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[
"Has the moon changed since the time of Galileo?"
] |
[
false
] |
[deleted]
|
[
"It has moved about ",
"14.15 meters farther away",
" on average. I'm not aware of any physical differences we could notice from Earth. It's still tidally locked so we always see the same side.",
"The 3.8cm is from ",
"http://curious.astro.cornell.edu/question.php?number=124"
] |
[
"What desimusxvii said. The moon does get hit periodically by meteorites and we do have ",
"footage of the flashes",
". Plus of course we (humans) have left a lot of junk there. Overall though 'Almost completely unchanged' would be a better way of saying it."
] |
[
"Definitely a lot of junk. What's cool is that the ",
"Lunar Laser Ranging Experiment",
" is still detectable from Earth."
] |
[
"Hey scientists, the colder it gets, the better my cellphone reception gets. Why?"
] |
[
false
] |
I live in the sticks, so cell reception can be pretty frustrating sometimes, but the last couple days I've actually had one bar of 4G, where usually I get two or three bars of 3G coverage. Is this a thing?
|
[
"Radio frequency (RF) energy is absorbed by, among other things, water. There is typically more water in the air when the air is warmer. Cold air cannot support as much atmospheric moisture so there is less absorption, and therefore more energy is able to make it from your transmitter to the cell site receiver.",
"Part of your experience may also be observer bias: on many cold days there is still enough humidity in the air to mess with your reception, but the times when you have had the best results were cold ",
" dry."
] |
[
"and snow/ice are much more transparent too."
] |
[
"Yep. The same goes for when you are in a crowded room. Lots of big bags of salt water (people) to muck up reception. "
] |
[
"Would drinking through two straws move more volume of liquid than drinking through one?"
] |
[
false
] |
Hi there, I really hope this question gets answered and taken seriously because it has been bugging me for a couple of days. I had a discussion with a few friends about this and we could not settle on an answer. Basically, assuming that there is an equal amount of suction, would drinking through two (or more) straws actually draw in more liquid than drinking through a single straw? To simplify the problem, we made a few assumptions. We idealized the movement as an adiabatic constant-area flow where friction had to be considered, essentially a . However, we also assumed that your mouth wouldn't be able to form as perfect a seal around several straws as it would around one, and there would therefore be pressure losses from the gaps in your mouth. I would be really interested in hearing the thoughts of some engineers, especially you fluids folks! :) Thanks.
|
[
"The tricky part of your question lays in this assumption : ",
"Without this assumption, the answer is easy, there is less pressure losses if you use 2 straws instead of one (The cross section is twice as big). ",
"As your assumption doesn't give a estimation of the pressure losses due to the gap. We cannot answer. ",
"In practice the answer is yes, you can empty a container quicker using two straws."
] |
[
"I think it depends more on the diameter of the straw and the viscoscity of the liquid. small straws are limited by friction loss of the fluid more than they are by your suction power. Adding another small straw should double your flow rate even with a small loss in suction due to lip gaps. A large straw such as a McDonalds straw does not have an issue with friction (unless your drinking a very viscous fluid like a milk-shake) and so the flow rate is limited only by how much suction you provide (up to a limit that is way beyond what your mouth can produce). Adding another straw here will induce large suction loses to the gaps without much benefit to fluid flow therefore you will actually decrease flow rate. ",
"I think there are too many variables to try to determine the tipping point between large/small straws to determine mathematically. you could try to find some experimentally, namely maximum mouth suction (Patm - Pmouth) available, and pressure loss due to lip gaps vs size of straw, flow rate of 1 straw of different sizes. ",
"And at this point i realize you should just get a few different size straws and time how long it takes you to suck a shot (of water) through 1,2,3.. of them. compile the data in excel and get back to me because now I am curious.",
"Edit: you should have a few friends go through the entire experiment to see how this varies person to person. Also get that loose chick down the hall to participate as I've heard she can suck a golfball through a garden hose."
] |
[
"Years ago I conducted empirical experiments using 1 vs 2 straws (always a fixed diameter) using liquids of a few different viscosities. I did a very poor job of documenting my results, but I can report that in all cases the fluid volume/time transferred was greater in the 2 straw case. "
] |
[
"What would happen to my body if I showered non stop for a year?"
] |
[
false
] |
Food and water would be brought to me and as for exercise, I would be able to do whatever you can do on about a square meter.
|
[
"aside from turgidity, you'd suffer from profound infection. "
] |
[
"Citation 1",
"Citation 2",
"Citation 3",
"Citation 4",
"Related search on PubMed",
"Image of trench foot",
"Other example of persistant exposure to moisture",
". Albeit anecdotal, it gets the point across I believe."
] |
[
"It doesn't take a biologist to answer such a question. While Slypsy is right, a pathogen needs to be present for infection. However, its hard to believe that within a year, after ones flesh falls off, one would be \"just fine\". I'm operating under the assumption that at least the feet will be covered in water the whole time and that's all it takes.",
"This is further exacerbated by the fact one has to defecate in said water. As a childrens book is titled, \"everybody poops\". "
] |
[
"What are the actual dangers of NOT turning off your cell phone before taking off in a plane?"
] |
[
false
] |
I have always wondered what might happen...
|
[
"Older models of planes used copper wire, not fiber optics or well insulated copper wires. ",
"Copper wires act like large antennas, and are subject to interference. Older electronics were more prone to emitting the types of electronic interference that ",
" mess with the long, uninsulated copper cables (things like static on the radio). ",
"Modern planes, and modern electronic devices (largely) aren't an issue. The real reason, mainly, is regulatory inertia.",
"You might ask \"if electronics ",
" cause interference, why aren't they banned entirely?\" And that's a good question - because take off and landing are the most dangerous times (by ",
") on a plane, and the risk is small anyway, so rather than interfering overly, a few minutes at either end of the flight to increase safety was deemed sufficient. ",
"It is not, contrary to popular opinion, to force you to pay attention to the safety briefings. If that was the case, you wouldn't be allowed to have books out, and you couldn't sleep - neither of which is prohibited. ",
"http://en.m.wikipedia.org/wiki/Mobile_phones_on_aircraft#section_1",
"[ABC came to conclusion] the primary reason for the ban on cell phone use in flight was that neither the FAA nor the FCC were willing to spend the money to perform conclusive safety tests.",
"Most people who do an overview of the situation come to similar conclusions. "
] |
[
"Also, when cell phones first came out, they were analog devices that put out far more power at the time. "
] |
[
"Time for a kickstarter to fund that study. Pass a hat down the aisle of your next flight. \"Change for Letting me Keep Reading my Dam Kindle\""
] |
[
"How can gravity possibly be accounted for by quantum theory?"
] |
[
false
] |
If what we perceive as gravity is a 3d representation of a 4d distortion of spacetime and not a force between two particles, then what is quantum theory looking for? Is it trying to explain the interaction between mass and spacetime? Is this what we're trying to represent with gravitons?
|
[
"What we don't know is how to solve for the curvature of a particle that doesn't have reasonably precise position and momentum (quantum particles). So far no approach we've thought of has really worked out right..."
] |
[
"... then what is quantum theory looking for? ",
"A more accurate description for the high-energy, short-wavelength gravitational physics. Relativity falls short and does not have a terribly accurate description of, for example, the border of a black hole. Consequently it cannot naturally explain observed phenomena like Hawking radiation.",
"Quantum mechanics started out as everyday normal classical mechanics, but eventually certain realizations allowed us to construct quantum theories that make more accurate predictions and can explain certain features of the fields in a more natural and less ad-hoc way. It even allowed for two of those theories (electrodynamics and electroweak theory) to be combined and derived from a more fundamental theory.",
"The great successes of quantum theories (like quantum electrodynamics and quantum chromodynamics) have led scientists to expect that a theory of quantum gravity would be similarly more accurate than its classical counterpart (general relativity). However, the problem of exactly how to accomplish constructing a valid theory of quantum gravity remains unsolved.",
"Is it trying to explain the interaction between mass and spacetime?",
"Not necessarily, though the explaination of that might be consequential. The goal of quantum theory is to produce a model of reality that is more accurate than current models (just as this is the goal of all theories). If a classical theory is more accurate than a quantum theory, then we have to roll with it (and currently, general relativity ",
" most accurate, of all theories of gravity).",
"And if either a classical or quantum theory just happens to explain the interaction between mass and spacetime (which general relativity already seems to do), then so be it! :)",
"Is this what we're trying to represent with gravitons?",
"Not quite. Gravitons are just a quantization of a gravitational wave. Gravitational waves still exist in general relativity, but in a quantized theory of gravity, the continuous gravitatonal wave is replaced by many small discrete gravitational particles (\"gravitons\"). Just like how in classical electromagnetics, light waves are replaced with photons."
] |
[
"Not always. There was a recent article on ",
"r/Science",
" about how the moon affects experiments at the LHC, and how operators there have to fine-tune the proton beams to correct for the disrepancies.",
"The reason the SM does not speak about gravity is because the SM is made up of gauge field theories (specifically, quantum electroweak theory and quantum chromodynamics) and there is no working gauge field theory of gravity that agrees with observations as well as general relativity does."
] |
[
"With current technology and unlimited budget, is draining the North sea and connecting Europe and England possible?"
] |
[
false
] |
Inspired by this thread here:
|
[
"Fill it with money."
] |
[
"dammit, you broke science."
] |
[
"Paper mache continent. What could go wrong?"
] |
[
"How are large natural magnets transported?"
] |
[
false
] |
What the methods used to transport large and powerful permanent magnets to where they're needed without having cyclists sticking to the side of the truck along the way?? So far the best answer I've found involved either using a lead lined box or thick plates to 'absorb' the magnetic field lines but then how do they remove the containers once the magnet is in place?? I'd really appreciate an answer! edit:grammar and terminology (thanks i_invented_the_ipod)
|
[
"Magnetic field strength decreases rapidly with distance. You don't need lead or plates or anything like that, just put the magnet on a wood pallet to keep it from sticking to the truck bed. "
] |
[
"This page",
" at KJ Magnetics gives the low-down on how they ship the big, dangerous magnets like ",
"this monster",
". Bottom line, they pack them with a lot of space and measure the field outside the box to make sure it meets regulations regarding external magnetic field strength.",
"Edit: ",
"or this monster",
". 1013 pounds pull force! Yikes."
] |
[
"By \"natural magnet\", I'm going to assume you actually mean permanent magnet. Actual natural magnets (lodestones) are extremely weak.",
"When transporting permanent magnets, you can either put enough packaging around the magnet to keep susceptible materials at a safe distance, or you can build a box around the magnet that provides a low-resistance magnetic path from one pole of the magnet to the other.",
"For particularly-large magnets, you might even do both - put the magnet in a wooden box, then line the outside of that box with soft steel sheeting to redirect the magnetic field back to the magnet."
] |
[
"Are any two given temperatures guaranteed to have every temperature between them?"
] |
[
false
] |
For example: if my hotpocket is 600 degrees in the middle, and 2 degrees on the outside, am i guaranteed to find every temperature between 2 and 600 in the hotpocket?
|
[
"Good question. The temperature in the hot pocket as a function of coordinates and time will be a solution to ",
"the heat equation",
".",
"At steady state, this simply becomes the ",
"Laplace equation",
", which shows up in many places in physics.",
"Solutions to the Laplace equation are continuous functions of the coordinates (clearly, as they must be twice-differentiable).",
"Since they're continuous, apply the intermediate value theorem. So yes."
] |
[
"Temperature is not defined for each individual particle. Temperature in the context of the heat equation is a scalar field which varies as a function of coordinates and time."
] |
[
"A single atom doesn't have a temperature."
] |
[
"When Pangea was the only one continent, were there big islands built by volcano like Hawaii around the world?"
] |
[
false
] | null |
[
"Yes, though the records of them are a bit more fragmentary than the large continental portions which made up the bulk of Pangea. In detail, there were both intra-oceanic island arcs formed above intra-oceanic subduction zones (e.g. modern day analogues would be things like Java and Sumatra on the extremely large end and the ",
"South Sandwich Islands",
" on the small end) and oceanic islands formed as a result of plumes (like Hawaii). The records for the former are not too bad because island arcs tend to be accreted as opposed to subducted, so there are accreted terranes on major continents now which resconstruct to having been intra-oceanic island arcs in the middle of Panthalassa, the large ocean that surrounded Pangea, e.g. ",
"van der Meer et al, 2012",
". Oceanic islands like Hawaii don't leave as much of a record, because after they move away from the plume, they tend to erode and sink, becoming seamounts (e.g. the ",
"Hawaii-Emperor seamount chain",
" represents a chain of islands that formed and then became seamounts as the Pacific plate moved over the formative mantle plume). Seamounts often are able to be subducted (meaning that there wouldn't be a record of their existence if they were), but sometimes they can be partially accreted and there is evidence of some accreted seamounts which may trace back to oceanic islands that would have been in the center of Panthalassa (e.g. ",
"Kimura et al, 1994",
" - link to research gate because the journal site was being glitchy when I accessed it). Because seamounts are not as readily accreted, there could have been more oceanic islands in Panthalassa for which we have no record."
] |
[
"Sure, the ones highlighted in the van der Meer reconstruction (with the references they cite) are the Kolyma–Omolon superterrane in NE Russia (e.g. ",
"Stone et al, 2003",
"), the Anadyr–Koryak terrane in Kamchatka (e.g. ",
"Filatova & Vishnevskaya, 1997",
"), the Oku-Niikappu terrane in Japan (e.g. ",
"Ueda & Miyashita, 2005",
"), and the Wrangelia and Stikinia terranes in British Columbia (e.g. ",
"Kent & Irving, 2010",
")."
] |
[
"Can you give examples of where these accreted terranes exist today?"
] |
[
"Are ants or other small insects able to communicate threats and dangers to the rest of their colonies?"
] |
[
false
] |
For example, if I spray part of a trail of ants with ant killer, will the survivors somehow communicate the danger to other ants so more ants don't continue moving towards it?
|
[
"Yes and no. It depends on where the threat is. I know two different ant systems pretty well, and I'll use them as two slightly different examples. ",
"Fungus farming ants, specifically leaf cutting ants, have a number of protective measures in place. If you disrupt a trail that is going out or coming back from collecting leaves, you might get attacked by a soldier that is near by, but protection is minimal. And it's not like the ants run back to the colony to get reinforcements. However, if you \"attack\" the entrance to the nest, you'll quickly be met with soldiers either trying to block your entrance, or coming out to try to defend their colony. If you start digging into said colony, it becomes mayhem, and they will start attacking you to try to defend their colony.",
" ants, some species of which live in ",
" trees, are great at protecting their tree. No one has completely worked out all the mechanisms, but if you tap the tree, ants RUSH out to attack ANYTHING that \"shouldn't\" be on the tree. There is some chemical signaling going on that if more ants are needed, more will come. This is also how general recruitment works. If an ant patrolling the tree finds a threat, she will chemically recruit her nestmates to come out and help her.",
"But to answer your question more specifically. Ants can and will mark certain areas as a 'go here, good things/food are over here' or 'don't go here, the way is blocked/poisonous'. It has to do with the chemical trails they lay down. For the average ant you might encounter in your house, ammonia based window cleaner is sufficient for this. Not only will it kill the ants, but it will also wipe out the chemical trail."
] |
[
"Ants do most of their chemical sensing with antennae. In general, chemical sensing works by having proteins on the cell membrane which match particular chemicals. Chemical hits them, they change configuration, often releasing a different chemical inside the cell, which triggers...well, whatever. I don't know if humans can sense ant signals, but you'd almost certainly sense them via smell if you could pick them up, and ants don't smell very strongly, so I'm going to guess that either we can't sense them or the concentrations are too low."
] |
[
"It's not hugely complicated, but it gets the job done. I think most ants use on the order of a dozen separate chemicals. But I don't remember exactly."
] |
[
"I'm tone deaf and cannot recognize different notes or any aspects of music aside from melody and rhythm, are there identified distinctions between the brains of musically gifted people and people who are not?"
] |
[
false
] | null |
[
"Are you sure you’re tone deaf? Most people who say things like this are commenting on their quality of musical talent or lack thereof. Neuroscientist Oliver Sacks has written extensively about music and the brain. \nMusical concepts can usually be learned/taught."
] |
[
"This doesn't answer your question at all, but Einstein's brain had a distinct omega shape in his right hemisphere that has been attributed as a characteristic of his proficiency at playing the violin. \nThough, the brain isn't born this way - meaning the signature omega shape of violinist's brains develops with time.",
"It would stand to reason that musical gift is, to a degree, a learned trait.",
"But this is postulation on my behalf. Not actual science. I don't know the answer to your question. But hopefully interesting nonetheless."
] |
[
"If you play 2 different keys on a piano, do you hear a difference?"
] |
[
"Are humans the only species with beauty perception of faces?"
] |
[
false
] |
Are there other animals that are atracted by simetric (?) faces? (pardon my english, not a native speaker)
|
[
"Humans have to rely on the face more than other species for sexual selection as a product of evolution and culture. I.E. we are social and get cues from the face and we wear clothes that conceal our body. It is likely that we are the most extreme version. "
] |
[
"Symmetric features typically indicate good genes. Mainly genes for proper growth during pregnancy, as it is when a fetus develops that most features develop and when most genes are expressed. It's important in realize that beauty is not a universal thing. We perceive beauty and are attracted to beautiful people because over thousands of generations those who were best at choosing a mate with good genes (and hence genes for symmetry) left behind more offspring than those who couldn't distinguish between good genes and bad genes. ",
"In all species of sexual animals there is some sort of tell that reveals how good the genes of an individual are. Peacocks attract peahens by showing off their large colorful tails. Walrus' fight for control over a harem. Songbirds sing complex and beautiful melodies to attract mates. In humans and other species we see \"beauty\" (among other things) and judge a potential mate that way. So in a way all animals have some perception of \"beauty\" even if it isn't the same as a human's. "
] |
[
"I'm not sure about other animals, but in humans, faces are primarily encoded in a part of the brain called the ",
"Fusiform Face Area (FFA)",
". Googling it might lead to more info."
] |
[
"How does solid salt melt solid ice if no solution is made?"
] |
[
false
] |
[deleted]
|
[
"You must consider three equilibiria:",
"Ice == Water delta(G)_1",
"Ice + Salt == Salt(aq) delta(G)_2",
"Water + Salt == Salt (aq) delta(G)_3",
"We know that salt dissolves in water spontaneously, then delta(G)_3 is negative. Further, below 0C, we know that delta(G)_1 is positive since melting does not occur spontaneously at this temperature. The question is then: is the sum of these (delta(G)_1 + delta(G)_3) negative? It is negative for a small range under 0C, this is the range of temperatures where salt melts ice, but ice does not spontaneously melt. "
] |
[
"It's the balance of all the factors in the reaction. There's also energy involved in breaking the hydrogen bonds in the water, and the ionic bonds in the salt, and the attraction of the ions to the water. In this case, though, most of those other factors are opposing the ice melting, and it's the increase in entropy that supplies the net favorability to melting. However, the entropy might not be able to drive it in favor of melting if it weren't for the fact that ions are also attracted to polar water molecules. So there are electrostatic interactions that are also supplying some of the needed energy. It depends on how you think about it, though. They might just be partially counteracting the loss of the energy in the bonds of the crystal lattice, or the energy of ice hydrogen bonding to itself. But this is part of why oil doesn't melt ice very well, but salt does. Oil is not attracted to water molecules, or vice versa. The increase in entropy of them mixing would be similar as with salt and water, but the electrostatic interactions prevent this."
] |
[
"It's the balance of all the factors in the reaction. There's also energy involved in breaking the hydrogen bonds in the water, and the ionic bonds in the salt, and the attraction of the ions to the water. In this case, though, most of those other factors are opposing the ice melting, and it's the increase in entropy that supplies the net favorability to melting. However, the entropy might not be able to drive it in favor of melting if it weren't for the fact that ions are also attracted to polar water molecules. So there are electrostatic interactions that are also supplying some of the needed energy. It depends on how you think about it, though. They might just be partially counteracting the loss of the energy in the bonds of the crystal lattice, or the energy of ice hydrogen bonding to itself. But this is part of why oil doesn't melt ice very well, but salt does. Oil is not attracted to water molecules, or vice versa. The increase in entropy of them mixing would be similar as with salt and water, but the electrostatic interactions prevent this."
] |
[
"If pepsin and trypsin break down proteins into peptides why are people worried about Estrogen in foods?"
] |
[
false
] |
For example: Growth Hormone, IGF-1, Estorgen, Phytoestrogen.
|
[
"Estrogen is not a peptide hormone, it is a cholesterol based hormone. It does not have peptide bonds that pepsin and trypsin target when they break down proteins. Similarly phytoestrogens are not molecules derived from linkages of amino acids so do not have the correct molecular shape to be targets of proteases like pepsin and trypsin.",
"IGF-1 and other peptide based hormones can get broken down so the amount of these molecules that you absorb largely depends on how much are in your foods since protein digestion is not 100% efficient."
] |
[
"Soy contains several molecules that fall into the category of phytoestrogens. They are molecules with a shape similar enough to the estrogen made in our bodies that they can often trick out bodies into thinking they are estrogen. They are not themselves becoming estrogen. Many of them are physically attached to sugar molecules in the soy plants, which makes them very difficult for our bodies to absorb. Our liver enzymes can break down the sugar attachments and make the phytoestrogens more easily absorbed into our bodies (this might be the metabolism the weightlifting sub users are referring to). ",
"A pertinent excerpt from: ",
"2016 NAMS/PFIZER—WULF H. UTIAN ENDOWED LECTURE",
"The history and basic science development of soy isoflavones",
"Kenneth D.R. Setchell, PhD",
"https://insights.ovid.com/crossref?an=00042192-201712000-00005",
"SOYBEAN ISOFLAVONE COMPOSITION, METABOLISM, AND BIOLOGICAL PROPERTIES All soybeans and most soy foods contain isoflavones in relatively high concentrations.19-24 The predominant forms of isoflavones in soybeans are genistein and daidzein and to a lesser extent glycitein, and these are conjugated to various sugars to form malonylglucosides, acetylglucosides, and glycosides, resulting in a complex and differing composition among foods (Fig. 1). The conjugated forms of isoflavones do not cross the enterocyte and are not bioavailable or bioactive.25 Hydrolysis by intestinal glucosidases is essential to release the bioactive aglycons from the sugars to afford absorption and biological activity.25,26 The isoflavone composition of soy foods is highly variable among different types of soy foods, especially with regard to the levels and relative proportions of these different isoflavone forms.19-24 Unless the soybean or soy food has undergone some form of fermentation process, there will be relatively small proportions of the biologically active unconjugated (aglycon) forms consumed.19,27 Soybeans, and most Western-style soy foods that are generally formulated from purified soy proteins (isolated soy protein, often referred to as ISP), contain the conjugated forms of isoflavones.19-24 Processing has a significant effect on isoflavone content and composition of the soy protein or food, whereby isoflavones can be lost and/or changed in highly processed soy food products.21,23,28 In general, foods made from purified soy proteins can be expected to contain approximately 1.0 to 1.5 mg isoflavones/g of protein, whereas higher isoflavone intakes can be achieved through the consumption of whole soy foods (3.0-3.5 mg/g). In contrast to Western soy food products, many Asian foods have higher proportions of the more bioavailable and biologically active aglycons.19,27,29 ",
""
] |
[
"You seem to know your stuff. I'd like to ask a follow-up question. I'm subscribed to a few weightlifting subs. Many users are convinced that soy somehow metabolizes into estrogen. Is that even possible?"
