilization. ",
"Ex."
] |
[
"The evolutionary “goal” of crossing over/recombination during meiosis is to generate gametes that have a chance of having higher success. There’s also a chance that that they have lower success, or are “not compatible.” Not compatible could mean having too many recessive alleles, leading to poor “fitness” either the offspring dies early or does not compete well with others."
] |
[
"What would you see if you were standing in the dead centre of a cylindrical mirror?"
] |
[
false
] |
Or if you were floating in the middle of a spherical mirror for that matter?
|
[
"i put this biped\n ",
"http://i.imgur.com/DLRwI.jpg",
"in a cylindrical mirror and got this",
"http://i.imgur.com/f3h1N.jpg"
] |
[
"What did you use to model this? And thanks :) It's just one of those things that has always intrigued me but also annoyed me knowing that I'll never be able to physically construct it."
] |
[
"i used 3ds max"
] |
[
"Is there something that determines if an animal can be domesticated?"
] |
[
false
] | null |
[
"A number of factors, not a single thing.",
"One is the animal's social structure in the wild. If for example they live in packs with a leader, then humans may be able to easily domesticate them by taking over that leader position. That's not absolute by any means, but it's one of the strongest factors.",
"The most key factor though doesn't determine whether they \"can be\" domesticated but rather if they will be: usefulness. Domestication takes a lot of effort over a long period of time. You can't really just domesticate something on a whim (though attempts are made). It needs to be economically useful. Dogs as hunting companions (primarily), cats as pest control, livestock as food sources, horses for mobiliyy, these things are enormous material leaps and bounds for a society. They unlock modes of production and living above what is otherwise available. "
] |
[
"Theoretically, with enough time and patience, any* species could be domesticated, since domestication is just breeding for favorable traits over successive generations. (Gonna address that asterisk in a minute.) The real question becomes one of resources and risk vs. reward that faced our ancestors.",
"Spotted hyenas, for example, are actually quite sweet-natured if they are acclimated to humans",
"As for the asterisk: If there's a limiting factor to domestication, intelligence may be it. The smarter a species is (specifically, the ones that might arguably be sentient), the worse they seem to fare in captivity. ",
"Elephants, for example, have never been technically domesticated; they breed poorly in captivity, making actual selective breeding impossible",
". Despite a history with humanity going 3,000 years, your average elephant is as just as wild as a tiger. Orcas have gotten a lot of attention recently, thanks to the documentary ",
" and the various Seaworld ethics scandals. A lot of self-mutilating behavior in \"pet\" birds is basically the result of a highly intelligent social being getting shoved in a small box and left alone, because they are nowhere near domesticated. ",
" of our great ape cousins are just too smart to try and domesticate, ",
" jokes aside. Any primatologist worth their salt would almost immediately start talking about the potential ethics violations in trying to breed an arguably sentient species for specific traits like docility, especially endangered species."
] |
[
"To expand on the eating point: The animal's diet also shouldn't be too specialised. It should be comfortable living off farm waste and table scraps. It's why we didn't domesticate anteaters.",
"Additional points:"
] |
[
"Evolution of viruses. Why kill the host?"
] |
[
false
] |
Forgive me if I sound overly ignorant here but I've recently come to accept that evolution is fact (long story: ex-JW). Anyway, I was thinking about how almost every species on this planet from bacteria to humans have evolved because of natural selection among other things. The point being that if a species survives it gets stronger or at least more capable of surviving. Which brings me to viruses. I know that not all viruses kill the host but what does the virus gain from killing the person or cells it has infected? If it kills the host doesn't it not also die? Seems counter intuitive to evolution but again I'm looking for more understanding.
|
[
"Good question! You're right. It is generally not advantageous for a virus to kill its host. You'll find that the vast majority of viruses do not. Sequencing studies have shown most people have more viral particles in and on their body than they do human cells, and for the most part these cause little or no noticeable effects on health. ",
"Why do some viruses kill humans? There can be many different reasons for this, some of the most common of which I'll try and cover.",
"1) Sickening humans aids in spreading the virus: This is pretty straight forward. Coughing, sneezing, and open pustules help infect new hosts, an evolutionary advantage that seems to out-weight the danger of killing the host for some viruses.",
"2) Humans are not the primary host: Many of the most deadly viruses we hear about like Ebola, SARS, or Hantaviruses are actually zoonotic infections. We sometimes pick them up from animals that are the virus' primary host. While the virus may be well adapted to infect a rat or a bat without doing much damage, this is not the case for humans, and problems ensue. ",
"3) Chronic infection means the virus is still able to spread even if the host dies: Certain viruses like HIV or Hepatitis C establish chronic infections. While these infections may eventually kill the host, this takes decades, meaning the virus still has plenty of time to spread to new hosts before this happens, so there's not really any pressure from an evolutionary perspective not to kill the host. "
] |
[
"Since other answers have talked about this affects humans, keep in mind the situation is pretty different for killing cells (either in a multicellular organism's body or among a population of single-celled organisms) and for killing a multi-celled host. Viruses need a host cell's machinery for reproducing, and often the most efficient way to do that ultimately kills the cell (and sometimes ends by breaking it open to release the viruses). This strategy of course depends on there being other cells to infect in the vicinity. Point being, a virus often has more to gain from killing an individual cell than from killing a multicellular host.",
"Also, natural selection only acts on what is being successful in the here and now. So if a strain emerges that kills a lot of its hosts but is effective at spreading, it can still be very \"successful\" from a selective standpoint until the epidemic burns itself out. (Also, the strain's virulence and transmissibility are controlled in large part not just by the virus itself but by the population's immunity to it. Most viruses are adapted to populations that have some immunity built up to them, and that can be disrupted if they transfer to a new population or species. Flu pandemics, for example, start when a strain transfers from birds or swine to humans. The new strain is more likely to kill the host than seasonal flu but it \"settles down\" into the new strain of seasonal flu after the pandemic has run its course.)"
] |
[
"Wow! That's really interesting. Never thought about the symptoms they cause also being a viable transmission system. "
] |
[
"Are there prisms and lenses for nonvisible wavelengths of the electromagnetic spectrum? What sort of things would they be used for?"
] |
[
false
] | null |
[
"Yes. There certainly exists a market for x-ray optical equipment, either to focus x-rays like you would need to do on the Chandra telescope (basically the Hubble telescope of the X-ray spectrum), or in x-ray spectrometers and microscopes. I would not be surprised if X-ray rated optical pieces would be what some specialist somewhere calls \"lab equipment.\" "
] |
[
"I do infrared spectroscopy, and there are all kinds of different optics for various infrared wavelengths. Metal mirrors are relatively straightforward, gold and aluminum have good reflectivity over a very broad region. Most often, people will use dielectric coated mirrors, which can be very highly reflective in the IR but transparent in the visible.",
"I find the windows most interesting. Many materials, like germanium, are completely opaque or even black to the eye, but transmit IR light well. ",
"I use them to steer IR laser beams around, basically. ",
"You can find some decent pictures of the optics at places like ThorLabs, if you're interested.",
"Not electromagnetic spectrum, but there are even mirror-like optics for neutron beams. "
] |
[
"Even so, very high quality & efficiency x-ray optics are notoriously difficult to make. There is a great demand for them to enable fine lithography for semiconductors, but so far that has been one of the barriers preventing introduction of such technology into manufacturing. We are stuck using \"deep UV\" and \"extreme UV\" for semiconductor patterning because no one can make X-ray lithography work well enough. (Photoresists are also a problem.) "
] |
[
"What is the study of genetic memory in animals called? For example elephants travelling vast distances knowing exactly where to go. And what evidence is there that animals are born with memories of past generations?"
] |
[
false
] | null |
[
"Geneticist here. I've never come across the term genetic memory before (in this context) and there is no evidence that animals are born with memories of their parents and ancestors. Animal migrations and movements are usually either learned from others of their species or instinctual. If you have a specific example that you think cannot be explained by learning or instinct I would be happy to discuss. "
] |
[
"What's the biological basis of \"instinct?\" It's something often stated without explanation, that instinct drives an animal. I just don't know if it's neurological, hormonal, or what?"
] |
[
"Some instincts are described as innate characteristics, as they can be explained by ",
"behavioral phenotypes",
".",
"See also ",
"Behavioral genetics"
] |
[
"Is there a maximum amount of energy that can be contained in a solar flare? Could the sun produce a solar flare beyond the X class?"
] |
[
false
] | null |
[
"I can't speak to the maximum energy of a solar flare, but the definition of the X class ( > 10",
" W/m",
" ) precludes there being a higher class. Within this class, there have been many examples of huge flares, like the X28 flare of 2003."
] |
[
"Forgive me, but I don't actually know if the scale is logarithmic, but I'll throw out some values and let someone better with math explain the proper mathematical term for this.",
"A C1 flare has an intensity of .000001 W/m",
" . C2 would then be .000002, C3 is .000003, etc. M1 has an intensity of .00001 W/m",
" . M2 is then .00002 and M9 is .00009. There's not an M10, because as you suggested, that's an X1.",
"An X28 is 28 times as powerful as an X1. I'm guessing there's not a higher classification because flares aren't expected to be a full order of magnitude larger than the X class. (Since the X28 is barely into the next order of magnitude.) However, I don't have much insight into this, as there are also superflares, which are millions of times more energetic, and not considered on the scale."
] |
[
"The scale is logarithmic, correct? Would a M10 solar flare be equivalent to an X1? ",
"If they have recorded solar flares that powerful in the past, wouldn't it make sense to use another letter for very large X category flares? Perhaps a \"Y\" scale? (Making the X28 flare a Y2.8 flare instead)."
] |
[
"Question about aerogel's electric properties."
] |
[
false
] |
Why aren't aerogels used as dielectric materials?
|
[
"Aerogel has a very low density and the majority of the volume is occupied by air. You could use it as a dielectric, but it would be very similar to using air as a dielectric."