] |
[
"What is the big deal with the determinant in linear algebra?"
] |
[
false
] |
Im taking differential equations and linear algebra for mechanical engineers in university. Im learning this math but Im not quite sure why the determinant is such a big deal? Surely Ill learn but Im curious.
|
[
"Linear algebra is a funny thing. It can really be quite interesting if it is taught well, but it is usually taught badly. The reason it is taught at all is because linear algebra is so useful in so many different applications, but too often, students aren't shown this, and are instead expected to learn rules and algorithms that anyone in the real world will just use a computer to apply.",
"The determinant of a matrix is a number that tells you properties of the matrix, but what that property means depends on what the matrix represents.",
"But most widely known, if the determinant of a matrix R, is zero, then there is not a simple solution R*x = y, given y. Also if you think about a matrix as representing a linear transform, and hence each column is a set of new basis vectors, then if the determinant is zero, then the transform that the matrix represents squishes data into a lower plane. For example, if a 2x2 matrix has a zero determinant, then it will transform any vector so that it ends up on a line. Because of this, we see why a matrix with a zero determinant is non-invertable. Another important detail about determinants is that they can be used to tell if a matrix is orthogonal: an orthogonal matrix has a determinant of 1 or -1. If you think of a matrix as a collection of linear equations, then if that matrix has a determinant of 0, then one of the rows is just a scalar multiple of the other.",
"If a lot of this isn't making sense, I strongly suggest watching this series of videos.\n",
"https://www.youtube.com/watch?v=fNk_zzaMoSs"
] |
[
"To expand on this answer: The determinant of a matrix / linear transformation is also a measure of size or scaling factor of the transformation.",
"If you consider the set of ",
" column vectors (or row vectors) of a matrix, then you can construct an ",
"-dimensional parallelepiped (which is the generalization of a parallelogram in 2 dimensions) spanned by the column vectors (or row vectors). The ",
"-volume of this shape is equal to the absolute value of the determinant.",
"So if you have a 2x2 matrix, the 2 column vectors together span a 2-dimensional parallelepiped, or parallelogram, with the surface area of the parallelogram being equal to the absolute value of the determinant.",
"The implications of a zero determinant also play a role here: If the determinant is zero, then one of the vectors is a scalar multiple of (some of) the others and the associated parallelepiped will have zero ",
"-volume. Consider the case of a 3x3 matrix: if 1 of the columns is a linear combination of the other 2, the associated parallelepiped will just be a parallelogram in 3D space, which has 0 volume."
] |
[
"I'll tag into these to give a real example to give some tangibility to these ideas.",
"In engineering, we use matrices (well, tensors) to define deformation of solid under loading. We take the load, apply it to the undeformed solid, and it gives us the deformed shape.",
"These tensors have to have certain properties, which can be seen by the determinant. When ",
"/u/NeuroBill",
" says 'if the determinant is zero, then the transform that the matrix represents squishes data into a lower plane', this is a no-no for our models! We can't have a 3D solid become 2D, that's not how things work. ",
"Similarly, the determinant of the deformation tensor describes the ",
" change of the object. So if the object gets smaller, the amount it gets smaller is the determinant.",
"This branch is called continuum mechanics, you can read about it ",
"here"
] |
[
"How exactly is the relation between permittivity and permeability of free space derived?"
] |
[
false
] |
While studying the Biot-Savart law, I came across the relation between permittivity and permeability of free space. Here it says, "1/ε c = µ " Where 'c' is the speed of light. My question is, how has this relation been derived? And who did it? Why is the speed of light a part of the equation?
|
[
"In the late 19th century, James Clerk Maxwell collected all the various electromagnetic field equations (from Gauss, Ampere, etc) and compiled them into what are now called ",
"Maxwell's equations.",
" The strength of electric fields depends on the dielectric constant, the strength of magnetic fields depends on the magnetic constant, and when a magnetic field changes an electric field is generated and vice versa. Combining all these, it's possible to show that Maxwell's equations imply an ",
"electromagnetic wave equation",
", where the squared velocity of the wave is 1/ε0µ0. Based on known values of these constants, Maxwell realized that multiplying them this way gave a value very close to the known speed of light, and suspected that light itself was an electromagnetic wave.",
"Note though that the definition of the Ampere is such that the magnetic constant has a value of exactly 4pi x10",
" in SI units, and the definition of the meter is such that c=299 792 458 m/s exactly."
] |
[
"Eh... The science is spot on. The history could be better.",
"\"The four modern Maxwell's equations can be found individually throughout his 1861 paper, derived theoretically using a molecular vortex model of Michael Faraday's \"lines of force\" and in conjunction with the experimental result of Weber and Kohlrausch. But it wasn't until 1884 that Oliver Heaviside, concurrently with similar work by Willard Gibbs and Heinrich Hertz, grouped the twenty set of equations together into a distinct set of only four. This group of four equations was known variously as the Hertz–Heaviside equations and the Maxwell–Hertz equations, and are sometimes still known as the Maxwell–Heaviside equations.\"\n-Wikipedia",
"In other words, Maxwell had about 20 equations. Heaviside, Gibbs, and Hertz managed to reduce them to four."
] |
[
"Thank you very much! I may need some more help on this topic soon..."
] |
[
"How can trees die of old age, yet successive cuttings of that tree can propagate indefinitely?"
] |
[
false
] | null |
[
"The reason the trees die is not because of old age, but because they outgrow their ability to successfully deliver the nutrients they need to sustain themselves because of sheer bulk."
] |
[
"as i understand it, senescence implies a deterioration, internally, of cellular functions which is not the case with trees not being able to supply nutrients because of size... the cells may still function normally but outside factors inhibit them from doing so leading to death... so i'd say it's more death by gravity"
] |
[
"Is there any way to combat this? If you own a tree, can you prevent this?"
] |
[
"How would gravity be affected if the Earth was a cuboid instead of spherical?"
] |
[
false
] |
Specifically, what would happen if you walked to one of the "edges" and jumped or tried to walk to the other side. Would the oceans just be pulled into space from the tide caused by the moon? Assume the axis is still 23 degrees and set up along two opposite vertexes, orbit is still the same, and moon still exists.
|
[
"The \"edges\" would be perceived like mountain ridges. The oceans would be convex puddles centered on each face of the cube, far enough away from the edges that tidal forces would not threaten to approach them. In fact, each side of the cube would be 10270 km, meaning the edges would be ~7262 km from the center of the Earth while the center of the faces would be only ~5135 km, an altitude differential 100-fold larger than the 19 km difference between the Mariana trench and Mt Everest. This would have a huge impact on the atmosphere and climate, and although the surface area of the Earth would be 24% greater, most of the surface would probably be uninhabitable for humans. If you had a pressurized oxygen suit and were on the edge, you'd be 33% lighter; if you were in the center of a face (assuming no ocean occupied that face), you'd be 54% heavier."
] |
[
"Of course, the gravity of Earth only allows for mountains to be about 10 - 15 km tall; beyond that height the rock at the base of the mountain is crushed by the weight of the rock above it. So this configuration is unstable based on the mass (gravitational strength) of Earth and the strength of it's rocks (estimate based on granite).",
"If you could somehow \"form\" Earth into a cube and press play, it would instantly and violently revert into a sphere.",
"Edit: spelling"
] |
[
"The Straight Dope had a column about this, and made an assumption that I think you are also making, namely that the person and the cube-shaped Earth are point masses. But they are not, which rather greatly affects the resulting \"heavier/lighter\" behavior over the surface of the cube faces.",
"A ridiculous amount of detail ",
"here",
". Briefly, you are never heavier-- at the center of a face, gravity is almost exactly 1 g; at the edges, you are only about 15% lighter, while at the corners, about 35% lighter."
] |
[
"Amplitude, wavelength: Why is the speed of light constant if these are both measures of distance?"
] |
[
false
] | null |
[
"The amplitude of a light wave is not a distance, it’s an electric or magnetic field strength. The wave shape is the field as a function of space and time, not the path of the wave through space."
] |
[
"Thanks. So the wavelength of a light wave is what, exactly?"
] |
[
"The distance from one peak to the next peak, or one trough to the next trough."
] |
[
"How do boneless animals have blood?"
] |
[
false
] |
I know that in humans, blood is formed in bone marrow. How do animals that don't have bones such as sharks or invertebrates, create blood?
|
[
"Spleens can make blood. They do it in human fetuses before the bone marrow comes online, and they do it in sharks."
] |
[
"Red blood cells are formed in marrow, not the entirety of the blood. Only vertebrates use red blood cells. Some invertebrates have freely dissolved hemoglobin (the protein contained in red blood cells) while others don't use hemoglobin at all."
] |
[
"What about species of boneless fish and sharks?"
] |
[
"Does a Planck length define the limits to the observable size of a particle?"
] |
[
false
] |
[deleted]
|
[
"Let's brush up on dimensional analysis. In other words, suppose I want to know what's the kinetic energy of a particle; I think mass and velocity have something to do with it, and by requiring that the dimensions line up, you get mv",
" as a rough ",
" of what the kinetic energy is. In this case, we can see that it's off by a factor of 2, but that might be good enough for lots of things. A similar procedure was followed by G. I. Taylor in estimating the power of a classified nuclear blast using two published photos (",
"http://en.wikipedia.org/wiki/Nuclear_weapon_yield#Calculating_yields_and_controversy",
"). A good rule of thumb about these things is that dimensionless constants are usually around one, so dimensional analysis gives you a rough idea of scale.",
"Planck length, and its associated friends are simply examples of doing the same thing. We don't see quantum effects of gravity in everyday life, but we might expect that the smaller you look, the more obvious it will get. We might then try and ask how small that would be, and use dimensional analysis --- throw in things like speed of light (something to do with relativity), Planck's constant (something to do with quantum mechanics) and Newton's constant (something to do with gravity) we end up being able to make quantities with the right units. ",
"There is absolutely no other evidence that these scales mean ",
". At the moment they're just heuristics to guide the mind --- experiments are so far from being able to access them that it's only in theoretical work that they are useful."
] |
[
"That paper is highly typical of the kind of questionable theory that people throw around. In the abstract they miss out one of the most important and questionable assumptions they have to make: spacetime is asymptotically flat. I repeat: without experiment, stating with certainty what happens in the Planck regime is simply scientifically unsound. Note that one can still speak of a Planck regime with good reason --- dimensional analysis!",
"On the issue of renormalisation technology --- our ability to play real games of renormalisation is extremely poor. In the context of conventional QFT we have some skills at finding regulators which obey the necessary symmetries (Poincaré and local gauge ones) and we can push the program through to arbitrary accuracy. However, once we step outside of that comfort zone we're actually very bad at it. Fundamentally it's a question of finding quasi-decoupled modes so that it makes sense to gradually coarse grain out details which we don't want; the existence of a nice Minkowski background gives you a breakdown for which this is possible. But lots of things (even simple lattice systems!) for which this is no longer possible."
] |
[
"There is absolutely no other evidence that these scales mean anything.",
"This is wrong, the Planck scale does have a special meaning. You can get them just for dimensional analysis, but it doesn't end in there. In QFT this is trivial because c = h = 1, so the Planck mass scale squared is just the inverse of the Newton's constant. But newton's constant does have a special significance when you go to high energies, let me tell you why.",
"But to really understand the meaning of the Planck scale you need to: know how black holes work and grasp the notion of renormalization, which is pretty much the central core of QFT and all of physics today. The idea is that the Newton's constant is the actual coupling constant for gravity, but since it has dimension of inverse mass squared, in order to actually calculate the perturbative amplitude for gravitational scattering, you need to multiply it by a mass scale - which is the typical energy of the stuff you're colliding.",
"But once you get to Planck scale energies, this ratio (E/Mp)",
" becomes of order 1, so gravity becomes very strongly coupled. That's just the statement that colliding heavy stuff will create black-holes. But you also know that in order to probe very small length scales you need to localize degrees of freedom within that small region and scatter it somehow. But this doesn't work out for gravity, because if you localize something within a Planck length, it will have a compton wavelength of the Planck length and therefore a momentum of the Planck mass, and thus you create a black-hole, since the Schwarzschild radius of a Planck mass ",
"So, although it has no deep meaningful significance in the formulation of your theory, Gravity doesn't allow degrees of freedom smaller than the Planck length to be probed. "
] |
[
"Is fat harder to burn, the longer you age with ?"
] |
[
false
] |
I mean the more time the fat spend in your body, is it more hard to burn it with time?
|
[
"In reality, adipose tissue is a very dynamic and constantly changing organ, and like bone being \"completely restructured\" every 20 years, a similar statement could be made for adipose. It is likely that the triglycerides stored in one's adipocytes is not the same as they were a week ago due to the constant flux of fatty acids into and out of the cells. ",
"But more pertinent to your question, the deposition of fat around your body is not an entirely random process and has many influences such as how the cells react to different stimuli (adrenaline, insulin and other metabolic hormones). Many times we characterize fat as subcutaneous (below the skin) or visceral (around the organs), and each react differently to lipogenic (fat building) or lipolytic (fat burning) stimuli. It is now quite clear that different areas of subcutaneous adipose tissue react differently as well and this can actually result in certain areas being easier to reduce as they can be stimulated to release their stores more readily than other depots around the body. This may give the illusion that depots that have been around longer are harder to reduce, but it is simply that the depot reacts differently than other areas that may have transiently grown due to a few bad months of intake/expenditure, and subsequently lost due to high reactivity to lipolytic stimuli.",
"TL;DR, It's likely not age of the tissue that is making it harder to get rid of, but rather how the cells are reacting to stimuli that promote fat storage or fat burning."
] |
[
"I believe he means, is the fat you've had for a long time harder to burn than fat you've gained recently. "
] |
[
"I believe he means, is the fat you've had for a long time harder to burn than fat you've gained recently. "
] |
[
"How does blood transfer oxygen to/take waste from organs if it circulates inside closed vessels?"
] |
[
false
] |
i'm trying to move beyond the simplistic model of "the blood circulates through the body via arteries and veins, carrying oxygen to and taking away waste from the body's organs", as if they're little UPS trucks...how does the blood stay in the vessels but the oxygen goes in and out?
|
[
"simply put, by diffusion.\noxygenated blood leaves the lungs via artery, disperse into arterioles then into capillaries, then depending on the CO2 level of the surrounding cell/tissue, RBCs will release some oxygen.. Higher CO2 concentration in tissue then the more oxygen will dissociate from the RBC (very rarely gives 100% oxygen, look up \"Bohr Effect\"), also it depends on how many oxygen is bound to the RBC, RBC's haemoglobin sometimes arent 100% oxygenated as it travels through the bloodstream. The RBC will also pick up the CO2 and store it as bicarbonate (dissolved CO2) in the cytoplasm. \nThis is possible due to the extremely short diffusion pathway, literally the capillary wall is one cell thick, and then it passively diffuses through cell plasma membranes"
] |
[
"oh and the RBCs are too big to fit through the capillary epithelium "
] |
[
"And once you've learned about diffusion, reading about ",
"Oxyhemoglobin dissociation curves",
", the ",
"Bohr Effect",
" and its inverse, the ",
"Haldane Effect",
" will explain why O2 binds to blood in the lungs, but then lets go to get into the tissues (because if Hb bound O2 too tightly, it could never come off, and too loosely and it wouldn't reliably bind at all). "
] |
[
"A spinning magnet can induce a current in a conductor, this is how a generator work. But what is the average rotational to electrical energy efficiency of these generator?"
] |
[
false
] | null |
[
">95% unless you operate it way outside its design range, for large generators in power plants typically something like 98%. They are extremely efficient.",
"article",
", ",
"plots"
] |
[
"for large generators in power plants typically something like 98% ",
"Even small machines like 3-400kW generators hit 98.5% efficiency. Bigger machines have lower losses typically.",
"ABB recently made a synchronous motor",
" with 99.05% efficiency."
] |
[
"The efficiency of steam drive however....."
] |
[
"Given that the speed of light changes based on the medium the light travels through, is it possible for matter or energy to travel faster than its local light due to moving through some highly refractive or dense medium?"
] |
[
false
] | null |
[
"Yes, 100% possible.",
"An earthly example: Cerenkov radiation is due to particles from nuclear reactors in water pools which emit particles travelling faster than the speed of light in water. ",
"https://www.iaea.org/newscenter/news/what-is-cherenkov-radiation"
] |
[
"Yes it's possible. The slowest light has been recorded at is around 27mph. There are situations where matter will move faster through the medium. The speed of light in a vacuum is the only universal speed limit.",
"EDIT: it looks like 27mph may have been a bad source, 38mph seems to be the consensus on the current record."
] |
[
"Not really, no. That's a common way to describe the phenomenon, but it's really more simple (and harder to understand) than that. The charged particles in a material set up an electromagnetic field that interacts with the photons of light changing the speed it can propagate. No bouncing around, just a change in the speed and wavelength."
] |
[
"Are there any evolutionary similarity between the scales of sea creatures and reptiles?"
] |
[
false
] |
snakes and fish for example
|
[
"No, they are fundamentally different kinds of structures. Fish scales grow from the mesoderm inside the skin, and are rather toothlike structures, in some fish (like sharks) containing bone, dentine, and enamel (though your standard fish has thin scales of collagen with a thin layer of harder material on top).",
"Fish style scales were lost at some point during the evolution of tetrapods. Later, reptiles evolved a different kind of scale forming from the epidermis instead of the mesoderm, and made out of keratin. "
] |
[
"This is the correct response. The fish scale forming from the mesoderm is a distinguishing factor between fish and reptile scale production. Also, as is stated, the same genes that are used to produce hair and teeth in mammals are used in the development of scales. This makes sense seeing as we have a common ancestor to fish. If you have ever watched a human embryo forming and maturing you will notice we go through stages where you can see gill structures (or the preliminary formation of said structures) form on the neck then be 'reabsorbed' as the process continues further along its course of action."
] |
[
"Are scales on reptiles related to feathers of birds, due to their classification now. "
] |
[
"What happens when you raise -1 to fractional powers other than 1/2?"
] |
[
false
] |
I know (-1) is i, but what would (-11/)3 be, for example? And how would it work if -1 were raised to an irrational power, like pi?
|
[
"(-1)",
" is (1+i*sqrt(3))/2.",
"We can write -1=e",
", and so (-1)",
"=e",
". If we keep in mind that e",
"=cos(t)+i*sin(t), then we can evaluate many of these exactly as in the case (-1)",
". ",
"There is some subtlety to this and the choices we make and how you choose roots. For instance, we can, instead, write -1=e",
", in which case we'd get (-1)",
"=-1 (this choice is conventional if you want to avoid complex numbers). You can also write (-1)=e",
", in which case we get (-1)",
"=(1-i*sqrt(3))/2. For every fractional power, there are different choices that you can make that lead to different results. Questions about what the heck is going on and how to make this precise is related to early work with Riemann Surfaces."
] |
[
"The n",
" roots of -1 are a collection of n points spaced evenly around the unit circle in the complex plane. For example, the only number which yields -1 when raised to the 1",
" power is -1. There are two numbers which yield -1 when raised to the 2",
" power: i and -i, diametrically opposite on the unit circle. There are three complex numbers yielding -1 when cubed, ",
"spaced evenly at 120 degree angles",
". Similarly there are ",
"four equally spaced points",
" yielding -1 when raised to the fourth power.",
"If you want x",
" to be a well-defined function you need to choose a specific root of -1 to be \"the cube root\" or \"the fourth root\" or whatever. This hides the n-points-around-the-circle property, but can demonstrate other interesting features. For example, one systematic way of choosing ",
" n",
" root of -1 for any n is: the first point you get on the unit circle starting at 1 and moving counterclockwise until you hit a solution to x",
" = -1. You can then define (-1)",
" as ((-1)",
")",
" for any integer m and positive integer n. This gives us all the rational number powers, at least, since all rational numbers can be represented in such a way. Then (-1)",
" for irrational x can be defined in terms of limits of increasingly good approximations, so for example we could say (-1)",
" is the limit of the sequence (-1)",
", (-1)",
", (-1)",
", (-1)",
", .... These definitions are fairly natural and give a very nice result when we graph it: ",
"http://www.wolframalpha.com/input/?i=plot+(-1)\\%5Ex",
", hinting at the connectedness between complex exponentiation and sinusoidal functions which can be formally expressed by Euler's theorem."
] |
[
"You get an irrational number, which has an infinitely long decimal expansion but is not an \"infinite value\".",
"-1",
" for example, is -0.90268... - 0.430301...i. Both the real and imaginary parts are irrational."
] |
[
"Could you polish two large stones so well that they would have low enough friction to slide against each other \"effortlessly\"?"
] |
[
false
] | null |
[
"And this is why a person can still get squashed by big rocks floating around in a zero G environment: inertia is a property of mass and is independent of weight."
] |
[
"You can polish them pretty well and get a very low coefficient of friction, but there is no such thing as \"effortlessly\" as in absolutely zero friction (one exception, I'll come back to that). The reason is that everything is made up of atoms and molecules and when two objects, polished rocks or whatever, are in contact, the electrons and atoms in the two objects will push and pull in each other, which will lead to a force that acts against movement of the two objects.",
"Then to the exception: Their is a weird quantum phenomenon where a liquid changed state to what is known as a ",
"superfluid",
" - a liquid with no internal friction/viscosity. It is however not possible to have a similar phenomenon for solids, except if you use a superfluid as lubrication between two solids."
] |
[
"To add: even if you polished them somehow down to zero friction, a stone still has mass so a large stone still has a large mass. So to move the stone, even if it's on a zero friction surface still means accelerating that large mass, which would require some input of force, which would (seemingly) be considered \"effort\"."
] |
[
"How did eusociality evolve in Hymenoptera (bees, ants, and wasps)? Did it occur multiple times or just once?"
] |
[
false
] |
I know that both ants and bees are descended from wasps. So was there a social wasp common ancestor that gave rise to bees, ants, and modern social wasps like yellowjackets? Or did all these groups evolve colony behavior independently? Eusociality in hymenoptera is so complex I have a hard time imagining how it could evolve once, let alone multiple times.
|
[
"Yes, it's evolved multiple times in the group (IIRC something like 10 times, much more frequently than any other group). There are several factors that make it relatively easy to evolve in hymenoptera specifically. This paper discuses some of them ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279739/",
"Note the overall conclusions are controversial (although I am somewhat favorable to them) but the description of factors involved is pretty uncontroversial, even if the weighting of how important they are is more controversial.",
"So, to summarize them:",
"Hymenoptera are ",
"haplodiploid",
", meaning males are haploid and females are diploid. The upshot of this is that females are more related to their siblings than to their own children...so helping their mother produce more sisters increases their evolutionary fitness a lot. This increase in genetic relatedness probably lowers the bar for eusociality to be a net benefit in terms of natural selection.",
"But it's not the only thing going on...some other insect groups are haplodiploid and have no eusocial members and eusocial species in other groups are usually not haplodiploid. You need more than just genetic relatedness. ",
"So another factor is how a species lives. Almost all eusocial species form some kind of defensible nest. Solitary hymenoptera often dig a hole or construct a small chamber where they keep their larvae and feed them. This provides a potential selective benefit for eusocial species because having more individuals to defend the nest means offspring are less likely to be lost. ",
"Eggs are also often laid in sequence...a solitary female often lays multiple eggs in a nest, staggered in time. Lay an egg, provision it with food, lay another egg, provide it with food, and so on. This means a solitary female doesn't get swamped caring for a bunch of eggs at once....but it also provides a mechanism for the evolution of eusociality. In solitary species when an offspring matures it disperses, but if some mutation breaks the dispersal instinct, the offspring will hang around the mother's nest...and bam, you've got primitive eusociality. Especially since the genetic programming for building a nest and caring for offspring is already present. The insect just has to apply that to the existing nest in front of it instead of the nest it would ordinarily make on its own. Of course it's not ",
" as simple as that but you can see the general outline."
] |
[
"Eusociality has definitely evolved multiple times within Hymenoptera. To start with, let's consider how this is actually defined. True eusociality has several requirements, including overlapping generations living together, concentration of reproduction into a subset of a colony (often a single individual), and cooperation in feeding and caring for new offspring. However, there are also several other forms of social behaviour which do not quite reach this threshold. You can see some definitions for these ",
"here",
", but I'll run through them briefly as well.",
"The large majority of hymenopterans are of course solitary, and it is quite clear that the ancestor of this group was as well. But some nest-building species can be communal, where multiple individuals live together but still produce and take care of their own offspring; they're effectively just \"roommates\". From there, some species may take it a step further and still have all members of a nest be reproductively active, but have everyone work on feeding all offspring rather than just their own (\"quasisocial\"). Next, some individuals may begin to make most of the offspring in the nest, leading to division into reproductive and worker castes (\"semisocial\"). However, this setup could still involve species which are just laying eggs, giving them food, and dying. For it to become truly eusocial, there must be overlapping generations of parents and offspring both living and working in the colony together.",
"To be clear, I'm not trying to imply that the evolution of eusociality always follows this path. These terms all describe the current state of at least a few species, and it's inaccurate to assume that true eusociality will be the \"end goal\" for all of them. And of course, current eusocial species may have acquired the features of this behaviour in a different order than I've laid out above. The point I'm trying to get across, though, is that eusociality doesn't evolve from nowhere; there are many plausible intermediate states documented in other living species.",
"The exact number of origins of eusociality is a bit tough to know for sure, but is probably somewhere in the ~8-10 range. These include:",
"ants",
"honey bees",
"bumble bees",
"stingless bees",
"allodapines",
"Rehan et al. 2012",
"several",
"independent",
"transitions",
"Brady et al. 2006",
"paper wasps",
"yellow jackets",
"hover wasps",
"Hines et al. 2007",
"Each of these contains at least one (but often multiple) transitions from presocial to eusocial behaviour, so the total number of origins of eusociality is probably somewhere in the ballpark of 10. ",
"Hughes et al. 2008",
" lay these out nicely in ",
"this figure",
". Since this figure excludes any ",
" groups and therefore may be a bit confusing, I'll also add ",
"this one",
" from ",
"So",
"vik et al. 2015",
"."
] |
[
"What about naked mole rats I'm pretty sure they are the only eusocial mammals, but then again I used to think that moose was another name for deer, so I may be wrong"
] |
[
"I have a question about super string theory, or M theory. I thought you guys might be able to help."
] |
[
false
] |
[deleted]
|
[
"Ah... this is a really important distinction and miscommunication between us then. I too don't really think that \"theory\" is an appropriate word here. Model perhaps. Idea. Scientific hypothesis, framework, something. ",
"But let's also remember what a theory ",
". It's a way of describing a bunch of separate observable data points within one unifying framework. String theory ",
" that. It describes the present observations, even if we must be a bit loose with ",
" string theory does this. (If I recall correctly, there's a number of string \"theories\" that do it well enough, and we need to distinguish between them in addition to verifying the whole theory). Anyways, what promotes a theory from a good framework for thinking about things to \"accepted theory\" is that the theory makes a prediction of some observation that the previous accepted theories did not. This is the limbo that string theory finds itself in at present. It seems like it's got some good structure to describe things, but it hasn't yet made a testable prediction, as you point out."
] |
[
"Try this",
".",
"The ten-dimensions thing is rubbish. It's not even sufficiently similar to science to be called pseudoscience. It's merely sciencey."
] |
[
"Look, I'm not sold on string theory myself, but this is way over the top. They have a theory that works mathematically, even if it must be massaged a bit. There are tests proposed for it, but we just don't have the technology to build them. Perhaps after they theorize a bit more they might have something that is technologically feasible to test. Which is a far sight from what we call an \"untestable\" prediction. It is ",
" by definition impossible to test. Just very difficult.",
"Some ideas are good scientific hypotheses. Some are pure crank physics. String theory is a good hypothesis, even if it's one you don't particularly care for. Save your anger for the crank physics, lest they all get painted with too broad a brush."
] |
[
"Diarrhea - What is happening in the body?"
] |
[
false
] |
I am very curious to know what the body and specific organs are doing when diarrhea is present. Many results on google give reasons and causes but what is the body doing or not doing, to make this happen?
|
[
"If you drink coffee (most of us do), and ever added cream or milk but ",
" stirred it, and watched it slowly dissolve into the coffee, you're observing a process known as diffusion. Substances with a higher concentration tend to diffuse to a lower concentration until both substances are balanced, in this case, the coffee is a lighter shade and the milk is mixed.",
"The cells that line your intestines are focused on maintaining a proper concentration of water + salts in the fluid on the interior of your intestines, and also absorbing as much of the water and nutrients from the digested food as possible. Normally once most of the nutrients and water are absorbed, it passes into the large intestines, and then…well, you get the idea.",
"As illiae mentioned, diarrhea can be caused from a number of reasons. The simplest to explain is if you take a laxative such as ",
"sorbitol",
". Sorbitol passes through your digestive tract largely unmetabolized, but when it is in the small and large intestine, it accumulates, and there is now a higher concentration of it compared to the interior of the cells (termed the osmotic gradient). This causes the cells to put water ",
" the interior of the intestines, instead of drawing water out, and thereby causing softening of stools, or in extreme cases diarrhea.",
"Diseases like ",
" can cause severe, life-threatening diarrhea by attacking the cells lining the intestines themselves, and hijacking the cells using a special ",
"toxin",
" into releasing Cl-, Na+, HCO3-, and K+ ions, and thereby massive amounts of water to compensate. If a person is sick with ",
" their life is in danger due to the massive loss of water and electrolytes in the diarrhea-giving them water will actually make their condition worse, they need to replenish salts somehow, like with gatorade."
] |
[
"Diarrhea can be caused by a number of things, from bacteria to viruses to tons of other things, such as illness or medication. Physiologically, after passing through the stomach, water and nutrients are absorbed from your partially digested food via the intestines to help solidify it into stool. Generally, diarrhea occurs when the intestines are compromised and cannot properly absorb water, such as with inflammation or damage, or when the still-digesting food passes through too quickly so that there isn't time to absorb enough water. Water, blood, mucus, etc can also leak into the forming stool and add moisture, causing diarrhea."
] |
[
"To summarize there are four different broad mechanisms of diarrhea: (More depending on the level of detail you require but let's make it four for the sake of simplicity)",
": ie stimulant laxatives like caffeine, Senna, and Bisacodyl can cause this. So can opiate withdrawal.",
": ie Cholera (kills through dehydration), Enterotoxigenic E. coli (ETEC). Some stimulant laxatives can increase secretion (This is one mechanism by which stimulant laxatives work). Senna and Bisacodyl increase secretion. Researching this topic I was surprised to learn that most GI viruses do not cause secretory or inflammatory diarrhea.",
": Often Osmotic: Unabsorbale molecules in the intestines cannot be broken down and fluid is pulled toward the lumen by an osmotic gradient. (ie sorbitol (found in prune juice), lactulose, miralax, lactose intolerance). Also inability to absorb due to \"short gut\" (the length of the digestive track is too small to absorb enough fluid) or due to Giardia which physically blocks absorption in the GI tract. Enteropathogenic E. coli (EPEC), Rotavirus, Norovirus, Astrovirus and Celiac disease can also results in loss of absorptive surface area.",
": Infections with Invasive E. coli (EIEC/EHEC), C. diff, Shigella, Salmonella, Campylobacter, Yersinia, Amoeba, or diseases such as Crohn's disease or Ulcerative Colitis. Leakage of blood and pus can cause diarrhea as well, this is sometimes classified as \"exudative diarrhea\" but since they are part of an inflammatory process I will include exudative here.",
"Here is a great resource for mechanisms of infectious diarrhea (one of my interests): ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3035144/"
] |
[
"How effective are nasal rinses, really, in reducing sinus problems?"
] |
[
false
] |
They all claim that by regularly cleaning out your sinuses you will reduce the number of sinus infections, problems from allergies, etc. Is this backed up by actual research? And are these claims regulated?
|
[
"It's well accepted that they reduce the symptoms of certain conditions when used with buffered hypotonic normal saline. ",
"Here",
"They're used to alleviate symptoms more than treat a condition. ",
"They are sometimes recommended post nasal surgery as well.",
"Long term continual use however ",
"may be linked to increased infections",
" but there are a lot of confounding factors for this.",
"There are some ongoing trials at irrigating with an antibiotic to treat current infections as well, I'm not certain what those are showing so far however."
] |
[
"Amebic encephalitis is a bad disease, but this can be easily prevented by boiling the water for sinus rinses. I recommend sinus rinses based on Teedy's data below; for some people they really seem to help. Especially around here, where it's particularly dry, it is helpful to get stuff hydrated and moved along."
] |
[
"RE: Amoebas",
"Doesn't matter if you're in a hot or cold country. It's a function of having amoebas in the water, and simply introducing water with the amoebas to your nasal cavity will allow them to burrow along your olfactory nerve into your brain and go to fucking town. ",
" infections turn up in the US and Europe fro mtime to time, and those are hardly \"hot\" countries."
] |
[
"If light speed isn't changed by the speed of the point of production, in the same amount of time, does one side of a light receive greater amounts of photons than the other side of the light?"
] |
[
false
] |
Theoretically, If you were to go half the speed of light, with a bulb lit on the top of your craft, then measure the amount of light in front of and behind the craft for the same amount of time, would the backside receive a lower count of photons? Edit: you guys are awesome
|
[
"Yes. Light going directly backwards or forwards will remain so in any frame, however light going mostly up and little forward in one frame can be going mostly up and a little backward in a different frame."
] |
[
"The other respondents have some disagreement. Allow me to clear it up:",
"So you're in a spaceship traveling at half the speed of light relative to some other reference frame. You've got a bulb on top of your craft. If ",
" (isotropic), because in your reference frame you're at rest, so it's no different than a lightbulb sitting in a room in your house on Earth-- it'll shine equally in all directions.",
"However, ",
" Instead, they will see the effects of ",
"relativistic beaming",
". The outside observer would see most of the light as being emitted forward from the spaceship.",
"This is not, as ",
"/u/I_Cant_Logoff",
" suggested, a result of doppler shifting alone. The difference in reference frames actually results in ",
"light being specifically beamed forward"
] |
[
"No. According to relativity, any constant-speed reference frame is the same as any other from the point of view of any experiments done within that reference frame. Therefore, the result of this experiment at half the speed of light will be the same as the results if done at rest. Assuming a symmetrical bulb, both front and back will receive an equal count of photons."
] |
[
"What's the significance of a eutectic/peritectic/eutectoid point and composition?"
] |
[
false
] |
It sounds an awful lot like an academic pursuit vs having any practical application. After all, a eutectic point is where liquid turns directly into two solid phases. I can't see any use in that because it's only the lowest melting point which seems like something one would want to avoid.
|
[
"This is actually a very very important property of a mixed phase system. If I take a rock made of two minerals and start heating it up, at what temperature do I get the first melt, and what is the composition of that melt? The answer is \"at the eutectic.\"",
"Similarly, let's say I want to distill ethanol from an ethanol and water mixture. Looking at the ",
"phase diagram",
" you can see that there is a minimum at 95.6% ethanol. That means that mixtures with an ethanol concentration below this point will have the vapor relatively enriched in ethanol (compared to the liquid) and that mixtures with ethanol concentrations above this number (<100% ethanol) will have liquids that are more enriched in ethanol than the vapor. However, you can never completely separate the ethanol and water by heating because of that behavior."
] |
[
"Some eutectics are useful ",
" you want a low melting point, e.g. traditional tin-lead solder, or other compositions used as a replacement for such. ",
"Other phase transition points are useful for the effects they can have on the microstructure of a material. The eutectoid transformation of ",
"austenite",
" (a higher-temperature phase of steel) into a mixture of ",
"ferrite",
" and ",
"cementite",
" has a very noticeable effect on the material properties, and careful heating and cooling of the steel can alter its final room-temperature properties in useful ways. Note that since all three phases are solid, you don't have to be exactly at the eutectoid composition - you'll just have \"extra\" cementite or ferrite, depending on whether you have more or less carbon than the eutectoid value. "
] |
[
"Eutetic compositions and Euctectoid temperatures are very important in any process where melting or freezing of a two or component system occurs. This could be a casting process, or heat treatment process. Understanding the eutectic compositions and temperatures will determine the phase compositions and phase crystal structure which is very important when performing industrial processes that involve alloying metals. Again understanding where the first liquid or first solid forms can be very important when melting or preventing melting such as a heat treatment process. Heating to the eutectic could induce phase separation. To create multi phase alloy, you must know where the eutectic is to ensure that cooling velocity will produce the desired grain size and properly disperse the phases."
] |
[
"[Engineering] How efficient are computer processors?"
] |
[
false
] |
From what I understand, heat generated by electronics is caused by it not being 100% efficient, better efficiency = lower heat. Please correct me if I'm wrong. But knowing that computer and graphics processors can reach up to 100°c before failing (or throttling). How efficient are processors really? I know high quality power supplies for computers are usually +85%, are the processors similar or way different?
|
[
"When a power supply is rated as 85% efficient, what they mean is that 85% of the energy that goes into the power supply makes it to the components that it is powering, and ~15% is released as heat.",
"CPUs/GPUs/etc don't work by directing the energy elsewhere, so it's not clear how you would rate their efficiency. They use all of the energy they receive, and it is all turned into heat.",
"You could do something like number of operations per second per watt of power (and this is in fact an important factor, especially in mobile processors), but that's not a percentage. ",
"It's a common misconception that CPUs receive energy, use some of it for computation, and release the rest as heat. This isn't true. It's the act of performing the computations that releases the heat. 100 watts into a CPU will produce 100 watts of heat."
] |
[
"It all depends on what you mean by efficiency, generally we measure it by energy in to energy out but a processor doesn’t output energy, at least not energy we care about. Therefore you could say its efficiency is 0% as there is no output power or 100% as all energy is used to calculate. I guess you might find a more valid measurement based off of the power loss in the copper traces compared to the power loss in the gate oxide but I’m not sure that would be meaning full either. The best measurement mighty be to compare different processer and measure their relative power usage compared to the number of operations it performed on a standard test set of data, but this would only give you a relative value probably not what you want. Hope that helps."
] |
[
"Well, not exactly 100% heat dissipated in the CPU itself. Some tiny current does flow over the data and address lines to peripherals to dissipate heat elsewhere. There's also RF emissions."
] |
[
"Can computers keep getting faster?"
] |
[
false
] |
or is there a limit to which our computational power will reach a constant which will be negligible to the increment of hardware power
|
[
"It depends what you mean by faster. There are many different measurements. I will focus on CPU speed here, but computer speed is a chain of many things, where the weakest link will cause a slowdown of everything.",
"The CPU: Here over the last 50 years processors have gotten vastly better at processing instructions in a smaller amount of time, as well as having more useful instructions, and being able to look at larger numbers at once. ",
"This is due to being able to cram more and more transistors into the same area, increasing the clock speed of the transistors, improvements to the design of the layout. ",
"These features (save the design) have been enabled by three things. \n1. Decreasing the size of transistors.\n2. Decreasing the voltage driving the transistors.\n3. Increasing cycles per second.",
"The first enables more and more transistors in the same area. We cannot make IC's very large due to propagation times of signals. The size of Processors cannot change much in future as the speed of light fundamentally limits propagation times. However by making the Transistors smaller we can smooch billions of transistors into very small areas 100-300 mm",
" Can this continue forever? No. Transistors cannot in principle be made smaller than 3 atoms, and much before we get down to that limit we have severe problems with electrons tunneling between the gate source and drain. Currently we can make transistors with a gate size of 14nm. This is around 90 Atoms per feature. ",
"The second allows for faster Cycle times. Going from TTL logic (5V) down to current levels 1.1-1.35 V allows for faster cycle times as less power is dissipated when the capacitors drain and fill. Can this continue forever? No. The thermal voltage of the silicon must be overcome to distinguish our data from noise. However as the thermal voltage is ~26 mV. As this is 50 times lower than our current voltage a lot of progress is left here. However it will require a lot of material science which may or may not be possible. The current FET transistors used experiance a very large slowdown when we decrease voltage due to slew rates.",
"Lastly if we simply cycle the processor faster we can get more use out of them. However this causes problems as the die will heat up as capacitors drain and fill. if we cannot remove heat fast enough the IC is destroyed. This limits the max cycle rate of the IC. Some progress is being made here still, however high power chips do not have much interest outside of the overclocking scene.",
"These three things together determine the \"speed\" of the processor in some sense. The amount of processing that can occur can be estimated by the number of transistors times the number of times each can cycle in a second. This is not a good way of actually looking at a processor, but is the gating our total processing power for a single core.",
"We have hit a block point in the last few years here for single cores. It is just too difficult to either increase the number of transistors within a region with high cycle numbers due to heat buildup, decreasing the voltage is hard with the current materials used. This is being solved via adding more cores. This can vastly increase the speed of processors in some measurements (Like Float Point Operations per Second) but on problems that are not parallel it does not increase the speed at all. So for single threaded non-parallel programs we haven't made as much progress as normal.",
"However the focus in the last few years really hasn't been on absolute speed of a single core anyway, but rather the efficiency of the cores. Due to mobile use and tablets a ton of money is being poured into trying to get the most computing power out of the least amount of electrical power. Here a huge amount of progress is still being made.",
"So for a simple answer.",
"\nCan computers keep getting faster? Yes. Things like FLOPS, and other measurements of a CPU's ability to do things have been getting much faster, and will continue to do so for the foreseeable future.",
"Can computers keep getting faster in the same way as the past? No. We do not know if its even possible to make transistors any smaller than 5nm. We will have to do things with parallel processors, more efficient lay outs, and lower power transistors."
] |
[
"No, quantum computing, in itself, has no effect on speed. What it does is make some algorithms available that normal CPUs can't natively execute. These new algorithms require less operations to arrive at the same result, meaning that specific problem gets solved faster. It does not mean that the processor is any faster, and there are many problems where a quantum computer simply doesn't have a faster algorithm available that can be used to solve the problem any faster."
] |
[
"I think the other answers have been overly-specific so far. Let me try. In short: yes, for quite some time. (As others have said, there are limits to density, but I don't think that was your question.)",
"Many answers have already talked about standard things like transistors, cores, and clock rates and blah blah. So let me talk about the other stuff.",
"For the last few years, clock rates have gone ",
" while singled-threaded performance has gone up by quite a lot. How is that? Well, because we started actually paying attention to what's important in performance. This has taken a few forms:",
"How much longer can we push single thread performance with this sort of thing? Not sure, but certainly a fair amount more than we have.",
"Next, if you look at GPUs, we're basically looking at relatively few real limits to their abilities. GPU-style work scales almost perfectly with number of cores. There's some memory issues you run into eventually, but those are solvable. At present we have GPUs with thousands of cores. I see no reason why that can't eventually be millions, really. I expect VR and deep learning to create enough demand that we see GPUs stay on their awesome scaling curve for quite a long time.",
"After that, there are quite a large number of possibilities for how things could continue to get faster.",
"I think I wrote a novel. But yeah, I see a lot of people pessimistic about computer performance and pointing to the impending end of Moore's law, but that's basically not relevant to performance, and I think they're wrong anyway. We had a small little scare because we were taking ordinary designs and just jamming tinier transistors with higher clocks speeds in there, and that doesn't work anymore. Turns out, it doesn't matter really. Everything's still getting on just fine.",
"People are unjustly suspicious of the fact that 6 year old computers (with enough RAM) are still \"fast enough\" these days. It makes them erroneously believe that modern computers aren't that much faster. Modern machines are still quite a lot faster, it's just that we used to make software less efficient in order to build it in a more maintainable way, and that meant older machines got unusably slower over time. But that change in how software is built is basically done. Software isn't really getting any more inefficient, so modern software still works fine on older machines. (I mean, really, even this awful modern trend of writing everything in javascript in the browser isn't as big of a loss of raw speed as the changes we used to make.)"