] |
[
"I've always been curious about aerogels. If there are experts in the room, here's some more aerogel questions:"
] |
[
"Ah, that makes sense. I guess thats why aerogels have such a low level of thermal conductivity, because air does. Thanks"
] |
[
"Can you 'catch' a mental illness?"
] |
[
false
] |
[deleted]
|
[
"Yes and no...\nWe don't really know what causes it nor can we predict if it will be triggered. We can detect preliminary risks with fMRI scans but it is still limited to research (i.e. by comparing with controls (healthy) subjects, we can see brain differences between them and schizophrenic patients for example; but we cannot take someone with no schizophrenic symptoms and diagnostic the mental illness based on his fMRI scan).",
"To the limit of my knowledge, you may have a predisposition to a certain mental illness (i.e. if your father was diagnosed with a severe depression or bipolar disorder; chances are you or one of your siblings might be at risk of developing it), , it may never be triggered, or it might be by a reaction to environmental stresses, genetic factors, biochemical imbalances, or a combination of these. ",
"As you requested a 101 on mental illness, ",
"here's",
" an interesting link explaining what it is in a simple way.\nI invite anyone to correct me or add more to my response.",
"Hope it helps!\nSource: Neuroscience graduate student"
] |
[
"Folie a deux",
" is a condition in which two or more people share delusions.",
"In Carl Sagan's book ",
", a gentleman by the pseudonym of Kirk Allen is brought up. Allegedly, he was a top-level physicist in the military who was referred to a psychologist. He told the psychologist that he could go into the future and he described it in a very detailed manner. After a period of time, the psychologist began to believe that his patient really could go into the future. Eventually, Kirk Allen revealed that he had made the entire thing up. Of course, I would take this story with a grain of salt."
] |
[
"What might trigger in some people and not other is the genetic predisposition to the mental illness in question.\nIf the family has a history of mental illness it means that the children have a risk/chance of having it too. Now whether it is dormant or not I do not know. If you have 2 children, there are chances that child #1 will have genetic predispositions and child #2 won't have any or vice versa, or both of them."
] |
[
"why don't companies like intel or amd just make their CPUs bigger with more nodes?"
] |
[
false
] | null |
[
"Conversely, this is one of the fundamental sources of instability when overclocking. It's possible that your processor will start giving you incorrect results before it starts overheating, and this means that you've found approximately how long it takes electrical signals to propagate through the longest paths in the CPU and for all the transistors to settle in time for the next clock cycle.",
"So this is why you can't just keep overclocking and cooling. I wasn't sure if that would be a problem but figured there was a physical limit."
] |
[
"Conversely, this is one of the fundamental sources of instability when overclocking. It's possible that your processor will start giving you incorrect results before it starts overheating, and this means that you've found approximately how long it takes electrical signals to propagate through the longest paths in the CPU and for all the transistors to settle in time for the next clock cycle.",
"So this is why you can't just keep overclocking and cooling. I wasn't sure if that would be a problem but figured there was a physical limit."
] |
[
"We past the \"propagation limit\" long ago. Modern CPUs do not work by having everything in lock-step of the clock. The clock signal propagates across the circuitry like a wave and the circuitry is designed around that propagation. In theory we could design larger chips and deal with the propagation, but the factors others have listed (heat, cost) make it pointless."
] |
[
"You live in an arctic igloo (with electricity). Will a refrigerator still be able to keep things at 40 degrees Fahrenheit?"
] |
[
false
] |
I once watched a documentary on an arctic outpost and the narrator said something like "the temperature here is 0 degrees. in this weather, you'd use a fridge to keep things WARM!". It was a bit cheesy, but makes me wonder whether a refrigerator DOES have heat capacity.
|
[
"I don't know where these other answers are coming from. ",
"Modern fridges have a complex mechanism to lower the interior temperature (that works better the colder the fridge's environment) and a different, very simple mechanism to briefly heat the interior to prevent frost buildup. I guess it might be possible to jigger this second mechanism to raise the interior temperature, but fridges aren't built that way: they're assumed to be used in an environment comfortable for humans, i.e. 50-80°F or so. So if the fridge is put in a really cold environment, the fridge would just not run but get colder and colder until it matched the outside temperature ",
" for the defrost cycle kicking on and off occasionally, which is a very small, limited heating mechanism.",
"So I think this is just a reporter using hyperbole."
] |
[
"Something that needs to be pointed out that most people here are getting wrong: assuming that igloos that are in use are at or below 0C inside. ",
"That's not the case",
". An in-use igloo can easily be >15C inside, purely from radiant body heat and an oil lamp.",
"Remember, when an Inuit person needs to build an igloo, they do so to keep ",
", not to keep ",
"."
] |
[
"What are you talking about? Fridges have to work a LOT less when the external temperature is lower. I mean not only are you gaining less heat through the case itself, but the colder the condenser coil the easier it is for the fridge to do its job."
] |
[
"Is there a relationship between droughts and the increased in carbon dioxide levels?"
] |
[
false
] |
i mean can it actually increase droughts in some parts of the world due to increase greenhouse gases?
|
[
"The short answer is \"Yes\". When people think of global warming, most people think of temperatures rising - which isn't surprising given the name! However, the temperature increase ",
" isn't actually the biggest problem. The real, major issues are the secondary effects that rising temperatures cause, such as changes in climate systems. All climate systems on the earth rely on energy and when you change the energy inputs (e.g. by changing the temperature), you can get very complex and significant changes.",
"The general view is that increasing temperatures will result in an increased risk of extreme weather, including drought",
". The climate is an incredibly complex system - some parts of the earth will get wetter - but generally speaking, climate change exacerbates existing weather trends. This means that areas that are already vulnerable to droughts are probably going to be more vulnerable in the future. ",
"There are many reasons why drought might become more likely. Here's an example. Many areas get their water from snow melt (e.g. the regions around the Himalaya). If you increase the temperature, that snow melts earlier and more suddenly. You get an earlier surge of water and naturally, it quickly runs out, leaving you deprived of water in the summer. You may also realise that, as paradoxical as it sounds, this also increases the chance of flooding as well as drought! On top of that, the ice sources that supply these people in the first place are getting smaller, decreasing the overall supply. According to the IPCC, a sixth of the world's population depends on melt water so this is quite a big problem. ",
"Increased greenhouse gas concentrations lead to higher temperatures which generally leads to more extreme weather and hence a higher overall risk of drought. So there is a relationship between increased CO2 levels and droughts, but it's not ",
" cause and effect."
] |
[
"Thanks kind stranger:)"
] |
[
"If greenhouse gases act as an insulator shouldn't it increase temperatures in hot areas, but also decrease temperatures in cold areas?"
] |
[
"Has anyone ever used EEG to monitor their own mental activity and adjusted their behavior in response?"
] |
[
false
] |
[deleted]
|
[
"Are you asking if this has been done, or are you asking for anecdotes/personal experience?"
] |
[
"Just google \"biofeedback EEG\".",
"If asking for anecdotes, this isn't really the subreddit for it."
] |
[
"It's called ",
"http://en.wikipedia.org/wiki/Neurofeedback",
" "
] |
[
"Why doesn't eating stimulate our gag reflex?"
] |
[
false
] |
How is it that our body stops us from retching every time we try to eat? And why do we still mostly puke when trying to eat things not identified as 'food'? Guess this is my first front page post. W00t.
|
[
"The medical name for the gag reflex is the Pharyngeal reflex, if you haven't read it yet the ",
"wikipedia page",
" has more information on it and ",
"swallowing",
". There doesn't seem to be anything conclusive on what triggers the different variations of the gag and swallowing reflexes tho.",
"One interesting thing I just learnt from that page is apparently ",
"1/3 people don't have a gag reflex",
" (and before you post that joke remember this is ",
"r/askscience",
"!)."
] |
[
"As for the second question, there is an area in the medulla called the area postrema that is responsible for detecting noxious substances and inducing vomiting through its connections to the nucleus and tractus solitarius. In addition, many poisonous substances have a bitter, unpleasant taste. For that reason we evolved our specialized \"bitter\" taste buds to provide early detection of possible poisons - nausea is a result; whether or not we vomit is up to the aforementioned area postrema.",
"Your first question is a little bit tougher for me to recall, since I haven't studied it in a while. I believe that swallowing is what's called a \"prepotent reflex.\" This means that it is essential for survival or avoiding harm, and is therefore given the ability to override other competing reflexes, in this case the gag reflex. Gagging is also the result of receptors mainly located in the posterior 1/3 of your mouth, behind the palatoglossal folds therefore in the oropharynx. The boundaries of the pharynx itself are usually only breached upon the actual act of swallowing, so you are at a lower risk of gagging. Note that you will still gag if you accidentally try to swallow something without chewing it, as the area is not prepared and in the act of swallowing."
] |
[
"Potentially stupid question: Is it dangerous to not have a gag reflex? Like, is one at a higher risk of choking on their underchewed food due to a lack of gag reflex?"
] |
[
"Is it easier to fly inward to the inner planet, closer to the sun, than outwards to the outer planets, away from the sun?"
] |
[
false
] |
On how presentation on how gravity works there's a bowling ball in the center of a trampoline and marbles are spun around the blowing ball moving inwards slowly. Would flying a space craft to the sun be like driving down hill and flying away be like driving up hill?
|
[
"It can actually be harder to fly to the inner planets than to the outer planets, at least for simple orbits.",
"The main problem is that there's no drag in space, and we are orbiting the Sun at 30 km/s. Escape velocity from the Solar System is about 42 km/s. So we only need another 12 km/s to move out from Earth to any outer planet in the Solar System.",
"But to fall inwards, we need to get rid of our current motion around the Sun. You need to slow down before you fall down, and that slowing down isn't \"free\". Depending on how close to the Sun you want to get, it could be up to almost the full 30 km/s, and cost a lot more than escaping the entire solar system!",
"You can use more complex orbits to make things cheaper, but it's definitely not the case that going to inner planets is automatically easier than going to outer planets."
] |
[
"Yup! A prime example of this is the Parker Solar Probe, launched in 2018 on the Delta 4 Heavy. It's a pretty small probe, but it needed the second biggest rocket we've got to give it enough push. Even that isn't enough to get the probe to the 8.5 solar diameter perihelion, so it is currently conducting a series of gravity assists with Venus to bleed off more energy and bring it down to the desired orbit.",
"Fun fact: when it's reached its final orbit, at perihelion it will be moving ~200km/s, making it the fastest manmade object in history!"
] |
[
"What if I point my rocket to always accelerate the probe towards the sun (along the probe to sun radial vector)? On second thought, I think once the rocket runs out of gas it the probe will just move along an elliptical orbit. It's been a while since I studied physics so I can't compute just how close the closest point on the orbit is to the sun."
] |
[
"Ethanol vs. neutral grain spirit?"
] |
[
false
] |
My lab needs non-denatured alcohol (but we don't need anhydrous). Unfortunately, we're also poor. Is there any reason whatsoever that we couldn't go down to the store and buy it 750 mL at a time in Everclear form? It looks cheaper than buying nondenatured ethanol from lab suppliers.
|
[
"Run it through a brita filter."
] |
[
"It's been a while since my ochem, but wouldn't charcoal absorb the alcohol (at least some of it)?"
] |
[
"I think it would absorb the by-products of fermentation more than it would absorb alcohol. Things like aromatic hydrocarbons, un-fermented sugars, etc that stayed in the bottle."
] |
[
"Energy Distortion of Space-Time Similar To Matter"
] |
[
false
] |
I get that things with Mass distort/bend/warp Space-Time. However, given that matter and energy are essentially interchangeable via Special Relativity (as I understand it), would a massive energy source like a gamma ray burst also distort Space-Time? Or am I completely missing something here. Not a Physicist, but rather a Neuroscientist that is fascinated by astrophysics.
|
[
"Energy isn't a thing, really. It's a number. And energy has two principle forms. Energy of \"restful existence\", mass, or energy of motion (in the form of momentum). A system of massless particles (like photons all traveling in different directions) may have a mass themselves. Any time you can find a \"rest\" frame for a system, and it has energy, then all that energy is, in a way, mass. ",
"It turns out when we want to calculate the curvature of space-time, we use not just mass-energy, but also motion-energy, ",
" other terms too. The whole thing is called a \"",
"stress-energy tensor (field)",
"\" and it includes stuff like pressure, and momentum flux, and shearing stress. "
] |
[
"Yeah. So this is in fact interesting and useful to us. For instance, we can choose a frame of reference in which the sun is at rest. And our orbit of that sun, at rest, is perfectly reasonable. ",
"But we can choose another frame of reference, where the sun is in motion, with some momentum. Now I ask you, do we orbit where the sun \"is\" or where it \"was\" 8 minutes ago? Since information can only travel at the speed of light, wouldn't the naive assumption be we're orbiting where the sun ",
"? And doesn't this conflict with our previous understanding, where the sun is at rest and we orbit where it ",
"? ",
"The answer is that the motion of the sun, its momentum, factors into the overall curvature equation that will govern our orbit. And it turns out, that equation will ",
" where the sun \"will have been\" (to abuse verb tensing) 8 minutes from 8 minutes ago. Ie, when we go to calculate where we orbit, it's as if we orbit the time-extrapolated position of the object, and all is right with the world (if we calculated its 8 minutes ago position, orbits would be unstable, so I'm told)."
] |
[
"To expand on shaveras answer; Yes, a massive gamma ray burst distorts space-time, as does a single photon. Also, a compressed spring distorts more than an uncompressed, as does a hot pot over cold, or a charged battery, or a strong magnet vs. weak. ",
"Also interesting to note that a large contribution to the mass of matter is the binding energy of the subatomic bits. "
] |
[
"How do scientists measure the mass of the earth?"
] |
[
false
] |
What method or formula do they use to calculate the total mass of the earth? Do They do one area and then use that as the baseline for the rest of the earth or what?
|
[
"We can measure the radius ",
" of Earth by various means. Then we can measure the gravitational force on an object at the surface by measuring the acceleration ",
" due to gravity. (Measuring ",
" is not as simple as it sounds since we have to account for the rotation of Earth and its effect on the effective acceleration if we want to get a value accurate beyond about 1 part in 1000.) The mass of Earth is then",
"M = gR",
"/G",
"We also need to have a good measurement of the gravitational constant ",
". Its value is so small though that it is surprisingly difficult to get an accurate measurement of it. See the ",
" for details of how to calculate it. For many purposes, however, the quantity ",
" = ",
" (which is called the standard gravitational parameter) is actually what is needed, and we can measure ",
" much more accurately than just ",
" (and hence ",
").",
"Once we get the mass of Earth, we can then use Kepler's third law to get first order estimates of the mass of the Moon (there are other ways to estimate its radius), the mass of the Sun, etc. But ultimately, measuring the mass of Earth is a matter of measuring ",
" and ",
".",
"So all of this gives a good estimate for the mass of Earth and is certainly how it was first calculated. Nowadays, the most accurate measurements of the mass of any planet in our solar system are calculated via accurate measurements of their positions and velocities using many satellite observations (",
"Wikipedia link here",
" and ",
"relevant journal paper here",
"). These position and velocity measurements are then fed into a complete n-body model of the solar system, from which the masses can be inferred."
] |
[
"The accuracy of G is interesting, and you can read about it ",
"here",
". Measurements of G actually vary periodically with the rotation rate of Earth (about a 6-year period). The relative error in these measurements is 1 part in 10,000 (so about 4 decimal places), so not really too accurate. Like I said, G is surprisingly difficult to measure. ",
" However, the product ",
" is known to much higher accuracy, something like 9 decimal places (instead of 4). Similarly, we can determine the ",
" of a planet's mass to Earth's mass very accurately also, since that is equivalent to calculating the ratio of ",
" for the two planets."
] |
[
"The Cavendish experiment he referred to earlier was done in 1798 and was 1% off (which gives you G and permits the calculations). The accuracy is pretty good. Here is an interesting read about how it's constantly changing: ",
"https://en.m.wikipedia.org/wiki/Earth_mass"
] |
[
"Is there a way to shift EM signal frequencies?"
] |
[
false
] |
Say can we shift IR to visible frequencies without receiving it on an IR sensor, reading it and reemitting it?
|
[
"Additionally to the non-linear effects that others mentioned in the thread small shifts in frequency can be realized by the use of ",
"acousto-optic modulator",
". It is very similar to optical non-linear interaction except one of the waves involved is made from phonons (so 'sound') instead of light."
] |
[
"I don't believe there is a simple way, but one method would be to take advantage of ",
"non-linear optics",
", where the polarisation response of a material is non-linear to the applied electric field. This causes additional frequencies to be generated which can be separated from the incident light.",
"A common example would be second harmonic generation. By getting the refractive index of the input beam and it's frequency doubled second harmonic to be the same (usually using a birefringent crystal), the generated second harmonic interferes constructively with itself and builds up.",
"Second harmonic generation is a special example of Sum-frequency generation, where two photons of different frequencies can be combined to make a third, whose frequency is the sum of the other two. Using something like an ",
"Optical parametric oscillator",
", you can take advantage of these effects to tune the output of a laser to a wide range of frequencies.",
"Non-linear effects are only really noticeable at extremely high intensities unless components such as micro-cavities are used so it's not very practical for most applications."
] |
[
"without receiving it on an IR sensor, reading it and reemitting it?",
"It depends how abstract you mean by \"sensor\" and \"re-emission\". It's impossible to shift frequency without inputting or extracting energy, doing so would violate conservation of energy and momentum. However, one can have \"passive\" \"sensing and remission\" with no humans involved. Others have mentioned some fancy technology, but I'd put forward something provided by nature: Fluorescence.",
"Something like UV goes in, visible comes out. It's from a certain perspective a \"passive photon down stepper\"."
] |
[
"Is \"Common Ancestor\" a Literal Concept of a Single Animal?"
] |
[
false
] |
We often see reference to our "common ancestor", particularly in genealogical "we're all related" type arguments, but it seems to me that life did not begin with a single organism and, esp., that evolutionary changes leading to populations created by sexual reproduction are not singular - i.e. there may have been 10 or 10000 "first humans" with different DNA and their bloodlines are not absolutely certain to have crossed in everyone - so is the popular concept of "a common ancestor" accurate?
|
[
"In evolutionary terms \"common ancestor\" is not used to represent an individual. The term defines a species from which two other species diverged. In the classical evolutionary tree schematic used to represent evolutionary history, a common ancestor is a point at which a branch forks. "
] |
[
"Two people can trace their respective lineages back to a single common ancestor, which will be another person. This is limited by how well the two family lines have kept records. Two species can be traced back to their common ancestral species. This is most accurately accomplished through analysis of genetic similarity."
] |
[
"It makes more sense to think of a common ancestral population rather than individual. It is always a population issue, not just an individual."
] |
[
"Most people I know rave about naps, but they make me feel sick -- why?"