] |
[
"Are animals born in litters genetically similar to twins compared to single birth animals?"
] |
[
false
] |
Say a cat gives birth, are the kittens in the litter twins by genetics like in humans? And would a second litter of kittens be genetically similar to siblings with the first litter? Apologies if I described it poorly.
|
[
"Usually not, they mostly develop from different eggs so they are fraternal twins not identical.",
"There have been cases found where splitting of an egg gives rise to identical twin animals in a litter. ",
"https://curiosity.com/topics/scientists-have-confirmed-the-first-identical-twin-puppies-and-its-a-big-surprise-curiosity/"
] |
[
"So many variables. Do the kittens between the litters have the same father? Do the kittens in the same litter have the same father?",
"Cats are capable of superfecundation and superfetation, which means that kittens in the same litter can have different dads:",
"\"A litter of kittens born to a single mother can have multiple fathers (superfecundation) and cats can become pregnant while already pregnant (superfetation). In such cases, the second litter may be born prematurely along with the first litter (which can be fatal for them), or they may hang on and be born at the normal time, which means that the mom will have extra kittens to deal with while still nursing the first litter, though feline moms usually do a good job of caring for all their kittens.\"",
"https://hitrecord.org/records/1618503/comments",
"If they've all got the same father between litters or within a litter, they're like full-blood siblings. Different fathers, and they're half-siblings. In a litter, it's also possible to have identical twins (or triplets etc), which could be demonstrated with a DNA test."
] |
[
"Thanks for the answer"
] |
[
"What is a topological insulator?"
] |
[
false
] |
[deleted]
|
[
"I don't have time for a full response with my own personal input, but see below:",
"The Hasan-Kane review article is a well-known one, and at the end of the intro section it references several of the other reviews: ",
"http://rmp.aps.org/abstract/RMP/v82/i4/p3045_1",
"This article in Physics Today is also nice for a broader, briefer perspective: ",
"http://physicstoday.org/journals/doc/PHTOAD-ft/vol_63/iss_1/33_1.shtml",
"I also refer you to the slides from a set of tutorial talks from the 2011 APS March Meeting, especially the first one by Joel Moore: ",
"https://sites.google.com/site/xlqistanford/home/talks",
"Materials growers are working hard to get these materials optimized for physics experiments beyond ARPES and STM, and I'm sure any scientists with relevant knowledge (i.e. physical chemists ;) ) would be welcome to help solve these problems. For example, one known issue is that the surfaces of these crystals degrade upon exposure to ambient atmospheric conditions. The electronic surface states are \"topologically\" protected as promised, i.e. they still exist, but their \"quality\" is significantly reduced (badger me and I can answer what \"quality\" means later). Note that surface states in other, \"non-topological\" systems typically get destroyed upon such exposure, so one of the interesting facts about TIs is the fact that the surface states are \"protected\", in a sense, regardless of how much the actual surface's structure gets screwed up. ",
"Hope this helps! If anyone has more questions, or wants more information, I can return later. ",
"*edit: more info"
] |
[
"Mathematician's perspective here. When thinking about geometry, you can think globally and locally. An example of thinking locally is thinking about the metric of a space at a point. It's quite intuitive to think about physics in terms of locally defined quantities in some geometric space.",
"However there is a global aspect to geometry. The nicest example I can think of is the ",
"Gauss-Bonnet theorem",
". The Gauss-Bonnet theorem tells you that if you integrate all the curvature of a surface and its boundary, you get a specific number that is a discrete multiple of 2*pi! That number doesn't depend on the curvature of the space at all, only the topological properties of the space. Topological properties are not affected by distortions of space. You can bend, twist, stretch all you want and the topology of the space stays the same. For example, a coffee cup and a donut are topologically the same. ",
"A nice picture courtesy of wikipedia.",
"Now what does this have to do with physics? Well, when you're talking about matter, you're talking about effective field theories. There's a class of such theories whose physics ",
". These are called topological quantum field theories. Since they don't depend on the metric, the only thing they can care about is the topology of the space. Hence, they only depend on 'global' properties."
] |
[
"I find that ",
"this brief intro",
" to topological insulators is generally well-received when I've referred it to others in the past."
] |
[
"How does the STAR detector at the Brookhaven Lab detect?"
] |
[
false
] |
I'm not sure how specific to be, this is a fairly new concept to me. For instance, what exactly are they looking for with the experiment
|
[
"Essentially, STAR is a detector designed to see what comes out of heavy ion collisions at the RHIC accelerator at Brookhaven National Lab. The accelerator sends large nuclei, such as gold atoms that are stripped of all electrons, around the accelerator's ring at nearly the speed of light. There are two \"beams\" of nuclei that circle the loop in opposite directions in separate \"lanes\" until they are focused into each other at a collision point. These collision points are the locations of detectors such as STAR, that essentially act like giant cameras to see what types of particles come out. The goal is to see the byproducts of a fundamental phase of matter called the quark-gluon plasma, where quarks and gluons are floating around freely in a soup-like medium.",
"Source: I used to work on a project that simulated these collisions to test models of how the quark-gluon plasma would \"flow.\""
] |
[
"Thank you, very helpful!"
] |
[
"Are you interested in which types of particle detectors are used in the STAR experiment, how the detectors are arranged, and what is the operating principle of each detector type?"
] |
[
"If phytoplankton contribute to half of the global oxygen output, has declined by 40% since the 50's, why is atmospheric oxygen not dropping noticeably?"
] |
[
false
] |
The global phytoplankton population has been found to have and are dropping by 1% per year, an alarming rate for a population of plankton that is contributing to 50% of the global oxygen output! Yet, by 0.7% of atmospheric oxygen in the past 800,000 years and can't figure out why that is so and calling it "atmospheric leaking". As if the assumption is that there is a decent balance here? I would have thought the atmospheric oxygen would be dropping over time because of the huge reduction of phytoplankton already. Why is it not? And what rate of oxygen depletion is reasonable to assume due to climate change and an ever reducing phytoplankton population?
|
[
"So there are a couple of factors at play here. Atmospheric O2 is decreasing over time, as can be ",
"seen in this chart from Scripps",
" (compare to the ",
"Keeling Curve, which monitors CO2",
"). This is largely due to burning of hydrocarbons, a general form of which could be given as CH+O2->CO2+H2O. While decreasing phytoplankton counts may also play some role in this decrease, it is important to note that atmospheric O2 has a residence time of ~4500 years, and one source dropping by half over 60 or so years is not going to have immediate impacts. "
] |
[
"Would lowered O2 levels be more detectable at altitude or ground level. I have heard reports of pilots experiencing hypoxia symptoms which could be due to lower O2 levels at altitude.",
"Would weather pressure systems have an impact with O2 levels e.g. a low pressure system implies reduced air density combined with high temperatures air density could get very low.",
"And what about CO2 density around cities displacing O2 levels."
] |
[
"I have heard reports of pilots experiencing hypoxia symptoms which could be due to lower O2 levels at altitude.",
"This is an effect of the altitude in general. The air is thinner if you go up. It has nothing to do with changing O2 concentrations, these are negligible over human timescales.",
"And what about CO2 density around cities displacing O2 levels.",
"For every molecule of CO2 there are ~500 molecules of O2 in the air. The CO2 concentration in a city might be a few percent higher than outside (this is a relative statement), maybe even less. It is completely irrelevant."
] |
[
"Would it ever be possible for humans to have gold-colored eyes (like cats, owls, wolves, bald eagles, etc.)?"
] |
[
false
] |
I am wondering if it would ever be possible, through a genetic-engineering perspective, for humans to have the gold-colored eyes that other animals have. Let's say you have a futuristic culture in which designer babies are the norm, and diseases have been all-but-eradicated in this better "breed" of human which has resulted through generations of careful genetic selection. If these futuristic peoples have the ability to pick and choose certain phenotypes for their children, isn't there some way for a gold eye color to come about (as it would be an alluring and desirable trait)? Can we not simply "inject" the pigments from other animals exhibiting golden eyes into human eyes, or splice the genes from these animals into human DNA to allow for this to be a new genotype able to be passed on from parent-to-parent? Please help... I've done tons of research but can't seem to find the answer anywhere. I need to know if this is possible for a novel I am writing.
|
[
"This may not be the best answer, but since you havent gotten any responses yet, I dont think there is much known about the genes underlying eye colour in animals, there may be a little known about cats perhaps, but even in humans we dont know all the genes and mutation involved in eye colour determination. I think we would need to know more about what is needed for yellow eyes to occur to know whether it is likely to happen by chance in humans, so that it could be selected for in babies. However, theoretically it should be possible to genetically engineer humans with yellow eyes, its just a long way off technology wise, and I suspect will probably require more work than just altering one gene or introducing a single mutation.\nInjecting pigments would probably not work, my understanding is that there is more to eye colour than just a simple pigment.",
"If it were me writing the novel I would have the yellow eyes genetically engineered into humans, the same way genetically engineered plants are produced, but would have them alter a few genes or regulatory regions of the genome to make it more believable."
] |
[
"There are at least two genes that influence eye color in humans, which is the explanation for why people with different forms of albinism might have blue eyes (only one pigmentation gene is coloring the eye) or pink eyes (neither of the genes that supply color to they eyes do so, which allows the underlying blood vessels--which are red, of course--to be the chief factor responsible for the resulting color).",
"In general, the genetics of human coloring are such: you either have a version of a gene that produces pigment (i.e. a gene for brown hair) or the version of that gene that produces no pigment (resulting in a lack of color, i.e. blond hair). The same goes for the pigmentation of human eyes, which explains how pink eyes can result from albinism. (This is a gross simplification, as there are quite a few genes that influence human hair color, but most of those genes work this way.)",
"The gold eye color we see in non-humans is best thought of as a variant of brown with a layer of white making it appear lighter. In cats, for example, ",
"there is a gene that codes for ",
" pigmentation--that is, it codes for a white pigment that essentially mixes with a darker pigment coded for by another eye-coloring gene",
". This is why cats eyes that might normally be brown end up looking orange, yellow, or gold. There's a layer of pigment in the eye that is lightening the overall color of the eye, which also is expressing genes for darker colors. Applying elementary school color mixing rules: Mix brown with white and you get orange/gold. I don't know for sure, but it's likely that a similar interaction happens in other species with gold eyes.",
"So, per your question: you'd need to genetically alter a human being to express genes that humans don't ordinarily have in order to end up with a human with gold/yellow eyes. But I don't see any reason why that's impossible, barring legal/ethical concerns. ",
"Good luck writing your novel! If you're looking for a technique that could be used to splice such genes, take a look at ",
"CRISPR",
"."
] |
[
"Thanks a lot! You've really helped me! :)"
] |
[
"Why aren't all known archaeological sites excavated?"
] |
[
false
] |
I've been reading a book about sites in County Clare (Ireland) that mentions that there are many sites that are not excavated, and that got me wondering about why. Is there a shortage of people capable of it? I'd imagine a new pyramid in Egypt would have people scrambling to unearth it as fast as possible, so why are there sites that aren't, ESPECIALLY given that some of these sites are over 1,500 years old, some even dating to the iron age.
|
[
"You bring up a lot of good reasons, but I'd like to add some. Excavation destroys/damages the thing being excavated. Excavation methods get better over time, so that they become less destructive and yield more information. So by not excavating a site now, we are preserving it for more capable future archaeologists. Therefore it is often a good idea to not excavate a known site unless it's being threatened by destruction in some other form (construction works, etc)"
] |
[
"You bring up a lot of good reasons, but I'd like to add some. Excavation destroys/damages the thing being excavated. Excavation methods get better over time, so that they become less destructive and yield more information. So by not excavating a site now, we are preserving it for more capable future archaeologists. Therefore it is often a good idea to not excavate a known site unless it's being threatened by destruction in some other form (construction works, etc)"
] |
[
"Thanks!"
] |
[
"Why does acetone cause things to cool down so quickly?"
] |
[
false
] |
I was cleaning a spray gun at work with acetone yesterday, and noticed the metal was much colder than room temperature when I was done. It also makes my hand much colder when I get it on me. It's been a while since chemistry. How does the acetone manage to suck so much heat out so quickly?
|
[
"Acetone has a high vapour pressure at room temperature. This means that it tends to vaporize rather easily.",
"Vaporization is an endothermic process - it requires heat to turn something from the liquid to gas phase. Therefore when something vaporizes, it sucks heat from its environment, so the temperature lowers.",
"This is known as ",
"."
] |
[
"To add, this is the process by which sweating works. The sweat evaporates, taking your body heat with it."
] |
[
"/u/rupert1920",
" is totally correct but fails to explain why vaporization is endothermic. ",
"Let us imagine a collection of acetone on a surface. Temperature is proportional to the average kinetic energy of the particles. The molecules that evaporate first are the ones with the highest kinetic energy (that is why they managed to escape the bonds whereas the others could not and have a combination of the binding energy and kinetic energy). Removing the molecules with the highest kinetic energy causes the average kinetic energy to drop and therefore, the temperature to drop. The remaining molecules are then heated up by their surroundings until more acetone molecules can evaporate. This process is then repeated. "
] |
[
"Have we learned anything new from mars that we didn't already know before landing there with a rover?"
] |
[
false
] | null |
[
"Of course we learned things about the planet from deploying rovers. Getting a vehicle with cameras and various sensors on the ground gives a wealth of information that cannot be garnered from Earth or even from an orbiter.",
"Probably the most significant data is that relating to water on Mars. Spirit and Opportunity sampled various rocks and made many observations that help deepen our understanding of Mars' history of water. Specifically, they found rocks and clays that only form in water. Curiosity also found evidence of water, in the form of unmistakable fluvial deposits. Curiosity also has advanced instruments to analyze rocks, which confirmed other findings.",
"There's lots more that has been discovered - dust devils, dunes that suggest a different planetary spin, less surface radiation than previously thought...the list goes on....",
"Check out the wikipedia articles on ",
"Spirit, Opportunity",
", and ",
"Curiosity",
") to read more. There are also articles like ",
"these",
", but they seem clickbatish to me and IMO lacking much content."
] |
[
"Two main reasons, is there a way for us to extract the water for use in an eventual human settlement? Both for drinking and power generation with fuel cells. Two, if it used to have lots of water and now doesn't, what happened? Could the same thing happen to earth? "
] |
[
"Thanks for including Spirit and Opportunity. I've seen posts discussing \"the rover\" like Curiosity is alone over there. I love them all."
] |
[
"How might a bacterial cell control copy number of its plasmid?"
] |
[
false
] |
To be a little more specific, if I put a plasmid with a gene (urease) that's normally under some pretty specific Nickel dependent (NikR) regulation instead under a constitutive T7 promoter, and the cells are making too much urease for their metabolic aims, does selection have any diversity to work on with regards to the plasmids themselves? It doesn't seem like it to me, so I guess any further selection in media would be dependent on novel mutations?
|
[
"The plasmid number won't be regulated, and your gene will only be regulated by whatever regulators your plasmid carries (e.g. Lac operon promoter). Plasmid number, as far as I know, is largely determined by the affinity for the DNA Synthase complex for its origin of replication and the bacteria's doubling time. ",
"That said, if your pathway has feedback inhibition on the enzyme level, that would likely still work. "
] |
[
"Not true, plasmid copy number is absolutely regulated. While your promotor will control transcription for that gene or operon, plasmids have their own origin of replication (similar to oriC, the chromosomal origin). These origins of replication will also control the frequency of replication for that entire plasmid.",
"Plasmids are typically classified as high, medium, or low copy plasmids. They are classified by how many copies a bacterial cell has on average - and so is directly related to how often that plasmid replicates. ",
"This can also control protein amounts to some extent, as if you have a high copy plasmid with hundreds of copies around, you will have more genes producing that protein."
] |
[
"I don't think the origin of replication has protein promoters, but I might be wrong. I mentioned that plasmid replication is affected by the bacteria's affinity for the origin of replication, which sounds like the regulation you're talking about. In that case, it affects the copy number, but the bacteria can't regulate it up and down based on protein levels on the plasmid itself. "
] |
[
"Why is the Earth's crust split into Tectonic plates?"
] |
[
false
] |
Whenever I have learned about this topic at various levels of education, we have simply been taught that the Earth is split into numerous tectonic plates, but WHY is this the case? Surely the earth's crust could be one joined together thing that moves as one on top of the mantles convection currents?
|
[
"You've erroneously assumed that all of the earth's crust is homogeneous, which is not the case. A fundamental driving force for plate tectonics is density contrasts, between the primarily basaltic, denser ",
"oceanic crust",
" and the variable composition, but lighter ",
"continental crust",
" and also between oceanic crust of different age (crust cools as at ages, becoming more dense, and thus more likely to subduct).",
"Additionally, as pointed out by ",
"u/Sevrael",
", there are currents within the mantle that may impose differently directed tractional forces on the base of the crust, however the role that mantle convection currents and traction forces play in driving plate motion is still unclear/somewhat controversial. Conventional ideas suggest that subduction and density contrasts as described above are the main driving force, but mantle traction likely plays some role."
] |
[
"Surely the earth's crust could be one joined together thing that moves as one on top of the mantles convection currents?",
"http://upload.wikimedia.org/wikipedia/commons/2/27/Oceanic_spreading.svg",
"The problem here is that the mantle isn't all moving in the same direction. The upper layer of the mantle moves away from areas where hot material rises, and towards the areas where cold material is sinking. Even if you did freeze the crust into a seamless sphere it would be pulled apart at areas of upwelling, producing continental rifts, and compressed at areas of sinking, producing subduction zones.",
"The lava lake at Erta Ale shows the same kind of convection on a small scale: ",
"https://www.youtube.com/watch?v=maSYZW8-8IQ&feature=player_detailpage#t=56"
] |
[
"As well as what ",
"/u/Sevrael",
" said, tectonic plates aren't fundamentally different from just rocks on the earth's crust. They are only classified as distinct individual pieces because they are very big, and surrounded by very big faults. And they don't really change in shape as quickly as smaller rocks."
] |
[
"Is it more environmentally friendly to get a real xmas tree from a tree lot every year or use the same artificial tree each year?"
] |
[
false
] | null |
[
"Hi blankiamyourfather 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.",
" ",
" "
] |
[
"Earth sciences"
] |
[
"'Earth Sciences'"
] |
[
"Why don’t vaccines carry over genetically?"
] |
[
false
] |
Just curious with everything going on why vaccines don’t essentially pass down to our children genetically if we’ve been immunised. Is it purely because we didn’t genetically start with that or purely down to the synthetic (well atleast not made naturally by the body) nature of the vaccinations?
|
[
"1) Vaccines do not alter your genetic information, i.e. those in the form of RNA (the new ones, because up until today they were protein based) do not integrate into the genome.",
"2) even if RNA vaccines could integrate into the DNA, you still wouldn't pass them on because vaccinations are injected into somatic cells, not into germ cells (inside testicules or oocytes, for instance...nobody would want that tbh). To pass genetic information on you need to alter the DNA of germ cells."
] |
[
"Others have explained that vaccines don't alter the genetics that you can pass down. However, it's not just what vaccines do, but none of the adaptive immunity can be passed down genetically, even though biologically speaking, it would be great if it could. Imagine being immune to smallpox or the plague and all of the various influenzas simply because your ancestors survived those disease.",
"The reason that this does not happen has to do with the specificity of the immune response. Infectious agents like bacteria, parasites, and viruses are made of the same biological material for the most part as our own cells. If the body wants to destroy infectious agents but not itself, it has to very very specifically identify what is itself and what is not itself. If this was passed down genetically, then the \"self\" would have to be the same every time, which would mean that we could not have variation in our genomes, which, by evolutionary theory would pretty much wipe out the species as soon as some disease presented itself, or other selective pressure was applied. So this is not good. That means that the immune system has to train itself to recognize what the \"self\" is early on with every new organism created. ",
"This leads to the second reason why we can't pass down our general immunity. If every time we have to figure out what is \"self\" and what is \"not-self\", we have to create a huge repertoire of antibodies which act like barcodes. Antibodies that match any part of our cell are destroyed, those that match some other cells or biological molecules are used to target the invaders for destruction. Since, on the molecular scale, there is a HUGE amount of diversity, we end up making a lot of antibodies, somewhere on the order of 1 billion to 1 trillion.",
"To pass down these sets of barcodes, we would need the genetic space do so. The human genome is about 4 billion base pairs of DNA. The variable domains of an antibody are about 1000 base pairs. If we wanted to pass down even just the smallest set of antibodies to our progeny, that would require increasing the genome by 1000 times. Not very practical. So instead we do pass down general archetypes of the antibodies, and let each one of the billions of immune cells make a different antibody through ways of ",
"introducing variance",
".",
"This all applies to the adaptive immune system, the specific one we try to trigger with vaccines. We do pass down genetically our innate immune system, which is more of a general quick response system. This is why we all get more or less similar symptoms when we get sick - such as fever - a shared, generically passed response to infection."
] |
[
"No. Our bodies can only pass down genes that were passed to them. They do not form new dna based on what the immune system learned. However natural selection would form a disease resistant species, if not for modern medicine. It would just be a sad process of everyone dying from disease, besides those with genetic immunities"
] |
[
"How high of a temperature would you theoretically need to break any combination of molecules apart from each other into their single elements?"
] |
[
false
] | null |
[
"As Qwerty222 said, there is certainly a question of molecular bond strength. It should be pretty easy to set an upperbound on this, however.",
"For covalent molecules, (excluding network solids) I'd suspect something on the order of 1500K in the absence of oxygen.",
"For network solids, maybe 3000K? This is a blind guess.",
"For ionic solids...hrm. I'm not even entirely sure if it would be possible simply by heating. Eventually you'd wind up in the gaseous ionic state but I don't think heating provides a mechanism by which to facilitate electron exchange and get you back in the elemental state.",
"The relevant calculation, if you wanted to know the temperatures for sure, would be to take the bond energy to be less than the boltzmann constant times the temperature (in Kelvin)."
] |
[
"Depends on the molecule's bond strength, and whether or not the reaction is exothermic. ",
"Thermal Decomposition",
"."