] |
[
false
] |
When I take a nap I always make sure I have at least 2 hours free with no disturbances because if I'm woken up before then (even if it is just 10 - 30 minutes) I feel nauseated, dizzy, and sort of heavy. I only get the "heavy" sensation if I nap. If I manage to get at least a 2 hour nap and wake up naturally from it, I still have some version of the heavy feeling (usually mild), but not the stomachache/dizziness. I never really feel refreshed no matter the length of nap I take, but longer ones are better than short ones. Any idea why this happens? It seems like I'm missing out. I'll add that being woken before 2 hours always seems to be accompanied by hot flashes which add to the sick feeling. I don't get the hot flashes if I'm left to wake up naturally (which is also always about 2 hours). The ill feeling I get is a lot like a hangover with hot flashes.
|
[
"Are you taking these naps within 8 hours of your regular bedtime or once it is dark? If so I would suggest taking them earlier in the day. Try to not go over 45 minutes of sleep as that will usually put you into another sleep cycle which is correlated with that upset feeling "
] |
[
"Not an answer to \"Why?\" but this may help. I get that sickly heavy feeling after a nap too. I have found that drinking a large glass of water as soon as I wake up helps immensely. "
] |
[
"Not an expert, but between trying out ",
"polyphasic sleep",
" and ",
"lucid dreaming",
", I have some half-remembered tidbits that may apply.",
"From what I recall, waking up during deep sleep (that is, ",
"N3 phase sleep",
") is generally correlated with grogginess and unsatisfying sleep. If you look at the hypnogram on the Wikipedia page I just linked, or ",
"this one from the NIH",
", you'll see that being in N3 20 minutes after falling asleep isn't out of the question. Likewise, those graphs show REM periods (which are not so unusual to wake up during; when you wake up from a dream, it's probably from REM sleep) at about 90 minutes, but it's not unreasonable to think that someone with a slightly different circadian rhythm might be in one at 2 hours.",
"Also relevant is the time at which the nap is taken: just after lunch is perfect, with the combined effect of the ",
"\"post-lunch dip\"",
" caused by our circadian rhythms and the ",
"postprandial dip",
" from eating lunch; after about 2:00, though, your circadian rhythm swings back towards restoring wakefulness and trying to take a nap would be fighting your body, leading to less satisfying sleep."
] |
[
"How far under the ocean does the water extend? Or better yet, how far under the ocean before the ground is dry again?"
] |
[
false
] |
I know under ground there are water tables, is it the same under the ocean? do they extend deep? how far down under say the pacific ocean floor would you have to go before you were at dryness again?
|
[
"The oceanic lithosphere (crust and part of the upper mantle) has a layered structure that comprises of various igneous rock which are crystalline and impermeable in varying structures (massive peridotites, dolomitic dykes, pillow basalts etc). On top of these there is a layer of sediment that varies in thickness depending on the age of the crust, which is in turn reliant on the type of ocean. (for example the pacific is a closing ocean and features far older crust than the atlantic which is currently opening. So near or at a spreading centre the thickness of sediment will be extremely small or non-existent leading to the impermeable basalt being on the ocean floor and as a result for it to become \"dry\" again merely venturing below the ocean floor would be required.",
"However further away from spreading centres thicker and varying sediment makes the question more complicated. This is because the water would penetrate the sediment to a certain extent, but how much would depend on a number of factors foremost of which being the type of sediment. The limiting factor on the penetration would be when the dewatering effect would take place, this is when the pressure would result in water being \"squeezed\" out of the sediment, and as a result it would be dry again."
] |
[
"Correct the atlantic ocean is slowing becoming larger while the pacific is becoming smaller."
] |
[
"What do you mean by closing and opening oceans? The continents are moving closer or farther apart? "
] |
[
"How will interstellar spacecraft deal with the extremely cold temperatures?"
] |
[
false
] |
We know that space is cold. Temperatures on Uranus have been measured as low as -224 degrees Celsius; and Uranus is still relatively close to the sun. During interstellar travel, there will be no stars nearby, so it will likely be even colder than on Uranus. How can we build a spaceship to withstand this extreme cold?
|
[
"Space is very cold indeed! However, it's also an excellent insulator, as there is nothing to conduct heat away. The only way to lose heat is by radiating it as photons. There's an equation that can tell you how much power you would radiate as a function of temperature and emissivity, the Stefan-Boltzmann law. You can ",
"try it out on wolfram alpha",
". You can find values for emissivity ",
"here",
" or ",
"here",
". ",
"A human being produces about 100W of power. If you were to put a human being in a space ship with 6 m",
" surface area made of polished aluminium (emissivity 0.04), even in deep space, the temperature would settle at around 20°C -- this is the temperature where 6 m",
" of polished aluminium emit 100W of black body radiation. However, that's without any additional power being used whatsoever. In reality, you'll have engines and computers and so on all producing heat, so you probably won't have to use highly polished metal to stay warm. In fact, you may want to create some surfaces on your space ship to radiate away some of that heat... because if our 100W human were to turn on a 100W computer, the temperature would stabilise at 75°C!"
] |
[
"That is absolutely amazing. I never considered that the void of space would effectively be an insulator, sort of like a vacuum carafe. :)"
] |
[
"If I remember correctly, they had significant problems with lack of power, so they turned everything off. However, the ship was still the same size as before, and therefore radiating as much energy as before. ",
"The ship was designed with all the heat-producing tech in mind. It had external heat radiators to remove heat for that reason. With so much less heat produced than the ship was designed for, everything got very cold.",
"[edit] I should probably add that I am not an expert on the apollo missions. "
] |
[
"Can earthquakes be predicted?"
] |
[
false
] |
So can they?
|
[
"In short, no, and the feasibility of someday developing prediction capabilities depends on your definition of \"predict\". Will we be able to say \"a magnitude 5.2 earthquake will occur at this location, at this time\", no. What we're working towards and have the beginnings of is more like weather forecasts, but these are on much longer timescales than a weather forecast. So just like a weather forecast doesn't \"predict\" exactly what rain distributions will look like or the exact temperature at each time of the day throughout a region, earthquake forecasts are more general and usually given as something like the probability that in some given time frame (e.g. 50 years) a particular area will experience ground shaking that exceeds some magnitude. That's the short version, let's break down the things that contribute to that answer.",
"So, why can't we predict earthquakes. In my mind, the big contributing factors are that fault systems are inherently complicated, we have incomplete or short records of prior earthquake events on those fault systems, and we have incomplete understanding of the mechanics of earthquakes and boundary conditions acting on particular faults. ",
" mean that an earthquake on one fault can load or unload a neighboring fault and that the exact location, magnitude and direction (earthquake ruptures have directionality along fault planes and this is a huge influence on the pattern of strain release associated with an earthquake) of that earthquake will change these patterns of loading and unloading on nearby faults. ",
" Instrumental records (measured by seismometer) only go back ~100 years, then there are historical records which give you a sense of large events, but without the accuracy of instrumental records and requires that people were in a location and writing things down about earthquakes in enough detail to be useful. Paleoseismology, which reconstructs past records of earthquake through examination of the stratigraphic record within fault zones, can significantly extend our record of earthquakes, but from these records we often are not sure of the magnitude of the event observed or other aspects of the event we'd like to know (direction, did it activate other faults, etc). ",
" Finally, to really predict earthquakes, or even forecast them as well as meteorologists are able to forecast weather, we need robust and predictive models of earthquakes. These models require all of the information above (where are the faults, how do they connect, where were past earthquakes, what were the details of those ruptures, etc) so the uncertainties and gaps in our knowledge of those propagate into the models. Additionally, we don't have key data like the detailed fault geometry (i.e. roughness), frictional properties along all fault planes of interest or the detailed state of stress of the crust within the models. If you think about it from the weather model analog, with that, we have the advantage of short time scales. We can run some simulations, produce a forecast, see whether that forecast was right in a few days and improve the simulation. With the earthquake models, if we're concerned primarily with large earthquakes, we can run a simulation, produce a forecast, and then wait 20-100 years to see if we're right. This long time scale makes model validation hard, to put it mildly.",
"However, all of these datasets are improving. As we grow our instrumental record we develop more complete understanding of how particular fault systems behave. Similarly, the more paleoseismological datasets we develop and as we expand the range of techniques applied to these, we build a more complete long term record of earthquakes. Our models of rupture on faults is also improving rapidly, but at the end of the day, there will also be uncertainties in all of these data which will impact our ability to \"predict\" an earthquake. Our forecasts will improve, but it may take a couple of seismic cycles (time between two major earthquakes on a particular fault/fault system) do really validate particular forecasts. The problem is that depending on the fault, the length of a seismic cycle ranges from decades to thousands of years."
] |
[
"Short answer: No",
"Slightly longer answer: No, not to the extent that you could put a time frame on it that would be of much use. If enough data exists you could maybe put a range that would normally cover periods in which they could happen. However they could be delayed or sooner than you expected. There is not enough know about the mechanics or data to accurately predict them. "
] |
[
"No.",
"The ",
"2008 Sichuan",
" huge earthquake (M 7.9) started as a limited earthquake with the apparent potential to reach perhaps around M7. The rupture propagated towards the north-east and overcame 4 barriers, one after the other. In two segments, slip exceeded 10 meters. It eventually travelled for 200 km until the end of the fault yielding a total energy tens of times the energy expected from the initial rupture.",
"How could one predict that an earthquake would produce 10m of slip more than 200 km away? How can one be sure that it will overcome this barrier but not the next one?",
"Intermediate-term forecasting of earthquakes is promising but still very far from being called \"prediction\". One of the many successful cases was the forecasting of earthquakes in Northern Aegean area: with the use of the Coulomb Stress Transfer model, and based on the accumulated knowledge on the fault geometries, earthquake mechanisms and kinematics of the region, a ",
"2001 paper",
" identified 3 areas with a potential for a big earthquake (M >= 6) within a 20-year period. That very year a 6.4 earthquake took place exactly where it was forecasted. Last year a 6.8 earthquake took place in another predicted area, and a 3rd area has not yet produced anything.",
"Ok, now one would say \"So we can predict earthquakes, nah?\". Wrong. This is nothing more than ",
" model. The scientific community uses it to make forecasts, then waits for the results, then assesses ",
". This particular model has shown promising results in ",
" areas in ",
" cases. But other models, which have shown promising results where the Coulomb Stress Transfer model failed, they failed elsewhere. Even for intermediate-term forecasting, the scientists cannot claim that they made a forecast, unless if they used multiple models and if they all tended to the same basic results.",
"Now, consider the scenario for a prediction. Say that one day they say \"A magnitude 6 earthquake will take place around X,Y coordinates around Z of the month\". What if the depth is 10 km deeper than predicted? What if the rupture starts from the west and propagates towards the east, contrary to the prediction? What if an alarming foreshock takes place? What if it hits in the night? What if it takes place in 2 waves, or a nearby parallel fault is activated instead? These small details have a ",
" impact on hazard.",
"Personally I believe that prediction will never become a reality. Intermediate-term forecasting is very promising and can be of use by the authorities. However, in Greece where I live, once an earthquake happens, seismologists tend to make contradictory claims. One of the best seismologists said after an earthquake \"We expected it\". This was a bad statement: 2 of the several models available agreed that an earthquake was expected there, but the rest of the models gave no indications. It is not smart to serve such thoughts to the public. It is smart to use whatever models you want and reach to whatever conclusions you want, but when talking to the public you have to be clear. A scientist often pursues his biases, tries to reach some results he wants, and this is good because it is a motivation. But when talking to the public as a scientist you have to talk on behalf of the whole domain, because the public has no interest in hearing your personal thoughts, but rather the product of the consensus of the scientific field as a whole."
] |
[
"How does Saran Wrap work? Why is it that it sticks together? How does it not melt in a microwave?"
] |
[
false
] | null |
[
"Any polar molecule will heat up in the microwave. Not just water."
] |
[
"Any polar molecule will heat up in the microwave. Not just water."
] |
[
"Saran Wrap is Low Density Polyethylene (polyethylene is the most common type of plastic), which, because of the way the monomers chain together, is highly ductile and malleable (very strechy). This is obviously desirable when making something that is going to be, well, ",
" over something else. As for the sticky part, many brands of food wrap add adhesive (glue) to the wrap, but polyethylene does have natural adhesive properties.",
"Saran wrap does not melt in a microwave because it is entirely non-polar, and so it can't easily absorb the microwave energy."
] |
[
"Why are we able to make vaccines for some viruses but not others?"
] |
[
false
] |
[deleted]
|
[
"Simply put, ",
"some viruses just change too fast",
". If a virus mutates enough, your immune system won't recognize it even if you've been previously infected with an older variety / inoculated with an older variety. HIV is notorious for mutating super quickly, which is why a successful HIV vaccine was never made. This is also why flu shots are annual -- the seasonal flu is different enough every year that even if you've had it before, your body won't recognize it a year later.",
"In other cases, viruses may not have vaccines because of who they effect -- vaccines for viruses that singularly affect more impoverished nations for example often do not get funded because pharmaceutical companies will not get as much of a return on their research investment."
] |
[
"Is the seasonal flu just the same flu that keeps evolving? Or does a new virus emerge?"
] |
[
"The most correct answer to this question is that seasonal flus are the same set of viruses, but primarily H3N2, that change slightly every year. Generally speaking the change from year to year is subtle enough that the viruses can still be considered the same species/strain (viruses are weird and so is their terminology). When larger mutations occur through a process called ",
"antigenic shift",
" you can get pandemic flus like swine flu, and these are considered to be distinct varieties."
] |
[
"How do mammals deal with placenta and the umbilical cord?"
] |
[
false
] |
With humans, if the placenta is left in the woman it can cause harm so it is removed. However, animals can't do this. Similarly, whilst not life-threatening, the umbilical cord can still be a danger if left unattended.
|
[
"Pregnant/postpartum mammals can, and do, die because of retained placentas/products of conception, as well as incomplete miscarriages/retained fetal tissues after a miscarriage, and complications during birth. ",
"And neonatal animals can, and do, die due to umbilical infections. ",
"Wild pregnant mammals cannot do anything about retained placentas or other complications related to pregnancy and birth, but they, for the most part, are attentive to their young, and mammal milk provides some protection, so umbilical infections are rare. If pregnancy or birth complications arise, nature takes course, and either the mother survives or dies. Same with neonatal mammals presenting with umbilical infections. They either recover, or die."
] |
[
"If he really wanted to go natural, he would have chewed thru the cord with his teeth and offered the placenta to his wife raw as a way to replenish her strength after the ordeal of childbirth"
] |
[
"Depends on the animal, but generally contractions continue until everything is out. The physiology is also a bit different here. Dogs for example have uterine \"horns\" so you basically have 2 tubes of puppies. Each fetus is in an individual sac with the amniotic fluid and placenta, so the placenta comes out with each puppy. Ideally the dog bites through the sac to eat the placenta and free the puppy, then cleans it before the next is born in the 30-60 min. The placenta is very calcium rich and stimulates further contractions. If one or more of the puppies do not descend they either are absorbed or can turn into an infection."
] |
[
"Whats the relation of entropy in physics and entropy in information theory?"
] |
[
false
] |
In thermodynamics entropy seems to be a measurement of stored enery per volume(or mass? or per system?) and in infromation theroy entropy is a measurement of information density. Both formulas seem to be very similar(an intergal/sum of all posible states) but ive never bee able to make the connection in meaning. Thermodynamic enropy incrases over time, can the same be said about informational entropy or is there an analogy in information theory for this increase?
|
[
"In thermodynamics entropy seems to be a measurement of stored enery per volume(or mass? or per system?) and in infromation theroy entropy is a measurement of information density. Both formulas seem to be very similar(an intergal/sum of all posible states) but ive never bee able to make the connection in meaning.",
"Hmm ... so, I worry this might come off a little disrespectful and I do apologize if it comes off that way ... but I think perhaps you are struggling to make a connection in meaning because your understanding of both thermodynamic and information entropy seems to be very wrong to begin with. :p",
"So, thermodynamic entropy is not a measure of energy density at all -- it is a measure of the \"degeneracy of a system's microstates.\" I'll try to explain what this means via a simple example.",
"A thermodynamic system can be assigned a set of \"microstates\" and \"macrostates\" -- microstates correspond to a set of assignments for every microscopic variable in a system, such as the position or momentum of every particle. Naturally, when you have a large number of particles, there are a huge number of these variables. Each possible assignment is a microstate, so the number of microstates available to a typical system is tremendous.",
"But you don't need to know all of these variables to understand how a system will behave thermodynamically. Instead you only need a few macroscopic variables that represent some sort of average or aggregate properties -- variables such as temperature and density. The possible sets of assignments for these macroscopic variables are the system's \"macrostates,\" and they are far fewer in number than the system's microstates.",
"Now, every microstate corresponds to some macrostate, but because there are so many more microstates than macrostates, by the pigeonhole principle at least some macrostates will have more than one microstate, making it \"degenerate\" (overloaded), and some macrostates will have more corresponding microstates than other macrostates.",
"Entropy, then, is a measure of \"how many microstates correspond to a given macrostate.\" Macrostates that have ",
" corresponding microstates have a higher entropy.",
"So here's the simple example: consider a set of two dice being rolled as part of a game. The microstates will be the individual face values rolled for each set of dice. So two six-sided dice have 6",
" = 36 possible microstates corresponding to the permutations of the possible dice values: {(1, 1), (1, 2), (2, 1), (3, 1), (3, 2) ... (6, 6)}.",
"But in a typical game, we don't care about the individual die values, we only care about the sum -- only the sum matters for deciding the future of the game. So there are 11 possible sums of two dice: {2, 3, 4 ... 12}. These are our macrostates, that determine the game's \"thermodynamic time-evolution\" so-to-speak.",
"We can then see how each microstate (pair of die values) corresponds to some macrostate. (1, 1) => 2, and (2, 1) => 3, etc.",
"But, because of how dice add up, the distribution of microstates to macrostates is not equal among all the macrostates. For example, the sums 2 and 12 only have a single corresponsing microstate: (1, 1) and (6, 6) respectively. But the sum 7 has as many as six corresponding microstates: (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), and (6, 1).",
"So, we say that the macrostate 7 has a higher entropy than the macrostates 2 and 12. If we were to roll the dice, we would expect our system to spend more of its time in the higher-entropy macrostates than the others.",
"Now, there's a lot that this example doesn't cover properly, but that's the gist of the idea. That's what entropy is really a measure of: the degeneracy of microstates for a macrostate. Because for real thermodynamic systems the number of microscopic variables is so tremendous, statistically a system in a lower-entropy state can almost always be expected to evolve into a higher-entropy state, and almost never vice-versa. Since the second law of thermodynamics is a ",
" law that only holds on average, there are counterexamples where it is possible for a system to spontaneously enter a low-entropy macrostate, but it will generally be fleeting and extremely rare.",
"Now then, lets look at information entropy. Just like how thermodynamic entropy is ",
" a measure of energy density, information entropy is ",
" a measure of information density. It's a measure of \"missing information\" that is needed to reconstruct a microstate from a macrostate.",
"Let's look again at our dice example. If we roll a sum of 2, how much information is missing that we need to know what microstate (individual die values) we rolled? Well ... none, right? We know the only possible microstate was (1, 1), so we don't need any missing information. This is basically the lowest possible information entropy (0 bits). But if we rolled a 7 instead, there are six possible microstates, so how many bits would we need to identify which of the six microstates we rolled? We could do a binary search of the set of microstates, where each bit tells us whether to look in the top half of the set or the bottom half. If we kept repeating this for the next bit in the selected half, eventually we would need 3 bits in total to uniquely identify all 6 microstates. ",
"For example, say we rolled a (5, 2). Out of our full set of microstates, the first bit tells us whether the first die was between 1-3 or 4-6, so we'd need to know the first bit is a 1 and not a 0. Then our next bit might tell us whether our microstate was in the sets {(4, 3)} or {(5, 2), (6, 1)} so we'd need to know the second bit is a 1. And then our last bit would tell us whether it was (5, 2) or (6, 1), so our last bit would be a 0, and all three bits together would be the bit string 110.",
"In general, the number of bits of missing information that you'd need scales with the ",
" of the number of microstates corresponding to a macrostate. In our simple example, we had 6 microstates for the macrostate 7, so we need log_2(6) ~= 2.58 bits (or in practice at least 3 bits).",
"And that's where the logarithmic relationship between ",
" the number of microstates and information entropy comes from! (Edited for correctness -- thanks to ",
"/u/un_om_de_cal",
" for catching the mistake!)",
"Hope that helps,"
] |
[
"This was an excellent explanation, thank you very much."