] |
[
"You're technically correct, but if you're implying that some bonds cannot be broken by adding heat just because their formation is endothermic, then that's wrong.",
"Unless the system is at very high density/pressure, free atoms will have a higher entropy than any bonded configuration; a sufficiently high temperature will break molecules into constituent atoms, and indeed atoms into a soup of particles. I think the quoted temperature in your wikipedia article of about 4000 K sounds good. For example, our sun is about 6000 K and there are no molecules there, only atoms."
] |
[
"How does my phone/laptop/device know how much charge is left on the battery?"
] |
[
false
] |
How does a device know how much charge is left on the battery? As in what is the mechanism that is used to extract and convey this information?
|
[
"At the full charge, the battery will have a certain voltage. As it is used, the voltage begins to drop, most likely the computer reads that voltage drop and displays it in a way that is useful to us."
] |
[
"Yes it would have the same voltage as a new battery, albeit for a shorter amount of time. "
] |
[
"A follow up question: would that mean that fully a charged older battery despite having a reduced charging capacity (or a memory effect) puts out the same voltage as a brand new battery at full charge?"
] |
[
"How would an observer view the universe if it were at the origin of the big bang?"
] |
[
false
] |
According to my knowledge the universe started expanding near the speed of light. When taking relativity into account wouldn't the observer see the Universe as a relatively small place due to Length-contraction? Wouldn't the observer think a lot less time has passed than what we humans on earth consider to be slightly less than 14 billion years? When taking these both into account I'd think that the observer would look at the universe being a very small and dense place with loads of mass that does not move(assuming the observer stays stationary when comparing to other matter, which is moving away from the observer at near c)
|
[
"Metric expansion is ",
" the same as motion. For all intents and purposes you can treat things as being at rest with space expanding between them. So metric expansion doesn't involve length contraction or time dilation. It's the same reason why sufficiently distant galaxies would appear ",
" they're moving away from here \"faster\" than c. They're not actually moving, there's just more than one light second of space created between us every second of time."
] |
[
"We have found solutions of space-time curvature that would be warped in such a way as to allow faster than light travel (on a global scale) while maintaining slower than light travel locally. The problem is that these solutions are also impossible to build. Not just technologically difficult, they require forms of matter that don't exist at all in our universe. They are unphysical solutions to the problem. General relativity has at its heart the Einstein Field Equations, which set a term describing curvature equal to a term describing the distribution of mass and energy and so forth. If we take the \"stress-energy\" tensor side of the equation, and fill in a distribution of matter we know to exist, say a spherical star, or a uniformly dense \"dust\" we get a curvature out the other side that we know can exist. But since it's an equation, we can feed in a curvature we'd like to see, and ask what energy configuration could create that curvature. But we're not guaranteed that the energy solution will be guaranteed to exist. That's the problem with wormholes and warp drives. They're good curvatures, but they're unphysical stress-energy tensors.",
"Dark energy is driving expansion right now. What dark energy is, we're not sure. But it's pushing apart more than mass is pulling together."
] |
[
"Thanks for this reply! So in theory if this process of metric expansion could be reversed or warped could we achieve \"faster than light\" travel under the laws of current physics?",
"Extra question: What force does the expanding of space? At öeast in conventional physics objects with mass should pull themselves closer to each other rather than expand away from each other."
] |
[
"As the light of more stars reaches the earth, will the night sky become brighter and brighter over time?"
] |
[
false
] |
Looking forward billions of years, if someone was able to look up at the night sky from earth (lets assume its still here), will there be some point in the future where the night sky is saturated with light?
|
[
"The opposite will happen, actually. ",
"Space is expanding faster than the speed of light. Except for a small bubble around the milky way, galaxies will move outside the observable universe until there are no stars left except ones in the milky way. According to the big rip theory, eventually, even those will go away as well. "
] |
[
"The galaxies aren't expanding. The space between them is. Or, if there is a repulsive force within the galaxy, it isn't nearly strong enough to overcome the attractive force of the galaxy that binds itself together. The repulsive force (we call it dark energy because we have no idea wtf it is, only that it exists) becomes stronger proportionally to distance. "
] |
[
"Because we are in the milky way. The expansion of the universe only has an effect at large scales - larger than our galaxy. "
] |
[
"Why India’s Chandrayaan-2 is taking 6 weeks to reach Moon and land their lunar lander, while Apollo missions typically landed astronauts on the moon in about 6+ hours?"
] |
[
false
] |
[deleted]
|
[
"After being placed into a 45,475 × 169 km ",
"parking orbit",
" by the launch vehicle,",
"[47]",
" the Chandrayaan-2 spacecraft stack gradually raised its orbit using on-board propulsion over 22 days. In this phase, one perigee-raising and five apogee-raising burns were performed to reach a highly eccentric orbit of 142,975 × 276 km",
"[94]",
" followed by ",
"trans-lunar injection",
" on 13 August 2019.",
"[95]",
" Such long Earth-bound phase with multiple orbit-raising manoeuvres exploiting the ",
"Oberth effect",
" was required because of the limited lifting capacity of the launch vehicle and thrust of the spacecraft's on-board propulsion system. A similar strategy was used for ",
"Chandrayaan-1",
" and the ",
"Mars Orbiter Mission",
" during their Earth-bound phase trajectory.",
"[110]",
" On 3 August 2019, the first set of Earth images were captured by the LI4 camera on the ",
" lander, showing ",
"North American",
" landmass.",
"[59]",
" ",
"https://en.wikipedia.org/wiki/Chandrayaan-2#Geocentric_phase",
"In other words, it's done in stages to increase the fuel efficiency to be able to lift more with a smaller launch vehicle. Since the payload doesn't contain any humans or similar highly sensitive cargo, it doesn't matter much that the mission takes a little longer."
] |
[
"More in depth explanation:",
"The Oberth effect: in layman's terms it is more efficient to do maneuvers when deep in a gravity well. So the closer to the Earth the rocket it when it has it's engine on the more efficient it will be and it will require less fuel. This effect applies to both Chandrayaan and Apollo because both did their burns while in low Earth orbit.",
"The difference is Apollo did this in one burn while Chandrayaan does it in multiple burns. Each burn raises the orbit on the opposite side of Earth. So for example it starts in a 250 km circular orbit and turns on its engine for a while. Now it's in a 250km x 500km elliptical orbit. It will go around Earth once, raising up to 500km then falling back down to 250km. When it reaches the low point it will turn its engine on again to raise the far side again. Now it's in a 250km x 5000 km orbit. It repeats this process until it has an orbit that reaches the Moon.",
"Another thing to note is that as the far side of the orbit gets higher it also becomes easier to raise it. So to lift it from 250km to 500km might take the same amount of fuel as raising it from 500km to 5000km. (these numbers aren't correct, just an example)",
"Apollo had humans on board and happened with late 1960's tech. So the longer the mission took meant more time the astronauts had to spend cramped in a tiny room together, it also meant more food and water had to be brought. So it was beneficial to have a fast mission. Having many burns also came with a risk. The engine on the spacecraft wasn't 100% reliable and every ignition came with the risk of breaking something which best case means no Moon landing and worst case means 3 dead astronauts.",
"Chandrayaan is a robot so it can take as long as it wants to do things. It also has a more modern and more reliable engine. This means it has the option to do many burns.",
"This still doesn't really explain why Chandrayaan uses multiple burns though. Both techniques actually require the same amount of energy per unit mass of spacecraft so why doesn't Chandrayaan use one burn just like Apollo and save some time?",
"The extra efficiency with multiple burns actually comes from using a very small rocket engine. Smaller rocket engines weigh a lot less which means you can use a smaller rocket to lift it off Earth or you can put more science instruments on the spacecraft. Chandrayaan uses an engine so small that by the time it burned through all its fuel it would have orbited half way around the Earth and wouldn't be pointed at the Moon anymore. So it has to do a short burn then wait one orbit to get back on the right side of Earth to do another short burn."
] |
[
"Good answers here, just wanted to add:",
"It took a ",
" longer than 6 hours to land astronauts on the Moon. Apollo 11 took 52 hours to get into lunar orbit, and a total of 110 hours from mission start until astronauts landed on the Moon.",
"The fastest any spacecraft has reached the Moon was New Horizons, which took 8.5 hours after a direct burn."
] |
[
"Do Photons get trapped behind your eyes when you close them?"
] |
[
false
] |
[deleted]
|
[
"Since your body, or anything for that matter, is constantly emitting ",
"thermal EM radiation",
" (photons with wavelengths below the wavelength we can see), the answer is kinda weird. When you close your eyes, there are tons of photons of these lower energies propagating around the inside of your eyeball because they are being emitted in there. Presumably there are also photons from cell and radio signals travelling through. As far as visible light goes, those photons get absorbed rather quickly by your tissue so no, they will not get trapped."
] |
[
"All electromagnetic radiation, including visible light, x-rays, and all those other waves, are made of photons, differing only in frequency"
] |
[
"If you close your eyes, you can tell if the light is on or off."
] |
[
"Why do we have to kill a horse when it broke its leg? What is the difference in biological processes between man and horse in bone mending?"
] |
[
false
] |
Edit: Thanks for popping my gold cherry kind stranger!
|
[
"Hi there.",
"The biological processes of bone healing are the same in both horses and humans. The problem is in their weight and behavior. And it depends on the location of the fracture whether or not the horse may need to be euthanized.",
"When humans break bones, they can take weight off by sitting down, using crutches, etc. Horses don't have this option. If they take the weight off of the leg by themselves by favoring the leg, especially if they are young, the other limb may become deformed due to the increased burden. Even if they do lie down, the act of standing back up can cause the fracture to break again. Smaller horses may heal from fractures better, and a few cases may do well with amputation, but these cases are few and far between.",
"Even if the leg is stabilized, it takes a very long time to heal. During this long time of inflammation, the horse may develop ",
"laminitis",
", which causes, in a word, the hooves to fall off. This is similar to having your fingernails pulled off, and for an animal that relies on supporting all of its weight on its \"fingernails\" this is incredibly painful and debilitating. (This is actually what happened to ",
"Barbaro",
"). Here is a look at ",
"Barbaro's radiographs",
" and how they attempted to stabilize his distal limb.",
"Also, practically, many horses have jobs (racers like thoroughbreds/standardbreds, work-horses like draft horses, etc), and their lives are sometimes seen as an investment. If the owner cannot afford to keep them on pasture, if it isn't a financially viable option, they may elect to euthanize.",
"Edit: added links and clarified"
] |
[
"Actually, there's one other detail you forgot to mention, which is that horses also cannot afford to lie down for prolonged periods of time as it messes up their internal organs. ",
"This is problematic as not only will having them support themselves on 3 legs cause damage to their intact legs, but you can't lie them down either or you get pressure sores, fluids accumulating in their lungs, etc.",
"To allow a horse to heal from a leg injury you pretty much need to keep it supported by a sling with a crane in a swimming pool (so that it's suspended in the water, without too much weight on the torso), which is insanely expensive and usually very distressing to the horse. It's pretty much never done."
] |
[
"Also, induction and emergence (going into and coming out of anesthesia) of horses is very scary and they can hurt themselves during the process. ",
"Their bones are huge, and the hardware to fix them has to be specially made, the hardware for humans doesn't fit their bones. ",
"Bones are harder than the surgical implants used for bony fixation. Horses are not known for their compliance with weight bearing restrictions, which could cause the hardware to break and compromise the reduction. ",
"I have personally been involved with the amputation on a horses leg with immediate placement on a prosthetic, so I know that is an option. I did not follow the animal after the surgery, so I can't comment on the ultimate success of the procedure."
] |
[
"What would humanity gain from increasing funding for space exploration?"
] |
[
false
] | null |
[
"Is \"awesomeness\" an acceptable answer?"
] |
[
"Survival."
] |
[
"The Sagan influence in me feels compelled to add that there's the fact that sending people to space is also freakin' awesome."
] |
[
"How Does Hawking Radiation Cause a Black Hole to Lose Mass?"
] |
[
false
] |
I am not a formal student of physics, but I am an engineering graduate and have several courses in fundamental physics and thermodynamics under my belt, and I have a layman's interest in theoretical physics. My understanding of Hawking radiation is that it occurs due to virtual particle pairs spawning near the event horizon of a black hole, where one of the particles escapes and the other falls into the black hole. Relative to the universe outside the black hole the energy of the escaping particle has a positive energy and the trapped particle has a negative energy. The in-falling particle, having negative energy, decreases the total energy, and therefore mass, of the black hole. What I don't understand is how negative energy is always assigned to the in-falling particle. Could not the escaping particle just as easily have negative energy and therefore decrease the energy of the outside universe?
|
[
"Virtual particles are a calculational tool. They are not something that can ever be observed (they don't even have the correct physical relationship between their energy , momentum, and mass). What you have outlined above is one way (sort of) to describe the first calculation that led Hawking to predict the evaporation of black holes.",
"When black holes are merged with quantum mechanics, it turns out that they can evaporate; what is emitted when the black hole evaporates is termed Hawking radiation. The physical process is as follows. The initial physical state is a black hole; the final physical state is a black hole with slightly less mass and a particle going away from the event horizon.",
"One version of this calculation uses virtual particles. In that calculation, the initial and final state are connected by a virtual particle. But I have to stress, that is just something that is a method of calculation. It is not an intrinsic physical part of what happens. However, within that calculational paradigm, the particle that escapes to infinity (away from the black hole) must have the right energy/mass/momentum relationship, and so it must have positive energy. The virtual particle (again, a calculational tool, not an observable thing) is not restricted in this way."
] |
[
"Hawking radiation is formed from the annihilation of pairs of particles at the horizon. ",
"This is simply incorrect."
] |
[
"Hawking radiation is formed from the annihilation of pairs of particles at the horizon. ",
"This is simply incorrect."
] |
[
"Halogen Heaters and Basil Plants."
] |
[
false
] |
[deleted]
|
[
"Unless it's ridiculously cold in your house, the limiting factor here is going to be light usable to the plant - photosynthetically active radiation. A halogen heater puts out a very small amount of PAR. The best thing you could do* is keep it near a sunny window and train several CFL lamps on the leaves (quite close to the leaves). Also, pinch off any flowers, as they will suck the plant's energy away from leaf production.",
"*this is the best thing you could do reasonably for not much money. If you wanted to, you could drop a ridiculous amount of money on lamps designed to maximize PAR and thereby the growth of your friend."
] |
[
"not saying it isn't appropriate here, but may I also suggest ",
"r/gardening",
"? They may have good tips."
] |
[
"You can make a cold frame (mini greenhouse) and by some plant growing lights. As long as it doesn't go below freezing it ",
" be fine. Alternatively,Basil is very easy to grow, you could take a cutting and place it in a sunny window and it will survive the winter. "
] |
[
"Why do we sometimes have blurry vision when we wake up?"
] |
[
false
] |
Is this something that only happens to people with glasses, or is this an occurrence for most people? EDIT: Sorry, if this came off as anecdotal.
|
[
"Eyes have some amounts of oil and mucus on them, and when adequately moisturized by the tear ducts we see fine through it. When tears dry up (which can happen overnight), the oil and mucus can appear somewhat blurry. "
] |
[
"Tear ducts are what drains the tears, not what produces them. The lacrimal gland makes tears."
] |
[
"I think you're referring to ",
"http://en.m.wikipedia.org/wiki/Rheum",
"It's a mucus that is meant to lubricate your eyes that doesn't get washed away while you sleep."
] |
[
"There is a redditor who attended the CERN OPERA briefing doing an AMA. Can we get a regular contributor to r/askscience to take a look and do a little peer review? (X-post link inside)"
] |
[
false
] |
[deleted]
|
[
"His summary seems reasonable. He's likely some sort of physics student (possibly grad). The results are almost definitely an unknown source of systematic bias, and should continue to be assumed so (unless you are a particle theorist who wants something fun to ponder about) until more independent experiments confirm with more independent verifications. If it was a new effect it likely doesn't destroy relativity but is warped extra dimensions."
] |
[
"Well, I kind of disagree with the 'doesn't disprove relativity' angle. I see where you're coming from with it, but I'm not sure it's a good way of expressing it. The point here is that SR is so ",
" ingrained in current theory, and has made so very many correct predictions (from anti-particles to QED in physics, to the color of gold and Pauli principle in chemistry), that it's essentially unfathomable that it'd be totally \"wrong\". In much the same way that SR itself didn't really invalidate classical physics.",
"But there's some differences; SR (and other modern theories) are a bit more well-grounded in terms of their underlying postulates. Before SR everyone had basically just ",
" that different observers would agree on measurements of time and space. SR invalidated that assumption, but people hadn't thought too much about it. But since Einstein, physics has spent tons of time on questioning and figuring out the basic postulates that underly it.",
"Since this result is rather blatantly at odds with SR, it means something must be wrong with some of our basic postulates. And it seems far from obvious which one(s) you could invalidate and still rescue most of what we know to be true. Who can really tell the scale of the theoretical ramifications? ",
"That said, it is of course most likely just a systematic instrument error, hidden somewhere in the very complicated accounting of systematic errors required to perform measurements at that scale and accuracy. ",
"To take a wild guess, if only to illustrate for people the kinds of complexities involved, it could be something like a miscalibrated or malfunctioning thermocouple in an electronic device. That, in turn, could cause an inaccurate temperature reading, causing an over or under-compensation when they were correcting the timings of their electronics for the systematic errors caused by thermal drift. It's the kind of stuff the people at CERN will likely be poring over in the months to come."
] |
[
"Since this result is rather blatantly at odds with SR, it means something must be wrong with some of our basic postulates. And it seems far from obvious which one(s) you could invalidate and still rescue most of what we know to be true. Who can really tell the scale of the theoretical ramifications?",
"I think that you raise the very good argument explaining why no one seriously believes or is even willing to consider that SR is not correct for normal matter and radiation (electrons, photons, etc...).",
"The only theoretical position that I have seen seriously considered is one of a higher dimensional GR, where photons and normal matter are confined to a plane in which SR holds, but high energy neutrinos can explore a higher dimensional bulk allowing them to move at higher velocity in the theory.",
"Figure 1 of ",
"this paper",
" illustrates the idea quite nicely. ",
"In such a theory, SR holds as expected in every measurement ever made for everything except high energy neutrinos. It should be noted that no one has ever measured high energy neutrinos with this degree of accuracy.",
"I refuse to guess at what is more likely - superluminal neutrinos, or systematic error - until MINOS chimes in with an independent measurement. Whatever the outcome, the only way to interpret the data is in such a way that is consistent with normal matter obeying SR exactly."
] |
[
"Why are there so many research stations on the Antartica and what are we actually researching?"
] |
[
false
] | null |
[
"You can get a lot of ",
"climate history from ice cores",
", and the dynamics of ice sheets are important for estimating future sea level rise in response to warming.",
"The waters around Antarctica have unique biology.",
"There is ",
"uniquely non-turbulent clear air for astronomical purposes",
".",
"You can ",
"detect neutrinos with huge blocks of ice",
".",
"Also helps that it's a big chunk of land which is currently outside of national boundaries, and part of the goal is to stake a claim to part of it if that should ever change."
] |
[
"To add two more:",
"The ",
"dry valleys are used as analogues of early earth",
".",
"There are ",
"extensive efforts",
" to collect meteorites in Antarctica (basically because they are easy to pick out on the ice)."
] |
[
"It's the continent least contaminated by human activity and much of it is frozen so there's unique opportunities to discover aspects of planetary,climate, and biological history. Think of how useful Pompeii was for historians since it was like a city frozen in time"
] |
[
"What are the physiological adaptations for hot climates?"
] |
[
false
] | null |
[
"Probably more than you wanted to know",
"Summary: Your sweat becomes more dilute and you sweat more and start sweating faster, your body water and plasma volume increase and you become thirstier, your metabolic rate and heart rate decrease, your resting core and skin temperatures drop, and you start producing heat shock proteins. Acclimatization takes a few days to weeks."
] |
[
"Some way to exchange heat with the environment. For example primates sweat, other animals like hares increase their surface area for heat exchange and others simply tolerate higher body temperatures or stay underground/in shade during the day."
] |
[
"IN hot climates, maintaining body heat is not a problem(the surrounding helps in that aspect), but dissipating it is the main concern",
"Increased melanin production, oily skin due to sweat to prevent the body from getting overheated(yes it is very common among people who live in the tropical regions). If you are a fair skinned person, you might notice your skin getting redder, because the blood vessels near the surface get dilated to allow more blood flow, so that it can dissipate the internal body heat into the environment more efficiently. There might even be a reduced rate of metabolism for people in such climates(can't be said to be true, as there are way too many exceptions)",
"Another thing, it's easier for a body to adapt to the heat rather than to the cold, hence why it's harder for people from the equatorial regions to adjust in a cold climate in a short period of time, usually takes months, whereas it takes a few weeks for a person in the North to adapt to the equatorial regions.",
"Check this wiki link out for more info: ",
"https://en.wikipedia.org/wiki/Cold_and_heat_adaptations_in_humans"
] |
[
"Why is coulomb not a fundamental unit?"
] |
[
false
] |
I know that Ampere is the fundamental unit in Electricity, but doesn't it make more sense to have coulombs to be the fundamental unit?
|
[
"It's easier to measure an ampere precisely than it is a coulomb."
] |
[
"...you take angles counterclockwise from the x axis."
] |
[
"This is the correct answer. However, it terms of what ought to be a fundamental unit, the Coulomb certain should be because the ampere is a measure of the amount of electric charge passing a point in an electric circuit per unit time with 6.241 × 1018 electrons, or one Coulomb per second constituting one ampere. Since amperes are expressed in terms of another fundamental unit, they're sort of crappy fundamental units. However, convention in measurement, as iorgfeflkd said, takes precedence here. "
] |
[
"Double Slit Question"
] |
[
false
] |
In the experiment, they found (correct me if I'm wrong) that the same principle applies to both photons electrons, i.e., an interference pattern is created so long as the path of the projectile is not observed. My understanding is that the interference pattern is created by the interference of the probability wave of the particle with itself. So what happens if you repeat the experiment, slightly increasing the size of the particle each time (or by using a different, and larger, particle/projectile all the way up to macroscopic objects)? How does the interference pattern created from each run of the experiment compare with the previous and next pattern? Would it eventually collapse into a 'double band' impression on the detector as the objects get larger?
|
[
"The general trend is that, as things get smaller, the quantum stuff (wave functions and whatnot) becomes more applicable. As things get larger, the quantum effects are still present, but classical behavior eventually drowns out the quantum effects. So, yes, after some point, you'd only see two lines at your detector. ",
"I guess you could shoot increasingly large particles through slits and observe how things change. I'm sure this has been done before; it'd be nice if one of the physics folks could link to an image of the experiment results. "
] |
[
"The interference pattern for buckyballs",
"."