] |
[
"Sort of. It is often described as the amount of disorder in a system, or a measure of how unavailable internal energy of the system is for doing work with, but these sorts of definitions are only approximate or subjective (for example I can think of systems that appear very ordered and predictable which are very high in entropy, and ones which are very chaotic and unpredictable but very low in entropy).",
"Thermodynamics emerges as a limit out of the statistical mechanics of quantum particles, so any really good definition of entropy is going to reflect in some capacity how the microscopic details translate over to macroscopic notions of entropy.",
"Hope that helps,"
] |
[
"Could we breed animals to make them more intelligent?"
] |
[
false
] |
There are certain tasks that animals perform that they could do better if they were smarter. One that comes to mind is service dogs and other service animals. Could we breed them to reach fairly high levels of intelligence? What might the upper reaches of this be? Which useful animals would be the best candidates? What ethical issues might come up?
|
[
"With the dog example we've been breeding them for thousands of years already with goals in mind and you now have breeds which are specialized to do different tasks but it would be hard to argue that some are more intelligent than others. If you try to rank them based on what task they do we'd probably encounter the anthropomorphic issue where we project what we perceive to be the hardest task donating more intelligence but that's just the way we think about the tasks. This also extends to pretty much all animal studies and is a common problem in the field of animal intelligence that how well an animal does something doesn't necessarily mean it's more or less intelligent. ",
"For example you could try and selectively breed chimps based on how well they pick up sign language (language is commonly seen as an intelligent feature) but you could easily be selecting the chimps based on how good they are at associative learning as apposed to how well they actually understand the sign language. So you could breed chimps to pick it up quicker but not necessarily understand it any better. It's a tough question but the idea is possible that you can breed for intelligence, we're finding human genes that are defiantly linked to intelligence so you could select for those genes but that's a world of ethical committees and a withdrawal of your funding Haha, and we're just not certain of those genes in other animals yet necessarily so if we understand more about the genetic makeup of intelligence them potentially in the future we could breed animals to be more intelligent based on their genetics as apposed to their ability to accomplish tasks. "
] |
[
"Within the field of behavioral research what denotes intelligence is still up for debate so yes we can't use our current definitions on animals or at least we can't use one and apply it to them all. On the flip side there's obviously features which most people would agree denotes a higher level of intelligence such as ability to live in social groups and how they interact with each other in those groups I.e theory of mind ways of measuring intelligence or at least how aware a species is of their actions. ",
"And you're of course right that there's a breadth of intelligence within a species, most easily seen in humans, it's very much a quantitative trait with many factors influencing it. And for humans id say it's easier to know what we would select for as we've many tests for cognitive ability, just that it becomes a lot harder to know what to select for in animals. "
] |
[
"Yes, there is a range in the intelligence both within humans and within animal species. Whenever there is already variation in a population for selection to act on you can make relatively quick changes to a population with strong selection. But that doesnt mean being able to have a dog be able to do maths over a short period of time, but you could breed them to solve puzzles or perform other tasks that require intelligence more quickly. There isn't really an upper reach, humans and dogs evolved from the same common ancestor after all. Theoretically you could breed dogs that can speak english and do maths if you bred and selected them for long enough, but that would take probably millions of generations.",
"There is some work done to breed working dogs like service dogs and police dogs to be better at their jobs. However intelligence isnt the most important trait in animals like guide dogs. Being easily trainable is important and that why labs are the most common guide dog, not because they are the smartest breed, but because they love food and thus are easy to train with food rewards. Also important for service animals is having the right temperament for the job. "
] |
[
"Pounds weight or mass?"
] |
[
false
] | null |
[
"It's both. Most of the time, without qualification, pound means mass. To distinguish you can say pound-mass or pound-force. 1 pound-force is the weight of one pound-mass. "
] |
[
"Thank you."
] |
[
"Hi leogorg thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"How do I know which color space is linear or non-linear ?"
] |
[
false
] |
The title says it all. How do I know which color space is linear or non linear ? Any recommendation (journal/paper) would be appreciated.
|
[
"The spec of the color space will define this somewhere. Usually with something called a \"transfer function\". The definition of \"transfer function\" is \"a mathematical function relating the output or response of a system such as a filter circuit to the input or stimulus.\", which is a fairly succinct description of it. A linear color space is one which has a linear transfer function. That is, at any power level, 2x luminance in results in 2x luminance out.",
"Most color spaces do not have a linear transfer function, as a non-linear one is often useful for display devices, as our eyes are not terribly linear. With a linear space, half your available values end up storing the highest \"stop\" that you can store. In other words, if 1.0 = 0EV, 0.5 = -1EV, and 0.25 = -2EV. A non-linear space pushes up values to better make use of the available bits. For example, in sRGB, -1EV is not 0.5, it's ~0.735. -2EV is approximately 0.537.",
"So essentially, for any given space, you'll need to dig up a specification document and find what the transfer function actually is. There's some info on the sRGB and rec709 transfer functions here: ",
"https://www.image-engineering.de/library/technotes/714-color-spaces-rec-709-vs-srgb",
".",
"Note that actual implementations get weirder. For example, DCI-P3 has its own transfer function. However, to simplify their implementation, Apple didn't use it for their P3 displays. They used the DCI-P3 chromaticities, but kept the sRGB transfer function and called the frankencolorspace \"Display P3\". Also, in graphics editing it's common to strip off/ignore the transfer function to treat all color spaces as linear, as this makes a lot of color blending math work better. So you'll see \"linear sRGB\" come up a lot in computer graphics, for example. ",
"Or to give another example, Lightroom internally uses a linear version of ProPhoto RGB, except for the viewer where it swaps in the sRGB transfer function.",
" Having fun yet?"
] |
[
"Depends on your definition of \"fun\". Thanks a lot !! also for articles recommendation. Actually, I'm working on image processing (in RGB) and trying to do color conversion for color deficiency, I'm yet to decide which colorspace will be the best option to go with so I do the conversion to all colorspaces and see the result. What I want to find out is among colorspaces : CIE, HSV/HSL, also LMS (? which represent 3 cones in human eyes) which one is linear ?? Because next I will have to do some calculation and I think it will be better and easier if I use linear colorspace."
] |
[
"What's the question behind the question? What are you actually doing? Basically whether or not a color space is non linear is just part of the definition of the color space. So it seems like there's a broader question here about \"how do I figure out what sort of color space some particular image is in?\" or \"how do I figure out general attributes of a given color space?\" or something like that."
] |
[
"Lunar Architecture"
] |
[
false
] |
Given the reduced gravity on the moon, just how high could you build a building? Also, is the gravity sufficient to make a fall fatal?
|
[
"Given enough time, any gravitational pull will accelerate you to speeds that would be fatal. Weaker gravity only changes how high you'd have to be for a fall to be fatal, not whether a fatal fall is possible at all."
] |
[
"To expand and clarify, this is true only in a vacuum. If terminal velocity is limited by an atmosphere it is possible that you could fall from any height (within the atmosphere) and survive. ",
"For example, a fall on titan would probably not be fatal from any height, provided you are protected from the cold and the atmospheric gasses."
] |
[
"Thank-you!"
] |
[
"Please stop saying \"This is Probably a stupid question\" or \"I know I am dumb, but...\" Ask your question, we will be nice and answer it. The objective of this sub-reddit is to have questions you do not know the answer to answered."
] |
[
false
] |
[deleted]
|
[
"eh, I just think it's easy enough for people reading to ignore the statement. If it helps people overcome their fear of asking a question, then ask away. But this is just, like, my opinion man."
] |
[
"This should be on the side bar or across the top!"
] |
[
"Submit: Any self-post which asks a question for which it is appropriate that Science attempts to find a satisfactory answer.",
"This is probably a stupid comment, but you didn't ask a question."
] |
[
"Question about learning about history of science..."
] |
[
false
] |
Hi everyone. I know this isn't strictly a science question, but lately I've found myself really interested in the history of science. Specifically from the scientific revolution to the Victorian era. I have a few books and I'm trying to find online courses and blogs on this subject. Can anybody here interested in the same subject matter share his or her resources? Pretty please?
|
[
"The Discoverers by Daniel Boorstin."
] |
[
"More on the \"human-interest\" side of things (i.e., not so much focus on the science itself), but nonetheless a good read (full of wonderful observations and interesting details) would be \"The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science\" by Richard Holmes. "
] |
[
"Thank you very much; this is right up my alley. It's downloading onto my kindle right now :)"
] |
[
"Would a wide mouth container fill faster than a narrow mouthed one when put out in the rain?"
] |
[
false
] | null |
[
"The rate of rain entering the container is dependent on the surface area of the opening, the rate at which the vessel fills is dependent on the incoming rate and the volume of the vessel. Everything else being equal the wider the mouth the better."
] |
[
"So if both vessels are say, 1m deep, the wider mouthed vessels fills up slower (on account of having a larger vol)? But doesn't it have a larger incoming rate due to the wider mouth and therefore larger area? Both vessels are in the rain so receive equal amounts. "
] |
[
"I think my previous post might be confusing because I wasn't talking about perfect cylinders, but things that could have wider or smaller openings than the rest of the container. What I meant by my last sentence is that if you have two different 1 L vessels but each has a different mouth size the bigger mouth fills faster. For a series of vessels that are all prefect cylinders, where the opening cross section is maintained for the whole height, then the rate of filling will be identical across all cylinders.",
"TL;DR: For perfect cylinders they fill at the same rate (in water height per unit time). For equal volumes with variable mouth sizes the bigger mouth fills faster."
] |
[
"Why do your eyes get puffy after waking up? What is going on near your eyes that causes this?"
] |
[
false
] | null |
[
"Sources?"
] |
[
"oh wow; that makes sense\nthank you :)"
] |
[
"When you sleep you lie down, this causes blood to move towards your head easier than it would while standing or sitting. This can cause puffy eyes and black eyes etc.",
"Try using extra pillows, my wife did this and it helped her black eyes."
] |
[
"How can we determine the curvature of the Universe while being inside of it?"
] |
[
false
] |
To describe the curvature of the Universe, wouldn't we need an external reference frame to compare with or something? That is, , I can only tell it is poorly drawn because of the regular, external pixel grid that supports it. Now if the pixel grid had the same shape as the triangle, I wouldn't be able to tell if the triangle really is poorly drawn. Another example would be . Now, , nothing has changed inside of my 2D Universe: distances and triangles are the same, and the observer wouldn't notice anything different ; yet the Universe has curvature now, but in an external reference frame. My point is, how can we tell if the Universe has curvature or not, if we happen to be in a Universe similar to my sheet of paper? observing that the Universe is flat does not disprove it has curvature elsewhere. There are surely numerous properties I'm missing in my oversimplified model of Universe. I also feel that I'm not talking about the usual curvature.
|
[
"You are confusing ",
" curvature and ",
" curvature. It is the latter that is always meant by the unmodified word \"curvature\" unless otherwise specified.",
"Extrinsic curvature is the curvature of a manifold when considered embedded in some other manifold. So a circle has positive curvature when considered as a 1-dimensional submanifold embedded in a 2-dimensional plane. Intrinsic curvature is the curvature of the manifold itself, which can be defined and calculated without that manifold being embedded in any other manifold. A circle, considered on its own not embedded in some other space, is a 1-dimensional manifold with zero curvature. (Actually, all 1-dimensional manifolds have zero curvature.)",
"So extrinsic curvature depends very much on the embedding space (although it's usually taken to be Euclidean), and intrinsic curvature depends only on the manifold itself.",
"In your example, the piece of paper is a flat plane, and so has zero curvature. If you curl it into a cylinder, it still has zero curvature. (If you consider the paper as embedded in Euclidean ambient 3-dimensional space, then the flat piece of paper has zero extrinsic curvature and the cylinder has non-zero extrinsic curvature.)",
"Intrinsic curvature is described by the ",
", which is a rank-4 tensor. A matrix is rank-2 because you need 2 indices to write the entries. So a rank-4 tensor needs 4 indices. To understand what the components mean, you transport a vector along a small infintesimal loop based at a fixed point. Depending on the direction of the path, when the vector comes back to the starting point, it may not be parallel to the original vector. (",
"See this image.",
") The components of the Riemann tensor essentially tell you how much a vector will deviate from its original when transported around a small loop.",
"So, in principle, someone living in a curved manifold can measure the local curvature by measuring how vectors transport around loops. There are other more physical characterizations of the curvature tensor though. It also measures how ",
" (the analogs of straight lines in curved manifolds) deviate from each other. That is, suppose two nearby geodesics are parallel to each other. If you follow the geodesics, they will eventually deviate and no longer remain parallel. This deviation is described by the curvature tensor. Physically, this geodesic deviation manifests itself as tidal acceleration, i.e., nearby free particles will be measured to accelerate relative to each other.",
"Okay, having said all that, how do we measure the curvature of the universe? In the current cosmological models, the spatial universe is isotropic and homogeneous (it looks the same at all points and in all directions). At any fixed time, the universe is some 3-dimensional manifold of constant curvature ",
". This curvature does not change over time. So how can we measure ",
"? Well, in principle, if we ",
" consider large enough loops or geodesics over a long enough time, we could measure ",
" via the failure of parallel transport or geodesic deviation. But that's not actually feasible. I think there are some experiments you can propose that could measure ",
", but most of them require many decades and a lot of money and some ideal conditions. (For instance, you could set up a relay of satellites and lasers to measure the angles of a large enough geodesic triangle and use a theorem that relates the sum of the angles to the ",
".)",
"Instead, we actually compare current CMB data with modeled CMB data or we compare luminosities with modeled luminosities. (Both the characteristic scale of the CMB anisotropies and the luminosity depend on the spatial curvature ",
".) ",
"This is a talk by Laurence Krauss",
" that explains how this actually done in more detail."
] |
[
"Thank you for this complete answer."
] |
[
"Thank you very much, this makes a lot more sense. Excellent breakdown."
] |
[
"Why does it take longer to recall certain memories?"
] |
[
false
] |
Does it have to do with how the memories are stored? Is there a priority system to the recollection?
|
[
"Memory research is such a hot topic in Psychology/Neuroscience right now. There's so much research out there because it's so easily testable. ",
"There's 3 stages of memory, encoding, storage and retrieval and changes in any of these stages will affect how a memory is stored and subsequently how it is recalled. For normal people (ie: people without lesions in their brains), the encoding phase is, I think, usually the most important in memory consolidation. ",
"There is a theory that elaborative rehearsal will aid memory. For example, when you see a stimulus, you can shallowly process it (ie: just look at it) or you can make more connections with other systems in your brain (ie: I saw this yesterday too or this other time, it was blue etc...). Elaborative rehearsal will always help encode memories better. This is why teachers and profs suggest finding a way to personalize the information you study or new ways to synthesize information. ",
"Another factor is what type of memory you're trying to recall. Episodic memories (memory of personal events - what we usually consider 'memory') will always be easier to recall than semantic (facts) and 'feel' more poignant because there's a lot of details associated. One theory that might explain why is that semantic memories are more generalized and abstract version of episodic memories to allow for application across different contexts and thus less details. ",
"Emotional impact is also a large factor as well. Events that are more emotionally salient will be remembered better than non-emotional events. There are various studies of this and if you want, I can suggest a few. ",
"Also you can't forget about learned associations (this is more into the realm of implicit memory (ie: skill memory and priming etc...). For example, if I always associate a certain classroom with a time when I failed a test, then I will always activate certain negative stereotypes when entering the room (a context) and end up activating other associated memories and thought about failing tests or times when I've failed. If you have strong associations between a context and a certain stimulus, you will have stronger activation scripts for activation of memories of that stimulus. ",
"Hopefully this will satiate your interest in memory research slightly until someone else can come along with a more detailed answer! c:",
"TLDR: the brain is mf'ing confusing. "
] |
[
"In addition to ",
"/u/Mackerie",
"'s good summary, when you're remembering a memory you've remembered in the past, you're often recalling a memory of your memory, not the original memory. So if you've recalled something recently, even if the original episode happened a longer time ago than a more recent episode, it may be easier to recall. "
] |
[
"That is all very interesting, I'm glad to see this subject is getting some interest among researchers. It always amazes me that my mind is so complex that it can't even fully understand itself yet. "
] |
[
"Does the observed state of a particle at a given time affect future evolutions in its wave function?"
] |
[
false
] |
I'm struggling to reconcile the physical and mathematical interpretations of the evolution of quantum particles. If an individual particle can be observed in a random (but predictable) state, does this observed state affect the probability of it being found in a given future state? If so, how can the properties of the wave function evolve deterministically?
|
[
"If you know the initial state of the particle and you allow it to undergo unitary time evolution, you can determine what its state will be at any subsequent time using the time-dependent Schrodinger equation.",
"The state at some time in the future will in general be different for different initial conditions."
] |
[
"That's actually a really good question, and touches directly upon the measurement problem.",
"An undisturbed wave function will indeed evolve deterministically. But the act of a measurement and the collapse of the wave function is (in standard QM) an instantaneous effect. If you collapse the wave function, you will indeed alter its state (unless it happened to be in a pure state) to collapse onto the observed measurement. The wave function will then evolve again deterministically from that collapsed state.",
"This is what's behind the ",
"quantum Zeno effect",
", in which you can prevent a state from decaying by measuring it repeatedly.",
"If you're wondering if this clashes with the deterministic nature of the Schrödinger equation, remember that the Schrödinger equation evolves an ",
" wave function within an external potential. There are no interactions with external particles, only interactions between particles ",
". A measurement is an external interaction, and thus not part of that Schrödinger evolution, but a disruption of it. If you wanted to describe it with a classical Schrödinger wave function, you'd have to include all particles of the measuring apparatus in the wave function as well."
] |
[
"Well it's a part of the measurement problem, in a way. If you take the simplified view that the observer and observation is somehow external to your system and need not be taken into account, then the wave function 'collapses' into an eigenstate of your observable. This is a non-unitary and (apparently) non-deterministic event. The time-evolution of the system from that eigenstate will of course be different from if you'd not performed the measurement. ",
"If you include the measuring interaction and thus the measuring apparatus ultimately the whole universe, then there's no collapse nor any non-unitary evolution, and the evolution of the whole big wave function must be entirely deterministic. ",
"So the crux of the so-called 'measurement problem' is how you reconcile these states of affairs, and the apparent determinism of the classical universe."
] |
[
"What phase is a flame?"