] |
[
"Last I heard, we don't know the cutoff where quantum effects stop. We can actually do the double slit experiment with large things like buckyballs, and even clouds of Bose-Einstein condensate."
] |
[
"Will a organ that was donated from a younger person to an older person help minimize the aging process? Also, will the organ age faster due to the already aged organs around it?"
] |
[
false
] | null |
[
"Transplantation isn't what you think. It doesn't restore a person. It's a kludge. But your thinking is common because the media's reports on transplants are biased and rarely discuss the negatives.",
"The organ is damaged by the surgeries and by being outside a body. The recipient must take pills for the rest of their life to prevent their immune system from attacking the organ. The pills are also toxic, harm the body, and have divers negative side effects. The immune system is slowed, but will eventually kill the organ unless the patient dies first. Having a transplant is considered a terminal disease.",
"Transplants have lifespans regardless of age. Young people who receive organs from young donors will generally need several transplants throughout their life."
] |
[
"I remember when ",
"Robert Altman was awarded a lifetime achievement Oscar in 2006",
". In his acceptance speech, he revealed that he'd had a heart transplant from a woman in her 30s, 10 years earlier, so he thought he had 40 years or more left. He did not survive the year (he died of cancer). Heart transplants last on average 10 years.",
"Transplantation is very hard on the transplanted organ, as well as the recipient's body. Organs degrade over time so they last if you're lucky 20 years. Sometimes more, which is great, but often less. So the organ ages differently than the rest of the body. It's not like you suddenly have a healthy, youthful organ in an old body. The immunosuppressants that transplant recipients must take are also pretty hard on a person, and they do things like increase risk of developing cancer. So while Altman wasn't unusual in dying of cancer at age 81, and that could have happened even without the transplant, the immunosuppressants didn't do him any favors. If you look at otherwise healthy people who get transplants, like the people who got face transplants or hand transplants, you'll see that getting a transplant ages you and shortens lifespan in many cases. The first person to get a face transplant died of 2 cancers within 10 years of the transplant, still in her 40s."
] |
[
"So... We make clones and then store them on an island until we need an organ."
] |
[
"Why are there so many volcanic eruptions recently? Are they somehow connected or is it a coincidence? Or is it just new media coverage?"
] |
[
false
] | null |
[
"The current level of activity is normal. On average, there are usually ~20 volcanoes in some stage of erupting at any given time. The recent news worthy eruptions (e.g. Hawaii and the recent one in Guatemala) are not connected. So the short answer it's just the coverage and/or the fact that these two eruptions are happening in populated places and that both are being filmed a lot by locals (mostly safely in the case of Hawaii and ",
" unsafely in the case of the Guatemalan eruption, you should never be as close to a pyroclastic flow as some of the people shooting video are). As for the rates, couldn't find any particularly good plots, but you can check out ",
"the smithsonian",
" weekly eruption report to 1) get a sense that there are lots of eruptions going on that aren't making the news and 2) if you go back into the archives, which span ~18 years, you can get a somewhat qualitative sense that this number of currently erupting volcanoes isn't particularly odd. As a side note, this is not quite real time, so this is the summary for last week so it doesn't yet include the eruption in Guatemala."
] |
[
"I think the ",
"Clustering Illusion",
" may be an answer to this question, at least in part."
] |
[
"Yes, ",
"apophenia",
" in general is a good explanation for lots of perceived patterns in natural phenomena, and especially those that get asked about here on AskScience. Not all patterns and apparent clustering in things like earthquakes, volcanoes, etc are devoid of meaning (e.g. aftershock sequences are good examples of a true pattern in earthquakes), but almost all of the, 'Why are there so many X recently? Is the rate of X increasing?' type observations/questions aren't meaningful when you look at time series of events. "
] |
[
"Are there any successful attempts to create a substance that is made up entirely with antimatter particles?"
] |
[
false
] | null |
[
"Yes, as long as you consider a small amount of antihydrogen-atoms as being a substance. CERN has successfully kept these antiatoms around for about 16 minutes. Here's the press release from 2011: ",
"http://press.cern/press-releases/2011/06/cern-experiment-traps-antimatter-atoms-1000-seconds",
"."
] |
[
"No. The (unfounded) concern was that, at the extremely high energy densities probed by CERN, microscopic black holes should be created, as any amount of energy/mass packed into a sufficiently small space will collapse into a black hole. However, Stephen Hawking's greatest contribution to physics was arguably his discovery that black holes evaporate, and that smaller black holes evaporate exponentially faster than large ones. The black holes formed in a particle collider are so short-lived that they don't stand a chance of interacting with anything.",
"The short of it is that cosmic rays (subatomic particles moving near the speed of light) smash into our atmosphere every second with energies exceeding that probed by CERN, and so if black holes didn't evaporate the Earth would have been swallowed up by a black hole very shortly after it formed. "
] |
[
"It was his consideration of what happens when a ",
"virtual particle pair",
", a consequence of quantum mechanics, comes into existence at the event horizon of a black hole. If one member of the pair goes into the black hole and is trapped while the other escapes, then energy conservation if violated because now the escaped member of the virtual particle pair is a regular particle that has come into existence permanently, increasing the total amount of energy in the universe. The only way for energy to be conserved is if the mass of the new real particle is subtracted from the black hole. So virtual particles coming into existence at the black hole's event horizon causes it to slowly evaporate.",
"The mathematics is of course much more complicated, but I think that that is a fairly accurate qualitative description. "
] |
[
"What's the smallest amount of collected atoms that can be detected by the human eye (not necessarily molecules because molecules can vary in size)? like a grain of sand, or.. A tiny piece of aluminum or gold."
] |
[
false
] | null |
[
"best possible human ",
"visual acuity",
" is around 20/10 (or 6/3); with this acuity you can discriminate between details or spots that are just one half arcminute of visual angle across (and separated by the same distance, so the limit of resolution is 1 discrimination per arcminute). you're going to need two good eyes to get such good resolution (basically for binocular noise correction).",
"the closest distance to your face you can converge both eyes and keep focused images on your retinas (assuming you're young and can still accommodate and have normal binocular vision) is (this is an educated guess) about 5±1cm.",
"with a little trigonometry (tangent of the angle of minimum resolution, times the speck distance, or 5cm*tan{1arcmin}), the tinest speck you can discriminate from other specks is 0.0015 cm wide, or about 15±3 microns. this is the size of a big ",
"cell",
" (e.g. human eggs are much bigger than this), and a little bigger than your typical bacterium.",
".",
"(this might sound amazing, and it would be dependent on perfect lighting and other sorts of conditions, but if you change the viewing distance, it's a little more believable. for example, under these perfect conditions, someone with 20/10 vision could see, at 1 meter, the spaces between the millimeter marks on a ruler. impressive, but not unbelievable..)"
] |
[
"That is a linear measure, assuming your 150k atom diameter, you are really looking at around 10",
" atoms for a minimally detectable sphere."
] |
[
"Assuming your length of 15um being the smallest diameter particle visible is correct(personally I can see 45um particles in the lab i work at), and if we work with a common opaque material, in this case common graphite, we can calculate the number of atoms.",
"As a single layer(graphene), its basically transparent(except under optimal lighting conditions and on a substrate like SiO2, where the sheet will have ~2.3% absorbance), but becomes functionally opaque at around 10 layers thick, so our platelet of graphite will be 15um across and 10 layers thick. The interlayer spacing of graphite is 6.708e-4 microns, so the thickness of our platelet with 10 layers will be 6.708e-3 microns.",
"Pure graphite has a density of 2.23g/cm",
" , and our platelet has a volume of Pix7.5",
" *6.708e-3 =1.1854 um",
" or 1.1854e-12 cm",
" which is 2.643442e-12 g.",
"Graphite has a molar mass of 12.011 g/mol. this means there are 2.20085e-13mol in this platelet.\n1 mol is 6.022141e23 atoms. This gives us a final count of 1.325e11 atoms.(1.325e10 atoms if your working with monolayer graphene)",
"Source: I make grahpite/graphene nanoplatelets for a living.\n",
"http://en.wikipedia.org/wiki/Carbon",
"\n",
"http://en.wikipedia.org/wiki/Graphene",
"\n",
"http://en.wikipedia.org/wiki/Graphite",
"I probably should have started from the bond length of the lattice which is .142nm. But its sunday morning, and I'm lazy."
] |
[
"Is there some sort of library for DNA of every living creature?"
] |
[
false
] |
It occurred to me that since cloning technology is becoming more advanced, why don't we keep an archive of DNA samples of every currently living creature so we could resurrect a species if it goes extinct? We might already, but I'm just curious.
|
[
"There are a few places like this, although I know of none with complete repositories, nor can I find reference to any such institution. It's also unlikely that we'd be able to save DNA samples from every \"creature\" (more on this later, though).",
"The American Museum of Natural History in NYC has put forth a project to deep freeze DNA samples from around 400 endangered species.\nYou can read ",
"an article about this in Scientific American",
".",
"Several Zoos operate \"frozen zoos,\" ",
"such as the San Diego zoo.",
"There is the ",
"Frozen Ark project",
".",
"Beyond this there is the ",
"Svalbard Global Seed Vault",
", a project to store a number of seeds in the arctic. While this would not include \"cloning\" as you mentioned, it is similar to the concept you are putting forth.",
"At the current state of the science of cloning, most of these would see more probable use in serving as genetic repositories to help a low-population species rebound without damaging inbreeding.",
"Basically, the idea is that there is extra genetic material to use for fertilization in a species which is endangered, but not yet extinct. If the species we may be able to make efforts to help a particular species population rebound, but if there is not enough genetic variability in the population itself to prevent inbreeding, it may be beneficial to \"seed\" (pun not intended) some additional genetic material into the population.",
"Reviving an extinct species has a long way to come before it would be viable. While we have had some success cloning different species, it is still troubled. Particular epigenetic disorders are more common in these types of births (as well as in vitro fertilization in humans).",
"These are caused when the \"epigenetic\" state of a cell is not properly maintained or reset. The epigenetic state or \"epigenomics\" of a cell is essentially a set of modifications to the DNA and the proteins which bind it which regulate which genes are turned \"on\" or \"off.\" Since some of these genes control factors such as whether a cell will become or be unable to become a particular type of \"differentiated cell\" (like neurons, muscle cells, etc), it is important for development and long term function that this is appropriately controlled.",
"Beyond this, cloning in animals still needs a female to carry the offspring to term. We have not yet achieved this. It would require a number of things to be simulated which you can read about ",
"on Wikipedia",
". With regards to this, a few groups have worked on individual components, such as artificial placentas with modest success. However, this is a long shot from a truly functioning uterus. One of the points which the previously linked Wikipedia page probably does not do justice is the complexity of creating a proper hormonal system. I would speculate that not properly controlling for the exchange of hormones between the \"mother system\" and the fetus would likely have dramatic effects on various aspects of development and/or the long-term regulation of those hormone systems in the child.",
"Depending on how you define a \"creature\" it may also be unrealistic to attempt this type of storage as well. If creature means \"endangered species,\" there are ~3000 animal and ~2500 plant species which are formerly considered endangered. This is an essentially arbitrary number based on organisms we already know to exist and how we want to define being \"endangered.\" The actual number of species who will soon be extinct is likely an underestimate as many species are unknown. However, it has the potential to be a very large number of species, even if only a small fraction of species go extinct each year, as the World Wildlife Fund describes ",
"here",
". This would be quite difficult to accomplish in terms of both collecting samples and storing them, but I would not doubt that given the initiative it could be done within a reasonable margin of error (you'll never find every species at risk) one day.",
"However, if \"creature\" is taken to mean all species, or even just all animals, the total number of species is probably far beyond anything that will be achievable in even the relatively distant future just because of the sheer size of such an endeavor. By one estimate of the number of species on the planet (~8.7 million) it would take about 990 straight YEARS worth of work to complete it, even if we were able to identify each organism as a unique one, collect the sample of each organism's DNA, transport it back to the facility, and store it at the highly generous speed of 1/hour. In reality, it would probably take much longer and would take much longer per sample and the work would have to be split between a great deal of people, who would not be able to work constantly. This is ignoring the immense financial constraints, as well as practical constraints such as our current inability to isolate many microorganisms who have obligate symbiotic relationships with other micro or macro organisms and cannot be cultured on their own.",
"One other poster mentioned GenBank, which I addressed partially as such:",
"To add to this comment, GenBank is a digital repository. It is not a \"bank\" where physical copies of these organism's DNA is held, as I think you were asked.",
"To elaborate more on this, there has been some success in making a \"synthetic\" organism off of an electronic genome sequence for an organism. This was done in a particularly simple bacteria though, and even then, the process was not very effective: while attempting to generate the organism, they first encountered several unintended mutations in critical genes. In higher ordered organisms, this would be even more difficult to achieve, as eukaryotes typically have \"epigenomes\" on top of their \"genomic\" data as I mentioned earlier. Currently we don't fully understand the \"code\" which is at work here, nor do we a way to recreate it from scratch."
] |
[
"I think he means do they have an archive of the actual physical genomes. Maybe in cryogenic storage of something. As far as I'm aware there is no big multi-species storage location. But for individual model organisms there are certain places with thousands of strains of that organism (e.g. mice, drosophila, zebrafish...)",
"Isn't there like an underground arctic seed bank?"
] |
[
"More or less, Yes. It's called GeneBank and it's run by the NCBI which itself is part of the NIH. It's a database where they accept whole genome data from labs.",
"\nHowever, most of the database is composed of \"popular\" organism like human and species used as model organisms like rats, microbes, Arabidopsis etc.",
"\nYou can check it out here ",
"https://www.ncbi.nlm.nih.gov/genbank/"
] |
[
"Why has there been no vaccine produced for SARS even though the first outbreak was in 2003, or MERS which was identified in 2012?"
] |
[
false
] |
Does the fact that we don’t have a vaccine for either illnesses despite 17 and 8 years having passed reflect on the likelihood of finding a vaccine for the current pandemic?
|
[
"For SARS, experimental vaccines were made and seemed to be reasonably safe and effective in animal models. For example (this is not the only one) ",
"Immunogenicity, safety, and protective efficacy of an inactivated SARS-associated coronavirus vaccine in rhesus monkeys",
" ",
"MERS hasn’t progressed as far, but there’s been progress there as well: ",
"Prospects for a MERS-CoV spike vaccine",
"Why weren’t vaccines made widely available? Because there was no real point. SARS was eliminated through quarantine and contact tracing by 2004. MERS has never spread well between humans. ",
"Vaccines aren’t put through the large and costly (and potentially risky) clinical trials needed for commercial licensure unless there’s a significant need for them. This is partly a commercial thing, but it’s also common sense; vaccines are only used to prevent disease, and if there’s no disease to be prevented there’s no point in using vaccines. ",
"There are many diseases like SARS and MERS, where vaccines have been produced in an academic lab, tested to some degree, and then set aside because there’s no immediate need. What that means is that when a new disease comes along (like COVID-19) this previous experience can be used to jump-start new vaccine production. All the experience with SARS vaccines is one of the reasons scientists are reasonable confident that a good vaccine for SARS-CoV-2 can be made."
] |
[
"Because we didn’t need those vaccines to stop the outbreaks. SARS and MERS are not very infective, and patients can’t infect others until they have shown symptoms for a few days already. This means that for SARS governments just put all patients in isolation, and for MERS (which is ongoing, and transmitted via infected camels in many Middle Eastern countries) any new cases are immediately locked down. So there’s very little spread and no need for a vaccine."
] |
[
"And two more things: firstly, it’s unlikely that a vaccine for those would be effective against corona, although it is possible; and secondly, it doesn’t reflect the likelihood of a vaccine for corona. It seems extremely likely that corona will become a seasonal illness, and a lot of attention will thus be devoted to creating a vaccine for it (as compared to a singular outbreak like SARS). It may take a long time (think 2-3 years) for a corona vaccine but one will be developed within 8 or 17 years."
] |
[
"Why is the FYA gene not present in Africans and why is it important?"
] |
[
false
] |
[deleted]
|
[
"The FY genotypes (FYA, FYB, FY3) encode slightly different variations of a protein present in the membrane of our red blood cells. ",
"It's important only so far as because this protein also happens to be the receptor that is recognized by ",
", the parasite that causes malaria. So, if you lack the FY antigen, you are slightly less susceptible to malaria.",
" ",
"A brief googling shows me that this particular gene is something that has been latched on to by a particular brand of racist, because whites and asians are more likely to be FYA or B, whereas blacks are more likely to be FY negative. This fact alone means almost nothing; only that people that lack FY (e.g. most black people) are slightly less susceptible to malaria. Bigots seem to have become interested in this because it is (in fact) a genuine genetic difference between most (~90%) of whites and most (~66%) of blacks, but its not like the FY protein has been shown to have any particularly huge impact outside of malaria. It's just a red blood cell surface marker.",
"Its likely that the reason people of african descent tend to be FY- is because malaria is endemic to Africa, exerting a selective pressure on those who can resist malaria, such as the FY- genotype.",
"http://en.wikipedia.org/wiki/Duffy_antigen_system"
] |
[
"To answer the first half of your question, the Fy glycoproteins are sticky little membrane proteins that are expressed on the surface of many cell types including immature red blood cells (reticulocytes), mature red blood cells (erythrocytes), epithelium of blood vessels, lung alveoli and parts of the brain. It acts as a non-specific receptor, and internalizes from the membrane into the cell in response to binding by a variety of immune signalling molecules called chemokines. This internalization can cause changes to occur in the cell, right now the strongest evidence being for neutrophil migration from the bloodstream into tissues.",
"People or mice lacking Fy appear normal with perhaps some trabecular bone structural changes (slightly decreased bone volume), and when gene targeted mice are challenged with an inflammatory stimulus (LPS), they have increased inflammatory infiltration to lung and liver tissue. ",
"The real story with Fy receptors is what ",
"/u/meaningless_name",
" has described, which is that expression of Fy is required for ",
" to enter red blood cells. Remove Fy = remove ",
" malaria infections!",
"More reading: [",
"Wikipedia",
"], [",
"OMIM",
"], [",
"Mouse Genome Informatics",
"]"
] |
[
"Came here hoping to see rational explanations for genetic differences. Did not disappoint.",
"Thanks for being askscience, and not worldnews, where anti-African opinions appear to be rampant. To the OP, you could also use the same conceptual situation to explain the difference between lactose tolerance in Europeans vs the rest of the world. Genetic differences arise but we're all pretty similar."
] |
[
"If the universe is infinite, how can it expand?"
] |
[
false
] |
If the universe is infinite, how can something infinite expand? Doesn't the word expand implies that the thing that expands is finite? Also, if the universe is expanding, what would happen if I travel faster than the universe expanding rate for long enough in one direction?
|
[
"We have rejected the infinite universe theory a long time ago, by accepting the idea of a big bang.",
"Au contraire, the most commonly used model for the Universe implies an infinite Universe. It's called \"flat Lambda CDM\"."
] |
[
"Sorry, but the size and cardinality of all countable infinite sets is identical.",
"This means there are not \"more\" even numbers than integers. You can match them 1:1 by the relationship n-->2n",
"edit: not all infinities are the same, but the infinities of your examples are the same."
] |
[
"Sorry, but the size and cardinality of all countable infinite sets is identical.",
"This means there are not \"more\" even numbers than integers. You can match them 1:1 by the relationship n-->2n",
"edit: not all infinities are the same, but the infinities of your examples are the same."
] |
[
"Why are diesel engines preferred over petrol in heavy towing/moving applications?"
] |
[
false
] | null |
[
"Diesel is preferred for the following:",
"I'm sure others will chime in soon; I work on airplanes, haha."
] |
[
"Here's",
" a Popular Mechanics article on that, the main points seem to be that, 1) diesel engines are intrinsically costlier because of reasons (higher compression ratio, the need for high-pressure pump and after-treatment system to comply with environmental regulations, etc), 2) both diesel and gas in the US are relatively cheap so it would take a lot of time to recoup the difference, 3) diesel is usually taxed more in the US, further decreasing end-user benefits."
] |
[
"Diesels are more efficient when they're bigger; ship engines have cylinders a metre across. Small diesels (for cars) were hard to do well, but Volkswagen's TDI changed that and now they're the leader in diesel cars."
] |
[
"Can babies get vaccine antibodies from mom through her breast milk?"
] |
[
false
] |
There’s a great body of research on transfer of immunity through the placenta wall, but I’m having difficulty in finding good information on how well antibodies are adopted when absorbed through the gut, whether it be through colostrum or breast milk. Also, considering the change in gut behavior from a closed gut to an open gut. Can anyone shed some light on the subject?
|
[
"Yes but I don't believe there are any studies testing thresholds for protection. Probably unethical.",
"For SARS-CoV-2 vaccines there is evidence of transfer through breast milk:",
"",
"This study found robust secretion of SARS-CoV-2 specific IgA and IgG antibodies in breast milk for 6 weeks after vaccination. IgA secretion was evident as early as 2 weeks after vaccination followed by a spike in IgG after 4 weeks (a week after the second vaccine). A few other studies have shown similar findings in women infected with COVID-19.",
"5",
" Antibodies found in breast milk of these women showed strong neutralizing effects, suggesting a potential protective effect against infection in the infant.",
"https://jamanetwork.com/journals/jama/fullarticle/2778766",
"",
"COVID-19 mRNA vaccines generated robust humoral immunity in pregnant and lactating women, with immunogenicity and reactogenicity similar to that observed in non-pregnant women. Vaccine-induced immune responses were significantly greater than the response to natural infection. Immune transfer to neonates occurred via placenta and breastmilk.",
"https://www.ajog.org/article/S0002-9378(21)00187-3/fulltext",
"00187-3/fulltext)",
"",
"We did not detect SARS-CoV-2 RNA in milk produced by women with mild-to-moderate COVID-19. Moreover, we demonstrated that milk contains anti-SARS-CoV-2 antibodies and that their concentrations are correlated with milk’s ability to effectively neutralize SARS-CoV-2 infectivity.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7885115/"
] |
[
"The “open” vs “closed” gut is a myth (",
"https://www.google.com/amp/s/scienceofmom.com/2016/05/03/whats-up-with-the-virgin-gut-do-babies-really-have-an-open-gut-until-6-months-of-age/amp/",
"). So even if they do get antibodies through the breast milk (which seems to be the case in several early papers), there is no way for them to enter the blood stream. The antibodies will only be present in mucosal surfaces."