] |
[
false
] | null |
[
"Typically just a gas phase reaction. Some flames can get hot enough for plasma to form but need to be at a very high temperature. The wikipedia article may be helpful, and even has a nice pun in the intro. ",
"http://en.wikipedia.org/wiki/Flame"
] |
[
"Right. The light is energy released as the bonds of CO2 are created (for the most part) and CO2 is a gas at room temperature, let alone after the heat gained in the reaction. Usually the particles are boiled into vapor during or just before ignition, also. "
] |
[
"There are a few different answers and it depends on what field you ask.",
"\"From a physics point of view,\" says DARPA on their site, \"flames are cold plasmas comprising mobile electrons and slower positive ions.\" ",
"Source",
"A flame is the visible, gaseous part of a fire. ",
"Source",
"But this fact is heavily debated in both fields. What constitutes the flame? Heat? Light? Both of those are by-products of the reaction. Is the reaction indicative of a flame?",
"Then again, there's this answer:",
"Fire is an oxidizing chemical reaction that releases heat and light. The actual flames that you see moving and glowing when something is burning are simply gas that is still reacting and giving off light. Of course, plasma and fire can both radiate visible light, So what's really the difference? If all fire were plasma, it would surely be noticeable. Plasma arc welding offers a good example of plasma and its qualities in comparison to fire. In plasma welding, gas is plasmized and in the process heated up to 20,000o Celsius and shot onto a material. The plasma gives off ultra-violet rays which can blind the welder if not protected, and cause tissue damage to bystanders. Can you imagine if candlelight were that strong? ",
"Source"
] |
[
"How far back can you go before carbon dating becomes unreliable?"
] |
[
false
] |
Yesterday I was speaking with a friend who is a Jehovah's Witness, so obviously he believes in the flood, and that humans have only been on the earth for 6,000. He says he knows a lot about carbon dating, and that it's only accurate if you're dating something that's within the last 3,500 years, after that, it can be very inaccurate. He also says that water will cause extreme variation in dating, do for example an object only 200 years old that's been in water for that time may be dated at 1,000 years old. So if you factor in a global flood, the dating of certain objects makes sense to say humans have only been on earth for 6,000 years. How much of this is true?
|
[
"How much of this is true?",
"To be blunt, virtually none of it (there is a sort of bastardization of one real thing, more on that in a minute). ",
"Wikipedia",
" has a pretty thorough and extensive discussion of radiocarbon dating, which I'd encourage you to look through along with our ",
"FAQ",
" on radiometric dating (a lot of which is focused on C",
" ). ",
"As for the effective range of C",
" , it's ~50,000 years, though it can sometimes be pushed back a little farther (the half life of C",
" is 5730 years, so saying that it's not accurate after 3500 years is just blatantly false). ",
"As for the water bit, I suspect they're (kind of poorly) describing a ",
"reservoir effect, specifically the marine effect",
". As described in the wiki article, CO2 (with some of the C atoms within the CO2 molecule being the radioactive C",
" is dissolved into surface waters of the ocean as carbonate and bicarbonate. These surface waters will eventually descend as part of larger ocean circulation patterns and stop exchanging with the atmosphere, so the dissolved carbonate in this water effectively begins to 'age' (i.e. C",
" atoms radioactively decay and thus the C",
" / C",
" ratio decreases). These deep waters eventually will reach the surface again, where some of this 'old' carbonate may be taken up by live organisms and incorporated into things like shells. When that organism dies, it would have an anomalously low C",
" / C",
" ratio (and thus appear older). This marine effect only applies to things living in the water (or in cases where terrestrial organisms almost exclusively consume marine species) so it is a real concern for things like shells, but something that's just 'been in the water for that time' would be unaffected (C",
" is essentially dating when an organism stopped taking up carbon from the atmosphere, so when it died, after it's dead, generally the only change to the C",
" / C",
" ratio is from the decay of C",
" That being said, this is a pretty well documented effect, and for material for which this is a concern it is something that is ",
"corrected for when reporting radiocarbon ages",
".",
"I think the final, crucial points are 1) radiocarbon is an incredibly well studied and robust geochronologic method that has been validated countless times, but also 2) it is just one of dozens of ",
"geochronologic methods",
" that operate across ranges of timescales from thousands to billions of years (and that are consistent with each other) that geologists / paleontologists / archeologists / anthropologists have used to establish the chronology of human and other organism evolution and the general geologic history of the Earth stretching back 4.5 billion years."
] |
[
"Beta counting is no longer the preferred method, it has mostly been replaced by AMS. Some of the same considerations apply, but with AMS, the effective age range of the technique is dictated by there being such a small ratio of C",
" to C",
" that it can no longer be effectively measured for old samples."
] |
[
"Hello, good answer here. I would like to add a bit about the probability of radioactive decay and radiation detection.",
"The reason there is a limit to carbon dating is essentially because:",
"1)Mathmatically, an exponential function such as a Half-Life would indicate that the quantity will never reach zero (it asymtotes). In reality, atoms are finite in number. Eventually you run out and there is a discontinuity.",
"2) The way detectors work, you generally detect atoms as they decay. Even before you run out of atoms, it becomes more difficult to detect them because the rate of atom decay will be that much less than the actual quantity. E.g. if there are X C14 left, and the half life is Y years, say you get a decay rate of 1 atom per day. Since it's random, you might have to wait a day and a half just to catch one atom, and that's assuming you have a 100% detection rate.",
"Assuming you did wait a day and a half, you might mis predict the quantity since you might think the rate is 1atom/1.5 days, but it isnt. It's 1atom/1day. In order to know it's 1atom/1day, you have to take a sample of points over time and predict the rate based on that sampling size, the larger your sample, generally the more confidence you would have that your rate prediction is accurate.",
"Edit: Yes, there are other methods, and yes, Destructive tests would not require the decay of atoms, but those detection methods will have their own limits where the same probability rules apply, especially if the detector is digital in any way. I was speaking generally about instrumentation and probability in regard to radioactive decay, not specifically about beta decay."
] |
[
"Provided that you have 20/20 vision, if you wear someone else's glasses, can you really see the way they see without glasses?"
] |
[
false
] | null |
[
"Please correct me if I am wrong but I think you would move the focal point in the wrong direction. I think you would need the prescription with the signs changed to see the way the person that needs glasses does. ",
"To test this theory out, I just put my glasses on with my contacts in and it is not the same as when I have my contacts out without glasses. It was making my eyes strain. My eyes do not strain like that without contacts or glasses."
] |
[
"No, you will not. Take for example a simple case of someone who is myopic (Their eye's cornea and lens has too much power for their eye - you may know this as nearsighted). Their glasses have a negative lens element in order to compensate for this. A negative lens reduces the power of an optical system. So, if an emmetrope (standard vision) individual wore a pair of glasses designed for a myope, they would have a lens system with too little power - exactly the opposite! Wearing a myope's glasses gives the impression of hyperopia (farsightedness). So, if you wanted to see what it is like to be nearsighted, find someone with the opposite prescription!"
] |
[
"This is not my topic at all but, seeing as glasses work by being either concave or convex (to varying degrees) - the glasses (flipped either way) will have the same effect."
] |
[
"How does one analyze the structure of a molecule?"
] |
[
false
] |
I'm a pretty visual guy, so analysis on the "meta" level escapes me quite often, no matter what the field is. Chemistry though is an extreme for me. I do have a middle-school idea about atoms, atomic bonds and how simple chemical reactions work. I do, however, have not the faintest clue about how a chemist identifies the structure of a molecule unknown to him. The reason I'm asking is - how can you know what parts make up a protein in the first place? Trying to figure out how it is folded seems like a (comparably) solvable dilemma to me once you know the structure - I'm guessing, you need to find out how all those different energies push everything into place - but how do you find out that something is (6aR,9R)- N,N- diethyl- 7-methyl- 4,6,6a,7,8,9- hexahydroindolo- [4,3-fg] quinoline- 9-carboxamide? What kind of qualitative analysis is happening here? What are the steps? How do you infer a certain structure from the information you've got? Basically, I wanna know how chemists can look at molecules without looking at them. Especially, since this has apparently been done for at least a hundred years.
|
[
"Much of it is empirically determined. For example, one can use chemical shift data from a ",
" simple molecule to learn how different bonds affect the NMR signal - and this will be applied to more complex molecules.",
"Take ethanol for example - given the molecular formula and the number of bonds each element can make, there is only one way the molecule can be arranged; the number of bonds each element can make is empirically determined as well prior to that, by stoichiometric methods such as combustion analysis.",
"Beyond that, other figures like J-coupling and multiplicity can give you even more information, and those are empirically correlated as well."
] |
[
"Yet those are all pretty recent methods and often required \"I know this is in there\" knowledge beforehand.",
"No prior knowledge of the compound is needed. Mass spectroscopy can give you the molecular formula, and ",
" fragmentation information. IR can identify the type of functional groups. NMR can give you chemical bonding, as well as proximity information. Together all three is enough for structural determination of small molecules, without prior knowledge of what your compound is.",
"Prior to all these methods, the simple answer is that chemists ",
"."
] |
[
"Not my line of work, but I've been reading this book, ",
"Nature's Robots: A History of Proteins",
". Unfortunately for your question, I haven't gotten very far into it yet, but I find it fascinating that the first determinations of the size of large proteins came from just burning them and looking at the ratios of the leftover molecules. So they found out that hemoglobin's chemical formula was C738H1166N812O203S2Fe, mainly from the two moles of sulfur and the one mole of iron they got when they burned a mole of hemoglobin. Well, they probably wouldn't use a whole mole, but you know what I'm saying.",
"From there, they went on to making crystals of hemoglobin, from which they determined that it must have a rigid structure. After that they did x-ray crystallography, and nowadays they do a lot of spectroscopy to find all those positional numbers in the name you gave for an example.",
"That's just the 50,000 foot view, I'm sure someone else will come along and explain it much more clearly. But if you're interested in that kind of thing, ",
" is a good book to get. It's not very long and it will give you a different perspective on how science works."
] |
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