] |
[
"Also, have there been any investigations on antibodies in babies? Babies get bloodwork done at 9 months. Have they tested that blood for antibodies in any cases?"
] |
[
"Why are the centers of galaxies so bright?"
] |
[
false
] |
Looking at picture, it seems that there's some space between the center of the galaxy and the clumps of matter/stars/gas that form the inner ring. Yet the center is visibly brighter. Is this an effect of the camera/photo, or is the center actually giving off that much light? I was under the impression that many galactic centers are supermassive black holes. Why would one give off so much light?
|
[
"If you're interested in this topic, you might also like to read up on ",
"active galactic nuclei.",
" Also ",
"here",
" and ",
"here",
"."
] |
[
"Spiral galaxies like the Milky Way and the Andromeda galaxy (M31, in your photo), are believed to have formed around black holes that were produced by some of the earliest, most massive stars in the Universe. Their gravity \"seeded\" the formation of entire galaxies, even though their masses constitute only a tiny fraction of the current structures.",
"The center of a spiral galaxy is far more densely populated than the arms or the rim. The light at the hub is not coming from the black hole at the core, but from the ",
" of stars that orbit it.",
"Some spiral galaxies funnel unthinkably vast quantities of matter into their central black hole, and the incredible amount of energy liberated as it falls into the hole often causes it to shine far brighter than all the stars in the host galaxy combined. These are quasars, the most energetic continuously-radiating sources in the known universe--but we'll save those for another discussion."
] |
[
"Spot on response! Thanks!",
"Some spiral galaxies funnel unthinkably vast quantities of matter into their central black hole, and the incredible amount of energy liberated as it falls into the hole often causes it to shine far brighter than all the stars in the host galaxy combined.",
"Is this process sustainable? How long until it runs out of (nearby, non-orbiting) matter and fizzles out?"
] |
[
"Would it be correct to think that sexual genetic heredity is patriarchal?"
] |
[
false
] |
Since fathers must pass their Y chromosome to their sons, but mothers can pass either one of their X to their daughters, that means the male hereditary line will always have an unbroken chain of Y's passed down. If a daughter can receive either one of their mother's X's (i.e. they're not enumerated in any way), then that will not always be the case for the female hereditary line. Is that quality something that can be observed in the phenotypes across generations of males in a species? Or does mutation and crossover (or whatever) mix it up so much that it is no longer significant? Then, depending on the answer, I have a few followup questions.
|
[
"Yeah, the y-chromosome is passed down from father to son for the most part unchanged, and the mitochondrial DNA is passed down by the mother mostly unchanged. That's why you can use Y and mtDNA to track genetic ancestry."
] |
[
"There aren't very many genes on the human Y chromosome (see ",
"wikipedia",
", so the Y probably doesn't have a huge impact on male phenotypes.",
"There are also some species (birds, some fish and insects) where sex determination is flipped around: males have two copies of the Z chromosome and females have one Z and one W. In these cases, the W is passed down from female to female. "
] |
[
"Y probably doesn't have a huge impact on male phenotypes",
"Cool, that's actually what I wanted to know most of all, actually. So yes, it is patriarchal, but it doesn't have much significance to the resulting phenotype.",
"If sex determination is flipped around, then what is used to determine sex? "
] |
[
"How did the genetic diversity of a species increase in the early evolutionary past?"
] |
[
false
] |
Apparently, in case of a mayor global disaster, say the zombie apocalypse, humanity would become extinct if the number of survivors goes below a certain threshold due to a lack of genetic diversity (inhibiting the ability of a species to create healthy offspring and in and other words; survive in the long term). If that is the case, and assuming that for every organism the population starts out small, how exactly did "our species" and others grow both in number and diversity in the evolutionary past?
|
[
"Random mutation.",
"There are several ways this can happen:",
"1) Radiation & chemical mutagens. Strong ionizing radiation can cause breaks in DNA, which are then repaired. Certain chemicals can also introduce mutations by physically damaging the DNA. Sometimes, the repairs aren't quite right and bases are lost, introduced, or otehrwise screwed up. Other forms of radiation can damage bases; a classis is the T-T dimer caused by UV radiation; two adjacent T's fuse together; this causes a kink in the DNA which is repaired, sometimes incorrectly. ",
"2) Jumping genes : these include viruses and transposons. For simplicity, I'll just talk about viruses here. Certain viruses insert themselves into the genome of the host and just sit there. We all have lots of these, and they can be passed to offspring in some cases. Under stress, these can pop back out as part of the life cycle of the virus and infect other tissues. However, this \"popping out\" is not always exact, and the virus can take along bits of your genome along with it. These will go and insert somewhere else, causing mutation. Imagine taking this post and randomly cutting a few lines of text and randomly pasting it somewhere else on Reddit. Most of the time it will be gibberish and be ignored, but it's possible it might sit down somewhere useful.",
"3) Chromosome stuff : Due to part of how we mix & match our genes during meiosis (forming sperm & eggs), big chunks of a chromosome can be duplicated (there are other mechanisms too, but this is one of the simplest and most common). This provide raw material, kind of a working copy that can accumulate mutations without too much damage. ",
"4) Directed mutation. This is directed only in the sense that the chance of random mutation is increased. What the mutations will be is not directed, just the rate at which the mutation happens. This is more common in simple life forms, but has to do with suppression of error correcting machinery. When DNA is replicated, there are systems that will monitor the new strands & check for errors, which are corrected. Sometimes, though, this system is suppressed, allowing an increase in error rate.",
"5) Error rate - crap, this should be first, but that would mean renumbering....DNA replication is pretty solid, but there is a base error rate. Sometimes, the machinery just copies the DNA wrong.",
"EDIT:",
"sorry, ignored this part:",
"assuming that for every organism the population starts out small",
"That's not a good assumption. The process of speciation is not a clear cut thing. It's a slow and messy process, a gradual thing that is only obvious at the extremes. For example: If you stay up all night, at what time, exactly, does it cease to be \"good evening\" and start to be \"good morning\"? 10PM is certainly night, and 6AM is certainly morning...but what about 1AM? 2AM? 3AM? It's not clear cut; everyone will have their opinion and you just have to be arbitrary about it.",
"Same thing for species, there isn't really a point where there's just one or two of a given species, it's a gardual process.",
"Even in rapid speciation, \"rapid\" is relative to evolution; we're still talking hundreds of thousands of years. 50,000 years is holy-crap fast in evolutionary terms for anything that's not a bacterium."
] |
[
"Mutation is a rare cause for evolution. It's usually isolated groups and genetic variability.",
"Where does the genetic variability come from?",
"I'm sorry, but this is totally wrong. You can't have anything to select on unless you have mutation. ",
"Mutation is rare at the per base pair level to be sure. Current estimates put mutation somewhere the vicinity of 10",
" mutations per base pair per generation. The human genome, however, has 3 billion base pairs in it, so taking these numbers as gospel (which the mutation rate one certainly isn't), each individual would have about 30 new mutations that their parents didn't. I've heard some estimates that place this number closer to 200.",
"That's for each individual. Now if you have even just a thousand individuals in the population (a rather small number, really), that means you're introducing 30,000 to 200,000 new mutations into the population each generation. That's quite a bit for selection to play with."
] |
[
"Why does everyone always go for the zombie apocalypse?",
"Anyways:",
"assuming that for every organism the population starts out small",
"This is not true. (Also, I'm assuming you meant \"species\" instead of \"organism\". The word organism refers to an individual. \"Species\" refers to the collective group of organisms there bear a great enough degree of genetic similarity such that we decide to declare them all the \"same\". Also, it seems like you have the ",
" misconception of a \"species\" being a discrete, or \"real\" thing. For that, I'll refer you to the first half of ",
"this post",
".)",
"Anyways, species don't start out from tiny little populations and grow to \"full, mature, species\". Evolution is really a branching process. ",
"Imagine you have a big, healthy population of some animal. Doesn't matter what, just pick your favorite one. Then imagine they live next to a mountain range (if you picked a fish, I guess you'll have to pick a different animal).",
"Now, if we take half of the population, and move it to the other side of the mountain range, the two populations won't be able to interbreed. Over time, they will diverge from one another genetically. This will happen because they will have totally different sets of random mutations (and klenow ",
"spelled out how that can happen",
" quite nicely), which could then be subject either to different selection pressures, or which will simply fix differently because of genetic drift (i.e. random survival of some individuals as opposed to others, unaffected by natural selection, which results in the random loss of some mutations from the population).",
"Eventually, these two populations will be so different that they cannot mate with one another. At no point, however, did they have to start out from some small population and grow into a larger one.",
"Does that make sense?",
"Also, I just want to add that the question of how new genetic material is created in general is a big one, and while I don't think you asked about it directly, it is relevant to your question. One of the most important factors is probably gene duplication. klenlow touched on it in his/her discussion of jumping genes, but I just wanted to expound a bit.",
"Imagine you had an organism with a really small genome. Say it only had two genes, we'll call them ",
" and ",
" (not really practical, except for maybe in some ",
"abiogenesis",
" scenarios, but it doesn't matter for out purposes). Now, sometimes, what can happen, is you'll have a whole genome duplication. So now, we have a total of four genes. We have ",
" and ",
", but we also have their duplicates, which we'll call ",
" and ",
".",
"The thing is, ",
" and ",
" can keep plugging away at their functions, but ",
" and ",
" are redundant, so they are free to evolve completely new functions via ",
"mutation",
" and ",
"selection",
".",
"Now in my example, we only have two genes available, but in reality, most present day organisms have thousands of genes, so you can imagine how much new genetic material duplications can create. This is thought to be one of the primary methods by which new genetic material is created."
] |
[
"How will/are human bodies adapt(ing) to increased body fat if obesity continues through many generations?"
] |
[
false
] |
Is there any evidence of human bodies adapting to obesity? If it is true that you can be genetically obese then are those humans better adapted for this? Would the human body be more likely to adapt to automatically store less fat, or to strengthen its organs/structure to be able to cope more easily with increased body fat?
|
[
"If being overweight has enough impact on a person's average reproductive success (i.e. total number of children who survive long enough to reproduce themselves), it's not impossible that we'll eventually see human evolution select for people who are less susceptible, perhaps because they retain less fat, have less interest in fatty/high-calorie foods, or are simply more healthy with high body fat. (There are plenty of animals that are perfectly healthy with lots of fat, and would be quite unhealthy without it--look at seals, for example.)",
"But it is way, way, way too soon to see any evidence of that right now. The \"obesity epidemic\" has been a thing for a couple of generations at most. Try back in a few thousand years.",
"(And even that seems like a stretch, honestly. Obesity kills, but it usually kills in middle age or later, after many people have already had kids.)"
] |
[
"Obesity ",
" affect fertility, but with our increasing abilities to raise or lower fertility that may not correlate as strongly with reproductive success as it would with other species any more.",
"Sometimes I wish for immortality just so I can see what happens next."
] |
[
"Imho we must make a difference between medieval fat/plump and our modern morbidly obese."
] |
[
"Career choices for Env. Scientist versus Chemist or Biologist?"
] |
[
false
] |
[deleted]
|
[
"Biologist here. The way you will decide the field you want is based more on the research experience you have rather than the classes you will take. So, don't sweat the specifics of your decision too much at this point. ",
"Take all the classes that are required plus anything that looks interesting, and when you meet a prof you like and whose work interests you, ask to work in his/her lab. At most schools, you can get credit for this type of lab work. ",
"When you ",
" the science, then you will know what you really love and want to commit to as a career. And you may actually decide research science is not applied enough for you or not your bag, and you may be more interested in something like policy work or teaching. You'll see! Good luck!"
] |
[
"I concur with twinklingyoureye. Your research experience will help you decide to a greater degree than the classes. I was originally in a similar position as yourself. I started undergraduate classes thinking I would go into environmental science. After freshman year I started research in a microbiology-type lab that did some field work, so it seemed like a great idea. ",
"Considering the PI in this lab was more on the Biology side of things, she told me I should take a couple of the classes she taught (Virology and Cell Biology).",
"At the same time, I was taking the required chemistry classes and after Organic Chemistry I decided to take an extra analytical chemistry class, which lead to another class taught by the same teacher. By that point all I needed was an advanced topics class in chemistry to get a B.A.",
"Therefore, I left undergrad with ample experience in Environmental Science, but degrees in Biology (B.S.) and Chemistry (B.A.). ",
"By the way, I am now doing something completely different- still in biology, but not environmental or chemistry based. However, all those experiences have helped get me here today."
] |
[
"I found out about the microbiology lab through my advisor, and it was not part of the curriculum. The only way you are going to find these opportunities is to ask. Most professors are willing to talk, if you want to go durring office hours or make an appointment, it doesnt really matter. Its what you talk about while there. Only briefly describe that you would like to do research in a lab, then ask what their lab normally does. PIs do enjoy explaining what their lab does. If they do happen to do what you like, then ask them if they have room in their lab. If they say that they cannot pay, you can still ask to volunteer on some level. There are many opportunities and typically the departments have money and/or housing for the summer breaks. "
] |
[
"We all know about trilobites, dinosaurs, pterodactyls and other animals that have gone extinct, but have we discovered any extinct plants with unique features not seen in plants today?"
] |
[
false
] | null |
[
"Paleontologists have found many interesting species of plants that no longer exist. Plants have been on land longer than animals have and they have had hundreds of millions of years to evolve. The unique adaptations in extinct plants were used to solve the same problems plants still have (how to reproduce, how to get water to all cells,..)",
"One of the best examples I have are seed ferns which were \"trees\" and shrubs that looked like ferns. These plants were filling in environmental niches of canopy and undergrowth before deciduous or coniferous plants existed. They may remind you of a palm tree or pineapple at times but they are really quite different because neither modern plant would exist for millions of years.",
"The problem with finding out just how unique a plant fossil is that most plant fossils are a small imprint (or a chunk of petrified wood). It is possible the leaves or roots of ancient plants could be organized in a totally different way from modern plants. However we would need to see the cell tissue to find out and all the tissues are long gone. ",
"At least visually there are quite a few different plant fossils that have been discovered including seed ferns. Sadly some parts of these ancient plants' uniqueness will never be known by humans."
] |
[
"Thank you for your clear answer - a bit sad that it's highly unlikely we'll ever now more. Nice example of convergent evolution with the seed ferns though!"
] |
[
"Silphium was a plant used by the romans, for several medicinal purposes and according to wikipedia it was used as a contraceptive. It was so used that it became extinct.",
"\nHere is the article ",
"http://en.wikipedia.org/wiki/Silphium",
"I dont know if that helps, but i hope it does"
] |
[
"New job in biology/similar to a very old guy (30) not in science?"
] |
[
false
] | null |
[
"No problems, trying also field specific subreddits like ",
"r/biology",
" is probably good."
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"A good home for this question is our sister subreddit ",
"/r/AskScienceDiscussion",
". It might be too open-ended or speculative for ",
"/r/askscience",
". ",
"/r/AskScienceDiscussion",
" is also a better place for advice on education, book suggestions or general questions about working in STEM. Please feel free to repost there!",
"Please see our ",
"guidelines",
".",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"I’m sorry, didn’t know about the sub. Thanks"
] |
[
"I've seen three huge tree plauges in my lifetime. Have they always been this common?"
] |
[
false
] | null |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"I was hoping for an evidence based discussion?"
] |
[
"Questions based on discussion, speculation, or opinion are better suited for ",
"r/asksciencediscussion",
"."
] |
[
"Light exposure influences our production of melatonin [right?] so does it affect the blind as well?"
] |
[
false
] |
does it 'affect' the blind any differently? This leads to my Are sleep cycles in general relatively different to the blind?
|
[
"http://jcem.endojournals.org/content/82/11/3763.full"
] |
[
"So basically:",
"These results indicate that a higher proportion of NPL subjects have abnormal melatonin rhythms compared to those with LP. ",
"LP: Light Perception",
"\nNPL: No Light Perceived."
] |
[
"Melatonin and melanin are different things. I'm not an expert so forgive me if I use wrong terminology, but melatonin production increases when you are in the dark, and makes you tired, eventually falling asleep. So OP's question was, do you have to see that it is dark, or does your body just know that it is dark?",
"Hope this helps you understand the original question."
] |
[
"Did the DDT ban cost humanity millions of lives lost to malaria?"
] |
[
false
] |
[deleted]
|
[
"No. The use of DDT for malarial control was not banned."
] |
[
"It was used for agricultural pest control as well as mosquito control. Its use as a crop spray was banned."
] |
[
"It was used for agricultural pest control as well as mosquito control. Its use as a crop spray was banned."
] |
[
"Is this statement regarding GMO Canola oil true? \"As a rule of thumb, if the bacteria that make things go bad won’t eat it, your liver will not be able to digest it either.\""
] |
[
false
] |
Source:
|
[
"Well that's just the silliest thing I've read. There are lots of reasons bacteria don't colonize a food, from it being sterilized to it being toxic to them (but not humans) to it being nutrient-poor for bacteria (but not for humans), etc...",
"Garlic takes forever to decompose, too, but no one is saying don't eat garlic. 99% of GMO \"caution\" is hysteria by people who have a poor, at best, understanding of biology."
] |
[
"The statement is misleading. The shelf life of oils are all relatively similar. ",
"Here is a table comparing shelf lives of different oils",
". Canola oil is no different than oils from other sources, so the point being made is kind of ...pointless. "
] |
[
"Two things:",
"1 ) No, it's not a good rule of thumb, since most bacterium cannot grow in oil. In fact, placing a layer of oil over things is used as a preservative, since it prevents stuff from landing on it and reduces gas exchange.",
"2 ) Strangely, the given history of Canola oil on the website seems to outline all the benefits of Canola oil, but then says 'But don't trust it, because GMO'. To me, that's reason to dismiss most of their claims.",
"Lets also remember that their claims that 'raw unfiltered unprocessed' oils are better for you are probably entirely false, given that churning bacteria or such into your oil is in fact less safe than pasturizing and sterilizing the stuff. ",
"Also, this:\n",
"http://www.snopes.com/medical/toxins/canola.asp"
] |
[
"How do deep space probes communicate with Earth?"
] |
[
false
] |
This one has been boggling me for a long time now. Let's say that a distant probe like Voyager 1 tries to communicate with earth. As per Voyager 1 is roughly 141 Astronomical Units away from earth which translates to roughly 19 light hours. AFAIK Voyager 1 needs to point it's antenna directly to Earth to communicate, so it locates Earth and sends a message. Since light speed is finite and it takes 19 hours the message to reach our Deep Space Network, the Earth has moved through space roughly 2 Million Kms. My question is, how is it possible for the radio wave to hit the Earth when it has moved 2 Millions Km? Is it because as the radio wave moves through space time the area it covers increases so it hits the earth because the message was sent to the general direction the earth was 19 hours before? or something in my previous assessments is flawed?
|
[
"Electrical Engineer here but my specialization was in radar specifically fields and waves so a physicist or someone more familiar will likely have more specifics.",
"Short answer: They point a dish as close to pointing directly at Earth (maybe they lead it a bit if transmitting, or trailing if receiving) and keep it pointed at earth. The same dish is the receiver and transmitter, then it comes down to a well scheduled pattern of communications.",
"So earth is only \"allowed\" to transmit to X probe at specific times so that when the signal gets to the probe the probe is listening. Also the probe has a preprogrammed location to point at earth so its listening but also listening in the right location to catch earth's signal.",
"The physics and engineering of the components are simple. A very sensitive receiver, and a relatively powerful transmitter.",
"\nThe hardest part is the timing and that's where some very very precise math comes in. As you get farther from earth the signal drops off but its also harder to point at the right location.",
"You are very much right that as a transmission travels it spreads out so yes receiving gets easier in the sense that it hits more space, but for the probe the transmission is less powerful and its easier to miss if its \"ear\" isn't pointed very accurately.",
"So it comes down to timing, a strict communications schedule, and hoping nothing gets in the way. For this reason comms with deep probes tend to be lots of repetition in case something interrupts a critical signal."
] |
[
"Arctan of 2 million km divided by 141 AU is approximately 0.005 degrees. Main lobe of Voyager antenna pattern must be much wider than that. Not only because it's difficult to form such a narrow beam with a relatively small antenna, but also because it's difficult to aim it so precisely."
] |
[
"Superb answer Malforus. I think I was missing the tight schedules and precise calculations part which in hindsight seem kinda obvious for this type of communications. Thanks for the detailed answer :)"
] |
[
"If every cell contains all our DNA, how does the body know to only translate certain genes in certain areas?"
] |
[
false
] |
For example, why is the gene coding for earwax only translated into a protein in the ear canal. Are genes suppressed in some way when cells are differentiated in development? Or is there some other mechanism at work?
|
[
"The posters here rightly talk about transcriptional regulation -- taking the DNA code and making it into mRNA. This is enormously complex and depends on lots of things, including DNA structure and folding and other \"epigenetic\" cues as well as signal transduction pathways, which convey signals from the outside environment to the nucleus. This lets a finger cell how far down the finger it is, or lets a cell know when it is confluent with its neighbors, or when exposed to a toxin or a disease or whatever. However, transcriptional control is just the first step in a whole chain of regulation, and represents only a fraction (less than 50% is usually noted) of control of how much protein eventually is produced by the cell. ",
"The mRNA gets processed, exported from the nucleus, made into protein (translation), which is then correctly folded and further processed. Each of these steps is highly regulated as well.",
"Here's",
" another thread similar to this one with some further information."
] |
[
"I'll try and give a broad but complete answer. This is assuming you have some cell biology background for terminology. ",
"Essentially, every unique cell type (say heart cell vs. cells in the ear canal) has built up a complex network of transcription factors and co-factors interacting with the genes of the cell. It's a huge, complex layer system and even though we have some understanding of how this happens (it goes ALL THE WAY back to development and cell differentiation) it resembles a cog system where it is hard to cell which cog is driving which other cog. Repressors, activators, co-repressors, etc.",
"On top of this, different protein expression patterns cause different effects on the DNA, allowing some genes to be open for expression and others to be closed. Another cog in the machine. Kind of chicken or the egg scenario. ",
"On top of THAT, there are also tissue specific promoters and other genetic regulatory elements (enhancers, etc.) that drive expression of certain genes only in specific tissue types. You can also \"sequester\" genes in certain areas that obscure them. ",
"On top of THAT, cells have several ways of mainfesting their differences by controlling the amount of protein that gets made at the gene or RNA level (either by degrading the RNA, splicing it differently or exporting it from the nucleus). Cells also control which mRNAs can translated into proteins or can shuttle proteins to different regions. ",
"And the final layer is cell-to-cell and environment-to-cell communication, where you have signals from one cell stimulating phenotypes in neighboring cells. ",
"So by the time development and differentiation has occurred, these networks have become so interwoven its hard to say what guides what. One hand washes the other."
] |
[
"This.",
"From an oversimplified base point, imagine that the moment a sperm hits the egg, a protein is produced. Diffusion will spread the protein around, but there'll be more in the front than the back, and more at the bottom from gravity's effect. As the cell divides, these concentrations give you forward/back up/down orientation and those concentrations dictate which proteins are expressed ad infinitum."
] |
[
"What is the smallest yield possible of a nuke?"
] |
[
false
] | null |
[
"At least the smallest weaponized nuclear payload was approximately 6 kilotons. The W54 nuclear warhead was equipped to the portable M-388 Davy Crockett nuclear launcher. The warheads would fit into small casings or backpack nukes.",
"If this is the absolute smallest possible, I don't know. This was the smallest weapon however."
] |
[
"The smallest intentional (non-fizzer) nuclear explosions are a few grams TNT equivalent.",
"The term you want is ",
"Hydronuclear",
".",
"When designing a nuclear weapon, you need to form a critical mass (obviously), and you do that by taking a subcritical mass and squeezing it in a conventional bomb.",
"You need to test the squeeze, because that's the hard bit to get right. You do that by putting a steel lump the shape of the plutonium core into the bomb pit, blow it up, and see if it compresses enough. This is called a hydrodynamic test. That's great, but it's hard to measure exactly what happened during the squeeze because the steel is elastic and partially bounces back once the pressure from the conventional explosion is removed.",
"So the more sophisticated test is hydronuclear - you use a tiny amount of plutonium, or an alloy with some plutonium, blow it up and you can then slice through the blank after testing and see how the atomic structure has changed to get a better idea of what the peak pressures were, and where they occurred. Then you can see which bits fissioned, which tells you what the upper limit of pressure was in that part of the blank. The plutonium in there will go bang, but not enough to destroy everything, and the fission byproducts will be embedded in the steel blank. It's a nuclear explosion (energy from the nucleus contributes to the blast) but ",
" small",
"Hydronuclear tests are usually <1kg TNT equivalent, often only a few grams TNT equivalent. They can of course be much bigger (up to a full-size nuke), but the point of them is to allow nuclear testing without violating any treaties, turning your sensors to vapor, or generally making a mess, so they are intentionally as small as possible to collect the required data."
] |
[
"and it was discontinued because even after firing it at it's max range of 3 miles, the crew would still be in range of radioactive fallout."
] |
[
"What is the margin of error in across the billiards shot list for anything from an easy to difficult shot?"
] |
[
false
] |
As the title says I want to know the amount of room for human error there is in various shots you would make in a game of pool/billiards.
|
[
"Speaking as a pool player:",
"For professional players, the margin for most common shots is < .5%. I'm basing this on their ability to run drills, as well as the high run numbers in straight pool (400-500 shots in a row, including difficult break shots), where a good number of those shots are difficult and require good positioning.",
"Now, of course in any game, there are going to be situations where the shot is more difficult, and those can range anywhere from 1% - 99%. A big part of the game is the player picking shots he is comfortable with, so called \"high percentage shots\". ",
"A good player is balancing shooting a 60% shot that leaves the player in a better position than another available 80% shot.... many factors go into this. Sometimes, without options, a player takes a 10% shot. ",
"In terms of the amount of human error, that can easily be 100%. a slight twitch in any muscle can easily cause any shot to fail. "
] |
[
"I'm not quite sure I understand your question. The game is played completely VIA human control. So depending on what they choose to do, there will be different amount of human error.",
"A complete newbie could completely miss the ball, while say a theoretical perfect player (CPU perhaps?) can calculate the exact velocity, angle, and trajectory needed to get a ball in.",
"So to your question, potential to basically infinite human error, but if you want to win, you just need to narrow your margin to less than the other player.",
"In case you are asking about allowed error between angle of contact between the balls, it would completely depend on the near infinite possible distances between them."
] |
[
"Ok so lets take a dead on shot straight to The center pocket. 6 inch spacing between pocket and ball and 6 between ball and cueball. How much area is there on the side of the curball to cleanly pocket the ball"
] |
[
"Is it possible that emotions were developed from a consistent response to similar situations?"
] |
[
false
] |
I would think that emotions didn't always exist throughout life and had to be developed. Would being exposed to the same or similar scenario eventually lead to developing that emotion? Examples: Seeing a potential mate could lead to Love Having food stolen could lead to Anger
|
[
"In order to answer this question, we need a working definition of 'emotion'. To this end, we can use the definition proposed by Tooby & Cosmides (1990) of ",
". In layman's terms, emotions help us make sense of our environments and circumstances.",
"From the standpoint of evolutionary psychology, it's likely that emotions developed and were cultivated/refined through the process of repeated encounters with stressors that required early humans to process information quickly and accurately. Situations such as mate-stealing, encroaching on territory, finding a mate, and death of other humans lead to recognizable patterns of behavior that became ingrained in human behavior as emotional responses. ",
"We can see a perfectly good example in ",
"Tooby & Cosmides (2000)",
". Most people experience fear when it is dark, to varying degrees. It is likely that this is a relic of a time when humans needed to be aware of nocturnal predators. Fear served the purpose of making early humans more cautious and avoiding situations where they may be hunted or killed. Humans that exhibited a fear of the dark and utilized it to avoid dangerous situations had a better survival rate than those that did not, leading to the residual fear of the dark we experience today."
] |
[
"I think you're considering the effect of repeated exposure to emotional stimulus ",
", rather than as a trait cemented into the species as a whole via natural selection. ",
"Yes, in individuals, as they are exposed to repeated stressors they experience diminished emotional responses. This is why the first time a friend jumps out from behind a door they scare you, but the hundredth time it's just annoying. ",
"What Tooby & Cosmides are suggesting in the linked study is that early humans that showed a predisposition toward a certain emotional response had a better rate of survival, effectively breeding those emotional responses into the human species. ",
"Going back to the fear of the dark, it's certainly plausible that a specific early human would experience desensitization to his fear of the dark throughout his life, but if he survives and another early human that does not have that fear does not, he will pass on his genetic predisposition to fear of the dark to his offspring, and so on."
] |
[
"While this makes sense on the surface in a Pavlovian way, I would like to ask how this works with desensitization over time to the same emotional stimulus. ",
"Wouldn't repeated encounters with stressors lead to less and less emotional response over time rather than cementing it into the evolutionary psyche?"
] |
[
"If we can let √(-1) equal to \"i\" to do more more complex mathematics, why cant we do the same for (1/0).?"
] |
[
false
] | null |
[
"There are fields in math where division by zero is okay. But you have to be careful of the context. If you think of division as an algebraic manipulation on numbers, then it doesn't make sense and you easily end up with contradictions like 1=0. However you can view things in a geometric way and get neat results.",
"Firstly, what you have to do is add what is called a \"Point at Infinity\" to the real line. You do this by taking the real line, wrapping it up into a hoop with a tiny gap at the ends and then adding an extra point to close off the hoop into a complete circle. You lose a lot of arithmetical properties when you do this, but gain a lot of geometric ones. What you then do is declare that 1/0=infinity. ",
"The important thing that this does is that now functions on the real line become ways of taking this circle and manipulating it in some way. You can then look at a function like f(x)=1/x and instead of being undefined at x=0, it becomes infinity. This then makes f(x) an operation on that circle and that operation flips it over, sending infinity to zero and zero to infinity. In fact, the leftmost and rightmost points on the circle that we get correspond to -1 and +1 respectively and the function f(x)=1/x flips the circle over about this equator. Other rational functions like f(x)=(x",
" -2)/(x",
" -1) no longer have asymptotes, it's just that now points get sent to infinity. ",
"This is part of the field of Projective Geometry. You can do the same thing to the complex plane and get what is called the ",
"Riemann Sphere",
" which is a very useful tool in math."
] |
[
"My favorite explanation of the Riemann sphere :",
"\"Riemann sphere, which is where we take a space shuttle and use it to fly over and drop a cow on top of a biodome, and then have the cow indiscriminately fire laser beams at the grass inside and around the biodome. That's my intuitive understanding of it anyway.\""
] |
[
"The way that we have defined zero, it doesn't make sense to.",
"Zero is a special number. It's such that zero added to anything has no effect, and multiplied by anything equals zero. This second definition is where we run into problems. Suppose we have x and y, where x=/=y. Then observe that x * 0 = y * 0 = 1 * 0 = 0 (zero is the only number that this holds). Then dividing by zero all the way through gives us x=y=1, a contradiction, since we already stated that x=/=y.",
"In other words, we don't define 1/0 to be anything because if we did, that number would have some crazy properties that we don't want, such as making inequal numbers be equal. These kinds of problems don't happen with i. If we let i be the number that i",
"=-1, then it doesn't really have any consequences that are undesirable. In fact, it makes a lot of things really easy!"
] |
[
"What evidence do we have that asymptomatic spread is significant with COVID?"
] |
[
false
] |
This is an honest question. Most searching I've done seems to indicate that we don't have much evidence. Articles citing evidence tend to just link to articles making claims, and the few studies I've found cite computer models, which I don't take as evidence. Evidence would consist of measuring the frequency with which COVID spreads from asymptomatic people who are followed up with later to make sure they never developed symptoms. Do these studies exist? How were they conducted? What have they shown? If they don't exist, why do we assume this is a major driver?
|
[
"The main issue isn't finding evidence of transmission from people with no symptoms, it's distinguishing presymptomatic from asymptomatic cases, and to some extent, distinguishing ",
" symptoms from ",
" symptoms -- it's a gradient of severity, not an on-off switch. But to an extent, that becomes irrelevant; if your symptoms are so mild that you don't notice them, then for practical purposes you're asymptomatic.",
"The problem of asymptomatic vs presymptomatic means you can't use a cross-sectional study (i.e. one measurement), you need to follow people for at least 14 days. However, some studies suggest that if you have a PCR-positive individual with no symptoms, most of them (roughly 75%) will in fact be asymptomatic.",
"Current data suggest that infected persons without symptoms—including both presymptomatic and asymptomatic persons—account for more than 40% of all SARS-CoV-2 transmission (75–77). The proportion of new infections caused by asymptomatic persons alone is uncertain, but when researchers in Wanzhou, China, analyzed epidemiologic data for “183 confirmed COVID-19 cases and their close contacts from five generations of transmission,” they determined that the asymptomatic cases, which made up 32.8% of infected persons, caused 19.3% of infections (78).",
"--",
"The Proportion of SARS-CoV-2 Infections That Are Asymptomatic: A Systematic Review",
"The references cited here are ",
"He X , Lau EHY , Wu P , et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med. 2020;26:672-675.",
"Ma S , Zhang J , Zeng M , et al. Epidemiological parameters of COVID-19: case series study. J Med Internet Res. 2020;22:e19994. ",
"Zhang H , Hong C , Zheng Q , et al. A multi-family cluster of COVID-19 associated with asymptomatic and pre-symptomatic transmission in Jixi City, Heilongjiang, China, 2020 [Letter]. Emerg Microbes Infect. 2020;9:2509-2514. ",
"Shi Q , Hu Y , Peng B , et al. Effective control of SARS-CoV-2 transmission in Wanzhou, China. Nat Med. 2020. ",
"Reference 78 spends quite a bit of time on asymptomatic cases, distinguishing them from presymptomatic, and summarizes -",
"Of the 171 close contacts of asymptomatic cases before their diagnosis, 9 (5.3%) were infected and showed symptoms, while 7 (4.1%) individuals were infected but asymptomatic ... 16 of the 83 infected close contacts (19.3%) were infected by asymptomatic source cases, while the remainder (80.7%) were infected by symptomatic source cases.",
"--",
"Effective control of SARS-CoV-2 transmission in Wanzhou, China",
"There are a handful of other studies that reach very similar conclusions: Asymptomatic individuals are less transmissible than symptomatic, but because there are a lot of asymptomatic people -- 20-40% of cases, depending on who's counting -- and because they don't tend to quarantine as strictly for obvious reasons, they remain an important part of the SARS-CoV-2 epidemic."
] |
[
"There are countless viruses out there which cause no noticeable symptoms. I'll be bold enough to say there are probably more viruses out there that cause no symptoms than ones which do - we just don't bother studying them (or are even aware there is something to study - it's difficult enough to find a virus you know about).",
"Your body is fighting off bacterial, fungal and viral infections literally constantly even when you feel healthy - its what the immune system evolved to do. Some reasons for symptoms would be the thing is exceptionally virulent, it affects particular tissues, it releases toxins, the immune system is overly responsive.",
"A virus has no particular goal to make you ill, and very often the best evolutionary path may result in a symptomless virus."
] |
[
"Thank you, that makes sense.",
"This virus is showing me how little I knew about viruses."
] |
[
"How would every nuke in existence detonated at the exact same place differ from just one?"
] |
[
false
] | null |
[
"This is fairly difficult to answer in very specific terms; the experiment has probably never even been simulated (even down in the deep dark heart of DOE classified computing).",
"But, in general, I think that we can draw some insight from the test sites out in the pacific (e.g. Bikini Atoll) where many nuclear weapons were detonated in short succession.",
"Pockmarked and cratered terrain. Formation of large amounts of Trinitite (sand fused in a nuclear explosion). Detonation in ",
" the same place will result in the excavation of a deeper crater, but it's not easy to say much on it's dimensions, or other soil dynamics. ",
"Massive soil contamination. Some of the atolls got so bad that their topsoil was removed, placed into a crater from a nuclear test, and capped with a concrete dome.",
"Unprecedented atmospheric contamination. A single source of contamination will result in a much larger than typical radioactive plum that will spread according to the prevalent winds. ",
"The total world nuclear arsenal is around 5000 megatons. Detonating all of these devices in the same area, simultaneously, is probably implausible due to technological limitations. Such a detonation would, in theory, be spectacular. It would be slightly inferior to the impact of a 1/2 kilometer diameter iron meteor impacting at a velocity of 18 km/s."
] |
[
"While I love your answer, I'm wondering where you got the last calculation from, and also why the analogy is helpful...have we experienced such a thing, or is it common to relate large explosions to iron meteors?"
] |
[
"True, I was just trying to avoid the phrase 'nuclear energy,' and I forgot we physicists tend to use terms like 'chemical energy' more loosely than they do in high school chemistry. "
] |
[
"Why does low frequency radar have poor resolution/accuracy when used to detect and track objects?"
] |
[
false
] |
[deleted]
|
[
"It is a fundamental property of waves. Waves with longer wavelengths simply can't carry as much information. More formally, the amount of information that a wave can carry is measured by its bandwidth. In simplified terms, a sine wave can carry information by tweaking its shape slightly. Mathematically, tweaking the shape of a sine wave with a certain wavelength is equivalent to adding to the base sine wave other sine waves with slightly different wavelengths. The range of different wavelengths that can be added to the carrier wave is called the bandwidth. The more details that we can add to the alterations in the shape of the carrier wave, the more information it carries. In other words, the greater the number of different wavelength sine waves we can add to the carrier wave (i.e. the greater the bandwidth), the more information it can carry. We can electronically add information to a wave using circuits, such as is done in a cell phone. Additionally, when waves scatter off of objects, such as radar waves, they get information about the scatterer added to them.",
"The key is that the bandwidth is ultimately limited by the wavelength of the carrier wave/center wavelength. For instance, consider a radar wave with center wavelength of 2 GHz. The lowest frequency that can be added to this is 0 GHz (or very close to 0 GHz since exactly at 0 GHz is not actually a wave), and the highest that can be added is 4 GHz. We could add a 5 GHz sine wave component, but at that point, the center frequency/carrier frequency would no longer be 2 GHz. So the ultimate largest bandwidth that a 2 GHz system can have is 4 GHz. In contrast, a 20 GHz system can have a max bandwidth of 40 GHz. So, shorter-wavelength radar waves simply can carry more information about the objects they are scattering off of.",
"There is another physical effect at work. Based on the physics of waves, a wave is scattered a very small amount by objects that are significantly smaller than the wavelength of the wave. As an approximate rule of thumb in radar, objects that smaller than a tenth of the wavelength of the radar wave are effectively invisible to the radar. In other words, a very low frequency radar imaging system pointed at a rocket can't image the screws along the body of the rocket because the reflected radio waves simply don't carry any information about the screws since they are too small."
] |
[
"You seem to be confusing pulse width (which is related to bandwidth) with wavelength. A single-wavelength wave containing no other wavelength components carries the same amount of information no matter what the wavelength is. The only information it carries is: intensity, polarization, and wavelength. In contrast, a series of pulses can carry a lot of information because each pulse can have a different intensity. In order to have a pulse, you have to many different wavelengths present. The narrower the pulse width, the more pulses you can cram into a meter, and the higher the resolution you get. The way to get a narrower pulse is by including more wavelengths, i.e. by having a higher bandwidth, exactly as I said before."
] |
[
"Long wavelengths travel farther. Also they can see \"through\" small objects like leaves. "
] |
[
"Why don't I receive a cell phone signal when I'm on a plane?"
] |
[
false
] | null |
[
"Cell towers generally have a relatively low power signal (a few miles to tens of miles of range), and are meant to cover a specific area. When you get close to the border of a cell you are handed off to the next cell.",
"You would not be likely to receive a cell signal in a plane at 35,000 feet for a couple of reasons... 1) the vast majority of the country doesn't really have much cell service. Look at a coverage map - all of those white areas have no coverage. and 2) You are moving so fast in the plane that your phone is not able to lock on to a particular tower, and if it does lock on it will be unable to hand you off to the next tower."
] |
[
"The FAA ban lift will presumably allow the installation of cellular infrastructure onboard aircraft providing service to mobile devices onboard. This would rely on satellite backhaul or dedicated air to ground communication, not terrestrial cellular networks.",
"This is different than the recent lifting of the ban on portable electronics during takeoff and landing."
] |
[
"The FAA ban lift will presumably allow the installation of cellular infrastructure onboard aircraft providing service to mobile devices onboard. This would rely on satellite backhaul or dedicated air to ground communication, not terrestrial cellular networks.",
"This is different than the recent lifting of the ban on portable electronics during takeoff and landing."
] |
[
"How did the first scientists discover that radiation was bad for you?"
] |
[
false
] |
Trying to understand exactly when we realized that certain elements, and or reactions were reactive, and that the results from those reactions were deadly. Did the early scientists pioneering this field just die as a result of discovering it? Or were they correctly able to theorize what elements would do and protect themselves before discovering radioactive elements?
|
[
"HJ Muller discovered that X rays cause mutations by giving fruit flies varying doses of radiation. However, Roentgen, discover of X rays, knew that x rays caused burns in high enough doses (although he didn't realize the cause)."
] |
[
"Weren't suspicions raised by early scientists who developed diseases as a result of working with radioactive materials?"
] |
[
"For a while, radioactivity was considered a cure-all.",
"Then people started getting sick."
] |
[
"Is it possible to detect an exoplanet by measuring the change in polarization of starlight as a iron-core planet transits in front of it?"
] |
[
false
] |
[deleted]
|
[
"In order for magnetic fields to affect light, the light must be traveling through (and not be completely absorbed or reflected by) a medium. At most, this implies that if the magnetic field is strong enough, light passing through the ",
" of the planet and then making its way to detectors on Earth could, potentially, maybe, have some sort of polarization. The degree of polarization would depend on how isotropic the planet's magnetic field is (the light would end up with no net polarization if the field is totally symmetric with respect to the path of the photons). However, depending on the ratio of the star's diameter to the planet's diameter, combined with the thickness of the atmosphere, the percentage of (weakly) polarized light which ",
" be present would probably be very difficult to detect relative to the total background, if not impossible. "
] |
[
"Since most planets rotate roughly on the same plane as their orbit, most polarization signatures would be significant."
] |
[
"I'm not understanding the part where polarization can only occur in a medium. Is there a source for that, that you're aware of.",
"Also, I wonder if that would therefor be useful in detecting planets with rings."
] |
[
"Is it possible for cavitation bubbles to be formed in gases?"
] |
[
false
] |
[deleted]
|
[
"Cavitation is specifically a phenomenon where the pressure in a liquid drops so low that it reaches the vapor pressure of the liquid and therefore induces the formation of a pocket of gas. There is no analogous phase transition for gases."
] |
[
"Not specifically cavitation, but an analogous process would be flow separation in gases. When this happens, the pressure in the separated region drops significantly, ",
"almost to the point of a full vacuum which causes moisture in the air to condense out.",
" ",
"Supersonic flow causes a similar but more violent effect. ",
"This used to occur in propeller blade tips that ended up inadvertently breaking the sound barrier in aerial maneuvers.",
" It was known to cause violent shaking, loud buzzing and sometimes structural damage. ",
"So yes- there are gas analogs to cavitation, but as ",
"/u/Coomb",
" said: cavitation is a specific term applied to these effects in liquids."
] |
[
"Yes. ",
"Form (parasitic) drag",
" increases with speed and creates a ",
" low pressure region behind objects moving through a fluid. "
] |
[
"Question from my 8 year old daughter: Can scientists invent something that isn't made up of atoms?"
] |
[
false
] |
I had absolutely no idea - can you give me an answer beyond yes or no? Her teacher told her that everything was made of atoms and we were talking about what atoms were made of, but I didn't have a good answer for this. EDIT: Thanks everyone - we googled quark gluon plasma last night and thanks to the term "squishy fire" I think she sort of has a loose concept of it. I had to laugh when she said "Internet scientists are pretty nice."
|
[
"Well, a quark gluon plasma is made of quarks and gluons but is too energetic for atoms to exist."
] |
[
"You can't make anything out of it. Basically it's a really short lived spark of squishy fire."
] |
[
"that, my friend, is up for debate"
] |
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